Electrochemical device, electrolyte solution, and additive used for electrolyte solution

Abstract

An electrochemical device which is provided with a positive electrode, a negative electrode and an electrolyte solution, wherein: the negative electrode contains a silicon-based active material; and the electrolyte solution contains a compound represented by formula (1).　In formula (1), each of R1 to R3 independently represents a hydrogen atom or a methyl group; and X represents a divalent organic group.

Description

Electrochemical devices, electrolytes, and additives used in electrolytes

[0001] The present invention relates to an electrochemical device, an electrolyte, and an additive for use in the electrolyte.

[0002] In recent years, the widespread use of portable electronic devices, electric vehicles, and the like has created a demand for high-performance electrochemical devices, such as nonaqueous electrolyte secondary batteries, typified by lithium-ion secondary batteries, and capacitors. As a means for improving the performance of electrochemical devices, for example, a method of adding a specific additive to an electrolyte has been investigated. For example, Patent Document 1 discloses a nonaqueous electrolyte containing a specific acrylate compound as an additive.

[0003] International Publication No. 2012 / 147502

[0004] According to the studies of the present inventors, it has been found that even when the same additive is used, the effect of the additive varies depending on the type of negative electrode (negative electrode active material, etc.) More specifically, among the acrylate compounds described in Patent Document 1, the effect of adding the acrylate compound varies greatly when used in an electrochemical device having a negative electrode containing a silicon-based active material.

[0005] An object of the present invention is to improve the cycle characteristics of an electrochemical device having a negative electrode containing a silicon-based active material.

[0006] The present inventors have found that the use of an electrolyte solution containing a specific acrylate compound in an electrochemical device having a negative electrode containing a silicon-based active material improves the cycle characteristics of the electrochemical device.

[0007] The present invention includes the following aspects: [1] An electrochemical device including a positive electrode, a negative electrode, and an electrolyte solution, wherein the negative electrode contains a silicon-based active material, and the electrolyte solution contains a compound represented by the following formula (1): In formula (1), R １ ~R ３ each independently represents a hydrogen atom or a methyl group, and X represents a divalent organic group. [2] R in formula (1) １ and R ２is a hydrogen atom. [3] The electrochemical device according to [1] or [2], wherein X in formula (1) is an alkylene group having 1 to 6 carbon atoms. [4] The electrochemical device according to [1] or [2], wherein X in formula (1) is an ethylene group. [5] The electrochemical device according to any one of [1] to [4], wherein the content of the compound represented by formula (1) is 0.001 mass % or more and 5 mass % or less, based on the total amount of the electrolyte. [6] The electrochemical device according to any one of [1] to [5], wherein the electrochemical device is a nonaqueous electrolyte secondary battery or a capacitor.

[0008] [7] An electrolyte solution for use in an electrochemical device having a negative electrode containing a silicon-based active material, the electrolyte solution containing a compound represented by the following formula (1): In formula (1), R １ ~R ３ each independently represents a hydrogen atom or a methyl group, and X represents a divalent organic group. [8] R in formula (1) １ and R ２ is a hydrogen atom. [9] The electrolyte solution according to [7] or [8], wherein X in formula (1) is an alkylene group having 1 to 6 carbon atoms.

[10] The electrolyte solution according to [7] or [8], wherein X in formula (1) is an ethylene group.

[11] The electrolyte solution according to any one of [7] to

[10] , wherein the content of the compound represented by formula (1) is 0.001 mass % or more and 5 mass % or less, based on the total amount of the electrolyte solution.

[0009]

[12] An additive used in an electrolyte solution of an electrochemical device having a negative electrode containing a silicon-based active material, the additive containing a compound represented by the following formula (1): In formula (1), R １ ~R ３ each independently represents a hydrogen atom or a methyl group, and X represents a divalent organic group.

[13] R in formula (1) １ and R ２

[14] The additive according to

[12] or

[13] , wherein X in formula (1) is an alkylene group having 1 to 6 carbon atoms.

[15] The additive according to

[12] or

[13] , wherein X in formula (1) is an ethylene group.

[0010] According to one aspect of the present invention, it is possible to improve the cycle characteristics of an electrochemical device having a negative electrode containing a silicon-based active material, and according to another aspect of the present invention, it is possible to reduce the direct current resistance (discharge DCR) during discharge after storing the electrochemical device at high temperatures.

[0011] 1 is a perspective view showing a nonaqueous electrolyte secondary battery as an electrochemical device according to one embodiment; FIG. 2 is an exploded perspective view showing an electrode group of the secondary battery shown in FIG. 1; FIG. 3 is a graph showing the results of cycle tests in Examples and Comparative Examples; FIG. 4 is a graph showing the measurement results of the resistance increase rates in Examples and Comparative Examples; FIG. 5 is a graph showing the results of CV measurement of the electrolyte in Evaluation Example; and FIG. 6 is a graph showing the results of pH measurement of the electrolyte in Evaluation Example.

[0012] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, although the present invention is not limited to the following embodiments.

[0013] FIG. 1 is a perspective view showing an electrochemical device according to one embodiment. In this embodiment, the electrochemical device is a nonaqueous electrolyte secondary battery. As shown in FIG. 1 , the nonaqueous electrolyte secondary battery 1 includes an electrode group 2 composed of a positive electrode, a negative electrode, and a separator, and a bag-shaped battery exterior 3 that houses the electrode group 2. The positive electrode and negative electrode are provided with a positive electrode current collector tab 4 and a negative electrode current collector tab 5, respectively. The positive electrode current collector tab 4 and the negative electrode current collector tab 5 protrude from the inside of the battery exterior 3 to the outside so that the positive electrode and the negative electrode can be electrically connected to the outside of the nonaqueous electrolyte secondary battery 1, respectively. The battery exterior 3 is filled with an electrolyte (not shown). The nonaqueous electrolyte secondary battery 1 may be a battery of a shape other than the so-called "laminated type" described above (e.g., a coin type, a cylindrical type, a stacked type, etc.).

[0014] The battery outer casing 3 may be a container formed of, for example, a laminate film. The laminate film may be a laminate film in which a resin film such as a polyethylene terephthalate (PET) film, a metal foil such as aluminum, copper, or stainless steel, and a sealant layer such as polypropylene are laminated in this order.

[0015] Fig. 2 is an exploded perspective view showing one embodiment of the electrode group 2 in the nonaqueous electrolyte secondary battery 1 shown in Fig. 1. As shown in Fig. 2, the electrode group 2 includes a positive electrode 6, a separator 7, and a negative electrode 8, in this order. The positive electrode 6 and the negative electrode 8 are arranged such that the surfaces facing the positive electrode mixture layer 10 and the negative electrode mixture layer 12 face the separator 7, respectively.

[0016] The positive electrode 6 includes a positive electrode current collector 9 and a positive electrode mixture layer 10 provided on the positive electrode current collector 9. The positive electrode current collector 9 is provided with a positive electrode current collecting tab 4.

[0017] The positive electrode current collector 9 is formed of, for example, aluminum, titanium, stainless steel, nickel, baked carbon, conductive polymer, conductive glass, etc. The positive electrode current collector 9 may be formed by treating the surface of aluminum, copper, etc. with carbon, nickel, titanium, silver, etc., for the purpose of improving adhesiveness, conductivity, and oxidation resistance. The thickness of the positive electrode current collector 9 is, for example, 1 to 50 μm from the viewpoint of electrode strength and energy density.

[0018] In one embodiment, the positive electrode mixture layer 10 contains a positive electrode active material, a conductive agent, and a binder. The thickness of the positive electrode mixture layer 10 is, for example, 20 to 200 μm.

[0019] The positive electrode active material may be, for example, lithium oxide. Examples of lithium oxide include Li ｘ CoO ２ , Li ｘ NiO ２ , Li ｘ MnO ２ , Li ｘ Co ｙ Ni １－ｙ O ２ , Li ｘ Co ｙ M １－ｙ O ｚ , Liｘ Ni １－ｙ M ｙ O ｚ , Li ｘ Mn ２ O ４ and Li ｘ Mn ２－ｙ M ｙ O ４ (In each formula, M represents at least one element selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Cu, Zn, Al, Cr, Pb, Sb, V, and B (provided that M is an element different from the other elements in each formula), x = 0 to 1.2, y = 0 to 0.9, and z = 2.0 to 2.3.) ｘ Ni １－ｙ M ｙ O ｚ The lithium oxide represented by Li ｘ Ni １－（ｙ１＋ｙ２） Co ｙ１ Mn ｙ２ O ｚ (where x and z are the same as those described above, y1=0 to 0.9, y2=0 to 0.9, and y1+y2=0 to 0.9), for example, LiNi １／３ Co １／３ Mn １／３ O ２ , LiNi ０．５ Co ０．２ Mn ０．３ O ２ , LiNi ０．６ Co ０．２ Mn ０．２ O ２、 LiNi ０．８ Co ０．１ Mn ０．１ O ２ Li ｘ Ni １－ｙ M ｙ O ｚ The lithium oxide represented by Li ｘ Ni １－（ｙ３＋ｙ４） Co ｙ３ Al ｙ４ O ｚ (where x and z are the same as those described above, y3 = 0 to 0.9, y4 = 0 to 0.9, and y3 + y4 = 0 to 0.9), for example, LiNi０．８ Co ０．１５ Al ０．０５ O ２ may be.

[0020] The positive electrode active material may be, for example, a lithium phosphate. Examples of lithium phosphate include lithium manganese phosphate (LiMnPO ４ ), lithium iron phosphate (LiFePO ４ ), lithium cobalt phosphate (LiCoPO ４ ) and lithium vanadium phosphate (Li ３ V ２ (P.O. ４ ) ３ ) are listed.

[0021] The content of the positive electrode active material may be 80% by mass or more, or 85% by mass or more, and may be 99% by mass or less, based on the total amount of the positive electrode mixture layer.

[0022] The conductive agent may be a carbon material such as carbon black (e.g., acetylene black, ketjen black), graphite, graphene, carbon nanotubes, etc. The content of the conductive agent may be, for example, 0.01% by mass or more, 0.1% by mass or more, or 1% by mass or more, and may be 50% by mass or less, 30% by mass or less, or 15% by mass or less, based on the total amount of the positive electrode mixture layer.

[0023] Examples of binders include resins such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubbers such as SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber, isoprene rubber, butadiene rubber, and ethylene-propylene rubber; and styrene-butadiene-styrene block copolymers or hydrogenated products thereof, EPDM (ethylene-propylene-diene terpolymer), styrene-ethylene-butadiene-ethylene copolymer, and styrene-isoprene-styrene block copolymer. thermoplastic elastomers such as olefins or hydrogenated products thereof; soft resins such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, and propylene-α-olefin copolymer; fluorine-containing resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene-ethylene copolymer, and polytetrafluoroethylene-vinylidene fluoride copolymer; resins having a nitrile group-containing monomer as a monomer unit; and polymer compositions having ionic conductivity for alkali metal ions (for example, lithium ions).

[0024] The content of the binder may be, for example, 0.1 mass % or more, 1 mass % or more, or 1.5 mass % or more, and may be 30 mass % or less, 20 mass % or less, or 10 mass % or less, based on the total amount of the positive electrode mixture layer.

[0025] The separator 7 is not particularly limited as long as it provides electronic insulation between the positive electrode 6 and the negative electrode 8 while allowing ions to pass therethrough, and is resistant to oxidation on the positive electrode 6 side and reduction on the negative electrode 8 side. Examples of materials for the separator 7 include resins and inorganic substances.

[0026] Examples of the resin include an olefin polymer, a fluorine-based polymer, a cellulose-based polymer, a polyimide, nylon, etc. From the viewpoint of being stable to the electrolytic solution and having excellent liquid retention properties, the separator 7 is preferably a porous sheet or nonwoven fabric formed of a polyolefin such as polyethylene or polypropylene.

[0027] Examples of inorganic materials include oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate. Separator 7 may be a separator in which a fibrous or particulate inorganic material is attached to a thin film substrate such as a nonwoven fabric, a woven fabric, or a microporous film.

[0028] The negative electrode 8 includes a negative electrode current collector 11 and a negative electrode mixture layer 12 provided on the negative electrode current collector 11. The negative electrode current collector 11 is provided with a negative electrode current collecting tab 5.

[0029] The negative electrode current collector 11 is formed of copper, stainless steel, nickel, aluminum, titanium, baked carbon, conductive polymer, conductive glass, aluminum-cadmium alloy, etc. The negative electrode current collector 11 may be made of copper, aluminum, etc., whose surface has been treated with carbon, nickel, titanium, silver, etc., for the purpose of improving adhesion, conductivity, and reduction resistance. The thickness of the negative electrode current collector 11 is, for example, 1 to 50 μm from the viewpoints of electrode strength and energy density.

[0030] The negative electrode mixture layer 12 contains a negative electrode active material. The shape of the negative electrode active material may be, for example, particulate. The negative electrode active material includes a silicon-based active material. The silicon-based active material includes at least silicon (Si) as a constituent element. The silicon-based active material may be simple silicon, or may be a compound containing silicon and other elements. The compound may be an alloy containing silicon and at least one element selected from the group consisting of nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium. The compound may be an oxide, nitride, or carbide of silicon. Examples of oxides of silicon include SiOx (SiO, SiO ２ Nitrides of silicon include, for example, Si ３ N ４ and Si ２ N ２ Examples of silicon carbides include SiC.

[0031] The negative electrode active material may further include a negative electrode active material other than a silicon-based active material. Examples of negative electrode active materials other than a silicon-based active material include a carbon-based active material. Examples of carbon materials constituting the carbon-based active material include amorphous carbon materials, natural graphite, composite carbon materials in which natural graphite is coated with an amorphous carbon material, and artificial graphite (obtained by firing resin raw materials such as epoxy resins and phenolic resins, or pitch-based raw materials obtained from petroleum, coal, etc.).

[0032] From the viewpoint of increasing the capacity of electrochemical devices, the carbon-based active material is preferably a graphite-based active material composed of graphite. In graphite, the carbon net plane interlayer distance (d002) measured by wide-angle X-ray diffraction is preferably less than 0.34 nm, more preferably 0.3354 nm or more and 0.337 nm or less. Carbon materials (graphite) that satisfy these conditions are sometimes referred to as pseudo-anisotropic carbon.

[0033] In addition to the above-described negative electrode active materials, the negative electrode active material may further include a negative electrode active material composed of a metal composite oxide, an oxide or nitride of a Group 4 element such as tin or germanium, lithium alone, or a lithium alloy such as a lithium-aluminum alloy.

[0034] From the viewpoint of further improving the performance of the electrochemical device, such as low-temperature input characteristics, the negative electrode active material preferably contains a silicon-based active material and a carbon-based active material, more preferably a silicon-based active material and a graphite-based active material. In this case, the content of the silicon-based active material may be 1 part by mass or more, 2 parts by mass or more, or 3 parts by mass or more, and may be 30 parts by mass or less, 20 parts by mass or less, or 10 parts by mass or less, relative to 100 parts by mass of the total amount of the silicon-based active material and the carbon-based active material.

[0035] The content of the negative electrode active material may be 80% by mass or more, or 85% by mass or more, and may be 99% by mass or less, based on the total amount of the negative electrode mixture layer.

[0036] The negative electrode mixture layer 12 may further contain a binder. The binder and its content may be the same as the binder and its content in the positive electrode mixture layer described above.

[0037] The negative electrode mixture layer 12 may further contain a thickener to adjust the viscosity. The thickener is not particularly limited, and may be carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphated starch, casein, salts thereof, etc. The thickener may be one type alone or a mixture of two or more types.

[0038] When the negative electrode mixture layer 12 contains a thickener, its content is not particularly limited. From the viewpoint of the coatability of the negative electrode mixture layer, the content of the thickener may be 0.1 mass% or more, preferably 0.2 mass% or more, and more preferably 0.5 mass% or more, based on the total amount of the negative electrode mixture layer. From the viewpoint of suppressing a decrease in battery capacity or an increase in resistance between the negative electrode active materials, the content of the thickener may be 5 mass% or less, preferably 3 mass% or less, and more preferably 2 mass% or less, based on the total amount of the negative electrode mixture layer.

[0039] In one embodiment, the electrolytic solution contains a compound represented by the following formula (1), an electrolyte salt, and a non-aqueous solvent. In formula (1), R １ ~R ３ each independently represents a hydrogen atom or a methyl group, and X represents a divalent organic group.

[0040] In other words, in one embodiment, the compound represented by formula (1) is an additive used in the electrolyte solution of the electrochemical device 1 .

[0041] R １ and R ２ is preferably a hydrogen atom. ３ is preferably a hydrogen atom from the viewpoint of further improving the cycle characteristics.

[0042] X may be, for example, a divalent hydrocarbon group or an alkylene group. The alkylene group may be linear or branched. The divalent hydrocarbon group and alkylene group may have, for example, 1 to 6 carbon atoms. The lower limit of the carbon number may be 2 or more. The upper limit of the carbon number may be 5 or less, or 4 or less. The alkylene group represented by X may be a methylene group, ethylene group, propylene group, butylene group, or pentylene group, and is preferably an ethylene group.

[0043] X may be, for example, a divalent group in which a divalent hydrocarbon group is partially substituted with a heteroatom. The heteroatom may be, for example, an oxygen atom. X may be, for example, a divalent group in which a divalent hydrocarbon group is partially substituted with an oxygen atom to have an ether structure. X may be, for example, a divalent group represented by the following formula (2): -X １ -O-X ２ - (2) In formula (2), X １ and X ２ Each of X independently represents an alkylene group. The alkylene group may be linear or branched. １ and X ２ The number of carbon atoms in the alkylene groups represented by each may independently be 1 to 6, 1 to 5, 1 to 4, 1 to 3, or 1 to 2.

[0044] From the viewpoint of further improving the performance (particularly the cycle characteristics) of the electrochemical device, the content of the compound represented by formula (1) is preferably 0.001 mass % or more, more preferably 0.005 mass % or more, even more preferably 0.01 mass % or more, particularly preferably 0.05 mass % or more, still more preferably 0.1 mass % or more, and may be preferably 8 mass % or less, more preferably 5 mass % or less, even more preferably 3 mass % or less, particularly preferably 2 mass % or less, and still more preferably 1 mass % or less, based on the total amount of the electrolyte solution.

[0045] The electrolyte salt may be, for example, a lithium salt. The lithium salt may be, for example, LiPF ６ , LiBF ４ , LiClO ４ , LiB(C ６ H５ ) ４ , LiCH ３ SO ３ , C.F. ３ SO ２ OLi, LiN(SO ２ F) ２ (Li[FSI], lithium bisfluorosulfonylimide), LiN(SO ２ CF ３ ) ２ (Li[TFSI], lithium bistrifluoromethanesulfonylimide), and LiN(SO ２ CF ２ CF ３ ) ２ The lithium salt is preferably LiPF 5 from the viewpoint of providing better solubility in a solvent and better charge / discharge characteristics, output characteristics, cycle characteristics, etc. of the secondary battery. ６ Includes:

[0046] From the viewpoint of excellent charge / discharge characteristics, the concentration of the electrolyte salt is preferably 0.5 mol / L or more, more preferably 0.7 mol / L or more, and even more preferably 0.8 mol / L or more, based on the total amount of the nonaqueous solvent, and is preferably 1.5 mol / L or less, more preferably 1.3 mol / L or less, and even more preferably 1.2 mol / L or less.

[0047] The non-aqueous solvent may be, for example, a chain carbonate compound such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl butyl carbonate; a cyclic carbonate compound such as ethylene carbonate, propylene carbonate, or butylene carbonate; a chain carboxylic acid ester compound such as methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, or propyl propionate; a cyclic carboxylic acid ester compound such as γ-butyl lactone; a chain ether compound such as dimethoxymethane, dimethoxyethane, or diethoxyethane; a cyclic ether compound such as tetrahydrofuran, tetrahydropyran, or dioxolane; a nitrile compound such as acetonitrile, or a sulfur compound such as sulfolane. The non-aqueous solvent may be one of these alone or a mixture of two or more thereof, preferably a mixture of two or more thereof.

[0048] The electrolyte solution may further contain other materials in addition to the compound represented by formula (1), the electrolyte salt, and the non-aqueous solvent. The other materials may be, for example, unsaturated cyclic carbonates, fluorine-containing cyclic carbonates, compounds containing a nitrogen atom, a sulfur atom, or a nitrogen atom and a sulfur atom other than the compound represented by formula (1), cyclic carboxylic acid esters, etc.

[0049] Examples of unsaturated cyclic carbonates include vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate (4,5-dimethyl vinylene carbonate), ethyl vinylene carbonate (4,5-diethyl vinylene carbonate), diethyl vinylene carbonate, and vinyl ethylene carbonate. Vinylene carbonate is preferred from the viewpoint of further improving the performance of electrochemical devices. Examples of fluorine-containing cyclic carbonates include 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, and 1,1,2,2-tetrafluoroethylene carbonate. Fluorine-containing cyclic carbonates include 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate; FEC). The nitrogen atom-containing compound other than the compound represented by formula (1) may be, for example, a nitrile compound such as succinonitrile, etc. The sulfur atom-containing compound other than the compound represented by formula (1) may be, for example, a cyclic sulfonate compound such as 1,3-propane sultone or 1-propene-1,3-sultone.

[0050] The present inventors have found that the use of an electrolyte solution containing the compound represented by formula (1) in an electrochemical device including a negative electrode containing a silicon-based active material can improve the cycle characteristics of the electrochemical device. The present inventors speculate that the effect of using an electrolyte solution containing the compound represented by formula (1) is as follows. That is, the compound represented by formula (1) forms a stable and dense coating on the negative electrode containing a silicon-based active material, and this coating suppresses decomposition of the electrolyte, thereby achieving the improvement in the cycle characteristics of the secondary battery. Furthermore, in one embodiment, by using an electrolyte solution containing the compound represented by formula (1) in an electrochemical device including a negative electrode containing a silicon-based active material, the compound represented by formula (1) forms a stable coating on the negative electrode containing a silicon-based active material, and this coating suppresses decomposition of the electrolyte, thereby reducing the direct current resistance (discharge DCR) during discharge of the electrochemical device after storage at high temperatures.

[0051] Next, a description will be given of a method for manufacturing the nonaqueous electrolyte secondary battery 1. The method for manufacturing the nonaqueous electrolyte secondary battery 1 includes a first step of obtaining the positive electrode 6, a second step of obtaining the negative electrode 8, a third step of housing the electrode group 2 in a battery exterior body 3, and a fourth step of injecting an electrolyte into the battery exterior body 3. The first to fourth steps may be performed in any order.

[0052] In the first step, the materials used for the positive electrode mixture layer 10 are dispersed in a dispersion medium using a kneader, disperser, or the like to obtain a slurry-like positive electrode mixture. This positive electrode mixture is then applied to the positive electrode current collector 9 by a doctor blade method, a dipping method, a spray method, or the like, and the dispersion medium is then volatilized to obtain the positive electrode 6. After volatilizing the dispersion medium, a compression molding step using a roll press may be performed as necessary. The positive electrode mixture layer 10 may be formed as a multilayered positive electrode mixture layer by performing the above-described steps from applying the positive electrode mixture to volatilizing the dispersion medium multiple times. The dispersion medium may be water, 1-methyl-2-pyrrolidone (hereinafter also referred to as NMP), or the like.

[0053] The second step may be the same as the first step described above, and the method for forming the negative electrode mixture layer 12 on the negative electrode current collector 11 may be the same as the method for the first step described above.

[0054] In the third step, a separator 7 is sandwiched between the fabricated positive electrode 6 and negative electrode 8 to form an electrode group 2. Next, this electrode group 2 is housed in a battery outer casing 3.

[0055] In the fourth step, an electrolyte solution is poured into the battery exterior body 3. The electrolyte solution can be prepared, for example, by first dissolving an electrolyte salt in a solvent and then dissolving other materials.

[0056] In another embodiment, the electrochemical device may be a capacitor. Similar to the nonaqueous electrolyte secondary battery 1 described above, the capacitor may include an electrode group composed of a positive electrode, a negative electrode, and a separator, and a bag-shaped battery exterior that houses the electrode group. Details of each component of the capacitor may be similar to those of the nonaqueous electrolyte secondary battery 1.

[0057] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0058] Example 1 [Preparation of Positive Electrode] Acetylene black (AB) (4 mass%) as a conductive agent and PVDF (4 mass%) as a binder were sequentially added to lithium nickel cobalt manganese oxide (92 mass%) as a positive electrode active material and mixed. NMP as a dispersion medium was added to the resulting mixture, and the mixture was kneaded to prepare a slurry positive electrode mixture. A predetermined amount of this positive electrode mixture was evenly and homogeneously applied to aluminum foil with a thickness of 20 μm as a positive electrode current collector. Thereafter, the dispersion medium was volatilized, and the mixture was pressed to a density of 2.8 g / cm. ３ The mixture was compacted to obtain a positive electrode.

[0059] [Fabrication of Negative Electrode] A silicon-based active material (SiOx (0<x<2.0), average particle size (50% particle size of volume cumulative particle size distribution): approximately 10 μm) and a graphite-based active material (artificial graphite, average particle size (D50): approximately 23 μm) were used as negative electrode active materials. SBR as a binder and carboxymethyl cellulose as a thickener were added to these active materials. The mass ratio between these was graphite active material: silicon-based active material: binder: thickener = 92:5:1.5:1.5. Water as a dispersion medium was added to the obtained mixture, and the mixture was kneaded to prepare a slurry-like negative electrode mixture. A predetermined amount of this negative electrode mixture was evenly and homogeneously applied to a rolled copper foil with a thickness of 10 μm as a negative electrode current collector. Thereafter, the dispersion medium was volatilized, and the mixture was pressed to obtain a negative electrode mixture with a density of 1.6 g / cm. ３ The mixture was compacted to obtain a negative electrode.

[0060] [Production of lithium ion secondary battery] 13.5 cm ２ The positive electrode cut into a square shape was sandwiched between a polyethylene porous sheet (thickness 30 μm) as a separator, and then a 14.3 cm ２ The negative electrodes cut into a square shape were stacked to prepare an electrode group. This electrode group was housed in a container (battery exterior) made of an aluminum laminate film (product name: Aluminum Laminate Film, manufactured by Dai Nippon Printing Co., Ltd.). Next, 1 mL of electrolyte was added to the container, and the container was heat-sealed to prepare a lithium-ion secondary battery for evaluation. The electrolyte was 1 mol / L LiPF ６ A mixed solution of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate = 1 / 1 / 1 (volume ratio) containing the above was added with 0.5 mass % of compound X represented by the following formula (X), 1 mass % of vinylene carbonate, and 1 mass % of fluoroethylene carbonate (all based on the total mass of the electrolyte solution).

[0061] Example 2 A lithium ion secondary battery was fabricated in the same manner as in Example 1, except that an electrolyte solution containing 0.2 mass % of compound X based on the total mass of the electrolyte solution was used.

[0062] Example 3 A lithium ion secondary battery was produced in the same manner as in Example 1, except that an electrolyte solution containing compound Y represented by the following formula (Y) added in an amount of 0.5 mass % based on the total mass of the electrolyte solution was used instead of compound X.

[0063] Comparative Example 1 A lithium ion secondary battery was fabricated in the same manner as in Example 1, except that Compound X was not added to the electrolyte solution.

[0064] Comparative Example 2 A lithium ion secondary battery was produced in the same manner as in Example 1, except that an electrolyte solution containing compound Z represented by the following formula (Z) added in an amount of 0.5 mass % based on the total mass of the electrolyte solution was used instead of compound X.

[0065] Comparative Example 3 A lithium ion secondary battery was fabricated in the same manner as in Example 1, except that an electrolyte solution containing hexamethylene diisocyanate (HDI) added in an amount of 0.2 mass % based on the total mass of the electrolyte solution instead of compound X was used.

[0066] [Initial Charge / Discharge] Each lithium-ion battery fabricated was subjected to an initial charge / discharge in the following manner. First, constant-current charging was performed at a current value of 0.1 C in an environment of 25°C up to an upper voltage of 4.2 V, followed by constant-voltage charging at 4.2 V. The charge termination condition was a current value of 0.01 C. Subsequently, constant-current discharging was performed at a current value of 0.1 C to an end voltage of 2.7 V. This charge / discharge cycle was repeated three times (the unit of current value, "C," means "current value (A) / battery capacity (Ah)").

[0067] [Evaluation of Cycle Characteristics] After the initial charge and discharge, the cycle characteristics of each secondary battery were evaluated by a cycle test in which charge and discharge were repeated. The charge pattern was as follows: for the secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2, constant-current charging was performed at a current value of 0.5 C up to an upper voltage of 4.2 V in an environment of 45° C., followed by constant-voltage charging at 4.2 V. The charge termination condition was a current value of 0.05 C. Regarding discharge, constant-current discharging was performed at 1.0 C down to 2.7 V, and the discharge capacity was determined. This series of charge and discharge cycles was repeated 500 times, and the discharge capacity was measured after each charge and discharge. The relative value of the discharge capacity at each cycle to the discharge capacity after the first charge and discharge cycle (discharge capacity retention rate (%)) was determined. The results of the cycle test are shown in FIG. 3.

[0068] The discharge capacity retention rates at the 500th cycle for Examples 1 to 3, which used electrolyte solutions containing Compound X or Compound Y, were 84.2%, 83.2%, and 83.7%, respectively. This revealed improved cycle characteristics compared to the discharge capacity retention rate (81.5%) at the 100th cycle for Comparative Example 1, which did not contain the compound. The reason for this is believed to be that Compound X or Compound Y formed a stable and dense coating on the negative electrode, which suppressed decomposition of the electrolyte, thereby achieving improved cycle characteristics for the secondary battery. Furthermore, the discharge capacity retention rates for Comparative Example 2, which used an electrolyte solution containing Compound Z, and Comparative Example 3, which used an electrolyte solution containing HDI, were 82.2% and 82.3%, respectively. Although these results indicated improved cycle characteristics compared to Comparative Example 1, which did not contain any compound, the improvement in cycle characteristics for Examples 1 to 3 was superior. Although the reason for this is unclear, it is believed that Compound X and Compound Y, compared to Compound Z and HDI, are able to form a stable and dense coating on the negative electrode even in small amounts, thereby significantly suppressing the decomposition of the electrolyte, resulting in improved cycle characteristics.

[0069] [High-Temperature Storage Test] After the above-described initial charge and discharge, each of the secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 3 was subjected to constant-current charging at a current value of 0.1 C in an environment of 25° C. up to an upper limit voltage of 4.2 V, followed by constant-voltage charging at 4.2 V. The charge termination condition was a current value of 0.01 C. Thereafter, the secondary batteries were stored in a constant-temperature bath at 60° C. for 4 weeks.

[0070] [Measurement of Discharge DCR] The discharge DCR (R1) of each secondary battery before high-temperature storage and the discharge DCR (R2) measured after leaving it in a 25°C environment for 30 minutes after high-temperature storage were measured, and the resistance increase rate (%) = R2 / R1 × 100 was calculated using the measured R1 and R2. The results are shown in Figure 4. The discharge DCR (DC resistance during discharge) was measured as follows. First, a constant current charge of 0.2 C was performed up to an upper limit voltage of 4.2 V, followed by a constant voltage charge at 4.2 V. The charge termination condition was a current value of 0.02 C. Subsequently, a constant current discharge was performed at a current value of 0.2 C to an end voltage of 2.7 V, and the current value at this time was calculated as I ０．２Ｃ , the voltage change 10 seconds after the start of discharge is ΔV ０．２Ｃ Next, constant current charging at 0.2 C was performed up to an upper limit voltage of 4.2 V, followed by constant voltage charging at 4.2 V (the charge termination condition was a current value of 0.02 C). Thereafter, constant current discharging was performed at a current value of 0.5 C to a termination voltage of 2.7 V, and the current value at this time was set to I ０．５Ｃ , the voltage change 10 seconds after the start of discharge is ΔV ０．５Ｃ From the same charge and discharge, the current value of 1C was I １Ｃ , voltage change ΔV 10 seconds after discharge start １Ｃ The three-point plot of the current value vs. voltage change (I ０．２Ｃ , ΔV ０．２Ｃ ), (I ０．５Ｃ , ΔV ０．５Ｃ ), (I １Ｃ , ΔV １Ｃ ) was fitted to the discharge DCR by a linear approximation line using the least squares method, and the slope of the line was used as the discharge DCR value.

[0071] Examples 1 to 3 showed resistance increase rates of 128%, 144%, and 138%, respectively, which revealed that the increase in resistance due to high-temperature storage could be suppressed more effectively than Comparative Examples 1 and 3 (resistance increase rates of 153% and 158%, respectively). The reason for this is thought to be that Compound X and Compound Y formed a stable coating on the negative electrode, which suppressed decomposition of the electrolyte, thereby suppressing the increase in resistance of the secondary battery due to high-temperature storage.

[0072] As described above, the lithium ion secondary batteries of Examples 1 to 3, in which an electrolyte solution containing compound X or compound Y was used, exhibited superior life characteristics and high-temperature storage characteristics compared to the lithium ion secondary battery of Comparative Example 1, which did not contain any of the compounds, the lithium ion secondary battery of Comparative Example 2, in which an electrolyte solution containing compound Z was used, and the lithium ion secondary battery of Comparative Example 3, in which an electrolyte solution containing HDI was used.

[0073] (Evaluation Examples 1-1 to 1-4) [Measurement of Electrolyte Reduction Stability] Cyclic voltammetry (CV) was measured to evaluate the reduction stability of the electrolyte. As a CV evaluation cell, a 2016-type coin cell was produced using a SUS working electrode, a metallic lithium counter electrode, a 30 μm-thick polyethylene microporous membrane separator, and an electrolyte. The electrolyte was 1 mol / L LiPF ６ The electrolyte solutions of Evaluation Examples 1-1 to 1-4 were prepared by adding the additives shown in Table 1 to a mixed solution of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate = 1 / 1 / 1 (volume ratio) containing the above in the amounts shown in Table 1, based on the total volume of the electrolyte. CV measurement conditions were a 25°C environment, and potential scanning was performed three times in a voltage range of 2.0 V to 0 V at 0.2 mV / s to evaluate the reduction stability of the electrolyte. The results of the CV measurement at the third cycle are shown in FIG.

[0074]

[0075] As a result of the CV measurement, the electrolyte solution of Evaluation Example 1-1 containing Compound X and the electrolyte solution of Evaluation Example 1-2 containing Compound Y had a smaller current between 2.0 V and 0 V than the electrolyte solution of Evaluation Example 1-3 containing no additive, which is considered to have suppressed reductive decomposition of the electrolyte solution. Furthermore, the electrolyte solution of Evaluation Example 1-4 containing Compound Z had a slightly smaller current than the electrolyte solution of Evaluation Example 1-3 containing no additive, but no significant effect was confirmed compared to the electrolyte solutions of Evaluation Examples 1-1 and 1-2. From these results, it is considered that the addition of compounds having the unique structures found in Compounds X and Y suppressed reductive decomposition of the electrolyte solution, thereby achieving the effects of improving life and suppressing resistance increase.

[0076] (Evaluation Examples 2-1 to 2-5) [Measurement of pH of Electrolyte] The pH of the electrolyte was measured under the following conditions.６ An electrolyte solution was prepared by adding 1% by mass of vinylene carbonate (based on the total volume of the electrolyte) to a mixed solution of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate = 1 / 1 / 1 (volume ratio) containing the above, and further adding the additives shown in Table 2 in the amounts shown in Table 2 (based on the total volume of the electrolyte). 3 ml of the above electrolyte solution was added to 50 ml of pure water, and the pH of the electrolyte solution was measured. The pH measurement was performed in a 25°C environment using an automatic titrator (product name: COM-A19S, manufactured by Hiranuma Sangyo Co., Ltd.). A glass electrode (GE-101B) and a reference electrode (RE-201) were used as electrodes. The pH measurement results are shown in Figure 6.

[0077]

[0078] As a result of the pH measurement, the pH of the electrolyte solutions of Evaluation Examples 2-1, 2-2, and 2-3 containing Compound X or Compound Y was 7.1, 6.0, and 6.4, respectively, which was higher than the pH of 3.9 of the electrolyte solution of Evaluation Example 2-4 containing no additive, and was found to be closer to neutral. Furthermore, the pH of the electrolyte solution of Evaluation Example 2-5 containing Compound Z was 4.0, which was found to be approximately the same pH as the electrolyte solution of Evaluation Example 2-4 containing no additive. From these measurement results, it was found that in the electrolyte solutions of Evaluation Examples 2-1, 2-2, and 2-3 containing Compound X or Compound Y, a lithium salt (LiPF ６ As a result, it is thought that the degradation of the silicon-based active material, such as elution caused by hydrofluoric acid, was suppressed, which is believed to have had the effect of suppressing the reduction in the lifespan of batteries containing silicon-based active materials.

[0079] 1... nonaqueous electrolyte secondary battery (electrochemical device), 2... electrode group, 3... battery exterior, 4... positive electrode current collector tab, 5... negative electrode current collector tab, 6... positive electrode, 7... separator, 8... negative electrode, 9... positive electrode current collector, 10... positive electrode mixture layer, 11... negative electrode current collector, 12... negative electrode mixture layer

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte solution, The negative electrode contains a silicon-based active material, The electrochemical device, wherein the electrolyte solution contains a compound represented by the following formula (1): 【Chemical 1】 [In formula (1), R １ ~R ３ each independently represents a hydrogen atom or a methyl group, and X represents a divalent organic group.

2. R in the formula (1) １ and R ２ The electrochemical device of claim 1 , wherein is a hydrogen atom.

3. 3. The electrochemical device according to claim 1, wherein X in the formula (1) is an alkylene group having 1 to 6 carbon atoms.

4. 3. The electrochemical device according to claim 1, wherein X in the formula (1) is an ethylene group.

5. 3. The electrochemical device according to claim 1, wherein the content of the compound represented by formula (1) is 0.001 mass % or more and 5 mass % or less based on the total amount of the electrolyte solution.

6. 3. The electrochemical device according to claim 1, wherein the electrochemical device is a non-aqueous electrolyte secondary battery or a capacitor.

7. An electrolyte solution for use in an electrochemical device having a negative electrode containing a silicon-based active material, An electrolyte solution containing a compound represented by the following formula (1): 【Chemistry 2】 [In formula (1), R １ ~R ３ each independently represents a hydrogen atom or a methyl group, and X represents a divalent organic group.

8. R in the formula (1) １ and R ２ The electrolyte according to claim 7, wherein is a hydrogen atom.

9. 9. The electrolyte solution according to claim 7, wherein X in the formula (1) is an alkylene group having 1 to 6 carbon atoms.

10. The electrolyte solution according to claim 7 or 8, wherein X in the formula (1) is an ethylene group.

11. The electrolyte solution according to claim 7 or 8, wherein the content of the compound represented by formula (1) is 0.001 mass % or more and 5 mass % or less based on the total amount of the electrolyte solution.

12. An additive used in an electrolyte solution of an electrochemical device having a negative electrode containing a silicon-based active material, An additive comprising a compound represented by the following formula (1): 【Chemistry 3】 [In formula (1), R １ ~R ３ each independently represents a hydrogen atom or a methyl group, and X represents a divalent organic group.

13. R in the formula (1) １ and R ２ The additive according to claim 12, wherein is a hydrogen atom.

14. The additive according to claim 12 or 13, wherein X in the formula (1) is an alkylene group having 1 to 6 carbon atoms.

15. The additive according to claim 12 or 13, wherein X in formula (1) is an ethylene group.

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