Binder composition for non-aqueous secondary battery and method for producing same, slurry composition for non-aqueous secondary battery electrode, electrode for non-aqueous secondary battery, and non-aqueous secondary battery

Abstract

The binder composition for a non-aqueous secondary battery according to the present invention is characterized by comprising: a particulate polymer including a graft polymer having an acidic graft chain and obtained by causing an acidic group-containing monomer and / or a macromonomer to undergo a graft polymerization reaction with respect to core particles containing a block copolymer having an aromatic vinyl block domain including an aromatic vinyl monomeric unit and an aliphatic conjugated diene block domain including an aliphatic conjugated diene monomeric unit; and an acidic group-containing water-soluble polymer having a weight-average molecular weight of at most 200,000.

Description

[Technical Field]

[0001] The present invention relates to a binder composition for a non-aqueous secondary battery and a method for producing the same, a slurry composition for a non-aqueous secondary battery electrode, an electrode for a non-aqueous secondary battery, and a non-aqueous secondary battery. [Background technology]

[0002] Non-aqueous secondary batteries such as lithium ion secondary batteries (hereinafter sometimes simply referred to as "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 with the aim of further improving the performance of non-aqueous 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, by applying a slurry composition containing an electrode active material and a binder composition containing a binding agent onto the current collector and then drying the applied slurry composition.

[0004] As the binding material contained in the binder composition, a particulate polymer made of a polymer having block regions made of aromatic vinyl monomer units has been conventionally used. For example, Patent Document 1 discloses a binder composition containing a particulate polymer made of a polymer having block regions composed of aromatic vinyl monomer units and having a tetrahydrofuran insoluble content of 5% by mass to 40% by mass. According to Patent Document 1, the stability of the slurry composition can be improved by further adding to the binder composition a water-soluble polymer having a hydrophilic group and a weight-average molecular weight of 15,000 to 500,000. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 107209 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, an electrode including an electrode mixture layer may be exposed to a high-humidity environment during transportation or storage, and therefore, the electrode including an electrode mixture layer is required to maintain good peel strength, i.e., to have excellent moisture resistance, even after being stored in a high-humidity environment.

[0007] However, the electrodes having electrode mixture layers formed using the conventional binder compositions have room for improvement in terms of moisture resistance.

[0008] Therefore, an object of the present invention is to provide a binder composition for a non-aqueous secondary battery that can form an electrode for a non-aqueous secondary battery that has excellent moisture resistance. Another object of the present invention is to provide a slurry composition for a non-aqueous secondary battery electrode that can form a non-aqueous secondary battery electrode having excellent moisture resistance. Another object of the present invention is to provide an electrode for a non-aqueous secondary battery that has excellent moisture resistance, and a non-aqueous secondary battery that includes the electrode for a non-aqueous secondary battery. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above-mentioned problems, and have found that a non-aqueous secondary battery electrode having excellent moisture resistance can be obtained by using a binder composition containing a particulate polymer made of a predetermined graft polymer and an acidic group-containing water-soluble polymer having a weight-average molecular weight of a predetermined value or less, thereby completing the present invention.

[0010] The present invention has an object to advantageously solve the above-mentioned problems, and the binder composition for a non-aqueous secondary battery of the present invention is characterized by comprising: a particulate polymer composed of a graft polymer having acidic graft chains, which is obtained by graft polymerization of an acidic group-containing monomer and / or a macromonomer onto core particles containing a block copolymer containing an aromatic vinyl block region composed of aromatic vinyl monomer units and an aliphatic conjugated diene block region composed of aliphatic conjugated diene monomer units; and an acidic group-containing water-soluble polymer having a weight-average molecular weight of 200,000 or less. Thus, by using a binder composition containing a particulate polymer composed of a predetermined graft polymer and an acidic group-containing water-soluble polymer having a weight-average molecular weight of a predetermined value or less, an electrode for a non-aqueous secondary battery having excellent moisture resistance can be obtained. In the present invention, the term "monomer unit" of a polymer means "a repeating unit derived from the monomer contained in a polymer obtained using the monomer." In the present invention, the weight average molecular weight of the acidic group-containing water-soluble polymer contained in the binder composition can be measured by the method described in the examples of this specification.

[0011] Here, the binder composition for a nonaqueous secondary battery of the present invention preferably has a viscosity of 3000 mPa s or less at a solids concentration of 40 mass % and a pH of 8.0. If the viscosity of the binder composition at a solids concentration of 40 mass % and a pH of 8.0 is equal to or less than the above-mentioned predetermined value, the moisture resistance of an electrode formed using the binder composition can be further improved, and the internal resistance of the secondary battery can be reduced. In the present invention, the viscosity of the binder composition at a solids concentration of 40% by mass and pH 8.0 can be measured by the method described in the examples of this specification.

[0012] Furthermore, the binder composition for a nonaqueous secondary battery of the present invention preferably has an acid amount, as measured by conductometric titration, of 0.02 mmol / g or more and 2.00 mmol / g or less. When the acid amount of the binder composition measured by conductometric titration is within the above-mentioned range, the viscosity stability of a slurry composition prepared using the binder composition can be increased and the peel strength of an electrode can be improved. When the acid amount of the binder composition measured by conductometric titration is within the above-mentioned range, the viscosity of the binder composition can be prevented from excessively increasing and the moisture resistance of the electrode can be further improved. Furthermore, when the acid amount of the binder composition measured by conductometric titration is within the above-mentioned range, the internal resistance of a secondary battery can be reduced. In the present invention, the acid amount of the binder composition by conductometric titration can be measured using the method described in the examples of this specification.

[0013] Furthermore, the binder composition for a non-aqueous secondary battery of the present invention preferably has a pH of 6.0 or more and 10.0 or less. When the pH of the binder composition is within the above-mentioned range, the viscosity stability of a slurry composition prepared using the binder composition can be improved.

[0014] The present invention also aims to advantageously solve the above-mentioned problems. The method for producing a binder composition for a non-aqueous secondary battery of the present invention is any of the methods for producing a binder composition for a non-aqueous secondary battery described above, and is characterized by including a step of graft-polymerizing the acidic group-containing monomer and / or macromonomer onto the core particles in the presence of a water-soluble chain transfer agent to obtain a dispersion of the particulate polymer. Thus, by graft-polymerizing the acidic group-containing monomer and / or macromonomer onto the core particles, a binder composition can be easily produced that includes a particulate polymer composed of a predetermined polymer and an acidic group-containing water-soluble polymer having a weight-average molecular weight of a predetermined value or less. Therefore, a binder composition for a non-aqueous secondary battery that can form an electrode for a non-aqueous secondary battery with excellent moisture resistance can be easily obtained.

[0015] Here, the method for producing a binder composition for a non-aqueous secondary battery of the present invention preferably further comprises a step of purifying the particulate polymer dispersion. Purifying the particulate polymer dispersion can further improve the moisture resistance of an electrode formed using the produced binder composition and reduce the internal resistance of the secondary battery.

[0016] Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and provides a slurry composition for a non-aqueous secondary battery electrode, which is characterized by containing an electrode active material and any one of the binder compositions for a non-aqueous secondary battery described above. In this way, a slurry composition for a non-aqueous secondary battery electrode, which contains an electrode active material and any one of the binder compositions for a non-aqueous secondary battery described above, can form an electrode with excellent moisture resistance.

[0017] The present invention also aims to advantageously solve the above-mentioned problems, and provides a non-aqueous secondary battery electrode comprising an electrode mixture layer formed using the above-mentioned non-aqueous secondary battery electrode slurry composition. Thus, a non-aqueous secondary battery electrode comprising an electrode mixture layer formed using the above-mentioned non-aqueous secondary battery electrode slurry composition has excellent moisture resistance.

[0018] Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and the nonaqueous secondary battery of the present invention is characterized by including the above-mentioned nonaqueous secondary battery electrode. By using the above-mentioned nonaqueous secondary battery electrode, a nonaqueous secondary battery that can exhibit excellent performance can be obtained. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a binder composition for a non-aqueous secondary battery that can form an electrode for a non-aqueous secondary battery that has excellent moisture resistance. Furthermore, according to the present invention, it is possible to provide a slurry composition for a non-aqueous secondary battery electrode that can form a non-aqueous secondary battery electrode having excellent moisture resistance. Furthermore, according to the present invention, it is possible to provide an electrode for a non-aqueous secondary battery having excellent moisture resistance, and a non-aqueous secondary battery including the electrode for a non-aqueous secondary battery. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a graph plotting electrical conductivity against the cumulative amount of hydrochloric acid added when calculating the acid amount of a binder composition by conductometric titration. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of the present invention will be described in detail. Here, the binder composition for non-aqueous secondary batteries of the present invention is used for manufacturing non-aqueous secondary batteries, and is particularly suitable for manufacturing electrodes for non-aqueous secondary batteries. For example, the binder composition for non-aqueous secondary batteries of the present invention can be used to prepare a slurry composition for non-aqueous secondary battery electrodes of the present invention. Furthermore, a slurry composition prepared using the binder composition of the present invention can be used to manufacture electrodes for non-aqueous secondary batteries such as lithium ion secondary batteries. Furthermore, the non-aqueous secondary battery of the present invention is characterized by using a non-aqueous secondary battery electrode of the present invention formed using the slurry composition of the present invention. The binder composition for a non-aqueous secondary battery, the slurry composition for a non-aqueous secondary battery electrode, and the electrode for a non-aqueous secondary battery of the present invention are preferably for use in a negative electrode, and the non-aqueous secondary battery of the present invention preferably uses the electrode for a non-aqueous secondary battery of the present invention as a negative electrode.

[0022] (Binder composition for non-aqueous secondary batteries) The binder composition for a non-aqueous secondary battery of the present invention contains a particulate polymer and an acidic group-containing water-soluble polymer, and optionally further contains other components that can be blended into the binder composition. The binder composition for a non-aqueous secondary battery of the present invention also typically contains a dispersion medium such as water. The binder composition of the present invention comprises a graft polymer obtained by graft polymerization of an acidic group-containing monomer and / or a macromonomer onto core particles containing a block copolymer in which the particulate polymer has an aromatic vinyl block region composed of aromatic vinyl monomer units and an aliphatic conjugated diene block region composed of aliphatic conjugated diene monomer units, and the weight-average molecular weight of the acidic group-containing water-soluble polymer is 200,000 or less. Therefore, an electrode for a non-aqueous secondary battery having excellent moisture resistance can be formed.

[0023] <Particulate polymer> The particulate polymer is a component that functions as a binder, and can hold components such as an electrode active material so that they do not detach from the electrode mixture layer when, for example, an electrode mixture layer is formed using a slurry composition containing the binder composition.

[0024] The particulate polymer is a water-insoluble particle formed by a predetermined graft polymer. In the present invention, the polymer particle being "water-insoluble" means that when 0.5 g of the polymer is dissolved in 100 g of water at 25°C, the insoluble content is 90 mass % or more.

[0025] <<Graft polymer>> The graft polymer forming the particulate polymer is obtained by providing acidic graft chains by graft polymerization of an acidic group-containing monomer and / or macromonomer onto core particles containing a block copolymer containing an aromatic vinyl block region composed of aromatic vinyl monomer units and an aliphatic conjugated diene block region composed of aliphatic conjugated diene monomer units.

[0026] [Core particle] The block copolymer constituting the core particle contains an aromatic vinyl block region composed of aromatic vinyl monomer units and an aliphatic conjugated diene block region composed of aliphatic conjugated diene monomer units, and optionally further contains a polymer chain portion (hereinafter sometimes abbreviated as "other region") in which repeating units other than the aromatic vinyl monomer units and the aliphatic conjugated diene monomer units are linked together. The core particle may also contain at least one of a hindered phenol-based antioxidant and a phosphite-based antioxidant, which will be described in detail later. The block copolymer may have only one aromatic vinyl block region or may have multiple regions. Similarly, the block copolymer may have only one aliphatic conjugated diene block region or may have multiple regions. Furthermore, the block copolymer may have only one other region or may have multiple regions. It is preferable that the block copolymer has only an aromatic vinyl block region and an aliphatic conjugated diene block region.

[0027] -Aromatic vinyl block region- As described above, the aromatic vinyl block region is a region containing only aromatic vinyl monomer units as repeating units. Here, one aromatic vinyl block region may be composed of only one type of aromatic vinyl monomer unit, or may be composed of multiple types of aromatic vinyl monomer units, but is preferably composed of only one type of aromatic vinyl monomer unit. Furthermore, one aromatic vinyl block region may contain a coupling site (i.e., the aromatic vinyl monomer units constituting one aromatic vinyl block region may be connected via a coupling site). When the polymer has a plurality of aromatic vinyl block regions, the types and proportions of the aromatic vinyl monomer units constituting the plurality of aromatic vinyl block regions may be the same or different, but are preferably the same.

[0028] Examples of aromatic vinyl monomers that can form the aromatic vinyl monomer units that constitute the aromatic vinyl block region include aromatic monovinyl compounds such as styrene, styrene sulfonic acid and its salts, α-methylstyrene, pt-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. Among these, styrene is preferred. These can be used alone or in combination of two or more, but it is preferred to use one alone.

[0029] The proportion of aromatic vinyl monomer units in the block copolymer is preferably 1% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, and preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less, when the amount of all repeating units (monomer units and structural units) in the block copolymer is taken as 100% by mass. If the proportion of aromatic vinyl monomer units in the block copolymer is equal to or greater than the above-mentioned lower limit, the viscosity stability of a slurry composition prepared using the binder composition can be improved, and the peel strength of an electrode can be improved. On the other hand, if the proportion of aromatic vinyl monomer units in the block copolymer is equal to or less than the above-mentioned upper limit, the stability of the binder composition can be improved. The proportion of the aromatic vinyl monomer units in the block copolymer usually coincides with the proportion of the aromatic vinyl block region in the block copolymer.

[0030] -Aliphatic conjugated diene block region- The aliphatic conjugated diene block region is a region containing an aliphatic conjugated diene monomer unit as a repeating unit.

[0031] Examples of aliphatic conjugated diene monomers that can constitute the aliphatic conjugated diene monomer units that constitute the aliphatic conjugated diene block region include conjugated diene compounds having 4 or more carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. These can be used alone or in combination of two or more. Among these, from the viewpoint of improving the peel strength of the electrode, 1,3-butadiene and isoprene are preferred, and 1,3-butadiene is more preferred.

[0032] The aliphatic conjugated diene block region may contain a coupling site (i.e., the aliphatic conjugated diene monomer units constituting one aliphatic conjugated diene block region may be connected via a coupling site).

[0033] Furthermore, the aliphatic conjugated diene block region may have a crosslinked structure (i.e., the aliphatic conjugated diene block region may contain a structural unit formed by crosslinking aliphatic conjugated diene monomer units).

[0034] Furthermore, the aliphatic conjugated diene monomer units contained in the aliphatic conjugated diene block region may be hydrogenated (i.e., the aliphatic conjugated diene block region may contain structural units (aliphatic conjugated diene hydride units) obtained by hydrogenating the aliphatic conjugated diene monomer units).

[0035] The structural unit obtained by crosslinking the aliphatic conjugated diene monomer unit can be introduced into the block copolymer by crosslinking a polymer containing an aromatic vinyl block region and an aliphatic conjugated diene block region.

[0036] The crosslinking can be carried out using a radical initiator, such as a redox initiator comprising a combination of an oxidizing agent and a reducing agent, without particular limitation. Examples of the oxidizing agent include organic peroxides such as diisopropylbenzene hydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, di-t-butyl peroxide, isobutyryl peroxide, and benzoyl peroxide. Examples of the reducing agent include compounds containing reduced metal ions, such as ferrous sulfate and cuprous naphthenate; sulfonic acid compounds, such as sodium methanesulfonate; and amine compounds, such as dimethylaniline. These organic peroxides and reducing agents may be used alone or in combination. The crosslinking may be carried out in the presence of a crosslinking agent such as a polyvinyl compound such as divinylbenzene, a polyallyl compound such as diallyl phthalate, triallyl trimellitate, or diethylene glycol bisallyl carbonate, or various glycols such as ethylene glycol diacrylate. Alternatively, the crosslinking may be carried out by irradiation with active energy rays such as gamma rays.

[0037] The method for introducing the aliphatic conjugated diene hydride units into the block copolymer is not particularly limited. For example, a method for obtaining a block copolymer by hydrogenating a polymer containing an aromatic vinyl block region and an aliphatic conjugated diene block region to convert the aliphatic conjugated diene monomer units into aliphatic conjugated diene hydride units is preferred because it allows for easy production of the block copolymer.

[0038] The total amount of the aliphatic conjugated diene monomer units, structural units formed by crosslinking the aliphatic conjugated diene monomer units, and aliphatic conjugated diene hydride units in the block copolymer is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, and is preferably 99% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less, when the amount of all repeating units (monomer units and structural units) in the block copolymer is taken as 100% by mass. When the total amount of the aliphatic conjugated diene monomer units, structural units formed by crosslinking the aliphatic conjugated diene monomer units, and aliphatic conjugated diene hydride units in the block copolymer is equal to or greater than the above-mentioned lower limit, the stability of the binder composition can be improved. On the other hand, when the total proportion of the aliphatic conjugated diene monomer units, the structural units formed by crosslinking the aliphatic conjugated diene monomer units, and the aliphatic conjugated diene hydride units in the block copolymer is not more than the above upper limit, the peel strength of the electrode can be increased. The proportions of the aliphatic conjugated diene monomer units, structural units obtained by crosslinking aliphatic conjugated diene monomer units, and aliphatic conjugated diene hydride units in the block copolymer usually coincide with the proportion of the aliphatic conjugated diene block region in the block copolymer.

[0039] -Other areas- As described above, the other region is a region containing only repeating units other than aromatic vinyl monomer units and aliphatic conjugated diene monomer units (hereinafter sometimes abbreviated as "other repeating units"). Here, one other region may be composed of one type of other repeating unit, or may be composed of multiple types of other repeating units. Furthermore, one other region may contain a coupling site (i.e., the other repeating units constituting one other region may be connected via a coupling site). When the polymer has a plurality of other regions, the types and proportions of the other repeating units constituting the plurality of other regions may be the same or different from one another.

[0040] The other repeating units are not particularly limited and include, for example, nitrile group-containing monomer units such as acrylonitrile units and methacrylonitrile units; (meth)acrylic acid ester monomer units such as acrylic acid alkyl ester units and methacrylic acid alkyl ester units; and acidic group-containing monomer units such as carboxyl group-containing monomer units, sulfonic acid group-containing monomer units, and phosphoric acid group-containing monomer units. Here, in the present invention, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid.

[0041] -Method for preparing core particles- The core particles containing the block copolymer described above can be prepared, for example, by a step of block polymerizing monomers such as the aromatic vinyl monomer and the aliphatic conjugated diene monomer in an organic solvent to obtain a solution of the block copolymer having an aromatic vinyl block region and an aliphatic conjugated diene block region (block copolymer solution preparation step), and a step of adding water to the obtained block copolymer solution to emulsify the block copolymer, thereby forming the block copolymer into particles (emulsification step).

[0042] = Block copolymer solution preparation step = The method of block polymerization in the block copolymer solution preparation step is not particularly limited. For example, a block copolymer can be prepared by adding a second monomer component different from the first monomer component to a solution obtained by polymerizing a first monomer component, and then polymerizing the second monomer component. If necessary, the addition and polymerization of the monomer component can be further repeated. The organic solvent used as the reaction solvent is also not particularly limited and can be appropriately selected depending on the type of monomer, etc. Here, the block copolymer obtained by block polymerization as described above is preferably subjected to a coupling reaction using a coupling agent prior to the emulsification step described below. By carrying out the coupling reaction, for example, the ends of the diblock structures contained in the block copolymer can be bonded with the coupling agent to convert them into a triblock structure (i.e., the amount of diblock can be reduced).

[0043] The coupling agent that can be used in the above coupling reaction is not particularly limited, and examples thereof include bifunctional coupling agents, trifunctional coupling agents, tetrafunctional coupling agents, and pentafunctional or higher coupling agents. Examples of bifunctional coupling agents include bifunctional halogenated silanes such as dichlorosilane, monomethyldichlorosilane, and dichlorodimethylsilane; bifunctional halogenated alkanes such as dichloroethane, dibromoethane, methylene chloride, and dibromomethane; and bifunctional tin halides such as dichlorotin, monomethyldichlorotin, dimethyldichlorotin, monoethyldichlorotin, diethyldichlorotin, monobutyldichlorotin, and dibutyldichlorotin. Examples of trifunctional coupling agents include trifunctional halogenated alkanes such as trichloroethane and trichloropropane; trifunctional halogenated silanes such as methyltrichlorosilane and ethyltrichlorosilane; and trifunctional alkoxysilanes such as methyltrimethoxysilane, phenyltrimethoxysilane, and phenyltriethoxysilane. Examples of tetrafunctional coupling agents include tetrafunctional halogenated alkanes such as carbon tetrachloride, carbon tetrabromide, and tetrachloroethane; tetrafunctional halogenated silanes such as tetrachlorosilane and tetrabromosilane; tetrafunctional alkoxysilanes such as tetramethoxysilane and tetraethoxysilane; and tetrafunctional tin halides such as tetrachlorotin and tetrabromotin. Examples of the pentafunctional or higher coupling agent include 1,1,1,2,2-pentachloroethane, perchloroethane, pentachlorobenzene, perchlorobenzene, octabromodiphenyl ether, and decabromodiphenyl ether. These can be used alone or in combination of two or more.

[0044] Among the above, dichlorodimethylsilane is preferred as the coupling agent. Note that, according to the coupling reaction using the coupling agent, a coupling moiety derived from the coupling agent is introduced into the polymer chain (e.g., triblock structure) constituting the block copolymer.

[0045] The block copolymer solution obtained after the above-described block polymerization and optional coupling reaction may be subjected to the emulsification step described below as it is. However, if necessary, at least one of a hindered phenol-based antioxidant and a phosphite-based antioxidant, preferably both a hindered phenol-based antioxidant and a phosphite-based antioxidant, may be added to the block copolymer solution before the emulsification step.

[0046] Examples of the hindered phenol antioxidant include, but are not limited to, 4-[[4,6-bis(octylthio)-1,3,5-triazin-2-yl]amino]-2,6-di-tert-butylphenol, 2,6-di-tert-butyl-p-cresol, stearyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 2,4,6-tris(3',5'-di-tert-butyl-4'-hydroxybenzyl)mesitylene. Among these, from the viewpoint of suppressing swelling of the electrode due to repeated charge and discharge, 4-[[4,6-bis(octylthio)-1,3,5-triazin-2-yl]amino]-2,6-di-tert-butylphenol and 2,6-di-tert-butyl-p-cresol are preferred, and from the viewpoint of improving the peel strength of the electrode while suppressing swelling of the electrode due to repeated charge and discharge, 4-[[4,6-bis(octylthio)-1,3,5-triazin-2-yl]amino]-2,6-di-tert-butylphenol is more preferred. These hindered phenol-based antioxidants may be used alone or in combination of two or more. The amount of the hindered phenol-based antioxidant used can be adjusted appropriately within a range that provides the desired effects of the present invention.

[0047] Furthermore, the phosphite antioxidant is not particularly limited, and examples thereof include 3,9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, 2,2-methylenebis(4,6-di-t-butylphenyl)2-ethylhexyl phosphite, and tris(2,4-di-tert-butylphenyl)phosphite. Among these, from the viewpoint of suppressing swelling of the electrode due to repeated charge and discharge, 3,9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane and tris(2,4-di-tert-butylphenyl)phosphite are preferred, and from the viewpoint of suppressing swelling of the electrode due to repeated charge and discharge while improving the peel strength of the electrode, 3,9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane is more preferred. These phosphite-based antioxidants may be used alone or in combination of two or more. The amount of the phosphite-based antioxidant used can be adjusted as appropriate within a range that provides the desired effects of the present invention.

[0048] =Emulsification process= The emulsification method in the emulsification step is not particularly limited, but a preferred method is, for example, a transfer emulsification method in which a premix of the block copolymer solution obtained in the above-mentioned block copolymer solution preparation step and an aqueous solution of an emulsifier is subjected to a transfer emulsification. As described above, the block copolymer solution may contain at least one of a hindered phenol-based antioxidant and a phosphite-based antioxidant, preferably both. Furthermore, for the phase inversion emulsification, for example, a known emulsifier and an emulsifying disperser can be used. Specifically, the emulsifying and dispersing machine is not particularly limited, and examples thereof include batch-type emulsifying and dispersing machines such as "Homogenizer" (manufactured by IKA Corporation), "Polytron" (manufactured by Kinematica Corporation), and "TK Auto Homo Mixer" (manufactured by Tokushu Kika Kogyo Co., Ltd.); "TK Pipeline Homo Mixer" (manufactured by Tokushu Kika Kogyo Co., Ltd.), "Colloid Mill" (manufactured by Kobe Steel Pantech Co., Ltd.), "Thrasher" (manufactured by Nippon Coke and Engineering Co., Ltd.), "Trigonal Wet Fine Grinding Mill" (manufactured by Mitsui Miike Chemical Engineering Co., Ltd.), "Cavitron" (manufactured by Eurotech Co., Ltd.), and "Milder" Examples of suitable emulsifying and dispersing machines include continuous emulsifying and dispersing machines such as "Microfluidizer" (manufactured by Mizuho Kogyo Co., Ltd.), "Nanomizer" (manufactured by Nanomizer Co., Ltd.), "APV Gaulin" (manufactured by Gaulin Co., Ltd.), and "LAB1000" (manufactured by SPXFLOW Co., Ltd.), high-pressure emulsifying and dispersing machines such as "Membrane Emulsifier" (manufactured by Reika Kogyo Co., Ltd.), vibration emulsifying and dispersing machines such as "Vibromixer" (manufactured by Reika Kogyo Co., Ltd.), and ultrasonic emulsifying and dispersing machines such as "Ultrasonic Homogenizer" (manufactured by Branson). The conditions for the emulsification operation using an emulsifying and dispersing machine (e.g., processing temperature, processing time, etc.) are not particularly limited and may be appropriately selected to achieve the desired dispersion state. Then, if necessary, the organic solvent may be removed from the emulsion obtained after the phase inversion emulsification by a known method, thereby obtaining an aqueous dispersion of core particles containing the block copolymer.

[0049] [Acidic graft chain] The acidic graft chains are not particularly limited, and can be introduced into the block copolymer constituting the core particle by graft polymerizing an acidic group-containing monomer or macromonomer onto the block copolymer.

[0050] Here, the acidic group monomer is not particularly limited, and examples thereof include carboxyl group-containing monomers, sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers.

[0051] Here, examples of the carboxyl group-containing monomer include monocarboxylic acids and derivatives thereof, dicarboxylic acids and acid anhydrides thereof, and derivatives thereof. 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, and α-chloro-β-E-methoxyacrylic 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 monoesters such as butyl 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, dimethyl maleic anhydride, and citraconic anhydride. Furthermore, as the carboxyl group-containing monomer, an acid anhydride that generates a carboxyl group upon hydrolysis can also be used. Furthermore, as the carboxyl group-containing monomer, ethylenically unsaturated polycarboxylic acids such as butenetricarboxylic acid, and partial esters of ethylenically unsaturated polycarboxylic acids such as monobutyl fumarate and mono-2-hydroxypropyl maleate can also be used.

[0052] Examples of sulfonic acid group-containing monomers include styrene sulfonic acid, vinyl sulfonic acid (ethylene sulfonic acid), methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, and 3-allyloxy-2-hydroxypropane sulfonic acid. In the present invention, "(meth)allyl" means allyl and / or methallyl.

[0053] Furthermore, examples of the phosphate group-containing monomer 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.

[0054] The above-mentioned acidic group-containing monomers may be used singly or in combination of two or more. The acidic group-containing monomers are preferably vinyl sulfonic acid, methacrylic acid, itaconic acid, and acrylic acid, more preferably methacrylic acid and acrylic acid, and even more preferably methacrylic acid.

[0055] The macromonomer is not particularly limited as long as it is a macropolymer containing an acidic group, but it is preferable to use, for example, a macromonomer of a polycarboxylic acid polymer.

[0056] -Method for preparing graft polymer- Here, the graft polymerization of the acidic graft chains is not particularly limited and can be carried out using a known graft polymerization method. Specifically, the introduction of the acidic graft chains by graft polymerization can be carried out using a radical initiator, such as a redox initiator comprising a combination of an oxidizing agent and a reducing agent. The oxidizing agent and the reducing agent can be the same as the oxidizing agent and the reducing agent described above as being usable for crosslinking a block polymer comprising a block region composed of an aromatic vinyl monomer unit and an aliphatic conjugated diene block region. When graft polymerization is performed using a redox initiator on a block copolymer having an aromatic vinyl block region and an aliphatic conjugated diene block region, the aliphatic conjugated diene monomer units in the block copolymer may be crosslinked when introducing acidic graft chains by graft polymerization. When preparing the graft polymer, crosslinking does not have to proceed simultaneously with graft polymerization, and only graft polymerization may proceed by adjusting the type of radical initiator and reaction conditions.

[0057] The graft polymerization reaction can be carried out, for example, by adding an acidic group-containing monomer and / or macromonomer to an aqueous dispersion of core particles containing a block copolymer and heating the mixture in the presence of the above-mentioned radical initiator.

[0058] Here, the total amount of the acidic monomer and macromonomer added during the graft polymerization reaction is preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 5 parts by mass or more, even more preferably 12 parts by mass or more, and preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of the block copolymer. When the total amount of the acidic monomer and macromonomer added during the graft polymerization reaction is equal to or greater than the above-mentioned lower limit, the viscosity stability of the slurry composition prepared using the binder composition can be improved, and the peel strength of the electrode can be improved. On the other hand, when the total amount of the acidic monomer and macromonomer added during the graft polymerization reaction is equal to or less than the above-mentioned upper limit, the viscosity of the binder composition can be prevented from excessively increasing, and the moisture resistance of the electrode can be further improved. Furthermore, when the total amount of the acidic monomer and macromonomer added during the graft polymerization reaction is equal to or less than the above-mentioned upper limit, the internal resistance of the secondary battery can be reduced.

[0059] It should be noted that the entire amount of the acidic-containing monomer and macromonomer added during the graft polymerization reaction may not be graft-polymerized onto the block copolymer constituting the core particle, and a portion of the acidic-containing monomer and / or macromonomer that is not graft-polymerized onto the block copolymer may polymerize with each other to form a water-soluble polymer as a by-product. The water-soluble polymer formed as a by-product may also be used as the acidic group-containing water-soluble polymer described below.

[0060] In addition, it is preferable to further use a water-soluble chain transfer agent in the graft polymerization reaction. Graft polymerization of an acidic group-containing monomer and / or macromonomer onto core particles containing a block polymer in the presence of the water-soluble chain transfer agent appropriately suppresses polymerization reactions between the acidic group-containing monomer and / or macromonomer that were not graft-polymerized onto the block copolymer, thereby preventing excessive increases in the weight-average molecular weight of the water-soluble polymer formed as a by-product. Therefore, the weight-average molecular weight of the acidic group-containing water-soluble polymer contained in the binder composition produced can be easily adjusted to the above-mentioned predetermined value or less, thereby further improving the moisture resistance of electrodes formed using the binder composition. Furthermore, by preventing excessive increases in the weight-average molecular weight of the water-soluble polymer formed as a by-product, the water-soluble polymer can be appropriately removed from the binder composition when microfiltration is performed as a purification step described below, thereby reducing the internal resistance of secondary batteries.

[0061] In the present invention, the chain transfer agent being "water-soluble" means that when 0.5 g of the chain transfer agent is dissolved in 100 g of water at 25°C, the insoluble content is less than 1 mass %.

[0062] Examples of water-soluble chain transfer agents include hypophosphites, phosphorous acids, mercaptans (thiols), secondary alcohols, and amines. Among these, from the viewpoint of further improving the moisture resistance of the electrode, mercaptans such as mercaptoacetic acid (thioglycolic acid), 2-mercaptosuccinic acid, 3-mercaptopropionic acid, and 3-mercapto-1,2-propanediol are preferred, with 3-mercapto-1,2-propanediol being particularly preferred. These water-soluble chain transfer agents may be used alone or in combination of two or more in any desired ratio.

[0063] The amount of the water-soluble chain transfer agent used is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.10 parts by mass or more, even more preferably 0.5 parts by mass or more, and preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 12 parts by mass or less, and even more preferably 1.8 parts by mass or less, relative to 100 parts by mass of the acidic group-containing monomer and / or macromonomer used in the graft polymerization reaction. When the amount of the water-soluble chain transfer agent used is equal to or greater than the above-mentioned lower limit, the moisture resistance of the electrode can be further improved. Furthermore, when the amount of the water-soluble chain transfer agent used is equal to or greater than the above-mentioned lower limit, the internal resistance of the secondary battery can be further reduced. On the other hand, when the amount of the water-soluble chain transfer agent used is equal to or less than the above-mentioned upper limit, the weight-average molecular weight of the water-soluble polymer formed as a by-product is prevented from becoming excessively small. Therefore, when microfiltration is performed as a purification step described below, a suitable amount of the water-soluble polymer remains in the binder composition. This improves the viscosity stability of the slurry composition prepared using the binder composition and improves the peel strength of the electrode.

[0064] <Acidic group-containing water-soluble polymer> The acidic group-containing water-soluble polymer is a component that can disperse well the blending components such as the particulate polymer described above in an aqueous medium. Here, the acidic group-containing water-soluble polymer is not particularly limited, but is preferably a synthetic polymer, more preferably an addition polymer produced through addition polymerization of monomers. The acidic group-containing water-soluble polymer may be in the form of a salt (a salt of the acidic group-containing water-soluble polymer). That is, in the present invention, the "acidic group-containing water-soluble polymer" also includes the salt of the acidic group-containing water-soluble polymer. In addition, in the present invention, a polymer being "water-soluble" means that when 0.5 g of the polymer is dissolved in 100 g of water at 25°C, the insoluble content is less than 1.0 mass%.

[0065] <<Acidic group>> Examples of acidic groups that the acidic group-containing water-soluble polymer may have include a carboxyl group, a sulfonic acid group, and a phosphate group. The acidic group-containing water-soluble polymer may have only one type of these hydrophilic groups, or may have two or more types. Among these, from the viewpoint of improving the viscosity stability of a slurry composition prepared using the binder composition, the acidic group is preferably a carboxyl group or a sulfonic acid group, and more preferably a carboxyl group.

[0066] Here, the method for introducing an acidic group into the acidic group-containing water-soluble polymer is not particularly limited, and the acidic group-containing water-soluble polymer may be obtained by addition polymerization of a monomer containing the above-mentioned acidic group (acidic group-containing monomer), or the water-soluble polymer having the above-mentioned acidic group may be obtained by modifying (e.g., terminally modifying) any polymer, with the former being preferred.

[0067] -Acidic group-containing monomer unit- From the viewpoint of improving the viscosity stability of a slurry composition prepared using the binder composition, the acidic group-containing water-soluble polymer preferably contains, as the acidic group-containing monomer unit, at least one acidic group-containing monomer unit selected from the group consisting of a carboxyl group-containing monomer unit, a sulfonic acid group-containing monomer unit, and a phosphoric acid group-containing monomer unit, more preferably at least one of a carboxyl group-containing monomer unit and a sulfonic acid group-containing monomer unit, and particularly preferably a carboxyl group-containing monomer unit. The acidic group-containing water-soluble polymer may contain only one type of the above-mentioned acidic group-containing monomer unit, or may contain two or more types.

[0068] Here, as the carboxyl group-containing monomer capable of forming a carboxyl group-containing monomer unit, the sulfonic acid group-containing monomer capable of forming a sulfonic acid group-containing monomer unit, and the phosphate group-containing monomer capable of forming a phosphate group-containing monomer unit, for example, an acidic group-containing monomer that can be used when forming the acidic graft chain of the particulate polymer described above can be used.

[0069] The proportion of the acidic group-containing monomer units in the acidic group-containing water-soluble polymer is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 40% by mass or more, and particularly preferably 60% by mass or more, when the amount of all repeating units in the acidic group-containing water-soluble polymer is taken as 100% by mass. If the proportion of the acidic group-containing monomer units in the acidic group-containing water-soluble polymer is 10% by mass or more, the viscosity stability of a slurry composition prepared using the binder composition can be improved. The upper limit of the proportion of the acidic group-containing monomer units in the acidic group-containing water-soluble polymer is not particularly limited, and can be 100% by mass or less.

[0070] -Other monomer units- The acidic group-containing water-soluble polymer may contain monomer units (other monomer units) other than the above-mentioned acidic group-containing monomer units. The other monomers that can form the other monomer units contained in the acidic group-containing water-soluble polymer are not particularly limited as long as they are copolymerizable with the above-mentioned acidic group-containing monomer. Examples of the other monomers include (meth)acrylic acid ester monomers, fluorine-containing (meth)acrylic acid ester monomers, crosslinkable monomers, and hydroxyl group-containing monomers. As the (meth)acrylic acid ester monomer, the fluorine-containing (meth)acrylic acid ester monomer, and the crosslinkable monomer, for example, those exemplified in JP-A-2015-70245 can be used. Examples of the hydroxyl group-containing monomer 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, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, and di-2-hydroxypropyl itaconate; and esters of ethylenically unsaturated carboxylic acids such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, di-4-hydroxybutyl maleate, and di-2-hydroxypropyl itaconate; a -COO-(C q H 2q O) p -H (wherein p is an integer of 2 to 9, q is an integer of 2 to 4, R arepresents a hydrogen atom 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, (meth)allyl-2-hydroxypropyl ether, (meth)allyl-3-hydroxypropyl ether, (meth)allyl-2-hydroxybutyl ether, (meth)allyl-3-hydroxybutyl ether, (meth)allyl-4-hydroxybutyl ether, and (meth)allyl-6-hydroxyhexyl ether; diethylene glycol mono(meth)allyl ether, dipropylene glycol mono(meth)allyl ethers of halogen- and hydroxy-substituted (poly)alkylene glycols, such as glycerin mono(meth)allyl ether, (meth)allyl-2-chloro-3-hydroxypropyl ether, and (meth)allyl-2-hydroxy-3-chloropropyl 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 amides having a hydroxyl group, such as N-hydroxymethylacrylamide (N-methylolacrylamide), N-hydroxymethylmethacrylamide, N-hydroxyethylacrylamide, and N-hydroxyethylmethacrylamide. The other monomers may be used singly or in combination of two or more.

[0071] [Method for preparing an acidic group-containing water-soluble polymer] The acidic group-containing water-soluble polymer can be produced by polymerizing a monomer composition containing the above-mentioned monomers in an aqueous solvent such as water. In this case, the content of each monomer in the monomer composition can be determined based on the content of each monomer unit in the acidic group-containing water-soluble 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. In addition, additives used in polymerization, such as emulsifiers, dispersants, polymerization initiators, polymerization aids, and molecular weight modifiers, may be those commonly used. The amounts of these additives used may also be those commonly used. The polymerization conditions may be appropriately adjusted depending on the polymerization method, the type of polymerization initiator, and the like.

[0072] In addition, when forming the acidic graft chains of the particulate polymer described above, a part of the acidic-containing monomers and / or macromonomers that have not been graft-polymerized to the block copolymer constituting the core particle are polymerized with each other to form a water-soluble polymer as a by-product, which can also be used as the acidic group-containing water-soluble polymer. That is, the graft polymerization reaction for forming the graft polymer constituting the particulate polymer and the polymerization reaction for forming the acidic group-containing water-soluble polymer can be carried out simultaneously.

[0073] [Weight average molecular weight] The weight-average molecular weight of the acidic group-containing water-soluble polymer contained in the binder composition of the present invention must be 200,000 or less, preferably 150,000 or less, more preferably 100,000 or less, even more preferably 85,000 or less, and preferably 15,000 or more, more preferably 20,000 or more, even more preferably 30,000 or more, and even more preferably 40,000 or more. If the weight-average molecular weight of the acidic group-containing water-soluble polymer exceeds 200,000, the electrode formed using the binder composition cannot exhibit excellent moisture resistance. On the other hand, if the weight-average molecular weight of the acidic group-containing water-soluble polymer is 200,000 or less, the electrode formed using the binder composition can exhibit excellent moisture resistance. Furthermore, if the weight-average molecular weight of the acidic group-containing water-soluble polymer is 15,000 or more, the viscosity stability of the slurry composition prepared using the binder composition can be improved and the peel strength of the electrode can be improved. The weight average molecular weight of the acidic group-containing water-soluble polymer can be adjusted by the type and amount of the water-soluble chain transfer agent and the type and amount of the polymerization initiator used in the polymerization reaction, as well as the conditions of the purification step described below.

[0074] <Aqueous medium> The aqueous medium contained in the binder composition of the present invention is not particularly limited as long as it contains water, and may be an aqueous solution or a mixed solution of water and a small amount of an organic solvent.

[0075] <Other ingredients> The binder composition of the present invention may contain components other than the above-mentioned components (other components). For example, the binder composition may contain a known particulate binder (such as a styrene-butadiene random copolymer or an acrylic polymer) other than the above-mentioned particulate polymer. The binder composition may also contain known additives. Examples of such known additives include antioxidants, antifoaming agents, dispersants (excluding those corresponding to the above-mentioned acidic group-containing water-soluble polymers), etc. Examples of the antioxidant include hindered phenol-based antioxidants and phosphite-based antioxidants that can be used when preparing the core particles of the above-mentioned particulate polymers. The other components may be used singly or in combination of two or more in any ratio.

[0076] <Acid Amount of Binder Composition Determined by Conductometric Titration Method> The acid content of the binder composition measured by conductometric titration is preferably 0.02 mmol / g or more, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, even more preferably 0.50 mmol / g or more, and preferably 2.00 mmol / g or less, more preferably 1.80 mmol / g or less, even more preferably 1.60 mmol / g or less, and even more preferably 1.40 mmol / g or less. When the acid content of the binder composition measured by conductometric titration is equal to or greater than the lower limit, the viscosity stability of the slurry composition prepared using the binder composition can be improved and the peel strength of the electrode can be improved. On the other hand, when the acid content of the binder composition measured by conductometric titration is equal to or less than the upper limit, the viscosity of the binder composition can be prevented from increasing excessively and the moisture resistance of the electrode can be further improved. Furthermore, if the acid amount of the binder composition measured by conductometric titration is equal to or less than the above upper limit, the internal resistance of the secondary battery can be reduced. The acid amount of the binder composition determined by conductometric titration can be adjusted by the amount of the acidic group-containing monomer added when preparing the graft polymer constituting the particulate polymer described above, and the conditions of the purification step described below.

[0077] <Acidic acid content in binder composition> Furthermore, the content of the acid in the binder composition is preferably 0.2 parts by mass or more, more preferably 1 part by mass or more, even more preferably 2 parts by mass or more, even more preferably 4 parts by mass or more, even more preferably 5 parts by mass or more, and preferably 20 parts by mass or less, more preferably 18 parts by mass or less, even more preferably 16 parts by mass or less, and even more preferably 14 parts by mass or less, relative to 100 parts by mass of the particulate polymer core particles. When the content of the acid in the binder composition is equal to or greater than the above-mentioned lower limit, the viscosity stability of the slurry composition prepared using the binder composition can be improved and the peel strength of the electrode can be improved. On the other hand, when the content of the acid in the binder composition is equal to or less than the above-mentioned upper limit, the viscosity of the binder composition can be prevented from excessively increasing and the moisture resistance of the electrode can be further improved. Furthermore, when the content of the acid in the binder composition is equal to or less than the above-mentioned upper limit, the internal resistance of the secondary battery can be reduced. The acid content in the binder composition can be measured by the method described in the examples of this specification. The content of the acid in the binder composition can be adjusted by the amount of the acidic group-containing monomer added when preparing the graft polymer constituting the particulate polymer described above, and the conditions of the purification step described below.

[0078] <Viscosity of binder composition> The viscosity of the binder composition when adjusted to a solids concentration of 40% by mass and a pH of 8.0 is preferably 3000 mPa·s or less, more preferably 1500 mPa·s or less, even more preferably 1000 mPa·s or less, even more preferably 250 mPa·s or less, and preferably 20 mPa·s or more, more preferably 40 mPa·s or more, and even more preferably 60 mPa·s or more. If the viscosity of the binder composition at a solids concentration of 40% by mass and a pH of 8.0 is equal to or less than the above upper limit, the moisture resistance of the electrode can be further improved and the internal resistance of the secondary battery can be reduced. On the other hand, if the viscosity of the binder composition at a solids concentration of 40% by mass and a pH of 8.0 is equal to or greater than the above lower limit, the viscosity stability of the slurry composition prepared using the binder composition can be improved and the peel strength of the electrode can be improved. The viscosity of the binder composition at a solids concentration of 40% by mass and pH 8.0 can be adjusted by the amount of the acidic group-containing monomer used in preparing the particulate polymer described above, the type and amount of the water-soluble chain transfer agent, and the conditions of the purification step described below.

[0079] <pH of binder composition> The pH of the binder composition is preferably 6.0 or higher, more preferably 7.0 or higher, and is preferably 10.0 or lower, more preferably 9.0 or lower. If the pH of the binder composition is within the above-mentioned range, the viscosity stability of a slurry composition prepared using the binder composition can be improved.

[0080] (Method for producing binder composition) The method for producing a binder composition of the present invention is the same as the method for producing the binder composition of the present invention described above, and includes a step (graft polymerization step) of grafting an acidic group-containing monomer and / or macromonomer onto core particles in the presence of a water-soluble chain transfer agent to obtain a dispersion of a particulate polymer. According to the method for producing a binder composition of the present invention, it is possible to easily produce a binder composition containing a particulate polymer made of a predetermined graft polymer and an acidic group-containing water-soluble polymer having a weight-average molecular weight of a predetermined value or less. Therefore, it is possible to easily obtain a binder composition for a non-aqueous secondary battery that can form an electrode for a non-aqueous secondary battery having excellent moisture resistance. The method for producing the binder composition of the present invention may further include other steps in addition to the purification step described above. The binder composition of the present invention described above can also be produced by a method other than the method for producing the binder composition of the present invention.

[0081] <Graft polymerization process> In the graft polymerization step, an acidic group-containing monomer and / or macromonomer is graft-polymerized onto the core particles in the presence of a water-soluble chain transfer agent to obtain a particulate polymer dispersion. Preparing a particulate polymer dispersion by graft-polymerizing the acidic group-containing monomer and / or macromonomer onto the core particles in the presence of a water-soluble chain transfer agent appropriately suppresses the polymerization reaction between the acidic group-containing monomer and / or macromonomer that is not graft-polymerized onto the block copolymer constituting the core particles, thereby preventing an excessive increase in the weight-average molecular weight of the acidic group-containing water-soluble polymer formed as a by-product. Therefore, the weight-average molecular weight of the acidic group-containing water-soluble polymer contained in the binder composition produced can be easily adjusted to the above-mentioned predetermined value or less. Therefore, electrodes formed using the binder composition can exhibit excellent moisture resistance. Furthermore, by preventing an excessive increase in the weight-average molecular weight of the acidic group-containing water-soluble polymer formed as a by-product, the acidic group-containing water-soluble polymer can be appropriately removed from the binder composition when microfiltration is performed as a purification step described below, thereby reducing the internal resistance of secondary batteries.

[0082] The graft polymerization reaction in the graft polymerization step can be carried out in the presence of a radical initiator such as a redox initiator.

[0083] The core particles used in the graft polymerization reaction can be prepared by the method for preparing core particles of particulate polymers described above in the section "Binder composition." The types and amounts of the radical initiator, water-soluble chain transfer agent, acidic group-containing monomer, and macromonomer used in the graft polymerization reaction may be the same as the types and amounts of each component that can be used in the method for preparing the graft polymer constituting the particulate polymer described above in the section "Binder composition."

[0084] The graft reaction in the graft polymerization step is usually carried out in the presence of water. When an aqueous dispersion of core particles is used in the graft reaction, the water contained in the aqueous dispersion can be used as is.

[0085] <Other processes> The method for producing the binder composition of the present invention may further include other steps in addition to the above-mentioned graft polymerization step. The method for producing the binder composition of the present invention preferably further includes, as the other step, a step of purifying the dispersion of the particulate polymer obtained in the graft polymerization step (purification step). The aqueous dispersion of the particulate polymer obtained in the graft polymerization step can also be used as the binder composition of the present invention without undergoing the purification step.

[0086] <<Purification process>> In the purification step, the particulate polymer dispersion is purified. Here, the particulate polymer dispersion obtained in the above-mentioned graft polymerization step is a mixture of the particulate polymer, the acidic group-containing water-soluble polymer formed as a by-product, and an aqueous medium (e.g., water). Then, in the purification step, the particulate polymer dispersion is purified, thereby removing a portion of the acidic group-containing water-soluble polymer formed as a by-product. In this way, by removing a portion of the acidic group-containing water-soluble polymer formed as a by-product from the particulate polymer dispersion, the weight-average molecular weight of the acidic group-containing water-soluble polymer remaining in the obtained binder composition can be further reduced and more easily adjusted to the above-mentioned predetermined value or less. Therefore, the moisture resistance of the electrode formed using the produced binder composition can be further improved, and the internal resistance of the secondary battery can also be further reduced.

[0087] The method for purifying the particulate polymer dispersion is not particularly limited as long as the desired effects of the present invention can be obtained, and methods such as filtration and centrifugation can be used. Among these, filtration is preferred from the viewpoint of the removal rate of the acidic group-containing water-soluble polymer. Specifically, it is preferred to remove a portion of the acidic group-containing water-soluble polymer from the particulate polymer dispersion by the following filtration method. That is, the particulate polymer dispersion is placed in a container (stock solution container) connected to a system equipped with a filtration membrane, and microfiltration is performed while circulating with a constant flow pump. Then, while adding a dispersion medium (e.g., water) to the stock solution container in an amount corresponding to the weight of the permeate discharged outside the filtration membrane, microfiltration is continued, and the liquid in the stock solution container can be obtained as a binder composition. As a system for microfiltration, the "Microza Pencil Module Type Module Tabletop Filtration Unit PX-02001" manufactured by Asahi Kasei Corporation can be used. The pore size of the filtration membrane provided in the system can be set appropriately within a range that achieves the desired effects of the present invention. Furthermore, conditions such as circulation flow rate, filtration pressure, and filtration time during microfiltration can also be adjusted as appropriate within ranges that achieve the desired effects of the present invention.

[0088] (Slurry composition for non-aqueous secondary battery electrodes) The slurry composition of the present invention is a composition used for forming an electrode mixture layer of an electrode, and contains the binder composition of the present invention described above and further contains an electrode active material. That is, the slurry composition of the present invention contains the particulate polymer, the acidic group-containing water-soluble polymer, the electrode active material, and an aqueous medium, and optionally further contains other components. Furthermore, since the slurry composition of the present invention contains the binder composition of the present invention described above, it is possible to form an electrode having excellent moisture resistance.

[0089] <Binder composition> As the binder composition, the above-mentioned binder composition of the present invention is used, which contains a particulate polymer made of a predetermined graft polymer and an acidic group-containing water-soluble polymer having a weight-average molecular weight of 200,000 or less. The amount of the binder composition in the slurry composition is not particularly limited, and may be, for example, 0.5 to 15 parts by mass, in terms of solid content, per 100 parts by mass of the electrode active material.

[0090] <Electrode active material> The electrode active material is not particularly limited, and known electrode active materials used in secondary batteries can be used. Specifically, for example, the electrode active material that can be used in the electrode mixture layer of a lithium ion secondary battery, which is an example of a secondary battery, is not particularly limited, and the following electrode active materials can be used.

[0091] [Cathode active material] The positive electrode active material to be blended in the positive electrode composite layer of the positive electrode of the lithium ion secondary battery can be, for example, a compound containing a transition metal, such as a transition metal oxide, a transition metal sulfide, or a composite metal oxide of lithium and a transition metal, etc. Examples of the transition metal include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo. Specifically, the positive electrode active material is not particularly limited, and examples include 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), and lithium-excess spinel compounds represented by Li 1+x Mn 2-x O4 (0 < X < 2), Li[Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 O2, LiNi 0.5 Mn 1.5 O4, etc. In addition, the above-mentioned positive electrode active material may be used alone or in combination of two or more kinds.

[0092] [Negative electrode active material] As the negative electrode active material incorporated in the negative electrode composite material layer of the negative electrode of the lithium-ion secondary battery, usually, a material capable of occluding and releasing lithium is used. Examples of the material capable of occluding and releasing lithium include carbon-based negative electrode active materials, non-carbon-based negative electrode active materials, and active materials combining these.

[0093] - Carbon-based negative electrode active material - Here, the carbon-based negative electrode active material refers to an active material having a carbon main skeleton into which lithium can be inserted (also referred to as "doped"). Examples of the carbon-based negative electrode active material include carbonaceous materials and graphite materials.

[0094] Carbonaceous materials are materials with a low degree of graphitization (i.e., low crystallinity) that are obtained by carbonizing a carbon precursor through heat treatment at 2000°C or less. The lower limit of the heat treatment temperature during carbonization is not particularly limited, but can be, for example, 500°C or higher. Examples of carbonaceous materials include graphitizable carbon, whose carbon structure can be easily changed depending on the heat treatment temperature, and non-graphitizable carbon, which has a structure similar to an amorphous structure, such as glassy carbon. Examples of graphitizable carbon include carbon materials made from tar pitch obtained from petroleum or coal. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber, and pyrolytic vapor-grown carbon fiber. Examples of non-graphitizable carbon include phenolic resin baked body, polyacrylonitrile carbon fiber, pseudo-isotropic carbon, furfuryl alcohol resin baked body (PFA), and hard carbon.

[0095] Graphite materials are materials with high crystallinity similar to that of graphite, obtained by heat treating graphitizable carbon at 2000°C or higher. The upper limit of the heat treatment temperature is not particularly limited, but can be set to, for example, 5000°C or lower. Examples of graphite materials include natural graphite and artificial graphite. Examples of artificial graphite include artificial graphite obtained by heat-treating carbon containing easily graphitized carbon mainly at 2800°C or higher, graphitized MCMB obtained by heat-treating MCMB at 2000°C or higher, and graphitized mesophase pitch-based carbon fiber obtained by heat-treating mesophase pitch-based carbon fiber at 2000°C or higher. In the present invention, natural graphite at least part of the surface of which is coated with amorphous carbon (amorphous-coated natural graphite) may be used as the carbon-based negative electrode active material.

[0096] -Non-carbon-based negative electrode active material- The non-carbon-based negative electrode active material is an active material other than a carbon-based negative electrode active material made solely of a carbonaceous material or graphite material, and examples of the non-carbon-based negative electrode active material include metal-based negative electrode active materials.

[0097] A metal-based negative electrode active material is an active material containing a metal, typically containing an element capable of intercalating lithium, and having a theoretical electrical capacity per unit mass of 500 mAh / g or more when lithium is intercalated. Examples of metal-based negative electrode active materials include lithium metal, elemental metals capable of forming lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.), alloys thereof, and oxides, sulfides, nitrides, silicides, carbides, and phosphides thereof. For example, a silicon-containing active material (silicon-based negative electrode active material) can be used as a metal-based negative electrode active material. The use of a silicon-based negative electrode active material can increase the capacity of lithium-ion secondary batteries.

[0098] Examples of silicon-based negative electrode active materials include silicon (Si), silicon-containing alloys, SiO, and SiO x and a composite of a Si-containing material and conductive carbon, which is obtained by coating or compounding a Si-containing material with conductive carbon. These silicon-based negative electrode active materials may be used alone or in combination of two or more.

[0099] Examples of alloys containing silicon include alloy compositions containing silicon and at least one element selected from the group consisting of titanium, iron, cobalt, nickel, and copper. Examples of alloys containing silicon also include alloy compositions containing silicon, aluminum, and a transition metal such as iron, and further containing tin and a rare earth element such as yttrium.

[0100] <Other ingredients> Other components that can be blended into the slurry composition are not particularly limited and include conductive materials and the same components as those that can be blended into the binder composition of the present invention. Note that the other components may be used alone or in combination of two or more in any ratio.

[0101] <Preparation of Slurry Composition> The method for preparing the slurry composition is not particularly limited. For example, a slurry composition can be prepared by mixing the binder composition, the electrode active material, and other components used as needed in the presence of an aqueous medium. The aqueous medium used in preparing the slurry composition also includes the one contained in the binder composition. The mixing method is not particularly limited, and mixing can be performed using a commonly used stirrer or disperser.

[0102] (Electrode for non-aqueous secondary batteries) The non-aqueous secondary battery electrode of the present invention includes an electrode mixture layer formed using the above-described slurry composition for a non-aqueous secondary battery electrode. Therefore, the electrode mixture layer is composed of a dried product of the above-described slurry composition, and typically contains an electrode active material, a component derived from a particulate polymer, an acidic group-containing water-soluble polymer, and optionally other components. The components contained in the electrode mixture layer are those contained in the above-described slurry composition for a non-aqueous secondary battery electrode, and the preferred ratios of the components are the same as the preferred ratios of the components in the slurry composition. Furthermore, although the particulate polymer exists in particulate form in the slurry composition, it may be in particulate form or any other shape in the electrode mixture layer formed using the slurry composition. The non-aqueous secondary battery electrode of the present invention has an electrode mixture layer formed using the above-mentioned slurry composition for a non-aqueous secondary battery electrode, and therefore has excellent moisture resistance.

[0103] <Production of electrodes for non-aqueous secondary batteries> The electrode mixture layer of the electrode for a non-aqueous secondary battery of the present invention can be formed, for example, by the following method. 1) A method in which the slurry composition of the present invention is applied to the surface of a current collector and then dried; 2) a method of immersing a current collector in the slurry composition of the present invention and then drying the same; and 3) A method in which the slurry composition of the present invention is applied to a release substrate, and dried to produce an electrode mixture layer, and the resulting electrode mixture layer is transferred to the surface of a current collector. Among these, the method 1) is particularly preferred because it allows for easy control of the thickness of the electrode mixture layer. Specifically, the method 1) includes a step of applying a 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 mixture layer on the current collector (drying step).

[0104] [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.

[0105] Here, the current collector to which the slurry composition is applied is made of a material that is electrically conductive and electrochemically durable. Specifically, the current collector may be made of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. Note that one of the above materials may be used alone, or two or more may be used in combination in any ratio.

[0106] [Drying process] The method for drying the slurry composition on the current collector is not particularly limited and any known method can be used, such as drying with warm air, hot air, or low-humidity air, vacuum drying, or drying by irradiation with infrared rays or 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 nonaqueous secondary battery electrode including the current collector and the electrode mixture layer can be obtained.

[0107] 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 improves the adhesion between the electrode mixture layer and the current collector and further increases the density of the resulting electrode mixture layer. In addition, when the electrode mixture layer contains a curable polymer, it is preferable to cure the polymer after the electrode mixture layer is formed.

[0108] (Non-aqueous secondary battery) The nonaqueous secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolyte, and a separator, and uses the above-described nonaqueous secondary battery electrode as at least one of the positive electrode and the negative electrode. The nonaqueous secondary battery of the present invention is manufactured using the above-described nonaqueous secondary battery electrode as at least one of the positive electrode and the negative electrode, and therefore can exhibit excellent battery characteristics. In the following, a case where the secondary battery is a lithium ion secondary battery will be described as an example, but the present invention is not limited to the following example.

[0109] <Electrode> Here, the electrodes other than the above-described nonaqueous secondary battery electrode of the present invention that can be used in the nonaqueous secondary battery of the present invention are not particularly limited, and known electrodes used in the manufacture of secondary batteries can be used. Specifically, the electrodes other than the above-described nonaqueous secondary battery electrode of the present invention can be electrodes formed by forming an electrode mixture layer on a current collector using a known manufacturing method.

[0110] <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 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 lithium ion conductivity tends to increase as the supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0111] 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), ethyl methyl carbonate (EMC), and vinylene carbonate (VC); 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 due to their high dielectric constant and wide stable potential range. Generally, the lower the viscosity of the solvent used, the higher the lithium ion conductivity. Therefore, the lithium ion conductivity can be adjusted by the type of solvent. The concentration of the electrolyte in the electrolytic solution can be adjusted as appropriate, and known additives can be added to the electrolytic solution.

[0112] <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.

[0113] 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. In the nonaqueous secondary battery of the present invention, the above-described nonaqueous secondary battery electrode is used as at least one of the positive electrode and negative electrode, preferably the negative electrode. The nonaqueous secondary battery of the present invention may be provided with a fuse, an overcurrent protection element such as a PTC element, an expanded metal, a lead plate, or the like, as necessary to prevent internal pressure buildup, overcharging and overdischarging, and the like within the secondary battery. The secondary battery may have any shape, such as a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, or a flat type. [Example]

[0114] 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. Furthermore, in a polymer produced by polymerizing multiple types of monomers, the proportion of monomer units formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of that certain monomer to all monomers used in the polymerization of the polymer, unless otherwise specified. In the examples and comparative examples, the weight average molecular weight of the acidic group-containing water-soluble polymer, the amount of acid in the binder composition determined by conductometric titration, the content of acid in the binder composition, the viscosity of the binder composition, the viscosity stability of the slurry composition, the peel strength and moisture resistance of the electrode, and the internal resistance of the secondary battery were measured and evaluated by the following methods.

[0115] <Weight-average molecular weight of acidic group-containing water-soluble polymer> 10 ml of 0.1 M Tris buffer (pH 9, 0.1 M potassium chloride added) was added to the binder composition to adjust the concentration to 0.05%. Then, ultracentrifugation (92,000 G) was performed, and the supernatant was filtered through a 0.5 μm filter to obtain a molecular weight measurement sample. The molecular weight of the obtained molecular weight measurement sample was then measured by GPC (gel permeation chromatography). The measurement conditions are shown below. Detector: Differential refractive index detector RI (Shimadzu RID-20A) Column: TSKgel guardcolumn PW XL 1 tube (φ6.0mm x 4cm, Tosoh), TSKgel GMPW XL 2 pieces (φ7.8mm x 30cm, Tosoh) Solvent: 0.1 M Tris buffer (pH 9, 0.1 M potassium chloride added) Flow rate: 0.7mL / min Column temperature: 40℃ Injection volume: 0.2mL Standard samples: Showa Denko monodisperse pullulan, sucrose, glucose Data processing: TRC GPC data processing system

[0116] <Acid Amount of Binder Composition Determined by Conductometric Titration Method> The resulting binder composition was diluted with ion-exchanged water to a solids concentration of 3%. The pH of the adjusted sample was then adjusted to 12.0 with a 3% aqueous solution of sodium hydroxide. A 1.5 g (solids equivalent) aliquot of the pH-adjusted sample was placed in a 100 mL beaker, to which 3 g of a 0.2% diluted aqueous solution of Kao Corporation's Emulgen 120 and 1 g of a 1% diluted aqueous solution of Toray Dow Corning Co., Ltd.'s SM5512 were added. While stirring uniformly with a stirrer, a 0.1 N aqueous solution of hydrochloric acid was added at a rate of 0.5 mL / 30 seconds, and electrical conductivity was measured every 30 seconds. The obtained electrical conductivity data was plotted on a graph with electrical conductivity on the vertical axis (Y-axis) and the cumulative amount of hydrochloric acid added on the horizontal axis (X-axis). This resulted in a hydrochloric acid amount-electrical conductivity curve with three inflection points, as shown in Figure 1. The X-coordinates of the three inflection points and the time when hydrochloric acid addition was completed were designated P1, P2, P3, and P4, respectively, in ascending order of value. Approximation lines L1, L2, L3, and L4 were calculated using the least squares method for the data in the four X-coordinate sections: from zero to P1, from P1 to P2, from P2 to P3, and from P3 to P4. The X-coordinate of the intersection of the approximated lines L1 and L2 was designated A1, the X-coordinate of the intersection of the approximated lines L2 and L3 was designated A2, and the X-coordinate of the intersection of the approximated lines L3 and L4 was designated A3. Then, the acid amount of the binder composition (acid amount per 1 g of solid content of the binder composition) was determined by conductometric titration using the following formula (a) as a hydrochloric acid equivalent value (mmol / g). (a) Acid content of binder composition = (A3 - A1) / 1.5g

[0117] <Acidic acid content in binder composition> Based on the acid amount of the binder composition obtained above by conductometric titration, the acid content in the binder composition was calculated as a relative amount to 100 parts by mass of the core particles of the particulate polymer.

[0118] <Viscosity of binder composition> The viscosity of the obtained binder composition was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., product name "TVB-10", rotation speed: 60 rpm).

[0119] <Viscosity stability of slurry composition> The viscosity η0 of the resulting slurry composition was measured using a Brookfield viscometer (manufactured by Toki Sangyo Co., Ltd., product name "TVB-10", rotation speed: 60 rpm). Next, the slurry composition whose viscosity had been measured was stirred for 24 hours using a planetary mixer (rotation speed: 60 rpm), and the viscosity η1 of the slurry composition after stirring was measured using the same Brookfield viscometer (rotation speed: 60 rpm) as above. The viscosity change rate of the slurry composition before and after stirring, Δη = {(η0 - η1) / η0} × 100 (%), was then calculated, and the viscosity stability of the slurry composition was evaluated according to the following criteria. The temperature during viscosity measurement was 25°C. The closer the absolute value of the viscosity change rate |Δη| is to 0, the better the viscosity stability of the slurry composition. A: The absolute value of the viscosity change rate |Δη| is 0% or more and less than 10% B: The absolute value of the viscosity change rate |Δη| is 10% or more and less than 20% C: The absolute value of the viscosity change rate |Δη| is 20% or more and less than 30% D: The absolute value of the viscosity change rate |Δη| is 30% or more

[0120] <Electrode peel strength> The prepared negative electrode was cut into a rectangle 100 mm long and 10 mm wide to prepare a test specimen. This test specimen was placed with the surface of the negative electrode composite layer facing down, and cellophane tape was attached to the surface of the negative electrode composite layer. Cellophane tape specified in JIS Z1522 was used as the cellophane tape. The cellophane tape was fixed to a test table. One end of the current collector was then pulled vertically upward at a pulling rate of 50 mm / min to measure the stress when peeled off. This measurement was performed three times, and the average value was calculated and used as the peel strength (A) of the electrode. Evaluation was then performed according to the following criteria, using the peel strength of Comparative Example 4 as the standard. A higher peel strength indicates a stronger adhesive strength of the negative electrode composite layer to the current collector, i.e., a higher adhesion strength. A: Peel strength 1.5 times or more of that of Comparative Example 2 B: 0.8 times or more and less than 1.5 times the peel strength of Comparative Example 2

[0121] <Moisture resistance of electrodes> The fabricated negative electrode was stored for 144 hours in a thermo-hygrostat chamber set at a temperature of 25°C and humidity of 85%, and then stored in a dry room with a dew point of -60°C for 24 hours. The negative electrode was then cut into a rectangular shape, 100 mm long and 10 mm wide, to prepare a test specimen. This test specimen was placed with the surface of the negative electrode composite layer facing downwards, and cellophane tape was attached to the surface of the negative electrode composite layer. Cellophane tape specified in JIS Z1522 was used for this purpose. The cellophane tape was also fixed to a test table. One end of the current collector was then pulled vertically upward at a pulling rate of 50 mm / min, and the stress when peeled was measured. This measurement was performed three times, and the average value was calculated. This average value was used as the peel strength (B) of the electrode after storage in a high-humidity environment. The peel strength retention rate was calculated from the peel strength (A) of the electrode immediately after production, obtained by the above-mentioned method for measuring the peel strength of an electrode, and the peel strength (B) of the electrode after storage in a high-humidity environment, using the formula: peel strength retention rate = {(B) / (A)} × 100 (%), and evaluated according to the following criteria. Note that a higher peel strength retention rate indicates a more excellent moisture resistance of the electrode. A: Peel strength retention rate is 95% or more B: Peel strength retention rate is 85% or more but less than 95% C: Peel strength retention rate is 75% or more but less than 85% D: Peel strength retention rate is less than 75%

[0122] <Internal resistance of secondary battery> To evaluate the internal resistance of the lithium-ion secondary battery, the IV resistance was measured as follows. A conditioning treatment was performed by charging at a charge rate of 0.1 C at 25°C until the voltage reached 4.2 V, resting for 10 minutes, and then discharging at a discharge rate of 0.1 C to 3.0 V three times. Subsequently, the battery was charged to 3.75 V at 1 C (C is a value expressed as rated capacity (mA) / hour (h)) in a −10°C atmosphere, and then charged and discharged for 20 seconds at 0.5 C, 1.0 C, 1.5 C, and 2.0 C, centered on 3.75 V. For each case, the battery voltage after 15 seconds on the charging side was plotted against the current value, and the slope was calculated as the IV resistance (Ω). The obtained IV resistance values ​​(Ω) were compared with the IV resistance of Comparative Example 4 and evaluated according to the following criteria. Note that a smaller IV resistance value indicates a lower internal resistance of the secondary battery. A: Less than 85% of the IV resistance of Comparative Example 2 B: 85% or more and less than 90% of the IV resistance of Comparative Example 2 C: 90% or more and less than 95% of the IV resistance of Comparative Example 2 D: IV resistance of Comparative Example 2

[0123] Example 1 <Preparation of binder composition for non-aqueous secondary battery negative electrode> [Preparation of cyclohexane solution of block polymer] A pressure-resistant reactor was charged with 233.3 kg of cyclohexane, 54.2 mmol of N,N,N',N'-tetramethylethylenediamine (TMEDA), and 31.0 kg of styrene as an aromatic vinyl monomer. While stirring these mixtures at 40°C, 1806.5 mmol of n-butyllithium as a polymerization initiator was added, and polymerization was carried out for 1 hour while the temperature was raised to 50°C. The polymerization conversion of styrene was 100%. Subsequently, while controlling the temperature to maintain a temperature of 50-60°C, 69.0 kg of 1,3-butadiene as an aliphatic conjugated diene monomer was continuously added to the pressure-resistant reactor over 1 hour. After the addition of 1,3-butadiene was completed, the polymerization reaction was continued for another 1 hour. The polymerization conversion of 1,3-butadiene was 100%. Next, 722.6 mmol of dichlorodimethylsilane was added to the pressure reactor as a coupling agent, and the coupling reaction was carried out for 2 hours to form a styrene-butadiene coupled block copolymer. Subsequently, 3612.9 mmol of methanol was added to the reaction solution to deactivate the active terminals and mixed thoroughly. Next, 0.05 parts of 4-[[4,6-bis(octylthio)-1,3,5-triazin-2-yl]amino]-2,6-di-tert-butylphenol as a hindered phenol-based antioxidant and 0.09 parts of 3,9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane as a phosphite-based antioxidant were added to 100 parts of this reaction solution (containing 30.0 parts of the polymer component) and mixed. The resulting mixed solution was gradually added dropwise to warm water at 85-95°C to volatilize the solvent and obtain a precipitate. The precipitate was then crushed and dried with hot air at 85°C to recover a dried product containing the block polymer. The recovered dried product was then dissolved in cyclohexane to prepare a block polymer solution with a block polymer concentration of 5.0%.

[0124] [Phase inversion emulsification] Sodium alkylbenzenesulfonate was dissolved in ion-exchanged water to prepare a 0.15% aqueous solution. Then, 1000 g of the obtained block polymer solution and 1400 g of the obtained aqueous solution were charged into a tank and premixed by stirring. Subsequently, the premix was transferred from the tank to a high-pressure emulsifying disperser "LAB1000" (manufactured by SPXFLOW) using a metering pump and circulated (number of passes: 5) to obtain an emulsion by phase inversion of the premix. Next, cyclohexane in the obtained emulsion was distilled off under reduced pressure using a rotary evaporator, and the distilled emulsion was then centrifuged at 7000 rpm for 10 minutes using a centrifuge (Hitachi Koki Co., Ltd., product name "Himac CR21N"), and the upper layer was removed for concentration. Finally, the upper layer was filtered through a 100-mesh wire screen to obtain an aqueous dispersion (block polymer latex) containing particulated block polymer (core particles).

[0125] [Graft polymerization and crosslinking] Distilled water was added to the obtained block polymer latex to dilute it to 850 parts of water per 100 parts of block polymer (equivalent to the solid content).The diluted block polymer latex was then charged into a nitrogen-substituted polymerization reaction vessel equipped with a stirrer, and heated to 30°C with stirring. In a separate vessel, 16 parts of methacrylic acid as an acidic group-containing monomer and 144 parts of distilled water were mixed to prepare a diluted methacrylic acid solution. This diluted methacrylic acid solution was added over 30 minutes to a polymerization reaction vessel heated to 30°C, thereby adding 16 parts of methacrylic acid per 100 parts of block polymer. Then, 1.0 part of 3-mercapto-1,2-propanediol as a water-soluble chain transfer agent per 100 parts of block polymer was added. Furthermore, a solution containing 7 parts of distilled water and 0.01 parts of ferrous sulfate (manufactured by Chubu Cherest Co., Ltd., trade name "Frost Fe") as a reducing agent was prepared in a separate container. The resulting solution was added to a polymerization reaction vessel, and 0.5 parts of 1,1,3,3-tetramethylbutyl hydroperoxide (manufactured by NOF Corporation, trade name "Perocta H") as an oxidizing agent was added. The reaction was allowed to proceed at 30°C for 1 hour, followed by a further reaction at 70°C for 2 hours. This resulted in graft polymerization of methacrylic acid onto the particulate block polymer and crosslinking of the block polymer, yielding an aqueous dispersion of particulate polymer. The polymerization conversion rate was 99%.

[0126] [Precision filtration] Ion-exchanged water was added to the obtained aqueous dispersion of the particulate polymer to dilute it to a solids concentration of 10%. A 5% aqueous sodium hydroxide solution was added to the diluted aqueous dispersion of the particulate polymer to adjust the pH to 8.0. 1500 g of the binder composition after pH adjustment was placed in a container (concentrate container) connected to the following system, and microfiltration was carried out under the conditions shown below while circulating it with a constant flow pump. System: Microza pencil module type module tabletop filtration unit PX-02001 (Asahi Kasei Corporation) Filtration membrane: Microza USP-043 (pore size 0.1μm) Circulation flow rate: 1000g / min Microfiltration was continued for 30 hours while adding water to the stock solution container in an amount equivalent to the weight of the permeate discharged outside the system (outside the filtration membrane). After that, microfiltration was continued while suspending the addition of water to the stock solution container. When the solids concentration of the binder composition reached 40%, microfiltration was terminated and the liquid in the stock solution container was collected as the binder composition. The resulting binder composition had a pH of 8.0 and a solids concentration of 40.0%. Using the resulting binder composition, the weight-average molecular weight of the acidic group-containing water-soluble polymer, the acid content of the binder composition by conductometric titration, the acid content of the binder composition, and the viscosity of the binder composition were measured. The results are shown in Table 1.

[0127] <Preparation of Slurry Composition for Non-Aqueous Secondary Battery Negative Electrode> A mixture was obtained by adding 97 parts of graphite (natural graphite) (capacity: 360 mAh / g) as the negative electrode active material and 1 part (solids equivalent) of carboxymethyl cellulose (CMC) as a thickener to a planetary mixer. The resulting mixture was then adjusted to a solids concentration of 60% with ion-exchanged water and kneaded for 60 minutes at a rotation speed of 45 rpm. Then, 1.5 parts (solids equivalent) of the binder composition prepared above was added and kneaded for 40 minutes at a rotation speed of 40 rpm. Ion-exchanged water was then added to obtain a negative electrode slurry composition with a viscosity of 3000±500 mPa·s (measured using a Brookfield viscometer at 25°C and a rotor rotation speed of 60 rpm). The viscosity stability of the resulting negative electrode slurry composition was evaluated, and the results are shown in Table 1.

[0128] <Formation of the negative electrode> The obtained negative electrode slurry composition was applied to a 15 μm-thick electrolytic copper foil current collector using a comma coater in an amount of 11±0.5 mg / cm 2 Thereafter, the copper foil coated with the negative electrode slurry composition was transported at a speed of 400 mm / min through an oven at a temperature of 1200°C for 2 minutes and then through an oven at a temperature of 130°C for 2 minutes, thereby drying the slurry composition on the copper foil and obtaining a negative electrode blank having a negative electrode composite layer formed on a current collector. Thereafter, the negative electrode composite layer side of the prepared negative electrode blank was roll-pressed in an environment at a temperature of 25±3°C, and the density of the negative electrode composite layer was adjusted to 1.60 g / cm 3 The negative electrode thus obtained was evaluated for peel strength and moisture resistance. The results are shown in Table 1.

[0129] <Formation of the positive electrode> The planetary mixer uses a Co-Ni-Mn lithium composite oxide active material NMC532 (LiNi 5 / 10 Co 2 / 10 Mn 3 / 1097 parts of acetylene black (product name "HS-100" manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, and 2 parts (solids equivalent) of polyvinylidene fluoride (product name "#7208" manufactured by Kureha Corporation) as a binder were added and mixed. Furthermore, N-methyl-2-pyrrolidone (NMP) as an organic solvent was gradually added, and the mixture was stirred at a temperature of 25±3°C and a rotation speed of 25 rpm to obtain a positive electrode slurry composition with a viscosity of 3600 mPa s (measured using a Brookfield viscometer at a temperature of 25±3°C, a rotor M4, and a rotor rotation speed of 60 rpm). The obtained slurry composition for the positive electrode was applied to a 20 μm thick aluminum foil current collector using a comma coater in an amount of 20±0.5 mg / cm 2 The aluminum foil was then transported at a speed of 200 mm / min through an oven at 120°C for 2 minutes and then through an oven at 130°C for 2 minutes to dry the slurry composition on the aluminum foil, thereby obtaining a positive electrode substrate having a positive electrode composite layer formed on the current collector. Thereafter, the positive electrode composite layer side of the prepared positive electrode blank was roll-pressed in an environment at a temperature of 25±3°C, and the density of the positive electrode composite layer was adjusted to 3.20 g / cm 3 A positive electrode of 1000 .mu.m was obtained.

[0130] <Preparing the separator> As a separator made of a separator substrate, a single-layer polypropylene separator (manufactured by Celgard Co., Ltd., product name "Celgard 2500") was prepared.

[0131] <Fabrication of lithium-ion secondary batteries> A single-layer laminate cell (with an initial design discharge capacity of 30 mAh) was fabricated using the above negative and positive electrodes and separators. It was then placed in an aluminum foil bag and vacuum dried at 60°C for 10 hours. A 1.0 M LiPF solution (solvent: ethylene carbonate (EC) / diethyl carbonate (DEC) = 5 / 5 (volume ratio), additive: vinylene carbonate 2 vol% (solvent ratio)) was then filled as the electrolyte. The aluminum foil was then heat-sealed at 150°C to seal the opening, completing the lithium-ion secondary battery. The internal resistance of this lithium-ion secondary battery was evaluated. The results are shown in Table 1.

[0132] Example 2 In preparing the slurry composition for a nonaqueous secondary battery negative electrode of Example 1, except that, instead of graphite (natural graphite), negative electrode active material 1 was used, which was a mixture of a silicon-containing alloy and artificial graphite in a mass ratio of silicon-containing alloy:artificial graphite = 50:50, a negative electrode binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were produced in the same manner as in Example 1. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0133] Example 3 In the preparation of the slurry composition for a non-aqueous secondary battery negative electrode of Example 1, silicon oxide (SiO) was used as the negative electrode active material instead of graphite (natural graphite). x and artificial graphite, x A negative electrode binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were produced in the same manner as in Example 1, except that a negative electrode active material 2 obtained by mixing the binder composition and the artificial graphite in a mass ratio of 30:70 was used. Evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

[0134] Example 4 A binder composition for a negative electrode, a slurry composition for a negative electrode, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were produced in the same manner as in Example 1, except that the amount of methacrylic acid added per 100 parts of the block polymer during graft polymerization and crosslinking in the preparation of the binder composition for a nonaqueous secondary battery negative electrode in Example 1 was changed from 16 parts to 10 parts. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0135] Example 5 Except for not performing microfiltration in the preparation of the binder composition for a non-aqueous secondary battery negative electrode in Example 1, a binder composition for a negative electrode, a slurry composition for a negative electrode, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were produced in the same manner as in Example 1. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0136] Example 6 A negative electrode binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were produced in the same manner as in Example 1, except that the amount of 3-mercapto-1,2-propanediol added as a water-soluble chain transfer agent during graft polymerization and crosslinking in the preparation of the nonaqueous secondary battery negative electrode binder composition of Example 1 was changed from 1.0 part to 0.4 part. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0137] Example 7 A binder composition for a negative electrode, a slurry composition for a negative electrode, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were produced in the same manner as in Example 1, except that the amount of 3-mercapto-1,2-propanediol added as a water-soluble chain transfer agent during graft polymerization and crosslinking in the preparation of the binder composition for a nonaqueous secondary battery negative electrode in Example 1 was changed from 1.0 part to 2.0 parts. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0138] Example 8 A negative electrode binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were prepared in the same manner as in Example 1, except that the water-soluble chain transfer agent added during graft polymerization and crosslinking in the preparation of the nonaqueous secondary battery negative electrode binder composition of Example 1 was changed to 1.0 part thioglycolic acid instead of 1.0 part 3-mercapto-1,2-propanediol. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0139] Example 9 A negative electrode binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were prepared in the same manner as in Example 1, except that the water-soluble chain transfer agent added during graft polymerization and crosslinking in the preparation of the nonaqueous secondary battery negative electrode binder composition of Example 1 was changed to 1.0 part of 3-mercaptopropionic acid instead of 1.0 part of 3-mercapto-1,2-propanediol. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0140] Example 10 A binder composition for a negative electrode, a slurry composition for a negative electrode, a negative electrode, a positive electrode, a separator, and a lithium ion secondary battery were produced in the same manner as in Example 1, except that during microfiltration in the preparation of the binder composition for a nonaqueous secondary battery negative electrode of Example 1, 5% aqueous ammonia was used instead of 5% aqueous sodium hydroxide, and the diluted aqueous dispersion of the particulate polymer was adjusted to pH 8.0. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0141] (Comparative Example 1) An attempt was made to obtain an aqueous dispersion of particulate polymer by the same procedure as in Example 1, except that 1.0 part of 3-mercapto-1,2-propanediol as a water-soluble chain transfer agent was not added during the graft polymerization and crosslinking steps in the preparation of the binder composition for a nonaqueous secondary battery negative electrode in Example 1. However, the mixture began to thicken during the graft polymerization and ultimately solidified into a pudding-like solid in the reaction vessel, making it impossible to obtain an aqueous dispersion of particulate polymer. Since a sample could not be obtained as a flowing liquid, subsequent microfiltration could not be performed. Therefore, the pudding-like solid was used as the binder composition for a negative electrode, and the weight-average molecular weight of the acidic group-containing water-soluble polymer was measured. The results are shown in Table 1. Since the negative electrode binder composition obtained above did not flow, it was not possible to measure the acid amount of the binder composition, the acid content of the particulate polymer in the binder composition, and the viscosity of the binder composition by conductometric titration. Furthermore, since the negative electrode binder composition obtained above did not flow, it was not possible to prepare a negative electrode slurry composition, a negative electrode, or a secondary battery, and various evaluations could not be carried out.

[0142] (Comparative Example 2) In the preparation of the binder composition for a non-aqueous secondary battery negative electrode in Example 1, the amount of styrene added during the preparation of the cyclohexane solution of the block polymer was changed from 31.0 kg to 25.0 kg, 75.0 kg of isoprene was added instead of 69.0 kg of 1,3-butadiene, the amount of methacrylic acid added during the graft polymerization and crosslinking was changed from 16 parts to 20 parts, 1.0 part of 3-mercapto-1,2-propanediol was not added as a water-soluble chain transfer agent, microfiltration was not performed, and the resulting aqueous dispersion of the particulate polymer was added with a 5% aqueous sodium hydroxide solution to adjust the pH to 8.0 and the solids concentration was adjusted to 40% for use as the binder composition for a negative electrode. The negative electrode binder composition, negative electrode slurry composition, negative electrode, positive electrode, separator, and lithium ion secondary battery were prepared in the same manner as in Example 1. Evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0143] In addition, in Table 1, "ST" indicates styrene, "BD" indicates 1,3-butadiene; "IP" indicates isoprene; "MAA" indicates methacrylic acid, "MPD" indicates "3-mercapto-1,2-propanediol" "TGA" stands for "thioglycolic acid" "MPA" stands for "3-mercaptopropionic acid" "NaOH" stands for "sodium hydroxide" "NH3" stands for "ammonia."

[0144] [Table 1]

[0145] From Table 1, it can be seen that by using the binder compositions for negative electrodes of Examples 1 to 10 containing a particulate polymer made of a predetermined graft polymer and an acidic group-containing water-soluble polymer having a weight average molecular weight of a predetermined value or less, a negative electrode having excellent moisture resistance can be obtained. On the other hand, when the binder composition for a negative electrode of Comparative Example 2 in which the molecular weight of the acidic group-containing water-soluble polymer exceeded a predetermined value was used, the formed negative electrode was found to have poor moisture resistance. The negative electrode binder composition of Comparative Example 1, in which the molecular weight of the acidic group-containing water-soluble polymer significantly exceeded the predetermined value, solidified into a pudding-like solid and did not flow, so that it was not possible to prepare a negative electrode slurry composition, and as a result, it was not possible to form a negative electrode. [Industrial Applicability]

[0146] According to the present invention, it is possible to provide a binder composition for a non-aqueous secondary battery that can form an electrode for a non-aqueous secondary battery that has excellent moisture resistance. Furthermore, according to the present invention, it is possible to provide a slurry composition for a non-aqueous secondary battery electrode that can form a non-aqueous secondary battery electrode having excellent moisture resistance. Furthermore, according to the present invention, it is possible to provide an electrode for a non-aqueous secondary battery having excellent moisture resistance, and a non-aqueous secondary battery including the electrode for a non-aqueous secondary battery.

Claims

1. a particulate polymer comprising a graft polymer having an acidic graft chain, which is obtained by graft polymerization of an acidic group-containing monomer and / or a macromonomer onto a core particle comprising a block copolymer containing an aromatic vinyl block region composed of an aromatic vinyl monomer unit and an aliphatic conjugated diene block region composed of an aliphatic conjugated diene monomer unit; an acidic group-containing water-soluble polymer having a weight average molecular weight of 20,000 or more and 85,000 or less; Including, the acidic group-containing water-soluble polymer is a by-product of the graft polymerization reaction, a viscosity of 3000 mPa s or less at a solids concentration of 40% by mass and a pH of 8.0; A binder composition for a non-aqueous secondary battery, having an acid amount measured by conductometric titration of 0.20 mmol / g or more and 1.80 mmol / g or less.

2. The binder composition for a nonaqueous secondary battery according to claim 1 , which has a pH of 6.0 or more and 10.0 or less.

3. A method for producing the binder composition for a non-aqueous secondary battery according to claim 1 or 2, a step of graft polymerization reaction of the acidic group-containing monomer and / or macromonomer with the core particles in the presence of a water-soluble chain transfer agent to obtain a dispersion of the particulate polymer.

4. The method for producing a binder composition for a non-aqueous secondary battery according to claim 3 , further comprising a step of purifying the dispersion of the particulate polymer.

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

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

7. A non-aqueous secondary battery comprising the electrode for a non-aqueous secondary battery according to claim 6.

Images