JP2016058239A - Method for operating power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for operating a power storage device, by which the pre-doping can be completed in a power storage device and there is no possibility of lithium remaining in the power storage device, a sufficient pre-doping amount can be obtained without utilizing the decomposition of an electrolytic solution, and degradation of the capacity of a power storage device can be prevented.SOLUTION: In a method for operating a power storage device having a positive electrode including at least two kinds of positive electrode active materials, i.e. a positive electrode active material (referred to as "positive electrode active material A") allowing an anion to go thereinto and go out thereof, and a positive electrode active material (referred to as "positive electrode active material B") lower than the positive electrode active material A in working potential and capable of releasing lithium ions while the power storage device is charged, a negative electrode including a negative electrode active material consisting of a carbon material allowing lithium to go thereinto or go out thereof, and a nonaqueous electrolyte, the power storage device is charged and discharged within a range where it does not reach a lower limit potential of the positive electrode active material B.SELECTED DRAWING: None

Description

  The present invention relates to a method for operating a storage element.

  In recent years, the characteristics of non-aqueous electrolyte secondary batteries as non-aqueous electrolyte storage elements having a high energy density have been improved and become widespread with the downsizing and higher performance of portable devices. 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, as a non-aqueous electrolyte secondary battery, a lithium ion secondary battery having a positive electrode such as a lithium cobalt composite oxide, a carbon negative electrode, and a non-aqueous electrolyte obtained by dissolving a lithium salt in a non-aqueous solvent Is often used.

  On the other hand, using a material such as a conductive polymer or carbonaceous material for the positive electrode, anions in the non-aqueous electrolyte are inserted or removed from the positive electrode, and lithium ions in the non-aqueous electrolyte are inserted into the negative electrode made of a carbonaceous material There is a non-aqueous electrolyte secondary battery (hereinafter, this type of battery may be referred to as a “dual carbon battery”) that is charged and discharged by desorption (see Non-Patent Document 1).

In the above dual carbon battery, as shown in the following reaction scheme, the positive electrode from a nonaqueous electrolytic solution, for example, PF ₆ ^- and the like anions are inserted, Li ⁺ is inserted into the negative electrode from a nonaqueous electrolytic solution Thus, charging is performed, and discharge is performed by desorption of an anion such as PF ₆ ⁻ from the positive electrode and Li ⁺ from the negative electrode into the non-aqueous electrolyte.

  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 in the dual carbon battery, it is necessary to increase the amount of non-aqueous electrolyte containing lithium salt in addition to the positive electrode active material and the negative electrode active material (see Non-Patent Document 1).

  As described above, the electric quantity of the battery in the dual carbon battery is proportional to the total amount of anions and cations in the non-aqueous electrolyte. Therefore, the energy stored in the battery is proportional to the total mass of the non-aqueous electrolyte in addition to the positive electrode active material and the negative electrode active material. For this reason, it is difficult to increase the weight energy density of the battery. When a non-aqueous electrolyte solution having a lithium salt concentration of about 1 mol / L, which is usually used for lithium ion secondary batteries, is used, a larger amount of non-aqueous electrolyte solution is required than lithium ion secondary batteries. On the other hand, when a non-aqueous electrolyte having a high lithium salt concentration of about 3 mol / L is used, there is a problem that the battery capacity is greatly reduced due to repeated charge and discharge of the battery.

In order to prevent this decrease in battery capacity, lithium pre-doping that reduces the resistance of the negative electrode is effective.
As a method for producing an electrode, a technique of forming a positive electrode and a negative electrode by forming a slurry containing an electrode active material and a conductive additive on both surfaces of a mesh-like or perforated current collector is known.
In such an electrode, the negative electrode can be pre-doped with lithium ions by bringing lithium metal into contact with the laminate of the positive electrode, the negative electrode, and the separator and leaving it in the electrolytic solution.
Lithium ions are transported in the thickness direction through the voids of the mesh current collector.
However, this method has a problem in terms of safety because lithium may remain in the battery in a metallic state.

  Patent Document 1 describes that the irreversible capacity of the positive electrode active material is used as a pre-doping capacity as a lithium pre-doping method. That is, the voltage after the second cycle is charged and discharged in a range lower than the voltage at the first cycle.

  In Patent Document 2, as a method of lithium pre-doping, an irreversible reaction capacity due to decomposition of the electrolyte is given to the positive electrode by applying a voltage higher than the withstand voltage of the electrolyte, and the irreversible capacity is used as the pre-dope capacity. . That is, charging / discharging is performed in a range where the voltage after the second cycle is lower than the voltage at the first cycle. In this method, gas is generated due to decomposition of the electrolytic solution, which causes early deterioration of the battery.

49th Battery Symposium 1B21 ^- the "PF ₆ Insert type graphite and mixing effect on the positive electrode characteristics of the composite electrode of the LiMn ₂ O _4", the composite, only mentions that the capacity can be increased, The problem of preventing the capacity deterioration of the electricity storage element has not been solved.

  An object of the present invention is to solve the above-described problems and achieve the following objects. That is, the present invention completes the pre-doping in the electricity storage device, and there is no possibility that lithium remains in the electricity storage device, and does not use the decomposition of the electrolytic solution. An object of the present invention is to provide a method for operating a power storage element that can prevent deterioration.

As a result of diligent investigations by the present inventors, a positive electrode active material capable of inserting or removing anions (referred to as a positive electrode active material A), an operating element lower than the positive electrode active material A, and lithium during charging as a power storage element A positive electrode including at least two kinds of positive electrode active materials (hereinafter referred to as positive electrode active material B) capable of releasing ions, a negative electrode including a negative electrode active material made of a carbon material capable of inserting or removing lithium, It was found that the above-mentioned problems can be solved by adopting an operation method in which charging and discharging are performed within a range that does not reach the lower limit potential of the positive electrode active material B using a power storage element having a water electrolyte. completed.
That is, the present invention is a method for operating a storage element as described in (1) below.

(1) a positive electrode active material capable of inserting or removing anions (referred to as positive electrode active material A);
A positive electrode containing at least two kinds of positive electrode active materials, a positive electrode active material having a lower operating potential than the positive electrode active material A and capable of releasing lithium ions during charging (referred to as a positive electrode active material B);
A negative electrode including a negative electrode active material made of a carbon material capable of inserting or removing lithium; and
With non-aqueous electrolyte
In a method for operating a storage element having
A method for operating a storage element that performs charge and discharge within a range that does not reach the lower limit potential of the positive electrode active material B.

  According to the present invention, the pre-doping is completed in the storage battery cell, and there is no possibility that lithium remains in the battery, the decomposition of the electrolytic solution is not utilized, and a sufficient amount of pre-doping is obtained, resulting in the capacity deterioration of the storage element. It is possible to provide a method for operating a power storage element that can prevent the above-described problem.

It is a charging / discharging curve of the 1st cycle of the electrical storage element which concerns on this invention. It is a typical charging / discharging curve after the 2nd cycle of the electrical storage element which concerns on this invention. It is the figure which showed the effect of the electrical storage element which concerns on this invention by transition of the capacity maintenance rate for every 10 cycles. FIG. 3 is a diagram showing a discharge capacity in Example 1. FIG. 6 is a diagram showing a discharge capacity in Example 2. FIG. 6 is a diagram showing a discharge capacity in Example 3. It is a figure which shows the discharge capacity in Example 4. FIG. It is a figure which shows the effect of the pre dope in Example 5. FIG. It is a figure which shows the effect of the pre dope in Example 6. FIG. It is a figure which shows the effect of the pre dope in Example 7. FIG. It is a figure which shows the effect of the pre dope in Example 8. FIG. It is a figure which shows the effect which can ensure the energy density of an electrical storage element when the density | concentration of a non-aqueous electrolyte is 2 mol / L or more. It is a figure which shows the effect of an additive.

  Embodiments according to the present invention will be described below. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims, The following description exemplifies an embodiment of the present invention and does not limit the scope of the claims.

  The power storage device of the present invention includes a positive electrode active material A (a positive electrode active material capable of inserting or removing anions) and a positive electrode active material B (a positive electrode having a lower operating potential than that of the positive electrode active material A and capable of releasing lithium ions during charging. A positive electrode including at least two types of positive electrode active materials (active material), a negative electrode including a negative electrode active material made of a carbon material into which lithium can be inserted or removed, and a non-aqueous electrolyte.

First, the structure of the electrical storage element of this invention is demonstrated in detail for every structural member.
<Positive electrode>
The positive electrode is not particularly limited as long as it contains a positive electrode active material, and can be appropriately selected according to the purpose. For example, a positive electrode including a positive electrode material having a positive electrode active material on a positive electrode current collector, and the like. Can be mentioned.
There is no restriction | limiting in particular as a shape of the said positive electrode, According to the objective, it can select suitably, For example, flat form etc. are mentioned.
There is no restriction | limiting in particular as the porosity of the said positive electrode, Although it can select suitably according to the objective, It is especially preferable that a porosity is 50% or more so that sufficient electrolyte solution can be hold | maintained in a positive electrode.

<< Positive electrode material >>
There is no restriction | limiting in particular as said positive electrode material, According to the objective, it can select suitably, For example, it contains a positive electrode active material at least, and also contains a electrically conductive agent, a binder, a thickener, etc. as needed. .

-Positive electrode active material-
――Positive electrode active material A――
The positive electrode active material A capable of inserting or removing anions is a substance capable of inserting or removing anions, and can be appropriately selected according to the purpose. Examples thereof include carbonaceous materials and conductive polymers. Is mentioned. Among these, a carbonaceous material is particularly preferable because of its high energy density.

Examples of the conductive polymer include polyaniline, polypyrrole, polyparaphenylene, and the like.
Examples of the carbonaceous material include graphite (graphite) such as coke, artificial graphite and natural graphite, and organic pyrolysis products under various pyrolysis conditions. Among these, artificial graphite, natural graphite, and soft carbon are particularly preferable.

The carbonaceous material is preferably a carbonaceous material having high crystallinity. The crystallinity can be evaluated by X-ray diffraction, Raman analysis, or the like. The BET specific surface area by nitrogen adsorption of the carbonaceous material is preferably 1 m ² / g or more and 100 m ² / g or less, and the average particle diameter (median diameter) determined by the laser diffraction / scattering method is 0.1 μm or more. It is preferable that it is 100 micrometers or less. When the thickness is less than 2 μm, the electrolytic solution is severely decomposed, and when the thickness exceeds 10 μm, the load characteristics are deteriorated.
――Positive electrode active material B――
The positive electrode active material B is not particularly limited as long as it has a lower operating voltage than the positive electrode active material A and can release Li ions during charging, and is appropriately selected according to the purpose. be able to. For example, an alkali metal transition complex oxide can be used.

Examples of the alkali metal transition composite oxide include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFePO _{4, and the} like. Among these, spinel-type and olivine-type materials are preferable from the viewpoint of stable structure, and LiMn ₂ O ₄ and LiFePO ₄ are particularly preferable from the viewpoint of safety and global environmental resources.
The capacity of the alkali metal transition composite oxide is preferably at least twice the capacity of the negative electrode.
If the capacity is less than this, the negative electrode is not sufficiently pre-doped, and a sufficient cycle characteristic improvement effect cannot be obtained.

-Binder-
The binder is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used in the production of the electrode, and can be appropriately selected according to the purpose. For example, polyvinylidene fluoride (PVDF), polytetra Examples thereof include a fluorine-based binder such as fluoroethylene (PTFE), styrene-butadiene rubber (SBR), isoprene rubber, and the like.
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.

-Conductive agent-
Examples of the conductive agent include metal materials such as copper and aluminum, and carbonaceous materials such as carbon black and acetylene black. These may be used individually by 1 type and may use 2 or more types together.

<< Positive electrode current collector >>
There is no restriction | limiting in particular as a material, a shape, a magnitude | size, and a structure of the said positive electrode electrical power collector, According to the objective, it can select suitably.
The material of the positive 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. For example, stainless steel, nickel, aluminum, copper, titanium , Tantalum, and the like. Among these, stainless steel and aluminum are particularly preferable.
There is no restriction | limiting in particular as a shape of the said 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 a power storage element, and can be appropriately selected according to the purpose.

-Method for producing positive electrode-
In the positive electrode, the positive electrode active material A and the positive electrode active material B are mixed with the binder, the thickener, the conductive agent, a solvent, etc. as necessary to form a slurry positive electrode material. It can be produced by applying on the body and drying. 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>
The negative electrode is not particularly limited as long as it includes a negative electrode active material made of a carbon material, and can be appropriately selected according to the purpose. For example, the negative electrode includes a negative electrode material having a negative electrode active material on a negative electrode current collector And a negative electrode.
There is no restriction | limiting in particular as a shape of the said 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 made of a carbon material, and further includes a binder, a conductive agent, and the like as necessary.

-Negative electrode active material-
The negative electrode active material is not particularly limited as long as it is made of a carbon material and functions at least in a non-aqueous solvent system, and can be appropriately selected according to the purpose.
Examples of the carbonaceous material include graphite such as coke, artificial graphite, and natural graphite. Among these, artificial graphite, natural graphite, hard carbon, and soft carbon are particularly preferable.

The amount of the negative electrode active material is preferably 1.1 to 6 times, and particularly preferably 2 to 4 times that of the positive electrode active material, as a capacity ratio. If it is less than 1.1 times, the influence of the lithium fluoride on the negative electrode is relatively large in the precipitation of lithium fluoride on the negative electrode derived from the hydrogen fluoride gas generated at the positive electrode, and more than 6 times. Since the amount of the negative electrode active material and the amount of the positive electrode active material B necessary for pre-doping increase, the energy density decreases.
The porosity of the negative electrode can be appropriately selected according to the purpose, but it is particularly preferable that the porosity capable of holding a sufficient electrolyte in the negative electrode is 55% or more.

-Binder-
There is no restriction | limiting in particular as said binder, According to the objective, it can select suitably, For example, fluorine-type binders, such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), ethylene-propylene-butadiene rubber ( EPBR), styrene-butadiene rubber (SBR), isoprene rubber, carboxymethylcellulose (CMC), and the like. These may be used individually by 1 type and may use 2 or more types together. Among these, fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), and carboxymethyl cellulose (CMC) are preferable, and the CMC is more preferable because the number of repeated charging and discharging is improved as compared with other binders. Particularly preferred.

-Conductive agent-
Examples of the conductive agent include metal materials such as copper and aluminum, and carbonaceous materials such as carbon black and acetylene black. These may be used individually by 1 type and may use 2 or more types together.

<< Negative electrode current collector >>
There is no restriction | limiting in particular as a material, a shape, a magnitude | size, and a structure of the said negative electrode collector, According to the objective, it can select suitably.
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. For example, stainless steel, nickel, aluminum, copper, etc. Is mentioned. Among these, stainless steel and copper are particularly preferable.
There is no restriction | limiting in particular as a shape of the said electrical power collector, According to the objective, it can select suitably.
The size of the current collector is not particularly limited as long as it is a size that can be used for a power storage element, and can be appropriately selected according to the purpose.

-Negative electrode manufacturing method-
The negative electrode is manufactured by applying a negative electrode material in a slurry form by adding the binder, the conductive agent, a solvent, or the like to the negative electrode active material as necessary, and drying the negative electrode current collector. be able to. As the solvent, the same solvent as that for the positive electrode can be used.
Further, the negative electrode active material added with the binder, the conductive agent and the like is roll-formed as it is to form a sheet electrode, a pellet electrode by compression molding, the negative electrode current collector by techniques such as vapor deposition, sputtering, and plating. A thin film of the negative electrode active material can be formed on the body.

<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 said 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, dimethyl carbonate (DMC) is preferable.

  The content of the chain carbonate is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 70% by mass or more, and more preferably 80% by mass or more based on the non-aqueous solvent. When the content of the chain carbonate is less than 70% by mass, when the remaining solvent is a cyclic substance having a high dielectric constant (such as cyclic carbonate or cyclic ester), the amount of the cyclic substance having a high dielectric constant is Therefore, when a non-aqueous electrolyte solution having a high concentration of 3M or more is produced, the viscosity becomes too high, which may cause problems in terms of penetration of the non-aqueous electrolyte solution into the electrode and ion diffusion.

Examples of the cyclic carbonate include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), and the like.
When a mixed solvent combining ethylene carbonate (EC) as the cyclic carbonate and dimethyl carbonate (DMC) as the chain carbonate is used, the mixing ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC) is particularly Although there is no restriction | limiting and it can select suitably according to the objective, Mass ratio (EC: DMC) is preferably 3:10 to 1:99, and more preferably 3:10 to 1:20.

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 (MA), ethyl acetate, etc.), formic acid alkyl ester (methyl formate (MF), ethyl formate, etc.), etc. Is mentioned.
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, and a combination of lithium and the following anions can be used. .
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.

The lithium salt is not particularly limited and may be appropriately selected depending on the intended purpose. For example, lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium chloride (LiCl), boron Lithium fluoride (LiBF ₄ ), lithium hexafluoride arsenic (LiAsF ₆ ), lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide (LiN (C ₂ F ₅ SO ₂ ) ₂ ), Lithium bisfurfluoroethylsulfonylimide (LiN (CF ₂ F ₅ SO ₂ ) ₂ ), and the like. These may be used individually by 1 type and may use 2 or more types together. Among these, LiPF6 is particularly preferable from the viewpoint of the amount of occlusion of anions in the carbon electrode.

Since the content of the electrolyte salt in the electricity storage device of the present invention is charged by co-insertion of an anion and a cation, it is preferably 2 mol / L or more in the non-aqueous solvent from the viewpoint of energy density improvement. 5 mol / L or less is preferable from the viewpoint of increasing the viscosity, increasing the ionic conductivity, and increasing the resistance. In particular, 2.5 mol / L to 4 mol / L is more preferable from the viewpoint of both the capacity and output of the energy storage device.
As an 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 porosity is 50% and the negative electrode porosity is 60%. In addition, the electrolytic solution that can be held on the positive electrode is 0.01 ml, the electrolytic solution that can be held on the negative electrode is 0.016 ml, and in order to obtain 67 μmol of the electrolyte necessary for charging the storage element from the electrolytic solution held on the positive electrode and the negative electrode, An electrolyte solution with an electrolyte concentration of at least 2.6 mol / L is required.

<< Additives >>
As the additive, as a compound capable of chemically binding an anion containing a fluorine atom (anion receptor), trishexafluoroisopropyl borate (THFIPB) and trispentafluorophenylborane (TPFPB) are particularly preferable. As a compound that forms SEI (solid electrolyte interface), a cyclic carbonate is preferable, and in particular, fluoroethylene carbonate (FEC) and EC that form good SEI on the negative electrode are preferable.
The anion receptor is in contact with the electrolyte so as to increase the conductivity of the non-aqueous electrolyte solution by binding to fluoride anions. Trishexafluoroisopropyl borate (THFIPB) and trispentafluorophenyl borane (TPFPB) have an effect of capturing hydrofluoric acid.

  The content of the compound having a site capable of binding an anion containing a halogen atom can be appropriately selected according to the purpose, but is preferably 0.5% by mass or more based on the non-aqueous electrolyte. Mass% to 5 mass% is more preferable, and 1 mass% to 3 mass% is still more preferable. When the content is less than 0.5% by mass, it may be difficult to obtain the effect. When the content exceeds 5% by mass, the ion diffusibility decreases due to an increase in viscosity and the charge / discharge efficiency decreases. There is.

  As for the mixing ratio of the cyclic carbonate, the mass ratio (EC or FEC: nonaqueous solvent) is preferably 3:10 to 1:99, more preferably 3:10 to 1:20.

  Note that the addition of a compound having a site capable of binding an anion containing a halogen atom (for example, TPFPB) is added to the inside of the electricity storage element, so that the electricity storage element is decomposed and the nonaqueous electrolytic solution is examined by gas chromatography or the like. Can be analyzed.

<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 as a material of the said 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 a power storage element, and can be appropriately selected according to the purpose.
A solid electrolyte can also be used.
The separator may have a single layer structure or a laminated structure.

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

<Method for manufacturing power storage element>
The electrical storage element of this invention is manufactured by assembling the said positive electrode, the said negative electrode, the said nonaqueous electrolyte, and the separator used as needed in a suitable shape. Furthermore, other constituent members such as a battery outer can can be used as necessary. There is no restriction | limiting in particular as a method of assembling the said electrical storage element, It can select suitably from the methods employ | adopted normally.

-Shape-
There is no restriction | limiting in particular about the shape of the electrical storage element of this invention, According to the use, it can select suitably from the various shapes generally employ | adopted. Examples of the shape 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, a cylinder type in an inside-out structure in which a pellet electrode and a separator are combined, and a pellet electrode and a separator are stacked. Coin type, and so on.

<Application>
There is no restriction | limiting in particular as a use of the electrical storage element of this invention, For example, it can use for various uses, For example, a notebook personal computer, pen input personal computer, a mobile personal computer, an electronic book player, a mobile telephone, a portable fax, a portable copy, a portable printer , Headphone stereo, video movie, LCD TV, handy cleaner, portable CD, minidisc, transceiver, electronic notebook, calculator, memory card, portable tape recorder, radio, backup power supply, motor, lighting equipment, toy, game device, clock, Strobe, camera, etc.

<Operation method of power storage element>
A method for operating the electricity storage device of the present invention will be described.
In explaining the operation method of the electricity storage device of the present invention, the electricity storage device assembled in the same manner as in Example 1 described later is used as a secondary battery, using the materials described below as materials constituting the electricity storage device. This will be described based on an example.
Positive electrode active material A: carbon powder
Cathode active material B: LiMn ₂ O ₄
Negative electrode active material: Carbon powder
Non-aqueous electrolyte: Solvent DMC electrolyte LiPF ₆ concentration 3M
Positive electrode current collector: Al foil
Negative electrode current collector: Cu foil

A coin-type energy storage device (2032 type) is assembled using the above materials, and set in a charge / discharge device.
(First charge / discharge)
The battery is charged to a final charge voltage of 5.2 V at a constant current of 0.5 mA / cm ² at room temperature (25 ° C.).
At the time of this charge, in the range of 3.0 V to 4.2 V, lithium ions are desorbed from LiMn ₂ O ₄ on the positive electrode side, and lithium ions are inserted on the negative electrode. The range of 5.2V from 4.2 V, the positive electrode side PF ₆ ^- is inserted ions, a negative electrode side is inserted lithium ions.
After the first charge, the battery is discharged to 4.2 V with a constant current of 0.5 mA / cm ² . During this discharge, PF ₆ ⁻ ions are desorbed on the positive electrode side and lithium ions are desorbed on the negative electrode side in the discharge up to 4.2V. In this operation, since the desorption of lithium ions corresponding to the capacity of LiMn ₂ O ₄ inserted on the negative electrode side at the time of the first charge has not started, lithium ions corresponding to the capacity released from LiMn ₂ O ₄ remain in the negative electrode. doing.
The charge / discharge curve in this first charge / discharge is shown in FIG.

(Charging / discharging after the second cycle)
After the second cycle, the battery is charged to a charge end voltage of 5.2 V at a constant current of 0.5 mA / cm ² at room temperature (25 ° C.). After this charging, the battery is discharged at a constant current of 0.5 mA / cm ² at room temperature (25 ° C.) to a charge end voltage of 4.2 V. This charging / discharging was made into 1 set, and the test repeated 100 times was done.
As a representative example of the charge / discharge curve in the second and subsequent cycles, the charge / discharge curve in the second cycle is shown in FIG.

(Changes in capacity maintenance rate)
FIG. 3 is a graph showing the transition of the capacity maintenance rate for every 10 cycles in the repeated charging / discharging of the electricity storage device in the operation method. From the results of FIG. 3, it can be seen that the cycle characteristics of the capacity retention rate can be improved by the operation method of the present invention.

In the first cycle, the carbon powder and LiMn ₂ O ₄ were charged by 5.2 V, and then the discharge was stopped before reaching the voltage at which the LiMn ₂ O ₄ discharge started. In the second and subsequent cycles, within the operating voltage of the carbon powder. Only charge and discharge. As a result, since the battery is repeatedly charged and discharged in the second and subsequent cycles while the amount of Li ions released from the LiMn ₂ O ₄ charged in the first cycle remains doped in the negative electrode, the same effect as lithium pre-doping is obtained. can get.

  In the present invention, by using a non-aqueous electrolyte solution having a high electrolyte concentration, in a power storage device in which the capacity cycle deterioration becomes large, by doping lithium ions into the negative electrode, the reaction resistance of the negative electrode is lowered, and the electrolyte concentration is reduced. Even if a high non-aqueous electrolyte is used, the cycle of capacity retention can be improved.

Moreover, although this invention concerns on the operating method of the electrical storage element of following (1), following (2)-(7) is also included as embodiment.
(1) a positive electrode active material capable of inserting or removing anions (referred to as positive electrode active material A);
A positive electrode containing at least two kinds of positive electrode active materials, a positive electrode active material having a lower operating potential than the positive electrode active material A and capable of releasing lithium ions during charging (referred to as a positive electrode active material B);
A negative electrode including a negative electrode active material made of a carbon material capable of inserting or removing lithium; and
With non-aqueous electrolyte
In a method for operating a storage element having
A method for operating a storage element that performs charge and discharge within a range that does not reach the lower limit potential of the positive electrode active material B.
(2) The method for operating a storage element according to claim 1, wherein the maximum value of the charging voltage is 5.5V.
(3) a positive electrode active material capable of inserting or removing anions (referred to as positive electrode active material A);
A positive electrode containing at least two kinds of positive electrode active materials, a positive electrode active material having a lower operating potential than the positive electrode active material A and capable of releasing lithium ions during charging (referred to as a positive electrode active material B);
A negative electrode including a negative electrode active material made of a carbon material capable of inserting or removing lithium; and
With non-aqueous electrolyte
A power storage device comprising:
The non-aqueous electrolyte has an electrolyte concentration of 2 mol / L or more,
A power storage device for use in the method for operating a power storage device according to (1) or (2).
(4) The storage element according to (3), wherein the positive electrode active material B is LiFePO ₄ or LiMn ₂ O ₄ .
(5) The electric storage element according to (4), wherein the positive electrode active material B is LiMn ₂ O ₄ , and the capacity of LiMnO ₄ is K and the negative electrode capacity is L, L / K <2.5.
(6) The electricity storage device according to any one of (3) to (5), wherein the non-aqueous electrolyte includes trishexafluoroisopropyl borate (THFIPB) and / or trispentafluorophenyl borane (TPFPB).
(7) The electricity storage device according to any one of (3) to (6), wherein at least one of the positive electrode active materials is a carbon material.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

[Example 1]
(Production Example 1 of positive electrode)
-Fabrication of positive electrode A-
A slurry to be an electrode film is prepared. This slurry is obtained by adding an active material to a basic composition liquid.
<< Basic composition liquid >>
As a thickener, 12.5 g of a 3% by weight aqueous solution of carboxymethylcellulose (CMC) is added and kneaded with 5 g of pure water, and 7.5 g of 20% acetylene black aqueous dispersion (manufactured by Mikuni Dye Co., Ltd.) is added and kneaded. did. Let the obtained basic composition liquid be [basic composition liquid 1].

<< Preparation of positive electrode material >>
Carbon powder (manufactured by TIMCAL, KS-6) was used as the positive electrode active material A. This carbon powder had a BET specific surface area of 20 m ² / g by nitrogen adsorption and an average particle diameter (median diameter) measured by a laser diffraction particle size distribution meter (SALD-2200, manufactured by Shimadzu Corporation) was 3.4 μm.
[Basic composition liquid 1] 4 g of the carbon powder (manufactured by TIMCAL, KS-6) as the positive electrode active material A was added to ₄ g and kneaded. Further, 2 g of LiMn ₂ O ₄ and pure water were added as the positive electrode active material B. 2 g was added and kneaded to prepare a positive electrode material layer composition (slurry). The positive electrode material layer composition was applied to an aluminum foil and vacuum dried at 120 ° C. for 4 hours to form a positive electrode material layer. This was punched into a round shape with a diameter of 16 mm to produce a positive electrode, which was designated as [Positive electrode A]. At this time, the mass of the positive electrode active material in the positive electrode material layer coated on the aluminum (Al) foil having a diameter of 16 mm was 20 mg, and the average thickness of the positive electrode material layer was 95.8 μm (0.00958 cm).
Moreover, the average porosity of the positive electrode material layer in [Positive electrode A] used in the examples (Examples 1, 2, and 5) was 50%.

(Negative electrode production example 1)
-Production of negative electrode A-
Carbon powder (manufactured by Hitachi Chemical Co., Ltd., MAGD) was used as the negative electrode active material. This carbon powder has a BET specific surface area of 4.5 m ² / g by nitrogen adsorption, an average particle diameter (median diameter) measured by a laser diffraction particle size distribution meter (SALD-2200, manufactured by Shimadzu Corporation), and a tap density of 630 kg. / M ³ .
Water is added to 10 g of carbon powder (graphite) and 2.5 g of 20% acetylene black water dispersion (manufactured by Mikuni Dye Co., Ltd.) and kneaded. Further, 10 g of 2% by weight aqueous solution of carboxymethyl cellulose (CMC) is added as a thickener. And kneaded to prepare a negative electrode material layer composition (slurry). The negative electrode material layer composition was applied to Cu foil and vacuum dried at 120 ° C. for 4 hours to form a negative electrode material layer. This was punched into a round shape with a diameter of 16 mm to produce a negative electrode.
This negative electrode was designated as [Negative electrode A]. At this time, the mass of the carbon powder (graphite) in the negative electrode material layer coated on the Cu foil having a diameter of 16 mm was 20 mg, and the average thickness of the negative electrode material layer was 130 μm (0.13 cm).
Moreover, the average porosity of the negative electrode material layer in [Negative electrode A] used in the examples (Examples 1, 4, and 6) was 63%.

<Non-aqueous electrolyte>
EC / DMC in which 1.0 mol / L LiPF ₆ was dissolved was prepared. This was designated as [Nonaqueous Electrolytic Solution 1].

<Separator>
A glass separator, GA-100 GLASS FIBER (GF) FILTER (manufactured by ADVANTEC) was prepared. This was designated as [Separator 1].

<Production of electricity storage element>
[Positive electrode A], [Separator 1], [Nonaqueous electrolyte 1], and [Negative electrode A] were placed in a decomposable bipolar cell (manufactured by Takumi Giken Co., Ltd.) to produce [Electric storage element 1]. The [electric storage element 1] has a L / K ratio of 3.65.

<Confirmation of pre-doping of positive electrode A and negative electrode A>
[Storage element 1] was charged to a final charge voltage of 5.2 V at a constant current of 0.5 mA / cm ² at room temperature (25 ° C.). After the first charge, the bipolar cell was disassembled in the glove box, and [Negative electrode A] was taken out.
[Negative electrode A], [Separator 1], [Nonaqueous electrolyte 1] and lithium (Honjo Metal Co., Ltd.) taken out in a can for producing a coin-type electricity storage device (2032 type, manufactured by Hosen Co., Ltd.) , A thickness of 200 μm) to form a negative electrode half cell. When this negative electrode half cell was discharged at a constant current of 0.5 mA / cm ² at room temperature (25 ° C.), discharge with a discharge capacity of 101.9 mAh / g was performed.
The discharge capacity of the electricity storage device of Example 1 is shown in FIG. FIG. 4 shows that pre-doping could be completed in the storage cell by the operation method of the present invention.

[Example 2]
(Negative electrode production example 2)
-Production of negative electrode B-
A negative electrode with an average thickness of the negative electrode material layer of 85 μm (0.0085 cm) was prepared in the same manner as in Example 1 except that the mass of the carbon powder (graphite) in the negative electrode material layer coated on the Cu foil was 10 mg. did. This negative electrode was designated as [Negative electrode B].
The average porosity of the negative electrode material layer in [Negative electrode B] used in the examples (Examples 2, 3, 5, 7, and 8) was 63%.

<Preparation of nonaqueous electrolyte storage element>
[Positive electrode A], [Separator 1], [Negative electrode B], and [Non-aqueous electrolyte 1] are put into a coin-type electric storage element manufacturing can (2032 type, manufactured by Hosen Co., Ltd.), and the can is caulked ( [Hakosen Co., Ltd.] was used to produce [Electric storage element 2].

<Confirmation of pre-doping of positive electrode A and negative electrode B>
The above-described [Positive electrode A], [Separator 1], [Nonaqueous electrolyte 1], and [Negative electrode B] were placed in a decomposable bipolar cell (manufactured by Takumi Giken Co., Ltd.) to constitute a storage element. This power storage element has an L / K ratio of 2.14. The electricity storage device was charged to a charge end voltage of 5.2 V with a constant current of 0.5 mA / cm ² at room temperature (25 ° C.). After the first charge, the bipolar cell was disassembled in the glove box, and [Negative electrode B] was taken out.
[Negative electrode B], [Separator 1], [Non-aqueous electrolyte 1] and lithium (Honjo Metal Co., Ltd.) taken out in a can for producing a coin-type electricity storage device (2032 type, manufactured by Hosen Co., Ltd.) , A thickness of 200 μm) to form a negative electrode half cell. When this negative electrode half cell was discharged at a constant current of 0.5 mA / cm ² at room temperature (25 ° C.), a discharge capacity of 173.7 mAh / g was discharged.

The discharge capacity of [electric storage element 2] is shown in FIG. FIG. 5 shows that pre-doping could be completed in the storage cell by the operation method of the present invention.
Further, when Example 2 is compared with Example 1 in which the capacity ratio of the positive electrode and the negative electrode is 2.5 or more, the discharge capacity in Example 1 is 101.9 mAh / g, and the discharge of the storage element in Example 2 is The capacity is 173.7 mAh / g. From the results of Example 2, when L / K is a small value, a sufficient amount of pre-doping can be obtained, and the negative electrode can be used in a stable region, and a storage element having stable cycle characteristics can be provided.

[Example 3]
(Production Example 2 of positive electrode)
-Production of positive electrode B-
<< Preparation of positive electrode material >>
Carbon powder (manufactured by TIMCAL, KS-6) was used as the positive electrode active material A. This carbon powder had a BET specific surface area of 20 m ² / g by nitrogen adsorption and an average particle diameter (median diameter) measured by a laser diffraction particle size distribution meter (SALD-2200, manufactured by Shimadzu Corporation) was 3.4 μm.
[Basic composition solution 1] 8 g of carbon powder (manufactured by TIMCAL, KS-6) as the positive electrode active material A was added to 8 g and kneaded, and 4 g of LiFePO ₄ and 3 g of pure water were added as the positive electrode active material B. And kneaded to prepare a positive electrode material layer composition (slurry). The positive electrode material layer composition was applied to an aluminum foil and vacuum dried at 120 ° C. for 4 hours to form a positive electrode material layer. This was punched into a round shape with a diameter of 16 mm to produce a positive electrode, which was designated as [Positive electrode B]. At this time, the mass of the positive electrode active material in the positive electrode material layer coated on the aluminum (Al) foil having a diameter of 16 mm was 20 mg, and the average thickness of the positive electrode material layer was 103.5 μm (0.1035 cm).
Moreover, the average porosity of the positive electrode material layer in [Positive electrode B] used in Examples (Examples 3, 4, 6, and 8) was 50%.

<Production of electricity storage element>
[Positive electrode B], [Separator 1], [Nonaqueous electrolyte 1] and [Negative electrode B] were put in a decomposable bipolar cell (manufactured by Takumi Giken Co., Ltd.) to produce [Storage element 3].

<Confirmation of pre-doping of positive electrode B and negative electrode B>
[Storage element 3] was charged to a final charge voltage of 5.2 V with a constant current of 0.5 mA / cm ² at room temperature (25 ° C.). After the first charge, the bipolar cell was disassembled in the glove box, and the negative electrode B was taken out.
[Negative electrode B], [Separator 1], [Non-aqueous electrolyte 1] and lithium (Honjo Metal Co., Ltd.) taken out in a can for producing a coin-type electricity storage device (2032 type, manufactured by Hosen Co., Ltd.) , A thickness of 200 μm) to form a negative electrode half cell. When the negative electrode half cell was discharged at a constant current of 0.5 mA / cm ² at room temperature (25 ° C.), a discharge capacity of 66.6 mAh / g was discharged.
The discharge capacity of the electricity storage device of Example 3 is shown in FIG. FIG. 6 shows that pre-doping could be completed in the storage cell by the operation method of the present invention.

[Example 4]
<Production of electricity storage element>
[Positive electrode B], [Separator 1], [Nonaqueous electrolyte 1], and [Negative electrode A] were placed in a decomposable bipolar cell (manufactured by Takumi Giken Co., Ltd.) to produce [Storage element 4].

<Confirmation of pre-doping of positive electrode B and negative electrode A>
[Storage element 4] was charged to a final charge voltage of 5.2 V at a constant current of 0.5 mA / cm ² at room temperature (25 ° C.). After the first charge, the bipolar cell was disassembled in the glove box, and [Negative electrode A] was taken out.
[Negative electrode A], [Separator 1], [Nonaqueous electrolyte 1] and lithium (Honjo Metal Co., Ltd.) taken out in a can for producing a coin-type electricity storage device (2032 type, manufactured by Hosen Co., Ltd.) , A thickness of 200 μm) to form a negative electrode half cell. When this negative electrode half cell was discharged at a constant current of 0.5 mA / cm ² at room temperature (25 ° C.), discharge with a discharge capacity of 41.2 mAh / g was performed.
The discharge capacity of the electricity storage device of Example 4 is shown in FIG. FIG. 7 shows that pre-doping could be completed in the storage cell by the operation method of the present invention.

[Example 5]
<Production of electricity storage element>
[Positive electrode A], [Separator 1], [Nonaqueous electrolyte 1], and [Negative electrode B] are put into a coin-type battery element canister (2032 type, manufactured by Hosen Co., Ltd.). ] Was produced. This power storage element has an L / K ratio of 2.14.
<Confirmation of pre-doping effect in positive electrode A and negative electrode B>
At room temperature (25 ° C.) to the storage element, a constant current of 0.5 mA / cm ^2, a constant current charging until 5.2V, then discharged at a constant current of 0.5 mA / cm ² to 4.2V One cycle of constant current discharge was performed, and this charge / discharge cycle was performed 100 times.
The maintenance rate of the discharge capacity of the electricity storage device of Example 5 is shown in FIG.
FIG. 8 shows the transition of the capacity retention rate (%) when the specific capacity in the second cycle is 100%.
From the results shown in FIG. 8, it can be seen that the capacity deterioration can be prevented by completing the pre-doping in the electric storage element.

[Example 6]
<Production of electricity storage element>
[Positive electrode B], [Separator 1], [Nonaqueous electrolyte 1], and [Negative electrode A] are put into a can (2032 type, manufactured by Hosen Co., Ltd.) for coin-type electricity storage device, ] Was produced.
<Confirmation of pre-doping effect in positive electrode B and negative electrode A>
At room temperature (25 ° C.) in the electric storage device 6, a constant current of 0.5 mA / cm ^2, a constant current charging until 5.2V, then a constant current of 0.5 mA / cm ² until 3.8V The constant current discharge to discharge was made into 1 cycle, and this charging / discharging cycle was performed 100 times.
The retention rate of the discharge capacity of the electricity storage device of Example 6 is shown in FIG.
FIG. 9 shows the transition of the capacity retention rate (%) when the specific capacity in the second cycle is 100%.
From the results shown in FIG. 9, it can be seen that the capacity deterioration can be prevented by completing the pre-doping in the electric storage element.

[Example 7]
(Production Example 3 of Positive Electrode)
-Fabrication of positive electrode C-
<< Preparation of positive electrode material >>
In the method for producing [Positive electrode B] in Example 3, the method for producing [Positive electrode B] in Example 3 except that the mass of the positive electrode active material in the positive electrode material layer coated on the aluminum (Al) foil was 10 mg. In the same manner as above, a positive electrode in which the average thickness of the positive electrode material layer was 59.5 μm (0.0595 cm) and the porosity of the positive electrode material layer was 50% was produced. This positive electrode was designated as [Positive electrode C].
<Production of electricity storage element>
[Positive electrode C], [Separator 1], [Non-aqueous electrolyte 1] and [Negative electrode B] are put into a can for producing a coin-type electricity storage device (2032 type, manufactured by Hosen Co., Ltd.). ] Was configured.

<Confirmation of pre-doping effect in positive electrode C and negative electrode B>
The electricity storage device is charged at a constant current of 0.5 mA / cm ^{2 to} 5.2 V at room temperature (25 ° C.), and then discharged to 3.8 V at a constant current of 0.5 mA / cm ^2. One cycle of constant current discharge was performed, and this charge / discharge cycle was performed 100 times.
The retention rate of the discharge capacity of the electricity storage device of Example 7 is shown in FIG.
FIG. 10 shows the transition of the capacity retention rate (%) when the specific capacity in the second cycle is 100%.
From the results shown in FIG. 10, it can be seen that capacity degradation can be prevented by completing pre-doping in the electric storage element.

[Example 8]
<Production of electricity storage element>
[Positive electrode B], [Separator 1], [Nonaqueous electrolyte 1] and [Negative electrode B] are put into a can for producing a coin-type electricity storage device (2032 type, manufactured by Hosen Co., Ltd.). ] Was produced.
<Confirmation of pre-doping effect in positive electrode B and negative electrode B>
At room temperature (25 ° C.) to the storage element 8, a constant current of 0.5 mA / cm ^2, a constant current charging until 5.2V, then a constant current of 0.5 mA / cm ² until 3.8V The constant current discharge to discharge was made into 1 cycle, and this charging / discharging cycle was performed 100 times.
The retention rate of the discharge capacity of the electricity storage device of Example 8 is shown in FIG.
FIG. 11 shows the transition of the capacity retention rate (%) when the specific capacity in the second cycle is 100%.
From the results shown in FIG. 11, it can be seen that capacity degradation can be prevented by completing pre-doping in the electric storage element.

[Comparative Example 1]
The [electric storage element 5] manufactured in Example 5 was charged at a constant current of 0.5 mA / cm ^{2 at} a constant current of 0.5 mA / cm ² up to 5.2 V and then a constant current of 0.5 mA / cm ² . The constant current discharge which discharges to 3V with electric current was made into 1 cycle, and this charging / discharging cycle was performed 100 times.
The maintenance rate of the discharge capacity of [Electric storage element 5] in Comparative Example 1 is shown in FIG.
From the results shown in FIG. 8, it can be seen that the capacity deterioration is occurring in the comparative example 1 compared to the example 5.

[Comparative Example 2]
The [electric storage element 6] manufactured in Example 6 was charged at a constant current of 0.5 mA / cm ^{2 at} a constant current of 0.5 mA / cm ^{2 to} 5.2 V, and then a constant current of 0.5 mA / cm ² . The constant current discharge which discharges to 3V with electric current was made into 1 cycle, and this charging / discharging cycle was performed 100 times.
The retention rate of the discharge capacity of [Electric storage element 6] in Comparative Example 2 is shown in FIG.
From the results shown in FIG. 9, it can be seen that the capacity deterioration is occurring in the comparative example 2 as compared with the example 6.

[Comparative Example 3]
The [electric storage element 7] manufactured in Example 7 was charged at a constant current of 0.5 mA / cm ^{2 to} 5.2 V at room temperature (25 ° C.), and then a constant current of 0.5 mA / cm ² . The charge / discharge cycle was performed 100 times with a constant current discharge that discharged to 3 V as a current.
The retention rate of the discharge capacity of [Electric storage element 7] in Comparative Example 3 is shown in FIG.
From the results shown in FIG. 10, it can be seen that the capacity deterioration is caused in the comparative example 3 as compared with the example 7.

[Comparative Example 4]
The [electric storage element 8] manufactured in Example 8 was charged at a constant current of 0.5 mA / cm ^{2 to} 5.2 V at room temperature (25 ° C.), and then a constant current of 0.5 mA / cm ² . The constant current discharge which discharges to 3V with electric current was made into 1 cycle, and this charging / discharging cycle was performed 100 times.
The retention rate of the discharge capacity of [Electric storage element 8] in Comparative Example 4 is shown in FIG.
From the results shown in FIG. 11, it can be seen that the capacity deterioration is occurring in the comparative example 4 compared to the example 8.

Hereinafter, reference examples of the present invention will be described.
The power storage device of the above example uses the positive electrode active material B for pre-doping, and the cycle test as the power storage device is performed on the carbon portion used as the positive electrode active material A. The following reference examples are shown in order to clarify the effect of the electrolyte concentration in a power storage device using carbon for the positive electrode.

[Reference Example 1]
In this reference example, the energy density of the electricity storage device can be secured by setting the concentration of the nonaqueous electrolyte of the electricity storage device to 2 mol / L or more, and the cycle can be stabilized by supplying a sufficient amount of anions and cations. It is for showing.

(Production Example 4 of Positive Electrode)
-Fabrication of positive electrode D-
Carbon powder (manufactured by TIMCAL, KS-6) was used as the positive electrode active material. This carbon powder had a BET specific surface area of 20 m ² / g by nitrogen adsorption and an average particle diameter (median diameter) measured by a laser diffraction particle size distribution meter (SALD-2200, manufactured by Shimadzu Corporation) was 3.4 μm.
19 g of this carbon powder and a 3% by weight aqueous solution of carboxymethylcellulose (CMC) as a thickener are added to 3.75 g of a 20% acetylene black aqueous dispersion (manufactured by Mikuni Dye Co., Ltd.) and kneaded, and further 5 g of pure water. Were added and kneaded to prepare a positive electrode material layer composition (slurry). The positive electrode material composition was coated on an aluminum foil and vacuum dried at 120 ° C. for 4 hours to form a positive electrode material layer. This was punched into a round shape with a diameter of 16 mm to produce a positive electrode. This was designated as [Positive electrode D]. At this time, the mass of the carbon powder (graphite) in the positive electrode material layer coated on the aluminum (Al) foil having a diameter of 16 mm was 10 mg, the average thickness of the positive electrode material layer was 69.5 μm, and the average porosity of the positive electrode material layer was It was 61.4%.

<Confirmation of cycle characteristics improvement in power storage elements>
<< Preparation of power storage element A1 >>
[Positive electrode D], [Separator 1], non-aqueous electrolyte (manufactured by Kishida Chemical Co., Ltd., 2 mol / L LiPF ₆ (DMC)) ) And [Negative electrode B] were added to form a storage element A1. At room temperature (25 ° C.) to the storage element A1, a constant current of 0.5 mA / cm ^2, a constant current charging until 5.2V, then a constant current of 0.5 mA / cm ² to 3.0V discharge The constant current discharge to be performed was one cycle, and this charge / discharge cycle was performed 100 times.
FIG. 12 shows the capacity-cycle relationship of the electricity storage element A1.

<<< Production of power storage element A2 >>>
[Positive electrode D], [Separator 1], non-aqueous electrolyte (manufactured by Kishida Chemical Co., Ltd., 1 mol / L LiPF ₆ (DMC)) ) And [Negative electrode B] were added to form a storage element A2. At room temperature (25 ° C.) to the storage element A2, a constant current of 0.5 mA / cm ^2, a constant current charging until 5.2V, then a constant current of 0.5 mA / cm ² to 3.0V discharge The constant current discharge to be performed was one cycle, and this charge / discharge cycle was performed 100 times.
FIG. 12 shows the capacity-cycle relationship of the electricity storage element A2.

  From the results shown in FIG. 12, the battery element A2 having a non-aqueous electrolyte concentration of 1 mol / L undergoes cycle deterioration due to a shortage of anions and cations necessary for charging the battery element. On the other hand, since the nonaqueous electrolyte concentration is 2 mol / L and the storage element A1 holds the anion and cation necessary for charging the storage element, cycle deterioration does not occur.

[Reference Example 2]
This reference example shows the effect of improving the cycle characteristics of the electricity storage device by adding trishexafluoroisopropyl borate (THFIPB) and trispentafluorophenylborane (TPFPB) to the non-aqueous electrolyte of the electricity storage device. is there.
<Confirmation of improved cycle characteristics in power storage devices>

<< Production of Power Storage Element B1 >>
[Positive electrode D], [Separator 1], non-aqueous electrolyte (2.5 mol / L LiPF ₆ (EMC) +1 wt% THFIPB or TPFPB) and [Negative electrode B] were added to form a storage element B1. At room temperature (25 ° C.) to the power storage device B1, a constant current of 0.5 mA / cm ^2, a constant current charging until 5.2V, then a constant current of 0.5 mA / cm ² to 3.0V discharge The constant current discharge is defined as one cycle, and this charge / discharge cycle was performed 100 times.
FIG. 13 shows the capacity-cycle relationship of the storage element B1.

<< Production of power storage element B2 >>
[Positive electrode D], [Separator 1], non-aqueous electrolyte (2.5 mol / L LiPF ₆ (EMC)), [negative electrode] B] was entered to form a power storage device B2.
At room temperature (25 ° C.) to the power storage device B2, a constant current of 0.5 mA / cm ^2, a constant current charging until 5.2V, then a constant current of 0.5 mA / cm ² to 3.0V discharge The constant current discharge is defined as one cycle, and this charge / discharge cycle was performed 100 times.
FIG. 13 shows the capacity-cycle relationship of the storage element B2.

  From the results shown in FIG. 12, in the power storage element B2 that does not contain an additive that captures hydrogen fluoride generated from the positive electrode, the capacity deteriorates due to the influence of hydrogen fluoride generated from the positive electrode. On the other hand, since the additive for trapping hydrogen fluoride generated from the positive electrode is added to the storage element B1, improvement in cycle characteristics can be confirmed.

JP 2012-212632 A JP 2008-91727 A

Journal of The ElectrochemicalSociety, 147 (3) 899-901 (2000)

Claims (7)

A positive electrode active material capable of inserting or releasing anions (referred to as positive electrode active material A);
A positive electrode containing at least two kinds of positive electrode active materials, a positive electrode active material having a lower operating potential than the positive electrode active material A and capable of releasing lithium ions during charging (referred to as a positive electrode active material B);
A negative electrode including a negative electrode active material made of a carbon material capable of inserting or removing lithium; and
With non-aqueous electrolyte
In a method for operating a storage element having
A method for operating a storage element that performs charge and discharge within a range that does not reach the lower limit potential of the positive electrode active material B.   The method for operating a storage element according to claim 1, wherein the maximum value of the charging voltage is 5.5V. A positive electrode active material capable of inserting or releasing anions (referred to as positive electrode active material A);
A positive electrode containing at least two kinds of positive electrode active materials, a positive electrode active material having a lower operating potential than the positive electrode active material A and capable of releasing lithium ions during charging (referred to as a positive electrode active material B);
A negative electrode including a negative electrode active material made of a carbon material capable of inserting or removing lithium; and
With non-aqueous electrolyte
A power storage device comprising:
The non-aqueous electrolyte has an electrolyte concentration of 2 mol / L or more,
A power storage element for use in the method for operating a power storage element according to claim 1. The electric storage element according to claim 3, wherein the positive electrode active material B is LiFePO ₄ or LiMn ₂ O ₄ . 5. The storage element according to claim 4, wherein the positive electrode active material B is LiMn ₂ O ₄ , and the capacity of LiMnO ₄ is K and the negative electrode capacity is L, L / K <2.5.   The electrical storage element as described in any one of Claims 3-5 in which the said non-aqueous electrolyte contains a tris hexafluoro isopropyl borate (THFIPB) and / or a tris pentafluorophenyl borane (TPFPB). The power storage element according to claim 3, wherein at least one of the positive electrode active materials is a carbon material.