JP2002246071A - Electricity storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a electricity storage device, capable of operating with a low-capacity battery, without needing capacity three to five times as much as that of normal usage, by using a lithium secondary battery as a main power source, even when high power consumption of the battery for a short time is required. SOLUTION: The lithium secondary battery 1 is connected in parallel with an electric double-layer capacitor 2, and the internal resistance value of the lithium secondary battery 1 is set to be lower than that of the electric double- layer capacitor 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power storage device using a lithium secondary battery as a main power supply, and more particularly to a power storage device which can reduce the load on the lithium secondary battery and can be used as a power source having good discharge characteristics.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of effective use of energy suitable for preserving the global environment and conserving resources, midnight power storage,
2. Description of the Related Art A household distributed power storage system for storing electric power by solar power generation, a power storage system for electric vehicles, and the like have attracted attention. For example, JP-A-6-86463 proposes a total system combining power supplied from a power plant, gas cogeneration, a fuel cell, a storage battery, and the like, as a system capable of supplying energy to energy consumers under optimal conditions. I have. The secondary batteries used in these power storage systems have an energy capacity of 10 W
Unlike small rechargeable batteries for portable devices of h or less, large capacity and large batteries are required. In these systems, a plurality of secondary batteries are connected in series, and the
It is a common practice to use a battery pack of up to 400 V. In most cases, a lead battery is connected and used.

[0003] Research and development for practical use of lithium secondary batteries has been conducted by the Lithium Battery Power Storage Technology Research Group (LI).
(BES), etc. Such a large lithium ion battery has an energy capacity of 100
About 400 Wh and a volume energy density of 20
It has reached the level of 0 to 300 Wh / l, which is comparable to that of a small secondary battery for portable equipment. Its shape is cylindrical, about 50-70mm in diameter and about 250-450mm in length, and 35mm-50mm in thickness.
A rectangular prism or a flat prism such as an oblong prism is typical.

[0004]

However, when a lithium secondary battery is used in a home distributed power storage system, the load on the lithium secondary battery is not excessive during normal load fluctuations, but the load on an air conditioner, a vacuum cleaner, or the like is small. When high power is required for a short time during use, the load on the lithium secondary battery increases. High loads can significantly reduce battery life,
Conventionally, in order to withstand a high load for a short time, a high load is assumed and a battery capacity equal to or more than a normal use capacity is required.

Accordingly, the present invention provides a lithium secondary battery as a main power source, which does not require an excess capacity of the lithium secondary battery even when short-time high power demand is required, and which can be covered by a battery capacity equivalent to a normally used capacity. It is intended to provide a device.

[0006]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted intensive studies while paying attention to the above-mentioned problems of the prior art, and as a result, have found that a lithium secondary battery and a specific capacitor have a specific condition. It has been found that when a power storage device connected in parallel is used, when the load is high, the capacitor is mainly discharged, and the load on the battery is reduced, and the present invention has been completed.

That is, the present invention relates to a power storage device in which a lithium secondary battery and an electric double layer capacitor are connected in parallel, wherein the internal resistance of the lithium secondary battery is equal to or more than the internal resistance of the electric double layer capacitor. It is characterized by. In addition,
The internal resistance is determined from the IR drop during discharge.

[0008] The lithium secondary battery has an energy capacity of 30 Wh or more and a volume energy density of 180
It is preferable that the battery has a flat shape of not less than Wh / l and a thickness of less than 12 mm.

The electric double layer capacitor has an electrode containing activated carbon, the activated carbon has a specific surface area of 1300 m ² / g or more and 2200 m ² / g or less by a BET method and a powder packing density of 0.45 g / cm. ³ or more 0.70 g / cm ³
And the average particle diameter is preferably 1 μm or more and 7 μm or less.

The activated carbon has a volume-based cumulative distribution of 90%.
% Particle diameter is preferably 6 μm or more and 22 μm or less, and the 10% particle diameter of the volume-based cumulative distribution is preferably 0.1 μm or more and 2 μm or less.

The pore volume of the activated carbon having a radius of 15 ° or less is preferably 0.8 ml / g or more.

Preferably, a non-aqueous electrolyte is used as the electrolyte of the double-layer capacitor.

The activated carbon has a capacity per unit weight of 40.
F / g or more, and the capacity per unit volume of the electrode is preferably 20 F / cm ³ or more.

It is preferable that a charging voltage of the electric double layer capacitor is 1.8 V or more and 3.3 V or less.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a power storage device according to the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a parallel connection of a lithium secondary battery and an electric double layer capacitor, FIG. 2 is a plan view and a side view of the lithium secondary battery, and FIG. 3 is a schematic diagram of the electric double layer capacitor. 4 is a graph showing a discharge curve of the power storage device, and FIG. 5 is a graph showing an enlarged view of FIG.

As shown in FIG. 1, for example, one lithium secondary battery 1 and an electric double layer capacitor 2 in which two unit cells 2 'are connected in series are connected in parallel. The terminal voltage (V4) is about 4.2 V when fully charged. The electric double layer capacitor 2 has a terminal voltage (V1) + (V2) of 4.2 V when fully charged by connecting two unit cells 2 ′ and 2 ″ in series.
It is.

When the electric double layer capacitor 2 has reached a predetermined charging voltage, it is preferable to provide a bypass circuit for bypassing the current so that the electric double layer capacitor 2 is not charged any more. For example, as shown in FIG. 6, the bypass circuit 5 is provided for each unit cell 2 ′, 2 ″, and includes a 2.1 V reference power supply 6, a comparator 7, a transistor 8, and a diode 9. In the illustrated example, the unit cells 2 ′ and 2 ″ of the electric double layer capacitor 2 have rated voltages of 2..
5V. When the unit cell 2 'or 2 "of the electric double layer capacitor reaches the reference voltage 2.1V, the transistor 8 is turned on by a signal (base current) from the comparator 7, and the current flows from the collector side of the transistor 8 to the emitter side. , The current to the unit cells 2 ′, 2 ″ is bypassed. This is because if the charging capacity varies between the unit cells 2 ′ and 2 ″ of the electric double layer capacitor 2, the durability of the electric double layer capacitor 2 is shortened, and furthermore, there is a possibility that the current may vary during discharging. This is because it is necessary to charge each unit cell 2 ′, 2 ″ equally. In addition, the deterioration of the electric double layer capacitor 2 is prevented by not exceeding the rated voltage of the unit cells 2 ', 2 ".

The connection in FIG. 1 may be such that three unit cells of the electric double layer capacitor 2 are connected in series with respect to one lithium secondary battery 1 or a plurality of unit cells are connected in series. A unit in which a plurality of unit cells of the electric double layer capacitor are connected in series may be used as a unit, and the units may be connected in series to increase the voltage. Further, if necessary, a plurality of unit cells of the lithium secondary battery 1 can be connected in series, and an electric double layer capacitor can be connected in parallel for each unit cell. A plurality of units connected in series can be used as a unit, and an electric double layer capacitor can be connected in parallel for each unit.

FIG. 2 shows a plan view and a side view of the lithium secondary battery. The illustrated lithium secondary battery includes a flat and rectangular battery case. The battery case is formed by welding and joining an upper lid 1a and a bottom container 1b at a peripheral edge A thereof. The upper lid 1a is provided with a positive electrode terminal 1c, a negative electrode terminal 1d, and a liquid inlet 1e. The injection port 1e is sealed with a sealing film 1f. The shape of the container of the lithium secondary battery 1 is not limited to the illustrated one. The lithium secondary battery 1 has an energy capacity of 30 Wh or more and a volume energy density of 1
A flat battery having a thickness of 80 Wh / l or more and a battery thickness of less than 12 mm is particularly suitable for this use.

FIG. 3 is a sectional view conceptually showing one embodiment of the electric double layer capacitor according to the present invention. In addition to the illustrated example, there are also a wound type and a laminated type.

The internal resistance (R1) of the lithium secondary battery 1 and the total internal resistance (R) of the unit cells of the electric double layer capacitor 2
2) is defined as R1 ≧ R2. In this case, the electric current value immediately after the discharge is larger in the electric double layer capacitor. That is, when a sudden load is applied to the power storage device, the electric double layer capacitor bears 50% or more of the current in the initial stage of discharge, and the discharge current of the lithium secondary battery is less than 50% of the load. But,
In the case of R1 <R2, the current value immediately after discharging is larger in the battery. In this case, the effect of providing the electric double layer capacitor 2 in parallel with the lithium secondary battery 1 is reduced.

When this power storage device is used in a household distributed power storage system, a predetermined number of units in which a lithium secondary battery and an electric double layer capacitor shown in FIG. 1 are connected in parallel are connected in series to obtain a predetermined voltage. The voltage is, for example, 10 units.
A voltage of 42 V may be obtained by connecting them in series, and this may be boosted to a voltage required for home use, for example, 320 V by a DC / DC converter. Moreover, you may directly connect in series with 320V.

The lithium secondary battery and the electric double layer capacitor are not limited, but the following ones are more effective.

That is, if the lithium secondary battery used has an energy capacity of 30 Wh or more, the volume energy density of the battery is 180 Wh / l or more, and the battery has a flat shape with a thickness of less than 12 mm, It is suitable for this purpose because the stacking space can be used effectively, and since the battery is thin, the heat dissipation design is easy and the capacity is high. The electric double layer capacitor includes an electrode containing activated carbon, and the activated carbon has a specific surface area of 1 according to a BET method.
300 meters ² / g or more 2200m and ² / g or less, the powder packing density is not more than 0.45 g / cm ³ or more 0.70 g / cm ^3, an electric double layer capacitor average particle diameter of 1μm or more 7μm or less More effective.

Hereinafter, an electric double layer capacitor according to an embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a schematic sectional view showing an embodiment of an electric double layer capacitor which is a component of the present invention.

As shown in FIG. 3, the electric double layer capacitor 2 has a pair of electrodes 2b, 2b ′ with a separator 2a interposed therebetween.
Is stored in the outer can 2c. The separator 2a and the electrodes 2b, 2b 'are impregnated with an electrolytic solution.
b and 2b 'each have a current collector 2d for extracting a current to the outside;
2d 'is electrically connected. Although the shape of the electric double layer capacitor 2 is not particularly limited,
Various shapes such as a film type, a coin type, a cylindrical type, and a box type can be manufactured.

The electrodes 2b and 2 of the electric double layer capacitor 2
b ′ is formed by molding activated carbon with a binder, and a conductive material or the like may be added as necessary. Electrodes 2b, 2
As a forming method of b ′, roll forming, press forming, such as a coating method of applying a slurry obtained by dispersing the above mixture in a solvent in the form of a metal foil, have been proposed for battery electrodes or electric double layer capacitor electrodes. Various methods can be used. When a conductive material is included in the electrodes 2b and 2b ', carbon materials such as acetylene black, carbon black, and graphite, metal powder, and the like can be used as the conductive material.

The shape of the electrodes 2b and 2b 'is appropriately determined depending on the shape or size of the electric double layer capacitor 2 or the characteristics to be satisfied by the capacitor. A disk-shaped electrode of about 1 mm to 30 mm, and a box-shaped electrode has a thickness of 0.1 mm to 30 mm.
In the case of a sheet-like electrode having a thickness of about mm, a cylindrical electrode or a cylindrical electrode or a material obtained by winding an electrode formed on a metal current collector foil such as aluminum or stainless steel having a thickness of about 0.02 mm to 2 mm, or the like is used. be able to.

The electrodes 2b and 2 of the electric double layer capacitor 2
The specific surface area of the activated carbon contained in b ′ by the BET method is 1
It is 300 m ² / g or more and 2200 m ² / g or less, preferably 1400 m ² / g or more and 2000 m ² / g or less.
When the specific surface area is less than 1300 m ² / g, the packing density is improved, but the capacity per weight is reduced or the liquid retention amount is reduced, so that it is not preferable because sufficient output characteristics cannot be obtained. On the other hand, when the specific surface area exceeds 2200 m ² / g, the packing density is lowered and a sufficient capacity cannot be obtained, which is not preferable.

The packing property of the activated carbon depends on the shape of the particles.
It depends on the shape, particle size distribution, surface condition, etc. Evaluation of this filling property
Tap density or powder packing density
I can do it. The present inventor has found that the powder packing density is
And high degree of correlation. That is, the electrode
The powder packing density of the activated carbon contained in 2b and 2b 'is 0.
45g / cm^Three0.70g / cm or more^ThreeLess and preferred
Or 0.45 g / cm ^Three0.65g / cm or more^ThreeBelow
is there. 0.45g / cm powder packing density^ThreeIf less than
It is preferable because the electrode density decreases and sufficient capacity cannot be obtained.
I don't. On the other hand, the powder packing density is 0.70 g / cm^ThreeOver
Powder packing density improves, but the capacity per weight
If the output volume decreases or the
It is not preferable because the property cannot be obtained.

Further, the average particle size of the activated carbon contained in the electrodes 2b and 2b 'is 1 μm or more and 7 μm or less, preferably 1 μm or more and 5 μm or less. Average particle size is 1μ
If it is less than m, secondary agglomeration and the like of the powder become intense and a problem occurs at the time of electrode molding, which is not preferable. On the other hand, when the average particle diameter exceeds 7 μm, the electrode density is lowered and a sufficient capacity cannot be obtained, which is not preferable. Further, in addition to the above-mentioned condition of the average particle size, the 90% particle size of the volume-based cumulative distribution of the activated carbon is 6 μm or more and 22 μm or less, and
10% particle size of the volume-based cumulative distribution is 0.1 μm or more 2
More preferably, the 90% particle diameter of the volume-based cumulative distribution of the activated carbon is 6 μm or more and 20 μm or less, and the 10% particle size of the volume-based cumulative distribution is 0.1 μm or less.
More preferably, it is 1 μm or more and 2 μm or less. In this case, a higher capacity per volume can be realized by the activated carbon having a relatively wide distribution of the particle size of the activated carbon and a small amount of fine powder of less than 0.1 μm and less large particles of more than 22 μm.

The pore volume of the activated carbon contained in the electrodes 2b and 2b 'having a radius of 15 ° or less is 0.8 ml / g or more, preferably 1.0 ml / g or more.
It is preferably 1.6 ml / g or less. When the pore volume is less than 0.8 ml / g, a sufficient capacity cannot be obtained, which is not preferable. When the pore volume exceeds 1.6 ml / g, the electrode density decreases and the capacity per volume decreases. Is not preferred.

If the above conditions are satisfied, the electrodes 2b, 2b
The method for producing the activated carbon contained in b ′ is not particularly limited,
As a general manufacturing method, for example, "New Edition" by Yuzo Sanada et al.
The method described in "Activated Carbon Basics and Applications" can be used. Therefore, the electric double layer capacitor of the present embodiment can be easily manufactured because a general method of manufacturing an electric double layer capacitor can be used except that the activated carbon is processed so as to satisfy the above conditions. it can. In general, activated carbon is manufactured in the form of powder or fiber having a size of 10 μm or more. Therefore, it is convenient and preferable to obtain activated carbon that satisfies the above-mentioned conditions using a crusher and a classifier such as a ball mill and a jet mill. The activated carbon satisfying the above conditions may be obtained by adjusting the raw material, the activation method, the shape of the activated carbon to be primarily synthesized, and the like.

As the binder used for the electrodes 2b and 2b ', known binders can be used. For example, fluorocarbon resins such as polytetrafluoroethylene and polyvinylidene fluoride, carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl alcohol, SBR Rubber, acrylic acid resin and the like can be mentioned, and one or more of these can be used. The amount of the binder to be added is not particularly limited, and is appropriately determined depending on the particle size, particle size distribution, particle shape, target electrode density, and the like of the activated carbon, and is generally 3% by weight to 20% by weight based on the activated carbon.

As the separator 2a, polyethylene,
Known materials such as a microporous membrane or nonwoven fabric made of polyolefin such as polypropylene, a porous membrane mainly made of pulp generally called electrolytic condenser paper, and the like can be used. As described above, in general, the electrodes are often separated by a porous separator impregnated with an electrolytic solution, but a solid electrolyte or a gel electrolyte may be used instead of the separator.

The electrolyte used for the electrodes 2b, 2b 'and the separator 2a is not particularly limited, but a non-aqueous electrolyte is preferably used, and an organic electrolyte having a high voltage per unit cell is more preferably used. . The organic electrolyte is prepared by adding 0.5 mol /
1 to 3.0 mol / l are preferable. As the organic solvent, known solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, sulfolane, and acetonitrile can be used. A plurality of types may be mixed and used. In addition, as the electrolyte, known materials such as tetraethylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, and tetraethylammonium hexafluorophosphate can be used, and one or a mixture of these may be used. Good.

The charging voltage of the electric double layer capacitor having the above-mentioned structure is as follows.
It is preferable to set the voltage between 8 V and 3.3 V. The charging voltage is appropriately determined depending on the type of activated carbon used for the electric double layer capacitor, the electrolytic solution, the operating temperature, and the intended life, but if it is less than 1.8 V, the usable capacity decreases, which is not preferable. If the voltage exceeds 3 V, the decomposition of the electrolytic solution becomes intense, which is not preferable.

[0038]

The present invention will be described more specifically below with reference to examples of the present invention.

Size: 150 × 21 as lithium secondary battery
A battery having a 0 × 6 mm thickness, an energy capacity of 37 Wh, and an energy density of 196 Wh / l was used. Internal resistance (R
1) was 14 mΩ.

As an electric double layer capacitor, the size φ40
A unit cell of × 125, a capacitance of 2000 F, and an internal resistance of 6 mΩ was connected in series with the lithium secondary battery in two series. Total internal resistance of electric double layer capacitor (R2)
Was 12 mΩ. That is, the relationship between the internal resistance values is R1>
R2. The connection method was the same as in FIG.

The battery was charged to 4.2 V with a current of 2 A, and then a constant current and constant voltage charge of applying a constant voltage of 4.2 V was performed for 7 hours, followed by (a) discharging at 20 A for 10 seconds, and (b) discharging for 20 seconds. The circuit is opened, and these operations (a) and (b)
Repeated 0 times. The result is shown in FIG. 4 and an enlarged view is shown in FIG.

The electric current of the electric double layer capacitor was initially discharged at 12 A, and the initial current value of the lithium secondary battery was 8 A. After discharging at 20A for 10 seconds,
For 20 seconds, there is no current flow to the external circuit of FIG. 1 in the open circuit state, and the current value of the ampere meter (A3) is 0 A, but between the lithium secondary battery 1 and the electric double layer capacitor 2 A current flow occurs, and the lithium secondary battery 1
Thus, it can be seen that a current flows to the side of the electric double layer capacitor 2 and the electric double layer capacitor 2 is charged from the lithium secondary battery. In this combination, since the initial current value of the battery current of the lithium secondary battery 1 was 8 A, the discharge rate of the lithium secondary battery was 0.8 C and the battery load was small.

Next, when a lithium secondary battery is used alone without discharging an electric double layer capacitor and discharges at 20 A, the discharge rate of the battery is as large as 2 C. Therefore, it has been found that when used in combination with an electric double layer capacitor, only a load of 0.8 C or less, which is 1/2 or less, is applied to the lithium secondary battery even at a load of 2 C.

[0044]

As is apparent from the above description, according to the power storage device of the present invention, a lithium secondary battery and an electric double layer capacitor are connected in parallel, and the internal resistance of the lithium secondary battery is reduced by By setting the internal resistance value of the electric double layer capacitor or more, the electric double layer capacitor can reduce the load of the lithium secondary battery and obtain good discharge characteristics.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating an embodiment of a power storage device according to the present invention.

2A and 2B show an example of a lithium secondary battery which is a component of a power storage device according to the present invention. FIG. 2A is a plan view and FIG.
(B) is a side view.

FIG. 3 is a cross-sectional view schematically showing an embodiment of an electric double layer capacitor which is a component of the power storage device according to the present invention.

FIG. 4 is a graph showing the results of a discharge experiment using a power storage device according to the present invention.

FIG. 5 is a graph showing a partially enlarged graph of FIG. 4;

FIG. 6 is a circuit diagram showing an example in which a bypass circuit is provided in the circuit of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lithium secondary battery 1a Top lid 1b Bottom container 1c Positive electrode terminal 1d Negative electrode terminal 1e Injection port 1f Sealing film 2 Electric double layer capacitor 2b, 2b 'Electrode 2a Separator 2d, 2d' Current collector 2c Outer can

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02J 7/02 H01G 9/00 301A 301D 301Z (72) Inventor Hajime Kinoshita Hajime Hiranocho, Chuo-ku, Osaka-shi, Osaka 1-2, Kansai New Technology Research Institute Co., Ltd. (72) Inventor Hisashi Satake 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi, Osaka, Japan Inside Kansai New Technology Research Institute Co., Ltd. (72) Inventor Shizukuni Yada Osaka 4-1-2 Hirano-cho, Chuo-ku, Osaka F-term in Kansai Research Institute of Technology (reference) 5G003 AA00 AA01 BA03 BA04 CA12 CC04 DA13 5H029 AJ02 BJ03 HJ04 HJ19 HJ20 5H030 AA01 AS01 BB21

Claims (9)

[Claims] 1. A power storage device in which a lithium secondary battery and an electric double layer capacitor are connected in parallel, wherein the internal resistance of the lithium secondary battery is equal to or greater than the internal resistance of the electric double layer capacitor. Power storage device. 2. The electric double-layer capacitor, wherein a plurality of unit cells of the electric double-layer capacitor are connected in series, and an internal resistance value of the lithium secondary battery is equal to that of the unit cell of the electric double-layer capacitor connected in series. The power storage device according to claim 1, wherein the power storage device has a total internal resistance value or more. 3. The energy capacity of the lithium secondary battery is 30 Wh or more, and the volume energy density of the battery is 180 Wh.
2. The power storage device according to claim 1, wherein the battery has a flat shape of not less than Wh / l and a thickness of less than 12 mm. 3. 4. The electric double layer capacitor includes an electrode containing activated carbon, the activated carbon has a specific surface area of 1300 m ² / g or more and 2200 m ² / g or less according to a BET method, and a powder packing density of 0.45 g / g. cm ³ or more 0.70 g / cm ³ or less, the electric storage device according to claim 1, wherein the average particle diameter of 1μm or more 7μm or less. 5. The activated carbon has a volume-based cumulative distribution of 9%.
5. The power storage device according to claim 4, wherein the 0% particle diameter is 6 μm to 22 μm, and the 10% particle diameter of the volume-based cumulative distribution is 0.1 μm to 2 μm. 6. 6. The power storage device according to claim 4, wherein a pore volume of the activated carbon having a radius of 15 ° or less is 0.8 ml / g or more. 7. A non-aqueous electrolytic solution is used as an electrolytic solution for the electric double layer capacitor.
The power storage device according to any one of the above. 8. The capacity per unit weight of the activated carbon is 4
8. The electrode according to claim 7, wherein the electrode has a capacity per unit volume of 20 F / cm ³ or more.
The power storage device according to claim 1. 9. The power storage device according to claim 7, wherein a charging voltage of the electric double layer capacitor is 1.8 V or more and 3.3 V or less.