Resin composition, carbon material dispersion composition, composite material slurry, electrode film, secondary battery, and vehicle

Abstract

The present invention provides a resin composition containing an alkali metal and a copolymer (X) having an alkylene structural unit and a nitrile group-containing structural unit, the content of the alkali metal being 50 ppm or more and less than 10,000 ppm, and the resistivity being 5,000-25,000 Omega cm (inclusive) when the non-volatile component content of the resin composition is 8 mass% by N-methyl-2-pyrrolidone.

Description

Technical Field

[0001] This disclosure relates to resin compositions and carbon material dispersion compositions. More specifically, it relates to carbon material dispersion compositions comprising resin compositions and carbon materials, composite slurries comprising carbon material dispersion compositions and active substances, electrode films formed by coating the like, secondary batteries having electrodes having electrode films and electrolytes, and vehicles having secondary batteries. Background Technology

[0002] With the increasing popularity of electric vehicles and the miniaturization, lightweighting, and high performance of portable devices, there is a demand for secondary batteries with high energy density and high capacity. Against this backdrop, non-aqueous electrolyte secondary batteries using non-aqueous electrolytes, especially lithium-ion secondary batteries, are being used in numerous devices due to their high energy density and high voltage characteristics.

[0003] As the negative electrode material used in these lithium-ion secondary batteries, carbon materials, represented by graphite, exhibit high charge-discharge capacity per unit mass at low potentials close to that of lithium (Li). However, the charge-discharge capacity per unit mass of these electrode materials has been utilized to near theoretical values, and the energy density per unit mass of the battery is approaching its limit. Therefore, in order to improve electrode utilization, research is underway to reduce conductive additives and binders that do not contribute to discharge capacity.

[0004] Conductive additives serve to form conductive channels within the electrode, and these channels must not be easily disrupted by the expansion and contraction of the electrode film. To maintain conductive channels with a small amount of conductive additive, using carbon materials with large specific surface areas, particularly carbon nanotubes (CNTs), a type of nanocarbon, is effective. However, carbon materials with large specific surface areas have strong cohesiveness, making it difficult to uniformly disperse them in composite slurries and electrode films.

[0005] Against this backdrop, numerous methods have been proposed for preparing carbon material dispersion compositions using various dispersants and for manufacturing composite material slurries from these carbon material dispersion compositions.

[0006] For example, Patent Documents 1 and 2 propose carbon material dispersion compositions in which the dispersibility is improved by adding alkaline compounds along with polymeric dispersants such as polyvinylpyrrolidone and hydrogenated nitrile rubber. However, while these dispersants can produce carbon material dispersion compositions with good dispersion, on the other hand, the dispersion of the carbon material sometimes becomes poor and the conductivity deteriorates during the formation of the electrode film.

[0007] Furthermore, in Patent Documents 3 and 4, it is proposed to use a mixture containing a predetermined Mooney viscosity (ML) 1+4A binder composition for electrodes using hydrogenated nitrile butadiene rubber (at 100°C) allows for good dispersion of carbon materials in composite slurries. Patent Document 5 proposes a dispersant composition using hydrogenated nitrile butadiene rubber with a weight-average molecular weight of 190,000 to 210,000 g / mol. However, these dispersants have low dispersing power, making it difficult to disperse carbon materials with large specific surface areas at high concentrations.

[0008] Therefore, Patent Document 6 proposes a technique that uses a copolymer with specific structural units and molecular weight as a dispersant to effectively disperse carbon materials in a solvent, maintaining good dispersion during the preparation of composite slurries and the fabrication of electrode films. However, to obtain the specific structure, a large amount of alkali needs to be added, and the reduction in electrode strength due to the decrease in the molecular weight of the dispersant and / or the deterioration of the binder resin becomes a problem.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2014-181140

[0012] Patent Document 2: Korean Patent No. 10-1831562

[0013] Patent Document 3: Japanese Patent No. 6848862

[0014] Patent Document 4: Japanese Patent No. 6863278

[0015] Patent Document 5: Japanese Patent Publication No. 2022-536304

[0016] Patent Document 6: Japanese Patent Application Publication No. 2021-122751 Summary of the Invention

[0017] The problem that the invention aims to solve

[0018] Therefore, the problem to be solved by this disclosure is to provide a resin composition that can achieve both good dispersibility and good electrode properties, as well as a carbon material dispersion composition. Furthermore, a composite material slurry that can produce an electrode film with high conductivity and adhesion is provided; more specifically, a secondary battery with excellent rate performance and cycle performance is provided, and a vehicle having improved safety and energy efficiency is provided by having this secondary battery.

[0019] Methods for solving problems

[0020] The inventors of this invention conducted in-depth research to solve the aforementioned problems. They discovered that by containing a copolymer (X) having a specific structure and 50 ppm to less than 10,000 ppm of an alkali metal, and by using N-methyl-2-pyrrolidone to achieve a non-volatile component content of 8% by mass in the resin composition, the aforementioned problems can be solved.

[0021] That is, this disclosure includes the following embodiments. The embodiments of this disclosure are not limited to the following.

[0022] [1] A resin composition comprising a copolymer (X) having alkylene structural units and nitrile structural units, and an alkali metal, wherein the content of the alkali metal is 50 ppm or more and less than 10,000 ppm, and the resistivity is 5,000 Ω·cm or more and 25,000 Ω·cm or less when the content of non-volatile components in the resin composition is 8% by mass by means of N-methyl-2-pyrrolidone.

[0023] [2] The resin composition according to [1], wherein the Z-average molecular weight of the copolymer (X) is 20,000 or more and 200,000 or less.

[0024] [3] The resin composition according to [1] or [2], wherein the ratio (Mz / Mw) of the Z-average molecular weight (Mz) to the weight-average molecular weight (Mw) of the aforementioned copolymer (X) is 2.0 or less.

[0025] [4] A carbon material dispersion composition comprising any one of [1] to [3], and a carbon material.

[0026] [5] A composite material slurry comprising the carbon material dispersion composition described in [4] and an active substance.

[0027] [6] An electrode film formed by coating the composite material slurry described in [5].

[0028] [7] A secondary battery comprising an electrode having an electrode membrane as described in [6] and an electrolyte.

[0029] [8] A vehicle having the secondary battery described in [7].

[0030] Invention Effects

[0031] The resin composition disclosed herein exhibits excellent dispersibility of dispersed materials such as carbon materials. By using a carbon material dispersion composition containing this resin composition, an electrode film with excellent conductivity and adhesion can be obtained. Furthermore, a secondary battery with excellent rate performance and cycle characteristics can be obtained. Therefore, it can be appropriately used even in vehicle applications such as hybrid electric vehicles, plug-in hybrid electric vehicles, and electric vehicles where high capacity, high output, and high durability of the secondary battery are required. Detailed Implementation

[0032] The following provides a detailed description of the resin composition, carbon material dispersion composition, composite material slurry, electrode film, and secondary battery disclosed herein, but is not intended to limit the scope of the invention. It should be noted that the numerical values ​​defined in this specification are values ​​obtained through the methods disclosed in the embodiments or examples.

[0033] In addition, in this specification, the numerical range defined by “~” includes the range of values ​​recorded before and after “~” as the lower and upper limits.

[0034] In this specification, “N-methyl-2-pyrrolidone” is sometimes labeled as “NMP”, “carbon black” as “CB”, “carbon nanotubes” as “CNT”, and “carbon material dispersion composition” as “dispersion composition”.

[0035] In addition, non-volatile components refer to the solid components after the solvent is removed. They are determined by measuring the content of residue remaining after the resin composition is heated to above the boiling point of the solvent.

[0036] It should be noted that the resin composition in the embodiments of this disclosure refers to the state before the addition of carbon materials and electrode active substances, and the carbon material dispersion composition refers to the state before the addition of electrode active substances. In this respect, the resin composition and carbon material dispersion composition can be distinguished from composite slurries containing electrode active substances.

[0037] In addition, this is a concept that excludes the intentional addition of carbon materials and electrode active substances to the resin composition. The amount of non-volatile components in the resin composition is used as a benchmark (100% by mass). The carbon materials and electrode active substances can be less than 1% by mass, less than 0.5% by mass, less than 0.1% by mass, or can be 0% by mass.

[0038] In addition, this is a concept that excludes the intentionally added electrode active material from the carbon material dispersion composition. The amount of non-volatile components in the carbon material dispersion composition is used as a basis (100% by mass). The electrode active material can be less than 1% by mass, less than 0.5% by mass, less than 0.1% by mass, or can be 0% by mass.

[0039] Unless otherwise specified, each ingredient mentioned in this instruction manual may be used individually or in combination with two or more other ingredients.

[0040] It should be noted that the values ​​determined in this specification are values ​​obtained by the methods disclosed in the implementation methods or embodiments.

[0041] Resin Compositions

[0042] The resin composition of this embodiment contains at least a copolymer (X) having alkylene structural units and nitrile structural units, and an alkali metal.

[0043] In addition, the content of alkali metals is 50 ppm or more and less than 10,000 ppm, and further, the resistivity is 5,000 Ω·cm or more and 25,000 Ω·cm or less when the content of non-volatile components in the resin composition is 8% by mass by N-methyl-2-pyrrolidone.

[0044] By using such a resin composition, it is possible to obtain a dispersion composition with excellent dispersibility and good stability of the dispersed material.

[0045] In the case where the dispersed material is carbon material, a carbon material dispersion composition with excellent dispersibility and oxidation resistance can be obtained, and the conductivity is also excellent. Therefore, the secondary battery using it can have excellent rate performance and high-temperature cycling performance.

[0046] In addition to carbon materials described later, any of the previously known inorganic pigments, organic pigments, etc., can be used as the dispersed material, and carbon materials can be used in particular.

[0047] Examples of inorganic pigments include gold, silver, copper, silver-plated copper powder, silver-copper composite powder, silver-copper alloy, amorphous copper, nickel, chromium, palladium, rhodium, ruthenium, indium, silicon, aluminum, tungsten, molybdenum, platinum, and other metal powders, inorganic powders coated with these metals, powders of metal oxides such as silver oxide, indium oxide, tin oxide, zinc oxide, and ruthenium oxide, inorganic powders coated with these metal oxides, as well as carbon nanotubes, carbon black, and graphite.

[0048] Examples of organic pigments include various pigments used in inks and the like. Examples of such pigments include soluble azo pigments, insoluble azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolineone pigments, isoindoline pigments, perylene pigments, perinone pigments, dioxazine pigments, anthraquinone pigments, dianthraquinone pigments, anthraquinone pigments, anthraquinone pigments, tanstanone pigments, yellow anthraquinone pigments, pinantrone pigments, and diketopyrrolopyrrole pigments.

[0049] When the content of non-volatile components in the resin composition disclosed herein is 8% by mass using N-methyl-2-pyrrolidone, the resistivity is 5,000 Ω·cm or more and 25,000 Ω·cm or less.

[0050] By using such a resin composition, it is possible to achieve both good dispersibility and good electrode properties.

[0051] It should be noted that the resistivity can be measured in advance by determining the non-volatile components of the resin composition, adding N-methyl-2-pyrrolidone at a non-volatile component content of 8% by mass, mixing, and preparing a liquid resistance measurement sample.

[0052] Resistivity can be measured using the methods described in the examples.

[0053] From the viewpoint of balancing the dispersibility of the dispersed material and the electrode resistance, the resistivity is preferably 5,000 Ω·cm or more and 20,000 Ω·cm or less, and more preferably 7,000 Ω·cm or more and 15,000 Ω·cm or less.

[0054] The resistivity of the resin composition can be adjusted by modifying the copolymer with alkaline compounds such as alkali metal compounds or by applying shear stress to the copolymer, thereby controlling the molecular weight, molecular weight distribution, ion concentration, etc. of the copolymer.

[0055] It should be noted that the modification of copolymers in this specification includes not only modifications such as hydrolysis of a portion of the structural units of the copolymer, but also changes in the viscoelasticity and molecular weight of the copolymer.

[0056] The initial viscosity of the resin composition in this embodiment is preferably 10 mPa·s or more and 2,000 mPa·s or less, as measured using a Type B viscometer at 100 rpm and 25°C; more preferably 100 mPa·s or more and 1,000 mPa·s or less; and even more preferably 100 mPa·s or more and 500 mPa·s or less. If it falls within the above range, the stability of the resin composition can be further improved.

[0057] Furthermore, when the resin composition contains alkali metal compounds, the precipitation of alkali metal compounds is suppressed, resulting in superior stability.

[0058] (Copolymer(X))

[0059] The copolymer (X) is a copolymer having alkylene structural units and nitrile-containing structural units. This copolymer may have other structural units.

[0060] From the viewpoint of the dispersibility of the dispersed material, based on 100% by mass of copolymer (X), the total content of alkylene structural units and nitrile structural units is preferably 50% by mass or more and 100% by mass or less, more preferably 80% by mass or more.

[0061] When copolymer (X) is a modified copolymer, from the viewpoint of dispersibility, based on 100% by mass of copolymer (X), the total content of alkylene structural units and nitrile-containing structural units is preferably 50% by mass or more and 100% by mass or less. Furthermore, when the nitrile-containing structural units are modified by hydrolysis, the total content is preferably 50% by mass or more and 97% by mass or less, more preferably 80% by mass or more and 95% by mass or less. The content of other structural units is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0062] In the case of amide-containing structural units obtained by modifying nitrile-containing structural units, the content of amide-containing structural units is preferably 5% by mass or less, more preferably 3% by mass or less, based on 100% by mass of copolymer (X). If the content of amide-containing structural units increases, the viscosity of the electrolyte will increase and the ionic conductivity may decrease significantly when the copolymer is dissolved in the electrolyte.

[0063] The modification of copolymer (X) is preferably achieved by adjusting the amount of alkaline compounds such as alkali metal compounds added, while maintaining the composition and controlling only properties such as molecular weight or viscoelasticity.

[0064] A structural unit refers to the state in which monomers are incorporated into a polymer after polymerization. Unless otherwise specified, the content of structural units formed by the polymerization of monomers is usually consistent with the ratio (input ratio) of the monomers in the total monomers used in the polymerization of that polymer. That is, the content of each monomer is set as the content of each structural unit based on the total content of all monomers.

[0065] The copolymer (X) can be a copolymer modified by adding an alkaline compound such as an alkali metal compound. When the nitrile groups in the nitrile-containing structural units of the copolymer are modified by hydrolysis or the like, the content of alkylene structural units and nitrile-containing structural units in the modified copolymer (X) is preferably within the above-mentioned range.

[0066] The content of alkylene structural units and nitrile-containing structural units can be calculated by IR determination. For example, it can be calculated using the method described in ISO 14558:2016. Alternatively, it can be determined by ATR method without using the KBr tablet method. By using the above methods, it is also possible to determine the structural units and their contents for copolymers (X) modified with basic compounds.

[0067] The number average molecular weight (Mn) of the copolymer (X) in this embodiment is preferably 70,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. Furthermore, it is preferably 10,000 or more.

[0068] When the number average molecular weight (Mn) of copolymer (X) is within the above range, the copolymer is easily adsorbed onto the dispersed material, and the dispersed material is easily wetted by the solvent.

[0069] The weight-average molecular weight (Mw) of the copolymer (X) in this embodiment is preferably 20,000 or more and 180,000 or less, more preferably 20,000 or more and 150,000 or less, and even more preferably 20,000 or more and 100,000 or less.

[0070] The Z-average molecular weight (Mz) of the copolymer (X) in this embodiment is preferably 20,000 or more and 250,000 or less, more preferably 20,000 or more and 200,000 or less, even more preferably 25,000 or more and 180,000 or less, and particularly preferably 30,000 or more and 100,000 or less.

[0071] When the weight-average molecular weight (Mw) and Z-average molecular weight (Mz) of the copolymer (X) are within the above-mentioned ranges, not only is dispersion easier when the resin composition contains dispersed materials such as carbon materials, but the viscosity of the resin composition also decreases. Furthermore, this further improves the efficiency of removing metallic foreign particles contained in the resin composition using filters and magnets.

[0072] Number-average molecular weight (Mn), weight-average molecular weight (Mw), and Z-average molecular weight (Mz) are values ​​converted from polystyrene and can be determined by gel permeation chromatography (GPC).

[0073] Z-average molecular weight is a weighted average calculated by using the squares of molecular weights as weights, and is therefore easily affected by high molecular weights. The copolymer (X) exhibits a molecular weight distribution, with low molecular weight components functioning to improve the wettability of the dispersed material. Conversely, high molecular weight components function to improve battery properties such as viscosity stability, oxidation resistance, and electrolyte solubility resistance.

[0074] By controlling the Z-average molecular weight of copolymer (X) within the above-mentioned range before adding dispersed materials such as carbon materials to the resin composition, the viscosity of the resin composition can be reduced, and the dispersed materials are easily wetted, making dispersion easier.

[0075] Furthermore, the viscosity of the carbon material dispersion composition described later is lower, thus allowing for good movement of the dispersion medium when using a disperser such as a bead mill. The kinetic energy of the dispersion medium is proportional to the square of its mass and velocity; therefore, by effectively moving the dispersion medium in the carbon material dispersion composition, not only can the target dispersion be achieved, but the carbon material dispersion composition can also be homogenized, resulting in a carbon material dispersion composition with excellent long-term stability and electrical conductivity.

[0076] The Z-average molecular weight (Mz) of copolymer (X) can be controlled by adjusting the synthesis conditions of copolymer (X) (composition, formulation amount, catalyst, reaction temperature, reaction time, etc.), modifying the copolymer, or applying shear stress to the copolymer. Regarding shear stress, the Z-average molecular weight can be reduced by applying mechanical shear stress using, for example, rollers or kneaders.

[0077] The polydispersity index (Mw / Mn) of the copolymer (X) in this embodiment is preferably 2.2 or less, more preferably 2.0 or less, and even more preferably 1.8 or less. Furthermore, it is preferably 1.2 or more.

[0078] When the polydispersity index (Mw / Mn) is within the above range, the ratio of low molecular weight components contained in the copolymer (X) is appropriate. In particular, when dispersing carbon materials, the wetting of the dispersed material proceeds rapidly, so dispersion is easy to carry out. A carbon material dispersion composition can be obtained while maintaining the structure of the carbon material, and electrode films and secondary batteries with high conductivity and adhesion can be easily obtained.

[0079] The ratio of the weight-average molecular weight (Mw) to the Z-average molecular weight (Mz) of the copolymer (X) (Mz / Mw) is preferably 2.2 or less, more preferably 2.0 or less, even more preferably 1.9 or less, and particularly preferably 1.8 or less. Furthermore, it is preferably 1.5 or more, more preferably 1.6 or more.

[0080] When the ratio of weight-average molecular weight (Mw) to Z-average molecular weight (Mz) (Mz / Mw) is within the above range, the proportion of high molecular weight components contained in the copolymer (X) is appropriate, and a dispersion composition with good dispersion stability of the dispersed material can be easily obtained.

[0081] The number-average molecular weight (Mn), weight-average molecular weight (Mw), and Z-average molecular weight (Mz) of the copolymer (X) can be adjusted, for example, by high-pressure dispersion of the copolymer and an amide-based polar solvent. Alternatively, the resin composition containing the amide-based polar solvent can be high-pressure dispersed.

[0082] For high-pressure dispersion, products such as "Star Burst" manufactured by SUGINO MACHINE can be used.

[0083] The number-average molecular weight (Mn) is preferably prepared by high-pressure dispersion of the copolymer and the amide-based polar solvent in the presence of an alkali metal.

[0084] [alkylene structural unit]

[0085] An alkylene structural unit is a structural unit containing an alkylene structure, preferably a structural unit consisting only of an alkylene structure. The alkylene structure is preferably a straight-chain alkylene structure or a branched alkylene structure.

[0086] The exception is the case where the structural unit has a nitrile group.

[0087] The alkylene structural unit preferably comprises the structural unit shown in the following general formula (1A).

[0088] General formula (1A)

[0089] [Chemistry 1]

[0090]

[0091] In general formula (1A), n represents an integer of 1 or more. n is preferably an integer of 2 or more, more preferably an integer of 3 or more. n is preferably an integer of 5 or less, more preferably an integer of 4 or less. Particularly preferred is n = 3.

[0092] The alkylene structural unit preferably comprises the structural unit shown in the following general formula (1B).

[0093] General formula (1B)

[0094] [Chemistry 2]

[0095]

[0096] In general formula (1B), n represents an integer greater than or equal to 1. n is preferably an integer of 4 or less, more preferably an integer of 3 or less, and even more preferably an integer of 2 or less. Particularly preferred is n = 2.

[0097] There are no particular limitations on the method of introducing alkylene structural units into the copolymer, for example, the following methods (1a) or (1b) can be cited.

[0098] In method (1a), a copolymer is prepared by polymerization using a monomer composition containing a conjugated diene monomer. The prepared copolymer comprises monomer units derived from the conjugated diene monomer. In this disclosure, "monomer units derived from the conjugated diene monomer" is sometimes referred to as "conjugated diene monomer units," and monomer units derived from other monomers are also sometimes omitted. Next, at least a portion of the conjugated diene monomer units is converted into alkylene structural units by hydrogenation. Hereinafter, "hydrogenation" is sometimes referred to as "hydrogenation." The final copolymer comprises units obtained by hydrogenating the conjugated diene monomer units as alkylene structural units.

[0099] It should be noted that the conjugated diene monomer unit comprises at least one monomer unit having a carbon-carbon double bond. For example, the 1,3-butadiene monomer unit, as a conjugated diene monomer unit, comprises at least one monomer unit selected from the group consisting of monomer units having a cis-1,4-structure, monomer units having a trans-1,4-structure, and monomer units having a 1,2-structure, and may also comprise two or more monomer units. Furthermore, the conjugated diene monomer unit may further comprise monomer units that do not have a carbon-carbon double bond and contain branch points. In this specification, "branch point" refers to a branch point in a branched polymer. When the conjugated diene monomer unit comprises a monomer unit containing a branch point, the copolymers and copolymers prepared above are branched polymers.

[0100] In method (1b), a copolymer is prepared by polymerization using a monomer composition containing an α-olefin monomer. The prepared copolymer contains α-olefin monomer units. The final copolymer contains α-olefin monomer units as alkylene structural units.

[0101] From the perspective of ease of copolymer production, method (1a) is preferred. The conjugated diene monomer has 4 or more carbon atoms, preferably 4 or more and 6 or less. Examples of conjugated diene monomers include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. 1,3-Butadiene is preferred. The alkylene structural unit preferably includes a structural unit obtained by hydrogenating a conjugated diene monomer unit (hydrogenated conjugated diene monomer unit), and more preferably includes a structural unit obtained by hydrogenating a 1,3-butadiene monomer unit (hydrogenated 1,3-butadiene monomer unit). One type of conjugated diene monomer may be used alone or in combination of two or more types.

[0102] Hydrogenation is preferably a method that can selectively hydrogenate conjugated diene monomer units.

[0103] As a method of hydrogenation, well-known methods such as oil layer hydrogenation or water layer hydrogenation can be cited.

[0104] Hydrogenation can be carried out by conventional methods. For example, hydrogenation can be performed by treating a copolymer having conjugated diene monomer units in a suitable solvent with hydrogen in the presence of a hydrogenation catalyst. Examples of hydrogenation catalysts include nickel, palladium, rhodium, platinum, and copper.

[0105] In method (1b), the α-olefin monomer has 2 or more carbon atoms, preferably 3 or more, and more preferably 4 or more. The α-olefin monomer preferably has 6 or fewer carbon atoms, and more preferably 5 or fewer. Examples of α-olefin monomers include ethylene, propylene, 1-butene, and 1-hexene. One type of α-olefin monomer may be used alone, or two or more may be used in combination.

[0106] The alkylene structural unit preferably comprises at least one type selected from the group consisting of structural units comprising a straight-chain alkylene structure and structural units comprising a branched alkylene structure; more preferably, it comprises at least one type selected from the group consisting of structural units consisting only of a straight-chain alkylene structure and structural units consisting only of a branched alkylene structure; and even more preferably, it comprises at least one type selected from the group consisting of structural units represented by formula (1A) and structural units represented by formula (1B).

[0107] Based on a total content of 100% by mass for alkylene structural units and nitrile-containing structural units, the content of alkylene structural units is preferably 50% by mass or more and 75% by mass or less, more preferably 55% by mass or more and 70% by mass or less, and even more preferably 55% by mass or more and 65% by mass or less. By maintaining the content of alkylene structural units within the above range, the adsorption of the dispersed material and its affinity for the dispersion medium can be controlled, allowing the dispersed material to exist stably in the dispersion medium. Furthermore, the affinity of the copolymer for the electrolyte can also be controlled, preventing adverse conditions such as the copolymer dissolving in the electrolyte within the battery and increasing the electrolyte resistance.

[0108] [Nitrile-based structural units]

[0109] The nitrile-containing structural unit is a structural unit containing a nitrile group, preferably containing a structural unit containing an alkylene structure substituted with a nitrile group, and more preferably containing a structural unit consisting only of an alkylene structure substituted with a nitrile group. The alkylene structure is preferably a straight-chain or branched alkylene structure. The nitrile-containing structural unit may further contain a structural unit containing an alkyl structure substituted with a nitrile group (or consisting only of an alkyl structure substituted with a nitrile group). The number of nitrile groups contained in the nitrile-containing structural unit is preferably one.

[0110] The nitrile-containing structural unit preferably comprises the structural unit shown in the following general formula (2A).

[0111] General formula (2A)

[0112] [Chemistry 3]

[0113]

[0114] In general formula (2A), n represents an integer of 2 or more. n is preferably an integer of 6 or less, more preferably an integer of 4 or less, and even more preferably an integer of 3 or less. Particularly preferred is n = 2.

[0115] The nitrile-containing structural unit may include the structural unit shown in the following general formula (2B).

[0116] General formula (2B)

[0117] [Chemistry 4]

[0118]

[0119] In general formula (2B), R represents methyl.

[0120] There are no particular limitations on the method of introducing nitrile-containing structural units into the copolymer, but a method of preparing the copolymer by polymerization of a monomer composition containing nitrile-containing monomers (method (2a)) is preferred. The resulting copolymer contains nitrile-containing structural units as nitrile-containing structural units. Examples of nitrile-containing monomers capable of forming nitrile-containing structural units include monomers containing polymerizable carbon-carbon double bonds and nitrile groups. For example, compounds containing α,β-olefinic unsaturated groups with nitrile groups can be mentioned, specifically acrylonitrile, methacrylonitrile, etc. In particular, from the viewpoint of improving the intermolecular forces between copolymers and / or between copolymers and the dispersed material (adsorbate), nitrile-containing monomers are preferably acrylonitrile. One nitrile-containing monomer may be used alone or in combination of two or more.

[0121] Based on a total content of 100% by mass for alkylene structural units and nitrile structural units, the content of nitrile structural units is preferably 25% by mass or more and 50% by mass or less, more preferably 30% by mass or more and 45% by mass or less, and even more preferably 35% by mass or more and 45% by mass or less. By maintaining the content of nitrile structural units within the above range, the adsorption of the dispersed material and its affinity for the dispersion medium can be controlled, allowing the dispersed material to exist stably in the dispersion medium. Furthermore, the affinity of the resin composition for the electrolyte can also be controlled, preventing adverse conditions such as the resin composition dissolving in the electrolyte within the battery, which could increase the electrolyte resistance.

[0122] [Other structural units]

[0123] To the extent that it does not impair the effects of this disclosure, structural units other than alkylene structural units and nitrile-containing structural units may be used as needed. Examples of other structural units include amide-containing monomers and carboxyl-containing structural units.

[0124] (Alkali metals)

[0125] The resin composition disclosed herein contains alkali metals. Furthermore, the content of the alkali metals in the resin composition is 50 ppm or more and less than 10,000 ppm.

[0126] Preferably, the concentration is 500 ppm or more and 8000 ppm or less, more preferably 2000 ppm or more and 5000 ppm or less.

[0127] By keeping the alkali metal content within the above range, the adsorption of the dispersed material and its affinity to the dispersion medium are improved when dispersing materials such as carbon, thereby enhancing the dispersibility.

[0128] Furthermore, if the amount of alkali metal in the resin composition is within the above range, the molecular weight of the copolymer (X) can be easily controlled within an appropriate range by using an alkali metal compound as a basic compound for modification, or by applying shear stress to the copolymer, thereby improving the dispersibility of the dispersed material.

[0129] Alkali metals are included in the resin composition through monomers used to synthesize the copolymer or copolymer (X) before modification, alkali metal compounds used to modify the copolymer, alkali metal compounds used as additives such as pH adjusters, or alkali metals contained in solvents, etc.

[0130] That is, the alkali metals contained in the resin composition include not only intentionally added alkali metal compounds, but also alkali metals from monomers, catalysts, additives, solvents, etc., which are used as raw materials.

[0131] Examples of alkali metals include lithium, sodium, and potassium.

[0132] The alkali metal content in the resin composition can be determined using an ICP-based luminescence spectrophotometer via the method described in the examples.

[0133] (solvent)

[0134] The resin composition of this embodiment preferably includes a solvent. As a solvent, any solvent capable of dissolving the copolymer is acceptable, and an amide-based polar solvent is preferred. Examples of amide-based polar solvents include N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and N-methylcaprolactam. More preferably, it includes at least one solvent selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone.

[0135] (Method for manufacturing the resin composition)

[0136] There are no particular limitations on the method for manufacturing the resin composition of this embodiment, and the resin composition can be manufactured by any method.

[0137] For example, a method can be described as follows: a copolymer is prepared by polymerization using a monomer composition containing a conjugated diene monomer and a nitrile monomer; hydrogen is then added to the conjugated diene monomer units of the copolymer to obtain a resin composition containing copolymer (X). Alternatively, a resin composition containing copolymer (X) can be prepared by modifying a copolymer having alkylene structural units and nitrile structural units with a basic compound such as an alkyl metal compound, or by applying shear stress.

[0138] Furthermore, as a method for achieving an alkali metal content of 50 ppm or more and less than 10,000 ppm, and a resistivity of 5,000 Ω·cm or more and 25,000 Ω·cm or less when the content of non-volatile components in the resin composition obtained by N-methyl-2-pyrrolidone is 8% by mass, in addition to the raw materials or formulation amounts used to manufacture this copolymer, the following methods can be cited as examples. <1> For copolymers containing alkali metals, methods such as using a pulverizer to apply shear stress are employed. <2> For copolymers, alkali metals or alkali metal compounds are added as modified copolymers, and shear stress is applied using the above-mentioned pulverizer method. <3> For copolymers, methods such as adding alkali metals or alkali metal compounds after applying shear stress using a pulverizer or similar means.

[0139] Among them, preferred <2> or <3> The method preferably uses an alkali metal compound with a maximum particle size of less than 150 μm, and sodium hydroxide is particularly preferred. In the presence of an alkali metal compound with a maximum particle size of less than 150 μm, by applying shear stress to the copolymer, the finely dispersed alkali metal compound absorbs moisture, comes into contact with the copolymer, and promotes the hydrolysis reaction of the copolymer, thus enabling control over the structure, molecular weight, and molecular weight distribution suitable for dispersing the dispersed material.

[0140] exist <2> or <3> In this process, alkali metal compounds used in the modification of copolymers can be, for example, alkali metal hydroxides or alkoxides. Alkali metal hydroxides are preferred.

[0141] That is, as a method for manufacturing a resin composition, it is preferable to include, for example, a step of mixing an alkali metal compound into a copolymer having alkylene structural units and nitrile structural units to manufacture a resin composition containing copolymer (X) and alkali metal.

[0142] At this point, the copolymer before modification is preferably a copolymer in which an alkali metal compound is mixed in a copolymer having alkylene structural units and nitrile structural units, having alkylene structural units with a content of 50% or more and 75% or less by mass, and nitrile structural units with a content of 25% or more and 50% or less by mass.

[0143] To prepare a resin composition that meets the above requirements, the unmodified copolymer is preferably dissolved in an amide-based polar solvent at a temperature of 60°C to 100°C. Furthermore, the alkali metal compound is preferably mixed at a temperature of 40°C to 100°C, and more preferably at a temperature of 60°C to 80°C.

[0144] Examples of alkali metal compounds include alkali metal hydroxides or alkali metal alkoxides, with alkali metal hydroxides being preferred.

[0145] Examples of alkali metal hydroxides that can be used include lithium hydroxide, sodium hydroxide, and potassium hydroxide. From the viewpoint of processability and operability, such as particle size control, sodium hydroxide is preferred due to its excellent dispersion stability.

[0146] Sodium hydroxide is hygroscopic and can be very effective in modifying a portion of the structural units of copolymers through hydrolysis and other methods.

[0147] Alkoxides of alkali metals, such as sodium ethoxide and sodium butoxide, can be used.

[0148] The maximum particle size of the alkali metal compound used for modifying the copolymer is preferably 150 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. Additionally, it is preferably 20 μm or more.

[0149] When the maximum particle size of the alkali metal compound is within the aforementioned range, precipitation of the alkali metal compound in the resin composition is suppressed, resulting in superior stability of the resin composition. The sedimentation rate of the alkali metal compound in the resin composition can be estimated using the Stokes equation. The viscosity of the resin composition and the density and particle size of the alkali metal compound are important in controlling the dispersion stability of the dispersed material. The maximum particle size of the alkali metal compound can be calculated, for example, by filtering a filter with a known mesh size.

[0150] Regarding the particle size of alkali metal compounds, it is preferable to perform and control the grinding process using conventionally known pulverizers in a dry and / or wet manner. Conventionally known pulverizers can be used for the grinding process.

[0151] By setting the maximum particle size of the alkali metal compound within the aforementioned range, it is possible not only to appropriately control the composition and structure of the structural units constituting the copolymer (X), but also to appropriately control changes in the molecular weight and other properties of the copolymer (X) accompanying the modification. Through such control of the molecular weight and molecular weight distribution of the copolymer (X), a dispersion composition with lower viscosity can be produced when dispersing the dispersed material.

[0152] When the maximum particle size of alkali metal compounds is large, not only do alkali metal compounds sometimes precipitate in the resin composition, making it impossible to control the molecular weight of the copolymer, but the long-term stability of the carbon material dispersion composition and composite slurry, as described later, may also decrease.

[0153] A pulverizer is a device that applies forces such as compression, impact, shearing, or friction to a sample to refine it into smaller particles. As devices for controlling particle size, various types of pulverizers can be used, including mortars, pin mills, hammer mills, pulverizers, attritors, jet mills, shear mills, ball mills, bead mills, colloid mills, cone mills, disc mills, edge mills, wonder crushers, vibratory mills, ultrasonic homogenizers, and high-speed shear mixers.

[0154] To control the alkali metal content and predetermined resistivity of the resin composition, the unmodified copolymer is preferably dissolved in a solvent at a temperature of 60°C to 100°C. Therefore, more preferably, the resin composition containing the solvent may contain 1 to 50, 2 to 40, 5 to 30, or 10 to 20% by mass relative to the total amount of the resin composition. More preferably, the solvent may contain an amide-based polar solvent. Furthermore, to prepare a resin composition that satisfies the above requirements, the alkali metal compound is preferably dissolved in a solvent at a temperature of 40°C to 100°C or 60°C to 80°C. Therefore, more preferably, the resin composition containing the solvent may contain 0.1 to 20%, 0.5 to 10%, 1 to 8%, or 2 to 5% by mass relative to the total amount of the resin composition. By ensuring that both the copolymer (X) and the alkali metal compound satisfy the above ranges relative to the total amount of the resin composition, the alkali metal content and predetermined resistivity of the resin composition can be controlled more easily.

[0155] To control the alkali metal content and predetermined resistivity of the resin composition, an alkali metal compound may be added during the manufacturing process of the resin composition. In this case, as one method of manufacturing the resin composition, the copolymer (X) and the alkali metal compound can be mixed while they are dissolved in a solvent. More preferably, a liquid obtained by dissolving the copolymer (A) in a solvent and a liquid obtained by dissolving the alkali metal compound in a solvent are prepared separately, and then mixed. An amide-based polar solvent is preferred as the solvent.

[0156] To control the alkali metal content and predetermined resistivity of a resin composition, as described above, there is a method for controlling the amount and method of adding the alkali metal compound during the manufacturing process of the resin composition. According to this method, the alkali metal content in the obtained resin composition can be controlled, and the predetermined resistivity can also be controlled simultaneously.

[0157] As another method for controlling the alkali metal content and predetermined resistivity of the resin composition, there are methods for controlling the molecular weight and molecular weight distribution of the copolymer (X). For example, even when the alkali metal content is low and the predetermined resistivity is high, the increase in the predetermined resistivity can be suppressed by reducing the molecular weight of the copolymer (X). Preferably, the number-average molecular weight Mn of the copolymer (X) is set to 70,000 or less, 60,000 or less, or 50,000 or less. Alternatively, it is preferable that the Mw / Mn of the copolymer (X) is 2.60 or less, 2.50 or less, or 2.40 or less. As a further preferred method, when the Mw / Mn of the copolymer (X) is 2.60 or less, 2.50 or less, or 2.40 or less, the Z-average molecular weight Mz is preferably 400,000 or less, 300,000 or less, or 250,000 or less. Several methods for controlling these molecular weights and molecular weight distributions include controlling the mixing time of the copolymer (X) and the alkali metal compound, the amount of alkali metal compound used, the content of the copolymer (X) and the alkali metal compound relative to the total amount of the resin composition, and the number of passes when using a through-type dispersion device.

[0158] Carbon Material Dispersion Compositions

[0159] The carbon material dispersion composition of this embodiment comprises at least carbon material and the resin composition of this embodiment. Additionally, a solvent is preferably included. By including a solvent in the carbon material dispersion composition, a well-dispersed carbon material dispersion composition is readily obtained.

[0160] (Carbon materials)

[0161] As carbon materials, various types of carbon black can be used, such as acetylene black, furnace black, hollow carbon black, channel black, thermal cracking black, and Ketjen black. Additionally, oxidized carbon black, graphitized carbon black, mesophase carbon black, amorphous carbon materials such as soft carbon and hard carbon, and carbon fibers such as carbon nanotubes or carbon nanofibers, and vapor-grown carbon fibers can also be used. Preferably, at least one of the materials selected from the group consisting of carbon black and carbon fibers is used, and carbon nanotubes are particularly preferred.

[0162] The carbon purity of the carbon material is based on the mass of the carbon material (with the mass of the carbon material set as 100% by mass), preferably 95% by mass or more, and more preferably 97% by mass or more.

[0163] Carbon nanotubes have a cylindrical structure formed by winding planar graphite and can include single-layer carbon nanotubes, multi-layer carbon nanotubes, or a mixture thereof. Multi-layer carbon nanotubes are preferred. Multi-layer carbon nanotubes have a structure consisting of two or three or more layers of wound graphite, while single-layer carbon nanotubes have a structure consisting of a single layer of wound graphite. The sidewalls of carbon nanotubes do not necessarily have to be graphite. For example, carbon nanotubes with amorphous sidewalls can also be used as the carbon material.

[0164] The average outer diameter of the carbon nanotubes is preferably 1 nm or more and 25 nm or less, more preferably 3 nm or more and 20 nm or less, and even more preferably 4 nm or more and 15 nm or less. When the average outer diameter is within the above range, a good conductive network can be easily formed in the electrode. During charging and discharging, the active material inside the secondary battery is utilized uniformly, thus suppressing the degradation of the active material and further improving the cycle characteristics of the secondary battery.

[0165] The preferred BET specific surface area of ​​carbon nanotubes is 100 m². 2 / g or more and 1000m 2 / g or less, more preferably 200m 2 / g or more and 700m 2 / g or less. With a BET specific surface area within the above range, a highly efficient conductive network can be formed with a small amount of material, reducing the amount of conductive material in the electrode. This increases the freedom of battery design in terms of active materials and binder resins. Furthermore, during the preparation of the composite slurry, the composite of the active material and carbon nanotubes becomes easier, thus easily obtaining an electrode film with a homogeneous conductive network of carbon nanotubes coated on the surface of the active material. This suppresses electrolyte decomposition reactions at the interface between the electrolyte and the active material, improving the battery's cycle characteristics.

[0166] BET specific surface area can be determined by the BET method as described in JIS Z 8830:2013.

[0167] Regarding the G / D ratio (the ratio of G-band peaks to D-band peaks) of carbon nanotubes, in Raman spectroscopy, the 1560 cm⁻¹ peak value... -1 ~1600cm -1 The maximum peak intensity within the range is set as G, and 1310 cm⁻¹ is used. -1 ~1350cm -1 When the maximum peak intensity within the range is set to D, the G / D ratio is preferably 0.5 to 10, more preferably 0.7 to 4.5.

[0168] It is believed that when the G / D ratio of carbon nanotubes is within the aforementioned range, the contact resistance between carbon nanotubes decreases, making it easier to obtain good electrical conductivity. Furthermore, it is speculated that this is due to the appropriate amount of functional groups on the surface of multilayer carbon nanotubes, resulting in good affinity with solvents and improved dispersibility.

[0169] The preferred volume resistivity of carbon nanotubes is 1.0 × 10⁻⁶. -2 Ω·cm ~3.0×10 -2 Ω·cm, more preferably 1.0×10 -2 Ω·cm ~ 2.0×10 -2 Ω·cm.

[0170] The volume resistivity of carbon nanotubes can be measured using a powder resistivity measuring device (Loresta GP Powder Resistivity Measuring System MCP-PD-51, manufactured by Mitsubishi Chemical Analytech Co., Ltd.). When the volume resistivity is within the above range, the conductivity of the electrode film tends to be good, making it easier to obtain a secondary battery with excellent rate performance and cycle characteristics.

[0171] Electromagnets are preferably used in carbon nanotubes to remove metallic foreign particles through magnetic force. For example, it is preferable to set up an electromagnet in the carbon nanotube crushing or filling process, so that it passes through the carbon nanotubes, thereby removing metallic foreign particles.

[0172] The higher the carbon purity of the carbon nanotubes, the better. Among 100% by mass of carbon nanotubes, it is preferred to be 98.0% by mass or more, more preferably 99.5% by mass or more, further preferably 99.8% by mass or more, and particularly preferably 99.9% by mass or more.

[0173] That is, the lower the content of metallic foreign particles, the better. In 100% by mass of carbon nanotubes, it is preferably 2.0% by mass or less, more preferably 0.5% by mass or less, even more preferably 0.2% by mass or less, and particularly preferably 0.1% by mass or less.

[0174] Carbon nanotubes prepared by methods that do not use metal catalysts as the core, or carbon nanotubes obtained by purification methods such as acid treatment, can have a metal foreign particle content of less than 0.5% by mass relative to 100% by mass of carbon nanotubes. This reduces the content of metal foreign particles in the carbon nanotube dispersion composition and improves the various characteristics of the secondary battery.

[0175] The carbon purity of carbon nanotubes can be determined using an ICP-based spectral analyzer, through the methods described in the examples.

[0176] The solvent is not particularly limited as long as it is mixable with the resin composition of this embodiment. Preferably, it is a solvent capable of dissolving the resin composition, and more preferably, it is a high dielectric constant solvent. It is also preferred that it comprises any one of the high dielectric constant solvents or a mixture of two or more high dielectric constant solvents. Alternatively, it may be used by mixing one or more other solvents with the high dielectric constant solvent.

[0177] As a high dielectric constant solvent, amide-based solvents (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclic solvents (cyclohexylpyrrolidone, 2-oxazolidinone, 1,3-dimethyl-2-imidazolium, γ-butyrolactone, etc.), sulfoxide-based solvents (dimethyl sulfoxide, etc.), sulfone-based solvents (hexamethylphosphoric triamine, sulfolane, etc.), lower ketone-based solvents (acetone, methyl ethyl ketone, etc.), carbonate-based solvents (diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, fluoroethylene carbonate, propylene carbonate, ethylene carbonate), as well as tetrahydrofuran, urea, acetonitrile, etc., are preferred. As a dispersion medium, an amide-based polar solvent is preferred, and more preferably, at least one solvent selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone is preferred. The relative permittivity of the high-dielectric-constant solvent can be set to a value described in solvent handbooks, etc., preferably 2.5 or higher at 20°C. By setting the solvent to a high-dielectric-constant solvent, the interaction between the nitrile groups, carbon materials, and solvent contained in the resin composition of this embodiment can be improved.

[0178] The water content in the solvent is preferably 100 ppm or more and 1500 ppm or less, more preferably 100 ppm or more and 1000 ppm or less. Within the above range, the alkali metal contained in the resin composition of this embodiment dissolves in the carbon material dispersion composition, and the dispersion stability of the carbon material dispersion composition tends to become good.

[0179] Regarding the solvent content in this embodiment, based on the mass of the carbon material dispersion composition (with the mass of the carbon material dispersion composition set to 100% by mass), it is preferably 90% to 99% by mass, more preferably 92% to 98% by mass. Within the above range, a carbon material dispersion composition with free flowability and excellent dispersion stability can be easily obtained. By using a carbon material dispersion composition with excellent dispersion stability, an electrode film with stable conductivity can be obtained, and the quality of the secondary battery can be easily stabilized.

[0180] To obtain the carbon material dispersion composition of this embodiment, it is preferable to perform a treatment that disperses the carbon material in a solvent. The dispersion apparatus used for performing this treatment is not particularly limited.

[0181] As a dispersing device, a dispersant commonly used in pigment dispersion and the like can be used. For example, it can be either a media-free dispersant or a media-type dispersant. Examples of media-free dispersants include dispersants, homogenizers, planetary mixers, etc.; homogenizers (such as BRANSON's Advanced Digital Sonifer (registered trademark), MODEL 450DA, M Technique's "CLEARMIX", PRIMIX's "FILMIX", Silverson's "Abramix"); paint conditioners (Red Devil), colloid mills (PUC's "PUC Colloid Mill", IKA's "Colloid Mill MK"), cone mills (IKA's "Cone Mill MKO"), etc. Examples of media-type dispersers include ball mills, sand mills (such as the "Dyno Mill" manufactured by Shinmaru Enterprises), grinding mills (Attritor), pearl mills (such as the "DCP MILL" manufactured by Eirich), compact ball mills (Co-ball mills), bead mills (manufactured by Ashizawa Finetech, Mugen Flow (registered trademark)), and media-type paint conditioners. Further examples include high-pressure homogenizers (such as the "Genus PY" manufactured by Genus, the "StarBurst" manufactured by SUGINO MACHINE, and the "Nanomizer" manufactured by Nanozer), medialess dispersers such as the "CLEARSS-5" manufactured by M Technique and the "MICROS" manufactured by Nara Machinery, as well as roller mills. Dispersers are not limited to these examples.

[0182] Based on the mass of the carbon material dispersion composition (with the mass of the carbon material dispersion composition set to 100% by mass), the content of carbon material contained in the carbon material dispersion composition is preferably 1% by mass or more and 20% by mass or less, more preferably 2% by mass or more and 15% by mass or less, and even more preferably 3% by mass or more and 10% by mass or less.

[0183] Based on the mass of the carbon material (setting the mass of the carbon material as 100% by mass), the content of the dispersant contained in the carbon material dispersion composition is preferably 5% by mass or more and 100% by mass or less, more preferably 10% by mass or more and 75% by mass or less, and even more preferably 20% by mass or more and 50% by mass or less. When the dispersant dosage is within the above range, the dispersion stability of the carbon material in the carbon material dispersion composition tends to become good. In addition, the peel strength of the electrode for secondary batteries becomes good.

[0184] The moisture content of the carbon material dispersion composition is preferably 100 ppm to 1500 ppm, more preferably 200 ppm to 1000 ppm. When the moisture content of the carbon material dispersion composition is within the above range, the gelation of the composite slurry described later is suppressed, and it is easy to obtain a composite slurry and electrode film with stable quality.

[0185] Regarding the initial viscosity of the carbon material dispersion composition of this embodiment, the viscosity measured using a Type B viscometer at 25°C and 100 rpm is preferably 100 mPa·s or more and 2,000 mPa·s or less, more preferably 200 mPa·s or more and 1,000 mPa·s or less. It is believed that when the initial viscosity of the carbon material dispersion composition is within the above range, the dispersion state of the carbon material contained in the carbon material dispersion composition is appropriate, and a conductive network is easily formed.

[0186] The viscosity of the carbon material dispersion composition of this embodiment, after being stored at 60°C for one week and cooled to 25°C, is preferably 500 mPa·s or more and 6,000 mPa·s or less, more preferably 500 mPa·s or more and 3,000 mPa·s or less, and even more preferably 500 mPa·s or more and 2,000 mPa·s or less, after being stored at 60°C for one week and cooled to 25°C.

[0187] The carbon material dispersion composition with viscosity within the above-mentioned range is considered to have appropriate composition ratios of carbon material, resin composition, and solvent, as well as a suitable dispersion process, resulting in good dispersion stability. Since the adsorption reaction of the resin composition on the carbon material surface is an endothermic reaction, the viscosity of the carbon material dispersion composition after storage at high temperatures can be evaluated to determine the sufficient amount of resin composition required to obtain a carbon material dispersion composition with excellent dispersion stability.

[0188] The carbon material dispersion composition of this embodiment preferably uses a material in which metallic foreign matter has been removed by a filter or a magnet.

[0189] [Process for removing metallic foreign particles]

[0190] There are no particular limitations on the methods for removing metallic foreign particles. Examples include filtration processes using filters and magnetic separation processes using electromagnets.

[0191] Preferably, the material includes both a filtration process and a magnetic separation process. This is because the magnetic separation process can remove metallic foreign particles contained in the carbon material, while the filtration process can recover metallic foreign particles that cannot be removed by a magnet.

[0192] Furthermore, it is preferable to perform a magnetic separation process after the filtration process. By performing a filtration process at the final stage before the carbon material dispersion composition leaves the factory, metallic foreign particles from piping and the like can also be removed.

[0193] (Magnetic separation process)

[0194] As a method for removing metallic foreign particles using magnetic force in a magnetic separation process, various conventionally known methods can be used. In particular, in the manufacturing process of a carbon material dispersion composition, it is preferable to use a method that removes metallic foreign particles by setting an electromagnet and passing the carbon material dispersion composition through it.

[0195] The magnetic flux density of the electromagnet is preferably 5,000 gauss or more and 20,000 gauss or less, more preferably 10,000 gauss or more and 20,000 gauss or less. By using an electromagnet within the above range, not only can metallic foreign particles contained in carbon materials be removed, but also metallic foreign particles generated during the manufacturing process can be removed.

[0196] Specifically, for example, you can use CS-150 HHH, CS-250 HHH, CS-300 HHH manufactured by Japan Magnetics Co., Ltd., DVF-50-6, DVF-50-9, DVF-50-12 manufactured by Japan Eliz Magnetics Co., Ltd., and EMF-100S, EMF-150S, EMF-250S, EMF-300S manufactured by Dae BoMagnetic Co., Ltd.

[0197] The flow rate when the carbon material dispersion composition comes into contact with the electromagnet is preferably 1 L / min or more and 300 L / min or less, and more preferably 30 L / min or more and 200 L / min or less.

[0198] The carbon material dispersion composition is preferably passed through the electromagnet three or more times. Fewer passes may fail to remove metallic foreign particles. When the electromagnet is passed through in a cyclic manner, a greater number of passes are preferable to ensure uniformity within the container used in the manufacturing process.

[0199] (Filtration process)

[0200] As a filter for filtering metallic foreign particles, it can be a surface filter such as a membrane filter, or a depth filter, more preferably a depth filter. Most metallic foreign particles are not spherical but oriented, so by using a depth filter, metallic foreign particles in a carbon material dispersion composition can be effectively removed.

[0201] Depth filters differ from surface filters (filters that primarily capture particulate matter in the fluid on the filter surface). Depth filters primarily capture particulate matter in the fluid within the filter media, exhibiting high particle retention and resistance to clogging. By using depth filters, metallic foreign particles in carbon material dispersion compositions can be removed more selectively.

[0202] As a depth filter, for example, the 3M(TM) PP nonwoven fabric depth cartridge NT-T series can be used.

[0203] The filtration accuracy of the filter is preferably 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 40 μm or less. To improve the removal rate of metallic foreign particles in the carbon material dispersion composition, when using a filter material with a small pore size, the removal efficiency of metallic foreign particles may decrease due to clogging of the carbon material. On the other hand, carbon material dispersion compositions filtered within the above-mentioned range exhibit high removal efficiency of metallic foreign particles when using the filter, thus easily yielding carbon material dispersion compositions with fewer metallic foreign particles.

[0204] Composite Material Slurry

[0205] The composite material slurry of this embodiment comprises a carbon material dispersion composition and an active substance. That is, it preferably contains at least the resin composition, carbon material, and active substance disclosed herein, and further comprises an adhesive resin.

[0206] Adhesive resins refer to resins used to bond carbon materials between substances. There are no particular limitations on adhesive resins; examples include: fluoropolymers; polymers or copolymers containing ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylates, methacrylic acid, methacrylates, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinylpyrrolidone, etc., as structural units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluoropolymers; cellulose resins such as carboxymethyl cellulose; rubbers such as styrene-butadiene rubber; and conductive resins such as polyaniline and polyacetylene.

[0207] From the perspective of electrochemical oxidation-reduction resistance, fluoropolymer resin is preferred as the adhesive resin.

[0208] The fluoropolymer used in this embodiment is preferably polyvinylidene fluoride, polyvinyl fluoride, or tetrafluoroethylene.

[0209] The weight-average molecular weight of the fluoropolymer is preferably 10,000 or more and 2,000,000 or less, more preferably 100,000 or more and 1,000,000 or less, and particularly preferably 200,000 or more and 1,000,000 or less.

[0210] Active materials are the fundamental materials for battery reactions. Based on electromotive force, active materials are classified into positive electrode active materials and negative electrode active materials. In this specification, positive electrode active materials and negative electrode active materials are sometimes referred to simply as "active materials".

[0211] As a positive electrode active material, there are no particular limitations; metal compounds such as metal oxides and metal sulfides that can be doped with or intercalated with lithium ions and sodium ions, as well as conductive polymers, can be used. Examples include oxides of transition metals such as Fe, Co, Ni, and Mn; composite oxides with lithium and sodium; inorganic compounds such as transition metal sulfides; polyanionic compounds; and Prussian blue compounds. Specifically, examples include MnO, V₂O₅, and V₆O. 13 The materials include transition metal oxide powders such as TiO2, layered lithium nickelate, lithium cobalt oxide, lithium manganese oxide, and spinel-structured lithium manganese oxide composite oxide powders, lithium iron phosphate materials as olivine-structured phosphoric acid compounds, transition metal sulfide powders such as TiS2 and FeS, layered sodium ferrite, sodium manganate, sodium chromate, sodium nickelate, and sodium iron phosphate materials as olivine-structured phosphoric acid compounds. Additionally, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Furthermore, a mixture of the above inorganic and organic compounds can be used.

[0212] The positive electrode active material is preferably a composite oxide of lithium with a transition metal such as Al, Fe, Co, Ni, Mn, etc., more preferably a composite oxide of lithium with any one of Al, Co, Ni, Mn, and particularly preferably a composite oxide of lithium containing Ni and / or Mn. When using these active materials, particularly good effects can be obtained.

[0213] As the negative electrode active material, there is no particular limitation as long as it can dope or intercalate lithium or sodium ions. For example, metal Li, alloy systems such as tin alloys, silicon alloys, and lead alloys as its alloys, LiXFe2O3, LiXFe3O4, LiXWO2 (x is a number between 0 and 1), metal oxide systems such as lithium titanate, lithium vanadate, and lithium silicate, conductive polymer systems such as polyacetylene and polyphenylene, amorphous carbonaceous materials such as soft carbon and hard carbon, artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, carbon black, mesophase carbon black, resin-fired carbon materials, gas-phase grown carbon fibers, carbon fiber and other carbon-based materials. These negative electrode active materials can be used alone or in combination.

[0214] The BET specific surface area of the active material is preferably 0.1 m 2 / g or more and 10 m 2 / g or less, more preferably 0.2 m 2 / g or more and 5 m 2 / g or less, and further preferably 0.3 m 2 / g or more and 3 m 2 / g or less.

[0215] The average particle size of the active material is preferably in the range of 0.05 μm to 100 μm, and further preferably in the range of 0.1 μm to 50 μm. The average particle size of the active material referred to in this specification means the average value of the particle sizes obtained by measuring the active material using an electron microscope.

[0216] To obtain the composite material slurry of this embodiment, it is preferable to add the active material to the carbon material dispersion composition and then perform a dispersion treatment. The dispersion device used for this treatment is not particularly limited. The composite material slurry can be obtained using the dispersion device described in the above carbon material dispersion composition.

[0217] Based on 100% by mass of the composite material slurry, the content rate of the active material in the composite material slurry is preferably 20% by mass to 85% by mass, and particularly preferably 40% by mass to 85% by mass.

[0218] Based on 100% by mass of the active material, the content rate of the carbon material in the composite material slurry is preferably 0.05% by mass to 10% by mass, preferably 0.1% by mass to 5% by mass, and preferably 0.1% by mass to 3% by mass.

[0219] Based on 100% by mass of active material, the content of binder resin in composite slurry is preferably 0.5% to 20% by mass, more preferably 1% to 10% by mass, and particularly preferably 1% to 5% by mass.

[0220] Based on 100% by mass of the composite material slurry, the concentration of solid components in the composite material slurry is preferably 30% to 90% by mass, and more preferably 40% to 85% by mass.

[0221] The water content in the composite slurry is preferably below 500 ppm, more preferably below 300 ppm, and particularly preferably below 100 ppm.

[0222] "electrode"

[0223] The electrode film of this embodiment includes a current collector and an electrode film formed from a composite material slurry. The electrode film is a coating film of the composite material slurry. For example, it is a coating film formed by coating the current collector with the composite material slurry and then drying it to form an electrode composite material layer.

[0224] The material and shape of the current collector used in the electrode film of this embodiment are not particularly limited, and various current collectors used in secondary batteries can be appropriately selected. For example, metals or alloys such as aluminum, copper, nickel, titanium, or stainless steel can be used as materials for the current collector. In addition, as for the shape, a flat foil is usually used, but current collectors with roughened surfaces, perforated foil-shaped current collectors, and mesh-shaped current collectors can also be used.

[0225] There are no particular limitations on the method for forming an electrode film by coating a composite material slurry onto a current collector; any known method may be used. Specifically, examples include mold coating, dip coating, roller coating, scraper coating, knife coating, spray coating, gravure coating, screen printing, or electrostatic coating. As for drying methods, methods such as placement drying, forced air drying, hot air drying, infrared heating, and far-infrared heating can be used, but these are not particularly limited to.

[0226] Alternatively, rolling processing using offset printing, calendering rolls, or the like can be performed after coating. The thickness of the electrode composite layer is typically 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

[0227] Secondary Batteries

[0228] The secondary battery of this embodiment includes an electrode having the electrode film of this disclosure and an electrolyte. Regarding the carbon material dispersion composition using the resin composition of this embodiment, since a good conductive network is formed within the secondary battery electrode, the rate performance is excellent. During charging and discharging, the active material is uniformly utilized, thus preventing the degradation of the active material. Furthermore, overcharging and over-discharging during charging and discharging are suppressed. Therefore, battery performance degradation caused by electrolyte decomposition and metal deposition is less likely to occur, resulting in excellent cycle performance.

[0229] As a positive electrode, an electrode film can be made by coating a current collector with a composite slurry containing a positive electrode active material and then drying it.

[0230] As a negative electrode, an electrode film can be made by coating a current collector with a composite slurry containing a negative electrode active material and then drying it.

[0231] As the electrolyte, various conventionally known electrolytes capable of ion mobility can be used. Examples include, but are not limited to, electrolytes containing lithium salts such as LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, Li(CF3SO2)3C, LiI, LiBr, LiCl, LiAlCl, LiHF2, LiSCN, or LiBPh4 (where Ph is phenyl). Electrolytes containing sodium salts can also be used. The electrolyte is preferably dissolved in a non-aqueous solvent for use as the electrolyte solution.

[0232] As a non-aqueous solvent, there are no particular limitations. Examples include carbonates such as ethylene carbonate, propylene carbonate, butyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octyl lactone; glycol dimethyl ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents can be used individually or in combination of two or more.

[0233] The secondary battery in this embodiment preferably includes a separator. Examples of separators include polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics obtained by hydrophilic treatment of these materials, but it is not particularly limited to these.

[0234] The structure of the secondary battery in this embodiment is not particularly limited. It is usually composed of a positive electrode, a negative electrode, and a separator provided as needed. It can be various shapes, such as paper type, cylindrical type, button type, and stacked type, depending on the purpose of use.

[0235] The application of the secondary battery in this embodiment is not particularly limited. Specifically, it can be used for power supply in civilian devices such as mobile phones, laptops, and digital cameras; as emergency power in hospitals, factories, and buildings; and in vehicles such as hybrid electric vehicles, plug-in hybrid electric vehicles, electric vehicles, electric-assisted bicycles, and railway vehicles. For example, the secondary battery can recover regenerative energy from vehicle power.

[0236] As a secondary battery with high charge-discharge performance and excellent cycle characteristics, it is suitable for use in vehicles, resulting in vehicles with high safety and improved energy efficiency. Furthermore, it also performs excellently in vehicle applications where high current charging and discharging is required.

[0237] The mounting location of the secondary battery in the vehicle according to this embodiment is not particularly limited. For example, when mounting the secondary battery in a car, it can be mounted in the engine compartment, at the rear of the vehicle body, or under the seats.

[0238] Example

[0239] The following examples illustrate the invention in more detail. This disclosure is not limited to these examples unless it departs from its spirit. It should be noted that, unless otherwise specified, "parts" means "parts by mass," and "%" means "% by mass." Furthermore, the quantities in the table are parts by mass. It should be noted that empty columns in the table indicate no mixing.

[0240] The materials used in the examples and comparative examples are shown below.

[0241] • Hydrogenated nitrile butadiene rubber (made by Zannan Scientech, liquid hydrogenated nitrile butadiene rubber, number average molecular weight 20,000, weight average molecular weight 35,000, Z-average molecular weight 60,000, alkylene structural units 66% by mass, nitrile structural units 34% by mass), hereinafter referred to as HNBR 1.

[0242] • Hydrogenated nitrile butadiene rubber (made by Zannan Scientech, ZN 35052, Mooney viscosity 20, number-average molecular weight 48,000, weight-average molecular weight 110,000, Z-average molecular weight 210,000, alkylene structural units 66% by mass, nitrile structural units 34% by mass), hereinafter referred to as HNBR 2.

[0243] • Hydrogenated nitrile butadiene rubber (made by Zannan Scientech, ZN 35053, Mooney viscosity 35, number-average molecular weight 53,000, weight-average molecular weight 133,000, Z-average molecular weight 270,000, alkylene structural units 64% by mass, nitrile structural units 36% by mass), hereinafter referred to as HNBR 3.

[0244] • Hydrogenated nitrile butadiene rubber (made by Zannan Scientech, ZN 35056, Mooney viscosity 65, number-average molecular weight 75000, weight-average molecular weight 183000, Z-average molecular weight 364000, alkylene structural units 64% by mass, nitrile structural units 36% by mass), hereinafter referred to as HNBR 4.

[0245] • Hydrogenated nitrile butadiene rubber (manufactured by ARLANXEO, Therban(R) 3406, Mooney viscosity 63, number average molecular weight 78,000, weight average molecular weight 209,000, Z-average molecular weight 434,000, alkylene structural units 66% by mass, nitrile structural units 34% by mass), hereinafter referred to as HNBR 5.

[0246] • Carbon nanotubes (manufactured by JEIO, JENOTUBE 6A, average outer diameter 6nm, BET specific surface area 650m²) 2 / g), hereinafter referred to as CNT 1.

[0247] • Carbon nanotubes (manufactured by JEIO, JENOTUBE 10B, average outer diameter 10 nm, BET specific surface area 230 m²) 2 / g), hereinafter referred to as CNT 2.

[0248] • HS-100: DENKA BLACK HS-100 (manufactured by Denka, acetylene black, average primary particle size 48nm, BET specific surface area 39m²) 2 / g), hereinafter referred to as CB 1.

[0249] The methods for determining the physical properties of the materials used in each embodiment and comparative example are described below.

[0250] Specific surface area

[0251] The BET specific surface area of ​​carbon nanotubes and carbon black can be determined according to JIS Z 8830:2013 by the BET method based on nitrogen adsorption.

[0252] <Average Outer Diameter>

[0253] The average outer diameter of carbon nanotubes can be calculated by observing and photographing them using a transmission electron microscope (TEM), then selecting any 300 carbon nanotubes from the resulting images and measuring their respective outer diameters. Similarly, the average primary particle size of carbon black can be calculated by first observing and photographing the carbon black using a TEM, then selecting any 100 spherical primary carbon black particles from the images and measuring their respective outer diameters.

[0254] Mooney viscosity

[0255] Regarding the Mooney viscosity of hydrogenated nitrile butadiene rubber, the Mooney viscosity was measured using an L-shaped rotor at 100°C according to Japanese Industrial Standard JIS K6300-1 (ML1+4, 100°C).

[0256] <Making a Standard Negative Electrode>

[0257] In a 150ml plastic container, add 0.5 parts by weight of acetylene black (DENKA BLACK HS-100, manufactured by Denka), 1 part by weight of MAC 500LC (Sunrose special type MAC 500L sodium carboxymethyl cellulose, manufactured by Nippon Paper Corporation, 100% non-volatile components), and 98.4 parts by weight of water. Then, using a rotary mixer (THINKY defoaming Rentarō, ARE-310), stir at 2000 rpm for 30 seconds. Further, add 92 parts by weight of artificial graphite (Nippon Graphite Industry, CGB-20) and 5 parts by weight of silicon oxide (Osaka Titanium Technology Co., Ltd., SILICON MONOOXIDE SiO 1.3C 5μm, 100% non-volatile components) as active materials, and stir at 3000 rpm for 10 minutes using a high-speed mixer. Next, 3.1 parts by weight of styrene-butadiene rubber (SBR, TRD2001, manufactured by JSR) were added, and the mixture was stirred at 2000 rpm for 30 seconds using the aforementioned rotary mixer to obtain a composite slurry for the negative electrode. Then, using a coating apparatus, the composite slurry for the negative electrode was prepared at a weight per unit area of ​​8 mg / cm³ for the electrode. 2 After being coated onto copper foil, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes. Further, it was rolled using a roller press (a 3t hydraulic roller press manufactured by THANK METAL Co., Ltd.) to produce a composite material layer with a density of 1.6 g / cm³. 3 The standard negative electrode.

[0258] <Preparation of Alkali Metal Compound Dispersions>

[0259] In a capacity of 2000cm 3Add 950 parts by weight of NMP and 50 parts by weight of NaOH (sodium hydroxide, manufactured by Tosoh Pearl Co., Ltd.) to a plastic container. Install a fine emulsifying sieve on a high-shear mixer (L5M-A, manufactured by SILVERSON) and disperse at 9000 rpm until the mixture becomes homogeneous. Then, use a filter bell to pass it through a nylon filter with a mesh size of 150 μm to prepare a NaOH dispersion (NaOH concentration 5% by weight).

[0260] The maximum particle size of sodium hydroxide is less than 150 μm.

[0261] Methods for Determination and Evaluation of Physical Properties

[0262] The methods for measuring and evaluating the physical properties of the resin compositions, carbon material dispersion compositions, electrode films, and secondary batteries used in the examples and comparative examples described below are as follows.

[0263] <Determination of number-average molecular weight, weight-average molecular weight, and Z-average molecular weight of copolymers>

[0264] (Preparation of samples for molecular weight determination)

[0265] To determine the number-average molecular weight (Mn), weight-average molecular weight (Mw), and Z-average molecular weight (Mz) of the copolymer, a sample for molecular weight determination was prepared by the following method.

[0266] The resin composition was added dropwise to purified water to precipitate the copolymer. The precipitate was then filtered using a Buchner funnel and recovered. The precipitate was rinsed directly over the Buchner funnel with purified water to dissolve it in tetrahydrofuran (THF), yielding a solution. This solution was then added dropwise to purified water again, and the filtration and washing with purified water steps described above were repeated to redissolve the precipitate in THF, thus preparing a sample for molecular weight determination.

[0267] (Determination of molecular weight)

[0268] Molecular weight determination samples were analyzed using gel permeation chromatography (GPC) equipped with an RI detector. An HLC-8320 GPC (manufactured by Tosoh Corporation) was used as the apparatus, with three separation columns connected in series. The packing media were sequentially filled with Tosoh Corporation's "TSK-GEL SUPER AW-4000", "AW-3000", and "AW-2500". The oven temperature was 40°C. The eluent was a solution of 30 mM triethylamine and 10 mM LiBr in N,N-dimethylformamide, and the flow rate was 0.6 mL / min. For the sample to be analyzed, the concentration was adjusted to 1% using a solvent prepared from the above eluent, and 20 μL was injected. The average molecular weight is a polystyrene equivalent.

[0269] <Content of alkylene structural units and nitrile-containing structural units in the copolymer>

[0270] (Preparation of samples for IR measurement)

[0271] The resin composition was added dropwise to purified water to precipitate the copolymer. The precipitate was then filtered using a Buchner funnel and recovered. The precipitate was rinsed directly with purified water over the Buchner funnel and then dried in a hot air oven at 140°C for 1 hour to prepare a sample for IR measurement.

[0272] (IR measurement)

[0273] Using IR measurement samples, Fourier transform infrared spectrometer (Thermo Fisher Scientific, Nicleti S5) was used to measure and calculate the content of alkylene structural units and nitrile structural units of the copolymer in the resin composition.

[0274] <Resistivity Measurement of Resin Compositions>

[0275] (Preparation of samples for resistivity measurement)

[0276] 250cm 3 In a plastic container, a resin composition and N-methyl-2-pyrrolidone were weighed to prepare 200 samples for liquid resistance measurement with a non-volatile component content of 8% by mass.

[0277] (Measurement of resistivity)

[0278] The resistivity at 25°C was calculated using a sample intended for liquid resistance measurement and a resistivity meter (IEST Yuaneng Technology (registered trademark), BATERRYSLURRY RESISTIVITY BSR2300). The resistivity value was obtained using measurements from Middlechannel.

[0279] Determination of Alkali Metal Content in Resin Compositions

[0280] After the resin composition was dried and cured using a hot air oven, acid decomposition was performed using a microwave sample pretreatment device (Milestone General, ETHOS1) to calculate the alkali metals (lithium, sodium, and potassium) content in the resin composition. The alkali metal content was the sum of the lithium, sodium, and potassium contents.

[0281] <Initial viscosity of carbon material dispersion composition>

[0282] After the carbon material dispersion composition was allowed to stand in a constant temperature bath at 25°C for more than 1 hour, the initial viscosity was immediately tested using a Type B viscometer at a rotor speed of 100 rpm. The initial viscosity evaluation criteria are as follows: 100 mPa·s or more and less than 500 mPa·s: ◎ (Excellent); 500 mPa·s or more and less than 1000 mPa·s: 〇 (Good); 1000 mPa·s or more and less than 2000 mPa·s: △ (Acceptable); more than 2000 mPa·s: × (Poor).

[0283] <Viscosity over time of carbon material dispersion composition>

[0284] After the carbon material dispersion composition was allowed to stand in a constant temperature bath at 60°C for one week, it was cooled to 25°C and then immediately tested using a Type B viscometer at a rotor speed of 100 rpm. The evaluation criteria for viscosity over time are as follows: ≥500 mPa·s and ≤2000 mPa·s: ◎ (Excellent); ≥2000 mPa·s and ≤3000 mPa·s: 〇 (Good); ≥3000 mPa·s and ≤6000 mPa·s: △ (Acceptable); ≥6000 mPa: × (Poor).

[0285] <60-degree mirror gloss of carbon material dispersion composition>

[0286] The surface smoothness of the coating film is evaluated by the gloss value as a measure of the dispersion of the dispersed material.

[0287] After coating a PET (polyethylene terephthalate) film with a rod coater No. 7, the carbon material dispersion composition was dried in a hot air oven at 120°C for 5 minutes. The gloss level of the coated surface was then measured at 60 degrees using a gloss meter (Nippon Denshoku Kogyo Co., Ltd., VG 7000) according to JIS Z8741. The evaluation criteria for 60-degree specular gloss are as follows: 50 degrees or more but less than 80 degrees: ◎ (Excellent); 40 degrees or more but less than 50 degrees, or 80 degrees or more but less than 90 degrees: 〇 (Good); 30 degrees or more but less than 40 degrees, or 90 degrees or more: △ (Acceptable); less than 30 degrees: × (Poor).

[0288] <Volume resistivity of electrode film>

[0289] The composite slurry was applied using a dressing applicator at a weight of 20 mg / cm² per unit area of ​​electrode. 2After being coated onto aluminum foil, the coating was dried in an electric oven at 120℃±5℃ for 25 minutes. Then, the surface resistivity (Ω / □) of the dried coating was measured using a Lorestar GP (MCP-T610, probe: AP2 probe (RMH333)) manufactured by Mitsubishi Chemical Analytech Co., Ltd. The measured resistivity was multiplied by the thickness of the electrode composite layer formed on the aluminum foil to obtain the volume resistivity (Ω·cm). For the thickness of the electrode composite layer, the volume resistivity (Ω·cm) was obtained by subtracting the aluminum foil thickness from the average value obtained from measuring three points on the electrode film using a film thickness gauge (NIKON, DIGIMICRO MH-15M). The evaluation criteria for volume resistivity are as follows: less than 8 Ω·cm: ◎ (Excellent); 8 Ω·cm or more but less than 12 Ω·cm: 〇 (Good); 12 Ω·cm or more but less than 15 Ω·cm: △ (Acceptable); 15 Ω·cm or more: × (Poor).

[0290] <Peel strength of electrode film>

[0291] The composite slurry was applied using a dressing applicator at a weight of 20 mg / cm² per unit area of ​​electrode. 2 After being coated onto aluminum foil, the coating was dried in an electric oven at 120℃±5℃ for 25 minutes. Then, the coating direction was used as the long axis to cut two 90mm×20mm rectangles. For peel strength determination, a benchtop tensile testing machine (Toyo Seiki Co., Ltd., Strograph E3) was used, and the results were evaluated using the 180-degree peel test method. Specifically, a 100mm×30mm double-sided tape (No. 5000 NS, Nitoms Co., Ltd.) was adhered to a stainless steel plate, ensuring the battery electrode composite material layer was in close contact with the other side of the tape. The tape was then pulled and peeled from bottom to top at a certain speed (50mm / min), and the average stress at this point was taken as the peel strength. The evaluation criteria for peel strength are as follows: 1.0 N / cm or above: ◎ (excellent); 0.7 N / cm or above and less than 1.0 N / cm: 〇 (good); 0.5 N / cm or above and less than 0.7 N / cm: △ (acceptable); less than 0.5 N / cm: × (poor).

[0292] <Evaluation of Rate Characteristics of Lithium-ion Secondary Batteries>

[0293] The laminated lithium-ion secondary battery was placed in a constant temperature chamber at 25°C and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Beidou Electric Co., Ltd.). After constant current and constant voltage charging at a charging current of 10mA (0.2C) and a charging termination voltage of 4.2V (cutoff current 1.0mA (0.02C)), constant current discharging at a discharging current of 10mA (0.2C) and a discharging termination voltage of 2.5V was performed. This operation was repeated three times. Then, constant current and constant voltage charging was performed at a charging current of 10mA (0.2C) and a charging termination voltage of 4.2V (cutoff current (1.0mA + 0.02C)), followed by constant current discharging at 0.2C and 3C until the discharging termination voltage of 2.5V was reached. The discharge capacity was calculated for each discharge. The rate characteristic can be expressed by the ratio of the 0.2C discharge capacity to the 3C discharge capacity, as shown in Equation 2 below.

[0294] (Equation 2) Rate capability = 3C discharge capacity / third 0.2C discharge capacity × 100 (%)

[0295] Regarding the evaluation criteria for rate capability, a rate capability of 80% or higher is set as ◎ (excellent), 70% or higher but less than 80% is set as 〇 (good), 60% or higher but less than 70% is set as △ (acceptable), and less than 60% is set as × (poor).

[0296] Evaluation of High-Temperature Cycling Characteristics of Lithium-ion Secondary Batteries

[0297] The laminated lithium-ion secondary battery was placed in a constant temperature chamber at 45°C and charge / discharge measurements were performed using a charge / discharge device (manufactured by Beidou Electric Co., Ltd., SM-8). After constant current and constant voltage charging at a charging current of 50mA (1C) and a charging termination voltage of 4.2V (cutoff current 1.25mA (0.025C)), constant current discharging was performed at a discharging current of 50mA (1C) and a discharging termination voltage of 2.5V. This operation was repeated 100 times. 1C is the current value at which the theoretical capacity of the positive electrode is discharged in 1 hour. The cycle characteristics can be expressed by the ratio of the 1C discharge capacity of the 100th cycle to the 1C discharge capacity of the third cycle at 45°C, as shown in Equation 3 below.

[0298] (Equation 3)

[0299] High-temperature cycling characteristics = (1C discharge capacity at the 100th cycle / 1C discharge capacity at the 3rd cycle) × 100 (%)

[0300] Regarding the evaluation criteria for high-temperature cycling characteristics, a cycling characteristic of 90% or more is set as ◎ (excellent); 85% or more but less than 90% is set as 〇 (good); 80% or more but less than 85% is set as △ (acceptable); and less than 80% is set as × (poor).

[0301] (Example 1-1)

[0302] 780 parts by weight of NMP were added to a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, and the mixture was purged with nitrogen. The reaction vessel was then heated to 80°C, and 200 parts by weight of HNBR 1 were added, stirring until the hydrogenated nitrile rubber was completely dissolved. Then, 20 parts by weight of NaOH dispersion were added, and air was added while stirring. The reaction vessel was kept at 80°C for 12 hours while being heated to obtain a resin composition (R-1) containing copolymer (A1) as copolymer (X) and an alkali metal.

[0303] Based on a total content of 100% by mass of alkylene structural units and nitrile structural units in copolymer (A1), the content of alkylene structural units is 66% by mass, the content of nitrile structural units is 34% by mass, the number average molecular weight (Mn) is 18,000, the weight average molecular weight (Mw) is 30,000, and the Z average molecular weight (Mz) is 49,000.

[0304] It should be noted that the other structural units constituting the copolymer (A1) are less than 3% by mass based on 100% by mass of the copolymer (A1).

[0305] In addition, the alkali metal content in the resin composition is 700 ppm.

[0306] (Examples 1-2 to 1-9), (Comparative Examples 1-1 to 1-5, 1-7 to 1-9)

[0307] Except for changing the conditions as described in Table 1, the resin compositions (R-2 to R-9) containing copolymers (X) and the comparative resin compositions (RRC-1 to RC5, RC-7 to RC9) described in Table 1 were obtained by the same method as in Examples 1-1.

[0308] (Examples 1-10)

[0309] For the resin composition 9 prepared in Examples 1-9, a three-pass dispersion process was performed using a high-pressure homogenizer (SUGINO MACHINE, Star Burst Labo). The dispersion process was carried out with a nozzle diameter of 0.17 mm and a pressure of 150 MPa to obtain a resin composition (R10) containing copolymer (E2).

[0310] (Examples 1-11)

[0311] For the resin composition 9 prepared in Examples 1-9, a five-pass dispersion process was performed using a high-pressure homogenizer (SUGINO MACHINE, Star Burst Labo). The dispersion process was carried out with a nozzle diameter of 0.17 mm and a pressure of 150 MPa to obtain a resin composition (R-11) containing copolymer (E3).

[0312] (Examples 1-12)

[0313] HNBR 1 was subjected to a 5-pass dispersion process using a high-pressure homogenizer (SUGINO MACHINE, Star Burst Labo). The dispersion process was carried out with a nozzle diameter of 0.17 mm and a pressure of 150 MPa to obtain a resin composition (R-12) containing the copolymer (A4).

[0314] (Comparative Examples 1-6)

[0315] Comparative resin composition 5 prepared in Comparative Examples 1-5 was subjected to a 5-pass dispersion process using a high-pressure homogenizer (SUGINO MACHINE, Star Burst Labo). The dispersion process was carried out at a nozzle diameter of 0.17 mm and a pressure of 150 MPa to obtain a resin composition (RC-6) containing copolymer (E5).

[0316] Table 2 lists the individual contents of alkylene structural units and nitrile-containing structural units, based on the total content of alkylene structural units and nitrile-containing structural units. It should be noted that in any copolymer, the other structural units constituting the copolymer are all less than 3% by mass, based on 100% by mass of the copolymer.

[0317] [Table 1]

[0318]

[0319] Table 2 shows the evaluation results of the resin compositions prepared in Examples 1-1 to Comparative Examples 1-9.

[0320] [Table 2]

[0321]

[0322] (Example 2-1)

[0323] 87.75 parts of N-methyl-2-pyrrolidone (NMP) and 8.75 parts of resin composition (R-1) were added to a stainless steel container and stirred using a dispersing mixer. Then, 3.5 parts of carbon nanotubes (JEIO, JENOTUBE 6A) were measured and added while stirring using a dispersing mixer. A fine emulsifying sieve was installed on a high-shear mixer (L5M-A, SILVERSON) and the mixture was intermittently dispersed at 9000 rpm until the mixture became homogeneous and the particle size was confirmed to be below 200 μm by a fineness gauge. The mixture was then passed through a high-magnetic-force magnetic filter (Eishin, surface magnetic flux density 17000 Gauss) to prepare a carbon material pre-dispersion composition. Next, the carbon material pre-dispersion composition is fed into a bead mill (manufactured by Ashizawa Finetech, Mugen Flow (registered trademark)) filled with zirconia beads of 1.0 mm diameter, and subjected to a cyclic dispersion process with a residence time of 10 minutes (bead filling rate 80%, circumferential speed 13 m / s). The number of cycles is 50. Then, the dispersed liquid is fed into a high-pressure homogenizer (manufactured by SUGINOMACHINE, Star Burst Labo) for 15 pass-through dispersion processes. The dispersion process was carried out using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa. The dispersed liquid was then supplied to an electromagnet (manufactured by Dae Bo Magnetic, EMF-100S, with a magnetic flux density of 16,000 Gauss, a volume of 1.7 L, and equipped with 31 grids with a diameter of 10 cm and a thickness of 1.3 cm). After three passes, the dispersed liquid was passed through two depth filters (3M, PP nonwoven fabric depth cartridge NT-T series, filtration accuracy of 20 μm) arranged in series to obtain carbon material dispersion composition 1.

[0324] (Examples 2-2 to 2-16), (Comparative Examples 2-1 to 2-9)

[0325] Except for the changes to the dispersion conditions, carbon material, resin composition, amount of resin composition added, and NMP as described in Table 3, carbon material dispersion compositions 2-16 and comparative carbon material dispersion compositions 1-9 were obtained by the same method as in Examples 2-1.

[0326] [Table 3]

[0327]

[0328] Table 4 shows the evaluation results of the carbon material dispersion compositions prepared in Examples 2-1 to 2-16 and Comparative Examples 2-1 to 2-9.

[0329] [Table 4]

[0330]

[0331] (Example 3-1)

[0332] 150cm 3 In a plastic container, 18.8 parts by weight of an NMP solution containing 8% by weight of PVDF (polyvinylidene fluoride, Solvay, Soflef#5130) and 14.5 parts by weight of NMP were weighed. Then, 11.4 parts by weight of a carbon material dispersion composition (carbon material dispersion composition 1) were added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotary mixer (defoaming Rentaro, ARE-310). Next, 98.1 parts by weight of a positive electrode active material (BASF Toda Battery Materials Co., Ltd., HED (registered trademark) NCM-111 1100) were added, and the mixture was stirred at 2000 rpm for 2.5 minutes using a rotary mixer (defoaming Rentaro, ARE-310) to obtain a composite material slurry (composite material slurry 1).

[0333] Next, using a dressing applicator, the composite slurry (composite slurry 1) was applied at a weight of 20 mg / cm² per unit area of ​​electrode. 2 After being coated onto aluminum foil, the coating was dried in an electric oven at 120℃±5℃ for 25 minutes to obtain an electrode film (electrode film 1). Then, the electrode film (electrode film 1) was rolled using a roller press (THANK METAL, 3t hydraulic roller press) to obtain the positive electrode (positive electrode 1). It should be noted that the weight per unit area of ​​the composite material layer is 20 mg / cm³. 2 The density of the composite material layer after rolling is 3.1 g / cc.

[0334] (Examples 3-2 to 3-5, Examples 3-8 to 3-16), (Comparative Examples 3-1 to 3-9)

[0335] As shown in Table 5, except that carbon material dispersion compositions 2-16 and comparative carbon material dispersion compositions 1-9 are used instead of carbon material dispersion composition 1, composite material slurries 2-5, 8-16, comparative composite material slurries 1-9, electrode films 2-5, 8-16, comparative electrode films 1-9, positive electrodes 2-16, and comparative positive electrodes 1-9 are obtained by the same method as in Example 3-1.

[0336] (Examples 3-6)

[0337] 150cm 3In a plastic container, 18.8 parts by weight of NMP solution containing 8% by weight of PVDF (polyvinylidene fluoride, Solvay, Soflef#5130) and 18.9 parts by weight of NMP were weighed. Then, 7.1 parts by weight of carbon material dispersion composition (carbon material dispersion composition 1) were added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotary mixer (defoaming Rentaro, ARE-310). Then, 98.1 parts by weight of positive electrode active material (BASF Toda Battery Materials Co., Ltd., HED (registered trademark) NCM-111 1100) were added, and the mixture was stirred at 2000 rpm for 2.5 minutes using a rotary mixer (defoaming Rentaro, ARE-310) to obtain composite material slurry (composite material slurry 6).

[0338] Next, using a dressing applicator, the composite slurry (composite slurry 6) was applied at a weight of 20 mg / cm² per unit area of ​​electrode. 2 After being coated onto aluminum foil, the coating was dried in an electric oven at 120℃±5℃ for 25 minutes to obtain an electrode film (electrode film 6). Then, the electrode film (electrode film 1) was rolled using a roller press (THANK METAL, 3t hydraulic roller press) to obtain the positive electrode (positive electrode 6). It should be noted that the weight per unit area of ​​the composite material layer is 20 mg / cm³. 2 The density of the composite material layer after rolling is 3.1 g / cc.

[0339] (Examples 3-7)

[0340] 150cm 3 In a plastic container, 18.8 parts by weight of NMP solution containing 8% by weight of PVDF (polyvinylidene fluoride, Solvay, Soflef#5130) and 21.6 parts by weight of NMP were weighed. Then, 5.0 parts by weight of carbon material dispersion composition (carbon material dispersion composition 1) were added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotary mixer (defoaming Rentaro, ARE-310). Then, 97.5 parts by weight of positive electrode active material (BASF Toda Battery Materials Co., Ltd., HED (registered trademark) NCM-111 1100) were added, and the mixture was stirred at 2000 rpm for 2.5 minutes using a rotary mixer (defoaming Rentaro, ARE-310) to obtain composite material slurry (composite material slurry 7).

[0341] Next, using a dressing applicator, the composite slurry (composite slurry 7) was applied at a weight of 20 mg / cm² per unit area of ​​electrode. 2After being coated onto aluminum foil, the coating was dried in an electric oven at 120℃±5℃ for 25 minutes to obtain an electrode film (electrode film 7). Then, the electrode film (electrode film 1) was rolled using a roller press (THANK METAL, 3t hydraulic roller press) to obtain the positive electrode (positive electrode 6). It should be noted that the weight per unit area of ​​the composite material layer is 20 mg / cm³. 2 The density of the composite material layer after rolling is 3.1 g / cc.

[0342] Table 5 shows the evaluation results of the electrode films prepared in Examples 3-1 to 3-16 and Comparative Examples 3-1 to 3-9.

[0343] [Table 5]

[0344]

[0345] (Example 4-1)

[0346] The positive electrode (positive electrode 1) and the standard negative electrode were punched to 45mm×40mm and 50mm×45mm respectively, and inserted into an aluminum laminated bag together with the separator (porous polypropylene membrane) inserted between them. The bags were then dried in an electric oven at 60°C for 1 hour. Then, in an argon-filled glove box, 2 mL of electrolyte (a non-aqueous electrolyte prepared by mixing ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a 1:1:1 (volume ratio) mixture, and further adding 2 parts by mass of VC (ethylene carbonate) relative to 100 parts by mass of the mixture as an additive, and then dissolving LiPF6 at a concentration of 1M) was injected. The aluminum laminated bag was then sealed to produce a laminated lithium-ion secondary battery (secondary battery 1).

[0347] (Examples 4-2 to 4-16), (Comparative Examples 4-1 to 4-9)

[0348] Except for changing the positive electrode to the one described in Table 6, laminated lithium-ion secondary batteries (secondary batteries 2) ~ (comparative secondary battery 9) are manufactured by the same method as the manufacturing of laminated lithium-ion secondary batteries (secondary batteries 1).

[0349] [Table 6]

[0350]

[0351] In the above embodiments, a resin composition containing copolymer (X) and 50 ppm or more but less than 10,000 ppm of alkali metal was used. The resistivity of the resin composition was 5,000 Ω·cm or more and 25,000 Ω·cm or less when the copolymer content of the resin composition was 8% by mass using N-methyl-2-pyrrolidone. In these embodiments, compared to the comparative example, a lithium-ion secondary battery exhibiting excellent viscosity stability over time, secondary battery characteristics, and particularly excellent high-temperature cycling characteristics of the carbon material dispersion composition was obtained. Therefore, it is clear that this disclosure can provide a lithium-ion secondary battery with high capacity, high output, and high durability that is difficult to achieve with conventional carbon material dispersion compositions.

[0352] Vehicles equipped with the lithium-ion secondary battery disclosed herein have high charge-discharge performance and excellent high-temperature cycle characteristics, thus enabling vehicles with high safety and improved energy efficiency.

[0353] The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above content. Various modifications that can be understood by those skilled in the art can be made to the structure and details of the present invention within the scope of the invention.

[0354] The present invention has been described with reference to the above-described embodiments, but the present invention is not limited to the above-described embodiments. Various modifications can be made to the structure and details of the invention within the scope of the present invention.

[0355] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-221779 filed on December 27, 2023, the entire disclosure of which is incorporated herein by reference.

Claims

1. A resin composition comprising a copolymer (X) having alkylene structural units and nitrile structural units, and an alkali metal, The content of the alkali metal is above 50 ppm and less than 10,000 ppm. When the content of non-volatile components in the resin composition is 8% by mass using N-methyl-2-pyrrolidone, the resistivity is 5,000 Ω·cm or more and 25,000 Ω·cm or less.

2. The resin composition according to claim 1, wherein, The copolymer (X) has a Z-average molecular weight of 20,000 or more and 200,000 or less.

3. The resin composition according to claim 1, wherein, The ratio of the Z-average molecular weight Mz to the weight-average molecular weight Mw of the copolymer (X), i.e., Mz / Mw, is less than 2.

0.

4. A carbon material dispersion composition comprising the resin composition according to any one of claims 1 to 3, and the carbon material.

5. A composite material slurry comprising the carbon material dispersion composition of claim 4 and an active substance.

6. An electrode film formed by coating the composite slurry of claim 5.

7. A secondary battery comprising an electrode having an electrode membrane as described in claim 6 and an electrolyte.

8. A vehicle comprising the secondary battery of claim 7.

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