WO2017013827A1 - Lithium ion secondary battery - Google Patents

Lithium ion secondary battery Download PDF

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WO2017013827A1
WO2017013827A1 PCT/JP2016/002784 JP2016002784W WO2017013827A1 WO 2017013827 A1 WO2017013827 A1 WO 2017013827A1 JP 2016002784 W JP2016002784 W JP 2016002784W WO 2017013827 A1 WO2017013827 A1 WO 2017013827A1
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active material
negative electrode
electrode active
positive electrode
ion secondary
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PCT/JP2016/002784
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French (fr)
Japanese (ja)
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達哉 江口
三好　学
斉藤　淳志
孝二 岩田
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株式会社豊田自動織機
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Priority to JP2017529437A priority Critical patent/JPWO2017013827A1/en
Publication of WO2017013827A1 publication Critical patent/WO2017013827A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0568—Liquid materials characterised by the solutes
    • 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
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • 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
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H01M50/491—Porosity
    • 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 lithium ion secondary battery.
  • non-aqueous electrolyte secondary batteries are recognized as essential for portable devices such as mobile phones and laptop computers.
  • non-aqueous electrolyte secondary batteries lithium ion secondary batteries are widely used because of their small size and large capacity. Lithium ion secondary batteries are also used in aircraft and automobiles.
  • lithium ion secondary batteries As negative electrode active materials for lithium ion secondary batteries, silicon-based materials such as silicon, silicon alloys, and silicon oxides having charge / discharge capacities far exceeding the theoretical capacity of carbon materials have been studied.
  • Patent Document 1 International Publication No. 2014/080608
  • CaSi 2 and an acid are reacted to synthesize a layered silicon compound containing layered polysilane as a main component, and the layered silicon compound is heated at 300 ° C. or higher.
  • a silicon material is manufactured by heating, and a lithium ion secondary battery including the silicon material as an active material.
  • Patent Document 2 Japanese Patent Laid-Open No. 2003-157854
  • Japanese Patent Laid-Open No. 2003-157854 describes a lithium ion secondary battery that did not ignite even when a nail penetration test was performed.
  • the electrode is divided into sheets having a specific shape.
  • the area and shape of the sheet into which the electrode is divided and the distance between the positive electrode current collector and the negative electrode current collector are defined by a certain relational expression, and the lithium ion secondary battery Multiple restrictions were imposed on the components.
  • Patent Document 3 Japanese Patent Application Laid-Open No. 2008-198591 discloses lithium ions in which an insulating member is interspersed at the interface between the current collector and the electrode mixture layer to increase the resistance between the positive electrode and the negative electrode. According to the secondary battery, it is disclosed that smoke does not occur even when a nail penetration test is performed. However, with the technique disclosed in Patent Document 3, there is a concern that the resistance as a battery increases and the output characteristics deteriorate.
  • the present invention has been made in view of such circumstances, and an object thereof is to provide a lithium ion secondary battery having high safety when an internal short circuit occurs.
  • a positive electrode active material containing a lithium nickel cobalt manganese composite oxide and a lithium iron phosphate compound and a silicon material having a structure in which a plate-like silicon body is laminated in the thickness direction It has been found that a lithium ion secondary battery having a negative electrode active material containing can withstand a nail penetration test and has high safety even during an internal short circuit.
  • the lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte
  • the positive electrode has a positive electrode active material layer including a positive electrode active material
  • the positive electrode active material is represented by the following formula ( 1) comprising a lithium nickel cobalt manganese composite oxide represented by the following formula and a lithium iron phosphate compound represented by the following formula (2), Li a Ni b Co c Mn (1-bcd) M 1 d O (2-e) (1)
  • M 1 represents at least one selected from the group consisting of Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr and W.
  • A, b, c, d and e are 0.8 ⁇ a ⁇ 1.2, 0 ⁇ b ⁇ 0.5, 0 ⁇ c ⁇ 0.5, 0 ⁇ d ⁇ 0.5, b + c + d ⁇ 1 , -0.1 ⁇ e ⁇ 0.2.)
  • Li p Fe q M 2 (1-q) PO 4 (2) (In the formula (2), M 2 is at least one of the group consisting of Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W and Zr.
  • the negative electrode has a negative electrode active material layer containing a negative electrode active material, and the negative electrode active material contains a silicon material having a structure in which plate-like silicon bodies are laminated in the thickness direction.
  • the density of the positive electrode active material layer is preferably 2.5 g / cm 3 or more and 3.5 g / cm 3 or less, and the density of the negative electrode active material layer is preferably 0.5 g / cm 3 or more and 2 g / cm 3 or less. .
  • the content of the silicon material is preferably 30 parts by mass or more and 80 parts by mass or less when the negative electrode active material layer is 100 parts by mass.
  • the content of the lithium nickel cobalt manganese composite oxide is preferably 50 parts by mass or more and 80 parts by mass or less when the positive electrode active material layer is 100 parts by mass, and the content of the lithium iron phosphate compound is positive electrode When the active material layer is 100 parts by mass, it is preferably 20 parts by mass or more and 40 parts by mass or less.
  • the separator preferably includes a porous film made of synthetic resin.
  • the non-aqueous electrolyte includes an electrolyte salt and a non-aqueous solvent
  • the electrolyte salt includes lithium hexafluorophosphate
  • the non-aqueous solvent includes fluoroethylene carbonate, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate. preferable.
  • the synergistic effect by using the specific negative electrode active material and the specific positive electrode active material a good result is obtained in the nail penetration test, and an excessive temperature rise at the time of short circuit is achieved. Can be suppressed.
  • FIG. 6 is a graph showing the relationship between the cell surface temperature, which is the nail penetration test result of the laminated lithium ion secondary batteries of Examples 1 to 7, and the mass part of the silicon material of each negative electrode.
  • the numerical range “a to b” described in this specification includes the lower limit “a” and the upper limit “b”.
  • the numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples.
  • numerical values arbitrarily selected from the numerical value range can be used as upper and lower numerical values.
  • the lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte.
  • the positive electrode has a positive electrode active material layer containing a positive electrode active material.
  • the positive electrode active material layer is disposed on the surface of the current collector.
  • a current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery.
  • the current collector material include metal materials such as stainless steel, titanium, nickel, aluminum, and copper, or conductive resins.
  • the material for the current collector is preferably aluminum or copper.
  • the current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like.
  • a metal foil such as a copper foil, a nickel foil, an aluminum foil, or a stainless steel foil can be suitably used.
  • the thickness of the current collector is preferably 10 ⁇ m to 50 ⁇ m.
  • the thickness of the current collector is particularly preferably 12 ⁇ m to 30 ⁇ m from the viewpoint of increasing battery capacity while maintaining high strength in the current collector.
  • the positive electrode active material layer has a positive electrode active material.
  • the positive electrode active material layer may include a binder and a conductive additive as necessary.
  • the positive electrode active material contains a lithium nickel cobalt manganese composite oxide represented by the following formula (1) and a lithium iron phosphate compound represented by the following formula (2).
  • M 1 represents at least one selected from the group consisting of Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr and W.
  • A, b, c, d and e are 0.8 ⁇ a ⁇ 1.2, 0 ⁇ b ⁇ 0.5, 0 ⁇ c ⁇ 0.5, 0 ⁇ d ⁇ 0.5, b + c + d ⁇ 1 , -0.1 ⁇ e ⁇ 0.2.
  • M 2 is at least one of the group consisting of Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W and Zr.
  • P is a value in the range of 0.9 ⁇ p ⁇ 1.1
  • q is a value in the range of 0 ⁇ q ⁇ 1)
  • lithium nickel cobalt manganese composite oxide represented by the formula (1) examples include LiCo 1/3 Ni 1/3 Mn 1/3 O 2 , LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0. .5 Co 0.2 Mn 0.3 O 2 and the like.
  • the lithium iron phosphate compound represented by the formula (2) include LiFePO 4.
  • the lithium ion secondary battery can obtain a higher energy density.
  • the lithium ion secondary battery is expected to be highly safe because the positive electrode active material contains a lithium iron phosphate compound represented by the formula (2).
  • the lithium iron phosphate compound represented by the formula (2) has an olivine type structure.
  • the olivine structure is based on hexagonal close-packing of oxygen, and phosphorus is located at the tetrahedral site and lithium and iron are located at the octahedral site.
  • a lithium iron phosphate compound having an olivine structure is less likely to release oxygen even at high temperatures because phosphorus and oxygen are covalently bonded.
  • the safety of the lithium ion secondary battery can be improved by using a lithium iron phosphate compound having an olivine type structure as the positive electrode active material of the lithium ion secondary battery.
  • the lithium iron phosphate compound represented by the formula (2) is preferably a carbon-coated surface.
  • the lithium ion secondary battery is higher. Energy density can be obtained and safety can be improved.
  • the content of the lithium nickel cobalt manganese composite oxide is preferably 50 parts by mass or more and 80 parts by mass or less, and 58 parts by mass or more and 78 parts by mass when the positive electrode active material layer is 100 parts by mass. More preferably, it is 65 parts by mass or more and 75 parts by mass or less, and the content of the lithium iron phosphate compound is 20 parts by mass when the positive electrode active material layer is 100 parts by mass. It is preferably no less than 40 parts by mass and no greater than 40 parts by mass, more preferably no less than 22 parts by mass and no greater than 35 parts by mass, and even more preferably no less than 24 parts by mass and no greater than 30 parts by mass.
  • the positive electrode active material layer may further include other lithium-containing oxides, other metal oxides, and other positive electrode active materials.
  • the positive electrode active material is preferably in the form of a powder having an average particle diameter D 50 of 1 ⁇ m to 20 ⁇ m.
  • the average particle diameter D 50 of the positive electrode active material is small, the specific surface area of the positive electrode active material is increased. Therefore, the average particle diameter D 50 of the positive electrode active material is too small, will be the reaction area of the cathode active material and an electrolytic solution is excessively increased, resulting in promoted decomposition of the electrolytic solution, the lithium ion secondary The cycle characteristics of the secondary battery may be deteriorated.
  • the average particle diameter D 50 of the positive electrode active material is too large, resistance of the lithium ion secondary battery increases, there is a possibility that the output characteristics of the lithium ion secondary battery decreases.
  • the average particle diameter D 50 refers to the particle size cumulative value of the volume distribution in the particle size distribution measurement by laser diffraction method is equivalent to 50%. That is, the average particle diameter D 50 means the median size measured by volume.
  • the binder plays a role of connecting the positive electrode active material to the current collector.
  • the binder for example, polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene / hexafluoropropylene copolymer (abbreviation FEP), fluorine-containing resin such as fluoro rubber, polypropylene, thermoplastic resin such as polyethylene, polyimide, Examples thereof include imide resins such as polyamide imide, acrylic resins such as poly (meth) acrylic acid, alkoxysilyl group-containing resins, styrene / butadiene rubber, carboxymethyl cellulose, polyethylene glycol, and polyacrylonitrile.
  • Positive electrode active material: binding agent 1: 0.005 to 1: 0.2 is more preferable, and 1: 0.01 to 1: 0.15 is further preferable. If the amount of the binder is too small, the moldability of the electrode may be lowered, and if the amount of the binder is too large, the energy density of the electrode may be lowered.
  • the conductive additive is added to the positive electrode active material layer as necessary in order to increase the conductivity of the electrode.
  • Carbon black, graphite, acetylene black (abbreviated as AB), ketjen black (registered trademark) (abbreviated as KB), vapor-grown carbon fiber (abbreviated as VGCF), etc., which are carbonaceous fine particles, are used alone or in combination as conductive aids. These can be used in combination.
  • the amount of the conductive aid used is not particularly limited, but can be, for example, about 1 to 30 parts by mass with respect to 100 parts by mass of the active material contained in the electrode.
  • a positive electrode active material layer-forming composition containing a positive electrode active material, a binder, and, if necessary, a conductive additive is prepared.
  • An appropriate solvent may be added to the product to form a paste, which may be applied to the surface of the current collector and then dried.
  • a coating method of the composition for forming a positive electrode active material layer conventionally known methods such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, a curtain coating method, a lip coating method, a comma coating method, and a die coating method are known. A method may be used.
  • solvent for adjusting the viscosity water, N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone and the like can be used.
  • the density of the positive electrode active material layer is preferably 2.5 g / cm 3 or more and 3.5 g / cm 3 or less, more preferably 2.6 g / cm 3 or more and 3.2 g / cm 3 or less. particularly preferably .8g / cm 3 or more 3.0 g / cm 3 or less.
  • the negative electrode has a negative electrode active material layer containing a negative electrode active material.
  • the negative electrode active material layer is disposed on the surface of the current collector.
  • the current collector is the same as that described for the positive electrode.
  • the negative electrode active material layer has a negative electrode active material.
  • the negative electrode active material layer may contain a binder and a conductive additive as necessary.
  • the binder and the conductive assistant are the same as those described for the positive electrode.
  • the negative electrode active material includes a silicon material having a structure in which plate-like silicon bodies are laminated in the thickness direction.
  • the structure of a silicon material having a structure in which plate-like silicon bodies are laminated in the thickness direction can be confirmed by observation with a scanning electron microscope or the like.
  • the plate-like silicon body has a thickness in the range of 10 nm to 100 nm for efficient insertion and removal of lithium ions. Are preferred, and those in the range of 20 nm to 50 nm are more preferred.
  • the length of the plate-like silicon body in the major axis direction is preferably in the range of 0.1 ⁇ m to 50 ⁇ m.
  • the plate-like silicon body preferably has a (length in the long axis direction) / (thickness) range of 2 to 1000.
  • the silicon material may be pulverized or classified to form particles having a certain particle size distribution.
  • D 50 can be exemplified within a range of 1 ⁇ m to 30 ⁇ m when measured by a general laser diffraction type particle size distribution measuring apparatus.
  • the silicon crystallite size is preferably nano-sized. Specifically, the silicon crystallite size is preferably in the range of 0.5 nm to 300 nm, more preferably in the range of 1 nm to 100 nm, further preferably in the range of 1 nm to 50 nm, and particularly in the range of 1 nm to 10 nm. preferable.
  • the silicon material can be manufactured by the following manufacturing process.
  • the production process includes a process of producing a layered silicon compound mainly composed of layered polysilane by reacting CaSi 2 and an acid, and a process of producing a silicon material by heating the layered silicon compound at 300 ° C. or higher.
  • CaSi 2 generally has a structure in which a Ca layer and a Si layer are laminated.
  • CaSi 2 may be synthesized by a known production method, or a commercially available one may be adopted.
  • CaSi 2 used for producing the layered silicon compound is preferably pulverized in advance.
  • Acids include hydrogen fluoride, hydrogen chloride, hydrogen bromide, hydrogen iodide, sulfuric acid, nitric acid, phosphoric acid, formic acid, acetic acid, methanesulfonic acid, tetrafluoroboric acid, hexafluorophosphoric acid, hexafluoroarsenic acid, fluoro Examples include antimonic acid, hexafluorosilicic acid, hexafluorogermanic acid, hexafluorotin (IV) acid, trifluoroacetic acid, hexafluorotitanic acid, hexafluorozirconic acid, trifluoromethanesulfonic acid, and fluorosulfonic acid. These acids may be used alone or in combination.
  • the acid is used as an aqueous solution from the viewpoint of easy work and safety, and removal of by-products.
  • Acid may be used in an amount capable of providing 2 or more equivalents of protons relative CaSi 2. Therefore, if a monovalent acid, the acid may be used in two moles or more relative to CaSi 2 1 mol.
  • the reaction conditions are preferably a reduced pressure condition such as vacuum or an inert gas atmosphere, and a temperature condition of room temperature or lower such as an ice bath. What is necessary is just to set reaction time suitably.
  • Si 6 H 6 which is polysilane corresponds to an ideal layered silicon compound. This reaction can also be considered to form a Si—H bond while Ca in the layered CaSi 2 is substituted with 2H.
  • the layered silicon compound has a layer shape because the basic skeleton of the Si layer in the raw material CaSi 2 is maintained.
  • the acid is preferably used as an aqueous solution in the reaction step of reacting CaSi 2 with the acid.
  • Si 6 H 6 can react with water, the layered silicon compound is rarely obtained only with a compound of Si 6 H 6 , and contains an element derived from oxygen or an acid.
  • ⁇ Heat is released from the layered silicon compound at 300 ° C. or higher to obtain a silicon material.
  • the process of heating the layered silicon compound at 300 ° C. or higher is sometimes referred to as a silicon material manufacturing process.
  • the silicon material manufacturing process is shown as an ideal reaction formula as follows.
  • the layered silicon compound actually used in the silicon material manufacturing process contains oxygen and acid-derived elements and also contains inevitable impurities
  • the actually obtained silicon material also contains oxygen and acid-derived elements. Further, inevitable impurities are also contained.
  • the molar amount of silicon when the molar amount of silicon is 100, the molar amount of oxygen element is preferably 50 or less, and particularly preferably 40 or less.
  • the molar amount of silicon when the molar amount of silicon is 100, the molar amount of the acid-derived element is preferably 8 or less, and particularly preferably 5 or less.
  • the silicon material production process is preferably performed in a non-oxidizing atmosphere having a lower oxygen content than in normal air.
  • the non-oxidizing atmosphere include a reduced pressure atmosphere including a vacuum and an inert gas atmosphere.
  • the heating temperature is preferably in the range of 350 ° C. to 1200 ° C., more preferably in the range of 400 ° C. to 1200 ° C. If the heating temperature is too low, hydrogen may not be released sufficiently, while if the heating temperature is too high, energy is wasted. What is necessary is just to set a heating time suitably according to heating temperature, and it is also preferable to determine a heating time, measuring the quantity of hydrogen etc. which escapes out of a reaction system.
  • the ratio of amorphous silicon and silicon crystallites contained in the silicon material to be manufactured, and the size of the silicon crystallites can also be adjusted, and further manufactured.
  • the shape and size of a nano-level layer containing amorphous silicon and silicon crystallites contained in the silicon material can also be prepared.
  • the silicon material covered with carbon may be only amorphous carbon, may be crystalline carbon, or may be a mixture of amorphous carbon and crystalline carbon.
  • the method for coating the silicon material with carbon is not particularly limited.
  • Carbon coating methods include mixing carbon powder and silicon material (for example, mechanical milling), heating the mixture obtained from the composite of resin and silicon material, and carbonizing the resin, and non-oxidizing silicon material. Examples thereof include a method (thermal CVD method) in which the organic gas is carbonized by being brought into contact with the organic gas in an atmosphere and heated.
  • the content of the silicon material in the negative electrode active material layer is preferably 30 parts by mass or more and 85 parts by mass or less, and preferably 40 parts by mass or more and 80 parts by mass or less when the negative electrode active material layer is 100 parts by mass. Is more preferable, and it is further more preferable that it is 50 to 75 mass parts.
  • the negative electrode active material layer may contain other negative electrode active materials in addition to the silicon material.
  • a carbon-based material capable of inserting and extracting lithium, an element capable of being alloyed with lithium, a compound having an element capable of being alloyed with lithium, a polymer material, or the like can be used.
  • the carbon-based material examples include graphite, non-graphitizable carbon, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon, and carbon blacks.
  • the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.
  • Elements that can be alloyed with lithium are Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn. , Pb, Sb, Bi.
  • Examples of the compound having an element that can be alloyed with lithium include ZnLiAl, AlSb, SiB 4 , SiB 6 , Mg 2 Si, Mg 2 Sn, Ni 2 Si, TiSi 2 , MoSi 2 , CoSi 2 , NiSi 2 , and CaSi. 2, CrSi 2, Cu 5 Si , FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 ⁇ v ⁇ 2), SnO w (0 ⁇ w ⁇ 2), SnSiO 3 , LiSiO or LiSnO can be used.
  • polyacetylene polypyrrole, or the like can be used as the polymer material.
  • the other negative electrode active material is preferably a carbon-based material.
  • the negative electrode active material is preferably in powder form.
  • the average particle diameter D 50 of the negative electrode active material is preferably 0.5 ⁇ m or more and 30 ⁇ m or less, and more preferably 1 ⁇ m or more and 20 ⁇ m or less.
  • the average particle diameter D 50 of the negative electrode active material is too small, the specific surface area of the powder of the negative electrode active material is increased, it increases the contact area of the powder of the anode active material and the electrolyte solution, proceed decomposition of the electrolyte solution Therefore, the cycle characteristics of the lithium ion secondary battery may be deteriorated.
  • the average particle diameter D 50 of the negative electrode active material is too large, conductivity of the whole electrode becomes uneven, charging and discharging characteristics may deteriorate.
  • the negative electrode active material layer can be disposed on the surface of the current collector in the same manner as the positive electrode active material layer is disposed on the surface of the current collector.
  • the density of the negative electrode active material layer is preferably 0.5 g / cm 3 or more and 2 g / cm 3 or less, more preferably 0.8 g / cm 3 or more and 1.5 g / cm 3 or less, and 1.0 g / Cm 3 or more and 1.3 g / cm 3 or less is particularly preferable.
  • the separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit of current due to contact between the two electrodes.
  • the separator include a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, polyethylene, polyester, and polyamide, or a porous film made of ceramics.
  • the separator preferably includes a porous film made of a synthetic resin so that it can easily follow expansion and contraction due to charging and discharging of the negative electrode including the silicon material.
  • the separator made of synthetic resin may have a single layer structure using a single synthetic resin or a laminated structure in which a plurality of synthetic resin layers are stacked.
  • the thickness of the separator is not particularly limited, but is preferably in the range of 5 ⁇ m to 100 ⁇ m, more preferably in the range of 10 ⁇ m to 50 ⁇ m, and particularly preferably in the range of 15 ⁇ m to 30 ⁇ m.
  • Non-aqueous electrolyte The nonaqueous electrolytic solution contains a nonaqueous solvent and an electrolyte dissolved in the nonaqueous solvent.
  • non-aqueous solvent examples include cyclic esters, chain esters, and ethers.
  • cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone.
  • chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, ethyl methyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester.
  • ethers examples include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane.
  • the non-aqueous solvent a compound in which part or all of hydrogen in the chemical structure of the specific non-aqueous solvent is substituted with fluorine may be employed.
  • the compound in which part or all of hydrogen in the chemical structure of the non-aqueous solvent is fluorine-substituted include, for example, fluoroethylene carbonate and difluoroethylene carbonate.
  • a lithium salt such as LiClO 4 , LiAsF 6 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN (FSO 2 ) 2 is used.
  • a lithium salt such as LiClO 4 , LiAsF 6 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN (FSO 2 ) 2 is used.
  • non-aqueous electrolyte for example, a lithium salt such as LiClO 4 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 , LiN (FSO 2 ) 2 is added to a solvent such as ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.
  • a solution dissolved at a concentration of about 5 mol / l to 1.7 mol / l can be used.
  • a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body.
  • the electrode body may be any of a stacked type in which a positive electrode, a separator and a negative electrode are stacked, or a wound type in which a positive electrode, a separator and a negative electrode are sandwiched.
  • a non-aqueous electrolyte is added to the electrode body and lithium is added. It is preferable to use an ion secondary battery.
  • the lithium ion secondary battery of this invention should just be charged / discharged in the voltage range suitable for the kind of active material contained in an electrode.
  • the shape of the lithium ion secondary battery is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be adopted.
  • the lithium ion secondary battery can be mounted on a vehicle. Since the lithium ion secondary battery has high safety, a vehicle equipped with the lithium ion secondary battery has high safety.
  • the vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source.
  • a vehicle that uses electric energy from a battery as a whole or a part of a power source.
  • an electric vehicle a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, an electric forklift, an electric wheelchair, and an electric assist.
  • Bicycles and electric motorcycles are examples.
  • LiNi 0.5 Co 0.2 Mn 0.3 O 2 having an average particle diameter D 50 of 6 ⁇ m as a positive electrode active material
  • LiFePO 4 having an average particle diameter D 50 of 1.5 ⁇ m having a carbon coating on the surface as a positive electrode active material
  • Acetylene black as a conductive additive and polyvinylidene fluoride (hereinafter referred to as PVDF) as a binder were mixed in a ratio of 67 parts by mass, 27 parts by mass, 3 parts by mass, and 3 parts by mass, respectively.
  • NMP N-methyl-2-pyrrolidone
  • An aluminum foil having a thickness of 15 ⁇ m was prepared as a current collector.
  • the positive electrode active material layer slurry was placed on the current collector, and the positive electrode active material layer slurry was applied in a film form using a comma coater.
  • the current collector coated with the positive electrode active material layer slurry was dried at 90 ° C. for 5 minutes and then dried at 120 ° C. for 5 minutes to volatilize and remove NMP. Thereafter, the current collector and the coated material on the current collector were firmly bonded by a roll press. At this time, the basis weight of the positive electrode active material layer was set to 27.0 mg / cm 2 .
  • the basis weight of the positive electrode active material layer was calculated from the equation: mass of positive electrode active material layer (g) ⁇ area of positive electrode active material layer (cm 2 ).
  • the bonded product was heated in a vacuum dryer at 120 ° C. for 6 hours.
  • the bonded product after heating was cut into a predetermined shape (rectangular shape of 40 mm ⁇ 80 mm) to obtain a positive electrode A.
  • the thickness of the positive electrode active material layer of the positive electrode A was about 90 ⁇ m.
  • the density of the positive electrode active material layer of the positive electrode A was 2.9 g / cm 3 .
  • (Positive electrode B) 94 parts by mass of LiNi 0.5 Co 0.2 Mn 0.3 O 2 having an average particle diameter D 50 of 6 ⁇ m as a positive electrode active material, acetylene black as a conductive additive, and PVDF as a binder,
  • a positive electrode B was prepared in the same manner as the positive electrode A, except that the mixture was mixed at a ratio of 3 parts by mass and the mixture was dispersed in an appropriate amount of NMP to prepare a positive electrode active material layer slurry.
  • the thickness of the positive electrode active material layer of the positive electrode B was about 80 ⁇ m.
  • the density of the positive electrode active material layer of the positive electrode B was 2.9 g / cm 3 .
  • acetylene black as a conductive assistant and PVDF as a binder are mixed in a ratio of 69 parts by mass, 25 parts by mass, 3 parts by mass, and 3 parts by mass, respectively, and this mixture is dispersed in an appropriate amount of NMP.
  • a positive electrode C was prepared in the same manner as the positive electrode A, except that the positive electrode active material layer slurry was prepared.
  • the thickness of the positive electrode active material layer of the positive electrode C was about 89 ⁇ m.
  • the density of the positive electrode active material layer of the positive electrode C was 2.9 g / cm 3 .
  • a silicon material coated with carbon was prepared as follows.
  • a mixed solution of 7 ml of an aqueous HF solution having a concentration of 46% by mass and 56 ml of an aqueous HCl solution having a concentration of 36% by mass was brought to 0 ° C. in an ice bath, and 3.3 g of CaSi 2 was added thereto in an argon gas stream. Stir. After confirming the completion of foaming, the mixed solution was warmed to room temperature, stirred for another 2 hours at room temperature, then added with 20 ml of distilled water, and further stirred for 10 minutes. At this time, yellow powder floated.
  • the obtained mixed solution was filtered, and the obtained residue was washed with 10 ml of distilled water and then with 10 ml of ethanol. The residue after washing was vacuum dried to obtain 2.5 g of layered polysilane.
  • the obtained silicon material was put into a rotary kiln type reactor and subjected to a carbonization process by thermal CVD under a condition of 850 ° C. and a residence time of 5 minutes under a flow of propane gas to obtain a silicon material coated with carbon. .
  • a carbonization process by thermal CVD under a condition of 850 ° C. and a residence time of 5 minutes under a flow of propane gas to obtain a silicon material coated with carbon.
  • the rotation speed of the reactor was 1 rpm.
  • the average particle diameter D 50 of the silicon material coated with this carbon was 5 [mu] m.
  • NiO having an average particle diameter D 50 of 4 ⁇ m and natural graphite having an average particle diameter D 50 of 15 ⁇ m were prepared.
  • a polyamide-imide resin was prepared as a binder resin.
  • Acetylene black was prepared as a conductive aid.
  • An appropriate amount of NMP was added as a solvent to the above mixture to prepare a negative electrode active material layer slurry.
  • a 20 ⁇ m copper foil was prepared as a negative electrode current collector.
  • the said slurry for negative electrode active material layers was apply
  • the copper foil coated with the negative electrode active material layer slurry was dried at 80 ° C. for 5 minutes to volatilize and remove NMP. Thereafter, the current collector and the coated material on the current collector were firmly bonded by a roll press.
  • the basis weight of the negative electrode active material layer was set to 7.5 mg / cm 2 .
  • the basis weight of the negative electrode active material layer was calculated from the equation: mass of negative electrode active material layer (g) ⁇ area of negative electrode active material layer (cm 2 ).
  • the joined product was heated in a vacuum dryer at 200 ° C. for 2 hours, and then cut into a predetermined shape (rectangular shape having a negative electrode active material layer area of 44 mm ⁇ 84 mm) to form a negative electrode A.
  • the thickness of the negative electrode active material layer of the negative electrode A was about 47 ⁇ m.
  • the density of the negative electrode active material layer of the negative electrode A was 1.6 g / cm 3 .
  • a negative electrode C was produced in the same manner as the negative electrode A, except that this negative electrode active material layer slurry was used and the basis weight of the negative electrode active material layer was 5.5 mg / cm 2 .
  • the thickness of the negative electrode active material layer of the negative electrode C was about 50 ⁇ m.
  • the density of the negative electrode active material layer of the negative electrode C was 1.1 g / cm 3 .
  • a negative electrode D was produced in the same manner as the negative electrode C, except that the density of the negative electrode active material layer was 1.2 g / cm 3 .
  • the thickness of the negative electrode active material layer of the negative electrode D was about 46 ⁇ m.
  • the basis weight of the negative electrode active material layer of the negative electrode D was 5.5 mg / cm 2 .
  • a negative electrode F was produced in the same manner as the negative electrode E, except that the density of the negative electrode active material layer was 1.2 g / cm 3 .
  • the thickness of the negative electrode active material layer of the negative electrode F was about 41 ⁇ m.
  • the basis weight of the negative electrode active material layer of the negative electrode F was 4.9 mg / cm 2 .
  • the negative electrode active material used in the negative electrode B, the conductive auxiliary agent used in the negative electrode A, and the binder resin are coated with carbon.
  • Silicon material: graphite: conductive auxiliary agent: binder resin 70: 15: 5: 10 Mixed.
  • An appropriate amount of NMP was added as a solvent to the above mixture to prepare a negative electrode active material layer slurry.
  • a negative electrode G was produced in the same manner as the negative electrode A, except that the basis weight of the negative electrode active material layer was 4.0 mg / cm 2 .
  • the thickness of the negative electrode active material layer of the negative electrode G was about 36 ⁇ m. Further, the density of the negative electrode active material layer of the negative electrode G was 1.1 g / cm 3 .
  • a negative electrode H was produced in the same manner as the negative electrode G, except that the density of the negative electrode active material layer was 1.2 g / cm 3 .
  • the thickness of the negative electrode active material layer of the negative electrode H was about 33 ⁇ m.
  • the basis weight of the negative electrode active material layer of the negative electrode H was 4.0 mg / cm 2 .
  • a negative electrode I was produced in the same manner as the negative electrode F, except that this negative electrode active material layer slurry was used and the density of the negative electrode active material layer was 1.1 g / cm 3 .
  • the thickness of the negative electrode active material layer of the negative electrode I was about 52 ⁇ m.
  • the basis weight of the negative electrode active material layer was 5.7 mg / cm 2 .
  • Example 1 The laminated lithium ion secondary battery of Example 1 was produced as follows.
  • a laminate type lithium ion secondary battery was manufactured using 30 positive electrodes A and 31 negative electrodes B. Specifically, a rectangular sheet (48 mm ⁇ 88 mm, thickness 25 ⁇ m) made of a porous polyethylene film as a separator was sandwiched between each positive electrode and each negative electrode, and laminated to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then an electrolyte solution was injected into the bag-like laminated film. The amount of electrolyte injected was 3.4 ml / Ah with respect to the battery capacity.
  • FEC fluoroethylene carbonate
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • DMC dimethyl carbonate
  • the positive electrode and the negative electrode have a tab portion that can be electrically connected to the outside, and a part of the tab portion extends to the outside of the laminated lithium ion secondary battery.
  • the laminated lithium ion secondary battery of Example 1 was produced through the above steps.
  • Example 2 A laminated lithium ion secondary battery of Example 2 was produced in the same manner as in Example 1 except that the negative electrode C was used instead of the negative electrode B in Example 1.
  • Example 3 A laminated lithium ion secondary battery of Example 3 was produced in the same manner as in Example 1 except that the negative electrode D was used instead of the negative electrode B in Example 1.
  • Example 4 A laminated lithium ion secondary battery of Example 4 was produced in the same manner as in Example 1 except that the negative electrode E was used instead of the negative electrode B in Example 1.
  • Example 5 A laminated lithium ion secondary battery of Example 5 was produced in the same manner as in Example 1 except that the negative electrode F was used instead of the negative electrode B in Example 1.
  • Example 6 A laminated lithium ion secondary battery of Example 6 was produced in the same manner as in Example 1 except that the negative electrode G was used instead of the negative electrode B in Example 1.
  • Example 7 A laminated lithium ion secondary battery of Example 7 was produced in the same manner as in Example 1 except that the negative electrode H was used instead of the negative electrode B in Example 1.
  • Example 8 The laminated lithium ion secondary battery of Example 8 was the same as Example 5 except that the amount of electrolyte injected in Example 5 was 1.7 ml / Ah with respect to the battery capacity. Produced.
  • Example 9 A laminated lithium ion secondary battery of Example 9 was produced in the same manner as in Example 5 except that the positive electrode C was used instead of the positive electrode A in Example 5.
  • Example 10 A laminated lithium ion secondary battery of Example 10 was produced in the same manner as in Example 9, except that the negative electrode I was used instead of the negative electrode F in Example 9.
  • Comparative Example 1 A laminated lithium ion secondary battery of Comparative Example 1 was prepared in the same manner as in Example 1 except that the positive electrode B was used instead of the positive electrode A in Example 1, and the negative electrode F was used instead of the negative electrode B in Example 1. Produced.
  • Comparative Example 2 Comparative Example as in Example 1, except that the negative electrode A was used instead of the negative electrode B in Example 1, and the amount of electrolyte injected was 4.1 ml / Ah with respect to the battery capacity. 2 laminate type lithium ion secondary battery was produced.
  • Comparative Example 3 A laminate type lithium ion secondary battery of Comparative Example 3 was produced in the same manner as Comparative Example 2, except that the amount of electrolyte injected was 2.8 ml / Ah with respect to the battery capacity.
  • each laminated lithium ion secondary battery was charged with a constant current (CC) until it reached 4.5 V at a current value of 3.0 A. Thereafter, charging was continued so as to maintain the voltage within 4.5 V ⁇ 0.02 V, and the charging was stopped when the total charging time reached 5 hours.
  • the capacity of each laminated lithium ion secondary battery is 7.5 Ah for the laminated lithium ion secondary batteries of Examples 1 to 10, and 7.5 Ah for the laminated lithium ion secondary battery of Comparative Example 1.
  • the laminate type lithium ion secondary batteries of Comparative Examples 2 and 3 were 7.0 Ah.
  • Each laminated lithium ion secondary battery subjected to the above-described charging treatment was placed on a restraining plate having a hole with a diameter of 20 mm.
  • a restraint plate was placed on a press machine with a nail attached to the top. The nail was moved from the top to the bottom at a speed of 20 mm / sec until the nail penetrated the laminated lithium ion secondary battery on the restraint plate and the tip of the nail was positioned inside the hole of the restraint plate.
  • a temperature measuring device capable of measuring the surface temperature was attached to the laminate type lithium ion secondary battery.
  • the nail was made of stainless steel (S45C defined by JIS G 4051), had a diameter of 8 mm, and a nail tip angle of 60 °.
  • the nail penetration test was performed while measuring the surface temperature of the laminated lithium ion secondary battery at room temperature and in the air. By this nail penetration test, the positive electrode and the negative electrode of the laminated lithium ion secondary battery were short-circuited.
  • the surface temperature of the laminated lithium ion secondary battery at the time of an internal short circuit was measured, and the state of the battery was observed. After the nail penetration, the surface temperature of each battery once increased and then gradually decreased.
  • Table 1 shows the cell surface temperatures observed in the nail penetration test of the laminated lithium ion secondary batteries of Examples 1 to 7 and Comparative Examples 1 and 2. As the cell surface temperature, the maximum temperature among the surface temperatures of each laminated lithium ion secondary battery is described.
  • FIG. 1 is a graph showing the relationship between the cell surface temperature, which is a nail penetration test result of the laminated lithium ion secondary batteries of Examples 1 to 7, and the mass part of the silicon material of each negative electrode.
  • a lithium ion secondary battery having a negative electrode including a silicon material and a positive electrode including NCM and LFP has an excessive increase in the cell surface temperature even when the positive electrode and the negative electrode are short-circuited by a nail penetration test. It turns out that does not happen.
  • the cell surface temperature during the nail penetration test of the laminated lithium ion secondary batteries of Examples 1 to 7 was compared, as shown in FIG. 1 and Table 1, the mass part of the silicon material in the negative electrode active material layer It was found that the greater the amount, the lower the cell surface temperature during the nail penetration test.
  • the density of the negative electrode active material layer was 1.2 g / cm 3.
  • the laminated lithium ion secondary batteries of Nos. 5 and 7 have a nail penetration test rather than the laminated type lithium ion secondary batteries of Examples 2, 4, and 6 in which the density of the negative electrode active material layer is 1.1 g / cm 3.
  • the cell surface temperature was found to be low.
  • the electrolyte solution is removed by nail penetration and the resistance increases, so that the amount of heat generation increases and the cell surface temperature rises.
  • the heat generation of the cell is suppressed by the heat of vaporization of the electrolyte. Therefore, from the viewpoint of safety, it is preferable that the amount of electrolyte contained in the laminated lithium ion secondary battery is larger. For example, 20 to 30% of the total volume of cells of a lithium ion secondary battery is preferably occupied by the electrolyte.
  • Table 2 shows the cell surface temperatures observed in the nail penetration test of the laminated lithium ion secondary batteries of Example 5, Example 8, Comparative Example 2 and Comparative Example 3.
  • the laminate type lithium ion secondary battery of Comparative Example 3 has a smaller amount of electrolyte than the laminate type lithium ion secondary battery of Comparative Example 2. Comparing the cell surface temperature during the nail penetration test of the laminate type lithium ion secondary battery of Comparative Example 2 and Comparative Example 3 in Table 2, the cell surface during the nail penetration test of the laminate type lithium ion secondary battery of Comparative Example 3 The temperature rose significantly compared to the cell surface temperature during the nail penetration test of the laminated lithium ion secondary battery of Comparative Example 2.
  • the laminate type lithium ion secondary battery of Example 8 has a smaller amount of electrolyte than the laminate type lithium ion secondary battery of Example 5, but the laminate type lithium ion of Examples 5 and 8 Comparing the cell surface temperature during the nail penetration test of the secondary battery, the laminate type lithium ion secondary battery of Example 8 and the laminate type lithium ion secondary battery of Example 5 have the cell surface temperature during the nail penetration test, There was little difference. In other words, it was found that the surface temperature of the cell during the nail penetration test does not increase excessively regardless of the amount of the electrolyte by including the silicon material in the negative electrode.
  • a lithium ion secondary battery having a negative electrode containing a silicon material and a positive electrode containing NCM and LFP has a cell surface at the time of a short circuit between the positive electrode and the negative electrode by a nail penetration test even when the amount of the electrolyte is small. It has been found that the effect that the temperature does not increase excessively is effectively exhibited.
  • Table 3 shows the cell surface temperatures observed in the nail penetration test of the laminated lithium ion secondary batteries of Example 5, Example 9, and Example 10.
  • the content ratios of NCM and LFP are different in each positive electrode.
  • the cell surface temperatures during the nail penetration test of the laminated lithium ion secondary batteries of Example 5 and Example 9 in Table 3 were compared, there was almost no difference. From this, in the positive electrode active material layer, if the content ratio of NCM is 50 parts by mass or more and 80 parts by mass or less and the content ratio of LFP is in the range of 20 parts by mass or more and 40 parts by mass or less, NCM and LFP It was found that the cell surface temperature did not increase excessively during the nail penetration test even when the content ratio changed.
  • the negative electrode of the laminated lithium ion secondary battery of Example 9 contains silicon material and graphite
  • the laminated lithium ion secondary of Example 10 The negative electrode of the battery contains a silicon material but does not contain graphite.

Abstract

Provided is a lithium ion secondary battery which exhibits high safety at the time of an internal short circuit. This lithium ion secondary battery comprises a positive electrode, a negative electrode, a separator and a nonaqueous electrolyte solution, and is characterized in that: the positive electrode has a positive electrode active material layer containing a positive electrode active material; the positive electrode active material contains a lithium nickel cobalt manganese composite oxide and a lithium iron phosphate compound; the negative electrode has a negative electrode active material layer containing a negative electrode active material; and the negative electrode active material contains a silicon material having a structure wherein plate-like silicon bodies are laminated in the thickness direction.

Description

リチウムイオン二次電池Lithium ion secondary battery
　本発明は、リチウムイオン二次電池に関するものである。 The present invention relates to a lithium ion secondary battery.
　非水電解質二次電池を用いた製品は、増加の一途を辿っている。一般に、非水電解質二次電池は、携帯電話やノート型パソコンなどの携帯機器には必須のものとして認識されている。非水電解質二次電池のうちリチウムイオン二次電池は、小型で大容量であるため、汎用されている。また、リチウムイオン二次電池は、航空機や自動車にも採用されている。 The number of products using non-aqueous electrolyte secondary batteries is increasing. In general, non-aqueous electrolyte secondary batteries are recognized as essential for portable devices such as mobile phones and laptop computers. Among non-aqueous electrolyte secondary batteries, lithium ion secondary batteries are widely used because of their small size and large capacity. Lithium ion secondary batteries are also used in aircraft and automobiles.
　近年、リチウムイオン二次電池に対する研究が盛んに行われている。リチウムイオン二次電池の負極活物質として、炭素材料の理論容量を大きく超える充放電容量を持つ珪素、珪素合金、珪素酸化物などの珪素系材料が、検討されている。 In recent years, research on lithium ion secondary batteries has been actively conducted. As negative electrode active materials for lithium ion secondary batteries, silicon-based materials such as silicon, silicon alloys, and silicon oxides having charge / discharge capacities far exceeding the theoretical capacity of carbon materials have been studied.
　例えば、特許文献１（国際公開第２０１４／０８０６０８号）には、ＣａＳｉ２と酸とを反応させ、層状ポリシランを主成分とする層状シリコン化合物を合成したこと、当該層状シリコン化合物を３００℃以上で加熱してシリコン材料を製造したこと、及び、当該シリコン材料を活物質として具備するリチウムイオン二次電池が記載されている。 For example, in Patent Document 1 (International Publication No. 2014/080608), CaSi 2 and an acid are reacted to synthesize a layered silicon compound containing layered polysilane as a main component, and the layered silicon compound is heated at 300 ° C. or higher. It describes that a silicon material is manufactured by heating, and a lithium ion secondary battery including the silicon material as an active material.
　さて、リチウムイオン二次電池を安全面からみると、リチウムイオン二次電池の内部短絡時の安全性を確保するのが重要である。 Now, from the viewpoint of safety of the lithium ion secondary battery, it is important to ensure safety when the lithium ion secondary battery is internally short-circuited.
　安全性の確認試験として、例えば、釘刺し試験を適用する場合には、釘刺し時に、短絡により、電池の過加熱が生じる可能性がある。リチウムイオン二次電池の安全性をより高めるためには、釘刺し試験のように試験条件の厳しい確認試験に耐え得る電池構成にすることが求められる。 For example, when a nail penetration test is applied as a safety confirmation test, overheating of the battery may occur due to a short circuit at the time of nail penetration. In order to further improve the safety of the lithium ion secondary battery, it is required to have a battery configuration that can withstand a confirmation test with severe test conditions such as a nail penetration test.
　釘刺し試験は、釘を電池に貫通させたときに、電池がどのような挙動を示すかを観察する試験である。実際に、特許文献２（特開２００３－１５７８５４号公報）には、釘刺し試験を行っても、発火しなかったリチウムイオン二次電池が記載されている。ここで、特許文献２に開示のリチウムイオン二次電池では、電極を特定の形状のシートに分割している。特許文献２に開示の技術では、電極を分割したシートの面積及び形状、並びに正極集電体と負極集電体の間の距離を一定の関係式で規定しており、リチウムイオン二次電池の構成要素に複数の制限が課せられていた。 The nail penetration test is a test for observing how the battery behaves when a nail is passed through the battery. Actually, Patent Document 2 (Japanese Patent Laid-Open No. 2003-157854) describes a lithium ion secondary battery that did not ignite even when a nail penetration test was performed. Here, in the lithium ion secondary battery disclosed in Patent Document 2, the electrode is divided into sheets having a specific shape. In the technique disclosed in Patent Document 2, the area and shape of the sheet into which the electrode is divided and the distance between the positive electrode current collector and the negative electrode current collector are defined by a certain relational expression, and the lithium ion secondary battery Multiple restrictions were imposed on the components.
　また、特許文献３（特開２００８－１９８５９１号公報）には、集電体と電極合剤層との界面に絶縁部材を点在させて、正極と負極との間の抵抗を大きくしたリチウムイオン二次電池によれば、釘刺し試験を行っても発煙しないことが開示されている。しかしながら、特許文献３に開示の技術では、電池としての抵抗が上昇して、出力特性が悪化することが懸念される。 Patent Document 3 (Japanese Patent Application Laid-Open No. 2008-198591) discloses lithium ions in which an insulating member is interspersed at the interface between the current collector and the electrode mixture layer to increase the resistance between the positive electrode and the negative electrode. According to the secondary battery, it is disclosed that smoke does not occur even when a nail penetration test is performed. However, with the technique disclosed in Patent Document 3, there is a concern that the resistance as a battery increases and the output characteristics deteriorate.
国際公開第２０１４／０８０６０８号International Publication No. 2014/080608 特開２００３－１５７８５４号公報JP 2003-157854 A 特開２００８－１９８５９１号公報JP 2008-198591 A
　本発明は、このような事情に鑑みて為されたものであり、内部短絡時に安全性が高いリチウムイオン二次電池を提供することを目的とする。 The present invention has been made in view of such circumstances, and an object thereof is to provide a lithium ion secondary battery having high safety when an internal short circuit occurs.
　本発明の発明者等は、鋭意研究の結果、リチウムニッケルコバルトマンガン複合酸化物及びリン酸鉄リチウム化合物を含む正極活物質と、板状シリコン体が厚さ方向に積層された構造を有するシリコン材料を含む負極活物質と、を有するリチウムイオン二次電池が、釘刺し試験に耐え、内部短絡時にも安全性が高いことを見出した。 As a result of earnest research, the inventors of the present invention have found that a positive electrode active material containing a lithium nickel cobalt manganese composite oxide and a lithium iron phosphate compound, and a silicon material having a structure in which a plate-like silicon body is laminated in the thickness direction It has been found that a lithium ion secondary battery having a negative electrode active material containing can withstand a nail penetration test and has high safety even during an internal short circuit.
　すなわち、本発明のリチウムイオン二次電池は、正極と負極とセパレータと非水電解液とを含み、正極は、正極活物質を含む正極活物質層を有し、正極活物質は、下記式（１）で表されるリチウムニッケルコバルトマンガン複合酸化物及び下記式（２）で表されるリン酸鉄リチウム化合物を含み、
　ＬｉａＮｉｂＣｏｃＭｎ（１－ｂ－ｃ－ｄ）Ｍ１ ｄＯ（２－ｅ）・・・・・（１）
　（式（１）中、Ｍ１は、Ｍｇ、Ａｌ、Ｂ、Ｔｉ、Ｖ、Ｃｒ、Ｆｅ、Ｃｕ、Ｚｎ、Ｚｒ、Ｍｏ、Ｓｎ、Ｃａ、Ｓｒ及びＷからなる群のうちの少なくとも１種を表し、ａ、ｂ、ｃ、ｄ及びｅは、０．８≦ａ≦１．２、０＜ｂ≦０．５、０＜ｃ≦０．５、０≦ｄ≦０．５、ｂ＋ｃ＋ｄ＜１、－０．１≦ｅ≦０．２の範囲内の値である。）
　ＬｉｐＦｅｑＭ２ （１－ｑ）ＰＯ４・・・・・（２）
　（式（２）中、Ｍ２は、Ｃｏ、Ｍｎ、Ｎｉ、Ｍｇ、Ａｌ、Ｂ、Ｔｉ、Ｖ、Ｎｂ、Ｃｕ、Ｚｎ、Ｍｏ、Ｃａ、Ｓｒ、Ｗ及Ｚｒからなる群のうちの少なくとも１種を表す。ｐは、０．９≦ｐ≦１．１の範囲内の値である。ｑは、０＜ｑ≦１の範囲内の値である。）
　負極は、負極活物質を含む負極活物質層を有し、負極活物質は板状シリコン体が厚さ方向に積層された構造を有するシリコン材料を含むことを特徴とする。 That is, the lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, the positive electrode has a positive electrode active material layer including a positive electrode active material, and the positive electrode active material is represented by the following formula ( 1) comprising a lithium nickel cobalt manganese composite oxide represented by the following formula and a lithium iron phosphate compound represented by the following formula (2),
Li a Ni b Co c Mn (1-bcd) M 1 d O (2-e) (1)
(In the formula (1), M 1 represents at least one selected from the group consisting of Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr and W. A, b, c, d and e are 0.8 ≦ a ≦ 1.2, 0 <b ≦ 0.5, 0 <c ≦ 0.5, 0 ≦ d ≦ 0.5, b + c + d <1 , -0.1 ≦ e ≦ 0.2.)
Li p Fe q M 2 (1-q) PO 4 (2)
(In the formula (2), M 2 is at least one of the group consisting of Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W and Zr. (P is a value in the range of 0.9 ≦ p ≦ 1.1, q is a value in the range of 0 <q ≦ 1)
The negative electrode has a negative electrode active material layer containing a negative electrode active material, and the negative electrode active material contains a silicon material having a structure in which plate-like silicon bodies are laminated in the thickness direction.
　正極活物質層の密度は、２．５ｇ／ｃｍ３以上３．５ｇ／ｃｍ３以下であり、負極活物質層の密度は、０．５ｇ／ｃｍ３以上２ｇ／ｃｍ３以下であることが好ましい。 The density of the positive electrode active material layer is preferably 2.5 g / cm 3 or more and 3.5 g / cm 3 or less, and the density of the negative electrode active material layer is preferably 0.5 g / cm 3 or more and 2 g / cm 3 or less. .
　シリコン材料の含有量は、負極活物質層を１００質量部としたときに、３０質量部以上８０質量部以下であることが好ましい。 The content of the silicon material is preferably 30 parts by mass or more and 80 parts by mass or less when the negative electrode active material layer is 100 parts by mass.
　リチウムニッケルコバルトマンガン複合酸化物の含有量は、正極活物質層を１００質量部としたときに、５０質量部以上８０質量部以下であることが好ましく、リン酸鉄リチウム化合物の含有量は、正極活物質層を１００質量部としたときに、２０質量部以上４０質量部以下であることが好ましい。 The content of the lithium nickel cobalt manganese composite oxide is preferably 50 parts by mass or more and 80 parts by mass or less when the positive electrode active material layer is 100 parts by mass, and the content of the lithium iron phosphate compound is positive electrode When the active material layer is 100 parts by mass, it is preferably 20 parts by mass or more and 40 parts by mass or less.
　セパレータは、合成樹脂製の多孔質膜を含むことが好ましい。 The separator preferably includes a porous film made of synthetic resin.
　非水電解液は、電解質塩と非水溶媒とを含み、電解質塩は六フッ化リン酸リチウムを含み、非水溶媒は、フルオロエチレンカーボネート、エチレンカーボネート、エチルメチルカーボネート及びジメチルカーボネートを含むことが好ましい。 The non-aqueous electrolyte includes an electrolyte salt and a non-aqueous solvent, the electrolyte salt includes lithium hexafluorophosphate, and the non-aqueous solvent includes fluoroethylene carbonate, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate. preferable.
　本発明のリチウムイオン二次電池によれば、特定の負極活物質及び特定の正極活物質を用いることによる相乗効果により、釘刺し試験において良好な結果が得られ、短絡時の過剰な温度上昇を抑制できる。 According to the lithium ion secondary battery of the present invention, the synergistic effect by using the specific negative electrode active material and the specific positive electrode active material, a good result is obtained in the nail penetration test, and an excessive temperature rise at the time of short circuit is achieved. Can be suppressed.
実施例１～実施例７のラミネート型リチウムイオン二次電池の釘刺し試験結果であるセル表面温度と、各負極のシリコン材料の質量部との関係を示すグラフである。6 is a graph showing the relationship between the cell surface temperature, which is the nail penetration test result of the laminated lithium ion secondary batteries of Examples 1 to 7, and the mass part of the silicon material of each negative electrode.
　以下に、本発明を実施するための形態を説明する。なお、特に断らない限り、本明細書に記載された数値範囲「ａ～ｂ」は、下限ａおよび上限ｂをその範囲に含む。そして、これらの上限値および下限値、ならびに実施例中に列記した数値も含めてそれらを任意に組み合わせることで、数値範囲を構成し得る。さらに数値範囲内から任意に選択した数値を、上限、下限の数値とすることができる。 Hereinafter, modes for carrying out the present invention will be described. Unless otherwise specified, the numerical range “a to b” described in this specification includes the lower limit “a” and the upper limit “b”. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from the numerical value range can be used as upper and lower numerical values.
　＜リチウムイオン二次電池＞
　本発明のリチウムイオン二次電池は、正極と負極とセパレータと非水電解液とを含む。 <Lithium ion secondary battery>
The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte.
　（正極）
　正極は、正極活物質を含む正極活物質層を有する。正極活物質層は、集電体の表面に配置される。 (Positive electrode)
The positive electrode has a positive electrode active material layer containing a positive electrode active material. The positive electrode active material layer is disposed on the surface of the current collector.
　集電体は、リチウムイオン二次電池の放電又は充電の間、電極に電流を流し続けるための化学的に不活性な電子高伝導体をいう。集電体の材料として、例えば、ステンレス鋼、チタン、ニッケル、アルミニウム、銅などの金属材料または導電性樹脂を挙げることができる。特に、電気伝導性、加工性、価格の面から、集電体の材料としては、アルミニウムまたは銅が好ましい。集電体は、箔、シート、フィルム、線状、棒状、メッシュなどの形態をとることができる。集電体として、例えば、銅箔、ニッケル箔、アルミニウム箔、ステンレス箔などの金属箔を好適に用いることができる。集電体が、箔、シートまたはフィルムの場合は、集電体の厚みは１０μｍ～５０μｍであることが好ましい。集電体に高い強度を保持しつつ電池容量を高くする点から、集電体の厚みは、１２μｍ～３０μｍであることが特に好ましい。 A current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. Examples of the current collector material include metal materials such as stainless steel, titanium, nickel, aluminum, and copper, or conductive resins. In particular, from the viewpoint of electrical conductivity, workability, and cost, the material for the current collector is preferably aluminum or copper. The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. As the current collector, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, or a stainless steel foil can be suitably used. When the current collector is a foil, sheet, or film, the thickness of the current collector is preferably 10 μm to 50 μm. The thickness of the current collector is particularly preferably 12 μm to 30 μm from the viewpoint of increasing battery capacity while maintaining high strength in the current collector.
　（正極活物質層）
　正極活物質層は、正極活物質を有する。正極活物質層は、必要に応じて結着剤及び導電助剤を含んでもよい。 (Positive electrode active material layer)
The positive electrode active material layer has a positive electrode active material. The positive electrode active material layer may include a binder and a conductive additive as necessary.
　正極活物質は、下記式（１）で表されるリチウムニッケルコバルトマンガン複合酸化物及び下記式（２）で表されるリン酸鉄リチウム化合物を含む。 The positive electrode active material contains a lithium nickel cobalt manganese composite oxide represented by the following formula (1) and a lithium iron phosphate compound represented by the following formula (2).
　ＬｉａＮｉｂＣｏｃＭｎ（１－ｂ－ｃ－ｄ）Ｍ１ ｄＯ（２－ｅ）・・・・・（１）
　（式（１）中、Ｍ１は、Ｍｇ、Ａｌ、Ｂ、Ｔｉ、Ｖ、Ｃｒ、Ｆｅ、Ｃｕ、Ｚｎ、Ｚｒ、Ｍｏ、Ｓｎ、Ｃａ、Ｓｒ及びＷからなる群のうちの少なくとも１種を表し、ａ、ｂ、ｃ、ｄ及びｅは、０．８≦ａ≦１．２、０＜ｂ≦０．５、０＜ｃ≦０．５、０≦ｄ≦０．５、ｂ＋ｃ＋ｄ＜１、－０．１≦ｅ≦０．２の範囲内の値である。） Li a Ni b Co c Mn (1-bcd) M 1 d O (2-e) (1)
(In the formula (1), M 1 represents at least one selected from the group consisting of Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr and W. A, b, c, d and e are 0.8 ≦ a ≦ 1.2, 0 <b ≦ 0.5, 0 <c ≦ 0.5, 0 ≦ d ≦ 0.5, b + c + d <1 , -0.1 ≦ e ≦ 0.2.)
　ＬｉｐＦｅｑＭ２ （１－ｑ）ＰＯ４・・・・・（２）
　（式（２）中、Ｍ２は、Ｃｏ、Ｍｎ、Ｎｉ、Ｍｇ、Ａｌ、Ｂ、Ｔｉ、Ｖ、Ｎｂ、Ｃｕ、Ｚｎ、Ｍｏ、Ｃａ、Ｓｒ、Ｗ及Ｚｒからなる群のうちの少なくとも１種を表す。ｐは、０．９≦ｐ≦１．１の範囲内の値である。ｑは、０＜ｑ≦１の範囲内の値である。） Li p Fe q M 2 (1-q) PO 4 (2)
(In the formula (2), M 2 is at least one of the group consisting of Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W and Zr. (P is a value in the range of 0.9 ≦ p ≦ 1.1, q is a value in the range of 0 <q ≦ 1)
　式（１）で表されるリチウムニッケルコバルトマンガン複合酸化物としては、ＬｉＣｏ１／３Ｎｉ１／３Ｍｎ１／３Ｏ２、ＬｉＮｉ０．６Ｃｏ０．２Ｍｎ０．２Ｏ２、ＬｉＮｉ０．５Ｃｏ０．２Ｍｎ０．３Ｏ２が挙げられる。 Examples of the lithium nickel cobalt manganese composite oxide represented by the formula (1) include LiCo 1/3 Ni 1/3 Mn 1/3 O 2 , LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0. .5 Co 0.2 Mn 0.3 O 2 and the like.
　式（２）で表されるリン酸鉄リチウム化合物としては、ＬｉＦｅＰＯ４が挙げられる。 The lithium iron phosphate compound represented by the formula (2) include LiFePO 4.
　正極活物質が式（１）で表されるリチウムニッケルコバルトマンガン複合酸化物を含むことにより、リチウムイオン二次電池は、より高いエネルギー密度を得ることができる。 When the positive electrode active material contains the lithium nickel cobalt manganese composite oxide represented by the formula (1), the lithium ion secondary battery can obtain a higher energy density.
　また、正極活物質が式（２）で表されるリン酸鉄リチウム化合物を含むことにより、リチウムイオン二次電池は、安全性が高くなることが期待される。式（２）で示されるリン酸鉄リチウム化合物は、オリビン型構造を有する。オリビン型構造とは、酸素の六方最密充填を基本とし、その４面体サイトにリンが、八面体サイトにリチウムと鉄とがそれぞれ位置する構造である。オリビン型構造を有するリン酸鉄リチウム化合物は、リンと酸素が共有結合しているため、高温においても酸素を放出しにくい。オリビン型構造を有するリン酸鉄リチウム化合物をリチウムイオン二次電池の正極活物質として使用することで、リチウムイオン二次電池の安全性を向上できると考えられる。また、式（２）で表されるリン酸鉄リチウム化合物は、その表面をカーボンコートしたものが好ましい。 In addition, the lithium ion secondary battery is expected to be highly safe because the positive electrode active material contains a lithium iron phosphate compound represented by the formula (2). The lithium iron phosphate compound represented by the formula (2) has an olivine type structure. The olivine structure is based on hexagonal close-packing of oxygen, and phosphorus is located at the tetrahedral site and lithium and iron are located at the octahedral site. A lithium iron phosphate compound having an olivine structure is less likely to release oxygen even at high temperatures because phosphorus and oxygen are covalently bonded. It is considered that the safety of the lithium ion secondary battery can be improved by using a lithium iron phosphate compound having an olivine type structure as the positive electrode active material of the lithium ion secondary battery. The lithium iron phosphate compound represented by the formula (2) is preferably a carbon-coated surface.
　正極活物質が、式（１）で表されるリチウムニッケルコバルトマンガン複合酸化物及び式（２）で表されるリン酸鉄リチウム化合物の両者を含むことにより、リチウムイオン二次電池は、より高いエネルギー密度を得ることができ、かつ、安全性を高めることができる。 When the positive electrode active material includes both the lithium nickel cobalt manganese composite oxide represented by the formula (1) and the lithium iron phosphate compound represented by the formula (2), the lithium ion secondary battery is higher. Energy density can be obtained and safety can be improved.
　正極活物質層において、リチウムニッケルコバルトマンガン複合酸化物の含有量は、正極活物質層を１００質量部としたときに、５０質量部以上８０質量部以下であることが好ましく、５８質量部以上７８質量部以下であることがより好ましく、６５質量部以上７５質量部以下であることがさらに好ましく、リン酸鉄リチウム化合物の含有量は、正極活物質層を１００質量部としたときに、２０質量部以上４０質量部以下であることが好ましく、２２質量部以上３５質量部以下であることがより好ましく、２４質量部以上３０質量部以下であることがさらに好ましい。 In the positive electrode active material layer, the content of the lithium nickel cobalt manganese composite oxide is preferably 50 parts by mass or more and 80 parts by mass or less, and 58 parts by mass or more and 78 parts by mass when the positive electrode active material layer is 100 parts by mass. More preferably, it is 65 parts by mass or more and 75 parts by mass or less, and the content of the lithium iron phosphate compound is 20 parts by mass when the positive electrode active material layer is 100 parts by mass. It is preferably no less than 40 parts by mass and no greater than 40 parts by mass, more preferably no less than 22 parts by mass and no greater than 35 parts by mass, and even more preferably no less than 24 parts by mass and no greater than 30 parts by mass.
　正極活物質層は、さらに、他のリチウム含有酸化物、他の金属酸化物及び他の正極活物質を含んでもよい。他のリチウム含有酸化物としては、例えば、層状構造を有するリチウムコバルト複合酸化物、層状構造を有するリチウムニッケル複合酸化物、スピネル構造を有するリチウムマンガン複合酸化物、一般式： ＬｉａＣｏｐＮｉｑＭｎｒＤｓＯｘ (ＤはＡｌ、Ｍｇ、Ｔｉ、Ｓｎ、Ｚｎ、Ｗ、Ｚｒ、Ｍｏ、Ｆｅ及びＮａから選択される少なくとも一種でありｐ＋ｑ＋ｒ＋ｓ＝１、０＜ｐ＜１、０≦ｑ＜１、０≦ｒ＜１、０≦ｓ＜１、０．８≦ａ＜２．０、－０．２≦ｘ－（ａ＋ｐ＋ｑ＋ｒ＋ｓ）≦０．２)で表される層状構造を有するリチウムコバルト含有複合金属酸化物、一般式：Ｌｉ２ＭＰＯ４Ｆで示されるフッ化オリビン型リチウムリン酸複合酸化物（ＭはＭｎ、Ｆｅ、Ｃｏ及びＮｉから選択される少なくとも一種）、一般式：Ｌｉ２ＭＳｉＯ４で示されるケイ酸塩系型リチウム複合酸化物（ＭはＭｎ、Ｆｅ、Ｃｏ及びＮｉから選択される少なくとも一種）が挙げられる。また、他の金属酸化物としては、例えば、酸化チタン、酸化バナジウム若しくは二酸化マンガンが挙げられる。他の正極活物質として、例えば、硫黄単体（Ｓ）、硫黄と炭素を複合化した化合物、ＴｉＳ２などの金属硫化物等が挙げられる。 The positive electrode active material layer may further include other lithium-containing oxides, other metal oxides, and other positive electrode active materials. Other lithium-containing oxides include, for example, a lithium cobalt composite oxide having a layered structure, a lithium nickel composite oxide having a layered structure, a lithium manganese composite oxide having a spinel structure, and a general formula: Li a Co p Ni q Mn r D s O x (D is at least one selected from Al, Mg, Ti, Sn, Zn, W, Zr, Mo, Fe and Na, and p + q + r + s = 1, 0 <p <1, 0 ≦ q < 1, 0 ≦ r <1, 0 ≦ s <1, 0.8 ≦ a <2.0, −0.2 ≦ x− (a + p + q + r + s) ≦ 0.2) containing lithium cobalt Composite metal oxide, general formula: fluorinated olivine-type lithium phosphate composite oxide represented by Li 2 MPO 4 F (M is at least one selected from Mn, Fe, Co and Ni), general formula: Li 2 silicate type lithium composite oxide represented by MSiO 4 (M is at least one selected from Mn, Fe, Co and Ni). Examples of other metal oxides include titanium oxide, vanadium oxide, and manganese dioxide. Other positive electrode active material, for example, elemental sulfur (S), the compound complexed with sulfur and carbon, and metal sulfides such as TiS 2.
　正極活物質は、その平均粒径Ｄ５０が１μｍ～２０μｍである粉末形状であることが好ましい。正極活物質の平均粒径Ｄ５０が小さいと、正極活物質の比表面積が大きくなる。このため、正極活物質の平均粒径Ｄ５０が小さすぎると、正極活物質と電解液との反応面積が過度に増えることになり、その結果、電解液の分解が促進されて、リチウムイオン二次電池のサイクル特性が悪くなるおそれがある。正極活物質の平均粒径Ｄ５０が大きすぎると、リチウムイオン二次電池の抵抗が大きくなり、リチウムイオン二次電池の出力特性が下がるおそれがある。 The positive electrode active material is preferably in the form of a powder having an average particle diameter D 50 of 1 μm to 20 μm. When the average particle diameter D 50 of the positive electrode active material is small, the specific surface area of the positive electrode active material is increased. Therefore, the average particle diameter D 50 of the positive electrode active material is too small, will be the reaction area of the cathode active material and an electrolytic solution is excessively increased, resulting in promoted decomposition of the electrolytic solution, the lithium ion secondary The cycle characteristics of the secondary battery may be deteriorated. When the average particle diameter D 50 of the positive electrode active material is too large, resistance of the lithium ion secondary battery increases, there is a possibility that the output characteristics of the lithium ion secondary battery decreases.
　なお、平均粒径Ｄ５０とはレーザー回析法による粒度分布測定における体積分布の積算値が５０％に相当する粒子径を意味する。つまり、平均粒径Ｄ５０とは、体積基準で測定したメディアン径を意味する。 Note that the average particle diameter D 50 refers to the particle size cumulative value of the volume distribution in the particle size distribution measurement by laser diffraction method is equivalent to 50%. That is, the average particle diameter D 50 means the median size measured by volume.
　結着剤は、上記正極活物質を集電体に繋ぎ止める役割を果たす。結着剤として、例えば、ポリフッ化ビニリデン、ポリテトラフルオロエチレン、テトラフルオロエチレン／ヘキサフルオロプロピレン共重合体（略称ＦＥＰ）、フッ素ゴム等の含フッ素樹脂、ポリプロピレン、ポリエチレン等の熱可塑性樹脂、ポリイミド、ポリアミドイミド等のイミド系樹脂、ポリ（メタ）アクリル酸などのアクリル系樹脂、アルコキシシリル基含有樹脂、スチレン・ブタジエンゴム、カルボキシメチルセルロース、ポリエチレングリコール、ポリアクリロニトリルが挙げられる。 The binder plays a role of connecting the positive electrode active material to the current collector. As the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene / hexafluoropropylene copolymer (abbreviation FEP), fluorine-containing resin such as fluoro rubber, polypropylene, thermoplastic resin such as polyethylene, polyimide, Examples thereof include imide resins such as polyamide imide, acrylic resins such as poly (meth) acrylic acid, alkoxysilyl group-containing resins, styrene / butadiene rubber, carboxymethyl cellulose, polyethylene glycol, and polyacrylonitrile.
　正極活物質層中の結着剤の配合割合は、質量比で、正極活物質：結着剤＝１：０．００１～１：０．３であるのが好ましい。正極活物質：結着剤＝１：０．００５～１：０．２であるのがより好ましく、１：０．０１～１：０．１５であるのがさらに好ましい。結着剤が少なすぎると、電極の成形性が低下するおそれがあり、また、結着剤が多すぎると、電極のエネルギー密度が低くなるおそれがある。 The compounding ratio of the binder in the positive electrode active material layer is preferably a positive electrode active material: binder = 1: 0.001 to 1: 0.3 in mass ratio. Positive electrode active material: binding agent = 1: 0.005 to 1: 0.2 is more preferable, and 1: 0.01 to 1: 0.15 is further preferable. If the amount of the binder is too small, the moldability of the electrode may be lowered, and if the amount of the binder is too large, the energy density of the electrode may be lowered.
　導電助剤は、電極の導電性を高めるために、必要に応じて、正極活物質層に添加される。導電助剤として、炭素質微粒子であるカーボンブラック、黒鉛、アセチレンブラック（略称ＡＢ）、ケッチェンブラック（登録商標）（略称ＫＢ）、気相法炭素繊維（略称ＶＧＣＦ）等を単独でまたは二種以上組み合わせて使用することができる。導電助剤の使用量については、特に限定的ではないが、例えば、電極に含有される活物質１００質量部に対して、１質量部～３０質量部程度とすることができる。 The conductive additive is added to the positive electrode active material layer as necessary in order to increase the conductivity of the electrode. Carbon black, graphite, acetylene black (abbreviated as AB), ketjen black (registered trademark) (abbreviated as KB), vapor-grown carbon fiber (abbreviated as VGCF), etc., which are carbonaceous fine particles, are used alone or in combination as conductive aids. These can be used in combination. The amount of the conductive aid used is not particularly limited, but can be, for example, about 1 to 30 parts by mass with respect to 100 parts by mass of the active material contained in the electrode.
　正極活物質層を集電体の表面に配置するには、正極活物質及び結着剤、並びに必要に応じて導電助剤を含む正極活物質層形成用組成物を調製し、さらに、この組成物に適当な溶剤を加えてペースト状にしてから、集電体の表面に塗布後、乾燥すればよい。なお、必要に応じて、電極密度を高めるべく正極活物質層が配置された集電体を圧縮してもよい。 In order to dispose the positive electrode active material layer on the surface of the current collector, a positive electrode active material layer-forming composition containing a positive electrode active material, a binder, and, if necessary, a conductive additive is prepared. An appropriate solvent may be added to the product to form a paste, which may be applied to the surface of the current collector and then dried. In addition, as needed, you may compress the electrical power collector in which the positive electrode active material layer is arrange | positioned in order to raise an electrode density.
　正極活物質層形成用組成物の塗布方法としては、ロールコート法、ディップコート法、ドクターブレード法、スプレーコート法、カーテンコート法、リップコート法、コンマコート法、ダイコート法などの従来から公知の方法を用いればよい。 As a coating method of the composition for forming a positive electrode active material layer, conventionally known methods such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, a curtain coating method, a lip coating method, a comma coating method, and a die coating method are known. A method may be used.
　粘度調整のための溶剤としては、水、Ｎ－メチル－２－ピロリドン、メタノール、メチルイソブチルケトンなどが使用可能である。 As the solvent for adjusting the viscosity, water, N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone and the like can be used.
　正極活物質層の密度は、２．５ｇ／ｃｍ３以上３．５ｇ／ｃｍ３以下であることが好ましく、２．６ｇ／ｃｍ３以上３．２ｇ／ｃｍ３以下であることがより好ましく、２．８ｇ／ｃｍ３以上３．０ｇ／ｃｍ３以下であることが特に好ましい。 The density of the positive electrode active material layer is preferably 2.5 g / cm 3 or more and 3.5 g / cm 3 or less, more preferably 2.6 g / cm 3 or more and 3.2 g / cm 3 or less. particularly preferably .8g / cm 3 or more 3.0 g / cm 3 or less.
　（負極）
　負極は、負極活物質を含む負極活物質層を有する。負極活物質層は、集電体の表面に配置される。集電体は、正極で説明したものと同様である。 (Negative electrode)
The negative electrode has a negative electrode active material layer containing a negative electrode active material. The negative electrode active material layer is disposed on the surface of the current collector. The current collector is the same as that described for the positive electrode.
　（負極活物質層）
　負極活物質層は、負極活物質を有する。負極活物質層は、必要に応じて結着剤及び導電助剤を含んでもよい。結着剤、導電助剤は、正極で説明したものと同様である。 (Negative electrode active material layer)
The negative electrode active material layer has a negative electrode active material. The negative electrode active material layer may contain a binder and a conductive additive as necessary. The binder and the conductive assistant are the same as those described for the positive electrode.
　負極活物質は、板状シリコン体が厚さ方向に積層された構造を有するシリコン材料を含む。 The negative electrode active material includes a silicon material having a structure in which plate-like silicon bodies are laminated in the thickness direction.
　板状シリコン体が厚さ方向に積層されてなる構造を有するシリコン材料の構造は、走査型電子顕微鏡などによる観察で確認できる。シリコン材料をリチウムイオン二次電池の活物質として使用することを考慮すると、リチウムイオンの効率的な挿入及び脱離反応のためには、板状シリコン体は厚さが１０ｎｍ～１００ｎｍの範囲内のものが好ましく、２０ｎｍ～５０ｎｍの範囲内のものがより好ましい。また、板状シリコン体の長軸方向の長さは、０．１μｍ～５０μｍの範囲内のものが好ましい。また、板状シリコン体は、（長軸方向の長さ）／（厚さ）が２～１０００の範囲内であるのが好ましい。 The structure of a silicon material having a structure in which plate-like silicon bodies are laminated in the thickness direction can be confirmed by observation with a scanning electron microscope or the like. Considering the use of a silicon material as an active material of a lithium ion secondary battery, the plate-like silicon body has a thickness in the range of 10 nm to 100 nm for efficient insertion and removal of lithium ions. Are preferred, and those in the range of 20 nm to 50 nm are more preferred. The length of the plate-like silicon body in the major axis direction is preferably in the range of 0.1 μm to 50 μm. Further, the plate-like silicon body preferably has a (length in the long axis direction) / (thickness) range of 2 to 1000.
　シリコン材料は、粉砕や分級を経て、一定の粒度分布の粒子としてもよい。シリコン材料の好ましい粒度分布としては、一般的なレーザー回折式粒度分布測定装置で測定した場合に、Ｄ５０が１μｍ～３０μｍの範囲内を例示できる。 The silicon material may be pulverized or classified to form particles having a certain particle size distribution. As a preferable particle size distribution of the silicon material, D 50 can be exemplified within a range of 1 μm to 30 μm when measured by a general laser diffraction type particle size distribution measuring apparatus.
　シリコン材料に対してＸ線回折測定（ＸＲＤ測定）を行い、得られたＸＲＤチャートのＳｉ（１１１）面の回折ピークの半値幅を用いたシェラーの式から、シリコン結晶子サイズが算出される。このシリコン結晶子のサイズとしては、ナノサイズのものが好ましい。具体的には、シリコン結晶子サイズは、０．５ｎｍ～３００ｎｍの範囲内が好ましく、１ｎｍ～１００ｎｍの範囲内がより好ましく、１ｎｍ～５０ｎｍの範囲内がさらに好ましく、１ｎｍ～１０ｎｍの範囲内が特に好ましい。 X-ray diffraction measurement (XRD measurement) is performed on the silicon material, and the silicon crystallite size is calculated from the Scherrer equation using the half-value width of the diffraction peak of the Si (111) plane of the obtained XRD chart. The silicon crystallite size is preferably nano-sized. Specifically, the silicon crystallite size is preferably in the range of 0.5 nm to 300 nm, more preferably in the range of 1 nm to 100 nm, further preferably in the range of 1 nm to 50 nm, and particularly in the range of 1 nm to 10 nm. preferable.
　上記シリコン材料は、下記の製造工程によって製造されることができる。製造工程は、ＣａＳｉ２と酸とを反応させ、層状ポリシランを主成分とする層状シリコン化合物を製造する工程と、層状シリコン化合物を３００℃以上で加熱してシリコン材料を製造する工程とを含む。 The silicon material can be manufactured by the following manufacturing process. The production process includes a process of producing a layered silicon compound mainly composed of layered polysilane by reacting CaSi 2 and an acid, and a process of producing a silicon material by heating the layered silicon compound at 300 ° C. or higher.
　ＣａＳｉ２は、一般にＣａ層とＳｉ層が積層した構造からなる。ＣａＳｉ２は、公知の製造方法で合成してもよく、市販されているものを採用してもよい。層状シリコン化合物の製造に用いるＣａＳｉ２は、あらかじめ粉砕しておくことが好ましい。 CaSi 2 generally has a structure in which a Ca layer and a Si layer are laminated. CaSi 2 may be synthesized by a known production method, or a commercially available one may be adopted. CaSi 2 used for producing the layered silicon compound is preferably pulverized in advance.
　酸としては、フッ化水素、塩化水素、臭化水素、ヨウ化水素、硫酸、硝酸、リン酸、蟻酸、酢酸、メタンスルホン酸、テトラフルオロホウ酸、ヘキサフルオロリン酸、ヘキサフルオロヒ素酸、フルオロアンチモン酸、ヘキサフルオロケイ酸、ヘキサフルオロゲルマン酸、ヘキサフルオロスズ(IV)酸、トリフルオロ酢酸、ヘキサフルオロチタン酸、ヘキサフルオロジルコニウム酸、トリフルオロメタンスルホン酸、フルオロスルホン酸が例示される。これらの酸を単独又は併用して使用すればよい。 Acids include hydrogen fluoride, hydrogen chloride, hydrogen bromide, hydrogen iodide, sulfuric acid, nitric acid, phosphoric acid, formic acid, acetic acid, methanesulfonic acid, tetrafluoroboric acid, hexafluorophosphoric acid, hexafluoroarsenic acid, fluoro Examples include antimonic acid, hexafluorosilicic acid, hexafluorogermanic acid, hexafluorotin (IV) acid, trifluoroacetic acid, hexafluorotitanic acid, hexafluorozirconic acid, trifluoromethanesulfonic acid, and fluorosulfonic acid. These acids may be used alone or in combination.
　また、酸は水溶液として用いられるのが、作業の簡便性及び安全性の観点、並びに、副生物の除去の観点から好ましい。 In addition, it is preferable that the acid is used as an aqueous solution from the viewpoint of easy work and safety, and removal of by-products.
　酸は、ＣａＳｉ２に対して２当量以上のプロトンを供給できる量で用いればよい。したがって、１価の酸であれば、ＣａＳｉ２１モルに対して酸を２モル以上で用いればよい。 Acid may be used in an amount capable of providing 2 or more equivalents of protons relative CaSi 2. Therefore, if a monovalent acid, the acid may be used in two moles or more relative to CaSi 2 1 mol.
　反応条件は、真空などの減圧条件又は不活性ガス雰囲気下とすることが好ましく、また、氷浴などの室温以下の温度条件とするのが好ましい。反応時間は、適宜設定すればよい。 The reaction conditions are preferably a reduced pressure condition such as vacuum or an inert gas atmosphere, and a temperature condition of room temperature or lower such as an ice bath. What is necessary is just to set reaction time suitably.
　さて、ＣａＳｉ２と酸とを反応させる反応工程において、酸として塩化水素を用いた場合を反応式で示すと、以下のとおりとなる。 Now, in the reaction step of reacting CaSi 2 and an acid, the case where hydrogen chloride is used as the acid is shown in the reaction formula as follows.
　３ＣａＳｉ２＋６ＨＣｌ→Ｓｉ６Ｈ６＋３ＣａＣｌ２ 3CaSi 2 + 6HCl → Si 6 H 6 + 3CaCl 2
　ポリシランであるＳｉ６Ｈ６が理想的な層状シリコン化合物に該当する。この反応は、層状のＣａＳｉ２のＣａが２Ｈで置換されつつ、Ｓｉ－Ｈ結合を形成すると考えることもできる。層状シリコン化合物は、原料のＣａＳｉ２におけるＳｉ層の基本骨格が維持されているため、層状をなす。 Si 6 H 6 which is polysilane corresponds to an ideal layered silicon compound. This reaction can also be considered to form a Si—H bond while Ca in the layered CaSi 2 is substituted with 2H. The layered silicon compound has a layer shape because the basic skeleton of the Si layer in the raw material CaSi 2 is maintained.
　ＣａＳｉ２と酸とを反応させる反応工程において、酸は水溶液として用いられるのが好ましいことは、前述した。ここで、Ｓｉ６Ｈ６は水と反応し得るため、通常は、層状シリコン化合物がＳｉ６Ｈ６なる化合物のみで得られることはほとんどなく、酸素や酸由来の元素を含有する。 As described above, the acid is preferably used as an aqueous solution in the reaction step of reacting CaSi 2 with the acid. Here, since Si 6 H 6 can react with water, the layered silicon compound is rarely obtained only with a compound of Si 6 H 6 , and contains an element derived from oxygen or an acid.
　層状シリコン化合物を３００℃以上で加熱することで水素などを離脱させ、シリコン材料とする。この層状シリコン化合物を３００℃以上で加熱する工程を、以下シリコン材料製造工程ということがある。 ・ Heat is released from the layered silicon compound at 300 ° C. or higher to obtain a silicon material. The process of heating the layered silicon compound at 300 ° C. or higher is sometimes referred to as a silicon material manufacturing process.
　シリコン材料製造工程を理想的な反応式で示すと、以下のとおりとなる。 The silicon material manufacturing process is shown as an ideal reaction formula as follows.
　Ｓｉ６Ｈ６→６Ｓｉ＋３Ｈ２↑ Si 6 H 6 → 6Si + 3H 2 ↑
　ただし、シリコン材料製造工程に実際に用いられる層状シリコン化合物は、酸素や酸由来の元素を含有し、さらに不可避不純物も含有するため、実際に得られるシリコン材料も酸素や酸由来の元素を含有し、さらに不可避不純物も含有するものとなる。シリコン材料は、ケイ素のモル量を１００としたとき、酸素元素のモル量が５０以下であることが好ましく、４０以下の量となるのが特に好ましい。また、ケイ素のモル量を１００としたとき、酸由来の元素のモル量が８以下の量であることが好ましく、５以下の量となるのが特に好ましい。 However, since the layered silicon compound actually used in the silicon material manufacturing process contains oxygen and acid-derived elements and also contains inevitable impurities, the actually obtained silicon material also contains oxygen and acid-derived elements. Further, inevitable impurities are also contained. In the silicon material, when the molar amount of silicon is 100, the molar amount of oxygen element is preferably 50 or less, and particularly preferably 40 or less. When the molar amount of silicon is 100, the molar amount of the acid-derived element is preferably 8 or less, and particularly preferably 5 or less.
　シリコン材料製造工程は、通常の大気下よりも酸素含有量の少ない非酸化性雰囲気下で行われるのが好ましい。非酸化性雰囲気としては、真空を含む減圧雰囲気、不活性ガス雰囲気を例示できる。加熱温度は、３５０℃～１２００℃の範囲内が好ましく、４００℃～１２００℃の範囲内がより好ましい。加熱温度が低すぎると、水素の離脱が十分でない場合があり、他方、加熱温度が高すぎると、エネルギーの無駄になる。加熱時間は、加熱温度に応じて適宜設定すれば良く、また、反応系外に抜けていく水素などの量を測定しながら加熱時間を決定するのも好ましい。 The silicon material production process is preferably performed in a non-oxidizing atmosphere having a lower oxygen content than in normal air. Examples of the non-oxidizing atmosphere include a reduced pressure atmosphere including a vacuum and an inert gas atmosphere. The heating temperature is preferably in the range of 350 ° C. to 1200 ° C., more preferably in the range of 400 ° C. to 1200 ° C. If the heating temperature is too low, hydrogen may not be released sufficiently, while if the heating temperature is too high, energy is wasted. What is necessary is just to set a heating time suitably according to heating temperature, and it is also preferable to determine a heating time, measuring the quantity of hydrogen etc. which escapes out of a reaction system.
　加熱温度及び加熱時間を適宜選択することにより、製造されるシリコン材料に含まれるアモルファスシリコン及びシリコン結晶子の割合、並びに、シリコン結晶子の大きさを調製することもでき、さらには、製造されるシリコン材料に含まれる、アモルファスシリコン及びシリコン結晶子を含むナノ水準の厚みの層の形状や大きさを調製することもできる。 By appropriately selecting the heating temperature and the heating time, the ratio of amorphous silicon and silicon crystallites contained in the silicon material to be manufactured, and the size of the silicon crystallites can also be adjusted, and further manufactured. The shape and size of a nano-level layer containing amorphous silicon and silicon crystallites contained in the silicon material can also be prepared.
　また、シリコン材料をリチウムイオン二次電池などの二次電池の負極活物質として使用する場合は、シリコン材料を炭素で被覆して用いるのが好ましい。炭素は、非晶質の炭素のみであってもよいし、結晶質の炭素のみであってもよいし、非晶質の炭素と結晶質の炭素とが混在していてもよい。 In addition, when a silicon material is used as a negative electrode active material of a secondary battery such as a lithium ion secondary battery, it is preferable to use the silicon material covered with carbon. The carbon may be only amorphous carbon, may be crystalline carbon, or may be a mixture of amorphous carbon and crystalline carbon.
　シリコン材料に炭素を被覆する方法は特に限定されない。炭素被覆方法としては、炭素粉末とシリコン材料を混合（例えばメカニカルミリング）する方法、樹脂とシリコン材料の複合化から得られる混合物を加熱処理して樹脂を炭素化する方法、シリコン材料を非酸化性雰囲気下にて有機物ガスと接触させ、加熱して有機物ガスを炭素化する方法(熱ＣＶＤ法)などが挙げられる。 The method for coating the silicon material with carbon is not particularly limited. Carbon coating methods include mixing carbon powder and silicon material (for example, mechanical milling), heating the mixture obtained from the composite of resin and silicon material, and carbonizing the resin, and non-oxidizing silicon material. Examples thereof include a method (thermal CVD method) in which the organic gas is carbonized by being brought into contact with the organic gas in an atmosphere and heated.
　上記シリコン材料が負極活物質に含まれると、リチウムイオン二次電池の釘刺し試験時の短絡により電池の過加熱が生じるのが抑制される。この理由として、以下のことが考えられる。シリコン材料は、充放電により膨張、収縮する。シリコン材料は、釘刺し試験における瞬間的な放電時に、大きく収縮すると考えられる。そのため、負極内において持続的な短絡経路が維持できず、リチウムイオン二次電池の発熱量が小さくなると推測される。また、上記シリコン材料は、理由は不明であるが、ＳｉＯｘと比較しても充放電時の膨張、収縮が大きいと推測される。 When the silicon material is contained in the negative electrode active material, overheating of the battery due to a short circuit during a nail penetration test of the lithium ion secondary battery is suppressed. The reason for this is considered as follows. Silicon material expands and contracts due to charge and discharge. Silicon material is thought to shrink significantly upon momentary discharge in the nail penetration test. Therefore, it is presumed that a continuous short circuit path cannot be maintained in the negative electrode, and the calorific value of the lithium ion secondary battery is reduced. Further, the reason for the silicon material is unknown, but it is presumed that expansion and contraction during charge / discharge are large even when compared with SiO x .
　負極活物質層におけるシリコン材料の含有量は、負極活物質層を１００質量部としたときに、３０質量部以上８５質量部以下であることが好ましく、４０質量部以上８０質量部以下であることがより好ましく、５０質量部以上７５質量部以下であることがさらに好ましい。シリコン材料が上記範囲で含まれることにより、リチウムイオン二次電池の短絡時の発熱量の低減効果がより顕著となる。 The content of the silicon material in the negative electrode active material layer is preferably 30 parts by mass or more and 85 parts by mass or less, and preferably 40 parts by mass or more and 80 parts by mass or less when the negative electrode active material layer is 100 parts by mass. Is more preferable, and it is further more preferable that it is 50 to 75 mass parts. By including the silicon material in the above range, the effect of reducing the amount of heat generated when the lithium ion secondary battery is short-circuited becomes more prominent.
　負極活物質層は、上記シリコン材料以外に他の負極活物質を含んでもよい。他の負極活物質としては、リチウムを吸蔵、放出可能な炭素系材料、リチウムと合金化可能な元素、リチウムと合金化可能な元素を有する化合物、あるいは高分子材料などを用いることができる。 The negative electrode active material layer may contain other negative electrode active materials in addition to the silicon material. As another negative electrode active material, a carbon-based material capable of inserting and extracting lithium, an element capable of being alloyed with lithium, a compound having an element capable of being alloyed with lithium, a polymer material, or the like can be used.
　炭素系材料としては、黒鉛、難黒鉛化性炭素、コークス類、グラファイト類、ガラス状炭素類、有機高分子化合物焼成体、炭素繊維、活性炭あるいはカーボンブラック類が挙げられる。ここで、有機高分子化合物焼成体とは、フェノール類やフラン類などの高分子材料を適当な温度で焼成して炭素化したものをいう。 Examples of the carbon-based material include graphite, non-graphitizable carbon, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon, and carbon blacks. Here, the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.
　リチウムと合金化可能な元素は、Ｎａ、Ｋ、Ｒｂ、Ｃｓ、Ｆｒ、Ｂｅ、Ｍｇ、Ｃａ、Ｓｒ、Ｂａ、Ｒａ、Ｔｉ、Ａｇ、Ｚｎ、Ｃｄ、Ａｌ、Ｇａ、Ｉｎ、Ｓｉ、Ｇｅ、Ｓｎ、Ｐｂ、Ｓｂ、Ｂｉの少なくとも１種である。 Elements that can be alloyed with lithium are Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn. , Pb, Sb, Bi.
　リチウムと合金化可能な元素を有する化合物としては、例えば、ＺｎＬｉＡｌ、ＡｌＳｂ、ＳｉＢ４、ＳｉＢ６、Ｍｇ２Ｓｉ、Ｍｇ２Ｓｎ、Ｎｉ２Ｓｉ、ＴｉＳｉ２、ＭｏＳｉ２、 ＣｏＳｉ２、ＮｉＳｉ２、ＣａＳｉ２、ＣｒＳｉ２、Ｃｕ５Ｓｉ、ＦｅＳｉ２、ＭｎＳｉ２、ＮｂＳｉ２、ＴａＳｉ２、ＶＳｉ２、ＷＳｉ２、ＺｎＳｉ２、ＳｉＣ、Ｓｉ３Ｎ４、Ｓｉ２Ｎ２Ｏ、ＳｉＯｖ（０＜ｖ≦２）、ＳｎＯｗ（０＜ｗ≦２）、ＳｎＳｉＯ３、ＬｉＳｉＯ あるいはＬｉＳｎＯなどが使用できる。 Examples of the compound having an element that can be alloyed with lithium include ZnLiAl, AlSb, SiB 4 , SiB 6 , Mg 2 Si, Mg 2 Sn, Ni 2 Si, TiSi 2 , MoSi 2 , CoSi 2 , NiSi 2 , and CaSi. 2, CrSi 2, Cu 5 Si , FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 <v ≦ 2), SnO w (0 <w ≦ 2), SnSiO 3 , LiSiO or LiSnO can be used.
　高分子材料としては、ポリアセチレン、ポリピロールなどが使用できる。 As the polymer material, polyacetylene, polypyrrole, or the like can be used.
　他の負極活物質としては、炭素系材料が好ましい。 The other negative electrode active material is preferably a carbon-based material.
　負極活物質は、粉末形状であることが好ましい。負極活物質が粉末形状の場合、負極活物質の平均粒径Ｄ５０は、０．５μｍ以上３０μｍ以下であることが好ましく、１μｍ以上２０μｍ以下であることがより好ましい。負極活物質の平均粒径Ｄ５０が小さすぎると、負極活物質の粉末の比表面積が大きくなり、負極活物質の粉末と電解液との接触面積が大きくなって、電解液の分解が進んでしまい、リチウムイオン二次電池のサイクル特性が悪くなるおそれがある。負極活物質の平均粒径Ｄ５０が大きすぎると、電極全体の導電性が不均一になり、充放電特性が低下するおそれがある。 The negative electrode active material is preferably in powder form. When the negative electrode active material is in a powder form, the average particle diameter D 50 of the negative electrode active material is preferably 0.5 μm or more and 30 μm or less, and more preferably 1 μm or more and 20 μm or less. When the average particle diameter D 50 of the negative electrode active material is too small, the specific surface area of the powder of the negative electrode active material is increased, it increases the contact area of the powder of the anode active material and the electrolyte solution, proceed decomposition of the electrolyte solution Therefore, the cycle characteristics of the lithium ion secondary battery may be deteriorated. When the average particle diameter D 50 of the negative electrode active material is too large, conductivity of the whole electrode becomes uneven, charging and discharging characteristics may deteriorate.
　負極活物質層を集電体の表面に配置するには、正極活物質層を集電体の表面に配置するのと同様にして行うことができる。 The negative electrode active material layer can be disposed on the surface of the current collector in the same manner as the positive electrode active material layer is disposed on the surface of the current collector.
　負極活物質層の密度は、０．５ｇ／ｃｍ３以上２ｇ／ｃｍ３以下であることが好ましく、０．８ｇ／ｃｍ３以上１．５ｇ／ｃｍ３以下であることがより好ましく、１．０ｇ／ｃｍ３以上１．３ｇ／ｃｍ３以下であることが特に好ましい。 The density of the negative electrode active material layer is preferably 0.5 g / cm 3 or more and 2 g / cm 3 or less, more preferably 0.8 g / cm 3 or more and 1.5 g / cm 3 or less, and 1.0 g / Cm 3 or more and 1.3 g / cm 3 or less is particularly preferable.
　(セパレータ)
　セパレータは、正極と負極とを隔離し、両極の接触による電流の短絡を防止しつつ、リチウムイオンを通過させるものである。セパレータとして、例えばポリテトラフルオロエチレン、ポリプロピレン、ポリエチレン、ポリエステル、ポリアミドなどの合成樹脂製の多孔質膜、またはセラミックス製の多孔質膜が挙げられる。シリコン材料を含む負極の充放電による膨張収縮に追随しやすくなるように、セパレータは合成樹脂製の多孔質膜を含むことが好ましい。 (Separator)
The separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit of current due to contact between the two electrodes. Examples of the separator include a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, polyethylene, polyester, and polyamide, or a porous film made of ceramics. The separator preferably includes a porous film made of a synthetic resin so that it can easily follow expansion and contraction due to charging and discharging of the negative electrode including the silicon material.
　合成樹脂製のセパレータは、単一の合成樹脂を用いた単層構造でもよいし、複数の合成樹脂の層を重ねた積層構造でもよい。セパレータの厚みは、特に制限されないが、５μｍ～１００μｍの範囲が好ましく、１０μｍ～５０μｍの範囲がより好ましく、１５μｍ～３０μｍの範囲が特に好ましい。 The separator made of synthetic resin may have a single layer structure using a single synthetic resin or a laminated structure in which a plurality of synthetic resin layers are stacked. The thickness of the separator is not particularly limited, but is preferably in the range of 5 μm to 100 μm, more preferably in the range of 10 μm to 50 μm, and particularly preferably in the range of 15 μm to 30 μm.
　(非水電解液)
　非水電解液は、非水溶媒と非水溶媒に溶解された電解質とを含んでいる。 (Non-aqueous electrolyte)
The nonaqueous electrolytic solution contains a nonaqueous solvent and an electrolyte dissolved in the nonaqueous solvent.
　非水溶媒として、例えば、環状エステル類、鎖状エステル類、エーテル類が挙げられる。環状エステル類として、例えばエチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、ガンマブチロラクトン、ビニレンカーボネート、２－メチル－ガンマブチロラクトン、アセチル－ガンマブチロラクトン、ガンマバレロラクトンが挙げられる。鎖状エステル類として、例えばジメチルカーボネート、ジエチルカーボネート、ジブチルカーボネート、ジプロピルカーボネート、エチルメチルカーボネート、プロピオン酸アルキルエステル、マロン酸ジアルキルエステル、酢酸アルキルエステルが挙げられる。エーテル類として、例えばテトラヒドロフラン、２－メチルテトラヒドロフラン、１，４－ジオキサン、１，２－ジメトキシエタン、１，２－ジエトキシエタン、１，２－ジブトキシエタンが挙げられる。非水溶媒としては、上記具体的な非水溶媒の化学構造のうち一部または全部の水素がフッ素に置換した化合物を採用してもよい。非水溶媒の化学構造のうち一部または全部の水素がフッ素置換された化合物としては、例えばフルオロエチレンカーボネート、ジフルオロエチレンカーボネートが挙げられる。 Examples of the non-aqueous solvent include cyclic esters, chain esters, and ethers. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of the chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, ethyl methyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. As the non-aqueous solvent, a compound in which part or all of hydrogen in the chemical structure of the specific non-aqueous solvent is substituted with fluorine may be employed. Examples of the compound in which part or all of hydrogen in the chemical structure of the non-aqueous solvent is fluorine-substituted include, for example, fluoroethylene carbonate and difluoroethylene carbonate.
　また上記非水電解液に溶解させる電解質として、例えばＬｉＣｌＯ４、ＬｉＡｓＦ６、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣＦ３ＳＯ３、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＮ（ＦＳＯ２）２等のリチウム塩を使用することができる。 Further, as an electrolyte to be dissolved in the non-aqueous electrolyte, for example, a lithium salt such as LiClO 4 , LiAsF 6 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN (FSO 2 ) 2 is used. Can be used.
　非水電解液として、例えば、エチレンカーボネート、ジメチルカーボネート、エチルメチルカーボネート、ジエチルカーボネートなどの溶媒にＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣＦ３ＳＯ３、ＬｉＮ（ＦＳＯ２）２などのリチウム塩を０．５ｍｏｌ／ｌから１．７ｍｏｌ／ｌ程度の濃度で溶解させた溶液を使用することができる。 As the non-aqueous electrolyte, for example, a lithium salt such as LiClO 4 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 , LiN (FSO 2 ) 2 is added to a solvent such as ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. A solution dissolved at a concentration of about 5 mol / l to 1.7 mol / l can be used.
　正極および負極にセパレータを挟装させ、電極体とする。電極体は、正極、セパレータ及び負極を重ねた積層型、又は、正極、セパレータ及び負極を捲いた捲回型のいずれの型にしてもよい。正極用集電体および負極用集電体から外部に通ずる正極タブ部および負極タブ部までの間を、集電用リード等を用いて接続した後に、電極体に非水電解液を加えてリチウムイオン二次電池とするとよい。また、本発明のリチウムイオン二次電池は、電極に含まれる活物質の種類に適した電圧範囲で、充放電を実行されればよい。 A separator is sandwiched between the positive electrode and the negative electrode to form an electrode body. The electrode body may be any of a stacked type in which a positive electrode, a separator and a negative electrode are stacked, or a wound type in which a positive electrode, a separator and a negative electrode are sandwiched. After connecting the current collector for the positive electrode and the current collector for the negative electrode to the positive electrode tab portion and the negative electrode tab portion that communicate with the outside using a current collector lead, etc., a non-aqueous electrolyte is added to the electrode body and lithium is added. It is preferable to use an ion secondary battery. Moreover, the lithium ion secondary battery of this invention should just be charged / discharged in the voltage range suitable for the kind of active material contained in an electrode.
　リチウムイオン二次電池の形状は、特に限定されるものでなく、円筒型、角型、コイン型、ラミネート型等、種々の形状を採用することができる。 The shape of the lithium ion secondary battery is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be adopted.
　上記リチウムイオン二次電池は、車両に搭載することができる。上記リチウムイオン二次電池は、安全性が高いため、そのリチウムイオン二次電池を搭載した車両は、安全性が高くなる。 The lithium ion secondary battery can be mounted on a vehicle. Since the lithium ion secondary battery has high safety, a vehicle equipped with the lithium ion secondary battery has high safety.
　車両としては、電池による電気エネルギーを動力源の全部または一部に使用する車両であればよく、例えば、電気自動車、ハイブリッド自動車、プラグインハイブリッド自動車、ハイブリッド鉄道車両、電動フォークリフト、電気車椅子、電動アシスト自転車、電動二輪車が挙げられる。 The vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source. For example, an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, an electric forklift, an electric wheelchair, and an electric assist. Bicycles and electric motorcycles are examples.
　以上、本発明のリチウムイオン二次電池の実施形態を説明したが、本発明は、上記実施形態に限定されるものではない。本発明の要旨を逸脱しない範囲において、当業者が行い得る変更、改良等を施した種々の形態にて実施することができる。 As mentioned above, although embodiment of the lithium ion secondary battery of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.
　以下、実施例を挙げて本発明を更に詳しく説明する。 Hereinafter, the present invention will be described in more detail with reference to examples.
　（正極の作成）
　（正極Ａ）
　正極活物質として平均粒径Ｄ５０が６μｍのＬｉＮｉ０．５Ｃｏ０．２Ｍｎ０．３Ｏ２と、正極活物質として表面をカーボンコートした平均粒径Ｄ５０が１．５μｍのＬｉＦｅＰＯ４と、導電助剤としてアセチレンブラックと、結着剤としてポリフッ化ビニリデン（以下ＰＶＤＦと称す。）とを、それぞれ６７質量部、２７質量部、３質量部、３質量部の割合で混合し、この混合物を適量のＮ－メチル－２－ピロリドン（以下ＮＭＰと称す。）に分散させて、正極活物質層用スラリーを作製した。 (Creation of positive electrode)
(Positive electrode A)
LiNi 0.5 Co 0.2 Mn 0.3 O 2 having an average particle diameter D 50 of 6 μm as a positive electrode active material, and LiFePO 4 having an average particle diameter D 50 of 1.5 μm having a carbon coating on the surface as a positive electrode active material, Acetylene black as a conductive additive and polyvinylidene fluoride (hereinafter referred to as PVDF) as a binder were mixed in a ratio of 67 parts by mass, 27 parts by mass, 3 parts by mass, and 3 parts by mass, respectively. Was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (hereinafter referred to as NMP) to produce a positive electrode active material layer slurry.
　集電体として厚み１５μｍのアルミニウム箔を準備した。集電体に、正極活物質層用スラリーをのせ、コンマコーターを用いて、正極活物質層用スラリーを膜状に塗布した。正極活物質層用スラリーが塗布された集電体を、９０℃で５分間乾燥し、次に、１２０℃で５分間乾燥して、ＮＭＰを揮発させて除去した。その後、ロ－ルプレス機により、集電体と集電体上の塗布物を強固に密着接合させた。この時、正極活物質層の目付は２７．０ｍｇ／ｃｍ２となるようにした。ここでいう正極活物質層の目付は、正極活物質層の質量（ｇ）÷正極活物質層の面積（ｃｍ２）の式より算出した。接合物を１２０℃で６時間、真空乾燥機で加熱した。加熱後の接合物を、所定の形状（４０ｍｍ×８０ｍｍの矩形状）に切り取り、正極Ａとした。正極Ａの正極活物質層の厚さは９０μｍ程度であった。また、正極Ａの正極活物質層の密度は２．９ｇ／ｃｍ３であった。 An aluminum foil having a thickness of 15 μm was prepared as a current collector. The positive electrode active material layer slurry was placed on the current collector, and the positive electrode active material layer slurry was applied in a film form using a comma coater. The current collector coated with the positive electrode active material layer slurry was dried at 90 ° C. for 5 minutes and then dried at 120 ° C. for 5 minutes to volatilize and remove NMP. Thereafter, the current collector and the coated material on the current collector were firmly bonded by a roll press. At this time, the basis weight of the positive electrode active material layer was set to 27.0 mg / cm 2 . Here, the basis weight of the positive electrode active material layer was calculated from the equation: mass of positive electrode active material layer (g) ÷ area of positive electrode active material layer (cm 2 ). The bonded product was heated in a vacuum dryer at 120 ° C. for 6 hours. The bonded product after heating was cut into a predetermined shape (rectangular shape of 40 mm × 80 mm) to obtain a positive electrode A. The thickness of the positive electrode active material layer of the positive electrode A was about 90 μm. Further, the density of the positive electrode active material layer of the positive electrode A was 2.9 g / cm 3 .
　(正極Ｂ)
　正極活物質として平均粒径Ｄ５０が６μｍのＬｉＮｉ０．５Ｃｏ０．２Ｍｎ０．３Ｏ２と、導電助剤としてアセチレンブラックと、結着剤としてＰＶＤＦとを、それぞれ９４質量部、３質量部、３質量部の割合で混合し、この混合物を適量のＮＭＰに分散させて、正極活物質層用スラリーを作製した以外は、正極Ａと同様にして、正極Ｂを作製した。正極Ｂの正極活物質層の厚さは８０μｍ程度であった。また、正極Ｂの正極活物質層の密度は２．９ｇ／ｃｍ３であった。 (Positive electrode B)
94 parts by mass of LiNi 0.5 Co 0.2 Mn 0.3 O 2 having an average particle diameter D 50 of 6 μm as a positive electrode active material, acetylene black as a conductive additive, and PVDF as a binder, A positive electrode B was prepared in the same manner as the positive electrode A, except that the mixture was mixed at a ratio of 3 parts by mass and the mixture was dispersed in an appropriate amount of NMP to prepare a positive electrode active material layer slurry. The thickness of the positive electrode active material layer of the positive electrode B was about 80 μm. Moreover, the density of the positive electrode active material layer of the positive electrode B was 2.9 g / cm 3 .
　(正極Ｃ)
　正極活物質として平均粒径Ｄ５０が６μｍのＬｉＮｉ０．５Ｃｏ０．２Ｍｎ０．３Ｏ２と、正極活物質として表面をカーボンコートした平均粒径Ｄ５０が１．５μｍのＬｉＦｅＰＯ４と、導電助剤としてアセチレンブラックと、結着剤としてＰＶＤＦとを、それぞれ６９質量部、２５質量部、３質量部、３質量部の割合で混合し、この混合物を適量のＮＭＰに分散させて、正極活物質層用スラリーを作製した以外は、正極Ａと同様にして、正極Ｃを作製した。正極Ｃの正極活物質層の厚さは８９μｍ程度であった。また、正極Ｃの正極活物質層の密度は２．９ｇ／ｃｍ３であった。 (Positive electrode C)
LiNi 0.5 Co 0.2 Mn 0.3 O 2 having an average particle diameter D 50 of 6 μm as a positive electrode active material, and LiFePO 4 having an average particle diameter D 50 of 1.5 μm having a carbon coating on the surface as a positive electrode active material, In addition, acetylene black as a conductive assistant and PVDF as a binder are mixed in a ratio of 69 parts by mass, 25 parts by mass, 3 parts by mass, and 3 parts by mass, respectively, and this mixture is dispersed in an appropriate amount of NMP. A positive electrode C was prepared in the same manner as the positive electrode A, except that the positive electrode active material layer slurry was prepared. The thickness of the positive electrode active material layer of the positive electrode C was about 89 μm. Further, the density of the positive electrode active material layer of the positive electrode C was 2.9 g / cm 3 .
　（負極の作製）
　（シリコン材料の作製）
　炭素で被覆されたシリコン材料を以下のように作製した。 (Preparation of negative electrode)
(Production of silicon material)
A silicon material coated with carbon was prepared as follows.
　濃度４６質量％のＨＦ水溶液７ｍｌと、濃度３６質量％のＨＣｌ水溶液５６ｍｌとの混合溶液を、氷浴中で０℃とし、アルゴンガス気流中にて、そこへ３．３ｇのＣａＳｉ２を加えて撹拌した。発泡が完了したのを確認した後に、混合溶液を室温まで昇温し、室温でさらに２時間撹拌した後、蒸留水２０ｍｌを加えて、さらに１０分間撹拌した。このとき、黄色粉末が浮遊した。 A mixed solution of 7 ml of an aqueous HF solution having a concentration of 46% by mass and 56 ml of an aqueous HCl solution having a concentration of 36% by mass was brought to 0 ° C. in an ice bath, and 3.3 g of CaSi 2 was added thereto in an argon gas stream. Stir. After confirming the completion of foaming, the mixed solution was warmed to room temperature, stirred for another 2 hours at room temperature, then added with 20 ml of distilled water, and further stirred for 10 minutes. At this time, yellow powder floated.
　得られた混合溶液を濾過し、得られた残渣を１０ｍｌの蒸留水で洗浄した後、１０ｍｌのエタノールで洗浄した。洗浄後の残渣を真空乾燥して、２．５ｇの層状ポリシランを得た。 The obtained mixed solution was filtered, and the obtained residue was washed with 10 ml of distilled water and then with 10 ml of ethanol. The residue after washing was vacuum dried to obtain 2.5 g of layered polysilane.
　この層状ポリシランを１ｇ秤量し、Ｏ２を１体積％以下の量で含むアルゴンガス中にて、５００℃で１時間保持する熱処理を行い、シリコン材料を得た。 1 g of this layered polysilane was weighed, and a heat treatment was performed in an argon gas containing O 2 in an amount of 1% by volume or less at 500 ° C. for 1 hour to obtain a silicon material.
　得られたシリコン材料を、ロータリーキルン型の反応器に入れ、プロパンガス通気下にて８５０℃、滞留時間５分間の条件で熱ＣＶＤによる炭素化工程を行い、炭素で被覆されたシリコン材料を得た。ロータリーキルン型の反応器では、回転式でシリコン材料を循環させながら加熱するため、炭素の被覆ムラがおこりにくい。反応器の回転速度は１ｒｐｍとした。この炭素で被覆されたシリコン材料の平均粒径Ｄ５０は、５μｍであった。 The obtained silicon material was put into a rotary kiln type reactor and subjected to a carbonization process by thermal CVD under a condition of 850 ° C. and a residence time of 5 minutes under a flow of propane gas to obtain a silicon material coated with carbon. . In the rotary kiln type reactor, since the silicon material is heated while being circulated in a rotary type, uneven coating of carbon hardly occurs. The rotation speed of the reactor was 1 rpm. The average particle diameter D 50 of the silicon material coated with this carbon was 5 [mu] m.
　(負極Ａ)
　負極活物質として、平均粒子径Ｄ５０が４μｍのＳｉＯ及び平均粒子径Ｄ５０が１５μｍの天然黒鉛を準備した。バインダー樹脂としてポリアミドイミド樹脂を準備した。導電助剤としてアセチレンブラックを準備した。 (Negative electrode A)
As the negative electrode active material, SiO having an average particle diameter D 50 of 4 μm and natural graphite having an average particle diameter D 50 of 15 μm were prepared. A polyamide-imide resin was prepared as a binder resin. Acetylene black was prepared as a conductive aid.
　上記負極活物質、導電助剤及びバインダー樹脂を、ＳｉＯ：黒鉛：導電助剤：バインダー樹脂＝３２：５０：８：１０の質量比で混合した。上記混合物に、溶媒としてＮＭＰを適量入れて調整して、負極活物質層用スラリーとした。 The negative electrode active material, conductive auxiliary agent and binder resin were mixed at a mass ratio of SiO: graphite: conductive auxiliary agent: binder resin = 32: 50: 8: 10. An appropriate amount of NMP was added as a solvent to the above mixture to prepare a negative electrode active material layer slurry.
　負極用集電体として、２０μｍの銅箔を準備した。銅箔にコンマコーターを用いて、上記負極活物質層用スラリーを、膜状に塗布した。負極活物質層用スラリーが塗布された銅箔を、８０℃で５分間乾燥して、ＮＭＰを揮発させて除去した。その後、ロ－ルプレス機により、集電体と集電体上の塗布物を強固に密着接合させた。この時、負極活物質層の目付は７．５ｍｇ／ｃｍ２となるようにした。ここでいう負極活物質層の目付は、負極活物質層の質量（ｇ）÷負極活物質層の面積（ｃｍ２）の式より算出した。接合物を２００℃で２時間、真空乾燥機で加熱した後、所定の形状（負極活物質層面積４４ｍｍ×８４ｍｍの矩形状）に切り取り、負極Ａとした。負極Ａの負極活物質層の厚さは、４７μｍ程度であった。また、負極Ａの負極活物質層の密度は、１．６ｇ／ｃｍ３であった。 A 20 μm copper foil was prepared as a negative electrode current collector. The said slurry for negative electrode active material layers was apply | coated to the film form using the comma coater for copper foil. The copper foil coated with the negative electrode active material layer slurry was dried at 80 ° C. for 5 minutes to volatilize and remove NMP. Thereafter, the current collector and the coated material on the current collector were firmly bonded by a roll press. At this time, the basis weight of the negative electrode active material layer was set to 7.5 mg / cm 2 . Here, the basis weight of the negative electrode active material layer was calculated from the equation: mass of negative electrode active material layer (g) ÷ area of negative electrode active material layer (cm 2 ). The joined product was heated in a vacuum dryer at 200 ° C. for 2 hours, and then cut into a predetermined shape (rectangular shape having a negative electrode active material layer area of 44 mm × 84 mm) to form a negative electrode A. The thickness of the negative electrode active material layer of the negative electrode A was about 47 μm. Moreover, the density of the negative electrode active material layer of the negative electrode A was 1.6 g / cm 3 .
　(負極Ｂ)
　負極活物質として、上記炭素で被覆されたシリコン材料と、上記天然黒鉛とを準備した。上記負極活物質、負極Ａで用いた導電助剤及びバインダー樹脂を、炭素で被覆されたシリコン材料：黒鉛：導電助剤：バインダー樹脂＝３２：５０：８：１０の質量比で混合した。上記混合物に、溶媒としてＮＭＰを適量入れて調整して、負極活物質層用スラリーとした。この負極活物質層用スラリーを用い、負極活物質層の目付が６．０ｍｇ／ｃｍ２となるようにした以外は、負極Ａと同様にして、負極Ｂを作製した。負極Ｂの負極活物質層の厚さは、５０μｍ程度であった。また、負極Ｂの負極活物質層の密度は、１．２ｇ／ｃｍ３であった。 (Negative electrode B)
As the negative electrode active material, the silicon material coated with carbon and the natural graphite were prepared. The negative electrode active material, the conductive auxiliary agent used in the negative electrode A, and the binder resin were mixed at a mass ratio of silicon material coated with carbon: graphite: conductive auxiliary agent: binder resin = 32: 50: 8: 10. An appropriate amount of NMP was added as a solvent to the above mixture to prepare a negative electrode active material layer slurry. A negative electrode B was produced in the same manner as the negative electrode A, except that this negative electrode active material layer slurry was used and the basis weight of the negative electrode active material layer was 6.0 mg / cm 2 . The thickness of the negative electrode active material layer of the negative electrode B was about 50 μm. Moreover, the density of the negative electrode active material layer of the negative electrode B was 1.2 g / cm 3 .
　(負極Ｃ)
　負極Ｂで用いた負極活物質、負極Ａで用いた導電助剤及びバインダー樹脂を、炭素で被覆されたシリコン材料：黒鉛：導電助剤：バインダー樹脂＝５０：３５：５：１０の質量比で混合した。上記混合物に、溶媒としてＮＭＰを適量入れて調整して、負極活物質層用スラリーとした。この負極活物質層用スラリーを用い、負極活物質層の目付が５．５ｍｇ／ｃｍ２となるようにした以外は、負極Ａと同様にして、負極Ｃを作製した。負極Ｃの負極活物質層の厚さは、５０μｍ程度であった。また、負極Ｃの負極活物質層の密度は、１．１ｇ／ｃｍ３であった。 (Negative electrode C)
The negative electrode active material used in the negative electrode B, the conductive auxiliary agent used in the negative electrode A, and the binder resin, silicon material coated with carbon: graphite: conductive auxiliary agent: binder resin = 50: 35: 5: 10 Mixed. An appropriate amount of NMP was added as a solvent to the above mixture to prepare a negative electrode active material layer slurry. A negative electrode C was produced in the same manner as the negative electrode A, except that this negative electrode active material layer slurry was used and the basis weight of the negative electrode active material layer was 5.5 mg / cm 2 . The thickness of the negative electrode active material layer of the negative electrode C was about 50 μm. Moreover, the density of the negative electrode active material layer of the negative electrode C was 1.1 g / cm 3 .
　(負極Ｄ) 
　負極活物質層の密度を、１．２ｇ／ｃｍ３とした以外は、負極Ｃと同様にして、負極Ｄを作製した。負極Ｄの負極活物質層の厚さは、４６μｍ程度であった。なお、負極Ｄの負極活物質層の目付は５．５ｍｇ／ｃｍ２であった。 (Negative electrode D)
A negative electrode D was produced in the same manner as the negative electrode C, except that the density of the negative electrode active material layer was 1.2 g / cm 3 . The thickness of the negative electrode active material layer of the negative electrode D was about 46 μm. The basis weight of the negative electrode active material layer of the negative electrode D was 5.5 mg / cm 2 .
　(負極Ｅ)
　負極Ｂで用いた負極活物質、負極Ａで用いた導電助剤及びバインダー樹脂を、炭素で被覆されたシリコン材料：黒鉛：導電助剤：バインダー樹脂＝５８：２４：７：１１の質量比で混合した。上記混合物に、溶媒としてＮＭＰを適量入れて調整して、負極活物質層用スラリーとした。そしてこの時、負極活物質層の目付が４．９ｍｇ／ｃｍ２となるようにした以外は、負極Ａと同様にして、負極Ｅを作製した。負極Ｅの負極活物質層の厚さは、４５μｍ程度であった。また負極Ｅの負極活物質層の密度は、１．１ｇ／ｃｍ３であった。 (Negative electrode E)
The negative electrode active material used in the negative electrode B, the conductive auxiliary agent used in the negative electrode A, and the binder resin are coated with carbon. Silicon material: graphite: conductive auxiliary agent: binder resin = 58: 24: 7: 11 Mixed. An appropriate amount of NMP was added as a solvent to the above mixture to prepare a negative electrode active material layer slurry. At this time, a negative electrode E was produced in the same manner as the negative electrode A, except that the basis weight of the negative electrode active material layer was 4.9 mg / cm 2 . The thickness of the negative electrode active material layer of the negative electrode E was about 45 μm. Further, the density of the negative electrode active material layer of the negative electrode E was 1.1 g / cm 3 .
　(負極Ｆ)
　負極活物質層の密度が１．２ｇ／ｃｍ３となるようにした以外は、負極Ｅと同様にして、負極Ｆを作製した。負極Ｆの負極活物質層の厚さは、４１μｍ程度であった。なお、負極Ｆの負極活物質層の目付は、４．９ｍｇ／ｃｍ２であった。 (Negative electrode F)
A negative electrode F was produced in the same manner as the negative electrode E, except that the density of the negative electrode active material layer was 1.2 g / cm 3 . The thickness of the negative electrode active material layer of the negative electrode F was about 41 μm. The basis weight of the negative electrode active material layer of the negative electrode F was 4.9 mg / cm 2 .
　(負極Ｇ)
　負極Ｂで用いた負極活物質、負極Ａで用いた導電助剤及びバインダー樹脂を、炭素で被覆されたシリコン材料：黒鉛：導電助剤：バインダー樹脂＝７０：１５：５：１０の質量比で混合した。上記混合物に、溶媒としてＮＭＰを適量入れて調整して、負極活物質層用スラリーとした。そしてこの時、負極活物質層の目付が４．０ｍｇ／ｃｍ２となるようにした以外は、負極Ａと同様にして、負極Ｇを作製した。負極Ｇの負極活物質層の厚さは、３６μｍ程度であった。また、負極Ｇの負極活物質層の密度は、１．１ｇ／ｃｍ３であった。 (Negative electrode G)
The negative electrode active material used in the negative electrode B, the conductive auxiliary agent used in the negative electrode A, and the binder resin are coated with carbon. Silicon material: graphite: conductive auxiliary agent: binder resin = 70: 15: 5: 10 Mixed. An appropriate amount of NMP was added as a solvent to the above mixture to prepare a negative electrode active material layer slurry. At this time, a negative electrode G was produced in the same manner as the negative electrode A, except that the basis weight of the negative electrode active material layer was 4.0 mg / cm 2 . The thickness of the negative electrode active material layer of the negative electrode G was about 36 μm. Further, the density of the negative electrode active material layer of the negative electrode G was 1.1 g / cm 3 .
　(負極Ｈ)
　負極活物質層の密度が１．２ｇ／ｃｍ３となるようにした以外は、負極Ｇと同様にして、負極Ｈを作製した。負極Ｈの負極活物質層の厚さは、３３μｍ程度であった。なお、負極Ｈの負極活物質層の目付は、４．０ｍｇ／ｃｍ２であった。 (Negative electrode H)
A negative electrode H was produced in the same manner as the negative electrode G, except that the density of the negative electrode active material layer was 1.2 g / cm 3 . The thickness of the negative electrode active material layer of the negative electrode H was about 33 μm. The basis weight of the negative electrode active material layer of the negative electrode H was 4.0 mg / cm 2 .
　（負極Ｉ）
　負極Ｂで用いた負極活物質、負極Ａで用いた導電助剤及びバインダー樹脂を、炭素で被覆されたシリコン材料：導電助剤：バインダー樹脂＝７３：１３：１４の質量比で混合した。上記混合物に、溶媒としてＮＭＰを適量入れて調整して、負極活物質層用スラリーとした。この負極活物質層用スラリーを用い、負極活物質層の密度を１．１ｇ／ｃｍ３とした以外は、負極Ｆと同様にして、負極Ｉを作製した。負極Ｉの負極活物質層の厚さは５２μｍ程度であった。なお、負極活物質層の目付は、５．７ｍｇ／ｃｍ２とであった。 (Negative electrode I)
The negative electrode active material used in the negative electrode B, the conductive auxiliary agent used in the negative electrode A, and the binder resin were mixed in a mass ratio of silicon material coated with carbon: conductive auxiliary agent: binder resin = 73: 13: 14. An appropriate amount of NMP was added as a solvent to the above mixture to prepare a negative electrode active material layer slurry. A negative electrode I was produced in the same manner as the negative electrode F, except that this negative electrode active material layer slurry was used and the density of the negative electrode active material layer was 1.1 g / cm 3 . The thickness of the negative electrode active material layer of the negative electrode I was about 52 μm. The basis weight of the negative electrode active material layer was 5.7 mg / cm 2 .
　＜ラミネート型リチウムイオン二次電池作製＞
　（実施例１）
　実施例１のラミネート型リチウムイオン二次電池を、次のようにして作製した。 <Production of laminated lithium-ion secondary battery>
Example 1
The laminated lithium ion secondary battery of Example 1 was produced as follows.
　上記の正極Ａを３０枚及び負極Ｂを３１枚用いて、ラミネート型リチウムイオン二次電池を製作した。詳しくは、各正極および各負極の間に、セパレータとして多孔性のポリエチレンフィルムからなる矩形状シート（４８ｍｍ×８８ｍｍ、厚さ２５μｍ）を挟装し、積層して極板群とした。この極板群を二枚一組のラミネートフィルムで覆い、三辺をシールした後、袋状となったラミネートフィルムに電解液を注入した。電解液の注液量は、電池容量に対して３．４ｍｌ／Ａｈとなるようにした。 A laminate type lithium ion secondary battery was manufactured using 30 positive electrodes A and 31 negative electrodes B. Specifically, a rectangular sheet (48 mm × 88 mm, thickness 25 μm) made of a porous polyethylene film as a separator was sandwiched between each positive electrode and each negative electrode, and laminated to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then an electrolyte solution was injected into the bag-like laminated film. The amount of electrolyte injected was 3.4 ml / Ah with respect to the battery capacity.
　電解液として、フルオロエチレンカーボネート（以下ＦＥＣと称す。）、エチレンカーボネート（以下ＥＣと称す。）と、エチルメチルカーボネート（以下ＥＭＣと称す。）と、ジメチルカーボネート（以下ＤＭＣと称す。）をＦＥＣ：ＥＣ：ＥＭＣ：ＤＭＣ＝０．４：２．６：３：４（体積比）で混合した溶媒にＬｉＰＦ6を１モル／ｌとなるように溶解した溶液を用いた。その後、残りの一辺をシールすることで、四辺が気密にシールされ、極板群および電解液が密閉されたラミネート型リチウムイオン二次電池を得た。なお、正極および負極は外部と電気的に接続可能なタブ部を備え、このタブ部の一部はラミネート型リチウムイオン二次電池の外側に延出している。以上の工程で、実施例１のラミネート型リチウムイオン二次電池を作製した。 As the electrolyte, fluoroethylene carbonate (hereinafter referred to as FEC), ethylene carbonate (hereinafter referred to as EC), ethyl methyl carbonate (hereinafter referred to as EMC), and dimethyl carbonate (hereinafter referred to as DMC) are FEC: A solution prepared by dissolving LiPF 6 in a solvent mixed at EC: EMC: DMC = 0.4: 2.6: 3: 4 (volume ratio) to 1 mol / l was used. Thereafter, the remaining one side was sealed to obtain a laminate type lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. The positive electrode and the negative electrode have a tab portion that can be electrically connected to the outside, and a part of the tab portion extends to the outside of the laminated lithium ion secondary battery. The laminated lithium ion secondary battery of Example 1 was produced through the above steps.
　（実施例２）
　実施例１における負極Ｂの代わりに負極Ｃを用いた以外は、実施例１と同様にして、実施例２のラミネート型リチウムイオン二次電池を作製した。 (Example 2)
A laminated lithium ion secondary battery of Example 2 was produced in the same manner as in Example 1 except that the negative electrode C was used instead of the negative electrode B in Example 1.
　（実施例３）
　実施例１における負極Ｂの代わりに負極Ｄを用いた以外は、実施例１と同様にして、実施例３のラミネート型リチウムイオン二次電池を作製した。 (Example 3)
A laminated lithium ion secondary battery of Example 3 was produced in the same manner as in Example 1 except that the negative electrode D was used instead of the negative electrode B in Example 1.
　（実施例４）
　実施例１における負極Ｂの代わりに負極Ｅを用いた以外は、実施例１と同様にして、実施例４のラミネート型リチウムイオン二次電池を作製した。 Example 4
A laminated lithium ion secondary battery of Example 4 was produced in the same manner as in Example 1 except that the negative electrode E was used instead of the negative electrode B in Example 1.
　（実施例５）
　実施例１における負極Ｂの代わりに負極Ｆを用いた以外は、実施例１と同様にして、実施例５のラミネート型リチウムイオン二次電池を作製した。 (Example 5)
A laminated lithium ion secondary battery of Example 5 was produced in the same manner as in Example 1 except that the negative electrode F was used instead of the negative electrode B in Example 1.
　（実施例６）
　実施例１における負極Ｂの代わりに負極Ｇを用いた以外は、実施例１と同様にして、実施例６のラミネート型リチウムイオン二次電池を作製した。 (Example 6)
A laminated lithium ion secondary battery of Example 6 was produced in the same manner as in Example 1 except that the negative electrode G was used instead of the negative electrode B in Example 1.
　（実施例７）
　実施例１における負極Ｂの代わりに負極Ｈを用いた以外は、実施例１と同様にして、実施例７のラミネート型リチウムイオン二次電池を作製した。 (Example 7)
A laminated lithium ion secondary battery of Example 7 was produced in the same manner as in Example 1 except that the negative electrode H was used instead of the negative electrode B in Example 1.
　（実施例８）
　実施例５における電解液の注液量を、電池容量に対して１．７ｍｌ／Ａｈとなるようにした以外は、実施例５と同様にして、実施例８のラミネート型リチウムイオン二次電池を作製した。 (Example 8)
The laminated lithium ion secondary battery of Example 8 was the same as Example 5 except that the amount of electrolyte injected in Example 5 was 1.7 ml / Ah with respect to the battery capacity. Produced.
　（実施例９）
　実施例５における正極Ａの代わりに正極Ｃを用いた以外は、実施例５と同様にして、実施例９のラミネート型リチウムイオン二次電池を作製した。 Example 9
A laminated lithium ion secondary battery of Example 9 was produced in the same manner as in Example 5 except that the positive electrode C was used instead of the positive electrode A in Example 5.
　（実施例１０）
　実施例９における負極Ｆの代わりに負極Ｉを用いた以外は、実施例９と同様にして、実施例１０のラミネート型リチウムイオン二次電池を作製した。 (Example 10)
A laminated lithium ion secondary battery of Example 10 was produced in the same manner as in Example 9, except that the negative electrode I was used instead of the negative electrode F in Example 9.
　（比較例１）
　実施例１における正極Ａに代わり正極Ｂを用い、実施例１における負極Ｂの代わりに負極Ｆを用いた以外は、実施例１と同様にして、比較例１のラミネート型リチウムイオン二次電池を作製した。 (Comparative Example 1)
A laminated lithium ion secondary battery of Comparative Example 1 was prepared in the same manner as in Example 1 except that the positive electrode B was used instead of the positive electrode A in Example 1, and the negative electrode F was used instead of the negative electrode B in Example 1. Produced.
　（比較例２）
　実施例１における負極Ｂの代わりに負極Ａを用い、電解液の注液量を、電池容量に対して４．１ｍｌ／Ａｈとなるようにした以外は、実施例１と同様にして、比較例２のラミネート型リチウムイオン二次電池を作製した。 (Comparative Example 2)
Comparative Example as in Example 1, except that the negative electrode A was used instead of the negative electrode B in Example 1, and the amount of electrolyte injected was 4.1 ml / Ah with respect to the battery capacity. 2 laminate type lithium ion secondary battery was produced.
　（比較例３）
　電解液の注液量を、電池容量に対して２．８ｍｌ／Ａｈとなるようにした以外は、比較例２と同様にして、比較例３のラミネート型リチウムイオン二次電池を作製した。 (Comparative Example 3)
A laminate type lithium ion secondary battery of Comparative Example 3 was produced in the same manner as Comparative Example 2, except that the amount of electrolyte injected was 2.8 ml / Ah with respect to the battery capacity.
　＜釘刺し試験＞
　実施例および比較例のラミネート型リチウムイオン二次電池について、釘刺し試験による安全性の評価をおこなった。詳しくは、各ラミネート型リチウムイオン二次電池を電流値３．０Ａで４．５Ｖに達するまで定電流（ＣＣ）充電した。その後、４．５Ｖ±０．０２Ｖ以内に電圧を維持するようにひきつづき充電を続け、全充電時間が５時間になったら充電を停止した。なお、各ラミネート型リチウムイオン二次電池の容量は、実施例１～１０のラミネート型リチウムイオン二次電池が７．５Ａｈ、比較例１のラミネート型リチウムイオン二次電池が７．５Ａｈであり、比較例２及び３のラミネート型リチウムイオン二次電池が７．０Ａｈであった。 <Nail penetration test>
The laminated lithium ion secondary batteries of Examples and Comparative Examples were evaluated for safety by a nail penetration test. Specifically, each laminated lithium ion secondary battery was charged with a constant current (CC) until it reached 4.5 V at a current value of 3.0 A. Thereafter, charging was continued so as to maintain the voltage within 4.5 V ± 0.02 V, and the charging was stopped when the total charging time reached 5 hours. The capacity of each laminated lithium ion secondary battery is 7.5 Ah for the laminated lithium ion secondary batteries of Examples 1 to 10, and 7.5 Ah for the laminated lithium ion secondary battery of Comparative Example 1. The laminate type lithium ion secondary batteries of Comparative Examples 2 and 3 were 7.0 Ah.
　上記の充電処理をおこなった各ラミネート型リチウムイオン二次電池を、径２０ｍｍの孔を有する拘束板上に配置した。上部に釘が取り付けられたプレス機に、拘束板を配置した。釘が拘束板上のラミネート型リチウムイオン二次電池を貫通して、釘の先端部が拘束板の孔内部に位置するまで、釘を上部から下部に２０ｍｍ／秒の速度で移動させた。ラミネート型リチウムイオン二次電池には、表面温度を測定可能な温度測定装置を取り付けた。釘はステンレススチール（ＪＩＳ　Ｇ　４０５１で規定するＳ４５Ｃ）製、直径φ８ｍｍ、かつ、釘の先端角度６０°であった。釘刺し試験は、室温かつ大気中でラミネート型リチウムイオン二次電池の表面温度を測定しつつ行った。この釘刺し試験によって、ラミネート型リチウムイオン二次電池の正極と負極とが短絡した。 Each laminated lithium ion secondary battery subjected to the above-described charging treatment was placed on a restraining plate having a hole with a diameter of 20 mm. A restraint plate was placed on a press machine with a nail attached to the top. The nail was moved from the top to the bottom at a speed of 20 mm / sec until the nail penetrated the laminated lithium ion secondary battery on the restraint plate and the tip of the nail was positioned inside the hole of the restraint plate. A temperature measuring device capable of measuring the surface temperature was attached to the laminate type lithium ion secondary battery. The nail was made of stainless steel (S45C defined by JIS G 4051), had a diameter of 8 mm, and a nail tip angle of 60 °. The nail penetration test was performed while measuring the surface temperature of the laminated lithium ion secondary battery at room temperature and in the air. By this nail penetration test, the positive electrode and the negative electrode of the laminated lithium ion secondary battery were short-circuited.
　内部短絡時のラミネート型リチウムイオン二次電池の表面温度を測定し、電池の様子を観察した。釘貫通後の各電池の表面温度は、いずれも一旦上昇した後に、徐々に低下した。 The surface temperature of the laminated lithium ion secondary battery at the time of an internal short circuit was measured, and the state of the battery was observed. After the nail penetration, the surface temperature of each battery once increased and then gradually decreased.
　表１には、実施例１～７及び比較例１及び２のラミネート型リチウムイオン二次電池の釘刺し試験で観測されたセル表面温度を示す。セル表面温度は、各ラミネート型リチウムイオン二次電池の表面温度のうち、最高温度を記載した。また図１に、実施例１～実施例７のラミネート型リチウムイオン二次電池の釘刺し試験結果であるセル表面温度と、各負極のシリコン材料の質量部との関係を示すグラフを示す。 Table 1 shows the cell surface temperatures observed in the nail penetration test of the laminated lithium ion secondary batteries of Examples 1 to 7 and Comparative Examples 1 and 2. As the cell surface temperature, the maximum temperature among the surface temperatures of each laminated lithium ion secondary battery is described. FIG. 1 is a graph showing the relationship between the cell surface temperature, which is a nail penetration test result of the laminated lithium ion secondary batteries of Examples 1 to 7, and the mass part of the silicon material of each negative electrode.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１の比較例２と実施例１のラミネート型リチウムイオン二次電池の釘刺し試験時のセル表面温度を比べると、負極にシリコン材料が含まれた実施例１のラミネート型リチウムイオン二次電池の釘刺し試験時のセル表面温度が、負極にシリコン材料を含まない比較例２のラミネート型リチウムイオン二次電池の釘刺し試験時のセル表面温度に比較して、大幅に低かった。また表１の比較例１と実施例５のラミネート型リチウムイオン二次電池の釘刺し試験時のセル表面温度を比べると、正極にＮＣＭを含み、ＬＦＰを含まない比較例１のラミネート型リチウムイオン二次電池の釘刺し試験時のセル表面温度に対して、正極にＮＣＭ及びＬＦＰの両方を含む実施例５のラミネート型リチウムイオン二次電池の釘刺し試験時のセル表面温度が大幅に低かった。 Comparing the cell surface temperature during the nail penetration test of the laminated lithium ion secondary battery of Comparative Example 2 and Example 1 of Table 1, the laminated lithium ion secondary battery of Example 1 in which the negative electrode contained a silicon material The cell surface temperature during the nail penetration test was significantly lower than the cell surface temperature during the nail penetration test of the laminated lithium ion secondary battery of Comparative Example 2 in which the negative electrode did not contain a silicon material. Moreover, when the cell surface temperature at the time of the nail penetration test of the laminated lithium ion secondary battery of Comparative Example 1 and Example 5 in Table 1 was compared, the laminated lithium ion of Comparative Example 1 containing NCM in the positive electrode and not containing LFP. The cell surface temperature during the nail penetration test of the laminate type lithium ion secondary battery of Example 5 including both NCM and LFP in the positive electrode was significantly lower than the cell surface temperature during the nail penetration test of the secondary battery. .
　このことから、シリコン材料を含む負極と、ＮＣＭとＬＦＰとを含む正極とを有するリチウムイオン二次電池は、釘刺し試験によって正極と負極の短絡が起こっても、セル表面温度の過剰な温度上昇がおこらないことがわかった。また実施例１～実施例７のラミネート型リチウムイオン二次電池の釘刺し試験時のセル表面温度を比べると、図１及び表１に見られるように、負極活物質層におけるシリコン材料の質量部が多いほど、釘刺し試験時のセル表面温度が低い、ということがわかった。また負極活物質層におけるシリコン材料の質量部を同じにした負極を有するラミネート型リチウムイオン二次電池同士を比較すると、負極活物質層の密度が１．２ｇ／ｃｍ３である実施例１、３、５、７のラミネート型リチウムイオン二次電池のほうが、負極活物質層の密度が１．１ｇ／ｃｍ３である実施例２、４、６のラミネート型リチウムイオン二次電池よりも釘刺し試験時のセル表面温度が低いことがわかった。 Therefore, a lithium ion secondary battery having a negative electrode including a silicon material and a positive electrode including NCM and LFP has an excessive increase in the cell surface temperature even when the positive electrode and the negative electrode are short-circuited by a nail penetration test. It turns out that does not happen. When the cell surface temperature during the nail penetration test of the laminated lithium ion secondary batteries of Examples 1 to 7 was compared, as shown in FIG. 1 and Table 1, the mass part of the silicon material in the negative electrode active material layer It was found that the greater the amount, the lower the cell surface temperature during the nail penetration test. Further, when comparing laminated lithium ion secondary batteries having negative electrodes with the same mass part of the silicon material in the negative electrode active material layer, the density of the negative electrode active material layer was 1.2 g / cm 3. The laminated lithium ion secondary batteries of Nos. 5 and 7 have a nail penetration test rather than the laminated type lithium ion secondary batteries of Examples 2, 4, and 6 in which the density of the negative electrode active material layer is 1.1 g / cm 3. The cell surface temperature was found to be low.
　また、一般的にラミネート型リチウムイオン二次電池の釘刺し試験時において、釘刺しにより電解液が抜け、抵抗が上がるため発熱量が上がり、セル表面温度が上昇すると考えられている。また電解液の気化熱によってセルの発熱上昇が抑制されるといわれている。そのため、安全性の観点から、ラミネート型リチウムイオン二次電池に含有される電解液量は多いほうが好ましいとされている。例えば、リチウムイオン二次電池のセルの全体積の２割～３割が電解液で占められることが好ましいとされている。 Also, it is generally considered that during the nail penetration test of a laminate type lithium ion secondary battery, the electrolyte solution is removed by nail penetration and the resistance increases, so that the amount of heat generation increases and the cell surface temperature rises. In addition, it is said that the heat generation of the cell is suppressed by the heat of vaporization of the electrolyte. Therefore, from the viewpoint of safety, it is preferable that the amount of electrolyte contained in the laminated lithium ion secondary battery is larger. For example, 20 to 30% of the total volume of cells of a lithium ion secondary battery is preferably occupied by the electrolyte.
　表２に、実施例５、実施例８、比較例２及び比較例３のラミネート型リチウムイオン二次電池の釘刺し試験で観測されたセル表面温度を示す。 Table 2 shows the cell surface temperatures observed in the nail penetration test of the laminated lithium ion secondary batteries of Example 5, Example 8, Comparative Example 2 and Comparative Example 3.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　表２に示すように、比較例３のラミネート型リチウムイオン二次電池は、比較例２のラミネート型リチウムイオン二次電池よりも電解液量が少ない。表２の比較例２及び比較例３のラミネート型リチウムイオン二次電池の釘刺し試験時のセル表面温度を比べると、比較例３のラミネート型リチウムイオン二次電池の釘刺し試験時のセル表面温度が、比較例２のラミネート型リチウムイオン二次電池の釘刺し試験時のセル表面温度に比べて、大幅に上昇した。 As shown in Table 2, the laminate type lithium ion secondary battery of Comparative Example 3 has a smaller amount of electrolyte than the laminate type lithium ion secondary battery of Comparative Example 2. Comparing the cell surface temperature during the nail penetration test of the laminate type lithium ion secondary battery of Comparative Example 2 and Comparative Example 3 in Table 2, the cell surface during the nail penetration test of the laminate type lithium ion secondary battery of Comparative Example 3 The temperature rose significantly compared to the cell surface temperature during the nail penetration test of the laminated lithium ion secondary battery of Comparative Example 2.
　これに対して、実施例８のラミネート型リチウムイオン二次電池は、実施例５のラミネート型リチウムイオン二次電池よりも電解液量が少ないが、実施例５及び実施例８のラミネート型リチウムイオン二次電池の釘刺し試験時のセル表面温度を比べると、実施例８のラミネート型リチウムイオン二次電池と実施例５のラミネート型リチウムイオン二次電池では釘刺し試験時のセル表面温度に、ほとんど違いはなかった。つまり、負極にシリコン材料が含まれることによって、電解液量に関係なく、釘刺し試験時のセルの表面温度が過剰に上昇しないことがわかった。 In contrast, the laminate type lithium ion secondary battery of Example 8 has a smaller amount of electrolyte than the laminate type lithium ion secondary battery of Example 5, but the laminate type lithium ion of Examples 5 and 8 Comparing the cell surface temperature during the nail penetration test of the secondary battery, the laminate type lithium ion secondary battery of Example 8 and the laminate type lithium ion secondary battery of Example 5 have the cell surface temperature during the nail penetration test, There was little difference. In other words, it was found that the surface temperature of the cell during the nail penetration test does not increase excessively regardless of the amount of the electrolyte by including the silicon material in the negative electrode.
　このことから、シリコン材料を含む負極と、ＮＣＭとＬＦＰとを含む正極とを有するリチウムイオン二次電池は、電解液量が少ない場合でも、釘刺し試験による正極と負極の短絡時において、セル表面温度の過剰な温度上昇がおこらないという効果が、有効に発揮されることがわかった。 Therefore, a lithium ion secondary battery having a negative electrode containing a silicon material and a positive electrode containing NCM and LFP has a cell surface at the time of a short circuit between the positive electrode and the negative electrode by a nail penetration test even when the amount of the electrolyte is small. It has been found that the effect that the temperature does not increase excessively is effectively exhibited.
　表３に、実施例５、実施例９及び実施例１０のラミネート型リチウムイオン二次電池の釘刺し試験で観測されたセル表面温度を示す。 Table 3 shows the cell surface temperatures observed in the nail penetration test of the laminated lithium ion secondary batteries of Example 5, Example 9, and Example 10.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　表３に示すように、実施例５のラミネート型リチウムイオン二次電池と実施例９のラミネート型リチウムイオン二次電池では、各正極において、ＮＣＭとＬＦＰの含有割合が異なる。表３の実施例５及び実施例９のラミネート型リチウムイオン二次電池の釘刺し試験時のセル表面温度を比べると、ほとんど違いはなかった。このことから、正極活物質層において、ＮＣＭの含有割合が５０質量部以上８０質量部以下であり、ＬＦＰの含有割合が２０質量部以上４０質量部以下の範囲内であれば、ＮＣＭとＬＦＰの含有割合が変化しても、釘刺し試験時にセル表面温度の過剰な温度上昇がおこらないことがわかった。 As shown in Table 3, in the laminate type lithium ion secondary battery of Example 5 and the laminate type lithium ion secondary battery of Example 9, the content ratios of NCM and LFP are different in each positive electrode. When the cell surface temperatures during the nail penetration test of the laminated lithium ion secondary batteries of Example 5 and Example 9 in Table 3 were compared, there was almost no difference. From this, in the positive electrode active material layer, if the content ratio of NCM is 50 parts by mass or more and 80 parts by mass or less and the content ratio of LFP is in the range of 20 parts by mass or more and 40 parts by mass or less, NCM and LFP It was found that the cell surface temperature did not increase excessively during the nail penetration test even when the content ratio changed.
　また、表３に示すように、実施例９のラミネート型リチウムイオン二次電池の負極には、シリコン材料と黒鉛とが含まれているのに対して、実施例１０のラミネート型リチウムイオン二次電池の負極には、シリコン材料は含まれているが、黒鉛は含まれていない。表３の実施例９及び実施例１０のラミネート型リチウムイオン二次電池の釘刺し試験時のセル表面温度を比べると、ほとんど違いはなかった。このことから、負極において、シリコン材料が含まれていれば、黒鉛が含まれていなくても、釘刺し試験時にセル表面温度の過剰な温度上昇がおこらないことがわかった。
  Moreover, as shown in Table 3, the negative electrode of the laminated lithium ion secondary battery of Example 9 contains silicon material and graphite, whereas the laminated lithium ion secondary of Example 10 The negative electrode of the battery contains a silicon material but does not contain graphite. When the cell surface temperatures during the nail penetration test of the laminated lithium ion secondary batteries of Example 9 and Example 10 in Table 3 were compared, there was almost no difference. From this, it was found that if the silicon material was included in the negative electrode, the cell surface temperature did not rise excessively during the nail penetration test even if graphite was not included.

Claims (6)

  1. 　正極と負極とセパレータと非水電解液とを含み、
    　前記正極は、正極活物質を含む正極活物質層を有し、
    　前記正極活物質は、下記式（１）で表されるリチウムニッケルコバルトマンガン複合酸化物及び下記式（２）で表されるリン酸鉄リチウム化合物を含み、
    　ＬｉａＮｉｂＣｏｃＭｎ（１－ｂ－ｃ－ｄ）Ｍ１ ｄＯ（２－ｅ）・・・・・（１）
    　（式（１）中、Ｍ１は、Ｍｇ、Ａｌ、Ｂ、Ｔｉ、Ｖ、Ｃｒ、Ｆｅ、Ｃｕ、Ｚｎ、Ｚｒ、Ｍｏ、Ｓｎ、Ｃａ、Ｓｒ及びＷからなる群のうちの少なくとも１種を表し、ａ、ｂ、ｃ、ｄ及びｅは、０．８≦ａ≦１．２、０＜ｂ≦０．５、０＜ｃ≦０．５、０≦ｄ≦０．５、ｂ＋ｃ＋ｄ＜１、－０．１≦ｅ≦０．２の範囲内の値である。）
    　ＬｉｐＦｅｑＭ２ （１－ｑ）ＰＯ４・・・・・（２）
    　（式（２）中、Ｍ２は、Ｃｏ、Ｍｎ、Ｎｉ、Ｍｇ、Ａｌ、Ｂ、Ｔｉ、Ｖ、Ｎｂ、Ｃｕ、Ｚｎ、Ｍｏ、Ｃａ、Ｓｒ、Ｗ及Ｚｒからなる群のうちの少なくとも１種を表す。ｐは、０．９≦ｐ≦１．１の範囲内の値である。ｑは、０＜ｑ≦１の範囲内の値である。）
    　前記負極は、負極活物質を含む負極活物質層を有し、
    　前記負極活物質は板状シリコン体が厚さ方向に積層された構造を有するシリコン材料を含むことを特徴とするリチウムイオン二次電池。     Including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte,
    The positive electrode has a positive electrode active material layer containing a positive electrode active material,
    The positive electrode active material includes a lithium nickel cobalt manganese composite oxide represented by the following formula (1) and a lithium iron phosphate compound represented by the following formula (2):
    Li a Ni b Co c Mn (1-bcd) M 1 d O (2-e) (1)
    (In the formula (1), M 1 represents at least one selected from the group consisting of Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr and W. A, b, c, d and e are 0.8 ≦ a ≦ 1.2, 0 <b ≦ 0.5, 0 <c ≦ 0.5, 0 ≦ d ≦ 0.5, b + c + d <1 , -0.1 ≦ e ≦ 0.2.)
    Li p Fe q M 2 (1-q) PO 4 (2)
    (In the formula (2), M 2 is at least one of the group consisting of Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W and Zr. (P is a value in the range of 0.9 ≦ p ≦ 1.1, q is a value in the range of 0 <q ≦ 1)
    The negative electrode has a negative electrode active material layer containing a negative electrode active material,
    The lithium ion secondary battery, wherein the negative electrode active material includes a silicon material having a structure in which plate-like silicon bodies are laminated in a thickness direction.
  2. 　前記正極活物質層の密度は、２．５ｇ／ｃｍ３以上３．５ｇ／ｃｍ３以下であり、前記負極活物質層の密度は、０．５ｇ／ｃｍ３以上２ｇ／ｃｍ３以下である請求項１に記載のリチウムイオン二次電池。 The density of the positive electrode active material layer is 2.5 g / cm 3 or more and 3.5 g / cm 3 or less, and the density of the negative electrode active material layer is 0.5 g / cm 3 or more and 2 g / cm 3 or less. Item 2. A lithium ion secondary battery according to Item 1.
  3. 　前記シリコン材料の含有量は前記負極活物質層を１００質量部としたときに３０質量部以上８５質量部以下である請求項１又は２に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to claim 1 or 2, wherein the content of the silicon material is 30 parts by mass or more and 85 parts by mass or less when the negative electrode active material layer is 100 parts by mass.
  4. 　前記リチウムニッケルコバルトマンガン複合酸化物の含有量は前記正極活物質層を１００質量部としたときに５０質量部以上８０質量部以下であり、
    　前記リン酸鉄リチウム化合物の含有量は前記正極活物質層を１００質量部としたときに２０質量部以上４０質量部以下である請求項１～３のいずれか一項に記載のリチウムイオン二次電池。     The content of the lithium nickel cobalt manganese composite oxide is 50 parts by mass or more and 80 parts by mass or less when the positive electrode active material layer is 100 parts by mass.
    The lithium ion secondary according to any one of claims 1 to 3, wherein a content of the lithium iron phosphate compound is 20 parts by mass or more and 40 parts by mass or less when the positive electrode active material layer is 100 parts by mass. battery.
  5. 　前記セパレータは合成樹脂製の多孔質膜を含む請求項１～４のいずれか一項に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to any one of claims 1 to 4, wherein the separator includes a porous film made of a synthetic resin.
  6. 　前記非水電解液は、電解質塩と非水溶媒とを含み、
    　前記電解質塩は六フッ化リン酸リチウムを含み、
    　前記非水溶媒は、フルオロエチレンカーボネート、エチレンカーボネート、エチルメチルカーボネート及びジメチルカーボネートを含む請求項１～５のいずれか一項に記載のリチウムイオン二次電池。
     
          The non-aqueous electrolyte includes an electrolyte salt and a non-aqueous solvent,
    The electrolyte salt includes lithium hexafluorophosphate,
    The lithium ion secondary battery according to any one of claims 1 to 5, wherein the non-aqueous solvent includes fluoroethylene carbonate, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

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