Dispersant for power storage device electrode

Abstract

To provide a dispersant for a power storage device electrode capable of scattering a carbon material system conductive material at a high level, and provide a manufacturing method.SOLUTION: The present invention provides a dispersant for a power storage device electrode, for scattering a carbon material system conductive material into a scattering medium in an aspect, in which a hydrocarbon group that the number of carbons is 1 or more and 10 or less is contained, and which is at least one type modified polymer of carboxymethyl cellulose and a salt of them. A replacement degree of a carboxymethyl group and their salt in the modified polymer is preferably 0.3 mol or more and 1.0 mol or less to one mol of absolute glucose unit of a cellulose.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a dispersant for electricity storage device electrodes and a method for producing the same, as well as a conductive material composition for electrodes or an electrode coating material composition containing the dispersant for electricity storage device electrodes. [Background technology]

[0002] Carbonaceous conductive materials such as carbon nanotubes and carbon black are used as conductive materials for the electrodes of lithium ion secondary batteries. These carbonaceous conductive materials have strong cohesive properties, making it difficult to disperse them uniformly in water. Because of the poor dispersibility of carbonaceous conductive materials, it is difficult to reduce the electrode resistance.

[0003] It is known that carboxymethyl cellulose (including a salt) is used as a dispersant in order to improve the dispersibility of carbon material-based conductive materials such as carbon nanotubes and carbon black in an aqueous system.

[0004] For example, Patent Document 1 discloses a single-walled carbon nanotube dispersion liquid using carboxymethylcellulose and / or a salt thereof having an etherification degree of 0.65 to 0.85 and a weight average molecular weight of 120,000 to 250,000, and a method for producing the same. Patent Document 2 discloses a carbon nanotube dispersion using carboxymethylcellulose having an etherification degree of 0.5 to 1.2 and / or a salt thereof, and an electrode composition for a non-aqueous electrolyte secondary battery containing the dispersion. Patent Document 3 discloses carboxymethylcellulose and / or a salt thereof having an amount of cations derived from alkali metal elements of 40,000 to 70,000 ppm and a degree of carboxymethyl substitution of 0.45 to 1.4. Patent Document 4 discloses an electrode-forming material containing a reaction product of a carboxyl group-containing polysaccharide and an epoxy compound, and a method for producing the same. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7194860 [Patent Document 2] International Publication No. 2022 / 070810 [Patent Document 3] Patent No. 2022-182384 [Patent Document 4] International Publication No. 2016 / 039271 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Documents 1 and 2 disclose carboxymethylcellulose and / or a salt thereof having a specified degree of carboxymethyl ether substitution as a dispersant for carbon nanotubes, but there is a demand for a dispersant that can further enhance dispersibility. Patent Documents 3 and 4 disclose that carboxymethyl cellulose and / or a salt thereof is used as a binder. However, these documents make no mention of improving the dispersibility of the carbon material-based conductive material.

[0007] The present disclosure has an object to provide a dispersant for electricity storage device electrodes that enables a carbon material-based conductive material to be highly dispersed, a method for producing the same, and a conductive material composition for electrodes or an electrode coating material composition that contains the dispersant for electricity storage device electrodes. [Means for solving the problem]

[0008] In one aspect, the present disclosure relates to a dispersant for an electrode of an electricity storage device for dispersing a carbon material-based conductive material in a dispersion medium, the dispersant for an electrode of an electricity storage device being at least one modified polymer selected from carboxymethyl cellulose and salts thereof, having a hydrocarbon group having 1 to 10 carbon atoms.

[0009] In one aspect, the present disclosure relates to a conductive material composition for electrodes, comprising the dispersant for an electrical storage device electrode of the present disclosure, a carbon material-based conductive material, and an aqueous solvent.

[0010] In one aspect, the present disclosure relates to an electrode coating material composition comprising the dispersant for an electricity storage device electrode of the present disclosure, a carbon material-based conductive material, an active material, a binder, and an aqueous solvent.

[0011] In one aspect, the present disclosure relates to a method for producing a dispersant for an electrode of an electricity storage device according to the present disclosure, the method including a step of reacting a compound having a hydrocarbon group having from 1 to 10 carbon atoms with at least one polymer selected from carboxymethyl cellulose and salts thereof to obtain the modified polymer.

[0012] In one aspect, the present disclosure relates to a method for producing a conductive material composition for electrodes, the method including a step of mixing and dispersing a dispersant for an electrical storage device electrode of the present disclosure, a carbon material-based conductive material, and an aqueous solvent. Effect of the Invention

[0013] In one aspect, the present disclosure can provide a dispersant for an electrode of an electricity storage device that can prepare an electrode conductive material composition having good dispersibility for a carbon material-based conductive material, and a method for producing the same. In one aspect, the present disclosure can provide a conductive material composition for electrodes, which makes it possible to prepare an electrode coating material composition capable of forming an electrode coating with a low resistance value. In one aspect, the present disclosure can provide an electrode coating material composition that can form an electrode coating having a low resistance value. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present disclosure is based on the new finding that the dispersibility of a carbon material-based conductive material in a dispersion medium is significantly improved by introducing a hydrocarbon group having a carbon number of 1 to 10 into at least one polymer of carboxymethyl cellulose and a salt thereof.

[0015] Although the details of the mechanism by which the effects of the present disclosure are manifested are not clear, it is presumed as follows.

[0016] Axial hydrogen of the cellulose structure (homopolysaccharide in which D-glucopyranose is glycosidic bonded by β(1→4)) interacts with the surface of the carbon material-based conductive material. Therefore, the cellulose structure has the property of adsorbing to the surface of the carbon material-based conductive material. The carboxy group (-COOH) or its salt constituting carboxymethylcellulose (CMC) or its salt expresses electrostatic repulsion and contributes to the dispersibility of the carbon material-based conductive material. In the dispersant for the electrode of the electric storage device of the present disclosure (hereinafter sometimes abbreviated as "dispersant of the present disclosure"), a hydrocarbon group having a carbon number of 1 to 10 is introduced into at least one polymer of CMC and its salt, so that the adsorption of the dispersant to the carbon material-based conductive material is improved compared to the polymer in which the hydrocarbon group is not introduced, and as a result, it is presumed that the dispersibility of the carbon material-based conductive material in the dispersion medium is significantly improved. However, the present disclosure is not interpreted as being limited to these mechanisms.

[0017] [Dispersants for power storage device electrodes] The dispersant of the present disclosure is a dispersant for dispersing a carbon material-based conductive material in a dispersion medium, and is at least one modified polymer selected from carboxymethyl cellulose (CMC) and salts thereof having a hydrocarbon group having 1 to 10 carbon atoms (hereinafter sometimes referred to as the "modified polymer of the present disclosure").

[0018] The dispersant of the present disclosure has a structure in which, for example, hydrogen atoms of some of the hydroxyl groups among the multiple hydroxyl groups contained in cellulose are substituted with at least one group selected from carboxymethyl groups and salts thereof (hereinafter, sometimes referred to as "carboxymethyl groups and / or salts thereof"), and hydrogen atoms of other hydroxyl groups among the multiple hydroxyl groups contained in cellulose are substituted with organic groups containing a hydrocarbon group having 1 to 10 carbon atoms. The modified polymer of the present disclosure may be only one of CMC and its salt having a hydrocarbon group having 1 to 10 carbon atoms, or may be a mixture of these. From the viewpoint of high dispersibility of the carbon material-based conductive material, the modified polymer of the present disclosure preferably contains a salt of CMC having a hydrocarbon group having 1 to 10 carbon atoms, more preferably is substantially a salt of CMC having a hydrocarbon group having 1 to 10 carbon atoms, and even more preferably is composed only of a salt of CMC having a hydrocarbon group having 1 to 10 carbon atoms.

[0019] X in the carboxymethyl group and / or its salt (—CHCOOX) constituting the modified polymer of the present disclosure is preferably at least one of a hydrogen atom, an alkali metal such as Na or K, an alkaline earth metal such as Ca or Mg, and a cation such as an ammonium salt (NH). Among these, from the viewpoint of high dispersibility of the carbon material-based conductive material, X is more preferably at least one selected from Na and K.

[0020] The degree of substitution of the carboxymethyl group and its salt in the modified polymer of the present disclosure is preferably 0.3 mol or more per mol of anhydrous glucose unit from the viewpoint of high dispersibility of the carbon material-based conductive material, and from the same viewpoint, is preferably 1.6 mol or less, more preferably 1.0 mol or less, and even more preferably 0.8 mol or less. The modified polymer of the present disclosure may be one type of modified polymer having the degree of substitution within the above-mentioned preferred range, or may be a mixture of two or more types of modified polymers having different degrees of substitution.

[0021] The degree of substitution of the carboxymethyl group and its salts is the sum of the degree of substitution of the carboxymethyl group and the degree of substitution of the salt (degree of etherification per anhydroglucose unit), and in the present disclosure, the degree of substitution of the carboxymethyl group and its salts is a value measured by the following method. In a 50 ml sample tube, take 1.0 g of the modified polymer or unmodified polymer of the present disclosure, add 10 ml of 1N HCl, and shake. Collect the solid matter by filtration, wash three times with 100 g of 80% aqueous methanol solution, and then wash twice with 100 g of methanol. Dry at 105°C under reduced pressure for 3 hours to obtain a dried polymer. 0.2 g of the dried polymer was placed in a 50 ml sample tube, 25 ml of 0.1 N NaOH was added, and the mixture was shaken to dissolve the solids. Excess NaOH in the resulting solution was back-titrated with 0.1 N HCl to quantify the amount of carboxyl groups. The titration was performed by potentiometric titration, and A was calculated from the amount of HCl required to reach an inflection point near pH 7 using the following formula (1). The value of A was then used to calculate the degree of substitution using the following formula (2). [Formula (1)] A = (100 x F1 - (HCl titration amount (ml)) x F2) x 10 / (weight of dried polymer collected) In the formula (1), F1 is the potency of 0.1N NaOH and F2 is the potency of 0.1N HCl. [Formula (2)] (degree of substitution)=0.162A / (1-0.058A)

[0022] (hydrocarbon group) The number of carbon atoms in the hydrocarbon group is 1 or more and 10 or less from the viewpoint of high dispersibility and foam suppression. When the number of carbon atoms in the hydrocarbon group exceeds 10, it is presumed that the intramolecular and intermolecular association of the modified polymer is promoted, so that the adsorption of the modified polymer to the surface of the carbon material-based conductive material is reduced, and the dispersibility of the carbon material-based conductive material is reduced. In addition, when the number of carbon atoms in the hydrocarbon group exceeds 10, it is presumed that the foamability of the electrode conductive material composition containing the modified polymer, the carbon material-based conductive material, and water is increased, and defects are likely to occur in the electrode coating film. In the modified polymer of the present disclosure, the number of carbon atoms in the hydrocarbon group is preferably 4 or more, more preferably 6 or more from the viewpoint of high dispersibility and foam suppression, and from the same viewpoint, it is preferably 8 or less.

[0023] From the viewpoint of high dispersibility and foaming suppression, the hydrocarbon group is preferably a monovalent substituted hydrocarbon group having 1 to 10 carbon atoms, and more preferably at least one alkyl group having 1 to 10 carbon atoms. From the viewpoint of high dispersibility and foaming suppression, the hydrocarbon group preferably does not contain polyoxyalkylene such as a polyoxyethylene chain. More specifically, the hydrocarbon group is preferably a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, a 2-ethylhexyl group, or the like. From the viewpoint of high dispersibility and foaming suppression, the hydrocarbon group is preferably at least one of a butyl group and a 2-ethylhexyl group.

[0024] The modified polymer of the present disclosure may have only one type of carbon atom in the hydrocarbon group (having 1 to 10 carbon atoms), but may contain two or more types of the hydrocarbon group (having 1 to 10 carbon atoms) having different carbon atoms. The modified polymer of the present disclosure may also be a mixture of two or more types of modified polymers having different carbon atoms in the hydrocarbon group (having 1 to 10 carbon atoms). The modified polymer of the present disclosure may also be a mixture of two or more types of modified polymers having different introduction rates of the hydrocarbon group (having 1 to 10 carbon atoms). The dispersant of the present disclosure may contain a small amount of a hydrocarbon group having a carbon atom number exceeding 10, as long as the effect of the present disclosure is not impaired.

[0025] An example of the modified polymer that is the dispersant of the present disclosure is a hydrocarbon group-containing polymer that includes a constitutional unit represented by the following formula (1) and a constitutional unit represented by the following formula (2). [ka]

[0026] However, R in the above formula (1) 1 At least one of the R 1 are the same or different and each is CHCOOX or H. R in the above formula (2) 2 At least one of R is CH2CH(OH)CH2OY, and the remaining R 2 are the same or different and are CH2COOX, CH2CH(OH)CH2OY, or H. X is a hydrogen atom, an alkali metal, an alkaline earth metal, or an ammonium salt. Y is a hydrocarbon group having 1 to 10 carbon atoms.

[0027] In the above formulas (1) and (2), the above Y corresponds to the above-mentioned hydrocarbon group having a carbon number of 1 to 10. The preferred form of the hydrocarbon group (carbon number, structure, etc.) is as described above.

[0028] In the above formula (1) and formula (2), the above CH2COOX corresponds to the above-mentioned carboxymethyl group and / or its salt. The preferred form (substitution degree, etc.) of the carboxymethyl group and / or its salt is as described above.

[0029] Dispersants of the present disclosure may contain unsubstituted anhydroglucose units as building blocks.

[0030] (Method of producing the dispersant of the present disclosure) Next, an example of a method for producing the dispersant of the present disclosure will be described. The dispersant of the present disclosure can be obtained, for example, by introducing a carboxymethyl group and / or a salt thereof, and an organic group containing a hydrocarbon group having 1 to 10 carbon atoms into cellulose.

[0031] The order of introduction of the carboxymethyl group and / or its salt and the organic group containing a hydrocarbon group having a carbon number of 1 to 10 into the cellulose does not matter, but from the viewpoint of ease of control of the solubility of the dispersant in water, it is preferable to introduce the organic group after the introduction of the carboxymethyl group and / or its salt. Also, instead of introducing the carboxymethyl group and / or its salt, at least one polymer of commercially available carboxymethyl cellulose (CMC) and its salt may be used.

[0032] The method for producing a dispersant of the present disclosure, in one embodiment, comprises reacting a compound containing a hydrocarbon group having a carbon number of 1 to 10 with at least one polymer selected from carboxymethyl cellulose and its salts to obtain a hydrocarbon group-containing polymer as the modified polymer of the present disclosure. The method for producing a dispersant of the present disclosure, in one embodiment, comprises reacting a compound containing a hydrocarbon group having a carbon number of 1 to 10 with at least one polymer selected from carboxymethyl cellulose and its salts to substitute and introduce an organic group containing a hydrocarbon group having a carbon number of 1 to 10 and derived from the compound containing a hydrocarbon group having a carbon number of 1 to 10 into the polymer.

[0033] The compound is preferably alkyl glycidyl ether or alkyl oxirane. The amount of the compound used in the reaction is preferably 0.1 mol or more, more preferably 0.3 mol or more, even more preferably 0.4 mol or more, and is preferably 1.5 mol or less, more preferably 1.2 mol or less, even more preferably 1.0 mol or less, relative to 1 mol of anhydroglucose unit of cellulose skeleton, from the viewpoint of high dispersibility and foam suppression. The theoretical introduction rate here refers to the molar amount of the organic groups per mole of anhydrous glucose unit when all of the organic groups contained in the compound charged to the reaction solution are replaced with hydrogen atoms of multiple hydroxyl groups contained in cellulose.

[0034] The reaction can be carried out in an aqueous solvent, which is preferable from the viewpoint of ease of preparation of an aqueous conductive material composition. From the viewpoint of increasing the concentration of a reaction liquid containing a compound containing a hydrocarbon group having a carbon number of 1 to 10 and at least one polymer selected from carboxymethyl cellulose and its salts, it is preferable to use a mixed solvent of water and an aqueous solvent as the aqueous solvent. As the aqueous solvent, alcohol, acetone, N-methylpyrrolidone, dimethylformamide, dimethylsulfoxide, etc. can be used, and from the viewpoint of the solubility of the polymer, alcohol is preferable. As the alcohol, methanol, ethanol, 2-propanol, 2-butanol, t-butanol, etc. are preferable. From the viewpoint of low viscosity and ease of handling, 2-propanol is particularly preferable. The ratio of the aqueous solvent in the mixed solvent 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 increasing the concentration of the reaction liquid.

[0035] The reaction can be carried out without a catalyst or with a catalyst. From the viewpoint of increasing the reaction rate of the reaction, the reaction is preferably carried out in the presence of an alkali hydroxide. Specifically, it is preferable to prepare a dispersion in which at least one polymer selected from carboxymethyl cellulose and its salts and an alkali hydroxide are dispersed in an aqueous solvent, and after the temperature of the dispersion reaches a value within a temperature range of preferably 30°C to 50°C, the compound containing a hydrocarbon group having a carbon number of 1 to 10 is added to the dispersion. The alkali hydroxide is preferably at least one selected from the group consisting of LiOH, NaOH and KOH. The amount of the alkali hydroxide used is preferably within a range of 0.1 to 1.0 molar equivalent, more preferably 0.2 to 0.9 molar equivalent, and further preferably 0.4 to 0.8 molar equivalent, relative to 1 mole of anhydrous glucose unit.

[0036] Next, the reaction liquid is stirred while being heated to a predetermined temperature, and the resulting reaction product (solid matter) is collected by filtration, washed, and then dried, thereby obtaining the dispersant (hydrocarbon-modified CMC) of the present disclosure. It is preferable to perform washing multiple times. The predetermined temperature is preferably 60°C or higher and 100°C or lower, and the preferred stirring time is 3 hours or higher and 24 hours or lower. The collection by filtration can be performed, for example, by filtering with filter paper. As the washing liquid for the washing, a mixture of water and an aqueous solvent, or a mixture of an aqueous solvent and a hydrophobic solvent can be used. As the aqueous solvent contained in the mixture of water and an aqueous solvent, methanol, ethanol, or 2-propanol is preferable, and 2-propanol is particularly preferable. As the aqueous solvent contained in the mixture of an aqueous solvent and a hydrophobic solvent, 2-propanol is preferable, and n-hexane is preferable as the hydrophobic solvent. It is preferable to perform washing multiple times. Drying is preferably performed by heating under vacuum (reduced pressure), for example, at a pressure of -100 kPa or more and -10 kPa or less and at a temperature of 50°C or more and 120°C or less.

[0037] The amount of hydrocarbon groups introduced into the resulting hydrocarbon group-containing polymer (modified polymer) can be analyzed by the method described by Ho and Klosiewicz in Anal. Chem 52, 913 (1980).

[0038] [Dispersant composition] The dispersant of the present disclosure may be supplied to the market as a solid, or may be supplied to the market as a dispersant composition in which the dispersant of the present disclosure is dissolved in an aqueous medium.

[0039] (Water-based solvent) The dispersant composition of the present disclosure contains an aqueous solvent as a solvent. The aqueous solvent is preferably water, specifically, preferably ion-exchanged water, distilled water or purified water. The aqueous solvent may contain a small amount of aqueous solvent. Preferred aqueous media are 2-propanol, ethanol, 2-butanol, t-butanol, acetone, N-methylpyrrolidone, etc. The content of the aqueous solvent in the dispersant composition of the present disclosure is the remainder excluding the dispersant of the present disclosure and the optional components described below.

[0040] (optional ingredient) The dispersant composition of the present disclosure may further contain other components to the extent that the effects of the present disclosure are not hindered. Examples of other components include antioxidants, antifoaming agents, preservatives, dehydrating agents, rust inhibitors, plasticizers, binders, etc.

[0041] The content of the dispersant of the present disclosure in the dispersant composition of the present disclosure is not particularly limited, but from the viewpoint of productivity in the step of preparing the dispersant into a dispersant composition and in the step of using the dispersant composition, it is preferably 0.5% by mass or more, more preferably 1% by mass or more, and from the viewpoint of solubility in aqueous solvents, it is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0042] [Conductive material composition] In one aspect, the present disclosure relates to a conductive material composition for an electrode of a power storage device. The conductive material composition of the present disclosure is an aqueous conductive material composition containing the dispersant of the present disclosure, a carbonaceous conductive material, and an aqueous solvent. The conductive material composition of the present disclosure contains the dispersant of the present disclosure, and therefore has good dispersibility of the carbonaceous conductive material. If the conductive material composition of the present disclosure is used to prepare an electrode coating material composition, it is possible to form an electrode coating film with low resistance. The preferred form of the dispersant of the present disclosure in this aspect is as described above.

[0043] (Carbon conductive material) As the carbonaceous conductive material contained in the conductive material composition, preferably, fibrous carbon, carbon black, acetylene black, etc. are used. From the viewpoint of electrical conductivity, fibrous carbon materials are particularly preferred. As the fibrous carbon materials, carbon nanotubes (hereinafter sometimes referred to as "CNT"), carbon nanofibers, etc. are preferred, and CNTs are particularly preferred.

[0044] CNTs include single-walled CNTs (SWCNTs) that have a single-wall structure and multi-walled CNTs (MWCNTs; multi-walled carbon nanotubes) that have a multi-layer structure. For the preparation of the conductive material composition of the present disclosure, single-walled CNTs, multi-walled CNTs, or mixtures thereof can be used. In general, single-walled CNTs are longer and more flexible than multi-walled CNTs, and therefore are more effective at improving conductivity, and are particularly preferred.

[0045] The average diameter of CNTs that can be used as a carbon material-based conductive material is not particularly limited, but from the viewpoint of improving the dispersibility of CNTs, it is preferably 1 nm or more, more preferably 2 nm or more, and from the viewpoint of improving the electrical conductivity, it is preferably 100 nm or less, more preferably 50 nm or less. In the present disclosure, the average diameter of CNTs can be measured by a scanning electron microscope (SEM) or an atomic force microscope (AFM).

[0046] The average length of the CNTs that can be used as the carbon material-based conductive material is not particularly limited, but from the viewpoint of improving the electrical conductivity, it is preferably 2 μm or more, more preferably 5 μm or more, and from the viewpoint of improving the dispersibility, it is preferably 500 μm or less, more preferably 300 μm or less. In the present disclosure, the average length of the CNTs can be measured by a scanning electron microscope (SEM) or an atomic force microscope (AFM).

[0047] (Content of Carbon-Based Conductive Material in Conductive Material Composition) The content of the carbon material-based conductive material in the conductive material composition of the present disclosure is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more for multi-walled CNTs from the viewpoint of improving the convenience of adjusting the concentration of the electrode coating material composition described in detail later, and is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less from the viewpoint of making the conductive material composition have an easy-to-handle viscosity. Similarly, the content of the carbon material-based conductive material in the single-walled CNTs is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, and is preferably 2% by mass or less, more preferably 1% by mass or less from the viewpoint of making the conductive material composition have an easy-to-handle viscosity.

[0048] (Content of the dispersant of the present disclosure in the conductive material composition) The content of the dispersant of the present disclosure in the conductive material composition of the present disclosure is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more for multi-walled CNTs relative to 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 is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 30 parts by mass or less for 100 parts by mass of the carbon material-based conductive material from the viewpoint of maintaining a high energy density of the electricity storage device. For single-walled CNTs, the content is preferably 40 parts by mass or more, more preferably 70 parts by mass or more, and even more preferably 100 parts by mass or more, and is 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 for 100 parts by mass of the carbon material-based conductive material from the viewpoint of maintaining a high energy density of the electricity storage device.

[0049] (Water-based solvent) The conductive material composition of the present disclosure contains an aqueous solvent as a dispersion medium. The aqueous solvent is preferably the same as the aqueous solvent contained in the dispersant composition described above. The content of the aqueous solvent in the conductive material composition of the present disclosure is the remainder excluding the dispersant of the present disclosure and the optional components described below.

[0050] (optional ingredient) The conductive material composition of the present disclosure may further contain other components within the scope of the present disclosure, such as antioxidants, antifoaming agents, preservatives, dehydrating agents, rust inhibitors, plasticizers, binders, etc.

[0051] (Method of manufacturing conductive composition) In one or more embodiments, the conductive material composition of the present disclosure can be prepared by mixing a mixture of the dispersant composition of the present disclosure, the carbon material-based conductive material, the aqueous solvent, and any optional components that are added as needed, in a mixer / disperser. In one or more embodiments, the conductive material composition of the present disclosure may also be prepared by mixing a mixture of the dispersant composition of the present disclosure, the carbon material-based conductive material, the aqueous solvent that is added as needed, and any optional components, in a mixer / disperser.

[0052] The mixing and dispersing machine may be at least one selected from, for example, an ultrasonic homogenizer, a vibration mill, a jet mill, a ball mill, a bead mill, a sand mill, a roll mill, a homogenizer, a high-pressure homogenizer, an ultrasonic device, an attritor, a dissolver, and a paint shaker. A part of the components of the conductive material composition may be mixed and then mixed with the rest, or each component may be added in a plurality of times rather than being added all at once. The dispersant of the present disclosure may be dissolved in water to form a dispersant composition and then mixed with other components such as a carbon material-based conductive material. The state of the carbon material-based conductive material before mixing with other components may be a dry state or may be a state dispersed in water or an aqueous solvent.

[0053] [Electrode coating material composition] In one aspect, the present disclosure relates to an electrode coating material composition comprising the dispersant of the present disclosure, a carbonaceous conductive material, an electrode active material, a binder, and an aqueous solvent. Preferred forms of the dispersant and the carbonaceous conductive material of the present disclosure in this aspect are as described above. The aqueous solvent in this aspect is preferably the same as the aqueous solvent contained in the dispersant composition and the conductive material composition described above.

[0054] Since the electrode coating material composition of the present disclosure contains the dispersant of the present disclosure, it is possible to form an electrode coating having a low resistance value.

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

[0056] As the negative electrode active material, carbon-based active materials such as natural graphite, artificial graphite, hard carbon, and soft carbon, metals capable of forming an alloy with lithium such as tin, zinc, aluminum, magnesium, titanium, and antimony, silicon-based compounds, and oxides thereof are used. From the viewpoint of electrode capacity, silicon-based compounds are preferred, and SiO is particularly preferred.

[0057] The content of the electrode active material in the electrode coating material composition of the present disclosure is, from the viewpoints of energy density and stability, preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more, and from the viewpoint of coatability onto a current collector, preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0058] The content of the electrode active material in the total solid content of the electrode coating material composition of the present disclosure may be the same as that in the total solid content of a conventionally known electrode, and is preferably 90.0 mass% or more in order to maintain a high energy density of the energy storage device, and is preferably 99.9 mass% or less in order to ensure the electrical conductivity and coating properties of the composite layer.

[0059] (binder) As the binder (binding agent), an emulsion of styrene-butadiene (SBR) resin or the like, crosslinked polyacrylic acid, polyacrylamide, water-soluble polymers such as carboxymethyl cellulose, or the like can be used alone or in combination.

[0060] The electrode coating material composition of the present disclosure may further contain other components (optional components) to the extent that the effects of the present disclosure are not hindered. Examples of other components include antioxidants, antifoaming agents, preservatives, dehydrating agents, rust inhibitors, plasticizers, dispersants other than the dispersants of the present disclosure, and the like.

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

[0062] (Content of the dispersant of the present disclosure in the electrode coating material composition) The content of the dispersant of the present disclosure in the electrode coating material composition of the present disclosure is, from the viewpoint of coating resistance, preferably 40 parts by mass or more, more preferably 100 parts by mass or more, and even more preferably 150 parts by mass or more, relative to 100 parts by mass of the carbon material-based conductive material, and from the viewpoint of high conductivity, it is 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.

[0063] (Binder Content in Electrode Coating Material Composition) The binder content in the total solid content of the electrode coating material composition of the present disclosure is preferably 0.05 mass % or more from the viewpoints of the coating properties of the composite layer and the binding property with the current collector, and is preferably 10.0 mass % or less from the viewpoint of maintaining a high energy density of the electricity storage device.

[0064] The solids concentration of the electrode coating material composition of the present disclosure, and the contents of the dispersant, electrode active material, binder, carbon material-based conductive material, aqueous solvent, and the above-mentioned optional components in the electrode coating material composition of the present disclosure can each be adjusted according to the viscosity suitable for applying the electrode coating material composition to a current collector. From the viewpoint of drying, a small amount of aqueous solvent is preferable, but from the viewpoint of uniformity of the composite layer (electrode coating) and surface smoothness, it is preferable that the viscosity of the electrode coating material composition is not too high. On the other hand, from the viewpoint of inhibiting drying and obtaining a sufficient film thickness of the composite layer, it is preferable that the viscosity of the electrode coating material composition is not too low.

[0065] (Method of manufacturing electrode coating material composition) In one or a plurality of embodiments, the electrode coating material composition of the present disclosure can be prepared by mixing and stirring the dispersant of the present disclosure, the electrode active material, the carbon material-based conductive material, the binder, an aqueous solvent (additional solvent) for adjusting the solids concentration, etc., and, as necessary, the optional components described above. A part of all the components used in preparing the electrode coating material composition may be premixed and then mixed with the remainder. For example, the conductive material composition of the present disclosure may be prepared, and then the electrode active material may be mixed with the conductive material composition. The conductive material composition and the electrode active material may be thoroughly stirred and mixed, and then a binder may be added thereto. The conductive material composition and the electrode active material may be thoroughly stirred and mixed, and then an additional conductive material composition of the present disclosure may be added thereto as necessary, and then these may be thoroughly mixed and stirred, and then a binder may be added. The state of the carbon material-based conductive material before mixing with other components may be in a dry state or in a state dispersed in an aqueous solvent such as water. In addition, each component may be added in multiple portions rather than in a single amount. This can reduce the mechanical load on the stirring device. In addition, a dispersant other than the dispersant of the present disclosure, a functional material, etc. may be added. A planetary mixer, a bead mill, a jet mill, etc. may be used for mixing and stirring these, and these may also be used in combination.

[0066] <Method of manufacturing electrode coating film> In one aspect, the present disclosure relates to a method for producing an electrode coating film using the electrode coating film material composition of the present disclosure. The production method of this aspect includes applying the electrode coating film material composition of the present disclosure to a current collector, followed by drying and pressing. In this aspect, the preferred form of the electrode coating film material composition of the present disclosure is as described above. In the production method of an electrode coating film of the present disclosure, the electrode coating film can be produced by a conventionally known method, except for using the electrode coating film material composition of the present disclosure. EXAMPLES

[0067] Examples and comparative examples of the present disclosure will be shown below, but the present disclosure is not limited thereto.

[0068] 1.Measuring methods for each parameter [Viscosity measurement of conductive composition] The viscosity (25° C.) of the conductive material composition was measured as follows. The sample was loaded between the stage and the parallel plate PP50 of a rheometer MCR302 (manufactured by Anton Paar) and subjected to a shear rate of 0.01 s at 25 °C. -1 From 1000s -1 (outbound), followed by 1000s -1 From 0.01s -1 The shear stress was measured while descending to 10 s (returning). -1 The apparent viscosity at this time is shown as the viscosity of the conductive material composition.

[0069] [Measurement of resistance value of electrode coating film] The conductive material composition was dropped onto a film (Cosmoshine 100A4360, manufactured by Panac Corporation) and uniformly coated with a 100 μm applicator. The resulting coating film was dried for 10 minutes on a hot plate at 80° C. A 20 mm×15 mm coating film was cut out from the dried coating film, the coating film thickness was measured with a micrometer, and the coating film volume resistance was measured using Loresta MCP-T610 (Mitsubishi Chemical Analytech).

[0070] [Evaluation of foam suppression] During the dispersion process using a Disperser and during the dispersion process using a cavitation mill, which will be described later, foaming was observed visually, and the foam-suppressing ability was evaluated according to the following evaluation criteria. (Evaluation Criteria) A: No foaming was observed during both dispersion processes. B: Foaming was observed during either dispersion process.

[0071] 2. Synthesis of dispersants for energy storage device electrodes [Synthesis Example 1] 103.6g of ion-exchanged water and 243.0g of 2-propanol were charged into a 500ml four-neck glass separable flask. Next, while stirring, 27.0g of carboxymethylcellulose Na salt (Sunrose F20LC, Nippon Paper Industries Co., Ltd., substitution degree 0.6 mol) was charged into the separable flask, and the mixture was heated to 40°C. After reaching 40°C, 8.46g of 48% NaOH aqueous solution was added to the mixture, and the mixture was stirred for 30 minutes. Then, 5.59g of methyl glycidyl ether was added, heated to 80°C, and stirring was continued for 5 hours. The amount of methyl glycidyl ether charged, 5.59g, is an amount equivalent to a theoretical introduction rate of methyl groups of 0.5 mol per 1 mol of anhydrous glucose unit of cellulose. The reaction product was collected by filtration using No. 2 filter paper (JIS P 3081 [filter paper (for chemical analysis)]), and the solid matter was washed in this order with 400 ml of a 70% 2-propanol aqueous solution, 400 ml of an 85% 2-propanol aqueous solution, and 400 ml of a 2-propanol / n-hexane mixed solvent (1 / 1 v / v). After washing, the solid matter was heated and dried under vacuum for 12 hours to obtain modified polymer 1 (dispersant for power storage device electrodes).

[0072] [Synthesis Example 2] A modified polymer 2 (dispersant for electricity storage device electrodes) was obtained in the same manner as in Synthesis Example 1, except that 6.48 g of ethyl glycidyl ether was used instead of 5.59 g of methyl glycidyl ether.

[0073] [Synthesis Example 3] A modified polymer 3 (dispersant for electricity storage device electrodes) was obtained in the same manner as in Synthesis Example 1, except that 8.26 g of n-butyl glycidyl ether was used instead of 5.59 g of methyl glycidyl ether.

[0074] [Synthesis Example 4] A modified polymer 4 (dispersant for electricity storage device electrodes) was obtained in the same manner as in Synthesis Example 1, except that 11.8 g of 2-ethylhexyl glycidyl ether was used instead of 5.59 g of methyl glycidyl ether.

[0075] [Synthesis Example 5] Modified polymer 5 (dispersant for electricity storage device electrodes) was obtained in the same manner as in Synthesis Example 4, except that the amount of 2-ethylhexyl glycidyl ether used was 17.7 g.

[0076] [Synthesis Example 6] A modified polymer 6 (dispersant for electrodes of electricity storage devices) was obtained in the same manner as in Synthesis Example 4, except that a carboxymethylcellulose Na salt (Sunrose F20HC manufactured by Nippon Paper Industries Co., Ltd., substitution degree 0.9 mol) was used instead of a carboxymethylcellulose Na salt (Sunrose F20LC manufactured by Nippon Paper Industries Co., Ltd., substitution degree 0.6 mol) and the amount of 2-ethylhexyl glycidyl ether used was 10.7 g.

[0077] [Synthesis Example 7] A modified polymer 7 (dispersant for electricity storage device electrodes) was obtained in the same manner as in Synthesis Example 1, except that 15.4 g of n-dodecyl glycidyl ether was used instead of 5.59 g of methyl glycidyl ether.

[0078] [Synthesis Example 8] A modified polymer 8 (dispersant for electrodes of electricity storage devices) was obtained in the same manner as in Synthesis Example 1, except that 57.3 g of Denacol EX-171 (lauryl alcohol (EO) 15 glycidyl ether, manufactured by Nagase ChemteX Corporation) was used instead of 5.59 g of methyl glycidyl ether.

[0079] 3. Preparation of electrode conductive material composition and electrode coating material composition [Example 1] (Preparation of Electrode Conductive Material Composition) In a 500 ml plastic bottle (a resin container made of polyethylene), 1.0 g of single-walled carbon nanotubes (CNT; TUBALL 01RW03 manufactured by Oxial Corporation), 150 g of a 1% aqueous solution of modified polymer 1, and 99.0 g of ion-exchanged water were placed, and the container was fixed in an ice bath. Next, the mixture in the container was stirred at 6000 rpm for 1 hour using a Lab-lution (manufactured by Primix Corporation) (Dispersion dispersion process), to obtain a CNT primary dispersion. Using a Lab-Cavitation Mill (manufactured by Advanced Nano Technology Corporation), the CNT primary dispersion was dispersed under a pressure of 150 MPa (Cavitation mill dispersion process). This series of dispersion processes was repeated four more times to obtain a conductive material composition for electrodes. The viscosity of the obtained conductive material composition for electrodes was measured according to the method described in [Measurement of viscosity of conductive material composition] above, and the results are shown in Table 1 below.

[0080] (Electrode coating material composition) In a dispersion vessel, 5.81 g of lithium iron phosphate (LFP-HS manufactured by Energy Materials Co., Ltd.) as an active material, 3.33 g of a 1.8 mass% aqueous solution of carboxymethylcellulose Na salt (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 1.80 g of purified water were placed and stirred with a spatula until homogenous. Next, the obtained dispersion was subjected to a dispersion treatment by stirring at 2000 rpm for 3 minutes using a rotation-revolution type mixer, Awatori Rentaro ARE-250 (manufactured by Thinky Corporation). After stirring the dispersion again with a spatula, a dispersion treatment was performed by stirring at 2000 rpm for 3 minutes using the ARE-250. Next, 0.75 g of the above electrode conductive material composition was added to the dispersion, stirred with a spatula, and then dispersed by stirring at 2000 rpm for 2 minutes using the ARE-250. Next, 0.30 g of binder BM-400B (manufactured by Zeon Corporation, solid content 40%, rubber-based negative electrode binder) was added to the dispersion liquid, and after lightly stirring with a spatula, the mixture was stirred at 2000 rpm for 2 minutes using an ARE-250, and then degassed for 30 seconds to obtain an electrode coating material composition.

[0081] [Examples 2 to 6, Comparative Examples 2 to 3] A conductive material composition for an electrode and an electrode coating material composition were prepared in the same manner as in Example 1, except that modified polymers 2 to 8 were used as dispersants for an electricity storage device electrode instead of modified polymer 1 in Example 1.

[0082] [Comparative Example 1] An electrode conductive material composition and an electrode coating material composition were prepared in the same manner as in Example 1, except that a 1% aqueous solution of carboxymethylcellulose Na salt (Sunrose F20LC, manufactured by Nippon Paper Industries Co., Ltd.) was used instead of the 1% aqueous solution of modified polymer 1.

[0083] [Table 1]

[0084] As shown in Table 1, Examples 1 to 6 have lower viscosity, lower coating resistance, and better foam suppression properties than Comparative Examples 1 to 3. [Industrial Applicability]

[0085] The use of the dispersant of the present disclosure makes it possible to prepare a low-viscosity electrode conductive material composition and a low-viscosity electrode coating material composition with good productivity. In addition, the use of the dispersant of the present disclosure makes it possible to produce a positive electrode for a power storage device and a power storage device having a reduced resistance.

Claims

1. A dispersant for energy storage device electrodes, for dispersing carbon material-based conductive materials in a dispersion medium, A dispersant for electrodes of energy storage devices, which is a modified polymer of at least one of carboxymethylcellulose and its salts having hydrocarbon groups with 1 to 10 carbon atoms.

2. The dispersant for energy storage device electrodes according to claim 1, wherein the degree of substitution of carboxymethyl groups and their salts in the modified polymer is 0.3 moles or more and 1.0 mole or less per mole of anhydrous glucose units of cellulose.

3. The dispersant for an energy storage device electrode according to claim 1 or 2, wherein the modified polymer comprises a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2). 【Chemistry 1】 However, R in formula (1) above 1 At least one of them is CH 2 COOX, and the remaining R 1 Each is either the same or different, CH 2 COOX or H, R in the above formula (2) 2 at least one of which is CH 2 CH(OH)CH 2 OY, and the remaining Rs 2 are each the same or different and are CH 2 COOX, CH 2 CH(OH)CH 2 OY or H, and X is a hydrogen atom, an alkali metal, an alkaline earth metal, or an ammonium salt. Y is a hydrocarbon group having between 1 and 10 carbon atoms.

4. A conductive material composition for electrodes comprising a dispersant for energy storage device electrodes according to claim 1 or 2, a carbon material-based conductive material, and an aqueous solvent.

5. The conductive material composition for electrodes according to claim 4, wherein the carbon material-based conductive material is a fibrous carbon material.

6. An electrode coating material composition comprising a dispersant for energy storage device electrodes according to claim 1 or 2, a carbon material-based conductive material, an active material, a binder, and an aqueous solvent.

7. The electrode coating material composition according to claim 6, wherein the active material is at least one selected from graphite, silicon material, and lithium iron phosphate.

8. The electrode coating material composition according to claim 6, wherein the binder is a styrene-butadiene resin, a polyacrylamide resin, or a crosslinked polyacrylic acid resin.

9. A method for producing a dispersant for electrodes of energy storage devices, comprising the step of reacting a compound containing a hydrocarbon group having 1 to 10 carbon atoms with at least one polymer selected from carboxymethylcellulose and its salts to obtain a modified polymer.

10. The method for producing a dispersant for an energy storage device electrode according to claim 9, wherein the compound is a glycidyl ether containing a hydrocarbon group having 1 to 10 carbon atoms.

11. A method for producing a dispersant for an energy storage device electrode according to claim 9 or 10, wherein the degree of substitution of carboxymethyl groups and their salts in at least one polymer from among carboxymethylcellulose and its salts is 0.3 moles or more and 1.0 mole or less per mole of anhydrous glucose units of cellulose.

12. The method for producing a dispersant for an energy storage device electrode according to claim 9 or 10, wherein the amount of the compound added is 0.1 moles or more and 1.5 moles or less per mole of anhydrous glucose units in at least one polymer of carboxymethylcellulose and its salts.

13. A method for producing a dispersant for an energy storage device electrode according to claim 9 or 10, wherein the reaction between the compound and the polymer is carried out in the presence of an alkali hydroxide.

14. A method for producing a dispersant for an energy storage device electrode according to claim 9 or 10, wherein the reaction between the compound and the polymer is carried out in a mixed solvent containing water and an aqueous solvent.

15. A method for producing a conductive material composition for electrodes, comprising the step of mixing and dispersing a dispersant for energy storage device electrodes according to claim 1 or 2 with a carbon material-based conductive material and an aqueous solvent.

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