WO2014128903A1 - Lithium ion secondary battery - Google Patents

Lithium ion secondary battery Download PDF

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Publication number
WO2014128903A1
WO2014128903A1 PCT/JP2013/054446 JP2013054446W WO2014128903A1 WO 2014128903 A1 WO2014128903 A1 WO 2014128903A1 JP 2013054446 W JP2013054446 W JP 2013054446W WO 2014128903 A1 WO2014128903 A1 WO 2014128903A1
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Prior art keywords
coating layer
ion secondary
secondary battery
lithium ion
composite coating
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PCT/JP2013/054446
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French (fr)
Japanese (ja)
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尚貴 木村
栄二 關
達哉 遠山
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株式会社 日立製作所
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Priority to PCT/JP2013/054446 priority Critical patent/WO2014128903A1/en
Publication of WO2014128903A1 publication Critical patent/WO2014128903A1/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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • 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
    • H01M4/58—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
    • H01M4/581—Chalcogenides or intercalation compounds thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—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
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • 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.
  • lithium-ion secondary batteries with high energy density
  • lithium-ion secondary batteries for consumer use are now available for mobile phones and laptop computers. Widely used.
  • electric vehicles (EV) and hybrid electric vehicles (HEV) that assist electric motors with some electric motors have been developed by each automobile manufacturer due to global warming and depleted fuel problems.
  • Lithium ion secondary batteries are required, and high safety is indispensable for popularization in the market.
  • Battery safety is determined by the standards of each country such as JIS (Japanese Industrial Standards), SAE (American Automotive Engineers Association), EUCAR (Europe) standards.
  • the safety test of each standard consists of needle puncture test, crushing (longitudinal / lateral) test, external short circuit test, heating test, overdischarge test, overcharge test, with or without ignition burst, although speed and time are different. Safety is judged by such factors. The most difficult of these tests is considered an overcharge test.
  • Non-Patent Documents 1 and 2 This thermal decomposition of the positive electrode generates a large amount of heat and may cause ignition if left untreated.
  • Patent Document 1 In order to suppress thermal decomposition of the positive electrode, in Patent Document 1, Al and Mg are substituted with metal sites in the positive electrode active material having a layered structure to suppress oxygen desorption. In Patent Document 2, protrusion-like Al-containing oxides and / or Al-containing hydroxides are uniformly distributed on the surface of the positive electrode material, and a phosphoric acid compound is adhered, so that the non-aqueous electrolyte is decomposed or cobalt is removed from the positive electrode material. And the like are suppressed from elution.
  • the phosphoric acid compound has an effect of suppressing the elution of elements from the positive electrode material
  • an example is described in which the phosphoric acid compound is arranged in the vicinity of the positive electrode material and the outer side thereof is coated with an Al compound.
  • Another object of the present invention is to suppress the amount and rate of oxygen desorption during overcharge and improve safety.
  • the present invention has optimized the coating compound and the coating structure on the positive electrode active material.
  • the present invention relates to a lithium ion secondary battery that includes a positive electrode or a negative electrode active material, a positive electrode capable of occluding and releasing lithium ions, a negative electrode, and a separator disposed between the positive and negative electrodes.
  • the positive electrode active material is oxidized on the surface.
  • the oxide or fluoride is a compound containing at least one of Mo, W, and Zr, and the Mo, W,
  • the atomic concentration of at least one of Zr is characterized in that the surface layer side is low and the positive electrode active material side is high.
  • the present invention contributes to improving the safety of lithium ion secondary batteries.
  • the present inventors examined a lithium ion secondary battery including a positive electrode that improves thermal stability during overcharge.
  • a lithium ion secondary battery including a positive electrode that improves thermal stability during overcharge.
  • the surface of the positive electrode active material is coated with a high-valence Mo, W, Zr oxide layer or the like, an excellent battery with high capacity, high cycle characteristics, and resistance to deterioration is obtained.
  • a composite coating layer using a phosphoric acid compound that is difficult to decompose at a high voltage can be used.
  • a composite coating layer containing a compound of an expensive element (Mo, W, Zr) is provided on the surface of the positive electrode, and a large amount of phosphate compound is arranged in the vicinity of the surface of the composite coating layer.
  • Expensive oxides prevent the active material from collapsing, and phosphoric acid compounds inhibit the reaction between the electrolyte and the positive electrode active material.
  • the starting temperature can also be high. As a result, it is considered that the risk of ignition burst during overcharge can be further suppressed. In particular, it is effective when applied to a positive electrode containing a large amount of Ni having a high capacity and not high thermal stability.
  • the positive electrode active material according to the present invention has one or more selected from the group consisting of a phosphoric acid compound and an expensive element A (A is Mo, W, Zr) on the surface of the lithium transition metal oxide. And a composite coating layer containing a compound (oxide or fluoride) containing the element.
  • A is Mo, W, Zr
  • a coating layer is formed. The content of the coating compound to be used is an important point.
  • the compound of the expensive element A contained in the composite coating layer is preferably 0.2 parts by weight or more and 1.5 parts by weight or less with respect to 100 parts by weight of the lithium transition metal oxide. It is desirable that the compound of the expensive element A covers the entire surface of the lithium transition metal oxide. Since the compound of the expensive element A has a high valence and a strong bond with oxygen, oxygen desorption of the lithium transition metal oxide is suppressed. In addition, it also serves as an intervening layer for coating the surface of the lithium transition metal oxide with a phosphate compound. If it is less than 0.2 parts by weight, the amount is small and it cannot be said to be sufficient to cover the entire surface of the lithium transition metal oxide.
  • the compound of the expensive element A has a high resistance, and when it exceeds 1.5 parts by weight, the battery capacity is significantly reduced due to the increase in resistance of the positive electrode.
  • it is preferably 0.4 parts by weight or more and 1.0 parts by weight or less.
  • the content rate of the phosphoric acid compound of a composite coating layer is 0.1 to 5.0 weight part with respect to 100 weight part of lithium transition metal oxides. If the content of the phosphoric acid compound is less than 0.1 part by weight, the entire surface of the lithium transition metal oxide cannot be covered, so that it cannot play a sufficient role. On the other hand, when the amount exceeds 5.0 parts by weight, the phosphoric acid compound itself does not contribute to the charge / discharge reaction, leading to an increase in resistance of the positive electrode and a decrease in battery capacity. More preferably, it is 0.5 parts by weight or more and 2.0 parts by weight or less.
  • the phosphoric acid compound forming the composite coating layer is preferably at least one selected from the group consisting of Li 3 PO 4 , Li 4 P 2 O 7 and LiPO 3 from the viewpoint of suppressing oxidative decomposition of the electrolytic solution. .
  • the thickness of the coating layer is preferably 2 nm or more and 80 nm or less.
  • the thickness of the coating layer is less than 2 nm, the particle size itself forming the coating compound needs to be smaller than that.
  • the coating compound particles of less than 2 nm tend to aggregate due to van der Waals force, and it is difficult to uniformly coat the lithium transition metal oxide surface.
  • the thickness of the coating layer exceeds 80 nm, the resistance increase due to the coating layer becomes remarkable, and the battery characteristics are deteriorated. More preferably, the thickness of the coating layer is 10 nm or more and 60 nm or less.
  • the phosphate compound in the composite coating layer has a role of suppressing oxidative decomposition of the electrolytic solution. Accordingly, the atomic concentration of phosphorus in the composite coating layer is preferably higher on the surface layer side (electrolyte side) of the coating layer than on the lithium transition metal oxide side.
  • the method for confirming the distribution of the phosphoric acid compound and the compound of the expensive element A in the composite coating layer is as follows.
  • Dividing the coating layer into two in the thickness direction that is, dividing the length from the interface on one side of the coating layer to the lithium transition metal oxide side to the interface on the other side of the coating layer electrolyte (electrolyte)
  • the interface side with the lithium transition metal oxide, which is the positive electrode active material is the lithium transition metal oxide side
  • the interface side with the electrolyte (electrolyte) is the surface layer side (electrolyte side).
  • the value was calculated. In consideration of measurement errors and the like, when the average value of the atomic concentration on the surface layer side (electrolyte side) is higher by 4 atom% or more than the average value of the atomic concentration on the lithium transition metal oxide side, it was determined that the atomic concentration was high.
  • the coating layer is formed on the surface of the lithium transition metal oxide, so that the phosphoric acid compound adjacent to the electrolytic solution suppresses the oxidative decomposition of the electrolytic solution and is adjacent to the lithium transition metal oxide during overcharge.
  • the method for surface treatment of the lithium transition metal oxide is not particularly limited in the present invention.
  • P in the phosphoric acid compound of the coating compound is preferably such that the atomic concentration on the surface layer side (electrolyte side) is higher than the atomic concentration on the lithium transition metal oxide side in the coating layer.
  • As a procedure for coating treatment for the lithium transition oxide forming such a coating layer there are the following methods. (1) After mixing the solution containing the expensive element A with the lithium transition metal oxide, the phosphoric acid compound is put into the solvent and further mixed at room temperature. In this state, the solvent is evaporated by vacuum drying or spray drying. A method of heat-treating the obtained powder in the air.
  • a solution containing an expensive element A is mixed with a lithium transition metal oxide, and the solvent is evaporated by vacuum drying or spray drying to form an oxide. Then, a phosphoric acid compound solution is added and mixed at room temperature. A method in which the solvent is further evaporated by vacuum drying or spray drying in the state, and the obtained powder is heat treated in the atmosphere. (3) After directly coating an oxide containing an expensive element A on a lithium transition metal oxide with a ball mill or the like, A method in which a phosphoric acid compound solution is added, mixed at room temperature, the solvent is evaporated by vacuum drying or spray drying, and the resulting powder is heat treated in the atmosphere.
  • the raw material of the phosphate compound is diammonium hydrogen phosphate ((NH 4 ) 2 HPO 4 ) or ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ).
  • a phosphoric acid compound is produced.
  • the phosphoric acid compound include Li 3 PO 4 , Li 4 P 2 O 7 , LiPO 3 , and the like.
  • the temperature of the heat treatment is 300 ° C. or higher and 800 ° C. or lower, more preferably 500 ° C. or higher and 700 ° C. or lower.
  • the heating time is 1 hour or more and 20 hours or less, preferably 3 hours or more and 8 hours or less.
  • F 2 fluorine
  • the hydroxide can be converted to fluoride.
  • nitrogen trifluoride gas is preferable.
  • the phosphoric acid compound can be increased on the surface layer side (electrolyte side) in the coating layer, particularly in the vicinity of the surface layer, and the atomic concentration of P can be increased.
  • the atomic concentration of the expensive element A near the lithium transition metal oxide is higher than the atomic concentration on the surface layer side (electrolyte side).
  • Li 3 PO 4 was used as the phosphate compound, and the lithium transition metal oxide was coated by the method (1).
  • the present invention is not limited to this.
  • the description will be made using a lithium ion secondary battery of a laminate cell having a stacked electrode group, but it may be a wound structure or a metal can sealed.
  • FIG. 1 is an exploded view of a laminated electrode group inside a laminated cell.
  • the stacked electrode group as shown in FIG. 1 has a structure in which a plate-like positive electrode 5 and a plate-like negative electrode 6 are sandwiched and stacked between separators 7.
  • the positive electrode has an aluminum foil as a positive electrode current collector foil, and a positive electrode active material is disposed on both sides of the aluminum foil. At this time, the positive electrode uncoated portion 3 where the positive electrode active material mixture is not applied is formed on a part of the aluminum foil. That is, in the positive electrode uncoated portion 3, the aluminum foil is exposed.
  • the positive electrode active material mixture applied to the positive electrode current collector foil was mixed with a carbon material conductive material and a polyvinylidene fluoride (hereinafter abbreviated as PVDF) binder. .
  • the weight ratio is 90: 5: 5 in order, and the mixture coating amount is 120 g / m2.
  • NMP N-methylpyrrolidone
  • the density of the positive electrode 5 was adjusted by a roll press after coating and drying, and this time, the density was 2.8 g / cm 3.
  • the negative electrode 6 has a copper foil as a negative electrode current collector foil. Artificial graphite was used as the negative electrode active material on both sides of the copper foil. In addition, a material capable of reversibly occluding and releasing lithium ions can be freely applied to the negative electrode active material, and carbon materials such as natural graphite and amorphous carbon, oxides and alloys can be used. .
  • As the negative electrode active material mixture acetylene black was used as a conductive material in addition to the negative electrode active material, and a PVDF binder was further used. The weight ratio was prepared in order 90: 5: 5, and the mixture coating amount was 70 g / m2.
  • the viscosity is adjusted with a dispersion solvent such as NMP.
  • the negative electrode uncoated portion 4 where the negative electrode active material mixture is not applied is formed on a part of the copper foil. That is, the copper foil is exposed in the negative electrode uncoated portion 4.
  • the density of the negative electrode 6 was adjusted by a roll press after drying, and this time the density was 1.5 g / cm 3.
  • a microporous membrane (such as polyolefin) that allows lithium ions to pass through was used as the separator.
  • Polyolefin is mainly characterized by containing at least one kind of polyethylene, polypropylene, etc., but may contain heat-resistant resin such as polyamide, polyamideimide, polyimide, polysulfone, polyethersulfone, polyphenylsulfone, polyacrylonitrile. Absent.
  • the inorganic filler layer is characterized by containing at least one of SiO 2 , Al 2 O 3 , montmorillonite, mica, ZnO, TiO 2 , BaTiO 3 , and ZrO 2 . From the viewpoint of cost and performance, it is most preferable to use SiO 2 or Al 2 O 3 .
  • the separator may be coated with an inorganic filler layer on one side or both sides.
  • the positive electrode uncoated portion 3 and the negative electrode uncoated portion 4 are bundled and ultrasonically welded to the positive electrode terminal 1 and the negative electrode terminal 2 that electrically connect the inside and outside of the battery.
  • the welding method other welding methods such as resistance welding can be appropriately selected.
  • the positive electrode terminal 1 and the negative electrode terminal 2 may be preliminarily coated with or attached to a sealing portion of the terminal in order to further seal the inside and outside of the battery.
  • the positive electrode active material of this example is a lithium transition metal oxide (LiNi a B b C (1-ab) O 2 ) having a coating layer made of an oxide containing a high number of metals A or a fluoride and a phosphate compound. ).
  • the positive electrode active materials of Examples and Comparative Examples used this time were prepared by changing the weight of the raw material or adjusting the coating layer. Further, from the prepared sample, the compound type of the positive electrode active material, the state of the coating layer, and the like were measured. Table 1 shows each positive electrode active material.
  • the thickness of the coating layer and the concentration distribution of the atoms in the coating layer were measured using a field emission transmission electron microscope (Hitachi HF-2000, equipped with an X-ray analyzer (NORAN TM System 300, hereinafter referred to as EDS) manufactured by Thermo Fisher). (Hereinafter abbreviated as TEM) and measured at an acceleration voltage of 200 kV.
  • EDS X-ray analyzer
  • the sample was sliced in advance by an Ar ion etching method using a polishing machine (600 type, manufactured by GATAN).
  • the elemental distribution of the coating layer includes TEM-EELS combining TEM and electron energy loss spectroscopy (EELS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), Auger electron spectroscopy (AES), etc. But it can be confirmed.
  • the bonding state of the surface coating compound (coating layer) was determined by using TEM, acquiring an electron diffraction image at an acceleration voltage of 200 kV, and comparing the diffraction point with information on the diffraction points of known compounds in the attached database. .
  • the weight ratio of the elements used for the surface treatment for forming the coating layer was measured using a high frequency inductively coupled plasma emission spectroscopy (hereinafter abbreviated as ICP) analyzer (P-4000 manufactured by Hitachi, Ltd.).
  • ICP inductively coupled plasma emission spectroscopy
  • 5 g of positive electrode material and 2 ml of nitric acid were added to 45 ml of ion exchange water in a beaker, and the mixture was stirred for 30 minutes with a stirrer (stirrer). After standing for 5 minutes, the filtrate filtered with filter paper was sprayed in a high-frequency atmosphere together with argon gas, and the light intensity peculiar to each excited element was measured to calculate the weight ratio of the elements.
  • Fig. 2 shows an exploded perspective view of the laminate cell.
  • the laminate cell has a structure in which the positive electrode terminal 1 and the negative electrode terminal 2 are passed through the edge of the laminate film in an electrically insulated state.
  • the electrode group 9 was sandwiched between laminate films 8 and 10, and the edge was thermally welded at 175 ° C. for 10 seconds and sealed. Sealing was performed by heat-welding and sealing while heat-welding first except the one side, injecting the electrolyte, and then vacuum-pressing the other side.
  • the heat welding location on the side that has become the liquid injection port is weaker in heat welding strength than the other sides and has the effect of a gas discharge valve.
  • an organic electrolytic solution in which a lithium salt is dissolved, or a known electrolyte used in a battery such as a solid electrolyte having a lithium ion conductivity, a gel electrolyte, or a molten salt can be used.
  • Non-aqueous solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ⁇ -butyrolactone, ⁇ -valerolactone, methyl acetate, ethyl acetate, methyl propionate, tetrahydrofuran, 2-methyl Tetrahydrofuran, 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 3-methyltetrahydrofuran, 1,2-dioxane, 1,3-dioxane, 1,4-dioxane, 1,3-dioxolane, 2-methyl At least one of -1,3-dioxolane, 4-methyl-1,3-dioxolane and the like can be used.
  • the electrolyte for example, a LiPF 6, LiBF 4, LiClO 4 , LiN (C 2 F 5 SO 2) at least one more like
  • Laminate Cell X in order to observe the overcharged positive electrode excluding the influence of temperature and gas, a laminate cell X having a constant temperature of 25 ° C. was produced.
  • electrolyte solution is injected into the entire internal volume of the laminate cell to improve heat dissipation, and a gas flow path is secured without thermally welding a part of one side of the laminate cell.
  • a thermocouple was passed inside, and a dedicated cooling fan was attached so that the internal temperature of the cell was kept constant at 25 ° C.
  • a normal laminate cell Y (a laminate battery cell in which the amount of electrolyte to be filled was reduced to give a margin with respect to the capacity of the laminate cell and all sides of the laminate cell were welded) was prepared.
  • the direct current resistance (R) was measured using the laminate cell X produced by combining the positive electrode of Table 1 and the negative electrode of graphite. First, constant current and constant voltage charging was performed for 4 hours at an upper limit voltage of 4.1 V with a current corresponding to 0.33 C, and then the circuit was opened for 10 minutes. After that, discharge was performed at a discharge current (I) of 3.5 A for 5 seconds, the open circuit voltage (V0) before discharge and the voltage (V5) at the 5th discharge were measured, and the difference between the two (V0 ⁇ V5) A certain voltage drop ( ⁇ V) was determined. The quotient ( ⁇ V / I) of this voltage drop and discharge current was defined as the direct current resistance (R).
  • Table 2 shows the DC resistance of the laminate cell X.
  • the batteries of Examples 1 to 10 using the positive electrode active material having a coating layer on the surface have a DC resistance equivalent to that of Comparative Examples 1 to 6 without coating.
  • Example 1 to 3 As a result, it was found that, compared with Comparative Examples 1 to 7 and 9 to 11, the Example had a higher oxygen desorption start temperature, a smaller oxygen desorption strength (desorption rate), and a smaller amount of oxygen desorption. .
  • the positive electrode active material having a large amount of Ni (Examples 1 to 3, 6 to 10) has a large effect.
  • the XRD of the electrode after the test was measured to investigate the crystal structure.
  • the laminate cells (X-1 to 20) of the examples were in a mixed state of a layered structure and a spinel structure, and no change in the crystal structure up to the rock salt structure was observed. In other words, it can be inferred that the crystal structure change during overcharge is suppressed in the examples.
  • the positive electrode active material has an oxide or fluorine containing at least one of Mo, W, and Zr on the surface.

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Abstract

The present invention is a lithium ion secondary battery which is provided with: positive and negative electrodes, each of which comprises a positive or negative electrode active material and is capable of absorbing and desorbing lithium ions; and a separator which is arranged between the positive electrode and the negative electrode. This lithium ion secondary battery is characterized in that: the positive electrode active material is mainly composed of a lithium transition metal oxide and has a composite coating layer on the surface, said composite coating layer being formed of a phosphoric acid compound and an oxide or fluoride containing one or more elements selected from among Mo, W and Zr; and with respect to the atomic concentration of at least one of Mo, W and Zr contained in the composite coating layer, the average atomic concentration from the center in the thickness direction of the composite coating layer to the lithium transition metal oxide is higher than the average atomic concentration from the center in the thickness direction of the composite coating layer to the electrolyte. The purpose of the present invention is to further improve safety of the battery by suppressing oxygen desorption at the time of overcharging as a result of the above-described configuration.

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 The present invention relates to a lithium ion secondary battery.
　近年、高エネルギー密度を有するリチウムイオン二次電池が着目され、その研究、開発及び商品化が急速に進められた結果、現在では、携帯電話やノートパソコン向けに小型民生用リチウムイオン二次電池が幅広く普及している。さらに、地球温暖化や枯渇燃料の問題から電気自動車（EV）や駆動の一部を電気モーターで補助するハイブリッド電気自動車（HEV）が各自動車メーカーで開発され、その電源として高容量で高出力なリチウムイオン二次電池が求められており、市場での普及には高い安全性が必要不可欠である。 In recent years, attention has been focused on lithium-ion secondary batteries with high energy density, and as a result of rapid progress in research, development and commercialization, lithium-ion secondary batteries for consumer use are now available for mobile phones and laptop computers. Widely used. Furthermore, electric vehicles (EV) and hybrid electric vehicles (HEV) that assist electric motors with some electric motors have been developed by each automobile manufacturer due to global warming and depleted fuel problems. Lithium ion secondary batteries are required, and high safety is indispensable for popularization in the market.
　電池の安全性は、JIS(日本工業規格)、SAE(米国自動車技術者協会)、EUCAR(欧州)規格など、各国それぞれの規格により判定されている。各規格の安全性試験は速度や時間などの条件が異なるものの、針刺し試験、圧壊(縦・横方向)試験、外部短絡試験、加熱試験、過放電試験、過充電試験から成り、発火破裂の有無などにより安全性を判定している。これら試験の中で最も難易度が高いのは、過充電試験と考えられている。 Battery safety is determined by the standards of each country such as JIS (Japanese Industrial Standards), SAE (American Automotive Engineers Association), EUCAR (Europe) standards. The safety test of each standard consists of needle puncture test, crushing (longitudinal / lateral) test, external short circuit test, heating test, overdischarge test, overcharge test, with or without ignition burst, although speed and time are different. Safety is judged by such factors. The most difficult of these tests is considered an overcharge test.
　過充電条件下では、電圧の影響で電解液の分解が始まり、徐々に温度が上昇し、約70℃でSEIの溶解再生成反応がはじまり、さらに温度が上昇する。そして、電圧と温度の影響で正極の熱分解が生じ、酸素が放出される。その際、一般に層状構造の正極は第一にスピネル構造、第二に岩塩構造へと変化すると考えられている(非特許文献１、２)。この正極の熱分解は発熱量が大きく、放置すると発火を引き起こす場合がある。 Under the overcharge condition, the decomposition of the electrolyte starts under the influence of voltage, the temperature gradually rises, the SEI dissolution and regeneration reaction begins at about 70 ° C, and the temperature further rises. The positive electrode is thermally decomposed by the influence of voltage and temperature, and oxygen is released. At that time, it is generally considered that the positive electrode having a layered structure changes into a spinel structure first and a rock salt structure second (Non-Patent Documents 1 and 2). This thermal decomposition of the positive electrode generates a large amount of heat and may cause ignition if left untreated.
　正極の熱分解を抑制するため、特許文献1では、層状構造を有する正極活物質にAlやMgを金属サイトに置換させて酸素脱離を抑制している。特許文献2では、正極材料表面に突起状のAl含有酸化物及び／又はAl含有水酸化物を均一に分布させるとともにリン酸化合物を付着させ、非水電解液が分解したり、正極材料からコバルト等の元素が溶出したりするのを抑制している。 In order to suppress thermal decomposition of the positive electrode, in Patent Document 1, Al and Mg are substituted with metal sites in the positive electrode active material having a layered structure to suppress oxygen desorption. In Patent Document 2, protrusion-like Al-containing oxides and / or Al-containing hydroxides are uniformly distributed on the surface of the positive electrode material, and a phosphoric acid compound is adhered, so that the non-aqueous electrolyte is decomposed or cobalt is removed from the positive electrode material. And the like are suppressed from elution.
　特に、リン酸化合物は正極材料からの元素の溶出を抑制する効果があるため、リン酸化合物を正極材料近傍に配置し、その外側にAl化合物を被覆する例が記載されている。 Especially, since the phosphoric acid compound has an effect of suppressing the elution of elements from the positive electrode material, an example is described in which the phosphoric acid compound is arranged in the vicinity of the positive electrode material and the outer side thereof is coated with an Al compound.
特開2004-220952JP2004-220952 特開2009-245917JP2009-245917
　しかしながら、更なる正極活物質の安全性の向上が要求されている。本発明はさらに過充電時の酸素脱離の量、速度を抑制し、安全性を向上させることを目的とする。 However, further improvement in the safety of the positive electrode active material is required. Another object of the present invention is to suppress the amount and rate of oxygen desorption during overcharge and improve safety.
　上記課題を解決するため、本発明は、正極活物質への被覆化合物および被覆構造を最適化した。本発明は、正極または負極活物質を備え、リチウムイオンを吸蔵放出できる正極、負極、及び正負極間に配置されたセパレータを備えるリチウムイオン二次電池であって、正極活物質は、表面に酸化物またはフッ化物と、リン酸化合物との複合被覆層を有し、前記酸化物またはフッ化物は、Ｍｏ，Ｗ，Ｚｒの少なくともいずれかを含む化合物であり、前記複合被覆層のＭｏ，Ｗ，Ｚｒの少なくともいずれか原子濃度は、表層側が低く、正極活物質側が高いことを特徴とする。複合被覆層のリンの原子濃度を正極活物質側よりも表層側を高くすることにより、過充電時の酸素脱離速度と量を低減させることが可能である。 In order to solve the above problems, the present invention has optimized the coating compound and the coating structure on the positive electrode active material. The present invention relates to a lithium ion secondary battery that includes a positive electrode or a negative electrode active material, a positive electrode capable of occluding and releasing lithium ions, a negative electrode, and a separator disposed between the positive and negative electrodes. The positive electrode active material is oxidized on the surface. The oxide or fluoride is a compound containing at least one of Mo, W, and Zr, and the Mo, W, The atomic concentration of at least one of Zr is characterized in that the surface layer side is low and the positive electrode active material side is high. By making the atomic concentration of phosphorus in the composite coating layer higher on the surface layer side than on the positive electrode active material side, the oxygen desorption rate and amount during overcharge can be reduced.
　本発明により、リチウムイオン二次電池の安全性向上に寄与する。 The present invention contributes to improving the safety of lithium ion secondary batteries.
ラミネートセル内部の積層型電極群の分解図Exploded view of the stacked electrode group inside the laminate cell ラミネートセルの分解斜視図Exploded perspective view of laminate cell
　本発明者らは、過充電時の熱安定性を向上させる正極を備えるリチウムイオン二次電池を検討した。正極活物質の表面に、価数の高いＭｏ，Ｗ，Ｚｒの酸化物層等で被覆したところ、高容量、かつ高サイクル特性、劣化しにくい優れた電池となる。さらなる熱安定性向上のため、高電圧で分解しにくいリン酸化合物を併せて用いた、複合被覆層を用いることができる。 The present inventors examined a lithium ion secondary battery including a positive electrode that improves thermal stability during overcharge. When the surface of the positive electrode active material is coated with a high-valence Mo, W, Zr oxide layer or the like, an excellent battery with high capacity, high cycle characteristics, and resistance to deterioration is obtained. In order to further improve thermal stability, a composite coating layer using a phosphoric acid compound that is difficult to decompose at a high voltage can be used.
　具体的には、正極表面に高価数元素（Ｍｏ，Ｗ，Ｚｒ）の化合物を含む複合被覆層を備え、更に複合被覆層の表面近傍部分にリン酸化合物を多く配した状態とする。高価数元素の酸化物は活物質の崩壊を防ぎ、リン酸化合物は電解液と正極活物質との反応を阻害するため、酸素の脱離量や、脱離速度が低減され、また酸素脱離開始温度も高温とすることができる。その結果、過充電時の発火破裂の危険性をさらに抑止することができると考える。特に、高容量で熱安定性の高くないＮｉを多く含む正極に適用すると効果的である。 Specifically, a composite coating layer containing a compound of an expensive element (Mo, W, Zr) is provided on the surface of the positive electrode, and a large amount of phosphate compound is arranged in the vicinity of the surface of the composite coating layer. Expensive oxides prevent the active material from collapsing, and phosphoric acid compounds inhibit the reaction between the electrolyte and the positive electrode active material. The starting temperature can also be high. As a result, it is considered that the risk of ignition burst during overcharge can be further suppressed. In particular, it is effective when applied to a positive electrode containing a large amount of Ni having a high capacity and not high thermal stability.
　以下、本発明について更に詳細を説明する。 Hereinafter, further details of the present invention will be described.
　(正極活物質)
  上述の通り、本発明に係る正極活物質は、リチウム遷移金属酸化物の表面に、リン酸化合物と、高価数元素Ａ（Ａは、Ｍｏ，Ｗ，Ｚｒからなる群より選択される一つ以上の元素）を含む化合物（酸化物またはフッ化物）とを含む複合被覆層を有する。充電状態で熱安定性に優れたリチウム遷移金属酸化物を得るには、リチウム遷移金属酸化物を被覆する被覆化合物(被覆層)の配置およびリチウム遷移金属酸化物の組成に加え、被覆層を形成する被覆化合物の含有量が重要なポイントである。 (Positive electrode active material)
As described above, the positive electrode active material according to the present invention has one or more selected from the group consisting of a phosphoric acid compound and an expensive element A (A is Mo, W, Zr) on the surface of the lithium transition metal oxide. And a composite coating layer containing a compound (oxide or fluoride) containing the element. In order to obtain a lithium transition metal oxide with excellent thermal stability in the charged state, in addition to the arrangement of the coating compound (coating layer) covering the lithium transition metal oxide and the composition of the lithium transition metal oxide, a coating layer is formed. The content of the coating compound to be used is an important point.
　複合被覆層に含まれる高価数元素Ａの化合物は、リチウム遷移金属酸化物１００重量部に対し、０．２重量部以上１．５重量部以下であることが好ましい。高価数元素Ａの化合物は、リチウム遷移金属酸化物を全面的に被覆していることが望ましい。高価数元素Ａの化合物は、価数が高く酸素との結合が強いためにリチウム遷移金属酸化物の酸素脱離を抑制する。また、リチウム遷移金属酸化物表面にリン酸化合物を被覆させるための介在層の役割も有する。０．２重量部未満では、量が少なくリチウム遷移金属酸化物の表面全体を被覆するのに十分とはいえない。また、高価数元素Ａの化合物は抵抗が高く、１．５重量部を超える場合、正極の抵抗上昇により電池容量の大幅な低下を招く。特に、0.4重量部以上1.0重量部以下であることが好ましい。 The compound of the expensive element A contained in the composite coating layer is preferably 0.2 parts by weight or more and 1.5 parts by weight or less with respect to 100 parts by weight of the lithium transition metal oxide. It is desirable that the compound of the expensive element A covers the entire surface of the lithium transition metal oxide. Since the compound of the expensive element A has a high valence and a strong bond with oxygen, oxygen desorption of the lithium transition metal oxide is suppressed. In addition, it also serves as an intervening layer for coating the surface of the lithium transition metal oxide with a phosphate compound. If it is less than 0.2 parts by weight, the amount is small and it cannot be said to be sufficient to cover the entire surface of the lithium transition metal oxide. Further, the compound of the expensive element A has a high resistance, and when it exceeds 1.5 parts by weight, the battery capacity is significantly reduced due to the increase in resistance of the positive electrode. In particular, it is preferably 0.4 parts by weight or more and 1.0 parts by weight or less.
　複合被覆層のリン酸化合物の含有率は、リチウム遷移金属酸化物１００重量部に対し、０．１重量部以上５．０重量部以下であることが好ましい。リン酸化合物の含有量が０．１重量部未満ではリチウム遷移金属酸化物表面を全体的に覆えないので十分な役割を果たすことができない。一方、５．０重量部を超える場合は、リン酸化合物自体は充放電反応に寄与しないため、正極の抵抗上昇につながり、電池容量の低下を招く。
より好ましくは、０．５重量部以上２．０重量部以下である。 It is preferable that the content rate of the phosphoric acid compound of a composite coating layer is 0.1 to 5.0 weight part with respect to 100 weight part of lithium transition metal oxides. If the content of the phosphoric acid compound is less than 0.1 part by weight, the entire surface of the lithium transition metal oxide cannot be covered, so that it cannot play a sufficient role. On the other hand, when the amount exceeds 5.0 parts by weight, the phosphoric acid compound itself does not contribute to the charge / discharge reaction, leading to an increase in resistance of the positive electrode and a decrease in battery capacity.
More preferably, it is 0.5 parts by weight or more and 2.0 parts by weight or less.
　複合被覆層を形成するリン酸化合物は、電解液の酸化分解抑制の観点から、Ｌｉ3ＰＯ4、Ｌｉ4Ｐ2Ｏ7、ＬｉＰＯ3からなる群より選択される一つ以上であることが好ましい。 The phosphoric acid compound forming the composite coating layer is preferably at least one selected from the group consisting of Li 3 PO 4 , Li 4 P 2 O 7 and LiPO 3 from the viewpoint of suppressing oxidative decomposition of the electrolytic solution. .
　被覆層の厚さは２ｎｍ以上８０ｎｍ以下であることが好ましい。被覆層の厚さが２ｎｍ未満の場合、被覆化合物を形成する粒子径自体をそれ以下にする必要がある。２ｎｍ未満の被覆化合物粒子はファンデルワールス力により凝集しやすく、リチウム遷移金属酸化物表面を均一に被覆することが困難である。一方、被覆層の厚さが８０ｎｍを超えると、被覆層による抵抗上昇が顕著になり、電池特性が低下してしまう。より好ましくは、被覆層の厚さは10nm以上60nm以下である。 The thickness of the coating layer is preferably 2 nm or more and 80 nm or less. When the thickness of the coating layer is less than 2 nm, the particle size itself forming the coating compound needs to be smaller than that. The coating compound particles of less than 2 nm tend to aggregate due to van der Waals force, and it is difficult to uniformly coat the lithium transition metal oxide surface. On the other hand, when the thickness of the coating layer exceeds 80 nm, the resistance increase due to the coating layer becomes remarkable, and the battery characteristics are deteriorated. More preferably, the thickness of the coating layer is 10 nm or more and 60 nm or less.
　複合被覆層のリン酸化合物は電解液の酸化分解を抑制する役割を有する。従って、複合被覆層のリンの原子濃度は、リチウム遷移金属酸化物側よりも被覆層の表層側（電解質側）で高いことが好ましい。なお、複合被覆層のリン酸化合物、高価数元素Ａの化合物の分布を確認する方法は下記のとおりである。被覆層を厚さ方向に２分割、すなわち被覆層のリチウム遷移金属酸化物側との一方側の界面から被覆層の電解液(電解質)との他方側の界面までの長さを２分割して、正極活物質であるリチウム遷移金属酸化物との界面側をリチウム遷移金属酸化物側、電解液(電解質)との界面側を表層側（電解質側）とし、それぞれの分割範囲の原子濃度の平均値を算出した。測定誤差等を考慮し、表層側（電解質側）の原子濃度の平均値がリチウム遷移金属酸化物側の原子濃度の平均値に対して４ａｔｏｍ％以上高い場合、原子濃度が高いと判断した。 The phosphate compound in the composite coating layer has a role of suppressing oxidative decomposition of the electrolytic solution. Accordingly, the atomic concentration of phosphorus in the composite coating layer is preferably higher on the surface layer side (electrolyte side) of the coating layer than on the lithium transition metal oxide side. The method for confirming the distribution of the phosphoric acid compound and the compound of the expensive element A in the composite coating layer is as follows. Dividing the coating layer into two in the thickness direction, that is, dividing the length from the interface on one side of the coating layer to the lithium transition metal oxide side to the interface on the other side of the coating layer electrolyte (electrolyte) The interface side with the lithium transition metal oxide, which is the positive electrode active material, is the lithium transition metal oxide side, and the interface side with the electrolyte (electrolyte) is the surface layer side (electrolyte side). The value was calculated. In consideration of measurement errors and the like, when the average value of the atomic concentration on the surface layer side (electrolyte side) is higher by 4 atom% or more than the average value of the atomic concentration on the lithium transition metal oxide side, it was determined that the atomic concentration was high.
　リチウム遷移金属酸化物は、一般式ＬｉＮｉaＢbＣ(1-a-b)Ｏ2(0.5≦a<1, 0≦b<0.4, B=Co,Mnのいずれか1種類以上, Ｃ＝Ｌｉ, Ｍｏ，Ｗ，Ｚｒ,Ａｌ，Ｍｇ，Ｔｉ，Ｃｕ，Ｎｂの少なくとも1種類以上)で表わされるものであると、効果が大きい。上記一般式で表される化合物は、Ｎｉの含有量が多めであり（Ｎｉリッチ）、熱安定性が悪いためである。 The lithium transition metal oxide has a general formula of LiNi a B b C (1-ab) O 2 (0.5 ≦ a <1, 0 ≦ b <0.4, B = Co, Mn, one or more types, C = Li, If it is represented by at least one of Mo, W, Zr, Al, Mg, Ti, Cu, and Nb), the effect is great. This is because the compound represented by the above general formula has a high Ni content (Ni-rich) and poor thermal stability.
　上記のように、被覆層をリチウム遷移金属酸化物の表面に形成する構成により、過充電時、電解液に隣接するリン酸化合物が電解液の酸化分解抑制し、かつリチウム遷移金属酸化物に隣接するＡを含む酸化物またはフッ化物がリチウム遷移金属酸化物の酸素脱離を抑制する。これらの役割を同時に果たすため、被覆効果を最大限に発揮し、過充電特性が向上する。 As described above, the coating layer is formed on the surface of the lithium transition metal oxide, so that the phosphoric acid compound adjacent to the electrolytic solution suppresses the oxidative decomposition of the electrolytic solution and is adjacent to the lithium transition metal oxide during overcharge. The oxide or fluoride containing A that suppresses oxygen desorption of the lithium transition metal oxide. Since these roles are played simultaneously, the covering effect is maximized and the overcharge characteristics are improved.
　＜リチウム遷移金属酸化物への表面処理方法＞
  リチウム遷移金属酸化物の表面処理の手法に関して、本発明において特に問わない。しかし、被覆化合物のリン酸化合物中のＰは、被覆層内において、表層側(電解液側)の原子濃度がリチウム遷移金属酸化物側の原子濃度よりも高くすることが好ましい。そのような被覆層を形成するリチウム遷移酸化物に対する被覆処理の手順として、以下のような方法がある。
  （１）高価数元素Ａを含む溶液をリチウム遷移金属酸化物と混合した後、リン酸化合物を溶媒中に投入し、室温でさらに混合し、この状態で真空乾燥や噴霧乾燥で溶媒を蒸発させ、得られた粉末を大気中で熱処理する方法。
  （２）高価数元素Ａを含む溶液をリチウム遷移金属酸化物と混合し、真空乾燥や噴霧乾燥で溶媒を蒸発させ、酸化物にした後、リン酸化合物溶液を投入し、室温で混合、この状態でさらに真空乾燥や噴霧乾燥で溶媒を蒸発させ、得られた粉末を大気中で熱処理し、得る方法。
  （３）高価数元素Ａを含む酸化物をボールミル等でリチウム遷移金属酸化物に直接被覆した後、
リン酸化合物溶液を投入し、室温で混合後、真空乾燥や噴霧乾燥で溶媒を蒸発させ、得られた粉末を大気中で熱処理し、得る方法。 <Surface treatment method for lithium transition metal oxide>
The method for surface treatment of the lithium transition metal oxide is not particularly limited in the present invention. However, P in the phosphoric acid compound of the coating compound is preferably such that the atomic concentration on the surface layer side (electrolyte side) is higher than the atomic concentration on the lithium transition metal oxide side in the coating layer. As a procedure for coating treatment for the lithium transition oxide forming such a coating layer, there are the following methods.
(1) After mixing the solution containing the expensive element A with the lithium transition metal oxide, the phosphoric acid compound is put into the solvent and further mixed at room temperature. In this state, the solvent is evaporated by vacuum drying or spray drying. A method of heat-treating the obtained powder in the air.
(2) A solution containing an expensive element A is mixed with a lithium transition metal oxide, and the solvent is evaporated by vacuum drying or spray drying to form an oxide. Then, a phosphoric acid compound solution is added and mixed at room temperature. A method in which the solvent is further evaporated by vacuum drying or spray drying in the state, and the obtained powder is heat treated in the atmosphere.
(3) After directly coating an oxide containing an expensive element A on a lithium transition metal oxide with a ball mill or the like,
A method in which a phosphoric acid compound solution is added, mixed at room temperature, the solvent is evaporated by vacuum drying or spray drying, and the resulting powder is heat treated in the atmosphere.
　なお、リン酸化合物の原料は、リン酸水素二アンモニウム（（NH4）2HPO4）やリン酸二水素アンモニウム（NH4H2PO4）である。これらの原料化合物を所定量溶解させ、LiOHを所定量加えると、リン酸化合物が生成する。リン酸化合物は、Ｌｉ3ＰＯ4、Ｌｉ4Ｐ2Ｏ7、ＬｉＰＯ3、などである。例えば、
  （ＮＨ4）2ＨＰＯ4＋３ＬｉＯＨ　→　Ｌｉ3ＰＯ4＋ＮＯ3 -＋５Ｈ2・・・（式１）
　リン酸化合物の原料、またはリン酸化合物を含む溶液をＡを含むリチウム遷移金属酸化物の溶液に加え、溶媒を蒸発させると、被覆層内の表層側(電解液側)近傍で、リン酸化合物中のＰの原子濃度を高くすることができる。 The raw material of the phosphate compound is diammonium hydrogen phosphate ((NH 4 ) 2 HPO 4 ) or ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ). When a predetermined amount of these raw material compounds are dissolved and a predetermined amount of LiOH is added, a phosphoric acid compound is produced. Examples of the phosphoric acid compound include Li 3 PO 4 , Li 4 P 2 O 7 , LiPO 3 , and the like. For example,
(NH 4 ) 2 HPO 4 + 3LiOH → Li 3 PO 4 + NO 3 − + 5H 2 (Formula 1)
When a phosphoric acid compound raw material or a solution containing a phosphoric acid compound is added to the lithium transition metal oxide solution containing A and the solvent is evaporated, the phosphoric acid compound is formed near the surface layer side (electrolyte side) in the coating layer. The atomic concentration of P inside can be increased.
　加熱処理の温度は、いずれも300℃以上800℃以下、より好ましくは500℃以上700℃以下である。加熱することで、リチウム遷移金属酸化物表面にＡを含む酸化物として被覆され、さらに、被覆層とリチウム遷移金属酸化物の間に強固な密着性を付与できる。加熱時間は1時間以上20時間以下、好ましくは、3時間以上8時間以下である。加熱処理をフッ素(F2)ガス雰囲気で実施することで、水酸化物をフッ化物にすることができる。フッ素ガスとしては三フッ化窒素ガスが好ましい。 The temperature of the heat treatment is 300 ° C. or higher and 800 ° C. or lower, more preferably 500 ° C. or higher and 700 ° C. or lower. By heating, the lithium transition metal oxide surface is coated as an oxide containing A, and further, strong adhesion can be imparted between the coating layer and the lithium transition metal oxide. The heating time is 1 hour or more and 20 hours or less, preferably 3 hours or more and 8 hours or less. By performing the heat treatment in a fluorine (F 2 ) gas atmosphere, the hydroxide can be converted to fluoride. As the fluorine gas, nitrogen trifluoride gas is preferable.
　これらの処理により、被覆層内の表層側(電解液側)で、特に表層近傍でリン酸化合物を多くし、Ｐの原子濃度を高くすることができる。一方、リチウム遷移金属酸化物近傍の高価数元素Ａの原子濃度が、表層側（電解質側）の原子濃度より高くなる。 By these treatments, the phosphoric acid compound can be increased on the surface layer side (electrolyte side) in the coating layer, particularly in the vicinity of the surface layer, and the atomic concentration of P can be increased. On the other hand, the atomic concentration of the expensive element A near the lithium transition metal oxide is higher than the atomic concentration on the surface layer side (electrolyte side).
　以下に詳細な実施例を挙げる。本実施例は、いずれもリン酸化合物としてＬｉ3ＰＯ4を用い、上記（１）の方法でリチウム遷移金属酸化物の被覆を行ったが、本発明はこれに限定されるものではない。また、本実施例では、積層型の電極群を備えるラミネートセルのリチウムイオン二次電池を用いて説明を行うが、捲回構造や、金属缶に封入されたものであってもかまわない。 Detailed examples are given below. In this example, Li 3 PO 4 was used as the phosphate compound, and the lithium transition metal oxide was coated by the method (1). However, the present invention is not limited to this. In this embodiment, the description will be made using a lithium ion secondary battery of a laminate cell having a stacked electrode group, but it may be a wound structure or a metal can sealed.
  ＜試験セルの作製＞
  図1はラミネートセル内部の積層型電極群の分解図である。図1のような積層型電極群では、板状の正極５と、板状の負極６とが、セパレータ７に挟まれて積層された構造を有する。 <Production of test cell>
FIG. 1 is an exploded view of a laminated electrode group inside a laminated cell. The stacked electrode group as shown in FIG. 1 has a structure in which a plate-like positive electrode 5 and a plate-like negative electrode 6 are sandwiched and stacked between separators 7.
　正極は、正極集電箔としてアルミニウム箔を有し、アルミニウム箔の両面に、正極活物質を配している。このとき、アルミニウム箔の一部に正極活物質合剤の塗工されない正極未塗工部３が形成される。すなわち、正極未塗工部3では、アルミニウム箔が露出している。 The positive electrode has an aluminum foil as a positive electrode current collector foil, and a positive electrode active material is disposed on both sides of the aluminum foil. At this time, the positive electrode uncoated portion 3 where the positive electrode active material mixture is not applied is formed on a part of the aluminum foil. That is, in the positive electrode uncoated portion 3, the aluminum foil is exposed.
　正極集電箔に塗布される正極活物質合剤には、正極活物質以外に、炭素材料の導電材およびポリフッ化ビニリデン（以下、PVDFと略記する。）のバインダ（結着材）を混合した。その重量比率は順に90：5：5で作製し、合剤塗工量は120g/m2である。アルミニウム箔への正極活物質合剤の塗工時には、N－メチルピロリドン（以下、NMPと略記する。）等の分散溶媒で粘度調整した。正極5は、塗布、乾燥後ロールプレスで密度が調整されており、今回密度は2.8g/cm3で作製した。 In addition to the positive electrode active material, the positive electrode active material mixture applied to the positive electrode current collector foil was mixed with a carbon material conductive material and a polyvinylidene fluoride (hereinafter abbreviated as PVDF) binder. . The weight ratio is 90: 5: 5 in order, and the mixture coating amount is 120 g / m2. When the positive electrode active material mixture was applied to the aluminum foil, the viscosity was adjusted with a dispersion solvent such as N-methylpyrrolidone (hereinafter abbreviated as NMP). The density of the positive electrode 5 was adjusted by a roll press after coating and drying, and this time, the density was 2.8 g / cm 3.
　負極6は、負極集電箔として銅箔を有している。銅箔の両面には、負極活物質として人造黒鉛を用いた。他にも、負極活物質にはリチウムイオンを可逆に吸蔵、放出可能な材料を自由に適用することができ、天然黒鉛、非晶質炭素などの炭素材料、酸化物や合金など用いることができる。負極活物質合剤には、負極活物質以外に、アセチレンブラックを導電材として用い、さらにPVDFのバインダを用いた。その重量比率は順に90：5：5で作製し、合剤塗工量は70g/m2で作製した。銅箔への負極活物質合剤の塗工時には、NMP等の分散溶媒で粘度調整される。このとき、銅箔の一部に負極活物質合剤の塗工されない負極未塗工部4が形成される。すなわち、負極未塗工部4では、銅箔が露出している。負極6は、乾燥後ロールプレスで密度が調整されており、今回密度は1.5g/cm3で作製した。 The negative electrode 6 has a copper foil as a negative electrode current collector foil. Artificial graphite was used as the negative electrode active material on both sides of the copper foil. In addition, a material capable of reversibly occluding and releasing lithium ions can be freely applied to the negative electrode active material, and carbon materials such as natural graphite and amorphous carbon, oxides and alloys can be used. . As the negative electrode active material mixture, acetylene black was used as a conductive material in addition to the negative electrode active material, and a PVDF binder was further used. The weight ratio was prepared in order 90: 5: 5, and the mixture coating amount was 70 g / m2. When the negative electrode active material mixture is applied to the copper foil, the viscosity is adjusted with a dispersion solvent such as NMP. At this time, the negative electrode uncoated portion 4 where the negative electrode active material mixture is not applied is formed on a part of the copper foil. That is, the copper foil is exposed in the negative electrode uncoated portion 4. The density of the negative electrode 6 was adjusted by a roll press after drying, and this time the density was 1.5 g / cm 3.
　セパレータとして、本実施例では、リチウムイオンを通す微多孔膜（ポリオレフィンなど）を用いた。ポリオレフィンは、主にポリエチレン、ポリプロピレンなどを少なくとも1種類を含むことを特徴とするが、ポリアミド、ポリアミドイミド、ポリイミド、ポリスルホン、ポリエーテルスルホン、ポリフェニルスルホン、ポリアクリロニトリルなどの耐熱性樹脂を含んでもかまわない。無機フィラー層は、ＳｉＯ2、Ａｌ2Ｏ3、モンモリロナイト、雲母、ＺｎＯ、ＴｉＯ2、ＢａＴｉＯ3、ＺｒＯ2の少なくとも1種類を含むことを特徴とする。コストや性能の観点からは、ＳｉＯ2またはＡｌ2Ｏ3を使用することが最も好ましい。またセパレータには、無機フィラー層を片面もしくは両面に塗っていてもかまわない。 In this example, a microporous membrane (such as polyolefin) that allows lithium ions to pass through was used as the separator. Polyolefin is mainly characterized by containing at least one kind of polyethylene, polypropylene, etc., but may contain heat-resistant resin such as polyamide, polyamideimide, polyimide, polysulfone, polyethersulfone, polyphenylsulfone, polyacrylonitrile. Absent. The inorganic filler layer is characterized by containing at least one of SiO 2 , Al 2 O 3 , montmorillonite, mica, ZnO, TiO 2 , BaTiO 3 , and ZrO 2 . From the viewpoint of cost and performance, it is most preferable to use SiO 2 or Al 2 O 3 . The separator may be coated with an inorganic filler layer on one side or both sides.
　正極未塗工部３および負極未塗工部4は、束ねて、電池内外を電気的に接続する正極端子1、負極端子2に超音波溶接されている。溶接方法は、抵抗溶接など他の溶接手法を適宜選択できる。なお、正極端子1、負極端子2は電池内外をより封止させるために、あらかじめ熱溶着樹脂を端子の封止箇所に塗る、または取り付けていてもよい。 The positive electrode uncoated portion 3 and the negative electrode uncoated portion 4 are bundled and ultrasonically welded to the positive electrode terminal 1 and the negative electrode terminal 2 that electrically connect the inside and outside of the battery. As the welding method, other welding methods such as resistance welding can be appropriately selected. Note that the positive electrode terminal 1 and the negative electrode terminal 2 may be preliminarily coated with or attached to a sealing portion of the terminal in order to further seal the inside and outside of the battery.
　本実施例の正極活物質は、高価数の金属Ａを含む酸化物またフッ化物とリン酸化合物とよりなる被覆層を備えるリチウム遷移金属酸化物（ＬｉＮｉaＢbＣ(1-a-b)Ｏ2）である。原料の重量を変更したり、被覆層を調整し、今回用いた実施例、比較例の正極活物質を作製した。また、作製した試料より、正極活物質の化合物種、被覆層の状態等を測定した。表１にそれぞれの正極活物質を示す。 The positive electrode active material of this example is a lithium transition metal oxide (LiNi a B b C (1-ab) O 2 ) having a coating layer made of an oxide containing a high number of metals A or a fluoride and a phosphate compound. ). The positive electrode active materials of Examples and Comparative Examples used this time were prepared by changing the weight of the raw material or adjusting the coating layer. Further, from the prepared sample, the compound type of the positive electrode active material, the state of the coating layer, and the like were measured. Table 1 shows each positive electrode active material.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　被覆層の厚さ、被覆層の原子の濃度分布は、Ｘ線分析装置（サーモフィッシャー社製　NORAN System 300、以下EDSと略す）を備えた電界放出形透過電子顕微鏡（日立製作所製　HF－2000、以下、TEMと略す）を用い、加速電圧200ｋＶで測定した。試料は研磨機（GATAN社製　600型）を用い、Ａｒイオンエッチング法により事前に薄片化した。なお、被覆層の元素分布は、TEMと電子エネルギ損失分光法（EELS）を組み合わせたTEM-EELSや、飛行時間型二次イオン質量分析法（TOF-SIMS）、オージェ電子分光法（AES）等でも確認することが可能である。 The thickness of the coating layer and the concentration distribution of the atoms in the coating layer were measured using a field emission transmission electron microscope (Hitachi HF-2000, equipped with an X-ray analyzer (NORAN ™ System 300, hereinafter referred to as EDS) manufactured by Thermo Fisher). (Hereinafter abbreviated as TEM) and measured at an acceleration voltage of 200 kV. The sample was sliced in advance by an Ar ion etching method using a polishing machine (600 type, manufactured by GATAN). The elemental distribution of the coating layer includes TEM-EELS combining TEM and electron energy loss spectroscopy (EELS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), Auger electron spectroscopy (AES), etc. But it can be confirmed.
　表面被覆化合物(被覆層)の結合状態は、TEMを用い、加速電圧200ｋVで電子線回折像を取得して、回折点を付属のデータベースの既知の化合物の回折点の情報と比較して決定した。 The bonding state of the surface coating compound (coating layer) was determined by using TEM, acquiring an electron diffraction image at an acceleration voltage of 200 kV, and comparing the diffraction point with information on the diffraction points of known compounds in the attached database. .
　被覆層を形成するための表面処理に用いた元素の重量比は、高周波誘導結合プラズマ発光分光（以下ICPと略す）分析装置（日立製作所製　P－4000）を用いて測定した。まず、ビーカに入れた45mlのイオン交換水に5ｇの正極材料と2mlの硝酸を投入し、スターラ(攪拌機)で30分間攪拌した。5分間放置後、濾紙で濾過した濾液をアルゴンガスと共に高周波雰囲気中に噴霧し、励起された各元素特有の光の強度を測定して元素の重量比を算出した。 The weight ratio of the elements used for the surface treatment for forming the coating layer was measured using a high frequency inductively coupled plasma emission spectroscopy (hereinafter abbreviated as ICP) analyzer (P-4000 manufactured by Hitachi, Ltd.). First, 5 g of positive electrode material and 2 ml of nitric acid were added to 45 ml of ion exchange water in a beaker, and the mixture was stirred for 30 minutes with a stirrer (stirrer). After standing for 5 minutes, the filtrate filtered with filter paper was sprayed in a high-frequency atmosphere together with argon gas, and the light intensity peculiar to each excited element was measured to calculate the weight ratio of the elements.
　図２にラミネートセルの分解斜視図を示す。ラミネートセルは、ラミネートフィルムのふちに、電気的に絶縁した状態で正極端子1と負極端子2を貫通させた構造となっている。 Fig. 2 shows an exploded perspective view of the laminate cell. The laminate cell has a structure in which the positive electrode terminal 1 and the negative electrode terminal 2 are passed through the edge of the laminate film in an electrically insulated state.
　ラミネートフィルム8、10で電極群9を挟み、ふちを175℃で10秒間熱溶着して封止した。封止は、1辺以外をはじめに熱溶着させ、電解液を注液した後に、残りの一辺を真空加圧しながら、熱溶着封止させた。注液口となった辺の熱溶着箇所は、その他の辺に比べ、熱溶着強度が弱く、ガス排出弁の効果を有する。なお、他の箇所に薄肉部など、ガス排出機構を設けてもよい。 The electrode group 9 was sandwiched between laminate films 8 and 10, and the edge was thermally welded at 175 ° C. for 10 seconds and sealed. Sealing was performed by heat-welding and sealing while heat-welding first except the one side, injecting the electrolyte, and then vacuum-pressing the other side. The heat welding location on the side that has become the liquid injection port is weaker in heat welding strength than the other sides and has the effect of a gas discharge valve. In addition, you may provide gas discharge mechanisms, such as a thin part, in another location.
　電解液には、リチウム塩を溶解させた有機電解液、あるいはリチウムイオンの伝導性を有する固体電解質、ゲル状電解質、溶融塩など、電池で使用される既知の電解質を用いることができる。本実施例では、エチレンカーボネート（EC）：エチルメチルカーボネート（EMC）＝１：３ｖｏｌ％の溶媒に、電解質として1MLiPF6を溶かしたものを用いた。 As the electrolytic solution, an organic electrolytic solution in which a lithium salt is dissolved, or a known electrolyte used in a battery such as a solid electrolyte having a lithium ion conductivity, a gel electrolyte, or a molten salt can be used. In this example, 1MLiPF 6 was used as an electrolyte in a solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1: 3 vol%.
　非水溶媒として、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、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、γ－ブチロラクトン、γ－バレロラクトン、メチルアセテート、エチルアセテート、メチルプロピオネート、テトラヒドロフラン、2－メチルテトラヒドロフラン、1，2－ジメトキシエタン、1－エトキシ－2－メトキシエタン、3－メチルテトラヒドロフラン、1，2－ジオキサン、1，3－ジオキサン、1，4－ジオキサン、1，3－ジオキソラン、2－メチル－1，3－ジオキソラン、4－メチル－1，3－ジオキソラン等より少なくとも1種を用いることができる。また、電解質として、例えば、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＣｌＯ4、ＬｉＮ（Ｃ2Ｆ5ＳＯ2）2等より少なくとも1種を使用できる。 Non-aqueous solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, γ-valerolactone, methyl acetate, ethyl acetate, methyl propionate, tetrahydrofuran, 2-methyl Tetrahydrofuran, 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 3-methyltetrahydrofuran, 1,2-dioxane, 1,3-dioxane, 1,4-dioxane, 1,3-dioxolane, 2-methyl At least one of -1,3-dioxolane, 4-methyl-1,3-dioxolane and the like can be used. Further, as the electrolyte, for example, a LiPF 6, LiBF 4, LiClO 4 , LiN (C 2 F 5 SO 2) at least one more like 2 can be used.
　なお、本実施例では、温度とガスの影響を除外して過充電正極を観察するため、25℃一定となるラミネートセルＸを作製した。ラミネートセルＸでは、ラミネートセルの内部体積全てに電解液を注入して放熱性に優れさせ、かつラミネートセルの1辺の一部分を熱溶着させずにガス流路を確保し、かつその部位からセル内部に熱電対を通し、セル内部温度が25℃一定となるように専用の冷却ファンを取り付けた。また、通常のラミネートセルＹ（ラミネートセルの容量に対し、充填する電解液量を少なくして余裕を持たせ、ラミネートセルの辺すべてを溶着したラミネート電池セル）を準備した。 In this example, in order to observe the overcharged positive electrode excluding the influence of temperature and gas, a laminate cell X having a constant temperature of 25 ° C. was produced. In Laminate Cell X, electrolyte solution is injected into the entire internal volume of the laminate cell to improve heat dissipation, and a gas flow path is secured without thermally welding a part of one side of the laminate cell. A thermocouple was passed inside, and a dedicated cooling fan was attached so that the internal temperature of the cell was kept constant at 25 ° C. In addition, a normal laminate cell Y (a laminate battery cell in which the amount of electrolyte to be filled was reduced to give a margin with respect to the capacity of the laminate cell and all sides of the laminate cell were welded) was prepared.
　（ラミネートセルの直流抵抗）
  表１の正極と、黒鉛の負極とを組み合わせ、作製したラミネートセルＸを用い、直流抵抗（Ｒ）を測定した。まず０．３３Ｃ相当の電流で上限電圧４．１Ｖで４時間の定電流定電圧充電を行った後、１０分間開回路状態とした。その後、放電電流（Ｉ）３．５Ａで５秒間の放電を行い、放電前の開回路電圧（Ｖ０）と放電５秒目の電圧（Ｖ５）を測定し、両者の差（Ｖ０－Ｖ５）である電圧低下（ΔＶ）を求めた。この電圧降下と放電電流の商（ΔＶ／Ｉ）を直流抵抗（Ｒ）とした。 (DC resistance of laminate cell)
The direct current resistance (R) was measured using the laminate cell X produced by combining the positive electrode of Table 1 and the negative electrode of graphite. First, constant current and constant voltage charging was performed for 4 hours at an upper limit voltage of 4.1 V with a current corresponding to 0.33 C, and then the circuit was opened for 10 minutes. After that, discharge was performed at a discharge current (I) of 3.5 A for 5 seconds, the open circuit voltage (V0) before discharge and the voltage (V5) at the 5th discharge were measured, and the difference between the two (V0−V5) A certain voltage drop (ΔV) was determined. The quotient (ΔV / I) of this voltage drop and discharge current was defined as the direct current resistance (R).
　表２にラミネートセルＸの直流抵抗を示す。表面に被覆層を有する正極活物質を用いた実施例１～１０の電池は、被覆無しの比較例１～６と同等の直流抵抗である。 Table 2 shows the DC resistance of the laminate cell X. The batteries of Examples 1 to 10 using the positive electrode active material having a coating layer on the surface have a DC resistance equivalent to that of Comparative Examples 1 to 6 without coating.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　（正極の酸素脱離挙動）
  次いで、ラミネートセルＸ(25℃一定)の過充電試験を行った。実施例、比較例のラミネートセル（Ｘ－１～２０）を電流値０．５ＣＡで２．５Ｖまで放電した後、電流値１ＣＡで2時間定電流充電させた。つまり、電解液の分解込みで２００％ＳＯＣに充電した。この際の温度は25℃で一定とした。充電時に実施例、比較例のラミネートセル（Ｘ－１～２０）には、いずれもセルの発火は見られなかった。この充電状態のセルを解体し、正極を取り出し、XRDを測定し、試験後の結晶構造を確認したところ、いずれも層状型結晶構造であり、構造変化は見られなかった。従って、過充電時の酸素脱離は電圧の効果だけではなく、温度の効果との複合により生じることがわかった。 (Oxygen desorption behavior of the positive electrode)
Subsequently, an overcharge test of the laminate cell X (constant at 25 ° C.) was performed. The laminate cells (X-1 to 20) of Examples and Comparative Examples were discharged to 2.5 V at a current value of 0.5 CA, and then charged with a constant current at a current value of 1 CA for 2 hours. That is, the battery was charged to 200% SOC by decomposition of the electrolytic solution. The temperature at this time was constant at 25 ° C. In the laminate cells (X-1 to 20) of Examples and Comparative Examples at the time of charging, no cell ignition was observed. This charged cell was disassembled, the positive electrode was taken out, XRD was measured, and the crystal structure after the test was confirmed. As a result, all had a layered crystal structure, and no structural change was observed. Therefore, it was found that oxygen desorption during overcharging occurs not only by the voltage effect but also by the combination with the temperature effect.
　次に、この充電状態の正極をφ15mmに打ち抜き、800℃まで加熱した際の酸素脱離挙動をTDS-MSで調べた。表３に酸素脱離挙動の測定結果を記載する。 Next, this charged positive electrode was punched out to 15 mm in diameter, and the oxygen desorption behavior when heated to 800 ° C. was examined by TDS-MS. Table 3 shows the measurement results of the oxygen desorption behavior.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　その結果、比較例１～７、９～１１に比べ、実施例は酸素脱離開始温度が高く、酸素脱離強度(脱離速度)が小さくなり、酸素脱離量も少なくなることがわかった。特に、Ｎｉ量が多い正極活物質（実施例１～３、６～１０）で効果が大きいことがわかった。 As a result, it was found that, compared with Comparative Examples 1 to 7 and 9 to 11, the Example had a higher oxygen desorption start temperature, a smaller oxygen desorption strength (desorption rate), and a smaller amount of oxygen desorption. . In particular, it has been found that the positive electrode active material having a large amount of Ni (Examples 1 to 3, 6 to 10) has a large effect.
　さらに試験後の電極のXRDを測定し、結晶構造を調査した。その結果、実施例のラミネートセル（Ｘ－１～２０）は、層状とスピネル構造の混合状態であり、岩塩構造までの結晶構造変化は見られなかった。つまり、実施例は過充電時の結晶構造変化が抑制されているものと推察できる。 Furthermore, the XRD of the electrode after the test was measured to investigate the crystal structure. As a result, the laminate cells (X-1 to 20) of the examples were in a mixed state of a layered structure and a spinel structure, and no change in the crystal structure up to the rock salt structure was observed. In other words, it can be inferred that the crystal structure change during overcharge is suppressed in the examples.
　(ラミネートセルの過充電試験)
  次に、電流値１ＣＡで２時間定電流充電(２００％ＳＯＣ)させ、ラミネートセルＹを過充電した。この試験では、ラミネートセルＸと異なり、冷却ファンをつけずに通常の過充電条件として行った。その結果、実施例のラミネートセルでは、いずれも発火・破裂はなかった。表４に、ラミネートセルＹの過充電結果を示す。 (Overcharge test of laminate cell)
Next, the laminate cell Y was overcharged by constant current charging (200% SOC) for 2 hours at a current value of 1CA. In this test, unlike the laminate cell X, a normal overcharge condition was performed without a cooling fan. As a result, none of the laminate cells of the examples were ignited or ruptured. Table 4 shows the overcharge result of the laminate cell Y.
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
　以上、リチウムイオンを吸蔵放出できる正極および負極とセパレータで構成されたリチウムイオン二次電池において、前記、正極活物質が、表面にＭｏ，Ｗ，Ｚｒのいずれか1種類以上を含む酸化物またはフッ化物と、リン酸化合物の複合被覆層を有しており、リンの原子濃度は、表層側が前記正極活物質側よりも高い事を特徴とするリチウムイオンイオン二次電池により、過充電時の酸素脱離速度と量の低減により、過充電時の発火破裂を抑止できる。 As described above, in a lithium ion secondary battery including a positive electrode and a negative electrode capable of occluding and releasing lithium ions and a separator, the positive electrode active material has an oxide or fluorine containing at least one of Mo, W, and Zr on the surface. A lithium-ion ion secondary battery characterized in that the surface concentration of the phosphorus is higher than that of the positive electrode active material. By reducing the detachment rate and amount, it is possible to suppress ignition burst during overcharge.
１.正極端子 
２.負極端子 
３.正極未塗工部 
４.負極未塗工部 
５.正極 
６.負極 
７.セパレータ 
８.ラミネートフィルム(ケース側)
９.電極群 
１０.ラミネートフィルム(ふた側) 1. Positive terminal
2. Negative terminal
3. Positive electrode uncoated part
4. Negative electrode uncoated part
5. Positive electrode
6. Negative electrode
7. Separator
8. Laminate film (case side)
9. Electrode group
10. Laminate film (lid side)

Claims (8)

  1. 　リチウムイオンを吸蔵放出する正極活物質を含む正極と、リチウムイオンを吸蔵放出する負極活物質を含む負極と、前記正負極間に配置されたセパレータと、を備えるリチウムイオン二次電池において、
    　前記正極活物質はリチウム遷移金属酸化物と、前記リチウム遷移金属酸化物の表面を被覆する複合被覆層を備え、前記複合被覆層は、Ｍｏ，Ｗ，Ｚｒのいずれか少なくとも1種を含む酸化物またはフッ化物と、リン酸化合物とを含み、
    　前記複合被覆層に含まれるＭｏ，Ｗ，Ｚｒのいずれか少なくとも1種の原子濃度は、前記複合被覆層の厚さ方向の中央部から前記リチウム遷移金属酸化物側の原子濃度の平均値が、前記複合被覆層の厚さ方向の中央部から電解質側の原子濃度の平均値よりも高いことを特徴とするリチウムイオン二次電池。     In a lithium ion secondary battery comprising: a positive electrode including a positive electrode active material that occludes and releases lithium ions; a negative electrode that includes a negative electrode active material that occludes and releases lithium ions; and a separator disposed between the positive and negative electrodes.
    The positive electrode active material includes a lithium transition metal oxide and a composite coating layer that covers a surface of the lithium transition metal oxide, and the composite coating layer includes an oxide containing at least one of Mo, W, and Zr. Or a fluoride and a phosphate compound,
    The atomic concentration of at least one of Mo, W, and Zr contained in the composite coating layer is an average value of atomic concentrations on the lithium transition metal oxide side from the central portion in the thickness direction of the composite coating layer. A lithium ion secondary battery characterized by being higher than the average value of the atomic concentration on the electrolyte side from the central portion in the thickness direction of the composite coating layer.
  2. 　請求項１記載のリチウムイオン二次電池において、
    　前記複合被覆層に含まれるＭｏ，Ｗ，Ｚｒのいずれか少なくとも1種の原子濃度は、前記複合被覆層の厚さ方向の中央部から電解質側の原子濃度の平均値が、前記被覆層の厚さ方向の中央部から前記リチウム遷移金属酸化物側の原子濃度の平均値に対して４ａｔｏｍ％以上低いことを特徴とするリチウムイオン二次電池。     The lithium ion secondary battery according to claim 1,
    The atomic concentration of at least one of Mo, W, and Zr contained in the composite coating layer is the average value of the atomic concentration on the electrolyte side from the center in the thickness direction of the composite coating layer. A lithium ion secondary battery characterized by being 4 atom% or more lower than the average value of the atomic concentration on the lithium transition metal oxide side from the central portion in the vertical direction.
  3. 　請求項１記載のリチウムイオン二次電池において、
    　前記複合被覆層に含まれるリン酸化合物は、Ｌｉ3ＰＯ4、Ｌｉ4Ｐ2Ｏ7、ＬｉＰＯ3からなる群より選択される少なくともいずれかを含むことを特徴とするリチウムイオン二次電池。     The lithium ion secondary battery according to claim 1,
    The lithium ion secondary battery, wherein the phosphoric acid compound contained in the composite coating layer includes at least one selected from the group consisting of Li 3 PO 4 , Li 4 P 2 O 7 and LiPO 3 .
  4. 　請求項１記載のリチウムイオン二次電池において、
    　前記リン酸化合物は、前記リチウム遷移金属酸化物１００重量部に対し、０．１重量部以上５．０重量部以下であることを特徴とするリチウムイオン二次電池。     The lithium ion secondary battery according to claim 1,
    The phosphoric acid compound is 0.1 parts by weight or more and 5.0 parts by weight or less based on 100 parts by weight of the lithium transition metal oxide.
  5. 　請求項１記載のリチウムイオン二次電池において、
    　前記Ｍｏ，Ｗ，Ｚｒのいずれか少なくとも1種を含む酸化物またはフッ化物は、前記リチウム遷移金属酸化物１００重量部に対し、０．２重量部以上１．５重量部以下であることを特徴とするリチウムイオン二次電池。     The lithium ion secondary battery according to claim 1,
    The oxide or fluoride containing at least one of Mo, W, and Zr is 0.2 to 1.5 parts by weight with respect to 100 parts by weight of the lithium transition metal oxide. Lithium ion secondary battery.
  6. 　請求項１記載のリチウムイオン二次電池において、
    　前記複合被覆層は、Ｍｏ，Ｗ，Ｚｒのいずれか少なくとも1種を含む酸化物またはフッ化物と、リン酸化合物とを含み、
    　前記複合被覆層に含まれるＭｏ，Ｗ，Ｚｒのいずれか少なくとも1種の原子濃度は、前記正極活物質側が表層側よりも高い事を特徴とするリチウムイオン二次電池。     The lithium ion secondary battery according to claim 1,
    The composite coating layer includes an oxide or fluoride containing at least one of Mo, W, and Zr, and a phosphoric acid compound,
    The lithium ion secondary battery, wherein the atomic concentration of at least one of Mo, W, and Zr contained in the composite coating layer is higher on the positive electrode active material side than on the surface layer side.
  7. 　請求項１記載のリチウムイオン二次電池において、
    　前記複合被覆層の厚さは、２ｎｍ以上８０ｎｍ以下であることを特徴とするリチウムイオン二次電池。     The lithium ion secondary battery according to claim 1,
    The lithium ion secondary battery, wherein the composite coating layer has a thickness of 2 nm to 80 nm.
  8. 　請求項１記載のリチウムイオン二次電池において、
    　前記リチウム遷移金属酸化物は、一般式 ＬｉＮｉaＢbＣ(1-a-b)Ｏ2(０．５≦ａ＜１, ０≦ｂ＜０．４, Ｂ=Ｃｏ，Ｍｎのいずれか1種類以上, Ｃ＝Ｌｉ, Ｍｏ，Ｗ，Ｚｒ, Ａｌ，Ｍｇ，Ｔｉ，Ｃｕ，Ｎｂの少なくとも1種類以上)で表される化合物であることを特徴とするリチウムイオン二次電池。     The lithium ion secondary battery according to claim 1,
    The lithium transition metal oxide has a general formula of LiNi a B b C (1-ab) O 2 (0.5 ≦ a <1, 0 ≦ b <0.4, B = Co, Mn, at least one kind) , C = Li, Mo, W, Zr, Al, Mg, Ti, Cu, and Nb).
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