Dispersant composition for electrodes of energy storage devices

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

[Technical Field]

[0001] The present invention relates to a dispersant composition for electrodes of energy storage devices. [Background technology]

[0002] In recent years, there has been a surge in the development of electric vehicles (EVs) that do not emit carbon dioxide, from the perspective of mitigating global warming. However, EVs have challenges compared to gasoline-powered vehicles, such as shorter driving ranges and longer battery charging times. To shorten charging times, it is necessary to increase the speed of electron movement in the positive electrode. Currently, carbon materials are used as conductive additives (conductive materials) in the positive electrodes of non-aqueous electrolyte batteries. In conductive material slurries where the conductive material is dispersed in an organic solvent, good dispersibility of the conductive material is important for forming good conductive paths in the positive electrode.

[0003] Patent Document 1 discloses a dispersant (C) used in the preparation of a conductive material dispersion for non-aqueous electrolyte secondary batteries, with the aim 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 alkyl (meth)acrylate esters, wherein the copolymer contains 40 to 99% by mass of the units derived from (meth)acrylonitrile, and has a weight-average molecular weight of 5,000 to 50,000.

[0004] Patent Document 2 discloses a dispersant used in the preparation of a dispersion, with the aim of providing 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 alkyl (meth)acrylate esters, wherein the copolymer contains 40 to 99% by mass of the units derived from (meth)acrylonitrile and has a weight-average molecular weight greater than 50,000 and less than or equal to 200,000.

[0005] Patent Document 3 discloses a binder used in the preparation of an electrochemical element electrode, with the aim of providing an electrochemical element electrode binder composition that is excellent in peel strength and powder fall resistance, and capable of forming an electrode composite layer that can exhibit high rate characteristics in 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. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-187991 [Patent Document 2] Japanese Patent Publication No. 2021-115523 [Patent Document 3] WO2020 / 004332 publication [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the use of the dispersants disclosed in Patent Documents 1 and 2 presents a problem in the dispersion process of carbon material-based conductive materials into the dispersion solvent: the viscosity is high, and in particular, the slurry becomes significantly thicker as the slurry temperature increases. When the slurry viscosity is high, the dispersion efficiency decreases, and the defibration of carbon material-based conductive materials such as CNTs does not proceed, resulting in a high resistance value of the electrode formed using the slurry. Therefore, when preparing the slurry, it is necessary to lower the viscosity by adding solvent or other methods to improve the dispersion efficiency. Furthermore, to reduce electrode resistance, it is desirable that the positive electrode coating (also called the positive electrode composite layer) adheres more tightly to the current collector, and that the dispersant has low solubility in the electrolyte. This is because if the dispersant has high solubility in the electrolyte, the dispersant dissolved in the electrolyte can clog the separator, which can lead to increased resistance and a decrease in the discharge capacity maintenance rate.

[0008] Therefore, in one embodiment, this disclosure provides a dispersant composition for the positive electrode of an energy storage device that enables the production of a conductive material slurry with low solubility of the dispersant in the electrolyte, low viscosity and good handling properties, and enables the formation of a coating film with high adhesion to the current collector. Furthermore, in one embodiment, this disclosure provides a carbon material-based conductive slurry or a positive electrode paste for an energy storage device, which includes the dispersant composition for the positive electrode of an energy storage device. Furthermore, this disclosure provides a positive electrode coating film for an energy storage device that is formed using the positive electrode paste for the energy storage device. [Means for solving the problem]

[0009] This disclosure is, in one manner, A copolymer (A), an inorganic or organic alkali component (B), and an organic solvent (C) are included. The copolymer (A) contains, with respect to 100% by mass of the total units, 30% to 99% by mass of unit I derived from (meth)acrylonitrile and 1% to 70% by mass of unit II derived from (meth)acrylamide. The present invention relates to a dispersant composition for electrodes of energy storage devices, wherein the mass ratio (B) / (A) of the copolymer (A) to an inorganic or organic alkaline component (B) is 0.2 or more and 2.0 or less.

[0010] This disclosure relates, in one embodiment, to a carbon material-based conductive material slurry containing the dispersant composition for electrodes of energy storage devices of this disclosure and a carbon material-based conductive material (D).

[0011] In one aspect, the present disclosure relates to a positive electrode paste for a power storage device, which includes a dispersant composition for a power storage device electrode, a positive electrode active material, a carbon material-based conductive material, and a binder.

[0012] In one aspect, the present disclosure relates to a method for manufacturing a positive electrode coating film for a power storage device, which includes coating a positive electrode paste for a power storage device according to the present disclosure on a current collector and then drying it.

[0013] In one aspect, the present disclosure is a method for manufacturing a dispersant composition for a power storage device electrode, which 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, based on 100% by mass of the total units, 30% to 99% by mass of unit I derived from (meth)acrylonitrile and 1% to 70% by mass of unit II derived from (meth)acrylamide. The present disclosure relates to a method for manufacturing a dispersant composition for a power storage device electrode, in which 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.

Advantages of the Invention

[0014] According to the present disclosure, in one aspect, it is possible to provide a dispersant composition for a power storage device positive electrode, which has low solubility of the dispersant in an electrolytic solution, enables the preparation of a conductive material slurry with low viscosity and good handling properties, and enables the formation of a coating film with high adhesion to a current collector. Also, according to the present disclosure, in one aspect, it is possible to provide a carbon material-based conductive material slurry with low viscosity and good handling properties. Also, according to the present disclosure, in one aspect, it is possible to provide a positive electrode paste for a power storage device, which has high adhesion to a current collector and enables the formation of a positive electrode coating film with low resistance. Also, according to the present disclosure, in one aspect, it is possible to provide a positive electrode coating film for a power storage device, which has high adhesion to a current collector and a low coating film resistance value.

Embodiments for Carrying Out the Invention

[0015] [Dispersant composition for electrodes of energy storage devices] This disclosure is based on the finding that a dispersant composition for positive electrodes of energy storage devices (hereinafter also referred to as "the dispersant composition of this disclosure") can be provided, which contains a specific copolymer (A) as a dispersant, and in which the specific copolymer (A) and a specific alkaline component (B) coexist in a specific mass ratio, thereby enabling the production of a conductive material slurry with low solubility of the dispersant in the electrolyte, low viscosity and good handling properties, and enabling the formation of a coating film with high adhesion to the current collector.

[0016] This disclosure relates, in one embodiment, to a dispersant composition for an energy storage device electrode comprising a copolymer (A), an inorganic or organic alkali component (B) (hereinafter sometimes abbreviated as "alkali component (B) of this disclosure"), and an organic solvent (C). The copolymer (A) is a copolymer (hereinafter sometimes abbreviated as "copolymer (A) of this disclosure") that contains 30% to 99% by mass of unit I derived from (meth)acrylonitrile and 1% to 70% by mass of unit II derived from (meth)acrylamide, based on 100% by mass of the total units, wherein some of the nitrile groups of unit I are modified into a cyclic structure, and the mass ratio (B) / (A) of copolymer (A) of this disclosure to alkali component (B) of this disclosure is 0.2 to 2.0.

[0017] By using the dispersant composition of this disclosure, a low-viscosity, easy-to-handle carbon-based conductive material slurry (hereinafter also referred to as "the conductive material slurry of this disclosure") can be prepared. Furthermore, by using the dispersant composition of this disclosure, a positive electrode paste for energy storage devices (hereinafter also referred to as "the positive electrode paste of this disclosure") that enables the formation of a coating film with high adhesion to the current collector can be prepared. In addition, by using the positive electrode paste of this disclosure containing the dispersant composition of this disclosure, a positive electrode coating film with low coating film resistance and an energy storage device with high discharge capacity retention can be manufactured.

[0018] Although the detailed mechanism of how the effects of this disclosure are realized is not clear, it can be inferred as follows. Of the total units of copolymer (A) in this disclosure, unit I, derived from (meth)acrylonitrile, is adsorbed onto the conductive material (hereinafter sometimes abbreviated as "conductive material") due to the interaction between the π electrons of its nitrile (CN) group and the π electrons of the conductive material, and is therefore considered to be a component that contributes to the dispersion of the conductive material. Furthermore, unit I derived from (meth)acrylonitrile also has high adsorption capacity to the current collector. On the other hand, unit II derived from (meth)acrylamide is an insoluble component in the electrolyte, and therefore suppresses the dissolution of copolymer (A) in the electrolyte, contributing to the suppression of the decrease in capacity retention rate. When the copolymer (A) and the alkali component (B) coexist, some of the nitrile groups of the unit I derived from (meth)acrylonitrile are modified into a cyclic structure through reaction with the alkali component (B), and it has been confirmed that the insolubility of unit I in organic solvents in the dispersant composition increases. Furthermore, since the cyclic structure has multiple π electrons, the π-π interaction between the cyclic structure and the conductive material enhances the adsorption capacity of the copolymer (A) to the conductive material. In addition, the modification of the nitrile groups into the cyclic structure improves the adsorption capacity of the copolymer (A) to the current collector, which is presumed to contribute to improving the peel strength of the positive electrode coating film from the current collector, and consequently to reducing the resistance of the positive electrode coating film and suppressing the decrease in discharge capacity maintenance rate. However, if the alkaline component (B) is present in excess in the dispersant composition, the copolymer (A) becomes too insoluble and aggregates, impairing the stability of the composition. In this disclosure, by setting the mixing ratio (B) / (A) of a specific copolymer (A) and a specific alkaline component (B) to 0.2 to 2.0 by mass ratio, the modification of the nitrile group to a cyclic structure appropriately insolubilizes unit I in the electrolyte and improves the adsorption force to the conductive material and current collector. As a result, it is presumed that it is possible to achieve both low solubility of the copolymer (A) in the electrolyte, suppression of viscosity increase during conductive slurry preparation, and high adhesion of the positive electrode coating to the current collector. Although the detailed mechanism is unknown, by referring to descriptions in "Polymer Chemistry 19, 653 (1962)," etc., the presence of the cyclic structure can be confirmed by the coloration of the dispersant composition due to the addition of alkaline component (B), and specifically by NMR or infrared spectroscopy.

[0019] [Copolymer (A)] (Unit I) Of the total units of copolymer (A) of the present disclosure, unit I derived from (meth)acrylonitrile acts as a component adsorbed on the surface of the conductive material. From the viewpoint of suppressing viscosity increase during conductive slurry preparation, the amount of 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 100% by mass of the total units of copolymer (A), and from the viewpoint of suppressing dissolution of copolymer (A) in the electrolyte, it is 99% by mass or less, preferably 90% by mass or less. Note that 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.

[0020] [ka]

[0021] (Unit II) Unit II, derived from (meth)acrylamide, of all units in copolymer (A) of this disclosure, is represented by the following formula (2). Because unit II has an amide group in its side chain, it has low solubility in the electrolyte. Therefore, it is possible to form a positive electrode coating film in which the dispersant (polymer (A)) dissolves little into the electrolyte, and as a result, an energy storage device can be obtained that maintains a high discharge capacity with repeated charging and discharging.

[0022] [ka]

[0023] From the viewpoint of suppressing the dissolution of copolymer (A) in the electrolyte and ensuring solubility in the solvent used for polymerization of copolymer (A) (hereinafter abbreviated as "polymerization solvent"), the aforementioned unit II is 1% by mass or more, preferably 5% by mass or more, more preferably 12% by mass or more, based on 100% by mass of the total units of copolymer (A), and from the same viewpoint, it is 50% by mass or less, preferably 25% by mass or less, and preferably 18% by mass or less.

[0024] Furthermore, the content of unit I in the total units of copolymer (A) can be considered as the ratio of the amount of monomer I used to the total amount of monomer used in polymerization. Monomer I is the monomer that gives unit I in the synthesis of copolymer (A). Also, the content of unit II in the total units of copolymer (A) can be considered as the ratio of the amount of monomer II used to the total amount of monomer used in polymerization. Monomer II is the monomer that gives unit II in the synthesis of copolymer (A).

[0025] The copolymer (A) may further contain unit III derived from monomers other than monomer I and monomer II (hereinafter referred to as "monomer III"). Examples of monomer III include alkyl (meth)acrylates such as 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, and behenyl (meth)acrylate. ;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, or caprolactone adducts of these monomers (number of adducted moles: 1-5); (meth)acrylic acid, (meth)acrylic acid dimer, itaconic acid, maleic acid, fumaric acid, crotonic acid, 2- Examples include (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 carboxyl group-containing monomers such as 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 the ease of introducing unit I into the dispersant (polymer (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.

[0026] The arrangement of each unit in copolymer (A) of this disclosure may be in blocks or random, but random arrangement is preferred from the viewpoint of preventing excessive cyclic structure modification and controlling the reaction.

[0027] 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 similarly 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 the value measured by GPC (gel permeation chromatography), and the details of the measurement conditions are as shown in the examples.

[0028] The content of copolymer (A) in the dispersant composition of this 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 carbon material-based conductive materials, and 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 flexibility in compounding in subsequent processes.

[0029] (Method for synthesizing copolymer (A)) The method for synthesizing copolymer (A) is not particularly limited, and methods commonly used for the polymerization of (meth)acrylic acid esters and vinyl monomers can be used. Examples of methods for synthesizing copolymer (A) include free radical polymerization, living radical polymerization, anionic polymerization, and living anionic polymerization. For example, when using free radical polymerization, it can be obtained by known methods such as polymerizing monomer components containing monomer I, monomer II, and optionally monomer III by solution polymerization.

[0030] As polymerization solvents, 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 because it can dissolve the binder during the preparation of the positive electrode paste.

[0031] The amount of solvent is preferably 0.5 to 10 times the mass of the total amount of monomer. Known radical polymerization initiators can be used as polymerization initiators, such as azo polymerization initiators, hydroperoxides, dialkyl peroxides, diacyl peroxides, and ketone peroxides. The amount of 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, relative to the total amount of monomer components. The polymerization reaction is preferably carried out under a nitrogen atmosphere at a temperature range of 40°C to 180°C, and the reaction time is preferably 0.5 hours to 20 hours. Furthermore, known chain transfer agents can be used during the polymerization. Examples of chain transfer agents include isopropyl alcohol and mercapto compounds such as mercaptoethanol.

[0032] [Inorganic or organic alkaline components (B)] Among the alkaline components (B) contained in the dispersant composition of this disclosure, examples of inorganic alkaline components include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of organic alkaline components include organic amines. Preferably, the organic amine is one or more organic amines selected from amine compound (i) and amine compound (ii) represented by the following formula (1), wherein amine compound (ii) is preferably at least one amine compound with a boiling point of 200°C or less, selected from aliphatic amines, aromatic amines, and heterocyclic amines. These amine compounds are considered to readily interact (cation-π interaction) between cations derived from the amine compound and π electrons derived from the conductive material. Furthermore, these amine compounds are preferred because, at the surface of the conductive material, the "cation-π" interaction blocks π-π interactions between conductive materials, thereby reducing the viscosity of the conductive material slurry.

[0033] [ka]

[0034] (Amine compound (i)) In the above formula (1), R 3 , , , , 5 , , 4 , 2 ,

[0038] ,

[0037] , 6 , represents a group represented by the following formula (2), and R 2 represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or -CH2CH2-OH. In the following formula (2), R 3 , R 4 , R 5 and R 6 are the same or different and represent a hydrogen atom, a methyl group, or -CH2OH.

[0035]

Chemical formula

[0036] The amine compound (primary or secondary amine) (i) represented by the above formula (1) is superior to the tertiary amine in which H in the formula (1) is substituted with a carbon atom because the steric hindrance is small and the cation-π interaction becomes easier. In the formula (1) representing a primary or secondary amine, R 2 is preferably a hydrogen atom (primary amine), an alkyl group having 1 to 4 carbon atoms (secondary amine), or -CH2CH2-OH (secondary amine) from the viewpoint of viscosity reduction, and a hydrogen atom, an alkyl group having 1 carbon atom (methyl group), or an alkyl group having 2 carbon atoms (ethyl group) is more preferable. Since the steric hindrance by a hydrogen atom, a methyl group, or an ethyl group is small, it is considered that the cation-π interaction becomes easier.

[0037] 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 viscosity reduction. A hydrogen atom or a methyl group has small steric hindrance, and it is considered that the cation-π interaction becomes easier.

[0038] 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 in one or more embodiments. Among these, from the viewpoint of achieving both improved dispersibility of the conductive material and low viscosity of the positive electrode paste, it is 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).

[0039] (Amine compounds (ii)) The amine compound (ii) is at least one selected from aliphatic amines, aromatic amines, and heterocyclic amines from the viewpoint of interaction with conductive materials and adsorption properties, 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 lower, preferably below the boiling point of the solvent of the positive electrode paste, more preferably below the boiling point of N-methylpyrrolidone (NMP), which is widely used as a solvent for positive electrode paste (boiling point 202°C), and even more preferably below 190°C from the viewpoint of reusing NMP. The lower limit of the boiling point of the amine compound (ii) is preferably 100°C or higher, and more preferably 120°C or higher, from the viewpoint of ease of handling.

[0040] Amine compounds reduce slurry viscosity by blocking π-π interactions between conductive materials through "cation-π" interactions on the conductive material surface. However, if electrically insulating amine compounds remain 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 maintenance rate of energy storage devices such as lithium-ion batteries. Therefore, in this disclosure, as the alkaline component (B), a tertiary aliphatic amine, primary aromatic amine, secondary aromatic amine, tertiary aromatic amine, or heterocyclic amine is used, which has a lower boiling point than NMP (boiling point 202°C), a solvent mainly used in positive electrode pastes, and does not undergo amidation. Alternatively, a secondary aliphatic amine, primary aromatic amine, secondary aromatic amine, tertiary aromatic amine, or heterocyclic amine is used, which is less likely to undergo amidation due to significant steric hindrance. It is presumed that this allows the amine compound to volatilize well along with the solvent when the coating dries, suppressing the increase in resistance value caused by the addition of amide compounds and preventing a decrease in the discharge capacity maintenance rate.

[0041] Amine compounds (ii) include secondary aliphatic amines such as dibutylamine (the values ​​in parentheses below indicate the 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); and N-methylcyclohexylamine. Examples include one or more amine compounds selected from secondary aromatic amines such as tilbenzylamine (at 186°C) and N-monomethylaniline (at 196°C); tertiary aromatic amines such as N,N-dimethylbenzylamine (at 183°C), N,N-dimethylaniline (at 194°C), and N,N-dimethyl-o-toluidine (at 186°C); and heterocyclic amines such as N-methylmorpholine (at 116°C), N-ethylmorpholine (at 135°C), and 4-isobutylmorpholine (at 167°C). Among these, from the viewpoint of achieving both improved dispersibility of conductive materials, lower viscosity of conductive slurries and positive electrode pastes, and reduction of resistance of positive electrode coatings and suppression of reduction in discharge capacity maintenance rate of energy storage devices, 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.

[0042] The mass ratio (B) / (A) of the copolymer (A) to the alkali component (B) is 0.2 or higher, preferably 0.3 or higher, and more preferably 0.6 or higher, from the viewpoint of achieving both improved dispersibility of the conductive material, lower viscosity of the conductive slurry and positive electrode paste, and suppression of a decrease in the resistance value of the positive electrode coating and a decrease in the discharge capacity maintenance rate of the energy storage device. Similarly, from the viewpoint of ensuring the stability of the dispersant composition, it is 2.0 or lower.

[0043] The content of the alkaline component (B) of the Dispersant Composition of the Disclosure in the Disclosure is, in one or more embodiments, 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 positive electrode paste, and from the viewpoint of effectively performing cyclization modification of nitrile groups, and from the viewpoint of the solubility of copolymer (A) and the control of cyclization modification of nitrile groups, it is 200 parts by mass or less per 100 parts by mass of copolymer (A).

[0044] [Organic solvent (C)] The organic solvent (C) contained in the dispersant composition of this disclosure is preferably one that can dissolve the binder resin contained in the positive electrode paste. Examples of organic solvents (C) include amide-type 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, or octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, or hexylene glycol; glycerin, Examples include polyhydric alcohols such as limethylolpropane, pentaerythritol, or 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, or tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, or cyclopentanone; and esters such as ethyl acetate. The organic solvent (C) may be one type or a combination of two or more types.

[0045] 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 alkali component (B), and preferably 98% by mass or less from the viewpoint of effectively dispersing the carbon material-based conductive material.

[0046] The dispersant compositions of this disclosure may further contain other components, to the extent that the effects of this disclosure are not impaired. Examples of other components include antioxidants, neutralizing agents, defoaming agents, preservatives, dehydrating agents, rust inhibitors, plasticizers, and binders (binder resins having a different structure from copolymer (A)).

[0047] [Method for producing dispersant compositions for energy storage devices] A method for producing the dispersant composition of this disclosure includes mixing a copolymer (A), an alkaline component (B), an organic solvent (C), and optional components to be added as needed, and mixing the copolymer (A) and the alkaline 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, for example, the same, the copolymer (A) may be mixed with the other components in the state of a polymer solution in which it is dissolved in the polymerization solvent.

[0048] Modification of nitrile groups to a cyclic structure can be carried out at room temperature (25°C), but heating is preferable from the viewpoint of promoting modification. Therefore, the method for producing the 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 an organic solvent (C). The copolymer (A) is a copolymer containing 30% to 99% by mass of unit I derived from (meth)acrylonitrile and 1% to 70% by mass of component II derived from (meth)acrylamide, based on 100% by mass of the total units. The mass ratio (B) / (A) of the copolymer (A) to the alkali component (B) in the mixed solution before the heat treatment is 0.05 to 2.0. The heating temperature for the heat treatment is preferably 25°C or higher, more preferably 50°C or higher, from the viewpoint of promoting modification, and preferably 100°C or lower, more preferably 80°C or lower, 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.

[0049] [Conductive material slurry for energy storage devices] This disclosure relates in one embodiment to a conductive material slurry for energy storage devices (hereinafter also referred to as "the conductive material slurry of this disclosure") which contains a carbon material-based conductive material (D) (hereinafter sometimes abbreviated as "conductive material") and the dispersant composition of this disclosure. The preferred form of the dispersant composition of this disclosure in this embodiment is as described above. In one or more embodiments, the conductive material slurry of this disclosure comprises a copolymer (A) of this disclosure, an alkaline component (B) of this disclosure, an organic solvent (C), and the conductive material (D) described later.

[0050] [Carbon material-based conductive material (D)] In one or more embodiments, the conductive material (D) of this disclosure may include carbon nanotubes (hereinafter sometimes referred to as "CNT"), carbon black, graphite, graphene, etc. Among these, at least one selected from carbon black, carbon nanotubes, and graphene is preferred from the viewpoint of achieving high conductivity, and from the same viewpoint, carbon nanotubes or graphene are more preferred, with carbon nanotubes being even more preferred. The conductive material (D) may be one type or a combination of two or more types.

[0051] (Carbon nanotubes) The average diameter of the CNTs that can be used as the conductive material (D) is not particularly limited, but from the viewpoint of improving the dispersibility and 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 even more preferably 5 nm or more. 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 this disclosure, the average diameter of the CNTs can be measured by scanning electron microscope (SEM) or atomic force microscope (AFM).

[0052] In this disclosure, CNT means a totality comprising multiple carbon nanotubes. The form of CNTs used in the production of conductive material slurry is not particularly limited, and may be, for example, multiple CNTs in an independent form, multiple CNTs in a bundle or entangled form, or a mixture of these forms. In order to achieve both conductivity and dispersibility, the CNTs may be a mixture of two or more types of CNTs with different number of layers or diameters. The CNTs may contain impurities derived from the process in the production of the CNTs (e.g., catalysts or amorphous carbon).

[0053] Examples of CNTs that can be used as conductive material (D) include Nanocyl's NC-7000 (the following values ​​are average diameters, 9.5nm), NX7100 (10nm), Cano's FT6100 (9nm), FT-6110 (9nm), FT-6120 (9nm), FT-7000 (9nm), FT-7010 (9nm), FT-7320 (9nm), FT-9000 (12.5nm), FT-9100 (12.5nm), FT-9110 (12.5nm), FT-9200 (19nm), FT-9220 (19nm), and Cabot Performance. Examples include HCNTs4 (4.5nm), CNTs5 (7.5nm), HCNTs5 (7.5nm), GCNTs5 (7.5nm), HCNTs10 (15nm), CNTs20 (25nm), and CNTs40 (40nm) from material (Shenzhen); CTUBE170 (13.5nm), CTUBE199 (8nm), and CTUBE298 (10nm) from CNT Korea; K-Nanos100P (11.5nm) from Kumho; CP-1001M (12.5nm) and BT-1003M (12.5nm) from LG Chem; 3003 (10nm) and 3021 (20nm) from Nano Tech Port; JENOTUBE8S (6.8nm) from JEIO; and TUBALL (1.6nm) from OCSIAL. Examples of combinations when using two types of CNTs include: a combination of Cabot Performance Material (Shenzhen)'s CNTs40 (40nm) and HCNTs4 (4.5nm) or HCNTs5 (7.5nm); a combination of CNTs40 (40nm) and GCNTs5 (7.5nm); a combination of CNTs40 (40nm) and Canano's FT-7010 (9nm); a combination of CNTs40 (40nm) and FT-9100 (12.5nm); and a combination of CNTs40 (40nm) and LG Chem's BT-1003M (12.5nm).

[0054] (Carbon Black) Various types of carbon black can be used as conductive material (D), including furnace black, channel black, thermal black, acetylene black, and Ketjen black. Oxidized carbon black and hollow carbon can also be used. Oxidation of carbon black involves treating the carbon black at high temperatures in air, or secondarily treating it with nitric acid, nitrogen dioxide, or ozone, thereby directly introducing (covalently bonding) oxygen-containing polar functional groups such as phenolic groups, quinone groups, carboxyl groups, and carbonyl groups to the carbon surface. These treatments are commonly 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 unoxidized carbon black.

[0055] The specific surface area of ​​carbon black that can be used as a conductive material (D) is advantageous in reducing the internal resistance of the electrode because a larger specific surface area increases the number of contact points between carbon black particles. Specifically, the specific surface area (BET) determined from the amount of nitrogen adsorbed is preferably 20 m². 2 / g or more, comfortably 50m 2 / g or more, more preferably 100m 2 It is 1500m or more per gram, and preferably 1500m 2 Less than / g, more preferably 1000m 2 / g or less, more preferably 800m 2 It is less than / g.

[0056] The primary particle size (diameter) of carbon black that can be used as a conductive material (D) is preferably 5 nm or larger, more preferably 10 nm or larger, more preferably 1000 nm or smaller, and more preferably 200 nm or smaller, from the viewpoint of conductivity. In this disclosure, the primary particle size of carbon black is the average of the particle sizes measured by an electron microscope or the like.

[0057] (Graphene) Graphene that can be used as a conductive material (D) is generally sp 2While the term "graphene" generally refers to a two-dimensional sheet (single-layer graphene) with a thickness of one atom, formed by hybridized carbon atoms creating a hexagonal honeycomb lattice, in this disclosure, the term "graphene" will also include materials that have a layered form of single-layer graphene.

[0058] There are no particular restrictions 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 are no particular restrictions on the size in the direction parallel to the graphene layer, but from the viewpoint of ensuring good conductivity at 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 and minimum diameters when observed from a direction perpendicular to the plane direction of the graphene.

[0059] ≪Content of conductive material (D) in conductive material slurry≫ The content of conductive material (D) in the conductive material slurry of this disclosure is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of improving the convenience of adjusting the concentration of the positive electrode paste, and preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 7% by mass or less, from the viewpoint of making the conductive material slurry easy to handle.

[0060] <Content of copolymer (A) in conductive material slurry> The content of copolymer (A) in the conductive material slurry of this disclosure is 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, per 100 parts by mass of conductive material (D), from the viewpoint of improving the dispersibility of conductive material (D), and from the viewpoint of high conductivity, preferably 1000 parts by mass or less, more preferably 200 parts by mass or less, even more preferably 100 parts by mass or even more preferably 50 parts by mass or less.

[0061] ≪Content of alkaline component (B) in conductive material slurry≫ From the viewpoint of improving the dispersibility of the carbon material-based conductive material, the content of the alkali component (B) in the conductive material slurry of this disclosure is 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, per 100 parts by mass of the carbon material-based conductive material (D). 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.

[0062] [Method for manufacturing conductive material slurry] The conductive material slurry of the present disclosure can be prepared in one or more embodiments by mixing the copolymer (A) of the present disclosure, the alkaline component (B) of the present disclosure, the conductive material (D), an organic solvent, and optional components to be added as needed, using a mixing disperser to disperse each component. The organic solvent is the same as the organic solvent (C) that can be used to prepare the dispersant composition of the present disclosure described above.

[0063] Examples of the mixing and dispersing machine include at least one selected from ultrasonic homogenizers, vibrating mills, jet mills, ball mills, bead mills, sand mills, roll mills, homogenizers, high-pressure homogenizers, ultrasonic devices, attritors, dissolvers, and paint shakers, but a media stirring type disperser is preferred for reasons of dispersion uniformity.

[0064] A media-agitated disperser works by applying rotational motion to beads within a grinding chamber, thereby miniaturizing the target material through collisions and shear forces between the beads, which generates heat. The bead material is primarily glass, alumina, or zirconia, but zirconia is preferred due to its hardness and the need to avoid impurities in the slurry. For larger target materials, larger beads are preferable, while smaller beads are preferred as the desired particle size becomes finer. For the dispersion of conductive materials, beads between 0.1 mm and 20 mm are preferred. The amount of beads introduced into the grinding chamber, i.e., the packing rate, is preferably 50% to 90% of the chamber's volume, and preferably 60% to 80% from the viewpoint of dispersion efficiency and heat generation. The rotational motion applied to the beads, i.e., the peripheral speed, 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 a tank to the disperser via a pump, dispersed by the rapidly agitated beads, and returned to the tank. This process is repeated to circulate the slurry and perform the dispersion treatment. In one embodiment, the method for producing a conductive material slurry of the present disclosure includes the step of dispersing each component in a mixture containing a copolymer (A), an alkaline component (B), a conductive material (D), an organic solvent, and optional components added as needed, using a media-stirred disperser to form a slurry, wherein in the step, the mixture in the process of dispersion (crude dispersion) is sent from the media-stirred disperser to a container (tank), the crude dispersion is sent from the tank to the media-stirred disperser via a pump for dispersion treatment, and this is repeated multiple times to obtain a conductive material slurry.

[0065] In the method for producing a conductive material slurry according to the present disclosure, some of the components of the conductive material slurry may be mixed before being mixed with the remainder, or each component may be added in multiple portions rather than all at once. For example, the dispersant composition according to the present disclosure may be prepared, and then the dispersant composition may be mixed with the conductive material (D) and, if necessary, other components such as additional organic solvents to disperse each component. The conductive material (D) may be mixed with the other components in a dry state, or it may be mixed with an organic solvent and then mixed with the other components.

[0066] [Positive electrode paste for energy storage devices] This disclosure relates, in one embodiment, to a positive electrode paste for an energy storage device comprising a copolymer (A) of the Disclosure, an alkaline component (B) of the 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 Disclosure contains a dispersant composition or a conductive material slurry of the Disclosure. Since the positive electrode paste of the Disclosure is prepared using a conductive material slurry or dispersant composition of the Disclosure containing copolymer (A) as a dispersant, which has low solubility in the electrolyte and good dispersion of the conductive material, a positive electrode for an energy storage device formed using the positive electrode paste of the Disclosure can achieve both a low volume resistivity and a high discharge capacity retention rate.

[0067] Preferred 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 this disclosure are as described above. In one or more embodiments, the positive electrode paste of this disclosure may further contain conductive materials 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.

[0068] (Cathode active material) As for the positive electrode active material, there are no particular restrictions as long as it is an inorganic compound; for example, compounds having an olivine structure or lithium transition metal composite oxides can be used. As for compounds having an olivine structure, the general formula Li x M1 s Examples of compounds represented by PO4 (where M1 is a 3d transition metal, 0≦x≦2, 0.8≦s≦1.2) can be used. Compounds having an olivine structure may be used coated with amorphous carbon or the like. Examples of lithium transition metal composite oxides include lithium manganese oxide having a spinel structure, and Li having a layered structure with the general formula Li x MO 2-Examples include lithium transition metal composite oxides represented by δ (where M is a transition metal, 0.4 ≤ x ≤ 1.2, and 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.

[0069] ≪Content of positive electrode active material in positive electrode paste≫ The content of the positive electrode active material in the positive electrode paste of this disclosure is not particularly limited, as long as it can be adjusted according to the viscosity suitable for the positive electrode paste to be applied to the current collector. However, from the viewpoint of energy density and the stability of the positive electrode paste, it is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0070] There are no particular restrictions on the content of the positive electrode active material in the total solid content of the positive electrode paste of this disclosure. The content of the positive electrode active material in the total solid content of the positive electrode paste of this disclosure may be the same as that in the total solid content of conventionally known positive electrode pastes. To maintain a high energy density of the energy storage device, it is preferable to have a content of 90.0% by mass or more, and to ensure the conductivity and coating properties of the positive electrode composite layer, it is preferable to have a content of 99.9% by mass or less.

[0071] (Binding agent (binder resin)) As a binder (binder resin), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer, styrene-butadiene rubber, polyacrylonitrile, etc., can be used alone or in combination.

[0072] ≪Binding agent content in positive electrode paste≫ The binder content in the positive electrode paste of this disclosure is preferably 0.05% by mass or more from the viewpoint of coating properties of the positive electrode composite layer and adhesion to the current collector, and preferably 10% by mass or less from the viewpoint of maintaining a high energy density of the energy storage device.

[0073] ≪Content of copolymer (A) in positive electrode paste≫ From the viewpoint of reducing the resistance of the cathode paste of this disclosure, the content of copolymer (A) is 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 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.

[0074] ≪Content of alkaline component (B) in positive electrode paste≫ The content of the alkaline component (B) in the positive electrode paste of this disclosure is preferably 0.012% by mass or more, more preferably 0.02% by mass or more, from the viewpoint of increasing the solid content concentration of the positive electrode paste and reducing viscosity, and preferably 0.2% by mass or less, more preferably 0.1% by mass or less, from the viewpoint of the solubility of the alkaline component (B) in organic solvents and the stability of the positive electrode paste.

[0075] ≪Content of conductive material (D) in positive electrode paste≫ From the viewpoint of conductivity of the positive electrode paste, the content of the conductive material (D) in the positive electrode paste of this disclosure is preferably 0.01% by mass or more in both the case of single-walled carbon nanotubes and multi-walled carbon nanotubes. In the case of multi-walled carbon nanotubes, it is more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, and from the viewpoint of maintaining a high energy density of the energy storage device, it is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less.

[0076] The positive electrode paste of this disclosure can be manufactured in one or more embodiments by mixing and stirring a positive electrode active material, a conductive material slurry of this disclosure, a binder (binder resin), and a solvent (additional solvent) for adjusting the solid content, etc. Other dispersants and functional materials may also 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 manufacture of the positive electrode paste of this disclosure, it is preferable to use a non-aqueous solvent as the solvent (additional solvent), and among these, it is more preferable to use NMP. A planetary mixer, bead mill, jet mill, etc. can be used for mixing and stirring, and these can also be used in combination.

[0077] The cathode paste of this disclosure may be manufactured by pre-mixing some of the components used in the production of the cathode paste and then mixing them with the remainder. Furthermore, each component may be added in multiple stages rather than all at once. This reduces the mechanical load on the stirring device.

[0078] The solid content concentration of the positive electrode paste, the amount of positive electrode active material, the amount of binder, the amount of conductive material slurry, the amount of additive components, and the amount of solvent in the positive electrode paste of this disclosure can be adjusted according to the viscosity suitable for applying the positive electrode paste to the current collector. From the viewpoint of drying properties, a smaller amount of solvent is preferable, but from the viewpoint of uniformity of the positive electrode composite layer (positive electrode coating) 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.

[0079] While a high concentration is preferable for the cathode paste of this disclosure from the viewpoint of manufacturing efficiency, a significant increase in viscosity is undesirable from the viewpoint of workability. By adding additives, it is possible to maintain a desirable viscosity range while maintaining a high concentration.

[0080] [Method for manufacturing positive electrode paste] The method for producing a positive electrode paste according to the present disclosure includes the step of mixing a conductive material, a positive electrode active material, a solvent, a binder, and the dispersant composition according to the present disclosure. The components may be mixed in any order. In one or more embodiments, the method for producing a positive electrode paste according to the present disclosure preferably includes the step of mixing the conductive material slurry, a binder, a solvent, and a positive electrode active material according to the present disclosure. The components may be mixed in any order. In another embodiment, a method is given in which the conductive material slurry, a solvent, and a binder according to the present disclosure are mixed, dispersed until homogeneous, and then the positive electrode active material is mixed and stirred until homogeneous to obtain a positive electrode paste, but the order in which these components are added is not limited to this.

[0081] Furthermore, the dispersant composition, conductive material slurry, and positive electrode paste of this disclosure may each further contain other components, to the extent that the effects of this disclosure are not impeded. Examples of other components include antioxidants, neutralizing agents, defoaming agents, preservatives, dehydrating agents, rust inhibitors, plasticizers, and binders.

[0082] [Method for manufacturing a positive electrode coating or positive electrode for an energy storage device] This disclosure relates, in one embodiment, to a method for manufacturing a positive electrode coating or a positive electrode for an energy storage device using the positive electrode paste of this disclosure. This embodiment includes coating the positive electrode paste of this disclosure onto a current collector and then drying it. In this embodiment, a preferred form of the positive electrode paste of this disclosure is as described above. In the method for manufacturing a positive electrode coating or a positive electrode for an energy storage device of this disclosure, the positive electrode coating or the positive electrode for an energy storage device can be manufactured by conventionally known methods, except for the use of the positive electrode paste of this disclosure.

[0083] A positive electrode coating or positive electrode for an energy storage device is manufactured, for example, by coating the above-mentioned positive electrode paste onto a current collector such as aluminum foil and drying it. To increase the density of the positive electrode coating, compaction can be performed using a press. A die head, Converse roll, direct roll, gravure roll, etc., can be used for coating the positive electrode paste. Drying after coating can be performed by heating, airflow, infrared irradiation, etc., individually 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 can no longer be present in the positive electrode paste after a drying time. The drying temperature is not particularly limited as long as it is below the thermal decomposition temperature of the binder resin in the environment in which drying is performed (under atmospheric pressure), but is preferably above the boiling point of the alkaline component (B), more preferably below the boiling points of the organic solvent (C) and additional solvent. Specifically, under normal pressure, 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. 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.

[0084] Examples and comparative examples of the present disclosure are shown below, but the present disclosure is not limited thereto.

[0085] 1. Measurement method for each parameter [Measurement of weight-average molecular weight of polymers] The weight-average molecular weight of the polymer was measured by GPC (Gravity Propagation). The detailed conditions are as follows: Measuring device: HLC-8320GPC (manufactured by Tosoh Corporation) Column: α-M + α-M (manufactured by Tosoh Corporation) Column temperature: 40℃ Detector: Differential refractive index Eluent: N,N-dimethylformamide (DMF) solution of 60 mmol / L H3PO4 and 50 mmol / L LiBr Flow rate: 1mL / min Standard sample used for calibration curve: Polystyrene Sample solution: DMF solution containing 0.5 wt% solid content of copolymer. Sample solution injection volume: 100 μL

[0086] [Electrolyte solubility] To confirm the solubility of the dispersant (polymer) 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 a nitrogen stream for more than 12 hours. 1 g of the obtained copolymer was added to 9 g of a mixed solvent of ethylene carbonate and diethylene carbonate (volume ratio 50 / 50) to prepare a 10% suspension. The obtained suspension was allowed to stand at 40°C for 1 hour. Then, it was filtered through a 0.5 μm PTFE filter to remove undissolved copolymer. The filtered solution was dried at 140°C under reduced pressure and under a nitrogen stream, and the mass of copolymer dissolved in the mixed solvent was measured. The solubility in the mixed solvent was calculated as the electrolyte solubility using the following formula. The obtained solubility (%) is shown in Tables 1 and 2 as the electrolyte solubility.

[0087]

number

[0088] [Viscosity measurement of conductive material slurry] The viscosity of the conductive material slurry at 25°C and 50°C was determined using an Anton Paar MCR302 rheometer equipped with a Complate CP50, at a shear rate of 10s. -1 Viscosity measurement was started, and the viscosity after 5 minutes was recorded, which is shown in Tables 1 and 2.

[0089] [Peel strength] The tests to evaluate the peel strength were conducted in accordance with JIS S0237:2009. Specifically, the positive electrode paste was applied to aluminum foil using a 200 μm applicator, dried, and a positive electrode coating was created. This coating was then applied at a density of 3.3 g / cm². 3The material was pressed to achieve the specified electrode density. Next, this coating was cut into 2cm x 7cm pieces to form the positive electrode, and its back side (the side opposite to the side in contact with the positive electrode coating on the aluminum foil) was attached to a 7cm x 15cm x 1mm stainless steel plate with double-sided tape. A 2cm wide aluminum tape (NITTO TAPE) was attached to the surface of the positive electrode coating, and it was pulled at a 180° angle at a speed of 100mm / min using a tensile strength testing machine. The resulting value was defined as the peel strength.

[0090] [Measurement of volume resistivity of positive electrode coating (positive electrode composite layer)] The positive electrode paste was dripped onto a polyester film and uniformly coated using a 100 μm applicator. This coated polyester film was dried at 100°C for 1 hour to obtain a positive electrode composite layer (positive electrode coating) with a thickness of 40 μm. The volume resistance was measured at a limit voltage of 10V using a Loresta-GP (manufactured by Mitsubishi Chemical Analytec) equipped with a PSP probe. The results are shown in Tables 1 and 2.

[0091] [Negative electrode] First, the negative electrode was manufactured. Specifically, 94.8 parts by mass of commercially available graphite for negative electrode active material, 1.7 parts by mass of acetylene black, 2 parts by mass of SBR (styrene-butadiene rubber), and 1.5 parts by mass of CMC (carboxymethylcellulose) were mixed. Subsequently, distilled water, which is used as a solvent, was added to this mixture to produce a slurry. Using a doctor blade, the slurry was applied to the surface of electrolytic copper foil to a thickness of approximately 100 μm, dried at 120°C, and then roll-pressed to manufacture the negative electrode.

[0092] [Positive electrode] The positive electrodes were manufactured by applying the positive electrode pastes 1 to 16, described later, to both sides of a 20 μm thick piece of aluminum foil, and then drying them.

[0093] [Electrolyte] An electrolyte was prepared by dissolving 1 M of LiPF6 as a solute in a non-aqueous organic solvent, which was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a 1:1 weight ratio.

[0094] [Discharge capacity maintenance rate] Coin cells were manufactured using the negative electrode, positive electrode, and electrolyte produced in this manner, and their battery characteristics (rate characteristic 5C) were measured. Specifically, the batteries were charged to 4.2V at 0.2C under the following conditions in a 25°C environment, and then discharged to 3V at 0.2C to determine the discharge capacity. Next, the 5C discharge capacity was determined in the same manner, and the 5C discharge capacity retention rate was calculated based on the 0.2C discharge capacity. The results are shown in Tables 1 and 2. (Charging conditions) 0.2C CC-CV 4.2V (0.02C Cut-off) (discharge conditions) 0.2,0.5,1,3,4,5,10C CC(3V Cut off) 5C discharge capacity retention rate (%) = (5C discharge capacity / 0.2C discharge capacity) × 100

[0095] 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 dropwise monomer solutions and dropwise initiator solutions were prepared. The dropwise monomer solutions were prepared by diluting the monomer with 1:1 NMP relative to the amount of monomer used in their preparation. Specifically, a dropwise monomer solution was prepared by adding 100 g of NMP to 99 g of AN (monomer I) and 1 g of MAAm (monomer II). For the dropwise initiator solution, we used a mixture of 1.6 g of V-65B (polymerization initiator) and 16 g of NMP (solvent).

[0096] Next, the separable flask, fitted with a reflux tubing, stirrer, thermometer, nitrogen inlet tube, and dropping funnel, was purged with nitrogen for more than one hour. Then, the monomer solution for dropping and the initiator solution for dropping were added dropwise to the flask at 70°C over 120 minutes. After the addition was complete, the flask was stirred for another hour while maintaining the temperature at 70°C. After that, the temperature in the flask was raised to 75°C and stirred for another hour. Subsequently, 80 g of NMP (solvent) was added and the solution was diluted to obtain a 35.1% by mass solution of copolymer 1. Its non-volatile content was 35.2% by mass, and the weight-average molecular weight of copolymer 1 was 36500.

[0097] Next, 89.2 g of NMP (solvent) was added to 4.3 g of a 35.1% by mass solution of copolymer 1 (solid content of copolymer 1 was 1.5 g), and then 1.5 g of 2-amino-2-methyl-1-propanol (AMP) was added to obtain a mixed solution. This mixed solution was then subjected to a heat treatment, in which it was left to stand for 12 hours while maintaining the liquid temperature at 80°C, to obtain dispersant composition 1 (indicated as "Composition 1" in Table 1, and the same applies hereinafter) with the composition shown in Table 1. Dispersant composition 1 was colored, and absorption at a wavelength of 620 nm was confirmed.

[0098] [Preparation of Dispersant Composition 2] Copolymer 2, used in the preparation of dispersant composition 2, was obtained by the following procedure. The following dropwise monomer solutions 1 to 3 and dropwise initiator solutions were prepared. Each of the dropwise monomer solutions 1 to 3 was prepared by diluting the monomer with 1:1 or 2:1 NMP relative to the amount of monomer used to prepare the dropwise monomer solution. A mixed solution consisting of 1:40g of SMA (monomer III) and 40g of NMP (solvent) for dropper application. Droplet monomer solution 2: A mixed solution consisting of 40g AN (monomer I) and 40g NMP. Droplet monomer solution 3: Mixed solution consisting of 20g MAAm (monomer II) and 40g NMP Droplet initiator solution: A mixed solution consisting of 1.6 g of V-65B (polymerization initiator) and 16 g of NMP (solvent).

[0099] Next, the separable flask, fitted with a reflux tubing, stirrer, thermometer, nitrogen inlet tube, and dropping funnel, was purged with nitrogen for more than one hour. Then, monomer solutions 1-3 and initiator solution were each added dropwise to a 70°C flask over 120 minutes. After the addition was complete, the flask was stirred for another hour while maintaining the temperature at 70°C. The temperature in the flask was then raised to 75°C and stirred for another hour. Subsequently, 49 g of NMP (solvent) was added and the solution was diluted to obtain a 35.1% by mass solution of copolymer 2. Its non-volatile content was 35.2% by mass, and the weight-average molecular weight of copolymer 2 was 38500.

[0100] Next, 89.2 g of NMP (solvent) was added to 4.3 g of a 35.1% by mass solution of copolymer 2 (solid content of copolymer 2 was 1.5 g), and then 0.75 g of 2-amino-2-methyl-1-propanol (AMP) was added to obtain a mixed solution. This mixed solution was then subjected to a heat treatment, in which it was left to stand for 12 hours while maintaining the liquid temperature at 80°C, to obtain dispersant composition 2 with the composition shown in Table 1. Dispersant resin composition 2 was colored, and absorption at a wavelength of 620 nm was confirmed.

[0101] [Preparation of dispersant compositions 3-9 and 11-15] Dispersant compositions 3-9 and 11-15 were prepared by changing the amounts of dropwise monomer solutions 1-3 and the type of alkaline component (B), respectively, as shown in Tables 1-2. The heat treatment conditions for the mixed solutions were as described in Tables 1 and 2. The concentrations of the copolymer solutions containing copolymers 1-5, 7, and 8 were all 35.1% by mass.

[0102] [Preparation of dispersant composition 10] Copolymer 6 was synthesized using the same dropper monomers as in copolymer 2, except that dropper monomer 4 was used instead of dropper monomer solution 1, with the amounts of each monomer changed as shown in Table 1, and the added NMP (solvent) changed to 39 g. Dispersant composition 10 with the composition shown in Table 1 was prepared in the same manner as dispersant composition 2, except that the type of copolymer was different. Droplet monomer solution 4: Mixed solution consisting of 20g MAA (monomer III) and 40g NMP

[0103] 3. Preparation of conductive material slurry Dispersant compositions 1 to 15, conductive material, and additional solvent (NMP) were uniformly mixed to obtain conductive material slurries 1 to 15 (in Table 1, "conductive material slurry 1" is indicated as "slurry 1," and the same applies hereafter).

[0104] Specifically, in 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 (Dynomill KDL-PILOT type 1.4, manufactured by Shinmaru Enterprises) at a flow rate of 300 g / min. The conditions of the disperser were zirconia beads with an average diameter of 0.5 mm packed at a density of 70% and a peripheral speed of 10 m / s. The crude dispersion that passed through the disperser was collected in a container, and then sent back to the disperser from that container. The temperature of the liquid coming out of the disperser before being sent back to the disperser reached approximately 50°C. This liquid circulation was carried out for 3 hours to obtain conductive material slurry 1.

[0105] 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 have the compositions shown in Tables 1 and 2.

[0106] 4. Preparation of positive electrode paste The conductive material slurries 1 to 15 shown in Tables 1 and 2, along with the positive electrode active material, binder solution, and NMP (additional solvent), were uniformly mixed to obtain a positive electrode paste. Specifically, in 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 mixed uniformly with a spatula. Then, 12 g of NCM523 (lithium nickel manganese cobalt oxide, manufactured by Nippon Chemical Corporation) was added as the positive electrode active material and mixed again with a spatula until uniform. Furthermore, the mixture was stirred for 5 minutes using a rotation-orbit mixer (AR-100, manufactured by Thinky Corporation) to obtain the positive electrode paste 1 of Example 1.

[0107] The positive electrode pastes 2-15 (Examples 2-10, Comparative Examples 1-5) were prepared in the same manner as positive electrode paste 1 in Example 1, except that conductive material slurries 2-15 were used instead of conductive material slurry 1.

[0108] [Table 1]

[0109] [Table 2]

[0110] As can be seen from Tables 1 and 2, a comparison of dispersant composition 2 (Example 2) and dispersant composition 12 (Comparative Example 2) shows that when the amount of alkali component (B) added to copolymer (A) is small and the mass ratio (B) / (A) is less than 0.2, the amount of nitrile groups that are modified into a cyclic structure is small, resulting in insufficient adsorption of the copolymer to the conductive material, poor dispersibility, and high slurry viscosity. Therefore, the volume resistivity of Comparative Example 2 was significantly higher than that of Example 2. On the other hand, in dispersant composition 14 (Comparative Example 4), the amount of alkali component (B) added to copolymer (A) was too large, and the mass ratio (B) / (A) exceeded 2.0, causing the copolymer to become insoluble and aggregate.

[0111] In the example 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 compared to Comparative Example 3, which contained copolymer 7 with a low unit I content as a dispersant. [Industrial applicability]

[0112] The dispersant composition of this disclosure can effectively disperse carbon-based conductive materials, thereby enabling lower viscosity of conductive material slurries and cathode pastes. Furthermore, using the dispersant of this disclosure in the preparation of conductive material pastes and cathode pastes can result in lower viscosity of both, contributing to lower resistance of the cathode coating.

Claims

1. The material comprises a copolymer (A), an inorganic or organic alkali component (B), and an organic solvent (C). The copolymer (A) contains, with respect to 100% by mass of the total units, 30% by mass or more and 99% by mass of unit I derived from (meth)acrylonitrile, and 1% by mass or more and 70% by mass of unit II derived from (meth)acrylamide. A dispersant composition for energy storage device electrodes, wherein the mass ratio (B) / (A) of the copolymer (A) to an inorganic or organic alkaline component (B) is 0.2 or more and 2.0 or less.

2. The dispersant composition for energy storage device electrodes according to claim 1, wherein the alkaline component (B) is an organic amine.

3. The organic amine is one or more organic amines selected from amine compound (i) and amine compound (ii) represented by the following formula (1): The dispersant composition for energy storage device electrodes according to claim 2, wherein the amine compound (ii) is at least one selected from secondary aliphatic amines, tertiary aliphatic amines, secondary aromatic amines, tertiary aromatic amines, and heterocyclic amines, and has a boiling point of 200°C or less. 【Chemistry 1】 In the above formula (1), R 1 represents a group represented by the following formula (2), and R 2 represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or -CH 2 CH 2 -OH. In the following formula (2), R 3 , R 4 , R 5 and R 6 are the same or different and each represents a hydrogen atom, a methyl group or -CH 2 OH 【Chemistry 2】

4. A carbon material-based conductive material slurry containing a dispersant composition for energy storage device electrodes according to any one of claims 1 to 3 and a carbon material-based conductive material (D).

5. The carbon material-based conductive material slurry according to claim 4, wherein the carbon material-based conductive material (D) is a carbon nanotube.

6. The carbon material-based conductive slurry according to claim 5, wherein the outer diameter of the carbon nanotubes is 10 nm or less.

7. A positive electrode paste for an energy storage device, comprising a dispersant composition for an energy storage 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.

8. A method for manufacturing a positive electrode coating, comprising applying the positive electrode paste for an energy storage device described in claim 7 to a current collector and then drying it.

9. The process includes a step of heating a mixed solution containing a copolymer (A), an inorganic or organic alkaline component (B), and an organic solvent (C). The copolymer (A) contains, with respect to 100% by mass of the total units, 30% by mass or more and 99% by mass of unit I derived from (meth)acrylonitrile, and 1% by mass or more and 70% by mass of unit II derived from (meth)acrylamide. A method for producing a dispersant composition for an energy storage device electrode, wherein the mass ratio (B) / (A) of the copolymer (A) to the inorganic or organic alkaline component (B) in the mixed solution is 0.2 or more and 2.0 or less.

Images