Leveling agent for energy storage devices

Abstract

In one embodiment, the present disclosure provides a leveling agent for energy storage devices that can improve the smoothness of an electrode coating by reducing the viscosity of the paste used for forming the electrode coating. [Solution] In one embodiment, this disclosure relates to a leveling agent for energy storage devices containing a compound represented by the following general formula (1). In the following general formula (1), R 1 represents an alkyl or alkenyl group having 6 to 14 carbon atoms, EO represents an ethyleneoxy group, PO represents a propyleneoxy group, n and m are the average number of moles added, which are between 0 and 8, and the sum of n and m is 8 or less, R 2 represents a hydrogen atom or a methyl group. R 1 -O-(EO) n (PO) m -R 2 (1)

Description

Technical Field

[0001] The present invention relates to a leveling agent for a power storage device, a leveling agent composition for a power storage device containing the same, a dispersant composition for a power storage device, a carbon material-based conductive material slurry, an electrode paste for a power storage device, and the like.

Background Art

[0002] In recent years, from the viewpoint of suppressing global warming, the development of electric vehicles that do not emit carbon dioxide has been actively carried out. Electric vehicles have problems such as a shorter driving range and longer battery charging time compared to gasoline vehicles. In order to shorten the charging time, it is necessary to increase the moving speed of electrons in the electrode. Currently, carbon material-based conductive materials such as carbon nanotubes and carbon black are used as conductive materials for electrodes. Since these carbon material-based conductive materials have strong cohesiveness, they increase the viscosity of the paste for forming the electrode coating film. After applying the paste, there is a problem that the coating film loses its smoothness and defects occur in the obtained electrode coating film before the electrode coating film is formed. Therefore, in order to improve the smoothness of the electrode coating film, it is known to use a leveling agent.

[0003] Patent Document 1 discloses a positive electrode composite material layer of a non-aqueous electrolyte secondary battery containing one or more film-forming agents selected from polyvinyl acetal, polyoxyalkylene, polyacrylic acid, polyvinyl pyrrolidone, alkylbenzene sulfonic acid, and their derivatives, for the purpose of providing a non-aqueous electrolyte secondary battery with excellent durability. Patent Document 2 discloses an amide-modified product of a copolymer of an olefin and maleic anhydride and / or its neutralized product as a dispersant for a power storage device electrode, which enables both the preparation of a conductive material slurry with good dispersibility of a carbon material-based conductive material and good solubility at room temperature in an organic solvent.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] It is known that the viscosity of the paste for forming an electrode coating film is reduced by improving the dispersibility of the carbon material-based conductive material. It is also known that the viscosity of the paste for forming an electrode coating film is reduced by highly dispersing the electrode active material in the paste.

[0006] Therefore, the present disclosure provides a leveling agent for a power storage device that can improve the smoothness of an electrode coating film by reducing the viscosity of the paste for forming the electrode coating film.

Means for Solving the Problems

[0007] In one aspect, the present disclosure relates to a leveling agent for a power storage device containing a compound represented by the following general formula (1). R 1 -O-(EO) n (PO) m -R 2 (1) In the above general formula (1), R 1 represents an alkyl group or an alkenyl group having 6 to 14 carbon atoms, EO represents an ethyleneoxy group, PO represents a propyleneoxy group, n and m are each the average number of added moles, are numbers of 0 or more and 8 or less, the sum of n and m is 8 or less, and R 2 represents a hydrogen atom or a methyl group.

[0008] In one aspect, the present disclosure relates to a leveling agent composition for a power storage device containing the leveling agent for a power storage device of the present disclosure and an organic solvent.

[0009] This disclosure relates, in one embodiment, to a dispersant composition for energy storage devices comprising the leveling agent for energy storage devices of this disclosure, a polymer dispersant, and an organic solvent.

[0010] This disclosure relates, in one embodiment, to a carbon material-based conductive material slurry containing the leveling agent for energy storage devices of this disclosure, a carbon material-based conductive material, a polymer dispersant, and an organic solvent.

[0011] This disclosure relates, in one aspect, to an electrode paste for an energy storage device comprising a leveling agent for energy storage devices, a carbon material-based conductive material, a binder resin, an electrode active material, a polymer dispersant, and an organic solvent.

[0012] This disclosure relates, in one embodiment, to a method for manufacturing an electrode for an energy storage device, which includes preparing an electrode coating using the electrode paste for energy storage devices of this disclosure.

[0013] This disclosure relates, in one embodiment, to a method for manufacturing an energy storage device, which includes incorporating an electrode for an energy storage device obtained by the method for manufacturing an electrode for an energy storage device of this disclosure. [Effects of the Invention]

[0014] In one embodiment, this disclosure provides a leveling agent for energy storage devices that enables the reduction of viscosity of electrode paste used for forming electrode coatings, thereby improving the smoothness of the electrode coatings. Furthermore, it provides a leveling agent composition for energy storage devices comprising the leveling agent and an organic solvent. In one embodiment, this disclosure includes a leveling agent for energy storage devices or a leveling agent composition for energy storage devices, thereby enabling the reduction of viscosity of electrode paste for energy storage devices used to form electrode coatings, and consequently improving the smoothness of the electrode coatings, and thus providing a dispersant composition for energy storage devices. In one aspect, the present disclosure includes a leveling agent for a power storage device of the present disclosure or a leveling agent composition for a power storage device of the present disclosure, and thus can provide a carbon material-based conductive material slurry with good dispersibility of the carbon material-based conductive material. In one aspect, the present disclosure includes a leveling agent for a power storage device of the present disclosure or a leveling agent composition for a power storage device of the present disclosure, and thus can provide an electrode paste for a power storage device that can form an electrode coating film with low viscosity and excellent smoothness. In one aspect, since an electrode coating film for a power storage device is produced using the electrode paste for a power storage device of the present disclosure, an electrode for a power storage device including an electrode coating film with excellent smoothness can be manufactured with good productivity. In one aspect, since the electrode for a power storage device of the present disclosure is incorporated, a power storage device can be manufactured with good productivity.

Embodiments for Carrying Out the Invention

[0015] The present disclosure is based on a new finding that by containing a compound represented by the following general formula (1) (hereinafter also referred to as a "leveling agent"), the viscosity of an electrode paste for a power storage device decreases, and the smoothness of an electrode coating film formed using the electrode paste for a power storage device is improved. R 1 -O-(EO) n (PO) m -R 2 (1) In the above general formula (1), R 1 represents an alkyl group or an alkenyl group having 6 to 14 carbon atoms, EO represents an ethyleneoxy group, PO represents a propyleneoxy group, n and m are each the average number of added moles, and are numbers from 0 to 8, and the sum of n and m is 8 or less, and R 2 represents a hydrogen atom or a methyl group.

[0016] Although the details of the mechanism of the effect expression of the present disclosure are not clear, it is presumed as follows. When the above leveling agent is included in an electrode paste for a power storage device containing a polymer dispersant, R 1The leveling agent adsorbs onto carbon-based conductive materials, contributing to improved dispersibility of the carbon-based conductive materials. EO and PO adsorb onto electrode active materials, contributing to improved dispersibility of the electrode active materials. Therefore, when an electrode paste for energy storage devices contains the leveling agent, the leveling agent contributes to a decrease in the viscosity of the electrode paste for energy storage devices. As a result, the viscosity-reducing effect of the leveling agent facilitates the volatilization of organic solvents during and after coating of the electrode paste for energy storage devices, improving the smoothness of the electrode coating obtained by drying the coating film. However, this disclosure shall not be interpreted as being limited to these mechanisms.

[0017] <Leveling agent for energy storage devices> This disclosure relates, in one embodiment, to a leveling agent for electrodes of energy storage devices. The leveling agent for energy storage devices of this disclosure (hereinafter sometimes abbreviated as "the leveling agent of this disclosure") includes a compound represented by the above general formula (1) (leveling agent).

[0018] [Leveling agent] In the above general formula (1), R 1 It adsorbs onto carbon-based conductive materials and contributes to improving the dispersibility of carbon-based conductive materials. 1 This plays a role in reducing viscosity in carbon material-based conductive material slurries and electrode pastes for energy storage devices. From a productivity standpoint, good solubility in organic solvents is also desirable for leveling agents. This organic solvent is used in the preparation of leveling agent compositions for energy storage devices, dispersant compositions for energy storage devices, carbon material-based conductive material slurries, and electrode pastes for energy storage devices. 1 The number of carbon atoms is 14 or less, preferably 12 or less, more preferably 10 or less, and even more preferably 8 or less, from the viewpoint of improving the solubility of the leveling agent in the organic solvent.

[0019] (EO) in the above general formula (1) n (PO) m It adsorbs onto the electrode active material and contributes to improving the dispersibility of the electrode active material. (EO) n (PO) mIt also plays a role in reducing viscosity in carbon material-based conductive material slurries and electrode pastes for energy storage devices. Of (EO) and (PO), (PO) has higher adsorption to electrode active materials. n is preferably 0, and (EO) n (PO) m (PO) m The sum of n and m is 8 or less, preferably 6 or less, more preferably 5 or less, even more preferably 4 or less, even more preferably 3 or less, and preferably 1 or more, even more preferably 2 or more, from the viewpoint of controlling the solubility of the leveling agent in organic solvents.

[0020] In the above general formula (1), R 2 From the viewpoint of controlling the solubility of the leveling agent in organic solvents, this is a methyl group or a hydrogen atom, preferably a hydrogen atom.

[0021] In one embodiment, the leveling agent of this disclosure may consist only of the compound (leveling agent) represented by the general formula (1), without containing any other leveling agents. However, it may also be a mixture of the compound (leveling agent) represented by the general formula (1) and other leveling agents, as long as the effects of the present invention are not impaired. From the viewpoint of reducing the viscosity of electrode paste for energy storage devices, the content of the compound (leveling agent) represented by the general formula (1) in the leveling agent of this disclosure is preferably substantially 100% by mass, more preferably 100% by mass.

[0022] <Leveling agent composition for energy storage devices> This disclosure relates, in one embodiment, to a leveling agent composition for electrodes of energy storage devices. The leveling agent composition for energy storage devices of this disclosure (hereinafter sometimes abbreviated as "the leveling agent composition of this disclosure") comprises the leveling agent of this disclosure and a solvent. The content of the solvent in the leveling agent composition of this disclosure is, for example, the residue after excluding the leveling agent and the optional components listed below.

[0023] [organic solvent] The solvent contained in the leveling agent composition of this disclosure is preferably an organic solvent. Specifically, the organic solvent is preferably at least one selected from the group consisting of dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), ethyl acetate, γ-butyrolactone, and ε-caprolactone, more preferably containing highly soluble N-methylpyrrolidone, and even more preferably N-methylpyrrolidone (NMP).

[0024] [Optional ingredients] The leveling agent 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, defoamers, preservatives, dehydrators, rust inhibitors, plasticizers, binders, and the like.

[0025] The leveling agent content in the leveling agent composition of this disclosure is not particularly limited, but from the viewpoint of productivity, it is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, and from the viewpoint of controlling solubility in organic solvents, it is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0026] The leveling agent composition of this disclosure can be prepared, for example, by mixing a mixture of the leveling agent and an organic solvent in a stirrer. Examples of the stirrer include rotary stirrers and high-speed stirrers.

[0027] <Dispersant composition for energy storage devices> This disclosure relates, in one embodiment, to a dispersant composition for energy storage devices. The dispersant composition for energy storage devices of this disclosure (hereinafter sometimes abbreviated as "the dispersant composition of this disclosure") comprises the leveling agent composition of this disclosure and a polymer dispersant. Therefore, the dispersant composition of this disclosure comprises the leveling agent of this disclosure, a polymer dispersant, and an organic solvent. The preferred leveling agent composition and leveling agent of this disclosure used in the preparation of the dispersant composition of this disclosure are as described above. The preferred organic solvent contained in the dispersant composition of this disclosure is the same as the organic solvent suitable for the preparation of the leveling agent composition of this disclosure. The content of the organic solvent in the dispersant composition of this disclosure is, for example, the residue after excluding the leveling agent, polymer dispersant, and the optional components listed below. The dispersant composition of this disclosure contains the leveling agent of this disclosure, which enables the reduction of viscosity of the electrode paste for energy storage devices used to form electrode coatings, and as a result, improves the smoothness of the electrode coating.

[0028] [Polymer dispersant] The polymeric dispersant included in the dispersant composition of this disclosure is not particularly limited, but examples include polyvinyl acetal, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl butyral, methylcellulose, styrene butadiene, acrylonitrile butadiene or a partially hydrogenated version thereof, acrylic copolymers, or polymeric dispersants obtained by neutralizing, as necessary, amide-modified copolymers of olefins and maleic anhydride (hereinafter, "polymeric dispersants obtained by neutralizing, as necessary, amide-modified copolymers of olefins and maleic anhydride" may be abbreviated as "polymeric dispersant A"). Among these, polyvinyl acetal and at least one of polymeric dispersant A are preferred. The degree of acetalization of the polyvinyl acetal is preferably 20 mol% to 80 mol%, and the weight-average molecular weight is preferably 10,000 to 50,000. As polymeric dispersant A, for example, the dispersant disclosed in Patent Document 2 can be used.

[0029] The polymer dispersant disclosed in Patent Document 2 includes a constituent unit represented by the following general formula (2) (hereinafter also referred to as "constituent unit I") and a constituent unit represented by the following general formula (3) (hereinafter also referred to as "constituent unit II"). When the amidation rate is less than 100 mol%, the polymer dispersant further includes a constituent unit represented by the following general formula (4) (hereinafter also referred to as "constituent unit III"). [ka]

[0030] Constituent units I, II, and III all contain a unit represented by the following general formula (5). This unit is responsible for solubility in organic solvents. M, which constitutes constituent units I and II, is a component that contributes to the dispersion of carbon material-based conductive materials in organic solvents. R, which constitutes constituent unit I. 5 It is a hydrophobic group and a component that functions as an adsorption group for carbon material-based conductive materials. At least R of constituent unit II 6 It functions as a spacer, and the long-chain alkyl group R 5 This suppresses the formation of association structures between the polymers and enhances the solubility of the polymer dispersant in organic solvents. [ka]

[0031] Let the molar fractions of structural unit I, structural unit II, and structural unit III be b, c, and a, respectively. Then b + c + a = 1. The sum b + c of the molar fraction b of structural unit I and the molar fraction c of structural unit II is also called the amidation rate or modification rate when a + b + c = 1. The molar fraction b of structural unit I is the modification rate to structural unit I, and the molar fraction c of structural unit II is the modification rate to structural unit II. The polymer dispersant A preferably satisfies the relational expressions of 0.50 < b + c ≤ 1.00 and 0.50 ≤ b / (b + c) ≤ 0.95. When the sum (b + c) of the molar fraction b and the molar fraction c exceeds 0.50, it means that the amidation rate with respect to maleic anhydride exceeds 50 mol%, and when the sum (b + c) of the molar fraction b and the molar fraction c is 1.00, it means that the amidation rate with respect to maleic anhydride is 100 mol%.

[0032] From the perspective of the adsorption property to the carbon material-based conductive material, the modification rate b is preferably 0.50 or more, more preferably 0.55 or more, still more preferably 0.60 or more, and from the perspective of improving the solubility in an organic solvent at room temperature, it is preferably 0.95 or less, more preferably 0.90 or less, still more preferably 0.85 or less, and even more preferably 0.80 or less. Incidentally, the modification rate b can be calculated from the usage amount of the amine compound having an alkyl group R with 16 or more and 22 or less carbon atoms used in the synthesis of the polymer dispersant A 5 having.

[0033] From the perspective of improving the solubility in an organic solvent at room temperature, the modification rate c is preferably 0.50 or less, more preferably 0.45 or less, still more preferably 0.40 or less, and from the perspective of improving the solubility in an organic solvent, it is preferably 0.10 or more, more preferably 0.15 or more, still more preferably 0.20 or more. Incidentally, the modification rate c can be calculated from the usage amount of the amine compound having R 6 and R 7 having.

[0034] The sum of the modification rates b and c is greater than 0.50, preferably 0.55 or higher, more preferably 0.65 or higher, even more preferably 0.70 or higher, even more preferably 0.75 or higher, and even more preferably 1.00. The polymer dispersant A may be one or more types selected from those in which the sum of the modification rates b and c is greater than 0.50 and 1.00 or less. Furthermore, the sum of denaturation rates b and c is used in the synthesis of polymer dispersant A. 5 The amount of amine compound having and R used 6 and R 7 It can be calculated from the total amount of amine compounds containing the specified compound used.

[0035] In the polymer dispersant A, from the viewpoint of adsorption to carbon material-based conductive materials, b / (b+c) is 0.50 or more, preferably 0.55 or more, more preferably 0.60 or more, and from the viewpoint of solubility at room temperature, it is 0.95 or less, preferably 0.90 or less, more preferably 0.85 or less, and even more preferably 0.80 or less. Note that b / (b+c) can be calculated from the amount of the amine compound used in the polymerization of the polymer dispersant A, as described later.

[0036] R 3 This is either a hydrogen atom or a methyl group, preferably a methyl group.

[0037] R 4 This is hydrogen, an alkyl group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group having 1 to 10 carbon atoms, or an unsubstituted alkyl group having 1 to 10 carbon atoms. The alkyl group may be linear or branched. 4 The number of carbon atoms is preferably 2 or more and 7 or less.

[0038] R 5 R is an alkyl group having 16 or more carbon atoms and 22 or less carbon atoms. 5 The number of carbon atoms is preferably 18 or more and 20 or less. 5Examples of amine compounds used to introduce these compounds include cetylamine, 1-aminoheptadecane, stearylamine, 1-aminononadecane, eicosylamine, and behenylamine.

[0039] M is hydrogen, NH4, a metal that yields a salt soluble in organic solvents, or an organic ammonium soluble in organic solvents, preferably hydrogen.

[0040] R 6 This is an alkyl group having 1 to 12 carbon atoms, a saturated hydrocarbon group having 1 to 12 carbon atoms including an alicyclic hydrocarbon group, or a saturated hydrocarbon group having 1 to 12 carbon atoms having a hydroxyl group. 6 The number of carbon atoms is R 5 From the perspective of suppressing the formation of association structures due to hydrophobic interactions between them, R 5 It is less than that. R 6 The number of carbon atoms is preferably 2 or more from the viewpoint of suppressing the formation of the associated structure, preferably 11 or less, and more preferably 10 or less from the viewpoint of availability and ease of synthesis of the dispersant. R 6 The number of hydroxyl groups is preferably 1 or more from the viewpoint of solubility, preferably 2 or less from the viewpoint of reactivity, and more preferably 1 or less. Spacer group R 6 From the viewpoint of solubility and availability, the position of the hydroxyl group is preferably at the end of the spacer group.

[0041] R 7 This refers to hydrogen, an alkyl group having 1 to 12 carbon atoms, a saturated hydrocarbon group having 1 to 12 carbon atoms including an alicyclic hydrocarbon group, or a saturated hydrocarbon group having 1 to 12 carbon atoms and a hydroxyl group. R 7 Preferably, the polymer dispersant is an alkyl group having 1 to 12 carbon atoms, a saturated hydrocarbon group having 1 to 12 carbon atoms including an alicyclic hydrocarbon group, or a saturated hydrocarbon group having 1 to 12 carbon atoms having a hydroxyl group, for the reason that it improves the solubility of the polymer dispersant in organic solvents at room temperature. R 7The number of carbon atoms is preferably 2 or more from the viewpoint of suppressing the formation of the associated structure, and preferably 11 or less, more preferably 10 or less, from the viewpoint of availability and ease of synthesis of the dispersant. R 7 The number of hydroxyl groups is preferably 1 or more from the viewpoint of solubility, preferably 2 or less from the viewpoint of reactivity, and more preferably 1 or less. Spacer group R 7 From the viewpoint of solubility and availability, the position of the hydroxyl group is preferably at the end of the spacer group.

[0042] R 6 and R 7 Examples of amine compounds used to introduce these compounds include isobutylamine, tert-butylamine, n-butylamine, isohexylamine, 2-ethylhexylamine, isooctylamine, n-octylamine, n-butylamine, isodecylamine, diethylamine, dibutylamine, dicyclohexylamine, 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.

[0043] The weight-average molecular weight of the polymer dispersant is preferably 3,000 or more, more preferably 5,000 or more, and even more preferably 10,000 or more, from the viewpoint of adsorption to carbon material-based conductive materials. Furthermore, from the viewpoint of solubility in organic solvents, dispersibility of carbon material-based conductive materials, and lower viscosity of carbon material-based conductive material slurries and electrode pastes for energy storage devices, it is preferably 100,000 or less, more preferably 70,000 or less, and even more preferably 50,000 or less. In this disclosure, the weight-average molecular weight of the polymer dispersant is the value measured by GPC (gel permeation chromatography), and the details of the measurement conditions are as shown in [Measurement of Weight-Average Molecular Weight] of the Examples.

[0044] From the viewpoint of productivity, the content of the leveling agent of the present disclosure in the dispersant composition of the present disclosure is preferably 0.1% or more, more preferably 0.5% by mass or more, and even more preferably 1.0% by mass or more, and from the viewpoint of solubility in the solvent, it is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less.

[0045] The content of the polymeric dispersant in the dispersant composition of this disclosure is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, from the viewpoint of productivity, and preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less, from the viewpoint of solubility in organic solvents at room temperature.

[0046] [Optional ingredients] 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, binders, and the like.

[0047] The dispersant composition of this disclosure can be prepared, for example, by mixing a mixture of the leveling agent composition and a polymer dispersant using a stirrer. A stirrer suitable for preparing the leveling agent composition of this disclosure can be used. The polymer dispersant may be mixed with the leveling agent composition after being dissolved in an organic solvent. The preferred organic solvent used to dissolve the polymer dispersant is the same as the organic solvent suitable for preparing the leveling agent composition.

[0048] <Carbon-based conductive material slurry> This disclosure relates, in one aspect, to a carbon material-based conductive material slurry (hereinafter also referred to as "the conductive material slurry of this disclosure") containing the leveling agent composition of this disclosure, the polymer dispersant, and a carbon material-based conductive material. Therefore, the conductive material slurry of this disclosure comprises a leveling agent, a polymer dispersant, a carbon material-based conductive material, and an organic solvent. Preferred leveling agents and leveling agent compositions of this disclosure used in the preparation of the conductive material slurry of this disclosure are as described above. Preferred organic solvents contained in the conductive material slurry of this disclosure are the same as organic solvents suitable for the preparation of the leveling agent composition and the dispersant composition of this disclosure. The content of organic solvents in the conductive material slurry of this disclosure is the remainder after excluding the leveling agent, the polymer dispersant, the carbon material-based conductive material, and the optional components listed below. The conductive material slurry of this disclosure contains the leveling agent of this disclosure, and therefore has good dispersibility of carbon material-based conductive materials and low viscosity.

[0049] [Carbon-based conductive materials] Examples of carbon material-based conductive materials include carbon nanotubes (hereinafter sometimes referred to as "CNT"), acetylene black, carbon black, graphite, graphene, etc., in one or more embodiments. Among these, at least one selected from acetylene black and CNT is preferred, and CNT is more preferred, from the viewpoint of achieving high conductivity. The carbon material-based conductive material may be one type or a combination of two or more types.

[0050] In one or more embodiments, carbon nanotubes (CNTs) that can be used as carbon material-based conductive materials have a cylindrical shape formed by winding a single sheet of graphite. Those wound in one layer are called single-walled carbon nanotubes (SWCNTs), those wound in two layers are called double-walled carbon nanotubes (DWCNTs), and those wound in three or more layers are called multi-walled carbon nanotubes (MWCNTs). Depending on the properties required for the electrode coating film formed using an electrode paste for energy storage devices containing CNTs, the conductive material slurry of this disclosure may contain single-walled, double-walled, or multi-walled CNTs, or mixtures thereof. The electrode coating film is a film-like layer obtained by coating an electrode substrate (current collector) with an electrode paste for energy storage devices and drying it.

[0051] The average diameter of the CNTs is not particularly limited, but from the viewpoint of improving the dispersibility of the CNTs, it is preferably 1 nm or more, more preferably 2 nm or more, and from the viewpoint of improving conductivity, it is preferably 100 nm or less, more preferably 50 nm or less. In this disclosure, the average diameter of the CNTs can be measured by scanning electron microscopy (SEM) or atomic force microscopy (AFM).

[0052] The average length of the CNTs is not particularly limited, but from the viewpoint of improving conductivity, it is preferably 2 μm or more, more preferably 5 μm or more, and from the viewpoint of improving dispersibility, it is preferably 1000 μm or less, more preferably 800 μm or less. In this disclosure, the average length of the CNTs can be measured by scanning electron microscope (SEM) or atomic force microscope (AFM).

[0053] (optional ingredient) The conductive slurry of this disclosure may further contain other components, to the extent that the effects of this disclosure are not impeded. Examples of other components include antioxidants, defoamers, preservatives, dehydrators, rust inhibitors, plasticizers, binders, and the like.

[0054] (Content of leveling agent in conductive material slurry) The content of the leveling agent in the conductive material slurry of the present disclosure is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, per 100 parts by mass of the carbon material-based conductive material, from the viewpoint of reducing the viscosity of the conductive material slurry, and preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the carbon material-based conductive material, from the viewpoint of controlling solubility in organic solvents.

[0055] (Content of carbon-based conductive material in conductive material slurry) The content of the carbon material-based conductive material in the conductive material slurry of this disclosure is preferably 1% by mass or more, 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 electrode paste for the energy storage device of this disclosure, which will be described in detail later, for multilayer CNTs, and preferably 10% by mass or less, more preferably 9% by mass or less, and even more preferably 8% by mass or less, from the viewpoint of making the conductive material slurry easy to handle. Similarly, for single-walled CNTs, the content is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, from the viewpoint of improving the convenience of adjusting the concentration of the electrode paste for the energy storage device of this disclosure, and preferably 2% by mass or less, and even more preferably 1% by mass or less, from the viewpoint of making the conductive material slurry easy to handle.

[0056] (Content of polymer dispersant in conductive material slurry) The content of the polymer dispersant in the conductive material slurry of this disclosure is preferably 3 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, per 100 parts by mass of the carbon material-based conductive material, from the viewpoint of improving the dispersibility of the carbon material-based conductive material, and preferably 300 parts by mass or less, more preferably 250 parts by mass or less, and even more preferably 200 parts by mass or less, per 100 parts by mass of the carbon material-based conductive material, from the viewpoint of maintaining a high energy density of the energy storage device.

[0057] (Method for manufacturing conductive material slurry) In one or more embodiments, the conductive material slurry of the present disclosure can be prepared by mixing a mixture of the leveling agent composition of the present disclosure, a polymer dispersant, a carbon material-based conductive material, an organic solvent and optional components as needed, in a mixing and dispersing machine.

[0058] Examples of the mixing and dispersing equipment include at least one selected from 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. Some components of the conductive material slurry may be mixed before mixing with the remainder, or each component may be added in multiple portions rather than all at once. The polymer dispersant may be dissolved in an organic solvent before being mixed with other components such as carbon material-based conductive materials. The state of the carbon material-based conductive material before mixing with other components may be dry or dispersed in an organic solvent.

[0059] <Electrode paste for energy storage devices> This disclosure relates, in one aspect, to an electrode paste for energy storage devices (hereinafter sometimes abbreviated as "the electrode paste of this disclosure") comprising the leveling agent composition of this disclosure, the polymer dispersant, a carbon material-based conductive material, an electrode active material, and a binder. Therefore, the electrode paste of this disclosure comprises the leveling agent of this disclosure, a polymer dispersant, a carbon material-based conductive material, an electrode active material, a binder, and an organic solvent. Preferred leveling agent compositions, leveling agents, polymer dispersants, and carbon material-based conductive materials used in the preparation of the electrode paste of the present disclosure are as described above. Preferred organic solvents contained in the electrode paste of the present disclosure are the same as those preferred for the preparation of the leveling agent compositions, dispersant compositions, and conductive material slurries of the present disclosure. The content of organic solvents in the electrode paste of the present disclosure is the remainder after excluding the leveling agents, polymer dispersants, carbon material-based conductive materials, electrode active materials, binders, and the optional components listed below. Since the electrode paste of this disclosure contains the leveling agent of this disclosure, it has good dispersibility of carbon material-based conductive materials, low viscosity, and can form an electrode coating film with good smoothness.

[0060] [Electrode active material] The electrode active material is, for example, the positive electrode active material. There are no particular restrictions on the positive electrode active material; 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 cited. Compounds having an olivine structure may be 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 M2O 2- Examples include lithium transition metal composite oxides represented by δ (where M2 is a transition metal, 0.4 ≤ x ≤ 1.2, 0 ≤ δ ≤ 0.5). The transition metal M2 may include Co, Ni, or Mn. The lithium transition metal composite oxide may further contain one or more elements selected from Al, Fe, Cr, Ti, Zn, P, and B. From the viewpoint of stability in aqueous systems, lithium transition metal composite oxides such as lithium iron phosphate and lithium manganese iron phosphate are preferred.

[0061] [binder] The binder is not particularly limited, but polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer, styrene-butadiene rubber, polyacrylonitrile, etc., can be used alone or in combination.

[0062] [Optional ingredients] The electrode paste of this disclosure may further contain other components (optional components) to the extent that the effects of this disclosure are not impeded. Examples of other components include antioxidants, defoamers, preservatives, dehydrating agents, rust inhibitors, plasticizers, and dispersants other than the polymer dispersants described above.

[0063] (Leveling agent content in electrode paste) The leveling agent content in the electrode paste of this disclosure is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, per 100 parts by mass of carbon material-based conductive material, from the viewpoint of improving the smoothness of the electrode coating film, and preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 5 parts by mass or less, from the viewpoint of suppressing the increase in resistance of the electrode coating film.

[0064] (Content of carbon-based conductive material in electrode paste) The content of the carbon material-based conductive material in the electrode paste of this disclosure is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, from the viewpoint of conductivity of the electrode coating film, and preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less, from the viewpoint of maintaining a high energy density of the energy storage device.

[0065] (Content of polymer dispersant in electrode paste) The content of the polymer dispersant in the electrode paste of this disclosure is preferably 3 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, per 100 parts by mass of the carbon material-based conductive material, from the viewpoint of suppressing an increase in the resistance of the electrode coating film, and preferably 300 parts by mass or less, more preferably 250 parts by mass or less, and even more preferably 200 parts by mass or less, from the viewpoint of high conductivity.

[0066] (Content of electrode active material in electrode paste) The content of the electrode active material in the electrode paste of this disclosure is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, from the viewpoint of energy density and stability, and preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less, from the viewpoint of coating properties on the current collector.

[0067] (Binder content in electrode paste) The binder content in the total solids of the electrode paste of this disclosure is preferably 0.05% by mass or more from the viewpoint of coating properties of the composite layer and adhesion to the current collector, and preferably 10.0% by mass or less from the viewpoint of maintaining a high energy density of the energy storage device.

[0068] The solid content concentration of the electrode paste of this disclosure, and the content of the leveling agent, polymer dispersant, electrode active material, binder, carbon material-based conductive material, organic solvent, and the above optional components in the electrode paste of this disclosure, can each be adjusted according to the viscosity suitable for applying the electrode paste to a current collector. From the viewpoint of drying properties, a small amount of organic solvent is preferable, but from the viewpoint of surface smoothness of the electrode coating film, it is preferable that the viscosity of the electrode paste is not too high. On the other hand, from the viewpoint of suppressing drying and obtaining a sufficient film thickness of the composite layer, it is preferable that the viscosity of the electrode paste is not too low.

[0069] (Method of manufacturing electrode paste) The electrode paste of the present disclosure can be prepared in one or more embodiments by mixing and stirring the dispersant composition of the present disclosure, the electrode active material, the carbon material-based conductive material, the binder, the organic solvent (additional solvent) for adjusting the solid content concentration, and any of the above optional components as needed. Some of the components used in preparing the electrode paste of this disclosure may be premixed before being mixed with the remainder. For example, the conductive material slurry of this disclosure may be prepared first, and then the electrode active material may be mixed into the conductive material slurry. Alternatively, the conductive material slurry and the electrode active material may be thoroughly stirred and mixed, and then the binder may be added. The state of the carbon material-based conductive material before mixing with other components may be dry or dispersed in an organic solvent. In addition, each component may be added in multiple portions rather than all at once. This reduces the mechanical load on the stirring device. A planetary mixer, bead mill, jet mill, etc., can be used for mixing and stirring, and these may also be used in combination.

[0070] <Method of manufacturing electrodes> This disclosure relates, in one embodiment, to a method for manufacturing an electrode using the electrode paste of this disclosure. The method for manufacturing an electrode in this embodiment includes coating the electrode paste of this disclosure onto a current collector, drying it, and obtaining an electrode coating. After drying the coating obtained by coating with the electrode paste, it may be pressed as necessary. In this embodiment, a preferred electrode paste of this disclosure is as described above. In the method for manufacturing an electrode of this disclosure, an electrode can be manufactured by conventionally known methods, except for the use of the electrode paste of this disclosure.

[0071] The positive electrode is manufactured, for example, by coating a positive electrode paste (electrode paste containing positive electrode active material) 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, Conn Reverse Roll, Direct Roll, Gravure Roll, etc., can be used to coat 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 organic 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 or vacuum), but it is preferably above the boiling point of the organic solvent. The drying temperature is preferably 60°C to 220°C, and the drying time is preferably 10 minutes to 24 hours. The positive electrode can be pressed using a roll press or the like. Alternatively, after pressing, the positive electrode may be processed to a size suitable for integration into an energy storage device, and then re-dried under the conditions described above.

[0072] <Leveling method for electrode coatings> This disclosure relates, in one embodiment, to a method for leveling an electrode coating. The electrode coating leveling method of this disclosure comprises applying an electrode paste of this disclosure, which includes a leveling agent of this disclosure, to a current collector. The electrode coating leveling method of the present disclosure further includes drying the electrode paste of the present disclosure applied to a current collector. The electrode coating leveling method of the present disclosure also includes, if necessary, pressing the dried electrode paste. The electrode paste that has been dried on the current collector and pressed if necessary forms an electrode coating. In this embodiment, a preferred electrode paste of the present disclosure is as described above. In the leveling method of the electrode coating of the present disclosure, the method of coating the electrode paste of the present disclosure onto the current collector, the drying means after coating, the drying temperature, the drying time, and the pressing method are the same as those of the electrode manufacturing method described above.

[0073] In the electrode coating leveling method of this disclosure, since the electrode paste of this disclosure contains the leveling agent of this disclosure, the viscosity of the electrode paste of this disclosure is low, and the organic solvent volatilizes easily during and after coating the electrode paste of this disclosure onto the current collector. As a result, the smoothness of the electrode coating obtained by drying the coating is improved.

[0074] <Manufacturing method for energy storage devices> This disclosure relates, in one embodiment, to a method for manufacturing an energy storage device. The method for manufacturing an energy storage device in this embodiment includes incorporating electrodes obtained by the electrode manufacturing method of this disclosure. Examples of energy storage devices in one or more embodiments include lithium-ion secondary batteries, lithium-air secondary batteries, sodium-ion batteries, sodium-sulfur secondary batteries, sodium-nickel chloride secondary batteries, organic radical batteries, zinc-air secondary batteries, and all-solid-state batteries.

[0075] The method for manufacturing an energy storage device according to the present disclosure includes steps similar to those of known methods for manufacturing energy storage devices, except that electrodes obtained by the method for manufacturing electrodes according to the present disclosure are used as electrodes for the energy storage device. The method for manufacturing an energy storage device according to the present disclosure includes, for example, the steps of overlapping two electrodes (a positive electrode and a negative electrode) via a separator and winding or laminating them into a battery shape, and placing the resulting winding or lamination into a battery container or laminate container, injecting an electrolyte into the container and sealing it. [Examples]

[0076] Examples and comparative examples of the present disclosure are shown below, but the present disclosure is not limited thereto.

[0077] 1. Measurement method for each parameter [Solubility of leveling agents in organic solvents] The solubility of the leveling agents in manufacturing examples 1-7 shown in Table 1 below in organic solvents (NMP) was confirmed under the following conditions. The leveling agent was added to an organic solvent (NMP) in a vial to a concentration of 10% by mass. The mixture was stirred at 200 rpm at room temperature for 2 hours to prepare the leveling agent composition. The solubility of the leveling agent in the organic solvent (NMP) at 25°C was evaluated by visual inspection of the obtained leveling agent composition according to the following criteria, and the results are shown in Table 2. A: The leveling agent composition is uniform and transparent, and the leveling agent has good solubility. B: The leveling agent composition is generally cloudy, and the solubility of the leveling agent is poor.

[0078] [Viscosity measurement of electrode paste] The viscosity of the electrode (positive electrode) paste (at 25°C) was measured as follows: An Anton Paar MCR302 rheometer was fitted with a CP50 cone plate, and the shear rate was set to 0.1 s. -1 from 1000s -1 After raising it up to (outbound), 1000s -1 from 0.1s -1 Return to the starting point (return trip), and the shear rate on the return trip is 1s -1 The shear viscosity was measured as the viscosity of the electrode paste. The results are shown in 3.

[0079] [Smoothness of electrode coating] The smoothness of the electrode coatings prepared using the electrode pastes of Examples 1-5 and Comparative Examples 1-5 was evaluated under the following conditions. Electrode paste was dripped onto a polyester film and coated using an applicator to a thickness of 200 μm. The polyester film coated with this electrode paste was dried at 80°C for 1 hour to obtain an electrode coating with a thickness of 150 μm. The appearance of the obtained electrode coating was visually inspected, and the smoothness of the electrode coating was evaluated according to the following criteria, and the results are shown in Table 3. A: The electrode coating is free of defects and has good smoothness. B: The electrode coating has slight defects, but the smoothness is relatively good. C: The electrode coating has numerous defects, and the overall smoothness is poor. A defect refers to an uneven surface caused by indentations of 100 μm or more.

[0080] [Measurement of weight-average molecular weight of polymer dispersants] The weight-average molecular weight of the polymer dispersant 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

[0081] 2. Leveling agent Leveling agents specified by the above general formula (1) and Table 1 were prepared. [Table 1]

[0082] 3. Preparation of Leveling Agent Composition The leveling agents 1 to 7 described above were each dissolved in NMP to obtain the leveling agent compositions of Production Examples 1 to 7. The concentration of the leveling agent in each leveling agent composition was 10% by mass. [Table 2]

[0083] 4. Polymer dispersants The following polymeric dispersants were prepared for the preparation of the dispersant composition and electrode paste. [Polymer dispersant A] In the above general formulas (2) and (3), R 3 CH3, R4 i-C5H 11 , R 5 C 18 H 37 , R 6 C4H9, R 7 A polymeric dispersant with C4H9, M being H, b+c=1.00, and b / b+c=0.70 (average molecular weight of polymerization Mw=23300). [Polymer Dispersant B] Polyvinyl acetal Esrec BL-1H (manufactured by Sekisui Chemical Co., Ltd., acetalization degree: approximately 69 mol%, molecular weight (catalog value) 2.0 × 10⁻⁶) 4 )

[0084] 5. Preparation of positive electrode paste (electrode paste) [Example 1] A dispersant composition was obtained by mixing 1.6 g of the leveling agent composition of Production Example 1 (10% by mass NMP solution) with 4 g of polymer dispersant A (30% by mass NMP solution). Next, 5.6 g of the dispersant composition was mixed with 4 g of MWCNT (FT6810, manufactured by Canno) and 0.4 g of NMP9 to obtain a crude dispersion. The obtained crude dispersion was dispersed in a paint shaker using zirconia beads as a medium for 12 hours to obtain a conductive material slurry. Next, 0.95 g of conductive material slurry, 1.714 g of NMP, and 2.375 g of PVDF (8 mass%) NMP solution (KF Polymer L#7208, manufactured by Kureha Corporation) were weighed into a 50 ml sample bottle and mixed uniformly with a spatula. Then, 14.96 g of NCM523 (lithium nickel manganese cobalt oxide 5E12D, manufactured by Beijing Dangsheng) was added as the positive electrode active material and mixed again with a spatula until uniform. The mixture was then stirred for 2 minutes using a rotation-orbit mixer (AR-100, manufactured by Thinky Corporation) to obtain the positive electrode paste of Example 1. The mass ratio of the positive electrode active material, binder (PVDF), carbon material-based conductive material (carbon nanotube), polymer dispersant A, and leveling agent was 98.415:1.25:0.25:0.075:0.01 (on a solid content basis), and the solid content (mass%) of the positive electrode paste was 76% by mass. The total solid content of the positive electrode paste is the sum of the masses of the positive electrode active material, binder, carbon material-based conductive material, polymer dispersant, and leveling agent contained in the positive electrode paste.

[0085] [Examples 2-5, Comparative Examples 2-4] The cathode pastes of Examples 2-5 and Comparative Examples 2-4 were prepared in the same manner as the cathode paste of Example 1, except that the polymer dispersant and leveling agent described in Table 3 were used.

[0086] [Comparative Example 1, Comparative Example 5] The cathode pastes of Comparative Example 1 and Comparative Example 5 were prepared in the same manner as the cathode paste of Example 1, except that they used the polymer dispersants listed in Table 3 and did not contain any leveling agents.

[0087] [Table 3]

[0088] The viscosity of the positive electrode pastes in the examples containing leveling agents 1-4 was lower than that of the positive electrode pastes in Comparative Examples 1, 3, and 5. Furthermore, the smoothness of the electrode coating film formed using the positive electrode pastes in the examples was superior to that formed using the positive electrode pastes in the comparative examples. Furthermore, in the case of Comparative Examples 2 and 4, the solubility of the leveling agent in NMP was poor, making it impossible to produce the cathode paste and electrode coating. [Industrial applicability]

[0089] The leveling agent composition of this disclosure enables the reduction of viscosity of electrode paste for energy storage devices used to form electrode coatings, thereby improving the smoothness of the electrode coatings. Using the leveling agent composition of this disclosure contributes to improving the yield of electrode coatings and, consequently, to improving the productivity of energy storage devices.

Claims

1. A leveling agent for energy storage devices, comprising a compound represented by the following general formula (1). 2 1 --(EO) n (0) m -2 2 (1) In the above general formula (1), R 1 R represents an alkyl or alkenyl group having 6 to 14 carbon atoms, EO represents an ethyleneoxy group, PO represents a propyleneoxy group, n and m are the average number of moles added, which are between 0 and 8, and the sum of n and m is 8 or less. 2 represents a hydrogen atom or a methyl group.

2. A leveling agent composition for energy storage devices comprising the leveling agent for energy storage devices described in claim 1 and an organic solvent.

3. The leveling agent composition for energy storage devices according to claim 2, wherein the content of the leveling agent is 1% by mass or more and 30% by mass or less.

4. A dispersant composition for energy storage devices, comprising the leveling agent for energy storage devices described in claim 1, a polymer dispersant, and an organic solvent.

5. The dispersant composition for energy storage devices according to claim 4, wherein the content of the leveling agent is 0.1% by mass or more and 10% by mass or less.

6. The dispersant composition for energy storage devices according to claim 4, wherein the content of the polymer dispersant is 10% by mass or more and 50% by mass or less.

7. The dispersant composition for energy storage devices according to claim 4, wherein the polymer dispersant is a vinyl polymer.

8. A carbon material-based conductive material slurry containing a leveling agent for energy storage devices as described in claim 1, a carbon material-based conductive material, a polymer dispersant, and an organic solvent.

9. The carbon material-based conductive material slurry according to claim 8, wherein the carbon material-based conductive material is one or more selected from acetylene black and carbon nanotubes.

10. An electrode paste for an energy storage device, comprising the leveling agent for an energy storage device described in claim 1, a carbon material-based conductive material, a binder resin, a positive electrode active material, a polymer dispersant, and an organic solvent.

11. A method for manufacturing an electrode for an energy storage device, comprising preparing an electrode coating film using the electrode paste for energy storage devices described in claim 10.

12. A method for manufacturing an energy storage device, comprising incorporating electrodes for an energy storage device obtained by the manufacturing method described in claim 11.

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