WO2013054743A1 - Lithium-ion rechargeable battery electrode, and method for producing same - Google Patents

Lithium-ion rechargeable battery electrode, and method for producing same Download PDF

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Publication number
WO2013054743A1
WO2013054743A1 PCT/JP2012/075858 JP2012075858W WO2013054743A1 WO 2013054743 A1 WO2013054743 A1 WO 2013054743A1 JP 2012075858 W JP2012075858 W JP 2012075858W WO 2013054743 A1 WO2013054743 A1 WO 2013054743A1
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Prior art keywords
positive electrode
repeating unit
unit based
active material
lithium
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PCT/JP2012/075858
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French (fr)
Japanese (ja)
Inventor
角崎　健太郎
丈裕 巨勢
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旭硝子株式会社
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Publication of WO2013054743A1 publication Critical patent/WO2013054743A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a positive electrode for a lithium ion secondary battery, a method for producing a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery.
  • a lithium ion secondary battery has a positive electrode, a negative electrode, and a nonaqueous electrolyte.
  • the positive electrode includes a positive electrode active material, a binder, and a conductive material.
  • a composite oxide of lithium and a transition metal hereinafter also referred to as a lithium-containing composite oxide
  • Li-rich positive electrode material As a method for improving the discharge capacity, there is a case where the positive electrode active material is a composite oxide in which the ratio of Li element to the transition metal element such as Ni, Co, and Mn is increased (hereinafter referred to as “Li-rich positive electrode material”). .) Is proposed. As an example of the Li-rich positive electrode material, a solid solution of LiMO 2 (M is at least one transition metal element selected from Ni, Co, and Mn) and Li 2 MnO 3 has been proposed.
  • Patent Document 1 in a lithium ion secondary battery using a Li-rich positive electrode material as a positive electrode active material, 800,000 atomic mass is used as a positive electrode binder so that the positive electrode active material can be filled more highly. It has been proposed to use polyvinylidene fluoride (PVDF) having an average molecular weight greater than the unit. Further, Patent Document 2 comprises a fluorine-containing copolymer having a repeating unit based on ethylene tetrafluoride having a weight average molecular weight of 10,000 to 300,000 and a repeating unit based on propylene in order to improve cycle characteristics. Binders have been proposed.
  • PVDF polyvinylidene fluoride
  • the present invention provides a positive electrode for a lithium ion secondary battery having a high discharge capacity, excellent adhesion between a positive electrode active material and a conductive material and a positive electrode current collector, and excellent cycle characteristics that do not easily deteriorate even after repeated charge / discharge cycles.
  • An object of the present invention is to provide a method for producing a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery including the lithium ion secondary battery positive electrode.
  • the positive electrode for a lithium ion secondary battery of the present invention is a positive electrode for a lithium ion secondary battery in which a positive electrode active material layer containing a positive electrode active material, a binder, and a conductive material is formed on the surface of the positive electrode current collector,
  • the positive electrode active material contains Li element and at least one transition metal element selected from the group consisting of Ni, Co, and Mn (provided that the molar amount of Li element is the total molar amount of the transition metal element)
  • the lithium-containing composite oxide is included, and the binder is at least one monomer selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride.
  • a fluorine-containing rubber having a fluorine content of 50 to 76% by mass.
  • the binder preferably contains a fluorinated rubber composed of a copolymer having a repeating unit based on ethylene tetrafluoride and a repeating unit based on propylene.
  • the copolymer having a repeating unit based on tetrafluoroethylene and a repeating unit based on propylene has a ratio of 40 to 70/60 to 30 (mol%) of the repeating unit based on ethylene tetrafluoride / the repeating unit based on propylene. It is preferable to have. It is preferable that the binder includes a fluorinated rubber made of a copolymer having a repeating unit based on ethylene tetrafluoride, a repeating unit based on propylene, and a repeating unit based on vinylidene fluoride.
  • the copolymer having a repeating unit based on ethylene tetrafluoride, a repeating unit based on propylene, and a repeating unit based on vinylidene fluoride is a repeating unit based on ethylene tetrafluoride / a repeating unit based on propylene / vinylidene fluoride. It is preferable to have a ratio of repeating units based on 30 to 70/20 to 60/1 to 40 (mol%).
  • the present invention is a method for producing a positive electrode for a lithium ion secondary battery of the present invention, comprising a mixing step of mixing the positive electrode active material and the binder to obtain a mixture, and a step of heat-treating the mixture.
  • a method for producing a positive electrode for a lithium ion secondary battery comprising a mixing step of mixing the positive electrode active material and the binder to obtain a mixture, and a step of heat-treating the mixture.
  • the positive electrode active material and the binder are preferably mixed in an organic solvent.
  • the present invention provides a lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery of the present invention, a negative electrode, and a nonaqueous electrolyte.
  • a lithium ion secondary battery having a high discharge capacity, excellent adhesion between a positive electrode active material and a conductive material and a positive electrode current collector, and excellent cycle characteristics that hardly deteriorate even after repeated charge and discharge cycles.
  • a positive electrode for use is obtained.
  • the lithium ion secondary battery of the present invention includes the positive electrode of the lithium ion secondary battery of the present invention, has a high discharge capacity, and excellent cycle characteristics.
  • the present invention is described in detail below.
  • the positive electrode active material in the present invention contains Li element and at least one transition metal element selected from Ni, Co, and Mn (provided that the molar amount of Li element is relative to the total molar amount of the transition metal element).
  • Including lithium-containing composite oxide hereinafter referred to as lithium-containing composite oxide (I)
  • a known positive electrode active material may be included in the lithium ion secondary battery.
  • 50 to 100% by mass of the positive electrode active material is preferably lithium-containing composite oxide (I), more preferably 75 to 100% by mass, and particularly preferably 100% by mass.
  • the shape of the positive electrode active material in the present invention is particulate.
  • the average particle size (D50) of the positive electrode active material is preferably 3 to 25 ⁇ m, more preferably 4 to 20 ⁇ m, and particularly preferably 5 to 15 ⁇ m.
  • the definition of the average particle diameter (D50) is as described later.
  • the composition ratio (molar ratio) of the Li element to the total molar amount of the transition metal element is preferably 1.25 to 1.70, and is 1.35 to 1.60. More preferably, it is particularly preferably 1.40 to 1.55.
  • the discharge capacity per unit mass of the lithium ion secondary battery can be further increased.
  • the lithium-containing composite oxide (I) contains at least one transition metal element selected from Ni, Co, and Mn. More preferably, Mn is included as an essential component, and it is particularly preferable that all elements of Ni, Co, and Mn are included.
  • the lithium-containing composite oxide (I) may contain a metal element other than Ni, Co, Mn, and Li (hereinafter referred to as other metal element). Examples of the other metal elements include at least one selected from Cr, Fe, Al, Ti, Zr, Mo, Nb, V, and Mg.
  • the proportion of the other metal elements is 0.001 to 0.1 mol in total when the total amount of metal elements other than Li in the lithium-containing composite oxide (I) is 1 mol. It is preferably 0.005 to 0.05 mol.
  • the lithium-containing composite oxide (I) is preferably a compound represented by the following formula (1).
  • the compound represented by Formula (1) in this invention is a composition before passing through the process of charging / discharging or activation.
  • activation means removing lithium oxide (Li 2 O) or lithium and lithium oxide from the lithium-containing composite oxide (I).
  • As a normal activation method there is an electrochemical activation method in which a voltage higher than 4.4 V or 4.6 V (expressed as a potential difference from the oxidation-reduction potential of Li + / Li) is applied.
  • the chemical activation method by performing chemical reaction using acids, such as a sulfuric acid, hydrochloric acid, or nitric acid, is mentioned.
  • Me is at least one element selected from Co, Ni, Cr, Fe, Al, Ti, Zr, Mo, Nb, V, and Mg.
  • Me is preferably one or more selected from Co, Ni, and Cr, and more preferably one or more selected from Co and Ni.
  • 0.09 ⁇ x ⁇ 0.3, y> 0, z> 0, 1.9 ⁇ p ⁇ 2.1, 0 ⁇ q ⁇ 0.1, and 0.4 ⁇ y / (y + z) ⁇ 0.8, x + y + z 1, 1.2 ⁇ (1 + x) / (y + z).
  • the ratio of Li exceeds 1.2 times mol with respect to the total of Mn and Me.
  • the formula (1) is also characterized in that it is a compound containing a specific amount of Mn, and the ratio of Mn to the total molar amount of Mn and Me is preferably 0.5 ⁇ y / (y + z) ⁇ 0.8, 0.55 ⁇ y / (y + z) ⁇ 0.75 is more preferable. If Mn is the said range, discharge capacity will become high capacity
  • the composition ratio of Li element with respect to the total molar amount of Mn and Me is preferably 1.25 ⁇ (1 + x) / (y + z) ⁇ 1.70, and 1.35 ⁇ (1 + x) / (y + z) ⁇ 1.60 is more preferable, and 1.40 ⁇ (1 + x) / (y + z) ⁇ 1.55 is particularly preferable.
  • the discharge capacity becomes high.
  • lithium-containing composite oxide (I) Li (Li 0.16 Ni 0.17 Co 0.08 Mn 0.59 ) O 2 , Li (Li 0.17 Ni 0.17 Co 0.17 Mn 0.49 ) O 2 , Li (Li 0.17 Ni 0.21 Co 0.08 Mn 0.54) O 2, Li (Li 0.17 Ni 0.14 Co 0.14 Mn 0.55 ) O 2 , Li (Li 0.18 Ni 0.12 Co 0.12 Mn 0.58 ) O 2 , Li (Li 0.18 Ni 0.16 Co 0.12 Mn 0.54 ) O 2 , Li (Li 0.20 Ni 0.12 Co 0.08 Mn 0.60 ) O 2 , Li (Li 0.20 Ni 0.16 Co 0.08 Mn 0.56 ) O 2 , Li (Li 0.20 Ni 0.13 Co 0.13 Mn 0.54 ) O 2 .
  • the shape of the lithium-containing composite oxide (I) is preferably particulate.
  • the average particle size (D50) of the lithium-containing composite oxide (I) is preferably 3 to 25 ⁇ m, more preferably 4 to 20 ⁇ m, and particularly preferably 5 to 15 ⁇ m.
  • the average particle size (D50) is a particle size distribution at a point where the cumulative curve is 50% in a cumulative curve where the particle size distribution is obtained on a volume basis and the total volume is 100%. It means% diameter.
  • the particle size distribution is obtained from a frequency distribution and a cumulative volume distribution curve measured with a laser scattering particle size distribution measuring apparatus.
  • the particle size is measured by sufficiently dispersing the powder in an aqueous medium by ultrasonic treatment or the like and measuring the particle size distribution (for example, a laser diffraction / scattering particle size distribution measuring device Partica LA-950VII manufactured by HORIBA, etc.). Used).
  • the specific surface area of the lithium-containing composite oxide (I) is preferably 0.3 ⁇ 10m 2 / g, particularly preferably 0.5 ⁇ 5m 2 / g.
  • the specific surface area is measured by a nitrogen gas adsorption BET (Brunauer, Emmett, Teller) method (for example, using a high precision gas / vapor adsorption amount measuring device BELSORP-max manufactured by Bell Japan).
  • the method for producing the lithium-containing composite oxide (I) includes a method in which a precursor of the lithium-containing composite oxide obtained by the coprecipitation method and a lithium compound are mixed and fired, a hydrothermal synthesis method, a sol-gel method, and a dry mixing method.
  • a method (solid phase method), an ion exchange method, or a glass crystallization method can be appropriately used.
  • the precursor of the lithium-containing composite oxide obtained by the coprecipitation method (coprecipitation composition) It is preferable to use a method of mixing and baking a lithium compound.
  • the lithium-containing composite oxide (I) used as the positive electrode active material has Mg, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Al, Ga, Y, La, Ce, Nd, Gd, on the surface. It is preferable that a coating layer (hereinafter referred to as coating layer (II)) made of an oxide containing at least one metal element selected from the group consisting of Er and Er is formed.
  • coating layer (II) made of an oxide containing at least one metal element selected from the group consisting of Er and Er is formed.
  • Al 2 O 3 , Ga 2 O 3 , Y 2 O 3 , La 2 O 3 , Ce 2 O 3 , Nd 2 O 3 , Gd 2 O 3 , or Er 2 O 3 is the cycle retention rate. Is particularly preferable because it can be greatly improved.
  • the coating layer (II) one or more of the above compounds may be used.
  • the coating layer (II) can be evaluated by transmission electron microscope-energy dispersive X-ray spectroscopy analysis (TEM-EDX) and X-ray electron spectroscopy (XPS).
  • TEM-EDX transmission electron microscope-energy dispersive X-ray spectroscopy analysis
  • XPS X-ray electron spectroscopy
  • the surface of the lithium-containing composite oxide (I) has Mg, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Al, Ga, It can be confirmed that there is an oxide of at least one metal element selected from the group consisting of Y, La, Ce, Nd, Gd, and Er.
  • the coating layer (II) may be crystalline or amorphous, and is preferably amorphous.
  • amorphous means that no peak attributed to the coating layer (II) is observed in the X-ray diffraction measurement (hereinafter also referred to as XRD). Although the reason is not clear, it is considered that when the coating layer (II) is amorphous, the coating layer (II) can more uniformly cover the surface of the lithium-containing composite oxide (I).
  • the total total molar amount of Mg, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Al, Ga, Y, La, Ce, Nd, Gd, and Er contained in the positive electrode active material is the positive electrode active material
  • the total molar amount of Ni, Co, and Mn in the total is 1 mol, it is preferably 0.0005 to 0.05 mol, more preferably 0.001 to 0.03 mol, Particularly preferred is 0.003 to 0.02 mol.
  • Mg, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Al, Ga, Y, La contained in the positive electrode active material with respect to the total molar amount of Ni, Co, and Mn in the positive electrode active material , Ce, Nd, Gd, and Er can be measured by dissolving the positive electrode active material in an acid and performing ICP (high frequency inductively coupled plasma) measurement. If it is difficult to obtain by ICP measurement, it may be calculated based on the amount of preparation.
  • ICP high frequency inductively coupled plasma
  • the lithium-containing composite oxide (I) is subjected to heat treatment after contacting with the compound containing the metal element. Is mentioned.
  • the spray method is particularly preferable because of its excellent productivity.
  • the temperature for the heat treatment is preferably 200 to 650 ° C, more preferably 300 to 550 ° C. When the heat treatment temperature is in the above range, an oxide can be efficiently generated, and an amorphous oxide is easily obtained.
  • At least one lithium compound selected from the group consisting of a lithium phosphate compound, a lithium sulfate compound, and a lithium fluoride may be attached to the surface of the lithium-containing composite oxide (I).
  • the lithium compound include LiF, Li 3 PO 4 , Li 2 SO 4 , and Li 2 SO 4 .H 2 O.
  • the binder in the present invention is at least one selected from the group consisting of ethylene tetrafluoride (hereinafter also referred to as TFE), hexafluoropropylene (hereinafter also referred to as HFP), and vinylidene fluoride (hereinafter also referred to as VdF).
  • TFE ethylene tetrafluoride
  • HFP hexafluoropropylene
  • VdF vinylidene fluoride
  • Fluorine-containing rubber hereinafter referred to as fluorine-containing rubber (III)
  • fluorine-containing rubber (III) comprising a copolymer having a repeating unit based on a monomer and having a fluorine content of 50 to 76% by mass is included.
  • the fluorine-containing rubber (III) is a copolymer composed of two or more kinds of repeating units, and is a copolymer consisting of repeating units based on two or three monomers selected from the group consisting of TFE, HFP, and VdF. It may be a coalescence, one or more repeating units based on one or more monomers selected from the group consisting of TFE, HFP, and VdF, and one or more other monomers copolymerizable with the monomers It may be a copolymer comprising repeating units based on.
  • the fluorine content of the fluorine-containing rubber (III) is preferably 50 to 74% by mass, more preferably 53 to 70% by mass.
  • the fluorine content of the fluorine-containing rubber is obtained by fluorine content analysis, and indicates the ratio of the mass of fluorine atoms to the total mass of all atoms constituting the fluorine-containing rubber.
  • the fluorine-containing rubber (III) has a repeating unit based on another monomer in addition to a repeating unit based on TFE, a repeating unit based on HFP, and a repeating unit based on VdF
  • P Propylene
  • E ethylene
  • PAVE perfluoro (alkyl vinyl ether)
  • PAVE perfluoro (methyl vinyl ether)
  • PMVE perfluoro (propyl vinyl ether)
  • PPVE perfluoro (propyl vinyl ether)
  • fluorine-containing rubber (III) examples include a TFE / P copolymer (meaning a copolymer comprising a repeating unit based on TFE and a repeating unit based on P. The same shall apply hereinafter), TFE / P / VdF copolymer.
  • TFE / P copolymer The ratio of the repeating unit based on TFE / the repeating unit based on P is 30 to 80/70 to 20 (mol%) (however, the repeating unit based on TFE and the repeating unit based on P are 100 mol% in total). The same shall apply hereinafter)), more preferably from 40 to 70/60 to 30 (mol%), and most preferably from 60 to 50/40 to 50 (mol%).
  • TFE / P / VdF copolymer The ratio of the repeating unit based on TFE / the repeating unit based on P / the repeating unit based on VdF is preferably in the range of 30 to 85/15 to 70 / 0.01 to 50 (mol%), more preferably 30 70/20 to 60/1 to 40 (mol%).
  • VdF / HFP copolymer The ratio of the repeating unit based on VdF / the repeating unit based on HFP is preferably 45 to 90/55 to 10 (mol%), and more preferably 50 to 80/50 to 20 (mol%).
  • VdF / TFE copolymer The ratio of the repeating unit based on VdF / the repeating unit based on HFP is preferably 50 to 90/50 to 10 (mol%).
  • TFE / VdF / HFP copolymer The ratio of the repeating unit based on TFE / the repeating unit based on VdF / the repeating unit based on HFP is preferably 2 to 50/30 to 90/1 to 35 (mol%).
  • TFE / PAVE copolymer The ratio of the repeating unit based on TFE / the repeating unit based on PAVE is preferably 50 to 90/50 to 10 (mol%), and more preferably 50 to 80/50 to 20 (mol%).
  • TFE / P / PAVE copolymer The ratio of the repeating unit based on TFE / the repeating unit based on P / the repeating unit based on PAVE is preferably 30 to 80/15 to 70 / 0.1 to 40 (mol%), and preferably 39 to 70/20 to More preferably 60/1 to 30 (mol%)
  • the weight average molecular weight of the fluorinated rubber (III) is preferably 10,000 to 300,000, more preferably 20,000 to 250,000, and even more preferably 30,000 to 190,000.
  • the weight average molecular weight (Mw) in the present specification is a molecular weight in terms of polystyrene obtained by measuring with gel permeation chromatography using a calibration curve prepared using a standard polystyrene sample having a known molecular weight.
  • the tensile elongation at break is preferably 500% or more, more preferably 800% or more, and particularly preferably 1000% or more. When the tensile elongation at break is less than 500%, the adhesion with the positive electrode current collector tends to be lowered.
  • the tensile strength of the fluorine-containing rubber (III) is preferably 1 to 50 MPa, more preferably 5 to 20 MPa. When the tensile strength is within the above range, the adhesion is excellent.
  • the values of the tensile elongation at break and the tensile strength of the fluorinated rubber (III) are values obtained by a method according to JISK6251.
  • the fluorine-containing rubber (III) contained in the positive electrode binder may be one type or two or more types.
  • the binder may contain other fluororesins such as polytetrafluoroethylene and other polymer compounds as necessary.
  • 60% by mass or more of the binder is preferably fluorine-containing rubber (III), more preferably 80% by mass or more, and particularly preferably 100% by mass.
  • the fluorine-containing rubber (III) can be produced by a known polymerization method, and among them, the radical copolymerization method is preferable.
  • the radical polymerization method is not particularly limited, and various radical polymerization methods are used, but those initiated by an organic or inorganic radical polymerization initiator, light, heat, ionizing radiation, or the like are preferable.
  • the form of polymerization can be produced by a conventionally known polymerization method such as bulk polymerization, suspension polymerization, emulsion polymerization, solution polymerization or the like, and emulsion polymerization is preferred. For example, a method of copolymerizing propylene and tetrafluoroethylene in an aqueous medium in the presence of a redox catalyst can be used.
  • a method for producing a fluorine-containing rubber (III) having a repeating unit based on TFE and a repeating unit based on P such as a TFE / P copolymer, an aqueous medium, an anionic emulsifier, and thermal decomposition type radical polymerization It has an emulsion polymerization step in which a monomer mixture containing tetrafluoroethylene and propylene is emulsion-polymerized at a polymerization temperature in the range of 50 ° C. to 100 ° C. to produce a fluorinated rubber (III) in the presence of an initiator.
  • a production method (hereinafter referred to as production method (IV)) can be preferably used.
  • the aqueous medium is composed of water alone or water and a water-soluble organic solvent, and the content of the water-soluble organic solvent is less than 1 part by mass with respect to 100 parts by mass of water.
  • the amount of the anionic emulsifier used is 1.5 to 5.0 parts by mass with respect to 100 parts by mass of the fluorine-containing rubber (III) to be produced.
  • the emulsion polymerization step can be performed by a known emulsion polymerization method. For example, it can be performed by the following procedure. According to this production method (IV), since the fluorinated rubber (III) can be produced without using a redox catalyst, a latex of the fluorinated rubber (III) having a low metal content can be obtained. Moreover, although the content of the organic solvent is small, good stability in the latex of the fluorine-containing rubber (III) can be obtained.
  • water-soluble organic solvents meaning organic solvents that can be dissolved in water
  • Alcohols are preferable, and tert-butanol is particularly preferable.
  • the content of the water-soluble organic solvent in the aqueous medium is preferably small.
  • the water-soluble organic solvent is less than 1 part by mass with respect to 100 parts by mass of water, preferably 0.5 parts by mass or less, more preferably 0.1 parts by mass or less, and particularly preferably zero. That is, it is particularly preferable to use water that does not contain a water-soluble organic solvent alone as the aqueous medium.
  • anionic emulsifier those known in the emulsion polymerization method can be used.
  • hydrocarbon emulsifiers such as sodium lauryl sulfate, sodium dodecylbenzene sulfonate, sodium alkyl sulfonate, sodium alkyl benzene sulfonate, sodium succinate dialkyl ester sulfonate, sodium alkyl diphenyl ether disulfonate; perfluoro Fluorine-containing alkyl carboxylates such as ammonium octanoate and ammonium perfluorohexanoate; compounds represented by the following formula (2), and the like.
  • X represents a fluorine atom or a perfluoroalkyl group having 1 to 3 carbon atoms
  • A represents a hydrogen atom, an alkali metal atom, or —NH 4
  • p represents an integer of 1 to 10
  • Q represents 0 or an integer of 1 to 3.
  • anionic emulsifier sodium lauryl sulfate is particularly preferable.
  • the amount of the anionic emulsifier used is 1.5 to 5.0 parts by mass, and 1.5 to 3.8 parts by mass with respect to 100 parts by mass of the fluorinated rubber (III) produced in the emulsion polymerization step.
  • the content of the emulsifier in the fluorine-containing rubber (III) latex is within this range, the stability of the latex is excellent, and excellent charge / discharge characteristics can be obtained when the latex is used as a binder composition. When there is too much content of this emulsifier, this charge / discharge characteristic will deteriorate easily.
  • the thermal decomposition type radical polymerization initiator is water-soluble and has a one-hour half-life temperature of 50 to 100 ° C. It can be appropriately selected from water-soluble polymerization initiators used in ordinary emulsion polymerization. Specific examples include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate; disuccinic acid peroxide; organic initiators such as azobisisobutylamidine dihydrochloride, and the like. Of these, persulfates are preferred, and ammonium persulfate is particularly preferred.
  • the amount of the thermal decomposition type radical polymerization initiator used is preferably 0.0001 to 3 parts by mass, and 0.001 to 1 part by mass with respect to 100 parts by mass of the fluorinated rubber (III) produced in the emulsion polymerization step. Is more preferable.
  • a pH adjuster may be added in the emulsion polymerization step of production method (IV).
  • Known inorganic salts can be used as the pH adjuster.
  • Specific examples include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate; carbonates such as sodium hydrogen carbonate and sodium carbonate; and the like. More preferable specific examples of the phosphate include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate.
  • the polymerization rate and the stability of the resulting latex can be improved.
  • the amount of the pH adjuster used is preferably as small as possible. Therefore, the emulsion polymerization process is preferably performed in the absence of a pH adjuster.
  • the positive electrode for a lithium ion secondary battery according to the present invention has a positive electrode active material layer containing the positive electrode active material, the binder, and a conductive material formed on the surface of a positive electrode current collector.
  • the conductive material include carbon black such as acetylene black, graphite, and ketjen black.
  • Examples of the positive electrode current collector include aluminum or an aluminum alloy.
  • the positive electrode for a lithium ion secondary battery of the present invention can be highly filled with the lithium-containing composite oxide (I) as a positive electrode active material, and can have a high capacity. Moreover, since the binder does not deteriorate even when charged at a high voltage, the cycle retention rate is excellent. That is, the discharge capacity can be improved by using the lithium-containing composite oxide (I) in which the molar amount of Li element is more than 1.2 times the total molar amount of the transition metal element as the positive electrode active material. .
  • the positive electrode for a lithium ion secondary battery using such a lithium-containing composite oxide (I) as the positive electrode active material it is preferable to activate the positive electrode active material at a high voltage, and for that purpose, the withstand voltage of the binder Is desired to be high. Furthermore, since lithium containing complex oxide (I) has comparatively low electroconductivity, it is desired to reduce the binder content in the positive electrode active material layer and increase the positive electrode active material content (high filling).
  • the positive electrode is interposed via the binder.
  • Good adhesion between the active material and conductive material layer and the positive electrode current collector can be obtained.
  • the content of the positive electrode active material in the positive electrode active material layer can be preferably 80 to 97% by mass. 85 to 95% by mass is more preferable.
  • the binder content in the positive electrode active material layer is preferably 1.5 to 10% by mass, more preferably 2.5 to 5% by mass.
  • the content of the conductive material in the positive electrode active material layer is preferably 1.5 to 10% by mass, and more preferably 2.5 to 5% by mass.
  • the content of the positive electrode active material, the binder, and the conductive material is within the above ranges, good conductivity can be obtained, and since the content of the positive electrode active material is large, the positive electrode has a high discharge capacity and is collected from the positive electrode active material. The adhesion of the electric body is improved.
  • the fluorine content of the fluorine-containing rubber (III) used as the binder is high, good voltage resistance is obtained, and the binder is hardly deteriorated even when charged at a high voltage. Further, the fluororubber (III) has good alkali resistance when it contains a repeating unit based on TFE and a repeating unit based on P. Therefore, even when the lithium-containing composite oxide (I) having a high Li element content is used as the positive electrode active material, the binder is hardly deteriorated, and a good cycle maintenance rate is obtained. Furthermore, since the fluorine-containing rubber (III) is excellent in flexibility, it has excellent followability to expansion and contraction of the positive electrode active material when charging and discharging are repeated, and contributes to improvement of cycle characteristics.
  • the positive electrode for a lithium ion secondary battery of the present invention can be manufactured by a method including a mixing step of mixing the positive electrode active material and the binder to obtain a mixture, and a step of heat-treating the mixture.
  • the mixture is preferably a slurry or a kneaded product further containing an organic solvent or an aqueous dispersion medium. That is, in the mixing step, it is preferable to mix the positive electrode active material and the binder in an organic solvent. Alternatively, in the mixing step, it is preferable to mix the positive electrode active material and the binder in an aqueous dispersion medium.
  • the conductive material is preferably contained in the mixture.
  • a conductive material When mixing the positive electrode active material and the binder, a conductive material may be added and mixed. Alternatively, the conductive material and the positive electrode active material may be mixed in advance and then mixed with the binder. The mixture is supported on the surface of the positive electrode current collector plate by coating or the like, and heat treated to remove the organic solvent and / or aqueous dispersion medium to form a positive electrode active material layer and the like, thereby forming a positive electrode for a lithium ion secondary battery Is obtained. The positive electrode active material layer may be further pressed.
  • the binder In the production of a positive electrode for a lithium ion secondary battery, the binder is preferably used as a binder composition containing a binder and an organic solvent or an aqueous dispersion medium.
  • the binder composition is preferably a binder composition containing a binder and an aqueous dispersion medium.
  • organic solvents examples include ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, hexane, octane, toluene, xylene, naphtha, acetonitrile, N-methylpyrrolidone, acetylpyridine, cyclopentanone, dimethylformamide, dimethyl sulfoxide , Methylformamide, methanol, ethanol and the like.
  • N-methylpyrrolidone or butyl acetate is preferable, and N-methylpyrrolidone is more preferable.
  • the organic solvent may be a single solvent or a mixed solvent of two or more solvents.
  • aqueous dispersion medium water alone or a mixture of water and a water-soluble organic solvent can be used.
  • water-soluble organic solvents include ketones such as acetone and methyl ethyl ketone; amines such as triethylamine and aniline; amides such as N-methylpyrrolidone and dimethylformamide; methanol, ethanol, propanol, isopropanol, n-butanol, and t-butanol.
  • alcohols Among these, alcohols or amides are preferable, and alcohols are more preferable.
  • methanol, isopropanol, or t-butanol is preferable, and t-butanol is more preferable.
  • Only one water-soluble organic solvent may be used in the aqueous dispersion medium, or two or more water-soluble organic solvents may be used in combination.
  • the ratio of the binder contained in the binder composition is preferably 5 to 60% by mass, and more preferably 10 to 50% by mass, based on the entire binder composition.
  • the fluorinated rubber (III) is preferably emulsified or dispersed in the aqueous dispersion medium, particularly in a latex state. preferable.
  • the production method of the binder composition is not particularly limited, but the fluorine-containing rubber (III) is produced by suspension polymerization, emulsion polymerization, solution polymerization, etc., and the fluorine-containing rubber (III) after polymerization is dissolved in an organic solvent.
  • the composition dispersed in an aqueous dispersion medium can be used as it is.
  • the solvent or dispersion medium used in the polymerization is preferably the same as the organic solvent or aqueous dispersion medium constituting the binder composition to be obtained.
  • the binder composition contains an organic solvent, the solution of fluorine-containing rubber (III) produced by solution polymerization can be used as it is.
  • the binder composition contains an aqueous dispersion medium
  • a composition produced by emulsion polymerization in which the fluorinated rubber (III) is dispersed in the aqueous dispersion medium can be used as it is.
  • the binder composition may be a composition obtained by purifying the fluorine-containing rubber obtained by polymerization to a solid state and dissolving the solid again in an organic solvent or dispersing in an aqueous dispersion medium.
  • the organic solvent or aqueous dispersion medium used in this case is preferably the aforementioned organic solvent or aqueous dispersion medium.
  • the lithium ion secondary battery in this invention contains the positive electrode for lithium ion secondary batteries of this invention, a negative electrode, and a nonaqueous electrolyte.
  • the negative electrode is formed by forming a negative electrode active material layer containing a negative electrode active material on a negative electrode current collector.
  • a slurry can be prepared by kneading a negative electrode active material with an organic solvent, and the prepared slurry can be applied to a negative electrode current collector, dried, and pressed.
  • the negative electrode current collector for example, a metal foil such as a nickel foil or a copper foil can be used.
  • the negative electrode active material may be any material that can occlude and release lithium ions at a relatively low potential.
  • Carbon compounds, silicon carbide compounds, silicon oxide compounds, titanium sulfide, boron carbide compounds, and the like can be used.
  • Examples of the carbon material of the negative electrode active material include non-graphitizable carbon, artificial graphite, natural graphite, pyrolytic carbon, coke such as pitch coke, needle coke, petroleum coke, graphite, glassy carbon, phenol Organic polymer compound fired bodies, carbon fibers, activated carbon, carbon blacks, etc., obtained by firing and carbonizing a resin, furan resin or the like at an appropriate temperature can be used.
  • the metal of the periodic table group 14 is, for example, silicon or tin, and most preferably silicon.
  • Non-silicon materials that can be used as the negative electrode active material include oxides such as iron oxide, ruthenium oxide, molybdenum oxide, tungsten oxide, titanium oxide, and tin oxide, and nitrides such as Li 2.6 Co 0.4 N. It is done.
  • non-aqueous electrolyte examples include a non-aqueous electrolyte obtained by dissolving an electrolyte salt in an organic solvent, a solid electrolyte containing an electrolyte salt, a solid electrolyte obtained by mixing or dissolving an electrolyte salt in a polymer electrolyte, a polymer compound, and the like. Or a gel electrolyte etc. are mentioned.
  • organic solvent those known as organic solvents for electrolytic solutions can be used.
  • propylene carbonate ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, Diglyme, triglyme, ⁇ -butyrolactone, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, acetic acid ester, butyric acid ester, propionic acid ester and the like
  • cyclic carbonates such as propylene carbonate or chain carbonates such as dimethyl carbonate and diethyl carbonate.
  • such an organic solvent may be used individually by 1 type, and may be used in mixture of 2 or more types.
  • any material having lithium ion conductivity may be used.
  • an inorganic solid electrolyte or a polymer solid electrolyte can be used.
  • lithium nitride lithium iodide, or the like
  • polymer solid electrolyte an electrolyte salt and a polymer compound that dissolves the electrolyte salt can be used.
  • the polymer compound include polyethylene oxide, polypropylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polyhexafluoropropylene, or derivatives, mixtures, and composites thereof. Can be used.
  • any gel electrolyte may be used as long as it absorbs the non-aqueous electrolyte and gels, and various polymers can be used.
  • the polymer material used for the gel electrolyte for example, fluorine-based polymers such as poly (vinylidene fluoride) and poly (vinylidene fluoride-co-hexafluoropropylene) can be used.
  • the polymer material used for the gel electrolyte for example, polyacrylonitrile and a copolymer of polyacrylonitrile, as well as an ether polymer such as polyethylene oxide, a copolymer of polyethylene oxide, and a crosslinked product thereof can be used. .
  • the copolymerization monomer examples include polypropylene oxide, methyl methacrylate, butyl methacrylate, methyl acrylate, and butyl acrylate.
  • the matrix of the gel electrolyte is particularly preferably a fluoropolymer from the viewpoint of stability against redox reaction.
  • any electrolyte salt can be used as long as it is used for this type of battery.
  • LiClO 4 , LiPF 6 , LiBF 4 , CH 3 SO 3 Li, LiCl, LiBr, or the like can be used.
  • the shape of the lithium ion secondary battery of the present invention can be appropriately selected from coin shapes, sheet shapes (film shapes), folded shapes, wound bottomed cylindrical shapes, button shapes, and the like depending on the application.
  • the mother liquor was placed in a 2 L baffled glass reaction vessel, heated to 50 ° C. with a mantle heater, and a pH adjusting solution was added so that the pH was 11.0.
  • the raw material solution was added at a rate of 5.0 g / min and the ammonia source solution was added at a rate of 1.0 g / min, and a composite hydroxide of nickel, cobalt, and manganese was added.
  • the pH adjusting solution was added so as to keep the pH in the reaction vessel at 11.0.
  • nitrogen gas was flowed at a flow rate of 0.5 L / min in the reaction tank so that the precipitated hydroxide was not oxidized. Further, the liquid was continuously extracted so that the amount of the liquid in the reaction tank did not exceed 2 L.
  • This precursor (20 g) and lithium carbonate (12.8 g) having a lithium content of 26.9 mol / kg were mixed and calcined at 900 ° C. for 12 hours in an oxygen-containing atmosphere to obtain a lithium-containing composite oxide of the example. It was.
  • the composition of the lithium-containing composite oxide of the obtained example is Li (Li 0.2 Ni 0.128 Co 0.134 Mn 0.538 ) O 2 .
  • the average particle diameter D50 of the lithium-containing composite oxide of the example was 8.4 ⁇ m, and the specific surface area measured using the nitrogen gas adsorption BET method was 1.4 m 2 / g. When the tap density of the lithium-containing composite oxide was measured, it was 1.8 g / cm 3 .
  • Al aqueous solution an aqueous solution in which the aluminum compound was dissolved (hereinafter also referred to as an Al aqueous solution).
  • Al aqueous solution aqueous solution in which the aluminum compound was dissolved
  • 1 g of the prepared Al aqueous solution was spray-sprayed and added to 10 g of the lithium-containing composite oxide of the example under stirring, and the lithium-containing composite oxide of the example and the Al aqueous solution were brought into contact with mixing.
  • the obtained mixture was dried at 90 ° C. for 2 hours, and then heated at 400 ° C. for 8 hours in an oxygen-containing atmosphere to form a coating layer (II) on the surface of the lithium-containing composite oxide to form a positive electrode active material (1 )
  • the coating layer (II) formed using the Al aqueous solution contains an oxide of Al.
  • the aluminum of the coating layer is in a molar ratio (coating amount) with respect to the total of nickel, cobalt, and manganese, which are transition metal elements of the lithium-containing composite oxide.
  • Binder composition As a binder composition, a solution was prepared in which a fluoropolymer as a binder was dissolved or dispersed in an organic solvent or water.
  • Reference Example 1 Preparation of binder composition containing fluorine-containing rubber A
  • ion exchange water After degassing the inside of a 3200 mL stainless steel pressure-resistant reactor equipped with an anchor blade for stirring, 1700 g of ion exchange water, 5 g of disodium hydrogen phosphate 12 hydrate, 2 0.0 g sodium hydroxide, 13.3 g sodium lauryl sulfate, and 4.4 g ammonium persulfate were added.
  • the anchor blade was rotated at 300 rpm to initiate the polymerization reaction.
  • the pressure in the reactor decreases.
  • the internal pressure of the reactor was increased to 2.51 MPaG. This was repeated, and the internal pressure of the reactor was maintained at 2.49 to 2.51 MPaG, and the polymerization reaction was continued.
  • the total amount of the TFE / P monomer mixed gas injected reaches 900 g
  • the internal temperature of the reactor is cooled to 10 ° C.
  • the polymerization reaction is stopped, and the latex containing the fine fluorine-containing rubber A This was used as a binder composition.
  • the polymerization time was 8 hours.
  • the solid content in the binder composition was 34% by mass.
  • the fluorine content of the obtained fluorinated rubber is shown in Table 1 (hereinafter the same).
  • EDTA ethylenediaminetetraacetic acid disodium salt dihydrate
  • ferrous sulfate heptahydrate ferrous sulfate heptahydrate
  • a 1.5% by mass aqueous solution of calcium chloride was added to the latex to agglomerate the fluorinated rubber B, which was filtered and recovered.
  • the fluorinated rubber B was washed with ion-exchanged water and dried in an oven at 100 ° C. for 15 hours to obtain a white fluorinated rubber B.
  • This fluorinated rubber B was dissolved in an N-methylpyrrolidone solution to prepare a binder composition having a fluorinated rubber B concentration of 10% by mass.
  • the fluorine-containing rubber A which is a binder of Reference Example 1 was added to the binder composition obtained in Reference Example 1 by adding a 1.5% by mass aqueous solution of calcium chloride to aggregate the fluorine-containing rubber A, and filtered. The recovered and dried product was used.
  • the fluorine-containing rubbers B and C which are binders of Reference Examples 2 and 3 the dried fluorine-containing rubbers B and C used for preparing the binder composition were used, respectively.
  • the binder of Reference Example 4 a dried product of the above polytetrafluoroethylene aqueous dispersion was used.
  • the binder of Reference Example 5 the above powdery polyvinylidene fluoride was used.
  • the binder of Reference Example 6 the above styrene-butadiene rubber was used.
  • Example 1 10 parts by weight of a 2% by weight aqueous solution of sodium carboxymethylcellulose as a viscosity modifier, the positive electrode active material (1) prepared above and acetylene black are mixed, and water is added so that the solid content concentration becomes 70% by weight. After that, the binder composition containing the fluorinated rubber A obtained in Reference Example 1 was added and stirred to prepare a uniform slurry (mixture). This slurry was applied on one side to a 20 ⁇ m thick aluminum foil (positive electrode current collector) using a doctor blade. And it heat-processed at 120 degreeC, it was made to dry, and the positive electrode sheet
  • the mass ratio of positive electrode active material / acetylene black / binder (fluorinated rubber A) was 85/15/5.
  • the positive electrode material sheet had good adhesion between the positive electrode active material layer and the positive electrode current collector.
  • a stainless steel simple sealed cell type lithium ion secondary battery was assembled in an argon glove box.
  • a metal lithium foil having a thickness of 500 ⁇ m is used for the negative electrode
  • a stainless steel plate having a thickness of 1 mm is used for the negative electrode current collector
  • a porous polypropylene having a thickness of 25 ⁇ m is used for the separator
  • a concentration is used for the electrolyte.
  • the following evaluation was performed using the lithium ion secondary battery manufactured above. That is, it charged to 4.6V with a load current of 20 mA per 1 g of the positive electrode active material, and discharged to 2.5 V with a load current of 20 mA per 1 g of the positive electrode active material.
  • the discharge capacity at this time is defined as the initial discharge capacity.
  • the initial discharge capacity was 270 mAh / g.
  • charging to 4.6 V with a load current of 60 mA per 1 g of the charge / discharge positive electrode active material and discharging to 2.5 V with a load current of 60 mA per 1 g of the positive electrode active material were further repeated 99 times.
  • the 99th discharge capacity / initial discharge capacity is defined as a cycle maintenance ratio.
  • the cycle maintenance rate was 96%.
  • Example 2 The positive electrode active material (1) produced above and acetylene black are mixed, the binder composition containing the fluorinated rubber B obtained in Reference Example 2 and N-methylpyrrolidone are added and stirred, and the solid content concentration is 65 A uniform slurry having a mass% was prepared. The mass ratio of positive electrode active material / acetylene black / binder (fluorinated rubber B) was 85/15/5. Thereafter, the same procedure as in Example 1 was performed.
  • Example 3 The same procedure as in Example 2 was performed except that the binder composition shown in Reference Example 3 was used as the binder composition.
  • Comparative Example 1 The same procedure as in Example 1 was performed except that the binder composition shown in Reference Example 4 was used as the binder composition.
  • the obtained positive electrode body sheet peels off due to insufficient adhesion between the positive electrode active material layer and the current collector.
  • the battery evaluation is performed on the positive electrode sheet that was not peeled off.
  • Comparative Example 2 It carries out similarly to Example 2 except having used the binder composition shown in the reference example 5 as a binder composition. Part of the obtained positive electrode sheet is peeled off due to insufficient adhesion between the positive electrode active material layer and the current collector.
  • the battery evaluation is performed on the positive electrode sheet that was not peeled off.
  • Comparative Example 3 The same procedure as in Example 2 was performed except that the binder composition shown in Reference Example 6 was used as the binder composition.
  • Comparative Example 4 The same procedure as in Example 1 was performed except that the positive electrode active material (1) was changed to the positive electrode active material (2).
  • Example 1 to 3 and Comparative Examples 1 to 4 are shown in Table 2.
  • the adhesion was evaluated by a cross-cut peel test of JISK5400. That is, a grid-like cut with a 1 mm interval was made with a cutter knife in the produced positive electrode sheet coating film, cellophane tape (trade name, manufactured by Nichiban Co., Ltd.) was applied, and the number of peeled and remaining eyes was measured. evaluate.
  • the number of remaining eyes is 70% or more, ⁇ , more than 40% to less than 70% is represented by ⁇ , and less than 40% is represented by ⁇ .
  • the initial discharge capacity is over 250 mAh / g, ⁇ , 200 to 250 mAh / g is ⁇ , and less than 200 mAh / g is x.
  • the cycle maintenance rate is over 90% as ⁇ , 80 to 90% as ⁇ , and less than 80% as x.
  • Comparative Example 4 is inferior in the initial discharge capacity because the molar amount of Li element in the lithium-containing composite oxide used as the positive electrode active material is as small as 1.0 times the total molar amount of transition metal elements.
  • a positive electrode for a lithium-in secondary battery having a high discharge capacity per unit mass and excellent cycle characteristics can be obtained.
  • the positive electrode can be used for electronic devices such as mobile phones and lithium ion secondary batteries for vehicles.

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Abstract

Provided is a lithium-ion rechargeable battery electrode, which has a high discharge capacity, excellent adhesion between a positive electrode active material and a conductive material and a positive electrode current collector, and excellent cycle characteristics that are not prone to degradation even when a charge-discharge cycle is repeated. The lithium-ion rechargeable battery electrode has a positive electrode active material layer containing a positive active material, binder and conductive material formed on a surface of the positive electrode current collector. The positive electrode active material contains a lithium-containing complex oxide that contains an Li element, and at least one type of transition metal element selected from a group comprising Ni, Co and Mn (where the molar quantity of the Li element is 1.2-fold the total molar quantity of said transition metal element(s)). The binder contains a fluorine-containing rubber, which comprises a copolymer having repeating units based on at least one type of monomer selected from a group comprising tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride, and a fluorine content of 50-76 mass %.

Description

リチウムイオン二次電池用正極、およびその製造方法Positive electrode for lithium ion secondary battery and method for producing the same
　本発明は、リチウムイオン二次電池用正極、リチウムイオン二次電池用正極の製造方法およびリチウムイオン二次電池に関する。 The present invention relates to a positive electrode for a lithium ion secondary battery, a method for producing a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery.
　近年、携帯型電子機器や車載用のリチウムイオン二次電池として小型化・軽量化が求められ、単位質量あたりの放電容量のさらなる向上が望まれている。また、充放電サイクルを繰り返した後に放電容量が低下しない特性（以下、サイクル特性ともいう。）のさらなる向上が望まれている。
　一般的に、リチウムイオン二次電池は、正極、負極、非水電解質を有する。正極としては、正極活物質、バインダー、導電材を有し、正極活物質としては、リチウムと遷移金属等との複合酸化物（以下、リチウム含有複合酸化物ともいう。）が用いられている。 In recent years, miniaturization and weight reduction have been demanded as portable electronic devices and in-vehicle lithium ion secondary batteries, and further improvement in discharge capacity per unit mass has been desired. Further, there is a demand for further improvement in characteristics (hereinafter also referred to as cycle characteristics) in which the discharge capacity does not decrease after repeated charge / discharge cycles.
Generally, a lithium ion secondary battery has a positive electrode, a negative electrode, and a nonaqueous electrolyte. The positive electrode includes a positive electrode active material, a binder, and a conductive material. As the positive electrode active material, a composite oxide of lithium and a transition metal (hereinafter also referred to as a lithium-containing composite oxide) is used.
　放電容量を向上させる方法としては、正極活物質としてＮｉ、Ｃｏ、およびＭｎ等の遷移金属元素に対するＬｉ元素の比率を高くした複合酸化物（以下、「Ｌｉ－ｒｉｃｈ系正極材料」という場合がある。）を用いることが提案されている。
　Ｌｉ－ｒｉｃｈ系正極材料の例として、ＬｉＭＯ２（ＭはＮｉ、Ｃｏ、およびＭｎから選ばれる少なくとも１種の遷移金属元素。）とＬｉ２ＭｎＯ３との固溶体が提案されている。 As a method for improving the discharge capacity, there is a case where the positive electrode active material is a composite oxide in which the ratio of Li element to the transition metal element such as Ni, Co, and Mn is increased (hereinafter referred to as “Li-rich positive electrode material”). .) Is proposed.
As an example of the Li-rich positive electrode material, a solid solution of LiMO 2 (M is at least one transition metal element selected from Ni, Co, and Mn) and Li 2 MnO 3 has been proposed.
　その他に、放電容量を向上させる方法として、正極中に正極活物質を高充填させることも提案されている。例えば、特許文献１には、Ｌｉ－ｒｉｃｈ系正極材料を正極活物質とするリチウムイオン二次電池において、正極活物質をより高充填できるようにするために、正極のバインダーとして８００，０００原子質量単位より大きい平均分子量を有するポリフッ化ビニリデン（ＰＶＤＦ）を使用することが提案されている。
　また特許文献２では、サイクル特性を向上させるために、重量平均分子量が１０，０００～３００，０００である四フッ化エチレンに基づく繰り返し単位及びプロピレンに基づく繰り返し単位を有する含フッ素共重合体からなるバインダーが提案されている。 In addition, as a method for improving the discharge capacity, it has been proposed to highly charge the positive electrode active material in the positive electrode. For example, in Patent Document 1, in a lithium ion secondary battery using a Li-rich positive electrode material as a positive electrode active material, 800,000 atomic mass is used as a positive electrode binder so that the positive electrode active material can be filled more highly. It has been proposed to use polyvinylidene fluoride (PVDF) having an average molecular weight greater than the unit.
Further, Patent Document 2 comprises a fluorine-containing copolymer having a repeating unit based on ethylene tetrafluoride having a weight average molecular weight of 10,000 to 300,000 and a repeating unit based on propylene in order to improve cycle characteristics. Binders have been proposed.
日本特表２０１１－５１９１２６号公報Japan Special Table 2011-519126 国際公開第２０１１／０５５７６０号International Publication No. 2011/055760
　しかしながら、本発明者等の知見によれば、ポリフッ化ビニリデン（ＰＶＤＦ）からなるバインダーは密着性が不十分となりやすく、特にＬｉ－ｒｉｃｈ系正極材料を高充填した際に集電体との密着性に劣るという問題がある。またＰＶＤＦは耐アルカリ性が不十分となりやすく、充放電サイクルによる劣化が生じやすいという問題がある。
　本発明は、放電容量が高く、正極活物質および導電材と正極集電体との密着性に優れ、充放電サイクルを繰り返しても劣化しにくいサイクル特性に優れた、リチウムイオン二次電池用正極、該リチウムイオン二次電池用正極の製造方法、および該リチウムイオン二次電池正極を備えたリチウムイオン二次電池を提供することを目的とする。 However, according to the knowledge of the present inventors, the binder made of polyvinylidene fluoride (PVDF) tends to have insufficient adhesion, and particularly when the Li-rich positive electrode material is highly filled, the adhesion to the current collector. There is a problem that it is inferior. Further, PVDF has a problem that alkali resistance tends to be insufficient, and deterioration due to charge / discharge cycles tends to occur.
The present invention provides a positive electrode for a lithium ion secondary battery having a high discharge capacity, excellent adhesion between a positive electrode active material and a conductive material and a positive electrode current collector, and excellent cycle characteristics that do not easily deteriorate even after repeated charge / discharge cycles. An object of the present invention is to provide a method for producing a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery including the lithium ion secondary battery positive electrode.
　本発明のリチウムイオン二次電池用正極は、正極活物質、バインダー、および導電材を含む正極活物質層が正極集電体の表面上に形成されたリチウムイオン二次電池用正極であって、前記正極活物質が、Ｌｉ元素と、Ｎｉ、Ｃｏ、およびＭｎからなる群より選ばれる少なくとも１種の遷移金属元素とを含む（ただし、Ｌｉ元素のモル量が該遷移金属元素の総モル量に対して１．２倍超である。）リチウム含有複合酸化物を含み、前記バインダーが、四フッ化エチレン、ヘキサフルオロプロピレン、およびフッ化ビニリデンからなる群より選ばれる少なくとも１種の単量体に基づく繰り返し単位を有する共重合体からなり、フッ素含有量が５０～７６質量％である含フッ素ゴムを含むことを特徴とする。 The positive electrode for a lithium ion secondary battery of the present invention is a positive electrode for a lithium ion secondary battery in which a positive electrode active material layer containing a positive electrode active material, a binder, and a conductive material is formed on the surface of the positive electrode current collector, The positive electrode active material contains Li element and at least one transition metal element selected from the group consisting of Ni, Co, and Mn (provided that the molar amount of Li element is the total molar amount of the transition metal element) The lithium-containing composite oxide is included, and the binder is at least one monomer selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride. And a fluorine-containing rubber having a fluorine content of 50 to 76% by mass.
　前記リチウム含有複合酸化物の表面にＭｇ、Ｃａ、Ｓｒ、Ｂａ、Ｔｉ、Ｚｒ、Ｈｆ、Ｎｂ、Ｔａ、Ａｌ、Ｇａ、Ｙ、Ｌａ、Ｃｅ、Ｎｄ、Ｇｄ、およびＥｒからなる群より選ばれる少なくとも１種の金属元素を含む酸化物からなる被覆層が形成されていることが好ましい。
　前記バインダーが、四フッ化エチレンに基づく繰り返し単位およびプロピレンに基づく繰り返し単位を有する共重合体からなる含フッ素ゴムを含むことが好ましい。
　前記四フッ化エチレンに基づく繰り返し単位およびプロピレンに基づく繰り返し単位を有する共重合体が、四フッ化エチレンに基づく繰り返し単位／プロピレンに基づく繰り返し単位の比率４０～７０／６０～３０（モル％）を有することが好ましい。
　前記バインダーが、四フッ化エチレンに基づく繰り返し単位、プロピレンに基づく繰り返し単位、およびフッ化ビニリデンに基づく繰り返し単位を有する共重合体からなる含フッ素ゴムを含むことが好ましい。
　前記四フッ化エチレンに基づく繰り返し単位、プロピレンに基づく繰り返し単位、およびフッ化ビニリデンに基づく繰り返し単位を有する共重合体が、四フッ化エチレンに基づく繰り返し単位／プロピレンに基づく繰り返し単位／フッ化ビニリデンに基づく繰り返し単位の比率３０～７０／２０～６０／１～４０（モル％）を有することが好ましい。 At least selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Al, Ga, Y, La, Ce, Nd, Gd, and Er on the surface of the lithium-containing composite oxide It is preferable that a coating layer made of an oxide containing one kind of metal element is formed.
The binder preferably contains a fluorinated rubber composed of a copolymer having a repeating unit based on ethylene tetrafluoride and a repeating unit based on propylene.
The copolymer having a repeating unit based on tetrafluoroethylene and a repeating unit based on propylene has a ratio of 40 to 70/60 to 30 (mol%) of the repeating unit based on ethylene tetrafluoride / the repeating unit based on propylene. It is preferable to have.
It is preferable that the binder includes a fluorinated rubber made of a copolymer having a repeating unit based on ethylene tetrafluoride, a repeating unit based on propylene, and a repeating unit based on vinylidene fluoride.
The copolymer having a repeating unit based on ethylene tetrafluoride, a repeating unit based on propylene, and a repeating unit based on vinylidene fluoride is a repeating unit based on ethylene tetrafluoride / a repeating unit based on propylene / vinylidene fluoride. It is preferable to have a ratio of repeating units based on 30 to 70/20 to 60/1 to 40 (mol%).
　本発明は、本発明のリチウムイオン二次電池用正極を製造する方法であって、前記正極活物質と前記バインダーを混合して混合物を得る混合工程と、該混合物を熱処理する工程を含むことを特徴とするリチウムイオン二次電池用正極の製造方法を提供する。 The present invention is a method for producing a positive electrode for a lithium ion secondary battery of the present invention, comprising a mixing step of mixing the positive electrode active material and the binder to obtain a mixture, and a step of heat-treating the mixture. Provided is a method for producing a positive electrode for a lithium ion secondary battery.
　前記混合工程において、有機溶媒中で前記正極活物質と前記バインダーとを混合することが好ましい。
　または、前記混合工程において、水性分散媒中で前記正極活物質と前記バインダーとを混合することが好ましい。
　本発明は、本発明のリチウムイオン二次電池用正極と、負極と、非水電解質とを含むリチウムイオン二次電池を提供する。 In the mixing step, the positive electrode active material and the binder are preferably mixed in an organic solvent.
Alternatively, in the mixing step, it is preferable to mix the positive electrode active material and the binder in an aqueous dispersion medium.
The present invention provides a lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery of the present invention, a negative electrode, and a nonaqueous electrolyte.
　本発明によれば、放電容量が高く、正極活物質および導電材と正極集電体との密着性に優れ、充放電サイクルを繰り返しても劣化しにくいサイクル特性に優れた、リチウムイオン二次電池用正極が得られる。
　本発明のリチウムイオン二次電池は、本発明のリチウムイオン二次電池正極を備えており、放電容量が高く、サイクル特性に優れる。 According to the present invention, a lithium ion secondary battery having a high discharge capacity, excellent adhesion between a positive electrode active material and a conductive material and a positive electrode current collector, and excellent cycle characteristics that hardly deteriorate even after repeated charge and discharge cycles. A positive electrode for use is obtained.
The lithium ion secondary battery of the present invention includes the positive electrode of the lithium ion secondary battery of the present invention, has a high discharge capacity, and excellent cycle characteristics.
　以下に、本発明を詳細に説明する。
［正極活物質］
　本発明における正極活物質は、Ｌｉ元素と、Ｎｉ、Ｃｏ、およびＭｎから選ばれる少なくとも１種の遷移金属元素とを含む（ただし、Ｌｉ元素のモル量が該遷移金属元素の総モル量に対して１．２倍超である。）リチウム含有複合酸化物（以下、リチウム含有複合酸化物（Ｉ）という。）を含む。該リチウム含有複合酸化物（Ｉ）のほかに、リチウムイオン二次電池において公知の正極活物質を含んでもよい。
　高い放電容量を得るために、正極活物質のうちの５０～１００質量％がリチウム含有複合酸化物（Ｉ）であることが好ましく、７５～１００質量％がより好ましく、１００質量％が特に好ましい。
　本発明における正極活物質の形状は粒子状である。正極活物質の平均粒子径（Ｄ５０）は、３～２５μｍが好ましく、４～２０μｍがより好ましく、５～１５μｍが特に好ましい。平均粒子径（Ｄ５０）の定義は、後述するとおりである。 The present invention is described in detail below.
[Positive electrode active material]
The positive electrode active material in the present invention contains Li element and at least one transition metal element selected from Ni, Co, and Mn (provided that the molar amount of Li element is relative to the total molar amount of the transition metal element). Including lithium-containing composite oxide (hereinafter referred to as lithium-containing composite oxide (I)). In addition to the lithium-containing composite oxide (I), a known positive electrode active material may be included in the lithium ion secondary battery.
In order to obtain a high discharge capacity, 50 to 100% by mass of the positive electrode active material is preferably lithium-containing composite oxide (I), more preferably 75 to 100% by mass, and particularly preferably 100% by mass.
The shape of the positive electrode active material in the present invention is particulate. The average particle size (D50) of the positive electrode active material is preferably 3 to 25 μm, more preferably 4 to 20 μm, and particularly preferably 5 to 15 μm. The definition of the average particle diameter (D50) is as described later.
　リチウム含有複合酸化物（Ｉ）において、遷移金属元素の総モル量に対するＬｉ元素の組成比（モル比）は、１．２５～１．７０であることが好ましく、１．３５～１．６０であることがより好ましく、１．４０～１．５５が特に好ましい。該組成比とすることにより、リチウムイオン二次電池の単位質量あたりの放電容量をより一層増加させうる。 In the lithium-containing composite oxide (I), the composition ratio (molar ratio) of the Li element to the total molar amount of the transition metal element is preferably 1.25 to 1.70, and is 1.35 to 1.60. More preferably, it is particularly preferably 1.40 to 1.55. By setting the composition ratio, the discharge capacity per unit mass of the lithium ion secondary battery can be further increased.
　リチウム含有複合酸化物（Ｉ）は、Ｎｉ、Ｃｏ、およびＭｎから選ばれる少なくとも１種の遷移金属元素を含む。Ｍｎを必須として含むことがより好ましく、Ｎｉ、Ｃｏ、およびＭｎの全ての元素を含むことが特に好ましい。
　リチウム含有複合酸化物（Ｉ）は、Ｎｉ、Ｃｏ、Ｍｎ、およびＬｉ以外の金属元素（以下、他の金属元素という。）を含んでいてもよい。他の金属元素としては、Ｃｒ、Ｆｅ、Ａｌ、Ｔｉ、Ｚｒ、Ｍｏ、Ｎｂ、Ｖ、およびＭｇから選ばれる少なくとも１種が挙げられる。他の金属元素の割合は、リチウム含有複合酸化物（Ｉ）中のＬｉ以外の金属元素の総量を１モルとするとき、そのうち他の金属元素の合計が０．００１～０．１モルであることが好ましく、０．００５～０．０５モルがより好ましい。 The lithium-containing composite oxide (I) contains at least one transition metal element selected from Ni, Co, and Mn. More preferably, Mn is included as an essential component, and it is particularly preferable that all elements of Ni, Co, and Mn are included.
The lithium-containing composite oxide (I) may contain a metal element other than Ni, Co, Mn, and Li (hereinafter referred to as other metal element). Examples of the other metal elements include at least one selected from Cr, Fe, Al, Ti, Zr, Mo, Nb, V, and Mg. The proportion of the other metal elements is 0.001 to 0.1 mol in total when the total amount of metal elements other than Li in the lithium-containing composite oxide (I) is 1 mol. It is preferably 0.005 to 0.05 mol.
　リチウム含有複合酸化物（Ｉ）は、下記式（１）で表される化合物であることが好ましい。本発明における式（１）で表される化合物は、充放電や活性化の工程を経る前の組成である。ここで、活性化とは、酸化リチウム（Ｌｉ２Ｏ）、または、リチウムおよび酸化リチウムを、リチウム含有複合酸化物（Ｉ）から取り除くことをいう。通常の活性化方法としては、４．４Ｖまたは４．６Ｖ（Ｌｉ＋／Ｌｉの酸化還元電位との電位差として表される。）より大きな電圧を加える電気化学的な活性化方法が挙げられる。また、硫酸、塩酸または硝酸等の酸を用いた化学反応を行うことによる、化学的な活性化方法が挙げられる。 The lithium-containing composite oxide (I) is preferably a compound represented by the following formula (1). The compound represented by Formula (1) in this invention is a composition before passing through the process of charging / discharging or activation. Here, activation means removing lithium oxide (Li 2 O) or lithium and lithium oxide from the lithium-containing composite oxide (I). As a normal activation method, there is an electrochemical activation method in which a voltage higher than 4.4 V or 4.6 V (expressed as a potential difference from the oxidation-reduction potential of Li + / Li) is applied. Moreover, the chemical activation method by performing chemical reaction using acids, such as a sulfuric acid, hydrochloric acid, or nitric acid, is mentioned.
　Ｌｉ（ＬｉｘＭｎｙＭｅｚ）ＯｐＦｑ　（１）
　式（１）において、Ｍｅは、Ｃｏ、Ｎｉ、Ｃｒ、Ｆｅ、Ａｌ、Ｔｉ、Ｚｒ、Ｍｏ、Ｎｂ、Ｖ、およびＭｇから選ばれる少なくとも１種の元素である。Ｍｅとしては、Ｃｏ、Ｎｉ、およびＣｒから選ばれる１種以上が好ましく、ＣｏおよびＮｉから選ばれる１種以上が特に好ましい。
　式（１）において、０．０９＜ｘ＜０．３、ｙ＞０、ｚ＞０、１．９＜ｐ＜２．１、０≦ｑ≦０．１であり、かつ、０．４≦ｙ／（ｙ＋ｚ）≦０．８、ｘ＋ｙ＋ｚ＝１、１．２＜（１＋ｘ）／（ｙ＋ｚ）である。すなわち、式（１）で表わされる化合物は、Ｌｉの割合が、ＭｎとＭeの合計に対して１．２倍モルを超える。また、式（１）はＭｎを特定量含む化合物である点も特徴であり、ＭｎとＭｅの総モル量に対するＭｎの割合は、０．５≦ｙ／（ｙ＋ｚ）≦０．８が好ましく、０．５５≦ｙ／（ｙ＋ｚ）≦０．７５がより好ましい。Ｍｎが前記の範囲であれば、放電容量が高容量となる。ｑはＦの割合を示すが、Ｆが存在しない場合、ｑは０である。ｐは、ｘ、ｙ、ｚおよびｑに応じて決まる値であり、１．９～２．１である。 Li (Li x Mn y Me z ) O p F q (1)
In the formula (1), Me is at least one element selected from Co, Ni, Cr, Fe, Al, Ti, Zr, Mo, Nb, V, and Mg. Me is preferably one or more selected from Co, Ni, and Cr, and more preferably one or more selected from Co and Ni.
In the formula (1), 0.09 <x <0.3, y> 0, z> 0, 1.9 <p <2.1, 0 ≦ q ≦ 0.1, and 0.4 ≦ y / (y + z) ≦ 0.8, x + y + z = 1, 1.2 <(1 + x) / (y + z). That is, in the compound represented by the formula (1), the ratio of Li exceeds 1.2 times mol with respect to the total of Mn and Me. The formula (1) is also characterized in that it is a compound containing a specific amount of Mn, and the ratio of Mn to the total molar amount of Mn and Me is preferably 0.5 ≦ y / (y + z) ≦ 0.8, 0.55 ≦ y / (y + z) ≦ 0.75 is more preferable. If Mn is the said range, discharge capacity will become high capacity | capacitance. q represents the proportion of F, but q is 0 when F is not present. p is a value determined according to x, y, z, and q, and is 1.9 to 2.1.
　式（１）において、ＭｎとＭｅの総モル量に対するＬｉ元素の組成比は１．２５≦（１＋ｘ）／（ｙ＋ｚ）≦１．７０が好ましく、１．３５≦（１＋ｘ）／（ｙ＋ｚ）≦１．６０がより好ましく、１．４０≦（１＋ｘ）／（ｙ＋ｚ）≦１．５５が特に好ましい。Ｌｉ元素の組成比が前記の範囲であれば、放電容量が高容量となる。 In the formula (1), the composition ratio of Li element with respect to the total molar amount of Mn and Me is preferably 1.25 ≦ (1 + x) / (y + z) ≦ 1.70, and 1.35 ≦ (1 + x) / (y + z) ≦ 1.60 is more preferable, and 1.40 ≦ (1 + x) / (y + z) ≦ 1.55 is particularly preferable. When the composition ratio of the Li element is in the above range, the discharge capacity becomes high.
　リチウム含有複合酸化物（Ｉ）としては、
Ｌｉ（Ｌｉ０．１３Ｎｉ０．２６Ｃｏ０．０９Ｍｎ０．５２）Ｏ２、
Ｌｉ（Ｌｉ０．１３Ｎｉ０．２２Ｃｏ０．０９Ｍｎ０．５６）Ｏ２、
Ｌｉ（Ｌｉ０．１３Ｎｉ０．１７Ｃｏ０．１７Ｍｎ０．５３）Ｏ２、
Ｌｉ（Ｌｉ０．１５Ｎｉ０．１７Ｃｏ０．１３Ｍｎ０．５５）Ｏ２、
Ｌｉ（Ｌｉ０．１６Ｎｉ０．１７Ｃｏ０．０８Ｍｎ０．５９）Ｏ２、
Ｌｉ（Ｌｉ０．１７Ｎｉ０．１７Ｃｏ０．１７Ｍｎ０．４９）Ｏ２、
Ｌｉ（Ｌｉ０．１７Ｎｉ０．２１Ｃｏ０．０８Ｍｎ０．５４）Ｏ２、
Ｌｉ（Ｌｉ０．１７Ｎｉ０．１４Ｃｏ０．１４Ｍｎ０．５５）Ｏ２、
Ｌｉ（Ｌｉ０．１８Ｎｉ０．１２Ｃｏ０．１２Ｍｎ０．５８）Ｏ２、
Ｌｉ（Ｌｉ０．１８Ｎｉ０．１６Ｃｏ０．１２Ｍｎ０．５４）Ｏ２、
Ｌｉ（Ｌｉ０．２０Ｎｉ０．１２Ｃｏ０．０８Ｍｎ０．６０）Ｏ２、
Ｌｉ（Ｌｉ０．２０Ｎｉ０．１６Ｃｏ０．０８Ｍｎ０．５６）Ｏ２、
Ｌｉ（Ｌｉ０．２０Ｎｉ０．１３Ｃｏ０．１３Ｍｎ０．５４）Ｏ２、
Ｌｉ（Ｌｉ０．２２Ｎｉ０．１２Ｃｏ０．１２Ｍｎ０．５４）Ｏ２、
Ｌｉ（Ｌｉ０．２３Ｎｉ０．１２Ｃｏ０．０８Ｍｎ０．５７）Ｏ２、が好ましい。 As the lithium-containing composite oxide (I),
Li (Li 0.13 Ni 0.26 Co 0.09 Mn 0.52 ) O 2 ,
Li (Li 0.13 Ni 0.22 Co 0.09 Mn 0.56 ) O 2 ,
Li (Li 0.13 Ni 0.17 Co 0.17 Mn 0.53 ) O 2 ,
Li (Li 0.15 Ni 0.17 Co 0.13 Mn 0.55 ) O 2 ,
Li (Li 0.16 Ni 0.17 Co 0.08 Mn 0.59 ) O 2 ,
Li (Li 0.17 Ni 0.17 Co 0.17 Mn 0.49 ) O 2 ,
Li (Li 0.17 Ni 0.21 Co 0.08 Mn 0.54) O 2,
Li (Li 0.17 Ni 0.14 Co 0.14 Mn 0.55 ) O 2 ,
Li (Li 0.18 Ni 0.12 Co 0.12 Mn 0.58 ) O 2 ,
Li (Li 0.18 Ni 0.16 Co 0.12 Mn 0.54 ) O 2 ,
Li (Li 0.20 Ni 0.12 Co 0.08 Mn 0.60 ) O 2 ,
Li (Li 0.20 Ni 0.16 Co 0.08 Mn 0.56 ) O 2 ,
Li (Li 0.20 Ni 0.13 Co 0.13 Mn 0.54 ) O 2 ,
Li (Li 0.22 Ni 0.12 Co 0.12 Mn 0.54 ) O 2 ,
Li (Li 0.23 Ni 0.12 Co 0.08 Mn 0.57 ) O 2 is preferred.
　特に好ましいリチウム含有複合酸化物（Ｉ）としては、
Ｌｉ（Ｌｉ０．１６Ｎｉ０．１７Ｃｏ０．０８Ｍｎ０．５９）Ｏ２、
Ｌｉ（Ｌｉ０．１７Ｎｉ０．１７Ｃｏ０．１７Ｍｎ０．４９）Ｏ２、
Ｌｉ（Ｌｉ０．１７Ｎｉ０．２１Ｃｏ０．０８Ｍｎ０．５４）Ｏ２、
Ｌｉ（Ｌｉ０．１７Ｎｉ０．１４Ｃｏ０．１４Ｍｎ０．５５）Ｏ２、
Ｌｉ（Ｌｉ０．１８Ｎｉ０．１２Ｃｏ０．１２Ｍｎ０．５８）Ｏ２、
Ｌｉ（Ｌｉ０．１８Ｎｉ０．１６Ｃｏ０．１２Ｍｎ０．５４）Ｏ２、
Ｌｉ（Ｌｉ０．２０Ｎｉ０．１２Ｃｏ０．０８Ｍｎ０．６０）Ｏ２、
Ｌｉ（Ｌｉ０．２０Ｎｉ０．１６Ｃｏ０．０８Ｍｎ０．５６）Ｏ２、
Ｌｉ（Ｌｉ０．２０Ｎｉ０．１３Ｃｏ０．１３Ｍｎ０．５４）Ｏ２、が挙げられる。 As particularly preferred lithium-containing composite oxide (I),
Li (Li 0.16 Ni 0.17 Co 0.08 Mn 0.59 ) O 2 ,
Li (Li 0.17 Ni 0.17 Co 0.17 Mn 0.49 ) O 2 ,
Li (Li 0.17 Ni 0.21 Co 0.08 Mn 0.54) O 2,
Li (Li 0.17 Ni 0.14 Co 0.14 Mn 0.55 ) O 2 ,
Li (Li 0.18 Ni 0.12 Co 0.12 Mn 0.58 ) O 2 ,
Li (Li 0.18 Ni 0.16 Co 0.12 Mn 0.54 ) O 2 ,
Li (Li 0.20 Ni 0.12 Co 0.08 Mn 0.60 ) O 2 ,
Li (Li 0.20 Ni 0.16 Co 0.08 Mn 0.56 ) O 2 ,
Li (Li 0.20 Ni 0.13 Co 0.13 Mn 0.54 ) O 2 .
　リチウム含有複合酸化物（Ｉ）の形状は粒子状であることが好ましい。リチウム含有複合酸化物（Ｉ）の平均粒子径（Ｄ５０）は、３～２５μｍが好ましく、４～２０μｍがより好ましく、５～１５μｍが特に好ましい。ここで、平均粒子径（Ｄ５０）とは、体積基準で粒度分布を求め、全体積を１００％とした累積カーブにおいて、その累積カーブが５０％となる点の粒子径である、体積基準累積５０％径を意味する。粒度分布は、レーザー散乱粒度分布測定装置で測定した頻度分布および累積体積分布曲線で求められる。粒子径の測定は、粉末を水媒体中に超音波処理などで充分に分散させて粒度分布を測定する（例えば、ＨＯＲＩＢＡ社製レーザー回折／散乱式粒子径分布測定装置Ｐａｒｔｉｃａ　ＬＡ－９５０ＶII、などを用いる）ことで行なわれる。 The shape of the lithium-containing composite oxide (I) is preferably particulate. The average particle size (D50) of the lithium-containing composite oxide (I) is preferably 3 to 25 μm, more preferably 4 to 20 μm, and particularly preferably 5 to 15 μm. Here, the average particle size (D50) is a particle size distribution at a point where the cumulative curve is 50% in a cumulative curve where the particle size distribution is obtained on a volume basis and the total volume is 100%. It means% diameter. The particle size distribution is obtained from a frequency distribution and a cumulative volume distribution curve measured with a laser scattering particle size distribution measuring apparatus. The particle size is measured by sufficiently dispersing the powder in an aqueous medium by ultrasonic treatment or the like and measuring the particle size distribution (for example, a laser diffraction / scattering particle size distribution measuring device Partica LA-950VII manufactured by HORIBA, etc.). Used).
　リチウム含有複合酸化物（Ｉ）の比表面積は、０．３～１０ｍ２／ｇであることが好ましく、０．５～５ｍ２／ｇが特に好ましい。該比表面積が、０．３～１０ｍ２／ｇであると容量が高く、緻密な正極電極層が形成できる。
　比表面積の測定は、窒素ガス吸着ＢＥＴ（Ｂｒｕｎａｕｅｒ，Ｅｍｍｅｔｔ，Ｔｅｌｌｅｒ）法（例えば、日本ベル社製高精度ガス／蒸気吸着量測定装置ＢＥＬＳＯＲＰ－ｍａｘ、などを用いる）により行なわれる。 The specific surface area of the lithium-containing composite oxide (I) is preferably 0.3 ~ 10m 2 / g, particularly preferably 0.5 ~ 5m 2 / g. When the specific surface area is 0.3 to 10 m 2 / g, the capacity is high and a dense positive electrode layer can be formed.
The specific surface area is measured by a nitrogen gas adsorption BET (Brunauer, Emmett, Teller) method (for example, using a high precision gas / vapor adsorption amount measuring device BELSORP-max manufactured by Bell Japan).
　リチウム含有複合酸化物（Ｉ）は、層状岩塩型結晶構造（空間群Ｒ－３ｍ）であることが好ましい。また、リチウム含有複合酸化物（Ｉ）は、遷移金属元素に対するＬｉ元素の比率が高いため、ＸＲＤ（Ｘ線回折）測定では層状Ｌｉ２ＭｎＯ３と同様に２θ＝２０～２５°の範囲にピークが観察される。 The lithium-containing composite oxide (I) preferably has a layered rock salt type crystal structure (space group R-3m). Further, since the lithium-containing composite oxide (I) has a high ratio of Li element to transition metal element, XRD (X-ray diffraction) measurement shows a peak in the range of 2θ = 20 to 25 ° as in the case of layered Li 2 MnO 3. Is observed.
　リチウム含有複合酸化物（Ｉ）の製造方法としては、共沈法により得られたリチウム含有複合酸化物の前躯体とリチウム化合物を混合して焼成する方法、水熱合成法、ゾルゲル法、乾式混合法（固相法）、イオン交換法、ガラス結晶化法を適宜用いることができる。なお、リチウム含有複合酸化物（Ｉ）中に遷移金属元素が均一に含有されると放電容量が向上するため、共沈法により得られたリチウム含有複合酸化物の前駆体（共沈組成物）とリチウム化合物とを混合して焼成する方法を用いることが好ましい。 The method for producing the lithium-containing composite oxide (I) includes a method in which a precursor of the lithium-containing composite oxide obtained by the coprecipitation method and a lithium compound are mixed and fired, a hydrothermal synthesis method, a sol-gel method, and a dry mixing method. A method (solid phase method), an ion exchange method, or a glass crystallization method can be appropriately used. In addition, since the discharge capacity is improved when the transition metal element is uniformly contained in the lithium-containing composite oxide (I), the precursor of the lithium-containing composite oxide obtained by the coprecipitation method (coprecipitation composition) It is preferable to use a method of mixing and baking a lithium compound.
　正極活物質として用いられるリチウム含有複合酸化物（Ｉ）は、表面にＭｇ、Ｃａ、Ｓｒ、Ｂａ、Ｔｉ、Ｚｒ、Ｈｆ、Ｎｂ、Ｔａ、Ａｌ、Ｇａ、Ｙ、Ｌａ、Ｃｅ、Ｎｄ、Ｇｄ、およびＥｒからなる群より選ばれる少なくとも１種の金属元素を含む酸化物よりなる被覆層（以下、被覆層（ＩＩ）という。）が形成されていることが好ましい。
　リチウム含有複合酸化物（Ｉ）を被覆層（ＩＩ）で被覆することによって、リチウム含有複合酸化物（Ｉ）と電解液との接触を減らすことができるため、リチウム含有複合酸化物（Ｉ）の表面から電解液へのＭｎ等の遷移金属元素の溶出が抑制でき、サイクル特性が向上すると考えられる。 The lithium-containing composite oxide (I) used as the positive electrode active material has Mg, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Al, Ga, Y, La, Ce, Nd, Gd, on the surface. It is preferable that a coating layer (hereinafter referred to as coating layer (II)) made of an oxide containing at least one metal element selected from the group consisting of Er and Er is formed.
By coating the lithium-containing composite oxide (I) with the coating layer (II), the contact between the lithium-containing composite oxide (I) and the electrolytic solution can be reduced. It is thought that elution of transition metal elements such as Mn from the surface to the electrolytic solution can be suppressed, and cycle characteristics are improved.
　被覆層（ＩＩ）としては、具体的には、ＭｇＯ、ＣａＯ、ＳｒＯ、ＢａＯ、ＴｉＯ２、ＺｒＯ２、ＨｆＯ２、Ｎｂ２Ｏ５、Ｔａ２Ｏ５、Ａｌ２Ｏ３、Ｇａ２Ｏ３、Ｙ２Ｏ３、Ｌａ２Ｏ３、Ｃｅ２Ｏ３、Ｎｄ２Ｏ３、Ｇｄ２Ｏ３、Ｅｒ２Ｏ３等が挙げられる。また、これらのなかでもＡｌ２Ｏ３、Ｇａ２Ｏ３、Ｙ２Ｏ３、Ｌａ２Ｏ３、Ｃｅ２Ｏ３、Ｎｄ２Ｏ３、Ｇｄ２Ｏ３、またはＥｒ２Ｏ３がサイクル維持率を大きく向上させ得るため特に好ましい。
　被覆層（ＩＩ）としては、前記化合物を１種または二種以上を用いてもよい。 Examples of the coating layer (II), specifically, MgO, CaO, SrO, BaO , TiO 2, ZrO 2, HfO 2, Nb 2 O 5, Ta 2 O 5, Al 2 O 3, Ga 2 O 3, Y 2 O 3, La 2 O 3, Ce 2 O 3, Nd 2 O 3, Gd 2 O 3, Er 2 O 3 and the like. Among these, Al 2 O 3 , Ga 2 O 3 , Y 2 O 3 , La 2 O 3 , Ce 2 O 3 , Nd 2 O 3 , Gd 2 O 3 , or Er 2 O 3 is the cycle retention rate. Is particularly preferable because it can be greatly improved.
As the coating layer (II), one or more of the above compounds may be used.
　被覆層（ＩＩ）は透過型電子顕微鏡－エネルギー分散型Ｘ線分光法分析（ＴＥＭ－ＥＤＸ）およびＸ線電子分光法（ＸＰＳ）により評価することができる。リチウム含有複合酸化物（Ｉ）を切断し、ＴＥＭ－ＥＤＸにより組成の面分析を行うことで、前記リチウム含有複合酸化物（Ｉ）の表面にＭｇ、Ｃａ、Ｓｒ、Ｂａ、Ｔｉ、Ｚｒ、Ｈｆ、Ｎｂ、Ｔａ、Ａｌ、Ｇａ、Ｙ、Ｌａ、Ｃｅ、Ｎｄ、Ｇｄ、およびＥｒからなる群より選ばれる少なくとも１種の金属元素を含む被覆層が形成されていることを確認することができる。また、リチウム含有複合酸化物（Ｉ）のＸＰＳ分析を行うことでリチウム含有複合酸化物（Ｉ）の表面にＭｇ、Ｃａ、Ｓｒ、Ｂａ、Ｔｉ、Ｚｒ、Ｈｆ、Ｎｂ、Ｔａ、Ａｌ、Ｇａ、Ｙ、Ｌａ、Ｃｅ、Ｎｄ、Ｇｄ、およびＥｒからなる群より選ばれる少なくとも１種の金属元素の酸化物が存在することが確認できる。 The coating layer (II) can be evaluated by transmission electron microscope-energy dispersive X-ray spectroscopy analysis (TEM-EDX) and X-ray electron spectroscopy (XPS). By cutting the lithium-containing composite oxide (I) and performing surface analysis of the composition by TEM-EDX, Mg, Ca, Sr, Ba, Ti, Zr, Hf are formed on the surface of the lithium-containing composite oxide (I). It can be confirmed that a coating layer containing at least one metal element selected from the group consisting of Nb, Ta, Al, Ga, Y, La, Ce, Nd, Gd, and Er is formed. Further, by performing XPS analysis of the lithium-containing composite oxide (I), the surface of the lithium-containing composite oxide (I) has Mg, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Al, Ga, It can be confirmed that there is an oxide of at least one metal element selected from the group consisting of Y, La, Ce, Nd, Gd, and Er.
　被覆層（ＩＩ）は、結晶性であってもよく、あるいは非晶質であってもよく、非晶質であることが好ましい。ここで、非晶質とは、Ｘ線回折測定（以下、ＸＲＤともいう。）において被覆層（ＩＩ）に帰属されるピークが観察されないことをいう。理由は明確ではないが、被覆層（ＩＩ）が非晶質である場合、被覆層（ＩＩ）がより均一にリチウム含有複合酸化物（Ｉ）の表面を覆うことができると考えられる。 The coating layer (II) may be crystalline or amorphous, and is preferably amorphous. Here, the term “amorphous” means that no peak attributed to the coating layer (II) is observed in the X-ray diffraction measurement (hereinafter also referred to as XRD). Although the reason is not clear, it is considered that when the coating layer (II) is amorphous, the coating layer (II) can more uniformly cover the surface of the lithium-containing composite oxide (I).
　正極活物質中に含まれるＭｇ、Ｃａ、Ｓｒ、Ｂａ、Ｔｉ、Ｚｒ、Ｈｆ、Ｎｂ、Ｔａ、Ａｌ、Ｇａ、Ｙ、Ｌａ、Ｃｅ、Ｎｄ、Ｇｄ、およびＥｒの合計総モル量は正極活物質中のＮｉ、Ｃｏ、およびＭｎを合わせた総モル量を１モルとすると、０．０００５～０．０５モルであることが好ましく、０．００１～０．０３モルであることがより好ましく、０．００３～０．０２モルであることが特に好ましい。 The total total molar amount of Mg, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Al, Ga, Y, La, Ce, Nd, Gd, and Er contained in the positive electrode active material is the positive electrode active material When the total molar amount of Ni, Co, and Mn in the total is 1 mol, it is preferably 0.0005 to 0.05 mol, more preferably 0.001 to 0.03 mol, Particularly preferred is 0.003 to 0.02 mol.
　正極活物質中のＮｉ、Ｃｏ、およびＭｎを合わせた総モル量に対する正極活物質中に含まれるＭｇ、Ｃａ、Ｓｒ、Ｂａ、Ｔｉ、Ｚｒ、Ｈｆ、Ｎｂ、Ｔａ、Ａｌ、Ｇａ、Ｙ、Ｌａ、Ｃｅ、Ｎｄ、Ｇｄ、およびＥｒの合計総モル量は、正極活物質を酸に溶解してＩＣＰ（高周波誘導結合プラズマ）測定を行うことによって測定することができる。なお、ＩＣＰ測定によって求めることが難しい場合には、仕込みの量に基づいて算出してもよい。 Mg, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Al, Ga, Y, La contained in the positive electrode active material with respect to the total molar amount of Ni, Co, and Mn in the positive electrode active material , Ce, Nd, Gd, and Er can be measured by dissolving the positive electrode active material in an acid and performing ICP (high frequency inductively coupled plasma) measurement. If it is difficult to obtain by ICP measurement, it may be calculated based on the amount of preparation.
　リチウム含有複合酸化物（Ｉ）の表面にＭｇ、Ｃａ、Ｓｒ、Ｂａ、Ｔｉ、Ｚｒ、Ｈｆ、Ｎｂ、Ｔａ、Ａｌ、Ｇａ、Ｙ、Ｌａ、Ｃｅ、Ｎｄ、Ｇｄ、およびＥｒからなる群より選ばれる少なくとも１種の金属元素を含む酸化物よりなる被覆層（ＩＩ）を形成する方法としては、リチウム含有複合酸化物（Ｉ）を前記金属元素を含む化合物とを接触させた後に加熱処理する方法が挙げられる。
　リチウム含有複合酸化物（Ｉ）を、前記金属元素を含む化合物と接触させる方法としては、リチウム含有複合酸化物（Ｉ）を前記金属元素を含む化合物が溶解した溶液に浸漬する湿式法や、リチウム含有複合酸化物（Ｉ）に前記金属元素を含む化合物が溶解した溶液をスプレーするスプレー法、リチウム含有複合酸化物（Ｉ）を前記金属元素を含む揮発性の化合物の蒸気と接触させる気相法等が挙げられる。これらの中で、生産性に優れていることからスプレー法が特に好ましい。
　加熱処理する温度は２００～６５０℃が好ましく、３００～５５０℃がより好ましい。加熱処理温度が前記範囲であると、酸化物を効率良く生成することができ、なおかつ非晶質の酸化物が得られやすい。 Selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Al, Ga, Y, La, Ce, Nd, Gd, and Er on the surface of the lithium-containing composite oxide (I) As a method of forming the coating layer (II) made of an oxide containing at least one kind of metal element, the lithium-containing composite oxide (I) is subjected to heat treatment after contacting with the compound containing the metal element. Is mentioned.
As a method of bringing the lithium-containing composite oxide (I) into contact with the compound containing the metal element, a wet method in which the lithium-containing composite oxide (I) is immersed in a solution in which the compound containing the metal element is dissolved, lithium Spray method of spraying solution in which compound containing metal element is dissolved in containing composite oxide (I), vapor phase method of contacting lithium containing composite oxide (I) with vapor of volatile compound containing metal element Etc. Among these, the spray method is particularly preferable because of its excellent productivity.
The temperature for the heat treatment is preferably 200 to 650 ° C, more preferably 300 to 550 ° C. When the heat treatment temperature is in the above range, an oxide can be efficiently generated, and an amorphous oxide is easily obtained.
　また、リチウム含有複合酸化物（Ｉ）の表面にリチウムのリン酸塩化合物、リチウムの硫酸塩化合物、およびリチウムのフッ化物からなる群より選ばれる少なくとも１種のリチウム化合物が付着していてもよい。該リチウム化合物として具体的にはＬｉＦ、Ｌｉ３ＰＯ４、Ｌｉ２ＳＯ４、Ｌｉ２ＳＯ４・Ｈ２Ｏが挙げられる。 Further, at least one lithium compound selected from the group consisting of a lithium phosphate compound, a lithium sulfate compound, and a lithium fluoride may be attached to the surface of the lithium-containing composite oxide (I). . Specific examples of the lithium compound include LiF, Li 3 PO 4 , Li 2 SO 4 , and Li 2 SO 4 .H 2 O.
［バインダー］
　本発明におけるバインダーは、四フッ化エチレン（以下ＴＦＥともいう。）、ヘキサフルオロプロピレン（以下ＨＦＰともいう。）、およびフッ化ビニリデン（以下ＶｄＦともいう。）からなる群より選ばれる少なくとも１種の単量体に基づく繰り返し単位を有する共重合体からなり、フッ素含有量が５０～７６質量％である含フッ素ゴム（以下、含フッ素ゴム（ＩＩＩ）という。）を含む。
　含フッ素ゴム（ＩＩＩ）は２種以上の繰り返し単位からなる共重合体であり、ＴＦＥ、ＨＦＰ、およびＶｄＦからなる群より選ばれる２種または３種の単量体に基づく繰り返し単位からなる共重合体であってもよく、ＴＦＥ、ＨＦＰ、およびＶｄＦからなる群より選ばれる１種以上の単量体に基づく繰り返し単位と、該単量体と共重合可能な他の単量体の１種以上に基づく繰り返し単位とからなる共重合体であってもよい。
　含フッ素ゴム（ＩＩＩ）のフッ素含有量は、５０～７４質量％が好ましく、５３～７０質量％がより好ましい。該フッ素含有量が５０質量％未満であると、耐アルカリ性、耐電圧性が不充分となりやすい。
　なお、含フッ素ゴムのフッ素含有量は、フッ素含有量分析により得られ、含フッ素ゴムを構成するすべての原子の総質量に対するフッ素原子の質量の割合を示す。 [binder]
The binder in the present invention is at least one selected from the group consisting of ethylene tetrafluoride (hereinafter also referred to as TFE), hexafluoropropylene (hereinafter also referred to as HFP), and vinylidene fluoride (hereinafter also referred to as VdF). Fluorine-containing rubber (hereinafter referred to as fluorine-containing rubber (III)) comprising a copolymer having a repeating unit based on a monomer and having a fluorine content of 50 to 76% by mass is included.
The fluorine-containing rubber (III) is a copolymer composed of two or more kinds of repeating units, and is a copolymer consisting of repeating units based on two or three monomers selected from the group consisting of TFE, HFP, and VdF. It may be a coalescence, one or more repeating units based on one or more monomers selected from the group consisting of TFE, HFP, and VdF, and one or more other monomers copolymerizable with the monomers It may be a copolymer comprising repeating units based on.
The fluorine content of the fluorine-containing rubber (III) is preferably 50 to 74% by mass, more preferably 53 to 70% by mass. When the fluorine content is less than 50% by mass, the alkali resistance and voltage resistance tend to be insufficient.
The fluorine content of the fluorine-containing rubber is obtained by fluorine content analysis, and indicates the ratio of the mass of fluorine atoms to the total mass of all atoms constituting the fluorine-containing rubber.
　含フッ素ゴム（ＩＩＩ）が、ＴＦＥに基づく繰り返し単位、ＨＦＰに基づく繰り返し単位、ＶｄＦに基づく繰り返し単位のほかに、その他の単量体に基づく繰り返し単位を有する場合、その他の単量体としては、プロピレン（以下Ｐともいう。）、エチレン（以下Ｅともいう。）、またはペルフルオロ（アルキルビニルエーテル）（以下ＰＡＶＥともいう。）が好ましい。
　ＰＡＶＥとしては、例えばペルフルオロ（メチルビニルエーテル）（以下ＰＭＶＥともいう。）、ペルフルオロ（プロピルビニルエーテル）（以下ＰＰＶＥともいう。）などが挙げられ、これらをそれぞれ単独で、または２種類以上任意に組み合わせて用いることができる。 When the fluorine-containing rubber (III) has a repeating unit based on another monomer in addition to a repeating unit based on TFE, a repeating unit based on HFP, and a repeating unit based on VdF, Propylene (hereinafter also referred to as P), ethylene (hereinafter also referred to as E), or perfluoro (alkyl vinyl ether) (hereinafter also referred to as PAVE) is preferable.
Examples of PAVE include perfluoro (methyl vinyl ether) (hereinafter also referred to as PMVE), perfluoro (propyl vinyl ether) (hereinafter also referred to as PPVE), and these are used alone or in any combination of two or more. be able to.
　含フッ素ゴム（ＩＩＩ）の具体例として、ＴＦＥ／Ｐ共重合体（ＴＦＥに基づく繰り返し単位とＰに基づく繰り返し単位とからなる共重合体を意味する。以下同様。）、ＴＦＥ／Ｐ／ＶｄＦ共重合体、ＶｄＦ／ＨＦＰ共重合体、ＶｄＦ／ＴＦＥ共重合体、ＴＦＥ／ＶｄＦ／ＨＦＰ共重合体、ＴＦＥ／ＰＡＶＥ共重合体、Ｅ／ＰＡＶＥ共重合体、Ｅ／Ｐ／ＰＡＶＥ共重合体、Ｅ／ＨＦＰ共重合体、ＴＦＥ／Ｐ／Ｅ共重合体、ＴＦＥ／Ｐ／ＰＡＶＥ共重合体、ＴＦＥ／Ｐ／ＶｄＦ／ＰＡＶＥ共重合体、ＶｄＦ／ＰＡＶＥ共重合体、ＶｄＦ／ＴＦＥ／ＰＡＶＥ共重合体、ＶｄＦ／ＴＦＥ／ＨＦＰ／ＰＡＶＥ共重合体、等が挙げられる。
　これらのうち、
ＴＦＥ／Ｐ共重合体、
ＴＦＥ／Ｐ／ＶｄＦ共重合体、
ＶｄＦ／ＨＦＰ共重合体、
ＶｄＦ／ＴＦＥ共重合体、
ＴＦＥ／ＶｄＦ／ＨＦＰ共重合体、
ＴＦＥ／ＰＡＶＥ共重合体、
ＴＦＥ／Ｐ／ＰＡＶＥ共重合体、
またはＴＦＥ／Ｐ／ＶｄＦ／ＰＡＶＥ共重合体が好ましく、
ＴＦＥ／Ｐ共重合体、またはＴＦＥ／Ｐ／ＶｄＦ共重合体が特に好ましい。 Specific examples of the fluorine-containing rubber (III) include a TFE / P copolymer (meaning a copolymer comprising a repeating unit based on TFE and a repeating unit based on P. The same shall apply hereinafter), TFE / P / VdF copolymer. Polymer, VdF / HFP copolymer, VdF / TFE copolymer, TFE / VdF / HFP copolymer, TFE / PAVE copolymer, E / PAVE copolymer, E / P / PAVE copolymer, E / HFP copolymer, TFE / P / E copolymer, TFE / P / PAVE copolymer, TFE / P / VdF / PAVE copolymer, VdF / PAVE copolymer, VdF / TFE / PAVE copolymer , VdF / TFE / HFP / PAVE copolymer, and the like.
Of these,
TFE / P copolymer,
TFE / P / VdF copolymer,
VdF / HFP copolymer,
VdF / TFE copolymer,
TFE / VdF / HFP copolymer,
TFE / PAVE copolymer,
TFE / P / PAVE copolymer,
Or a TFE / P / VdF / PAVE copolymer is preferred,
A TFE / P copolymer or a TFE / P / VdF copolymer is particularly preferred.
　含フッ素ゴム（ＩＩＩ）のより好ましい組成を以下に述べる。共重合組成が以下の範囲であると、正極集電体との密着性に優れ、優れた耐アルカリ性、耐電圧性が得られやすい。
　ＴＦＥ／Ｐ共重合体：
　ＴＦＥに基づく繰り返し単位／Ｐに基づく繰り返し単位の比率が、３０～８０／７０～２０（モル％）（ただし、ＴＦＥに基づく繰り返し単位とＰに基づく繰り返し単位とは合計で１００モル％である。以下同じ。）であることが好ましく、４０～７０／６０～３０（モル％）であることがより好ましく、６０～５０／４０～５０（モル％）であることが最も好ましい。 A more preferred composition of the fluorinated rubber (III) is described below. When the copolymer composition is in the following range, the adhesiveness to the positive electrode current collector is excellent, and excellent alkali resistance and voltage resistance are easily obtained.
TFE / P copolymer:
The ratio of the repeating unit based on TFE / the repeating unit based on P is 30 to 80/70 to 20 (mol%) (however, the repeating unit based on TFE and the repeating unit based on P are 100 mol% in total). The same shall apply hereinafter)), more preferably from 40 to 70/60 to 30 (mol%), and most preferably from 60 to 50/40 to 50 (mol%).
　ＴＦＥ／Ｐ／ＶｄＦ共重合体：
　ＴＦＥに基づく繰り返し単位／Ｐに基づく繰り返し単位／ＶｄＦに基づく繰り返し単位の比率が、３０～８５／１５～７０／０．０１～５０（モル％）の範囲であることが好ましく、より好ましくは３０～７０／２０～６０／１～４０（モル％）である。 TFE / P / VdF copolymer:
The ratio of the repeating unit based on TFE / the repeating unit based on P / the repeating unit based on VdF is preferably in the range of 30 to 85/15 to 70 / 0.01 to 50 (mol%), more preferably 30 70/20 to 60/1 to 40 (mol%).
　ＶｄＦ／ＨＦＰ共重合体：
　ＶｄＦに基づく繰り返し単位／ＨＦＰに基づく繰り返し単位の比率が、４５～９０／５５～１０（モル％）であることが好ましく、５０～８０／５０～２０（モル％）であることがより好ましい。 VdF / HFP copolymer:
The ratio of the repeating unit based on VdF / the repeating unit based on HFP is preferably 45 to 90/55 to 10 (mol%), and more preferably 50 to 80/50 to 20 (mol%).
　ＶｄＦ／ＴＦＥ共重合体：
　ＶｄＦに基づく繰り返し単位／ＨＦＰに基づく繰り返し単位の比率が、５０～９０／５０～１０（モル％）であることが好ましい。 VdF / TFE copolymer:
The ratio of the repeating unit based on VdF / the repeating unit based on HFP is preferably 50 to 90/50 to 10 (mol%).
　ＴＦＥ／ＶｄＦ／ＨＦＰ共重合体：
　ＴＦＥに基づく繰り返し単位／ＶｄＦに基づく繰り返し単位／ＨＦＰに基づく繰り返し単位の比率が、２～５０／３０～９０／１～３５（モル％）であることが好ましい。 TFE / VdF / HFP copolymer:
The ratio of the repeating unit based on TFE / the repeating unit based on VdF / the repeating unit based on HFP is preferably 2 to 50/30 to 90/1 to 35 (mol%).
　ＴＦＥ／ＰＡＶＥ共重合体：
　ＴＦＥに基づく繰り返し単位／ＰＡＶＥに基づく繰り返し単位の比率が、５０～９０／５０～１０（モル％）であることが好ましく、５０～８０／５０～２０（モル％）であることがより好ましい。 TFE / PAVE copolymer:
The ratio of the repeating unit based on TFE / the repeating unit based on PAVE is preferably 50 to 90/50 to 10 (mol%), and more preferably 50 to 80/50 to 20 (mol%).
　ＴＦＥ／Ｐ／ＰＡＶＥ共重合体：
　ＴＦＥに基づく繰り返し単位／Ｐに基づく繰り返し単位／ＰＡＶＥに基づく繰り返し単位の比率が、３０～８０／１５～７０／０．１～４０（モル％）であることが好ましく、３９～７０／２０～６０／１～３０（モル％）であることがより好ましい TFE / P / PAVE copolymer:
The ratio of the repeating unit based on TFE / the repeating unit based on P / the repeating unit based on PAVE is preferably 30 to 80/15 to 70 / 0.1 to 40 (mol%), and preferably 39 to 70/20 to More preferably 60/1 to 30 (mol%)
　含フッ素ゴム（ＩＩＩ）の重量平均分子量は、１０，０００～３００，０００が好ましく、２０，０００～２５０，０００がより好ましく、３０，０００～１９０，０００がさらに好ましい。該重量平均分子量が前記範囲の下限値以上であると、正極活物質層のバインダーとして用いた場合に電解液に膨潤し難く、前記範囲の上限値以下であると、密着性に優れる。
　本明細書における重量平均分子量（Ｍｗ）は、分子量既知の標準ポリスチレン試料を用いて作成した検量線を用い、ゲルパーミエーションクロマトグラフィーで測定することによって得られるポリスチレン換算分子量である。 The weight average molecular weight of the fluorinated rubber (III) is preferably 10,000 to 300,000, more preferably 20,000 to 250,000, and even more preferably 30,000 to 190,000. When the weight average molecular weight is not less than the lower limit of the above range, it is difficult to swell in the electrolyte when used as the binder of the positive electrode active material layer, and when it is not more than the upper limit of the above range, the adhesion is excellent.
The weight average molecular weight (Mw) in the present specification is a molecular weight in terms of polystyrene obtained by measuring with gel permeation chromatography using a calibration curve prepared using a standard polystyrene sample having a known molecular weight.
　含フッ素ゴム（ＩＩＩ）の引張特性として、引張破断伸びが５００％以上であることが好ましく、８００％以上がより好ましく、１０００％以上が特に好ましい。引張破断伸びが５００％未満であると、正極集電体との密着性が低下しやすい。
　また、含フッ素ゴム（ＩＩＩ）の引張強度は１～５０ＭＰａが好ましく、５～２０ＭＰａがより好ましい。該引張強度が前記の範囲であると密着性に優れる。含フッ素ゴム（ＩＩＩ）の引張破断伸びおよび引張強度の値は、ＪＩＳＫ６２５１に準処する方法で求められる値である。 As tensile properties of the fluorine-containing rubber (III), the tensile elongation at break is preferably 500% or more, more preferably 800% or more, and particularly preferably 1000% or more. When the tensile elongation at break is less than 500%, the adhesion with the positive electrode current collector tends to be lowered.
The tensile strength of the fluorine-containing rubber (III) is preferably 1 to 50 MPa, more preferably 5 to 20 MPa. When the tensile strength is within the above range, the adhesion is excellent. The values of the tensile elongation at break and the tensile strength of the fluorinated rubber (III) are values obtained by a method according to JISK6251.
　正極のバインダーに含まれる含フッ素ゴム（ＩＩＩ）は１種でもよく２種以上でもよい。バインダーは、含フッ素ゴム（ＩＩＩ）の他に、必要に応じてポリ四フッ化エチレンなどの他のフッ素樹脂や、他の高分子化合物を含んでもよい。バインダーのうちの６０質量％以上が含フッ素ゴム（ＩＩＩ）であることが好ましく、８０質量％以上がより好ましく、１００質量％が特に好ましい。 The fluorine-containing rubber (III) contained in the positive electrode binder may be one type or two or more types. In addition to the fluorine-containing rubber (III), the binder may contain other fluororesins such as polytetrafluoroethylene and other polymer compounds as necessary. 60% by mass or more of the binder is preferably fluorine-containing rubber (III), more preferably 80% by mass or more, and particularly preferably 100% by mass.
［含フッ素ゴムの製造方法］
　含フッ素ゴム（ＩＩＩ）は公知の重合方法により製造することができ、中でもラジカル共重合法が好ましい。ラジカル重合法は、特に限定されるものではなく、種々のラジカル重合法が用いられるが、有機または無機のラジカル重合開始剤、光、熱、電離放射線などによって開始されるものが好ましい。重合の形態としては塊状重合、懸濁重合、乳化重合、溶液重合等の従来公知の重合方法により製造することができるが、好ましくは乳化重合である。
　例えば、プロピレンとテトラフルオロエチレンとを水性媒体中で、レドックス触媒の存在下に共重合させる方法を用いることができる。 [Method for producing fluorine-containing rubber]
The fluorine-containing rubber (III) can be produced by a known polymerization method, and among them, the radical copolymerization method is preferable. The radical polymerization method is not particularly limited, and various radical polymerization methods are used, but those initiated by an organic or inorganic radical polymerization initiator, light, heat, ionizing radiation, or the like are preferable. The form of polymerization can be produced by a conventionally known polymerization method such as bulk polymerization, suspension polymerization, emulsion polymerization, solution polymerization or the like, and emulsion polymerization is preferred.
For example, a method of copolymerizing propylene and tetrafluoroethylene in an aqueous medium in the presence of a redox catalyst can be used.
　または、特に、ＴＦＥ／Ｐ共重合体など、ＴＦＥに基づく繰り返し単位とＰに基づく繰り返し単位を有する含フッ素ゴム（ＩＩＩ）を製造する方法として、水性媒体、アニオン性乳化剤、および熱分解型ラジカル重合開始剤の存在下で、テトラフルオロエチレンとプロピレンとを含む単量体混合物を、重合温度５０℃～１００℃の範囲で乳化重合して、含フッ素ゴム（ＩＩＩ）を生成させる乳化重合工程を有する製造方法（以下、製造方法（ＩＶ）という。）を好ましく用いることができる。
　前記水性媒体は、水単独、または水と水溶性有機溶媒とからなり、該水溶性有機溶媒の含有量が水１００質量部に対して１質量部未満であるものを用いる。
　前記アニオン性乳化剤の使用量は、生成する含フッ素ゴム（ＩＩＩ）１００質量部に対して、１．５～５．０質量部とする。
　乳化重合工程は、公知の乳化重合法により行うことができる。例えば以下の手順で行うことができる。
　この製造方法（ＩＶ）によれば、レドックス触媒を使用せずに含フッ素ゴム（ＩＩＩ）を製造できるため、金属分の含有量が少ない含フッ素ゴム（ＩＩＩ）のラテックスが得られる。また、有機溶剤の含有量が少ないにもかかわらず、含フッ素ゴム（ＩＩＩ）のラテックスにおける良好な安定性が得られる。 Or, in particular, as a method for producing a fluorine-containing rubber (III) having a repeating unit based on TFE and a repeating unit based on P, such as a TFE / P copolymer, an aqueous medium, an anionic emulsifier, and thermal decomposition type radical polymerization It has an emulsion polymerization step in which a monomer mixture containing tetrafluoroethylene and propylene is emulsion-polymerized at a polymerization temperature in the range of 50 ° C. to 100 ° C. to produce a fluorinated rubber (III) in the presence of an initiator. A production method (hereinafter referred to as production method (IV)) can be preferably used.
The aqueous medium is composed of water alone or water and a water-soluble organic solvent, and the content of the water-soluble organic solvent is less than 1 part by mass with respect to 100 parts by mass of water.
The amount of the anionic emulsifier used is 1.5 to 5.0 parts by mass with respect to 100 parts by mass of the fluorine-containing rubber (III) to be produced.
The emulsion polymerization step can be performed by a known emulsion polymerization method. For example, it can be performed by the following procedure.
According to this production method (IV), since the fluorinated rubber (III) can be produced without using a redox catalyst, a latex of the fluorinated rubber (III) having a low metal content can be obtained. Moreover, although the content of the organic solvent is small, good stability in the latex of the fluorine-containing rubber (III) can be obtained.
　製造方法（ＩＶ）において、水性媒体における水溶性有機溶媒（水に溶解可能な有機溶媒を意味する。）は公知のものを適宜用いることができる。好ましくはアルコール類であり、ｔｅｒｔ－ブタノールが特に好ましい。
　水性媒体中の水溶性有機溶媒の含有量は少ない方が好ましい。具体的には、水の１００質量部に対して、水溶性有機溶媒は１質量部未満であり、０．５質量部以下が好ましく、０．１質量部以下がより好ましく、ゼロが特に好ましい。
　すなわち、水性媒体として水溶性有機溶媒を含まない水を単独で用いることが特に好ましい。
　水溶性有機溶媒の含有量が上記の範囲であると、得られる含フッ素ゴム（ＩＩＩ）ラテックスを蓄電デバイス用バインダーとして用いた場合、製造工程によって作業環境対策等の取扱いの問題が生じる可能性が低減でき、好ましい。 In the production method (IV), known water-soluble organic solvents (meaning organic solvents that can be dissolved in water) in an aqueous medium can be appropriately used. Alcohols are preferable, and tert-butanol is particularly preferable.
The content of the water-soluble organic solvent in the aqueous medium is preferably small. Specifically, the water-soluble organic solvent is less than 1 part by mass with respect to 100 parts by mass of water, preferably 0.5 parts by mass or less, more preferably 0.1 parts by mass or less, and particularly preferably zero.
That is, it is particularly preferable to use water that does not contain a water-soluble organic solvent alone as the aqueous medium.
When the content of the water-soluble organic solvent is in the above range, when the obtained fluorinated rubber (III) latex is used as a binder for an electricity storage device, there may be a problem in handling such as measures for working environment depending on the production process. This is preferable because it can be reduced.
　製造方法（ＩＶ）において、アニオン性乳化剤としては、乳化重合法において公知のものが使用できる。具体例としては、ラウリル硫酸ナトリウム、ドデシルベンゼンスルホン酸ナトリウム、アルキルスルホン酸ナトリウム塩、アルキルベンゼンスルホン酸ナトリウム塩、コハク酸ジアルキルエステルスルホン酸ナトリウム塩、アルキルジフェニルエーテルジスルホン酸ナトリウム塩等の炭化水素系乳化剤；ペルフルオロオクタン酸アンモニウム、ペルフルオロヘキサン酸アンモニウム等の含フッ素アルキルカルボン酸塩；下記式（２）で表される化合物等が挙げられる。
　Ｆ（ＣＦ２）ｐＯ（ＣＦ（Ｘ）ＣＦ２Ｏ）ｑＣＦ（Ｘ）ＣＯＯＡ　・・・（２）
　式（２）中、Ｘはフッ素原子または炭素原子数１～３のペルフルオロアルキル基を表し、Ａは、水素原子、アルカリ金属原子、または－ＮＨ４を表し、ｐは１～１０の整数を表し、ｑは０または１～３の整数を表す。
　アニオン性乳化剤としては、ラウリル硫酸ナトリウムが特に好ましい。
　アニオン性乳化剤の使用量は、乳化重合工程で生成される含フッ素ゴム（ＩＩＩ）の１００質量部に対して、１．５～５．０質量部であり、１．５～３．８質量部が好ましく、１．７～３．２質量部が特に好ましい。
　含フッ素ゴム（ＩＩＩ）ラテックスにおける乳化剤の含有量がこの範囲であると、ラテックスの安定性に優れ、該ラテックスをバインダー組成物として用いた場合に優れた充放電特性が得られる。該乳化剤の含有量が多すぎると該充放電特性が劣化しやすくなる。 In the production method (IV), as the anionic emulsifier, those known in the emulsion polymerization method can be used. Specific examples include hydrocarbon emulsifiers such as sodium lauryl sulfate, sodium dodecylbenzene sulfonate, sodium alkyl sulfonate, sodium alkyl benzene sulfonate, sodium succinate dialkyl ester sulfonate, sodium alkyl diphenyl ether disulfonate; perfluoro Fluorine-containing alkyl carboxylates such as ammonium octanoate and ammonium perfluorohexanoate; compounds represented by the following formula (2), and the like.
F (CF 2 ) pO (CF (X) CF 2 O) qCF (X) COOA (2)
In the formula (2), X represents a fluorine atom or a perfluoroalkyl group having 1 to 3 carbon atoms, A represents a hydrogen atom, an alkali metal atom, or —NH 4 , and p represents an integer of 1 to 10 , Q represents 0 or an integer of 1 to 3.
As the anionic emulsifier, sodium lauryl sulfate is particularly preferable.
The amount of the anionic emulsifier used is 1.5 to 5.0 parts by mass, and 1.5 to 3.8 parts by mass with respect to 100 parts by mass of the fluorinated rubber (III) produced in the emulsion polymerization step. It is preferably 1.7 to 3.2 parts by mass.
When the content of the emulsifier in the fluorine-containing rubber (III) latex is within this range, the stability of the latex is excellent, and excellent charge / discharge characteristics can be obtained when the latex is used as a binder composition. When there is too much content of this emulsifier, this charge / discharge characteristic will deteriorate easily.
　製造方法（ＩＶ）において、熱分解型ラジカル重合開始剤としては、水溶性であって、１時間半減期温度が５０～１００℃のものが用いられる。通常の乳化重合に用いられる水溶性重合開始剤から適宜選択して使用することができる。具体例としては、過硫酸アンモニウム、過硫酸ナトリウム、過硫酸カリウム等の過硫酸類；ジコハク酸過酸化物；アゾビスイソブチルアミジン二塩酸塩等の有機系開始剤等が挙げられる。これらのうちで過硫酸類が好ましく、過硫酸アンモニウム塩が特に好ましい。
　熱分解型ラジカル重合開始剤の使用量は、乳化重合工程で生成される含フッ素ゴム（ＩＩＩ）の１００質量部に対して、０．０００１～３質量部が好ましく、０．００１～１質量部がより好ましい。 In the production method (IV), the thermal decomposition type radical polymerization initiator is water-soluble and has a one-hour half-life temperature of 50 to 100 ° C. It can be appropriately selected from water-soluble polymerization initiators used in ordinary emulsion polymerization. Specific examples include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate; disuccinic acid peroxide; organic initiators such as azobisisobutylamidine dihydrochloride, and the like. Of these, persulfates are preferred, and ammonium persulfate is particularly preferred.
The amount of the thermal decomposition type radical polymerization initiator used is preferably 0.0001 to 3 parts by mass, and 0.001 to 1 part by mass with respect to 100 parts by mass of the fluorinated rubber (III) produced in the emulsion polymerization step. Is more preferable.
　製造方法（ＩＶ）の乳化重合工程においてｐＨ調整剤を添加してもよい。ｐＨ調整剤として公知の無機塩を用いることができる。具体例としてはリン酸水素二ナトリウム、リン酸二水素ナトリウムなどのリン酸塩；炭酸水素ナトリウム、炭酸ナトリウムなどの炭酸塩；などが挙げられる。リン酸塩のより好ましい具体例としては、リン酸水素二ナトリウム２水和物、リン酸水素二ナトリウム１２水和物等が挙げられる。また、所望のｐＨに調整するために、水酸化ナトリウム、水酸化カリウムなどの塩基類；硫酸、塩酸、硝酸などの酸類；などを併用してもよい。
　ｐＨ調整剤を添加することにより、重合速度や、得られるラテックスの安定性を向上させることができる。
　含フッ素ゴム（ＩＩＩ）ラテックス中の金属分の含有量を低減させるためには、ｐＨ調整剤の使用量はできるだけ少ない方が好ましい。そのために、乳化重合工程はｐＨ調整剤の非存在下で行うことが好ましい。 A pH adjuster may be added in the emulsion polymerization step of production method (IV). Known inorganic salts can be used as the pH adjuster. Specific examples include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate; carbonates such as sodium hydrogen carbonate and sodium carbonate; and the like. More preferable specific examples of the phosphate include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate. Moreover, in order to adjust to desired pH, you may use together bases, such as sodium hydroxide and potassium hydroxide; Acids, such as a sulfuric acid, hydrochloric acid, and nitric acid;
By adding a pH adjuster, the polymerization rate and the stability of the resulting latex can be improved.
In order to reduce the metal content in the fluorinated rubber (III) latex, the amount of the pH adjuster used is preferably as small as possible. Therefore, the emulsion polymerization process is preferably performed in the absence of a pH adjuster.
＜リチウムイオン二次電池用正極＞
　本発明のリチウムイオン二次電池用正極は、前記の正極活物質、前記のバインダー、および導電材を含む正極活物質層が、正極集電体の表面上に形成されてなる。
　導電材としては、アセチレンブラック、黒鉛、ケッチェンブラックなどのカーボンブラック等が挙げられる。
　正極集電体としては、アルミニウムまたはアルミニウム合金が挙げられる。 <Positive electrode for lithium ion secondary battery>
The positive electrode for a lithium ion secondary battery according to the present invention has a positive electrode active material layer containing the positive electrode active material, the binder, and a conductive material formed on the surface of a positive electrode current collector.
Examples of the conductive material include carbon black such as acetylene black, graphite, and ketjen black.
Examples of the positive electrode current collector include aluminum or an aluminum alloy.
　本発明のリチウムイオン二次電池用正極は、正極活物質としてリチウム含有複合酸化物（Ｉ）を高充填することができ高い容量を得ることができる。また、バインダーによる密着性に優れ、高電圧で充電してもバインダーが劣化しないためサイクル維持率に優れる。
　すなわち、正極活物質としてＬｉ元素のモル量が該遷移金属元素の総モル量に対して１．２倍超であるリチウム含有複合酸化物（Ｉ）を用いることにより放電容量を向上させることができる。
　正極活物質として、かかるリチウム含有複合酸化物（Ｉ）を用いたリチウムイオン二次電池用正極にあっては、正極活物質を高電圧で活性化させることが好ましく、そのためにバインダーの耐電圧性が高いことが望まれる。さらにリチウム含有複合酸化物（Ｉ）は導電性が比較的低いため、正極活物質層におけるバインダーの含有量を少なくし、正極活物質の含有量を多く（高充填）することが望まれる。 The positive electrode for a lithium ion secondary battery of the present invention can be highly filled with the lithium-containing composite oxide (I) as a positive electrode active material, and can have a high capacity. Moreover, since the binder does not deteriorate even when charged at a high voltage, the cycle retention rate is excellent.
That is, the discharge capacity can be improved by using the lithium-containing composite oxide (I) in which the molar amount of Li element is more than 1.2 times the total molar amount of the transition metal element as the positive electrode active material. .
In the positive electrode for a lithium ion secondary battery using such a lithium-containing composite oxide (I) as the positive electrode active material, it is preferable to activate the positive electrode active material at a high voltage, and for that purpose, the withstand voltage of the binder Is desired to be high. Furthermore, since lithium containing complex oxide (I) has comparatively low electroconductivity, it is desired to reduce the binder content in the positive electrode active material layer and increase the positive electrode active material content (high filling).
　本発明によれば、バインダーとして含フッ素ゴム（ＩＩＩ）を用いることにより、後述の実施例に示されるように、正極活物質層において正極活物質を高充填した場合にも、バインダーを介して正極活物質および導電材層と正極集電体との良好な密着性が得られる。
　例えば、正極活物質層における正極活物質の含有量を好ましくは８０～９７質量％とすることができる。８５～９５質量％がより好ましい。
　正極活物質層におけるバインダーの含有量は１．５～１０質量％が好ましく、２．５～５質量％がより好ましい。
　正極活物質層における導電材の含有量は１．５～１０質量％が好ましく、２．５～５質量％がより好ましい。
　正極活物質、バインダー、導電材の含有量が前記の範囲であると、良好な導電性が得られるとともに、正極活物質の含有量が多いため放電容量の高い正極となり、かつ正極活物質と集電体の密着性が良好となる。 According to the present invention, by using the fluorine-containing rubber (III) as a binder, even when the positive electrode active material layer is highly filled in the positive electrode active material layer, as shown in the examples described later, the positive electrode is interposed via the binder. Good adhesion between the active material and conductive material layer and the positive electrode current collector can be obtained.
For example, the content of the positive electrode active material in the positive electrode active material layer can be preferably 80 to 97% by mass. 85 to 95% by mass is more preferable.
The binder content in the positive electrode active material layer is preferably 1.5 to 10% by mass, more preferably 2.5 to 5% by mass.
The content of the conductive material in the positive electrode active material layer is preferably 1.5 to 10% by mass, and more preferably 2.5 to 5% by mass.
When the content of the positive electrode active material, the binder, and the conductive material is within the above ranges, good conductivity can be obtained, and since the content of the positive electrode active material is large, the positive electrode has a high discharge capacity and is collected from the positive electrode active material. The adhesion of the electric body is improved.
　また、バインダーとして用いる含フッ素ゴム（ＩＩＩ）のフッ素含有量が高いため、良好な耐電圧性が得られ、高電圧で充電してもバインダーの劣化が生じにくい。
　さらに含フッ素ゴム（ＩＩＩ）はＴＦＥに基づく繰り返し単位とＰに基づく繰り返し単位を含む場合は耐アルカリ性が良好である。したがって、正極活物質としてＬｉ元素の含有比率が高いリチウム含有複合酸化物（Ｉ）を用いてもバインダーの劣化が生じにくく、良好なサイクル維持率が得られる。
　さらに、含フッ素ゴム（ＩＩＩ）は柔軟性に優れるため、充放電が繰り返される際の、正極活物質の膨張、収縮に対する追従性に優れ、サイクル特性の向上に寄与する。 Further, since the fluorine content of the fluorine-containing rubber (III) used as the binder is high, good voltage resistance is obtained, and the binder is hardly deteriorated even when charged at a high voltage.
Further, the fluororubber (III) has good alkali resistance when it contains a repeating unit based on TFE and a repeating unit based on P. Therefore, even when the lithium-containing composite oxide (I) having a high Li element content is used as the positive electrode active material, the binder is hardly deteriorated, and a good cycle maintenance rate is obtained.
Furthermore, since the fluorine-containing rubber (III) is excellent in flexibility, it has excellent followability to expansion and contraction of the positive electrode active material when charging and discharging are repeated, and contributes to improvement of cycle characteristics.
＜リチウムイオン二次電池用正極の製造方法＞
　本発明のリチウムイオン二次電池用正極は、前記正極活物質と前記バインダーとを混合して混合物を得る混合工程と、該混合物を熱処理する工程を含む方法で製造できる。
　該混合物は、さらに有機溶媒または水系分散媒を含む、スラリーまたは混練物であることが好ましい。すなわち、前記混合工程において、有機溶媒中で正極活物質とバインダーとを混合することが好ましい。または、前記混合工程において、水性分散媒中で正極活物質とバインダーとを混合することが好ましい。
　導電材は前記混合物に含有させることが好ましい。正極活物質とバインダーとを混合する際に、導電材を加えて混合してもよく、予め導電材と正極活物質とを混合した後、これらとバインダーを混合してもよい。
　該混合物を正極集電板の表面上に塗布等により担持させ、熱処理して有機溶媒および／または水系分散媒を除去して正極活物質層等を形成することにより、リチウムイオン二次電池用正極が得られる。該正極活物質層に、さらにプレス処理を施してもよい。 <Method for producing positive electrode for lithium ion secondary battery>
The positive electrode for a lithium ion secondary battery of the present invention can be manufactured by a method including a mixing step of mixing the positive electrode active material and the binder to obtain a mixture, and a step of heat-treating the mixture.
The mixture is preferably a slurry or a kneaded product further containing an organic solvent or an aqueous dispersion medium. That is, in the mixing step, it is preferable to mix the positive electrode active material and the binder in an organic solvent. Alternatively, in the mixing step, it is preferable to mix the positive electrode active material and the binder in an aqueous dispersion medium.
The conductive material is preferably contained in the mixture. When mixing the positive electrode active material and the binder, a conductive material may be added and mixed. Alternatively, the conductive material and the positive electrode active material may be mixed in advance and then mixed with the binder.
The mixture is supported on the surface of the positive electrode current collector plate by coating or the like, and heat treated to remove the organic solvent and / or aqueous dispersion medium to form a positive electrode active material layer and the like, thereby forming a positive electrode for a lithium ion secondary battery Is obtained. The positive electrode active material layer may be further pressed.
［バインダー組成物］
　リチウムイオン二次電池用正極の製造において、バインダーは、バインダーと有機溶媒または水性分散媒とを含有するバインダー組成物として用いることが好ましい。
　有機溶媒は可燃性である場合が多く、取り扱いに注意を要することから、バインダー組成物としては、バインダーと水性分散媒とを含有するバインダー組成物であることがより好ましい。 [Binder composition]
In the production of a positive electrode for a lithium ion secondary battery, the binder is preferably used as a binder composition containing a binder and an organic solvent or an aqueous dispersion medium.
In many cases, the organic solvent is flammable and needs attention in handling. Therefore, the binder composition is preferably a binder composition containing a binder and an aqueous dispersion medium.
　有機溶媒としては、酢酸エチル、酢酸ブチル、アセトン、メチルエチルケトン、メチルイソブチルケトン、ヘキサン、オクタン、トルエン、キシレン、ナフサ、アセトニトリル、Ｎ－メチルピロリドン、アセチルピリジン、シクロペンタノン、ジメチルホルムアミド、ジメチルスルフォキシド、メチルホルムアミド、メタノール、エタノール等が例示される。これらの中でも、Ｎ－メチルピロリドン、または酢酸ブチルが好ましく、Ｎ－メチルピロリドンがより好ましい。有機溶媒は、１種のみからなる溶媒であってもよく、２種以上の溶媒の混合溶媒であってもよい。 Examples of organic solvents include ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, hexane, octane, toluene, xylene, naphtha, acetonitrile, N-methylpyrrolidone, acetylpyridine, cyclopentanone, dimethylformamide, dimethyl sulfoxide , Methylformamide, methanol, ethanol and the like. Among these, N-methylpyrrolidone or butyl acetate is preferable, and N-methylpyrrolidone is more preferable. The organic solvent may be a single solvent or a mixed solvent of two or more solvents.
　水性分散媒としては、水単独、または水と水溶性有機溶媒との混合物を使用することができる。水溶性有機溶媒としては、アセトン、メチルエチルケトン等のケトン類；トリエチルアミン、アニリン等のアミン類；Ｎ－メチルピロリドン、ジメチルホルムアミド等のアミド類；メタノール、エタノール、プロパノール、イソプロパノール、ｎ－ブタノール、ｔ－ブタノール等のアルコール類などが挙げられる。これらの中でもアルコール類、またはアミド類が好ましく、アルコール類がより好ましい。
　また、アルコール類の中でも、メタノール、イソプロパノール、またはｔ－ブタノールが好ましく、ｔ-ブタノールがより好ましい。水性分散媒に使用する水溶性有機溶媒は１種のみでもよく、２種以上を組み合わせて使用してもよい。 As the aqueous dispersion medium, water alone or a mixture of water and a water-soluble organic solvent can be used. Examples of water-soluble organic solvents include ketones such as acetone and methyl ethyl ketone; amines such as triethylamine and aniline; amides such as N-methylpyrrolidone and dimethylformamide; methanol, ethanol, propanol, isopropanol, n-butanol, and t-butanol. And alcohols. Among these, alcohols or amides are preferable, and alcohols are more preferable.
Of the alcohols, methanol, isopropanol, or t-butanol is preferable, and t-butanol is more preferable. Only one water-soluble organic solvent may be used in the aqueous dispersion medium, or two or more water-soluble organic solvents may be used in combination.
　バインダー組成物に含まれるバインダーの割合は、バインダー組成物全体の５～６０質量％が好ましく、より好ましくは１０～５０質量％である。
　バインダー組成物が、含フッ素ゴム（ＩＩＩ）と水性分散媒を含有する場合、含フッ素ゴム（ＩＩＩ）は、水性分散媒に乳化または分散していることが好ましく、特にラテックスの状態であることが好ましい。 The ratio of the binder contained in the binder composition is preferably 5 to 60% by mass, and more preferably 10 to 50% by mass, based on the entire binder composition.
When the binder composition contains the fluorinated rubber (III) and the aqueous dispersion medium, the fluorinated rubber (III) is preferably emulsified or dispersed in the aqueous dispersion medium, particularly in a latex state. preferable.
　バインダー組成物の製造方法については特に限定されないが、含フッ素ゴム（ＩＩＩ）を懸濁重合、乳化重合、溶液重合等で製造し、重合後の含フッ素ゴム（ＩＩＩ）が有機溶媒に溶解した状態、または水性分散媒に分散した状態の組成物をそのまま使用することができる。この場合は、重合の際に用いる溶媒または分散媒を、得ようとするバインダー組成物を構成する有機溶媒または水性分散媒と同じにすることが好ましい。
　バインダー組成物が、有機溶媒を含有する場合、溶液重合で製造された、含フッ素ゴム（ＩＩＩ）の溶液をそのまま使用することができる。
　また、バインダー組成物が水性分散媒を含有する場合、乳化重合により製造された、含フッ素ゴム（ＩＩＩ）が水性分散媒に分散した組成物をそのまま使用することができる。
　また、バインダー組成物は、重合によって得られた含フッ素ゴムを精製して固体の状態とし、該固体を再度、有機溶媒に溶解または水性分散媒に分散させた組成物であってもよい。この場合に使用する有機溶媒または水性分散媒は、前述の有機溶媒または水性分散媒であることが好ましい。 The production method of the binder composition is not particularly limited, but the fluorine-containing rubber (III) is produced by suspension polymerization, emulsion polymerization, solution polymerization, etc., and the fluorine-containing rubber (III) after polymerization is dissolved in an organic solvent. Alternatively, the composition dispersed in an aqueous dispersion medium can be used as it is. In this case, the solvent or dispersion medium used in the polymerization is preferably the same as the organic solvent or aqueous dispersion medium constituting the binder composition to be obtained.
When the binder composition contains an organic solvent, the solution of fluorine-containing rubber (III) produced by solution polymerization can be used as it is.
Further, when the binder composition contains an aqueous dispersion medium, a composition produced by emulsion polymerization in which the fluorinated rubber (III) is dispersed in the aqueous dispersion medium can be used as it is.
The binder composition may be a composition obtained by purifying the fluorine-containing rubber obtained by polymerization to a solid state and dissolving the solid again in an organic solvent or dispersing in an aqueous dispersion medium. The organic solvent or aqueous dispersion medium used in this case is preferably the aforementioned organic solvent or aqueous dispersion medium.
＜リチウムイオン二次電池＞
　本発明におけるリチウムイオン二次電池は、本発明のリチウムイオン二次電池用正極と、負極と非水電解質とを含むものである。
　負極は、負極集電体上に、負極活物質を含有する負極活物質層が形成されてなる。たとえば、負極活物質を有機溶媒と混錬することによってスラリーを調製し、調製したスラリーを負極集電体に塗布、乾燥、プレスすることによって製造できる。 <Lithium ion secondary battery>
The lithium ion secondary battery in this invention contains the positive electrode for lithium ion secondary batteries of this invention, a negative electrode, and a nonaqueous electrolyte.
The negative electrode is formed by forming a negative electrode active material layer containing a negative electrode active material on a negative electrode current collector. For example, a slurry can be prepared by kneading a negative electrode active material with an organic solvent, and the prepared slurry can be applied to a negative electrode current collector, dried, and pressed.
　負極集電体としては、たとえばニッケル箔、銅箔等の金属箔を用いることができる。
　負極活物質としては、比較的低い電位でリチウムイオンを吸蔵、放出可能な材料であればよく、たとえば、リチウム金属、リチウム合金、炭素材料、周期表１４、１５族の金属を主体とする酸化物、炭素化合物、炭化ケイ素化合物、酸化ケイ素化合物、硫化チタンおよび炭化ホウ素化合物等を用いることができる。 As the negative electrode current collector, for example, a metal foil such as a nickel foil or a copper foil can be used.
The negative electrode active material may be any material that can occlude and release lithium ions at a relatively low potential. For example, an oxide mainly composed of lithium metal, lithium alloy, carbon material, periodic table 14 or group 15 metal. Carbon compounds, silicon carbide compounds, silicon oxide compounds, titanium sulfide, boron carbide compounds, and the like can be used.
　負極活物質の炭素材料としては、たとえば、難黒鉛化性炭素、人造黒鉛、天然黒鉛、熱分解炭素類、ピッチコークス、ニードルコークス、石油コークス等のコークス類、グラファイト類、ガラス状炭素類、フェノール樹脂やフラン樹脂等を適当な温度で焼成し炭素化した有機高分子化合物焼成体、炭素繊維、活性炭、カーボンブラック類等を用いることができる。
　周期表１４族の金属としては、たとえば、ケイ素またはスズであり、最も好ましくはケイ素である。
　その他に負極活物質として用いることができる材料としては酸化鉄、酸化ルテニウム、酸化モリブデン、酸化タングステン、酸化チタン、酸化スズ等の酸化物やＬｉ２．６Ｃｏ０．４Ｎ等の窒化物が挙げられる。 Examples of the carbon material of the negative electrode active material include non-graphitizable carbon, artificial graphite, natural graphite, pyrolytic carbon, coke such as pitch coke, needle coke, petroleum coke, graphite, glassy carbon, phenol Organic polymer compound fired bodies, carbon fibers, activated carbon, carbon blacks, etc., obtained by firing and carbonizing a resin, furan resin or the like at an appropriate temperature can be used.
The metal of the periodic table group 14 is, for example, silicon or tin, and most preferably silicon.
Other materials that can be used as the negative electrode active material include oxides such as iron oxide, ruthenium oxide, molybdenum oxide, tungsten oxide, titanium oxide, and tin oxide, and nitrides such as Li 2.6 Co 0.4 N. It is done.
　非水電解質としては、例えば、有機溶媒に電解質塩を溶解させた非水電解液、電解質塩を含有させた固体電解質、高分子電解質、高分子化合物等に電解質塩を混合または溶解させた固体状もしくはゲル状電解質等が挙げられる。
　有機溶媒としては、電解液用の有機溶媒として公知のものを用いることができ、たとえば、プロピレンカーボネート、エチレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、１，２－ジメトキシエタン、１，２－ジエトキシエタン、ジグライム、トリグライム、γ－ブチロラクトン、ジエチルエーテル、スルホラン、メチルスルホラン、アセトニトリル、酢酸エステル、酪酸エステル、プロピオン酸エステル等を用いることができる。特に、電圧安定性の点からは、プロピレンカーボネート等の環状カーボネート類、またはジメチルカーボネート、ジエチルカーボネート等の鎖状カーボネート類を使用することが好ましい。また、このような有機溶媒は、１種類を単独で用いてもよく、２種類以上を混合して用いてもよい。 Examples of the non-aqueous electrolyte include a non-aqueous electrolyte obtained by dissolving an electrolyte salt in an organic solvent, a solid electrolyte containing an electrolyte salt, a solid electrolyte obtained by mixing or dissolving an electrolyte salt in a polymer electrolyte, a polymer compound, and the like. Or a gel electrolyte etc. are mentioned.
As the organic solvent, those known as organic solvents for electrolytic solutions can be used. For example, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, Diglyme, triglyme, γ-butyrolactone, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, acetic acid ester, butyric acid ester, propionic acid ester and the like can be used. In particular, from the viewpoint of voltage stability, it is preferable to use cyclic carbonates such as propylene carbonate or chain carbonates such as dimethyl carbonate and diethyl carbonate. Moreover, such an organic solvent may be used individually by 1 type, and may be used in mixture of 2 or more types.
　固体電解質としては、リチウムイオン伝導性を有する材料であればよく、たとえば、無機固体電解質および高分子固体電解質のいずれをも用いることができる。 As the solid electrolyte, any material having lithium ion conductivity may be used. For example, either an inorganic solid electrolyte or a polymer solid electrolyte can be used.
　無機固体電解質としては、窒化リチウム、ヨウ化リチウム等を用いることができる。
　高分子固体電解質としては、電解質塩と該電解質塩を溶解する高分子化合物を用いることができる。そして、この高分子化合物としては、ポリエチレンオキサイド、ポリプロピレンオキサイド、ポリホスファゼン、ポリアジリジン、ポリエチレンスルフィド、ポリビニルアルコール、ポリフッ化ビニリデン、および、ポリヘキサフルオロプロピレン、もしくは、これらの誘導体、混合物、および複合体を用いることができる。 As the inorganic solid electrolyte, lithium nitride, lithium iodide, or the like can be used.
As the polymer solid electrolyte, an electrolyte salt and a polymer compound that dissolves the electrolyte salt can be used. Examples of the polymer compound include polyethylene oxide, polypropylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polyhexafluoropropylene, or derivatives, mixtures, and composites thereof. Can be used.
　ゲル状電解質等としては、前記の非水電解液を吸収してゲル化するものであればよく、種々の高分子を用いることができる。また、ゲル状電解質に用いられる高分子材料としては、たとえば、ポリ（ビニリデンフルオロライド）、ポリ（ビニリデンフルオロライド－ｃｏ－ヘキサフルオロプロピレン）などのフッ素系高分子等を使用できる。また、ゲル状電解質に用いられる高分子材料としては、たとえば、ポリアクリロニトリルおよびポリアクリロニトリルの共重合体の他、ポリエチレンオキサイドおよびポリエチレンオキサイドの共重合体、同架橋体などのエーテル系高分子を使用できる。共重合モノマーとしては、たとえば、ポリプロピレンオキサイド、メタクリル酸メチル、メタクリル酸ブチル、アクリル酸メチル、アクリル酸ブチル等を挙げることができる。
　また、 ゲル状電解質のマトリックスとしては、酸化還元反応に対する安定性の観点から、特にフッ素系高分子が好ましい。 Any gel electrolyte may be used as long as it absorbs the non-aqueous electrolyte and gels, and various polymers can be used. In addition, as the polymer material used for the gel electrolyte, for example, fluorine-based polymers such as poly (vinylidene fluoride) and poly (vinylidene fluoride-co-hexafluoropropylene) can be used. As the polymer material used for the gel electrolyte, for example, polyacrylonitrile and a copolymer of polyacrylonitrile, as well as an ether polymer such as polyethylene oxide, a copolymer of polyethylene oxide, and a crosslinked product thereof can be used. . Examples of the copolymerization monomer include polypropylene oxide, methyl methacrylate, butyl methacrylate, methyl acrylate, and butyl acrylate.
In addition, the matrix of the gel electrolyte is particularly preferably a fluoropolymer from the viewpoint of stability against redox reaction.
　電解質塩は、この種の電池に用いられるものであればいずれも使用可能であり、たとえば、ＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＢＦ４、ＣＨ３ＳＯ３Ｌｉ、ＬｉＣｌ、ＬｉＢｒ等を用いることができる。
　本発明のリチウムイオン二次電池の形状は、コイン型、シート状（フィルム状）、折り畳み状、巻回型有底円筒型、ボタン型等の形状を、用途に応じて適宜選択できる。 Any electrolyte salt can be used as long as it is used for this type of battery. For example, LiClO 4 , LiPF 6 , LiBF 4 , CH 3 SO 3 Li, LiCl, LiBr, or the like can be used.
The shape of the lithium ion secondary battery of the present invention can be appropriately selected from coin shapes, sheet shapes (film shapes), folded shapes, wound bottomed cylindrical shapes, button shapes, and the like depending on the application.
　以下に、本発明の更に詳しい説明を実施例によって行うが、本発明は、これら実施例にのみ限定されるものではない。 Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.
 [正極活物質（１）の合成例]
　硫酸ニッケル（ＩＩ）六水和物（６３０ｇ）、硫酸コバルト（ＩＩ）七水和物（６６９ｇ）、および硫酸マンガン（ＩＩ）五水和物（２３２１ｇ）に蒸留水（５９８０ｇ）を加えて均一に溶解させて原料溶液とした。硫酸アンモニウム（４００ｇ）に蒸留水（１６００ｇ）を加えて均一に溶解させてアンモニア源溶液とした。硫酸アンモニウム（７９．２ｇ）に蒸留水（１９２０．８ｇ）を加えて均一に溶解させて母液とした。水酸化ナトリウム（１２０ｇ）に蒸留水（１８００ｇ）を加えて均一に溶解させてｐＨ調整液とした。 [Synthesis Example of Positive Electrode Active Material (1)]
Distilled water (5980 g) was added uniformly to nickel (II) sulfate hexahydrate (630 g), cobalt (II) sulfate heptahydrate (669 g), and manganese (II) sulfate pentahydrate (2321 g). A raw material solution was prepared by dissolving. Distilled water (1600 g) was added to ammonium sulfate (400 g) and dissolved uniformly to obtain an ammonia source solution. Distilled water (1920.8 g) was added to ammonium sulfate (79.2 g) and dissolved uniformly to obtain a mother liquor. Distilled water (1800 g) was added to sodium hydroxide (120 g) and dissolved uniformly to obtain a pH adjusting solution.
　２Ｌのバッフル付きガラス製反応槽に母液を入れてマントルヒーターで５０℃に加熱し、ｐＨが１１．０となるようにｐＨ調整液を加えた。反応槽内の溶液をアンカー型の攪拌翼で攪拌しながら原料溶液を５．０ｇ／分、アンモニア源溶液を１．０ｇ／分の速度で添加し、ニッケル、コバルト、およびマンガンの複合水酸化物を析出させた。原料溶液を添加している間、反応槽内のｐＨを１１．０に保つようにｐＨ調整溶液を添加した。また、析出した水酸化物が酸化しないように反応槽内に窒素ガスを流量０．５Ｌ／分で流した。また、反応槽内の液量が２Ｌを超えないように連続的に液の抜き出しを行った。 The mother liquor was placed in a 2 L baffled glass reaction vessel, heated to 50 ° C. with a mantle heater, and a pH adjusting solution was added so that the pH was 11.0. While stirring the solution in the reaction vessel with an anchor-type stirring blade, the raw material solution was added at a rate of 5.0 g / min and the ammonia source solution was added at a rate of 1.0 g / min, and a composite hydroxide of nickel, cobalt, and manganese was added. Was precipitated. During the addition of the raw material solution, the pH adjusting solution was added so as to keep the pH in the reaction vessel at 11.0. Moreover, nitrogen gas was flowed at a flow rate of 0.5 L / min in the reaction tank so that the precipitated hydroxide was not oxidized. Further, the liquid was continuously extracted so that the amount of the liquid in the reaction tank did not exceed 2 L.
　得られたニッケル、コバルト、およびマンガンの複合水酸化物から不純物イオンを取り除くため、加圧ろ過と蒸留水への分散を繰返して洗浄した。ろ液の電気伝導度が２５μＳ／ｃｍとなった時点で洗浄を終了し、１２０℃で１５時間乾燥させて前駆体とした。
　ＩＣＰで前駆体のニッケル、コバルト、およびマンガンの含有量を測定したところ、それぞれ１１．３質量％、１１．９質量％、４４．５質量％であった（モル比でニッケル：コバルト：マンガン＝０．１６０：０．１６８：０．６７３）。 In order to remove impurity ions from the resulting composite hydroxide of nickel, cobalt, and manganese, washing was repeated by pressure filtration and dispersion in distilled water. When the electrical conductivity of the filtrate reached 25 μS / cm, the washing was finished and dried at 120 ° C. for 15 hours to obtain a precursor.
When the contents of the precursors nickel, cobalt, and manganese were measured by ICP, they were 11.3 mass%, 11.9 mass%, and 44.5 mass%, respectively (molar ratio of nickel: cobalt: manganese = 0.160: 0.168: 0.673).
　この前駆体（２０ｇ）とリチウム含有量が２６．９ｍｏｌ／ｋｇの炭酸リチウム（１２．８ｇ）を混合して酸素含有雰囲気下９００℃で１２時間焼成し、実施例のリチウム含有複合酸化物を得た。得られた実施例のリチウム含有複合酸化物の組成はＬｉ（Ｌｉ０．２Ｎｉ０．１２８Ｃｏ０．１３４Ｍｎ０．５３８）Ｏ２となる。実施例のリチウム含有複合酸化物の平均粒子径Ｄ５０は８．４μｍであり、窒素ガス吸着ＢＥＴ法を用いて測定した比表面積は１．４ｍ２／ｇであった。リチウム含有複合酸化物のタップ密度を測定したところ１．８ｇ／ｃｍ３であった。 This precursor (20 g) and lithium carbonate (12.8 g) having a lithium content of 26.9 mol / kg were mixed and calcined at 900 ° C. for 12 hours in an oxygen-containing atmosphere to obtain a lithium-containing composite oxide of the example. It was. The composition of the lithium-containing composite oxide of the obtained example is Li (Li 0.2 Ni 0.128 Co 0.134 Mn 0.538 ) O 2 . The average particle diameter D50 of the lithium-containing composite oxide of the example was 8.4 μm, and the specific surface area measured using the nitrogen gas adsorption BET method was 1.4 m 2 / g. When the tap density of the lithium-containing composite oxide was measured, it was 1.8 g / cm 3 .
　次いで、乳酸アルミニウム水溶液（Ａｌ含量４．５質量％、ｐＨ４．６）の７．０ｇに、蒸留水を３．０ｇ加えてアルミニウム化合物が溶解した水溶液（以下、Ａｌ水溶液ともいう。）を調製した。攪拌中の実施例のリチウム含有複合酸化物１０ｇに対して、調製したＡｌ水溶液１ｇをスプレーコート噴霧して添加し、実施例のリチウム含有複合酸化物とＡｌ水溶液とを混合しながら接触させた。 Next, 3.0 g of distilled water was added to 7.0 g of an aluminum lactate aqueous solution (Al content: 4.5 mass%, pH 4.6) to prepare an aqueous solution in which the aluminum compound was dissolved (hereinafter also referred to as an Al aqueous solution). . 1 g of the prepared Al aqueous solution was spray-sprayed and added to 10 g of the lithium-containing composite oxide of the example under stirring, and the lithium-containing composite oxide of the example and the Al aqueous solution were brought into contact with mixing.
　次に、得られた混合物を９０℃で２時間乾燥した後に酸素含有雰囲気下４００℃で８時間加熱し、リチウム含有複合酸化物の表面に被覆層（ＩＩ）を形成して正極活物質（１）を得た。前記Ａｌ水溶液を用いて形成された該被覆層（ＩＩ）はＡｌの酸化物を含む。
　本例で得られた正極活物質（１）において、該被覆層のアルミニウムは、リチウム含有複合酸化物の遷移金属元素であるニッケル、コバルト、マンガンの合計に対して、モル比（被覆量）で｛（被覆層のＡｌのモル数）／（被覆する前のリチウム含有複合酸化物のＮｉ、Ｃｏ、Ｍｎの合計モル数）｝＝０．０１３である。
 [正極活物質（２）］
　ＡＧＣセイミケミカル社製、商品名「セリオンＬ」（ＬｉＮｉ０．５Ｃｏ０．２Ｍｎ０．３Ｏ２、タップ密度２．４ｇ／ｃｍ３、平均粒子径：１２μｍ）を正極活物質（２）として使用した。 Next, the obtained mixture was dried at 90 ° C. for 2 hours, and then heated at 400 ° C. for 8 hours in an oxygen-containing atmosphere to form a coating layer (II) on the surface of the lithium-containing composite oxide to form a positive electrode active material (1 ) The coating layer (II) formed using the Al aqueous solution contains an oxide of Al.
In the positive electrode active material (1) obtained in this example, the aluminum of the coating layer is in a molar ratio (coating amount) with respect to the total of nickel, cobalt, and manganese, which are transition metal elements of the lithium-containing composite oxide. {(Number of moles of Al in coating layer) / (total number of moles of Ni, Co and Mn of lithium-containing composite oxide before coating)} = 0.013.
[Positive electrode active material (2)]
Product name “Selion L” (LiNi 0.5 Co 0.2 Mn 0.3 O 2 , tap density 2.4 g / cm 3 , average particle size: 12 μm) manufactured by AGC Seimi Chemical Co., Ltd., positive electrode active material (2) Used as.
[バインダー組成物の調製例]
　バインダー組成物として、バインダーである含フッ素重合体が、有機溶媒または水に、溶解または分散した溶液を調製した。
（参考例１：含フッ素ゴムＡを含むバインダー組成物の調製）
　攪拌用アンカー翼を備えた内容積３２００ｍＬのステンレス鋼製の耐圧反応器の内部を脱気した後、該反応器に、１７００ｇのイオン交換水、５ｇのリン酸水素二ナトリウム１２水和物、２．０ｇの水酸化ナトリウム、１３．３ｇのラウリル硫酸ナトリウム、および４．４ｇの過硫酸アンモニウムを加えた。
　ついで、７５℃で、ＴＦＥ／Ｐ＝８８／１２（モル比）の単量体混合ガスを、反応器の内圧が２．５０ＭＰａＧになるように圧入した。アンカー翼を３００ｒｐｍで回転させ、重合反応を開始させた。
　重合の進行に伴い、反応器内の圧力が低下するので、反応器の内圧が２．４９ＭＰａＧに降下した時点で、ＴＦＥ／Ｐ＝５６／４４（モル比）の単量体混合ガスを自圧で圧入し、反応器の内圧を２．５１ＭＰａＧまで昇圧させた。これを繰り返し、反応器の内圧を２．４９～２．５１ＭＰａＧに保持し、重合反応を続けた。ＴＦＥ／Ｐの単量体混合ガスの圧入量の総量が９００ｇとなった時点で、反応器の内温を１０℃まで冷却し、重合反応を停止し、微粒子状の含フッ素ゴムＡを含むラテックスを得、これをバインダー組成物とした。重合時間は８時間であった。バインダー組成物中の固形分は３４質量％であった。含フッ素ゴムＡの重量平均分子量は１３万であり、共重合組成は、ＴＦＥに基づく繰り返し単位／Ｐに基づく繰り返し単位＝５６／４４（モル比）であった。得られた含フッ素ゴムのフッ素含有量を表１に示す（以下、同様）。 [Preparation Example of Binder Composition]
As a binder composition, a solution was prepared in which a fluoropolymer as a binder was dissolved or dispersed in an organic solvent or water.
(Reference Example 1: Preparation of binder composition containing fluorine-containing rubber A)
After degassing the inside of a 3200 mL stainless steel pressure-resistant reactor equipped with an anchor blade for stirring, 1700 g of ion exchange water, 5 g of disodium hydrogen phosphate 12 hydrate, 2 0.0 g sodium hydroxide, 13.3 g sodium lauryl sulfate, and 4.4 g ammonium persulfate were added.
Next, a monomer mixed gas of TFE / P = 88/12 (molar ratio) was injected at 75 ° C. so that the internal pressure of the reactor was 2.50 MPaG. The anchor blade was rotated at 300 rpm to initiate the polymerization reaction.
As the polymerization proceeds, the pressure in the reactor decreases. When the internal pressure of the reactor drops to 2.49 MPaG, the monomer mixed gas of TFE / P = 56/44 (molar ratio) is self-pressured. And the internal pressure of the reactor was increased to 2.51 MPaG. This was repeated, and the internal pressure of the reactor was maintained at 2.49 to 2.51 MPaG, and the polymerization reaction was continued. When the total amount of the TFE / P monomer mixed gas injected reaches 900 g, the internal temperature of the reactor is cooled to 10 ° C., the polymerization reaction is stopped, and the latex containing the fine fluorine-containing rubber A This was used as a binder composition. The polymerization time was 8 hours. The solid content in the binder composition was 34% by mass. The weight average molecular weight of the fluorinated rubber A was 130,000, and the copolymer composition was a repeating unit based on TFE / a repeating unit based on P = 56/44 (molar ratio). The fluorine content of the obtained fluorinated rubber is shown in Table 1 (hereinafter the same).
（参考例２：含フッ素ゴムＢを含むバインダー組成物の調製）
　攪拌用アンカー翼を備えた内容積３２００ｍＬのステンレス鋼製の耐圧反応器の内部を脱気した後、該反応器に、１７００ｇのイオン交換水、５８ｇのリン酸水素二ナトリウム１２水和物、１．０ｇの水酸化ナトリウム、９ｇのラウリル硫酸ナトリウム、および４．４ｇの過硫酸アンモニウムを加えた。さらに、２００ｇのイオン交換水に０．４ｇのＥＤＴＡ（エチレンジアミン四酢酸２ナトリウム塩・２水和物）および０．３ｇの硫酸第一鉄７水和物を溶解させた水溶液を、反応器に加えた。
　ついで、２５℃で、ＴＦＥ／Ｐ／ＶｄＦ＝２５／６／６９（モル比）の単量体混合ガスを、反応器の内圧が２．５０ＭＰａＧになるように圧入した。アンカー翼を３００ｒｐｍで回転させ、水酸化ナトリウムでｐＨを１０．０に調整したロンガリットの６．９質量％水溶液（以下、ロンガリット６．９質量％水溶液と記す。）を反応器に加え、重合反応を開始させた。以降、ロンガリット６．９質量％水溶液を、高圧ポンプを用いて連続的に反応器に加えた。
　重合の進行に伴い、反応器内の圧力が低下するので、反応器の内圧が２．４９ＭＰａＧに降下した時点で、ＴＦＥ／Ｐ／ＶｄＦ＝３９／２６／３５（モル比）の単量体混合ガスを自圧で圧入し、反応器の内圧を２．５１ＭＰａＧまで昇圧させた。これを繰り返し、反応器の内圧を２．４９～２．５１ＭＰａＧに保持し、重合反応を続けた。ＴＦＥ／Ｐ／ＶｄＦの単量体混合ガスの圧入量の総量が９００ｇとなった時点で、ロンガリット６．９質量％水溶液の添加を停止し、反応器の内温を１０℃まで冷却し、重合反応を停止し、含フッ素ゴムＢを含むラテックスを得た。ラテックス中の固形分は３４質量％であり、含フッ素ゴムＢの重量平均分子量は２２万であり、共重合組成は、ＴＦＥに基づく繰り返し単位／Ｐに基づく繰り返し単位／ＶｄＦに基づく繰り返し単位＝３９／２６／３５（モル比）であった。
　前記ラテックスに塩化カルシウムの１．５質量％水溶液を添加して、含フッ素ゴムＢを凝集させ、ろ過し、回収した。ついで、含フッ素ゴムＢをイオン交換水により洗浄し、１００℃のオーブンで１５時間乾燥させ、白色の含フッ素ゴムＢを得た。この含フッ素ゴムＢをＮ－メチルピロリドン溶液に溶解し、含フッ素ゴムＢの濃度が１０質量％のバインダー組成物を調製した。 (Reference Example 2: Preparation of binder composition containing fluorine-containing rubber B)
After degassing the inside of a 3200 mL stainless steel pressure-resistant reactor equipped with an anchor blade for stirring, 1700 g of ion-exchange water, 58 g of disodium hydrogen phosphate 12 hydrate, 0.0 g sodium hydroxide, 9 g sodium lauryl sulfate, and 4.4 g ammonium persulfate were added. Further, an aqueous solution in which 0.4 g of EDTA (ethylenediaminetetraacetic acid disodium salt dihydrate) and 0.3 g of ferrous sulfate heptahydrate were dissolved in 200 g of ion-exchanged water was added to the reactor. It was.
Then, a monomer mixed gas of TFE / P / VdF = 25/6/69 (molar ratio) was injected at 25 ° C. so that the internal pressure of the reactor was 2.50 MPaG. The anchor blade was rotated at 300 rpm, and a 6.9% by mass aqueous solution of Rongalite adjusted to pH 10.0 with sodium hydroxide (hereinafter referred to as Rongalit's 6.9% by mass aqueous solution) was added to the reactor, followed by polymerization reaction. Was started. Thereafter, Rongalite 6.9% by mass aqueous solution was continuously added to the reactor using a high-pressure pump.
As the polymerization proceeds, the pressure in the reactor decreases, so when the internal pressure of the reactor drops to 2.49 MPaG, monomer mixing of TFE / P / VdF = 39/26/35 (molar ratio) The gas was injected under its own pressure, and the internal pressure of the reactor was increased to 2.51 MPaG. This was repeated, and the internal pressure of the reactor was maintained at 2.49 to 2.51 MPaG, and the polymerization reaction was continued. When the total amount of TFE / P / VdF monomer mixture gas injection reaches 900 g, the addition of Rongalite 6.9% by mass aqueous solution is stopped, the internal temperature of the reactor is cooled to 10 ° C., and polymerization is performed. The reaction was stopped, and a latex containing fluorine-containing rubber B was obtained. The solid content in the latex is 34% by mass, the weight average molecular weight of the fluorinated rubber B is 220,000, and the copolymer composition is a repeating unit based on TFE / a repeating unit based on P / a repeating unit based on VdF = 39. / 26/35 (molar ratio).
A 1.5% by mass aqueous solution of calcium chloride was added to the latex to agglomerate the fluorinated rubber B, which was filtered and recovered. Next, the fluorinated rubber B was washed with ion-exchanged water and dried in an oven at 100 ° C. for 15 hours to obtain a white fluorinated rubber B. This fluorinated rubber B was dissolved in an N-methylpyrrolidone solution to prepare a binder composition having a fluorinated rubber B concentration of 10% by mass.
（参考例３：含フッ素ゴムＣを含むバインダー組成物の調製）
　バインダーとして、含フッ素ゴムＢの代わりに、ＶｄＦ／ＨＦＰ／ＴＦＥ＝４８／２２／３０（モル比）の含フッ素ゴムＣを用いた以外は参考例２と同様にして、含フッ素ゴムＣが濃度１０質量％でＮ－メチルピロリドンに溶解したバインダー組成物を調製した。 (Reference Example 3: Preparation of binder composition containing fluorine-containing rubber C)
The concentration of the fluorine-containing rubber C was the same as in Reference Example 2 except that the fluorine-containing rubber C of VdF / HFP / TFE = 48/22/30 (molar ratio) was used instead of the fluorine-containing rubber B as the binder. A binder composition dissolved in N-methylpyrrolidone at 10% by mass was prepared.
（参考例４：ポリ四フッ化エチレン水性分散液の調製）
　バインダー組成物として、ポリ四フッ化エチレン水性分散液（旭硝子社製、製品名：Ｆｌｕｏｎ　ＰＴＦＥＡＤ、固形分濃度６０％）を用いた。
（参考例５：ポリフッ化ビニリデン溶液の調製）
　バインダーとして、含フッ素ゴムＢの代わりに、粉末状のポリフッ化ビニリデンを用いた以外は参考例２と同様にして、ポリフッ化ビニリデンが濃度１０質量％でＮ－メチルピロリドンに溶解したバインダー組成物を調製した。
（参考例６：スチレン－ブタジエンゴム溶液の調製）
　バインダーとして、含フッ素ゴムＢの代わりに、スチレン－ブタジエンゴムを用いた以外は参考例２と同様にして、スチレン－ブタジエンゴムが濃度１０質量％でＮ－メチルピロリドンに溶解したバインダー組成物を調製した。 (Reference Example 4: Preparation of polytetrafluoroethylene aqueous dispersion)
As the binder composition, an aqueous polytetrafluoroethylene dispersion (Asahi Glass Co., Ltd., product name: Fluon PTFEAD, solid content concentration 60%) was used.
(Reference Example 5: Preparation of polyvinylidene fluoride solution)
A binder composition in which polyvinylidene fluoride was dissolved in N-methylpyrrolidone at a concentration of 10% by mass in the same manner as in Reference Example 2 except that powdered polyvinylidene fluoride was used in place of fluorine-containing rubber B as a binder. Prepared.
(Reference Example 6: Preparation of styrene-butadiene rubber solution)
A binder composition in which styrene-butadiene rubber was dissolved in N-methylpyrrolidone at a concentration of 10% by mass was prepared in the same manner as in Reference Example 2 except that styrene-butadiene rubber was used in place of fluorine-containing rubber B. did.
[バインダーの機械特性評価］
　各例のバインダー組成物中のバインダーのみ厚さ２ｍｍのシートに圧縮成形し、該シートから３号ダンベルの形状の試験片を切り出し、ＪＩＳＫ６２５１に従い、引張特性（引張強度および引張破断伸び）を評価した。各バインダーの物性評価結果を表１に示す。 [Mechanical property evaluation of binder]
Only the binder in the binder composition of each example was compression-molded into a sheet having a thickness of 2 mm, a test piece having a No. 3 dumbbell shape was cut out from the sheet, and tensile properties (tensile strength and tensile elongation at break) were evaluated according to JISK6251. . Table 1 shows the physical property evaluation results of each binder.
　なお、参考例１のバインダーである含フッ素ゴムＡは、参考例１で得たバインダー組成物に塩化カルシウムの１．５質量％水溶液を添加して、含フッ素ゴムＡを凝集させ、ろ過し、回収し、乾燥させたものを用いた。
　参考例２、３のバインダーである含フッ素ゴムＢ、Ｃは、それぞれ、バインダー組成物の調製に用いた乾燥物の含フッ素ゴムＢ、Ｃを用いた。
　参考例４のバインダーとしては、上記ポリ四フッ化エチレン水性分散液の乾燥物を用いた。
　参考例５のバインダーとしては、上記粉末状のポリフッ化ビニリデンを用いた。
　参考例６のバインダーとしては、上記スチレン－ブタジエンゴムを用いた。 In addition, the fluorine-containing rubber A which is a binder of Reference Example 1 was added to the binder composition obtained in Reference Example 1 by adding a 1.5% by mass aqueous solution of calcium chloride to aggregate the fluorine-containing rubber A, and filtered. The recovered and dried product was used.
As the fluorine-containing rubbers B and C which are binders of Reference Examples 2 and 3, the dried fluorine-containing rubbers B and C used for preparing the binder composition were used, respectively.
As the binder of Reference Example 4, a dried product of the above polytetrafluoroethylene aqueous dispersion was used.
As the binder of Reference Example 5, the above powdery polyvinylidene fluoride was used.
As the binder of Reference Example 6, the above styrene-butadiene rubber was used.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
（実施例１）
　粘度調整剤としてのカルボキシメチルセルロースナトリウムの２質量％水溶液１０質量部、上記で製造した正極活物質（１）とアセチレンブラックを混合し、固形分濃度が７０質量％となるように水を加えて攪拌したのち、参考例１で得られた含フッ素ゴムＡを含むバインダー組成物を加えて攪拌し、均一なスラリー（混合物）を作製した。このスラリーを、厚さ２０μｍのアルミニウム箔（正極集電体）に、ドクターブレードを用いて片面塗工した。そして、１２０℃で熱処理して乾燥させ、ロールプレス圧延を２回行うことにより、正極体シートを作製した。この際、正極活物質／アセチレンブラック／バインダー（含フッ素ゴムＡ）の質量比は８５／１５／５とした。正極材シートは正極活物質層と正極集電体との密着性が良好であった。
　得られた正極体シートを正極に用い、ステンレス鋼製簡易密閉セル型のリチウムイオン二次電池をアルゴングローブボックス内で組み立てた。この際、厚さ５００μｍの金属リチウム箔を負極に用い、負極集電体に厚さ１ｍｍのステンレス板を使用し、セパレータには厚さ２５μｍの多孔質ポリプロピレンを用い、さらに、電解液には濃度１ｍｏｌ／ｄｍ３のＬｉＰＦ６／ＥＣ（エチレンカーボネート）＋ＤＥＣ（ジエチルカーボネート）（１：１）溶液（ＬｉＰＦ６を溶質とするＥＣとＤＥＣとの体積比（ＥＣ：ＤＥＣ＝１：１）の混合溶液を意味する。）を用いた。 Example 1
10 parts by weight of a 2% by weight aqueous solution of sodium carboxymethylcellulose as a viscosity modifier, the positive electrode active material (1) prepared above and acetylene black are mixed, and water is added so that the solid content concentration becomes 70% by weight. After that, the binder composition containing the fluorinated rubber A obtained in Reference Example 1 was added and stirred to prepare a uniform slurry (mixture). This slurry was applied on one side to a 20 μm thick aluminum foil (positive electrode current collector) using a doctor blade. And it heat-processed at 120 degreeC, it was made to dry, and the positive electrode sheet | seat was produced by performing roll press rolling twice. At this time, the mass ratio of positive electrode active material / acetylene black / binder (fluorinated rubber A) was 85/15/5. The positive electrode material sheet had good adhesion between the positive electrode active material layer and the positive electrode current collector.
Using the obtained positive electrode sheet as a positive electrode, a stainless steel simple sealed cell type lithium ion secondary battery was assembled in an argon glove box. At this time, a metal lithium foil having a thickness of 500 μm is used for the negative electrode, a stainless steel plate having a thickness of 1 mm is used for the negative electrode current collector, a porous polypropylene having a thickness of 25 μm is used for the separator, and a concentration is used for the electrolyte. 1 mol / dm 3 LiPF 6 / EC (ethylene carbonate) + DEC (diethyl carbonate) (1: 1) solution (mixed solution of EC and DEC in volume ratio (EC: DEC = 1: 1) using LiPF 6 as a solute) Is used.)
　前記で製造したリチウムイオン二次電池を用いて下記の評価を行った。
　すなわち、正極活物質１ｇにつき２０ｍＡの負荷電流で４．６Ｖまで充電し、正極活物質１ｇにつき２０ｍＡの負荷電流にて２．５Ｖまで放電した。このときの放電容量を初回放電容量とする。初回放電容量は２７０ｍＡｈ／ｇであった。
　次いで、充放電正極活物質１ｇにつき６０ｍＡの負荷電流で４．６Ｖまで充電し、正極活物質１ｇにつき６０ｍＡの負荷電流にて２．５Ｖまで放電することをさらに９９回繰り返した。９９回目の放電容量／初回放電容量をサイクル維持率とする。サイクル維持率は９６％であった。 The following evaluation was performed using the lithium ion secondary battery manufactured above.
That is, it charged to 4.6V with a load current of 20 mA per 1 g of the positive electrode active material, and discharged to 2.5 V with a load current of 20 mA per 1 g of the positive electrode active material. The discharge capacity at this time is defined as the initial discharge capacity. The initial discharge capacity was 270 mAh / g.
Next, charging to 4.6 V with a load current of 60 mA per 1 g of the charge / discharge positive electrode active material and discharging to 2.5 V with a load current of 60 mA per 1 g of the positive electrode active material were further repeated 99 times. The 99th discharge capacity / initial discharge capacity is defined as a cycle maintenance ratio. The cycle maintenance rate was 96%.
（実施例２）
　上記で製造した正極活物質（１）とアセチレンブラックを混合し、参考例２で得られた含フッ素ゴムＢを含むバインダー組成物、およびＮ－メチルピロリドンを加えて攪拌し、固形分濃度が６５質量％である均一なスラリーを作製した。正極活物質／アセチレンブラック／バインダー（含フッ素ゴムＢ）の質量比は８５／１５／５とした。以降は実施例１と同様に行った。 (Example 2)
The positive electrode active material (1) produced above and acetylene black are mixed, the binder composition containing the fluorinated rubber B obtained in Reference Example 2 and N-methylpyrrolidone are added and stirred, and the solid content concentration is 65 A uniform slurry having a mass% was prepared. The mass ratio of positive electrode active material / acetylene black / binder (fluorinated rubber B) was 85/15/5. Thereafter, the same procedure as in Example 1 was performed.
（実施例３）
　バインダー組成物として参考例３に示すバインダー組成物を用いた以外は実施例２と同様に行う。
（比較例１）
　バインダー組成物として参考例４に示すバインダー組成物を用いた以外は実施例１と同様に行う。得られた正極体シートは正極活物質層と集電体との密着性が不十分で剥離してしまう。電池評価は剥離しなかった正極体シートで行う。
（比較例２）
　バインダー組成物として参考例５に示すバインダー組成物を用いた以外は実施例２と同様に行う。得られた正極体シートの一部は正極活物質層と集電体との密着性が不十分で剥離してしまう。電池評価は剥離しなかった正極体シートで行う。
（比較例３）
　バインダー組成物として参考例６に示すバインダー組成物を用いた以外は実施例２と同様に行う。
（比較例４）
　正極活物質（１）を正極活物質（２）に変更した以外は、実施例１と同様に行う。 (Example 3)
The same procedure as in Example 2 was performed except that the binder composition shown in Reference Example 3 was used as the binder composition.
(Comparative Example 1)
The same procedure as in Example 1 was performed except that the binder composition shown in Reference Example 4 was used as the binder composition. The obtained positive electrode body sheet peels off due to insufficient adhesion between the positive electrode active material layer and the current collector. The battery evaluation is performed on the positive electrode sheet that was not peeled off.
(Comparative Example 2)
It carries out similarly to Example 2 except having used the binder composition shown in the reference example 5 as a binder composition. Part of the obtained positive electrode sheet is peeled off due to insufficient adhesion between the positive electrode active material layer and the current collector. The battery evaluation is performed on the positive electrode sheet that was not peeled off.
(Comparative Example 3)
The same procedure as in Example 2 was performed except that the binder composition shown in Reference Example 6 was used as the binder composition.
(Comparative Example 4)
The same procedure as in Example 1 was performed except that the positive electrode active material (1) was changed to the positive electrode active material (2).
（評価）
　実施例１～３および比較例１～４の結果を表２に示す。なお、密着性は、ＪＩＳＫ５４００の碁盤目剥離試験により評価した。すなわち、作製した正極体シート塗膜にカッターナイフで１ｍｍ間隔の碁盤目状の切込みを入れ、セロハンテープ（商品名、ニチバン社製）を貼り付けた後、剥離し残存する目数を計測して評価する。残存する目数が７０％以上のものを○、４０％超～７０％未満を△、４０％未満を×とする。
　初回放電容量は２５０ｍＡｈ／ｇ超を○、２００～２５０ｍＡｈ／ｇを△、２００ｍＡｈ／ｇ未満を×とする。
　サイクル維持率は９０％超を○、８０～９０％を△、８０％未満を×とする。 (Evaluation)
The results of Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 2. The adhesion was evaluated by a cross-cut peel test of JISK5400. That is, a grid-like cut with a 1 mm interval was made with a cutter knife in the produced positive electrode sheet coating film, cellophane tape (trade name, manufactured by Nichiban Co., Ltd.) was applied, and the number of peeled and remaining eyes was measured. evaluate. The number of remaining eyes is 70% or more, ◯, more than 40% to less than 70% is represented by Δ, and less than 40% is represented by ×.
The initial discharge capacity is over 250 mAh / g, ◯, 200 to 250 mAh / g is Δ, and less than 200 mAh / g is x.
The cycle maintenance rate is over 90% as ◯, 80 to 90% as △, and less than 80% as x.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　実施例１～実施例３および比較例１～４の結果より、本発明のリチウムイオン二次電池用正極を適用してリチウムイオン二次電池を構成した場合には、初期放電容量が高く、また、優れたサイクル維持率が得られることが明らかとなる。比較例１、比較例２のバインダーを用いた場合はバインダーの引張破断伸びが小さくゴム弾性を有さないため、正極活物質を高充填した場合に集電体との密着性が不十分である。比較例３のバインダーはフッ素含有量が小さいため耐電圧性が不十分であり、初期放電容量とサイクル維持率に劣る。実施例１、実施例２で用いたバインダーはＴＦＥに基づく繰り返し単位とＰに基づく繰り返し単位を有するため、実施例３で用いたバインダーよりも耐アルカリ性が高い。このため実施例１と実施例２では特にサイクル維持率が高い。
　比較例４は、正極活物質として使用したリチウム含有複合酸化物におけるＬｉ元素のモル量が遷移金属元素の総モル量の１．０倍と少ないため、初期放電容量に劣る。 From the results of Examples 1 to 3 and Comparative Examples 1 to 4, when the lithium ion secondary battery was configured by applying the positive electrode for a lithium ion secondary battery of the present invention, the initial discharge capacity was high, It is clear that an excellent cycle maintenance ratio can be obtained. When the binders of Comparative Examples 1 and 2 are used, the tensile elongation at break of the binder is small and the rubber does not have elasticity. Therefore, when the positive electrode active material is highly filled, the adhesion with the current collector is insufficient. . Since the binder of Comparative Example 3 has a low fluorine content, the voltage resistance is insufficient, and the initial discharge capacity and cycle retention rate are inferior. Since the binder used in Example 1 and Example 2 has a repeating unit based on TFE and a repeating unit based on P, the alkali resistance is higher than that of the binder used in Example 3. For this reason, in Example 1 and Example 2, a cycle maintenance factor is especially high.
Comparative Example 4 is inferior in the initial discharge capacity because the molar amount of Li element in the lithium-containing composite oxide used as the positive electrode active material is as small as 1.0 times the total molar amount of transition metal elements.
　本発明によれば、単位質量あたりの放電容量が高く、かつ、サイクル特性に優れるリチウムイン二次電池用正極を得ることができる。正極は、携帯電話等の電子機器、車載用のリチウムイオン二次電池用に利用できる。
　なお、２０１１年１０月１４日に出願された日本特許出願２０１１－２２６７６３号の明細書、特許請求の範囲、及び要約書の全内容をここに引用し、本発明の明細書の開示として、取り入れるものである。 According to the present invention, a positive electrode for a lithium-in secondary battery having a high discharge capacity per unit mass and excellent cycle characteristics can be obtained. The positive electrode can be used for electronic devices such as mobile phones and lithium ion secondary batteries for vehicles.
It should be noted that the entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2011-226863 filed on October 14, 2011 are incorporated herein as the disclosure of the specification of the present invention. Is.

Claims (10)

  1. 　正極活物質、バインダー、および導電材を含む正極活物質層が正極集電体の表面上に形成されたリチウムイオン二次電池用正極であって、
    　前記正極活物質が、Ｌｉ元素と、Ｎｉ、Ｃｏ、およびＭｎからなる群より選ばれる少なくとも１種の遷移金属元素とを含む（ただし、Ｌｉ元素のモル量が該遷移金属元素の総モル量に対して１．２倍超である。）リチウム含有複合酸化物を含み、
    　前記バインダーが、四フッ化エチレン、ヘキサフルオロプロピレン、およびフッ化ビニリデンからなる群より選ばれる少なくとも１種の単量体に基づく繰り返し単位を有する共重合体からなり、フッ素含有量が５０～７６質量％である含フッ素ゴムを含むことを特徴とするリチウムイオン二次電池用正極。     A positive electrode for a lithium ion secondary battery in which a positive electrode active material layer including a positive electrode active material, a binder, and a conductive material is formed on the surface of a positive electrode current collector,
    The positive electrode active material contains Li element and at least one transition metal element selected from the group consisting of Ni, Co, and Mn (provided that the molar amount of Li element is the total molar amount of the transition metal element) More than 1.2 times) including a lithium-containing composite oxide;
    The binder comprises a copolymer having a repeating unit based on at least one monomer selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride, and has a fluorine content of 50 to 76 mass. %, A positive electrode for a lithium ion secondary battery.
  2. 　前記リチウム含有複合酸化物の表面にＭｇ、Ｃａ、Ｓｒ、Ｂａ、Ｔｉ、Ｚｒ、Ｈｆ、Ｎｂ、Ｔａ、Ａｌ、Ｇａ、Ｙ、Ｌａ、Ｃｅ、Ｎｄ、Ｇｄ、およびＥｒからなる群より選ばれる少なくとも１種の金属元素を含む酸化物からなる被覆層が形成されている請求項１に記載のリチウムイオン二次電池用正極。 At least selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Al, Ga, Y, La, Ce, Nd, Gd, and Er on the surface of the lithium-containing composite oxide The positive electrode for a lithium ion secondary battery according to claim 1, wherein a coating layer made of an oxide containing one kind of metal element is formed.
  3. 　前記バインダーが、四フッ化エチレンに基づく繰り返し単位およびプロピレンに基づく繰り返し単位を有する共重合体からなる含フッ素ゴムを含む請求項１または２に記載のリチウムイオン二次電池用正極。 The positive electrode for a lithium ion secondary battery according to claim 1 or 2, wherein the binder includes a fluorine-containing rubber made of a copolymer having a repeating unit based on tetrafluoroethylene and a repeating unit based on propylene.
  4. 　前記四フッ化エチレンに基づく繰り返し単位およびプロピレンに基づく繰り返し単位を有する共重合体が、四フッ化エチレンに基づく繰り返し単位／プロピレンに基づく繰り返し単位の比率４０～７０／６０～３０（モル％）を有する請求項３に記載のリチウムイオン二次電池用正極。 The copolymer having a repeating unit based on tetrafluoroethylene and a repeating unit based on propylene has a ratio of 40 to 70/60 to 30 (mol%) of the repeating unit based on ethylene tetrafluoride / the repeating unit based on propylene. The positive electrode for a lithium ion secondary battery according to claim 3.
  5. 　前記バインダーが、四フッ化エチレンに基づく繰り返し単位、プロピレンに基づく繰り返し単位、およびフッ化ビニリデンに基づく繰り返し単位を有する共重合体からなる含フッ素ゴムを含む請求項１または２に記載のリチウムイオン二次電池用正極。 3. The lithium ion catalyst according to claim 1, wherein the binder comprises a fluorine-containing rubber comprising a copolymer having a repeating unit based on ethylene tetrafluoride, a repeating unit based on propylene, and a repeating unit based on vinylidene fluoride. Positive electrode for secondary battery.
  6. 　前記四フッ化エチレンに基づく繰り返し単位、プロピレンに基づく繰り返し単位、およびフッ化ビニリデンに基づく繰り返し単位を有する共重合体が、四フッ化エチレンに基づく繰り返し単位／プロピレンに基づく繰り返し単位／フッ化ビニリデンに基づく繰り返し単位の比率３０～７０／２０～６０／１～４０（モル％）を有する請求項５に記載のリチウムイオン二次電池用正極。 The copolymer having a repeating unit based on ethylene tetrafluoride, a repeating unit based on propylene, and a repeating unit based on vinylidene fluoride is a repeating unit based on ethylene tetrafluoride / a repeating unit based on propylene / vinylidene fluoride. 6. The positive electrode for a lithium ion secondary battery according to claim 5, having a ratio of repeating units based on 30 to 70/20 to 60/1 to 40 (mol%).
  7. 　請求項１～６のいずれか一項に記載のリチウムイオン二次電池用正極を製造する方法であって、前記正極活物質と前記バインダーを混合して混合物を得る混合工程と、該混合物を熱処理する工程を含むリチウムイオン二次電池用正極の製造方法。 A method for producing a positive electrode for a lithium ion secondary battery according to any one of claims 1 to 6, comprising a mixing step of mixing the positive electrode active material and the binder to obtain a mixture, and heat-treating the mixture. The manufacturing method of the positive electrode for lithium ion secondary batteries including the process to carry out.
  8. 　前記混合工程において、有機溶媒中で前記正極活物質と前記バインダーとを混合する請求項７に記載のリチウムイオン二次電池用正極の製造方法。 The method for producing a positive electrode for a lithium ion secondary battery according to claim 7, wherein the positive electrode active material and the binder are mixed in an organic solvent in the mixing step.
  9. 　前記混合工程において、水性分散媒中で前記正極活物質と前記バインダーとを混合する請求項７に記載のリチウムイオン二次電池用正極の製造方法。 The method for producing a positive electrode for a lithium ion secondary battery according to claim 7, wherein in the mixing step, the positive electrode active material and the binder are mixed in an aqueous dispersion medium.
  10. 　請求項１～６のいずれか一項に記載のリチウムイオン二次電池用正極と、負極と、非水電解質とを含むリチウムイオン二次電池。 A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to any one of claims 1 to 6, a negative electrode, and a nonaqueous electrolyte.
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