Binder composition for secondary battery, composition for electrode, electrode sheet and secondary battery, and method for manufacturing the electrode sheet and secondary battery

Abstract

A secondary battery binder composition that includes water and a water-soluble cross-linked polymer that is formed by using an aziridine compound to cross-link a copolymer that contains, as constituent components, a (meth)acrylic acid component and a (meth)acrylic acid ester component. An electrode composition, an electrode sheet, a secondary battery, a production method for the electrode sheet, and a production method for the secondary battery.

Description

[Technical field]

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

[0002] Secondary batteries, such as lithium-ion secondary batteries, are used as power sources for portable electronic devices such as personal computers, video cameras, mobile phones, etc. Recently, against the backdrop of the global environmental challenge of reducing carbon dioxide emissions, they have become widespread as power sources for transportation equipment such as automobiles, and for storing electricity such as nighttime electricity and electricity generated by natural energy sources.

[0003] The electrodes (positive and negative electrodes) of a lithium ion secondary battery have electrode active material layers (positive and negative active material layers), and these electrode active material layers contain electrode active material particles capable of absorbing or releasing lithium ions during charging and discharging. In addition, since electron transport also occurs between the electrode active material particles or between the electrode active material particles and the current collector, it is required to ensure electronic conductivity. To improve the efficiency of this electronic conduction, the binding property between the electrode active material particles or between the electrode active material particles and the current collector is important, and the electrode active material layer usually has a binder. However, the binder itself has low electron transport ability, and improvement of binding property and improvement of electronic conductivity are usually in a so-called trade-off relationship with each other.

[0004] Electrodes for lithium ion secondary batteries are usually formed by applying an electrode-forming composition (slurry) onto a current collector and drying it. Therefore, the slurry for forming the electrode is prepared by dispersing an electrode active material and a binder in a liquid medium. In recent years, with the background of increasing interest in environmental issues, there has been a demand for aqueous liquid media, and water-soluble (meth)acrylic binders suitable for aqueous slurries have been developed. For example, Patent Document 1 describes a negative electrode agent for non-aqueous electrolyte secondary batteries that contains at least an active material and a binder, and describes that the binder contains a first linear water-soluble polymer that has been crosslinked and a second linear water-soluble polymer that has not been crosslinked. It describes that this negative electrode agent provides an active material layer that is highly durable against internal stresses caused by volumetric expansion and contraction during charging and discharging, and makes it possible to suppress the continuous destruction and generation of SEI (Solid Electrolyte Interphase) that accompanies repeated charging and discharging.

[0005] In recent years, in order to realize a further increase in the capacity of lithium-ion secondary batteries, the use of silicon-based active materials as negative electrode active materials has been actively studied. The use of silicon-based active materials in the negative electrode enables a high energy density. However, silicon-based active materials absorb a large amount of lithium ions and expand significantly during charging, and the degree of contraction of the silicon-based active material during discharging is also large. Therefore, in lithium-ion batteries using silicon-based active materials as negative electrode active materials, the volume change of the negative electrode active material during charging and discharging is large, and the battery performance is easily deteriorated by repeated charging and discharging. In other words, there are limitations to improving the cycle life. As a technique for dealing with such problems, for example, Patent Document 2 describes a negative electrode agent for non-aqueous electrolyte secondary batteries that includes a negative electrode active material, a conductive assistant, and a binder, and describes that the binder is composed of a mixture of an aqueous polymer crosslinked by adding a crosslinking agent such as an aziridine-based crosslinking agent to calcium polyacrylate or polyacrylic acid ester having a molecular weight of 1 million to 5 million, and an aqueous polymer having a molecular weight of 1,000 to 1 million. Patent Document 2 describes that the mechanical strength of the negative electrode agent can be improved, and that it is possible to suppress the continuous destruction and generation of SEI that accompanies repeated charging and discharging. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2016 / 051811 [Patent Document 2] JP 2017-004682 A Summary of the Invention [Problem to be solved by the invention]

[0007] As the use of non-aqueous secondary batteries expands, non-aqueous secondary batteries are required to have higher energy density, lower resistance, and further improved cycle life. However, as a result of the inventors' investigation of conventional electrode binders, including the electrode binders described in the above patent documents, it has become clear that when a silicon-based active material is used as the negative electrode active material to increase the energy density of a non-aqueous secondary battery, it is difficult to sufficiently suppress the battery resistance, and the cycle life has not yet reached the desired high level. In addition, it has become clear that when the above conventional electrode binders are used, there are limitations to improving the dispersibility of solid particles such as electrode active materials and conductive assistants in an electrode composition containing a solvent.

[0008] An object of the present invention is to provide a binder composition for secondary batteries which, by mixing with solid particles such as an electrode active material, a conductive assistant, etc., can obtain a composition (slurry) having excellent dispersibility of these solid particles, and which, when an electrode active material layer is formed using this composition, can sufficiently increase the binding between electrode active material particles or between the electrode active material particles and a current collector, and can satisfactorily reduce the resistance of the obtained secondary battery and sufficiently extend the cycle life of this secondary battery, even when an electrode active material that undergoes a large volume change during charging and discharging is used. Another object of the present invention is to provide an electrode composition comprising the binder composition and an electrode active material, an electrode sheet and a secondary battery using the electrode composition, and a method for producing the electrode sheet and the secondary battery. [Means for solving the problem]

[0009] That is, the above-mentioned object of the present invention has been achieved by the following means. <1> A binder composition for secondary batteries comprising water and a water-soluble crosslinked polymer obtained by crosslinking a copolymer containing a (meth)acrylic acid component and a (meth)acrylic acid ester component as constituent components with an aziridine compound. <2> The water-soluble crosslinked polymer has a solubility in water at 20°C of 10 g / L or more. <1> The binder composition for a secondary battery according to claim 1. <3> The (meth)acrylic acid ester component contains a component having a glass transition temperature of 20° C. or lower. <1> or <2> The binder composition for a secondary battery according to claim 1. <4> The water-soluble crosslinked polymer satisfies the following <Condition I>, <1> ~ <3> 13. The binder composition for a secondary battery according to claim 12 . <Condition I> In an aqueous dispersion in which the acetylene black content is 60 parts by mass, the water-soluble crosslinked polymer content is 50 parts by mass, and the total content of the acetylene black and the water-soluble crosslinked polymer is 0.015% by mass, the average particle size of particles in this aqueous dispersion is 9.0 μm or less. <5> The aziridine compound is a compound represented by any one of the following general formulas (1) to (3): <1> ~ <4> 13. The binder composition for a secondary battery according to claim 12 . [ka] In the formula, R 11 represents a hydrogen atom, a halogen atom or an alkyl group. 11 ~L 18 represents a single bond or a divalent linking group. <6> The aziridine compound is a compound represented by the general formula (1) or (2). <5> The binder composition for a secondary battery according to claim 1. <7> The water-soluble crosslinked polymer satisfies the following <Condition II>, <1> ~ <6> 13. The binder composition for a secondary battery according to claim 12 . <Condition II> The water-soluble crosslinked polymer has a swelling ratio of 1% by mass or more and less than 100% by mass in a mixed solvent obtained by mixing 2 parts by mass of ethyl methyl carbonate with 1 part by mass of ethylene carbonate. <8> The (meth)acrylic acid component includes a component having a (meth)acrylate salt structure. <1> ~ <7> 13. The binder composition for a secondary battery according to claim 12 . <9> The (meth)acrylate salt structure has a counter ion derived from a polyvalent amine. <8> The binder composition for a secondary battery according to claim 1. <10> The viscosity of a 10% by mass aqueous solution of the water-soluble crosslinked polymer is 300 mPa s to 50,000 mPa s. <1> ~ <9> 13. The binder composition for a secondary battery according to claim 12 . <11> The weight average molecular weight of the copolymer is 100,000 or more. <1> ~ <10> 13. The binder composition for a secondary battery according to claim 12 . <12> <1> ~ <11> and an active material capable of inserting and releasing ions of a metal belonging to Group 1 or 2 of the periodic table. <13> <12> An electrode sheet having a layer constituted by the electrode composition according to claim 1. <14> A secondary battery having a positive electrode, a separator, and a negative electrode in this order, wherein at least one of a positive electrode active material layer constituting the positive electrode and a negative electrode active material layer constituting the negative electrode is <12> A secondary battery, comprising a layer formed from the electrode composition according to claim 1. <15> <12> forming a film of the electrode composition according to claim 1 and drying the film. <16> <15> and incorporating the electrode sheet obtained by the manufacturing method described in claim 1 into an electrode of the secondary battery. Effect of the Invention

[0010] The binder composition for secondary batteries of the present invention can be mixed with solid particles such as an electrode active material, a conductive assistant, etc. to obtain a composition (slurry) with excellent dispersibility of these solid particles. The binder composition for secondary batteries, the composition for electrodes, and the electrode sheet of the present invention can sufficiently increase the binding between electrode active material particles or between the electrode active material particles and a current collector in a secondary battery in which an electrode is produced using these, and can realize low resistance of the secondary battery even when an electrode active material with a large volume change during charging and discharging is used, and can also sufficiently extend the cycle life of the secondary battery. The secondary battery of the present invention has sufficiently enhanced adhesion between electrode active material particles or between the electrode active material particles and the current collector, and can achieve low resistance during battery operation even when an electrode active material that undergoes a large volume change during charging and discharging is used, and has a sufficiently long cycle life. According to the method for producing an electrode sheet of the present invention, the electrode sheet of the present invention can be obtained. Also, according to the method for producing a secondary battery of the present invention, the secondary battery of the present invention can be obtained. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a vertical cross-sectional view showing a schematic diagram of a basic layered structure of an embodiment of a secondary battery according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] In the description of the present invention, a numerical range expressed using "to" means a range including the numerical values ​​before and after "to" as the lower and upper limits. In the present invention, the indication of a compound, a component, or a substituent is used to include not only the compound itself, the component itself, or the substituent itself, but also their salts and ions. For example, a group having a dissociable hydrogen atom (a group in which a hydrogen atom dissociates under the action of a base) such as a carboxy group in a compound may have an ionic structure or a salt structure when the hydrogen atom is dissociated. That is, in the present invention, the "carboxy group of a compound or a component" means a carboxylate ion or a salt thereof. The counter ion when forming the above salt structure can be described below when the (meth)acrylic acid component has a salt structure. In the case of a salt structure, the type of salt may be one type or two or more types may be mixed, the salt type and free acid structure groups may be mixed in the compound (polymer), and further, a compound of a salt structure and a compound of a free acid structure may be mixed. In addition, it is meant to include those in which a part of the structure has been changed within the scope of the effects of the present invention. Furthermore, for compounds or components not specified as substituted or unsubstituted in the present invention, it is meant that they may have any substituent within the scope of the effects of the present invention. This also applies to substituents (for example, groups expressed as "alkyl group", "methyl group", "methyl", etc.) and linking groups (for example, groups expressed as "alkylene group", "methylene group", "methylene", etc.). Among such optional substituents, the preferred substituents in the present invention are those selected from the substituent group Q described below. In the present invention, when there are a plurality of substituents or linking groups, etc., represented by a specific symbol or formula (hereinafter referred to as "substituents, etc."), or when a plurality of substituents, etc., are specified at the same time, the respective substituents, etc. may be the same or different from each other, unless otherwise specified. This also applies to the constituent components of the polymer. In the present invention, the term "(meth)acrylic" refers to a concept that includes both methacryl and acrylic, and the term "(meth)acryloyl" refers to a concept that includes both methacryloyl and acryloyl. In the present invention, one type of each component may be contained, or two or more types may be contained. In the present invention, the term "nonaqueous secondary battery" includes nonaqueous electrolyte secondary batteries and all-solid-state secondary batteries. In the present invention, the term "nonaqueous electrolyte" means an electrolyte that does not substantially contain water. That is, the "nonaqueous electrolyte" may contain a small amount of water within a range that does not impede the effects of the present invention. In the present invention, the "nonaqueous electrolyte" has a water concentration of 200 ppm (by mass) or less, preferably 100 ppm or less, and more preferably 20 ppm or less. Note that it is practically difficult to make a nonaqueous electrolyte completely anhydrous, and it usually contains 1 ppm or more of water. The term "all-solid-state secondary battery" means a secondary battery that does not use a liquid as an electrolyte, but uses a solid electrolyte such as an inorganic solid electrolyte or a solid polymer electrolyte. In the present invention, when the number of carbon atoms of a certain group is specified, this carbon number means the number of carbon atoms of the group itself unless otherwise specified in the present invention or this specification. In other words, when this group further has a substituent, the number of carbon atoms means the number of carbon atoms counted without including the number of carbon atoms of the substituent. In the present invention, the term "solid content" used when describing the content or content ratio means components other than water and the liquid medium described below.

[0013] [Binder composition for secondary batteries] The binder composition for secondary batteries of the present invention (hereinafter, also referred to as "the binder composition of the present invention") is a binder composition suitable as a material for forming a member or a constituent layer constituting a secondary battery, preferably a non-aqueous secondary battery, more preferably a non-aqueous electrolyte secondary battery. Typically, the binder composition of the present invention can be suitably used for forming an electrode active material layer in an electrode of a secondary battery. Specifically, the binder composition of the present invention can be mixed with an electrode active material (used to include a positive electrode active material or a negative electrode active material, and these are also simply referred to as "active material") to form an electrode (positive electrode and / or negative electrode) active material layer of a non-aqueous secondary battery. The binder composition of the present invention can be used by applying it to the surface of a separator of a secondary battery to form a heat-resistant layer, or as a binder for coating a current collector.

[0014] The binder composition of the present invention contains water and a water-soluble crosslinked polymer obtained by crosslinking a copolymer containing a (meth)acrylic acid component and a (meth)acrylic acid ester component as constituent components with an aziridine compound. The water-soluble crosslinked polymer contained in the binder composition of the present invention functions as a binder for binding solid particles (electrode active material, conductive assistant, etc.) to each other in a layer formed from a composition obtained by mixing the binder composition of the present invention with solid particles, and may also function as a binder for binding a current collector to the solid particles. Furthermore, when the water-soluble crosslinked polymer is present in the aqueous dispersion of the solid particles, it adsorbs to the surfaces of the solid particles and functions as a dispersant for the solid particles in the aqueous medium. This can increase the dispersibility or dispersion stability of the solid particles in the aqueous dispersion of the solid particles. Here, the adsorption of the water-soluble crosslinked polymer to the solid particles includes not only physical adsorption but also chemical adsorption (adsorption by chemical bond formation, adsorption by electron transfer, etc.).

[0015] The above-mentioned prior art documents 1 and 2 disclose a binder made of a mixture of two types of homopolymers, one of which has a crosslinked structure. However, the cycle life cannot be sufficiently improved with the binder made of these mixtures. In contrast, in the present invention, a copolymer having a (meth)acrylic acid component and a (meth)acrylic acid ester component as constituent components is crosslinked with aziridine to obtain a water-soluble crosslinked polymer. By using such a water-soluble crosslinked polymer as a binder for a secondary battery, an excellent cycle life can be realized. Although the reason for this is unclear, it is difficult to finely control the hydrophilicity and hydrophobicity of a polymer with a homopolymer, whereas it is possible with a copolymer. One of the reasons is thought to be that the dispersibility or dispersion stability of solid particles, including electrode active materials, can be improved by forming a water-soluble crosslinked polymer by aziridine crosslinking a specific copolymer.

[0016] <Water-soluble cross-linked polymer> The binder composition of the present invention contains, as a binder, a water-soluble crosslinked polymer obtained by crosslinking a copolymer having a component derived from (meth)acrylic acid and a component derived from a (meth)acrylic acid ester with an aziridine compound.

[0017] The term "water-soluble" in the above water-soluble crosslinked polymer means that the solubility in water at 20°C is 0.1 g / L or more (meaning that 0.1 grams of the water-soluble crosslinked polymer dissolves in 1 liter of water), preferably 1 g / L or more, more preferably 10 g / L or more, even more preferably 50 g / L or more, and even more preferably 100 g / L or more.

[0018] The water-soluble crosslinked polymer preferably satisfies the following <Condition I>. <Condition I> In an aqueous dispersion in which acetylene black is dispersed in water such that the content of acetylene black is 60 parts by mass, the content of water-soluble crosslinked polymer is 50 parts by mass, and the total content of the acetylene black and the water-soluble crosslinked polymer is 0.015% by mass, the average particle size of particles in this aqueous dispersion is 9.0 μm or less. However, the above aqueous dispersion does not contain any components other than the water-soluble crosslinked polymer, acetylene black, and water. The acetylene black has an average particle size of 30 to 40 nm and a specific surface area of ​​65 to 70 m 2 The average particle size of acetylene black means the volume average particle size, and the specific surface area means the value measured by the BET method. 2 A specific example of acetylene black that satisfies the condition of / g is Denka Black powder (average particle size: 35 nm, specific surface area: 68 m 2 / g (representative value listed on Denka's website) should be used. Other conditions for preparing the aqueous dispersion and conditions for measuring the same are as described in the Examples below. The average particle size of the particles in the aqueous dispersion as specified in the above <Condition I> is a value measured by a dynamic light scattering method using a zeta potential meter.

[0019] When the water-soluble crosslinked polymer satisfies the above <Condition I>, the acetylene black is dispersed in water with the water-soluble crosslinked polymer adsorbed therearound, and thus the aggregation of the acetylene black particles is effectively suppressed. Therefore, the water-soluble crosslinked polymer that satisfies the above <Condition I> has excellent dispersibility or dispersion stability of the acetylene black in the aqueous dispersion, and when it is mixed with solid particles such as an electrode active material or a conductive assistant, a composition having excellent dispersibility or dispersion stability of the solid particles can be obtained. In addition, by using this composition to form an electrode for a secondary battery, the binding property between the solid particles and the current collector (hereinafter also simply referred to as binding property) can be further improved, and the cycle characteristics of the obtained secondary battery can be effectively improved.

[0020] The average particle size of the particles in the above <Condition I> is preferably 8.0 μm or less, more preferably 6.0 μm or less, even more preferably 4.0 μm or less, and particularly preferably 2.5 μm or less.

[0021] The water-soluble crosslinked polymer has a structure in which a copolymer containing a (meth)acrylic acid component and a (meth)acrylic acid ester component as constituent components is crosslinked with an aziridine compound, and exhibits a predetermined viscosity. From the viewpoint of improving the coatability of the electrode composition to a substrate such as a current collector, the viscosity of a 10 mass % aqueous solution of the water-soluble crosslinked polymer is preferably 300 mPa·s to 50,000 mPa·s, more preferably 500 mPa·s to 30,000 mPa·s, and even more preferably 500 mPa·s to 20,000 mPa·s. The above viscosity can be obtained by measuring the viscosity of a 10% by mass aqueous solution of the water-soluble crosslinked polymer using a VISCOMETER TVB-10 (product name, manufactured by Toki Sangyo Co., Ltd.) with a rotor No. M4, a rotation speed of 12 rpm, a measurement temperature of 20°C, and a measurement time of 2 minutes.

[0022] (Copolymer containing (meth)acrylic acid component and (meth)acrylic acid ester component as constituent components) (1) (Meth)acrylic acid component The (meth)acrylic acid component contained as a constituent of the copolymer has a carboxy group or a salt structure thereof, and therefore contributes to the dispersion of solid particles such as silicon-based active materials in the water-soluble crosslinked polymer by groups capable of adsorbing to the surfaces of solid particles, and also serves the function of imparting water solubility to the water-soluble crosslinked polymer. The (meth)acrylic acid component preferably contains a component having a (meth)acrylate structure. As described later, it is also preferable that a crosslinked structure different from the crosslinked structure by an aziridine compound described later is formed by neutralization with a divalent or higher metal or a polyfunctional organic base. By crosslinking the copolymer containing the above-mentioned (meth)acrylic acid component having a salt structure as a constituent with an appropriate amount of an aziridine compound, the content of the salt structure in the water-soluble crosslinked polymer can be adjusted, and the water solubility of the polymer can be increased to a desired level. In addition, the interaction with the surface of the active material or current collector is also increased, which is thought to contribute to improving the binding property.

[0023] As the counter ion for forming the (meth)acrylate structure, a common cation can be used. Examples of cations as counter ions include metal cations, such as cations of metals belonging to Group 1 of the periodic table, such as sodium ion, lithium ion, or potassium ion; cations of metals belonging to Group 2 of the periodic table, such as calcium ion or magnesium ion; and zinc ion. It is also preferable that the counter ion has a cation derived from an amine. Such an amine may be a monovalent amine, a divalent or higher polyvalent amine, a low molecular weight compound, or a high molecular weight compound such as a polymer. As the monovalent amine, monoalkylamines such as pentylamine, hexylamine, and octylamine, dialkylamines such as dibutylamine, trialkylamines such as triethylamine, alcoholamines such as ethanolamine, aromatic ring-containing amines such as benzylamine and dimethylaminopyridine, and polycyclic amines such as diazabicycloundecene can be preferably used. As the polyamine, a low molecular weight polyamine such as ethylenediamine or histidine, or a polymeric polyamine having an amino group in a polymer structural unit such as polyethyleneimine can be preferably used, and a polymeric polyamine is more preferred. In the case of a polyamine, the amines present in the molecule may each independently be any of primary amines, secondary amines, and tertiary amines. In the case of a polymeric polyamine, the polymer structure may be either linear or branched, and branched is preferred. The weight average molecular weight of the polymeric polyamine is preferably 1000 to 50000, and more preferably 5000 to 30000. The counter ion preferably contains a cation of a metal belonging to Group 1 of the periodic table, more preferably contains a sodium ion or a lithium ion, and further preferably contains a sodium ion. When sodium ions are contained as counter ions, and the water-soluble crosslinked polymer contains one type of (meth)acrylic acid ester component described below, the resistance and cycle characteristics of the secondary battery can be further improved, and when the water-soluble crosslinked polymer contains two or more types of (meth)acrylic acid ester components described below, the cycle characteristics can be further improved. It is also preferable to contain, as a counter ion, a cation derived from an amine, particularly a cation derived from a polyvalent amine, from the viewpoint of improving the breaking energy of the water-soluble crosslinked polymer. To form a salt structure, two or more kinds of counter ions may be used. For example, it is preferable to use a metal cation and a cation derived from an amine in combination, more preferably a cation of a metal belonging to Group 1 of the periodic table in combination with a cation derived from a polyvalent amine, and even more preferably a sodium ion in combination with a cation derived from polyethyleneimine. When a metal cation and an amine-derived cation are used in combination, the water-soluble crosslinked polymer may have one or more types of (meth)acrylic acid ester components described below. The proportion of cations of metals belonging to Group 1 of the periodic table in the counter ions is preferably 50 mol % or more, more preferably 70 mol % or more, and even more preferably 90 mol % or more. There is no particular upper limit, and it can be 100 mol % or less. The proportion of cations derived from polyvalent amines in the counter ions is preferably 50 mol % or less, more preferably 30 mol % or less, and even more preferably 10 mol % or less. There is no particular restriction on the lower limit, and it can be 0 mol % or more.

[0024] The (meth)acrylic acid component preferably contains a component having a hydrogen atom at the end of the carboxylic acid and a component having a (meth)acrylate structure (i.e., a component having a non-hydrogen atom at the end of the carboxylic acid). In this case, the content ratio of the component having a (meth)acrylate structure in all (meth)acrylic acid components, i.e., the neutralization degree of the copolymer, is preferably 20 mol% or more, more preferably 40 mol% or more, even more preferably 50 mol% or more, and particularly preferably 70 mol% or more. The neutralization degree of the polymer may be 100 mol%, preferably 95 mol% or less, and more preferably 90 mol% or less. The above-mentioned neutralization degree means the neutralization degree of the copolymer before being crosslinked with the aziridine compound. The neutralization degree can be measured by the method described in the examples below.

[0025] The above-mentioned component having a (meth)acrylate structure can be obtained by reacting a (meth)acrylic acid component with a neutralizing agent. There is no particular restriction on the timing of reacting the neutralizing agent, but it is preferable to react the neutralizing agent with the above-mentioned copolymer. Examples of the neutralizing agent include inorganic bases such as hydroxides, carbonates, and hydrogen carbonates of metals belonging to Group 1 of the periodic table, hydroxides, and carbonates of metals belonging to Group 2 of the periodic table, and organic bases such as monoamines, polyamines, diazabicycloundecene, and pyridine. The neutralizing agent may be used alone or in combination of two or more. Preferred neutralizing agents include lithium hydroxide, sodium hydroxide, and polyethyleneimine.

[0026] Specific examples of the (meth)acrylic acid component are shown below, but the (meth)acrylic acid component in the present invention is not limited to these, and the acrylic acid portion in the specific examples below may be methacrylic acid, or may have a salt structure other than the specific examples below.

[0027] [ka]

[0028] (2) (Meth)acrylic acid ester component The (meth)acrylic acid ester component contained as a constituent of the copolymer contributes to improving the breaking energy by lowering the glass transition temperature (also abbreviated as Tg) of the water-soluble crosslinked polymer and increasing the breaking elongation in a tensile test. The (meth)acrylic acid ester component preferably contains a (meth)acrylic acid alkyl ester component or a (meth)acrylic acid aryl ester component, and more preferably contains a (meth)acrylic acid alkyl ester component. The alkyl ester moiety constituting the (meth)acrylic acid alkyl ester component and the aryl ester moiety constituting the (meth)acrylic acid aryl ester component may have a substituent, such as a hydroxy group, a carboxy group, an amino group, an alkoxy group, a phenyl group, an aliphatic ring group (e.g., an aliphatic hydrocarbon ring group, a cyclic ether group), or a halogen atom. From the viewpoint of adjusting the Tg of the water-soluble crosslinked polymer to a low temperature, it is preferable that the (meth)acrylic acid ester component does not contain a carboxylate. In addition, from the viewpoint of suppressing gelation of the water-soluble crosslinked polymer by the non-aqueous electrolyte, it is preferable that the (meth)acrylic acid ester component exhibits high solubility in the non-aqueous electrolyte and does not have a functional group (e.g., a cyano group, a methoxycarbonyl group, etc.) that is likely to gel by the non-aqueous electrolyte. It is preferable that the (meth)acrylic acid ester component does not have two or more structures derived from a (meth)acryloyloxy group in one constituent component.

[0029] From the viewpoint of further improving the dispersibility or dispersion stability of solid particles, the (meth)acrylic acid ester component preferably contains a component (hereinafter also referred to as component T) having a glass transition temperature of 20° C. or lower. The glass transition temperature of component T is preferably 15° C. or lower, more preferably 10° C. or lower. There is no particular restriction on the lower limit, but it is practical to have a glass transition temperature of −100° C. or higher. The glass transition temperature of the component T means the glass transition temperature of a homopolymer of the component T, and the value of the glass transition temperature in the table in Chapter 36 of the 4th edition of the POLYMER HANDBOOK can be used. If the glass transition temperature is not described in the above literature, the value measured using a differential scanning calorimeter (DSC) under the measurement conditions described in the Examples is used. Examples of monomers that lead to the above component T include methyl acrylate (8°C), ethyl acrylate (-20°C), butyl acrylate (-55°C), isoamyl acrylate (-45°C), 2-ethylhexyl acrylate (-70°C), lauryl acrylate (-3°C), methoxy-triethylene glycol acrylate (-50°C), phenoxyethyl acrylate (-22°C), phenoxy-polyethylene glycol acrylate (for example, Light Acrylate P-200A, a product name manufactured by Kyoeisha Chemical Co., Ltd., is at -25°C), 2-hydroxyethyl acrylate (-7°C), and 2-acryloyloxyethyl-succinic acid (-40°C). The temperature in parentheses is the glass transition temperature. However, the monomers that lead to the above component T are not limited to these. In addition, it is known that homopolymers of (meth)acrylic acid ester components have a glass transition temperature of 20°C or less when the alkyl group of the methacrylic acid ester component has 4 to 16 carbon atoms, and when the alkyl group of the acrylic acid ester component has 1 to 14 carbon atoms, and therefore, can be appropriately selected based on this.

[0030] In the water-soluble crosslinked polymer, the content of the component T in the (meth)acrylic acid ester component is preferably 40% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. There is no particular upper limit, and it can be 100% by mass. The content of the component T in the total components of the copolymer is preferably more than 20% by mass, and more preferably more than 80% by mass.

[0031] The (meth)acrylic acid ester component is preferably represented by the following general formula (E-1).

[0032] [ka]

[0033] In the above formula, R 31 R represents a hydrogen atom or a methyl group. 31The methyl group which may be taken as the methyl group is preferably an unsubstituted methyl group.

[0034] R 32 R represents a hydrogen atom, a hydroxyl group, a carboxyl group, an amino group, an alkyl group having 1 to 12 carbon atoms, a phenyl group, an aliphatic ring group, or a halogen atom. 32 The chemical formula weight is preferably 1 to 2000, more preferably 15 to 500, and further preferably 17 to 200. The alkyl group having 1 to 12 carbon atoms may be linear or branched. The alkyl group preferably has 1 to 6 carbon atoms, and more preferably has 1 to 4 carbon atoms. R 32 Preferred examples of the aliphatic cyclic group that can be used include an aliphatic hydrocarbon cyclic group and a cyclic ether group. The number of carbon atoms in the aliphatic hydrocarbon ring group is preferably 3 to 18, and more preferably 3 to 12. An example thereof is isobornyl. The cyclic ether group is preferably a 3- to 6-membered ring, more preferably a 5- or 6-membered ring, for example, tetrahydrofuryl. R 32 The amino group which can be taken as may have a nitrogen atom substituted with an alkyl group or an aryl group. As the amino group, -NH2 or an amino group in which the nitrogen atom is substituted with an alkyl group is preferred, and a dialkylamino group is more preferred. R 32 is preferably a hydrogen atom, a hydroxy group, a carboxy group, an alkyl group having 1 to 12 carbon atoms or an aliphatic ring group, more preferably a hydroxy group, a carboxy group, an alkyl group having 1 to 12 carbon atoms or an aliphatic ring group, and even more preferably a hydroxy group.

[0035] L 41 represents an alkylene group having 1 to 16 carbon atoms, an arylene group having 6 to 12 carbon atoms, an oxygen atom, a sulfur atom, a carbonyl group, or a linking group combining these, provided that the bond to the (meth)acryloyloxy group is an alkylene group having 1 to 16 carbon atoms or an arylene group having 6 to 12 carbon atoms, and L 41 R 32 When the side bonded to is an alkylene group having 1 to 16 carbon atoms, R 32represents a hydrogen atom, a hydroxyl group, a carboxyl group, an amino group, a phenyl group or a halogen atom (preferably a fluorine atom or a chlorine atom). The alkylene group having 1 to 16 carbon atoms preferably has 1 to 12 carbon atoms, more preferably 1 to 10 carbon atoms, further preferably 1 to 8 carbon atoms, and particularly preferably 1 to 6 carbon atoms. L 41 The chemical formula weight of L is preferably 14 to 2000, more preferably 28 to 500, and further preferably 40 to 200. 41 The alkylene group having 1 to 16 carbon atoms may be linear or branched. The alkylene group preferably has 1 to 12 carbon atoms, more preferably 1 to 10 carbon atoms, further preferably 1 to 8 carbon atoms, and particularly preferably 1 to 6 carbon atoms. L 41 Examples of the linking group that can be taken as a combination of an alkylene group having 1 to 16 carbon atoms, an arylene group having 6 to 12 carbon atoms, an oxygen atom, a sulfur atom, or a carbonyl group include -[alkylene-O having 1 to 16 carbon atoms] m Preferred examples thereof include -, -[alkylene having 1 to 16 carbon atoms]-[O-carbonyl]-[alkylene having 1 to 16 carbon atoms]-. m represents the average number of repetitions and is 1 to 50, preferably 1 to 10, and more preferably 2 or 3. L 41 Examples of the alkylene group include an alkylene group having 1 to 16 carbon atoms, -[alkylene-O having 1 to 16 carbon atoms] m - or -[alkylene having 1 to 16 carbon atoms]-[O-carbonyl]-[alkylene having 1 to 16 carbon atoms]- is preferred, and an alkylene group having 1 to 16 carbon atoms is more preferred. The above description can be applied to the number of carbon atoms of the alkylene group.

[0036] The (meth)acrylic acid ester component has a chemical formula weight of preferably 80-4,100, and more preferably 80-1,100.

[0037] The (meth)acrylic acid ester component preferably contains a hydroxyalkyl (meth)acrylate component from the viewpoint of further improving the dispersibility or dispersion stability of solid particles. The ratio of the hydroxyalkyl (meth)acrylate component to the total (meth)acrylic acid ester components contained in the water-soluble crosslinked polymer is preferably 40% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 85% by mass or more, and especially preferably 90% by mass or more. There is no particular limit to the upper limit, and it can be 100% by mass. The content ratio of the hydroxyalkyl (meth)acrylate component to the total constituent components of the copolymer is preferably more than 20% by mass, more preferably more than 80% by mass. In particular, from the viewpoint of further improving the resistance (reducing the resistance) of the secondary battery and further improving the cycle characteristics, it is preferable that all of the (meth)acrylic acid ester components constituting the water-soluble crosslinked polymer are hydroxyalkyl (meth)acrylate components, i.e., it is particularly preferable that the copolymer is composed of a (meth)acrylic acid component and a hydroxyalkyl (meth)acrylate component.

[0038] Specific examples of the (meth)acrylic acid ester component are shown below, but the (meth)acrylic acid ester component in the present invention is not limited to these. In the structural formulas below, ( ) denotes a repeating unit, and the number of repeats is the same as m above.

[0039] [ka]

[0040] (3) Other components The copolymer may contain components other than the (meth)acrylic acid component and the (meth)acrylic acid ester component (hereinafter also referred to as other components) within the range in which the effects of the present invention are achieved. As the other components, any components that can be used in binders for secondary batteries can be used without any particular limitation. For example, vinyl-based components such as (meth)acrylonitrile, vinyl acetate, and styrene, and (meth)acrylamide components can be used.

[0041] In all the constituent components of the copolymer, the content of the (meth)acrylic acid component is preferably from 1 to 50 mass %, more preferably from 3 to 40 mass %, further preferably from 5 to 30 mass %, and particularly preferably from 5 to 20 mass %. In all the constituent components of the copolymer, the content of the (meth)acrylic acid ester component is preferably from 50 to 99 mass%, more preferably from 60 to 97 mass%, further preferably from 70 to 95 mass%, and particularly preferably from 80 to 95 mass%. The content of the other components in the total components of the copolymer is, for example, preferably 0 to 49 mass%, more preferably 0 to 37 mass%, further preferably 0 to 25 mass%, and particularly preferably 0 to 15 mass%.

[0042] (Aziridine Compounds) The aziridine compound is not particularly limited as long as it can crosslink the copolymer, and any compound known as an aziridine crosslinking agent can be used without particular limitation. The number of aziridinyl groups in the aziridine compound may be two or more, preferably from two to four, and more preferably two or three. The molecular weight of the aziridine compound is not particularly limited as long as the effects of the present invention are achieved.

[0043] The aziridine compound is preferably a compound represented by any one of the following general formulas (1) to (3), and more preferably a compound represented by the following general formula (1) or (2).

[0044] [ka]

[0045] In the formula, R 11 represents a hydrogen atom, a halogen atom or an alkyl group; L 11 ~L 18 represents a single bond or a divalent linking group, and a divalent linking group is preferable.

[0046] R 11 The alkyl group and halogen atom which can be taken as the substituent Q have the same meanings as the alkyl group and halogen atom in the substituent group Q described later, and the preferred ranges are also the same. R 11 The alkyl group that can be taken as R may be unsubstituted or may have a substituent. 11 Examples of the substituent that the alkyl group in the formula (I) may have include substituents selected from the substituent group Q described below. R 11 The alkyl group which can be taken as the alkyl group preferably has 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms, further preferably 1 to 6 carbon atoms, and particularly preferably 1 to 3 carbon atoms. R 11 Examples of the halogen atom that can be taken include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, with a fluorine atom or a chlorine atom being preferred. R 11 is preferably an alkyl group.

[0047] L 11 ~L 18 The divalent linking group that can be taken as the linking group is not limited as long as it can bond to the nitrogen atom in the aziridinyl group (functions as a linking group), and examples thereof include an alkylene group, an arylene group, -O-, -S-, -COO-, and -CONR 50 -, or a divalent linking group formed by combining two or more of these groups. 50 represents a hydrogen atom or an alkyl group. L 11 ~L 18 The alkylene group constituting the divalent linking group which can be taken as the alkylene group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, further preferably 1 to 6 carbon atoms, particularly preferably 1 to 4 carbon atoms, and most preferably 1 or 2 carbon atoms. L 11~L 18 The number of carbon atoms in the arylene group constituting the divalent linking group which can be taken as the carbon atom is preferably 6 to 14, more preferably 6 to 10, and further preferably 6. As the arylene group, a 1,4-phenylene group is most preferable. R 50 The alkyl group that can be taken as R 11 The description of the alkyl group in the above can be preferably applied. R 50 is preferably a hydrogen atom. L 11 The number of linking atoms of the divalent linking group which can be taken as is preferably 1 to 30, more preferably 3 to 25, and further preferably 5 to 20. L 12 ~L 18 The number of linking atoms of the divalent linking group which can be taken as is preferably 1 to 20, more preferably 1 to 15, and further preferably 3 to 10. In the present invention, "L 11 The number of linking atoms of the divalent linking group that can be taken as the linking group L means the number of linking atoms that constitute the shortest molecular chain that links the nitrogen atoms of the two aziridinyl groups. For example, in the case of Chemitite DZ-22E (trade name, manufactured by Nippon Shokubai Co., Ltd.), which is an aziridinyl compound described below, 11 The atomic number of is 13. In the present invention, "L 12 ~L 18 The number of linking atoms of the divalent linking group that can be taken as R 11 or the carbon atom to which L is bonded 15 ~L 18 For example, in the case of Chemitite PZ-33 (trade name, manufactured by Nippon Shokubai Co., Ltd.), which is an aziridine compound described below, the linking group L 12 ~L 14 The number of atoms in each is 5. Linking group L 11 ~L 18 The divalent linking group that can constitute the above group is -COO- or -CONR 50 It is more preferable that the group is a group containing at least one of -COO- or -CONR50 It is more preferable that the linking group is a divalent linking group which contains at least one of - and is formed by bonding to one or more groups selected from an alkylene group and an arylene group. Linking group L 11 ~L 18 The above alkylene groups, arylene groups, -O-, -S-, -COO- and -CONR 50 The number of combinations of - is preferably 1 to 7, and more preferably 1 to 5. Linking group L 11 Specific examples of the group include -CONH-arylene-alkylene-arylene-NHCO-. Linking group L 12 ~L 18 Specific examples include alkylene-COO-alkylene.

[0048] The ratio of the content of the structural part derived from the copolymer constituting the water-soluble crosslinked polymer to the content of the structural part derived from the aziridine compound is not particularly limited as long as the copolymer is crosslinked and the effects of the present invention are exhibited. For example, the content of the structural part derived from the aziridine compound is preferably 0.3 to 10 parts by mass, more preferably 0.7 to 7.0 parts by mass, and even more preferably 1.0 to 5.0 parts by mass, per 100 parts by mass of the structural part derived from the copolymer.

[0049] - Substituent group Q - In the present invention, preferred examples of the substituent include those selected from the following substituent group Q. In the present invention, when a group is merely described as a substituent, this refers to the substituent group Q, and when a group, for example, an alkyl group, is merely described, the corresponding group in the substituent group Q is preferably applied. Furthermore, in this specification, when the alkyl group is described in distinction from the cyclic (cyclo) alkyl group, the alkyl group is used to include linear alkyl groups and branched alkyl groups. On the other hand, when the alkyl group is not described in distinction from the cyclic alkyl group, and unless otherwise specified, the alkyl group is used to include linear alkyl groups, branched alkyl groups, and cycloalkyl groups. This also applies to groups (alkoxy groups, alkylthio groups, alkenyloxy groups, etc.) that contain groups that can have a cyclic structure (alkyl groups, alkenyl groups, alkynyl groups, etc.) and compounds that contain groups that can have a cyclic structure. When a group can form a cyclic skeleton, the lower limit of the number of atoms of the group that forms the cyclic skeleton is 3 or more, and preferably 5 or more, regardless of the lower limit of the number of atoms specifically described below for groups that can have this structure. In the description of the substituent group Q below, a linear or branched structure group and a cyclic structure group, for example, an alkyl group and a cycloalkyl group, are sometimes described separately in order to clarify the linear or branched structure group and the cyclic structure group.

[0050] The substituent group Q includes the following groups. Alkyl groups (preferably alkyl groups having 1 to 20 carbon atoms, for example, methyl, ethyl, isopropyl, t-butyl, pentyl, heptyl, 1-ethylpentyl, benzyl, 2-ethoxyethyl, 1-carboxymethyl, etc.), alkenyl groups (preferably alkenyl groups having 2 to 20 carbon atoms, for example, vinyl, allyl, oleyl, etc.), alkynyl groups (preferably alkynyl groups having 2 to 20 carbon atoms, for example, ethynyl, butadiynyl, phenylethynyl, etc.), cycloalkyl groups (preferably cycloalkyl groups having 3 to 20 carbon atoms, for example , cyclopropyl, cyclopentyl, cyclohexyl, 4-methylcyclohexyl, etc.), aryl groups (preferably aryl groups having 6 to 26 carbon atoms, for example, phenyl, 1-naphthyl, 4-methoxyphenyl, 2-chlorophenyl, 3-methylphenyl, etc.), heterocyclic groups (preferably heterocyclic groups having 2 to 20 carbon atoms, more preferably a 5- or 6-membered heterocyclic group having at least one of an oxygen atom, a sulfur atom, and a nitrogen atom as a ring-constituting atom. The heterocyclic group includes an aromatic heterocyclic group and an aliphatic heterocyclic group. For example, tetrahydropyridine, a tetrahydrofuran ring group, 2-pyridyl, 4-pyridyl, 2-imidazolyl, 2-benzoimidazolyl, 2-thiazolyl, 2-oxazolyl, etc.), an alkoxy group (preferably an alkoxy group having 1 to 20 carbon atoms, for example, methoxy, ethoxy, isopropyloxy, benzyloxy, etc.), an aryloxy group (preferably an aryloxy group having 6 to 26 carbon atoms, for example, phenoxy, 1-naphthyloxy, 3-methylphenoxy, 4-methoxyphenoxy, etc.), a heterocyclic oxy group (a group in which the above heterocyclic group is bonded to an -O- group), an aryloxy group (preferably an aryloxy group having 6 to 26 carbon atoms, for example, phenoxy, 1-naphthyloxy, 3-methylphenoxy, 4-methoxyphenoxy, etc.), a heterocyclic oxy group (a group in which an -O- group is bonded to the above heterocyclic ... an alkoxycarbonyl group (preferably an alkoxycarbonyl group having 2 to 20 carbon atoms, such as ethoxycarbonyl or 2-ethylhexyloxycarbonyl), an aryloxycarbonyl group (preferably an aryloxycarbonyl group having 6 to 26 carbon atoms, such as phenoxycarbonyl, 1-naphthyloxycarbonyl, 3-methylphenoxycarbonyl, or 4-methoxyphenoxycarbonyl), an amino group (preferably an amino group having 0 to 20 carbon atoms, including an amino group substituted with a group selected from an alkyl group and an aryl group).For example, amino (-NH2), N,N-dimethylamino, N,N-diethylamino, N-ethylamino, anilino, etc.), sulfamoyl group (preferably a sulfamoyl group having 0 to 20 carbon atoms, including a sulfamoyl group substituted with a group selected from an alkyl group and an aryl group, for example, sulfamoyl (-SO2NH2), N,N-dimethylsulfamoyl, N-phenylsulfamoyl, etc.), acyl group (including an alkylcarbonyl group, an alkenylcarbonyl group, an alkynylcarbonyl group, an arylcarbonyl group, and a heterocyclic carbonyl group, preferably an acyl group having 1 to 20 carbon atoms, for example, acetyl, propionyl, butyryl, octanoyl, hexadecanoyl, acryloyl, methacryloyl, crotonoyl, benzoyl, naphthoyl, nicotinoyl, etc.), acyloxy group (alkylcarbonyloxy group, alkene Examples of the acyloxy group include an arylcarbonyloxy group, an alkynylcarbonyloxy group, an arylcarbonyloxy group, and a heterocyclic carbonyloxy group, and are preferably acyloxy groups having 1 to 20 carbon atoms, such as acetyloxy, propionyloxy, butyryloxy, octanoyloxy, hexadecanoyloxy, acryloyloxy, methacryloyloxy, crotonoyloxy, benzoyloxy, naphthoyloxy, and nicotinoyloxy; a carbamoyl group (preferably a carbamoyl group having 1 to 20 carbon atoms, and including a carbamoyl group substituted with a group selected from an alkyl group and an aryl group, such as N,N-dimethylcarbamoyl and N-phenylcarbamoyl); an acylamino group (preferably an acylamino group having 1 to 20 carbon atoms, and preferred examples of the acyl group in the acylamino group include the above-mentioned acyl groups.For example, acetylamino, benzoylamino, etc.), alkylthio groups (preferably alkylthio groups having 1 to 20 carbon atoms, for example, methylthio, ethylthio, isopropylthio, benzylthio, etc.), arylthio groups (preferably arylthio groups having 6 to 26 carbon atoms, for example, phenylthio, 1-naphthylthio, 3-methylphenylthio, 4-methoxyphenylthio, etc.), arylsilyl groups (preferably arylsilyl groups having 6 to 42 carbon atoms, for example, triphenylsilyl, etc.), heterocyclic thio groups (the above heterocyclic groups having an -S- group bonded thereto, a group having a carbon number of 0 to 20, such as, for example, -OP(=O)(OH)(R. P )), a hypophosphite group (preferably a hypophosphite group having 0 to 20 carbon atoms, for example, -OP(=O)(R P )2), a phosphoryl group (preferably a phosphoryl group having 0 to 20 carbon atoms, for example, -P(=O)(R P )2), a phosphinyl group (preferably a phosphinyl group having 0 to 20 carbon atoms, for example, -P(R P )2), sulfo group (sulfonic acid group, -S(=O)2(OH)), phosphoric acid group (-OP(=O)(OH)2), phosphonic acid group (-P(=O)(OH)2), carboxy group, hydroxy group, sulfanyl group, cyano group, halogen atom (e.g. fluorine atom, chlorine atom, bromine atom, iodine atom). P is a hydrogen atom or a substituent (preferably a group selected from the substituent group Q). Furthermore, each of the groups listed in the substituent group Q may further have the above-mentioned substituent group Q as a substituent.

[0051] The water-soluble crosslinked polymer, which is a binder component constituting the binder composition of the present invention, preferably has low swelling property in an electrolytic solution, from the viewpoint that swelling in the electrolytic solution is suppressed, thereby enabling the electrode structure to be sufficiently maintained and the cycle life to be extended. For example, the water-soluble crosslinked polymer preferably satisfies the following <Condition II>. <Condition II> The water-soluble crosslinked polymer has a swelling rate of 1% by mass or more and less than 100% by mass in a mixed solvent obtained by mixing 2 parts by mass of ethyl methyl carbonate with 1 part by mass of ethylene carbonate. That is, the swelling ratio of the water-soluble crosslinked polymer in a solvent (pseudo electrolyte) in which ethylene carbonate and ethyl methyl carbonate are mixed at a mass ratio of ethylene carbonate / ethyl methyl carbonate=1 / 2 is preferably 1% by mass or more and less than 100% by mass, more preferably 1% by mass or more and less than 50% by mass, even more preferably 1% by mass or more and less than 20% by mass, and particularly preferably 1% by mass or more and less than 10% by mass. Here, when the water-soluble crosslinked polymer does not swell in the solvent, the swelling ratio is 0% by mass. The swelling ratio is determined by the method described in the examples below.

[0052] In addition, the water-soluble crosslinked polymer, which is a binder component constituting the binder composition of the present invention, preferably exhibits a certain degree of breaking energy from the viewpoint of being able to follow the repeated swelling and shrinkage of the active material and of expressing the desired binding property to extend the cycle life. The breaking energy of the water-soluble crosslinked polymer is preferably 4.0 to 15.0 MPa, more preferably 4.5 to 13.0 MPa, and even more preferably 4.8 to 11.0 MPa. The breaking energy is measured and calculated by the method described in the Examples below.

[0053] The weight-average molecular weight of the copolymer is preferably 100,000 or more, more preferably 200,000 or more, and even more preferably 300,000 or more. If the weight-average molecular weight of the copolymer is sufficiently large, when a water-soluble crosslinked polymer obtained by crosslinking the copolymer with an aziridine compound is used as a binder for a secondary battery, a large binding property is obtained, and the cycle life of a secondary battery formed by using the binder composition containing the water-soluble crosslinked polymer is extended. The upper limit is practically 3,000,000 or less, and preferably 2,000,000 or less.

[0054] In the present invention, the weight average molecular weight is a weight average molecular weight calculated as sodium polyacrylate by gel permeation chromatography (GPC), and the value measured by the method under the following measurement condition 1 is used. However, an appropriate eluent can be selected and used depending on the sample to be measured. (Measurement condition 1) Measuring instrument: HLC-8220GPC (product name, manufactured by Tosoh Corporation) Columns: TOSOH TSKgel 5000PWXL (product name, manufactured by Tosoh Corporation), TOSOH TSKgel G4000PWXL (product name, manufactured by Tosoh Corporation), and TOSOH TSKgel G2500PWXL (product name, manufactured by Tosoh Corporation) are connected together. Carrier: 200mM sodium nitrate aqueous solution Measurement temperature: 40℃ Carrier flow rate: 1.0mL / min Sample concentration: 0.2% Detector: RI (refractive index) detector

[0055] When the weight average molecular weight cannot be measured under the above measurement condition 1, for example when the sample to be measured is a polymer having a crosslinked structure, the weight average molecular weight is measured by static light scattering under the following measurement condition 2. Measuring instrument: DLS-8000 (product name, manufactured by Otsuka Electronics Co., Ltd.) Measured concentration: 0.25, 0.50, 0.75, 1.00mg / mL Diluent: 0.1M NaCl aqueous solution Laser wavelength: 633nm Pinhole: PH1=Open, PH2=Slit Measurement angles: 60, 70, 80, 90, 100, 110, 120, 130 degrees Analysis method: Molecular weight was measured from Zimm square root plot. dn / dc required for analysis was measured with Abbe refractometer.

[0056] The binder composition of the present invention may contain one kind of the water-soluble crosslinked polymer alone or may contain two or more kinds of the water-soluble crosslinked polymer alone. It is preferable that the binder composition of the present invention contains one kind of the water-soluble crosslinked polymer alone. The binder composition of the present invention may contain, in addition to the water-soluble crosslinked polymer, other polymers commonly used as binders for batteries. In this case, the weight-average molecular weight of the other polymers is preferably more than 10,000. However, the content of the water-soluble crosslinked polymer in all the polymers contained in the binder composition of the present invention is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. It may also be 100% by mass.

[0057] The water-soluble crosslinked polymer can be synthesized by combining monomers that lead to the above-mentioned constituent components according to the purpose, synthesizing a copolymer by addition polymerization in the presence of a catalyst (including a polymerization initiator, a chain transfer agent, etc.) as necessary, and then reacting the obtained copolymer with the above-mentioned aziridine compound to crosslink it. The method and conditions for addition polymerization and the method and conditions for reacting the aziridine compound are not particularly limited, and ordinary methods and conditions can be appropriately selected.

[0058] The binder composition of the present invention contains water. The content of water in the binder composition of the present invention is not particularly limited, but may be, for example, 10% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 50% by mass or more. The binder composition of the present invention may contain 60% by mass or more of water, 70% by mass or more, or 80% by mass or more. There is no particular upper limit, but 95% by mass or less is practical. The binder composition of the present invention may contain a liquid medium other than water. Examples of the liquid medium other than water include organic solvents that are miscible with water without phase separation when mixed with water (hereinafter referred to as water-soluble organic solvents), and preferred examples thereof include N-methylpyrrolidone, methanol, ethanol, acetone, and tetrahydrofuran. The water-soluble crosslinked polymer, which is a binder component, may or may not be dissolved in the liquid medium constituting the binder composition of the present invention.

[0059] The content of the water-soluble crosslinked polymer in the binder composition of the present invention may be appropriately set depending on the purpose. For example, the content of the water-soluble crosslinked polymer in the binder composition may be 2 to 50% by mass, preferably 4 to 30% by mass, and more preferably 5 to 20% by mass. The binder composition of the present invention may contain other components depending on the purpose in addition to the water-soluble crosslinked polymer, water, and a liquid medium other than water. Examples of other components include polyhydric alcohols (alcohols having two or more hydroxyl groups). However, when the composition contains an active material capable of inserting and releasing ions of a metal belonging to Group 1 or Group 2 of the periodic table, which will be described later, this composition is not the binder composition of the present invention but the electrode composition of the present invention. The binder composition of the present invention can also be prepared by diluting the synthesis liquid of the water-soluble crosslinked polymer, etc. Therefore, the binder composition of the present invention may contain the compounds used in the synthesis of the copolymer and the water-soluble crosslinked polymer, or by-products produced after the reaction thereof.

[0060] [Composition for electrode] The electrode composition of the present invention contains the binder composition of the present invention and an active material capable of inserting and releasing ions of a metal belonging to Group 1 or Group 2 of the periodic table. If necessary, a conductive assistant and other additives may be further contained. The active material may be a positive electrode active material or a negative electrode active material. When the electrode composition contains a positive electrode active material, the electrode composition can be used as a slurry for forming a positive electrode active material layer of a secondary battery. When the electrode composition contains a negative electrode active material, the electrode composition can be used as a slurry for forming a negative electrode active material layer. The above binder composition can be applied to either a positive electrode or a negative electrode composition, but is preferably used for a negative electrode, and is particularly preferably used for a negative electrode composition having a silicon atom-containing active material. The active material, conductive assistant, and other additives are not particularly limited, and may be appropriately selected from those commonly used in secondary batteries according to the purpose.

[0061] The content of the binder composition of the present invention in the electrode composition of the present invention is a ratio calculated from the amount of solids constituting each composition (the ratio of the solids of the binder composition to the solids of the electrode composition), and is preferably 0.5 to 30 mass%, more preferably 1.0 to 20 mass%, further preferably 1.5 to 15 mass%, and particularly preferably 2.5 to 10 mass%. Typically, the solids in the binder composition of the present invention refer to the binder component (water-soluble crosslinked polymer), and the solids in the electrode composition of the present invention refer to the binder component, solid particles (electrode active material, conductive assistant, other additives, etc.), etc.

[0062] (Cathode active material) The positive electrode active material is preferably one that can reversibly insert and release lithium ions. The material is not particularly limited as long as it has the above-mentioned characteristics, and may be a transition metal oxide, an organic material, an element that can be composited with Li, such as sulfur, or a composite of sulfur and a metal. Among them, it is preferable to use a transition metal oxide as the positive electrode active material, and a transition metal element M aIt is more preferable that the transition metal oxide contains an element M (one or more elements selected from Co, Ni, Fe, Mn, Cu and V). b (Elements of Group 1 (Ia) of the periodic table other than lithium, elements of Group 2 (IIa), Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, etc.) may be mixed. b The amount of the transition metal element M a The transition metal element M is preferably 0 to 30 moles per 100 moles. a Molar ratio of Li to a It is more preferable that the ratio of the two components be 0.3 to 2.2. Specific examples of transition metal oxides include (MA) transition metal oxides having a layered rock salt structure, (MB) transition metal oxides having a spinel structure, (MC) lithium-containing transition metal phosphate compounds, (MD) lithium-containing transition metal halide phosphate compounds, and (ME) lithium-containing transition metal silicate compounds.

[0063] (MA) Specific examples of transition metal oxides with a layered rock-salt structure include LiCoO2 (lithium cobalt oxide [LCO]), LiNi2O2 (lithium nickel oxide), and LiNi 0.85 Co 0.10 Al 0.05 O2 (Lithium Nickel Cobalt Aluminum Oxide [NCA]), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (Lithium Nickel Manganese Cobalt Oxide [NMC]) and LiNi 0.5 Mn 0.5 O2 (lithium manganese nickel oxide). (MB) Specific examples of transition metal oxides having a spinel structure include LiMn2O4 (LMO), LiCoMnO4, Li2FeMn3O8, Li2CuMn3O8, Li2CrMn3O8, and Li2NiMn3O8. (MC) Examples of lithium-containing transition metal phosphate compounds include olivine-type iron phosphates such as LiFePO4 and Li3Fe2(PO4)3, iron pyrophosphates such as LiFeP2O7, cobalt phosphates such as LiCoPO4, and monoclinic Nasicon-type vanadium phosphates such as Li3V2(PO4)3 (lithium vanadium phosphate). (MD) Examples of lithium-containing transition metal halophosphate compounds include fluorophosphate iron salts such as Li2FePO4F, fluorophosphate manganese salts such as Li2MnPO4F, and fluorophosphate cobalt salts such as Li2CoPO4F. (ME) Examples of lithium-containing transition metal silicate compounds include Li2FeSiO4, Li2MnSiO4, and Li2CoSiO4. In the present invention, transition metal oxides having a layered rock-salt structure (MA) are preferred, with LCO or NMC being more preferred.

[0064] The shape of the positive electrode active material is not particularly limited, but particulate is preferred. The average particle size (average particle size converted into a sphere) of the positive electrode active material is not particularly limited. For example, it can be 0.1 to 50 μm. In order to adjust the positive electrode active material to a predetermined particle size, it may be prepared by a conventional method using a grinder or a classifier. The method of adjusting the negative electrode active material to a predetermined particle size described later can also be applied. The positive electrode active material obtained by the baking method may be used after washing with water, an acidic aqueous solution, an alkaline aqueous solution, an organic solvent, or the like.

[0065] The positive electrode active materials may be used alone or in combination of two or more. When forming a positive electrode active material layer, the unit area (cm 2 The mass (mg) (weight per unit area) of the positive electrode active material is not particularly limited and can be appropriately determined depending on the designed battery capacity.

[0066] The content of the positive electrode active material in the electrode composition of the present invention is not particularly limited, and is preferably 10 to 99 mass%, more preferably 30 to 98 mass%, further preferably 50 to 97 mass%, and particularly preferably 55 to 95 mass%, based on the total solid content.

[0067] (Negative electrode active material) The negative electrode active material is preferably one that can reversibly absorb and release lithium ions. The material is not particularly limited as long as it has the above characteristics, and examples thereof include carbonaceous materials, silicon-based materials (meaning materials containing silicon atoms), metal oxides, metal composite oxides, lithium alone, lithium alloys, and negative electrode active materials that can form alloys with lithium. Among these, carbonaceous materials and silicon-based materials are preferably used from the viewpoint of reliability.

[0068] The carbonaceous material used as the negative electrode active material is a material that is substantially made of carbon. For example, carbon black such as petroleum pitch, graphite (natural graphite such as flake graphite and lump graphite, artificial graphite such as vapor-grown graphite and fibrous graphite, expanded graphite, etc.), activated carbon, carbon fiber, coke, soft carbon, hard carbon, and carbonaceous materials obtained by firing various synthetic resins such as PAN (polyacrylonitrile)-based resins or furfuryl alcohol resins can be mentioned. In addition, various carbon fibers such as PAN-based carbon fibers, cellulose-based carbon fibers, pitch-based carbon fibers, vapor-grown carbon fibers, dehydrated PVA (polyvinyl alcohol)-based carbon fibers, lignin carbon fibers, glassy carbon fibers, and activated carbon fibers, mesophase microspheres, graphite whiskers, and plate-like graphite can also be mentioned.

[0069] The metal oxide and metal composite oxide used as the negative electrode active material are not particularly limited as long as they are oxides capable of absorbing and releasing lithium, and amorphous oxides are preferred, and chalcogenides that are reaction products of metal elements and elements of group 16 of the periodic table are also preferred. The term "amorphous" as used herein means that the oxide has a broad scattering band with a peak in the region of 20° to 40° in 2θ value in an X-ray diffraction method using CuKα radiation, and may have crystalline diffraction lines. Among the compound group consisting of the above amorphous oxides and chalcogenides, the amorphous oxides and the above chalcogenides of metalloid elements are more preferred, and the oxides or chalcogenides consisting of one or more of the elements of Groups 13 (IIIB) to 15 (VB) of the periodic table, Al, Ga, Si, Sn, Ge, Pb, Sb and Bi are particularly preferred.Specific examples of preferred amorphous oxides and chalcogenides include Ga2O3, GeO, PbO, PbO2, Pb2O3, Pb2O4, Pb3O4, Sb2O3, Sb2O4, Sb2O8Bi2O3, Sb2O8Si2O3, Sb2O5, Bi2O3, Bi2O4, GeS, PbS, PbS2, Sb2S3 and Sb2S5.

[0070] The metal (composite) oxide and the above chalcogenide preferably contain at least one of titanium and lithium as a constituent from the viewpoint of high current density charge / discharge characteristics. Examples of the metal composite oxide containing lithium (lithium composite metal oxide) include composite oxides of lithium oxide and the above metal (composite) oxide or the above chalcogenide, more specifically Li2SnO2.

[0071] The negative electrode active material preferably contains titanium atoms. More specifically, TiNb2O7 (niobium titanate oxide [NTO]), Li4Ti5O 12 Lithium titanate (LTO) is preferred because it has excellent rapid charge / discharge characteristics due to its small volumetric change when absorbing and releasing lithium ions, and because it suppresses electrode deterioration and can improve the life of lithium ion secondary batteries.

[0072] The lithium alloy as the negative electrode active material is not particularly limited as long as it is an alloy that is usually used as a negative electrode active material for secondary batteries, and an example thereof is a lithium aluminum alloy.

[0073] The lithium-alloyable negative electrode active material is not particularly limited as long as it is commonly used as the negative electrode active material of a secondary battery. Such an active material has a large expansion and contraction due to charge and discharge, and as is usually the case, the binding property between solid particles or between solid particles and the current collector decreases. However, in the present invention, a high binding property can be achieved by the water-soluble crosslinked polymer functioning as a binder. Examples of such active materials include negative electrode active materials having a silicon atom or a tin atom, and various metals such as Al and In. A negative electrode active material having a silicon atom (silicon atom-containing active material), which enables a higher battery capacity, is preferable, and a silicon atom-containing active material having a silicon atom content of 40 mol% or more of all constituent atoms is more preferable. Generally, a negative electrode containing these negative electrode active materials (for example, a Si negative electrode containing a silicon atom-containing active material, a Sn negative electrode containing an active material having a tin atom) can occlude more Li ions than a negative electrode composed only of a carbonaceous material (graphite, carbon black, etc.). That is, the amount of Li ions occluded per unit mass increases. Therefore, the battery capacity (energy density) can be increased. As a result, there is an advantage that the battery driving time can be extended. Thus, a negative electrode active material having a silicon atom or a tin atom is also referred to as a high-capacity active material. Examples of the silicon atom-containing active material include silicon materials such as Si and SiOx (0 < x ≦ 1), and further alloys containing titanium, vanadium, chromium, manganese, nickel, copper, or lanthanum (for example, LaSi2, VSi2), or organized active materials (for example, LaSi2 / Si). In addition, active materials containing a silicon atom and a tin atom such as SnSiO3 and SnSiS3 can also be mentioned. Note that SiOx can be used as a negative electrode active material (semi-metal oxide) itself, and can also be used as an active material (its precursor material) alloyable with lithium because Si is generated during the operation of the battery. Examples of the negative electrode active material having a tin atom include Sn, SnO, SnO2, SnS, SnS2, and further active materials containing the above silicon atom and tin atom. In addition, composite oxides with lithium oxide, for example, Li2SnO2, are also included.

[0074] The shape of the negative electrode active material is not particularly limited, but a particulate shape is preferred. The average particle diameter of the negative electrode active material is preferably 0.1 to 60 μm. To obtain a predetermined particle diameter, it can be prepared by a conventional method using a pulverizer or a classifier. For example, a mortar, a ball mill, a sand mill, a vibration ball mill, a satellite ball mill, a planetary ball mill, a swirling air flow type jet mill, a sieve, etc. are preferably used. During pulverization, wet pulverization in the coexistence of water or an organic solvent such as methanol can also be carried out. In order to obtain a desired particle diameter, it is preferable to perform classification. The classification method is not particularly limited, and a sieve, an air classifier, etc. can be used as desired. Classification can be used both in dry and wet forms.

[0075] The above negative electrode active material may be used alone or in combination of two or more. Among them, a combination of a silicon atom-containing active material and a carbonaceous material is preferred, and a combination of SiOx (0 < x ≤ 1) and graphite is particularly preferred. When combining SiOx (0 < x ≤ 1) and graphite, the mass ratio of SiOx to graphite (SiOx / graphite) is preferably 2 or less, more preferably 1 or less, and still more preferably 0.5 or less. There is no particular limitation on the lower limit value of the mass ratio of SiOx to graphite, but 0.05 or more is practical. When forming the negative electrode active material layer, the mass (mg) of the negative electrode active material per unit area (cm 2 ) (coating weight) is not particularly limited. It can be appropriately determined according to the designed battery capacity.

[0076] The content of the negative electrode active material in the electrode composition of the present invention is not particularly limited, and is preferably 10 to 99% by mass, more preferably 30 to 98% by mass, still more preferably 50 to 97% by mass, and particularly preferably 55 to 95% by mass based on the total solid content.

[0077] The chemical formula of the compound obtained by the above firing method can be calculated from the mass difference of the powder before and after firing as a simple method using inductively coupled plasma (ICP) emission spectrometry as a measurement method.

[0078] In the present invention, when the negative electrode active material layer is formed by charging the battery, ions of a metal belonging to Group 1 or 2 of the periodic table that are generated in the secondary battery can be used instead of the above-mentioned negative electrode active material. The negative electrode active material layer can be formed by bonding these ions with electrons and precipitating them as a metal.

[0079] (Coating of active material) The surfaces of the positive electrode active material and the negative electrode active material may be surface-coated with another metal oxide. Examples of the surface coating agent include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specific examples include titanate spinel, tantalum-based oxides, niobium-based oxides, and lithium niobate-based compounds. More specifically, Li4Ti5O 12 , Li2Ti2O5, LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4, Li2MoO4, Li3BO3, LiBO2, Li2CO3, Li2SiO3, SiO2, TiO2, ZrO2, Al2O3, B2O3, etc. The electrode surface containing the positive electrode active material or the negative electrode active material may be surface-treated with sulfur or phosphorus. Furthermore, the particle surfaces of the positive electrode active material or the negative electrode active material may be subjected to a surface treatment with active light or active gas (plasma, etc.) before or after the above-mentioned surface coating.

[0080] (Conductive assistant) The electrode composition of the present invention may contain a conductive assistant, and in particular, it is preferable that the silicon atom-containing active material as the negative electrode active material is used in combination with a conductive assistant. The conductive assistant is not particularly limited, and may be any known conductive assistant. For example, it may be an electron conductive material such as carbon blacks, such as acetylene black, ketjen black, furnace black, amorphous carbon, such as needle coke, carbon fibers, such as vapor-grown carbon fibers or carbon nanotubes, carbonaceous materials, such as graphene or fullerene, metal powders, metal fibers, such as copper or nickel, or conductive polymers, such as polyaniline, polypyrrole, polythiophene, polyacetylene, or polyphenylene derivatives. In the present invention, when an active material and a conductive assistant are used in combination, among the above-mentioned conductive assistants, those that do not insert or release Li when the battery is charged and discharged and do not function as an active material are considered to be conductive assistants. Therefore, among the conductive assistants, those that can function as an active material in the active material layer when the battery is charged and discharged are classified as active materials rather than conductive assistants. Whether or not a conductive assistant functions as an active material when the battery is charged and discharged is not unique, but is determined by the combination with the active material.

[0081] The conductive assistant may be used alone or in combination of two or more. The content of the conductive assistant in the electrode composition of the present invention is preferably 0.5 to 60 mass %, more preferably 1.0 to 50 mass %, further preferably 1.5 to 40 mass %, and particularly preferably 2.5 to 35 mass %, based on the total solid content.

[0082] The shape of the conductive assistant is not particularly limited, but is preferably particulate. The median diameter D50 of the conductive assistant is not particularly limited, but is, for example, preferably 0.01 to 50 μm, and more preferably 0.02 to 10.0 μm.

[0083] (Other additives) The electrode composition of the present invention may contain, as desired, a lithium salt, an ionic liquid, a thickener, a defoamer, a leveling agent, a dehydrating agent, an antioxidant, and the like, as components other than the above-mentioned components. For the above active materials, conductive assistants, and other additives, reference can be made to, for example, International Publication No. 2019 / 203334 and JP-A-2015-46389.

[0084] (solvent) The electrode composition of the present invention contains water as a solvent, and may contain a liquid medium other than water. As the liquid medium other than water, for example, the description of the liquid medium other than water in the binder composition of the present invention can be applied. The water-soluble crosslinked polymer, which is a binder component, may or may not be dissolved in the liquid medium constituting the electrode composition of the present invention, so long as it disperses solid particles such as an electrode active material and a conductive assistant in the electrode composition of the present invention.

[0085] The content of the solvent in the electrode composition of the present invention can be adjusted to, for example, 10 to 90 mass %, preferably 20 to 80 mass %, and more preferably 30 to 70 mass %.

[0086] [Electrode sheet] The electrode sheet of the present invention has a layer (electrode active material layer, i.e., anode active material layer or cathode active material layer) formed using the electrode composition of the present invention. The electrode sheet of the present invention may be an electrode sheet having an electrode active material layer, and may be a sheet in which the electrode active material layer is formed on a substrate such as a current collector, or a sheet in which the electrode active material layer is formed only with the electrode active material layer (anode active material layer or cathode active material layer) without a substrate. This electrode sheet is usually a sheet having a configuration in which the electrode active material layer is laminated on the current collector, and the density of the electrode mixture is not particularly limited, but may be, for example, 1.4 to 1.6 g / cm. 3 The electrode sheet of the present invention may have, as other layers, for example, a protective layer such as a release sheet, and a coating layer. The electrode sheet of the present invention can be suitably used as a material constituting the negative electrode active material layer or the positive electrode active material layer of a secondary battery.

[0087] [Manufacturing method of electrode sheet] The electrode sheet of the present invention can be obtained by forming an electrode active material layer using the electrode composition of the present invention. For example, the electrode sheet of the present invention can be manufactured by forming a film using the electrode composition of the present invention. Specifically, a current collector or the like is used as a substrate, and the electrode composition of the present invention is applied thereon (may be via another layer) to form a coating film, which is then dried to obtain an electrode sheet having an active material layer (coated and dried layer) on the substrate. The secondary battery of the present invention can be obtained by incorporating the electrode sheet obtained by the above-mentioned method for producing an electrode sheet into an electrode of the secondary battery.

[0088] [Secondary battery] The secondary battery of the present invention means a general device in which ions pass between positive and negative electrodes via an electrolyte by charging and discharging, and energy is stored and released at the positive and negative electrodes. That is, the secondary battery in the present invention includes both batteries and capacitors (e.g., lithium ion capacitors). From the viewpoint of the amount of energy stored, it is preferable that the secondary battery of the present invention is used for battery applications (not as a capacitor).

[0089] The secondary battery of the present invention will be described taking a nonaqueous electrolyte secondary battery as an example, however, the secondary battery of the present invention is not limited to a nonaqueous electrolyte secondary battery and broadly includes all secondary batteries including all-solid-state secondary batteries. A nonaqueous electrolyte secondary battery according to a preferred embodiment of the present invention includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The positive electrode has a positive electrode current collector and a positive electrode active material layer in contact with the positive electrode current collector, and the negative electrode has a negative electrode current collector and a negative electrode active material layer in contact with the negative electrode current collector. In the nonaqueous electrolyte secondary battery of the present invention, at least one of the positive electrode active material layer and the negative electrode active material layer is formed using the electrode composition of the present invention. The nonaqueous electrolyte secondary battery of the present invention functions as a secondary battery by charging and discharging by filling the space between the positive electrode and the negative electrode with a nonaqueous electrolyte.

[0090] FIG. 1 is a cross-sectional view showing a schematic of the laminated structure of a general nonaqueous electrolyte secondary battery 10, including the working electrodes when the battery is operated. The nonaqueous electrolyte secondary battery 10 has a laminated structure having, in this order, a negative electrode current collector 1, a negative electrode active material layer 2, a separator 3, a positive electrode active material layer 4, and a positive electrode current collector 5, as viewed from the negative electrode side. The space between the negative electrode active material layer and the positive electrode active material layer is filled with a nonaqueous electrolyte (not shown), and is separated by the separator 3. The separator 3 has pores, and during normal battery use, it functions as a positive / negative electrode separator that insulates between the positive and negative electrodes while allowing the electrolyte and ions to pass through the pores. With this structure, for example, in the case of a lithium-ion secondary battery, electrons (e - ) is supplied, and at the same time, lithium ions (Li + ) moves and accumulates in the negative electrode. On the other hand, during discharge, the lithium ions (Li + ) is returned to the positive electrode side through the electrolyte, and electrons are supplied to the operating part 6. In the illustrated example, a light bulb is used as the operating part 6, and it is lit by the discharge. In the present invention, the negative electrode current collector 1 and the negative electrode active material layer 2 are collectively referred to as the negative electrode, and the positive electrode active material layer 4 and the positive electrode current collector 5 are collectively referred to as the positive electrode.

[0091] The materials, nonaqueous electrolyte, members, etc. used in the nonaqueous electrolyte secondary battery are not particularly limited except that a specific layer is formed using the binder composition or electrode composition of the present invention. These materials, members, etc. can be appropriately applied to those used in normal nonaqueous electrolyte secondary batteries. In addition, as for the method of producing a nonaqueous electrolyte secondary battery, a normal method through the production of an electrode sheet can be appropriately adopted except that a specific layer is formed using the binder composition or electrode composition of the present invention. For example, JP-A-2016-201308, JP-A-2005-108835, JP-A-2012-185938, etc. can be appropriately referred to. A preferred form of the non-aqueous electrolyte will now be described in more detail.

[0092] (electrolyte) The electrolyte used in the non-aqueous electrolyte is preferably a salt of a metal ion belonging to Group 1 or Group 2 of the periodic table. The salt of the metal ion to be used is appropriately selected depending on the purpose of the non-aqueous electrolyte. For example, lithium salt, potassium salt, sodium salt, calcium salt, magnesium salt, etc. can be mentioned, and when used in a secondary battery, etc., lithium salt is preferred from the viewpoint of output. When the non-aqueous electrolyte of the present invention is used as a non-aqueous electrolyte for a lithium ion secondary battery, lithium salt may be selected as the salt of the metal ion. As the lithium salt, lithium salts usually used in electrolytes for non-aqueous electrolytes for lithium ion secondary batteries are preferred, and for example, the following lithium salts can be mentioned.

[0093] (L-1) Inorganic lithium salts: inorganic fluoride salts such as LiPF6, LiBF4, LiAsF6, LiSbF6, etc., perhalogenates such as LiClO4, LiBrO4, LiIO4, etc., inorganic chloride salts such as LiAlCl4, etc.

[0094] (L-2) Fluorine-containing organic lithium salts: perfluoroalkanesulfonates such as LiCF3SO3, perfluoroalkanesulfonylimide salts such as LiN(CF3SO2)2, LiN(CF3CF2SO2)2, LiN(FSO2)2, LiN(CF3SO2)(C4F9SO2), perfluoroalkanesulfonylmethide salts such as LiC(CF3SO2)3, perfluoroalkyl fluorophosphates such as Li[PF5(CF2CF2CF3)], Li[PF4(CF2CF2CF3)2], Li[PF3(CF2CF2CF3)3], Li[PF5(CF2CF2CF2CF3)], Li[PF4(CF2CF2CF2CF3)2], Li[PF3(CF2CF2CF2CF3)3], etc.

[0095] (L-3) Oxalatoborate salts: lithium bis(oxalato)borate, lithium difluorooxalatoborate, etc.

[0096] Among these, LiPF6, LiBF4, LiAsF6, LiSbF6, LiClO4, Li(R f1 SO3), LiN(R f1SO2)2, LiN(FSO2)2, and LiN(R f1 SO2)(R f2 SO2) is preferred, LiPF6, LiBF4, LiN(R f1 SO2)2, LiN(FSO2)2 and LiN(R f1 SO2)(R f2 More preferred are lithium imide salts such as lithium iodide salts, where R f1 , R f2 Each represents a perfluoroalkyl group. The electrolytes used in the nonaqueous electrolyte solution may be one type used alone or two or more types used in any combination.

[0097] The salt concentration of the electrolyte (preferably ions of a metal belonging to Group 1 or Group 2 of the periodic table or a metal salt thereof) in the non-aqueous electrolyte is appropriately selected depending on the purpose of use of the non-aqueous electrolyte, but is generally 10 to 50 mass % of the total mass of the non-aqueous electrolyte, and more preferably 15 to 30 mass %. The molar concentration is preferably 0.5 to 1.5 M. When evaluating the concentration of the ions, it may be calculated in terms of a salt with the suitably applied metal.

[0098] (Non-aqueous solvent) The non-aqueous electrolyte contains a non-aqueous solvent. As the non-aqueous solvent, an aprotic organic solvent is preferable, and among them, an aprotic organic solvent having 2 to 10 carbon atoms is more preferable. Examples of such non-aqueous solvents include linear or cyclic carbonate compounds, lactone compounds, linear or cyclic ether compounds, ester compounds, nitrile compounds, amide compounds, oxazolidinone compounds, nitro compounds, linear or cyclic sulfone or sulfoxide compounds, and phosphate esters. In addition, compounds having an ether bond, a carbonyl bond, an ester bond or a carbonate bond are preferred. These compounds may have a substituent, for example, a substituent selected from the above-mentioned substituent group Q.

[0099] Examples of non-aqueous solvents include ethylene carbonate, fluorinated ethylene carbonate, vinylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, methyl acetate, Examples of the solvent include ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, ethyl trimethylacetate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, N,N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N,N'-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, dimethyl sulfoxide phosphate, etc. These may be used alone or in combination of two or more. Among them, at least one selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and γ-butyrolactone is preferred, and in particular, a combination of a high-viscosity (high-dielectric constant) solvent (e.g., relative dielectric constant ε≧30) such as ethylene carbonate or propylene carbonate with a low-viscosity solvent (e.g., viscosity≦1 mPa s) such as dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate is more preferred. By using a mixed solvent of such a combination, the dissociation of the electrolyte salt and the mobility of the ions are improved. However, the non-aqueous solvent used in the present invention is not limited to these.

[0100] The secondary battery of the present invention can be mounted in electronic devices such as notebook computers, pen-input computers, mobile computers, electronic book players, mobile phones, cordless phone sub-units, pagers, handheld terminals, mobile fax machines, mobile copiers, mobile printers, headphone stereos, video movie machines, liquid crystal televisions, handheld cleaners, portable CDs, mini-discs, electric shavers, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power sources, and memory cards. It can also be mounted in consumer products such as automobiles, electric vehicles, motors, lighting equipment, toys, game equipment, road conditioners, watches, strobes, cameras, and medical equipment (pacemakers, hearing aids, shoulder massagers, and the like). It can also be combined with solar cells. EXAMPLES

[0101] The present invention will be described in more detail below based on examples. The materials, amounts, ratios, processing contents, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited to the following examples. In the following examples, the units "parts" and "%" representing compositions are based on mass unless otherwise specified.

[0102] (1) Synthesis of binder B-1 260.0 g of distilled water was added to a 1 L three-neck flask equipped with a reflux condenser and a gas inlet cock. Nitrogen gas was introduced at a flow rate of 200 mL / min for 60 minutes, and then the temperature was raised to 75° C. In a separate container, 5.4 g of acrylic acid, 48.6 g of hydroxyethyl acrylate, 80.0 g of distilled water, and 0.46 g of VA-057 (trade name, water-soluble azo polymerization initiator, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were stirred to prepare mixed solution A. The mixed solution A prepared above was dropped into the three-necked flask over 1 hour. After completion of the dropwise addition, stirring was continued at 75°C for 3 hours. After that, it was cooled in an ice bath, and 5.00g of 48% aqueous sodium hydroxide solution was added. Then, 171.54g of distilled water was added. Next, a solution obtained by diluting 1.0g of Chemitite PZ-33 (trade name, aziridine compound, manufactured by Nippon Shokubai Co., Ltd.) with 9.0g of distilled water was added to obtain an aqueous solution of binder B-1 with a solid content concentration of 10.0% by mass. The copolymer before crosslinking with the aziridine compound had a weight average molecular weight of 331000 and a neutralization degree of 80 mol%. (Measurement of acid value (degree of neutralization)) Approximately 10 g of the binder aqueous solution prepared above was precisely weighed as a sample, and 150 mL of water was added to dissolve it to prepare a sample solution. Potentiometric titration was performed on the sample solution using a titrant under the following measurement conditions, and the acid value (degree of neutralization) was calculated using the following formula. A blank test was performed using 150 mL of water instead of the sample solution. Acid value (mgKOH / g)={(VB)×f×0.1×56.11} / (W×solids concentration×0.01) In the above formula, V is the titration amount (mL) of the titrant to the sample solution, f is the titer of the titrant, B is the titration amount (mL) of the titrant in the blank test, and W is the amount of sample (g). The solid content concentration is the solid content concentration (mass%) of the sample. (Measurement conditions) Measuring device: Automatic titrator GT-100 (product name, manufactured by Nitto Seiko Analytech Co., Ltd.) Reference electrode: Double junction type Ag / AgCl reference electrode (Internal solution: 1 mol / L potassium chloride aqueous solution, External solution: 1 mol / L potassium nitrate aqueous solution) Indicator electrode: glass electrode Titrant: 0.1 mol / L potassium hydroxide solution

[0103] (2) Synthesis of binders B-2 to B-10, BC-1 to BC-3, and BC-5 As shown in Table 1 below, aqueous solutions of binders B-2 to B-10, BC-1 to BC-3, and BC-5 were prepared in the same manner as in the synthesis of binder B-1, except that the monomer components, neutralizing agent, and crosslinking agent were changed. The solid content concentration of each aqueous solution was 10.0 mass%. The neutralization degree and weight average molecular weight (Mw) of the polymer before crosslinking are as shown in Table 1 below.

[0104] (3) Synthesis of binder BC-4 Based on the synthesis method described in JP-T No. 2016-528357, binder BC-4 was synthesized as follows. In a 1000cc reactor in which nitrogen gas was refluxed and a cooling device was installed to facilitate temperature control, a monomer mixture consisting of 58g of n-butyl acrylate, 40g of methoxyethyl acrylate, and 2g of hydroxybutyl acrylate, 0.02g of n-dodecanethiol as a chain transfer agent, and 150g of ethyl acetate were added as a solvent. Next, in order to remove oxygen, the mixture was purged with nitrogen gas at 60°C for 60 minutes and then maintained at 60°C. After the mixture was homogenized, 0.04g of azobisisobutyronitrile was added as a reaction initiator. The mixture was reacted for 8 hours. Next, a solution in which 2.0g of Chemitite PZ-33 (trade name, aziridine compound, manufactured by Nippon Shokubai Co., Ltd.) was diluted with 18.0g of ethyl acetate was added to obtain an ethyl acetate solution of binder BC-4.

[0105] The structures of binders B-1 to B-10 and BC-1 to BC-5 are shown below.

[0106] [ka]

[0107] (Weight average molecular weight) The weight average molecular weight of the binder prepared above is a weight average molecular weight calculated as sodium polyacrylate by gel permeation chromatography (GPC), and is a value measured under the following conditions. Measuring instrument: HLC-8220GPC (product name, manufactured by Tosoh Corporation) Columns: TOSOH TSKgel 5000PWXL (product name, manufactured by Tosoh Corporation), TOSOH TSKgel G4000PWXL (product name, manufactured by Tosoh Corporation), and TOSOH TSKgel G2500PWXL (product name, manufactured by Tosoh Corporation) were connected. Carrier: 200mM sodium nitrate aqueous solution Measurement temperature: 40℃ Carrier flow rate: 1.0mL / min Sample concentration: 0.2% by mass Detector: RI (refractive index) detector

[0108] The weight average molecular weight of binders B-4 and B-7 could not be measured under the above measurement conditions, so they were measured by static light scattering under the following conditions. Measuring instrument: DLS-8000 (product name, manufactured by Otsuka Electronics Co., Ltd.) Measured concentration: 0.25, 0.50, 0.75, 1.00mg / mL Diluent: 0.1M NaCl aqueous solution Laser wavelength: 633nm Pinhole: PH1=Open, PH2=Slit Measurement angles: 60, 70, 80, 90, 100, 110, 120, 130 degrees Analysis method: Molecular weight was measured from Zimm square root plot. dn / dc required for analysis was measured by Abbe refractometer.

[0109] (glass transition temperature) The glass transition temperature (Tg) of the homopolymer of the monomer component from which each constituent of the copolymer is derived was taken from the glass transition temperature table in Chapter 36 of POLYMER HANDBOOK 4th. If the glass transition temperature was not described in the above literature, the value measured under the following measurement conditions was used. The homopolymers used as measurement samples had a number average molecular weight of 10,000 to 50,000. - Measurement of glass transition temperature - The glass transition temperature (Tg) was measured using a dry homopolymer sample with a differential scanning calorimeter: X-DSC7000 (trade name, manufactured by SII Nano Technology Co., Ltd.) under the following measurement conditions. The measurement was performed twice using the same sample, and the second measurement result was used. (Measurement conditions) Atmosphere in the measurement chamber: Nitrogen gas (50mL / min) Heating rate: 5℃ / min Measurement start temperature: -80℃ End of measurement temperature: 250℃ Sample pan: Aluminum pan Mass of measurement sample: 5mg Calculation of Tg: Tg is calculated by rounding off the average of the temperature at which the baseline of the DSC chart begins to change due to the glass transition (start point of the decline) and the temperature at which it returns to the baseline (end point of the decline).

[0110] [Test Example 1] Evaluation of swelling rate in simulated electrolyte The binder solution prepared above was placed on a SUS plate, dried at 50°C for 6 hours, and then the binder film was peeled off from the SUS plate. The obtained binder film was dried at 150°C under vacuum conditions (10 Torr or less) for 6 hours, and dried sufficiently to remove the solvent. 0.10 g of each binder film after drying was weighed into a glass bottle, and 1.90 g of a solvent mixed with ethylene carbonate / ethyl methyl carbonate = 1 / 2 by mass ratio was added as a simulated electrolyte solution, and heated at 60°C for 24 hours. The binder film after heating was taken out of the glass bottle and the mass Ws was measured. The binder film was dried under vacuum conditions (10 Torr or less) at 150°C for 5 hours, and the mass Wd was measured again. The obtained values ​​of Ws and Wd were applied to the following formula to calculate the swelling ratio. The results are shown in Table 1. Swelling ratio = [(Ws-Wd) / Wd] x 100

[0111] [Test Example 2] Evaluation of Breaking Energy (Polymer Tensile Test) The binder solution prepared above was applied onto a PET (polyethylene terephthalate) release film, dried for 10 hours under conditions of 150°C and 10 Torr or less, and peeled off to prepare a binder film with a thickness of 0.030 to 0.150 mm. This binder film was cut into a rectangular shape of 3 cm in length and 1 cm in width to prepare a test piece. The top and bottom of the test piece were covered with aluminum tape for 1 cm, the covered area was fixed to a jig, and a stress-strain curve was obtained from the results of measuring the load against the displacement using a tensile tester (product name: FGS-TV, manufactured by Nidec-Shimpo Corporation). The room temperature during the measurement was 23°C. The breaking energy was calculated from the area value (energy until breaking) of the obtained stress-strain curve. The results are shown in Table 1.

[0112] [Test Example 3] Evaluation of AB dispersibility The binder solution prepared above and AB (acetylene black, product name: Denka Black (powder), average particle size: 35 nm, specific surface area: 68 m) were placed in a 60 mL ointment container (Umano Chemical Co., Ltd.). 2 / g, manufactured by Denka Co., Ltd.) was added so that the mass ratio of the binder (solid content) to AB was 50 / 60, distilled water was added so that the concentration of the total solid content was 2.2 mass%, and dispersion was repeated three times for 3 minutes at 2000 rpm using Awatori Rentaro (trade name, manufactured by THINKY Co., Ltd.). Distilled water was further added to the dispersed liquid so that the concentration of the total solid content was 0.015 mass%, and dispersion was performed for 3 minutes at 2000 rpm using Awatori Rentaro (trade name, manufactured by THINKY Co., Ltd.). One minute after the dispersion treatment was completed, the particle size of AB in the obtained dispersion liquid was measured by dynamic light scattering using a zeta potential meter (trade name: ELSZ-1000, manufactured by Otsuka Electronics Co., Ltd.). The total solid content means the binder and AB. The results are shown in Table 1.

[0113] [Table 1]

[0114] (Table Notes) "-": indicates that the ingredient is not contained. PEI: Polyethyleneimine (weight average molecular weight: 10,000, Fujifilm Wako Pure Chemical Industries, Ltd.) PZ-33: Chemitite PZ-33 (trade name, manufactured by Nippon Shokubai Co., Ltd.), and DZ-22E: Chemitite DZ-22E (trade name, manufactured by Nippon Shokubai Co., Ltd.) are compounds having the following structures.

[0115] [ka]

[0116] EX-810: Deconal EX-810 (product name, ethylene glycol diglycidyl ether, manufactured by Nagase ChemteX Corporation) TDI: Tolylene diisocyanate is a mixture of the following compounds:

[0117] [ka]

[0118] M-1 to M-3 represent monomer components leading to each constituent component of the copolymer, and each has the following structure: The temperature shown under each monomer component is the Tg of the corresponding homopolymer, and the method of determining it is as described above.

[0119] [ka]

[0120] <Preparation of composition for secondary battery electrode> In a 60 mL ointment container (Umano Chemical Co., Ltd.), 1.35 g of silicon monoxide (average particle size: 5 μm, Osaka Titanium Co., Ltd.), 3.15 g of graphite (product name: MAG-D, Hitachi Chemical Co., Ltd.), and acetylene black (product name: Denka Black (powder), average particle size: 35 nm, specific surface area: 68 m 20.25 g of 100% ethanol (1.00 g / g, manufactured by Denka Co., Ltd.), 2.50 g of an aqueous solution of binder B-1 (solid content 0.25 g), and 1.6 g of distilled water were added and dispersed for 10 minutes at 2000 rpm using a foaming mixer (trade name, manufactured by THINKY Co., Ltd.). 1.3 g of distilled water was added to the dispersed liquid and dispersed for 10 minutes at 2000 rpm using a foaming mixer (trade name, manufactured by THINKY Co., Ltd.) to prepare a secondary battery electrode composition C-1. Compositions C-2 to C-10 and CC-1 to CC-5 for secondary battery electrodes were prepared in the same manner as in the preparation of the composition C-1 for secondary battery electrodes, except that the binder was changed to one shown in Table 2 below so that the solid content of the binder was the same.

[0121] <Preparation of electrode sheet> The obtained secondary battery electrode composition was applied onto a copper foil having a thickness of 20 μm using an applicator (product name: SA-204 micrometer-equipped film applicator, manufactured by Tester Sangyo Co., Ltd.) and dried at 80° C. for 1 hour. Thereafter, pressure was applied using a roll press machine until the density of the electrode mixture became 1.5 g / cm. 3 Thereafter, the electrode sheet was dried at 150° C. under vacuum conditions (10 Torr or less) for 6 hours to form an electrode active material layer with a thickness of 25 μm, thereby obtaining an electrode sheet with a total thickness of 45 μm.

[0122] [Test Example 4] Evaluation of binding ability A test piece 10 mm wide and 50 mm long was cut out from the electrode sheet prepared above, and an adhesive tape of the same width was attached to the surface of the electrode active material layer side of this test piece so as to cover the entire surface of the electrode active material layer. The average stress was measured when the tape was peeled off in the length direction at an angle of 90° at a speed of 100 mm / min. The above measurement was repeated eight times, and the average value of the eight average stresses was assigned to the following evaluation rank to evaluate the adhesion. The pass level of this test is an evaluation criterion of "3" or higher. The results are shown in Table 2. - Evaluation rank of adhesiveness - 6: 0.6N or more 5: 0.4N or more, less than 0.6N 4: 0.2N or more, less than 0.4N 3: 0.1N or more, less than 0.2N 2: 0.05N or more, less than 0.1N 1: Less than 0.05N

[0123] <Making a 2032-type coin battery> The electrode sheet prepared above was cut into a disk shape with a diameter of 13.0 mm and used as the negative electrode. A lithium foil (thickness 50 μm, 14.5 mmφ) and a polypropylene separator (thickness 25 μm, 16.0 mmφ) were stacked in this order, and 200 μL of the following electrolyte A was soaked into the separator. 200 μL of the following electrolyte A was further added (soaked) on top of the separator, and the negative electrode was stacked so that the electrode active material layer surface was in contact with the separator. Then, a 2032-type coin case was crimped to prepare a coin battery (secondary battery). This coin battery is composed of Li foil, a separator, a negative electrode active material layer, and a copper foil stacked in this order. (Electrolyte A) 1M electrolyte of LiPF6 in a mixed solvent of ethylene carbonate / ethyl methyl carbonate = 1 / 2 by mass

[0124] [Test Example 5] Evaluation of cycle characteristics As the battery characteristics of the secondary battery, cycle characteristics were evaluated based on the discharge capacity retention rate. Specifically, the discharge capacity retention rate of the secondary battery prepared above was measured using a charge / discharge evaluation device: TOSCAT-3000 (product name, manufactured by Toyo Systems Co., Ltd.). Charging was performed at a C rate of 0.2C (a rate at which the battery is fully charged in 5 hours) until the battery voltage reached 0.02V. Discharging was performed at a C rate of 0.2C until the battery voltage reached 1.5V. This cycle of charging and discharging was counted as one charge / discharge cycle, and three cycles of charging and discharging were repeated to initialize the secondary battery. After initialization, charging was performed at 0.5C until the battery voltage reached 0.02V, and then discharging was performed at 0.5C until the battery voltage reached 1.5V. This cycle of charging and discharging was repeated 50 times. The discharge capacity retention rate (the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity) was measured when the discharge capacity at the first cycle after initialization (initial discharge capacity) was set to 100%, and the cycle characteristics were evaluated by applying the discharge capacity retention rate to the following evaluation rank. The pass level of this test is an evaluation standard of "3" or higher. The results are shown in Table 2. The initial discharge capacity of all of the secondary batteries C-1 to C-10 was sufficient for them to function as secondary batteries. - Evaluation ranking of cycle characteristics - 6: 92% or more 5: 87% or more, less than 92% 4: 80% or more, less than 87% 3: 70% or more, but less than 80% 2: 50% or more, less than 70% 1: Less than 50%

[0125] [Test Example 6] Evaluation of resistance The resistance was evaluated as a battery characteristic of the secondary battery. The secondary battery prepared above was initialized in the same manner as in the evaluation of cycle characteristics. After initialization, charging was performed at a C rate of 0.2C until the battery voltage reached 0.02V, and discharging was performed at 2C until the battery voltage reached 1.5V. The ratio of discharge capacity A at this time to the discharge capacity at the third cycle at initialization was assigned to the following evaluation ranks to evaluate the resistance. The smaller the ratio of discharge capacity A (discharge capacity maintenance rate), the higher the resistance. The pass level for this test is an evaluation standard of "3" or higher. The results are shown in Table 2. - Resistance rating rank - 6: 96% or more 5: 94% or more, less than 96% 4: 92% or more, less than 94% 3: 87% or more, less than 92% 2: 80% or more, less than 87% 1: Less than 80%

[0126] [Table 2]

[0127] In the above Table 2, the content (mass %) of each component is the content of each component in the total solid content of the composition. The results in Tables 1 and 2 above reveal the following: Both binders BC-1 and BC-2 are water-soluble crosslinked polymers obtained by aziridine-crosslinking a homopolymer of acrylic acid, and do not contain a (meth)acrylic acid ester component. These binders BC-1 and BC-2 were poor in dispersibility of solid particles and had low breaking energy. Secondary batteries No. CC-1 and CC-2 equipped with electrode active material layers prepared using compositions containing these binders were poor in binding properties and cycle characteristics. Binder BC-3 is a water-soluble crosslinked polymer obtained by crosslinking a copolymer containing a (meth)acrylic acid component and a (meth)acrylic acid ester component with an isocyanate compound, and BC-5 is a water-soluble crosslinked polymer obtained by crosslinking a copolymer containing a (meth)acrylic acid component and a (meth)acrylic acid ester component with a glycidyl compound. These binders BC-3 and BC-5 had high swelling ratios in simulated electrolytes and low breaking energy. Secondary batteries No. CC-3 and CC-5 equipped with electrode active material layers made using compositions containing these binders had poor cycle characteristics. Binder BC-4 is a water-insoluble crosslinked polymer obtained by aziridine-crosslinking a copolymer containing a (meth)acrylic acid ester component, but does not contain a (meth)acrylic acid component. This binder BC-4 is water-insoluble and has a high swelling ratio in a simulated electrolyte, so that it was difficult to apply it to an aqueous slurry in the first place. In contrast, the water-soluble crosslinked polymers B-1 to B-10 defined in the present invention all have excellent dispersibility of solid particles, low swelling ratio in simulated electrolyte, and high breaking energy. Moreover, it was found that the electrode sheets prepared using the binder compositions of the present invention containing these water-soluble crosslinked polymers have excellent binding properties, and secondary batteries Nos. C-1 to C-10 equipped with these electrode sheets have sufficiently low resistance and sufficiently long cycle life.

[0128] This application claims priority based on Japanese Patent Application No. 2020-166584, filed in Japan on September 30, 2020, the contents of which are incorporated herein by reference as part of the present specification. [Explanation of symbols]

[0129] 10 Nonaqueous electrolyte secondary battery 1 Negative electrode current collector 2 Negative electrode active material layer 3. Separator 4 Cathode active material layer 5 Positive electrode current collector 6. Working part (light bulb)

Claims

1. A binder composition for a secondary battery comprising: water; and a water-soluble crosslinked polymer obtained by crosslinking a copolymer containing, as constituent components, a (meth)acrylic acid component and a (meth)acrylic acid ester component with an aziridine compound; and no active material capable of inserting or releasing ions of a metal belonging to Group 1 or Group 2 of the periodic table.

2. The binder composition for a secondary battery according to claim 1 , wherein the water-soluble crosslinked polymer has a solubility in water at 20° C. of 10 g / L or more.

3. The binder composition for a secondary battery according to claim 1 or 2, wherein the (meth)acrylic acid ester component includes a component having a glass transition temperature of 20° C. or lower.

4. The binder composition for a secondary battery according to any one of claims 1 to 3, wherein the water-soluble crosslinked polymer satisfies the following <Condition I>. <Condition I> In an aqueous dispersion in which the content of acetylene black is 60 parts by mass, the content of the water-soluble crosslinked polymer is 50 parts by mass, and the total content of the acetylene black and the water-soluble crosslinked polymer is 0.015% by mass, the average particle size of particles in the aqueous dispersion is 9.0 μm or less.

5. The binder composition for a secondary battery according to any one of claims 1 to 4, wherein the aziridine compound is a compound represented by any one of the following general formulas (1) to (3): [Formula 1] In the formula, R １１ represents a hydrogen atom, a halogen atom or an alkyl group. １１ ~L １８ represents a single bond or a divalent linking group.

6. The binder composition for a secondary battery according to claim 5 , wherein the aziridine compound is a compound represented by the general formula (1) or (2).

7. The binder composition for a secondary battery according to any one of claims 1 to 6, wherein the water-soluble crosslinked polymer satisfies the following <Condition II>: <Condition II> The water-soluble crosslinked polymer has a swelling ratio of 1% by mass or more and less than 100% by mass in a mixed solvent obtained by mixing 2 parts by mass of ethyl methyl carbonate with 1 part by mass of ethylene carbonate.

8. The binder composition for a secondary battery according to any one of claims 1 to 7, wherein the (meth)acrylic acid component includes a component having a (meth)acrylate structure.

9. The binder composition for a secondary battery according to claim 8 , wherein the (meth)acrylate structure has a counter ion derived from a polyamine.

10. The binder composition for secondary batteries according to any one of claims 1 to 9, wherein a 10 mass % aqueous solution of the water-soluble crosslinked polymer has a viscosity of 300 mPa·s to 50,000 mPa·s.

11. The binder composition for a secondary battery according to any one of claims 1 to 10, wherein the copolymer has a weight average molecular weight of 100,000 or more.

12. 12. A composition for an electrode comprising the binder composition for a secondary battery according to claim 1 and an active material capable of inserting and releasing ions of a metal belonging to Group 1 or Group 2 of the periodic table.

13. An electrode sheet having a layer constituted of the electrode composition according to claim 12.

14. 13. A secondary battery comprising a positive electrode, a separator, and a negative electrode in this order, wherein at least one of a positive electrode active material layer constituting the positive electrode and a negative electrode active material layer constituting the negative electrode is a layer constituted by the electrode composition according to claim 12.

15. A method for producing an electrode sheet, comprising forming a film of the electrode composition according to claim 12 and drying the film.

16. A method for producing a secondary battery, comprising incorporating the electrode sheet obtained by the method according to claim 15 into an electrode of the secondary battery.

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