JP2024067508A - Dispersant composition for power storage device electrodes - Google Patents

Abstract

To provide a dispersant composition for power storage device positive electrodes of which the dissolubility of a dispersant with respect to an electrolyte is low and which is capable of preparing a conductive material slurry of low viscosity and satisfactory handleability and forming a coating of high adhesiveness to a collector.SOLUTION: A dispersant composition for power storage device positive electrodes contains a copolymer (A), an inorganic or organic alkali component (B) and an organic solvent (C). The copolymer (A) contains a meta acrylonitrile-derived unit I in 30 mass% or more and 99 mass% or less and a meta acrylamide-derived unit II in 1 mass% or more and 0 mass% or less with respect to total 100 mass% of all the units, and a mass ratio (B)/(A) of the copolymer (A) and the alkali component (B) is 0.2 or more and 2.0 or less.SELECTED DRAWING: None

Description

The present invention relates to a dispersant composition for use in electrodes of electrical storage devices.

In recent years, electric vehicles that do not emit carbon dioxide have been actively developed in order to curb global warming. Electric vehicles have the problem that they have a shorter driving distance and take longer to charge their batteries than gasoline-powered vehicles. To shorten the charging time, it is necessary to increase the speed at which electrons move in the positive electrode. Currently, carbon materials are used as conductive additives (conductive materials) in the positive electrodes of non-aqueous electrolyte batteries, but in the conductive material slurry in which the conductive material is dispersed in an organic solvent, it is important for the conductive material to have good dispersibility in order to form a good conductive path in the positive electrode.

Patent Document 1 discloses a dispersant (C) used in the preparation of a conductive material dispersion for non-aqueous electrolyte secondary batteries for the purpose of obtaining an electrode film with high adhesion and conductivity. Dispersant (C) is a copolymer containing units derived from (meth)acrylonitrile and one or more monomer units selected from the group consisting of active hydrogen group-containing monomers, basic monomers, and (meth)acrylic acid alkyl esters, and the copolymer contains 40 to 99 mass% of the units derived from (meth)acrylonitrile and has a weight average molecular weight of 5,000 to 50,000.

Patent Document 2 discloses a dispersant used in the preparation of a dispersion with excellent dispersibility and storage stability. The dispersant is a copolymer containing units derived from (meth)acrylonitrile and one or more monomer units selected from the group consisting of active hydrogen group-containing monomers, basic monomers, and (meth)acrylic acid alkyl esters, and the copolymer contains 40 to 99% by mass of units derived from (meth)acrylonitrile and has a weight average molecular weight of more than 50,000 and not more than 200,000.

Patent Document 3 discloses a binder used in the preparation of an electrochemical element electrode binder composition that is excellent in peel strength and powder shedding resistance and can form an electrode mixture layer that can provide high rate characteristics to an electrochemical element. Patent Document 3 discloses a polyacrylonitrile copolymer (PAN1) containing 93% by mass of acrylonitrile units and 1% by mass of acrylamide, and a polyacrylonitrile copolymer (PAN2) containing 65% by mass of acrylonitrile units and 1% by mass of acrylamide, as one component of the binder.

JP 2020-187991 A JP 2021-115523 A WO2020/004332

However, the use of the dispersants disclosed in Patent Documents 1 and 2 has a problem that the viscosity is high during the dispersion process of the carbon material-based conductive material in the dispersion solvent, and in particular, the viscosity of the slurry increases significantly as the temperature of the slurry increases. If the viscosity of the slurry is high, the dispersion efficiency decreases, the defibration of the carbon material-based conductive material such as CNT does not progress, and the resistance value of the electrode formed using the slurry increases. Therefore, when preparing the slurry, it is necessary to reduce the viscosity by a method such as adding additional solvent to improve the dispersion efficiency.
In order to reduce the resistance of the electrode, it is also desirable that the positive electrode coating film (also called the positive electrode composite layer) has better adhesion to the current collector and that the dispersant has low solubility in the electrolyte. If the dispersant has high solubility in the electrolyte, the dispersant dissolved in the electrolyte clogs the separator, which causes an increase in resistance and a decrease in the discharge capacity retention rate.

Therefore, in one aspect, the present disclosure provides a dispersant composition for a positive electrode of an electricity storage device, which enables the preparation of a conductive material slurry having low solubility of the dispersant in an electrolyte solution, low viscosity and good handleability, and enables the formation of a coating film having high adhesion to a current collector.
In one aspect, the present disclosure provides a carbon material-based conductive material slurry or a positive electrode paste for an electricity storage device, comprising the dispersant composition for a positive electrode of an electricity storage device.
The present disclosure also provides a positive electrode coating for an electricity storage device formed using the positive electrode paste for an electricity storage device.

The present disclosure provides, in one aspect, a method for producing a method for manufacturing a semiconductor device comprising:
A copolymer (A), an inorganic or organic alkali component (B), and an organic solvent (C),
The copolymer (A) contains, relative to 100 mass% of the total of all units, 30 mass% or more and 99 mass% or less of units I derived from (meth)acrylonitrile and 1 mass% or more and 70 mass% or less of units II derived from (meth)acrylamide,
The present invention relates to a dispersant composition for an electric storage device electrode, in which a mass ratio (B)/(A) of the copolymer (A) to the inorganic or organic alkali component (B) is 0.2 or more and 2.0 or less.

In one aspect, the present disclosure relates to a carbonaceous conductive material slurry containing the dispersant composition for an electrode of an electric storage device of the present disclosure and a carbonaceous conductive material (D).

In one aspect, the present disclosure relates to a positive electrode paste for an electricity storage device, comprising the dispersant composition for an electricity storage device electrode of the present disclosure, a positive electrode active material, a carbon material-based conductive material, and a binder.

In one aspect, the present disclosure relates to a method for producing a positive electrode coating for an electricity storage device, which includes applying the positive electrode paste for an electricity storage device of the present disclosure to a current collector and then drying the applied coating.

In one aspect, the present disclosure provides a method for producing a dispersant composition for an electric storage device electrode, comprising:
The method includes a step of heat-treating a mixed solution containing a copolymer (A), an inorganic or organic alkali component (B), and an organic solvent (C),
The copolymer (A) contains, relative to 100 mass% of the total of all units, 30 mass% or more and 99 mass% or less of units I derived from (meth)acrylonitrile and 1 mass% or more and 70 mass% or less of units II derived from (meth)acrylamide,
the mass ratio (B)/(A) of the copolymer (A) to the inorganic or organic alkali component (B) in the mixed solution is 0.2 or more and 2.0 or less.

According to one aspect of the present disclosure, it is possible to provide a dispersant composition for a positive electrode of an electricity storage device, which makes it possible to prepare a conductive material slurry having low solubility of the dispersant in an electrolyte solution, low viscosity, and good handleability, and which makes it possible to form a coating film having high adhesion to a current collector.
Moreover, according to one embodiment of the present disclosure, a carbon material-based conductive material slurry having low viscosity and good handleability can be provided.
Moreover, according to one aspect of the present disclosure, it is possible to provide a positive electrode paste for an electricity storage device that enables the formation of a positive electrode coating film that has high adhesion to a current collector and low resistance.
Moreover, according to one embodiment of the present disclosure, it is possible to provide a positive electrode coating film for an electricity storage device that has high adhesion to a current collector and a low coating resistance value.

[Dispersant composition for power storage device electrodes]
The present disclosure is based on the finding that it is possible to provide a dispersant composition for a positive electrode of an electricity storage device (hereinafter also referred to as the "dispersant composition of the present disclosure") that contains a specific copolymer (A) as a dispersant, and that coexists with a specific alkaline component (B) in a specific mass ratio, thereby making it possible to prepare a conductive material slurry that has low solubility in an electrolyte solution, is low in viscosity, and has good handleability, and that makes it possible to form a coating film that has high adhesion to a current collector.

In one embodiment, the present disclosure relates to a dispersant composition for an electrode of a power storage device, comprising a copolymer (A), an inorganic or organic alkali component (B) (hereinafter sometimes abbreviated as "alkali component (B) of the present disclosure"), and an organic solvent (C). The copolymer (A) is a copolymer (hereinafter sometimes abbreviated as "copolymer (A) of the present disclosure") that contains 30% by mass or more and 99% by mass or less of units I derived from (meth)acrylonitrile and 1% by mass or more and 70% by mass or less of units II derived from (meth)acrylamide, relative to 100% by mass of the total of all units, and a part of the nitrile groups of the units I is modified to a cyclic structure, and the mass ratio (B)/(A) of the copolymer (A) of the present disclosure to the alkali component (B) of the present disclosure is 0.2 or more and 2.0 or less.

By using the dispersant composition of the present disclosure, it is possible to prepare a carbon material-based conductive material slurry of the present disclosure (hereinafter, also referred to as the "conductive material slurry of the present disclosure") that has low viscosity and good handling properties. In addition, by using the dispersant composition of the present disclosure, it is possible to prepare a positive electrode paste for an electricity storage device of the present disclosure (hereinafter, also referred to as the "positive electrode paste of the present disclosure") that enables the formation of a coating film with high adhesion to a current collector. In addition, by using the positive electrode paste of the present disclosure that contains the dispersant composition of the present disclosure, it is possible to manufacture a positive electrode coating film with a low coating film resistance value and an electricity storage device with a high discharge capacity retention rate.

Although the details of the mechanism by which the effects of the present disclosure are manifested are not clear, it is presumed as follows.
Among all the units of the copolymer (A) of the present disclosure, the unit I derived from (meth)acrylonitrile is adsorbed to the conductive material due to the interaction between the π electrons of the nitrile (CN) group and the π electrons of the carbon material-based conductive material (hereinafter sometimes abbreviated as "conductive material"). Therefore, it is considered to be a component that contributes to the dispersion of the conductive material. Furthermore, the unit I derived from (meth)acrylonitrile also has a high adsorption force to the current collector. On the other hand, the unit II derived from (meth)acrylamide is a component that is insoluble in the electrolyte, so it suppresses the dissolution of the copolymer (A) in the electrolyte and contributes to suppressing the decrease in the capacity retention rate.
It has been confirmed that when such copolymer (A) and the alkali component (B) coexist, some of the nitrile groups of the unit I derived from the (meth)acrylonitrile are modified into a cyclic structure by reaction with the alkali component (B), and the insolubility of the unit I in the organic solvent in the dispersant composition is increased. In addition, since the cyclic structure has multiple π electrons, the adsorption ability of the copolymer (A) to the conductive material is enhanced by π-π interaction between the cyclic structure and the conductive material. In addition, the modification of the nitrile groups into the cyclic structure also improves the adsorption of the copolymer (A) to the current collector, which is presumed to contribute to improving the peel strength of the positive electrode coating film against the current collector, thereby reducing the resistance of the positive electrode coating film and suppressing the decrease in the discharge capacity retention rate.
However, if the alkali component (B) is contained in an excessive amount in the dispersant composition, the copolymer (A) becomes too insoluble and aggregates, resulting in a loss of stability of the composition.
In the present disclosure, it is presumed that by setting the mixing ratio (B)/(A) of the specific copolymer (A) and the specific alkaline component (B) to a mass ratio of 0.2 to 2.0, the unit I is appropriately insolubilized in the electrolyte solution and the adsorptivity to the conductive material and the current collector is appropriately improved by modifying the nitrile group into a cyclic structure, and as a result, it is possible to achieve both low solubility of the copolymer (A) in the electrolyte solution, suppression of an increase in viscosity during preparation of a conductive slurry, and high adhesion of the positive electrode coating film to the current collector.
Although the detailed mechanism is unclear, referring to the description in Polymer Chemistry 19, 653 (1962) and the like, the presence of the cyclic structure can be confirmed by the coloring of the dispersant composition due to the addition of the alkali component (B), and specifically, the presence can be confirmed by NMR or infrared spectroscopic analysis.

[Copolymer (A)]
(Unit I)
The unit I derived from (meth)acrylonitrile among all the units of the copolymer (A) of the present disclosure acts as a component adsorbed to the surface of the conductive material. The unit I is 30% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on the total of all the units of the copolymer (A) in terms of suppressing the increase in viscosity during preparation of the conductive slurry, and is 99% by mass or less, preferably 90% by mass or less, based on the viewpoint of suppressing the dissolution of the copolymer (A) in the electrolytic solution. The unit I derived from (meth)acrylonitrile includes not only the unit represented by the following formula (3), but also those modified into a cyclic structure.

(Unit II)
The unit II derived from (meth)acrylamide among all the units of the copolymer (A) of the present disclosure is represented by the following formula (2). The unit II has an amide group in the side chain, and therefore has low solubility in the electrolyte. Therefore, a positive electrode coating film with little dissolution of the dispersant (copolymer (A)) into the electrolyte can be formed, and as a result, an electricity storage device with a high discharge capacity retention rate due to repeated charging and discharging can be obtained.

The unit II is 1% by mass or more, preferably 5% by mass or more, and more preferably 12% by mass or more, based on 100% by mass of the total of all units of the copolymer (A), from the viewpoint of suppressing dissolution of the copolymer (A) in the electrolyte and ensuring solubility in the solvent used in the polymerization of the copolymer (A) (hereinafter abbreviated as "polymerization solvent"). From the same viewpoint, the unit II is 50% by mass or less, preferably 25% by mass or less, and more preferably 18% by mass or less.

The content of unit I in all units of copolymer (A) can be regarded as the ratio of the amount of monomer I used to the total amount of monomers used in polymerization. Monomer I is a monomer that provides unit I when synthesizing copolymer (A). The content of unit II in all units of copolymer (A) can be regarded as the ratio of the amount of monomer II used to the total amount of monomers used in polymerization. Monomer II is a monomer that provides unit II when synthesizing copolymer (A).

The copolymer (A) may further contain a unit III derived from a monomer other than the monomers I and II (hereinafter referred to as "monomer III"). Examples of the monomer III include (meth)acrylic acid alkyl esters such as 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, and behenyl (meth)acrylate ; Examples of the monomers include hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycerol mono(meth)acrylate, 4-hydroxyvinylbenzene, 2-hydroxy-3-phenoxypropyl acrylate, and caprolactone adducts of these monomers (the number of moles added is 1 to 5); and carboxyl group-containing monomers such as (meth)acrylic acid, (meth)acrylic acid dimer, itaconic acid, maleic acid, fumaric acid, crotonic acid, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxypropyl phthalate, 2-(meth)acryloyloxyethyl hexahydrophthalate, 2-(meth)acryloyloxypropyl hexahydrophthalate, ethylene oxide-modified succinic acid (meth)acrylate, β-carboxyethyl (meth)acrylate, and monofunctional alcohol adducts of acid anhydride group-containing monomers such as maleic anhydride, itaconic anhydride, and citraconic acid. Among these, from the viewpoint of improving the dispersibility of the conductive material and easiness of introducing unit I into the dispersant (copolymer (A)), at least one selected from methacrylic acid (MAA), lauryl (meth)acrylate, stearyl (meth)acrylate, and behenyl (meth)acrylate is preferred, at least one selected from methacrylic acid (MAA), stearyl (meth)acrylate, and behenyl (meth)acrylate is more preferred, at least one selected from methacrylic acid (MAA), stearyl methacrylate (SMA), and behenyl methacrylate (BeMA) is even more preferred, and stearyl methacrylate is even more preferred.

The arrangement of each unit in the copolymer (A) of the present disclosure may be block or random, but random is preferred from the viewpoint of preventing excessive modification to cyclic structures and controlling the reaction.

The weight average molecular weight of copolymer (A) (dispersant) is preferably 5,000 or more, more preferably 7,000 or more, and even more preferably 10,000 or more, from the viewpoint of improving the dispersibility of the conductive material and the solubility of the dispersant in the polymerization solvent, and from the same viewpoint, is preferably 500,000 or less, more preferably 200,000 or less, and even more preferably 100,000 or less. In this disclosure, the weight average molecular weight is a value measured by GPC (gel permeation chromatography), and the details of the measurement conditions are as shown in the examples.

The content of copolymer (A) in the dispersant composition of the present disclosure is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1.2% by mass or more, from the viewpoint of effectively dispersing the carbon material-based conductive material, and is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, from the viewpoint of ensuring the degree of freedom of blending in the subsequent steps.

(Method of synthesizing copolymer (A))
The synthesis method of copolymer (A) is not particularly limited, and the method used for polymerization of ordinary (meth)acrylic acid esters and vinyl monomers is used.The synthesis method of copolymer (A) can be, for example, free radical polymerization method, living radical polymerization method, anionic polymerization method, living anionic polymerization method, etc. For example, when using free radical polymerization method, it can be obtained by a known method such as polymerizing monomer components including monomer I, monomer II, and if necessary, monomer III by solution polymerization method.

As the polymerization solvent, for example, organic solvents such as hydrocarbons (hexane, heptane), aromatic hydrocarbons (toluene, xylene, etc.), lower alcohols (ethanol, isopropanol, etc.), ketones (acetone, methyl ethyl ketone), ethers (tetrahydrofuran, diethylene glycol dimethyl ether), and N-methyl-2-pyrrolidone can be used, but N-methyl-2-pyrrolidone is preferred, as it can dissolve the binder when preparing the positive electrode paste.

The amount of the solvent is preferably 0.5 to 10 times the total amount of the monomers in terms of mass ratio. 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, or ketone peroxides. The amount of the polymerization initiator is preferably 0.01 mol% or more, more preferably 0.05 mol% or more, even more preferably 0.1 mol% or more, and preferably 5 mol% or less, more preferably 4 mol% or less, and even more preferably 3 mol% or less, based on the total amount of the monomer components. The polymerization reaction is preferably carried out in a temperature range of 40°C to 180°C under a nitrogen stream, and the reaction time is preferably 0.5 hours 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.

[Inorganic or organic alkaline component (B)]
Among the alkali components (B) contained in the dispersant composition of the present disclosure, examples of inorganic alkali components include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of organic alkali components include organic amines. The organic amine is preferably one or more organic amines selected from amine compound (i) and amine compound (ii) represented by the following formula (1), and the amine compound (ii) is preferably at least one amine compound having a boiling point of 200°C or less selected from aliphatic amines, aromatic amines, and heterocyclic amines. It is considered that these amine compounds are likely to have an interaction (cation-π interaction) between cations derived from the amine compound and π electrons derived from the conductive material. In addition, the amine compound is preferable because it blocks the π-π interaction between conductive materials on the surface of the conductive material by the "cation-π" interaction, thereby reducing the viscosity of the conductive material slurry.

(Amine compound (i))
In the above formula (1), ^R1 represents a group represented by the following formula (2), and ^R2 represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or _{--CH2CH2 --} OH. In the following formula (2), ^R3 , ^R4 , ^R5 , and ^R6 may be the same or different and represent a hydrogen atom, a methyl group, or _--CH2OH .

The amine compound (primary or secondary amine) (i) represented by the above formula (1) is superior to a tertiary amine in which H in formula (1) is replaced by a carbon atom, because the steric hindrance is small and the cation-π interaction is easily formed. In formula (1) showing a primary or secondary amine, from the viewpoint of reducing viscosity, R ² is preferably a hydrogen atom (primary amine), an alkyl group having 1 to 4 carbon atoms (secondary amine) or -CH ₂ CH ₂ -OH (secondary amine), and more preferably a hydrogen atom, an alkyl group having 1 carbon atom (methyl group) or an alkyl group having 2 carbon atoms (ethyl group). Since the steric hindrance due to a hydrogen atom, a methyl group or an ethyl group is small, the cation-π interaction is easily formed.

In the above formula (2), R ³ , R ⁴ , R ⁵ and R ⁶ are the same or different and are preferably a hydrogen atom or a methyl group from the viewpoint of reducing viscosity. A hydrogen atom or a methyl group is considered to have small steric hindrance and to facilitate the cation-π interaction.

In one or more embodiments, the organic alkali component (B) (amine compound (i)) is preferably one or more compounds selected from ethanolamine, N-methylethanolamine, N-ethylethanolamine, 2-amino-1-propanol, 2-amino-2-methyl-1-propanol, 1-amino-2-propanol, 2-amino-1,3, propanediol, and diethanolamine. Among these, from the viewpoint of improving the dispersibility of the conductive material and achieving a low viscosity of the positive electrode paste at the same time, more preferably at least one selected from ethanolamine, N-methylethanolamine, N-ethylethanolamine, 2-amino-2-methyl-1-propanol (AMP), 1-amino-2-propanol, and diethanolamine, and even more preferably at least one selected from N-methylethanolamine, N-ethylethanolamine, and 2-amino-2-methyl-1-propanol (AMP).

(Amine compound (ii))
The amine compound (ii) is at least one selected from aliphatic amines, aromatic amines, and heterocyclic amines from the viewpoint of interaction and adsorption with the conductive material, and is preferably at least one selected from secondary aliphatic amines, tertiary aliphatic amines, secondary aromatic amines, tertiary aromatic amines, and heterocyclic amines. The boiling point of the amine compound (ii) is 200°C or less, but is preferably the boiling point of the solvent of the positive electrode paste or less, more preferably the boiling point of N-methylpyrrolidone (NMP) (boiling point 202°C) or less, which is often used as a solvent for the positive electrode paste, and from the viewpoint of reusing NMP, it is even more preferably 190°C or less. The lower limit of the boiling point of the amine compound (ii) is preferably 100°C or more from the viewpoint of handleability, and more preferably 120°C or more.

Amine compounds block π-π interactions between conductive materials through "cation-π" interactions on the surface of the conductive material, reducing the viscosity of the slurry. However, if an electrically insulating amine compound remains in the positive electrode coating, it can cause a decrease in the resistance value of the positive electrode coating and a decrease in the discharge capacity retention rate of a storage device such as a lithium-ion battery. Therefore, in the present disclosure, as the alkaline component (B), a tertiary aliphatic amine, a primary aromatic amine, a secondary aromatic amine, a tertiary aromatic amine, or a heterocyclic amine that has a lower boiling point than the solvent NMP (boiling point 202°C) mainly used in positive electrode pastes and does not undergo amidate, or a secondary aliphatic amine, a primary aromatic amine, a secondary aromatic amine, a tertiary aromatic amine, or a heterocyclic amine that is difficult to undergo amidate due to large steric hindrance, is used. As a result, the amine compound is well volatilized together with the solvent when the coating is dried, and it is presumed that the increase in the resistance value caused by the addition of the amide compound is suppressed, and the decrease in the discharge capacity retention rate is suppressed.

Examples of the amine compound (ii) include secondary aliphatic amines such as dibutylamine (boiling point: 159°C), dihexylamine (193°C), N-methylcyclohexylamine (148°C), and N-ethylcyclohexylamine (164°C); tertiary aliphatic amines such as tripropylamine (156°C), dimethyloctylamine (195°C), and dimethylcyclohexylamine (160°C); primary aromatic amines such as benzylamine (185°C); N-methylcyclohexylamine (160°C), and Examples of the amine compound include one or more amine compounds selected from secondary aromatic amines such as N-ethylbenzylamine (same temperature 186°C), N-monomethylaniline (same temperature 196°C), etc.; tertiary aromatic amines such as N,N-dimethylbenzylamine (same temperature 183°C), N,N-dimethylaniline (same temperature 194°C), N,N-dimethyl-o-toluidine (same temperature 186°C), etc.; and heterocyclic amines such as N-methylmorpholine (same temperature 116°C), N-ethylmorpholine (same temperature 135°C), 4-isobutylmorpholine (same temperature 167°C), etc. Among these, from the viewpoint of improving the dispersibility of the conductive material, lowering the viscosity of the conductive slurry or positive electrode paste, lowering the resistance value of the positive electrode coating film, and suppressing the decrease in the discharge capacity retention rate of the power storage device, at least one selected from dibutylamine, dihexylamine, tripropylamine, N-methylcyclohexylamine, benzylamine, N-methylbenzylamine, N,N-dimethylbenzylamine, N-methylmorpholine, and N-ethylmorpholine is preferred, at least one selected from tripropylamine, dihexylamine, N,N-dimethylbenzylamine, N-methylbenzylamine, benzylamine, and N-ethylmorpholine is more preferred, at least one selected from tripropylamine, dihexylamine, benzylamine, and N-ethylmorpholine is even more preferred, and at least one selected from dihexylamine, benzylamine, and N-ethylmorpholine is even more preferred.

The mass ratio (B)/(A) of the copolymer (A) to the alkaline component (B) is 0.2 or more, preferably 0.3 or more, more preferably 0.6 or more, from the viewpoint of improving the dispersibility of the conductive material, reducing the viscosity of the conductive slurry or positive electrode paste, and simultaneously reducing the resistance value of the positive electrode coating film and suppressing the decrease in the discharge capacity retention rate of the electricity storage device, and from the similar viewpoint, is 2.0 or less, from the viewpoint of ensuring the stability of the dispersant composition.

In one or more embodiments, the content of the alkali component (B) of the present disclosure in the dispersant composition of the present disclosure is preferably 20 parts by mass or more, more preferably 50 parts by mass or more, and even more preferably 70 parts by mass or more, per 100 parts by mass of copolymer (A) from the viewpoint of reducing the viscosity of the conductive material slurry and the positive electrode paste and from the viewpoint of effectively carrying out the cyclization modification of the nitrile groups, and is 200 parts by mass or less, per 100 parts by mass of copolymer (A), from the viewpoint of the solubility of copolymer (A) and the viewpoint of controlling the cyclization modification of the nitrile groups.

[Organic solvent (C)]
The organic solvent (C) contained in the dispersant composition of the present disclosure is preferably one capable of dissolving the binder (binder resin) contained in the positive electrode paste. Examples of the organic solvent (C) include amide polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, and octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol; glycerin, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol; Examples of the organic solvent include polyhydric alcohols such as dimethylolpropane, pentaerythritol, and sorbitol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, and cyclopentanone; and esters such as ethyl acetate. The organic solvent (C) may be one type or a combination of two or more types.

In one or more embodiments, the content of the organic solvent (C) in the dispersant composition of the present disclosure is preferably 30% by mass or more, more preferably 70% by mass or more, and even more preferably 85% by mass or more, from the viewpoint of the solubility of the copolymer (A) and the solubility of the alkali component (B), and is preferably 98% by mass or less, from the viewpoint of effectively dispersing the carbon material-based conductive material.

The dispersant composition of the present disclosure may further contain other components to the extent that the effects of the present disclosure are not hindered. Examples of other components include antioxidants, neutralizing agents, defoamers, preservatives, dehydrating agents, rust inhibitors, plasticizers, and binders (binder resins having a structure different from that of copolymer (A)).

[Method of producing dispersant composition for power storage device]
The method for producing a dispersant composition of the present disclosure includes a step of mixing the copolymer (A), an alkali component (B), an organic solvent (C), and an optional component added as necessary, and mixing the copolymer (A) and the alkali component (B) with the organic solvent (C). The copolymer (A) may be added to the organic solvent (C) in a dry state obtained by volatilizing the polymerization solvent used in the production of the copolymer (A), but if the polymerization solvent and the organic solvent (C) are the same, the copolymer (A) may be mixed with other components in the state of a polymer solution in which the copolymer is dissolved in the polymerization solvent.

The modification of the nitrile group to a cyclic structure can be carried out at room temperature (25°C), but heating is preferred from the viewpoint of promoting the modification. Therefore, the method for producing a dispersant composition of the present disclosure preferably includes a step of heat-treating a mixed solution containing the copolymer (A) of the present disclosure, the alkali component (B), and the organic solvent (C). The copolymer (A) is a copolymer containing 30% by mass or more and 99% by mass or less of unit I derived from (meth)acrylonitrile and 1% by mass or more and 70% by mass or less of structure II derived from (meth)acrylamide, relative to 100% by mass of the total of all units. In the mixed solution before the heat treatment, the mass ratio (B)/(A) of the copolymer (A) to the alkali component (B) is 0.05 or more and 2.0 or less. The heating temperature of the heat treatment is preferably 25°C or more, more preferably 50°C or more, from the viewpoint of promoting the modification, and is preferably 100°C or less, more preferably 80°C or less, from the viewpoint of suppressing the volatilization of the alkali component (B) and the organic solvent (C). The heating time for the heat treatment is preferably 0.5 hours or more, more preferably 1 hour or more, and preferably 24 hours or less, more preferably 12 hours or less.

[Conductive material slurry for power storage device]
In one aspect, the present disclosure relates to a conductive material slurry for an electrical storage device (hereinafter also referred to as the "conductive material slurry of the present disclosure") containing a carbon material-based conductive material (D) (hereinafter sometimes abbreviated as "conductive material") and a dispersant composition of the present disclosure. A preferred form of the dispersant composition of the present disclosure in this aspect is as described above. In one or more embodiments, the conductive material slurry of the present disclosure contains the copolymer (A) of the present disclosure, the alkali component (B) of the present disclosure, an organic solvent (C), and a conductive material (D) described below.

[Carbon-based conductive material (D)]
In one or more embodiments, the conductive material (D) of the present disclosure may be carbon nanotubes (hereinafter, sometimes referred to as "CNT"), carbon black, graphite, graphene, etc., and among these, from the viewpoint of realizing high conductivity, at least one selected from carbon black, carbon nanotubes, and graphene is preferable, and from the same viewpoint, carbon nanotubes or graphene are more preferable, and carbon nanotubes are more preferable. The conductive material (D) may be one type or a combination of two or more types.

(carbon nanotube)
The average diameter of the CNTs usable as the conductive material (D) is not particularly limited, and from the viewpoint of improving the dispersibility and electrical conductivity of the CNTs, it is preferably 1 nm or more, more preferably 2 nm or more, even more preferably 3 nm or more, even more preferably 5 nm or more, and from the same viewpoint, it is preferably 100 nm or less, more preferably 70 nm or less, even more preferably 50 nm or less, and even more preferably 10 nm or less. In the present disclosure, the average diameter of the CNTs can be measured by a scanning electron microscope (SEM) or an atomic force microscope (AFM).

In this disclosure, CNT refers to an entity including multiple carbon nanotubes. The form of the CNT used in the production of the conductive material slurry is not particularly limited, and may be, for example, a form in which multiple CNTs are independent of each other, a form in which multiple CNTs are bundled or entangled, or a mixture of these forms. In order to achieve both electrical conductivity and dispersibility, the CNT may be a mixture of two or more types of CNTs with different numbers of layers or diameters. The CNT may contain impurities (e.g., catalysts and amorphous carbon) derived from the process in which the CNTs are produced.

Examples of CNTs that can be used as the conductive material (D) include Nanocyl's NC-7000 (hereinafter, the numerical values are average diameter, 9.5 nm) and NX7100 (10 nm), Cnano's FT6100 (9 nm), FT-6110 (9 nm), FT-6120 (9 nm), FT-7000 (9 nm), FT-7010 (9 nm), FT-7320 (9 nm), FT-9000 (12.5 nm), FT-9100 (12.5 nm), FT-9110 (12.5 nm), FT-9200 (19 nm), FT-9220 (19 nm), and Cabot Performance Examples of such nanotubes include HCNTs4 (4.5 nm), CNTs5 (7.5 nm), HCNTs5 (7.5 nm), GCNTs5 (7.5 nm), HCNTs10 (15 nm), CNTs20 (25 nm), and CNTs40 (40 nm) from CNT Materials (Shenzhen), CTUBE170 (13.5 nm), CTUBE199 (8 nm), and CTUBE298 (10 nm) from Korea CNT Company, K-Nanos100P (11.5 nm) from Kumho, CP-1001M (12.5 nm), and BT-1003M (12.5 nm) from LG Chem, 3003 (10 nm), and 3021 (20 nm) from Nano Tech Port, JENOTUBE8S (6.8 nm) from JEIO, and TUBALL (1.6 nm) from OCSIAL.
Combinations when two types of CNTs are used include, for example, a combination of Cabot Performance Materials (Shenzhen) CNTs40 (40 nm) and HCNTs4 (4.5 nm) or HCNTs5 (7.5 nm), a combination of CNTs40 (40 nm) and GCNTs5 (7.5 nm), a combination of CNTs40 (40 nm) and Cnano's FT-7010 (9 nm), a combination of CNTs40 (40 nm) and FT-9100 (12.5 nm), and a combination of CNTs40 (40 nm) and LG Chem's BT-1003M (12.5 nm).

(Carbon black)
As the carbon black that can be used as the conductive material (D), various types such as furnace black, channel black, thermal black, acetylene black, and ketjen black can be used. In addition, carbon black that has been subjected to a commonly performed oxidation treatment, hollow carbon, and the like can also be used. The oxidation treatment of carbon black is a treatment in which oxygen-containing polar functional groups such as phenol groups, quinone groups, carboxyl groups, and carbonyl groups are directly introduced (covalently bonded) to the carbon surface by treating carbon black at high temperatures in air or by secondary treatment with nitric acid, nitrogen dioxide, ozone, and the like. These treatments are generally performed to improve the dispersibility of carbon black. However, since the conductivity of carbon black generally decreases as the amount of functional groups introduced increases, it is preferable to use carbon black that has not been subjected to an oxidation treatment.

The larger the specific surface area of the carbon black usable as the conductive material (D), the more the number of contact points between the carbon black particles increases, which is advantageous for lowering the internal resistance of the electrode. Specifically, the specific surface area (BET) calculated from the amount of nitrogen adsorption is preferably ²⁰ m2/g or more, more preferably ⁵⁰ m2/g or more, even more preferably ¹⁰⁰ m2/g or more, and is preferably 1500 ^m2 /g or less, more preferably 1000 ^m2 /g or less, even more preferably 800 ^m2 /g or less.

From the viewpoint of electrical conductivity, the primary particle size (diameter) of carbon black that can be used as the conductive material (D) is preferably 5 nm or more, more preferably 10 nm or more, and is preferably 1000 nm or less, more preferably 200 nm or less. In this disclosure, the primary particle size of carbon black is the average particle size measured with an electron microscope or the like.

(Graphene)
Graphene that can be used as the conductive material (D) generally refers to a two-dimensional sheet (single-layer graphene) in which ^sp2 hybridized carbon atoms form a hexagonal honeycomb lattice and have a thickness of one atom. In the present disclosure, however, the term graphene also refers to substances having a flake-like form in which single-layer graphene is stacked.

There is no particular restriction on the thickness of the graphene that can be used as the conductive material (D), but it is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 20 nm or less. There is no particular restriction on the size in the direction parallel to the graphene layer, but from the viewpoint of ensuring good conductivity in the positive electrode, it is preferably 0.5 μm or more, more preferably 0.7 μm or more, and even more preferably 1 μm or more. Here, the size in the direction parallel to the graphene layer refers to the average of the maximum diameter and the minimum diameter when observed from a direction perpendicular to the surface direction of the graphene.

<Containing amount of conductive material (D) in conductive material slurry>
The content of the conductive material (D) in the conductive material slurry of the present disclosure is, from the viewpoint of improving the convenience of adjusting the concentration of the positive electrode paste, preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, and still more preferably 3% by mass or more, and from the viewpoint of making the conductive material slurry have a viscosity that is easy to handle, preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 7% by mass or less.

<Content of copolymer (A) in conductive material slurry>
The content of the copolymer (A) in the conductive material slurry of the present disclosure is, from the viewpoint of improving the dispersibility of the conductive material (D), preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 5 parts by mass or more, relative to 100 parts by mass of the conductive material (D); and, from the viewpoint of high conductivity, it is preferably 1,000 parts by mass or less, more preferably 200 parts by mass or less, even more preferably 100 parts by mass or less, and even more preferably 50 parts by mass or less.

<Content of alkaline component (B) in conductive material slurry>
The content of the alkali component (B) in the conductive material slurry of the present disclosure is, from the viewpoint of improving the dispersibility of the carbon material-based conductive material, preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, even more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, relative to 100 parts by mass of the carbon material-based conductive material (D), and from the viewpoint of high conductivity, it is preferably 500 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 50 parts by mass or less, and even more preferably 30 parts by mass or less.

[Method of producing conductive slurry]
In one or more embodiments, the conductive material slurry of the present disclosure can be prepared by mixing the copolymer (A) of the present disclosure, the alkali component (B) of the present disclosure, the conductive material (D), an organic solvent, and any optional components added as necessary using a mixer/disperser to disperse each component. Examples of the organic solvent include the same organic solvent (C) that can be used in the preparation of the dispersant composition of the present disclosure described above.

The mixing and dispersing machine may be at least one selected from the group consisting of ultrasonic homogenizers, vibration mills, jet mills, ball mills, bead mills, sand mills, roll mills, homogenizers, high-pressure homogenizers, ultrasonic devices, attritors, dissolvers, and paint shakers. For reasons of dispersion uniformity, a media stirring type dispersing machine is preferred.

A media agitation type disperser applies a rotational motion to beads in a grinding chamber to reduce the size of the target material by collisions between the beads and shearing forces, which generates heat. The beads are mainly made of glass, alumina, and zirconia, but zirconia is preferred from the viewpoints of hardness of the beads and avoiding impurities from being mixed into the slurry. For large targets, large diameter beads are preferred, and the finer the target particle size, the smaller the diameter is preferred. For dispersing conductive materials, beads of 0.1 mm to 20 mm are preferred. The amount of beads put into the grinding chamber, i.e., the filling rate, is preferably 50% to 90% of the volume of the grinding chamber, and from the viewpoints of dispersion efficiency and heat generation, it is preferably 60% to 80%. The rotational motion, i.e., the peripheral speed, given to the beads is preferably 5 m/s or more, more preferably 7 m/s or more, from the viewpoint of dispersion efficiency, and preferably 16 m/s or less, more preferably 14 m/s or less, from the viewpoint of heat generation. The conductive material slurry is sent from the tank to the disperser via a pump, dispersed by the beads being agitated at high speed, and returned to the tank. By repeating this process, the slurry is circulated and dispersion processing can be performed. In one embodiment, the method for producing a conductive material slurry of the present disclosure includes a step of dispersing each component in a mixture containing a copolymer (A), an alkali component (B), a conductive material (D), an organic solvent, and optional components added as necessary, using a media-agitation type disperser to form a slurry, and in the step, the mixture in the middle of dispersion (crude dispersion) is sent from the media-agitation type disperser to a container (tank), and the crude dispersion is sent from the tank via a pump to the media-agitation type disperser for dispersion processing, and this process is repeated multiple times to obtain a conductive material slurry.

In the method for producing the conductive material slurry of the present disclosure, some of the components constituting the conductive material slurry may be mixed and then mixed with the remainder, or each component may be added in multiple batches rather than all at once. For example, the dispersant composition of the present disclosure may be prepared, and then the dispersant composition, the conductive material (D), and other components such as an additional organic solvent, if necessary, may be mixed to disperse each component. The conductive material (D) may be mixed with the other components in a dry state, or may be mixed with an organic solvent and then mixed with the other components.

[Positive electrode paste for power storage devices]
In one aspect, the present disclosure relates to a positive electrode paste for an electric storage device, comprising the copolymer (A) of the present disclosure, the alkaline component (B) of the present disclosure, a conductive material (D), a positive electrode active material, a binder, and an organic solvent. In one or more embodiments, the positive electrode paste of the present disclosure contains the dispersant composition of the present disclosure or the conductive material slurry of the present disclosure. The positive electrode paste of the present disclosure is prepared using the conductive material slurry or the dispersant composition of the present disclosure, which contains the copolymer (A) as a dispersant, which has low solubility in an electrolyte and improves the dispersion of the conductive material, and therefore, in the positive electrode for an electric storage device formed using the positive electrode paste of the present disclosure, both a low volume resistance value and a high discharge capacity retention rate can be achieved.

Preferable forms of the copolymer (A), alkaline component (B), organic solvent (C), conductive material (D), dispersant composition, and conductive material slurry contained in the positive electrode paste of the present disclosure are as described above. In one or more embodiments, the positive electrode paste of the present disclosure may further contain a conductive material other than the carbon material-based conductive material (D). Examples of conductive materials other than the carbon material-based conductive material (D) include conductive polymers such as polyaniline.

(Positive Electrode Active Material)
The positive electrode active material is not particularly limited as long as it is an inorganic compound, and for example, a compound having an olivine structure or a lithium transition metal composite oxide can be used. Examples of the compound having an olivine structure include a compound represented by the general formula Li _x M1 _s PO ₄ (where M1 is a 3d transition metal, 0≦x≦2, 0.8≦s≦1.2). The compound having an olivine structure may be used after being coated with amorphous carbon or the like. Examples of the lithium transition metal composite oxide include lithium manganese oxide having a spinel structure, and lithium transition metal composite oxide having a layered structure and represented by the general formula Li _x MO _2- δ (where M is a transition metal, 0.4≦x≦1.2, 0≦δ≦0.5). The lithium transition metal composite oxide may further contain one or more elements selected from Al, Mn, Fe, Ni, Co, Cr, Ti, Zn, P, and B. The transition metal M may include Co, Ni, or Mn.

<Content of positive electrode active material in positive electrode paste>
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.

There are no particular limitations 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 a conventionally known positive electrode paste, and is preferably 90.0 mass% or more in order to maintain a high energy density of the energy storage device, and is preferably 99.9 mass% or less in order to ensure the conductivity and coating properties of the positive electrode mixture layer.

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

<Binder content in positive electrode paste>
The content of the binder in the positive electrode paste of the present disclosure is preferably 0.05% by mass or more from the viewpoint of the coating properties of the positive electrode mixture layer and the binding property with the current collector, and is preferably 10% by mass or less from the viewpoint of maintaining a high energy density of the electricity storage device.

<Content of copolymer (A) in positive electrode paste>
The content of the copolymer (A) in the positive electrode paste of the present disclosure is, from the viewpoint of reducing the resistance of the positive electrode mixture layer, preferably 0.01% by mass or more, more preferably 0.02% by mass or more, even more preferably 0.03% by mass or more, and is preferably 2.0% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less.

<Content of alkaline component (B) in positive electrode paste>
The content of the alkaline component (B) in the positive electrode paste of the present disclosure is preferably 0.012 mass % or more, and more preferably 0.02 mass % or more, from the viewpoint of increasing the solids concentration of the positive electrode paste and reducing the viscosity, and is preferably 0.2 mass % or less, and more preferably 0.1 mass % or less, from the viewpoint of the solubility of the alkaline component (B) in an organic solvent and the stability of the positive electrode paste.

<Contains conductive material (D) in positive electrode paste>
The content of the conductive material (D) in the positive electrode paste of the present disclosure is preferably 0.01% by mass or more in both the case of single-walled carbon nanotubes and multi-walled carbon nanotubes from the viewpoint of the conductivity of the positive electrode mixture layer, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more in the case of multi-walled carbon nanotubes, and from the viewpoint of maintaining a high energy density of the electricity storage device, is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less.

In one or more embodiments, the positive electrode paste of the present disclosure can be produced by mixing and stirring the positive electrode active material, the conductive material slurry of the present disclosure, a binder (binder resin), and a solvent (additional solvent) for adjusting the solid content, etc. Other dispersants, functional materials, etc. may be added. As the solvent (additional solvent), non-aqueous solvents such as N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or water can be used. In addition, in the production of the positive electrode paste of the present disclosure, it is preferable to use a non-aqueous solvent as the solvent (additional solvent), and among them, it is more preferable to use NMP. A planetary mixer, a bead mill, a jet mill, etc. can be used for mixing and stirring, and these can also be used in combination.

The positive electrode paste of the present disclosure can be prepared by premixing some of the components used in the manufacture 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.

The solids concentration of the positive electrode paste of the present disclosure, the amount of the positive electrode active material, the amount of the binder, the amount of the conductive material slurry, the amount of the additive component, and the amount of the solvent can be adjusted according to the viscosity suitable for applying the positive electrode paste to the current collector. From the viewpoint of drying, a smaller amount of the solvent is preferable, but from the viewpoint of uniformity of the positive electrode composite layer (positive electrode coating film) 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 positive electrode composite layer, it is preferable that the viscosity of the positive electrode paste is not too low.

The positive electrode paste of the present disclosure is preferably high in concentration from the viewpoint of manufacturing efficiency, but a significant increase in viscosity is undesirable from the viewpoint of workability. By adding an additive, it is possible to maintain a high concentration while maintaining a preferred viscosity range.

[Method of manufacturing positive electrode paste]
The method for producing a positive electrode paste of the present disclosure includes a step of mixing a conductive material, a positive electrode active material, a solvent, a binder, and a dispersant composition of the present disclosure. The components may be mixed in any order. In one or more embodiments, the method for producing a positive electrode paste of the present disclosure preferably includes a step of mixing a conductive material slurry of the present disclosure, a binder, a solvent, and a positive electrode active material. The components may be mixed in any order. In one or more embodiments, the conductive material slurry of the present disclosure, a solvent, and a binder are mixed, dispersed 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, but the order of addition of these components is not limited to this.

The dispersant composition, conductive material slurry, and positive electrode paste of the present disclosure may each further contain other components to the extent that the effects of the present disclosure are not hindered. Examples of other components include antioxidants, neutralizing agents, defoamers, preservatives, dehydrating agents, rust inhibitors, plasticizers, binders, etc.

[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 using the positive electrode paste of the present disclosure. This aspect includes applying the positive electrode paste of the present disclosure to a current collector and then drying it. In this aspect, the preferred form of the positive electrode paste of the present disclosure is as described above. In the method for producing a positive electrode coating film or a positive electrode for an electricity storage device 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.

The positive electrode coating film or the positive electrode for a storage device is prepared, for example, by applying the above-mentioned positive electrode paste to a collector such as an aluminum foil and drying the same. In order to increase the density of the positive electrode coating film, compaction can also be performed using a press. A die head, a cone reverse roll, a direct roll, a gravure roll, etc. can be used for coating the positive electrode paste. Drying after coating can be performed by heating, air flow, infrared irradiation, etc. alone or in combination. Drying after coating is performed at a temperature at which the alkaline component (B), organic solvent (C) and additional solvent in the positive electrode paste cannot be present in the positive electrode paste due to the drying time. There are no particular restrictions on the drying temperature as long as it is equal to or lower than the thermal decomposition temperature of the binder resin in the environment (atmospheric pressure) in which the drying is performed, but it is preferably a temperature equal to or higher than the boiling point of the alkaline component (B), and more preferably a temperature equal to or lower than the boiling point of the organic solvent (C) and additional solvent. Specifically, it is preferably 60°C or higher, more preferably 80°C or higher, and preferably 220°C or lower, more preferably 200°C or lower, under normal pressure. The drying time is preferably 10 minutes or more, more preferably 20 minutes or more, and preferably 90 minutes or less, more preferably 60 minutes or less. The positive electrode can be pressed using a roll press or the like.

The following are examples and comparative examples of the present disclosure, but the present disclosure is not limited to these.

1. Measurement method for each parameter [Measurement of weight average molecular weight of polymer]
The weight average molecular weight of the polymer was measured by a GPC method under the following detailed conditions.
Measuring device: HLC-8320GPC (manufactured by Tosoh Corporation)
Column: α-M + α-M (Tosoh Corporation)
Column temperature: 40°C
Detector: Differential refractive index Eluent: 60 mmol/L H ₃ PO ₄ and 50 mmol/L LiBr in N,N-dimethylformamide (DMF) Flow rate: 1 mL/min
Standard sample used for calibration curve: polystyrene Sample solution: DMF solution containing 0.5 wt% solids of copolymer Amount of sample solution injected: 100 μL

[Electrolyte solubility]
In order to confirm the solubility of the dispersant (copolymer) in the electrolyte, the solubility in the solvent used in the electrolyte was measured. The obtained copolymer solution was placed in a petri dish and dried under reduced pressure at 140 ° C. under nitrogen gas flow for 12 hours or more. 9 g of a mixed solvent (volume ratio 50/50) of ethylene carbonate and diethylene carbonate was added to 1 g of the obtained copolymer to prepare a 10% suspension. The obtained suspension was left to stand at 40 ° C. for 1 hour. Then, it was filtered with a 0.5 μm PTFE filter to remove the undissolved copolymer. The filtered solution was dried at 140 ° C. under reduced pressure under nitrogen gas flow to measure the mass of the copolymer dissolved in the mixed solvent. The solubility in the mixed solvent was calculated as the electrolyte solubility from the following formula. The obtained solubility (%) is shown in Tables 1 and 2 as the electrolyte solubility.

[Measurement of viscosity of conductive material slurry]
The viscosities of the conductive slurry at 25° C. and 50° C. were measured using a Complate CP50 mounted on an Anton Paar MCR302 rheometer, starting at a shear rate of ¹⁰ s. The viscosities after 5 minutes were recorded and shown in Tables 1 and 2.

[Peel strength]
The test for evaluating the peel strength was carried out in accordance with JIS S0237:2009.
Specifically, the positive electrode paste was applied to an aluminum foil using a 200 μm applicator, dried, and a positive electrode coating film was prepared. This was pressed to an electrode density of 3.3 g/cm ^3. Next, this coating film was cut into 2 cm x 7 cm to form a positive electrode, and its back surface (the surface opposite to the surface of the aluminum foil that contacted the positive electrode coating film) was attached and fixed to a 7 cm x 15 cm x 1 mm stainless steel plate with double-sided tape. A 2 cm wide aluminum tape (NITTO TAPE) was attached to the surface of the positive electrode coating film, and pulled at an angle of 180° at a speed of 100 mm/min using a tensile strength measuring tester, and the obtained value was taken as the peel strength.

[Measurement of volume resistance of positive electrode coating film (positive electrode mixture layer)]
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 100° C. for 1 hour to obtain a positive electrode mixture layer (positive electrode coating film) having a thickness of 40 μm.
The volume resistivity 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 Tables 1 and 2.

[Negative electrode]
First, the negative electrode was prepared. Specifically, 94.8 parts by weight of graphite, which is commercially available as a negative electrode active material, 1.7 parts by weight of acetylene black, 2 parts by weight of SBR (styrene butadiene rubber), and 1.5 parts by weight of CMC (carboxymethyl cellulose) were mixed. Then, distilled water, which is a solvent, was added to the mixture to prepare a slurry. The slurry was applied to a surface of an electrolytic copper foil to a thickness of about 100 μm using a doctor blade, dried at 120° C., and then a roll press process was performed to prepare a negative electrode.

[Positive electrode]
Positive electrode pastes 1 to 16, which will be described later, were each applied to both sides of an aluminum foil having a thickness of 20 μm, and then dried to produce positive electrodes.

[Electrolyte]
An electrolyte solution was prepared by dissolving _1M of LiPF6 as a solute in a non-aqueous organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a weight ratio of 1:1.

[Discharge capacity retention rate]
A coin battery was manufactured using the negative electrode, positive electrode, and electrolyte thus manufactured, and the battery characteristics (rate characteristics 5C) were measured. Specifically, the battery was charged to 4.2V at 0.2C according to the following conditions in an environment of 25°C, and then discharged to 3V at 0.2C to obtain the discharge capacity. The discharge capacity at 5C was then obtained in the same manner, and the discharge capacity retention rate at 5C was obtained based on the discharge capacity at 0.2C. The results are shown in Tables 1 and 2.
(Charging conditions)
0.2C CC-CV4.2V (0.02C Cut off)
(Discharge conditions)
0.2,0.5,1,3,4,5,10C CC (3V Cut off)
5C discharge capacity maintenance rate (%)=(5C discharge capacity/0.2C discharge capacity)×100

2. Preparation of Dispersant Composition [Preparation of Dispersant Composition 1]
Copolymer 1 used in the preparation of dispersant composition 1 was obtained by the following procedure.
The following monomer solution for dropping and initiator solution for dropping were prepared: The monomer solution for dropping was prepared by diluting the monomer with NMP in an amount equal to the amount of the monomer used in the preparation.
Specifically, 100 g of NMP was added to 99 g of AN (monomer I) and 1 g of MAAm (monomer II) to prepare a monomer solution for dropping.
The initiator solution to be dropped was prepared by mixing 1.6 g of V-65B (polymerization initiator) with 16 g of NMP (solvent).

Next, the atmosphere in the separable flask, which was equipped with a reflux tube, a stirrer, a thermometer, a nitrogen inlet tube, and a dropping funnel, was replaced with nitrogen for at least 1 hour. After that, the monomer solution for dropping and the initiator solution for dropping were each dropped into the flask at 70°C over 120 minutes. After the dropping was completed, the mixture was stirred for another hour while maintaining the temperature in the tank at 70°C. The temperature in the flask was then raised to 75°C and the mixture was stirred for another hour. Next, 80 g of NMP (solvent) was added to dilute the mixture, thereby obtaining a 35.1% by mass solution of copolymer 1. The non-volatile content was 35.2% by mass, and the weight average molecular weight of copolymer 1 was 36,500.

Next, 89.2 g of NMP (solvent) was added to 4.3 g of the 35.1% by mass solution of copolymer 1 (solid content of copolymer 1 was 1.5 g), and 1.5 g of 2-amino-2-methyl-1-propanol (AMP) was further added to obtain a mixed solution, which was then subjected to a heat treatment in which the mixed solution was left for 12 hours while maintaining the liquid temperature at 80°C, to obtain dispersant composition 1 (shown as "composition 1" in Table 1, and the same applies below) having the composition shown in Table 1. Dispersant composition 1 was colored, and absorption at a wavelength of 620 nm was confirmed.

[Preparation of Dispersant Composition 2]
Copolymer 2 used in the preparation of dispersant composition 2 was obtained by the following procedure.
The following monomer solutions 1 to 3 for dropping and an initiator solution for dropping were prepared. Each of the monomer solutions 1 to 3 for dropping was prepared by diluting the monomer with NMP in an amount 1 or 2 times the amount of the monomer used to prepare the monomer solution for dropping.
Monomer solution 1 for dropping: A mixed solution consisting of 40 g of SMA (monomer III) and 40 g of NMP (solvent) Monomer solution 2 for dropping: A mixed solution consisting of 40 g of AN (monomer I) and 40 g of NMP Monomer solution 3 for dropping: A mixed solution consisting of 20 g of MAAm (monomer II) and 40 g of NMP Initiator solution for dropping: A mixed solution consisting of 1.6 g of V-65B (polymerization initiator) and 16 g of NMP (solvent)

Next, the atmosphere in the separable flask, which was equipped with a reflux tube, a stirrer, a thermometer, a nitrogen inlet tube, and a dropping funnel, was replaced with nitrogen for at least 1 hour. Then, the monomer solutions 1 to 3 for dropping and the initiator solution for dropping were each dropped into the flask at 70°C over 120 minutes. After the dropping was completed, the mixture was stirred for another hour while maintaining the temperature in the tank at 70°C. The temperature in the flask was then raised to 75°C and the mixture was stirred for another hour. Next, 49 g of NMP (solvent) was added to dilute the mixture, and a 35.1% by mass solution of copolymer 2 was obtained. The non-volatile content was 35.2% by mass, and the weight average molecular weight of copolymer 2 was 38,500.

Next, 89.2 g of NMP (solvent) was added to 4.3 g of the 35.1% by mass solution of copolymer 2 (solid content of copolymer 2 is 1.5 g), and 0.75 g of 2-amino-2-methyl-1-propanol (AMP) was further added to obtain a mixed solution, which was then subjected to a heat treatment in which the mixed solution was left for 12 hours while maintaining the liquid temperature at 80°C, thereby obtaining dispersant composition 2 having the composition shown in Table 1. Dispersant resin composition 2 was colored, and absorption at a wavelength of 620 nm was confirmed.

[Preparation of Dispersant Compositions 3 to 9 and 11 to 15]
By changing the amounts of monomer solutions 1 to 3 for dropping and the type of alkaline component (B), dispersant compositions 3 to 9 and 11 to 15 having the compositions shown in Tables 1 and 2 were prepared. The conditions for the heat treatment of the mixed solutions were as shown in Tables 1 and 2. The concentrations of the copolymer solutions containing copolymers 1 to 5, 7, and 8, respectively, were all 35.1% by mass.

[Preparation of Dispersant Composition 10]
Except for using the dropping monomer 4 below instead of the dropping monomer solution 1, the same dropping monomers as those used in copolymer 2 were used, the amount of each monomer was changed as shown in Table 1, and the amount of added NMP (solvent) was changed to 39 g to synthesize copolymer 6. Dispersant composition 10 having the composition shown in Table 1 was prepared in the same manner as dispersant composition 2 except that the type of copolymer was different.
Monomer solution 4 for dropping: A mixed solution consisting of 20 g of MAA (monomer III) and 40 g of NMP

3. Preparation of Conductive Material Slurry Dispersant compositions 1 to 15, a conductive material, and an additional solvent (NMP) were uniformly mixed to obtain conductive material slurries 1 to 15 (in Table 1, "Conductive material slurry 1" is represented as "Slurry 1", and the same applies below).

Specifically, in the case of Example 1, 200 g of conductive material and 3800 g of dispersant composition 1 were mixed at room temperature to prepare a crude dispersion. The obtained crude dispersion was passed through a media stirring type disperser (Dyno Mill KDL-PILOT type 1.4, manufactured by Shinmaru Enterprises) at a flow rate of 300 g/min. The conditions of the dispersing device were a filling rate of 70% with zirconia beads having an average diameter of 0.5 mm and a peripheral speed of 10 m/s. The crude dispersion that passed through the disperser was collected in a container, and was sent from the container to the disperser again. The temperature of the liquid that passed through the disperser and came out before being sent to the disperser again reached about 50°C. This liquid circulation was carried out for 3 hours to obtain conductive material slurry 1.

Conductive material slurries 2 to 15 were prepared in the same manner as conductive material slurry 1, except that the type of dispersant composition, the type of conductive material, and the amount used were appropriately changed to obtain the compositions shown in Tables 1 and 2.

4. Preparation of Positive Electrode Paste Conductive material slurries 1 to 15 shown in Tables 1 and 2, a positive electrode active material, a binder solution, and NMP (additional solvent) were uniformly mixed to obtain a positive electrode paste.
Specifically, in the case of Example 1, 0.61 g of conductive material slurry 1, 2.51 g of NMP, and 1.9 g of PVDF (8%) NMP solution (KF Polymer L#7208, manufactured by Kureha Corporation) as a binder solution were weighed into a 50 ml sample bottle and uniformly mixed with a spatula. Then, 12 g of NCM523 (lithium nickel manganese cobalt oxide, manufactured by Nippon Kagaku Co., Ltd.) was added as a positive electrode active material, and the mixture was stirred again with a spatula until it became uniform. The mixture was further stirred for 5 minutes with a planetary centrifugal mixer (AR-100, manufactured by Thinky Corporation) to obtain a positive electrode paste 1 of Example 1.

Positive electrode pastes 2 to 15 (Examples 2 to 10, Comparative Examples 1 to 5) were prepared in the same manner as positive electrode paste 1 in Example 1, except that conductive material slurry 2 to 15 were used instead of conductive material slurry 1.

As can be seen from Tables 1 and 2, a comparison between Dispersant Composition 2 (Example 2) and Dispersant Composition 12 (Comparative Example 2) shows that when the amount of alkali component (B) added to the copolymer (A) is small and the mass ratio (B)/(A) is less than 0.2, the amount of nitrile groups modified to a cyclic structure is small, the adsorption force of the copolymer to the conductive material is insufficient, dispersibility is poor, and the viscosity of the slurry is high. Therefore, the volume resistivity in Comparative Example 2 was significantly higher than that in Example 2.
On the other hand, in the case of dispersant composition 14 (Comparative Example 4), the amount of the alkali component (B) added relative to the copolymer (A) was too large, and the mass ratio (B)/(A) exceeded 2.0, so that the copolymer became insolubilized and aggregated.

In the examples containing copolymer (A) as a dispersant, the viscosity of the conductive material slurry was lower, the peel strength was higher, the volume resistivity was significantly lower, and the discharge capacity retention rate was higher than in Comparative Example 3, which contains copolymer 7, which has a lower content of unit I, as a dispersant.

The dispersant composition of the present disclosure can disperse carbonaceous conductive materials well, thereby enabling the viscosity of the conductive material slurry and the positive electrode paste to be reduced. Furthermore, if the dispersant of the present disclosure is used to prepare the conductive material paste or the positive electrode paste, the viscosity of the conductive material slurry and the positive electrode paste will also be low, which can contribute to reducing the resistance of the positive electrode coating film.

Claims (9)

A copolymer (A), an inorganic or organic alkali component (B), and an organic solvent (C),
The copolymer (A) contains, relative to 100 mass% of the total of all units, 30 mass% or more and 99 mass% or less of units I derived from (meth)acrylonitrile and 1 mass% or more and 70 mass% or less of units II derived from (meth)acrylamide,
a mass ratio (B)/(A) of the copolymer (A) to the inorganic or organic alkali component (B) is 0.2 or more and 2.0 or less. The dispersant composition for an electric storage device electrode according to claim 1, wherein the alkaline component (B) is an organic amine. The organic amine is one or more organic amines selected from amine compound (i) and amine compound (ii) represented by the following formula (1):
3. The dispersant composition for an electric storage device electrode according to claim 1 or 2, wherein the amine compound (ii) is at least one selected from the group consisting of secondary aliphatic amines, tertiary aliphatic amines, secondary aromatic amines, tertiary aromatic amines, and heterocyclic amines, and is an amine compound having a boiling point of 200° C. or lower.
In the above formula (1), ^R1 represents a group represented by the following formula (2), and ^R2 represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or _{--CH2CH2 --} OH. In the following formula (2), ^R3 , ^R4 , ^R5 , and ^R6 may be the same or different and represent a hydrogen atom, a methyl group, or _--CH2OH .
A carbon material-based conductive material slurry containing the dispersant composition for an electric storage device electrode according to any one of claims 1 to 3 and a carbon material-based conductive material (D). The carbonaceous conductive material slurry according to claim 4, wherein the carbonaceous conductive material (D) is a carbon nanotube. The carbon material-based conductive material slurry according to claim 5, wherein the carbon nanotubes have an outer diameter of 10 nm or less. A positive electrode paste for a storage battery device, comprising the dispersant composition for a storage battery device electrode according to any one of claims 1 to 3, a positive electrode active material, a carbon material-based conductive material (D), and a binder. A method for producing a positive electrode coating film, comprising applying the positive electrode paste for an electricity storage device according to claim 7 to a current collector and then drying the applied paste. The method includes a step of heat-treating a mixed solution containing a copolymer (A), an inorganic or organic alkali component (B), and an organic solvent (C),
The copolymer (A) contains, relative to 100 mass% of the total of all units, 30 mass% or more and 99 mass% or less of units I derived from (meth)acrylonitrile and 1 mass% or more and 70 mass% or less of units II derived from (meth)acrylamide,
a mass ratio (B)/(A) of the copolymer (A) to the inorganic or organic alkali component (B) in the mixed solution is 0.2 or more and 2.0 or less.