WO2011037142A1 - リチウムイオン二次電池負極及びリチウムイオン二次電池 - Google Patents
リチウムイオン二次電池負極及びリチウムイオン二次電池 Download PDFInfo
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- WO2011037142A1 WO2011037142A1 PCT/JP2010/066421 JP2010066421W WO2011037142A1 WO 2011037142 A1 WO2011037142 A1 WO 2011037142A1 JP 2010066421 W JP2010066421 W JP 2010066421W WO 2011037142 A1 WO2011037142 A1 WO 2011037142A1
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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
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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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
- H01M4/134—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
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/364—Composites as mixtures
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
- H01M4/622—Binders being polymers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- 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
- H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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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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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Definitions
- the present invention relates to a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery including the same.
- Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries (hereinafter sometimes simply referred to as “batteries”) are frequently used as secondary batteries used for the power sources of these portable terminals.
- Batterys are required to have more comfortable portability, and are rapidly becoming smaller, thinner, lighter, and higher in performance.
- portable terminals are used in various places.
- the battery used as a power source with the expansion of the range of use is required to be smaller, thinner, lighter, and higher in performance, as is the case with mobile terminals. Is required. For this reason, various members and materials of lithium secondary batteries have been actively improved in performance, and in particular, increasing the capacity of batteries using a negative electrode active material has become more important.
- carbon-based active materials such as graphite are mainly used as negative electrode active materials, and those having a discharge capacity of about 350 to 360 mAh / g and values close to the theoretical capacity of 372 mAh / g of graphite have been put into practical use.
- alloy active materials such as silicon, tin, zinc, aluminum, gallium, copper, silver, germanium, and indium. It has been found that theoretical capacity can be obtained.
- silicon has an extremely large theoretical capacity of 4200 mAh / g, but due to expansion and contraction associated with charge and discharge, the adhesion strength of the electrode is lowered, resulting in deterioration of the negative electrode material and shortening the cycle life of the battery. was there. Therefore, for the purpose of increasing discharge capacity and improving cycle characteristics, silicon powder is mixed with carbon powder, graphite powder and silicon powder, or silicon powder on the surface of carbon powder or graphite powder. There has been proposed an alloy-based active material having a surface coated with a pitch coated on the surface thereof.
- Patent Document 1 it is proposed to use a negative electrode obtained by using a slurry obtained by dispersing a silicon compound and a carbon material in a binder such as polyester.
- the binder absorbs the volume change of the silicon compound negative electrode during lithium doping / dedoping, the volume change of the negative electrode active material layer as a whole is suppressed, and cycle deterioration is suppressed.
- Patent Document 2 proposes a negative electrode material for a lithium secondary battery that includes silicon particles and a plurality of types of carbonaceous materials and has voids.
- carbonaceous materials of a plurality of types carbonaceous material A having relatively high electron conductivity selected from graphite, carbon black, carbon nanotube, carbon fiber, etc., and pitch-based materials, tar-based materials, resin-based materials, etc.
- a carbonaceous material B which is selected amorphous carbon.
- Patent Document 2 a composite obtained by mixing carbonaceous material B or a precursor of carbonaceous material B, silicon particles, and carbonaceous material A using a biaxial heating kneader or the like and then performing a heat treatment.
- Patent Document 1 the mixing ratio of the carbon material to the silicon compound is high, and when a binder such as polyester is used, the carbon material is not sufficiently dispersed and is unevenly distributed in the electrode. Therefore, the binder cannot absorb the expansion / contraction of the silicon compound localized in the electrode, the silicon compound is pulverized, and the resistance in the electrode is increased, so that the cycle characteristics are deteriorated. Furthermore, many silicon-based alloy active materials have an angular particle shape, and the adhesive force between the particles tends to decrease in the rolling process of the electrode plate. This tendency is particularly noticeable in an electrode having an active material layer density of 1.6 g / cm 3 or more.
- the composite particles composed of silicon particles and a carbonaceous material have voids, thereby exhibiting cycle characteristics. Although the cycle characteristics are improved, the battery capacity per volume tends to be low.
- a composite material is produced by mixing and heat-treating silicon particles and a carbonaceous material, and then sifting to remove impurities with hydrochloric acid, followed by filtration and vacuum drying to obtain a negative electrode material. , Production processes increase, and manufacturing costs increase. Furthermore, when preparing a slurry for an electrode, a submicron carbon material may be detached from the composite particles, and this carbon material forms a structure in the slurry through the binder, which increases the viscosity of the slurry. .
- an object of the present invention is to provide a lithium ion secondary battery negative electrode capable of providing a lithium ion secondary battery that suppresses a decrease in the adhesion strength of the electrode and has little life deterioration without complexing an active material, and
- the object is to provide a slurry for a negative electrode of a lithium ion secondary battery to be used.
- the inventors of the present invention have prepared an alloy-based active material as an electrode active material in producing a lithium ion secondary battery negative electrode containing a negative electrode active material and an active material layer containing a binder on a current collector.
- an alloy-based active material as an electrode active material in producing a lithium ion secondary battery negative electrode containing a negative electrode active material and an active material layer containing a binder on a current collector.
- the stability of the slurry can be improved by improving the stability of the binder during slurry blending. It has been found that an increase in viscosity can be suppressed.
- the presence of the carbon-based active material in the system can reduce the adhesion point between the alloy-based active material particles, and the presence of a specific amount of the specific functional group in the binder enables the adhesion within the active material layer.
- the adhesion between the active material layer and the current collector that is, the decrease in the adhesion strength of the electrode is suppressed, the expansion and contraction of the alloy-based active material in the battery is mitigated, and the internal resistance of the negative electrode is further reduced. It has been found that the life characteristics of the obtained lithium ion secondary battery are improved.
- a lithium ion secondary battery negative electrode having a current collector and an active material layer containing a negative electrode active material and a binder provided on the current collector, wherein the negative electrode active material is an alloy-based active material.
- a weight ratio of the alloy-based active material and the carbon-based active material in the active material layer is 20:80 to 50:50, and the binder is ethylenic.
- the lithium ion secondary battery negative electrode according to (1) wherein the active material layer further contains 1 to 20 parts by weight of a conductive material with respect to 100 parts by weight of the active material.
- the binder has a glass transition temperature of 25 ° C. or lower.
- (5) contains a negative electrode active material, a binder, and a solvent
- the negative electrode active material contains an alloy-based active material and a carbon-based active material
- the weight ratio of the alloy-based active material to the carbon-based active material is
- the slurry for a negative electrode of a lithium ion secondary battery is 20:80 to 50:50
- the binder contains 0.1 to 15% by weight of polymerized units of an ethylenically unsaturated carboxylic acid monomer.
- a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolytic solution, wherein the negative electrode is the lithium ion secondary battery negative electrode according to any one of (1) to (5) above.
- a slurry obtained by blending a binder containing 1 to 15% by weight and a solvent the alloy-based active material and the carbon-based active material are uniformly distributed in the active material layer.
- the adhesion point of the active material layer and the current collector are reduced, that is, the binder contains a polymerized unit of an ethylenically unsaturated carboxylic acid monomer, and the adhesion strength between the active material layer and the current collector, that is, the electrode
- the adhesion strength of is improved. Furthermore, since the expansion and contraction of the alloy-based active material is relaxed by the carbon-based active material and the internal resistance of the negative electrode is reduced, a battery with little life deterioration can be obtained.
- the lithium ion secondary battery negative electrode slurry of the present invention contains a negative electrode active material, a binder and a solvent, and contains an alloy-based active material and a carbon-based active material as the negative electrode active material.
- the alloy-based active material used in the present invention includes an element capable of inserting lithium in the structure, and has a theoretical electric capacity of 500 mAh / g or more when lithium is inserted (the upper limit of the theoretical electric capacity is particularly Although not limited, the active material can be, for example, 5000 mAh / g or less.) Specifically, lithium metal, a single metal forming a lithium alloy and an alloy thereof, and oxides and sulfides thereof Nitride, silicide, carbide, phosphide and the like are used.
- Examples of single metals and alloys forming lithium alloys include compounds containing metals such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, and Zn. Is mentioned. Among these, silicon (Si), tin (Sn) or lead (Pb) simple metals, alloys containing these atoms, or compounds of these metals are used.
- the alloy-based active material used in the present invention may further contain one or more nonmetallic elements.
- SiC, SiO x C y (hereinafter referred to as “Si—O—C”) (0 ⁇ x ⁇ 3, 0 ⁇ y ⁇ 5), Si 3 N 4 , Si 2 N 2 O, Examples thereof include SiO x (0 ⁇ x ⁇ 2), SnO x (0 ⁇ x ⁇ 2), LiSiO, LiSnO, etc.
- SiO x C y capable of inserting and releasing lithium at a low potential is preferable.
- SiO x C y can be obtained by firing a polymer material containing silicon.
- the range of 0.8 ⁇ x ⁇ 3 and 2 ⁇ y ⁇ 4 is preferably used in view of the balance between capacity and cycle characteristics.
- oxides, sulfides, nitrides, silicides, carbides, and phosphides include oxides, sulfides, nitrides, silicides, carbides, and phosphides of lithium-insertable elements.
- Oxides are particularly preferred. Specifically, an oxide such as tin oxide, manganese oxide, titanium oxide, niobium oxide, vanadium oxide, or a lithium-containing metal composite oxide material containing a metal element selected from the group consisting of Si, Sn, Pb, and Ti atoms is used. It has been.
- the silicon oxide include materials such as silicon carbide (Si—O—C).
- a lithium titanium composite oxide represented by Li x Ti y M z O 4 (0.7 ⁇ x ⁇ 1.5, 1.5 ⁇ y ⁇ 2.3, 0 ⁇ z ⁇ 1.6, M includes Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb), among which Li 4/3 Ti 5/3 O 4 , Li1Ti 2 O 4 and Li 4/5 Ti 11/5 O 4 are used.
- materials containing silicon are preferable, and Si—O—C is more preferable.
- the volume average particle diameter of the alloy-based active material used in the present invention is preferably 0.1 to 50 ⁇ m, more preferably 0.5 to 20 ⁇ m, and most preferably 1 to 10 ⁇ m. If the particle diameter of the alloy-based active material is within this range, the electrode slurry described later can be easily produced.
- the carbon-based active material used in the present invention refers to an active material having carbon as a main skeleton into which lithium can be inserted, and specifically includes a carbonaceous material and a graphite material.
- the carbonaceous material is generally low in graphitization in which a carbon precursor is heat-treated (carbonized) at 2000 ° C. or less (the lower limit of the treatment temperature is not particularly limited, but can be, for example, 500 ° C. or more).
- a carbon material (low crystallinity) is shown, and a graphitic material is a heat treatment of graphitizable carbon at 2000 ° C. or higher (the upper limit of the processing temperature is not particularly limited, but can be, for example, 5000 ° C. or higher).
- similar to the graphite obtained by this is 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.
- Carbon fiber made from Examples of the non-graphitizable carbon include phenol resin fired bodies, polyacrylonitrile-based carbon fibers, pseudo-isotropic carbon, and furfuryl alcohol resin fired bodies (PFA).
- Examples of graphite materials include natural graphite and artificial graphite.
- Examples of artificial graphite include artificial graphite heat-treated at 2800 ° C. or higher, graphitized MCMB heat-treated MCMB at 2000 ° C. or higher, and graphitized mesophase pitch carbon fiber heat-treated at 2000 ° C. or higher. It is done.
- a graphite material is preferable.
- the density of the active material layer is 1.6 g / cm 3 or more (the upper limit of the density is not particularly limited, but 2.2 g / cm 3
- the negative electrode can be easily prepared as follows. If the negative electrode has an active material layer having a density in the above range, the effect of the present invention is remarkably exhibited.
- the volume average particle diameter of the carbon-based active material used in the present invention is preferably 0.1 to 100 ⁇ m, more preferably 0.5 to 50 ⁇ m, and most preferably 1 to 30 ⁇ m. If the particle diameter of the carbon-based active material is within this range, the electrode slurry described later can be easily produced.
- Examples of the method for mixing the alloy-based active material and the carbon-based active material include dry mixing and wet mixing. However, dry mixing is preferable because the binder can be prevented from being specifically adsorbed on one of the active materials.
- the dry mixing here refers to mixing the powder of the alloy-based active material and the powder of the carbon-based active material using a mixer.
- the solid content concentration at the time of mixing is 90% by weight. More than, preferably 95% by weight or more, more preferably 97% by weight or more. If the solid content concentration at the time of mixing is in the above range, it can be uniformly dispersed while maintaining the particle shape, and aggregation of the active material can be prevented.
- Mixers used for dry mixing include dry tumblers, super mixers, Henschel mixers, flash mixers, air blenders, flow jet mixers, drum mixers, ribocorn mixers, pug mixers, nauter mixers, ribbon mixers, and Spartan Luzers.
- a Redige mixer and a planetary mixer and examples thereof include a screw type kneader, a defoaming kneader, a paint shaker, and a kneader such as a pressure kneader and a two-roller.
- mixers such as a planetary mixer that can be dispersed by stirring, and planetary mixers and Henschel mixers are particularly preferred.
- the mixing ratio of the alloy-based active material and the carbon-based active material is 20: 80-50: 50, preferably 20: 80-40: 60, by weight.
- the binder used in the present invention contains 0.1 to 15% by weight of polymerized units of an ethylenically unsaturated carboxylic acid monomer.
- the binder used in the present invention contains 0.1 to 15% by weight of a polymerized unit of ethylenically unsaturated carboxylic acid monomer, the stability of the binder is maintained, the increase in the viscosity of the slurry over time is suppressed, and the electrode The adhesion strength of is improved.
- a polymerized unit of a monomer means a polymerized unit in a polymer formed by the polymerization reaction of the monomer.
- the “polymerized unit of acrylic acid” in polyacrylic acid is a unit — (CH 2 —CH (COOH)) —.
- the polymerization unit of the ethylenically unsaturated carboxylic acid monomer in the binder used in the present invention is less than 0.1% by weight, the above effect is not exhibited, and the polymerization unit of the ethylenically unsaturated carboxylic acid monomer is 15% by weight.
- Exceeds the water content in the binder used for hydration of the carboxylic acid group the viscosity of the binder itself increases significantly, causing the viscosity of the slurry to increase, and the adhesion strength between the active material layer and the current collector decreases. End up.
- the content of polymerized units of the ethylenically unsaturated carboxylic acid monomer in the binder used in the present invention is preferably 0.5 to 10% by weight, more preferably 1 to 5% by weight.
- the content of the polymerization unit of the ethylenically unsaturated carboxylic acid monomer in the binder is within the above range, the stability of the binder is maintained, and the increase in the viscosity of the slurry over time can be further suppressed. In addition, the adhesion strength of the electrode is further improved.
- the ethylenically unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, itaconic acid, and fumaric acid.
- the polymerization unit of the ethylenically unsaturated carboxylic acid monomer can be introduced by using the ethylenically unsaturated carboxylic acid monomer as a monomer constituting the binder described later.
- the binder is a solution or dispersion in which binder (polymer) particles having binding properties are dissolved or dispersed in water or an organic solvent (hereinafter, these may be collectively referred to as “binder dispersion”). ).
- binder dispersion is aqueous, it is usually a polymer particle dispersion, for example, a diene polymer particle dispersion, an acrylic polymer particle dispersion, a fluorine polymer particle dispersion, or a silicon polymer particle.
- a dispersion liquid etc. are mentioned.
- a diene polymer particle dispersion or an acrylic polymer particle dispersion is preferable because it has excellent binding properties to the active material and the strength and flexibility of the obtained negative electrode.
- a diene polymer particle dispersion or an acrylic polymer particle dispersion When a diene polymer particle dispersion or an acrylic polymer particle dispersion is used, it has high binding properties with the active material, and thus the negative electrode does not easily peel off. As a result, the binder does not easily peel off due to the expansion / contraction of the active material during charging / discharging, so that the active material is prevented from peeling off from the current collector and the resistance increase of the negative electrode is suppressed. As a result, high cycle characteristics can be exhibited.
- the diene polymer particle dispersion is an aqueous dispersion of a polymer containing monomer units obtained by polymerizing conjugated dienes such as butadiene and isoprene.
- the proportion of the monomer unit obtained by polymerizing the conjugated diene in the diene polymer is usually 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more.
- the diene polymer include a copolymer of a conjugated diene, an ethylenically unsaturated carboxylic acid monomer, and a copolymerizable monomer.
- copolymerizable monomer examples include ⁇ , ⁇ -unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl Styrene monomers such as naphthalene, chloromethylstyrene, hydroxymethylstyrene, ⁇ -methylstyrene, divinylbenzene; olefins such as ethylene and propylene; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl acetate, vinyl propionate, Vinyl esters such as vinyl butyrate and vinyl benzoate; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, and butyl vinyl ether; Methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ket
- ⁇ , ⁇ -unsaturated nitrile compounds and styrene monomers are preferable, and styrene monomers are particularly preferable.
- the proportion of polymerized units derived from these copolymerizable monomers is preferably 5 to 70% by weight, more preferably 10 to 60% by weight.
- the acrylic polymer particle dispersion is an aqueous dispersion of a polymer containing monomer units obtained by polymerizing an acrylic ester and / or a methacrylic ester.
- the proportion of monomer units obtained by polymerizing acrylic acid ester and / or methacrylic acid ester in the acrylic polymer is usually 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more.
- the acrylic polymer include a copolymer of an acrylic ester and / or a methacrylic ester, an ethylenically unsaturated carboxylic acid monomer, and a monomer copolymerizable therewith.
- Examples of the copolymerizable monomer include carboxylic acid ester monomers having two or more carbon-carbon double bonds such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate; styrene, chlorostyrene, vinyl Styrene monomers such as toluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, ⁇ -methylstyrene, divinylbenzene; acrylamide, N-methylol aquaamide, acrylamide Amide monomers such as -2-methylpropanesulfonic acid; ⁇ , ⁇ -unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; olefins such as ethylene and propylene; Diene monomers such as diene and isoprene;
- Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; and heterocyclic ring-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine, and vinyl imidazole.
- ⁇ , ⁇ -unsaturated nitrile compounds and styrene monomers are preferable, and ⁇ , ⁇ -unsaturated nitrile compounds are particularly preferable.
- the proportion of polymerized units derived from these copolymerizable monomers is preferably 3 to 50% by weight, and more preferably 5 to 40% by weight.
- the pH of the binder dispersion used in the present invention is preferably 7 to 12, and more preferably 8 to 10.
- the pH of the binder is within the above range, the electrostatic repulsion effect of the binder is expressed, the stability of the binder is maintained, and the increase in the viscosity of the slurry with time is suppressed.
- the binder dispersion may be an aqueous binder using water as a dispersion medium, or may be a non-aqueous binder using an organic solvent as a dispersion medium, but from the aspect of environmental load and the dispersibility of the conductive material, An aqueous binder is preferably used.
- the aqueous binder can be produced, for example, by emulsion polymerization of the above monomer in water.
- the non-aqueous binder can be produced by replacing the aqueous binder with an organic solvent.
- the number average particle size of the binder particles in the binder dispersion is preferably 50 nm to 500 nm, more preferably 70 nm to 400 nm. When the number average particle diameter of the binder particles is within this range, the strength and flexibility of the obtained negative electrode are improved.
- the glass transition temperature of the binder is preferably 25 ° C. or less, more preferably from ⁇ 100 ° C. to + 25 ° C., still more preferably from ⁇ 80 ° C. to + 10 ° C., and most preferably from ⁇ 80 ° C. to 0 ° C. is there.
- the glass transition temperature of the binder is within the above range, characteristics such as flexibility, binding and winding properties of the negative electrode, and adhesion between the active material layer and the current collector layer are highly balanced and suitable.
- the total content of the alloy-based active material, the carbon-based active material and the binder in the negative electrode slurry of the present invention is preferably 10 to 90 parts by weight, more preferably 30 to 80 parts by weight with respect to 100 parts by weight of the slurry. Part.
- the binder content (solid content equivalent amount) relative to the total amount of the alloy-based active material and the carbon-based active material is preferably 0.1 with respect to 100 parts by weight of the total amount of the alloy-based active material and the carbon-based active material. -5 parts by weight, more preferably 0.5-2 parts by weight.
- the viscosity of the resulting negative electrode slurry is optimized so that the coating can be performed smoothly.
- sufficient adhesion strength can be obtained without increasing the resistance of the obtained electrode.
- peeling of the binder from the active material in the electrode plate pressing step can be suppressed.
- the solvent is not particularly limited as long as it can uniformly disperse the above-described solid content (alloy-based active material, carbon-based active material, binder, conductive material, thickener, and optional components described later).
- the solvent used for the negative electrode slurry either water or an organic solvent can be used.
- organic solvents examples include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; acetone, ethyl methyl ketone, disopropyl ketone, cyclohexanone, methylcyclohexane, and ethylcyclohexane.
- Ketones chlorinated aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; esters such as ethyl acetate, butyl acetate, ⁇ -butyrolactone and ⁇ -caprolactone; acylonitriles such as acetonitrile and propionitrile; tetrahydrofuran; Ethers such as ethylene glycol diethyl ether: alcohols such as methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether; Examples include amides such as loridone and N, N-dimethylformamide.
- solvents may be used alone, or two or more of these may be mixed and used as a mixed solvent.
- a solvent having a low boiling point and high volatility is preferable because it can be removed at a low temperature in a short time.
- acetone, toluene, cyclohexanone, cyclopentane, tetrahydrofuran, cyclohexane, xylene, water, N-methylpyrrolidone, or a mixed solvent thereof is preferable.
- the negative electrode slurry of the present invention may further contain a thickener.
- thickeners include cellulosic polymers such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof; (modified) poly (meth) acrylic acid and ammonium salts and alkali metal salts thereof; ) Polyvinyl alcohols such as polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified Examples include polyacrylic acid, oxidized starch, phosphate starch, casein, various modified starches, and ammonium salts and alkali metal salts of carboxymethyl cellulose are preferred. It is needed. This is because the thickener is easy to cover the surface of the active material uniformly during slurry preparation, and thus has an effect
- the blending amount of the thickener is preferably 0.5 to 2.0 parts by weight based on 100 parts by weight of the total amount of the alloy-based active material and the carbon-based active material. When the blending amount of the thickener is within this range, the coating property and the adhesion with the current collector are good.
- “(modified) poly” means “unmodified poly” or “modified poly”
- “(meth) acryl” means “acryl” or “methacryl”.
- the negative electrode slurry of the present invention preferably contains a conductive material.
- a conductive material conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor-grown carbon fiber, and carbon nanotube can be used.
- the content of the conductive material in the negative electrode slurry is preferably 1 to 20 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the total amount of the alloy-based active material and the carbon-based active material.
- the negative electrode slurry of the present invention may further contain optional components such as a reinforcing material, a dispersing agent, a leveling agent, and an electrolytic solution additive having a function of suppressing electrolytic decomposition. It may be contained in the secondary battery negative electrode described later. These are not particularly limited as long as they do not affect the battery reaction.
- the reinforcing material various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used.
- a reinforcing material By using a reinforcing material, a tough and flexible negative electrode can be obtained, and excellent long-term cycle characteristics can be exhibited.
- the content of the conductive material and the reinforcing agent in the negative electrode slurry is usually 0.01 to 20 parts by weight, preferably 1 to 10 parts by weight, based on 100 parts by weight of the total amount of the alloy-based active material and the carbon-based active material. When the content of the conductive material or the reinforcing agent is within the above range, high capacity and high load characteristics can be exhibited.
- the dispersant examples include anionic compounds, cationic compounds, nonionic compounds, and polymer compounds.
- a dispersing agent is selected according to the kind of negative electrode active material and electrically conductive material to be used.
- the content of the dispersant in the negative electrode slurry is preferably 0.01 to 10 parts by weight based on 100 parts by weight of the total amount of the alloy-based active material and the carbon-based active material. When the content of the dispersant is in the above range, the slurry has excellent stability, a smooth negative electrode can be obtained, and a high battery capacity can be exhibited.
- the leveling agent examples include surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants.
- surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants.
- the electrolytic solution additive vinylene carbonate used in the negative electrode slurry and the electrolytic solution can be used.
- the content of the electrolyte solution additive in the negative electrode slurry is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the total amount of the alloy-based active material and the carbon-based active material.
- the cycle characteristics and the high temperature characteristics are excellent.
- Other examples include nanoparticles such as fumed silica and fumed alumina. By mixing the nanoparticles, the thixotropy of the negative electrode slurry can be controlled, and the leveling property of the negative electrode obtained thereby can be improved.
- the content of the nanoparticles in the negative electrode slurry is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the total amount of the alloy-based active material and the carbon-based active material.
- the content of the nanoparticles is in the above range, the slurry stability and productivity are excellent, and high battery characteristics are exhibited.
- the slurry for the negative electrode of a lithium ion secondary battery is obtained by mixing the binder, a mixture of an alloy-based active material and a carbon-based active material, a thickener used as necessary, a conductive material, and the like in a solvent.
- 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. Further, a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, and a planetary kneader can be used.
- a negative electrode for a lithium ion secondary battery according to the present invention is a negative electrode for a lithium ion secondary battery having a current collector and an active material layer containing a negative electrode active material and a binder provided on the current collector.
- the negative electrode active material includes an alloy-based active material and a carbon-based active material, and the weight ratio of the alloy-based active material to the carbon-based active material in the active material layer is a ratio of 20:80 to 50:50.
- the binder contains 0.1 to 15% by weight of polymerized units of an ethylenically unsaturated carboxylic acid monomer.
- the negative electrode for a lithium ion secondary battery of the present invention has an active material layer formed by applying and drying the negative electrode slurry of the present invention on a current collector.
- the manufacturing method of the negative electrode of this invention is not specifically limited, For example, the method of apply
- the method for applying the negative electrode slurry on the current collector is not particularly limited. Examples of the method 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.
- drying method examples 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 time is usually 5 to 30 minutes, and the drying temperature is usually 40 to 180 ° C.
- the method includes a step of reducing the porosity of the active material layer by pressure treatment using a die press or a roll press after applying and drying the negative electrode slurry on the current collector.
- a preferable range of the porosity is 5% to 30%, more preferably 7% to 20%. If the porosity is too high, charging efficiency and discharging efficiency are deteriorated. When the porosity is too low, it is difficult to obtain a high volume capacity, and there arises a problem that the active material layer is easily peeled off from the current collector. Further, when a curable polymer is used as the binder, it is preferably cured.
- the thickness of the active material layer of the negative electrode for a lithium ion secondary battery is usually 5 to 300 ⁇ m, preferably 30 to 250 ⁇ m, for both the positive electrode and the negative electrode.
- the negative electrode thickness is in the above range, both load characteristics and cycle characteristics are high.
- the total content of the alloy-based active material and the carbon-based active material in the active material layer of the negative electrode is preferably 85 to 99% by weight, more preferably 88 to 97% by weight.
- the density of the active material layer of the negative electrode for a lithium ion secondary battery preferably 1.6 ⁇ 1.9g / cm 3, more preferably 1.65 ⁇ 1.85g / cm 3.
- the density of the active material layer of the negative electrode is in the above range, a high-capacity battery can be obtained.
- the current collector used in the present invention is not particularly limited as long as it is an electrically conductive and electrochemically durable material.
- a metal material is preferable because it has heat resistance.
- iron, copper, aluminum Nickel, stainless steel, titanium, tantalum, gold, platinum and the like are particularly preferable for the negative electrode of a lithium ion secondary battery.
- the shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 to 0.5 mm is preferable.
- the current collector is preferably used after roughening in advance. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical 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. Further, an intermediate layer may be formed on the current collector surface in order to increase the adhesive strength and conductivity of the mixture.
- the lithium ion secondary battery of this invention has a positive electrode, a negative electrode, a separator, and electrolyte solution, and a negative electrode is the said negative electrode for secondary batteries.
- 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 alone or in admixture of two or more.
- 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 is lowered, and the charging characteristics and discharging characteristics of the battery are degraded.
- 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 alone or in admixture of two or more. 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 lithium sulfide, LiI, and Li 3 N.
- the separator is a porous substrate having pores, and usable separators include (a) a porous separator having pores, and (b) a porous material having a polymer coating layer formed on one or both sides. There is a separator or (c) a porous separator on which a porous resin coat layer containing an inorganic ceramic powder is formed.
- Non-limiting examples of these include polypropylene, polyethylene, polyolefin, or aramid porous Polymer film for solid polymer electrolyte or gel polymer electrolyte such as conductive separator, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or polyvinylidene fluoride hexafluoropropylene copolymer, and gelled polymer coating layer Coated separator or inorganic filler And the like porous membrane layer made of an inorganic filler dispersant is coated separator.
- the electrode for a lithium ion secondary battery positive electrode is formed by laminating a positive electrode active material layer containing a positive electrode active material and a binder on a current collector.
- the electrode active material (positive electrode active material) for the positive electrode of the non-aqueous electrolyte secondary battery uses an active material capable of occluding and releasing lithium ions, and is broadly classified into an inorganic compound and an organic compound.
- the positive electrode active material made of an inorganic compound include transition metal oxides, transition metal sulfides, lithium-containing composite metal oxides of lithium and transition metals, and the like.
- the transition metal 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. Among them, MnO, V 2 O 5 , V 6 O 13 and TiO 2 are preferable from the viewpoint of cycle stability and capacity.
- 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 lithium-containing cobalt oxide (LiCoO 2 ), lithium-containing nickel oxide (LiNiO 2 ), Co—Ni—Mn lithium composite oxide, Ni—Mn—Al lithium
- lithium-containing cobalt oxide (LiCoO 2 ) lithium-containing nickel oxide (LiNiO 2 ), Co—Ni—Mn lithium composite oxide, Ni—Mn—Al lithium
- examples thereof include composite oxides and lithium composite oxides of Ni—Co—Al.
- 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 (wherein 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, Li X MPO 4 as the 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 by allowing a carbon source material to coexist during reduction firing. These compounds may be partially element-substituted.
- the positive electrode active material for a lithium ion secondary battery may be a mixture of the above inorganic compound and organic compound.
- the average particle diameter of the positive electrode active material is usually 1 to 50 ⁇ m, preferably 2 to 30 ⁇ m.
- the amount of binder when preparing a slurry to be described later can be reduced, the decrease in the capacity of the battery can be suppressed, and the slurry is adjusted to a viscosity suitable for application. And a uniform electrode can be obtained.
- the content ratio of the positive electrode active material in the positive electrode active material layer of the positive electrode is preferably 90 to 99.9% by weight, more preferably 95 to 99% by weight.
- the binder for the lithium ion secondary battery positive electrode is not particularly limited and a known binder can be used.
- a known binder can be used.
- Resins such as derivatives and polyacrylonitrile derivatives
- soft polymers such as acrylic soft polymers, diene soft polymers, olefin soft polymers, and vinyl soft polymers can be used. These may be used alone or in combination of two or more.
- the positive electrode for a lithium ion secondary battery further includes optional components such as a dispersant used in the above-described negative electrode for a secondary battery and an electrolyte additive having a function of inhibiting decomposition of the electrolyte, etc. May be included. These are not particularly limited as long as they do not affect the battery reaction.
- the electrode for a lithium ion secondary battery positive electrode is formed by forming a positive electrode active material comprising a positive electrode active material and a binder on a current collector.
- the current collector can be the current collector used for the negative electrode of the secondary battery described above, and is not particularly limited as long as the material has electrical conductivity and is electrochemically durable. Aluminum is particularly preferable for the positive electrode of the ion secondary battery.
- the thickness of the positive electrode active material layer for a lithium ion secondary battery is usually 5 to 300 ⁇ m, preferably 10 to 250 ⁇ m. When the thickness of the positive electrode active material layer is in the above range, both load characteristics and energy density are high.
- the positive electrode for lithium ion secondary batteries can be produced in the same manner as the negative electrode for lithium ion secondary batteries described above.
- the manufacturing method of the lithium ion secondary battery of the present invention is not particularly limited.
- the negative electrode and the positive electrode are overlapped via a separator, and this is wound or folded according to the shape of the battery and placed in the battery container, and the electrolytic solution is injected into the battery container and sealed.
- an expanded metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate and the like can be inserted to prevent an increase in pressure inside the battery and overcharge / discharge.
- the shape of the battery may be any of a laminated cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, and the like.
- Electrode adhesion strength Each negative electrode was cut into a rectangle having a width of 1 cm and a length of 10 cm to form a test piece, and fixed with the electrode active material layer surface facing up. After applying the cellophane tape to the surface of the electrode active material layer of the test piece, the stress was measured when the cellophane tape was peeled off from one end of the test piece in the 180 ° direction at a speed of 50 mm / min. The measurement was performed 10 times, the average value was obtained, and this was used as the peel strength. It shows that the adhesion strength of an electrode is so large that peel strength is large.
- Example 1 Manufacture of negative electrode slurry
- CMC carboxymethyl cellulose
- 1.0% CMC aqueous solution was prepared using “Daicel 2200” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.
- a planetary mixer with a disper 70 parts of artificial graphite having a volume average particle diameter of 24.5 ⁇ m as a carbon-based active material and 30 parts of a Si—O—C based active material having a volume average particle diameter of 10 ⁇ m as an alloy-based active material Then, 5 parts of acetylene black was added as a conductive material and stirred for 20 minutes using only a low speed blade. Thereafter, the above 1% CMC aqueous solution was added to 1.0 part on the basis of solid content, adjusted to a solid content concentration of 55% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes.
- the binder contains 49% butadiene polymer units, 47% styrene polymer units, 4% acrylic acid polymer units, a solid content concentration of 40%, a glass transition temperature of ⁇ 17 ° C., and a number average.
- a styrene-butadiene polymer particle aqueous dispersion having a particle size of 100 nm and a pH of 8.5 is added so as to be 1.0 part on a solid basis, and ion exchange water is further added to obtain a final solid content concentration of 48%.
- ion exchange water is further added to obtain a final solid content concentration of 48%.
- Table 2 shows the evaluation results of the viscosity change rate of the negative electrode slurry.
- the negative electrode slurry was applied to one side of a 20 ⁇ m thick copper foil with a comma coater so that the film thickness after drying was about 200 ⁇ m, and dried at 60 ° C. for 2 minutes at a rate of 0.5 m / min. Heat treatment was performed at 120 ° C. for 2 minutes to obtain an electrode raw material.
- This electrode original fabric was rolled with a roll press to obtain a negative electrode having an active material layer thickness of 80 ⁇ m and a density of 1.7 g / cm 3 .
- the negative electrode was cut into a disk shape having a diameter of 12 mm.
- a separator made of a disc-shaped polypropylene porous film having a diameter of 18 mm and a thickness of 25 ⁇ m, metallic lithium used as a positive electrode, and expanded metal are laminated in this order, and this is made into a polypropylene packing.
- a stainless steel coin-type outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm).
- the electrolyte is poured into the container so that no air remains, and the outer container is fixed with a 0.2 mm thick stainless steel cap through a polypropylene packing, and the battery can is sealed, and the diameter is A half cell of 20 mm and a thickness of about 2 mm was produced.
- Table 2 shows the evaluation results of the performance of the coin-type battery. The evaluation results of the negative electrode are also shown in Table 2.
- Example 2 A negative electrode slurry, an electrode and a half cell were prepared in the same manner as in Example 1, except that silicon particles having a volume average average particle size of about 20 ⁇ m were used as the active material instead of the Si—O—C based active material. Were prepared and evaluated. The results are shown in Table 2.
- Example 3 A negative electrode slurry, an electrode and a half cell were prepared in the same manner as in Example 1 except that the blending amount of the artificial graphite was 50 parts and the blending amount of the Si—O—C-based active material was 50 parts. These evaluations were made. The results are shown in Table 2.
- Example 4 Except not using an electrically conductive material, operation similar to Example 1 was performed, the slurry for negative electrodes, the electrode, and the half cell were produced, and these evaluation was performed. The results are shown in Table 2.
- Example 5 As a binder, it contains 49% butadiene polymer units, 50.5% styrene polymer units, 0.5% acrylic acid polymer units, 40% solid content, -10 ° C glass transition temperature, number average A negative electrode slurry was prepared in the same manner as in Example 1 except that 1.0 part (based on solid content) of a styrene-butadiene polymer particle aqueous dispersion having a particle size of 105 nm and a pH of 8.5 was used. Electrodes and half cells were prepared and evaluated. The results are shown in Table 2.
- Example 6 The binder contains 47% butadiene polymer units, 50.5% styrene polymer units and 2.5% acrylic acid polymer units, a solid content concentration of 40%, a glass transition temperature of ⁇ 8 ° C., and a number average.
- a negative electrode slurry was prepared in the same manner as in Example 1 except that 1.0 part (based on solid content) of a styrene-butadiene polymer particle aqueous dispersion having a particle size of 97 nm and a pH of 8.5 was used. Electrodes and half cells were prepared and evaluated. The results are shown in Table 2.
- Example 7 As a binder, it contains 44% butadiene polymer units, 46% styrene polymer units and 10% acrylic acid polymer units, a solid content concentration of 40%, a glass transition temperature of ⁇ 5 ° C., and a number average particle diameter of 150 nm. Except that 1.0 part (based on solid content) of an aqueous dispersion of styrene-butadiene polymer particles having a pH of 8.5 was used, the same operation as in Example 1 was carried out to obtain a slurry for the negative electrode, an electrode, and a half cell. Were prepared and evaluated. The results are shown in Table 2.
- the binder contains 32% butadiene polymer units, 64% styrene polymer units, 4% acrylic acid polymer units, a solid content concentration of 40%, a glass transition temperature of 10 ° C., a number average particle size of 98 nm, Except that 1.0 part (based on solid content) of a styrene-butadiene polymer particle aqueous dispersion having a pH of 8.5 was used, the same operation as in Example 1 was performed to prepare a negative electrode slurry, an electrode and a half cell. Fabricated and evaluated. The results are shown in Table 2.
- Example 9 The negative electrode slurry is applied, applied to one side of the copper foil so that the film thickness after drying is about 80 ⁇ m, and the electrode raw material is rolled by a roll press to have a thickness of 140 ⁇ m and a density of 1.3 g / cm 3 . Except having used the electrode for negative electrodes, operation similar to Example 1 was performed, the negative electrode slurry, the electrode, and the half cell were produced, and these evaluation was performed. The results are shown in Table 2.
- Example 10 As a binder, it contains 49% butadiene polymer units, 47% styrene polymer units, 4% itaconic acid polymer units, a solid content concentration of 40%, a glass transition temperature of ⁇ 15 ° C., and a number average particle size of 98 nm. Except that 1.0 part (based on solid content) of an aqueous dispersion of styrene-butadiene polymer particles having a pH of 8.5 was used, the same operation as in Example 1 was carried out to obtain a slurry for the negative electrode, an electrode, and a half cell. Were prepared and evaluated. The results are shown in Table 2.
- Example 1 A negative electrode slurry, an electrode and a half cell were prepared in the same manner as in Example 1 except that 100 parts of Si—O—C based active material was used as the active material without using artificial graphite. Was evaluated. The results are shown in Table 2.
- Comparative Example 2 As a binder, it contains no polymerized units of ethylenically unsaturated carboxylic acid monomer, 50% of polymerized units of butadiene, 50% of polymerized units of styrene, solid content concentration of 40%, glass transition temperature of ⁇ 12 ° C., number The same procedure as in Example 1 was performed, except that 1.0 part (based on solid content) of an aqueous styrene-butadiene polymer particle dispersion having an average particle size of 150 nm and a pH of 8.0 was used. Slurries, electrodes and half cells were prepared and evaluated. The results are shown in Table 2.
- the binder contains 45% butadiene polymer units, 37% styrene polymer units, 18% methacrylic acid polymer units, a solid content concentration of 40%, a glass transition temperature of 5 ° C., a number average particle size of 130 nm, Except that 1.0 part (based on solid content) of a styrene-butadiene polymer particle aqueous dispersion having a pH of 8.0 was used, the same operation as in Example 1 was performed to prepare a negative electrode slurry, an electrode, and a half cell. Fabricated and evaluated. The results are shown in Table 2.
- Example 4 An electrode and a half cell were produced in the same manner as in Example 1 except that the blending amount of the artificial graphite was 20 parts and the blending amount of the Si—O—C based active material was 80 parts. Went. The results are shown in Table 2.
- the electrode active material layer containing the electrode active material and the binder contains the alloy active material and the carbon active material, and the alloy active material and the carbon active material
- the weight ratio to the active material is 20:80 to 50:50 and the binder contains 0.1 to 15% by weight of polymerized units of ethylenically unsaturated carboxylic acid monomer, slurry stability, electrode adhesion strength, cycle A lithium ion secondary battery having excellent characteristics can be obtained.
- a Si—O—C based active material is used as the alloy based active material, and the weight ratio of the alloy active material to the carbon based active material is in the range of 20:80 to 40:60, and the binder is The glass transition temperature is in the range of ⁇ 80 ° C. to 0 ° C., the polymerization unit of acrylic acid or itaconic acid is contained in the range of 1 to 5% by weight, and the conductive material is in the range of 1 to 20 parts by weight.
- Example 1 Example 6 and Example 10 are most excellent in all of slurry stability, electrode adhesion strength, and cycle characteristics.
Abstract
Description
このため、リチウム二次電池の各種の部材や材料の高性能化も活発に試みられ、中でも負極活物質による電池の高容量化は重要度を増している。
特許文献2では、ケイ素粒子と炭素質材料とからなる複合粒子が空隙を有することにより、サイクル特性を発揮しており、サイクル特性は向上するものの、体積あたりの電池容量が低くなる傾向にある。また、特許文献2では、ケイ素粒子と炭素質材料を混合、熱処理して複合粒子を作成し、その後ふるいをかけ更に塩酸で不純物を除去し、ろ過・真空乾燥することによって負極材料を得ており、生産工程が増加し、製造コストが増大する。
さらに電極用スラリー作製の際に、複合粒子からサブミクロンの炭素材料が脱離することがあり、この炭素材料がバインダーを通じてスラリー中で構造体を形成し、スラリーの粘度が上昇するという問題がある。
従って、本発明の目的は、活物質を複合化することなく、電極の密着強度の低下を抑制し、かつ寿命劣化の少ないリチウムイオン二次電池を提供可能なリチウムイオン二次電池負極、およびそれに用いるリチウムイオン二次電池負極用スラリーを提供することにある。
(1)集電体、及び前記集電体上に設けられた、負極活物質及びバインダーを含有する活物質層を有するリチウムイオン二次電池負極であって、前記負極活物質が、合金系活物質及び炭素系活物質を含み、かつ前記活物質層における前記合金系活物質と前記炭素系活物質との重量比率が、20:80~50:50の比率であり、前記バインダーが、エチレン性不飽和カルボン酸モノマーの重合単位を0.1~15重量%含むリチウムイオン二次電池負極。
(2)前記活物質層が、活物質100重量部に対して1~20重量部の導電材をさらに含有する上記(1)に記載のリチウムイオン二次電池負極。
(3)前記バインダーのガラス転移温度が、25℃以下である上記(1)又は(2)に記載のリチウムイオン二次電池負極。
(4)前記活物質層の密度が1.6~1.9g/cm3である上記(1)~(3)のいずれかに記載のリチウムイオン二次電池負極。
(5)負極活物質、バインダー、及び溶媒を含有し、前記負極活物質が合金系活物質及び炭素系活物質を含み、かつ、前記合金系活物質と炭素系活物質との重量比率が、20:80~50:50であり、前記バインダーがエチレン性不飽和カルボン酸モノマーの重合単位を0.1~15重量%含むリチウムイオン二次電池負極用スラリー。
(6)正極、負極、セパレーター及び電解液を有し、前記負極が、上記(1)~(5)のいずれかに記載のリチウムイオン二次電池負極である、リチウム二次電池。
本発明のリチウムイオン二次電池負極用スラリーは、負極活物質、バインダー及び溶媒を含有し、前記負極活物質として合金系活物質と炭素系活物質を含有する。
本発明で用いる合金系活物質とは、リチウムの挿入可能な元素を構造に含み、リチウムが挿入された場合の重量あたりの理論電気容量が500mAh/g以上(当該理論電気容量の上限は、特に限定されないが、例えば5000mAh/g以下とすることができる。)である活物質をいい、具体的には、リチウム金属、リチウム合金を形成する単体金属およびその合金、及びそれらの酸化物や硫化物、窒化物、珪化物、炭化物、燐化物等が用いられる。
リチウム合金を形成する単体金属及び合金としては、Ag、Al、Ba、Bi、Cu、Ga、Ge、In、Ni、P、Pb、Sb、Si、Sn、Sr、Zn等の金属を含有する化合物が挙げられる。それらの中でもケイ素(Si)、スズ(Sn)または鉛(Pb)の単体金属若しくはこれら原子を含む合金、または、それらの金属の化合物が用いられる。
本発明で用いる合金系活物質は、さらに、一つ以上の非金属元素を含有していてもよい。具体的には、例えばSiC、SiOxCy(以下、「Si-O-C」と呼ぶ)(0<x≦3、0<y≦5)、Si3N4、Si2N2O、SiOx(0<x≦2)、SnOx(0<x≦2)、LiSiO、LiSnO等が挙げられ、中でも低電位でリチウムの挿入脱離が可能なSiOxCyが好ましい。例えば、SiOxCyは、ケイ素を含む高分子材料を焼成して得ることができる。SiOxCyの中でも、容量とサイクル特性の兼ね合いから、0.8≦x≦3、2≦y≦4の範囲が好ましく用いられる。
リチウム含有金属複合酸化物としては、更にLixTiyMzO4で示されるリチウムチタン複合酸化物(0.7≦x≦1.5、1.5≦y≦2.3、0≦z≦1.6、Mは、Na、K、Co、Al、Fe、Ti、Mg、Cr、Ga、Cu、ZnおよびNb)が挙げられ、中でもLi4/3Ti5/3O4、Li1Ti2O4、Li4/5Ti11/5O4が用いられる。
これらの中でもケイ素を含む材料が好ましく、中でもSi-O-Cがさらに好ましい。この化合物では高電位でSi(ケイ素)、低電位ではC(炭素)へのLiの挿入脱離が起こると推測され、他の合金系活物質よりも膨張・収縮が抑制されるため、本発明の効果がより得られ易い。
本発明に用いる合金系活物質の体積平均粒子径は、0.1~50μmであることが好ましく、0.5~20μmがさらに好ましく、1~10μmが最も好ましい。合金系活物質の粒子径がこの範囲内であれば後述する電極用スラリーの作製が容易となる。
本発明に用いる炭素系活物質とは、リチウムが挿入可能な炭素を主骨格とする活物質をいい、具体的には、炭素質材料と黒鉛質材料が挙げられる。炭素質材料とは一般的に炭素前駆体を2000℃以下(当該処理温度の下限は、特に限定されないが、例えば500℃以上とすることができる)で熱処理(炭素化)された黒鉛化の低い(結晶性の低い)炭素材料を示し、黒鉛質材料とは易黒鉛性炭素を2000℃以上(当該処理温度の上限は、特に限定されないが、例えば5000℃以上とすることができる)で熱処理することによって得られた黒鉛に近い高い結晶性を有する黒鉛質材料を示す。
易黒鉛性炭素としては石油や石炭から得られるタールピッチを原料とした炭素材料が挙げられ、例えば、コークス、メソカーボンマイクロビーズ(MCMB)、メソフェーズピッチ系炭素繊維、熱分解気相成長炭素繊維などが挙げられる。MCMBとはピッチ類を400℃前後で過熱する過程で生成したメソフェーズ小球体を分離抽出した炭素微粒子であり、メソフェーズピッチ系炭素繊維とは、前記メソフェーズ小球体が成長、合体して得られるメソフェーズピッチを原料とする炭素繊維である。
難黒鉛性炭素としては、フェノール樹脂焼成体、ポリアクリロニトリル系炭素繊維、擬等方性炭素、フルフリルアルコール樹脂焼成体(PFA)などが挙げられる。
ここでいう乾式混合とは、合金系活物質の粉体と炭素系活物質の粉体同士を混合機を用いて混合することをいい、具体的には混合時の固形分濃度が90重量%以上、好ましくは95重量%以上、より好ましくは97重量%以上で混合することをいう。混合時の固形分濃度が、前記範囲であれば粒子形状を維持したまま均一に分散させることができ、活物質の凝集を防ぐことができる。
乾式混合の際に用いる混合機としては、乾式タンブラー、スーパーミキサー、ヘンシェルミキサー、フラッシュミキサー、エアーブレンダー、フロージェットミキサー、ドラムミキサー、リボコーンミキサー、パグミキサー、ナウターミキサー、リボンミキサー、スパルタンリューザー、レディゲミキサー、プラネタリーミキサーがあげられ、スクリュー型ニーダー、脱泡ニーダー、ペイントシェーカー等の装置、加圧ニーダー、二本ロールなどの混練機を例示できる。
上述した方法の中で比較的容易にできるものとして、攪拌による分散が可能なプラネタリーミキサーなどのミキサー類が挙げられ、プラネタリーミキサー、ヘンシェルミキサーが特に好ましい。
本発明に用いるバインダーは、エチレン性不飽和カルボン酸モノマーの重合単位を0.1~15重量%含む。本発明に用いるバインダーが、エチレン性不飽和カルボン酸モノマーの重合単位を0.1~15重量%含むことにより、バインダーの安定性が保持され、経時でのスラリーの粘度上昇が抑制され、さらに電極の密着強度が向上する。
本願において、あるモノマーの重合単位とは、当該モノマーが重合反応することにより形成される、重合体中の重合単位を意味する。具体例を挙げれば、ポリアクリル酸における、「アクリル酸の重合単位」は、単位-(CH2-CH(COOH))-である。
本発明に用いるバインダー中のエチレン性不飽和カルボン酸モノマーの重合単位が0.1重量%未満であると、前記効果が発現せず、またエチレン性不飽和カルボン酸モノマーの重合単位が15重量%を超えると、バインダー中の水分がカルボン酸基の水和に用いられ、バインダー自身の粘度上昇が顕著に起こり、スラリーの粘度上昇を引き起こし、活物質層と集電体の密着強度が低下してしまう。
本発明に用いるバインダー中のエチレン性不飽和カルボン酸モノマーの重合単位の含有量は、好ましくは0.5~10重量%、より好ましくは1~5重量%である。バインダー中のエチレン性不飽和カルボン酸モノマーの重合単位の含有量が前記範囲であることにより、バインダーの安定性が保持され、経時でのスラリーの粘度上昇をより抑制することができる。また、電極の密着強度がより向上する。
エチレン性不飽和カルボン酸モノマーとしては、アクリル酸、メタクリル酸、イタコン酸、フマル酸などが挙げられる。中でも、バインダーの表面に官能基を存在させやすいという点で、アクリル酸やイタコン酸が好ましい。
エチレン性不飽和カルボン酸モノマーの重合単位は、エチレン性不飽和カルボン酸モノマーを後述するバインダーを構成するモノマーとして用いることにより導入することができる。
溶媒としては、上記固形分(合金系活物質、炭素系活物質、バインダー、導電材、増粘剤、後述する任意の成分)、を均一に分散し得るものであれば特に制限されない。
負極用スラリーに用いる溶媒としては、水および有機溶媒のいずれも使用できる。有機溶媒としては、シクロペンタン、シクロヘキサンなどの環状脂肪族炭化水素類;トルエン、キシレン、エチルベンゼンなどの芳香族炭化水素類;アセトン、エチルメチルケトン、ジソプロピルケトン、シクロヘキサノン、メチルシクロヘキサン、エチルシクロヘキサンなどのケトン類;メチレンクロライド、クロロホルム、四塩化炭素など塩素系脂肪族炭化水素;酢酸エチル、酢酸ブチル、γ-ブチロラクトン、ε-カプロラクトンなどのエステル類;アセトニトリル、プロピオニトリルなどのアシロニトリル類;テトラヒドロフラン、エチレングリコールジエチルエーテルなどのエーテル類:メタノール、エタノール、イソプロパノール、エチレングリコール、エチレングリコールモノメチルエーテルなどのアルコール類;N-メチルピロリドン、N,N-ジメチルホルムアミドなどのアミド類があげられる。
これらの溶媒は、単独で使用しても、これらを2種以上混合して混合溶媒として使用してもよい。これらの中でも沸点が低く揮発性が高い溶媒が、短時間でかつ低温で除去できるので好ましい。具体的には、アセトン、トルエン、シクロヘキサノン、シクロペンタン、テトラヒドロフラン、シクロヘキサン、キシレン、水、若しくはN-メチルピロリドン、またはこれらの混合溶媒が好ましい。
本発明の負極用スラリーは、さらに増粘剤を含有してもよい。増粘剤としては、カルボキシメチルセルロース、メチルセルロース、ヒドロキシプロピルセルロースなど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、各種変性デンプンなどが挙げられ、カルボキシメチルセルロースのアンモニウム塩並びにアルカリ金属塩が好ましく用いられる。これは上記増粘剤がスラリー作製時に活物質の表面を均一に覆いやすいため、活物質間の接着を向上させる効果があるためである。
本発明の負極用スラリーは、導電材を含有することが好ましい。導電材としては、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、グラファイト、気相成長カーボン繊維、および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。導電材を含有することにより、活物質同士の電気的接触を向上させることができ、リチウムイオン二次電池に用いる場合に放電レート特性を改善することができる。負極用スラリーにおける導電材の含有量は、合金系活物質と炭素系活物質の総量100重量部に対して、好ましくは1~20重量部、より好ましくは1~10重量部である。
リチウムイオン二次電池負極用スラリーは、上記バインダー、合金系活物質と炭素系活物質の混合物、および必要に応じ用いられる増粘剤、導電材等とを溶媒中で混合して得られる。
混合法は特に限定はされないが、例えば、撹拌式、振とう式、および回転式などの混合装置を使用した方法が挙げられる。また、ホモジナイザー、ボールミル、サンドミル、ロールミル、および遊星式混練機などの分散混練装置を使用した方法が挙げられる。
本発明のリチウムイオン二次電池負極は、集電体、及び前記集電体上に設けられた、負極活物質及びバインダーを含有する活物質層を有するリチウムイオン二次電池負極であって、前記負極活物質が、合金系活物質及び炭素系活物質を含み、かつ前記活物質層における前記合金系活物質と前記炭素系活物質との重量比が、20:80~50:50の比率であり、前記バインダーが、エチレン性不飽和カルボン酸モノマーの重合単位を0.1~15重量%含む。
好ましい態様において、本発明のリチウムイオン二次電池用負極は、集電体上に、本発明の負極用スラリーを塗布乾燥してなる活物質層を有する。
本発明の負極の製造方法は、特に限定されないが、例えば、前記負極用スラリーを集電体の少なくとも片面、好ましくは両面に塗布、乾燥し、活物質層を形成する方法が挙げられる。
負極用スラリーを集電体上に塗布する方法は特に限定されない。例えば、ドクターブレード法、ディップ法、リバースロール法、ダイレクトロール法、グラビア法、エクストルージョン法、およびハケ塗り法などの方法が挙げられる。
乾燥方法としては、例えば、温風、熱風、低湿風による乾燥、真空乾燥、(遠)赤外線や電子線などの照射による乾燥法が挙げられる。乾燥時間は通常5~30分であり、乾燥温度は通常40~180℃である。
さらに、バインダーとして硬化性の重合体を用いる場合は、硬化させることが好ましい。
本発明で用いる集電体は、電気導電性を有しかつ電気化学的に耐久性のある材料であれば特に制限されないが、耐熱性を有するため金属材料が好ましく、例えば、鉄、銅、アルミニウム、ニッケル、ステンレス鋼、チタン、タンタル、金、白金などが挙げられる。中でも、リチウムイオン二次電池の負極用としては銅が特に好ましい。集電体の形状は特に制限されないが、厚さ0.001~0.5mm程度のシート状のものが好ましい。集電体は、活物質層との接着強度を高めるため、予め粗面化処理して使用するのが好ましい。粗面化方法としては、機械的研磨法、電解研磨法、化学研磨法などが挙げられる。機械的研磨法においては、研磨剤粒子を固着した研磨布紙、砥石、エメリバフ、鋼線などを備えたワイヤーブラシ等が使用される。また、合剤の接着強度や導電性を高めるために、集電体表面に中間層を形成してもよい。
本発明のリチウムイオン二次電池は、正極、負極、セパレーター及び電解液を有し、負極が、前記二次電池用負極である。
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。
また前記電解液には添加剤を含有させて用いることも可能である。添加剤としてはビニレンカーボネート(VC)などのカーボネート系の化合物が好ましい。
セパレーターは気孔部を有する多孔性基材であって、使用可能なセパレーターとしては、(a)気孔部を有する多孔性セパレーター、(b)片面または両面上に高分子コート層が形成された多孔性セパレーター、または(c)無機セラミック粉末を含む多孔質の樹脂コート層が形成された多孔性セパレーターがあり、これらの非制限的な例としては、ポリプロピレン系、ポリエチレン系、ポリオレフィン系、またはアラミド系多孔性セパレーター、ポリビニリデンフルオリド、ポリエチレンオキシド、ポリアクリロニトリルまたはポリビニリデンフルオリドヘキサフルオロプロピレン共重合体などの固体高分子電解質用またはゲル状高分子電解質用の高分子フィルム、ゲル化高分子コート層がコートされたセパレーター、または無機フィラー、無機フィラー用分散剤からなる多孔膜層がコートされたセパレーターなどがある。
リチウムイオン二次電池正極用電極は、正極活物質及びバインダーを含む正極活物質層が、集電体上に積層されてなる。
非水電解質二次電池正極用の電極活物質(正極活物質)は、リチウムイオンの吸蔵放出可能な活物質が用いられ、無機化合物からなるものと有機化合物からなるものとに大別される。
無機化合物からなる正極活物質としては、遷移金属酸化物、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。
遷移金属硫化物としては、TiS2、TiS3、非晶質MoS2、FeS等が挙げられる。
リチウム含有複合金属酸化物としては、層状構造を有するリチウム含有複合金属酸化物、スピネル構造を有するリチウム含有複合金属酸化物、オリビン型構造を有するリチウム含有複合金属酸化物などが挙げられる。
スピネル構造を有するリチウム含有複合金属酸化物としてはマンガン酸リチウム(LiMn2O4)やMnの一部を他の遷移金属で置換したLi[Mn3/2M1/2]O4(ここでMは、Cr、Fe、Co、Ni、Cu等)等が挙げられる。
オリビン型構造を有するリチウム含有複合金属酸化物としてはLiXMPO4(式中、Mは、Mn,Fe,Co,Ni,Cu,Mg,Zn,V,Ca,Sr,Ba,Ti,Al,Si,B及びMoから選ばれる少なくとも1種、0≦X≦2)であらわされるオリビン型燐酸リチウム化合物が挙げられる。
電気伝導性に乏しい、鉄系酸化物は、還元焼成時に炭素源物質を共存させることで、炭素材料で覆われた電極活物質として用いてもよい。また、これら化合物は、部分的に元素置換したものであってもよい。リチウムイオン二次電池用の正極活物質は、上記の無機化合物と有機化合物の混合物であってもよい。
リチウムイオン二次電池正極用バインダーとしては、特に制限されず公知のものを用いることができる。例えば、前述のリチウムイオン二次電池負極用に使用される、ポリエチレン、ポリテトラフルオロエチレン(PTFE)、ポリフッ化ビニリデン(PVDF)、テトラフルオロエチレン-ヘキサフルオロプロピレン共重合体(FEP)、ポリアクリル酸誘導体、ポリアクリロニトリル誘導体などの樹脂や、アクリル系軟質重合体、ジエン系軟質重合体、オレフィン系軟質重合体、ビニル系軟質重合体等の軟質重合体を用いることができる。これらは単独で使用しても、これらを2種以上併用してもよい。
集電体は、前述の二次電池負極用に使用される集電体を用いることができ、電気導電性を有しかつ電気化学的に耐久性のある材料であれば特に制限されないが、リチウムイオン二次電池の正極用としてはアルミニウムが特に好ましい。
本発明のリチウムイオン二次電池の製造方法は、特に限定されない。例えば、負極と正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する。さらに必要に応じてエキスパンドメタルや、ヒューズ、PTC素子などの過電流防止素子、リード板などを入れ、電池内部の圧力上昇、過充放電の防止をすることもできる。電池の形状は、ラミネートセル型、コイン型、ボタン型、シート型、円筒型、角形、扁平型などいずれであってもよい。
実施例および比較例において、各種物性は以下のように評価した。
電極用スラリー作製1時間後のスラリー粘度(η1h)と5時間後のスラリー粘度(η5h)とから、下記式によりスラリー粘度変化率を求め、以下の基準で判定した。
スラリー粘度変化率(%)=100×(η5h-η1h)/η1h
A:5%未満
B:5%以上10%未満
C:10%以上15%未満
D:15%以上20%未満
E:20%以上25%未満
F:25%以上
なお、スラリーの粘度は、JIS Z8803:1991に準じて単一円筒形回転粘度計(25℃、回転数=60rpm、スピンドル形状:4)により測定した。
負極を、それぞれ、幅1cm×長さ10cmの矩形に切って試験片とし、電極活物質層面を上にして固定した。試験片の電極活物質層表面にセロハンテープを貼り付けた後、試験片の一端からセロハンテープを50mm/分の速度で180°方向に引き剥がしたときの応力を測定した。測定を10回行い、その平均値を求めてこれをピール強度とし、下記基準にて判定を行った。ピール強度が大きいほど、電極の密着強度が大きいことを示す。
A:6N/m以上
B:5N/m以上~6N/m未満
C:4N/m以上~5N/m未満
D:3N/m以上~4N/m未満
E:2N/m以上~3N/m未満
F:2N/m未満
得られたコインセル型電池を用いて、それぞれ25℃で0.1Cの定電流定電圧充電法という方式で、0.02Vになるまで定電流で充電し、得られた容量を初期充電容量とした。
得られたコインセル型電池を用いて、それぞれ25℃で0.1Cの定電流定電圧充電法という方式で、0.02Vになるまで定電流で充電、その後定電圧で充電し、また0.1Cの定電流で3.0Vまで放電する充放電サイクルを行った。充放電サイクルは50サイクルまで行い、初期放電容量に対する50サイクル目の放電容量の比を容量維持率とし、下記の基準で判定した。この値が大きいほど繰り返し充放電による容量減が少ないことを示す。
A:80%以上
B:75%以上80%未満
C:70%以上75%未満
D:65%以上70%未満
E:60%以上65%未満
F:60%未満
(負極用スラリーの製造)
カルボキシメチルセルロース(CMC)として、第一工業製薬株式会社製「ダイセル2200」を用い、1.0%のCMC水溶液を調製した。
その後、上記1%のCMC水溶液を固形分基準で1.0部となるように加え、イオン交換水で固形分濃度55%に調整した後、25℃で60分間混合した。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分間混合した。
次に、バインダーとして、ブタジエンの重合単位を49%、スチレンの重合単位を47%、アクリル酸の重合単位を4%を含み、固形分濃度が40%、ガラス転移温度が-17℃、個数平均粒子径が100nm、pHが8.5であるスチレン-ブタジエン重合体粒子水分散液を固形分基準で1.0部となるように入れ、さらにイオン交換水を入れて最終固形分濃度48%となるように調整し、さらに10分間混合した。これを減圧下で脱泡処理して流動性の良い負極用スラリーを得た。
負極用スラリーの粘度変化率の評価結果を表2に示す。
上記負極用スラリーを、コンマコーターで、厚さ20μmの銅箔の片面に、乾燥後の膜厚が200μm程度になるように塗布し、0.5m/minの速度で60℃で2分間乾燥、120℃で2分間加熱処理して電極原反を得た。この電極原反をロールプレスで圧延して活物質層の厚みが80μm、密度が1.7g/cm3の負極用電極を得た。
このコイン型電池の性能の評価結果を表2に示す。負極の評価結果も表2に示す。
Si-O-C系の活物質のかわりに体積平均平均粒子径約20μmのケイ素粒子を活物質として使用したこと以外は、実施例1と同様の操作を行って、負極用スラリー、電極及びハーフセルを作製し、これらの評価を行った。結果を表2に示す。
人造黒鉛の配合量を50部、Si-O-C系の活物質の配合量を50部としたこと以外は実施例1と同様の操作を行って、負極用スラリー、電極及びハーフセルを作製し、これらの評価を行った。結果を表2に示す。
導電材を使用しないこと以外は実施例1と同様の操作を行って、負極用スラリー、電極及びハーフセルを作製し、これらの評価を行った。結果を表2に示す。
バインダーとして、ブタジエンの重合単位を49%、スチレンの重合単位を50.5%、アクリル酸の重合単位を0.5%含み、固形分濃度が40%、ガラス転移温度が-10℃、個数平均粒子径が105nm、pHが8.5のスチレン-ブタジエン重合体粒子水分散液を1.0部(固形分基準)用いたこと以外は、実施例1と同様の操作を行って、負極用スラリー、電極及びハーフセルを作製し、これらの評価を行った。結果を表2に示す。
バインダーとして、ブタジエンの重合単位を47%、スチレンの重合単位50.5%、アクリル酸の重合単位を2.5%を含み、固形分濃度が40%、ガラス転移温度が-8℃、個数平均粒子径が97nm、pHが8.5のスチレン-ブタジエン重合体粒子水分散液を1.0部(固形分基準)用いたこと以外は、実施例1と同様の操作を行って、負極用スラリー、電極及びハーフセルを作製し、これらの評価を行った。結果を表2に示す。
バインダーとして、ブタジエンの重合単位を44%、スチレンの重合単位を46%、アクリル酸の重合単位を10%含み、固形分濃度が40%、ガラス転移温度が-5℃、個数平均粒子径が150nm、pHが8.5のスチレン-ブタジエン重合体粒子水分散液を1.0部(固形分基準)用いたこと以外は、実施例1と同様の操作を行って、負極用スラリー、電極及びハーフセルを作製し、これらの評価を行った。結果を表2に示す。
バインダーとして、ブタジエンの重合単位を32%、スチレンの重合単位を64%、アクリル酸の重合単位を4%含み、固形分濃度が40%、ガラス転移温度が10℃、個数平均粒子径が98nm、pHが8.5のスチレン-ブタジエン重合体粒子水分散液を1.0部(固形分基準)用いたこと以外は、実施例1と同様の操作を行って、負極用スラリー、電極及びハーフセルを作製し、これらの評価を行った。結果を表2に示す。
負極用スラリーを塗布、乾燥後の膜厚が80μm程度になるように、銅箔の片面に塗布し、この電極原反をロールプレスで圧延して厚さ140μm、密度1.3g/cm3の負極用電極を使用したこと以外は、実施例1と同様の操作を行って、負極用スラリー、電極及びハーフセルを作製し、これらの評価を行った。結果を表2に示す。
バインダーとして、ブタジエンの重合単位を49%、スチレンの重合単位を47%、イタコン酸の重合単位を4%含み、固形分濃度が40%、ガラス転移温度が-15℃、個数平均粒子径が98nm、pHが8.5のスチレン-ブタジエン重合体粒子水分散液を1.0部(固形分基準)用いたこと以外は、実施例1と同様の操作を行って、負極用スラリー、電極及びハーフセルを作製し、これらの評価を行った。結果を表2に示す。
活物質として、人造黒鉛を用いず、Si-O-C系の活物質を100部用いたこと以外は実施例1と同様の操作を行って、負極用スラリー、電極及びハーフセルを作製し、これらの評価を行った。結果を表2に示す。
バインダーとして、エチレン性不飽和カルボン酸モノマーの重合単位を含まず、ブタジエンの重合単位を50%、スチレンの重合単位を50%含み、固形分濃度が40%、ガラス転移温度が-12℃、個数平均粒子径が150nm、pHが8.0のスチレン-ブタジエン重合体粒子水分散液を1.0部(固形分基準)用いたこと以外は、実施例1と同様の操作を行って、負極用スラリー、電極及びハーフセルを作製し、これらの評価を行った。結果を表2に示す。
バインダーとして、ブタジエンの重合単位を45%、スチレンの重合単位を37%、メタクリル酸の重合単位を18%含み、固形分濃度が40%、ガラス転移温度が5℃、個数平均粒子径が130nm、pHが8.0のスチレン-ブタジエン重合体粒子水分散液を1.0部(固形分基準)用いたこと以外は、実施例1と同様の操作を行って、負極用スラリー、電極及びハーフセルを作製し、これらの評価を行った。結果を表2に示す。
人造黒鉛の配合量を20部、Si-O-C系の活物質の配合量を80部としたこと以外は実施例1と同様の操作を行って、電極及びハーフセルを作製し、これらの評価を行った。結果を表2に示す。
本発明によれば、実施例1~10に示すように、電極活物質及びバインダーを含む電極活物質層中に合金系活物質及び炭素系活物質を含み、かつ前記合金系活物質と炭素系活物質との重量比が20:80~50:50で、バインダーがエチレン性不飽和カルボン酸モノマーの重合単位を0.1~15重量%含むことにより、スラリー安定性、電極の密着強度、サイクル特性に優れるリチウムイオン二次電池を得ることができる。また、実施例の中でも、合金系活物質としてSi-O-C系の活物質を用い、合金活物質と炭素系活物質の重量比で20:80~40:60の範囲にあり、バインダーが、ガラス転移温度が-80℃~0℃の範囲にあり、かつアクリル酸またはイタコン酸の重合単位を1~5重量%の範囲で含むものであり、導電材を1~20重量部の範囲で含む実施例1、実施例6や実施例10が、スラリー安定性、電極の密着強度、サイクル特性の全てに最も優れている。
一方、電極活物質層に合金系活物質を単独で用いた場合(比較例1)、バインダーとしてエチレン性不飽和カルボン酸モノマーの重合単位を含まないものを用いた場合(比較例2)、バインダーとしてエチレン性不飽和カルボン酸モノマーの重合単位が15重量%を超えるものを用いた場合(比較例3)、合金系活物質と炭素系活物質の重量比を80:20としたものを用いた場合(比較例4)は、特にピール強度、充放電サイクル特性が著しく劣る。
Claims (6)
- 集電体、及び前記集電体上に設けられた、負極活物質及びバインダーを含有する活物質層を有するリチウムイオン二次電池負極であって、
前記負極活物質が、合金系活物質及び炭素系活物質を含み、かつ前記活物質層における前記合金系活物質と前記炭素系活物質との重量比が、20:80~50:50の比率であり、
前記バインダーが、エチレン性不飽和カルボン酸モノマーの重合単位を0.1~15重量%含むリチウムイオン二次電池負極。 - 前記活物質層が、活物質100重量部に対して1~20重量部の導電材をさらに含有する請求項1に記載のリチウムイオン二次電池負極。
- 前記バインダーのガラス転移温度が、25℃以下である請求項1に記載のリチウムイオン二次電池負極。
- 前記活物質層の密度が1.6~1.9g/cm3である請求項1に記載のリチウムイオン二次電池負極。
- 負極活物質、バインダー、及び溶媒を含有し、
前記負極活物質が合金系活物質及び炭素系活物質を含み、かつ、
前記合金系活物質と前記炭素系活物質との重量比が、20:80~50:50であり、前記バインダーがエチレン性不飽和カルボン酸モノマーの重合単位を0.1~15重量%含むリチウムイオン二次電池負極用スラリー。 - 正極、負極、セパレーター及び電解液を有し、前記負極が、請求項1に記載のリチウムイオン二次電池負極である、リチウム二次電池。
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KR101628430B1 (ko) | 2016-06-08 |
KR20120081987A (ko) | 2012-07-20 |
US9263733B2 (en) | 2016-02-16 |
JPWO2011037142A1 (ja) | 2013-02-21 |
CN102576858A (zh) | 2012-07-11 |
CN102576858B (zh) | 2015-09-30 |
US20120189913A1 (en) | 2012-07-26 |
JP5673545B2 (ja) | 2015-02-18 |
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