JP2018152158A - Operation method of nonaqueous power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an operation method of a nonaqueous power storage device excellent in cycle characteristics.SOLUTION: Provided is an operation method of a nonaqueous power storage device 10 comprising: a positive electrode 11 containing a graphite-based carbon material into or from which an anion can be intercalated or deintercalated; a negative electrode 12 containing a negative electrode active material into or from which lithium ions can be adsorbed or desorbed; and a nonaqueous electrolyte. When charging the nonaqueous power storage device 10, the operation method of the nonaqueous power storage device 10 uses three reaction potential regions, having the lowest to the third lowest potential, among the four reaction potential regions where the anion is intercalated into the graphite-based carbon material.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a method for operating a non-aqueous power storage element.

  Conventionally, as a nonaqueous secondary battery, a lithium salt is dissolved in a nonaqueous solvent as a positive electrode including a positive electrode active material such as lithium cobalt composite oxide, a negative electrode including a negative electrode active material such as carbon, and a nonaqueous electrolyte. Many lithium ion secondary batteries having non-aqueous electrolytes and solid electrolytes have been developed.

  On the other hand, carbon is used as the positive electrode active material, and anions in the nonaqueous electrolyte are inserted or desorbed from carbon as the positive electrode active material, and lithium ions in the nonaqueous electrolyte are inserted into carbon as the negative electrode active material. There is a non-aqueous secondary battery (dual carbon battery) that is charged or discharged after being detached (see, for example, Patent Document 1).

In the dual carbon battery, an anion such as PF ₆ ⁻ is inserted into the positive electrode active material from the non-aqueous electrolyte, and Li ⁺ is inserted into the negative electrode active material from the non-aqueous electrolyte. Discharge occurs when an anion such as PF ₆ ⁻ is desorbed from the positive electrode active material, and Li ⁺ is desorbed from the negative electrode active material to the nonaqueous electrolyte.

デュアルカーボン電池の正極反応では、リチウムコバルト複合酸化物等の正極活物質を用いる場合と異なり、アニオンが利用される。アニオンは、リチウムイオンと異なり、ほとんど溶媒和しない。このため、デュアルカーボン電池の正極反応では、リチウムコバルト複合酸化物等の正極活物質を用いる場合と異なり、アニオンが挿入される過程で脱溶媒和を必要としない、このことは、デュアルカーボン電池を用いると、急速な充放電が可能であることを意味している。また、炭素は、リチウムコバルト複合酸化物等の正極活物質と異なり、構造中に酸素を含まない。このため、炭素は、加熱状態や、過充電状態においても、酸素を放出することなく、使用することができる安全な材料となっている。

Unlike the case of using a positive electrode active material such as a lithium cobalt composite oxide, the anion is used in the positive electrode reaction of the dual carbon battery. Unlike lithium ions, anions hardly solvate. Therefore, unlike the case of using a positive electrode active material such as lithium cobalt composite oxide, the dual carbon battery does not require desolvation in the process of anion insertion. When used, it means that rapid charge / discharge is possible. Further, carbon does not contain oxygen in the structure, unlike a positive electrode active material such as a lithium cobalt composite oxide. For this reason, carbon is a safe material that can be used without releasing oxygen even in a heated state or an overcharged state.

  The discharge capacity of the dual carbon battery includes the amount of anions inserted into the positive electrode active material, the amount capable of desorbing the anions of the positive electrode active material, the amount of cations inserted into the negative electrode active material, and the negative electrode active material It is determined by the amount capable of desorbing cations, the amount of anions and the amount of cations in the non-aqueous electrolyte. For this reason, in the dual carbon battery, in order to increase the discharge capacity, it is necessary to increase the amount of the non-aqueous electrolyte containing a lithium salt in addition to the positive electrode active material and the negative electrode active material (for example, Non-Patent Document 1). reference).

  As described above, the anion is inserted into the positive electrode active material from the non-aqueous electrolyte, and the cation is inserted into the negative electrode active material from the non-aqueous electrolyte, and the anion is desorbed from the positive electrode active material into the non-aqueous electrolyte. In a non-aqueous secondary battery that is discharged by desorption of cations from the negative electrode active material into the non-aqueous electrolyte, a sufficient amount of electrolyte salt is required.

  When a secondary battery using a lithium titanate (LTO) having a spinel structure as a negative electrode active material is charged / discharged, the crystal lattice size and structure of LTO hardly change. For this reason, it is known that LTO has extremely high cycle stability, and a secondary battery using LTO as a negative electrode active material has high cycle stability and safety.

  From the above, the secondary battery using carbon as the positive electrode active material and LTO as the negative electrode active material can be rapidly charged and discharged, and has high cycle stability and safety ( For example, see Patent Document 2).

However, the carbon used as the positive electrode active material has a problem that the cycle characteristics of the secondary battery are deteriorated due to generation of F ^{− which} is considered to be caused by decomposition of anions in charge and discharge in a high potential range. Along with this, there is a concern that the swelling and shrinkage of carbon occurs, the geometrical destruction of the electrode structure proceeds, and the cycle characteristics of the secondary battery deteriorate. For this reason, it is not preferable to use a high potential range as a potential range that is normally used, that is, continuously used for general purposes, and an appropriate potential range for continuous use for general purposes has not been known.

  An object of the present invention is to provide a method for operating a non-aqueous power storage element that is excellent in cycle characteristics in view of the above-described problems of the prior art.

  One embodiment of the present invention includes a positive electrode including a graphite-based carbon material capable of inserting or desorbing anions, a negative electrode including a negative electrode active material capable of inserting or extracting lithium ions, and a non-aqueous electrolyte. A method of operating a non-aqueous storage element having, when charging the non-aqueous storage element, from among the four reaction potential regions into which the anion is inserted into the graphite-based carbon material, from the one having a lower potential, Use up to the third reaction potential region.

  ADVANTAGE OF THE INVENTION According to this invention, the operating method of the non-aqueous electrical storage element which is excellent in cycling characteristics can be provided.

3 is a cyclic voltammogram of a nonaqueous storage element for evaluation of Reference Example 1. FIG. It is a figure which shows the measurement result of the charge characteristic of the positive electrode of the non-aqueous electrical storage element for evaluation of the reference example 1. FIG. It is a figure which shows the measurement result of the cycle characteristic of the non-aqueous electrical storage element for evaluation of Examples 1, 2 and Comparative Example 1. It is a figure which shows the measurement result of the swelling of the positive electrode a of the non-aqueous electrical storage element for evaluation of the reference example 3. It is the schematic which shows an example of the non-aqueous electrical storage element of this embodiment.

(Operation method of non-aqueous storage element)
The operation method of the non-aqueous power storage device of this embodiment includes a positive electrode including a graphite-based carbon material capable of inserting or desorbing anions, and a negative electrode including a negative electrode active material capable of inserting or extracting lithium ions. And a method of operating a non-aqueous storage element having a non-aqueous electrolyte.

  The operation method of the non-aqueous storage element of the present embodiment is the third of the four reaction potential regions in which the anion is inserted into the graphite-based carbon material when the non-aqueous storage element is charged. Up to the reaction potential region. Thereby, the cycle characteristic of a non-aqueous electrical storage element can be improved.

  The non-aqueous electricity storage device of this embodiment preferably includes a separator, and further includes other members as necessary.

  Hereinafter, the operation method of the non-aqueous storage element of this embodiment will be further described.

  FIG. 1 shows a cyclic voltammogram in which an oxidation-reduction reaction in a positive electrode containing graphite (positive electrode active material) when a negative electrode made of lithium (negative electrode active material) is used (see Reference Example 1 described later).

  Here, the oxidation reaction and the reduction reaction at the positive electrode correspond to a charging reaction in which anions are inserted (intercalated) into graphite and a discharge reaction in which anions from graphite are desorbed (deintercalated), respectively.

From FIG. 1, it can be seen that graphite has roughly four reaction potential regions on the oxidation reaction side. First, the first reaction potential region is observed in the measurement in the potential range of 3.0-4.662 V vs Li / Li ⁺ . Next, the first reaction potential region and the second reaction potential region are observed in the measurement in the potential range of 3.0-4.783 Vvs Li / Li ⁺ . Next, in the measurement in the potential range of 3.0-4.969 V vs Li / Li ⁺ , the third reaction potential region is seen from the first reaction potential region. Next, in the measurement in the potential range of 3.0-5.2 V vs Li / Li ⁺ , the fourth reaction potential region is seen from the first reaction potential region.

  FIG. 2 shows the measurement results of the charge characteristics (change in potential due to the charge reaction) of the positive electrode containing graphite (positive electrode active material) when a negative electrode made of lithium (negative electrode active material) was used (see Reference Example 2 described later). ).

As can be seen from FIG. 2, there are four plateau regions (potential flat portions) corresponding to FIG. Specifically, the potential range of 3.0 to 4.9 V vs Li / Li ⁺ corresponds to the first reaction potential region and the second reaction potential region in FIG. Next, the potential range of 4.9-5.0 V vs. Li / Li ⁺ corresponds to the third reaction potential region in FIG. Furthermore, the potential range of 5.0-5.2 V vs Li / Li ⁺ corresponds to the fourth reaction potential region in FIG.

  FIG. 3 shows the cycle characteristics (cycle dependency of discharge capacity retention rate) when a negative electrode containing LTO (negative electrode active material) is used and the potential of a positive electrode containing graphite (positive electrode active material) is controlled to carry out a charge / discharge cycle. The measurement results are shown (see Examples 1 and 2 and Comparative Example 1 described later).

From FIG. 3, a potential range of 3.0 to 4.98 V vs Li / Li ⁺ (Example 2 described later), that is, a region corresponding to the first reaction potential region to the third reaction potential region (particularly, 3.0 It can be seen that the cycle characteristics of the non-aqueous storage element are excellent in the potential range of −4.85 V vs Li / Li ⁺ (Example 1 described later), that is, the first reaction potential region and the second reaction potential region.

This is considered to be caused by the swelling of the positive electrode containing graphite (positive electrode active material) and the generation of F ⁻ which seems to be due to the decomposition of the anion.

  FIG. 4 shows the measurement results of the swelling of the positive electrode containing graphite (positive electrode active material) when using the Li electrode (negative electrode) (see Reference Example 3 described later).

  From FIG. 4, in the first charge (oxidation), the swelling Δh of the positive electrode containing graphite (positive electrode active material) is measured in any reaction potential region. Specifically, Δh to the second reaction potential region is 10 μm, Δh to the third reaction potential region is 32 μm, and Δh to the fourth reaction potential region is 48 μm.

  On the other hand, in the second charge (oxidation), Δh to the second reaction potential region, Δh to the third reaction potential region are ˜0 μm, and Δh to the fourth reaction potential region is 5 μm. From this, it can be seen that the positive electrode containing graphite (positive electrode active material) swells significantly when used up to the fourth reaction potential region when charging the nonaqueous storage element.

Table 1, LTO using a negative electrode containing a (negative active material), graphite (positive electrode active material) non-aqueous electrolyte solution after controlling the potential of the positive electrode was carried discharge cycle 140 hours including F ^- of The result of having measured the density | concentration and the result of having measured the ratio of F of the surface of a negative electrode are shown (refer below Example 3 and 4 and the comparative example 2).

表１から、充放電サイクルにおける電位範囲が３．０−５．２０Ｖ ｖｓ Ｌｉ／Ｌｉ^＋の電位範囲、即ち、第一反応電位領域から第四反応電位領域に相当する領域になると、充放電サイクル後の負極の表面のＦの割合が顕著に増えることがわかる。

From Table 1, when the potential range in the charge / discharge cycle is the potential range of 3.0-5.20 V vs Li / Li ⁺ , that is, the region corresponding to the first reaction potential region to the fourth reaction potential region, the charge / discharge cycle It can be seen that the proportion of F on the surface of the subsequent negative electrode increases significantly.

  From FIG. 3, FIG. 4 and Table 1, it has been found that the cycle characteristics of the non-aqueous storage element are improved when the operation method of the non-aqueous storage element of the present embodiment is used.

(Non-aqueous storage element)
Hereinafter, the positive electrode, the negative electrode, the non-aqueous electrolyte, and the separator of the non-aqueous storage element of this embodiment will be described in order.

<Positive electrode>
The positive electrode is not particularly limited as long as it contains a graphite-based carbon material (such as a positive electrode active material), and can be appropriately selected according to the purpose. For example, a positive electrode containing a positive electrode active material on a positive electrode current collector Examples include a positive electrode provided with a material.

  There is no restriction | limiting in particular as a shape of a positive electrode, According to the objective, it can select suitably, For example, flat form etc. are mentioned.

<< Positive electrode material >>
The positive electrode material includes a positive electrode active material, and further includes a conductive agent, a binder, a thickener, and the like as necessary.

-Positive electrode active material-
The positive electrode active material is a graphite-based carbon material capable of reversibly inserting or desorbing anions.

  Examples of the graphite-based carbon material include graphite such as artificial graphite and natural graphite.

  The graphite-based carbon material preferably has high crystallinity.

  The crystallinity of the graphite-based carbon material can be evaluated by X-ray diffraction, Raman analysis, or the like.

The graphite-based carbon material has, for example, a diffraction peak intensity I at _{2θ = 22.3 °} and a diffraction peak intensity I at 2θ = 26.4 ° in a powder X-ray diffraction pattern using CuKα rays. it is preferable _{2 [Theta] = 26.4 °} of the intensity ratio _{I 2θ = 22.3 ° / I 2θ} = 26.4 ° is 0.4 or less.

Graphite carbon material, that the BET specific surface area by nitrogen adsorption of preferably not more than ^{1 m} 2 / g or more 100 m ² / g, a median diameter determined by laser diffraction-scattering method is 0.1μm or more 100μm or less preferable.

-Binder-
The binder is not particularly limited as long as it is a solvent, a non-aqueous electrolyte, and a material that is stable with respect to an applied potential used when manufacturing the positive electrode, and can be appropriately selected according to the purpose. Examples thereof include fluorine-based binders such as vinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), isoprene rubber, and polyacrylate. These may be used alone or in combination of two or more.

-Thickener-
Examples of the thickener include carboxymethyl cellulose (CMC), methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein. These may be used alone or in combination of two or more.

-Conductive agent-
Examples of the conductive agent include carbonaceous materials such as carbon black and acetylene black. These may be used alone or in combination of two or more.

<< Positive electrode current collector >>
There is no restriction | limiting in particular as a material, a shape, a magnitude | size, and a structure of a 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 a conductive material and is stable with respect to the applied potential, and can be appropriately selected according to the purpose. For example, aluminum, titanium, tantalum, etc. Is mentioned. Among these, aluminum is particularly preferable because it is lightweight, inexpensive, and has high oxidation resistance.

  There is no restriction | limiting in particular as a shape of a positive electrode electrical power collector, According to the objective, it can select suitably.

  The size of the positive electrode current collector is not particularly limited as long as it is a size that can be used for a non-aqueous storage element, and can be appropriately selected according to the purpose.

-Method for producing positive electrode-
The positive electrode is coated with a positive electrode active material and, if necessary, a binder, a thickener, a conductive agent, a solvent, etc., and applied to the positive electrode current collector in a slurry state, and then dried. Then, it can be produced by forming a positive electrode material.

  There is no restriction | limiting in particular as a 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 and alcohol.

  Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP) and toluene.

  In addition, the positive electrode composition in which a binder, a thickener, a conductive agent, and the like are added to the positive electrode active material as necessary can be roll-molded into a sheet electrode, or can be compressed into a pellet electrode. .

<Negative electrode>
The negative electrode is not particularly limited as long as it contains a negative electrode active material capable of occluding or releasing lithium ions, and can be appropriately selected according to the purpose. For example, the negative electrode active material on the negative electrode current collector And a negative electrode provided with a negative electrode material.

  There is no restriction | limiting in particular as a shape of a negative electrode, According to the objective, it can select suitably, For example, flat form etc. are mentioned.

<< Anode Material >>
A negative electrode material contains a negative electrode active material, and further contains a binder, a electrically conductive agent, etc. as needed.

-Negative electrode active material-
Examples of the negative electrode active material include lithium, lithium alloys, graphite (artificial graphite, natural graphite), graphitizable carbon, non-graphitizable carbon, and pyrolysis products of organic substances under various pyrolysis conditions. Among these, LTO is preferable because the insertion and release of lithium ions is fast and the swelling and shrinkage accompanying the charge / discharge cycle hardly occurs.

-Binder-
The binder is not particularly limited as long as it is a solvent, a non-aqueous electrolyte, and a material that is stable with respect to an applied potential used when manufacturing the negative electrode, and can be appropriately selected according to the purpose. Fluorine binders such as vinylidene 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 alone or in combination of two or more. Among these, fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) are preferable.

-Conductive agent-
Examples of the conductive agent include carbonaceous materials such as carbon black and acetylene black. These may be used alone or in combination of two or more.

<< Negative electrode current collector >>
The material, shape, size, and structure of the negative electrode current collector can be appropriately selected according to the purpose.

  The material of the negative electrode current collector is not particularly limited as long as it is a conductive material and is stable with respect to the applied potential, and can be appropriately selected according to the purpose. For example, stainless steel, nickel, aluminum , Copper and the like. Among these, stainless steel, copper, and aluminum are particularly preferable.

  There is no restriction | limiting in particular as a shape of a negative electrode electrical power collector, According to the objective, it can select suitably.

  The size of the negative electrode current collector is not particularly limited as long as it is a size that can be used for a non-aqueous storage element, and can be appropriately selected according to the purpose.

-Negative electrode manufacturing method-
The negative electrode is prepared by adding a binder, a conductive agent, a solvent, etc. to the negative electrode active material as necessary, and applying a slurry-like coating liquid for negative electrode material on the negative electrode current collector, followed by drying. It can be manufactured by forming a material.

  As the solvent, a solvent similar to the method for manufacturing the positive electrode can be used.

  In addition, the negative electrode composition obtained by adding a binder, a conductive agent and the like to the negative electrode active material may be roll-molded to form a sheet electrode, or compression-molded to form a pellet electrode.

  Further, the negative electrode material can be formed by forming a thin film of a negative electrode active material on the negative electrode current collector by a technique such as vapor deposition, sputtering, or plating.

<Nonaqueous electrolyte>
As the nonaqueous electrolyte, a solid electrolyte or a nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a nonaqueous solvent can be used.

<< Solid electrolyte >>
A polymer can be used for the solid electrolyte.

  There is no restriction | limiting in particular as a polymer used for a solid electrolyte, According to the objective, it can select suitably, For example, a polyvinylidene fluoride, a vinylidene fluoride-hexafluoropropylene copolymer, a vinylidene fluoride-ethylene copolymer , Vinylidene fluoride-monofluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer Vinylidene fluoride polymers such as: acrylonitrile-methyl methacrylate copolymer, acrylonitrile-methyl acrylate copolymer, acrylonitrile-ethyl methacrylate copolymer, acrylonitrile-ethyl acrylate copolymer, acrylonitrile -Acrylic nitrile polymers such as methacrylic acid copolymer, acrylonitrile-acrylic acid copolymer, acrylonitrile-vinyl acetate copolymer; polyethylene oxide, ethylene oxide-propylene oxide copolymer, Examples include coalescence. These may be used alone or in combination of two or more.

  Note that the solid electrolyte may be a gel made by adding an electrolytic solution to a polymer, or an ion conductive polymer may be used as it is.

<< Non-aqueous solvent >>
There is no restriction | limiting in particular as a non-aqueous solvent, Although it can select suitably according to the objective, An aprotic organic solvent is used suitably.

  As the aprotic organic solvent, carbonate-based organic solvents such as chain carbonates and cyclic carbonates are used, and solvents having low viscosity are preferable. Among these, a chain carbonate is preferable because the solubility of the electrolyte salt is high.

  Examples of the chain carbonate include dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). Among these, dimethyl carbonate (DMC) is preferable.

  The content of chain carbonate in the non-aqueous solvent is preferably 50% by mass or more. As a result, even when a non-aqueous electrolyte solution having a high concentration of 2M or more is produced, the viscosity is low, so that the non-aqueous electrolyte solution is likely to penetrate into the electrode and ion diffusion is facilitated.

  Examples of the cyclic carbonate include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), and the like.

  In addition, as a 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.) and the like. It is done.

  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 is a compound containing lithium ions that dissolves in a non-aqueous solvent and exhibits high ionic conductivity, but a compound containing a halogen atom is preferable.

Examples of the anion constituting the electrolyte salt include BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , and (C ₂ F ₅ SO ₂ ) ₂ N ^−. Etc.

As the electrolyte salt is not particularly limited and may be appropriately selected depending on the purpose, for example, lithium hexafluorophosphate (LiPF _6), boric lithium fluoride (LiBF _4), hexafluoride arsenic lithium (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 alone or in combination of two or more. Among these, LiPF ₆ is preferable from the viewpoint of the amount of anion inserted into the graphite-based carbon material, and LiBF ₄ is preferable from the viewpoint of being difficult to decompose.

  The concentration of the electrolyte salt in the nonaqueous electrolytic solution is preferably 2 mol / L or more. Thereby, the amount of ions necessary for charging is not lost, and a sufficient charging capacity can be secured.

  Further, the concentration of the electrolyte salt in the nonaqueous electrolytic solution is preferably 6 mol / L or less, and more preferably 4 mol / L or less. When the concentration of the electrolyte salt in the nonaqueous electrolytic solution is 6 mol / L or less, the viscosity of the nonaqueous electrolytic solution becomes low, the nonaqueous electrolytic solution is likely to penetrate into the electrode, and the ionic conductivity is improved.

<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 a separator, a shape, a magnitude | size, and a structure, According to the objective, it can select suitably.

  Examples of the separator include paper such as kraft paper, vinylon mixed paper, synthetic pulp mixed paper, cellophane, polyethylene graft membrane, polyolefin nonwoven fabric such as polypropylene melt blown nonwoven fabric, polyamide nonwoven fabric, glass fiber nonwoven fabric, and micropore membrane.

  The separator preferably has a porosity of 50% from the viewpoint of holding the non-aqueous electrolyte.

  As the shape of the separator, since the porosity is high, the nonwoven fabric type is preferable to the thin film type having micropores.

  The average thickness of the separator is preferably 15 μm or more and 100 μm or less. When the average thickness of the separator is 15 μm or more, the amount of non-aqueous electrolyte retained is increased, and when it is 100 μm or less, the energy density of the non-aqueous storage element is improved.

  The size of the separator is not particularly limited as long as it is a size that can be used for a non-aqueous energy storage device, and can be appropriately selected according to the purpose.

  The structure of the separator may be a single layer structure or a laminated structure.

  Note that when a solid electrolyte is used as the non-aqueous electrolyte, a separator is not necessary.

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

<Method for producing non-aqueous energy storage device>
The non-aqueous electricity storage device of this embodiment can be manufactured by assembling, for example, a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator into an appropriate shape. At this time, it is also possible to use other members such as an outer can if necessary.

  There is no restriction | limiting in particular as a method of assembling a non-aqueous electrical storage element, It can select suitably from the methods employ | adopted normally.

-Shape of non-aqueous storage element-
There is no restriction | limiting in particular as a shape of the non-aqueous electrical storage element of this embodiment, Although it can select suitably according to the use from various shapes generally employ | adopted, For example, a sheet electrode and a separator Cylinder type with spiral shape, cylinder type with inside-out structure combining pellet electrode and separator, coin type with pellet electrode and separator laminated, type with sheet electrode and separator laminated, then packaged with laminate film, etc. It is done.

  FIG. 5 shows an example of the non-aqueous storage element of this embodiment.

  In the nonaqueous storage element 10, a positive electrode 11, a negative electrode 12, and a separator 13 are accommodated in an outer can 14, and the separator 13 is filled with a nonaqueous electrolytic solution. In addition, lead wires 15 and 16 are provided on the positive electrode 11 and the negative electrode 12, respectively.

  Examples of the non-aqueous storage element of this embodiment include a secondary battery and a capacitor.

<Applications of non-aqueous energy storage devices>
The application of the non-aqueous storage element of the present embodiment is not particularly limited and can be used for various applications. For example, a notebook computer, pen input personal computer, mobile personal computer, electronic book player, mobile phone, mobile fax, mobile copy , Portable printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, mini-discs, transceivers, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, lighting equipment, toys, game equipment , Watches, strobes, cameras, etc.

  EXAMPLES Hereinafter, examples will be described, but the present invention is not limited to these examples.

<Preparation of positive electrode>
-Positive electrode a-
After adding and kneading 2.7 g of graphite powder KS-6 (manufactured by TIMCAL) as a positive electrode active material and 0.2 g of a conductive agent (acetylene black), carboxymethyl cellulose (CMC) as a thickener Then, 5 g of a 2% by weight aqueous solution was added and kneaded to prepare a slurry for a positive electrode material.

Here, graphite powder KS-6 (manufactured by TIMCAL) has a BET specific surface area of 20 m ² / g by nitrogen adsorption, and a median diameter measured by a laser diffraction particle size distribution analyzer SALD-2200 (manufactured by Shimadzu Corporation) is 3. .4 μm.

  Next, after applying a slurry for a positive electrode material on an aluminum foil as a positive electrode current collector, the positive electrode material was formed by vacuum drying at 130 ° C. for 12 hours. The aluminum foil on which the positive electrode material was formed was punched into a round shape having a diameter of 15 mm to produce a positive electrode a.

<Production of negative electrode>
-Negative electrode a-
As a negative electrode active material, lithium titanate (made by Ishihara Sangyo Co., Ltd.) 2.19 g, carbon powder MAGD (made by Hitachi Chemical Co., Ltd.) 0.6 g, conductive agent (acetylene black) 0.15 g was added and kneaded. Thereafter, 4 g of a 3% by weight aqueous solution of carboxymethylcellulose (CMC) as a thickener was added and kneaded to prepare a slurry for negative electrode material.

  Next, after applying the slurry for negative electrode materials on the aluminum foil as a negative electrode collector, it vacuum-dried at 130 degreeC for 12 hours, and formed the negative electrode material. The aluminum foil on which the negative electrode material was formed was punched into a round shape having a diameter of 15 mm to produce a negative electrode a.

<Preparation of non-aqueous electrolyte>
-Non-aqueous electrolyte a-
After mixing propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate at a mass ratio of 1: 1: 1, 1.8 mol / L LiPF ₆ and 0.2 mol / L LiBF ₄ are dissolved, and the non-aqueous electrolyte a Was made.

<Separator>
-Separator a-
A cellulose separator (manufactured by Nippon Kogyo Paper Co., Ltd.) having an average thickness of 25 μm was prepared, and five sheets were stacked and used as the separator a.

[Reference Example 1]
In an inert gas atmosphere, a working electrode, a counter electrode, a separator a, and 180 μl of a nonaqueous electrolytic solution a are placed in an electrochemical test cell ECC-Ref (manufactured by EL-CELL) to produce a nonaqueous storage element for evaluation. did. At this time, positive electrode a, lithium (Honjo Metal Co., Ltd.) were used as the working electrode, and lithium (Honjo Metal Co., Ltd.) was used as the reference electrode. At this time, the positive electrode a was punched into a diameter of 13 mm.

  With respect to the reference electrode, the potential of the positive electrode was controlled, and the oxidation-reduction characteristics of the nonaqueous storage element for evaluation were evaluated by cyclic voltammetry. At this time, the potential sweep rate was 0.1 mV / sec, and the following procedures a) to d) were continuously performed.

a) After sweeping the potential of the positive electrode from the natural soaking potential to the high potential side of 4.662 V vs Li / Li ^{+ and} then to the low potential side of 3.0 V vs Li / Li ⁺ to the first natural soaking potential The operation to be performed was defined as one cycle, and two cycles were performed.

b) The potential of the positive electrode is swept from the natural immersion potential to the high potential side of 4.783 V vs Li / Li ^{+ and} then to the low potential side of 3.0 V vs Li / Li ⁺ to the first natural immersion potential. The operation to be performed was defined as one cycle, and two cycles were performed.

c) The potential of the positive electrode is swept from the natural soaking potential to the high potential side 4.969V vs Li / Li ^{+ and} then to the low potential side 3.0V vs Li / Li ⁺ to the first natural soaking potential. The operation to be performed was defined as one cycle, and two cycles were performed.

d) After sweeping the positive electrode potential from the natural immersion potential to the high potential side of 5.2 V vs Li / Li ^{+ and} then to the low potential side of 3.0 V, the operation of sweeping to the first natural immersion potential is one cycle. As a result, two cycles were carried out.

  FIG. 1 shows a cyclic voltammogram of a nonaqueous storage element for evaluation. FIG. 1 shows a cyclic voltammogram for the second cycle of steps a) to d).

From FIG. 1, it can be seen that graphite has roughly four reaction potential regions on the oxidation reaction side. First, in the measurement in the potential range of 3.0-4.662V vs Li / Li ⁺ in the procedure (a), the first reaction potential region is seen. Next, the first reaction potential region and the second reaction potential region are observed in the measurement in the potential range of 3.0-4.783 V vs Li / Li ⁺ in the procedure (b). Next, in the measurement in the potential range of 3.0 to 4.969 V vs Li / Li ⁺ in the procedure (c), the third reaction potential region is seen from the first reaction potential region. Next, in the measurement in the potential range of 3.0-5.2 V vs Li / Li ⁺ in the procedure (d), the fourth reaction potential region is seen from the first reaction potential region.

[Reference Example 2]
Using the evaluation non-aqueous energy storage device of Reference Example 1, the charge characteristics of the positive electrode were measured. Specifically, first, charging was started by flowing a constant current of 0.12 mA between the positive and negative electrodes, and the charging was terminated when the potential of the positive electrode with respect to the reference electrode became 5.2 V vs Li / Li ^+. The state was left for 5 minutes. Next, a constant current of 0.12 mA was passed between the positive and negative electrodes to start discharge, and when the potential of the positive electrode with respect to the reference electrode reached 3.0 V vs Li / Li ⁺ , the discharge was terminated. Left for a minute. This charge / discharge cycle was performed four times.

  In FIG. 2, the measurement result of the charge characteristic of the positive electrode of the nonaqueous electrical storage element for evaluation is shown. In FIG. 2, the charge characteristics of the positive electrode for four times are overwritten, but the charge characteristics of the positive electrode were the same results for all four times.

As can be seen from FIG. 2, there are four plateau regions (potential flat portions) corresponding to FIG. Specifically, the potential range of 3-4.9V vs Li / Li ⁺ corresponds to the first reaction potential region and the second reaction potential region in FIG. Next, the potential range of 4.9-5.0 V vs. Li / Li ⁺ corresponds to the third reaction potential region in FIG. Furthermore, the potential range of 5.0-5.2 V vs Li / Li ⁺ corresponds to the fourth reaction potential region in FIG.

[Example 1]
In an inert gas atmosphere, the positive electrode a, the negative electrode a, and 800 μl of the nonaqueous electrolytic solution a were put into a battery evaluation batch cell SB1A (manufactured by EC Frontier Co., Ltd.) to produce a nonaqueous storage element for evaluation. At this time, lithium (made by Honjo Metal Co., Ltd.) was used as a reference electrode.

  In this cell, the positive and negative electrodes are separated by a certain distance (5 mm), the separator is not used, and the effective charge / discharge region diameter of the positive and negative electrodes is 13 mm.

  In order to initialize the nonaqueous storage element for evaluation, the following procedure was performed.

a) A constant current of 0.067 mA was passed between the positive and negative electrodes to charge the positive electrode until the potential of the positive electrode reached the upper limit potential, and left in that state for 5 minutes. At this time, the upper limit potential was 4.85 V vs Li / Li ⁺ (see Reference Example 2).

  b) A constant current of 0.067 mA was passed between the positive and negative electrodes to discharge the positive electrode until the potential of the positive electrode reached 3.0 V, and this state was left for 5 minutes.

c) A constant current of 0.335 mA was passed between the positive and negative electrodes to charge the positive electrode until the potential of the positive electrode reached the upper limit potential (4.85 V vs Li / Li ⁺ ), and left in that state for 5 minutes.

  d) A constant current of 0.335 mA was passed between the positive and negative electrodes to discharge the positive electrode until the potential of the positive electrode reached 3.0 V, and left in that state for 5 minutes.

  e) The charge / discharge cycle consisting of steps c) and d) was carried out 10 times.

  f) Procedures a) and b) were performed.

  After the above procedure was performed to initialize the evaluation non-aqueous energy storage device, the non-aqueous electrolyte a was discarded. Next, the inside of the cell was washed twice with 800 μl of the non-aqueous electrolyte a, and then the non-aqueous electrolyte a was discarded.

  After putting 800 μl of the non-aqueous electrolyte a in the cell, the charge / discharge cycle consisting of procedures c) and d) was carried out for 140 hours (66 times), and the cycle characteristics of the evaluation non-aqueous power storage element were measured. As a result, the non-aqueous storage element for evaluation had a discharge capacity maintenance rate of 103%. At this time, the discharge capacity of the nonaqueous storage element for evaluation when the fifth charge / discharge cycle was performed was set to 100%.

[Example 2]
The cycle characteristics of the non-aqueous storage element for evaluation were measured in the same manner as in Example 1 except that the upper limit potential was changed to 4.98 V vs Li / Li ⁺ (see Reference Example 2). As a result, the non-aqueous storage element for evaluation had a discharge capacity maintenance rate of 92%.

[Comparative Example 1]
The cycle characteristics of the nonaqueous storage element for evaluation were measured in the same manner as in Example 1 except that the upper limit potential was changed to 5.2 V vs Li / Li ⁺ (see Reference Example 2). As a result, the non-aqueous storage element for evaluation had a discharge capacity maintenance rate of 74%.

  In FIG. 3, the measurement result of the cycle characteristic of the non-aqueous power storage element for evaluation of Examples 1 and 2 and Comparative Example 1 is shown.

  From FIG. 3, it can be seen that the operation method of the non-aqueous storage element of Examples 1 and 2 (particularly, Example 1) has excellent cycle characteristics.

  On the other hand, since the charge / discharge cycle includes the fourth reaction potential region (see Reference Examples 1 and 2), the cycle characteristics of the operation method of the non-aqueous storage element of Comparative Example 1 are deteriorated.

[Reference Example 3]
In an inert gas atmosphere, an electrochemical dilatometer ECD-2 (manufactured by EL-Cell) is charged with positive electrode a, lithium (manufactured by Honjo Metal Co., Ltd.), and electrolytic solution a as a negative electrode. Then, the charge / discharge cycle was carried out twice, and the swelling of the positive electrode a was measured. At this time, the positive electrode a was punched into a diameter of 10 mm.

  In FIG. 4, the measurement result of the swelling of the positive electrode a is shown.

  From FIG. 4, in the first charge (oxidation), the bulge Δh of the positive electrode a is measured in any reaction potential region. Specifically, Δh to the second reaction potential region is 10 μm, Δh to the third reaction potential region is 32 μm, and Δh to the fourth reaction potential region is 48 μm.

  On the other hand, in the second charge (oxidation), Δh is obtained up to the second reaction potential region, Δh up to the third reaction potential region is ˜0 μm, and Δh up to the fourth reaction potential region is 5 μm. From this, it can be seen that the positive electrode a swells significantly when used up to the fourth reaction potential region when charging the non-aqueous storage element.

[Example 3]
In an inert gas atmosphere, the positive electrode a, the negative electrode a, and 800 μl of the nonaqueous electrolytic solution a were put into a battery evaluation batch cell SB1A (manufactured by EC Frontier Co., Ltd.) to produce a nonaqueous storage element for evaluation. At this time, lithium (made by Honjo Metal Co., Ltd.) was used as a reference electrode.

  In this cell, the positive and negative electrodes are separated by a certain distance (5 mm), the separator is not used, and the effective charge / discharge region diameter of the positive and negative electrodes is 13 mm.

  In order to initialize the nonaqueous storage element for evaluation, the following procedure was performed.

a) A constant current of 0.067 mA was passed between the positive and negative electrodes to charge the positive electrode until the potential of the positive electrode reached the upper limit potential, and left in that state for 5 minutes. At this time, the upper limit potential was 4.85 V vs Li / Li ⁺ (see Reference Example 2).

  b) A constant current of 0.067 mA was passed between the positive and negative electrodes to discharge the positive electrode until the potential of the positive electrode reached 3.0 V, and this state was left for 5 minutes.

c) A constant current of 0.335 mA was passed between the positive and negative electrodes to charge the positive electrode until the potential of the positive electrode reached the upper limit potential (4.85 V vs Li / Li ⁺ ), and left in that state for 5 minutes.

  d) A constant current of 0.335 mA was passed between the positive and negative electrodes to discharge the positive electrode until the potential of the positive electrode reached 3.0 V, and left in that state for 5 minutes.

  e) The charge / discharge cycle consisting of steps c) and d) was carried out 10 times.

  f) Procedures a) and b) were performed.

  After the above procedure was performed to initialize the evaluation non-aqueous energy storage device, the non-aqueous electrolyte a was discarded. Next, the inside of the cell was washed twice with 800 μl of the non-aqueous electrolyte a, and then the non-aqueous electrolyte a was discarded.

One hour after putting 800 μl of the non-aqueous electrolyte a in the cell, 40 μl of the non-aqueous electrolyte a was sampled twice from the cell. The concentration of F ^{− in} the collected non-aqueous electrolyte a was measured and used as the initial value of the F ⁻ concentration.

After carrying out the charge / discharge cycle consisting of procedures c) and d) for 140 hours (66 times), 40 μl of the non-aqueous electrolyte a was sampled twice from the cell. When the concentration of F ⁻ of the collected non-aqueous electrolyte a was measured, the difference from the initial value, that is, the amount of change in the concentration of F ⁻ in the non-aqueous electrolyte a after the charge / discharge cycle was −2 ppm. .

In addition, the density | concentration of F < ^- > in the non-aqueous electrolyte a was measured by the ion chromatograph ICS1500 (made by DIONEX).

  Next, the cell was disassembled, the negative electrode a was taken out, washed twice with dimethyl carbonate, and then dried. Next, after introducing the negative electrode a into the field emission scanning electron microscope MERLIN (manufactured by SII Nanotech), the ratio of F on the surface of the negative electrode a was measured by an energy dispersive X-ray spectrometer attached to the scanning electron microscope. 23.7%.

[Example 4]
Except for changing the upper limit potential to 4.98 V vs Li / Li ⁺ , the amount of F ⁻ concentration change in the non-aqueous electrolyte a after the charge / discharge cycle and F on the surface of the negative electrode a were the same as in Example 3. When the ratio of was measured, they were 20 ppm and 27.2%, respectively.

[Comparative Example 2]
Except for changing the upper limit potential to 5.2 V vs Li / Li ⁺ , the amount of change in the concentration of F ⁻ in the non-aqueous electrolyte a after the charge / discharge cycle and the surface F of the negative electrode a were the same as in Example 3. When the ratio of was measured, they were 13 ppm and 38.9%, respectively.

Table 2 shows the measurement of the amount of change in F ⁻ concentration in the non-aqueous electrolyte a and the ratio of F on the surface of the negative electrode a after the charge / discharge cycle of the non-aqueous storage element for evaluation in Examples 3 and 4 and Comparative Example 2. Results are shown.

表２から、比較例２の評価用非水系蓄電素子は、実施例３、４の評価用非水系蓄電素子よりも、充放電サイクル後の負極ａの表面のＦの割合が増えていることがわかる。

From Table 2, the ratio of F on the surface of the negative electrode a after the charge / discharge cycle is increased in the nonaqueous storage element for evaluation in Comparative Example 2 than in the nonaqueous storage element for evaluation in Examples 3 and 4. Recognize.

DESCRIPTION OF SYMBOLS 10 Non-aqueous electrical storage element 11 Positive electrode 12 Negative electrode 13 Separator 14 Exterior cans 15, 16 Lead wire

JP-A-2005-251472 JP 2003-77544 A

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

Claims (4)

Operation of a non-aqueous storage element having a positive electrode including a graphite-based carbon material capable of inserting or desorbing anions, a negative electrode including a negative-electrode active material capable of inserting or extracting lithium ions, and a non-aqueous electrolyte A way to
When charging the non-aqueous energy storage device, use of the four reaction potential regions into which the anion is inserted into the graphite-based carbon material, from the one having the lowest potential to the third reaction potential region. A method for operating a non-aqueous energy storage device.   When charging the non-aqueous energy storage device, use of the four reaction potential regions in which the anion is inserted into the graphite-based carbon material, from the one having the lowest potential to the second reaction potential region. The method for operating a non-aqueous storage element according to claim 1, wherein   The method for operating a non-aqueous storage element according to claim 1, wherein the non-aqueous electrolyte is a non-aqueous electrolyte solution having an electrolyte salt concentration of 2 mol / L or more.   The method for operating a non-aqueous storage element according to any one of claims 1 to 3, wherein the negative electrode active material is lithium titanate.

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