Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers

Definitions

• the present invention relates to a composition for secondary battery electrodes.
• fibrous carbon materials such as carbon nanotubes and VGCF have been expected to be put to practical use in a wide range of fields such as electronics because they exhibit excellent electrical properties.
• research has been carried out on adding it as a conductive additive to electrodes for secondary batteries and transparent electrodes.
• Patent Document 1 discloses a composition containing fine particles made of polyvinyl acetal resin, a fibrous conductive substance, and a liquid dispersion medium containing 50% by weight or more of water.
• Patent Document 2 discloses a fine carbon fiber dispersion liquid comprising fine carbon fibers, a dispersion medium, a polymer dispersant such as polyvinyl acetal, and a basic compound having a pKa of 7.5 or more. There is.
• JP2014-209435A Japanese Patent Application Publication No. 2014-181140
• fibrous carbon materials have a problem in that they have low solubility and dispersibility and cannot maintain a stable dispersion state in a solvent. Furthermore, although fibrous carbon materials have excellent electrical, thermal, and mechanical properties, their very large aspect ratio makes them easy to tangle, making it difficult to obtain high-performance composite materials that take full advantage of their properties. There is a problem. In order to solve the above problem, it is necessary to add a large amount of a resin component as a dispersant, but there is a problem that the properties of the fibrous carbon material are impaired. Furthermore, when a dispersion medium with a high moisture content is used as in Patent Document 1, there is a problem that the calculated dispersion state due to the hydrophobic interaction of the fibrous carbon material cannot be maintained sufficiently. Furthermore, the composition disclosed in Patent Document 2 has a problem in that it gels when mixed with a basic active material.
• the present invention has excellent coating properties and adhesive properties, and is capable of achieving both high electronic conductivity and dispersibility and dispersion stability of fibrous carbon materials, and suppresses gelation.
• An object of the present invention is to provide a composition for a secondary battery electrode that can produce a high-performance secondary battery.
• the present disclosure (1) contains an active material, a hydrophobic solvent, a fibrous carbon material, and a polyvinyl acetal resin, the water content is 10% by weight or less, and the polyvinyl acetal resin has a hydroxyl group content. is 30 mol% or less.
• the present disclosure (2) is the composition for a secondary battery electrode according to the present disclosure (1), wherein the polyvinyl acetal resin has a structural unit having an acidic functional group.
• the present disclosure (3) provides a secondary battery electrode according to the present disclosure (1) or (2), wherein the acidic functional group is at least one selected from the group consisting of a carboxylic acid group, a sulfur-containing group, and a phosphorus-containing group. It is a composition.
• the present disclosure (4) is the present disclosure (2) or (3), wherein the content of the structural unit having an acidic functional group with respect to all the structural units of the polyvinyl acetal resin is 0.01 mol% or more and 10 mol% or less.
• This is a composition for secondary battery electrodes.
• the present disclosure (5) is a composition for a secondary battery electrode in any combination with any of the present disclosures (1) to (4), in which the average degree of polymerization of the polyvinyl acetal resin is 150 or more and 1500 or less.
• the present disclosure (6) provides the present disclosure (2) to (5), wherein the acidic functional group is a Br ⁇ nsted acidic group, and the Br ⁇ nsted acid amount in the polyvinyl acetal resin is 0.2 mg/g or more and 250 mg/g or less.
• the present disclosure (7) is a composition for a secondary battery electrode in any combination with any of the present disclosures (1) to (6), further containing polyvinylidene fluoride.
• the present disclosure (8) is a composition for a secondary battery electrode in any combination with any of the present disclosures (1) to (7), in which the fibrous carbon material is a carbon nanotube.
• the present disclosure (9) is a composition for a secondary battery electrode in any combination with any of the present disclosures (1) to (8), in which the pH of the active material is 9 or more and 12 or less. The present invention will be explained in detail below.
• the present inventors have found that by combining an active material, a fibrous carbon material, a hydrophobic solvent, and a polyvinyl acetal resin having a specific structure, and further reducing the water content to a predetermined amount or less, In addition to having excellent coating properties and adhesive properties, it is possible to achieve both high electronic conductivity and dispersibility and dispersion stability of the fibrous carbon material, suppressing gelation and manufacturing high-performance secondary batteries. This discovery led to the completion of the present invention.
• the secondary battery electrode composition contains an active material.
• the active material include a positive electrode active material and a negative electrode active material.
• the positive electrode active material include lithium nickel oxide (e.g., LiNiO 2 ), lithium cobalt oxide (e.g., LiCoO 2 ), lithium manganese oxide (e.g., LiMn 2 O 4 ), and lithium nickel manganese oxide (e.g., LiNi 0 ) . .5 Mn 1.5 O 4 ), lithium nickel cobalt manganese oxide (e.g. LiNi 1/3 Co 1/3 Mn 1/3 O 2 ), lithium nickel cobalt aluminum oxide (e.g.
• LiNi 0.8 Co 0.15 examples include particles of an oxide (lithium transition metal oxide) containing lithium and a transition metal element as constituent metal elements, such as Al 0.05 O 2 ). Further, examples include particles of phosphates containing lithium and a transition metal element as constituent metal elements, such as lithium manganese phosphate (LiMnPO 4 ) and lithium iron phosphate (LiFePO 4 ). Note that these may be used alone or in combination of two or more.
• negative electrode active material for example, materials conventionally used as negative electrode active materials of lithium secondary batteries can be used, such as carbon-based materials such as graphite, natural graphite, graphite carbon, amorphous carbon, lithium transition Examples include metal oxides, lithium transition metal nitrides, silicon, and silicon compounds such as silicon oxide.
• the composition ratio of metal elements in the lithium transition metal oxide containing nickel is preferably such that the composition ratio of Ni atoms is 30 at% or more, and 50 at% It is more preferably at least 98 atom %, more preferably at most 95 atom %.
• the composition ratio of the Ni atoms is preferably 30 to 98 atomic %, more preferably 50 to 95 atomic %.
• the above active material is required to contain a large amount of Li in its structure in order to increase battery capacity. Since the manufacturing method differs depending on the active material, the pH of the obtained active material changes depending on the amount of basic compound such as Li hydroxide used.
• the pH of the active material is preferably 9 or higher, more preferably 10 or higher, preferably 12 or lower, and preferably 11 or lower.
• the above pH is preferably 9 to 12, more preferably 10 to 11.
• the pH of the active material can be determined by measuring the pH of an aqueous solution in which the active material is added to water at a concentration of 1.0% by weight using a pH meter.
• the average particle diameter of the active material is preferably 0.1 ⁇ m or more, more preferably 0.5 ⁇ m or more, even more preferably 1.0 ⁇ m or more, preferably 100 ⁇ m or less, more preferably 50 ⁇ m or less, and even more preferably 20 ⁇ m or less.
• the average particle diameter is preferably 0.1 to 100 ⁇ m, more preferably 0.5 to 50 ⁇ m, and even more preferably 1.0 to 20 ⁇ m.
• the average particle diameter can be determined, for example, by measuring the maximum diameter of 50 arbitrary active materials observed using a scanning electron microscope and calculating the average value.
• the density of the active material is preferably 3.0 g/cm 3 or more, more preferably 3.5 g/cm 3 or more, preferably 6.0 g/cm 3 or less, and more preferably 5.5 g/cm 3 or less.
• the density is preferably 3.0 to 6.0 g/cm 3 , more preferably 3.5 to 5.5 g/cm 3 .
• the above density can be measured by a method based on JIS Z8807.
• the specific surface area of the active material is preferably 0.1 m 2 /g or more, more preferably 0.2 m 2 /g or more, preferably 5.0 m 2 /g or less, and more preferably 4.5 m 2 /g or less.
• the specific surface area is preferably 0.1 to 5.0 m 2 /g, more preferably 0.2 to 4.5 m 2 /g.
• the specific surface area can be measured, for example, using a specific surface area measuring device ("ASAP-2000" manufactured by Shimadzu Corporation).
• the secondary battery electrode composition contains a hydrophobic solvent.
• a hydrophobic solvent By containing a hydrophobic solvent, it is possible to prevent moisture from entering and suppress side reactions in the battery.
• the hydrophobic solvent refers to a "solvent having an octanol/water partition coefficient of 0.1 or more.” The above distribution coefficient can be measured by a method based on JIS Z7260-117:2006.
• hydrophobic solvent examples include organic solvents such as ketones, alcohols, aromatic hydrocarbons, esters, carbonates, and amides.
• ketones include acetone, methyl ethyl ketone, dipropyl ketone, diisobutyl ketone, and the like.
• alcohols include methanol, ethanol, isopropanol, butanol, and the like.
• aromatic hydrocarbons include toluene and xylene.
• esters include methyl propionate, ethyl propionate, butyl propionate, methyl butanoate, ethyl butanoate, butyl butanoate, methyl pentanoate, ethyl pentanoate, butyl pentanoate, methyl hexanoate, ethyl hexanoate, Examples include butyl hexanoate, 2-ethylhexyl acetate, butyl butyrate, 2-ethylhexyl butyrate, and the like.
• methyl cellosolve, ethyl cellosolve, butyl cellosolve, terpineol, dihydroterpineol, butyl cellosolve acetate, butyl carbitol acetate, terpineol acetate, dihydroterpineol acetate, etc. can also be used.
• the carbonates include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and the like.
• the amides include dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, diethylformamide, and the like.
• the content of the hydrophobic solvent in the secondary battery electrode composition is preferably 20.0% by weight or more, more preferably 25.0% by weight or more, and preferably 50.0% by weight or less.
• the content of the hydrophobic solvent is preferably 20.0 to 50.0% by weight, more preferably 25.0 to 50.0% by weight.
• the secondary battery electrode composition contains a fibrous carbon material. By containing the fibrous carbon material, conductive properties can be improved.
• the above-mentioned fibrous carbon material means a carbon material having an aspect ratio (average fiber length/average fiber diameter) of 30 or more.
• the aspect ratio (average fiber length/average fiber diameter) of the above-mentioned fibrous carbon material is preferably 50 or more, more preferably 100 or more, still more preferably 200 or more, and even more preferably 400 or more. more 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, particularly preferably 20,000 or less.
• the aspect ratio is preferably 30 to 500,000, more preferably 50 to 300,000, even more preferably 100 to 100,000, even more preferably 200 to 50,000, and particularly preferably 400 to 20,000.
• Examples of the fibrous carbon material include carbon fibers and carbon nanotubes.
• Examples of the carbon fibers include PAN carbon fibers, pitch carbon fibers, cellulose carbon fibers, vapor grown carbon fibers (VGCF), and the like.
• the carbon nanotube is a cylindrical carbon material, and includes single-walled carbon nanotubes, multi-walled carbon nanotubes, and the like. Among these, carbon nanotubes are preferred because they have high crystallinity and excellent conductivity.
• the average fiber diameter of the fibrous carbon material is preferably 0.40 nm or more, more preferably 0.50 nm or more, still more preferably 1.00 nm or more, and 5.00 nm or more from the viewpoint of increasing the conductivity per unit weight. It is even more preferably 200.00 nm or less, more preferably 150.00 nm or less, even more preferably 100.00 nm or less.
• the average fiber diameter is preferably 0.40 to 200.00 nm, more preferably 0.50 to 150.00 nm, and even more preferably 1.00 to 100.00 nm.
• the average fiber diameter can be measured using, for example, a scanning laser microscope or a transmission laser microscope.
• the average fiber length of the fibrous carbon material is preferably 0.10 ⁇ m or more, more preferably 0.50 ⁇ m or more, even more preferably 1.00 ⁇ m or more, and 5.00 ⁇ m or more from the viewpoint of increasing the conductivity per unit weight. It is even more preferably 500.00 ⁇ m or less, more preferably 250.00 ⁇ m or less, even more preferably 200.00 ⁇ m or less, and even more preferably 100.00 ⁇ m or less.
• the average fiber length is preferably 0.10 to 500.00 ⁇ m, more preferably 0.50 to 250.00 ⁇ m, and even more preferably 1.00 to 100.00 ⁇ m.
• the average fiber length can be measured using, for example, a scanning laser microscope or a transmission laser microscope.
• the density of the fibrous carbon material is preferably 1.0 g/cm 3 or more, more preferably 1.1 g/cm 3 or more, and still more preferably 1.2 g/cm 3 or more from the viewpoint of increasing the conductivity per unit weight. It is preferably 1.8 g/cm 3 or more, even more preferably 2.5 g/cm 3 or less, more preferably 2.3 g/cm 3 or less, and even more preferably 2.1 g/cm 3 or less.
• the above density is preferably 1.0 to 2.5 g/cm 3 , more preferably 1.1 to 2.3 g/cm 3 , even more preferably 1.2 to 2.1 g/cm 3 , and still more preferably 1.8 to 2 .1 g/cm 3 is even more preferred.
• the above density can be measured by a method based on JIS Z8807.
• the specific surface area of the fibrous carbon material is preferably 8 m 2 /g or more, more preferably 13 m 2 /g or more, even more preferably 100 m 2 /g or more, and 200 m 2 /g from the viewpoint of increasing the conductivity per unit weight. It is even more preferable that the area is at least 3000 m 2 /g, more preferably at most 1500 m 2 /g, even more preferably at most 1200 m 2 /g, and even more preferably at most 1000 m 2 /g.
• the specific surface area is preferably 8 to 3000 m 2 /g, more preferably 13 to 1500 m 2 /g, even more preferably 100 to 1200 m 2 /g, and even more preferably 200 to 1000 m 2 /g.
• the specific surface area can be measured, for example, using a specific surface area measuring device ("ASAP-2000" manufactured by Shimadzu Corporation).
• the peak intensity ratio (G/D ratio) between the G band and the D band in the fibrous carbon material is preferably 0.1 or more, and 0.5 or more, since the higher the crystallinity, the higher the conductivity. More preferably, it is 100 or less, and even more preferably 95 or less.
• the above G/D ratio is preferably 0.1 to 100, more preferably 0.5 to 95.
• the above G/D ratio can be determined, for example, by measuring a Raman spectrum using Raman spectroscopy. When the above fibrous carbon material was measured by Raman spectroscopy, two peaks were clearly observed: the G band (near 1580 cm -1 ) corresponding to sp2 bonds and the D band (near 1360 cm -1 ) corresponding to sp3 bonds. Ru.
• the carbon material is crystalline
• one of the two bands described above becomes minimum.
• the G band near 1580 cm -1 is hardly observed.
• the D band near 1360 cm ⁇ 1 hardly appears.
• the fibrous carbon material may be a discontinuous fiber whose fibers are intermittently divided, or a continuous fiber which is not divided.
• the shape of the fibers is not particularly limited, but may be, for example, in addition to fibers, sheet shapes such as woven fabrics, knitted fabrics, and nonwoven fabrics.
• the content of the fibrous carbon material in the secondary battery electrode composition 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, 1. It is even more preferably 5% by weight or more, preferably 15.0% by weight or less, and even more preferably 10.0% by weight or less.
• the above content is preferably 0.05 to 15.0% by weight, more preferably 0.1 to 10.0% by weight, even more preferably 0.5 to 10.0% by weight, and even more preferably 1.5 to 10.0% by weight. % by weight is even more preferred.
• the surface area (specific surface area (m 2 /g) x content (g)) of the active material is X
• the surface area (specific surface area (m 2 /g)) of the fibrous carbon material is x content (g))
• the surface area ratio (X/Y) is preferably 0.01 or more, preferably 6.0 or less, and more preferably 0.05 or more, from the viewpoint of conductivity. It is more preferably 4.5 or less, and even more preferably 3.0 or less.
• the surface area ratio (X/Y) is preferably 0.01 to 6.0, more preferably 0.05 to 4.5, and even more preferably 0.05 to 3.0.
• the secondary battery electrode composition may contain particulate carbon material in addition to the fibrous carbon material.
• particulate carbon materials include graphite such as artificial graphite, flaky graphite, exfoliated graphite, natural graphite, acid-treated graphite, expandable graphite, and expanded graphite, acetylene black, Ketjen black, thermal black, and furnace black.
• carbon black such as black and channel black.
• the average particle diameter of the particulate carbon material is preferably 10 nm or more, more preferably 15 ⁇ m or more, even more preferably 20 ⁇ m or more, preferably 100 ⁇ m or less, more preferably 75 ⁇ m or less, and even more preferably 50 ⁇ m or less.
• the average particle diameter is preferably 10 to 100 ⁇ m, more preferably 15 to 75 ⁇ m, and even more preferably 20 to 50 ⁇ m.
• the density of the particulate carbon material is preferably 1.0 g/cm 3 or more, more preferably 1.1 g/cm 3 or more, even more preferably 1.2 g/cm 3 or more, and even more preferably 1.8 g/cm 3 or more. It is more preferably 2.5 g/cm 3 or less, more preferably 2.3 g/cm 3 or less, even more preferably 2.1 g/cm 3 or less.
• the above density is preferably 1.0 to 2.5 g/cm 3 , more preferably 1.1 to 2.3 g/cm 3 , even more preferably 1.2 to 2.1 g/cm 3 , and still more preferably 1.8 to 2 .1 g/cm 3 is even more preferred.
• the above density can be measured by a method based on JIS Z8807.
• the specific surface area of the particulate carbon material is preferably 20 m 2 /g or more, more preferably 50 m 2 /g or more, preferably 1000 m 2 /g or less, and more preferably 800 m 2 /g or less.
• the specific surface area is preferably 20 to 1000 m 2 /g, more preferably 50 to 800 m 2 /g.
• the specific surface area can be measured, for example, using a specific surface area measuring device ("ASAP-2000" manufactured by Shimadzu Corporation).
• the total content of the fibrous carbon material and the particulate carbon material in the secondary battery electrode composition is preferably 0.05% by weight or more, more preferably 0.1% by weight or more, and 0.5% by weight. % or more, still more preferably 1.5% by weight or more, preferably 15.0% by weight or less, and more preferably 10.0% by weight or less.
• the above total content is preferably 0.05 to 15.0% by weight, more preferably 0.1 to 10.0% by weight, even more preferably 0.5 to 10.0% by weight, and even more preferably 1.5 to 10.0% by weight. Even more preferred is 0% by weight.
• the secondary battery electrode composition contains a polyvinyl acetal resin.
• the polyvinyl acetal resin has a hydroxyl group content of 30 mol% or less.
• the above-mentioned polyvinyl acetal resin usually contains a structural unit having a hydroxyl group represented by the following formula (1-1), a constitutional unit having an acetyl group represented by the following formula (1-2), and a structural unit having a hydroxyl group represented by the following formula (1-2), and a structural unit having a hydroxyl group represented by the following formula (1-2). It has a structural unit having an acetal group represented by 3).
• R 1 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.
• R 1 is an alkyl group having 1 to 20 carbon atoms
• examples of the alkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group.
• the content of the structural unit having a hydroxyl group represented by the above formula (1-1) (hereinafter also referred to as "hydroxyl group amount”) is 30 mol% or less.
• hydroxyl group amount is preferably 10 mol% or more, more preferably 15 mol% or more, preferably 30 mol% or less, more preferably 28 mol% or less, and even more preferably 25 mol% or less.
• the amount of hydroxyl groups is preferably 10 to 30 mol%, more preferably 15 to 28 mol%, even more preferably 15 to 25 mol%.
• the amount of hydroxyl groups can be measured, for example, by NMR.
• the content of the structural unit having an acetyl group represented by the above formula (1-2) is preferably 0.1 mol % or more, and 5 mol %. % or more, preferably 30 mol% or less, more preferably 20 mol% or less, even more preferably 15 mol% or less.
• the amount of acetyl groups is preferably 0.1 to 30 mol%, more preferably 5 to 20 mol%, even more preferably 5 to 15 mol%.
• the amount of acetyl groups can be measured, for example, by NMR.
• the content of the structural unit having an acetal group represented by the above formula (1-3) (hereinafter also referred to as "acetal group amount”) is more preferably 60 mol% or more, and 70 mol%.
• the above is more preferable, 80 mol% or less is more preferable, and even more preferably 75 mol% or less.
• the amount of acetal groups is preferably 60 to 80 mol%, more preferably 70 to 75 mol%. Within the above range, the dispersibility of the fibrous carbon material can be further improved.
• the structural unit having an acetal group is replaced by the structural unit having a hydroxyl group.
• Calculate the amount of acetal groups by counting by converting into two parts.
• the amount of acetal groups can be measured, for example, by NMR.
• the polyvinyl acetal resin may have an ionic functional group.
• ionic functional groups include sulfur-containing groups such as carboxylic acid groups, sulfonic acid groups, sulfinic acid groups, and sulfenic acid groups, phosphorus-containing groups such as phosphoric acid groups and phosphonic acid groups, amino groups, and salts thereof. It will be done. Among these, it is preferable to have a structural unit having an acidic functional group, and it is more preferable to have a structural unit having a Br ⁇ nsted acidic group.
• Examples of the Bronsted acidic group include a carboxylic acid group, a sulfonic acid group, a sulfinic acid group, a sulfenic acid group, a phosphoric acid group, a phosphonic acid group, or salts thereof.
• a carboxylic acid group, a sulfur-containing group, and a phosphorus-containing group is preferable from the viewpoint of being able to increase adsorption to fibrous carbon materials, and carboxylic acid groups, sulfonic acid groups, and phosphonic acid groups are preferred. At least one selected from the group is more preferred. Since the modified polyvinyl acetal resin has the structural unit having the acidic functional group, the dispersibility of the fibrous carbon material can be improved even with a small amount added.
• the above structural unit having an ionic functional group may have a structure in which an ionic functional group as a side chain is directly bonded to carbon constituting the main chain, or an ionic functional group may be bonded directly to carbon constituting the main chain through an alkylene group. It may also have a structure in which a sexual functional group is bonded. Further, the above structural unit having an ionic functional group may have a structure in which the ionic functional group is bonded to carbon forming the main chain via an acetal bond.
• the above structural unit having an ionic functional group may have a three-dimensional structure in which two ionic functional groups are bonded to the same carbon constituting the main chain, or one ionic functional group is bonded to the same carbon constituting the main chain. It may be a three-dimensional structure in which two bonds are made. Alternatively, it may be a three-dimensional structure in which one ionic functional group is bonded to each adjacent carbon that makes up the main chain, or an ionic functional group is bonded to only one of the adjacent carbons that make up the main chain. It may be a three-dimensional structure.
• it has a three-dimensional structure in which two ionic functional groups are bonded to the same carbon that makes up the main chain, or a three-dimensional structure in which one ionic functional group is bonded to each adjacent carbon that makes up the main chain. is preferred.
• the above-mentioned structural unit having an ionic functional group may have a three-dimensional structure in which the ionic functional group is bonded in the same direction to the carbon constituting the main chain, which is an isotactic configuration. It may have a syndiotactic three-dimensional structure in which ionic functional groups are alternately bonded to carbon atoms on opposite sides. Furthermore, it may have a three-dimensional structure in which the ionic functional groups are randomly bonded in an atactic configuration.
• the alkylene group is an alkylene group having 1 to 10 carbon atoms. It is preferably an alkylene group having 1 to 5 carbon atoms, more preferably an alkylene group having 1 to 3 carbon atoms.
• Examples of the alkylene group having 1 to 10 carbon atoms include a linear alkylene group, a branched alkylene group, and a cyclic alkylene group.
• Examples of the linear alkylene group include a methylene group, a vinylene group, an n-propylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, an octamethylene group, and a decamethylene group.
• Examples of the branched alkylene group include methylmethylene group, methylethylene group, 1-methylpentylene group, and 1,4-dimethylbutylene group.
• cyclic alkylene group examples include a cyclopropylene group, a cyclobutylene group, and a cyclohexylene group.
• a linear alkylene group is preferred, a methylene group, a vinylene group, and an n-propylene group are more preferred, and a methylene group and a vinylene group are even more preferred.
• Examples of the above-mentioned structural units having an ionic functional group include structural units represented by the following formulas (2-1) to (2-4).
• R 2 , R 4 , R 6 , R 8 , R 10 and R 12 are each independently a single bond or an alkylene group having 1 to 10 carbon atoms.
• R 3 , R 5 , R 7 , R 9 , R 11 and R 13 each represent an ionic functional group.
• the above R 2 , R 4 , R 6 , R 8 , R 10 and R 12 are preferably a single bond or an alkylene group having 1 to 5 carbon atoms, and are a single bond or an alkylene group having 1 to 3 carbon atoms. More preferably, it is an alkylene group.
• Examples of the alkylene group having 1 to 10 carbon atoms include a linear alkylene group, a branched alkylene group, and a cyclic alkylene group.
• Examples of the linear alkylene group include a methylene group, an ethylene group, a trimethylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, an octamethylene group, and a decamethylene group.
• Examples of the branched alkylene group include methylmethylene group, methylethylene group, 1-methylpentylene group, and 1,4-dimethylbutylene group.
• cyclic alkylene group examples include a cyclopropylene group, a cyclobutylene group, and a cyclohexylene group.
• a linear alkylene group is preferred, a methylene group, an ethylene group, and a trimethylene group are more preferred, and a methylene group and an ethylene group are even more preferred.
• examples of the structural unit having a carboxylic acid group include structural units represented by the following formulas (3-1) to (3-3).
• R 14 to R 18 are each independently a single bond or an alkylene group having 1 to 10 carbon atoms
• X 1 to X 5 are each independently , represents a hydrogen atom, a metal atom or a methyl group.
• Examples of the above alkylene group having 1 to 10 carbon atoms include those similar to R 2 in the above formula (2-1).
• the metal atoms include sodium atoms, lithium atoms, potassium atoms, and the like. Among these, a sodium atom is preferred.
• Examples of the structural unit having a sulfonic acid group include a structural unit represented by the following formula (4).
• R 19 represents a single bond or an alkylene group having 1 to 10 carbon atoms
• X 6 represents a hydrogen atom, a metal atom, or a methyl group.
• Examples of the above alkylene group having 1 to 10 carbon atoms include those similar to R 2 in the above formula (2-1).
• Examples of the metal atom include those similar to X 1 in the above formula (3-1).
• Examples of the above-mentioned structural unit having a phosphonic acid group include a structural unit represented by the following formula (5).
• R 20 is a single bond or an alkylene group having 1 to 10 carbon atoms
• X 7 and X 8 each independently represent a hydrogen atom, a metal atom, or a methyl group.
• Examples of the above alkylene group having 1 to 10 carbon atoms include those similar to R 2 in the above formula (2-1).
• Examples of the metal atom include those similar to X 1 in the above formula (3-1).
• Examples of the above-mentioned structural unit having an amino group include a structural unit represented by the following formula (6).
• R 21 represents a single bond or an alkylene group having 1 to 10 carbon atoms.
• Examples of the above alkylene group having 1 to 10 carbon atoms include those similar to R 2 in the above formula (2-1).
• the content of the structural unit having an ionic functional group with respect to all the structural units of the polyvinyl acetal resin is preferably 0.01 mol% or more, and 0.1 mol% or more from the viewpoint of dispersibility of the fibrous carbon material. It is more preferably 0.5 mol% or more, still more preferably 20 mol% or less, more preferably 15 mol% or less, even more preferably 10 mol% or less, and even more preferably 5 mol% or less.
• the content of the structural unit having an ionic functional group is preferably 0.01 to 20 mol%, more preferably 0.1 to 15 mol%, even more preferably 0.5 to 10 mol%, and even more preferably 0.5 to 20 mol%. Even more preferred is 5 mol%.
• the content of the structural unit having an ionic functional group can be measured, for example, by NMR.
• the amount of Bronsted acid in the polyvinyl acetal resin is preferably 0.2 mg/g or more, more preferably 10 mg/g or more, and preferably 350 mg/g or less, and 250 mg/g. The following is more preferable, and 150 mg/g or less is still more preferable.
• the amount of Br ⁇ nsted acid is preferably 0.2 to 350 mg/g, more preferably 10 to 250 mg/g, even more preferably 10 to 150 mg/g.
• the above-mentioned amount of Bronsted acid means the amount of potassium hydroxide required to neutralize the Bronsted acid contained in the polyvinyl acetal resin.
• the amount of Br ⁇ nsted acid can be measured, for example, by acid-base titration according to a method based on JIS K0070-1992.
• the polyvinyl acetal resin has an acetal group having an ionic functional group represented by the above formula (2-4) as a structural unit having an ionic functional group
• the polyvinyl acetal resin has an acetal group having an ionic functional group represented by the above formula (2-4).
• -4) and the content of structural units having an acetal group represented by the above formula (1-3) (hereinafter referred to as "total acetal group content").
• total acetal group content is preferably 45 mol% or more, more preferably 60 mol% or more, preferably 85 mol% or less, and more preferably 75 mol% or less.
• the total amount of acetal groups is preferably 45 to 85 mol%, more preferably 60 to 75 mol%.
• the average degree of polymerization of the polyvinyl acetal resin is preferably 150 or more, more preferably 200 or more, even more preferably 300 or more, since it can sufficiently improve the dispersibility of the fibrous carbon material and exhibit high electronic conductivity. It is preferably 1,500 or less, more preferably 1,200 or less, and even more preferably 900 or less.
• the average degree of polymerization is preferably from 150 to 1,500, more preferably from 200 to 1,200, even more preferably from 300 to 900.
• the average degree of polymerization can be measured, for example, by gel permeation chromatography (GPC).
• the content of the polyvinyl acetal resin in the secondary battery electrode composition is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, preferably 30.0% by weight or less, and 15.0% by weight. % or less is more preferable.
• the above content is preferably 0.1 to 30.0% by weight, more preferably 0.5 to 15.0% by weight.
• the ratio of the content of the polyvinyl acetal resin to the content of the fibrous carbon material in the composition for secondary battery electrodes is 0.1 or more. is preferable, 0.2 or more is more preferable, 2 or less is preferable, and 1.5 or less is more preferable.
• the above ratio is preferably 0.1 to 2, more preferably 0.2 to 1.5.
• the fibrous carbon material has good dispersibility, making it easier to form conductive paths. As a result, electronic conductivity becomes even more excellent.
• the ratio of the content (g) of the polyvinyl acetal resin to the surface area (specific surface area (m 2 /g) x content (g)) of the fibrous carbon material Resin content/surface area of fibrous carbon material) is preferably 0.0001 or more, preferably 0.04 or less, more preferably 0.001 or more, more preferably 0.035 or less, and still more preferably 0.005 or more. It is preferably 0.03 or less, and more preferably 0.03 or less.
• the above ratio is preferably 0.0001 to 0.04, more preferably 0.001 to 0.035, and even more preferably 0.005 to 0.03.
• a polyvinyl acetate resin obtained by polymerizing a monomer such as vinyl acetate is saponified by adding an acid or an alkali, and purified to contain Na ions.
• Examples include a method of acetalizing polyvinyl alcohol resin in an adjusted amount.
• polyvinyl alcohol resin conventionally known polyvinyl alcohol resins such as resins produced by saponifying polyvinyl acetate resin with alkali, acid, aqueous ammonia, etc. can be used.
• the above-mentioned polyvinyl alcohol resin may be completely saponified, but it is completely saponified if there is at least one unit having a double hydroxyl group in the meso or racemo position at least at one location in the main chain. It is not necessary, and a partially saponified polyvinyl alcohol resin may be used.
• polyvinyl alcohol resin a copolymer of vinyl alcohol and a monomer that can be copolymerized with vinyl alcohol, such as an ethylene-vinyl alcohol copolymer resin or a partially saponified ethylene-vinyl alcohol copolymer resin, may also be used. be able to.
• the polyvinyl acetate resin include ethylene-vinyl acetate copolymer.
• polyvinyl acetal resin having a structural unit having an ionic functional group for example, polyvinyl acetate obtained by copolymerizing a monomer having an ionic functional group and vinyl acetate is saponified.
• examples include a method of acetalizing the obtained polyvinyl alcohol by a conventionally known method.
• an ionic functional group may be introduced by post-modifying a polyvinyl acetal resin obtained by acetalizing unmodified polyvinyl alcohol by a conventionally known method.
• Examples of the monomer having a carboxylic acid group include monocarboxylic acids such as acrylic acid, crotonic acid, methacrylic acid, and oleic acid, methylene malonic acid, itaconic acid, 2-methylene glutaric acid, 2-methylene adipic acid, -Dicarboxylic acids such as methylene sebacic acid, maleic anhydride, and metal salts thereof.
• Examples of the monomer having a sulfonic acid group include vinylsulfonic acid, sodium vinylsulfonate, beta-styrenesulfonic acid, and the like.
• Examples of the monomer having a phosphonic acid group include vinyl phosphoric acid, sodium vinyl phosphate, dimethyl vinyl phosphonate, diethyl vinyl phosphonate, and the like.
• Examples of the above-mentioned monomer having an amino group include vinylamine, allylamine, and the like.
• the amount of residual acetyl groups in the polyvinyl alcohol resin is preferably 0.1 mol% or more and 20.0 mol% or less, more preferably 5.0 mol% or more and 15.0 mol% or less.
• the acetalization can be carried out using a known method, and is preferably carried out in an aqueous solvent, in a mixed solvent of water and an organic solvent with which water is compatible, or in an organic solvent.
• an organic solvent that is compatible with water for example, an alcohol-based organic solvent can be used.
• the organic solvent include alcohol-based organic solvents, aromatic organic solvents, aliphatic ester-based solvents, ketone-based solvents, lower paraffinic solvents, ether-based solvents, amide-based solvents, amine-based solvents, and the like.
• the alcoholic organic solvent include methanol, ethanol, n-propanol, isopropanol, n-butanol, and tert-butanol.
• Examples of the aromatic organic solvent include xylene, toluene, ethylbenzene, methyl benzoate, and the like.
• Examples of the aliphatic ester solvent include methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, methyl acetoacetate, and ethyl acetoacetate.
• Examples of the ketone solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methylcyclohexanone, benzophenone, and acetophenone.
• Examples of the lower paraffinic solvent include hexane, pentane, octane, cyclohexane, decane, and the like.
• Examples of the ether solvent include diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol diethyl ether, and the like.
• Examples of the amide solvent include N,N-dimethylformamide, N,N-dimethyltesetamide, N-methylpyrrolidone, acetanilide, and the like.
• amine solvent examples include ammonia, trimethylamine, triethylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, aniline, N-methylaniline, N,N-dimethylaniline, and pyridine. These solvents can be used alone or in a mixture of two or more. Among these, ethanol, n-propanol, isopropanol, and tetrahydrofuran are particularly preferred from the viewpoint of solubility in the resin and ease of purification.
• the acetalization is preferably performed in the presence of an acid catalyst.
• the above acid catalysts are not particularly limited, and include mineral acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, carboxylic acids such as formic acid, acetic acid, and propionic acid, methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, and paratoluenesulfonic acid. Examples include sulfonic acids such as acids.
• These acid catalysts may be used alone or in combination of two or more kinds of compounds. Among these, hydrochloric acid, nitric acid, and sulfuric acid are preferred, and hydrochloric acid is particularly preferred.
• aldehyde used in the acetalization examples include aldehydes having a chain aliphatic group, a cyclic aliphatic group, or an aromatic group having 1 to 10 carbon atoms. As these aldehydes, conventionally known aldehydes can be used.
• the aldehyde used in the acetalization reaction is not particularly limited, and examples thereof include aliphatic aldehydes, aromatic aldehydes, and the like.
• Examples of the aliphatic aldehydes include formaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, n-valeraldehyde, n-hexylaldehyde, 2-ethylbutyraldehyde, 2-ethylhexylaldehyde, n-heptylaldehyde, and n-octylaldehyde.
• Examples include octeraldehyde, n-nonylaldehyde, n-decylaldehyde, amylaldehyde and the like.
• aromatic aldehyde examples include benzaldehyde, cinnamaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylbutyraldehyde, and ⁇ -phenylpropionaldehyde.
• aldehydes examples include aldehydes.
• cyclic multimers such as paraldehyde and metaldehyde can be used. These aldehydes may be used alone or in combination of two or more.
• aldehydes examples include formaldehyde, butyraldehyde, butyraldehyde, and 2-ethylhexylaldehyde, which have excellent acetalization reactivity and can provide a sufficient internal plasticizing effect to the resulting resin, resulting in good flexibility.
• n-nonylaldehyde and paraldehyde are preferred.
• formaldehyde, n-butyraldehyde, and paraldehyde are more preferred because they yield an adhesive composition that is particularly excellent in impact resistance and adhesion to metals.
• the amount of the aldehyde added can be appropriately set depending on the amount of acetal groups in the target polyvinyl acetal resin. In particular, it is preferable to use 10 to 65 mol %, preferably 15 to 60 mol %, based on 100 mol % of polyvinyl alcohol, because the acetalization reaction can be carried out efficiently and unreacted aldehyde can be easily removed.
• the secondary battery electrode composition has a water content of 10% by weight or less. By setting it as the said range, the dispersion stability of a fibrous carbon material can be improved.
• the water content is preferably 5% by weight or less, more preferably 1% by weight or less. Further, the lower limit is not particularly limited, and is, for example, 0% by weight or more.
• the water content is preferably 0 to 10% by weight, more preferably 0 to 5% by weight, and even more preferably 0 to 1% by weight.
• the water content can be measured using, for example, an infrared moisture meter.
• the secondary battery electrode composition further contains a binder resin.
• the binder resin include fluorine-containing resins such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), and polymethyl acrylate (PMA).
• acrylic resins such as polymethyl methacrylate (PMMA), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), polyethernitrile (PEN), polyethylene (PE), polypropylene (PP),
• PMMA polymethyl methacrylate
• PMMA polyvinyl acetate
• PA polyamide
• PVC polyvinyl chloride
• PEN polyethernitrile
• PE polyethylene
• PP polypropylene
• PAN polyacrylonitrile
• PAN acrylonitrile-butadiene rubber
• styrene-butadiene rubber poly(meth)acrylic acid
• carboxymethyl cellulose hydroxyethyl cellulose
• polyvinyl alcohol polyvinyl alcohol
• the ratio of the content of the polyvinyl acetal resin to the content of the binder resin in the composition for secondary battery electrodes improves electrical properties and improves dispersibility.
• it is preferably 0.1 or more, more preferably 0.2 or more, preferably 2.0 or less, and more preferably 1.0 or less.
• the above ratio is preferably 0.1 to 2.0, more preferably 0.2 to 1.0.
• the secondary battery electrode composition may further contain additives such as a conductive additive, a flame retardant additive, an antifoaming agent, a leveling agent, and an adhesion imparting agent, within a range that does not impair the effects of the present invention. Good too.
• the method for producing the secondary battery electrode composition is not particularly limited, and for example, a polyvinyl acetal resin obtained by acetalizing raw material polyvinyl alcohol, an active material, and a fibrous carbon material are added to a hydrophobic solvent.
• a polyvinyl acetal resin obtained by acetalizing raw material polyvinyl alcohol, an active material, and a fibrous carbon material are added to a hydrophobic solvent.
• Examples include a method of mixing. Examples of the above-mentioned mixing method include methods using various mixers such as a ball mill, a blender mill, and a three-roll mixer.
• a lithium secondary battery electrode can be formed by applying the composition for a secondary battery electrode onto a conductive substrate and drying the composition, for example.
• various coating methods can be employed, including, for example, an extrusion coater, a reverse roller, a doctor blade, an applicator, and the like.
• a composition for a secondary battery electrode that can be used to manufacture a secondary battery can be provided.
• Carboxylic acid-modified polyvinyl alcohol resin (average degree of polymerization 600, residual acetyl group 1.0 mol%, content of structural units represented by formula (3-1) (R 14 is a methylene group, X 1 is a hydrogen atom) content 1 0 mol %) was added to 2500 g of pure water and stirred at 90° C. for 2 hours to dissolve. This solution was cooled to 40°C, 10g of hydrochloric acid with a concentration of 35% by weight was added thereto, the temperature was lowered to 5°C, 85g of n-butyraldehyde was added, and this temperature was maintained to carry out the acetalization reaction. The reaction product was precipitated.
• the reaction was completed by keeping the liquid temperature at 65° C. for 5 hours, and 40 g of an aqueous sodium hydroxide solution was added to perform a neutralization reaction. Thereafter, 5000 g of pure water was added and stirred, and then 5000 g of water was removed by decantation. Furthermore, the process of adding 5000 g of pure water, stirring, and removing water by decantation was repeated three times in total. Thereafter, the solid content of the resin was adjusted to 20% by weight using ion-exchanged water to obtain a polyvinyl acetal resin (PVB-A1).
• PVB-A1 polyvinyl acetal resin
• the amount of acetal groups, the amount of hydroxyl groups, and the amount of acetyl groups were measured using 1 H-NMR (nuclear magnetic resonance spectrum), and the results were as shown in Table 1.
• 1 H-NMR measurement used heavy DMSO as a solvent.
• the amount of Br ⁇ nsted acid was measured by acid-base titration method in accordance with JIS K0070-1992. Specifically, it was measured by the following method. First, as a main test, about 1 g of the obtained polyvinyl acetal resin was accurately weighed into an Erlenmeyer flask, and 40 ml of a mixed solvent of ethanol/water (volume ratio 9:1) was added and dissolved by shaking.
• Br ⁇ nsted acid amount [(AB) x f x (1/50) x (C/1000)] x 100/D
• n - A polyvinyl acetal resin (PVB-A14) was obtained in the same manner as in Production Example 1 except that the amount of butyraldehyde added was 75 g.
• Examples 1 to 18, Comparative Examples 1 to 8 An active material, a hydrophobic solvent, a carbon material, a polyvinyl acetal resin, a binder resin, and water were mixed according to the formulation shown in Table 2 to obtain a composition for a secondary battery electrode. Note that the following were used as the active material, hydrophobic solvent, carbon material, and binder resin. Further, the pH of the active material was measured by adding the active material into water at a concentration of 1.0% by weight, and measuring the pH of the resulting aqueous solution using a pH meter (manufactured by Horiba, Ltd.). Moreover, the water content was measured using an infrared moisture meter (manufactured by KETT).
• LFP-1 Lithium iron phosphate (LiFePO 4 ) (pH 9, average particle size 1.0 ⁇ m, density 3.4 g/cm 3 , specific surface area 10.7 m 2 /g)
• LFP-2 Lithium iron phosphate (LiFePO 4 ) (pH 10, average particle size 1.5 ⁇ m, density 3.7 g/cm 3 , specific surface area 12.0 m 2 /g)
• LFP-3 Lithium iron phosphate (LiFePO 4 ) (pH 9, average particle size 5.5 ⁇ m, density 3.6 g/cm 3 , specific surface area 0.8 m 2 /g)
• NCM-1 Lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ) (pH 12, average particle size 10.0 ⁇ m, density 3.5 g/cm 3 , specific surface area 0.5 m 2 /g)
• NCM-2 Lithium nickel cobalt manganese oxide
• the obtained secondary battery electrode composition was coated onto a glass plate using a doctor blade, and dried at 150° C. for 5 minutes in an air circulating oven to obtain a coating film.
• the resulting coating film was visually observed and evaluated based on the following criteria. ⁇ : There were no cracks or fissures on the coating film surface, and the film thickness was uniform. ⁇ : Slight cracks and fissures were observed on the surface of the coating film. ⁇ : Cracks and fissures were observed on the coating film surface, and there were variations in film thickness.
• Viscosity change rate is less than 150%
• Viscosity change rate is 150% or more and less than 250%
• Viscosity change rate is 250% or more
• the storage modulus of the obtained secondary battery electrode composition was measured using RHEOSTRESS (manufactured by Thermo Scientific) at 25°C and a strain of 0.1, and the storage elastic modulus was measured according to the following criteria. It was evaluated by ⁇ : Storage modulus is less than 1000 ⁇ : Storage modulus is 1000 or more, less than 5000 ⁇ : Storage modulus is 5000 or more If the viscoelasticity evaluation is high, the paste has excellent fluidity and is difficult to gel.
• a composition for a secondary battery electrode that can be used to manufacture a secondary battery can be provided.

Landscapes

• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Battery Electrode And Active Subsutance (AREA)
• Compositions Of Macromolecular Compounds (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=88101472

Family Applications (1)

Country Status (3)

Cited By (2)

Citations (3)

• 2023
  • 2023-03-15 JP JP2023522511A patent/JPWO2023182090A1/ja active Pending
  • 2023-03-15 WO PCT/JP2023/010029 patent/WO2023182090A1/ja not_active Ceased
  • 2023-03-16 TW TW112109755A patent/TW202347850A/zh unknown

Patent Citations (3)

Also Published As

Similar Documents

Legal Events