WO2013161786A1 - リチウムイオン二次電池 - Google Patents
リチウムイオン二次電池 Download PDFInfo
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- WO2013161786A1 WO2013161786A1 PCT/JP2013/061846 JP2013061846W WO2013161786A1 WO 2013161786 A1 WO2013161786 A1 WO 2013161786A1 JP 2013061846 W JP2013061846 W JP 2013061846W WO 2013161786 A1 WO2013161786 A1 WO 2013161786A1
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- negative electrode
- ion secondary
- lithium ion
- positive electrode
- secondary battery
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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
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/134—Electrodes based on metals, Si or alloys
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- 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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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
- H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
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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
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
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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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative 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
- H01M4/621—Binders
- H01M4/622—Binders being polymers
- H01M4/623—Binders being polymers fluorinated polymers
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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
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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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
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/70—Energy storage systems for electromobility, e.g. batteries
Definitions
- the present invention relates to a lithium ion secondary battery that has a large capacity and suppresses the swelling of cells after charging and discharging.
- Lithium ion secondary batteries have a high energy density and are used in fields such as mobile phones and notebook personal computers. Further, with the expansion and development of applications, electrochemical devices are required to have further improved performance such as low resistance and large capacity.
- Patent Document 1 a polyamide imide binder having a tensile strength, a tensile elongation, and a tensile elastic modulus of a predetermined value or more is used by using an SBR binder having an elongation at break of a predetermined value or more in Patent Document 2. By using it, cycle characteristics are improved.
- a silicon-based material such as Si or silicon oxide (SiO x ) is used as the negative electrode active material.
- Si or silicon oxide (SiO x ) is used as the negative electrode active material.
- the negative electrode using the binder described in Patent Document 1 or 2 is produced, and there is a problem that the swelling of the cell becomes large when a lithium ion secondary battery is used.
- the lithium ion secondary battery is required to have good performance even in a high temperature environment or a low temperature environment.
- An object of the present invention is to provide a lithium ion secondary battery that can suppress the swelling of a cell and has good performance in a high temperature environment and a low temperature environment.
- the present inventor can suppress cell swelling even when a silicon-based material is used as the negative electrode active material by using a binder having a predetermined swelling degree and repeated tensile strength, and The inventors have found that a lithium ion secondary battery having good performance can be obtained even in a high temperature environment and a low temperature environment, and have completed the present invention.
- a lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolytic solution, and a separator, wherein the negative electrode comprises a particulate polymer A containing an aliphatic conjugated diene monomer unit. And an electrolytic solution in which an electrolyte is dissolved in a solvent having a solubility parameter of 8 to 13 (cal / cm 3 ) 1/2.
- the negative electrode binder composition has a swelling degree of 1 to 2 times that of the negative electrode binder composition, and the negative tensile binder composition swollen by the electrolytic solution has a low tensile modulus of 15% and 0.5 to 20 kg / cm.
- the positive electrode comprises a positive electrode binder composition comprising a particulate polymer B containing an ethylenically unsaturated carboxylic acid monomer unit, and a positive electrode slurry composition comprising a positive electrode active material
- the positive electrode binder composition has a swelling degree of 1 with respect to the electrolytic solution in which an electrolyte is dissolved in a solvent including a positive electrode active material layer formed from a material and having a solubility parameter of 8 to 13 (cal / cm 3 ) 1/2.
- Lithium ion secondary characterized in that the repetitive tensile strength of the positive electrode binder composition swollen by the electrolyte is 0.2 to 5 Kg / cm 2 at a low elongation modulus of 15%.
- the particulate polymer A contains an aromatic vinyl monomer unit, and the content of the aromatic vinyl monomer unit in the particulate polymer A is 50 to 75% by weight.
- the particulate polymer A contains an ethylenically unsaturated carboxylic acid monomer unit, and the content of the ethylenically unsaturated carboxylic acid monomer unit in the particulate polymer A is 0.5 to
- the binder composition for a negative electrode further includes a water-soluble polymer having an ethylenically unsaturated carboxylic acid monomer unit, and the water-soluble polymer contains the ethylenically unsaturated carboxylic acid monomer unit.
- the particulate polymer B contains an ethylenically unsaturated carboxylic acid monomer unit, and the content of the ethylenically unsaturated carboxylic acid monomer unit in the particulate polymer B is 20 to 50 weights.
- the particulate polymer B contains a (meth) acrylic acid ester monomer unit, and the content ratio of the (meth) acrylic acid ester monomer unit in the particulate polymer B is 50 to 80 wt. % Of the lithium ion secondary battery according to any one of (1) to (7), (9)
- the lithium ion secondary battery according to any one of (1) to (8), which is a stacked type, is provided.
- the lithium ion secondary battery of the present invention it is possible to suppress the swelling of the cell and to have good performance in a high temperature environment and a low temperature environment.
- the lithium ion secondary battery of the present invention is a lithium ion secondary battery including a positive electrode, a negative electrode, an electrolytic solution, and a separator, and the negative electrode includes a particulate polymer A including an aliphatic conjugated diene monomer unit.
- a negative electrode active material layer formed from a negative electrode slurry composition comprising a negative electrode binder composition and a negative electrode active material, and having a solubility parameter of 8 to 13 (cal / cm 3 ) 1/2
- the swelling degree of the negative electrode binder composition with respect to the electrolytic solution in which the electrolyte is dissolved is 1 to 2 times, and the repeated tensile strength of the negative electrode binder composition swollen by the electrolytic solution is a low elongation modulus of 15%.
- the positive electrode a positive electrode binder composition comprising a particulate polymer B containing ethylenically unsaturated carboxylic acid monomer units, the positive electrode active material
- the positive electrode is formed from a slurry composition includes a positive electrode active material layer, the solubility parameter is 8 ⁇ 13 (cal / cm 3 ) the positive electrode binder with respect to the electrolytic solution prepared by dissolving an electrolyte in a solvent is half including bets
- the degree of swelling of the composition is 1 to 5 times, and the repeated tensile strength of the positive electrode binder composition swollen by the electrolytic solution is 0.2 to 5 kg / cm 2 at a low elongation modulus of 15%.
- the binder composition for a negative electrode used for the lithium ion secondary electrode of the present invention comprises a particulate polymer A containing an aliphatic conjugated diene monomer unit, and the particulate polymer A and medium or particulate weight. It is preferable that the polymer A comprises a water-soluble polymer and a medium.
- the aliphatic conjugated diene monomer unit means a structural unit formed by polymerizing an aliphatic conjugated diene monomer.
- Examples of the aliphatic conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, chloroprene, and the like. Is mentioned. Of these, 1,3-butadiene and isoprene are preferable, and 1,3-butadiene is more preferable. These aliphatic conjugated diene monomers can be used alone or in combination of two or more.
- the content ratio of the aliphatic conjugated diene monomer unit in the particulate polymer A is the total unit amount contained in the particulate polymer A from the viewpoint of balancing the cycle characteristics and adhesion of the secondary battery.
- the amount is preferably 20 to 50% by weight, more preferably 25 to 45% by weight, particularly preferably 30 to 40% by weight based on 100% by weight of the body unit.
- the content ratio of the aliphatic conjugated diene monomer unit is too large, the adhesion between the negative electrode active materials may be reduced when the negative electrode active material layer is formed.
- the content of the aliphatic conjugated diene monomer unit is too small, cell swelling may increase when used as a negative electrode, and cycle characteristics may deteriorate. .
- the particulate polymer A preferably further contains an aromatic vinyl monomer unit.
- the aromatic vinyl monomer unit refers to a structural unit formed by polymerizing an aromatic vinyl monomer.
- the aromatic vinyl monomer include styrene, ⁇ -methylstyrene, vinyltoluene, divinylbenzene, sodium p-styrenesulfonate, and the like. Among these, styrene and sodium p-styrenesulfonate are preferable, and styrene is more preferable.
- the content ratio of the aromatic vinyl monomer unit in the particulate polymer A is the total monomer contained in the particulate polymer A from the viewpoint of achieving a balance between the adhesion and cycle characteristics of the secondary battery.
- the amount is preferably 50 to 75% by weight, more preferably 55 to 70% by weight, and particularly preferably 60 to 65% by weight with respect to 100% by weight of the unit.
- the particulate polymer A preferably further contains an ethylenically unsaturated carboxylic acid monomer unit.
- An ethylenically unsaturated carboxylic acid monomer unit means a structural unit formed by polymerizing an ethylenically unsaturated carboxylic acid monomer.
- Examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid; ethylenically unsaturated carboxylic acids such as itaconic acid, maleic acid, fumaric acid, maleic anhydride, and citraconic anhydride.
- saturated polyvalent carboxylic acids and anhydrides thereof saturated polyvalent carboxylic acids and anhydrides thereof; partially esterified products of ethylenically unsaturated polyvalent carboxylic acids such as monobutyl fumarate, monobutyl maleate, mono-2-hydroxypropyl maleate; and the like.
- acrylic acid, methacrylic acid, and itaconic acid it is preferable to use itaconic acid.
- the content ratio of the ethylenically unsaturated carboxylic acid monomer unit in the particulate polymer A is all that is contained in the particulate polymer A from the viewpoint that the adhesion and voltage resistance of the secondary battery can be balanced.
- the amount is preferably 0.5 to 10% by weight, more preferably 1 to 8% by weight, and particularly preferably 1.5 to 6% by weight with respect to 100% by weight of the monomer unit. If the content of the ethylenically unsaturated carboxylic acid monomer unit is too large, the durability of the lithium ion secondary battery may be reduced when the lithium ion secondary battery negative electrode is formed. Moreover, when there is too little content rate of an ethylenically unsaturated carboxylic acid monomer unit, when forming a negative electrode active material layer, there exists a possibility that the adhesiveness of negative electrode active materials may fall.
- the particle polymer A includes other monomers that can be copolymerized therewith. It may contain body units.
- the other monomer unit copolymerizable with these refers to a structural unit obtained by polymerizing other monomers copolymerizable with these, and as such other monomer units, Examples thereof include an unsaturated carboxylic acid alkyl ester monomer unit, a vinyl cyanide monomer unit, an unsaturated monomer unit containing a hydroxyalkyl group, and an unsaturated carboxylic acid amide monomer unit.
- the content ratio of the other monomer units copolymerizable with these is preferably a total ratio, preferably 0 to 20% by weight, more preferably 0.1 to 15% by weight. It is particularly preferably 0.2 to 10% by weight.
- the glass transition temperature of the particulate polymer A can improve the breaking strength and flexibility of the particulate polymer A.
- the temperature is preferably ⁇ 40 to + 50 ° C., more preferably ⁇ 30 to + 40 ° C., and further preferably ⁇ 20 to + 30 ° C. .
- the particulate polymer A can be obtained by polymerizing a monomer mixture containing the above-described monomers in an aqueous medium.
- polymerization can be used as a medium contained in the binder composition for negative electrodes.
- the polymerization method of the particulate polymer A is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used.
- any reaction such as ionic polymerization, radical polymerization, and living radical polymerization can be used.
- polymerization initiators used for polymerization include lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3,3,5-trimethylhexanoyl peroxide, and the like.
- the degree of swelling of the negative electrode binder composition of the present invention with respect to the electrolytic solution is 1 to 2 times, preferably 1 to 1.8 times, and more preferably 1 to 1.6 times.
- the degree of swelling of the negative electrode binder composition indicates the degree of swelling with respect to an electrolytic solution obtained by dissolving an electrolyte in a solvent having a solubility parameter of 8 to 13 (cal / cm 3 ) 1/2 .
- the solubility parameter (SP value) H Although it can be obtained by the method described in the edition of Immergut "Polymer Handbook” VII Solidity Parametic Values, pp 519-559 (John Wiley & Sons, 3rd edition, published in 1989), those which are not described in this publication can be obtained. It can be obtained according to the proposed “molecular attraction constant method”.
- the SP value ( ⁇ ) is calculated from the characteristic value of the functional group (atomic group) constituting the compound molecule, that is, the statistics of the molecular attractive constant (G), the molecular weight (M), and the specific gravity (d) according to the following formula. It is a method to seek.
- the tensile strength of the repetition of the negative electrode binder composition for use in a lithium ion secondary battery of the present invention 0.5 ⁇ 20Kg / cm 2 with 15% low elongation modulus, preferably 1 ⁇ 18Kg / cm 2, more preferably Is from 5 to 15 kg / cm 2 .
- the tensile strength with a low elongation modulus of 15% is that a film composed of the negative electrode binder composition swollen with the above-described electrolyte solution is repeatedly subjected to a strength corresponding to 15% elongation a predetermined number of times in accordance with, for example, JIS-K7312. It is a measured value.
- the type and amount of the polymerizable monomer constituting the particulate polymer A can be adjusted, You can adjust the amount. Specifically, it can be adjusted by decreasing the content ratio of the aliphatic conjugated diene monomer unit constituting the particulate polymer A or increasing the content ratio of the aromatic vinyl monomer unit.
- the repeated tensile strength of the binder composition for negative electrode is too large, the adhesion between the negative electrode active materials decreases when the negative electrode active material layer is formed. Moreover, when the repetition tensile strength of the binder composition for negative electrodes is too small, the lifetime of a battery when it is set as a lithium ion secondary battery will fall.
- the tetrahydrofuran insoluble content of the binder composition for negative electrode used in the lithium ion secondary battery of the present invention is preferably 75 to 95%, more preferably 80 to 95%.
- the tetrahydrofuran insoluble content is a value representing the weight ratio of the solid content insoluble in tetrahydrofuran among the total solid content of the negative electrode binder composition. If the tetrahydrofuran-insoluble content of the negative electrode binder composition is too large, the adhesion between the negative electrode active materials may be reduced when the negative electrode active material layer is formed.
- the type and amount of the polymerizable monomer constituting the particulate polymer A are adjusted, or the type and amount of the water-soluble polymer described later. You can adjust.
- the glass transition temperature of the particulate polymer A that is, the content ratio of the aliphatic conjugated diene monomer unit or the aromatic vinyl monomer unit, or preparing the particulate polymer A It can adjust by changing the kind and quantity of the molecular weight modifier to be used.
- the number average particle diameter of the particulate polymer A is preferably from 50 to 500 nm, more preferably from 70 to 500 nm, from the viewpoint of improving the strength and flexibility of the obtained negative electrode for secondary battery. 400 nm.
- the number average particle diameter can be easily measured by transmission electron microscopy, Coulter counter, laser diffraction scattering method, or the like.
- the content ratio of the particulate polymer A in the binder composition is preferably 50 to 100% by weight, more preferably 60 to 99% by weight.
- the negative electrode binder composition used in the lithium ion secondary battery of the present invention preferably contains a water-soluble polymer.
- the water-soluble polymer used in the negative electrode binder composition of the present invention is not particularly limited, but from the viewpoint of improving the stability of the slurry, a cellulose polymer such as carboxymethyl cellulose (CMC), an ethylenically unsaturated carboxylic acid monomer Polymers containing body units are preferred.
- the monomer constituting the polymer can be used for the above-described negative electrode binder composition.
- an ethylenically unsaturated carboxylic acid monomer can be used, among these, it is preferable to use acrylic acid and methacrylic acid, and it is more preferable to use methacrylic acid.
- the content ratio of the ethylenically unsaturated carboxylic acid monomer unit in the polymer containing the ethylenically unsaturated carboxylic acid monomer unit is preferably 100% by weight based on the total monomer units contained in the polymer. It is 20 to 60% by weight, more preferably 25 to 55% by weight, particularly preferably 30 to 50% by weight.
- a unit of another monomer that can be copolymerized May be contained.
- other monomer units include crosslinkable monomer units, fluorine-containing (meth) acrylate monomer units, reactive surfactant units, and fluorine-containing (meth) acrylate esters.
- examples include (meth) acrylic acid ester monomer units other than the monomer units.
- the crosslinkable monomer for forming the crosslinkable monomer unit a monomer capable of forming a crosslinked structure upon polymerization can be used.
- the crosslinkable monomer include monomers having two or more reactive groups per molecule. Examples of such a monomer include a thermally crosslinkable crosslinkable group and one monomer per molecule. And monofunctional monomers having one olefinic double bond, and polyfunctional monomers having two or more olefinic double bonds per molecule.
- the heat-crosslinkable crosslinkable group contained in the monofunctional monomer include an epoxy group, an N-methylolamide group, an oxetanyl group, an oxazoline group, and the like.
- the content of the crosslinkable monomer unit in the polymer containing the ethylenically unsaturated carboxylic acid monomer unit is preferably 0 from the viewpoint of improving the water solubility and dispersibility of the water-soluble polymer. 0.1 to 2% by weight, more preferably 0.2 to 1.5% by weight, still more preferably 0.5 to 1% by weight.
- the content ratio of the fluorine-containing (meth) acrylic acid ester monomer unit in the polymer containing the ethylenically unsaturated carboxylic acid monomer unit is preferably 1 to 20% by weight, more preferably 2 to 15% by weight, More preferably, it is 5 to 10% by weight.
- R 1 represents a hydrogen atom or a methyl group
- R 2 represents a C 1-18 hydrocarbon group containing a fluorine atom.
- the number of fluorine atoms contained in R 2 may be 1 or 2 or more.
- the content ratio of the (meth) acrylate monomer unit other than the fluorine-containing (meth) acrylate monomer unit in the polymer containing the ethylenically unsaturated carboxylic acid monomer unit is preferably 30 to It is 70% by weight, more preferably 35 to 70% by weight, still more preferably 40 to 70% by weight.
- the reactive surfactant that forms the reactive surfactant unit has a polymerizable group that can be copolymerized with other monomers, and has a surfactant group (hydrophilic group and hydrophobic group). It is a monomer.
- the reactive surfactant usually has a polymerizable unsaturated group, and this group also acts as a hydrophobic group after polymerization.
- Examples of the polymerizable unsaturated group possessed by the reactive surfactant include a vinyl group, an allyl group, a vinylidene group, a propenyl group, an isopropenyl group, and an isobutylidene group.
- Such polymerizable unsaturated groups may be of one type or two or more types.
- the content of the reactive surfactant unit in the polymer containing the ethylenically unsaturated carboxylic acid monomer unit is preferably 0.1 to 15% by weight, more preferably 0.2 to 10% by weight, and still more preferably. Is 0.5 to 5% by weight.
- Examples of the (meth) acrylate monomer constituting the (meth) acrylate monomer unit other than the fluorine-containing (meth) acrylate monomer unit include methyl acrylate, ethyl acrylate, n- Acrylic acid alkyl esters such as propyl acrylate, isopropyl acrylate and n-butyl acrylate; Methacrylic acid alkyl esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate and n-butyl methacrylate; These (meth) acrylic acid ester monomers may be used individually by 1 type, and may be used in combination of 2 or more types.
- the content ratio of the (meth) acrylate monomer units other than the fluorine-containing (meth) acrylate monomer units in the polymer containing the ethylenically unsaturated carboxylic acid monomer units is preferably 30. It is ⁇ 70% by weight, more preferably 35 to 70% by weight, still more preferably 40 to 70% by weight.
- the content of the water-soluble polymer in the negative electrode binder composition is preferably 0.1 to 50 parts by weight, more preferably 0.2 to 40 parts by weight with respect to 100 parts by weight of the particulate polymer A.
- the negative electrode active material used in the lithium ion secondary battery of the present invention includes a Si (containing) compound that occludes and releases lithium.
- the Si (containing) compound include SiOC, SiC, and SiOx.
- a transition metal such as Sn or Zn that absorbs and releases lithium may be used. Of these, it is preferable to use SiOC, SiC, or SiOx.
- SiO x (0.01 ⁇ x ⁇ 2) is formed of at least one of SiO and SiO 2 and Si.
- SiO x is usually obtained by cooling and precipitating silicon monoxide gas generated by heating a mixture of SiO 2 and Si (metal silicon).
- SiOC and SiC are preferably formed by combining at least one of an oxygen-containing Si compound (SiO, SiO 2 , SiO x ) and metallic silicon with conductive carbon.
- the swell of the negative electrode active material itself can be suppressed by combining with the conductive carbon.
- the compounding method includes a method of compounding by coating an oxygen-containing Si compound and / or metal silicon with conductive carbon, and at least one of the oxygen-containing Si compound and metal silicon and conductive carbon. The method of compounding by granulating a mixture etc. is mentioned.
- the method for coating at least one of the oxygen-containing Si compound and metal silicon with carbon is not particularly limited, but the oxygen-containing i compound and / or metal silicon is heat treated to disproportionately. And a method of performing chemical vapor deposition by applying a heat treatment to the oxygen-containing Si compound and / or metal silicon.
- SiO x is a temperature range of 900 to 1400 ° C., preferably 1000 to 1400 ° C., more preferably 1050 to 1300 ° C., and still more preferably 1100 to 1200 ° C. in an atmosphere containing at least an organic gas and / or steam.
- a method of performing disproportionation by performing a heat treatment in a temperature range of 1100 to 1300 ° C. is preferable.
- a dispersion (slurry) in which the mixture is dispersed in a solvent is prepared.
- spray granulation method in which the dispersion is spray-dried with an atomizer or the like to produce granulated particles.
- carbon in addition to the above-mentioned Si (containing) compound and / or transition metal.
- examples of carbon include carbonaceous materials and graphite materials.
- a carbonaceous material generally indicates a carbon material having a low graphitization (low crystallinity) obtained by heat-treating (carbonizing) a carbon precursor at 2000 ° C. or lower.
- a graphitic material having high crystallinity close to that of the graphite obtained by heat treatment as described above will be shown.
- Examples of the carbonaceous material include graphitizable carbon that easily changes the carbon structure depending on the heat treatment temperature and non-graphitic carbon having a structure close to an amorphous structure typified by glassy carbon.
- Examples of graphitizable carbon include carbon materials made from tar pitch obtained from petroleum and coal, such as coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, pyrolytic vapor-grown carbon fibers, etc. Is mentioned.
- MCMB is carbon fine particles obtained by separating and extracting mesophase spherules produced in the process of heating the pitches at around 400 ° C.
- mesophase pitch-based carbon fiber is mesophase pitch obtained by growing and coalescing the mesophase spherules. Is a carbon fiber made from a raw material.
- non-graphitizable carbon examples include phenol resin fired bodies, polyacrylonitrile-based carbon fibers, pseudo-isotropic carbon, and furfuryl alcohol resin fired bodies (PFA).
- Graphite materials include natural graphite and artificial graphite.
- artificial graphite artificial graphite heat treated at 2800 ° C or higher, graphitized MCMB heat treated at 2000 ° C or higher, graphitized mesophase pitch carbon fiber heat-treated mesophase pitch carbon fiber at 2000 ° C or higher, etc. are used. Is done.
- the negative electrode active material preferably contains 3 to 60 parts by weight of silicon with respect to 100 parts by weight of the total carbon contained in the negative electrode active material, and further contains 4 to 50 parts by weight of silicon. preferable. If the amount of silicon contained in the negative electrode active material is too large, the life of the battery as a lithium ion secondary battery is reduced. Moreover, when there is too little quantity of the silicon contained in a negative electrode active material, the battery capacity when it is set as a lithium ion secondary battery will fall.
- the negative electrode active material is preferably particle-sized.
- the shape of the particles is spherical, a higher density electrode can be formed during electrode molding.
- the volume average particle diameter is usually 0.1 to 100 ⁇ m, preferably 1 to 50 ⁇ m, more preferably 5 to 20 ⁇ m.
- the negative electrode slurry composition comprises the above-mentioned negative electrode binder composition, negative electrode active material, water-soluble polymer, and medium for adjusting the viscosity of the slurry used as necessary, preservative, thickener, conductivity imparting It can be obtained by mixing a material such as a material, a reinforcing material, a dispersant, a leveling agent, an antioxidant, an electrolytic solution additive having a function of inhibiting decomposition of the electrolytic solution and the like.
- the content ratio of the particulate polymer A in the negative electrode slurry composition is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, and particularly preferably 1 part by weight with respect to 100 parts by weight of the negative electrode active material. 0.5 parts by weight or more, preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and particularly preferably 3 parts by weight or less.
- the mixing method is not particularly limited, and examples thereof include a method using a mixing apparatus such as a stirring type, a shaking type, and a rotary type.
- a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader can be used.
- the medium the same solvent as that used in the polymerization of the negative electrode binder composition can be used.
- the ratio of the medium is not particularly limited, and can be appropriately adjusted so that the slurry has a property suitable for the subsequent process. Specifically, solids in the slurry composition for the negative electrode (drying and heating of the slurry are performed). After that, the ratio of the substance remaining as a constituent component of the electrode active material layer) can be adjusted to 30 to 70% by weight, preferably 40 to 60% by weight.
- Preservative Any preservative can be used as the preservative, and in particular, a benzoisothiazoline compound represented by the following general formula (2), 2-methyl-4-isothiazolin-3-one, or a mixture thereof Is preferable, and a mixture of these is particularly preferable.
- R represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.
- R represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.
- these ratios are 1:10 to 10: 1 by weight.
- the content of the preservative in the negative electrode slurry composition is preferably 0.001 to 0.1 parts by weight, based on 100 parts by weight of the monomer composition, and 0.001 to 0.05 parts by weight. Part is more preferable, and 0.001 to 0.01 part by weight is more preferable.
- thickener As the thickener, the above-mentioned cellulosic polymers and their ammonium salts and alkali metal salts; (modified) poly (meth) acrylic acid and their ammonium salts and alkali metal salts; (modified) polyvinyl alcohol, acrylic acid or acrylic Polyvinyl alcohols such as copolymers of acid salts 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, phosphorus Examples include acid starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydride, and the like.
- (modified) poly means “unmodified poly” or “modified poly”
- (meth) acryl means “acryl” or “methacryl”.
- the content of the thickener in the negative electrode slurry composition can increase the dispersibility of the active material and the like in the slurry, can obtain a smooth electrode, and the resulting secondary battery has an excellent load. From the viewpoint of showing characteristics and cycle characteristics, the content is preferably 0.1 to 10% by weight.
- Conductivity imparting material As the conductivity-imparting material, conductive carbon such as acetylene black, ketjen black, carbon black, vapor-grown carbon fiber, and carbon nanotube can be used. Alternatively, carbon powder such as graphite, fibers or foils of various metals can be used. By using the conductivity imparting material, the electrical contact between the electrode active materials can be improved. In particular, when used in a lithium ion secondary battery, the discharge load characteristics can be improved.
- 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 obtained.
- the content ratio of the conductivity-imparting material and the reinforcing agent in the negative electrode slurry composition is usually 0.01 to 20 parts by weight, preferably 100 parts by weight with respect to 100 parts by weight of the negative electrode active material, in view of high capacity and high load characteristics. 1 to 10 parts by weight.
- Dispersant examples include an anionic compound, a cationic compound, a nonionic compound, and a polymer compound.
- a dispersing agent is selected according to the electrode active material and electrically conductive agent to be used.
- the content of the dispersant in the negative electrode slurry composition is preferably from the viewpoint of obtaining a smooth electrode and a high capacity battery from the viewpoint of obtaining a negative electrode slurry composition having excellent stability. 01 to 10% by weight.
- 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 improve the smoothness of the negative electrode.
- the content of the leveling agent in the negative electrode slurry composition is preferably 0.01 to 10% by weight from the viewpoint of productivity, smoothness, and battery characteristics during electrode production.
- 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 200 to 1000, preferably 600 to 700 is preferably used.
- the content of the antioxidant in the negative electrode slurry composition is preferably 0.01 to 10% by weight, more preferably 0.05 to 5% from the viewpoint of the stability, battery capacity and cycle characteristics of the negative electrode slurry composition. % By weight.
- the lithium ion secondary battery negative electrode of the present invention is an electrode having a negative electrode active material layer and a current collector formed by applying and drying a negative electrode slurry composition.
- the manufacturing method of a negative electrode is not specifically limited, It is the method of apply
- the method for applying the negative electrode slurry composition to the current collector is not particularly limited. Examples thereof include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a comma direct coating, a slide die coating, and a brush coating method.
- Examples of the drying method include drying with warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams.
- the drying time is usually 5 to 30 minutes, and the drying temperature is usually 40 to 180 ° C.
- the active material layer may be formed by repeating application and drying a plurality of times.
- the current collector is not particularly limited as long as it is an electrically conductive and electrochemically durable material, but is preferably a metal material because of its heat resistance, for example, iron, copper, aluminum, nickel, stainless steel. Examples include steel, titanium, tantalum, gold, and platinum.
- the shape of the current collector is not particularly limited, but a sheet shape 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.
- an intermediate layer may be formed on the surface of the current collector in order to increase the adhesive strength and conductivity of the negative electrode active material layer.
- the press working is performed using, for example, a roll press or a sheet press using a metal roll, an elastic roll, or a heating roll.
- the pressing temperature may be performed at room temperature or may be performed as long as the temperature is lower than the temperature for drying the coating film of the negative electrode active material layer. Is 15 to 35 ° C.).
- Roll pressing Pressing with a roll press machine (roll pressing) is preferable because a long sheet-like negative electrode plate can be continuously pressed.
- a stereotaxic press or a constant pressure press may be performed.
- the thickness of the negative electrode active material layer is not particularly limited, but is preferably 5 to 300 ⁇ m, more preferably 30 to 250 ⁇ m.
- the binder composition for a positive electrode used for the lithium ion secondary battery of the present invention comprises a particulate polymer B containing an ethylenically unsaturated carboxylic acid monomer unit, and the particulate polymer B and a dispersion medium or particles It is preferable to comprise a polymer B, a fluoropolymer and a medium.
- the ethylenically unsaturated carboxylic acid monomer constituting the ethylenically unsaturated carboxylic acid monomer unit include an ethylenically unsaturated carboxylic acid monomer that can be used in the above-mentioned binder composition for a negative electrode.
- the content ratio of the ethylenically unsaturated carboxylic acid monomer units in the particulate polymer B is preferably 20 to 50% by weight with respect to 100% by weight of all monomer units contained in the particulate polymer B. More preferably, it is 25 to 45% by weight, particularly preferably 30 to 40% by weight. If the content of the ethylenically unsaturated carboxylic acid monomer unit contained in the particulate polymer B is too large, the durability of the lithium ion secondary battery when used for the positive electrode of the lithium ion secondary battery may be reduced. .
- the particulate polymer B further contains a (meth) acrylic acid ester monomer unit.
- the monomer that gives the (meth) acrylic acid ester monomer unit include a (meth) acrylic acid alkyl ester monomer and a (meth) acrylic acid ester monomer having a functional group in the side chain. Among these, (meth) acrylic acid alkyl ester monomers are preferable.
- (meth) acrylic acid alkyl ester monomers examples include 2-ethylhexyl acrylate (2-EHA), ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, and t-acrylate.
- 2-EHA 2-ethylhexyl acrylate
- ethyl acrylate propyl acrylate
- isopropyl acrylate n-butyl acrylate
- isobutyl acrylate isobutyl acrylate
- t-acrylate examples include 2-ethylhexyl acrylate (2-EHA), ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, and t-acrylate.
- Acrylic acid alkyl esters such as butyl, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, hexyl acrylate, nonyl acrylate, lauryl acrylate, stearyl acrylate; ethyl methacrylate, Propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethyl methacrylate Hexyl, be octyl methacrylate, isodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, and the like compounds such as methacrylic acid alkyl esters such as
- the content ratio of the (meth) acrylic acid ester monomer in the particulate polymer B is 50 to 80% by weight, preferably 55 to 80% by weight with respect to 100% by weight of all monomer units contained in the particulate polymer B. 75% by weight, more preferably 60 to 70% by weight.
- the particulate polymer B contains, in addition to the above-mentioned ethylenically unsaturated carboxylic acid monomer unit and (meth) acrylic acid ester monomer unit, other monomer units copolymerizable therewith. May be.
- the other monomer unit copolymerizable with these refers to a structural unit obtained by polymerizing other monomers copolymerizable with these, and as such other monomer units, Examples thereof include vinyl cyanide monomer units, unsaturated monomer units containing a hydroxyalkyl group, and unsaturated carboxylic acid amide monomer units.
- the content of other monomer units that can be copolymerized with these and the like is a total ratio, preferably 0 to 40% by weight, more preferably 0.5 to 35% by weight. It is particularly preferably 1 to 30% by weight.
- the glass transition temperature of the particulate polymer B is preferably ⁇ 40 to + 50 ° C., more preferably ⁇ 30 to + 40 ° C., and further preferably ⁇ 20 to + 30 ° C.
- the number average particle size of the particulate polymer B is preferably 50 to 500 nm, more preferably 70 to 500 nm from the viewpoint of improving the strength and flexibility of the obtained negative electrode for secondary battery. 400 nm.
- the number average particle diameter can be easily measured by transmission electron microscopy, Coulter counter, laser diffraction scattering method, or the like.
- the content of the particulate polymer B in the positive electrode binder composition is preferably 50 to 100% by weight, more preferably 60 to 99% by weight.
- a fluorine-based polymer such as polytetrafluoroethylene and polyvinylidene fluoride may be used for the positive electrode binder composition.
- the method for producing a positive electrode binder composition used in the lithium ion secondary battery of the present invention is not particularly limited, and the same method as the above-described method for producing a negative electrode binder composition can be used. That is, the particulate polymer B can be obtained by polymerizing a monomer mixture containing the above-described monomers in an aqueous medium. In addition, as a medium contained in the binder composition for positive electrodes, the aqueous medium used for superposition
- the degree of swelling of the binder composition for positive electrode of the present invention with respect to the electrolytic solution is 1 to 5 times, preferably 1 to 4 times, and more preferably 1 to 3 times.
- the degree of swelling of the negative electrode binder composition indicates the degree of swelling with respect to an electrolytic solution obtained by dissolving an electrolyte in a solvent having the solubility parameter described above of 8 to 13 (cal / cm 3 ) 1/2 . If the degree of swelling of the positive electrode binder composition is too large, the durability of the lithium ion secondary battery when used as a lithium ion secondary battery positive electrode may be reduced.
- the type and amount of the polymerizable monomer constituting the particulate polymer B may be adjusted. Specifically, it can be adjusted by reducing the content ratio of the ethylenically unsaturated carboxylic acid monomer unit or increasing the carbon number of the ester group of the (meth) acrylic acid ester monomer unit. .
- the repeated tensile strength of the positive electrode binder composition used in the lithium ion secondary battery of the present invention is 0.2 to 5 kg / cm 2 , preferably 0.5 to 4.5 kg / cm 2 at a low elongation modulus of 15%. 2 and more preferably 1 to 4 Kg / cm 2 .
- the type and amount of the polymerizable monomer constituting the particulate polymer B may be adjusted. Specifically, the content ratio of the ethylenically unsaturated carboxylic acid monomer unit constituting the particulate polymer B is decreased, or the carbon number of the ester group of the (meth) acrylic acid ester monomer unit is increased. Can be adjusted.
- the repeated tensile strength of the positive electrode binder composition is too large, the adhesion between the positive electrode active materials may be reduced when the positive electrode active material layer is formed. Moreover, when the repeated tensile strength of the binder composition for positive electrodes is too small, there is a possibility that the life of the battery as a lithium ion secondary battery is reduced.
- Electrode active material examples of the electrode active material for the positive electrode of the lithium ion secondary battery include transition metal oxides, transition metal sulfides, lithium-containing composite metal oxides of lithium and transition metals, and organic compounds.
- the transition metal examples include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo.
- transition metal oxides include MnO, MnO 2 , V 2 O 5 , V 6 O 13 , TiO 2 , Cu 2 V 2 O 3 , amorphous V 2 O—P 2 O 5 , MoO 3 , V 2 O 5 , V 6. O 13 and the like, MnO from among them cycling stability and capacity, V 2 O 5, V 6 O 13, TiO 2 is preferred.
- the lithium-containing composite metal oxide include a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure.
- lithium-containing composite metal oxide having a layered structure examples include lithium-containing cobalt oxide (LiCoO 2 ), lithium-containing nickel oxide (LiNiO 2 ), Co—Ni—Mn lithium composite oxide, and Ni—Mn—Al lithium. Examples thereof include composite oxides and lithium composite oxides of Ni—Co—Al. Examples of the lithium-containing composite metal oxide having a spinel structure include lithium manganate (LiMn 2 O 4 ) and Li [Mn 3/2 M 1/2 ] O 4 in which a part of Mn is substituted with another transition metal (here, M may be Cr, Fe, Co, Ni, Cu or the like.
- Li x MPO 4 (wherein, M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, and the like) is a lithium-containing composite metal oxide having an olivine structure.
- An olivine type lithium phosphate compound represented by at least one selected from Si, B, and Mo, 0 ⁇ X ⁇ 2) may be mentioned.
- 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 in the presence of a carbon source material during reduction firing. These compounds may be partially element-substituted.
- the positive electrode active material for a lithium secondary battery may be a mixture of the above-described inorganic compound (transition metal oxide, transition metal sulfide, lithium-containing composite metal oxide, etc.) and an organic compound.
- a Si (containing) compound when used as the negative electrode active material, it is preferable to use a material containing Ni as the positive electrode active material.
- the average particle diameter of the positive electrode active material can reduce the amount of the positive electrode binder composition when preparing the positive electrode slurry composition described below, and can suppress the decrease in battery capacity, and the positive electrode slurry composition From the viewpoint that it becomes easy to prepare a product with a viscosity suitable for coating and a uniform electrode can be obtained, it is usually 1 to 50 ⁇ m, preferably 2 to 30 ⁇ m. .
- the content ratio of the positive electrode active material in the positive electrode active material layer is preferably 90 to 99.9% by weight, more preferably 95 to 99% by weight.
- the positive electrode slurry composition can be obtained by mixing the positive electrode binder composition, the positive electrode active material, and other optional substances used as necessary.
- examples of such an optional substance include the same substances as those described above as those that can be contained in the negative electrode slurry composition, and the content ratio of these optional substances is also the content ratio in the negative electrode slurry composition. The same can be said.
- the method for preparing the positive electrode slurry composition and the method for forming the positive electrode active material layer using the same are carried out in the same manner as the method for preparing the negative electrode slurry composition and the method for forming the negative electrode active material layer using the same. be able to.
- the lithium secondary battery positive electrode is formed by laminating a positive electrode active material layer containing a positive electrode active material and a positive electrode binder composition on a current collector.
- the lithium ion secondary battery positive electrode can be obtained by a production method similar to the above-described method for producing a lithium ion secondary battery negative electrode.
- the collector used for the above-mentioned lithium ion secondary battery negative electrode can be used.
- the thickness of the positive electrode active material layer is not particularly limited, but is preferably 5 to 300 ⁇ m, more preferably 10 to 250 ⁇ m.
- a porous film having a fine pore diameter that has no electron conductivity and ion conductivity and high resistance to an organic solvent can be used. Specifically, any of the following (i) to (iv) can be used.
- Microporous membrane made of resin (ii) Woven fabric woven with resin fibers or nonwoven fabric of the fibers (iii) Aggregate layer of non-conductive fine particles (iv) (i) to (iii) above Among these, a laminate comprising a combination of two or more layers (i) or (ii) (iii) a separator formed with a layer, a lithium ion secondary battery negative electrode and / or a positive electrode (iii It is preferable to use a separator having a layer formed thereon.
- the microporous membrane (i) is one in which a number of fine pores are formed after the resin film is formed. Examples of a method for forming such a microporous film include the following methods.
- the material of the microporous membrane (i) includes polyolefin resins (polyethylene, polypropylene, polybutene, polyvinyl chloride) and other resins such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimide. Examples thereof include resins such as amide, polyaramid, polycycloolefin, nylon, and polytetrafluoroethylene.
- any of the polyolefin-based resins, a mixture thereof, or a resin such as a copolymer easily forms a complex with the above (iii) (the slurry for forming the layer of (iii) is coated well.
- the separator thickness can be reduced and the active material ratio in the battery can be increased to increase the capacity per volume.
- the woven or non-woven fiber material is also preferably a polyolefin-based resin similar to the microporous membrane material (i).
- examples of the polyolefin resin used as the material of the separator (i) or (ii) include homopolymers such as polyethylene and polypropylene, copolymers, and mixtures thereof.
- examples of the polyethylene include low density, medium density, and high density polyethylene, and high density polyethylene is preferable from the viewpoint of piercing strength and mechanical strength. These polyethylenes may be mixed in two or more types for the purpose of imparting flexibility.
- the polymerization catalyst used for the preparation of these polyethylenes is not particularly limited, and examples thereof include Ziegler-Natta catalysts, Philips catalysts, metallocene catalysts, and the like.
- the viscosity average molecular weight of polyethylene is preferably 100,000 or more and 12 million or less, more preferably 200,000 or more and 3 million or less.
- polypropylene include homopolymers, random copolymers, and block copolymers, and one kind or a mixture of two or more kinds can be used.
- the polymerization catalyst is not particularly limited, and examples thereof include Ziegler-Natta catalysts and metallocene catalysts.
- the stereoregularity is not particularly limited, and isotactic, syndiotactic or atactic can be used. However, it is desirable to use isotactic polypropylene because it is inexpensive.
- an appropriate amount of a polyolefin other than polyethylene or polypropylene, and an additive such as an antioxidant or a nucleating agent may be added to the polyolefin resin within a range not impairing the effects of the present invention.
- the thickness of the separator (i) or (ii) is usually 0.5 to 40 ⁇ m, preferably from the viewpoint of reducing resistance by the separator in the battery and good workability at the time of coating on the separator, preferably The thickness is 1 to 30 ⁇ m, more preferably 1 to 10 ⁇ m. .
- the aggregated layer of non-conductive fine particles (iii) can be obtained by curing a mixture containing non-conductive fine particles and a binder resin that can be added if necessary.
- a mixture is typically a slurry
- the layer of (iii) is obtained by applying and curing the slurry on the film of (i) above or another member such as a woven or non-woven fabric of (ii). Can be obtained.
- the nonconductive fine particles constituting the layer (iii) exist stably in the use environment of the lithium ion secondary battery and are also stable electrochemically.
- various non-conductive inorganic fine particles and organic fine particles can be used, and organic fine particles are preferably used.
- the inorganic fine particles include oxide particles such as iron oxide, silicon oxide, aluminum oxide, magnesium oxide, and titanium oxide; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystal particles such as silicon and diamond; barium sulfate, Examples include slightly soluble ionic crystal particles such as calcium fluoride and barium fluoride; those obtained by subjecting the above various particles to element substitution, surface treatment, solid solution treatment, and the like, or combinations of two or more thereof. Among these, oxide particles are preferable from the viewpoints of stability in an electrolytic solution and potential stability.
- the organic fine particles particles made of various polymer materials such as polystyrene, polyethylene, polyimide, melamine resin, and phenol resin can be used.
- the polymer material forming the particles can be used as a mixture, a modified product, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, a crosslinked product, and the like. There may be two or more different polymeric material regions within the particle.
- a conductive metal such as carbon black, graphite, SnO 2 , ITO, metal powder, and the fine powder of conductive compound or oxide
- a surface treatment with the non-conductive material exemplified above, It is also possible to use particles having electrical insulating properties.
- nonconductive fine particles constituting the layer (iii) two or more of the various inorganic fine particles and organic fine particles described above may be used in combination.
- the average particle diameter (volume average D50 average particle diameter) of the non-conductive fine particles constituting the layer (iii) is preferably from the viewpoint of easy control of the dispersion state and easy to obtain a film having a uniform predetermined thickness. Is from 5 nm to 10 ⁇ m, more preferably from 10 nm to 5 ⁇ m. . It is particularly preferable that the average particle diameter of the non-conductive fine particles is in the range of 50 nm or more and 2 ⁇ m or less because the dispersion, the ease of coating, and the controllability of the voids are excellent.
- the BET specific surface area of the non-conductive fine particles is preferably 0.9 to 200 m 2 / g from the viewpoint of suppressing the aggregation of the particles and optimizing the fluidity of the slurry. More preferably, it is 150 m 2 / g.
- the shape of the non-conductive fine particles constituting the layer (iii) is not particularly limited, such as a spherical shape, a needle shape, a rod shape, a conical shape, a plate shape, and a scale shape, but a spherical shape, a acicular shape, a conical shape and the like are preferable. Porous particles can also be used.
- the content ratio of the non-conductive fine particles in the layer (iii) is preferably 5 to 99% by weight, more preferably 50 to 98% by weight, from the viewpoint that a layer exhibiting high thermal stability and strength can be obtained.
- the layer (iii) contains the non-conductive fine particles described above as an essential component, but preferably further contains a binder as necessary.
- the binder By including the binder, the strength of the layer (iii) increases, and problems such as cracking can be prevented.
- the binder is not particularly limited, and various resin components and soft polymers can be used.
- polyethylene polytetrafluoroethylene
- PVDF polyvinylidene fluoride
- FEP tetrafluoroethylene-hexafluoropropylene copolymer
- polyacrylic acid derivatives polyacrylonitrile derivatives, etc.
- resin component polytetrafluoroethylene
- PVDF polyvinylidene fluoride
- FEP tetrafluoroethylene-hexafluoropropylene copolymer
- polyacrylic acid derivatives polyacrylonitrile derivatives, etc.
- Soft polymers include polybutyl acrylate, polybutyl methacrylate, polyhydroxyethyl methacrylate, polyacrylamide, polyacrylonitrile, butyl acrylate / styrene copolymer, butyl acrylate / acrylonitrile copolymer, butyl acrylate / acrylonitrile / glycidyl methacrylate copolymer
- An acrylic soft polymer which is a homopolymer of acrylic acid or a methacrylic acid derivative, or a copolymer with a monomer copolymerizable therewith;
- Isobutylene-based soft polymers such as polyisobutylene, isobutylene-isoprene rubber, isobutylene-styrene copolymer; Polybutadiene, polyisoprene, butadiene / styrene random copolymer, isoprene / styrene random cop
- Olefinic soft polymers of Vinyl-based soft polymers such as polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, vinyl acetate / styrene copolymer; Epoxy-based soft polymers such as polyethylene oxide, polypropylene oxide, epichlorohydrin rubber; Fluorine-containing soft polymers such as vinylidene fluoride rubber and tetrafluoroethylene-propylene rubber; Other soft polymers such as natural rubber, polypeptide, protein, polyester-based thermoplastic elastomer, vinyl chloride-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, and the like are mentioned. Of these, acrylic-based soft polymers are preferable, and more preferable.
- an acrylic soft polymer containing acrylonitrile polymerized units is preferred.
- the binder is the copolymer, elution into the electrolytic solution is reduced, and deformation of the layer (iii) can be made difficult to occur. Furthermore, it is difficult to elute while maintaining the swellability of the electrolyte even at high temperatures, and can exhibit excellent high temperature characteristics. Therefore, the safety of the layer (iii) can be further improved by combining such a binder and the nonconductive fine particles.
- the glass transition temperature of the binder constituting the layer (iii) can give flexibility to the layer (iii) at room temperature, cracks during winding and winding, chipping of the layer (iii), etc. From the viewpoint of suppressing the above, it is preferably 15 ° C. or lower, more preferably 0 ° C. or lower.
- the glass transition temperature of the binder can be adjusted by changing the use ratio of the monomer constituting the polymer.
- the weight average molecular weight of the binder constituting the layer (iii) is preferably 5,000 or more, more preferably from the viewpoint of improving the dispersibility of the non-conductive fine particles and the strength of the layer (iii). It is preferably 10,000 or more and preferably 10,000,000 or less. .
- the content ratio of the binder in the layer (iii) increases the resistance by inhibiting the migration of lithium ions while maintaining the binding property between the non-conductive fine particles and the binding property to the electrode and flexibility.
- the amount is preferably 0.1 to 10 parts by weight, more preferably 1 to 5 parts by weight with respect to 100 parts by weight of the nonconductive fine particles. be able to.
- the layer (iii) can contain an optional component, if necessary, in addition to the nonconductive fine particles and the binder.
- optional components include a dispersant and an electrolytic solution additive having a function of suppressing electrolytic decomposition. These are not particularly limited as long as they do not affect the battery reaction.
- dispersant examples include anionic compounds, cationic compounds, nonionic compounds, and polymer compounds.
- the dispersant can be selected according to the non-conductive fine particles to be used, but when organic fine particles are used as the non-conductive fine particles, it is preferable to use a water-soluble polymer such as carboxymethyl cellulose.
- nanoparticles such as fumed silica and fumed alumina: surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants.
- surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants.
- the content ratio of the surfactant in the layer (iii) is preferably within a range that does not affect the battery characteristics, and is preferably 10% by weight or less.
- the layer (iii) may further contain particles other than non-conductive fine particles and fiber compounds for the purpose of controlling strength, hardness, and heat shrinkage rate.
- a low molecular weight compound or a high molecular weight compound is used in advance for the purpose of improving adhesion or improving the liquid impregnation property by lowering the surface tension with the electrolytic solution.
- the surface of the other member on which the layer (iii) is provided with the molecular compound may be subjected to coating treatment, electromagnetic radiation treatment such as ultraviolet rays, or plasma treatment such as corona discharge / plasma gas.
- the layer (iii) is a layer (iii) forming slurry containing a dispersion medium and the above-described various components constituting the layer (iii) dispersed therein, and is applied onto another member and dried. Can be formed. For example, by applying a slurry for forming a layer (iii) containing organic fine particles (iii) on the separator (i) or (ii) and drying, a separator in which the organic fine particle porous film is laminated (the above (iv)) can be obtained. it can.
- a lithium ion secondary battery negative electrode and / or a lithium ion secondary battery positive electrode on which a fine particle porous film (polymer layer) is laminated can be obtained.
- the solvent used for the slurry for forming the layer (iii) either water or an organic solvent can be used.
- organic solvent examples include aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene, and chlorinated aliphatic hydrocarbons include methylene chloride, chloroform, and carbon tetrachloride.
- Others include pyridine, acetone, dioxane, dimethylformamide, methyl ethyl ketone, diisopropyl ketone, cyclohexanone, tetrahydrofuran, n-butyl phthalate, methyl phthalate, ethyl phthalate, tetrahydrofurfuryl alcohol, ethyl acetate, butyl acetate, 1-nitropropane, disulfide Examples include carbon, tributyl phosphate, cyclohexane, cyclopentane, xylene, methylcyclohexane, ethylcyclohexane, N-methylpyrrolidone and the like. These solvents can be used alone or as a mixed solvent.
- solvents may be used alone or as a mixed solvent by mixing two or more of them.
- a solvent having excellent dispersibility of the nonconductive fine particles and having a low boiling point and high volatility is preferable because the solvent can be removed at a low temperature in a short time.
- acetone, cyclohexanone, cyclopentane, tetrahydrofuran, cyclohexane, xylene, water, N-methylpyrrolidone, or a mixed solvent thereof is preferable.
- cyclohexanone, xylene, N-methylpyrrolidone, or a mixed solvent thereof is particularly preferable because it has low volatility and excellent workability during slurry coating.
- the solid concentration of the slurry for forming the layer (iii) is not particularly limited as long as it can be applied and immersed and has a fluid viscosity, but is generally about 20 to 50% by weight.
- the method for producing the slurry for forming the layer (iii) is not particularly limited, and a slurry in which non-conductive fine particles 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 the components can be mixed uniformly, and a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, and the like can be used. It is particularly preferable to use a high dispersion apparatus such as a bead mill, a roll mill, or a fill mix that can add a high dispersion share.
- the method for applying the layer (iii) forming slurry onto other members is not particularly limited. Examples thereof include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. Among them, the dip method and the gravure method are preferable in that a uniform layer can be obtained.
- 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 drying temperature varies depending on the type of solvent used.
- a low-volatility solvent such as N-methylpyrrolidone
- it is preferably dried at a high temperature of 120 ° C. or higher with a blower-type dryer.
- a highly volatile solvent when used, it can be dried at a low temperature of 100 ° C. or lower.
- the layer (iii) formed by the above-described forming method may have a structure in which non-conductive fine particles are bound via a binder, and voids are formed between the non-conductive fine particles. it can. Since the electrolytic solution can penetrate into the voids, a favorable battery reaction can be obtained.
- the thickness of the layer (iii) is not particularly limited and can be appropriately set according to the type of the lithium ion secondary battery in which the layer (iii) is used, but if it is too thin, a uniform film cannot be formed. If the thickness is too large, the capacity per volume (weight) in the battery decreases, so 0.1 to 50 ⁇ m is preferable, 0.2 to 10 ⁇ m is more preferable, and 0.5 to 10 ⁇ m is particularly preferable.
- the electrolytic solution used in the present invention is not particularly limited.
- a solution obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent can be used.
- the lithium salt include 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 other lithium salts.
- 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 preferably used. These can be used individually or in mixture of 2 or more types.
- the amount of the supporting electrolyte is usually 1% by weight or more, preferably 5% by weight or more, and usually 30% by weight or less, preferably 20% by weight or less with respect to the electrolytic solution. If the amount of the supporting electrolyte is too small or too large, the ionic conductivity decreases, and the charging characteristics and discharging characteristics of the battery decrease.
- the solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte.
- Alkyl carbonates such as carbonate (BC), and methyl ethyl carbonate (MEC); esters such as ⁇ -butyrolactone, methyl formate, ethers such as 1,2-dimethoxyethane, and tetrahydrofuran; sulfolane, dimethyl sulfoxide, and the like Sulfur-containing compounds are used.
- dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferable because high ion conductivity is easily obtained and the use temperature range is wide. These can be used individually or in mixture of 2 or more types. Moreover, it is also possible to use the electrolyte solution by containing an additive. As the additive, carbonate compounds such as vinylene carbonate (VC) are preferable.
- VC vinylene carbonate
- Examples of the electrolytic solution other than the above include a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide and polyacrylonitrile with an electrolytic solution, and an inorganic solid electrolyte such as LiI and Li 3 N.
- the configuration of the lithium ion secondary battery of the present invention is not particularly limited as long as the lithium ion secondary battery negative electrode, the lithium ion secondary battery positive electrode, the electrolytic solution, and the separator are provided, and the configuration of a normal lithium ion secondary battery Can be adopted as appropriate.
- a lithium ion secondary battery positive electrode and a lithium ion secondary battery negative electrode are overlapped via a separator, wound in accordance with the shape of the battery, folded into a battery container, and an electrolyte solution is injected into the battery container. And the battery can be configured.
- the negative electrode of the lithium ion secondary battery, the positive electrode of the lithium ion secondary battery, and the separator may have a laminated structure in which these are stacked as a flat layer that is not curved.
- a negative electrode active material layer or a positive electrode active material is formed on both sides of a flat plate current collector, and a laminate having a layer structure of (negative electrode active material layer)-(current collector)-(negative electrode active material layer) ( A conductive adhesive layer may optionally be interposed between the current collector and the negative electrode active material layer) and (positive electrode active material layer)-(current collector)-(positive electrode active material layer)
- a laminate having a layer structure (a conductive adhesive layer may optionally be interposed between the current collector and the positive electrode active material layer) is formed, and these are combined (current collector) -(Positive electrode active material layer)-(separator)-(negative electrode active material layer)-(current collector)-(negative electrode active material layer)-(separator)-(positive
- the lithium ion secondary battery of the present invention can be provided with optional components such as an expanded metal, an overcurrent prevention element such as a fuse and a PTC element, a lead plate, and the like as necessary. It is also possible to prevent internal pressure rise and overcharge / discharge.
- the shape of the outer shape of the battery includes a coin type, a button type, a sheet type, a cylindrical type, a square type, a laminated type, and the like, and the laminated type is preferable in terms of excellent output density and safety.
- the use of the lithium ion secondary battery of the present invention is not particularly limited, and can be used for the same use as a conventional secondary battery.
- it has a large capacity, can maintain a high capacity even during rapid charging / discharging and charging / discharging in a low temperature environment, and has a high safety. It can be used as a power source for electronic devices and large devices such as electric vehicles.
- a cellophane tape (specified in JIS Z1522) is attached to the surface of the electrode composition layer with the negative electrode active material layer surface of the dried lithium ion secondary battery negative electrode and the positive electrode active material layer surface of the lithium ion secondary electrode positive electrode facing down, respectively.
- the stress was measured when one end of the current collector was pulled in the vertical direction at a pulling speed of 50 mm / min and peeled off (the cellophane tape was fixed to the test stand). The measurement was performed three times, and the average value was obtained and used as the peel strength. The higher the peel strength, the greater the binding force of the negative electrode active material layer and the positive electrode active material layer to the current collector, that is, the higher the adhesion strength.
- Lithium ion secondary batteries manufactured in Examples and Comparative Examples were allowed to stand at 25 ° C. for 24 hours, and then charged at a charge voltage of 4.2 V, a discharge voltage of 3.0 V, and a charge of 0.1 C at 25 ° C. The charge / discharge operation was performed, and the initial capacity C 0 was measured. Further, charging and discharging (charging voltage 4.2 V, discharging voltage 3.0 V, charging and discharging rate 0.1 C) were repeated under a 60 ° C. environment, and the capacity C 2 after 100 cycles was measured.
- Lithium ion secondary batteries produced in Examples and Comparative Examples were allowed to stand at 25 ° C. for 24 hours, and then charged at 25 ° C. at a charge rate of 4.2 V and 0.1 C. Thereafter, a discharge operation was performed at a 1 C discharge rate in an environment of ⁇ 25 ° C., and the voltage V 10 seconds after the start of discharge was measured.
- the swelling degree and tensile strength of the negative electrode binder composition and the positive electrode binder composition were measured as follows.
- the repeated tensile strength (low elongation modulus 15%) of the negative electrode binder composition and the positive electrode binder composition produced in the examples and comparative examples is the same as the above-described method for measuring the degree of swelling. According to JIS-K7312, the film was stretched at a speed of 50 mm / min, and the strength corresponding to 15% elongation was measured 1000 times.
- Example 1 (Production of water-soluble polymers) In a 5 MPa pressure vessel with a stirrer, 35 parts of methacrylic acid (MAA), 65 parts of ethyl acrylate, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water and 0.5 part of potassium persulfate as a polymerization initiator After stirring sufficiently, the mixture was heated to 60 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain an aqueous dispersion containing a water-soluble polymer.
- MAA methacrylic acid
- ethyl acrylate 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier
- ion-exchanged water 150 parts
- potassium persulfate potassium persulfate
- the swelling degree of the binder composition for negative electrode comprising 1 part of an aqueous dispersion containing the particulate polymer A (solid content basis) and 1 part of a 5% aqueous solution of water-soluble polymer is 1.4 times, and the tensile strength (low elongation) (Modulus 15%) was 12.8 Kg / cm 2 , and tetrahydrofuran insoluble content was 88.5%.
- the blending ratio of the particulate polymer A and the water-soluble polymer in the negative electrode binder composition was 0.4: 0.05 as a solid content equivalent ratio.
- the obtained slurry composition for negative electrode was applied on a copper foil having a thickness of 20 ⁇ m with a comma coater so that the film thickness after drying was about 150 ⁇ m, and dried for 2 minutes (at a rate of 0.5 m / min). , 60 ° C.) and heat treatment (120 ° C.) for 2 minutes to obtain a negative electrode raw material.
- This negative electrode original fabric was rolled with a roll press to obtain a secondary battery negative electrode having a negative electrode active material layer thickness of 80 ⁇ m.
- the swelling degree of this positive electrode binder composition was 2.4 times, and the tensile strength (low elongation modulus 15%) was 1.55 Kg / cm 2 .
- a slurry composition for a positive electrode was prepared by mixing a 40% aqueous dispersion with a planetary mixer so that the solid content was 5 parts corresponding to the solid content and the total solid content concentration was 40% with ion-exchanged water.
- the obtained positive electrode slurry composition was applied on a 20 ⁇ m thick aluminum foil with a comma coater so that the film thickness after drying was about 200 ⁇ m, and dried for 2 minutes (at a rate of 0.5 m / min, 60 ° C.) and heat treatment (120 ° C.) for 2 minutes to obtain an electrode raw material.
- This positive electrode raw material was rolled with a roll press to obtain a secondary battery positive electrode having a positive electrode active material layer thickness of 80 ⁇ m.
- the slurry for organic fine particle porous film 1 is dried on the single layer polypropylene separator film (width 65 mm, length 500 mm, thickness 25 ⁇ m, manufactured by dry method, porosity 55%). Coating was performed using a wire bar so that the thickness of the layer was 5 ⁇ m, followed by drying at 60 ° C. for 30 seconds to form an organic fine particle porous film, thereby obtaining a separator with an organic fine particle porous film.
- Example 2 In the same manner as in Example 1, except that the composition of the monomer in producing the particulate polymer A was 57 parts of styrene, 39.5 parts of 1,3-butadiene, and 3.5 parts of itaconic acid. The next battery was manufactured.
- the swelling degree of the binder composition for negative electrode comprising 1 part of an aqueous dispersion containing the particulate polymer A of Example 2 (based on solid content) and 1 part of a 5% aqueous solution of water-soluble polymer is 1.7 times tensile.
- the strength (low elongation modulus: 15%) was 9.5 kg / cm 2 , and the tetrahydrofuran insoluble content was 90.8%.
- Example 3 In the same manner as in Example 1, except that the composition of the monomer in producing the particulate polymer A was 68 parts of styrene, 28.5 parts of 1,3-butadiene, and 3.5 parts of itaconic acid. The next battery was manufactured.
- the swelling degree of the binder composition for negative electrode which consists of 1 part of aqueous dispersion containing the particulate polymer A of Example 3 (solid content basis) and 1 part of 5% aqueous solution of water-soluble polymer is 1.67 times, tensile The strength (low elongation modulus: 15%) was 8.8 kg / cm 2 , and the tetrahydrofuran insoluble content was 83.2%.
- Example 4 A lithium ion secondary battery was produced in the same manner as in Example 1 except that the composition of the monomer in producing the particulate polymer B was 72 parts of 2-ethylhexyl acrylate and 28 parts of methacrylic acid.
- the positive electrode binder composition of Example 4 had a degree of swelling of 3.1 times and a tensile strength (low elongation modulus of 15%) of 0.94 Kg / cm 2 .
- Example 5 A lithium ion secondary battery was produced in the same manner as in Example 1, except that the monomer composition for producing the particulate polymer B was 78 parts of 2-ethylhexyl acrylate and 22 parts of methacrylic acid. In addition, the swelling degree of the positive electrode binder composition of Example 5 was 4.1 times, and the tensile strength (low elongation modulus 15%) was 0.25 kg / cm 2 .
- Example 6 A lithium ion secondary battery was produced in the same manner as in Example 1 except that the water-soluble polymer contained in the negative electrode binder composition was not used.
- the negative electrode binder composition of Example 6 had a degree of swelling of 1.4, a tensile strength (low elongation modulus of 15%) of 7.8 kg / cm 2 , and a tetrahydrofuran insoluble content of 90.2%.
- Example 7 A lithium ion secondary battery was produced in the same manner as in Example 1 except that the composition of the negative electrode active material contained in the negative electrode slurry composition was 90 parts of artificial graphite and 10 parts of SiC.
- Example 8 A lithium ion secondary battery was produced in the same manner as in Example 1 except that the composition of the negative electrode active material contained in the negative electrode slurry composition was 95 parts of artificial graphite and 5 parts of SiC.
- Example 9 A lithium ion secondary battery was produced in the same manner as in Example 1, except that the composition of the negative electrode active material contained in the negative electrode slurry composition was 70 parts of artificial graphite and 30 parts of SiOC.
- Example 10 A lithium ion secondary battery was produced in the same manner as in Example 1 except that the composition of the negative electrode active material contained in the negative electrode slurry composition was 70 parts of artificial graphite and 30 parts of SiO x .
- Example 11 A lithium ion secondary battery was produced in the same manner as in Example 1, except that the composition of the negative electrode active material contained in the negative electrode slurry composition was 90 parts of artificial graphite and 10 parts of the Si negative electrode material A.
- the Si negative electrode material A is obtained by mixing Si fine particles (volume average particle diameter of 20 nm) with artificial graphite using water, and spray drying by spray drying.
- Example 12 A lithium ion secondary battery was produced in the same manner as in Example 1 except that the composition of the negative electrode active material contained in the negative electrode slurry composition was 85 parts of artificial graphite and 15 parts of Si negative electrode material B.
- the Si negative electrode material B is obtained by firing the Si negative electrode material A at 2000 degrees.
- Example 13 A lithium ion secondary battery was produced in the same manner as in Example 1 except that the composition of the negative electrode active material contained in the negative electrode slurry composition was 80 parts of artificial graphite and 20 parts of Si negative electrode material C.
- the Si negative electrode material C is obtained by firing the Si negative electrode material A at 2500 degrees.
- the monomer composition for producing the particulate polymer A is 40 parts of styrene, 55.5 parts of 1,3-butadiene, and 4.5 parts of methacrylic acid. Except that the composition of the body was 95 parts butyl acrylate (BA), 5 parts methacrylic acid, no water-soluble polymer was used, and the organic fine particle porous film was not formed on the single-layer polypropylene separator film.
- a lithium ion secondary battery was produced in the same manner as in Example 1.
- the negative electrode binder composition of Comparative Example 1 had a swelling degree of 2.4 times, a tensile strength (low elongation modulus of 15%) of 0.45 Kg / cm 2 , and a tetrahydrofuran insoluble content of 67.7%. Moreover, the swelling degree of the positive electrode binder composition of Comparative Example 1 was 7.8 times, and the tensile strength (low elongation modulus 15%) was 0.08 Kg / cm 2 .
- Comparative Example 2 The composition of the monomer when producing the particulate polymer A is 70.5 parts of styrene, 26 parts of 1,3-butadiene, 3.5 parts of methacrylic acid, and a negative electrode active material made only of artificial graphite is used. Produced a lithium ion secondary battery in the same manner as in Comparative Example 1.
- the swelling ratio of the negative electrode binder composition of Comparative Example 2 was 1.4 times, the tensile strength (low elongation modulus 15%) was 7.8 kg / cm 2 , and the tetrahydrofuran insoluble content was 68%.
- Example 3 A lithium ion secondary battery was produced in the same manner as in Example 1 except that a negative electrode active material composed only of artificial graphite was used.
- the composition of the monomer is 70 parts butyl acrylate, 10 parts methacrylic acid, 20 parts acrylonitrile, and a negative electrode active material consisting only of artificial graphite, for a single-layer polypropylene separator.
- a lithium ion secondary battery was produced in the same manner as in Comparative Example 1 except that the organic fine particle porous film was not formed on the film.
- the swelling ratio of the positive electrode binder composition of Comparative Example 1 was 7.5 times, and the tensile strength (low elongation modulus 15%) was 0.001 Kg / cm 2 .
- the electrolyte was added to a solvent containing an aliphatic conjugated diene monomer unit and a particulate polymer A and having a solubility parameter of 8 to 13 (cal / cm 3 ) 1/2.
- the binder composition for a negative electrode has a degree of swelling of 1 to 2 times with respect to an electrolyte solution in which an aqueous solution is dissolved, and a repeated tensile strength when swollen with the electrolyte solution is 0.5 to 20 kg / cm 2 at a low elongation modulus of 15%.
- a positive electrode including a positive electrode active material layer formed from a positive electrode slurry composition including a positive electrode binder composition containing 5% and 0.2 to 5 kg / cm 2 , a positive electrode active material, an electrolyte solution, and a separator.
- a positive electrode active material layer formed from a positive electrode slurry composition including a positive electrode binder composition containing 5% and 0.2 to 5 kg / cm 2 , a positive electrode active material, an electrolyte solution, and a separator.
Abstract
Description
さらに、リチウムイオン二次電池は、高温環境下や低温環境下においても良好な性能を有することが求められる。
(1) 正極、負極、電解液およびセパレータを備えるリチウムイオン二次電池であって、前記負極は、脂肪族共役ジエン単量体単位を含む粒子状重合体Aを含んでなる負極用バインダー組成物と、負極活物質とを含む負極用スラリー組成物から形成される負極活物質層を含み、溶解度パラメータが8~13(cal/cm3)1/2である溶媒に電解質を溶解した前記電解液に対する前記負極用バインダー組成物の膨潤度が1~2倍であって、前記電解液により膨潤した前記負極用バインダー組成物の繰り返しの引張り強度は低伸張モジュラス15%で0.5~20Kg/cm2であり、前記正極は、エチレン性不飽和カルボン酸単量体単位を含む粒子状重合体Bを含んでなる正極用バインダー組成物と、正極活物質とを含む正極用スラリー組成物から形成される正極活物質層を含み、溶解度パラメータが8~13(cal/cm3)1/2である溶媒に電解質を溶解した前記電解液に対する前記正極用バインダー組成物の膨潤度が1~5倍であって、前記電解液により膨潤した前記正極用バインダー組成物の繰り返しの引張り強度は低伸張モジュラス15%で0.2~5Kg/cm2であることを特徴とするリチウムイオン二次電池、
(2) 前記負極活物質は、リチウムを吸蔵し放出するSi化合物を含むことを特徴とする(1)記載のリチウムイオン二次電池、
(3) 前記粒子状重合体Aは、芳香族ビニル単量体単位を含み、前記粒子状重合体Aにおける前記芳香族ビニル単量体単位の含有割合は50~75重量%であることを特徴とする(1)または(2)記載のリチウムイオン二次電池、
(4) 前記粒子状重合体Aは、エチレン性不飽和カルボン酸単量体単位を含み、前記粒子状重合体Aにおける前記エチレン性不飽和カルボン酸単量体単位の含有割合は0.5~10重量%であることを特徴とする(1)~(3)の何れかに記載のリチウムイオン二次電池、
(5) 前記粒子状重合体Aのテトラヒドロフラン不溶分が、75~95%であることを特徴とする(1)~(4)の何れかに記載のリチウムイオン二次電池、
(6) 前記負極用バインダー組成物は、さらにエチレン性不飽和カルボン酸単量体単位を有する水溶性高分子を含み、前記水溶性高分子における前記エチレン性不飽和カルボン酸単量体単位の含有割合は20~60重量%であることを特徴とする(1)~(5)の何れかに記載のリチウムイオン二次電池、
(7) 前記粒子状重合体Bは、エチレン性不飽和カルボン酸単量体単位を含み、前記粒子状重合体Bにおける前記エチレン性不飽和カルボン酸単量体単位の含有割合は20~50重量%であることを特徴とする(1)~(6)の何れかに記載のリチウムイオン二次電池、
(8) 前記粒子状重合体Bは、(メタ)アクリル酸エステル単量体単位を含み、前記粒子状重合体Bにおける前記(メタ)アクリル酸エステル単量体単位の含有割合は50~80重量%であることを特徴とする(1)~(7)の何れかに記載のリチウムイオン二次電池、
(9) 積層型であることを特徴とする(1)~(8)の何れかに記載のリチウムイオン二次電池
が提供される。
本発明のリチウムイオン二次電極に用いる負極用バインダー組成物は、脂肪族共役ジエン単量体単位を含む粒子状重合体Aを含んでなり、粒子状重合体A及び媒体、又は、粒子状重合体A、水溶性高分子及び媒体を含んでなることが好ましい。脂肪族共役ジエン単量体単位とは、脂肪族共役ジエン単量体を重合して形成される構造単位のことをいう。脂肪族共役ジエン単量体としては、たとえば、1,3-ブタジエン、イソプレン、2,3-ジメチル-1,3-ブタジエン、2-エチル-1,3-ブタジエン、1,3-ペンタジエン、クロロプレンなどが挙げられる。これらのなかでも、1,3-ブタジエン、イソプレンが好ましく、1,3-ブタジエンがさらに好ましい。これらの脂肪族共役ジエン単量体は単独でまたは2種以上を組み合わせて用いることができる。
粒子状重合体Aにおける、前記これらと共重合他可能な他の単量体単位の含有割合は、合計の割合で、好ましくは0~20重量%、より好ましくは0.1~15重量%であり、特に好ましくは0.2~10重量%である。
δ=ΣG/V=dΣG/M(V;比容、M;分子量、d;比重)
負極用バインダー組成物の膨潤度が大きすぎると、リチウムイオン二次電池負極としたときのリチウムイオン二次電池の耐久性が低下する。
負極用バインダー組成物の膨潤度を上記範囲にするためには、粒子状重合体Aを構成する重合性単量体の種類や量を調整したり、後述する水溶性高分子の種類や量を調整したりすればよい。具体的には、脂肪族共役ジエン単量体単位の含有割合を減らしたり、芳香族ビニル単量体単位の含有割合を増やしたりすることにより調整することができる。
負極用バインダー組成物の繰り返しの引張強度を上記範囲にするためには、粒子状重合体Aを構成する重合性単量体の種類や量を調整したり、後述する水溶性高分子の種類や量を調整したりすればよい。具体的には、粒子状重合体Aを構成する脂肪族共役ジエン単量体単位の含有割合を減らしたり、芳香族ビニル単量体単位の含有割合を増やしたりすることにより調整することができる。
負極用バインダー組成物のテトラヒドロフラン不溶分を上記範囲にするためには、粒子状重合体Aを構成する重合性単量体の種類や量を調整したり、後述する水溶性高分子の種類や量を調整したりすればよい。具体的には、粒子状重合体Aのガラス転移温度、すなわち、脂肪族共役ジエン単量体単位や芳香族ビニル単量体単位の含有割合を変えたり、粒子状重合体Aの調製する際に用いる分子量調整剤の種類や量を変えることにより、調整することができる。
本発明のリチウムイオン二次電池に用いる負極用バインダー組成物は、水溶性高分子を含むことが好ましい。本発明の負極用バインダー組成物に用いられる水溶性高分子は、特に限定されないが、スラリーの安定性の向上の点からカルボキシメチルセルロース(CMC)などのセルロース系ポリマー、エチレン性不飽和カルボン酸単量体単位を含む重合体等が好ましい。
エチレン性不飽和カルボン酸単量体単位を含む重合体における、架橋性単量体単位の含有割合は、水溶性高分子の水に対する可溶性及び分散性を良好なものとする観点から、好ましくは0.1~2重量%、より好ましくは0.2~1.5重量%、さらに好ましくは0.5~1重量%である。
反応性界面活性剤は、通常、重合性不飽和基を有し、この基が重合後に疎水性基としても作用する。反応性界面活性剤が有する重合性不飽和基の例としては、ビニル基、アリル基、ビニリデン基、プロペニル基、イソプロペニル基、イソブチリデン基などが挙げられる。このような重合性不飽和基の種類は、1種類でもよく、2種類以上でもよい。
本発明のリチウムイオン二次電池に用いられる負極活物質は、リチウムを吸蔵し放出するSi(含有)化合物を含む。Si(含有)化合物としては、SiOC、SiC、SiOx等が挙げられる。また、負極活物質としては、リチウムを吸蔵し放出するSn、Zn等の遷移金属を用いてもよい。これらのなかでもSiOC、SiC、SiOxを用いることが好ましい。
負極用スラリー組成物は、上述の負極用バインダー組成物、負極活物質、水溶性高分子、および必要に応じ用いられるスラリーの粘度を調整するための媒体、防腐剤、増粘剤、導電性付与材、補強材、分散剤、レベリング剤、酸化防止剤、電解液分解抑制等の機能を有する電解液添加剤等の物質を混合することにより得ることができる。
負極用スラリー組成物における、上述の粒子状重合体Aの含有割合は、負極活物質100重量部に対して、好ましくは0.5重量部以上、より好ましくは1重量部以上、特に好ましくは1.5重量部以上であり、好ましくは10重量部以下、より好ましくは5重量部以下、特に好ましくは3重量部以下である。
媒体としては、負極用バインダー組成物の重合に際して用いた溶媒と同様のものを用いることができる。媒体の割合は、特に限定されず、スラリーがその後の工程に適した性状となるよう、適宜調整することができ、具体的には負極用スラリー組成物中の固形物(スラリーの乾燥、加熱を経て電極活物質層の構成成分として残留する物質)の割合が30~70重量%、好ましくは40~60重量%となるよう調整することができる。
前記防腐剤としては、任意の防腐剤を用いることができるが、特に、下記の一般式(2)で表わされるベンゾイソチアゾリン系化合物、2-メチル-4-イソチアゾリン-3-オン、又はこれらの混合物を用いることが好ましく、特にこれらの混合物であることがより好ましい。
増粘剤としては、上述のセルロース系ポリマーおよびこれらのアンモニウム塩並びにアルカリ金属塩;(変性)ポリ(メタ)アクリル酸およびこれらのアンモニウム塩並びにアルカリ金属塩;(変性)ポリビニルアルコール、アクリル酸又はアクリル酸塩とビニルアルコールの共重合体、無水マレイン酸又はマレイン酸もしくはフマル酸とビニルアルコールの共重合体などのポリビニルアルコール類;ポリエチレングリコール、ポリエチレンオキシド、ポリビニルピロリドン、変性ポリアクリル酸、酸化スターチ、リン酸スターチ、カゼイン、各種変性デンプン、アクリロニトリル-ブタジエン共重合体水素化物などが挙げられる。ここで、「(変性)ポリ」は「未変性ポリ」又は「変性ポリ」を意味し、「(メタ)アクリル」は、「アクリル」又は「メタアクリル」を意味する。負極用スラリー組成物中の増粘剤の含有割合は、スラリー中の活物質等の分散性を高めることができ、平滑な電極を得ることができる観点、及び得られる二次電池が優れた負荷特性及びサイクル特性を示す観点から、好ましくは0.1~10重量%である。
導電付与材としては、アセチレンブラック、ケッチェンブラック、カーボンブラック、気相成長カーボン繊維、カーボンナノチューブ等の導電性カーボンを使用することができる。または、黒鉛などの炭素粉末、各種金属のファイバーや箔などを使用することもできる。導電性付与材を用いることにより電極活物質同士の電気的接触を向上させることができ、特にリチウムイオン二次電池に用いる場合に放電負荷特性を改善したりすることができる。
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得ることができる。
分散剤としてはアニオン性化合物、カチオン性化合物、非イオン性化合物、高分子化合物が例示される。分散剤は用いる電極活物質や導電剤に応じて選択される。負極用スラリー組成物中の分散剤の含有割合は、安定性に優れた負極用スラリー組成物を得られるため平滑な電極を得られる観点及び高い容量の電池を得られる観点から、好ましくは0.01~10重量%である。
レベリング剤としては、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が挙げられる。前記界面活性剤を混合することにより、塗工時に発生するはじきを防止したり、負極の平滑性を向上させたりすることができる。負極用スラリー組成物中のレベリング剤の含有割合は、電極作製時の生産性、平滑性及び電池特性の観点から好ましくは0.01~10重量%である。
酸化防止剤としては、フェノール化合物、ハイドロキノン化合物、有機リン化合物、硫黄化合物、フェニレンジアミン化合物、ポリマー型フェノール化合物等が挙げられる。ポリマー型フェノール化合物は、分子内にフェノール構造を有する重合体であり、重量平均分子量が200~1000、好ましくは600~700のポリマー型フェノール化合物が好ましく用いられる。負極用スラリー組成物中の酸化防止剤の含有割合は、負極用スラリー組成物の安定性、電池容量及びサイクル特性の観点から好ましくは0.01~10重量%、更に好ましくは0.05~5重量%である。
本発明のリチウムイオン二次電池負極は、負極用スラリー組成物を塗布、乾燥してなる負極活物質層および集電体を有する電極である。負極の製造方法は、特に限定されないが、集電体の少なくとも片面、好ましくは両面に負極用スラリー組成物を塗布、加熱乾燥して負極活物質層を形成する方法である。
本発明のリチウムイオン二次電池に用いる正極用バインダー組成物は、エチレン性不飽和カルボン酸単量体単位を含む粒子状重合体Bを含んでなり、粒子状重合体B及び分散媒、又は粒子状重合体B、フッ素系重合体及び媒体を含んでなることが好ましい。エチレン性不飽和カルボン酸単量体単位を構成するエチレン性不飽和カルボン酸単量体としては、上述の負極用バインダー組成物に用いることができるエチレン性不飽和カルボン酸単量体を挙げることができるが、これらのなかでも、アクリル酸、メタクリル酸、イタコン酸が好ましく、アクリル酸、メタクリル酸がより好ましい。前記粒子状重合体Bにおけるエチレン性不飽和カルボン酸単量体単位の含有割合は、前記粒子状重合体Bに含まれる全単量体単位100重量%に対して、好ましくは20~50重量%、より好ましくは25~45重量%、特に好ましくは30~40重量%である。粒子状重合体Bに含まれるエチレン性不飽和カルボン酸単量体単位の含有割合が多すぎるとリチウムイオン二次電池正極に用いたときのリチウムイオン二次電池の耐久性が低下する虞がある。また、エチレン性不飽和カルボン酸単量体単位の含有割合が少なすぎるとリチウムイオン二次電池正極に用いたときのリチウムイオン二次電池の寿命が低下する虞がある。
粒子状重合体Bにおける、前記これらと共重合他可能な他の単量体単位の含有割合は、合計の割合で、好ましくは0~40重量%、より好ましくは0.5~35重量%であり、特に好ましくは1~30重量%である。
正極用バインダー組成物の膨潤度を上記範囲にするためには、粒子状重合体Bを構成する重合性単量体の種類や量を調整すればよい。具体的には、エチレン性不飽和カルボン酸単量体単位の含有割合を減らしたり、(メタ)アクリル酸エステル単量体単位のエステル基の炭素数を増やしたりすることにより、調整することができる。
正極用バインダー組成物の繰り返しの引張強度を上記範囲にするためには、粒子状重合体Bを構成する重合性単量体の種類や量を調整すればよい。具体的には、粒子状重合体Bを構成するエチレン性不飽和カルボン酸単量体単位の含有割合を減らしたり、(メタ)アクリル酸エステル単量体単位のエステル基の炭素数を増やしたりすることにより、調整することができる。
リチウムイオン二次電池の正極用の電極活物質としては、遷移金属酸化物、遷移金属硫化物、リチウムと遷移金属とのリチウム含有複合金属酸化物、有機化合物などが挙げられる。上記の遷移金属としては、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Mo等が使用される。
正極用スラリー組成物は、正極用バインダー組成物、正極活物質および必要に応じて用いられるその他の任意の物質を混合することにより得ることができる。かかる任意の物質としては、負極用スラリー組成物が含みうるものとして上述したものと同様の物質を挙げることができ、それら任意の物質の含有割合も、負極用スラリー組成物におけるそれらの含有割合と同様とすることができる。
リチウム二次電池正極は、正極活物質及び正極用バインダー組成物を含む正極活物質層が、集電体上に積層されてなる。リチウムイオン二次電池正極は、上述のリチウムイオン二次電池負極の製造方法と同様の製造方法により得ることができる。また、集電体としては、上述のリチウムイオン二次電池負極に用いられる集電体を用いることができる。
本発明に用いるセパレータとしては、電子伝導性がなくイオン伝導性があり、有機溶媒に対する耐性が高い、孔径の微細な多孔質膜を用いることができる。具体的には、下記(i)~(iv)のいずれかを用いることができる。
(ii)樹脂の繊維を織った織布、または当該繊維の不織布
(iii)非導電性微粒子の集合体の層
(iv)上記(i)~(iii)のうちの1種以上の層を2層以上組み合わせた積層体
これらのなかでも、(i)または(ii)に(iii)層を形成したセパレータ、リチウムイオン二次電池負極および/または正極に(iii)層を形成したセパレータを用いることが好ましい。
(i)の微多孔膜とは、樹脂のフィルムを形成した後微細な孔を多数形成したものである。かかる微多孔膜の形成方法としては、下記の方法を挙げることができる。
(i-2)炭化水素溶媒と、必要に応じて添加しうる任意の低分子材料と、樹脂とを混合し、当該混合物のフィルムを形成し、その後、非晶相に溶媒や低分子材料が集まり島相を形成し始めた時点で、この溶媒や低分子材料を他の揮発し易い溶媒を用いて除去し、微多孔膜を形成する湿式方法
(i-1)の乾式方法及び(i-2)の湿式方法のうちでは、抵抗を下げうる大きな空隙を得やすい点で、乾式方法が好ましい。
(iii)の、非導電性微粒子の集合体の層は、非導電性微粒子と、必要に応じて添加しうる結着樹脂とを含む混合物を硬化させて得ることができる。かかる混合物は典型的にはスラリーであり、かかるスラリーを、上記(i)の膜、又は(ii)の織布若しくは不織布等の他の部材上に塗布し硬化させることにより、(iii)の層を得ることができる。
層(iii)を構成する非導電性微粒子は、リチウムイオン二次電池の使用環境下で安定に存在し、電気化学的にも安定であることが望まれる。例えば各種の非導電性の無機微粒子、有機微粒子を使用することができ、有機微粒子を用いることが好ましい。
本発明において、層(iii)は、上に述べた非導電性微粒子を必須成分として含むが、さらに必要に応じて結着剤を含むことが好ましい。結着剤を含むことにより、層(iii)の強度が上がり、割れ等の問題を防ぐことができる。
ポリイソブチレン、イソブチレン・イソプレンゴム、イソブチレン・スチレン共重合体などのイソブチレン系軟質重合体;
ポリブタジエン、ポリイソプレン、ブタジエン・スチレンランダム共重合体、イソプレン・スチレンランダム共重合体、アクリロニトリル・ブタジエン共重合体、アクリロニトリル・ブタジエン・スチレン共重合体、ブタジエン・スチレン・ブロック共重合体、スチレン・ブタジエン・スチレン・ブロック共重合体、イソプレン・スチレン・ブロック共重合体、スチレン・イソプレン・スチレン・ブロック共重合体などジエン系軟質重合体;
ジメチルポリシロキサン、ジフェニルポリシロキサン、ジヒドロキシポリシロキサンなどのケイ素含有軟質重合体;
液状ポリエチレン、ポリプロピレン、ポリ-1-ブテン、エチレン・α-オレフィン共重合体、プロピレン・α-オレフィン共重合体、エチレン・プロピレン・ジエン共重合体(EPDM)、エチレン・プロピレン・スチレン共重合体などのオレフィン系軟質重合体;
ポリビニルアルコール、ポリ酢酸ビニル、ポリステアリン酸ビニル、酢酸ビニル・スチレン共重合体などビニル系軟質重合体;
ポリエチレンオキシド、ポリプロピレンオキシド、エピクロルヒドリンゴムなどのエポキシ系軟質重合体;
フッ化ビニリデン系ゴム、四フッ化エチレン-プロピレンゴムなどのフッ素含有軟質重合体;
天然ゴム、ポリペプチド、蛋白質、ポリエステル系熱可塑性エラストマー、塩化ビニル系熱可塑性エラストマー、ポリアミド系熱可塑性エラストマーなどのその他の軟質重合体 などが挙げられ、中でもアクリル系軟質重合体が好ましく、さらに好ましくはアクリロニトリル重合単位を含むアクリル系軟質重合体が好ましい。結着剤が、前記共重合体であることにより、電解液への溶出が低減され、層(iii)の変形を生じにくくすることができる。さらに、高温においても電解液の膨潤性を保ちながら溶出しにくく、優れた高温特性を示しうる。したがって、このような結着剤と前記非導電性微粒子とを組み合わせることで、層(iii)の安全性をさらに向上することができる。
層(iii)は、上記非導電性微粒子及び結着剤に加えて、必要に応じて任意の成分を含むことができる。かかる任意の成分としては、分散剤や電解液分解抑制等の機能を有する電解液添加剤等を挙げることができる。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。
層(iii)は、分散媒と、その中に分散された層(iii)を構成する上記各種の成分とを含有する層(iii)形成用スラリーを、他の部材上に塗布し、乾燥して形成することができる。例えば、セパレータ(i)または(ii)上に有機微粒子を含む層(iii)形成用スラリーを塗布、乾燥することにより、有機微粒子多孔膜が積層されたセパレータ(上記(iv))を得ることができる。
上述の形成方法により形成された層(iii)においては、非導電性微粒子が結着剤を介して結着された性状を呈し、非導電性微粒子間に空隙が形成された構造とすることができる。この空隙中には電解液が浸透可能であるため、良好な電池反応を得ることができる。
本発明に用いられる電解液は、特に限定されないが、例えば、非水系の溶媒に支持電解質としてリチウム塩を溶解したものが使用できる。リチウム塩としては、例えば、LiPF6、LiAsF6、LiBF4、LiSbF6、LiAlCl4、LiClO4、CF3SO3Li、C4F9SO3Li、CF3COOLi、(CF3CO)2NLi、(CF3SO2)2NLi、(C2F5SO2)NLiなどのリチウム塩が挙げられる。特に溶媒に溶けやすく高い解離度を示すLiPF6、LiClO4、CF3SO3Liは好適に用いられる。これらは、単独または2種以上を混合して用いることができる。支持電解質の量は、電解液に対して、通常1重量%以上、好ましくは5重量%以上、また通常は30重量%以下、好ましくは20重量%以下である。支持電解質の量が少なすぎても多すぎてもイオン導電度は低下し、電池の充電特性、放電特性が低下する。
本発明のリチウムイオン二次電池の構成は、前記リチウムイオン二次電池負極、リチウムイオン二次電池正極、電解液、及びセパレータを備える限りにおいて特に限定されず、通常のリチウムイオン二次電池の構成を適宜採用することができる。例えば、リチウムイオン二次電池正極とリチウムイオン二次電池負極とをセパレータを介して重ね合わせ、これを電池形状に応じて巻く、折るなどして電池容器に入れ、電池容器に電解液を注入して封口し、電池を構成することができる。
実施例および比較例で製造するリチウムイオン二次電池負極およびリチウムイオン二次電池正極をそれぞれ長さ100mm、幅10mmの長方形に切り出して試験片とし、電解液(1.0mol/LのLiPF6/EC+DEC(EC/DEC=1/2体積比))に60℃、72時間浸漬した後に乾燥した。乾燥したリチウムイオン二次電池負極の負極活物質層面およびリチウムイオン二次電極正極の正極活物質層面をそれぞれ下にして電極組成物層表面にセロハンテープ(JIS Z1522に規定されるもの)を貼り付け、集電体の一端を垂直方向に引張り速度50mm/分で引っ張って剥がしたときの応力を測定した(なお、セロハンテープは試験台に固定されている。)。測定を3回行い、その平均値を求めてこれをピール強度とした。ピール強度が大きいほど負極活物質層および正極活物質層の集電体への結着力が大きい、すなわち密着強度が大きいことを示す。
実施例および比較例で製造するリチウムイオン二次電池負極を用いて、ラミネート型セルのリチウムイオン二次電池を作製し、25℃で24時間静置させた後に、25℃で充電電圧4.2V、放電電圧3.0V、0.1Cの充放電レートにて充放電の操作を行い、初期容量C0を測定した。さらに、4.2Vに充電し、60℃、7日間保存した後、25℃で、充電電圧4.2V、放電電圧3.0V、0.1Cの充放電レートにて充放電の操作を行い、高温保存後の容量C1を測定した。高温保存特性は、ΔC=C1/C0×100(%)で示す容量変化率にて評価し、この値が高いほど高温保存特性に優れることを示す。即ち、この値が高いほど活物質間を強固に繋ぎとめ、容量低下が抑制されたことを示す。
実施例および比較例で製造するリチウムイオン二次電池を、25℃で24時間静置させた後に、25℃で、充電電圧4.2V、放電電圧3.0V、0.1Cの充放電レートにて充放電の操作を行い、初期容量C0を測定した。さらに、60℃環境下で、充放電(充電電圧4.2V、放電電圧3.0V、充放電レート0.1C)を繰り返し、100サイクル後の容量C2を測定した。高温サイクル特性は、ΔC=C2/C0×100(%)で示す容量変化率にて評価し、この値が高いほど高温サイクル特性に優れることを示す。即ち、この値が高いほど活物質間を強固に繋ぎとめ、容量低下が抑制されたことを示す。
実施例および比較例で製造するリチウムイオン二次電池を、25℃で24時間静置させた後に、25℃で4.2V、0.1Cの充電レートにて充電の操作をいった。その後、-25℃環境下で、1C放電レートにて放電の操作を行い、放電開始10秒後の電圧Vを測定した。低温出力特性は、ΔV=4.2V-Vで示す電圧変化にて評価し、この値が小さいほど低温出力特性に優れることを示す。即ち、この値が小さいほど活物質間を強固に繋ぎとめ、放電時の分極が抑制されたことを示す。
実施例および比較例で作製したリチウムイオン二次電池を、25℃で24時間静置させた後に、60℃、充電電圧4.2V、放電電圧3.0V、1Cの充放電レートにて200サイクル充放電の操作を行った後のセルの厚み(d2)を測定した。そして、リチウムイオン二次電池の作製直後のセルの厚み(d0)に対する変化率(Δd2=(d2-d0)/d0×100(%))を求めた。この値が小さいほど充放電の繰り返しによるセルの膨らみが抑制されたことを示す。
負極用バインダー組成物および正極用バインダー組成物からなる1×1cm2のフィルムを作製し、重量M0を測定した。その後、フィルムを1.0mol/LのLiPF6/EC+DEC(EC/DEC=1/2:体積比)に60℃、72時間浸漬し、重量M1を測定した。膨潤度はM1/M0より算出した。
実施例および比較例で製造する負極用バインダー組成物および正極用バインダー組成物の繰り返しの引張強度(低伸張モジュラス15%)は、上述の膨潤度の測定の要領と同様に膨潤させたバインダーフィルムをJIS-K7312に準じて、50mm/minの速度で伸張し、15%伸びに相当する強度を1000回測定した。
(水溶性高分子の製造)
攪拌機付き5MPa耐圧容器に、メタクリル酸(MAA)35部、アクリル酸エチル65部、乳化剤としてドデシルベンゼンスルホン酸ナトリウム1.0部、イオン交換水150部及び重合開始剤として過硫酸カリウム0.5部を入れ、十分に攪拌した後、60℃に加温して重合を開始した。重合転化率が96%になった時点で冷却し反応を停止して、水溶性高分子を含む水分散液を得た。
攪拌機付き5MPa耐圧容器に、スチレン(ST)62.5部、1,3-ブタジエン(BD)34部、イタコン酸(IA)3.5部、乳化剤としてドデシルベンゼンスルホン酸ナトリウム4部、イオン交換水150部及び重合開始剤として過硫酸カリウム0.5部を入れ、十分に攪拌した後、50℃に加温して重合を開始した。重合転化率が96%になった時点で冷却し反応を停止した。そして、5%水酸化ナトリウム水溶液を添加して、pH8に調整後、加熱減圧蒸留によって未反応単量体の除去を行った後、30℃以下まで冷却し、所望の粒子状重合体Aを含む水分散液を得た。
ディスパー付きのプラネタリーミキサーに、負極活物質として比表面積4m2/gの人造黒鉛(平均粒子径:24.5μm)を70部およびSiCを30部、上記水溶性高分子の5%水溶液1部をそれぞれ加え、イオン交換水で固形分濃度55%に調整した後、25℃で60分混合した。次に、イオン交換水で固形分濃度52%に調整した後、さらに25℃で15分混合し混合液を得た。
得られた負極用スラリー組成物を、コンマコーターで、厚さ20μmの銅箔の上に、乾燥後の膜厚が150μm程度になるように塗布し、2分間乾燥(0.5m/分の速度、60℃)し、2分間加熱処理(120℃)して負極原反を得た。この負極原反をロールプレスで圧延して負極活物質層の厚みが80μmの二次電池負極を得た。
攪拌機付き5MPa耐圧容器に、アクリル酸2-エチルヘキシル(2-EHA)65部、メタクリル酸(MAA)35部、乳化剤としてドデシルベンゼンスルホン酸ナトリウム4部、イオン交換水150部及び重合開始剤として過硫酸カリウム0.5部を入れ、十分に攪拌した後、50℃に加温して重合を開始した。重合転化率が96%になった時点で冷却し反応を停止した。そして、5%水酸化ナトリウム水溶液を添加して、pH8に調整後、加熱減圧蒸留によって未反応単量体の除去を行った後、30℃以下まで冷却し、粒子状重合体Bを含む水分散液(正極用バインダー組成物)を得た。
正極活物質として、LiNiO2を100部、分散剤としてカルボキシメチルセルロースの1%水溶液(CMC、第一工業製薬株式会社製「BSH-12」)を固形分相当で1部、正極用バインダー組成物の40%水分散液を固形分相当で5部、及びイオン交換水で全固形分濃度が40%となるようにプラネタリーミキサーにより混合し、正極用スラリー組成物を調製した。
得られた正極スラリー組成物を、コンマコーターで、厚さ20μmのアルミ箔の上に、乾燥後の膜厚が200μm程度になるように塗布し、2分間乾燥(0.5m/分の速度、60℃)し、2分間加熱処理(120℃)して電極原反を得た。この正極原反をロールプレスで圧延して、正極活物質層の厚みが80μmの二次電池正極を得た。
有機微粒子(ポリスチレンビーズ,体積平均粒径1.0μm)と、上述の正極用バインダー組成物と、カルボキシメチルセルロース(CMC、第一工業製薬株式会社製「BSH-12」)とを、100:3:1(固形分相当比)となるように混合し、更にイオン交換水を固形分濃度が40%になるように混合し、次いでビーズミルを用いて分散させて、有機微粒子多孔膜用スラリーを調製した。
正極の正極活物質層側の面上に、セパレータを配置した。さらに、セパレータ上に負極を、負極活物質層側の面がセパレータに対向するように、セパレータは有機微粒子多孔膜が負極活物質層に対向するように配置した。さらに、負極の集電体面に接するようにラミネートフィルムを配置し、ラミネートセル型のリチウムイオン二次電池を製造した。電解液としては、1.0mol/LのLiPF6/EC+DEC(EC/DEC=1/2(体積比))を用いた。
粒子状重合体Aを製造する際の単量体の組成をスチレン57部、1,3-ブタジエン39.5部、イタコン酸3.5部とした以外は、実施例1と同様にリチウムイオン二次電池の製造を行った。なお、実施例2の粒子状重合体Aを含む水分散液1部(固形分基準)と水溶性高分子5%水溶液1部からなる負極用バインダー組成物の膨潤度は1.7倍、引張強度(低伸張モジュラス15%)は9.5Kg/cm2、テトラヒドロフラン不溶分は90.8%であった。
粒子状重合体Aを製造する際の単量体の組成をスチレン68部、1,3-ブタジエン28.5部、イタコン酸3.5部とした以外は、実施例1と同様にリチウムイオン二次電池の製造を行った。なお、実施例3の粒子状重合体Aを含む水分散液1部(固形分基準)と水溶性高分子5%水溶液1部からなる負極用バインダー組成物の膨潤度は1.67倍、引張強度(低伸張モジュラス15%)は8.8Kg/cm2、テトラヒドロフラン不溶分は83.2%であった。
粒子状重合体Bを製造する際の単量体の組成をアクリル酸2-エチルヘキシル72部、メタクリル酸28部とした以外は、実施例1と同様にリチウムイオン二次電池の製造を行った。なお、実施例4の正極用バインダー組成物の膨潤度は3.1倍、引張強度(低伸張モジュラス15%)は0.94Kg/cm2であった。
粒子状重合体Bを製造する際の単量体の組成をアクリル酸2-エチルヘキシル78部、メタクリル酸22部とした以外は、実施例1と同様にリチウムイオン二次電池の製造を行った。なお、実施例5の正極用バインダー組成物の膨潤度は4.1倍、引張強度(低伸張モジュラス15%)は0.25Kg/cm2であった。
負極用バインダー組成物に含まれる水溶性高分子を用いなかった以外は、実施例1と同様にリチウムイオン二次電池の製造を行った。なお、実施例6の負極用バインダー組成物の膨潤度は1.4、引張強度(低伸張モジュラス15%)は7.8Kg/cm2、テトラヒドロフラン不溶分は90.2%であった。
負極用スラリー組成物に含まれる負極活物質の組成を人造黒鉛90部およびSiC10部とした以外は実施例1と同様にリチウムイオン二次電池の製造を行った。
負極用スラリー組成物に含まれる負極活物質の組成を人造黒鉛95部およびSiC5部とした以外は実施例1と同様にリチウムイオン二次電池の製造を行った。
負極用スラリー組成物に含まれる負極活物質の組成を人造黒鉛70部およびSiOC30部とした以外は、実施例1と同様にリチウムイオン二次電池の製造を行った。
負極用スラリー組成物に含まれる負極活物質の組成を人造黒鉛70部およびSiOx30部とした以外は、実施例1と同様にリチウムイオン二次電池の製造を行った。
負極用スラリー組成物に含まれる負極活物質の組成を人造黒鉛90部およびSi負極物質A10部とした以外は、実施例1と同様にリチウムイオン二次電池の製造を行った。Si負極物質Aは、人造黒鉛にSi微粒子(体積平均粒子径20nm)を水を用いて混合し、スプレードライで噴霧乾燥することで得られたものである。
負極用スラリー組成物に含まれる負極活物質の組成を人造黒鉛85部およびSi負極物質B15部とした以外は、実施例1と同様にリチウムイオン二次電池の製造を行った。Si負極物質Bは、前記Si負極物質Aを2000度に焼成して得られたものである。
負極用スラリー組成物に含まれる負極活物質の組成を人造黒鉛80部およびSi負極物質C20部とした以外は、実施例1と同様にリチウムイオン二次電池の製造を行った。Si負極物質Cは、前記Si負極物質Aを2500度に焼成して得られたものである。
粒子状重合体Aを製造する際の単量体の組成をスチレン40部、1,3-ブタジエン55.5部、メタクリル酸4.5部とし、粒子状重合体Bを製造する際の単量体の組成をアクリル酸ブチル95部(BA)、メタクリル酸5部とし、水溶性高分子を用いず、単層のポリプロピレン製セパレータ用フィルム上に有機微粒子多孔膜を形成しなかった以外は、実施例1と同様にリチウムイオン二次電池の製造を行った。なお、比較例1の負極用バインダー組成物の膨潤度は2.4倍、引張強度(低伸張モジュラス15%)は0.45Kg/cm2、テトラヒドロフラン不溶分は67.7%であった。また、比較例1の正極用バインダー組成物の膨潤度は7.8倍、引張強度(低伸張モジュラス15%)は0.08Kg/cm2であった。
粒子状重合体Aを製造する際の単量体の組成をスチレン70.5部、1,3-ブタジエン26部、メタクリル酸3.5部とし、人造黒鉛のみからなる負極活物質を用いた以外は、比較例1と同様にリチウムイオン二次電池の製造を行った。なお、比較例2の負極用バインダー組成物の膨潤度は1.4倍、引張強度(低伸張モジュラス15%)は7.8Kg/cm2、テトラヒドロフラン不溶分は68%であった。
人造黒鉛のみからなる負極活物質を用いた以外は、実施例1と同様にリチウムイオン二次電池の製造を行った。
粒子状重合体Bを製造する際の単量体の組成をアクリル酸ブチル70部、メタクリル酸10部、アクリロニトリル20部とし、人造黒鉛のみからなる負極活物質を用い、単層のポリプロピレン製セパレータ用フィルム上に有機微粒子多孔膜を形成しなかった以外は、比較例1と同様にリチウムイオン二次電池の製造を行った。なお、比較例1の正極用バインダー組成物の膨潤度は7.5倍、引張強度(低伸張モジュラス15%)は0.001Kg/cm2であった。
Claims (9)
- 正極、負極、電解液およびセパレータを備えるリチウムイオン二次電池であって、
前記負極は、脂肪族共役ジエン単量体単位を含む粒子状重合体Aを含んでなる負極用バインダー組成物と、負極活物質とを含む負極用スラリー組成物から形成される負極活物質層を含み、
溶解度パラメータが8~13(cal/cm3)1/2である溶媒に電解質を溶解した前記電解液に対する前記負極用バインダー組成物の膨潤度が1~2倍であって、
前記電解液により膨潤した前記負極用バインダー組成物の繰り返しの引張り強度は低伸張モジュラス15%で0.5~20Kg/cm2であり、
前記正極は、エチレン性不飽和カルボン酸単量体単位を含む粒子状重合体Bを含んでなる正極用バインダー組成物と、正極活物質とを含む正極用スラリー組成物から形成される正極活物質層を含み、
溶解度パラメータが8~13(cal/cm3)1/2である溶媒に電解質を溶解した前記電解液に対する前記正極用バインダー組成物の膨潤度が1~5倍であって、
前記電解液により膨潤した前記正極用バインダー組成物の繰り返しの引張り強度は低伸張モジュラス15%で0.2~5Kg/cm2であることを特徴とするリチウムイオン二次電池。 - 前記負極活物質は、リチウムを吸蔵し放出するSi化合物を含むことを特徴とする請求項1記載のリチウムイオン二次電池。
- 前記粒子状重合体Aは、芳香族ビニル単量体単位を含み、
前記粒子状重合体Aにおける前記芳香族ビニル単量体単位の含有割合は50~75重量%であることを特徴とする請求項1または2記載のリチウムイオン二次電池。 - 前記粒子状重合体Aは、エチレン性不飽和カルボン酸単量体単位を含み、
前記粒子状重合体Aにおける前記エチレン性不飽和カルボン酸単量体単位の含有割合は0.5~10重量%であることを特徴とする請求項1~3の何れか一項に記載のリチウムイオン二次電池。 - 前記粒子状重合体Aのテトラヒドロフラン不溶分が、75~95%であることを特徴とする請求項1~4の何れか一項に記載のリチウムイオン二次電池。
- 前記負極用バインダー組成物は、さらにエチレン性不飽和カルボン酸単量体単位を有する水溶性高分子を含み、
前記水溶性高分子における前記エチレン性不飽和カルボン酸単量体単位の含有割合は20~60重量%であることを特徴とする請求項1~5の何れか一項に記載のリチウムイオン二次電池。 - 前記粒子状重合体Bは、エチレン性不飽和カルボン酸単量体単位を含み、
前記粒子状重合体Bにおける前記エチレン性不飽和カルボン酸単量体単位の含有割合は20~50重量%であることを特徴とする請求項1~6の何れか一項に記載のリチウムイオン二次電池。 - 前記粒子状重合体Bは、(メタ)アクリル酸エステル単量体単位を含み、
前記粒子状重合体Bにおける前記(メタ)アクリル酸エステル単量体単位の含有割合は50~80重量%であることを特徴とする請求項1~7の何れか一項に記載のリチウムイオン二次電池。 - 積層型であることを特徴とする請求項1~8の何れか一項に記載のリチウムイオン二次電池。
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WO2020208799A1 (ja) * | 2019-04-12 | 2020-10-15 | 花王株式会社 | 蓄電デバイス正極用分散剤 |
US11894559B2 (en) | 2019-04-12 | 2024-02-06 | Kao Corporation | Dispersant composition for carbon nanotube |
US11891502B2 (en) | 2019-04-12 | 2024-02-06 | Kao Corporation | Dispersant for power storage device positive electrode |
CN111952658A (zh) * | 2019-05-15 | 2020-11-17 | Sk新技术株式会社 | 锂二次电池 |
US11876217B2 (en) | 2019-05-15 | 2024-01-16 | Sk On Co., Ltd. | Lithium secondary battery |
CN111952658B (zh) * | 2019-05-15 | 2024-04-19 | Sk新能源株式会社 | 锂二次电池 |
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US20150132643A1 (en) | 2015-05-14 |
EP2843739A4 (en) | 2015-12-23 |
KR20150010706A (ko) | 2015-01-28 |
EP2843739B1 (en) | 2020-05-06 |
JPWO2013161786A1 (ja) | 2015-12-24 |
EP2843739A1 (en) | 2015-03-04 |
CN104247109A (zh) | 2014-12-24 |
JP6506553B2 (ja) | 2019-04-24 |
KR102063540B1 (ko) | 2020-03-02 |
CN104247109B (zh) | 2016-08-24 |
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