WO2011002016A1 - 二次電池用電極、二次電池電極用スラリー及び二次電池 - Google Patents
二次電池用電極、二次電池電極用スラリー及び二次電池 Download PDFInfo
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- WO2011002016A1 WO2011002016A1 PCT/JP2010/061132 JP2010061132W WO2011002016A1 WO 2011002016 A1 WO2011002016 A1 WO 2011002016A1 JP 2010061132 W JP2010061132 W JP 2010061132W WO 2011002016 A1 WO2011002016 A1 WO 2011002016A1
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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
- H01M4/04—Processes of manufacture in general
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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
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
- H01G11/22—Electrodes
- H01G11/30—Electrodes characterised by their material
- H01G11/32—Carbon-based
- H01G11/38—Carbon pastes or blends; Binders or additives therein
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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
- H01M4/24—Electrodes for alkaline accumulators
- H01M4/242—Hydrogen storage electrodes
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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
- H01M4/24—Electrodes for alkaline accumulators
- H01M4/32—Nickel oxide or hydroxide electrodes
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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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- 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
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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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- 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
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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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
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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
- Y02E60/13—Energy storage using capacitors
Definitions
- the present invention relates to an electrode slurry used for a secondary battery electrode such as a lithium ion secondary battery, a secondary battery electrode, and a secondary battery.
- Lithium ion secondary batteries show the highest energy density among practical batteries, and are widely used especially for small electronics. In addition, expansion to automobile applications is also expected, and there is a demand for improved output characteristics and stable operation over a wide temperature range.
- a positive electrode of a lithium ion secondary battery is generally used as a positive electrode active material (hereinafter, also referred to as a “positive electrode active material”) on a current collector, such as LiCoO 2 , LiMn 2 O 4 and LiFePO 4.
- An electrode active material layer is formed by bonding a lithium-containing metal oxide or the like with a binder (also referred to as a binder) such as polyvinylidene fluoride.
- the negative electrode is a carbonaceous (amorphous) carbon material, metal oxide or metal sulfide used as a negative electrode active material (hereinafter also referred to as “negative electrode active material”) on the current collector.
- Etc. are bonded with a binder such as a styrene-butadiene copolymer.
- Patent Document 1 discloses that by using a polymer having a cationic group and an anion corresponding to the cationic group as a binder, the dispersibility of the electrode active material is improved, and as a result, the dispersibility of the conductive agent is also improved. By doing so, it is disclosed that a battery excellent in surface smoothness and output characteristics of the electrode can be obtained.
- Patent Document 2 discloses that an electrode having an anionic functional group and a binder containing a compound having an anionic functional group and a cationic functional group can be used for adhesion to a current collector and an electrode. It is described that the mobility of lithium ions in the vicinity of the surface is improved.
- Patent Document 3 discloses that an electrode is formed using a graphite material as a negative electrode active material and polyethylene or ethylene / vinyl acetate copolymer as a binder, and then heat-treating at a temperature equal to or higher than the melting point of the binder to bind the electrode. Has been shown to improve.
- JP 2006-278303 A JP 2009-123523 A JP 11-238505 A (US Pat. No. 6,436,573)
- an object of the present invention is to provide an electrode for a lithium ion secondary battery that suppresses lithium metal deposition and the resulting secondary battery exhibits excellent low-temperature characteristics.
- the inventors of the present invention include an electrode including the electrode active material containing a polymer having a cationic group and an anion corresponding to the cationic group, By setting the cation density in the polymer within a predetermined range, the polymer is selectively present near the surface of the electrode active material, lithium deposition is suppressed, and the low-temperature discharge capacity of the obtained secondary battery is improved. I found out that This is because the polymer is selectively present in the vicinity of the surface of the electrode active material, so that the desolvation resistance at the time of lithium insertion is greatly reduced, and the precipitation of the lithium not inserted on the electrode surface can be suppressed. It depends. Based on these findings, the present invention has been completed.
- the present invention for solving the above-mentioned problems includes the following matters as a gist.
- An electrode active material layer comprising a polymer having a cationic group, an anion corresponding to the cationic group, and an electrode active material, and the cation density in the polymer is 0.1 to
- the electrode for secondary batteries which is 15 meq / g.
- the electrode for a secondary battery wherein the electrode active material layer further contains a particulate polymer.
- a mass ratio of the polymer having the cationic group to the particulate polymer in the electrode active material layer is 5:95 to 40:60.
- a slurry for a secondary battery electrode comprising a polymer having a cationic group, an anion corresponding to the cationic group, an electrode active material, and a solvent, wherein the cation density in the polymer is 0.00.
- this polymer suppresses resistance during lithium insertion on the surface of the electrode active material, It is possible to obtain a secondary battery electrode in which lithium deposition does not occur on the electrode surface and the obtained secondary battery exhibits a high discharge capacity including a low temperature range of 0 ° C. or lower.
- the electrode for a secondary battery of the present invention (hereinafter sometimes simply referred to as “electrode”) includes a polymer having a cationic group and an anion corresponding to the cationic group (hereinafter referred to as “counter anion”). And an electrode active material layer containing an electrode active material (also referred to as an “electrode mixture layer”).
- the anion corresponding to the cationic group represents an anion that can bind to the cationic group.
- the cationic group refers to an atom or an atomic group that is positively charged by releasing electrons.
- a cationic group which the polymer used for this invention has what contains a hetero atom is preferable.
- a heteroatom is defined as an atom other than hydrogen, carbon and metal.
- it since it has a moderate interaction with the electrolyte solution described later and easily suppresses the precipitation of lithium metal, it preferably contains at least one of nitrogen, phosphorus, sulfur, oxygen and boron, Most preferred is one containing at least one of nitrogen, phosphorus and sulfur.
- the cationic group containing a hetero atom include a compound represented by the formula (I) (In the formula, A represents a hetero atom.
- R 1 to R 3 may be the same or different from each other, 1 to 2 may be hydrogen atoms, and 1 to 3 are substituted.
- each of R 1 to R 3 independently represents a hydrogen atom or an optionally substituted alkyl group, but the aliphatic group represented by the formula (I)
- at least one of R 1 to R 3 is an optionally substituted alkyl group, and therefore one or two of R 1 to R 3 may be a hydrogen atom.
- R 1 ⁇ R 3 is an aliphatic cationic group that is represented by the.) that removed as a hydrogen atom, Formula (II): (In the formula, A represents a hetero atom. Q 1 represents an optionally substituted aliphatic ring group. R 1 represents a hydrogen atom or an optionally substituted alkyl group.) Cyclic cationic groups, Or formula (III): (Wherein, A represents a hetero atom, Q 2 represents an optionally substituted heteroaromatic ring group), and the like.
- the primary cationic group can be classified into the quaternary cationic group according to the number of R 1 to R 3 hydrogen atoms contained in the above formula.
- R 1 to R 3 hydrogen atoms contained in the above formula.
- a quaternary cationic group when a hydrogen atom is not included among R 1 to R 3, a quaternary cationic group, a tertiary cationic group when one is a hydrogen atom, and a hydrogen atom when two are hydrogen atoms Is called a secondary cationic group.
- R 1 when R 1 is a hydrogen atom, it is called a tertiary cationic group, and when R 1 is other than hydrogen, it is called a quaternary cationic group.
- R 1 when R 1 is a hydrogen atom, it is called a tertiary cationic group, and when R 1 is other than hydrogen, it is called a quaternary cationic group.
- a heterocyclic cationic group all
- Examples of the optionally substituted alkyl group in the formula (I) and the formula (II) include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group.
- Linear, branched or cyclic unsubstituted having 1 to 18 carbon atoms such as pentyl group, pentyl group, neopentyl group, hexyl group, isohexyl group, decyl group, dodecyl group, octadecyl group, cyclopentyl group, cyclohexyl group, etc.
- Examples of the substituent of the optionally substituted alkyl group include an aryl group such as a phenyl group; a disubstituted amino group such as a dimethylamino group; a nitro group; a cyano group; a carboxyl group; and a formyl group, an acetyl group, and the like.
- substituted alkyl group examples include, for example, 1-methoxyethyl group, 2- (dimethylamino) methyl group, benzyl group, 1-phenylethyl group, 2-phenylethyl group, 2-methoxyethyl group, 2- ( 2-methoxyethoxy) ethyl group, allyl group and the like.
- Examples of the optionally substituted aliphatic ring group in the formula (II) include a pyrrolidyl group, a 2-methylpyrrolidyl group, a 3-methylpyrrolidyl group, a 2-ethylpyrrolidyl group, and a 3-ethylpyrrolidyl group.
- Examples of the optionally substituted heteroaromatic ring group in the formula (III) include a pyridyl group, a 2-methylpyridyl group, a 3-methylpyridyl group, a 4-methylpyridyl group, a 2,6-dimethylpyridyl group, 2-methyl-6-ethylpyridyl group, 1-methylimidazolyl group, 1,2-dimethylimidazolyl group, 1-ethylimidazolyl group, 1-propylimidazolyl group, 1-butylimidazolyl group, 1-pentylimidazolyl group, 1- Hexylimidazolyl, thiophene, thiazolyl, 1-methylthiazolyl, 1,2-dimethylthiazolyl, 1-ethylthiazolyl, 1-propylthiazolyl, 1-butylthiazolyl, 1-pentylthiazolyl Group, 1-hexyl thiazolyl group and the like
- the obtained electrode has a high binding property between the electrode active material and the binder, and at the time of forming an electrode slurry (also referred to as an electrode forming slurry).
- an electrode slurry also referred to as an electrode forming slurry.
- a tertiary cationic group or a quaternary cationic group is preferred, and a quaternary cationic group is particularly preferred.
- the alicyclic cationic group represented by the formula (II) and the heterocyclic cationic group represented by the formula (III) Groups are preferred.
- the cation density in the polymer used in the present invention is 0.1 meq / g or more and 15 meq / g or less per the polymer.
- the cation density is preferably 0.5 meq / g or more, more preferably 1 meq / g or more, and particularly preferably 2 meq / g or more. Yes, preferably 10 meq / g or less, more preferably 7.5 meq / g or less, and particularly preferably 5 meq / g or less.
- the cation density is preferably 2 meq / g or more, more preferably 4 meq / g or more, and still more preferably 5 meq / g or more.
- it is 12 meq / g or less, More preferably, it is 9 meq / g or less, More preferably, it is 8 meq / g or less, Most preferably, it is 7 meq / g or less, Most preferably, it is 6 meq / g or less.
- the electrode active material layer contains a particulate polymer containing an anion, and the cation density is 2 meq / g or more and 5 meq / g or less.
- the cation density is less than 0.1 meq / g, precipitation of lithium is observed during discharge and the low-temperature characteristics tend to be inferior.
- it is more than 15 meq / g the stability of the slurry for secondary battery electrodes described later is lowered, and an increase in battery failure rate is observed due to a decrease in productivity during electrode production and a decrease in electrode surface smoothness.
- meq / g represents a milliequivalent of a cationic group per gram of the polymer
- 1 eq is a value represented by “1 mol / ion valence”.
- the cation density in the polymer having a cationic group used in the present invention can be measured by colloid titration.
- the quaternary amine group can be measured by colloidal titration using potassium polyvinyl sulfate as a standard anion.
- the anion (that is, the counter anion) corresponding to the cationic group used in the present invention contains an anion, and the anion preferably contains a halogen element or a chalcogen element.
- the “halogen element” means an atomic group consisting of fluorine, chlorine, bromine, iodine and astatine which are Group 17 elements.
- chlorine, bromine and iodine are preferable because a strong electrolyte having a high degree of dissociation can be formed, and at least one selected from the group consisting of chlorine ions, bromine ions and iodine ions is preferable as the counter anion.
- the “chalcogen element” means an atomic group consisting of oxygen, sulfur, selenium, tellurium and polonium which are group 16 elements. Among these, at least one selected from the group consisting of sulfonate ions, sulfate ions and nitrate ions containing sulfur and oxygen as chalcogen elements is preferable because a strong electrolyte having a high degree of dissociation can be formed.
- counter anions are usually bonded to the cationic group of the polymer having a cationic group, but may not necessarily form a bond with the cationic group as long as the effects of the present invention are exhibited. Good. Moreover, you may couple
- the counter anion is bound to the polymer having a cationic group by a bond other than the bond with the cationic group or the cationic group, the polymer having the cationic group is a cationic group and It will have a counter anion.
- the amount of the counter anion is arbitrary as long as the effect of the present invention is obtained. Since the counter anion corresponds to the cationic group of the polymer used in the present invention, the counter anion usually has the same equivalent density (meq / g) as the corresponding cationic group.
- the weight average molecular weight of the polymer having a cationic group used in the present invention is a standard polyethylene oxide measured by gel permeation chromatography (hereinafter sometimes referred to as “GPC”) using an aqueous solution of sodium nitrate as a developing solvent.
- the converted value is preferably 1,000 or more, more preferably 5,000 or more, still more preferably 10,000 or more, preferably 500,000 or less, more preferably 300,000 or less, and still more preferably 200,000. Hereinafter, it is particularly preferably 100,000 or less.
- the polymer having a cationic group When the weight average molecular weight of the polymer having a cationic group is within the above range, the polymer having a cationic group exhibits high adsorption stability to the surface of the electrode active material inside the electrode, and has an appropriate mobility. Thus, excellent low-temperature characteristics are exhibited, and the stability of the electrode slurry is excellent, so that productivity can be improved and a smooth electrode can be obtained.
- the glass transition temperature (Tg) of the polymer having a cationic group used in the present invention is preferably 30 ° C. or less, more preferably 0 ° C. or less from the viewpoint of improving the flexibility and bending resistance of the electrode.
- the lower limit of the glass transition temperature (Tg) is preferably ⁇ 100 ° C. or higher, more preferably ⁇ 70 ° C. or higher.
- the polymer having a cationic group used in the present invention is usually prepared as a solution or dispersion containing the polymer and a solvent in order to produce an electrode.
- the viscosity of the solution or dispersion is usually 1 mPa ⁇ S or more, preferably 50 mPa ⁇ S or more, and usually 300,000 mPa ⁇ S or less, preferably 10,000 mPa ⁇ S or less.
- the viscosity is a value measured using a B-type viscometer at 25 ° C. and a rotation speed of 60 rpm.
- the solvent used in the solution or dispersion of the polymer having a cationic group used in the present invention is not particularly limited as long as it can uniformly dissolve or disperse the polymer, but a solvent that can dissolve is preferable. This is because the solution tends to have an effect of promoting lithium desolvation on the surface of the electrode active material because a larger amount of polymer can be present on the surface of the electrode active material during electrode production. Moreover, since it mixes with the solvent used for the slurry for electrodes at the time of preparation of the slurry for electrodes mentioned later, it is desirable to use the same solvent as the solvent used for the slurry for electrodes.
- acetone, toluene, cyclohexanone, cyclopentane, tetrahydrofuran, cyclohexane, xylene, water, N-methylpyrrolidone, or a mixed solvent thereof is preferable.
- water is particularly preferable because the polymer used in the present invention has high solubility and is often used as a solvent for an electrode slurry.
- a method for producing a polymer having a cationic group used in the present invention for example, (first method) a method of homopolymerizing a monomer having a cationic group, or a copolymerization with a copolymerizable monomer (Second method) a method of adding a compound having a cationic group to a polymer obtained from a polymerizable monomer; (third method) using a compound having a tertiary cationic group as a polymerization catalyst A method of anionic polymerization of a polymerizable monomer; (fourth method) a method of polymerizing a monomer having a secondary cationic group under a basic condition and neutralizing the obtained polymer with an acid, etc. Can be mentioned.
- Examples of the monomer having a cationic group used in the (first method) include the aforementioned unsaturated monomers having a cationic group.
- a counter anion corresponding to the cationic group is usually bonded to the monomer having a cationic group.
- the presence of a cation having a specific density range and a counter anion corresponding to the cationic group is a requirement for achieving the effects of the present invention, and therefore, regardless of the type of cation and counter anion.
- the effect of the present invention can be exhibited. Therefore, the combination is not particularly limited, and the effect of the present invention can be obtained with any combination.
- monomers include, for example, when the counter anion is a chloride ion, such as vinylalkylammonium chloride, (meth) acryloylalkylammonium chloride, (di) allylalkylammonium chloride, aminoalkyl (meth) acrylamide, etc.
- a chloride ion such as vinylalkylammonium chloride, (meth) acryloylalkylammonium chloride, (di) allylalkylammonium chloride, aminoalkyl (meth) acrylamide, etc.
- the polymer having a cationic group used in the present invention may be obtained by homopolymerizing a monomer having a cationic group or by copolymerizing a polymerizable monomer copolymerizable therewith.
- the copolymerizable monomer include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; 2 such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate.
- Carboxylic acid esters having one or more carbon-carbon double bonds having one or more carbon-carbon double bonds; styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, ⁇ -Styrene monomers such as methylstyrene and divinylbenzene; Amide monomers such as acrylamide, N-methylol aquaylamide, and acrylamide-2-methylpropanesulfonic acid; ⁇ such as acrylonitrile and methacrylonitrile , ⁇ -unsaturated nitrile compounds; olefins such as ethylene and propylene; diene monomers such as butadiene and isoprene; monomers containing halogen atoms such as vinyl chloride and vinylidene chloride; vinyl acetate
- the content ratio of the copolymerizable monomer unit in the polymer having a cationic group used in the present invention is preferably 1% by mass or more, more preferably 10% by mass or more, and preferably 90% by mass or less. More preferably, it is 50 mass% or less.
- the polymerization method in the (first method) is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method can be used.
- the polymerization initiator used for the polymerization include peroxides such as hydrogen peroxide and tert-butyl hydroperoxide; reductions of these peroxides and divalent iron (Fe ++), Na 2 SO 3 , ascorbic acid, and the like.
- Redox initiator comprising a combination with an agent: lauroyl peroxide, disopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butylperoxypivalate, 3,5,5-trimethylhexanoylper Organic peroxides such as oxides; azo compounds such as ⁇ , ⁇ ′-azobisisobutyronitrile; persulfates such as ammonium persulfate and potassium persulfate;
- an aqueous medium As the solvent used in solution polymerization, an aqueous medium is preferable.
- the aqueous medium include water, inorganic acid (hydrochloric acid, sulfuric acid, phosphoric acid, polyphosphoric acid, etc.) aqueous solution, organic acid aqueous solution, inorganic acid salt (sodium chloride, zinc chloride, calcium chloride, magnesium chloride, etc.) aqueous solution, and the like.
- suspending agent used in suspension polymerization examples include synthetic polymers such as polyvinyl alcohol, partially saponified polyvinyl acetate, cellulose derivatives such as methylcellulose, polyvinylpyrrolidone, maleic anhydride-vinyl acetate copolymer, and polyacrylamide.
- synthetic polymers such as polyvinyl alcohol, partially saponified polyvinyl acetate, cellulose derivatives such as methylcellulose, polyvinylpyrrolidone, maleic anhydride-vinyl acetate copolymer, and polyacrylamide.
- synthetic polymers such as polyvinyl alcohol, partially saponified polyvinyl acetate, cellulose derivatives such as methylcellulose, polyvinylpyrrolidone, maleic anhydride-vinyl acetate copolymer, and polyacrylamide.
- substances and natural polymer substances such as starch and gelatin.
- emulsifier used in the emulsion polymerization examples include anionic emulsifiers such as sodium alkylbenzene sulfonate and sodium lauryl sulfate, and nonionic emulsifiers such as polyoxyethylene alkyl ether and polyoxyethylene sorbitan fatty acid partial ester. Further, a molecular weight adjusting agent such as trichlorethylene, thioglycol or dodecyl mercaptan can be used as necessary.
- the above-described polymerization initiator, monomer, suspending or emulsifying agent, molecular weight adjusting agent, etc. may be added to the polymerization system all together at the start of polymerization, or may be added in portions during the polymerization. The polymerization is usually carried out at a temperature of 35 to 80 ° C. with stirring.
- a polymer is first formed, and then a compound having a cationic group is added to the polymer.
- a counter anion corresponding to the cationic group is bonded to the compound having a cationic group.
- the polymerization method any of the solution polymerization method, the suspension polymerization method, and the emulsion polymerization method can be used as described above, and it is optimal depending on the conditions of the subsequent addition reaction and the characteristics of the polymer to be obtained.
- a suitable manufacturing method may be selected. For example, when the addition reaction is carried out in an aqueous system, it is advantageous to obtain the polymer as fine aqueous dispersion particles by emulsion polymerization.
- a solution polymerization method or a suspension polymerization method using a lower alcohol such as methanol as a polymerization medium is preferable, but a normal suspension polymerization method can also be used.
- a tertiary amine is reacted in the presence or absence of an acid. And a method of adding them together.
- Tertiary amines include saturated tertiary amines such as pyridine, dimethyl lauryl amine, dimethyl stearyl amine, triethyl amine and dimethyl methoxyethyl amine; dimethylallyl amine, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylamide and the like.
- Saturated tertiary amines can be used.
- the acid include saturated carboxylic acids such as acetic acid and lactic acid; and unsaturated carboxylic acids such as (meth) acrylic acid and crotonic acid.
- the reaction for adding the polymer and the tertiary amine may be carried out in a solvent in which both are dissolved or may be carried out by directly melting and mixing the two, but in a solvent at 40 to 60 ° C. Is preferred.
- the pH of the polymer having a cationic group in the present invention is preferably 6 or more, more preferably 7 or more, preferably 12 or less, and more preferably 10 or less.
- the polymer having a cationic group used in the present invention is obtained through a particulate metal removal step of removing particulate metal contained in the polymer solution or the polymer dispersion in the polymer production process.
- a particulate metal removal step of removing particulate metal contained in the polymer solution or the polymer dispersion in the polymer production process.
- the content of the particulate metal component contained in the polymer solution or polymer dispersion is 10 ppm or less, metal ion cross-linking between polymers in the electrode slurry described later is prevented, and the viscosity is increased. Can be prevented.
- there is little concern about an increase in self-discharge due to internal short circuit of the secondary battery or dissolution or precipitation during charging and the cycle characteristics and safety of the battery are improved.
- the method for removing the particulate metal component from the polymer solution or polymer dispersion in the particulate metal removal step is not particularly limited.
- the removal method by filtration using a filtration filter, the removal method by a vibrating screen, centrifugation Examples thereof include a method of removing by separation and a method of removing by magnetic force.
- the removal target is a metal component
- the metal foreign matter component can be selectively and efficiently removed.
- the method for removing by magnetic force is not particularly limited as long as it is a method capable of removing a metal component. However, in consideration of productivity and removal efficiency, it is preferably performed by arranging a magnetic filter in a polymer production line. .
- the content ratio of the polymer having a cationic group in the electrode active material layer is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and preferably 5% by mass or less. More preferably, it is 3 mass% or less, Most preferably, it is 1 mass% or less.
- the counter anion is bonded to a polymer having a cationic group, it is preferable that the content of the polymer including the mass of the counter anion falls within the above range. Since the content ratio of the polymer having a cationic group in the electrode active material layer is in the above range, excellent low-temperature characteristics are exhibited, and the electrode slurry is excellent in stability and productivity, and a smooth electrode. Can be obtained.
- Electrode active material What is necessary is just to select the electrode active material used for the electrode for secondary batteries of this invention according to the secondary battery in which an electrode is utilized.
- the secondary battery include a lithium ion secondary battery and a nickel hydride secondary battery.
- the positive electrode active material is roughly classified into those made of an inorganic compound and those made of an organic compound.
- the positive electrode active material made of an inorganic compound include transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides.
- the transition metal Fe, Co, Ni, Mn and the like are used.
- the inorganic compound used for the positive electrode active material include LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiFePO 4 , LiFeVO 4, and other lithium-containing composite metal oxides; TiS 2 , TiS 3 , non- Transition metal sulfides such as crystalline MoS 2 ; transition metal oxides such as Cu 2 V 2 O 3 , amorphous V 2 O—P 2 O 5 , MoO 3 , V 2 O 5 , V 6 O 13 ; Is mentioned. These compounds may be partially element-substituted.
- the positive electrode active material made of an organic compound for example, a conductive polymer such as polyacetylene or poly-p-phenylene can be used.
- An iron-based oxide having poor electrical conductivity may be used as an electrode active material covered with a carbon material by allowing a carbon source material to be present during reduction firing. These compounds may be partially element-substituted.
- the positive electrode active material for a lithium ion secondary battery may be a mixture of the above inorganic compound and organic compound.
- the particle diameter of the positive electrode active material is appropriately selected in consideration of other constituent elements of the battery. From the viewpoint of improving battery characteristics such as load characteristics and cycle characteristics, the 50% volume cumulative diameter is usually 0.1 ⁇ m. Above, preferably 1 ⁇ m or more, usually 50 ⁇ m or less, preferably 20 ⁇ m or less. When the 50% volume cumulative diameter is within this range, a secondary battery having a large charge / discharge capacity can be obtained, and handling of the slurry for electrodes and the electrodes is easy.
- the 50% volume cumulative diameter can be determined by measuring the particle size distribution by laser diffraction.
- examples of the negative electrode active material include carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads, and pitch-based carbon fibers. Examples thereof include materials and conductive polymers such as polyacene.
- carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads, and pitch-based carbon fibers. Examples thereof include materials and conductive polymers such as polyacene.
- metals such as silicon, tin, zinc, manganese, iron, nickel, alloys thereof, oxides or sulfates of the metals or alloys are used.
- lithium alloys such as lithium metal, Li—Al, Li—Bi—Cd, and Li—Sn—Cd, lithium transition metal nitride, silicon, and the like can be used.
- An electrode active material having a conductive agent attached to the surface by a mechanical modification method can also be used.
- the particle diameter of the negative electrode active material is appropriately selected in consideration of other constituent elements of the battery. From the viewpoint of improving battery characteristics such as initial efficiency, load characteristics, and cycle characteristics, a 50% volume cumulative diameter is usually It is 1 ⁇ m or more, preferably 15 ⁇ m or more, and is usually 50 ⁇ m or less, preferably 30 ⁇ m or less.
- examples of the positive electrode active material include nickel hydroxide particles.
- the nickel hydroxide particles may be dissolved in cobalt, zinc, cadmium, or the like, or may be coated with a cobalt compound whose surface is subjected to an alkali heat treatment.
- the hydrogen storage alloy particles are hydrogen generated electrochemically in an alkaline electrolyte when the battery is charged.
- the possible storage, yet as long as the storage of hydrogen can be easily released upon discharge well is not particularly limited, AB 5 type system, preferably particles made of TiNi system and TiFe system hydrogen absorbing alloy.
- LaNi 5 , MmNi 5 (Mm is a misch metal), LmNi 5 (Lm is at least one selected from rare earth elements including La), and a part of Ni of these alloys is Al, Mn, Co Multi-element hydrogen storage alloy particles substituted with one or more elements selected from the group consisting of Ti, Cu, Zn, Zr, Cr, and B can be used.
- hydrogen storage having a composition represented by the general formula: L m Ni w Co x Mn y Al z (the total value of atomic ratios w, x, y and z is 4.80 ⁇ w + x + y + z ⁇ 5.40)
- the alloy particles are suitable because the pulverization accompanying the progress of the charge / discharge cycle is suppressed and the charge / discharge cycle characteristics are improved.
- the content ratio of the electrode active material in the electrode active material layer is preferably 90% by mass or more, more preferably 95% by mass or more, preferably 99.9% by mass or less, more preferably 99% by mass or less.
- the electrode active material layer is a particulate polymer (also referred to as a particulate polymer) in addition to a polymer having a cationic group, a counter anion corresponding to the cationic group, and an electrode active material. May be included.
- the particulate polymer By including the particulate polymer, the binding property of the electrode is improved, the strength against the mechanical force applied during the process of winding the electrode is increased, and the electrode active material layer in the electrode is less likely to be detached. For this reason, the risk of a short circuit due to the desorbed material is reduced.
- the particulate polymer is prepared as a dispersion in which polymer particles having binding properties are dispersed in water or an organic solvent (hereinafter, these may be collectively referred to as “binder dispersion”).
- binder dispersion is an aqueous dispersion
- examples of the particulate polymer include polymer particles such as a diene polymer, an acrylic polymer, a fluorine polymer, and a silicon polymer. Among these, non-fluorinated polymers that do not contain fluorine are preferred. If the particulate polymer contains fluorine, the lithium metal precipitation suppressing effect may be reduced due to the interaction with the cation due to high electronegativity.
- the particulate polymer is more preferably an amorphous polymer. Since the particulate polymer is amorphous, the electrode active material layer is excellent in flexibility, and the lithium metal deposition suppressing effect is highly expressed by the mobility of the polymer inside the battery.
- the degree of crystallinity of the particulate polymer is preferably 10% or less, more preferably 5% or less.
- a diene polymer or an acrylic polymer is preferable because of excellent binding properties with an electrode active material and strength and flexibility of the obtained electrode.
- the particulate polymer is usually polyethylene, polypropylene, polyisobutylene, polyvinyl chloride, polyvinylidene chloride, polyfluoride.
- Vinyl polymers such as vinylidene, polytetrafluoroethylene, polyvinyl acetate, polyvinyl alcohol, polyvinyl isobutyl ether, polyacrylonitrile, polymethacrylonitrile, polymethyl methacrylate, polymethyl acrylate, polyethyl methacrylate, allyl acetate, polystyrene Diene polymers such as polybutadiene and polyisoprene; ether polymers containing heteroatoms in the main chain such as polyoxymethylene, polyoxyethylene, polycyclic thioether, and polydimethylsiloxane; Poly cyclic anhydride, polyethylene terephthalate, condensation ester polymer such as polycarbonate; nylon 6, nylon 66, poly -m- phenylene isophthalamide, poly -p- phenylene terephthalamide, poly pyromellitic imide.
- the diene polymer is a polymer containing monomer units obtained by polymerizing conjugated dienes such as butadiene and isoprene, and the binder dispersion is usually an aqueous dispersion.
- the proportion of the monomer unit obtained by polymerizing the conjugated diene in the diene polymer is usually 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more, and usually 100% or less.
- Examples of the diene polymer include homopolymers of conjugated dienes such as polybutadiene and polyisoprene; and copolymers with monomers copolymerizable with conjugated dienes.
- Examples of the copolymerizable monomer include ⁇ , ⁇ -unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; styrene, chlorostyrene, Styrene monomers such as vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, ⁇ -methyl styrene, divinylbenzene; olefins such as ethylene and propylene Diene monomers such as butadiene and isoprene; monomers containing halogen atoms such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; methyl
- the acrylic polymer is a polymer containing monomer units obtained by polymerizing acrylic acid ester and / or methacrylic acid ester, and the binder dispersion liquid is usually an aqueous dispersion liquid.
- the proportion of monomer units formed by polymerizing acrylic acid ester and / or methacrylic acid ester is usually 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more, and usually 100% or less. is there.
- the acrylic polymer include homopolymers of acrylic acid esters and / or methacrylic acid esters, and copolymers with monomers copolymerizable therewith.
- Examples of the copolymerizable monomer include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; two or more carbons such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate.
- unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid
- two or more carbons such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate.
- Carboxylates having carbon double bonds including styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, ⁇ -methyl styrene, Styrene monomers such as divinylbenzene; Amide monomers such as acrylamide, N-methylol aquaylamide, acrylamide-2-methylpropanesulfonic acid; ⁇ , ⁇ - such as acrylonitrile and methacrylonitrile Saturated nitrile compounds; olefins such as ethylene and propylene; diene monomers such as butadiene and isoprene; monomers containing halogen atoms such as vinyl chloride and vinylidene chloride; vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate Vinyl esters such as
- an acrylic polymer which is a saturated polymer having no unsaturated bond in the polymer main chain is preferable because of excellent oxidation resistance during charging.
- a diene polymer is preferable.
- the particulate polymer used for the secondary battery electrode of the present invention preferably contains an anion from the viewpoint of improving the adhesion to the current collector.
- the anion contained in the particulate polymer is an anion different from the counter anion corresponding to the cationic group, and is contained in the particulate polymer.
- An anion can be contained in the particulate polymer as an anionic group, and a monomer containing an anionic group is used as a monomer constituting the particulate polymer, or an emulsifier and an initiator used in the polymerization described later.
- an anionic group can be contained in a polymerization additive such as a terminator, so that it can be contained in the particulate polymer.
- the content of the anion with respect to the total amount of the particulate polymer varies depending on whether the anionic group is contained in the monomer unit, the emulsifier, the initiator, or the like. Each preferable content is mentioned later.
- a method for obtaining a particulate polymer containing an anion (1) a method using a monomer containing an anionic group as a polymerizable monomer; (2) an emulsifier containing an anionic group using a polymerizable monomer Examples include a method used for solubilization; (3) a method using an initiator containing an anionic group as a polymerization initiator; and (4) a method combining the above (1) to (3).
- Examples of the monomer having an anionic group include a monomer having a carboxyl group, a monomer having a phosphonic acid group, a monomer having a phosphinic acid group, and a monomer having a sulfonic acid group.
- a monomer having a carboxyl group or a monomer having a sulfonic acid group is preferable from the viewpoint of the stability of the particulate polymer.
- Examples of the monomer having a carboxyl group include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid and fumaric acid.
- Monomers having a sulfonic acid group include 2-acrylamido-2-methylpropanesulfonic acid, 2-[(2-propenyloxy) methoxy] ethenesulfonic acid, 3- (2-propenyloxy) -1-propene-1- Sulfonic acid, vinyl sulfonic acid, 2-vinyl benzene sulfonic acid, 3-vinyl benzene sulfonic acid, 4-vinyl benzene sulfonic acid, 4-vinyl benzyl sulfonic acid, 2-methyl-1-pentene-1-sulfonic acid, 1- Examples include octene-1-sulfonic acid.
- the content of the monomer unit comprising an anionic group with respect to the total amount of the particulate polymer is preferably 0.5% by mass or more, more preferably 1% by mass or more, preferably 10% by mass or less, more preferably Is 5% by mass or less.
- an electrostatic repulsion effect will express in a particulate polymer and the stability in the slurry mixing for electrodes will improve.
- adhesion between the particulate polymer and the current collector is improved in the electrode.
- the emulsifier containing an anionic group examples include an anionic surfactant such as a surfactant having a carboxyl group, a surfactant having a sulfonic acid group, and a surfactant having a phosphate group.
- an anionic surfactant such as a surfactant having a carboxyl group, a surfactant having a sulfonic acid group, and a surfactant having a phosphate group.
- a surfactant having a sulfonic acid group is preferable for the reason of stability of the particulate polymer.
- surfactants having a sulfonic acid group include sulfates of higher alcohols, alkylbenzene sulfonates, and aliphatic sulfonates.
- sodium dodecylbenzene sulfonate sodium dodecyl phenyl ether sulfonate, and the like.
- Benzene sulfonates alkyl sulfates such as sodium lauryl sulfate and sodium tetradodecyl sulfate; sulfosuccinates such as sodium dioctyl sulfosuccinate and sodium dihexyl sulfosuccinate, polyoxyethylene lauryl ether sulfate sodium salt, polyoxyethylene nonylphenyl ether Ethoxy sulfate salts such as tersulfate sodium salt; alkane sulfonate salts; and the like.
- the anionic surfactant may be used alone or in combination with another surfactant.
- examples of other surfactants include nonionic surfactants, cationic surfactants, and amphoteric surfactants.
- nonionic surfactant known ones can be used. Specifically, polyethylene glycol alkyl ester type, alkyl ether type, alkylphenyl ether type and the like are used.
- cationic surfactant known ones can be used, and examples thereof include primary amine salts, secondary amine salts, tertiary amine salts, and quaternary ammonium salts.
- amphoteric surfactants include those having a carboxylate, sulfate, sulfonate, and phosphate ester salt as the anion moiety, and an amine salt and quaternary ammonium salt as the cation moiety.
- Betaines such as lauryl betaine and stearyl betaine; those of amino acid type such as lauryl- ⁇ -alanine, stearyl- ⁇ -alanine, lauryl di (aminoethyl) glycine, octyldi (aminoethyl) glycine, etc.
- the content of the emulsifier with respect to the total amount of the particulate polymer is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, preferably 10% by mass or less, more preferably 5% by mass or less.
- polymerization initiator examples include persulfates such as potassium persulfate and ammonium persulfate, and organic peroxides such as hydrogen peroxide, benzoyl peroxide and cumene hydroperoxide. These may be used alone or as a redox polymerization initiator used in combination with a reducing agent such as acidic sodium sulfite, sodium thiosulfate, or ascorbic acid.
- persulfates such as potassium persulfate and ammonium persulfate
- organic peroxides such as hydrogen peroxide, benzoyl peroxide and cumene hydroperoxide.
- a reducing agent such as acidic sodium sulfite, sodium thiosulfate, or ascorbic acid.
- the content of the polymerization initiator with respect to the total amount of the particulate polymer is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, preferably 5% by mass or less, more preferably 3% by mass or less. is there. By being included in the said range, even if it mix
- Polymerization terminators include diethylhydroxylamine, hydroxyaminesulfonic acid, and its metal alkali salts, hydroxyamine sulfate, hydroxydimethylbenzenethiocarboxylic acid, hydroxydibutylbenzenethiocarboxylic acid and other hydroxydithiocarboxylic acids and their alkali metal salts, hydroquinone derivatives And catechol derivatives.
- hydroxyamine sulfonic acid containing an anionic group and its alkali metal salt, hydroxydithiocarboxylic acid and its alkali metal salt are preferably used.
- the content of the polymerization terminator with respect to the total amount of the particulate polymer is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, preferably 2% by mass or less, more preferably 1% by mass or less. is there. By being included in the said range, even if it mix
- the content of the anion in the particulate polymer is calculated from the ratio of the structural component having an anionic group in the particulate polymer, preferably 0.25% by mass or more, more preferably 0.5% by mass or more. 1 mass% or more is especially preferable, 20 mass% or less is preferable, 10 mass% or less is more preferable, and 8 mass% or less is especially preferable.
- the particulate polymer used for the secondary battery electrode of the present invention can be produced by emulsion polymerization, suspension polymerization or the like.
- emulsion polymerization a known method can be employed, and the emulsion polymerization can be carried out using an emulsifier, a polymerization initiator, a molecular weight regulator and the like in an aqueous medium.
- the binder dispersion may be an aqueous dispersion (aqueous binder) using water as a dispersion medium or a non-aqueous dispersion (non-aqueous binder) using an organic solvent as a dispersion medium.
- aqueous binder aqueous binder
- non-aqueous dispersion non-aqueous binder
- an aqueous binder is preferably used.
- the aqueous dispersion can be produced, for example, by emulsion polymerization of the above monomers in water.
- the non-aqueous dispersion can be produced by replacing the aqueous dispersion with an organic solvent.
- the number average particle size of the particulate polymer in the binder dispersion is preferably 50 nm or more, more preferably 70 nm or more, preferably 500 nm or less, and more preferably 400 nm or less. When the number average particle diameter of the particulate polymer is within this range, the strength and flexibility of the obtained electrode are good.
- the glass transition temperature (Tg) of the particulate polymer is appropriately selected according to the purpose of use, but is usually ⁇ 150 ° C. or higher, preferably ⁇ 100 ° C. or higher, more preferably ⁇ 70 ° C. or higher, more preferably ⁇ 50. ° C or higher, particularly preferably -35 ° C or higher, usually + 100 ° C or lower, preferably + 25 ° C or lower, more preferably + 5 ° C or lower.
- Tg glass transition temperature
- the amount of the particulate polymer in the secondary battery electrode of the present invention is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, particularly preferably 100 parts by mass of the electrode active material. It is 0.5 parts by mass or more, preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and particularly preferably 3 parts by mass or less.
- the amount of the particulate polymer in the electrode active material layer is in the above range, it is possible to prevent the electrode active material from dropping from the electrode without inhibiting the battery reaction.
- the mass ratio of the polymer having a cationic group in the electrode active material layer to the particulate polymer is preferably 5:95 to 40:60, and 10:90 to 30:70. More preferably.
- the electrode for a secondary battery of the present invention is further added with an electrolytic solution having functions such as a conductive agent, a reinforcing material, a dispersing agent, a leveling agent, an antioxidant, a thickener, and an electrolytic decomposition inhibition.
- an agent such as an agent may be included.
- these other components may be contained in the slurry for secondary battery electrodes mentioned later. These are not particularly limited as long as they do not affect the battery reaction.
- conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor-grown carbon fiber, and carbon nanotube can be used. Examples thereof include carbon powders such as graphite, and fibers and foils of various metals.
- the electrical contact between the electrode active materials can be improved by using the conductive agent, and the discharge load characteristics can be improved particularly when used in a lithium ion secondary battery.
- the reinforcing material various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used. By using a reinforcing material, a tough and flexible electrode can be obtained, and excellent long-term cycle characteristics can be exhibited.
- the content of the conductive agent or reinforcing agent in the electrode active material layer is usually 0.01 parts by mass or more, preferably 1 part by mass or more, and usually 20 parts by mass or less, preferably 100 parts by mass of the electrode active material. Is 10 parts by mass or less. By being included in the range, high capacity and high load characteristics can be exhibited.
- the dispersant examples include anionic compounds, cationic compounds, nonionic compounds, and polymer compounds.
- a dispersing agent is selected according to the electrode active material and electrically conductive agent to be used.
- the content ratio of the dispersant in the electrode active material layer is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the electrode active material.
- the electrode slurry is excellent in stability, a smooth electrode can be obtained, and a high battery capacity can be exhibited.
- the leveling agent examples include surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants. By mixing the surfactant, it is possible to prevent the repelling that occurs during coating or to improve the smoothness of the electrode.
- the content ratio of the leveling agent in the electrode active material layer is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the electrode active material. When the content of the leveling agent in the electrode active material layer is in the above range, the productivity, smoothness, and battery characteristics during electrode production are excellent.
- the antioxidant examples include a phenol compound, a hydroquinone compound, an organic phosphorus compound, a sulfur compound, a phenylenediamine compound, and a polymer type phenol compound.
- the polymer type phenol compound is a polymer having a phenol structure in the molecule, and a polymer type phenol compound having a weight average molecular weight of usually 200 or more, preferably 600 or more, usually 1000 or less, preferably 700 or less is preferably used.
- the content ratio of the antioxidant in the electrode active material layer is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, preferably 10 parts by mass or less, with respect to 100 parts by mass of the electrode active material. More preferably, it is 5 parts by mass or less. When the content of the antioxidant in the electrode active material layer is within the above range, the electrode slurry stability, battery capacity, and cycle characteristics are excellent.
- thickeners include cellulose polymers such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof; (modified) poly (meth) acrylic acid and ammonium salts and alkali metal salts thereof; ) Polyvinyl alcohols such as polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified Polyacrylic acid, oxidized starch, phosphoric acid starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydride, and the like.
- cellulose polymers such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof; (modified) poly (meth) acrylic acid and ammonium salts and alkali metal salts thereof
- (modified) poly means “unmodified poly” or “modified poly”
- “(meth) acryl” means “acryl” or “methacryl”.
- the content ratio of the thickener in the electrode active material layer is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the electrode active material.
- the electrode active material in the electrode slurry is excellent in dispersibility and a smooth electrode can be obtained, and excellent load characteristics and cycle characteristics. Indicates.
- the electrolytic solution additive vinylene carbonate used in an electrode slurry and an electrolytic solution described later can be used.
- the content ratio of the electrolytic solution additive in the electrode active material is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the electrode active material.
- the cycle characteristics and the high temperature characteristics are excellent.
- Other examples include nanoparticles such as fumed silica and fumed alumina: surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants.
- the content ratio of the nanoparticles in the electrode active material layer is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the electrode active material.
- the slurry for an electrode is excellent in stability and productivity, and high battery characteristics are exhibited.
- the content ratio of the surfactant in the electrode active material is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the electrode active material.
- a polymer having a cationic group, a counter anion corresponding to the cationic group, and an electrode active material layer containing an electrode active material may be formed on the current collector.
- the current collector is not particularly limited as long as it is an electrically conductive and electrochemically durable material. From the viewpoint of having heat resistance, for example, iron, copper, aluminum, nickel, stainless steel, etc. Metal materials such as titanium, tantalum, gold, and platinum are preferable. Among these, aluminum is particularly preferable for the positive electrode of the lithium ion secondary battery, and copper is particularly preferable for the negative electrode of the lithium ion secondary battery.
- the shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 to 0.5 mm is preferable.
- the current collector is preferably used after roughening in advance.
- the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method.
- the mechanical polishing method an abrasive cloth paper with a fixed abrasive particle, a grindstone, an emery buff, a wire brush provided with a steel wire or the like is used.
- the method for producing an electrode for a secondary battery of the present invention may be any method in which an electrode active material layer is bound in a layered manner on at least one surface, preferably both surfaces of the current collector.
- an electrode slurry described later is applied to a current collector, dried, and then heated at 120 ° C. or higher for 1 hour or longer to form an electrode.
- the method for applying the electrode slurry to the current collector is not particularly limited. Examples thereof include a doctor blade method, a zip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.
- Examples of the drying method include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams.
- the preferable range of the porosity is preferably 5% or more, more preferably 7% or more, preferably 15% or less, more preferably 13% or less. If the porosity is too high, charging efficiency and discharging efficiency are deteriorated. When the porosity is too low, there are problems that it is difficult to obtain a high volume capacity, or that the electrodes are easily peeled off and are likely to be defective. Further, when a curable polymer is used, it is preferably cured.
- the thickness of the secondary battery electrode of the present invention is usually 5 ⁇ m or more, preferably 10 ⁇ m or more, and usually 300 ⁇ m or less, preferably 250 ⁇ m or less, for both the positive electrode and the negative electrode. When the electrode thickness is in the above range, both load characteristics and energy density are high.
- the slurry for secondary battery electrodes of the present invention includes a polymer having a cationic group, a counter anion corresponding to the cationic group, an electrode active material, and a solvent.
- Examples of the polymer having a cationic group, the counter anion corresponding to the cationic group, and the electrode active material include those described for the electrode.
- solvent As a solvent used for the slurry for electrodes, any solid component (polymer having a cationic group, counter anion corresponding to the cationic group, electrode active material, and other components) can be uniformly dispersed. There is no particular limitation.
- the solvent used for the electrode slurry either water or an organic solvent can be used.
- organic solvents examples include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; acetone, ethyl methyl ketone, disopropyl ketone, cyclohexanone, methylcyclohexane, and ethylcyclohexane.
- Ketones chlorinated aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; esters such as ethyl acetate, butyl acetate, ⁇ -butyrolactone and ⁇ -caprolactone; acylonitriles such as acetonitrile and propionitrile; tetrahydrofuran; Ethers such as ethylene glycol diethyl ether: alcohols such as methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether; Examples include amides such as loridone and N, N-dimethylformamide.
- solvents may be used alone, or two or more of these may be mixed and used as a mixed solvent.
- a solvent having excellent solubility of the polymer of the present invention, excellent dispersibility of the electrode active material and the conductive agent, and having a low boiling point and high volatility is preferable because it can be removed at a low temperature in a short time.
- Acetone, toluene, cyclohexanone, cyclopentane, tetrahydrofuran, cyclohexane, xylene, water, N-methylpyrrolidone, or a mixed solvent thereof is preferable, and water is particularly preferable.
- the solid content concentration of the slurry for the secondary battery electrode of the present invention is not particularly limited as long as it can be applied and immersed and has a fluid viscosity, but is generally about 10 to 80% by mass. is there.
- the slurry for the secondary battery electrode further includes a dispersant used in the electrode.
- a dispersant used in the electrode such as an electrolyte additive having a function of suppressing decomposition of the electrolyte and the like may be included. These are not particularly limited as long as they do not affect the battery reaction.
- the method for producing the slurry for the secondary battery electrode is not particularly limited, and a polymer having a cationic group, a counter anion corresponding to the cationic group, an electrode active material, and a solvent are added as necessary. Obtained by mixing other ingredients.
- a polymer having a cationic group, a counter anion corresponding to the cationic group, an electrode active material, and a solvent are added as necessary. Obtained by mixing other ingredients.
- an electrode slurry in which the electrode active material and the conductive agent are highly dispersed can be obtained regardless of the mixing method and the mixing order.
- the mixing device is not particularly limited as long as it can uniformly mix the above-mentioned components.
- the viscosity of the electrode slurry is preferably 10 mPa ⁇ s or more, more preferably 100 mPa ⁇ s or more, preferably 100,000 mPa ⁇ s or less, more preferably 50, from the viewpoint of uniform coating properties and electrode slurry aging stability. 1,000 mPa ⁇ s or less.
- the viscosity is a value measured using a B-type viscometer at 25 ° C. and a rotation speed of 60 rpm.
- the secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolytic solution, and at least one of the positive electrode and the negative electrode has a polymer having a cationic group, a counter anion corresponding to the cationic group, and an electrode activity. It consists of an electrode including an electrode active material layer containing a substance.
- Examples of the secondary battery of the present invention include a lithium ion secondary battery, a nickel metal hydride secondary battery, etc., but safety improvement is most demanded and the effect of improving low temperature characteristics is the highest, and in addition, in the operating temperature range.
- a lithium ion secondary battery is preferable because expansion is cited as a problem.
- the case where it uses for a lithium ion secondary battery is demonstrated.
- separator for lithium ion secondary battery
- known ones such as a microporous film or non-woven fabric made of polyolefin such as polyethylene and polypropylene; a porous resin coat containing inorganic ceramic powder; and the like can be used.
- a separator for a lithium ion secondary battery a known one such as a microporous film or non-woven fabric containing a polyolefin resin such as polyethylene or polypropylene or an aromatic polyamide resin; a porous resin coat containing an inorganic ceramic powder; Can do.
- polyolefin polymers polyethylene, polypropylene, polybutene, polyvinyl chloride
- microporous membranes made of resins such as mixtures or copolymers thereof, polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide
- a microporous membrane made of a resin such as amide, polyaramid, polycycloolefin, nylon, and polytetrafluoroethylene, or a woven fabric of polyolefin fibers, a nonwoven fabric thereof, an aggregate of insulating substance particles, and the like.
- a microporous film made of a polyolefin-based resin is preferable because the thickness of the entire separator can be reduced and the electrode active material ratio in the battery can be increased to increase the capacity per volume.
- the thickness of the organic separator is usually 0.5 ⁇ m or more, preferably 1 ⁇ m or more, and is usually 40 ⁇ m or less, preferably 30 ⁇ m or less, more preferably 10 ⁇ m or less. Within this range, the resistance due to the separator in the battery is reduced, and the workability during battery production is excellent.
- Electrode for lithium ion secondary battery As the electrolytic solution for the lithium ion secondary battery, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is used. A lithium salt is used as the supporting electrolyte.
- the lithium salt is not particularly limited, LiPF 6, LiAsF 6, LiBF 4, LiSbF 6, LiAlCl 4, LiClO 4, CF 3 SO 3 Li, C 4 F 9 SO 3 Li, CF 3 COOLi, (CF 3 CO) 2 NLi, (CF 3 SO 2 ) 2 NLi, (C 2 F 5 SO 2 ) NLi, and the like.
- LiPF 6 , LiClO 4 , and CF 3 SO 3 Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferable. Two or more of these may be used in combination. Since the lithium ion conductivity increases as the supporting electrolyte having a higher degree of dissociation is used, the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.
- the organic solvent used in the electrolyte for the lithium ion secondary battery is not particularly limited as long as it can dissolve the supporting electrolyte, but dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene Carbonates such as carbonate (PC), butylene carbonate (BC) and methyl ethyl carbonate (MEC); esters such as ⁇ -butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfolane and dimethyl sulfoxide Sulfur-containing compounds such as: are preferably used. Moreover, you may use the liquid mixture of these solvents.
- DMC dimethyl carbonate
- EC ethylene carbonate
- DEC diethyl carbonate
- PC butylene carbonate
- MEC methyl ethyl carbonate
- esters such as ⁇ -butyrolactone and methyl formate
- ethers such as 1,2-
- carbonates are preferable because they have a high dielectric constant and a wide stable potential region. Since the lithium ion conductivity increases as the viscosity of the solvent used decreases, the lithium ion conductivity can be adjusted depending on the type of the solvent. Moreover, it is also possible to use the electrolyte solution by containing an additive. Examples of the additive include carbonate compounds such as vinylene carbonate (VC) used in the above-described slurry for secondary battery electrodes.
- VC vinylene carbonate
- concentration of the supporting electrolyte in the electrolyte solution for lithium ion secondary batteries is 1 mass% or more normally, Preferably it is 5 mass% or more, and is 30 mass% or less normally, Preferably it is 20 mass% or less.
- concentration is usually 0.5 to 2.5 mol / L depending on the type of the supporting electrolyte. If the concentration of the supporting electrolyte is too low or too high, the ionic conductivity tends to decrease.
- the electrolytic solution other than the above include polymer electrolytes such as polyethylene oxide and polyacrylonitrile, gelled polymer electrolytes in which the polymer electrolyte is impregnated with an electrolytic solution, and inorganic solid electrolytes such as LiI and Li 3 N.
- a positive electrode and a negative electrode are overlapped via a separator, and this is wound into a battery container according to the shape of the battery.
- the method of injecting and sealing is mentioned. If necessary, an expanded metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate, or the like can be inserted to prevent an increase in pressure inside the battery and overcharge / discharge.
- the shape of the battery may be any of a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.
- the particulate polymer and the polymer having a cationic group partially form a complex. From the presence of this complex, The electrode active material surface is prevented from being completely covered, and a lithium ion entrance route to the electrode active material surface is selectively secured, while the effect of improving the mobility of thium ions by the polymer having a cationic group. It becomes possible to hold. Therefore, precipitation of lithium metal on the electrode surface is suppressed.
- a secondary battery electrode having an electrode active material layer containing a polymer having a cationic group, a particulate polymer, and an electrode active material.
- the electrode for a secondary battery wherein the mass ratio of the polymer having the cationic group and the particulate polymer in the electrode active material layer is 5:95 to 40:60.
- the electrode for a secondary battery wherein the particulate polymer contains an anion.
- the electrode for a secondary battery, wherein the particulate polymer has a glass transition temperature of 25 ° C. or lower.
- the electrode for a secondary battery, wherein the cationic group contains a hetero atom.
- the electrode for a secondary battery containing at least one of nitrogen, phosphorus, sulfur, oxygen, and boron as the heteroatom.
- a slurry for a secondary battery electrode comprising a polymer having a cationic group, a particulate polymer, an electrode active material and a solvent.
- a method for producing a secondary battery electrode comprising a step of applying and drying the slurry for a secondary battery electrode on a current collector.
- a secondary battery including a positive electrode, a negative electrode, a separator, and an electrolytic solution, wherein at least one of the positive electrode and the negative electrode is the electrode.
- the electrode active material layer necessarily includes a particulate polymer and does not necessarily include a counter anion corresponding to the cationic group. It is the same as the secondary battery electrode of the present invention except that the cation density is not limited to 0.1 to 15 meq / g.
- the slurry for a secondary battery electrode according to another invention necessarily includes a particulate polymer and does not necessarily include a counter anion corresponding to a cationic group, and the cation density in the polymer having a cationic group Is the same as that of the slurry for secondary battery electrodes of the present invention except that is not limited to 0.1 to 15 meq / g.
- the manufacturing method of the electrode for secondary batteries which concerns on another invention is 2nd of this invention except using the slurry for secondary battery electrodes which concerns on another invention instead of the slurry for secondary battery electrodes of this invention. It is the same as the manufacturing method of the electrode for secondary batteries.
- the secondary battery according to another invention is the same as the secondary battery according to the present invention except that the secondary battery electrode according to another invention is used instead of the secondary battery electrode according to the present invention.
- the polymer having a cationic group and a particulate polymer are contained in the electrode active material layer, so that these polymers have a resistance when lithium is inserted on the surface of the electrode active material. It is possible to obtain a secondary battery electrode that is suppressed, lithium deposition does not occur on the electrode surface, and the obtained secondary battery has a high charge capacity including a low temperature range of 0 ° C. or lower.
- CV (meq / g) N / 400 PVSK solution titration ⁇ N / 400 PVSK solution titer ⁇ 1/2
- the blank titer is calculated by adding the titer of the N / 400 PVSK solution.
- Each electrode is cut into a rectangular shape having a width of 1 cm and a length of 10 cm to form a test piece, which is fixed with the electrode active material layer surface facing up.
- the stress was measured when the cellophane tape was peeled off from one end of the test piece in the 180 ° direction at a speed of 50 mm / min. The measurement was performed 10 times, the average value was obtained, and this was used as the peel strength. It shows that the adhesion strength of an electrode plate is so large that this value is large.
- Polymer D An aqueous solution of quaternary salt of N, N-dimethylaminopropylacrylamide methyl chloride (manufactured by Kojin Co., Ltd. DMAPAA-Q 75% aqueous solution) in a reactor equipped with a reflux condenser, thermometer, dropping funnel, stirrer, and gas introduction tube 150 parts was added, and ion exchange water was further added to prepare a monomer concentration of 30%. Furthermore, 2 parts of polyoxyethylene alkyl ether (Emulgen 1150S-60 manufactured by Kao Corporation) was added and stirred to prepare an emulsion.
- Emulgen 1150S-60 manufactured by Kao Corporation
- the temperature inside the system was raised to 60 ° C. while introducing nitrogen gas, and 0.2 part of a water-soluble azo polymerization initiator (VA-050 manufactured by Wako Pure Chemical Industries, Ltd.) was added as a polymerization initiator.
- VA-050 water-soluble azo polymerization initiator manufactured by Wako Pure Chemical Industries, Ltd.
- the reaction started.
- the reaction was continued at 60 ° C. for 4 hours, then heated to 80 ° C. and continued for 4 hours, and then cooled to complete the reaction. Thereby, the polymer D was obtained.
- the polymerization conversion rate determined from the solid content concentration was 96%.
- the cation density of the polymer D determined by the colloid titration method was 4.8 meq / g.
- required from GPC was about 50,000.
- the temperature inside the system was raised to 60 ° C. while introducing nitrogen gas, and 0.2 part of a water-soluble azo polymerization initiator (VA-050 manufactured by Wako Pure Chemical Industries, Ltd.) was added as a polymerization initiator.
- VA-050 water-soluble azo polymerization initiator manufactured by Wako Pure Chemical Industries, Ltd.
- the reaction started.
- the reaction was continued at 60 ° C. for 4 hours, then heated to 80 ° C. and continued for 4 hours, and then cooled to complete the reaction.
- a polymer E was obtained.
- the polymerization conversion rate determined from the solid content concentration was 95%.
- the cation density of the polymer E determined by the colloid titration method was 5.2 meq / g.
- required from GPC was about 80,000.
- the reaction was further continued for 3 hours, and then the temperature was raised to 80 ° C. and the reaction was continued for 3 hours, followed by cooling to complete the reaction. Thereby, the polymer I was obtained.
- the polymerization conversion rate determined from the solid content concentration was 96%.
- an appropriate amount of ion-exchanged water was added to adjust the solid content concentration to 25%.
- the cation density of polymer I determined by colloid titration was 0.05 meq / g.
- polymers A to C, F, G, and H are ion-exchanged water and a 20% strength aqueous solution is prepared and used, and polymers D, E, and I are used as they are. did.
- Particulate polymer 1 To Polymerization Can A, 5 parts of styrene, 10 parts of butadiene, 3 parts of polyoxyethylene alkyl ether (Emulgen 1150S-60 manufactured by Kao Corporation) and 70 parts of ion-exchanged water were added and stirred sufficiently. Thereafter, the temperature was adjusted to 70 ° C., 0.3 parts of a water-soluble azo polymerization initiator (VA-086 manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator and 10 parts of ion-exchanged water were added and stirred for 120 minutes.
- VA-086 water-soluble azo polymerization initiator
- Porate polymer 2 To polymerization can A, 12 parts of butyl acrylate, 2 parts of acrylonitrile, 2 parts of polyoxyethylene alkyl ether, and 60 parts of ion-exchanged water were added and sufficiently stirred. Thereafter, the temperature was set to 70 ° C., 0.25 part of a water-soluble azo polymerization initiator and 10 parts of ion-exchanged water were added as a polymerization initiator, and the mixture was stirred for 60 minutes.
- Fine polymer 3 To polymerization can A, 1 part of itaconic acid, 1.0 part of sodium dodecylbenzenesulfonate, and 80 parts of ion-exchanged water were added and sufficiently stirred. On the other hand, 50 parts of butadiene, 48 parts of styrene, 1 part of itaconic acid, 1.0 part of sodium dodecylbenzenesulfonate, and 45 parts of ion-exchanged water were added to another polymerization vessel B and stirred to prepare an emulsion.
- the polymerization can A was set to 70 ° C., and 1/30 of the emulsion prepared in the polymerization can B was continuously added from the polymerization can B to the polymerization can A.
- Porate polymer 4 To polymerization can A, 12 parts of 2-ethylhexyl acrylate, 5 parts of styrene, 0.05 part of sodium lauryl sulfate, and 70 parts of ion-exchanged water were added and sufficiently stirred. Thereafter, the temperature was adjusted to 70 ° C., 0.2 parts of ammonium persulfate and 10 parts of ion-exchanged water were added as a polymerization initiator, and the mixture was stirred for 120 minutes.
- Fine polymer 5 To the polymerization vessel A, 0.2 part of itaconic acid, 0.3 part of sodium dodecylbenzenesulfonate, and 80 parts of ion-exchanged water were added and sufficiently stirred. On the other hand, 35 parts of butadiene, 64.6 parts of styrene, 0.2 part of itaconic acid, 0.5 part of sodium dodecylbenzenesulfonate, and 45 parts of ion-exchanged water are added to another polymerization vessel B and stirred to obtain an emulsion. Was made.
- the polymerization can A was set to 70 ° C., and 1/30 of the emulsion prepared in the polymerization can B was sequentially added from the polymerization can B to the polymerization can A.
- Example 1 (Production of slurry for electrodes) As carboxymethyl cellulose (CMC), 1.0% CMC aqueous solution was prepared using “Daicel 2200” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.
- the electrode slurry was applied to one side of a copper foil having a thickness of 18 ⁇ m with a comma coater so that the film thickness after drying was about 200 ⁇ m, dried at 50 ° C. for 20 minutes, and then heat-treated at 110 ° C. for 20 minutes. As a result, an electrode raw material was obtained.
- the raw electrode was rolled with a roll press to obtain a negative electrode having an electrode active material layer thickness of 80 ⁇ m. When the coating thickness of the obtained electrode was measured, the film thickness was almost uniform.
- the negative electrode is cut into a disk shape having a diameter of 15 mm, and a separator made of a porous polypropylene film having a diameter of 18 mm and a thickness of 25 ⁇ m on the surface of the negative electrode active material layer, metallic lithium used as the positive electrode, and expanded metal in this order.
- This was laminated and stored in a stainless steel coin-type outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm) provided with polypropylene packing.
- the electrolyte is poured into the container so that no air remains, and the outer container is fixed with a 0.2 mm thick stainless steel cap through a polypropylene packing, and the battery can is sealed, and the diameter is A negative electrode half cell having a thickness of 20 mm and a thickness of about 2 mm was produced.
- Example 2 Except that the particulate polymer 2 was used instead of the particulate polymer 1, the same operation as in Example 1 was performed to prepare an electrode slurry and a negative electrode half cell, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 3 Except that the polymer B was used instead of the polymer A, the same operation as in Example 2 was performed to prepare an electrode slurry and a negative electrode half cell, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 4 Except that the polymer C was used instead of the polymer A, the same operation as in Example 2 was performed to prepare an electrode slurry and a negative electrode half cell, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 5 Except having used the polymer D instead of the polymer A, operation similar to Example 1 was performed, the electrode slurry and the negative electrode half cell were produced, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 6 Except that the polymer E was used instead of the polymer A, the same operation as in Example 1 was performed to prepare an electrode slurry and a negative electrode half cell, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 7 The polymer F is used in place of the polymer A, the particulate polymer 3 is used in place of the particulate polymer 1, and the mixing ratio of the polymer having a cationic group and the particulate polymer is 20 by mass ratio. : Except that it was set to 80, the same operation as Example 1 was performed, the electrode slurry and the negative electrode half cell were produced, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 8 Except that the polymer B was used instead of the polymer F, the same operation as in Example 7 was performed to prepare an electrode slurry and a negative electrode half cell, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 9 An electrode slurry and a negative electrode half cell were prepared by performing the same operation as in Example 7 except that the blending ratio of the polymer having a cationic group and the particulate polymer was 6:94 by mass ratio, and this battery was prepared. The performance was evaluated. The results are shown in Table 2.
- Example 10 An electrode slurry and a negative electrode half cell were prepared by performing the same operation as in Example 7 except that the blending ratio of the polymer having a cationic group and the particulate polymer was 40:60 by mass ratio, and this battery was prepared. The performance was evaluated. The results are shown in Table 2.
- Example 11 Except that the particulate polymer 4 was used instead of the particulate polymer 3, the same operation as in Example 7 was performed to prepare an electrode slurry and a negative electrode half cell, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 12 Except that the particulate polymer 5 was used instead of the particulate polymer 3, the same operation as in Example 7 was performed to prepare an electrode slurry and a negative electrode half cell, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 13 100 parts of spinel manganese (LiMn 2 O 4 ) as an electrode active material, 0.1 part (based on solid content) of polymer A as a polymer having a cationic group, acetylene black (HS-100: Electrochemical Industry) 5 parts, 1.0 part (based on solid content) of an aqueous dispersion of particulate polymer 2 having a solid content concentration of 40% as a particulate polymer, and the degree of etherification as a thickener is 0.8.
- a slurry for positive electrode was prepared by stirring 40 parts of a certain aqueous solution of carboxymethyl cellulose (solid concentration 2%) and an appropriate amount of water with a planetary mixer. Table 3 shows the evaluation results of the viscosity change rate after 5 hours of the positive electrode slurry.
- the positive electrode slurry was applied on one side onto a 20 ⁇ m thick aluminum foil with a comma coater, dried at 60 ° C. for 20 minutes, and then heat-treated at 120 ° C. for 20 minutes to obtain an electrode stock.
- This electrode fabric was rolled with a roll press to obtain an electrode for a positive electrode having an electrode active material layer thickness of 70 ⁇ m. When the coating thickness of the obtained electrode was measured, the film thickness was almost uniform.
- the positive electrode is cut out into a disk shape having a diameter of 15 mm, and a separator made of a disk-shaped porous polypropylene film having a diameter of 18 mm and a thickness of 25 ⁇ m is formed on the electrode active material layer side of the positive electrode, metallic lithium used as the negative electrode, and expanded metal in this order.
- This was laminated and stored in a stainless steel coin-type outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm) provided with polypropylene packing.
- the electrolyte is poured into the container so that no air remains, and the outer container is fixed with a 0.2 mm thick stainless steel cap through a polypropylene packing, and the battery can is sealed, and the diameter is A positive electrode half cell having a thickness of 20 mm and a thickness of about 2 mm was produced.
- the performance evaluation results of this battery are shown in Table 3.
- NMP N-methylpyrrolidone
- Example 15 Except that the polymer G was used instead of the polymer A, the same operation as in Example 1 was performed to prepare an electrode slurry and a negative electrode half cell, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 16 Except having used the polymer C instead of the polymer A, operation similar to Example 1 was performed, the electrode slurry and the negative electrode half cell were produced, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 17 instead of particulate polymer 1, polyvinylidene fluoride-hexafluoropropylene copolymer particles (hereinafter referred to as “PVDF-HFP polymer particles”) having a solid content concentration of 40% and a glass transition temperature of ⁇ 5 ° C.
- PVDF-HFP polymer particles having a solid content concentration of 40% and a glass transition temperature of ⁇ 5 ° C.
- the same operation as in Example 1 was carried out except that a slurry for an electrode and a negative electrode half cell were produced, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 18 Except that the polymer F was used instead of the polymer A, the same operation as in Example 1 was performed to prepare an electrode slurry and a negative electrode half cell, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 19 Except that the polymer H was used instead of the polymer A, the same operation as in Example 1 was performed to prepare an electrode slurry and a negative electrode half cell, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 20 Except that the polymer B was used instead of the polymer A, the same operation as in Example 1 was performed to prepare an electrode slurry and a negative electrode half cell, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 2 The same operation as in Example 7 except that 2-aminoethanesulfonic acid, which is a cation-containing low molecular weight composition, was used instead of the polymer B instead of a cation-containing polymer (that is, a polymer having a cationic group).
- the electrode slurry and the negative electrode half cell were prepared, and the performance of the battery was evaluated. The results are shown in Table 2.
- Example 3 (Comparative Example 3) Except that the polymer having a cationic group was not used, the same operation as in Example 7 was performed to prepare an electrode slurry and a negative electrode half cell, and the performance of this battery was evaluated. The results are shown in Table 2.
- Example 4 A slurry for an electrode and a negative electrode half cell were prepared in the same manner as in Example 7 except that a polyethyleneimine polymer (trade name, Epomin SP-200) was used instead of the polymer A. Was evaluated. The results are shown in Table 2.
- a polyethyleneimine polymer trade name, Epomin SP-200
- Example 5 (Comparative Example 5) Except that the polymer having a cationic group was not used, the same operation as in Example 13 was performed to produce a positive electrode slurry and a positive electrode half cell, and the performance of this battery was evaluated. The results are shown in Table 3.
- Examples 1 to 20 by using a polymer having a cationic group having a predetermined cation density and a counter anion, slurry stability, low temperature characteristics, lithium precipitation suppression can be achieved.
- a lithium ion secondary battery excellent in all can be obtained.
- an acrylate particulate polymer having no anion is used in combination, the cation density is in the range of 5 to 7 meq / g, and the molecular weight is in the range of 5,000 to 300,000.
- Examples 2 and 13 using a class cation are particularly excellent in slurry stability, low temperature characteristics, and lithium precipitation suppression.
- Example 7 in which a particulate polymer having a predetermined amount of anion is used in combination, the cation density is in the range of 2 to 5 meq / g, and the molecular weight is in the range of 5,000 to 300,000 is In addition, it has high peel strength and is excellent in all properties.
- those having a cation density outside the predetermined range Comparative Examples 1 and 4
- having a low molecular composition containing a cation without having a polymer having a cationic group and a counter anion Comparative Example 2
- Those having no polymer having a cationic group and a counter anion are particularly inferior in low-temperature characteristics and lithium precipitation suppression.
Abstract
Description
例えば、特許文献1には、カチオン性基を有する重合体及び該カチオン性基に対応するアニオンをバインダーに用いることにより、電極活物質の分散性が向上し、その結果導電剤の分散性も向上することにより、電極の表面平滑性さらには出力特性に優れた電池が得られる旨開示されている。
従って、本発明の目的は、リチウム金属の析出を抑制し、得られる二次電池が優れた低温特性を示すリチウムイオン二次電池用電極を提供することにある。
これは、重合体が電極活物質表面近傍に選択的に存在する結果、リチウム挿入時の脱溶媒和抵抗が大幅に低減し、挿入されなかったリチウムの電極表面への析出を抑制できると考えたことによる。そしてこれらの知見により本発明を完成するに至った。
〔1〕 カチオン性基を有する重合体、該カチオン性基に対応するアニオン、及び電極活物質を含有してなる、電極活物質層を有し、前記重合体中のカチオン密度が0.1~15meq/gである二次電池用電極。
〔2〕 前記電極活物質層がさらに粒子状重合体を含有してなる前記の二次電池用電極。
〔3〕 前記電極活物質層における前記カチオン性基を有する重合体と、前記粒子状重合体との質量比が5:95~40:60である前記の二次電池用電極。
〔4〕 前記粒子状重合体が、アニオンを含むものである前記の二次電池用電極。
〔5〕 前記カチオン性基が、脂環式カチオン性基または複素環式カチオン性基である前記の二次電池用電極。
〔6〕 カチオン性基を有する重合体、該カチオン性基に対応するアニオン、電極活物質及び溶媒を含有してなる二次電池電極用スラリーであって、前記重合体中のカチオン密度が0.1~15meq/gである二次電池電極用スラリー。
〔7〕 正極、負極、セパレーター及び電解液を含む二次電池であって、前記正極及び負極の少なくともいずれかが前記の二次電池用電極である、二次電池。
本発明の二次電池用電極(以下、単に「電極」ということがある。)は、カチオン性基を有する重合体、該カチオン性基に対応するアニオン(以下、「対アニオン」という場合がある。)、及び電極活物質を含有してなる電極活物質層(「電極合剤層」ともいう。)を有する。ここで、カチオン性基に対応するアニオンとは、カチオン性基に結合し得るアニオンのことを表す。
本発明において、カチオン性基とは、電子を放出して正の電荷を帯びた原子、または原子団を示す。本発明に用いられる重合体が有するカチオン性基としては、ヘテロ原子を含むものが好ましい。本発明においてヘテロ原子とは、水素、炭素及び金属以外の原子と定義される。これらの中でも、後述の電解液溶媒との適度な相互作用を有しリチウム金属の析出を抑制しやすいことから、窒素、りん、硫黄、酸素及びホウ素の少なくともいずれか1つを含むものが好ましく、窒素、りん及び硫黄の少なくともいずれか1つを含むものが最も好ましい。
式(II):
又は式(III):
例えば、脂肪族カチオン性基ではR1~R3のうち水素原子が含まれない場合は第四級カチオン性基、1つが水素原子の場合は第三級カチオン性基、2つが水素原子の場合は第二級カチオン性基と呼ぶ。脂環式カチオン性基では、R1が水素原子の場合は第三級カチオン性基、R1が水素以外の場合は第四級カチオン性基と呼ぶ。複素環式カチオン性基の場合は全て第四級カチオン性基である。
本発明に用いられる、前記カチオン性基に対応するアニオン(すなわち、対アニオン)は、陰イオンを含んでなり、陰イオンとしてはハロゲン元素またはカルコゲン元素を含むものが好ましい。
ここで、「ハロゲン元素」とは、第17族元素であるフッ素、塩素、臭素、ヨウ素、アスタチンからなる原子群を意味する。これらの中でも、解離度の大きい強電解質を形成し得ることから、塩素、臭素及びヨウ素が好ましく、対アニオンとしては塩素イオン、臭素イオン及びヨウ素イオンからなる群から選ばれる少なくとも1つが好ましい。
「カルコゲン元素」とは、第16族元素である酸素、硫黄、セレン、テルル、ポロニウムからなる原子群を意味する。これらの中でも、解離度の大きい強電解質を形成し得ることからカルコゲン元素として硫黄、酸素を含有する、スルホン酸イオン、硫酸イオン及び硝酸イオンからなる群から選ばれる少なくとも1つが好ましい。
本発明に用いるカチオン性基を有する重合体の重量平均分子量は、硝酸ナトリウム水溶液を展開溶媒としたゲル・パーミエーション・クロマトグラフィー(以下、「GPC」ということがある。)で測定した標準ポリエチレンオキサイド換算値で、好ましくは1,000以上、より好ましくは5,000以上、更に好ましくは10,000以上であり、好ましくは500,000以下、より好ましくは300,000以下、更に好ましくは200,000以下、特に好ましくは100,000以下である。カチオン性基を有する重合体の重量平均分子量が前記範囲にあると、カチオン性基を有する重合体が、電極内部において電極活物質表面への高い吸着安定性を示し、また適度な運動性を有することから優れた低温特性を示し、且つ電極用スラリーの安定性に優れて生産性の向上及び平滑な電極を得ることができる。
本発明においては、特定の密度範囲のカチオンと、そのカチオン性基に対応する対アニオンとが存在していることが、本発明の効果を奏する要件となるので、カチオンと対アニオンの種類にかかわらず本発明の効果が発現できる。よってその組み合わせには特に制限がなく、いずれの組み合わせであっても本発明の効果が得られる。
単量体の例を挙げると、例えば対アニオンが塩素イオンの場合、ビニルアルキルアンモニウムクロライド、(メタ)アクリロイルアルキルアンモニウムクロライド、(ジ)アリルアルキルアンモニウムクロライド、アミノアルキル(メタ)アクリルアミド等の、式(I)で示される含窒素脂肪族カチオンを有する不飽和単量体;ビニルアルキルピロリジニウムクロライド、(メタ)アクリロイルアルキルピロリジニウムクロライド、(ジ)アリルアルキルピロリジニウムクロライド、ビニルアルキルピペリジニウムクロライド、(メタ)アクリロイルアルキルピペリジニウムクロライド、(ジ)アリルアルキルピペリジニウムクロライド、ビニルアルキルモルホリニウムクロライド、(メタ)アクリロイルアルキルモルホリニウムクロライド、(ジ)アリルアルキルモルホリニウムクロライド等の、式(II)で示される含窒素脂環式カチオンを有する不飽和単量体;ビニルピリジニウムクロライド、(メタ)アクリロイルアルキルピリジニウムクロライド、(ジ)アリルアルキルピリジニウムクロライド、ビニルイミダゾリウムクロライド、(メタ)アクリロイルアルキルイミダゾリウムクロライド、(ジ)アリルアルキルイミダゾリウムクロライド等の、式(III)で示される含窒素複素環式カチオンを有する不飽和単量体;ビニルアルキルホスホニウムクロライド、(メタ)アクリロイルアルキルホスホニウムクロライド、(ジ)アリルアルキルホスホニウムクロライド等の、含リン脂肪族カチオンを有する不飽和単量体;ビニルアルキルスルホニウムクロライド、(メタ)アクリロイルアルキルスルホニウムクロライド、(ジ)アリルアルキルスルホニウムクロライド等の、含硫黄脂肪族カチオンを有する不飽和単量体;が挙げられる。
本発明に用いるカチオン性基を有する重合体中の前記共重合可能な単量体単位の含有割合は、好ましくは1質量%以上、より好ましくは10質量%以上であり、好ましくは90質量%以下、より好ましくは50質量%以下である。
重合に用いられる重合開始剤としては、例えば過酸化水素、tert-ブチルヒドロパーオキシドなどの過酸化物;これらの過酸化物と二価鉄(Fe++)、Na2SO3、アスコルビン酸などの還元剤との組合わせからなるレドックス系開始剤;過酸化ラウロイル、ジソプロピルパーオキシジカーボネート、ジ2-エチルヘキシルパーオキシジカーボネート、t-ブチルパーオキシピバレート、3,5,5-トリメチルヘキサノイルパーオキシドなどの有機過酸化物;α,α’-アゾビスイソブチロニトリルなどのアゾ化合物;過硫酸アンモニウム、過硫酸カリウムなどの過硫酸塩;などが挙げられる。
前記した重合開始剤、単量体、懸濁剤または乳化剤、分子量調整剤などは重合開始時に一括して重合系に添加してもよいし、重合中に分割して添加することもできる。重合は通常35~80℃の温度で撹拌下にて行われる。
この場合、重合方法としては、前記と同様に、溶液重合法、懸濁重合法、乳化重合法のいずれも用いることができ、後の付加反応の条件や得られる重合体の特性に応じて最適な製造方法を選択すればよい。例えば、付加反応を水系で行う場合には、乳化重合により微細な水性分散粒子として重合体を得るのが有利である。また、付加反応を溶剤系で行う場合には、溶液重合法またはメタノールなどの低級アルコールを重合媒体とする懸濁重合法が好ましいが、通常の懸濁重合法も用いることができる。
前記粒子状金属除去工程における重合体溶液もしくは重合体分散液から粒子状の金属成分を除去する方法は特に限定されず、例えば、濾過フィルターによる濾過により除去する方法、振動ふるいにより除去する方法、遠心分離により除去する方法、磁力により除去する方法等が挙げられる。中でも、除去対象が金属成分であるので、金属異物成分の選択的かつ効率的な除去ができることから磁力により除去する方法が好ましい。磁力により除去する方法としては、金属成分が除去できる方法であれば特に限定はされないが、生産性および除去効率を考慮すると、好ましくは重合体の製造ライン中に磁気フィルターを配置することで行われる。
本発明の二次電池用電極に用いられる電極活物質は、電極が利用される二次電池に応じて選択すればよい。前記二次電池としては、リチウムイオン二次電池やニッケル水素二次電池が挙げられる。
無機化合物からなる正極活物質としては、遷移金属酸化物、リチウムと遷移金属との複合酸化物、遷移金属硫化物などが挙げられる。上記の遷移金属としては、Fe、Co、Ni、Mn等が使用される。正極活物質に使用される無機化合物の具体例としては、LiCoO2、LiNiO2、LiMnO2、LiMn2O4、LiFePO4、LiFeVO4などのリチウム含有複合金属酸化物;TiS2、TiS3、非晶質MoS2等の遷移金属硫化物;Cu2V2O3、非晶質V2O-P2O5、MoO3、V2O5、V6O13などの遷移金属酸化物;などが挙げられる。これらの化合物は、部分的に元素置換したものであってもよい。有機化合物からなる正極活物質としては、例えば、ポリアセチレン、ポリ-p-フェニレンなどの導電性重合体を用いることもできる。電気伝導性に乏しい、鉄系酸化物は、還元焼成時に炭素源物質を存在させることで、炭素材料で覆われた電極活物質として用いてもよい。また、これら化合物は、部分的に元素置換したものであってもよい。
本発明において、電極活物質層は、カチオン性基を有する重合体、前記カチオン性基に対応する対アニオン、及び電極活物質の他に、更に粒子状重合体(粒子状高分子ともいう。)を含んでもよい。粒子状重合体を含むことにより電極の結着性が向上し、電極の撒回時等の工程上においてかかる機械的な力に対する強度が上がり、また電極中の電極活物質層が脱離しにくくなることから、脱離物による短絡等の危険性が小さくなる。
これらの中でもフッ素を含有しない非フッ素系重合体が好ましい。粒子状重合体がフッ素を含有すると、高い電気陰性度からカチオンとの相互作用により、リチウム金属析出抑制効果が小さくなる恐れがある。
粒子状重合体は、非結晶性重合体であることがより好ましい。粒子状重合体が非結晶性であることにより電極活物質層の柔軟性に優れ、また電池内部での重合体の運動性によりリチウム金属析出抑制効果が高く発現される。粒子状重合体の結晶化度は、好ましくは10%以下、更に好ましくは5%以下である。非フッ素系重合体かつ非結晶性重合体の中でも、電極活物質との結着性および得られる電極の強度や柔軟性に優れるため、ジエン系重合体、又はアクリル系重合体が好ましい。
スルホン酸基を持つ界面活性剤としては、高級アルコールの硫酸エステル、アルキルベンゼンスルホン酸塩、脂肪族スルホン酸塩などが挙げられ、具体的にはドデシルベンゼンスルホン酸ナトリウム、ドデシルフェニルエーテルスルホン酸ナトリウムなどのベンゼンスルホン酸塩;ラウリル硫酸ナトリウム、テトラドデシル硫酸ナトリウムなどのアルキル硫酸塩;ジオクチルスルホコハク酸ナトリウム、ジヘキシルスルホコハク酸ナトリウムなどのスルホコハク酸塩、ポリオキシエチレンラウリルエーテルサルフェートナトリウム塩、ポリオキシエチレンノニルフェニルエ-テルサルフェートナトリウム塩などのエトキシサルフェート塩;アルカンスルホン酸塩;などが挙げられる。
他の界面活性剤としては、ノニオン性界面活性剤、カチオン性界面活性剤、両性界面活性剤が挙げられる。
ノニオン界面活性剤としては、公知のものが使用でき、具体的にはポリエチレングリコールのアルキルエステル型、アルキルエーテル型、アルキルフェニルエーテル型などが用いられる。
カチオン性界面活性剤としては、公知のものが使用でき、第1級アミンの塩、第2級アミンの塩、第3級アミンの塩、第4級アンモニウム塩などが挙げられる。
両性界面活性剤としては、アニオン部分としてカルボン酸塩、硫酸エステル塩、スルホン酸塩、燐酸エステル塩を、カチオン部分としてアミン塩、第4級アンモニウム塩を持つものが挙げられ、具体的には、ラウリルベタイン、ステアリルベタインなどのベタイン類;ラウリル-β-アラニン、ステアリル-β-アラニン、ラウリルジ(アミノエチル)グリシン、オクチルジ(アミノエチル)グリシンなどのアミノ酸タイプのものなどが用いられる。
本発明の二次電池用電極には、上記成分のほかに、さらに導電剤、補強材、分散剤、レベリング剤、酸化防止剤、増粘剤、電解液分解抑制等の機能を有する電解液添加剤等の、他の成分が含まれていてもよい。また、これらの他の成分は、後述の二次電池電極用スラリー中に含まれていてもよい。これらは電池反応に影響を及ぼさないものであれば特に限られない。
補強材としては、各種の無機および有機の球状、板状、棒状または繊維状のフィラーが使用できる。補強材を用いることにより強靭で柔軟な電極を得ることができ、優れた長期サイクル特性を示すことができる。
導電剤や補強剤の電極活物質層中の含有量は、電極活物質100質量部に対して、通常0.01質量部以上、好ましくは1質量部以上であり、通常20質量部以下、好ましくは10質量部以下である。前記範囲に含まれることにより、高い容量と高い負荷特性を示すことができる。
その他には、フュームドシリカやフュームドアルミナなどのナノ微粒子:アルキル系界面活性剤、シリコン系界面活性剤、フッ素系界面活性剤、金属系界面活性剤などの界面活性剤等が挙げられる。
前記ナノ微粒子を混合することにより電極用スラリーのチキソ性をコントロールすることができ、さらにそれにより得られる電極のレベリング性を向上させることができる。電極活物質層中のナノ微粒子の含有割合は、電極活物質100質量部に対して、好ましくは0.01~10質量部である。電極活物質層中のナノ微粒子の含有量が上記範囲であることにより電極用スラリー安定性、生産性に優れ、高い電池特性を示す。
前記界面活性剤を混合することにより電極用スラリー中の電極活物質等の分散性を向上することができ、さらにそれにより得られる電極の平滑性を向上させることができる。電極活物質中の界面活性剤の含有割合は、電極活物質100質量部に対して、好ましくは0.01~10質量部である。電極活物質中の界面活性剤の含有量が上記範囲であることにより電極用スラリー安定性、電極平滑性に優れ、高い生産性を示す。
本発明の二次電池用電極は、カチオン性基を有する重合体、該カチオン性基に対応する対アニオン及び電極活物質を含む電極活物質層が集電体上に形成されていてもよい。
集電体は、電気導電性を有しかつ電気化学的に耐久性のある材料であれば特に制限されないが、耐熱性を有するとの観点から、例えば、鉄、銅、アルミニウム、ニッケル、ステンレス鋼、チタン、タンタル、金、白金などの金属材料が好ましい。中でも、リチウムイオン二次電池の正極用としてはアルミニウムが特に好ましく、リチウムイオン二次電池の負極用としては銅が特に好ましい。集電体の形状は特に制限されないが、厚さ0.001~0.5mm程度のシート状のものが好ましい。集電体は、電極の接着強度を高めるため、予め粗面化処理して使用するのが好ましい。粗面化方法としては、機械的研磨法、電解研磨法、化学研磨法などが挙げられる。機械的研磨法においては、研磨剤粒子を固着した研磨布紙、砥石、エメリバフ、鋼線などを備えたワイヤーブラシ等が使用される。また、電極の接着強度や導電性を高めることを目的に、集電体表面に中間層を形成してもよい。
本発明の二次電池用電極の製造方法は、前記集電体の少なくとも片面、好ましくは両面に電極活物質層を層状に結着させる方法であればよい。例えば、後述する電極用スラリーを集電体に塗布、乾燥し、次いで、120℃以上で1時間以上加熱処理して電極を形成する。電極用スラリーを集電体へ塗布する方法は特に制限されない。例えば、ドクターブレード法、ジップ法、リバースロール法、ダイレクトロール法、グラビア法、エクストルージョン法、ハケ塗り法などの方法が挙げられる。乾燥方法としては例えば温風、熱風、低湿風による乾燥、真空乾燥、(遠)赤外線や電子線などの照射による乾燥法が挙げられる。
本発明の二次電池電極用スラリーは、カチオン性基を有する重合体、該カチオン性基に対応する対アニオン、電極活物質、及び溶媒を含む。カチオン性基を有する重合体、該カチオン性基に対応する対アニオン、電極活物質としては、電極で説明したものと同様のものが挙げられる。
電極用スラリーに用いる溶媒としては、上記固形分(カチオン性基を有する重合体、該カチオン性基に対応する対アニオン、電極活物質、及びその他の成分)を均一に分散し得るものであれば特に制限されない。
電極用スラリーに用いる溶媒としては、水および有機溶媒のいずれも使用できる。有機溶媒としては、シクロペンタン、シクロヘキサンなどの環状脂肪族炭化水素類;トルエン、キシレン、エチルベンゼンなどの芳香族炭化水素類;アセトン、エチルメチルケトン、ジソプロピルケトン、シクロヘキサノン、メチルシクロヘキサン、エチルシクロヘキサンなどのケトン類;メチレンクロライド、クロロホルム、四塩化炭素など塩素系脂肪族炭化水素;酢酸エチル、酢酸ブチル、γ-ブチロラクトン、ε-カプロラクトンなどのエステル類;アセトニトリル、プロピオニトリルなどのアシロニトリル類;テトラヒドロフラン、エチレングリコールジエチルエーテルなどのエーテル類:メタノール、エタノール、イソプロパノール、エチレングリコール、エチレングリコールモノメチルエーテルなどのアルコール類;N-メチルピロリドン、N,N-ジメチルホルムアミドなどのアミド類等があげられる。
これらの溶媒は、単独で使用しても、これらを2種以上混合して混合溶媒として使用してもよい。これらの中でも特に、本発明の重合体の溶解性に優れ、電極活物質及び導電剤の分散性にすぐれ、沸点が低く揮発性が高い溶媒が、短時間でかつ低温で除去できるので好ましい。アセトン、トルエン、シクロヘキサノン、シクロペンタン、テトラヒドロフラン、シクロヘキサン、キシレン、水、若しくはN-メチルピロリドン、またはこれらの混合溶媒が好ましく、特に水が好ましい。
本発明においては、二次電池電極用スラリーの製法は、特に限定はされず、カチオン性基を有する重合体、該カチオン性基に対応する対アニオン、電極活物質、及び溶媒と必要に応じ添加される他の成分を混合して得られる。
本発明においては上記成分を用いることにより、混合方法や混合順序にかかわらず、電極活物質と導電剤が高度に分散された電極用スラリーを得ることができる。混合装置は、上記成分を均一に混合できる装置であれば特に限定されず、ビーズミル、ボールミル、ロールミル、サンドミル、顔料分散機、擂潰機、超音波分散機、ホモジナイザー、プラネタリーミキサー、フィルミックスなどを使用することができるが、中でも高濃度での分散が可能なことから、ボールミル、ロールミル、顔料分散機、擂潰機、プラネタリーミキサーを使用することが特に好ましい。
電極用スラリーの粘度は、均一塗工性、電極用スラリー経時安定性の観点から、好ましくは10mPa・s以上、更に好ましくは100mPa・s以上であり、好ましくは100,000mPa・s以下、更に50,000mPa・s以下である。前記粘度は、B型粘度計を用いて25℃、回転数60rpmで測定した時の値である。
本発明の二次電池は、正極、負極、セパレーター及び電解液を含み、前記正極及び負極の少なくともいずれかが、カチオン性基を有する重合体、該カチオン性基に対応する対アニオン、及び電極活物質を含有してなる電極活物質層を含む電極からなる。
セパレーターとしては、ポリエチレン、ポリプロピレンなどのポリオレフィン製の微孔膜または不織布;無機セラミック粉末を含む多孔質の樹脂コート;など公知のものを用いることができる。
リチウムイオン二次電池用セパレーターとしては、ポリエチレン、ポリプロピレンなどのポリオレフィン樹脂や芳香族ポリアミド樹脂を含んでなる微孔膜または不織布;無機セラミック粉末を含む多孔質の樹脂コート;など公知のものを用いることができる。例えばポリオレフィン系重合体(ポリエチレン、ポリプロピレン、ポリブテン、ポリ塩化ビニル)、及びこれらの混合物あるいは共重合体等の樹脂からなる微多孔膜、ポリエチレンテレフタレート、ポリシクロオレフィン、ポリエーテルスルフォン、ポリアミド、ポリイミド、ポリイミドアミド、ポリアラミド、ポリシクロオレフィン、ナイロン、ポリテトラフルオロエチレン等の樹脂からなる微多孔膜またはポリオレフィン系の繊維を織ったもの、またはその不織布、絶縁性物質粒子の集合体等が挙げられる。これらの中でも、セパレーター全体の膜厚を薄くし電池内の電極活物質比率を上げて体積あたりの容量を上げることができるため、ポリオレフィン系の樹脂からなる微多孔膜が好ましい。
有機セパレーターの厚さは、通常0.5μm以上、好ましくは1μm以上であり、通常40μm以下、好ましくは30μm以下、より好ましくは10μm以下である。この範囲であると電池内でのセパレーターによる抵抗が小さくなり、また電池作製時の作業性に優れる。
リチウムイオン二次電池用の電解液としては、有機溶媒に支持電解質を溶解した有機電解液が用いられる。支持電解質としては、リチウム塩が用いられる。リチウム塩としては、特に制限はないが、LiPF6、LiAsF6、LiBF4、LiSbF6、LiAlCl4、LiClO4、CF3SO3Li、C4F9SO3Li、CF3COOLi、(CF3CO)2NLi、(CF3SO2)2NLi、(C2F5SO2)NLiなどが挙げられる。中でも、溶媒に溶けやすく高い解離度を示すLiPF6、LiClO4、CF3SO3Liが好ましい。これらは、二種以上を併用してもよい。解離度の高い支持電解質を用いるほどリチウムイオン伝導度が高くなるので、支持電解質の種類によりリチウムイオン伝導度を調節することができる。
また前記電解液には添加剤を含有させて用いることも可能である。添加剤としては前述の二次電池電極用スラリー中に使用されるビニレンカーボネート(VC)などのカーボネート系の化合物が挙げられる。
上記以外の電解液としては、ポリエチレンオキシド、ポリアクリロニトリルなどのポリマー電解質や前記ポリマー電解質に電解液を含浸したゲル状ポリマー電解質や、LiI、Li3Nなどの無機固体電解質を挙げることができる。
本発明者らは、上記課題を解決すべく鋭意研究を進めた結果、前記電極活物質を含む電極に、カチオン性基を有する重合体及び粒子状重合体を含有させることにより、リチウムの析出が抑制され、さらに得られる二次電池の低温放電容量が向上されることを見出した。
カチオン性基を有する重合体が電極活物質の表面に存在すると、リチウムイオンの移動度が向上するが、カチオン性基を有する重合体が電極活物質の表面を完全に被覆してしまうと抵抗体となってしまう。そこで、粒子状重合体とカチオン性基を有する重合体とを併用することにより、粒子状重合体とカチオン性基を有する重合体が部分的に複合体を形成し、この複合体の存在より、電極活物質表面が完全に被覆されるのが抑制され、リチウムイオンの電極活物質表面への進入経路が選択的に確保されつつ、カチオン性基を有する重合体によるチウムイオンの移動度の向上効果を保持することが可能となる。よってリチウム金属の電極表面への析出が抑制される。
〔I〕 カチオン性基を有する重合体、粒子状重合体及び電極活物質を含有してなる電極活物質層を有する二次電池用電極。
〔II〕 前記電極活物質層における前記カチオン性基を有する重合体と、前記粒子状重合体との質量比が5:95~40:60である前記の二次電池用電極。
〔III〕 前記粒子状重合体が、アニオンを含むものである前記の二次電池用電極。
〔IV〕 前記粒子状重合体のガラス転移温度が、25℃以下である前記の二次電池用電極。
〔V〕 前記カチオン性基が、ヘテロ原子を含む前記の二次電池用電極。
〔VI〕 前記ヘテロ原子として、窒素、りん、硫黄、酸素及びホウ素の少なくともいずれか1つを含む前記の二次電池用電極。
〔VII〕 前記カチオン性基を有する重合体の重量平均分子量が、1,000~500,000である前記の二次電池用電極。
〔VIII〕 カチオン性基を有する重合体、粒子状重合体、電極活物質及び溶媒を含有してなる二次電池電極用スラリー。
〔IX〕 集電体上に、前記の二次電池電極用スラリーを塗布、乾燥する工程を含む二次電池用電極の製造方法。
〔X〕 正極、負極、セパレーター及び電解液を含む二次電池であって、前記正極及び負極の少なくともいずれかが前記の電極である、二次電池。
また、別の発明に係る二次電池電極用スラリーは、粒子状重合体を必ず含み、カチオン性基に対応する対アニオンを必ずしも含まなくてもよく、カチオン性基を有する重合体中のカチオン密度が0.1~15meq/gに限られないこと以外は、本発明の二次電池電極用スラリーと同様である。
また、別の発明に係る二次電池用電極の製造方法は、本発明の二次電池電極用スラリーの代わりに別の発明に係る二次電池電極用スラリーを用いること以外は、本発明の二次電池用電極の製造方法と同様である。
さらに、別の発明に係る二次電池は、本発明の二次電池用電極の代わりに別の発明に係る二次電池用電極を用いること以外は、本発明の二次電池と同様である。
実施例および比較例において、各種物性は以下のように評価する。
ビーカーに蒸留水90ミリリットルをとり、濃度を500ppmに調整したカチオン性基を有する重合体の水溶液を10ミリリットル加え、1N(1モル/リットル)HCl溶液でpH3.0以下にする。約1分間撹拌したのち、トルイジンブルー指示薬を2~3滴加え、N/400(0.0025モル/リットル)PVSK(ポリビニル硫酸カリウム)溶液で滴定し、CV値を以下の式により求めた。本試験法をコロイド滴定法と呼ぶ。
CV(meq/g)=N/400PVSK溶液滴定量×N/400PVSK溶液の力価×1/2
なお、四級化物の場合は、ブランク滴定量にN/400PVSK溶液の滴定量をプラスして計算する。
電極用スラリー作製1時間後のスラリー粘度(η1h)と5時間後のスラリー粘度(η5h)とから、下記式によりスラリー粘性変化率を求め、以下の基準で判定した。
スラリー粘度変化率(%)=100×(η5h-η1h)/η1h
この値が小さいほどスラリーの安定性が高いことを示す。
A:5%未満
B:5%以上10%未満
C:10%以上15%未満
D:15%以上20%未満
E:20%以上25%未満
F:25%以上
なお、スラリーの粘度は、JIS Z8803:1991に準じて単一円筒形回転粘度計(25℃、回転数=60rpm、スピンドル形状:4)により測定した。
電極を、それぞれ、幅1cm×長さ10cmの矩形に切って試験片とし、電極活物質層面を上にして固定する。試験片の電極活物質層表面にセロハンテープを貼り付けた後、試験片の一端からセロハンテープを50mm/分の速度で180°方向に引き剥がしたときの応力を測定した。測定を10回行い、その平均値を求めてこれをピール強度とし、下記基準にて判定を行った。この値が大きいほど、極板の密着強度が大きいことを示す。
A:6N/m以上
B:5N/m以上~6N/m未満
C:4N/m以上~5N/m未満
D:3N/m以上~4N/m未満
E:2N/m以上~3N/m未満
F:2N/m未満
(1)低温特性(0℃)
得られた負極ハーフセルを用いて、それぞれ25℃で充放電レートを0.1Cとし、定電流定電圧充電法にて、0.2Vになるまで定電流で充電し、定電圧で充電する。充電後に1.5Vまで放電する充放電を各2回繰り返し、その後0℃に設定した恒温槽内で0.1Cで定電流定電圧充電を行った。この定電流定電圧充電における定電流時に得られた電池容量をリチウム受け入れ性の指標とし、下記の基準で判定した。この値が大きいほど、低温特性が優れ、リチウム受入性のよい電池であることを示す。
A:220mAh/g以上
B:200mAh/g以上220mAh/g未満
C:180mAh/g以上200mAh/g未満
D:160mAh/g以上180mAh/g未満
E:140mAh/g以上160mAh/g未満
F:140mAh/g未満
得られた負極ハーフセルを用いて、それぞれ25℃で充放電レートを0.1Cとし、定電流定電圧充電法にて、0.2Vになるまで定電流で充電し、定電圧で充電する。充電後に1.5Vまで放電する充放電を各2回繰り返し、その後-30℃に設定した恒温槽内で0.1Cで定電流定電圧充電を行った。この定電流定電圧充電における定電流時に得られた電池容量をリチウム受け入れ性の指標とし、下記の基準で判定した。この値が大きいほど、低温特性が優れ、リチウム受入性のよい電池であることを示す。
A:60mAh/g以上
B:50mAh/g以上60mAh/g未満
C:40mAh/g以上50mAh/g未満
D:20mAh/g以上40mAh/g未満
E:10mAh/g以上20mAh/g未満
F:10mAh/g未満
得られた負極ハーフセルを用いて上記方法と同様に、0.1Cで充電と放電を繰り返した後、0℃に設定した恒温層にて0.1Cで充電し、充電後のハーフセルを解体し、負極電極表面の形態観察を行った。それぞれ10セルずつ試験を行い、リチウムの析出が目視で観察できたセルの数を求める。リチウムの析出が見られるセルが少ないほど、リチウム金属の析出が抑制されていることを示す。
A:0セル
B:1~2セル
C:3~5セル
D:6~8セル
E:9セル以上
得られた正極ハーフセルを用いて、それぞれ25℃で充放電レートを0.2Cとし、定電流法にて、4.3Vになるまで充電する。充電後に3.0Vまで放電する充放電を各2回繰り返し、その後0℃に設定した恒温槽内で0.1Cで定電流充電を行った。この0℃定電流充電にて得られた充電容量と、25℃低電流充電で得られた充電容量の比(%)で表される正極低温特性を求め、下記の基準で判定した。この値が大きいほど、低温特性に優れることを示す。
A:70%以上
B:50%以上70%未満
C:30%以上50%未満
D:30%未満
(重合体A)
還流冷却器、温度計、滴下ロート、攪拌装置およびガス導入管を備えた反応器にジアリルジメチルアンモニウムクロリド(60%)400部、アクリルアミド(40%)40部、およびイオン交換水250部を入れ、窒素ガスを流入させながら、系内温度を70℃に昇温した。攪拌下で滴下ロートを用いて、重合開始剤として過硫酸アンモニウム(25%)30部を4時間にわたり滴下した。滴下終了後、更に1時間反応を続け、粘稠な淡黄色液状物を得た。
重合体Aの収率は80%であった。
コロイド滴定法で求めた重合体Aのカチオン密度は、5.9meq/gであった。
また、GPCより求めた重合体Aの重量平均分子量(展開溶媒:硝酸ナトリウム水溶液、標準物質:ポリエチレンオキサイド)は、約20万であった。
なお、後述の重量平均分子量も、全て展開溶媒は硝酸ナトリウム水溶液、標準物質はポリエチレンオキサイドにて測定を行った。
還流冷却器、温度計、滴下ロート、攪拌装置およびガス導入管を備えた反応器にN-メチルジアリルアミン塩酸塩(60%)500部およびイオン交換水50部を入れ、窒素ガスを流入させながら、系内温度を80℃に昇温した。攪拌下で滴下ロートを用いて、重合開始剤として過硫酸アンモニウム(25%)30部を4時間にわたり滴下した。滴下終了後、更に1時間反応を続け、粘稠な淡黄色液状物を得た。
重合体Bの収率は78%であった。
コロイド滴定法で求めた重合体Bのカチオン密度は、6.8meq/gであった。
また、GPCより求めた重合体Bの重量平均分子量は、約2万であった。
還流冷却器、温度計、滴下ロート、攪拌装置およびガス導入管を備えた反応器にジアリルジメチルアンモニウムエチル硫酸塩(60%)400部およびイオン交換水50部を入れ、窒素ガスを流入させながら、系内温度を80℃に昇温した。攪拌下で滴下ロートを用いて、重合開始剤として過硫酸アンモニウム(25%)30部を4時間にわたり滴下した。滴下終了後、更に1時間反応を続け、粘稠な淡黄色液状物を得た。
重合体Cの収率は75%であった。
コロイド滴定法で求めた重合体Cのカチオン密度は、4.2meq/gであった。
また、GPCより求めた重合体Cの重量平均分子量は、約3.7万であった。
還流冷却器、温度計、滴下ロート、攪拌装置およびガス導入管を備えた反応器にN,N-ジメチルアミノプロピルアクリルアミド塩化メチル4級塩の水溶液((株)興人製 DMAPAA-Q 75%水溶液)150部を入れ、更にイオン交換水を加えてモノマー濃度が30%になるように調製した。さらに、ポリオキシエチレンアルキルエーテル(花王(株)製 エマルゲン 1150S-60)2部を添加し、攪拌混合してエマルジョンを作製した。
コロイド滴定法で求めた重合体Dのカチオン密度は、4.8meq/gであった。
また、GPCより求めた重合体Dの重量平均分子量は、約5万であった。
還流冷却器、温度計、滴下ロート、攪拌装置およびガス導入管を備えた反応器にN,N-ジメチルアミノエチルアクリレート塩化メチル4級塩の水溶液((株)興人製 DMAEA-Q 79%水溶液)150部を入れ、更にイオン交換水を加えてモノマー濃度が30%になるように調製した。さらに、ポリオキシエチレンアルキルエーテル(花王(株)製 エマルゲン 1150S-60)2部を添加し、攪拌混合してエマルジョンを作製した。
コロイド滴定法で求めた重合体Eのカチオン密度は、5.2meq/gであった。
また、GPCより求めた重合体Eの重量平均分子量は、約8万であった。
還流冷却器、温度計、滴下ロート、攪拌装置およびガス導入管を備えた反応器にジアリルメチルエチルアンモニウムエチル硫酸塩(60%)400部、およびマレイン酸(40%)200部を入れ、窒素ガスを流入させながら系内温度を65℃に昇温した。攪拌下で滴下ロートを用いて、重合開始剤として過硫酸アンモニウム(25%)30部を6時間にわたり滴下した。滴下終了後、更に2時間反応を続け、粘稠な淡黄色液状物を得た。
重合体Fの収率は80%であった。
コロイド滴定法で求めた重合体Fのカチオン密度は、2.6meq/gであった。
また、GPCより求めた重合体Fの重量平均分子量は、約1万であった。
還流冷却器、温度計、滴下ロート、攪拌装置およびガス導入管を備えた反応器にジアリルジメチルアンモニウムクロリド(60%)400部、アクリルアミド(40%)40部、およびイオン交換水250部を入れ、窒素ガスを流入させながら、系内温度を80℃に昇温した。攪拌下で滴下ロートを用いて、重合開始剤として過硫酸アンモニウム(25%)30部を3時間にわたり滴下した。滴下終了後、更に1時間反応を続け、粘稠な淡黄色液状物を得た。
重合体Gの収率は85%であった。
コロイド滴定法で求めた重合体Gのカチオン密度は、5.9meq/gであった。
また、GPCより求めた重合体Gの重量平均分子量は、約1万であった。
還流冷却器、温度計、滴下ロート、攪拌装置およびガス導入管を備えた反応器にジアリルジメチルアンモニウムクロリド(60%)450部、およびイオン交換水250部を入れ、窒素ガスを流入させながら、系内温度を80℃に昇温した。攪拌下で滴下ロートを用いて、重合開始剤として過硫酸アンモニウム(25%)30部を4時間にわたり滴下した。滴下終了後、更に1時間反応を続け、粘稠な淡黄色液状物を得た。
重合体Hの収率は83%であった。
コロイド滴定法で求めた重合体Hのカチオン密度は、6.2meq/gであった。
また、GPCより求めた重合体Hの重量平均分子量は、約4万であった。
還流冷却器、温度計、滴下ロート、攪拌装置およびガス導入管を備えた反応器にイオン交換水230部、アクリル酸2-エチルヘキシル77部、メタクリル酸グリシジル2部、アクリロニトリル20部、メタアクリロイルオキシエチルトリメチルアンモニウムクロリド1部、ポリオキシエチレンラウリルエーテル5部およびアゾ重合開始剤(和光純薬工業(株)製 V-601)1部を入れ、十分に撹拌した後、70℃に加温して重合を開始した。更に3時間反応を継続し、その後80℃に昇温して3時間反応を継続した後、冷却して反応を終了した。これにより、重合体Iを得た。なお、固形分濃度から求めた重合転化率は、96%であった。その後イオン交換水を適量加え、固形分濃度を25%に調整した。コロイド滴定法で求めた重合体Iのカチオン密度は、0.05meq/gであった。
(粒子状重合体1)
重合缶Aにスチレン5部、ブタジエン10部、ポリオキシエチレンアルキルエーテル(花王株式会社製 エマルゲン 1150S-60)3部、およびイオン交換水70部を加え、十分攪拌した。その後、70℃とし、重合開始剤として水溶性アゾ重合開始剤(和光純薬工業製 VA-086)0.3部、およびイオン交換水10部を加え120分攪拌した。
他方、別の重合缶Bに、スチレン47部、ブタジエン38部、ポリオキシエチレンアルキルエーテル10部、およびイオン交換水30部を加えて攪拌して、エマルジョンを作製した。
その後、作製したエマルジョンを約300分かけて重合缶Bから重合缶Aに連続添加した後、約180分攪拌してモノマー消費量が95%になったところで冷却して反応を終了した。これにより、固形分濃度が40%、個数平均粒子径が150nm、ガラス転移温度が-15℃であるスチレンーブタジエン粒子状重合体1の水分散液を得た。
重合缶Aにブチルアクリレート12部、アクリロニトリル2部、ポリオキシエチレンアルキルエーテル2部、およびイオン交換水60部を加え、十分攪拌した。その後、70℃とし、重合開始剤として水溶性アゾ重合開始剤0.25部、およびイオン交換水10部を加え60分攪拌した。
他方、別の重合缶Bに、ブチルアクリレート70部、アクリロニトリル16部、ポリオキシエチレンアルキルエーテル3部、およびイオン交換水46部を加えて攪拌して、エマルジョンを作製した。
その後、作製したエマルジョンを約180分かけて重合缶Bから重合缶Aに連続添加した後、約120分攪拌してモノマー消費量が95%になったところで冷却して反応を終了した。これにより、固形分濃度が40%、個数平均粒子径が200nm、ガラス転移温度が-35℃であるブチルアクリレート-アクリロニトリル粒子状重合体2の水分散液を得た。
重合缶Aにイタコン酸1部、ドデシルベンゼンスルホン酸ナトリウム1.0部、およびイオン交換水80部を加えて十分攪拌した。
他方、別の重合缶Bに、ブタジエン50部、スチレン48部、イタコン酸1部、ドデシルベンゼンスルホン酸ナトリウム1.0部、およびイオン交換水45部を加えて攪拌して、エマルジョンを作製した。
その後、重合缶Aを70℃とし、重合缶Bで作製したエマルジョンのうち1/30を、重合缶Bから重合缶Aに連続添加した。その5分後に、重合缶Aに重合開始剤として過硫酸アンモニウム0.5部、およびイオン交換水10部を添加し、重合缶Bの残りのエマルジョンを300分かけて重合缶Aに連続添加した。その後、約240分攪拌してモノマー消費量が95%になったところで冷却して、反応を終了した。これにより、イタコン酸由来の構造単位を2%(アニオン(アニオン性基)を含んでなる単量体由来の構造単位の含有量2%)含み、個数平均粒子径が100nm、ガラス転移温度が-17℃であるスチレン-ブタジエン粒子状重合体3の水分散液を得た。
重合缶Aに2-エチルヘキシルアクリレート12部、スチレン5部、ラウリル硫酸ナトリウム0.05部、およびイオン交換水70部を加え、十分攪拌した。その後、70℃とし、重合開始剤として過硫酸アンモニウム0.2部、およびイオン交換水10部を加え120分攪拌した。
他方、別の重合缶Bに、2-エチルヘキシルアクリレート53部、スチレン28部、メタクリル酸2部、ラウリル硫酸ナトリウム0.2部、およびイオン交換水30部を加えて攪拌して、エマルジョンを作製した。
その後、作製したエマルジョンを約420分かけて重合缶Bから重合缶Aに連続添加した後、約300分攪拌してモノマー消費量が95%になったところで冷却して反応を終了した。これにより、固形分濃度が40%、個数平均粒子径が150nm、ガラス転移温度が-26℃である2-エチルヘキシルアクリレート-スチレン粒子状重合体4の水分散液を得た。
重合缶Aにイタコン酸0.2部、ドデシルベンゼンスルホン酸ナトリウム0.3部、およびイオン交換水80部を加えて十分攪拌した。
他方、別の重合缶Bに、ブタジエン35部、スチレン64.6部、イタコン酸0.2部、ドデシルベンゼンスルホン酸ナトリウム0.5部、およびイオン交換水45部を加えて攪拌して、エマルジョンを作製した。
その後、重合缶Aを70℃とし、重合缶Bで作製したエマルジョンのうち1/30を、重合缶Bから重合缶Aに逐次添加した。その5分後に、重合缶Aに重合開始剤として過硫酸アンモニウム0.5部、およびイオン交換水10部を添加し、重合缶Bの残りのエマルジョンを300分かけて重合缶Aに連続添加した。その後、約240分攪拌してモノマー消費量が95%になったところで冷却して反応を終了した。これにより、イタコン酸由来の構造単位を0.4%(アニオン(アニオン性基)を含んでなる単量体由来の構造単位の含有量2%)含み、個数平均粒子径が130nm、ガラス転移温度が10℃であるスチレン-ブタジエン粒子状重合体5の水分散液を得た。得られた粒子状重合体5の水分散液にイオン交換水を適量加え、固形分濃度を40%に調整した。
(電極用スラリーの製造)
カルボキシメチルセルロース(CMC)として、第一工業製薬株式会社製「ダイセル2200」を用い、1.0%のCMC水溶液を調製した。
次に、粒子状重合体として固形分濃度が40%の粒子状重合体1の水分散液を1.0部(固形分基準)を入れ、更にイオン交換水を加えて、最終固形分濃度55%となるように調整し、さらに10分間混合した。これを減圧下で脱泡処理して流動性の良い電極用スラリー(電極用スラリー組成物)を得た。この時のカチオン性基を有する重合体と粒子状重合体の比は、固形分基準で9:91(質量比)となる。
電極用スラリーの5時間後の粘性変化率の評価結果を表2に示す。
上記電極用スラリーをコンマコーターで、厚さ18μmの銅箔上に、乾燥後の膜厚が200μm程度になるように片面に塗布し、50℃で20分乾燥後、110℃で20分間加熱処理して電極原反を得た。この電極原反をロールプレスで圧延して、電極活物質層の厚みが80μmの負極用電極を得た。得られた電極の塗布厚を測定したところ、膜厚はほぼ均一であった。
この電池の性能の評価結果を表2に示す。
粒子状重合体1のかわりに粒子状重合体2を使用した事以外は実施例1と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
重合体Aのかわりに重合体Bを使用した事以外は実施例2と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
重合体Aのかわりに重合体Cを使用した事以外は実施例2と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
重合体Aのかわりに重合体Dを使用した事以外は実施例1と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
重合体Aのかわりに重合体Eを使用した事以外は実施例1と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
重合体Aのかわりに重合体Fを使用し、粒子状重合体1のかわりに粒子状重合体3を使用し、カチオン性基を有する重合体と粒子状重合体の配合割合を質量比で20:80にした事以外は実施例1と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
重合体Fのかわりに重合体Bを使用した事以外は実施例7と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
カチオン性基を有する重合体と粒子状重合体の配合割合を質量比で6:94にした事以外は実施例7と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
カチオン性基を有する重合体と粒子状重合体の配合割合を質量比で40:60にした事以外は実施例7と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
粒子状重合体3のかわりに粒子状重合体4を使用した事以外は実施例7と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
粒子状重合体3のかわりに粒子状重合体5を使用した事以外は実施例7と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
電極活物質としてスピネルマンガン(LiMn2O4)100部と、カチオン性基を有する重合体として重合体Aを0.1部(固形分基準)と、アセチレンブラック(HS-100:電気化学工業)5部と、粒子状重合体として固形分濃度が40%の粒子状重合体2の水分散液を1.0部(固形分基準)と、増粘剤としてのエーテル化度が0.8であるカルボキシメチルセルロース水溶液40部(固形分濃度2%)と、適量の水とをプラネタリーミキサーにて攪拌し、正極用スラリーを調製した。正極用スラリーの5時間後の粘性変化率の評価結果を表3に示す。
上記正極用スラリーをコンマコーターで、厚さ20μmのアルミ箔上に片面に塗布し、60℃で20分乾燥後、120℃で20分間加熱処理して電極原反を得た。この電極原反をロールプレスで圧延して電極活物質層の厚みが70μmの正極用電極を得た。得られた電極の塗布厚を測定したところ、膜厚はほぼ均一であった。
この電池の性能の評価結果を表3に示す。
固形分濃度が40%の粒子状重合体2の水分散液に対して、分散液全体に対して3倍の質量のN-メチルピロリドン(NMP)を加え、エバポレーターで水分を蒸発させ、NMPで固形分濃度10%に調整し、粒子状重合体2のNMP溶解物を得た。カチオン性基を有する重合体Aに対しても同様に、溶液全体に対して3倍の質量のNMPを加え、エバポレーターで水分を蒸発させ、NMPで固形分濃度10%に調整し、重合体AのNMP溶解物を得た。
電極用スラリーの5時間後の粘性変化率の評価結果を表2に示す。
その後、実施例1と同様に負極ハーフセルを作製し、電池の性能の評価を行った。評価結果を表2に示す。
重合体Aのかわりに重合体Gを使用した事以外は実施例1と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
重合体Aのかわりに重合体Cを使用した事以外は実施例1と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
粒子状重合体1のかわりに固形分濃度が40%、ガラス転移温度が-5℃であるポリフッ化ビニリデン-ヘキサフルオロプロピレン共重合体粒子(以下、「PVDF-HFP重合体粒子」ということがある)を使用した事以外は実施例1と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
重合体Aのかわりに重合体Fを使用した事以外は実施例1と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
重合体Aのかわりに重合体Hを使用した事以外は実施例1と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
重合体Aのかわりに重合体Bを使用した事以外は実施例1と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
重合体Aのかわりに重合体Iを使用し、粒子状重合体を使用しなかった事以外は実施例1と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
重合体Bのかわりにカチオン含有重合体(即ち、カチオン性基を有する重合体)ではなくカチオン含有低分子組成物である2-アミノエタンスルホン酸を使用した事以外は実施例7と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
カチオン性基を有する重合体を使用しなかった事以外は実施例7と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
重合体Aのかわりにポリエチレンイミン重合体(商品名、エポミンSP-200)を使用した事以外は実施例7と同様の操作を行って、電極用スラリー及び負極ハーフセルを作製し、この電池の性能の評価を行った。結果を表2に示す。
カチオン性基を有する重合体を使用しなかった事以外は実施例13と同様の操作を行って、正極用スラリー及び正極ハーフセルを作製し、この電池の性能の評価を行った。結果を表3に示す。
本発明によれば、実施例1~実施例20に示すように、所定のカチオン密度を示すカチオン性基及び対アニオンを有する重合体を用いることにより、スラリー安定性、低温特性、リチウム析出抑制の全てに優れるリチウムイオン二次電池を得ることができる。また、実施例の中でも、アニオンを有さないアクリレートの粒子状重合体を併用し、カチオン密度が5~7meq/gの範囲にあり、分子量が5,000~300,000の範囲である第4級カチオンを用いた実施例2、13は、スラリー安定性、低温特性、リチウム析出抑制に特に優れている。更には、所定量のアニオンを有する粒子状重合体を併用し、カチオン密度が2~5meq/gの範囲にあり、分子量が5,000~300,000の範囲である実施例7は、上記特性に加えてピール強度も高く、全ての特性において優れている。
一方、カチオン密度が所定の範囲以外のもの(比較例1、4)、カチオン性基及び対アニオンを有する重合体を有さずに、カチオンを含む低分子組成物を含むもの(比較例2)、カチオン性基及び対アニオンを有する重合体を有さないものは(比較例3、5)は、特に低温特性、リチウム析出抑制が著しく劣る。
Claims (7)
- カチオン性基を有する重合体、該カチオン性基に対応するアニオン、及び電極活物質を含有してなる、電極活物質層を有し、前記重合体中のカチオン密度が0.1~15meq/gである二次電池用電極。
- 前記電極活物質層がさらに粒子状重合体を含有してなる請求項1に記載の二次電池用電極。
- 前記電極活物質層における前記カチオン性基を有する重合体と、前記粒子状重合体との質量比が5:95~40:60である請求項2記載の二次電池用電極。
- 前記粒子状重合体が、アニオンを含むものである請求項2に記載の二次電池用電極。
- 前記カチオン性基が、脂環式カチオン性基または複素環式カチオン性基である請求項1に記載の二次電池用電極。
- カチオン性基を有する重合体、該カチオン性基に対応するアニオン、電極活物質及び溶媒を含有してなる二次電池電極用スラリーであって、前記重合体中のカチオン密度が0.1~15meq/gである二次電池電極用スラリー。
- 正極、負極、セパレーター及び電解液を含む二次電池であって、前記正極及び負極の少なくともいずれかが請求項1に記載の二次電池用電極である、二次電池。
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Cited By (11)
Publication number | Priority date | Publication date | Assignee | Title |
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JP2013004241A (ja) * | 2011-06-14 | 2013-01-07 | Toyota Motor Corp | リチウムイオン二次電池 |
JPWO2013031690A1 (ja) * | 2011-08-30 | 2015-03-23 | 日本ゼオン株式会社 | 二次電池負極用バインダー組成物、二次電池用負極、負極用スラリー組成物、製造方法及び二次電池 |
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JPWO2014185381A1 (ja) * | 2013-05-14 | 2017-02-23 | 日本ゼオン株式会社 | リチウムイオン二次電池用バインダー組成物、リチウムイオン二次電池用スラリー組成物、リチウムイオン二次電池用電極、リチウムイオン二次電池、並びにリチウムイオン二次電池用バインダー組成物の製造方法 |
JP2015106489A (ja) * | 2013-11-29 | 2015-06-08 | Jsr株式会社 | 蓄電デバイス電極用バインダー組成物、蓄電デバイス電極用スラリー、蓄電デバイス電極、および蓄電デバイス |
JPWO2016024383A1 (ja) * | 2014-08-11 | 2017-05-25 | 日本ゼオン株式会社 | 二次電池電極用バインダー組成物、二次電池電極用スラリー組成物、二次電池用電極および二次電池 |
US10529989B2 (en) | 2014-08-11 | 2020-01-07 | Zeon Corporation | Binder composition for secondary battery electrode, slurry composition for secondary battery electrode, electrode for secondary battery, and secondary battery |
JP2016225135A (ja) * | 2015-05-29 | 2016-12-28 | 三菱化学株式会社 | 非水系二次電池負極用活物質並びにそれを用いた負極及び非水系二次電池 |
JP2015166887A (ja) * | 2015-06-04 | 2015-09-24 | Dic株式会社 | 重合性液晶組成物 |
JP2017068976A (ja) * | 2015-09-29 | 2017-04-06 | Fdk株式会社 | アルカリ二次電池用の負極及びこの負極を用いたアルカリ二次電池 |
JP2022505211A (ja) * | 2018-10-16 | 2022-01-14 | ハーキュリーズ エルエルシー | 電極用水性バインダー組成物、及びその製造方法 |
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US8877376B2 (en) | 2014-11-04 |
US20120107690A1 (en) | 2012-05-03 |
CN102473898A (zh) | 2012-05-23 |
CN102473898B (zh) | 2015-03-04 |
EP2450985A4 (en) | 2014-02-26 |
EP2450985B1 (en) | 2017-09-27 |
KR101530756B1 (ko) | 2015-06-22 |
JPWO2011002016A1 (ja) | 2012-12-13 |
PL2450985T3 (pl) | 2018-03-30 |
KR20120028339A (ko) | 2012-03-22 |
JP5626209B2 (ja) | 2014-11-19 |
EP2450985A1 (en) | 2012-05-09 |
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