Binder composition for electrochemical element, slurry composition for electrochemical element electrode, electrode for electrochemical element, and electrochemical element

Abstract

The purpose of the present invention is to provide a novel technology which is capable of decreasing the IV resistance of an electrochemical element at low temperatures, and is capable of improving the storage characteristics of the electrochemical element at high temperatures, while sufficiently suppressing heat generation in the event of an internal short circuit of the electrochemical element. A binder composition for electrochemical elements according to the present invention contains a binder and a thermally decomposable material. The thermally decomposable material contains a foaming agent. The thermally decomposable material has a thermal decomposition temperature of from 150°C to 400°C, a number average particle diameter of from 0.01 μm to 10 μm, a ratio of the number average particle diameter to the volume average particle diameter of from 0.05 to 1, and a circularity of from 0.05 to 0.95.

Description

[Technical Field]

[0001] The present invention relates to a binder composition for an electrochemical device, a slurry composition for an electrode for an electrochemical device, an electrode for an electrochemical device, and an electrochemical device. [Background technology]

[0002] Electrochemical devices such as lithium ion secondary batteries, electric double layer capacitors, and lithium ion capacitors are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications.

[0003] An electrode used in an electrochemical element typically includes a current collector and an electrode mixture layer formed on the current collector. The electrode mixture layer is formed, for example, by applying a slurry composition containing an electrode active material and a binder composition containing a binding agent onto the current collector and then drying the applied slurry composition.

[0004] However, electrochemical elements may experience thermal runaway due to an internal short circuit between electrodes, and therefore attempts have been made to suppress heat generation in electrochemical elements and ensure safety even when an internal short circuit occurs between electrodes. For example, Patent Document 1 discloses a positive electrode including a current collector and a positive electrode composite layer, the positive electrode composite layer containing a positive electrode active material and a melamine acid salt, which is a salt of melamine and an acid. According to Patent Document 1, the use of this positive electrode can improve input / output characteristics and charge / discharge efficiency while ensuring the safety of the non-aqueous electrolyte. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2014 / 119315 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the above-mentioned conventional technology has room for further improvement in terms of further suppressing heat generation during an internal short circuit in an electrochemical element, while at the same time reducing the IV resistance at low temperatures (hereinafter sometimes abbreviated as "low-temperature IV resistance") and improving high-temperature storage characteristics.

[0007] Therefore, an object of the present invention is to provide a new technology that can sufficiently suppress heat generation during an internal short circuit in an electrochemical element, while reducing the IV resistance of the electrochemical element at low temperatures and improving its high-temperature storage characteristics. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems, and have found that forming a battery component such as an electrode using a binder composition containing, in addition to a binder, a thermally decomposable material having a thermal decomposition temperature within a predetermined range and predetermined particle properties can sufficiently suppress heat generation during an internal short circuit of an electrochemical element, and can also improve the high-temperature storage characteristics of the electrochemical element while reducing the low-temperature IV resistance, thereby completing the present invention.

[0009] The present invention has an object to advantageously solve the above-mentioned problems, and provides a binder composition for electrochemical elements comprising a binder and a thermally decomposable material, wherein the thermally decomposable material contains a foaming agent, and the thermally decomposable material has a thermal decomposition temperature of 150°C to 400°C, a number-average particle diameter of 0.01 μm to 10 μm, a ratio of the number-average particle diameter to the volume-average particle diameter of 0.05 to 1, and a circularity of 0.05 to 0.95. Thus, by using a binder composition containing a thermally decomposable material and a binder, whose thermal decomposition temperature, number-average particle diameter, ratio of the number-average particle diameter to the volume-average particle diameter (hereinafter sometimes abbreviated as "particle diameter ratio"), and circularity are each within the above-mentioned ranges, it is possible to produce an electrochemical element in which heat generation during an internal short circuit is sufficiently suppressed, low low-temperature IV resistance, and excellent high-temperature storage characteristics are exhibited.

[0010] In the present invention, the "foaming agent" contained in the thermally decomposable material means a compound that generates a non-flammable gas such as nitrogen, carbon dioxide, ammonia, or water vapor upon thermal decomposition. In the present invention, the "thermal decomposition temperature" of the thermally decomposable material can be measured using the method described in the Examples. In the present invention, the "number average particle size" of a thermally decomposable material means the particle size at 50% of the cumulative value in the particle size distribution (number basis) measured using a laser diffraction particle size distribution analyzer. In the present invention, the "volume average particle size" of a thermally decomposable material means the particle size at an integrated value of 50% in the particle size distribution (volume basis) measured using a laser diffraction particle size distribution measuring device. In the present invention, the "circularity" of a thermally decomposable material is determined by the formula: circularity=4πS / L, where S is the area of ​​a two-dimensional image of the thermally decomposable material and L is the perimeter. 2 The circularity is calculated as follows. The circularity takes a value greater than 0 and less than or equal to 1, with a perfect circle having a circularity of 1. The more complex the two-dimensional image, the smaller the circularity value.

[0011] In the binder composition for electrochemical elements of the present invention, the thermally decomposable material preferably further contains a surfactant, and has a core-shell structure including a core made of the foaming agent and a shell made of the surfactant that covers at least a portion of the outer surface of the core. If the thermally decomposable material has the core-shell structure in which the foaming agent is coated with the surfactant, the low-temperature IV resistance of the electrochemical element can be further reduced, while the high-temperature storage characteristics can be further improved.

[0012] In addition, in the binder composition for electrochemical elements of the present invention, the proportion of the surfactant in the total amount of the foaming agent and the surfactant is preferably 0.01% by mass or more and 10% by mass or less. When the ratio of the foaming agent and surfactant that form the core-shell structure is within the above-mentioned range, the electrode mixture layer formed using the binder composition can be well adhered to the current collector (i.e., the peel strength of the electrode can be increased), and heat generation during an internal short circuit in the electrochemical element can be further suppressed. Furthermore, the low-temperature IV resistance of the electrochemical element can be further reduced, while the high-temperature storage characteristics can be further improved. In the present invention, the "proportion of the surfactant in the total amount of the foaming agent and the surfactant" in the thermally decomposable material can be measured by thermogravimetric analysis, pyrolysis GC-MS, or the like.

[0013] In the binder composition for electrochemical elements of the present invention, the melting point of the surfactant is preferably 50°C or higher and 350°C or lower. If the melting point of the surfactant is within the above range, heat generation during an internal short circuit in the electrochemical element can be further suppressed. In addition, the low-temperature IV resistance of the electrochemical element can be further reduced, while the high-temperature storage characteristics can be further improved.

[0014] In the binder composition for electrochemical elements of the present invention, the surfactant is preferably an anionic surfactant, which can increase the peel strength of the electrode and further reduce the low-temperature IV resistance of the electrochemical element.

[0015] In addition, in the binder composition for electrochemical elements of the present invention, the surfactant is preferably at least one of an aliphatic carboxylic acid and its salt. If an aliphatic carboxylic acid and / or a salt of an aliphatic carboxylic acid (hereinafter, these may be collectively abbreviated as "aliphatic carboxylic acid (salt)") is used as the surfactant, the peel strength of the electrode can be further increased and the low-temperature IV resistance of the electrochemical element can be further reduced.

[0016] In the binder composition for electrochemical elements of the present invention, the binder is preferably a polymer having at least one functional group selected from the group consisting of a carboxylic acid group, a hydroxyl group, a nitrile group, an amino group, an epoxy group, an oxazoline group, a sulfonic acid group, an ester group, and an amide group. Use of a polymer having at least one of the above-mentioned functional groups as the binder can further increase the peel strength of the electrode and further reduce the low-temperature IV resistance of the electrochemical element.

[0017] In the binder composition for electrochemical elements of the present invention, the foaming agent is preferably a nitrogen-based foaming agent. Using a nitrogen-based foaming agent as the foaming agent contained in the thermally decomposable material can further suppress heat generation during an internal short circuit in the electrochemical element. Furthermore, the low-temperature IV resistance of the electrochemical element can be further reduced, while the high-temperature storage characteristics can be further improved. In the present invention, the term "nitrogen-based blowing agent" refers to a blowing agent that generates nitrogen as a non-flammable gas by thermal decomposition.

[0018] The binder composition for an electrochemical element of the present invention may further contain a solvent.

[0019] The present invention also aims to advantageously solve the above-mentioned problems, and provides a slurry composition for an electrochemical element electrode, which comprises an electrode active material and the above-mentioned binder composition for an electrochemical element containing a solvent. An electrode obtained using a slurry composition containing the above-mentioned binder composition of the present invention can be used to produce an electrochemical element in which heat generation during an internal short circuit is sufficiently suppressed, low low-temperature IV resistance is low, and high-temperature storage characteristics are excellent.

[0020] The present invention also aims to advantageously solve the above-mentioned problems, and provides an electrode for an electrochemical device, characterized in that it comprises an electrode mixture layer formed using the above-mentioned slurry composition for an electrochemical device electrode of the present invention. By using an electrode comprising an electrode mixture layer formed from the above-mentioned slurry composition of the present invention, it is possible to produce an electrochemical device in which heat generation during an internal short circuit is sufficiently suppressed, low low-temperature IV resistance is low, and high-temperature storage characteristics are excellent.

[0021] The present invention aims to advantageously solve the above-mentioned problems, and provides an electrochemical device comprising the above-mentioned electrode for an electrochemical device of the present invention. An electrochemical device comprising the above-mentioned electrode of the present invention is excellent in safety because heat generation during an internal short circuit is sufficiently suppressed. Furthermore, the electrochemical device has low low-temperature IV resistance and excellent high-temperature storage characteristics. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a binder composition for electrochemical elements, a slurry composition for electrochemical element electrodes, and an electrode for electrochemical elements, which are capable of sufficiently suppressing heat generation during an internal short circuit of an electrochemical element, reducing IV resistance at low temperatures, and enabling the electrochemical element to exhibit excellent high-temperature storage properties. Furthermore, according to the present invention, it is possible to provide an electrochemical element in which heat generation during an internal short circuit is sufficiently suppressed, which has low IV resistance at low temperatures, and which has excellent high-temperature storage characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described in detail. The binder composition for electrochemical elements of the present invention is used for producing element components such as electrodes that constitute electrochemical elements. For example, the binder composition for electrochemical elements of the present invention can be used for preparing a slurry composition for electrochemical element electrodes. Furthermore, the slurry composition for an electrochemical element electrode of the present invention is prepared using the binder composition for an electrochemical element of the present invention, and can be used to form an electrode mixture layer of an electrode for an electrochemical element. Furthermore, the electrode for electrochemical elements of the present invention can be used as an electrode for electrochemical elements such as lithium ion secondary batteries, electric double layer capacitors, and lithium ion capacitors, and has an electrode mixture layer formed using the slurry composition for electrochemical element electrodes of the present invention. The electrochemical device of the present invention comprises the electrode for an electrochemical device of the present invention.

[0024] (Binder composition for electrochemical elements) The binder composition of the present invention includes a binder and a thermally decomposable material, and optionally includes a solvent and / or other components. The thermally decomposable material also includes a foaming agent and optionally includes a surfactant. Here, the binder composition of the present invention requires that the thermal decomposition temperature of the above-mentioned thermally decomposable material is 150°C or higher and 400°C or lower, the number average particle size is 0.01 μm or higher and 10 μm or lower, the particle size ratio is 0.05 or higher and 1 or lower, and the circularity is 0.05 or higher and 0.95 or lower.

[0025] Furthermore, in the binder composition of the present invention, the thermally decomposable material containing a foaming agent has a thermal decomposition temperature within the above-mentioned specified range and has the specified particle properties. Therefore, when the binder composition is used to prepare element components such as electrodes, heat generation during an internal short circuit in an electrochemical element can be sufficiently suppressed, the low-temperature IV resistance can be reduced, and the high-temperature storage characteristics can be improved.

[0026] <Binding material> The binder is not particularly limited as long as it is a polymer that can exhibit binding ability inside the electrochemical element, and any polymer can be used. Suitable examples of polymers used as binders, from the viewpoints of increasing the peel strength of the electrode and further reducing the low-temperature IV resistance of the electrochemical element, include polymers mainly containing aliphatic conjugated diene monomer units and their hydrogenated products (diene polymers), polymers mainly containing (meth)acrylic acid ester monomer units (acrylic polymers), polymers mainly containing (meth)acrylonitrile (nitrile polymers), and polymers mainly containing fluorine-containing monomer units (fluorine-containing polymers). Among these, diene polymers, acrylic polymers, and nitrile polymers are more preferred, and diene polymers are even more preferred. The binder may be used alone or in combination of two or more kinds in any ratio.

[0027] Here, in the present invention, "(meth)acrylic" means acrylic and / or methacrylic, and "(meth)acrylo" means acrylo and / or methacrylo. In the present invention, the phrase "containing a monomer unit" means that "a polymer obtained using the monomer contains a repeating unit derived from the monomer." Furthermore, in the present invention, the phrase "mainly comprising" a certain monomer unit means that "when the amount of all repeating units contained in the polymer is taken as 100% by mass, the content of the monomer unit exceeds 50% by mass." In the present invention, the content ratio of each monomer unit in the polymer is 1 It can be measured using nuclear magnetic resonance (NMR) techniques such as H-NMR.

[0028] <<Specific functional group>> The binder is preferably a polymer having a functional group. Examples of functional groups that the binder has include a carboxylic acid group, a hydroxyl group, a nitrile group, an amino group, an epoxy group, an oxazoline group, a sulfonic acid group, an ester group, and an amide group (hereinafter, these functional groups may be collectively referred to as "specific functional groups"). The polymer used as the binder may have one or more of the specific functional groups described above. The use of a polymer having these specific functional groups as a binder can increase the peel strength of the electrode and further reduce the low-temperature IV resistance of the electrochemical device. From the viewpoint of further increasing the peel strength of the electrode and further reducing the low-temperature IV resistance of the electrochemical device, the polymer used as a binder preferably has at least one selected from the group consisting of a carboxylic acid group, a hydroxyl group, and a nitrile group, more preferably has at least one of a carboxylic acid group and a nitrile group, and even more preferably has both a carboxylic acid group and a nitrile group.

[0029] Here, the method for introducing the specific functional group into the polymer is not particularly limited. For example, a polymer may be prepared using a monomer having the specific functional group (specific functional group-containing monomer) to obtain a polymer containing the specific functional group-containing monomer unit, or a polymer into which the specific functional group has been introduced may be obtained by modifying an arbitrary polymer, but the former is preferred. That is, the polymer used as a binder preferably contains at least one of a carboxylic acid group-containing monomer unit, a hydroxyl group-containing monomer unit, a nitrile group-containing monomer unit, an amino group-containing monomer unit, an epoxy group-containing monomer unit, an oxazoline group-containing monomer unit, a sulfonic acid group-containing monomer unit, an ester group-containing monomer unit, and an amide group-containing monomer unit, more preferably at least one of a carboxylic acid group-containing monomer unit, a hydroxyl group-containing monomer unit, and a nitrile group-containing monomer unit, even more preferably at least one of a carboxylic acid group-containing monomer unit and a nitrile group-containing monomer unit, and particularly preferably both a carboxylic acid group-containing monomer unit and a nitrile group-containing monomer unit.

[0030] <<Carboxylic acid group-containing monomer unit>> Examples of the carboxylic acid group-containing monomer capable of forming the carboxylic acid group-containing monomer unit include monocarboxylic acids and derivatives thereof, dicarboxylic acids and acid anhydrides thereof, and derivatives thereof. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid. Examples of the monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, and α-chloro-β-E-methoxyacrylic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid monoesters such as nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate. Examples of the acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Furthermore, as the carboxylic acid group-containing monomer, an acid anhydride that generates a carboxylic acid group upon hydrolysis can also be used. Among these, acrylic acid and methacrylic acid are preferred as the carboxylic acid group-containing monomer. Note that the carboxylic acid group-containing monomer may be used alone or in combination of two or more in any ratio.

[0031] <<Hydroxyl group-containing monomer units>> Examples of hydroxyl group-containing monomers that can form hydroxyl group-containing monomer units include ethylenically unsaturated alcohols such as (meth)allyl alcohol, 3-butene-1-ol, and 5-hexene-1-ol; alkanol esters of ethylenically unsaturated carboxylic acids such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, and di-2-hydroxypropyl itaconate; and esters of ethylenically unsaturated carboxylic acids such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, di-4-hydroxybutyl maleate, and di-2-hydroxypropyl itaconate; a -COO-(C q H 2q O) p -H (wherein p is an integer of 2 to 9, q is an integer of 2 to 4, R arepresents a hydrogen atom or a methyl group) and (meth)acrylic acid esters; mono(meth)acrylic acid esters of dihydroxy esters of dicarboxylic acids such as 2-hydroxyethyl-2'-(meth)acryloyloxyphthalate and 2-hydroxyethyl-2'-(meth)acryloyloxysuccinate; vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; mono(meth)allyl ethers of alkylene glycols such as (meth)allyl-2-hydroxyethyl ether, (meth)allyl-2-hydroxypropyl ether, (meth)allyl-3-hydroxypropyl ether, (meth)allyl-2-hydroxybutyl ether, (meth)allyl-3-hydroxybutyl ether, (meth)allyl-4-hydroxybutyl ether, and (meth)allyl-6-hydroxyhexyl ether; diethylene glycol mono(meth)allyl ether, dipropylene glycol Examples of the hydroxyl group-containing monomer include polyoxyalkylene glycol mono(meth)allyl ethers such as glycerin mono(meth)allyl ether, (meth)allyl-2-chloro-3-hydroxypropyl ether, and (meth)allyl-2-hydroxy-3-chloropropyl ether; mono(meth)allyl ethers of halogen- and hydroxy-substituted (poly)alkylene glycols, such as glycerin mono(meth)allyl ether, (meth)allyl-2-chloro-3-hydroxypropyl ether; mono(meth)allyl ethers of polyhydric phenols such as eugenol and isoeugenol, and halogen-substituted derivatives thereof; (meth)allyl thioethers of alkylene glycols, such as (meth)allyl-2-hydroxyethyl thioether and (meth)allyl-2-hydroxypropyl thioether; and amides having a hydroxyl group, such as N-hydroxymethylacrylamide (N-methylolacrylamide), N-hydroxymethylmethacrylamide, N-hydroxyethylacrylamide, and N-hydroxyethylmethacrylamide. The hydroxyl group-containing monomer may be used alone or in combination of two or more in any ratio. In the present invention, "(meth)allyl" means allyl and / or methallyl, and "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0032] <<Nitrile group-containing monomer unit>> Examples of nitrile group-containing monomers capable of forming nitrile group-containing monomer units include α,β-ethylenically unsaturated nitrile monomers. Specifically, the α,β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group, and examples thereof include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile and α-ethylacrylonitrile. The nitrile group-containing monomers may be used alone or in combination of two or more in any ratio.

[0033] <<Amino group-containing monomer unit>> Examples of amino group-containing monomers capable of forming amino group-containing monomer units include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, aminoethyl vinyl ether, dimethylaminoethyl vinyl ether, etc. The amino group-containing monomers may be used alone or in combination of two or more in any ratio. In the present invention, the term "(meth)acrylate" means acrylate and / or methacrylate.

[0034] <<Epoxy group-containing monomer unit>> The epoxy group-containing monomer capable of forming the epoxy group-containing monomer unit includes a monomer containing a carbon-carbon double bond and an epoxy group. Examples of the monomer containing a carbon-carbon double bond and an epoxy group include unsaturated glycidyl ethers such as vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, and o-allylphenyl glycidyl ether; diene or polyene monoepoxides such as butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, and 1,2-epoxy-5,9-cyclododecadiene; and 3,4-epoxy-1- Examples of the epoxy group-containing monomer include alkenyl epoxides such as butene, 1,2-epoxy-5-hexene, and 1,2-epoxy-9-decene; and glycidyl esters of unsaturated carboxylic acids such as glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl 4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl 4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexenecarboxylic acid, and glycidyl ester of 4-methyl-3-cyclohexenecarboxylic acid. The epoxy group-containing monomer may be used alone or in combination of two or more in any ratio.

[0035] <<Oxazoline group-containing monomer unit>> Examples of oxazoline group-containing monomers capable of forming oxazoline group-containing monomer units include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, etc. The oxazoline group-containing monomers may be used alone or in combination of two or more in any ratio.

[0036] <<Sulfonic acid group-containing monomer unit>> Examples of sulfonic acid group-containing monomers capable of forming sulfonic acid group-containing monomer units include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, styrene sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, etc. The sulfonic acid group-containing monomers may be used alone or in combination of two or more in any ratio.

[0037] <<Ester group-containing monomer units>> Examples of the ester group-containing monomer capable of forming the ester group-containing monomer unit include (meth)acrylic acid ester monomers. Examples of the (meth)acrylic acid ester monomer include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, butyl acrylates such as n-butyl acrylate and t-butyl acrylate, octyl acrylates such as pentyl acrylate, hexyl acrylate, heptyl acrylate and 2-ethylhexyl acrylate, alkyl acrylates such as nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate and stearyl acrylate; and Examples of the ester group-containing monomer include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, butyl methacrylates such as n-butyl methacrylate and t-butyl methacrylate, octyl methacrylates such as pentyl methacrylate, hexyl methacrylate, heptyl methacrylate and 2-ethylhexyl methacrylate, and methacrylic acid alkyl esters such as nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate and stearyl methacrylate. The ester group-containing monomer may be used alone or in combination of two or more at any ratio. In the present invention, when a certain monomer has a specific functional group other than an ester group, the monomer is not included in the ester group-containing monomer.

[0038] <<Amide group-containing monomer unit>> Examples of amide group-containing monomers capable of forming amide group-containing monomer units include acrylamide, methacrylamide, vinylpyrrolidone, etc. The amide group-containing monomers may be used alone or in combination of two or more in any ratio.

[0039] Here, when the amount of all repeating units contained in the polymer as a binder is taken as 100% by mass, the content of the specific functional group-containing monomer unit in the polymer is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, from the viewpoints of increasing the peel strength of the electrode and further reducing the low-temperature IV resistance of the electrochemical device. Note that the upper limit of the content of the specific functional group-containing monomer unit in the polymer as a binder is not particularly limited, and can be 100% by mass or less, for example, 99% by mass or less.

[0040] <<Other repeating units>> The polymer serving as the binder may contain repeating units (other repeating units) other than the specific functional group-containing monomer units described above. Such other repeating units are not particularly limited, but when the polymer is a diene-based monomer, examples of such other repeating units include aliphatic conjugated diene-based monomer units. Examples of aliphatic conjugated diene monomers that can form aliphatic conjugated diene monomer units include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. These may be used alone or in combination of two or more in any ratio. In the present invention, the "aliphatic conjugated diene monomer unit" also includes a structural unit (hydride unit) obtained by further hydrogenating a monomer unit contained in a polymer obtained using an aliphatic conjugated diene monomer. Among the above-mentioned aliphatic conjugated diene monomers, 1,3-butadiene and isoprene are preferred. In other words, as the aliphatic conjugated diene monomer unit, a 1,3-butadiene unit, an isoprene unit, a 1,3-butadiene hydride unit, and an isoprene hydride unit are preferred, and a 1,3-butadiene hydride unit and an isoprene hydride unit are more preferred.

[0041] Here, when the polymer used as a binder contains an aliphatic conjugated diene monomer unit, the content of the diene monomer unit in the polymer, when the amount of all repeating units contained in the polymer is taken as 100% by mass, is preferably more than 50% by mass, more preferably 60% by mass or more, and is preferably 90% by mass or less, preferably 80% by mass or less, and even more preferably 70% by mass or less, from the viewpoints of increasing the peel strength of the electrode and further reducing the low-temperature IV resistance of the electrochemical device.

[0042] <<How to prepare the binder>> The method for preparing the binder is not particularly limited. A polymeric binder is produced, for example, by polymerizing a monomer composition containing one or more monomers in an aqueous solvent, and optionally hydrogenating or modifying the monomer composition. The content of each monomer in the monomer composition can be determined based on the content of the desired monomer unit in the polymer. The polymerization method is not particularly limited, and any of solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. can be used. The polymerization reaction can be any of ionic polymerization, radical polymerization, living radical polymerization, various condensation polymerizations, addition polymerization, etc. Known emulsifiers and polymerization initiators can be used during polymerization, if necessary. Hydrogenation and modification can be carried out by known methods.

[0043] <Pyrolytic materials> As described above, the thermally decomposable material is a component containing at least a foaming agent that generates a non-flammable gas upon thermal decomposition. When an electrode mixture layer is formed using a binder composition containing a thermally decomposable material containing such a foaming agent, if the electrochemical element experiences thermal runaway and the temperature inside the element rises, the foaming agent in the electrode mixture layer decomposes (foams) to generate a non-flammable gas. This generation of non-flammable gas dilutes flammable gases generated by high-temperature decomposition of the electrolyte, preventing the spread of fire. Furthermore, the foaming of the thermally decomposable material to generate a non-flammable gas destroys the electrode structure (e.g., the electrode active material is detached from the current collector), thereby breaking the conductive path. As a result, the generation of Joule heat is suppressed, and further temperature increases inside the electrochemical element can be suppressed.

[0044] <<Foaming agent>> Here, the foaming agent contained in the thermally decomposable material is not particularly limited as long as it is a compound that decomposes when heated to generate a non-flammable gas. However, from the viewpoint of further suppressing heat generation during an internal short circuit of the electrochemical device, further reducing the low-temperature IV resistance, and further improving the high-temperature storage characteristics, a nitrogen-based foaming agent is preferred, a compound having at least one selected from the group consisting of an amino group, an azo group, a hydrazino group, a hydrazo group, and a nitroso group, a derivative thereof, or a salt thereof is more preferred, a compound having at least one of an amino group and an azo group, a derivative thereof, or a salt thereof is even more preferred, and a melamine compound is particularly preferred. The foaming agent may be used alone or in combination of two or more kinds in any ratio.

[0045] [Melamine compounds] The melamine compounds include melamine, melamine derivatives, and salts thereof. Examples of melamine and melamine derivatives include compounds represented by the following formula (I):

[0046] [ka]

[0047] In formula (I), each A is independently a hydroxyl group or NR 1 R 2 (R 1 and R 2 each independently represents a hydrogen atom, a hydrocarbon group, or a hydroxyl group-containing hydrocarbon group. 1 If there are multiple R 1 may be the same or different, and R 2 If there are multiple R 2 may be the same or different.

[0048] where R 1 and R 2 When the hydrocarbon group and hydroxyl group-containing hydrocarbon group have two or more carbon atoms, one or more oxygen atoms (-O-) may be present between the carbon atoms (however, when two or more oxygen atoms are present, they are not adjacent to each other). 1 and R 2 The number of carbon atoms in the hydrocarbon group and the hydroxyl group-containing hydrocarbon group is not particularly limited, but is preferably 1 or more and 5 or less.

[0049] Furthermore, salts of melamine and melamine derivatives are not particularly limited, but include sulfates, cyanurates, and the like.

[0050] As the melamine compound, from the viewpoints of further reducing the low-temperature IV resistance of the electrochemical element and further enhancing the high-temperature storage characteristics while improving the peel strength of the electrode, melamine, ammeline, ammelide, and their salts with cyanuric acid are preferred, melamine and melamine cyanurate (melamine cyanurate) are more preferred, and melamine cyanurate is even more preferred. The melamine compounds may be used singly or in combination of two or more kinds in any ratio.

[0051] [Other foaming agents] Examples of blowing agents other than the above-mentioned melamine compounds include azobisisobutyronitrile, p-toluenesulfonylhydrazide, 5-methyl-1H-benzotriazole, oxybisbenzenesulfonylhydrazide, trihydrazinetriazine, azodicarbonamide, hydrazodicarbonamide, dinitrosopentamethylenetetramine, p-toluenesulfonylsemicarbazide, p,p'-oxybisbenzenesulfonylsemicarbazide, and sodium hydrogen carbonate. These other blowing agents may be used alone or in combination of two or more in any ratio.

[0052] <<Thermal decomposition temperature>> The thermal decomposition temperature of the thermally decomposable material must be 150°C or higher and 400°C or lower, preferably 200°C or higher, more preferably 300°C or higher, and preferably 380°C or lower, and more preferably 360°C or lower. If the thermal decomposition temperature of the thermally decomposable material is lower than 150°C, the thermally decomposable material may unexpectedly decompose during normal operation or storage of the electrochemical device, increasing the low-temperature IV resistance of the electrochemical device and reducing its high-temperature storage characteristics. On the other hand, if the thermal decomposition temperature of the thermally decomposable material is higher than 400°C, it becomes difficult for the thermally decomposable material to generate non-flammable gases at the appropriate time, and the heat generation suppression effect during an internal short circuit that is expected from the use of the thermally decomposable material cannot be fully achieved. The thermal decomposition temperature of the thermally decomposable material can be adjusted by changing the type of foaming agent contained in the thermally decomposable material.

[0053] <<Particle properties>> The thermally decomposable material has predetermined particle properties. Specifically, the thermally decomposable material is required to have a number average particle size of 0.01 to 10 μm, a particle size ratio of 0.05 to 1, and a circularity of 0.05 to 0.95. It is presumed that the reason for this is that, when the thermally decomposable material has the particle properties described above, the behavior of the thermally decomposable material can be controlled during application and drying when forming an electrode mixture layer from a slurry composition containing a binder composition, and that the thermally decomposable material (especially a thermally decomposable material with a relatively small size) can be prevented from excessively covering the electrode active material in the resulting electrode mixture layer.This achieves effects such as a reduction in low-temperature IV resistance and improved high-temperature storage characteristics while fully ensuring the effect of suppressing heat generation during internal short circuits caused by the foaming agent contained in the thermally decomposable material.

[0054] [Number average particle size] First, the thermally decomposable material must have a number-average particle size of 0.01 μm or more and 10 μm or less, preferably 0.05 μm or more, more preferably 0.3 μm or more, even more preferably 0.4 μm or more, preferably 5 μm or less, more preferably 4 μm or less, and even more preferably 1.2 μm or less. If the number-average particle size of the thermally decomposable material is less than 0.01 μm, the expected effect of suppressing heat generation during an internal short circuit due to the use of the thermally decomposable material cannot be fully achieved, and the low-temperature IV resistance of the electrochemical element increases. On the other hand, if the number-average particle size of the thermally decomposable material exceeds 10 μm, the low-temperature IV resistance of the electrochemical element increases.

[0055] [Volume average particle size] Furthermore, the thermally decomposable material preferably has a volume average particle diameter of 0.01 μm or more, more preferably 0.1 μm or more, even more preferably 1 μm or more, particularly preferably 2 μm or more, and preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 5 μm or less. If the volume average particle diameter of the thermally decomposable material is 0.01 μm or more, the low-temperature IV resistance of the electrochemical device can be further reduced and the high-temperature storage characteristics can be further improved. On the other hand, if the volume average particle diameter of the thermally decomposable material is 10 μm or less, heat generation during an internal short circuit of the electrochemical device can be further suppressed and the low-temperature IV resistance can be further reduced.

[0056] [Particle size ratio] The ratio of the number-average particle size to the volume-average particle size of the thermally decomposable material must be 0.05 or more and 1 or less, preferably 0.2 or more, more preferably 0.3 or more, even more preferably 0.5 or more, and preferably 0.95 or less, and more preferably 0.8 or less. If the particle size ratio of the thermally decomposable material is less than 0.05, the low-temperature IV resistance of the electrochemical element increases and the high-temperature storage characteristics deteriorate. On the other hand, if the particle size ratio of the thermally decomposable material is 0.95 or less, the heat generation suppression effect during an internal short circuit, which is expected from the use of the thermally decomposable material, can be more fully obtained.

[0057] Circularity In addition, the thermally decomposable material must have a circularity of 0.05 or more and 0.95 or less, preferably 0.5 or more, more preferably 0.6 or more, even more preferably 0.75 or more, preferably 0.9 or less, and more preferably 0.85 or less. If the circularity of the thermally decomposable material is less than 0.05, the peel strength of the electrode will decrease, and the low-temperature IV resistance of the electrochemical element will increase, resulting in poor high-temperature storage characteristics. On the other hand, if the circularity of the thermally decomposable material is more than 0.95, the low-temperature IV resistance of the electrochemical element will increase, resulting in poor high-temperature storage characteristics.

[0058] The particle properties of the thermally decomposable material can be controlled by changing the preparation conditions of the thermally decomposable material. For example, when preparing a thermally decomposable material containing melamine cyanurate as a foaming agent, the number-average particle size and volume-average particle size can be controlled by changing the solid concentration in the reaction from melamine and cyanuric acid to obtain melamine cyanurate, or by subjecting the obtained melamine cyanurate to a pulverization treatment using a bead mill, etc. Furthermore, when preparing a thermally decomposable material containing melamine cyanurate as a foaming agent, the circularity can be controlled by changing the pH in the reaction from melamine and cyanuric acid to obtain melamine cyanurate. Furthermore, the particle properties of the thermally decomposable material can also be controlled by changing the granulation conditions when preparing the thermally decomposable material.

[0059] <<Structure>> Here, the thermally decomposable material having the above-mentioned thermal decomposition temperature and particle properties is not particularly limited as long as it contains at least a foaming agent, and may be composed essentially of only the foaming agent. However, from the viewpoint of further reducing the low-temperature IV resistance of the electrochemical device and further improving the high-temperature storage characteristics, the thermally decomposable material preferably has a core-shell structure comprising a core made of a foaming agent and a shell made of a surfactant that covers at least a portion of the outer surface of the core. It is not clear why the thermally decomposable material having the above-mentioned core-shell structure can further reduce the low-temperature IV resistance of the electrochemical element while further improving the high-temperature storage characteristics. However, it is presumed that this is because a thermally decomposable material having a structure in which the foaming agent is covered with a surfactant does not excessively adsorb to the electrode active material, and as a result, sufficient electrical contact between the electrode active materials is ensured.

[0060] [Surfactants] As the surfactant capable of forming a shell that covers the foaming agent core, any of anionic surfactants, nonionic surfactants and cationic surfactants can be used.

[0061] Examples of anionic surfactants include aliphatic carboxylic acids (salts) such as lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, and their metal salts (sodium salt, lithium salt, potassium salt, calcium salt, magnesium salt, aluminum salt, zinc salt); alkyl sulfates such as sodium 2-ethylhexyl sulfate and sodium lauryl sulfate; dialkyl sulfosuccinates such as sodium di-2-ethylhexyl-sulfosuccinate; and alkylbenzene sulfonates. Examples of nonionic surfactants include ether-type surfactants such as polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, and polyoxyethylene-2-ethylhexyl ether; and ester-type surfactants such as polyoxyethylene monolaurate, polyoxyethylene monostearate, sorbitan monostearate, sorbitan monolaurate, sorbitan trioleate, and glycerin stearic acid ester. Examples of cationic surfactants include amine salt types such as tetradecylamine acetate and octadecylamine acetate; and trimethyl types such as dodecyltrimethyl-ammonium chloride and octadecyltrimethyl-ammonium chloride. The surfactant may be used alone or in any combination of two or more in any ratio. From the viewpoints of increasing the peel strength of the electrode and further reducing the low-temperature IV resistance of the electrochemical device, the surfactant is preferably an anionic surfactant, more preferably an aliphatic carboxylic acid (salt), further preferably sodium stearate or lithium stearate, and particularly preferably sodium stearate.

[0062] The surfactant preferably has a molecular weight of 50 g / mol or more, more preferably 100 g / mol or more, and even more preferably 250 g / mol or more, and preferably 1,000 g / mol or less, more preferably 800 g / mol or less, and even more preferably 500 g / mol or less. If the surfactant has a molecular weight of 50 g / mol or more, the high-temperature storage characteristics of the electrochemical element can be further improved, and if it is 1,000 g / mol or less, the low-temperature IV resistance of the electrochemical element can be further reduced.

[0063] In addition, the surfactant preferably has a melting point of 50°C or higher, more preferably 200°C or higher, even more preferably 250°C or higher, and preferably 350°C or lower, more preferably 330°C or lower, and even more preferably 320°C or lower. If the melting point of the surfactant is 50°C or higher, the low-temperature IV resistance of the electrochemical device can be further reduced while the high-temperature storage characteristics can be further improved. On the other hand, if the melting point of the surfactant is 350°C or lower, heat generation in the event of an internal short circuit in the electrochemical device can be further suppressed.

[0064] The amount of surfactant contained in the thermally decomposable material having the core-shell structure described above is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 1% by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 4% by mass or less, based on 100% by mass of the total amount of the foaming agent and surfactant (usually the total amount of the thermally decomposable material). When the proportion of surfactant in the total amount of the foaming agent and surfactant is 0.01% by mass or more, the low-temperature IV resistance of the electrochemical device can be further reduced while further improving the high-temperature storage characteristics. On the other hand, when the proportion of surfactant in the total amount of the foaming agent and surfactant is 10% by mass or less, the peel strength of the electrode can be increased while further suppressing heat generation in the event of an internal short circuit in the electrochemical device.

[0065] <<Ratio of binder to degradable material>> The amount of thermally decomposable material contained in the binder composition is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 90 parts by mass or more, particularly preferably 95 parts by mass or more, and preferably 150 parts by mass or less, more preferably 130 parts by mass or less, even more preferably 110 parts by mass or less, and particularly preferably 105 parts by mass or less, per 100 parts by mass of binder. If the content of the thermally decomposable material in the binder composition is 50 parts by mass or more per 100 parts by mass of binder, the peel strength of the electrode can be increased while further suppressing heat generation during an internal short circuit in the electrochemical element. On the other hand, if the content of the thermally decomposable material in the binder composition is 150 parts by mass or less per 100 parts by mass of binder, the low-temperature IV resistance of the electrochemical element can be further reduced while further improving the high-temperature storage characteristics.

[0066] <<Method for preparing thermally decomposable materials>> The thermally decomposable material can be prepared, for example, by granulating a composition containing at least a foaming agent and, optionally, a surfactant and a dispersing medium (hereinafter referred to as a "composition for thermally decomposable material"). Here, the preferred ratio of the foaming agent to the surfactant in the composition for thermally decomposable materials can be the same as the preferred ratio of the foaming agent (core) to the surfactant (shell) in the desired thermally decomposable material. The dispersion medium can be appropriately used depending on the granulation method, and the type of the dispersion medium can be appropriately selected from water and known organic solvents depending on the granulation method.

[0067] [Granulation] The granulation method for obtaining a thermally decomposable material from the above-mentioned composition for a thermally decomposable material is not particularly limited as long as it can obtain a thermally decomposable material having the desired particle properties, but examples include spray granulation, fluidized bed granulation, coagulant precipitation, pH precipitation, dry mixing, and a method of wet mixing followed by drying and granulation. Among these, spray granulation is preferred.

[0068] In the spray granulation method, a slurry composition containing a foaming agent and a dispersant, and optionally a surfactant, as a composition for a thermally decomposable material (hereinafter referred to as "slurry composition for a thermally decomposable material") is spray-dried to obtain a thermally decomposable material having predetermined particle properties.

[0069] The method for preparing the slurry composition for thermally decomposable materials is not particularly limited, and can be carried out by mixing the above-mentioned components using a known mixer. Known mixers include ball mills, sand mills, bead mills, pigment dispersers, crushers, ultrasonic dispersers, homogenizers, and planetary mixers. Mixing is usually carried out at a temperature ranging from room temperature to 80°C for 10 minutes to several hours.

[0070] The slurry composition for pyrolyzable materials obtained by the above-described mixing is sprayed using a spray dryer, and the sprayed droplets of the slurry composition for pyrolyzable materials are dried inside a drying tower. This allows for the production of a particulate pyrolyzable material. When the slurry composition for pyrolyzable materials contains a surfactant, the surfactant adheres physically and / or chemically to the outer surface of the foaming agent contained in the droplets, resulting in a pyrolyzable material in which at least a portion of the outer surface of the foaming agent is covered with the surfactant. The temperature of the sprayed slurry composition for pyrolyzable materials is typically room temperature, but it may be heated to a temperature higher than room temperature. The hot air temperature during spray drying is preferably below the thermal decomposition temperature of the pyrolyzable material, e.g., 80°C to 250°C, preferably 100°C to 200°C.

[0071] <Solvent> Examples of solvents that may be optionally contained in the binder composition include water and organic solvents, with organic solvents being preferred. Examples of organic solvents that can be used include acetonitrile, N-methylpyrrolidone, acetylpyridine, cyclopentanone, N,N-dimethylacetamide, dimethylformamide, dimethyl sulfoxide, methylformamide, methyl ethyl ketone, furfural, and ethylenediamine. Among these, N-methyl-2-pyrrolidone (NMP) is particularly preferred from the viewpoints of ease of handling, safety, and ease of synthesis. The solvent may be used alone or in combination of two or more kinds in any ratio.

[0072] <Other ingredients> In addition to the components described above, the binder composition of the present invention may contain known components such as a conductive material, a crosslinking agent, a reinforcing material, an antioxidant, a dispersant, a rheology modifier, and an electrolyte additive having the function of suppressing decomposition of the electrolyte. The conductive material is not particularly limited, and examples thereof include conductive carbon materials such as carbon black (e.g., acetylene black, Ketjen Black (registered trademark), furnace black, etc.), single-walled or multi-walled carbon nanotubes (multi-walled carbon nanotubes include cup-stacked types), carbon nanohorns, vapor-grown carbon fibers, milled carbon fibers obtained by crushing polymer fibers after firing, single-walled or multi-walled graphene, and carbon nonwoven fabric sheets obtained by firing nonwoven fabric made of polymer fibers, as well as fibers or foils of various metals. The other components may be used singly or in combination of two or more in any ratio.

[0073] <Method for preparing binder composition> The binder composition of the present invention can be prepared by mixing the binder, the thermally decomposable material, and the solvent and / or other components used as needed by a known method. There are no particular limitations on the mixing method used to obtain the binder composition, and general mixing devices such as a disper, mill, or kneader can be used.

[0074] (Slurry composition for electrochemical element electrodes) The slurry composition for electrochemical element electrodes of the present invention is a slurry-like composition containing at least an electrode active material and the above-mentioned binder composition for electrochemical elements of the present invention, which contains a solvent. In other words, the slurry composition of the present invention is typically a composition in which an electrode active material, the above-mentioned binder, the above-mentioned thermally decomposable material, and the above-mentioned other components, which are optionally blended, are dissolved and / or dispersed in the above-mentioned solvent. Furthermore, since the slurry composition of the present invention contains the above-mentioned binder composition of the present invention, an electrode having an electrode mixture layer formed from the slurry composition of the present invention can be used to produce an electrochemical element in which heat generation during internal short circuits is sufficiently suppressed, low low-temperature IV resistance, and excellent high-temperature storage characteristics are achieved.

[0075] <Electrode active material> Here, the electrode active material is a material that transfers electrons at the electrode of the electrochemical device. For example, when the electrochemical device is a lithium ion secondary battery, the electrode active material is usually a material that can absorb and release lithium. In the following, an example will be described in which the slurry composition for an electrochemical element electrode is a slurry composition for a lithium ion secondary battery electrode, but the present invention is not limited to the following example.

[0076] Positive electrode active materials for lithium ion secondary batteries are not particularly limited, and include lithium-containing cobalt oxide (lithium cobalt oxide, LiCoO2), lithium manganese oxide (LiMn2O4), lithium-containing nickel oxide (LiNiO2), lithium-containing composite oxide of Co-Ni-Mn (Li(Co Mn Ni)O2), lithium-containing composite oxide of Ni-Mn-Al, lithium-containing composite oxide of Ni-Co-Al, olivine-type lithium iron phosphate (LiFePO4), olivine-type lithium manganese phosphate (LiMnPO4), Li2MnO3-LiNiO2 solid solution, Li 1+x Mn 2-xA lithium-excess spinel compound represented by O4 (0 < X < 2), Li[Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 O2, LiNi 0.5 Mn 1.5 O4 and other known cathode active materials can be mentioned. In addition, the blending amount and particle diameter of the cathode active material are not particularly limited and can be the same as those of the conventionally used cathode active materials.

[0077] In addition, examples of the anode active material for a lithium-ion secondary battery include a carbon-based anode active material, a metal-based anode active material, and an anode active material combining these.

[0078] Here, the carbon-based anode active material refers to an active material having a carbon main skeleton into which lithium can be inserted (also referred to as "doped"). Examples of the carbon-based anode active material include a carbonaceous material and a graphite material.

[0079] And examples of the carbonaceous material include graphitizable carbon and non-graphitizable carbon having a structure close to an amorphous structure typified by glassy carbon. Here, examples of the graphitizable carbon include carbon materials obtained from tar pitch obtained from petroleum or coal as a raw material. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, pyrolytic vapor deposition carbon fibers, and the like. In addition, examples of the non-graphitizable carbon include a phenol resin fired body, a polyacrylonitrile-based carbon fiber, quasi-isotropic carbon, a furfuryl alcohol resin fired body (PFA), hard carbon, and the like.

[0080] Furthermore, examples of the graphite material include natural graphite, artificial graphite, and the like. Examples of artificial graphite include artificial graphite obtained by heat-treating carbon containing easily graphitized carbon mainly at 2800°C or higher, graphitized MCMB obtained by heat-treating MCMB at 2000°C or higher, and graphitized mesophase pitch-based carbon fiber obtained by heat-treating mesophase pitch-based carbon fiber at 2000°C or higher.

[0081] Furthermore, a metal-based negative electrode active material is an active material containing a metal, typically an active material containing an element capable of intercalating lithium, and having a theoretical electrical capacity per unit mass of 500 mAh / g or more when lithium is intercalated. Examples of metal-based active materials include lithium metal, elemental metals capable of forming lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.), alloys thereof, and oxides, sulfides, nitrides, silicides, carbides, and phosphides thereof. Among these, silicon-containing active materials (silicon-based negative electrode active materials) are preferred as metal-based negative electrode active materials. This is because the use of silicon-based negative electrode active materials can increase the capacity of lithium-ion secondary batteries.

[0082] Examples of silicon-based negative electrode active materials include silicon (Si), silicon-containing alloys, SiO, and SiO x and a composite of a Si-containing material and conductive carbon, which is obtained by coating or compounding a Si-containing material with conductive carbon. These silicon-based negative electrode active materials may be used alone or in combination of two or more. The amount and particle size of the negative electrode active material are not particularly limited, and may be the same as those of conventionally used negative electrode active materials.

[0083] <Binder composition> As the binder composition, the binder composition for electrochemical elements of the present invention is used. Here, the content of the binder composition in the slurry composition for electrochemical element electrodes is preferably such that the amount of binder per 100 parts by mass of electrode active material is 0.3 parts by mass or more, more preferably 0.7 parts by mass or more, preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less. Adding the binder composition to the slurry composition in an amount that results in a binder amount of 0.3 parts by mass or more can improve the peel strength of the electrode. On the other hand, adding the binder composition to the slurry composition in an amount that results in a binder amount of 5 parts by mass or less can ensure the proportion of electrode active material in the electrode mixture layer and sufficiently increase the capacity of the electrochemical element.

[0084] <Other ingredients> Other components that can be blended into the slurry composition are not particularly limited and include the same components as those that can be blended into the binder composition described above. Furthermore, the other components may be used alone or in combination of two or more in any ratio.

[0085] <Method for preparing slurry composition> The above-mentioned slurry composition can be prepared by mixing the above-mentioned components. Specifically, the slurry composition can be prepared by mixing the above-mentioned components with an optional solvent using a mixer such as a ball mill, sand mill, bead mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, or Filmix. Note that the solvent optionally added when preparing the slurry composition can be the same as the solvent described in the binder composition section.

[0086] (Electrodes for electrochemical elements) The electrode for electrochemical devices of the present invention comprises an electrode mixture layer formed using the above-described slurry composition for electrochemical device electrodes of the present invention. For example, the electrode of the present invention comprises a current collector and an electrode mixture layer formed on the current collector, and the electrode mixture layer is a dried product of the slurry composition for electrochemical device electrodes of the present invention. The electrode for electrochemical devices of the present invention may optionally comprise layers other than the electrode mixture layer (e.g., an adhesive layer or a porous membrane layer). The electrode for electrochemical devices of the present invention can be used as an electrode for electrochemical devices such as lithium ion secondary batteries, electric double layer capacitors, and lithium ion capacitors. Furthermore, by using the electrode of the present invention, it is possible to produce an electrochemical device in which heat generation during an internal short circuit is sufficiently suppressed, the low-temperature IV resistance is low, and high-temperature storage characteristics are excellent.

[0087] <Current collector> The current collector included in the electrode for an electrochemical device is not particularly limited as long as it is an electrically conductive and electrochemically durable material, and may be selected depending on the type of electrochemical device. When the electrode for an electrochemical device is an electrode for a lithium ion secondary battery, examples of materials constituting the current collector include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum. Among these, copper foil is particularly preferred as the current collector used for the negative electrode. Aluminum foil is particularly preferred as the material constituting the current collector used for the positive electrode. These materials may be used singly or in combination of two or more in any ratio.

[0088] <Electrode composite layer> The electrode mixture layer formed using the slurry composition for electrochemical element electrodes of the present invention is, for example, a dried product of the slurry composition for electrochemical element electrodes. Here, each component contained in the electrode mixture layer is the same as that contained in the slurry composition for electrochemical element electrodes of the present invention, and the preferred abundance ratio of each component is the same as the preferred abundance ratio of each component in the slurry composition for electrochemical element electrodes of the present invention.

[0089] <Method of manufacturing an electrode for an electrochemical element> Here, the method for producing an electrode for an electrochemical element is not particularly limited, and for example, the electrode for an electrochemical element can be produced by a step of applying a slurry composition for an electrochemical element electrode to at least one surface of a current collector (application step), and a step of drying the slurry composition for an electrochemical element electrode applied to at least one surface of the current collector to form an electrode composite layer on the current collector (drying step).

[0090] <<Coating process>> The method for applying the slurry composition for an electrochemical element electrode onto a current collector is not particularly limited, and any known method can be used. Specific examples of the application method include a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. The thickness of the slurry film on the current collector after application and before drying can be appropriately set depending on the thickness of the electrode mixture layer obtained by drying.

[0091] <<Drying process>> The method for drying the slurry composition for electrochemical element electrodes on the current collector is not particularly limited, and any known method can be used, including drying with warm air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with infrared rays or electron beams, etc. By drying the slurry composition for electrochemical element electrodes on the current collector in this manner, an electrode mixture layer can be formed on the current collector, and an electrochemical element electrode comprising the current collector and the electrode mixture layer can be obtained.

[0092] After the drying step, the electrode mixture layer may be subjected to pressure treatment using a mold press, a roll press, etc. Pressure treatment can improve the peel strength of the electrode.

[0093] (electrochemical element) The electrochemical device of the present invention is characterized by comprising the above-described electrode for an electrochemical device. The electrochemical device of the present invention is not particularly limited and may be, for example, a lithium ion secondary battery, an electric double layer capacitor, or a lithium ion capacitor, and is preferably a lithium ion secondary battery. Since the electrochemical device of the present invention comprises the electrode of the present invention, heat generation during an internal short circuit is sufficiently suppressed, maintaining a high level of safety. Furthermore, the electrochemical device of the present invention has low IV resistance at low temperatures and excellent high-temperature storage characteristics.

[0094] Hereinafter, a case where the electrochemical element is a lithium ion secondary battery will be described as an example, but the present invention is not limited to the following example. A lithium ion secondary battery as the electrochemical element of the present invention usually comprises electrodes (positive electrode and negative electrode), an electrolyte, and a separator, and uses the electrode for electrochemical elements of the present invention for at least one of the positive electrode and the negative electrode.

[0095] <Electrode> Here, the electrode other than the above-described electrode for electrochemical elements of the present invention that can be used in the lithium ion secondary battery as the electrochemical element of the present invention is not particularly limited, and any known electrode can be used. Specifically, the electrode other than the above-described electrode for electrochemical elements can be an electrode obtained by forming an electrode mixture layer on a current collector using a known manufacturing method.

[0096] <Electrolyte> As the electrolyte, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent is typically used. For example, a lithium salt is used as the supporting electrolyte. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, CF4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)NLi. Among these, LiPF6, LiClO4, and CF3SO3Li are preferred, with LiPF6 being particularly preferred, because they are easily soluble in solvents and exhibit a high degree of dissociation. One type of electrolyte may be used alone, or two or more types may be used in combination at any ratio. Generally, the use of a supporting electrolyte with a higher degree of dissociation tends to result in higher lithium ion conductivity, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0097] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. For example, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate (EMC) are preferred. Other suitable solvents include γ-butyrolactone, methyl formate, and other esters. Ethers such as 1,2-dimethoxyethane and tetrahydrofuran are also suitable. Sulfur-containing compounds such as sulfolane and dimethyl sulfoxide are also suitable. Mixtures of these solvents may also be used. Among these, carbonates are preferred because of their high dielectric constant and wide stable potential range. A mixture of ethylene carbonate and ethyl methyl carbonate is even more preferred. The concentration of the electrolyte in the electrolytic solution can be adjusted appropriately, and is preferably 0.5 to 15 mass%, more preferably 2 to 13 mass%, and even more preferably 5 to 10 mass%. The electrolytic solution may also contain known additives, such as vinylene carbonate, fluoroethylene carbonate, and ethyl methyl sulfone.

[0098] <Separator> The separator is not particularly limited, and for example, the one described in JP 2012-204303 A can be used. Among these, a microporous membrane made of a polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred because it can reduce the overall separator thickness, thereby increasing the ratio of electrode active material particles in the lithium ion secondary battery and increasing the capacity per volume. Furthermore, a separator with a functional layer, in which a functional layer (porous membrane layer or adhesive layer) is provided on one or both sides of a separator substrate, may be used as the separator.

[0099] <Method of manufacturing lithium-ion secondary batteries> The lithium ion secondary battery according to the present invention can be produced, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the resulting structure as necessary according to the battery shape, placing the resultant structure in a battery container, injecting an electrolyte into the battery container, and sealing the container. To prevent internal pressure buildup, overcharging and overdischarging, and the like, a fuse, an overcurrent protection element such as a PTC element, an expanded metal, a lead plate, or the like may be provided as necessary. The shape of the secondary battery may be any of a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, a flat type, and the like. [Example]

[0100] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. Furthermore, in a polymer produced by copolymerizing multiple types of monomers, the proportion of a monomer unit formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of the certain monomer to all the monomers used in the polymerization of the polymer, unless otherwise specified. In the examples and comparative examples, the thermal decomposition temperature, average particle size (number average particle size, volume average particle size, particle size ratio), circularity, and the proportion of the amount of surfactant in the total amount of the foaming agent and surfactant in the thermally decomposable material, the peel strength of the positive electrode, the low-temperature IV resistance, high-temperature storage characteristics, and heat generation suppression during internal short circuit of the lithium ion secondary battery were measured or evaluated using the following methods.

[0101] <Thermal decomposition temperature> In thermogravimetric analysis using a thermogravimetric differential thermal analyzer (Hitachi High-Tech Science Corporation, product name "TG / DTA7200"), the weight of the thermally decomposable material was measured while the temperature was raised from 25°C to 500°C at a rate of 10°C / min in a nitrogen atmosphere, and the temperature at which the measured weight was 95% of the mass at the start of the measurement (25°C) (5% weight loss temperature) was defined as the thermal decomposition temperature of the thermally decomposable material. <Average particle size> The number-average particle size and volume-average particle size of the thermally decomposable material were measured using a laser diffraction particle size analyzer (Microtrac-Bell, product name "MT3000II"), and the particle size ratio was calculated. <Circularity> The circularity of 1,000 particles was measured using a particle image analyzer (Malvern Panalytical, product name "Morphologi (registered trademark) G3") and the average value was calculated to evaluate the circularity of the thermally decomposable material. <Proportion of surfactant amount in the total amount of foaming agent and surfactant> In thermogravimetric analysis using a thermogravimetric differential thermal analyzer (Hitachi High-Tech Science Corporation, product name "TG / DTA7200"), the weight of the thermally decomposable material was measured while the temperature was raised from 25°C to 500°C at a rate of 10°C / min in a nitrogen atmosphere, and the weight loss at temperatures other than the thermal decomposition temperature of the foaming agent was calculated as the surfactant content. <Peel strength> The positive electrode was cut into a rectangular shape 100 mm long and 10 mm wide to prepare a test piece. Cellophane tape (compliant with JIS Z1522) was attached to the surface of the positive electrode composite layer with the side having the positive electrode composite layer facing downwards, and one end of the current collector was pulled vertically at a pulling rate of 60 mm / min to measure the stress when peeled off (note that the cellophane tape was fixed to the test table). A total of three measurements were performed, and the average was calculated and evaluated according to the following criteria. A higher average stress value indicates better peel strength for the positive electrode, indicating stronger adhesion between the positive electrode composite layer and the current collector. A: The average stress is 30N / m or more B: Average stress is 25N / m or more and less than 30N / m C: Average stress is 20N / m or more and less than 25N / m D: Average stress is less than 20N / m <Low temperature IV resistance> After the electrolyte was injected, the lithium-ion secondary battery was left standing at 25°C for 5 hours. It was then charged at 25°C at a constant current of 0.2C to a cell voltage of 3.65V, followed by aging at 60°C for 12 hours. It was then discharged at 25°C at a constant current of 0.2C to a cell voltage of 3.00V. It was then subjected to CC-CV charging at a constant current of 0.2C (upper cell voltage: 4.35V) and CC discharging at a constant current of 0.2C to 3.00V. This 0.2C charge-discharge cycle was repeated three times. It was then charged at 0.2C to a state of charge (SOC) of 50% in a 25°C environment, and the voltage V0 was measured after 3 hours of standing at -10°C. It was then discharged at a discharge rate of 1C, and the voltage V1 was measured 10 seconds after the start of discharge. The value of low-temperature IV resistance (mΩ)=(V0-V1) / 200×1000 was evaluated according to the following criteria: The smaller this value, the better the low-temperature IV resistance of the lithium ion secondary battery. A: Low temperature IV resistance is 40mΩ or less B: Low temperature IV resistance is over 40mΩ and 42mΩ or less C: Low temperature IV resistance is over 42mΩ and 44mΩ or less D: Low temperature IV resistance is over 44mΩ and 46mΩ or less E: Low temperature IV resistance > 46mΩ <High temperature storage characteristics> After the electrolyte was poured into the lithium-ion secondary battery, it was left standing at 25°C for 5 hours. Next, it was charged at 25°C at a constant current of 0.2C to a cell voltage of 3.65V, and then aged at 60°C for 12 hours. Then, it was discharged at 25°C at a constant current of 0.2C to a cell voltage of 3.00V. Then, it was subjected to CC-CV charging at a constant current of 0.2C (upper limit cell voltage 4.35V), and CC discharging at a constant current of 0.2C to 3.00V. This 0.2C charge-discharge cycle was repeated three times. The discharge capacity obtained during the final charge-discharge was designated X1. Thereafter, the cell was charged at 25° C. to a cell voltage of 4.35 V and left for 10 days in an environment at a temperature of 45° C. Thereafter, the cell was discharged at 25° C. using a constant current method of 0.2 C to a cell voltage of 3.00 V. This discharge capacity was designated as X2. Using the discharge capacities X1 and X2, the capacity retention rate, expressed as ΔC = (X2 / X1) × 100 (%), was calculated and evaluated according to the following criteria: The larger the value of this capacity retention rate ΔC, the better the high-temperature storage characteristics of the lithium-ion secondary battery. A: ΔC is 85% or more B: ΔC is 83% or more and less than 85% C: ΔC is 80% or more and less than 83% D: ΔC is less than 80% <Heat suppression during internal short circuit (forced internal short circuit test)> After injecting the electrolyte, the lithium-ion secondary batteries in the Examples and Comparative Examples were left standing at 25°C for 5 hours. Next, they were charged at 25°C at a constant current of 0.2C to a cell voltage of 3.65V, and then aged at 60°C for 12 hours. Then, they were discharged at 25°C at a constant current of 0.2C to a cell voltage of 3.00V. Then, they were subjected to CC-CV charging at a constant current of 0.2C (upper cell voltage: 4.35V), and CC discharging at a constant current of 0.2C to 3.00V. This 0.2C charge-discharge cycle was repeated three times. Then, they were charged at a charge rate of 0.2C to 4.35V (cutoff condition: 0.02C) using a constant voltage-constant current (CC-CV) method in a 25°C atmosphere. Then, a 3mm diameter, 10cm long iron nail was driven into the center of the lithium-ion secondary battery at a rate of 5m / min, forcing it to short-circuit. This forced short circuit was performed on five lithium-ion secondary batteries (test specimens) each fabricated using the same procedure, and the number of test specimens that did not burst or catch fire was used to evaluate them according to the following criteria: The greater the number of test specimens that did not burst or catch fire, the better the lithium-ion secondary battery's ability to suppress heat generation during an internal short circuit. A: The number of test specimens that did not burst or ignite was 4 or 5. B: The number of test specimens that did not explode or ignite was three. C: The number of test specimens that did not explode or ignite was 2. D: The number of test specimens that did not burst or ignite was 1 or 0.

[0102] Example 1 <Preparation of binder> 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzenesulfonate, 30 parts of acrylonitrile as a nitrile group-containing monomer, 5 parts of methacrylic acid as a carboxylic acid group-containing monomer, and 0.25 parts of t-dodecyl mercaptan as a chain transfer agent were placed in an autoclave equipped with a stirrer, in this order, and the inside of the bottle was purged with nitrogen. Then, 65 parts of 1,3-butadiene as an aliphatic conjugated diene monomer were pressurized, and 0.25 parts of ammonium persulfate were added, followed by polymerization at a reaction temperature of 40°C. A polymer containing acrylonitrile units, methacrylic acid units, and 1,3-butadiene units was obtained. The polymerization conversion was 85%. The resulting polymer was adjusted to a total solids concentration of 12% with water, and 400 mL of the resulting solution (48 g total solids) was placed in a 1 L autoclave equipped with a stirrer. After 10 minutes of nitrogen gas flow to remove dissolved oxygen from the solution, 75 mg of palladium acetate as a hydrogenation catalyst was dissolved in 180 mL of ion-exchanged water containing 4 times the molar amount of nitric acid relative to Pd and added. After the system was purged with hydrogen gas twice, the contents of the autoclave were heated to 50 °C under a pressure of 3 MPa with hydrogen gas, and the hydrogenation reaction (first-stage hydrogenation reaction) was carried out for 6 hours. Next, the autoclave was returned to atmospheric pressure, and 25 mg of palladium acetate was dissolved in 60 mL of water containing 4 times the molar amount of nitric acid relative to Pd as a hydrogenation catalyst and added. After the system was purged with hydrogen gas twice, the contents of the autoclave were heated to 50°C while pressurized with hydrogen gas to 3 MPa, and a hydrogenation reaction (second-stage hydrogenation reaction) was carried out for 6 hours to obtain an aqueous dispersion of hydrogenated nitrile rubber. An appropriate amount of NMP was added to the obtained aqueous dispersion of hydrogenated nitrile rubber to obtain a mixture. Thereafter, vacuum distillation was carried out at 90°C to remove water and excess NMP from the mixture, and an NMP solution of hydrogenated nitrile rubber (solid concentration: 8%) was obtained. <Preparation of thermally decomposable materials> Equimolar amounts of 63.0 g of melamine ground to a volume average particle size of 100 μm and 64.5 g of cyanuric acid were added to a reactor. Potassium hydroxide was then added at 1% relative to the total amount of melamine and cyanuric acid (100%), and ion-exchanged water was added to adjust the solids concentration to 55%. The mixture was then heated to 75°C with stirring and continued for 120 minutes to produce a slurry containing melamine cyanurate (a foaming agent) as the core of the thermally decomposable material. To the resulting slurry, 3 parts of anionic surfactant sodium stearate (molecular weight 306.5 g / mol, melting point: 305°C) were added to 97 parts of melamine cyanurate. Ion-exchanged water was added to adjust the solids concentration to 20%. The mixture was further stirred for 30 minutes to obtain a slurry composition for thermally decomposable materials. The resulting slurry composition was spray-dried at 140°C to obtain a thermally decomposable material. The thermal decomposition temperature, average particle size, circularity, and the ratio of the amount of surfactant to the total amount of the foaming agent and surfactant were measured for this thermally decomposable material, and the particle size ratio was calculated. The results are shown in Table 1. <Preparation of Binder Composition> 100 parts (solid content equivalent) of the NMP solution of the hydrogenated nitrile rubber and 100 parts of the thermally decomposable material were mixed, and NMP was further added to prepare a binder composition with a solid content concentration of 8%. <Preparation of Slurry Composition for Positive Electrode> 96 parts of lithium cobalt oxide as a positive electrode active material, 2.0 parts in solids equivalent of carbon black (manufactured by Denka, product name "Li-100") as a conductive material, and 2.0 parts in solids equivalent of the binder composition were charged into a planetary mixer and mixed, and NMP was gradually added thereto, followed by stirring and mixing at a temperature of 25±3°C and a rotation speed of 60 rpm. A positive electrode slurry composition was obtained by adjusting the viscosity to 3,600 mPa s at 25±3°C using a Brookfield viscometer at 60 rpm (rotor M4). <Production of positive electrodes> The positive electrode slurry composition was applied to a 20 μm thick aluminum foil current collector using a comma coater in an amount of 20±0.5 mg / cm 2The cathode slurry composition on the aluminum foil was then dried by transporting the aluminum foil at a speed of 0.5 m / min through an oven at 90°C for 2 minutes and then through an oven at 120°C for 2 minutes, thereby obtaining a cathode raw sheet with a cathode composite layer formed on the current collector. Thereafter, the cathode composite layer side of the prepared cathode raw sheet was roll-pressed under a temperature of 25±3°C and a load of 14 t, and the density of the cathode composite layer was determined to be 3.80 g / cm. 3 The peel strength of the obtained positive electrode was evaluated. The results are shown in Table 1. <Production of negative electrodes> A 5 MPa pressure vessel equipped with a stirrer was charged with 63 parts of styrene as an aromatic vinyl monomer, 34 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 2 parts of itaconic acid as a carboxylic acid group-containing monomer, 1 part of 2-hydroxyethyl acrylate as a hydroxyl group-containing monomer, 0.3 parts of t-dodecyl mercaptan as a molecular weight modifier, 5 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water as a solvent, and 1 part of potassium persulfate as a polymerization initiator. After thorough stirring, the mixture was heated to 55°C to initiate polymerization. The reaction was stopped by cooling when the monomer consumption reached 95.0%. A 5% aqueous sodium hydroxide solution was added to the resulting aqueous dispersion containing the polymer to adjust the pH to 8. Unreacted monomer was then removed by heated vacuum distillation. The mixture was then cooled to a temperature of 30°C or below to obtain an aqueous dispersion containing a negative electrode binder (a negative electrode binder composition). A planetary mixer was charged with 48.75 parts of artificial graphite (theoretical capacity 360 mAh / g) as a negative electrode active material, 48.75 parts of natural graphite (theoretical capacity 360 mAh / g), and 1 part of carboxymethyl cellulose as a thickener (solids equivalent). The mixture was then diluted with ion-exchanged water to a solids concentration of 60% and kneaded for 60 minutes at a rotation speed of 45 rpm. Then, 1.5 parts (solids equivalent) of the negative electrode binder composition obtained above was added and kneaded for 40 minutes at a rotation speed of 40 rpm. Ion-exchanged water was then added to the mixture to a viscosity of 3000±500 mPa·s (measured with a Brookfield viscometer at 25°C and 60 rpm), thereby preparing a negative electrode slurry composition. The negative electrode slurry composition was applied to the surface of a 15 μm thick copper foil current collector using a comma coater in an amount of 11±0.5 mg / cm 2 The copper foil coated with the negative electrode slurry composition was then transported at a speed of 400 mm / min through an oven at 80°C for 2 minutes and then through an oven at 110°C for 2 minutes, thereby drying the negative electrode slurry composition on the copper foil and obtaining a negative electrode blank with a negative electrode composite layer formed on the current collector. The negative electrode composite layer side of the prepared negative electrode blank was then roll-pressed under a temperature of 25±3°C and a linear pressure of 11 t (tons), until the density of the negative electrode composite layer reached 1.60 g / cm. 3 A negative electrode of 1000 .mu.m was obtained. <Preparing the separator> A single-layer polypropylene separator (manufactured by Celgard, product name "#2500") was prepared. <Fabrication of lithium-ion secondary batteries> A laminated cell (with an initial design discharge capacity of 3 Ah) was fabricated using the negative electrode, positive electrode, and separator described above. It was then placed in an aluminum foil bag and vacuum dried at 60°C for 10 hours. A 1.0 M LiPF solution (solvent: ethylene carbonate (EC) / diethyl carbonate (DEC) = 3 / 7 (volume ratio), additive: vinylene carbonate 2 vol% (solvent ratio)) was then filled as the electrolyte. The aluminum foil was then heat-sealed at 150°C to seal the opening, completing the lithium-ion secondary battery. The resulting lithium-ion battery was evaluated for low-temperature IV resistance, high-temperature storage characteristics, and heat generation suppression during internal short circuits. The results are shown in Table 1.

[0103] (Examples 2 and 3) In preparing the thermally decomposable material, the solid content of the mixture for obtaining melamine cyanurate was changed from 55% to 60% (Example 2) and 70% (Example 3), respectively. Except for this, a binder, a thermally decomposable material, a binder composition, a positive electrode slurry composition, a positive electrode, a negative electrode, a separator, and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0104] (Examples 4 and 5) In preparing the thermally decomposable material, the amount of potassium hydroxide added was changed from 1% to 0.5% (Example 4) and 2.0% (Example 5) relative to the total amount of melamine and cyanuric acid (100%), respectively. Except for this, a binder, a thermally decomposable material, a binder composition, a positive electrode slurry composition, a positive electrode, a negative electrode, a separator, and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0105] (Examples 6 and 7) In preparing the thermally decomposable material, except that the amounts of melamine cyanurate and sodium stearate were changed as follows, a binder, a thermally decomposable material, a binder composition, a positive electrode slurry composition, a positive electrode, a negative electrode, a separator, and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1. Example 6: 92 parts melamine cyanurate, 8 parts sodium stearate Example 7: Melamine cyanurate 99.5 parts, sodium stearate 0.5 parts

[0106] (Examples 8 to 11) In preparing the thermally decomposable material, except that the following surfactants were used instead of sodium stearate, an anionic surfactant, a binder, a thermally decomposable material, a binder composition, a positive electrode slurry composition, a positive electrode, a negative electrode, a separator, and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2. Example 8: Sorbitan monostearate (molecular weight: 430.6, melting point: 50°C, nonionic) Example 9: Tetradecylamine acetate (molecular weight: 273.5 g / mol, melting point: 65°C, cationic) Example 10: Lithium stearate (molecular weight: 290.4 g / mol, melting point: 220°C, anionic) Example 11: Sodium 2-ethylhexyl sulfate (232.3 g / mol, melting point: 150°C, anionic)

[0107] Example 12 Except for using the thermally decomposable material prepared as follows, a binder, a binder composition, a positive electrode slurry composition, a positive electrode, a negative electrode, a separator, and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2. <Preparation of thermally decomposable materials> Ion-exchanged water was added to 50.0 g of melamine as a foaming agent to a solids concentration of 5%, yielding a mixture. The mixture was then heated to 90°C with stirring and stirred for 10 minutes to produce a slurry containing melamine as the core of a thermally decomposable material. To the resulting slurry, 3 parts of anionic surfactant sodium stearate (molecular weight 306.5 g / mol, melting point: 305°C) was added per 97 parts of melamine, and the mixture was stirred for an additional 30 minutes to yield a slurry composition for a thermally decomposable material. The resulting slurry composition was spray-dried at 140°C to yield a thermally decomposable material.

[0108] Example 13 Except for using the thermally decomposable material prepared as follows, a binder, a binder composition, a positive electrode slurry composition, a positive electrode, a negative electrode, a separator, and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2. <Preparation of thermally decomposable materials> A pre-dispersion (premix) was prepared using a Three-One Motor (Shintokagaku Co., Ltd., product name "BL300") with 100.0 g of azodicarbonamide as a foaming agent. The resulting pre-dispersion was milled for 5 minutes using a bead mill (Ashizawa Finetech Co., Ltd., product name "LMZ-015") at a bead diameter of 1.0 mm, a bead filling rate of 80%, and a peripheral speed of 8 m / s to produce a slurry containing azodicarbonamide as the core of the thermally decomposable material. To the resulting slurry, 3 parts of anionic surfactant sodium stearate (molecular weight 306.5 g / mol, melting point: 305 °C) were added to 97 parts of azodicarbonamide and stirred for an additional 30 minutes to obtain a slurry composition for thermally decomposable materials. The resulting slurry composition was spray-dried at 140 °C to obtain a thermally decomposable material.

[0109] Example 14 Except for using the binder prepared as follows, a thermally decomposable material, a binder composition, a positive electrode slurry composition, a positive electrode, a negative electrode, a separator, and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 3. <Preparation of binder> In a reactor A equipped with a mechanical stirrer and a condenser, 85 parts of ion-exchanged water and 0.2 parts of sodium dodecylbenzenesulfonate were placed under a nitrogen atmosphere, and the mixture was heated to 55 ° C. with stirring. 0.3 parts of potassium persulfate was added as a 5.0% aqueous solution to the reactor A. Next, in another vessel B equipped with a mechanical stirrer, under a nitrogen atmosphere, 94.0 parts of acrylonitrile as a nitrile group-containing monomer, 1.0 parts of acrylamide as an amide group-containing monomer, 2.0 parts of acrylic acid as a carboxylic acid group-containing monomer, and 3.0 parts of n-butyl acrylate as an ester group-containing monomer, as well as 0.6 parts of sodium dodecylbenzenesulfonate, 0.035 parts of t-dodecyl mercaptan, 0.4 parts of polyoxyethylene lauryl ether, and 80 parts of ion-exchanged water were added, and the mixture was stirred and emulsified to prepare a monomer mixture. Then, this monomer mixture was added to reactor A at a constant rate over 5 hours while being stirred and emulsified, and the reaction was continued until the polymerization conversion rate reached 95%, thereby obtaining an aqueous dispersion of polyacrylonitrile. An appropriate amount of NMP was added to the obtained aqueous dispersion of polyacrylonitrile to obtain a mixture. Thereafter, water and excess NMP were removed from the mixture by vacuum distillation at 90°C, and an NMP solution of polyacrylonitrile (solid concentration: 8%) was obtained.

[0110] Example 15 Except for using the binder prepared as follows, a thermally decomposable material, a binder composition, a positive electrode slurry composition, a positive electrode, a negative electrode, a separator, and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 3. <Preparing the binding material> Polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd., product name "L#7200") was dissolved in NMP to prepare an NMP solution of polyvinylidene fluoride (solid content concentration: 8%).

[0111] Example 16 Except for using the thermally decomposable material prepared as follows, a binder, a binder composition, a positive electrode slurry composition, a positive electrode, a negative electrode, a separator, and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 3. <Preparation of thermally decomposable materials> Equimolar amounts of 63.0 g of melamine pulverized to a volume average particle size of 100 μm and 64.5 g of cyanuric acid were added to a reactor. Potassium hydroxide was then added at 1% relative to the total amount of melamine and cyanuric acid (100%), and ion-exchanged water was added to adjust the solids concentration to 55% to obtain a mixture. The mixture was then heated to 75°C with stirring and continued for 120 minutes to produce a slurry containing melamine cyanurate (a foaming agent) as the core of the thermally decomposable material. Ion-exchanged water was added to the resulting slurry to adjust the solids concentration to 20% and milled for 5 minutes using a bead mill (manufactured by Ashizawa Finetech Co., Ltd., product name "LMZ-015") with a bead diameter of 1.0 mm, a bead filling rate of 80%, and a peripheral speed of 8 m / s. Next, 3 parts of anionic surfactant sodium stearate (molecular weight 306.5 g / mol, melting point: 305°C) was added to 97 parts of melamine cyanurate, and the mixture was stirred for another 30 minutes to obtain a slurry composition for a thermally decomposable material. The obtained slurry composition was dried by spray drying at 140°C to obtain a thermally decomposable material.

[0112] Example 17 Except for using the thermally decomposable material prepared as follows, a binder, a binder composition, a positive electrode slurry composition, a positive electrode, a negative electrode, a separator, and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 3. <Preparation of thermally decomposable materials> Equimolar amounts of 63.0 g of melamine pulverized to a volume average particle size of 100 μm and 64.5 g of cyanuric acid were added to a reactor. Potassium hydroxide was then added at 1% relative to the total amount of melamine and cyanuric acid (100%), and ion-exchanged water was added to adjust the solids concentration to 55%, yielding a mixture. The mixture was then heated to 75°C with stirring and continued for 120 minutes to yield a slurry composition for a thermally decomposable material containing melamine cyanurate (a foaming agent). The resulting slurry composition was spray-dried at 140°C to yield a thermally decomposable material.

[0113] (Comparative Example 1) Except for using the thermally decomposable material prepared as follows, a binder, a binder composition, a positive electrode slurry composition, a positive electrode, a negative electrode, a separator, and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 3. <Preparation of thermally decomposable materials> Melamine cyanurate (Nissan Chemical Corporation, product name "MC-6000") was added with ion-exchanged water to adjust the solids concentration to 40%, creating a slurry containing melamine cyanurate (a foaming agent) as the core of the thermally decomposable material. To the resulting slurry, 3 parts of the anionic surfactant sodium stearate (molecular weight 306.5 g / mol, melting point: 305°C) were added to 97 parts of melamine cyanurate, and ion-exchanged water was added to adjust the solids concentration to 20%. The mixture was stirred for an additional 30 minutes to obtain a slurry composition for the thermally decomposable material. The resulting slurry composition was spray-dried at 140°C to obtain the thermally decomposable material.

[0114] (Comparative Example 2) Except for using the thermally decomposable material prepared as follows, a binder, a binder composition, a positive electrode slurry composition, a positive electrode, a negative electrode, a separator, and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 3. <Preparation of thermally decomposable materials> Equimolar amounts of 63.0 g of melamine pulverized to a volume average particle diameter of 100 μm and 64.5 g of cyanuric acid were added to a reactor. Potassium hydroxide was then added at 1% relative to the total amount of melamine and cyanuric acid (100%), and ion-exchanged water was added to adjust the solids concentration to 55% to obtain a mixture. The mixture was then heated to 75°C with stirring and continued for 120 minutes to produce a slurry containing melamine cyanurate (a blowing agent) as the core of the thermally decomposable material. The resulting slurry was dried at 80°C for 12 hours, and the resulting dried material was subjected to a spheronization treatment using a mechanical spheronizer (EarthTechnica, product name "Kryptron Orb CSH0"). Ion-exchanged water was added to the dried spheronized material to adjust the solids concentration to 40%, producing a slurry containing melamine cyanurate (a blowing agent) as the core of the thermally decomposable material. To the resulting slurry, 97 parts of melamine cyanurate and 3 parts of anionic surfactant sodium stearate (molecular weight 306.5 g / mol, melting point: 305°C) were added, and ion-exchanged water was added to make the solids concentration 20%, followed by stirring for another 30 minutes to obtain a slurry composition for a thermally decomposable material. The resulting slurry composition was dried by spray drying at 140°C to obtain a thermally decomposable material.

[0115] In addition, in the following Tables 1 to 3, "HNBR" indicates hydrogenated nitrile rubber; "PAN" indicates polyacrylonitrile; "PVDF" refers to polyvinylidene fluoride; "CN" represents a nitrile group; "COOH" represents a carboxylic acid group; "COO" represents an ester group; "CONH2" represents an amide group, "MC" indicates melamine cyanurate; "ADCA" refers to azodicarbonamide.

[0116] [Table 1]

[0117] [Table 2]

[0118] [Table 3]

[0119] Tables 1 to 3 show that in Examples 1 to 17, which contain a binder and a thermally decomposable material containing a foaming agent, and in which the thermal decomposition temperature, number-average particle size, particle size ratio, and circularity of the thermally decomposable material are each within a predetermined range, electrochemical elements were produced that sufficiently suppressed heat generation during an internal short circuit, had low low-temperature IV resistance, and were excellent in high-temperature storage characteristics. On the other hand, Table 3 shows that in Comparative Example 1, in which the particle size ratio of the thermally decomposable material was outside the specified range, heat generation during an internal short circuit in the electrochemical element was not sufficiently suppressed, the low-temperature IV resistance was high, and the high-temperature storage characteristics were poor. Furthermore, Table 3 shows that in Comparative Example 2, in which the circularity of the thermally decomposable material was outside the predetermined range, the electrochemical element had a high low-temperature IV resistance and poor high-temperature storage characteristics. [Industrial Applicability]

[0120] According to the present invention, it is possible to provide a binder composition for electrochemical elements, a slurry composition for electrochemical element electrodes, and an electrode for electrochemical elements, which are capable of sufficiently suppressing heat generation during an internal short circuit of an electrochemical element, reducing IV resistance at low temperatures, and enabling the electrochemical element to exhibit excellent high-temperature storage properties. Furthermore, according to the present invention, it is possible to provide an electrochemical element in which heat generation during an internal short circuit is sufficiently suppressed, which has low IV resistance at low temperatures, and which has excellent high-temperature storage characteristics.

Claims

1. A binder composition for an electrochemical element, comprising a binder and a thermally decomposable material, the thermally decomposable material contains a foaming agent and a surfactant; the thermally decomposable material has a core-shell structure including a core made of the foaming agent and a shell made of the surfactant that covers at least a part of the outer surface of the core, the surfactant is at least one of an aliphatic carboxylic acid and a salt thereof, and the thermally decomposable material has a thermal decomposition temperature of 150°C or more and 400°C or less, a number average particle diameter of 0.01 μm or more and 10 μm or less, a ratio of the number average particle diameter to the volume average particle diameter of 0.05 or more and 1 or less, and a circularity of 0.05 or more and 0.95 or less.

2. 2. The binder composition for an electrochemical element according to claim 1, wherein a ratio of the amount of the surfactant to a total amount of the foaming agent and the surfactant is 0.01% by mass or more and 10% by mass or less.

3. 3. The binder composition for an electrochemical element according to claim 1, wherein the surfactant has a melting point of 50°C or higher and 350°C or lower.

4. 4. The binder composition for electrochemical elements according to claim 1, wherein the binder is a polymer having at least one functional group selected from the group consisting of a carboxylic acid group, a hydroxyl group, a nitrile group, an amino group, an epoxy group, an oxazoline group, a sulfonic acid group, an ester group, and an amide group.

5. 5. The binder composition for an electrochemical element according to claim 1, wherein the foaming agent is a nitrogen-based foaming agent.

6. The binder composition for an electrochemical element according to any one of claims 1 to 5, further comprising a solvent.

7. A slurry composition for an electrochemical element electrode, comprising an electrode active material and the binder composition for an electrochemical element according to claim 6.

8. An electrode for an electrochemical element, comprising an electrode mixture layer formed using the slurry composition for an electrochemical element electrode according to claim 7.

9. An electrochemical device comprising the electrode for an electrochemical device according to claim 8 .

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