Binder for secondary battery, mixture for secondary battery electrode, electrode for secondary battery, and secondary battery

Abstract

To provide a binder used for an aqueous electrode mixture slurry to improve battery performance.SOLUTION: A binder for secondary batteries comprising a water-soluble polymer compound, wherein the water-soluble polymer compound comprises a repeating unit A represented by the formula (1) and a repeating unit B containing two or more acid groups, and when the total of the repeating unit A and the repeating unit B is 100mol%, the repeating unit B is 1mol% or more and 40mol% or less. In formula (1), M1 is each independently hydrogen or alkali. ] SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a binder for a secondary battery, a mixture for a secondary battery electrode, an electrode for a secondary battery, and a secondary battery. [Background technology]

[0002] BACKGROUND ART In recent years, with growing interest in solving environmental problems and realizing a sustainable recycling-based society, non-aqueous electrolyte secondary batteries, typified by lithium ion secondary batteries, have been actively researched.

[0003] Electrodes for lithium ion secondary batteries are usually produced by applying an electrode mixture slurry (hereinafter sometimes simply referred to as slurry) to a current collector, the electrode mixture slurry being prepared by mixing an active material and a conductive additive with a binder solution or slurry in which an electrode binder (hereinafter sometimes simply referred to as binder) is dissolved in a solvent or dispersed in a dispersion medium, and then removing the solvent or dispersion medium by a method such as drying.

[0004] In recent years, from the viewpoint of environmental concerns, interest has been shifting from slurries using organic solvents to aqueous slurries using water as a dispersant, and various binders for use in aqueous slurries such as those disclosed in Patent Document 1 have been investigated. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-177061 [Patent Document 2] Japanese Patent Application Publication No. 7-240201 [Patent Document 3] Japanese Patent Application Publication No. 10-294112 [Non-patent literature]

[0006] [Non-Patent Document 1] Lithium Secondary Batteries, p.132 (Ohmsha Co., Ltd., published March 20, 2008) Summary of the Invention [Problem to be solved by the invention]

[0007] With the expansion of lithium-ion secondary batteries, electrode reactions have been increasing, mainly for the purpose of increasing battery capacity. The use of various graphites as negative electrode active materials that directly contribute to the reaction has been investigated. In addition, silicon-containing particles such as silicon particles and silicon oxide particles are inexpensive and have been widely investigated (Patent Documents 2 and 3 and Non-Patent Document 1).

[0008] However, when silicon-containing particles such as silicon particles or silicon oxide particles are used as a negative electrode active material, there is a problem in that the battery performance deteriorates due to volume changes of the negative electrode active material caused by the lithium ion absorption and desorption reactions during charging and discharging.

[0009] Under these circumstances, a main object of the present invention is to provide a binder for secondary batteries that can improve the battery performance of secondary batteries. Another object of the present invention is to provide a secondary battery electrode mixture and a secondary battery electrode that can improve the battery performance of secondary batteries, as well as a secondary battery with improved battery performance. [Means for solving the problem]

[0010] The binder for secondary batteries of the present invention is a binder for secondary batteries containing a water-soluble polymer compound, characterized in that the water-soluble polymer compound contains a repeating unit A represented by formula (1) and a repeating unit B containing two or more acid groups, and when the total of the repeating unit A and the repeating unit B is taken as 100 mol %, the repeating unit B accounts for 1 mol % or more and 40 mol % or less.

[0011] [ka]

[0012] [In formula (1), M 1 are each independently a hydrogen atom or an alkali metal atom. The acid group is preferably a carboxy group or a group corresponding to a salt thereof.

[0013] The repeating unit B is preferably a repeating unit represented by formula (2).

[0014] [ka]

[0015] [In formula (2), M 2 are each independently a hydrogen atom or an alkali metal atom. The weight-average molecular weight of the water-soluble polymer compound is preferably 50,000 or more and 300,000 or less.

[0016] The total amount of the repeating unit A and the repeating unit B is preferably 10 mol % or more and 90 mol % or less based on the total amount of all repeating units constituting the water-soluble polymer compound.

[0017] The water-soluble polymer compound preferably contains a repeating unit C represented by formula (3).

[0018] [ka]

[0019] The mixture for a secondary battery electrode of the present invention contains the above-mentioned binder for a secondary battery and an active material.

[0020] The active material preferably contains a carbon material.

[0021] The active material preferably contains at least one of silicon and silicon oxide.

[0022] The secondary battery electrode of the present invention contains the above-mentioned secondary battery electrode mixture.

[0023] The secondary battery of the present invention includes the above-described secondary battery electrode. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide a binder for secondary batteries that can improve the battery performance (particularly, cycle characteristics) of secondary batteries. Also, according to the present invention, it is possible to provide a secondary battery electrode mixture and a secondary battery electrode, and a secondary battery (such as a lithium ion secondary battery), that can improve the battery performance (particularly, cycle characteristics). DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, embodiments of the present invention will be described in detail.

[0026] <Binder> The binder for secondary batteries of the present invention contains a water-soluble polymer compound, which contains a repeating unit A represented by formula (1) and a repeating unit B containing two or more acid groups, and when the total of the repeating units A and B is taken as 100 mol %, the repeating unit B accounts for 1 mol % or more and 40 mol % or less.

[0027] [ka]

[0028] [In formula (1), M 1 are each independently a hydrogen atom or an alkali metal atom. The water-soluble polymer compound includes a copolymer essentially comprising a repeating unit A represented by formula (1) and a repeating unit B containing two or more acid groups. The arrangement of the copolymer may be random or block.

[0029] Monomers that form the repeating unit A include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxyethyl acrylate.

[0030] The repeating unit B may be a repeating unit derived from an unsaturated hydrocarbon compound containing two or more acid groups. Examples of the acid group include a group corresponding to a carboxy group or a salt thereof (-COOM), -OP(O)(OM)2, -O-NO2, a group corresponding to an oxysulfonic acid group or a salt thereof (-O-SO3M), and -O-SO2M (wherein M is a hydrogen atom or an alkali metal atom).

[0031] In particular, repeating unit B preferably contains a carboxy group or a group corresponding to a salt thereof as the acid group. For example, repeating unit B may be a repeating unit derived from an unsaturated dicarboxylic acid, an unsaturated tricarboxylic acid, or an unsaturated hydrocarbon compound containing four or more carboxylic acids. Repeating unit B may also be a repeating unit containing both a carboxy group and another acid group.

[0032] Examples of the monomer that forms the repeating unit B include itaconic acid, maleic acid, and fumaric acid.

[0033] [ka]

[0034] [In formula (2), M 2 are each independently a hydrogen atom or an alkali metal atom. The water-soluble polymer compound can be obtained by copolymerizing, in the presence of a polymerization initiator, a monomer forming a repeating unit A represented by formula (1) and a monomer forming a repeating unit B containing two or more acid groups. If necessary, saponification may be carried out in the presence of an alkali in a mixed solvent of water and an aqueous organic solvent.

[0035] When the sum of repeating units A and B is 100 mol%, the repeating unit B is 1 mol% to 40 mol%, preferably 5 mol% to 40 mol%, and more preferably 10 mol% to 40 mol%. When the repeating unit B is 1 mol% or more, a significant effect on battery performance can be obtained. From the viewpoint of reactivity, the repeating unit B is preferably 40 mol% or less.

[0036] The weight-average molecular weight of the water-soluble polymer compound is preferably 50,000 or more and 300,000 or less. From the viewpoint of slurry dispersibility, the weight-average molecular weight is preferably 50,000 or more. When the weight-average molecular weight is 300,000 or less, the water-soluble polymer compound is easily synthesized.

[0037] The total amount of repeating units A and B may be 10 mol% or more and 90 mol% or less, preferably 10 mol% or more and 70 mol% or less, and more preferably 15 mol% or more and 60 mol% or less, based on the total amount of all repeating units constituting the water-soluble polymer compound. From the viewpoint of reactivity, the total amount of repeating units A and B is preferably 10 mol% or more. From the viewpoint of slurry dispersibility, the total amount of repeating units A and B is preferably 90 mol% or less.

[0038] The water-soluble polymer compound preferably contains a repeating unit C represented by formula (3).

[0039] [ka]

[0040] The water-soluble polymer compound may be obtained by copolymerizing a monomer that forms a repeating unit A represented by formula (1), a monomer that forms a repeating unit B containing two or more acid groups, and a monomer that forms a repeating unit C represented by formula (3) in the presence of a polymerization initiator, and then saponifying the copolymer in a mixed solvent of water and an aqueous organic solvent in the presence of an alkali.

[0041] The viscosity of a 2.5% aqueous solution of the water-soluble polymer compound at 25° C. may be 5 mPa·s or more and 40 mPa·s or less, and preferably 10 mPa·s or more and 20 mPa·s or less. When the viscosity is within this range, the slurry has good handleability.

[0042] <Combination drug> The mixture for a secondary battery electrode of the present invention contains the above-mentioned binder for a secondary battery and an active material.

[0043] <Active material> The active material is an electrode active material, and may be a negative electrode active material or a positive electrode active material. When the active material is a negative electrode active material, it may contain, for example, a carbon material, and may also contain, for example, at least one of silicon and silicon oxide. Specific examples of the negative electrode active material and the positive electrode active material are shown below.

[0044] (Cathode active material) The positive electrode active material may be any positive electrode active material used in the art. The positive electrode active material may be a lithium-containing composite oxide. Examples of lithium-containing composite oxides include LiMnO2, LiFeO2, LiCoO2, LiMn2O4, Li2FeSiO4, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi x Co y M a z O2 (However, 0.01 <x<1、0≦y≦1、0≦z≦1、x+y+z=1であり、M a is at least one element selected from the group consisting of Mn, V, Mg, Mo, Nb, Fe, Cu and Al), LiMn (1-w) Few PO4 (where 0 < w < 1), LiFePO4, etc. may be mentioned.

[0045] (Negative electrode active material) As the negative electrode active material, materials capable of occluding and releasing a large amount of lithium ions such as crystalline graphite such as graphite, silicon (Si), tin (Sn), titanium (Ti), etc. can be used. For such materials, any of simple substances, alloys, compounds, solid solutions, and composite active materials including silicon-containing materials, tin-containing materials, and titanium-containing materials may be used. As the silicon-containing materials, Si, SiO x (0.05 < x < 1.95), or alloys, compounds, or solid solutions in which a part of Si is substituted with at least one element selected from the group consisting of B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, Ta, V, W, Zn, C, N, Sn can be used. These can be referred to as silicon, silicon compounds, or silicon oxides. As the tin-containing materials, Ni2Sn4, Mg2Sn, SnO x (0 < x < 2), SnO2, SnSiO3, LiSnO, etc. can be applied. As the titanium-containing materials, lithium titanates such as Li2TiO3, Li4Ti5O 12 etc., titanium niobium composite compounds, etc. can be applied. These materials may be used individually or in combination of two or more. Among these, silicon or silicon oxides such as elemental Si and silicon oxide are preferable.

[0046] <Conductive assistant> The binder for the electrode of the present invention may contain a conductive assistant.

[0047] The conductive additive is not particularly limited as long as it has conductivity, but carbon powder is preferred. Examples of carbon powder include commonly used carbon materials such as acetylene black (AB), ketjen black (KB), graphite, carbon fiber, carbon tube, graphene, amorphous carbon, hard carbon, soft carbon, glassy carbon, carbon nanofiber, and carbon nanotube. These may be used alone or in combination of two or more. Among these, carbon nanofiber or carbon nanotube is preferred from the viewpoint of improving conductivity.

[0048] <Dispersion aid> The electrode mixture of the present invention may further contain a dispersing aid.

[0049] Preferred dispersing aids are organic acids containing at least one substituent selected from the group consisting of a hydroxy group, an amino group, and an imino group, and a carboxy group, or humic acid. Examples of organic acids containing a hydroxy group and a carboxy group include lactic acid, tartaric acid, citric acid, malic acid, glycolic acid, tartronic acid, glucuronic acid, and humic acid. Examples of organic acids containing an amino group and a carboxy group include glycine, alanine, phenylalanine, 4-aminobutyric acid, leucine, isoleucine, lysine, glutamic acid, aspartic acid, glutamine, asparagine, histidine, tryptophan, cysteine, and polymers thereof. Examples of organic acids containing an imino group and a carboxy group include proline, 3-hydroxyproline, 4-hydroxyproline, and pipecolic acid. Among these, glucuronic acid, humic acid, glycine, polyglycine, aspartic acid, and glutamic acid are preferred due to their availability.

[0050] <Preparation of combination drug> The mixture of the present invention is prepared using the binder of the present invention and an active material by a known method. For example, the electrode mixture may be obtained by adding a conductive additive, a dispersing agent, and water to the active material and binder as needed to form a paste-like slurry. The binder may be dispersed or dissolved in water before use, or powders of the active material, binder, conductive additive, and dispersing agent may be mixed in advance, and then water may be added and mixed.

[0051] The amount of water used may be, for example, 10% by mass or more and 2000% by mass or less, and preferably 30% by mass or more and 1000% by mass or less, assuming that the total of the active material, the conductive additive, and the binder is 100% by mass. Within this range, the slurry becomes easy to handle.

[0052] The binder is used for the purpose of bonding the active materials together, the active materials and the conductive additive, and these and the current collectors, i.e., to form a good active material layer when the slurry is applied to the current collectors of both electrodes and dried.

[0053] The amount of binder used is, for example, preferably 0.5% by mass to 30% by mass, more preferably 1% by mass to 20% by mass, and even more preferably 2% by mass to 10% by mass, based on the total mass of the active material, binder, and conductive additive. If the amount of binder used exceeds 30% by mass, the content of the active material decreases relatively, making it difficult to obtain a high capacity during charging and discharging of the battery, and if the amount of binder used is less than 0.5% by mass, the cycle characteristics are likely to deteriorate due to insufficient binding strength.

[0054] The amount of conductive additive used is, for example, preferably 0.1% by mass to 30% by mass, more preferably 0.5% by mass to 10% by mass, and even more preferably 2% by mass to 5% by mass, based on the total mass of the active material, binder, and conductive additive. If the amount of conductive additive used is less than 0.1% by mass, the conductivity of the electrode may not be sufficiently improved. If the amount of conductive additive used exceeds 30% by mass, the content of the active material decreases relatively, making it difficult to obtain high capacity during charging and discharging of the battery.

[0055] The amount of the dispersion aid used is 0.01% by mass or more relative to the total mass of the active material, binder, and conductive aid, so that the active material and other components can be efficiently and effectively finely dispersed during preparation of the active material dispersion. Note that an amount of 5.0% by mass or less is often sufficient to maintain fine dispersion and dispersion stability. [Example]

[0056] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0057] Example 1 A reactor equipped with a stirrer, thermometer, N2 gas inlet tube, reflux condenser, and dropping funnel was charged with N2 gas to remove oxygen from the system. Then, 80 g of methanol, 173.0 g of vinyl acetate, 7.2 g of methyl acrylate, and 6.5 g of itaconic acid were charged to the reactor and stirred. The temperature inside the reactor was raised to 53°C while stirring, and then 0.6 g of 2,2'-azobis(2,4-dimethylvaleronitrile) was added to the reactor. A solution containing 30.8 g of methyl acrylate and 12.6 g of methanol was added dropwise to the reactor over 8 hours while stirring. Then, 0.2 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride was added to the reactor and the mixture was kept warm for 3 hours. Then, 304.8 g of methanol was added to prepare the reaction solution.

[0058] A reaction vessel equipped with a stirrer, thermometer, N2 gas inlet tube, reflux condenser, and dropping funnel was charged with 270.9 g of the above reaction solution, 111.3 g of water, 0.2 g of hydrazine, and 96.3 g of 48% aqueous sodium hydroxide solution, and stirred at 30°C for 3 hours. After stirring was completed, 470.8 g of methanol was added, and acetic acid was added to adjust the pH of the reaction solution to 7.7-7.8. The solid was then filtered, washed with methanol, and dried at 60°C for 8 hours to obtain a copolymer containing repeating units A represented by formula (1), B represented by formula (2), and C represented by formula (3). When the sum of repeating units A and B is taken as 100 mol%, repeating unit B accounts for 10.2 mol%.

[0059] The molecular weight of the resulting copolymer was measured using a molecular weight analyzer (Viscotek TDA302, manufactured by Asahi Techneion Corporation). The weight-average molecular weight calculated based on a standard polyethylene glycol / polyethylene oxide equivalent was 110,000. 5.4 g of the resulting copolymer was weighed out, 194.6 g of water was added, and the mixture was heated and dissolved at 95°C for 7 hours to prepare a 2.5% aqueous solution of the copolymer. After keeping the resulting 2.5% aqueous solution at 25°C, the viscosity was measured using a Brookfield DV1MLVTJ0 type B viscometer with a LV-1 spindle. The resulting viscosity was 16.3 mPa·s.

[0060] Example 2 A reactor equipped with a stirrer, thermometer, N2 gas inlet tube, reflux condenser, and dropping funnel was charged with N2 gas to remove oxygen from the system. Then, 141.4 g of methanol, 260.1 g of vinyl acetate, 35.5 g of acrylic acid, and 34.5 g of itaconic acid were charged to the reactor and stirred. The temperature inside the reactor was raised to 60°C while stirring, and 2.0 g of 2,2'-azobis(2,4-dimethylvaleronitrile) was added to the reactor. Then, 109.7 g of acrylic acid and 149.7 g of methanol were added dropwise to the reactor over 8 hours while stirring. Then, 3.4 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride was added to the reactor and kept warm for 3 hours. Then, 357.8 g of methanol was added to prepare a reaction solution.

[0061] A similar reaction vessel was charged with 250.1 g of the reaction solution, 109.9 g of water, 30.6 g of methanol, 0.2 g of hydrazine, and 108.2 g of 48% aqueous sodium hydroxide solution, and the mixture was stirred at 30°C for 3 hours. After stirring, 484.5 g of methanol was added, and acetic acid was added to adjust the pH of the reaction solution to 7.7-7.8. The solid was then filtered, washed with methanol, and dried at 60°C for 8 hours to obtain a copolymer containing repeating units A represented by formula (1), B represented by formula (2), and C represented by formula (3). When the sum of repeating units A and B is taken as 100 mol%, the proportion of B is 11.6 mol%.

[0062] The molecular weight of the obtained copolymer was measured in the same manner as in Example 1. The weight-average molecular weight calculated in terms of standard polyethylene glycol / polyethylene oxide was 100,000. 5.3 g of the obtained copolymer was weighed out, and 194.7 g of water was added. The mixture was heated and dissolved at 95°C for 7 hours to prepare a 2.5% aqueous solution of the copolymer. The obtained 2.5% aqueous solution was kept at 25°C, and then the viscosity was measured in the same manner as in Example 1. The resulting viscosity was 13.9 mPa s.

[0063] Example 3 A copolymer containing repeating unit A represented by formula (1), repeating unit B represented by formula (2), and repeating unit C represented by formula (3) was obtained in the same manner as in Example 2, except that the dropwise addition time of acrylic acid and methanol was changed from 8 hours to 5 hours in Example 2. When the total of repeating unit A and repeating unit B is taken as 100 mol %, repeating unit B accounts for 11.6 mol %.

[0064] The molecular weight of the obtained copolymer was measured in the same manner as in Example 1. The weight-average molecular weight calculated in terms of standard polyethylene glycol / polyethylene oxide was 120,000. 5.3 g of the obtained copolymer was weighed out, and 194.7 g of water was added. The mixture was heated and dissolved at 95°C for 7 hours to prepare a 2.5% aqueous solution of the copolymer. The obtained 2.5% aqueous solution was kept at 25°C, and then the viscosity was measured in the same manner as in Example 1. The resulting viscosity was 15.7 mPa s.

[0065] Example 4 A copolymer containing repeating units A represented by formula (1), repeating units B represented by formula (2), and repeating units C represented by formula (3) was obtained in the same manner as in Example 2, except that the amounts of acrylic acid (145.2 g) were changed to 122.2 g (1.7 mol), itaconic acid (34.5 g) to 137.9 g (1.1 mol), and vinyl acetate (260.1 g) to 219.1 g (2.5 mol). When the sum of repeating units A and B is taken as 100 mol%, repeating units B account for 38.5 mol%.

[0066] The molecular weight of the obtained copolymer was measured in the same manner as in Example 1. The weight-average molecular weight calculated in terms of standard polyethylene glycol / polyethylene oxide was 200,000. 5.4 g of the obtained copolymer was weighed out, and 194.6 g of water was added. The mixture was heated and dissolved at 95°C for 7 hours to prepare a 2.5% aqueous solution of the copolymer. The obtained 2.5% aqueous solution was kept at 25°C, and then the viscosity was measured in the same manner as in Example 1. The resulting viscosity was 10.9 mPa s.

[0067] (Comparative Example 1) A reactor equipped with a stirrer, thermometer, N2 gas inlet tube, reflux condenser, and dropping funnel was charged with 768.0 g of water and 12.0 g of anhydrous sodium sulfate, and N2 gas was blown in to remove oxygen from the system. Next, 1.0 g of partially saponified polyvinyl alcohol (saponification degree 88%) and 1.0 g of lauryl peroxide were charged to the reactor and stirred. While stirring, the temperature inside the reactor was raised to 60°C, and then 51.8 g of methyl acrylate and 208.0 g of vinyl acetate were added dropwise to the reactor over 4 hours. The internal temperature was then maintained at 65°C for 2 hours. The solids were then filtered off.

[0068] The solid content, 450.0 g of methanol, 420.0 g of water, 132 g of sodium hydroxide, and 0.5 g of hydrazine were charged into a reaction vessel similar to that described above and stirred at 30°C for 3 hours. After stirring was completed, the solid was filtered off, washed with methanol, and dried at 60°C for 8 hours to obtain a copolymer containing repeating units A represented by formula (1) and repeating units C represented by formula (3). Note that since repeating unit B was not contained, when the sum of repeating units A and B is 100 mol%, repeating unit B is 0 mol%.

[0069] The molecular weight of the obtained copolymer was measured in the same manner as in Example 1. The weight-average molecular weight calculated in terms of standard polyethylene glycol / polyethylene oxide was 440,000. 5.4 g of the obtained copolymer was weighed out, and 194.6 g of water was added. The mixture was heated and dissolved at 95°C for 7 hours to prepare a 2.5% aqueous solution of the copolymer. The obtained 2.5% aqueous solution was kept at 25°C, and then the viscosity was measured in the same manner as in Example 1. The resulting viscosity was 99.7 mPa s.

[0070] (Comparative Example 2) A reactor equipped with a stirrer, thermometer, N2 gas inlet tube, reflux condenser, and dropping funnel was charged with 215.2 g of pure water, and N2 gas was blown in to remove oxygen from the system. Then, 15.1 g of acrylic acid, 16.9 g of 48% aqueous sodium hydroxide solution, 26.0 g of acrylonitrile, and 0.8 g of potassium persulfate were charged to the reactor and stirred. The temperature inside the reactor was maintained at 70°C for 6 hours while stirring. The reaction solution was then filtered to obtain an acrylic acid / acrylonitrile copolymer. Since the sample did not contain repeating unit B, if the sum of repeating unit A and repeating unit B is 100 mol%, repeating unit B is 0 mol%.

[0071] The molecular weight of the obtained copolymer was measured in the same manner as in Example 1. The weight-average molecular weight calculated in terms of standard polyethylene glycol / polyethylene oxide was 350,000. The obtained copolymer was prepared into a 2.5% aqueous solution and dissolved by heating at 95°C for 3 hours. The solution was then kept at 25°C, and the viscosity was measured in the same manner as in Example 1. The resulting viscosity was 43.6 mPa s.

[0072] [Preparation of secondary battery electrode mixture, electrode, and secondary battery] The copolymers obtained in the above examples and comparative examples were used as 10% by mass binder aqueous solutions. Next, 23.3 g of artificial graphite (G-49, manufactured by Jiangxi Zichen Technology Co., Ltd.) and 5.8 g of silicon monoxide (KSC-1265, manufactured by Shin-Etsu Chemical Co., Ltd.) were added as electrode active materials, and the 10% by mass binder aqueous solution (copolymer content: 0.9 g) was mixed and kneaded. 13.6 g of water was then added and kneaded to a solids concentration of 58% by mass to prepare a negative electrode mixture slurry. The resulting negative electrode mixture was applied to a rolled copper foil with a thickness of 18 μm and dried. After that, the rolled copper foil and the coating were tightly bonded together using a roll press (manufactured by Ohno Roll Co., Ltd.), and dried (reduced pressure, 100°C, 12 hours) to prepare a negative electrode. The thickness of the active material layer in the resulting negative electrode was 36 μm, and the capacity density of the negative electrode was 3.5 mAh / cm. 2 It was.

[0073] LiNi as the positive electrode active material 0.5 Co 0.2 Mn 0.3 A positive electrode sheet containing O2 (manufactured by Hachiyama Co., Ltd.) and a glass filter (trade name GA-100, manufactured by Advantec Co., Ltd.) were prepared as a separator. The positive electrode sheet had an aluminum foil (thickness 20 μm) as a positive electrode current collector and a positive electrode active material layer formed on one side of the aluminum foil. The positive electrode active material layer contained LiNi 0.5 Co 0.2 Mn 0.3 The material contained O2, carbon black (CB) and carbon (KS) as conductive additives, and polyvinylidene fluoride (PVdF) as a binder. The mass ratio of these was: LiNi 0.5 Co 0.2 Mn 0.3 The O2:CB:KS:PVdF ratio was 92:2.5:2.5:3.

[0074] Next, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1 to obtain a mixed nonaqueous solvent. LiPF6 was dissolved in the obtained mixed nonaqueous solvent to a concentration of 1 mol / L as an electrolyte. 1% by mass of vinylene carbonate (VC) and 1% by mass of fluoroethylene carbonate (FEC) were added to the obtained solution as electrolyte additives to prepare a nonaqueous electrolyte.

[0075] The gasket, positive electrode, and separator were placed in a coin cell (CR2032) case, and the electrolyte was poured in. The negative electrode, spacer, and washer were then placed, and the coin cell was then sealed with a cap to prepare it.

[0076] [Evaluation of battery characteristics] (Aging process) Each coin cell was charged at 30°C to 4.2 V at a current equivalent to 0.1 C and discharged to 2.5 V at a current equivalent to 0.1 C for three cycles, and then charged to 4.2 V at a current equivalent to 0.5 C and discharged to 2.5 V at a current equivalent to 0.5 C for two cycles to age the battery.

[0077] (Charge-discharge cycle test) Each coin cell that had undergone the aging process was subjected to a charge-discharge cycle test at 30°C, with a charge rate of 1.0 C, a discharge rate of 1.0 C, a charge cut-off voltage of 4.2 V, and a discharge cut-off voltage of 2.5 V. The capacity retention rate after 200 cycles is shown in Table 1. The "capacity retention rate (%)" after 200 cycles is the ratio (percentage) of the discharge capacity (mAh) after 200 cycles to the initial discharge capacity (mAh).

[0078] [Table 1]

Claims

1. A binder for a secondary battery containing a water-soluble polymer compound, the water-soluble polymer compound contains a repeating unit A represented by formula (1) and a repeating unit B containing two or more acid groups, The binder for a secondary battery, wherein the repeating unit B accounts for 1 mol % or more and 40 mol % or less when the total of the repeating unit A and the repeating unit B is 100 mol %. 【Chemistry 1】 [In formula (1), M １ are each independently a hydrogen atom or an alkali metal atom.

2. 2. The binder for a secondary battery according to claim 1, wherein the acid group is a carboxy group or a group corresponding to a salt thereof.

3. The binder for a secondary battery according to claim 1 , wherein the repeating unit B is represented by formula (2): 【Chemistry 2】 [In formula (2), M ２ are each independently a hydrogen atom or an alkali metal atom.

4. 2. The binder for a secondary battery according to claim 1, wherein the water-soluble polymer compound has a weight average molecular weight of 50,000 or more and 300,000 or less.

5. 2. The binder for a secondary battery according to claim 1, wherein a total amount of the repeating unit A and the repeating unit B is 10 mol % or more and 90 mol % or less based on a total amount of all repeating units constituting the water-soluble polymer compound.

6. The binder for a secondary battery according to claim 1 , wherein the water-soluble polymer compound contains a repeating unit C represented by formula (3): 【Transformation 3】

7. A secondary battery electrode mixture comprising the binder for a secondary battery according to claim 1 and an active material.

8. The secondary battery electrode mixture according to claim 7 , wherein the active material comprises a carbon material.

9. 8. The secondary battery electrode mixture according to claim 7, wherein the active material contains at least one of silicon and silicon oxide.

10. A secondary battery electrode comprising the electrode mixture for a secondary battery according to any one of claims 7 to 9.

11. A secondary battery comprising the electrode for a secondary battery according to claim 10.

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