Binders for secondary battery electrodes and their applications

Abstract

The present invention provides a secondary battery electrode binder that exhibits superior binding capacity as compared to conventional binders and that makes it possible to reduce slurry viscosity, even when the solid concentration of an electrode slurry is high.　A secondary battery electrode binder according to the present invention contains a block polymer having a polymer block (A) and a polymer block (B), wherein: the polymer block (A) includes a structural unit derived from an ethylenically unsaturated carboxylic acid monomer; the content of a structural unit derived from an ethylenically unsaturated carboxylic acid monomer in the polymer block (B) is less than 30 mass% (and is different from that in the polymer block (A)) relative to all structural units of the polymer block (B); the ratio of the polymer block (A) in the block polymer is 10-90 mass%; and the block polymer does not contain a structural unit derived from a crosslinkable monomer.

Description

[Technical Field]

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

[0002] Various energy storage devices such as nickel-metal hydride batteries, lithium-ion batteries, and electric double-layer capacitors have been put into practical use as secondary batteries. The electrodes used in these secondary batteries are manufactured by coating and drying a composition for forming an electrode mixture layer containing an active material and a binder onto a current collector. For example, in lithium-ion batteries, an aqueous binder containing styrene-butadiene rubber (SBR) latex and carboxymethylcellulose (CMC) is used as the binder for the negative electrode mixture layer composition. In addition, binders containing aqueous solutions or aqueous dispersions of acrylic acid polymers are known to have excellent dispersibility and binding properties. On the other hand, an N-methyl-2-pyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) is widely used as the binder for the positive electrode mixture layer.

[0003] In recent years, as the applications of various secondary batteries have expanded, there has been a growing demand for improved energy density, reliability, and durability. For example, to increase the electrical capacity of lithium-ion secondary batteries, there is an increasing trend towards using silicon-based active materials as the negative electrode active material. However, silicon-based active materials are known to undergo large volume changes during charging and discharging, and repeated use can lead to peeling or detachment of the electrode mixture layer, resulting in a decrease in battery capacity and deterioration of cycle characteristics (durability). To suppress such problems, it is generally effective to improve the binding properties of the binder, and research is being conducted on improving the binding properties of the binder in order to improve durability.

[0004] A binder utilizing the above-mentioned acrylic acid polymer has been proposed as a binder that exhibits good binding properties and is effective in improving durability.

[0005] Patent Document 1 describes that by using a polymer crosslinked with a specific crosslinking agent to form polyacrylic acid as a binder, it is possible to provide an electrode in which the electrode structure is not destroyed even when an active material containing silicon is used. Patent Document 2 describes a binder for lithium batteries consisting of a polymer that contains monomer units derived from acrylic acid as a component and is crosslinked with a specific crosslinking agent, and describes that it exhibits a high capacity retention rate even after repeated charging and discharging.

[0006] Furthermore, Patent Document 3, which also aims to improve performance such as binding properties, discloses a binder that utilizes block polymers, which includes a block copolymer having a segment containing a vinyl monomer structural unit having an acid component, and a segment containing an alkyl (meth)acrylate monomer structural unit. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2014 / 065407 [Patent Document 2] International Publication No. 2015 / 163302 [Patent Document 3] Japanese Patent Publication No. 2012-204303 [Overview of the project] [Problems that the invention aims to solve]

[0008] The binders disclosed in Patent Documents 1 to 3 can all provide good binding properties, but with the improvement of secondary battery performance, there is a growing demand for binders with even higher binding strength. In general, secondary battery electrodes are obtained by coating an electrode mixture layer composition (hereinafter also referred to as "electrode slurry") containing an active material, binder, and medium onto the surface of an electrode current collector and then removing the medium. In this case, it is advantageous to increase the solid content concentration of the electrode slurry in order to improve the drying efficiency of the electrode slurry and improve the productivity of electrodes.

[0009] However, as the solid content concentration of the electrode slurry increases, the slurry viscosity also increases, making it difficult to ensure good coating properties.

[0010] The present invention has been made in view of these circumstances, and provides a binder for secondary battery electrodes that exhibits superior binding properties compared to conventional binders and can reduce slurry viscosity even when the solid content concentration of the electrode slurry is high. In addition, the present invention also provides a composition for a secondary battery electrode mixture layer and a secondary battery electrode obtained using the above binder. [Means for solving the problem]

[0011] As a result of diligent research to solve the above problems, the present inventors have found that a binder for secondary battery electrodes containing a "block polymer having a polymer block (A) containing structural units derived from ethylenically unsaturated carboxylic acid monomers and a polymer block (B) having a content of the same structural units below a specific amount, and in which the proportion of polymer block (A) is within a specific range," can reduce the slurry viscosity even when the solid content concentration of the electrode slurry is high, and can exhibit superior binding properties compared to conventional binders, thus completing the present invention.

[0012] The present invention is as follows: 〔1〕A secondary battery electrode binder containing a block polymer having a polymer block (A) and a polymer block (B), wherein the polymer block (A) contains a structural unit derived from an ethylenically unsaturated carboxylic acid monomer, and the polymer block (B) has a content of a structural unit derived from an ethylenically unsaturated carboxylic acid monomer based on all the structural units of the polymer block (B) of less than 30% by mass (however, it is different from the polymer block (A)), the proportion of the polymer block (A) in the block polymer is 10% by mass or more and 90% by mass or less, and the block polymer does not contain a structural unit derived from a crosslinkable monomer. A secondary battery electrode binder. 〔2〕The secondary battery electrode binder according to 〔1〕, wherein the polymer block (A) contains 50% by mass or more of a structural unit derived from an ethylenically unsaturated carboxylic acid monomer with respect to all its structural units. 〔3〕The secondary battery electrode binder according to 〔1〕 or 〔2〕, wherein the polymer block (B) contains a structural unit derived from a (meth)acrylate monomer. 〔4〕The secondary battery electrode binder according to any one of 〔1〕 to 〔3〕, wherein the polymer block (B) contains 50% by mass or more of a structural unit derived from an ethylenically unsaturated monomer (excluding monomers classified as ethylenically unsaturated carboxylic acid monomers; hereinafter also referred to as "monomer (b1)") having a solubility in 100 g of water at 20 °C of 20 g or less with respect to all its structural units. 〔5〕The secondary battery electrode binder according to any one of 〔1〕 to 〔4〕, wherein the block polymer further has a polymer block (C) (however, it is different from the polymer block (A) and the polymer block (B)). 〔6〕The secondary battery electrode binder according to 〔5〕, wherein the polymer block (C) contains 50% by mass or more of a structural unit derived from an ethylenically unsaturated monomer (excluding ethylenically unsaturated carboxylic acid monomers and monomers classified as the monomer (b1)) having a solubility in 100 g of water at 20 °C of 1.0 g or less with respect to all its structural units. 〔7〕The binder for a secondary battery electrode according to any one of 〔1〕to 〔6〕, wherein 80 mol% or more of the carboxyl groups of the block polymer are neutralized salts. 〔8〕The binder for a secondary battery electrode according to any one of 〔1〕to 〔7〕, wherein the number average molecular weight of the block polymer is 50,000 or more in terms of the number average molecular weight of the methyl esterified product of the carboxyl group contained in the block polymer in terms of polystyrene. 〔9〕A composition for a secondary battery electrode binder layer containing the binder for a secondary battery electrode according to any one of 〔1〕to 〔8〕, an active material, and water. 〔10〕A secondary battery electrode provided with a binder layer formed from the composition for a secondary battery electrode binder layer according to 〔9〕on the surface of a current collector. 〔11〕A method for producing a block polymer used as a binder for a secondary battery electrode, The block polymer has a polymer block (A) and a polymer block (B), A step of producing the polymer block (A) by polymerizing a monomer component containing an ethylenically unsaturated carboxylic acid monomer by a living radical polymerization method, A step of producing the polymer block (B) (however, different from the polymer block (A)) by polymerizing a monomer component in which the content of the ethylenically unsaturated carboxylic acid monomer is less than 30% by mass in the presence of the polymer block (A), and has, The ratio of the polymer block (A) in the block polymer is 10% by mass or more and 90% by mass or less, and the block polymer does not contain a structural unit derived from a crosslinkable monomer. 〔12〕The method for producing a block polymer according to 〔11〕, wherein the living radical polymerization method is a reversible addition-fragmentation chain transfer polymerization method (RAFT method). 〔13〕The method for producing a block polymer according to 〔11〕or 〔12〕, wherein the polymerization is aqueous solution polymerization.

Advantages of the Invention

[0013] According to the binder for secondary battery electrodes of the present invention, even when the solid content concentration of the electrode slurry is high, the slurry viscosity can be reduced, and superior binding properties can be achieved compared to conventional methods. [Modes for carrying out the invention]

[0014] The binder for secondary battery electrodes of the present invention contains a block polymer and can be mixed with an active material and water to form a composition for a secondary battery electrode mixture layer (hereinafter also referred to as "this composition"). The above composition may be in a slurry state that can be applied to a current collector, or it may be prepared in a wet powder state to accommodate press processing on the surface of the current collector. By forming a mixture layer formed from the above composition on the surface of a current collector such as copper foil or aluminum foil, the secondary battery electrode of the present invention can be obtained.

[0015] The binder for secondary battery electrodes, the composition for secondary battery electrode mixture layer obtained using the binder, the secondary battery electrode, and the secondary battery of the present invention will be described in detail below.

[0016] In this specification, "(meth)acrylic" means acrylic and / or methacrylic, and "(meth)acrylate" means acrylate and / or methacrylate. Also, "(meth)acryloyl group" means acryloyl group and / or methacryloyl group. 1. Binder The binder for secondary battery electrodes of the present invention comprises a block polymer (hereinafter also referred to as "this block polymer"). This block polymer has polymer blocks (A) containing structural units derived from ethylenically unsaturated carboxylic acid monomers, and polymer blocks (B) having a content of structural units derived from ethylenically unsaturated carboxylic acid monomers of less than 30% by mass. The proportion of polymer block (A) in this block polymer is 10% by mass or more and 90% by mass or less. This block polymer does not contain structural units derived from crosslinkable monomers.

[0017] Here, the above-mentioned crosslinkable monomers include polyfunctional polymerizable monomers having two or more polymerizable unsaturated groups, and monomers having self-crosslinkable functional groups such as hydrolyzable silyl groups. The following provides a detailed description of this block polymer.

[0018] <Polymer block (A)> Polymer block (A) is a polymer block containing structural units derived from ethylenically unsaturated carboxylic acid monomers, and can be obtained, for example, by polymerizing a monomer composition containing ethylenically unsaturated carboxylic acid monomers. Because this block polymer has carboxyl groups due to the presence of these structural units, its adhesion to the current collector is improved, and it exhibits excellent lithium ion desolvation effect and ionic conductivity, resulting in an electrode with low resistance and excellent high-rate characteristics.

[0019] Examples of ethylenically unsaturated carboxylic acid monomers include (meth)acrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid; (meth)acrylamide alkyl carboxylic acids such as (meth)acrylamidehexanoic acid and (meth)acrylamidedodecanoic acid; ethylenically unsaturated monomers having carboxyl groups such as monohydroxyethyl (meth)acrylate succinate, ω-carboxy-caprolactone mono(meth)acrylate, and β-carboxyethyl (meth)acrylate, or their (partially) alkali neutralized products. One of these may be used alone, or two or more may be used in combination. Among the above, compounds having an acryloyl group as a polymerizable functional group are preferred because they yield polymers with long primary chain lengths due to their high polymerization rate and good binder binding strength, and acrylic acid is particularly preferred. When acrylic acid is used as the ethylenically unsaturated carboxylic acid monomer, polymers with a high carboxyl group content can be obtained.

[0020] The polymer block (A) is not particularly limited in its content of structural units derived from ethylenically unsaturated carboxylic acid monomers based on all structural units of the polymer block (A), but for example, it is 50% by mass or more, for example 60% by mass or more, for example 70% by mass or more, for example 80% by mass or more, and for example 90% by mass or more.

[0021] By including structural units derived from ethylenically unsaturated carboxylic acid monomers within this range, excellent adhesion to the current collector can be easily ensured. When the lower limit of structural units derived from (meth)acrylic acid is 50% by mass or more, the dispersion stability of the composition is improved, and a higher bonding strength is obtained, which is more preferable.

[0022] Furthermore, there are no particular restrictions on structural units derived from monomers other than ethylenically unsaturated carboxylic acid monomers (hereinafter also referred to as "monomer (a)").

[0023] Examples of monomer (a) include aromatic vinyl monomers, maleimide compounds, (meth)acrylic acid ester monomers, (meth)acrylamide and its derivatives, and nitrile group-containing ethylenically unsaturated monomers. The amount of each monomer used is, for example, 50% by mass or less, 40% by mass or more, 30% by mass or more, 20% by mass or more, or 10% by mass or more, relative to the total amount of monomers constituting the polymer block (A).

[0024] Examples of aromatic vinyl monomers include styrene, α-methylstyrene, vinylnaphthalene, and isopropenylnaphthalene. One of these may be used alone, or two or more may be used in combination.

[0025] Maleimide compounds include maleimides and N-substituted maleimide compounds. Examples of N-substituted maleimide compounds include N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, N-isopropylmaleimide, Nn-butylmaleimide, N-isobutylmaleimide, N-tert-butylmaleimide, N-pentylmaleimide, N-hexylmaleimide, N-heptylmaleimide, N-octylmaleimide, N-laurylmaleimide, N-stearylmaleimide, and other N-alkyl-substituted maleimide compounds; N-cyclopentylmaleimide, N-cyclohexylmaleimide, and others. Examples include N-cycloalkyl-substituted maleimide compounds such as xylmaleimide; and N-aryl-substituted maleimide compounds such as N-phenylmaleimide, N-(4-hydroxyphenyl)maleimide, N-(4-acetylphenyl)maleimide, N-(4-methoxyphenyl)maleimide, N-(4-ethoxyphenyl)maleimide, N-(4-chlorophenyl)maleimide, N-(4-bromophenyl)maleimide, and N-benzylmaleimide. One or more of these can be used.

[0026] Examples of (meth)acrylic acid monomers include alkyl (meth)acrylic acid compounds such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; Aromatic (meth)acrylic acid ester compounds such as phenyl (meth)acrylate, phenylmethyl (meth)acrylate, phenylethyl (meth)acrylate, and phenoxyethyl (meth)acrylate; Alkoxyalkyl ester compounds of (meth)acrylates such as 2-methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; Examples include hydroxyalkyl ester compounds of (meth)acrylate such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate. One of these may be used alone, or two or more may be used in combination.

[0027] Examples of (meth)acrylamide derivatives include N-alkyl(meth)acrylamide compounds such as isopropyl(meth)acrylamide and t-butyl(meth)acrylamide; N-alkoxyalkyl(meth)acrylamide compounds such as Nn-butoxymethyl(meth)acrylamide and N-isobutoxymethyl(meth)acrylamide; N,N-dialkyl(meth)acrylamide compounds such as dimethyl(meth)acrylamide and diethyl(meth)acrylamide; and cyclic(meth)acrylamide compounds such as 4-acryloylmorpholine. One of these may be used alone, or two or more may be used in combination.

[0028] Examples of nitrile group-containing ethylenically unsaturated monomers include (meth)acrolinitrile; cyanoalkyl (meth)acrylate compounds such as cyanomethyl (meth)acrylate and cyanoethyl (meth)acrylate; cyano group-containing unsaturated aromatic compounds such as 4-cyanostyrene and 4-cyano-α-methylstyrene; and vinylidene cyanide. One of these may be used alone, or two or more may be used in combination.

[0029] The number-average molecular weight (Mn) of the polymer block (A) is not particularly limited, but is preferably in the range of 1,000 to 1,000,000. If the number-average molecular weight is 1,000 or more, it can exhibit high cohesive force as a binder and contribute to improving the bonding properties of electrodes. If it is 1,000,000 or less, good fluidity can be ensured, which is preferable as it makes handling easier during manufacturing, etc. The number-average molecular weight of the block polymer (A) is preferably 5,000 or more, more preferably 8,000 or more, even more preferably 10,000 or more, and even more preferably 20,000 or more. The upper limit is preferably 800,000 or less, more preferably 600,000 or less, even more preferably 400,000 or less, even more preferably 200,000 or less, and even more preferably 100,000 or less.

[0030] Furthermore, the molecular weight distribution (Mw / Mn) obtained by dividing the weight-average molecular weight (Mw) of polymer block (A) by the number-average molecular weight (Mn) is preferably 3.0 or less from the viewpoint of binding properties. More preferably it is 2.5 or less, even more preferably 2.0 or less, still more preferably 1.5 or less, and even more preferably 1.3 or less. The lower limit of the molecular weight distribution (Mw / Mn) is usually 1.0.

[0031] Furthermore, the Mw and Mn of polymer block (A) can both be measured as the Mw and Mn of the methyl esterified carboxyl group (methyl esterification rate 100%) contained in polymer block (A) by gel permeation chromatography (GPC) using polystyrene as a standard substance. The details of the GPC measurement conditions can be those disclosed in the examples below.

[0032] The glass transition temperature (Tg) of the polymer block (A) is preferably 50°C or higher from the viewpoint of obtaining good binding properties. Tg may be, for example, 70°C or higher, 80°C or higher, 90°C or higher, or 100°C or higher. Due to limitations on the usable constituent monomer units, the upper limit of Tg is 350°C. Tg may be, for example, 300°C or lower, 280°C or lower, or 250°C or lower.

[0033] In this specification, the Tg of polymer block (A) can be obtained by analyzing the block polymer using differential scanning calorimetry (DSC). Here, the Tg of polymer block (A) is a value based on structural units, including the neutralized salt of the carboxyl group derived from the ethylenically unsaturated carboxylic acid monomer of polymer block (A).

[0034] Furthermore, if DSC measurement is not possible, the Tg can be calculated using FOX's formula from the Tg of each monomer homopolymer constituting the polymer block. The same applies to other polymer blocks such as polymer block (B) and polymer block (C) described later. <Polymer Block (B)> Polymer block (B) is a polymer block different from polymer block (A), and is a polymer block in which the content of structural units derived from ethylenically unsaturated carboxylic acid monomers based on its total structural units is less than 30% by mass. In order to obtain secondary battery electrodes with excellent binding properties, the content is preferably less than 25% by mass, more preferably less than 20% by mass, even more preferably less than 15% by mass, and even more preferably less than 10% by mass. Polymer block (B) can be obtained, for example, by polymerizing a monomer composition in which the content of ethylenically unsaturated carboxylic acid monomers is less than 30% by mass.

[0035] Furthermore, the structural units derived from the ethylenically unsaturated carboxylic acid monomers of polymer block (B) may consist of unreacted ethylenically unsaturated carboxylic acid monomers from the time of production of polymer block (A), and their content is less than 30% by mass, with the preferred amount being the same as described above.

[0036] Polymer block (B) is a relatively hydrophobic segment, and when this block polymer is used as a binder, it tends to adsorb easily onto surfaces such as carbon-based active materials. As a result, it becomes possible to firmly bond the active materials together, and a secondary battery electrode with excellent bonding properties can be obtained.

[0037] The monomers constituting polymer block (B) may include ethylenically unsaturated carboxylic acid monomers and / or other non-crosslinkable ethylenically unsaturated monomers copolymerizable therewith (hereinafter also referred to as "monomer (b)"). Monomer (b) can be the same monomers as monomer (a) described above as constituting polymer block (A), and one of these may be used alone or two or more may be used in combination.

[0038] The proportion of monomer (b) can be 70% by mass or more and 100% by mass or less relative to the total amount of non-crosslinkable monomers constituting the polymer block (B). The proportion of monomer (b) may be 75% by mass or more and 99% by mass or less, 80% by mass or more and 98% by mass or less, 85% by mass or more and 96% by mass or less, or 90% by mass or more and 95% by mass or less. The range of monomer (b) content can be a combination of these lower and upper limits as appropriate. Furthermore, when monomer (b) is contained in an amount of 70% by mass or more relative to the total amount of non-crosslinkable monomers, the affinity to the electrolyte is improved, and therefore, an effect of improved lithium ion conductivity can also be expected.

[0039] Examples of monomer (b) include (meth)acrylic acid ester monomers such as alkyl (meth)acrylate compounds, aromatic (meth)acrylate compounds, and alkoxyalkyl (meth)acrylate compounds, as well as styrenes and aliphatic conjugated diene monomers.

[0040] Among these, alkyl (meth)acrylate compounds and aromatic (meth)acrylate compounds are preferred in terms of their excellent binder flexibility, and alkyl (meth)acrylate compounds are even more preferred. Among alkyl (meth)acrylate compounds, compounds with a homopolymer glass transition temperature (Tg) of 20°C or lower are more preferred in that they can impart flexibility to the binder and maintain high binding properties even when the active material swells or shrinks during lithium ion storage.

[0041] Examples of alkyl (meth)acrylate compounds include aliphatic alkyl (meth)acrylates and alicyclic alkyl (meth)acrylates.

[0042] Examples of aliphatic alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Examples of alicyclic alkyl (meth)acrylates include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, cyclodecyl (meth)acrylate, cyclododecyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and dicyclopentanyl (meth)acrylate. One of these may be used alone, or two or more may be used in combination.

[0043] Examples of aromatic (meth)acrylic acid ester compounds include phenyl (meth)acrylate, phenylmethyl (meth)acrylate, phenylethyl (meth)acrylate, and phenoxyethyl (meth)acrylate. One of these may be used alone, or two or more may be used in combination.

[0044] Examples of (meth)acrylate alkoxyalkyl ester compounds include 2-methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, and one of these may be used alone or two or more may be used in combination.

[0045] Examples of styrenes include styrene, α-methylstyrene, β-methylstyrene, vinylxylene, vinylnaphthalene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o-ethylstyrene, m-ethylstyrene, p-ethylstyrene, pn-butylstyrene, p-isobutylstyrene, pt-butylstyrene, o-methoxystyrene, m-methoxystyrene, p-methoxystyrene, o-chloromethylstyrene, p-chloromethylstyrene, o-chlorostyrene, p-chlorostyrene, o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, divinylbenzene, etc. One of these may be used alone, or two or more may be used in combination.

[0046] Examples of aliphatic conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and 2-chloro-1,3-butadiene. One of these may be used alone, or two or more may be used in combination.

[0047] As monomer (b), compounds having an acryloyl group are preferred because they yield polymers with long primary chain lengths due to their rapid polymerization rate, resulting in good binder binding strength.

[0048] Furthermore, as monomer (b), (meth)acrylic acid ester monomers are preferred in terms of their excellent binder flexibility. Among (meth)acrylic acid ester monomers, polymer block (B) is preferably composed of structural units derived from ethylenically unsaturated monomers (excluding monomers classified as ethylenically unsaturated carboxylic acid monomers; hereinafter also referred to as "monomer (b1)") whose total structural units have a solubility of 20 g or less in 100 g of water at 20°C (hereinafter also simply referred to as "water solubility").

[0049] The proportion of monomers (b1) is not particularly limited, but is, for example, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, relative to the total structural units of polymer block (B).

[0050] By containing monomer (b1) within this range, the polymer block (B) becomes a relatively hydrophobic segment, and when this block polymer is used as a binder, it tends to adsorb easily onto surfaces such as carbon-based active materials. As a result, it becomes possible to firmly bond the active materials together, and a secondary battery electrode with excellent bonding properties can be obtained.

[0051] Here, the water solubility is preferably more than 1g, more preferably 2g or more, even more preferably 4g or more, even more preferably 8g or more, and even more preferably 10g or more.

[0052] The number-average molecular weight (Mn) of the polymer block (B) is not particularly limited, but is preferably in the range of 1,000 to 1,000,000. If the number-average molecular weight is 1,000 or more, it can be adsorbed onto the active material, contributing to improved electrode binding. If it is 1,000,000 or less, good fluidity can be ensured, which is preferable as it facilitates handling during manufacturing, etc. The number-average molecular weight of the block polymer (B) is preferably 5,000 or more, more preferably 8,000 or more, even more preferably 10,000 or more, and even more preferably 20,000 or more. The upper limit is preferably 800,000 or less, more preferably 600,000 or less, even more preferably 400,000 or less, even more preferably 200,000 or less, and even more preferably 100,000 or less.

[0053] The glass transition temperature (Tg) of the polymer block (B) is preferably -80°C or higher from the viewpoint of obtaining good binding properties. Tg may be, for example, -70°C or higher, -60°C or higher, -50°C or higher, -40°C or higher, -30°C or higher, or -20°C or higher. Due to limitations on the usable constituent monomer units, the upper limit of Tg is 350°C. Tg may be, for example, 300°C or lower, 200°C or lower, 150°C or lower, 150°C or lower, 100°C or lower, or 50°C or lower. <Polymer Block (C)> Polymer block (C) is a polymer block different from polymer block (A) and polymer block (B), and may contain structural units derived from an ethylenically unsaturated carboxylic acid monomer and / or a monomer similar to monomers (a) and monomer (b) described above (hereinafter also referred to as "monomer (c)"). Polymer block (C) can be obtained, for example, by polymerizing a monomer composition containing an ethylenically unsaturated carboxylic acid monomer and / or monomer (c), and one of monomer (c) may be used alone, or two or more may be used in combination.

[0054] Examples of monomer (c) include (meth)acrylic acid ester monomers such as alkyl (meth)acrylate compounds and aromatic (meth)acrylate compounds, styrenes, and aliphatic conjugated diene monomers.

[0055] Among these, alkyl (meth)acrylate compounds and aromatic (meth)acrylate compounds are preferred, and aromatic (meth)acrylate compounds are more preferred, due to their excellent adsorption properties to active materials.

[0056] In particular, in terms of excellent adsorption to active materials, it is preferable that the polymer block (C) contains structural units derived from an ethylenically unsaturated acid monomer (excluding ethylenically unsaturated carboxylic acid monomers and monomers classified as monomer (b1); hereinafter also referred to as "monomer (c1)") whose total structural units have a solubility of 1.0 g or less in 100 g of water at 20°C (water solubility).

[0057] Here, among the aromatic (meth)acrylic acid ester compounds mentioned above, those classified as monomers (c1), such as phenoxyethyl acrylate, phenolethylene oxide-modified (e.g., n=2) acrylate, and benzyl acrylate, are particularly preferred.

[0058] The proportion of monomers (c1) is not particularly limited, but is, for example, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, relative to the total structural units of the polymer block (C).

[0059] By containing monomer (c1) within this range, the polymer block (C) becomes a hydrophobic segment, and when this block polymer is used as a binder, it tends to adsorb easily onto surfaces such as carbon-based active materials. As a result, it becomes possible to firmly bond the active materials together, and a secondary battery electrode with excellent bonding properties can be obtained.

[0060] Here, the water solubility is preferably 0.8 g or less, more preferably 0.7 g or less, even more preferably 0.6 g or less, even more preferably 0.5 g or less, and even more preferably 0.4 g or less.

[0061] The number-average molecular weight (Mn) of the polymer block (C) is not particularly limited, but is preferably in the range of 1,000 to 1,000,000. If the number-average molecular weight is 1,000 or more, it can be adsorbed onto the active material, contributing to improved electrode binding. If it is 1,000,000 or less, good fluidity can be ensured, which is preferable as it facilitates handling during manufacturing, etc. The number-average molecular weight of the block polymer (C) is preferably 2,000 or more, more preferably 3,000 or more, and even more preferably 5,000 or more. The upper limit is preferably 500,000 or less, more preferably 300,000 or less, and even more preferably 100,000 or less.

[0062] The glass transition temperature (Tg) of the polymer block (C) is preferably -90°C or higher from the viewpoint of obtaining good binding properties. Tg may be, for example, -80°C or higher, -70°C or higher, -60°C or higher, -50°C or higher, -40°C or higher, or -30°C or higher. Due to limitations on the usable constituent monomer units, the upper limit of Tg is 350°C. Tg may be, for example, 300°C or lower, 250°C or lower, 200°C or lower, 150°C or lower, 100°C or lower, or 50°C or lower.

[0063] <This block polymerization> The block polymer only needs to have one or more polymer blocks (A) and polymer blocks (B). Examples include a (AB) diblock composed of polymer block (A) and polymer block (B), an (ABA) triblock composed of polymer block (A) / polymer block (B) / polymer block (A), or a (BAB) triblock. Furthermore, it may also have a structure such as (ABC) or (ABCA), which includes polymer block (C) other than polymer block (A) and polymer block (B).

[0064] In particular, the block polymer preferably has an ABC structure. This structure is advantageous because it provides both high binder cohesiveness and adsorption properties for active materials. The ABC structure only needs to be present in all or part of the copolymer; for example, a copolymer consisting of an ABCA structure may also be used. The block polymer may also be a mixture of two or more block polymers belonging to the above-mentioned diblock and triblock types. In addition to the block polymer, the polymer may also contain polymers consisting only of polymer block (A) or polymers consisting only of polymer block (B).

[0065] The proportion of polymer blocks (A) in this block polymer can be 10% by mass or more and 90% by mass or less, from the viewpoint of binding properties. The proportion of polymer blocks (A) may be 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, or 30% by mass or more. The proportion of polymer blocks (A) may be 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less.

[0066] On the other hand, the proportion of polymer blocks (B) in this block polymer can be 20% by mass or more and 80% by mass or less. Within this range, good binding properties can be achieved. The proportion of polymer blocks (B) may be 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, or 50% by mass or more. The proportion of polymer blocks (B) may be 90% by mass or less, 80% by mass or less, 75% by mass or less, 70% by mass or less, 65% by mass or less, 60% by mass or less, or 55% by mass or less.

[0067] In this block polymer, the proportion of the total amount of polymer block (A) and polymer block (B) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more. The proportion of the total amount of polymer block (A) and polymer block (B) may be 100% by mass.

[0068] The mass ratio of polymer block (A) to polymer block (B) in this block polymer is not particularly limited, but can be, for example, 0.1 to 80 / 20 to 99.9. Good binding properties can be achieved within this range. The mass ratio may also be, for example, 0.5 to 70 / 30 to 99.5, 1.0 to 50 / 50 to 99, 5.0 to 30 / 70 to 95, or 10 to 30 / 70 to 99.

[0069] The number-average molecular weight (Mn) of this block polymer is not particularly limited, but is preferably in the range of 10,000 to 10,000,000. If the number-average molecular weight is 10,000 or more, it can exhibit sufficient performance as a binder. Furthermore, if it is 10,000,000 or less, good fluidity can be ensured, which is preferable as it facilitates handling during manufacturing, etc. The number-average molecular weight of this block polymer is preferably 20,000 or more, more preferably 30,000 or more, even more preferably 50,000 or more, even more preferably 75,000 or more, and even more preferably 100,000 or more. Furthermore, the upper limit is preferably 5,000,000 or less, more preferably 3,000,000 or less, even more preferably 1,000,000 or less, even more preferably 500,000 or less, and even more preferably 300,000 or less.

[0070] The molecular weight distribution (Mw / Mn) obtained by dividing the weight-average molecular weight (Mw) of this block polymer by the number-average molecular weight (Mn) is preferably 3.0 or less from the viewpoint of binding properties. More preferably it is 2.5 or less, even more preferably 2.0 or less, still more preferably 1.5 or less, and even more preferably 1.3 or less. The lower limit of the molecular weight distribution (Mw / Mn) is usually 1.0.

[0071] Furthermore, the Mw and Mn of this block polymer can both be measured as the Mw and Mn of the methyl esterified carboxyl group contained in this block polymer (methyl esterification rate is 100%) by gel permeation chromatography (GPC) using polystyrene as a standard substance. The detailed GPC measurement conditions can be those disclosed in the examples below.

[0072] In this composition, the block polymer is preferably used in the form of a salt, with the acidic groups such as carboxyl groups derived from the ethylenically unsaturated carboxylic acid monomer neutralized to a degree of neutralization of 50 mol% or more. The degree of neutralization is more preferably 60 mol% or more, even more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 85 mol% or more, and particularly preferably 90 mol% or more. The upper limit of the degree of neutralization is 100 mol%, but it may also be 98 mol% or less, or 95 mol% or less. The range of the degree of neutralization can be appropriately combined from the lower and upper limits above, for example, it may be 50 mol% or more and 100 mol% or less, 70 mol% or more and 100 mol% or less, or 80 mol% or more and 100 mol% or less. A degree of neutralization of 50 mol% or more is preferable because it results in good solubility in water and makes it easier to obtain good slurry coating properties. Furthermore, if the degree of neutralization is 80 mol% or higher, the viscosity of the composition (electrode slurry) containing the active material is greatly reduced. This is preferable because it allows for the acquisition of electrodes with a smooth surface. In addition, since the concentration of the composition can be increased, the amount of solvent to be removed by drying can be reduced, which is also preferable from the viewpoint of productivity.

[0073] In this specification, the degree of neutralization can be calculated from the input values ​​of monomers having acidic groups such as carboxyl groups and the neutralizing agent used for neutralization. The degree of neutralization can be confirmed by IR measurement of the powder obtained by drying the crosslinked polymer or its salt at 80°C for 3 hours under reduced pressure, and by the intensity ratio of the peak derived from the C=O group of the carboxylic acid and the peak derived from the C=O group of the carboxylate salt.

[0074] The type of salt used in this block polymer is not particularly limited, but examples include alkali metal salts such as lithium, sodium, and potassium; alkaline earth metal salts such as magnesium salts, calcium salts, and barium salts; other metal salts such as aluminum salts; ammonium salts and organic amine salts. Among these, alkali metal salts and alkaline earth metal salts are preferred because they do not adversely affect battery characteristics, alkali metal salts are more preferred, and lithium salts and potassium salts are even more preferred. <Method for producing this block polymer> The block polymer is not particularly limited as long as it is obtained as a block polymer having polymer block (A) and polymer block (B), and known manufacturing methods can be employed. For example, methods using various controlled polymerization methods such as living radical polymerization and living anionic polymerization, or methods of coupling polymers having functional groups can be used. In addition, for example, a method is included in which a macromonomer having polymer block (A) is copolymerized with a monomer constituting polymer block (B) to obtain a polymer having a structural unit consisting of polymer block (A) / polymer block (B) / the polymer block (A) in the molecule. Among these, living radical polymerization is preferred from the viewpoint of being easy to operate and applicable to a wide range of monomers.

[0075] Living radical polymerization can employ any of the following processes: batch process, semi-batch process, tubular continuous polymerization process, or continuous stirred tank process (CSTR). Furthermore, the polymerization method can be applied to various forms, including solvent-free bulk polymerization, solvent-based solution polymerization, aqueous emulsion polymerization, miniemulsion polymerization, or suspension polymerization. Among these, aqueous solution polymerization is preferred due to its controllability, ease of implementation, and the ability to obtain block polymers with excellent binding properties.

[0076] There are no particular restrictions on the type of living radical polymerization method, and various polymerization methods can be employed, such as reversible addition-cleavage chain transfer polymerization (RAFT), nitroxy radical polymerization (NMP), atom transfer radical polymerization (ATRP), polymerization using organotellurium compounds (TERP), polymerization using organoantimony compounds (SBRP), polymerization using organobismuth compounds (BIRP), and iodine transfer polymerization. Among these, the RAFT method is preferred because it offers excellent controllability of polymerization, ease of implementation, and the ability to obtain block polymers with superior binding properties.

[0077] In the RAFT method, polymerization proceeds via a reversible chain transfer reaction in the presence of a polymerization control agent (RAFT agent) and a free radical polymerization initiator. Examples of RAFT agents include dithioester compounds represented by formula (1) or their salts, trithiocarbonate compounds represented by formula (2) or their salts, dithiocarbamate compounds represented by formula (3) or their salts, and xanthate compounds represented by formula (4) or their salts. The RAFT agent may be monofunctional, having only one active site, or it may be bifunctional or multifunctional.

[0078] Furthermore, the amount of RAFT agent used is adjusted as appropriate depending on the monomer and type of RAFT agent used.

[0079] [ka] (In the formula, R 1 ~R 9represents an alkyl group which may have a substituent, an aryl group which may have a substituent, a heteroaryl group which may have a substituent, or an aralkyl group which may have a substituent, and R 6 and R 7 may be bonded to each other to form a ring together with adjacent nitrogen atoms, and the ring may have a substituent.) R 1 ~R 9 Examples of the "alkyl group" of the alkyl group which may have a substituent represented by R 1 ~R 9 include a linear or branched alkyl group having 1 to 16 carbon atoms (preferably 1 to 12 carbon atoms, more preferably 1 to 6 carbon atoms, particularly preferably 1 to 4 carbon atoms). Specifically, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, etc. may be mentioned. When the alkyl group has a substituent, examples of the substituent include a carboxyl group, an ester group (such as an alkoxycarbonyl group), a cyano group, a hydroxyl group, an alkoxy group, etc. The alkyl group may have 1 to 4 substituents selected from these substituents. R 1 ~R 9 Examples of the "aryl group" of the aryl group which may have a substituent represented by R 1 ~R 9 include a monocyclic or bicyclic aryl group. Specifically, a phenyl group, a toluyl group, a xylyl group, a naphthyl group, etc. may be mentioned. When the aryl group has a substituent, examples of the substituent include a carboxyl group, an ester group (such as an alkoxycarbonyl group), a cyano group, a hydroxyl group, an alkoxy group, a halogen atom, etc. The aryl group may have 1 to 5 substituents selected from these substituents.

[0080] R 1 ~R 9Examples of a heteroaryl group that may have substituents as shown include monocyclic or bicyclic heteroaryl groups containing at least one heteroatom selected from the group consisting of oxygen, nitrogen, and sulfur atoms as a ring constituent atom. Specifically, examples include pyridyl groups, pyrimidinyl groups, and pyrazinyl groups. If the heteroaryl group has substituents, examples of substituents include carboxyl groups, ester groups (alkoxycarbonyl groups, etc.), cyano groups, hydroxyl groups, alkoxy groups, halogen atoms, etc. The heteroaryl group may have 1 to 4 substituents selected from these substituents.

[0081] R 1 ~R 9 The term "aralkyl group" in the aralkyl group which may have substituents as shown by means of an alkyl group substituted with an aryl group, such as a benzyl group or a phenethyl group. If the aralkyl group has substituents, such substituents may include, for example, a carboxyl group, an ester group (such as an alkoxycarbonyl group), a cyano group, a hydroxyl group, an alkoxy group, or a halogen atom. The aryl group in the aralkyl group may have 1 to 5 substituents selected from these substituents.

[0082] Furthermore, R represented by equation (3) 6 and R 7 These atoms may be bonded to each other to form a ring with adjacent nitrogen atoms, and the ring may have substituents. Examples of such rings include pyrrolidine rings, piperidine rings, and morpholine rings. If the ring has substituents, examples of such substituents include alkyl groups and oxo groups (=O). The ring may have 1 to 3 substituents selected from these substituents. Here, as the RAFT agent in aqueous solution polymerization, a water-soluble RAFT agent is preferred, and examples include compounds and / or salts thereof having a thiocarbonylthio group (-CS-S-) and a hydrophilic group (e.g., a carboxyl group) in the molecule.

[0083] Examples of salts of compounds represented by formulas (1) to (4) include alkali metal salts (sodium salts, potassium salts, etc.) and ammonium salts when the compound has an acidic group, and organic salts of carboxylates (acetate salts, etc.) and sulfonates (p-toluenesulfonate, etc.) when the compound has a basic group.

[0084] Of the above RAFT agents, the compound represented by formula (2) or a salt thereof is preferred. 3 and R 4 The alkyl groups are the same or different and may have substituents. Preferably, they are alkyl groups having 1 to 12 carbon atoms (more preferably 1 to 6 carbon atoms) and may have at least one (particularly 1 to 3) substituents selected from the group consisting of carboxyl groups, ester groups (such as alkoxycarbonyl groups), cyano groups, hydroxyl groups, and alkoxy groups. Particularly preferred are alkyl groups having 1 to 4 carbon atoms and may have one carboxyl group.

[0085] Examples of compounds represented by formula (2) include formula (2A): (wherein R 3A and R 4A This refers to an alkylene group having 1 to 6 carbon atoms (particularly 1 to 4 carbon atoms) which may have at least one (particularly 1 to 3) substituents selected from the group consisting of ester groups (such as alkoxycarbonyl groups), cyano groups, hydroxyl groups, and alkoxy groups, either identical or different. 3A and R 4A The alkylene group having 1 to 3 carbon atoms is preferred, and examples include 2-{[(2-carboxyethyl)sulfanylthiocarbonyl]sulfanyl}propanoic acid and 4-[(2-carboxyethylsulfanylthiocarbonyl)sulfanyl]-4-cyanopentanoic acid. [ka]

[0086] As polymerization initiators used in polymerization by the RAFT method, known radical polymerization initiators such as azo compounds, organic peroxides, and persulfates can be used, but azo compounds are preferred because they are easy to handle safely and less likely to cause side reactions during radical polymerization. Examples of the above azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), dimethyl-2,2'-azobis(2-methylpropionate), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitride), 2,2'-azobis[N-(2-propenyl)-2-methylpropionamide], and 2,2'-azobis(N- Examples include 2-methylpropionamide, 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis[2-(2-imidazolin-2-yl)propane], 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis[2-(-imidazolin-2-yl)propane] disulfate dihydrate, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] hydrate. The above radical polymerization initiators may be used individually or in combination of two or more.

[0087] Here, as the polymerization initiator in aqueous solution polymerization, a water-soluble polymerization initiator is preferred, for example, a compound having a hydrophilic group (e.g., a carboxyl group) and / or a salt or hydrate thereof, among which 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis[2-(-imidazolin-2-yl)propane] disulfate dihydrate, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] hydrate, etc. are preferred.

[0088] While there are no particular restrictions on the proportion of radical polymerization initiator used, it is preferable to use 0.5 mol or less of radical polymerization initiator per 1 mol of RAFT agent, and more preferably 0.2 mol or less, from the viewpoint of obtaining polymers with a smaller molecular weight distribution. Furthermore, from the viewpoint of stably carrying out the polymerization reaction, the lower limit of the amount of radical polymerization initiator used per 1 mol of RAFT agent is 0.001 mol. Therefore, the amount of radical polymerization initiator used per 1 mol of RAFT agent is preferably in the range of 0.001 mol to 0.5 mol, and more preferably in the range of 0.005 mol to 0.2 mol.

[0089] The reaction temperature during polymerization by the RAFT method is preferably 30°C to 120°C, more preferably 40°C to 110°C, and even more preferably 50°C to 100°C. A reaction temperature of 30°C or higher allows the polymerization reaction to proceed smoothly. On the other hand, a reaction temperature of 120°C or lower suppresses side reactions and relaxes restrictions on the initiators and solvents that can be used.

[0090] TERP polymerization is a method for polymerizing water-soluble vinyl monomers, typically in the presence of an organotellurium compound. For example, see Chemical Review, 2009, 109, pp. 5051-5068.

[0091] SBPR polymerization is a method for polymerizing water-soluble vinyl monomers, typically in the presence of an organic antimony compound. For example, see Chemical Review, 2009, 109, pp. 5051-5068.

[0092] BIRP polymerization is a method for polymerizing water-soluble vinyl monomers, typically in the presence of an organobismuth compound. For example, see Chemical Review, 2009, 109, pp. 5051-5068.

[0093] For information on iodine transfer polymerization, see, for example, Chemical Review, 2006, 106, pp. 3936-3962.

[0094] In this disclosure, known polymerization solvents can be used in living radical polymerization. Specifically, these include aromatic compounds such as benzene, toluene, xylene, and anisole; ester compounds such as methyl acetate, ethyl acetate, propyl acetate, and butyl acetate; ketone compounds such as acetone and methyl ethyl ketone; dimethylformamide, acetonitrile, dimethyl sulfoxide, alcohols, and water. Among these, water, which is used in aqueous polymerization, is preferred because it offers controllability of polymerization, ease of implementation, and the ability to obtain block polymers with excellent binding properties.

[0095] Polymer block (A) may be produced by carrying out a polymerization reaction in the presence of a basic compound. By carrying out the polymerization reaction in the presence of a basic compound, the polymerization reaction can be carried out stably even under high monomer concentration conditions. The monomer concentration may be 13.0% by mass or more, preferably 15.0% by mass or more, more preferably 17.0% by mass or more, even more preferably 19.0% by mass or more, and even more preferably 20.0% by mass or more. The monomer concentration is still preferably 22.0% by mass or more, and even more preferably 25.0% by mass or more. In general, the higher the monomer concentration during polymerization, the higher the molecular weight can be, and if the polymer is a crosslinked polymer, a polymer with a long primary chain length can be produced.

[0096] The upper limit of monomer concentration varies depending on the type of monomer and solvent used, as well as the polymerization method and various polymerization conditions. However, if the heat of polymerization reaction can be removed, it is generally around 50% for solution polymerization, around 50% for suspension polymerization, and around 70% for emulsion polymerization.

[0097] The above-mentioned base compound is a so-called alkaline compound, and either an inorganic or organic base compound may be used. By carrying out the polymerization reaction in the presence of the base compound, the polymerization reaction can be carried out stably even under high monomer concentration conditions, such as exceeding 13.0% by mass. Furthermore, polymers obtained by polymerization at such high monomer concentrations have excellent binding properties due to their high molecular weight (long primary chain length).

[0098] Examples of inorganic base compounds include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide, and alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide. One or more of these can be used.

[0099] Examples of organic base compounds include ammonia, as well as organic amine compounds such as monoethylamine, diethylamine, and triethylamine. One or more of these can be used. Among these, organic amine compounds are preferred from the viewpoint of polymerization stability and the binding properties of the resulting polymer or binder containing its salt.

[0100] In this specification, the amount of base compound used represents the molar concentration of the base compound used relative to the ethylenically unsaturated carboxylic acid monomer, and does not indicate the degree of neutralization. In other words, the valency of the base compound used is not considered.

[0101] The block polymer can be obtained in powder form by reducing the pressure and / or heating the reaction solution containing the block polymer and removing the solvent by distillation. In this case, it is preferable to perform a washing treatment using reprecipitation or the like immediately following the polymerization reaction in order to remove unreacted monomers (and their salts), impurities derived from the initiator, etc., before distilling off the solvent. When the above washing treatment is performed, the block polymer exhibits good performance in terms of binding properties and battery characteristics because any remaining unreacted monomers are removed.

[0102] In this manufacturing method, an alkaline compound may be added to the dispersion containing the block polymer obtained after the polymerization reaction to neutralize the block polymer (hereinafter also referred to as "process neutralization"), and then the solvent may be removed in the drying process. Alternatively, after obtaining the polymer powder without performing the above process neutralization treatment, an alkaline compound may be added when preparing the electrode slurry to neutralize the polymer (hereinafter also referred to as "post-neutralization"). Of the above, process neutralization is preferred because it tends to dissolve more easily in the electrode slurry. 2. Composition for secondary battery electrode mixture layer The secondary battery electrode composite layer composition of the present invention comprises a binder containing the block polymer, an active material, and water.

[0103] The amount of this block polymer used in this composition is, for example, 0.1 parts by mass or more and 20 parts by mass or less, per 100 parts by mass of the total amount of active material. The above amount can also be, for example, 0.2 parts by mass or more and 10 parts by mass or less, for example, 0.3 parts by mass or more and 8 parts by mass or less, or for example, 0.4 parts by mass or more and 5 parts by mass or less. If the amount of this block polymer used is less than 0.1 parts by mass, sufficient binding properties may not be obtained. In addition, the dispersion stability of the active material may be insufficient, and the uniformity of the resulting mixture layer may decrease. On the other hand, if the amount of this block polymer used exceeds 20 parts by mass, the composition may become highly viscous, and its coating properties on the current collector may decrease. As a result, bumps and irregularities may occur in the resulting mixture layer, which may adversely affect the electrode characteristics.

[0104] If the amount of this block polymer used is within the above range, a composition with excellent dispersion stability can be obtained, as well as a composite layer with extremely high adhesion to the current collector, resulting in improved battery durability. Furthermore, this block polymer exhibits sufficiently high binding properties even in small amounts (e.g., 5% by mass or less) relative to the active material, and because it contains carboxyanions, electrodes with low interfacial resistance and excellent high-rate characteristics can be obtained.

[0105] Of the above active materials, lithium salts of transition metal oxides can be used as the positive electrode active material. For example, layered rock salt type and spinel type lithium-containing metal oxides can be used. Specific compounds of the layered rock salt type positive electrode active material include lithium cobaltate, lithium nickelate, and NCM{Li(Ni}, which are called ternary systems. x Co y ,Mn z ), x+y+z=1} and NCA{Li(Ni 1-a-b Co a Al b Examples include )}. In addition, lithium manganate is an example of a spinel-type positive electrode active material. Besides oxides, phosphates, silicates, and sulfur can also be used, and examples of phosphates include olivine-type lithium iron phosphate. As a positive electrode active material, one of the above may be used alone, or two or more may be combined and used as a mixture or composite.

[0106] Furthermore, when a positive electrode active material containing layered rock salt-type lithium-containing metal oxide is dispersed in water, the dispersion becomes alkaline due to the exchange of lithium ions on the surface of the active material with hydrogen ions in the water. This may cause corrosion of common positive electrode current collector materials such as aluminum foil (Al). In such cases, it is preferable to neutralize the alkali leaching from the active material by using the unneutralized or partially neutralized block polymer as a binder. Moreover, it is preferable to use the unneutralized or partially neutralized block polymer in such an amount that the amount of unneutralized carboxyl groups in the block polymer is equivalent to or greater than the amount of alkali leaching from the active material.

[0107] Since positive electrode active materials all have low electrical conductivity, they are generally used with the addition of a conductive additive. Examples of conductive additives include carbon-based materials such as carbon black, carbon nanotubes, carbon fibers, graphite powder, and carbon fibers. Of these, carbon black, carbon nanotubes, and carbon fibers are preferred because they easily provide excellent conductivity. Ketjenblack and acetylene black are preferred as carbon blacks. One of the above conductive additives may be used alone, or two or more may be used in combination. From the viewpoint of balancing conductivity and energy density, the amount of conductive additive used can be, for example, 0.2 to 20 parts by mass, or for example, 0.2 to 10 parts by mass, per 100 parts by mass of the total amount of active material. The positive electrode active material may also be one that has been surface-coated with a conductive carbon-based material.

[0108] On the other hand, examples of negative electrode active materials include carbon-based materials, lithium metal, lithium alloys, and metal oxides, and one or more of these can be used in combination. Among these, active materials made of carbon-based materials such as natural graphite, artificial graphite, hard carbon, and soft carbon (hereinafter also referred to as "carbon-based active materials") are preferred, with graphite such as natural graphite and artificial graphite, and hard carbon being more preferred. In the case of graphite, spheroidized graphite is preferably used in terms of battery performance, and the preferred range of particle size is, for example, 1 to 20 μm, or for example, 5 to 15 μm. Furthermore, in order to increase the energy density, metals or metal oxides that can absorb lithium, such as silicon and tin, can also be used as negative electrode active materials. Among these, silicon has a higher capacity than graphite, and active materials made of silicon-based materials such as silicon, silicon alloys, and silicon oxides such as silicon monoxide (SiO) (hereinafter also referred to as "silicon-based active materials") can be used. However, while the silicon-based active material has high capacity, it undergoes large volume changes during charging and discharging. For this reason, it is preferable to use it in combination with the carbon-based active material. In this case, if the amount of silicon-based active material is too high, it can lead to the breakdown of the electrode material, and the cycle characteristics (durability) may be greatly reduced. From this perspective, when using silicon-based active material in combination, the amount used should be, for example, 60% by mass or less, or for example, 30% by mass or less, relative to the carbon-based active material.

[0109] The binder containing this block polymer has structural units derived from ethylenically unsaturated carboxylic acid monomers, and these structural units have a high affinity for silicon-based active materials, exhibiting good binding properties. Therefore, the binder of the present invention exhibits excellent binding properties even when using high-volume active materials containing silicon-based active materials, and is therefore considered effective in improving the durability of the resulting electrodes.

[0110] Since carbon-based active materials possess good electrical conductivity on their own, it is not always necessary to add conductive additives. When conductive additives are added for purposes such as further reducing resistance, the amount used should be, for example, 10 parts by mass or less, or 5 parts by weight or less, per 100 parts by mass of the total amount of active material, from the perspective of energy density.

[0111] When the composition is in slurry form, the amount of active material used is, for example, in the range of 10 to 75% by mass, or in the range of 30 to 65% by mass, relative to the total amount of the composition. If the amount of active material used is 10% by mass or more, migration of binders, etc., is suppressed, and it is also advantageous in terms of the drying cost of the medium. On the other hand, if it is 75% by mass or less, the fluidity and coating properties of the composition can be ensured, and a uniform mixture layer can be formed.

[0112] Furthermore, when preparing this composition in a wet powder state, the amount of active material used is, for example, in the range of 60 to 97% by mass, or in the range of 70 to 90% by mass, relative to the total amount of the composition. Also, from the viewpoint of energy density, non-volatile components other than the active material, such as binders and conductive additives, should be kept as small as possible while ensuring the necessary binding properties and conductivity.

[0113] This composition uses water as the medium. Furthermore, to adjust the properties and drying properties of the composition, a mixed solvent with lower alcohols such as methanol and ethanol, carbonates such as ethylene carbonate, ketones such as acetone, tetrahydrofuran, or N-methylpyrrolidone may be used. The proportion of water in the mixed medium is, for example, 50% by mass or more, and also, for example, 70% by mass or more.

[0114] When this composition is in a coatable slurry state, the content of the water-containing medium in the whole composition can be, for example, in the range of 25 to 90% by mass, or for example, in the range of 35 to 70% by mass, from the viewpoint of the coatability of the slurry, the energy cost required for drying, and productivity. Furthermore, when the composition is in a pressable wet powder state, the content of the above medium can be, for example, in the range of 3 to 40% by mass, or for example, in the range of 10 to 30% by mass, from the viewpoint of the uniformity of the mixture layer after pressing.

[0115] The binder of the present invention may consist solely of this block polymer, but other binder components such as styrene / butadiene latex (SBR), acrylic latex, and polyvinylidene fluoride latex may also be used in combination. When other binder components are used in combination, the amount used can be, for example, 0.1 to 5 parts by mass or less, or for example, 0.1 to 2 parts by mass or less, or for example, 0.1 to 1 part by mass or less, per 100 parts by mass of the total amount of active material. If the amount of other binder components used exceeds 5 parts by mass, the resistance may increase, and the high-rate properties may become insufficient. Among the above, styrene / butadiene latex is preferred because it has an excellent balance of binding properties and flexural resistance.

[0116] The above-mentioned styrene / butadiene latex refers to an aqueous dispersion of a copolymer having structural units derived from an aromatic vinyl monomer such as styrene and structural units derived from an aliphatic conjugated diene monomer such as 1,3-butadiene. Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, vinyltoluene, and divinylbenzene, and one or more of these can be used. The amount of structural units derived from the aromatic vinyl monomer in the copolymer can be in the range of, for example, 20 to 70% by mass, or in the range of, for example, 30 to 60% by mass, mainly from the viewpoint of binding properties.

[0117] Examples of the above-mentioned aliphatic conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, etc., and one or more of these can be used. The structural units derived from the above-mentioned aliphatic conjugated diene monomers in the copolymer can be in the range of, for example, 30 to 70% by mass, or in the range of 40 to 60% by mass, in order to ensure good binder binding and flexibility of the resulting electrode.

[0118] In addition to the monomers mentioned above, styrene / butadiene latex may also use other monomers as copolymer monomers to further improve properties such as binding ability, including nitrile group-containing monomers such as (meth)acrylonitrile, carboxyl group-containing monomers such as (meth)acrylic acid, itanconic acid, and maleic acid, and ester group-containing monomers such as (meth)acrylate.

[0119] The structural units derived from the other monomers in the copolymer can be in the range of, for example, 0 to 30% by mass, or in the range of, for example, 0 to 20% by mass.

[0120] This composition comprises the above-mentioned active material, water, and binder as essential components, and is obtained by mixing each component using known means. The method of mixing each component is not particularly limited, and known methods can be used, but it is preferable to dry blend the powder components such as the active material, conductive additive, and carboxyl group-containing polymer particles which are the binder, and then mix them with a dispersion medium such as water and disperse and knead them. When obtaining the electrode mixture layer composition in slurry form, it is preferable to produce a slurry that is free from poor dispersion and aggregation. As a mixing means, known mixers such as planetary mixers, thin-film swirling mixers, and orbital mixers can be used, but it is preferable to use a thin-film swirling mixer because a good dispersion state can be obtained in a short time. Furthermore, when using a thin-film swirling mixer, it is preferable to pre-disperse with a stirrer such as a disper beforehand. The viscosity of the slurry can be, for example, in the range of 100 to 10,000 mPa·s as a B-type viscosity at 20 rpm, or in the range of 1,000 to 5,000 mPa·s.

[0121] On the other hand, when obtaining this composition in a wet powder state, it is preferable to knead it using a Henschel mixer, blender, planetary mixer, twin-shaft kneader, etc., until it reaches a uniform state without uneven concentration. 3. Secondary battery electrode The secondary battery electrode of the present invention comprises a composite layer formed from this composition on the surface of a current collector made of copper or aluminum. The composite layer is formed by coating the surface of the current collector with this composition and then drying and removing a medium such as water. The method of coating with this composition is not particularly limited, and known methods such as the doctor blade method, dip method, roll coating method, comma coating method, curtain coating method, gravure coating method, and extrusion method can be employed. Furthermore, the drying can be carried out by known methods such as hot air blowing, reduced pressure, (far) infrared radiation, and microwave irradiation.

[0122] Typically, the mixture layer obtained after drying is subjected to compression treatment using a die press or roll press. Compression brings the active material and binder into close contact, improving the strength of the mixture layer and its adhesion to the current collector. Compression can adjust the thickness of the mixture layer to, for example, 30-80% of its original thickness, and the thickness of the mixture layer after compression is generally around 4-200 μm. 4. Secondary battery A secondary battery can be manufactured by providing a separator and an electrolyte to the secondary battery electrode of the present invention. The electrolyte may be in liquid or gel form.

[0123] The separator is placed between the positive and negative electrodes of a battery and plays a role in preventing short circuits caused by contact between the two electrodes and in retaining the electrolyte to ensure ionic conductivity. The separator is preferably a film-like insulating microporous membrane with good ionic permeability and mechanical strength. Specific materials that can be used include polyethylene, polyolefins such as polypropylene, and polytetrafluoroethylene.

[0124] The electrolyte can be a known one commonly used depending on the type of active material. In lithium-ion secondary batteries, specific solvents include cyclic carbonates with high dielectric constant and high electrolyte solubility, such as propylene carbonate and ethylene carbonate, as well as low-viscosity chain carbonates, such as ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate. These can be used alone or as mixed solvents. The electrolyte is used by dissolving lithium salts such as LiPF6, LiSbF6, LiBF4, LiClO4, and LiAlO4 in these solvents. In nickel-metal hydride secondary batteries, an aqueous potassium hydroxide solution can be used as the electrolyte. Secondary batteries are obtained by housing positive and negative electrode plates, separated by a separator, in a spiral or stacked structure in a case or the like.

[0125] As described above, the secondary battery electrode mixture layer composition (electrode slurry) containing the secondary battery electrode binder disclosed herein has a low slurry viscosity and exhibits excellent bonding with the electrode material and excellent adhesion to the current collector in the electrode mixture layer, and is therefore expected to exhibit good durability (cycle characteristics). For this reason, a secondary battery equipped with electrodes obtained using the above binder is expected to ensure good integrity and exhibit good durability (cycle characteristics) even after repeated charging and discharging, making it suitable for automotive secondary batteries and the like. [Examples]

[0126] The present invention will be described in detail below based on the following examples. However, the present invention is not limited to these examples. In the following, "parts" and "%" mean parts by mass and mass%, respectively, unless otherwise specified.

[0127] <Molecular weight measurement> An aqueous solution containing the polymer obtained in the production example and comparative production example (0.01 g as polymer solid content) was taken, diluted with 2 g of methanol, and then trimethylsilyldiazomethane (manufactured by Tokyo Chemical Industry Co., Ltd., 10% hexane solution) was added until the polymer solution turned yellow to obtain a methyl ester of the carboxyl group (methyl esterification rate of 100%). The methyl ester was measured by gel permeation chromatography (GPC) under the conditions described below to obtain the number-average molecular weight (Mn) and weight-average molecular weight (Mw) in polystyrene equivalent. The molecular weight distribution (Mw / Mn) was also calculated from the obtained values.

[0128] (GPC measurement conditions) Columns: 4 x TSKgel SuperMultiporeHZ-M (manufactured by Tosoh Corporation) Solvent: tetrahydrofuran Temperature: 40℃ Detector: RI Flow rate: 600μL / min

[0129] <Measurement of monomer reaction rate> First, a sample of the solution before polymerization began and a portion of the polymerization solution at a predetermined time were collected and dissolved in methanol to prepare a 2 wt% solution. Then, 0.02 g of dimethyl sulfoxide was added as an internal standard to obtain the measurement sample. Next, the sample was subjected to gas chromatography (GC) measurement to obtain the monomer concentration X in the solution before polymerization began and the monomer concentration Y in the polymerization solution after a predetermined time. The monomer reaction rate was then determined using the following formula. Reaction rate of monomers (%) = (XY) / X × 100

[0130] (GC measurement conditions) Equipment: Agilent Technologies 7820A Column: GL Sciences Co., Ltd. CP-Sil 5CB (dimethylpolysiloxane) Column length 30m, column diameter 0.32mm, df = 0.3μm Carrier gas: He Gas flow rate: 1.5 mL / min Split ratio: 40:1 Injection volume: 1.0μL Inlet temperature: 230℃ Detector: FID Detector temperature: 250℃ H2 flow rate: 40mL / min Air flow rate: 450mL / min N2 flow rate: 25mL / min Heating conditions: 50°C (5 min) → 10°C / min → 230°C (5 min)

[0131] <Glass transition temperature (Tg)> The glass transition temperature (Tg) of each polymer block of the obtained block polymer was determined from the intersection of the baseline and the tangent at the inflection point of the heat flux curve obtained by differential scanning calorimeter (DSC) analysis of the block polymer. The heat flux curve was obtained under the following conditions: approximately 10 mg of the sample was cooled to -50°C, held for 5 minutes, then heated to 300°C at a rate of 10°C / min, subsequently cooled to -50°C, held for 5 minutes, and then heated to 350°C at a rate of 10°C / min. Measuring instrument: DSC6220 manufactured by SII Nanotechnology Co., Ltd. Measurement atmosphere: Under a nitrogen atmosphere

[0132] <Composition ratio of block polymers> The composition ratio (mass ratio) of the obtained block polymer is: 1 Identified and calculated by 1H-NMR measurement.

[0133] <Method for measuring solid content concentration> Approximately 0.5 g of the sample was placed in weighing bottles whose weights had been measured in advance [weight of weighing bottle = B (g)], and after accurately weighing the bottles together [W0 (g)], the samples and weighing bottles together were placed in an airless drying oven and dried at 155°C for 45 minutes, and the weight of the weighing bottles together was measured at that time [W1 (g)], and the solid content concentration was calculated using the following formula. Solid content concentration (mass%)=(W1-B) / (W0-B)×100

[0134] ≪Polymer Manufacturing≫ (Manufacturing Example 1: Manufacturing of Polymer A) In a 2L flask equipped with a stirrer and thermometer, 0.28 parts of 2-{[(2-carboxyethyl)sulfanylthiocarbonyl]sulfanyl}propanoic acid (hereinafter also referred to as "CBSTSP"), 0.014 parts of 4,4'-azobis(4-cyanovaleric acid) (hereinafter also referred to as "ACVA"), 33.4 parts of acrylic acid (hereinafter also referred to as "AA"), and 134.6 parts of deionized water were charged. The mixture was thoroughly degassed by nitrogen bubbling, and polymerization was started in a 70°C constant temperature bath. After 4 hours, the reaction was stopped by cooling to room temperature. At this point, the reaction rate of AA was 95%. The molecular weights were Mn 32,000, Mw 36,200, and Mw / Mn 1.13. Next, 2-methoxyethyl acrylate (hereinafter also referred to as "MEA") (78.9 parts), ACVA (0.014 parts), and deionized water (315.5 parts) were charged into the polymerization solution. The mixture was thoroughly degassed by nitrogen bubbling, and polymerization was started in a constant temperature bath at 70°C. After 3 hours, the mixture was cooled to room temperature to stop the reaction. At this point, the reaction rate of MEA was 92%, and polymer block (B) contained structural units derived from unreacted AA during the production of polymer block (A), with an AA content of 2% by mass. The molecular weights were Mn 104,000, Mw 138,000, and Mw / Mn 1.33. Next, 187.5 parts of deionized water were added, followed by an aqueous solution of lithium hydroxide monohydrate (hereinafter also referred to as "LiOH·H2O") (17.5 parts) dissolved in 232.4 parts of deionized water. The mixture was stirred at 25°C for 1 hour to neutralize it, thereby obtaining an aqueous solution containing polymer A (Li salt, degree of neutralization 98 mol%).

[0135] (Manufacturing Examples 2-5 and Comparative Manufacturing Examples 1-2: Production of Polymers B-E, O, and P) Except for changing the types and amounts of raw materials charged into the flask as shown in Table 1, and adjusting the reaction time as appropriate, the same procedure as in Production Example 1 was performed to obtain aqueous solutions containing polymers B to E, polymer O, and polymer P, respectively. However, in the production of polymer Q in comparative production example 1, the second polymerization step was not performed.

[0136] (Manufacturing Example 6: Manufacturing of Polymer F) A 2L flask equipped with a stirrer and thermometer was charged with CBSTSP (0.28 parts), ACVA (0.014 parts), AA (33.5 parts), and deionized water (135.0 parts). The flask was thoroughly degassed by nitrogen bubbling, and polymerization was started in a 70°C constant temperature bath. After 4 hours, the reaction was stopped by cooling to room temperature. At this point, the reaction rate of AA was 94%. The molecular weights were Mn 31,800, Mw 36,100, and Mw / Mn 1.14. Next, MEA (67.6 parts), ACVA (0.014 parts), and deionized water (314.8 parts) were added to the polymerization solution, and the mixture was thoroughly degassed by nitrogen bubbling. Polymerization was then started in a constant temperature bath at 70°C. After 1 hour, the mixture was cooled to room temperature to stop the reaction. The reaction rate of MEA was 97%, and polymer block (B) contained structural units derived from unreacted AA during the production of polymer block (A), with an AA content of 3% by mass. The molecular weights were Mn 96,800, Mw 118,000, and Mw / Mn 1.22. Next, phenoxyethyl acrylate (Viscote #192, manufactured by Osaka Organic Chemical Industry Co., Ltd., hereinafter also referred to as "PEA") (11.1 parts) was added to the polymerization solution, and the mixture was thoroughly degassed by nitrogen bubbling. Polymerization was then started in a constant temperature bath at 70°C. After 2 hours, the mixture was cooled to room temperature to stop the reaction. At this point, the reaction rate of PEA was 98%, and the molecular weights were Mn 108,000, Mw 168,000, and Mw / Mn 1.56. Next, 187.4 parts of deionized water were added, followed by an aqueous solution of LiOH·H2O (17.5 parts) dissolved in 232.7 parts of deionized water. The mixture was stirred at 25°C for 1 hour to neutralize it, yielding an aqueous solution containing polymer F (Li salt, degree of neutralization 98 mol%).

[0137] (Manufacturing Examples 7-16: Manufacturing of Polymer G to Polymer P) Except for changing the types and amounts of raw materials added to the flask as shown in Tables 1 and 2, and adjusting the reaction time as appropriate, the same procedure as in Production Example 6 was performed to obtain aqueous solutions containing polymers G to P.

[0138] (Comparative manufacturing example 3) (Production of polymer S) In a 1 L flask equipped with a stirrer and thermometer, 0.23 parts of CBSTSP, 0.022 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name "V-65"), 100 parts of MEA, and 66.8 parts of acetonitrile were charged. The mixture was thoroughly degassed by nitrogen bubbling, and polymerization was started in a 60°C constant temperature bath. After 2 hours, the mixture was cooled to room temperature to stop the reaction. The polymerization solution was reprecipitated and purified from methanol / water = 90 / 10 (vol%), and the first polymer of polymer P was obtained by vacuum drying. The reaction rate of MEA, based on gas chromatography measurements, was 90%. The molecular weights, measured by GPC (polystyrene equivalent), were Mn 99000, Mw 133700, and Mw / Mn 1.35. Next, 567 parts of acetonitrile, 2.20 parts of deionized water, 98 parts of AA, 0.90 parts of trimethylolpropanediallyl ether (manufactured by Osaka Soda Co., Ltd., trade name "Neoallyl T-20"), 2.0 parts of the primary polymer of the above-mentioned polymer P as the resin component, and triethylamine equivalent to 1.0 mol% of the above-mentioned AA were charged into a 2L flask equipped with a stirrer and thermometer. After thoroughly purging the reactor with nitrogen, the internal temperature was raised to 55°C. After confirming that the internal temperature had stabilized at 55°C, 0.040 parts of V-65 were added as a polymerization initiator, and turbidity was observed in the reaction solution, so this point was taken as the polymerization initiation point. The monomer concentration was calculated to be 15.0%. The polymerization reaction was continued while maintaining the internal temperature at 55°C by adjusting the external temperature (water bath temperature), and the internal temperature was raised to 65°C 6 hours after the polymerization initiation point. The internal temperature was maintained at 65°C, and cooling of the reaction solution was started 12 hours after the polymerization initiation point. After the internal temperature dropped to 25°C, 52.4 parts of LiOH·H2O powder were added. After the addition, stirring was continued at room temperature for 12 hours to obtain a slurry-like polymerization reaction solution in which particles of block polymer S (Li salt, degree of neutralization 90 mol%) were dispersed in the medium. The reaction rate of AA was 97% 12 hours after the polymerization initiation point. The obtained polymerization reaction solution was centrifuged to settle the polymer particles, and the supernatant was removed. Subsequently, the precipitate was redispersed in acetonitrile of the same weight as the polymerization reaction solution, and the washing operation of settling the polymer particles by centrifugation and removing the supernatant was repeated twice. The precipitate was collected and dried under reduced pressure at 80°C for 3 hours to remove volatile components, thereby obtaining block polymer S powder. Since block polymer S is hygroscopic, it was stored sealed in a container with water vapor barrier properties.

[0139] Of the polymers, polymers A to E, polymer R, and polymer S are block polymers composed of AB diblocks, polymers F to P are block polymers composed of ABC triblocks, and polymer Q is a non-block polymer.

[0140] The raw materials and physical properties of polymers A to S obtained above are listed in Tables 1 and 2.

[0141] [Table 1]

[0142] [Table 2]

[0143] Details of the compounds used in Tables 1 and 2 are shown below. AA: Acrylic acid • ACMO:4-Acryloylmorpholine MEA: 2-methoxyethyl acrylate • MA: Methyl acrylate • EA: Ethyl acrylate PEA: Phenoxyethyl acrylate • CBSTSP: 2-{[(2-carboxyethyl)sulfanylthiocarbonyl]sulfanyl}propanoic acid • ACVA: 4,4'-Azobis(4-cyanovaleric acid) ·LiOH·H2O: Lithium hydroxide monohydrate Example 1 <Preparation of the composition for the electrode active material layer (electrode slurry)> As the active material, a material obtained by coating carbon on the surface of SiOx (0.8 < x < 1.2) by CVD method (hereinafter also referred to as "Si-based active material") was prepared, and a mixture of graphite (manufactured by Nippon Graphite Co., Ltd., trade name "CGB-10") and Si-based active material was used. Using water as the diluting solvent so that the solid content concentration becomes 56% by mass, ion-exchanged water was added so that the mass ratio of graphite: Si-based active material: polymer A = 90: 10: 3.2 (solid content), and pre-dispersion was performed with a disper. Then, using a thin-film swing mixer (manufactured by Primix Co., Ltd., FM-56-30), the main dispersion was performed for 15 seconds under the condition of a peripheral speed of 20 m / s to prepare an electrode slurry. The slurry viscosity of the electrode slurry using each polymer salt as a binder was measured.

[0144] <Viscosity measurement of the electrode slurry> Regarding the electrode slurry obtained above, using a rheometer (Physica MCR301) manufactured by Anton Paar, with a CP25-5 cone plate (diameter 25 mm, cone angle 5°), the shear rate at 25°C was 60 s -1 When the slurry viscosity was measured, it was 1,800 mPa·s, which was a viscosity suitable for coating.

[0145] (Fabrication of the negative electrode plate) Next, using a variable applicator, the above electrode slurry was applied onto a current collector (copper foil) with a thickness of 20 μm, and drying was performed at 100°C for 15 minutes in a ventilation dryer to form an active material layer. Then, rolling was performed so that the thickness of the active material layer was 50 ± 5 μm and the packing density was 1.60 ± 0.10 g / cm 3 to obtain a negative electrode plate.

[0146] Regarding the above negative electrode plate, the peel strength between the active material layer and the current collector (that is, the binding property of the binder) was measured. <90° peel strength (binding property)> A sample for peel testing was prepared by attaching the composite layer surface of the above-mentioned negative electrode plate, measuring 100 mm x 25 mm, to a 120 mm x 30 mm acrylic plate using double-sided tape (Nichiban Co., Ltd. Nicetack NW-20). After drying at 60°C overnight under reduced pressure, the bonding properties were evaluated by measuring the peel strength between the composite layer and the copper foil using a tensile testing machine (ORIENTEC RTE-1210 Tensilon universal testing material machine) at a measurement temperature of 25°C and a tensile speed of 50 mm / min for 90° peeling. The peel strength was high at 10.0 N / m, indicating good performance. Examples 2-16 and Comparative Examples 1-3 Electrode slurries were prepared by the same procedure as in Example 1, except that the polymer used as the binder was as shown in Table 3. The viscosity of each electrode slurry and the 90° peel strength (binding strength) of the obtained negative electrode were evaluated, and the results are shown in Table 3.

[0147] [Table 3] <<Evaluation Results>> As is clear from the results of Examples 1 to 16, the secondary battery electrode composite layer composition (electrode slurry) containing the secondary battery electrode binder of the present invention had low slurry viscosity and excellent binding properties.

[0148] Among these, focusing on the proportion of polymer blocks (A) in the block polymer (Examples 1, 2, and 5), the lower the proportion of polymer blocks (A) in the range of 21% by mass (Example 2) to 79% by mass (Example 5), the better the binding performance. This is presumed to be due to the high flexibility of the block polymer.

[0149] Furthermore, focusing on the content of structural units derived from ethylenically unsaturated carboxylic acid monomers based on the total structural units of polymer block (B) (Examples 1, 3, and 4), it was found that in the range of 2% by mass (Example 1) to 17% by mass (Example 4), the lower the content, the better the binding performance. This is presumed to be due to the high flexibility of the block polymer.

[0150] Furthermore, focusing on the structure of the block polymer, the ABC structure (Example 6), which has polymer block (C) that is different from polymer block (A) and polymer block (B), showed even better binding properties than the AB structure (Example 1), which has polymer block (A) and polymer block (B). This is presumed to be because the adsorption to the active material was improved by introducing hydrophobic polymer block (C), which contains 50% by mass or more of structural units derived from ethylenically unsaturated monomers whose solubility in 100g of water at 20°C is 1.0g or less.

[0151] Furthermore, focusing on the Mn content of the block polymer, the Mn content of 189,000 (Example 11) showed even better binding properties than that of 108,000 (Example 6). This is presumed to be because the higher the Mn content, the better the adsorption to the active material.

[0152] In contrast, when a non-block polymer (Comparative Example 1) or a block polymer with a polymer block (A) proportion exceeding 90% by mass (Comparative Example 2) was used as a binder, the binding properties were significantly inferior. Furthermore, when a block polymer containing structural units derived from crosslinkable monomers (Comparative Example 3) was used, the electrode slurry with a high solid content concentration had high viscosity. Therefore, in order to improve coating properties in practical terms, it was necessary to reduce the solid content concentration, which presented challenges in electrode productivity. [Industrial applicability]

[0153] The secondary battery electrode mixture layer composition (electrode slurry) containing the binder for secondary battery electrodes of the present invention exhibits low slurry viscosity and excellent bonding properties with the electrode material and current collector in the electrode mixture layer, and is therefore expected to show good durability (cycle characteristics). For this reason, secondary batteries equipped with electrodes obtained using the above binder are expected to show good durability (cycle characteristics) and are expected to be applied to automotive secondary batteries. Furthermore, it is also useful for the use of silicon-containing active materials and is expected to contribute to increasing the capacity of batteries. The binder for secondary battery electrodes of the present invention can be suitably used in non-aqueous electrolyte secondary battery electrodes, and is particularly useful in non-aqueous electrolyte lithium-ion secondary batteries with high energy density.

Claims

1. A binder for secondary battery electrodes containing a block polymer having polymer block (A) and polymer block (B), The polymer block (A) contains 50% by mass or more of structural units derived from ethylenically unsaturated carboxylic acid monomers based on the total structural units of the polymer block (A), The polymer block (B) contains, based on the total structural units of the polymer block (B), 1% by mass or more and less than 17% by mass of structural units derived from an ethylenically unsaturated carboxylic acid monomer. A binder for secondary battery electrodes, wherein the block polymer does not contain structural units derived from crosslinkable monomers, and contains 18% by mass or more and 38% by mass or less of the polymer block (A).

2. The polymer block (B) contains, based on all structural units of the polymer block (B), 1% by mass or more and less than 10% by mass of structural units derived from the ethylenically unsaturated carboxylic acid monomer, The binder for secondary battery electrodes according to claim 1, wherein the block polymer contains 18% by mass or more and 38% by mass or less of the polymer block (A).

3. The binder for secondary battery electrodes according to claim 1 or 2, wherein the polymer block (B) comprises structural units derived from a (meth)acrylic acid ester monomer.

4. The polymer block (B) contains 50% by mass or more of structural units derived from an ethylenically unsaturated monomer (excluding monomers classified as ethylenically unsaturated carboxylic acid monomers; hereinafter referred to as "monomer (b1)") whose solubility in 100 g of water at 20°C is 20 g or less, with respect to all of its structural units, as described in any one of claims 1 to 3 for a secondary battery electrode binder.

5. The binder for secondary battery electrodes according to any one of claims 1 to 4, wherein the block polymer further comprises a polymer block (C) (but different from the polymer block (A) and the polymer block (B)).

6. The binder for secondary battery electrodes according to claim 5, wherein the polymer block (C) contains 50% by mass or more of structural units derived from ethylenically unsaturated monomers (excluding ethylenically unsaturated carboxylic acid monomers and monomers classified as monomer (b1)) whose solubility in 100 g of water at 20°C is 1.0 g or less, with respect to all of its structural units.

7. The binder for secondary battery electrodes according to any one of claims 1 to 6, wherein the block polymer is a salt in which 80 mol% or more of the carboxyl groups of the block polymer are neutralized.

8. The binder for secondary battery electrodes according to any one of claims 1 to 7, wherein the number-average molecular weight of the block polymer is 50,000 or more as the number-average molecular weight of the methyl esterified carboxyl group contained in the block polymer on a polystyrene basis.

9. A composition for a secondary battery electrode mixture layer comprising a binder for secondary battery electrodes, an active material, and water according to any one of claims 1 to 8.

10. A secondary battery electrode comprising a composite layer formed from the secondary battery electrode composite layer composition described in claim 9 on the surface of a current collector.

11. A method for producing a block polymer used in secondary battery electrode binders, The aforementioned block polymer comprises polymer block (A) and polymer block (B), A step of producing the polymer block (A) by polymerizing monomer components containing ethylenically unsaturated carboxylic acid monomers using a living radical polymerization method, The process includes a step of polymerizing a monomer component having an ethylenically unsaturated carboxylic acid monomer content of less than 30% by mass in the presence of the polymer block (A) to produce the polymer block (B), The polymer block (A) contains 50% by mass or more of structural units derived from ethylenically unsaturated carboxylic acid monomers based on the total structural units of the polymer block (A), The polymer block (B) contains 1% by mass or more and less than 17% by mass of structural units derived from ethylenically unsaturated carboxylic acid monomers based on the total structural units of the polymer block (B), A method for producing the aforementioned block polymer, wherein the block polymer does not contain structural units derived from crosslinkable monomers, and contains 18% by mass or more and 38% by mass or less of the polymer block (A).

12. The method for producing a block polymer according to claim 11, wherein the living radical polymerization method is a reversible addition-fraction chain transfer polymerization (RAFT) method.

13. A method for producing a block polymer according to claim 11 or 12, wherein the polymerization is aqueous solution polymerization.

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