Conductive slurry for power storage devices

Abstract

To provide a conductive material slurry for a power storage device in which carbon nanotubes are well dispersed and which can contribute to improvement in high temperature cycle characteristics.SOLUTION: A conductive material slurry for a power storage device includes a conductive material containing carbon nanotubes, a dispersing agent which is a polymer containing vinyl alcohol units, vinyl acetate units, and units of formula (1), and an organic solvent. The content of vinyl alcohol units in the conductive material slurry is 20 to 100 parts by mass with respect to 100 parts by mass of the carbon nanotubes.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a conductive material slurry, a positive electrode paste for an electricity storage device, and a positive electrode for an electricity storage device. [Background technology]

[0002] In recent years, there has been active development of electric vehicles that do not emit carbon dioxide, with a view to curbing global warming. Electric vehicles have the drawback of having a shorter driving range and longer battery charging times than gasoline-powered vehicles. To shorten charging times, it is necessary to increase the electron transfer rate in the positive electrode. Currently, carbon black is used as a conductive material in the positive electrodes of non-aqueous electrolyte batteries, but there is a demand for a conductive material with lower electronic resistance than carbon black.

[0003] Carbon nanotubes (hereinafter sometimes referred to as "CNTs") are a conductive material with lower electronic resistance than carbon black, and their physical and chemical properties make them promising for application in a variety of fields. CNTs have a high aspect ratio and can form conductive paths with a small amount. CNTs are essentially nanocarbon materials that have the shape of a single sheet of graphite rolled into a cylindrical shape; those rolled in a single layer are called single-walled CNTs, and those rolled coaxially in multiple layers are called multi-walled CNTs.

[0004] In order to reduce the coating resistance of the positive electrode, it is necessary to uniformly disperse the carbon material in an organic solvent. Patent Document 1 discloses a conductive paste for lithium-ion battery positive electrodes that uses a polyvinyl alcohol resin containing 10 mass% of structural units derived from 2-hydroxyethyl methacrylate (HEMA) and having a saponification degree of 90 mol% as a dispersant for acetylene black. Patent Document 2 discloses the use of polyvinyl alcohol as a dispersant for CNTs. Patent Document 3 discloses a slurry composition for secondary battery electrodes that contains CNTs as the carbon material and a polyvinyl alcohol resin with a saponification degree of 98 mol% as a dispersant. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-130443 [Patent Document 2] Patent Publication No. 2021-50106 [Patent Document 2] WO2020 / 137403 publication Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a polyvinyl alcohol resin has a high degree of saponification (high polarity), the dispersant's adsorption to the carbon material improves, but its solubility in the solvent deteriorates, resulting in poor productivity of the conductive material slurry. The solubility of the dispersant in the solvent is a factor that also affects the dispersibility of the carbon material, and poor solubility of the dispersant in the solvent is disadvantageous in improving the dispersibility of the carbon material. Patent Document 1 discloses that by including a polymerizable unsaturated group-containing monomer (A1-1) such as 2-hydroxyethyl methacrylate (HEMA) as a constituent component of a polymer dispersant, it is possible to achieve both solubility in the solvent and adsorption to the carbon material. However, there is still room for improvement in terms of improving the dispersibility of the carbon material in the conductive material slurry. On the other hand, since an electricity storage device is repeatedly charged and discharged, it is desirable that the degree of deterioration of the electrodes due to the charge and discharge be small. The durability of an electrode against charge and discharge can be evaluated, for example, by high-temperature cycle characteristics, but Patent Documents 1 to 3 do not consider the relationship between the dispersant and high-temperature cycle characteristics.

[0007] Therefore, the present disclosure provides a conductive material slurry for an electricity storage device that exhibits good CNT dispersibility and can contribute to improving high-temperature cycle characteristics. The present disclosure also provides a positive electrode paste for an electricity storage device prepared using the conductive material slurry for an electricity storage device. The present disclosure also provides a positive electrode for an electricity storage device formed using the conductive material slurry for an electricity storage device. [Means for solving the problem]

[0008] In one aspect, the present disclosure provides a conductive material slurry for an electrical storage device, the conductive material slurry comprising a carbon material-based conductive material, a dispersant, and an organic solvent, the carbonaceous conductive material includes carbon nanotubes, The dispersant is a polymer containing a vinyl alcohol unit, a vinyl acetate unit, and a structural unit represented by the following general formula (1): The polymer contains, in one molecule, 62 to 98 mass% of the vinyl alcohol unit and 1 to 25 mass% of the constitutional unit represented by the general formula (1), a ratio of the mass of the vinyl alcohol unit to the total mass of the vinyl alcohol unit and the vinyl acetate unit in one molecule of the polymer is 83 to 99%; The present invention relates to a conductive material slurry for an electricity storage device, wherein the content of the vinyl alcohol unit in the conductive material slurry is 20 to 100 parts by mass with respect to 100 parts by mass of the carbon nanotubes. [ka] However, in the above general formula (1), R 1 is hydrogen or a methyl group, p is an integer of 1 or 2, and q is an integer of 2 or 3.

[0009] In one aspect, the present disclosure provides a positive electrode paste for an electricity storage device, comprising a positive electrode active material, a binder, a carbonaceous conductive material, a dispersant, and an organic solvent, the carbonaceous conductive material includes carbon nanotubes, The dispersant is a polymer containing a vinyl alcohol unit, a vinyl acetate unit, and a structural unit represented by the following general formula (1): The polymer contains, in one molecule, 62 to 98 mass% of the vinyl alcohol unit and 1 to 25 mass% of the constitutional unit represented by the general formula (1), a ratio of the mass of the vinyl alcohol unit to the total mass of the vinyl alcohol unit and the vinyl acetate unit in one molecule of the polymer is 83 to 99%; The present invention relates to a positive electrode paste for an electricity storage device, wherein the content of the vinyl alcohol units in the positive electrode paste is 20 to 100 parts by mass per 100 parts by mass of the carbon nanotubes. [ka] However, in the above general formula (1), R 1 is hydrogen or a methyl group, p is an integer of 1 or 2, and q is an integer of 2 or 3.

[0010] In one aspect, the present disclosure provides a positive electrode for an electricity storage device, including a positive electrode mixture layer, the positive electrode mixture layer includes a positive electrode active material, a carbon material-based conductive material, a dispersant, and a binder, the carbonaceous conductive material includes carbon nanotubes, The dispersant is a polymer containing a vinyl alcohol unit, a vinyl acetate unit, and a structural unit represented by the following general formula (1): The polymer contains, in one molecule, 62 to 98 mass% of the vinyl alcohol unit and 1 to 25 mass% of the constitutional unit represented by the general formula (1), a ratio of the mass of the vinyl alcohol unit to the total mass of the vinyl alcohol unit and the vinyl acetate unit in one molecule of the polymer is 83 to 99%; The present invention relates to a positive electrode for an electricity storage device, wherein the content of the vinyl alcohol units in the positive electrode mixture layer is 20 to 100 parts by mass per 100 parts by mass of the carbon nanotubes. [ka] However, in the above general formula (1), R 1 is hydrogen or a methyl group, p is an integer of 1 or 2, and q is an integer of 2 or 3. [Effects of the Invention]

[0011] The conductive material slurry for an electricity storage device of the present disclosure contains the above polymer as a dispersant, and the content of vinyl alcohol units in the conductive material slurry is 20 to 100 parts by mass per 100 parts by mass of carbon nanotubes, which allows for good dispersion of CNTs in the conductive material slurry for an electricity storage device and can contribute to improving high-temperature cycle characteristics. The positive electrode paste for an electricity storage device of the present disclosure is prepared using the conductive material slurry for an electricity storage device of the present disclosure, and therefore it is possible to reduce the coating resistance of the positive electrode mixture layer and improve the high-temperature cycle characteristics. The positive electrode for an electricity storage device according to the present disclosure has a positive electrode composite layer formed using the positive electrode paste for a battery according to the present disclosure prepared using the conductive material slurry for an electricity storage device according to the present disclosure, and therefore has good high-temperature cycle characteristics and low coating resistance of the positive electrode composite layer. DETAILED DESCRIPTION OF THE INVENTION

[0012] The conductive material slurry for an electricity storage device of the present disclosure (hereinafter also referred to as "conductive material slurry") contains, as a dispersant, a polymer containing, in one molecule, vinyl alcohol units, vinyl acetate units, and units represented by general formula (1) in a specific mass ratio, and is based on the new finding that by setting the amount of vinyl alcohol units to 100 parts by mass of CNTs in the conductive material slurry to a specific amount, the dispersibility of CNTs in the conductive material slurry is improved, and the high-temperature cycle characteristics of a positive electrode for an electricity storage device formed using the conductive material slurry are improved.

[0013] In the present disclosure, the details of the mechanism by which the dispersibility of CNTs in the conductive material slurry and the high-temperature cycle characteristics are improved are not clear, but are presumed as follows. In polymers (dispersants) containing vinyl alcohol units and vinyl acetate units, it is known that the vinyl alcohol units exhibit adsorption to CNTs, while the vinyl acetate units are the component responsible for solubility in solvents. However, when the dispersant becomes highly polar, its solubility in organic solvents such as NMP decreases. If the dispersant's solubility is low, it takes a long time to dissolve in the solvent, reducing productivity, and the dispersant's stability in the solvent decreases, resulting in reduced dispersibility. On the other hand, if the dispersant's solubility in organic solvents is too high, the vinyl alcohol units become less likely to adsorb to CNTs, resulting in poor CNT dispersibility. In the present disclosure, the content of the dispersant in the conductive material slurry is set to 20 to 100 parts by mass of the vinyl alcohol units per 100 parts by mass of CNTs, and the content of the vinyl alcohol units in one polymer molecule is set to 62 to 98% by mass, thereby ensuring the necessary adsorptive power for CNTs for high CNT dispersibility. The mass ratio of the vinyl alcohol units to the total mass of the vinyl alcohol units and the vinyl acetate units in one polymer molecule is set to 83 to 99% by mass, and the polymer molecule contains 1 to 25% by mass of a structural unit represented by the following general formula (1), thereby improving the solubility of the polymer containing vinyl alcohol units and vinyl acetate units without impairing the necessary adsorptive power for CNTs, thereby increasing productivity and ensuring the stability of the dispersant in the solvent. Furthermore, in the present disclosure, the polymer contains 1 to 25 mass % of the following general formula (1) per molecule, and therefore the glass transition temperature (Tg) of the dispersant is lower than, for example, a single-component polymer composed of vinyl alcohol units or a binary copolymer composed of vinyl alcohol units and vinyl acetate units. Therefore, the composite layer formed using the conductive slurry of the present disclosure has high adhesion to the current collector, and the composite layer becomes moderately soft while maintaining appropriate strength, which is thought to mitigate the adverse effects on the positive electrode of expansion and contraction associated with charging and discharging of the power storage device and improve the high-temperature cycle characteristics. However, the present invention is not limited to these mechanisms. The decrease in glass transition temperature (Tg) caused by introducing a constituent unit represented by the following general formula (1) into a polymer containing vinyl alcohol units and vinyl acetate units can be confirmed by the Fox equation.

[0014] <Conductive slurry> In one embodiment, the conductive material slurry of the present disclosure contains a carbon material-based conductive material (hereinafter sometimes abbreviated as "conductive material"), a dispersant, and an organic solvent, and the conductive material contains CNTs.

[0015] [Conductive material] In the conductive material slurry of the present disclosure, preferably 80 mass % or more, more preferably 90 mass % or more, even more preferably 95 mass % or more, still more preferably 98 mass % or more, still more preferably substantially 100 mass %, and still more preferably 100 mass % of the conductive material is CNT. Examples of conductive materials other than CNT contained in the conductive material slurry of the present disclosure include carbon material-based conductive materials such as acetylene black, ketjen black, and graphite, and these can be used alone or in combination of two or more.

[0016] In the present disclosure, CNT refers to a whole including multiple CNTs. The form of the CNTs used in preparing the conductive material slurry of the present disclosure is not particularly limited, and may be, for example, multiple CNTs that are independent of each other, multiple CNTs that are bundled or entangled, or a mixture of these forms. The CNTs may have various numbers of walls or diameters. The CNTs may contain impurities (e.g., catalysts and amorphous carbon) derived from the CNT manufacturing process.

[0017] In one or more embodiments, the CNT has a cylindrical shape formed by rolling one surface of graphite. CNTs rolled into one layer are called single-walled CNTs (SWCNTs), CNTs rolled into two layers are called double-walled CNTs (DWCNTs), and CNTs rolled into three or more layers are called multi-walled CNTs (MWCNTs). Depending on the properties required for the positive electrode composite layer formed using a positive electrode paste for an electricity storage device containing the conductive material slurry of the present disclosure (hereinafter sometimes abbreviated as "positive electrode paste"), single-walled, double-walled, or multi-walled CNTs, or a mixture thereof, can be used. To obtain a positive electrode composite layer with good CNT dispersion and low resistance, it is preferable to use multi-walled CNTs.

[0018] The average diameter of CNTs is measured using a scanning electron microscope (SEM) or an atomic force microscope (AFM). In the present disclosure, the average diameter is not particularly limited, but from the viewpoint of improving CNT dispersibility, it is preferably 3 nm or more, more preferably 5 nm or more, and even more preferably 8 nm or more. From the viewpoint of improving conductivity, it is preferably 100 nm or less, more preferably 50 nm or less, even more preferably 30 nm or less, still more preferably 20 nm or less, and even more preferably 15 nm or less. Specifically, the average diameter of CNTs is preferably 3 to 100 nm, more preferably 3 to 50 nm, even more preferably 3 to 30 nm, still more preferably 5 to 20 nm, still more preferably 8 to 20 nm, and even more preferably 8 to 15 nm.

[0019] The average length of the CNTs is measured using a scanning electron microscope (SEM) or an atomic force microscope (AFM). In the present disclosure, the average length is not particularly limited, but from the viewpoint of improving electrical conductivity, it is preferably 2 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and even more preferably 30 μm or more. From the viewpoint of improving dispersibility, it is preferably 500 μm or less, more preferably 300 μm or less, even more preferably 200 μm or less, and even more preferably 120 μm or less. Specifically, the average length of the CNTs is preferably 2 to 500 μm, more preferably 5 to 300 μm, even more preferably 10 to 200 μm, and even more preferably 30 to 120 μm.

[0020] The impurity content in CNTs is measured by methods such as thermogravimetric analysis, and in the present disclosure, the lower the better. From the viewpoint of achieving a high concentration of useful CNT content, the impurity content in CNTs is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, even more preferably 10% by mass or less, and even more preferably substantially 0% by mass.

[0021] The content of the conductive material in the conductive material slurry of the present disclosure is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more, from the viewpoint of improving the convenience of adjusting the concentration of the positive electrode paste, and is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, from the viewpoint of imparting a viscosity that makes the conductive material slurry easy to handle. Specifically, the content of the conductive material in the conductive material slurry of the present disclosure is preferably 0.5 to 10% by mass, more preferably 1.0 to 5% by mass, and even more preferably 1.5 to 3% by mass.

[0022] [Dispersant] The dispersant contained in the conductive material slurry of the present disclosure (hereinafter, sometimes referred to as the "dispersant of the present disclosure" or the "polymer of the present disclosure") is a polymer containing, in one molecule, a vinyl alcohol unit, a vinyl acetate unit, and a constitutional unit represented by the following general formula (1). The vinyl alcohol unit is represented by -CH2-CH(OH)-. The vinyl acetate unit is represented, for example, by -(CH3COO)CH-CH2-. The vinyl alcohol unit is a component that contributes to adsorption to CNTs, and the vinyl acetate unit is a component that contributes to dissolution in organic solvents such as NMP. The constitutional unit represented by the following general formula (1) is a component that contributes to improving solubility in organic solvents and high-temperature cycle characteristics. [ka] However, in the above general formula (1), R 1 is hydrogen or a methyl group, p is an integer of 1 or 2, and q is an integer of 2 or 3.

[0023] [Vinyl alcohol unit, vinyl acetate unit] The content of vinyl alcohol units per molecule of the polymer of the present disclosure is 62% by mass or more from the viewpoint of improving CNT dispersibility. When the content of vinyl alcohol units per molecule is 62% by mass or more, the vinyl alcohol units adsorb to the CNTs and hold the CNTs, and the polyvinyl structure, which is the main chain of the polymer, spreads over the CNT surface. It is presumed that the steric repulsion of the polymer causes strong steric repulsion between the CNTs, making the CNTs highly dispersible in the solvent. The content of vinyl alcohol units per molecule of the polymer of the present disclosure is preferably 69% by mass or more, more preferably 75% by mass or more, from the viewpoint of improving CNT dispersibility. On the other hand, from the viewpoints of productivity and the stability of the conductive material slurry, it is preferably 98% by mass or less, more preferably 95% by mass or less.

[0024] In the polymer of the present disclosure, the ratio (100×a / (a+b)) of the mass (a) of vinyl alcohol units to the sum of the mass (a) of vinyl alcohol units and the mass (b) of vinyl acetate units in one molecule is 83 to 99% by mass. When the ratio (100×a / (a+b)) is 83% by mass or more, excessive dissolution of the polymer in organic solvents such as N-methyl-2-pyrrolidone (NMP) is suppressed, while sufficient adsorption of the polymer to CNTs is ensured, which is thought to contribute to improved dispersibility. When the ratio (100×a / (a+b)) is 99% by mass or less, the polymer is moderately soluble in organic solvents, in combination with the effect of the structural unit represented by general formula (1). Therefore, preparation of the conductive material slurry does not take an excessively long time, and the conductive material slurry is stable. The mass a of the vinyl alcohol unit and the mass b of the vinyl acetate unit can be calculated from the amount of vinyl acetate used in the synthesis of the polymer of the present disclosure and the amount of sodium hydroxide used in the saponification reaction, respectively.

[0025] The above-mentioned ratio 100×a / (a+b) within one molecule of the polymer of the present disclosure is 83 mass% or more, preferably 90 mass% or more, and more preferably 94 mass% or more from the viewpoint of improving the dispersibility of CNTs, and is 99 mass% or less, preferably 98 mass% or less, and more preferably 95 mass% or less from the viewpoint of productivity and the stability of the conductive material slurry.

[0026] [Constituent unit represented by general formula (1)] The constitutional unit represented by the general formula (1) is as described above. However, from the viewpoint of high-temperature cycle properties, R 1 is preferably a methyl group, p is preferably 2, and q is preferably 2. Examples of monomers that provide the structural unit represented by the above general formula (1) include 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate, and among these, 2-hydroxyethyl (meth)acrylate is preferred, and 2-hydroxyethyl methacrylate is more preferred.

[0027] The content of the structural unit represented by general formula (1) in one molecule of the polymer of the present disclosure is 1% by mass or more, preferably 3% by mass or more, and more preferably 5% by mass or more, from the viewpoints of improving productivity by improving the solubility of the polymer and improving high-temperature cycle characteristics. On the other hand, from the viewpoints of suppressing a decrease in the adsorption force of the polymer to CNTs due to excessive dissolution of the polymer and suppressing a decrease in the strength of the composite layer, the content is 25% by mass or less, preferably 15% by mass or less, and more preferably 10% by mass or less. In the present disclosure, the content of the structural unit represented by general formula (1) in one molecule of the polymer of the present disclosure is specifically 1 to 25% by mass, preferably 3 to 15% by mass, and more preferably 5 to 10% by mass. The content (mass %) of the constitutional unit represented by general formula (1) in one molecule of the polymer of the present disclosure can be considered as the mass ratio of the monomer that provides the constitutional unit represented by general formula (1) to all reactive monomers used in the synthesis of the polymer of the present disclosure.

[0028] [Other building blocks] The polymer of the present disclosure may contain other structural units in addition to vinyl alcohol units, vinyl acetate units, and the structural units represented by the general formula (1) above. Examples of such other structural units include one or more structural units selected from vinyl ester units other than vinyl acetate, vinyl butyral units, styrene units, ethylene units, and butadiene units. The vinyl ester units other than vinyl acetate are derived from vinyl ester monomers used as raw material monomers for the polymer. Examples of vinyl ester monomers include vinyl propionate, vinyl butyrate, and vinyl laurate.

[0029] The degree of polymerization of the polymer of the present disclosure is preferably 20 or more, more preferably 50 or more, even more preferably 200 or more, and even more preferably 300 or more, from the viewpoint of improving the dispersibility of CNTs by suitably coating the CNTs with a polyvinyl structure, and is preferably 5000 or less, more preferably 3000 or less, even more preferably 2000 or less, and even more preferably 1000 or less, from the viewpoint of improving the dispersibility of CNTs by improving the dispersibility of the polymer itself. In the present disclosure, the degree of polymerization of the polymer is specifically preferably 20 to 5000, more preferably 50 to 3000, even more preferably 200 to 2000, and even more preferably 300 to 1000.

[0030] If the content of the vinyl alcohol units in the conductive material slurry of the present disclosure is too low, the CNTs will aggregate, and the stability of the conductive material slurry will not be maintained. If the content is too high, the aggregation effect of the vinyl alcohol units during solvent drying will hinder contact between the CNTs, resulting in an increase in the coating resistance of the positive electrode coating film. Here, "the content of the vinyl alcohol units in the conductive material slurry" means the total amount of vinyl alcohol units contained in the conductive material slurry.

[0031] The content of vinyl alcohol units in the conductive material slurry of the present disclosure is 20 parts by mass or more, preferably 23 parts by mass or more, per 100 parts by mass of CNTs, from the viewpoint of high dispersibility of CNTs and stability of the conductive material slurry, and 100 parts by mass or less, preferably 30 parts by mass or less, per 100 parts by mass of CNTs, from the viewpoint of coating film resistance. The content of vinyl alcohol units in the conductive material slurry of the present disclosure is specifically 20 to 100 parts by mass, preferably 23 to 30 parts by mass, per 100 parts by mass of CNTs. The content of dispersant in the conductive material slurry is an amount such that the amount of vinyl alcohol units is 20 to 100 parts by mass, preferably 23 to 30 parts by mass, per 100 parts by mass of CNTs.

[0032] [Polymer manufacturing method] The polymer of the present disclosure may be synthesized by any known method, for example, by polymerizing vinyl acetate and a monomer that provides a structural unit represented by general formula (1) and saponifying the resulting copolymer.

[0033] [Organic solvents] The solvent contained in the conductive material slurry of the present disclosure is preferably an organic solvent capable of dissolving the binder contained in the positive electrode paste. Examples of the organic solvent include amide polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, and octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol; glycerin, trimethylolpropane, pentanediol, and the like. Examples of suitable organic solvents include polyhydric alcohols such as pentane, thiaerythritol, or sorbitol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, or tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, or cyclopentanone; and esters such as ethyl acetate, γ-butyl lactone, and ε-propiolactone. The organic solvent contained in the conductive material slurry may be one type or a combination of two or more types. When the binder is PVDF (polyvinylidene fluoride resin), which is contained in conventional battery positive electrode pastes, the organic solvent is generally N-methyl-2-pyrrolidone (NMP). NMP is particularly preferred as the organic solvent from the viewpoint of improving the dispersibility of CNTs.

[0034] (binder) The binder contained in the positive electrode paste of the present disclosure, which will be described later, may be added to the conductive material slurry or the positive electrode active material of the present disclosure when preparing the positive electrode paste. In one embodiment, the binder may be contained in the conductive material slurry of the present disclosure in advance.

[0035] The binder is not particularly limited, and known binders used in the production of battery electrodes can be used. For example, vinylidene fluoride polymers such as polyvinylidene fluoride (PVDF), vinylidene fluoride copolymers with hexafluoropropylene or monochlorotrifluoroethylene, and modified vinylidene fluoride with carboxylic acid can be used. There are no particular limitations on the weight-average molecular weight of these vinylidene fluoride polymers, but vinylidene fluoride polymers with a molecular weight of 100,000 to 1,500,000 are generally used. The vinylidene fluoride polymer may be mixed with styrene-butadiene rubber, polyacrylonitrile, or the like.

[0036] The amount of binder contained in the conductive material slurry, positive electrode paste, or positive electrode mixture layer of a positive electrode for an electricity storage device according to the present disclosure is preferably 150 parts by mass or more, more preferably 300 parts by mass or more, and even more preferably 500 parts by mass or more, relative to 100 parts by mass of vinyl alcohol units in the conductive material slurry, positive electrode paste, or positive electrode mixture layer of a positive electrode for an electricity storage device, from the viewpoint of ensuring the integrity of the positive electrode mixture layer and the adhesion between the positive electrode mixture layer and the current collector; and from the viewpoint of dispersibility of CNTs and preventing a loss of dispersion stability of the conductive material slurry or positive electrode paste due to an increase in the viscosity of the conductive material slurry or positive electrode paste associated with the addition of the binder, the amount of binder is preferably 800 parts by mass or less, more preferably 700 parts by mass or less, and even more preferably 660 parts by mass or less, relative to 100 parts by mass of vinyl alcohol units in the conductive material slurry, positive electrode paste, or positive electrode mixture layer of a positive electrode for an electricity storage device. Specifically, the amount of binder contained in the conductive material slurry, the positive electrode paste, or the positive electrode mixture layer of the positive electrode for the electricity storage device is preferably 150 to 800 parts by mass, more preferably 300 to 700 parts by mass, and even more preferably 500 to 660 parts by mass, relative to 100 parts by mass of vinyl alcohol units in the conductive material slurry, the positive electrode paste, or the positive electrode mixture layer of the positive electrode for the electricity storage device.

[0037] [Nitrogen-containing organic compounds] In one embodiment, the positive electrode paste and the positive electrode composite layer of the positive electrode of the present disclosure, which will be described later, may further contain a nitrogen-containing organic compound. The nitrogen-containing organic compound may be added to the conductive material slurry and other components of the present disclosure when preparing the positive electrode paste. In one embodiment, the nitrogen-containing organic compound may be pre-contained in the conductive material slurry of the present disclosure. The addition of the nitrogen-containing organic compound allows the preparation of a conductive material slurry and a positive electrode paste that have low viscosity and good handleability.

[0038] Although the details of the mechanism by which the addition of a nitrogen-containing organic compound reduces viscosity are unclear, the polymer of the present disclosure does not cover the entire surface of the carbonaceous conductive material, and exposed portions exist on the surface of the carbonaceous conductive material. Therefore, adjacent carbonaceous conductive materials aggregate in an organic solvent due to π-π interactions and hydrogen bonding between polar groups present on the surface of the carbonaceous conductive material. However, when a nitrogen-containing organic compound is included, the nitrogen-containing organic compound interacts with the polar groups (neutralization reaction or dipole-dipole interaction) to suppress hydrogen bonding between the carbonaceous conductive materials. Furthermore, the amine (cation) interacts with the π electrons of the carbonaceous conductive material to suppress π-π interactions between the carbonaceous conductive materials. It is presumed that the suppression of hydrogen bonding and the suppression of π-π interactions improves the dispersibility of the carbonaceous conductive material, resulting in a lower viscosity compared to when the nitrogen-containing organic compound is not added. However, the present disclosure should not be interpreted as being limited to these mechanisms.

[0039] The nitrogen-containing organic compound is preferably a compound having at least one primary, secondary, or tertiary amino group in the molecule (hereinafter referred to as a primary, secondary, or tertiary amine). In the present application, a primary, secondary, or tertiary amino group refers to a structure in which all three bonds to the central nitrogen atom are single bonds. As long as the nitrogen-containing organic compound has one such primary, secondary, or tertiary amino group, it may have other nitrogen atoms in the molecule, and the other nitrogen atoms may be primary, secondary, or tertiary amino groups or may constitute an imino group having a double bond. When other nitrogen atoms are present in the molecule, it is preferable that they are not adjacent to the nitrogen atom of the amino group.

[0040] The primary to tertiary amines are preferably aliphatic amines, and may be linear (branched or linear) or cyclic. In the case of cyclic amines, saturated rings are preferred. Non-cyclic amines may have an unsaturated group such as an imino group along with an amino group. The hydrocarbon group portion of the aliphatic amine may be substituted with OH, an amino group, COOH, or the like. In addition, -CH2- in the aliphatic group may be replaced with O (oxygen atom), and in this case, it is preferable that the O (oxygen atom) is not adjacent to the nitrogen atom of the amino group. Examples of the primary to tertiary amines include alkylamines, amino group-containing alcohols, carboxyl-substituted alkylamines, imidazoles, piperazines, guanidines, piperidines, and pyrrolidines.

[0041] The alkylamines are preferably primary, secondary, or tertiary amines in which the alkyl groups present are each independently a branched or linear alkyl group, and more preferably have alkyl groups such that the total number of carbon atoms in the molecule is 15 or less. Specific examples include hexylamine, octylamine, diethylamine, dibutylamine, trimethylamine, triethylamine, tributylamine, N-propylethylamine, N-butylethylamine, and N,N-dimethylcyclohexylamine. The alkyl groups may be substituted with amino groups, in which case the amine contains two or more primary, secondary, or tertiary amino groups, and examples thereof include di- or triamines such as ethylenediamine and diethylenediaminetriamine.

[0042] As the amino group-containing alcohol, compounds in which hydrogen of the alkyl group in the above-mentioned alkylamine is substituted with OH are preferred, and examples thereof include monoethanolamine, diethanolamine, triethanolamine, N-butyldiethanolamine, N,N-dimethylaminoethanol, Nn-butylethanolamine, 2-(methylamino)ethanol, N-methylethanolamine, N-ethylethanolamine, 2-amino-1-propanol, 2-amino-2-methyl-1-propanol, 1-amino-2-propanol, 2-amino-1,3-propanediol, etc. Among them, 2-amino-1,3-propanediol is preferred.

[0043] Carboxyl-substituted alkylamines include compounds in which hydrogen atoms in the alkyl group of the above-mentioned alkylamines are substituted with COOH, such as ethylenediaminetetraacetic acid, 1,3-propanediaminetetraacetic acid, 1,2-propanediaminetetraacetic acid, 1,3-diamino-2-hydroxypropanetetraacetic acid, glycol ether diaminetetraacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid, hexamethylenediaminetetraacetic acid, dicarboxymethylglutamic acid, dicarboxymethylaspartic acid, S,S-ethylenediaminedisuccinic acid, ethylenediaminedi(o-hydroxyphenyl)acetic acid, hydroxyethyliminodiacetic acid, ethylenediaminediacetic acid, iminodiacetic acid, ethylenediaminedipropionic acid, nitrilotriacetic acid, hydroxyethylenediaminetriacetic acid, nitrilotripropionic acid, methylglycinediacetic acid, diethylenetriaminepentaacetic acid, and triethylenetetraminehexaacetic acid. Furthermore, some or all of the carboxyl groups may form a salt with an alkali metal such as sodium.

[0044] Specific examples of imidazoles include 1,2-dimethylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 4-ethyl-2-methylimidazole, and 1-methyl-4-ethylimidazole.

[0045] Preferred piperazines are unsubstituted or alkyl-substituted piperazines, where the alkyl group may further have an amino group. The alkyl group may be substituted at any position on the piperazine ring, either on a nitrogen atom or on a carbon atom. Specific examples include piperazine, 1-methylpiperazine, 1-ethylpiperazine, 1-propylpiperazine, 1,4-dimethylpiperazine, 1,4-diethylpiperazine, 1,4-dipropylpiperazine, 2-methylpiperazine, 2-ethylpiperazine, 3-propylpiperazine, 2,6-dimethylpiperazine, 2,6-diethylpiperazine, 2,6-dipropylpiperazine, 2,5-dimethylpiperazine, 2,5-diethylpiperazine, and 2,5-dipropylpiperazine. Also preferred are piperazines substituted with an aminoalkyl group, such as 1-aminoethylpiperazine.

[0046] Other examples of the nitrogen-containing organic compound include guanidines, piperidines, and pyrrolidines. Specific examples include guanidine and guanidine salts, piperidine, 1-methylpiperidine, 1-ethylpiperidine, 1-propylpiperidine, 2, 3, or 4-methylpiperidine, 2, 3, or 4-ethylpiperidine, 2,6-dimethylpiperidine, 2,6-diethylpiperidine, 2,6-dipropylpiperidine, 2,4-dimethylpiperidine, 2,4-diethylpiperidine, 1-aminoethylpiperidine, morpholine, pyrrolidine, 1-methylpyrrolidine, 1-ethylpyrrolidine, 1-propylpyrrolidine, 2 or 3-methylpyrrolidine, 2 or 3-ethylpyrrolidine, 2,5-dimethylpyrrolidine, 2,5-diethylpyrrolidine, 2,5-dipropylpyrrolidine, 2,4-dimethylpiperidine, 2,4-diethylpiperidine, and 1-aminoethylpyrrolidine.

[0047] The content of the nitrogen-containing organic compound contained in the conductive material slurry, positive electrode paste, or positive electrode mixture layer of a positive electrode for an electrical storage device is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 5 parts by mass or more, relative to 100 parts by mass of the conductive material, from the viewpoint of improving the dispersibility of the conductive material, and is preferably 2000 parts by mass or less, more preferably 1000 parts by mass or less, and even more preferably 500 parts by mass or less, from the viewpoint of high conductivity. Specifically, the content of the nitrogen-containing organic compound contained in the conductive material slurry, positive electrode paste, or positive electrode mixture layer of a positive electrode for an electrical storage device is preferably 0.5 to 2000 parts by mass, more preferably 1 to 1000 parts by mass, and even more preferably 5 to 500 parts by mass, relative to 100 parts by mass of the conductive material.

[0048] The conductive material slurries of the present disclosure may further contain other components, such as antioxidants, neutralizing agents, antifoaming agents, preservatives, dehydrating agents, rust inhibitors, plasticizers, etc. (hereinafter also referred to as additives), to the extent that the effects of the present disclosure are not impaired.

[0049] [Method for producing conductive slurry] In one or more embodiments, the conductive material slurry of the present disclosure can be prepared by mixing a conductive material, a dispersant of the present disclosure, an organic solvent, and, as necessary, components such as a binder, a nitrogen-containing organic compound, or an additive using a mixer / disperser, and performing a dispersion treatment until a uniform composition is achieved. In one aspect, a method for producing a conductive material slurry of the present disclosure includes the steps of: dissolving a dispersant of the present disclosure in an organic solvent to obtain a dispersant solution; adding a conductive material to the dispersant solution; and performing a dispersion treatment using a mixer / disperser on the dispersant solution to which the conductive material has been added.

[0050] The mixer / disperser may be at least one selected from an ultrasonic homogenizer, a vibration mill, a jet mill, a ball mill, a bead mill, a sand mill, a roll mill, a homogenizer, a high-pressure homogenizer, an ultrasonic device, an attritor, a dissolver, and a paint shaker.

[0051] The dispersion treatment is preferably carried out while circulating the crude dispersion by, for example, discharging it from the mixer-disperser and then injecting it back into the mixer-disperser, and the circulation is preferably carried out 2 to 40 times, and the discharging and injecting rate of the dispersion is preferably 10 to 60 g / min.

[0052] In the method for producing a conductive material slurry of the present disclosure, some of the components constituting the conductive material slurry may be mixed and then mixed with the remainder, or each component may be added in multiple batches rather than all at once. The conductive material may be mixed with the other components in a dry state, or may be mixed with a solvent and then mixed with the other components. Examples of the solvent include the same organic solvents as described above. It is preferable that the binder is dissolved in a solvent, i.e., the binder solution is mixed with the other components. Examples of the solvent include the same organic solvents as described above.

[0053] When preparing a conductive material slurry of the present disclosure containing a binder, it is preferable to mix a binder solution with a crude dispersion containing a conductive material, a dispersant of the present disclosure, an organic solvent, and, as necessary, a nitrogen-containing organic compound or an additive, etc., and it is preferable to agitate the mixture containing the crude dispersion and the binder solution with a mixer or the like, and then supply the mixture to a mixer / disperser.

[0054] The viscosity of the conductive material slurry of the present disclosure at 25°C is preferably low, and from the viewpoint of improving handleability during preparation of the positive electrode paste, it is preferably 90 Pa·s or less, more preferably 70 Pa·s or less, and even more preferably 60 Pa·s or less.

[0055] <Positive electrode paste for energy storage devices> In one aspect, the present disclosure relates to a positive electrode paste for an electrical storage device, comprising a conductive material slurry of the present disclosure and a positive electrode active material. The positive electrode paste of the present disclosure prepared using the conductive material slurry of the present disclosure has good CNT dispersibility, thereby reducing the coating resistance of the positive electrode mixture layer and improving high-temperature cycle characteristics.

[0056] In one aspect, the present disclosure relates to a positive electrode paste for an electricity storage device, comprising a positive electrode active material, a binder, a conductive material, the dispersant of the present disclosure, and an organic solvent, wherein the carbonaceous conductive material contains CNTs, and the content of the vinyl alcohol units in the positive electrode paste of the present disclosure is 20 to 100 parts by mass per 100 parts by mass of CNTs. "The content of the vinyl alcohol units in the positive electrode paste" refers to the total amount of vinyl alcohol units contained in the positive electrode paste of the present disclosure.

[0057] The positive electrode paste of the present disclosure contains the dispersant of the present disclosure in an amount such that the content of the vinyl alcohol units in the positive electrode paste of the present disclosure is 20 to 200 parts by mass per 100 parts by mass of CNTs. This results in good dispersion of CNTs in the positive electrode paste, a reduction in the coating resistance of the positive electrode mixture layer, and improved high-temperature cycle characteristics.

[0058] [Cathode active material] The positive electrode active material may be any active material capable of absorbing and releasing lithium and capable of undergoing charge-discharge reactions, such as LiCoO2, LiNiO2, LiMn2O4, ternary (NMC) LiNi x Mn y Co z O2, Li-rich (Li(Li x Me 1-x )O2 (Me=Co, Ni, Mn, etc.), Ni-rich type (LiNi x Co y Al z Examples of the positive electrode active material include lithium metal composite oxides such as SiO2. The positive electrode active material is used in the form of particles. The average particle size can be, for example, 1 μm or more and 40 μm or less.

[0059] (Content of positive electrode active material in positive electrode paste) The content of the positive electrode active material in the positive electrode paste of the present disclosure is, in terms of solid content, preferably 80% by mass or more, and more preferably 90% by mass or more, from the viewpoint of increasing the energy density and capacity, and is preferably 99.5% by mass or less, and more preferably 99% by mass or less, from the viewpoint of improving the binding strength of the positive electrode mixture layer to the current collector.

[0060] The content of the positive electrode active material in the positive electrode paste or the positive electrode mixture layer of the energy storage device positive electrode described later, expressed as the ratio of the mass of the positive electrode active material to the total mass of the vinyl alcohol units in the positive electrode paste or the positive electrode mixture layer (positive electrode active material / vinyl alcohol units), is preferably 150 or more, more preferably 300 or more, and even more preferably 500 or more, from the viewpoints of suppressing aggregation of the positive electrode active materials and of maintaining the stability of the positive electrode paste. Furthermore, from the viewpoints of suppressing aggregation of the positive electrode active materials in the positive electrode mixture layer after solvent removal, which is caused by covering the positive electrode active material with an excessive amount of dispersant, and suppressing an increase in the coating resistance of the positive electrode mixture layer, the content of the positive electrode active material in the positive electrode paste or the positive electrode mixture layer, expressed as the mass ratio (positive electrode active material / vinyl alcohol units), is preferably 800 or less, more preferably 750 or less, and even more preferably 700 or less. The content of the positive electrode active material in the positive electrode paste is preferably 150 to 800, more preferably 300 to 750, and even more preferably 500 to 700, when expressed in terms of the mass ratio (positive electrode active material / vinyl alcohol unit).

[0061] (Dispersant content in positive electrode paste) The content of the dispersant (polymer) in the positive electrode paste of the present disclosure is, in terms of solid content, preferably 0.05% by mass or more, more preferably 0.10% by mass or more, from the viewpoint of reducing the resistance of the positive electrode mixture layer, and preferably 1% by mass or less, more preferably 0.5% by mass or less, from the viewpoint of maintaining a high energy density of the power storage device. Specifically, the content of the dispersant (polymer) in the positive electrode paste of the present disclosure is preferably 0.05 to 1% by mass, more preferably 0.10 to 0.5% by mass.

[0062] (Conductive material content in positive electrode paste) The content of the conductive material in the positive electrode paste of the present disclosure is preferably 0.3 mass% or more, more preferably 0.5 mass% or more, calculated as solid content, from the viewpoint of the conductivity of the positive electrode mixture layer, and is preferably 2 mass% or less, more preferably 1 mass% or less, from the viewpoint of maintaining a high energy density of the electricity storage device. Specifically, the content of the conductive material in the positive electrode paste of the present disclosure is preferably 0.3 to 2 mass%, more preferably 0.5 to 1 mass%.

[0063] (Binder content in positive electrode paste) The binder content in the positive electrode paste of the present disclosure is preferably 0.5 mass% or more, more preferably 0.8 mass% or more, calculated as solid content, from the viewpoints of the coating properties of the positive electrode mixture layer and the binding strength with the current collector, and is preferably 1.5 mass% or less, more preferably 1.2 mass% or less, from the viewpoint of maintaining a high energy density of the electricity storage device. Specifically, the binder content in the positive electrode paste of the present disclosure is preferably 0.5 to 1.5 mass%, more preferably 0.8 to 1.2 mass%.

[0064] The positive electrode pastes of the present disclosure may further contain other components, such as antioxidants, neutralizing agents, antifoaming agents, preservatives, dehydrating agents, rust inhibitors, and plasticizers, as long as the effects of the present disclosure are not impaired.

[0065] (Positive electrode paste manufacturing method) In one or more embodiments, the positive electrode paste of the present disclosure can be produced by mixing and stirring a positive electrode active material, the conductive material slurry of the present disclosure, a solvent (additional solvent) for adjusting the solid content, etc., and, if necessary, a binder, etc. The components may be mixed in any order. Examples of the solvent (additional solvent) include the same organic solvents as those described above, with NMP being preferred. A planetary mixer, a bead mill, a jet mill, etc. can be used for mixing and stirring, or these can be used in combination.

[0066] The positive electrode paste of the present disclosure may be prepared by premixing some of the components used in the preparation of the positive electrode paste and then mixing the premixed components with the remaining components. Alternatively, each component may be added in multiple batches rather than all at once. This reduces the mechanical load on the stirring device. The solids concentration of the positive electrode paste of the present disclosure may be adjusted according to the viscosity suitable for applying the positive electrode paste to the current collector. Alternatively, components other than the positive electrode active material may be mixed and dispersed until homogeneous, after which the positive electrode active material may be added and stirred until further homogeneous. In one aspect, the method for producing a positive electrode paste of the present disclosure includes a step of adding and dispersing a positive electrode active material into the conductive slurry of the present disclosure. In another aspect, the method for producing a positive electrode paste of the present disclosure includes adding a binder solution prepared by dissolving a binder in an organic solvent to the conductive slurry of the present disclosure, mixing the two, and then adding and dispersing the positive electrode active material.

[0067] <Positive electrodes for energy storage devices> In one aspect, the present disclosure relates to a positive electrode for an electricity storage device, including a current collector and a positive electrode mixture layer bonded to the current collector, the positive electrode mixture layer being formed using the positive electrode paste of the present disclosure. Also, in one aspect, the present disclosure relates to a positive electrode for an electricity storage device, including a positive electrode mixture layer, the positive electrode mixture layer including a positive electrode active material, a carbon material conductive material, a dispersant of the present disclosure, and a binder, the carbon material conductive material including CNTs, and the content of the vinyl alcohol units in the positive electrode mixture layer is 20 to 100 parts by mass per 100 parts by mass of CNTs. The "content of the vinyl alcohol units in the positive electrode mixture layer" refers to the total amount of vinyl alcohol units contained in the positive electrode mixture layer, and can be considered as the total amount of vinyl alcohol units contained in the positive electrode paste used to form the positive electrode mixture layer.

[0068] The positive electrode for an electricity storage device according to the present disclosure contains the dispersant according to the present disclosure in an amount such that the content of the vinyl alcohol units in the positive electrode mixture layer is 20 to 100 parts by mass per 100 parts by mass of CNTs. This results in good dispersibility of CNTs in the positive electrode mixture layer, a reduction in coating resistance of the positive electrode mixture layer, and improved high-temperature cycle characteristics.

[0069] In the method for manufacturing a positive electrode for an electricity storage device according to the present disclosure, the positive electrode paste according to the present disclosure is applied to a current collector such as aluminum foil, and then dried to form a positive electrode composite layer. To increase the density of the positive electrode, compaction can be performed using a press. A die head, a cone reverse roll, a direct roll, a gravure roll, or the like can be used to apply the positive electrode paste. Drying after application can be performed using heating, airflow, infrared irradiation, or a combination thereof. The positive electrode can be pressed using a roll press or the like. [Example]

[0070] The present invention will be described in more detail below with reference to Production Examples, Examples and Comparative Examples.

[0071] <Production of dispersants> (Dispersant a1) A copolymerization reaction was carried out at 60°C in a reaction vessel equipped with a thermometer, reflux condenser, nitrogen gas inlet tube, and stirrer using 95 parts by mass of vinyl acetate and 5 parts by mass of 2-hydroxyethyl methacrylate (monomer (C)) as polymerizable monomers, methanol as solvent, and azobisisobutyronitrile as a polymerization initiator, to obtain a resin solution. Next, a methanol solution of sodium hydroxide was added to the resin solution to carry out a saponification reaction, and after thorough washing, the solution was dried in a hot air dryer to obtain dispersant a1 with a degree of polymerization of 300 and the composition shown in Table 1. 6 parts of the obtained dispersant a1 (6 parts solid content) were added to 962 parts of N-methyl-2-pyrrolidone (NMP) (solvent) heated to 80°C and mixed to completely dissolve the dispersant a1. The time required for complete dissolution was 4 hours. The time required for complete dissolution was measured by mixing 6 parts of dispersant a1 with 962 parts of N-methyl-2-pyrrolidone (NMP) and heating the mixture to 80°C, and measuring the time required for the presence of undissolved aggregates to disappear when visually inspected.

[0072] By controlling the usage amounts (parts by mass) of vinyl acetate and monomer (C) described in the above (dispersant a1) and the saponification reaction, dispersants a2 to a9 described in Table 1 were prepared. The time required for complete dissolution of the obtained dispersant in NMP is shown in Table 2.

[0073]

Table 1

[0074] <Preparation of CNT Slurry> As an example of the conductive material slurry, CNT slurries A1 to A12 in Table 2 were prepared by the following method.

[0075] (CNT Slurry A1) 2 g of multi-walled carbon nanotubes (MWCNT, average diameter 12 nm, average length 40 μm) as fibrous carbon nanostructures was added to 100 g of an NMP solution of dispersant a1 (solid content 0.624 g) to obtain a crude dispersion. Then, the crude dispersion containing MWCNT and dispersant a1 was filled into a high-pressure homogenizer (manufactured by Mikari Co., Ltd., product name "BERYU MINI") having a multi-stage pressure control device (multi-stage pressure reducer) that applies back pressure during dispersion, and the dispersion treatment of the crude dispersion was performed at a pressure of 100 MPa. Specifically, while applying back pressure, a shear force was applied to the crude dispersion to disperse MWCNT, and CNT slurry A1 as a fibrous carbon nanostructure dispersion was obtained. The dispersion treatment was performed while circulating the dispersion by discharging it from the high-pressure homogenizer and injecting it back into the high-pressure homogenizer again. This circulation was performed 20 times, and the discharge and injection rates of the dispersion were 30 g / min. The content (total amount) of vinyl alcohol units in CNT slurry A1 was 28.1 parts by mass with respect to 100 parts by mass of the CNT content.

[0076] (CNT Slurries A2 to A12) CNT slurries A2 to A12 were each prepared by the same operation as the preparation of CNT slurry A1 so as to have the composition described in Table 2. The nitrogen-containing organic compound used for the adjustment of CNT slurry A7 is 2-amino-1,3-propanediol.

[0077] [Viscosity measurement] The viscosity (25°C) of the conductive material slurry was measured as follows: An Anton Paar MCR302 rheometer was equipped with a parallel plate PP50, and the shear rate was set to 0.1 s -1 From the 1000s -1 After increasing the shear rate to 1000 s -1 to 0.1 seconds -1 Return to (return route), return shear rate 1s -1 The viscosity at 1000 kJ / min was measured and is shown in Table 2.

[0078] [Particle size measurement] The CNT slurries A1 to A12 prepared as described above were each diluted 500 times with NMP. These were then placed in glass cells as measurement targets, and the cells were attached to a Malvern Panalytical Zetasizer Nano-S to measure the particle size of the CNTs when the temperature of the measurement target was 20°C.

[0079] [Preparation of positive electrode paste] (Preparation of Positive Electrode Pastes B1 to B12) 7.5 g of CNT slurries A1 to A12, 4.3 g of NMP, and 3.0 g of PVDF (8%) NMP solution (KF Polymer L#7208, manufactured by Kureha Corporation) were weighed into a 50 ml sample bottle and mixed uniformly with a spatula. 24.0 g of LCO (lithium cobalt oxide, manufactured by Nippon Chemical Industry Co., Ltd., CellSeed C-8hV) was then added as the positive electrode active material, and the mixture was again mixed with a spatula until uniform. The mixture was further stirred for 5 minutes using a planetary centrifugal mixer (AR-100, manufactured by Thinky Corporation) to obtain positive electrode pastes B1 to B12, respectively.

[0080] In the positive electrode pastes B1 to B12, the contents (mass %) of the positive electrode active material, binder (PVDF), dispersant (polymer), and conductive material (CNT) are as follows, converted into solid content.

[0081] (mass ratio) Positive electrode paste B1~B4, B7, B8, B10~B12 (solid content concentration: 62% by mass) Positive electrode active material: binder: dispersant: conductive material = 98.23:0.98:0.19:0.60 Positive electrode paste B5, B6, B9 (solid content: 62% by mass) Positive electrode active material: binder: dispersant: conductive material = 97.82:0.98:0.60:0.60

[0082] [Measurement of the coating resistance value of the positive electrode composite layer] The positive electrode paste prepared according to the above [Preparation of Positive Electrode Paste] was dropped onto a polyester film and uniformly coated with a 100 μm applicator. This coated polyester film was dried at 100 °C for 1 hour to obtain a positive electrode composite layer with a thickness of 40 μm. The coating resistance was measured at a limit voltage of 10 V using a Loresta-GP (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) equipped with a PSP probe. The results are shown in Table 2.

[0083] [Preparation of electrode (cathode) and battery] The positive electrode paste prepared according to the above [Preparation of positive electrode paste] was applied to an Al foil having a thickness of 20 μm so that the positive electrode capacity was 3 mAh / cm 2 The mixture was coated onto a current collector and vacuum dried at 100°C for 12 hours to produce an electrode material (positive electrode material). This positive electrode material was punched out to a diameter of 13 mm and pressed to produce an electrode (positive electrode). A 19 mm diameter separator and a 15 mm diameter, 0.5 mm thick coin-shaped lithium metal were placed on the positive electrode to produce a 2032-type coin cell (test half cell). The electrolyte used was 1M LiPF6 EC / DEC (volume ratio) = 3 / 7.

[0084] [High temperature cycle characteristic measurement] The battery was charged at 0.2 C to 4.2 V and discharged to 3.0 V in a 25°C environment, and this cycle was repeated three times. Then, in a 60°C environment, the battery was charged at 1 C until the battery voltage reached 4.2 V and then discharged at 1 C until the battery voltage reached 3.0 V. This cycle was repeated 200 times. The capacity retention rate ΔC = (C1 / C0) × 100 (%) was calculated from the first discharge capacity (C0) and the 200th discharge capacity (C1), and the high-temperature cycle characteristics were evaluated according to the following criteria. A higher capacity retention rate indicates less discharge capacity loss and better high-temperature cycle characteristics. A: ΔC is 90% or more B: ΔC is 80% or more but less than 90% C: ΔC is 60% or more and less than 80% D: ΔC is less than 60% (Charge / discharge conditions) 30℃, 0.2C, charge 4.45V CC / CV 1 / 10C cutoff Discharge CC3.0V cutoff

[0085] [Table 2]

[0086] As shown in Table 2, the Examples, in which the content of vinyl alcohol units in one molecule of the dispersant is 62 to 98 mass%, the content of structural units derived from HEMA is 1 to 25 mass%, 100×a / (a+b) is 83 to 99 mass%, and 20 to 100 mass parts of vinyl alcohol units are contained per 100 mass parts of CNT, are more suitable overall than the Comparative Examples in terms of productivity, CNT dispersibility, coating film resistance, and high-temperature cycle characteristics. [Industrial Applicability]

[0087] The conductive material slurry of the present disclosure has good dispersibility of CNTs, which results in a low viscosity of the conductive material slurry. Furthermore, when the conductive material slurry of the present disclosure is used to prepare a positive electrode paste, the viscosity of the positive electrode paste is low, which can contribute to lowering the resistance of the positive electrode coating film. It can also contribute to improving the high-temperature cycle characteristics.

Claims

1. A conductive material slurry for an electricity storage device, comprising a carbon material-based conductive material, a dispersant, and an organic solvent, the carbonaceous conductive material includes carbon nanotubes, The dispersant is a polymer containing a vinyl alcohol unit, a vinyl acetate unit, and a structural unit represented by the following general formula (1): The polymer contains, in one molecule, 62 to 98% by mass of the vinyl alcohol unit and 1 to 25% by mass of the constitutional unit represented by general formula (1), a ratio of the mass of the vinyl alcohol unit to the total mass of the vinyl alcohol unit and the vinyl acetate unit in one molecule of the polymer is 83 to 99%; The conductive material slurry for an electricity storage device has a content of the vinyl alcohol unit in the conductive material slurry of 20 to 100 parts by mass per 100 parts by mass of the carbon nanotubes. 【Chemical 1】 However, in the above general formula (1), R 1 is hydrogen or a methyl group, p is an integer of 1 or 2, and q is an integer of 2 or 3.

2. Further containing a binder, 2. The conductive material slurry for a power storage device according to claim 1, wherein a content of the binder in the conductive material slurry is 150 to 800 parts by mass per 100 parts by mass of the vinyl alcohol unit in the conductive material slurry.

3. The conductive material slurry for an electricity storage device according to claim 1 or 2, further comprising a nitrogen-containing organic compound.

4. A positive electrode paste for an electricity storage device, comprising a positive electrode active material, a binder, a carbon material-based conductive material, a dispersant, and an organic solvent, the carbonaceous conductive material includes carbon nanotubes, The dispersant is a polymer containing a vinyl alcohol unit, a vinyl acetate unit, and a structural unit represented by the following general formula (1): The polymer contains, in one molecule, 62 to 98% by mass of the vinyl alcohol unit and 1 to 25% by mass of the constitutional unit represented by general formula (1), a ratio of the mass of the vinyl alcohol unit to the total mass of the vinyl alcohol unit and the vinyl acetate unit in one molecule of the polymer is 83 to 99%; The positive electrode paste for an electricity storage device has a content of the vinyl alcohol unit in the positive electrode paste of 20 to 100 parts by mass per 100 parts by mass of the carbon nanotubes. 【Chemistry 2】 However, in the above general formula (1), R 1 is hydrogen or a methyl group, p is an integer of 1 or 2, and q is an integer of 2 or 3.

5. 5. The positive electrode paste for an electricity storage device according to claim 4, wherein the content of the binder in the positive electrode paste is 150 to 800 parts by mass per 100 parts by mass of the vinyl alcohol unit in the positive electrode paste.

6. 6. The positive electrode paste for an electricity storage device according to claim 4, wherein the ratio of the mass of the positive electrode active material to the total mass of the vinyl alcohol units in the positive electrode paste (the positive electrode active material / vinyl alcohol units) is 150 to 800.

7. The positive electrode paste for an electricity storage device according to any one of claims 4 to 6, further comprising a nitrogen-containing organic compound.

8. A positive electrode for an electricity storage device including a positive electrode mixture layer, the positive electrode mixture layer includes a positive electrode active material, a carbon material-based conductive material, a polymer, and a binder, the carbonaceous conductive material includes carbon nanotubes, The dispersant is a polymer containing a vinyl alcohol unit, a vinyl acetate unit, and a structural unit represented by the following general formula (1): The polymer contains, in one molecule, 62 to 98% by mass of the vinyl alcohol unit and 1 to 25% by mass of the constitutional unit represented by general formula (1), a ratio of the mass of the vinyl alcohol unit to the total mass of the vinyl alcohol unit and the vinyl acetate unit in one molecule of the polymer is 83 to 99%; The positive electrode for an electricity storage device, wherein the content of the vinyl alcohol unit in the positive electrode mixture layer is 20 to 100 parts by mass per 100 parts by mass of the carbon nanotubes. 【Chemistry 3】 However, in the above general formula (1), R 1 is hydrogen or a methyl group, p is an integer of 1 or 2, and q is an integer of 2 or 3.

9. 9. The positive electrode for an electricity storage device according to claim 8, wherein the content of the binder in the positive electrode mixture layer is 150 to 800 parts by mass per 100 parts by mass of the vinyl alcohol unit in the positive electrode mixture layer.

10. 10. The positive electrode for an electricity storage device according to claim 8 or 9, wherein the ratio of the mass of the positive electrode active material to the total mass of the vinyl alcohol units in the positive electrode mixture layer (the positive electrode active material / vinyl alcohol units) is 150 to 800.

11. The positive electrode for an electricity storage device according to any one of claims 8 to 10, wherein the positive electrode mixture layer further contains a nitrogen-containing organic compound.

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