Composition, positive electrode composition for lithium ion battery, and dispersant

Abstract

The objective of the present invention is to provide a composition that contains a dispersant having improved voltage resistance and that is capable of maintaining high storage stability.　The composition according to the present invention is characterized by containing: a dispersant that includes a polymer (I) of monomers including a nitrile group-containing monomer (A), an acidic group-containing monomer (B), and an alkyl group-containing monomer (C) having an alkyl group with 12 or more carbon atoms, and in which the molar ratio [(B) / (A)] of the acidic group-containing monomer (B) unit to the nitrile group-containing monomer (A) unit is greater than 0 and at most 2.00; a conductive auxiliary agent; and a solvent.

Description

COMPOSITION, POSITIVE ELECTRODE COMPOSITION FOR LITHIUM ION BATTERY AND DISPERSANT - Patent application

[0001] The present invention relates to a composition containing a dispersant and a conductive additive, a positive electrode composition for a lithium ion battery, and a dispersant.

[0002] In recent years, lithium-ion batteries have become widely used as power sources for electronic devices and electric vehicles. A lithium-ion battery generally has a positive electrode including a current collector and a positive electrode composite layer formed on the current collector. The positive electrode composite layer is produced using a positive electrode composition including a positive electrode active material, a binder resin, and a solvent. For example, the positive electrode composite layer is formed by applying the positive electrode composition to a current collector and then removing the solvent.

[0003] The positive electrode active material can absorb and release lithium ions. However, the positive electrode active material has low conductivity, which increases the internal resistance of the lithium-ion battery. Therefore, the positive electrode mixture layer further contains a conductive additive. Examples of the conductive additive include carbon materials such as carbon black and carbon nanotubes.

[0004] In order to improve the conductivity of the positive electrode active material, it is necessary to uniformly disperse the conductive additive in the positive electrode mixture layer without agglomeration. Therefore, the conductive additive is used as a composition dispersed in a solvent by a dispersant. Then, this composition is mixed with a positive electrode active material and a binder resin to prepare a positive electrode composition. The positive electrode mixture layer formed using such a positive electrode composition contains the conductive additive and the dispersant in addition to the positive electrode active material and the binder resin.

[0005] A polymeric dispersant is used as a dispersant for dispersing a conductive additive. For example, Patent Document 1 discloses a dispersant (A) containing an acidic group-containing monomer unit (a), a monomer unit (b) having 10 to 40 carbon atoms, and a monomer unit (c) having one or more moieties selected from a nitrile group and a heterocyclic ring.

[0006] In a composition using such a polymeric dispersant, the polymeric dispersant is adsorbed onto the surface of the conductive additive, thereby imparting electrostatic repulsion between the conductive additives, making it possible to disperse the conductive additives.

[0007] Patent Publication No. 2023-100291

[0008] In recent years, efforts have been made to increase the energy density of lithium-ion batteries in order to extend the operating time of electronic devices and the driving distance of electric vehicles. As a result, efforts are being made to increase the voltage of lithium-ion batteries.

[0009] However, conventional polymer dispersants have the problem of low voltage resistance. Therefore, when a lithium-ion battery is charged at high voltage, the polymer dispersant contained in the positive electrode mixture layer can undergo oxidative decomposition. In such cases, the oxidative decomposition of the polymer dispersant generates gas, which increases the internal resistance of the lithium-ion battery and reduces battery performance.

[0010] On the other hand, as described above, the polymer dispersant has the role of adsorbing to the surface of the conductive additive and imparting electrostatic repulsion, etc. However, when attempting to improve the voltage resistance of the polymer dispersant, the solvent may separate during long-term storage of a composition containing the polymer dispersant, resulting in a decrease in storage stability. If the storage stability is low in this way, when a positive electrode composite layer is formed using this composition after long-term storage, the conductive additive may not be uniformly dispersed in the positive electrode composite layer, resulting in an increase in the internal resistance of the lithium-ion battery. Therefore, it has been difficult to improve the voltage resistance of the polymer dispersant while maintaining the storage stability of the composition.

[0011] Therefore, an object of the present invention is to provide a composition that contains a dispersant with improved voltage resistance and that can maintain high storage stability.

[0012] The present invention provides a composition comprising: a dispersant containing polymer (I) of monomers including a nitrile group-containing monomer (A), an acidic group-containing monomer (B), and an alkyl group-containing monomer (C) having an alkyl group having 12 or more carbon atoms, wherein the molar ratio of acidic group-containing monomer (B) units to nitrile group-containing monomer (A) units [(B) / (A)] is greater than 0 and 2.00 or less; a conductive auxiliary; and a solvent.

[0013] The present invention provides a composition comprising a dispersant, a conductive aid, and a solvent, wherein the dispersant comprises a polymer (I) of monomers comprising: a nitrile group-containing monomer (A), an acidic group-containing monomer (B), and an alkyl group-containing monomer (C) having an alkyl group having 12 or more carbon atoms; and wherein in the polymer (I), the molar ratio of the acidic group-containing monomer (B) units to the nitrile group-containing monomer (A) units [(B) / (A)] is more than 0 and 2.00 or less.

[0014] The present invention also provides a positive electrode composition for a lithium ion battery, comprising the above composition, a positive electrode active material, and a binder resin.

[0015] The present invention provides a dispersant characterized by containing a polymer (I) of monomers comprising a nitrile group-containing monomer (A), an acidic group-containing monomer (B), and an alkyl group-containing monomer (C) having an alkyl group having 12 or more carbon atoms, wherein the molar ratio of the acidic group-containing monomer (B) units to the nitrile group-containing monomer (A) units [(B) / (A)] is greater than 0 and not greater than 2.00.

[0016] The present invention provides a dispersant comprising a polymer (I) of monomers comprising: a nitrile group-containing monomer (A); an acidic group-containing monomer (B); and an alkyl group-containing monomer (C) having an alkyl group having 12 or more carbon atoms, wherein in the polymer (I), the molar ratio of the acidic group-containing monomer (B) units to the nitrile group-containing monomer (A) units [(B) / (A)] is greater than 0 and not greater than 2.00.

[0017] Here, (meth)acryloyloxy means acryloyloxy or methacryloyloxy. (Meth)acrylic acid means acrylic acid or methacrylic acid. (Meth)acrylic means acrylic or methacrylic. (Meth)acrylate means acrylate or methacrylate.

[0018] According to the present invention, it is possible to provide a composition that contains a dispersant with improved voltage resistance and that can maintain high storage stability.

[0019] FIG. 1 is a three-component composition diagram in which the composition ratios (mol %) of three components consisting of nitrile group-containing monomer (A) units, acidic group-containing monomer (B) units, and alkyl group-containing monomer (C) units in the polymer (I) of the present invention are represented by triangular coordinates (A, B, C).

[0020] In the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. In the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in an example or a value that can be unambiguously derived from an example. In this specification, a numerical value connected with "to" means a numerical range that includes the numbers before and after "to" as the lower and upper limits.

[0021] <Composition> The present invention relates to a composition comprising a dispersant, a conductive aid, and a solvent. The dispersant comprises a polymer (I) of monomers comprising a nitrile group-containing monomer (A), an acidic group-containing monomer (B), and an alkyl group-containing monomer (C) having an alkyl group having 12 or more carbon atoms. In the polymer (I), the molar ratio of the acidic group-containing monomer (B) units to the nitrile group-containing monomer (A) units [(B) / (A)] is greater than 0 and not greater than 2.00.

[0022] The content of the dispersant, conductive aid, and solvent is preferably 80% by mass or more, more preferably 90% by mass or more, more preferably 95% by mass or more, and still more preferably 97% by mass or more, relative to 100% by mass of the total mass of the composition.

[0023] As described above, in the composition of the present invention, a polymer (I) obtained by polymerizing monomers including a nitrile group-containing monomer (A), an acidic group-containing monomer (B), and an alkyl group-containing monomer (C) is used as a dispersant for dispersing the conductive additive.

[0024] The alkyl group-containing monomer (C) contains an alkyl group having a predetermined number of carbon atoms, which allows the polymer (I) to be adsorbed onto the surface of the conductive additive. Furthermore, the acidic group contained in the acidic group-containing monomer (B) can impart electrostatic repulsion between the conductive additives. This allows the polymer (I) to uniformly disperse the conductive additive in the solvent.

[0025] The present inventors have conducted various studies on the voltage resistance of the polymer (I) used as such a dispersant, and as a result, they have speculated that when a lithium ion battery is charged under high voltage, electrons are extracted from the lone electron pair of the acidic group of the acidic group-containing monomer (B), causing oxidative decomposition of the polymer (I), which is a factor in reducing the voltage resistance of the polymer (I).

[0026] Therefore, in the composition of the present invention, a nitrile group-containing monomer (A) is used to reduce oxidative decomposition of the acidic group in the acidic group-containing monomer (B). The nitrile group in the nitrile group-containing monomer (A) has electron-withdrawing properties, which is thought to stabilize the lone electron pair of the acidic group in the acidic group-containing monomer (B), thereby reducing oxidative decomposition of the acidic group in the acidic group-containing monomer (B) under high voltage.

[0027] Furthermore, by adjusting the molar ratio of the acidic group-containing monomer (B) units to the nitrile group-containing monomer (A) units [(B) / (A)] in the polymer (I) to 2.00 or less, the polymer (I) has high voltage resistance and the composition can maintain high storage stability, which makes it difficult for solvent separation to occur in the composition during long-term storage, and allows the solvent to be maintained in a uniformly dispersed state.

[0028] (Polymer (I)) The polymer (I) contained as a dispersant in the composition of the present invention is obtained by polymerizing monomers including a nitrile group-containing monomer (A), an acidic group-containing monomer (B), and an alkyl group-containing monomer (C) having an alkyl group having 12 or more carbon atoms.

[0029] (Nitrile Group-Containing Monomer (A)) The nitrile group-containing monomer (A) preferably has a nitrile group and an ethylenically unsaturated double bond in one molecule.

[0030] The nitrile group-containing monomer (A) may be an acrylic monomer containing a nitrile group, such as acrylonitrile or methacrylonitrile. Acrylonitrile is preferred. The nitrile group-containing monomer (A) may be used alone or in combination of two or more.

[0031] The content of the nitrile group-containing monomer (A) units in the polymer (I) is preferably 1 mol% or more, more preferably 5 mol% or more, more preferably 9 mol% or more, more preferably 15 mol% or more, and more preferably 25 mol% or more, based on 100 mol% of the total amount of the nitrile group-containing monomer (A) units, the acidic group-containing monomer (B) units, and the alkyl group-containing monomer (C) units. The content of the nitrile group-containing monomer (A) units in the polymer (I) is preferably 95 mol% or less, more preferably 90 mol% or less, more preferably 75 mol% or less, and more preferably 65 mol% or less, based on 100 mol% of the total amount of the nitrile group-containing monomer (A) units, the acidic group-containing monomer (B) units, and the alkyl group-containing monomer (C) units.

[0032] By setting the content of the nitrile group-containing monomer (A) unit to 1 mol % or more, it is possible to further reduce the oxidative decomposition of the acidic group of the acidic group-containing monomer (B) under high voltage, and it is possible to further improve the voltage resistance of the dispersant. By setting the content of the nitrile group-containing monomer (A) unit to 95 mol % or less, it is possible to improve the dispersibility of the conductive additive and the storage stability of the composition.

[0033] In the following, when describing the content of each monomer unit in polymer (I), "100 mol % in total of nitrile group-containing monomer (A) units, acidic group-containing monomer (B) units, and alkyl group-containing monomer (C) units" in polymer (I) will also be simply referred to as "100 mol % in total of base monomer units." In other words, "100 mol % in total of base monomer units" means "100 mol % in total of nitrile group-containing monomer (A) units, acidic group-containing monomer (B) units, and alkyl group-containing monomer (C) units" in polymer (I).

[0034] (Acidic Group-Containing Monomer (B)) The acidic group-containing monomer (B) has an acidic group. The acidic group-containing monomer (B) preferably has an acidic group and an ethylenically unsaturated double bond in one molecule. Examples of the acidic group include a carboxy group (-COOH), a phosphate group (H2PO4-), and a sulfonic acid group (-SO3H). The phosphate group is a group represented by the following chemical formula (1). Among these, the carboxy group and the phosphate group are preferred, and the phosphate group is more preferred, as they provide excellent dispersibility of the conductive additive and storage stability of the composition. The phosphate group is preferred, as they provide excellent voltage resistance of the dispersant. The acidic groups may be used alone or in combination of two or more.

[0035]

[0036] Examples of the acidic group-containing monomer (B) include carboxyl group-containing monomers, phosphate group-containing monomers, and sulfonic acid group-containing monomers, with the carboxyl group-containing monomers and phosphate group-containing monomers being preferred, and the phosphate group-containing monomers being more preferred because they can further improve the voltage resistance of the dispersant. The acidic group-containing monomer (B) may be used alone or in combination of two or more.

[0037] Examples of the carboxy group-containing monomer include acrylic acid, methacrylic acid, crotonic acid, fumaric acid, maleic acid, itaconic acid, citraconic acid, (meth)acryloyloxyethyl succinic acid, (meth)acryloyloxyethyl phthalate, (meth)acryloyloxypropyl phthalate, (meth)acryloyloxyethyl hexahydrophthalate, (meth)acryloyloxypropyl hexahydrophthalate, (meth)acryloyloxypropyl hydrogen phthalate, (meth)acryloyloxyethyl hydrogen phthalate, ethylene oxide-modified succinic acid (meth)acrylate, ε-caprolactone-added (meth)acrylic acid, and β-carboxyethyl (meth)acrylate.

[0038] Examples of the phosphate group-containing monomer include phosphate group-containing (meth)acrylates such as 2-(meth)acryloyloxyethyl acid phosphate, 3-(meth)acryloyloxypropyl acid phosphate, (meth)acryloyloxypolyoxyethylene glycol acid phosphate, and (meth)acryloyloxypolyoxypropylene glycol acid phosphate. Among these, 2-(meth)acryloyloxyethyl acid phosphate and 3-(meth)acryloyloxypropyl acid phosphate are preferred, 2-(meth)acryloyloxyethyl acid phosphate is more preferred, and 2-methacryloyloxyethyl acid phosphate is even more preferred.

[0039] The phosphate group-containing monomer is preferably a (meth)acryloyloxyalkyl acid phosphate represented by the following formula (I).

[0040] (In formula (I), R 1 represents a hydrogen atom or a methyl group, and R 2 represents an ethylene group (-CH-CH-) or a propylene group (-CH-CH-CH-).

[0041] The content of the acidic group-containing monomer (B) units in the polymer (I) is preferably 1 mol% or more, more preferably 5 mol% or more, relative to 100 mol% of the total amount of the base monomer units. The content of the acidic group-containing monomer (B) units in the polymer (I) is preferably 65 mol% or less, more preferably 60 mol% or less, more preferably 45 mol% or less, and more preferably 30 mol% or less, relative to 100 mol% of the total amount of the base monomer units. By making the content of the acidic group-containing monomer (B) units 1 mol% or more, it is possible to further improve the dispersibility of the conductive assistant and the storage stability of the composition. By making the content of the acidic group-containing monomer (B) units 65 mol% or less, it is possible to further improve the dispersibility of the conductive assistant and the storage stability of the composition.

[0042] In the polymer (I), the molar ratio of the acidic group-containing monomer (B) units to the nitrile group-containing monomer (A) units [(B) / (A)] exceeds 0, preferably 0.001 or more, more preferably 0.01 or more, more preferably 0.05 or more, and more preferably 0.07 or more. In the polymer (I), the molar ratio of the acidic group-containing monomer (B) units to the nitrile group-containing monomer (A) units [(B) / (A)] is 2.00 or less, preferably 1.85 or less, more preferably 1.50 or less, and more preferably 1.00 or less. By having the molar ratio [(B) / (A)] exceeding 0, it is possible to further improve the dispersibility of the conductive additive and the storage stability of the composition. By setting the molar ratio [(B) / (A)] to 2.00 or less, it is possible to provide a composition in which the polymer (I) has high voltage resistance and can maintain high storage stability.

[0043] In the polymer (I), the molar ratio [(C) / (B)] of the alkyl group-containing monomer (C) units to the acidic group-containing monomer (B) units is preferably 0.1 or more, more preferably 1.0 or more. In the polymer (I), the molar ratio [(C) / (B)] of the alkyl group-containing monomer (C) units to the acidic group-containing monomer (B) units is preferably 20 or less, more preferably 18 or less, and even more preferably 13 or less. By setting the molar ratio [(C) / (B)] to 0.1 or more, the dispersibility of the conductive assistant and the storage stability of the composition can be improved. By setting the molar ratio [(C) / (B)] to 20 or less, the dispersibility of the conductive assistant and the storage stability of the composition can be further improved.

[0044] (Alkyl group-containing monomer (C)) The number of carbon atoms in the alkyl group of the alkyl group-containing monomer (C) is 12 or more, preferably 16 or more, and more preferably 18 or more. The number of carbon atoms in the alkyl group of the alkyl group-containing monomer (C) is preferably 35 or less, more preferably 30 or less, more preferably 26 or less, and more preferably 23 or less. By making the number of carbon atoms in the alkyl group 12 or more, the polymer (I) has a moderate affinity to the conductive assistant, and the polymer (I) can be sufficiently adsorbed to the surface of the conductive assistant, thereby improving the dispersibility of the conductive assistant. By making the number of carbon atoms in the alkyl group 35 or less, when the solvent is a polar solvent, the affinity of the polymer (I) to the polar solvent can be maintained, and it is easy to maintain the state in which the polymer (I) is adsorbed to the surface of the conductive assistant.

[0045] The alkyl group-containing monomer (C) preferably has an alkyl group and an ethylenically unsaturated double bond in one molecule. Examples of the alkyl group-containing monomer (C) include alkyl group-containing (meth)acrylates.

[0046] Examples of the alkyl group-containing monomer (C) include linear alkyl group-containing (meth)acrylates such as lauryl (meth)acrylate, tridecyl (meth)acrylate, myristyl (meth)acrylate, pentadecyl (meth)acrylate, palmityl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, nonadecyl (meth)acrylate, icosyl (meth)acrylate, heneicosyl (meth)acrylate, and behenyl (meth)acrylate; and branched alkyl group-containing (meth)acrylates such as isododecyl (meth)acrylate, isotridecyl (meth)acrylate, isomyristyl (meth)acrylate, isopentadecyl (meth)acrylate, isohexadecyl (meth)acrylate, isoheptadecyl (meth)acrylate, and isostearyl (meth)acrylate.

[0047] The alkyl group-containing monomer (C) is preferably an alkyl group-containing (meth)acrylate, more preferably a linear alkyl group-containing (meth)acrylate, more preferably behenyl (meth)acrylate, and more preferably behenyl acrylate. The alkyl group-containing monomer (C) may be used alone or in combination of two or more.

[0048] The content of the alkyl group-containing monomer (C) units in the polymer (I) is preferably 1 mol% or more, more preferably 3 mol% or more, more preferably 10 mol% or more, more preferably 15 mol% or more, more preferably 20 mol% or more, more preferably 25 mol% or more, and more preferably 30 mol% or more, relative to the total amount of the base monomer units (100 mol%). The content of the alkyl group-containing monomer (C) units in the polymer (I) is preferably 95 mol% or less, more preferably 90 mol% or less, and more preferably 80 mol% or less, relative to the total amount of the base monomer units (100 mol%). By making the content of the alkyl group-containing monomer (C) units 1 mol% or more, the dispersibility of the conductive additive and the storage stability of the composition can be further improved, and the volume resistivity of the positive electrode mixture layer can be reduced. By making the content of the alkyl group-containing monomer (C) units 95 mol% or less, the dispersibility of the conductive additive can be improved and the volume resistivity of the positive electrode mixture layer can be reduced.

[0049] Furthermore, from the viewpoint of the voltage resistance of the polymer (I), the content of the alkyl group-containing monomer (C) units in the polymer (I) is more preferably 15 mol % or less, more preferably 10 mol % or less, and still more preferably 5 mol % or less, relative to 100 mol % of the total amount of the base monomer units. By setting the content of the alkyl group-containing monomer (C) units to 15 mol % or less, the voltage resistance of the polymer (I) can be improved.

[0050] In the polymer (I), the molar ratio [(A) / (C)] of the nitrile group-containing monomer (A) units to the alkyl group-containing monomer (C) units is preferably 0.01 or more, more preferably 0.1 or more, more preferably 0.2 or more, and more preferably 0.4 or more. In the polymer (I), the molar ratio [(A) / (C)] of the nitrile group-containing monomer (A) units to the alkyl group-containing monomer (C) units is preferably 30 or less, more preferably 10 or less, more preferably 5 or less, and more preferably 3 or less. By setting the molar ratio [(A) / (C)] to 0.01 or more, the dispersibility of the conductive additive can be improved, and the volume resistivity of the positive electrode mixture layer can be reduced. By setting the molar ratio [(A) / (C)] to 30 or less, the compatibility of the polymer (I) with the solvent can be improved. This makes it possible to further improve the dispersibility of the conductive additive and the storage stability of the composition.

[0051] In the polymer (I), the total content of the nitrile group-containing monomer (A) units, the acidic group-containing monomer (B) units, and the alkyl group-containing monomer (C) units is preferably 50 mol% or more, more preferably 75 mol% or more, more preferably 85 mol% or more, more preferably 90 mol% or more, more preferably 95 mol% or more, more preferably 98 mol% or more, and particularly preferably 100 mol%, based on 100 mol% of the total amount of all monomer units constituting the polymer (I).

[0052] The monomers constituting the polymer (I) may contain other monomers in addition to the above-mentioned nitrile group-containing monomer (A), acidic group-containing monomer (B), and alkyl group-containing monomer (C).

[0053] Examples of other monomers include alkyl group-containing monomers having an alkyl group with less than 12 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, and decyl (meth)acrylate; aromatic (meth)acrylates such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxydiethylene glycol (meth)acrylate; N-substituted (meth)acrylamides such as (meth)acrylamide, N,N-dimethyl (meth)acrylamide, and N,N-diethyl (meth)acrylamide; Examples of suitable vinyl compounds include N-alkylene allylamines such as N-methylene allylamine, N-(2,2-dimethylpropylidene) allylamine, and N-(2-furylmethylene) allylamine; nitriles such as (meth)acrylonitrile; styrene-based monomers such as styrene, α-methylstyrene, p-hydroxystyrene, chloromethylstyrene, vinyltoluene, and indene; and vinylpyridines such as 2-vinylpyridine and 4-vinylpyridine.

[0054] The weight-average molecular weight of the polymer (I) is preferably at least 500. The weight-average molecular weight of the polymer (I) is preferably at most 30,000, more preferably at most 20,000, and even more preferably at most 10,000. When the weight-average molecular weight of the polymer (I) is within the above range, the polymer (I) is easily adsorbed to the surface of the conductive additive, and is more likely to function as a dispersant from the viewpoint of storage stability.

[0055] The content of the polymer (I) in the composition is preferably 1 part by mass or more, more preferably 5 parts by mass or more, more preferably 10 parts by mass or more, more preferably 20 parts by mass or more, more preferably 30 parts by mass or more, and more preferably 35 parts by mass or more, relative to 100 parts by mass of the conductive additive. The content of the polymer (I) in the composition is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, more preferably 70 parts by mass or less, and more preferably 65 parts by mass or less, relative to 100 parts by mass of the conductive additive. By making the content of the polymer (I) 1 part by mass or more relative to 100 parts by mass of the conductive additive, the dispersibility of the conductive additive and the storage stability of the composition can be improved. Furthermore, even when the content of the polymer (I) is set to a low value of 100 parts by mass or less relative to 100 parts by mass of the conductive additive, the conductive additive can be sufficiently dispersed. Therefore, the content of the conductive additive in the positive electrode mixture layer can be reduced, which makes it easier to increase the amount of positive electrode active material and binder, thereby increasing the design freedom of the positive electrode mixture layer. As a result, depending on the application, it becomes easier to increase the adhesion of the positive electrode mixture layer to the current collector and to achieve a high energy density of the lithium ion battery.

[0056] The method for producing the polymer (I) is not particularly limited. For example, the polymer (I) can be produced by polymerizing monomers including the nitrile group-containing monomer (A), the acidic group-containing monomer (B), and the alkyl group-containing monomer (C) in the presence of a polymerization initiator (P).

[0057] As the polymerization initiator (P), a thermal polymerization initiator is preferably used. Examples include azo compounds such as 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(isobutyronitrile), and 2,2'-azobis(2-methylpropionamidine); and organic peroxides such as methyl ethyl ketone peroxide, acetylacetone peroxide, t-butyl peroxybenzoate, benzoyl peroxide, dicumyl peroxide, cumene hydroperoxide, and tert-butylperoxy-2-ethylhexanoate. The polymerization of the monomers is preferably carried out under heating. The polymerization temperature is preferably 60 to 120°C.

[0058] The composition contains the polymer (I) as a dispersant. The content of the polymer (I) in the dispersant is preferably 50% by mass or more, more preferably 75% by mass or more, more preferably 85% by mass or more, still more preferably 95% by mass or more, and particularly preferably 100% by mass.

[0059] (Conductive Aid) The composition of the present invention contains a conductive aid in addition to the polymer (I) described above. The conductive aid may be any conductive aid as long as it has conductivity.

[0060] Examples of conductive additives include carbon materials, metal powders, metal fibers, and conductive ceramics. Of these, carbon materials are preferred. Examples of carbon materials include carbon black, graphite, graphene, and carbon fibers. Examples of carbon black include acetylene black, ketjen black, furnace black, channel black, lamp black, and thermal black. One type of conductive additive may be used alone, or two or more types may be used in combination.

[0061] The content of the carbon material in the conductive additive is preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, more preferably 95% by mass or more, more preferably 98% by mass or more, and more preferably 100% by mass.

[0062] Among carbon materials, carbon fibers have high surface energy and are therefore prone to aggregation due to van der Waals forces, making it difficult to uniformly disperse them. However, even such carbon fibers can be uniformly dispersed and maintained in this dispersed state by using the polymer (I) used in the composition of the present invention. Therefore, it is particularly preferable to use carbon fibers as the carbon material, as they can particularly exhibit the effects of the present invention.

[0063] Examples of carbon fibers include carbon fibers, carbon nanofibers, and carbon nanotubes. Of these, carbon nanotubes are preferred. Examples of carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes, with multi-walled carbon nanotubes being preferred. Carbon fibers may be used alone or in combination of two or more types.

[0064] The average fiber length of the carbon fibers is preferably 1 μm or more, more preferably 10 μm or more, and even more preferably 30 μm or more. The average fiber length of the carbon fibers is preferably 300 μm or less, and even more preferably 200 μm or less.

[0065] The average fiber diameter of the carbon fibers is preferably 1 nm or more, more preferably 3 nm or more, and is preferably 30 nm or less, more preferably 15 nm or less.

[0066] (Solvent) The composition of the present invention contains a solvent. Examples of the solvent include water and organic solvents.

[0067] Examples of organic solvents include monohydric alcohols such as methanol, ethanol, propanol, isopropanol, butanol, and isobutanol; polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, and hexanetriol; polyhydric alcohol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol monobutyl ether; amines such as ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, and tetramethylpropylenediamine; Examples thereof include amides such as N-cyclohexylpyrrolidone, N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and N-methylcaprolactam.

[0068] Preferred solvents are monohydric alcohols, polyhydric alcohols, and amides. In particular, polar solvents are preferred as the solvent, and aprotic polar solvents are more preferred. Aprotic polar solvents have excellent compatibility with the polymer (I), and can maintain high storage stability of the composition. Examples of aprotic polar solvents include the amides described above. Specific examples of amides include N-cyclohexylpyrrolidone, N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and N-methylcaprolactam. Of these, N-methyl-2-pyrrolidone (NMP) is preferred. One type of solvent may be used alone, or two or more types may be used in combination.

[0069] The content of the organic solvent in the solvent is preferably 95% by mass or more, more preferably 98% by mass or more, and particularly preferably 100% by mass.

[0070] The content of the solvent in the composition is preferably 80% by mass or more, more preferably 90% by mass or more, more preferably 95% by mass or more, and more preferably 97% by mass or more, relative to the total mass of the composition (100% by mass). The content of the solvent in the composition is preferably 99.7% by mass or less, more preferably 99.5% by mass or less, more preferably 99% by mass or less, and more preferably 98% by mass or less, relative to the total mass of the composition (100% by mass).

[0071] The composition may further contain additives in addition to the polymer (I) and the conductive aid, such as a leveling agent, an anti-sagging agent, an anti-settling agent, an anti-color separation agent, an antioxidant, a pH adjuster, a colorant, a neutralizing agent, an antifoaming agent, an antiseptic, a dehydrating agent, an anti-rust agent, and a plasticizer.

[0072] The method for producing the composition is not particularly limited. For example, the composition can be obtained by mixing the polymer (I), the conductive aid, and the solvent, and, if necessary, additives. Examples of mixing means include a disper, a homomixer, a ball mill, a sand mill, a bead mill, an ultrasonic disperser, a homogenizer, a planetary mixer, a film mix, and a jet mill.

[0073] In the composition of the present invention, the polymer (I) allows the conductive assistant to be uniformly dispersed. Furthermore, the polymer (I) has excellent compatibility with solvents, allowing the composition to maintain its storage stability. Therefore, the polymer (I) allows the conductive assistant to be maintained in a uniformly dispersed state for a long period of time. In particular, the conductive assistant is prone to aggregation in high-temperature environments. Therefore, in conventional compositions, in order to prevent aggregation of the conductive assistant, it is necessary to maintain the storage temperature at a low temperature, such as room temperature, which places a heavy burden on temperature control, especially in the summer. However, the polymer (I) allows high storage stability to be maintained even in high-temperature environments of about 40°C, thereby reducing the burden of maintaining the composition at a low storage temperature. The dispersant can be preferably used as a dispersant for the conductive assistant. The dispersant can be more preferably used as a dispersant for the conductive assistant containing a carbon material (preferably carbon fiber). The dispersant can be more preferably used as a dispersant for the conductive assistant containing carbon nanotubes.

[0074] Furthermore, as described above, in the composition of the present invention, the polymer (I) used as a dispersant allows the conductive additive to be uniformly dispersed and maintain this dispersed state for a long period of time. Therefore, such a composition is suitable for use in forming a positive electrode composite layer of a lithium ion battery. This allows a positive electrode composite layer in which the conductive additive is uniformly dispersed to be provided, thereby reducing the internal resistance of the lithium ion battery. Furthermore, because the polymer (I) used as a dispersant has excellent voltage resistance, even when the lithium ion battery is charged under high voltage, oxidative decomposition of the polymer (I) in the positive electrode composite layer is reduced, thereby reducing the increase in the internal resistance of the lithium ion battery. Therefore, the composition of the present invention can provide a lithium ion battery that can be stably charged even under high voltage, and is therefore suitable for use as a positive electrode composition for a lithium ion battery for forming a positive electrode composite layer of the lithium ion battery.

[0075] <Positive electrode composition for lithium ion battery> The positive electrode composition for lithium ion battery contains the composition of the present invention described above, a positive electrode active material, and a binder resin. The positive electrode active material is capable of absorbing and releasing lithium ions.

[0076] Examples of the positive electrode active material include inorganic compounds such as oxides of transition metals, composite oxides of transition metals and lithium, and transition metal sulfides. Examples of the transition metal include Fe, Co, Ni, and Mn. Specific examples of the positive electrode active material include lithium cobalt oxide (LiCoO), lithium manganese oxide (LiMnO), lithium nickel phosphate (LiNiO), and lithium-containing composite oxides of Co—Ni—Mn (Li(CoMnNi)O; LiNiO). x Co y Mn z O2) (X+Y+Z=1)), lithium-containing composite oxides of Ni—Mn—Al, lithium-containing composite oxides of Ni—Co—Al, and olivine-type lithium iron phosphate (LiFePO4).

[0077] Examples of binder resins include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF), as well as carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyimide (PI), polyamideimide (PAI), and polyacrylic acid (PAA). Polyvinylidene fluoride (PVDF) is preferred as the binder resin.

[0078] The method for producing the positive electrode composition for a lithium ion battery is not particularly limited. For example, the positive electrode composition for a lithium ion battery can be obtained by mixing the composition of the present invention, a positive electrode active material, a binder resin, and, if necessary, a solvent.

[0079] The method for producing a positive electrode composition for a lithium ion battery preferably includes a first step of mixing the composition of the present invention, a binder resin, and a solvent to obtain a mixture, and a second step of mixing this mixture with a positive electrode active material to obtain a positive electrode composition for a lithium ion battery.

[0080] The solvent used in the first step is for adjusting the viscosity, and the same solvent as that described above for the composition of the present invention is used.

[0081] (Positive electrode for lithium ion battery) The positive electrode composition for lithium ion battery can be used to form a positive electrode for lithium ion battery. The positive electrode for lithium ion battery includes a current collector and a positive electrode mixture layer formed using the positive electrode composition for lithium ion battery of the present invention. The positive electrode mixture layer includes a dispersant, a conductive additive, a positive electrode active material, and a binder resin.

[0082] The method for forming the positive electrode mixture layer is not particularly limited, and a known method can be used. For example, the positive electrode mixture layer can be obtained by applying a positive electrode composition for a lithium ion battery onto a current collector and drying it.

[0083] (Lithium-ion battery) The lithium-ion battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode can be the above-described positive electrode for a lithium-ion battery. The shape of the lithium-ion battery is not particularly limited, and examples thereof include a coin type, a laminate type, a button type, a sheet type, a cylindrical type, a rectangular type, and a flat type.

[0084] The negative electrode may be a conventionally known negative electrode. The negative electrode preferably includes a current collector and a negative electrode mixture layer formed on the current collector. The negative electrode mixture layer preferably includes a negative electrode active material and a binder resin.

[0085] The separator is not particularly limited, and examples thereof include microporous films containing synthetic resins such as polyethylene, polypropylene, polybutene, and polyvinyl chloride.

[0086] The electrolytic solution contains an electrolyte and an organic solvent. Examples of the electrolyte include lithium salts such as LiPF6, LiClO4, and CF3SO3Li. The organic solvent is not particularly limited as long as it can dissolve the electrolyte. Examples of the organic solvent include carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and ethyl methyl carbonate (EMC). Preferred organic solvents are ethylene carbonate (EC) and diethyl carbonate (DEC). One type of electrolytic solution may be used alone, or two or more types may be used in combination.

[0087] In a lithium ion battery, a positive electrode and a negative electrode are stacked with a separator interposed therebetween. After obtaining a laminate in which the positive electrode and the negative electrode are stacked with the separator interposed therebetween, the laminate is housed in a battery container, and an electrolyte solution is poured into the laminate and the container is sealed to obtain a lithium ion battery. A plurality of laminates may be housed in a stacked state, or a long laminate may be housed in a wound state.

[0088] The present invention will be described in more detail below using examples, but the present invention is not limited thereto. Specific numerical values ​​of blending ratios (content ratios), physical property values, parameters, etc. used in the following description can be replaced with the upper limit values ​​(numeric values ​​defined as "equal to or less than") or lower limit values ​​(numeric values ​​defined as "equal to or greater than") of the corresponding blending ratios (content ratios), physical property values, parameters, etc. described in the "Summary of the Invention" and "Description of the Invention."

[0089] Synthesis Example 1 6.891 g of acrylonitrile, 2-methacryloyloxyethyl acid phosphate (the compound represented by the above formula (I) [R 1 represents a methyl group, and R 2 represents an ethylene group.], 0.577 g of a phosphate group-containing monomer represented by the formula (product name "Light Ester P-1M" manufactured by Kyoeisha Chemical Co., Ltd.), 1.25 g of a polymerization initiator (P1) (2,2'-azobis(2-methylbutyronitrile) manufactured by Nippon Finechem Co., Ltd., product name "ABN-E"), and 54.6 g of N-methyl-2-pyrrolidone (NMP) were mixed together to prepare a monomer solution for dropping.

[0090] Next, 1.773 g of behenyl acrylate (manufactured by NOF Corporation, product name "Blemmer VA") and 117.1 g of N-methyl-2-pyrrolidone (NMP) were placed in a separable flask, and then a reflux condenser, a stirrer, a thermometer, and a nitrogen-filled tube were attached to the separable flask. The atmosphere inside the separable flask was replaced with nitrogen, and the temperature inside the separable flask was heated to 82°C, and the monomer solution for dropping was added dropwise over 2 hours. 30 minutes after the end of the dropwise addition, an additional polymerization initiator solution (a solution prepared by dissolving 0.13 g of polymerization initiator (P2) (2,2'-azobis(2-methylbutyronitrile), manufactured by Nippon Finechem Co., Ltd., product name "ABN-E") in 0.5 g of NMP) was added three times at 30-minute intervals. The temperature was then maintained at 82°C and the mixture was stirred for 2 hours, thereby obtaining an NMP solution containing polymer (I).

[0091] (Synthesis Examples 2 to 10, and Comparative Synthesis Examples 1 and 2) NMP solutions containing polymer (I) were obtained in the same manner as in Synthesis Example 1, except that the blending amounts of acrylonitrile, 2-methacryloyloxyethyl acid phosphate (phosphate group-containing monomer), behenyl acrylate, polymerization initiator (P1), and polymerization initiator (P2) were changed as shown in Table 1.

[0092] The contents (mol %) of the nitrile group-containing monomer (A) unit, the acidic group-containing monomer (B) unit, and the alkyl group-containing monomer (C) unit in the obtained polymer (I) relative to 100 mol % of the total amount of the base monomer units are shown in Table 2.

[0093] [Evaluation] The storage stability, the voltage resistance of the dispersant, and the resistance of the positive electrode mixture layer were evaluated according to the following procedures. The results are shown in Table 2 and FIG.

[0094] [Storage Stability] (Examples 1 to 10 and Comparative Examples 1 and 2) 1. Preparation of Composition (I) A vial was charged with 1.5 g of carbon nanotubes (multi-walled carbon nanotubes, product name "K-Nanos 501T" manufactured by Kumho Petrochemical Co., Ltd.), 12 g of an NMP solution containing polymer (I), and 86.5 g of N-methyl-2-pyrrolidone (NMP) to obtain a premix. In this case, the NMP solution containing polymer (I) prepared in the above Synthesis Example or Comparative Synthesis Example was used as the NMP solution containing polymer (I), as shown in Table 2. Next, the premix was mixed in a high-pressure jet mill at a pressure of 150 MPa in one pass, thereby obtaining composition (I).

[0095] Composition (I) contained 1.5 mass% of carbon nanotubes (CNT), 0.6 mass% of polymer (I), and 97.9 mass% of N-methyl-2-pyrrolidone (NMP). Therefore, in composition (I), the content of polymer (I) per 100 mass parts of carbon nanotubes was 40 mass parts.

[0096] 2. Evaluation of storage stability The prepared composition (I) was left to stand at 40°C for one month, and the presence or absence of separation of N-methyl-2-pyrrolidone (NMP) was visually determined and evaluated according to the following criteria: A: No separation of NMP was observed. B: Slight separation of NMP was observed on the surface of composition (I). C: Separation of NMP was clearly observed on the surface of composition (I).

[0097] [Voltage resistance of dispersant] (Examples 1 to 10 and Comparative Examples 1 and 2) 1. Preparation of composition (II) Composition (II) was prepared in the same manner as in the preparation of composition (I) above, except that a premixture was prepared by supplying 2 g of carbon nanotubes (multi-walled carbon nanotubes, average fiber diameter of 5 to 7 nm, average fiber length of 50 to 150 μm, product name "JENOTUBE 6A" by JEIO), 24 g of an NMP solution containing polymer (I), and 74 g of N-methyl-2-pyrrolidone (NMP) to a vial.

[0098] Composition (II) contained 2 mass% of carbon nanotubes (CNT), 1.2 mass% of polymer (I), and 96.8 mass% of N-methyl-2-pyrrolidone (NMP). Therefore, in composition (II), the content of polymer (I) per 100 mass parts of carbon nanotubes was 60 mass parts.

[0099] 2. Preparation of coin cells for voltage resistance tests Composition (II) and polyvinylidene fluoride (PVDF) were weighed into a 240 ml sample bottle so that the PVDF:CNT:polymer (I) (mass ratio) was 63.0:23.0:14.0, and the mixture was stirred for 1 minute at 800 rpm and 528 rpm using a planetary centrifugal mixer (manufactured by Kurabo Industries, Ltd., product name "Mazerustar KK-2000") to obtain a mixture. NMP was then added to the mixture to reduce the viscosity, and a slurry for voltage resistance tests was prepared.

[0100] The slurry was applied to aluminum foil using an applicator and dried at 100°C for 1 hour to obtain a positive electrode film. The aluminum foil and positive electrode film were punched out to a diameter of 14 mm and dried overnight at 120°C in an argon gas atmosphere to obtain a positive electrode. The mass of the 14 mm positive electrode film was 2.70 mg (dry state). Using the positive electrode, a coin cell to be measured was assembled in a glove box purged with argon gas. Metallic lithium was used as the negative electrode. The electrolyte solution used was a 1 mol / L electrolyte (LiPF6) dissolved in an organic solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) in a 1:1 EC:DEC (volume ratio).

[0101] Furthermore, blank coin cells were prepared using the same procedure as above, except that when preparing the slurry for the voltage resistance test, composition (II) not containing polymer (I) was used as composition (II), and the mass of the φ14 mm positive electrode film was 2.32 mg (dry state). The compositions of the positive electrode films contained in the coin cell to be measured and the blank coin cell were as shown below. [Composition of the positive electrode film of the coin cell to be measured] PVDF: 63.0 mass%, CNT: 23.0 mass%, polymer (I): 14.0 mass% [Composition of the positive electrode film of the blank coin cell] PVDF: 73.2 mass%, CNT: 26.8 mass%, polymer (I): 0 mass%

[0102] 3. Cyclic Voltammetry (CV) Measurements Cyclic voltammetry (CV) measurements were carried out on each coin cell using a potentiostat (HZ-Pro 2CH, manufactured by Hokuto Denko Corporation) at a sweep voltage of 2.5 V to 5.0 V and a sweep rate of 10 mV / s.

[0103] The current value when a voltage of 5 V was applied was measured for each of the coin cell to be measured and the blank coin cell, and the current value ratio (Is / Ib) = (current value of the coin cell to be measured) / (current value of the blank coin cell) was calculated.

[0104] When a voltage is applied to the coin cell to be measured, if decomposition of the dispersant occurs, the current value increases and the graph rises. Therefore, if the current value ratio (Is / Ib) exceeds 1, it can be determined that decomposition of the dispersant has occurred.

[0105] [Resistance of Positive Electrode Composite Layer] (Examples 1 to 10 and Comparative Examples 1 and 2) Composition (I) was obtained according to the same procedure as in the preparation of composition (I) in the evaluation of storage stability described above. Composition (I) and a solution of polyvinylidene fluoride (PVDF) dissolved in N-methyl-2-pyrrolidone (NMP) (PVDF: 8% by mass, manufactured by Kureha Corporation, product name "KF Polymer L#7208") were weighed into a 240 ml sample bottle and stirred for 1 minute at a rotation speed of 800 rpm and a revolution speed of 528 rpm using a planetary centrifugal mixer (manufactured by Kurabo Industries, Ltd., product name "Mazerustar KK-2000").

[0106] Thereafter, lithium cobalt oxide (LiCoO) was added to the sample bottle as a positive electrode active material, and the mixture was stirred for 1 minute using a planetary centrifugal mixer (manufactured by Kurabo Industries, Ltd., product name "Mazerustar KK-2000") at a planetary centrifugal speed of 800 rpm and a revolution speed of 528 rpm, to obtain a positive electrode composition in a slurry form.

[0107] The mass ratio (positive electrode active material: PVDF: carbon nanotubes: polymer (I)) in the positive electrode was 97.3:2.42:0.20:0.08.

[0108] The positive electrode composition was applied to the surface of aluminum foil using an applicator and dried at 100°C for 1 hour to obtain a positive electrode composite layer. The positive electrode composite layer was pressed using a roll press (manufactured by Hosen Co., Ltd., product name "Ultra-small manual roll press: HSHRP-40120"). The aluminum foil and the positive electrode composite layer were punched out to a diameter of 14 mm to obtain a positive electrode for measuring DC resistance. The positive electrode composite layer had a volume density of 3.0 g / cm. 3 The mass was 29 to 32 mg and the thickness was 62 to 64 μm.

[0109] The volume resistivity (Ω·cm) of the positive electrode mixture layer of the produced positive electrode was measured in a 25° C. environment using an electrode resistance system (manufactured by Hioki E.E. Corporation, product name "RM2610").

[0110]

[0111]

[0112] 1 shows a three-component composition diagram (ternary composition diagram) in which the composition ratios of the three components in the polymer (I) of the present invention, consisting of nitrile group-containing monomer (A) units, acidic group-containing monomer (B) units, and alkyl group-containing monomer (C) units, are expressed as the content (mol %) of each unit relative to 100 mol % of the total amount of base monomer units, using triangular coordinates (A, B, C). Therefore, in the triangular coordinates (A, B, C), A + B + C = 100 (mol %).

[0113] In the polymer (I), the nitrile group-containing monomer (A) unit, the acidic group-containing monomer (B) unit, and the alkyl group-containing monomer (C) unit are essential units, but the polymer (I) may contain other monomer units in addition to the above units.

[0114] In the equilateral triangular three-component composition diagram shown in Figure 1, the base of the equilateral triangle (A axis) represents the content (mol %) of nitrile group-containing monomer (A) units in polymer (I) relative to 100 mol % of the total amount of base monomer units. The apex A of the equilateral triangle represents a composition in which the content of nitrile group-containing monomer (A) units is 100 mol % [(A, B, C) = (100, 0, 0)]. The scale lines for the content of nitrile group-containing monomer (A) units are shown in 10% increments as straight lines parallel to the right side (C axis) of the equilateral triangle from the base of the equilateral triangle (A axis).

[0115] In the equilateral triangular three-component composition diagram shown in Figure 1, the left side of the equilateral triangle (B axis) represents the content (mol %) of acidic group-containing monomer (B) units in the polymer (I) relative to 100 mol % of the total amount of base monomer units. The apex B of the equilateral triangle represents a composition in which the content of acidic group-containing monomer (B) units is 100 mol % [(A, B, C) = (0, 100, 0)]. The scale line for the content of acidic group-containing monomer (B) units is a straight line parallel to the left side of the equilateral triangle (B axis) and the base of the equilateral triangle (A axis), and is shown in 10% increments.

[0116] In the equilateral triangular three-component composition diagram shown in Figure 1, the right side of the equilateral triangle (C axis) represents the content (mol %) of alkyl group-containing monomer (C) units in the polymer (I) relative to 100 mol % of the total amount of base monomer units. The vertex C of the equilateral triangle represents a composition in which the content of alkyl group-containing monomer (C) units is 100 mol % [(A, B, C) = (0, 0, 100)]. The scale lines for the content of alkyl group-containing monomer (C) units are shown in 10% increments as straight lines parallel to the right side of the equilateral triangle (C axis) and the left side of the equilateral triangle (B axis).

[0117] In the triangular coordinate system of the three-component composition diagram of Figure 1, the region surrounded by the dashed-dotted line, the A axis, and the B axis (including the dashed-dotted line and excluding the A axis and the B axis) is the range in which the molar ratio of the acidic group-containing monomer (B) units to the nitrile group-containing monomer (A) units [(B) / (A)] in the polymer (I) is greater than 0 and 2.00 or less. In Examples 1 to 10, by using a polymer (I) whose composition ratio falls within this region, good evaluation results were obtained in terms of storage stability, the voltage resistance of the dispersant, and the resistance of the positive electrode mixture layer.

[0118] (Cross-reference to related applications) This application claims priority to Japanese Patent Application No. 2024-89561, filed on May 31, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0119] According to the present invention, it is possible to provide a composition that contains a dispersant with improved voltage resistance and that can maintain high storage stability.

Claims

1. A composition comprising: a dispersant containing polymer (I) of monomers including a nitrile group-containing monomer (A), an acidic group-containing monomer (B), and an alkyl group-containing monomer (C) having an alkyl group with 12 or more carbon atoms, wherein the molar ratio of acidic group-containing monomer (B) units to nitrile group-containing monomer (A) units [(B) / (A)] is greater than 0 and 2.00 or less; a conductive additive; and a solvent.

2. The composition according to claim 1, wherein the content of alkyl group-containing monomer (C) units in polymer (I) is 15 mol % or more relative to 100 mol % of the total amount of nitrile group-containing monomer (A) units, acidic group-containing monomer (B) units, and alkyl group-containing monomer (C) units.

3. The composition according to claim 1, wherein the acid group-containing monomer (B) comprises a phosphoric acid group-containing (meth)acrylate.

4. The composition according to claim 1, characterized in that the alkyl group-containing monomer (C) has 18 or more and 23 or less carbon atoms.

5. The composition according to claim 1, wherein the conductive additive comprises a carbon material.

6. The composition according to claim 1, wherein the conductive additive comprises carbon nanotubes.

7. A positive electrode composition for a lithium ion battery, comprising the composition according to claim 1, a positive electrode active material, and a binder resin.

8. A dispersant characterized by containing a polymer (I) of monomers comprising a nitrile group-containing monomer (A), an acidic group-containing monomer (B), and an alkyl group-containing monomer (C) having an alkyl group having 12 or more carbon atoms, wherein the molar ratio of the acidic group-containing monomer (B) units to the nitrile group-containing monomer (A) units [(B) / (A)] is greater than 0 and not greater than 2.00.

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