WO2018003448A1 - Positive electrode material for lithium secondary cell, and positive electrode for lithium secondary cell and lithium secondary cell in which said positive electrode material for lithium secondary cell is used - Google Patents

Positive electrode material for lithium secondary cell, and positive electrode for lithium secondary cell and lithium secondary cell in which said positive electrode material for lithium secondary cell is used Download PDF

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WO2018003448A1
WO2018003448A1 PCT/JP2017/021288 JP2017021288W WO2018003448A1 WO 2018003448 A1 WO2018003448 A1 WO 2018003448A1 JP 2017021288 W JP2017021288 W JP 2017021288W WO 2018003448 A1 WO2018003448 A1 WO 2018003448A1
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positive electrode
lithium secondary
active material
secondary battery
electrode active
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PCT/JP2017/021288
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French (fr)
Japanese (ja)
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博史 春名
所　久人
大郊 高松
達哉 遠山
崇 中林
心 高橋
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日立金属株式会社
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Priority to JP2018525005A priority Critical patent/JP6642710B2/en
Publication of WO2018003448A1 publication Critical patent/WO2018003448A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0568—Liquid materials characterised by the solutes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • 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 material used for a positive electrode of a lithium secondary battery and a lithium secondary battery using the same.
  • Lithium secondary batteries are power supplies for mobile communications such as mobile phones and laptop computers, power supplies for household electrical appliances, stationary power supplies such as power storage devices and uninterruptible power supplies, drive power supplies for ships, railways, automobiles, etc. Widely used in the field.
  • lithium metal, a lithium alloy, a metal oxide, carbon, or the like is used as the negative electrode active material, and a lithium composite compound containing lithium and a transition metal is used as the positive electrode active material.
  • a positive electrode for a lithium secondary battery is prepared by kneading a positive electrode active material and a binder in a dispersion medium to prepare a paste-like positive electrode mixture, and applying this positive electrode mixture to a substrate such as a current collector In general, it is produced by drying and molding.
  • a binder such as polyvinylidene fluoride (PVDF)
  • PVDF polyvinylidene fluoride
  • LiMO 2 (M represents a metal element such as Ni, Co, or Mn) having an ⁇ -NaFeO 2 type crystal structure
  • Patent Document 1 discloses that the general formula Li x Ni 1-y A y O 2 (0.98 ⁇ x ⁇ 1.10, 0.05 ⁇ y ⁇ 0.30, A is Co, Al, Mg, Ca , Ti, V, Cr, Mn, Zr, Nb, Mo, and W are selected from the group consisting of oxides of zirconium and titanium on the surface of the positive electrode active material particles having a high Ni ratio.
  • a technique for providing a coating layer is disclosed.
  • Patent Document 1 after chelating a specific organic zirconium compound and / or an organic titanium compound with acetylacetone, a specific solvent is added to prepare a coating solution, and this coating solution is mixed with nickel composite oxide particles. It is said that a positive electrode active material having a coating layer is obtained by heat treatment, and gelation of a paste-like composition used for manufacturing a positive electrode can be suppressed.
  • the lithium secondary battery is configured to include an electrolytic solution in which a lithium salt such as LiPF 6 or LiBF 4 is dissolved.
  • a lithium salt such as LiPF 6 or LiBF 4
  • the interface resistance between the electrolytic solution and the active material the electrolytic solution It is important to reduce the degradation of.
  • Patent Document 2 discloses a technique in which a cyclic boroxine compound is added to at least one solvent selected from carbonates and borate esters and LiBF 4 .
  • a positive electrode active material that has been surface-treated by applying a voltage in an electrolytic solution to which a cyclic boroxine compound has been added has a low interface resistance.
  • Patent Document 3 discloses a positive electrode in which a lithium transition metal oxide and a boron-containing compound are dry-mixed and heat-treated, and the surface of the lithium transition metal oxide is coated with boron lithium oxide. It is said that by heat-treating a boron-containing compound, lithium impurities present on the lithium transition metal oxide can be converted into a structurally stable boron lithium oxide.
  • JP 2016-24968 A International Publication No. 2012/133556 Special table 2015-536558 gazette
  • the gelation of the positive electrode mixture used for the production of the positive electrode can be suppressed by the inorganic coating layer of zirconium and / or titanium formed on the surface of the positive electrode active material.
  • the technique disclosed in Patent Document 1 since a highly insulating inorganic coating layer is formed, the charge / discharge reaction is hindered in the lithium secondary battery, and it is difficult to avoid high resistance of the battery. is there.
  • the present invention provides a positive electrode material for a lithium secondary battery capable of producing a positive electrode of a lithium secondary battery while suppressing modification of the positive electrode mixture, a positive electrode for a lithium secondary battery and a lithium secondary battery using the same.
  • An object is to provide a battery.
  • a positive electrode material for a lithium secondary battery includes a positive electrode active material represented by the following formula (1) and a borate ester represented by the following formula (2). It is characterized by. Li 1 + a Ni b Mn c Co d M e O 2 + ⁇ ⁇ (1)
  • the positive electrode for a lithium secondary battery according to the present invention comprises the positive electrode material for a lithium secondary battery.
  • the lithium secondary battery according to the present invention is a lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes the positive electrode material for a lithium secondary battery. To do.
  • the positive electrode material for lithium secondary batteries which can suppress the modification
  • a positive electrode material for a lithium secondary battery according to an embodiment of the present invention (hereinafter, simply referred to as a positive electrode material), a positive electrode for a lithium secondary battery and a lithium secondary battery using the same will be described in detail. To do.
  • the positive electrode material according to the present embodiment is a material used for manufacturing a positive electrode of a lithium secondary battery, and includes a powdered positive electrode active material.
  • the positive electrode material according to the present embodiment is a lithium composite compound (positive electrode active material) having a layered rock salt type crystal structure (hereinafter sometimes referred to as a layered structure) belonging to the space group R-3m. And a borate ester having a boroxine ring structure.
  • This positive electrode material becomes a material for a positive electrode mixture used in the manufacture of a positive electrode for a lithium secondary battery, together with a binder for binding particles such as a positive electrode active material and a conductive material added to supplement conductivity. And mixed in a dispersion medium to form a positive electrode mixture.
  • the lithium composite compound as the positive electrode active material has the following formula (1): Li 1 + a Ni b Mn c Co d M e O 2 + ⁇ ⁇ (1)
  • a is ⁇ 0.1 or more and 0.2 or less.
  • M ′ represents a metal element other than Li in the formula (1). The less lithium, the higher the valence of the transition metal before charging, the lower the rate of transition metal valence change when lithium is desorbed, and the better the charge / discharge cycle characteristics of the positive electrode active material. On the other hand, when lithium is excessive, the charge / discharge capacity of the positive electrode active material is lowered.
  • a more preferable range of a is ⁇ 0.05 or more and 0.1 or less. If a is ⁇ 0.05 or more, a sufficient amount of lithium is ensured to contribute to charge and discharge, and thus the capacity of the positive electrode active material can be increased. Moreover, if a is 0.1 or less, charge compensation due to a change in the valence of the transition metal is sufficiently performed, so that both high charge / discharge capacity and good charge / discharge cycle characteristics can be achieved.
  • b is more than 0.7 and 0.9 or less.
  • the more nickel the more advantageous is to increase the charge / discharge capacity.
  • the thermal stability of the positive electrode active material may be reduced. Therefore, by defining b within the above range, the capacity of the positive electrode active material can be stably increased.
  • a more preferable range of b is 0.75 or more and 0.85 or less. When b is 0.75 or more, the charge / discharge capacity is further increased.
  • c is 0 or more and less than 0.3.
  • manganese When manganese is added, the layered structure is stably maintained even when lithium is desorbed by charging. On the other hand, when manganese is excessive, the ratio of other transition metals, such as nickel, will become low, and the charge / discharge capacity of a positive electrode active material will fall. Therefore, by defining c within the above range, it is possible to stably maintain the crystal structure of the positive electrode active material even when lithium insertion and extraction are repeated by charging and discharging. Therefore, good charge / discharge cycle characteristics, thermal stability, and the like can be obtained together with a high charge / discharge capacity.
  • a more preferable range of c is 0.10 or more and 0.25 or less.
  • c is 0.10 or more, the crystal structure of the positive electrode active material is further stabilized. Moreover, since the ratio of other transition metals, such as nickel, will become high if c is 0.25 or less, it becomes difficult to impair the charging / discharging capacity
  • d is 0 or more and less than 0.3.
  • d is 0.10 or more and 0.25 or less.
  • d is 0.10 or more, the charge / discharge capacity and the charge / discharge cycle characteristics are further improved.
  • d 0.25 or less, the raw material cost is lower, and the productivity of the positive electrode active material is improved.
  • e is 0 or more and 0.25 or less.
  • M element selected from the group consisting of Mg, Al, Ti, Zr, Mo and Nb
  • Electrode performance including stability and charge / discharge cycle characteristics can be improved.
  • M element selected from the group consisting of Mg, Al, Ti, Zr, Mo and Nb
  • M is excessive, the ratio of other transition metals such as nickel is decreased, and the charge / discharge capacity of the positive electrode active material is decreased. Therefore, by defining e in the above range, both high charge / discharge capacity and good electrochemical characteristics can be achieved.
  • ⁇ is set to ⁇ 0.2 or more and 0.2 or less.
  • ⁇ represents the excess or deficiency of oxygen (O) from the stoichiometric ratio of the positive electrode active material represented by the chemical formula LiM′O 2 .
  • O oxygen
  • LiM′O 2 the excess or deficiency of oxygen
  • the positive electrode active material according to the present embodiment may include primary particles of a lithium composite compound in which individual particles are separated, and include secondary particles in which a plurality of primary particles are bonded by granulation, sintering, or the like. Also good. Secondary particles may be granulated by either dry granulation or wet granulation.
  • a granulator such as a spray dryer or a rolling fluidized bed apparatus can be used.
  • the average particle diameter of the primary particles of the positive electrode active material is preferably 0.1 ⁇ m or more and 2 ⁇ m or less. When the average particle size is within this range, the positive electrode active material filling property of the positive electrode is improved, so that a positive electrode having a high energy density can be manufactured. In addition, since the scattering and aggregation of the powdered positive electrode active material are reduced, the handleability is improved.
  • the average particle diameter of the secondary particles of the positive electrode active material can be, for example, 3 ⁇ m or more and 50 ⁇ m or less.
  • the BET specific surface area of the positive electrode active material is preferably 0.2 m 2 / g or more and 2.0 m 2 / g or less.
  • the BET specific surface area of the powdered positive electrode active material composed of a collection of primary particles and secondary particles is within this range, the positive electrode active material filling property in the positive electrode is improved, and a positive electrode with higher energy density can be produced. It becomes possible.
  • the BET specific surface area can be measured using, for example, an automatic specific surface area measuring device.
  • the crystal structure of the positive electrode active material can be confirmed by, for example, X-ray diffraction (XRD).
  • XRD X-ray diffraction
  • the composition of the positive electrode active material can be confirmed by high frequency inductively coupled plasma (ICP) emission spectroscopic analysis, atomic absorption spectrometry (AAS), or the like.
  • ICP inductively coupled plasma
  • AAS atomic absorption spectrometry
  • the particle fracture strength of the positive electrode active material is preferably 50 MPa or more and 100 MPa or less.
  • the particle breaking strength per particle of the positive electrode active material is within this range, the positive electrode active material particles are hardly broken in the process of producing the electrode, and the positive electrode mixture slurry containing the positive electrode active material in the positive electrode current collector When the positive electrode mixture layer is formed by coating, coating defects such as peeling are less likely to occur.
  • the particle breaking strength of the positive electrode active material can be measured using, for example, a micro compression tester.
  • the positive electrode active material according to the present embodiment is synthesized mainly through a mixing step and a firing step using a compound containing lithium and a compound containing a metal element other than Li constituting the positive electrode active material as raw materials. Can do.
  • a compound containing lithium and a compound containing a metal element other than Li constituting the positive electrode active material are mixed.
  • the compound containing lithium include lithium carbonate, lithium acetate, lithium nitrate, lithium hydroxide, lithium chloride, and lithium sulfate.
  • lithium carbonate is particularly preferable.
  • Lithium carbonate is stable in supply, has good procurement, and is inexpensive. Moreover, since melting
  • the compound containing a metal element other than Li constituting the positive electrode active material a compound containing nickel, a compound containing manganese, a compound containing cobalt, or a compound containing an element represented by M is mixed.
  • the compound containing nickel, the compound containing manganese, or the compound containing cobalt for example, oxides, hydroxides, carbonates, acetates, and the like can be used. Among these, it is particularly preferable to use an oxide, a hydroxide, or a carbonate.
  • a compound containing the element represented by M carbonate, an oxide, a hydroxide, acetate, nitrate etc. can be used, for example. Among these, it is particularly preferable to use carbonate, oxide, or hydroxide.
  • each compound as a raw material is weighed at a predetermined elemental composition ratio corresponding to the above formula, and each compound is pulverized and mixed to prepare a powdery mixture in which each compound is mixed.
  • a pulverizer for pulverizing the compound for example, a general precision pulverizer such as a ball mill, a jet mill, or a sand mill can be used.
  • the raw material compound is preferably pulverized by wet pulverization, and from an industrial viewpoint, wet pulverization using water as a dispersion medium is particularly preferable.
  • the solid-liquid mixture obtained by wet pulverization may be dried using, for example, a dryer.
  • a dryer for example, a spray dryer, a fluidized bed dryer, an evaporator or the like can be used.
  • the mixture obtained in the mixing step is fired to obtain a lithium composite compound having a layered structure.
  • heat treatment can be performed using an appropriate heat treatment apparatus. Specifically, for example, a roller hearth kiln, a tunnel furnace, a pusher furnace, a rotary kiln, a batch furnace or the like can be used.
  • the firing step preferably includes a first heat treatment step for forming the first precursor, a second heat treatment step for forming the second precursor, and a third heat treatment step which is a finish heat treatment.
  • the positive electrode active material represented by the general formula: LiNiO 2 has a higher capacity than the positive electrode active material represented by the general formula: LiCoO 2 , but is more alkaline after firing than the positive electrode active material represented by LiCoO 2. Tends to remain. According to the method of sequentially performing each of these heat treatment steps, residual alkali components can be reduced.
  • the mixture obtained in the mixing step is preferably heat treated at a heat treatment temperature of 200 ° C. or more and 400 ° C. or less for 0.5 hours or more and 5 hours or less.
  • a first precursor is obtained by this heat treatment.
  • the first heat treatment step is performed mainly for removing a highly vaporizable component such as moisture that hinders the synthesis reaction of the positive electrode active material from the mixture obtained in the mixing step.
  • carbon dioxide gas generated due to thermal decomposition of raw materials such as lithium carbonate or combustion of impurities is excluded from the mixture together with moisture.
  • the heat treatment temperature is less than 200 ° C., the combustion reaction of impurities and the thermal decomposition reaction of raw materials may be insufficient.
  • the heat treatment temperature in the first heat treatment step is preferably 250 ° C. or more and 400 ° C. or less, and more preferably 250 ° C. or more and 380 ° C. or less. If the heat treatment temperature is within this range, the progress of crystallization in this step can be suppressed while efficiently removing moisture, impurities and the like.
  • the heat treatment time in the first heat treatment step can be set to an appropriate time according to, for example, the heat treatment temperature, the amount of moisture and impurities contained in the mixture, the removal target of moisture and impurities, and the like.
  • the first heat treatment step may be performed in an oxidizing gas atmosphere, a non-oxidizing gas atmosphere, or a reduced pressure atmosphere.
  • the oxidizing gas atmosphere may be either an oxygen gas atmosphere or an air atmosphere. If it is an air atmosphere, the structure of a heat processing apparatus can be simplified and the manufacturing cost of a positive electrode active material can be reduced. Further, the reduced-pressure atmosphere may be a reduced-pressure condition with an appropriate degree of vacuum such as an atmospheric pressure or lower.
  • the first heat treatment step under an atmosphere gas flow or exhaust with a pump.
  • the gas generated from the mixture can be efficiently eliminated.
  • the atmospheric gas flow or the flow rate of the exhaust gas by the pump be larger than the volume of gas generated from the mixture.
  • the volume of gas generated from the mixture is, for example, a temperature set by estimating the amount of gas generated based on the mass of the raw material contained in the mixture and the ratio of components expected to be desorbed from the raw material. What is necessary is just to calculate about conditions.
  • the first precursor obtained in the first heat treatment step is preferably heat treated at a heat treatment temperature of 450 ° C. or higher and 900 ° C. or lower for 0.1 hour or more and 50 hours or less.
  • a second precursor is obtained by this heat treatment.
  • the second heat treatment step is performed mainly for oxidizing nickel in the first precursor from divalent to trivalent to crystallize a lithium composite compound having a layered structure.
  • the heat treatment temperature is lower than 450 ° C., the reaction rate of the solid phase reaction is slowed, and there is a possibility that the raw materials such as lithium carbonate remain excessively.
  • the heat treatment temperature in the second heat treatment step is more preferably 600 ° C. or higher. If it is 600 degreeC or more, the reaction efficiency of a solid-phase reaction will improve more.
  • the heat treatment temperature in the second heat treatment step is more preferably 800 ° C. or lower. If it is 800 degrees C or less, it will become difficult to coarsen a crystal grain.
  • the heat treatment time in the second heat treatment step is more preferably 0.1 hour or more and 5 hours or less.
  • the heat treatment time is 5 hours or less, the time required for producing the positive electrode active material is shortened, and the productivity can be improved.
  • the second heat treatment step is preferably an oxidizing atmosphere having an oxygen concentration of 90% or more, more preferably an oxidizing atmosphere having an oxygen concentration of 95% or more, and an oxygen concentration of 100%. It is more preferable to use an oxidizing atmosphere. Moreover, it is preferable to perform a 2nd heat treatment process under the airflow by oxidizing gas. When heat treatment is performed in a stream of oxidizing gas having a high oxygen concentration, nickel can be reliably oxidized, and gas generated by thermal decomposition of the raw material can be reliably excluded.
  • the second precursor obtained in the second heat treatment step is preferably heat treated at a heat treatment temperature of 700 ° C. or higher and 900 ° C. or lower.
  • a lithium composite compound having a layered structure is obtained.
  • the third heat treatment step is carried out mainly for the purpose of sufficiently oxidizing nickel in the second precursor from divalent to trivalent and growing crystal grains of a lithium composite compound having a layered structure. That is, this step is a heat treatment step for performing an oxidation reaction of nickel in the second precursor and grain growth of the lithium composite compound crystal grains.
  • the heat treatment temperature is less than 700 ° C., the grain growth of the lithium composite compound may not proceed promptly.
  • the heat treatment time is preferably 0.1 hours or more and 50 hours or less, more preferably 0.5 hours or more and 5 hours or less.
  • the oxygen partial pressure is low, heat is required to promote the oxidation reaction of nickel. Therefore, when the oxygen supply to the second precursor is insufficient in the third heat treatment step, it is necessary to increase the heat treatment temperature.
  • the heat treatment temperature is raised, decomposition of the layered structure is unavoidable, so that a high-capacity lithium composite compound cannot be obtained.
  • the heat treatment time is 0.1 hour or longer, the second precursor can be sufficiently reacted with oxygen.
  • the third heat treatment step is preferably an oxidizing atmosphere having an oxygen concentration of 90% or more, more preferably an oxidizing atmosphere having an oxygen concentration of 95% or more, and an oxygen concentration of 100%. It is more preferable to use an oxidizing atmosphere. Moreover, it is preferable to perform a 3rd heat treatment process under the airflow by oxidizing gas. When heat treatment is performed in a stream of oxidizing gas having a high oxygen concentration, the oxygen partial pressure in the atmosphere is difficult to decrease, and nickel can be reliably oxidized without increasing the heat treatment temperature.
  • the positive electrode active material synthesized through the above mixing step and the firing step has a nickel (Ni) coefficient b in the formula (1) of more than 0.7 and not more than 0.9, and the inclusion of nickel Due to the high rate, unreacted alkali components may remain after firing.
  • the remaining alkali component reacts with an organic binder such as PVDF used as a binder when preparing the positive electrode mixture, and gelation of the positive electrode mixture is caused by the polymerization reaction of the organic binder.
  • the positive electrode mixture may be thickened.
  • the molecule of the organic binder is modified to cause a defluorination reaction such as PVDF.
  • the modification of the positive electrode mixture is suppressed by allowing a borate ester having a boroxine ring structure and the positive electrode active material to coexist.
  • the borate ester having a boroxine ring structure is represented by the following formula (2): (BO) 3 (OR) 3 (2) [However, in Formula (2), R is an organic group having 1 or more carbon atoms. ].
  • the borate ester represented by the formula (2) is a boroxine derivative having a molecular structure in which hydrogen of boroxine is substituted.
  • the organic group (R) in the formula (2) may be linear or branched, and may have a ring structure or an arbitrary substituent.
  • the substituent may be a halogen atom such as a fluorine atom, a chlorine atom or a bromine atom, or a group having a nitrogen atom, a sulfur atom or the like.
  • the upper limit of the carbon number of the organic group (R) is not particularly limited, but is preferably 6 or less from the viewpoint of easy synthesis.
  • the organic group (R) in the formula (2) is preferably an alkyl group or a cycloalkyl group.
  • the alkyl group may be a chain alkyl group or a branched alkyl group. Specific examples of the chain alkyl group include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group and n-nonyl group. And n-decyl group.
  • branched alkyl group examples include isopropyl group, 1-methyl-propyl group, 1-ethyl-propyl group, 2-methyl-propyl group, 1-methyl-butyl group, 1-ethyl-butyl group, 2 -Methyl-butyl group, 2-ethyl-butyl group, 3-methyl-butyl group, 1-methyl-pentyl group, 1-ethyl-pentyl group, 1-propyl-pentyl group, 2-methyl-pentyl group, 2- Ethyl-pentyl group, 2-propyl-pentyl group, 3-methyl-pentyl group, 3-ethyl-pentyl group, 4-methyl-pentyl group, 1-methyl-hexyl group, 1-ethyl-hexyl group, 1-propyl -Hexyl, 1-butyl-hexyl, 1-pentyl-hexyl, 2-methyl-hexyl, 2-ethyl
  • the boric acid ester represented by the formula (2) is, in particular, triisopropoxyboroxine ((BO) 3 (O (CH) (CH 3 ) 2 ) 3 ), trimethoxyboroxine ((BO) 3 ( Either OCH 3 ) 3 ) or tricyclohexoxyboroxine ((BO) 3 (O (C 6 H 11 )) 3 ) is preferred.
  • these boric acid esters corresponding to alkoxy substitution products of boroxine the effect of suppressing denaturation of the binder can be effectively obtained as compared with alkyl substitution products such as trimethylboroxine.
  • a borate ester having high hydrolyzability may be hydrolyzed by exposure to air. Therefore, when using a highly hydrolyzable borate ester, it is preferable to handle it in an inert atmosphere.
  • the positive electrode mixture slurry is preferably prepared in an inert atmosphere.
  • the borate ester represented by the formula (2) is preferably less than 5.0% by mass with respect to the total amount of the positive electrode active material and borate ester, and is 0.5% by mass or more and 2.0% by mass. The following is more preferable. If the ratio of borate ester is less than 5.0% by mass, it can be expected that a lithium secondary battery having low internal resistance can be produced by suppressing modification of the positive electrode mixture. The effect which suppresses modification
  • the boric acid ester represented by the formula (2) may coexist with the positive electrode active material in a powder state, or may coexist with the positive electrode active material in a liquid state. However, in terms of quality control of the positive electrode active material, it is preferable to mix with the positive electrode active material in a powder state to obtain a positive electrode material.
  • the borate ester represented by the formula (2) is preferably coexisted with the positive electrode active material before the positive electrode active material and the binder are brought into contact with each other. .
  • the alkali component contained in the positive electrode active material and the binder react to defluorinate a fluorinated polyolefin such as PVDF, and fluorine generated by defluorination
  • a fluorinated polyolefin such as PVDF
  • fluorine generated by defluorination the positive electrode active material represented by the formula (1) or a solution thereof (dispersion) is mixed with the boric acid ester represented by the formula (2) or a solution thereof (dispersion).
  • a binder or a solution thereof (dispersion) is added to the obtained mixture and kneaded to prepare a positive electrode mixture, and the positive electrode mixture is applied to a substrate such as a positive electrode current collector, and then dried and pressed.
  • a positive electrode for a lithium secondary battery it is preferable to produce a positive electrode for a lithium secondary battery by molding.
  • a nonaqueous solvent such as N-methyl-2-pyrrolidone (NMP) as a solvent (dispersion medium) for preparing a solution (dispersion).
  • NMP N-methyl-2-pyrrolidone
  • the conductive material may be added to the positive electrode active material at any stage.
  • the boric acid represented by the formula (2) reacts with the alkali component remaining after firing of the positive electrode active material to neutralize the alkali component and suppress the modification of the organic binder such as PVDF. Therefore, the gelation of the positive electrode mixture and the defluorination reaction of the binder are suppressed, and as a result, the denaturation of the positive electrode mixture is suppressed, so that the internal resistance is low without difficulty due to gelation in the manufacturing process. It becomes possible to provide a positive electrode for a lithium secondary battery and a lithium secondary battery.
  • the binding strength between the particles and between the particles and the base material is increased, and the uniformity of the distribution of the particles in the positive electrode mixture layer is also increased. can get. That is, according to this positive electrode material, unlike the case where the boroxine derivative is directly added to the electrolytic solution, it is possible to reliably eliminate the cause of the high resistance that occurs before the battery is assembled. The discharge cycle characteristics can also be improved.
  • FIG. 1 is a cross-sectional view schematically showing a lithium secondary battery according to an embodiment of the present invention.
  • a lithium secondary battery 1 according to this embodiment includes a positive electrode 10, a separator 11, a negative electrode 12, a battery container 13, a positive electrode current collecting tab 14, a negative electrode current collecting tab 15, an inner lid 16, and release of internal pressure.
  • a valve 17, a gasket 18, a positive temperature coefficient (PTC) resistance element 19, a battery lid 20, and an axis 21 are provided.
  • the battery lid 20 is an integrated part composed of the inner lid 16, the internal pressure release valve 17, the gasket 18 and the resistance element 19.
  • the positive electrode 10 and the negative electrode 12 are provided in a sheet shape, and are overlapped with each other with the separator 11 interposed therebetween.
  • the positive electrode 10, the separator 11, and the negative electrode 12 are wound around the axis 21 to form a cylindrical electrode group.
  • the shaft center 21 can be provided in any cross-sectional shape suitable for supporting the positive electrode 10, the separator 11, and the negative electrode 12.
  • Examples of the cross-sectional shape include a cylindrical shape, a columnar shape, a rectangular tube shape, and a square shape.
  • the shaft center 21 can be made of any material having good insulation. Examples of the material of the shaft center 21 include polypropylene and polyphenylene sulfide. Glass fiber or the like may be added to improve the mechanical strength of the shaft core.
  • the battery container 13 can be formed of an active material having corrosion resistance to the electrolyte, such as aluminum, stainless steel, nickel-plated steel, and the like.
  • the active material is prevented from being deteriorated due to corrosion of the battery container 13 or alloying with lithium in a portion in contact with the electrolytic solution. Is selected.
  • the inner surface of the battery container 13 may be subjected to a surface treatment for improving corrosion resistance and adhesion.
  • a positive current collecting tab 14 and a negative current collecting tab 15 for drawing current are connected to the positive electrode 10 and the negative electrode 12 by spot welding, ultrasonic welding, or the like.
  • An electrode group provided with the positive electrode current collecting tab 14 and the negative electrode current collecting tab 15 is accommodated in the battery container 13.
  • the positive electrode current collecting tab 14 is electrically connected to the bottom surface of the battery lid 20.
  • the negative electrode current collecting tab 15 is electrically connected to the inner wall of the battery container 13.
  • a plurality of the positive electrode current collecting tabs 14 and the negative electrode current collecting tabs 15 may be provided for the electrode group as shown in FIG. By providing a plurality, it becomes possible to cope with a large current.
  • the positive electrode 10 is a lithium containing a positive electrode active material represented by the formula (1) and a borate ester represented by the formula (2) as a positive electrode active material capable of reversibly occluding and releasing lithium ions. It is comprised including the positive electrode material for secondary batteries.
  • the positive electrode 10 includes, for example, a positive electrode mixture layer composed of a positive electrode active material, a conductive material, and a binder, and a positive electrode assembly in which the positive electrode mixture layer is coated on one side or both sides. Electric body. That is, the positive electrode 10 is produced using a positive electrode material for a lithium secondary battery.
  • the conductive material for example, carbon particles such as graphite, carbon black, acetylene black, ketjen black, and channel black, carbon fibers, and the like can be used.
  • One of these conductive materials may be used alone, or a plurality of these conductive materials may be used in combination.
  • the amount of the conductive material is preferably 5% by mass or more and 20% by mass or less with respect to the positive electrode active material. When the amount of the conductive material is within such a range, good conductivity can be obtained and a high capacity can be secured.
  • an organic binder such as polyvinylidene fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, or a copolymer of vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, or the like is used. be able to.
  • organic binder By using only the organic binder as the binder in the positive electrode, it is possible to avoid hydrolysis of the boric acid ester represented by the formula (2).
  • These organic binders may be used individually by 1 type, and may use multiple types together. Further, a thickening material such as carboxymethylcellulose may be used in combination.
  • the organic binder is preferably a halogenated polyolefin, more preferably a fluorinated polyolefin, particularly preferably polyvinylidene fluoride, from the viewpoint of making effective the effect of the boric acid ester represented by the formula (2).
  • the amount of the binder in the positive electrode is preferably 1% by mass or more and 7% by mass or less based on the total amount of the positive electrode active material, the conductive material, and the binder.
  • the amount of the binder is within such a range, the capacity is not reduced and the internal resistance is rarely excessive.
  • strength of a positive mix layer are hard to be impaired.
  • the positive electrode current collector for example, an appropriate material such as a metal foil, a metal plate, a foam metal plate, an expanded metal, or a punching metal made of aluminum, stainless steel, titanium, or the like can be used.
  • a metal foil it is good also as perforated foil perforated by the hole diameter of about 0.1 mm or more and 10 mm or less, for example. It is preferable that the thickness of the metal foil is substantially 10 ⁇ m or more and 100 ⁇ m or less.
  • the positive electrode 10 is prepared by mixing a positive electrode active material, a conductive material, and a binder together with an appropriate solvent to form a positive electrode mixture, and applying the positive electrode mixture to the positive electrode current collector, followed by drying and compression molding. It can produce by doing.
  • a method for applying the positive electrode mixture for example, a doctor blade method, a dipping method, a spray method, or the like can be used.
  • a method of compression molding the positive electrode mixture for example, a roll press or the like can be used.
  • the thickness of the positive electrode mixture layer can be set to an appropriate thickness in consideration of the specifications of the lithium secondary battery to be manufactured and the balance with the negative electrode, but when applied to both surfaces of the positive electrode current collector 50 ⁇ m or more and 200 ⁇ m or less is preferable.
  • the thickness of the positive electrode mixture layer can be set according to the specifications of the capacity, resistance value, etc. of the lithium secondary battery, but if this amount of coating, the distance between the electrodes becomes excessive, There is little distribution of lithium ion storage and release.
  • the particle diameter of the positive electrode active material is usually not more than the thickness of the positive electrode mixture layer. In the case where coarse particles are present in the synthesized positive electrode active material powder, it is preferable that the average particle size of the positive electrode active material is made smaller than the thickness of the positive electrode mixture layer by performing sieving classification, wind classification, and the like in advance.
  • the density of the positive electrode mixture layer can be set to an appropriate density in consideration of the specifications of the lithium secondary battery to be manufactured and the balance with the negative electrode, but the viewpoint of securing the capacity of the lithium secondary battery Is preferably 60% or more of the true density.
  • the separator 11 is provided to prevent the positive electrode 10 and the negative electrode 12 from coming into direct contact with each other and causing a short circuit.
  • a microporous film such as polyethylene, polypropylene, and aramid resin, a film in which the surface of such a microporous film is coated with a heat resistant material such as alumina particles, and the like can be used.
  • the negative electrode 12 includes a negative electrode active material capable of reversibly occluding and releasing lithium ions.
  • the negative electrode 12 includes, for example, a negative electrode active material, a binder, and a negative electrode current collector.
  • the negative electrode active material an appropriate type used in a general lithium secondary battery can be used.
  • Specific examples of the negative electrode active material include those obtained by treating a graphitizable active material obtained from natural graphite, petroleum coke, pitch coke, and the like at a high temperature of 2500 ° C. or higher, mesophase carbon, amorphous carbon, and non-graphite surface.
  • a material coated with crystalline carbon a carbon material whose surface crystallinity has been lowered by mechanically treating the surface of natural graphite or artificial graphite, an active material in which organic substances such as polymers are coated and adsorbed on the carbon surface, Carbon fiber, lithium metal, lithium and aluminum, alloys of tin, silicon, indium, gallium, magnesium, etc., silicon particles or active materials carrying metal on the surface of carbon particles, metals such as tin, silicon, iron, titanium An oxide etc. are mentioned.
  • the metal to be supported include lithium, aluminum, tin, silicon, indium, gallium, magnesium, and alloys thereof.
  • the binder in the negative electrode it is possible to use either an aqueous binder that dissolves, swells or disperses in water and an organic binder that does not dissolve, swell or disperse in water.
  • the water-based binder include a styrene-butadiene copolymer, an acrylic polymer, a polymer having a cyano group, and a copolymer thereof.
  • the organic binder include polyvinylidene fluoride, polytetrafluoroethylene, and copolymers thereof. These binders may be used individually by 1 type, and may use multiple types together. Further, a thickening material such as carboxymethylcellulose may be used in combination.
  • the amount of the binder in the negative electrode is preferably 0.8% by mass to 1.5% by mass with respect to the total amount of the negative electrode active material and the binder for the aqueous binder.
  • an organic binder it is preferable to set it as 3 to 6 mass% with respect to the total of a negative electrode active material and a binder.
  • an appropriate active material such as metal foil made of copper, a copper alloy containing copper as a main component, a metal plate, a metal foam plate, an expanded metal, a punching metal, or the like can be used.
  • metal foil it is good also as perforated foil perforated by the hole diameter of about 0.1 mm or more and 10 mm or less, for example.
  • the thickness of the metal foil is preferably 7 ⁇ m or more and 25 ⁇ m or less.
  • the negative electrode 12 is produced, for example, by mixing a negative electrode active material and a binder together with an appropriate solvent to form a negative electrode mixture, applying this negative electrode mixture to the negative electrode current collector, and then drying and compression molding the mixture. can do.
  • a method for applying the negative electrode mixture for example, a doctor blade method, a dipping method, a spray method, or the like can be used.
  • a method of compression-molding the negative electrode mixture for example, a roll press or the like can be used.
  • the thickness of the negative electrode mixture layer can be set to an appropriate thickness in consideration of the specifications of the lithium secondary battery to be manufactured and the balance with the positive electrode, but when applied to both sides of the negative electrode current collector 50 ⁇ m or more and 200 ⁇ m or less is preferable.
  • the thickness of the negative electrode mixture layer can be set according to the specifications of the lithium secondary battery capacity, resistance value, etc., but if this amount of coating, the distance between the electrodes becomes excessive, There is little distribution of lithium ion storage and release.
  • an electrolytic solution configured to contain an electrolyte and an electrolytic solution solvent
  • an electrolytic solution that contains a small amount of free acid such as moisture and hydrofluoric acid is generally used as the electrolytic solution sealed in the battery container 13. .
  • LiPF 6 lithium hexafluorophosphate
  • LiPF 6 it has high solubility in carbonate used as non-aqueous solvent to be described later, bulky PF 6 - ion conductivity of the electrolyte after dissolution is high dissociation degree of Li +, from a non-aqueous solvent by a group High degree.
  • LiPF 6 reacts with the boric acid ester represented by the formula (2), and the reaction product suppresses the increase in battery resistance.
  • the electrolyte only LiPF 6 may be used alone, or other lithium salts may be used in combination.
  • lithium salts used in combination with LiPF 6 include LiBF 4 , LiClO 4 , LiAsF 6 , LiCF 3 SO 2 , Li (CF 3 SO 2 ) 2 N, Li (C 2 F 5 SO 2 ) 2 N, Li (F 2 SO 2 ) 2 N, LiF, Li 2 CO 3 , LiPF 4 (CF 3 ) 2 , LiPF 4 (CF 3 SO 2 ) 2 , LiBF 3 (CF 3 ), LiBF 2 (CF 3 SO 2 ) 2 etc. are mentioned.
  • the concentration of the electrolyte is preferably in the range of 0.6 mol / L or more and 1.5 mol / L or less.
  • concentration is 0.6 mol / L or more, good ion conductivity can be realized.
  • concentration is 1.5 mol / L or less, the resistance of ion conduction is suppressed to a small value, and the reaction rate of lithium ions is increased, so that deterioration of battery characteristics can be suppressed.
  • non-aqueous solvent used in the electrolytic solution examples include a chain carbonate, a cyclic carbonate, a chain carboxylic acid ester, a cyclic carboxylic acid ester, a chain ether, a cyclic ether, an organic phosphorus compound, an organic sulfur compound, and the like. These compounds may be used individually by 1 type, and may use multiple types together.
  • chain carbonate examples include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.
  • cyclic carbonate examples include ethylene carbonate, propylene carbonate, vinylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, and the like.
  • Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, and propyl propionate.
  • Examples of the cyclic carboxylic acid ester include ⁇ -butyrolactone, ⁇ -valerolactone, and ⁇ -valerolactone.
  • chain ether examples include dimethoxymethane, diethoxymethane, 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,3-dimethoxypropane and the like.
  • cyclic ether examples include tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran and the like.
  • organic phosphorus compound examples include phosphoric acid esters such as trimethyl phosphate, triethyl phosphate, and triphenyl phosphate, phosphorous acid esters such as trimethyl phosphite, triethyl phosphite, and triphenyl phosphite, And trimethylphosphine oxide.
  • organic sulfur compound examples include 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, sulfolane, sulfolene, dimethyl sulfone, ethyl methyl sulfone, methyl phenyl sulfone, and ethyl phenyl sulfone.
  • These compounds used as a non-aqueous solvent may have a substituent or may be a compound in which an oxygen atom is substituted with a sulfur atom.
  • halogen atoms such as a fluorine atom, a chlorine atom, a bromine atom, are mentioned, for example.
  • a compound having a high relative dielectric constant such as a cyclic carbonate or a cyclic lactone and a relatively high viscosity, and a viscosity such as a chain carbonate are relatively It is preferable to combine with a low compound.
  • the electrolytic solution preferably contains carbonates such as vinylene carbonate and monofluorinated ethylene carbonate as additives.
  • carbonates such as vinylene carbonate and monofluorinated ethylene carbonate
  • SEI A surface film called a solid (Electrolyte Interphase) film is formed.
  • the SEI film exhibits an action of suppressing the decomposition of the nonaqueous solvent, but is generated by consuming electric charge in the battery reaction, and thus contributes to a reduction in the capacity of the battery.
  • vinylene carbonate or the like is added, the SEI film can be formed while suppressing a decrease in capacity.
  • the addition amount of additives such as vinylene carbonate is preferably 2% by mass or less based on the total weight of the electrolytic solution.
  • the addition amount is within such a range, it is advantageous in that the capacity and output can be reduced little when excess vinylene carbonate or the like is oxidized and decomposed.
  • the electrolyte may contain carboxylic acid anhydride, sulfur compounds such as 1,3-propane sultone, boron compounds such as lithium bisoxalate borate (LiBOB), trimethyl borate (TMB), and the like as additives. Good.
  • the electrolyte is an overcharge inhibitor that suppresses overcharge of the battery, a flame retardant that improves the flame retardancy (self-extinguishing) of the electrolyte, and a wettability improver that improves the wettability of electrodes and separators.
  • an additive for suppressing elution of Mn from the positive electrode active material, an additive for improving the ionic conductivity of the electrolytic solution, and the like may be contained. The total amount of these additives is preferably less than 10% by mass per electrolyte solution.
  • overcharge inhibitor examples include biphenyl, biphenyl ether, terphenyl, methyl terphenyl, dimethyl terphenyl, cyclohexylbenzene, dicyclohexylbenzene, triphenylbenzene, hexaphenylbenzene, adiponitrile, dioxane, and the like.
  • the flame retardant for example, organic phosphorus compounds such as trimethyl phosphate and triethyl phosphate, fluorides of the above non-aqueous solvents including borate esters, and the like can be used.
  • the wettability improver for example, chain ethers such as 1,2-dimethoxyethane can be used.
  • the lithium secondary battery having the above configuration uses the battery lid as the positive electrode external terminal and the bottom of the battery can as the negative electrode external terminal, and accumulates power supplied from the outside in the wound electrode group and also in the wound electrode group. Can be supplied to an external device or the like.
  • the lithium secondary battery of this embodiment is, for example, a small power source such as a portable electronic device or a household electric device, a stationary power source such as an uninterruptible power source or a power leveling device, a ship, a railway, a hybrid vehicle, an electric vehicle, etc. It can be used as a drive power supply.
  • the electrode group and the battery container 13 are formed in a cylindrical shape.
  • the form of the electrode group includes various forms exemplified by a form wound in a flat circular shape, a form in which strip-shaped electrodes are laminated, a form in which a bag-like separator containing electrodes is laminated to form a multilayer structure, etc. It is also possible to adopt the form.
  • the battery case 13 can have an appropriate shape such as a cylindrical shape, a flat elliptical shape, a flat elliptical shape, a square shape, a coin shape, or a button shape according to the form of the electrode group. Further, it is possible to adopt a form in which the axis 21 is not provided.
  • Example 1 Using a positive electrode material containing a positive electrode active material represented by the formula (1) and triisopropoxyboroxine as a borate ester represented by the formula (2), a lithium secondary A battery was produced.
  • lithium carbonate, nickel hydroxide, cobalt carbonate, and manganese carbonate were prepared as starting materials for the positive electrode active material.
  • the mixing process which mixes these starting materials was implemented. Specifically, the starting material is weighed so that Li: Ni: Co: Mn is 1.04: 0.80: 0.15: 0.05 by atomic ratio, and is pulverized and mixed to obtain a powder form A mixture of was obtained.
  • a firing step for firing the obtained mixture was performed. Specifically, the mixed powder obtained by the mixing step was subjected to a first heat treatment step to obtain a first precursor. Thereafter, the first precursor was subjected to a second heat treatment step to obtain a second precursor, and then the second precursor was subjected to a third heat treatment step to calcine the lithium composite compound.
  • the first heat treatment step 1 kg of the mixed powder obtained in the mixing step is filled into an alumina container having a length of 300 mm, a width of 300 mm, and a height of 100 mm, and then, for 1 hour at a heat treatment temperature of 350 ° C. in an air atmosphere by a continuous transfer furnace. To obtain a first precursor powder. In this step, water vapor accompanying thermal decomposition of nickel hydroxide and carbon dioxide accompanying thermal decomposition of cobalt carbonate and manganese carbonate are generated.
  • the powder of the first precursor obtained in the first heat treatment step is replaced with an atmosphere having an oxygen concentration of 90% or more for 10 hours at a heat treatment temperature of 600 ° C. in an oxygen stream.
  • a second precursor powder was obtained by heat treatment.
  • cobalt carbonate and manganese carbonate that could not be reacted in the first heat treatment step are thermally decomposed to generate carbon dioxide.
  • carbon dioxide is generated by the reaction of lithium carbonate with Ni, Co, and Mn.
  • the positive electrode active material obtained by the above steps was subjected to elemental analysis by ICP emission spectroscopic analysis, it was confirmed to be Li 1.02 Ni 0.8 Mn 0.05 Co 0.15 O 2 .
  • the negative electrode was produced using natural graphite having an interplanar spacing of 0.368 nm, an average particle size of 20 ⁇ m, and a specific surface area of 5 m 2 / g as a negative electrode active material.
  • natural graphite as a negative electrode active material and an aqueous dispersion of carboxymethyl cellulose were sufficiently mixed, and an aqueous dispersion of a styrene-butadiene copolymer was added to prepare a negative electrode mixture slurry.
  • Natural graphite, carboxymethyl cellulose, and styrene butadiene copolymer were mixed in an amount such that the mass ratio was 98: 1: 1. And this negative electrode mixture slurry was uniformly apply
  • the cylindrical lithium secondary battery shown in FIG. 1 was produced using the produced positive electrode and negative electrode.
  • a positive electrode lead and a negative electrode lead for drawing current were formed on the positive electrode and the negative electrode, respectively, by ultrasonic welding.
  • the positive electrode lead and the negative electrode lead are made of the same material as the current collector, and are stacked with a polyethylene separator sandwiched between the tabbed positive electrode and negative electrode, wound in a spiral shape, and stored in a cylindrical battery container. did.
  • electrolyte solution was inject
  • LiPF 6 lithium hexafluorophosphate
  • EMC ethyl methyl carbonate
  • Example 2 Lithium was treated in the same manner as in Example 1 except that the amount of triisopropoxyboroxine ((BO) 3 (O (CH) (CH 3 ) 2 ) 3 ) mixed with the positive electrode active material was 0.5% by mass. A secondary battery was produced.
  • (BO) 3 (O (CH) (CH 3 ) 2 ) 3 triisopropoxyboroxine
  • Example 3 Lithium was obtained in the same manner as in Example 1 except that the amount of triisopropoxyboroxine ((BO) 3 (O (CH) (CH 3 ) 2 ) 3 ) mixed with the positive electrode active material was 2.0% by mass. A secondary battery was produced.
  • Example 4 Lithium was obtained in the same manner as in Example 1 except that the amount of triisopropoxyboroxine ((BO) 3 (O (CH) (CH 3 ) 2 ) 3 ) mixed in the positive electrode active material was 5.0% by mass. A secondary battery was produced.
  • Example 5 A lithium secondary battery was produced in the same manner as in Example 1 except that the boric acid ester mixed with the positive electrode active material was trimethoxyboroxine ((BO) 3 (OCH 3 ) 3 ).
  • Example 6 The boric acid ester mixed with the positive electrode active material was trimethoxyboroxine ((BO) 3 (OCH 3 ) 3 ) and the amount thereof was changed to 0.5% by mass. A battery was produced.
  • the boric acid ester to be mixed with the positive electrode active material was trimethoxyboroxine ((BO) 3 (OCH 3 ) 3 ), and the amount thereof was set to 2.0% by mass. A battery was produced.
  • Example 8 The boric acid ester mixed with the positive electrode active material was trimethoxyboroxine ((BO) 3 (OCH 3 ) 3 ) and the amount thereof was 5.0% by mass. A battery was produced.
  • Example 9 A lithium secondary battery was produced in the same manner as in Example 1 except that the boric acid ester mixed with the positive electrode active material was tricyclohexoxyboroxine ((BO) 3 (O (C 6 H 11 )) 3 ). .
  • the boric acid ester mixed with the positive electrode active material was tricyclohexoxyboroxine ((BO) 3 (O (C 6 H 11 )) 3 ), and the amount thereof was changed to 0.5% by mass. Similarly, a lithium secondary battery was produced.
  • the boric acid ester mixed with the positive electrode active material was tricyclohexoxyboroxine ((BO) 3 (O (C 6 H 11 )) 3 ), and the amount thereof was set to 2.0 mass%. Similarly, a lithium secondary battery was produced.
  • the boric acid ester mixed with the positive electrode active material was tricyclohexoxyboroxine ((BO) 3 (O (C 6 H 11 )) 3 ), and the amount thereof was 5.0 mass%. Similarly, a lithium secondary battery was produced.
  • Example 2 A lithium secondary battery was produced in the same manner as in Example 1 except that 1.0% by mass of lithium bisoxalate borate was mixed with the positive electrode mixture slurry instead of boric acid esters.
  • the initial DC internal resistance was measured by the following procedure. First, the battery was charged with a constant current and a constant voltage for 5 hours with an upper limit voltage of 4.2 V and a current value of 1.8 A. Next, the battery was discharged at a constant current with a final voltage of 3.0 V and a current value of 1.8 A. Then, this charge / discharge operation was repeated up to a total of 3 cycles. Subsequently, the battery was charged with a constant current and a constant voltage for 5 hours with an upper limit voltage of 4.2 V and a current value of 1.8 A.
  • the current value was set to 1.8 A and discharged for 10 seconds, and the voltage drop due to the discharge at this time was measured. Then, the initial DC internal resistance value was obtained by dividing the displacement of the voltage value by the current value.
  • the amount of the boric acid ester represented by the formula (2) is preferably less than 5.0% by mass. Further, in Comparative Examples 2 and 3, gelation of the positive electrode mixture slurry was observed, and the internal resistance was higher than those in Examples 1, 5, and 9, respectively. Therefore, the boric acid ester represented by the formula (2) is effective in suppressing the denaturation of the binder, and it is considered that boroxine derivatives in which hydrogen is alkyl-substituted and other boric acids are not suitable.
  • the positive electrode active material represented by Li 1.02 Ni 0.8 Mn 0.05 Co 0.15 O 2 was examined for the effect of suppressing the gelation of the positive electrode mixture slurry.
  • the other positive electrode active material represented by (1) also has a high Ni content and tends to have a large amount of residual alkali. Therefore, by adding the boric acid ester represented by the above formula (2) As in Examples 1 to 12, gelation of the positive electrode mixture slurry can be suppressed.

Abstract

The present invention provides: a positive electrode material for a lithium secondary cell with which it is possible to manufacture a positive electrode of a lithium secondary cell while suppressing denaturation of a positive electrode mixture; and a positive electrode for a lithium secondary cell and a lithium secondary cell in which said positive electrode material for a lithium secondary cell is used. The positive electrode material for a lithium secondary cell contains a positive electrode active material represented by formula (1) below, and a boric acid ester represented by formula (2) below. : Li1+aNibMncCodMeO2+α (1): [In formula (1), M is at least one element selected from the group consisting of Mg, Al, Ti, Zr, Mo, and Nb, and a, b, c, d, e, and α are numbers that satisfy –0.1 ≤ a ≤ 0.2, 0.7 < b ≤ 0.9, 0 ≤ c < 0.3, 0 ≤ d < 0.3, 0 ≤ e ≤ 0.25, b + c + d + e = 1, and –0.2 ≤ α ≤ 0.2.] : (BO)3(OR)3 (2): [In formula (2), R is a C1 or higher organic group.]

Description

リチウム二次電池用正極材料、それを用いたリチウム二次電池用正極及びリチウム二次電池Positive electrode material for lithium secondary battery, positive electrode for lithium secondary battery and lithium secondary battery using the same
　本発明は、リチウム二次電池の正極に用いられる正極材料及びそれを用いたリチウム二次電池に関する。 The present invention relates to a positive electrode material used for a positive electrode of a lithium secondary battery and a lithium secondary battery using the same.
　リチウム二次電池は、携帯電話、ノートパソコン等の移動体通信用電源、家庭用電気機器用電源、電力貯蔵装置、無停電電源装置等の定置用電源、船舶、鉄道、自動車等の駆動電源等の分野において広く実用化が進められている。リチウム二次電池には、例えば、負極活物質として、リチウム金属やリチウム合金、金属酸化物、カーボン等が用いられ、正極活物質として、リチウムと遷移金属とを含むリチウム複合化合物が用いられる。 Lithium secondary batteries are power supplies for mobile communications such as mobile phones and laptop computers, power supplies for household electrical appliances, stationary power supplies such as power storage devices and uninterruptible power supplies, drive power supplies for ships, railways, automobiles, etc. Widely used in the field. In the lithium secondary battery, for example, lithium metal, a lithium alloy, a metal oxide, carbon, or the like is used as the negative electrode active material, and a lithium composite compound containing lithium and a transition metal is used as the positive electrode active material.
　リチウム二次電池用正極は、正極活物質と結着剤等とを分散媒中で混練して、ペースト状の正極合剤を調製し、この正極合剤を集電体等の基材に塗布し、乾燥、成形して作製するのが一般的である。リチウムを含む原料を用いて正極を作製するとき、ポリフッ化ビニリデン（ＰＶＤＦ）等の結着剤がアルカリ成分に晒されると、結着剤の分子鎖同士がアルカリ成分と反応して三次元的な架橋を形成し、スラリー状の正極合剤がゲル化することが知られている。 A positive electrode for a lithium secondary battery is prepared by kneading a positive electrode active material and a binder in a dispersion medium to prepare a paste-like positive electrode mixture, and applying this positive electrode mixture to a substrate such as a current collector In general, it is produced by drying and molding. When producing a positive electrode using a raw material containing lithium, if a binder such as polyvinylidene fluoride (PVDF) is exposed to an alkali component, the molecular chains of the binder react with the alkali component to form a three-dimensional structure. It is known that crosslinks are formed and the slurry-like positive electrode mixture is gelled.
　リチウム二次電池用正極に用いられるリチウム複合化合物としては、α－ＮａＦｅＯ２型の結晶構造を有するＬｉＭＯ２（Ｍは、Ｎｉ、Ｃｏ、Ｍｎ等の金属元素を示す。）が知られている。例えば、特許文献１には、一般式ＬｉｘＮｉ１－ｙＡｙＯ２（０．９８≦ｘ≦１．１０、０．０５≦ｙ≦０．３０、ＡはＣｏ、Ａｌ、Ｍｇ、Ｃａ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｚｒ、Ｎｂ、ＭｏおよびＷからなる群より選択される１種以上）で表されるＮｉの割合が高い正極活物質粒子の表面にジルコニウムやチタニウムの酸化物の被覆層を設ける技術が開示されている。 As a lithium composite compound used for a positive electrode for a lithium secondary battery, LiMO 2 (M represents a metal element such as Ni, Co, or Mn) having an α-NaFeO 2 type crystal structure is known. For example, Patent Document 1 discloses that the general formula Li x Ni 1-y A y O 2 (0.98 ≦ x ≦ 1.10, 0.05 ≦ y ≦ 0.30, A is Co, Al, Mg, Ca , Ti, V, Cr, Mn, Zr, Nb, Mo, and W are selected from the group consisting of oxides of zirconium and titanium on the surface of the positive electrode active material particles having a high Ni ratio. A technique for providing a coating layer is disclosed.
　特許文献１によると、特定の有機ジルコニウム化合物および／又は有機チタニウム化合物をアセチルアセトンによりキレート化した後、特定の溶媒を添加してコーティング液を作製し、このコーティング液をニッケル複合酸化物粒子と混合すると、熱処理により被覆層を具備した正極活物質が得られ、正極の製造に用いるペースト状組成物のゲル化を抑制することができるとされている。 According to Patent Document 1, after chelating a specific organic zirconium compound and / or an organic titanium compound with acetylacetone, a specific solvent is added to prepare a coating solution, and this coating solution is mixed with nickel composite oxide particles. It is said that a positive electrode active material having a coating layer is obtained by heat treatment, and gelation of a paste-like composition used for manufacturing a positive electrode can be suppressed.
　ところで、リチウム二次電池は、ＬｉＰＦ６、ＬｉＢＦ４等のリチウム塩を溶解した電解液を含んで構成され、電池性能の向上のためには、電解液と活物質との界面抵抗や、電解液の分解を低減することが重要である。例えば、特許文献２には、炭酸エステル及びホウ酸エステルから選ばれる少なくとも１種の溶媒と、ＬｉＢＦ４とに、環状ボロキシン化合物を添加する技術が開示されている。特許文献２によると、環状ボロキシン化合物を添加した電解液中で電圧を印加して表面処理した正極活物質は、界面抵抗が小さくなるとされている。また、特許文献３には、リチウム遷移金属酸化物及びボロン含有化合物を乾式混合して熱処理し、リチウム遷移金属酸化物の表面をホウ素リチウム酸化物でコーティングした正極が開示されている。ボロン含有化合物を熱処理することにより、リチウム遷移金属酸化物上に存在するリチウム不純物を構造的に安定したホウ素リチウム酸化物に転換させることができるとされている。 By the way, the lithium secondary battery is configured to include an electrolytic solution in which a lithium salt such as LiPF 6 or LiBF 4 is dissolved. In order to improve battery performance, the interface resistance between the electrolytic solution and the active material, the electrolytic solution It is important to reduce the degradation of. For example, Patent Document 2 discloses a technique in which a cyclic boroxine compound is added to at least one solvent selected from carbonates and borate esters and LiBF 4 . According to Patent Document 2, a positive electrode active material that has been surface-treated by applying a voltage in an electrolytic solution to which a cyclic boroxine compound has been added has a low interface resistance. Patent Document 3 discloses a positive electrode in which a lithium transition metal oxide and a boron-containing compound are dry-mixed and heat-treated, and the surface of the lithium transition metal oxide is coated with boron lithium oxide. It is said that by heat-treating a boron-containing compound, lithium impurities present on the lithium transition metal oxide can be converted into a structurally stable boron lithium oxide.
特開２０１６－２４９６８号公報JP 2016-24968 A 国際公開第２０１２／１３３５５６号International Publication No. 2012/133556 特表２０１５－５３６５５８号公報Special table 2015-536558 gazette
　リチウム二次電池用の正極を作製するにあたって、結着剤がアルカリ成分と反応すると、ゲル化により増粘して正極合剤の塗工性が悪化する。また、ＰＶＤＦ等の結着剤は脱フッ素化により結着性が低下するので、電池の内部抵抗が増大する虞がある。特に、正極活物質についてニッケルの含有率が高い場合、正極活物質の焼成時にニッケルの酸化が不十分になり易いため、未反応のリチウムが焼成後に残留し、結着剤とアルカリ成分との反応が起こり易い傾向がある。 In producing a positive electrode for a lithium secondary battery, when the binder reacts with an alkali component, the viscosity of the positive electrode mixture is deteriorated by thickening due to gelation. In addition, since the binding property of PVDF or the like decreases due to defluorination, the internal resistance of the battery may increase. In particular, when the content of nickel in the positive electrode active material is high, oxidation of nickel tends to be insufficient at the time of firing the positive electrode active material, so that unreacted lithium remains after firing, and the reaction between the binder and the alkali component Tends to occur.
　特許文献１に開示された技術によると、正極活物質の表面に形成されたジルコニウムおよび／又はチタニウムの無機物の被覆層によって、正極の作製に用いる正極合剤のゲル化を抑制できるとされている。しかしながら、特許文献１に開示された技術では、絶縁性が高い無機物の被覆層が形成されるため、リチウム二次電池中で充放電反応が妨げられ、電池の高抵抗化は避け難いという課題がある。 According to the technique disclosed in Patent Document 1, it is said that the gelation of the positive electrode mixture used for the production of the positive electrode can be suppressed by the inorganic coating layer of zirconium and / or titanium formed on the surface of the positive electrode active material. . However, in the technique disclosed in Patent Document 1, since a highly insulating inorganic coating layer is formed, the charge / discharge reaction is hindered in the lithium secondary battery, and it is difficult to avoid high resistance of the battery. is there.
　一方、特許文献２に開示された技術によると、電解質にＬｉＢＦ４を用い、環状ボロキシンを添加した電解液中で正極活物質を表面処理すると、界面抵抗が小さくなるとされている。しかしながら、特許文献２に開示された技術では、４．８Ｖ（ｖｓ　Ｌｉ＋／Ｌｉ）程度の高い電位が印加されるため、電解液自体あるいは結着剤、正極を構成する炭素成分への電解質の挿入による分解反応などが生じ、電池の高抵抗化を避けられない可能性がある。また、特許文献３に開示された技術によると、リチウム遷移金属酸化物の表面にコーティング層を形成するために、初期抵抗の増加により電気化学的特性が低下する虞がある。 On the other hand, according to the technique disclosed in Patent Document 2, when the positive electrode active material is surface-treated in an electrolytic solution using LiBF 4 as an electrolyte and added with cyclic boroxine, the interface resistance is reduced. However, in the technique disclosed in Patent Document 2, since a high potential of about 4.8 V (vs Li + / Li) is applied, the electrolyte is inserted into the electrolyte itself, the binder, or the carbon component constituting the positive electrode. There is a possibility that a high resistance of the battery cannot be avoided due to a decomposition reaction caused by the above. In addition, according to the technique disclosed in Patent Document 3, since the coating layer is formed on the surface of the lithium transition metal oxide, there is a possibility that the electrochemical characteristics are deteriorated due to an increase in initial resistance.
　そこで、本発明は、正極合剤の変性を抑制してリチウム二次電池の正極を製造することが可能なリチウム二次電池用正極材料、それを用いたリチウム二次電池用正極及びリチウム二次電池を提供することを目的とする。 Accordingly, the present invention provides a positive electrode material for a lithium secondary battery capable of producing a positive electrode of a lithium secondary battery while suppressing modification of the positive electrode mixture, a positive electrode for a lithium secondary battery and a lithium secondary battery using the same. An object is to provide a battery.
　前記課題を解決するために本発明に係るリチウム二次電池用正極材料は、下記式（１）によって表される正極活物質と、下記式（２）によって表されるホウ酸エステルとを含むことを特徴とする。
　Ｌｉ１＋ａＮｉｂＭｎｃＣｏｄＭｅＯ２＋α・・・（１）
［但し、式（１）中、Ｍは、Ｍｇ、Ａｌ、Ｔｉ、Ｚｒ、Ｍｏ及びＮｂからなる群より選択される少なくとも１種の元素であり、ａ、ｂ、ｃ、ｄ、ｅ及びαは、－０．１≦ａ≦０．２、０．７＜ｂ≦０．９、０≦ｃ＜０．３、０≦ｄ＜０．３、０≦ｅ≦０．２５、ｂ＋ｃ＋ｄ＋ｅ＝１、及び、－０．２≦α≦０．２、を満たす数である。］
　（ＢＯ）３（ＯＲ）３・・・（２）
［但し、式（２）中、Ｒは、炭素数１以上の有機基である。］ In order to solve the above problems, a positive electrode material for a lithium secondary battery according to the present invention includes a positive electrode active material represented by the following formula (1) and a borate ester represented by the following formula (2). It is characterized by.
Li 1 + a Ni b Mn c Co d M e O 2 + α ··· (1)
[In the formula (1), M is at least one element selected from the group consisting of Mg, Al, Ti, Zr, Mo and Nb, and a, b, c, d, e and α are , −0.1 ≦ a ≦ 0.2, 0.7 <b ≦ 0.9, 0 ≦ c <0.3, 0 ≦ d <0.3, 0 ≦ e ≦ 0.25, b + c + d + e = 1, And a number satisfying −0.2 ≦ α ≦ 0.2. ]
(BO) 3 (OR) 3 (2)
[However, in Formula (2), R is an organic group having 1 or more carbon atoms. ]
　また、本発明に係るリチウム二次電池用正極は、前記のリチウム二次電池用正極材料を含んでなる。 The positive electrode for a lithium secondary battery according to the present invention comprises the positive electrode material for a lithium secondary battery.
　また、本発明に係るリチウム二次電池は、正極と、負極と、電解質と、を備えるリチウム二次電池であって、前記正極は、前記のリチウム二次電池用正極材料を含むことを特徴とする。 The lithium secondary battery according to the present invention is a lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes the positive electrode material for a lithium secondary battery. To do.
　本発明によれば、正極合剤の変性を抑制してリチウム二次電池の正極を製造することが可能なリチウム二次電池用正極材料、それを用いたリチウム二次電池用正極及びリチウム二次電池を提供することができる。 ADVANTAGE OF THE INVENTION According to this invention, the positive electrode material for lithium secondary batteries which can suppress the modification | denaturation of a positive electrode mixture, and can manufacture the positive electrode of a lithium secondary battery, the positive electrode for lithium secondary batteries using the same, and a lithium secondary A battery can be provided.
本発明の一実施形態に係るリチウム二次電池を模式的に示す断面図である。It is sectional drawing which shows typically the lithium secondary battery which concerns on one Embodiment of this invention.
　以下、本発明の一実施形態に係るリチウム二次電池用正極材料（以下、単に正極材料と言うことがある。）、それを用いたリチウム二次電池用正極及びリチウム二次電池について詳細に説明する。 Hereinafter, a positive electrode material for a lithium secondary battery according to an embodiment of the present invention (hereinafter, simply referred to as a positive electrode material), a positive electrode for a lithium secondary battery and a lithium secondary battery using the same will be described in detail. To do.
　本実施形態に係る正極材料は、リチウム二次電池の正極の製造に用いられる材料であって、粉末状の正極活物質を含んで構成される。本実施形態に係る正極材料は、具体的には、空間群Ｒ－３ｍに帰属される層状岩塩型の結晶構造（以下、層状構造ということがある。）を有するリチウム複合化合物（正極活物質）と、ボロキシン環構造を有するホウ酸エステルとを含んでなる。この正極材料は、リチウム二次電池の正極の製造において用いられる正極合剤の材料となり、正極活物質等の粒子を結着させる結着剤や、導電性を補うために添加される導電材と共に、分散媒中で混和されて正極合剤とされる。 The positive electrode material according to the present embodiment is a material used for manufacturing a positive electrode of a lithium secondary battery, and includes a powdered positive electrode active material. Specifically, the positive electrode material according to the present embodiment is a lithium composite compound (positive electrode active material) having a layered rock salt type crystal structure (hereinafter sometimes referred to as a layered structure) belonging to the space group R-3m. And a borate ester having a boroxine ring structure. This positive electrode material becomes a material for a positive electrode mixture used in the manufacture of a positive electrode for a lithium secondary battery, together with a binder for binding particles such as a positive electrode active material and a conductive material added to supplement conductivity. And mixed in a dispersion medium to form a positive electrode mixture.
　正極活物質としてのリチウム複合化合物は、次の式（１）：
　Ｌｉ１＋ａＮｉｂＭｎｃＣｏｄＭｅＯ２＋α・・・（１）
［但し、式（１）中、Ｍは、Ｍｇ、Ａｌ、Ｔｉ、Ｚｒ、Ｍｏ及びＮｂからなる群より選択される少なくとも１種の元素であり、ａ、ｂ、ｃ、ｄ、ｅ及びαは、－０．１≦ａ≦０．２、０．７＜ｂ≦０．９、０≦ｃ＜０．３、０≦ｄ＜０．３、０≦ｅ≦０．２５、ｂ＋ｃ＋ｄ＋ｅ＝１、及び、－０．２≦α≦０．２、を満たす数である。］で表される。 The lithium composite compound as the positive electrode active material has the following formula (1):
Li 1 + a Ni b Mn c Co d M e O 2 + α ··· (1)
[In the formula (1), M is at least one element selected from the group consisting of Mg, Al, Ti, Zr, Mo and Nb, and a, b, c, d, e and α are , −0.1 ≦ a ≦ 0.2, 0.7 <b ≦ 0.9, 0 ≦ c <0.3, 0 ≦ d <0.3, 0 ≦ e ≦ 0.25, b + c + d + e = 1, And a number satisfying −0.2 ≦ α ≦ 0.2. ].
　以下、前記式（１）におけるａ、ｂ、ｃ、ｄ、ｅ及びαの規定範囲について説明する。 Hereinafter, the prescribed ranges of a, b, c, d, e, and α in the formula (1) will be described.
　前記式におけるａは、－０．１以上かつ０．２以下とする。ａは、一般式；ＬｉＭ´Ｏ２で表される正極活物質の量論比、すなわちＬｉ：Ｍ´：Ｏ＝１：１：２からのＬｉの過不足量を表している。ここで、Ｍ´は、前記式（１）におけるＬｉ以外の金属元素を表す。リチウムが少ないほど、充電前の遷移金属の価数が高くなって、リチウムが脱離した時の遷移金属の価数変化の割合が低減され、正極活物質の充放電サイクル特性が向上する。その反面、リチウムが過剰であると、正極活物質の充放電容量は低下する。よって、ａを前記の範囲に規定することで、正極活物質の充放電サイクル特性を向上させ、かつ充放電容量を高くすることができる。より好ましいａの範囲は、－０．０５以上かつ０．１以下である。ａが－０．０５以上であれば、充放電に寄与するのに十分な量のリチウムが確保されるため、正極活物質の高容量化を図ることができる。また、ａが０．１以下であれば、遷移金属の価数変化による電荷補償が十分になされるので、高い充放電容量と、良好な充放電サイクル特性とを両立させることができる。 In the above formula, “a” is −0.1 or more and 0.2 or less. a represents the stoichiometric ratio of the positive electrode active material represented by the general formula; LiM′O 2 , that is, the excess and deficiency of Li from Li: M ′: O = 1: 1: 2. Here, M ′ represents a metal element other than Li in the formula (1). The less lithium, the higher the valence of the transition metal before charging, the lower the rate of transition metal valence change when lithium is desorbed, and the better the charge / discharge cycle characteristics of the positive electrode active material. On the other hand, when lithium is excessive, the charge / discharge capacity of the positive electrode active material is lowered. Therefore, by defining a in the above range, the charge / discharge cycle characteristics of the positive electrode active material can be improved and the charge / discharge capacity can be increased. A more preferable range of a is −0.05 or more and 0.1 or less. If a is −0.05 or more, a sufficient amount of lithium is ensured to contribute to charge and discharge, and thus the capacity of the positive electrode active material can be increased. Moreover, if a is 0.1 or less, charge compensation due to a change in the valence of the transition metal is sufficiently performed, so that both high charge / discharge capacity and good charge / discharge cycle characteristics can be achieved.
　前記式において、ｂは、０．７を超えかつ０．９以下とする。ニッケルが多いほど、充放電容量を高くするのに有利である。一方、ニッケルが過剰であると、正極活物質の熱的安定性が低下する虞がある。よって、ｂを前記の範囲に規定することで、正極活物質を安定的に高容量化することができる。より好ましいｂの範囲は、０．７５以上かつ０．８５以下である。ｂが０．７５以上であれば、充放電容量がより高くなる。 In the above formula, b is more than 0.7 and 0.9 or less. The more nickel, the more advantageous is to increase the charge / discharge capacity. On the other hand, if nickel is excessive, the thermal stability of the positive electrode active material may be reduced. Therefore, by defining b within the above range, the capacity of the positive electrode active material can be stably increased. A more preferable range of b is 0.75 or more and 0.85 or less. When b is 0.75 or more, the charge / discharge capacity is further increased.
　前記式において、ｃは、０以上かつ０．３未満とする。マンガンが添加されていると、充電によってリチウムが脱離しても層状構造が安定に維持されるようになる。一方、マンガンが過剰であると、ニッケル等の他の遷移金属の割合が低くなり、正極活物質の充放電容量が低下する。よって、ｃを前記の範囲に規定することで、充放電によってリチウムの挿入と脱離とが繰り返されたとしても、正極活物質の結晶構造を安定に維持することが可能になる。よって、高い充放電容量と共に、良好な充放電サイクル特性や、熱的安定性等を得ることができる。より好ましいｃの範囲は、０．１０以上かつ０．２５以下である。ｃが０．１０以上であれば、正極活物質の結晶構造がより安定化する。また、ｃが０．２５以下であれば、ニッケル等の他の遷移金属の割合が高くなるので、正極活物質の充放電容量が損なわれ難くなる。 In the above formula, c is 0 or more and less than 0.3. When manganese is added, the layered structure is stably maintained even when lithium is desorbed by charging. On the other hand, when manganese is excessive, the ratio of other transition metals, such as nickel, will become low, and the charge / discharge capacity of a positive electrode active material will fall. Therefore, by defining c within the above range, it is possible to stably maintain the crystal structure of the positive electrode active material even when lithium insertion and extraction are repeated by charging and discharging. Therefore, good charge / discharge cycle characteristics, thermal stability, and the like can be obtained together with a high charge / discharge capacity. A more preferable range of c is 0.10 or more and 0.25 or less. If c is 0.10 or more, the crystal structure of the positive electrode active material is further stabilized. Moreover, since the ratio of other transition metals, such as nickel, will become high if c is 0.25 or less, it becomes difficult to impair the charging / discharging capacity | capacitance of a positive electrode active material.
　前記式において、ｄは、０以上かつ０．３未満とする。コバルトが添加されていると、充放電容量が大きく損なわれること無く、充放電サイクル特性が向上する。一方、コバルトが過剰であると、原料費が高価となるので、正極活物質の工業的な生産において不利になる虞がある。よって、ｄを前記の範囲に規定することで、良好な生産性をもって、高い充放電容量と、良好な充放電サイクル特性とを両立させることができる。より好ましいｄの範囲は、０．１０以上かつ０．２５以下である。ｄが０．１０以上であれば、充放電容量や充放電サイクル特性がより向上する。また、ｄが０．２５以下であれば、原料費がより低廉となるので、正極活物質の生産性が良くなる。 In the above formula, d is 0 or more and less than 0.3. When cobalt is added, the charge / discharge cycle characteristics are improved without significantly impairing the charge / discharge capacity. On the other hand, when cobalt is excessive, the raw material cost becomes expensive, which may be disadvantageous in industrial production of the positive electrode active material. Therefore, by defining d within the above range, it is possible to achieve both high charge / discharge capacity and good charge / discharge cycle characteristics with good productivity. A more preferable range of d is 0.10 or more and 0.25 or less. When d is 0.10 or more, the charge / discharge capacity and the charge / discharge cycle characteristics are further improved. In addition, when d is 0.25 or less, the raw material cost is lower, and the productivity of the positive electrode active material is improved.
　前記式において、ｅは、０以上かつ０．２５以下とする。Ｍｇ、Ａｌ、Ｔｉ、Ｚｒ、Ｍｏ及びＮｂからなる群より選択される少なくとも１種の元素（Ｍ）が添加されていると、正極活物質の電気化学的活性を維持しながらも、結晶構造の安定性や、充放電サイクル特性をはじめとする電極性能を向上させることができる。一方、Ｍが過剰であると、ニッケル等の他の遷移金属の割合が低くなり、正極活物質の充放電容量が低下する。よって、ｅを前記の範囲に規定することで、高い充放電容量と、良好な電気化学的特性とを両立させることができる。 In the above formula, e is 0 or more and 0.25 or less. When at least one element (M) selected from the group consisting of Mg, Al, Ti, Zr, Mo and Nb is added, while maintaining the electrochemical activity of the positive electrode active material, Electrode performance including stability and charge / discharge cycle characteristics can be improved. On the other hand, when M is excessive, the ratio of other transition metals such as nickel is decreased, and the charge / discharge capacity of the positive electrode active material is decreased. Therefore, by defining e in the above range, both high charge / discharge capacity and good electrochemical characteristics can be achieved.
　前記式において、αは、－０．２以上かつ０．２以下とする。αは、化学式ＬｉＭ´Ｏ２で表される正極活物質の量論比からの酸素（Ｏ）の過不足量を表している。αが前記の範囲であれば、正極活物質の結晶構造の欠陥は少なく、良好な電気化学的特性が得られる。但し、αは、正極活物質に要求される性能によっては、層状構造をより安定的に維持する観点から、－０．１以上かつ０．１以下であることが好ましい。 In the above formula, α is set to −0.2 or more and 0.2 or less. α represents the excess or deficiency of oxygen (O) from the stoichiometric ratio of the positive electrode active material represented by the chemical formula LiM′O 2 . When α is in the above range, there are few defects in the crystal structure of the positive electrode active material, and good electrochemical characteristics can be obtained. However, α is preferably −0.1 or more and 0.1 or less from the viewpoint of more stably maintaining the layered structure depending on the performance required for the positive electrode active material.
　本実施形態に係る正極活物質は、個々の粒子が分離したリチウム複合化合物の一次粒子を含んでいてもよく、複数の一次粒子が造粒、焼結等によって結合した二次粒子を含んでいてもよい。二次粒子は、乾式造粒及び湿式造粒のうちのいずれによって造粒されたものであってもよい。造粒手段としては、例えば、スプレードライヤや、転動流動層装置等の造粒機を利用することができる。 The positive electrode active material according to the present embodiment may include primary particles of a lithium composite compound in which individual particles are separated, and include secondary particles in which a plurality of primary particles are bonded by granulation, sintering, or the like. Also good. Secondary particles may be granulated by either dry granulation or wet granulation. As the granulating means, for example, a granulator such as a spray dryer or a rolling fluidized bed apparatus can be used.
　正極活物質の一次粒子の平均粒径は、０．１μｍ以上かつ２μｍ以下であることが好ましい。平均粒径がこの範囲であると、正極における正極活物質の充填性が良くなるため、エネルギ密度が高い正極を製造することができる。また、粉末状の正極活物質の飛散や凝集等が低減されるので、取り扱い性も良くなる。正極活物質の二次粒子の平均粒径は、例えば、３μｍ以上かつ５０μｍ以下とすることができる。 The average particle diameter of the primary particles of the positive electrode active material is preferably 0.1 μm or more and 2 μm or less. When the average particle size is within this range, the positive electrode active material filling property of the positive electrode is improved, so that a positive electrode having a high energy density can be manufactured. In addition, since the scattering and aggregation of the powdered positive electrode active material are reduced, the handleability is improved. The average particle diameter of the secondary particles of the positive electrode active material can be, for example, 3 μm or more and 50 μm or less.
　正極活物質のＢＥＴ比表面積は、０．２ｍ２／ｇ以上かつ２．０ｍ２／ｇ以下であることが好ましい。一次粒子や二次粒子の集合からなる粉末状の正極活物質のＢＥＴ比表面積がこの範囲であると、正極における正極活物質の充填性が改善し、エネルギ密度がより高い正極を製造することが可能になる。なお、ＢＥＴ比表面積は、例えば、自動比表面積測定装置を用いて測定することができる。 The BET specific surface area of the positive electrode active material is preferably 0.2 m 2 / g or more and 2.0 m 2 / g or less. When the BET specific surface area of the powdered positive electrode active material composed of a collection of primary particles and secondary particles is within this range, the positive electrode active material filling property in the positive electrode is improved, and a positive electrode with higher energy density can be produced. It becomes possible. The BET specific surface area can be measured using, for example, an automatic specific surface area measuring device.
　正極活物質の結晶構造は、例えば、Ｘ線回折法（X-ray diffraction；ＸＲＤ）等によって確認することができる。また、正極活物質の組成は、高周波誘導結合プラズマ（Inductively Coupled Plasma；ＩＣＰ）発光分光分析、原子吸光分析（Atomic Absorption Spectrometry；ＡＡＳ）等によって確認することができる。 The crystal structure of the positive electrode active material can be confirmed by, for example, X-ray diffraction (XRD). The composition of the positive electrode active material can be confirmed by high frequency inductively coupled plasma (ICP) emission spectroscopic analysis, atomic absorption spectrometry (AAS), or the like.
　正極活物質の粒子破壊強度は、５０ＭＰａ以上かつ１００ＭＰａ以下であることが好ましい。正極活物質の一粒子当たりの粒子破壊強度がこの範囲であると、電極を作製する過程で正極活物質の粒子が破壊され難くなり、正極集電体に正極活物質を含む正極合剤スラリーを塗工して正極合剤層を形成するとき、剥がれ等の塗工不良が発生し難くなる。正極活物質の粒子破壊強度は、例えば、微小圧縮試験機を用いて測定することができる。 The particle fracture strength of the positive electrode active material is preferably 50 MPa or more and 100 MPa or less. When the particle breaking strength per particle of the positive electrode active material is within this range, the positive electrode active material particles are hardly broken in the process of producing the electrode, and the positive electrode mixture slurry containing the positive electrode active material in the positive electrode current collector When the positive electrode mixture layer is formed by coating, coating defects such as peeling are less likely to occur. The particle breaking strength of the positive electrode active material can be measured using, for example, a micro compression tester.
　本実施形態に係る正極活物質は、リチウムを含む化合物と、正極活物質を組成するＬｉ以外の金属元素を含む化合物とを原料として、主に、混合工程と、焼成工程とを経て合成することができる。 The positive electrode active material according to the present embodiment is synthesized mainly through a mixing step and a firing step using a compound containing lithium and a compound containing a metal element other than Li constituting the positive electrode active material as raw materials. Can do.
　混合工程では、リチウムを含む化合物と、正極活物質を組成するＬｉ以外の金属元素を含む化合物とを混合する。リチウムを含む化合物としては、炭酸リチウム、酢酸リチウム、硝酸リチウム、水酸化リチウム、塩化リチウム、硫酸リチウム等が挙げられる。これらの中でも、炭酸リチウムが特に好ましい。炭酸リチウムは、供給が安定していて調達性が良く、低廉である。また、融点が高いので、製造装置へのダメージが少なく、工業利用性及び実用性に優れている。 In the mixing step, a compound containing lithium and a compound containing a metal element other than Li constituting the positive electrode active material are mixed. Examples of the compound containing lithium include lithium carbonate, lithium acetate, lithium nitrate, lithium hydroxide, lithium chloride, and lithium sulfate. Among these, lithium carbonate is particularly preferable. Lithium carbonate is stable in supply, has good procurement, and is inexpensive. Moreover, since melting | fusing point is high, there is little damage to a manufacturing apparatus and it is excellent in industrial utilization and practicality.
　正極活物質を組成するＬｉ以外の金属元素を含む化合物としては、ニッケルを含む化合物や、マンガンを含む化合物や、コバルトを含む化合物や、Ｍで表される元素を含む化合物を混合する。 As the compound containing a metal element other than Li constituting the positive electrode active material, a compound containing nickel, a compound containing manganese, a compound containing cobalt, or a compound containing an element represented by M is mixed.
　ニッケルを含む化合物や、マンガンを含む化合物や、コバルトを含む化合物としては、例えば、酸化物、水酸化物、炭酸塩、酢酸塩等を用いることができる。これらの中でも、特に、酸化物、水酸化物、又は、炭酸塩を用いることが好ましい。また、Ｍで表される元素を含む化合物としては、例えば、炭酸塩、酸化物、水酸化物、酢酸塩、硝酸塩等を用いることができる。これらの中でも、特に、炭酸塩、酸化物、又は、水酸化物を用いることが好ましい。 As the compound containing nickel, the compound containing manganese, or the compound containing cobalt, for example, oxides, hydroxides, carbonates, acetates, and the like can be used. Among these, it is particularly preferable to use an oxide, a hydroxide, or a carbonate. Moreover, as a compound containing the element represented by M, carbonate, an oxide, a hydroxide, acetate, nitrate etc. can be used, for example. Among these, it is particularly preferable to use carbonate, oxide, or hydroxide.
　混合工程では、具体的には、前記式に対応する所定の元素組成比で原料の各化合物を秤量し、各化合物を粉砕及び混合して、各化合物が混和した粉末状の混合物を調製する。化合物を粉砕する粉砕機としては、例えば、ボールミル、ジェットミル、サンドミル等の一般的な精密粉砕機を用いることができる。 In the mixing step, specifically, each compound as a raw material is weighed at a predetermined elemental composition ratio corresponding to the above formula, and each compound is pulverized and mixed to prepare a powdery mixture in which each compound is mixed. As a pulverizer for pulverizing the compound, for example, a general precision pulverizer such as a ball mill, a jet mill, or a sand mill can be used.
　原料の化合物の粉砕は、湿式粉砕とすることが好ましく、工業的な観点からは、水を分散媒とした湿式粉砕が特に好ましい。湿式粉砕して得られる固液混合物は、例えば、乾燥機を用いて乾燥させてよい。乾燥機としては、例えば、噴霧乾燥機、流動床乾燥機、エバポレータ等を使用することができる。 The raw material compound is preferably pulverized by wet pulverization, and from an industrial viewpoint, wet pulverization using water as a dispersion medium is particularly preferable. The solid-liquid mixture obtained by wet pulverization may be dried using, for example, a dryer. As the dryer, for example, a spray dryer, a fluidized bed dryer, an evaporator or the like can be used.
　焼成工程では、混合工程で得られた混合物を焼成して層状構造を有するリチウム複合化合物を得る。焼成工程においては、適宜の熱処理装置を用いて熱処理を実施することができる。具体的には、例えば、ローラーハースキルン、トンネル炉、プッシャー炉、ロータリーキルン、バッチ炉等を用いることができる。 In the firing step, the mixture obtained in the mixing step is fired to obtain a lithium composite compound having a layered structure. In the firing step, heat treatment can be performed using an appropriate heat treatment apparatus. Specifically, for example, a roller hearth kiln, a tunnel furnace, a pusher furnace, a rotary kiln, a batch furnace or the like can be used.
　焼成工程は、第１前駆体を形成する第１熱処理工程と、第２前駆体を形成する第２熱処理工程と、仕上の熱処理である第３熱処理工程と、を有することが好ましい。一般式：ＬｉＮｉＯ２で表される正極活物質は、一般式：ＬｉＣｏＯ２で表される正極活物質よりも高容量である反面、ＬｉＣｏＯ２で表される正極活物質よりも、焼成後にアルカリ成分が残留し易い。これらの各熱処理工程を順に実施する方法によれば、アルカリ成分の残留を低減させることができる。 The firing step preferably includes a first heat treatment step for forming the first precursor, a second heat treatment step for forming the second precursor, and a third heat treatment step which is a finish heat treatment. The positive electrode active material represented by the general formula: LiNiO 2 has a higher capacity than the positive electrode active material represented by the general formula: LiCoO 2 , but is more alkaline after firing than the positive electrode active material represented by LiCoO 2. Tends to remain. According to the method of sequentially performing each of these heat treatment steps, residual alkali components can be reduced.
　第１熱処理工程では、混合工程で得られた混合物を２００℃以上かつ４００℃以下の熱処理温度で、０．５時間以上かつ５時間以下にわたって熱処理することが好ましい。この熱処理によって第１前駆体が得られる。第１熱処理工程は、混合工程で得られた混合物から、正極活物質の合成反応を妨げる水分等のような気化性が高い成分を除去することを主な目的として行われる。この工程では、炭酸リチウム等の原料の熱分解や不純物の燃焼等に伴って発生した炭酸ガス等が、水分と共に混合物から排除される。第１熱処理工程において、熱処理温度が２００℃未満であると、不純物の燃焼反応や原料の熱分解反応が不十分となる虞がある。一方、熱処理温度が４００℃を超えると、この工程でリチウム複合化合物の結晶化が進み、水分、不純物等を含むガスの存在下で欠陥が多い結晶構造が形成される虞がある。これに対して、前記の熱処理温度であれば、水分、不純物等が十分に除去され、以降の焼成に適した第１前駆体を得ることができる。 In the first heat treatment step, the mixture obtained in the mixing step is preferably heat treated at a heat treatment temperature of 200 ° C. or more and 400 ° C. or less for 0.5 hours or more and 5 hours or less. A first precursor is obtained by this heat treatment. The first heat treatment step is performed mainly for removing a highly vaporizable component such as moisture that hinders the synthesis reaction of the positive electrode active material from the mixture obtained in the mixing step. In this step, carbon dioxide gas generated due to thermal decomposition of raw materials such as lithium carbonate or combustion of impurities is excluded from the mixture together with moisture. In the first heat treatment step, if the heat treatment temperature is less than 200 ° C., the combustion reaction of impurities and the thermal decomposition reaction of raw materials may be insufficient. On the other hand, when the heat treatment temperature exceeds 400 ° C., crystallization of the lithium composite compound proceeds in this step, and a crystal structure with many defects may be formed in the presence of a gas containing moisture, impurities, and the like. On the other hand, if it is the said heat processing temperature, a water | moisture content, an impurity, etc. will fully be removed and the 1st precursor suitable for subsequent baking can be obtained.
　第１熱処理工程における熱処理温度は、２５０℃以上かつ４００℃以下であることが好ましく、２５０℃以上かつ３８０℃以下であることがより好ましい。熱処理温度がこの範囲内であれば、水分、不純物等を効率的に除去しつつ、この工程における結晶化の進行については抑制することができる。なお、第１熱処理工程における熱処理時間は、例えば、熱処理温度、混合物に含まれている水分、不純物等の量、水分、不純物等の除去目標等に応じて、適宜の時間とすることができる。 The heat treatment temperature in the first heat treatment step is preferably 250 ° C. or more and 400 ° C. or less, and more preferably 250 ° C. or more and 380 ° C. or less. If the heat treatment temperature is within this range, the progress of crystallization in this step can be suppressed while efficiently removing moisture, impurities and the like. The heat treatment time in the first heat treatment step can be set to an appropriate time according to, for example, the heat treatment temperature, the amount of moisture and impurities contained in the mixture, the removal target of moisture and impurities, and the like.
　第１熱処理工程は、酸化性ガス雰囲気下で行ってもよいし、非酸化性ガス雰囲気下で行ってもよいし、減圧雰囲気下で行ってもよい。酸化性ガス雰囲気としては、酸素ガス雰囲気及び大気雰囲気のいずれであってもよい。大気雰囲気であれば、熱処理装置の構成を簡略化し、正極活物質の製造コストを削減することができる。また、減圧雰囲気としては、例えば、大気圧以下等のような適宜の真空度の減圧条件であってよい。 The first heat treatment step may be performed in an oxidizing gas atmosphere, a non-oxidizing gas atmosphere, or a reduced pressure atmosphere. The oxidizing gas atmosphere may be either an oxygen gas atmosphere or an air atmosphere. If it is an air atmosphere, the structure of a heat processing apparatus can be simplified and the manufacturing cost of a positive electrode active material can be reduced. Further, the reduced-pressure atmosphere may be a reduced-pressure condition with an appropriate degree of vacuum such as an atmospheric pressure or lower.
　第１熱処理工程は、雰囲気ガスの気流下、又は、ポンプによる排気下で行うことが好ましい。このような雰囲気下で熱処理を行うことにより、混合物から発生するガスを効率的に排除することができる。雰囲気ガスの気流やポンプによる排気の流量は、混合物から発生するガスの体積よりも多くすることが好ましい。混合物から発生するガスの体積は、例えば、混合物に含まれる原料の質量と、その原料から脱離すると見込まれる成分の比率とに基いて、発生するガスの物質量を見積もり、設定している温度条件について算出すればよい。 It is preferable to perform the first heat treatment step under an atmosphere gas flow or exhaust with a pump. By performing the heat treatment in such an atmosphere, the gas generated from the mixture can be efficiently eliminated. It is preferable that the atmospheric gas flow or the flow rate of the exhaust gas by the pump be larger than the volume of gas generated from the mixture. The volume of gas generated from the mixture is, for example, a temperature set by estimating the amount of gas generated based on the mass of the raw material contained in the mixture and the ratio of components expected to be desorbed from the raw material. What is necessary is just to calculate about conditions.
　第２熱処理工程では、第１熱処理工程で得た第１前駆体を４５０℃以上かつ９００℃以下の熱処理温度で、０．１時間以上かつ５０時間以下にわたって熱処理することが好ましい。この熱処理によって第２前駆体が得られる。第２熱処理工程は、第１前駆体中のニッケルを２価から３価へと酸化し、層状構造を有するリチウム複合化合物を結晶化させることを主な目的として行われる。第２熱処理工程において、熱処理温度が４５０℃未満であると、固相反応の反応速度が遅くなって炭酸リチウム等の原料が過剰に残留する虞がある。一方、熱処理温度が９００℃を超えると、この工程でリチウム複合化合物の粒成長が過剰に進行し、高容量の正極活物質が得られなくなる虞が高い。これに対して、前記の熱処理温度であれば、固相反応が全体で進んでいながら、粗大な結晶粒が少ない第２前駆体を得ることができる。 In the second heat treatment step, the first precursor obtained in the first heat treatment step is preferably heat treated at a heat treatment temperature of 450 ° C. or higher and 900 ° C. or lower for 0.1 hour or more and 50 hours or less. A second precursor is obtained by this heat treatment. The second heat treatment step is performed mainly for oxidizing nickel in the first precursor from divalent to trivalent to crystallize a lithium composite compound having a layered structure. In the second heat treatment step, if the heat treatment temperature is lower than 450 ° C., the reaction rate of the solid phase reaction is slowed, and there is a possibility that the raw materials such as lithium carbonate remain excessively. On the other hand, when the heat treatment temperature exceeds 900 ° C., there is a high possibility that the grain growth of the lithium composite compound proceeds excessively in this step and a high-capacity positive electrode active material cannot be obtained. On the other hand, if it is the said heat processing temperature, the 2nd precursor with few coarse crystal grains can be obtained, while solid-phase reaction is progressing on the whole.
　第２熱処理工程における熱処理温度は、６００℃以上とすることがより好ましい。６００℃以上であれば、固相反応の反応効率がより向上する。また、第２熱処理工程における熱処理温度は、８００℃以下とすることがより好ましい。８００℃以下であれば、結晶粒がより粗大化し難くなる。 The heat treatment temperature in the second heat treatment step is more preferably 600 ° C. or higher. If it is 600 degreeC or more, the reaction efficiency of a solid-phase reaction will improve more. The heat treatment temperature in the second heat treatment step is more preferably 800 ° C. or lower. If it is 800 degrees C or less, it will become difficult to coarsen a crystal grain.
　第２熱処理工程における熱処理時間は、０．１時間以上かつ５時間以下とすることがより好ましい。熱処理時間を５時間以下とすると、正極活物質の製造に要する時間が短縮され、生産性を向上させることができる。 The heat treatment time in the second heat treatment step is more preferably 0.1 hour or more and 5 hours or less. When the heat treatment time is 5 hours or less, the time required for producing the positive electrode active material is shortened, and the productivity can be improved.
　ニッケルの割合が７０原子％を超える正極活物質に高容量を発現させるためには、特に、ニッケルの価数を２価から３価へ十分に酸化させることが肝要である。２価のニッケルは、層状構造を有するＬｉＭ´Ｏ２において容易にリチウムサイトに置換してしまい、正極活物質の容量を低下させる原因となるからである。そのため、第２熱処理工程では、第１前駆体を酸素が十分に給気される酸化性雰囲気下で熱処理し、ニッケルの価数を確実に２価から３価へ変化させることが好ましい。 In order to develop a high capacity in the positive electrode active material in which the nickel ratio exceeds 70 atomic%, it is particularly important to sufficiently oxidize the valence of nickel from divalent to trivalent. This is because divalent nickel easily substitutes for lithium sites in LiM′O 2 having a layered structure, and causes a decrease in the capacity of the positive electrode active material. Therefore, in the second heat treatment step, it is preferable to heat-treat the first precursor in an oxidizing atmosphere in which oxygen is sufficiently supplied, and to surely change the valence of nickel from divalent to trivalent.
　第２熱処理工程は、具体的には、酸素濃度が９０％以上の酸化性雰囲気とすることが好ましく、酸素濃度が９５％以上の酸化性雰囲気とすることがより好ましく、酸素濃度が１００％の酸化性雰囲気とすることがさらに好ましい。また、第２熱処理工程は、酸化性ガスによる気流下で行うことが好ましい。酸素濃度が高い酸化性ガスの気流下で熱処理を行うと、ニッケルを確実に酸化させることができるし、原料の熱分解により生じるガスを確実に排除することができる。 Specifically, the second heat treatment step is preferably an oxidizing atmosphere having an oxygen concentration of 90% or more, more preferably an oxidizing atmosphere having an oxygen concentration of 95% or more, and an oxygen concentration of 100%. It is more preferable to use an oxidizing atmosphere. Moreover, it is preferable to perform a 2nd heat treatment process under the airflow by oxidizing gas. When heat treatment is performed in a stream of oxidizing gas having a high oxygen concentration, nickel can be reliably oxidized, and gas generated by thermal decomposition of the raw material can be reliably excluded.
　第３熱処理工程では、第２熱処理工程で得た第２前駆体を７００℃以上かつ９００℃以下の熱処理温度で熱処理することが好ましい。この熱処理によって層状構造を有するリチウム複合化合物が得られる。第３熱処理工程は、第２前駆体中のニッケルを２価から３価へと十分に酸化させると共に、層状構造を有するリチウム複合化合物の結晶粒を成長させることを主な目的として行われる。すなわち、この工程は、第２前駆体中のニッケルの酸化反応とリチウム複合化合物の結晶粒の粒成長を行う熱処理工程である。第３熱処理工程において、熱処理温度が７００℃未満であると、リチウム複合化合物の粒成長が速やかに進まない虞がある。一方、熱処理温度が９００℃を超えると、リチウム複合化合物の粒成長が過剰に進行したり、層状構造が分解して２価のニッケルが生成されたりして、高容量の正極活物質が得られなくなる虞が高い。これに対して、前記の熱処理温度であれば、高容量のリチウム複合化合物を効率的に得ることができる。 In the third heat treatment step, the second precursor obtained in the second heat treatment step is preferably heat treated at a heat treatment temperature of 700 ° C. or higher and 900 ° C. or lower. By this heat treatment, a lithium composite compound having a layered structure is obtained. The third heat treatment step is carried out mainly for the purpose of sufficiently oxidizing nickel in the second precursor from divalent to trivalent and growing crystal grains of a lithium composite compound having a layered structure. That is, this step is a heat treatment step for performing an oxidation reaction of nickel in the second precursor and grain growth of the lithium composite compound crystal grains. In the third heat treatment step, if the heat treatment temperature is less than 700 ° C., the grain growth of the lithium composite compound may not proceed promptly. On the other hand, when the heat treatment temperature exceeds 900 ° C., the grain growth of the lithium composite compound proceeds excessively, or the layered structure is decomposed to produce divalent nickel, thereby obtaining a high capacity positive electrode active material. There is a high risk of disappearing. On the other hand, if it is the said heat processing temperature, a high capacity | capacitance lithium complex compound can be obtained efficiently.
　第３熱処理工程は、熱処理時間が、０．１時間以上かつ５０時間以下であることが好ましく、０．５時間以上かつ５時間以下であることがより好ましい。第３熱処理工程において、酸素分圧が低いと、ニッケルの酸化反応を促進させるために熱が必要となる。したがって、第３熱処理工程において第２前駆体への酸素供給が不十分である場合、熱処理温度を上昇させる必要が生じる。ところが、熱処理温度を上昇させると層状構造の分解が不可避となるため、高容量のリチウム複合化合物を得ることができなくなる。これに対して、熱処理時間が０．１時間以上であれば、第２前駆体を酸素と十分に反応させることができる。 In the third heat treatment step, the heat treatment time is preferably 0.1 hours or more and 50 hours or less, more preferably 0.5 hours or more and 5 hours or less. In the third heat treatment step, if the oxygen partial pressure is low, heat is required to promote the oxidation reaction of nickel. Therefore, when the oxygen supply to the second precursor is insufficient in the third heat treatment step, it is necessary to increase the heat treatment temperature. However, when the heat treatment temperature is raised, decomposition of the layered structure is unavoidable, so that a high-capacity lithium composite compound cannot be obtained. On the other hand, if the heat treatment time is 0.1 hour or longer, the second precursor can be sufficiently reacted with oxygen.
　第３熱処理工程は、具体的には、酸素濃度が９０％以上の酸化性雰囲気とすることが好ましく、酸素濃度が９５％以上の酸化性雰囲気とすることがより好ましく、酸素濃度が１００％の酸化性雰囲気とすることがさらに好ましい。また、第３熱処理工程は、酸化性ガスによる気流下で行うことが好ましい。酸素濃度が高い酸化性ガスの気流下で熱処理を行うと、雰囲気中の酸素分圧が低下し難くなり、熱処理温度を上昇させなくともニッケルを確実に酸化させることができる。 Specifically, the third heat treatment step is preferably an oxidizing atmosphere having an oxygen concentration of 90% or more, more preferably an oxidizing atmosphere having an oxygen concentration of 95% or more, and an oxygen concentration of 100%. It is more preferable to use an oxidizing atmosphere. Moreover, it is preferable to perform a 3rd heat treatment process under the airflow by oxidizing gas. When heat treatment is performed in a stream of oxidizing gas having a high oxygen concentration, the oxygen partial pressure in the atmosphere is difficult to decrease, and nickel can be reliably oxidized without increasing the heat treatment temperature.
　以上の混合工程と、焼成工程とを経て合成される正極活物質は、前記式（１）におけるニッケル（Ｎｉ）の係数ｂが、０．７を超えかつ０．９以下であり、ニッケルの含有率が高いため、焼成後に未反応のアルカリ成分が残留していることがある。残留しているアルカリ成分は、正極合剤を調製するときに結着剤として用いるＰＶＤＦ等の有機バインダと反応し、有機バインダの高分子化反応により正極合剤のゲル化を生じ、ペースト状の正極合剤を増粘させることがある。また、アルカリ成分とＰＶＤＦ等の有機バインダとの反応により、有機バインダの分子が変性し、ＰＶＤＦ等の脱フッ素反応を生じる。このように結着剤が変性する結果、結着剤による正極活物質、導電材、集電体等の結着強度が低下し、電極を安定且つ実質的に均一に作製することが困難になる。このような課題に対し、本実施形態に係る正極材料では、ボロキシン環構造を有するホウ酸エステルと正極活物質とを共存させることにより正極合剤の変性を抑制するものとした。 The positive electrode active material synthesized through the above mixing step and the firing step has a nickel (Ni) coefficient b in the formula (1) of more than 0.7 and not more than 0.9, and the inclusion of nickel Due to the high rate, unreacted alkali components may remain after firing. The remaining alkali component reacts with an organic binder such as PVDF used as a binder when preparing the positive electrode mixture, and gelation of the positive electrode mixture is caused by the polymerization reaction of the organic binder. The positive electrode mixture may be thickened. In addition, due to the reaction between the alkali component and an organic binder such as PVDF, the molecule of the organic binder is modified to cause a defluorination reaction such as PVDF. As a result of the modification of the binder as described above, the binding strength of the positive electrode active material, the conductive material, the current collector and the like due to the binder is lowered, and it becomes difficult to stably and substantially uniformly produce the electrode. . For such a problem, in the positive electrode material according to the present embodiment, the modification of the positive electrode mixture is suppressed by allowing a borate ester having a boroxine ring structure and the positive electrode active material to coexist.
　ボロキシン環構造を有するホウ酸エステルは、具体的には、次の式（２）：
　（ＢＯ）３（ＯＲ）３・・・（２）
［但し、式（２）中、Ｒは、炭素数１以上の有機基である。］で表される。 Specifically, the borate ester having a boroxine ring structure is represented by the following formula (2):
(BO) 3 (OR) 3 (2)
[However, in Formula (2), R is an organic group having 1 or more carbon atoms. ].
　前記式（２）で表されるホウ酸エステルは、ボロキシンの水素が置換された分子構造を持つボロキシン誘導体である。前記式（２）における有機基（Ｒ）は、直鎖状及び分枝状のいずれであってもよいし、環構造や任意の置換基を有していてもよい。置換基は、フッ素原子、塩素原子、臭素原子等のハロゲン原子であってもよいし、窒素原子、硫黄原子等を有する基であってもよい。有機基（Ｒ）の炭素数は、上限について特に制限されないが、合成が容易となる点から、６以下であることが好ましい。 The borate ester represented by the formula (2) is a boroxine derivative having a molecular structure in which hydrogen of boroxine is substituted. The organic group (R) in the formula (2) may be linear or branched, and may have a ring structure or an arbitrary substituent. The substituent may be a halogen atom such as a fluorine atom, a chlorine atom or a bromine atom, or a group having a nitrogen atom, a sulfur atom or the like. The upper limit of the carbon number of the organic group (R) is not particularly limited, but is preferably 6 or less from the viewpoint of easy synthesis.
　前記式（２）における有機基（Ｒ）としては、アルキル基又はシクロアルキル基が好ましい。アルキル基は、鎖状アルキル基及び分枝状アルキル基のいずれであってもよい。鎖状アルキル基の具体例としては、メチル基、エチル基、ｎ－プロピル基、ｎ－ブチル基、ｎ－ペンチル基、ｎ－ヘキシル基、ｎ－ヘプチル基、ｎ－オクチル基、ｎ－ノニル基、ｎ－デシル基等が挙げられる。分枝状アルキル基の具体例としては、イソプロピル基、１－メチル－プロピル基、１－エチル－プロピル基、２－メチル－プロピル基、１－メチル－ブチル基、１－エチル－ブチル基、２－メチル－ブチル基、２－エチル－ブチル基、３－メチル－ブチル基、１－メチル－ペンチル基、１－エチル－ペンチル基、１－プロピル－ペンチル基、２－メチル－ペンチル基、２－エチル－ペンチル基、２－プロピル－ペンチル基、３－メチル－ペンチル基、３－エチル－ペンチル基、４－メチル－ペンチル基、１－メチル－ヘキシル基、１－エチル－ヘキシル基、１－プロピル－ヘキシル基、１－ブチル－ヘキシル基、１－ペンチル－ヘキシル基、２－メチル－ヘキシル基、２－エチル－ヘキシル基、２－プロピル－ヘキシル基、２－ブチル－ヘキシル基、３－メチル－ヘキシル基、３－エチル－ヘキシル基、３－プロピル－ヘキシル基、４－メチル－ヘキシル基、４－エチル－ヘキシル基、５－メチル－ヘキシル基等が挙げられる。 The organic group (R) in the formula (2) is preferably an alkyl group or a cycloalkyl group. The alkyl group may be a chain alkyl group or a branched alkyl group. Specific examples of the chain alkyl group include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group and n-nonyl group. And n-decyl group. Specific examples of the branched alkyl group include isopropyl group, 1-methyl-propyl group, 1-ethyl-propyl group, 2-methyl-propyl group, 1-methyl-butyl group, 1-ethyl-butyl group, 2 -Methyl-butyl group, 2-ethyl-butyl group, 3-methyl-butyl group, 1-methyl-pentyl group, 1-ethyl-pentyl group, 1-propyl-pentyl group, 2-methyl-pentyl group, 2- Ethyl-pentyl group, 2-propyl-pentyl group, 3-methyl-pentyl group, 3-ethyl-pentyl group, 4-methyl-pentyl group, 1-methyl-hexyl group, 1-ethyl-hexyl group, 1-propyl -Hexyl, 1-butyl-hexyl, 1-pentyl-hexyl, 2-methyl-hexyl, 2-ethyl-hexyl, 2-propyl-hexyl, 2-butyl-hexyl Group, 3-methyl - hexyl group, 3-ethyl - hexyl group, 3-propyl - hexyl group, 4-methyl - hexyl group, 4-ethyl - hexyl, 5-methyl - hexyl.
　前記式（２）で表されるホウ酸エステルは、特に、トリイソプロポキシボロキシン（（ＢＯ）３（Ｏ（ＣＨ）（ＣＨ３）２）３）、トリメトキシボロキシン（（ＢＯ）３（ＯＣＨ３）３）、及び、トリシクロヘキソキシボロキシン（（ＢＯ）３（Ｏ（Ｃ６Ｈ１１））３）のうちのいずれかが好ましい。ボロキシンのアルコキシ置換体に相当するこれらのホウ酸エステルによれば、トリメチルボロキシンのようなアルキル置換体と比較して、結着剤の変性を抑制する効果を有効に得ることができる。なお、前記式（２）で表されるホウ酸エステルの中には、加水分解性の高い物質がある。加水分解性の高いホウ酸エステルは、空気暴露によって加水分解する虞がある。そのため、加水分解性の高いホウ酸エステルを用いる場合は、不活性雰囲気で取り扱うことが好ましい。特に正極合剤スラリーは、不活性雰囲気で作製することが好ましい。 The boric acid ester represented by the formula (2) is, in particular, triisopropoxyboroxine ((BO) 3 (O (CH) (CH 3 ) 2 ) 3 ), trimethoxyboroxine ((BO) 3 ( Either OCH 3 ) 3 ) or tricyclohexoxyboroxine ((BO) 3 (O (C 6 H 11 )) 3 ) is preferred. According to these boric acid esters corresponding to alkoxy substitution products of boroxine, the effect of suppressing denaturation of the binder can be effectively obtained as compared with alkyl substitution products such as trimethylboroxine. In addition, in the boric acid ester represented by the formula (2), there is a substance having high hydrolyzability. A borate ester having high hydrolyzability may be hydrolyzed by exposure to air. Therefore, when using a highly hydrolyzable borate ester, it is preferable to handle it in an inert atmosphere. In particular, the positive electrode mixture slurry is preferably prepared in an inert atmosphere.
　前記式（２）で表されるホウ酸エステルは、正極活物質とホウ酸エステルの合計量に対する割合が５．０質量％未満であることが好ましく、０．５質量％以上２．０質量％以下であることがより好ましい。ホウ酸エステルの割合が５．０質量％未満であれば、正極合剤の変性を抑制して、内部抵抗が低いリチウム二次電池を作製できると見込める。０．５質量％以上であると、正極合剤の変性を抑制する効果がより有効となる。一方、２．０質量％以下であれば、正極合剤の変性を抑制するために添加したホウ酸エステルがもたらす、正極合剤の密着性の悪化や内部抵抗の増大等の副作用を、確実に軽減することができる。 The borate ester represented by the formula (2) is preferably less than 5.0% by mass with respect to the total amount of the positive electrode active material and borate ester, and is 0.5% by mass or more and 2.0% by mass. The following is more preferable. If the ratio of borate ester is less than 5.0% by mass, it can be expected that a lithium secondary battery having low internal resistance can be produced by suppressing modification of the positive electrode mixture. The effect which suppresses modification | denaturation of a positive electrode mixture becomes more effective as it is 0.5 mass% or more. On the other hand, if it is 2.0% by mass or less, side effects such as deterioration of the adhesion of the positive electrode mixture and increase in internal resistance caused by the added boric acid ester for suppressing the modification of the positive electrode mixture are surely achieved. Can be reduced.
　前記式（２）によって表されるホウ酸エステルは、粉末状の状態で正極活物質と共存していてもよいし、液体の状態で正極活物質と共存していてもよい。但し、正極活物質の品質管理上は、粉末状の状態で正極活物質と混合して正極材料とすることが好ましい。 The boric acid ester represented by the formula (2) may coexist with the positive electrode active material in a powder state, or may coexist with the positive electrode active material in a liquid state. However, in terms of quality control of the positive electrode active material, it is preferable to mix with the positive electrode active material in a powder state to obtain a positive electrode material.
　前記式（２）によって表されるホウ酸エステルは、正極合剤を調製するにあたり、正極活物質と結着剤とが接触下におかれる以前に、正極活物質と共存させておくことが好ましい。正極活物質と結着剤とが接触すると、正極活物質中に含まれるアルカリ成分と結着剤とが反応して、ＰＶＤＦのようなフッ素化ポリオレフィンが脱フッ素化し、脱フッ素化により発生したフッ素が、リチウム二次電池中で電解液の劣化等を引き起こすためである。具体的には、例えば、前記式（１）によって表される正極活物質又はその溶液（分散液）と、前記式（２）によって表されるホウ酸エステル又はその溶液（分散液）とを混合し、得られた混合物に結着剤又はその溶液（分散液）を添加、混練して正極合剤を調製し、正極合剤を正極集電体等の基材に塗布し、乾燥及び加圧成形してリチウム二次電池用正極を製造することが好ましい。このような製造方法において、溶液（分散液）を調製するための溶媒（分散媒）としては、Ｎ－メチル－２－ピロリドン（ＮＭＰ）等の非水溶媒を用いることが好ましい。なお、導電材は、正極活物質に対していずれの段階で加えてもよい。 In preparing the positive electrode mixture, the borate ester represented by the formula (2) is preferably coexisted with the positive electrode active material before the positive electrode active material and the binder are brought into contact with each other. . When the positive electrode active material and the binder come into contact, the alkali component contained in the positive electrode active material and the binder react to defluorinate a fluorinated polyolefin such as PVDF, and fluorine generated by defluorination However, this is because it causes deterioration of the electrolyte in the lithium secondary battery. Specifically, for example, the positive electrode active material represented by the formula (1) or a solution thereof (dispersion) is mixed with the boric acid ester represented by the formula (2) or a solution thereof (dispersion). Then, a binder or a solution thereof (dispersion) is added to the obtained mixture and kneaded to prepare a positive electrode mixture, and the positive electrode mixture is applied to a substrate such as a positive electrode current collector, and then dried and pressed. It is preferable to produce a positive electrode for a lithium secondary battery by molding. In such a production method, it is preferable to use a nonaqueous solvent such as N-methyl-2-pyrrolidone (NMP) as a solvent (dispersion medium) for preparing a solution (dispersion). Note that the conductive material may be added to the positive electrode active material at any stage.
　以上のとおり、前記式（１）によって表される正極活物質と、前記式（２）によって表されるホウ酸エステルとを併用した正極材料によると、前記式（２）によって表されるホウ酸エステルが、正極活物質の焼成後に残留しているアルカリ成分と反応してアルカリ成分を中和し、ＰＶＤＦ等の有機バインダの変性を抑制する。そのため、正極合剤のゲル化や結着剤の脱フッ素反応が抑制され、ひいては、正極合剤の変性が抑制されることで、製造工程上でゲル化による困難を伴わず、内部抵抗が低いリチウム二次電池用正極やリチウム二次電池を提供することが可能になる。更に、結着剤の機能が適切に維持されることにより、粒子同士や、粒子と基材との結着強度が高くなり、正極合剤層中の粒子の分布の均一性も高くなる効果が得られる。すなわち、この正極材料によると、電解液にボロキシン誘導体を直接的に添加する場合とは異なり、電池を組み付ける前に生じる高抵抗化の要因を確実に排除することができ、リチウム二次電池の充放電サイクル特性も改善することができる。 As described above, according to the positive electrode material in which the positive electrode active material represented by the formula (1) and the boric acid ester represented by the formula (2) are used in combination, the boric acid represented by the formula (2) The ester reacts with the alkali component remaining after firing of the positive electrode active material to neutralize the alkali component and suppress the modification of the organic binder such as PVDF. Therefore, the gelation of the positive electrode mixture and the defluorination reaction of the binder are suppressed, and as a result, the denaturation of the positive electrode mixture is suppressed, so that the internal resistance is low without difficulty due to gelation in the manufacturing process. It becomes possible to provide a positive electrode for a lithium secondary battery and a lithium secondary battery. Furthermore, by appropriately maintaining the function of the binder, the binding strength between the particles and between the particles and the base material is increased, and the uniformity of the distribution of the particles in the positive electrode mixture layer is also increased. can get. That is, according to this positive electrode material, unlike the case where the boroxine derivative is directly added to the electrolytic solution, it is possible to reliably eliminate the cause of the high resistance that occurs before the battery is assembled. The discharge cycle characteristics can also be improved.
　次に、本実施形態に係るリチウム二次電池及びリチウム二次電池用正極について説明する。 Next, the lithium secondary battery and the positive electrode for a lithium secondary battery according to this embodiment will be described.
　図１は、本発明の一実施形態に係るリチウム二次電池を模式的に示す断面図である。
　図１に示すように、本実施形態に係るリチウム二次電池１は、正極１０、セパレータ１１、負極１２、電池容器１３、正極集電タブ１４、負極集電タブ１５、内蓋１６、内圧開放弁１７、ガスケット１８、正温度係数（Positive Temperature Coefficient；ＰＴＣ）抵抗素子１９、電池蓋２０、軸心２１を備えている。電池蓋２０は、内蓋１６、内圧開放弁１７、ガスケット１８及び抵抗素子１９からなる一体化部品である。 FIG. 1 is a cross-sectional view schematically showing a lithium secondary battery according to an embodiment of the present invention.
As shown in FIG. 1, a lithium secondary battery 1 according to this embodiment includes a positive electrode 10, a separator 11, a negative electrode 12, a battery container 13, a positive electrode current collecting tab 14, a negative electrode current collecting tab 15, an inner lid 16, and release of internal pressure. A valve 17, a gasket 18, a positive temperature coefficient (PTC) resistance element 19, a battery lid 20, and an axis 21 are provided. The battery lid 20 is an integrated part composed of the inner lid 16, the internal pressure release valve 17, the gasket 18 and the resistance element 19.
　正極１０及び負極１２は、シート状に設けられており、セパレータ１１を挟んで互いに重ねられている。そして、正極１０、セパレータ１１及び負極１２が軸心２１の周りに捲回されることによって、円筒形状の電極群が形成されている。 The positive electrode 10 and the negative electrode 12 are provided in a sheet shape, and are overlapped with each other with the separator 11 interposed therebetween. The positive electrode 10, the separator 11, and the negative electrode 12 are wound around the axis 21 to form a cylindrical electrode group.
　軸心２１は、正極１０、セパレータ１１及び負極１２の支持に適した任意の断面形状に設けることができる。断面形状としては、例えば、円筒形状、円柱形状、角筒形状、角形状等が挙げられる。また、軸心２１は、絶縁性が良好な任意の材質で設けることができる。軸心２１の材料としては、例えば、ポリプロピレン、ポリフェニレンサルファイド等が挙げられる。軸芯の機械強度の向上のため、ガラス繊維などを添加してもよい。 The shaft center 21 can be provided in any cross-sectional shape suitable for supporting the positive electrode 10, the separator 11, and the negative electrode 12. Examples of the cross-sectional shape include a cylindrical shape, a columnar shape, a rectangular tube shape, and a square shape. Further, the shaft center 21 can be made of any material having good insulation. Examples of the material of the shaft center 21 include polypropylene and polyphenylene sulfide. Glass fiber or the like may be added to improve the mechanical strength of the shaft core.
　電池容器１３は、電解液に対して耐食性のある活物質、例えば、アルミニウム、ステンレス鋼、ニッケルメッキ鋼等によって形成することができる。電池容器１３を正極１０又は負極１２と電気的に接続する場合に、電解液と接触している部分において電池容器１３の腐食やリチウムとの合金化による活物質の変質が起こらないように活物質を選定する。電池容器１３の内面には、耐食性や密着性を向上させるための表面加工処理が施されていてもよい。 The battery container 13 can be formed of an active material having corrosion resistance to the electrolyte, such as aluminum, stainless steel, nickel-plated steel, and the like. When the battery container 13 is electrically connected to the positive electrode 10 or the negative electrode 12, the active material is prevented from being deteriorated due to corrosion of the battery container 13 or alloying with lithium in a portion in contact with the electrolytic solution. Is selected. The inner surface of the battery container 13 may be subjected to a surface treatment for improving corrosion resistance and adhesion.
　正極１０及び負極１２には、電流引き出し用の正極集電タブ１４、負極集電タブ１５のそれぞれが、スポット溶接、超音波溶接等によって接続されている。正極集電タブ１４と負極集電タブ１５とが設けられた電極群が電池容器１３に収納されている。正極集電タブ１４は、電池蓋２０の底面に電気的に接続されている。また、負極集電タブ１５は、電池容器１３の内壁に電気的に接続されている。正極集電タブ１４や負極集電タブ１５は、図１に示すように電極群に対して複数設けてもよい。複数設けることによって、大電流への対応が可能となる。 A positive current collecting tab 14 and a negative current collecting tab 15 for drawing current are connected to the positive electrode 10 and the negative electrode 12 by spot welding, ultrasonic welding, or the like. An electrode group provided with the positive electrode current collecting tab 14 and the negative electrode current collecting tab 15 is accommodated in the battery container 13. The positive electrode current collecting tab 14 is electrically connected to the bottom surface of the battery lid 20. Further, the negative electrode current collecting tab 15 is electrically connected to the inner wall of the battery container 13. A plurality of the positive electrode current collecting tabs 14 and the negative electrode current collecting tabs 15 may be provided for the electrode group as shown in FIG. By providing a plurality, it becomes possible to cope with a large current.
　正極１０は、リチウムイオンを可逆的に吸蔵及び放出可能な正極活物質として、前記の式（１）によって表される正極活物質と、式（２）によって表されるホウ酸エステルとを含むリチウム二次電池用正極材料を含んで構成される。正極１０は、詳細には、例えば、正極活物質と、導電材と、結着剤とを含んで組成される正極合剤層と、正極合剤層が片面又は両面に塗工された正極集電体とを備える。すなわち、正極１０は、リチウム二次電池用正極材料を材料として作製されるものである。 The positive electrode 10 is a lithium containing a positive electrode active material represented by the formula (1) and a borate ester represented by the formula (2) as a positive electrode active material capable of reversibly occluding and releasing lithium ions. It is comprised including the positive electrode material for secondary batteries. Specifically, the positive electrode 10 includes, for example, a positive electrode mixture layer composed of a positive electrode active material, a conductive material, and a binder, and a positive electrode assembly in which the positive electrode mixture layer is coated on one side or both sides. Electric body. That is, the positive electrode 10 is produced using a positive electrode material for a lithium secondary battery.
　導電材としては、例えば、黒鉛、カーボンブラック、アセチレンブラック、ケッチェンブラック、チャンネルブラック等の炭素粒子や、炭素繊維等を用いることができる。これらの導電材は、一種を単独で用いてもよいし、複数種を併用してもよい。導電材の量は、正極活物質に対して５質量％以上２０質量％以下とすることが好ましい。導電材の量がこのような範囲であると、良好な導電性が得られると共に、高い容量も確保することができる。 As the conductive material, for example, carbon particles such as graphite, carbon black, acetylene black, ketjen black, and channel black, carbon fibers, and the like can be used. One of these conductive materials may be used alone, or a plurality of these conductive materials may be used in combination. The amount of the conductive material is preferably 5% by mass or more and 20% by mass or less with respect to the positive electrode active material. When the amount of the conductive material is within such a range, good conductivity can be obtained and a high capacity can be secured.
　正極における結着剤としては、例えば、ポリフッ化ビニリデン、ポリテトラフルオロエチレン、ポリクロロトリフルオロエチレン等や、フッ化ビニリデン、テトラフルオロエチレン、クロロトリフルオロエチレン等の共重合体等の有機バインダを用いることができる。正極における結着剤として有機バインダのみを用いることにより、式（２）によって表されるホウ酸エステルが加水分解するのを避けることができる。これらの有機バインダは、一種を単独で用いてもよいし、複数種を併用してもよい。また、カルボキシメチルセルロース等の増粘性の材料を併用してもよい。有機バインダとしては、前記式（２）によって表されるホウ酸エステルによる効果を有効にする観点から、好ましくはハロゲン化ポリオレフィン、より好ましくはフッ素化ポリオレフィン、特に好ましくはポリフッ化ビニリデンが用いられる。 As the binder in the positive electrode, for example, an organic binder such as polyvinylidene fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, or a copolymer of vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, or the like is used. be able to. By using only the organic binder as the binder in the positive electrode, it is possible to avoid hydrolysis of the boric acid ester represented by the formula (2). These organic binders may be used individually by 1 type, and may use multiple types together. Further, a thickening material such as carboxymethylcellulose may be used in combination. The organic binder is preferably a halogenated polyolefin, more preferably a fluorinated polyolefin, particularly preferably polyvinylidene fluoride, from the viewpoint of making effective the effect of the boric acid ester represented by the formula (2).
　正極における結着剤の量は、正極活物質、導電材及び結着剤の総計に対して１質量％以上７質量％以下とすることが好ましい。結着剤の量がこのような範囲であると、容量が小さくなったり、内部抵抗が過大になったりすることが少ない。また、正極合剤層の塗布性及び成形性や、正極合剤層の強度が損なわれ難い。 The amount of the binder in the positive electrode is preferably 1% by mass or more and 7% by mass or less based on the total amount of the positive electrode active material, the conductive material, and the binder. When the amount of the binder is within such a range, the capacity is not reduced and the internal resistance is rarely excessive. Moreover, the applicability | paintability and moldability of a positive mix layer, and the intensity | strength of a positive mix layer are hard to be impaired.
　正極集電体としては、例えば、アルミニウム、ステンレス鋼、チタン等を材質とする金属箔、金属板、発泡金属板、エキスパンドメタル、パンチングメタル等の適宜の材料を用いることができる。金属箔については、例えば、０．１ｍｍ以上１０ｍｍ以下程度の孔径に穿孔された穿孔箔としてもよい。実質的に金属箔の厚さは、１０μｍ以上１００μｍ以下とすることが好ましい。 As the positive electrode current collector, for example, an appropriate material such as a metal foil, a metal plate, a foam metal plate, an expanded metal, or a punching metal made of aluminum, stainless steel, titanium, or the like can be used. About metal foil, it is good also as perforated foil perforated by the hole diameter of about 0.1 mm or more and 10 mm or less, for example. It is preferable that the thickness of the metal foil is substantially 10 μm or more and 100 μm or less.
　正極１０は、例えば、正極活物質と、導電材と、結着剤とを適宜の溶媒と共に混合して正極合剤とし、この正極合剤を正極集電体に塗布した後、乾燥、圧縮成形することによって作製することができる。正極合剤を塗布する方法としては、例えば、ドクターブレード法、ディッピング法、スプレー法等を用いることができる。また、正極合剤を圧縮成形する方法としては、例えば、ロールプレス等を用いることができる。 For example, the positive electrode 10 is prepared by mixing a positive electrode active material, a conductive material, and a binder together with an appropriate solvent to form a positive electrode mixture, and applying the positive electrode mixture to the positive electrode current collector, followed by drying and compression molding. It can produce by doing. As a method for applying the positive electrode mixture, for example, a doctor blade method, a dipping method, a spray method, or the like can be used. Moreover, as a method of compression molding the positive electrode mixture, for example, a roll press or the like can be used.
　正極合剤層の厚さは、製造しようとするリチウム二次電池の仕様や、負極とのバランスを考慮して、適宜の厚さとすることができるが、正極集電体の両面に塗布した場合、５０μｍ以上２００μｍ以下とすることが好ましい。正極合剤層の厚さは、リチウム二次電池の容量、抵抗値等の仕様に応じて設定することができるが、この程度の塗布量であれば、電極間の距離が過大になったり、リチウムイオンの吸蔵及び放出について分布が生じたりすることは少ない。 The thickness of the positive electrode mixture layer can be set to an appropriate thickness in consideration of the specifications of the lithium secondary battery to be manufactured and the balance with the negative electrode, but when applied to both surfaces of the positive electrode current collector 50 μm or more and 200 μm or less is preferable. The thickness of the positive electrode mixture layer can be set according to the specifications of the capacity, resistance value, etc. of the lithium secondary battery, but if this amount of coating, the distance between the electrodes becomes excessive, There is little distribution of lithium ion storage and release.
　正極活物質の粒径は、通常、正極合剤層の厚さ以下とされる。合成した正極活物質の粉末中に粗粒がある場合は、あらかじめ篩分級、風流分級等を行い、正極活物質の平均粒径を正極合剤層の厚さより小さくしておくことが好ましい。 The particle diameter of the positive electrode active material is usually not more than the thickness of the positive electrode mixture layer. In the case where coarse particles are present in the synthesized positive electrode active material powder, it is preferable that the average particle size of the positive electrode active material is made smaller than the thickness of the positive electrode mixture layer by performing sieving classification, wind classification, and the like in advance.
　正極合剤層の密度は、製造しようとするリチウム二次電池の仕様や、負極とのバランスを考慮して、適宜の密度とすることができるが、リチウム二次電池についての容量を確保する観点からは、真密度の６０％以上の密度とすることが好ましい。 The density of the positive electrode mixture layer can be set to an appropriate density in consideration of the specifications of the lithium secondary battery to be manufactured and the balance with the negative electrode, but the viewpoint of securing the capacity of the lithium secondary battery Is preferably 60% or more of the true density.
　セパレータ１１は、正極１０と負極１２とが直接接触して短絡が生じるのを防止するために備えられる。セパレータ１１としては、ポリエチレン、ポリプロピレン、アラミド樹脂等の微多孔質フィルムや、このような微多孔質フィルムの表面にアルミナ粒子等の耐熱性物質を被覆したフィルム等を用いることができる。なお、セパレータ１１の機能は、電池性能を損なわない程度で、正極１０及び負極１２自体に具備させてもよい。 The separator 11 is provided to prevent the positive electrode 10 and the negative electrode 12 from coming into direct contact with each other and causing a short circuit. As the separator 11, a microporous film such as polyethylene, polypropylene, and aramid resin, a film in which the surface of such a microporous film is coated with a heat resistant material such as alumina particles, and the like can be used. In addition, you may provide the function of the separator 11 in the positive electrode 10 and the negative electrode 12 itself to such an extent that battery performance is not impaired.
　負極１２は、リチウムイオンを可逆的に吸蔵及び放出可能な負極活物質を含んでなる。負極１２は、例えば、負極活物質と、結着剤と、負極集電体とを備えて構成される。 The negative electrode 12 includes a negative electrode active material capable of reversibly occluding and releasing lithium ions. The negative electrode 12 includes, for example, a negative electrode active material, a binder, and a negative electrode current collector.
　負極活物質としては、一般的なリチウム二次電池において用いられる適宜の種類を用いることができる。負極活物質の具体例としては、天然黒鉛、石油コークス、ピッチコークス等から得られる易黒鉛化活物質を２５００℃以上の高温で処理したもの、メソフェーズカーボン、非晶質炭素、黒鉛の表面に非晶質炭素を被覆したもの、天然黒鉛又は人造黒鉛の表面を機械的処理することにより表面の結晶性を低下させた炭素材、高分子等の有機物を炭素表面に被覆・吸着させた活物質、炭素繊維、リチウム金属、リチウムとアルミニウム、スズ、ケイ素、インジウム、ガリウム、マグネシウム等との合金、シリコン粒子又は炭素粒子の表面に金属を担持した活物質、スズ、ケイ素、鉄、チタン等の金属の酸化物等が挙げられる。担持させる金属としては、例えば、リチウム、アルミニウム、スズ、ケイ素、インジウム、ガリウム、マグネシウム、これらの合金等が挙げられる。 As the negative electrode active material, an appropriate type used in a general lithium secondary battery can be used. Specific examples of the negative electrode active material include those obtained by treating a graphitizable active material obtained from natural graphite, petroleum coke, pitch coke, and the like at a high temperature of 2500 ° C. or higher, mesophase carbon, amorphous carbon, and non-graphite surface. A material coated with crystalline carbon, a carbon material whose surface crystallinity has been lowered by mechanically treating the surface of natural graphite or artificial graphite, an active material in which organic substances such as polymers are coated and adsorbed on the carbon surface, Carbon fiber, lithium metal, lithium and aluminum, alloys of tin, silicon, indium, gallium, magnesium, etc., silicon particles or active materials carrying metal on the surface of carbon particles, metals such as tin, silicon, iron, titanium An oxide etc. are mentioned. Examples of the metal to be supported include lithium, aluminum, tin, silicon, indium, gallium, magnesium, and alloys thereof.
　負極における結着剤としては、水に溶解、膨潤又は分散する水系バインダ、及び、水に溶解、膨潤又は分散しない有機バインダのいずれを用いることも可能である。水系バインダの具体例としては、スチレン－ブタジエン共重合体、アクリル系ポリマ、シアノ基を有するポリマ、これらの共重合体等が挙げられる。有機バインダの具体例としては、ポリフッ化ビニリデン、ポリテトラフルオロエチレン、これらの共重合体等が挙げられる。これらの結着剤は、一種を単独で用いてもよいし、複数種を併用してもよい。また、カルボキシメチルセルロース等の増粘性の材料を併用してもよい。 As the binder in the negative electrode, it is possible to use either an aqueous binder that dissolves, swells or disperses in water and an organic binder that does not dissolve, swell or disperse in water. Specific examples of the water-based binder include a styrene-butadiene copolymer, an acrylic polymer, a polymer having a cyano group, and a copolymer thereof. Specific examples of the organic binder include polyvinylidene fluoride, polytetrafluoroethylene, and copolymers thereof. These binders may be used individually by 1 type, and may use multiple types together. Further, a thickening material such as carboxymethylcellulose may be used in combination.
　負極における結着剤の量は、水系バインダについては、負極活物質及び結着剤の総計に対して０．８質量％以上１．５質量％以下とすることが好ましい。一方、有機バインダについては、負極活物質及び結着剤の総計に対して３質量％以上６質量％以下とすることが好ましい。結着剤の量がこのような範囲であると、電池容量が小さくなったり、内部抵抗が過大になったりすることは少ない。また、負極合剤層の塗布性及び成形性や、負極合剤層の強度が損なわれ難い。 The amount of the binder in the negative electrode is preferably 0.8% by mass to 1.5% by mass with respect to the total amount of the negative electrode active material and the binder for the aqueous binder. On the other hand, about an organic binder, it is preferable to set it as 3 to 6 mass% with respect to the total of a negative electrode active material and a binder. When the amount of the binder is within such a range, the battery capacity is less likely to be small and the internal resistance is not excessive. Moreover, the applicability | paintability and moldability of a negative mix layer, and the intensity | strength of a negative mix layer are hard to be impaired.
　負極集電体としては、例えば、銅、銅を主成分とする銅合金等を材質とする金属箔、金属板、発泡金属板、エキスパンドメタル、パンチングメタル等の適宜の活物質を用いることができる。金属箔については、例えば、０．１ｍｍ以上１０ｍｍ以下程度の孔径に穿孔された穿孔箔としてもよい。金属箔の厚さは、７μｍ以上２５μｍ以下とすることが好ましい。 As the negative electrode current collector, for example, an appropriate active material such as metal foil made of copper, a copper alloy containing copper as a main component, a metal plate, a metal foam plate, an expanded metal, a punching metal, or the like can be used. . About metal foil, it is good also as perforated foil perforated by the hole diameter of about 0.1 mm or more and 10 mm or less, for example. The thickness of the metal foil is preferably 7 μm or more and 25 μm or less.
　負極１２は、例えば、負極活物質と、結着剤とを適宜の溶媒と共に混合して負極合剤とし、この負極合剤を負極集電体に塗布した後、乾燥、圧縮成形することによって作製することができる。負極合剤を塗布する方法としては、例えば、ドクターブレード法、ディッピング法、スプレー法等を用いることができる。また、負極合剤を圧縮成形する方法としては、例えば、ロールプレス等を用いることができる。 The negative electrode 12 is produced, for example, by mixing a negative electrode active material and a binder together with an appropriate solvent to form a negative electrode mixture, applying this negative electrode mixture to the negative electrode current collector, and then drying and compression molding the mixture. can do. As a method for applying the negative electrode mixture, for example, a doctor blade method, a dipping method, a spray method, or the like can be used. Moreover, as a method of compression-molding the negative electrode mixture, for example, a roll press or the like can be used.
　負極合剤層の厚さは、製造しようとするリチウム二次電池の仕様や、正極とのバランスを考慮して、適宜の厚さとすることができるが、負極集電体の両面に塗布した場合、５０μｍ以上２００μｍ以下とすることが好ましい。負極合剤層の厚さは、リチウム二次電池の容量、抵抗値等の仕様に応じて設定することができるが、この程度の塗布量であれば、電極間の距離が過大になったり、リチウムイオンの吸蔵及び放出について分布が生じたりすることは少ない。 The thickness of the negative electrode mixture layer can be set to an appropriate thickness in consideration of the specifications of the lithium secondary battery to be manufactured and the balance with the positive electrode, but when applied to both sides of the negative electrode current collector 50 μm or more and 200 μm or less is preferable. The thickness of the negative electrode mixture layer can be set according to the specifications of the lithium secondary battery capacity, resistance value, etc., but if this amount of coating, the distance between the electrodes becomes excessive, There is little distribution of lithium ion storage and release.
　電池容器１３に封入される電解液は、電解質と電解液溶媒とを含んで構成される電解液としては、水分、フッ酸等の遊離酸の含有量が少ないものを用いることが一般的である。 As an electrolytic solution configured to contain an electrolyte and an electrolytic solution solvent, an electrolytic solution that contains a small amount of free acid such as moisture and hydrofluoric acid is generally used as the electrolytic solution sealed in the battery container 13. .
　電解質としては、ヘキサフルオロリン酸リチウム（ＬｉＰＦ６）が少なくとも用いられる。ＬｉＰＦ６は、後述する非水溶媒として用いられるカーボネートへの溶解度が高いこと、嵩高いＰＦ６ －基によりＬｉ＋の解離度が高いこと、から非水溶媒に溶解した後の電解液のイオン伝導度が高い。また、ＬｉＰＦ６は前記式（２）で表されるホウ酸エステルと反応し、反応生成物が電池抵抗の上昇を抑制する。電解質としては、ＬｉＰＦ６のみを単独で用いてもよいし、その他のリチウム塩を併用してもよい。ＬｉＰＦ６と併用するその他のリチウム塩としては、例えば、ＬｉＢＦ４、ＬｉＣｌＯ４、ＬｉＡｓＦ６、ＬｉＣＦ３ＳＯ２、Ｌｉ（ＣＦ３ＳＯ２）２Ｎ、Ｌｉ（Ｃ２Ｆ５ＳＯ２）２Ｎ、Ｌｉ（Ｆ２ＳＯ２）２Ｎ、ＬｉＦ、Ｌｉ２ＣＯ３、ＬｉＰＦ４（ＣＦ３）２、ＬｉＰＦ４（ＣＦ３ＳＯ２）２、ＬｉＢＦ３（ＣＦ３）、ＬｉＢＦ２（ＣＦ３ＳＯ２）２等が挙げられる。 As the electrolyte, at least lithium hexafluorophosphate (LiPF 6 ) is used. LiPF 6, it has high solubility in carbonate used as non-aqueous solvent to be described later, bulky PF 6 - ion conductivity of the electrolyte after dissolution is high dissociation degree of Li +, from a non-aqueous solvent by a group High degree. Moreover, LiPF 6 reacts with the boric acid ester represented by the formula (2), and the reaction product suppresses the increase in battery resistance. As the electrolyte, only LiPF 6 may be used alone, or other lithium salts may be used in combination. Examples of other lithium salts used in combination with LiPF 6 include LiBF 4 , LiClO 4 , LiAsF 6 , LiCF 3 SO 2 , Li (CF 3 SO 2 ) 2 N, Li (C 2 F 5 SO 2 ) 2 N, Li (F 2 SO 2 ) 2 N, LiF, Li 2 CO 3 , LiPF 4 (CF 3 ) 2 , LiPF 4 (CF 3 SO 2 ) 2 , LiBF 3 (CF 3 ), LiBF 2 (CF 3 SO 2 ) 2 etc. are mentioned.
　電解質の濃度は、０．６ｍｏｌ／Ｌ以上１．５ｍｏｌ／Ｌ以下の範囲とすることが好ましい。濃度が０．６ｍｏｌ／Ｌ以上であると、良好なイオン伝導性を実現することができる。また、濃度が１．５ｍｏｌ／Ｌ以下であると、イオン伝導の抵抗が小さく抑えられ、リチウムイオンの反応速度も速くなるため、電池特性の低下を抑制することができる。 The concentration of the electrolyte is preferably in the range of 0.6 mol / L or more and 1.5 mol / L or less. When the concentration is 0.6 mol / L or more, good ion conductivity can be realized. Further, when the concentration is 1.5 mol / L or less, the resistance of ion conduction is suppressed to a small value, and the reaction rate of lithium ions is increased, so that deterioration of battery characteristics can be suppressed.
　電解液に用いる非水溶媒は、例えば、鎖状カーボネート、環状カーボネート、鎖状カルボン酸エステル、環状カルボン酸エステル、鎖状エーテル、環状エーテル、有機リン化合物、有機硫黄化合物等が挙げられる。これらの化合物は、一種を単独で用いてもよいし、複数種を併用してもよい。 Examples of the non-aqueous solvent used in the electrolytic solution include a chain carbonate, a cyclic carbonate, a chain carboxylic acid ester, a cyclic carboxylic acid ester, a chain ether, a cyclic ether, an organic phosphorus compound, an organic sulfur compound, and the like. These compounds may be used individually by 1 type, and may use multiple types together.
　鎖状カーボネートは、例えば、ジメチルカーボネート、エチルメチルカーボネート、ジエチルカーボネート、メチルプロピルカーボネート、エチルプロピルカーボネート等が挙げられる。また、環状カーボネートとしては、例えば、エチレンカーボネート、プロピレンカーボネート、ビニレンカーボネート、１、２－ブチレンカーボネート、２、３－ブチレンカーボネート等が挙げられる。 Examples of the chain carbonate include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, vinylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, and the like.
　鎖状カルボン酸エステルは、例えば、酢酸メチル、酢酸エチル、酢酸プロピル、酢酸ブチル、プロピオン酸メチル、プロピオン酸エチル、プロピオン酸プロピル等が挙げられる。また、環状カルボン酸エステルとしては、例えば、γ－ブチロラクトン、γ－バレロラクトン、δ－バレロラクトン等が挙げられる。 Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, and propyl propionate. Examples of the cyclic carboxylic acid ester include γ-butyrolactone, γ-valerolactone, and δ-valerolactone.
　鎖状エーテルは、例えば、ジメトキシメタン、ジエトキシメタン、１、２－ジメトキシエタン、１－エトキシ－２－メトキシエタン、１、３－ジメトキシプロパン等が挙げられる。また、環状エーテルとしては、例えば、テトラヒドロフラン、２－メチルテトラヒドロフラン、３－メチルテトラヒドロフラン等が挙げられる。 Examples of the chain ether include dimethoxymethane, diethoxymethane, 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,3-dimethoxypropane and the like. Examples of the cyclic ether include tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran and the like.
　有機リン化合物としては、例えば、リン酸トリメチル、リン酸トリエチル、リン酸トリフェニル等のリン酸エステルや、亜リン酸トリメチル、亜リン酸トリエチル、亜リン酸トリフェニル等の亜リン酸エステルや、トリメチルホスフィンオキシド等が挙げられる。また、有機硫黄化合物としては、例えば、１、３－プロパンスルトン、１、４－ブタンスルトン、メタンスルホン酸メチル、スルホラン、スルホレン、ジメチルスルホン、エチルメチルスルホン、メチルフェニルスルホン、エチルフェニルスルホン等が挙げられる。 Examples of the organic phosphorus compound include phosphoric acid esters such as trimethyl phosphate, triethyl phosphate, and triphenyl phosphate, phosphorous acid esters such as trimethyl phosphite, triethyl phosphite, and triphenyl phosphite, And trimethylphosphine oxide. Examples of the organic sulfur compound include 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, sulfolane, sulfolene, dimethyl sulfone, ethyl methyl sulfone, methyl phenyl sulfone, and ethyl phenyl sulfone. .
　非水溶媒として用いられるこれらの化合物は、置換基を有していてもよいし、酸素原子が硫黄原子で置換された化合物であってもよい。置換基としては、例えば、フッ素原子、塩素原子、臭素原子等のハロゲン原子が挙げられる。非水溶媒として二種以上の化合物を併用する場合は、環状カーボネートや環状ラクトン等のように比誘電率が高く粘度が相対的に高い化合物と、鎖状カーボネート等のように粘度が相対的に低い化合物とを組み合わせることが好ましい。混合された電解液のイオン伝導度の点で、エチレンカーボネートと、エチルメチルカーボネート又はジエチルカーボネートの何れかを含む組成にすることが好ましい。 These compounds used as a non-aqueous solvent may have a substituent or may be a compound in which an oxygen atom is substituted with a sulfur atom. As a substituent, halogen atoms, such as a fluorine atom, a chlorine atom, a bromine atom, are mentioned, for example. When two or more compounds are used in combination as a non-aqueous solvent, a compound having a high relative dielectric constant such as a cyclic carbonate or a cyclic lactone and a relatively high viscosity, and a viscosity such as a chain carbonate are relatively It is preferable to combine with a low compound. In view of the ionic conductivity of the mixed electrolyte, it is preferable to use a composition containing ethylene carbonate and either ethyl methyl carbonate or diethyl carbonate.
　電解液は、ビニレンカーボネート、モノフッ素化エチレンカーボネート等のカーボネート類を添加剤として含有することが好ましい。負極活物質の表面には、Ｃ＝Ｏ、Ｃ－Ｈ、ＣＯＯ等の官能基が存在しており、これらの官能基は、電池反応に伴い非水溶媒と不可逆的に反応して、ＳＥＩ（Solid Electrolyte Interphase）被膜と呼ばれる表面被膜を形成する。ＳＥＩ被膜は、非水溶媒の分解を抑制する作用を示すが、電池反応における電荷を消費して生成されるため電池の容量を低下させる一因となる。これに対して、ビニレンカーボネート等を添加しておくと、容量の低下を抑制してＳＥＩ被膜を形成させることができる。ビニレンカーボネート等の添加剤の添加量は、電解液の総重量当たり、２質量％以下とすることが好ましい。添加量がこのような範囲であると、過剰なビニレンカーボネート等が酸化分解されたときに容量や出力の低下が小さくて済む点で有利である。 The electrolytic solution preferably contains carbonates such as vinylene carbonate and monofluorinated ethylene carbonate as additives. There are functional groups such as C═O, C—H, and COO on the surface of the negative electrode active material, and these functional groups react irreversibly with a non-aqueous solvent in accordance with the battery reaction, and SEI ( A surface film called a solid (Electrolyte Interphase) film is formed. The SEI film exhibits an action of suppressing the decomposition of the nonaqueous solvent, but is generated by consuming electric charge in the battery reaction, and thus contributes to a reduction in the capacity of the battery. On the other hand, when vinylene carbonate or the like is added, the SEI film can be formed while suppressing a decrease in capacity. The addition amount of additives such as vinylene carbonate is preferably 2% by mass or less based on the total weight of the electrolytic solution. When the addition amount is within such a range, it is advantageous in that the capacity and output can be reduced little when excess vinylene carbonate or the like is oxidized and decomposed.
　電解液には、カルボン酸無水物、１、３－プロパンスルトン等の硫黄化合物、リチウムビスオキサレートボレート（ＬｉＢＯＢ）、ホウ酸トリメチル（ＴＭＢ）等のホウ素化合物等を添加剤として含有していてもよい。また、電解液は、電池の過充電を抑制する過充電抑制剤、電解液の難燃性（自己消火性）を向上させる難燃化剤、電極やセパレータの濡れ性を改善する濡れ性改善剤、正極活物質からのＭｎの溶出を抑制する添加剤、電解液のイオン伝導性を向上させるための添加剤等を含有していてもよい。これらの添加剤の添加量の総計は、電解液当たり、１０質量％未満とすることが好ましい。 The electrolyte may contain carboxylic acid anhydride, sulfur compounds such as 1,3-propane sultone, boron compounds such as lithium bisoxalate borate (LiBOB), trimethyl borate (TMB), and the like as additives. Good. In addition, the electrolyte is an overcharge inhibitor that suppresses overcharge of the battery, a flame retardant that improves the flame retardancy (self-extinguishing) of the electrolyte, and a wettability improver that improves the wettability of electrodes and separators. Further, an additive for suppressing elution of Mn from the positive electrode active material, an additive for improving the ionic conductivity of the electrolytic solution, and the like may be contained. The total amount of these additives is preferably less than 10% by mass per electrolyte solution.
　過充電抑制剤としては、例えば、ビフェニル、ビフェニルエーテル、ターフェニル、メチルターフェニル、ジメチルターフェニル、シクロヘキシルベンゼン、ジシクロヘキシルベンゼン、トリフェニルベンゼン、ヘキサフェニルベンゼン、アジポニトリル、ジオキサン類等が挙げられる。また、難燃化剤としては、例えば、リン酸トリメチル、リン酸トリエチル等の有機リン化合物、ホウ酸エステル等をはじめとする前記の非水溶媒のフッ化物等を用いることができる。また、濡れ性改善剤としては、例えば、１、２－ジメトキシエタン等をはじめとする鎖状エーテル等を用いることができる。 Examples of the overcharge inhibitor include biphenyl, biphenyl ether, terphenyl, methyl terphenyl, dimethyl terphenyl, cyclohexylbenzene, dicyclohexylbenzene, triphenylbenzene, hexaphenylbenzene, adiponitrile, dioxane, and the like. As the flame retardant, for example, organic phosphorus compounds such as trimethyl phosphate and triethyl phosphate, fluorides of the above non-aqueous solvents including borate esters, and the like can be used. As the wettability improver, for example, chain ethers such as 1,2-dimethoxyethane can be used.
　以上の構成を有するリチウム二次電池は、電池蓋を正極外部端子、電池缶の底部を負極外部端子として、外部から供給された電力を捲回電極群に蓄積するとともに、捲回電極群に蓄積した電力を外部の装置等に供給することができる。本実施形態のリチウム二次電池は、例えば、携帯電子機器や家庭用電気機器等の小型電源、無停電電源や電力平準化装置等の定置用電源、船舶、鉄道、ハイブリット自動車、電気自動車等の駆動電源として使用することができる。 The lithium secondary battery having the above configuration uses the battery lid as the positive electrode external terminal and the bottom of the battery can as the negative electrode external terminal, and accumulates power supplied from the outside in the wound electrode group and also in the wound electrode group. Can be supplied to an external device or the like. The lithium secondary battery of this embodiment is, for example, a small power source such as a portable electronic device or a household electric device, a stationary power source such as an uninterruptible power source or a power leveling device, a ship, a railway, a hybrid vehicle, an electric vehicle, etc. It can be used as a drive power supply.
　なお、以上の実施形態では、電極群及び電池容器１３が、円筒形状に形成されている。しかしながら、電極群の形態は、扁平円形状に捲回した形態、短冊状の電極を積層した形態、電極が収納された袋状のセパレータを積層して多層構造とした形態等に例示される種々の形態とすることも可能である。また、電池容器１３は、電極群の形態に応じて、円筒形状、扁平楕円形状、扁長楕円形状、角形状、コイン形状、ボタン形状等の適宜の形状とすることができる。また、軸心２１を備えない形態とすることも可能である In the above embodiment, the electrode group and the battery container 13 are formed in a cylindrical shape. However, the form of the electrode group includes various forms exemplified by a form wound in a flat circular shape, a form in which strip-shaped electrodes are laminated, a form in which a bag-like separator containing electrodes is laminated to form a multilayer structure, etc. It is also possible to adopt the form. In addition, the battery case 13 can have an appropriate shape such as a cylindrical shape, a flat elliptical shape, a flat elliptical shape, a square shape, a coin shape, or a button shape according to the form of the electrode group. Further, it is possible to adopt a form in which the axis 21 is not provided.
　以上、図面を用いて本発明の実施の形態を詳述してきたが、具体的な構成はこの実施形態に限定されるものではなく、本発明の要旨を逸脱しない範囲における設計変更等があっても、それらは本発明に含まれるものである。 The embodiment of the present invention has been described in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.
　以下、実施例を示して本発明について具体的に説明するが、本発明の技術的範囲はこれに限定されるものではない。 Hereinafter, the present invention will be specifically described with reference to examples, but the technical scope of the present invention is not limited thereto.
（実施例１）
　前記式（１）によって表される正極活物質と、前記式（２）によって表されるホウ酸エステルとしてトリイソプロポキシボロキシンと、を含む正極材料を用いて、以下の手順にしたがってリチウム二次電池を作製した。 Example 1
Using a positive electrode material containing a positive electrode active material represented by the formula (1) and triisopropoxyboroxine as a borate ester represented by the formula (2), a lithium secondary A battery was produced.
　はじめに、正極活物質の出発原料として、炭酸リチウム、水酸化ニッケル、炭酸コバルト、及び、炭酸マンガンを用意した。次に、これら出発原料を混合する混合工程を実施した。具体的には、出発原料を、原子比でＬｉ：Ｎｉ：Ｃｏ：Ｍｎが、１．０４：０．８０：０．１５：０．０５となるように秤量して粉砕及び混合し、粉末状の混合物を得た。 First, lithium carbonate, nickel hydroxide, cobalt carbonate, and manganese carbonate were prepared as starting materials for the positive electrode active material. Next, the mixing process which mixes these starting materials was implemented. Specifically, the starting material is weighed so that Li: Ni: Co: Mn is 1.04: 0.80: 0.15: 0.05 by atomic ratio, and is pulverized and mixed to obtain a powder form A mixture of was obtained.
　次に、得られた混合物を焼成する焼成工程を実施した。具体的には、混合工程によって得られた混合粉を、第１熱処理工程に供して第１前駆体を得た。その後、第１前駆体を第２熱処理工程に供して第２前駆体を得てから、第２前駆体を第３熱処理工程に供してリチウム複合化合物を焼成した。 Next, a firing step for firing the obtained mixture was performed. Specifically, the mixed powder obtained by the mixing step was subjected to a first heat treatment step to obtain a first precursor. Thereafter, the first precursor was subjected to a second heat treatment step to obtain a second precursor, and then the second precursor was subjected to a third heat treatment step to calcine the lithium composite compound.
　第１熱処理工程では、混合工程によって得られた１ｋｇの混合粉を、縦３００ｍｍ、横３００ｍｍ、高さ１００ｍｍのアルミナ容器に充填し、連続搬送炉によって、大気雰囲気で３５０℃の熱処理温度で１時間にわたって熱処理して第１前駆体の粉末を得た。この工程では、水酸化ニッケルの熱分解に伴う水蒸気と、炭酸コバルト及び炭酸マンガンの熱分解に伴う二酸化炭素が発生する。 In the first heat treatment step, 1 kg of the mixed powder obtained in the mixing step is filled into an alumina container having a length of 300 mm, a width of 300 mm, and a height of 100 mm, and then, for 1 hour at a heat treatment temperature of 350 ° C. in an air atmosphere by a continuous transfer furnace. To obtain a first precursor powder. In this step, water vapor accompanying thermal decomposition of nickel hydroxide and carbon dioxide accompanying thermal decomposition of cobalt carbonate and manganese carbonate are generated.
　第２熱処理工程では、第１熱処理工程で得られた第１前駆体の粉末を、酸素濃度９０％以上の雰囲気に置換した連続搬送炉によって、酸素気流中で６００℃の熱処理温度で１０時間にわたって熱処理して第２前駆体の粉末を得た。この工程では、第１熱処理工程で反応しきれなかった炭酸コバルト及び炭酸マンガンが熱分解し、二酸化炭素が発生する。さらに、炭酸リチウムとＮｉ、Ｃｏ、Ｍｎとの反応が進むことにより、二酸化炭素が発生する。 In the second heat treatment step, the powder of the first precursor obtained in the first heat treatment step is replaced with an atmosphere having an oxygen concentration of 90% or more for 10 hours at a heat treatment temperature of 600 ° C. in an oxygen stream. A second precursor powder was obtained by heat treatment. In this step, cobalt carbonate and manganese carbonate that could not be reacted in the first heat treatment step are thermally decomposed to generate carbon dioxide. Furthermore, carbon dioxide is generated by the reaction of lithium carbonate with Ni, Co, and Mn.
　以上の工程によって得られた正極活物質は、ＩＣＰ発光分光分析によって元素分析を行ったところ、Ｌｉ１．０２Ｎｉ０．８Ｍｎ０．０５Ｃｏ０．１５Ｏ２であることが確認された。 When the positive electrode active material obtained by the above steps was subjected to elemental analysis by ICP emission spectroscopic analysis, it was confirmed to be Li 1.02 Ni 0.8 Mn 0.05 Co 0.15 O 2 .
　次に、得られた正極活物質に、塊状黒鉛及びアセチレンブラックを混合した。また、ホウ酸エステルとして、トリイソプロポキシボロキシン（（ＢＯ）３（Ｏ（ＣＨ）（ＣＨ３）２）３）を、正極活物質とホウ酸エステルの合計量に対する割合が１質量％となるように混合した。更に、ポリフッ化ビニリデン（ＰＶＤＦ）をＮ－メチル－２－ピロリドン（ＮＭＰ）に溶解した溶液を混合して正極合剤スラリーを調製した。なお、正極活物質、塊状黒鉛、アセチレンブラック、及び、ＰＶＤＦは、質量比が８５：８：２：５となる量を混合した。そして、この正極合剤スラリーを厚さ２０μｍのアルミニウム箔（正極集電体）の片面に均一に塗布し、８０℃の温度で乾燥した。また、アルミニウム箔の反対側の面にも、同様にして正極合剤スラリーを塗布し、乾燥した。その後、ロールプレス機により圧縮成形し、塗布幅５．４ｃｍ、塗布長さ５０ｃｍとなるよう切断して正極とした。作製した正極を観察したところ、正極活物質の表面に被覆層は生成されていないことが確認できた。 Next, massive graphite and acetylene black were mixed with the obtained positive electrode active material. In addition, as a borate ester, triisopropoxyboroxine ((BO) 3 (O (CH) (CH 3 ) 2 ) 3 ) is 1% by mass with respect to the total amount of the positive electrode active material and the borate ester. Mixed. Further, a positive electrode mixture slurry was prepared by mixing a solution of polyvinylidene fluoride (PVDF) dissolved in N-methyl-2-pyrrolidone (NMP). Note that the positive electrode active material, massive graphite, acetylene black, and PVDF were mixed in an amount such that the mass ratio was 85: 8: 2: 5. And this positive mix slurry was apply | coated uniformly on the single side | surface of 20-micrometer-thick aluminum foil (positive electrode electrical power collector), and it dried at the temperature of 80 degreeC. Similarly, the positive electrode mixture slurry was applied to the opposite surface of the aluminum foil and dried. Then, it compression-molded with the roll press machine, and it cut | disconnected so that it might become a coating width 5.4cm and coating length 50cm, and it was set as the positive electrode. When the produced positive electrode was observed, it was confirmed that no coating layer was formed on the surface of the positive electrode active material.
　負極は、面間隔が０．３６８ｎｍ、平均粒径が２０μｍ、比表面積が５ｍ２／ｇの天然黒鉛を負極活物質として作製した。はじめに、負極活物質の天然黒鉛とカルボキシメチルセルロースの水分散液とを充分に混合し、スチレンブタジエン共重合体の水分散液を加えて負極合剤スラリーを調製した。天然黒鉛、カルボキシメチルセルロース、及び、スチレンブタジエン共重合体は、質量比が９８：１：１となる量を混合した。そして、この負極合剤スラリーを厚さ１０μｍの圧延銅箔（負極集電体）に均一に塗布し、その後、正極と同様に乾燥、圧縮成形等して負極を作製した。 The negative electrode was produced using natural graphite having an interplanar spacing of 0.368 nm, an average particle size of 20 μm, and a specific surface area of 5 m 2 / g as a negative electrode active material. First, natural graphite as a negative electrode active material and an aqueous dispersion of carboxymethyl cellulose were sufficiently mixed, and an aqueous dispersion of a styrene-butadiene copolymer was added to prepare a negative electrode mixture slurry. Natural graphite, carboxymethyl cellulose, and styrene butadiene copolymer were mixed in an amount such that the mass ratio was 98: 1: 1. And this negative electrode mixture slurry was uniformly apply | coated to the 10-micrometer-thick rolled copper foil (negative electrode electrical power collector), and dried and compression-molded similarly to the positive electrode, and the negative electrode was produced.
　次に、作製した正極と負極とを用いて、図１に示す円筒型のリチウム二次電池を作製した。正極及び負極には、それぞれ電流引き出し用の正極リード及び負極リードを超音波溶接により形成した。正極リード及び負極リードは、集電体とそれぞれ同じ材質とし、タブ付けされた正極及び負極間にポリエチレン製のセパレータを挟んで重ね、螺旋状に捲いて電極群とし、円筒状の電池容器に収納した。そして、電池容器内に電解液を注入して密封し、リチウム二次電池とした。電解液としては、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）を、ＥＣ：ＥＭＣ＝１：２の体積比で混合した混合溶液に、ヘキサフルオロリン酸リチウム（ＬｉＰＦ６）を１．０ｍｏｌ／Ｌの濃度となるように添加して用いた。このリチウム二次電池の設計容量は、１．８Ａｈであった。 Next, the cylindrical lithium secondary battery shown in FIG. 1 was produced using the produced positive electrode and negative electrode. A positive electrode lead and a negative electrode lead for drawing current were formed on the positive electrode and the negative electrode, respectively, by ultrasonic welding. The positive electrode lead and the negative electrode lead are made of the same material as the current collector, and are stacked with a polyethylene separator sandwiched between the tabbed positive electrode and negative electrode, wound in a spiral shape, and stored in a cylindrical battery container. did. And electrolyte solution was inject | poured and sealed in the battery container, and it was set as the lithium secondary battery. As the electrolytic solution, 1.0 mol / liter of lithium hexafluorophosphate (LiPF 6 ) was added to a mixed solution in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of EC: EMC = 1: 2. It added and used so that it might become the density | concentration of L. The design capacity of this lithium secondary battery was 1.8 Ah.
（実施例２）
　正極活物質に混合するトリイソプロポキシボロキシン（（ＢＯ）３（Ｏ（ＣＨ）（ＣＨ３）２）３）の量を０．５質量％にした以外は、実施例１と同様にしてリチウム二次電池を作製した。 (Example 2)
Lithium was treated in the same manner as in Example 1 except that the amount of triisopropoxyboroxine ((BO) 3 (O (CH) (CH 3 ) 2 ) 3 ) mixed with the positive electrode active material was 0.5% by mass. A secondary battery was produced.
（実施例３）
　正極活物質に混合するトリイソプロポキシボロキシン（（ＢＯ）３（Ｏ（ＣＨ）（ＣＨ３）２）３）の量を２．０質量％にした以外は、実施例１と同様にしてリチウム二次電池を作製した。 (Example 3)
Lithium was obtained in the same manner as in Example 1 except that the amount of triisopropoxyboroxine ((BO) 3 (O (CH) (CH 3 ) 2 ) 3 ) mixed with the positive electrode active material was 2.0% by mass. A secondary battery was produced.
（実施例４）
　正極活物質に混合するトリイソプロポキシボロキシン（（ＢＯ）３（Ｏ（ＣＨ）（ＣＨ３）２）３）の量を５．０質量％にした以外は、実施例１と同様にしてリチウム二次電池を作製した。 (Example 4)
Lithium was obtained in the same manner as in Example 1 except that the amount of triisopropoxyboroxine ((BO) 3 (O (CH) (CH 3 ) 2 ) 3 ) mixed in the positive electrode active material was 5.0% by mass. A secondary battery was produced.
（実施例５）
　正極活物質に混合するホウ酸エステルをトリメトキシボロキシン（（ＢＯ）３（ＯＣＨ３）３）にした以外は、実施例１と同様にしてリチウム二次電池を作製した。 (Example 5)
A lithium secondary battery was produced in the same manner as in Example 1 except that the boric acid ester mixed with the positive electrode active material was trimethoxyboroxine ((BO) 3 (OCH 3 ) 3 ).
（実施例６）
　正極活物質に混合するホウ酸エステルをトリメトキシボロキシン（（ＢＯ）３（ＯＣＨ３）３）とし、その量を０．５質量％にした以外は、実施例１と同様にしてリチウム二次電池を作製した。 (Example 6)
The boric acid ester mixed with the positive electrode active material was trimethoxyboroxine ((BO) 3 (OCH 3 ) 3 ) and the amount thereof was changed to 0.5% by mass. A battery was produced.
（実施例７）
　正極活物質に混合するホウ酸エステルをトリメトキシボロキシン（（ＢＯ）３（ＯＣＨ３）３）とし、その量を２．０質量％にした以外は、実施例１と同様にしてリチウム二次電池を作製した。 (Example 7)
The boric acid ester to be mixed with the positive electrode active material was trimethoxyboroxine ((BO) 3 (OCH 3 ) 3 ), and the amount thereof was set to 2.0% by mass. A battery was produced.
（実施例８）
　正極活物質に混合するホウ酸エステルをトリメトキシボロキシン（（ＢＯ）３（ＯＣＨ３）３）とし、その量を５．０質量％にした以外は、実施例１と同様にしてリチウム二次電池を作製した。 (Example 8)
The boric acid ester mixed with the positive electrode active material was trimethoxyboroxine ((BO) 3 (OCH 3 ) 3 ) and the amount thereof was 5.0% by mass. A battery was produced.
（実施例９）
　正極活物質に混合するホウ酸エステルをトリシクロヘキソキシボロキシン（（ＢＯ）３（Ｏ（Ｃ６Ｈ１１））３）にした以外は、実施例１と同様にしてリチウム二次電池を作製した。 Example 9
A lithium secondary battery was produced in the same manner as in Example 1 except that the boric acid ester mixed with the positive electrode active material was tricyclohexoxyboroxine ((BO) 3 (O (C 6 H 11 )) 3 ). .
（実施例１０）
　正極活物質に混合するホウ酸エステルをトリシクロヘキソキシボロキシン（（ＢＯ）３（Ｏ（Ｃ６Ｈ１１））３）とし、その量を０．５質量％にした以外は、実施例１と同様にしてリチウム二次電池を作製した。 (Example 10)
The boric acid ester mixed with the positive electrode active material was tricyclohexoxyboroxine ((BO) 3 (O (C 6 H 11 )) 3 ), and the amount thereof was changed to 0.5% by mass. Similarly, a lithium secondary battery was produced.
（実施例１１）
　正極活物質に混合するホウ酸エステルをトリシクロヘキソキシボロキシン（（ＢＯ）３（Ｏ（Ｃ６Ｈ１１））３）とし、その量を２．０質量％にした以外は、実施例１と同様にしてリチウム二次電池を作製した。 (Example 11)
The boric acid ester mixed with the positive electrode active material was tricyclohexoxyboroxine ((BO) 3 (O (C 6 H 11 )) 3 ), and the amount thereof was set to 2.0 mass%. Similarly, a lithium secondary battery was produced.
（実施例１２）
　正極活物質に混合するホウ酸エステルをトリシクロヘキソキシボロキシン（（ＢＯ）３（Ｏ（Ｃ６Ｈ１１））３）とし、その量を５．０質量％にした以外は、実施例１と同様にしてリチウム二次電池を作製した。 (Example 12)
The boric acid ester mixed with the positive electrode active material was tricyclohexoxyboroxine ((BO) 3 (O (C 6 H 11 )) 3 ), and the amount thereof was 5.0 mass%. Similarly, a lithium secondary battery was produced.
（比較例１）
　正極合剤スラリーにホウ酸エステル類を添加すること無く、実施例１と同様にしてリチウム二次電池を作製した。 (Comparative Example 1)
A lithium secondary battery was produced in the same manner as in Example 1 without adding boric acid esters to the positive electrode mixture slurry.
（比較例２）
　正極合剤スラリーにホウ酸エステル類に代えてリチウムビスオキサレートボレートを１．０質量％混合した以外は、実施例１と同様にしてリチウム二次電池を作製した。 (Comparative Example 2)
A lithium secondary battery was produced in the same manner as in Example 1 except that 1.0% by mass of lithium bisoxalate borate was mixed with the positive electrode mixture slurry instead of boric acid esters.
（比較例３）
　正極合剤スラリーにホウ酸エステル類に代えてトリメチルボロキシン（（ＢＯ）３（ＣＨ３）３）を１．０質量％混合した以外は、実施例１と同様にしてリチウム二次電池を作製した。 (Comparative Example 3)
A lithium secondary battery was produced in the same manner as in Example 1 except that 1.0% by mass of trimethylboroxine ((BO) 3 (CH 3 ) 3 ) was mixed with the positive electrode mixture slurry instead of boric acid esters. did.
　作製した実施例１乃至１２に係るリチウム二次電池、及び、比較例１乃至３に係るリチウム二次電池について、初期の直流内部抵抗を、以下の手順で測定した。はじめに、上限電圧を４．２Ｖ、電流値を１．８Ａとして、定電流定電圧で５時間充電した。次いで、終止電圧を３．０Ｖ、電流値を１．８Ａとして、定電流で放電した。その後、この充放電操作を計３サイクルまで繰り返した。続いて、上限電圧を４．２Ｖ、電流値を１．８Ａとして、定電流定電圧で５時間充電した。そして、１５分間休止した後、電流値を１．８Ａとして１０秒間放電し、このときの放電による電圧降下を測定した。そして、電圧値の変位を電流値で除算して、初期の直流内部抵抗値を求めた。 For the lithium secondary batteries according to Examples 1 to 12 and the lithium secondary batteries according to Comparative Examples 1 to 3, the initial DC internal resistance was measured by the following procedure. First, the battery was charged with a constant current and a constant voltage for 5 hours with an upper limit voltage of 4.2 V and a current value of 1.8 A. Next, the battery was discharged at a constant current with a final voltage of 3.0 V and a current value of 1.8 A. Then, this charge / discharge operation was repeated up to a total of 3 cycles. Subsequently, the battery was charged with a constant current and a constant voltage for 5 hours with an upper limit voltage of 4.2 V and a current value of 1.8 A. Then, after resting for 15 minutes, the current value was set to 1.8 A and discharged for 10 seconds, and the voltage drop due to the discharge at this time was measured. Then, the initial DC internal resistance value was obtained by dividing the displacement of the voltage value by the current value.
　実施例１乃至１２に係るリチウム二次電池、及び、比較例１乃至３に係るリチウム二次電池について求めた直流内部抵抗値（内部抵抗）と、目視により確認された正極合剤スラリー性状の結果を表１に示す。なお、表のスラリー性状において、正極合剤スラリーのゲル化が認められない場合を「○」、正極合剤スラリーのゲル化は認められないものの正極合剤の密着性が悪化する場合を「△」、正極合剤スラリーのゲル化が認められる場合を「×」として示す。また、内部抵抗は、比較例１の結果を１００としたときの相対値である。 DC internal resistance value (internal resistance) obtained for the lithium secondary batteries according to Examples 1 to 12 and the lithium secondary batteries according to Comparative Examples 1 to 3, and the results of the positive electrode mixture slurry properties visually confirmed Is shown in Table 1. In the slurry properties in the table, “◯” indicates that the gelation of the positive electrode mixture slurry is not recognized, and “Δ” indicates that the adhesion of the positive electrode mixture deteriorates although the gelation of the positive electrode mixture slurry is not recognized. ”, The case where gelation of the positive electrode mixture slurry is observed is indicated by“ x ”. The internal resistance is a relative value when the result of Comparative Example 1 is 100.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１に示すように、実施例１乃至１２では、正極合剤スラリーのゲル化が認められず、正極合剤スラリーを正極集電体に塗布するとき、粘度が高過ぎるようなことは無かった。実施例１乃至１２のように、ニッケルを高い割合で含む前記式（１）によって表される正極活物質を用いる場合、正極合剤スラリーの調製時にアルカリ度が高くなり易いが、前記式（１）によって表される正極活物質と前記式（２）によって表されるホウ酸エステルとが共存していることにより、アルカリ成分による結着剤の変性が抑制されたものと考えられる。また、実施例１乃至３、５乃至７、９乃至１１では、リチウム二次電池の内部抵抗が、比較例１よりも低くなった。この理由は、結着剤の変性が抑制されたことにより、正極合剤層中の粒子同士や、粒子と正極集電体との結着強度が向上し、粒子の分布のむらが低減された為であると考えられる。 As shown in Table 1, in Examples 1 to 12, no gelation of the positive electrode mixture slurry was observed, and when the positive electrode mixture slurry was applied to the positive electrode current collector, the viscosity was not too high. . When using the positive electrode active material represented by the formula (1) containing a high proportion of nickel as in Examples 1 to 12, the alkalinity tends to be high when preparing the positive electrode mixture slurry, but the formula (1) ) And the boric acid ester represented by the formula (2) coexist, it is considered that the denaturation of the binder by the alkali component is suppressed. In Examples 1 to 3, 5 to 7, and 9 to 11, the internal resistance of the lithium secondary battery was lower than that of Comparative Example 1. The reason for this is that by suppressing the denaturation of the binder, the binding strength between the particles in the positive electrode mixture layer and between the particles and the positive electrode current collector is improved, and the uneven distribution of the particles is reduced. It is thought that.
　また、実施例４、８、１２では、正極合剤スラリーのゲル化は認められなかったものの、正極合剤の密着性が悪化し、内部抵抗も比較例１より高くなった。よって、前記式（２）によって表されるホウ酸エステルの量は、５．０質量％未満が好ましいといえる。また、比較例２及び３では、正極合剤スラリーのゲル化が認められ、内部抵抗が実施例１、５及び９のそれぞれより高くなった。よって、前記式（２）によって表されるホウ酸エステルが結着剤の変性の抑制に有効であり、水素をアルキル置換したボロキシン誘導体や、他のホウ酸類は適していないと考えられる。 In Examples 4, 8, and 12, gelation of the positive electrode mixture slurry was not observed, but the adhesion of the positive electrode mixture was deteriorated and the internal resistance was higher than that of Comparative Example 1. Therefore, it can be said that the amount of the boric acid ester represented by the formula (2) is preferably less than 5.0% by mass. Further, in Comparative Examples 2 and 3, gelation of the positive electrode mixture slurry was observed, and the internal resistance was higher than those in Examples 1, 5, and 9, respectively. Therefore, the boric acid ester represented by the formula (2) is effective in suppressing the denaturation of the binder, and it is considered that boroxine derivatives in which hydrogen is alkyl-substituted and other boric acids are not suitable.
　実施例及び比較例では、Ｌｉ１．０２Ｎｉ０．８Ｍｎ０．０５Ｃｏ０．１５Ｏ２で表される正極活物質について正極合剤スラリーのゲル化抑制の効果を検討したが、前記式（１）で表される他の正極活物質についても、Ｎｉ含有割合が高く、残アルカリ量が多い傾向にあるため、前記式（２）で表されるホウ酸エステルを添加することにより、実施例１～１２と同様に正極合剤スラリーのゲル化を抑制できる。 In Examples and Comparative Examples, the positive electrode active material represented by Li 1.02 Ni 0.8 Mn 0.05 Co 0.15 O 2 was examined for the effect of suppressing the gelation of the positive electrode mixture slurry. The other positive electrode active material represented by (1) also has a high Ni content and tends to have a large amount of residual alkali. Therefore, by adding the boric acid ester represented by the above formula (2) As in Examples 1 to 12, gelation of the positive electrode mixture slurry can be suppressed.
１　リチウム二次電池
１０　正極
１１　セパレータ
１２　負極
１３　電池容器
１４　正極集電タブ
１５　負極集電タブ
１６　内蓋
１７　内圧開放弁
１８　ガスケット
１９　正温度係数抵抗素子
２０　電池蓋
２１　軸心 DESCRIPTION OF SYMBOLS 1 Lithium secondary battery 10 Positive electrode 11 Separator 12 Negative electrode 13 Battery container 14 Positive electrode current collection tab 15 Negative electrode current collection tab 16 Inner cover 17 Internal pressure release valve 18 Gasket 19 Positive temperature coefficient resistance element 20 Battery cover 21 Axis center

Claims (9)

  1. 　下記式（１）によって表される正極活物質と、下記式（２）によって表されるホウ酸エステルとを含むことを特徴とするリチウム二次電池用正極材料。
    　Ｌｉ１＋ａＮｉｂＭｎｃＣｏｄＭｅＯ２＋α・・・（１）
    ［但し、式（１）中、Ｍは、Ｍｇ、Ａｌ、Ｔｉ、Ｚｒ、Ｍｏ及びＮｂからなる群より選択される少なくとも１種の元素であり、ａ、ｂ、ｃ、ｄ、ｅ及びαは、－０．１≦ａ≦０．２、０．７＜ｂ≦０．９、０≦ｃ＜０．３、０≦ｄ＜０．３、０≦ｅ≦０．２５、ｂ＋ｃ＋ｄ＋ｅ＝１、及び、－０．２≦α≦０．２、を満たす数である。］
    　（ＢＯ）３（ＯＲ）３・・・（２）
    ［但し、式（２）中、Ｒは、炭素数１以上の有機基である。］     A positive electrode material for a lithium secondary battery comprising a positive electrode active material represented by the following formula (1) and a borate ester represented by the following formula (2).
    Li 1 + a Ni b Mn c Co d M e O 2 + α ··· (1)
    [In the formula (1), M is at least one element selected from the group consisting of Mg, Al, Ti, Zr, Mo and Nb, and a, b, c, d, e and α are , −0.1 ≦ a ≦ 0.2, 0.7 <b ≦ 0.9, 0 ≦ c <0.3, 0 ≦ d <0.3, 0 ≦ e ≦ 0.25, b + c + d + e = 1, And a number satisfying −0.2 ≦ α ≦ 0.2. ]
    (BO) 3 (OR) 3 (2)
    [However, in Formula (2), R is an organic group having 1 or more carbon atoms. ]
  2. 　請求項１に記載のリチウム二次電池用正極材料であって、
    　前記ホウ酸エステルが、トリイソプロポキシボロキシン、トリメトキシボロキシン及びトリシクロヘキソキシボロキシンのいずれかであることを特徴とするリチウム二次電池用正極材料。     The positive electrode material for a lithium secondary battery according to claim 1,
    The positive electrode material for a lithium secondary battery, wherein the borate ester is any of triisopropoxyboroxine, trimethoxyboroxine, and tricyclohexoxyboroxine.
  3. 　請求項１又は２に記載のリチウム二次電池用正極材料であって、
    　前記正極活物質と前記ホウ酸エステルの合計量に対する前記ホウ酸エステルの割合が５．０質量％未満であることを特徴とするリチウム二次電池用正極材料。     The positive electrode material for a lithium secondary battery according to claim 1 or 2,
    A positive electrode material for a lithium secondary battery, wherein a ratio of the borate ester to a total amount of the positive electrode active material and the borate ester is less than 5.0% by mass.
  4. 　請求項３に記載のリチウム二次電池用正極材料であって、
    　前記正極活物質と前記ホウ酸エステルの合計量に対する前記ホウ酸エステルの割合が０．５質量％以上２．０質量％以下であることを特徴とするリチウム二次電池用正極材料。     The positive electrode material for a lithium secondary battery according to claim 3,
    A positive electrode material for a lithium secondary battery, wherein a ratio of the borate ester to a total amount of the positive electrode active material and the borate ester is 0.5% by mass or more and 2.0% by mass or less.
  5. 　請求項１乃至４のいずれか一項に記載のリチウム二次電池用正極材料を含んでなるリチウム二次電池用正極。 A positive electrode for a lithium secondary battery comprising the positive electrode material for a lithium secondary battery according to any one of claims 1 to 4.
  6. 　請求項５に記載のリチウム二次電池用正極であって、
    　結着剤として有機バインダを含むことを特徴とするリチウム二次電池用正極。     The positive electrode for a lithium secondary battery according to claim 5,
    A positive electrode for a lithium secondary battery, comprising an organic binder as a binder.
  7. 　正極と、負極と、電解質と、を備えるリチウム二次電池であって、
    　前記正極は、請求項１乃至４のいずれか一項に記載のリチウム二次電池用正極材料を含むことを特徴とするリチウム二次電池。     A lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte,
    The said positive electrode contains the positive electrode material for lithium secondary batteries as described in any one of Claims 1 thru | or 4. The lithium secondary battery characterized by the above-mentioned.
  8. 　請求項７に記載のリチウム二次電池であって、
    　前記電解質は、ヘキサフルオロリン酸リチウムを含むことを特徴とするリチウム二次電池。     The lithium secondary battery according to claim 7,
    The lithium secondary battery, wherein the electrolyte includes lithium hexafluorophosphate.
  9. 　請求項７又は８に記載のリチウム二次電池であって、
    　前記正極は、結着剤を含み、
    　前記結着剤は、有機バインダであることを特徴とするリチウム二次電池。     The lithium secondary battery according to claim 7 or 8,
    The positive electrode includes a binder,
    The lithium secondary battery, wherein the binder is an organic binder.
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