WO2018198252A1

WO2018198252A1 - Secondary battery, secondary battery system, and electricity-generating system

Info

Publication number: WO2018198252A1
Application number: PCT/JP2017/016629
Authority: WO
Inventors: 修一郎足立; 北川　雅規; 明博織田; 祐一利光; 酒井　政則; 杉政　昌俊; 渉太伊藤
Original assignee: 日立化成株式会社
Priority date: 2017-04-26
Filing date: 2017-04-26
Publication date: 2018-11-01

Abstract

This secondary battery is provided with a positive electrode, a negative electrode, an electrolytic solution which contains an active material, and a pair of bipolar plates disposed on the side of the positive electrode and on the side of the negative electrode, the sides being opposite to the facing sides of the positive electrode and the negative electrode, wherein: the positive electrode and/or the negative electrode has at least two regions that have mutually different porosities in the thickness direction; and the positive electrode and/or the negative electrode has a higher porosity therein on the facing side facing the positive electrode or negative electrode than that on the bipolar plate side opposite to the facing side facing the positive electrode or negative electrode.

Description

Secondary battery, secondary battery system and power generation system

The present invention relates to a secondary battery, a secondary battery system, and a power generation system.

In recent years, as a countermeasure against global warming, the demand for renewable natural energy to replace fossil fuels has increased, and the renewable energy market is expected to grow steadily in the future. In such a background, as one of countermeasures against output fluctuation, which is a problem of power generation using natural power such as sunlight and wind power, power storage technology using a storage battery has been highlighted. Among them, the flow battery that performs charging and discharging by causing the electrolyte to flow and causing an oxidation-reduction reaction of the active material has a long charge / discharge cycle life, and output / capacity design according to the application is possible, In particular, it is attracting attention as a large-capacity storage battery.

Other forms to which a flow battery can be applied as a large-capacity storage battery include, for example, a use on the power supply side and a use on the power demand side. The former is expected to be applied to, for example, securing power generation reserves and surplus power storage in thermal power plants, and frequency control, securing supply surplus and load leveling in substations. For the latter, in industrial facilities such as factories, peak cuts or time shifts for the purpose of reducing power costs, instantaneous power outages (instantaneous power outages), uninterruptible power supplies (Uninterruptable Power Supply, UPS) or emergency It is expected that it will be applied to applications such as power sources for automobiles.

A flow battery is composed of a positive electrode and a negative electrode, a positive electrode electrolyte and a negative electrode electrolyte, a positive electrode electrolyte reservoir and a negative electrode electrolyte reservoir, a liquid feed pump, a pipe, and the like. Charging / discharging is performed by circulating between the liquid reservoir and the negative electrode electrolyte circulating between the negative electrode and the negative electrode electrolyte reservoir. The positive electrode and the negative electrode are usually separated by a diaphragm, and mixing of the positive electrode electrolyte and the negative electrode electrolyte is prevented. Here, as the active material in the flow battery, ions whose valence changes can be candidates. Among these, vanadium (V / V) flow batteries and the like have been put into practical use from the viewpoint of safety and the like.

The electrode reaction of the V / V flow battery is shown below.
Positive: ^{VO 2+} _{_{^{(4-valent) + H 2 O⇔VO 2 + (}}} 5 ^{^{valence) + 2H + + e - ···}} (1)
Negative electrode: V ³⁺ (trivalent) + e ⁻ ⇔V ²⁺ (divalent) (2)
Here, a reaction from left to right represents a charging reaction, and a reaction from right to left represents a discharging reaction. When the reaction from the left to the right occurs, the supplied electric power is consumed in changing the valence of V ions in the positive electrode and the negative electrode, and is stored in the electrolytic solution. Moreover, at the time of discharge, the electric power stored in electrolyte solution can be taken out by reverse reaction.

As a V / V type flow battery, a two-layer liquid-permeable porous layer having a high surface porous electrode layer made of carbon fiber on the diaphragm side and a low surface porous electrode layer made of carbon fiber on the bipolar plate side A configuration using electrodes has been proposed (see, for example, Patent Document 1).

In addition, as a V / V flow battery, for example, from the viewpoint of suppressing electrode deterioration, the positive electrode and the negative electrode have an end portion close to the side where the electrolyte is supplied and an end portion close to the outflow side. There has been proposed a configuration in which at least one of the portions has a surface area per electrode unit volume smaller than a central portion therebetween (see, for example, Patent Document 2). Further, in Patent Document 2, from the viewpoint of suppressing electrode deterioration, the positive electrode and the negative electrode are electrode layers in which a plurality of layered electrodes are stacked, and per electrode unit volume in the electrode layer closer to the diaphragm. The remaining electrode layer is smaller in at least one of the end portion near the side where the electrolyte solution is supplied and the end portion near the side where the electrolyte solution flows out than the central portion therebetween. A configuration is also proposed.

JP-A-8-287938 JP 2000-188123 A

V / V flow batteries have a long history of development and are undergoing large-scale demonstration tests at home and abroad. On the other hand, V / V type flow batteries have problems in terms of raw material cost and energy density, and a system using alternative materials is expected. Examples of the alternative material include cerium / zinc (Ce / Zn), zinc / bromine (Zn / Br), zinc / iodine (Zn / I), and iron / chromium (Fe / Cr). .

Incidentally, a carbon felt electrode whose surface is activated may be used for a flow battery in view of the activity of electrode reaction, acid resistance, reaction area, and the like. A carbon felt electrode is a method in which polyacrylonitrile (PAN) or rayon fibers are flame-resistant in air at a temperature of 200 ° C. to 300 ° C. and then made into a nonwoven fabric and carbonized at a temperature of about 1000 ° C. It is manufactured using a direct carbonization method or the like.

Further, in order to increase the reaction area, it is preferable to increase the specific surface area of the carbon felt electrode. In this case, the diameter of the fibers constituting the carbon felt electrode is reduced, and the gap is fine. However, when the specific surface area of the carbon felt electrode is increased, the pressure loss when the electrolyte is circulated and the electrolyte is supplied to the electrode, that is, the fluid dynamic energy loss per unit time unit flow rate increases. As a result, when the pressure loss increases, the energy efficiency of the entire flow battery, including the power loss of the liquid feed pump, decreases, for example, when the pump is driven by the power of the flow battery itself.

Particularly, among the compositions other than the V / V system mentioned above, in the Zn / I system and the Zn / Br system, metal Zn is deposited on the negative electrode during the charging reaction. At this time, it is considered that the pressure loss further increases when deposition of metal or the like proceeds in the carbon felt electrode.

Here, in the technique described in Patent Document 1, in order to activate the electrode reaction while suppressing the pressure loss of the electrolytic solution, the electrode layer close to the diaphragm side where the battery reaction actively occurs has a high surface area density ( High-density) electrode layer. In such a structure, the V / V composition shown in Patent Document 1 can be expected to have a certain effect, but in other compositions (especially, the composition accompanied by precipitation of metal or the like as described above). It is thought that it cannot respond to a flow battery. In particular, since the electrode layer close to the diaphragm side has a high density, the gap of the electrode is blocked by a solid such as a metal deposited during the charging reaction or discharging reaction, and the reactivity in this portion is reduced. There is a possibility that the internal resistance of the flow battery increases and the pressure loss increases.

In addition, the technique described in Patent Document 2 is provided with a portion where the surface area per unit volume of the electrode is smaller than that of the central portion in order to prevent deterioration of the electrode, and does not correspond to prevention of pressure loss of the flow battery. Absent. Specifically, the flow of the electrolyte is directional, and when the battery reaction does not occur uniformly in the electrode in the direction of the flow of the electrolyte, the current density is a relative characteristic as a general characteristic of the battery. In particular, there is a tendency for deterioration in a high electrode region. In particular, the current density tends to be relatively high on the positive electrode outlet side during charging and the negative electrode inlet side during discharging, and deterioration of the electrodes tends to become obvious. A flow battery is composed of a laminated structure of single cells of a battery, and a bipolar plate (bipolar plate, electrode) structure that most easily matches this structure with a current collecting function is often used as a positive electrode and negative electrode structure. Here, in Patent Document 2, since the deterioration of the electrode becomes significant on the side of the bipolar plate having a relatively high current density, the surface area per unit electrode volume is adjusted to the electrode layer on the side of the bipolar plate, and the reactivity is ensured. From this point, it is considered that the electrode layer on the diaphragm side has no surface area gradient per unit electrode volume. However, in the composition other than the V / V system (especially, the composition accompanied by the deposition of metal or the like as described above), the electrode layer close to the diaphragm side has a high density, and thus deposited during the charging reaction or discharging reaction. The void portion of the electrode is blocked by a solid such as metal, and the reactivity at this portion is reduced, which may increase the internal resistance of the flow battery and increase the pressure loss.

An object of one embodiment of the present invention is to provide a secondary battery in which an increase in pressure loss is suppressed when an electrolytic solution is flowed, and a secondary battery system and a power generation system including the secondary battery.

Specific means for solving the above-described problems include the following embodiments.

<1> A secondary battery comprising a positive electrode, a negative electrode, and an electrolytic solution containing an active material, and satisfying any one of the following (1) to (3).
(1) It further includes a pair of bipolar plates provided on the opposite side of the positive electrode and the negative electrode opposite to the side where the positive electrode and the negative electrode face each other, and at least one of the positive electrode and the negative electrode is in the thickness direction. The bipolar plate having at least two regions having different porosity, wherein the porosity of the electrode on the side where the positive electrode and the negative electrode face each other is opposite to the side where the positive electrode and the negative electrode face each other It is higher than the porosity of the electrode on the side.
(2) It further includes a reservoir for supplying the electrolytic solution to the positive electrode and the negative electrode, respectively, and at least one of the positive electrode and the negative electrode has at least two regions having different porosity in the flow direction of the electrolytic solution. The porosity of the electrode on the side into which the electrolyte solution flows is higher than the porosity of the electrode on the side from which the electrolyte solution flows out.
(3) A pair of bipolar plates provided on the opposite side of the positive electrode and the negative electrode on the opposite side of the positive electrode and the negative electrode, respectively, and a reservoir for supplying the electrolyte to the positive electrode and the negative electrode, respectively. And at least one of the positive electrode and the negative electrode is an electrode having at least two regions having different porosity in the flow direction of the electrolyte, and the porosity of the electrode on the side into which the electrolyte flows Is higher than the porosity of the electrode on the side from which the electrolyte flows out, and the electrode having at least two regions having different porosity in the flow direction of the electrolyte has different porosity in the thickness direction. It has at least two areas.

<2> The secondary battery according to <1>, wherein the electrode contains carbon fiber.

<3> When the above (1) is satisfied, the porosity of the electrode increases from the bipolar plate side toward the side where the positive electrode and the negative electrode face each other, and when the above (3) is satisfied, the bipolar plate The porosity of the electrode increases from the side facing the positive electrode and the negative electrode, or from the side facing the positive electrode and the negative electrode toward the bipolar plate side. When the above (2) or (3) is satisfied, the porosity of the electrode increases from the side from which the electrolytic solution flows to the side from which the electrolytic solution flows, <1> or <2 The secondary battery as described in>.

<4> When satisfying the above (1), a position where a length of 5.0% enters from the at least part of the electrode on the side where the positive electrode and the negative electrode face each other in the thickness direction The difference between the porosity of the electrode at 95.0% and the porosity of the electrode at the position where the length penetrated 95.0% is 1.0% to 50.0%, and when the above (3) is satisfied, The porosity of the electrode at a position where a length of 5.0% has penetrated in the thickness direction from at least a part of the end of the electrode facing the positive electrode and the negative electrode, and a length of 95 When the absolute value of the difference from the porosity of the electrode at the position where 0.0% penetrates is 1.0% to 50.0% and satisfies the above (2) or (3), The position at a position where the length has penetrated 5.0% from at least a part of the end on the side where the electrolyte flows into the flow direction. Any one of <1> to <3>, wherein the difference between the porosity of the electrode and the porosity of the electrode at the position where the length penetrates 95.0% is 1.0% to 50.0% Secondary battery described in 1.

<5> When satisfying the above (1) or (3), the porosity distribution of the electrode in the thickness direction from at least a part of the end side of the electrode where the positive electrode and the negative electrode face each other The absolute value of the average change rate of the porosity of the electrode obtained from the slope of the straight line approximated by the least square method is 0.5% / mm to 8.0% / mm, In the case where (2) or (3) is satisfied, a minimum of two in the graph in which the distribution of the porosity of the electrode in the flow direction is plotted from at least a part of the end of the electrode on the side into which the electrolyte flows. Any of <1> to <4>, in which the absolute value of the average change rate of the porosity of the electrode obtained from the slope of the straight line approximated by multiplication is 0.1% / cm to 3.0% / cm The secondary battery as described in any one.

<6> The secondary battery according to any one of <1> to <5>, wherein the electrode is accompanied by precipitation of the active material in a charging reaction or a discharging reaction.

<7> The secondary battery according to <6>, wherein the deposit contains a metal.

<8> The secondary battery according to any one of <1> to <7>, wherein the porosity of the electrode is determined by weight measurement.

<9> The secondary battery according to any one of <1> to <8>, wherein the electrolytic solution contains at least one of iodine ions and iodine molecules as the active material.

<10> The secondary battery according to any one of <1> to <9>, wherein the electrolytic solution contains at least one of zinc ions and zinc as the active material.

<11> The secondary battery according to any one of <1> to <10>, further including a storage unit that supplies the electrolytic solution to the positive electrode and the negative electrode when the above (1) is satisfied.

<12> The secondary battery according to <11>, comprising a positive electrode electrolyte containing a positive electrode active material and a negative electrode electrolyte containing a negative electrode active material as the electrolyte.

<13> The secondary battery according to <12>, wherein the positive electrode active material contains at least one of iodine ions and iodine molecules, and the negative electrode active material contains at least one of zinc ions and zinc.

<14> The reservoir is a positive electrolyte reservoir that stores the positive electrolyte and a negative electrolyte reservoir that stores the negative electrolyte, and is between the positive electrode and the positive electrolyte reservoir. The secondary battery according to <12> or <13>, wherein the secondary battery is a flow battery further including a liquid feeding unit that circulates the positive electrode electrolyte and circulates the negative electrode electrolyte between the negative electrode and the negative electrode electrolyte reservoir. battery.

<15> A secondary battery system comprising: the secondary battery according to any one of <1> to <14>, and a control unit that controls charging and discharging of the secondary battery.

<16> A power generation system comprising a power generation device and a secondary battery system according to <15>.

<17> The power generation system according to <16>, wherein the power generation device generates power using renewable energy.

It is a mimetic diagram showing an example of member composition of a flow battery of this indication. It is a schematic diagram of the flow battery of this indication. It is a schematic diagram of the flow battery which has a cell stack structure. It is a schematic diagram which shows the structure of the electrode which concerns on 1st embodiment, and the combination of the electrode from which the porosity differs. It is a schematic diagram which shows the structure of the electrode which concerns on 1st embodiment, and the combination of the electrode from which the porosity differs. It is a figure which shows distribution of the porosity of the electrode in an electrode thickness direction. It is a figure which shows distribution of the porosity of the electrode in an electrode thickness direction. It is a figure which shows distribution of the porosity of the electrode in an electrode thickness direction. It is a figure which shows distribution of the porosity of the electrode in an electrode thickness direction. It is a schematic diagram which shows the structure of the electrode which concerns on 2nd embodiment, and the combination of the electrode from which the porosity differs. It is a schematic diagram which shows the structure of the electrode which concerns on 2nd embodiment, and the combination of the electrode from which the porosity differs. It is a figure which shows the change of the porosity distribution of the electrode before and behind compression among the structures of the electrode which concerns on 2nd embodiment. It is a figure which shows the change of the porosity distribution of the electrode before and behind compression among the structures of the electrode which concerns on 2nd embodiment. It is a figure which shows the change of the porosity distribution of the electrode before and behind compression among the structures of the electrode which concerns on 2nd embodiment. It is a figure which shows distribution of the porosity of the electrode in an electrolyte solution distribution direction. It is a figure which shows distribution of the porosity of the electrode in an electrolyte solution distribution direction. It is a figure which shows distribution of the porosity of the electrode in an electrolyte solution distribution direction. It is a figure which shows distribution of the porosity of the electrode in an electrolyte solution distribution direction. It is a figure which shows distribution of the porosity of the electrode in an electrolyte solution distribution direction. It is a figure which shows distribution of the porosity of the electrode in an electrolyte solution distribution direction. It is a schematic diagram which shows the structure of the electrode which concerns on 3rd embodiment, and the combination of the electrode from which the porosity differs. It is a schematic diagram which shows the structure of the electrode which concerns on 3rd embodiment, and the combination of the electrode from which the porosity differs. It is a schematic diagram which shows the structure of the electrode which concerns on 3rd embodiment, and the combination of the electrode from which the porosity differs. It is a schematic diagram which shows the structure of the electrode which concerns on 3rd embodiment, and the combination of the electrode from which the porosity differs. It is a schematic diagram which shows the structure of the electrode which concerns on 3rd embodiment, and the combination of the electrode from which the porosity differs. It is a schematic diagram which shows the structure of the electrode which concerns on 3rd embodiment, and the combination of the electrode from which the porosity differs.

Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including element steps and the like) are not essential unless otherwise specified. The same applies to numerical values and ranges thereof, and the present invention is not limited thereto.

In the present disclosure, numerical ranges indicated using “to” indicate ranges including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.
In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerical description. . Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples.
In the present disclosure, the content of each component in the electrolytic solution is the total of the plurality of types of substances present in the electrolytic solution unless there is a specific indication when there are multiple types of substances corresponding to the respective components in the electrolytic solution. Mean content.
Further, in the present disclosure, “content ratio” represents mass% of each component when the total amount of each electrolytic solution is 100 mass% unless otherwise specified.

In the present disclosure, the term “solid” refers to a material that is deposited by an electrochemical reaction on at least one of a positive electrode and a negative electrode used in a secondary battery, and specifically includes a metal solid and a nonmetal solid. . Examples of the non-metallic solid include molecular solids such as iodine molecules (I ₂ ) described later, and organic molecular solids such as polymers and plastics. Further, the non-metallic solid may be a complex such as a complex.

In the present disclosure, the “thickness direction” in the positive electrode refers to the direction from the side facing the negative electrode that is the counter electrode to the opposite side (for example, the direction of the bipolar plate side that exchanges electrons with the positive electrode). Indicates the direction from the side facing the positive electrode, which is the counter electrode, to the opposite side (for example, the direction from the side of the bipolar plate that exchanges electrons with the negative electrode).

In the present disclosure, the “porosity gradient” means that at least two regions having different porosity exist in an electrode in a certain direction, and the gradient of the porosity (a constant ratio) is present in at least a part of the electrode in a certain direction. However, the present invention is not limited to a configuration having a continuous change).

In the present disclosure, “the porosity of the electrode on the side where the positive electrode and the negative electrode face each other” refers to the length of 5.0% from the end surface on the side facing the counter electrode in the thickness direction of the electrode. Refers to the porosity of at least a portion of the region.
In the present disclosure, “the porosity of the electrode on the side of the bipolar plate” is defined as “a positive electrode and a positive electrode on the basis of a surface that penetrates 50% in the thickness direction of the electrode from the end surface facing the counter electrode”. It refers to the porosity of a region that is plane-symmetric with the region from which the “porosity of the electrode on the side facing the negative electrode” is obtained.

In the present disclosure, “the porosity of the electrode on the side into which the electrolyte solution flows” refers to a region from the end side of the electrode on which the electrolyte solution flows into the length of 5.0% in the flow direction. The porosity of at least a part of
In the present disclosure, the “porosity of the electrode on the side from which the electrolyte flows out” refers to a surface that has entered a length of 50% from the end surface on the side into which the electrolyte flows into the flow direction. It refers to the porosity of a region that is plane-symmetric with the region from which the “porosity of the electrode on the side from which the electrolyte flows out”.

[First embodiment]
[Secondary battery]
The secondary battery according to the first embodiment of the present disclosure includes a positive electrode, a negative electrode, and an electrolytic solution containing an active material. (1) The side of the positive electrode and the negative electrode opposite to the side where the positive electrode and the negative electrode face each other. And at least one of the positive electrode and the negative electrode is an electrode having at least two regions having different porosity in the thickness direction, and the electrode on the side where the positive electrode and the negative electrode face each other Is higher than the porosity of the electrode on the side of the bipolar plate opposite to the side where the positive electrode and the negative electrode face each other (that is, the side of the bipolar plate that exchanges electrons with the electrode). In the following description of the present embodiment, “an electrode having at least two regions having different porosity” is also referred to as “an electrode having a porosity gradient”.

The secondary battery of the present disclosure is provided with the above-described porosity gradient in the thickness direction on at least one of the positive electrode and the negative electrode. As a result, even when an electrode provided with a porosity gradient is accompanied by a deposition reaction of metal or the like by a charge / discharge reaction, an increase in pressure loss is suppressed when the electrolyte is flowed, and a liquid feed pump Therefore, a high current density and a high output characteristic can be obtained in the secondary battery.

(Positive electrode and negative electrode)
The secondary battery of the present disclosure includes a positive electrode and a negative electrode. At least one of the positive electrode and the negative electrode is an electrode having a porosity gradient in the thickness direction, and the porosity of the electrode on the side facing the counter electrode is the porosity of the electrode on the side of the bipolar plate that exchanges electrons with the electrode Higher than. This suppresses an increase in pressure loss when the electrolyte is flowed, and also suppresses power loss of the liquid feed pump. These reasons are considered as follows, for example.

In the secondary battery, when the charge / discharge reaction is accompanied by the deposition of an active material metal or the like, a large amount of metal or the like tends to be deposited on the counter electrode side where the battery reaction occurs actively. This is because, in principle, a position closer to the counter electrode has a small absolute value of ohmic loss and is an advantageous position in terms of potential as an electrochemical reaction field. For example, when the porosity of the negative electrode is uniform or the porosity is small on the positive electrode side which is the counter electrode, and there is precipitation of metal or the like of the active material in the charge / discharge reaction, precipitation of metal or the like occurs on the side closer to the positive electrode It is easy to close the gap. As a result, on the side closer to the positive electrode, the flow of the electrolytic solution is hindered and the pressure loss increases, the ion conductivity through the electrolytic solution is impaired, and the battery reaction is difficult to proceed. As a result, the power loss of the liquid feed pump increases, and the output such as current density and discharge capacity decreases.

On the other hand, in the secondary battery of the present disclosure, in at least one of the positive electrode and the negative electrode, the porosity of the electrode on the side facing the counter electrode is higher than the porosity of the electrode on the bipolar plate side that exchanges electrons with the electrode. Yes. Therefore, the deposition of metal or the like is less likely to occur on the side closer to the counter electrode where an electrochemical reaction is likely to occur, and the gap is less likely to be blocked. As a result, on the side closer to the counter electrode, it is possible to suppress the flow of the electrolytic solution from being inhibited and increase the pressure loss, and it is also possible to prevent the electrochemical reaction from proceeding easily. As a result, an increase in power loss of the liquid feed pump is suppressed, and a decrease in output such as current density and discharge capacity is suppressed, and a secondary battery having a high current density and high output can be maintained for a long time.

As a positive electrode and a negative electrode, what is used for a conventionally well-known secondary battery can be used. Specific examples include metals such as aluminum, copper, and zinc, and carbon (graphite). In addition, conductive materials such as InSnO ₂ , SnO ₂ , ZnO, In ₂ O ₂ , fluorine-doped tin oxide (SnO ₂ : F), antimony-doped tin oxide (SnO ₂ : Sb), tin-doped indium oxide (In ₂ O _3). : Sn), Al-doped zinc oxide (ZnO: Al), Ga-doped zinc oxide (ZnO: Ga) and other conductive materials doped with impurities such as single layer or multiple layers were formed on glass or polymer. Things. Examples of the shape of the positive electrode and the negative electrode include a plate shape and a mesh shape.

The electrode provided with at least one of the positive electrode and the negative electrode, preferably a porosity gradient, preferably contains carbon fiber from the viewpoint of increasing the reaction field as an electron transfer with the active material, that is, the electrode area.

When the electrode provided with at least one of the positive electrode and the negative electrode, preferably a porosity gradient, contains carbon fiber, it may be a porous body made of carbon fiber from the viewpoint of handling, processability, manufacturability and surface area. preferable. Specifically, examples of the porous body made of carbon fibers include carbon felt, carbon cloth, and carbon paper. Among them, it is preferable to use carbon felt from the viewpoint of reaction activity and surface area during charge / discharge.

Examples of carbon fiber raw material fibers include carbonizable fibers, and specific examples include cellulose-based, acrylic-based, rayon-based, phenol-based, aromatic polyamide-based, pitch-based fibers, and polyacrylonitrile-based fibers.

As a method for producing carbon felt, raw fibers before firing are laminated and spread into a sheet shape, and then a web is formed. Then, a gap between fibers is appropriately determined by a known method such as a needle punch method, a thermal bond method, or a stitch bond method. There is a method of bonding, finishing in a felt shape, and finally performing a heat treatment.

The conditions for the heat treatment are not particularly limited, and include, for example, a step (carbonization treatment) in which a felt material made of raw material fibers is heat treated in an inert gas at a temperature of 800 ° C. to 2000 ° C. In addition, if necessary, a step of heat treatment at a temperature of 100 ° C. to 500 ° C. before the carbonization treatment (flame resistance) and a step of heat treatment at a temperature of 2000 ° C. to 3000 ° C. after the carbonization treatment (graphitization treatment) are included. You may go out. By performing the graphitization treatment, the carbonized raw material fibers are further graphitized, the crystal structure as graphite becomes regular, and excess functional groups on the carbon fiber surface are removed, so that the electrode physical properties such as conductivity are improved. There is a tendency.

Other conditions for heat treatment include, for example, a step (activation treatment) of heat treating a felt material made of raw material fibers at a temperature of 800 ° C. to 2000 ° C. in a water vapor atmosphere. Thereby, the carbonized raw material fibers become porous and become activated carbon fibers, and the adsorption efficiency of the active material onto the fiber surface tends to be increased.

In addition, carbon cloth and carbon paper can also be suitably manufactured by performing heat treatment after finishing the raw fiber into a cloth shape or a paper shape by a known method.

The fiber diameter of the carbon fiber is preferably 1.0 μm to 30.0 μm, preferably 1.5 μm to 25 μm, from the viewpoints of physical properties as a carbon felt, production method, efficiency of electron transfer reaction with the electrolyte active material, and the like. The thickness is more preferably 0.0 μm, and further preferably 2.0 μm to 20.0 μm.

As shown in FIGS. 2 and 3, the positive electrode and the negative electrode are preferably compressed in the thickness direction when mounted (filled) in the flow battery. Thereby, the electrical conductivity of the material which comprises a positive electrode and a negative electrode (in the case of carbon felt, carbon fiber) and a bipolar plate improves, and it exists in the tendency which can reduce cell resistance.

When the positive electrode and the negative electrode are used after being compressed, the ratio of the thickness before and after compression (thickness before compression / thickness after compression) is preferably 1.1 to 4.0, preferably 1.2 to 3 Is more preferably 0.8, and still more preferably 1.3 to 3.6.

In the secondary battery, at least one of the positive electrode and the negative electrode is an electrode having a porosity gradient, and the porosity of the electrode on the side facing the counter electrode is the porosity of the electrode on the side of the bipolar plate that exchanges electrons with the electrode. Higher than. The porosity of this electrode can be determined by weight measurement, for example.

When using a material that changes its porosity before and after compression, such as carbon felt, for the electrode provided with a porosity gradient, the porosity of the electrode after compression (when used as an electrode for a secondary battery) It is preferable to calculate. In addition, when the relationship between the compression ratio and the porosity calculated from the thickness of the electrode before and after compression is known, the porosity of the electrode that is not mounted on the secondary battery and is not compressed is measured. The porosity of the electrode after compression may be calculated.

When calculating the porosity from weight measurement, the following equation (3) may be used.
φ = (1−V / V ′) × 100 (3)
In equation (3), φ is the porosity (%), V is the true volume (cm ³ ) of the electrode, and V ′ is the apparent volume (cm ³ ) of the electrode. The true volume V of the electrode can be calculated by dividing the mass of the material constituting the electrode by the density (g / cm ³ ) of the material.

It is preferable that at least one of the positive electrode and the negative electrode has a higher porosity of the electrode from the side of the bipolar plate that transmits and receives electrons toward the side facing the counter electrode. At this time, the porosity of the electrode may increase stepwise or discontinuously from the side of the bipolar plate toward the side facing the counter electrode, or the porosity of the electrode may increase continuously. That is, it is preferable that the porosity of the electrode tends to increase from the side of the bipolar plate that transmits and receives electrons toward the side facing the counter electrode.

Both the positive electrode and the negative electrode are electrodes provided with a porosity gradient, and the porosity of the electrode on the side facing the counter electrode may be higher than the porosity of the electrode on the side of the bipolar plate that exchanges electrons with the electrode. At this time, the degree of the porosity gradient may be the same or different between the positive electrode and the negative electrode.

<Example of electrode provided with porosity gradient>
Examples of electrodes provided with a porosity gradient used in the first embodiment are shown in FIGS. 4A and 4B. In Figure 4A, by combining the porosity phi ₁ of the electrode and the porosity phi ₂ of the electrode, a positive electrode 1a and the anode 1b porosity gradient is provided are formed. In Figure 4A, satisfies the φ _1> φ ₂ relationship, the porosity of the counter electrode and the opposite side (phi ₁₎ is higher than the bipolar plate (not shown) side porosity (phi _2).

In Figure 4B, the porosity phi ₁ of the electrode, combined with porosity phi ₂ of the electrode, the electrode porosity phi _3, the positive electrode 1a and the anode 1b porosity gradient is provided are formed. In FIG. 4B, the relationship of φ ₁ > φ ₂ > φ ₃ is satisfied, and the porosity of the electrode increases from the bipolar plate side (φ ₃ ) to the side (φ ₁ ) facing the counter electrode.

The following two methods can be given as examples of the method of giving the electrode a porosity gradient. The first is a method in which members having different porosity before compression are arranged from the side facing the counter electrode to the bipolar plate in order of increasing porosity, and these are compressed to form an electrode having a porosity gradient. It is. At this time, the order of the porosity of the electrode after compression (a state used as an electrode of the secondary battery) is also in the same order as before compression.

The second method is to provide a difference in the porosity of the electrode material when a structure such as carbon felt is manufactured, particularly when a porous body made of carbon fiber is used. That is, the porosity can be changed continuously or discontinuously in the same electrode member by selecting conditions for the web lamination method and the needle punch method.

In the thickness direction of the electrode, the porosity of the electrode at a position where the length has penetrated 5.0% from at least a part of the end side facing the counter electrode of the electrode in the thickness direction; The difference from the porosity of the electrode at the position where 0% penetrated (the porosity of the electrode at the position where the length entered 5.0% −the porosity of the electrode at the position where the length entered 95.0%) was 1. It is preferably 0% to 50.0%, more preferably 1.5% to 45.0%, still more preferably 2.0% to 40.0%, and more preferably 2.0% to 30.0% is particularly preferable, 2.0% to 20.0% is even more preferable, and 2.0% to 10.0% is even more preferable. When the above-described difference in porosity is 1.0% or more, the pressure loss of the electrolytic solution tends to be effectively suppressed even when a deposition reaction of metal or the like is involved in the electrode. Moreover, when the above-described difference in porosity is 50.0% or less, the uniformity of the reaction of the active material in the electrode is increased, and the activity of the charge / discharge reaction tends to be improved.

Further, in a graph in which the distribution of the porosity of the electrode in the thickness direction is plotted (for example, plotted at an equal interval of 0.05 mm) from at least a part of the end facing the counter electrode, the least square method is used. The absolute value of the average change rate of the porosity of the electrode obtained from the slope of the approximated straight line is preferably 0.5% / mm to 8.0% / mm, and preferably 0.75% / mm to 7. It is more preferably 0% / mm, further preferably 1.0% / mm to 6.5% / mm, particularly preferably 1.0% / mm to 6.0% / mm. . When the absolute value of the average change rate is 0.5% / mm or more, the pressure loss of the electrolytic solution tends to be effectively suppressed even when a deposition reaction of metal or the like is involved in the electrode. . In addition, when the absolute value of the average change rate is 8.0% / mm or less, the uniformity of the reaction of the active material in the electrode is increased, and the charge / discharge reaction activity tends to be improved.

The absolute value of the average change rate of the porosity in the electrode thickness direction can be obtained, for example, as follows. First, the coordinate in the thickness direction of the electrode (distance from the end of the electrode facing the counter electrode) is plotted on the horizontal axis, and the porosity of the electrode is plotted on the vertical axis. Next, linear approximation is performed by the least square method to obtain an approximate expression. When the porosity of the electrode increases from the bipolar plate side to the side facing the counter electrode, since the slope of the approximate expression is negative, the value obtained by multiplying the slope in the approximate expression by minus 1 (−1) is the gap. It can be the absolute value of the average rate of change of the rate.

For example, the absolute value of the average change rate of porosity is calculated as follows. First, as shown in FIGS. 5A to 5D, the coordinate in the thickness direction of the electrode (distance from the end on the diaphragm side) is plotted on the horizontal axis, and the porosity of the electrode is plotted on the vertical axis, and plotted on a graph. Next, linear approximation is performed by the least square method to obtain an approximate expression. When the porosity of the electrode increases from the bipolar plate side to the side facing the counter electrode, since the slope of the approximate expression is negative, the value obtained by multiplying the slope in the approximate expression by minus 1 (−1) is the gap. It can be the absolute value of the average rate of change of the rate. For example, FIG. 5A shows a calculation result when two types of electrodes having a porosity of 91.2% and 85.3% are arranged at a ratio (length) shown on the horizontal axis of the graph. 5B shows two types of electrodes with porosity of 95.6% and 85.3%, and FIG. 5C shows three types of electrodes with porosity of 93.3%, 89.0% and 87.2%. FIG. 5D shows calculation results when three types of electrodes having a porosity of 91.5%, 90.4%, and 89.3% are arranged at the ratios (lengths) indicated on the horizontal axis of the graph. It is shown.

In addition to the porosity of the electrode, a bulk density is an example of an index that defines the density of the electrode. The bulk density is defined as a density in a unit volume including a void portion.
The bulk density of the electrode after compression (state used as an electrode of a secondary battery) is not particularly limited, for ^example, is preferably 0.04g / cm 3 ~ 0.50g / cm 3, 0.045g / more preferably ^cm 3 ~ is 0.45 g / cm ^{^3,} further preferably 0.05g / cm 3 ~ 0.40g / cm 3. When the bulk density of the electrode is 0.04 g / cm ³ or more, the pressure loss of the electrolytic solution tends to be suppressed. For example, the compressive stress when mounted on a flow battery is improved, and the cell resistance is reduced. There is a tendency to be able to. Moreover, when the bulk density of the electrode is 0.50 g / cm ³ or less, the pressure loss of the electrolytic solution tends to be effectively reduced.

The surface area of the positive electrode and the surface area of the negative electrode are each independently preferably 1 m ² / g to 100 m ² / g, more preferably 2 m ² / g to 80 m ² / g, and 3 m ² / g to 60 m ^2. More preferably, it is / g. It exists in the tendency which can improve the reaction activity in charging / discharging reaction because the surface area of a positive electrode or the surface area of a negative electrode is 1 m < ² > / g or more. Moreover, it exists in the tendency which can suppress a pressure loss effectively because the surface area of a positive electrode or the surface area of a negative electrode is 100 m < ² > / g or less. For measuring the surface area of the positive electrode and the surface area of the negative electrode, a normal BET method or the like can be used.

(diaphragm)
The secondary battery may further include a diaphragm between the positive electrode and the negative electrode. The diaphragm is not particularly limited as long as it can withstand the usage conditions of the secondary battery. Examples of the diaphragm include an ion conductive polymer film capable of conducting ions, an ion conductive solid electrolyte film, a polyolefin porous film, and a cellulose porous film.

Examples of the ion conductive polymer membrane include a cation exchange membrane and an anion exchange membrane, and more specifically, Seleion APS (registered trademark) (AGC), Nafion (registered trademark) (DuPont) and Neoceptor. (Registered trademark) (Astom).

(Electrolyte)
The secondary battery includes an electrolytic solution containing an active material. The electrolyte solution may be a one-component electrolyte solution containing a positive electrode active material and a negative electrode active material, or a positive electrode electrolyte solution containing a positive electrode active material and a negative electrode electrolyte solution containing a negative electrode active material. Good.
Further, the electrolytic solution may contain a liquid medium in which the active material is dispersed or dissolved.

When an electrolytic solution containing a positive electrode active material and a negative electrode active material is used, this electrolytic solution is supplied to an electrode chamber in which the positive electrode and the negative electrode are arranged, the positive electrode active material is collected on the positive electrode side, and the negative electrode active material is on the negative electrode side. It is preferable to arrange the positive electrode and the negative electrode so as to gather. In the one-component electrolyte solution containing the positive electrode active material and the negative electrode active material, the positive electrode active material and the negative electrode active material are the positive electrode active material and the negative electrode contained in the negative electrode electrolyte, respectively. An active material may be used.

When a positive electrode electrolyte containing a positive electrode active material and a negative electrode electrolyte containing a negative electrode active material are used as the electrolyte, the positive electrode electrolyte is supplied to the positive electrode and the negative electrode electrolyte is supplied to the negative electrode. Further, it is preferable that the positive electrode electrolyte is supplied from one end side of the positive electrode toward the other end side, and the negative electrode electrolyte solution is supplied from one end side of the negative electrode toward the other end side. A plate-like, rod-like positive electrode and negative electrode are arranged along the vertical direction, and a positive electrode electrolyte is supplied along the vertical direction (for example, vertically upward) from one end side of the positive electrode to the other end side. More preferably, the liquid is supplied from one end side of the negative electrode to the other end side along the vertical direction (for example, vertically upward direction).

The active material in the electrolytic solution preferably contains ions whose valence changes, and known materials can be used.
Specifically, the active material in the electrolytic solution is an oxidant / reductant satisfying the following reaction formula (4) or the reaction formula (5) (hereinafter sometimes referred to as a redox pair). May be contained.
A ^{n +} + xe ⁻ ⇔A ^{(n−x) +} (4)
A ⁿ⁻ + xe ⁻ ⇔A ^{(n + x) −} (5)
In the general formula (4), n and x are integers and n ≧ x, and in the general formula (5), n and x are positive integers.

Examples of the redox pair satisfying the general formula (4) or (5) include Fe ³⁺ / Fe ²⁺ , Cr ³⁺ / Cr ²⁺ , Ga ³⁺ / Ga ²⁺ , Ti ³⁺ / Ti ²⁺ , Co ³⁺ / Co ²⁺ , Cu ²⁺ / Cu ⁺ , V ³⁺ / V ²⁺ , V ⁵⁺ / V ⁴⁺ , Ce ⁴⁺ / Ce ³⁺ , Cl ⁻ / Cl ³⁻ , Br ⁻ / Br ³⁻ , Zn ²⁺ / Zn, Pb ²⁺ / Pb, Fe ²⁺ / Fe, Cr ²⁺ / Cr, Ga ²⁺ / Ga, Ti ²⁺ / Ti, Mn ²⁺ / Mn, Mg ²⁺ / Mg, Mg ⁺ / Mg, Ag ⁺ / Ag, Cd ²⁺ / Cd, Co ²⁺ / Co, Cu ²⁺ / Cu, Cu ⁺ / Cu, Hg ²⁺ / Hg, and the like.
Examples of the redox _couple other than the redox _couple satisfying the general formula (4) or the general formula (5) include I ₃ ⁻ / I ⁻ and S ₄ ²⁻ / S ₂ ²⁻ .

In addition, the secondary battery of the present disclosure is at least one of a positive electrode and a negative electrode, and the electrode provided with the above-described porosity gradient is preferably accompanied by precipitation of an active material by a charge reaction or a discharge reaction. Moreover, it is more preferable that the precipitate contains a metal. By depositing the active material in the electrolytic solution in the charging reaction or discharging reaction, for example, the movement of ions from the positive electrode side to the negative electrode side through the diaphragm is suppressed, and the increase in ionic conduction resistance is suppressed, and the high current density is suppressed. In addition, it tends to be a high-power secondary battery. However, in an ordinary secondary battery, when the electrolyte is flowed, the void of the electrode is blocked by a solid such as a metal deposited during the charge reaction or the discharge reaction, and the reactivity at this part decreases. As a result, the internal resistance increases and the pressure loss may increase. On the other hand, in the secondary battery of the present disclosure, the porosity gradient is formed in the thickness direction at the electrode accompanied by the deposition of the active material, and therefore, when the electrolytic solution is flowed, an increase in pressure loss is suppressed. There is a tendency.

Examples of the oxidation-reduction pair that involves precipitation of metal or the like at the negative electrode during the charge reaction include, for example, Zn ²⁺ / Zn, Pb ²⁺ / Pb, Fe ²⁺ / Fe, Cr ²⁺ / Cr, Ga ²⁺ / Ga, Ti ²⁺ / Ti, Mn ²⁺ / Mn, Mg ²⁺ / Mg, Mg ⁺ / Mg, Ag ⁺ / Ag, Cd ²⁺ / Cd, Co ²⁺ / Co, Cu ²⁺ / Cu, Cu ⁺ / Cu, Hg ²⁺ / Hg, etc. It is done. Therefore, in the secondary battery of the present disclosure, an electrolytic solution containing these redox couples as a negative electrode active material may be used, or a negative electrode electrolytic solution containing these redox couples as a negative electrode active material may be used. .
In addition, you may use the positive electrode electrolyte solution which contains these redox couples as a positive electrode active material, and the negative electrode electrolyte solution which contains these redox couples as a negative electrode active material. At this time, a combination of the positive electrode active material and the negative electrode active material may be selected so that the standard redox potential of the negative electrode is lower than the standard redox potential of the positive electrode.

The deposit preferably contains a metal, and more preferably a metal. Further, the volume resistivity of the metal is preferably 1.0 × 10 ⁻⁵ Ωcm or less. When the deposit is a metal and the volume resistivity of the metal is 1.0 × 10 ⁻⁵ Ωcm or less, the metal deposited on the electrode becomes a new current collector during charge and discharge, It tends to be able to suppress a decrease in the efficiency of electron transfer reaction during charging and discharging.

The electrolytic solution preferably contains at least one of zinc ions (Zn ²⁺ ) and zinc (Zn) as an active material, and more preferably an aqueous solution system containing water as a liquid medium. By making the electrolytic solution into an aqueous solution system, the viscosity of the electrolytic solution can be lowered, and particularly when the electrolytic solution is flowed, the secondary battery tends to have a higher output. In addition, by containing at least one of zinc ions and zinc as an active material, a secondary battery having excellent safety, low environmental load, and high energy density can be realized. The zinc ion may be derived from a compound containing zinc. The compounds containing zinc include zinc iodide, zinc acetate, zinc nitrate, zinc terephthalate, zinc sulfate, zinc chloride, zinc bromide, zinc oxide, zinc peroxide, zinc selenide, zinc diphosphate, acrylic acid Examples thereof include zinc, zinc hydroxide carbonate, zinc stearate, zinc propionate, zinc fluoride, and zinc citrate. Of these, zinc chloride and zinc sulfate are preferable.

The electrolytic solution preferably contains at least one of iodine ions and iodine molecules as an active material, and more preferably an aqueous solution system containing water as a liquid medium. By making the electrolytic solution into an aqueous solution system, the viscosity of the electrolytic solution can be lowered, and particularly when the electrolytic solution is flowed, the secondary battery tends to have a higher output. In addition, by containing at least one of iodine ions and iodine molecules as an active material, a secondary battery having excellent safety, low environmental load, and high energy density can be realized. At least one of iodine ions and iodine molecules is preferably used in a state of being dispersed or dissolved in a liquid medium.

Examples of iodine ions include I ⁻ , I ₃ ⁻ , I ₅ ^{− and the} like. Therefore, when the electrolytic solution contains at least one of iodine ions and iodine molecules as an active material, for example, it only needs to contain at least one of I ⁻ , I ₃ ⁻ , I ₅ ⁻ and I ₂ .

Further, the electrolyte may contain an iodine compound, the iodine _{_{compound, CuI, ZnI 2, NaI,}} KI, HI, LiI, NH 4 I, BaI 2, CaI 2, MgI 2, SrI 2, CI ₄ , AgI, NI ₃ , tetraalkylammonium iodide, pyridinium iodide, pyrrolidinium iodide, sulfonium iodide and the like can be mentioned.

Iodine ions are preferably dissolved in the electrolytic solution. When water is used as the liquid medium, the iodine compound is preferably at least one of NaI, KI, and NH ₄ I. Since NaI, KI, and NH ₄ I have high solubility in water, the energy density of the secondary battery can be further improved by using at least one of NaI, KI, and NH ₄ I.

When the electrolytic solution contains at least one of iodine ions and iodine molecules as the positive electrode active material, the main redox pair in the charge / discharge reaction is I ⁻ / I ₃ ⁻ , and the reaction formula of the following formula (6) Happens.
3I ⁻ ⇔I ₃ ⁻ + 2e ⁻ (6)
In the reaction of this formula (6), iodine molecules do not precipitate, and high current density and high output characteristics can be realized in the secondary battery.

When the electrolytic solution contains at least one of iodine ions and iodine molecules as the positive electrode active material, in addition to the reaction of the formula (6), a reaction such as the following formula (7) is involved depending on charge / discharge conditions and the like. Sometimes.
^{_{^{2I - ⇔I 2 + 2e - ···}}} (7)
In the reaction of the formula (7), it means that the I ⁻ ion is oxidized during the charging to generate I ₂ . When I ₂ is generated, I ₂ may be deposited on the electrode surface as a solid, which may increase the pressure loss. For this reason, when using at least one of iodine ions and iodine molecules as the positive electrode active material, from the point of suppressing the increase in pressure loss, the positive electrode diaphragm side, that is, the side opposite to the negative electrode in the positive electrode, than the bipolar plate side. It is preferable to increase the porosity of the positive electrode.

In the electrolytic solution, the total content of iodine compounds and iodine molecules is preferably 1% by mass to 80% by mass, more preferably 3% by mass to 70% by mass, and 5% by mass to 50% by mass. More preferably. By setting the total content of the iodine compound and iodine molecules to 1% by mass or more, a secondary battery suitable for practical use with a high capacity tends to be obtained. Moreover, it exists in the tendency for the solubility or dispersibility in a liquid medium to become favorable because the total content rate of an iodine compound and an iodine molecule shall be 80 mass% or less. The iodine compound and iodine molecule content ratio represents the total content of ions derived from iodine compounds and iodine molecules in the electrolytic solution, and ions derived from iodine compounds in the electrolytic solution (for example, I ⁻ and I _3). ^- , I ₅ ^- and their counter ions) and the total content of iodine molecules (I ₂ ).

Moreover, electrolyte solution may contain oxidation-reduction substances other than an iodine molecule and an iodine ion as a positive electrode active material. The redox substance other than molecular iodine and iodine ^ions, _I - / I ₂ and ^I - / _{I 3} ^- system to form a mixed potential of the ^I - / _{I 2} and ^I - / _{I 3} ^- system of positive electrode potential Those in which the decrease in the thickness does not manifest are preferable.

Examples of redox substances other than iodine molecules and iodine ions include chromium, vanadium, zinc, quinone compounds, lithium cobaltate, sodium manganate, lithium nickelate, cobalt-nickel-lithium manganate, and lithium iron phosphate. .

As the electrolytic solution, a combination of a positive electrode electrolytic solution containing at least one of iodine molecules and iodine ions as a positive electrode active material and a negative electrode electrolytic solution containing a redox pair that accompanies deposition of a metal or the like as a negative electrode active material. Preferably, a combination of a positive electrode electrolyte containing at least one of iodine molecules and iodine ions as a positive electrode active material and a negative electrode electrolyte containing at least one of zinc and zinc ions as a negative electrode active material is more preferable. Further, if necessary, the positive electrode electrolyte may contain the above-described oxidation-reduction substances other than iodine molecules and iodine ions as the positive electrode active material, and if necessary, the negative electrode electrolyte may be used as the negative electrode active material. An oxidation-reduction substance other than the above-described oxidation-reduction pair may be contained.

The content of the positive electrode active material in the positive electrode electrolyte is not particularly limited, and is preferably 0.1% by mass to 80.0% by mass, for example, 0.5% by mass from the viewpoint of charge / discharge reaction activity. More preferably, it is ˜75.0% by mass, and further preferably 1.0% by mass to 70.0% by mass.

The content of the negative electrode active material in the negative electrode electrolyte is not particularly limited, and is preferably 0.1% by mass to 80.0% by mass, for example, 0.5% by mass from the viewpoint of the activity of the charge / discharge reaction. More preferably, it is ˜75.0% by mass, and further preferably 1.0% by mass to 70.0% by mass.

<Liquid medium>
The electrolytic solution is preferably one in which at least one active material is dissolved or dispersed in a liquid medium. A liquid medium means a medium in a liquid state at room temperature (25 ° C.).

Liquid media include acetone, methyl ethyl ketone, methyl-n-propyl ketone, methyl isopropyl ketone, methyl-n-butyl ketone, methyl isobutyl ketone, methyl-n-pentyl ketone, methyl-n-hexyl ketone, diethyl ketone, dipropyl ketone Ketone solvents such as diisobutyl ketone, trimethylnonanone, cyclohexanone, cyclopentanone, methylcyclohexanone, 2,4-pentanedione, acetonylacetone; diethyl ether, methyl ethyl ether, methyl-n-propyl ether, diisopropyl ether, Tetrahydrofuran, methyltetrahydrofuran, dioxane, dimethyldioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol -N-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl n-propyl ether, diethylene glycol methyl n-butyl ether, diethylene glycol di-n-propyl ether, diethylene glycol Di-n-butyl ether, diethylene glycol methyl-n-hexyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, triethylene glycol methyl-n-butyl ether, triethylene glycol di-n-butyl ether, Triethylene glycol Cyl-n-hexyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, tetraethylene glycol methyl-n-butyl ether, tetraethylene glycol di-n-butyl ether, tetraethylene glycol methyl-n- Hexyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di-n-propyl ether, propylene glycol di-n-butyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol methyl ethyl ether, dipropylene glycol Methyl-n-butyl ether, dipropylene glycol Recall di-n-propyl ether, dipropylene glycol di-n-butyl ether, dipropylene glycol methyl-n-hexyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether, tripropylene glycol methyl ethyl ether, tripropylene glycol methyl-n -Butyl ether, tripropylene glycol di-n-butyl ether, tripropylene glycol methyl-n-hexyl ether, tetrapropylene glycol dimethyl ether, tetrapropylene glycol diethyl ether, tetrapropylene glycol methyl ethyl ether, tetrapropylene glycol methyl-n-butyl ether, tetra Propylene glycol di-n-butyl ether, tetrapro Ether solvents such as lenglycol methyl-n-hexyl ether; carbonate solvents such as propylene carbonate, ethylene carbonate, diethyl carbonate; methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, Sec-butyl acetate, n-pentyl acetate, sec-pentyl acetate, 3-methoxybutyl acetate, methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, 2- (2-butoxyethoxy) ethyl acetate, benzyl acetate, acetic acid Cyclohexyl, methyl cyclohexyl acetate, nonyl acetate, methyl acetoacetate, ethyl acetoacetate, diethylene glycol methyl ether acetate, diethylene glycol monoethyl ether acetate, dipropylene glycol methyl ether acetate , Dipropylene glycol ethyl ether acetate, glycol diacetate, methoxytriethylene glycol acetate, ethyl propionate, n-butyl propionate, isoamyl propionate, diethyl oxalate, di-n-butyl oxalate, methyl lactate, ethyl lactate, N-butyl lactate, n-amyl lactate, ethylene glycol methyl ether propionate, ethylene glycol ethyl ether propionate, ethylene glycol methyl ether acetate, ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, Ester solvents such as propylene glycol propyl ether acetate, γ-butyrolactone, γ-valerolactone; acetonitrile, N- Aprotic polarities such as tilpyrrolidinone, N-ethylpyrrolidinone, N-propylpyrrolidinone, N-butylpyrrolidinone, N-hexylpyrrolidinone, N-cyclohexylpyrrolidinone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide Solvent: methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, t-butanol, n-pentanol, isopentanol, 2-methylbutanol, sec-pentanol, t-pentanol , 3-methoxybutanol, n-hexanol, 2-methylpentanol, sec-hexanol, 2-ethylbutanol, sec-heptanol, n-octanol, 2-ethylhexanol, sec-o Octanol, n-nonyl alcohol, n-decanol, sec-undecyl alcohol, trimethylnonyl alcohol, sec-tetradecyl alcohol, sec-heptadecyl alcohol, cyclohexanol, methylcyclohexanol, benzyl alcohol, ethylene glycol, 1,2- Alcohol solvents such as propylene glycol, 1,3-butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, Diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether Ter, diethylene glycol mono-n-hexyl ether, triethylene glycol monoethyl ether, tetraethylene glycol mono-n-butyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether, etc. And terpene solvents such as α-terpinene, myrcene, alloocimene, limonene, dipentene, α-pinene, β-pinene, terpineol, carvone, ocimene, and ferrandrene; water and the like. A liquid medium may be used individually by 1 type, and may use 2 or more types together. Among these, water is preferable as the liquid medium. By using water as the liquid medium, the electrolyte solution tends to have a low viscosity, and the secondary battery tends to have a high output.

<Polymer>
When the electrolytic solution, preferably the positive electrode electrolytic solution contains at least one of iodine molecules and iodine ions, it may contain a polymer that forms a complex with iodine ions. When the electrolytic solution contains a polymer that forms a complex with iodine ions, precipitation of iodine molecules that may occur during the oxidation-reduction reaction of iodine ions is suppressed, and the secondary battery tends to have high output. Polymers that form complexes with iodine ions include nylon 6, polytetrahydrofuran, polyvinyl alcohol, polyacrylonitrile, poly-4-vinylpyridine, polyvinylpyrrolidone, polymethyl (meth) acrylate, polytetramethylene ether glycol, polyacrylamide, polypropylene glycol , Polyethylene glycol, polyethylene oxide and the like. These polymers may be used individually by 1 type, and may use 2 or more types together.

<Good solvent for iodine molecules>
In addition, when the electrolytic solution, preferably the positive electrode electrolytic solution contains at least one of iodine molecules and iodine ions, it is preferable to contain a good solvent for iodine molecules in addition to water. When the electrolytic solution contains a good solvent for iodine molecules, the film formed on the positive electrode during the charge reaction is thinned, and the inhibition of the charge / discharge reaction by the film tends to be suppressed. Good solvents for iodine molecules include amides such as dimethylformamide, diethylformamide, acetamide, dimethylacetamide, N-methylpyrrolidone and N-ethylpyrrolidone, ketones such as acetone and methylethylketone, methyl acetate, ethyl acetate and methyl nicotinate. Examples thereof include esters, sulfoxides such as dimethyl sulfoxide, alcohols such as ethanol and ethylene glycol, ethers such as diethyl ether, pyridine derivatives such as nicotinamide and cyanopyridine. As a good solvent for halogen molecules, one kind may be used alone, or two or more kinds may be used in combination.

(Bipolar plate)
The secondary battery is provided on a side opposite to the side facing the counter electrode, and includes a pair of bipolar plates that respectively exchange electrons with the positive electrode and the negative electrode. Examples of the bipolar plate include a carbon material system and a metal material system, and it is preferable to use a carbon material system from the viewpoints of cost and corrosion resistance against an electrolytic solution. The bipolar plate is preferably a plate-like bipolar plate obtained by subjecting a composite material obtained by kneading graphite powder, a binder or the like to molding such as pressing or injection.
In addition, in the case of a single cell structure in which the secondary battery has one positive electrode and one negative electrode, from the point of suppressing corrosion of the current collector plate such as Cu, between the current collector plate and the positive electrode, and between the current collector plate and the negative electrode A bipolar plate may be provided between the two. Moreover, in the case of a single cell structure, it is not limited to the structure provided with both a current collecting plate and a bipolar plate, A current collecting plate may serve as the bipolar plate.

(Reference electrode)
The secondary battery may include a positive electrode reference electrode for measuring the positive electrode potential, or may include a negative electrode reference electrode for measuring the negative electrode potential. In the secondary battery, the positive electrode reference electrode and the negative electrode reference electrode are not indispensable components. If necessary, the positive electrode reference electrode and the negative electrode reference electrode are used, and the positive electrode potential and the negative electrode potential in the secondary battery are used. May be measured.

The positive electrode reference electrode and the negative electrode reference electrode may be any one that can be converted into a potential with respect to a standard hydrogen electrode potential and can exhibit a stable electrochemical potential. The reference electrode used as the electrochemical potential standard is indicated in textbooks and the like as the basics of electrochemistry (for example, “Allen J. Bard and Larry R. Faulkner,“ ELECTROCHEMICAL METHODS ”p. 3, (1980), John Wiley & Sons, Inc. "). Reference electrodes include Ag / AgCl reference electrodes, saturated calomel electrodes, and the like, with Ag / AgCl reference electrodes being preferred.
When an Ag / AgCl reference electrode is used as the reference electrode, for example, a RE-1CP saturated KCl silver-silver chloride reference electrode (BAS) may be used.
Further, a reference electrode other than the Ag / AgCl reference electrode may be used as the positive electrode reference electrode and the negative electrode reference electrode, and the measured potential may be converted into the potential of the Ag / AgCl reference electrode.

The secondary battery of the present disclosure may be a flow battery. For example, the secondary battery includes, as a storage unit, a positive electrode electrolyte storage unit that stores a positive electrode electrolyte solution, and a negative electrode electrolyte storage unit that stores a negative electrode electrolyte solution, and the positive electrode and the positive electrode electrolyte storage unit The flow battery may further include a liquid feeding unit that circulates the positive electrode electrolyte between them and circulates the negative electrode electrolyte between the negative electrode and the negative electrode reservoir.
Hereinafter, each configuration of the flow battery will be described.

(Cathode electrolyte reservoir and anode electrolyte reservoir)
The flow battery includes a positive electrode electrolyte storage part that stores a positive electrode electrolyte and a negative electrode electrolyte storage part that stores a negative electrode electrolyte. As a positive electrode electrolyte storage part and a negative electrode electrolyte storage part, an electrolyte storage tank is mentioned, for example.

(Liquid feeding part)
The flow battery includes a liquid feeding unit that circulates the positive electrode electrolyte between the positive electrode and the positive electrode electrolyte reservoir, and circulates the negative electrode electrolyte between the negative electrode and the negative electrode electrolyte reservoir. The positive electrode electrolyte stored in the positive electrode electrolyte reservoir is supplied to the positive electrode chamber where the positive electrode is disposed through the liquid delivery unit, and the negative electrode electrolyte stored in the negative electrode electrolyte reservoir is disposed through the liquid feeder. Supplied to the negative electrode chamber.

In the flow battery, for example, the liquid supply unit circulates the positive electrode electrolyte between the positive electrode chamber and the positive electrode electrolyte storage unit and circulates the negative electrode electrolyte between the negative electrode chamber and the negative electrode electrolyte storage unit. And a liquid feed pump.

The amount of the positive electrode electrolyte to be circulated between the positive electrode chamber and the positive electrode electrolyte reservoir and the amount of the negative electrode electrolyte to be circulated between the negative electrode chamber and the negative electrode electrolyte reservoir are appropriately adjusted using a liquid feed pump, respectively. What is necessary is just to set suitably according to a battery scale, for example.

(Electrolyte pressure loss)
In the flow battery, the pressure loss of the electrolytic solution can be measured by a known method. Specifically, a method of measuring the pressure on the inflow side and the outflow side of the electrolyte solution in the positive electrode and the negative electrode using a pressure sensor, and calculating the difference between the pressure and the like.
Any pressure sensor may be used as long as it can measure the pressure of a fluid such as pure water, a liquid containing a chemical solution, or a gas.

(Charge / discharge characteristics of secondary battery)
The charge / discharge characteristics of the secondary battery include current efficiency (CE), voltage efficiency (VE), and power efficiency (EE) in addition to battery capacity.
The current efficiency CE is a ratio between the amount of electricity obtained by discharging and the amount of electricity required for charging. The voltage efficiency VE is a ratio of the average voltage during discharging and the average voltage during charging. The power efficiency EE is a ratio between the discharged electric energy and the charged electric energy.

FIG. 1 is a schematic diagram showing an example of the configuration of the members of the flow battery according to the present embodiment. The positive electrode 1 a and the negative electrode 1 b are separated by a diaphragm 2. During the charge / discharge reaction, electrons are exchanged between each electrode and the bipolar plate 5. The bipolar plate 5 may be used as the bipolar plate frame 6. The bipolar plate frame 6 has a structure in which the outer peripheral portion is surrounded by the sealing material 3 or the like in a state where the bipolar plate 5 having the same area as each electrode is exposed. Further, the bipolar plate 5 is in contact with the current collector plate 9 and is connected to an external terminal for charging and discharging. Moreover, the sealing material 3 and the liquid separation plate 4 are arrange | positioned in the outer peripheral part of each electrode, The slit (a groove | channel, not shown) is formed in the liquid separation plate 4, and electrolyte solution (not shown) is each shown. It can be distributed in the electrode.

Specifically, the positive electrode electrolyte injected from the positive electrode electrolyte electrode chamber inlet 8a reaches the positive electrode separator 4 and flows into the positive electrode 1a via the slit. Here, the flow direction of the positive electrode electrolyte in FIG. 1 is from the bottom to the top. Next, through the slit formed in the positive electrode separator plate 4 from the upper end of the positive electrode 1a, the ends of the positive electrode seal material 3, the diaphragm 2, the negative electrode seal material 3, the negative electrode separator plate 4, and the negative electrode bipolar plate frame 6 are provided. It flows out from the positive electrode electrolyte electrode chamber outlet 8b through the positive electrode electrolyte flow path (sometimes called a manifold) formed in the section.

The negative electrode electrolyte injected from the negative electrode electrolyte electrode chamber inlet 8c reaches the negative electrode separator 4 and flows into the negative electrode 1b through the slit. Here, the flow direction of the negative electrode electrolyte in FIG. 1 is from the bottom to the top. Next, through the slit formed in the negative electrode separation plate 4 from the upper end of the negative electrode 1b, the ends of the negative electrode sealing material 3, the diaphragm 2, the positive electrode sealing material 3, the positive electrode liquid separation plate 4, and the positive electrode bipolar plate frame 6 It flows out from the negative electrode electrolyte electrode chamber outlet 8d through a negative electrode electrolyte flow path (sometimes called a manifold) formed in the section.

FIG. 2 is a schematic diagram of a flow battery. That is, the positive electrode electrolyte solution 10a flowing out from the positive electrode electrolyte electrode chamber outlet 8b passes through the pipe (circulation path) 13 and is stored in the positive electrode electrolyte storage part 11a. Further, the negative electrode electrolyte 10b flowing out from the negative electrode electrolyte electrode chamber outlet 8d passes through the pipe (circulation path) 13 and is stored in the negative electrode electrolyte storage part 11b. In this way, during the charge / discharge reaction, the positive electrode electrolyte 10a and the negative electrode electrolyte 10b are circulated in the positive electrode 1a and the negative electrode 1b by operating the liquid feed pump 12, respectively, and the positive electrode electrolyte reservoir 11a. And the cycle which returns to the negative electrode electrolyte storage part 11b again is repeated. Electrical control when charging / discharging is performed using the power supply 14 and the external load 15.

FIG. 3 is a schematic view of a flow battery in a state where a combination of positive electrode and negative electrode members (also referred to as cells) shown in FIG. 2 is electrically connected in series to form a stack structure. By increasing the number of cells and forming a stack structure, the output voltage of the flow battery can be increased. Here, the positive electrode 1a and the negative electrode 1b of the adjacent cells are electrically connected via the bipolar plate 5, and can exchange electrons during charging and discharging. Moreover, the positive electrode electrolyte solution 10a and the negative electrode electrolyte solution 10b are the same as FIG. 2 except having changed the structure of the piping (circulation path) 13 so that it can distribute | circulate in parallel with each electrode arrange | positioned in series. In the secondary battery in a stack structure, preferably in the flow battery in a stack structure, the side where the positive electrode and the negative electrode face each other is the side where no bipolar plate is provided between the positive electrode and the negative electrode. In FIG. 3, the side where the diaphragm 2 exists between the positive electrode 1a and the negative electrode 1b is indicated.

[Secondary battery system]
The secondary battery system of the present disclosure includes the above-described secondary battery of the present disclosure and a control unit that controls charging / discharging of the secondary battery. The secondary battery system of the present disclosure may be a flow battery system in which the secondary battery is a flow battery, and the control unit may be configured to control charge / discharge of the flow battery.

(Control part)
The secondary battery system includes a control unit that controls charging and discharging of the secondary battery. For example, the control unit may be configured to control the charging voltage in the secondary battery system, the charging potential of the positive electrode and the negative electrode, and the like.
The charging voltage indicates a potential difference between the negative electrode and the positive electrode, and the charging potential indicates a potential difference with respect to a reference electrode (reference electrode) having a constant reference potential.

[Power generation system]
A power generation system of the present disclosure includes a power generation device and the above-described secondary battery system of the present disclosure. The power generation system of the present disclosure can level and stabilize power fluctuations or stabilize power supply and demand by combining a secondary battery system and a power generation device.

The power generation system includes a power generation device. The power generation device is not particularly limited, and examples thereof include a power generation device that generates power using renewable energy, a hydroelectric power generation device, a thermal power generation device, and a nuclear power generation device. Among them, a power generation device that generates power using renewable energy is preferable. .

The amount of power generated by power generators using renewable energy varies greatly depending on weather conditions, etc., but when combined with a secondary battery system, the generated power can be leveled and supplied to the power system. it can.

Renewable energy includes wind power, sunlight, wave power, tidal power, running water, tide, geothermal heat, etc., preferably wind power or sunlight.

The generated power generated using renewable energy such as wind power and sunlight may be supplied to a high-voltage power system. In general, wind power generation and solar power generation are affected by weather such as wind direction, wind power, and weather, and thus generated power is not constant and tends to fluctuate greatly. If the generated power that is not constant is supplied to the high-voltage power system as it is, it is not preferable because it promotes instability of the power system. For example, the power generation system of the present embodiment can level the generated power waveform to the target power fluctuation level by superimposing the charge / discharge waveform of the secondary battery system on the generated power waveform.

[Second Embodiment]
[Secondary battery]
The secondary battery of the second embodiment of the present disclosure includes a positive electrode, a negative electrode, and an electrolytic solution containing an active material, and (2) further includes a storage unit that supplies the electrolytic solution to the positive electrode and the negative electrode, respectively. At least one of the positive electrode and the negative electrode is an electrode having at least two regions having different porosity in the flow direction of the electrolytic solution, and the porosity of the electrode on the side into which the electrolytic solution flows is the electrode on the side from which the electrolytic solution flows out It is higher than the porosity. In addition, in the secondary battery of 2nd embodiment, the description is abbreviate | omitted about the matter which is common in the secondary battery of above-mentioned 1st embodiment. In the following description of the present embodiment, “an electrode having at least two regions having different porosity” is also referred to as “an electrode provided with a porosity gradient”.

In the secondary battery of the present disclosure, a porosity gradient is provided in the flow direction of the electrolyte in at least one of the positive electrode and the negative electrode. As a result, even when an electrode provided with a porosity gradient is accompanied by a deposition reaction of metal or the like by a charge / discharge reaction, an increase in pressure loss is suppressed when the electrolyte is flowed, and a liquid feed pump Therefore, a high current density and a high output characteristic can be obtained in the secondary battery.

(Positive electrode and negative electrode)
The secondary battery of the present disclosure includes a positive electrode and a negative electrode. At least one of the positive electrode and the negative electrode is an electrode having a porosity gradient in the flow direction of the electrolytic solution, and the porosity of the electrode on the electrolyte flowing side is the porosity of the electrode on the electrolyte flowing side. Higher than. This suppresses an increase in pressure loss when the electrolyte is flowed, and also suppresses power loss of the liquid feed pump. These reasons are considered as follows, for example.

When a fluid flows through a space, it is subject to resistance due to friction with the material it contacts. This is the basic cause of pressure loss. The pressure loss in the laminar flow can be obtained by the so-called Hagen-Poiseille equation.
There is a clear relationship between the reaction rate of the electrochemical reaction between the positive electrode and the negative electrode, which is the basic constituent reaction of the battery reaction, and the pressure loss. When the pressure loss changes, it means that the flow velocity changes in the space in which the electrolyte for evaluating it flows. Regarding the relationship between the rate of the electrochemical reaction and the flow rate of the reaction field, the reaction rate is higher in the high flow rate field than in the low flow rate field. This is because the mass flow layer at the electrode interface is thinner in the high flow field than in the low flow field, and the flux (mol / (cm ² · sec)), which is the supply speed of the active material, is increased. Therefore, when the potential of the reaction field is controlled to be constant, the reaction rate on the side into which the electrolyte solution flows becomes faster than the side on which the electrolyte solution in which pressure loss has occurred. In the case of constant current control, that is, when the reaction rate of the reaction field is made constant by external control, there is a change in the difference in the reaction overvoltage of the battery reaction due to pressure loss between the electrolyte inflow side and the electrolyte outflow side. Arise. That is, the rate of increase of the overvoltage of the electrochemical reaction on the side where the electrolyte flows in, which is a place where the flow rate of the electrolyte is fast, can be suppressed lower than the rate of increase of the overvoltage of the electrochemical reaction on the side where the electrolyte flows. . Thus, pressure loss and battery reaction characteristics are closely related.

The same applies to the case where a metal or the like is deposited on the electrode due to the charge / discharge reaction and affects the flow path area of the electrolytic solution. However, when the battery reaction involves a precipitation reaction, the influence of the pressure loss on the battery reaction becomes more obvious. For example, when the deposition of metal or the like occurs in the negative electrode due to a charging reaction, the pressure loss is further amplified. The reason for this is that the reaction rate is fast on the side where the electrolytic solution flows, so that the channel area on the side where the electrolytic solution flows becomes smaller with the charging time due to the deposited metal or the like. If the flow path area decreases with the charging time, the region on the side into which the electrolyte solution flows is covered with the solid produced by the charging reaction, and the electrolyte solution may not flow. When the electrolyte stops flowing, it is no longer a flow battery, and the battery function stops.

For example, when zinc is deposited on the negative electrode in the charging reaction, first, zinc is deposited on the side on which the electrolytic solution having a high reaction rate flows, so that the flow area decreases from the side on which the electrolytic solution flows and pressure loss is reduced. As a result, the power loss of the liquid feed pump increases, and the electrolyte does not flow easily. In order to suppress these, the porosity of the electrode on the upstream side where the electrolyte solution flows in is made higher than the porosity of the electrode on the downstream side where the electrolyte solution flows out. Thereby, obstruction | occlusion of the electrode by precipitation of a metal etc. can be suppressed and the increase in pressure loss can also be suppressed.

In the secondary battery, at least one of the positive electrode and the negative electrode is an electrode having a porosity gradient, and the porosity of the electrode on the side into which the electrolyte solution flows is higher than the porosity of the electrode on the side from which the electrolyte solution flows out. high. The porosity of this electrode can be determined by weight measurement in the same manner as in the first embodiment described above, for example.

It is preferable that at least one of the positive electrode and the negative electrode has a higher porosity of the electrode from the side from which the electrolytic solution flows out to the side from which the electrolytic solution flows. At this time, the porosity of the electrode may increase stepwise or discontinuously from the side from which the electrolytic solution flows out to the side from which the electrolytic solution flows, or the porosity of the electrode may increase continuously. Good. That is, it is preferable that the porosity of the electrode tends to increase from the side from which the electrolytic solution flows out to the side from which the electrolytic solution flows.

Both the positive electrode and the negative electrode are electrodes provided with a porosity gradient, and the porosity of the electrode on the side into which the electrolyte solution flows may be higher than the porosity of the electrode on the side from which the electrolyte solution flows out. At this time, the degree of the porosity gradient may be the same or different between the positive electrode and the negative electrode.

Further, in the secondary battery of the second embodiment, similarly to the secondary battery of the first embodiment, the positive electrode and the negative electrode are provided on the side opposite to the side where the positive electrode and the negative electrode face each other, and exchange of electrons with the positive electrode and the negative electrode is performed. In the case of further including a pair of bipolar plates for performing each of the above, at least one of the positive electrode and the negative electrode may be an electrode having a porosity gradient in the thickness direction. At this time, unlike the secondary battery of the first embodiment, the porosity of the electrode on the bipolar plate side may be higher than the porosity of the electrode on the side facing the counter electrode. Thereby, the secondary battery can cope with high rate discharge and high output design. By increasing the porosity on the side of the bipolar plate, the flow rate on the side of the bipolar plate increases when the electrolyte is circulated. As a result, the supply speed of the active material into the electrode on the side facing the counter electrode is increased, and as a result, the secondary battery tends to have a higher output.

<Example of electrode provided with porosity gradient>
Hereinafter, the example of the electrode provided with the porosity gradient used by 2nd embodiment is shown to FIG. 6A and FIG. 6B. In Figure 6A, by combining the porosity phi ₁ of the electrode and the porosity phi ₂ of the electrode, the electrode 1 porosity gradient is provided are formed. In FIG. 6A, the relationship of φ ₁ > φ ₂ is satisfied, and the porosity (φ ₁ ) on the side into which the electrolytic solution flows is higher than the porosity (φ ₂ ) on the side from which the electrolytic solution flows out.

In Figure 6B, the porosity phi ₁ of the electrode, combined with porosity phi ₂ of the electrode, the electrode porosity phi _3, the electrode 1 porosity gradient is provided are formed. In FIG. 6B, the relationship of φ ₁ > φ ₂ > φ ₃ is satisfied, and the porosity of the electrode increases from the side (φ ₃ ) from which the electrolyte flows out to the side (φ ₁ ) from which the electrolyte flows. .

For example, the following three methods can be given as a method for giving the electrode a porosity gradient. First, as shown in FIG. 7A, members having different porosity before compression are arranged on the side from which the electrolyte flows in from the side where the electrolyte flows in order from the highest porosity, and these are compressed. In this method, the electrode is provided with a porosity gradient. At this time, the order of the porosity of the electrode after compression (a state used as an electrode of the secondary battery) is also in the same order as before compression.

Second, as shown in FIG. 7B, the electrolyte solution flows out from the side where the electrolyte solution flows in the members having the same porosity and different thicknesses before compression in the order of decreasing thickness. It is the method of arrange | positioning and compressing until each member becomes the same thickness. At this time, since the degree of compression increases from the electrolyte inflow side to the electrolyte outflow side, the porosity of the electrode increases from the electrolyte outflow side to the electrolyte inflow side. .
At this time, as shown in FIG. 7C, a trapezoidal member having a constant porosity is prepared, and compressed until the width (thickness) in the thickness direction of the electrode becomes the same in the flow direction of the electrolyte. Also good. Thereby, the porosity is high from the side where the electrolytic solution flows out to the side where the electrolytic solution flows, and an electrode having a constant porosity gradient can be formed.

The third method is to provide a difference in the porosity of the electrode material when a structure such as carbon felt is manufactured, particularly when a porous body made of carbon fiber is used. That is, the porosity can be changed continuously or discontinuously in the same electrode member by selecting conditions for the web lamination method and the needle punch method.

The porosity of the electrode at a position where the length penetrates 5.0% and the position where the length penetrates 95.0% from at least a part of the end of the electrode on the side into which the electrolyte flows. The difference from the porosity of the electrode (the porosity of the electrode at the position where the length penetrates 5.0% −the porosity of the electrode at the position where the length penetrates 95.0%) is 1.0% to 50.0% It is preferably 1.5% to 45.0%, more preferably 2.0% to 40.0%, and further preferably 2.0% to 30.0%. Is particularly preferably 2.0% to 20.0%, more preferably 2.0% to 10.0%. When the above-described difference in porosity is 1.0% or more, the pressure loss of the electrolytic solution tends to be effectively suppressed even when a deposition reaction of metal or the like is involved in the electrode. Moreover, when the above-described difference in porosity is 50.0% or less, the uniformity of the reaction of the active material in the electrode is increased, and the activity of the charge / discharge reaction tends to be improved.

Further, in a graph in which the distribution of the porosity of the electrode in the flow direction is plotted (for example, plotted at an equal interval of 0.1 cm) from at least a part of the end of the electrode on the side where the electrolyte flows in, the least square method is used. The absolute value of the average change rate of the porosity of the electrode obtained from the slope of the approximated straight line is preferably 0.1% / cm to 3.0% / cm, preferably 0.15% / cm to 2. It is more preferably 8% / cm, further preferably 0.2% / cm to 2.75% / cm, particularly preferably 0.25% / cm to 2.5% / cm. 0.3% / cm to 2.0% / cm is even more preferable, 0.3% / cm to 1.5% / cm is still more preferable, and 0.3% / cm to It is especially more preferable that it is 1.0% / cm. When the absolute value of the average change rate is 0.1% / cm or more, the pressure loss of the electrolytic solution tends to be effectively suppressed even when a deposition reaction of metal or the like is involved in the electrode. Moreover, when the absolute value of the average change rate is 3.0% / cm or less, the uniformity of the reaction of the active material in the electrode is increased, and the activity of the charge / discharge reaction tends to be improved.

For example, the absolute value of the average change rate of porosity is calculated as follows. First, as shown in FIGS. 8A to 8F, the horizontal axis represents the coordinate in the flow direction of the electrolytic solution (distance from the end of the electrode on the side where the electrolytic solution flows), and the vertical axis represents the porosity of the electrode. Plot on graph. Next, linear approximation is performed by the least square method to obtain an approximate expression. When the porosity of the electrode increases from the electrolyte outflow side to the electrolyte inflow side, since the slope of the approximate expression is negative, the slope in the approximate expression is multiplied by minus 1 (−1). The absolute value can be used as the average change rate of the porosity. FIG. 8A and FIG. 8B show calculation results when two types of electrodes having different porosity are arranged at a ratio (length) shown on the horizontal axis of the graph. 8C to 8F show calculation results when three types of electrodes having different porosity are arranged at a ratio (length) shown on the horizontal axis of the graph.

[Third embodiment]
[Secondary battery]
The secondary battery according to the third embodiment of the present disclosure includes a positive electrode, a negative electrode, and an electrolytic solution containing an active material. (3) The side of the positive electrode and the negative electrode opposite to the side where the positive electrode and the negative electrode face each other. And a reservoir for supplying the electrolyte solution to the positive electrode and the negative electrode, respectively, and at least one of the positive electrode and the negative electrode has at least a region having a different porosity in the flow direction of the electrolyte solution. The porosity of the electrode on the side into which the electrolyte solution flows is higher than the porosity of the electrode on the side from which the electrolyte solution flows out, and at least a region having a different porosity in the flow direction of the electrolyte solution. The electrode having two or more has at least two regions having different porosity in the thickness direction. In addition, in the secondary battery of 3rd embodiment, the description is abbreviate | omitted about the matter which is common in the secondary battery of above-mentioned 1st embodiment. In the following description of the present embodiment, “an electrode having at least two regions having different porosity” is also referred to as “an electrode provided with a porosity gradient”.

The secondary battery of the third embodiment includes an electrode provided with a porosity gradient in the flow direction of the electrolytic solution and further provided with a porosity gradient in the thickness direction. As a result, even when an electrode provided with a porosity gradient is accompanied by a deposition reaction of metal or the like by a charge / discharge reaction, an increase in pressure loss is suppressed when the electrolyte is flowed, and a liquid feed pump Therefore, a high current density and a high output characteristic can be obtained in the secondary battery. In addition, in 3rd embodiment, since the preferable structure of the porosity gradient of the distribution direction of electrolyte solution is the same as that of above-mentioned 2nd embodiment, the description is abbreviate | omitted.

In the secondary battery of the present disclosure, the porosity of the electrode on the side where the positive electrode and the negative electrode face each other is higher than the porosity of the electrode on the side of the bipolar plate that transmits and receives electrons to and from the point of suppressing an increase in pressure loss. Alternatively, from the viewpoint of higher output, the porosity of the electrode on the side of the bipolar plate that transfers electrons to and from the electrode may be higher than the porosity of the electrode on the side where the positive electrode and the negative electrode face each other.

Both the positive electrode and the negative electrode are electrodes provided with a porosity gradient, and the porosity of the electrode on the side facing the counter electrode may be higher than the porosity of the electrode on the bipolar plate side that exchanges electrons with the electrode, The porosity of the electrode on the side of the bipolar plate that exchanges electrons with the electrode may be higher than the porosity of the electrode on the side of the bipolar plate that exchanges electrons with the electrode. At this time, the degree of the porosity gradient may be the same or different between the positive electrode and the negative electrode.

<Example of electrode provided with porosity gradient>
Examples of electrodes provided with a porosity gradient used in the third embodiment are shown in FIGS. 9A to 9F. In FIG. 9A, a positive electrode 1a and a negative electrode 1b each having a porosity gradient are formed by combining four electrodes having a porosity φ ₁ to a porosity φ ₄ . In FIG. 9A, the relationship of φ ₁ > φ ₂ > φ ₃ > φ ₄ is satisfied, and the porosity (φ ₁ and φ ₂ ) on the side where the electrolyte flows in is the porosity (φ ₃ on the side where the electrolyte flows out. And φ ₄ ).

It is preferable that at least one of the positive electrode and the negative electrode has a higher porosity in a direction from the bipolar plate side toward the side facing the counter electrode or in a direction from the side facing the counter electrode toward the bipolar plate side. That is, it is preferable that the porosity of at least one of the positive electrode and the negative electrode has a distribution that decreases in a direction from the side facing the counter electrode toward the bipolar plate side, or from the bipolar plate side toward the side facing the counter electrode. At this time, the porosity may be a stepwise or non-continuous distribution or a continuous distribution.

In FIG. 9B, a positive electrode 1a and a negative electrode 1b each having a porosity gradient are formed by combining six electrodes having a porosity φ ₁ to a porosity φ ₆ . In FIG. 9B, the relationship of φ ₁ > φ ₂ > φ ₃ > φ ₄ > φ ₅ > φ ₆ is satisfied, and the porosity decreases from the side where the electrolytic solution flows to the side where the electrolytic solution flows.

Further, as shown in FIGS. 9C to 9F, in at least one of the positive electrode and the negative electrode, there is a region where a porosity gradient is not formed from the electrolyte flowing side to the electrolyte flowing side, And the porosity gradient may be formed in the thickness direction.

In at least one of the positive electrode and the negative electrode, there is a region where the porosity gradient is not formed in the thickness direction, and the porosity gradient is formed from the side where the electrolytic solution flows to the side where the electrolytic solution flows. May be.

The following two methods can be given as examples of the method of giving the electrode a porosity gradient. First, as shown in FIGS. 9A to 9F, members having different porosity before compression are arranged so that the porosity is in the order shown in the figure, and these are compressed to provide a porosity gradient. This is a method of forming an electrode. At this time, the order of the porosity of the electrode after compression (a state used as an electrode of the secondary battery) is also in the same order as before compression.

The porosity of the electrode at the position where the length of 5.0% penetrated from at least a part of the end of the electrode facing the positive electrode and the negative electrode in the thickness direction, and the length of 95.0% entered. The absolute value of the difference from the porosity of the electrode at the position is preferably 1.0% to 50.0%, more preferably 1.5% to 45.0%, and more preferably 2.0% to It is more preferably 40.0%, particularly preferably 2.0% to 30.0%, still more preferably 2.0% to 20.0%, and more preferably 2.0% to 10%. More preferably, it is 0.0%.
In addition, from the point of suppressing an increase in pressure loss, the difference between the porosity of the electrode at the position where the length of 5.0% penetrates and the porosity of the electrode at the position where the length penetrates 95.0%. It is preferable that (the porosity of the electrode at the position where the length penetrates 5.0% −the porosity of the electrode at the position where the length penetrates 95.0%) is 1.0% to 50.0%. It is more preferably 5% to 45.0%, further preferably 2.0% to 40.0%, particularly preferably 2.0% to 30.0%, % To 20.0% is even more preferable, and 2.0% to 10.0% is even more preferable.
Further, from the viewpoint of high output, the difference (length) between the porosity of the electrode at the position where the length of 5.0% enters and the porosity of the electrode at the position where the length penetrates 95.0%. The porosity of the electrode at the position where it penetrates 5.0% -the porosity of the electrode at the position where the length penetrates 95.0%) is preferably -50.0% to -1.0%,- It is more preferably 45.0% to -1.5%, further preferably -40.0% to -2.0%, and more preferably -30.0% to -2.0%. Particularly preferred is -20.0% to -2.0%, even more preferred is -10.0% to -2.0%.

Moreover, in a graph plotting the distribution of the porosity of the electrode in the thickness direction from at least a part of the end side of the electrode facing the positive electrode and the negative electrode (for example, plotted at equal intervals of 0.05 mm), The absolute value of the average change rate of the porosity of the electrode obtained from the slope of the straight line approximated by the least square method is preferably 0.5% / mm to 8.0% / mm, preferably 0.75% / mm. More preferably, it is from mm to 7.0% / mm, more preferably from 1.0% / mm to 6.5% / mm, and from 1.0% / mm to 6.0% / mm. It is particularly preferred.
In order to suppress an increase in pressure loss, the average rate of change is preferably −8.0% / mm to −0.5% / mm, and preferably −7.0% / mm to −0. More preferably, it is 75% / mm, more preferably −6.5% / mm to −1.0% / mm, and −6.0% / mm to −1.0% / mm. It is particularly preferred.
Further, from the viewpoint of high output, the above average change rate is preferably 0.5% / mm to 8.0% / mm, and preferably 0.75% / mm to 7.0% / mm. More preferably, it is 1.0% / mm to 6.5% / mm, still more preferably 1.0% / mm to 6.0% / mm.

The absolute value of the average change rate of the porosity in the flow direction of the electrolytic solution can be obtained by the same method as in the second embodiment.

The absolute value of the average change rate of the porosity in the electrode thickness direction can be obtained, for example, as follows. First, the coordinate in the thickness direction of the electrode (distance from the end of the electrode facing the counter electrode) is plotted on the horizontal axis, and the porosity of the electrode is plotted on the vertical axis. Next, linear approximation is performed by the least square method to obtain an approximate expression. When the porosity of the electrode increases from the bipolar plate side to the side facing the counter electrode, since the slope of the approximate expression is negative, the value obtained by multiplying the slope in the approximate expression by minus 1 (−1) is the gap. It can be the absolute value of the average rate of change of the rate. On the other hand, when the porosity of the electrode increases from the side facing the counter electrode toward the bipolar plate, the slope of the approximate expression is positive, so that the value can be the absolute value of the average change rate of the porosity. .
In addition, the average change rate of the porosity in the thickness direction of the electrode corresponds to the slope in the above-described similar equation.

Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to these examples.

<Example 1-A>
(A) Production of positive electrode and negative electrode As the positive electrode and the negative electrode, electrodes having a porosity gradient in the thickness direction as shown below were prepared. In order to prepare these electrodes, no. 1 and no. Two carbon felt electrodes were used. First, as shown in FIG. 4A, two types of electrodes were evenly arranged in the thickness direction of the electrodes. In addition, when attaching a positive electrode and a negative electrode to a flow battery, it compressed so that the thickness of a positive electrode and a negative electrode might be 2.5 mm. Moreover, the area of the surface perpendicular | vertical to the thickness direction of a positive electrode and a negative electrode was 150 mm x 100 mm. Thereby, the positive electrode and negative electrode which have the same porosity gradient in the thickness direction were produced. Details are as shown in Table 2.
Therefore, No. after compression. 1 and No. 1 The porosity of the electrode of 2 is 91.2% and 85.3%, respectively, using the density of carbon felt and the density of graphite (2.26 g / cm ³ ). In FIG. 4A, from the side close to the diaphragm (the side where the positive electrode and the negative electrode face each other), no. 1 (porosity φ ₁ ) and No. ₁ 2 (porosity φ ₂ ) electrodes were arranged in this order. Moreover, the absolute value of the average change rate of the porosity of the electrode in such an arrangement was 3.41% / mm.

(B) Preparation of Electrolytic Solution For the positive electrode electrolytic solution, an aqueous solution containing 6.0 mol / L sodium iodide (NaI) was prepared. In addition, an aqueous solution containing 2.0 mol / L of zinc chloride (ZnCl ₂ ) and 2.5 mol / L of ammonium chloride (NH ₄ Cl) as a pH adjuster was prepared as the negative electrode electrolyte.

(C) Production of Flow Battery In addition to the positive electrode and negative electrode produced above and the electrolyte, a cation exchange membrane “Nafion 117” as a diaphragm, and a bipolar plate made of highly conductive graphite fine powder as a bipolar plate (Showa Denko) 1 using an ethylene propylene rubber sheet as a sealing material, a copper (Cu) plate plated with nickel (Ni) as a current collecting plate, and a PVC tank and piping and a circulation pump (Iwaki Pump Co., Ltd.). A single cell type flow battery as shown in FIG. 2 was produced. Note that, as described above, the member in the portion sandwiched between the current collector plates was appropriately compressed so that the attached positive electrode and negative electrode had a thickness of 2.5 mm. At this time, it was confirmed that there were no gaps and steps at the boundary between the compression-filled electrodes.

(D) Evaluation of Flow Battery Characteristics A pressure sensor (HPS-24-F, Surpass Kogyo Co., Ltd.) was attached to the inflow side and outflow side piping sections of each electrolyte solution of the produced flow battery. Next, 0.50 L each of the positive electrode electrolyte and the negative electrode electrolyte prepared above are stored in the positive electrode electrolyte reservoir and the negative electrode electrolyte reservoir, respectively, and the flow rates of the positive electrode electrolyte and the negative electrode electrolyte are adjusted using a circulation pump. The positive electrode electrolyte and the negative electrode electrolyte were circulated through the positive electrode and the negative electrode, respectively, while adjusting the output of the circulation pump to be 0.20 L / min.
Thereafter, after confirming that the flow rates of the positive electrode electrolyte and the negative electrode electrolyte were constant, a charge / discharge experiment was performed at a current density of 50 mA / cm ² . Specifically, the current density is made constant, the battery is charged until the cell voltage reaches 1.5V, and then discharged at the same current density until the cut-off voltage becomes 0.7V, and the electric capacity (Ah) of the battery is obtained. It was.
Furthermore, the pressure loss at the start and end of charging was measured for each of the positive electrode electrolyte and the negative electrode electrolyte.
When evaluating the characteristics of the flow battery, the temperature was kept at 25 ° C.

<Example 2-A>
A flow battery was prepared and the characteristics were evaluated in the same manner as in Example 1-A, except that the electrodes used in Example 1-A were changed as shown in Tables 1 and 2.
The absolute value of the average change rate of the porosity of the electrode was 6.02% / mm.

<Example 3-A>
A flow battery was prepared and the characteristics were evaluated in the same manner as in Example 1-A, except that the electrodes used in Example 1-A were changed as shown in Tables 1 and 2.
The absolute value of the average change rate of the porosity of the electrode was 3.27% / mm.

<Example 4-A>
A flow battery was prepared and the characteristics were evaluated in the same manner as in Example 1-A, except that the electrodes used in Example 1-A were changed as shown in Tables 1 and 2.
The absolute value of the average change rate of the porosity of the electrode was 1.13% / mm.

<Example 5-A>
In Example 1-A, a flow battery was fabricated in the same manner as Example 1-A, except that the current density at the time of evaluating the characteristics of the flow battery was changed from 50 mA / cm ² to 100 mA / cm ^2. The characteristics were evaluated.

<Example 6-A>
In Example 1-A, except that the flow rate of the electrolytic solution for evaluating the characteristics of the flow battery was changed from 0.20 L / min to 0.35 L / min, the flow was the same as in Example 1-A. A battery was fabricated and the characteristics were evaluated.

<Comparative Example 1-A>
In Example 1-A, only one type of electrode was used (No. 2 carbon felt electrode in Table 1). A flow battery was prepared and the characteristics were evaluated in the same manner as in Example 1-A except that no porosity gradient was provided in the positive electrode and the negative electrode.

<Comparative Example 2-A>
In Comparative Example 1-A, a flow battery was produced in the same manner as Comparative Example 1-A, except that the current density at the time of evaluating the characteristics of the flow battery was changed from 50 mA / cm ² to 100 mA / cm ^2. The characteristics were evaluated.

Table 3 shows the measurement results of the pressure loss before and after charging and discharging and the discharge capacity in each produced flow battery. As shown in Examples and Comparative Examples, it was confirmed that the discharge capacity can be increased by using a structure in which the porosity of the electrode on the diaphragm side is higher than that on the bipolar plate side.
Focusing on the pressure loss, even in the flow battery produced in the example, although the pressure loss after charging is slightly increased particularly on the negative electrode side, the increase is suppressed as compared with the comparative example. This is because, on the side of the diaphragm having a high reaction activity, considering the reduction of voids due to the precipitation of zinc, the porosity is improved in advance, so that even when zinc is deposited during charging, the deposition rate of the electrode is This is probably because the film was distributed with high uniformity in the thickness direction.

<Example 1-B>
(A) Preparation of positive electrode and negative electrode As the positive electrode and the negative electrode, electrodes having a porosity gradient in the flow direction of the electrolyte as shown below were prepared. In order to prepare these electrodes, no. 1 and no. Two carbon felt electrodes were used. First, as shown in FIG. 6A, two types of electrodes were evenly arranged in the length direction of the electrodes (the direction from the electrolyte inlet to the outlet). In addition, when attaching a positive electrode and a negative electrode to a flow battery, it compressed so that the thickness of a positive electrode and a negative electrode might be 2.2 mm. Moreover, the area of the surface perpendicular | vertical to the thickness direction of a positive electrode and a negative electrode was 150 mm x 100 mm. Thereby, the positive electrode and negative electrode which have the same porosity gradient in the distribution direction of electrolyte solution were produced. Details are as shown in Table 5.
Therefore, No. after compression. 1 and No. 1 The porosity of the electrode of 2 is 95.0% and 91.7%, respectively, using the density of carbon felt and the density of graphite (2.26 g / cm ³ ). In FIG. 6A, No. 1 is from the side near the electrolyte inlet. 1 (porosity φ ₁ ) and No. ₁ 2 (porosity φ ₂ ) electrodes were arranged in this order. Moreover, the absolute value of the average change rate of the porosity of the electrode in such an arrangement was 0.33% / cm.

(B) Preparation of Electrolytic Solution As the positive electrode electrolyte and the negative electrode electrolyte, aqueous solutions similar to those of Example 1-A were prepared.

(C) Production of flow battery Using the positive electrode and the negative electrode produced above, the members sandwiched between the current collector plates were appropriately compressed so that the thickness of the attached positive electrode and negative electrode was 2.2 mm. A flow battery was fabricated in the same manner as in Example 1-A except for the above.

(D) Evaluation of flow battery characteristics The characteristics of the produced flow battery were evaluated in the same manner as in Example 1-A.

<Example 2-B>
A flow battery was prepared and the characteristics were evaluated in the same manner as in Example 1-B, except that the electrodes used in Example 1-B were changed as shown in Tables 4 and 5.
The absolute value of the average change rate of the porosity of the electrode was 0.46% / cm.

<Example 3-B>
A flow battery was prepared and the characteristics were evaluated in the same manner as in Example 1-B, except that the electrodes used in Example 1-B were changed as shown in Tables 4 and 5.
The absolute value of the average change rate of the porosity of the electrode was 0.39% / cm.

<Example 4-B>
A flow battery was prepared and the characteristics were evaluated in the same manner as in Example 1-B, except that the electrodes used in Example 1-B were changed as shown in Tables 4 and 5.
The absolute value of the average change rate of the porosity of the electrode was 0.41% / cm.

<Example 5-B>
A flow battery was prepared and the characteristics were evaluated in the same manner as in Example 1-B, except that the electrodes used in Example 1-B were changed as shown in Tables 4 and 5.
The absolute value of the average change rate of the porosity of the electrode was 0.52% / cm.

<Example 6-B>
In Example 1-B, a flow battery was fabricated in the same manner as in Example 1-B, except that the current density at the time of evaluating the characteristics of the flow battery was changed from 50 mA / cm ² to 100 mA / cm ^2. The characteristics were evaluated.

<Example 7-B>
In Example 1-B, except that the flow rate of the electrolytic solution for evaluating the characteristics of the flow battery was changed from 0.20 L / min to 0.35 L / min, the flow was the same as Example 1-B. A battery was fabricated and the characteristics were evaluated.

<Comparative Example 1-B>
In Example 1-B, only one type of electrode was used (No. 5 carbon felt electrode in Table 4), and the same as Example 1-B, except that no porosity gradient was provided on the positive and negative electrodes. Then, a flow battery was produced and the characteristics were evaluated.

<Comparative Example 2-B>
In Comparative Example 1-B, a flow battery was fabricated in the same manner as Comparative Example 1-B, except that the current density for evaluating the characteristics of the flow battery was changed from 50 mA / cm ² to 100 mA / cm ^2. The characteristics were evaluated.

Table 6 shows the measurement results of the pressure loss before and after charging and discharging and the discharge capacity in each produced flow battery. As shown in Examples and Comparative Examples, it was confirmed that the discharge capacity can be increased by using a structure in which the porosity of the electrode on the side into which the electrolyte solution flows is higher than on the side on which the electrolyte solution flows out.
Focusing on the pressure loss, even in the flow battery produced in the example, although the pressure loss after charging is slightly increased particularly on the negative electrode side, the increase is suppressed as compared with the comparative example. This is because, on the inflow side of the electrolyte solution with high reaction activity, considering the reduction of voids due to the precipitation of zinc, the porosity is improved in advance, so that even when zinc is deposited during charging, the precipitation ratio is This is probably because the electrolyte solution was distributed with high uniformity in the flow direction.

<Example 1-C>
(A) Preparation of positive electrode and negative electrode As the positive electrode and the negative electrode, electrodes having a porosity gradient in the thickness direction and a porosity gradient in the flow direction of the electrolyte were prepared as shown below. In order to prepare these electrodes, no. 1-No. 4 carbon felt electrodes were used. First, as shown in FIG. 9A, four types of electrodes were equally arranged. In addition, when attaching a positive electrode and a negative electrode to a flow battery, it compressed so that the thickness of an electrode might be 2.5 mm. Moreover, the area of the surface perpendicular | vertical to the thickness direction of a positive electrode and a negative electrode was 150 mm x 100 mm. Thereby, the positive electrode and negative electrode which have the same porosity gradient in the thickness direction and the distribution direction of electrolyte solution were produced. Details are as shown in Table 8.
Therefore, No. after compression. 1-No. The porosity of electrode 4 is 93.6%, 92.0%, 87.3%, and 84.1%, respectively, using the density of carbon felt and the density of graphite (2.26 g / cm ³ ). . In FIG. 9A, No. is located on the electrolyte inlet side and on the side close to the diaphragm. 1 (porosity φ ₁ ) on the electrolyte inlet side and No. 1 No. 1 at a position adjacent to the electrode No. 1 No. ₂ electrode (porosity φ ₂ ) on the electrolyte outflow side and the side close to the diaphragm. No. ₃ electrode (porosity φ ₃ ) on the electrolyte outflow side and No. 3 in a position adjacent to the electrode No. 3 Four electrodes (porosity φ ₄ ) were respectively arranged. In addition, the absolute value of the average change rate of the porosity of the electrodes in each direction in such an arrangement is as shown in Table 9.

(C) Production of flow battery A flow battery was produced in the same manner as in Example 1-A, except that the positive electrode and negative electrode produced above were used.

<Example 2-C>
As a positive electrode and a negative electrode, No. 1 in Table 7 was used. 1-No. 6 carbon felt electrodes were used. When the six types of electrodes are evenly arranged as shown in FIG. 9B, No. 2 is placed on the electrolyte inlet side and the side close to the diaphragm. 1 (porosity φ ₁ ) on the electrolyte inlet side and No. 1 No. 1 at a position adjacent to the electrode No. 1 No. ₂ electrode (porosity φ ₂ ) on the electrolyte outflow side and the side close to the diaphragm. 5 (porosity φ ₅ ) on the electrolyte outflow side and No. 5 No. 5 at a position adjacent to the electrode No. 5. No. ₆ electrode (porosity φ ₆ ) is located on the side close to the diaphragm. 1 and No. 1 No. 5 between the No. 5 electrodes. 3 (porosity φ ₃ ), No. ₃ Adjacent to the electrode of No. 3, 2 and No. 2 Between the electrodes of No. 6 Four electrodes (porosity φ ₄ ) were respectively arranged. The absolute value of the average rate of change in the electrode porosity in each direction when such an arrangement is used is as shown in Table 9.
A flow battery was prepared and the characteristics were evaluated in the same manner as in Example 1-C except that the electrodes were arranged as described above.

<Example 3-C>
As a positive electrode and a negative electrode, No. 1 in Table 7 was used. 3, no. 4 and no. 5 carbon felt electrodes were used. When the three types of electrodes are arranged as shown in FIG. 9C, No. 2 is placed on the electrolyte inlet side and on the side close to the diaphragm. No. 3 (porosity φ ₁ ) No. 3 on the electrolyte outflow side and the side close to the diaphragm. No. 4 electrode (porosity φ ₂ ) 3 and No. 3 No. 4 on the bipolar plate side. 5 electrodes (porosity φ ₃ ) were respectively arranged. The absolute value of the average rate of change in the electrode porosity in each direction when such an arrangement is used is as shown in Table 9.
A flow battery was prepared and the characteristics were evaluated in the same manner as in Example 1-C except that the electrodes were arranged as described above.

<Example 4-C>
As a positive electrode and a negative electrode, No. 1 in Table 1 was used. 1, no. 3 and no. 4 carbon felt electrodes were used. When the three types of electrodes are arranged as shown in FIG. 9D, No. 2 is placed on the electrolyte inlet side and the side close to the diaphragm. No. 3 (porosity φ ₁ ) No. 3 on the electrolyte outflow side and the side close to the diaphragm. No. 4 electrode (porosity φ ₂ ) 3 and No. 3 No. 4 on the bipolar plate side. 1 electrodes (porosity φ ₃ ) were respectively arranged. The absolute value of the average rate of change in the electrode porosity in each direction when such an arrangement is used is as shown in Table 9.
A flow battery was prepared and the characteristics were evaluated in the same manner as in Example 1-C except that the electrodes were arranged as described above.

<Example 5-C>
As the positive electrode electrolyte, an aqueous solution containing 6.0 mol / L sodium iodide (NaI) and 10.0% by mass of polyvinylpyrrolidone “PVP K30” (Wako Pure Chemical Industries, Ltd., number average molecular weight is 40,000) is used. did.
A flow battery was prepared and the characteristics were evaluated in the same manner as in Example 1-C, except that the composition of the positive electrode electrolyte was changed as described above.

<Comparative Example 1-C>
In Example 1-C, only one type of electrode was used (No. 4 carbon felt electrode in Table 7). A flow battery was prepared and the characteristics were evaluated in the same manner as in Example 1-C except that no porosity gradient was provided in the positive electrode and the negative electrode.

In Table 10, the measurement result of the pressure loss before and behind charging / discharging in each produced flow battery and discharge capacity are shown. As shown in the examples and comparative examples, the discharge capacity is obtained by using a structure in which the porosity of the electrode on the side into which the electrolyte flows is higher than the side on which the electrolyte flows out and a porosity gradient is provided in the thickness direction of the electrode. Confirmed that it can be increased.
Focusing on the pressure loss, even in the flow battery produced in the example, although the pressure loss after charging is slightly increased particularly on the negative electrode side, the increase is suppressed as compared with the comparative example. This is because, on the inflow side of the electrolyte solution having a high reaction activity, considering the decrease of the void portion due to the precipitation of zinc, by increasing the porosity in advance, even when zinc is precipitated during charging, the precipitation ratio is It is thought that it was possible to distribute with high uniformity in the flowing direction of the electrolytic solution and the thickness direction of the electrode.
In Example 5-C, polyvinylpyrrolidone was added to the positive electrode electrolyte as a compound capable of forming a complex with iodine molecules or iodide ions, and the viscosity of the positive electrode electrolyte was increased. The pressure loss before charging and the pressure loss after charging are larger than those of Example 4-C. Even in such a case, the pressure loss before charging and the pressure loss after charging are smaller than those of Comparative Example 1-C, and also in Example 5-C, the electrode has the above-described structure, so that the pressure during charging is reduced. It was found that the increase in loss can be suppressed and the discharge capacity can be kept higher.

All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually stated to be incorporated by reference, Incorporated herein by reference.

DESCRIPTION OF SYMBOLS 1 ... Electrode, 1a ... Positive electrode, 1b ... Negative electrode, 2 ... Diaphragm, 3 ... Sealing material, 4 ... Separation plate, 5 ... Bipolar plate, 6 ... Dipolar plate frame, 7 ... Polar chamber, 8a ... Positive electrode cathode chamber Inlet, 8b ... Positive electrode electrolyte electrode chamber outlet, 8c ... Negative electrode electrolyte electrode chamber inlet, 8d ... Negative electrode electrolyte electrode chamber outlet, 9 ... Current collector plate, 10a ... Positive electrode electrolyte, 10b ... Negative electrode electrolyte, 11a ... Positive electrode Electrolyte storage part, 11b ... Negative electrode electrolyte storage part, 12 ... Liquid feed pump, 13 ... Pipe (circulation path), 14 ... Power source, 15 ... External load

Claims

A positive electrode, a negative electrode, and an electrolytic solution containing an active material,
A secondary battery satisfying any one of the following (1) to (3).
(1) It further includes a pair of bipolar plates provided on the opposite side of the positive electrode and the negative electrode opposite to the side where the positive electrode and the negative electrode face each other, and at least one of the positive electrode and the negative electrode is in the thickness direction. The bipolar plate having at least two regions having different porosity, wherein the porosity of the electrode on the side where the positive electrode and the negative electrode face each other is opposite to the side where the positive electrode and the negative electrode face each other It is higher than the porosity of the electrode on the side.
(2) It further includes a reservoir for supplying the electrolytic solution to the positive electrode and the negative electrode, respectively, and at least one of the positive electrode and the negative electrode has at least two regions having different porosity in the flow direction of the electrolytic solution. The porosity of the electrode on the side into which the electrolyte solution flows is higher than the porosity of the electrode on the side from which the electrolyte solution flows out.
(3) A pair of bipolar plates provided on the opposite side of the positive electrode and the negative electrode on the opposite side of the positive electrode and the negative electrode, respectively, and a reservoir for supplying the electrolyte to the positive electrode and the negative electrode, respectively. And at least one of the positive electrode and the negative electrode is an electrode having at least two regions having different porosity in the flow direction of the electrolyte, and the porosity of the electrode on the side into which the electrolyte flows Is higher than the porosity of the electrode on the side from which the electrolyte flows out, and the electrode having at least two regions having different porosity in the flow direction of the electrolyte has different porosity in the thickness direction. It has at least two areas.
The secondary battery according to claim 1, wherein the electrode contains carbon fiber.
When the above (1) is satisfied, the porosity of the electrode increases from the bipolar plate side toward the side where the positive electrode and the negative electrode face each other,
When satisfying (3), the porosity of the electrode increases from the bipolar plate side toward the side where the positive electrode and the negative electrode face each other, or from the side where the positive electrode and the negative electrode face each other. The porosity of the electrode increases toward the bipolar plate side,
The porosity of the electrode increases from the side from which the electrolytic solution flows out to the side from which the electrolytic solution flows in when the above (2) or (3) is satisfied. Secondary battery.
When satisfying the above (1), the electrode at the position where the length has penetrated 5.0% from at least a part of the end side of the electrode facing the positive electrode and the negative electrode in the thickness direction. The difference between the porosity of the electrode and the porosity of the electrode at the position where the length penetrated 95.0% is 1.0% to 50.0%,
When satisfying the above (3), the electrode at a position where a length of 5.0% has penetrated from at least a part of the electrode on the side where the positive electrode and the negative electrode face each other in the thickness direction. The absolute value of the difference between the porosity of the electrode and the porosity of the electrode at the position where the length penetrated 95.0% is 1.0% to 50.0%,
When satisfying the above (2) or (3), at a position where a length of 5.0% has penetrated from at least a part of an end side of the electrode into which the electrolyte solution flows in the flow direction. The difference between the porosity of the electrode and the porosity of the electrode at a position where the length penetrates 95.0% is 1.0% to 50.0%. A secondary battery according to item.
When satisfying the above (1) or (3), the distribution of the porosity of the electrode in the thickness direction was plotted from at least a part of the end side of the electrode where the positive electrode and the negative electrode face each other. In the graph, the absolute value of the average change rate of the porosity of the electrode obtained from the slope of the straight line approximated by the least square method is 0.5% / mm to 8.0% / mm,
In the case of satisfying the above (2) or (3), in the graph plotting the distribution of the porosity of the electrode in the flow direction from at least a part of the end side of the electrode into which the electrolyte solution flows, The absolute value of the average change rate of the porosity of the electrode obtained from the slope of the straight line approximated by the square method is 0.1% / cm to 3.0% / cm. The secondary battery according to any one of the above.
The secondary battery according to any one of claims 1 to 5, wherein the electrode is accompanied by precipitation of the active material by a charging reaction or a discharging reaction.
The secondary battery according to claim 6, wherein the deposit contains a metal.
The secondary battery according to any one of claims 1 to 7, wherein the porosity of the electrode is determined by weight measurement.
The secondary battery according to any one of claims 1 to 8, wherein the electrolytic solution contains at least one of iodine ions and iodine molecules as the active material.
10. The secondary battery according to claim 1, wherein the electrolytic solution contains at least one of zinc ions and zinc as the active material.
The secondary battery according to any one of claims 1 to 10, further comprising a storage unit that supplies the electrolytic solution to the positive electrode and the negative electrode, respectively, when the condition (1) is satisfied.
The secondary battery according to claim 11, comprising a positive electrode electrolyte containing a positive electrode active material and a negative electrode electrolyte containing a negative electrode active material as the electrolyte.
The secondary battery according to claim 12, wherein the positive electrode active material contains at least one of iodine ions and iodine molecules, and the negative electrode active material contains at least one of zinc ions and zinc.
The reservoir is a positive electrolyte reservoir that stores the positive electrolyte and a negative electrolyte reservoir that stores the negative electrolyte,
A flow battery further comprising a liquid feeding part for circulating the positive electrode electrolyte between the positive electrode and the positive electrode electrolyte reservoir and circulating the negative electrolyte between the negative electrode and the anode electrolyte reservoir; The secondary battery according to claim 12 or claim 13, wherein
A secondary battery according to any one of claims 1 to 14,
A control unit for controlling charge and discharge of the secondary battery;
A secondary battery system comprising:
A power generator,
A power generation system comprising: the secondary battery system according to claim 15.
The power generation system according to claim 16, wherein the power generation device generates power using renewable energy.