Dispersant for electrodes of energy storage devices

Abstract

In one embodiment, the objective is to provide a dispersant for electrodes of energy storage devices that enables further improvement in the dispersibility of carbon materials for conductive materials. [Solution] In one embodiment, this disclosure relates to a polysaccharide-modified polymer, the modified polymer comprising at least one ionic group selected from the group consisting of sulfo groups and salts thereof, and a hydrocarbon group having 1 to 10 carbon atoms, as a dispersant for electrodes of energy storage devices. The degree of substitution of the ionic group in the modified polymer is preferably 50 to 1000 per 1000 units of anhydrous glucose of cellulose. The degree of substitution of the hydrocarbon group in the modified polymer is 1 to 100 per 1000 units of anhydrous glucose of cellulose.

Description

[Technical Field]

[0001] The present invention relates to a dispersant for electrodes of energy storage devices, and to a conductive material composition for electrodes and an electrode coating material composition containing the dispersant for electrodes of energy storage devices. [Background technology]

[0002] In recent years, there has been a surge in the development of electric vehicles (EVs) that do not emit carbon dioxide, as a way to mitigate global warming. However, EVs have challenges compared to gasoline-powered vehicles, such as shorter driving ranges and longer battery charging times. To shorten charging times, it is necessary to increase the speed of electron movement within the electrodes. Currently, carbon materials such as carbon nanotubes and carbon black are used as conductive materials in electrodes. Because these carbon materials have strong cohesive properties, it is difficult to disperse them uniformly in water.

[0003] In aqueous systems, it is known that carboxymethylcellulose (including its salts), polyvinylpyrrolidone, and hydroxyethylcellulose are used as dispersants to improve the dispersibility of conductive carbon materials such as carbon nanotubes and carbon black. Carboxymethylcellulose and / or its salts with specified degrees of carboxymethyl ether substitution have been disclosed in patent information, but there has been a need for dispersants that can further improve dispersibility in order to improve the performance of energy storage devices.

[0004] Furthermore, Reference 1 discloses a binder for lithium-ion battery positive electrodes, which binds a positive electrode active material, a conductive additive, and a current collector at the positive electrode of a lithium-ion battery, and comprises a polysaccharide having at least one ion exchange group selected from the group consisting of sulfate groups and alkali metal sulfates. Reference 2 discloses a topical skin preparation containing as an active ingredient a compound selected from sulfated cellulose obtained from crystalline cellulose and its salts, having a solubility of 3 g / L or more in pure water at 20°C and a sulfur content of 13.1 to 15.4% by weight. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2021 / 177134 [Patent Document 2] Japanese Patent Publication No. 2006-274245 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to provide a dispersant for energy storage device electrodes that enables further improvement of the dispersibility of carbon materials for conductive materials, and to provide an electrode conductive material composition and an electrode coating material composition containing the dispersant for energy storage device electrodes. [Means for solving the problem]

[0007] In one aspect, this disclosure relates to a polysaccharide-modified polymer, the modified polymer comprising at least one ionic group selected from the group consisting of sulfo groups and salts thereof, and a hydrocarbon group having 1 to 10 carbon atoms, as a dispersant for electrodes of energy storage devices.

[0008] This disclosure relates, in one aspect, to an electrode conductive material composition comprising a dispersant for energy storage device electrodes according to this disclosure, a carbon material-based conductive material, and an aqueous solvent.

[0009] This disclosure relates, in one aspect, to an electrode coating material composition comprising a dispersant for energy storage device electrodes, a carbon material-based conductive material, an active material, a binder, and an aqueous solvent.

[0010] This disclosure relates, in one aspect, to 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 this disclosure, a carbon material-based conductive material, and an aqueous solvent. [Effects of the Invention]

[0011] In one embodiment, this disclosure provides a dispersant for energy storage device electrodes that can highly disperse carbon material-based conductive materials in an aqueous solvent and exhibits excellent foam suppression properties. In one aspect, this disclosure provides an electrode conductive material composition containing an aqueous solvent in which a carbon material-based conductive material is highly dispersed and foam generation during preparation is suppressed, as well as a method for producing the same. In one aspect, this disclosure provides an electrode coating material composition containing an aqueous solvent in which a carbon material-based conductive material is highly dispersed and foam generation is suppressed during preparation. [Modes for carrying out the invention]

[0012] This disclosure is based on a novel finding that using a modified polysaccharide polymer containing a hydrocarbon group having 1 to 10 carbon atoms and at least one ionic group selected from the group consisting of sulfo groups and their salts significantly improves the dispersibility of carbon material-based conductive materials in dispersion media, particularly in aqueous solvents.

[0013] The detailed mechanism of action of this disclosure is not clear, but it can be inferred as follows.

[0014] The dispersant for energy storage device electrodes of this disclosure (hereinafter sometimes abbreviated as "the dispersant of this disclosure") is a modified polymer as described above, and it is presumed that the dispersant has high adsorption properties to carbon material-based conductive materials, and that the dispersibility of carbon material-based conductive materials is significantly improved due to the improved dispersibility of carbon material-based conductive materials through electrostatic repulsion and improved solubility in water.

[0015] More specifically, the axial hydrogen of the cellulose structure (a homopolysaccharide in which D-glucopyranose is β(1→4)-glycosidically bonded) forms a CH-π interaction 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. And the hydrocarbon group having 1 to 10 carbon atoms adsorbs to the surface of the carbon material-based conductive material by an action based on hydrophobic interaction. The sulfonic group (-SO3H) or its salt exhibits electrostatic repulsion and contributes to the dispersibility of the carbon material-based conductive material. Further, the sulfonic group (-SO3H) or its salt is an ionic group and has high hydrophilicity, so it also contributes to the improvement of the solubility of the dispersant of the present disclosure in an aqueous solvent, and suppresses the generation of bubbles during the preparation of the conductive material composition for electrodes and the electrode coating material composition prepared using the dispersant of the present disclosure. Thus, in the dispersant of the present invention, the adsorption property of the dispersant to the carbon material-based conductive material by the hydrocarbon group having 1 to 10 carbon atoms and the electrostatic repulsion by the ionic group significantly improve the dispersibility of the carbon material-based conductive material in the dispersion medium, and it is presumed that the generation of bubbles is suppressed during the preparation of the conductive material composition for electrodes and the electrode coating material composition. However, the present disclosure is not construed as being limited to these mechanisms.

[0016] [Dispersant for Electrodes of Energy Storage Devices] The dispersant of the present disclosure is a dispersant for dispersing a carbon material-based conductive material in a dispersion medium. The dispersant of the present disclosure is a modified polymer of a polysaccharide (hereinafter may also be referred to as "the modified polymer of the present disclosure"). The modified polymer of the present disclosure has a structure in which the hydroxyl group of the anhydroglucose unit constituting the polysaccharide is substituted by the hydrocarbon group and the ionic group.

[0017] (Polysaccharide) The polysaccharide is preferably at least one selected from hydroxyethyl cellulose (HEC), hydroxypropyl cellulose, methyl cellulose, and cellulose, more preferably at least one selected from hydroxyethyl cellulose and cellulose. From the viewpoint of improving the dispersibility of the carbon material-based conductive material, the molecular weight of these polysaccharides is preferably 1,000,000 or less, more preferably 800,000 or less, and still more preferably 200,000 or less. The molecular weight of these polysaccharides may be referred to as the catalog molecular weight, but can also be measured by weight-average GPC (gel permeation chromatography) and determined by a conversion standard substance.

[0018] (Hydrocarbon group) From the viewpoints of high dispersibility and foam suppression properties of the carbon material-based conductive material, the number of carbon atoms in the hydrocarbon group is 1 or more and 10 or less. From the viewpoints of high dispersibility and foam suppression properties of the carbon material-based conductive material, the number of carbon atoms in the hydrocarbon group is preferably 4 or more, more preferably 6 or more, and from the same viewpoints, preferably 8 or less. When the number of carbon atoms in the hydrocarbon group is 10 or less, it is presumed that the association within and between molecules is suppressed, the adsorption of the dispersant onto the surface of the carbon material is favorably performed, and the carbon material-based conductive material can be highly dispersed. Further, it is presumed that the generation of bubbles during the preparation of the conductive material composition for electrodes and the electrode coating material composition described in detail later can be suppressed, and the occurrence of defects due to these bubbles in the electrode coating film (composite layer) formed using them can be suppressed.

[0019] The hydrocarbon group is preferably at least one selected from methyl group, ethyl group, propyl group, iso-propyl group, butyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, 2-ethylhexyl group, phenyl group, benzyl group, furfuryl group, and 2-methylphenyl ether group. From the viewpoints of high dispersibility and foam suppression properties of the carbon material-based conductive material, among them, at least one of butyl group, 2-ethylhexyl group, phenyl group, and benzyl group is more preferable, and at least one of butyl group, 2-ethylhexyl group, and benzyl group is still more preferable.

[0020] From the viewpoint of high dispersibility and anti-foaming properties of carbon material-based conductive materials, the degree of substitution of the hydrocarbon group in the modified polymer of this disclosure is preferably 0.5 or more, more preferably 1 or more, even more preferably 3 or more, even more preferably 10 or more, and even more preferably 14 or more, per 1000 units of anhydrous glucose of cellulose. From the same viewpoint, it is preferably 100 or less, more preferably 80 or less, even more preferably 60 or less, even more preferably 50 or less, and even more preferably 38 or less. The degree of substitution of the hydrocarbon group is measured using 1H-NMR, and specifically the value obtained by the method described in the examples.

[0021] The modified polymer of this disclosure may consist of only one hydrocarbon group, but it may also contain two or more hydrocarbon groups with different numbers of carbon atoms. Furthermore, the modified polymer of this disclosure may be a mixture of two or more modified polymers with different numbers of carbon atoms in the hydrocarbon groups. Also, the modified polymer of this disclosure may be a mixture of two or more modified polymers with different degrees of substitution of hydrocarbon groups. The dispersant of this disclosure may contain a small amount of hydrocarbon groups with more than 10 carbon atoms, as long as this does not impair the effects of this disclosure.

[0022] (Ionic group) The X in the sulfo group and / or salt thereof (-SO3X) constituting the modified polymer of this disclosure is preferably one or more of the following: a hydrogen atom, an alkali metal such as Na and K, an alkaline earth metal such as Ca and Mg, and a cation such as an ammonium salt (NH4). Among these, from the viewpoint of high dispersibility and anti-foaming properties of carbon material-based conductive materials, it is more preferably at least one selected from Na, K and NH4, and even more preferably at least one selected from Na and K.

[0023] The degree of substitution of at least one ionic group selected from the group consisting of sulfo groups and their salts constituting the modified polymer of this disclosure [ / 1000 units] is preferably 50 or more, more preferably 80 or more, even more preferably 100 or more, even more preferably 150 or more, and even more preferably 170 or more per 1000 units of anhydrous glucose of cellulose, from the viewpoint of improving the dispersibility of carbon material-based conductive materials due to electrostatic repulsion, and preferably 1000 or less, more preferably 700 or less, even more preferably 500 or less, even more preferably 300 or less, and even more preferably 240 or less, from the viewpoint of good adsorption to carbon material-based conductive materials. The degree of substitution of the above ionic group is measured using colloidal titration, and specifically the value obtained by measuring by the method described in the examples. When the modified polymer of this disclosure has both a sulfo group and its salt, the degree of substitution is the sum of the degree of substitution of the sulfo group and the degree of substitution of its salt (degree of etherification per unit of anhydrous glucose).

[0024] The ionic groups constituting the modified polymer of this disclosure may be one type or two or more types. Furthermore, the modified polymer of this disclosure may be a mixture of two or more modified polymers with different ionic groups. Furthermore, the modified polymer of this disclosure may be a mixture of two or more modified polymers with different degrees of substitution of the ionic groups. Furthermore, the dispersant of this disclosure may contain small amounts of ionic groups other than at least one ionic group selected from the group consisting of sulfo groups and their salts, such as carboxymethyl groups and / or their salts, to the extent that it does not impair the effects of this disclosure, but it is preferable that it does not contain any ionic groups other than at least one ionic group selected from the group consisting of sulfo groups and their salts.

[0025] The viscosity (at 25°C) of a 3% by mass aqueous solution of the modified polymer of this disclosure is preferably 500 mPa·s or less, more preferably 300 mPa·s or less, even more preferably 150 mPa·s or less, and even more preferably 75 mPa·s or less, from the viewpoint of improving the dispersibility of the carbon material-based conductive material, preventing foaming, and avoiding thickening of the dispersion. Furthermore, the lower limit of the viscosity (at 25°C) of a 3% by mass aqueous solution of the modified polymer of this disclosure is usually 0.5 mPa·s or more.

[0026] From the viewpoint of high dispersibility of carbon material-based conductive materials, the modified polymers of this disclosure preferably include a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (2). [ka]

[0027] R in the general formula (1) 1 At least one of these is -X-SO3M. The X comprises a structure containing one or more groups from a hydrocarbon group, an oxyalkylene group, and a polyoxyalkylene group. The hydrocarbon group may have substituents, may be linear or branched, and preferably has 1 to 6 carbon atoms. The hydrocarbon group is more preferably an alkylene group that may have substituents, may be linear or branched, and has 1 to 6 carbon atoms. The substituents are preferably hydroxyl groups, oxo groups, etc. The oxyalkylene group and the polyoxyalkylene group are derived from the polysaccharide and are therefore not particularly limited, but the oxyalkylene group is preferably an oxyethylene group (CH2CH2O) or an oxypropylene group (CH2CH2CH2O). The polyoxyalkylene group preferably contains either an oxyethylene group or an oxypropylene group, or both. The number of moles of polyoxyalkylene groups added is preferably 0 to 10. M is a hydrogen atom, an alkali metal, an alkaline earth metal, or an ammonium salt, preferably at least one selected from Na, K, and NH4, and more preferably Na or K. The remaining R in the general formula (1) above 1 is a hydrogen atom, a methyl group, a hydroxypropyl group, an alkali metal, an alkaline earth metal, an ammonium salt, or -YZ in the general formula (2), preferably a hydrogen atom, a methyl group, a hydroxypropyl group, or -YZ in the general formula (2), and particularly preferably a hydrogen atom or -YZ in the general formula (2). In the above general formula (1), -X-SO3M is preferably at least one of the following general formulas (3) and (4). -(AO)nA-SO3M (3) -(AO)n-SO3M (4) In the above general formulas (3) and (4), (AO) is an oxyalkylene group, and n is the number of moles added, which is between 0 and 10. (AO)n preferably contains either an oxyethylene group or an oxypropylene group, or both. A is an alkylene group having 1 to 6 carbon atoms, being linear or branched, and may have the substituents mentioned above. Preferred substituents include hydroxyl groups, oxo groups, etc. Preferred M is as described above.

[0028] In the above general formula (2), R 2 At least one of these is -YZ. The Y comprises a structure containing one or more groups from a hydrocarbon group, an oxyalkylene group, and a polyoxyalkylene group. The hydrocarbon group may have substituents, may be linear or branched, and preferably has 1 to 6 carbon atoms. The hydrocarbon group is more preferably an alkylene group that may have substituents, may be linear or branched, and has 1 to 6 carbon atoms. The substituents are preferably hydroxyl groups, oxo groups, etc. The oxyalkylene group and the polyoxyalkylene group are derived from the polysaccharide and are therefore not particularly limited, but the oxyalkylene group is preferably an oxyethylene group (CH2CH2O) or an oxypropylene group (CH2CH2CH2O). The polyoxyalkylene group preferably contains either an oxyethylene group or an oxypropylene group, or both. The number of moles of polyoxyalkylene groups added is preferably 0 to 10. The aforementioned Z is a hydrocarbon group, which may have substituents, and may be linear, branched, or contain an aromatic ring, and preferably has 2 to 10 carbon atoms, more preferably 6 to 8 carbon atoms. The remaining R in the general formula (2) above 2 is a hydrogen atom, a methyl group, a hydroxypropyl group, an alkali metal, an alkaline earth metal, an ammonium salt, or -X-SO3M from the general formula (1), preferably a hydrogen atom, a methyl group, a hydroxypropyl group, or -X-SO3M from the general formula (1). In the above general formula (2), -YZ is at least one of the following general formulas (5) and (6). -(AO)nBOZ (5) -(AO)nOZ (6) In the above general formulas (5) and (6), (AO) is an oxyalkylene group, and n is the number of moles added, which is between 0 and 10. (AO)n preferably includes either an oxyethylene group or an oxypropylene group, or both. B is an alkylene group having 1 to 6 carbon atoms, being linear or branched, and may have the substituents mentioned above. Preferred substituents include hydroxyl groups, oxo groups, etc. O is an oxygen atom, and the preferred Z is as described above.

[0029] The dispersant of this disclosure can be produced by introducing the hydrocarbon group and the ionic group into a polysaccharide containing the cellulose skeleton. The method for introducing these groups can be carried out by conventionally known methods.

[0030] [Dispersant composition] The dispersant of this disclosure may be supplied to the market as a solid, or it may be supplied to the market as a dispersant composition in which the dispersant of this disclosure is dissolved in an aqueous medium.

[0031] (Aqueous solvent) The dispersant compositions of this disclosure contain an aqueous solvent as a solvent. The aqueous solvent is preferably water, and more specifically, preferably deionized water, distilled water, or purified water. The aqueous solvent may contain a small amount of aqueous solvent. Preferred aqueous media include 2-propanol, ethanol, 2-butanol, t-butanol, acetone, N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, etc. The content of the aqueous solvent in the dispersant compositions of this disclosure is the remainder after excluding the dispersant of this disclosure and the optional components listed below.

[0032] (optional ingredient) 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, defoamers, preservatives, dehydrators, rust inhibitors, plasticizers, binders, and the like.

[0033] 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 of 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.

[0034] [Conductive material composition for electrodes] This disclosure relates, in one embodiment, to a conductive material composition for electrodes of energy storage devices (hereinafter sometimes abbreviated as "conductive material composition"). The conductive material composition of this disclosure is an aqueous conductive material composition comprising the dispersant of this disclosure, a carbon material-based conductive material, and an aqueous solvent. Because the conductive material composition of this disclosure contains the dispersant of this disclosure, the dispersibility of the carbon material-based conductive material is good. If the conductive material composition of this disclosure is used in the preparation of an electrode coating material composition, it is possible to form an electrode coating with low resistance. The preferred form of the dispersant of this disclosure in this embodiment is as described above.

[0035] (Carbon-based conductive materials) Preferably, the carbon material-based conductive material included in the conductive material composition of this disclosure is fibrous carbon, carbon black, acetylene black, graphene, etc. From the viewpoint of conductivity, fibrous carbon material is particularly preferred. Preferred fibrous carbon material is carbon nanotube (hereinafter sometimes referred to as "CNT"), carbon nanofiber, etc., with CNT being particularly preferred.

[0036] CNTs include single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), multi-walled carbon nanotubes (FWCNTs), and multi-walled carbon nanotubes (MWCNTs). Any of these CNTs can be used to prepare the conductive material composition of this disclosure, and mixtures thereof can also be used. Generally, single-walled carbon nanotubes are preferred because they are longer and more flexible than other types of CNTs, resulting in a higher effect on improving conductivity.

[0037] The average diameter of carbon nanotubes (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 conductivity, it is preferably 100 nm or less, more preferably 50 nm or less. In this disclosure, the average diameter of CNTs can be measured by scanning electron microscope (SEM) or atomic force microscope (AFM).

[0038] The average length of carbon nanotubes (CNTs) that can be used as a carbon material-based conductive material 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 CNTs can be measured by scanning electron microscope (SEM) or atomic force microscope (AFM).

[0039] (Content of carbon-based conductive material in the conductive material composition) The content of the carbon material-based conductive material in the conductive material composition of this 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 multilayer CNTs, from the viewpoint of improving the convenience of adjusting the concentration of the electrode coating material composition, which will be described in detail later. From the viewpoint of making the conductive material composition easy to handle, it is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less. Similarly, for single-walled CNTs, it 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. From the viewpoint of making the conductive material composition easy to handle, it is preferably 2% by mass or less, and even more preferably 1% by mass or less.

[0040] (Content of the dispersant of this disclosure in the conductive material composition) The content of the dispersant of this disclosure in the conductive material composition of this disclosure is not particularly limited, but from the viewpoint of improving the dispersibility of the carbon material-based conductive material, it is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 60 parts by mass or more, per 100 parts by mass of the carbon material-based conductive material, and from the viewpoint of maintaining a high energy density of the energy storage device, 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, per 100 parts by mass of the carbon material-based conductive material.

[0041] (Aqueous solvent) The conductive material composition of this disclosure preferably 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 this disclosure is the remainder after excluding the dispersant of this disclosure and the optional components listed below.

[0042] (optional ingredient) The conductive material compositions 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.

[0043] (Method for manufacturing conductive material composition) In one or more embodiments, the conductive material composition of this disclosure can be prepared by mixing a mixture of the dispersant of this disclosure, a carbon material-based conductive material, an aqueous solvent, and optionally additional components in a mixing disperser. Alternatively, in one or more embodiments, the conductive material composition of this disclosure may be prepared by mixing a mixture of the dispersant composition of this disclosure, a carbon material-based conductive material, an optionally additional aqueous solvent, and optional components in a mixing disperser.

[0044] Examples of mixing and dispersing machines 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 composition may be mixed before being mixed with the remainder, or each component may be added in multiple portions rather than all at once. The dispersant of this disclosure may be dissolved in water to form a dispersant composition and then 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 water or an aqueous solvent.

[0045] [Electrode coating material composition] This disclosure relates, in one embodiment, to an electrode coating material composition comprising a dispersant of the Disclosure, a carbon material-based conductive material, an electrode active material, a binder, and an aqueous solvent. Preferred forms of the dispersant and carbon material-based conductive material of the Disclosure in this embodiment are as described above. The aqueous solvent in this embodiment is preferably the same as the aqueous solvent contained in the dispersant composition and conductive material composition described above.

[0046] Since the electrode coating material composition of this disclosure contains the dispersant of this disclosure, it is possible to form an electrode coating (composite layer) with low resistance.

[0047] (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. Examples of compounds having an olivine structure include those with the general formula Li x M1 s Examples of compounds represented by PO4 (where M1 is a 3d transition metal, 0≦x≦2, 0.8≦s≦1.2) can be used. Compounds having an olivine structure may be 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.

[0048] As the negative electrode active material, carbon-based active materials such as natural graphite, artificial graphite, hard carbon, and soft carbon, metals that can form alloys with lithium such as tin, zinc, aluminum, magnesium, titanium, and antimony, or silicon-based materials are used. Silicon-based materials include oxides and mixed systems of graphite and silicon materials. From the viewpoint of electrode capacity, silicon-based materials (SiOx, X≧0) are preferred, and SiO is particularly preferred.

[0049] The content of the electrode active material in the electrode coating material composition of this disclosure is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more, from the viewpoint of energy density and stability, and preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less, from the viewpoint of coating properties on current collectors.

[0050] The content of electrode active material in the total solid content of the electrode coating material composition disclosed herein may be the same as that in the total solid content of conventionally known electrodes. Preferably, it is 90.0% by mass or more in order to maintain a high energy density of the energy storage device, and preferably 99.9% by mass or less in order to ensure the conductivity and coating properties of the composite layer.

[0051] (binder) The binder is not particularly limited, but emulsions of styrene-butadiene (SBR) resins, crosslinked polyacrylic acid resins, polyacrylamide resins, or water-soluble polymers of carboxymethylcellulose can be used alone or in combination.

[0052] The electrode coating material composition 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 dispersants of this disclosure.

[0053] (Content of carbon-based conductive material in electrode coating material composition) The content of the carbon material-based conductive material in the electrode coating material composition 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 composite layer, 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.

[0054] (Content of the dispersant of this 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 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, per 100 parts by mass of carbon material-based conductive material, from the viewpoint of coating resistance, 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.

[0055] (Binder content in electrode coating material composition) The binder content in the total solids of the electrode coating material composition disclosed herein 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.

[0056] The solid content concentration of the electrode coating material composition of this disclosure, and the content of the dispersant, electrode active material, binder, carbon material-based conductive material, aqueous solvent, and the above optional components in the electrode coating material composition of this 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 properties, 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 suppressing 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.

[0057] (Method for manufacturing electrode coating material composition) The electrode coating material composition of this disclosure can be prepared in one or more embodiments by mixing and stirring the dispersant, electrode active material, carbon material-based conductive material, binder, aqueous solvent (additional solvent) for adjusting the solid content concentration, etc., and optionally the above-mentioned optional components. Some of the components used in preparing the electrode coating material composition may be premixed before mixing with the remainder. For example, the conductive material composition of this disclosure may be prepared and then the electrode active material may be mixed into the conductive material composition. Alternatively, the conductive material composition and the electrode active material may be thoroughly stirred and mixed, and then the binder may be added. Alternatively, the conductive material composition and the electrode active material may be thoroughly stirred and mixed, and then additional conductive material composition of this disclosure may be added as needed, and after thoroughly mixing and stirring these, 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 aqueous solvent such as water. In addition, each component may not be added in its entirety at once, but in multiple portions. This reduces the mechanical load on the stirring device. Other dispersants and functional materials other than the dispersant of this disclosure may also be added. A planetary mixer, bead mill, jet mill, etc., can be used for mixing and stirring, and these can also be used in combination.

[0058] <Method for manufacturing electrode coating> This disclosure relates, in one embodiment, to a method for manufacturing an electrode coating using the electrode coating material composition of this disclosure. The manufacturing method in this embodiment includes coating the electrode coating material composition of this disclosure onto a current collector, drying it, and pressing it. In this embodiment, a preferred form of the electrode coating material composition of this disclosure is as described above. In the method for manufacturing an electrode coating of this disclosure, an electrode coating can be manufactured by conventionally known methods, except for using the electrode coating material composition of this disclosure. [Examples]

[0059] Examples and comparative examples of the present disclosure are shown below, but the present disclosure is not limited thereto.

[0060] [Degree of substitution of sulfo group] The degree of substitution of sulfo groups and / or their salts in the following dispersants for energy storage devices was measured by colloidal titration. Specifically, it was measured by the method described below. 10 mg of a dispersant for energy storage devices was weighed into a sample bottle and dissolved in 4 g of deionized water. Next, 5.00 mL of N / 200 methyl glycol chitosan solution and 3 drops of toluidine blue indicator were added and the mixture was stirred for 10 minutes. Titration was performed using a burette with N / 400 potassium polyvinyl sulfate. The titration endpoint was defined as the point where the indicator changed color and no further color change occurred after 30 seconds of stirring. The degree of sulfo group substitution DS was calculated from the titration volume. From the calculated value, the degree of sulfo group substitution per 1000 units of anhydrous glucose was calculated and is shown in Table 1.

[0061] [Degree of substitution of alkyl chains] 150 mg of the following energy storage device dispersant was weighed into a sample bottle and dissolved in 1 g of heavy water. 0.5 g of sulfuric acid and 0.5 g of heavy water were then added, and the mixture was heated and stirred at 60°C for 11 hours. The resulting solution was measured by 1H-NMR under the following conditions, and the degree of alkyl chain substitution DS was analyzed. From the analysis results, the degree of alkyl chain substitution relative to 1000 units of anhydrous glucose was calculated and is shown in Table 1. (1H-NMR measurement) Measuring equipment: Bruker Avance NEO 400 Measurement conditions: 32 cumulative measurements, 20-second relaxation time.

[0062] [Viscosity measurement of aqueous dispersant solutions for energy storage devices] The viscosity (at 25°C) of a 3% aqueous solution (sample) of a dispersant for energy storage devices was measured as follows. The sample was loaded between the stage and cone plate CP50 of a rheometer MCR302 (manufactured by Anton Paar), and the shear viscosity was measured at 25°C at a rotation speed of 10 rpm for 120 seconds. The average shear viscosity from 100 to 120 seconds was taken as the viscosity of a 3% aqueous solution of the dispersant for energy storage devices, and is shown in Table 1.

[0063] [Preparation of CNT slurry (conductive material composition)] Into a 500 mL polyvinyl container, 1.0 g of single-walled carbon nanotubes (CNT, TUBALL 01RW03 manufactured by OCSiAL, average diameter 1.6 nm), 150 g of a 1 mass% aqueous solution of a dispersant for a power storage device, and 99.0 g of ion-exchanged water were added, and the container was fixed in an ice bath. Using a biomixer BM-2 (manufactured by Nippon Seiki Co., Ltd.), the mixture in the container was stirred at 18,000 rpm for 1 hour (homogenizer dispersion process) to obtain a primary dispersion of CNT. Next, using a laboratory cavitation mill (manufactured by Advanced Nano Technology), the primary dispersion of CNT was dispersed under a pressure of 150 MPa (cavitation mill dispersion process). This series of dispersion treatments was performed 5 more times to obtain a CNT slurry.

[0064] In Example 1, the dispersant for a power storage device of Synthesis Example 1 below was used. In Example 2, the dispersant for a power storage device of Synthesis Example 2 below was used. In Example 3, the dispersant for a power storage device of Synthesis Example 3 below was used. In Comparative Example 1, the dispersant for a power storage device of Synthesis Example 4 below was used, and CNT slurries were prepared according to the above [Preparation of CNT slurry (conductive material composition)]. In Comparative Example 2, a CNT slurry was prepared in the same manner as in Example 1 except that water was used instead of the 1 mass% aqueous solution of the dispersant for a power storage device.

[0065] [Evaluation of CNT slurry] Measurement of the dispersion particle size of CNT Using a laser diffraction / scattering particle size distribution measuring device LA-950 (manufactured by Horiba, Ltd.), the particle size measurement (volume basis) of CNT in the CNT slurry was performed. The relative refractive index was set to 1.44. The median diameter (D50) of the measurement results was shown in Table 1 as the CNT dispersion particle size.

[0066] Viscosity measurement of CNT slurry The viscosity (25 °C) of the CNT slurry was measured as follows. A sample was loaded between the stage of a rheometer MCR302 (manufactured by Anton Paar) and a parallel plate; PP50, and at 25 °C, the shear rate was changed from 0.01 s -1 to 1000 s -1 while increasing (forward path), and then, from 1000 s-1 from 0.01s -1 The shear stress was measured while descending to the return path (return trip). Table 1 below shows the shear stress at a shear rate of 10s on the return trip. -1 The apparent viscosity at that time is shown as the viscosity of the CNT slurry (25°C).

[0067] [Evaluation of foam suppression properties] 1.0 g of single-walled carbon nanotubes (CNTs, TUBALL 01RW03, manufactured by OCSiAL), 150 g of a 1% aqueous solution of a dispersant for energy storage devices, and 99.0 g of deionized water were placed in a 500 mL poly bottle (container), 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-Solution (manufactured by Primix) (homogenizer dispersion process) to obtain a CNT dispersion. Foaming was observed visually during the homogenizer dispersion process, and the foam suppression properties were evaluated according to the evaluation criteria below. The results are shown in Table 1. (Evaluation Criteria) A: No foaming was observed. B: Foaming was observed.

[0068] 2. Synthesis of dispersants for energy storage device electrodes [Synthesis Example 1] In a 1L glass four-neck separable flask equipped with a stirring blade and a condenser, 35.0g of hydroxyethylcellulose (Ashland Natrosol 250LR, molecular weight 90,000 (catalog value)) and 280.0g of an 80% by mass 2-propanol aqueous solution were charged and mixed. Next, 2.4g of a 48% by mass sodium hydroxide aqueous solution was added and the mixture was stirred at room temperature for 20 minutes. Then, 1.68g of a 30% by mass sodium 3-chloro-2-hydroxypropanesulfonate aqueous solution (Fujifilm Wako Pure Chemical Industries) was added and the mixture was stirred for 1 hour. After adding 2.39g of 2-ethylhexylglycidyl ether (Tokyo Chemical Industries), the mixture was heated to 80°C and stirred for 8 hours. The resulting reaction solution was cooled to 50°C. To this solution, 126.3 g of 30% by mass sodium 3-chloro-2-hydroxypropanesulfonate aqueous solution, 16.1 g of 48% by mass sodium hydroxide aqueous solution (Fujifilm Wako Pure Chemical Industries), 164.5 g of 2-propanol (Fujifilm Wako Pure Chemical Industries), and 2.1 g of deionized water were added, and the mixture was stirred at 50°C for 7 hours. After the resulting reaction solution was cooled to room temperature, it was neutralized with 14.6 g of acetic acid (Fujifilm Wako Pure Chemical Industries). The precipitate was then collected, and the collected material was washed three times with 600.0 g of 75% by mass 2-propanol aqueous solution, followed by two washes with 250 g of 2-propanol. The washed material was heat-dried to obtain the dispersant (modified polymer) for energy storage devices of Example 1. In the obtained modified polymer, the degree of substitution of alkyl chains was 14 per 1000 units of anhydrous glucose of cellulose, and the degree of substitution of sulfo groups was 230 per 1000 units of anhydrous glucose of cellulose. The resulting modified polymer contains the constituent units represented by the general formula (1) and the constituent units represented by the general formula (2). 1 One of them is expressed by general formula (3), and the other two R 1 These are, respectively, one of H, general formula (3), and general formula (5). The three R 2 One of them is expressed by general formula (5), and the other two R 2Each of the following is H, general formula (3), and general formula (5). In general formula (3), n is 0 or 1, and A is an alkylene group having one hydroxyl group and 3 carbon atoms. M is Na. In general formula (5), n is 0 or 1, and B is an alkylene group having one hydroxyl group and 3 carbon atoms. Z is an ethylhexyl group.

[0069] [Synthesis Examples 2-4] In Synthesis Examples 2 to 4, polysaccharide-modified polymers (dispersants for energy storage devices) containing a constituent unit represented by general formula (1) and a constituent unit represented by general formula (2) were obtained according to the method described in [Synthesis Example 1]. In Synthesis Example 2, butyl glycidyl ether (Tokyo Chemical Industries) was used instead of the 2-ethylhexyl glycidyl ether used in Synthesis Example 1. The resulting modified polymer is the same as the dispersant for energy storage device electrodes in Synthesis Example 1, except that Z in general formula (5) is a butyl group. In Synthesis Example 3, benzyl glycidyl ether (Tokyo Chemical Industries) was used instead of the 2-ethylhexyl glycidyl ether used in Synthesis Example 1. The resulting modified polymer is the same as the dispersant for energy storage device electrodes in Synthesis Example 1, except that Z in general formula (5) is a benzyl group. In Synthesis Example 4, instead of the hydroxyethylcellulose with a molecular weight (catalog value) of 90,000 used in Synthesis Example 1, a hydroxyethylcellulose with a molecular weight (catalog value) of 1,500,000 was used. Also, instead of the 2-ethylhexylglycidyl ether used in Synthesis Example 1, stearyl glycidyl ether (Tokyo Chemical Industries) was used.

[0070] [Table 1]

[0071] As shown in Table 1, in Examples 1-3, the dispersed particle size of CNTs in the CNT slurry was significantly smaller compared to Comparative Examples 1-2, and the viscosity of the CNT slurry at 25°C was also lower. Therefore, the CNT slurries of Examples 1-3 had a higher degree of dispersion of CNTs than the slurries of Comparative Examples 1-2. In addition, the CNT slurries of Examples 1-3 exhibited good foam suppression properties, similar to the CNT slurry of Comparative Example 2. [Industrial applicability]

[0072] Using the dispersant of this disclosure, low-viscosity conductive material compositions for electrodes and low-viscosity electrode coating material compositions can be prepared with high productivity. Furthermore, using the dispersant of this disclosure, low-resistance positive electrode electrodes for energy storage devices and energy storage devices can be manufactured.

Claims

1. A dispersant for electrodes of energy storage devices, comprising a modified polymer of polysaccharides, wherein the modified polymer contains at least one ionic group selected from the group consisting of sulfo groups and salts thereof, and a hydrocarbon group having 1 to 10 carbon atoms.

2. The dispersant for energy storage device electrodes according to claim 1, wherein the degree of substitution of the ionic group in the modified polymer is 50 or more and 1000 or less per 1000 units of anhydrous glucose of cellulose.

3. The dispersant for energy storage device electrodes according to claim 1, wherein the degree of substitution of the hydrocarbon group in the modified polymer is 1 or more and 100 or less per 1000 units of anhydrous glucose of cellulose.

4. The dispersant for an electrode of an energy storage device according to claim 1, wherein the modified polymer comprises a constituent unit represented by the following general formula (1) and a constituent unit represented by the following general formula (2). 【Chemistry 1】 In the above general formula (1), R 1 At least one of them is -X-SO 3 It is M, The aforementioned X includes a structure containing one or more groups from among hydrocarbon groups, oxyalkylene groups, and polyoxyalkylene groups. The hydrocarbon group may have substituents and may be linear or branched. M is a hydrogen atom, an alkali metal, an alkaline earth metal, or an ammonium salt. Remaining R 1 is a hydrogen atom, a methyl group, a hydroxypropyl group, an alkali metal, an alkaline earth metal, an ammonium salt, or -Y-Z in the following general formula (2). 【Chemistry 2】 In the above general formula (2), R 2 At least one of them is -Y-Z, The Y has a structure that includes one or more groups from among a hydrocarbon group, an oxyalkylene group, and a polyoxyalkylene group. The hydrocarbon group may have substituents and may be linear or branched. The aforementioned Z is a hydrocarbon group that may have substituents, is linear, branched, or contains an aromatic ring. Remaining R 2 This is a hydrogen atom, a methyl group, a hydroxypropyl group, an alkali metal, an alkaline earth metal, an ammonium salt, or -X-SO in the general formula (1) above. 3 It is M.

5. The dispersant for energy storage device electrodes according to claim 1, wherein the polysaccharide is at least one selected from the group consisting of hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose, and cellulose.

6. The dispersant for energy storage device electrodes according to claim 1, wherein the viscosity of a 3% by mass aqueous solution of the modified polymer at 25°C is 500 mPa·s or less.

7. The dispersant for an electrode in an energy storage device, as described in claim 1, which is a dispersant for the negative electrode of an energy storage device.

8. A conductive material composition for electrodes comprising a dispersant for energy storage device electrodes according to any one of claims 1 to 7, a carbon material-based conductive material, and an aqueous solvent.

9. The conductive material composition for electrodes according to claim 8, wherein the carbon material-based conductive material is a fibrous carbon material.

10. An electrode coating material composition comprising a dispersant for energy storage device electrodes according to any one of claims 1 to 7, a carbon material-based conductive material, an active material, a binder, and an aqueous solvent.

11. The electrode coating material composition according to claim 10, wherein the active material is at least one selected from graphite, silicon-based materials, lithium iron phosphate, and lithium iron manganese phosphate.

12. 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 any one of claims 1 to 7, a carbon material-based conductive material, and an aqueous solvent.

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