JP2011086502A - Lithium secondary battery - Google Patents

Abstract

A lithium secondary battery having an electrolytic solution is provided.
The lithium secondary battery of the present invention is a lithium secondary battery having at least a positive electrode, a negative electrode, and an electrolyte solution interposed between the positive electrode and the negative electrode, wherein the negative electrode is at least a negative electrode A current collector and a negative electrode active material layer, wherein the electrolytic solution contains an ionic liquid, and the negative electrode active material layer is interposed between a part or all of at least one side of the negative electrode current collector and the electrolytic solution. There is no intervening portion where the electrolyte solution, the negative electrode current collector, and the negative electrode active material layer are in contact with each other at the same time.
[Selection] Figure 1

Description

  The present invention relates to a lithium secondary battery having an electrolytic solution.

  The secondary battery can convert the decrease in chemical energy associated with the chemical reaction into electrical energy and perform discharge. In addition, the secondary battery converts electrical energy into chemical energy by flowing current in the opposite direction to that during discharge. A battery that can be stored (charged). Among secondary batteries, lithium secondary batteries are widely used as power sources for notebook personal computers, mobile phones, and the like because of their high energy density.

In the lithium secondary battery, when graphite (expressed as C ₆ ) is used as the negative electrode active material, the reaction of the formula (1) proceeds at the negative electrode during discharge.
C ₆ Li → C ₆ + Li ⁺ + e ⁻ (1)
The electrons generated by the equation (1) reach the positive electrode after working with an external load via an external circuit. Then, lithium ions (Li ⁺ ) generated in the formula (1) move from the negative electrode side to the positive electrode side by electroosmosis in the electrolyte sandwiched between the negative electrode and the positive electrode.

Further, when lithium cobaltate (Li _0.4 CoO ₂ ) is used as the positive electrode active material, the reaction of the formula (2) proceeds at the positive electrode during discharge.
Li _0.4 CoO ₂ + 0.6 Li ⁺ + 0.6e ⁻ → LiCoO ₂ (2)
At the time of charging, the reverse reactions of the above formulas (1) and (2) proceed in the negative electrode and the positive electrode, respectively, and in the negative electrode, graphite (C ₆ Li) into which lithium has entered by graphite intercalation is present in the positive electrode. Since lithium cobaltate (Li _0.4 CoO ₂ ) is regenerated, re-discharge is possible.

In the conventional lithium secondary battery, an organic solvent having flammability and volatility is used for the electrolytic solution, and thus there is a limit to improving safety.
On the other hand, a lithium secondary battery using an ionic liquid as an electrolyte has been conventionally known as an effort to increase safety. Here, the ionic liquid refers to a salt that is liquid at 100 ° C. or lower, and generally has flame retardancy and non-volatility. Such a flame-retardant electrolyte not only can improve safety, but also has an advantage of having a relatively wide potential window (potential region) and relatively high ion conductivity.
Patent Document 1 discloses a technique of an ionic liquid-added electrolytic solution characterized in that oxygen is dissolved in an ionic liquid-added electrolytic solution obtained by adding an ionic liquid to an electrolytic solution.

JP 2009-123382 A

In the technique relating to the ionic liquid-added electrolyte disclosed in Patent Document 1, no consideration is given to the possibility of battery deactivation due to electrolyte decomposition.
The present invention has been accomplished in view of the above circumstances, and an object thereof is to provide a lithium secondary battery having an electrolytic solution.

  The lithium secondary battery of the present invention is a lithium secondary battery having at least a positive electrode, a negative electrode, and an electrolyte solution interposed between the positive electrode and the negative electrode, and the negative electrode includes at least a negative electrode current collector and A negative electrode active material layer, wherein the electrolytic solution contains an ionic liquid, and the negative electrode active material layer is interposed between part or all of at least one side of the negative electrode current collector and the electrolytic solution, There is no portion where the electrolyte solution, the negative electrode current collector, and the negative electrode active material layer are in contact with each other at the same time.

  In the lithium secondary battery having such a configuration, the negative electrode current collector is completely cut off from the electrolyte solution containing the ionic liquid by at least the negative electrode active material layer. Simultaneous contact of the negative electrode active material layer and the electrolyte can be avoided, and decomposition of the ionic liquid due to the reaction of the three can be prevented.

  As one form of the lithium secondary battery of the present invention, a protective layer is further provided, and the negative electrode active material layer and the protection are provided between a part or all of at least one side of the negative electrode current collector and the electrolytic solution. A configuration in which layers are interposed can be employed.

  In the lithium secondary battery having such a configuration, the negative electrode current collector is completely cut off from the electrolyte solution containing the ionic liquid by at least the negative electrode active material layer and the protective layer. Simultaneous contact of the three members of the electric body, the negative electrode active material layer, and the electrolytic solution can be avoided, and decomposition of the ionic liquid due to the reaction of the three members can be prevented.

  As one form of the lithium secondary battery of the present invention, at least a portion of the one side of the negative electrode current collector on which the protective layer is laminated at least on the outer peripheral edge and the protective layer on the one side is not laminated. The negative electrode active material layer can be configured to be laminated on the entire surface.

  As one form of the lithium secondary battery of the present invention, the negative electrode current collector is installed around the outer periphery of the negative electrode active material layer, and the entire surface of the one surface side of the negative electrode current collector and the negative electrode active material layer A configuration in which the protective layer is partially laminated can be employed.

  As one form of the lithium secondary battery of the present invention, the negative electrode active material layer is laminated on a part or all of one surface side of the negative electrode current collector, and the negative electrode active material layer is in contact with the negative electrode current collector. It is possible to adopt a configuration in which the protective layer is laminated at least on the outer peripheral edge of the surface that is not.

  As one form of the lithium secondary battery of the present invention, the negative electrode active material layer is laminated on one surface side of the negative electrode current collector, and the protective layer includes the negative electrode current collector and the negative electrode active material layer. It can be installed around the outer periphery of the interface, and a structure comprising the negative electrode current collector, the negative electrode active material layer, and the protective layer is immersed in the electrolytic solution.

  As one form of the lithium secondary battery of this invention, the structure called a lithium air battery can be taken.

  According to the present invention, since the negative electrode current collector is completely shielded from the electrolyte solution containing the ionic liquid by at least the negative electrode active material layer, the negative electrode current collector, the negative electrode active material layer, and Simultaneous contact of the three electrolyte solutions can be avoided, and decomposition of the ionic liquid due to the reaction of the three parties can be prevented.

It is the figure which showed typically the cross section cut | disconnected in the lamination direction about a part of typical example of the lithium secondary battery which concerns on this invention. It is the figure which showed typically the cross section cut | disconnected in the lamination direction about a part of modification of the lithium secondary battery which concerns on this invention. It is a cross-sectional schematic diagram of the lithium air secondary battery of an Example. It is the figure which showed typically the cross section cut | disconnected in the lamination direction about the negative electrode part of the lithium secondary battery of a prior art. It is a cross-sectional schematic diagram of the lithium air secondary battery of a comparative example.

  The lithium secondary battery of the present invention is a lithium secondary battery having at least a positive electrode, a negative electrode, and an electrolyte solution interposed between the positive electrode and the negative electrode, and the negative electrode includes at least a negative electrode current collector and A negative electrode active material layer, wherein the electrolytic solution contains an ionic liquid, and the negative electrode active material layer is interposed between part or all of at least one side of the negative electrode current collector and the electrolytic solution, There is no portion where the electrolyte solution, the negative electrode current collector, and the negative electrode active material layer are in contact with each other at the same time.

The term “lithium secondary battery” as used in the present invention refers to a lithium ion secondary battery using a solid positive electrode active material such as LiCoO ₂ and a lithium air secondary battery using a gas positive electrode active material such as air or oxygen. Both are included. That is, it is not particularly limited as long as it is a secondary battery in which lithium ions are involved in the electrode reaction, and is included in the lithium secondary battery referred to in the present invention.
The state of “there is no site where the three parts of the electrolytic solution, the negative electrode current collector, and the negative electrode active material layer are in contact simultaneously” in the present invention specifically refers to the negative electrode current collector and the negative electrode active material layer. The state in which the electrolytic solution does not enter the interface.

FIG. 4 is a diagram schematically showing a cross section cut in the stacking direction of the negative electrode portion of the lithium secondary battery of the prior art. As shown in FIG. 4, in the lithium secondary battery of the prior art, a laminated body in which the negative electrode active material layer 12 is laminated as it is on the negative electrode current collector 11 is used as the negative electrode. As shown in a portion surrounded by a broken line in FIG. 4, such a lithium secondary battery has a portion where the negative electrode current collector 11, the negative electrode active material layer 12, and the ionic liquid 4 are in contact with each other at the same time. To do.
In the course of research and development of a lithium secondary battery, the inventors have decomposed the ionic liquid when the three-part coexistence site as shown in FIG. 4 exists, resulting in a decrease in power generation performance of the secondary battery, and It has been found that the battery life is shortened. Although details are not clear, the following two reasons are presumed as the reason for the ionic liquid decomposition. That is, the first reason is that oxygen is desorbed from the passive state of SUS or the like normally used as a negative electrode current collector, and as a result, the decomposition of the ionic liquid is promoted by the negative electrode current collector in a state where oxygen is desorbed. This is considered to be because of this. The second reason is that when lithium metal is used in the negative electrode active material layer and a metal having a higher corrosion potential (ie, standard electrode potential E ⁰ ) than lithium metal is used in the negative electrode current collector, the negative electrode This is probably because the current collector, the negative electrode active material layer, and the ionic liquid locally constitute an internal battery, resulting in partial decomposition of the ionic liquid.

  As a result of diligent efforts, the inventors of the present invention have a lithium secondary battery according to the present invention having a structure in which there is no site where the electrolyte solution, the negative electrode current collector, and the negative electrode active material layer are in contact at the same time. It was found that the decomposition of the ionic liquid due to the reaction involved can be avoided. As a result, it has been clarified that the lithium secondary battery according to the present invention can achieve a longer life as compared with a conventional lithium secondary battery having an electrolytic solution. Furthermore, the lithium secondary battery according to the present invention can prevent a side reaction caused by the decomposition product of the electrolytic solution and does not generate a gas accompanying the decomposition of the electrolytic solution. It has been found that safety can be improved without causing the above problems.

FIG. 1 is a diagram schematically showing a cross section cut in a stacking direction of a part of a typical example of a lithium secondary battery according to the present invention. In addition, the double wavy line in the figure means omission of the figure.
In this typical example, the negative electrode current collector 1 processed into a cylindrical shape is used, and the negative electrode current collector 1 is arranged so that the substantially planar portion of the cylinder is on the top in FIG. Furthermore, in the cylindrical negative electrode current collector 1, a substantially planar portion of the cylinder is completely covered with the negative electrode active material layer 2.
As shown in the figure, this typical example has a structure in which the negative electrode current collector 1 is not in direct contact with the ionic liquid 4 filled in the container 3. With this structure, simultaneous contact of the negative electrode current collector, the negative electrode active material layer, and the electrolyte can be avoided, and decomposition of the ionic liquid due to the reaction of the three parties can be prevented.

  As one form of the lithium secondary battery of the present invention, a protective layer is further provided, and the negative electrode active material layer and the protection are provided between a part or all of at least one side of the negative electrode current collector and the electrolytic solution. A configuration in which layers are interposed can be employed.

Here, the protective layer refers to a layer that protects the negative electrode current collector from the electrolytic solution so that the electrolytic solution containing the ionic liquid does not contact the negative electrode current collector.
The material that can be used for the protective layer is not particularly limited as long as it is a material that has resistance to an electrolytic solution containing an ionic liquid and does not affect the power generation performance of the lithium secondary battery. It is preferable that the material can maintain high.
Specifically, as the protective layer having the above conditions, it is preferable to use a sealing material, more specifically, gaskets such as rubber gaskets, O-rings, metal gaskets, packings such as lip packings, oil seals, etc. Can be used. As these sealing materials, any of sealing materials made of organic materials such as natural rubber, synthetic rubber and Teflon (registered trademark), and sealing materials made of inorganic materials such as iron alloy, ceramic, graphite, and asbestos can be used. .

FIG. 2 is a diagram schematically showing a cross section cut in the stacking direction of a part of a modification of the lithium secondary battery according to the present invention. In addition, the double wavy line in the figure means omission of the figure.
FIG. 2 (a) shows a first modification of the lithium secondary battery according to the present invention, that is, a protective layer is laminated at least on the outer peripheral edge of one surface of the negative electrode current collector, A configuration example in which a negative electrode active material layer is stacked on at least the entire surface of a portion where the protective layer is not stacked is shown.
As shown in FIG. 2 (a), in the first modification, a seal material 9 is placed on the outer peripheral edge of one surface side of the negative electrode current collector 1, and further, in the central portion of the negative electrode current collector 1. The negative electrode active material layer 2 is applied. The outer peripheral edge of the negative electrode active material layer 2 is in contact with the sealing material 9 without any gap. In such a lithium secondary battery, since the sealing material 9 serving as the negative electrode active material layer 2 or the protective layer is interposed between the one surface side of the negative electrode current collector 1 and the electrolytic solution 4, the electrolytic solution 4 Does not leak to the negative electrode current collector 1 side, and therefore, the electrolyte solution, the negative electrode current collector, and the negative electrode active material layer do not contact at the same time.

FIG. 2B shows a second modification of the lithium secondary battery according to the present invention, that is, the negative electrode current collector is installed around the outer periphery of the negative electrode active material layer. An example of a structure in which a protective layer is laminated on the entire surface and a part of the negative electrode active material layer is shown.
As shown in FIG. 2 (b), in the second modification, the negative electrode current collector 1 surrounds the negative electrode active material layer 2, and further, the entire one surface side of the negative electrode current collector 1, The packing 10 is placed on the edge of the one surface side of the negative electrode active material layer 2, and the sealing material 9 is placed on the one surface side of the packing 10. In such a lithium secondary battery, since the negative electrode active material layer 2 or the sealing material 9 serving as a protective layer and the packing 10 are interposed between the one surface side of the negative electrode current collector 1 and the electrolytic solution 4, The electrolyte solution 4 does not leak to the negative electrode current collector 1 side, and the three components of the electrolyte solution, the negative electrode current collector, and the negative electrode active material layer do not contact at the same time.

FIG. 2C shows a third modification of the lithium secondary battery according to the present invention, that is, a negative electrode active material layer laminated on a part or all of one surface side of the negative electrode current collector. The structural example that the protective layer is laminated | stacked at least on the outer periphery part of the surface which is not in contact with the negative electrode collector is shown.
As shown in FIG. 2C, in the third modification, a negative electrode active material layer 2 is laminated on one surface side of the negative electrode current collector 1, and a seal is formed on the edge of one surface side of the negative electrode active material layer 2. It has a structure in which the material 9 is placed. In the case of the third modification, the negative electrode active material layer 2 is not necessarily laminated on the entire surface of the negative electrode current collector 1. In such a lithium secondary battery, since the negative electrode active material layer 2 or the sealing material 9 serving as a protective layer is interposed between the one surface side of the negative electrode current collector 1 and the electrolytic solution 4, the electrolytic solution 4 is There is no leakage to the negative electrode current collector 1 side, and the three components of the electrolytic solution, the negative electrode current collector, and the negative electrode active material layer do not contact at the same time.

FIG. 2D shows a fourth modification of the lithium secondary battery according to the present invention, that is, a negative electrode active material layer is laminated on one side of the negative electrode current collector, and the protective layer is a negative electrode current collector. And a structure composed of a negative electrode current collector, a negative electrode active material layer, and a protective layer (hereinafter simply referred to as a structure) is immersed in the electrolyte solution. A configuration example is shown.
As shown in FIG. 2D, in the fourth modification, a negative electrode active material layer 2 is laminated on one surface side of the negative electrode current collector 1, and the negative electrode current collector 1, the negative electrode active material layer 2, and the like. The seal material 9 is applied around the interface. In such a lithium secondary battery, even when the structure is placed in the electrolytic solution 4, the negative electrode active material layer 2 or the protective layer is provided between the one surface side of the negative electrode current collector 1 and the electrolytic solution 4. Therefore, the electrolyte solution 4 does not leak to the negative electrode current collector 1 side, and the three components of the electrolyte solution, the negative electrode current collector, and the negative electrode active material layer do not contact at the same time. .

  As described above, in any of the modifications shown in FIG. 2, the three parts of the electrolytic solution, the negative electrode current collector, and the negative electrode active material layer are not in contact with each other at the same time. Can prevent decomposition

  Hereinafter, the positive electrode and the negative electrode, the electrolytic solution containing the ionic liquid, and other components (such as a separator), which are the components of the lithium secondary battery of the present invention, will be described separately.

(Positive electrode and negative electrode)
The positive electrode of the lithium secondary battery according to the present invention preferably has a positive electrode active material layer having a positive electrode active material, and is usually connected to the positive electrode current collector and the positive electrode current collector. It has a positive electrode lead. In addition, when the lithium secondary battery which concerns on this invention is a lithium air battery, it has an air electrode containing an air electrode layer instead of the said positive electrode.
The negative electrode of the lithium secondary battery according to the present invention has the negative electrode laminate according to the present invention described above, and in addition to this, in general, the negative electrode connected to the negative electrode current collector of the negative electrode laminate. It has a lead.

(Positive electrode active material layer)
Hereinafter, the case where the positive electrode which has a positive electrode active material layer as a positive electrode is employ | adopted is demonstrated.
Specific examples of the positive electrode active material used in the present invention include LiCoO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNiPO ₄ , LiMnPO ₄ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoMnO _4. , Li ₂ NiMn ₃ O ₈ , Li ₃ Fe ₂ (PO ₄ ) _3, Li ₃ V ₂ (PO ₄ ) _{3 and the} like. Among these, in the present invention, LiCoO ₂ is preferably used as the positive electrode active material.

  The thickness of the positive electrode active material layer used in the present invention varies depending on the intended use of the lithium secondary battery, but is preferably in the range of 10 μm to 250 μm, and in the range of 20 μm to 200 μm. It is particularly preferred that it is most preferably in the range of 30 μm to 150 μm.

  The average particle diameter of the positive electrode active material is, for example, preferably in the range of 1 μm to 50 μm, more preferably in the range of 1 μm to 20 μm, and particularly preferably in the range of 3 μm to 5 μm. If the average particle size of the positive electrode active material is too small, the handleability may be deteriorated. If the average particle size of the positive electrode active material is too large, it may be difficult to obtain a flat positive electrode active material layer. Because. The average particle diameter of the positive electrode active material can be determined by measuring and averaging the particle diameter of the active material carrier observed with, for example, a scanning electron microscope (SEM).

The positive electrode active material layer may contain a conductive material, a binder, and the like as necessary.
The conductive material included in the positive electrode active material layer used in the present invention is not particularly limited as long as the conductivity of the positive electrode active material layer can be improved. For example, carbon black such as acetylene black and ketjen black Etc. Moreover, although content of the electrically conductive material in a positive electrode active material layer changes with kinds of electrically conductive material, it is in the range of 1 mass%-10 mass% normally.

  Examples of the binder included in the positive electrode active material layer used in the present invention include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Further, the content of the binder in the positive electrode active material layer may be an amount that can fix the positive electrode active material or the like, and is preferably smaller. The content of the binder is usually in the range of 1% by mass to 10% by mass.

(Positive electrode current collector)
The positive electrode current collector used in the present invention has a function of collecting the positive electrode active material layer. Examples of the material for the positive electrode current collector include aluminum, SUS, nickel, iron, and titanium. Of these, aluminum and SUS are preferable. Moreover, as a shape of a positive electrode electrical power collector, foil shape, plate shape, mesh shape etc. can be mentioned, for example, Foil shape is preferable.

  The electrode active material layer of at least one of the positive electrode and the negative electrode can also be configured to contain at least an electrode active material and an electrode electrolyte. In this case, as the electrode electrolyte, a solid electrolyte such as a solid oxide electrolyte or a solid sulfide electrolyte, a polymer electrolyte described later, a gel electrolyte, or the like can be used.

  The method for producing the positive electrode used in the present invention is not particularly limited as long as it is a method capable of obtaining the positive electrode. In addition, after forming a positive electrode active material layer, in order to improve an electrode density, you may press a positive electrode active material layer.

(Air electrode layer)
Hereinafter, the case where the air electrode which has an air electrode layer as a positive electrode is employ | adopted is demonstrated. The air electrode layer used in the present invention contains at least a conductive material. Furthermore, you may contain at least one of a catalyst and a binder as needed.

  The conductive material used for the air electrode layer used in the present invention is not particularly limited as long as it has conductivity, and examples thereof include a carbon material. Furthermore, the carbon material may have a porous structure or may not have a porous structure. However, in the present invention, the carbon material preferably has a porous structure. This is because the specific surface area is large and many reaction fields can be provided. Specific examples of the carbon material having a porous structure include mesoporous carbon. On the other hand, specific examples of the carbon material having no porous structure include graphite, acetylene black, carbon nanotube, and carbon fiber. As content of the electroconductive material in an air electrode layer, it is preferable to exist in the range of 65 mass%-99 mass%, for example in the range of 75 mass%-95 mass% especially. If the content of the conductive material is too small, the reaction field may decrease and the battery capacity may be reduced. If the content of the conductive material is too large, the content of the catalyst is relatively reduced and sufficient. This is because it may not be possible to exert a proper catalytic function.

Examples of the catalyst used for the air electrode layer used in the present invention include cobalt phthalocyanine and manganese dioxide. The catalyst content in the air electrode layer is, for example, preferably in the range of 1% by mass to 30% by mass, and more preferably in the range of 5% by mass to 20% by mass. If the catalyst content is too low, sufficient catalytic function may not be achieved. If the catalyst content is too high, the content of the conductive material is relatively reduced, the reaction field is reduced, and the battery capacity is reduced. This is because there is a possibility that a decrease in the number of times will occur.
From the viewpoint that the electrode reaction is performed more smoothly, the conductive material described above preferably supports a catalyst.

  The air electrode layer only needs to contain at least a conductive material, but preferably further contains a binder for fixing the conductive material. Examples of the binder include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE). Although it does not specifically limit as content of the binder in an air electrode layer, For example, it is preferable that it is in the range of 30 mass% or less, especially 1 mass%-10 mass%.

The thickness of the air electrode layer is different depending on the use of the air battery, for example, 2 μm to
It is preferable to be in the range of 500 μm, especially in the range of 5 μm to 300 μm.

(Air current collector)
The air electrode current collector used in the present invention collects current in the air electrode layer. The material for the air electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include stainless steel, nickel, aluminum, iron, titanium, and carbon. Examples of the shape of the air electrode current collector include a foil shape, a plate shape, and a mesh (grid) shape. Especially, in this invention, it is preferable that the shape of an air electrode electrical power collector is a mesh form. This is because the current collection efficiency is excellent. In this case, usually, a mesh-shaped air electrode current collector is disposed inside the air electrode layer. Furthermore, the secondary battery of the present invention may have another air electrode current collector (for example, a foil-shaped current collector) that collects the charges collected by the mesh-shaped air electrode current collector. good. In the present invention, a battery case to be described later may also have the function of an air electrode current collector.
The thickness of the air electrode current collector is, for example, preferably in the range of 10 μm to 1000 μm, and more preferably in the range of 20 μm to 400 μm.

(Negative electrode active material layer)
The negative electrode active material used for the negative electrode active material layer is not particularly limited as long as it can occlude / release lithium ions. For example, metal lithium, lithium alloy, metal oxide, metal sulfide, Examples thereof include metal nitrides and carbon materials such as graphite. The negative electrode active material may be in the form of a powder or a thin film.

The negative electrode active material layer may contain a conductive material, a binder, and the like as necessary.
As the binder and the conductive material that can be used in the negative electrode active material layer, those already described in the description of the positive electrode active material layer can be used. Moreover, it is preferable to select the usage-amount of a binder and a electrically conductive material suitably according to the use etc. of a lithium secondary battery. Further, the film thickness of the negative electrode active material layer is not particularly limited, but for example, it is preferably in the range of 10 μm to 100 μm, and more preferably in the range of 10 μm to 50 μm.

(Negative electrode current collector)
As the material and shape of the negative electrode current collector, the same materials and shapes as those of the positive electrode current collector described above can be employed.
As a manufacturing method of the negative electrode used in the present invention, a method similar to the manufacturing method of the positive electrode as described above can be adopted.

(Electrolyte containing ionic liquid)
The electrolytic solution containing an ionic liquid used in the present invention performs lithium ion exchange between the above-described positive electrode active material layer or air electrode layer and negative electrode active material. As the electrolytic solution containing the ionic liquid, the ionic liquid itself may be used, or a polymer electrolyte or gel electrolyte containing the ionic liquid may be used.
In addition, an ionic liquid is a substance which consists only of the ionic molecule which combined the cation and the anion, and points out the substance which is a liquid at normal temperature (15 to 25 degreeC).

  Examples of the cation species of the ionic liquid that can be used in the present invention include 2-ethylimidazolium, 3-propylimidazolium, 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1,3 - imidazolium such as dimethyl imidazolium diethyl methyl ammonium, tetrabutyl ammonium, cyclohexyl trimethylammonium methyl tri -n- octyl ammonium, triethyl (2-methoxyethoxymethyl) ammonium, benzyl dimethyl tetradecyl ammonium, ammonium and benzyl trimethylammonium Other examples include alkylpyridinium, dialkylpyrrolidinium, tetraalkylphosphonium, and trialkylsulfonium.

Examples of the anionic species of the ionic liquid that can be used in the present invention include halide anions such as Cl ⁻ , Br ⁻ and I ⁻ ; BF ₄ ⁻ , B (CN) ₄ ⁻ , B (C ₂ O ₄ ) ₂ ^{− and the} like. Boronide anion of amide anion or imide anion such as (CN) ₂ N ⁻ , [N (CF ₃ ) ₂ ] ⁻ , [N (SO ₂ CF ₃ ) ₂ ] ⁻ ; RSO ₃ ⁻ (hereinafter R is fat Sulfate anion such as RSO ₄ ⁻ , R ^f SO ₃ ⁻ (hereinafter, R ^f represents a fluorinated halogenated hydrocarbon group), R ^f SO ₄ ^{— and the} like. Or sulfonate anions; phosphate anions such as R ^f ₂ P (O) O ⁻ , PF ₆ ⁻ , R ^f ₃ PF ₃ ^— ; antimony anions such as SbF ₆ ; other, lactate, nitrate ions, trif Examples include uroacetate.

Further, a supporting salt may be dissolved in the ionic liquid. Examples of the supporting salt include salts composed of lithium ions and the above anions, such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiTFSI, and LiBETI. Two or more such supporting salts may be used in combination. Moreover, although the addition amount of the supporting salt with respect to an ionic liquid is not specifically limited, It is preferable to set it as about 0.1-1 mol / kg.

The polymer electrolyte that can be used together with the ionic liquid preferably contains a lithium salt and a polymer. The lithium salt is not particularly limited as long as it is a lithium salt used in a general lithium secondary battery. For example, LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , Examples include LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) _3, and LiClO ₄ . The polymer is not particularly limited as long as it forms a complex with a lithium salt, and examples thereof include polyethylene oxide.

The gel electrolyte that can be used together with the ionic liquid preferably contains a lithium salt, a polymer, and a nonaqueous solvent.
The lithium salt described above can be used as the lithium salt.
The non-aqueous solvent is not particularly limited as long as it can dissolve the lithium salt. For example, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1 , 2-diethoxyethane, acetonitrile, propionitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone, and the like. These nonaqueous solvents may be used alone or in combination of two or more. Moreover, room temperature molten salt can also be used as a non-aqueous electrolyte.
The polymer is not particularly limited as long as it can be gelled, and examples thereof include polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride (PVDF), polyurethane, polyacrylate, cellulose and the like. Can be mentioned.

(Other components)
As another component, a separator can be used for the lithium secondary battery of the present invention. The separator is disposed between the positive electrode current collector and the negative electrode current collector described above when two or more batteries are stacked, and usually prevents contact between the positive electrode active material layer and the negative electrode active material layer. And has a function of holding the electrolyte. Examples of the material for the separator include resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Among these, polyethylene and polypropylene are preferable. The separator may have a single layer structure or a multilayer structure. Examples of the separator having a multilayer structure include a separator having a two-layer structure of PE / PP and a separator having a three-layer structure of PP / PE / PP. Furthermore, in the present invention, the separator may be a nonwoven fabric such as a resin nonwoven fabric or a glass fiber nonwoven fabric. Moreover, the film thickness of the said separator is not specifically limited, It is the same as the film thickness of the separator used for a general lithium secondary battery.
Moreover, the battery case which accommodates the lithium secondary battery of this invention can also be used as another component. The shape of the battery case is not particularly limited as long as it can accommodate the above-described positive electrode, negative electrode, electrolyte, and the like, and specific examples include a cylindrical shape, a square shape, a coin shape, a laminate shape, and the like. be able to. When the lithium secondary battery of the present invention is a lithium air secondary battery, the battery case may be an open-air battery case or a sealed battery case. An open-air battery case is a battery case having a structure in which at least the air electrode layer can sufficiently come into contact with the atmosphere. On the other hand, when the battery case is a sealed battery case, it is preferable to provide a gas (air) introduction pipe and an exhaust pipe in the sealed battery case. In this case, the gas to be introduced / exhausted preferably has a high oxygen concentration, and more preferably pure oxygen. In addition, it is preferable to increase the oxygen concentration during discharging and decrease the oxygen concentration during charging.

1. Production of lithium secondary battery [Example]
First, a lithium metal thin film was prepared as a negative electrode active material layer, and a cylindrical SUS was prepared as a negative electrode current collector. A lithium metal thin film was covered on the substantially planar portion of the cylindrical SUS to complete the negative electrode.

Next, as raw materials for the positive electrode active material layer, Ketjen Black (KB) (manufactured by Mitsubishi Chemical Corporation: ECP600JD) 110 mg, manganese dioxide (MnO ₂ ) (Mitsui Metal Mining: HM370) 6.7 mg, polyvinylidene fluoride 500 mg of an N-methyl-2-pyrrolidone solution of resin (PVdF / NMP) (manufactured by Kureha Co., Ltd .: KF1320) and 3 g of N-methyl-2-pyrrolidone (NMP) as a solvent were added to the ointment container. Sealed with film (registered trademark).

  Next, an adapter for an ointment container was set in a rotation / revolution kneader, and an ointment container (weight: about 165 g) to which the raw material and solvent were added was set in the adapter. Kneading was performed under the conditions of a kneading rotation speed of 2000 rpm and a kneading time of 5 minutes, and defoaming was performed under conditions of a defoaming rotation speed of 2200 rpm and a defoaming time of 5 minutes.

  Next, as a positive electrode current collector, SUS304 mesh (manufactured by Iseya Wire Mesh Industry Co., Ltd .: # 50, wire diameter 0.12 mm) was punched into f15 mm and processed. The mesh was weighed to be 58 mg.

Next, an appropriate amount of paste after defoaming was applied to tweezers for coating, and coating was performed so as to sandwich the positive electrode current collector mesh. Then, it pre-dried with the dryer until the appearance dried.
After the pre-drying, main drying was performed using a hot plate under the conditions of a drying temperature of 150 ° C. and a drying time of 30 minutes to complete the positive electrode. When the positive electrode after the main drying was weighed and the difference between the weight of the entire laminate and the mesh weight was calculated, the weight of the positive electrode was 3.0 mg.

  FIG. 3 is a schematic cross-sectional view of a lithium-air secondary battery of an example incorporating the negative electrode and the positive electrode prepared by the above-described steps. In the cylindrical negative electrode current collector 1, the substantially planar portion of the cylinder is completely covered with the negative electrode active material layer 2. For this reason, the negative electrode current collector 1 is configured not to be in direct contact with the ionic liquid 4 filled in the Teflon (registered trademark) container 3. Oxygen (1 atm) is supplied from the oxygen tank 6 to the air electrode 5 facing the negative electrode active material layer 2 with the ionic liquid 4 interposed therebetween. Further, a negative electrode lead 7 was installed on the negative electrode active material layer 2 side, and an air electrode lead 8 was installed on the air electrode 5 side. The distance between the negative electrode active material layer 2 and the air electrode 5 was 2 cm. As the ionic liquid used as the electrolytic solution, N-methyl-N-propylpiperidinium-bis (trifluoromethylsulfonyl) amine (hereinafter referred to as PP13-TFSA) was used.

[Comparative example]
The production of the lithium secondary battery of the comparative example was performed in the same manner as in the above example except for the negative electrode.
FIG. 5 is a schematic sectional view of a lithium-air secondary battery of a comparative example, and is the same as the apparatus shown in FIG. 3 except for the negative electrode portion. The device shown in FIG. 5 uses a negative electrode in which the negative electrode active material layer 12 is laminated on the negative electrode current collector 11 as it is. The negative electrode active material layer 12 does not cover one surface side of the negative electrode current collector 11, and therefore, the negative electrode current collector 11, the negative electrode active material layer 12, and the ions are surrounded by a broken line in FIG. 5. There are three coexisting sites of liquid 4.

2. Gas analysis after charge / discharge
Using the lithium-air secondary battery shown in FIG. 3 and FIG. 5, after charging and discharging once for 250 hours, the amount of propylene gas and methylpiperidine gas generated along with the decomposition of PP13-TFSA as an electrolytic solution Analysis was carried out. A gas chromatograph (GSLJ9810, manufactured by Agilent Technologies) was used for gas analysis.

As can be seen from Table 1 above, when the lithium secondary battery of the comparative example was used, the generation amounts of propylene gas and methylpiperidine gas were both 0.4%. On the other hand, when the lithium secondary battery of the example was used, the generation amounts of propylene gas and methylpiperidine gas were both below the detection limit of the analytical instrument.
From the above, in the lithium secondary battery of the comparative example having a portion where the negative electrode current collector, the negative electrode active material layer, and the ionic liquid that is the electrolytic solution are in contact with each other at the same time, the decomposition of PP13-TFSA that is the ionic liquid In contrast, in the lithium secondary battery of the example in which these three members do not have a portion in contact with each other at the same time, it became clear that the ionic liquid was not decomposed at all.

DESCRIPTION OF SYMBOLS 1 Negative electrode collector 2 Negative electrode active material layer 3 Container 4 Ionic liquid 5 Air electrode 6 Oxygen tank 7 Negative electrode lead 8 Air electrode lead 9 Sealing material 10 Packing 11 Negative electrode current collector 12 Negative electrode active material layer

Claims (7)

A lithium secondary battery having at least a positive electrode, a negative electrode, and an electrolyte solution interposed between the positive electrode and the negative electrode,
The negative electrode includes at least a negative electrode current collector and a negative electrode active material layer,
The electrolyte includes an ionic liquid;
The negative electrode active material layer is interposed between part or all of at least one side of the negative electrode current collector and the electrolytic solution,
A lithium secondary battery characterized in that there is no portion where the electrolyte solution, the negative electrode current collector, and the negative electrode active material layer are in contact with each other at the same time. In addition, with a protective layer,
The lithium secondary battery according to claim 1, wherein the negative electrode active material layer and the protective layer are interposed between a part or all of at least one side of the negative electrode current collector and the electrolytic solution. The protective layer is laminated at least on the outer peripheral edge of one surface side of the negative electrode current collector,
3. The lithium secondary battery according to claim 2, wherein the negative electrode active material layer is laminated on at least the entire surface of the portion where the protective layer on the one surface side is not laminated. The negative electrode current collector is installed around the outer periphery of the negative electrode active material layer;
The lithium secondary battery according to claim 2, wherein the protective layer is laminated on the entire surface of one surface of the negative electrode current collector and a part of the negative electrode active material layer. The negative electrode active material layer is laminated on a part or all of one surface side of the negative electrode current collector,
The lithium secondary battery according to claim 2, wherein the protective layer is laminated at least on the outer peripheral edge of the surface of the negative electrode active material layer that is not in contact with the negative electrode current collector. The negative electrode active material layer is laminated on one side of the negative electrode current collector,
The protective layer is disposed around the outer periphery of the interface between the negative electrode current collector and the negative electrode active material layer;
The lithium secondary battery according to claim 2, wherein a structure including the negative electrode current collector, the negative electrode active material layer, and the protective layer is immersed in the electrolytic solution.   The lithium secondary battery according to claim 1, which is a lithium air battery.

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