WO2020050285A1 - Lithium ion secondary battery, method for producing same, and electrode for lithium ion secondary batteries - Google Patents

Lithium ion secondary battery, method for producing same, and electrode for lithium ion secondary batteries Download PDF

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Publication number
WO2020050285A1
WO2020050285A1 PCT/JP2019/034664 JP2019034664W WO2020050285A1 WO 2020050285 A1 WO2020050285 A1 WO 2020050285A1 JP 2019034664 W JP2019034664 W JP 2019034664W WO 2020050285 A1 WO2020050285 A1 WO 2020050285A1
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negative electrode
insulating layer
active material
electrode active
binder
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PCT/JP2019/034664
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French (fr)
Japanese (ja)
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寛大 奥田
利絵 寺西
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積水化学工業株式会社
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Priority to JP2020541248A priority Critical patent/JPWO2020050285A1/en
Publication of WO2020050285A1 publication Critical patent/WO2020050285A1/en

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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
    • 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
    • H01M10/058—Construction or manufacture
    • H01M10/0585—Construction or manufacture of accumulators having only flat construction elements, i.e. flat positive electrodes, flat negative electrodes and flat separators
    • 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
    • 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
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to an electrode for a lithium ion secondary battery having an insulating layer on a negative electrode, a method for producing the same, and a lithium ion secondary battery.
  • Lithium-ion secondary batteries are used as large stationary power sources for power storage and power sources for electric vehicles, etc.
  • a lithium ion secondary battery includes both electrodes having an electrode active material layer formed on a surface of a current collector made of a metal foil or the like, and a separator disposed between both electrodes.
  • the separator plays a role in preventing a short circuit between the two electrodes and holding the electrolytic solution.
  • a polyolefin-based porous film such as polyethylene or polypropylene is generally used.
  • lithium-ion secondary batteries have been attempted to be separatorless without using the porous film for the purpose of reducing the number of parts.
  • it has been studied to form an insulating layer on the surface of the electrode active material layer and prevent a short circuit between both electrodes by the insulating layer.
  • the insulating layer a layer having a three-dimensional network void structure including insulating particles and a binder for bonding the insulating particles to each other is known.
  • the present invention provides a lithium-ion secondary battery and a negative electrode for a lithium-ion secondary battery which can improve all of safety, charge / discharge characteristics, and output characteristics even without a separator. That is the task.
  • the present inventors have conducted intensive studies and as a result, used a predetermined binder as a negative electrode binder for forming a negative electrode active material layer and a predetermined binder for an insulating layer binder for forming an insulating layer. It has been found that the above problem can be solved by adjusting the thickness of the insulating layer within a predetermined range, and the present invention described below has been completed.
  • the gist of the present invention is the following [1] to [9].
  • a lithium ion secondary battery including a positive electrode and a negative electrode,
  • the negative electrode includes a negative electrode active material layer containing a negative electrode active material and a negative electrode binder, and an insulating layer provided on a surface of the negative electrode active material layer and containing insulating fine particles and an insulating layer binder.
  • the insulating layer is disposed so as to contact the positive electrode,
  • the negative electrode binder contains a water-soluble polymer and a particulate binder,
  • the insulating layer binder contains an organic solvent-soluble polymer, and the content of the organic solvent-soluble polymer is 15 to 45% by volume based on the total amount of the insulating layer;
  • a lithium ion secondary battery wherein the thickness of the insulating layer is 10 to 20 ⁇ m.
  • a separator-less negative electrode for a lithium ion secondary battery There is no separator between the positive electrode and the negative electrode, a separator-less negative electrode for a lithium ion secondary battery, A negative electrode active material layer containing a negative electrode active material and a negative electrode binder, and an insulating layer provided on the surface of the negative electrode active material layer and containing insulating fine particles and an insulating layer binder,
  • the negative electrode binder contains a water-soluble polymer and a particulate binder
  • the insulating layer binder contains an organic solvent-soluble polymer, and the content of the organic solvent-soluble polymer is 15 to 45% by volume based on the total amount of the insulating layer;
  • a negative electrode for a lithium ion secondary battery wherein the thickness of the insulating layer is 10 to 20 ⁇ m.
  • FIG. 1 is a schematic cross-sectional view showing one embodiment of a lithium ion secondary battery of the present invention.
  • the lithium ion secondary battery 10 includes a negative electrode 11 and a positive electrode 21.
  • the negative electrode 11 includes a negative electrode active material layer 12 and an insulating layer 13 provided on a surface of the negative electrode active material layer 12.
  • the lithium ion secondary battery 10 is a so-called separator-less type, and no separator is provided between the negative electrode 11 and the positive electrode 21 as a member separate from these electrodes. Therefore, the insulating layer 13 provided on the surface of the negative electrode active material layer 12 is arranged to be in contact with the positive electrode 21.
  • the negative electrode 11 is preferably bonded to the positive electrode 21 by pressing or the like via the insulating layer 13 so that the negative electrode 11 and the positive electrode 21 may form an integrated laminate.
  • the charge / discharge characteristics, output characteristics, and the like can be easily improved.
  • the negative electrode 11 usually includes a negative electrode current collector 14, and the negative electrode active material layer 12 is stacked on the negative electrode current collector 14.
  • the positive electrode 21 includes a positive electrode active material layer 22.
  • the positive electrode active material layer 22 is usually stacked on the electrode current collector 24.
  • a surface layer such as an insulating layer may be provided on the surface of the positive electrode active material layer 22 (the surface opposite to the surface on the positive electrode current collector 24 side). No layer is provided, and the insulating layer 13 of the negative electrode 11 directly contacts the positive electrode active material layer 22.
  • FIG. 1 shows a configuration in which the negative electrode active material layer 12 and the positive electrode active material layer 22 are provided only on one surface of each of the negative electrode current collector 14 and the positive electrode current collector 24. May be provided with a negative electrode active material layer 12.
  • the insulating layer 13 is preferably provided on the surface of each negative electrode active material layer 12.
  • the positive electrode current collector 24 may be provided with the positive electrode active material layers 22 on both surfaces.
  • the negative electrode 11 and the positive electrode 21 each having the negative electrode active material layer 12 and the positive electrode active material layer 22 on both surfaces are used, the negative electrode 11 and the positive electrode 21 are alternately arranged so that a plurality of layers are provided, respectively. It is preferable that the insulating layer 13 provided on the surface of the layer 12 be disposed so as to be in contact with the positive electrode 21 (the positive electrode active material layer 22).
  • the negative electrode active material layer 12 includes a negative electrode active material and a negative electrode binder.
  • the negative electrode active material used for the negative electrode active material layer include carbon materials such as graphite and hard carbon, a composite of a tin compound and silicon and carbon, and lithium. Among these, carbon materials are preferable, and graphite is preferable. More preferred.
  • One kind of the negative electrode active material may be used alone, or two or more kinds may be used in combination.
  • the negative electrode active material is not particularly limited, but preferably has an average particle size of 0.5 to 50 ⁇ m, more preferably 1 to 30 ⁇ m.
  • the average particle diameter means the particle diameter (D50) at a volume integration of 50% in the particle size distribution of the negative electrode active material obtained by a laser diffraction / scattering method, and the same applies to the average particle diameter of other particles. .
  • the content of the negative electrode active material in the negative electrode active material layer 11 is preferably 50 to 98.5% by mass, more preferably 60 to 98% by mass, and further preferably 70 to 98% by mass, based on the total amount of the negative electrode active material layer.
  • an appropriate amount of the negative electrode active material is blended in the negative electrode active material layer 12, and the charge / discharge characteristics and output characteristics of the lithium ion secondary battery can be easily improved.
  • the amount to be equal to or less than the upper limit it becomes possible to make the anode active material layer 12 contain an appropriate amount of binder.
  • the negative electrode active material layer 12 may contain a conductive auxiliary.
  • a conductive additive a material having higher conductivity than the above-described negative electrode active material is used, and specific examples thereof include carbon materials such as Ketjen black, acetylene black, carbon nanotube, and rod-like carbon.
  • the conductive auxiliary may be used alone or in combination of two or more.
  • the content of the conductive auxiliary is preferably 1 to 30% by mass, and more preferably 2 to 25% by mass, based on the total amount of the negative electrode active material layer. Is more preferable. When the content is within these ranges, appropriate conductivity is imparted to the negative electrode active material, and various performances of the lithium ion secondary battery are easily improved.
  • the negative electrode active material layer 12 does not contain a conductive auxiliary.
  • the negative electrode active material layer 12 is formed by binding a negative electrode active material or a negative electrode active material and a conductive auxiliary with a negative electrode binder.
  • the binder for the negative electrode contains a water-soluble polymer and a particulate binder.
  • a water-soluble polymer is a polymer having high solubility in water. Since the water-soluble polymer has high solubility in water, the water-soluble polymer forms an insulating layer described later, and is hardly compatible with an insulating layer binder containing an organic solvent-soluble polymer. Thus, the negative electrode active material layer and the insulating layer are separated from each other as layers without the negative electrode active material and the insulating fine particles described later being mixed. Therefore, the negative electrode active material layer 12 and the insulating layer 13 can easily exhibit desired performance, respectively, and the charge / discharge characteristics and the output characteristics are likely to be good.
  • a solid content concentration decrease amount is used as an index indicating solubility.
  • the solid content concentration decrease amount is an index indicating how much insoluble solids remain when a binder is dissolved in a solvent at a predetermined temperature and a predetermined concentration.The lower the value, the higher the solubility. Is shown.
  • the specific method of measuring the amount of decrease in the solid content is as described in Examples. Since the binder for the negative electrode has a water-soluble polymer, the amount of decrease in the solid content concentration with respect to water is reduced.
  • the amount of decrease in the solid content of the binder for the negative electrode with respect to water is, for example, 5% by mass or less, more preferably 3% by mass or less, and further preferably 1.5% by mass or less.
  • the lowering of the solid content concentration of the binder for the negative electrode with respect to water is preferably as low as possible, and may be 0% by mass or more, but practically 0.5% by mass or more.
  • water-soluble polymers have low solubility in organic solvents.
  • the water-soluble polymer has low solubility in N-methylpyrrolidone (NMP), and therefore, the binder for the negative electrode has a large decrease in the solid concentration with respect to NMP.
  • the amount of decrease in the solid concentration of the binder for the negative electrode with respect to NMP is, for example, 10% by mass or more, preferably 15% by mass or more, and more preferably 18% by mass or more. By setting the lower limit or more, the binder for the negative electrode becomes more difficult to be compatible with the binder for the insulating layer.
  • the lowering of the solid content concentration of the binder for the negative electrode with respect to NMP is preferably as high as 100% by mass or less, but practically 50% by mass or less.
  • NMP was used as an index of solubility in an organic solvent is that NMP has excellent solubility in various substances among organic solvents, and is generally used as a solvent for a composition for an insulating layer. It is.
  • the water-soluble polymer examples include a cellulose compound and a salt thereof, polyvinyl alcohol, and polyvinylpyrrolidone. These may be used alone or in combination of two or more.
  • the cellulose compound and its salt include hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, and their sodium and ammonium salts.
  • the water-soluble polymer preferably contains at least one selected from the group consisting of carboxymethylcellulose and salts thereof, hydroxyethylcellulose and salts thereof, polyvinyl alcohol, and polyvinylpyrrolidone, and is selected from carboxymethylcellulose and salts thereof. At least one is particularly preferred.
  • carboxymethyl cellulose a sodium salt is preferable.
  • the carboxymethyl cellulose salt has a viscosity of, for example, 10 to 5000 mPa ⁇ s, preferably 200 to 4000 mPa ⁇ s at 25 ° C. and 60 rpm measured by a B-type viscometer when dissolved in water at a concentration of 1% by mass. It is.
  • Rubber particles can be used as the particulate binder.
  • the rubber include a conjugated diene-based polymer having a constituent unit derived from a conjugated diene-based monomer such as butadiene, and, for example, a rubber having a constituent unit derived from an aromatic vinyl monomer and a constituent unit derived from butadiene. Is mentioned. Specific preferred compounds include styrene butadiene rubber.
  • Another specific example of the particulate binder includes an acrylic resin. Examples of the acrylic resin include an acrylic polymer having a structural unit derived from a (meth) acrylate such as an alkyl (meth) acrylate.
  • polymers of alkyl (meth) acrylates having about 1 to 8 carbon atoms such as polymethyl methacrylate and polybutyl acrylate, and two or more copolymers selected from these.
  • the particulate binder among the above, one or more selected from styrene-butadiene rubber and acrylic resin are preferable, and styrene-butadiene rubber is particularly preferable. Therefore, it is particularly preferable to use at least one selected from carboxymethylcellulose and its salts as the negative electrode binder, and to use styrene-butadiene rubber as the particulate binder.
  • the average particle diameter of the particulate binder is not particularly limited, but is preferably 10 to 500 nm, more preferably 50 to 300 nm. When the average particle diameter of the particulate binder is within these ranges, the particulate binder can be appropriately dispersed in the negative electrode active material layer 12, and the performance of the negative electrode active material layer 12 is excellent. Becomes
  • the total amount of the water-soluble polymer and the particulate binder is preferably 1.5 to 40% by mass, more preferably 2.0 to 25% by mass, based on the total amount of the negative electrode active material layer. 2.0-20% by mass is more preferred.
  • the negative electrode active material, or the negative electrode active material and the conductive assistant can be appropriately fixed to the negative electrode active material layer 12 by the negative electrode binder.
  • the content is not less than the upper limit, it is possible to prevent the amount of the binder from being excessively large and prevent the performance of the negative electrode from being lowered.
  • the mass ratio of the particulate binder to the water-soluble polymer is preferably 1/4 to 4, more preferably 1/2 to 2, and 2/3 to 3/2. More preferred.
  • the negative electrode active material, or the negative electrode active material and the conductive assistant are appropriately held by the negative electrode binder.
  • the compatibility with the insulating layer in which an organic solvent-soluble polymer described later is used as a binder is low. This makes it difficult for the negative electrode active material layer and the insulating layer to mix.
  • each negative electrode active material layer 12 is not particularly limited, but is preferably 10 to 100 ⁇ m, and more preferably 20 to 80 ⁇ m.
  • the negative electrode active material layer 12 may contain other optional components other than the negative electrode active material, the conductive assistant, and the negative electrode binder as long as the effects of the present invention are not impaired.
  • the negative electrode binder preferably comprises a water-soluble polymer and a particulate binder, but may contain other binders. Other binders may be used in amounts that do not impair the effects of the present invention. For example, the amount is less than 10% by mass, preferably less than 5% by mass, based on the total amount of the binder for the negative electrode.
  • the total mass of the negative electrode active material layer 12 the total content of the negative electrode active material, the conductive auxiliary, the water-soluble polymer, and the particulate binder is preferably 90% by mass or more, and 95% by mass or more. More preferably, it is the above.
  • the density (electrode density) of the negative electrode active material layer 12 is preferably 1.3 to 2.0 g / cc, and more preferably 1.4 to 1.8 g / cc. By setting the electrode density within these ranges, the performance of the negative electrode active material layer 12 is improved. Further, when the content is not less than these lower limits, the composition for an insulating layer described later (that is, the insulating layer 12) becomes more difficult to permeate into the negative electrode active material layer 12, and the negative electrode active material layer 12 and the insulating layer 13 are mixed. The charge / discharge characteristics, output characteristics, and the like are likely to be good.
  • the density of the negative electrode active material layer 12 can be calculated from the mass per unit area of the negative electrode active material layer and the thickness of the negative electrode active material layer. For example, a plurality of measurement samples prepared by punching the negative electrode before forming the insulating layer into a predetermined size (for example, a diameter of 16 mm) are prepared. The mass of each measurement sample is weighed with a precision balance, and the mass is measured. By subtracting the previously measured mass of the negative electrode current collector from the measurement result, the mass of the negative electrode active material layer in the measurement sample can be calculated. In addition, the thickness of the negative electrode active material layer is measured by a known method such as observing a measurement sample subjected to cross-section processing with an SEM.
  • the density of the negative electrode active material layer can be calculated from the average of the measured values based on the following equation (1).
  • Density of negative electrode active material layer (g / cc) mass of negative electrode active material layer (g) / [(thickness of negative electrode active material (cm) ⁇ area of punched negative electrode (cm 2 )] (1)
  • the insulating layer 13 contains insulating fine particles and a binder for the insulating layer.
  • the insulating layer 13 is formed by binding insulating fine particles with an insulating layer binder.
  • the binder for the insulating layer contains an organic solvent-soluble polymer.
  • the organic solvent-soluble polymer is a polymer that is soluble in an organic solvent and has high solubility in an organic solvent.
  • the organic solvent-soluble polymer is hardly compatible with the water-soluble polymer forming the negative electrode active material layer 12, the insulating layer 13 and the negative electrode active material layer 12 are separated from each other as layers, and each has a desired performance. Easy to demonstrate. Therefore, the lithium ion secondary battery has favorable charge / discharge characteristics and output characteristics.
  • the content of the organic solvent-soluble polymer in the insulating layer 13 is 15 to 45% by volume based on the total amount of the insulating layer.
  • the content of the organic solvent-soluble polymer is preferably 18% by volume or more, more preferably 20% by volume or more, and more preferably 23% by volume or more, from the viewpoint of enhancing safety and improving charge / discharge characteristics. It is more preferred that there be.
  • the content of the organic solvent-soluble polymer is preferably 40% by volume or less, more preferably 35% by volume or less, and further preferably 29% by volume or less, in order to make the void amount in the insulating layer 13 an appropriate amount and enhance the output characteristics. preferable.
  • the content of the insulating fine particles is, for example, 55 to 85% by volume based on the volume of the entire insulating layer.
  • the content of the insulating fine particles is preferably 60% by volume or more, more preferably 65% by volume or more, and still more preferably 71% by volume or more, in order to make the void amount in the insulating layer 13 an appropriate amount and enhance output characteristics.
  • the content of the insulating fine particles is preferably 82% by volume or less, more preferably 80% by volume or less, and further preferably 77% by volume or more, from the viewpoint of enhancing safety and improving charge / discharge characteristics. preferable.
  • the thickness of the insulating layer 13 is 10 to 20 ⁇ m. If the thickness is less than 10 ⁇ m, it becomes difficult to ensure insulation even if the content of the organic solvent-soluble polymer is within the above-mentioned predetermined range, and safety is reduced. On the other hand, when the thickness is larger than 20 ⁇ m, the insulating layer becomes thicker than necessary, and the output characteristics deteriorate.
  • the thickness of the insulating layer 13 is preferably 11 ⁇ m or more, and more preferably 13 ⁇ m or more, from the viewpoint of enhancing the charge / discharge characteristics and safety. In addition, from the viewpoint of improving output characteristics, the thickness of the insulating layer 13 is preferably equal to or less than 19 ⁇ m, and more preferably equal to or less than 17 ⁇ m.
  • the insulating fine particles used in the present invention are not particularly limited as long as they are insulating, and may be either organic particles or inorganic particles.
  • Specific organic particles include, for example, cross-linked polymethyl methacrylate, cross-linked styrene-acrylic acid copolymer, cross-linked acrylonitrile resin, polyamide resin, polyimide resin, poly (lithium 2-acrylamido-2-methylpropanesulfonate), Examples include particles composed of an organic compound such as a polyacetal resin, an epoxy resin, a polyester resin, a phenol resin, and a melamine resin.
  • the inorganic particles include silicon dioxide, silicon nitride, alumina, boehmite, titania, zirconia, boron nitride, zinc oxide, tin dioxide, niobium oxide (Nb 2 O 5 ), tantalum oxide (Ta 2 O 5 ), potassium fluoride, and fluoride.
  • examples include particles composed of inorganic compounds such as lithium chloride, clay, zeolite, and calcium carbonate.
  • the inorganic particles may be particles composed of a known composite oxide such as a niobium-tantalum composite oxide or a magnesium-tantalum composite oxide.
  • the insulating fine particles may be particles in which each of the above-mentioned materials is used alone or in combination of two or more.
  • the insulating fine particles may be fine particles containing both an inorganic compound and an organic compound.
  • inorganic-organic composite particles in which an inorganic oxide is coated on the surface of particles made of an organic compound may be used.
  • inorganic particles are preferable, and among them, alumina particles and boehmite particles are preferable, and alumina particles are particularly preferable.
  • the average particle diameter of the insulating fine particles is smaller than the thickness of the insulating layer, and is, for example, 0.001 to 1 ⁇ m, preferably 0.05 to 0.8 ⁇ m, and more preferably 0.1 to 0.6 ⁇ m. .
  • the porosity can be easily adjusted within the above range.
  • the insulating fine particles one kind having an average particle diameter within the above range may be used alone, or two kinds of insulating fine particles having different average particle diameters may be mixed and used.
  • Organic solvent soluble polymer is soluble in an organic solvent, particularly an organic solvent for forming an insulating layer, but is preferably soluble in N-methylpyrrolidone (NMP). Since NMP is generally used as a diluting solvent for a composition for an insulating layer for forming an insulating layer, it is easy to form an insulating layer appropriately by being soluble in NMP.
  • NMP N-methylpyrrolidone
  • the binder for the insulating layer contains the organic solvent-soluble polymer, so that the solid content concentration decrease with respect to NMP is reduced, for example, 1% by mass or less, more preferably 0.4% by mass or less, further preferably 0.1% by mass or less. % By mass or less.
  • the lowering of the solid content concentration of the binder for the insulating layer with respect to the NMP is preferably low, and therefore it is sufficient that the amount is 0% by mass or more.
  • the binder for the insulating layer containing the polymer soluble in an organic solvent has a large decrease in the solid concentration with respect to water.
  • the amount of decrease in the solid content of the binder for the insulating layer with respect to water is, for example, 50% by mass or more, preferably 75% by mass or more, and more preferably 85% by mass or more.
  • the lowering of the solid content concentration of the binder for the insulating layer with respect to water is preferably as high as 100% by mass or less, but is practically 99% by mass or less.
  • the organic solvent-soluble polymer itself has a low decrease in solid content concentration with respect to NMP, and specifically, is 1% by mass or less, more preferably 0.4% by mass or less, and further preferably 0.1% by mass or less. % By mass or less. Further, the lowering of the solid content concentration of the organic solvent-soluble polymer with respect to NMP is better, and it is sufficient that the amount is 0% by mass or more.
  • organic solvent-soluble polymer examples include fluorine-containing resins such as polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), acrylic resin, polyvinyl acetate, polyimide (PI), and polyamide (PA). ), Polyvinyl chloride (PVC), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP), polyacrylonitrile (PAN), and the like. These may be used alone or in combination of two or more. Among these, at least one selected from polyvinylidene fluoride and an acrylic resin is preferable, and an acrylic resin is more preferable.
  • PVDF polyvinylidene fluoride
  • PVDF-HFP polyvinylidene fluoride-hexafluoropropylene copolymer
  • acrylic resin polyvinyl acetate, polyimide (PI), and polyamide (PA).
  • PVC Polyviny
  • the binder for the insulating layer is hardly compatible with the binder for the negative electrode, and the insulating layer and the negative electrode active material layer are likely to be present as separate layers. It becomes easy to exhibit the function well. Therefore, the charge / discharge characteristics and the output characteristics of the lithium ion secondary battery are improved.
  • an acrylic resin is used, the adhesive strength of the insulating layer binder is increased, and the adhesiveness to the positive electrode active material layer 22 and the negative electrode active material layer 12 is increased.
  • the acrylic resin used as the organic solvent-soluble polymer includes an acrylic polymer having a structural unit derived from a (meth) acrylic ester. Specifically, it is preferable to have a structural unit derived from an alkyl (meth) acrylate, and the structural unit derived from an alkyl (meth) acrylate is, for example, 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more. contains.
  • the alkyl (meth) acrylate is preferably an alkyl acrylate having an alkyl group having 1 to 12, more preferably 2 to 8, carbon atoms.
  • the acrylic polymer preferably contains 50% by mass or more, more preferably 70% by mass or more, and still more preferably 90% by mass or more of a main unit of an alkyl acrylate-derived structural unit having 2 to 8 carbon atoms in the alkyl group. Contains on top.
  • alkyl acrylate having 2 to 8 carbon atoms in the alkyl group examples include ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, and octyl acrylate.
  • the alkyl group in these may be a straight-chain alkyl group or a branched alkyl group which is a structural isomer thereof, such as 2-ethylhexyl acrylate.
  • the acrylic polymer may be a copolymer of an alkyl (meth) acrylate and a vinyl monomer other than the alkyl (meth) acrylate.
  • vinyl monomers other than alkyl (meth) acrylate examples include vinyl group-containing (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, amino group-containing (meth) acrylates, nitrile group-containing vinyl monomers such as acrylonitrile, and (meth) acrylic.
  • vinyl group-containing (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, amino group-containing (meth) acrylates, nitrile group-containing vinyl monomers such as acrylonitrile, and (meth) acrylic.
  • carboxyl group-containing vinyl monomers such as acid and itaconic acid
  • aromatic ring-containing (meth) acrylates such as phenoxyethyl (meth) acrylate.
  • acrylic polymers include polybutyl acrylate.
  • acrylic polymer may be cross-linked, and specific examples thereof include cross-linked polybutyl acrylate.
  • (meth) acrylate means one or both of acrylate and methacrylate, and the same applies to other similar terms.
  • the binder for the negative electrode containing the water-soluble polymer, the binder for the insulating layer containing the organic solvent-soluble polymer becomes difficult to be compatible, the charge and discharge characteristics, and the more excellent output characteristics. Is what you do.
  • the water-soluble polymer is one or more selected from carboxymethylcellulose and salts thereof, hydroxyethylcellulose, polyvinyl alcohol, and polyvinylpyrrolidone
  • the organic solvent-soluble polymer is polyvinylidene fluoride
  • at least one selected from acrylic resins It is particularly preferable that the water-soluble polymer is one or more selected from carboxymethylcellulose and salts thereof, and the organic solvent-soluble polymer is an acrylic resin.
  • the insulating layer may contain other optional components other than the insulating fine particles and the binder for the insulating layer as long as the effects of the present invention are not impaired.
  • the binder for the insulating layer may be composed of an organic solvent-soluble polymer, but may contain other binders other than the organic solvent-soluble polymer as long as the effects of the present invention are not impaired. Other binders may be used in amounts that do not impair the effects of the present invention. For example, the amount is less than 10% by mass, preferably less than 5% by mass, based on the total amount of the binder for the insulating layer.
  • the total volume of the insulating layer is preferably 85% by volume or more, more preferably 90% by volume or more, and more preferably 95% by volume or more. Is more preferred.
  • Examples of a material constituting the negative electrode current collector 14 include conductive metals such as copper, aluminum, titanium, nickel, and stainless steel. Among these, aluminum or copper is preferable, and copper is more preferable.
  • the negative electrode current collector 14 is generally made of a metal foil, and its thickness is not particularly limited, but is preferably 1 to 50 ⁇ m.
  • the positive electrode 21 includes the positive electrode active material layer 22 as described above.
  • the positive electrode active material layer 22 typically includes a positive electrode active material and a positive electrode binder. Although it does not specifically limit as a positive electrode active material, a lithium metal oxide compound is mentioned. Examples of the lithium metal oxide compound include lithium cobaltate (LiCoO 2 ), lithium nickelate (LiNiO 2 ), lithium manganate (LiMn 2 O 4 ), and the like. Further, olivine-type lithium iron phosphate (LiFePO 4 ) may be used.
  • a plurality of metals other than lithium may be used, and a ternary NCM (nickel-cobalt-manganese) -based oxide, an NCA (nickel-cobalt-aluminum-based) -based oxide, or the like may be used.
  • a ternary NCM nickel-cobalt-manganese
  • NCA nickel-cobalt-aluminum-based
  • the binder for the positive electrode is not particularly limited, and a binder conventionally used for a positive electrode can be appropriately selected and used.
  • a binder conventionally used for a positive electrode can be appropriately selected and used.
  • one or two or more selected from the above-mentioned organic solvent-soluble polymers and water-soluble polymers may be used.
  • a water-soluble polymer is used, one or more selected from the above-mentioned particulate binders may be further added.
  • the positive electrode active material layer preferably further contains a conductive auxiliary.
  • the conductive aid one or more of the conductive aids described above may be appropriately selected and used.
  • the content of the positive electrode active material in the positive electrode active material layer 22 is preferably 50 to 98.5% by mass, more preferably 60 to 98% by mass, based on the total amount of the positive electrode active material layer. Further, the content of the positive electrode binder in the positive electrode active material layer 22 is preferably 1.5 to 40% by mass, more preferably 2.0 to 25% by mass, based on the total amount of the positive electrode active material layer. When the positive electrode active material layer 22 contains a conductive auxiliary, the content of the conductive auxiliary is preferably 1 to 30% by mass, and more preferably 2 to 25% by mass based on the total amount of the positive electrode active material layer. Is more preferable.
  • the thickness of each positive electrode active material layer 22 is not particularly limited, but is preferably 10 to 100 ⁇ m, and more preferably 20 to 80 ⁇ m.
  • the material constituting the positive electrode current collector 24 may be appropriately selected from the compounds used for the negative electrode current collector 14, and preferably used is aluminum or copper, and more preferably aluminum.
  • the thickness of the positive electrode current collector 24 is not particularly limited, but is preferably 1 to 50 ⁇ m.
  • the lithium ion secondary battery usually includes a casing, and the above-described positive electrode and negative electrode may be housed in the casing.
  • the casing is not particularly limited, but may be an exterior can or an exterior film.
  • the exterior film may be provided between two exterior films or one exterior film may be folded in two, for example, and the negative electrode and the positive electrode may be arranged between the exterior films.
  • the lithium ion secondary battery includes a wound type and a stacked type, and the lithium ion secondary battery of the present invention is preferably a stacked type.
  • a negative electrode 11 in which a negative electrode active material layer 12 is provided on both surfaces of a negative electrode current collector 14 and a positive electrode 21 in which a positive electrode active material layer 22 is provided on both surfaces of a positive electrode current collector 24 Respectively.
  • Each of the negative electrode 11 and the positive electrode 21 has a planar shape, and these are stacked so as to be alternated along the thickness direction.
  • the insulating layer 13 provided on the surface of each negative electrode active material layer 12 contacts the adjacent positive electrode 21 (for example, the positive electrode active material layer 22), and preferably contacts the positive electrode 21 (for example, the positive electrode active material layer 22). Glue.
  • the plurality of negative electrode current collectors 14 constituting each negative electrode 11 are put together and attached to a negative electrode tab or the like, and connected to the negative electrode terminal via the negative electrode tab or the like.
  • the plurality of positive electrode current collectors 24 constituting each positive electrode 21 are put together and attached to a positive electrode tab or the like, and connected to a positive electrode terminal via the positive electrode tab or the like.
  • the type of the binder for the insulating layer, the amount of each component constituting the insulating layer, the thickness, and the like are adjusted as described above, so that the insulating layer 13 is cracked when bent or the like.
  • the negative electrode 11 is arranged in a plane in the stacked type, it is not bent. Therefore, in the present invention, a laminated lithium ion secondary battery having high mechanical strength and good durability can be provided.
  • a lithium ion secondary battery usually includes an electrolyte.
  • the electrolyte is not particularly limited, and a known electrolyte used in a lithium ion secondary battery may be used.
  • an electrolyte is used as the electrolyte.
  • the electrolyte include an electrolyte containing an organic solvent and an electrolyte salt.
  • organic solvent examples include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ⁇ -butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane And polar solvents such as tetrohydrafuran, 2-methyltetrahydrofuran, dioxolane and methyl acetate, or a mixture of two or more of these solvents.
  • polar solvents such as tetrohydrafuran, 2-methyltetrahydrofuran, dioxolane and methyl acetate, or a mixture of two or more of these solvents.
  • a complex such as a lithium hydride of an organic acid-boron trifluoride complex or a complex hydride such as LiBH 4 may be used.
  • These salts or complexes may be used alone or as a mixture of two or more.
  • the electrolyte may be a gel electrolyte further containing a polymer compound in the above-mentioned electrolytic solution.
  • the polymer compound include a fluorine-based polymer such as polyvinylidene fluoride and a polyacryl-based polymer such as poly (methyl meth) acrylate.
  • the gel electrolyte may be used as a separator.
  • the electrolyte may be disposed between the negative electrode and the positive electrode. Therefore, for example, the electrolyte is filled in a casing in which the above-described negative electrode and positive electrode are housed. Further, the electrolyte may be, for example, applied on the negative electrode or the positive electrode and disposed between the negative electrode and the positive electrode.
  • the method for producing an electrode for a lithium ion secondary battery includes a step of applying a composition for an insulating layer on the surface of a negative electrode active material layer to form an insulating layer, thereby producing a negative electrode. (A negative electrode manufacturing step) and a step of pressing the negative electrode to the positive electrode via the insulating layer (pressure bonding step). In addition, it usually includes a step of producing a positive electrode (positive electrode production step).
  • a negative electrode manufacturing step and a step of pressing the negative electrode to the positive electrode via the insulating layer
  • it usually includes a step of producing a positive electrode (positive electrode production step).
  • the present manufacturing method will be described in detail for each step.
  • a negative electrode active material layer is formed.
  • a negative electrode active material layer composition including a negative electrode active material, a negative electrode binder, and a solvent is prepared.
  • the composition for a negative electrode active material layer may include other components such as a conductive auxiliary compounded as necessary.
  • the negative electrode active material, the negative electrode binder, the conductive auxiliary, and the like are as described above.
  • the composition for the negative electrode active material layer becomes a slurry.
  • Water is used as the solvent in the negative electrode active material layer composition.
  • the water-soluble polymer used as the negative electrode binder can be easily dissolved in the negative electrode active material layer composition.
  • the particulate binder and other binders are preferably mixed with water in the form of an emulsion.
  • the solid concentration of the composition for a negative electrode active material layer is preferably 5 to 75% by mass, more preferably 20 to 65% by mass.
  • the negative electrode active material layer may be formed by a known method using the negative electrode active material layer composition.
  • the negative electrode active material layer composition is applied on a negative electrode current collector and dried. Can be formed.
  • the negative electrode active material layer may be formed by applying the composition for a negative electrode active material layer on a substrate other than the negative electrode current collector and drying the composition.
  • a substrate other than the negative electrode current collector a known release sheet may be used.
  • the negative electrode active material layer formed on the substrate is preferably formed by forming an insulating layer, and then peeling the negative electrode active material layer from the substrate and transferring the negative electrode active material layer onto the negative electrode current collector.
  • the negative electrode active material layer formed on the negative electrode current collector or the substrate is preferably pressed under pressure. By pressing under pressure, the density of the negative electrode can be increased.
  • the pressure press may be performed by a roll press or the like.
  • a composition for an insulating layer is applied over the surface of the negative electrode active material layer to form an insulating layer.
  • the composition for an insulating layer used for forming an insulating layer contains insulating fine particles, a binder for an insulating layer, and a solvent.
  • the binder for the insulating layer contains the organic solvent-soluble binder as described above, but may also contain a binder other than the organic solvent-soluble binder.
  • the composition for an insulating layer may include other optional components that are blended as necessary. Details of the insulating fine particles, the binder for the insulating layer, and the like are as described above.
  • the composition for an insulating layer becomes a slurry (slurry for an insulating layer).
  • the solvent used for the composition for an insulating layer is an organic solvent.
  • the organic solvent include one or more selected from N-methylpyrrolidone, N-ethylpyrrolidone, dimethylacetamide, and dimethylformamide. Among these, N-methylpyrrolidone is particularly preferred.
  • the composition for an insulating layer containing an organic solvent is applied on the surface of the negative electrode active material layer to form an insulating layer, but the negative electrode active material layer has low solubility in the organic solvent. Water-soluble polymers are used. Therefore, the insulating layer is formed with almost no compatibility of the composition for an insulating layer with the negative electrode active material layer.
  • the insulating fine particles are prevented from being mixed into the negative electrode active material layer, or the negative electrode active material is prevented from being mixed into the insulating layer, and the insulating layer and the negative electrode active material layer each easily exhibit desired functions, The charge and discharge characteristics, output characteristics, and the like are improved.
  • the solid content of the composition for an insulating layer is preferably 10 to 60% by mass, more preferably 20 to 50% by mass.
  • the viscosity of the composition for an insulating layer is preferably 100 to 4000 mPa ⁇ s, more preferably 1500 to 2500 mPa ⁇ s.
  • the viscosity is a viscosity measured by a B-type viscometer at 60 rpm under a temperature condition at the time of coating.
  • the insulating layer can be formed by applying the composition for an insulating layer to the surface of the negative electrode active material layer and then drying the composition.
  • the method for applying the composition for an insulating layer to the surface of the negative electrode active material layer is not particularly limited, and examples thereof include a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a bar coating method, a gravure coating method, and screen printing. And the like. Among these, the gravure coating method is preferable from the viewpoint of uniformly applying the insulating layer.
  • the drying temperature is not particularly limited as long as the solvent can be removed, but is, for example, 50 to 130 ° C., preferably 60 to 100 ° C.
  • the drying time is not particularly limited, but is, for example, 30 seconds to 30 minutes, preferably 2 to 20 minutes.
  • a positive electrode active material layer is preferably formed over a positive electrode current collector.
  • a positive electrode active material layer composition including a positive electrode active material, a positive electrode binder, and a solvent is prepared.
  • the composition for a positive electrode active material layer may include other components such as a conductive auxiliary compounded as necessary.
  • the positive electrode active material, the positive electrode binder, the conductive additive, and the like are as described above.
  • the composition for the positive electrode active material layer becomes a slurry.
  • the solvent in the composition for the positive electrode active material layer it is preferable to use a solvent that dissolves the binder for the positive electrode, and may be appropriately selected depending on the type of the binder for the positive electrode, and may use water or an organic solvent. May be used.
  • the organic solvent may be appropriately selected from the above-mentioned organic solvents.
  • the solid concentration of the composition for a positive electrode active material layer is preferably 5 to 75% by mass, and more preferably 20 to 65% by mass.
  • the positive electrode active material layer may be formed by a known method using the positive electrode active material layer composition.
  • the positive electrode active material layer composition is applied on a positive electrode current collector and dried. Can be formed.
  • the positive electrode active material layer may be formed by applying the composition for a positive electrode active material layer on a substrate other than the positive electrode current collector and drying the composition.
  • a substrate other than the positive electrode current collector a known release sheet may be used.
  • the positive electrode active material layer formed on the substrate may be peeled off from the substrate and transferred onto the positive electrode current collector.
  • the positive electrode active material layer formed on the positive electrode current collector or the substrate is preferably pressed under pressure. By pressing under pressure, it is possible to increase the density of the positive electrode.
  • the pressure press may be performed by a roll press or the like.
  • the negative electrode obtained as described above may be pressed against the positive electrode to form a laminate including the negative electrode and the positive electrode.
  • the insulating layer may be disposed so as to be in contact with the positive electrode, typically the positive electrode active material layer, and the negative electrode may be press-bonded to the positive electrode via the insulating layer.
  • the negative electrode and the positive electrode are laminated in a plurality of layers, respectively, the negative electrode and the positive electrode are laminated in a plurality of layers so as to be alternately arranged in the thickness direction. It is good to let.
  • the specific method of crimping the negative electrode and the positive electrode is to press the stacked negative electrode and the positive electrode (if there are multiple layers, alternately arranged and stacked) with a press machine or the like. It is good to do in.
  • the pressing is preferably performed under such a condition that the negative electrode active material layer and the positive electrode active material layer are not compressed more than necessary and the insulating layer is bonded to the positive electrode.
  • the pressing temperature is 50 to 130 ° C., preferably 60 to 100 ° C.
  • the pressing pressure is, for example, 0.2 to 3 MPa, preferably 0.4 to 1.5 MPa.
  • the pressing time is, for example, 15 seconds to 15 minutes, preferably 30 seconds to 10 minutes.
  • the laminated body of the negative electrode and the positive electrode obtained as described above is, for example, connected to the negative electrode current collector to the negative electrode terminal and the positive electrode current collector to the positive electrode terminal, and housed in a casing, so that the lithium ion
  • the above manufacturing method is one embodiment of the manufacturing method of the lithium ion secondary battery of the present invention, and is not limited to the above.
  • the negative electrode and the positive electrode may be simply overlapped without being pressed.
  • the method for evaluating the electrode for an ion secondary battery and the method for measuring various physical properties are as follows. (Charge / discharge characteristics evaluation) The lithium ion secondary batteries prepared in each of the examples and the comparative examples were charged at a constant current of 0.1 A, then the current was decreased as soon as the voltage reached 4.2 V, and the charging was completed when the current reached 0.02 A. Was done. Thereafter, a constant current discharge of 0.1 A was performed, and discharge was completed when the discharge was completed to 2.5 V. Thereafter, the battery was allowed to stand for 30 minutes, and the voltage was measured after 30 minutes. In each of Examples and Comparative Examples, a test was performed on a 15-cell lithium ion secondary battery, and an average value was calculated. A: Average value of 2.5 V or more B: Average value of 2.0 V or more and less than 2.5 V C: Average value of 1.0 V or more and less than 2.0 V D: Average value of less than 1.0 V
  • the lithium ion secondary batteries produced in each of the examples and comparative examples were evaluated by calculating the discharge capacity as described below.
  • the battery was charged at a constant current of 0.1 A, and then the current was reduced as soon as 4.2 V was reached. Thereafter, a constant current discharge of 1 A was performed, and when the discharge was completed to 2.5 V, a discharge was completed to complete the discharge, and the discharge capacity was calculated.
  • the output characteristics were evaluated based on the following criteria.
  • B The discharge capacity at 1 A is 20% or more and less than 30% as compared with the discharge capacity at a constant current of 0.1 A.
  • C The discharge capacity at 1 A is 10% or more and less than 20% as compared with the discharge capacity at a constant current of 0.1 A.
  • D The discharge capacity at 1 A is less than 10% as compared with the discharge capacity at a constant current of 0.1 A.
  • the components used as the binder for the insulating layer, the binder for the negative electrode, or the organic solvent-soluble polymer are the same as the ratio of each component in the binder for the insulating layer, the binder for the negative electrode, or the organic solvent-soluble polymer, and the solid content concentration.
  • 500 g of the prepared binder solution was filtered through a stainless steel filter having a mesh size of 72 ⁇ m. Preparation of the binder solution and filtration of the binder solution were performed at 25 ° C. The filtered binder solution was dried on a hot plate at 150 ° C.
  • the thickness of the insulating layer was measured by the following method. A cross section of the negative electrode on which the negative electrode active material layer and the insulating layer were formed was exposed by an ion milling method. The exposed cross section was observed with a field emission scanning electron microscope (FE-SEM). The observation was made so that the surface of the insulating layer of the electrode could be seen from the surface to the bottom. The section magnification was 20000 times. For the obtained image, the length from the interface between the electrode active material and the insulating layer to the surface of the insulating layer was randomly measured using image analysis software (Image J) in a direction perpendicular to the electrode current collector. Ten points were measured for one image, and the average value was taken as the thickness of the insulating layer. (Thickness of negative electrode active material layer and positive electrode active material layer) The thicknesses of the negative electrode active material layer and the positive electrode active material layer were measured using “MF-101” manufactured by Nikon Corporation.
  • Example 1 [Preparation of positive electrode] 100 parts by mass of Li (Ni—Co—Al) O 2 (NCA-based oxide) having an average particle diameter of 10 ⁇ m as a positive electrode active material, 4 parts by mass of acetylene black as a conductive additive, and a binder for an electrode 4 parts by mass of polyvinylidene fluoride (PVdF) and N-methylpyrrolidone (NMP) as a solvent were mixed to obtain a composition for a positive electrode active material layer adjusted to a solid concentration of 60% by mass.
  • PVdF polyvinylidene fluoride
  • NMP N-methylpyrrolidone
  • the composition for a positive electrode active material layer was applied on both sides of a 15 ⁇ m-thick aluminum foil as a positive electrode current collector, and was preliminarily dried and then vacuum dried at 120 ° C. Thereafter, the positive electrode current collector coated with the composition for a positive electrode active material layer on both sides is pressed under a pressure of 400 kN / m, and further punched into a 40 mm ⁇ 50 mm square of the electrode dimensions. A positive electrode having a certain positive electrode active material layer was obtained. Among these dimensions, the area where the positive electrode active material layer was formed was 40 mm ⁇ 45 mm.
  • composition for a negative electrode active material layer was applied to both surfaces of a copper foil having a thickness of 12 ⁇ m as a negative electrode current collector, and dried at 100 ° C. under vacuum.
  • the negative electrode current collector having both sides coated with the negative electrode active material layer composition was pressed under a linear pressure of 500 kN / m to obtain a negative electrode active material layer having a thickness of 50 ⁇ m.
  • the density of the negative electrode active material layer was 1.55 g / cc.
  • the dimension of the negative electrode was 45 mm ⁇ 55 mm, and the area where the negative electrode active material layer was applied was 45 mm ⁇ 50 mm.
  • a polymer solution was prepared by dissolving crosslinked polybutyl acrylate as an organic solvent-soluble polymer in NMP at a concentration of 10% by mass.
  • Alumina particles as insulating fine particles (manufactured by Nippon Light Metal Co., Ltd., product name: AHP200, average particle diameter 0.4 ⁇ m).
  • the solution was mixed while applying moderate shear to prepare an insulating layer composition (insulating layer slurry).
  • the solid content concentration in the insulating layer slurry was 40% by mass.
  • the obtained slurry for an insulating layer was applied to both surfaces of the negative electrode active material layer by gravure coating at a temperature of 25 ° C. while applying a shearing force.
  • the viscosity of the slurry for the insulating layer at the time of coating was 2000 mPa ⁇ s. Thereafter, the coating film was dried at 90 ° C. for 10 minutes using a heating oven to form insulating layers on both surfaces of the negative electrode. The thickness of the insulating layer after drying was 15 ⁇ m per side.
  • LiPF 6 as an electrolyte salt was dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7 (EC: DEC) so as to have a concentration of 1 mol / liter, and the electrolytic solution was dissolved.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • the laminated body was sandwiched between aluminum laminated films, the terminal tabs were projected outside, and three sides were sealed by laminating. From one side left without sealing, the electrolyte solution obtained above was injected, and vacuum sealing was performed to produce a laminated lithium ion secondary battery (cell).
  • Example 1 was carried out in the same manner as in Example 1 except that the solid content concentration of the slurry for the insulating layer was 45% by mass, and the thickness of the insulating layer formed on the negative electrode active material was changed to 19 ⁇ m.
  • Example 1 was the same as Example 1 except that the solid content concentration of the slurry for the insulating layer was 35% by mass and the thickness of the insulating layer formed on the negative electrode active material was changed to 11 ⁇ m.
  • Example 4 The procedure was performed in the same manner as in Example 1 except that the composition for the insulating layer was prepared so that the organic solvent-soluble polymer was 40 parts by volume with respect to 60 parts by volume of the alumina particles.
  • Example 1 was carried out in the same manner as in Example 1 except that the composition for an insulating layer was prepared so that the organic solvent-soluble polymer was 18 parts by volume with respect to 82 parts by volume of alumina particles.
  • Example 1 In addition to 25 negative electrodes and 24 positive electrodes having an insulating layer manufactured in the same manner as in Example 1, 50 separators were laminated to obtain a laminate. Here, the negative electrode and the positive electrode were alternately arranged, and the negative electrode or the positive electrode was arranged between the separators. As the separator, a polyethylene microporous membrane separator having a thickness of 16 ⁇ m and an air permeability of 110 sec / 100 cc air was used. The ends of the exposed portions of the positive electrode current collector of each positive electrode were joined together by ultrasonic fusion, and a terminal tab projecting to the outside was joined.
  • Example 2 The same operation as in Example 1 was performed except that the solid content concentration of the slurry for the insulating layer was 15% by mass, and the thickness of the insulating layer formed on the negative electrode active material was changed to 4 ⁇ m.
  • Example 3 The procedure was performed in the same manner as in Example 1 except that the composition for an insulating layer was prepared so that the organic solvent-soluble polymer was 5 parts by volume with respect to 95 parts by volume of alumina particles.
  • Example 1 was carried out in the same manner as in Example 1 except that the composition for an insulating layer was prepared such that the organic solvent-soluble polymer was 50 parts by volume with respect to 50 parts by volume of alumina particles.
  • Example 5 The procedure was the same as that of Example 1 except that the solid content concentration of the slurry for the insulating layer was 55% by mass, and the thickness of the insulating layer formed on the negative electrode active material was changed to 30 ⁇ m.
  • Example 1 was carried out in the same manner as in Example 1 except that the insulating layer was formed using the insulating layer composition (insulating layer slurry) prepared as follows.
  • Alumina particles as insulating fine particles product name: AHP200, manufactured by Nippon Light Metal Co., Ltd., average particle diameter 0.4 ⁇ m
  • CMC carboxymethylcellulose
  • a slurry for an insulating layer was prepared.
  • the slurry for the insulating layer was adjusted so that CMC was 5 parts by volume, SBR was 20 parts by volume, and the solid content concentration was 50% by mass with respect to 100 parts by volume of alumina.
  • the binder for the negative electrode contains the water-soluble polymer and the particulate binder
  • the binder for the insulating layer contains the polymer soluble in an organic solvent
  • the volume% of the polymer soluble in the organic solvent By adjusting the thickness of the layer within a predetermined range, all of the safety, charge / discharge characteristics, and output characteristics were improved.

Abstract

An electrode 10 for lithium ion secondary batteries according to the present invention is provided with a positive electrode 21 and a negative electrode 11. The negative electrode 11 is provided with: a negative electrode active material layer 12 that contains a negative electrode active material and a binder for negative electrodes; and an insulating layer 13 that is provided on the surface of the negative electrode active material layer 12, while containing insulating fine particles and a binder for insulating layers. The insulating layer 13 is arranged to be in contact with the positive electrode 21. The binder for negative electrodes contains a water-soluble polymer and a particulate binder. The binder for insulating layers contains an organic solvent-soluble polymer; and the content of the organic solvent-soluble polymer is 15-45% by volume based on the total amount of the insulating layer. The insulating layer 13 has a thickness of 10-20 μm.

Description

リチウムイオン二次電池、その製造方法、及びリチウムイオン二次電池用電極Lithium ion secondary battery, method of manufacturing the same, and electrode for lithium ion secondary battery
　本発明は、負極に絶縁層を備えるリチウムイオン二次電池用電極、その製造方法、及びリチウムイオン二次電池に関する。 The present invention relates to an electrode for a lithium ion secondary battery having an insulating layer on a negative electrode, a method for producing the same, and a lithium ion secondary battery.
　リチウムイオン二次電池は、電力貯蔵用の大型定置用電源、電気自動車用等の電源として利用されており、近年では電池の小型化及び薄型化の研究が進展している。リチウムイオン二次電池は、金属箔などからなる集電体の表面に電極活物質層を形成した両電極と、両電極の間に配置されるセパレータを備えるものが一般的である。セパレータは、両電極間の短絡防止や電解液を保持する役割を果たす。セパレータとしては、一般的にポリエチレン、ポリプロピレン等のポリオレフィン系多孔質フィルムが用いられる。 (4) Lithium-ion secondary batteries are used as large stationary power sources for power storage and power sources for electric vehicles, etc. In recent years, research into miniaturization and thinning of batteries has been advanced. Generally, a lithium ion secondary battery includes both electrodes having an electrode active material layer formed on a surface of a current collector made of a metal foil or the like, and a separator disposed between both electrodes. The separator plays a role in preventing a short circuit between the two electrodes and holding the electrolytic solution. As the separator, a polyolefin-based porous film such as polyethylene or polypropylene is generally used.
　従来、リチウムイオン二次電池は、部品点数を少なくすることなどを目的として、上記多孔質フィルムを使用しないセパレータレスとすることが試みられている。セパレータレスとするために、電極活物質層表面に絶縁層を形成し、絶縁層により両電極間の短絡を防止することが検討されている。絶縁層としては、特許文献１に開示されるように、絶縁性粒子と、絶縁性粒子同士を結合させるバインダーを含み、３次元網目空隙構造を有するものが知られている。 Conventionally, lithium-ion secondary batteries have been attempted to be separatorless without using the porous film for the purpose of reducing the number of parts. In order to eliminate the separator, it has been studied to form an insulating layer on the surface of the electrode active material layer and prevent a short circuit between both electrodes by the insulating layer. As disclosed in Patent Document 1, as the insulating layer, a layer having a three-dimensional network void structure including insulating particles and a binder for bonding the insulating particles to each other is known.
特許第３２５３６３２号Patent No. 3253632
　ところで、リチウムイオン二次電池には、加熱されたときに熱暴走しないなどの安全性を確保しつつ、充放電特性、出力特性などを高めることが求められている。しかし、従来のセパレータレスで使用される絶縁層は、絶縁層の構成や電極活物質層との組み合わせが十分に検討されているとはいえず、安全性、充放電特性、及び出力特性が十分に高められているとはいえない。 By the way, there is a demand for a lithium ion secondary battery to improve charge / discharge characteristics, output characteristics, and the like while ensuring safety such as not causing thermal runaway when heated. However, it cannot be said that the structure of the insulating layer and the combination with the electrode active material layer of the conventional insulating layer used without a separator have not been sufficiently studied, and the safety, charge / discharge characteristics, and output characteristics are not sufficient. It cannot be said that it has been raised.
　そこで、本発明は、セパレータレスであっても、安全性、充放電特性、及び出力特性をいずれも良好にすることが可能なリチウムイオン二次電池、及びリチウムイオン二次電池用負極を提供することを課題とする。 Therefore, the present invention provides a lithium-ion secondary battery and a negative electrode for a lithium-ion secondary battery which can improve all of safety, charge / discharge characteristics, and output characteristics even without a separator. That is the task.
　本発明者らは、鋭意検討の結果、負極活物質層を形成するための負極用バインダー、絶縁層を形成するための絶縁層用バインダーに所定のバインダーを使用し、さらに、絶縁層におけるバインダー量、及び絶縁層の厚さを所定の範囲内に調整することで、上記課題が解決できることを見出し、以下の本発明を完成させた。本発明の要旨は、以下の［１］～［９］である。
［１］正極と、負極とを備えるリチウムイオン二次電池であって、
　前記負極が、負極活物質と負極用バインダーとを含有する負極活物質層と、前記負極活物質層の表面上に設けられ、絶縁性微粒子と絶縁層用バインダーとを含有する絶縁層とを備え、
　前記絶縁層が前記正極に接触するように配置され、
　前記負極用バインダーが水溶性ポリマーと粒子状結着剤を含み、      
　前記絶縁層用バインダーが有機溶剤可溶性ポリマーを含み、かつ前記有機溶剤可溶性ポリマーの含有量が、絶縁層全量基準で１５～４５体積％であり、
　前記絶縁層の厚さが１０～２０μｍである、リチウムイオン二次電池。
［２］前記有機溶剤可溶性ポリマーが、Ｎ－メチルピロリドンに可溶である上記［１］に記載のリチウムイオン二次電池。
［３］前記有機溶剤可溶性ポリマーが、ポリフッ化ビニリデン、及びアクリル樹脂からなる群から選択される少なくとも１種である上記［１］又は［２］に記載のリチウムイオン二次電池。
［４］前記水溶性ポリマーが、カルボキシメチルセルロース及びその塩、ヒドロキシエチルセルロース、ポリビニルアルコール、並びにポリビニルピロリドンからなる群から選択される少なくとも１種である上記［１］～［３］のいずれか１項に記載のリチウムイオン二次電池。
［５］前記粒子状結着剤が、スチレンブタジエンゴム、及びアクリル樹脂からなる群から選択される少なくとも１種である上記［１］～［４］のいずれか１項に記載のリチウムイオン二次電池。
［６］前記正極が正極活物質層を備え、前記絶縁層が前記正極活物質層に接触するように配置される上記［１］～［５］のいずれか１項に記載のリチウムイオン二次電池。
［７］積層型である、上記［１］～［６］のいずれか１項に記載のリチウムイオン二次電池。
［８］上記［１］～［７］のいずれか１項に記載のリチウムイオン二次電池の製造方法であって、
　前記負極活物質と前記負極用バインダーとを含有する負極活物質層の表面上に、絶縁層用組成物を塗布して絶縁層を形成して、負極を得る工程と、
　前記絶縁層を介して前記負極を正極に圧着させる工程とを備え、
　前記絶縁層用組成物が、前記絶縁性微粒子と前記絶縁層用バインダーと有機溶剤とを含む、リチウムイオン二次電池の製造方法。
［９］正極と負極の間にセパレータがない、セパレータレスのリチウムイオン二次電池用負極であって、
　負極活物質と負極用バインダーとを含有する負極活物質層と、前記負極活物質層の表面上に設けられ、絶縁性微粒子と絶縁層用バインダーとを含有する絶縁層とを備え、
　前記負極用バインダーが水溶性ポリマーと粒子状結着剤を含み、
　前記絶縁層用バインダーが有機溶剤可溶性ポリマーを含み、かつ前記有機溶剤可溶性ポリマーの含有量が、絶縁層全量基準で１５～４５体積％であり、
　前記絶縁層の厚さが１０～２０μｍである、リチウムイオン二次電池用負極。 The present inventors have conducted intensive studies and as a result, used a predetermined binder as a negative electrode binder for forming a negative electrode active material layer and a predetermined binder for an insulating layer binder for forming an insulating layer. It has been found that the above problem can be solved by adjusting the thickness of the insulating layer within a predetermined range, and the present invention described below has been completed. The gist of the present invention is the following [1] to [9].
[1] A lithium ion secondary battery including a positive electrode and a negative electrode,
The negative electrode includes a negative electrode active material layer containing a negative electrode active material and a negative electrode binder, and an insulating layer provided on a surface of the negative electrode active material layer and containing insulating fine particles and an insulating layer binder. ,
The insulating layer is disposed so as to contact the positive electrode,
The negative electrode binder contains a water-soluble polymer and a particulate binder,
The insulating layer binder contains an organic solvent-soluble polymer, and the content of the organic solvent-soluble polymer is 15 to 45% by volume based on the total amount of the insulating layer;
A lithium ion secondary battery, wherein the thickness of the insulating layer is 10 to 20 μm.
[2] The lithium ion secondary battery according to the above [1], wherein the organic solvent-soluble polymer is soluble in N-methylpyrrolidone.
[3] The lithium ion secondary battery according to the above [1] or [2], wherein the organic solvent-soluble polymer is at least one selected from the group consisting of polyvinylidene fluoride and an acrylic resin.
[4] The method according to any one of [1] to [3], wherein the water-soluble polymer is at least one selected from the group consisting of carboxymethylcellulose and salts thereof, hydroxyethylcellulose, polyvinyl alcohol, and polyvinylpyrrolidone. The lithium ion secondary battery according to the above.
[5] The lithium ion secondary according to any one of [1] to [4], wherein the particulate binder is at least one selected from the group consisting of styrene butadiene rubber and acrylic resin. battery.
[6] The lithium ion secondary according to any one of [1] to [5], wherein the positive electrode includes a positive electrode active material layer, and the insulating layer is arranged to be in contact with the positive electrode active material layer. battery.
[7] The lithium ion secondary battery according to any one of the above [1] to [6], which is a stacked type.
[8] The method for producing a lithium ion secondary battery according to any one of the above [1] to [7],
A step of applying an insulating layer composition to form an insulating layer on the surface of the negative electrode active material layer containing the negative electrode active material and the negative electrode binder, to obtain a negative electrode,
Pressure bonding the negative electrode to the positive electrode via the insulating layer,
A method for producing a lithium ion secondary battery, wherein the composition for an insulating layer contains the insulating fine particles, the binder for the insulating layer, and an organic solvent.
[9] There is no separator between the positive electrode and the negative electrode, a separator-less negative electrode for a lithium ion secondary battery,
A negative electrode active material layer containing a negative electrode active material and a negative electrode binder, and an insulating layer provided on the surface of the negative electrode active material layer and containing insulating fine particles and an insulating layer binder,
The negative electrode binder contains a water-soluble polymer and a particulate binder,
The insulating layer binder contains an organic solvent-soluble polymer, and the content of the organic solvent-soluble polymer is 15 to 45% by volume based on the total amount of the insulating layer;
A negative electrode for a lithium ion secondary battery, wherein the thickness of the insulating layer is 10 to 20 μm.
　本発明によれば、セパレータレスのリチウムイオン二次電池において、安全性、充放電特性、及び出力特性をいずれも良好にできる。 According to the present invention, in a separator-less lithium ion secondary battery, safety, charge / discharge characteristics, and output characteristics can all be improved.
本発明のリチウムイオン二次電池の一実施形態を示す概略断面図である。FIG. 1 is a schematic cross-sectional view showing one embodiment of a lithium ion secondary battery of the present invention.
＜リチウムイオン二次電池＞
　以下、本発明のリチウムイオン二次電池について詳細に説明する。
　図１に示すように、リチウムイオン二次電池１０は、負極１１と、正極２１とを備える。負極１１は、負極活物質層１２と、負極活物質層１２の表面上に設けられる絶縁層１３とを備える。リチウムイオン二次電池１０は、いわゆるセパレータレスであって、負極１１と正極２１の間にはこれら電極とは別部材として構成されるセパレータが設けられない。したがって、負極活物質層１２の表面上に設けられた絶縁層１３は、正極２１に接触するように配置されることになる。
　また、負極１１は、好ましくは絶縁層１３を介して、正極２１に圧着などにより接着して、負極１１と正極２１は一体的な積層体を構成するとよい。負極１１は、正極２１に圧着などにより接着することで、充放電特性、及び出力特性などを高めやすくなる。 <Lithium ion secondary battery>
Hereinafter, the lithium ion secondary battery of the present invention will be described in detail.
As shown in FIG. 1, the lithium ion secondary battery 10 includes a negative electrode 11 and a positive electrode 21. The negative electrode 11 includes a negative electrode active material layer 12 and an insulating layer 13 provided on a surface of the negative electrode active material layer 12. The lithium ion secondary battery 10 is a so-called separator-less type, and no separator is provided between the negative electrode 11 and the positive electrode 21 as a member separate from these electrodes. Therefore, the insulating layer 13 provided on the surface of the negative electrode active material layer 12 is arranged to be in contact with the positive electrode 21.
In addition, the negative electrode 11 is preferably bonded to the positive electrode 21 by pressing or the like via the insulating layer 13 so that the negative electrode 11 and the positive electrode 21 may form an integrated laminate. By adhering the negative electrode 11 to the positive electrode 21 by pressure bonding or the like, the charge / discharge characteristics, output characteristics, and the like can be easily improved.
　リチウムイオン二次電池１０において、負極１１は、通常、負極集電体１４を備え、負極活物質層１２は、負極集電体１４の上に積層される。正極２１は、正極活物質層２２を備える。正極２１において、正極活物質層２２は、通常、電極集電体２４の上に積層される。正極活物質層２２の表面（正極集電体２４側の面とは反対側の面）には、絶縁層などの表面層（図示しない）が設けられてもよいが、典型的には、表面層が設けられず、負極１１の絶縁層１３が正極活物質層２２に直接接触する。 In the lithium ion secondary battery 10, the negative electrode 11 usually includes a negative electrode current collector 14, and the negative electrode active material layer 12 is stacked on the negative electrode current collector 14. The positive electrode 21 includes a positive electrode active material layer 22. In the positive electrode 21, the positive electrode active material layer 22 is usually stacked on the electrode current collector 24. A surface layer (not shown) such as an insulating layer may be provided on the surface of the positive electrode active material layer 22 (the surface opposite to the surface on the positive electrode current collector 24 side). No layer is provided, and the insulating layer 13 of the negative electrode 11 directly contacts the positive electrode active material layer 22.
　なお、図１は、負極活物質層１２及び正極活物質層２２が、負極集電体１４、正極集電体２４それぞれの片面のみに設けられた構成を示すが、負極集電体１４の両面に負極活物質層１２が設けられてもよい。その場合、各負極活物質層１２の表面に絶縁層１３が設けられるとよい。また、正極集電体２４も同様に両面に正極活物質層２２が設けられるとよい。
　それぞれ両面に負極活物質層１２及び正極活物質層２２を有する、負極１１及び正極２１を使用する場合、負極１１及び正極２１は、それぞれ複数層設けられるように交互に配置され、各負極活物質層１２の表面に設けられた絶縁層１３が正極２１（正極活物質層２２）に接触するように配置されるとよい。 FIG. 1 shows a configuration in which the negative electrode active material layer 12 and the positive electrode active material layer 22 are provided only on one surface of each of the negative electrode current collector 14 and the positive electrode current collector 24. May be provided with a negative electrode active material layer 12. In that case, the insulating layer 13 is preferably provided on the surface of each negative electrode active material layer 12. Similarly, the positive electrode current collector 24 may be provided with the positive electrode active material layers 22 on both surfaces.
When the negative electrode 11 and the positive electrode 21 each having the negative electrode active material layer 12 and the positive electrode active material layer 22 on both surfaces are used, the negative electrode 11 and the positive electrode 21 are alternately arranged so that a plurality of layers are provided, respectively. It is preferable that the insulating layer 13 provided on the surface of the layer 12 be disposed so as to be in contact with the positive electrode 21 (the positive electrode active material layer 22).
［負極］
　以下、リチウムイオン二次電池の負極１１を構成する各層について詳細に説明する。
（負極活物質層）
　負極活物質層１２は、負極活物質と、負極用バインダーとを含む。
　負極活物質層に使用される負極活物質としては、グラファイト、ハードカーボンなどの炭素材料、スズ化合物とシリコンと炭素の複合体、リチウムなどが挙げられるが、これら中では炭素材料が好ましく、グラファイトがより好ましい。負極活物質は１種単独で使用してもよいし、２種以上を併用してもよい。
　負極活物質は、特に限定されないが、その平均粒子径が０．５～５０μｍであることが好ましく、１～３０μｍであることがより好ましい。
　なお、平均粒子径は、レーザー回折・散乱法によって求めた負極活物質の粒度分布において、体積積算が５０％での粒径（Ｄ５０）を意味し、他の粒子における平均粒子径も同様である。 [Negative electrode]
Hereinafter, each layer constituting the negative electrode 11 of the lithium ion secondary battery will be described in detail.
(Negative electrode active material layer)
The negative electrode active material layer 12 includes a negative electrode active material and a negative electrode binder.
Examples of the negative electrode active material used for the negative electrode active material layer include carbon materials such as graphite and hard carbon, a composite of a tin compound and silicon and carbon, and lithium. Among these, carbon materials are preferable, and graphite is preferable. More preferred. One kind of the negative electrode active material may be used alone, or two or more kinds may be used in combination.
The negative electrode active material is not particularly limited, but preferably has an average particle size of 0.5 to 50 μm, more preferably 1 to 30 μm.
The average particle diameter means the particle diameter (D50) at a volume integration of 50% in the particle size distribution of the negative electrode active material obtained by a laser diffraction / scattering method, and the same applies to the average particle diameter of other particles. .
　負極活物質層１１における負極活物質の含有量は、負極活物質層全量基準で、５０～９８．５質量％が好ましく、６０～９８質量％がより好ましく、７０～９８質量％がさらに好ましい。これら下限値以上とすることで、負極活物質層１２に適度な量の負極活物質が配合されることになり、リチウムイオン二次電池の充放電特性、出力特性などを良好にしやすくなる。また、上限値以下とすることで、負極活物質層１２に適度な量のバインダーを含有させることが可能になる。 負極 The content of the negative electrode active material in the negative electrode active material layer 11 is preferably 50 to 98.5% by mass, more preferably 60 to 98% by mass, and further preferably 70 to 98% by mass, based on the total amount of the negative electrode active material layer. By setting the lower limit or more, an appropriate amount of the negative electrode active material is blended in the negative electrode active material layer 12, and the charge / discharge characteristics and output characteristics of the lithium ion secondary battery can be easily improved. In addition, by setting the amount to be equal to or less than the upper limit, it becomes possible to make the anode active material layer 12 contain an appropriate amount of binder.
　負極活物質層１２は、導電助剤を含有してもよい。導電助剤は、上記負極活物質よりも導電性が高い材料が使用され、具体的には、ケッチェンブラック、アセチレンブラック、カーボンナノチューブ、棒状カーボンなどの炭素材料などが挙げられる。導電助剤は１種単独で使用してもよいし、２種以上を併用してもよい。
　負極活物質層１１において、導電助剤が含有される場合、導電助剤の含有量は、負極活物質層全量基準で、１～３０質量％であることが好ましく、２～２５質量％であることがより好ましい。これら範囲内とすることで、負極活物質に適度な導電性を付与して、リチウムイオン二次電池の各種性能を向上させやすくなる。ただし、負極活物質層１２は導電助剤を含有しないほうが好ましい。 The negative electrode active material layer 12 may contain a conductive auxiliary. As the conductive additive, a material having higher conductivity than the above-described negative electrode active material is used, and specific examples thereof include carbon materials such as Ketjen black, acetylene black, carbon nanotube, and rod-like carbon. The conductive auxiliary may be used alone or in combination of two or more.
When the negative electrode active material layer 11 contains a conductive auxiliary, the content of the conductive auxiliary is preferably 1 to 30% by mass, and more preferably 2 to 25% by mass, based on the total amount of the negative electrode active material layer. Is more preferable. When the content is within these ranges, appropriate conductivity is imparted to the negative electrode active material, and various performances of the lithium ion secondary battery are easily improved. However, it is preferable that the negative electrode active material layer 12 does not contain a conductive auxiliary.
＜負極用バインダー＞
　負極活物質層１２は、負極活物質、又は負極活物質及び導電助剤が負極用バインダーによって結着されて構成される。本発明において、負極用バインダーは、水溶性ポリマーと粒子状結着剤を含む。 <Binder for negative electrode>
The negative electrode active material layer 12 is formed by binding a negative electrode active material or a negative electrode active material and a conductive auxiliary with a negative electrode binder. In the present invention, the binder for the negative electrode contains a water-soluble polymer and a particulate binder.
　水溶性ポリマーは、水に対する溶解性が高いポリマーである。水溶性ポリマーは、水に対する溶解度が高いことで、後述する絶縁層を構成し、有機溶剤可溶性ポリマーを含有する絶縁層用バインダーとは相溶しにくい。そのため、負極活物質と後述する絶縁性微粒子とが混ざり合わずに、負極活物質層と絶縁層とは互いに層として分離する。したがって、負極活物質層１２と絶縁層１３はそれぞれ所望の性能を発揮しやすくなり、充放電特性、出力特性が良好となりやすい。 A water-soluble polymer is a polymer having high solubility in water. Since the water-soluble polymer has high solubility in water, the water-soluble polymer forms an insulating layer described later, and is hardly compatible with an insulating layer binder containing an organic solvent-soluble polymer. Thus, the negative electrode active material layer and the insulating layer are separated from each other as layers without the negative electrode active material and the insulating fine particles described later being mixed. Therefore, the negative electrode active material layer 12 and the insulating layer 13 can easily exhibit desired performance, respectively, and the charge / discharge characteristics and the output characteristics are likely to be good.
　本明細書において、溶解性を示す指標として固形分濃度低下量を用いる。固形分濃度低下量とは、所定の温度及び所定の濃度でバインダーを溶媒に溶解させたときに、不溶分の固形分がどの程度残るかを示す指標であり、値が低いほど溶解度が高いことを示す。固形分濃度低下量の具体的な測定方法は実施例に示すとおりである。
　負極用バインダーは、水溶性ポリマーを有することで、水に対する固形分濃度低下量が低くなる。負極用バインダーの水に対する固形分濃度低下量は、例えば５質量％以下、より好ましくは３質量％以下、さらに好ましくは１．５質量％以下である。負極用バインダーの水に対する固形分濃度低下量は、低いほうがよく、したがって０質量％以上であればよいが、実用的には０．５質量％以上である。 In the present specification, a solid content concentration decrease amount is used as an index indicating solubility. The solid content concentration decrease amount is an index indicating how much insoluble solids remain when a binder is dissolved in a solvent at a predetermined temperature and a predetermined concentration.The lower the value, the higher the solubility. Is shown. The specific method of measuring the amount of decrease in the solid content is as described in Examples.
Since the binder for the negative electrode has a water-soluble polymer, the amount of decrease in the solid content concentration with respect to water is reduced. The amount of decrease in the solid content of the binder for the negative electrode with respect to water is, for example, 5% by mass or less, more preferably 3% by mass or less, and further preferably 1.5% by mass or less. The lowering of the solid content concentration of the binder for the negative electrode with respect to water is preferably as low as possible, and may be 0% by mass or more, but practically 0.5% by mass or more.
　一方で、水溶性ポリマーは、有機溶剤に対する溶解性は低い。具体的には、水溶性ポリマーは、Ｎ－メチルピロリドン（ＮＭＰ）に対する溶解性が低く、したがって、負極用バインダーは、ＮＭＰに対する固形分濃度低下量が高くなる。具体的には、負極用バインダーのＮＭＰに対する固形分濃度低下量は、例えば１０質量％以上、好ましくは１５質量％以上、より好ましくは１８質量％以上である。これら下限値以上とすることで、負極用バインダーは、絶縁層用バインダーに対してより相溶しにくくなる。
　負極用バインダーのＮＭＰに対する固形分濃度低下量は、高いほうがよく、１００質量％以下であればよいが、実用的には５０質量％以下程度である。なお、ここで、有機溶剤に対する溶解度の指標としてＮＭＰを使用した理由は、ＮＭＰが有機溶媒の中でも様々な物質に対する溶解性に優れ、かつ絶縁層用組成物の溶媒として一般的に使用されるからである。 On the other hand, water-soluble polymers have low solubility in organic solvents. Specifically, the water-soluble polymer has low solubility in N-methylpyrrolidone (NMP), and therefore, the binder for the negative electrode has a large decrease in the solid concentration with respect to NMP. Specifically, the amount of decrease in the solid concentration of the binder for the negative electrode with respect to NMP is, for example, 10% by mass or more, preferably 15% by mass or more, and more preferably 18% by mass or more. By setting the lower limit or more, the binder for the negative electrode becomes more difficult to be compatible with the binder for the insulating layer.
The lowering of the solid content concentration of the binder for the negative electrode with respect to NMP is preferably as high as 100% by mass or less, but practically 50% by mass or less. Here, the reason why NMP was used as an index of solubility in an organic solvent is that NMP has excellent solubility in various substances among organic solvents, and is generally used as a solvent for a composition for an insulating layer. It is.
　水溶性ポリマーの具体例としては、セルロール系化合物、及びその塩、ポリビニルアルコール、並びにポリビニルピロリドンなどが挙げられる。これらは１種単独で使用してもよいし、２種以上を併用してもよい。
　セルロール系化合物及びその塩としては、例えば、ヒドロキシエチルセルロース、ヒドロキシプロピルセルロース、メチルセルロース、カルボキシメチルセルロースおよびこれらのナトリウム塩、アンモニウム塩などが挙げられる。
　水溶性ポリマーとしては、上記した中では、カルボキシメチルセルロース及びその塩、ヒドロキシエチルセルロース及びその塩、ポリビニルアルコール、並びにポリビニルピロリドンより選択される少なくとも１種を含むことが好ましく、カルボキシメチルセルロース及びその塩から選択される少なくとも１種が特に好ましい。なお、カルボキシメチルセルロースの塩としては、ナトリウム塩が好ましい。
　カルボキシメチルセルロースの塩は、水へ濃度１質量％で溶解させたときのＢ型粘度計によって測定した２５℃、６０ｒｐｍ条件での粘度が、例えば、１０～５０００ｍＰａ・ｓ、好ましくは２００～４０００ｍＰａ・ｓである。 Specific examples of the water-soluble polymer include a cellulose compound and a salt thereof, polyvinyl alcohol, and polyvinylpyrrolidone. These may be used alone or in combination of two or more.
Examples of the cellulose compound and its salt include hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, and their sodium and ammonium salts.
The water-soluble polymer preferably contains at least one selected from the group consisting of carboxymethylcellulose and salts thereof, hydroxyethylcellulose and salts thereof, polyvinyl alcohol, and polyvinylpyrrolidone, and is selected from carboxymethylcellulose and salts thereof. At least one is particularly preferred. In addition, as a salt of carboxymethyl cellulose, a sodium salt is preferable.
The carboxymethyl cellulose salt has a viscosity of, for example, 10 to 5000 mPa · s, preferably 200 to 4000 mPa · s at 25 ° C. and 60 rpm measured by a B-type viscometer when dissolved in water at a concentration of 1% by mass. It is.
　粒子状結着剤としては、ゴム粒子を使用することができる。ゴムとしては、ブタジエンなどの共役ジエン系モノマー由来の構成単位を有する共役ジエン系重合体などが挙げられ、例えば、芳香族系ビニル単量体由来の構成単位とブタジエン由来の構成単位とを有するゴムが挙げられる。具体的な好適な化合物としては、スチレンブタジエンゴムが挙げられる。
　また、粒子状結着剤の別の具体例としては、アクリル樹脂からなるものが挙げられる。アクリル樹脂としては、アルキル（メタ）アクリル酸エステルなどの（メタ）アクリル酸エステル由来の構成単位を有するアクリル系重合体が挙げられる。具体的には、ポリメタクリル酸メチルやポリアクリル酸ブチルなどの炭素数１～８程度のアルキル（メタ）アクリル酸エステルの重合体、及びこれらから選択される２以上の共重合体などが挙げられる。
　粒子状結着剤としては、上記した中では、スチレンブタジエンゴム及びアクリル樹脂から選択される１種又は２種以上が好ましいが、特に好ましくはスチレンブタジエンゴムである。したがって、負極用バインダーとしては、カルボキシメチルセルロース及びその塩から選択される１種以上を使用し、かつ粒子状結着剤としてスチレンブタジエンゴムを使用することが特に好ましい。 Rubber particles can be used as the particulate binder. Examples of the rubber include a conjugated diene-based polymer having a constituent unit derived from a conjugated diene-based monomer such as butadiene, and, for example, a rubber having a constituent unit derived from an aromatic vinyl monomer and a constituent unit derived from butadiene. Is mentioned. Specific preferred compounds include styrene butadiene rubber.
Another specific example of the particulate binder includes an acrylic resin. Examples of the acrylic resin include an acrylic polymer having a structural unit derived from a (meth) acrylate such as an alkyl (meth) acrylate. Specific examples include polymers of alkyl (meth) acrylates having about 1 to 8 carbon atoms, such as polymethyl methacrylate and polybutyl acrylate, and two or more copolymers selected from these. .
As the particulate binder, among the above, one or more selected from styrene-butadiene rubber and acrylic resin are preferable, and styrene-butadiene rubber is particularly preferable. Therefore, it is particularly preferable to use at least one selected from carboxymethylcellulose and its salts as the negative electrode binder, and to use styrene-butadiene rubber as the particulate binder.
　粒子状結着剤の平均粒子径は、特に限定されないが、好ましくは１０～５００ｎｍ、より好ましくは５０～３００ｎｍである。粒子状結着剤の平均粒子径がこれら範囲内であることで、粒子状結着剤を負極活物質層１２中に適切に分散することができ、負極活物質層１２の性能が優れたものとなる。 平均 The average particle diameter of the particulate binder is not particularly limited, but is preferably 10 to 500 nm, more preferably 50 to 300 nm. When the average particle diameter of the particulate binder is within these ranges, the particulate binder can be appropriately dispersed in the negative electrode active material layer 12, and the performance of the negative electrode active material layer 12 is excellent. Becomes
　本発明において、水溶性ポリマーと粒子状結着剤の合計量は、負極活物質層全量基準で、１．５～４０質量％であることが好ましく、２．０～２５質量％がより好ましく、２．０～２０質量％がより好ましい。これら下限値以上とすることで、負極用バインダーによって、負極活物質、又は負極活物質及び導電助剤を負極活物質層１２に適切に定着させることが可能である。また、これら上限値以上とすることで、バインダー量が多くなりすぎて、負極の性能が低下するのを防止する。 In the present invention, the total amount of the water-soluble polymer and the particulate binder is preferably 1.5 to 40% by mass, more preferably 2.0 to 25% by mass, based on the total amount of the negative electrode active material layer. 2.0-20% by mass is more preferred. By setting the lower limit value or more, the negative electrode active material, or the negative electrode active material and the conductive assistant can be appropriately fixed to the negative electrode active material layer 12 by the negative electrode binder. In addition, when the content is not less than the upper limit, it is possible to prevent the amount of the binder from being excessively large and prevent the performance of the negative electrode from being lowered.
　水溶性ポリマーに対する粒子状結着剤の質量比（粒子状結着剤／水溶性ポリマー）は、１／４～４が好ましく、１／２～２がより好ましく、２／３～３／２がさらに好ましい。これら範囲内とすることで、負極活物質、又は負極活物質及び導電助剤が負極用バインダーによって適切に保持される。また、上限値以下とすることで、負極活物質層は、一定量の水溶性ポリマーが含有することになるので、後述する有機溶剤可溶性ポリマーがバインダーとして使用される絶縁層との相溶性が低くなり、負極活物質層と絶縁層とが混ざり合いにくくなる。 The mass ratio of the particulate binder to the water-soluble polymer (particulate binder / water-soluble polymer) is preferably 1/4 to 4, more preferably 1/2 to 2, and 2/3 to 3/2. More preferred. When the content is within these ranges, the negative electrode active material, or the negative electrode active material and the conductive assistant are appropriately held by the negative electrode binder. In addition, by being equal to or less than the upper limit, since the negative electrode active material layer contains a certain amount of water-soluble polymer, the compatibility with the insulating layer in which an organic solvent-soluble polymer described later is used as a binder is low. This makes it difficult for the negative electrode active material layer and the insulating layer to mix.
　各負極活物質層１２の厚さは、特に限定されないが、１０～１００μｍが好ましく、２０～８０μｍがより好ましい。
　負極活物質層１２は、本発明の効果を損なわない範囲内において、負極活物質、導電助剤、及び負極用バインダー以外の他の任意成分を含んでもよい。また、負極用バインダーは、水溶性ポリマーと粒子状結着剤からなることが好ましいが、その他のバインダーを含有してもよい。その他のバインダーは、本発明の効果を損なわない量であればよいが、例えば、負極用バインダー全量に対して、１０質量％未満、好ましくは５質量％未満の量である。
　ただし、負極活物質層１２の総質量のうち、負極活物質、導電助剤、水溶性ポリマー、及び粒子状結着剤の合計含有量は、９０質量％以上であることが好ましく、９５質量％以上であることがより好ましい。 The thickness of each negative electrode active material layer 12 is not particularly limited, but is preferably 10 to 100 μm, and more preferably 20 to 80 μm.
The negative electrode active material layer 12 may contain other optional components other than the negative electrode active material, the conductive assistant, and the negative electrode binder as long as the effects of the present invention are not impaired. The negative electrode binder preferably comprises a water-soluble polymer and a particulate binder, but may contain other binders. Other binders may be used in amounts that do not impair the effects of the present invention. For example, the amount is less than 10% by mass, preferably less than 5% by mass, based on the total amount of the binder for the negative electrode.
However, in the total mass of the negative electrode active material layer 12, the total content of the negative electrode active material, the conductive auxiliary, the water-soluble polymer, and the particulate binder is preferably 90% by mass or more, and 95% by mass or more. More preferably, it is the above.
　負極活物質層１２の密度（電極密度）は、好ましくは１．３～２．０ｇ／ｃｃ、より好ましくは１．４～１．８ｇ／ｃｃである。電極密度をこれら範囲内とすることで、負極活物質層１２の性能が良好となる。また、これら下限値以上とすることで、後述する絶縁層用組成物（すなわち、絶縁層１２）がより一層負極活物質層１２に染み込みにくくなり、負極活物質層１２と絶縁層１３とが混ざりにくくなり、充放電特性、出力特性などが良好となりやすい。 密度 The density (electrode density) of the negative electrode active material layer 12 is preferably 1.3 to 2.0 g / cc, and more preferably 1.4 to 1.8 g / cc. By setting the electrode density within these ranges, the performance of the negative electrode active material layer 12 is improved. Further, when the content is not less than these lower limits, the composition for an insulating layer described later (that is, the insulating layer 12) becomes more difficult to permeate into the negative electrode active material layer 12, and the negative electrode active material layer 12 and the insulating layer 13 are mixed. The charge / discharge characteristics, output characteristics, and the like are likely to be good.
　なお、負極活物質層１２の密度は、負極活物質層の単位面積当たりの質量と、負極活物質層の厚さを得て、これらより算出することができる。
　例えば、絶縁層形成前の負極を所定の大きさ（例えば、直径１６ｍｍ）で打ち抜いた測定試料を複数枚準備する。各測定試料の質量を精密天秤にて秤量し、質量を測定する。予め測定した負極集電体の質量を測定結果から差し引くことにより、測定試料中の負極活物質層の質量を算出することができる。また、断面出し加工した測定試料をＳＥＭで観察するなどの公知の方法によって、負極活物質層の厚みを測定する。各測定値の平均値から下記式（１）に基づいて、負極活物質層の密度を算出することができる。
　負極活物質層の密度（ｇ／ｃｃ）＝負極活物質層の質量（ｇ）／［（負極活物質の厚み
（ｃｍ）×打ち抜いた負極の面積（ｃｍ２）］・・・（１） The density of the negative electrode active material layer 12 can be calculated from the mass per unit area of the negative electrode active material layer and the thickness of the negative electrode active material layer.
For example, a plurality of measurement samples prepared by punching the negative electrode before forming the insulating layer into a predetermined size (for example, a diameter of 16 mm) are prepared. The mass of each measurement sample is weighed with a precision balance, and the mass is measured. By subtracting the previously measured mass of the negative electrode current collector from the measurement result, the mass of the negative electrode active material layer in the measurement sample can be calculated. In addition, the thickness of the negative electrode active material layer is measured by a known method such as observing a measurement sample subjected to cross-section processing with an SEM. The density of the negative electrode active material layer can be calculated from the average of the measured values based on the following equation (1).
Density of negative electrode active material layer (g / cc) = mass of negative electrode active material layer (g) / [(thickness of negative electrode active material (cm) × area of punched negative electrode (cm 2 )] (1)
（絶縁層）
　絶縁層１３は、絶縁性微粒子と絶縁層用バインダーとを含有する。
　絶縁層１３は、絶縁性微粒子が絶縁層用バインダーによって結着されて構成される。本発明において、絶縁層用バインダーは、有機溶剤可溶性ポリマーを含む。
　有機溶剤可溶性ポリマーは、有機溶剤に可溶なポリマーであり、有機溶剤に対する溶解性が高いポリマーである。本発明では、有機溶剤可溶性ポリマーは、負極活物質層１２を形成する水溶性ポリマーと相溶しにくいため、絶縁層１３と負極活物質層１２とは互いに層として分離し、それぞれ所望の性能を発揮しやすくなる。そのため、リチウムイオン二次電池は、充放電特性、出力特性が良好となる。 (Insulating layer)
The insulating layer 13 contains insulating fine particles and a binder for the insulating layer.
The insulating layer 13 is formed by binding insulating fine particles with an insulating layer binder. In the present invention, the binder for the insulating layer contains an organic solvent-soluble polymer.
The organic solvent-soluble polymer is a polymer that is soluble in an organic solvent and has high solubility in an organic solvent. In the present invention, since the organic solvent-soluble polymer is hardly compatible with the water-soluble polymer forming the negative electrode active material layer 12, the insulating layer 13 and the negative electrode active material layer 12 are separated from each other as layers, and each has a desired performance. Easy to demonstrate. Therefore, the lithium ion secondary battery has favorable charge / discharge characteristics and output characteristics.
＜各成分の含有量＞
　本発明では、絶縁層１３における有機溶剤可溶性ポリマーの含有量は、絶縁層全量基準で１５～４５体積％である。この含有量が１５体積％未満であると、絶縁層の強度が不十分となることで、絶縁性の維持が難しくなり安全性が低下したりする。また、４５体積％を超えると、絶縁層１３には必要な空隙が形成されずに出力特性が低下したりする。
　有機溶剤可溶性ポリマーの含有量は、安全性を高め、充放電特性も良好にする観点から、１８体積％以上であることが好ましく、２０体積％以上であることがより好ましく、２３体積％以上であることがさらに好ましい。
　有機溶剤可溶性ポリマーの含有量は、絶縁層１３における空隙量を適切な量にして、出力特性を高めるために、４０体積％以下が好ましく、３５体積％以下がより好ましく、２９体積％以下がさらに好ましい。 <Content of each component>
In the present invention, the content of the organic solvent-soluble polymer in the insulating layer 13 is 15 to 45% by volume based on the total amount of the insulating layer. When the content is less than 15% by volume, the strength of the insulating layer becomes insufficient, so that it is difficult to maintain the insulating property and the safety is reduced. On the other hand, when the content exceeds 45% by volume, necessary voids are not formed in the insulating layer 13 and output characteristics are deteriorated.
The content of the organic solvent-soluble polymer is preferably 18% by volume or more, more preferably 20% by volume or more, and more preferably 23% by volume or more, from the viewpoint of enhancing safety and improving charge / discharge characteristics. It is more preferred that there be.
The content of the organic solvent-soluble polymer is preferably 40% by volume or less, more preferably 35% by volume or less, and further preferably 29% by volume or less, in order to make the void amount in the insulating layer 13 an appropriate amount and enhance the output characteristics. preferable.
　一方で、絶縁性微粒子の含有量は、絶縁層全体の体積基準で、例えば５５～８５体積％である。５５体積％以上となることで、絶縁層１３に必要な空隙が形成され、出力特性が良好となる。また、８５体積％以下となることで、絶縁層の強度が高くなり、絶縁性を確保しやすくなる。
　絶縁性微粒子の含有量は、絶縁層１３における空隙量を適切な量にして、出力特性を高めるために、６０体積％以上が好ましく、６５体積％以上がより好ましく、７１体積％以上がさらに好ましい。
　絶縁性微粒子の含有量は、安全性を高め、充放電特性も良好にする観点から、８２体積％以下が好ましく、８０体積％以下であることがより好ましく、７７体積％以上であることがさらに好ましい。 On the other hand, the content of the insulating fine particles is, for example, 55 to 85% by volume based on the volume of the entire insulating layer. When the content is 55% by volume or more, necessary voids are formed in the insulating layer 13, and the output characteristics are improved. Further, when the content is 85% by volume or less, the strength of the insulating layer is increased, and the insulating property is easily ensured.
The content of the insulating fine particles is preferably 60% by volume or more, more preferably 65% by volume or more, and still more preferably 71% by volume or more, in order to make the void amount in the insulating layer 13 an appropriate amount and enhance output characteristics. .
The content of the insulating fine particles is preferably 82% by volume or less, more preferably 80% by volume or less, and further preferably 77% by volume or more, from the viewpoint of enhancing safety and improving charge / discharge characteristics. preferable.
＜厚さ＞
　さらに、本発明では、絶縁層１３の厚さが１０～２０μｍである。厚さが１０μｍ未満となると、有機溶剤可溶性ポリマーの含有量を上記した所定の範囲としても、絶縁性の確保が難しくなり、安全性が低下する。一方で、２０μｍより大きくなると、絶縁層が必要以上に厚くなり、出力特性が低下する。
　絶縁層１３の厚さは、充放電特性及び安全性を高める観点から、１１μｍ以上が好ましく、１３μｍ以上がより好ましい。また、出力特性を高める観点からは、絶縁層１３の厚さは、１９μｍ以下が好ましく、１７μｍ以下がより好ましい。 <Thickness>
Further, in the present invention, the thickness of the insulating layer 13 is 10 to 20 μm. If the thickness is less than 10 μm, it becomes difficult to ensure insulation even if the content of the organic solvent-soluble polymer is within the above-mentioned predetermined range, and safety is reduced. On the other hand, when the thickness is larger than 20 μm, the insulating layer becomes thicker than necessary, and the output characteristics deteriorate.
The thickness of the insulating layer 13 is preferably 11 μm or more, and more preferably 13 μm or more, from the viewpoint of enhancing the charge / discharge characteristics and safety. In addition, from the viewpoint of improving output characteristics, the thickness of the insulating layer 13 is preferably equal to or less than 19 μm, and more preferably equal to or less than 17 μm.
＜絶縁性微粒子＞
　本発明で使用する絶縁性微粒子は、絶縁性であれば特に限定されず、有機粒子、無機粒子の何れであってもよい。具体的な有機粒子としては、例えば、架橋ポリメタクリル酸メチル、架橋スチレン－アクリル酸共重合体、架橋アクリロニトリル樹脂、ポリアミド樹脂、ポリイミド樹脂、ポリ（２－アクリルアミド－２－メチルプロパンスルホン酸リチウム）、ポリアセタール樹脂、エポキシ樹脂、ポリエステル樹脂、フェノール樹脂、メラミン樹脂等の有機化合物から構成される粒子が挙げられる。無機粒子としては二酸化ケイ素、窒化ケイ素、アルミナ、ベーマイト、チタニア、ジルコニア、窒化ホウ素、酸化亜鉛、二酸化スズ、酸化ニオブ（Ｎｂ２Ｏ５）、酸化タンタル（Ｔａ２Ｏ５）、フッ化カリウム、フッ化リチウム、クレイ、ゼオライト、炭酸カルシウム等の無機化合物から構成される粒子が挙げられる。また、無機粒子は、ニオブ－タンタル複合酸化物、マグネシウム－タンタル複合酸化物等の公知の複合酸化物から構成される粒子であってもよい。
　絶縁性微粒子は、上記した各材料が１種単独で使用される粒子であってもよいし、２種以上が併用される粒子であってもよい。また、絶縁性微粒子は、無機化合物と有機化合物の両方を含む微粒子であってもよい。例えば、有機化合物からなる粒子の表面に無機酸化物をコーティングした無機有機複合粒子であってもよい。
　これらの中では、無機粒子が好ましく、中でもアルミナ粒子、ベーマイト粒子が好ましく、アルミナ粒子が特に好ましい。 <Insulating fine particles>
The insulating fine particles used in the present invention are not particularly limited as long as they are insulating, and may be either organic particles or inorganic particles. Specific organic particles include, for example, cross-linked polymethyl methacrylate, cross-linked styrene-acrylic acid copolymer, cross-linked acrylonitrile resin, polyamide resin, polyimide resin, poly (lithium 2-acrylamido-2-methylpropanesulfonate), Examples include particles composed of an organic compound such as a polyacetal resin, an epoxy resin, a polyester resin, a phenol resin, and a melamine resin. Examples of the inorganic particles include silicon dioxide, silicon nitride, alumina, boehmite, titania, zirconia, boron nitride, zinc oxide, tin dioxide, niobium oxide (Nb 2 O 5 ), tantalum oxide (Ta 2 O 5 ), potassium fluoride, and fluoride. Examples include particles composed of inorganic compounds such as lithium chloride, clay, zeolite, and calcium carbonate. Further, the inorganic particles may be particles composed of a known composite oxide such as a niobium-tantalum composite oxide or a magnesium-tantalum composite oxide.
The insulating fine particles may be particles in which each of the above-mentioned materials is used alone or in combination of two or more. Further, the insulating fine particles may be fine particles containing both an inorganic compound and an organic compound. For example, inorganic-organic composite particles in which an inorganic oxide is coated on the surface of particles made of an organic compound may be used.
Among these, inorganic particles are preferable, and among them, alumina particles and boehmite particles are preferable, and alumina particles are particularly preferable.
　絶縁性微粒子の平均粒子径は、絶縁層の厚さよりも小さくなるものであり、例えば０．００１～１μｍ、好ましくは０．０５～０．８μｍ、より好ましくは０．１～０．６μｍである。絶縁層の平均粒子径をこれら範囲内することで、空隙率を上記範囲内に調整しやすくなる。
　絶縁性微粒子は、平均粒子径が上記範囲内の１種が単独で使用されてもよいし、平均粒子径の異なる２種の絶縁性微粒子が混合されて使用されてもよい。 The average particle diameter of the insulating fine particles is smaller than the thickness of the insulating layer, and is, for example, 0.001 to 1 μm, preferably 0.05 to 0.8 μm, and more preferably 0.1 to 0.6 μm. . By setting the average particle diameter of the insulating layer within these ranges, the porosity can be easily adjusted within the above range.
As the insulating fine particles, one kind having an average particle diameter within the above range may be used alone, or two kinds of insulating fine particles having different average particle diameters may be mixed and used.
＜有機溶剤可溶性ポリマー＞
　上記した有機溶剤可溶性ポリマーは、有機溶剤、特に、絶縁層を形成するための有機溶剤に対して可溶であるものであるが、好ましくはＮ－メチルピロリドン（ＮＭＰ）に可溶である。ＮＭＰは、一般的に絶縁層を形成するための絶縁層用組成物の希釈溶媒として使用されるため、ＮＭＰに可溶であることで、絶縁層を適切に形成しやすくなる。 <Organic solvent soluble polymer>
The organic solvent-soluble polymer described above is soluble in an organic solvent, particularly an organic solvent for forming an insulating layer, but is preferably soluble in N-methylpyrrolidone (NMP). Since NMP is generally used as a diluting solvent for a composition for an insulating layer for forming an insulating layer, it is easy to form an insulating layer appropriately by being soluble in NMP.
　したがって、絶縁層用バインダーは、有機溶剤可溶性ポリマーを含有することでＮＭＰに対する固形分濃度低下量が低くなり、例えば１質量％以下、より好ましくは０．４質量％以下、さらに好ましくは０．１質量％以下である。絶縁層用バインダーのＮＭＰに対する固形分濃度低下量は、低いほうがよく、したがって０質量％以上であればよい。 Accordingly, the binder for the insulating layer contains the organic solvent-soluble polymer, so that the solid content concentration decrease with respect to NMP is reduced, for example, 1% by mass or less, more preferably 0.4% by mass or less, further preferably 0.1% by mass or less. % By mass or less. The lowering of the solid content concentration of the binder for the insulating layer with respect to the NMP is preferably low, and therefore it is sufficient that the amount is 0% by mass or more.
　一方で、有機溶剤可溶性ポリマーは、水に対する溶解性は低い。そのため、有機溶剤可溶性ポリマーを含有する絶縁層用バインダーは、水に対する固形分濃度低下量が高くなる。絶縁層用バインダーの水に対する固形分濃度低下量は、例えば５０質量％以上、好ましくは７５質量％以上、より好ましくは８５質量％以上である。これら下限値以上とすることで、絶縁層が、負極活物質層に対してより相溶しにくくなる。絶縁層用バインダーの水に対する固形分濃度低下量は、高いほうがよく、１００質量％以下であればよいが、実用的には９９質量％以下程度である。 On the other hand, organic solvent-soluble polymers have low solubility in water. Therefore, the binder for the insulating layer containing the polymer soluble in an organic solvent has a large decrease in the solid concentration with respect to water. The amount of decrease in the solid content of the binder for the insulating layer with respect to water is, for example, 50% by mass or more, preferably 75% by mass or more, and more preferably 85% by mass or more. By setting the lower limit or more, the insulating layer becomes more difficult to be compatible with the negative electrode active material layer. The lowering of the solid content concentration of the binder for the insulating layer with respect to water is preferably as high as 100% by mass or less, but is practically 99% by mass or less.
　なお、有機溶剤可溶性ポリマーは、それ自体も、ＮＭＰに対する固形分濃度低下量が低いものであり、具体的には１質量％以下、より好ましくは０．４質量％以下、さらに好ましくは０．１質量％以下である。また、有機溶剤可溶性ポリマーのＮＭＰに対する固形分濃度低下量は、低いほうがよく、したがって０質量％以上であればよい。 In addition, the organic solvent-soluble polymer itself has a low decrease in solid content concentration with respect to NMP, and specifically, is 1% by mass or less, more preferably 0.4% by mass or less, and further preferably 0.1% by mass or less. % By mass or less. Further, the lowering of the solid content concentration of the organic solvent-soluble polymer with respect to NMP is better, and it is sufficient that the amount is 0% by mass or more.
　有機溶剤可溶性ポリマーとしては、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリフッ化ビニリデン－ヘキサフルオロプロピレン共重合体（ＰＶＤＦ－ＨＦＰ）等のフッ素含有樹脂、アクリル樹脂、ポリ酢酸ビニル、ポリイミド（ＰＩ）、ポリアミド（ＰＡ）、ポリ塩化ビニル（ＰＶＣ）、ポリエーテルニトリル（ＰＥＮ）、ポリエチレン（ＰＥ）、ポリプロピレン（ＰＰ）、ポリアクリロニトリル（ＰＡＮ）などが挙げられる。これらは１種単独で使用してよいし、２種以上を併用してもよい。
　これらの中では、ポリフッ化ビニリデン、及びアクリル樹脂から選択される少なくとも１種であることが好ましく、アクリル樹脂がより好ましい。これら樹脂を使用することで、本発明では、絶縁層用バインダーは、負極用バインダーと相溶しにくくなり、絶縁層及び負極活物質層がそれぞれ別の層として存在しやすくなり、各層が所望の機能を良好に発揮しやすくなる。そのため、リチウムイオン二次電池の充放電特性、及び出力特性が良好となる。また、アクリル樹脂を使用すると、絶縁層用バインダーの接着力が高められ、正極活物質層２２や負極活物質層１２に対する接着性が高められる。 Examples of the organic solvent-soluble polymer include fluorine-containing resins such as polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), acrylic resin, polyvinyl acetate, polyimide (PI), and polyamide (PA). ), Polyvinyl chloride (PVC), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP), polyacrylonitrile (PAN), and the like. These may be used alone or in combination of two or more.
Among these, at least one selected from polyvinylidene fluoride and an acrylic resin is preferable, and an acrylic resin is more preferable. By using these resins, in the present invention, the binder for the insulating layer is hardly compatible with the binder for the negative electrode, and the insulating layer and the negative electrode active material layer are likely to be present as separate layers. It becomes easy to exhibit the function well. Therefore, the charge / discharge characteristics and the output characteristics of the lithium ion secondary battery are improved. When an acrylic resin is used, the adhesive strength of the insulating layer binder is increased, and the adhesiveness to the positive electrode active material layer 22 and the negative electrode active material layer 12 is increased.
　有機溶剤可溶性ポリマーとして使用されるアクリル樹脂は、（メタ）アクリル酸エステル由来の構成単位を有するアクリル系重合体が挙げられる。具体的には、アルキル（メタ）アクリレート由来の構成単位を有することが好ましく、アルキル（メタ）アクリレート由来の構成単位を例えば５０質量％以上、好ましくは７０質量％以上、より好ましくは９０質量％以上含有する。
　アルキル（メタ）アクリレートは、好ましくはアルキル基の炭素数が１～１２、より好ましくは２～８のアルキルアクリレートである。そして、アクリル系重合体は、アルキル基の炭素数が２～８のアルキルアクリレート由来の構成単位を好ましくは５０質量％以上、より好ましくは７０質量％以上、さらに好ましくは９０質量％以上を主鎖上に含有する。 The acrylic resin used as the organic solvent-soluble polymer includes an acrylic polymer having a structural unit derived from a (meth) acrylic ester. Specifically, it is preferable to have a structural unit derived from an alkyl (meth) acrylate, and the structural unit derived from an alkyl (meth) acrylate is, for example, 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more. contains.
The alkyl (meth) acrylate is preferably an alkyl acrylate having an alkyl group having 1 to 12, more preferably 2 to 8, carbon atoms. The acrylic polymer preferably contains 50% by mass or more, more preferably 70% by mass or more, and still more preferably 90% by mass or more of a main unit of an alkyl acrylate-derived structural unit having 2 to 8 carbon atoms in the alkyl group. Contains on top.
　アルキル基の炭素数が２～８のアルキルアクリレートとしては、エチルアクリレート、プロピルアクリレート、ブチルアクリレート、ペンチルアクリレート、ヘキシルアクリレート、オクチルアクリレートなどが挙げられる。これらにおけるアルキル基は、直鎖アルキル基であってもよいし、その構造異性体である分岐アルキル基であってもよく、例えば２－エチルヘキシルアクリレートなどであってもよい。
　また、アクリル系重合体は、アルキル（メタ）アクリレートと、アルキル（メタ）アクリレート以外のビニルモノマーとの共重合体であってもよい。アルキル（メタ）アクリレート以外のビニルモノマーとしては、２－ヒドロキシエチル（メタ）アクリレートなどの水酸基含有（メタ）アクリレート、アミノ基含有（メタ）アクリレート、アクリロニトリルなどのニトリル基含有ビニルモノマー、（メタ）アクリル酸、イタコン酸などのカルボキシル基含有ビニルモノマー、フェノキシエチル（メタ）アクリレートなど芳香環含有（メタ）アクリレートなどが挙げられる。 Examples of the alkyl acrylate having 2 to 8 carbon atoms in the alkyl group include ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, and octyl acrylate. The alkyl group in these may be a straight-chain alkyl group or a branched alkyl group which is a structural isomer thereof, such as 2-ethylhexyl acrylate.
Further, the acrylic polymer may be a copolymer of an alkyl (meth) acrylate and a vinyl monomer other than the alkyl (meth) acrylate. Examples of vinyl monomers other than alkyl (meth) acrylate include vinyl group-containing (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, amino group-containing (meth) acrylates, nitrile group-containing vinyl monomers such as acrylonitrile, and (meth) acrylic. Examples include carboxyl group-containing vinyl monomers such as acid and itaconic acid, and aromatic ring-containing (meth) acrylates such as phenoxyethyl (meth) acrylate.
　好適なアクリル系重合体の具体例としては、ポリブチルアクリレートが挙げられる。
　また、アクリル系重合体は、架橋していてもよく、好ましい具体例としては、架橋ポリブチルアクリレートなどが挙げられる。
　なお、本明細書においては、（メタ）アクリレートとは、アクリレート及びメタクリレートの一方又は両方を意味し、他の類似する用語も同様である。 Specific examples of suitable acrylic polymers include polybutyl acrylate.
In addition, the acrylic polymer may be cross-linked, and specific examples thereof include cross-linked polybutyl acrylate.
In this specification, (meth) acrylate means one or both of acrylate and methacrylate, and the same applies to other similar terms.
　本発明は、上記のように、水溶性ポリマーを含む負極用バインダーと、有機溶剤可溶性ポリマーを含む絶縁層用バインダーとが相溶しにくくなり、充放電特性、及び出力特性をより優れたものとするものである。そのような観点から、水溶性ポリマーが、カルボキシメチルセルロース及びその塩、ヒドロキシエチルセルロース、ポリビニルアルコール、並びにポリビニルピロリドンから選択される１種又は２種以上であるとともに、有機溶剤可溶性ポリマーが、ポリフッ化ビニリデン、及びアクリル樹脂から選択される１種又は２種以上であることが好ましい。また、中でも、水溶性ポリマーが、カルボキシメチルセルロース及びその塩から選択される１種又は２種以上であるとともに、有機溶剤可溶性ポリマーがアクリル樹脂であることが特に好ましい。 The present invention, as described above, the binder for the negative electrode containing the water-soluble polymer, the binder for the insulating layer containing the organic solvent-soluble polymer becomes difficult to be compatible, the charge and discharge characteristics, and the more excellent output characteristics. Is what you do. From such a viewpoint, the water-soluble polymer is one or more selected from carboxymethylcellulose and salts thereof, hydroxyethylcellulose, polyvinyl alcohol, and polyvinylpyrrolidone, and the organic solvent-soluble polymer is polyvinylidene fluoride, And at least one selected from acrylic resins. It is particularly preferable that the water-soluble polymer is one or more selected from carboxymethylcellulose and salts thereof, and the organic solvent-soluble polymer is an acrylic resin.
　絶縁層は、本発明の効果を損なわない範囲内において、絶縁性微粒子及び絶縁層用バインダー以外の他の任意成分を含んでもよい。また、絶縁層用バインダーは、有機溶剤可溶性ポリマーからなるものでもよいが、本発明の効果の損なわない範囲内において、有機溶剤可溶性ポリマー以外のその他のバインダーを含有してもよい。その他のバインダーは、本発明の効果を損なわない量であればよいが、例えば、絶縁層用バインダー全量に対して、１０質量％未満、好ましくは５質量％未満である。
　ただし、絶縁層の総体積のうち、絶縁性微粒子及び有機溶剤可溶性ポリマーの合計体積は、８５体積％以上であることが好ましく、９０体積％以上であることがより好ましく９５体積％以上であることがさらに好ましい。 The insulating layer may contain other optional components other than the insulating fine particles and the binder for the insulating layer as long as the effects of the present invention are not impaired. The binder for the insulating layer may be composed of an organic solvent-soluble polymer, but may contain other binders other than the organic solvent-soluble polymer as long as the effects of the present invention are not impaired. Other binders may be used in amounts that do not impair the effects of the present invention. For example, the amount is less than 10% by mass, preferably less than 5% by mass, based on the total amount of the binder for the insulating layer.
However, in the total volume of the insulating layer, the total volume of the insulating fine particles and the organic solvent-soluble polymer is preferably 85% by volume or more, more preferably 90% by volume or more, and more preferably 95% by volume or more. Is more preferred.
（負極集電体）
　負極集電体１４を構成する材料としては、例えば、銅、アルミニウム、チタン、ニッケル、ステンレス鋼等の導電性を有する金属が挙げられ、これらの中ではアルミニウム又は銅が好ましく、銅がより好ましい。負極集電体１４は、一般的に金属箔からなり、その厚さは、特に限定されないが、１～５０μｍが好ましい。 (Negative electrode current collector)
Examples of a material constituting the negative electrode current collector 14 include conductive metals such as copper, aluminum, titanium, nickel, and stainless steel. Among these, aluminum or copper is preferable, and copper is more preferable. The negative electrode current collector 14 is generally made of a metal foil, and its thickness is not particularly limited, but is preferably 1 to 50 μm.
［正極］
　次に、リチウムイオン二次電池１０の正極２１について詳細に説明する。
（正極活物質層）
　正極２１は、上記のように正極活物質層２２を含む。正極活物質層２２は、典型的には、正極活物質と、正極用バインダーとを備える。
　正極活物質としては、特に限定されないが、金属酸リチウム化合物が挙げられる。金属酸リチウム化合物としては、コバルト酸リチウム（ＬｉＣｏＯ２）、ニッケル酸リチウム（ＬｉＮｉＯ２）、マンガン酸リチウム（ＬｉＭｎ２Ｏ４）等が例示できる。また、オリビン型リン酸鉄リチウム（ＬｉＦｅＰＯ４）などであってもよい。さらに、リチウム以外の金属を複数使用したものでもよく、三元系と呼ばれるＮＣＭ（ニッケルコバルトマンガン）系酸化物、ＮＣＡ（ニッケルコバルトアルミニウム系）系酸化物などを使用してもよい。 [Positive electrode]
Next, the positive electrode 21 of the lithium ion secondary battery 10 will be described in detail.
(Positive electrode active material layer)
The positive electrode 21 includes the positive electrode active material layer 22 as described above. The positive electrode active material layer 22 typically includes a positive electrode active material and a positive electrode binder.
Although it does not specifically limit as a positive electrode active material, a lithium metal oxide compound is mentioned. Examples of the lithium metal oxide compound include lithium cobaltate (LiCoO 2 ), lithium nickelate (LiNiO 2 ), lithium manganate (LiMn 2 O 4 ), and the like. Further, olivine-type lithium iron phosphate (LiFePO 4 ) may be used. Further, a plurality of metals other than lithium may be used, and a ternary NCM (nickel-cobalt-manganese) -based oxide, an NCA (nickel-cobalt-aluminum-based) -based oxide, or the like may be used.
　正極用バインダーとしては、特に限定されず、従来正極に使用しているバインダーを適宜選択して使用することができる。例えば、上記した有機溶剤可溶性ポリマー及び水溶性ポリマーから選択される１種又は２種以上であってもよい。また、水溶性ポリマーを使用する場合には、上記した粒子状結着剤から選択される１種又は２種以上がさらに加えられてもよい。
　また、正極活物質層は、さらに導電助剤を含有することが好ましい。導電助剤としては、上記した導電助剤から１種又は２種以上を適宜選択して使用すればよい。 The binder for the positive electrode is not particularly limited, and a binder conventionally used for a positive electrode can be appropriately selected and used. For example, one or two or more selected from the above-mentioned organic solvent-soluble polymers and water-soluble polymers may be used. When a water-soluble polymer is used, one or more selected from the above-mentioned particulate binders may be further added.
Further, the positive electrode active material layer preferably further contains a conductive auxiliary. As the conductive aid, one or more of the conductive aids described above may be appropriately selected and used.
　正極活物質層２２における正極活物質の含有量は、正極活物質層全量基準で、５０～９８．５質量％が好ましく、６０～９８質量％がより好ましい。また、正極活物質層２２における正極用バインダーの含有量は、正極活物質層全量基準で、１．５～４０質量％であることが好ましく、２．０～２５質量％がより好ましい。
　正極活物質層２２において、導電助剤が含有される場合、導電助剤の含有量は、正極活物質層全量基準で、１～３０質量％であることが好ましく、２～２５質量％であることがより好ましい。
　各正極活物質層２２の厚さは、特に限定されないが、１０～１００μｍが好ましく、２０～８０μｍがより好ましい。 The content of the positive electrode active material in the positive electrode active material layer 22 is preferably 50 to 98.5% by mass, more preferably 60 to 98% by mass, based on the total amount of the positive electrode active material layer. Further, the content of the positive electrode binder in the positive electrode active material layer 22 is preferably 1.5 to 40% by mass, more preferably 2.0 to 25% by mass, based on the total amount of the positive electrode active material layer.
When the positive electrode active material layer 22 contains a conductive auxiliary, the content of the conductive auxiliary is preferably 1 to 30% by mass, and more preferably 2 to 25% by mass based on the total amount of the positive electrode active material layer. Is more preferable.
The thickness of each positive electrode active material layer 22 is not particularly limited, but is preferably 10 to 100 μm, and more preferably 20 to 80 μm.
（正極集電体）
　正極集電体２４を構成する材料は、上記負極集電体１４に使用される化合物から適宜選択して使用すればよいが、好ましくはアルミニウム又は銅、より好ましくはアルミニウムが使用される。正極集電体２４の厚さは、特に限定されないが、１～５０μｍが好ましい。 (Positive electrode current collector)
The material constituting the positive electrode current collector 24 may be appropriately selected from the compounds used for the negative electrode current collector 14, and preferably used is aluminum or copper, and more preferably aluminum. The thickness of the positive electrode current collector 24 is not particularly limited, but is preferably 1 to 50 μm.
［ケーシング］
　リチウムイオン二次電池は、通常、ケーシングを備え、上記した正極及び負極をケーシング内に収納とするとよい。ケーシングとしては、特に限定されないが、外装缶などであてもよいし、外装フィルムであってもよい。外装フィルムは、２枚の外装フィルムの間、或いは、１枚の外装フィルムが例えば２つ折りで折り畳まれ、その外装フィルムの間に負極、及び正極を配置するとよい。 [casing]
The lithium ion secondary battery usually includes a casing, and the above-described positive electrode and negative electrode may be housed in the casing. The casing is not particularly limited, but may be an exterior can or an exterior film. The exterior film may be provided between two exterior films or one exterior film may be folded in two, for example, and the negative electrode and the positive electrode may be arranged between the exterior films.
［リチウムイオン二次電池の構造］
　リチウムイオン二次電池は、巻回型、積層型などがあるが、本発明のリチウムイオン二次電池は、積層型であることが好ましい。
　積層型のリチウムイオン二次電池では、負極集電体１４の両面に負極活物質層１２が設けられた負極１１と、正極集電体２４の両面に正極活物質層２２が設けられた正極２１をそれぞれ複数枚備える。負極１１及び正極２１は、いずれも平面状であり、これらは厚さ方向に沿って交互となるように積層される。また、各負極活物質層１２の表面に設けられた絶縁層１３は、隣接する正極２１（例えば、正極活物質層２２）に接触し、好ましくは正極２１（例えば、正極活物質層２２）に接着する。 [Structure of lithium ion secondary battery]
The lithium ion secondary battery includes a wound type and a stacked type, and the lithium ion secondary battery of the present invention is preferably a stacked type.
In the stacked lithium ion secondary battery, a negative electrode 11 in which a negative electrode active material layer 12 is provided on both surfaces of a negative electrode current collector 14 and a positive electrode 21 in which a positive electrode active material layer 22 is provided on both surfaces of a positive electrode current collector 24 , Respectively. Each of the negative electrode 11 and the positive electrode 21 has a planar shape, and these are stacked so as to be alternated along the thickness direction. The insulating layer 13 provided on the surface of each negative electrode active material layer 12 contacts the adjacent positive electrode 21 (for example, the positive electrode active material layer 22), and preferably contacts the positive electrode 21 (for example, the positive electrode active material layer 22). Glue.
　各負極１１を構成する複数の負極集電体１４は、纏められて負極タブなどに取り付けられ、負極タブなどを介して負極端子に接続される。また、各正極２１を構成する複数の正極集電体２４は、纏められて正極タブなどに取り付けられ、正極タブなどを介して正極端子に接続される。 The plurality of negative electrode current collectors 14 constituting each negative electrode 11 are put together and attached to a negative electrode tab or the like, and connected to the negative electrode terminal via the negative electrode tab or the like. The plurality of positive electrode current collectors 24 constituting each positive electrode 21 are put together and attached to a positive electrode tab or the like, and connected to a positive electrode terminal via the positive electrode tab or the like.
　本発明では、絶縁層用バインダーの種類、絶縁層を構成する各成分の量、及び厚さなどを、上記のように調整することで、絶縁層１３は、曲げられたりすると割れ等が発生するおそれがあるが、積層型では、負極１１が平面状に配置されるので、曲げられたりすることもない。そのため、本発明では、機械強度が高く、かつ耐久性の良好な積層型のリチウムイオン二次電池を提供できる。 In the present invention, the type of the binder for the insulating layer, the amount of each component constituting the insulating layer, the thickness, and the like are adjusted as described above, so that the insulating layer 13 is cracked when bent or the like. Although there is a possibility that the negative electrode 11 is arranged in a plane in the stacked type, it is not bent. Therefore, in the present invention, a laminated lithium ion secondary battery having high mechanical strength and good durability can be provided.
［電解質］
　リチウムイオン二次電池は、通常は電解質を備える。電解質は特に限定されず、リチウムイオン二次電池で使用される公知の電解質を使用すればよい。電解質としては例えば電解液を使用する。
　電解液としては、有機溶媒と、電解質塩を含む電解液が例示できる。有機溶媒としては、例えば、エチレンカーボネート、プロピレンカーボネート、ジメチルカーボネート、ジエチルカーボネート、γ－ブチロラクトン、スルホラン、ジメチルスルホキシド、アセトニトリル、ジメチルホルムアミド、ジメチルアセトアミド、１，２－ジメトキシエタン、１，２－ジエトキシエタン、テトロヒドラフラン、２－メチルテトラヒドロフラン、ジオキソラン、メチルアセテートなどの極性溶媒、又はこれら溶媒の２種類以上の混合物が挙げられる。電解質塩としては、ＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＡｓＦ６、ＬｉＳｂＦ６、ＬｉＣＦ３ＣＯ２、ＬｉＮ（ＳＯ２ＣＦ３）２、ＬｉＮ（ＳＯ２ＣＦ２ＣＦ３）２、ＬｉＮ（ＣＯＣＦ３）２及びＬｉＮ（ＣＯＣＦ２ＣＦ３）２、リチウムビスオキサレートボラート（ＬｉＢ（Ｃ２Ｏ４）２)等のリチウムを含む塩が挙げられる。また、有機酸リチウム塩－三フッ化ホウ素錯体、ＬｉＢＨ４等の錯体水素化物等の錯体が挙げられる。これらの塩又は錯体は、１種単独で使用してもよいが、２種以上の混合物であってもよい。
　また、電解質は、上記電解液に更に高分子化合物を含むゲル状電解質であってもよい。高分子化合物としては、例えば、ポリフッ化ビニリデン等のフッ素系ポリマー、ポリ（メタ）アクリル酸メチル等のポリアクリル系ポリマーが挙げられる。なお、ゲル状電解質は、セパレータとして使用されてもよい。
　電解質は、負極及び正極間に配置されればよい。したがって、例えば、電解質は、上記した負極及び正極が内部に収納されたケーシング内に充填される。また、電解質は、例えば、負極又は正極上に塗布されて負極及び正極間に配置されてもよい。 [Electrolytes]
A lithium ion secondary battery usually includes an electrolyte. The electrolyte is not particularly limited, and a known electrolyte used in a lithium ion secondary battery may be used. For example, an electrolyte is used as the electrolyte.
Examples of the electrolyte include an electrolyte containing an organic solvent and an electrolyte salt. Examples of the organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane And polar solvents such as tetrohydrafuran, 2-methyltetrahydrofuran, dioxolane and methyl acetate, or a mixture of two or more of these solvents. As the electrolyte salt, LiClO 4 , LiPF 6 , LiBF 4 , LiAsF 6 , LiSbF 6 , LiCF 3 CO 2 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 CF 2 CF 3 ) 2 , LiN (COCF 3 ) And lithium-containing salts such as LiN (COCF 2 CF 3 ) 2 and lithium bisoxalate borate (LiB (C 2 O 4 ) 2 ). Further, a complex such as a lithium hydride of an organic acid-boron trifluoride complex or a complex hydride such as LiBH 4 may be used. These salts or complexes may be used alone or as a mixture of two or more.
Further, the electrolyte may be a gel electrolyte further containing a polymer compound in the above-mentioned electrolytic solution. Examples of the polymer compound include a fluorine-based polymer such as polyvinylidene fluoride and a polyacryl-based polymer such as poly (methyl meth) acrylate. Note that the gel electrolyte may be used as a separator.
The electrolyte may be disposed between the negative electrode and the positive electrode. Therefore, for example, the electrolyte is filled in a casing in which the above-described negative electrode and positive electrode are housed. Further, the electrolyte may be, for example, applied on the negative electrode or the positive electrode and disposed between the negative electrode and the positive electrode.
＜リチウムイオン二次電池の製造方法＞
　次に、リチウムイオン二次電池用電極の製造方法の一実施形態について詳細に説明する。本発明の一実施形態に係るリチウムイオン二次電池用電極の製造方法は、負極活物質層の表面上に、絶縁層用組成物を塗布して絶縁層を形成して、負極を作製する工程（負極作製工程）と、絶縁層を介して負極を正極に圧着させる工程（圧着工程）とを備える。また、通常、正極を作製する工程（正極作製工程）も含む。以下、本製造方法について各工程ごとに詳細に説明する。 <Production method of lithium ion secondary battery>
Next, an embodiment of a method for manufacturing an electrode for a lithium ion secondary battery will be described in detail. The method for producing an electrode for a lithium ion secondary battery according to one embodiment of the present invention includes a step of applying a composition for an insulating layer on the surface of a negative electrode active material layer to form an insulating layer, thereby producing a negative electrode. (A negative electrode manufacturing step) and a step of pressing the negative electrode to the positive electrode via the insulating layer (pressure bonding step). In addition, it usually includes a step of producing a positive electrode (positive electrode production step). Hereinafter, the present manufacturing method will be described in detail for each step.
［負極作製工程］
　以下では、まず、負極の作製方法について説明する。
（負極活物質層の形成）
　負極の作製においては、まず、負極活物質層を形成する。負極活物質層の形成においては、最初に負極活物質と、負極用バインダーと、溶媒とを含む負極活物質層用組成物を用意する。負極活物質層用組成物は、必要に応じて配合される導電助剤などのその他成分を含んでもよい。負極活物質、負極用バインダー、導電助剤などは上記で説明したとおりである。負極活物質層用組成物は、スラリーとなる。 [Negative electrode fabrication process]
Hereinafter, first, a method for manufacturing a negative electrode will be described.
(Formation of negative electrode active material layer)
In manufacturing a negative electrode, first, a negative electrode active material layer is formed. In forming the negative electrode active material layer, first, a negative electrode active material layer composition including a negative electrode active material, a negative electrode binder, and a solvent is prepared. The composition for a negative electrode active material layer may include other components such as a conductive auxiliary compounded as necessary. The negative electrode active material, the negative electrode binder, the conductive auxiliary, and the like are as described above. The composition for the negative electrode active material layer becomes a slurry.
　負極活物質層用組成物における溶媒は、水を使用する。水を使用することで、負極用バインダーとして使用する水溶性ポリマーを負極活物質層用組成物中に容易に溶解できる。また、粒子状結着剤やその他のバインダーは、水にエマルションの形態で配合させるとよい。負極活物質層用組成物の固形分濃度は、好ましくは５～７５質量％、より好ましくは２０～６５質量％である。 水 Water is used as the solvent in the negative electrode active material layer composition. By using water, the water-soluble polymer used as the negative electrode binder can be easily dissolved in the negative electrode active material layer composition. Further, the particulate binder and other binders are preferably mixed with water in the form of an emulsion. The solid concentration of the composition for a negative electrode active material layer is preferably 5 to 75% by mass, more preferably 20 to 65% by mass.
　負極活物質層は、上記負極活物質層用組成物を使用して公知の方法で形成すればよく、例えば、上記負極活物質層用組成物を負極集電体の上に塗布し、乾燥することによって形成することができる。
　また、負極活物質層は、負極活物質層用組成物を、負極集電体以外の基材上に塗布し、乾燥することにより形成してもよい。負極集電体以外の基材としては、公知の剥離シートが挙げられる。基材の上に形成した負極活物質層は、好ましくは絶縁層を形成した後、基材から負極活物質層を剥がして負極集電体の上に転写すればよい。
　負極集電体又は基材の上に形成した負極活物質層は、好ましくは加圧プレスする。加圧プレスすることで、負極密度を高めることが可能になる。加圧プレスは、ロールプレスなどにより行えばよい。 The negative electrode active material layer may be formed by a known method using the negative electrode active material layer composition. For example, the negative electrode active material layer composition is applied on a negative electrode current collector and dried. Can be formed.
Further, the negative electrode active material layer may be formed by applying the composition for a negative electrode active material layer on a substrate other than the negative electrode current collector and drying the composition. As a substrate other than the negative electrode current collector, a known release sheet may be used. The negative electrode active material layer formed on the substrate is preferably formed by forming an insulating layer, and then peeling the negative electrode active material layer from the substrate and transferring the negative electrode active material layer onto the negative electrode current collector.
The negative electrode active material layer formed on the negative electrode current collector or the substrate is preferably pressed under pressure. By pressing under pressure, the density of the negative electrode can be increased. The pressure press may be performed by a roll press or the like.
（絶縁層の形成）
　負極の作製においては、負極活物質層を形成した後に、負極活物質層の表面上に、絶縁層用組成物を塗布して絶縁層を形成する。
　絶縁層の形成に使用する絶縁層用組成物は、絶縁性微粒子と、絶縁層用バインダーと、溶媒とを含む。絶縁層用バインダーは、上記のように有機溶剤可溶性バインダーを含むが、有機溶剤可溶性バインダー以外のバインダーを含んでいてもよい。また、絶縁層用組成物は、必要に応じて配合されるその他の任意成分を含んでいてもよい。絶縁性微粒子、絶縁層用バインダーなどの詳細は上記で説明したとおりである。絶縁層用組成物はスラリー（絶縁層用スラリー）となる。 (Formation of insulating layer)
In manufacturing a negative electrode, after forming a negative electrode active material layer, a composition for an insulating layer is applied over the surface of the negative electrode active material layer to form an insulating layer.
The composition for an insulating layer used for forming an insulating layer contains insulating fine particles, a binder for an insulating layer, and a solvent. The binder for the insulating layer contains the organic solvent-soluble binder as described above, but may also contain a binder other than the organic solvent-soluble binder. In addition, the composition for an insulating layer may include other optional components that are blended as necessary. Details of the insulating fine particles, the binder for the insulating layer, and the like are as described above. The composition for an insulating layer becomes a slurry (slurry for an insulating layer).
　本製造方法において、絶縁層用組成物に使用する溶媒は、有機溶剤である。有機溶剤の具体例としては、Ｎ－メチルピロリドン、Ｎ－エチルピロリドン、ジメチルアセトアミド、及びジメチルホルムアミドから選択される１種又は２種以上が挙げられる。これらの中では、Ｎ－メチルピロリドンが特に好ましい。
　本製造方法においては、有機溶剤を含む絶縁層用組成物を、負極活物質層の表面上に塗布して、絶縁層を形成するが、負極活物質層には、有機溶剤に対する溶解性が低い水溶性ポリマーが使用される。したがって、絶縁層用組成物が負極活物質層と殆ど相溶することなく、絶縁層が形成される。そのため、絶縁性微粒子が負極活物質層中に混入し、或いは、負極活物質が絶縁層中に混入することが防止され、絶縁層及び負極活物質層それぞれが所望の機能を発揮しやすくなり、充放電特性、出力特性などが良好となる。 In the present production method, the solvent used for the composition for an insulating layer is an organic solvent. Specific examples of the organic solvent include one or more selected from N-methylpyrrolidone, N-ethylpyrrolidone, dimethylacetamide, and dimethylformamide. Among these, N-methylpyrrolidone is particularly preferred.
In the present production method, the composition for an insulating layer containing an organic solvent is applied on the surface of the negative electrode active material layer to form an insulating layer, but the negative electrode active material layer has low solubility in the organic solvent. Water-soluble polymers are used. Therefore, the insulating layer is formed with almost no compatibility of the composition for an insulating layer with the negative electrode active material layer. Therefore, the insulating fine particles are prevented from being mixed into the negative electrode active material layer, or the negative electrode active material is prevented from being mixed into the insulating layer, and the insulating layer and the negative electrode active material layer each easily exhibit desired functions, The charge and discharge characteristics, output characteristics, and the like are improved.
　絶縁層用組成物の固形分濃度は、好ましくは１０～６０質量％、より好ましくは２０～５０質量％である。
　また、絶縁層用組成物の粘度は、好ましくは１００～４０００ｍＰａ・ｓ、より好ましくは１５００～２５００ｍＰａ・ｓである。なお、粘度とは、Ｂ型粘度計で６０ｒｐｍ、塗布時の温度条件で測定した粘度である。
　粘度及び固形分粘度を上記範囲内とすることで、所定の厚さを有する絶縁層を形成しやすくなる。また、粘度を上記した範囲内の粘度とすることで、絶縁層用組成物が負極活物質層に染み込んだりすることが防止され、負極活物質層と絶縁層とが層として分離しやすくなる。 The solid content of the composition for an insulating layer is preferably 10 to 60% by mass, more preferably 20 to 50% by mass.
The viscosity of the composition for an insulating layer is preferably 100 to 4000 mPa · s, more preferably 1500 to 2500 mPa · s. The viscosity is a viscosity measured by a B-type viscometer at 60 rpm under a temperature condition at the time of coating.
By setting the viscosity and the solid content viscosity within the above ranges, an insulating layer having a predetermined thickness can be easily formed. By setting the viscosity within the above range, the composition for the insulating layer is prevented from seeping into the negative electrode active material layer, and the negative electrode active material layer and the insulating layer are easily separated as a layer.
　絶縁層は、絶縁層用組成物を、負極活物質層の表面に塗布した後、乾燥することによって形成できる。絶縁層用組成物を負極活物質層の表面に塗布する方法は特に限定されず、例えば、ディップコート法、スプレーコート法、ロールコート法、ドクターブレード法、バーコート法、グラビアコート法、スクリーン印刷法等が挙げられる。これらの中では、絶縁層を均一に塗布する観点などから、グラビアコート法が好ましい。
　また、乾燥温度は、上記溶媒を除去できれば特に限定されないが、例えば５０～１３０℃、好ましくは６０～１００℃である。また、乾燥時間は、特に限定されないが、例えば、３０秒～３０分間、好ましくは２～２０分間である。 The insulating layer can be formed by applying the composition for an insulating layer to the surface of the negative electrode active material layer and then drying the composition. The method for applying the composition for an insulating layer to the surface of the negative electrode active material layer is not particularly limited, and examples thereof include a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a bar coating method, a gravure coating method, and screen printing. And the like. Among these, the gravure coating method is preferable from the viewpoint of uniformly applying the insulating layer.
The drying temperature is not particularly limited as long as the solvent can be removed, but is, for example, 50 to 130 ° C., preferably 60 to 100 ° C. The drying time is not particularly limited, but is, for example, 30 seconds to 30 minutes, preferably 2 to 20 minutes.
［正極作製工程］
　正極の作製においては、正極集電体の上に正極活物質層を形成するとよい。正極活物質層の形成においては、最初に正極活物質と、正極用バインダーと、溶媒とを含む正極活物質層用組成物を用意する。正極活物質層用組成物は、必要に応じて配合される導電助剤などのその他成分を含んでもよい。正極活物質、正極用バインダー、導電助剤などは上記で説明したとおりである。正極活物質層用組成物はスラリーとなる。 [Positive electrode preparation process]
In manufacturing a positive electrode, a positive electrode active material layer is preferably formed over a positive electrode current collector. In forming the positive electrode active material layer, first, a positive electrode active material layer composition including a positive electrode active material, a positive electrode binder, and a solvent is prepared. The composition for a positive electrode active material layer may include other components such as a conductive auxiliary compounded as necessary. The positive electrode active material, the positive electrode binder, the conductive additive, and the like are as described above. The composition for the positive electrode active material layer becomes a slurry.
　正極活物質層用組成物における溶媒は、正極用バインダーを溶解する溶媒を使用することが好ましく、正極用バインダーの種類に応じて適宜選択すればよく、水を使用してもよいし、有機溶剤を使用してもよい。有機溶剤としては、上記した有機溶剤から適宜選択すればよい。正極活物質層用組成物の固形分濃度は、好ましくは５～７５質量％、より好ましくは２０～６５質量％である。 As the solvent in the composition for the positive electrode active material layer, it is preferable to use a solvent that dissolves the binder for the positive electrode, and may be appropriately selected depending on the type of the binder for the positive electrode, and may use water or an organic solvent. May be used. The organic solvent may be appropriately selected from the above-mentioned organic solvents. The solid concentration of the composition for a positive electrode active material layer is preferably 5 to 75% by mass, and more preferably 20 to 65% by mass.
　正極活物質層は、上記正極活物質層用組成物を使用して公知の方法で形成すればよく、例えば、上記正極活物質層用組成物を正極集電体の上に塗布し、乾燥することによって形成することができる。
　また、正極活物質層は、正極活物質層用組成物を、正極集電体以外の基材上に塗布し、乾燥することにより形成してもよい。正極集電体以外の基材としては、公知の剥離シートが挙げられる。基材の上に形成した正極活物質層は、基材から剥がして正極集電体の上に転写すればよい。
　正極集電体又は基材の上に形成した正極活物質層は、好ましくは加圧プレスする。加圧プレスすることで、正極密度を高めることが可能になる。加圧プレスは、ロールプレスなどにより行えばよい。 The positive electrode active material layer may be formed by a known method using the positive electrode active material layer composition. For example, the positive electrode active material layer composition is applied on a positive electrode current collector and dried. Can be formed.
In addition, the positive electrode active material layer may be formed by applying the composition for a positive electrode active material layer on a substrate other than the positive electrode current collector and drying the composition. As a substrate other than the positive electrode current collector, a known release sheet may be used. The positive electrode active material layer formed on the substrate may be peeled off from the substrate and transferred onto the positive electrode current collector.
The positive electrode active material layer formed on the positive electrode current collector or the substrate is preferably pressed under pressure. By pressing under pressure, it is possible to increase the density of the positive electrode. The pressure press may be performed by a roll press or the like.
［圧着工程］
　上記のようにして得られた負極は、正極に圧着させて、負極と正極からなる積層体を形成するとよい。ここで、より具体的には、負極は、絶縁層を正極、典型的には正極活物質層に接触するように配置し、負極を絶縁層を介して正極に圧着させるよい。
　また、負極と正極とをそれぞれ複数層積層する場合には、負極と正極とを厚さ方向に交互となるようにそれぞれ複数層積層して、各負極と正極間は、絶縁層を介して圧着させるとよい。 [Crimping process]
The negative electrode obtained as described above may be pressed against the positive electrode to form a laminate including the negative electrode and the positive electrode. Here, more specifically, in the negative electrode, the insulating layer may be disposed so as to be in contact with the positive electrode, typically the positive electrode active material layer, and the negative electrode may be press-bonded to the positive electrode via the insulating layer.
When the negative electrode and the positive electrode are laminated in a plurality of layers, respectively, the negative electrode and the positive electrode are laminated in a plurality of layers so as to be alternately arranged in the thickness direction. It is good to let.
　負極と正極とを圧着させる具体的な方法は、負極と正極とを重ね合わせたもの（それぞれが複数層ある場合には、交互に配置して重ね合わせたもの）をプレス機などによりプレスすることで行うとよい。プレス条件は、負極活物質層及び正極活物質層が必要以上に圧縮せず、かつ絶縁層が正極に接着する程度の条件で行うとよい。具体的には、プレス温度は、５０～１３０℃、好ましくは６０～１００℃であり、プレス圧力は、例えば、０．２～３ＭＰａ、好ましくは０．４～１．５ＭＰａである。また、プレス時間は、例えば、１５秒～１５分間、好ましくは３０秒～１０分間である。 The specific method of crimping the negative electrode and the positive electrode is to press the stacked negative electrode and the positive electrode (if there are multiple layers, alternately arranged and stacked) with a press machine or the like. It is good to do in. The pressing is preferably performed under such a condition that the negative electrode active material layer and the positive electrode active material layer are not compressed more than necessary and the insulating layer is bonded to the positive electrode. Specifically, the pressing temperature is 50 to 130 ° C., preferably 60 to 100 ° C., and the pressing pressure is, for example, 0.2 to 3 MPa, preferably 0.4 to 1.5 MPa. The pressing time is, for example, 15 seconds to 15 minutes, preferably 30 seconds to 10 minutes.
　上記のようにして得られた負極と正極の積層体は、例えば、負極集電体を負極端子に、正極集電体を正極端子に接続させ、かつケーシング内に収納することで、リチウムイオン二次電池を得ることができる。
　なお、以上の製造方法は、本発明のリチウムイオン二次電池の製造方法の一実施形態であって、上記に限定されない。例えば、負極が正極に接着しない場合には、負極と正極とは圧着させずにこれらを重ね合わせるだけでもよい。 The laminated body of the negative electrode and the positive electrode obtained as described above is, for example, connected to the negative electrode current collector to the negative electrode terminal and the positive electrode current collector to the positive electrode terminal, and housed in a casing, so that the lithium ion The following battery can be obtained.
The above manufacturing method is one embodiment of the manufacturing method of the lithium ion secondary battery of the present invention, and is not limited to the above. For example, when the negative electrode does not adhere to the positive electrode, the negative electrode and the positive electrode may be simply overlapped without being pressed.
　以下に実施例を用いて本発明をさらに詳しく説明するが、本発明はこれら実施例に限定されるものではない。 The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
　イオン二次電池用電極の評価方法、及び各種物性の測定方法は以下の通りである。
（充放電特性評価）
　各実施例、比較例で作製したリチウムイオン二次電池について、０．１Ａの定電流充電を行い、次いで４．２Ｖ到達次第電流を減少させ０．０２Ａとなった時点で充電完了する定電圧充電を行った。その後、０．１Ａの定電流放電を行い、２．５Ｖまで放電させた時点で放電完了とする放電を行った。その後、３０分電池を静置し、３０分後に電圧を測定した。各実施例、比較例において、１５セルのリチウムイオン二次電池について試験を行い、平均値を計算した。
　　Ａ：平均値２．５Ｖ以上
　　Ｂ：平均値２．０Ｖ以上２．５Ｖ未満
　　Ｃ：平均値１．０Ｖ以上２．０Ｖ未満
　　Ｄ：平均値１．０Ｖ未満 The method for evaluating the electrode for an ion secondary battery and the method for measuring various physical properties are as follows.
(Charge / discharge characteristics evaluation)
The lithium ion secondary batteries prepared in each of the examples and the comparative examples were charged at a constant current of 0.1 A, then the current was decreased as soon as the voltage reached 4.2 V, and the charging was completed when the current reached 0.02 A. Was done. Thereafter, a constant current discharge of 0.1 A was performed, and discharge was completed when the discharge was completed to 2.5 V. Thereafter, the battery was allowed to stand for 30 minutes, and the voltage was measured after 30 minutes. In each of Examples and Comparative Examples, a test was performed on a 15-cell lithium ion secondary battery, and an average value was calculated.
A: Average value of 2.5 V or more B: Average value of 2.0 V or more and less than 2.5 V C: Average value of 1.0 V or more and less than 2.0 V D: Average value of less than 1.0 V
（出力特性評価）
　各実施例、比較例で作製したリチウムイオン二次電池について、以下のように放電容量を求めることで評価した。
　０．１Ａの定電流充電を行い、次いで４．２Ｖ到達次第電流を減少させ０．０２Ａとなった時点で充電完了する定電圧充電を行った。その後、１Ａの定電流放電を行い、２．５Ｖまで放電させた時点で放電完了とする放電を行い、放電容量を計算した。以下の基準で出力特性を評価した。
　　Ａ：０．１Ａの定電流の放電容量に比べ、１Ａの放電容量が３０％以上である。
　　Ｂ：０．１Ａの定電流の放電容量に比べ、１Ａの放電容量が２０％以上３０％未満である。
　　Ｃ：０．１Ａの定電流の放電容量に比べ、１Ａの放電容量が１０％以上２０％未満である。
　　Ｄ：０．１Ａの定電流の放電容量に比べ、１Ａの放電容量が１０％未満である。 (Output characteristic evaluation)
The lithium ion secondary batteries produced in each of the examples and comparative examples were evaluated by calculating the discharge capacity as described below.
The battery was charged at a constant current of 0.1 A, and then the current was reduced as soon as 4.2 V was reached. Thereafter, a constant current discharge of 1 A was performed, and when the discharge was completed to 2.5 V, a discharge was completed to complete the discharge, and the discharge capacity was calculated. The output characteristics were evaluated based on the following criteria.
A: The discharge capacity at 1 A is 30% or more as compared with the discharge capacity at a constant current of 0.1 A.
B: The discharge capacity at 1 A is 20% or more and less than 30% as compared with the discharge capacity at a constant current of 0.1 A.
C: The discharge capacity at 1 A is 10% or more and less than 20% as compared with the discharge capacity at a constant current of 0.1 A.
D: The discharge capacity at 1 A is less than 10% as compared with the discharge capacity at a constant current of 0.1 A.
（安全性評価）
　各実施例、比較例で作製したリチウムイオン二次電池について、０．１Ａの定電流充電を行い、次いで４．２Ｖ到達次第電流を減少させ０．０２Ａとなった時点で充電完了する定電圧充電を行った。その後電池を加熱し、１１０℃として保管した。１１０℃到達後１時間保持したときの電池の最高温度を測定した。
　　Ａ：最高温度１１５℃未満
　　Ｂ：最高温度１１５℃以上１４０℃未満
　　Ｃ：最高温度１４０℃以上２００℃未満
　　Ｄ：最高温度２００℃以上 (Safety evaluation)
The lithium ion secondary batteries prepared in each of the examples and the comparative examples were charged at a constant current of 0.1 A, then the current was decreased as soon as the voltage reached 4.2 V, and the charging was completed when the current reached 0.02 A. Was done. Thereafter, the battery was heated and stored at 110 ° C. The maximum temperature of the battery when it was held for 1 hour after reaching 110 ° C. was measured.
A: Maximum temperature of less than 115 ° C B: Maximum temperature of 115 ° C or more and less than 140 ° C C: Maximum temperature of 140 ° C or more and less than 200 ° C D: Maximum temperature of 200 ° C or more
（固形分濃度低下量）
　絶縁層用バインダー、負極用バインダー、又は有機溶剤可溶性ポリマーとして使用する各成分を、絶縁層用バインダー、負極用バインダー、又は有機溶剤可溶性ポリマーそれぞれにおける各成分の比率と同様になり、かつ固形分濃度が５質量％となるように、水又はＮＭＰに希釈したバインダー液を用意した。用意したバインダー液５００ｇを、目開き７２μｍのステンレス製フィルターを通して濾過した。バインダー液の準備、及びバインダー液の濾過は２５℃にて行った。
　濾過した得られたバインダー液を、１５０℃のホットプレートで３０分間乾燥させて、乾燥後の固形分量を測定し、下記の計算式（２）により、濾過後のバインダー液の濃度を求めた。
（バインダー濃度）（％）＝（加熱後の固形分量）÷（加熱前の溶液量）×１００　　（２）
　濾過前のバインダー液も、同様にホットプレートで乾燥させて上記計算式（２）により、濾過前のバインダー液の濃度を求めた。
　下記の計算式（３）により、バインダーの固形分濃度低下量を測定し、水又はＮＭＰに対するバインダーの溶解性とした。なお、固形分濃度低下量が低いほど、濾過により取り除かれる不溶分が少なく、溶解性が高いことを意味する。
　（固形分濃度低下量）（％）＝（濾過前のバインダー液の濃度）（％）－（濾過後のバインダー液の濃度）（％）　　　（３） (Decrease in solid content concentration)
The components used as the binder for the insulating layer, the binder for the negative electrode, or the organic solvent-soluble polymer are the same as the ratio of each component in the binder for the insulating layer, the binder for the negative electrode, or the organic solvent-soluble polymer, and the solid content concentration. Was adjusted to 5% by mass to prepare a binder solution diluted with water or NMP. 500 g of the prepared binder solution was filtered through a stainless steel filter having a mesh size of 72 μm. Preparation of the binder solution and filtration of the binder solution were performed at 25 ° C.
The filtered binder solution was dried on a hot plate at 150 ° C. for 30 minutes, the solid content after drying was measured, and the concentration of the filtered binder solution was determined by the following formula (2).
(Binder concentration) (%) = (solid content after heating) / (solution volume before heating) × 100 (2)
The binder liquid before filtration was also dried on a hot plate in the same manner, and the concentration of the binder liquid before filtration was determined by the above formula (2).
The amount of decrease in the solid content of the binder was measured by the following formula (3), and the solubility of the binder in water or NMP was determined. It should be noted that the lower the solid content concentration decrease amount, the smaller the insoluble content removed by filtration and the higher the solubility.
(Amount of decrease in solid content concentration) (%) = (concentration of binder solution before filtration) (%)-(concentration of binder solution after filtration) (%) (3)
　絶縁層の厚さは、以下の方法により測定した。
　負極活物質層、及び絶縁層が形成された負極に対し、イオンミリング方式で断面を露出させた。露出した断面を電界放出型走査電子顕微鏡（ＦＥ-ＳＥＭ）にて観察した。観察は電極の絶縁層の表層から底部まで見えるような視野とした。断面倍率は、２００００倍で行った。得られた画像に対し、画像解析ソフト（Ｉｍａｇｅ　Ｊ）を使用しランダムに電極活物質と絶縁層の界面から絶縁層表面までの長さを、電極集電体に対して垂直方向に計測した。１枚の画像につき、１０点測定し、平均値を絶縁層の厚さとした。
（負極活物質層及び正極活物質層の厚さ）
　負極活物質層及び正極活物質層の厚さは、株式会社ニコン製「ＭＦ－１０１」を使用して測定した。 The thickness of the insulating layer was measured by the following method.
A cross section of the negative electrode on which the negative electrode active material layer and the insulating layer were formed was exposed by an ion milling method. The exposed cross section was observed with a field emission scanning electron microscope (FE-SEM). The observation was made so that the surface of the insulating layer of the electrode could be seen from the surface to the bottom. The section magnification was 20000 times. For the obtained image, the length from the interface between the electrode active material and the insulating layer to the surface of the insulating layer was randomly measured using image analysis software (Image J) in a direction perpendicular to the electrode current collector. Ten points were measured for one image, and the average value was taken as the thickness of the insulating layer.
(Thickness of negative electrode active material layer and positive electrode active material layer)
The thicknesses of the negative electrode active material layer and the positive electrode active material layer were measured using “MF-101” manufactured by Nikon Corporation.
［実施例１］
［正極の作製］
　正極活物質としての平均粒子径１０μｍのＬｉ（Ｎｉ－Ｃｏ－Ａｌ）Ｏ２（ＮＣＡ系酸化物）を１００質量部と、導電助剤としてのアセチレンブラックを４質量部と、電極用バインダーとしてのポリフッ化ビニリデン（ＰＶｄＦ）４質量部と、溶媒としてのＮ－メチルピロリドン（ＮＭＰ）とを混合し、固形分濃度６０質量％に調整した正極活物質層用組成物を得た。この正極活物質層用組成物を、正極集電体としての厚さ１５μｍのアルミニウム箔の両面に塗布し、予備乾燥後、１２０℃で真空乾燥した。その後、両面に正極活物質層用組成物を塗布した正極集電体を、４００ｋＮ／ｍで加圧プレスし、更に電極寸法の４０ｍｍ×５０ｍｍ角に打ち抜いて、両面にそれぞれの厚さが５０μｍである正極活物質層を有する正極とした。該寸法のうち、正極活物質層が形成された面積は４０ｍｍ×４５ｍｍであった。 [Example 1]
[Preparation of positive electrode]
100 parts by mass of Li (Ni—Co—Al) O 2 (NCA-based oxide) having an average particle diameter of 10 μm as a positive electrode active material, 4 parts by mass of acetylene black as a conductive additive, and a binder for an electrode 4 parts by mass of polyvinylidene fluoride (PVdF) and N-methylpyrrolidone (NMP) as a solvent were mixed to obtain a composition for a positive electrode active material layer adjusted to a solid concentration of 60% by mass. The composition for a positive electrode active material layer was applied on both sides of a 15 μm-thick aluminum foil as a positive electrode current collector, and was preliminarily dried and then vacuum dried at 120 ° C. Thereafter, the positive electrode current collector coated with the composition for a positive electrode active material layer on both sides is pressed under a pressure of 400 kN / m, and further punched into a 40 mm × 50 mm square of the electrode dimensions. A positive electrode having a certain positive electrode active material layer was obtained. Among these dimensions, the area where the positive electrode active material layer was formed was 40 mm × 45 mm.
［負極の作製］
（負極活物質層の形成）
　負極活物質としてのグラファイト（平均粒子径１０μｍ）１００質量部（９７質量％）と、粒子状結着剤としてのスチレンブタジエンゴム（ＳＢＲ、平均粒子径：１８０ｎｍ）の水分散体を固形分量として１．５質量部（１．５質量％）と、水溶性ポリマーとしてのカルボキシメチルセルロース（ＣＭＣ）のナトリウム塩（水へ濃度１質量％で溶解させたときのＢ型粘度計によって測定した２５℃、６０ｒｐｍ条件での粘度：３０００ｍＰａ・ｓ）を１．５質量部（１．５質量％）と、溶媒としての水とを混合し、固形分濃度５０質量％に調整した負極活物質層用組成物を得た。
　この負極活物質層用組成物を、負極集電体としての厚さ１２μｍの銅箔の両面に塗布して１００℃で真空乾燥した。その後、両面に負極活物質層用組成物を塗布した負極集電体を、線圧５００ｋＮ／ｍで加圧プレスして各厚さが５０μｍの負極活物質層を得た。負極活物質層の密度は１．５５ｇ／ｃｃであった。なお、負極の寸法は４５ｍｍ×５５ｍｍであり、該寸法のうち、負極活物質層が塗布された面積は４５ｍｍ×５０ｍｍであった。 [Preparation of negative electrode]
(Formation of negative electrode active material layer)
An aqueous dispersion of 100 parts by mass (97% by mass) of graphite (average particle size: 10 μm) as a negative electrode active material and styrene butadiene rubber (SBR, average particle size: 180 nm) as a particulate binder was used as a solid content. 0.5 mass parts (1.5 mass%) and sodium salt of carboxymethyl cellulose (CMC) as a water-soluble polymer (25 ° C., 60 rpm measured by a B-type viscometer when dissolved in water at a concentration of 1 mass%) Viscosity under the conditions: 3000 mPa · s) was mixed with 1.5 parts by mass (1.5% by mass) and water as a solvent to adjust the solid content concentration to 50% by mass. Obtained.
The composition for a negative electrode active material layer was applied to both surfaces of a copper foil having a thickness of 12 μm as a negative electrode current collector, and dried at 100 ° C. under vacuum. Thereafter, the negative electrode current collector having both sides coated with the negative electrode active material layer composition was pressed under a linear pressure of 500 kN / m to obtain a negative electrode active material layer having a thickness of 50 μm. The density of the negative electrode active material layer was 1.55 g / cc. In addition, the dimension of the negative electrode was 45 mm × 55 mm, and the area where the negative electrode active material layer was applied was 45 mm × 50 mm.
（絶縁層の形成）
　有機溶剤可溶性ポリマーとしての架橋ポリブチルアクリレートを、濃度１０質量％でＮＭＰに溶解したポリマー溶液を用意した。絶縁性微粒子としてのアルミナ粒子（日本軽金属社製、製品名：ＡＨＰ２００、平均粒子径０．４μｍ）に、アルミナ粒子７５体積部に対して有機溶剤可溶性ポリマーが２５体積部となるように、上記ポリマー溶液を中程度のせん断をかけながら混合して、絶縁層用組成物（絶縁層用スラリー）を調製した。絶縁層用スラリーにおける固形分濃度は４０質量％であった。
　得られた絶縁層用スラリーを負極活物質層の両面に温度２５℃でグラビア塗工により、せん断力をかけながら塗布した。塗布時の絶縁層用スラリーの粘度は２０００ｍＰａ・ｓであった。その後、加熱オーブンを用いて塗膜を９０℃で１０分間乾燥させ、負極の両面に絶縁層を形成した。乾燥後の絶縁層の厚さは片面あたり１５μｍであった。 (Formation of insulating layer)
A polymer solution was prepared by dissolving crosslinked polybutyl acrylate as an organic solvent-soluble polymer in NMP at a concentration of 10% by mass. Alumina particles as insulating fine particles (manufactured by Nippon Light Metal Co., Ltd., product name: AHP200, average particle diameter 0.4 μm). The solution was mixed while applying moderate shear to prepare an insulating layer composition (insulating layer slurry). The solid content concentration in the insulating layer slurry was 40% by mass.
The obtained slurry for an insulating layer was applied to both surfaces of the negative electrode active material layer by gravure coating at a temperature of 25 ° C. while applying a shearing force. The viscosity of the slurry for the insulating layer at the time of coating was 2000 mPa · s. Thereafter, the coating film was dried at 90 ° C. for 10 minutes using a heating oven to form insulating layers on both surfaces of the negative electrode. The thickness of the insulating layer after drying was 15 μm per side.
（電解液の調製）
　エチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）を３：７の体積比（ＥＣ：ＤＥＣ）で混合した溶媒に、電解質塩としてＬｉＰＦ６を１モル／リットルとなるように溶解して、電解液を調製した。 (Preparation of electrolyte solution)
LiPF 6 as an electrolyte salt was dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7 (EC: DEC) so as to have a concentration of 1 mol / liter, and the electrolytic solution was dissolved. Prepared.
（リチウムイオン二次電池の製造）
　上記で得た絶縁層を有する負極２５枚と、正極２４枚を積層し仮積層体を得た。ここで、負極と正極は交互に配置した。平板型ホットプレス機を用いて、上記仮積層体を、８０℃、０．６ＭＰａの条件で１分間プレスし積層体を得た。
　各正極の正極集電体の露出部の端部を纏めて超音波融着で接合するとともに、外部に突出する端子用タブを接合した。同様に、各負極の負極集電体の露出部の端部を纏めて超音波融着で接合するとともに、外部に突出する端子用タブを接合した。
　次いで、アルミラミネートフィルムで上記積層体を挟み、端子用タブを外部に突出させ、三辺をラミネート加工によって封止した。封止せずに残した一辺から、上記で得た電解液を注入し、真空封止することによって積層型のリチウムイオン二次電池（セル）を製造した。 (Manufacture of lithium ion secondary batteries)
Twenty-five negative electrodes having the insulating layer obtained above and twenty-four positive electrodes were laminated to obtain a temporary laminate. Here, the negative electrode and the positive electrode were alternately arranged. The temporary laminate was pressed at 80 ° C. and 0.6 MPa for 1 minute using a flat plate hot press to obtain a laminate.
The ends of the exposed portions of the positive electrode current collector of each positive electrode were joined together by ultrasonic fusion, and a terminal tab projecting to the outside was joined. Similarly, the ends of the exposed portions of the negative electrode current collectors of the respective negative electrodes were joined together by ultrasonic fusion, and terminal tabs projecting to the outside were joined.
Next, the laminated body was sandwiched between aluminum laminated films, the terminal tabs were projected outside, and three sides were sealed by laminating. From one side left without sealing, the electrolyte solution obtained above was injected, and vacuum sealing was performed to produce a laminated lithium ion secondary battery (cell).
［実施例２］
　絶縁層用スラリーの固形分濃度を４５質量％として、負極活物質上に形成される絶縁層の厚さを１９μｍに変更した点を除いて実施例１と同様にした。 [Example 2]
Example 1 was carried out in the same manner as in Example 1 except that the solid content concentration of the slurry for the insulating layer was 45% by mass, and the thickness of the insulating layer formed on the negative electrode active material was changed to 19 μm.
［実施例３］
　絶縁層用スラリーの固形分濃度を３５質量％として、負極活物質上に形成される絶縁層の厚さを１１μｍに変更した点を除いて実施例１と同様にした。 [Example 3]
Example 1 was the same as Example 1 except that the solid content concentration of the slurry for the insulating layer was 35% by mass and the thickness of the insulating layer formed on the negative electrode active material was changed to 11 μm.
［実施例４］
　アルミナ粒子６０体積部に対して有機溶剤可溶性ポリマーが４０体積部となるように絶縁層用組成物を調製した以外は実施例１と同様に実施した。 [Example 4]
The procedure was performed in the same manner as in Example 1 except that the composition for the insulating layer was prepared so that the organic solvent-soluble polymer was 40 parts by volume with respect to 60 parts by volume of the alumina particles.
［実施例５］
　アルミナ粒子８２体積部に対して有機溶剤可溶性ポリマーが１８体積部となるように絶縁層用組成物を調製した以外は実施例１と同様に実施した。 [Example 5]
Example 1 was carried out in the same manner as in Example 1 except that the composition for an insulating layer was prepared so that the organic solvent-soluble polymer was 18 parts by volume with respect to 82 parts by volume of alumina particles.
［比較例１］
　実施例１と同様に作製した絶縁層を有する負極２５枚及び正極２４枚に加えて、セパレータ５０枚を積層して積層体を得た。ここで、負極と正極は交互に配置し、かつ各セパレータの間に負極又は正極が配置した。また、セパレータとしては、厚さが１６μｍ、透気度が１１０ｓｅｃ／１００ｃｃ　ａｉｒであるポリエチレン製微多孔膜セパレータを用いた。
　各正極の正極集電体の露出部の端部を纏めて超音波融着で接合するとともに、外部に突出する端子用タブを接合した。同様に、各負極の負極集電体の露出部の端部を纏めて超音波融着で接合するとともに、外部に突出する端子用タブを接合した。その後、実施例１と同様にして積層型のリチウムイオン二次電池（セル）を製造した。 [Comparative Example 1]
In addition to 25 negative electrodes and 24 positive electrodes having an insulating layer manufactured in the same manner as in Example 1, 50 separators were laminated to obtain a laminate. Here, the negative electrode and the positive electrode were alternately arranged, and the negative electrode or the positive electrode was arranged between the separators. As the separator, a polyethylene microporous membrane separator having a thickness of 16 μm and an air permeability of 110 sec / 100 cc air was used.
The ends of the exposed portions of the positive electrode current collector of each positive electrode were joined together by ultrasonic fusion, and a terminal tab projecting to the outside was joined. Similarly, the ends of the exposed portions of the negative electrode current collectors of the respective negative electrodes were joined together by ultrasonic fusion, and terminal tabs projecting to the outside were joined. Thereafter, a laminated lithium ion secondary battery (cell) was manufactured in the same manner as in Example 1.
［比較例２］
　絶縁層用スラリーの固形分濃度を１５質量％として、負極活物質上に形成される絶縁層の厚さを４μｍに変更した点を除いて実施例１と同様にした。 [Comparative Example 2]
The same operation as in Example 1 was performed except that the solid content concentration of the slurry for the insulating layer was 15% by mass, and the thickness of the insulating layer formed on the negative electrode active material was changed to 4 μm.
［比較例３］
　アルミナ粒子９５体積部に対して有機溶剤可溶性ポリマーが５体積部となるように絶縁層用組成物を調製した以外は実施例１と同様に実施した。 [Comparative Example 3]
The procedure was performed in the same manner as in Example 1 except that the composition for an insulating layer was prepared so that the organic solvent-soluble polymer was 5 parts by volume with respect to 95 parts by volume of alumina particles.
［比較例４］
　アルミナ粒子５０体積部に対して有機溶剤可溶性ポリマーが５０体積部となるように絶縁層用組成物を調製した以外は実施例１と同様に実施した。 [Comparative Example 4]
Example 1 was carried out in the same manner as in Example 1 except that the composition for an insulating layer was prepared such that the organic solvent-soluble polymer was 50 parts by volume with respect to 50 parts by volume of alumina particles.
［比較例５］
　絶縁層用スラリーの固形分濃度を５５質量％として、負極活物質上に形成される絶縁層の厚さを３０μｍに変更した点を除いて実施例１と同様にした。 [Comparative Example 5]
The procedure was the same as that of Example 1 except that the solid content concentration of the slurry for the insulating layer was 55% by mass, and the thickness of the insulating layer formed on the negative electrode active material was changed to 30 μm.
［比較例６］
　以下のように調製した絶縁層組成物（絶縁層用スラリー）を使用して絶縁層を形成した以外は、実施例１と同様に実施した。
　絶縁性微粒子としてのアルミナ粒子（日本軽金属社製、製品名：ＡＨＰ２００、平均粒子径０．４μｍ）と、カルボキシメチルセルロースのナトリウム塩（ＣＭＣ、水へ濃度１質量％で溶解させたときのＢ型粘度計によって測定した２５℃、６０ｒｐｍ条件での粘度：５０ｍＰａ・ｓ）と、スチレンブタジエンゴム（ＳＢＲ，平均粒子径：１８０ｎｍ）の水分散体と、溶媒としての水を、中程度のせん断をかけながら混合して、絶縁層用スラリーを調製した。絶縁層用スラリーでは、アルミナ１００体積部に対して、ＣＭＣが５体積部、ＳＢＲが２０体積部となり、固形分濃度が５０質量％となるように調整した。 [Comparative Example 6]
Example 1 was carried out in the same manner as in Example 1 except that the insulating layer was formed using the insulating layer composition (insulating layer slurry) prepared as follows.
Alumina particles as insulating fine particles (product name: AHP200, manufactured by Nippon Light Metal Co., Ltd., average particle diameter 0.4 μm) and sodium salt of carboxymethylcellulose (CMC, B-type viscosity when dissolved in water at a concentration of 1% by mass) Viscosity at 25 ° C. and 60 rpm measured by a meter: 50 mPa · s), an aqueous dispersion of styrene-butadiene rubber (SBR, average particle diameter: 180 nm), and water as a solvent were subjected to moderate shearing. By mixing, a slurry for an insulating layer was prepared. The slurry for the insulating layer was adjusted so that CMC was 5 parts by volume, SBR was 20 parts by volume, and the solid content concentration was 50% by mass with respect to 100 parts by volume of alumina.
Figure JPOXMLDOC01-appb-T000001
 ※比較例６における絶縁層用バインダーには、水溶性ポリマーと粒子状結着剤を使用した。
※有機溶剤可溶性ポリマーの固形分濃度低下量の値は、絶縁層用バインダーの固形分濃度低下量の値と同じである。
※評価欄における“－”は、充放電できないため評価できなかったことを示す。
Figure JPOXMLDOC01-appb-T000001
 * A water-soluble polymer and a particulate binder were used as the binder for the insulating layer in Comparative Example 6.
* The value of the decrease in the solid concentration of the organic solvent-soluble polymer is the same as the value of the decrease in the solid concentration of the binder for the insulating layer.
* "-" In the evaluation column indicates that evaluation was not possible because charging / discharging was not possible.
　以上のように、各実施例では、負極用バインダーが水溶性ポリマーと粒子状結着剤とを含み、絶縁層用バインダーが有機溶剤可溶性ポリマーを含み、かつ有機溶剤可溶性ポリマーの体積％、及び絶縁層の厚さを所定の範囲内に調整することで、安全性、充放電特性、及び出力特性がいずれも良好になった。 As described above, in each example, the binder for the negative electrode contains the water-soluble polymer and the particulate binder, the binder for the insulating layer contains the polymer soluble in an organic solvent, and the volume% of the polymer soluble in the organic solvent, By adjusting the thickness of the layer within a predetermined range, all of the safety, charge / discharge characteristics, and output characteristics were improved.
　１０　リチウムイオン二次電池
　１１　負極
　１２　負極活物質層
　１３　絶縁層
　１４　負極集電体
　２１　正極
　２２　正極活物質層
　２４　正極集電体 Reference Signs List 10 lithium ion secondary battery 11 negative electrode 12 negative electrode active material layer 13 insulating layer 14 negative electrode current collector 21 positive electrode 22 positive electrode active material layer 24 positive electrode current collector

Claims (9)

  1. 　正極と、負極とを備えるリチウムイオン二次電池であって、
    　前記負極が、負極活物質と負極用バインダーとを含有する負極活物質層と、前記負極活物質層の表面上に設けられ、絶縁性微粒子と絶縁層用バインダーとを含有する絶縁層とを備え、
    　前記絶縁層が前記正極に接触するように配置され、
    　前記負極用バインダーが水溶性ポリマーと粒子状結着剤を含み、
    　前記絶縁層用バインダーが有機溶剤可溶性ポリマーを含み、かつ前記有機溶剤可溶性ポリマーの含有量が、絶縁層全量基準で１５～４５体積％であり、
    　前記絶縁層の厚さが１０～２０μｍである、リチウムイオン二次電池。     A lithium ion secondary battery including a positive electrode and a negative electrode,
    The negative electrode includes a negative electrode active material layer containing a negative electrode active material and a negative electrode binder, and an insulating layer provided on a surface of the negative electrode active material layer and containing insulating fine particles and an insulating layer binder. ,
    The insulating layer is disposed so as to contact the positive electrode,
    The negative electrode binder contains a water-soluble polymer and a particulate binder,
    The insulating layer binder contains an organic solvent-soluble polymer, and the content of the organic solvent-soluble polymer is 15 to 45% by volume based on the total amount of the insulating layer;
    A lithium ion secondary battery, wherein the thickness of the insulating layer is 10 to 20 μm.
  2. 　前記有機溶剤可溶性ポリマーが、Ｎ－メチルピロリドンに可溶である請求項１に記載のリチウムイオン二次電池。 (4) The lithium ion secondary battery according to (1), wherein the organic solvent-soluble polymer is soluble in N-methylpyrrolidone.
  3. 　前記有機溶剤可溶性ポリマーが、ポリフッ化ビニリデン、及びアクリル樹脂からなる群から選択される少なくとも１種である請求項１又は２に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to claim 1 or 2, wherein the organic solvent-soluble polymer is at least one selected from the group consisting of polyvinylidene fluoride and an acrylic resin.
  4. 　前記水溶性ポリマーが、カルボキシメチルセルロース及びその塩、ヒドロキシエチルセルロース、ポリビニルアルコール、並びにポリビニルピロリドンからなる群から選択される少なくとも１種である請求項１～３のいずれか１項に記載のリチウムイオン二次電池。 The lithium ion secondary according to any one of claims 1 to 3, wherein the water-soluble polymer is at least one selected from the group consisting of carboxymethylcellulose and salts thereof, hydroxyethylcellulose, polyvinyl alcohol, and polyvinylpyrrolidone. battery.
  5. 　前記粒子状結着剤が、スチレンブタジエンゴム、及びアクリル樹脂からなる群から選択される少なくとも１種である請求項１～４のいずれか１項に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to any one of claims 1 to 4, wherein the particulate binder is at least one selected from the group consisting of styrene butadiene rubber and acrylic resin.
  6. 　前記正極が正極活物質層を備え、前記絶縁層が前記正極活物質層に接触するように配置される請求項１～５のいずれか１項に記載のリチウムイオン二次電池。 (6) The lithium ion secondary battery according to any one of (1) to (5), wherein the positive electrode includes a positive electrode active material layer, and the insulating layer is arranged to be in contact with the positive electrode active material layer.
  7. 　積層型である、請求項１～６のいずれか１項に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to any one of claims 1 to 6, which is a stacked type.
  8. 　請求項１～７のいずれか１項に記載のリチウムイオン二次電池の製造方法であって、
    　前記負極活物質と前記負極用バインダーとを含有する負極活物質層の表面上に、絶縁層用組成物を塗布して絶縁層を形成して、負極を得る工程と、
    　前記絶縁層を介して前記負極を正極に圧着させる工程とを備え、
    　前記絶縁層用組成物が、前記絶縁性微粒子と前記絶縁層用バインダーと有機溶剤とを含む、リチウムイオン二次電池の製造方法。     The method for producing a lithium ion secondary battery according to any one of claims 1 to 7, wherein
    A step of applying an insulating layer composition to form an insulating layer on the surface of the negative electrode active material layer containing the negative electrode active material and the negative electrode binder, and obtaining a negative electrode;
    Pressure bonding the negative electrode to the positive electrode via the insulating layer,
    A method for producing a lithium ion secondary battery, wherein the composition for an insulating layer includes the insulating fine particles, a binder for the insulating layer, and an organic solvent.
  9. 　正極と負極の間にセパレータがない、セパレータレスのリチウムイオン二次電池用負極であって、
    　負極活物質と負極用バインダーとを含有する負極活物質層と、前記負極活物質層の表面上に設けられ、絶縁性微粒子と絶縁層用バインダーとを含有する絶縁層とを備え、
    　前記負極用バインダーが水溶性ポリマーと粒子状結着剤を含み、
    　前記絶縁層用バインダーが有機溶剤可溶性ポリマーを含み、かつ前記有機溶剤可溶性ポリマーの含有量が、絶縁層全量基準で１５～４５体積％であり、
    　前記絶縁層の厚さが１０～２０μｍである、リチウムイオン二次電池用負極。     There is no separator between the positive electrode and the negative electrode, a separator-less negative electrode for a lithium ion secondary battery,
    A negative electrode active material layer containing a negative electrode active material and a negative electrode binder, and an insulating layer provided on the surface of the negative electrode active material layer and containing insulating fine particles and an insulating layer binder,
    The negative electrode binder contains a water-soluble polymer and a particulate binder,
    The insulating layer binder contains an organic solvent-soluble polymer, and the content of the organic solvent-soluble polymer is 15 to 45% by volume based on the total amount of the insulating layer;
    A negative electrode for a lithium ion secondary battery, wherein the thickness of the insulating layer is 10 to 20 μm.
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