WO2020129750A1 - 二次電池電極用バインダー及びその利用 - Google Patents
二次電池電極用バインダー及びその利用 Download PDFInfo
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- WO2020129750A1 WO2020129750A1 PCT/JP2019/048274 JP2019048274W WO2020129750A1 WO 2020129750 A1 WO2020129750 A1 WO 2020129750A1 JP 2019048274 W JP2019048274 W JP 2019048274W WO 2020129750 A1 WO2020129750 A1 WO 2020129750A1
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- 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
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F293/00—Macromolecular compounds obtained by polymerisation on to a macromolecule having groups capable of inducing the formation of new polymer chains bound exclusively at one or both ends of the starting macromolecule
- C08F293/005—Macromolecular compounds obtained by polymerisation on to a macromolecule having groups capable of inducing the formation of new polymer chains bound exclusively at one or both ends of the starting macromolecule using free radical "living" or "controlled" polymerisation, e.g. using a complexing agent
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- 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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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- 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
- H01M4/621—Binders
- H01M4/622—Binders being polymers
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F2438/00—Living radical polymerisation
- C08F2438/03—Use of a di- or tri-thiocarbonylthio compound, e.g. di- or tri-thioester, di- or tri-thiocarbamate, or a xanthate as chain transfer agent, e.g . Reversible Addition Fragmentation chain Transfer [RAFT] or Macromolecular Design via Interchange of Xanthates [MADIX]
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- 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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Definitions
- the present invention relates to a binder for a secondary battery electrode and its use.
- the electrodes used in these secondary batteries are produced by applying a composition for forming an electrode mixture layer containing an active material, a binder and the like onto a current collector and drying the composition.
- a composition for forming an electrode mixture layer containing an active material, a binder and the like onto a current collector and drying the composition.
- an aqueous binder containing styrene-butadiene rubber (SBR) latex and carboxymethyl cellulose (CMC) is used as a binder used in the composition for the negative electrode mixture layer.
- a binder having excellent dispersibility and binding property a binder containing an acrylic acid polymer aqueous solution or an aqueous dispersion is known.
- a polyvinylidene fluoride (PVDF) N-methyl-2-pyrrolidone (NMP) solution is widely used as a binder for the positive electrode mixture layer.
- Patent Document 1 As a binder having a good binding property and an effect of improving durability, a binder using the acrylic acid-based polymer has been proposed.
- Patent Document 1 by using a polymer obtained by cross-linking polyacrylic acid with a specific cross-linking agent as a binder, the electrode structure is not destroyed even when an active material containing silicon is used. It is described that it can be provided.
- Patent Document 2 describes a binder for a lithium battery, which comprises a polymer containing a monomer unit derived from acrylic acid as a constituent component and cross-linked with a specific cross-linking agent, and has a high capacity even when charging and discharging are repeated. It is described that the maintenance rate is shown.
- Patent Document 3 in which a binder using a block polymer is also investigated for the purpose of improving performance such as binding property, a segment including a structural unit of a vinyl monomer having an acid component, and (meth)acrylic are disclosed. Binders are disclosed that include block copolymers having segments that include structural units of acid alkyl ester monomers.
- binders disclosed in Patent Documents 1 to 3 are all capable of imparting good binding properties, but as the performance of the secondary battery is improved, electrodes having higher binding properties are required. ing.
- the present invention has been made in view of the above circumstances, and provides a binder for a secondary battery electrode, which can obtain a secondary battery electrode having a higher binding property than conventional.
- the present invention also provides a composition for a secondary battery electrode and a secondary battery electrode containing the above binder.
- the present inventors contain a block polymer having a block having a small number of structural units derived from (meth)acrylic acid and a block containing a specific amount of the structural unit. It was found that when the binder is used, the binding property of the obtained electrode mixture layer can be made higher. According to the present disclosure, the following means are provided based on these findings.
- a binder for a secondary battery electrode comprising a block polymer having a polymer block (A) and a polymer block (B),
- the polymer block (A) has less than 30% by mass of structural units derived from (meth)acrylic acid based on all the structural units of the polymer block (A),
- the polymer block (B) has 30% by mass or more and 100% by mass or less of structural units derived from (meth)acrylic acid based on all structural units of the polymer block (B). binder.
- the ratio of the polymer block (A) in the block polymer is 0.1% by mass or more and 80% by mass or less
- Tg glass transition temperature
- the polymer block (B) is a polymer block obtained by polymerizing a monomer composition containing (meth)acrylic acid and a crosslinkable monomer, [1] to [4]
- a method for producing a block polymer used for a secondary battery electrode binder comprising: The block polymer has a polymer block (A) and a polymer block (B), A step of polymerizing a monomer component having a (meth)acrylic acid content of less than 30% by mass by a living radical polymerization method to produce the polymer block (A), Producing a polymer block (B) by polymerizing a monomer component containing 30% by mass or more and 100% by mass or less of (meth)acrylic acid in the presence of the polymer block (A). , A method for producing a block polymer. [9] The method for producing a block polymer according to [8], wherein the living radical polymerization method is a reversible addition-cleavage chain transfer polymerization method (RAFT method).
- RAFT method reversible addition-cleavage chain transfer polymerization method
- the binder for secondary battery electrodes of the present invention exhibits excellent binding properties to electrode active materials and the like. Further, the binder can exhibit good adhesiveness with the current collector. Therefore, the electrode mixture layer containing the binder and the electrode provided with the binder layer have excellent binding properties and can maintain their integrity.
- the binder for a secondary battery electrode of the present invention contains a block polymer and is mixed with an active material and water to form a composition for a secondary battery electrode mixture layer (hereinafter, also referred to as “present composition”). ) Can be.
- the above composition may be in a slurry state in which it can be applied to the current collector, or may be prepared in a wet powder state so that it can be pressed to the surface of the current collector.
- the secondary battery electrode of the present invention can be obtained by forming a mixture layer formed of the above composition on the surface of a current collector such as copper foil or aluminum foil.
- (meth)acryl means acryl and/or methacryl
- (meth)acrylate means acrylate and/or methacrylate
- (meth)acryloyl group means an acryloyl group and/or a methacryloyl group.
- Binder The binder for a secondary battery electrode of the present invention contains a block polymer (hereinafter, also referred to as “present block polymer”).
- This block polymer has a structural unit derived from (meth)acrylic acid of less than 30% by mass, and a structural unit derived from (meth)acrylic acid of 30% by mass or more and 100% by mass. It has the following polymer blocks (B): Hereinafter, the block polymer will be described in detail.
- the polymer block (A) is a polymer block having a structural unit derived from (meth)acrylic acid of less than 30% by mass, and for example, a unit amount of the content of (meth)acrylic acid of less than 30% by mass. It can be obtained by polymerizing the body composition.
- the content of (meth)acrylic acid in the monomer composition may be 20% by mass or less, 10% by mass or less, and 0% by mass.
- the polymer block (A) may have a structural unit derived from (meth)acrylic acid of less than 30% by mass.
- the structural unit derived from a monomer other than (meth)acrylic acid (hereinafter, also referred to as “component (a)”) is not particularly limited.
- Examples of the component (a) include ethylenically unsaturated carboxylic acid monomers other than (meth)acrylic acid, aromatic vinyl monomers, maleimide compounds, (meth)acrylic acid ester monomers, (meth)acrylamides. And derivatives thereof, nitrile group-containing ethylenically unsaturated monomers and the like.
- the amount of each monomer used may be, for example, 10% by mass or more, or 30% by mass or more, based on the total amount of the monomers constituting the polymer block (A), 50 It may be mass% or more, or may be 70 mass% or more.
- the upper limit is 100% by mass or less, 90% by mass or less, or 80% by mass or less.
- the total amount of the component (a) with respect to all the constituent monomers of the polymer block (A) is more than 70% by mass, may be 80% by mass or more, may be 90% by mass or more, and may be 100% by mass. It may be %.
- Examples of the ethylenically unsaturated carboxylic acid monomer excluding (meth)acrylic acid include ethylenically unsaturated dicarboxylic acids such as itaconic acid, maleic acid and citraconic acid, and acid anhydrides thereof; (meth)acrylamidohexanoic acid and ( (Meth) acrylamido dodecanoic acid and other (meth) acrylamidoalkylcarboxylic acids; ethylene such as crotonic acid, succinic acid monohydroxyethyl (meth) acrylate, ⁇ -carboxy-caprolactone mono (meth) acrylate and ⁇ -carboxyethyl (meth) acrylate
- Examples of the unsaturated carboxylic acid include polyunsaturated monocarboxylic acid, and one of these may be used alone, or two or more thereof may be used in combination.
- the ethylenically unsaturated carboxylic acid monomer may be in the form
- aromatic vinyl monomer examples include styrene, ⁇ -methylstyrene, vinylnaphthalene, and isopropenylnaphthalene. One of these may be used alone, or two or more of them may be used. You may use it in combination.
- Maleimide compounds include maleimide and N-substituted maleimide compounds.
- Examples of the N-substituted maleimide compound include N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, N-isopropylmaleimide, Nn-butylmaleimide, N-isobutylmaleimide, N-tert-butylmaleimide.
- N-alkyl-substituted maleimide compounds such as N-pentylmaleimide, N-hexylmaleimide, N-heptylmaleimide, N-octylmaleimide, N-laurylmaleimide and N-stearylmaleimide; N-cyclopentylmaleimide, N-cyclohexylmaleimide and the like N-cycloalkyl-substituted maleimide compounds; N-phenylmaleimide, N-(4-hydroxyphenyl)maleimide, N-(4-acetylphenyl)maleimide, N-(4-methoxyphenyl)maleimide, N-(4-ethoxyphenyl) ) N-aryl-substituted maleimide compounds such as maleimide, N-(4-chlorophenyl)maleimide, N-(4-bromophenyl)maleimide, N-benzylmaleimide, etc., and
- Examples of the (meth)acrylic acid ester monomer include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.
- (Meth)acrylic acid alkyl ester compounds such as; Aromatic (meth)acrylic acid ester compounds such as phenyl (meth)acrylate, phenylmethyl (meth)acrylate, phenylethyl (meth)acrylate, and phenoxyethyl (meth)acrylate; (Meth)acrylic acid alkoxyalkyl ester compounds such as 2-methoxyethyl (meth)acrylic acid and ethoxyethyl (meth)acrylate; (Meth)acrylic acid hydroxyalkyl ester compounds such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate and hydroxybutyl (meth)acrylate, and the like, and one of these may be used alone. Alternatively, two or more kinds may be used in combination. From the viewpoint of adhesion to the active material and cycle characteristics, an aromatic (meth)acrylic acid ester compound can be preferably used.
- Examples of the (meth)acrylamide derivative include N-alkyl(meth)acrylamide compounds such as isopropyl(meth)acrylamide and t-butyl(meth)acrylamide; Nn-butoxymethyl (meth)acrylamide, N-isobutoxymethyl.
- N-alkoxyalkyl(meth)acrylamide compounds such as (meth)acrylamide; N,N-dialkyl(meth)acrylamide compounds such as dimethyl(meth)acrylamide, diethyl(meth)acrylamide and the like. They may be used alone or in combination of two or more.
- nitrile group-containing ethylenically unsaturated monomer examples include (meth)acrylonitrile; (meth)acrylic acid cyanoalkyl ester compounds such as cyanomethyl (meth)acrylate and cyanoethyl (meth)acrylate; 4-cyanostyrene Cyano group-containing unsaturated aromatic compounds such as 4-cyano- ⁇ -methylstyrene; vinylidene cyanide and the like.
- One of these may be used alone, or two or more thereof may be used in combination. May be used.
- acrylonitrile is preferable because it has a large nitrile group content.
- the glass transition temperature (Tg) of the polymer block (A) is preferably ⁇ 30° C. or higher from the viewpoint of obtaining good binding properties.
- Tg may be, for example, ⁇ 20° C. or higher, 0° C. or higher, 20° C. or higher, 50° C. or higher, or 80° C. or higher.
- the upper limit of Tg is 350° C. due to the limitation of constituent monomer units that can be used.
- Tg may be, for example, 300° C. or lower, 280° C. or lower, or 250° C. or lower.
- the Tg of the polymer block (A) can be obtained by differential scanning calorimetry (DSC). Further, when the DSC measurement cannot be performed, it can be calculated from the Tg of the homopolymer of each monomer constituting the polymer block by using the formula of FOX. The same applies to other polymer blocks such as the polymer block (B) described later.
- the number average molecular weight (Mn) of the polymer block (A) is not particularly limited, but is preferably in the range of 1,000 or more and 1,000,000 or less. When the number average molecular weight is 1,000 or more, it can be adsorbed on the active material or the like and contribute to the improvement of the binding property of the electrode. Further, if it is 1,000,000 or less, good fluidity can be secured, and handling at the time of production and the like is facilitated, which is preferable.
- the number average molecular weight of the block polymer (A) is preferably 5,000 or more, more preferably 8,000 or more, still more preferably 10,000 or more.
- the upper limit is preferably 500,000 or less, more preferably 300,000 or less, and further preferably 100,000 or less.
- the molecular weight distribution (Mw/Mn) obtained by dividing the value of the weight average molecular weight (Mw) of the polymer block (A) by the value of the number average molecular weight (Mn) is 3 from the viewpoint of binding property. It is preferably 0.0 or less. It is more preferably 2.5 or less, still more preferably 2.0 or less, still more preferably 1.5 or less, and even more preferably 1.3 or less.
- the lower limit of the molecular weight distribution (Mw/Mn) is usually 1.0.
- the polymer block (A) is a relatively hydrophobic segment, and when this block polymer is used as a binder, it tends to be adsorbed on the surface of, for example, a carbon-based active material. As a result, the active materials can be firmly bound to each other, and a secondary battery electrode having excellent binding properties can be obtained.
- the polymer block (B) is a polymer block in which the structural unit derived from (meth)acrylic acid is 30% by mass or more and 100% by mass or less, and for example, the content of (meth)acrylic acid is 30% by mass. As described above, it can be obtained by polymerizing 100% by mass or less of the monomer composition. By containing the structural unit derived from (meth)acrylic acid in such a range, excellent adhesiveness to the current collector can be easily ensured. When the lower limit of the structural unit derived from (meth)acrylic acid is 50% by mass or more, the dispersion stability of the present composition is good, and a higher binding force is obtained, which is more preferable.
- the lower limit may be 60% by mass or more, 70% by mass or more, and 80% by mass or more.
- the upper limit value is, for example, 99.9% by mass or less, or, for example, 99.5% by mass or less, or, for example, 99% by mass or less, or, for example, 98% by mass or less, or, for example, 95% by mass.
- the range can be a range in which the lower limit and the upper limit are appropriately combined, but is, for example, 50% by mass or more and 100% by mass or less, and for example, 50% by mass or more and 99.9% by mass or less, Further, it may be, for example, 50% by mass or more and 99% by mass or less, or, for example, 70% by mass or more and 99% by mass or less, and for example, 80% by mass or more and 99% by mass or less.
- the monomer constituting the polymer block (B) is, in addition to (meth)acrylic acid, other non-crosslinkable ethylenically unsaturated monomer copolymerizable therewith (hereinafter, also referred to as “component (b)”). ).
- component (b) the same monomer as the component (a) described above as a monomer constituting the polymer block (A) can be used, and one of these can be used alone. Alternatively, two or more kinds may be used in combination.
- the ratio of the component (b) can be 0% by mass or more and 70% by mass or less with respect to the total amount of the non-crosslinkable monomers constituting the polymer block (B).
- the ratio of the component (b) may be 1% by mass or more and 50% by mass or less, 5% by mass or more and 50% by mass or less, and 10% by mass or more and 50% by mass or less. It may be 20% by mass or more and 40% by mass or less. Further, when the component (b) is contained in an amount of 1% by mass or more based on the total amount of the non-crosslinkable monomer, the affinity for the electrolytic solution is improved, and the effect of improving lithium ion conductivity can also be expected.
- (meth)acrylic acid hydroxyalkyl ester compounds such as (meth)acrylic acid hydroxyethyl, (meth)acrylic acid hydroxypropyl, and (meth)acrylic acid hydroxybutyl are preferable.
- a hydroxyl group is introduced into the polymer block (B).
- the binder containing the obtained block copolymer is preferable because it can impart excellent binding properties.
- an ether bond such as (meth)acrylic acid alkoxyalkyl ester such as (meth)acrylic acid 2-methoxyethyl and (meth)acrylic acid 2-ethoxyethyl is used.
- the compound having is preferable, and 2-methoxyethyl (meth)acrylate is more preferable.
- a compound having an acryloyl group is preferable in that a polymer having a long primary chain length can be obtained because of its high polymerization rate, and the binding force of the binder becomes good.
- a compound having a homopolymer glass transition temperature (Tg) of 0° C. or lower is preferable in that the obtained electrode has good bending resistance.
- the monomer constituting the polymer block (B) may include a crosslinkable monomer.
- the crosslinkable monomer in the present specification includes a polyfunctional polymerizable monomer having two or more polymerizable unsaturated groups, and a monofunctional crosslinkable functional group such as a hydrolyzable silyl group. Examples thereof include a polymer.
- the polyfunctional polymerizable monomer is a compound having two or more polymerizable functional groups such as a (meth)acryloyl group and an alkenyl group in the molecule, and a polyfunctional (meth)acrylate compound, a polyfunctional alkenyl compound, ( Examples thereof include compounds having both a (meth)acryloyl group and an alkenyl group. These compounds may be used alone or in combination of two or more. Among these, a polyfunctional alkenyl compound is preferable because a uniform crosslinked structure is easily obtained, and a polyfunctional allyl ether compound having two or more allyl ether groups in the molecule is particularly preferable.
- polyfunctional (meth)acrylate compound examples include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di( Di(meth)acrylates of dihydric alcohols such as (meth)acrylate; trimethylolpropane tri(meth)acrylate, trimethylolpropane ethylene oxide modified tri(meth)acrylate, glycerin tri(meth)acrylate, pentaerythritol tri( Poly(meth)acrylates such as tri(meth)acrylates of trihydric or higher polyhydric alcohols such as (meth)acrylates, pentaerythritol tetra(meth)acrylates, tetra(meth)acrylates; methylenebisacrylamide, hydroxyethylenebisacrylamide, etc. Examples thereof include bisamides.
- polyfunctional alkenyl compound examples include trimethylolpropane diallyl ether, trimethylolpropane triallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, tetraallyloxyethane, polyallyl saccharose and the like; diallyl phthalate and the like. And polyfunctional allyl compounds; and polyfunctional vinyl compounds such as divinylbenzene.
- Examples of the compound having both a (meth)acryloyl group and an alkenyl group include allyl (meth)acrylate, isopropenyl (meth)acrylate, butenyl (meth)acrylate, pentenyl (meth)acrylate, and (meth)acrylic acid. 2-(2-vinyloxyethoxy)ethyl and the like can be mentioned.
- the monomer having a self-crosslinkable crosslinkable functional group include a hydrolyzable silyl group-containing vinyl monomer, N-methylol (meth)acrylamide, N-methoxyalkyl (meth)acrylate and the like. Are listed. These compounds can be used alone or in combination of two or more.
- the hydrolyzable silyl group-containing vinyl monomer is not particularly limited as long as it is a vinyl monomer having at least one hydrolyzable silyl group.
- vinylsilanes such as vinyltrimethoxysilane, vinyltriethoxysilane, vinylmethyldimethoxysilane and vinyldimethylmethoxysilane
- silyl compounds such as trimethoxysilylpropyl acrylate, triethoxysilylpropyl acrylate and methyldimethoxysilylpropyl acrylate.
- Group-containing acrylic acid esters silyl group-containing methacrylic acid esters such as trimethoxysilylpropyl methacrylate, triethoxysilylpropyl methacrylate, methyldimethoxysilylpropyl methacrylate, dimethylmethoxysilylpropyl methacrylate; trimethoxysilylpropyl vinyl ether, etc.
- silyl group-containing vinyl ethers include silyl group-containing vinyl esters such as trimethoxysilyl vinyl undecanoate.
- the amount of the cross-linkable monomer used is 100 total amount of monomers other than the cross-linkable monomer (non-cross-linkable monomer). It is preferably 0.1 parts by mass or more and 2.0 parts by mass or less, more preferably 0.3 parts by mass or more and 1.5 parts by mass or less, and further preferably 0.5 parts by mass or more and 1 part by mass with respect to parts by mass. It is 0.5 parts by mass or less.
- the amount of the crosslinkable monomer used is 0.1 part by mass or more, the binding property and the stability of the electrode slurry are improved, which is preferable.
- the amount of the crosslinkable monomer used is 0.02 to 0.7 mol% based on the total amount of the monomers other than the crosslinkable monomer (non-crosslinkable monomer). It is more preferably 0.03 to 0.4 mol %.
- the glass transition temperature (Tg) of the polymer block (B) is preferably 50° C. or higher from the viewpoint of obtaining good binding properties.
- Tg may be, for example, 70° C. or higher, 80° C. or higher, 90° C. or higher, and 100° C. or higher.
- the upper limit of Tg is 350° C. due to the limitation of constituent monomer units that can be used.
- Tg may be, for example, 300° C. or lower, 280° C. or lower, or 250° C. or lower.
- the block copolymer may have at least one polymer block (A) and at least one polymer block (B), for example, the polymer block (A) and the polymer block (B) (AB ) A diblock body, a (ABA) triblock body composed of a polymer block (A)/a polymer block (B)/a polymer block (A), a (BAB) triblock body, and the like. Further, it may have a structure such as (ABC) or (ABCA) containing a polymer block (C) other than the polymer block (A) and the polymer block (B). Above all, the block copolymer preferably has an A-(BA)n (n is an integer of 1 or more) structure.
- the microphase-separated structure expressed by the present block copolymer is preferable in that it forms a bridge structure between domains.
- the A-(BA)n structure may be present in all or part of the copolymer, and may be, for example, a copolymer having a (BABAB) structure.
- the block polymer may be a mixture of two or more block polymers belonging to the diblock body, triblock body and the like. Further, in addition to the block polymer, a polymer composed only of the polymer block (A) or a polymer composed only of the polymer block (B) may be contained.
- the proportion of the polymer block (A) in the present block copolymer is not particularly limited, but from the viewpoint of binding properties, it can be, for example, 0.1% by mass or more and 80% by mass or less.
- the proportion of the polymer block (A) may be 0.5% by mass or more, 1.0% by mass or more, or 2.0% by mass or more, and 5.0% by mass. It may be more than 10% by mass, may be 10% by mass or more, and may be 20% by mass or more.
- the proportion of the polymer block (A) may be 70% by mass or less, 50% by mass or less, 30% by mass or less, and 10% by mass or less.
- the ratio of the polymer block (B) in the present block polymer can be 20% by mass or more and 99.9% by mass or less.
- the proportion of the polymer block (B) may be 30% by mass or more, 50% by mass or more, 70% by mass or more, and 90% by mass or more.
- the proportion of the polymer block (B) may be 99.5% by mass or less, 99% by mass or less, 98% by mass or less, and 95% by mass or less. It may be 90% by mass or less, or 80% by mass or less.
- the proportion of the total amount of the polymer block (A) and the polymer block (B) is preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 80% by mass. It is at least mass%, more preferably at least 90 mass%.
- the proportion of the total amount of the polymer block (A) and the polymer block (B) may be 100% by mass.
- the mass ratio of the polymer block (A) and the polymer block (B) in the present block copolymer is not particularly limited, but may be, for example, 0.1 to 80/20 to 99.9. it can. Within such a range, good binding properties can be exhibited.
- the mass ratio may be, for example, 0.5 to 70/30 to 99.5, 1.0 to 50/50 to 99, or 5.0 to 30/70 to 95. It may be 10 to 30/70 to 99.
- an acid group such as a carboxyl group derived from an ethylenically unsaturated carboxylic acid monomer is neutralized so that the degree of neutralization in the composition is 50 mol% or more, and a salt form is obtained.
- the degree of neutralization is more preferably 60 mol% or more, further preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 85 mol% or more, and particularly preferably It is 90 mol% or more.
- the upper limit of the degree of neutralization is 100 mol% and may be 98 mol% or less, or 95 mol% or less.
- the range of the degree of neutralization can be appropriately combined with the lower limit value and the upper limit value, and may be, for example, 50 mol% or more and 100 mol% or less, or 70 mol% or more and 100 mol% or less. , 80 mol% or more and 100 mol% or less.
- the degree of neutralization is 50 mol% or more, the water swellability is good and the dispersion stabilizing effect is easily obtained, which is preferable.
- the degree of neutralization is 80 mol% or more, the viscosity of the present composition (electrode slurry) containing an active material and the like is greatly reduced. In this case, an electrode having a smooth surface can be obtained, which is preferable.
- the concentration of the present composition can be increased, the amount of solvent removed by drying can be reduced, which is also preferable from the viewpoint of productivity.
- the type of salt of the block polymer is not particularly limited, but alkali metal salts such as lithium, sodium and potassium; alkaline earth metal salts such as calcium salt and barium salt; other metal salts such as magnesium salt and aluminum salt.
- alkali metal salts and magnesium salts are preferred, alkali metal salts are more preferred, and lithium salts and potassium salts are even more preferred, because they are unlikely to adversely affect battery characteristics.
- the particle size (dry particle size) of the block polymer at the time of drying is not particularly limited, but for example, the volume-based median size can be in the range of 0.03 ⁇ m or more and 3 ⁇ m or less.
- the range of the particle diameter may be 0.1 ⁇ m or more and 1 ⁇ m or less, or 0.3 ⁇ m or more and 0.8 ⁇ m or less.
- the water-swollen particle size of the block polymer is not particularly limited, but can be, for example, a volume-based median size of 0.1 ⁇ m or more and 10.0 ⁇ m or less.
- the particle size range may be 0.1 ⁇ m or more and 8.0 ⁇ m or less, 0.1 ⁇ m or more and 7.0 ⁇ m or less, or 0.2 ⁇ m or more and 5.0 ⁇ m or less. It may be 0.5 ⁇ m or more and 3.0 ⁇ m or less.
- the water-swollen particle size can be obtained by measuring the particle size of a block polymer having a degree of neutralization based on the carboxyl groups of 80 to 100 mol% when dispersed in water.
- the particle size distribution which is a value obtained by dividing the volume-based average particle size of the water-swollen particle size by the number-based average particle size, is, for example, 10 or less, may be 5.0 or less, and is 3.0 or less. It may be 1.5 or less.
- the lower limit of the particle size distribution is usually 1.0.
- the block copolymer is not particularly limited as long as a block copolymer having the polymer block (A) and the polymer block (B) is obtained, and a known production method can be adopted. For example, a method utilizing various control polymerization methods such as living radical polymerization and living anionic polymerization, a method of coupling polymers having functional groups, and the like can be mentioned.
- a polymer block (A)/polymer block (B )/Method for obtaining a polymer having a structural unit consisting of the polymer block (A) is also included.
- the living radical polymerization method is preferable from the viewpoints of easy operation and application to a wide range of monomers.
- any process such as a batch process, a semi-batch process, a tubular continuous polymerization process, and a continuous stirred tank type process (CSTR) may be adopted.
- the polymerization method can be applied to various modes such as bulk polymerization without using a solvent, solvent-based solution polymerization, water-based emulsion polymerization, mini-emulsion polymerization or suspension polymerization.
- the type of living radical polymerization method is also not particularly limited, and reversible addition-cleavage chain transfer polymerization method (RAFT method), nitroxy radical method (NMP method), atom transfer radical polymerization method (ATRP method), organic tellurium compound
- RAFT method reversible addition-cleavage chain transfer polymerization method
- NMP method nitroxy radical method
- ATRP method atom transfer radical polymerization method
- organic tellurium compound It is possible to employ various polymerization methods such as a polymerization method using a (TERP method), a polymerization method using an organic antimony compound (SBRP method), a polymerization method using an organic bismuth compound (BIRP method), and an iodine transfer polymerization method.
- the RAFT method is preferable from the viewpoint of obtaining a block polymer having excellent controllability of polymerization, simple implementation, and binding property.
- RAFT agent a specific polymerization control agent
- RAFT agent a specific polymerization control agent
- RAFT agent various known RAFT agents such as a dithioester compound, a xanthate compound, a trithiocarbonate compound and a dithiocarbamate compound can be used.
- the RAFT agent may be a monofunctional one having only one active site, or a bifunctional or higher functional one.
- a bifunctional RAFT agent is preferably used from the viewpoint of easily obtaining the block copolymer having the A-(BA) n-type structure efficiently.
- the amount of RAFT agent used is appropriately adjusted depending on the type of monomer and RAFT agent used.
- a known radical polymerization initiator such as an azo compound, an organic peroxide and a persulfate can be used as a polymerization initiator used in the polymerization by the RAFT method.
- Azo compounds are preferred because side reactions are unlikely to occur.
- azo compound examples include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2, 4-dimethylvaleronitrile), dimethyl-2,2'-azobis(2-methylpropionate), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-) Carbonitrile), 2,2′-azobis[N-(2-propenyl)-2-methylpropionamide], 2,2′-azobis(N-butyl-2-methylpropionamide) and the like.
- the radical polymerization initiators may be used alone or in combination of two or more.
- the ratio of the radical polymerization initiator used is not particularly limited, but from the viewpoint of obtaining a polymer having a smaller molecular weight distribution, the amount of the radical polymerization initiator used is preferably 0.5 mol or less relative to 1 mol of the RAFT agent, It is more preferable that the amount is 0.2 mol or less. Further, from the viewpoint of stably performing the polymerization reaction, the lower limit of the amount of the radical polymerization initiator used with respect to 1 mol of the RAFT agent is 0.001 mol.
- the amount of the radical polymerization initiator used with respect to 1 mol of the RAFT agent is preferably in the range of 0.001 mol or more and 0.5 mol or less, and more preferably in the range of 0.005 mol or more and 0.2 mol or less.
- the reaction temperature in the polymerization reaction by the RAFT method is preferably 30°C or higher and 120°C or lower, more preferably 40°C or higher and 110°C or lower, and further preferably 50°C or higher and 100°C or lower.
- the reaction temperature is 30° C. or higher, the polymerization reaction can proceed smoothly.
- the reaction temperature is 120° C. or lower, side reactions can be suppressed, and restrictions on usable initiators and solvents can be relaxed.
- known polymerization solvents can be used in living radical polymerization.
- aromatic compounds such as benzene, toluene, xylene and anisole
- ester compounds such as methyl acetate, ethyl acetate, propyl acetate and butyl acetate
- ketone compounds such as acetone and methyl ethyl ketone
- dimethylformamide, acetonitrile, dimethyl sulfoxide examples thereof include alcohol and water.
- the polymer block (B) is preferably obtained by precipitation polymerization and suspension polymerization (reverse phase suspension polymerization) from the viewpoint of productivity.
- Heterogeneous polymerization methods such as precipitation polymerization, suspension polymerization, and emulsion polymerization are preferable, and precipitation polymerization method is more preferable, from the viewpoint of obtaining better performance in terms of binding property and the like.
- Precipitation polymerization is a method for producing a polymer by carrying out a polymerization reaction in a solvent that dissolves an unsaturated monomer as a raw material but does not substantially dissolve a produced polymer.
- Dispersion stabilizers can also be used to control the particle size of the polymer.
- the secondary aggregation can be suppressed by selecting a dispersion stabilizer, a polymerization solvent and the like.
- precipitation polymerization in which secondary aggregation is suppressed is also called dispersion polymerization.
- a solvent selected from water, various organic solvents, and the like can be used as the polymerization solvent in consideration of the types of monomers to be used.
- a solvent having a small chain transfer constant include water-soluble solvents such as methanol, t-butyl alcohol, acetone, methyl ethyl ketone, acetonitrile and tetrahydrofuran, as well as benzene, ethyl acetate, dichloroethane, n-hexane, cyclohexane and n-heptane.
- the water-soluble solvent refers to one having a solubility in water at 20° C. of more than 10 g/100 ml.
- Methyl ethyl ketone and acetonitrile are preferable in that they are easy), a polymer having a small chain transfer constant and a large degree of polymerization (primary chain length) can be obtained, and that the operation is easy when neutralizing the step described later. ..
- a highly polar solvent water and methanol are preferably mentioned.
- the amount of the highly polar solvent used is preferably 0.05 to 20.0% by mass, more preferably 0.1 to 10.0% by mass, and still more preferably 0.1 to 5%, based on the total mass of the medium. It is 0.0% by mass, and more preferably 0.1 to 1.0% by mass. If the proportion of the highly polar solvent is 0.05% by mass or more, the effect on the neutralization reaction is recognized, and if it is 20.0% by mass or less, no adverse effect on the polymerization reaction is observed.
- the monomer concentration at the time of polymerization for obtaining the polymer block (B) is preferably higher from the viewpoint of obtaining a polymer having a longer primary chain length.
- the monomer concentration at the start of the polymerization is generally in the range of about 2 to 40% by mass, preferably 5 to 40% by mass.
- the “monomer concentration” refers to the monomer concentration in the reaction solution at the time of starting the polymerization.
- the polymer block (B) may be produced by carrying out a polymerization reaction in the presence of a basic compound. By carrying out the polymerization reaction in the presence of a base compound, the polymerization reaction can be stably carried out even under high monomer concentration conditions.
- the monomer concentration may be 13.0% by mass or more, preferably 15.0% by mass or more, more preferably 17.0% by mass or more, and further preferably 19.0% by mass or more. And more preferably 20.0 mass% or more.
- the monomer concentration is more preferably 22.0% by mass or more, and even more preferably 25.0% by mass or more. Generally, the higher the monomer concentration at the time of polymerization, the higher the molecular weight can be made, and when the present polymer is a cross-linked polymer, a polymer having a long primary chain length can be produced.
- the upper limit of the monomer concentration varies depending on the type of the monomer and the solvent used, and the polymerization method and various polymerization conditions, but if the heat of the polymerization reaction can be removed, as described above in the precipitation polymerization. It is about 40%, about 50% for suspension polymerization, and about 70% for emulsion polymerization.
- the basic compound is a so-called alkaline compound, and either an inorganic basic compound or an organic basic compound may be used.
- the polymerization reaction can be stably carried out even under a high monomer concentration condition of, for example, more than 13.0 mass %. Further, the polymer obtained by polymerizing at such a high monomer concentration has a high molecular weight (because of its long primary chain length), and thus has excellent binding properties.
- the inorganic base compound include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide, and the like. One kind or two or more kinds can be used.
- organic base compound examples include ammonia, and organic amine compounds such as monoethylamine, diethylamine and triethylamine, and one or more of them can be used.
- organic amine compound is preferable from the viewpoint of polymerization stability and the binding property of the binder containing the obtained polymer or its salt.
- the amount of the base compound used is preferably in the range of 0.001 mol% or more and 4.0 mol% or less based on the ethylenically unsaturated carboxylic acid monomer. When the amount of the base compound used is within this range, the polymerization reaction can be smoothly carried out.
- the amount used may be 0.05 mol% or more and 4.0 mol% or less, 0.1 mol% or more and 4.0 mol% or less, and 0.1 mol% or more and 3.0 mol% or less. % Or less, or 0.1 mol% or more and 2.0 mol% or less.
- the amount of the basic compound used represents the molar concentration of the basic compound used with respect to the ethylenically unsaturated carboxylic acid monomer, and does not mean the degree of neutralization. That is, the valence of the basic compound used is not considered.
- the block polymer can be obtained in a powder state by distilling off the solvent by subjecting the reaction liquid containing the block polymer to pressure reduction and/or heat treatment. At this time, before distilling off the solvent, unreacted monomers (and salts thereof), for the purpose of removing impurities derived from the initiator, etc., following the polymerization reaction, solid-liquid separation treatment such as centrifugation and filtration, It is preferable to perform a washing treatment using water, methanol, or the same solvent as the polymerization solvent.
- an alkali compound is added to the dispersion containing the block polymer obtained after the polymerization reaction to neutralize the block polymer (hereinafter, also referred to as “step neutralization”), and then in a drying step.
- the solvent may be removed.
- an alkali compound is added when preparing the electrode slurry to neutralize the polymer (hereinafter, also referred to as “post-neutralization”). You may say).
- the step neutralization is preferable because the secondary aggregate tends to be easily loosened.
- composition for secondary battery electrode mixture layer of the present invention contains a binder containing the block polymer, an active material and water.
- the amount of the block polymer used in the composition is, for example, 0.1 part by mass or more and 20 parts by mass or less based on 100 parts by mass of the total amount of the active material.
- the amount used is, for example, 0.2 parts by mass or more and 10 parts by mass or less, for example 0.3 parts by mass or more and 8 parts by mass or less, and for example, 0.4 parts by mass or more and 5 parts by mass or less. .. If the amount of the block polymer used is less than 0.1 part by mass, sufficient binding properties may not be obtained.
- the dispersion stability of the active material and the like becomes insufficient, and the uniformity of the mixture layer formed may decrease.
- the amount of the block polymer used exceeds 20 parts by mass, the composition may have a high viscosity and the coatability on the current collector may be deteriorated. As a result, the obtained mixture layer may have bumps or irregularities, which may adversely affect the electrode characteristics.
- the amount of the block polymer used is within the above range, a composition having excellent dispersion stability can be obtained, and a mixture layer having extremely high adhesion to the current collector can be obtained, resulting in a battery. Durability is improved. Furthermore, the present block polymer exhibits a sufficiently high binding property to the active material even in a small amount (for example, 5% by mass or less), and since it has a carboxy anion, it has a low interfacial resistance and an electrode having excellent high rate characteristics. Is obtained.
- a lithium salt of a transition metal oxide can be used as the positive electrode active material, and for example, layered rock salt-type and spinel-type lithium-containing metal oxides can be used.
- spinel type positive electrode active materials include lithium manganate.
- phosphates include olivine-type lithium iron phosphate.
- the positive electrode active material one of the above may be used alone, or two or more thereof may be used in combination as a mixture or composite.
- the conductive aid include carbon-based materials such as carbon black, carbon nanotubes, carbon fibers, fine graphite powder, and carbon fibers. Among them, carbon black, carbon nanotubes, and carbon fibers are easy to obtain excellent conductivity. , Are preferred. Moreover, as the carbon black, Ketjen black and acetylene black are preferable.
- the conductive auxiliary agent one type described above may be used alone, or two or more types may be used in combination.
- the amount of the conductive aid used can be, for example, 0.2 to 20 parts by mass with respect to 100 parts by mass of the total amount of the active material from the viewpoint of achieving both conductivity and energy density, and can be, for example, 0. It can be 2 to 10 parts by mass.
- a surface-coated carbon-based material having conductivity may be used as the positive electrode active material.
- examples of the negative electrode active material include carbon-based materials, lithium metals, lithium alloys, metal oxides, and the like, and one or more of these may be used in combination.
- active materials made of carbon-based materials such as natural graphite, artificial graphite, hard carbon and soft carbon (hereinafter, also referred to as “carbon-based active material”) are preferable, and graphite such as natural graphite and artificial graphite, and Hard carbon is more preferred.
- graphite spheroidized graphite is preferably used from the viewpoint of battery performance, and the preferable particle size range is, for example, 1 to 20 ⁇ m and, for example, 5 to 15 ⁇ m.
- a metal or metal oxide capable of occluding lithium such as silicon and tin can be used as the negative electrode active material.
- silicon has a higher capacity than graphite, and active materials made of silicon-based materials such as silicon, silicon alloys, and silicon oxides such as silicon monoxide (SiO) (hereinafter, also referred to as “silicon-based active material”).
- silicon-based active material has a high capacity, but on the other hand, its volume changes greatly with charge and discharge. Therefore, it is preferable to use the carbon-based active material together.
- the amount of the silicon-based active material added is large, the electrode material may be collapsed, and the cycle characteristics (durability) may be significantly reduced.
- the amount thereof is, for example, 60% by mass or less, and for example, 30% by mass or less, based on the carbon-based active material.
- the binder containing this block polymer has a structural unit (component (a)) derived from an ethylenically unsaturated carboxylic acid monomer.
- component (a) has a high affinity for the silicon-based active material and exhibits a good binding property. Therefore, the binder of the present invention exhibits excellent binding properties even when a high-capacity type active material containing a silicon-based active material is used, and is therefore effective for improving the durability of the obtained electrode. Thought to be a thing.
- the carbon-based active material itself has good electrical conductivity, it is not always necessary to add a conductive auxiliary agent.
- a conductive additive is added for the purpose of further reducing the resistance, the amount used is, for example, 10 parts by mass or less, and 5 parts by mass or so with respect to 100 parts by mass of the total amount of the active material from the viewpoint of energy density. It is less than or equal to parts by weight.
- the amount of the active material used is, for example, in the range of 10 to 75% by mass, or in the range of 30 to 65% by mass, based on the total amount of the composition.
- the amount of the active material used is 10% by mass or more, migration of the binder and the like can be suppressed, and it is also advantageous in terms of medium drying cost.
- it is 75% by mass or less, the fluidity and coatability of the composition can be secured, and a uniform mixture layer can be formed.
- the amount of the active material used is in the range of, for example, 60 to 97% by mass, or 70 to 90% by mass, based on the total amount of the composition. It is a range. From the viewpoint of energy density, it is preferable that the amount of non-volatile components other than the active material such as the binder and the conductive additive be as small as possible within the range in which the required binding property and conductivity are ensured.
- the composition uses water as a medium.
- lower alcohols such as methanol and ethanol
- carbonates such as ethylene carbonate
- ketones such as acetone
- water-soluble organic solvents such as tetrahydrofuran and N-methylpyrrolidone.
- the proportion of water in the mixed medium is, for example, 50% by mass or more and, for example, 70% by mass or more.
- the content of the medium containing water in the entire composition is the coatability of the slurry, and the energy cost required for drying, from the viewpoint of productivity, for example,
- the amount may be in the range of 25 to 90% by mass, and may be, for example, 35 to 70% by mass.
- the content of the medium can be, for example, in the range of 3 to 40 mass% from the viewpoint of the uniformity of the mixture layer after pressing, and is, for example, 10%. It can be in the range of up to 30% by mass.
- the binder of the present invention may be composed of only the block polymer, but other binder components such as styrene/butadiene latex (SBR), acrylic latex and polyvinylidene fluoride latex may be used. You may use together.
- SBR styrene/butadiene latex
- acrylic latex acrylic latex
- polyvinylidene fluoride latex based on 100 parts by mass of the total amount of the active material.
- the amount can be less than or equal to parts, and can be, for example, 0.1 to 1 part by weight or less. If the amount of the other binder component used exceeds 5 parts by mass, the resistance may increase and the high rate property may become insufficient.
- a styrene/butadiene latex is preferable because it has an excellent balance of binding property and flex resistance.
- the styrene/butadiene latex is a copolymer having a structural unit derived from an aromatic vinyl monomer such as styrene and a structural unit derived from an aliphatic conjugated diene monomer such as 1,3-butadiene.
- An aqueous dispersion is shown.
- the aromatic vinyl monomer include ⁇ -methylstyrene, vinyltoluene, divinylbenzene and the like in addition to styrene, and one or more of these can be used.
- the structural unit derived from the aromatic vinyl monomer in the copolymer may be in the range of, for example, 20 to 70% by mass mainly from the viewpoint of binding property, and may be, for example, 30 to 60. It can be in the range of mass%.
- Examples of the aliphatic conjugated diene-based monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3- Butadiene and the like can be mentioned, and one or more of these can be used.
- the structural unit derived from the aliphatic conjugated diene-based monomer in the copolymer is, for example, 30 to 70% by mass in that the binding property of the binder and the flexibility of the obtained electrode are good. It may be in the range of, and for example, in the range of 40 to 60% by mass.
- the styrene/butadiene-based latex is a nitrile group-containing monomer such as (meth)acrylonitrile, or (meth), in order to further improve performance such as binding property.
- a carboxyl group-containing monomer such as acrylic acid, itanconic acid or maleic acid, or an ester group-containing monomer such as methyl (meth)acrylate may be used as the copolymerization monomer.
- the structural unit derived from the other monomer in the copolymer can be, for example, in the range of 0 to 30% by mass, and can be in the range of, for example, 0 to 20% by mass.
- the present composition has the above-mentioned active material, water and binder as essential constituent components, and can be obtained by mixing the components using a known means.
- the mixing method of each component is not particularly limited, and a known method can be adopted, but after dry blending the powder components such as the active material, the conductive additive and the carboxyl group-containing polymer particles that are the binder, A method of mixing with a dispersion medium such as water and kneading with dispersion is preferable.
- a dispersion medium such as water and kneading with dispersion is preferable.
- a known mixer such as a planetary mixer, a thin film swirl mixer, and a revolving mixer can be used, but a thin film swirl mixer is used in that a good dispersion state can be obtained in a short time. It is preferable to carry out.
- a thin film swirling mixer it is preferable to carry out preliminary dispersion with a stirrer such as a disper in advance.
- the viscosity of the slurry may be, for example, in the range of 500 to 100,000 mPa ⁇ s as the B-type viscosity at 60 rpm, and may be in the range of 1,000 to 50,000 mPa ⁇ s. it can.
- composition when the composition is obtained in a wet powder state, it is preferable to use a Henschel mixer, a blender, a planetary mixer, a twin-screw kneader, or the like to knead the mixture to a uniform state without unevenness in concentration.
- the secondary battery electrode of the present invention comprises a mixture layer formed of the present composition on the surface of a collector such as copper or aluminum.
- the mixture layer is formed by applying the present composition on the surface of a current collector and then removing a medium such as water by drying.
- the method for applying the present composition is not particularly limited, and a known method such as a doctor blade method, a dip method, a roll coating method, a comma coating method, a curtain coating method, a gravure coating method and an extrusion method may be adopted. it can. Further, the drying can be performed by a known method such as blowing hot air, reducing pressure, (far) infrared rays, or irradiating with microwaves.
- the mixture layer obtained after drying is subjected to compression treatment by a die press, a roll press or the like.
- compression treatment By compressing, the active material and the binder can be brought into close contact with each other, and the strength of the mixture layer and the adhesion to the current collector can be improved.
- the thickness of the mixture layer can be adjusted by compression to, for example, about 30 to 80% before compression, and the thickness of the mixture layer after compression is generally about 4 to 200 ⁇ m.
- the electrolytic solution may be liquid or gel.
- the separator is disposed between the positive electrode and the negative electrode of the battery, and plays a role of preventing a short circuit due to contact of both electrodes and holding an electrolytic solution to ensure ionic conductivity.
- the separator is preferably a film-like insulating microporous film having good ion permeability and mechanical strength.
- polyolefins such as polyethylene and polypropylene, polytetrafluoroethylene and the like can be used.
- the electrolytic solution a known one that is generally used depending on the type of active material can be used.
- a specific solvent a cyclic carbonate having a high dielectric constant such as propylene carbonate and ethylene carbonate and a high ability to dissolve an electrolyte, and a chain having a low viscosity such as ethylmethyl carbonate, dimethyl carbonate and diethyl carbonate. Carbonates and the like, which can be used alone or as a mixed solvent.
- the electrolytic solution is used by dissolving a lithium salt such as LiPF 6 , LiSbF 6 , LiBF 4 , LiClO 4 , LiAlO 4 in these solvents.
- an aqueous solution of potassium hydroxide can be used as the electrolytic solution.
- the secondary battery is obtained by accommodating a positive electrode plate and a negative electrode plate, which are partitioned by a separator, in a spiral shape or a laminated structure in a case or the like.
- the secondary battery electrode binder disclosed in the present specification exhibits excellent binding properties with the electrode material and excellent adhesion properties with the current collector in the mixture layer. Therefore, the secondary battery provided with the electrode obtained by using the binder is expected to be able to ensure good integrity and to show good durability (cycle characteristics) even after repeated charging and discharging. Suitable for secondary batteries for automobiles.
- Tg Glass transition temperature (Tg) measurement conditions
- the Tg of the resulting polymer was determined from the intersection of the tangent line at the inflection point with the baseline of the heat flux curve obtained using a differential scanning calorimeter.
- the heat flux curve was such that about 10 mg of the sample was cooled to ⁇ 60° C., held for 5 minutes, heated to 250° C. at 10° C./min, subsequently cooled to ⁇ 60° C., held for 5 minutes, and then heated to 10° C./min. It was obtained under the condition that the temperature was raised to 250° C. in min.
- Measuring instrument TA Instrument (Q-100) Measurement atmosphere: under nitrogen atmosphere
- the reaction rate based on the gas chromatography measurement was 79% with respect to the total amount of phenoxyethyl acrylate, and the result of GPC measurement under the same conditions as in Production Example 1-1 showed that Mn9,100, Mw10,700 and Mw/Mn were 1 It was 0.17.
- the Tg measured by DSC was -20°C.
- the reaction rate based on the gas chromatography measurement was 77% with respect to the total amount of BA used, and the GPC measurement was conducted under the same conditions as in Production Example 1-1.
- Mn8,900, Mw10,200, and Mw/Mn were 1 It was .15.
- the Tg measured by DSC was -50°C.
- the reaction rate based on the total amount of anhydrous MLA and St used was 71% based on the gas chromatography measurement.
- Mn 13,800, Mw 22,200, and Mw/Mn were It was 1.61.
- the Tg measured by DSC was 107°C.
- the reaction rate based on the gas chromatography measurement was 74% with respect to the total amount of PhMI and St used.
- Mn 13,100, Mw 31,100 and Mw/Mn were 2 It was .37.
- the Tg measured by DSC was 213°C.
- St Styrene PhMI: N-phenylmaleimide
- AN Acrylonitrile
- PEA Phenoxyethyl acrylate
- BA n-Butyl acrylate
- MLA Maleic anhydride
- ACMO Acryloylmorpholine
- DBTTC Dibenzyltrithiocarbonate
- PEI 1-phenylethyl Iodide
- ABN-E 2,2'-azobis(2-methylbutyronitrile) (manufactured by Nippon Finechem Co., Ltd.)
- the internal temperature was maintained at 65° C., cooling of the reaction solution was started 12 hours after the start of polymerization, and the internal temperature was lowered to 25° C., after which lithium hydroxide monohydrate (hereinafter, referred to as “LiOH 52.4 parts of a powder of "H 2 O”) was added. After the addition, stirring was continued at room temperature for 12 hours to obtain a slurry-like polymerization reaction liquid in which particles of the block polymer R-1 (Li salt, neutralization degree: 90 mol%) consisting of ABA triblock were dispersed in a medium. It was The reaction rate of AA at the time point 12 hours after the initiation of polymerization was 97%.
- Production Examples 2-2 to 2-13, Comparative Production Examples 2-1 to 2-2: Production of Polymers R-2 to R-15 The same operation as in Production Example 2-1 was carried out except that the amounts of the respective raw materials charged were as shown in Table 2, to obtain a polymerization reaction liquid containing the polymers R-2 to R-15. Then, the same operation as in Production Example 2-1 was performed on each of the polymerization reaction liquids to obtain powdery polymers R-2 to R-15. Each polymer was hermetically stored in a container having a water vapor barrier property. In Production Example 2-11, polymer Na salt (neutralization degree: 90 mol%) was obtained by using NaOH instead of the LiOH.H 2 O powder.
- the polymers R-2 to R-7 and R-9 to R-13 are block polymers composed of ABA triblocks, and R-8 is a block polymer composed of AB diblocks. is there.
- R-14 and R-15 are non-block polymers.
- AA Acrylic acid
- HEA 2-Hydroxyethyl acrylate
- St Styrene
- T-20 Trimethylolpropane diallyl ether (manufactured by Daiso, trade name "Neoallyl T-20")
- TEA triethylamine
- V-65 2,2'-azobis(2,4-dimethylvaleronitrile) (Fuji Film Wako Pure Chemical Industries, Ltd.)
- LiOH/H 2 O Lithium hydroxide monohydrate
- NaOH Sodium hydroxide
- Example>> Regarding the composition for an electrode mixture layer using graphite, which is an active material for a negative electrode, or graphite and silicon particles as an active material, and using a block polymer as a binder, the viscosity (electrode slurry viscosity) and formation of the composition The peeling strength (that is, the binding property of the binder) between the prepared mixture layer/current collector was measured. Natural graphite (manufactured by Nippon Graphite Co., Ltd., trade name “CGB-10”) was used as the graphite, and Si nanopowder (manufactured by Sigma-Aldrich, particle diameter ⁇ 100 nm) was used as the silicon particles.
- Natural graphite manufactured by Nippon Graphite Co., Ltd., trade name “CGB-10”
- Si nanopowder manufactured by Sigma-Aldrich, particle diameter ⁇ 100 nm
- Example 1 3.2 parts of the powdery block polymer R-1 was weighed in 100 parts of natural graphite, mixed well in advance, 210 parts of ion-exchanged water was added and predispersed with a disper, and then a thin film swirling mixer ( Using FM-56-30 manufactured by Primix Co., Ltd., main dispersion was performed for 15 seconds at a peripheral speed of 20 m/sec to obtain a slurry composition for electrode mixture layer (electrode slurry). The solid content concentration of the electrode slurry was calculated to be 33.0%.
- the above electrode slurry was applied onto a 12 ⁇ m thick copper foil (manufactured by Furukawa Electric Co., Ltd.) and dried at 100° C. for 15 minutes in a ventilation dryer to form a mixture layer. .. Then, the mixture layer was rolled so that the thickness was 50 ⁇ 5 ⁇ m and the packing density was 1.60 ⁇ 0.20 g/cm 3 to obtain a negative electrode.
- the negative electrode obtained above was cut into a strip having a width of 25 mm, and the mixture layer surface of the negative electrode was attached to a double-sided tape fixed on a horizontal surface to prepare a sample for peel test. After the test sample was dried under reduced pressure conditions at 60° C. overnight, 90° peeling (measurement temperature 23° C.) at a pulling speed of 50 mm/min was performed to measure the peel strength between the mixture layer and the copper foil. The peel strength was as high as 12.8 N/m, which was good.
- Examples 2 to 15 and Comparative Examples 1 to 2 An electrode slurry was prepared by performing the same operations as in Example 1 except that the carboxyl group-containing polymer salt used as the active material and the binder was used as shown in Table 3.
- the carboxyl group-containing polymer salt used as the active material and the binder was used as shown in Table 3.
- natural graphite and silicon particles were stirred at 400 rpm for 1 hour using a planetary ball mill (P-5, manufactured by FRITSCH), and the resulting mixture was used as a powdery block polymer.
- 3.2 parts of R-3 (Li salt) was weighed and mixed well in advance, and then the same operation as in Example 1 was performed to prepare an electrode slurry. The viscosity of each electrode slurry and the 90° peel strength (binding property) of the obtained negative electrode were evaluated, and the results are shown in Table 3.
- Each of the examples is a composition for an electrode mixture layer containing a binder for a secondary battery electrode according to the present invention and an electrode prepared by using the composition.
- the peel strength between the mixture layer of the electrode and the current collector obtained from the composition for each electrode mixture layer (electrode slurry) was high, showing excellent binding properties. It was Further, in comparison with Example 7 in which the Tg of the polymer block (A) is less than ⁇ 30° C., in other examples in which the Tg of the polymer block (A) is ⁇ 30° C. or more, the peel strength is further improved. It was found to be high and preferable in terms of binding property.
- the degree of neutralization of the block polymer is 80 mol% or more.
- the electrode slurry had a low viscosity and was preferable in terms of coatability and productivity.
- the peel strengths of the polymers having no polymer block (A) in Comparative Examples 1 and 2 were lower than those of the Examples.
- the binder for secondary battery electrodes of the present invention exhibits excellent binding properties in the mixture layer. Therefore, the secondary battery provided with the electrode obtained by using the binder is expected to exhibit good durability (cycle characteristics), and is expected to be applied to a vehicle-mounted secondary battery. It is also useful for using an active material containing silicon, and is expected to contribute to higher capacity of batteries.
- the binder for secondary battery electrodes of the present invention can be suitably used particularly for non-aqueous electrolyte secondary battery electrodes, and is particularly useful for non-aqueous electrolyte lithium ion secondary batteries having high energy density.
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Abstract
Description
特許文献1では、特定の架橋剤によりポリアクリル酸を架橋したポリマーを結着剤として用いることにより、シリコンを含む活物質を用いた場合であっても電極構造が破壊されることのない電極の提供が可能であることが記載されている。特許文献2には、アクリル酸由来のモノマー単位を構成成分に含み、特定の架橋剤により架橋したポリマーからなるリチウム電池用結着剤が記載され、充放電を繰り返した場合であっても高い容量維持率を示すことが記載されている。
また、同じく結着性等の性能向上を目的として、ブロック重合体を利用したバインダーが検討されている特許文献3には、酸成分を有するビニルモノマーの構造単位を含むセグメント、及び(メタ)アクリル酸アルキルエステルモノマーの構造単位を含むセグメントを有するブロック共重合体を含むバインダーが開示されている。
〔1〕重合体ブロック(A)及び重合体ブロック(B)を有するブロック重合体を含む二次電池電極用バインダーであって、
前記重合体ブロック(A)は、当該重合体ブロック(A)の全構造単位に基づく(メタ)アクリル酸に由来する構造単位が30質量%未満であり、
前記重合体ブロック(B)は、当該重合体ブロック(B)の全構造単位に基づく(メタ)アクリル酸に由来する構造単位が30質量%以上、100質量%以下である、二次電池電極用バインダー。
〔2〕前記ブロック重合体における前記重合体ブロック(A)の割合は、0.1質量%以上、80質量%以下であり、
前記ブロック重合体における前記重合体ブロック(B)の割合は、20質量%以上、99.9質量%以下である、〔1〕に記載の二次電池電極用バインダー。
〔3〕前記重合体ブロック(A)は、ガラス転移温度(Tg)が-30℃以上である、〔1〕又は〔2〕に記載の二次電池電極用バインダー。
〔4〕前記ブロック重合体は、当該ブロック重合体が有するカルボキシル基の80モル%以上が中和された塩である、〔1〕~〔3〕のいずれか一に記載の二次電池電極用バインダー。
〔5〕前記重合体ブロック(B)が、(メタ)アクリル酸及び架橋性単量体を含む単量体組成物を重合して得られる重合体ブロックである、〔1〕~〔4〕のいずれか一に記載の二次電池電極用バインダー。
〔6〕〔1〕~〔5〕のいずれか一に記載の二次電池電極用バインダー、活物質及び水を含む二次電池電極合剤層用組成物。
〔7〕集電体表面に、〔1〕~〔5〕のいずれか一に記載の二次電池電極用バインダー含有する電極合剤層を備えた二次電池電極。
〔8〕二次電池電極バインダーに用いるブロック重合体の製造方法であって、
前記ブロック重合体は、重合体ブロック(A)及び重合体ブロック(B)を有し、
リビングラジカル重合法により(メタ)アクリル酸の含有量が30質量%未満である単量体成分を重合し、前記重合体ブロック(A)を製造する工程と、
前記重合体ブロック(A)の存在下、(メタ)アクリル酸を30質量%以上、100質量%以下含む単量体成分を重合して前記重合体ブロック(B)を製造する工程と、を有する、ブロック重合体の製造方法。
〔9〕前記リビングラジカル重合法が、可逆的付加-開裂連鎖移動重合法(RAFT法)である、〔8〕に記載のブロック重合体の製造方法。
尚、本明細書において、「(メタ)アクリル」とは、アクリル及び/又はメタクリルを意味し、「(メタ)アクリレート」とは、アクリレート及び/又はメタクリレートを意味する。また、「(メタ)アクリロイル基」とは、アクリロイル基及び/又はメタクリロイル基を意味する。
本発明の二次電池電極用バインダーは、ブロック重合体(以下、「本ブロック重合体」ともいう)を含む。本ブロック重合体は、(メタ)アクリル酸に由来する構造単位が30質量%未満である重合体ブロック(A)、及び(メタ)アクリル酸に由来する構造単位が30質量%以上、100質量%以下である重合体ブロック(B)を有する。以下、本ブロック重合体について詳述する。
重合体ブロック(A)は、(メタ)アクリル酸に由来する構造単位が30質量%未満である重合体ブロックであり、例えば、(メタ)アクリル酸の含有量が30質量%未満である単量体組成物を重合することにより得ることができる。上記単量体組成物における(メタ)アクリル酸の含有量は、20質量%以下であってもよく、10質量%以下であってもよく、0質量%であってもよい。
重合体ブロック(A)の全構成単量体に対する(a)成分の総量は、70質量%超であり、80質量%以上であってもよく、90質量%以上であってもよく、100質量%であってもよい。
(メタ)アクリル酸フェニル、(メタ)アクリル酸フェニルメチル、(メタ)アクリル酸フェニルエチル、(メタ)アクリル酸フェノキシエチル等の芳香族(メタ)アクリル酸エステル化合物;
(メタ)アクリル酸2-メトキシエチル、(メタ)アクリル酸エトキシエチル等の(メタ)アクリル酸アルコキシアルキルエステル化合物;
(メタ)アクリル酸ヒドロキシエチル、(メタ)アクリル酸ヒドロキシプロピル及び(メタ)アクリル酸ヒドロキシブチル等の(メタ)アクリル酸ヒドロキシアルキルエステル化合物等が挙げられ、これらの内の1種を単独で使用してもよいし、2種以上を組み合わせて使用してもよい。活物質との密着性及びサイクル特性の観点からは、芳香族(メタ)アクリル酸エステル化合物を好ましく用いることができる。
重合体ブロック(B)は、(メタ)アクリル酸に由来する構造単位が30質量%以上、100質量%以下である重合体ブロックであり、例えば、(メタ)アクリル酸の含有量が30質量%以上、100質量%以下である単量体組成物を重合することにより得ることができる。係る範囲で(メタ)アクリル酸に由来する構造単位を含有することで、集電体に対する優れた接着性を容易に確保することができる。(メタ)アクリル酸に由来する構造単位の下限が50質量%以上の場合、本組成物の分散安定性が良好となり、より高い結着力が得られるためより好ましい。下限は、60質量%以上であってもよく、70質量%以上であってもよく、80質量%以上であってもよい。また、上限値は、例えば、99.9質量%以下であり、また例えば99.5質量%以下であり、また例えば99質量%以下であり、また例えば98質量%以下であり、また例えば95質量%以下であり、また例えば90質量%以下であり、また例えば80質量%以下である。範囲としては、こうした下限及び上限を適宜組み合わせた範囲とすることができるが、例えば、50質量%以上、100質量%以下であり、また例えば50質量%以上、99.9質量%以下であり、また例えば50質量%以上、99質量%以下であり、また例えば70質量%以上、99質量%以下であり、また例えば80質量%以上、99質量%以下などとすることができる。
同様に、上記架橋性単量体の使用量は、架橋性単量体以外の単量体(非架橋性単量体)の総量に対して0.02~0.7モル%であることが好ましく、0.03~0.4モル%であることがより好ましい。
本ブロック共重合体は、重合体ブロック(A)及び重合体ブロック(B)を各々1つ以上有していればよく、例えば重合体ブロック(A)及び重合体ブロック(B)からなる(AB)ジブロック体、重合体ブロック(A)/重合体ブロック(B)/重合体ブロック(A)からなる(ABA)トリブロック体又は(BAB)トリブロック体等が挙げられる。また、重合体ブロック(A)及び重合体ブロック(B)以外の重合体ブロック(C)を含む、(ABC)又は(ABCA)等の構造を有するものであってもよい。中でも、本ブロック共重合体は、A-(BA)n(nは1以上の整数)構造を有することが好ましい。係る構造であると、本ブロック共重合体によって発現するミクロ相分離構造が、ドメイン間で橋掛け構造を形成する点で好適である。尚、上記A-(BA)n構造は共重合体の全部又は一部に存在すればよく、例えば(BABAB)構造からなる共重合体などであってもよい。本ブロック重合体は、上記ジブロック体及びトリブロック体等に属する2種以上のブロック重合体の混合物であってもよい。また、ブロック重合体以外に、重合体ブロック(A)のみからなる重合体、又は重合体ブロック(B)のみからなる重合体等を含んでいてもよい。
一方、本ブロック重合体における重合体ブロック(B)の割合は、20質量%以上、99.9質量%以下とすることができる。こうした範囲であれば、良好な結着性を発揮することができる。重合体ブロック(B)の割合は、30質量%以上であってもよく、50質量%以上であってもよく、70質量%以上であってもよく、90質量%以上であってもよい。重合体ブロック(B)の割合は、99.5質量%以下であってもよく、99質量%以下であってもよく、98質量%以下であってもよく、95質量%以下であってもよく、90質量%以下であってもよく、80質量%以下であってもよい。
本明細書では、上記中和度は、カルボキシル基等の酸基を有する単量体及び中和に用いる中和剤の仕込み値から計算により算出することができる。なお、中和度は架橋重合体又はその塩を、減圧条件下、80℃で3時間乾燥処理後の粉末をIR測定し、カルボン酸のC=O基由来のピークとカルボン酸塩のC=O基由来のピークの強度比より確認することができる。
水膨潤粒子径は、本ブロック重合体が有するカルボキシル基に基づく中和度が80~100モル%であるものを水中に分散させた際の粒子径を測定することにより得られる。架橋重合体が未中和若しくは中和度80モル%未満の場合は、アルカリ金属水酸化物等により中和度80~100モル%に中和し、水中に分散させた際の粒子径を測定すればよい。
水膨潤粒子径の体積基準平均粒子径を個数基準平均粒子径で除した値である粒子径分布は、例えば10以下であり、5.0以下であってもよく、3.0以下であってもよく、1.5以下であってもよい。上記粒子径分布の下限値は、通常は1.0である。
本ブロック共重合体は、重合体ブロック(A)及び重合体ブロック(B)を有するブロック共重合体を得る限りにおいて特段の制限を受けるものではなく、公知の製造方法を採用することができる。例えば、リビングラジカル重合及びリビングアニオン重合等の各種制御重合法を利用する方法や、官能基を有する重合体同士をカップリングする方法等を挙げることができる。また、例えば、重合体ブロック(A)を有するマクロモノマーを、重合体ブロック(B)を構成する単量体とともに共重合することにより、分子内に重合体ブロック(A)/重合体ブロック(B)/前記重合体ブロック(A)からなる構造単位を有する重合体を得る方法も含まれる。これらの中でも、操作が簡便であり、広い範囲の単量体に対して適用することができる観点から、リビングラジカル重合法が好ましい。
リビングラジカル重合法の種類についても特段の制限はなく、可逆的付加-開裂連鎖移動重合法(RAFT法)、ニトロキシラジカル法(NMP法)、原子移動ラジカル重合法(ATRP法)、有機テルル化合物を用いる重合法(TERP法)、有機アンチモン化合物を用いる重合法(SBRP法)、有機ビスマス化合物を用いる重合法(BIRP法)及びヨウ素移動重合法等の各種重合方法を採用することができる。これらの内でも、重合の制御性と実施の簡便さ、及び結着性に優れるブロック重合体が得られる点から、RAFT法が好ましい。
また、RAFT剤の使用量は、用いる単量体及びRAFT剤の種類等により適宜調整される。
沈殿重合は、原料である不飽和単量体を溶解するが、生成する重合体を実質溶解しない溶媒中で重合反応を行うことにより重合体を製造する方法である。重合の進行とともにポリマー粒子は凝集及び成長により大きくなり、数十nm~数百nmの一次粒子が数μm~数十μmに二次凝集したポリマー粒子の分散液が得られる。ポリマーの粒子サイズを制御するために分散安定剤を使用することもできる。
尚、分散安定剤や重合溶剤等を選定することにより上記二次凝集を抑制することもできる。一般に、二次凝集を抑制した沈殿重合は、分散重合とも呼ばれる。
具体的な重合溶媒としては、メタノール、t-ブチルアルコール、アセトン、メチルエチルケトン、アセトニトリル及びテトラヒドロフラン等の水溶性溶剤の他、ベンゼン、酢酸エチル、ジクロロエタン、n-ヘキサン、シクロヘキサン及びn-ヘプタン等が挙げられ、これらの1種を単独であるいは2種以上を組み合わせて用いることができる。又は、これらと水との混合溶媒として用いてもよい。本発明において水溶性溶剤とは、20℃における水への溶解度が10g/100mlより大きいものを指す。
上記の内、粗大粒子の生成や反応器への付着が小さく重合安定性が良好であること、析出した重合体微粒子が二次凝集しにくい(若しくは二次凝集が生じても水媒体中で解れやすい)こと、連鎖移動定数が小さく重合度(一次鎖長)の大きい重合体が得られること、及び後述する工程中和の際に操作が容易であること等の点で、メチルエチルケトン及びアセトニトリルが好ましい。
なお、本明細書において「単量体濃度」とは、重合を開始する時点における反応液中の単量体濃度を示す。
無機塩基化合物としては、水酸化リチウム、水酸化ナトリウム、水酸化カリウム等のアルカリ金属水酸化物、水酸化カルシウム、水酸化マグネシウム等のアルカリ土類金属水酸化物等が挙げられ、これらの内の1種又は2種以上を用いることができる。
有機塩基化合物としては、アンモニア、並びに、モノエチルアミン、ジエチルアミン及びトリエチルアミン等有機アミン化合物が挙げられ、これらの内の1種又は2種以上を用いることができる。中でも、重合安定性及び得られる重合体又はその塩を含むバインダーの結着性の観点から、有機アミン化合物が好ましい。
尚、本明細書では、塩基化合物の使用量は、エチレン性不飽和カルボン酸単量体に対して用いた塩基化合物のモル濃度を表したものであり、中和度を意味するものではない。すなわち、用いる塩基化合物の価数は考慮しない。
本発明の二次電池電極合剤層用組成物は、本ブロック重合体を含有するバインダー、活物質及び水を含む。
本組成物における本ブロック重合体の使用量は、活物質の全量100質量部に対して、例えば、0.1質量部以上20質量部以下である。上記使用量は、また例えば、0.2質量部以上10質量部以下であり、また例えば0.3質量部以上8質量部以下であり、また例えば0.4質量部以上5質量部以下である。本ブロック重合体の使用量が0.1質量部未満の場合、十分な結着性が得られないことがある。また、活物質等の分散安定性が不十分となり、形成される合剤層の均一性が低下する場合がある。一方、本ブロック重合体の使用量が20質量部を超える場合、本組成物が高粘度となり集電体への塗工性が低下することがある。その結果、得られた合剤層にブツや凹凸が生じて電極特性に悪影響を及ぼす虞がある。
上記共重合体中における上記その他の単量体に由来する構造単位は、例えば、0~30質量%の範囲とすることができ、また例えば、0~20質量%の範囲とすることができる。
本発明の二次電池電極は、銅又はアルミニウム等の集電体表面に本組成物から形成される合剤層を備えてなるものである。合剤層は、集電体の表面に本組成物を塗工した後、水等の媒体を乾燥除去することにより形成される。本組成物を塗工する方法は特に限定されず、ドクターブレード法、ディップ法、ロールコート法、コンマコート法、カーテンコート法、グラビアコート法及びエクストルージョン法などの公知の方法を採用することができる。また、上記乾燥は、温風吹付け、減圧、(遠)赤外線、マイクロ波照射等の公知の方法により行うことができる。
通常、乾燥後に得られた合剤層には、金型プレス及びロールプレス等による圧縮処理が施される。圧縮することにより活物質及びバインダーを密着させ、合剤層の強度及び集電体への密着性を向上させることができる。圧縮により合剤層の厚みを、例えば、圧縮前の30~80%程度に調整することができ、圧縮後の合剤層の厚みは4~200μm程度が一般的である。
本発明の二次電池電極にセパレータ及び電解液を備えることにより、二次電池を作製することができる。電解液は液状であってもよく、ゲル状であってもよい。
セパレータは電池の正極及び負極間に配され、両極の接触による短絡の防止や電解液を保持してイオン導電性を確保する役割を担う。セパレータにはフィルム状の絶縁性微多孔膜であって、良好なイオン透過性及び機械的強度を有するものが好ましい。具体的な素材としては、ポリエチレン及びポリプロピレン等のポリオレフィン、ポリテトラフルオロエチレン等を使用することができる。
(製造例1-1:重合体Aの製造)
攪拌機、温度計を装着した1Lフラスコにジベンジルトリチオカーボネート(二官能RAFT剤、以下「DBTTC」ともいう)2.0部、2,2’-アゾビス(2-メチルブチロニトリル)(日本ファインケム社製、商品名「ABN-E」)0.014部、N-フェニルマレイミド(以下、「PhMI」ともいう)62部、スチレン(以下、「St」ともいう)38部およびアセトニトリル222部を仕込み、窒素バブリングで十分脱気し、70℃の恒温槽で重合を開始した。4時間後、室温まで冷却し反応を停止した。上記重合溶液を、メタノール/水=90/10(vоl%)から再沈殿精製、真空乾燥することにより重合体Aを得た。ガスクロマトグラフィー測定に基づくPhMI及びStの総使用量に対する反応率は75%であった。以下に示す条件によりGPC測定した結果、重合体Aのポリスチレン換算による数平均分子量(Mn)は10,200、重量平均分子量(Mw)は15,300であり、Mw/Mnは1.51と算出された。更に、以下に示す条件によるDSC測定による重合体Aのガラス転移点(Tg)は、210℃であった。
カラム:東ソー製TSKgel SuperMultiporeHZ-M×4本
溶媒:テトラヒドロフラン
温度:40℃
検出器:RI
流速:600μL/min
得られた重合体のTgは、示差走査熱量計を用いて得られた熱流束曲線のベースラインと変曲点での接線の交点から決定した。熱流束曲線は試料約10mgを-60℃まで冷却し、5分間保持した後、10℃/minで250℃まで昇温し、引き続き-60℃まで冷却し、5分間保持した後、10℃/minで250℃まで昇温する条件で得た。
測定機器:TA Instrument製(Q-100)
測定雰囲気:窒素雰囲気下
攪拌機、温度計を装着した1LフラスコにDBTTC2.0部、ABN-E0.41部、アクリロニトリル(以下、「AN」ともいう)25部、St75部およびアニソール67部を仕込み、窒素バブリングで十分脱気し、80℃の恒温槽で重合を開始した。4時間後、室温まで冷却し反応を停止した。上記重合溶液を、メタノール/水=90/10(vоl%)から再沈殿精製、真空乾燥することにより重合体Bを得た。ガスクロマトグラフィー測定に基づくAN及びStの総使用量に対する反応率は72%であり、製造例1-1と同様の条件でGPC測定した結果、Mn11,900、Mw15,500、Mw/Mnは1.30であった。また、DSC測定によるTgは、101℃であった。
攪拌機、温度計を装着した1LフラスコにDBTTC2.0部、ABN-E0.019部、フェノキシエチルアクリレート(共栄社化学社製、商品名「ライトアクリレートPO-A」)100部およびアセトニトリル53部を仕込み、窒素バブリングで十分脱気し、70℃の恒温槽で重合を開始した。3時間後、室温まで冷却し反応を停止した。上記重合溶液を、メタノール/水=90/10(vоl%)から再沈殿精製、真空乾燥することにより重合体Cを得た。ガスクロマトグラフィー測定に基づくフェノキシエチルアクリレートの総使用量に対する反応率は79%であり、製造例1-1と同様の条件でGPC測定した結果、Mn9,100、Mw10,700、Mw/Mnは1.17であった。また、DSC測定によるTgは、-20℃であった。
攪拌機、温度計を装着した1LフラスコにDBTTC2.0部、ABN-E0.019部、アクリル酸ブチル(以下、「BA」ともいう)100部およびアセトニトリル53部を仕込み、窒素バブリングで十分脱気し、70℃の恒温槽で重合を開始した。3時間後、室温まで冷却し反応を停止した。上記重合溶液を、メタノール/水=90/10(vоl%)から再沈殿精製、真空乾燥することにより重合体Dを得た。ガスクロマトグラフィー測定に基づくBAの総使用量に対する反応率反応率は77%であり、製造例1-1と同様の条件でGPC測定した結果、Mn8,900、Mw10,200、Mw/Mnは1.15であった。また、DSC測定によるTgは、-50℃であった。
攪拌機、温度計を装着した1LフラスコにDBTTC2.0部、ABN-E0.070部、無水マレイン酸(以下、「無水MLA」ともいう)48部、St52部およびアセトニトリル207部を仕込み、窒素バブリングで十分脱気し、70℃の恒温槽で重合を開始した。4時間後、室温まで冷却し反応を停止した。上記重合溶液を、トルエンから再沈殿精製、真空乾燥することにより重合体Eを得た。ガスクロマトグラフィー測定に基づく無水MLA及びStの総使用量に対する反応率は71%であり、製造例1-1と同様の条件でGPC測定した結果、Mn13,800、Mw22,200、Mw/Mnは1.61であった。また、DSC測定によるTgは、107℃であった。
攪拌機、温度計を装着した1LフラスコにDBTTC2.0部、ABN-E0.022部、アクリロイルモルフォリン(以下、「ACMO」ともいう)100部およびアセトニトリル78部を仕込み、窒素バブリングで十分脱気し、70℃の恒温槽で重合を開始した。4時間後、室温まで冷却し反応を停止した。上記重合溶液を、メタノールから再沈殿精製、真空乾燥することにより重合体Fを得た。ガスクロマトグラフィー測定に基づくACMOの総使用量に対する反応率は93%であり、GPC測定の結果から、Mn12,500、Mw13,400、Mw/Mnは1.07を得た。尚、PACMOはTHFへの溶解性が低いため、重合体FのGPCは以下の条件により測定した。また、DSC測定によるTgは、145℃であった。
カラム:東ソー製TSKgel SuperMultiporeHM-M×3本
溶媒:10mM LiBr/DMF
温度:40℃
検出器:RI
流速:300μL/min
攪拌機、温度計を装着した1Lフラスコに1-フェニルエチルヨージド(以下、「1-PEI」ともいう)3.24部、ABN-E0.019部、PhMI62部、St38部およびアセトニトリル221部を仕込み、窒素バブリングで十分脱気し、70℃の恒温槽で重合を開始した。4時間後、室温まで冷却し反応を停止した。上記重合溶液を、メタノール/水=90/10(vоl%)から再沈殿精製、真空乾燥することにより重合体Gを得た。ガスクロマトグラフィー測定に基づくPhMI及びStの総使用量に対する反応率は74%であり、製造例1-1と同様の条件でGPC測定した結果、Mn13,100、Mw31,100、Mw/Mnは2.37であった。また、DSC測定によるTgは、213℃であった。
St:スチレン
PhMI:N-フェニルマレイミド
AN:アクリロニトリル
PEA:フェノキシエチルアクリレート
BA:アクリル酸n-ブチル
無水MLA:無水マレイン酸
ACMO:アクリロイルモルフォリン
DBTTC:ジベンジルトリチオカーボネート
1-PEI:1-フェニルエチルヨージド
ABN-E:2,2’-アゾビス(2-メチルブチロニトリル)(日本ファインケム社製)
(製造例2-1:ブロック重合体R-1の製造)
重合には、攪拌翼、温度計、還流冷却器及び窒素導入管を備えた反応器を用いた。
反応器内にアセトニトリル567部、イオン交換水2.20部、アクリル酸(以下、「AA」という)100部、トリメチロールプロパンジアリルエーテル(ダイソー社製、商品名「ネオアリルT-20」)0.90部、製造例1-1で得られた重合体A1.0部、及び上記AAに対して1.0モル%に相当するトリエチルアミンを仕込んだ。反応器内を十分に窒素置換した後、加温して内温を55℃まで昇温した。内温が55℃で安定したことを確認した後、重合開始剤として2,2’-アゾビス(2,4-ジメチルバレロニトリル)(和光純薬工業社製、商品名「V-65」)0.040部を添加したところ、反応液に白濁が認められたため、この点を重合開始点とした。単量体濃度は15.0%と算出された。外温(水バス温度)を調整して内温を55℃に維持しながら重合反応を継続し、重合開始点から6時間経過した時点で内温を65℃まで昇温した。内温を65℃で維持し、重合開始点から12時間経過した時点で反応液の冷却を開始し、内温が25℃まで低下した後、水酸化リチウム・一水和物(以下、「LiOH・H2O」という)の粉末52.4部を添加した。添加後室温下12時間撹拌を継続して、ABAトリブロック体からなるブロック重合体R-1(Li塩、中和度90モル%)の粒子が媒体に分散したスラリー状の重合反応液を得た。なお、重合開始点から12時間経過した時点におけるAAの反応率は、97%であった。
各原料の仕込み量を表2に記載の通りとした以外は製造例2-1と同様の操作を行い、重合体R-2~R-15を含む重合反応液を得た。
次いで、各重合反応液について製造例2-1と同様の操作を行い、粉末状の重合体R-2~R-15を得た。各重合体は、水蒸気バリア性を有する容器に密封保管した。尚、製造例2-11では、LiOH・H2Oの粉末の代わりにNaOHを用いることにより、重合体Na塩(中和度90モル%)を得た。
各重合体の内、重合体R-2~R-7及びR-9~R-13はABAトリブロック体からなるブロック重合体であり、R-8はABジブロック体からなるブロック重合体である。また、R-14及びR-15は非ブロック重合体である。
AA:アクリル酸
HEA:アクリル酸2-ヒドロキシエチル
St:スチレン
T-20:トリメチロールプロパンジアリルエーテル(ダイソー社製、商品名「ネオアリルT-20」)
TEA:トリエチルアミン
V-65:2,2’-アゾビス(2,4-ジメチルバレロニトリル)(冨士フィルム和光純薬社製)
LiOH・H2O:水酸化リチウム・一水和物
NaOH:水酸化ナトリウム
活物質として、負極用活物質である黒鉛、又は、黒鉛及びケイ素粒子を用い、ブロック重合体をバインダーとして用いた電極合剤層用組成物について、当該組成物の粘度(電極スラリー粘度)及び形成された合剤層/集電体間の剥離強度(すなわちバインダーの結着性)を測定した。黒鉛としては天然黒鉛(日本黒鉛社製、商品名「CGB-10」)、ケイ素粒子としてはSiナノパウダー(Sigma-Aldrich社製、粒子径<100nm)を使用した。
天然黒鉛100部に粉末状のブロック重合体R-1を3.2部秤量し、予めよく混合した後、イオン交換水210部を加えてディスパーで予備分散を行った後、薄膜旋回式ミキサー(プライミクス社製、FM-56-30)を用いて周速度20m/秒の条件で本分散を15秒間行うことにより、スラリー状の電極合剤層用組成物(電極スラリー)を得た。電極スラリーの固形分濃度は、33.0%と算出された。
上記で得られた電極スラリーについて、アントンパール社製レオメーター(Physica MCR301)を用い、CP25-5のコーンプレート(直径25mm、コーン角度5°)にて、25℃におけるせん断速度60s-1のスラリー粘度を測定したところ、5,000mPa・sであった。
上記で得られた負極電極を25mm幅の短冊状に裁断した後、水平面に固定された両面テープに当該負極電極の合剤層面を貼付け、剥離試験用試料を作成した。試験用試料を60℃、1晩減圧条件下で乾燥させた後、引張速度50mm/分における90°剥離(測定温度23℃)を行い、合剤層と銅箔間の剥離強度を測定した。剥離強度は12.8N/mと高く、良好であった。
活物質及びバインダーとして使用するカルボキシル基含有重合体塩を表3の通り用いた以外は実施例1と同様の操作を行うことにより、電極スラリーを調製した。なお、実施例4及び実施例5では、天然黒鉛及びケイ素粒子を、遊星ボールミル(FRITSCH社製、P-5)を用いて400rpmで1時間撹拌し、得られた混合物に粉末状のブロック重合体R-3(Li塩)を3.2部秤量し、予めよく混合した後、実施例1と同様の操作を行うことにより、電極スラリーを調製した。各電極スラリーの粘度及び得られた負極電極の90°剥離強度(結着性)を評価し、結果を表3に示した。
一方、重合体ブロック(A)を有さない重合体による比較例1及び2の剥離強度は、実施例と比較すると低い値であった。
本発明の二次電池電極用バインダーは、特に非水電解質二次電池電極に好適に用いることができ、中でも、エネルギー密度が高い非水電解質リチウムイオン二次電池に有用である。
Claims (9)
- 重合体ブロック(A)及び重合体ブロック(B)を有するブロック重合体を含む二次電池電極用バインダーであって、
前記重合体ブロック(A)は、当該重合体ブロック(A)の全構造単位に基づく(メタ)アクリル酸に由来する構造単位が30質量%未満であり、
前記重合体ブロック(B)は、当該重合体ブロック(B)の全構造単位に基づく(メタ)アクリル酸に由来する構造単位が30質量%以上、100質量%以下である、二次電池電極用バインダー。 - 前記ブロック重合体における前記重合体ブロック(A)の割合は、0.1質量%以上、80質量%以下であり、
前記ブロック重合体における前記重合体ブロック(B)の割合は、20質量%以上、99.9質量%以下である、請求項1に記載の二次電池電極用バインダー。 - 前記重合体ブロック(A)は、ガラス転移温度(Tg)が-30℃以上である、請求項1又は2に記載の二次電池電極用バインダー。
- 前記ブロック重合体は、当該ブロック重合体が有するカルボキシル基の80モル%以上が中和された塩である、請求項1~3のいずれか1項に記載の二次電池電極用バインダー。
- 前記重合体ブロック(B)が、(メタ)アクリル酸及び架橋性単量体を含む単量体組成物を重合して得られる重合体ブロックである、請求項1~4のいずれか1項に記載の二次電池電極用バインダー。
- 請求項1~5のいずれか1項に記載の二次電池電極用バインダー、活物質及び水を含む二次電池電極合剤層用組成物。
- 集電体表面に、請求項1~5のいずれか1項に記載の二次電池電極用バインダーを含有する電極合剤層を備えた二次電池電極。
- 二次電池電極バインダーに用いるブロック重合体の製造方法であって、
前記ブロック重合体は、重合体ブロック(A)及び重合体ブロック(B)を有し、
リビングラジカル重合法により(メタ)アクリル酸の含有量が30質量%未満である単量体成分を重合し、前記重合体ブロック(A)を製造する工程と、
前記重合体ブロック(A)の存在下、(メタ)アクリル酸を30質量%以上、100質量%以下含む単量体成分を重合して前記重合体ブロック(B)を製造する工程と、を有する、ブロック重合体の製造方法。 - 前記リビングラジカル重合法が、可逆的付加-開裂連鎖移動重合法(RAFT法)である、請求項8に記載のブロック重合体の製造方法。
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WO2022138613A1 (ja) * | 2020-12-25 | 2022-06-30 | 東亞合成株式会社 | 二次電池電極用バインダー及びその利用 |
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JPWO2020129750A1 (ja) | 2021-10-28 |
US20220059845A1 (en) | 2022-02-24 |
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