JP2014127656A - Nonaqueous electrolyte storage element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte storage element excellent in cycle characteristics of charging and discharging.SOLUTION: The nonaqueous electrolyte storage element comprises a positive electrode comprising a positive electrode active substance that can reversibly store or discharge anions, a negative electrode comprising a negative electrode active substance that can reversibly store or discharge cations; and a nonaqueous electrolytic solution containing an electrolyte salt, in which a capacitance of the negative electrode per unit area is 4 times or more of a capacitance of the positive electrode per unit area. In preferred embodiments, the capacitance of the negative electrode per unit area is 6 to 10 times of the capacitance of the positive electrode per unit area, the capacitance of the negative electrode per unit area ranges from 0.5 mAh/cmto 5 mAh/cm, or cations are preliminarily stored in the negative electrode active substance of the negative electrode.

Description

  The present invention relates to a non-aqueous electrolyte storage element.

In recent years, with the miniaturization and high performance of portable devices, the characteristics of non-aqueous electrolyte storage elements having a high energy density have been improved and become widespread. In addition, attempts are being made to improve the weight energy density of non-aqueous electrolyte storage elements with the aim of developing applications in electric vehicles.
Conventionally, as a non-aqueous electrolyte storage element, a lithium ion non-aqueous electrolysis 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. Many liquid storage elements are 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 storage element (hereinafter, this type of battery may be referred to as “dual carbon storage element”) that is charged and discharged by desorption (see Patent Document 1).
In the dual carbon energy storage device, as shown in the following reaction formula, for example, an anion such as PF ₆ ⁻ is inserted from the non-aqueous electrolyte to the positive electrode, and Li ⁺ is inserted from the non-aqueous electrolyte to the negative electrode. Thus, charging is performed, and discharging 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 energy storage device 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 electricity storage device, 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 amount of electricity of the battery in the dual carbon electricity storage element is proportional to the total amount of anions and cations in the non-aqueous electrolyte. Therefore, the energy stored in the power storage element 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 raise the weight energy density of an electrical storage element. When a non-aqueous electrolyte solution having a lithium salt concentration of about 1 mol / L, which is usually used for lithium ion storage elements, is used, a larger amount of non-aqueous electrolyte solution is required than lithium ion storage elements. 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 in that the capacity of the power storage element is greatly reduced due to repeated charge / discharge of the power storage element.
The dual carbon energy storage device has an operating voltage range of about 2.5 V to 5.4 V, and the maximum voltage is about 1 V higher than about 4.2 V of the lithium ion energy storage device. For this reason, the non-aqueous electrolyte is easily decomposed. Decomposition of the non-aqueous electrolyte causes deterioration such as a reduction in the capacity of the storage element due to gas generation and excessive film formation of fluoride on the electrode surface, so a countermeasure against fluoride by decomposition of the non-aqueous electrolyte is necessary. .

In addition, when the non-aqueous electrolyte storage element is charged at a high voltage of about 5 V, or when the electrolyte salt concentration is increased to about 3 mol / L, the non-aqueous electrolyte is easily decomposed, and fluorine ( F) The component is released. When the fluorine (F) component is liberated, an excessive film formation of fluoride on the surface of the electrode (particularly the negative electrode) causes deterioration such as a reduction in the capacity of the storage element and deterioration of the charge / discharge cycle characteristics.
Therefore, it is desired to provide a nonaqueous electrolyte storage element that is excellent in charge / discharge cycle characteristics.

  An object of the present invention is to solve the above-described problems and achieve the following objects. That is, an object of the present invention is to provide a nonaqueous electrolyte storage element that is excellent in charge / discharge cycle characteristics.

The nonaqueous electrolyte storage element of the present invention as a means for solving the above problems includes a positive electrode containing a positive electrode active material capable of reversibly accumulating or releasing anions, and a negative electrode capable of reversibly accumulating or releasing cations. Comprising a negative electrode containing an active material and a non-aqueous electrolyte containing an electrolyte salt;
The capacity per unit area of the negative electrode is four times or more the capacity per unit area of the positive electrode.

  ADVANTAGE OF THE INVENTION According to this invention, the said various problems in the past can be solved, the said objective can be achieved, and the non-aqueous-electrolyte electrical storage element which is excellent in the cycling characteristics of charging / discharging can be provided.

FIG. 1 is a schematic view showing an example of the nonaqueous electrolyte storage element of the present invention. FIG. 2 is a graph showing the relationship between the number of cycles and the capacity retention rate in the example.

(Non-aqueous electrolyte storage element)
The nonaqueous electrolyte storage element of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, and further includes other members as necessary.
There is no restriction | limiting in particular as said non-aqueous electrolyte electrical storage element, According to the objective, it can select suitably, For example, a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte capacitor, etc. are mentioned.

In the non-aqueous electrolyte storage element using an electrode that accumulates anions on the positive electrode, the present inventors performed high voltage charging when the content of the electrolyte salt in the non-aqueous electrolyte is increased to about 3 mol / L. As a result of intensive studies on the mechanism of the phenomenon in which the capacity of the storage element decreases in this case, when LiPF ₆ is used as the electrolyte salt, the fluorine component derived from the decomposition of the anion PF ₆ ⁻ is the electrode (particularly the negative electrode). It was found that the cause was the formation of a film on the surface. When the non-aqueous electrolyte storage element is charged, LiPF ₆ in the non-aqueous electrolyte is dissociated and PF ₆ ⁻ as an anion is inserted into the positive electrode. At this time, a part of PF ₆ ⁻ is decomposed to release fluorine ions. Fluorine ions dissociated from PF ₆ ⁻ react with lithium, become Li fluoride and cover the electrode surface to increase the internal resistance, thereby deteriorating the storage element capacity and the like. When the cell after repeated charging and discharging was disassembled and the negative electrode was analyzed, the presence of Li fluoride was observed. It has been found that this phenomenon occurs when a fluorine-based electrolyte salt is used.
As a result of intensive studies by the present inventors based on the above findings, it is effective to reduce the decrease in capacity per unit area of the negative electrode due to the deterioration of the negative electrode in order to maintain the stability of repeated charge and discharge. In addition, it has been found that making the capacity per unit area of the negative electrode larger than the capacity per unit area of the positive electrode is effective in improving the reduction in discharge capacity associated with repeated charge / discharge cycles.

In this invention, the capacity | capacitance per unit area of the said negative electrode is 4 times or more of the capacity | capacitance per unit area of the said positive electrode, and 6 times-10 times are preferable. If the capacity ratio (negative electrode capacity / positive electrode capacity) is less than 4 times, the charge / discharge cycle characteristics may be reduced. If the capacity ratio exceeds 10 times, the capacity of the storage element can be improved by maintaining the amount of electrolyte. Although the charge / discharge cycle characteristics can be maintained, it is not preferable because the energy density of the storage element itself is lowered.
Here, the capacity per unit area of the positive electrode and the capacity per unit area of the negative electrode mean the capacity of the positive electrode alone or the negative electrode alone. For example, when the positive electrode is lithium, The capacity to charge and discharge to a voltage. The predetermined voltage generally corresponds to the charging method when the non-electrolyte storage element of the present invention is configured. In the case of the negative electrode, this is the amount of electricity discharged when cation accumulation is performed up to 0 V and cation emission is performed up to 2 V with respect to the lithium electrode.

The capacitance per unit area of the negative electrode is not particularly limited and may be appropriately selected depending on the intended ^purpose, preferably ^{0.5mAh / cm 2 ~5mAh / cm 2} , 1.6mAh / cm 2 ~4. 3 mAh / cm ² is more preferable. Capacity per unit area of the negative electrode is more than 0.5 mAh / cm ² and less than 5 mAh / cm ^2, substantial energy density may decrease.
The capacity per unit area of the negative electrode is not particularly limited and can be appropriately selected depending on the purpose. For example, by changing the average thickness of the negative electrode material layer and changing the content of the negative electrode active material, Can be adjusted.

Moreover, it is preferable that the negative electrode active material of the negative electrode has cations accumulated in advance from the viewpoint of further improving the charge / discharge cycle characteristics. That is, after the negative electrode material layer is formed on the surface of the negative electrode current collector, a predetermined amount of cations is preferably accumulated in advance in the negative electrode active material of the negative electrode.
The accumulation amount of the cation is not particularly limited and may be appropriately selected depending on the intended purpose. However, it is preferable to accumulate at least an electric capacity corresponding to the positive electrode capacity, and is about 0. It is more preferable to accumulate cations corresponding to up to 1V.
There is no particular limitation on the method for pre-doping cation (for example, lithium ion) in the negative electrode active material, and it can be appropriately selected according to the purpose. For example, mechanical charging method, electrochemical charging Method, chemical charging method, and the like.

  According to the mechanical charging method, for example, charging is performed by mechanically contacting a material (such as lithium metal) having a lower potential than the negative electrode active material with the negative electrode active material. More specifically, for example, a predetermined amount of metallic lithium is attached to the negative electrode surface, or a metallic lithium film is directly formed on the negative electrode surface by a vacuum process such as vapor deposition, or on a plastic substrate subjected to a release treatment. The produced lithium metal may be transferred to the negative electrode surface and then charged. Further, in the mechanical charging method, after the material having a lower potential than the negative electrode active material is brought into contact with the surface of the negative electrode, the negative electrode is heated to accelerate the progress of the charging reaction, thereby shortening the time required for the charging reaction. Is possible.

According to the electrochemical charging method, for example, the negative electrode is charged by immersing the negative electrode and the counter electrode in an electrolytic solution and passing a current between the negative electrode and the counter electrode. At this time, for example, metallic lithium can be used as the counter electrode. As the electrolytic solution, for example, a non-aqueous solvent in which a lithium salt is dissolved can be used.
In the electrochemical charging method, it is preferable that charging is performed until the end-of-charge voltage of the negative electrode with respect to metallic lithium is 0.05 V to 1.0 V.
If the end-of-charge voltage of the negative electrode is less than 0.05V, metallic lithium may be deposited on the surface of the negative electrode. If it exceeds 1.0V, the effect of increasing the capacity due to pre-doping on the negative electrode is reduced. May end up.

By setting the capacity per unit area of the negative electrode to be four times or more the capacity per unit area of the positive electrode, and preferably by previously storing cations in the negative electrode active material, a high voltage of a final charge voltage of 5.2 V is obtained. Further, it is possible to prevent the storage element capacity from being reduced by repeated charging and discharging under the condition of a high concentration electrolytic solution having an electrolyte salt concentration of 3 mol / L.
Hereinafter, the positive electrode, the negative electrode, the non-aqueous electrolyte, and the separator of the non-aqueous electrolyte storage element will be sequentially described.

<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 layer having a positive electrode active material on a positive electrode current collector, etc. Is 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.

<< Cathode Material Layer >>
There is no restriction | limiting in particular as said positive electrode material layer, 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. Become.

-Positive electrode active material-
The positive electrode active material is not particularly limited as long as it is a substance capable of reversibly accumulating or releasing anions, and can be appropriately selected according to the purpose. Examples thereof include carbonaceous materials and conductive polymers. Can be 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 and natural graphite 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, and the like. For example, in a powder X-ray diffraction pattern using CuKα rays, the diffraction peak intensity I _{2θ = 22.3 ° at 2θ = 22.3 °} The intensity ratio I _{2θ = 22.3 °} / I 2θ = 26.4 ° of the diffraction peak intensity I _{2θ = 26.4 °} at _{2θ = 26.4 °} is preferably 0.4 or less.
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 size (median diameter) obtained by the laser diffraction / scattering method is 0.1 μm or more and 100 μm or less. preferable.

-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.

  There is no restriction | limiting in particular in the average thickness of the said positive electrode material layer, Although it can select suitably according to the objective, 35 micrometers-280 micrometers are preferable and 70 micrometers-210 micrometers are more preferable. When the average thickness is less than 35 μm, the energy density may be reduced, and when it exceeds 280 μm, the current characteristics may be deteriorated.

<< 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 non-aqueous electrolyte storage element, and can be appropriately selected according to the purpose.

-Method for producing positive electrode-
The positive electrode is obtained by applying a positive electrode material composition in a slurry form by adding the binder, the thickener, the conductive agent, a solvent, and the like to the positive electrode active material as necessary. The positive electrode material layer can be formed by 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 contains a negative electrode active material, and can be appropriately selected according to the purpose. For example, a negative electrode including a negative electrode material layer having a negative electrode active material on a negative electrode current collector, etc. Is mentioned.
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 Layer >>
The negative electrode material layer includes at least a negative electrode active 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 a substance capable of reversibly accumulating or releasing cations, and can be appropriately selected according to the purpose. For example, an alkali metal ion, an alkaline earth metal, or Metal oxides that can be occluded and released; alkali metal ions, metals that can be alloyed with alkaline earth metals, alloys containing these metals, composite alloy compounds; non-reactions due to physical adsorption of ions such as carbonaceous materials with a high specific surface area And the like. Among these, a substance capable of reversibly storing or releasing at least one of lithium and lithium ions is preferable in terms of energy density, and a non-reactive electrode is more preferable in terms of cycle characteristics.
Specifically, the anode active material can be alloyed with lithium such as carbonaceous material, antimony tin oxide, lithium oxide such as silicon monoxide, and other metal oxides, aluminum, tin, silicon, zinc, etc. Or a metal alloy capable of being alloyed with lithium, a composite alloy compound of lithium and an alloy containing the metal, and lithium metal nitride such as cobalt lithium nitride. These may be used individually by 1 type and may use 2 or more types together. Among these, carbonaceous materials are particularly preferable from the viewpoint of safety and cost.
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 and natural graphite are particularly preferable.

-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.

  There is no restriction | limiting in particular in the average thickness of the said negative electrode material layer, Although it can select suitably according to the objective, 35 micrometers-280 micrometers are preferable and 70 micrometers-210 micrometers are more preferable. When the average thickness is less than 35 μm, the energy density may be reduced, and when it exceeds 280 μm, the current characteristics may be deteriorated.

<< 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 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 a non-aqueous electrolyte storage element, and can be appropriately selected according to the purpose.

-Negative electrode manufacturing method-
The negative electrode is obtained by applying a negative electrode material composition in a slurry form by adding the binder, the conductive agent, a solvent, etc. to the negative electrode active material as necessary, and drying the negative electrode current collector. A negative electrode material layer can be formed. 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 that the electrolyte salt has a high dissolving power.
Examples of the chain carbonate include dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl propionate (MP), and the like. Among these, dimethyl carbonate (DMC) is preferable.
The content of the DMC is not particularly limited and can be appropriately selected according to the purpose. However, the content is preferably 70% by mass or more and more preferably 90% by mass or more with respect to the non-aqueous solvent. If the content of the DMC is less than 70% by mass, the amount of the cyclic substance having a high dielectric constant increases when the remaining solvent is a cyclic substance (cyclic carbonate, cyclic ester, etc.) having a high dielectric constant. When a non-aqueous electrolyte solution having a high concentration of 3 mol / L 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 the following cation and the following anion can be used. It is.
Examples of the cation include alkali metal ions, alkaline earth metal ions, tetraalkylammonium ions, spiro quaternary ammonium ions, and the like.
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.

Among the electrolyte salts containing a halogen atom, a lithium salt is particularly preferable from the viewpoint of improving the storage element capacity.
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 hexafluoroarsenide (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, LiPF ₆ is particularly preferable from the viewpoint of the amount of occlusion of anions in the carbon electrode.

  There is no restriction | limiting in particular as content of the said electrolyte salt, Although it can select suitably according to the objective, 3 mol / L or more is preferable in the said nonaqueous solvent, and 3 mol / L-6 mol / L are more preferable. From the viewpoint of achieving both the storage element capacity and the output, 3 mol / L to 4 mol / L is more preferable.

<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 flow nonwoven fabric, polyamide nonwoven fabric, and glass fiber nonwoven fabric. .
Among these, those having a porosity of 50% or more are preferable from the viewpoint of holding the non-aqueous electrolyte.
As the shape of the separator, the non-woven fabric type is preferred from the point of high porosity than the thin-film type having micropores.
There is no restriction | limiting in particular in the average thickness of the said separator, Although it can select suitably according to the objective, 20 micrometers-100 micrometers are preferable. When the average thickness is less than 20 μm, the amount of electrolyte retained may be reduced, and when it exceeds 100 μm, the energy density may be reduced.
More preferably, a microporous film (micropore film) of 30 μm or less is arranged on the negative electrode side in order to prevent a positive / negative short circuit due to precipitation of alkali metal or alkaline earth metal on the negative electrode side, and the thickness on the positive electrode side is 20 μm to It is preferable to use a non-woven fabric with a porosity of 100 μm and a porosity of 50% or more.
Examples of the shape of the separator include a sheet shape.
There is no restriction | limiting in particular as long as the magnitude | size of the said separator is a magnitude | size which can be used for a non-aqueous electrolyte electrical storage element, It can select suitably according to the objective.
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, an armored 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 is manufactured by assembling the positive electrode, the negative electrode, and the non-aqueous electrolyte and a separator used as necessary into an appropriate shape. Furthermore, it is also possible to use other components such as an outer can if necessary. There is no restriction | limiting in particular as a method of assembling the said non-aqueous electrolyte electrical storage element, It can select suitably from the methods employ | adopted normally.

  The non-aqueous electrolyte storage element of the present invention is not particularly limited and can be appropriately selected according to the purpose. However, the maximum voltage during charge / discharge is preferably 4.3 V to 6.0 V. If the maximum voltage at the time of charging / discharging is less than 4.3V, the anion cannot be accumulated sufficiently and the capacity may decrease. If it exceeds 6.0V, the solvent and the electrolyte salt are not easily decomposed and deteriorated. May be faster.

  Here, FIG. 1 is a schematic diagram showing an example of the nonaqueous electrolyte storage element of the present invention. This nonaqueous electrolyte storage element 10 includes a positive electrode 1 including a positive electrode active material capable of reversibly storing or releasing anions and a negative electrode active material capable of reversibly storing and releasing cations in an outer can 4. A negative electrode 2 and a separator 3 are accommodated between the positive electrode 1 and the negative electrode 2, and the positive electrode 1, the negative electrode 2, and the separator 3 are non-aqueous electrolytes (non-aqueous electrolytes) obtained by dissolving an electrolyte salt in a non-aqueous solvent. It is immersed in the figure. In addition, 5 is a negative electrode lead wire and 6 is a positive electrode lead wire.

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

<Application>
The use of the non-aqueous electrolyte storage element of the present invention is not particularly limited and can be used for various purposes. For example, a notebook computer, pen input personal computer, mobile personal computer, electronic book player, mobile phone, mobile fax, mobile phone Copy, 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 Equipment, watch, strobe, camera, etc.

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

<Average thickness of positive electrode material layer and negative electrode material layer>
The average thickness of the positive electrode material layer and the negative electrode material layer was determined by measuring the thickness of the electrode with a micrometer (Ozaki Mfg. Co., Ltd. G2-205), subtracting the current collector thickness, and obtaining the thickness. The thickness of the positive electrode material layer or the negative electrode material layer was measured, and an average value was obtained.

<Measuring method of capacity per unit area of positive electrode and capacity per unit area of negative electrode>
The capacity per unit area of the positive electrode and the capacity per unit area of the negative electrode are capacities for charging and discharging to a predetermined voltage when lithium is used as a counter electrode in the case of the positive electrode. The predetermined voltage corresponds to the charging method when the nonaqueous electrolyte storage element of the present invention is configured. In the case of the negative electrode, this is the amount of electricity discharged when cation accumulation is performed up to 0 V and cation emission is performed up to 2 V with respect to the lithium counter electrode. Specifically, the counter electrode is Li in a two-electrode cell HS manufactured by Hosen Co., Ltd., and the positive electrode is charged to a predetermined voltage (5.2 V in the embodiment) at 0.5 mA / cm ² and 0.5 mA. The capacity was measured by discharging to a predetermined voltage at 3 cm / cm ² (3 V in the example).
(In the example 0V) the predetermined voltage at 0.5 mA / cm ² if the negative electrode charged to, was measured capacity by (2V in this embodiment) discharged at 0.5 mA / cm ² up to a predetermined voltage. In addition, the measurement was performed using the charging / discharging apparatus (TOSCAT3001, Toyo System Co., Ltd. product).

Example 1
-Fabrication of non-aqueous electrolyte storage element-
<Preparation of positive electrode>
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.
Carbon powder (manufactured by TIMCAL, KS-6) 2.7 g and a conductive agent (acetylene black) 0.2 g are kneaded by adding water, and further 5 g of carboxymethyl cellulose (CMC) 2 mass% aqueous solution as a thickener. In addition, the mixture was kneaded to prepare a positive electrode material composition (slurry). The positive electrode material composition was applied to an aluminum foil and vacuum dried at 120 ° C. for 4 hours to form a positive electrode material layer having an average thickness of 70 μm. This was punched into a round shape with a diameter of 16 mm to obtain a positive electrode. 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 capacity per unit area of the positive electrode was 0.46 mAh / cm ² .

<Production of negative electrode>
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 .
A mixture of 3 g of carbon powder (graphite) and 0.15 g of conductive agent (acetylene black) is kneaded with water, and 4 g of a 3% by weight aqueous solution of carboxymethylcellulose (CMC) is added as a thickener and kneaded to form a negative electrode material composition A product (slurry) was prepared. The negative electrode material composition was applied to Cu foil and vacuum dried at 120 ° C. for 4 hours to form a negative electrode material layer having an average thickness of 70 μm. This was punched into a round shape with a diameter of 16 mm to obtain a negative electrode. 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 11 mg. The capacity per unit area of the negative electrode was 1.86 mAh / cm ² , which was 4.04 times the capacity per unit area of the positive electrode.

<Non-aqueous electrolyte>
As a non-aqueous electrolyte, 0.3 mL of dimethyl carbonate (DMC) in which 3 mol / L LiPF ₆ was dissolved was prepared.

<Separator>
An experimental filter paper (manufactured by ADVANTEC, GA-100 GLASS FIBER FILTER) was prepared as a separator.

<Preparation of nonaqueous electrolyte storage element>
In the argon dry box, as shown in FIG. 1, a non-aqueous electrolyte solution was injected by injecting a non-aqueous electrolyte solution by placing a separator between the produced positive electrode and negative electrode and adjoining the separator.

(Example 2)
-Negative electrode pre-doping-
A negative electrode was produced in the same manner as in Example 1. Next, in an argon dry box, a cell was produced using the produced negative electrode of Example 1, lithium metal as a counter electrode, a separator, and a non-aqueous electrolyte. An HS cell manufactured by Hosen Co., Ltd. was used as such a cell.
With respect to the cell, the negative electrode was doped with lithium ions by charging to a final charge voltage of 0.1 V at a current of 0.5 mA / cm ² at room temperature (25 ° C.).

-Fabrication of non-aqueous electrolyte storage element-
The pre-doped cell was disassembled in an argon dry box, and the pre-doped negative electrode was taken out.
In Example 1, the nonaqueous electrolyte storage element of Example 2 was produced in the same manner as in Example 1 except that the pre-doped negative electrode was used as the negative electrode. The capacity per unit area of the negative electrode was 1.86 mAh / cm ² , which was 4.04 times the capacity per unit area of the positive electrode.

(Example 3)
-Fabrication of non-aqueous electrolyte storage element-
In Example 2, the non-aqueous electrolyte electricity storage of Example 3 was the same as Example 2 except that the average thickness of the negative electrode material layer was 103 μm and the mass of the carbon powder (graphite) of the negative electrode material layer was 16 mg. An element was produced. The capacity per unit area of the negative electrode was 2.76 mAh / cm ² , which was 6.0 times the capacity per unit area of the positive electrode.

Example 4
-Fabrication of non-aqueous electrolyte storage element-
In Example 2, the non-aqueous electrolyte storage battery of Example 4 was the same as Example 2 except that the average thickness of the negative electrode material layer was 171 μm and the mass of the carbon powder (graphite) of the negative electrode material layer was 27 mg. An element was produced. The capacity per unit area of the negative electrode was 4.6 mAh / cm ² , which was 10.0 times the capacity per unit area of the positive electrode.

(Example 5)
-Fabrication of non-aqueous electrolyte storage element-
In Example 1, the non-aqueous electrolyte electricity storage of Example 5 was the same as Example 1 except that the average thickness of the negative electrode material layer was 103 μm and the mass of the carbon powder (graphite) of the negative electrode material layer was 16 mg. An element was produced. The capacity per unit area of the negative electrode was 2.76 mAh / cm ² , which was 6.0 times the capacity per unit area of the positive electrode.

(Example 6)
-Fabrication of non-aqueous electrolyte storage element-
In Example 1, the non-aqueous electrolyte electricity storage of Example 6 is the same as Example 1 except that the average thickness of the negative electrode material layer is 170 μm and the mass of the carbon powder (graphite) of the negative electrode material layer is 27 mg. An element was produced. The capacity per unit area of the negative electrode was 4.6 mAh / cm ² , which was 10.0 times the capacity per unit area of the positive electrode.

(Example 7)
-Fabrication of non-aqueous electrolyte storage element-
In Example 1, the non-aqueous electrolyte storage battery of Example 7 was the same as Example 1 except that the average thickness of the negative electrode material layer was 190 μm and the mass of the carbon powder (graphite) of the negative electrode material layer was 30 mg. An element was produced. The capacity per unit area of the negative electrode was 5.06 mAh / cm ² , which was 11.0 times the capacity per unit area of the positive electrode.

(Comparative Example 1)
-Fabrication of non-aqueous electrolyte storage element-
In Example 1, the non-aqueous electrolysis of Comparative Example 1 was performed in the same manner as in Example 1 except that the average thickness of the negative electrode material layer was 34 μm and the mass of the carbon powder (graphite) of the negative electrode material layer was 5.5 mg. A liquid storage element was produced. The capacity per unit area of the negative electrode was 0.92 mAh / cm ² , which was 2.0 times the capacity per unit area of the positive electrode.

(Comparative Example 2)
-Fabrication of non-aqueous electrolyte storage element-
In Example 1, the non-aqueous electrolysis of Comparative Example 2 was performed in the same manner as in Example 1 except that the average thickness of the negative electrode material layer was 52 μm and the mass of the carbon powder (graphite) of the negative electrode material layer was 8.1 mg. A liquid storage element was produced. The capacity per unit area of the negative electrode was 1.38 mAh / cm ² , which was 3.0 times the capacity per unit area of the positive electrode.

  Next, charge / discharge characteristics were repeatedly evaluated for each of the produced nonaqueous electrolyte storage elements as follows. The results are shown in Tables 1 to 3 and FIG.

<Evaluation of repeated charge / discharge characteristics>
The obtained nonaqueous electrolyte storage element 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, initial charge / discharge was performed by discharging to 2.5 V at a constant current of 0.5 mA / cm ² . And about the non-aqueous-electrolyte electrical storage element after an initial stage charge / discharge, constant current charge was performed to 5.2V with the constant current of 0.5 mA / cm < ² >. Next, a constant current discharge that discharges to 2.5 V at a constant current of 0.5 mA / cm ² is defined as one cycle, this charge / discharge cycle is performed up to 200 cycles, and the discharge capacity at the fifth cycle is a reference (100%) As a result, the capacity retention rate (%) for each 50 cycles was determined and evaluated according to the following criteria. In addition, the measurement was performed using the charging / discharging apparatus (TOSCAT3001, Toyo System Co., Ltd. product).
〔Evaluation criteria〕
○: Capacity maintenance rate 85% or more Δ: Capacity maintenance rate 55% or more and less than 85% ×: Capacity maintenance rate less than 55%

From the results of Tables 1 to 3, it can be seen that when Comparative Examples 1 and 2 and Example 1 are compared, the charge / discharge cycle life is improved when the capacity ratio (negative electrode capacity / positive electrode capacity) is increased by 4 times or more. It was.
Moreover, when Example 1 and Example 2 were contrasted, it turned out that the cycle life of charging / discharging further improves by performing pre dope of a negative electrode. The effect of increasing the capacity ratio (negative electrode capacity / positive electrode capacity) can be further obtained by pre-doping the negative electrode. When comparing Examples 2, 3, and 4, it was found that the charge / discharge cycle life was improved as the capacity ratio (negative electrode capacity / positive electrode capacity) increased.
From the above results, it was found that it is effective to pre-dope the negative electrode by setting the capacity ratio (negative electrode capacity / positive electrode capacity) to 4 times or more in order to keep the charge / discharge cycle characteristics favorable.

The aspect of the present invention is as follows.
<1> A positive electrode including a positive electrode active material capable of reversibly accumulating or releasing anions, a negative electrode including a negative electrode active material capable of reversibly accumulating or releasing cations, and a non-aqueous electrolyte including an electrolyte salt. And
A capacity of the negative electrode per unit area is four times or more of a capacity per unit area of the positive electrode.
<2> The non-aqueous electrolyte storage element according to <1>, wherein the capacity per unit area of the negative electrode is 6 to 10 times the capacity per unit area of the positive electrode.
<3> The nonaqueous electrolyte storage element according to any one of <1> to <2>, wherein the capacity per unit area of the negative electrode is 0.5 mAh / cm ^{2 to 5} mAh / cm ² .
<4> The nonaqueous electrolyte storage element according to any one of <1> to <3>, wherein cations are accumulated in advance in the negative electrode active material of the negative electrode.
<5> The nonaqueous electrolyte storage element according to any one of <1> to <4>, wherein a maximum voltage during charge / discharge is 4.3 V to 6.0 V.
<6> The nonaqueous electrolyte storage element according to any one of <1> to <5>, wherein the content of the electrolyte salt in the nonaqueous electrolyte is 3 mol / L or more.
<7> The nonaqueous electrolyte storage element according to any one of <1> to <6>, wherein the negative electrode active material is a carbonaceous material.
<8> The nonaqueous electrolyte storage element according to any one of <1> to <7>, wherein the positive electrode active material is a carbonaceous material.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Exterior can 5 Negative electrode lead wire 6 Positive electrode lead wire 10 Nonaqueous electrolyte storage element

JP-A-2005-251472

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

Claims (8)

A positive electrode including a positive electrode active material capable of reversibly storing or releasing anions; a negative electrode including a negative electrode active material capable of reversibly storing or releasing cations; and a non-aqueous electrolyte including an electrolyte salt. ,
The nonaqueous electrolyte storage element, wherein a capacity per unit area of the negative electrode is four times or more a capacity per unit area of the positive electrode.   The non-aqueous electrolyte storage element according to claim 1, wherein the capacity per unit area of the negative electrode is 6 to 10 times the capacity per unit area of the positive electrode. Capacitance per unit area of the negative ^electrode, nonaqueous electrolytic capacitor element according to any one of claims 1 to 2 which is ^{0.5mAh / cm 2 ~5mAh / cm 2} .   The nonaqueous electrolyte storage element according to any one of claims 1 to 3, wherein cations are accumulated in advance in the negative electrode active material of the negative electrode.   The non-aqueous electrolyte storage element according to any one of claims 1 to 4, wherein a maximum voltage during charging / discharging is 4.3V to 6.0V.   The non-aqueous electrolyte storage element according to claim 1, wherein the content of the electrolyte salt in the non-aqueous electrolyte is 3 mol / L or more.   The nonaqueous electrolyte storage element according to claim 1, wherein the negative electrode active material is a carbonaceous material.   The nonaqueous electrolyte storage element according to claim 1, wherein the positive electrode active material is a carbonaceous material.