JP2016081801A - Electrode for positive electrode, and nonaqueous electrolyte power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a positive electrode, which enables the increase in charge and discharge efficiencies without decreasing the capacity of a nonaqueous electrolyte power storage device, and enables the suppression of self discharge.SOLUTION: (1) An electrode for a positive electrode of a nonaqueous electrolyte power storage device comprises: a positive electrode current collector; and a positive electrode material layer formed on the positive electrode current collector, including at least a positive electrode active material consisting of soft carbon which allows anions to go thereinto and out thereof, and a conductive assistant. As to the quantity of the conductive assistant per unit area in a thickness direction of the positive electrode material layer, the following condition holds: Positive electrode current collector interface>Electrolyte interface. (2) A nonaqueous electrolyte power storage device comprises at least, a positive electrode, a negative electrode and a nonaqueous electrolyte; the electrode for a positive electrode as described in (1) is used as the positive electrode.SELECTED DRAWING: None

Description

  The present invention relates to a positive electrode and a non-aqueous electrolyte storage element using the same.

In recent years, with the miniaturization and high performance of portable devices, non-aqueous electrolyte secondary batteries having a high energy density have become widespread. Attempts have also been made to improve the weight energy density of non-aqueous electrolyte secondary batteries with the aim of developing applications in electric vehicles.
Conventionally, a lithium ion secondary battery having a positive electrode such as a lithium cobalt composite oxide, a carbon negative electrode, and a nonaqueous electrolytic solution in which a lithium salt is dissolved in a nonaqueous solvent has been widely used.
On the other hand, materials such as conductive polymers and carbonaceous materials are used for the positive electrode, and anions in the non-aqueous electrolyte are inserted into or removed from the positive electrode, and lithium ions in the non-aqueous electrolyte are converted into carbonaceous materials. A non-aqueous electrolyte secondary battery (hereinafter sometimes referred to as “dual carbon battery”) that is charged and discharged by being inserted into or removed from a negative electrode made of a material is known (see Non-Patent Document 1). ).

In the dual carbon battery, for example, as shown in the following reaction formula, an anion such as PF ₆ ⁻ is inserted into the positive electrode from the nonaqueous electrolytic solution, and Li ⁺ is inserted into the negative electrode from the nonaqueous electrolytic solution. Charging is performed, and an anion such as PF ₆ ⁻ is desorbed from the positive electrode, and Li ⁺ is desorbed from the negative electrode, thereby discharging.

The discharge capacity of the dual carbon battery is determined by the anion storage amount of the positive electrode, the anion release amount of the positive electrode, the cation storage amount of the negative electrode, the cation release amount of the negative electrode, the anion amount and the cation amount in the non-aqueous electrolyte. For this reason, in order to increase the discharge capacity of the dual carbon battery, in addition to the positive electrode active material and the negative electrode active material, it is necessary to increase the amount of the non-aqueous electrolyte containing a lithium salt (see Non-Patent Document 1).
The dual carbon battery can be charged at a high voltage of 5 V or more. However, under a high voltage, the decomposition of the electrolytic solution is increased and the charge / discharge efficiency is deteriorated. The reaction area of the liquid is reduced, and charge / discharge efficiency can be improved. In order to reduce the reaction area, an active material having a small surface area may be selected or the amount of the conductive aid in the electrode may be reduced. However, since the performance of the battery depends on the active material, it is difficult to change the active material.
Therefore, to improve the charge / discharge efficiency, it is effective to reduce the conductive assistant in the electrode near the electrolyte interface. However, in order to bring out the capacity of the battery, the conductive path between the current collector and the electrode must be sufficient, so there is a minimum amount of conductive aid at the electrolyte and electrode interface, and the current collector and electrode interface. It is effective to improve the characteristics of the battery.

Further, the dual carbon battery has a problem of suppressing self-discharge. In order to suppress self-discharge, it is effective to increase the resistance at the interface between the electrolyte and the electrode so that ions in the electrode are not easily emitted.
As a known technique, Patent Document 1 discloses an invention in which a conductive film is formed on the surface of a current collector by an electrodeposition coating method to increase the adhesion between the electrode and the current collector, thereby reducing the internal resistance.
Patent Document 2 discloses an invention in which the content of the conductive additive in the electrode is changed to enable high output of the power storage element.
Non-Patent Document 2 discloses a technique for reducing the internal resistance of a battery by applying a carbon base layer to an aluminum current collector.

An object of this invention is to provide the electrode for positive electrodes which can improve charging / discharging efficiency and suppress self-discharge, without reducing the capacity | capacitance of a non-aqueous electrolyte storage element.
Note that the inventions of Patent Documents 1 and 2 are different from the present invention in subject and configuration, and cannot solve the problem of the present invention. Moreover, the said nonpatent literature 2 does not have description regarding the subject of this invention, and it is unknown whether the subject of this invention can be solved.

The above problem is solved by the following invention 1).
1) A positive electrode for a non-aqueous electrolyte storage element in which a positive electrode active material composed of soft carbon capable of inserting and releasing anions and a positive electrode material layer containing at least a conductive additive are formed on a positive electrode current collector. The positive electrode is characterized in that the amount of the conductive additive per unit area in the thickness direction of the positive electrode material layer is positive electrode collector interface> electrolyte interface.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode for positive electrodes which can improve charging / discharging efficiency and suppress self-discharge can be provided, without reducing the capacity | capacitance of a non-aqueous-electrolyte electrical storage element.

It is a schematic diagram which shows the structure of the electrode for positive electrodes of this invention. The figure which shows the discharge capacity in each cycle of Examples 1-2 and the comparative example 1. FIG. The figure which shows the charging / discharging efficiency in each cycle of Examples 1-2 and the comparative example 1. FIG. The figure which shows the capacity | capacitance maintenance factor of Examples 1-2 and the comparative example 1. FIG.

Hereinafter, the present invention 1) will be described in detail, but the following 2) to 6) are also included in the embodiment, and these will also be described together.
2) A positive electrode material layer that does not include a positive electrode active material and includes a conductive additive is formed on the positive electrode current collector side, and a positive electrode material layer that includes a positive electrode active material and does not include a conductive additive is formed thereon. The electrode for positive electrodes as described in 1).
3) A positive electrode material layer containing a positive electrode active material and a conductive auxiliary agent is formed on the positive electrode current collector side, and a positive electrode material layer containing a positive electrode active material and no conductive auxiliary agent is formed thereon 1 The electrode for positive electrodes as described in).
4) A non-aqueous electrolyte storage element comprising at least a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode according to any one of 1) to 3) is used as the positive electrode.
5) The nonaqueous electrolyte storage element according to 4), wherein the concentration of the electrolyte salt contained in the nonaqueous electrolyte is 2 mol / L or more.
6) The working voltage range of the positive electrode is 2.5 V to 5.5 V vs Li / Li ⁺ , and the nonaqueous electrolyte storage element according to 5).

<Configuration of positive electrode>
FIG. 1 is a schematic diagram showing the configuration of the positive electrode of the present invention.
As shown in FIG. 1, the positive electrode of the present invention has a positive electrode material layer containing at least a positive electrode active material made of soft carbon capable of inserting and removing anions and a conductive additive on a positive electrode current collector. The distribution state of the conductive additive in the positive electrode material layer (the amount of conductive additive per unit area in the electrode thickness direction) is positive electrode collector interface> electrolyte interface. This feature improves the charge / discharge efficiency by reducing the amount of conductive additive present at the interface between the electrolyte and the positive electrode compared to the conventional positive electrode, and suppresses self-discharge because the resistance at the interface increases. The
It is preferable that the difference in the amount of the conductive additive between the positive electrode current collector interface and the electrolyte solution interface in the positive electrode material layer is large. Further, the positive electrode material layer at the positive electrode current collector interface may be composed of a positive electrode material that does not contain a positive electrode active material and contains a conductive additive, or the positive electrode material layer at the electrolyte solution interface contains a positive electrode active material and a conductive additive. You may be comprised with the positive electrode material which does not contain.

The positive electrode layer as described above is, for example, a slurry-like positive electrode material composition (1) that does not contain a positive electrode active material and contains a conductive additive, or a slurry-like positive electrode material composition (2 that contains a positive electrode active material and a conductive additive). And a slurry-like positive electrode material composition (3) which contains a positive electrode active material and does not contain a conductive additive or contains a conductive auxiliary agent less than (2), and a positive electrode on the positive electrode current collector It can be formed by applying the material composition (1) or (2), and then applying the positive electrode material composition (3) thereon and drying it. There is no restriction | limiting in particular in the thickness of each layer which consists of said positive electrode material composition (1)-(3), According to the objective, it can change suitably.
Moreover, it is also possible to set it as the positive electrode agent layer of the 3 or more layer structure which changed content of the conductive support agent so that it might become positive electrode collector interface> electrolyte solution interface as needed.

<Non-aqueous electrolyte storage element>
The non-aqueous electrolyte storage element of the present invention includes a positive electrode, a negative electrode, a non-aqueous electrolyte, a separator, and other members.
<Positive electrode>
The configuration of the positive electrode (positive electrode) is as described above, and includes at least a positive electrode material layer and a positive electrode current collector.
There is no restriction | limiting in particular in the shape of a positive electrode, According to the objective, it can select suitably, For example, flat form etc. are mentioned.

<< Positive electrode material >>
The positive electrode material is not particularly limited and may be appropriately selected depending on the purpose. However, it includes at least a positive electrode active material composed of soft carbon capable of inserting and removing anions and a conductive additive, and optionally includes a binder and a thickening agent. Including agents.

-Positive electrode active material-
As the positive electrode active material, soft carbon whose (002) plane spacing d (002) measured by X-ray diffraction is 0.34 nm to 0.36 nm is used. If d (002) is smaller than 0.34 nm, it generally exhibits the properties of graphite and has a high capacity, but it has poor load characteristics, particularly large current charging characteristics. On the other hand, when d (002) is larger than 0.36 nm, it generally exhibits the properties of non-graphitized carbon or activated carbon, and the anion is only adsorbed on the surface and hardly intercalates between the layers. I can't get it.
Examples of the soft carbon include those obtained by firing coke, meso-face pitch or the like at a temperature of about 2000 ° C. or less.

-Conductive aid-
As a conductive support agent, carbonaceous materials, such as metal materials, such as copper and aluminum, carbon black, and acetylene black, etc. are mentioned, for example. These may be used individually by 1 type and may use 2 or more types together.

-Binder-
The binder is not particularly limited as long as it is a material that is stable with respect to a solvent, an electrolytic solution, and an applied potential that are used in the production of the positive electrode, and can be appropriately selected according to the purpose.
Examples thereof include fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), isoprene rubber, and polyacrylate. These may be used individually by 1 type and may use 2 or more types together.

-Thickener-
Examples of the thickener include carboxymethyl cellulose (CMC), methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphate starch, and casein. These may be used individually by 1 type and may use 2 or more types together.

<< Positive electrode current collector >>
The material, shape, size, and structure of the positive electrode current collector are not particularly limited and can be appropriately selected according to the purpose.
The material of the positive electrode current collector is not particularly limited as long as it is made of a conductive material and is stable with respect to the applied potential, and can be appropriately selected according to the purpose. Examples thereof include stainless steel, nickel, aluminum, titanium, tantalum, and the like. Among these, stainless steel and aluminum are particularly preferable, and aluminum that is easy to manufacture foil and inexpensive is particularly preferable.
There is no restriction | limiting in particular in the shape of a positive electrode electrical power collector, According to the objective, it can select suitably.
The size of the positive electrode current collector is not particularly limited as long as it is a size that can be used for the nonaqueous electrolyte storage element, and can be appropriately selected according to the purpose.

-Method for producing positive electrode-
The positive electrode can be produced by applying a positive electrode active material, a conductive additive, and, if necessary, a positive electrode material composition in a slurry form by adding a binder, a thickener, a solvent, and the like onto the positive electrode current collector and drying it. . In the case of forming a layer consisting of only a conductive aid or a layer having a different content of the conductive aid, a positive electrode material composition in which the content of the conductive aid is appropriately changed may be prepared.
There is no restriction | limiting in particular as said solvent, According to the objective, it can select suitably, For example, an aqueous solvent, an organic solvent, etc. are mentioned. Examples of the aqueous solvent include water, alcohol, and the like. Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP), toluene, and the like.
In addition, the positive electrode active material can be roll-formed as it is to form a sheet electrode, or a pellet electrode by compression molding.

<Negative electrode>
There is no restriction | limiting in particular in a negative electrode, According to the objective, it can select suitably, For example, the negative electrode which formed the negative electrode material layer which has a negative electrode active material on a negative electrode collector etc. are mentioned.
There is no restriction | limiting in particular in the shape of a negative electrode, According to the objective, it can select suitably, For example, flat form etc. are mentioned.

<< Anode Material >>
The negative electrode material includes at least a negative electrode active material, and further includes a binder, a conductive auxiliary agent, and the like as necessary.

-Negative electrode active material-
The negative electrode active material is not particularly limited as long as it is a substance that functions at least in a non-aqueous solvent system, and can be appropriately selected according to the purpose. Examples thereof include graphite (graphite) such as artificial graphite and natural graphite, hard carbon, soft carbon, coke, lithium titanate, spinel compound, and the like. Among these, artificial graphite, natural graphite, hard carbon, and soft carbon are particularly preferable.

-Binder-
There is no restriction | limiting in particular as a binder, According to the objective, it can select suitably. Examples include fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), ethylene-propylene-butadiene rubber (EPBR), styrene-butadiene rubber (SBR), isoprene rubber, carboxymethylcellulose (CMC). ), Etc. These may be used individually by 1 type and may use 2 or more types together. Among these, fluorine-based binders such as PVDF and PTFE and CMC are preferable, and CMC is particularly preferable because the number of repeated charge / discharge cycles is improved as compared with other binders.

-Conductive aid-
As a conductive support agent, carbonaceous materials, such as metal materials, such as copper and aluminum, carbon black, and acetylene black, etc. are mentioned, for example. These may be used individually by 1 type and may use 2 or more types together.

<< Negative electrode current collector >>
The material, shape, size, and structure of the negative electrode current collector are not particularly limited and can be appropriately selected depending on the purpose.
The material of the negative electrode current collector is not particularly limited as long as it is formed of a conductive material, and can be appropriately selected according to the purpose. Examples thereof include stainless steel, nickel, aluminum, and copper. . Among these, stainless steel and copper are particularly preferable.
There is no restriction | limiting in particular in the shape of a negative electrode electrical power collector, According to the objective, it can select suitably.
The size of the negative electrode current collector is not particularly limited as long as it is a size that can be used for the nonaqueous electrolyte storage element, and can be appropriately selected according to the purpose.

-Negative electrode manufacturing method-
The negative electrode can be produced by applying a negative electrode material composition in the form of a slurry by adding a binder, a conductive additive, a solvent and the like to the negative electrode active material as necessary, and drying the composition.
As the solvent, the same solvent as in the method for manufacturing the positive electrode can be used.
In addition, a negative electrode active material added with a binder, a conductive additive, etc. can be roll-formed as it is to form a sheet electrode, a pellet electrode by compression molding, or vapor deposition, sputtering, plating, etc. on the negative electrode current collector A thin film of a negative electrode active material can also be formed.

<Non-aqueous electrolyte>
The nonaqueous electrolytic solution is an electrolytic solution containing a nonaqueous solvent and an electrolyte salt.

<< Non-aqueous solvent >>
There is no restriction | limiting in particular as a non-aqueous solvent, Although it can select suitably according to the objective, An aprotic organic solvent is suitable.
As the aprotic organic solvent, carbonate-based organic solvents such as chain carbonates and cyclic carbonates are used, and low viscosity solvents are preferred. Among these, a chain carbonate is preferable from the viewpoint of low viscosity and high electrolyte salt dissolving power.
Examples of the chain carbonate include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and the like. Among these, DMC is preferable.
There is no restriction | limiting in particular in content of the said chain carbonate, According to the objective, it can select suitably.

Examples of the cyclic carbonate include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), and the like.
The mixing ratio in the case of using a mixed solvent of EC of the cyclic carbonate and DMC of the chain carbonate is not particularly limited and can be appropriately selected according to the purpose. However, EC: DMC = 3: 10 to 1:99 are preferable, and 3:10 to 1:20 are more preferable.

In addition, as said non-aqueous solvent, ester type organic solvents, such as cyclic ester and chain ester, ether type organic solvents, such as cyclic ether and chain ether, etc. can be used as needed.
Examples of the cyclic ester include γ-butyrolactone (γBL), 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, and γ-valerolactone.
Examples of the chain ester include propionic acid alkyl ester, malonic acid dialkyl ester, acetic acid alkyl ester (methyl acetate, ethyl acetate, etc.), formic acid alkyl ester (methyl formate, ethyl formate, etc.), and the like.
Examples of the cyclic ether include tetrahydrofuran, alkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane, and the like.
Examples of the chain ether include 1,2-dimethoxyethane (DME), diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, and tetraethylene glycol dialkyl ether.

<< Electrolyte salt >>
The electrolyte salt is not particularly limited as long as it contains a halogen atom, dissolves in a non-aqueous solvent, and exhibits high ionic conductivity, but a salt composed of lithium and various anions is preferable.
Examples of the anion include Cl ⁻ , Br ⁻ , I ⁻ , ClO ₄ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , SbF ₆ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ , and the like.

There is no restriction | limiting in particular as said lithium salt, According to the objective, it can select suitably. Examples thereof include lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium chloride (LiCl), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), tri Lithium fluorometasulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide [LiN (C ₂ F ₅ SO ₂ ) ₂ ], lithium bisfurfluoroethylsulfonylimide [LiN (CF ₂ F ₅ SO ₂ ) ₂ ] , Etc. These may be used individually by 1 type and may use 2 or more types together. Among these, LiPF ₆ is particularly preferable from the viewpoint of the amount of occlusion of anions in the carbon electrode.

In the nonaqueous electrolyte storage element of the present invention, charging is performed by co-insertion of an anion and a cation. Therefore, the concentration of the electrolyte salt is preferably 2 mol / L or more in the non-aqueous solvent from the viewpoint of improving the energy density. Moreover, 5 mol / L or less is preferable so that the viscosity of the non-aqueous electrolyte does not increase to increase the ionic conductivity and increase the resistance. In particular, 2.5 to 4 mol / L is preferable from the viewpoint of both the capacity and output of the electricity storage element.
For example, assuming that the porosity of the separator is as close to 0 as possible, in an electrode having an active material specific capacity of 180 mAh, a diameter of 16 mm, and a thickness of 150 μm, the positive electrode has a porosity of 0.5 and the negative electrode has a porosity of 0.6. Sometimes, the electrolyte that can be held on the positive electrode is 0.01 mL, and the electrolyte that can be held on the negative electrode is 0.016 mL. From the electrolyte held on the positive electrode and the negative electrode, 67 μmol of the electrolyte required for charging the storage element can be obtained. An electrolyte solution having an electrolyte concentration of at least 2.6 mol / L is required.

<< Additives >>
As the additive, trishexafluoroisopropyl borate (THFIPB) and trispentafluorophenylborane (TPFPB), which are compounds having a site capable of chemically binding an anion containing a halogen atom, are preferable. Moreover, as a compound which forms interphase solid electrolyte (SEI) on the negative electrode surface, a cyclic carbonate is preferable and especially fluoroethylene carbonate (FEC) and EC which form favorable SEI on a negative electrode are preferable.
The content of the compound having a moiety capable of binding an anion containing a halogen atom can be appropriately selected according to the purpose.
Whether or not a compound having a portion capable of binding an anion containing a halogen atom is contained in the nonaqueous electrolyte storage element is determined by decomposing the nonaqueous electrolyte storage element and gas chromatography. It can be confirmed by analyzing with a graph.

<Separator>
The separator is provided between the positive electrode and the negative electrode in order to prevent a short circuit between the positive electrode and the negative electrode.
There is no restriction | limiting in particular in the material of a separator, a shape, a magnitude | size, and a structure, According to the objective, it can select suitably.
Examples of the material of the separator include paper such as kraft paper, vinylon mixed paper, synthetic pulp mixed paper, cellophane, polyethylene graft film, polyolefin nonwoven fabric such as polypropylene melt blown nonwoven fabric, polyamide nonwoven fabric, and glass fiber nonwoven fabric.
Examples of the shape of the separator include a sheet shape.
The size of the separator is not particularly limited as long as it is a size that can be used for the nonaqueous electrolyte storage element, and can be appropriately selected according to the purpose.
The structure of the separator may be a single layer structure or a laminated structure.

<Other members>
There is no restriction | limiting in particular as another member, According to the objective, it can select suitably, For example, a battery can, an electrode extraction line, etc. are mentioned.

<Method for Manufacturing Nonaqueous Electrolyte Storage Element>
The non-aqueous electrolyte storage element of the present invention can be produced by assembling the positive electrode, the negative electrode, the non-aqueous electrolyte, and the separator used as necessary into an appropriate shape. Furthermore, other constituent members such as a battery outer can can be used as necessary.
There is no restriction | limiting in particular in the said assembly method, It can select suitably from the methods employ | adopted normally.
There is no restriction | limiting in particular in the shape of the said nonaqueous electrolyte storage element, It can select suitably from the various shapes generally employ | adopted according to the use.
Examples include a cylinder type in which a sheet electrode and a separator are spiraled, a laminate cell type in which a sheet electrode and a separator are stacked, an inside-out structure cylinder type in which a pellet electrode and a separator are combined, a coin in which a pellet electrode and a separator are stacked. Type, etc.

<Operation method of nonaqueous electrolyte storage element>
The working voltage range of the nonaqueous electrolyte storage element of the present invention is preferably 2.5 V to 5.5 V vs Li / Li ⁺ . When the voltage is less than 2.5 V vs Li / Li ⁺ , sufficient capacity of the power storage element cannot be obtained, and when the voltage exceeds 5.5 V vs Li / Li ⁺ , the decomposition reaction of the electrolyte is dominant, and the power storage element Because it will break.

<Application of non-aqueous electrolyte storage element>
There is no restriction | limiting in particular in the use of the nonaqueous electrolyte storage element of this invention, It can use for various uses. Examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, and transceivers. Electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, lighting equipment, toys, game machines, watches, strobes, cameras, etc.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated further more concretely, this invention is not limited at all by these Examples. In the examples, “%” is “mass%”.

Comparative Example 1
-Fabrication of positive electrode A-
(The positive electrode A does not satisfy the requirements of the present invention, and the amount of the conductive additive per unit area in the electrode thickness direction is the current collector interface = electrolyte interface).
<< Positive electrode material composition A >>
19% 2% aqueous solution of carboxymethylcellulose (CMC) as a thickener, 3.75 g of 20% acetylene black aqueous dispersion (manufactured by Mikuni Dye Co., Ltd.) as a conductive additive, 10 g of soft carbon powder of positive electrode active material (SMC manufactured by Hitachi Chemical Co., Ltd.) Then, 2 g of pure water was added to 0.746 g of an acrylate binder (manufactured by JSR: TRD202A) and kneaded to prepare a slurry-like positive electrode material composition A (slurry A).

<< Preparation of Positive Electrode Material Layer A and Positive Electrode A >>
Slurry A was applied onto an aluminum foil current collector, dried at room temperature for 2 hours, and further dried with warm air at 120 ° C. for 5 minutes to form positive electrode material layer A. Next, the obtained laminate was punched into a round shape with a diameter of 16 mm to produce a positive electrode A. The mass of the positive electrode active material in the positive electrode A was 20 mg, and the average thickness of the positive electrode material layer A was 142 μm.

-Production of negative electrode A-
Carbon is added to 10 g of carbon powder of negative electrode active material (graphite: manufactured by Hitachi Chemical Co., Ltd., MAGD) and 2.5 g of 20% acetylene black aqueous dispersion of conductive additive (manufactured by Mikuni Dye Co., Ltd.). 10 g of a CMC 2% aqueous solution of the material was added and kneaded to prepare a slurry-like negative electrode material layer composition. Next, this slurry was applied onto a copper foil current collector, dried at room temperature for 2 hours, and further dried at 120 ° C. for 5 minutes to form a negative electrode material layer. Next, the obtained laminate was punched into a round shape with a diameter of 16 mm to produce a negative electrode A. The mass of the carbon powder (graphite) in the negative electrode A was 20 mg, and the average thickness of the negative electrode material layer was 130 μm.

<Non-aqueous electrolyte>
2.0 mol / L LiPF ₆ was dissolved in a mixture of dimethyl carbonate (DMC), ethylene carbonate (EC) and fluoroethylene carbonate (FEC) [DMC / EC / FEC = 96/2/2 (vol%)]. A non-aqueous electrolyte was prepared.

<Separator>
A glass separator, GA-100 GLASS FIBER (GF) FILTER (manufactured by ADVANTEC) was prepared.

<Measurement of Charge / Discharge Efficiency of Nonaqueous Electrolyte Storage Element (Secondary Battery) A Using Positive Electrode A>
The positive electrode A, the separator, the non-aqueous electrolyte solution, and the negative electrode A were placed in a can for producing a coin-type electricity storage device (2032 type, manufactured by Hosen Co., Ltd.) to prepare a non-aqueous electrolyte storage device A.
About this electrical storage element A, the following charging / discharging tests were done using TOSCAT-3100 (made by Toyo System Co., Ltd.) as a test apparatus.
The storage element A was charged to a charge end voltage of 5.2 V at a constant current of 0.5 mA / cm ² : ² mA at room temperature (25 ° C.). Next, the battery was discharged to a final discharge voltage of 3.0 V with a constant current of 0.5 mA / cm ² : ² mA. This was defined as one cycle, and 10 cycles of charge / discharge were performed.
The discharge capacity in each cycle is shown in FIG.
Moreover, the value of the discharge capacity / charge capacity in each cycle is the charge / discharge efficiency, which is shown in Table 1 and FIG.

<Measurement of Self-Discharge of Nonaqueous Electrolyte Storage Element (Secondary Battery) A Using Positive Electrode A>
About the said electrical storage element A, the following tests were done using the same test apparatus as the above.
The storage element A was charged to a charge end voltage of 5.2 V at a constant current of 0.5 mA / cm ² : ² mA at room temperature (25 ° C.). Next, the battery was discharged to a final discharge voltage of 3.0 V with a constant current of 0.5 mA / cm ² : ² mA. The discharge capacity at this time is defined as a discharge capacity X1.
Thereafter, the battery was allowed to stand at a constant current of 0.5 mA / cm ² : ² mA up to a charge end voltage of 5.2 V, and then further left for 6 hours. Thereafter, the battery was discharged at a constant current of 0.5 mA / cm ² : ² mA to a final discharge voltage of 3V. The discharge capacity at this time is defined as a discharge capacity Y1.
The discharge capacity X1 / discharge capacity Y1 is a capacity maintenance rate in 6 hours self-discharge.
Next, the battery was charged to a charge end voltage of 5.2 V at a constant current of 0.5 mA / cm ² : ² mA at room temperature (25 ° C.). Next, the battery was discharged to a final discharge voltage of 3.0 V with a constant current of 0.5 mA / cm ² : ² mA. The discharge capacity at this time is defined as a discharge capacity X2.
Thereafter, the battery was allowed to stand at a constant current of 0.5 mA / cm ² : ² mA up to a charge end voltage of 5.2 V, and then further left for 12 hours. Thereafter, the battery was discharged to a final discharge voltage of 3 V at a constant current of 0.5 mA / cm ² : ² mA. The discharge capacity at this time is defined as a discharge capacity Y2.
The discharge capacity X2 / discharge capacity Y2 is the capacity retention rate in 12 hours self-discharge.
As a result of the above test, the capacity retention rate in 6 hours self-discharge was 86.34%, and the capacity retention rate in 12 hours self-discharge was 79.41%. This is shown in FIG.

Example 1
-Production of positive electrode B-
<< Positive electrode material composition B >>
A slurry of CMC 2% aqueous solution of thickener 19 g, soft carbon powder of positive electrode active material (SMC manufactured by Hitachi Chemical Co., Ltd.) 10 g, 0.746 g of acrylate binder (manufactured by JSR: TRD202A) 0.76 g of pure water, kneaded and kneaded into slurry -Shaped positive electrode material composition B (slurry B) was produced.

<< Preparation of Positive Electrode Material Layer B and Positive Electrode B >>
The slurry A produced in Comparative Example 1 was applied onto an aluminum foil current collector, dried with warm air at 120 ° C. for 5 minutes, then coated with the slurry B, dried at room temperature for 2 hours, and further dried at 120 ° C. Was dried with warm air for 5 minutes to form a positive electrode material layer B having a two-layer structure. Next, the obtained laminate was punched into a round shape with a diameter of 16 mm to produce a positive electrode B. The thickness of the positive electrode material composition A in the positive electrode B was 35 μm, and the thickness of the positive electrode material composition B was 125 μm. Moreover, the mass of the positive electrode active material in the positive electrode B was 20 mg, and the average thickness of the positive electrode material layer B was 141 μm.

<Measurement of Charge / Discharge Efficiency of Nonaqueous Electrolyte Storage Element (Secondary Battery) B Using Positive Electrode B>
Except that the positive electrode A in the electricity storage device A of Comparative Example 1 was changed to the positive electrode B, a non-aqueous electrolyte electricity storage device B was prepared in the same manner as in Comparative Example 1, and a charge / discharge test was performed.
The discharge capacity in each cycle is shown in FIG.
The charge / discharge efficiency in each cycle is shown in Table 1 and FIG.

<Measurement of Self-Discharge of Nonaqueous Electrolyte Storage Element (Secondary Battery) B Using Positive Electrode B>
The electricity storage device B was tested in the same manner as in Comparative Example 1.
That is, the battery element B was charged to a charge end voltage of 5.2 V at a constant current of 0.5 mA / cm ² : ² mA at room temperature (25 ° C.). Next, the battery was discharged to a final discharge voltage of 3.0 V with a constant current of 0.5 mA / cm ² : ² mA. The discharge capacity at this time is defined as a discharge capacity X3.
Thereafter, the battery was allowed to stand at a constant current of 0.5 mA / cm ² : ² mA up to a charge end voltage of 5.2 V, and then further left for 6 hours. Thereafter, the battery was discharged at a constant current of 0.5 mA / cm ² : ² mA to a final discharge voltage of 3V. The discharge capacity at this time is defined as a discharge capacity Y3.
The discharge capacity X3 / discharge capacity Y3 is the capacity retention rate in self-discharge for 6 hours.
Next, the battery was charged to a charge end voltage of 5.2 V at a constant current of 0.5 mA / cm ² : ² mA at room temperature (25 ° C.). Next, the battery was discharged to a final discharge voltage of 3.0 V with a constant current of 0.5 mA / cm ² : ² mA. The discharge capacity at this time is defined as a discharge capacity X4.
Thereafter, the battery was allowed to stand at a constant current of 0.5 mA / cm ² : ² mA up to a charge end voltage of 5.2 V, and then further left for 12 hours. Thereafter, the battery was discharged to a final discharge voltage of 3 V at a constant current of 0.5 mA / cm ² : ² mA. The discharge capacity at this time is defined as a discharge capacity Y4.
The discharge capacity X4 / discharge capacity Y4 is the capacity retention rate in 12 hours self-discharge.
As a result of the above test, the capacity retention rate at 6 hours self-discharge was 91.96%, and the capacity retention rate at 12 hours self-discharge was 88.67%. This is shown in FIG.

Example 2
-Production of positive electrode C-
<< Preparation of Positive Material Layer C and Positive Electrode C >>
A 20% acetylene black aqueous dispersion of conductive additive (manufactured by Mikuni Dye Co., Ltd.) was applied onto an aluminum foil current collector, dried with warm air at 120 ° C. for 5 minutes, and then the slurry produced in Example 1 thereon. B was applied, dried at room temperature for 2 hours, and further dried with warm air at 120 ° C. for 5 minutes to form a positive electrode material layer C having a two-layer structure. Next, the obtained laminate was punched into a round shape with a diameter of 16 mm to produce a positive electrode C. The thickness of the acetylene black layer in the positive electrode C was 20 μm, and the thickness of the positive electrode material composition B was 145 μm. Moreover, the mass of the positive electrode active material in the positive electrode C was 20 mg, and the average thickness of the positive electrode material layer was 145 μm.

<Measurement of Charge / Discharge Efficiency of Nonaqueous Electrolyte Storage Element (Secondary Battery) C Using Positive Electrode C>
Except that the positive electrode A in the electricity storage device A of Comparative Example 1 was changed to the positive electrode C, a nonaqueous electrolyte electricity storage device C was prepared in the same manner as in Comparative Example 1, and a charge / discharge test was performed.
The discharge capacity in each cycle is shown in FIG.
The charge / discharge efficiency in each cycle is shown in Table 1 and FIG.

<Measurement of Self-Discharge of Nonaqueous Electrolyte Storage Element (Secondary Battery) C Using Positive Electrode C>
The storage element C was tested in the same manner as in Comparative Example 1.
That is, the storage element C was charged to a charge end voltage of 5.2 V at a constant current of 0.5 mA / cm ² : ² mA at room temperature (25 ° C.). Next, the battery was discharged to a final discharge voltage of 3.0 V with a constant current of 0.5 mA / cm ² : ² mA. The discharge capacity at this time is defined as a discharge capacity X5.
Thereafter, the battery was allowed to stand at a constant current of 0.5 mA / cm ² : ² mA up to a charge end voltage of 5.2 V, and then further left for 6 hours. Thereafter, the battery was discharged at a constant current of 0.5 mA / cm ² : ² mA to a final discharge voltage of 3V. The discharge capacity at this time is defined as a discharge capacity Y5.
The discharge capacity X5 / discharge capacity Y5 is the capacity retention rate in self-discharge for 6 hours.
Next, the battery was charged to a charge end voltage of 5.2 V at a constant current of 0.5 mA / cm ² : ² mA at room temperature (25 ° C.). Next, the battery was discharged to a final discharge voltage of 3.0 V with a constant current of 0.5 mA / cm ² : ² mA. The discharge capacity at this time is defined as a discharge capacity X6.
Thereafter, the battery was allowed to stand at a constant current of 0.5 mA / cm ² : ² mA up to a charge end voltage of 5.2 V, and then further left for 12 hours. Thereafter, the battery was discharged to a final discharge voltage of 3 V at a constant current of 0.5 mA / cm ² : ² mA. The discharge capacity at this time is defined as a discharge capacity Y6.
The discharge capacity X6 / discharge capacity Y6 is the capacity retention rate in 12 hours self-discharge.
As a result of the above test, the capacity retention rate at 6 hours self-discharge was 92.23%, and the capacity retention rate at 12 hours self-discharge was 90.19%. This is shown in FIG.

As can be seen from FIG. 2, the nonaqueous electrolyte storage element using the positive electrode of the present invention maintains the same discharge capacity as can be seen from FIG. 2, as can be seen from FIG. The capacity retention rate is high and self-discharge can be suppressed, and charge and discharge efficiency is good as can be seen from Table 1 and FIG.
As described above, when the positive electrode of the present invention is used, it is possible to improve the charge / discharge efficiency and suppress self-discharge without reducing the capacity of the nonaqueous electrolyte storage element.
This is presumably because the electrode for positive electrode of the present invention has a small amount of conductive additive present at the interface with the electrolytic solution, and therefore the reaction of the electrolytic solution at the interface is small.

JP 2013-235680 A JP 2007-280687 A

Journal of The Electrochemical Society, 147 (3) 899-901 (2000). Abstract # 1097, Honolul PRIMe 2012, c 2012 The Electrochemical Society

Claims (6)

  An electrode for a positive electrode of a non-aqueous electrolyte storage element, wherein a positive electrode active material comprising a soft carbon capable of inserting and releasing anions on a positive electrode current collector and a positive electrode material layer containing at least a conductive additive are formed. The positive electrode is characterized in that the amount of the conductive additive per unit area in the thickness direction of the positive electrode material layer is positive electrode collector interface> electrolyte interface.   A positive electrode material layer that does not contain a positive electrode active material and contains a conductive auxiliary agent is formed on the positive electrode current collector side, and a positive electrode material layer that contains a positive electrode active material and does not contain a conductive auxiliary agent is formed thereon. Item 4. The positive electrode according to Item 1.   2. A positive electrode material layer containing a positive electrode active material and a conductive auxiliary agent is formed on the positive electrode current collector side, and a positive electrode material layer containing a positive electrode active material and no conductive auxiliary agent is formed thereon. The electrode for positive electrodes as described in 2.   A non-aqueous electrolyte storage element comprising at least a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode according to claim 1 is used as the positive electrode.   The nonaqueous electrolyte storage element according to claim 4, wherein the concentration of the electrolyte salt contained in the nonaqueous electrolyte is 2 mol / L or more. The non-aqueous electrolyte storage element according to claim 5, wherein a working voltage range of the positive electrode is 2.5 V to 5.5 V vs Li / Li ⁺ .