Carbonaceous material dispersions and electrode slurries for all-solid-state lithium-ion secondary batteries

Abstract

The present invention provides a carbonaceous material dispersion for all-solid-state lithium-ion secondary batteries that, when used as a conductive additive for all-solid-state lithium-ion secondary batteries, suppresses the degradation of the solid electrolyte, allows for high-concentration and uniform dispersion of carbonaceous materials, and, when mixed with electrode active materials, allows for low-viscosity and high-concentration dispersion of solid components, thereby contributing to the excellent conductivity of the secondary battery. [Solution] A carbonaceous material dispersion for an all-solid-state lithium-ion secondary battery, comprising a carbonaceous material and a dispersant dispersed in a dispersion medium, The dispersion medium consists solely of a carboxylic acid ester such as butyl butyrate, or a mixed solvent of the carboxylic acid ester and a nonpolar solvent. It contains at least polyvinyl butyral as a dispersant, The amount of carbonaceous material in the dispersion is 10 to 25% by mass relative to the total mass of the dispersion, and the amount of dispersant is 5% by mass or more and less than 20% by mass relative to the mass of the carbonaceous material. This is a carbonaceous material dispersion having a viscosity of 500 mPa·s or less at 25°C.

Description

[Technical Field]

[0001] The present invention relates to a carbonaceous material dispersion for all-solid-state lithium-ion secondary batteries and an electrode slurry for all-solid-state lithium-ion secondary batteries. More specifically, the present invention relates to a carbonaceous material dispersion for all-solid-state lithium-ion secondary batteries that, when used as a conductive additive for all-solid-state lithium-ion secondary batteries, can suppress the degradation of the solid electrolyte, and in which the carbonaceous material is dispersed at a high concentration and uniformly, and in which the solid content is dispersed at a low viscosity and high concentration when mixed with the electrode active material, and an electrode slurry for all-solid-state lithium-ion secondary batteries using the same. [Background technology]

[0002] In recent years, high-capacity, high-output lithium-ion rechargeable batteries have been widely used in many fields, including electronic devices such as portable personal computers, smartphones, and mobile phones, as well as automobiles such as electric vehicles and hybrid vehicles.

[0003] In lithium-ion secondary batteries, electrolytes using flammable organic solvents as diluents have conventionally been used as the medium for moving ions. However, batteries using such electrolytes may experience problems such as electrolyte leakage, ignition, and explosion.

[0004] To address these problems, development is underway on all-solid-state lithium-ion secondary batteries, which use a solid electrolyte instead of a liquid electrolyte and are composed entirely of solid components. All-solid-state lithium-ion secondary batteries have very low charge transfer resistance between the solid electrolyte and lithium ions, thus reducing the internal resistance of the battery. Furthermore, because the electrolyte is solid, there is less risk of ignition, leakage is unlikely, and problems such as degradation of battery performance due to corrosion are less likely to occur.

[0005] All-solid-state lithium-ion secondary batteries are equipped with a positive electrode layer, a negative electrode layer, and a solid electrolyte layer placed between them, and the electrolyte is made of solid material.

[0006] When constructing an electrode layer using only electrode active material by powder molding as a solid electrolyte layer, the electrolyte is solid, making it difficult for it to penetrate into the electrode layer. This reduces the interface between the electrode active material and the electrolyte, resulting in decreased battery performance. Furthermore, because the electrode layer is made of solid material, it lacks flexibility and processability, making it difficult to handle.

[0007] To address these problems, it has been proposed to form an electrode layer using a slurry prepared by dispersing an electrode active material, a solid electrolyte material, and a binder in a solvent.

[0008] Conventional lithium-ion secondary batteries use electrode slurries in which active materials and conductive additives are dispersed in a polymer solution obtained by dissolving polyvinylidene fluoride (PVDF) as a binder in N-methyl-2-pyrrolidone (NMP) solvent, or electrode slurries in which active materials and conductive additives are dispersed in an aqueous solution obtained by emulsifying styrene-butadiene rubber (SBR) as a binder in an aqueous solvent, with the addition of a thickener such as carboxymethylcellulose (CMC). However, in the case of all-solid-state lithium-ion secondary batteries, if the solid electrolyte is exposed to a highly polar solvent, the ionic conductivity decreases, and sufficient battery performance cannot be obtained. Therefore, NMP and water cannot be used as solvents for electrode slurries for electrode preparation.

[0009] For example, Patent Document 1 proposes a slurry for forming a positive electrode mixture layer, which consists of a positive electrode active material, a solid electrolyte material, a binder, a conductive agent, and a solvent, and is used to form a positive electrode mixture layer in an all-solid-state lithium-ion secondary battery. The slurry uses a styrene-containing binder resin such as styrene-butadiene rubber (SBR) or styrene-ethylene-butylene-styrene block copolymer (SEBS) as the binder, carbon fibers as the conductive agent, and a nonpolar solvent such as a normal alkane such as heptane, toluene, or xylene as the solvent. It has been shown that this improves electrical conductivity and results in a positive electrode current collector in which a positive electrode mixture layer with high flexibility and strength is formed.

[0010] However, it has also been reported that when carbon black is used as a conductive agent instead of carbon fiber, which is more expensive, and a styrene-containing binder resin is used as a binder, the electrical resistance increases compared to a positive electrode mixture layer with only a silicone-based polymer added.

[0011] Furthermore, Patent Document 2 proposes a slurry for forming a negative electrode mixture layer, which is used to form a negative electrode mixture for an all-solid-state lithium-ion secondary battery, comprising a negative electrode active material, a solid electrolyte material, a binder, a conductive agent, and a solvent. The slurry comprises a negative electrode active material containing Si, a solid electrolyte containing a sulfide solid electrolyte, a conductive material made of a fibrous carbonaceous material having a six-membered carbon ring, a binder made of a polymer compound having an aromatic ring such as SBR or SEBS, and at least one solvent selected from the group consisting of 1,3,5-trimethylbenzene, isopropylbenzene, and methylphenyl ether. It is also disclosed that the binder may contain polymer compounds other than polymer compounds having an aromatic ring, such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), butylene rubber (BR), polyvinyl butyral (PVB), and acrylic resin, in a range of 5% by mass or less. Furthermore, it has been shown that with this composition, when a negative electrode active material containing Si is used, the occurrence of poor contact between the conductive material and the negative electrode active material due to repeated charge-discharge cycles of the negative electrode mixture can be suppressed, thereby suppressing the increase in internal resistance.

[0012] However, even in this case, considering the dispersibility when using carbon fibers having a six-membered carbon ring as a conductive agent, binders consisting of polymer compounds having aromatic rings such as SBR and SEBS, and solvents having aromatic rings such as 1,3,5-trimethylbenzene, isopropylbenzene, and methylphenyl ether are selected. It has also been reported that, for example, when using flake-shaped carbonaceous material as a conductive agent, the increase in internal resistance cannot be suppressed even if similar materials having aromatic rings are used as binders and solvents.

[0013] In Patent Document 3, for example, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl acetate, polymethyl methacrylate, polyethylene, etc. are used as the binder, and for example, aromatic hydrocarbons such as toluene, xylene, decalin, and tetrahydronaphthalene, saturated hydrocarbons such as hexane, pentane, ethylhexane, heptane, decane, and cyclohexane, unsaturated hydrocarbons such as hexene, heptene, and cyclohexene are used as the solvent, and it has been proposed to form the positive electrode mixture layer by wet mechano-chemical treatment.

[0014] Furthermore, in Patent Document 4, in preparing a slurry for an all-solid-state lithium-ion secondary battery, conventionally, butyl butyrate, heptane, etc. have been used as a low-polarity solvent. However, since the affinity with PVDF is not sufficient, the molecular chains of PVDF cannot spread sufficiently in the solvent, the viscosity of the electrode slurry cannot be increased sufficiently, the electrode slurry cannot be uniformly coated, non-uniformity occurs in the electrode, and the battery performance deteriorates. In order to solve such problems, an acrylic copolymer having a predetermined structure is used as the binder, and for example, butyl ether (butyl butyrate, butyl propionate, butyl valerate) and alkane solvents (hexane, cyclohexane, heptane, cycloheptane, octane, cyclooctane) are used as the solvent.

Prior Art Documents

Patent Documents

[0015]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0016] However, when using the conventional solvent and binder combination described above as an electrode slurry for all-solid-state lithium-ion secondary batteries, or a carbonaceous material dispersion prepared by dispersing carbonaceous material in a solvent, problems of solid electrolyte degradation occur. Furthermore, it is difficult to disperse the carbonaceous material at a high concentration and uniformly in the slurry or dispersion. As a result, when mixed with the electrode active material, the solid components cannot be dispersed at a low viscosity and high concentration, and the charge-discharge characteristics, cycle characteristics, and electrode conductivity of the resulting all-solid-state lithium-ion secondary battery cannot be sufficiently improved, especially its conductivity.

[0017] Accordingly, the present invention aims to provide a carbonaceous material dispersion for all-solid-state lithium-ion secondary batteries and an electrode slurry for all-solid-state lithium-ion secondary batteries that solve the above problems. The present invention also aims to provide a carbonaceous material dispersion for all-solid-state lithium-ion secondary batteries and an electrode slurry for all-solid-state lithium-ion secondary batteries using the same, which, when used as a conductive additive for all-solid-state lithium-ion secondary batteries, can suppress the degradation of the solid electrolyte, and in which the carbonaceous material is dispersed at a high concentration and uniformly, exhibiting excellent conductivity. [Means for solving the problem]

[0018] To solve the above problems, the present inventors conducted diligent studies and research, and as a result, discovered that by blending a carbonaceous material dispersion for all-solid-state lithium-ion secondary batteries with a carbonaceous material, particularly carbon black, a dispersant containing at least polyvinyl butyral as a dispersant, and an ester-based solvent as a solvent in a predetermined ratio, the degradation of the solid electrolyte can be suppressed, the carbonaceous material can be dispersed at a high concentration and uniformly, and excellent conductivity can be achieved, leading to the present invention.

[0019] In other words, the present invention, which solves the above problems, is a carbonaceous material dispersion for an all-solid-state lithium-ion secondary battery, wherein a carbonaceous material and a dispersant are dispersed in a dispersion medium, and the dispersion medium contains at least an ester-based solvent, and the dispersant contains at least polyvinyl butyral, the amount of carbonaceous material in the dispersion is 10 to 25% by mass of the total mass of the dispersion, and the amount of dispersant is 5% by mass or more and less than 20% by mass of the mass of the carbonaceous material, and the viscosity at 25°C is 500 mPa·s or less.

[0020] In one embodiment of the carbonaceous material dispersion according to the present invention, the viscoelasticity of the carbonaceous material dispersion at 25°C is such that the shear rate is 10 to 1000 s. -1 A carbonaceous material dispersion is presented that is characterized by having a minimum value within a certain range.

[0021] In one embodiment of the carbonaceous material dispersion according to the present invention, the dispersion medium is a carbonaceous material dispersion containing 10% by mass or more of an ester-based solvent by the total amount of the dispersion medium.

[0022] In one embodiment of the carbonaceous material dispersion according to the present invention, the ester solvent is at least one selected from the group consisting of propyl acetate, butyl butyrate, butyl pentanoate, butyl hexanoate, pentyl butyrate, pentyl pentanoate, pentyl hexanoate, hexyl butyrate, hexyl pentanoate, and hexyl hexanoate.

[0023] In one embodiment of the carbonaceous material dispersion according to the present invention, the carbonaceous material dispersion is shown in which the ester solvent is butyl butyrate.

[0024] In one embodiment of the carbonaceous material dispersion according to the present invention, a carbonaceous material dispersion is shown in which the carbonaceous material is carbon black.

[0025] In one embodiment of the carbonaceous material dispersion according to the present invention, a carbonaceous material dispersion is further shown in which carbon black is acetylene black.

[0026] In one embodiment of the carbonaceous material dispersion according to the present invention, a carbonaceous material dispersion further containing a pH adjusting agent is shown.

[0027] The present invention, which solves the above problems, also provides an electrode slurry for an all-solid-state lithium-ion secondary battery comprising a carbonaceous material, a dispersant, a binder resin, and a positive electrode active material or a negative electrode active material in a dispersion medium, This is an electrode slurry for an all-solid-state lithium-ion secondary battery, characterized in that the dispersion medium contains at least an ester-based solvent, the dispersant contains at least polyvinyl butyral, and the amount of the dispersant in the solid content of the slurry is 5% by mass or more and less than 20% by mass relative to the mass of the carbonaceous material.

[0028] In one embodiment of the electrode slurry for an all-solid-state lithium-ion secondary battery according to the present invention, the slurry has a solid content concentration of 65 to 75% by mass, and a viscosity of 500 to 5000 mPa·s at 25°C. [Effects of the Invention]

[0029] According to the present invention, when used as a conductive additive for all-solid-state lithium-ion secondary batteries, a carbonaceous material dispersion can be provided that can suppress the degradation of the solid electrolyte and exhibit excellent conductivity by dispersing the carbonaceous material at a high concentration and uniformly. As a result, an electrode slurry for all-solid-state lithium-ion secondary batteries using the same can be provided, making it possible to manufacture secondary batteries with excellent and stable performance in terms of charge-discharge characteristics, cycle characteristics, electrode conductivity, etc. [Modes for carrying out the invention]

[0030] The present invention will be described in detail below based on embodiments.

[0031] <Carbonaceous material dispersion> A carbonaceous material dispersion for an all-solid-state lithium-ion secondary battery according to a first aspect of the present invention is a carbonaceous material dispersion for an all-solid-state lithium-ion secondary battery comprising a carbonaceous material and a dispersant dispersed in a dispersion medium, wherein the dispersion medium contains at least an ester-based solvent, and the dispersant contains at least polyvinyl butyral, the amount of carbonaceous material in the dispersion is 10 to 25% by mass of the total mass of the dispersion, the amount of dispersant is 5% by mass or more and less than 20% by mass of the mass of the carbonaceous material, and the viscosity at 25°C is 500 mPa·s or less.

[0032] First, we will explain the components that make up the carbonaceous material dispersion for all-solid-state lithium-ion secondary batteries, relating to the first aspect.

[0033] (carbonaceous material) The carbonaceous material used is not particularly limited as long as it is conductive and can take the form of a powder or granule. Examples include carbon black (CB), carbon nanotubes (CNT), carbon nanofibers (CNF), graphene, fullerene, natural graphite, artificial graphite, non-graphitizable carbon, cokes, graphites, etc. These can be used individually or in combination of two or more. CB is particularly preferred as the carbonaceous material. Examples of CB include furnace black, Ketjen black, channel black, acetylene black, and thermal black, and any of these can be used. Of these, acetylene black is preferred because its manufacturing process inherently results in a low metal content.

[0034] In addition, conventionally treated carbon black, such as oxidized carbon black or graphitized carbon black, can also be used. Oxidation of carbon black involves treating the carbon black at high temperatures in air or secondarily treating it with nitric acid, nitrogen dioxide, ozone, etc., to directly introduce (covalently bond) oxygen-containing polar functional groups such as phenol groups, quinone groups, carboxyl groups, and carbonyl groups onto the carbon black surface, thereby improving the dispersibility of the carbon black.

[0035] The carbonaceous material may also be subjected to dry magnetic separation to remove any metallic impurities introduced prior to the production of a carbonaceous material dispersion, and / or, after the carbonaceous material has been dispersed in an ester-based solvent to prepare a dispersion, it may be subjected to wet magnetic separation.

[0036] In this specification, the "granular" form of carbonaceous material used as a raw material dispersed in a dispersion medium is not limited to any form that can be dispersed in an ester-based solvent, as described later. Furthermore, its shape is not particularly limited and is not limited to a generally spherical shape, but may include elliptical, flaky, needle-like or short-fiber-like, amorphous, etc.

[0037] Regarding carbon black, as explained on the website of the Carbon Black Association (https: / / carbonblack.biz / index.html), for example, the smallest non-degradable unit of carbon black is the aggregate (primary aggregate), and a part of it (domain) is commonly referred to as a particle. This particle can be considered to correspond to the particle defined as the smallest unit in nanomaterials, but it is only a part of the aggregate. The aggregate forms agglomerate (secondary aggregate) through physical forces such as van der Waals forces. Furthermore, carbon black products are almost always transported and sold in the form of processed particles called beads, which are compressed or granulated to prevent scattering and improve handling.

[0038] For example, this may include primary aggregates with an average particle size of about 10 to 100 nm, secondary aggregates formed by the aggregation of such primary aggregates with an average particle size of about 0.1 to 100 μm, or particles that have been further processed to have an average particle size of about 500 to 5000 μm through compression or granulation treatment, taking into consideration handling properties.

[0039] Furthermore, from the viewpoint of carbon black conductivity, aggregates of conductive carbon nanoparticles, in which primary particles are linked together to form a chain-like or cluster-like structure, are preferred. The linkage of primary particles in the aggregate is also called a structure, and the degree of such development can be determined by particle size distribution measurement (dynamic light scattering method or laser diffraction / light scattering method) or electron microscope observation (either scanning or transmission type can be used). Such structures can efficiently form conductive paths between electrode active material particles. Therefore, excellent conductivity can be imparted to the electrode active material layer with a smaller amount of material used.

[0040] (dispersion medium) The dispersion medium constituting the carbonaceous material dispersion for all-solid-state lithium-ion secondary batteries according to the first aspect of the present invention contains at least an ester-based solvent. The reason for using an ester-based solvent is that, as will be described later, polyvinyl butyral is mainly used as the dispersant in the carbonaceous material dispersion for all-solid-state lithium-ion secondary batteries according to the first aspect of the present invention, and the ester-based solvent exhibits good solubility with polyvinyl butyral, is hydrophobic, and has low reactivity with solid electrolytes.

[0041] The dispersion medium according to the present invention is not particularly limited in terms of the proportion of the ester-based solvent in the dispersion medium, as long as it exhibits good solubility for polyvinyl butyral as a dispersant as described above. However, for example, it is preferable for the ester-based solvent to be present in an amount of 10% by mass or more, more preferably 20% by mass or more, of the total amount of the dispersion medium, in order to obtain a good dispersion. Of course, it is one preferred embodiment that the entire amount (100% by mass) of the dispersion medium is composed of the ester-based solvent.

[0042] Furthermore, the ester solvent used is not particularly limited, as long as it exhibits good solubility in polyvinyl butyral and has low reactivity with solid electrolytes. For example, R 1 -COOR 2 (However, R in the formula) 1 R is a hydrocarbon group of C1-C8. 2 is a C2-C8 alkyl group. Carboxylic acid esters represented by ) can be used.

[0043] Specifically, for example, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate, amyl propionate, hexyl propionate, heptyl propionate, octyl propionate, ethyl butyrate, propyl butyrate, butyl butyrate, amyl butyrate, hexyl butyrate, heptyl butyrate, octyl butyrate, ethyl pentanoate, propyl pentanoate, butyl pentanoate, amyl pentanoate, hexyl pentanoate, heptyl pentanoate, octyl pentanoate, ethyl hexanoate, hexyl Propyl sunate, butyl hexanoate, amyl hexanoate, hexyl hexanoate, heptyl hexanoate, octyl hexanoate, ethyl heptanoate, propyl heptanoate, butyl heptanoate, amyl heptanoate, hexyl heptanoate, heptyl heptanoate, octyl heptanoate, ethyl octanoate, propyl octanoate, butyl octanoate, amyl octanoate, hexyl octanoate, heptyl octanoate, octyl octanoate, etc. can be used individually or in combination of two or more.

[0044] Of these, propyl acetate, butyl butyrate, butyl pentanoate, butyl hexanoate, pentyl butyrate, pentyl pentanoate, pentyl hexanoate, hexyl butyrate, hexyl pentanoate, and hexyl hexanoate are preferred, with butyl butyrate being particularly preferred.

[0045] Furthermore, other solvents that can be used together with the ester-based solvent as a dispersion medium according to the present invention are not particularly limited as long as they do not significantly impair the solubility of the resin component and the dispersibility of the carbonaceous material by the ester-based solvent, but it is preferable to use a nonpolar solvent. Using a nonpolar solvent prevents a decrease in the ionic conductivity of the solid electrolyte, which can occur when using polar solvents such as water or NMP.

[0046] The nonpolar solvents that can be used with the above-mentioned ester-based solvents as dispersion media according to the present invention are not particularly limited, but specifically include, for example, nonaqueous linear and / or branched or cyclic alkanes having 4 to 30 carbon atoms, such as pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, methylcyclohexane, etc.; linear and / or branched and / or cyclic haloalkanes having 1 to 30 carbon atoms, such as dichloromethane, chloroform. tetrachloromethane, dichloroethane, trichloroethane, tetrachloroethane, chlorocyclohexane, etc.; aromatic compounds with 6 to 22 carbon atoms, e.g., benzene, toluene, xylene, mesitylene, etc.; hydrogenated aromatic compounds with 10 to 22 carbon atoms, e.g., tetralin, cis-decalin and trans-decalin, etc.; halogenated aromatic compounds with 6 to 22 carbon atoms, e.g., chlorobenzene, fluorobenzene, dichlorobenzene or difluorobenzene, trichlorobenzene or trifluorobenzene, chloronaphthalene or f Luoronaphthalene, etc.; linear and / or branched and / or cyclic ethers, e.g., diethyl ether, dipropyl ether, tert-butyl methyl ether, tert-amyl methyl ether, tert-amyl ethyl ether, dimethoxyethane, diethoxyethane, methoxybenzene, methylthiobenzene, ethoxybenzene, petroleum ether, etc.; linear and / or branched and / or cyclic ketones, e.g., acetone, trichloroacetone, butanone, pentanone, hexanone, heptanone, octanone, nonanone, cyclopene Tanone, cyclohexanone, acetophenone, acetylacetone, etc.; linear and / or branched and / or cyclic nitroalkanes, e.g., nitromethane, nitroethane, nitrocyclohexane, etc.; nitroaromatic compounds having 6 to 22 carbon atoms, e.g., nitrobenzene, etc.; linear and / or branched and / or cyclic amines, preferably tert-butylamine, diaminoethane, diethylamine, triethylamine, tributylamine, pyrrolidine, piperidine, morpholine, N-methylaniline, and N,N-dimethylaniline, etc.;Hexamethyldisilane, diphenyldimethylsilane, chlorophenyltrimethylsilane, phenyltrimethylsilane, phenethyltris(trimethylsiloxy)silane, phenyltris(trimethylsiloxy)silane, polydimethylsiloxane, tetraphenyltetramethyltrisiloxane, poly(3,3,3-trifluoropropylmethylsiloxane), 3,5,7-triphenylnonamethylpentasiloxane, 3,5-diphenyloctamethyltetrasiloxane, 1,1,5,5-tetraphenyl-1,3,3,5-tetramethyl Silicone oils such as tyl-trisiloxane and hexamethylcyclotrisiloxane; fluorinated solvents, such as hydrofluoroethers, chlorodifluoromethane, 1,1,1,2-tetrafluoroethane, pentafluoroethane, difluoromethane, trifluoromethane, 1,1,1,2,3,3,3-heptafluoropropane, 1,1-difluoroethane, 1,1,1,3,3,3-hexafluoropropane, octafluoropropane, etc.; or mixtures of nonpolar solvents as described above in any proportion may be included.

[0047] Among these, cyclohexane, n-hexane, benzene, toluene, and xylene are particularly desirable as nonpolar solvents.

[0048] The dispersion medium according to the present invention is preferably composed solely of the above-mentioned ester solvent, or a mixed solvent of an ester solvent and a nonpolar solvent, wherein the ester solvent content in the mixed solvent is 10% by mass or more and less than 100% by mass, and the nonpolar solvent content is 0% by mass or more and less than 90% by mass (provided the total is 100% by mass).

[0049] (Dispersant) The dispersant constituting the carbonaceous material dispersion for all-solid-state lithium-ion secondary batteries according to the first aspect of the present invention contains at least polyvinyl butyral.

[0050] As a dispersant, polyvinyl butyral is the main component, and it is particularly desirable that it be 80% by mass or more. In one particularly preferred embodiment, the entire amount of the dispersant, i.e., 100% by mass, is polyvinyl butyral. In a carbonaceous material dispersion for all-solid-state lithium-ion secondary batteries, by using polyvinyl butyral as a dispersant in this way and combining it with the ester-based solvent described above as a dispersion medium, good dispersibility of the carbonaceous material in the carbonaceous material dispersion can be obtained, and low viscosity can be achieved. Furthermore, as will be described later, when preparing an electrode slurry for all-solid-state lithium-ion secondary batteries, the solid content can be dispersed at a low viscosity and high concentration when mixed with the electrode active material. In addition, it has the effect of moderately increasing the viscosity of the slurry, reducing the settling rate of the electrode constituting materials such as electrode active material and carbonaceous material, and uniformly coating the slurry on the current collector, and it is possible to bind the materials constituting the electrode, such as between active materials, between active materials and conductive additives, and between conductive additives, with appropriate strength, adhesion, and conductivity.

[0051] While not particularly limited, polyvinyl butyral is preferable if it has a relatively low hydroxyl group content, specifically, for example, a hydroxyl group content in the polymer of 5% to 25% by mass, more preferably 10% to 20% by mass, and even more preferably 12.5% ​​to 17.5% by mass, as this results in good solubility in the aforementioned dispersion medium, the ester-based solvent. Furthermore, while not particularly limited, the acetate group content of the polyvinyl butyral is preferably about 1 to 7% by mass, and the viscosity of a 10% by mass ethanol solution of polyvinyl butyral, measured at 20°C in accordance with DIN53015, is preferably about 10 to 100 mPa·s, particularly 20 to 60 mPa·s.

[0052] Other dispersants that can be used in combination with polyvinyl butyral as dispersants include, for example, resin-based dispersants other than polyvinyl butyral, and surfactants as exemplified below.

[0053] (Other resin-based dispersants) Other resin-based dispersants besides polyvinyl butyral include polyvinyl acetal, polyvinyl acetate, polyester resin, epoxy resin, polyether resin, alkyd resin, and urethane resin. When other resin-based components are blended in addition to polyvinyl butyral as a dispersant, the composition shall be such that polyvinyl butyral is present in an amount of 80% by mass or more and less than 100% by mass, and the other components described above are present in an amount of less than 20% by mass and more than 0% by mass (however, the total is 100% by mass). If the amount of other components blended is less than 20% by mass, it is possible to maintain the viscosity of the carbonaceous material dispersion according to the present invention at 25°C at the desired value, specifically, for example, 500 mPa·s or less, and improve the bonding between active materials, between active materials and conductive additives, between conductive additives, and other materials constituting the electrodes when the final prepared slurry is coated onto a current collector.

[0054] (pH adjuster) In the carbonaceous material dispersion for all-solid-state lithium-ion secondary batteries according to the first aspect of the present invention, a pH adjuster may be added as needed. Examples of pH adjusting agents include tertiary amines, secondary amines, primary amines, cyclic amines, and alkanolamines or amino alcohols which are compounds having an amino group and a hydroxyl group in an alkane skeleton, or amine compounds such as diglycolamine, tris(hydroxymethyl)aminomethane (THAM), morpholine, and other amines. While not particularly limited, among these, 2-methylaminoethanol, 2-amino-1-butanol, 4-ethylamino-1-butanol, triethylamine, 2-amino-2-ethyl-1,3-propanediol (AEPD), 2-amino-2-methyl-1-propanol (AMP), and THAM are particularly preferred.

[0055] (Surfactants) In the carbonaceous material dispersion for all-solid-state lithium-ion secondary batteries according to the first aspect of the present invention, a surfactant may be added as a dispersant if necessary. While not particularly limited, examples of surfactants include anionic surfactants such as sodium dodecylbenzenesulfonate and sodium lauryl sulfate, cationic surfactants such as tetramethylammonium chloride, and nonionic surfactants such as polyoxyethylene alkyl ether compounds and polyoxyethylene fatty acid ester compounds.

[0056] When other components are added in addition to polyvinyl butyral as a dispersant, the composition shall be such that polyvinyl butyral is present in an amount of 80% by mass or more and less than 100% by mass, and the other components are present in an amount of less than 20% by mass and more than 0% by mass (however, the total is 100% by mass). If the amount of other components added is less than 20% by mass, it is possible to maintain the viscosity of the carbonaceous material dispersion according to the present invention at 25°C at the desired value, specifically, for example, 500 mPa·s or less, and improve the bonding between active materials, between active materials and conductive additives, between conductive additives, etc., when the final prepared slurry is coated onto a current collector.

[0057] (Formulation ratio in the dispersion) In the carbonaceous material dispersion for all-solid-state lithium-ion secondary batteries according to the first aspect of the present invention, the carbonaceous material is present in a dispersion medium containing at least an ester-based solvent, with a concentration of 10 to 25% by mass, more preferably 12 to 18% by mass, relative to the total mass of the dispersion, and the amount of dispersant is adjusted to be 5% by mass or more and less than 20% by mass, more preferably 6% by mass or more and less than 12% by mass, relative to the mass of the carbonaceous material (i.e., relative to 100% by mass of the carbonaceous material). If the amounts of carbonaceous material and dispersant are within this range, it is possible to create a dispersion containing a high concentration of carbonaceous material while maintaining good dispersibility and low viscosity of the carbonaceous material. If the concentration of carbonaceous material is lower than the above, the energy required for solvent removal in product manufacturing increases, and the transportation costs of the dispersion and the cost of the solvent increase. On the other hand, if the concentration of carbonaceous material is higher than the above, it becomes difficult to obtain sufficient fluidity, resulting in poor handling. Furthermore, if the concentration of the dispersant is lower than the above, it becomes difficult to obtain fluidity, while if the concentration of the dispersant is higher than the above, the proportion of insulating components in the dispersion increases, which may reduce the conductivity of the final product.

[0058] Furthermore, as mentioned above, when a pH adjuster is added, the amount of the pH adjuster added should be approximately 0.01 to 5%, more preferably 0.05 to 3%, relative to the total amount of the dispersion. By adding a pH adjuster within this range, it is possible to obtain better dispersibility of carbonaceous materials.

[0059] (Viscosity of dispersion) Furthermore, by performing a dispersion treatment on the composition and proportions described above, for example, as illustrated below, the carbonaceous material dispersion according to the present invention can have a viscosity of 500 mPa·s or less at 25°C, preferably around 50 to 300 mPa·s.

[0060] In this specification, the viscosity of the carbonaceous material dispersion is the value measured immediately after sufficiently stirring (for example, for 1 minute) the dispersion with a spatula at a measurement temperature of 25°C and a B-type viscometer rotor rotation speed of 60 rpm using a B-type viscometer.

[0061] Since the carbonaceous material dispersion according to the present invention has the above-described predetermined composition and blending ratio and exhibits the above-described predetermined viscosity, the carbonaceous material is dispersed at a high concentration and uniformly, showing stable fluidity. When mixed with an electrode active material to prepare an electrode slurry for an all-solid-state lithium-ion secondary battery, the electrode active material can be dispersed at a high concentration with an appropriate low viscosity suitable for construction.

[0062] Such characteristics can be objectively evaluated, for example, by the aspect that the carbonaceous material dispersion according to the present invention has a minimum value in the range of a viscoelasticity at 25°C of a shear rate of 10 to 1000 s -1 Preferably in the range of 10 to 500 s -1 More preferably in the range of 10 to 100 s -1 in the range.

[0063] In this specification, the viscoelasticity of this carbonaceous material dispersion is a value using a rheometer with the temperature condition of the dispersion being 25°C and the shear rate being changed from 0.1 s -1 to 1000 s -1 and measuring the shear viscosity, and is an index value based on the shear rate range showing the minimum value of the viscosity.

[0064] (Manufacture of Carbonaceous Material Dispersion) As a method for manufacturing a carbonaceous material dispersion for an all-solid-state lithium-ion secondary battery according to the first aspect of the present invention, although not particularly limited, the carbonaceous material and the dispersant are added to an ester-based solvent as a dispersion medium at the above-described predetermined ratio, stirred and mixed, and dispersed.

[0065] The dispersion device is not particularly limited, and any dispersion machine commonly used for pigment dispersion can be used. For example, mixers such as dispersers, homomixers, and planetary mixers; homogenizers (such as M-Technic's "Clearmix," PRIMIX's "Filmix," and Silverson's "Abramix"); paint conditioners (Red Devil); colloid mills (such as PUC's "PUC Colloid Mill" and IKA's "Colloid Mill MK"); cone mills (such as IKA's "Corn Mill MKO"); ball mills; and sand mills (Shinmaru). Examples include, but are not limited to, media-type dispersers such as Enterprises' "Dinomill," Atlighter, Pearlmill (Eirich's "DCPmill," etc.), Coballmill, wet jet mills (Genus' "Genus PY," Sugino Machine's "Starburst," Nanomizer's "Nanomizer," etc.), media-less dispersers such as M-Technique's "CREA SS-5" and Nara Machinery's "MICROS," and other roll mills.

[0066] Preferably, the carbonaceous material is ultimately prepared by dispersing it in a media mill, particularly a media mill using beads with an average particle size of 0.05 to 2 mm. More preferably, the material is prepared by first performing a dispersion treatment using a shear-type dispersion device, as detailed below, prior to the dispersion treatment with such a media mill, and then subsequently performing the dispersion treatment with a media mill.

[0067] Furthermore, if the particle size of the beads used in the media mill is too small, there is a risk that carbonaceous materials such as primary aggregates of carbon black may be finely fractured, and excessive energy will be required for the dispersion process. Also, handling becomes difficult, so it is preferable that the average particle size of the beads be 0.05 mm or larger, and particularly preferable that it be 0.5 mm or larger. On the other hand, if the beads are too large, the number of beads per unit volume decreases, reducing the dispersion efficiency, resulting in insufficient pulverization of the carbonaceous material, and the carbonaceous material particles may exist with a large aspect ratio, which may prevent the desired liquid properties from being obtained as a paint or coating agent. For this reason, it is preferable that the average diameter of the beads be 2 mm or less, and particularly preferable that it be 1.5 mm or less.

[0068] The material of the beads used as dispersion media in the media mill is not particularly limited; for example, alumina, zirconia, steel, chromium steel, and glass can be used. However, considering contamination of the product and the magnitude of kinetic energy due to specific gravity, it is preferable to use zirconia beads.

[0069] While there are no particular restrictions on the shape of the beads, spherical beads are generally used.

[0070] The structure of a media mill is not particularly limited, and various known media mills can be applied. Specifically, these include various known attritors, sand mills, and bead mills.

[0071] The bead filling ratio in the vessel can be determined by the vessel, stirring mechanism, and structure, and is not particularly limited. However, if the ratio is too low, it may not be able to exert sufficient crushing or cutting action on carbonaceous materials. On the other hand, if the ratio is too high, it may require a large driving force for rotation and may cause increased contamination of the processing medium due to bead wear. For this reason, it is desirable that the bead filling ratio be approximately 70 to 85% of the effective volume of the vessel.

[0072] Furthermore, operating conditions such as processing time, shaft rotation speed, vessel internal pressure, and motor load depend on the amount of carbonaceous material blended and the properties of the resin to be dispersed, particularly viscosity and compatibility with the carbonaceous material, and should be set appropriately according to the purpose.

[0073] Furthermore, prior to dispersion processing using such a media mill, it is possible to perform preliminary dispersion processing using other stirring devices, such as shear-type stirrers like dispersers and homomixers.

[0074] By performing this dispersion treatment, a dispersion with a viscosity of 500 mPa·s or less, preferably 50 to 300 mPa·s, at 25°C is prepared.

[0075] <Electrode slurry for all-solid-state lithium-ion secondary batteries> The carbonaceous material dispersion according to the first aspect of the present invention, as detailed above, can be prepared as an electrode slurry by containing the following electrode active material.

[0076] In other words, the electrode slurry for an all-solid-state lithium-ion secondary battery according to the second aspect of the present invention is an electrode slurry for an all-solid-state lithium-ion secondary battery comprising a carbonaceous material, a dispersant, a binder resin, and a positive electrode active material or a negative electrode active material in a dispersion medium, wherein the dispersion medium contains at least an ester-based solvent, the dispersant contains at least polyvinyl butyral, and the amount of the dispersant in the solid content of the slurry is 5% by mass or more and less than 20% by mass, more preferably 6% by mass or more and less than 12% by mass, relative to the mass of the carbonaceous material.

[0077] The manufacturing process and the order of adding each component to the electrode slurry for all-solid-state lithium-ion secondary batteries according to the second aspect of the present invention are not limited, and any of the following can be used: (a) a method of manufacturing an electrode slurry for all-solid-state lithium-ion secondary batteries by dispersing and mixing all components together; (b) a method of manufacturing an electrode slurry for all-solid-state lithium-ion secondary batteries by preparing a carbonaceous material dispersion according to the first aspect of the present invention as described above, and then blending a positive electrode active material or a negative electrode active material with this carbonaceous material dispersion; (c) a method of preparing a carbonaceous material dispersion in which a carbonaceous material (and dispersant) is dispersed in a part of the dispersion medium, and an electrode active material dispersion in which a positive electrode active material or a negative electrode active material (and dispersant) is dispersed in a part of the dispersion medium, and then mixing the carbonaceous material dispersion and the electrode active material dispersion to manufacture an electrode slurry for all-solid-state lithium-ion secondary batteries.

[0078] (Dispersant, carbonaceous material, dispersant, and pH adjuster) Regarding the components of the electrode slurry for all-solid-state lithium-ion secondary batteries according to the second aspect of the present invention, the dispersion medium, carbonaceous material, and dispersant are the same as those described for the carbonaceous material dispersion according to the first aspect of the present invention, so their description will be omitted here to avoid duplication. Furthermore, the electrode slurry for all-solid-state lithium-ion secondary batteries according to the second aspect of the present invention may also contain, if necessary, pH adjusting agents as described above, similar to the carbonaceous material dispersion according to the first aspect of the present invention.

[0079] (electrode active material) In the electrode slurry for an all-solid-state lithium-ion secondary battery according to a second aspect of the present invention, the positive electrode active material that can be incorporated is not particularly limited, but metal compounds such as metal oxides and metal sulfides that can dope or intercalate lithium ions, and conductive polymers can be used.

[0080] Examples include oxides of transition metals such as Fe, Co, Ni, and Mn, complex oxides with lithium, and inorganic compounds such as transition metal sulfides. Specifically, MnO, V2O5, V6O 13Examples include transition metal oxide powders such as TiO2, lithium-transition metal composite oxide powders such as layered lithium nickelate, lithium cobaltate, lithium manganate, and spinel-structured lithium manganate, lithium iron phosphate-based materials which are olivine-structured phosphoric acid compounds, and transition metal sulfide powders such as TiS2 and FeS. Conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Furthermore, the above inorganic and organic compounds may be mixed and used.

[0081] On the other hand, in the electrode slurry for an all-solid-state lithium-ion secondary battery according to the second aspect of the present invention, the negative electrode active material that can be incorporated is not particularly limited as long as it can dope or intercalate lithium ions. For example, metallic Li, alloys thereof such as tin alloys, silicon alloys, lead alloys, etc. X Fe2O3, Li X Fe3O4, Li X Examples of carbonaceous materials include metal oxides such as WO2, lithium titanate, lithium vanadate, and lithium siliconate; conductive polymers such as polyacetylene and poly-p-phenylene; amorphous carbonaceous materials such as soft carbon and hard carbon; artificial graphite such as highly graphitized carbonaceous materials; carbonaceous powders such as natural graphite; carbon black; mesophase carbon black; resin-fired carbonaceous materials; vapor-grown carbon fibers; and carbon fibers. These negative electrode active materials can be used individually or in combination.

[0082] These electrode active materials preferably have an average particle diameter in the range of 0.05 to 100 μm, and more preferably in the range of 0.1 to 50 μm. In this specification, the average particle diameter of the electrode active material refers to the average value of particle diameters measured with an electron microscope.

[0083] (Binder resin) In the electrode slurry for an all-solid-state lithium-ion secondary battery according to the second aspect of the present invention, the binder resin blended in the dispersion medium is not particularly limited, but polymers that are insoluble in water can be used. Specifically, for example, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyamide, polyamide-imide, butadiene rubber, isobutylene rubber, styrene-butadiene rubber, ethylene propylene rubber, and nitrile-butadiene rubber can be used. Of these, styrene-butadiene rubber is particularly preferred. In some cases, the same resin-based dispersants that can be blended in the carbonaceous material dispersion according to the first aspect of the present invention may function as the binder resin.

[0084] For manufacturing this electrode slurry, the same type of apparatus used for preparing the dispersion of the present invention described above can be used.

[0085] In one embodiment of an electrode slurry for an all-solid-state lithium-ion secondary battery according to a second aspect of the present invention, by using the predetermined components described above, when the solid content concentration of the slurry is 65 to 75% by mass, the viscosity of the slurry at 25°C can be made 500 to 5000 mPa·s, more preferably 1000 to 4000 mPa·s, thereby improving workability. [Examples]

[0086] The present invention will be described in detail below based on examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. In these examples, "parts" represents parts by mass, and "%" represents mass percent.

[0087] Example 1 With a total dispersion mass of 100% by mass, the following components were blended: 82.5% by mass of butyl butyrate (manufactured by Tokyo Chemical Industry Co., Ltd.) as the dispersion medium, 1.5% by mass of polyvinyl butyral (Eslec BL, manufactured by Sekisui Chemical Co., Ltd.) as the dispersant (10% by mass relative to acetylene black), 15% by mass of acetylene black (Denka Black (trademark) granular product, manufactured by Denka Co., Ltd.), and 1% by mass of 2-amino-2-ethyl-1,3-propanediol. The mixture was then dispersed using a laboratory bead mill (manufactured by AIMEX Co., Ltd.). For the dispersion process using a bead mill, zirconia beads with a diameter of 1 mm were used, the bead filling rate in the vessel was set to 30% of the vessel's effective volume, and the volume ratio of the dispersion to the beads was set to approximately 1:1. Dispersion was carried out in the vessel at a rotation speed of approximately 2000 rpm until the viscosity reached approximately 100 mPa·s.

[0088] The carbonaceous material dispersion (acetylene black dispersion) prepared in this manner was allowed to stand for more than 24 hours after dispersion treatment, and its viscosity was measured at 25°C, where it was 104 mPa·s. A B-type viscometer (TVB-15M, manufactured by Toki Sangyo Co., Ltd.) was used for the measurement. The measurement was performed immediately after thoroughly stirring the dispersion composition with a spatula at a measurement temperature of 25°C and a B-type viscometer rotor rotation speed of 60 rpm. Rotor No. 21 was used. Subsequently, the shear rate was measured at 0.1 s using a rheometer (Kinexus, manufactured by Malvern Panalytical). -1 ~1000s -1 The shear viscosity was measured while varying the viscosity up to 10s. -1 ~1000s -1 range (250s) -1 I confirmed that it was located in ).

[0089] To 4 parts of the prepared carbonaceous material dispersion, 18 parts of a binder solution in which styrene-butadiene rubber was dissolved in 10% by mass butyl butyrate were added, and the mixture was uniformly mixed using a rotational stirring defoamer to prepare a coating paste. The paste was applied to a glass plate using an applicator (manufactured by Yoshimitsu Seiki Co., Ltd.) and dried under reduced pressure at 100°C for 2 hours to obtain a coating film (film thickness after drying: 30 μm). The resistance value was measured using a low resistivity meter (Loresta-GX, manufactured by Mitsubishi Chemical Analytec Co., Ltd.) and was found to be 1211 Ω, indicating good conductivity.

[0090] Example 2 To 10.0 g of the carbonaceous material dispersion prepared in Example 1 above, LiNi was used as the positive electrode active material. 1 / 3 Co 1 / 3 Mn 1 / 3 30.0 g of O2 powder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., particle size 1 to several μm), a binder solution prepared by dissolving styrene-butadiene rubber in 10% by mass butyl butyrate, and butyl butyrate were mixed to achieve a total solids content of 65% by mass. The mixture was then treated for 5 minutes using a rotary-rotating agitator and defoamer at a rotational speed of 1200 rpm in both directions, resulting in a fluid slurry.

[0091] Here, the viscosity of the resulting slurry for forming the positive electrode composite layer was measured using the rheometer described above to determine if it had the appropriate viscosity for coating. The measurement conditions with the rheometer were a constant temperature of 25°C and a shear rate of 10s. -1 The viscosity of the slurry was then determined by taking the average of five measurements taken every 60 seconds. As a result, the viscosity of the slurry was 3746 mPa·s.

[0092] Example 3 Assuming a total mass of 100% by mass of the dispersion, 83.2% by mass of butyl butyrate was used as the dispersion medium, 0.8% by mass of polyvinyl butyral (Eslec BL, manufactured by Sekisui Chemical Co., Ltd.) (5.3% by mass relative to acetylene black) was used as the dispersant, 15% by mass of acetylene black (Denka Black (trademark) granular product, manufactured by Denka Co., Ltd.) was used as the dispersant, and 1% by mass of 2-amino-2-ethyl-1,3-propanediol was blended and dispersed using a bead mill. The dispersion conditions using the bead mill were the same as those in Example 1, except that dispersion was carried out until the viscosity reached approximately 300 mPa·s.

[0093] The viscosity of the carbonaceous material dispersion (acetylene black dispersion) prepared in this manner was measured in the same manner as in Example 1. As a result, the viscosity of the dispersion was 345 mPa·s. Subsequently, the shear rate was measured at 0.1 s using a rheometer, as in Example 1. -1 ~1000s -1 The shear viscosity was measured while varying the viscosity up to 10s. -1 ~1000s -1 range (630s) -1 I confirmed that it was located in ). Subsequently, a dried coating was prepared in the same manner as in Example 1, and the resistance value was measured to be 1079Ω, indicating good conductivity.

[0094] Example 4 With a total mass of 100% by mass of the dispersion, 81.5% by mass of butyl butyrate was used as the dispersion medium, 2.5% by mass of polyvinyl butyral (Eslec BL, manufactured by Sekisui Chemical Co., Ltd.) (16.7% by mass relative to acetylene black) was used as the dispersant, 15% by mass of acetylene black (Denka Black (trademark) granular product, manufactured by Denka Co., Ltd.) was used as the dispersant, and 1% by mass of 2-amino-2-ethyl-1,3-propanediol was added and dispersed using a bead mill. The dispersion processing conditions using the bead mill were the same as those in Example 1.

[0095] The viscosity of the carbonaceous material dispersion (acetylene black dispersion) prepared in this manner was measured in the same manner as in Example 1. As a result, the viscosity of the dispersion was 79 mPa·s. Subsequently, the shear rate was measured at 0.1 s using a rheometer, similar to Example 1. -1 ~1000s -1 The shear viscosity was measured while varying the viscosity up to 10s. -1 ~1000s -1 range (250s) -1I confirmed that it was located in ). Subsequently, a dried coating film was prepared in the same manner as in Example 1, and the resistance value was measured to be 1371 Ω, indicating good conductivity.

[0096] Comparative Examples 1-2 Dispersion treatment was carried out in a bead mill in the same manner as in Example 1, except that cellulose acetate or polyvinylpyrrolidone (both manufactured by Kanto Chemical Co., Ltd.) was used instead of polyvinyl butyral as the dispersant. However, in all cases, the resin components did not dissolve well in butyl butyrate as a dispersion medium, and a homogeneous dispersion of acetylene black could not be obtained.

[0097] Comparative Example 3 Assuming a total mass of 100% by mass of the dispersion, 83.4% by mass of butyl butyrate was used as the dispersion medium, 0.6% by mass of polyvinyl butyral (Eslec BL, manufactured by Sekisui Chemical Co., Ltd.) (4% by mass relative to acetylene black) was used as the dispersant, 15% by mass of acetylene black (Denka Black (trademark) granular product, manufactured by Denka Co., Ltd.) was used as the dispersant, and 1% by mass of 2-amino-2-ethyl-1,3-propanediol was added. Dispersion treatment was performed using a bead mill, but the dispersion did not exhibit sufficient fluidity.

[0098] Comparative Example 4 The total mass of the dispersion was set to 100% by mass. The mixture consisted of 81% by mass of butyl butyrate as the dispersion medium, 3% by mass of polyvinyl butyral (Eslec BL, manufactured by Sekisui Chemical Co., Ltd.) as a dispersant (20% by mass relative to acetylene black), 15% by mass of acetylene black (Denka Black (trademark) granular product, manufactured by Denka Co., Ltd.), and 1% by mass of 2-amino-2-ethyl-1,3-propanediol. Dispersion was performed using a bead mill. The dispersion conditions using the bead mill were the same as those in Example 1.

[0099] The viscosity of the carbonaceous material dispersion (acetylene black dispersion) prepared in this manner was measured in the same manner as in Example 1. As a result, the viscosity of the dispersion was 137 mPa·s. Subsequently, the shear rate was measured at 0.1 s using a rheometer, as in Example 1. -1 ~1000s -1 When the shear viscosity was measured while varying the viscosity up to a certain point, the minimum viscosity was found to be 10s. -1 ~1000s -1 range (250s) -1 It was located in ). Subsequently, a dried coating film was prepared in the same manner as in Example 1, and the resistance value was measured to be 1953Ω, indicating poor conductivity.

Claims

1. A carbonaceous material dispersion for all-solid-state lithium-ion secondary batteries, comprising a carbonaceous material and a dispersant dispersed in a dispersion medium, The dispersion medium is R １ - COOR ２ (However, R in the formula) １ R is a C1-C8 hydrocarbon group, ２ It is an alkyl group from C2 to C8.) It consists only of carboxylic acid esters represented by ). Alternatively, the mixed solvent consists of the carboxylic acid ester and a nonpolar solvent, wherein the content of the carboxylic acid ester in the mixed solvent is 10% by mass or more and less than 100% by mass, and the content of the nonpolar solvent is 0% by mass or more and less than 90% by mass (provided the total is 100% by mass). The nonpolar solvent is at least one selected from the group consisting of nonaqueous linear and / or branched or cyclic alkanes having 4 to 30 carbon atoms, linear and / or branched and / or cyclic haloalkanes having 1 to 30 carbon atoms, aromatic compounds having 6 to 22 carbon atoms, halogenated aromatic compounds having 6 to 22 carbon atoms, linear and / or branched and / or cyclic ethers, linear and / or branched and / or cyclic ketones, linear and / or branched and / or cyclic nitroalkanes, nitroaromatic compounds having 6 to 22 carbon atoms, linear and / or branched and / or cyclic amines, silicone oils, and fluorine-containing solvents. It contains at least polyvinyl butyral as a dispersant, A carbonaceous material dispersion characterized in that the amount of carbonaceous material in the dispersion is 10 to 25% by mass relative to the total mass of the dispersion, the amount of dispersant is 5% by mass or more and less than 20% by mass relative to the mass of the carbonaceous material, and the viscosity at 25°C is 500 mPa·s or less.

2. The viscoelasticity of the carbonaceous material dispersion at 25°C is such that the shear rate is 10 to 1000 s. －１ The carbonaceous material dispersion according to claim 1, characterized in that it has a minimum value within the range.

3. The carbonaceous material dispersion according to claim 1 or 2, wherein the dispersion medium contains 10% by mass or more of an ester-based solvent by the total amount of the dispersion medium.

4. The carbonaceous material dispersion according to any one of claims 1 to 3, wherein the carboxylic acid ester is at least one selected from the group consisting of propyl acetate, butyl butyrate, butyl pentanoate, butyl hexanoate, pentyl butyrate, pentyl pentanoate, pentyl hexanoate, hexyl butyrate, hexyl pentanoate, and hexyl hexanoate.

5. The carbonaceous material dispersion according to any one of claims 1 to 3, wherein the carboxylic acid ester is butyl butyrate.

6. A carbonaceous material dispersion according to any one of claims 1 to 5, wherein the carbonaceous material is carbon black.

7. The carbonaceous material dispersion according to claim 6, wherein the carbon black is acetylene black.

8. A carbonaceous material dispersion according to any one of claims 1 to 7, further containing a pH adjusting agent.