Resin Composition

Abstract

This invention provides a resin composition with excellent coatability and adhesion, and which can balance high electronic conductivity with the dispersibility and dispersion stability of fibrous carbon materials, thereby achieving a lithium secondary battery with high capacity retention. This invention is a resin composition comprising fibrous carbon materials, a non-aqueous solvent, and a polyvinyl acetal resin, wherein the polyvinyl acetal resin has structural units with acidic functional groups, an average degree of polymerization of 150 or more and 1500 or less, and a hydroxyl content of 40.0 mol% or more and 80.0 mol% or less.

Description

Technical Field

[0001] This invention relates to a resin composition that has excellent coatability and adhesion, and can balance high electronic conductivity with the dispersibility and dispersion stability of fibrous carbon materials, thereby obtaining a lithium secondary battery with high capacity retention. Background Technology

[0002] In recent years, fibrous carbon materials such as carbon nanotubes and VGCF have shown excellent electrical properties and are expected to be applied in a wide range of fields, including the electronics industry. For example, their use as conductive additives in electrodes for secondary batteries and transparent electrodes is under investigation.

[0003] Fibrous carbon materials are typically produced using compositions dispersed in water or organic solvents.

[0004] For example, Patent Document 1 discloses a conductive resin composition having a resin component comprising polyvinyl acetal (A) and a curable resin (B), and a carbon component comprising carbon nanotubes (C) with an aspect ratio and an average fiber diameter within a specified range.

[0005] In addition, Patent Document 2 discloses a microfiber dispersion comprising microfibers, a dispersion medium, a polymeric dispersant, and an alkaline compound with a pKa of 7.5 or higher.

[0006] In addition, Patent Document 3 discloses a composition containing microparticles comprising polyvinyl acetal resin, a fibrous conductive substance, and a liquid dispersion medium.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2014-28900

[0010] Patent Document 2: Japanese Patent Application Publication No. 2014-181140

[0011] Patent Document 3: Japanese Patent Application Publication No. 2014-209435 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] However, fibrous carbon materials suffer from low solubility and dispersibility, and cannot maintain a stable dispersion in solvents. In particular, they are known to be unable to maintain a dispersion in non-aqueous solvents. Furthermore, while fibrous carbon materials possess excellent electrical, thermal, and mechanical properties, their aspect ratio is very large, making them prone to entanglement and hindering the development of high-performance composite materials that fully utilize their properties.

[0014] To address the aforementioned problems, a large amount of resin component is required as a dispersant; however, this can hinder the properties of the fibrous carbon material. Even the compositions disclosed in Patent Documents 1-3 are insufficient to maintain both the high electronic conductivity and high dispersibility of the fibrous carbon material.

[0015] The purpose of this invention is to provide a resin composition that has excellent coatability and adhesion, and can balance high electronic conductivity with the dispersibility and dispersion stability of fibrous carbon materials, thereby obtaining a lithium secondary battery with high capacity retention.

[0016] Methods for solving problems

[0017] This invention relates to a resin composition comprising fibrous carbon material, a non-aqueous solvent, and polyvinyl acetal resin.

[0018] The above-mentioned polyvinyl acetal resin has structural units with acidic functional groups, an average degree of polymerization of 150 or more and 1500 or less, and a hydroxyl content of 40.0 mol% or more and 80.0 mol% or less.

[0019] The present invention will now be described in detail.

[0020] The inventors conducted in-depth research and discovered that by combining fibrous carbon materials, non-aqueous solvents, and polyvinyl acetal resins with a specific structure, excellent coatability and adhesion are achieved, while simultaneously maintaining high electronic conductivity and good dispersibility of the fibrous carbon materials. Furthermore, it was found that by using the above-described resin composition, lithium-ion secondary batteries with high capacity retention can be obtained, thus completing this invention.

[0021] The resin composition of the present invention contains fibrous carbon material.

[0022] By incorporating fibrous carbon materials, electrical conductivity can be improved.

[0023] The aforementioned fibrous carbon materials refer to carbon materials with a longitudinal-to-transverse dimension ratio (average fiber length / average fiber diameter) of 30 or higher.

[0024] Regarding the aspect ratio (average fiber length / average fiber diameter) of the aforementioned fibrous carbon material, from the viewpoint of efficiently forming electron conduction pathways, it is preferably 50 or more, more preferably 100 or more, even more preferably 200 or more, even more preferably 400 or more, and preferably 500,000 or less, more preferably 300,000 or less, even more preferably 100,000 or less, even more preferably 50,000 or less, and particularly preferably 20,000 or less.

[0025] Examples of fibrous carbon materials include carbon fibers and carbon nanotubes.

[0026] Examples of the aforementioned carbon fibers include PAN-based carbon fibers, pitch-based carbon fibers, cellulose-based carbon fibers, and vapor-grown carbon fibers (VGCF).

[0027] The aforementioned carbon nanotubes are cylindrical carbon materials, including single-layer carbon nanotubes and multi-layer carbon nanotubes.

[0028] Regarding the average fiber diameter of the aforementioned fibrous carbon material, from the viewpoint of efficiently forming electron conduction paths, it is preferably 0.40 nm or more, more preferably 0.50 nm or more, even more preferably 1.0 nm or more, even more preferably 5.0 nm or more, and preferably 200.0 nm or less, more preferably 150.0 nm or less, and even more preferably 100.0 nm or less.

[0029] The average fiber diameter mentioned above can be determined, for example, by Raman spectroscopy.

[0030] Regarding the average fiber length of the aforementioned fibrous carbon material, from the viewpoint of efficiently forming electron conduction pathways, it is preferably 0.10 μm or more, more preferably 0.50 μm or more, even more preferably 1.0 μm or more, even more preferably 5.0 μm or more, and preferably 500.0 μm or less, more preferably 250.0 μm or less, even more preferably 200.0 μm or less, and even more preferably 100.0 μm or less.

[0031] The average fiber length mentioned above can be determined, for example, by Raman spectroscopy.

[0032] Regarding the specific gravity of the aforementioned fibrous carbon material, from the viewpoint of maintaining a stable dispersion state, it is preferably 1.0 or more, more preferably 1.3 or more, even more preferably 1.5 or more, and even more preferably 1.8 or more, and preferably 2.5 or less, more preferably 2.3 or less, and even more preferably 2.1 or less.

[0033] The above specific gravity can be determined according to the method of JIS Z8807.

[0034] Regarding the specific surface area of ​​the aforementioned fibrous carbon material, from the viewpoint of improving electrical conductivity while maintaining dispersibility, an area of ​​8 m² is preferred. 2 / g or more, preferably 13m 2 / g or more, further preferably 100m 2 / g or more, more preferably 200m 2 / g or more, and preferably 3000m 2 / g or less, more preferably 1500m 2 / g or less, more preferably 1200m 2 / g or less, more preferably 1000m 2 / g or less.

[0035] The aforementioned specific surface area can be measured, for example, using a specific surface area measuring device (Shimadzu Corporation's "ASAP-2000").

[0036] Regarding the peak intensity ratio (G / D ratio) of the G band to the D band of the aforementioned fibrous carbon material, from the viewpoint of improving electronic conductivity, it is preferably 0.1 or more, more preferably 5 or more, even more preferably 10 or more, and preferably 100 or less, more preferably 85 or less, and even more preferably 70 or less.

[0037] The aforementioned G / D ratio can be determined by measuring the Raman spectrum using Raman spectrophotometry.

[0038] When the above-mentioned fibrous carbon material was measured by Raman spectroscopy, the G band corresponding to the sp2 bond (1580 cm⁻¹) was clearly observed. -1 (nearby) and the D band corresponding to the sp3 bond (1360cm) -1 These two peaks (nearby) are noteworthy. It should be noted that when the carbon material is crystalline, one of these two bands is minimized. For example, the 1580 cm⁻¹ peak is practically unobservable in single-crystal diamond. -1 The nearby G-band. On the other hand, in the case of a high-purity graphite structure, 1360 cm⁻¹ -1 The nearby D-band is almost never seen.

[0039] The aforementioned fibrous carbon material can be a discontinuous fiber with the fiber intermittently cut, or it can be a continuous fiber without being cut.

[0040] In addition, the shape of the above-mentioned fibers is not particularly limited. For example, in addition to fibrous form, they can also be sheet-like, such as fabric, woven fabric, or non-woven fabric.

[0041] The content of the fibrous carbon material in the resin composition of the present invention is preferably 0.05% by weight or more, more preferably 0.1% by weight or more, even more preferably 0.5% by weight or more, even more preferably 1.5% by weight or more, and preferably 15.0% by weight or less, more preferably 10.0% by weight or less.

[0042] The resin composition of the present invention contains a non-aqueous solvent.

[0043] The aforementioned non-aqueous solvents refer to solvents in which the water content, calculated by weight, is less than 100 ppm.

[0044] Examples of non-aqueous solvents include ketones, alcohols, aromatic hydrocarbons, esters, and amides.

[0045] Examples of ketones mentioned above include acetone, methyl ethyl ketone, dipropyl ketone, and diisobutyl ketone.

[0046] Examples of alcohols mentioned above include methanol, ethanol, isopropanol, and butanol.

[0047] Examples of aromatic hydrocarbons mentioned above include toluene and xylene.

[0048] Examples of the aforementioned esters include methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, butyl butyrate, methyl valerate, ethyl valerate, butyl valerate, methyl hexanoate, ethyl hexanoate, butyl hexanoate, 2-ethylhexyl acetate, and 2-ethylhexyl butyrate.

[0049] Alternatively, methyl cellosolve, ethyl cellosolve, butyl cellosolve, terpineol, dihydroterpineol, butyl cellosolve acetate, butyl carbitol acetate, terpineol acetate, dihydroterpineol acetate, etc., can also be used.

[0050] Examples of the aforementioned carbonates include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate.

[0051] As for the aforementioned amides, compounds containing a lactam structure are preferred, more preferably containing a 3- to 6-membered ring lactam structure, and even more preferably containing a 5-membered ring lactam structure. Specifically, examples of the aforementioned amides include dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and diethylformamide.

[0052] The content of the above-mentioned non-aqueous solvent in the resin composition of the present invention is preferably 60.0% by weight or more, more preferably 70.0% by weight or more, and preferably 99.9% by weight or less.

[0053] The resin composition of the present invention contains polyvinyl acetal resin.

[0054] The above-mentioned polyvinyl acetal resin has structural units with acidic functional groups, an average degree of polymerization of 150 or more and 1500 or less, and a hydroxyl content of 40.0 mol% or more and 80.0 mol% or less.

[0055] By including the above-mentioned polyvinyl acetal resin, even if the amount of polyvinyl acetal resin added as a dispersant is reduced, the dispersibility of fibrous carbon materials can be sufficiently improved, thus balancing high electronic conductivity and the dispersibility of fibrous carbon materials.

[0056] The aforementioned polyvinyl acetal resin possesses structural units with acidic functional groups.

[0057] The acidic functional group mentioned above is preferably a proton acidic group.

[0058] Examples of proton-acidic groups include carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, sulfinic acid groups, hyposulfonic acid groups, phosphonic acid groups, or their salts.

[0059] Preferably, it is selected from at least one of the carboxylic acid group, sulfonic acid group and phosphate group.

[0060] By equipping the modified polyvinyl acetal resin with structural units having the aforementioned acidic functional groups, the dispersibility of fibrous carbon materials can be improved even with a small amount of addition.

[0061] The structural unit having the above-mentioned acidic functional groups can be a structure in which acidic functional groups as side chains are directly bonded to the carbons constituting the main chain, or a structure in which acidic functional groups are bonded to the carbons constituting the main chain via alkylene bonds. Alternatively, the structural unit having the above-mentioned acidic functional groups can be a structure in which acidic functional groups are bonded to the carbons constituting the main chain via acetal bonds.

[0062] The structural unit having the aforementioned acidic functional groups can be a three-dimensional structure in which two acidic functional groups are bonded to the same carbon atom constituting the main chain, or a three-dimensional structure in which one acidic functional group is bonded to the carbon atom constituting the main chain. Alternatively, it can be a three-dimensional structure in which one acidic functional group is bonded to each of the adjacent carbon atoms constituting the main chain, or a three-dimensional structure in which an acidic functional group is bonded to only one of the adjacent carbon atoms constituting the main chain. Preferably, it has a three-dimensional structure in which two acidic functional groups are bonded to the same carbon atom constituting the main chain, or a three-dimensional structure in which one acidic functional group is bonded to each of the adjacent carbon atoms constituting the main chain. Furthermore, since steric hindrance can be increased, the network structure of the cured product obtained by combination with epoxy resin is expanded, resulting in improved flexibility of the obtained cured product; therefore, a three-dimensional structure in which two acidic functional groups are bonded to the same carbon atom constituting the main chain is preferred.

[0063] Furthermore, the structural units having the aforementioned acidic functional groups can have either an isotactic or a syndiotactic configuration. The isotactic configuration involves acidic functional groups bonded to the carbon atoms constituting the main chain along the same direction, while the syndiotactic configuration involves acidic functional groups bonded to the carbon atoms constituting the main chain alternately on opposite sides. Additionally, a atactic configuration is also possible, where the acidic functional groups are randomly bonded.

[0064] When the structural unit having the above-mentioned acidic functional group has a structure in which the carbon constituting the main chain is bonded with an acidic functional group via an alkylene group, the alkylene group is preferably an alkylene group having 1 to 10 carbon atoms, more preferably an alkylene group having 1 to 5 carbon atoms, and even more preferably an alkylene group having 1 to 3 carbon atoms.

[0065] Examples of alkylene groups having 1 to 10 carbon atoms include straight-chain alkylene groups, branched alkylene groups, and cyclic alkylene groups.

[0066] Examples of linear alkylene compounds include methylene, vinylene, n-propylene, tetramethylene, pentamethylene, hexamethylene, octamethylene, and decamethylene.

[0067] Examples of branched alkylene compounds include methylmethylene, methylethylene, 1-methylpentane, and 1,4-dimethylbutylene.

[0068] Examples of the aforementioned cyclic alkylene groups include cyclopropylene, cyclobutylene, and cyclohexylene.

[0069] Among them, linear alkylene groups are preferred, methylene, vinylene, and n-propylene groups are more preferred, and methylene and vinylene groups are even more preferred.

[0070] As a structural unit having the above-mentioned acidic functional groups, examples of structural units shown in equations (1-1) to (1-5) can be cited.

[0071] [Chemistry 1]

[0072]

[0073] In the above equations (1-1) to (1-5), R 1 R 3 R 5 R 7 R 9 R 11 R 13 R 15 Each independently represents a single bond or an alkylene group having 1 to 10 carbon atoms, R 2 R 4 R 6 R 8 R 10 R 12 R 14 R 16 It represents an acidic functional group.

[0074] As mentioned above, R 1 R 3 R 5 R 7 R 9 R11 R 13 R 15 Preferably, it is a single bond or an alkylene group having 1 to 5 carbon atoms, more preferably a single bond or an alkylene group having 1 to 3 carbon atoms.

[0075] Examples of alkylene groups having 1 to 10 carbon atoms include straight-chain alkylene groups, branched alkylene groups, and cyclic alkylene groups.

[0076] Examples of linear alkylene compounds include methylene, vinylene, n-propylene, tetramethylene, pentamethylene, hexamethylene, octamethylene, and decamethylene.

[0077] Examples of branched alkylene compounds include methylmethylene, methylethylene, 1-methylpentane, and 1,4-dimethylbutylene.

[0078] Examples of the aforementioned cyclic alkylene groups include cyclopropylene, cyclobutylene, and cyclohexylene.

[0079] Among them, linear alkylene groups are preferred, methylene, vinylene, and n-propylene groups are more preferred, and methylene and vinylene groups are even more preferred.

[0080] When the acidic functional group is a carboxylic acid group, the structural units having a carboxyl group can be, for example, the structural units shown in formula (2-1), formula (2-2), formula (2-3), and formula (2-4).

[0081] [Chemistry 2]

[0082]

[0083] In equations (2-1) to (2-4) above, R 17 ~R 23 Each independently represents a single bond or an alkylene group having 1 to 10 carbon atoms, X 17 ~X 23 Each can be used independently to represent a hydrogen atom, a metal atom, or a methyl group.

[0084] Examples of alkylene groups having 1 to 10 carbon atoms, such as R in formula (1-1), can be cited. 1 The same alkylene group.

[0085] Examples of metal atoms mentioned above include sodium atoms, lithium atoms, and potassium atoms. Among them, sodium atoms are preferred.

[0086] As a structural unit with a sulfonic acid group, the structural unit shown in the following formula (3) can be cited.

[0087] [Chemistry 3]

[0088]

[0089] In equation (3) above, R 24 X represents a single bond or an alkylene group having 1 to 10 carbon atoms. 24 It represents a hydrogen atom, a metal atom, or a methyl group.

[0090] Examples of alkylene groups having 1 to 10 carbon atoms, such as R in formula (1-1), can be cited. 1 The same alkylene group.

[0091] As the aforementioned metal atom, examples can be given of X in equation (2-1) above. 17 The same metal atoms.

[0092] As a structural unit with a phosphate group, the structural unit shown in the following formula (4) can be cited.

[0093] [Chemistry 4]

[0094]

[0095] In equation (4) above, R 25 X represents a single bond or an alkylene group having 1 to 10 carbon atoms. 25 and X 26 Each can be used independently to represent a hydrogen atom, a metal atom, or a methyl group.

[0096] Examples of alkylene groups having 1 to 10 carbon atoms, such as R in formula (1-1), can be cited. 1 The same alkylene group.

[0097] As the aforementioned metal atom, examples can be given of X in equation (2-1) above. 17 The same metal atoms.

[0098] The content of the structural units having the above-mentioned acidic functional groups in the polyvinyl acetal resin is preferably 0.01 mol% or more, and preferably 20.0 mol% or less, relative to all structural units.

[0099] If the above range is met, the dispersibility of fibrous carbon materials can be further improved.

[0100] The content of structural units having the above-mentioned acidic functional groups is more preferably 0.1 mol% or more, more preferably 0.5 mol% or more, even more preferably 1.0 mol% or more, and more preferably 15.0 mol% or less, even more preferably 12.0 mol% or less, and even more preferably 10.0 mol% or less.

[0101] The content of structural units with the aforementioned acidic functional groups can be determined, for example, by NMR.

[0102] The amount of protic acid in the above-mentioned polyvinyl acetal resin is preferably 0.1 mg / g or more, and more preferably 200 mg / g or less.

[0103] If the above range is met, the dispersibility of fibrous carbon materials can be further improved.

[0104] The amount of protic acid mentioned above is more preferably 0.2 mg / g or more, and more preferably 175 mg / g or less.

[0105] The above-mentioned amount of protic acid refers to the amount of potassium hydroxide required to neutralize the protic acid contained in polyvinyl acetal resin.

[0106] The aforementioned proton acid content can be determined, for example, by acid-base titration based on the method according to JIS K0070-1992.

[0107] The above-mentioned polyvinyl acetal resin preferably has a structural unit with an acetal group as shown in formula (5-1), a structural unit with a hydroxyl group as shown in formula (5-2), and a structural unit with an acetyl group as shown in formula (5-3).

[0108] [Chemistry 5]

[0109]

[0110] In the above equation (5-1), R 26 The alkyl group represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. The alkyl group preferably has 1 or more carbon atoms, and more preferably 10 or less, and more preferably 5 or less.

[0111] In the above equation (5-1), in R 26 When the alkyl group has 1 to 20 carbon atoms, examples of such alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, and octadecyl. Among these, methyl and n-propyl are preferred.

[0112] In the above-mentioned polyvinyl alcohol acetal resin, the content of the structural unit with acetal group shown in the above formula (5-1) (hereinafter also referred to as "acetal group amount") is preferably 5.0 mol% or more, and preferably 60.0 mol% or less.

[0113] If the above range is met, the dispersibility of fibrous carbon materials can be further improved.

[0114] The amount of the acetal group is more preferably 7.0 mol% or more, more preferably 10.0 mol% or more, even more preferably 15.0 mol% or more, and more preferably 50.0 mol% or less, even more preferably 40.0 mol% or less, and even more preferably 35.0 mol% or less.

[0115] It should be noted that, in this specification, the method for calculating the amount of acetal group mentioned above is based on the fact that the acetal group of polyvinyl alcohol acetal resin is a group obtained by acetalizing two hydroxyl groups. Therefore, the method of counting the two acetalized hydroxyl groups is used to calculate the amount of acetal group.

[0116] The amount of the aforementioned acetal group can be determined, for example, by NMR.

[0117] Furthermore, when the polyvinyl acetal resin described above has an acetal group with acidic modified groups as a structural unit having acidic modified groups as shown in formula (1-5), the total content of the structural unit with acidic modified groups as shown in formula (1-5) and the content of the structural unit with acetal groups as shown in formula (5-1) in the polyvinyl acetal resin (hereinafter also referred to as "total acetal content") is preferably 15.0 mol% or more, more preferably 20.0 mol% or more, and preferably 60.0 mol% or less, more preferably 50.0 mol% or less.

[0118] In the above-mentioned polyvinyl acetal resin, the content of the structural unit with hydroxyl groups shown in the above formula (5-2) (hereinafter also referred to as "hydroxyl content") is 40.0 mol% or more and 80.0 mol% or less.

[0119] By setting the parameters within the aforementioned range, the dispersibility and dispersion stability of fibrous carbon materials can be significantly improved, and their high electronic conductivity can be achieved.

[0120] The amount of hydroxyl groups is preferably 45.0 mol% or more, more preferably 50.0 mol% or more, even more preferably 55.0 mol% or more, and preferably 75.0 mol% or less, more preferably 70.0 mol% or less, and even more preferably 65.0 mol% or less.

[0121] The amount of hydroxyl groups mentioned above can be determined, for example, by NMR.

[0122] In the above-mentioned polyvinyl acetal resin, the content of the structural unit with acetyl groups shown in the above formula (5-3) (hereinafter also referred to as "acetyl content") is preferably 0.1 mol% or more, more preferably 1.0 mol% or more, even more preferably 2.0 mol% or more, even more preferably 5.0 mol% or more, and preferably 20.0 mol% or less, more preferably 15.0 mol% or less, even more preferably 12.0 mol% or less, and even more preferably 8.0 mol% or less.

[0123] If the amount of acetyl groups is within the above range, thickening can be suppressed, and coating properties can be further improved.

[0124] The amount of acetyl groups mentioned above can be determined, for example, by NMR.

[0125] The average degree of polymerization of the above-mentioned polyvinyl alcohol acetal resin is above 150 and below 1500.

[0126] If it falls within the above range, the dispersibility of fibrous carbon materials can be significantly improved, and high electronic conductivity can be achieved.

[0127] The average degree of polymerization is preferably 200 or higher, and more preferably 1000 or lower.

[0128] The aforementioned average degree of polymerization can be determined, for example, by gel permeation chromatography (GPC).

[0129] Regarding the glass transition temperature of the aforementioned polyvinyl acetal resin, from the viewpoint of balancing dispersibility and adhesion, it is preferably 60°C or higher, more preferably 65°C or higher, and preferably 115°C or lower, more preferably 100°C or lower.

[0130] The glass transition temperature mentioned above can be determined, for example, by differential scanning calorimetry.

[0131] The content of the polyvinyl acetal resin in the resin composition of the present invention is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and preferably 30.0% by weight or less, more preferably 15.0% by weight or less.

[0132] The ratio of the content of the polyvinyl acetal resin to the content of the fibrous carbon material in the resin composition of the present invention (content of polyvinyl acetal resin / content of fibrous carbon material) is preferably 0.1 or more, and preferably 2.0 or less.

[0133] If the material falls within the aforementioned range, the fibrous carbon material becomes well-dispersed, facilitating the formation of conductive pathways. As a result, its electronic conductivity becomes significantly improved.

[0134] The ratio of the above-mentioned content is more preferably 0.2 or more, and more preferably 1.5 or less.

[0135] As a method for producing the above-mentioned polyvinyl alcohol acetal resin, for example, the following method can be used: the polyvinyl acetate resin obtained by polymerizing monomers such as vinyl acetate is saponified by adding acid or alkali and then purified, thereby acetalizing the polyvinyl alcohol resin with adjusted Na ion content.

[0136] As the aforementioned polyvinyl alcohol-based resin, conventionally known polyvinyl alcohol-based resins can be used, such as those manufactured by saponifying polyvinyl acetate-based resins with alkali, acid, ammonia, etc.

[0137] The aforementioned polyvinyl alcohol-based resins can be completely saponified; however, if at least one of two linked units with hydroxyl groups is present at least one position on the main chain relative to the meso and racemic positions, complete saponification is not necessary, and partially saponified polyvinyl alcohol-based resins are also permissible. Furthermore, ethylene-vinyl alcohol copolymer resins, partially saponified ethylene-vinyl alcohol copolymer resins, and copolymers of monomers capable of copolymerizing with ethylene alcohol can also be used as the aforementioned polyvinyl alcohol-based resins.

[0138] Examples of polyvinyl acetate resins mentioned above include ethylene-vinyl acetate copolymers.

[0139] As a method for producing a polyvinyl alcohol acetal resin having structural units possessing the aforementioned acidic functional groups, an example method can be given as follows: copolymerizing a monomer possessing acidic functional groups with vinyl acetate, saponifying the resulting polyvinyl acetate, and acetalizing the resulting polyvinyl alcohol using a conventionally known method. Alternatively, a method can be used whereby unmodified polyvinyl alcohol is acetalized using a conventionally known method, and the resulting polyvinyl alcohol acetal resin is post-modified, thereby introducing acidic functional groups.

[0140] Examples of monomers having the aforementioned acidic functional groups include monocarboxylic acids such as acrylic acid, crotonic acid, methacrylic acid, and oleic acid; dicarboxylic acids such as methylene malonic acid, itaconic acid, 2-methylene glutaric acid, 2-methylene adipic acid, and 2-methylene sebacic acid; maleic anhydride; and their metal salts.

[0141] The degree of saponification of the above-mentioned polyvinyl alcohol resin is preferably 80.0 mol% or more and 99.9 mol% or less, more preferably 85.0 mol% or more and 95.0 mol% or less.

[0142] By using the above-mentioned polyvinyl alcohol-based resin, the dispersibility of fibrous carbon materials can be further improved.

[0143] The above-mentioned acetalization can be carried out using known methods, preferably in an aqueous solvent, in a mixed solvent of water and an organic solvent compatible with water, or in an organic solvent.

[0144] For example, alcohol-based organic solvents can be used as the aforementioned organic solvents that are compatible with water.

[0145] Examples of organic solvents mentioned above include alcohol-based organic solvents, aromatic organic solvents, aliphatic ester-based solvents, ketone-based solvents, lower alkane-based solvents, ether-based solvents, amide-based solvents, and amine-based solvents.

[0146] Examples of alcohol-based organic solvents include methanol, ethanol, n-propanol, isopropanol, n-butanol, and tert-butanol.

[0147] Examples of aromatic organic solvents include xylene, toluene, ethylbenzene, and methyl benzoate.

[0148] Examples of aliphatic ester solvents include methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, methyl acetoacetate, and ethyl acetoacetate.

[0149] Examples of ketone solvents mentioned above include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl cyclohexanone, benzophenone, and acetophenone.

[0150] Examples of lower alkane solvents include hexane, pentane, octane, cyclohexane, and decane.

[0151] Examples of ether solvents include diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol diethyl ether.

[0152] Examples of amide solvents include N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and acetanilide.

[0153] Examples of amine solvents include ammonia, trimethylamine, triethylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, aniline, N-methylaniline, N,N-dimethylaniline, and pyridine.

[0154] The solvents mentioned above can be used alone or in combination of two or more. Among them, ethanol, n-propanol, isopropanol, and tetrahydrofuran are particularly preferred from the viewpoint of resin solubility and ease of purification.

[0155] The above acetalization is preferably carried out in the presence of an acid catalyst.

[0156] The acid catalysts mentioned above are not particularly limited, and examples include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid; carboxylic acids such as formic acid, acetic acid, and propionic acid; and sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, and p-toluenesulfonic acid. These acid catalysts can be used alone or in combination with two or more compounds. Among them, hydrochloric acid, nitric acid, and sulfuric acid are preferred, with hydrochloric acid being particularly preferred.

[0157] Examples of aldehydes used in the above acetalization process include chain-like aliphatic groups, cyclic aliphatic groups, or aromatic groups having 1 to 10 carbon atoms. Aldehydes known in the art can be used as these aldehydes. The aldehyde used in the above acetalization reaction is not particularly limited; for example, aliphatic aldehydes and aromatic aldehydes can be included.

[0158] Examples of aliphatic aldehydes mentioned above include formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, n-pentanaldehyde, n-hexanaldehyde, 2-ethylbutanaldehyde, 2-ethylhexanaldehyde, n-heptanaldehyde, n-octanaldehyde, n-nonanaldehyde, n-decanaldehyde, and pentanaldehyde.

[0159] Examples of aromatic aldehydes mentioned above include benzaldehyde, cinnamaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, β-phenylpropanal, and other aromatic aldehydes.

[0160] Alternatively, cyclic polymers such as metaldehyde and tetraacetaldehyde can be used.

[0161] These aldehydes can be used alone or in combination of two or more. Among the aldehydes, formaldehyde, acetaldehyde, butyraldehyde, 2-ethylhexanal, n-nonanal, and metaldehyde are preferred because they exhibit excellent acetalization reactivity, provide sufficient internal plasticizing effect to the resulting resin, and thus impart good flexibility. Furthermore, from the perspective of obtaining adhesive compositions with particularly excellent impact resistance and adhesion to metals, formaldehyde, acetaldehyde, butyraldehyde, and metaldehyde are more preferred.

[0162] The amount of aldehyde added can be appropriately set to match the amount of acetal groups in the target polyvinyl alcohol acetal resin. In particular, if it is set to 10 to 65 mol%, preferably 15 to 60 mol%, relative to 100 mol% of polyvinyl alcohol, the acetalization reaction can be carried out efficiently, and unreacted aldehydes can be easily removed, which is therefore preferred.

[0163] The resin composition of the present invention may further include other binders, conductive agents, flame retardants, defoamers, leveling agents, and adhesion promoters, etc., without impairing the effects of the present invention.

[0164] Furthermore, the resin composition of the present invention preferably does not contain a curable resin.

[0165] There are no particular limitations on the method for preparing the resin composition of the present invention. For example, a method can be described by adding a polyvinyl acetal resin obtained by acetalizing a raw material polyvinyl alcohol and a fibrous carbon material to a non-aqueous solvent and mixing them.

[0166] As a method for mixing as described above, examples include using various mixers such as ball mills, stirred mills, and three-roll mills.

[0167] By adding an active substance to the resin composition of the present invention, a composition for lithium secondary battery electrodes can be prepared.

[0168] Examples of the aforementioned active materials include positive electrode active materials and negative electrode active materials.

[0169] Examples of positive electrode active materials include lithium nickel oxide (e.g., LiNiO2), lithium cobalt oxide (e.g., LiCoO2), lithium manganese oxide (e.g., LiMn2O4), and their composites (e.g., LiNiO2). 0.5 Mn 1.5 O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / Particles such as lithium transition metal oxides (lithium transition metal oxides) containing lithium and transition metal elements as constituent metal elements, such as lithium manganese phosphate (LiMnPO4) and lithium iron phosphate (LiFePO4).

[0170] It should be noted that they can be used individually or in combination of two or more.

[0171] As the aforementioned negative electrode active material, materials that have been used as negative electrode active materials in lithium secondary batteries can be used, such as carbon-based materials such as graphite, natural graphite, graphitic carbon, and amorphous carbon, lithium transition metal oxides, lithium transition metal nitrides, silicon, silicon oxide, and other silicon compounds.

[0172] There are no particular limitations on the method for manufacturing the above-mentioned lithium secondary battery electrode composition. For example, a method can be described by mixing the above-mentioned active material, the resin composition of the present invention, and various additives added as needed using a ball mill, a stirred mill, a three-roll mill, or other mixers.

[0173] The aforementioned lithium secondary battery electrode composition is formed, for example, by a process of coating onto a conductive substrate and drying.

[0174] As for the above-mentioned coating method, various coating methods such as extrusion coating machines, reverse rollers, scrapers, and applicators can be used.

[0175] Invention Effects

[0176] According to the present invention, a resin composition is provided that has excellent coatability and adhesion, and can take into account both high electronic conductivity and the dispersibility and dispersion stability of fibrous carbon materials, thereby obtaining a lithium secondary battery with high capacity retention. Detailed Implementation

[0177] The present invention will be described in more detail below with reference to the embodiments provided; however, the present invention is not limited to these embodiments.

[0178] (Manufacturing Example 1)

[0179] The carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 150, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) was used. 17 Methylene, X 17 500g of a solution containing 0.01 mol% hydrogen atoms was added to 2500g of pure water and stirred at 90°C for 2 hours to dissolve. The solution was cooled to 40°C, and 10g of 35% hydrochloric acid was added. The temperature was then lowered to 5°C, and 62.99g of acetaldehyde was added. The acetalization reaction was carried out at this temperature, causing the reaction product to precipitate. The temperature was set to 65°C and maintained for 5 hours to stop the reaction. 40g of sodium hydroxide aqueous solution was added for neutralization. Then, 5000g of pure water was added, stirred, and the water was removed by decantation. This process was repeated a total of 3 times. Finally, the solid content of the resin was adjusted to 20% by weight using deionized water to obtain polyvinyl alcohol acetal resin A1.

[0180] For the obtained polyvinyl acetal resin, use 1 The amounts of acetal, hydroxyl, and acetyl groups were determined by H-NMR (nuclear magnetic resonance spectroscopy), and the results are shown in Table 1. 1 The H-NMR determination used deuterated DMSO as the solvent.

[0181] In addition, the amount of protic acid was determined by acid-base titration according to JIS K0070-1992. Specifically, it was determined by the following method. First, as in this test, the obtained polyvinyl acetal resin was used as the sample. Approximately 1 g of the sample was accurately weighed into an Erlenmeyer flask, and 40 ml of a mixed solvent of ethanol / water (volume ratio 9:1) was added and shaken to dissolve. After dissolution, using 1% wt% phenolphthalein solution as an indicator, a 0.02 mol / L potassium hydroxide-ethanol solution was used, and titrated with a microburette until a light red color was maintained for more than 30 seconds. A blank test was then performed, and the amount of protic acid was determined by the following formula. The result was 0.2 mg / g.

[0182] Proton acidity = [(AB)×f×(1 / 50)×(C / 1000)]×100 / D

[0183] A: The volume (mL) of potassium hydroxide-ethanol solution added in this experiment.

[0184] B: Volume (mL) of potassium hydroxide-ethanol solution added in the blank test

[0185] C: Molecular weight of structural units with acidic functional groups

[0186] D: Sample volume (g)

[0187] f: Titration rate of 0.02 mol / L potassium hydroxide-ethanol solution

[0188] Subsequently, the glass transition temperature (Tg) of the obtained polyvinyl acetal resin was determined using a differential scanning calorimeter (DSC) at a heating rate of 10 °C / min. The result was 93 °C.

[0189] (Manufacturing Example 2)

[0190] In addition to using sulfonic acid modified polyvinyl alcohol resin (average degree of polymerization 500, degree of saponification 98 mol%), the structural unit (R) shown in formula (3) is used. 24 Methylene, X 24 Polyvinyl acetal resin A2 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 1.0 mol% and the amount of acetaldehyde added was set to 32.99 g.

[0191] (Manufacturing Example 3)

[0192] In addition to using phosphate-modified polyvinyl alcohol resin (average degree of polymerization 1000, degree of saponification 92 mol%, structural unit (R) shown in formula (4) 25 Methylene, X 25 X 26 Polyvinyl acetal resin A3 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 10.0 mol% and the amount of acetaldehyde added was set to 46.99 g.

[0193] (Manufacturing Example 4)

[0194] In addition to using phosphate-modified polyvinyl alcohol resin (average degree of polymerization 1250, degree of saponification 98 mol%), the structural unit (R) shown in formula (4) is used. 25 For vinylidene, X 25 X 26 Polyvinyl acetal resin A4 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 0.1 mol% and the amount of acetaldehyde added was set to 22.9 g.

[0195] (Manufacturing Example 5)

[0196] In addition to using sulfonic acid modified polyvinyl alcohol resin (average degree of polymerization 1500, degree of saponification 98 mol%), the structural unit (R) shown in formula (3) is used. 24 Methylene, X 24 Polyvinyl acetal resin A5 was obtained in the same manner as in Manufacturing Example 1, except that the content of sodium element was 10.0 mol% and the amount of acetaldehyde added was set to 53 g.

[0197] (Manufacturing Example 6)

[0198] Using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 500, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) was employed.17 Methylene, X 17 The following were prepared: 250g of unmodified polyvinyl alcohol resin (average degree of polymerization 500, degree of saponification 98 mol%) and 250g of acetaldehyde (1.0 mol%). Additionally, 52g of acetaldehyde was added. Polyvinyl alcohol acetal resin A6 was obtained in the same manner as in Manufacturing Example 1, except as described above.

[0199] (Manufacturing Example 7)

[0200] Using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 1000, degree of saponification 92 mol%), the structural unit (R) shown in formula (2-1) was employed. 17 Methylene, X 17 The content of hydrogen atoms is 0.1 mol%) 250g and sulfonic acid modified polyvinyl alcohol resin (average degree of polymerization 1000, degree of saponification 92 mol%), the structural unit (R) shown in formula (3) 24 For vinylidene, X 24 The content of hydrogen atoms (0.1 mol%) was 250 g. Additionally, the amount of acetaldehyde added was set to 26.9 g. Except as described above, polyvinyl acetal resin A7 was obtained in the same manner as in Manufacturing Example 1.

[0201] (Manufacturing Example 8)

[0202] Using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 1250, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) was employed. 17 Methylene, X 17 250g of 250g of phosphate-modified polyvinyl alcohol resin (average degree of polymerization 1250, degree of saponification 98 mol%) and structural unit (R) as shown in formula (4). 25 Methylene, X 25 X 26 The content of sodium atoms was 0.1 mol% (250 g). Additionally, the amount of acetaldehyde added was set to 42.89 g. Except as described above, polyvinyl acetal resin A8 was obtained in the same manner as in Manufacturing Example 1.

[0203] (Manufacturing Example 9)

[0204] In addition to using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 1250, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) 17 Methylene, X 17 Polyvinyl acetal resin A9 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 15.0 mol% and the amount of acetaldehyde added was set to 38 g.

[0205] (Manufacturing Example 10)

[0206] In addition to using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 100, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) is also used. 17 Methylene, X 17 Polyvinyl acetal resin B1 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 0.1 mol% and the amount of acetaldehyde added was set to 57.9 g.

[0207] (Manufacturing Example 11)

[0208] In addition to using sulfonic acid modified polyvinyl alcohol resin (average degree of polymerization 1700, degree of saponification 98 mol%), the structural unit (R) shown in formula (3) is used. 24 Methylene, X 24 Polyvinyl acetal resin B2 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 10.0 mol% and the amount of acetaldehyde added was set to 53 g.

[0209] (Manufacturing Example 12)

[0210] In addition to using phosphate-modified polyvinyl alcohol resin (average degree of polymerization 500, degree of saponification 98 mol%), the structural unit (R) shown in formula (4) is used. 25 For vinylidene, X 25 X 26 Polyvinyl acetal resin B3 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 1.0 mol% and the amount of acetaldehyde added was set to 67 g.

[0211] (Manufacturing Example 13)

[0212] In addition to using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 1250, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) 17 Methylene, X 17 Polyvinyl acetal resin B4 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 0.01 mol% and the amount of acetaldehyde added was set to 17.99 g.

[0213] (Manufacturing Example 14)

[0214] Except that unmodified polyvinyl alcohol resin (average degree of polymerization 500, degree of saponification 92 mol%) was used and the amount of acetaldehyde added was set to 37 g, polyvinyl alcohol acetal resin B5 was obtained in the same manner as in Manufacturing Example 1.

[0215] (Manufacturing Example 15)

[0216] In addition to using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 1700, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) 17 Methylene, X 17Except for the content of hydrogen atoms (0.01 mol%), polyvinyl acetal resin B6 was obtained in the same manner as in manufacturing example 1.

[0217] (Manufacturing Example 16)

[0218] In addition to using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 150, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) 17 Methylene, X 17 Polyvinyl acetal resin B7 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 0.01 mol% and the amount of acetaldehyde added was set to 73.0 g.

[0219] (Manufacturing Example 17)

[0220] In addition to using sulfonic acid modified polyvinyl alcohol resin (average degree of polymerization 500, degree of saponification 98 mol%), the structural unit (R) shown in formula (3) is used. 24 Methylene, X 24 Polyvinyl acetal resin A10 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 1.0 mol% and 62 g of butyraldehyde was added instead of acetaldehyde.

[0221] (Manufacturing Example 18)

[0222] In addition to using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 150, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) 17 Methylene, X 17 Polyvinyl acetal resin A11 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 0.1 mol% and 62 g of butyraldehyde was added instead of acetaldehyde.

[0223] (Manufacturing Example 19)

[0224] In addition to using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 500, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) 17 Methylene, X 17 Polyvinyl acetal resin A12 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 0.1 mol% and 52.9 g of hexanal was added instead of acetaldehyde.

[0225] (Manufacturing Example 20)

[0226] In addition to using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 500, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) 17 Methylene, X 17Polyvinyl acetal resin A13 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 0.005 mol% and butyraldehyde was added instead of acetaldehyde.

[0227] (Manufacturing Example 21)

[0228] In addition to using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 500, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) 17 Methylene, X 17 Polyvinyl acetal resin A14 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 0.001 mol% and butyraldehyde was added instead of acetaldehyde (63.0 g).

[0229] (Manufacturing Example 22)

[0230] In addition to using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 500, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) 17 Methylene, X 17 Polyvinyl acetal resin A15 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 14.5 mol% and butyraldehyde was added instead of acetaldehyde.

[0231] (Manufacturing Example 23)

[0232] In addition to using phosphate-modified polyvinyl alcohol resin (average degree of polymerization 500, degree of saponification 98 mol%), the structural unit (R) shown in formula (4) is used. 25 Methylene, X 25 X 26 Polyvinyl acetal resin A16 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 1.0 mol% and butyraldehyde was added instead of acetaldehyde.

[0233] (Manufacturing Example 24)

[0234] Except for using unmodified polyvinyl alcohol resin (average degree of polymerization 150, degree of saponification 98 mol%) and adding 63.0 g of butyraldehyde instead of acetaldehyde, polyvinyl alcohol acetal resin B8 was obtained in the same manner as in Manufacturing Example 1.

[0235] (Manufacturing Example 25)

[0236] In addition to using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 150, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) 17 Methylene, X 17 Polyvinyl acetal resin B9 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 0.01 mol% and butyraldehyde was added instead of acetaldehyde.

[0237] (Manufacturing Example 26)

[0238] In addition to using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 100, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) is also used. 17 Methylene, X 17 Polyvinyl acetal resin B10 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 0.01 mol% and butyraldehyde was added instead of acetaldehyde.

[0239] (Manufacturing Example 27)

[0240] In addition to using carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 500, degree of saponification 98 mol%), the structural unit (R) shown in formula (2-1) 17 Methylene, X 17 Polyvinyl acetal resin B11 was obtained in the same manner as in Manufacturing Example 1, except that the content of hydrogen atoms was 0.01 mol% and butyraldehyde was added instead of acetaldehyde.

[0241] [Table 1]

[0242]

[0243] (Examples 1-23, Comparative Examples 1-15)

[0244] A resin composition is obtained by mixing polyvinyl acetal resin, fibrous carbon material and non-aqueous solvent as shown in Table 2.

[0245] It should be noted that the following substances are used as non-aqueous solvents, carbon materials, and resins.

[0246] <Non-aqueous solvents>

[0247] N-Methylpyrrolidone

[0248] <Carbon Materials>

[0249] MW-1: Multilayer carbon nanotubes (manufactured by Sigma Aldrich, average fiber diameter 9 nm, average fiber length 13 μm, specific gravity 1.8, specific surface area 200 m²). 2 / g, G / D ratio 8.0)

[0250] MW-2: Multilayer carbon nanotubes (manufactured by Cnano Corporation, average fiber diameter 10 nm, average fiber length 150 μm, specific gravity 1.9, specific surface area 3000 m²). 2 / g, G / D ratio 20)

[0251] MW-3: Multilayer carbon nanotubes (manufactured by Cnano Corporation, average fiber diameter 10 nm, average fiber length 15 μm, specific gravity 1.8, specific surface area 250 m²). 2 / g, G / D ratio 20)

[0252] VGCF: Vapor-grown carbon fiber (manufactured by Showa Denko Corporation, average fiber diameter 150 nm, average fiber length 15 μm, specific gravity 2.1, specific surface area 13 m²). 2 / g, G / D ratio 5.5)

[0253] SW-1: Monolayer carbon nanotubes (manufactured by OCSIAL, average fiber diameter 1.2±0.5nm, average fiber length ≥4μm, specific gravity 1.3, G / D ratio 80)

[0254] AB: Particulate acetylene black (manufactured by DENKA Corporation, average particle size 35nm, specific surface area 68m²) 2 / g, G / D ratio 1.27)

[0255] <Resin>

[0256] PVDF: Polyvinylidene fluoride (manufactured by Kureha, weight average molecular weight 630,000)

[0257] PVP: Polyvinylpyrrolidone (manufactured by Tokyo Chemical Industry Co., Ltd., weight average molecular weight 40,000)

[0258] <Evaluation>

[0259] The resin compositions obtained in the examples and comparative examples were evaluated as follows. The results are shown in Table 2.

[0260] (1) Average surface roughness (dispersion)

[0261] The obtained resin composition is coated onto a polyethylene terephthalate (PET) film after demolding treatment to a film thickness of 20 μm after drying, and then peeled off from the PET film after drying to produce a sheet.

[0262] The average surface roughness Ra of the obtained sheets was determined according to JIS B 0601 (1994), and evaluated according to the following criteria.

[0263] 〇: Ra is less than 5μm.

[0264] △: Ra is greater than 5μm and less than 8μm.

[0265] ×: Ra is 8 or higher.

[0266] If the average surface roughness Ra is low, then it can be said that the smoothness and dispersibility are excellent.

[0267] (2) Adhesion

[0268] The obtained resin composition was coated on an aluminum foil (20 μm thick) to make the film thickness 20 μm after drying, and then dried to obtain a test piece with the resin composition formed on the aluminum foil.

[0269] The test piece was cut into 1cm length and 2cm width. Using an AUTOGRAPH (manufactured by Shimadzu Corporation, “AGS-J”), the test piece was lifted while it was fixed in place. The peeling force (N) required to completely peel the aluminum foil off the sheet was then measured, and the following criteria were used for judgment.

[0270] 〇: Peeling force is above 8.0N.

[0271] △: Peeling force is 5.0N or more and less than 8.0N.

[0272] ×: Peeling force is less than 5.0N.

[0273] (3) Coating properties

[0274] The obtained resin composition was applied to a glass plate using a scraper and dried in an air-circulating oven at 150°C for 5 minutes to obtain a coating film. The obtained coating film was evaluated by visual inspection according to the following criteria.

[0275] 〇: There are no cracks or fissures on the coating surface, and the film thickness is uniform.

[0276] △: Slight cracks and fissures can be observed on the coating surface.

[0277] ×: Cracks and fissures can be observed on the coating surface, and the film thickness is deviated.

[0278] (4) Thickening properties (dispersion stability)

[0279] Ten parts by weight of the obtained resin composition were subjected to a rheometer (Reologica Instruments: using a parallel plate with a diameter of 10 mm) at a shear rate of 0.1–1000 s. -1 Measure the viscosity. Determine the shear rate over 1 second. -1 The viscosity at that time is set as the paste viscosity of the sample. It should be noted that the measurement temperature is set to 20℃.

[0280] In addition, the viscosity was measured after being placed at 20°C for one week. It should be noted that the viscosity increase rate was calculated using the following formula based on the viscosity immediately after manufacturing and after one week, and the evaluation was conducted according to the following criteria.

[0281] Viscosity increase rate (%) = (Viscosity after 1 week / Viscosity immediately after manufacturing) × 100

[0282] 〇: The viscosity increase rate is less than 150%.

[0283] △: The viscosity increase rate is greater than 150% and less than 300%.

[0284] ×: Viscosity increase rate is greater than 300%.

[0285] If the viscosity increase rate is small, it can be said that the dispersion stability is excellent.

[0286] (5) Electrical conductivity

[0287] A resin composition is coated onto a polyethylene terephthalate (PET) film that has undergone a demolding process, resulting in a film thickness of 20 μm after drying. The film is then peeled off from the PET film to produce a sheet.

[0288] The electrode resistance values ​​of the obtained plates were measured using an electrode resistance meter (manufactured by Hioki Electric Co., Ltd.), and evaluated according to the following criteria.

[0289] 〇: Electrode resistance value is less than 100Ω / sq.

[0290] △: Electrode resistance is above 100Ω / sq and less than 200Ω / sq.

[0291] ×: Electrode resistance value is greater than 200Ω / sq.

[0292] If the surface resistivity is low, it can be said that the electronic conductivity is excellent.

[0293] (6) DC resistance

[0294] 10g of NCM622 (LiNi) as the positive electrode active material was added to the obtained resin composition. 0.6 Co 0.2 Mn 0.2 A positive electrode composition was obtained by mixing O2 and 0.2 g of PVDF#7200 (polyvinylidene fluoride, manufactured by Kureha Corporation). The obtained positive electrode composition was coated onto an aluminum foil (20 μm thick) and dried to obtain a positive electrode sheet with a thickness of 80 μm. This sheet was then punched to a diameter of φ11 mm to obtain the positive electrode layer. Separately, a 100 μm thick lithium metal foil was punched to a diameter of φ11 mm to obtain the negative electrode layer. Using a mixed solvent containing 1 mol / L LiPF6 with an EC:DEC:EMC ratio of 3:4:3 as the electrolyte, the positive current collector, positive electrode layer, porous PP film spacer (25 μm thick), and lithium metal foil (negative electrode layer) were stacked in the following order. Pressure was applied using a riveting machine to obtain a sealed button cell battery. The DC resistance of the obtained button cell battery was measured using a charge-discharge test apparatus (manufactured by Hokuto Electric Co., Ltd.).

[0295] Measure the voltage when a current of 0.2C, 1.0C, 8.0C, and 16.0C is applied, calculate the DC resistance value using Ohm's law, and evaluate it according to the following criteria.

[0296] 〇: DC resistance value below 8Ω

[0297] △: DC resistance value greater than 8Ω and less than 15Ω

[0298] ×: DC resistance value greater than 15Ω

[0299] (7) Capacity retention rate

[0300] The capacity retention of the obtained button cells was measured using a charge-discharge test apparatus (manufactured by Hosen Corporation). The capacity retention was measured in a voltage range of 0.1 to 1.5 V and an evaluation temperature of 25°C. The capacity retention (%) was calculated as the capacity of the 100th cycle relative to the discharge capacity of the 5th cycle, and the evaluation was performed according to the following criteria.

[0301] 〇: Capacity retention rate is above 90%

[0302] △: Capacity retention rate is above 70% and below 90%.

[0303] ×: Capacity retention rate less than 70%

[0304] [Table 2]

[0305]

[0306] Industrial availability

[0307] According to the present invention, a resin composition is provided that has excellent coatability and adhesion, and can take into account both high electronic conductivity and the dispersibility and dispersion stability of fibrous carbon materials, thereby obtaining a lithium secondary battery with high capacity retention.

Claims

1. A resin composition comprising a fibrous carbon material, a non-aqueous solvent, and a polyvinyl acetal resin. The polyvinyl acetal resin contains structural units with acidic functional groups, has an average degree of polymerization of 150 or more and 1500 or less, and a hydroxyl content of 40.0 mol% or more and 80.0 mol% or less. The content of structural units with acidic functional groups is 0.01 mol% or more and 20.0 mol% or less, relative to all structural units of polyvinyl acetal resin. The content of the non-aqueous solvent is 60.0% by weight or more and 99.9% by weight or less. The non-aqueous solvent is N-methylpyrrolidone. The fibrous carbon material is carbon nanotubes.

2. The resin composition according to claim 1, wherein, The acidic functional group is selected from at least one of the carboxylic acid group, sulfonic acid group and phosphate group.

3. The resin composition according to claim 1 or 2, wherein, The acidic functional group is a proton acidic group, and the amount of proton acid in polyvinyl acetal resin is above 0.1 mg / g and below 200 mg / g.

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