Viscosity reducer for positive electrode of power storage device

Abstract

To provide a viscosity reducer for an electrode of a power storage device, which enables a reduction in the yield value of a positive electrode paste and the formation of a positive electrode coating film with a low resistance value.SOLUTION: In an embodiment, the present disclosure relates to a viscosity reducer for a power storage device electrode, which is a polymer containing a structural unit (A) represented by the following general formula (1), in which the molar fraction a of the structural unit (A) relative to all structural units of the polymer is 0.10 to 0.60. In the following general formula (1), X is (CH2)n, n is 0 or 1, R1 is an aromatic ring or a heteroaromatic ring, R2 is hydrogen, an aromatic ring, a heteroaromatic ring, or an aliphatic hydrocarbon, and M1 is hydrogen, NH4, an alkali metal atom, or an organic ammonium.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a viscosity reducer for a positive electrode of an electricity storage device. [Background technology]

[0002] In recent years, the positive electrode manufacturing process for lithium-ion batteries has increasingly used carbon nanotubes as a conductive additive in addition to the positive electrode active materials such as lithium metal oxide and the binder resin that binds them. In addition, the positive electrode active materials (particles) are becoming finer.

[0003] The positive electrode is produced by preparing a paste-like paint (positive electrode paste) by mixing and dispersing these materials in an organic solvent, and then coating and drying this on aluminum foil or other current collectors (current collectors). However, the positive electrode paste cannot be uniformly coated, which can lead to poor productivity and adverse effects on the resistance of the positive electrode coating. The positive electrode coating is a film-like layer obtained by coating the electrode substrate (current collector). It has generally been thought that the cause of this phenomenon is the high viscosity of the positive electrode paste. It is also known that the viscosity of the positive electrode paste is greatly affected by the dispersibility of the carbon material-based conductive material.

[0004] The following Patent Documents 1 to 3 each disclose a dispersant used for dispersing a carbon material in a non-aqueous solvent. Specifically, Patent Document 1 discloses a dispersant useful as a dispersant for carbon black, which is obtained by reacting a copolymer of diisobutylene and maleic anhydride with ammonia or a saturated lower amine at a reaction rate of almost 100%. Patent Document 2 discloses a dispersant composition for printing inks, which contains 100% amidation product of a copolymer of diisobutylene and maleic anhydride with stearylamine, methyl isobutyl ketone (MIBK) as an organic solvent, and carbon black as a pigment. Patent Document 3 discloses an oil-based dispersion composition for electronic materials, which contains an amidation product of a copolymer of diisobutylene and maleic anhydride with oleylamine, propylene glycol methyl ether acetate (PEGMA) as an organic solvent, and carbon black. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 41-17852 [Patent Document 2] JP 2018-168285 A [Patent Document 3] JP 2009-138115 A Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, Patent Documents 1 to 3 all focus on the dispersibility of carbon materials (carbon black). However, they do not disclose that the dispersion state of the positive electrode active material affects the coatability of the positive electrode paste and, in turn, the coating resistance. In addition, they do not disclose that the coatability of the positive electrode paste can be improved by taking some measures against the positive electrode active material.

[0007] In one aspect, the present disclosure provides a viscosity reducer for a positive electrode of an electricity storage device, which enables a reduction in the yield value of a positive electrode paste and the formation of a positive electrode coating film with a low resistance value. The present disclosure also provides a viscosity reducer composition for use in a positive electrode of an electricity storage device and a positive electrode paste, each of which contains the viscosity reducer for use in a positive electrode of an electricity storage device. The present disclosure also provides a method for producing a positive electrode for an electricity storage device using the positive electrode paste, and a method for producing an electricity storage device using the positive electrode for an electricity storage device. [Means for solving the problem]

[0008] In one aspect, the present disclosure relates to a viscosity reducer for a positive electrode of an electricity storage device, which is a polymer including a structural unit (A) represented by the following general formula (1), wherein the molar fraction a of the structural unit (A) relative to all structural units of the polymer is 0.10 or more and 0.60 or less. [ka] However, in the above general formula (1), X is (CH2) n , n is 0 or 1; R 1 is an aromatic ring or a heteroaromatic ring, R 2 is hydrogen, an aromatic ring, a heteroaromatic ring, or an aliphatic hydrocarbon; M 1 is hydrogen, NH4, an alkali metal atom or an organic ammonium.

[0009] In one aspect, the present disclosure relates to a viscosity reducer composition for a positive electrode of an electricity storage device, comprising the viscosity reducer for a positive electrode of an electricity storage device of the present disclosure and an organic solvent.

[0010] In one aspect, the present disclosure relates to a positive electrode paste for an electricity storage device, comprising the viscosity reducer for a positive electrode of an electricity storage device of the present disclosure, a carbon material-based conductive material, a positive electrode active material, and an organic solvent.

[0011] In one aspect, the present disclosure relates to a method for producing a positive electrode for an electricity storage device, the method comprising applying the positive electrode paste for an electricity storage device of the present disclosure to a current collector and drying the applied paste.

[0012] In one aspect, the present disclosure relates to a method for producing an electricity storage device, comprising incorporating a positive electrode for the electricity storage device of the present disclosure. Effect of the Invention

[0013] According to one aspect of the present disclosure, it is possible to provide a viscosity reducer for a positive electrode of an electricity storage device, which enables a reduction in the yield value of a positive electrode paste and the formation of a positive electrode coating film having a low resistance value. According to one aspect of the present disclosure, it is possible to provide a viscosity reducer composition for a positive electrode of an electricity storage device, which enables a reduction in the yield value of a positive electrode paste and the formation of a positive electrode coating film having a low resistance value. According to the present disclosure, in one aspect, it is possible to provide a positive electrode paste for an electricity storage device, which contains the viscosity reducer for a positive electrode of an electricity storage device of the present disclosure and is capable of forming a positive electrode coating film having a low yield value and a low resistance value. According to the present disclosure, in one aspect, a positive electrode for an electricity storage device is produced using the positive electrode paste for an electricity storage device of the present disclosure, so that a positive electrode for an electricity storage device with low resistance can be manufactured. According to one embodiment of the present disclosure, an electricity storage device is produced using the electricity storage device positive electrode of the present disclosure, and therefore, an electricity storage device with low resistance can be manufactured. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The inventors of the present application believed that factors that make it difficult to uniformly apply the positive electrode paste include friction between particles of the positive electrode active material and aggregation of the carbonaceous conductive material with a large specific surface area, etc. They believed that in order to improve the application properties of the positive electrode paste and ultimately to reduce the coating resistance, it was necessary to control the structure in the positive electrode paste, that is, to appropriately control the yield value of the positive electrode paste, and therefore designed the viscosity reducer (polymer) for the positive electrode of the present disclosure (hereinafter sometimes abbreviated as the "viscosity reducer of the present disclosure"). The present disclosure is based on the new finding that the yield value of a positive electrode paste for an electricity storage device can be controlled to a desired value by including a polymer (thickening agent) that contains a structural unit (A) represented by the following general formula (1) and has a molar fraction a of the structural unit (A) of 0.10 or more and 0.60 or less with respect to all structural units: [ka] In the above general formula (1), X is (CH2) n , n is 0 or 1, and R 1 is an aromatic ring or a heteroaromatic ring, R 2 is hydrogen, an aromatic ring, a heteroaromatic ring, or an aliphatic hydrocarbon; M 1 is hydrogen, NH4, an alkali metal atom or an organic ammonium.

[0015] Although the details of the mechanism by which the effects of the present disclosure are exerted are not clear, R 1 However, the positive electrode active material and the carbon material-based conductive material exhibit high adsorption properties in a polar solvent, and thus the positive electrode active material and the carbon material-based conductive material are dispersed well in the solvent. 2 is R 1 In cooperation with the above, it contributes to the expression of the affinity of the viscosity reducer of the present disclosure with an appropriate solvent, that is, it plays a role in controlling the solubility of the viscosity reducer of the present disclosure in the solvent. In addition, it is presumed that the carboxyl group of the structural unit (A) or the salt structure obtained by neutralizing the carboxyl group contributes to improving the dispersibility of the positive electrode active material and the carbon material-based conductive material in the polar solvent by its electrostatic repulsion, thereby suppressing friction between the positive electrode active material particles and aggregation of the carbon material-based conductive material having a large specific surface area, enabling a reduction in the yield value of the positive electrode paste, and ultimately enabling a reduction in the resistance of the coating film formed using the positive electrode paste. However, the present disclosure is not limited to these mechanisms.

[0016] <Deviscosity reducer for positive electrodes of power storage devices> Unit In one aspect, the present disclosure relates to a viscosity reducer for a positive electrode of an electricity storage device such as a non-aqueous secondary battery. The viscosity reducer for a positive electrode of an electricity storage device of the present disclosure (hereinafter also referred to as the "viscosity reducer of the present disclosure") is a polymer containing a structural unit (A) represented by the following general formula (1). The molar fraction a of the structural unit (A) relative to all structural units of the polymer is 0.10 or more and 0.60 or less from the viewpoint of obtaining a desired yield value. [ka]

[0017] The viscosity reducing agent of the present disclosure is, for example, a copolymer of an olefin and maleic anhydride that is amidated to form an aromatic ring or a heteroaromatic ring R 1 and R is hydrogen, an aromatic ring, a heteroaromatic ring, or an aliphatic hydrocarbon. 2The structural unit (A) represented by the above general formula (1) is derived from maleic anhydride which has been amide-modified and, if necessary, the carboxyl group formed by the amidation is neutralized.

[0018] The structural unit (A) plays a role in improving the dispersibility of the positive electrode active material and the carbon material-based conductive material blended in the positive electrode paste. 1 It is speculated that this is due to the polarity of the aromatic ring, which is shown by R, interacting with the positive electrode active material particles and the carbon material-based conductive material. 1 is an aromatic ring or a heteroaromatic ring, preferably a heteroaromatic ring such as a pyridine ring, a benzene ring or a naphthalene ring, more preferably a pyridine ring or a benzene ring, and further preferably a pyridine ring, from the viewpoint of acting on the positive electrode active material particles and the carbon material-based conductive material and controlling the yield value of the positive electrode paste.

[0019] In the above general formula (1), R 2 R plays a role in controlling the solubility in the solvent. 2 may be any one of hydrogen, an aromatic ring, a heteroaromatic ring, or an aliphatic hydrocarbon, but is preferably hydrogen. Examples of the aromatic ring or heteroaromatic ring include a heteroaromatic ring such as a pyridine ring, a benzene ring, and a naphthalene ring. The carbon number of the aliphatic hydrocarbon is 1 or more from the viewpoint of ease of synthesis of the viscosity reducer and the solubility of the viscosity reducer, and is preferably 10 or less, more preferably 6 or less, and even more preferably 4 or less, from the viewpoint of the solubility of the viscosity reducer in organic solvents. Also, R 1 and R 2 From the viewpoint of the solubility of the viscosity reducer in an organic solvent, the total carbon number is preferably 20 or less, more preferably 10 or less, even more preferably 7 or less, and still more preferably 6 or less.

[0020] In the above general formula (1), X is derived from the synthetic raw material (CH2) n where n is 0 or 1.

[0021] In the above general formula (1), a carboxy group or a neutralized carboxy group (COOM 1 ) is R 2 It is a factor that controls the solubility in a solvent, just like M 1 is hydrogen, NH4, an alkali metal atom, or organic ammonium (salt of an organic amine). Among them, organic ammonium is preferable from the viewpoint of improving the solubility in a solvent. Examples of the metal include Na, Ca, and Mg. The organic amine is not particularly limited as long as it functions as a neutralizing agent, and examples thereof include amine compounds such as monoethanolamine, methylamine, dimethylamine, ethylamine, dimethylbenzylamine, methylbenzylamine, 2-N-dibutylaminoethanol, 1-phenylmethanamine, N,N-diethylaminoethanol, 2-dimethylaminoethanol, 1-amino-2-butanol, 2-(ethylamino)ethanol, 2-amino-2-methyl-1-propanol, DL-1-amino-2-propanol, N-methyl-2-aminoethanol, 1-(2-hydroxyethyl)piperazine, and N-ethyldiethanolamine. In order to distinguish it from "organic amine B2" described later, the above organic amine used as the neutralizing agent is called organic amine B1.

[0022] In the above general formula (1), a is the molar fraction of the structural unit (A) relative to all structural units of the viscosity reducer (polymer) of the present disclosure. The molar fraction a of the structural unit (A) is 0.10 or more and 0.60 or less from the viewpoint of controlling the yield value of the positive electrode paste within a desired range, and is preferably 0.10 or more and 0.50 or less from the viewpoint of the practicality of the produced polymer. In the present disclosure, the molar fraction a is R with respect to the monomer I described below used in the polymerization of the viscosity reducing agent of the present disclosure. 1 and R 2 It can be calculated from the amount of amine compound A1 used for introducing the formula:

[0023] Constituent Unit The following structural unit (C) is a structural unit derived from the above-mentioned olefin. The structural unit (C) is a factor that controls the polymerizability (ease of synthesis of the viscosity reducer). [ka]

[0024] In the above general formula (3), R 5 From the viewpoint of improving solubility in a solvent, represents hydrogen or a methyl group, and is preferably a methyl group.

[0025] In the above general formula (3), R 6 From the viewpoint of improving the solubility of the viscosity reducer in a solvent, R is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group having 1 to 10 carbon atoms and either substituted or unsubstituted. 6 From the viewpoint of improving solubility in a solvent, is preferably an alkyl group having from 1 to 10 carbon atoms, or an aromatic hydrocarbon group having from 1 to 10 carbon atoms and either substituted or unsubstituted, more preferably an alkyl group having from 1 to 10 carbon atoms, or a naphthyl group or phenyl group having from 1 to 10 carbon atoms and either substituted or unsubstituted, and even more preferably an alkyl group having from 1 to 10 carbon atoms. The alkyl group may be either linear or branched.

[0026] R 6 From the viewpoint of monomer polymerizability, the carbon number of is 1 or more, preferably 2 or more, and from the same viewpoint, it is 10 or less, preferably 7 or less.

[0027] In the above general formula (3), c is the molar fraction of the structural unit (C) relative to all structural units of the viscosity reducer (polymer) of the present disclosure. From the viewpoint of ease of synthesis of the viscosity reducer, the molar fraction c of the structural unit (C) is preferably 0.40 or more, more preferably 0.45 or more, and from the same viewpoint, is preferably 0.65 or less, more preferably 0.55 or less. In the present disclosure, the molar fraction c can be calculated from the amount of monomer II used in the polymerization of the viscosity reducer of the present disclosure, which will be described later.

[0028] The configuration of the structural units (A) and (C) may be either a block type or a random type, but from the viewpoint of polymer productivity, a random type is preferred.

[0029] [Block] From the viewpoint of improving the carbon material-based conductive material (conductive assistant) blended in the positive electrode paste, the viscosity reducer of the present disclosure preferably further contains a structural unit (B) represented by the following general formula (2). [ka]

[0030] In the above general formula (2), R 3 is hydrogen, R 4 is an aliphatic hydrocarbon group having 14 to 22 carbon atoms; M 2 is hydrogen, NH4, an alkali metal atom or an organic ammonium.

[0031] In the above general formula (2), R 4 From the viewpoint of dispersing the carbonaceous conductive material to be mixed in the positive electrode paste, R is preferably an aliphatic alkyl group having 14 to 22 carbon atoms. 4 From the viewpoint of dispersing the carbon material-based conductive material blended in the positive electrode paste, the number of carbon atoms is 14 or more, preferably 18 or more, and from the same viewpoint, it is 22 or less.

[0032] In the above general formula (2), a carboxy group or a neutralized carboxy group (COOM 2 ) is COOM 1 and R 2 It is a factor that controls the solubility in a solvent, just like M 2 is hydrogen, NH4, an alkali metal atom, or an organic ammonium (a salt of an organic amine B1). Among them, from the viewpoint of improving the solubility in a solvent, an organic ammonium (a salt of an organic amine B1) is preferable. Specific examples of the alkali metal atom and the organic amine B1 are each the same as those described above for M 1 The same as those in the previous section can be mentioned.

[0033] In the above general formula (2), b is the molar fraction of the structural unit (B) relative to all structural units of the viscosity reducer (polymer) of the present disclosure. The molar fraction b of the structural unit (B) is preferably 0.10 or more and 0.30 or less, from the viewpoints of high adsorption to the carbon material-based conductive material, solvent solubility, and maximizing the action (adsorption) on the positive electrode active material particles, and is a value that satisfies the relational expression b / a≦2.5, preferably 0.3≦b / a≦2.5, and more preferably 0.3≦b / a≦1.0. In the present disclosure, the molar fraction b is R with respect to the monomer I described below used in the polymerization of the viscosity reducing agent of the present disclosure. 3 and R 4 It can be calculated from the amount of amine compound A2 used for introducing the formula:

[0034] Unit When the amidation of the copolymer of olefin and maleic anhydride is carried out on a portion of the maleic anhydride, the viscosity reducer of the present disclosure further contains a structural unit (D) derived from maleic anhydride represented by the following general formula (4). [ka]

[0035] In the following general formula (4), d is the molar fraction of the structural unit (D) relative to all structural units of the viscosity reducer (polymer) of the present disclosure. The molar fraction d of the structural unit (D) is preferably 0.20 or less, more preferably 0.15 or less, and even more preferably 0, from the viewpoint of controlling the yield value of the positive electrode paste within a desired range and from the viewpoint of reducing the coating resistance.

[0036] The viscosity reducer of the present disclosure is, for example, a modified copolymer obtained by neutralizing an amidated product of a copolymer of an olefin and maleic anhydride as necessary, and the weight average molecular weight of the copolymer before the amide modification is preferably 3,000 or more, more preferably 5,000 or more, and even more preferably 10,000 or more from the viewpoint of adsorption to the positive electrode active material and the carbon material-based conductive material. From the viewpoint of solubility in organic solvents, dispersibility of the positive electrode active material and the carbon material-based conductive material, and low viscosity of the positive electrode paste, the weight average molecular weight is preferably 100,000 or less, more preferably 70,000 or less, and even more preferably 50,000 or less. In the present disclosure, the weight average molecular weight of the copolymer of a vinyl ether monomer and maleic anhydride before amide modification is a value measured by GPC (gel permeation chromatography), and the details of the measurement conditions are as shown in [Measurement of weight average molecular weight] in the Examples.

[0037] The monomer I which gives the structural unit (A), the structural unit (B), and the structural unit (D) can be, for example, maleic anhydride or maleic acid. 1 and R 2 , if necessary R 3 and R 4 Since it is easy to introduce maleic anhydride having a structure reactive with amines, maleic anhydride is preferred.

[0038] From the viewpoint of good solubility in organic solvents, the monomer II which gives the structural unit (C) is R 5 and R 6 Specific examples of the α-olefin include isobutylene, 1-pentene, 1-heptene, 1-butene, 1-oxene, diisobutylene (2,4,4-trimethyl-1-pentene), 1-decene, styrene, α-methylstyrene, etc. Among these, from the viewpoint of good solubility in organic solvents, at least one of styrene, diisobutylene, and isobutylene is preferred, and diisobutylene is more preferred.

[0039] The viscosity reducer of the present disclosure can be produced, for example, by polymerization of a vinyl monomer. For example, Monomer I and Monomer II are mixed in a solvent, and the monomers are polymerized by a solution polymerization method to obtain a copolymer to be subjected to amidation. The copolymer to be subjected to amidation can be a commercially available product, for example, Isoban (manufactured by Kuraray Co., Ltd.), which is a copolymer of isobutylene and maleic anhydride. 1 and R 2 By adding an amine compound A1 having the formula: 1 and R 2 (amide modified copolymer containing structural unit A). 3 and R 4 To the monomer I, an amine compound A2 having the formula 3 and R 4 is introduced (amide modified copolymer containing structural units A and B). The solution containing the amide-modified copolymer thus obtained is neutralized in whole or in part by using a neutralizing agent as necessary. Thereafter, as necessary, the solvent in the solution containing the amide-modified copolymer is replaced with a poor solvent for the amide-modified copolymer, such as an aqueous solvent, to precipitate the amide-modified copolymer, thereby obtaining the viscosity reducer of the present disclosure. The viscosity reducer may be neutralized during the preparation of the viscosity reducer composition.

[0040] R 1 and R 2 Examples of the amine compound A1 having the formula include 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, N-phenyl-1-naphthylamine, benzylamine, N-methylbenzylamine, N-methylaniline, and N-ethylaniline.

[0041] R 3 and R 4 Examples of the amine compound A2 having the formula include tetradecylamine, pentadecylamine, cetylamine, stearylamine, nonadecylamine, icosylamine, and behenylamine.

[0042] Examples of the solvent used in the synthesis of the viscosity reducer of the present disclosure include organic solvents such as hydrocarbons (hexane, heptane), aromatic hydrocarbons (toluene, xylene, etc.), ketones (acetone, methyl ethyl ketone), ethers (tetrahydrofuran, diethylene glycol dimethyl ether), N-methylpyrrolidone, etc. The amount of the solvent is preferably 0.5 to 10 times the total amount of the monomers in terms of mass ratio.

[0043] The polymerization initiator used in the polymerization may be a known radical polymerization initiator, such as an azo polymerization initiator, hydroperoxides, dialkyl peroxides, diacyl peroxides, and ketone peroxides. The amount of the polymerization initiator is preferably 0.01 to 5 mol% based on the total amount of the monomer components. The polymerization reaction is preferably carried out in a nitrogen stream at a temperature range of 40 to 180°C, and the reaction time is preferably 0.5 to 20 hours. In addition, a known chain transfer agent may be used during the polymerization. Examples of the chain transfer agent include mercapto compounds such as isopropyl alcohol and mercaptoethanol.

[0044] <Viscosity reducer composition for power storage device electrodes> The viscosity reducer of the present disclosure may be supplied to the market in the form of a polymer containing the structural unit (A) itself, or may be supplied to the market as a viscosity reducer composition for an electrical storage device electrode (hereinafter, sometimes abbreviated as "viscosity reducer composition") dissolved in an organic solvent (hereinafter, for ease of explanation, referred to as "organic solvent C").

[0045] The viscosity reducer composition of the present disclosure contains the viscosity reducer of the present disclosure. Therefore, by using the viscosity reducer composition of the present disclosure, it is possible to prepare a positive electrode paste for an electricity storage device that has good coatability and is capable of forming a positive electrode coating film with a low resistance value.

[0046] The content of the viscosity reducer in the viscosity reducer composition of the present disclosure is not particularly limited, but from the viewpoint of productivity, it is preferably 10 mass% or more, more preferably 15 mass% or more, and even more preferably 20 mass% or more, and from the viewpoint of solubility in organic solvents, it is preferably 70 mass% or less, more preferably 60 mass% or less, and even more preferably 50 mass% or less.

[0047] In one embodiment, the viscosity reducer composition of the present disclosure may also contain an organic amine soluble in organic solvent C (hereinafter, also referred to as "organic amine B2" to distinguish it from the organic amine B1 used for neutralizing the viscosity reducer) from the viewpoint of reducing the viscosity of the positive electrode paste and reducing the coating resistance. The boiling point of organic amine B2 is preferably 260°C or lower from the viewpoint of suppressing residue on the electrode.

[0048] The boiling point of the organic amine B2 of the present disclosure is preferably 260° C. or lower, but from the viewpoint of reducing the resistance of the electrode of the power storage device, it is preferably a temperature at which it volatilizes during drying in the manufacturing process of the electrode, and is more preferably lower than the boiling point of a solvent commonly used as a solvent for positive electrode paste, for example, more preferably lower than the boiling point of N-methylpyrrolidone (NMP) (boiling point 202° C.), and from the viewpoint of reusing NMP, it is even more preferably lower than 190° C. The lower limit of the boiling point of the organic amine B2 of the present disclosure is preferably 100° C. or higher, more preferably 120° C. or higher, from the viewpoint of handleability.

[0049] Organic amine B2 may be the same as organic amine B1. In that case, when preparing the viscosity reducer composition of the present disclosure, the total amount of organic amine as organic amine B1 and organic amine as organic amine B2 may be added to the unneutralized viscosity reducer. Since the added organic amine is preferentially consumed to neutralize the carboxy groups, by definition, the amount of organic amine that can neutralize all the carboxy groups is the amount added as organic amine B1, and the remainder is the amount added as organic amine B2.

[0050] [Organic solvent C] Examples of the organic solvent C include amide-based polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP), ketone-based polar organic solvents such as methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and ester-based polar organic solvents such as ethyl acetate, γ-butyllactone, and ε-caprolactone. It is more preferable to use N-methylpyrrolidone, which has high solubility for the viscosity reducing agent of the present disclosure, and it is even more preferable to use N-methylpyrrolidone. The organic solvent C may be one of these organic solvents or a combination of two or more of them.

[0051] The viscosity reducer composition of the present disclosure may further contain other components to the extent that the effects of the present disclosure are not impaired. Examples of other components include antioxidants, antifoaming agents, preservatives, dehydrating agents, rust inhibitors, plasticizers, binders, etc.

[0052] <Positive electrode paste for power storage devices> In one aspect, the present disclosure relates to a positive electrode paste for an electrical storage device (hereinafter also referred to as the "positive electrode paste of the present disclosure"), which contains the viscosity reducer of the present disclosure, a carbon material-based conductive material, a positive electrode active material, an organic solvent, and, if necessary, an organic amine B2. The preferred form of the viscosity reducer of the present disclosure in this aspect is as described above. The organic solvent in this aspect is preferably the same as the organic solvent C described above, and more preferably NMP. The positive electrode paste of the present disclosure contains the viscosity reducer of the present disclosure, and therefore can form a positive electrode coating film with a low resistance value.

[0053] The positive electrode paste of the present disclosure may further include a binder. In one or more embodiments, the positive electrode paste of the present disclosure may further include a conductive material other than the carbon material-based conductive material. Examples of the conductive material other than the carbon material-based conductive material include conductive polymers such as polyaniline.

[0054] [Carbon-based conductive materials] In one or more embodiments, the carbon material-based conductive material may be carbon nanotubes (hereinafter, sometimes referred to as "CNTs"), carbon black, graphite, graphene, etc., and among these, at least one selected from carbon black and carbon nanotubes is preferable, and CNTs are more preferable. As the carbon material-based conductive material, one or more of the above may be used. The average diameter of CNTs that can be used as a carbon material-based conductive material is not particularly limited, but from the viewpoint of improving the dispersibility of the CNTs, it is preferably 1 nm or more, more preferably 2 nm or more, and even more preferably 5 nm or more, and from the viewpoint of improving the electrical conductivity, it is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 20 nm or less. The average length of the CNTs is not particularly limited, but from the viewpoint of improving the electrical conductivity, it is preferably 2 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and even more preferably 30 μm or more, and from the viewpoint of improving the dispersibility, it is preferably 500 μm or less, more preferably 300 μm or less, even more preferably 200 μm or less, and even more preferably 120 μm or less. Two or more types of CNTs having different diameters or lengths may be mixed and used. In this disclosure, the average diameter and average length of the CNTs can be measured by a scanning electron microscope (SEM) or an atomic force microscope (AFM). Depending on the properties required for the positive electrode coating, the CNTs may be single-walled, double-walled, or multi-walled, or a mixture of these.

[0055] (Cathode active material) The positive electrode active material is not particularly limited as long as it is an inorganic compound. For example, a compound having an olivine structure or a lithium transition metal composite oxide can be used. The compound having an olivine structure is represented by the general formula Li x M1 s Examples of the lithium transition metal complex oxide include a compound represented by the formula Li PO4 (wherein M1 is a 3d transition metal, 0≦x≦2, 0.8≦s≦1.2). The compound having an olivine structure may be coated with amorphous carbon or the like before use. Examples of the lithium transition metal complex oxide include a lithium manganese oxide having a spinel structure, a lithium manganese oxide having a layered structure, and a lithium manganese oxide having a general formula Lix M2O 2- Examples of the lithium transition metal composite oxide include a lithium transition metal composite oxide represented by x≦x≦1.2 and 0≦δ≦0.5 (wherein M2 is a transition metal, 0.4≦x≦1.2, 0≦δ≦0.5). The transition metal M2 may include Co, Ni, or Mn. The lithium transition metal composite oxide may further include one or more elements selected from Al, Fe, Cr, Ti, Zn, P, and B.

[0056] The content of the positive electrode active material in the positive electrode paste of the present disclosure is not particularly limited, as long as it can be adjusted in accordance with the viscosity suitable for applying the positive electrode paste to a current collector. From the viewpoints of energy density and stability of the positive electrode paste, however, the content is preferably 40 mass % or more, more preferably 50 mass % or more, even more preferably 60 mass % or more, and is preferably 90 mass % or less, more preferably 85 mass % or less, and even more preferably 80 mass % or less.

[0057] There is no particular restriction on the content of the positive electrode active material in the total solid content of the positive electrode paste of the present disclosure. The content of the positive electrode active material in the total solid content of the positive electrode paste of the present disclosure may be the same as that in the total solid content of the conventionally known positive electrode paste, and is preferably 90.0 mass% or more in order to maintain a high energy density of the power storage device, and is preferably 99.9 mass% or less in order to ensure the electrical conductivity and coating properties of the composite layer.

[0058] (Binding agent) As the binder (binder resin), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, styrene-butadiene rubber, polyacrylonitrile, etc. can be used alone or in combination.

[0059] The content of the binder in the total solid content of the positive electrode paste of the present disclosure is preferably 0.05 mass % or more from the viewpoints of the coating properties of the mixture layer and the binding property with the current collector, and is preferably 9.95 mass % or less from the viewpoint of maintaining a high energy density of the electricity storage device.

[0060] (Content of viscosity reducer in positive electrode paste) The content of the viscosity reducer of the present disclosure in the positive electrode paste of the present disclosure is preferably 0.01 mass % or more, and more preferably 0.02 mass % or more, from the viewpoint of yield value control, and is preferably 2.0 mass % or less, and more preferably 1.0 mass % or less, from the viewpoint of reducing the coating resistance.

[0061] (Content of carbon-based conductive material in positive electrode paste) The content of the carbon material-based conductive material in the positive electrode paste of the present disclosure is, from the viewpoint of the conductivity of the composite layer, preferably 0.01 mass % or more, more preferably 0.05 mass % or more, and even more preferably 0.1 mass % or more, and from the viewpoint of maintaining a high energy density of the electricity storage device, preferably 5 mass % or less, more preferably 3 mass % or less, and even more preferably 2 mass % or less.

[0062] In one or more embodiments, the positive electrode paste of the present disclosure can be prepared by mixing and stirring a positive electrode active material, a binder, a viscosity reducer composition of the present disclosure, a carbon material-based conductive material, an organic solvent (additional solvent) for adjusting the solid content concentration, and the like. In addition, the above-mentioned organic amine B2, a dispersant, a functional material, and the like may be added. As the organic solvent (additional solvent), the above-mentioned organic solvent C is preferably used, and NMP is more preferably used. A planetary mixer, a bead mill, a jet mill, and the like can be used for mixing and stirring these, and these can also be used in combination.

[0063] The positive electrode paste of the present disclosure may be prepared by premixing some of the components used in the preparation of the positive electrode paste and then mixing the premixed components with the remainder. Also, each component may be added in multiple batches rather than all at once. This can reduce the mechanical load on the stirring device.

[0064] The solids concentration of the positive electrode paste of the present disclosure, the amount of the viscosity reducer of the present disclosure, the amount of the positive electrode active material, the amount of the binder, the amount of the conductive material, the amount of the additive component, and the amount of the organic solvent can be adjusted according to the viscosity of the positive electrode paste suitable for application to the current collector. From the viewpoint of drying, it is preferable to use a small amount of organic solvent, but from the viewpoint of uniformity of the positive electrode mixture layer and surface smoothness, it is preferable that the viscosity of the positive electrode paste is not too high. On the other hand, from the viewpoint of suppressing drying and obtaining a sufficient film thickness of the mixture layer (positive electrode coating film), it is preferable that the viscosity of the positive electrode paste is not too low.

[0065] The positive electrode paste of the present disclosure is preferably capable of being adjusted to a high concentration from the viewpoint of production efficiency, but a significant increase in viscosity is not preferable from the viewpoint of workability. The additive allows the high concentration to be maintained while maintaining a preferred viscosity range.

[0066] The conductive material slurry and the positive electrode paste of the present disclosure may each further contain other components, such as antioxidants, neutralizing agents, defoamers, preservatives, dehydrating agents, rust inhibitors, plasticizers, and binders, to the extent that the effects of the present disclosure are not impaired.

[0067] (Positive electrode paste manufacturing method) In one or more embodiments, the method for producing a positive electrode paste of the present disclosure may include a step of mixing the viscosity reducer composition of the present disclosure, a carbon material-based conductive material, a binder, a positive electrode active material, and, if necessary, an additional organic solvent or organic amine B2. In one or more embodiments, the method for producing a positive electrode paste of the present disclosure may include preparing a conductive material slurry containing a carbon material-based conductive material, an organic solvent, and, if necessary, a viscosity reducer and / or organic amine B2 of the present disclosure, and then mixing the conductive slurry, the binder, and the positive electrode active material. The conductive material slurry may be a commercially available product. In one or more embodiments, the conductive material slurry, the additional organic solvent, and the binder are mixed and stirred until they are homogeneous, and then the positive electrode active material is mixed and stirred until they are homogeneous to obtain a positive electrode paste. The order of addition of these components is not limited to this.

[0068] <Method of manufacturing positive electrode coating film or positive electrode for power storage device> In one aspect, the present disclosure relates to a method for producing a positive electrode coating film or a positive electrode for an electricity storage device produced using the positive electrode paste of the present disclosure. The production method of this aspect includes applying the positive electrode paste of the present disclosure to a current collector, drying and pressing the current collector. In this aspect, the preferred form of the positive electrode paste of the present disclosure is as described above. In the production method of the present disclosure, the positive electrode coating film or the positive electrode for an electricity storage device can be produced by a conventionally known method, except for using the positive electrode paste of the present disclosure.

[0069] The positive electrode coating film or the positive electrode for a storage battery device is prepared, for example, by coating the positive electrode paste on a current collector such as an aluminum foil and drying the same. In order to increase the density of the positive electrode coating film, compaction can be performed using a press. A die head, a cone reverse roll, a direct roll, a gravure roll, or the like can be used for coating the positive electrode paste. Drying after coating can be performed by heating, air flow, infrared irradiation, or the like, alone or in combination. Drying after coating is performed at a temperature at which the organic solvent in the positive electrode paste cannot be present in the positive electrode paste after the drying time has elapsed. The drying temperature is not particularly limited as long as it is equal to or lower than the thermal decomposition temperature of the binder resin in the environment in which the drying is performed (under atmospheric pressure or vacuum), but is preferably equal to or higher than the boiling point of the organic solvent. The drying temperature is preferably 60° C. or higher and 220° C. or lower, and the drying time is preferably 10 minutes to 24 hours. Pressing of the positive electrode can be performed using a roll press machine or the like. After pressing, the positive electrode for an electricity storage device may be processed into a size suitable for incorporation into an electricity storage device, and then may be dried again under the above conditions.

[0070] <Electricity storage device and method for producing same> In one aspect, the present disclosure relates to an electricity storage device including a positive electrode for an electricity storage device obtained by the method for producing a positive electrode for an electricity storage device of the present disclosure, and a method for producing the same. In one or a plurality of embodiments, examples of the power storage device include a lithium ion secondary battery, a lithium-air secondary battery, a sodium ion battery, a sodium-sulfur secondary battery, a sodium-nickel chloride secondary battery, an organic radical battery, a zinc-air secondary battery, and an all-solid-state battery.

[0071] The method for producing an electricity storage device according to the present disclosure includes the same steps as those of known methods for producing electricity storage devices, except that the positive electrode for an electricity storage device according to the present disclosure is used as the positive electrode for an electricity storage device. The method for producing an electricity storage device according to the present disclosure includes, for example, a step of overlapping two electrodes (a positive electrode and a negative electrode) with a separator interposed therebetween, and winding or stacking the electrodes into a battery shape, and a step of placing the resulting wound body or stacked body in a battery container or laminate container, injecting an electrolyte into the container, and sealing the container. EXAMPLES

[0072] Examples and comparative examples of the present disclosure will be shown below, but the present disclosure is not limited thereto.

[0073] 1.Measuring methods for each parameter [Measurement of weight average molecular weight] The weight average molecular weight of the copolymer before the amide modification was measured by a GPC method under the following detailed conditions. Measuring device: HLC-8320GPC (Tosoh Corporation) Column: α-M + α-M (Tosoh Corporation) Column temperature: 40℃ Detector: Differential refractive index Eluent: 60mmol / L H3PO4 and 50mmol / L LiBr in N,N-dimethylformamide (DMF) Flow rate: 1mL / min Standard sample used for calibration curve: Polystyrene Sample solution: DMF solution containing 0.5 wt% of copolymer solids Sample solution injection volume: 100μL

[0074] [Yield value measurement of positive electrode paste] The yield value (25° C.) of the positive electrode paste was measured as follows. The Anton Paar MCR302 rheometer was equipped with a cone plate CP50 and the shear rate was set to 0.1 s -1 From 1000s -1 After raising it to 1000s (outward trip), -1 From 0.1s -1 (return trip), and the shear rate on the return trip is 1000s -1 From 500s -1 The shear stress at the specimen was measured, and the intercept of the linear approximation was taken as the yield value. The results are shown in Table 2.

[0075] [Measurement of the resistance value of the positive electrode coating film] The positive electrode paste was dropped onto a polyester film and uniformly coated with a 100 μm applicator. The coated polyester film was dried at 80° C. for 1 hour to obtain a positive electrode coating film with a thickness of 40 μm. The coating resistance was measured using a Loresta-GP (manufactured by Mitsubishi Chemical Analytech) equipped with a PSP probe at a limit voltage of 10 V. The results are shown in Table 3.

[0076] [Example 1] (Synthesis of Viscosity Reducer) In a glass reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a nitrogen inlet tube, and a dropping funnel, 621.8 g of diisobutylene (manufactured by Maruzen Petrochemical Co., Ltd.) and 3.1 g of Lutonal A-50 (manufactured by BASF, polyvinyl ethyl ether) were charged. The reaction vessel was filled with nitrogen and stirring was started. The contents of the reaction vessel were heated to 105°C, and the temperature of the contents of the reaction vessel was kept at 105°C until the polymerization reaction was completed. 190.0 g of liquid maleic anhydride (manufactured by Mitsui Chemicals Polyurethane Co., Ltd.) kept at 70°C, and an initiator solution obtained by dissolving 9.2 g of Perbutyl O (polymerization initiator, manufactured by NOF Corporation, t-butylperoxy-2-ethylhexanoate, "Perbutyl" is a registered trademark) in 23.1 g of diisobutylene were each dropped into the reaction vessel from separate dropping funnels over a period of 4 hours. 20 minutes after the end of the dropwise addition, an additional initiator solution obtained by dissolving 1.2 g of Perbutyl O in 7.3 g of diisobutylene was added to the reaction vessel, and the polymerization reaction was completed by aging for another 2 hours and 40 minutes to obtain a solution containing a copolymer. 800 g of ion-exchanged water was added to the reaction vessel to precipitate a copolymer precipitate. Next, unreacted diisobutylene was distilled off by steam distillation. The steam distillation was performed by heating the reaction vessel at normal pressure until the temperature of the reaction vessel contents reached 100°C and distillation of diisobutylene ceased. Next, water was removed by decantation, and the precipitate of the copolymer wetted with water was dried at 105°C and under reduced pressure of 100 mmHg for 24 hours to obtain a diisobutylene / maleic anhydride copolymer having a weight average molecular weight of 28,000.

[0077] In a 1 L four-neck glass separable flask, 138.2 g of the obtained diisobutylene / maleic anhydride copolymer and 248.6 g of N-methyl-2-pyrrolidone (NMP) (manufactured by Mitsubishi Chemical) were placed, and the mixture was stirred and dissolved under a nitrogen atmosphere. Then, 61.8 g of 2-aminopyridine (manufactured by Wako Pure Chemical Industries, Ltd.) was dropped into the flask at room temperature, and the reaction solution in the flask was heated to 72°C and held for 2 hours to be amidated, thereby obtaining a viscosity reducer A solution with a non-volatile content of 42% by mass as a viscosity reducer composition B1.

[0078] (Preparation of conductive slurry) A crude dispersion was obtained by mixing 4.2 parts by mass of multi-walled carbon nanotubes (FT6810 manufactured by Cnano, diameter 7 to 12 nm, length 50 to 250 μm (catalog value)), 1.6 parts by mass of polyvinylpyrrolidone (K-30 manufactured by Wako Pure Chemical Industries, Ltd.), and 98.2 parts by mass of NMP. The crude dispersion was treated for 12 hours using a paint shaker (manufactured by Asada Iron Works Co., Ltd.) to obtain a conductive material slurry.

[0079] (Preparation of Positive Electrode Paste) 0.93 g of the conductive material slurry prepared above, 0.51 g of NMP, 2.44 g of PVDF (8%) NMP solution (KF Polymer L#7208, manufactured by Kureha Corporation), and 0.8 g of the viscosity reducer composition B1 prepared above diluted to 1% solid content were weighed into a 50 ml sample bottle and uniformly stirred with a spatula. Then, LiNi 0.5 Co 0.2 Mn 0.3 15.4 g of O2 (NCM523-ME5E12D, manufactured by Beijing Dangsheng) was added, and the mixture was again mixed with a spatula until it became homogenous. The mixture was further mixed for 2 minutes with a planetary centrifugal mixer (AR-100, manufactured by Thinky Corporation) to obtain a positive electrode paste.

[0080] The mass ratio of the positive electrode active material, binder (PVDF), conductive material (carbon nanotubes), and viscosity reducer was 98.45:1.25:0.25:0.05 (solid content equivalent), and the solid content (mass%) of the positive electrode paste was 78 mass%. The total solid content of the positive electrode paste is the total mass of the positive electrode active material, binder, conductive material, and viscosity reducer contained in the positive electrode paste.

[0081] [Examples 2 to 11, Comparative Example 1] The type or amount of the amine compound used in the synthesis of the viscosity reducer, and the amount of the diisobutylene / maleic anhydride copolymer added were changed to prepare viscosity reducer solutions containing viscosity reducers B to L listed in Table 1 below as viscosity reducer compositions B2 to B8 and B10 to B12. The content of viscosity reducers B to H and J to L in the viscosity reducer compositions B2 to B8 and B10 to B12 was 42.0 mass%, with the remainder being NMP. The amine compounds used were as follows. For Example 9, the diisobutylene / maleic anhydride copolymer was amidated using 2-aminopyridine and stearylamine, and then 2-amino-2-methyl-1-propanol (AMP) was added in an amount sufficient to neutralize all carboxy groups in the viscosity reducer solution to obtain a viscosity reducer composition B9 containing 42 mass% of the neutralized viscosity reducer I. Example 2 2-Aminopyridine Examples 3 to 5, 9 2-Aminopyridine, stearylamine Example 6 2-Aminopyridine, Tetradecylamine Examples 7 and 10 Benzylamine, stearylamine Example 8 N-phenyl-1-naphthylamine Comparative Example 1 Tetradecylamine

[0082] Next, a conductive slurry was prepared in the same manner as in [Example 1], and then positive electrode pastes D2 to D12 were each prepared.

[0083] [Table 1]

[0084] [Table 2]

[0085] As shown in Table 2, the yield values ​​of the positive electrode pastes D1 to D11 containing the viscosity reducers of Examples 1 to 11 are lower than the yield value of the positive electrode paste D12 containing the viscosity reducer of Comparative Example 1. 1In the case where R is a pyridine ring, the value was 15% or more lower than that in Comparative Example 1 (see Examples 1 to 6, 9, and 11). 4 However, when the aliphatic alkyl group had a carbon number of 18 or more and 22 or less, a significant decrease in the yield value was observed (see Examples 3 to 5, 9, and 11). In particular, when the molar fraction ratio of the structural unit (A) to the structural unit (B) was 0.50 or less, a significant decrease in the yield value was observed (see Examples 4 and 9).

[0086] Positive electrode coating films were produced using the positive electrode pastes D1 to D11 containing the viscosity reducers of Examples 1 to 11 according to the method described in [Measurement of resistance value of positive electrode coating film] above. The coatability of the positive electrode pastes D1 to D11 was all good. As shown in Table 3 below, the resistance of the positive electrode coating film produced using the positive electrode pastes D1 to D11 was lower than the resistance of the positive electrode coating film produced using the positive electrode paste D12 containing the viscosity reducer of Comparative Example 1.

[0087] [Table 3] [Industrial Applicability]

[0088] The viscosity reducer of the present disclosure enables a reduction in the yield value of the positive electrode paste, so that the positive electrode paste can be prepared with good productivity. In addition, the use of the viscosity reducer of the present disclosure enables the formation of a positive electrode coating film with a low resistance value, so that a positive electrode for a power storage device and a power storage device with low resistance can be produced with good productivity.

Claims

1. A viscosity reducer for energy storage device electrodes, comprising a polymer containing a constituent unit (A) represented by the following general formula (1), wherein the mole fraction a of the constituent unit (A) relative to the total constituent units of the polymer is 0.10 or more and 0.60 or less. 【Chemistry 1】 However, in the above general formula (1), X is (CH 2 ) n n is 0 or 1, R 1 is an aromatic ring or a heteroaromatic ring, R 2 is hydrogen, an aromatic ring, a heteroaromatic ring, or an aliphatic hydrocarbon. M 1 is hydrogen, NH 4 These are alkali metal atoms or organic ammonium compounds.

2. The polymer includes a constituent unit (B) represented by the following general formula (2): The viscosity reducing agent for an energy storage device electrode according to claim 1, wherein the mole fraction a of the constituent unit (A) and the mole fraction b of the constituent unit (B) satisfy the following relationship. Relationship: b / a ≤ 2.5 【Chemistry 2】 In the above general formula (2), R 3 is hydrogen, R 4 This is an aliphatic hydrocarbon group having 14 to 22 carbon atoms. M 2 is hydrogen, NH 4 , an alkali metal atom, or an organic ammonium.

3. The polymer includes a constituent unit (C) represented by the following general formula (3): The viscosity reducing agent for energy storage device electrodes according to claim 1, wherein the mole fraction c of the constituent unit (C) is 0.40 or more and 0.65 or less. 【Transformation 3】 In the above general formula (3), R 5 is a hydrogen or methyl group, R 6 This is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group having 1 to 10 substituents or being unsubstituted.

4. The polymer includes a constituent unit (D) represented by the following general formula (4): The viscosity reducing agent for energy storage device electrodes according to claim 1, wherein the mole fraction d of the constituent unit (D) is 0 or more and 0.20 or less. 【Chemistry 4】

5. A viscosity reducing agent composition for energy storage device electrodes, comprising a viscosity reducing agent for energy storage device electrodes according to any one of claims 1 to 4 and an organic solvent.

6. A positive electrode paste for an energy storage device, comprising a viscosity reducer for energy storage device electrodes according to any one of claims 1 to 4, a carbon material-based conductive material, a positive electrode active material, and an organic solvent.

7. The positive electrode paste for an energy storage device according to claim 6, wherein the carbon material-based conductive material is at least one selected from carbon black and carbon nanotubes.

8. A method for manufacturing a positive electrode for an energy storage device, comprising applying the positive electrode paste for an energy storage device described in claim 6 to a current collector and drying it.

9. A method for manufacturing an energy storage device, comprising incorporating a positive electrode for an energy storage device obtained by the method of claim 8.

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