JP6164011B2 - Electrode for nonaqueous electrolyte storage element - Google Patents

Description

  The present invention relates to an electrode for a nonaqueous electrolyte storage element and a nonaqueous electrolyte storage element using the same.

Currently, negative electrode active materials used in non-aqueous electrolyte electricity storage devices represented by lithium ion secondary batteries and the like are mainly graphite-based carbonaceous materials. Graphite carbon material can reversibly insert and desorb 1 lithium atom with respect to 6 carbon atoms, and its theoretical electricity is 372 mAh / g.
In recent years, nonaqueous electrolyte storage elements have come to be used as power sources for electric vehicles, and higher capacities are required to improve the cruising distance of electric vehicles.

In order to further increase the capacity of the nonaqueous electrolyte storage element, it is necessary to develop a high-capacity material that replaces the conventional graphitic carbon material. Examples of such a high-capacity material include a substance containing silicon, and typical examples include silicon (Si), silicon oxide (SiO _x , x is 0 <x ≦ 2), silicon alloy, and the like. Can do.

  Although the substance containing silicon has a large theoretical charge / discharge capacity, the substance undergoes a large volume change with insertion and extraction of lithium (Li) in the charge / discharge cycle. Degradation of power storage elements such as dropping or peeling of substance particles from the current collector due to this volume change, and increase in irreversible capacity due to pulverization of substance particles has become a problem, and efforts to solve these problems are in progress. It is made.

Patent Document 1 discloses “a negative electrode for a lithium ion secondary battery in which a conductive organic thin film layer having a film thickness of 0.1 μm or more is formed on a copper base material to be a current collector.” A technique that can provide a negative electrode for a lithium ion secondary battery having excellent cycle characteristics (charge / discharge characteristics) is disclosed.
Further, “the organic thin film layer is made of a polyimide thin film layer in which conductive particles are dispersed” (Claim 4), “an active material layer made of Sn-based material or Si-based material is formed on the organic thin film layer. (Claim 5).

  Patent Document 2 discloses “a negative electrode material for Li ion secondary battery, characterized in that an organic thin film containing conductive particles and an active material made of SiO powder is formed on a copper base material” (claim). Item 1), “The organic thin film has a concentration gradient such that the active material concentration gradually increases from the copper substrate side.” (Claim 2) Thus, a technique is disclosed in which a Li-ion secondary battery negative electrode material that can prevent peeling of the active material can be obtained.

Patent Document 3 states that "in an electrode mixture layer formed by laminating an electrode mixture paste obtained by kneading electrode raw material powder together with a binder and a solvent on a current collector, the binder in the electrode mixture layer" An electrode for a non-aqueous electrolyte secondary battery characterized in that the concentration is increased near the current collector. "(Claim 1), whereby adhesion between the current collector and the electrode mixture layer is achieved. There is disclosed a technique capable of providing an electrode for a non-aqueous electrolyte secondary battery that can reduce the amount of binder and improve charge / discharge characteristics and a method for manufacturing the same without reducing the amount of the binder.
Further, “a nonaqueous electrolyte secondary battery electrode characterized in that the binder concentration near the surface of the electrode mixture layer is set to be higher than the center side” (Claim 2). "The binder concentration in the center is 50 to 90% compared to the binder concentration near the current collector" (Claim 3).

JP 2010-272399 A JP 2010-205659 A JP-A-10-270013

  In Patent Document 1, an organic thin film layer having conductivity different from that of an active material layer is formed on a copper base material serving as a current collector, and further, a polyimide thin film in which conductive particles are dispersed in the organic thin film layer It is described that it consists of layers. However, since the binder used for the active material layer in the examples is polyvinylidene fluoride (PVdF), which is a binder made of a material different from that of the polyimide thin film layer, the thickness of the negative electrode accompanying the charge / discharge cycle is reduced. The ability to suppress expansion is not sufficient.

  In Patent Document 2, an electrodeposition liquid containing a binder composed of a polyimide liquid, conductive particles composed of acetylene black, and an active material composed of SiO powder is electrophoretically deposited, and the current density at the time of electrodeposition is sequentially reduced. Thus, it is described that a concentration gradient is provided in the organic thin film so that the active material concentration gradually increases from the copper substrate side. However, the specific ratio of the binder in the vicinity of the surface of the organic thin film layer and the center of the organic thin film layer is unknown, and the ability to suppress the negative electrode thickness expansion associated with the charge / discharge cycle of the lithium ion secondary battery is Not necessarily enough.

  In Patent Document 3, the binder concentration in the electrode mixture layer is not uniform, and the binder concentration is set so that the binder concentration near the surface of the electrode mixture layer is higher than the center side. Is 50-90% of the binder concentration near the current collector. However, in the examples, a carbon material is used as an active material and polyvinylidene fluoride (PVdF) is used as a binder. In the case of using an active material that reaches four times the particle volume before discharge, it cannot be said that the ability to suppress the expansion of the negative electrode thickness accompanying the charge / discharge cycle is sufficient.

  The present invention has been made in view of the above-described problems, and provides an electrode for a nonaqueous electrolyte storage element in which the expandability of the electrode thickness associated with a charge / discharge cycle is improved, and a nonaqueous electrolyte storage element using the same There is to do.

  The configuration and effects of the present invention will be described with a technical idea. However, the action mechanism includes estimation, and the correctness does not limit the present invention. It should be noted that the present invention can be implemented in various other forms without departing from the spirit or main features thereof. For this reason, the following embodiments or experimental examples are merely examples in all respects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

The present invention comprises a current collector, a mixture layer containing a silicon-containing substance and a polyimide binder, and a thickness of 0.5 to 5 μm between the mixture layer and the current collector , It is an electrode for a nonaqueous electrolyte electricity storage element provided with a layer made of a polyimide resin.
The present invention also includes a current collector, a mixture layer containing a silicon-containing substance and a polyimide-based binder, and a thickness of 0.5 on the side of the mixture layer opposite to the current collector. It is an electrode for nonaqueous electrolyte elements provided with a layer made of polyimide resin of ˜5 μm .

  ADVANTAGE OF THE INVENTION According to this invention, the electrode for nonaqueous electrolyte electrical storage elements with which the expansibility of the electrode thickness accompanying a charging / discharging cycle was improved, and a nonaqueous electrolyte electrical storage element using the same can be provided.

FIG. 3 is a diagram showing a measurement result of electron beam microanalyzer (EPMA) measurement of the electrode for a nonaqueous electrolyte storage element of Example 1.

An electrode for a nonaqueous electrolyte storage element according to the present invention includes a current collector, a mixture layer containing a silicon-containing substance and a polyimide-based binder, and the current collector side of the mixture layer or the current collector. The electrode for a non-aqueous electrolyte storage element includes a layer made of a polyimide resin on the surface opposite to the body.

When a silicon-containing substance is used as an active material, by using a polyimide-based binder, the expansion in the thickness direction of the mixture layer due to the volume change accompanying the charge / discharge cycle of the compound containing silicon is suppressed. Can do.
The binder used for the electrode for the non-aqueous electrolyte element includes polyvinylidene fluoride (PVDF), polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, and styrene, which are used in lithium batteries. Butadiene rubber (SBR) and the like are well known. However, in the present invention, since a silicon-containing substance is used as an active material, in these binders, the expansion of the mixture layer in the thickness direction caused by the volume change accompanying the charge / discharge cycle of the compound containing silicon Is not preferable because it is difficult to sufficiently suppress the electrochemical property, and the electrochemical characteristics of the electrode for the nonaqueous electrolyte storage element are likely to deteriorate.

Further, the current collector-side or surface opposite to the collector of the mixture layer, in Rukoto a layer made of a polyimide resin, in the thickness direction of the non-aqueous electrolyte energy storage element electrodes associated with charge and discharge cycles Expansion can be suppressed.

Here, the layer made of polyimide resin may be provided on at least a part of the current collector side of the mixture layer or the surface opposite to the current collector. From the viewpoint of improving the expandability of the electrode thickness associated with the charge / discharge cycle, it is preferable that the area of the layer made of polyimide resin is larger, and the layer made of polyimide resin is the current collector side of the mixture layer or the current collector Most preferably, it is provided over the entire opposite surface.

The concentration of the polyimide binder contained in the layer made of the polyimide resin and the mixture layer, as described later in the examples, the cut surface of the electrode for the nonaqueous electrolyte storage element by an electron beam microanalyzer (EPMA), It is measured by analyzing the element distribution and performing quantitative analysis on nitrogen (N) contained in the polyimide binder.

In addition, as a polyimide binder for the layer made of the polyimide resin and the mixture layer, a non-aqueous electrolyte can be obtained by using a polyimide resin having the same type of polyimide, the same kind of solvent, or the composition of the polyimide contained in the binder. This is preferable because the manufacturing process of the electrode for the storage element can be simplified.

Further, as shown in the examples below, the collector of the mixture layer by providing a layer made of a polyimide resin on the opposite side, comprises a layer made of a polyimide resin on the collector side of the mixture layer It is preferable because the effect of the present invention can be enhanced.

The thickness of the layer made of the polyimide resin in the nonaqueous electrolyte storage element electrode according to the present invention is preferably 0.5 to 5 μm from the viewpoint of suppressing the expansion of the thickness of the nonaqueous electrolyte storage element electrode. At this time , it is preferable that the thickness of the mixture layer provided with the layer which consists of a polyimide-type resin is 1-70 micrometers .

The layer made of the polyimide resin may contain a substance other than the polyimide binder as long as the effects of the present invention are not impaired .

In the electrode for nonaqueous electrolyte storage elements according to the present invention, it is preferable to provide a carbon material in the mixture layer because charge / discharge cycle characteristics can be improved.
Examples of the carbon material include carbon nanotubes, amorphous carbon, natural graphite, artificial graphite, flake graphite, carbon black, acetylene black, ketjen black, carbon whisker and the like. Further, for the purpose of improving the characteristics of the carbon material itself or the nonaqueous electrolyte storage element, a different element such as boron may be added.
Among these, it is preferable to use scale-like graphite.
The proportion of scaly graphite contained in the carbon material is preferably 40% by mass or more. More preferably, it is 40-60 mass%.

As the flake graphite, it is preferable to use flake graphite having a BET specific surface area of 6 to 10 m ² / g by a flow method nitrogen gas adsorption method because charge / discharge cycle characteristics can be improved. The 50% particle diameter (D50) in the particle size distribution measurement is preferably 7 to 15 μm, and the R value in Raman spectroscopy is preferably R ≦ 0.17.

As the substance containing silicon used for the electrode for the nonaqueous electrolyte storage element according to the present invention, silicon, silicon oxide or silicon alloy can be used alone or in combination of two or more. For example, a substance represented by the general formula SiO _x (0 ≦ x <2) can be given .
In addition, a small amount of typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Excluding inclusion of typical metal elements such as Ge, transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W Absent.

In the substance represented by the general formula SiO _x (0 ≦ x <2), it is preferable to use a material containing both phases of SiO ₂ and Si. Such a material has a small volume expansion due to insertion and extraction of lithium into and from Si in the SiO ₂ matrix. Therefore, by mixing them at an optimum ratio, a substance having a large discharge capacity and excellent charge / discharge cycle characteristics can be obtained.

Furthermore, in the substance represented by the general formula SiO _x (0 ≦ x <2), the range of 2θ = 46 ° to 49 ° in the X-ray diffraction measurement (XRD) profile measured using CuKα rays. When the half width of the peak appearing in is less than 3 °, the charge / discharge cycle characteristics are excellent, which is preferable.

  The average particle diameter of the substance containing silicon is preferably 5 μm or less. Furthermore, it is more preferably 1 μm or less for the purpose of improving the charge / discharge cycle characteristics of the nonaqueous electrolyte storage element.

In addition, the crystallinity of a silicon-containing substance can be used from a highly crystalline one to an amorphous one, but the high crystalline one has a large reversible potential change when it is made amorphous by a charge / discharge cycle. Therefore, it is preferable to use an amorphous material.
Furthermore, it is possible to use a silicon-containing substance that has been washed with an acid such as hydrofluoric acid or sulfuric acid or that has been reduced with hydrogen.

An active material in which a silicon-containing substance is coated with a conductive substance can suppress any separation between the particles and the conductive substance that accompanies a volume change of the silicon-containing substance accompanying charge / discharge. It is preferable because good charge / discharge characteristics can be obtained even in a state.
The conductive substance that coats the substance containing silicon is not particularly limited as long as it is a substance that is more excellent in electrical conductivity than the substance containing silicon. Examples thereof include carbon, metal, metal compound, metal fiber, conductive polymer, conductive ceramic and the like. Among these, it is preferable to use carbon from the balance of the influence on the ease of a coating process, manufacturing cost, electrical conductivity, and characteristics of the nonaqueous electrolyte storage element. Examples of carbon include carbon nanotubes, amorphous carbon, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon whiskers. Further, for the purpose of improving the characteristics of the carbon or non-aqueous electrolyte storage element, a different element such as boron may be added.

  The method for coating a silicon-containing substance with a conductive substance is not particularly limited. For example, silicon is contained by decomposing in a gas phase using benzene, toluene, xylene, methane, or the like as a carbon source. CVD method for chemical vapor deposition on the surface of a substance, method of heating in an inert or reducing atmosphere after mixing a silicon-containing substance and an organic compound, or between a silicon-containing substance and a carbon material Examples thereof include a mechanical milling method in which mechanical energy is applied to form a composite. Among them, a method of coating low crystalline carbon on the surface of a substance containing silicon by a CVD method is preferable.

The coating amount of the conductive material covering the silicon-containing material contained in the active material is preferably 1 to 30% by mass. More preferably, it is 2-10 mass%. By setting the coating amount of the conductive material within the above range, the charge / discharge characteristics of the active material can be made excellent.
When the coating amount of the conductive material is less than 1% by mass, the amount of the conductive material that assists the electronic conductivity of the silicon-containing material is too small, which is not preferable because the charge / discharge capacity decreases. In addition, when the coating amount of the conductive material exceeds 30% by mass, ion conduction between the silicon-containing material and the nonaqueous electrolyte is inhibited by the conductive material, which is not preferable because the charge / discharge capacity is reduced.

The counter electrode of the electrode for a nonaqueous electrolyte storage element according to the present invention is not particularly limited as long as the electrode has a different reversible potential due to charge / discharge. Examples of the counter electrode include LiCoO ₂ , LiMn ₂ O ₄ , LiNiCoO ₂ , LiNiMnCoO ₂ , Li (Ni _0.5 Mn _1.5 ) O ₄ , Li ₄ Ti ₅ O ₁₂ , LiV ₃ O _{8 and} other lithium transition metal composite oxides, Lithium-rich transition metal complex oxides such as Li [LiNiMnCo] O ₂ , polyanion compounds such as LiFePO ₄ , LiMnPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , iron sulfide, iron fluoride, sulfur And the like.

A polyimide-based binder is used as the binder used in the mixture layer of the electrode for the nonaqueous electrolyte storage element according to the present invention. Examples of the polyimide binder include polyimide and polyamideimide. Polyimide is particularly preferable.
1-50 mass% is preferable with respect to the total mass of a mixture layer, and, as for content of the binder in a mixture layer, 2-30 mass% is especially preferable.

The electrode is produced by sequentially forming a mixture layer and a layer made of a polyimide resin on a current collector such as a copper foil. The order of forming the layer composed of the mixture layer and the polyimide resin on the current collector is arbitrary.

  The mixture layer is prepared by kneading a silicon-containing substance and a polyimide resin binder into an organic solvent such as N-methylpyrrolidone and toluene, or water and then mixing the resulting mixture. It is preferably produced by applying it on a current collector or a surface layer and performing a heat drying treatment at a temperature of about 50 ° C to 250 ° C. About the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited.

A layer made of a polyimide resin was prepared by mixing a polyimide compound with an organic solvent such as N-methylpyrrolidone or toluene or water, and then applying the obtained mixture on a current collector or a mixture layer at 50 ° C. It is preferably produced by performing a heat drying treatment at a temperature of about ~ 250 ° C. About the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited.

  The nonaqueous electrolyte used for the nonaqueous electrolyte electricity storage device according to the present invention is not limited, and those generally proposed for use in lithium batteries and the like can be used. Nonaqueous solvents used for the nonaqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof Examples thereof include a conductor alone or a mixture of two or more thereof, but are not limited thereto.

Examples of the electrolyte salt used for the non-aqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, and NaBr. , KClO ₄ , KSCN, and other inorganic ion salts containing one of lithium (Li), sodium (Na), or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ (SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H _{9) 4, NClO 4, (} n-C 4 H 9) 4 NI, (C 2 H 5) 4 N-maleate, (C 2 H 5) 4 N-benzoate, (C 2 H 5) 4 N-pht h Alate, lithium stearyl sulfonate, lithium octyl sulfonate, organic ion salts such as lithium dodecyl benzenesulfonic acid and the like, it is possible to use a mixture of these ionic compounds alone, or two or more kinds.

Further, by using a mixture of LiPF ₆ or LiBF ₄ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ , the viscosity of the electrolyte can be further reduced, The low temperature characteristics can be further improved, and self-discharge can be suppressed, which is more desirable.

  Moreover, you may use normal temperature molten salt and an ionic liquid as a nonaqueous electrolyte.

  The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, more preferably 0.5 mol / l in order to reliably obtain a non-aqueous electrolyte storage element having high power storage element characteristics. -2.5 mol / l.

  As the separator, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the material constituting the separator include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene copolymer. , Vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoro Acetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoro Ethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

  The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

  The separator may be a polymer gel composed of a polymer and an electrolyte such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, and vinylidene fluoride. Use of the non-aqueous electrolyte in the gel state as described above is preferable in that it has an effect of preventing leakage.

  Furthermore, it is desirable that the separator be used in combination with the above-described porous film, non-woven fabric, or the like and a polymer gel because the liquid retention of the electrolyte is improved. That is, by forming a film in which the surface of the polyethylene microporous membrane and the microporous wall are coated with a solvophilic polymer having a thickness of several μm or less, and holding the electrolyte in the micropores of the film, Gels.

  Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. The monomer can be subjected to a crosslinking reaction using a radical initiator in combination with heating or ultraviolet rays (UV), or using an actinic ray such as an electron beam (EB).

  The shape of the nonaqueous electrolyte storage element is not particularly limited, and examples thereof include a cylindrical shape, a square shape, a flat shape, and a button shape.

Example 1
Polyimide was used as the polyimide resin . Are treated with the dispersion medium N- methylpyrrolidone (NMP), polyimide a solution containing such a solid content of 17.5 wt% was prepared, further added and mixed NMP of the solution and the mass, polyimide A solution of the resin was prepared. After this coating paste was applied to a copper foil current collector having a thickness of 20 μm, vacuum drying was performed at 350 ° C. for 5 hours to prepare a layer made of polyimide resin .

Silicon oxide coated with carbon (carbon content: 5.9% by mass, D50 = 4.5 μm) as a material containing silicon as an active material, and flaky graphite (manufactured by TIMCAL Ltd., SFG-) 6) was mixed so that the mass ratio was 4: 6. Subsequently, the polyimide as the binder was mixed so that the mass ratio of the mixture of the active material and the conductive agent to the binder was (active material + conductive agent): binder = 9: 1. Further, an appropriate amount of N-methylpyrrolidone was added as a dispersion medium and kneaded and dispersed to prepare a coating paste for the mixture layer. After this coating paste was applied over the entire layer made of the polyimide resin , vacuum drying was performed at 350 ° C. for 5 hours, and roll pressing was performed to produce a nonaqueous electrolyte storage element electrode. When the thickness and coating mass of the produced electrode for a nonaqueous electrolyte storage element were measured, the electrode thickness was 49 μm and the coating mass was 2.68 mg / cm ² . The thickness of the combined layer obtained by subtracting the thickness of the copper foil of the current collector from the electrode thickness and the layer made of the polyimide resin were 29 μm.

(Example 2)
In the step of producing an electrode for a nonaqueous electrolyte storage element , the mixture layer coating paste was applied onto a copper foil current collector and vacuum-dried. Throughout over the mixture layer, applying a solution of the polyimide resin, and vacuum drying, with the exception that was roll press, the non-aqueous in Example 2 in the same manner as in Example 1 An electrolyte storage element was produced. The electrode thickness was 48 μm, and the coating mass was 3.35 mg / cm ² . The thickness of the combined layer of the mixture layer and the polyimide resin layer was 28 μm.

(Comparative Example 1)
In the step of preparing a non-aqueous electrolyte energy storage element electrodes, on a copper foil current collector, applying a solution of the polyimide resin, and vacuum drying, except that the formation of the only layer composed of the polyimide resin In the same manner as in Example 1, a nonaqueous electrolyte electricity storage device of Comparative Example 1 was produced. The electrode thickness was 22 μm, and the coating mass was 0.15 mg / cm ² . The thickness of the layer made of polyimide resin was 2 μm.

(Comparative Example 2)
In the step of preparing a non-aqueous electrolyte energy storage element electrodes, on a copper foil current collector, applying a coating paste for the mixture layer, followed by vacuum drying, except that it was formed only mix layer, A nonaqueous electrolyte electricity storage device of Comparative Example 2 was produced in the same manner as Example 1. The electrode thickness was 46 μm and the coating mass was 2.78 mg / cm ² . Moreover, the thickness of the mixture layer was 26 μm.

(Electron beam microanalyzer (EPMA) measurement)
For the electrodes for nonaqueous electrolyte storage elements of Examples 1 and 2 and Comparative Examples 1 and 2, EPMA measurement of the electrode cross section was performed.
First, each non-aqueous electrolyte storage element electrode is sandwiched and fixed by an acrylic plate from the thickness direction of the electrode, and this is used for a non-aqueous electrolyte storage element using a cross section polisher (IB-09020CP, manufactured by JEOL Ltd.) The electrode was cut in the thickness direction, and the cut surface was smoothed. This is set on the sample stage of an electron beam microanalyzer (manufactured by Shimadzu Corporation, EPMA-1610) so that the cut surface of the electrode can be measured, and in the cross section, nitrogen (N), copper (Cu), silicon ( Si), carbon (C) and oxygen (O) line analysis (acceleration voltage: 10 kV, beam size: 1 μm, beam intensity: 200 nA, number of integrations: 1, counting time: 1 second), characteristics of each element X-ray intensity was measured.
The measurement result of the electrode of Example 1 is shown in FIG. This figure shows the concentration and distribution of nitrogen (N) element and copper (Cu) element in the electrode cross section of Example 1. FIG. From the left side of the figure, the region where the Cu concentration is high corresponds to the Cu current collector, and the region where the concentration of N is high (X in the drawing) from the point where the Cu concentration suddenly decreases is a layer containing a polyimide binder. The region with a low N concentration (Y in the figure) present on the right side corresponds to the mixture layer. Here, the N element count number in the central portion (x) in the thickness direction of the surface layer relative to the maximum value of the N element count number is defined as the binder concentration (A) of the surface layer, and the total value for the N element count number is The count number of the N element at the center (y) in the thickness direction of the agent layer is defined as the binder concentration (B) of the mixture layer. And ratio A / B of the binder density | concentration (A) of the layer containing a polyimide binder and the binder density | concentration (B) of a mixture layer was computed. The values of A / B calculated for Examples 1 and 2 are shown in Table 1.

  Further, from the results of the line analysis of Si, C, and O of Example 1 and Example 2, the surface layer of Example 1 is free of a substance containing silicon as an active material, and the surface layer of Example 2 It has been found that a substance containing silicon as an active material exists to some extent.

(Preparation of non-aqueous electrolyte element)
Lithium metal was used as a counter electrode for the non-aqueous electrolyte storage element electrode. A stainless steel (product name: SUS316) mesh current collector to which a stainless steel (product name: SUS316) terminal is attached is bonded to both sides of a 300 μm thick lithium metal foil and pressed to form a counter electrode.

  In addition, a reference electrode was prepared by attaching a lithium metal piece to the tip of a current collector rod made of stainless steel (product name: SUS316).

A nonaqueous electrolyte was prepared by dissolving LiClO ₄ as an electrolyte salt at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1. The amount of water in the non-aqueous electrolyte was less than 40 ppm.

  A glass non-aqueous electrolyte storage element was assembled in an Ar box having a dew point of −40 ° C. or lower. A non-aqueous electrolyte storage element is sandwiched between a non-aqueous electrolyte storage element electrode, a counter electrode, and a reference electrode, each of which has been cut to have the same area as the counter electrode, on a gold-plated clip whose lead is fixed to the lid of the container in advance. The device electrode and the counter electrode were fixed so as to face each other. The reference electrode was fixed at a position on the back side of the electrode for the nonaqueous electrolyte storage element as viewed from the counter electrode. Next, a non-aqueous electrolyte electricity storage element is installed by placing a polypropylene cup containing a certain amount of electrolyte in a glass container and covering the nonaqueous electrolyte electricity storage element electrode, counter electrode, and reference electrode. Assembled.

(Initial activation process)
The non-aqueous electrolyte electricity storage device produced as described above was transferred to a thermostat set at 25 ° C. and subjected to an initial activation step. The initial activation process is composed of four charge / discharge cycles. First, the initial charging conditions were constant current and constant voltage charging with a current value of 0.1 CmA and a potential of 0.02 V. The charging time was 16 hours from the start of energization. The initial discharge conditions were constant current discharge with a current of 0.1 CmA and a final voltage of 2.0V. Subsequently, the charging conditions in the second to fourth cycles were constant current and constant voltage charging with a current value of 0.2 CmA and a potential of 0.02 V. The charging time was 8 hours from the start of energization. The discharge conditions for the second to fourth cycles were constant current discharge with a current of 0.2 CmA and a final voltage of 2.0 V. In all cycles, a 30 minute rest period was set after charging and discharging.
Here, the current value 1 CmA applied to each of the nonaqueous electrolyte storage elements of Examples 1 and 2 and Comparative Examples 1 and 2 was set to 6 mA.

(Charge / discharge cycle test)
Each nonaqueous electrolyte storage element after the initial activation step was subjected to a charge / discharge cycle test of 30 cycles. The charging conditions were constant current and constant voltage charging with a current value of 1 CmA and a potential of 0.02 V. The charging time was 3 hours from the start of energization. The discharge conditions were a constant current discharge with a current of 1 CmA and a final voltage of 2.0V.

(Measurement of electrode thickness for nonaqueous electrolyte storage element)
Each non-aqueous electrolyte electricity storage element for which the discharge cycle test was completed was disassembled in an Ar box having a dew point of −40 ° C. or lower, and an electrode for the non-aqueous electrolyte electricity storage element was taken out. The taken out electrode for the non-aqueous electrolyte storage element was washed with lithium salt attached to the electrode for the non-aqueous electrolyte storage element with dimethyl carbonate (DMC) and then vacuum-dried. By measuring the thickness of the electrode for the nonaqueous electrolyte storage element after drying and subtracting the thickness of the copper foil as the current collector from the value, the mixture for the electrode for the nonaqueous electrolyte storage element of Examples 1 and 2 the total thickness of the layers comprising a layer and a polyimide resin, non-aqueous electrolyte energy storage element electrodes of Comparative examples 1 and 2 were respectively determined the thickness of the layer and the mixture layer made of a polyimide resin. And about each Example and a comparative example, the ratio of the thickness after the charging / discharging cycle test with respect to immediately after preparation of the electrode for nonaqueous electrolyte electrical storage elements was computed, and it shows in Table 1 as "thickness change rate (%)."

As can be seen from Table 1, in an electrode in which only a layer made of a polyimide resin is formed on the current collector of Comparative Example 1 and an electrode in which only a mixture layer is formed on the current collector as in Comparative Example 2, By performing the charge / discharge cycle, the thickness of the electrode is greatly increased. Nevertheless, as in Examples 1 and 2, in the electrode for a nonaqueous electrolyte storage element formed by combining a mixture layer and a layer made of a polyimide resin , surprisingly, the thickness of the electrode after the charge / discharge cycle The increase of is suppressed. Although details about the reason for this phenomenon are not understood, it is presumed that some kind of interaction worked between the mixture layer and the polyimide resin layer.

Moreover, since the increase in the thickness of the electrode of the nonaqueous electrolyte storage element electrode of Example 2 is suppressed more than that of the nonaqueous electrolyte storage element electrode of Example 1, the current collector of the mixture layer An electrode having a layer made of a polyimide resin on the opposite surface is more preferable.

  In addition, the inventor applied a mixture layer coating paste on the current collector foil, and after placing a surface layer prepared in advance on the mixture layer formed by vacuum drying, It has been confirmed that the same result as in Example 2 can be obtained even with the electrode for a non-aqueous electrolyte storage element produced by roll pressing.

  Since the electrode for a nonaqueous electrolyte storage element of the present invention can suppress an increase in the thickness of the electrode accompanying a charge / discharge cycle, the swelling of the nonaqueous electrolyte storage element is suppressed and the influence on adjacent devices is reduced. Therefore, it can be effectively used for nonaqueous electrolyte power storage elements such as electric vehicle power supplies, electronic device power supplies, and power storage power supplies.

Claims (3)

A current collector, a mixture layer containing a silicon-containing substance and a polyimide binder , and a polyimide resin having a thickness of 0.5 to 5 μm between the mixture layer and the current collector The electrode for nonaqueous electrolyte electrical storage elements provided with the layer which becomes. A current collector, a mixture layer containing a silicon-containing substance and a polyimide binder, and a polyimide system having a thickness of 0.5 to 5 μm on the opposite side of the mixture layer from the current collector An electrode for a non-aqueous electrolyte element, comprising a resin layer. Nonaqueous electricity storage device having a non-aqueous electrolyte energy storage device electrode according to claim 1 or 2.