Binder composition for secondary battery electrodes, conductive paste composition for secondary battery electrodes, slurry composition for secondary battery electrodes, secondary battery electrodes, and secondary batteries

Abstract

The binder composition for a secondary battery electrode comprises a polymer that contains a nitrile group-containing monomer unit, an aromatic vinyl monomer unit, and a linear alkylene structural unit, but does not contain a hydrophilic group-containing monomer unit.

Description

[Technical Field]

[0001] The present invention relates to a binder composition for secondary battery electrodes, a conductive paste composition for secondary battery electrodes, a slurry composition for secondary battery electrodes, an electrode for a secondary battery, and a secondary battery. [Background technology]

[0002] Secondary batteries such as lithium-ion secondary batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications. Therefore, in recent years, improvements to battery components such as electrodes have been investigated in order to further improve the performance of secondary batteries.

[0003] Here, an electrode used in a secondary battery such as a lithium-ion secondary battery usually includes a current collector and an electrode mixture layer (positive electrode mixture layer or negative electrode mixture layer) formed on the current collector. This electrode mixture layer is formed, for example, using a slurry composition obtained by dispersing an electrode active material and a binder composition containing a binding agent in a dispersion medium.

[0004] Therefore, in recent years, attempts have been made to improve the binder composition used in forming the electrode mixture layer in order to achieve further improvements in the performance of secondary batteries. Specifically, for example, Patent Document 1 discloses a binder composition for a secondary battery positive electrode, which is a binder containing polymerization units having a nitrile group, aromatic vinyl polymerization units, polymerization units having a hydrophilic group, and linear alkylene polymerization units having 4 or more carbon atoms, and in which the content of aromatic vinyl polymerization units is 5 to 50%. By using such a binder composition, a secondary battery excellent in cycle characteristics and the like can be provided. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-179040 Summary of the Invention [Problem to be solved by the invention]

[0006] However, even when the conventional binder composition for a positive electrode is used, it is difficult to sufficiently increase the dispersibility of the conductive material in the conductive material paste or slurry composition, and it is not possible to obtain a slurry composition with sufficiently high stability over time. Furthermore, the positive electrode prepared using the conventional binder composition for a positive electrode has room for improvement in terms of further reducing gas generation due to repeated charge and discharge.

[0007] Therefore, an object of the present invention is to provide a binder composition for secondary battery electrodes, which can prepare a conductive material paste having sufficiently high dispersibility of the conductive material, can prepare a slurry composition having sufficiently high stability over time, and can also produce an electrode with a low amount of gas generation. Another object of the present invention is to provide a conductive material paste composition for secondary battery electrodes, which can prepare a slurry composition having sufficiently high dispersibility of a conductive material and sufficiently high stability over time, and which can produce an electrode with a low amount of gas generation. A further object of the present invention is to provide a slurry composition for secondary battery electrodes which has sufficiently high stability over time and can produce electrodes with low gas generation. Another object of the present invention is to provide an electrode that generates a low amount of gas and a secondary battery that includes such an electrode. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems, and have found that a binder composition for a secondary battery electrode containing a polymer that includes a nitrile group-containing monomer unit, an aromatic vinyl monomer unit, and a linear alkylene structural unit, but does not include a hydrophilic group-containing monomer unit, makes it possible to prepare a conductive material paste with sufficiently high dispersibility of the conductive material, to prepare a slurry composition with sufficiently high stability over time, and to produce an electrode that generates a low amount of gas, thereby completing the present invention.

[0009]

[0009] The present invention has an object to advantageously solve the above-mentioned problems, and provides a binder composition for a secondary battery electrode, which comprises a polymer, wherein the polymer contains nitrile group-containing monomer units, aromatic vinyl monomer units, and linear alkylene structural units, but does not contain hydrophilic group-containing monomer units. Thus, if the polymer contained in the binder composition contains nitrile group-containing monomer units, aromatic vinyl monomer units, and linear alkylene structural units, but does not contain hydrophilic group-containing monomer units, it is possible to prepare a conductive material paste with sufficiently high conductive material dispersibility, a slurry composition with sufficiently high stability over time, and further, it is possible to produce an electrode with low gas generation. The phrase "containing a monomer unit" means that "a polymer obtained using the monomer contains a structural unit derived from the monomer." Furthermore, the phrase "containing a linear alkylene structural unit" means that a polymer contains a structural unit derived from the monomer. n H 2n - [where n is an integer]. Furthermore, the presence or absence of monomer units and structural units in the polymer and the content ratio thereof can be determined, for example, by the following formula: 1 It can be determined or measured by H-NMR.

[0010] In the binder composition for a secondary battery electrode of the present invention, the polymer preferably has an iodine value of 120 mg / 100 mg or less. If the iodine value of the polymer is 120 mg / 100 mg or less, a conductive material paste having a higher dispersibility of the conductive material can be prepared, and in turn, when a slurry composition is prepared, the dispersibility of the conductive material in the slurry composition can be improved. The "iodine value" of the polymer can be measured in accordance with JIS K6235 (2006).

[0011] In the binder composition for a secondary battery electrode of the present invention, the polymer preferably contains the aromatic vinyl monomer unit in a proportion of 3% by mass to 80% by mass. If the content of the aromatic vinyl monomer unit in the polymer is within the above range, it is possible to prepare a conductive material paste having a higher dispersibility of the conductive material and a slurry composition having higher stability over time.

[0012] The present invention also aims to advantageously solve the above-mentioned problems, and provides a conductive material paste composition for secondary battery electrodes, which is characterized by containing a conductive material and any one of the above-mentioned binder compositions for secondary battery electrodes. When the paste composition contains any one of the above-mentioned binder compositions for secondary battery electrodes, it is possible to prepare a slurry composition in which the conductive material has sufficiently high dispersibility in the paste composition and which has sufficiently high stability over time, and further, it is possible to produce an electrode that generates a low amount of gas.

[0013] In the conductive material paste composition for a secondary battery electrode of the present invention, the conductive material may contain carbon nanotubes. When the paste composition contains the binder composition, the carbon nanotubes as the conductive material can be well dispersed in the paste composition.

[0014] The present invention also aims to advantageously solve the above-mentioned problems, and provides a slurry composition for a secondary battery electrode, which is characterized by comprising an electrode active material, a solvent, and any one of the binder compositions for a secondary battery electrode described above. When the slurry composition contains any one of the binder compositions for a secondary battery electrode described above, it is possible to produce an electrode that has sufficiently high stability over time and generates a low amount of gas.

[0015] Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and the secondary battery electrode of the present invention is characterized by comprising an electrode mixture layer formed using the above-mentioned secondary battery electrode slurry composition. Thus, the electrode formed using the above-mentioned secondary battery electrode slurry composition generates a low amount of gas.

[0016] The present invention aims to advantageously solve the above-mentioned problems, and provides a secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein at least one of the positive electrode and the negative electrode is the above-mentioned secondary battery electrode. In this way, by using the above-mentioned secondary battery electrode, the amount of gas generated in the secondary battery is small, and excellent battery characteristics can be exhibited over a long period of time. [Effects of the Invention]

[0017] According to the present invention, it is possible to prepare a conductive material paste having a sufficiently high dispersibility of the conductive material, to prepare a slurry composition having a sufficiently high stability over time, and further to provide a binder composition for a secondary battery electrode, which is capable of producing an electrode with a low amount of gas generation. Furthermore, according to the present invention, it is possible to prepare a slurry composition having sufficiently high dispersibility of a conductive material and sufficiently high stability over time, and further, it is possible to provide a conductive material paste composition for secondary battery electrodes, which can produce an electrode with a low amount of gas generation. Furthermore, according to the present invention, it is possible to provide a slurry composition for secondary battery electrodes which has sufficiently high stability over time and which can produce electrodes with low gas generation. According to the present invention, it is possible to provide an electrode that generates a low amount of gas and a secondary battery that includes such an electrode. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described in detail. Here, the binder composition for secondary battery electrodes of the present invention can be suitably used when preparing a conductive material paste composition for secondary battery electrodes (hereinafter, sometimes simply referred to as "conductive material paste") and a slurry composition for secondary battery electrodes (hereinafter, sometimes simply referred to as "slurry composition"). Furthermore, a slurry composition for secondary battery electrodes prepared using the binder composition for secondary battery electrodes of the present invention can be suitably used when forming a positive electrode of a secondary battery such as a lithium ion secondary battery. Furthermore, the secondary battery of the present invention is characterized by using a secondary battery electrode formed using the slurry composition for secondary battery electrodes of the present invention.

[0019] (Binder composition for secondary battery electrodes) The binder composition for secondary battery electrodes of the present invention is characterized by containing a polymer containing nitrile group-containing monomer units, aromatic vinyl monomer units, and linear alkylene structural units, but containing no hydrophilic group-containing monomers. A polymer of this composition can sufficiently enhance the dispersibility of the conductive material in the conductive paste or slurry composition and further suppress the tendency of the slurry composition to thicken over time after preparation. Furthermore, the inclusion of a polymer of this composition enables the formation of an electrode with reduced gas generation due to repeated charging and discharging. These advantages can be achieved by the specific composition of the polymer described above. In particular, the absence of hydrophilic group-containing monomer units in the polymer suppresses the thickening of the slurry composition over time after preparation, and suppresses gas generation from the electrode when the slurry composition is used to form an electrode. Furthermore, the inclusion of nitrile group-containing monomer units in the polymer appropriately increases the solubility of the polymer in organic solvents such as N-methylpyrrolidone, making it possible to adjust the viscosity of the conductive paste or slurry composition within an appropriate range. As a result, the dispersibility of solid components such as the conductive material in the conductive material paste or slurry composition can be improved. Furthermore, when the polymer contains aromatic vinyl monomer units, the dispersibility of solid components such as the conductive material can be improved when the conductive material paste or slurry composition is prepared. And, when the polymer contains linear alkylene structural units, the solid components such as the conductive material in the slurry composition can be prevented from aggregating over time after the preparation of the slurry composition, thereby improving the dispersion stability of the slurry composition.

[0020] <Polymer> The polymer is a component that functions as a binder and prevents components contained in the electrode mixture layer from being detached from the electrode mixture layer in an electrode manufactured by forming an electrode mixture layer on a current collector using a slurry composition for a secondary battery electrode prepared using the binder composition. The polymer must contain nitrile group-containing monomer units, aromatic vinyl monomer units, and linear alkylene structural units, but must not contain hydrophilic group-containing monomer units. The polymer may optionally contain other monomer units as long as the effects of the present invention are not impaired. Furthermore, the polymer is preferably a hydrogenated polymer obtained by hydrogenating, by a known method, a polymer obtained by polymerizing a monomer composition containing a nitrile group-containing monomer, an aromatic vinyl monomer, and a conjugated diene monomer, but not containing a hydrophilic group-containing monomer.

[0021] [Nitrile group-containing monomer unit] The nitrile group-containing monomer unit is a repeating unit derived from a nitrile group-containing monomer. Even if the monomer unit contains a nitrile group, a unit that can be classified as a hydrophilic group-containing monomer unit, i.e., a monomer unit containing a hydrophilic group such as an acidic group or a hydroxyl group, is not included in the "nitrile group-containing monomer unit" that is a constituent element of the polymer of the present invention. Furthermore, since the polymer contains the nitrile group-containing monomer unit, it has high solubility in organic solvents such as N-methylpyrrolidone, and can effectively increase the viscosity of the resulting slurry composition. Furthermore, by suppressing viscosity change over time, the viscosity stability of the slurry composition can also be effectively improved.

[0022] Here, examples of nitrile group-containing monomers capable of forming nitrile group-containing monomer units include α,β-ethylenically unsaturated nitrile monomers. Specifically, the α,β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group, and examples thereof include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile and α-ethylacrylonitrile. Among these, from the viewpoint of increasing the binding strength of the polymer, acrylonitrile and methacrylonitrile are preferred as nitrile group-containing monomers, and acrylonitrile is more preferred. These may be used alone or in combination of two or more.

[0023] The content of the nitrile group-containing monomer units in the polymer is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 38% by mass or less, based on 100% by mass of all repeating units in the polymer. By setting the content of the nitrile group-containing monomer units in the polymer at or above the lower limit, the solubility of the polymer in organic solvents such as N-methylpyrrolidone is appropriately increased, making it possible to adjust the viscosity of a conductive material paste or slurry composition within an appropriate range when the composition is prepared. As a result, the dispersibility of solid components such as conductive materials in the conductive material paste or slurry composition can be improved. Furthermore, when an electrode is formed using such a slurry composition, the polymer can exhibit good binding strength, thereby increasing the peel strength of the electrode. Furthermore, the output characteristics of a secondary battery including such an electrode can be further improved. Furthermore, by setting the content of the nitrile group-containing monomer units in the polymer at or below the upper limit, the output characteristics of the secondary battery can be further improved. This is presumably because, when the content ratio of the nitrile group-containing monomer unit in the polymer is equal to or less than the above upper limit, the degree of swelling of the polymer in the electrolyte can be effectively prevented from increasing excessively, and the internal resistance of the secondary battery can be reduced.

[0024] [Aromatic vinyl monomer unit] The aromatic vinyl monomer unit is a repeating unit derived from an aromatic vinyl monomer. Even if the repeating unit is derived from an aromatic vinyl monomer, a unit that can be classified as a hydrophilic group-containing monomer unit, i.e., a unit containing a hydrophilic group such as an acidic group or a hydroxyl group, is not included in the "aromatic vinyl monomer unit" that is a constituent element of the polymer of the present invention. Furthermore, a polymer containing an aromatic vinyl monomer unit can enhance the dispersibility of solid components such as conductive materials in a conductive material paste or slurry composition.

[0025] Examples of the monomer capable of forming an aromatic vinyl polymerization unit include aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, etc. Among these, styrene is preferred because it has good copolymerizability with other monomers and relatively little side reactions such as branching, chain formation, and intermolecular crosslinking of the polymer.

[0026] The content of the aromatic vinyl monomer units in the polymer is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 65% ​​by mass or less, when the total amount of repeating units in the polymer is taken as 100% by mass. By setting the content of the aromatic vinyl monomer units in the polymer to the above-mentioned lower limit or more, the dispersibility of solid components such as conductive materials can be effectively improved when a conductive material paste or slurry composition is prepared. Furthermore, by setting the content of the aromatic vinyl monomer units in the polymer to the above-mentioned upper limit or less, the dispersibility of solid components such as conductive materials can also be effectively improved when a conductive material paste or slurry composition is prepared. Furthermore, by setting the content of the aromatic vinyl monomer units in the polymer within the above-mentioned range, it is possible to suppress changes in the viscosity of the slurry composition when the slurry composition is left standing for a certain period of time after preparation, and to effectively improve the dispersion stability of solid components such as conductive materials in the slurry composition.

[0027] [Straight-chain alkylene structural unit] The linear alkylene structural unit (hereinafter, sometimes simply referred to as "alkylene structural unit") is represented by the general formula: -C n H 2n - [where n is an integer]. Even if the repeating unit is composed of only a linear alkylene structure, units that may fall under the category of hydrophilic group-containing monomer units, i.e., structural units containing hydrophilic groups such as acidic groups and hydroxyl groups, are not included in the "linear alkylene structural unit" that is a constituent element of the polymer of the present invention. Furthermore, since the polymer has a linear alkylene structural unit, it is possible to suppress aggregation of solid components such as conductive materials in the slurry composition over time after preparation of the slurry composition, thereby improving the dispersion stability of the slurry composition. To further enhance this effect, the linear alkylene structural unit is preferably a linear alkylene structural unit having 4 or more carbon atoms, and it is preferable that n in the above general formula be an integer of 4 or more.

[0028] The method for introducing the linear alkylene structural unit into the polymer is not particularly limited, but may be, for example, the following method (1) or (2): (1) A method in which a polymer is prepared from a monomer composition containing a conjugated diene monomer, and the polymer is hydrogenated to convert the conjugated diene monomer units into linear alkylene structural units. (2) A method for preparing a polymer from a monomer composition containing a 1-olefin monomer such as 1-butene or 1-hexene. These conjugated diene monomers and 1-olefin monomers can be used either alone or in combination of two or more. Among these, method (1) is preferred because it is easy to produce the polymer.

[0029] Examples of conjugated diene monomers that can be used in the above method (1) include conjugated diene compounds such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Among these, 1,3-butadiene is preferred. That is, the linear alkylene structural unit is preferably a structural unit (conjugated diene hydride unit) obtained by hydrogenating a conjugated diene monomer unit, and more preferably a structural unit (1,3-butadiene hydride unit) obtained by hydrogenating a 1,3-butadiene unit. The hydrogenation can be carried out using a known method, as described below.

[0030] The content of the linear alkylene structural unit in the polymer is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, and preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 55% by mass or less, when the total repeating units in the polymer (the sum of structural units and monomer units) is taken as 100% by mass. By setting the content of the linear alkylene structural unit at or above the lower limit, aggregation of the solid components, such as the conductive material, in the slurry composition can be more effectively suppressed over time after preparation of the slurry composition, thereby more effectively improving the dispersion stability of the slurry composition. Furthermore, by setting the content of the linear alkylene structural unit at or below the upper limit, the solubility of the polymer in organic solvents, such as N-methylpyrrolidone, can be appropriately increased, and the viscosity of the conductive material paste or slurry composition can be more effectively adjusted within an appropriate range. As a result, the dispersibility of the solid components, such as the conductive material, in the conductive material paste or slurry composition can be more effectively improved.

[0031] As described above, when the polymer is a hydrogenated polymer obtained by hydrogenating a polymer obtained by polymerizing a monomer composition containing a conjugated diene, the hydrogenated polymer may contain linear alkylene structural units and units derived from other conjugated dienes (for example, including unhydrogenated conjugated diene units). In this case, it is preferable that the total content of the linear alkylene structural units and units derived from other conjugated dienes in the hydrogenated polymer (hereinafter also referred to as the "content of units derived from conjugated dienes") is within the preferred content range described above for the "content of linear alkylene structural units." By setting the total content of the units derived from conjugated dienes within the above range, the effects described for the upper and lower limits of the content of linear alkylene structural units can be achieved.

[0032] [Other monomer units] Furthermore, the other monomers capable of forming the other monomer units are not particularly limited, and examples thereof include known monomers copolymerizable with the above-mentioned monomers, such as (meth)acrylic acid ester monomers, fluorine-containing monomers, (meth)acrylamide compounds, and epoxy group-containing unsaturated compounds, which are monomers or compounds not containing a hydrophilic group, as described below. These monomers can be used alone or in combination of two or more. In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0033] The content of other monomer units in the polymer is preferably 20% by mass or less, more preferably 10% by mass or less, and may be 0% by mass.

[0034] [Hydrophilic group-containing monomer unit as non-containing unit] The polymer of the present invention is required to be free of hydrophilic group-containing monomer units. Here, the hydrophilic group-containing monomer units are repeating units derived from hydrophilic group-containing monomers. Examples of hydrophilic groups include acidic groups and hydroxyl groups. Examples of acidic groups include carboxylic acid groups, sulfonic acid groups, and phosphoric acid groups.

[0035] Examples of the monomer having a carboxylic acid group include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides and their derivatives. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid. Examples of the monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, and β-diaminoacrylic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid esters such as methylallyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleates. Examples of the acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Furthermore, as the compound having a carboxylic acid group, an acid anhydride that generates a carboxyl group upon hydrolysis can also be used. Other examples include monoesters and diesters of α,β-ethylenically unsaturated polycarboxylic acids such as monoethyl maleate, diethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, monocyclohexyl fumarate, dicyclohexyl fumarate, monoethyl itaconate, diethyl itaconate, monobutyl itaconate, and dibutyl itaconate.

[0036] Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, styrene sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid. In the present invention, "(meth)allyl" means allyl and / or methallyl.

[0037] Examples of the monomer having a phosphate group include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate. In the present invention, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0038] Examples of the monomer having a hydroxyl group include ethylenically unsaturated alcohols such as (meth)allyl alcohol, 3-butene-1-ol, and 5-hexene-1-ol; alkanol esters of ethylenically unsaturated carboxylic acids such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate; and monomers having the general formula CH₂=CR₂. 1 -COO-(C n H 2n O) m -H (wherein m is an integer of 2 to 9, n is an integer of 2 to 4, R 1represents hydrogen or a methyl group) and (meth)acrylic acid esters; mono(meth)acrylic acid esters of dihydroxy esters of dicarboxylic acids such as 2-hydroxyethyl-2'-(meth)acryloyloxyphthalate and 2-hydroxyethyl-2'-(meth)acryloyloxysuccinate; vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; mono(meth)allyl ethers of alkylene glycols such as (meth)allyl-2-hydroxyethyl ether and (meth)allyl-2-hydroxypropyl ether; diethylene glycol mono(meth)allyl ether mono(meth)allyl ethers of halogen- and hydroxy-substituted (poly)alkylene glycols, such as glycerin mono(meth)allyl ether and (meth)allyl-2-chloro-3-hydroxypropyl ether; mono(meth)allyl ethers of polyhydric phenols, such as eugenol and isoeugenol, and halogen-substituted products thereof; (meth)allyl thioethers of alkylene glycols, such as (meth)allyl-2-hydroxyethyl thioether and (meth)allyl-2-hydroxypropyl thioether; and the like.

[0039] The above-mentioned nitrile group-containing monomer units, aromatic vinyl monomer units, linear alkylene structural units, and other monomer units do not include carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, and hydroxyl groups.

[0040] [Iodine value] Furthermore, the polymer preferably has an iodine value of 120 mg / 100 mg or less, more preferably 80 mg / 100 mg or less, and even more preferably 50 mg / 100 mg or less. A polymer having an iodine value equal to or less than the above upper limit makes it possible to prepare a conductive material paste with higher dispersibility of the conductive material, and thus, when a slurry composition is prepared, the dispersibility of the conductive material in the slurry composition can be improved. The iodine value of the polymer may be, for example, 2 mg / 100 mg or more. When the polymer is a hydrogenated polymer, the iodine value of the polymer can be adjusted by changing the hydrogenation conditions.

[0041] [Weight average molecular weight] Furthermore, the polymer has a weight average molecular weight of 10×10 3 It is preferable that the value is 20×10 or more. 3 More preferably, it is 200×10 3 Preferably, it is 90 x 10 3 It is more preferable that the weight-average molecular weight of the polymer is equal to or greater than the above lower limit. If the weight-average molecular weight of the polymer is equal to or greater than the above lower limit, excessive swelling of the polymer in the electrolyte solution can be suppressed, and an increase in the internal resistance of the resulting secondary battery can be effectively suppressed. Furthermore, if the weight-average molecular weight of the polymer is equal to or less than the above upper limit, an increase in the viscosity of the conductive material paste, which would otherwise result in a decrease in the dispersibility of the conductive material, can be effectively suppressed when the conductive material paste is prepared. Furthermore, if the weight-average molecular weight of the polymer is equal to or less than the above upper limit, polymers in the slurry composition can be easily aggregated, and the viscosity of the slurry composition can be effectively prevented from changing over time.

[0042] [Method for preparing polymer] The method for preparing the above-mentioned polymer is not particularly limited. For example, the polymer can be prepared by polymerizing a monomer composition containing the above-mentioned monomers, optionally in the presence of a molecular weight modifier such as t-dodecyl mercaptan, to obtain a polymer, and then hydrogenating (hydrogenating) the obtained polymer.

[0043] Here, the content of each monomer in the monomer composition used to prepare the polymer can be determined according to the content of each repeating unit in the polymer. The polymerization method is not particularly limited, and any of solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. The polymerization reaction may be any of ionic polymerization, radical polymerization, living radical polymerization, etc. Furthermore, the method for hydrogenating the polymer is not particularly limited, and general methods using a catalyst, such as oil phase hydrogenation, aqueous phase direct hydrogenation, and aqueous phase indirect hydrogenation (see, for example, WO 2013 / 080989, etc.), can be used.

[0044] [solvent] The binder composition may contain a solvent. The solvent is not particularly limited, and any organic solvent can be used. Examples of the organic solvent include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, and amyl alcohol; ketones such as acetone, ethyl methyl ketone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; ethers such as diethyl ether, dioxane, and tetrahydrofuran; amide-based polar organic solvents such as N,N-dimethylformamide and N-methylpyrrolidone (NMP); and aromatic hydrocarbons such as toluene, xylene, chlorobenzene, orthodichlorobenzene, and paradichlorobenzene. These solvents may be used alone or in combination. Among these, NMP is preferred as the solvent.

[0045] [Other ingredients] In addition to the above components, the binder composition of the present invention may contain other components such as a polymer having a different composition from the above polymer, and known additives such as those described in JP-A-2013-179040. These components may be used alone or in combination of two or more in any ratio.

[0046] For example, polymers having a different composition from the above-mentioned polymers include fluorine-containing polymers such as polyvinylidene fluoride (PVdF), polyacrylonitrile, and polymethyl methacrylate. These polymers differ from the above-mentioned polymers in that they do not contain at least one of a nitrile group-containing monomer unit, an aromatic vinyl monomer unit, and a linear alkylene structural unit. From the viewpoint of further suppressing gas generation from the resulting secondary battery electrode, it is preferable that the binder composition does not contain a polymer containing a hydrophilic group-containing monomer unit.

[0047] <Method for preparing binder composition> The binder composition of the present invention can be prepared by mixing the above-mentioned components with a solvent. The mixing method is not particularly limited, and examples thereof include mixing methods using a mixer such as a ball mill, sand mill, bead mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, or Filmix.

[0048] (Conductive paste composition for secondary battery electrodes) The conductive material paste composition for secondary battery electrodes of the present invention (hereinafter sometimes simply referred to as "conductive material paste composition") is characterized by containing the above-mentioned binder composition of the present invention and a conductive material. Because the conductive material paste composition of the present invention contains the binder composition of the present invention, it is possible to prepare a slurry composition that has sufficiently high dispersibility of the conductive material and sufficiently high stability over time, and further it is possible to produce an electrode that generates a low amount of gas.

[0049] <Conductive material> The conductive material is a component that can be blended to promote electrical contact between electrode active materials in the electrode mixture layer. Examples of conductive materials that can be used include conductive carbon materials such as carbon black (e.g., acetylene black, Ketjen Black (registered trademark), furnace black, etc.), graphite, carbon fiber, and carbon flakes; and fibers and foils of various metals. Among these, the conductive material preferably contains carbon fiber, more preferably contains ultrashort carbon fibers such as carbon nanotubes and vapor-grown carbon fibers, and even more preferably contains carbon nanotubes. These may be used alone or in combination of two or more.

[0050] The BET specific surface area of ​​the conductive material is preferably 100 m 2 / g or more, more preferably 150m 2 / g or more, usually 2500m 2 / g or less. When the BET specific surface area of ​​the conductive material is equal to or greater than the above lower limit, a good conductive path is formed in the electrode mixture layer, and the output characteristics of the secondary battery can be further improved. Furthermore, when the BET specific surface area of ​​the conductive material is equal to or less than the above upper limit, aggregation of the conductive material can be suppressed, and the dispersibility of the conductive material can be ensured.

[0051] Generally, conductive materials with a large BET specific surface area and fibrous conductive materials such as carbon nanotubes tend to aggregate and are difficult to disperse. However, the slurry composition for a secondary battery electrode of the present invention uses a binder composition containing a polymer of the above-described predetermined composition, so that even conductive materials with a large BET specific surface area can be dispersed well and stably.

[0052] <Other ingredients> Other components that can be blended into the conductive paste are not particularly limited and include the same components as those that can be blended into the binder composition of the present invention. Furthermore, the other components may be used alone or in combination of two or more in any ratio.

[0053] <Method of manufacturing conductive paste> The conductive material paste can be prepared by mixing the binder composition of the present invention described above, a conductive material, and any other components such as a solvent. The mixing method is not particularly limited, and examples include the mixing methods described above under "Method for Preparing Binder Composition." Here, the content ratio of the conductive material and the polymer of the specific composition in the conductive material paste is preferably 1 part by mass or more of the polymer (i.e., 1 / 100 or more of the mass content of the conductive material), more preferably 2 parts by mass or more (i.e., 1 / 50 or more of the mass content of the conductive material), even more preferably 5 parts by mass or more (i.e., 1 / 20 or more of the mass content of the conductive material), and preferably 100 parts by mass or less (i.e., equal to or less than the mass content of the conductive material), more preferably 50 parts by mass or less (i.e., half or less of the mass content of the conductive material), and even more preferably 25 parts by mass or less (i.e., 1 / 4 or less of the mass content of the conductive material). The solid content of the conductive paste is, for example, 1% by mass or more, preferably 2% by mass or more, more preferably 3% by mass or more, and 30% by mass or less, preferably 25% by mass or less, more preferably 20% by mass or less. The viscosity of the conductive paste is measured with a rheometer (MCR302 manufactured by Anton Paar) at a temperature of 25°C and a shear rate of 0.1 s -1 When the viscosity is measured under the above conditions, it is usually 10,000 Pa·s or less, preferably 5,000 Pa·s or less, more preferably 1,000 Pa·s or less, even more preferably less than 500 Pa·s, particularly preferably less than 250 Pa·s, and usually 50 Pa·s or more.

[0054] (Slurry composition for secondary battery electrodes) The slurry composition for a secondary battery electrode of the present invention contains an electrode active material, a solvent, and the above-mentioned binder composition, and optionally further contains a conductive material and other components. That is, the slurry composition for a secondary battery electrode of the present invention contains an electrode active material, a solvent, and the above-mentioned polymer, and optionally further contains a conductive material and other components. Furthermore, since the slurry composition for a secondary battery electrode of the present invention contains the above-mentioned binder composition, it is possible to produce an electrode that has sufficiently high stability over time and generates a low amount of gas. In the following, as an example, the case where the slurry composition for a secondary battery electrode is a slurry composition for a positive electrode of a lithium-ion secondary battery will be described, but the present invention is not limited to the following example.

[0055] <Electrode active material> The electrode active material is a substance that transfers electrons in the electrode of a secondary battery. And, as the positive electrode active material for a lithium-ion secondary battery, usually, a substance capable of occluding and releasing lithium is used.

[0056] Specifically, the positive electrode active material for a lithium-ion secondary battery is not particularly limited, and includes lithium-containing cobalt oxide (LiCoO2), lithium manganate (LiMn2O4), lithium-containing nickel oxide (LiNiO2), lithium-containing composite oxides of Co-Ni-Mn, lithium-containing composite oxides of Ni-Mn-Al, lithium-containing composite oxides of Ni-Co-Al, olivine-type lithium iron phosphate (LiFePO4), olivine-type lithium manganese phosphate (LiMnPO4), Li [[ID=eleven]] 1+x [[ID=twelve]]Mn [[ID=thirteen]] 2-x [[ID=fourteen]]O4 (0 <X <2), a lithium-excess spinel compound represented by Li[Ni [[ID=fifteen]] 0.17 [[ID=sixteen]]Li [[ID=seventeen]] 0.2 [[ID=eighteen]]Co [[ID=nineteen]] 0.07 [[ID=twenty]]Mn [[ID=twenty-one]] 0.56 [[ID=twenty-two]]]O2, LiNi [[ID=twenty-three]] 0.5 [[ID=twenty-four]]Mn [[ID=twenty-five]] 1.5 [[ID=twenty-six]]O4, and other known positive electrode active materials. Incidentally, as the lithium-containing composite oxide of Co-Ni-Mn, Li(Ni [[ID=twenty-seven]] 0.5 [[ID=twenty-eight]]Co [[ID=twenty-nine]] 0.2 [[ID=thirty]]Mn [[ID=thirty-one]] 0.3 [[ID=thirty-two]])O2, Li(Ni [[ID=thirty-three]] 1 / 3 [[ID=thirty-four]]Co [[ID=thirty-five]] 1 / 3 [[ID=thirty-six]]Mn [[ID=thirty-seven]] 1 / 3 [[ID=thirty-eight]])O2, and the like can be mentioned. [[ID=thirty-nine]] [[ID=forty]]Among those described above, from the viewpoint of improving the battery capacity and the like of the secondary battery, as the positive electrode active material, lithium-containing cobalt oxide (LiCoO2), lithium-containing nickel oxide (LiNiO2), lithium-containing composite oxides of Co-Ni-Mn, Li[Ni [[ID=forty-one]] 0.17 [[ID=forty-two]]Li [[ID=forty-three]] 0.2 [[ID=forty-four]]Co [[ID=forty-five]] 0.07 [[ID=forty-six]]Mn [[ID=forty-seven]] 0.56 [[ID=forty-eight]]]O2 or LiNi0.5 Mn 1.5 It is preferable to use O4, and it is more preferable to use a lithium-containing composite oxide of Co-Ni-Mn. The amount and particle size of the positive electrode active material are not particularly limited, and may be the same as those of conventionally used positive electrode active materials.

[0057] <Conductive material> As the conductive material, those described above in the section (Conductive material paste composition for secondary battery electrodes) can be suitably used.

[0058] <Binder composition> As the binder composition, the above-mentioned binder composition for a secondary battery electrode of the present invention is used.

[0059] <Solvent> As the solvent, the same solvents as those listed as solvents that can be contained in the binder composition for a secondary battery electrode of the present invention can be used.

[0060] <Content ratio> The content ratio of the conductive material in the slurry composition is preferably 0.01 to 20 parts by mass, based on 100 parts by mass of the electrode active material. When the content ratio of the conductive material is equal to or greater than the lower limit, electrical contact between the positive electrode active materials can be promoted. Furthermore, when the content of the conductive material is equal to or less than the upper limit, dispersion stability can be improved. Furthermore, a suitable content ratio of the polymer in the slurry composition may be within a suitable range that can be derived from the suitable range of the polymer relative to the conductive material described above in the section <Method for producing conductive material paste> and the content ratio between the electrode active material and the conductive material described at the beginning of this paragraph.

[0061] <Other ingredients> Other components that can be incorporated into the slurry composition are not particularly limited and include the same components as those that can be incorporated into the binder composition of the present invention. Furthermore, the other components may be used singly or in any combination of two or more in any ratio. In particular, when the slurry composition for a secondary battery electrode is a slurry composition for a lithium-ion secondary battery positive electrode, it is preferable to use a fluorine-containing polymer such as polyvinylidene fluoride (PVdF) as a second polymer in addition to the above-mentioned polymer (hereinafter sometimes referred to as the "predetermined polymer"). When a second polymer is used in combination as an additional component, the amount of the predetermined polymer used is preferably 10% by mass or less, more preferably 5% by mass or less, based on 100% by mass of the total content of the predetermined polymer and the second polymer.

[0062] <Method for producing slurry composition> The above-described slurry composition can be prepared by dissolving or dispersing each of the above components in a solvent such as an organic solvent. For example, the slurry composition can be prepared by mixing each of the above components with a solvent using a known dispersion or mixing method, as described in the section <Method for Preparing Binder Composition>. Alternatively, the slurry composition can be prepared by adding an electrode active material and any of the above-described optional components to the conductive material paste of the present invention and subjecting the mixture to a known dispersion or mixing method. The solvent contained in the binder composition may be used as the solvent used to prepare the slurry composition. The order of addition of the components during preparation is not particularly limited, and the components may be mixed all at once or in stages. From the viewpoint of improving the dispersibility of the conductive material, it is preferable to perform a step of adding and mixing a positive electrode active material, a solvent, a second polymer, and any other optional components to the conductive material paste after obtaining the above-described conductive material paste. The viscosity of the slurry composition (measured using a single cylindrical rotational viscometer in accordance with JIS Z8803:1991 at 25°C and 60 rpm) is preferably 1500 mPa·s or more, more preferably 4000 mPa·s or more, and is preferably 20000 mPa·s or less, more preferably 5000 mPa·s or less.

[0063] (Electrode for secondary batteries) The secondary battery electrode of the present invention comprises a current collector and an electrode mixture layer formed on the current collector, the electrode mixture layer being formed using the above-mentioned slurry composition for a secondary battery electrode. That is, the electrode mixture layer contains at least an electrode active material and a polymer. Note that the components contained in the electrode mixture layer are the same as those contained in the above-mentioned slurry composition for a secondary battery electrode, and the preferred abundance ratios of the components are the same as the preferred abundance ratios of the components in the slurry composition. Furthermore, since the secondary battery electrode of the present invention is produced using a slurry composition containing the secondary battery electrode binder composition of the present invention, the electrode generates a small amount of gas when incorporated into a secondary battery and used for repeated charging and discharging.

[0064] <Electrode manufacturing method> The secondary battery electrode of the present invention is produced, for example, through a step of applying the above-described slurry composition onto a current collector (application step) and a step of drying the slurry composition applied onto the current collector to form an electrode composite layer on the current collector (drying step).

[0065] [Coating process] The method for applying the slurry composition to the current collector is not particularly limited, and known methods can be used. Specifically, examples of the application method include a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. In this case, the slurry composition may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the slurry film on the current collector after application and before drying can be appropriately set depending on the thickness of the electrode mixture layer obtained by drying.

[0066] Here, a material having electrical conductivity and electrochemical durability is used as the current collector to which the slurry composition is applied. Specifically, a current collector made of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. can be used as the current collector. Among them, aluminum foil is particularly preferred as the current collector used for the positive electrode, and copper foil is particularly preferred as the current collector used for the negative electrode. Note that the above materials may be used alone or in combination of two or more types in any ratio.

[0067] [Drying process] The method for drying the slurry composition on the current collector is not particularly limited and any known method can be used, including, for example, drying with warm air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with infrared rays, electron beams, etc. By drying the slurry composition on the current collector in this manner, an electrode mixture layer can be formed on the current collector, and a secondary battery electrode including the current collector and the electrode mixture layer can be obtained.

[0068] After the drying step, the electrode mixture layer may be subjected to a pressure treatment using a mold press, a roll press, or the like. The pressure treatment can effectively increase the density of the electrode mixture layer and improve the adhesion between the electrode mixture layer and the current collector. Furthermore, when the electrode mixture layer contains a curable polymer, it is preferable to cure the polymer after the electrode mixture layer is formed.

[0069] (Secondary battery) The secondary battery of the present invention comprises a positive electrode, a negative electrode, an electrolyte, and a separator, and at least one of the positive electrode and the negative electrode is the secondary battery electrode of the present invention. The secondary battery of the present invention has excellent battery characteristics (particularly, output characteristics) because it comprises the secondary battery electrode of the present invention. In the following, as an example, a case will be described in which the secondary battery is a lithium ion secondary battery and the positive electrode is made of the secondary battery electrode of the present invention, but the present invention is not limited to the following example.

[0070] <Negative electrode> As the negative electrode, a known negative electrode can be used, specifically, for example, a negative electrode made of a thin plate of metallic lithium or a negative electrode formed by forming a negative electrode mixture layer on a current collector. The current collector can be made of a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, or platinum. The negative electrode composite layer can be a layer containing a negative electrode active material and a binder. The binder is not particularly limited, and any known material can be used.

[0071] <Electrolyte> As the electrolyte, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. For example, a lithium salt is used as the supporting electrolyte of a lithium ion secondary battery. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, CF4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)NLi. Among these, LiPF6, LiClO4, and CF3SO3Li are preferred, with LiPF6 being particularly preferred, because they are easily soluble in solvents and exhibit a high degree of dissociation. One type of electrolyte may be used alone, or two or more types may be used in combination at any ratio. Generally, the use of a supporting electrolyte with a higher degree of dissociation tends to result in higher lithium ion conductivity, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte. The concentration of the supporting electrolyte in the electrolytic solution (at 25° C.) can be, for example, 0.5 mol / L or more and 2.0 mol / L or less.

[0072] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. Suitable examples include carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and ethyl methyl carbonate (EMC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. Mixtures of these solvents may also be used. Among these, carbonates are preferred because of their high dielectric constant and wide stable potential range, and a mixture of ethylene carbonate and diethyl carbonate is preferred. Additives such as vinylene carbonate (VC), fluoroethylene carbonate, and ethyl methyl sulfone may also be added to the electrolyte.

[0073] <separator> The separator is not particularly limited, and can be, for example, one described in JP 2012-204303 A. Among these, a microporous film made of a polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred because it can reduce the overall separator thickness, thereby increasing the proportion of electrode active material in the secondary battery and increasing capacity per volume.

[0074] <Secondary battery manufacturing method> The secondary battery of the present invention can be produced, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the stack as necessary according to the battery shape, placing the stack in a battery container, injecting an electrolyte into the battery container, and sealing the container. To prevent internal pressure rise, overcharge / discharge, and the like, a fuse, an overcurrent protection element such as a PTC element, an expanded metal, a lead plate, or the like may be provided as necessary. The shape of the secondary battery may be any of a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, a flat type, and the like. [Example]

[0075] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. Pressure is gauge pressure. In the examples and comparative examples, the polymer composition, iodine value, weight average molecular weight, dispersibility of the conductive material in the conductive material paste, dispersion stability of the solid content in the slurry composition, initial resistance of the secondary battery, and amount of gas generated from the electrode were measured and evaluated by the following methods.

[0076] <Polymer composition> In all examples and comparative examples, 1 The H-NMR measurement confirmed the presence of linear alkylene structural units (1,3-butadiene hydride units) having 4 or more carbon atoms. <Iodine value of polymer> 100 g of the aqueous dispersion of the polymer prepared in each of the Examples and Comparative Examples was coagulated with 1 L of methanol and then vacuum dried for 12 hours at 60° C. The iodine value of the resulting dried polymer was measured in accordance with JIS K6235 (2006). <Weight average molecular weight of polymer> The weight-average molecular weights of the polymers prepared in the examples and comparative examples were measured by gel permeation chromatography (GPC). Specifically, a calibration curve was prepared using polystyrene as a standard substance, and the weight-average molecular weights were calculated as values ​​converted from the standard substance. The measurement conditions were as follows: <<Measurement conditions>> Column: TSKgel α-M x 2 (inner diameter 7.8 mm x 30 cm x 2, manufactured by Tosoh Corporation) Eluent: dimethylformamide (50 mM lithium bromide, 10 mM phosphoric acid) Flow rate: 0.5mL / min. Sample concentration: Approximately 0.5 g / L (solid concentration) Injection volume: 200μL Column temperature: 40℃ Detector: Differential refractive index detector RI (Tosoh HLC-8320 GPC RI detector) Detector conditions: RI: Pol(+), Res(1.0s) Molecular weight marker: Tosoh standard polystyrene kit PStQuick K

[0077] <Dispersibility of conductive material in conductive paste> The viscosity of the conductive paste prepared in the examples and comparative examples was measured using a rheometer (MCR302 manufactured by Anton Paar) at a temperature of 25°C and a shear rate of 0.1 s -1 At the same solid content concentration, the lower the viscosity, the better the dispersibility of the conductive material. A: Viscosity less than 250 Pa·s B: Viscosity is 250 Pa·s or more but less than 500 Pa·s C: Viscosity is 500 Pa·s or more

[0078] <Dispersion stability of solid content in slurry composition> The viscosity of the positive electrode slurry compositions prepared in the Examples and Comparative Examples was measured immediately after preparation using a Brookfield viscometer at a temperature of 25°C and a rotation speed of 60 rpm, and the obtained viscosity was designated as η0. Next, the positive electrode slurry compositions were sealed and left to stand at 25°C for one week (168 hours). The viscosity of the positive electrode slurry composition after standing for one week was then measured under the same conditions as before standing for one week, and the obtained viscosity was designated as η1. The viscosity retention rate Δη = (η1 / η0) × 100% was calculated from η0 and η1. The closer the viscosity retention rate is to 100%, the more excellent the dispersion stability of the solids in the positive electrode slurry composition is. A: Viscosity retention rate Δη is less than 150% B: Viscosity retention rate Δη is 150% or more and less than 300% C: Viscosity maintenance rate Δη is 300% or more

[0079] <Initial resistance of secondary battery> The secondary batteries prepared in the Examples and Comparative Examples were charged at a constant current of 0.2 C at 25°C until the battery voltage reached 4.2 V, and then charged at a constant voltage of 0.02 C at 4.2 V. Subsequently, the batteries were discharged at a constant current of 0.2 C until the battery voltage reached 3.87 V (SOC 50%), and then the voltage change after 30 seconds of discharge was measured at 0.2 C, 0.5 C, 1.0 C, 2.0 C, 2.5 C, and 3.0 C. The discharge current and the measured voltage change were plotted, and the slope was taken as the initial resistance (Ω). The calculated initial resistance was evaluated according to the following criteria. A: Initial resistance is less than 4Ω B: Initial resistance is 4Ω or more and less than 6Ω C: Initial resistance is 6Ω or more

[0080] <Gas generation rate of electrode> The secondary batteries prepared in the examples and comparative examples were left standing for 24 hours in a 25°C environment. Then, they were charged to 4.35 V at 0.1 C and discharged to 2.75 V at 0.1 C in a 25°C environment. The battery cells were immersed in liquid paraffin, and the cell volume X0 was measured. Furthermore, the battery cells were subjected to 1,000 cycles of charge and discharge under the same conditions as above in a 60°C environment. After 1,000 cycles, the battery cells were immersed in liquid paraffin, and the cell volume X1 was measured. The cell volume change rate ΔX before and after the high-temperature cycle test, in which 1,000 charge and discharge cycles were repeated, was calculated as ΔX (%) = (X1 - X0) / X0 × 100. The smaller the cell volume change rate ΔX, the less gas was generated from the electrode, indicating that the electrode had excellent gas generation suppression capabilities. A: Less than 20% B: 20% or more but less than 45% C: 45% or more

[0081] Example 1 <Preparation of Polymer> A reactor was charged with 180 parts of ion-exchanged water, 25 parts of a 10% aqueous solution of sodium dodecylbenzenesulfonate (emulsifier for emulsion polymerization), 23 parts of acrylonitrile as a nitrile group-containing monomer, 43 parts of styrene as an aromatic vinyl monomer, and 2 parts of t-dodecyl mercaptan as a molecular weight modifier, in that order. The internal gas was replaced with nitrogen three times, and then 34 parts of 1,3-butadiene as a conjugated diene monomer was charged. The reactor was then kept at 10 ° C., and 0.1 parts of cumene hydroperoxide and 0.1 parts of ferrous sulfate were charged as polymerization initiators. The polymerization reaction was continued with stirring, and when the polymerization conversion rate reached 85%, 0.1 parts of a 10% aqueous solution of hydroquinone as a polymerization terminator was added to terminate the polymerization reaction. Next, the residual monomer was removed at a water temperature of 80 ° C., and an aqueous dispersion of a polymer precursor (particulate polymer) was obtained. <Polymer hydrogenation> The particulate polymer obtained above was hydrogenated according to the aqueous phase direct hydrogenation method. The aqueous dispersion and a palladium catalyst (a solution of 1% palladium acetate acetone solution mixed with an equal mass of ion-exchanged water) were added to an autoclave so that the palladium content relative to the mass of solids contained in the aqueous dispersion of the polymer precursor was 5,000 ppm. The hydrogenation reaction was carried out at a hydrogen pressure of 3 MPa and a temperature of 50°C for 6 hours to obtain the target hydrogenated polymer. The iodine value and weight-average molecular weight of the polymer were measured according to the above method, and the results are shown in Table 1.

[0082] <Preparation of Binder Composition for Positive Electrode> The aqueous dispersion of the polymer was mixed with an appropriate amount of N-methylpyrrolidone (NMP) as an organic solvent to obtain a mixed solution, and then the water contained in the mixed solution was evaporated under reduced pressure to obtain a binder composition for a positive electrode containing the polymer and NMP.

[0083] <Preparation of conductive paste for positive electrode> Carbon nanotubes as conductive materials (specific surface area: 150 m 2 3.0 parts of the cellulose acetate copolymer (wt. / g), 0.6 parts of the binder composition (solid content equivalent), and 96.4 parts of NMP were stirred using a disper (3000 rpm, 10 minutes), and then mixed for 1 hour at a peripheral speed of 8 m / s using a bead mill using zirconia beads with a diameter of 1 mm, to produce a conductive material paste with a solid content concentration of 3.6 mass %. The resulting conductive material paste was then evaluated for dispersibility of the conductive material in the conductive material paste as described above. The results are shown in Table 1.

[0084] <Preparation of Slurry Composition for Positive Electrode> The conductive paste for the positive electrode obtained as described above was mixed with 0.04 parts in terms of polymer solid content and a ternary active material (Li(Ni) 0.5 Co 0.2 Mn 0.3A positive electrode slurry composition was prepared by adding 100 parts of 100% ethylenediamine fluoride (O2, average particle size: 10 μm), 0.96 parts (solids equivalent) of polyvinylidene fluoride (PVdF) as a second polymer, and NMP as an organic solvent, and stirring with a planetary mixer (60 rpm, 30 minutes). The amount of NMP added was adjusted so that the viscosity of the resulting positive electrode slurry composition (measured with a single cylindrical rotational viscometer in accordance with JIS Z8803:1991, temperature: 25°C, rotation speed: 60 rpm) was within the range of 4000 to 5000 mPa·s. The resulting positive electrode slurry composition was then evaluated for dispersion stability of the solids in the slurry composition as described above. The results are shown in Table 1.

[0085] <Preparation of positive electrode> An aluminum foil having a thickness of 20 μm was prepared as a current collector. The positive electrode slurry composition was applied to the aluminum foil using a comma coater so that the coating weight after drying was 20 mg / cm. 2 The coating was applied so that the density became 3.2 g / cm 3 , and the coating was dried at 90°C for 20 minutes and at 120°C for 20 minutes, and then heat-treated at 60°C for 10 hours to obtain a positive electrode blank. This positive electrode blank was rolled using a roll press to obtain a positive electrode blank with a density of 3.2 g / cm 3 . 3 A sheet-shaped positive electrode was fabricated from the positive electrode composite layer and aluminum foil. The thickness of the sheet-shaped positive electrode was 70 μm. This sheet-shaped positive electrode was cut into a width of 4.8 cm and a length of 50 cm to prepare a positive electrode for a lithium-ion secondary battery.

[0086] <Preparation of negative electrode> 90 parts of spherical artificial graphite (volume average particle diameter: 12 μm) as the negative electrode active material and SiO X A mixture of 10 parts of cellulose acetate (volume average particle diameter: 10 μm), 1 part of styrene-butadiene polymer as a binder, 1 part of carboxymethyl cellulose as a thickener, and an appropriate amount of water as a dispersion medium was stirred in a planetary mixer to prepare a slurry composition for a negative electrode. Next, a copper foil having a thickness of 15 μm was prepared as a current collector. The negative electrode slurry composition was applied to both sides of the copper foil in an amount of 10 mg / cm after drying. 2The coating was applied so that the density became 1.8 g / cm 3 , and then dried at 60°C for 20 minutes and at 120°C for 20 minutes. After that, the coating was heated at 150°C for 2 hours to obtain a negative electrode blank. This negative electrode blank was rolled using a roll press to a density of 1.8 g / cm 3 . 3 A sheet-shaped negative electrode was fabricated consisting of the negative electrode mixture layer (both sides) and copper foil, and the sheet-shaped negative electrode was cut into a width of 5.0 cm and a length of 52 cm to prepare a negative electrode for a lithium ion secondary battery.

[0087] <Preparing the separator> A single-layer polypropylene separator (manufactured by Celgard, product name "Celgard 2500") was cut into a size of 120 cm x 5.5 cm.

[0088] <Manufacturing lithium-ion secondary batteries> The positive electrode and the negative electrode were wound around a core having a diameter of 20 mm with the separator interposed therebetween to obtain a wound body. The wound body was then compressed in one direction at a speed of 10 mm / sec until it reached a thickness of 4.5 mm. The wound body after compression had an elliptical shape in a plan view, and the ratio of its major axis to its minor axis (major axis / minor axis) was 7.7. In addition, an electrolyte solution (composition: LiPF6 solution with a concentration of 1.0 M (the solvent is a mixed solution in which 5 mass% of fluoroethylene carbonate is added to a mixed solvent of ethylene carbonate / ethyl methyl carbonate = 3 / 7 (mass ratio) and 2 volume% of vinylene carbonate is added as an additive)) was prepared. The compressed wound body was then placed in an aluminum laminate case together with 3.2 g of nonaqueous electrolyte. A nickel lead wire was connected to a designated location on the negative electrode, and an aluminum lead wire was connected to a designated location on the positive electrode. The opening of the case was then thermally sealed to obtain a lithium-ion secondary battery. This lithium-ion secondary battery was a pouch-shaped battery measuring 35 mm wide, 48 mm high, and 5 mm thick, with a nominal capacity of 700 mAh. The initial resistance of the secondary battery and the amount of gas generated from the electrodes were evaluated according to the procedures described above. The results are shown in Table 1.

[0089] Example 2 A hydrogenated polymer, a positive electrode conductive material paste, a positive electrode binder composition, a positive electrode slurry composition, a secondary battery positive electrode, a secondary battery negative electrode, and a secondary battery were produced in the same manner as in Example 1, except that the amounts of the various monomers used in preparing the polymer were changed to 39 parts acrylonitrile, 5 parts styrene, and 56 parts 1,3-butadiene, respectively. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

[0090] Example 3 A hydrogenated polymer, a positive electrode conductive material paste, a positive electrode binder composition, a positive electrode slurry composition, a secondary battery positive electrode, a secondary battery negative electrode, and a secondary battery were produced in the same manner as in Example 1, except that the amounts of the various monomers used in preparing the polymer were changed to 35 parts acrylonitrile, 15 parts styrene, and 50 parts 1,3-butadiene, respectively. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

[0091] Example 4 A hydrogenated polymer, a positive electrode conductive material paste, a positive electrode binder composition, a positive electrode slurry composition, a secondary battery positive electrode, a secondary battery negative electrode, and a secondary battery were produced in the same manner as in Example 1, except that the amounts of the various monomers used in preparing the polymer were changed to 12 parts acrylonitrile, 69 parts styrene, and 19 parts 1,3-butadiene, respectively. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

[0092] Example 5 <Preparation of Polymer> The hydrogenation method used was oil phase hydrogenation. A portion of the aqueous dispersion of the polymer precursor obtained in Example 1 was added to an aqueous solution of magnesium sulfate in an amount equivalent to 12% by mass relative to the solids mass, and the mixture was stirred to coagulate the latex. The mixture was then washed with water and filtered. The coagulated material was then vacuum dried at 60°C for 12 hours to obtain the hydrogenation target. The resulting hydrogenation target was then dissolved in acetone to a concentration of 12% by mass, obtaining an acetone solution of the hydrogenation target. This solution was then placed in an autoclave, and 200 ppm by mass of palladium-silica catalyst was added relative to 100% by mass of the hydrogenation target. The hydrogenation reaction was then carried out at a hydrogen pressure of 3.0 MPa for 6 hours to obtain the hydrogenation target. After the hydrogenation reaction was completed, the hydrogenation target was poured into a large amount of water to coagulate the product, filtered, and dried to obtain the desired polymer.

[0093] <Preparation of Binder Composition for Positive Electrode> The polymer and an appropriate amount of NMP as an organic solvent were mixed under heating to obtain a binder composition for a positive electrode containing the polymer and NMP. Thereafter, a conductive paste for a positive electrode, a slurry composition for a positive electrode, a positive electrode for a secondary battery, a negative electrode for a secondary battery, and a secondary battery were produced in the same manner as in Example 1. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

[0094] (Comparative Example 1) A hydrogenated polymer, a positive electrode conductive material paste, a positive electrode binder composition, a positive electrode slurry composition, a secondary battery positive electrode, a secondary battery negative electrode, and a secondary battery were produced in the same manner as in Example 1, except that 23 parts of acrylonitrile, 43 parts of styrene, and 5 parts of methacrylic acid were charged as monomers, and 2 parts of t-dodecyl mercaptan as a molecular weight modifier, in that order, during the preparation of the polymer, and the amount of 1,3-butadiene added was changed to 29 parts. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

[0095] (Comparative Example 2) A hydrogenated polymer, a positive electrode conductive material paste, a positive electrode binder composition, a positive electrode slurry composition, a secondary battery positive electrode, a secondary battery negative electrode, and a secondary battery were produced in the same manner as in Example 1, except that 23 parts of acrylonitrile, 43 parts of styrene, 0.1 parts of methacrylic acid, and 2 parts of t-dodecyl mercaptan as a molecular weight modifier were charged in this order during the preparation of the polymer, and the amount of 1,3-butadiene added was changed to 33.9 parts. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

[0096] (Comparative Example 3) A hydrogenated polymer, a positive electrode conductive material paste, a positive electrode binder composition, a positive electrode slurry composition, a secondary battery positive electrode, a secondary battery negative electrode, and a secondary battery were produced in the same manner as in Example 1, except that styrene was not added during the preparation of the polymer, and the amount of acrylonitrile added was changed to 35 parts and the amount of 1,3-butadiene added was changed to 65 parts. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

[0097] In Table 1, "AN" stands for acrylonitrile unit, "ST" stands for styrene unit, "H-BD" refers to a structural unit represented by the general formula -C2H4-, which is a 1,3-butadiene hydride unit, "BD" refers to units derived from 1,3-butadiene monomers other than H-BD. "NCM" is Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, "PVdF" stands for polyvinylidene fluoride.

[0098] [Table 1]

[0099] From Table 1, it can be seen that the binder compositions of Examples 1 to 5 made it possible to prepare conductive material pastes with sufficiently high dispersibility of the conductive material, to prepare slurry compositions with sufficiently high stability over time, and further to produce electrodes with low gas generation. On the other hand, it can be seen that in Comparative Examples 1 and 2, which used a polymer containing a hydrophilic group-containing monomer unit, and Comparative Example 3, which used a polymer not containing an aromatic vinyl monomer unit, it was not possible to obtain the good attributes achieved in Examples 1 to 5. [Industrial Applicability]

[0100] According to the present invention, it is possible to prepare a conductive material paste having a sufficiently high dispersibility of the conductive material, to prepare a slurry composition having a sufficiently high stability over time, and further to provide a binder composition for a secondary battery electrode, which is capable of producing an electrode with a low amount of gas generation. Furthermore, according to the present invention, it is possible to prepare a slurry composition having sufficiently high dispersibility of a conductive material and sufficiently high stability over time, and further, it is possible to provide a conductive material paste composition for secondary battery electrodes, which can produce an electrode with a low amount of gas generation. Furthermore, according to the present invention, it is possible to provide a slurry composition for secondary battery electrodes which has sufficiently high stability over time and which can produce electrodes with low gas generation. According to the present invention, it is possible to provide an electrode that generates a low amount of gas and a secondary battery that includes such an electrode.

Claims

1. A binder composition for a secondary battery electrode comprising a polymer, the polymer contains a nitrile group-containing monomer unit, an aromatic vinyl monomer unit, and a linear alkylene structural unit, but does not contain a hydrophilic group-containing monomer unit; the polymer contains the aromatic vinyl monomer unit in a proportion of 10% by mass or more and 65% by mass or less, the linear alkylene structural unit in a proportion of 55% by mass or less, and further contains other monomer units in a proportion of 0% by mass or more and 10% by mass or less; A binder composition for secondary battery electrodes.

2. 2. The binder composition for a secondary battery electrode according to claim 1, wherein the polymer has an iodine value of 120 mg / 100 mg or less.

3. A conductive material paste composition for a secondary battery electrode, comprising a conductive material and the binder composition for a secondary battery electrode according to claim 1 or 2.

4. The conductive paste composition for a secondary battery electrode according to claim 3 , wherein the conductive material comprises carbon nanotubes.

5. A slurry composition for a secondary battery electrode, comprising an electrode active material, a solvent, and the binder composition for a secondary battery electrode according to claim 1 or 2.

6. A secondary battery electrode comprising an electrode mixture layer formed using the slurry composition for a secondary battery electrode according to claim 5 .

7. A battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator; A secondary battery, wherein at least one of the positive electrode and the negative electrode is the electrode for a secondary battery according to claim 6.

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