Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
• • 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
• • 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
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/0402—Methods of deposition of the material
  • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
• • 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
• • 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
  • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
• • 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
• • 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
• • 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
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
• • 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
• • 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 slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery.
• Lithium ion secondary batteries are small and light, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, in recent years, improvement of battery members such as electrodes has been studied for the purpose of further improving the performance of lithium ion secondary batteries.
• the silicon-based negative electrode active material has a high theoretical capacity and can increase the battery capacity of the lithium ion secondary battery, it greatly expands and contracts with charge and discharge. Accordingly, in a negative electrode using a silicon-based negative electrode active material, deterioration of the silicon-based negative electrode active material itself (that is, structural destruction of the silicon-based negative electrode active material) due to expansion and contraction of the silicon-based negative electrode active material due to repeated charge / discharge. Miniaturization) and / or destruction of the electrode plate structure, and the conductive path in the electrode is destroyed. That is, a lithium ion secondary battery including a negative electrode using a silicon-based negative electrode active material has a problem in that cycle characteristics deteriorate due to large expansion and contraction of the silicon-based negative electrode active material.
• the above-mentioned conventional technology cannot sufficiently suppress the expansion and contraction of the silicon-based negative electrode active material due to charge / discharge, and it is a high dimension to increase the capacity of the lithium ion secondary battery and suppress the deterioration of the cycle characteristics. It was not possible to achieve both.
• a negative electrode for a lithium ion secondary battery is prepared by applying a negative electrode slurry composition in which a negative electrode active material and a binder are dispersed in a dispersion medium on a current collector and drying the negative electrode active material and It is manufactured by forming a negative electrode composite material layer containing a binder on a current collector.
• the viscosity of the slurry composition for negative electrode is increased when the blending amount or molecular weight of polyacrylic acid is increased in order to suppress the expansion and contraction of the silicon-based negative electrode active material.
• the coating property was lowered due to the increase.
• the present invention can increase the battery capacity while suppressing the expansion and contraction of the silicon-based negative electrode active material that accompanies charge / discharge when used for the formation of the negative electrode, and is a lithium ion secondary that is excellent in coatability. It aims at providing the slurry composition for battery negative electrodes. Moreover, an object of this invention is to provide the negative electrode for lithium ion secondary batteries which can provide the lithium ion secondary battery which has the outstanding battery capacity and cycling characteristics. Another object of the present invention is to provide a lithium ion secondary battery having a high battery capacity and excellent cycle characteristics.
• the present inventor has intensively studied for the purpose of solving the above problems. And this inventor made the ratio of the silicon type negative electrode active material in a negative electrode active material into a predetermined range, and mix
• the slurry composition for a lithium ion secondary battery negative electrode of the present invention comprises a negative electrode active material, polyacrylic acid, and water.
• the negative electrode active material contains a silicon-based negative electrode active material in a proportion of 5% by mass to 40% by mass
• the polyacrylic acid has a viscosity of 1% by mass aqueous solution with respect to the viscosity of the 0.5% by mass aqueous solution.
• the ratio viscosity of 1% by mass aqueous solution / viscosity of 0.5% by mass aqueous solution) is 2.0 or more.
• the polyacrylic acid in which the ratio of the viscosity of the 1% by mass aqueous solution to the viscosity of the 0.5% by mass aqueous solution satisfies the predetermined size, with the negative electrode active material having a silicon-based negative electrode active material content in the predetermined range.
• the battery capacity can be increased while suppressing the expansion and contraction of the silicon-based negative electrode active material.
• the slurry composition is excellent in coatability.
• viscosity of an aqueous solution of polyacrylic acid is a condition of temperature 25 ° C., pH 8, rotor M4, rotation speed 60 rpm in accordance with JIS K7117-1, using a B-type viscometer. It refers to the viscosity of the polyacrylic acid aqueous solution measured below.
• the slurry composition for a lithium ion secondary battery negative electrode of the present invention further contains a carboxymethyl cellulose salt. This is because the storage stability of the slurry composition can be improved by adding carboxymethylcellulose salt.
• the negative electrode for lithium ion secondary batteries of this invention is either of the slurry composition for lithium ion secondary battery negative electrodes mentioned above. It has the negative mix layer obtained by using, It is characterized by the above-mentioned.
• the negative electrode mixture layer formed using the lithium ion secondary battery negative electrode slurry composition expansion and contraction associated with charge and discharge of a silicon-based negative electrode active material having a high theoretical capacity can be suppressed. Therefore, if a negative electrode having the negative electrode composite material layer is used, a lithium ion secondary battery having excellent battery capacity and cycle characteristics can be provided.
• the lithium ion secondary battery of this invention is the negative electrode for lithium ion secondary batteries mentioned above, a positive electrode, electrolyte solution, And a separator.
• a lithium ion secondary battery using the negative electrode for a lithium ion secondary battery has a high battery capacity and excellent cycle characteristics.
• a lithium ion secondary when used for forming a negative electrode, a lithium ion secondary that can increase the battery capacity while suppressing the expansion and contraction of the silicon-based negative electrode active material due to charge / discharge and that is excellent in coatability.
• a slurry composition for a battery negative electrode can be provided.
• the negative electrode for lithium ion secondary batteries which can provide the lithium ion secondary battery which has the outstanding battery capacity and cycling characteristics can be provided.
• a lithium ion secondary battery having a high battery capacity and excellent cycle characteristics can be provided.
• the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention is used for forming a negative electrode of a lithium ion secondary battery.
• the negative electrode for lithium ion secondary batteries of this invention can be manufactured using the slurry composition for lithium ion secondary batteries negative electrode of this invention.
• the lithium ion secondary battery of the present invention is characterized by using the negative electrode for a lithium ion secondary battery of the present invention.
• the lithium ion secondary battery negative electrode slurry composition of the present invention is an aqueous slurry composition containing a negative electrode active material, polyacrylic acid, and water.
• the negative electrode active material of the slurry composition for lithium ion secondary battery negative electrodes of this invention contains a silicon type negative electrode active material in the ratio of 5 to 40 mass%.
• the polyacrylic acid of the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention is a ratio of the viscosity of a 1% by weight aqueous solution to the viscosity of a 0.5% by weight aqueous solution (viscosity of 1% by weight aqueous solution / 0.5% by weight % Aqueous solution) is 2.0 or more.
• the slurry composition for lithium ion secondary battery negative electrodes of this invention may contain other components, such as a carboxymethylcellulose salt and a particulate binder other than a negative electrode active material and polyacrylic acid.
• a negative electrode active material contains a silicon-type negative electrode active material in the ratio of 5 mass% or more, the battery capacity of a lithium ion secondary battery is raised.
• a negative electrode that can be formed can be formed.
• the negative electrode active material contains a silicon-based negative electrode active material in a proportion of 40% by mass or less, and the viscosity ratio of polyacrylic acid (1 (Viscosity of mass% aqueous solution / viscosity of 0.5 mass% aqueous solution) is 2.0 or more, so that when the negative electrode is formed, the decrease in the coating property of the slurry composition is suppressed. Expansion and contraction associated with charging / discharging can be suppressed.
• each component contained in the said slurry composition for lithium ion secondary battery negative electrodes is demonstrated.
• the negative electrode active material is a material that transfers electrons in the negative electrode of the lithium ion secondary battery. And as a negative electrode active material of a lithium ion secondary battery, the substance which can occlude and discharge
• the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention uses a negative electrode active material containing a silicon-based negative electrode active material in order to increase the battery capacity of the lithium ion secondary battery. That is, in the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention, a silicon-based negative electrode active material and another negative electrode active material are used in combination as the negative electrode active material.
• the slurry composition for lithium ion secondary battery negative electrodes of this invention needs the ratio of the silicon type negative electrode active material in a negative electrode active material to be 5 mass% or more and 40 mass% or less. This is because when the ratio of the silicon-based negative electrode active material is less than 5% by mass, the capacity of the lithium ion secondary battery cannot be sufficiently increased. In addition, when the proportion of the silicon-based negative electrode active material is less than 5% by mass, the expansion and contraction of the entire negative electrode is small, so that the cycle characteristics are hardly deteriorated without using in combination with polyacrylic acid described later. When used in combination with acrylic acid, the negative electrode composite material layer becomes too hard and the cycle characteristics of the lithium ion secondary battery may be deteriorated.
• the content ratio of the silicon-based negative electrode active material in the negative electrode active material is 35% by mass or less. It is preferably 30% by mass or less, more preferably 10% by mass or more, and further preferably 20% by mass or more.
• the silicon-based negative electrode active material is an active material containing silicon.
• silicon (Si) an alloy containing silicon, SiO, SiO x , a Si-containing material formed by coating or compounding a Si-containing material with conductive carbon, and conductive carbon. Examples include composites.
• these silicon type negative electrode active materials may be used individually by 1 type, and may be used in combination of 2 types.
• the alloy containing silicon examples include an alloy composition containing silicon and at least one element selected from the group consisting of titanium, iron, cobalt, nickel, and copper.
• the alloy containing silicon examples include an alloy composition containing silicon, aluminum, and a transition metal such as iron, and further containing a rare earth element such as tin and yttrium.
• a rare earth element such as tin and yttrium.
• an alloy containing silicon (A) an amorphous phase containing silicon; (B) a nanocrystalline phase comprising tin, indium, and yttrium, lanthanide elements, actinide elements, or combinations thereof; Of the mixture.
• an alloy containing silicon the following general formula: Si a Al b T c Sn d In e M f Li g [Wherein T is a transition metal, M is yttrium, a lanthanide element, an actinide element, or a combination thereof, and the sum of a + b + c + d + e + f is equal to 1, and 0.35 ⁇ a ⁇ 0.70, 0 .01 ⁇ b ⁇ 0.45, 0.05 ⁇ c ⁇ 0.25, 0.01 ⁇ d ⁇ 0.15, e ⁇ 0.15, 0.02 ⁇ f ⁇ 0.15, 0 ⁇ g ⁇ ⁇ 4.4 ⁇ (a + d + e) + b ⁇ ]
• the alloy composition represented by these is mentioned.
• Such an alloy can be prepared, for example, by a method described in JP2013-65569A, specifically, a melt spinning method.
• SiO x is a compound containing at least one of SiO and SiO 2 and Si, and x is usually 0.01 or more and less than 2. Then, SiO x, for example, can be formed by using a disproportionation reaction of silicon monoxide (SiO). Specifically, SiO x can be prepared by heat-treating SiO, optionally in the presence of a polymer such as polyvinyl alcohol, to produce silicon and silicon dioxide. The heat treatment can be performed at a temperature of 900 ° C. or higher, preferably 1000 ° C. or higher, in an atmosphere containing an organic gas and / or vapor after grinding and mixing SiO and optionally a polymer.
• SiO x can be prepared by heat-treating SiO, optionally in the presence of a polymer such as polyvinyl alcohol, to produce silicon and silicon dioxide. The heat treatment can be performed at a temperature of 900 ° C. or higher, preferably 1000 ° C. or higher, in an atmosphere containing an organic gas and / or
• a composite of Si-containing material and conductive carbon for example, a pulverized mixture of SiO, a polymer such as polyvinyl alcohol, and optionally a carbon material is heat-treated in an atmosphere containing, for example, an organic gas and / or steam.
• an organic gas and / or steam can be mentioned.
• a method of coating the surface of the SiO particles by a chemical vapor deposition method using an organic gas a method of forming composite particles (granulation) of the SiO particles and graphite or artificial graphite by a mechanochemical method, etc. It can also be obtained by a known method.
• the silicon-based negative electrode active material is preferably an alloy containing silicon and SiO x .
• Examples of the negative electrode active material used in combination with the silicon negative electrode active material in the slurry composition for a negative electrode of the lithium ion secondary battery of the present invention include a carbon negative electrode active material and a metal negative electrode active material.
• the carbon-based negative electrode active material refers to an active material having carbon as a main skeleton capable of inserting lithium (also referred to as “dope”).
• examples of the carbon-based negative electrode active material include carbonaceous materials and graphite. Quality materials.
• the carbonaceous material is a material having a low degree of graphitization (ie, low crystallinity) obtained by carbonizing a carbon precursor by heat treatment at 2000 ° C. or lower.
• the minimum of the heat processing temperature at the time of carbonizing is not specifically limited, For example, it can be 500 degreeC or more.
• the carbonaceous material include graphitizable carbon that easily changes the carbon structure depending on the heat treatment temperature, and non-graphitizable carbon having a structure close to an amorphous structure typified by glassy carbon.
• the graphitizable carbon for example, a carbon material using tar pitch obtained from petroleum or coal as a raw material can be mentioned.
• examples of the non-graphitizable carbon include a phenol resin fired body, polyacrylonitrile-based carbon fiber, pseudo-isotropic carbon, furfuryl alcohol resin fired body (PFA), and hard carbon.
• the graphite material is a material having high crystallinity close to that of graphite obtained by heat-treating graphitizable carbon at 2000 ° C. or higher.
• the upper limit of heat processing temperature is not specifically limited, For example, it can be 5000 degrees C or less.
• the graphite material include natural graphite and artificial graphite.
• the artificial graphite for example, artificial graphite obtained by heat-treating carbon containing graphitizable carbon mainly at 2800 ° C. or higher, graphitized MCMB heat-treated at 2000 ° C. or higher, and mesophase pitch-based carbon fiber at 2000 ° C. Examples thereof include graphitized mesophase pitch-based carbon fibers that have been heat-treated.
• the metal-based negative electrode active material is an active material containing a metal, and usually contains an element capable of inserting lithium in the structure, and the theoretical electric capacity per unit mass when lithium is inserted is 500 mAh / g or more. Is an active material.
• the metal-based negative electrode active material include simple metals other than Si that can form lithium metal and lithium alloys (for example, Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, and Sb). , Sn, Sr, Zn, Ti, etc.) and alloys thereof, and oxides, sulfides, nitrides, carbides, phosphides, and the like thereof.
• the negative electrode active material is preferably a mixture of a silicon-based negative electrode active material and a carbon-based negative electrode active material such as artificial graphite.
• polyacrylic acid binds each component in the negative electrode mixture layer or each component and the current collector. At the same time, the expansion and contraction of the negative electrode active material accompanying charge / discharge are suppressed. That is, polyacrylic acid functions as a binder in the negative electrode mixture layer and breaks the conductive path due to the large expansion and contraction of the silicon negative electrode active material accompanying charge / discharge (structure of the silicon negative electrode active material). The reduction in cycle characteristics of the lithium ion secondary battery is suppressed by preventing miniaturization due to destruction and / or destruction of the electrode plate structure).
• the polyacrylic acid used for the slurry composition for lithium ion secondary battery negative electrodes of this invention is ratio of the viscosity of 1 mass% aqueous solution with respect to the viscosity of 0.5 mass% aqueous solution (viscosity of 1 mass% aqueous solution / 0.5
• the viscosity of the mass% aqueous solution needs to be 2.0 or more.
• Polyacrylic acid having a ratio of the viscosity of the 1% by mass aqueous solution to the viscosity of the 0.5% by mass aqueous solution (hereinafter sometimes simply referred to as “viscosity ratio”) of 2.0 or more is a condition where the polyacrylic acid concentration is low.
• the slurry composition for negative electrode containing polyacrylic acid having a viscosity ratio of 2.0 or more has low viscosity and good coatability in the state of the slurry composition having a low polyacrylic acid concentration.
• the negative electrode mixture layer is formed by drying the slurry composition for negative electrode. High strength is exhibited in the composite layer, and the expansion and contraction of the negative electrode active material (particularly, the silicon-based negative electrode active material) is suppressed.
• the viscosity ratio is preferably 3.0 or more, more preferably 6.0 or less, and still more preferably 4.5 or less.
• the reasons for focusing on the viscosity of the 1% by mass aqueous solution and the viscosity of the 0.5% by mass aqueous solution are as follows. That is, when the concentration of the aqueous solution is less than 0.5% by mass, the measured value of the viscosity varies greatly. In addition, since polyacrylic acid having a viscosity ratio of 2.0 or more usually does not have high solubility in water, an aqueous solution having a concentration of more than 1% by mass may not be prepared.
• the viscosity of 0.5 mass% aqueous solution of polyacrylic acid is 0.3 Pa.s or more and 10.0 Pa.s or less. It is because there exists a possibility that the applicability
• the viscosity of the 1.0 mass% polyacrylic acid aqueous solution is 0.6 Pa.s or more and 15.0 Pa.s or less. It is because there exists a possibility that the applicability
• the polyacrylic acid having the above-described viscosity property is not particularly limited, and can be obtained by copolymerizing acrylic acid or a salt thereof, a crosslinkable monomer, and optionally another polymerizable monomer.
• Cross-linked polyacrylic acid can be mentioned.
• 70 mass% or more of the whole monomer used for manufacture of a copolymer is acrylic acid or its salt.
• the amount of the crosslinkable monomer used for the production of the crosslinkable polyacrylic acid is 2.0 parts by mass or less with respect to 100 parts by mass of the total amount of monomers other than the crosslinkable monomer. Preferably, it is 1.0 mass part or less.
• acrylic acid or a salt thereof examples include acrylic acid and alkali metal salts such as sodium salt and potassium salt or ammonium salt thereof. These may be used alone or in combination of two or more.
• crosslinkable monomer examples include polyalkenyl polyether monomers and polyvalent vinyl monomers. Specifically, tetraallyloxyethane, pentaerythritol tetraallyl ether, pentaerythritol triallyl ether, pentaerythritol diallyl ether, allyl saccharose, trimethylolpropane diallyl ether, trimethylolpropane triallyl ether, ethylene glycol diallyl ether, glyceryl diallyl Examples include ether, glyceryl triallyl ether, triallyl isocyanurate, allyl acrylate, allyl methacrylate, diallyl phthalate, ethylene glycol diacrylate, polyethylene glycol diacrylate, ethylene glycol dimethacrylate, and polyethylene glycol dimethacrylate.
• crosslinkable monomer ethylene glycol dimethacrylate, tetraallyloxyethane, and pentaerythritol triallyl ether are preferable.
• Examples of other polymerizable monomers include styrene, alkyl vinyl ether, vinylidene chloride, acrylic acid esters, methacrylic acid esters, acrylamides, methacrylamides, N-vinylformamide, N-vinylacetamide, vinyl acetate, Examples include vinyl pyrrolidone, acrylonitrile, and methacrylonitrile. These may be used alone or in combination of two or more.
• acrylic esters and methacrylic esters include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, (meth) acrylic.
• (Meth) acrylic acid alkyl esters such as octyl acid;
• (meth) acrylic acid esters having an ether bond such as 2-methoxyethyl acrylate and 2-ethoxyethyl acrylate; 2-hydroxyethyl acrylate and 2-hydroxypropyl methacrylate Hydroxy group-containing (meth) acrylic acid esters; glycidyl methacrylate and the like.
• acrylamides and methacrylamides examples include acrylamide, methacrylamide, dimethylacrylamide, diethylacrylamide, dimethylaminopropylacrylamide and the like.
• macromonomers such as terminal methacrylate polymethyl methacrylate, terminal styryl polymethyl methacrylate, terminal methacrylate polystyrene, terminal methacrylate polyethylene glycol, and terminal methacrylate acrylonitrile styrene copolymer can be used. is there.
• esters such as maleic acid, fumaric acid and itaconic acid can be used, and trimethoxyvinylsilane, triethoxyvinylsilane, ⁇ -methacryloxypropyltrimethoxysilane and the like can also be used. Can be mentioned. These may be used alone or in combination of two or more.
• acrylamides are preferable, and acrylamide is more preferable.
• (meth) acryl means acryl and / or methacryl.
• the above-mentioned cross-linked polyacrylic acid can be produced by using a general radical polymerization initiator and copolymerizing the above-described monomers.
• the copolymerization is not particularly limited, and can be performed using a precipitation polymerization method in an organic solvent in which the monomer is dissolved but the polymer is not dissolved.
• the radical polymerization initiator a compound selected from peroxides, azo initiators, and the like, or a mixture thereof can be used.
• the cross-linked polyacrylic acid as the polyacrylic acid having the above-mentioned viscosity property can also be produced by mixing and reacting uncrosslinked polyacrylic acid and a cross-linking agent.
• a specific production method for example, an aqueous solution of uncrosslinked polyacrylic acid is prepared, and a crosslinking agent capable of crosslinking polyacrylic acid is added thereto to add uncrosslinked polyacrylic acid and a crosslinking agent. The method of making it react is mentioned.
• Uncrosslinked polyacrylic acid can be obtained by polymerizing acrylic acid or a salt thereof and optionally another polymerizable monomer by a known method.
• acrylic acid or salt thereof and “other polymerizable monomer”
• the above-mentioned “acrylic acid or salt thereof” and “other polymerizable monomer” can be used.
• the number average molecular weight is 200,000 or more from the viewpoint of being excellent in dispersibility of the negative electrode active material and capable of suppressing precipitation and further improving the cycle characteristics of the lithium ion secondary battery.
• Those having a number average molecular weight of 300,000 or more and 2 million or less are more preferable, and those having a number average molecular weight of 500,000 or more and 1,500,000 or less are particularly preferable.
• “number average molecular weight” can be calculated
• the ratio of uncrosslinked polyacrylic acid in the aqueous solution of uncrosslinked polyacrylic acid is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and preferably 10% by mass. Less than, more preferably less than 5% by mass.
• Crosslinking agent examples include polyfunctional epoxy compounds, oxazoline compounds, and carbodiimide compounds.
• a polyfunctional epoxy compound is a compound having two or more epoxy groups in one molecule. And as a polyfunctional epoxy compound, the compound which has an epoxy group preferably in less than 6 in a molecule
• polyfunctional epoxy compound for example, polyfunctional glycidyl ether compounds such as aliphatic polyglycidyl ether, aromatic polyglycidyl ether, and diglycidyl ether are preferable.
• the oxazoline compound is not particularly limited as long as it has two or more oxazoline groups.
• 2,2′-bis (2-oxazoline), 2,2′-bis (4-methyl-) is used.
• 2,2′-bis (2-oxazoline) is preferable from the
• Suitable examples include polycarbodiimides and / or modified polycarbodiimides having a repeating unit represented by the formula:
• the modified polycarbodiimide refers to a resin obtained by reacting a reactive compound with polycarbodiimide.
• the reactive compound one group having reactivity with polycarbodiimide (a group having an active hydrogen such as a carboxyl group or a primary or secondary amino group), and another functional group
• examples of such carbodiimide compounds include SV-02, V-02 manufactured by Nisshinbo Chemical.
• the crosslinking agent it is preferable to use an oxazoline compound or a carbodiimide compound from the viewpoint of allowing the crosslinking reaction to proceed uniformly throughout the system.
• the amount of the crosslinking agent in the case of mixing and reacting the uncrosslinked polyacrylic acid and the crosslinking agent is preferably 0.1 parts by mass or more, more preferably, 100 parts by mass of the uncrosslinked polyacrylic acid. Is 0.5 parts by mass or more, preferably 10 parts by mass or less, more preferably 5 parts by mass or less. If the amount of the crosslinking agent is too small, the cycle characteristics of the resulting lithium ion secondary battery may be deteriorated. If the amount is too large, undissolved gel may remain when slurried and the negative electrode may be cracked. Because there is.
• the viscosity ratio of the crosslinked polyacrylic acid obtained as described above, the viscosity of the 0.5 mass% aqueous solution, and the viscosity of the 1.0 mass% aqueous solution are, for example, the crosslinking density and crosslinking of the crosslinked polyacrylic acid. It can be adjusted by changing the distance between points. Specifically, for example, the viscosity ratio of cross-linked polyacrylic acid can be improved by increasing the cross-linking density by increasing the amount of cross-linkable monomer or cross-linking agent used.
• the water absorption of the polyacrylic acid present in the negative electrode mixture layer prepared using the slurry composition for negative electrodes is increased. Can be lowered. As a result, it is possible to reduce hydrogen fluoride produced by the reaction between the electrolyte and the water in the negative electrode mixture layer when forming a lithium ion secondary battery, so that internal resistance, water absorption and gas generation amount Can be obtained.
• the polyacrylic acid may be a polyacrylate. This is because when at least a part of the carboxyl group is neutralized, the molecular chain of polyacrylic acid is likely to spread, and the expansion and contraction of the negative electrode active material accompanying charge / discharge are easily suppressed.
• the salt used for neutralization of polyacrylic acid is not particularly limited.
• a monovalent base is preferable from the viewpoint of easily spreading the molecular chain of polyacrylic acid, and examples thereof include sodium hydroxide and lithium hydroxide.
• lithium hydroxide is preferable from the viewpoint of the characteristics of the lithium ion secondary battery.
• the degree of neutralization of the polyacrylic acid is preferably 0.4 or more and 1.0 or less, and 0.7 or more and 1.0 or less. More preferably.
• the degree of neutralization of polyacrylic acid is preferably 0.4 or more and 1.0 or less, and 0.7 or more and 1.0 or less. More preferably it is.
• the degree of neutralization can be measured according to the following method for measuring the degree of neutralization. [[Method for measuring degree of neutralization]]
• the target neutralization degree is calculated from the value measured by the method according to JIS K0113-1997.
• the method according to JIS K0113-1997 is a method in which a 0.1N potassium hydroxide aqueous solution is used as a titrant to perform potentiometric titration and the end point is determined by an inflection point method.
• the neutralization degree of acrylic acid (number of moles of acrylate after neutralization ⁇ acrylic before neutralization)
• the degree of neutralization can also be determined from the number of moles of acid.
• the slurry composition for a lithium ion secondary battery negative electrode of the present invention preferably contains polyacrylic acid in a proportion of 0.5 parts by mass or more per 100 parts by mass of the negative electrode active material. More preferably, it is contained at a rate of 10 parts by mass or less, more preferably at a rate of 5 parts by mass or less, particularly preferably at a rate of 3 parts by mass or less, Most preferably, it is contained in a proportion of 2 parts by mass or less.
• the content of polyacrylic acid per 100 parts by mass of the negative electrode active material is 0.5 parts by mass or more, the expansion and contraction of the negative electrode active material (particularly, the silicon-based negative electrode active material) accompanying charge / discharge is sufficiently suppressed. be able to.
• content of polyacrylic acid is 10 mass parts or less, it can fully suppress that the viscosity of a slurry composition rises and coating property falls.
• the slurry composition for a lithium ion secondary battery negative electrode of the present invention preferably contains a carboxymethyl cellulose salt.
• a carboxymethyl cellulose salt By using polyacrylic acid and carboxymethylcellulose salt in combination, the dispersibility of the negative electrode active material and the like can be improved, and the storage stability of the negative electrode slurry composition can be improved.
• carboxymethyl cellulose salt is not particularly limited, and a sodium salt or ammonium salt of carboxymethyl cellulose can be used.
• the viscosity of a 1% by mass aqueous solution of carboxymethyl cellulose salt is preferably 1.0 Pa ⁇ s or more.
• the viscosity of a 1% by mass aqueous solution of carboxymethyl cellulose salt is preferably 12 Pa ⁇ s or less, and preferably 10 Pa ⁇ s. More preferably, it is as follows.
• the content of the carboxymethyl cellulose salt is preferably 0.1 to 9 times the content of polyacrylic acid, The content is more preferably 0.25 to 4 times the content, and still more preferably 0.25 to 2.3 times the polyacrylic acid content.
• the content of the carboxymethyl cellulose salt is within the above range, it is possible to further suppress the expansion and contraction of the negative electrode active material accompanying charge / discharge while sufficiently increasing the storage stability of the slurry composition for negative electrode.
• the slurry composition for a lithium ion secondary battery negative electrode of the present invention preferably contains a particulate binder.
• the particulate binder is composed of the components in the negative electrode mixture layer together with the polyacrylic acid described above. Alternatively, each component and the current collector are bound. Therefore, if a particulate binder is blended with the slurry composition for a negative electrode of a lithium ion secondary battery, the binding properties between the components in the negative electrode mixture layer or between each component and the current collector can be further improved.
• a polymer such as a conjugated diene polymer or an acrylic polymer can be used as the particulate binder described above.
• An acrylic polymer is a polymer containing a (meth) acrylic acid ester monomer unit.
• the acrylic polymer includes a carboxyl group-containing monomer unit, an ⁇ , ⁇ -unsaturated nitrile monomer unit, and any other monomer unit. May be included.
• “comprising a monomer unit” means “a monomer-derived structural unit is contained in a polymer obtained using the monomer”.
• (meth) acrylic acid ester monomers that can be used for the production of acrylic polymers include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, and t-butyl acrylate.
• Alkyl acrylates such as pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate , Hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, etc.
• acid alkyl esters Such as acid alkyl esters.
• the ratio of the (meth) acrylic acid ester monomer unit in the acrylic polymer is preferably 50% by mass or more, more preferably 55% by mass or more, particularly preferably 58% by mass or more, and preferably 98% by mass. % Or less, more preferably 97% by mass or less, particularly preferably 96% by mass or less.
• Examples of the carboxyl group-containing monomer that can be used for the production of the acrylic polymer include ethylenically unsaturated monocarboxylic acid and derivatives thereof, ethylenically unsaturated dicarboxylic acid and acid anhydrides thereof, and derivatives thereof. It is done.
• Examples of the ethylenically unsaturated monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid and the like.
• Examples of the ethylenically unsaturated monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, ⁇ -acetoxyacrylic acid, ⁇ -trans-aryloxyacrylic acid, ⁇ -chloro- ⁇ -E-methoxyacrylic.
• Acid ⁇ -diaminoacrylic acid and the like.
• ethylenically unsaturated dicarboxylic acid examples include maleic acid, fumaric acid, itaconic acid and the like.
• acid anhydrides of ethylenically unsaturated dicarboxylic acids include maleic anhydride, diacrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, and the like.
• examples of ethylenically unsaturated dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, diphenyl maleate, nonyl maleate, decyl maleate , Dodecyl maleate, octadecyl maleate, fluoroalkyl maleate and the like. These may be used alone or in combination of two or more.
• the ratio of the carboxyl group-containing monomer unit in the acrylic polymer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, preferably 10% by mass or less, more preferably 5%. It is below mass%.
• Examples of the ⁇ , ⁇ -unsaturated nitrile monomer that can be used in the production of the acrylic polymer include acrylonitrile and methacrylonitrile. These may be used alone or in combination of two or more.
• the proportion of ⁇ , ⁇ -unsaturated nitrile monomer units in the acrylic polymer is preferably 1% by mass or more, more preferably 2% by mass or more, preferably 50% by mass or less, more preferably 35%. It is below mass%.
• the monomer copolymerizable with the monomer mentioned above is mentioned.
• the optional monomers include hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.
• Crosslinkable monomer crosslinkable monomer: Styrene such as styrene, chlorostyrene, vinyltoluene, t-butylstyrene, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, ⁇ -methylstyrene, divinylbenzene Monomers; ethylene, propylene, etc.
• diene monomers such as butadiene and isoprene
• halogen atom-containing monomers such as vinyl chloride and vinylidene chloride
• vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate
• methyl vinyl ether vinyl ethers
• Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone and isopropenyl vinyl ketone
• Heterocycles such as N-vinyl pyrrolidone, vinyl pyridine and vinyl imidazole -Containing vinyl compounds
• amino group-containing monomers such as aminoethyl vinyl ether and dimethylaminoethyl vinyl ether; These may be used alone or in combination of two or more.
• the ratio of the arbitrary monomer unit in the acrylic polymer is not particularly limited, but is preferably 10% by mass or less, more preferably 8% by mass or less, and more preferably 0.5% by mass or more in total amount. Is preferable, and 1.0 mass% or more is more preferable.
• the method for producing the acrylic polymer 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 may be used.
• a solution polymerization method a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method
• addition polymerization such as ionic polymerization, radical polymerization, and living radical polymerization can be used.
• the conjugated diene polymer is a polymer containing a conjugated diene monomer unit, and includes hydrogenated products thereof.
• Specific examples of conjugated diene polymers include aliphatic conjugated diene polymers such as polybutadiene and polyisoprene; aromatic vinyl / aliphatic conjugated diene copolymers such as styrene / butadiene copolymer (SBR); acrylonitrile / butadiene.
• Examples include vinyl cyanide / conjugated diene copolymers such as copolymers (NBR); hydrogenated SBR, hydrogenated NBR, and the like.
• NBR copolymers
• aromatic vinyl monomer, aliphatic conjugated diene monomer, carboxyl group-containing monomer, hydroxyl group-containing used for the production of aromatic vinyl / aliphatic conjugated diene copolymer preferred as conjugated diene polymer Monomers and other optional monomers will be described in detail.
• examples of the aromatic vinyl monomer that can be used for the production of the aromatic vinyl / aliphatic conjugated diene copolymer include styrene, ⁇ -methylstyrene, vinyltoluene, and divinylbenzene. These may be used alone or in combination of two or more.
• the ratio of the aromatic vinyl monomer unit in the aromatic vinyl / aliphatic conjugated diene copolymer is preferably 30% by mass or more, more preferably 35% by mass or more, and preferably 79.5% by mass or less. More preferably, it is 69 mass% or less.
• Examples of the aliphatic conjugated diene monomer that can be used in the production of the aromatic vinyl / aliphatic conjugated diene copolymer include 1,3-butadiene, 2-methyl-1,3-butadiene, and 2,3-dimethyl-1. , 3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like. These may be used alone or in combination of two or more.
• the ratio of the aliphatic conjugated diene monomer unit in the aromatic vinyl / aliphatic conjugated diene copolymer is preferably 20% by mass or more, more preferably 30% by mass or more, and preferably 70% by mass or less. More preferably, it is 60 mass% or less, Most preferably, it is 55 mass% or less.
• Examples of the carboxyl group-containing monomer that can be used for the production of the aromatic vinyl / aliphatic conjugated diene copolymer include those similar to those mentioned above that can be used for the production of the acrylic polymer. It is done.
• the ratio of the carboxyl group-containing monomer unit in the aromatic vinyl / aliphatic conjugated diene copolymer is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and preferably 10% by mass. % Or less, more preferably 8% by mass or less.
• the ratio of the hydroxyl group-containing monomer unit in the aromatic vinyl / aliphatic conjugated diene copolymer is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and preferably 10% by mass. % Or less, more preferably 8% by mass or less.
• the monomer copolymerizable with the monomer mentioned above is mentioned.
• the optional monomer from the above-mentioned acrylic polymers, those that can be used as other monomers, aromatic vinyl monomers, aliphatic conjugated diene monomers And those other than those corresponding to the hydroxyl group-containing monomer, and ⁇ , ⁇ -unsaturated nitrile monomers can be used. These other monomers may be used alone or in combination of two or more.
• the proportion of any monomer unit in the aromatic vinyl / aliphatic conjugated diene copolymer is not particularly limited, but is preferably 10% by mass or less, more preferably 8% by mass or less in total. 0.5 mass% or more is preferable, and 1.0 mass% or more is more preferable.
• the production method of the conjugated diene polymer 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 may be used.
• a solution polymerization method a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method
• addition polymerization such as ionic polymerization, radical polymerization, and living radical polymerization can be used.
• the slurry composition for lithium ion secondary battery negative electrodes of this invention contains a particulate binder in the ratio of 4 mass parts or more per 100 mass parts of polyacrylic acid, and is 20 mass parts or less. It is preferable to contain in a ratio, and it is still more preferable to contain in the ratio of 10 mass parts or less. If the content of the particulate binder per 100 parts by mass of polyacrylic acid is 4 parts by mass or more, the binding property is sufficiently increased, and the powder falling off from the negative electrode produced using the negative electrode slurry composition Occurrence can be suppressed.
• the content of the particulate binder per 100 parts by mass of polyacrylic acid is 20 It is preferable to set it as a mass part or less.
• the amount of the particulate binder is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more per 100 parts by mass of the negative electrode active material. 1.0 mass part or less, preferably 0.6 mass part or less, more preferably 0.5 mass part or less.
• the particulate binder preferably has a gel content of 50% by mass or more, more preferably 80% by mass or more, preferably 98% by mass or less, more preferably 95% by mass or less.
• the gel content of the particulate binder is less than 50% by mass, the cohesive force of the particulate binder may be reduced, and the adhesion strength with the current collector or the like may be insufficient.
• the gel content of the particulate binder is more than 98% by mass, the particulate binder may lose toughness and become brittle, resulting in insufficient adhesion strength.
• the “gel content” of the particulate binder can be measured using the measuring method described in the examples of the present specification.
• the particulate binder has a glass transition temperature (Tg) of preferably ⁇ 30 ° C. or higher, more preferably ⁇ 20 ° C. or higher, preferably 80 ° C. or lower, more preferably 30 ° C. or lower.
• Tg glass transition temperature
• the components in the slurry composition for secondary battery negative electrode are prevented from aggregating and settling, and the stability of the slurry composition is ensured. be able to.
• the glass transition temperature of a particulate-form binder is 80 degrees C or less.
• the “glass transition temperature (Tg)” of the particulate binder can be measured using the measuring method described in the examples of the present specification.
• the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention may contain components such as a conductive material, a reinforcing material, a leveling agent, and an electrolytic solution additive in addition to the above components. These are not particularly limited as long as they do not affect the battery reaction, and known ones such as those described in International Publication No. 2012/115096 can be used. These components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
• the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention can be prepared by dispersing each of the above components in an aqueous medium as a dispersion medium. Specifically, the above components and the aqueous medium are mixed using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a grinder, an ultrasonic disperser, a homogenizer, a planetary mixer, or a fill mix. Thus, a slurry composition can be prepared.
• water is usually used as the aqueous medium, but an aqueous solution of an arbitrary compound or a mixed solution of a small amount of an organic medium and water may be used.
• the negative electrode for lithium ion secondary batteries of this invention can be manufactured using the slurry composition for negative electrodes of lithium ion secondary batteries of this invention.
• the negative electrode for a lithium ion secondary battery of the present invention includes a current collector and a negative electrode mixture layer formed on the current collector, and the negative electrode mixture layer includes at least a negative electrode active material, Contains polyacrylic acid.
• each component contained in the negative electrode composite material layer was contained in the slurry composition for a lithium ion secondary battery negative electrode of the present invention, and a suitable abundance ratio of each of these components is It is the same as the suitable abundance ratio of each component in the slurry composition for use.
• the negative electrode mixture layer contains the above-described negative electrode active material containing a silicon-based negative electrode active material and the above-described polyacrylic acid.
• the battery capacity can be improved while preventing the deterioration of the cycle characteristics of the battery.
• the negative electrode for a lithium ion secondary battery of the present invention is applied, for example, to a step of applying the above-described slurry composition for a negative electrode of a lithium ion secondary battery on a current collector (application step), and a current collector.
• the lithium ion secondary battery negative electrode slurry composition is dried to form a negative electrode mixture layer on the current collector (drying step).
• a method for applying the slurry composition for a lithium ion secondary battery negative electrode on the current collector is not particularly limited, and a known method can be used. Specifically, as a coating method, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, or the like can be used. At this time, the slurry composition for negative electrode may be applied only to one side of the current collector, or may be applied to both sides.
• the thickness of the slurry film on the current collector after coating and before drying can be appropriately set according to the thickness of the negative electrode mixture layer obtained by drying.
• the thickness of the negative electrode mixture layer can be preferably 1 to 200 ⁇ m, more preferably 3 to 100 ⁇ m.
• the current collector to which the slurry composition for negative electrode is applied a material having electrical conductivity and electrochemical durability is used.
• a current collector made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like can be used.
• a copper foil is particularly preferable as the current collector used for the negative electrode.
• the said material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
• a method for drying the slurry composition for the negative electrode on the current collector is not particularly limited, and a known method can be used, for example, drying with hot air, hot air, low-humidity air, vacuum drying, infrared rays, electron beam, etc. The drying method by irradiation is mentioned.
• a negative electrode mixture layer is formed on the current collector, and the negative electrode for a lithium ion secondary battery comprising the current collector and the negative electrode mixture layer Can be obtained.
• the negative electrode mixture layer may be subjected to pressure treatment using a die press or a roll press. By the pressure treatment, the adhesion between the negative electrode mixture layer and the current collector can be improved. Furthermore, when the negative electrode mixture layer contains a curable polymer, the polymer is preferably cured after the formation of the negative electrode mixture layer.
• the lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolytic solution, and a separator, and the negative electrode for a lithium ion secondary battery of the present invention is used as the negative electrode. And since the lithium ion secondary battery of this invention uses the negative electrode for lithium ion secondary batteries of this invention, its battery capacity is high and it is excellent in cycling characteristics.
• a positive electrode of a lithium ion secondary battery As a positive electrode of a lithium ion secondary battery, a known positive electrode used as a positive electrode for a lithium ion secondary battery can be used. Specifically, as the positive electrode, for example, a positive electrode formed by forming a positive electrode mixture layer on a current collector can be used. As the current collector, one made of a metal material such as aluminum can be used. As the positive electrode mixture layer, a layer containing a known positive electrode active material, a conductive material, and a binder can be used.
• an electrolytic solution in which an electrolyte is dissolved in a solvent can be used.
• the solvent an organic solvent capable of dissolving the electrolyte can be used.
• the solvent include alkyl carbonate solvents such as ethylene carbonate, propylene carbonate, and ⁇ -butyrolactone, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl acetate, dimethoxyethane. , Dioxolane, methyl propionate, methyl formate and the like can be used.
• a lithium salt can be used as the electrolyte.
• the lithium salt for example, those described in JP 2012-204303 A can be used.
• LiPF 6 , LiClO 4 , and CF 3 SO 3 Li are preferable as the electrolyte because they are easily dissolved in an organic solvent and exhibit a high degree of dissociation.
• ⁇ Separator> As the separator, for example, those described in JP 2012-204303 A can be used. Among these, the thickness of the separator as a whole can be reduced, thereby increasing the ratio of the electrode active material in the lithium ion secondary battery and increasing the capacity per volume.
• a microporous film made of a series resin polyethylene, polypropylene, polybutene, polyvinyl chloride is preferred.
• a positive electrode and a negative electrode are overlapped via a separator, and this is wound into a battery container according to the battery shape as necessary, and placed in the battery container. It can manufacture by inject
• an overcurrent prevention element such as a fuse or a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary.
• the shape of the lithium ion secondary battery may be any of, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.
• ⁇ Viscosity ratio> About 0.5 mass% aqueous solution and 1.0 mass% aqueous solution of polyacrylic acid, using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., TVB-10M), temperature 25 ° C., pH 8.0, rotation speed 60 rpm The viscosity at (rotor: M4) was measured according to JIS K7117-1. Then, the viscosity ratio ( viscosity of 1 mass% aqueous solution / viscosity of 0.5 mass% aqueous solution) was calculated. The pH was adjusted using sodium hydroxide or lithium hydroxide.
• ⁇ Glass transition temperature> The aqueous dispersion containing the particulate binder was dried for 3 days in an environment of 50% humidity and a temperature of 23 to 26 ° C. to obtain a film having a thickness of 1 ⁇ 0.3 mm. This film was dried with a vacuum dryer at a temperature of 60 ° C. for 10 hours. Then, using the dried film as a sample, in accordance with JIS K7121, measurement temperature: ⁇ 100 ° C. to 180 ° C., temperature increase rate: 5 ° C./min, a differential scanning calorimeter (DSC6220SII, manufactured by Nanotechnology, Inc.) ) was used to measure the glass transition temperature.
• DSC6220SII differential scanning calorimeter
• ⁇ Gel content> An aqueous dispersion containing a particulate binder was prepared, and the aqueous dispersion was dried in an environment of 50% humidity and a temperature of 23 to 25 ° C. to form a film having a thickness of 1 ⁇ 0.3 mm. This film was dried with a vacuum dryer at a temperature of 60 ° C. for 10 hours. Thereafter, the dried film was cut into 3 to 5 mm square, and about 1 g was precisely weighed. The mass of the film piece obtained by cutting is defined as w0. This film piece was immersed in 50 g of tetrahydrofuran (THF) for 24 hours.
• THF tetrahydrofuran
• Gel content (mass%) (w1 / w0) ⁇ 100 ⁇ Smoothness of negative electrode>
• the coating amount was measured at 10 points every 10 mm in the length direction.
• the difference between the minimum value and the maximum value of the 10 measured values was evaluated according to the following criteria. It shows that the coating property of the slurry composition for negative electrodes used for formation of a negative electrode is excellent, so that a difference is small.
• Powder fall residual rate is 99.98% or more
• B Powder fall residual rate is 99.96% or more and less than 99.98%
• C Powder fall residual rate is less than 99.96% ⁇ Design capacity of negative electrode> The mass average theoretical capacity (mAh / g) of the used negative electrode active material was calculated and evaluated according to the following criteria.
• Theoretical capacity exceeds 800 mAh / g
• C Theoretical capacity is 470 mAh / g or less ⁇ Initial efficiency>
• the laminated cell type lithium ion secondary battery thus prepared was allowed to stand at 25 ° C. for 5 hours after electrolyte injection, and then subjected to a cell voltage of 3.C under the condition of 25 ° C. by a constant current method of 0.2C.
• the battery was charged to 65 V (the charge amount is defined as “C1 (mAh)”). Thereafter, an aging treatment is performed at a temperature of 60 ° C.
• Initial efficiency ⁇ (D1 + D2) / (C1 + C2) ⁇ ⁇ 100 (%) A: Initial efficiency is 88% or more B: Initial efficiency is 85% or more and less than 88% C: Initial efficiency is 81% or more and less than 85% D: Initial efficiency is less than 81% ⁇ Cycle characteristics>
• the lithium ion secondary battery used in the evaluation of the initial efficiency was discharged to a cell voltage of 2.75 V by a constant current method of 0.1 C under the condition of a temperature of 25 ° C. Thereafter, 100 cycles of charge / discharge operation were performed at a charge / discharge rate of charge voltage 4.2V, discharge voltage 2.75V, and 0.5C under the condition of a temperature of 45 ° C.
• ⁇ C ′ (X2 / X1) ⁇ 100 (%). Evaluation was made according to the following criteria. The higher the value of the capacity change rate ⁇ C ′, the better the cycle characteristics. A: ⁇ C ′ is 85% or more B: ⁇ C ′ is 83% or more and less than 85% C: ⁇ C ′ is 80% or more and less than 83% D: ⁇ C ′ is less than 80%
• Example 1 ⁇ Preparation of negative electrode active material> Artificial graphite (manufactured by Hitachi Chemical, theoretical capacity: 360 mAh / g) as a carbon-based negative electrode active material and SiO x (manufactured by Shin-Etsu Chemical, theoretical capacity: 2300 mAh / g) as a silicon-based negative electrode active material were prepared.
• ⁇ Preparation of particulate binder> In a 5 MPa pressure vessel equipped with a stirrer, 62 parts of styrene as an aromatic vinyl monomer, 35 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 2 parts of itaconic acid as a carboxyl group-containing monomer, and a hydroxyl group-containing monomer 1 part of 2-hydroxyethyl acrylate (2-hydroxyethyl acrylate) as a monomer, 0.3 part of t-dodecyl mercaptan as a molecular weight regulator, 5 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water as a solvent And 1 part of potassium persulfate was added as a polymerization initiator, and after sufficiently stirring, the mixture was heated to 55 ° C.
• the reaction was stopped by cooling.
• the aqueous dispersion containing the polymer thus obtained was adjusted to pH 8 by adding a 5% aqueous sodium hydroxide solution.
• the unreacted monomer was removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion of the particulate binder.
• the gel content and glass transition temperature were measured by the methods described above. As a result of the measurement, the gel content was 92% and the glass transition temperature (Tg) was 10 ° C.
• ⁇ Preparation of slurry composition for negative electrode of lithium ion secondary battery> 90 parts of artificial graphite as a carbon-based negative electrode active material, 10 parts of SiO x (manufactured by Shin-Etsu Chemical) as a silicon-based negative electrode active material, cross-linked sodium polyacrylate (manufactured by Toagosei Co., Ltd., Rhegic 260H) 1 part by weight of a 1% by weight aqueous solution of 1.5 parts by weight, and 1.5 parts by weight of a 1% by weight aqueous solution of a carboxymethyl cellulose salt (MAC800LC, Nippon Paper Chemicals, sodium salt of carboxymethyl cellulose) in a solid content.
• MAC800LC carboxymethyl cellulose salt
• the obtained negative electrode raw material was pressed with a roll press so that the density was 1.63 to 1.67 g / cm 3, and further, under vacuum conditions for the purpose of removing moisture and further promoting crosslinking.
• the negative electrode was obtained by placing in an environment of 120 ° C. for 10 hours. About the obtained negative electrode, smoothness and dust-proof property were evaluated. The results are shown in Table 1.
• the obtained slurry composition for a lithium ion secondary battery positive electrode was applied with a comma coater onto an aluminum foil having a thickness of 20 ⁇ m so that the amount applied was 30.5 to 31.5 mg / cm 2 . Thereafter, the aluminum foil coated with the slurry composition for a positive electrode of a lithium ion secondary battery was dried by conveying it in an oven at a temperature of 60 ° C. at a rate of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a positive electrode raw material. The obtained positive electrode raw material was pressed with a roll press machine so that the density after pressing was 3.40 to 3.50 g / cm 3 , and further, the temperature was 120 ° C.
• a single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 ⁇ m; manufactured by a dry method; porosity 55%) was prepared and cut into a 5 cm ⁇ 5 cm square.
• the aluminum packaging material exterior was prepared as a battery exterior.
• the produced positive electrode was cut out to 3.8cm x 2.8cm, and it has arrange
• the square separator was placed on the surface of the positive electrode mixture layer of the positive electrode.
• the produced negative electrode was cut out to 4.0 cm x 3.0 cm, and this was arrange
• heat sealing at 150 ° C. was performed to seal and close the opening of the aluminum packaging material exterior, and a laminated cell type lithium ion secondary battery was manufactured. The initial efficiency and cycle characteristics of the lithium ion secondary battery were evaluated. The results are shown in Table 1.
• Example 2 The negative electrode of the lithium ion secondary battery in the same manner as in Example 1 except that the blending amount of the artificial graphite as the carbon-based negative electrode active material was 75 parts and the blending amount of SiO x as the silicon-based negative electrode active material was 25 parts. Slurry composition, negative electrode, positive electrode, and lithium ion secondary battery were prepared. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
• Example 3 The negative electrode of the lithium ion secondary battery in the same manner as in Example 1 except that the compounding amount of the artificial graphite as the carbon-based negative electrode active material was 65 parts and the compounding amount of SiO x as the silicon-based negative electrode active material was 35 parts. Slurry composition, negative electrode, positive electrode, and lithium ion secondary battery were prepared. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
• Example 4 A slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the carboxymethyl cellulose salt was not blended. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
• Example 5 A slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the particulate binder was not blended. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
• Example 6 A slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the amount of the particulate binder was 0.225 parts corresponding to the solid content. Produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
• Example 7 Implemented except that 3 parts of polyacrylic acid 2 below was used in place of 1.5 parts of cross-linked sodium polyacrylate (Rheojic 260H) as polyacrylic acid, and carboxymethylcellulose salt and particulate binder were not added.
• a slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
• ⁇ Preparation of polyacrylic acid 2> In a reaction vessel, uncrosslinked polyacrylic acid (manufactured by Aldrich, number average molecular weight: 1.25 million) was dissolved at a solid content concentration of 2% and stirred. Thereafter, the reaction vessel was heated to 60 ° C., and a carbodiimide compound (manufactured by Nisshinbo Chemical Co., Ltd., SV-02, diluted to a solid content concentration of 0.5%) was gradually added dropwise over 1 hour. Stir for 8 hours. Thereafter, the pH was adjusted to 8.0 with a 1% aqueous sodium hydroxide solution, and water was evaporated from the obtained aqueous solution under vacuum drying conditions at 60 ° C. to obtain polyacrylic acid 2.
• uncrosslinked polyacrylic acid manufactured by Aldrich, number average molecular weight: 1.25 million
• a carbodiimide compound manufactured by Nisshinbo Chemical Co., Ltd., SV-02, diluted to a solid
• Example 8 (Example 8) Implemented except that 3 parts of polyacrylic acid 3 below was used in place of 1.5 parts of cross-linked sodium polyacrylate (Rheodic 260H) as polyacrylic acid, and carboxymethyl cellulose salt and particulate binder were not added.
• a slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
• Example 9 A slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary material were prepared in the same manner as in Example 1 except that the blending amount of a 1% by mass aqueous solution of carboxymethylcellulose salt was 0.375 parts corresponding to the solid content. A secondary battery was produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
• Example 1 (Comparative Example 1) In the same manner as in Example 1 except that only 100 parts of artificial graphite was used as the negative electrode active material and SiO x was not used as the silicon negative electrode active material, the slurry composition for the negative electrode of the lithium ion secondary battery, the negative electrode, A positive electrode and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
• Example 2 Lithium ion secondary battery negative electrode in the same manner as in Example 1 except that the amount of artificial graphite as the carbon-based negative electrode active material was 50 parts and the amount of SiO x as the silicon-based negative electrode active material was 50 parts. Slurry composition, negative electrode, positive electrode, and lithium ion secondary battery were prepared. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
• Example 5 The same procedure as in Example 1 was used except that polyacrylic acid 6 (manufactured by Toa Gosei Co., Ltd., cross-linked sodium polyacrylate, Rheotic 262L) was used as the polyacrylic acid instead of the cross-linked sodium polyacrylate (Rheodic 260H).
• a slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
• Example 6 A slurry composition for a negative electrode of a lithium ion secondary battery in the same manner as in Example 1, except that no polyacrylic acid was blended and the blending amount of a 1% by weight aqueous solution of carboxymethylcellulose salt was 3.0 parts in terms of solid content. A negative electrode, a positive electrode, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
• a lithium ion secondary when used for forming a negative electrode, a lithium ion secondary that can increase the battery capacity while suppressing the expansion and contraction of the silicon-based negative electrode active material due to charge / discharge and that is excellent in coatability.
• a slurry composition for a battery negative electrode can be provided.
• the negative electrode for lithium ion secondary batteries which can provide the lithium ion secondary battery which has the outstanding battery capacity and cycling characteristics can be provided.
• a lithium ion secondary battery having a high battery capacity and excellent cycle characteristics can be provided.

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