WO2015011884A1 - Positive electrode for non-aqueous secondary battery, and non-aqueous secondary battery - Google Patents

Positive electrode for non-aqueous secondary battery, and non-aqueous secondary battery Download PDF

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WO2015011884A1
WO2015011884A1 PCT/JP2014/003603 JP2014003603W WO2015011884A1 WO 2015011884 A1 WO2015011884 A1 WO 2015011884A1 JP 2014003603 W JP2014003603 W JP 2014003603W WO 2015011884 A1 WO2015011884 A1 WO 2015011884A1
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positive electrode
metal oxide
secondary battery
aqueous secondary
transition metal
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PCT/JP2014/003603
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French (fr)
Japanese (ja)
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直人 安田
雄太 中川
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株式会社豊田自動織機
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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
    • H01M10/05—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
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a positive electrode for a non-aqueous secondary battery and a non-aqueous secondary battery.
  • Non-aqueous secondary batteries such as lithium ion secondary batteries are small and have high energy density, and are widely used as power sources for portable electronic devices.
  • the positive electrode active material containing Ni has low thermal stability, and it has been reported that the battery ignites at high temperatures. The reason is considered that oxygen is released from the positive electrode active material at a high temperature because the bonding force between nickel and oxygen is weak. A technique for increasing the thermal stability of the positive electrode is required.
  • Patent Document 1 in a winding structure in which a positive electrode and a negative electrode are wound through a separator, a positive electrode active material is provided on the outer peripheral surface side of the current collector at the outermost peripheral portion of the positive electrode. A portion where the containing coating film is not formed is provided. The portion where the positive electrode active material-containing coating film is not formed is opposed to the negative electrode through the separator, and the lead body welded to the negative electrode current collector is not directly opposed to the positive electrode through the separator.
  • the positive electrode active material does not exist in the short-circuit portion at the outermost peripheral portion of the positive electrode. A battery having this configuration is less likely to reach a thermal runaway temperature even if it generates heat, and is highly safe.
  • LiNi 0.5 Mn 1.5 O 4 having a spinel structure has a high upper limit potential of 4.5 V (Li reference) or more, and is used as a positive electrode active material for high voltage use.
  • a battery using a high-voltage positive electrode active material is charged and discharged at a high potential, and it has been pointed out that the cycle characteristics of the battery deteriorate due to oxidative decomposition of the electrolytic solution.
  • the causes of the oxidative decomposition of the electrolytic solution are considered to be that the positive electrode is exposed to a high oxidation state and that the positive electrode active material is easily dissolved in an acid such as hydrofluoric acid generated by the decomposition of the electrolytic solution. Therefore, development of a positive electrode material having a function of improving the stability of the battery at a high potential is desired.
  • the inventor of the present application diligently searched to develop a highly safe non-aqueous secondary battery by a method different from the technique described in Patent Document 1 above.
  • This invention is made
  • Another problem is to provide a positive electrode for a non-aqueous secondary battery and a non-aqueous secondary battery that can be used stably even at a high potential.
  • the positive electrode for a non-aqueous secondary battery of the present invention has a positive electrode active material having a Ni-containing metal oxide containing Ni and a transition metal oxide having a transition element, and the transition element can be taken after the initial charge. It has an oxidation number smaller than the maximum oxidation number.
  • the positive electrode for a non-aqueous secondary battery of the present invention has a transition metal oxide having a transition element in addition to a positive electrode active material having a Ni-containing metal oxide.
  • the transition element contained in the transition metal oxide has an oxidation number smaller than the maximum oxidation number that can be taken after the first charge. For this reason, heat_generation
  • Example 1 and Comparative Example 1 The DSC curve of Example 1 and Comparative Example 1 is shown.
  • the discharge capacities of Examples 3 and 4 and Comparative Example 2 when a cycle test is performed at 25 ° C. are shown.
  • the discharge capacities of Examples 3 and 4 and Comparative Example 2 when a cycle test is performed at 60 ° C. are shown.
  • the positive electrode for non-aqueous secondary battery and the non-aqueous secondary battery of the present invention will be described in detail.
  • the positive electrode for a non-aqueous secondary battery of the present invention has a Ni-containing metal oxide and a transition metal oxide.
  • the negative electrode active material and the SEI film (passive film) formed on the surface of the negative electrode active material react with the electrolytic solution and generate heat.
  • the separator is decomposed to further promote heat generation.
  • the Ni-containing metal oxide in the positive electrode contains nickel element.
  • the binding force of the Ni—O bond in the Ni-containing metal oxide is smaller than that of other metal-oxygen bonds.
  • the Ni—O bond in the Ni-containing metal oxide is decomposed, and the Ni-containing metal oxide releases oxygen.
  • the released oxygen causes a violent oxidation (exothermic) reaction with the organic solvent of the electrolyte, causing thermal runaway.
  • the transition element in the transition metal oxide contained in the positive electrode has an oxidation number smaller than the maximum oxidation number that can be taken after the initial charge.
  • the transition metal oxide absorbs oxygen before the oxygen released from the Ni-containing metal oxide reacts with the electrolyte.
  • the oxidation number of the transition element in the transition metal oxide is smaller than the maximum oxidation number that the transition element can take.
  • the transition element in the transition metal oxide is oxidized by oxygen to increase the oxidation number, and oxygen is absorbed by the transition metal oxide. For this reason, the calorific value of the positive electrode is greatly suppressed in the temperature range where oxygen is released from the Ni-containing metal oxide. Also, the stable temperature range of the positive electrode can be expanded to the high temperature side.
  • the transition element in the transition metal oxide contained in the positive electrode has an oxidation number smaller than the maximum oxidation number that can be taken after the initial charge.
  • the transition element in the transition metal oxide absorbs oxygen and increases its valence. For this reason, the oxidative decomposition of electrolyte solution is suppressed effectively.
  • the non-aqueous electrolyte has a compound having fluorine
  • the decomposition of the compound contained in the non-aqueous electrolyte is suppressed and the generation of hydrofluoric acid is suppressed. Dissolution of the positive electrode active material by hydrofluoric acid is prevented. This effect is remarkably exhibited when the potential is high.
  • the transition element contained in the transition metal oxide includes a transition element whose valence does not change by the initial charge and a transition element whose valence decreases by the initial charge.
  • the transition metal oxide has a transition element having an oxidation number smaller than the maximum possible oxidation number after the initial charge means that the transition element (for example, Fe) whose valence is reduced by the initial charge is the initial charge. Later, it means having a valence less than the maximum valence.
  • a transition element (for example, Mn, Co) whose valence does not change by the first charge has a valence smaller than the maximum valence both before and after the first charge.
  • the upper limit potential for charging the Ni-containing metal oxide contained in the positive electrode is preferably 4.5 V (Li counter electrode reference) or more.
  • the upper limit potential of charging is a value converted to a lithium counter electrode based on the charge and discharge curves of the positive and negative electrodes measured in advance.
  • Such Ni-containing metal oxides include LiNi 0.5 Mn 1.5 O 4 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , and LiNi 1/3 Co 1/3 Mn 1/3 O 2. Can be mentioned.
  • the transition metal oxide has a transition element. Unlike the Ni-containing metal oxide of the positive electrode active material, the transition metal oxide does not participate in the battery reaction or has a much smaller reaction amount than the Ni-containing metal oxide even though it participates in the battery reaction. At least in the operating potential range of the battery, it is preferable that the transition metal oxide does not participate in the battery reaction or has a much smaller reaction amount than the Ni-containing metal oxide even though it participates in the battery reaction.
  • the transition element in the transition metal oxide has an oxidation number smaller than the maximum possible oxidation number after the first charge.
  • Transition elements are elements that can take several oxidation numbers. Transition elements are more likely to be oxidized and oxygen uptake than typical elements. If the transition element has an oxidation number smaller than the maximum possible oxidation number, the transition element is easily oxidized, and the oxidation number can be increased toward the maximum oxidation number.
  • the average oxidation number of the transition element in the transition metal oxide is, for example, preferably from 1 to less than 3, and more preferably from 1 to less than 2, although it depends on the type of the transition element. In this case, the transition element is easily oxidized and easily absorbs oxygen.
  • the transition element in the transition metal oxide is preferably oxidized more easily than Ni contained in the Ni-containing metal oxide. That is, the transition element in the transition metal oxide preferably has a lower standard reduction potential than Ni contained in the Ni-containing metal oxide. In this case, oxygen released from the Ni-containing metal oxide can be immediately absorbed by the transition metal oxide.
  • the transition metal oxide contains one or more transition elements.
  • the transition element contained in the transition metal oxide may be a transition element other than Ni. This is because Ni has a weak binding force with O (oxygen), and therefore when the transition metal oxide contains Ni, the oxygen absorption performance of the transition metal oxide is reduced.
  • the transition metal oxide is a first transition element (3d transition element). Examples of the transition element include Mn, Co, Fe, Cu, and the like.
  • the transition metal oxide contains at least a transition element and an oxygen element.
  • the transition metal oxide may be composed of only a transition element and an oxygen element, and the transition metal oxide in this case is represented by the general formula: M 1 x O y (M 1 is one selected from the transition elements) As described above, x and y are integers of 1 or more) (Expression 1).
  • Transition element M 1 in the transition metal oxide for example, Mn, Co, Fe, Cu, V and the like.
  • M 1 in Formula 1 may be a transition element that does not participate in the battery reaction. When the transition metal oxide is a compound represented by Formula 1, the transition metal oxide does not participate in the battery reaction.
  • the transition metal oxide may contain a metal element other than the transition element.
  • the general formula is M 2 z M 1 x O y (M 1 is one or more selected from the transition elements, M 1 2 is a metal element other than a transition element, and x, y, and z are integers of 1 or more) (Expression 2).
  • M 1 in the formula 2 is the same as M 1 in formula 1.
  • Examples of M 2 in Formula 2 include Li and Na.
  • M 2 in Formula 2 may be a cation as an ionic conductor. In this case, the transition metal oxide decomposes and discharges the cation M 2 during the first charge, and the cation M 2 is doped into the negative electrode active material. Most of the transition metal oxides are preferably M 1 x O y not containing M 2 .
  • Table 1 lists the maximum oxidation number of the transition element that can be contained in the transition metal oxide, the oxidation number that is smaller than the maximum oxidation number and that can be taken, and the transition metal oxide containing the transition element.
  • the transition metal oxide is not limited to those listed in Table 1.
  • MnO and CoO are preferable. Furthermore, MnO is desirable. Metals Fe and Cu generated from FeO and Cu 2 O are easy to dissolve when the voltage is high, but metals Mn and Co generated from MnO and CoO are difficult to dissolve even when the voltage is high. MnO is stable in the atmosphere and can absorb oxygen at room temperature.
  • the transition metal oxide is preferably a compound having an inverted fluorite structure.
  • the transition metal oxide is preferably a compound having a reverse fluorite structure and including a lithium element, a transition element, and an oxygen element.
  • Such compounds include the formula: Li a M 1 b O c (4.5 ⁇ a ⁇ 6.5, 0.5 ⁇ b ⁇ 1.5, 3.5 ⁇ c ⁇ 4.5, M 1 : Co, It may be a lithium metal composite oxide represented by at least one selected from the group consisting of Mn and Fe.
  • the transition metal oxide is preferably composed of at least one selected from the group consisting of Li 6 MnO 4 , Li 6 CoO 4 , and Li 5 FeO 4 .
  • These compounds are lithium metal composite oxides having an inverted fluorite structure.
  • the lithium metal composite oxide decomposes during the initial charge to generate MnO, CoO, and FeO, respectively, and releases lithium ions.
  • the negative electrode active material can be doped with lithium, and the discharge capacity can be increased.
  • transition elements contained in MnO, CoO, and FeO have an oxidation number smaller than the maximum oxidation number, and can absorb oxygen released from the positive electrode active material.
  • transition metal oxides When these transition metal oxides absorb oxygen, the oxidation number of the transition element contained in the transition metal oxide is increased to MnO 2 , CoO 2 , and Fe 2 O 3 .
  • the above compound having an inverted fluorite structure can serve as a lithium doping material and an oxygen absorbing material. For this reason, the thermal runaway of the battery by combustion is suppressed. Further, when the electrolytic solution contains fluorine, the generation of hydrofluoric acid can be suppressed and dissolution of the positive electrode active material can be suppressed.
  • the positive electrode active material contained in the positive electrode has a Ni-containing metal oxide having at least Ni (nickel) and O (oxygen).
  • Ni-containing metal oxide has the formula: LiNi 1-xy Co x Mn y O 2 (0 ⁇ x ⁇ 1,0 ⁇ y ⁇ 1,0 ⁇ 1-xy), or / and Formula: LiNi 2-xy Co x Mn y O 4 (0 ⁇ x ⁇ 2, 0 ⁇ y ⁇ 2, 0 ⁇ 2-xy) is preferable.
  • Formula: LiNi 1-xy Co x Mn y O 2 (0 ⁇ x ⁇ 1,0 ⁇ y ⁇ 1,0 ⁇ 1-xy) compound represented by is a layered compound.
  • Ni-containing metal oxides include LiNi 1/3 Co 1/3 Mn 1/3 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiNiO 2 , LiNi 1-x Co x O. 2 (0 ⁇ x ⁇ 1), LiNi 0.5 Mn 1.5 O 4 and the like.
  • the Ni-containing metal oxide used as the positive electrode active material may be based on the above composition formula as a basic composition, and a metal element included in the basic composition may be substituted with another metal element, Mg, etc. Other metal elements may be added to the basic composition to form a metal oxide.
  • the positive electrode active material may contain other positive electrode active material components responsible for the battery reaction in addition to the Ni-containing metal oxide.
  • other positive electrode active material components include LiMn 2 O 4 and LiMnO 2 .
  • the content of the transition metal oxide when the Ni-containing metal oxide as the positive electrode active material is 100 parts by mass is preferably 5 parts by mass or more and 40 parts by mass or less, and more preferably 10 parts by mass or more and 20 parts by mass or more. It is preferable that it is below mass parts. In this case, oxygen released from the Ni-containing metal oxide can be sufficiently absorbed by the transition metal oxide, and the thermal stability of the positive electrode is excellent.
  • the positive electrode preferably has a positive electrode mixture having a positive electrode active material and a transition metal oxide, and a current collector whose surface is coated with the positive electrode mixture.
  • the positive electrode current collector is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material to be used. For example, silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin , Indium, titanium, ruthenium, tantalum, chromium, molybdenum, and metal materials such as stainless steel.
  • the positive electrode for a non-aqueous secondary battery includes a current collector and a positive electrode mixture that covers the surface of the current collector and has the positive electrode active material and the transition metal oxide, and the positive electrode mixture is 100 masses. %,
  • the content of the transition metal oxide contained in the positive electrode mixture is preferably 1% by mass to 15% by mass, and more preferably 5% by mass to 10% by mass. preferable. In this case, the oxygen absorption performance of the transition metal oxide can be improved while increasing the battery capacity.
  • 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. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector.
  • a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector.
  • the thickness is preferably in the range of 1 ⁇ m to 100 ⁇ m.
  • the positive electrode mixture may contain a conductive additive.
  • the conductive assistant is added to increase the conductivity of the electrode.
  • Examples of the conductive assistant include carbon black, graphite, acetylene black (AB), ketjen black (KB), and vapor grown carbon fiber (Vapor Grown Carbon Fiber: VGCF).
  • the amount of the conductive aid used is not particularly limited, but can be, for example, 1 to 30 parts by mass with respect to 100 parts by mass of the positive electrode active material.
  • the positive electrode mixture may contain a binder.
  • the binder serves to bind the active material, transition metal oxide and conductive additive to the surface of the current collector.
  • the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins. be able to.
  • a conventionally known method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method is used.
  • the positive electrode mixture may be applied to the surface of the current collector.
  • an active material layer-forming composition containing an active material, a transition metal oxide and, if necessary, a binder and a conductive aid is prepared, and an appropriate solvent is added to the composition to make a paste. Then, after applying to the surface of the current collector, it is dried.
  • the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, the dried product may be compressed.
  • Non-aqueous secondary battery of the present invention includes the positive electrode for a non-aqueous secondary battery, a negative electrode, and a non-aqueous electrolyte.
  • the above-mentioned positive electrode for a non-aqueous secondary battery contains a transition metal oxide.
  • the transition element in the transition metal oxide has an oxidation number smaller than the maximum possible oxidation number after the first charge.
  • the transition metal oxide absorbs oxygen. In the temperature range where oxygen is released from the Ni-containing metal oxide, the calorific value of the positive electrode is greatly suppressed.
  • the non-aqueous electrolyte has a compound having fluorine, decomposition of the compound contained in the non-aqueous electrolyte is suppressed, and the generation of hydrofluoric acid is suppressed. Dissolution of the positive electrode active material by hydrofluoric acid is prevented.
  • the negative electrode used in the non-aqueous secondary battery of the present invention has a current collector and a negative electrode mixture bonded to the surface of the current collector.
  • the negative electrode mixture has a negative electrode active material.
  • the negative electrode mixture preferably contains a conductive additive or / and a binder in addition to the negative electrode active material.
  • the conductive auxiliary agent and / or binder that may be contained in the negative electrode mixture the same conductive assistant or / and binder as may be contained in the positive electrode mixture can be used.
  • the negative electrode current collector is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material to be used, and for example, the one described for the positive electrode current collector can be adopted.
  • the negative electrode active material a material that can occlude and release metal ions such as lithium ions can be used. Therefore, there is no particular limitation as long as it is a simple substance, alloy, or compound that can occlude and release metal ions such as lithium ions.
  • a negative electrode active material Li, group 14 elements such as carbon, silicon, germanium and tin, group 13 elements such as aluminum and indium, group 12 elements such as zinc and cadmium, group 15 elements such as antimony and bismuth, magnesium , Alkaline earth metals such as calcium, and group 11 elements such as silver and gold may be employed alone.
  • silicon or the like is employed as the negative electrode active material, one silicon atom reacts with a plurality of lithiums.
  • the alloy or compound in which other elements such as transition are combined in a simple substance such as a negative electrode active material.
  • the alloy or compound include tin-based materials such as Ag—Sn alloy, Cu—Sn alloy, Co—Sn alloy, carbon-based materials such as various graphites, SiOx (0 which disproportionates into silicon simple substance and silicon dioxide). .3 ⁇ x ⁇ 1.6), silicon simple substance, or a composite of a silicon-based material and a carbon-based material.
  • the non-aqueous electrolyte used for the non-aqueous secondary battery of the present invention has a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent.
  • 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 examples include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester.
  • ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. These nonaqueous solvents may be used alone or in combination with the electrolyte.
  • Examples of the electrolyte include lithium salts such as LiClO 4 , LiAsF 6 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 , and LiN (CF 3 SO 2 ) 2 .
  • the non-aqueous electrolyte may have a compound having fluorine.
  • the compound in the electrolytic solution may be decomposed under high voltage to generate hydrofluoric acid.
  • the generated hydrofluoric acid is immediately absorbed by the transition metal oxide having a transition metal having a valence smaller than the maximum valence. For this reason, the amount of hydrofluoric acid in the electrolyte is extremely reduced.
  • the positive electrode active material that has come into contact with the electrolytic solution is prevented from being dissolved by hydrofluoric acid, and the cycle characteristics are improved.
  • examples of the compound having fluorine include fluorinated ethylene carbonate as a non-aqueous solvent
  • examples of the electrolyte include LiAsF 6 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2, and the like. It is done.
  • a separator is used for non-aqueous secondary batteries as necessary.
  • the separator separates the positive electrode and the negative electrode and allows metal ions such as lithium ions to pass while preventing a short circuit of current due to contact between the two electrodes.
  • a separator is sandwiched between the positive electrode and the negative electrode as necessary to form an electrode body.
  • the electrode body may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched.
  • the positive electrode for a non-aqueous secondary battery according to this example includes a current collector and a positive electrode mixture that covers the current collector.
  • the positive electrode mixture includes a positive electrode active material and a transition metal oxide.
  • the positive electrode active material is made of LiNi 0.5 Mn 0.3 Co 0.2 O 2 having a layered structure.
  • the transition metal oxide is made of Li 6 MnO 4 .
  • the content of Li 6 MnO 4 is 4% by mass and the content of LiNi 0.5 Mn 0.3 Co 0.2 O 2 is 90% by mass when the entire positive electrode mixture is 100% by mass.
  • the positive electrode mixture further contains 3% by mass of acetylene black as a conductive additive and 3% by mass of PVdF as a binder.
  • the current collector is made of an aluminum foil having a thickness of 20 ⁇ m.
  • the electrolytic solution is composed of a mixed solvent and LiPF 6 as a lithium salt.
  • the mixed solvent consists of ethylene carbonate (EC) and diethyl carbonate (DEC).
  • the volume ratio of EC to DEC in the mixed solvent was 3: 7.
  • the concentration of LiPF 6 in the electrolytic solution is 1 mol / L.
  • This half cell was charged to 4.5 V at the Li reference potential. Thereafter, the half cell was disassembled and the positive electrode was taken out.
  • This positive electrode was subjected to differential scanning calorimetry.
  • 3 mg of this positive electrode and 1.8 ⁇ L of the electrolytic solution were placed in a stainless steel pan, and the pan was sealed. Using a sealed pan, under a nitrogen atmosphere, the heating rate was 20 ° C / min.
  • Differential scanning calorimetry was performed under the conditions of the above to obtain a DSC curve. Rigaku DSC8230 was used as a differential scanning calorimeter. The measured DSC curve of Example 1 is shown in FIG.
  • the main calorific value was 500 J / g, and the main exothermic reaction temperature was 271 ° C.
  • the main calorific value was measured in the range of 250 to 300 ° C. where main heat generation occurred in the positive electrode.
  • Example 1 The positive electrode of this example is different from Example 1 in that it does not contain a transition metal oxide. Others are the same as in the first embodiment.
  • Example 2 For this positive electrode, a half cell was prepared in the same manner as in Example 1 and charged to 4.5V. Thereafter, the half cell was disassembled, and the positive electrode was taken out. Differential scanning calorimetry was performed on the positive electrode in the same manner as in Example 1 to obtain a DSC curve.
  • the DSC curve of Comparative Example 1 is shown in FIG. Moreover, as shown in Table 2, the main calorific value was 750 J / g, and the main exothermic reaction temperature was 258 ° C.
  • the positive electrode of Example 1 had less main heat generation and a higher main exothermic reaction temperature than the positive electrode of Comparative Example 1.
  • the reason is considered as follows. Li 6 MnO 4 is decomposed by charging to produce MnO. MnO absorbed oxygen released from the Ni-containing metal oxide to become MnO 2 , and the calorific value was suppressed.
  • the positive electrode of Example 1 was produced by decomposing the transition metal oxide Li 6 MnO 4 in addition to the Ni-containing metal oxide LiNi 0.5 Mn 0.3 Co 0.2 O 2 as the positive electrode active material. Contains MnO. In the vicinity of 230 to 240 ° C., MnO starts absorbing oxygen released from the Ni-containing metal oxide and generates MnO 2 as represented by the following formula (3). In the vicinity of 240 to 270 ° C., MnO 2 is actively generated. In the vicinity of 270 to 280 ° C., Mn in MnO 2 begins to release O (oxygen), and O 2 oxygen reacts with the electrolyte and generates heat, as shown in the following formula (4).
  • Example 1 Li 6 MnO 4 absorbs oxygen released from the Ni-containing metal oxide at around 255 ° C. For this reason, reaction of oxygen and electrolyte solution is suppressed. Further, MnO 2 that has absorbed oxygen releases oxygen at around 275 ° C., and oxygen and the electrolytic solution react. Thus, the main exothermic reaction temperature between oxygen and the electrolyte shifts to the high temperature side. Therefore, the stable temperature range of the positive electrode can be expanded to the high temperature side.
  • the transition metal oxide having an inverse fluorite structure in addition to the Li 6 MnO 4, Li 6 CoO 4, Li 5 FeO 4 may be used.
  • Li 6 CoO 4 and Li 5 FeO 4 are both decomposed into CoO and FeO during the initial charge.
  • CoO and FeO are oxides that do not participate in the battery reaction and can absorb oxygen. For this reason, the oxygen released from the Ni-containing metal oxide of the positive electrode active material is absorbed to improve the stability of the positive electrode.
  • Example 2 The positive electrode of this example is different from Example 1 in that MnO is used instead of Li 6 MnO 4 as a transition metal oxide.
  • the content of MnO was 4% by mass when the entire positive electrode mixture was 100% by mass.
  • a half cell was prepared in the same manner as in Example 1 and charged to 4.5 V on the basis of the Li counter electrode. Thereafter, the half cell was disassembled, and the positive electrode was taken out. Differential scanning calorimetry was performed on the positive electrode in the same manner as in Example 1, and the DSC curve was observed.
  • LiNi 0.5 Mn 1.5 O 4 having a spinel structure As the positive electrode active material, LiNi 0.5 Mn 1.5 O 4 having a spinel structure was used. In this LiNi 0.5 Mn 1.5 O 4 , primary particles aggregated to form secondary particles. The primary particle size was about 200 nm, the secondary particle size was 15 ⁇ m, and the specific surface area was 8.5 m 2 / g.
  • the positive electrode active material 80 parts by weight of the positive electrode active material, 10 parts by weight of acetylene black, and 10 parts by weight of PVdF were mixed with an NMP solvent to form a slurry.
  • the slurry was applied to one side of a 15 ⁇ m thick aluminum foil so that the slurry had a thickness of 20 ⁇ m and a solid content of about 7 mg / cm 2 , dried and pressed to obtain a positive electrode.
  • This positive electrode was punched into a diameter of 14 mm.
  • metallic lithium was used.
  • separator a polyethylene nonwoven fabric having a thickness of 25 ⁇ m was used.
  • the electrolytic solution is composed of a mixed solvent composed of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) and LiPF 6 as a lithium salt.
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • LiPF 6 LiPF 6 as a lithium salt.
  • the concentration of LiPF 6 in the electrolytic solution is 1.2 mol / L. Using these, a 2032 type coin battery was produced. All battery fabrication operations were performed in a glove box filled with argon gas. The obtained battery was referred to as Example 1.
  • Example 3 A slurry was prepared by mixing 76 parts by weight of the positive electrode active material, 4 parts by weight of commercially available 5 ⁇ m MnO, 10 parts by weight of acetylene black, and 10 parts by weight of PVDF with an NMP solvent.
  • the positive electrode active material was the same as in Comparative Example 2.
  • a battery was produced in the same manner as in Comparative Example 2 using this slurry. This battery was referred to as Example 3.
  • Example 4 A slurry was prepared by mixing 71.3 parts by weight of the positive electrode active material, 8.7 parts by weight of Li 6 MnO 4 , 10 parts by weight of acetylene black, and 10 parts by weight of PVdF with an NMP solvent.
  • the positive electrode active material was the same as in Comparative Example 2.
  • a battery was produced in the same manner as in Comparative Example 2 using this slurry. This battery was referred to as Example 4.
  • ⁇ Cycle test> A cycle test was performed on the batteries of Comparative Example 2 and Examples 3 and 4.
  • the conditions of the cycle test are as follows: the positive electrode active material LiNi 0.5 Mn 1.5 O 4 has a capacity of 120 mAh / g. After the elapse of time, the battery was discharged to 3.0 V at a 0.1 C rate with a rest time of 10 minutes. Charging and discharging were taken as one cycle and repeated 50 cycles.
  • the test was performed in an environment of 25 ° C. and 60 ° C., respectively.
  • FIG. 2 shows the discharge capacity of each battery when the cycle test is conducted at 25 ° C.
  • FIG. 3 shows the discharge capacity of each battery when the cycle test is conducted at 60 ° C.
  • Examples 3 and 4 had a higher discharge capacity during the cycle than Comparative Example 2.
  • the difference in discharge capacity between Examples 3 and 4 and Comparative Example 2 was large at a high temperature of 60 ° C. Under high temperature, LiPF 6 in the electrolytic solution is easily decomposed to generate hydrofluoric acid.
  • Example 3 since the generated hydrofluoric acid was absorbed by MnO, it is considered that the superiority with Comparative Example 2 was increased at high temperatures.
  • Li 6 MnO 4 releases Li and decomposes into MnO at the time of charging, particularly at the first charging. MnO absorbs hydrofluoric acid generated in the electrolytic solution. For this reason, it is considered that the cycle characteristics of the battery of Example 5 were improved as compared with Comparative Example 2.

Abstract

Provided is a positive electrode for a non-aqueous secondary battery, the positive electrode being highly safe and being able to be stably used at a high potential. Also provided is a non-aqueous secondary battery. This positive electrode for a non-aqueous secondary battery has: a positive electrode active material having a Ni-containing metal oxide; and a transition metal oxide having a transition element. After the initial charge, the transition element has a lower oxidation number than the maximum oxidation number that said transition element can have.

Description

非水系二次電池用正極及び非水系二次電池Positive electrode for non-aqueous secondary battery and non-aqueous secondary battery
　本発明は、非水系二次電池用正極及び非水系二次電池に関する。 The present invention relates to a positive electrode for a non-aqueous secondary battery and a non-aqueous secondary battery.
　リチウムイオン二次電池などの非水系二次電池は、小型でエネルギー密度が高く、ポータブル電子機器の電源として広く用いられている。リチウムイオン二次電池の正極活物質としては、主としてＬｉＣｏＯ２、ＬｉＮｉＯ２、Ｌｉ（ＮｉｘＣｏｙＭｎｚ）Ｏ２（ｘ+ｙ+ｚ＝１）などの層状岩塩構造をもつ金属複合酸化物が用いられている。層状岩塩構造をもつ金属複合酸化物は、Ｎｉ（ニッケル）を構成元素に含むものが多い。 Non-aqueous secondary batteries such as lithium ion secondary batteries are small and have high energy density, and are widely used as power sources for portable electronic devices. As the positive electrode active material of the lithium ion secondary battery mainly LiCoO 2, LiNiO 2, Li ( Ni x Co y Mn z) O 2 (x + y + z = 1) metal composite oxide having a layered rock salt structure, such as Is used. Many metal complex oxides having a layered rock salt structure contain Ni (nickel) as a constituent element.
　Ｎｉを含む正極活物質は熱的な安定性が低く、高温で電池が発火する問題が報告されている。その理由としては、ニッケルと酸素との結合力が弱いため、高温で正極活物質から酸素が放出されるからであると考えられる。正極の熱安定性を高める技術が必要とされる。 The positive electrode active material containing Ni has low thermal stability, and it has been reported that the battery ignites at high temperatures. The reason is considered that oxygen is released from the positive electrode active material at a high temperature because the bonding force between nickel and oxygen is weak. A technique for increasing the thermal stability of the positive electrode is required.
　そこで、従来、特許文献１に開示されているように、正極と負極とをセパレータを介して巻回してなる巻回構造において、正極の最外周部の集電体の外周面側に正極活物質含有塗膜を形成していない部分を設ける。正極活物質含有塗膜を形成していない部分がセパレータを介して負極と対向し、負極集電体に溶接したリード体がセパレータを介して正極と直接対向しないようにしている。正極の最外周部の短絡個所には正極活物質が存在しない。この構成をもつ電池は、発熱しても熱暴走温度までには至りにくく、安全性が高い。 Therefore, as disclosed in Patent Document 1, conventionally, in a winding structure in which a positive electrode and a negative electrode are wound through a separator, a positive electrode active material is provided on the outer peripheral surface side of the current collector at the outermost peripheral portion of the positive electrode. A portion where the containing coating film is not formed is provided. The portion where the positive electrode active material-containing coating film is not formed is opposed to the negative electrode through the separator, and the lead body welded to the negative electrode current collector is not directly opposed to the positive electrode through the separator. The positive electrode active material does not exist in the short-circuit portion at the outermost peripheral portion of the positive electrode. A battery having this configuration is less likely to reach a thermal runaway temperature even if it generates heat, and is highly safe.
　また、近年、非水系二次電池を高電圧で使用したいという要望がある。このため、正極活物質として、高電位で使用可能な材料の研究がなされている。たとえば、スピネル構造をもつＬｉＮｉ０．５Ｍｎ１．５Ｏ４は、その上限電位が４．５Ｖ（Ｌｉ基準）以上と高く、高電圧使用の正極活物質として用いられている。高電圧使用の正極活物質を用いた電池は高電位で充放電を行うため、電解液の酸化分解による電池のサイクル特性の悪化が指摘されている。電解液の酸化分解の原因は、正極が高い酸化状態に晒されること、及び電解液の分解で発生したフッ酸などの酸に正極活物質が溶解し易いこと、と考えられている。
　そこで、高電位で電池の安定性を向上させる機能を有する正極材料の開発が望まれている。 In recent years, there is a demand to use a non-aqueous secondary battery at a high voltage. For this reason, studies have been made on materials that can be used at a high potential as the positive electrode active material. For example, LiNi 0.5 Mn 1.5 O 4 having a spinel structure has a high upper limit potential of 4.5 V (Li reference) or more, and is used as a positive electrode active material for high voltage use. A battery using a high-voltage positive electrode active material is charged and discharged at a high potential, and it has been pointed out that the cycle characteristics of the battery deteriorate due to oxidative decomposition of the electrolytic solution. The causes of the oxidative decomposition of the electrolytic solution are considered to be that the positive electrode is exposed to a high oxidation state and that the positive electrode active material is easily dissolved in an acid such as hydrofluoric acid generated by the decomposition of the electrolytic solution.
Therefore, development of a positive electrode material having a function of improving the stability of the battery at a high potential is desired.
特開２００３－１９７２６７号公報JP 2003-197267 A
　本願発明者は、上記の特許文献１に記載した技術とは異なる方法で、安全性の高い非水系二次電池を開発すべく鋭意探求した。また、高電位で安定に使用できる正極を開発した。 The inventor of the present application diligently searched to develop a highly safe non-aqueous secondary battery by a method different from the technique described in Patent Document 1 above. We have also developed a positive electrode that can be used stably at a high potential.
　本発明はかかる事情に鑑みてなされたものであり、安全性の高い非水系二次電池用正極及び非水系二次電池を提供することを課題とする。もう一つの課題は、高電位でも安定に使用できる非水系二次電池用正極及び非水系二次電池を提供することである。 This invention is made | formed in view of this situation, and makes it a subject to provide the positive electrode for non-aqueous secondary batteries and a non-aqueous secondary battery with high safety | security. Another problem is to provide a positive electrode for a non-aqueous secondary battery and a non-aqueous secondary battery that can be used stably even at a high potential.
　本発明の非水系二次電池用正極は、Ｎｉを含むＮｉ含有金属酸化物を有する正極活物質と、遷移元素を有する遷移金属酸化物とをもち、前記遷移元素は、初回充電後において取り得る最大酸化数よりも小さい酸化数をもつことを特徴とする。 The positive electrode for a non-aqueous secondary battery of the present invention has a positive electrode active material having a Ni-containing metal oxide containing Ni and a transition metal oxide having a transition element, and the transition element can be taken after the initial charge. It has an oxidation number smaller than the maximum oxidation number.
　本発明の非水系二次電池用正極は、Ｎｉ含有金属酸化物を有する正極活物質の他に、遷移元素を有する遷移金属酸化物をもつ。遷移金属酸化物に含まれる遷移元素は、初回充電後において、取り得る最大酸化数よりも小さい酸化数をもつ。このため、発熱が抑えられ、安全性の高い非水系二次電池用正極及び非水系二次電池を提供することができる。また、高電位でも安定に使用できる非水系二次電池用正極及び非水系二次電池を提供することができる。 The positive electrode for a non-aqueous secondary battery of the present invention has a transition metal oxide having a transition element in addition to a positive electrode active material having a Ni-containing metal oxide. The transition element contained in the transition metal oxide has an oxidation number smaller than the maximum oxidation number that can be taken after the first charge. For this reason, heat_generation | fever is suppressed and the positive electrode for non-aqueous secondary batteries and a non-aqueous secondary battery with high safety | security can be provided. In addition, it is possible to provide a positive electrode for a non-aqueous secondary battery and a non-aqueous secondary battery that can be used stably even at a high potential.
実施例１及び比較例１のＤＳＣ曲線を示す。The DSC curve of Example 1 and Comparative Example 1 is shown. ２５℃でサイクル試験を行ったときの実施例３，４及び比較例２の放電容量を示す。The discharge capacities of Examples 3 and 4 and Comparative Example 2 when a cycle test is performed at 25 ° C. are shown. ６０℃でサイクル試験を行ったときの実施例３，４及び比較例２の放電容量を示す。The discharge capacities of Examples 3 and 4 and Comparative Example 2 when a cycle test is performed at 60 ° C. are shown.
　本発明の非水系二次電池用正極及び非水系二次電池について詳細に説明する。 The positive electrode for non-aqueous secondary battery and the non-aqueous secondary battery of the present invention will be described in detail.
　（非水系二次電池用正極）
　本発明の非水系二次電池用正極は、Ｎｉ含有金属酸化物と、遷移金属酸化物とを有している。 (Positive electrode for non-aqueous secondary batteries)
The positive electrode for a non-aqueous secondary battery of the present invention has a Ni-containing metal oxide and a transition metal oxide.
　ここで、電池の発熱過程について説明する。まず、負極活物質や負極活物質表面に形成されるＳＥＩ皮膜（不動態皮膜）が、電解液と反応して発熱する。電解液の温度上昇によりセパレータが分解し発熱を更に促進させる。正極の中のＮｉ含有金属酸化物はニッケル元素を含む。Ｎｉ含有金属酸化物の中のＮｉ－Ｏ結合の結合力は、他の金属―酸素間結合の結合力よりも小さい。高温になると、Ｎｉ含有金属酸化物の中のＮｉ－Ｏ結合が分解して、Ｎｉ含有金属酸化物は酸素を放出する。放出された酸素は、電解液の有機溶媒と激しい酸化（発熱）反応を起こし、熱暴走の要因となる。 Here, the heat generation process of the battery will be described. First, the negative electrode active material and the SEI film (passive film) formed on the surface of the negative electrode active material react with the electrolytic solution and generate heat. As the temperature of the electrolyte rises, the separator is decomposed to further promote heat generation. The Ni-containing metal oxide in the positive electrode contains nickel element. The binding force of the Ni—O bond in the Ni-containing metal oxide is smaller than that of other metal-oxygen bonds. When the temperature rises, the Ni—O bond in the Ni-containing metal oxide is decomposed, and the Ni-containing metal oxide releases oxygen. The released oxygen causes a violent oxidation (exothermic) reaction with the organic solvent of the electrolyte, causing thermal runaway.
　本発明においては、正極に含まれる遷移金属酸化物の中の遷移元素が、初回充電後において、取り得る最大酸化数よりも小さい酸化数をもつ。本発明では、Ｎｉ含有金属酸化物から放出された酸素が電解液と反応をする前に、遷移金属酸化物が酸素を吸収する。遷移金属酸化物の中の遷移元素の酸化数は、該遷移元素の取り得る最大酸化数よりも小さい。遷移金属酸化物の中の遷移元素は、酸素により酸化されて酸化数を上げて、酸素は遷移金属酸化物に吸収される。このため、Ｎｉ含有金属酸化物から酸素が放出される温度域において、正極の発熱量が大幅に抑制される。また、正極の安定な温度領域も高温側に拡大させることができる。 In the present invention, the transition element in the transition metal oxide contained in the positive electrode has an oxidation number smaller than the maximum oxidation number that can be taken after the initial charge. In the present invention, the transition metal oxide absorbs oxygen before the oxygen released from the Ni-containing metal oxide reacts with the electrolyte. The oxidation number of the transition element in the transition metal oxide is smaller than the maximum oxidation number that the transition element can take. The transition element in the transition metal oxide is oxidized by oxygen to increase the oxidation number, and oxygen is absorbed by the transition metal oxide. For this reason, the calorific value of the positive electrode is greatly suppressed in the temperature range where oxygen is released from the Ni-containing metal oxide. Also, the stable temperature range of the positive electrode can be expanded to the high temperature side.
　また、本発明においては、正極に含まれる遷移金属酸化物の中の遷移元素が、初回充電後において、取り得る最大酸化数よりも小さい酸化数をもつ。この遷移金属酸化物の中の遷移元素は、酸素を吸収して価数を上げる。このため、電解液の酸化分解が効果的に抑制される。非水電解液がフッ素を有する化合物をもつ場合には、非水電解液に含まれる該化合物の分解が抑制されてフッ酸の生成が抑制される。フッ酸による正極活物質の溶解が防止される。この効果は高電位のときに顕著に発揮される。 In the present invention, the transition element in the transition metal oxide contained in the positive electrode has an oxidation number smaller than the maximum oxidation number that can be taken after the initial charge. The transition element in the transition metal oxide absorbs oxygen and increases its valence. For this reason, the oxidative decomposition of electrolyte solution is suppressed effectively. When the non-aqueous electrolyte has a compound having fluorine, the decomposition of the compound contained in the non-aqueous electrolyte is suppressed and the generation of hydrofluoric acid is suppressed. Dissolution of the positive electrode active material by hydrofluoric acid is prevented. This effect is remarkably exhibited when the potential is high.
　本発明において、遷移金属酸化物に含まれる遷移元素は、初回充電により価数が変化しないものや、初回充電により価数が小さくなるものがある。「遷移金属酸化物は、初回充電後において、取り得る最大酸化数よりも小さい酸化数をもつ遷移元素を有する」は、初回充電により価数が小さくなる遷移元素（例えば、Fe）は、初回充電後において、最大価数よりも小さい価数をもつという意味である。初回充電により価数が変化しない遷移元素（例えば、Mn、Co）については、初回充電の前後のいずれでも、最大価数よりも小さい価数をもつ。 In the present invention, the transition element contained in the transition metal oxide includes a transition element whose valence does not change by the initial charge and a transition element whose valence decreases by the initial charge. “The transition metal oxide has a transition element having an oxidation number smaller than the maximum possible oxidation number after the initial charge” means that the transition element (for example, Fe) whose valence is reduced by the initial charge is the initial charge. Later, it means having a valence less than the maximum valence. A transition element (for example, Mn, Co) whose valence does not change by the first charge has a valence smaller than the maximum valence both before and after the first charge.
　正極に含まれるＮｉ含有金属酸化物の充電の上限電位は、４．５Ｖ（Ｌｉ対極基準）以上であることがよい。充電の上限電位は、事前に測定した正負極の充放電曲線に基づき、リチウム対極に換算した値にする。かかるＮｉ含有金属酸化物としては、ＬｉＮｉ０．５Ｍｎ１．５Ｏ４、ＬｉＮｉ０．５Ｃｏ０．２Ｍｎ０．３Ｏ２、ＬｉＮｉ１／３Ｃｏ１／３Ｍｎ１／３Ｏ２が挙げられる。 The upper limit potential for charging the Ni-containing metal oxide contained in the positive electrode is preferably 4.5 V (Li counter electrode reference) or more. The upper limit potential of charging is a value converted to a lithium counter electrode based on the charge and discharge curves of the positive and negative electrodes measured in advance. Such Ni-containing metal oxides include LiNi 0.5 Mn 1.5 O 4 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , and LiNi 1/3 Co 1/3 Mn 1/3 O 2. Can be mentioned.
　ここで、遷移金属酸化物は、遷移元素をもつ。遷移金属酸化物は、正極活物質のＮｉ含有金属酸化物と異なって、電池反応に関与しないか、電池反応に関与していてもＮｉ含有金属酸化物に比べてはるかに反応量が小さい。少なくとも電池の作動電位範囲では、遷移金属酸化物は、電池反応に関与しないか、電池反応に関与していてもＮｉ含有金属酸化物に比べてはるかに反応量が小さいことがよい。 Here, the transition metal oxide has a transition element. Unlike the Ni-containing metal oxide of the positive electrode active material, the transition metal oxide does not participate in the battery reaction or has a much smaller reaction amount than the Ni-containing metal oxide even though it participates in the battery reaction. At least in the operating potential range of the battery, it is preferable that the transition metal oxide does not participate in the battery reaction or has a much smaller reaction amount than the Ni-containing metal oxide even though it participates in the battery reaction.
　遷移金属酸化物の中の遷移元素は、初回充電後において、とり得る最大酸化数よりも小さい酸化数をもつ。遷移元素は、いくつかの酸化数をとることができる元素である。遷移元素は、典型元素と比べて酸化されやすく、酸素を取り込みやすい。遷移元素が、とり得る最大酸化数よりも小さい酸化数をもつと、遷移元素は、酸化されやすく、最大酸化数に向かって酸化数を大きくすることが可能である。 The transition element in the transition metal oxide has an oxidation number smaller than the maximum possible oxidation number after the first charge. Transition elements are elements that can take several oxidation numbers. Transition elements are more likely to be oxidized and oxygen uptake than typical elements. If the transition element has an oxidation number smaller than the maximum possible oxidation number, the transition element is easily oxidized, and the oxidation number can be increased toward the maximum oxidation number.
　遷移金属酸化物の中の遷移元素の平均酸化数は、遷移元素の種類にもよるが、例えば、１以上３未満であることがよく、更には、１以上２未満であることがよい。この場合には、遷移元素は酸化されやすく、酸素を吸収しやすい。 The average oxidation number of the transition element in the transition metal oxide is, for example, preferably from 1 to less than 3, and more preferably from 1 to less than 2, although it depends on the type of the transition element. In this case, the transition element is easily oxidized and easily absorbs oxygen.
　遷移金属酸化物の中の遷移元素は、Ｎｉ含有金属酸化物に含まれるＮｉよりも酸化されやすいことがよい。即ち、遷移金属酸化物の中の遷移元素は、Ｎｉ含有金属酸化物に含まれるＮｉよりも標準還元電位が低いことがよい。この場合には、Ｎｉ含有金属酸化物から放出された酸素を、遷移金属酸化物により即座に吸収することができる。 The transition element in the transition metal oxide is preferably oxidized more easily than Ni contained in the Ni-containing metal oxide. That is, the transition element in the transition metal oxide preferably has a lower standard reduction potential than Ni contained in the Ni-containing metal oxide. In this case, oxygen released from the Ni-containing metal oxide can be immediately absorbed by the transition metal oxide.
　遷移金属酸化物は、１種以上の遷移元素を含む。遷移金属酸化物に含まれる遷移元素は、Ｎｉ以外の遷移元素であるとよい。ＮｉはＯ（酸素）との結合力が弱いため、遷移金属酸化物にＮｉが含まれると、遷移金属酸化物の酸素吸収性能が低下するからである。好ましくは、遷移金属酸化物は、第１遷移元素（３ｄ遷移元素）であることがよい。遷移元素は、例えば、Ｍn、Ｃｏ、Ｆｅ、Ｃｕなどが挙げられる。 The transition metal oxide contains one or more transition elements. The transition element contained in the transition metal oxide may be a transition element other than Ni. This is because Ni has a weak binding force with O (oxygen), and therefore when the transition metal oxide contains Ni, the oxygen absorption performance of the transition metal oxide is reduced. Preferably, the transition metal oxide is a first transition element (3d transition element). Examples of the transition element include Mn, Co, Fe, Cu, and the like.
　遷移金属酸化物は、少なくとも遷移元素と酸素元素を含む。遷移金属酸化物は、遷移元素と酸素元素とだけからなる場合でもよく、この場合の遷移金属酸化物は、一般式：Ｍ１ ｘＯｙ（Ｍ１は、遷移元素の中から選ばれる１種以上、ｘ、ｙは１以上の整数）（式１）で表わされる。遷移金属酸化物の中の遷移元素Ｍ１は、例えば、Ｍｎ、Ｃｏ、Ｆｅ、Ｃｕ、Ｖが挙げられる。式１のＭ１は、電池反応に関与しない遷移元素であるとよい。遷移金属酸化物が式１で表わされる化合物である場合には、遷移金属酸化物は電池反応には関与しない。 The transition metal oxide contains at least a transition element and an oxygen element. The transition metal oxide may be composed of only a transition element and an oxygen element, and the transition metal oxide in this case is represented by the general formula: M 1 x O y (M 1 is one selected from the transition elements) As described above, x and y are integers of 1 or more) (Expression 1). Transition element M 1 in the transition metal oxide, for example, Mn, Co, Fe, Cu, V and the like. M 1 in Formula 1 may be a transition element that does not participate in the battery reaction. When the transition metal oxide is a compound represented by Formula 1, the transition metal oxide does not participate in the battery reaction.
　遷移金属酸化物は、遷移元素以外の金属元素を含んでいてもよく、この場合の一般式はＭ２ ｚＭ１ ｘＯｙ（Ｍ１は、遷移元素の中から選ばれる１種以上、Ｍ２は遷移元素以外の金属元素、ｘ、ｙ、ｚは１以上の整数）（式２）で表わされる。式２の中のＭ１は、式１の中のＭ１と同様である。式２の中のＭ２は、例えば、Ｌｉ、Ｎａが挙げられる。式２の中のＭ２は、イオン伝導体としてのカチオンであってもよい。この場合には、初回の充電時に遷移金属酸化物は分解して、カチオンＭ２を放出し、カチオンＭ２は負極活物質にドープされる。遷移金属酸化物の多くはＭ２を含まないＭ１ ｘＯｙとなるとよい。 The transition metal oxide may contain a metal element other than the transition element. In this case, the general formula is M 2 z M 1 x O y (M 1 is one or more selected from the transition elements, M 1 2 is a metal element other than a transition element, and x, y, and z are integers of 1 or more) (Expression 2). M 1 in the formula 2 is the same as M 1 in formula 1. Examples of M 2 in Formula 2 include Li and Na. M 2 in Formula 2 may be a cation as an ionic conductor. In this case, the transition metal oxide decomposes and discharges the cation M 2 during the first charge, and the cation M 2 is doped into the negative electrode active material. Most of the transition metal oxides are preferably M 1 x O y not containing M 2 .
　遷移金属酸化物に含まれ得る遷移元素の最大酸化数、最大酸化数よりも小さく且つ取り得る酸化数、遷移元素を含む遷移金属酸化物を表１に列挙する。なお、遷移金属酸化物は、表１に列挙されたものに限定されない。 Table 1 lists the maximum oxidation number of the transition element that can be contained in the transition metal oxide, the oxidation number that is smaller than the maximum oxidation number and that can be taken, and the transition metal oxide containing the transition element. The transition metal oxide is not limited to those listed in Table 1.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　ＭｎＯ、ＣｏＯ、ＦｅＯ、Ｃｕ２Ｏの中において、ＭｎＯ、ＣｏＯが好ましい。更には、ＭｎＯが望ましい。ＦｅＯ、Ｃｕ２Ｏから生成した金属Ｆｅ、Ｃｕは電圧が高いと溶けやすいが、ＭｎＯ、ＣoＯから生成した金属Ｍｎ、Ｃｏは電圧が高くても溶けにくい。ＭｎＯは、大気中で安定であり、室温で酸素を吸収できる。 Among MnO, CoO, FeO, and Cu 2 O, MnO and CoO are preferable. Furthermore, MnO is desirable. Metals Fe and Cu generated from FeO and Cu 2 O are easy to dissolve when the voltage is high, but metals Mn and Co generated from MnO and CoO are difficult to dissolve even when the voltage is high. MnO is stable in the atmosphere and can absorb oxygen at room temperature.
　遷移金属酸化物は、逆蛍石構造をもつ化合物がよい。特に、非水系二次電池がリチウムイオン二次電池の場合には、遷移金属酸化物は、逆蛍石構造をもち、且つリチウム元素と遷移元素と酸素元素を含む化合物であることがよい。かかる化合物としては、式：ＬiａＭ１ ｂＯｃ（４．５≦ａ≦６．５、０．５≦ｂ≦１．５、３．５≦ｃ≦４．５、Ｍ１：Ｃｏ、Ｍｎ、Ｆｅの群から選ばれる１種以上）で表されるリチウム金属複合酸化物であるとよい。 The transition metal oxide is preferably a compound having an inverted fluorite structure. In particular, when the non-aqueous secondary battery is a lithium ion secondary battery, the transition metal oxide is preferably a compound having a reverse fluorite structure and including a lithium element, a transition element, and an oxygen element. Such compounds include the formula: Li a M 1 b O c (4.5 ≦ a ≦ 6.5, 0.5 ≦ b ≦ 1.5, 3.5 ≦ c ≦ 4.5, M 1 : Co, It may be a lithium metal composite oxide represented by at least one selected from the group consisting of Mn and Fe.
　遷移金属酸化物は、Ｌｉ６ＭｎＯ４、Ｌｉ６ＣｏＯ４、及びＬｉ５ＦｅＯ４の群から選ばれた１種以上からなることが好ましい。これらの化合物は逆蛍石構造をもつリチウム金属複合酸化物である。これらのリチウム金属複合酸化物を遷移金属酸化物として正極に含めることにより、リチウム金属複合酸化物は初回充電時に分解してそれぞれＭｎＯ、ＣｏＯ、ＦｅＯを生成するとともにリチウムイオンを放出する。負極活物質にリチウムをドープすることができ、放電容量を増加させることができる。生成した分解物のうちＭｎＯ、ＣｏＯ、ＦｅＯに含まれる遷移元素は、最大酸化数よりも小さい酸化数をもち、正極活物質から放出された酸素を吸収することができる。これらの遷移金属酸化物は、酸素を吸収すると、遷移金属酸化物に含まれる遷移元素の酸化数が増えて、ＭｎＯ２、ＣｏＯ２、Ｆｅ２Ｏ３となる。このように、逆蛍石構造の上記化合物は、リチウムドープ材と酸素吸収材としての役割を担うことができる。このため、燃焼による電池の熱暴走を抑制する。また、電解液にフッ素を含む場合にはフッ酸生成を抑制して正極活物質の溶解を抑制することができる。 The transition metal oxide is preferably composed of at least one selected from the group consisting of Li 6 MnO 4 , Li 6 CoO 4 , and Li 5 FeO 4 . These compounds are lithium metal composite oxides having an inverted fluorite structure. By including these lithium metal composite oxides as transition metal oxides in the positive electrode, the lithium metal composite oxide decomposes during the initial charge to generate MnO, CoO, and FeO, respectively, and releases lithium ions. The negative electrode active material can be doped with lithium, and the discharge capacity can be increased. Of the generated decomposition products, transition elements contained in MnO, CoO, and FeO have an oxidation number smaller than the maximum oxidation number, and can absorb oxygen released from the positive electrode active material. When these transition metal oxides absorb oxygen, the oxidation number of the transition element contained in the transition metal oxide is increased to MnO 2 , CoO 2 , and Fe 2 O 3 . Thus, the above compound having an inverted fluorite structure can serve as a lithium doping material and an oxygen absorbing material. For this reason, the thermal runaway of the battery by combustion is suppressed. Further, when the electrolytic solution contains fluorine, the generation of hydrofluoric acid can be suppressed and dissolution of the positive electrode active material can be suppressed.
　正極に含まれる正極活物質は、少なくともＮｉ（ニッケル）とＯ（酸素）とを有するＮｉ含有金属酸化物を有する。Ｎｉ含有金属酸化物は、式：ＬｉＮｉ１-x-yＣｏxＭｎyＯ２(0≦x＜1、0≦y＜1、0＜1-x-y )、又は／及び式：ＬｉＮｉ２-x-yＣｏxＭｎyＯ４(0≦x＜2、0≦y＜2、0＜2-x-y )で表されることが好ましい。式：ＬｉＮｉ１-x-yＣｏxＭｎyＯ２(0≦x＜1、0≦y＜1、0＜1-x-y )で表わされる化合物は、層状化合物である。式：ＬｉＮｉ２-x-yＣｏxＭｎyＯ４(0≦x＜2、0≦y＜2、0＜2-x-y )で表される化合物は、スピネル化合物である。Ｎｉ含有金属酸化物の具体例として、ＬｉＮｉ１／３Ｃｏ１／３Ｍｎ１／３Ｏ２、ＬｉＮｉ０．５Ｃｏ０．２Ｍｎ０．３Ｏ２、ＬｉＮｉＯ２、ＬｉＮｉ１－ｘＣｏｘＯ２（０≦ｘ≦１）、ＬｉＮｉ０．５Ｍｎ１．５Ｏ４などが挙げられる。 The positive electrode active material contained in the positive electrode has a Ni-containing metal oxide having at least Ni (nickel) and O (oxygen). Ni-containing metal oxide has the formula: LiNi 1-xy Co x Mn y O 2 (0 ≦ x <1,0 ≦ y <1,0 <1-xy), or / and Formula: LiNi 2-xy Co x Mn y O 4 (0 ≦ x <2, 0 ≦ y <2, 0 <2-xy) is preferable. Formula: LiNi 1-xy Co x Mn y O 2 (0 ≦ x <1,0 ≦ y <1,0 <1-xy) compound represented by is a layered compound. Formula: LiNi 2-xy Co x Mn y O 4 (0 ≦ x <2,0 ≦ y <2,0 <2-xy) compound represented by a spinel compound. Specific examples of Ni-containing metal oxides include LiNi 1/3 Co 1/3 Mn 1/3 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiNiO 2 , LiNi 1-x Co x O. 2 (0 ≦ x ≦ 1), LiNi 0.5 Mn 1.5 O 4 and the like.
　正極活物質として用いられるＮｉ含有金属酸化物は、上記の組成式を基本組成とすればよく、基本組成に含まれる金属元素を他の金属元素で置換したものも使用可能であるし、Ｍｇなどの他の金属元素を基本組成のものに加えて金属酸化物としてもよい。 The Ni-containing metal oxide used as the positive electrode active material may be based on the above composition formula as a basic composition, and a metal element included in the basic composition may be substituted with another metal element, Mg, etc. Other metal elements may be added to the basic composition to form a metal oxide.
　正極活物質は、Ｎｉ含有金属酸化物のほかに、電池反応を担う他の正極活物質成分を含んでいてもよい。例えば、他の正極活物質成分としては、ＬｉＭｎ２Ｏ４、ＬｉＭｎＯ２等がある。 The positive electrode active material may contain other positive electrode active material components responsible for the battery reaction in addition to the Ni-containing metal oxide. For example, other positive electrode active material components include LiMn 2 O 4 and LiMnO 2 .
　正極において、正極活物質であるＮｉ含有金属酸化物を１００質量部としたときの遷移金属酸化物の含有量は５質量部以上４０質量部以下であることがよく、更には１０質量部以上２０質量部以下であることが好ましい。この場合には、Ｎｉ含有金属酸化物から放出される酸素を遷移金属酸化物により十分に吸収することができ、正極の熱安定性に優れる。 In the positive electrode, the content of the transition metal oxide when the Ni-containing metal oxide as the positive electrode active material is 100 parts by mass is preferably 5 parts by mass or more and 40 parts by mass or less, and more preferably 10 parts by mass or more and 20 parts by mass or more. It is preferable that it is below mass parts. In this case, oxygen released from the Ni-containing metal oxide can be sufficiently absorbed by the transition metal oxide, and the thermal stability of the positive electrode is excellent.
　正極は、正極活物質と遷移金属酸化物とを有する正極合材と、前記正極合材で表面が被覆された集電体とを有することがよい。正極の集電体は、使用する活物質に適した電圧に耐え得る金属であれば特に制限はなく、例えば、銀、銅、金、アルミニウム、タングステン、コバルト、亜鉛、ニッケル、鉄、白金、錫、インジウム、チタン、ルテニウム、タンタル、クロム、モリブデンから選ばれる少なくとも一種、並びにステンレス鋼などの金属材料を例示することができる。 The positive electrode preferably has a positive electrode mixture having a positive electrode active material and a transition metal oxide, and a current collector whose surface is coated with the positive electrode mixture. The positive electrode current collector is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material to be used. For example, silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin , Indium, titanium, ruthenium, tantalum, chromium, molybdenum, and metal materials such as stainless steel.
　前記非水系二次電池用正極は、集電体と、前記集電体の表面を被覆するとともに前記正極活物質及び前記遷移金属酸化物を有する正極合材とをもち、正極合材を１００質量％としたときに、前記正極合材に含まれる前記遷移金属酸化物の含有量は１質量％以上１５質量％以下であることがよく、更には５質量％以上１０質量％以下であることが好ましい。この場合には、電池容量も高くしつつ、遷移金属酸化物の酸素吸収性能を向上させることができる。 The positive electrode for a non-aqueous secondary battery includes a current collector and a positive electrode mixture that covers the surface of the current collector and has the positive electrode active material and the transition metal oxide, and the positive electrode mixture is 100 masses. %, The content of the transition metal oxide contained in the positive electrode mixture is preferably 1% by mass to 15% by mass, and more preferably 5% by mass to 10% by mass. preferable. In this case, the oxygen absorption performance of the transition metal oxide can be improved while increasing the battery capacity.
　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。そのため、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、フィルム形態の場合は、その厚みが１μｍ～１００μｍの範囲内であることが好ましい。 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. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 1 μm to 100 μm.
　正極合材は導電助剤を含んでもよい。導電助剤は、電極の導電性を高めるために添加される。導電助剤としては、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（ＡＢ）、ケッチェンブラック（登録商標）（ＫＢ）、気相法炭素繊維（Vapor Grown Carbon Fiber：ＶＧＣＦ）が例示される。導電助剤の使用量については特に制限はないが、例えば、正極活物質１００質量部に対して１～３０質量部とすることができる。 The positive electrode mixture may contain a conductive additive. The conductive assistant is added to increase the conductivity of the electrode. Examples of the conductive assistant include carbon black, graphite, acetylene black (AB), ketjen black (KB), and vapor grown carbon fiber (Vapor Grown Carbon Fiber: VGCF). . The amount of the conductive aid used is not particularly limited, but can be, for example, 1 to 30 parts by mass with respect to 100 parts by mass of the positive electrode active material.
　正極合材は結着剤を含んでもよい。結着剤は、活物質、遷移金属酸化物及び導電助剤を集電体の表面に繋ぎ止める役割を果たすものである。結着剤としては、ポリフッ化ビニリデン、ポリテトラフルオロエチレン、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、アルコキシシリル基含有樹脂を例示することができる。正極合材中の結着剤の配合割合は、質量比で、活物質：結着剤＝１：０．００５～１：０．３であるのが好ましい。結着剤が少なすぎると電極の成形性が低下し、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ためである。 The positive electrode mixture may contain a binder. The binder serves to bind the active material, transition metal oxide and conductive additive to the surface of the current collector. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins. be able to. The mixing ratio of the binder in the positive electrode mixture is preferably active material: binder = 1: 0.005 to 1: 0.3 in mass ratio. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.
　集電体の表面に正極合材からなる層を形成させるには、ロールコート法、ダイコート法、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、カーテンコート法などの従来から公知の方法を用いて、集電体の表面に正極合材を塗布すればよい。具体的には、活物質、遷移金属酸化物並びに必要に応じて結着剤及び導電助剤を含む活物質層形成用組成物を調製し、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、乾燥する。溶剤としては、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、水を例示できる。電極密度を高めるべく、乾燥後のものを圧縮してもよい。 In order to form a layer made of a positive electrode mixture on the surface of the current collector, a conventionally known method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method is used. The positive electrode mixture may be applied to the surface of the current collector. Specifically, an active material layer-forming composition containing an active material, a transition metal oxide and, if necessary, a binder and a conductive aid is prepared, and an appropriate solvent is added to the composition to make a paste. Then, after applying to the surface of the current collector, it is dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, the dried product may be compressed.
　（非水系二次電池）
　本発明の非水系二次電池は、上記の非水系二次電池用正極と、負極と、非水電解液とを備えている。 (Non-aqueous secondary battery)
The non-aqueous secondary battery of the present invention includes the positive electrode for a non-aqueous secondary battery, a negative electrode, and a non-aqueous electrolyte.
　上記の非水系二次電池用正極には、遷移金属酸化物が含まれる。この遷移金属酸化物の中の遷移元素は、初回充電後において、取り得る最大酸化数よりも小さい酸化数をもつ。上記のように、正極活物質としてのＮｉ含有金属酸化物から酸素が放出されると、遷移金属酸化物は酸素を吸収する。Ｎｉ含有金属酸化物から酸素が放出される温度域において、正極の発熱量が大幅に抑制される。また、非水電解液がフッ素を有する化合物をもつ場合には、非水電解液に含まれる該化合物の分解が抑制されてフッ酸の生成が抑制される。フッ酸による正極活物質の溶解が防止される。 The above-mentioned positive electrode for a non-aqueous secondary battery contains a transition metal oxide. The transition element in the transition metal oxide has an oxidation number smaller than the maximum possible oxidation number after the first charge. As described above, when oxygen is released from the Ni-containing metal oxide as the positive electrode active material, the transition metal oxide absorbs oxygen. In the temperature range where oxygen is released from the Ni-containing metal oxide, the calorific value of the positive electrode is greatly suppressed. Further, when the non-aqueous electrolyte has a compound having fluorine, decomposition of the compound contained in the non-aqueous electrolyte is suppressed, and the generation of hydrofluoric acid is suppressed. Dissolution of the positive electrode active material by hydrofluoric acid is prevented.
　本発明の非水系二次電池に用いられる負極は、集電体と、集電体の表面に結着させた負極合材を有する。負極合材は、負極活物質を有する。負極合材は、負極活物質のほかに、導電助剤又は／及び結着剤を含むことがよい。負極合剤に含まれることがある導電助剤又は／及び結着剤は、正極合材に含まれることがある導電助剤又は／及び結着剤と同様のものを用いることができる。負極の集電体は、使用する活物質に適した電圧に耐え得る金属であれば特に制限はなく、例えば、正極の集電体で説明したものを採用できる。 The negative electrode used in the non-aqueous secondary battery of the present invention has a current collector and a negative electrode mixture bonded to the surface of the current collector. The negative electrode mixture has a negative electrode active material. The negative electrode mixture preferably contains a conductive additive or / and a binder in addition to the negative electrode active material. As the conductive auxiliary agent and / or binder that may be contained in the negative electrode mixture, the same conductive assistant or / and binder as may be contained in the positive electrode mixture can be used. The negative electrode current collector is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material to be used, and for example, the one described for the positive electrode current collector can be adopted.
　負極活物質としては、リチウムイオンなどの金属イオンを吸蔵及び放出し得る材料が使用可能である。したがって、リチウムイオンなどの金属イオンを吸蔵及び放出可能である単体、合金または化合物であれば特に限定はない。たとえば、負極活物質としてＬｉや、炭素、ケイ素、ゲルマニウム、錫などの１４族元素、アルミニウム、インジウムなどの１３族元素、亜鉛、カドミウムなどの１２族元素、アンチモン、ビスマスなどの１５族元素、マグネシウム、カルシウムなどのアルカリ土類金属、銀、金などの１１族元素をそれぞれ単体で採用すればよい。ケイ素などを負極活物質に採用すると、ケイ素１原子が複数のリチウムと反応する。このため、ケイ素などは、高容量の活物質となる一方、リチウムの吸蔵及び放出に伴う体積の膨張及び収縮が顕著となるとの問題が生じる恐れがあるため、当該恐れの軽減のために、ケイ素などの単体に遷移などの他の元素を組み合わせた合金又は化合物を負極活物質として採用するのも好適である。合金又は化合物の具体例としては、Ａｇ－Ｓｎ合金、Ｃｕ－Ｓｎ合金、Ｃｏ－Ｓｎ合金等の錫系材料、各種黒鉛などの炭素系材料、ケイ素単体と二酸化ケイ素に不均化するＳｉＯｘ（０．３≦ｘ≦１．６）などのケイ素系材料、ケイ素単体若しくはケイ素系材料と炭素系材料を組み合わせた複合体が挙げられる。また、負極活物質して、Ｎｂ２Ｏ５、ＴｉＯ２、Ｌｉ４Ｔｉ５Ｏ１２、ＷＯ２、ＭｏＯ２、Ｆｅ２Ｏ３等の酸化物、又は、Ｌｉ３－ｘＭｘＮ（Ｍ＝Ｃｏ、Ｎｉ、Ｃｕ）で表される窒化物を採用しても良い。負極活物質として、これらのものの一種以上を使用することができる。 As the negative electrode active material, a material that can occlude and release metal ions such as lithium ions can be used. Therefore, there is no particular limitation as long as it is a simple substance, alloy, or compound that can occlude and release metal ions such as lithium ions. For example, as a negative electrode active material, Li, group 14 elements such as carbon, silicon, germanium and tin, group 13 elements such as aluminum and indium, group 12 elements such as zinc and cadmium, group 15 elements such as antimony and bismuth, magnesium , Alkaline earth metals such as calcium, and group 11 elements such as silver and gold may be employed alone. When silicon or the like is employed as the negative electrode active material, one silicon atom reacts with a plurality of lithiums. For this reason, while silicon and the like become a high-capacity active material, there is a possibility that a problem that the expansion and contraction of the volume accompanying the occlusion and release of lithium becomes significant. It is also preferable to employ an alloy or compound in which other elements such as transition are combined in a simple substance such as a negative electrode active material. Specific examples of the alloy or compound include tin-based materials such as Ag—Sn alloy, Cu—Sn alloy, Co—Sn alloy, carbon-based materials such as various graphites, SiOx (0 which disproportionates into silicon simple substance and silicon dioxide). .3 ≦ x ≦ 1.6), silicon simple substance, or a composite of a silicon-based material and a carbon-based material. Further, as the negative electrode active material, oxides such as Nb 2 O 5 , TiO 2 , Li 4 Ti 5 O 12 , WO 2 , MoO 2 , Fe 2 O 3 , or Li 3-x M x N (M = A nitride represented by (Co, Ni, Cu) may be employed. One or more of these materials can be used as the negative electrode active material.
　本発明の非水系二次電池に用いられる非水電解液は、非水溶媒と、非水溶媒に溶解された電解質とを有する。非水溶媒としては、環状エステル類、鎖状エステル類、エーテル類等が使用できる。環状エステル類としては、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を例示できる。鎖状エステル類としては、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、メチルエチルカーボネート、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等を例示できる。エーテル類としては、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－ジブトキシエタンを例示できる。電解液には、これらの非水溶媒を単独で用いてもよいし、又は、複数を併用してもよい。 The non-aqueous electrolyte used for the non-aqueous secondary battery of the present invention has a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent. As the non-aqueous solvent, cyclic esters, chain esters, ethers and the like can be used. 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 chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl 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. These nonaqueous solvents may be used alone or in combination with the electrolyte.
　電解質としては、ＬｉＣｌＯ４、ＬｉＡｓＦ６、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣＦ３ＳＯ３、ＬｉＮ（ＣＦ３ＳＯ２）２等のリチウム塩を例示できる。 Examples of the electrolyte include lithium salts such as LiClO 4 , LiAsF 6 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 , and LiN (CF 3 SO 2 ) 2 .
　非水電解液は、フッ素を有する化合物をもつことがある。この場合には、高電圧下で電解液中の該化合物が分解されてフッ酸が生成されることがある。しかし、生成したフッ酸は、最大価数よりも小さい価数をもつ遷移金属をもつ遷移金属酸化物に即座に吸収される。このため、電解液中のフッ酸量が極めて少なくなる。電解液に触れた正極活物質が、フッ酸により溶解することが抑制され、サイクル特性が向上する。ここで、フッ素を有する化合物は、非水溶媒としてフッ化エチレンカーボネートなどが挙げられ、電解質としてはＬｉＡｓＦ６、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣＦ３ＳＯ３、ＬｉＮ（ＣＦ３ＳＯ２）２等が挙げられる。 The non-aqueous electrolyte may have a compound having fluorine. In this case, the compound in the electrolytic solution may be decomposed under high voltage to generate hydrofluoric acid. However, the generated hydrofluoric acid is immediately absorbed by the transition metal oxide having a transition metal having a valence smaller than the maximum valence. For this reason, the amount of hydrofluoric acid in the electrolyte is extremely reduced. The positive electrode active material that has come into contact with the electrolytic solution is prevented from being dissolved by hydrofluoric acid, and the cycle characteristics are improved. Here, examples of the compound having fluorine include fluorinated ethylene carbonate as a non-aqueous solvent, and examples of the electrolyte include LiAsF 6 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2, and the like. It is done.
　非水系二次電池には必要に応じてセパレータが用いられる。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、リチウムイオンなどの金属イオンを通過させるものである。 A separator is used for non-aqueous secondary batteries as necessary. The separator separates the positive electrode and the negative electrode and allows metal ions such as lithium ions to pass while preventing a short circuit of current due to contact between the two electrodes.
　正極および負極に必要に応じて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良い。正極の集電体および負極の集電体から外部に通ずる正極端子および負極端子までの間を、集電用リード等を用いて接続した後に、電極体に電解液を加えて非水系二次電池とするとよい。 A separator is sandwiched between the positive electrode and the negative electrode as necessary to form an electrode body. The electrode body may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched. After connecting between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal connected to the outside using a current collecting lead or the like, an electrolyte is added to the electrode body to add a non-aqueous secondary battery It is good to do.
　（実施例１）
　本例の非水系二次電池用正極は、集電体と、集電体を被覆する正極合材とからなる。正極合材は、正極活物質と、遷移金属酸化物とを有する。正極活物質は、層状構造を有するＬｉＮｉ０．５Ｍｎ０．３Ｃｏ０．２Ｏ2からなる。遷移金属酸化物は、Ｌｉ６ＭｎＯ４からなる。正極合材全体を１００質量％としたときに、Ｌｉ６ＭｎＯ４の含有量は４質量％、ＬｉＮｉ０．５Ｍｎ０．３Ｃｏ０．２Ｏ2の含有量は９０質量％である。正極合材には、更に、導電助剤としてのアセチレンブラックを３質量％と、結着剤としてのＰＶｄＦを３質量％とを含んでいる。集電体は、厚み２０μｍのアルミニウム箔からなる。 Example 1
The positive electrode for a non-aqueous secondary battery according to this example includes a current collector and a positive electrode mixture that covers the current collector. The positive electrode mixture includes a positive electrode active material and a transition metal oxide. The positive electrode active material is made of LiNi 0.5 Mn 0.3 Co 0.2 O 2 having a layered structure. The transition metal oxide is made of Li 6 MnO 4 . The content of Li 6 MnO 4 is 4% by mass and the content of LiNi 0.5 Mn 0.3 Co 0.2 O 2 is 90% by mass when the entire positive electrode mixture is 100% by mass. The positive electrode mixture further contains 3% by mass of acetylene black as a conductive additive and 3% by mass of PVdF as a binder. The current collector is made of an aluminum foil having a thickness of 20 μm.
　この正極を用いてハーフセルを作製した。ハーフセルの対極はリチウム金属からなる。正極と対極の間には、セパレータを介在させた。セパレータはポリプロピレンからなる薄膜である。電解液は、混合溶媒と、リチウム塩としてのＬｉＰＦ６とからなる。混合溶媒は、エチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）とからなる。混合溶媒の中のＥＣとＤＥＣの体積比は、３：７であった。電解液の中のＬｉＰＦ６濃度は、１ｍｏｌ／Ｌである。 A half cell was produced using this positive electrode. The counter electrode of the half cell is made of lithium metal. A separator was interposed between the positive electrode and the counter electrode. The separator is a thin film made of polypropylene. The electrolytic solution is composed of a mixed solvent and LiPF 6 as a lithium salt. The mixed solvent consists of ethylene carbonate (EC) and diethyl carbonate (DEC). The volume ratio of EC to DEC in the mixed solvent was 3: 7. The concentration of LiPF 6 in the electrolytic solution is 1 mol / L.
　このハーフセルについて、Ｌｉ基準電位で４．５Ｖまで充電を行った。その後ハーフセルを解体して正極を取り出した。この正極について示差走査熱量分析を行った。正極の示差走査熱量分析のために、この正極３ｍｇ及び電解液１．８μＬをステンレス製のパンに入れ、該パンを密閉した。密閉パンを用いて、窒素雰囲気下、昇温速度２０℃／ｍｉｎ．の条件で示差走査熱量分析を行い、ＤＳＣ曲線を得た。示差走査熱量測定装置としてRigaku　DSC8230を使用した。測定された実施例１のＤＳＣ曲線を図１に示した。また、表２に示すように、主発熱量は５００Ｊ／ｇであり、主発熱反応温度は２７１℃であった。尚、主発熱量は正極において主要な発熱が生じる２５０～３００℃の範囲で測定した。 This half cell was charged to 4.5 V at the Li reference potential. Thereafter, the half cell was disassembled and the positive electrode was taken out. This positive electrode was subjected to differential scanning calorimetry. For the differential scanning calorimetric analysis of the positive electrode, 3 mg of this positive electrode and 1.8 μL of the electrolytic solution were placed in a stainless steel pan, and the pan was sealed. Using a sealed pan, under a nitrogen atmosphere, the heating rate was 20 ° C / min. Differential scanning calorimetry was performed under the conditions of the above to obtain a DSC curve. Rigaku DSC8230 was used as a differential scanning calorimeter. The measured DSC curve of Example 1 is shown in FIG. Moreover, as shown in Table 2, the main calorific value was 500 J / g, and the main exothermic reaction temperature was 271 ° C. The main calorific value was measured in the range of 250 to 300 ° C. where main heat generation occurred in the positive electrode.
　（比較例１）
　本例の正極は、遷移金属酸化物を含んでいない点が、実施例１と相違する。その他は、実施例１と同様である。 (Comparative Example 1)
The positive electrode of this example is different from Example 1 in that it does not contain a transition metal oxide. Others are the same as in the first embodiment.
　この正極について実施例１と同様にハーフセルを作製し、４．５Ｖまで充電を行った。その後ハーフセルを解体し、正極を取り出した。正極について実施例１と同様に示差走査熱量分析を行い、ＤＳＣ曲線を得た。比較例１のＤＳＣ曲線を図１に示した。また、表２に示すように、主発熱量は７５０Ｊ／ｇであり、主発熱反応温度は２５８℃であった。 For this positive electrode, a half cell was prepared in the same manner as in Example 1 and charged to 4.5V. Thereafter, the half cell was disassembled, and the positive electrode was taken out. Differential scanning calorimetry was performed on the positive electrode in the same manner as in Example 1 to obtain a DSC curve. The DSC curve of Comparative Example 1 is shown in FIG. Moreover, as shown in Table 2, the main calorific value was 750 J / g, and the main exothermic reaction temperature was 258 ° C.
　図１及び表２に示すように、実施例１の正極は、比較例１の正極よりも主発熱量が少なく、また主発熱反応温度が高くなった。この理由は以下のように考えられる。充電によりＬｉ６ＭｎＯ４が分解してＭｎＯが生成する。ＭｎＯは、Ｎｉ含有金属酸化物から放出された酸素を吸収してＭｎＯ２となり、発熱量が抑えられた。 As shown in FIG. 1 and Table 2, the positive electrode of Example 1 had less main heat generation and a higher main exothermic reaction temperature than the positive electrode of Comparative Example 1. The reason is considered as follows. Li 6 MnO 4 is decomposed by charging to produce MnO. MnO absorbed oxygen released from the Ni-containing metal oxide to become MnO 2 , and the calorific value was suppressed.
　比較例１では、２４０℃付近で、正極活物質であるＮｉ含有金属酸化物ＬｉＮｉ０．５Ｍｎ０．３Ｃｏ０．２Ｏ2からの酸素の放出が開始され、発熱反応が活発化する。２６５℃付近で、放出された酸素が電解液と激しく反応し、発熱量が最大値となる。その後、Ｎｉ含有金属酸化物からの酸素の放出量が低下し、急激に発熱量が低下する。 In Comparative Example 1, release of oxygen from the Ni-containing metal oxide LiNi 0.5 Mn 0.3 Co 0.2 O 2 that is the positive electrode active material is started around 240 ° C., and the exothermic reaction is activated. At around 265 ° C., the released oxygen reacts violently with the electrolyte and the calorific value reaches its maximum value. Thereafter, the amount of released oxygen from the Ni-containing metal oxide decreases, and the calorific value rapidly decreases.
　実施例１の正極は、正極活物質であるＮｉ含有金属酸化物ＬｉＮｉ０．５Ｍｎ０．３Ｃｏ０．２Ｏ2のほかに、遷移金属酸化物Ｌｉ６ＭｎＯ４が分解して生成されたＭｎＯを含んでいる。２３０～２４０℃付近で、ＭｎＯは、Ｎｉ含有金属酸化物から放出された酸素の吸収を開始して、以下の式（３）に表わすようにＭｎＯ２を生成する。２４０～２７０℃付近では、ＭｎＯ２が積極的に生成する。２７０～２８０℃付近では、以下の式（４）に表わすように、ＭｎＯ２の中のＭｎがＯ（酸素）を離し始め、Ｏ２酸素が電解液と反応し発熱する。 The positive electrode of Example 1 was produced by decomposing the transition metal oxide Li 6 MnO 4 in addition to the Ni-containing metal oxide LiNi 0.5 Mn 0.3 Co 0.2 O 2 as the positive electrode active material. Contains MnO. In the vicinity of 230 to 240 ° C., MnO starts absorbing oxygen released from the Ni-containing metal oxide and generates MnO 2 as represented by the following formula (3). In the vicinity of 240 to 270 ° C., MnO 2 is actively generated. In the vicinity of 270 to 280 ° C., Mn in MnO 2 begins to release O (oxygen), and O 2 oxygen reacts with the electrolyte and generates heat, as shown in the following formula (4).
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000001
　このように、実施例１では、２５５℃付近で、Ｌｉ６ＭｎＯ４が、Ｎｉ含有金属酸化物から放出された酸素を吸収する。このため、酸素と電解液との反応が抑えられる。また、酸素を吸収したＭｎＯ２は、２７５℃付近で酸素を離し、酸素と電解液とが反応する。このように、酸素と電解液との主発熱反応温度が高温側にシフトする。ゆえに、正極の安定な温度領域を高温側まで拡大させることができる。 Thus, in Example 1, Li 6 MnO 4 absorbs oxygen released from the Ni-containing metal oxide at around 255 ° C. For this reason, reaction of oxygen and electrolyte solution is suppressed. Further, MnO 2 that has absorbed oxygen releases oxygen at around 275 ° C., and oxygen and the electrolytic solution react. Thus, the main exothermic reaction temperature between oxygen and the electrolyte shifts to the high temperature side. Therefore, the stable temperature range of the positive electrode can be expanded to the high temperature side.
　逆蛍石構造をもつ遷移金属酸化物としては、上記Ｌｉ６ＭｎＯ４の他に、Ｌｉ６ＣｏＯ４、Ｌｉ５ＦｅＯ４も用いることができる。このうちＬｉ６ＣｏＯ４、Ｌｉ５ＦｅＯ４は、いずれも初回充電時に分解してＣｏＯ、ＦｅＯとなる。ＣｏＯ、ＦｅＯは、電池反応に関与しない酸化物であり、酸素を吸収し得る。このため、正極活物質のＮｉ含有金属酸化物から放出された酸素を吸収して、正極の安定性を向上させる。 The transition metal oxide having an inverse fluorite structure, in addition to the Li 6 MnO 4, Li 6 CoO 4, Li 5 FeO 4 may be used. Of these, Li 6 CoO 4 and Li 5 FeO 4 are both decomposed into CoO and FeO during the initial charge. CoO and FeO are oxides that do not participate in the battery reaction and can absorb oxygen. For this reason, the oxygen released from the Ni-containing metal oxide of the positive electrode active material is absorbed to improve the stability of the positive electrode.
　（実施例２）
　本例の正極は、遷移金属酸化物として、Ｌｉ６ＭｎＯ４の代わりにＭｎＯを用いた点が実施例１と相違する。正極合材全体を１００質量％としたときに、ＭｎＯの含有量は４質量％とした。 (Example 2)
The positive electrode of this example is different from Example 1 in that MnO is used instead of Li 6 MnO 4 as a transition metal oxide. The content of MnO was 4% by mass when the entire positive electrode mixture was 100% by mass.
　この正極について実施例１と同様にハーフセルを作製し、Li対極基準で４．５Ｖまで充電を行った。その後ハーフセルを解体し、正極を取り出した。正極について実施例１と同様に示差走査熱量分析を行い、ＤＳＣ曲線を観察した。 For this positive electrode, a half cell was prepared in the same manner as in Example 1 and charged to 4.5 V on the basis of the Li counter electrode. Thereafter, the half cell was disassembled, and the positive electrode was taken out. Differential scanning calorimetry was performed on the positive electrode in the same manner as in Example 1, and the DSC curve was observed.
　ＭｎＯを含む充電後の正極に示差走査熱量分析を行った場合にも、主発熱量が比較例１よりも小さく、また主発熱反応温度が高温側にシフトしていた。２４０～２６０℃付近で、ＭｎＯは、Ｎｉ含有金属酸化物から放出された酸素の吸収を開始してＭｎＯ２を生成し、ＭｎＯ２から酸素が放出されるのは、実施例１より高温の２８０～２９０℃であり、その温度までは正極は安定に維持された。主発熱反応温度が実施例１の方が低い理由としては、Ｌｉ６ＭｎＯ４が分解して生成されたＭｎＯは比表面積が実施例２のＭｎＯより大きくなるためと考えられる。 Also when the differential scanning calorimetry was performed on the positive electrode containing MnO, the main calorific value was smaller than that of Comparative Example 1, and the main exothermic reaction temperature was shifted to the high temperature side. Near 240 ~ 260 ° C., MnO is, Ni-containing absorption of oxygen released from the metal oxide starting generate MnO 2, from MnO 2 of oxygen is released, 280 of high temperature than Example 1 The positive electrode was stably maintained up to that temperature. The reason why the main exothermic reaction temperature is lower in Example 1 is considered that MnO produced by decomposition of Li 6 MnO 4 has a specific surface area larger than that of MnO in Example 2.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　次に、比較例２及び実施例３、４の電池を作成し、サイクル特性を測定した。 Next, batteries of Comparative Example 2 and Examples 3 and 4 were prepared, and cycle characteristics were measured.
　（比較例２）
　正極活物質として、スピネル構造をもつＬiＮｉ０．５Ｍｎ１．５Ｏ４を用いた。このＬiＮｉ０．５Ｍｎ１．５Ｏ４は、一次粒子が凝集して二次粒子を形成していた。一次粒子径は約２００ｎｍ、二次粒子径は15μｍ、比表面積は８．５ｍ２／ｇであった。 (Comparative Example 2)
As the positive electrode active material, LiNi 0.5 Mn 1.5 O 4 having a spinel structure was used. In this LiNi 0.5 Mn 1.5 O 4 , primary particles aggregated to form secondary particles. The primary particle size was about 200 nm, the secondary particle size was 15 μm, and the specific surface area was 8.5 m 2 / g.
　正極活物質８０重量部、アセチレンブラック１０重量部、ＰＶｄＦ１０重量部をＮＭＰ溶媒で混合してスラリーとした。１５μｍ厚のアルミニウム箔の片面に、スラリーを厚さ２０μｍ、固形分にして約７ｍｇ／ｃｍ２程度になるように塗工し、乾燥、プレスすることにより正極を得た。 80 parts by weight of the positive electrode active material, 10 parts by weight of acetylene black, and 10 parts by weight of PVdF were mixed with an NMP solvent to form a slurry. The slurry was applied to one side of a 15 μm thick aluminum foil so that the slurry had a thickness of 20 μm and a solid content of about 7 mg / cm 2 , dried and pressed to obtain a positive electrode.
　この正極を直径14mmの大きさに打ち抜いた。負極は、金属リチウムを用いた。セパレータとしては、厚さ２５ μ ｍ のポリエチレン製不織布を用いた。電解液は、エチレンカーボネート（ＥＣ）とエチルメチルカーボネート（ＥＭＣ）とからなる混合溶媒と、リチウム塩としてのＬｉＰＦ６とからなる。ＥＣとＥＭＣの配合比はEC:EMC = 3:7（体積比）である。電解液の中のＬｉＰＦ６濃度は、１．２ｍｏｌ／Ｌである。これらを用いて２０３２型コイン電池を作製した。電池作製の作業は全てアルゴンガスで満たされたグローブボックス内で行った。得られた電池を実施例１とした。 This positive electrode was punched into a diameter of 14 mm. As the negative electrode, metallic lithium was used. As the separator, a polyethylene nonwoven fabric having a thickness of 25 μm was used. The electrolytic solution is composed of a mixed solvent composed of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) and LiPF 6 as a lithium salt. The blending ratio of EC and EMC is EC: EMC = 3: 7 (volume ratio). The concentration of LiPF 6 in the electrolytic solution is 1.2 mol / L. Using these, a 2032 type coin battery was produced. All battery fabrication operations were performed in a glove box filled with argon gas. The obtained battery was referred to as Example 1.
　（実施例３）
　正極活物質７６重量部、市販の５μｍのＭｎＯを４重量部、アセチレンブラック１０重量部、ＰＶＤＦ１０重量部をＮＭＰ溶媒で混合してスラリーとした。正極活物質は、比較例２と同様のものを用いた。このスラリーを用いて、比較例２と同様に電池を作製した。この電池を実施例３とした。 Example 3
A slurry was prepared by mixing 76 parts by weight of the positive electrode active material, 4 parts by weight of commercially available 5 μm MnO, 10 parts by weight of acetylene black, and 10 parts by weight of PVDF with an NMP solvent. The positive electrode active material was the same as in Comparative Example 2. A battery was produced in the same manner as in Comparative Example 2 using this slurry. This battery was referred to as Example 3.
　（実施例４）
　正極活物質７１．３重量部、Ｌｉ６ＭｎＯ４を８．７重量部、アセチレンブラック１０重量部、ＰＶｄＦ１０重量部をＮＭＰ溶媒で混合してスラリーとした。正極活物質は、比較例２と同様のものを用いた。このスラリーを用いて、比較例２と同様に電池を作製した。この電池を実施例４とした。 Example 4
A slurry was prepared by mixing 71.3 parts by weight of the positive electrode active material, 8.7 parts by weight of Li 6 MnO 4 , 10 parts by weight of acetylene black, and 10 parts by weight of PVdF with an NMP solvent. The positive electrode active material was the same as in Comparative Example 2. A battery was produced in the same manner as in Comparative Example 2 using this slurry. This battery was referred to as Example 4.
　＜サイクル試験＞
　比較例２及び実施例３，４の電池についてサイクル試験を行った。サイクル試験の条件は、正極活物質LiNi0.5Mn1.5O4の容量を120mAh/gとした場合の0.1Cレートで４．９Ｖ（Ｌｉ基準）まで充電しその後定電圧充電を行い、総充電時間１２時間経過後、休止時間を１０分おいて０．１Ｃレートにて３．０ Ｖ まで放電を行った。充電及び放電を１サイクルとし、５０サイクル繰り返した。試験は、２５℃と６０℃の環境下でそれぞれ行った。図２は２５℃でサイクル試験を行ったときの各電池の放電容量を示し、図３は、６０℃でサイクル試験を行ったときの各電池の放電容量を示す。 <Cycle test>
A cycle test was performed on the batteries of Comparative Example 2 and Examples 3 and 4. The conditions of the cycle test are as follows: the positive electrode active material LiNi 0.5 Mn 1.5 O 4 has a capacity of 120 mAh / g. After the elapse of time, the battery was discharged to 3.0 V at a 0.1 C rate with a rest time of 10 minutes. Charging and discharging were taken as one cycle and repeated 50 cycles. The test was performed in an environment of 25 ° C. and 60 ° C., respectively. FIG. 2 shows the discharge capacity of each battery when the cycle test is conducted at 25 ° C., and FIG. 3 shows the discharge capacity of each battery when the cycle test is conducted at 60 ° C.
　図２，図３に示すように、実施例３，４は比較例２に比べてサイクル時の放電容量が高かった。特に６０℃の高温下では実施例３，４と比較例２の放電容量の差が大きかった。高温下では、電解液中のＬｉＰＦ６が分解してフッ酸が発生しやすい。実施例３では、発生したフッ酸をＭｎＯが吸収したため、高温下で、比較例２との優位差が大きくなったと考えられる。実施例４では、Ｌｉ６ＭｎＯ４が充電時、特に初回充電時にＬｉを放ちＭｎＯに分解する。ＭｎＯが、電解液で発生したフッ酸を吸収する。このため、比較例２に比べて、実施例５の電池のサイクル特性が向上したと考えられる。 As shown in FIGS. 2 and 3, Examples 3 and 4 had a higher discharge capacity during the cycle than Comparative Example 2. In particular, the difference in discharge capacity between Examples 3 and 4 and Comparative Example 2 was large at a high temperature of 60 ° C. Under high temperature, LiPF 6 in the electrolytic solution is easily decomposed to generate hydrofluoric acid. In Example 3, since the generated hydrofluoric acid was absorbed by MnO, it is considered that the superiority with Comparative Example 2 was increased at high temperatures. In Example 4, Li 6 MnO 4 releases Li and decomposes into MnO at the time of charging, particularly at the first charging. MnO absorbs hydrofluoric acid generated in the electrolytic solution. For this reason, it is considered that the cycle characteristics of the battery of Example 5 were improved as compared with Comparative Example 2.

Claims (10)

  1. 　Ｎｉを含むＮｉ含有金属酸化物を有する正極活物質と、遷移金属酸化物とをもち、
    　前記遷移金属酸化物は、遷移元素を有する遷移金属酸化物とをもち、前記遷移元素は、初回充電後において取り得る最大酸化数よりも小さい酸化数をもつことを特徴とする非水系二次電池用正極。     A positive electrode active material having a Ni-containing metal oxide containing Ni, and a transition metal oxide;
    The transition metal oxide has a transition metal oxide having a transition element, and the transition element has an oxidation number smaller than a maximum oxidation number that can be obtained after initial charge. Positive electrode.
  2. 　前記遷移金属酸化物は、一般式：Ｍ１ ｘＯｙ（Ｍ１は、遷移元素の中から選ばれる１種以上、ｘ、ｙは１以上の整数）（式１）で表わされる請求項１記載の非水系二次電池用正極。 The transition metal oxide is represented by a general formula: M 1 x O y (M 1 is one or more selected from transition elements, x and y are integers of 1 or more) (Formula 1) The positive electrode for non-aqueous secondary batteries as described.
  3. 　前記遷移金属酸化物は、ＭｎＯ、Ｃｕ２Ｏ、ＦｅＯ、及びＣｏＯの群から選ばれる１種以上からなる請求項２記載の非水系二次電池用正極。 The positive electrode for a non-aqueous secondary battery according to claim 2 , wherein the transition metal oxide is at least one selected from the group consisting of MnO, Cu 2 O, FeO, and CoO.
  4. 　前記遷移金属酸化物は、式：ＬiａＭ１ ｂＯｃ（４．５≦ａ≦６．５、０．５≦ｂ≦１．５、３．５≦ｃ≦４．５、Ｍ１：Ｃｏ、Ｍｎ、Ｆｅの群から選ばれる１種以上）で表されるリチウム金属複合酸化物からなる請求項１記載の非水系二次電池用正極。 The transition metal oxide has the formula: Li a M 1 b O c (4.5 ≦ a ≦ 6.5, 0.5 ≦ b ≦ 1.5, 3.5 ≦ c ≦ 4.5, M 1 : The positive electrode for a non-aqueous secondary battery according to claim 1, comprising a lithium metal composite oxide represented by one or more selected from the group consisting of Co, Mn, and Fe).
  5. 　前記遷移金属酸化物は、Ｌｉ６ＭｎＯ４、Ｌｉ６ＣｏＯ４、及びＬｉ５ＦｅＯ４の群から選ばれた１種以上からなる請求項４記載の非水系二次電池用正極。 5. The positive electrode for a non-aqueous secondary battery according to claim 4 , wherein the transition metal oxide is composed of one or more selected from the group consisting of Li 6 MnO 4 , Li 6 CoO 4 , and Li 5 FeO 4 .
  6. 　前記Ｎｉ含有金属酸化物は、式：ＬｉＮｉ１-x-yＣｏxＭｎyＯ２(0≦x＜1、0≦y＜1、0＜1-x-y )、又は／及び式：ＬｉＮｉ２-x-yＣｏxＭｎyＯ４(0≦x＜2、0≦y＜2、0＜2-x-y )で表される請求項１～５のいずれか１項に記載の非水系二次電池用正極。 The Ni-containing metal oxide has the formula: LiNi 1-xy Co x Mn y O 2 (0 ≦ x <1,0 ≦ y <1,0 <1-xy), or / and Formula: LiNi 2-xy Co x Mn y O 4 (0 ≦ x <2,0 ≦ y <2,0 <2-xy) for nonaqueous secondary battery positive electrode according to any one of claims 1 to 5 represented by.
  7. 　集電体と、前記集電体の表面を被覆するとともに前記正極活物質と前記遷移金属酸化物とをもつ正極合材とをもち、
    　前記正極合材を１００質量％としたときに、前記正極合材に含まれる前記遷移金属酸化物の含有量は１質量％以上１５質量％以下である請求項１～６のいずれか１項に記載の非水系二次電池用正極。     Having a current collector and a positive electrode mixture covering the surface of the current collector and having the positive electrode active material and the transition metal oxide;
    The content of the transition metal oxide contained in the positive electrode mixture is 1% by mass or more and 15% by mass or less when the positive electrode mixture is 100% by mass. The positive electrode for non-aqueous secondary batteries as described.
  8. 　前記Ｎｉ含有金属酸化物の充電の上限電位は、４．５Ｖ（Ｌｉ基準）以上である請求項１～７のいずれか１項に記載の非水系二次電池用正極。 The positive electrode for a non-aqueous secondary battery according to any one of claims 1 to 7, wherein an upper limit potential for charging the Ni-containing metal oxide is 4.5 V (Li reference) or more.
  9. 　請求項１～８のいずれか１項に記載の非水系二次電池用正極と、負極と、非水電解液とを備えた非水系二次電池。 A non-aqueous secondary battery comprising the positive electrode for a non-aqueous secondary battery according to any one of claims 1 to 8, a negative electrode, and a non-aqueous electrolyte.
  10. 　前記非水電解液は、フッ素を有する化合物をもつ請求項９記載の非水系二次電池。 The non-aqueous secondary battery according to claim 9, wherein the non-aqueous electrolyte has a fluorine-containing compound.
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