WO2023243437A1 - Positive electrode active material, method for producing same, and nonaqueous electrolyte secondary battery - Google Patents

Positive electrode active material, method for producing same, and nonaqueous electrolyte secondary battery Download PDF

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WO2023243437A1
WO2023243437A1 PCT/JP2023/020617 JP2023020617W WO2023243437A1 WO 2023243437 A1 WO2023243437 A1 WO 2023243437A1 JP 2023020617 W JP2023020617 W JP 2023020617W WO 2023243437 A1 WO2023243437 A1 WO 2023243437A1
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positive electrode
electrode active
active material
secondary battery
producing
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PCT/JP2023/020617
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French (fr)
Japanese (ja)
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裕一郎 滝本
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愛知製鋼株式会社
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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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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 active material, a method for producing the same, and a non-aqueous electrolyte secondary battery.
  • Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries can easily increase energy density. Taking advantage of these characteristics, nonaqueous electrolyte secondary batteries have recently been used in a wide range of applications, including small electronic devices such as mobile phones and laptop computers, and large electric drive devices such as electric cars and hybrid cars.
  • LiNi 0.33 Mn 0.33 Co 0.33 O 2 (so-called NMC111) containing Li (lithium), Ni (nickel), Mn (manganese) and Co (cobalt), and Li , LiNi 0.8 Co 0.15 Al 0.05 O 2 (so-called NCA) containing Ni, Co and Al (aluminum) have been put into practical use.
  • NMC111 LiNi 0.33 Mn 0.33 Co 0.33 O 2
  • NCA LiNi 0.8 Co 0.15 Al 0.05 O 2
  • these positive electrode active materials contain Co, which is a rare element, there is a relatively high risk that raw material costs will increase due to various reasons such as changes in the supply and demand situation.
  • Patent Document 1 describes the general formula Li a Ni b Mn 1-b W c O 2 (where 1 ⁇ a ⁇ 1.2, 0.5 ⁇ b ⁇ 0.7, A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium-transition metal composite oxide represented by 0 ⁇ c ⁇ 0.02) is described.
  • the present invention has been made in view of this background, and provides a positive electrode active material that can reduce raw material costs, has high discharge capacity, and has excellent thermal stability and output characteristics, a method for producing the same, and a positive electrode active material that can reduce raw material costs, has high discharge capacity, and has excellent thermal stability and output characteristics.
  • the present invention aims to provide a non-aqueous electrolyte secondary battery using a positive electrode active material.
  • One embodiment of the present invention is a positive electrode active material used in a non-aqueous electrolyte secondary battery, comprising: Composition formula of Li a Ni b Mn c W d Mg e Of (however, a to f in the above composition formula are 0.9 ⁇ a ⁇ 1.2, 0.45 ⁇ b ⁇ 0.6, 0.25 ⁇ c ⁇ 0.5, 0 ⁇ d ⁇ 0.06, 0 ⁇ e ⁇ 0.1, 1.9 ⁇ f ⁇ 2.1.)
  • the positive electrode active material has a layered rock salt type crystal structure that can be assigned to space group R-3m.
  • Another aspect of the present invention is a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolyte,
  • the positive electrode is in a non-aqueous electrolyte secondary battery that includes the positive electrode active material of the above embodiment.
  • the positive electrode active material has the specific composition and crystal structure. Since the positive electrode active material does not contain Co, the risk of an increase in raw material costs can be reduced. Further, in the positive electrode active material, a portion of Mn in the Li--Ni--Mn-based positive electrode active material is replaced with W and Mg. In this way, by adding W and Mg to the Li--Ni--Mn-based positive electrode active material, it is possible to improve the thermal stability of the positive electrode active material while ensuring high discharge capacity and excellent output characteristics.
  • the positive electrode active material has high discharge capacity, excellent thermal stability and output characteristics, and can easily reduce raw material costs.
  • the non-aqueous electrolyte secondary battery of the above embodiment has a positive electrode containing the specific positive electrode active material. Therefore, the non-aqueous electrolyte secondary battery can easily reduce raw material cost, has high discharge capacity, and is excellent in thermal stability and output characteristics.
  • FIG. 1 is a developed view showing the internal structure of a secondary battery in an example.
  • the positive electrode active material has a composition formula of Li a Ni b Mn c W d Mg e Of (however, a to f in the composition formula are 0.9 ⁇ a ⁇ 1.2, 0.45 ⁇ b ⁇ 0 .6, 0.25 ⁇ c ⁇ 0.5, 0 ⁇ d ⁇ 0.06, 0 ⁇ e ⁇ 0.1, 1.9 ⁇ f ⁇ 2.1.) have.
  • the value of a in the above compositional formula that is, the molar ratio of Li to the total number of moles of Li, Ni, Mn, W, Mg, and O is greater than 0.9 and less than 1.2.
  • a phenomenon called cation mixing in which lithium ion sites are replaced by transition metal ions, tends to occur in the crystal lattice of the positive electrode active material. Therefore, in this case, it becomes difficult to form a sufficient diffusion path for lithium ions in the positive electrode active material, which may lead to a decrease in discharge capacity and output characteristics.
  • the value of a in the above compositional formula is 1.2 or more, a lithium-excess layered rock salt crystal structure belonging to the space group C2/m is likely to be formed in the positive electrode active material, and the output characteristics This may lead to a decrease in
  • the value of d in the above composition formula that is, the molar ratio of W to the total number of moles of Li, Ni, Mn, W, Mg, and O is greater than 0 and less than 0.06.
  • the value of e in the composition formula that is, the molar ratio of Mg to the total number of moles of Li, Ni, Mn, W, Mg, and O is greater than 0 and less than 0.1.
  • the value of d in the compositional formula is 0, that is, if only Mg of W and Mg is added to the positive electrode active material, there is a risk that the discharge capacity and output characteristics will deteriorate.
  • the value of d in the composition formula is preferably 0.005 or more, and more preferably 0.01 or more.
  • a crystalline phase having a crystal structure other than the specific layered rock salt type crystal structure is likely to be formed in the positive electrode active material, and the discharge capacity and thermal This may lead to a decrease in stability.
  • the value of e in the compositional formula is 0, that is, if only W out of W and Mg is added to the positive electrode active material, there is a risk that the thermal stability of the positive electrode active material will decrease. be.
  • the value of e in the composition formula is preferably 0.005 or more, and more preferably 0.01 or more.
  • the values of b, c, and f in the above compositional formula that is, the molar ratio of Ni, Mn, or O to the total number of moles of Li, Ni, Mn, W, Mg, and O, are each within a range that satisfies the above relationship. .
  • a crystal phase having a crystal structure other than the specific layered rock salt crystal structure is likely to be formed in the positive electrode active material, This may lead to a decrease in discharge capacity.
  • the value of b in the compositional formula is preferably greater than 0.5 and less than 0.6.
  • the positive electrode active material has a composition formula of Li a Ni b Mn c W d Mg e Of (however, a to f in the composition formula are 0.9 ⁇ a ⁇ 1.2, 0.5 ⁇ b ⁇ 0.6, 0.25 ⁇ c ⁇ 0.5, 0 ⁇ d ⁇ 0.06, 0 ⁇ e ⁇ 0.1, 1.9 ⁇ f ⁇ 2.1.) It is preferable to have the following composition.
  • the value of c in the composition formula is preferably more than 0.25 and less than 0.42.
  • the positive electrode active material has a composition formula of Li a Ni b Mn c W d Mg e Of (however, a to f in the above composition formula are 0.9 ⁇ a ⁇ 1.2, 0.45 ⁇ b ⁇ 0.6, 0.25 ⁇ c ⁇ 0.42, 0 ⁇ d ⁇ 0.06, 0 ⁇ e ⁇ 0.1, 1.9 ⁇ f ⁇ 2.1.) It is preferable to have the following composition.
  • the positive electrode active material has a composition formula of Li a Ni b Mn c W d Mg e Of (however, a to f in the above composition formula are 0.9 ⁇ a ⁇ 1.2, 0.5 ⁇ b ⁇ 0.6, 0.25 ⁇ c ⁇ 0.42, 0 ⁇ d ⁇ 0.06, 0 ⁇ e ⁇ 0.1, 1.9 ⁇ f ⁇ 2.1.) It is more preferable to have a composition of Li a Ni b Mn c W d Mg e Of (however, a to f in the above composition formula are 0.9 ⁇ a ⁇ 1.2, 0. The following relationships are satisfied: 5 ⁇ b ⁇ 0.6, 0.25 ⁇ c ⁇ 0.42, 0.01 ⁇ d ⁇ 0.06, 0 ⁇ e ⁇ 0.08, 1.9 ⁇ f ⁇ 2.1. ) It is more preferable to have a composition represented by:
  • the a-axis length in the crystal lattice of the positive electrode active material is 2.880 ⁇ or more and 2.900 ⁇ or less, and the c-axis length is 14.290 ⁇ or more and 14.360 ⁇ or less.
  • the positive electrode active material has a diffraction angle of 64.5 ⁇ 1 with respect to a half-width w 44 of a peak appearing in a diffraction angle range of 44.4 ⁇ 1° in an X-ray diffraction pattern obtained by the ⁇ -2 ⁇ method. It is preferable to have a crystal structure in which the ratio w 64 / w 44 of the half width w 64 of the peak appearing in the range of 1.10 to 1.30 is obtained.
  • the positive electrode active material may contain a crystal phase having a crystal structure other than the specific layered rock salt type crystal structure as long as the above-described effects are not impaired.
  • the content of the crystalline phase having a crystal structure other than the specific layered rock salt crystal structure is preferably 20% by mass or less, more preferably 15% by mass or less, and preferably 10% by mass or less. More preferred.
  • the content of the crystalline phase in the positive electrode active material described above can be calculated based on the X-ray diffraction pattern obtained by powder X-ray diffraction method. More specifically, the scanning range of the diffraction angle 2 ⁇ in the powder X-ray diffraction method is 10° to 90°, the scanning speed is 2°/min, the sampling width is 0.02°, and the X-ray light source is CuK ⁇ radiation. shall be.
  • the above-mentioned positive electrode active material is usually used in a powder form from the viewpoint of further shortening the diffusion distance of lithium ions in the positive electrode active material. It is preferable that the positive electrode active material is composed of particles having a particle size of 10 ⁇ m or less. That is, the positive electrode active material may be composed of primary particles having a particle size distribution such that the maximum particle size is 10 ⁇ m or less, or may be formed by agglomeration of primary particles such that the maximum particle size is 10 ⁇ m or less.
  • the secondary particles may have a particle size distribution. In this case, the diffusion distance of lithium ions in the positive electrode active material can be made shorter, and the internal resistance in the non-aqueous electrolyte secondary battery can be more easily reduced. From the viewpoint of further shortening the diffusion distance of lithium ions in the positive electrode active material, the positive electrode active material is preferably composed of primary particles having a particle size of 1 ⁇ m or less.
  • the particle diameter of the primary particles of the positive electrode active material described above can be measured based on an enlarged photograph obtained by observing the positive electrode active material using a scanning electron microscope (SEM). More specifically, for 50 or more positive electrode active material particles randomly selected from enlarged photographs observed with SEM, the circumscribed circle for each particle is determined, and the diameter is taken as the particle diameter of each particle. . The maximum value of these particle sizes is defined as the particle size of the positive electrode active material. Further, the particle diameter of the secondary particles of the positive electrode active material described above can be measured using a laser scattering type particle size distribution measuring device.
  • SEM scanning electron microscope
  • Method for producing positive electrode active material for example, a solid phase method can be adopted. Specifically, after preparing a mixture containing a compound serving as a Li source, a compound serving as a Ni source, a compound serving as a Mn source, a compound serving as a W source, and a compound serving as a Mg source, the mixture is heated under an oxidizing gas atmosphere. You can bake it with The ratio of each compound in the mixture may be appropriately set according to the desired compositional formula of the crystal phase in the positive electrode active material.
  • the mixture is a powder.
  • each raw material compound can be uniformly dispersed in the mixture. As a result, the deviation in composition of the fired body after firing can be further reduced, and the content of the crystal phase can be further increased.
  • the raw material compounds When producing a powdery mixture, the raw material compounds may be pulverized as necessary.
  • the pulverization method manual pulverization using a mortar, mechanical pulverization using a ball mill, etc. can be adopted.
  • the particle size of the mixture may be adjusted by classifying the raw material compound using a sieve or the like. By reducing the particle size of the mixture as much as possible using these techniques, the raw material compounds can be more uniformly dispersed. As a result, the deviation in composition of the fired body after firing can be further reduced, and the content of the crystal phase can be further increased.
  • a fired body of the positive electrode active material containing the specific crystal phase can be obtained.
  • the oxidizing gas for example, the atmosphere can be used.
  • the firing temperature during firing can be appropriately set within the range of 800 to 1100°C.
  • the holding time during firing can be appropriately set within the range of 0.5 to 50 hours.
  • a powdered positive electrode active material can be obtained by crushing the obtained fired body.
  • the method for crushing the fired body is not particularly limited. For example, various methods such as manual crushing using a mortar, mechanical crushing using a ball mill, etc. can be used as the crushing method. Further, after crushing the fired body, the powder may be classified as necessary to adjust the particle size of the positive electrode active material.
  • a coprecipitation method may be employed as a method for producing the positive electrode active material.
  • a coprecipitation method for example, an alkaline reaction solution, a raw material solution containing ions of two or more metal elements excluding Li among the metal elements constituting the positive electrode active material, and an alkaline Prepare a pH adjustment solution. Thereafter, the raw material solution containing the ions is dropped into the reaction solution, and at the same time, a pH adjustment solution is added dropwise to adjust the pH of the reaction solution after the raw material solution has been dropped. As a result, a precursor containing the aforementioned metal element is precipitated in the reaction solution.
  • the concentration of each ion in the raw material solution may be appropriately set according to the desired compositional formula of the crystal phase in the positive electrode active material.
  • a compound serving as a Li source and other raw materials added as necessary are mixed with the precursor to prepare a mixture.
  • a fired body of the positive electrode active material containing the specific crystal phase can be obtained.
  • the atmosphere can be used as the oxidizing gas.
  • the firing temperature during firing can be appropriately set within the range of 800 to 1100°C.
  • the holding time during firing can be appropriately set within the range of 0.5 to 50 hours.
  • a powdered positive electrode active material can be obtained by crushing the obtained fired body.
  • the method for crushing the fired body is not particularly limited. For example, various methods such as manual crushing using a mortar, mechanical crushing using a ball mill, etc. can be used as the crushing method. Further, after crushing the fired body, the powder may be classified as necessary to adjust the particle size of the positive electrode active material.
  • a precursor containing all metal elements other than Li in the composition is produced by a coprecipitation method, and a mixture is produced by mixing the precursor and a compound containing Li. death, It is preferable to obtain the positive electrode active material by firing the mixture in an oxidizing gas atmosphere.
  • the distribution of each metal element in the precursor can be made more uniform. Then, by mixing such a precursor and a compound serving as a Li source and then firing the mixture, a more homogeneous positive electrode active material can be obtained. According to this method, the discharge capacity, output characteristics, and thermal stability of the positive electrode active material can be improved in a better balance.
  • the number of raw material solutions dropped into the reaction solution may be one or two or more.
  • some of the compounds may be difficult to dissolve in the raw material solution, making it difficult to adjust the ratio of metal elements in the precursor to a desired range.
  • this raw material solution may be dropped into the reaction solution. More specifically, when producing the precursor, a reaction solution exhibiting alkalinity, a first raw material solution containing W, a second raw material solution containing a metal element other than Li and W in the composition, Prepare, Dropping the first raw material solution into the second raw material solution to create a mixed solution, Thereafter, the mixed solution can be dropped into the reaction solution to produce the precursor.
  • all the raw material solutions may be dropped into the reaction solution at the same time. More specifically, when producing the precursor, a reaction solution exhibiting alkalinity, a first raw material solution containing W, a second raw material solution containing a metal element other than Li and W in the composition, Prepare, The precursor can also be produced by simultaneously dropping the first raw material solution and the second raw material solution into the reaction solution.
  • a pH adjusting solution exhibiting alkalinity is prepared, and the pH adjusting solution is dropped into the reaction solution together with the first raw material solution, the second raw material solution, or the mixed solution.
  • the precursor may be produced by In this case, changes in the pH of the reaction solution due to dropping of the raw material solution can be suppressed, and a precursor having a desired composition can be produced more reliably.
  • the positive electrode active material is used in nonaqueous electrolyte secondary batteries, and is particularly suitable for lithium ion secondary batteries.
  • the secondary battery can include a positive electrode containing the positive electrode active material, a negative electrode, a separator, a non-aqueous electrolyte, an additive, a case housing these, and the like as main components.
  • the shape of the secondary battery includes, for example, a coin shape, a cylindrical shape, a stacked type, a square shape, and the like.
  • the positive electrode of the secondary battery includes a positive electrode active material and a positive electrode current collector that holds the positive electrode active material.
  • a positive electrode current collector various conductors can be used, such as metal foils such as copper foil, aluminum foil, and nickel foil, stainless steel mesh, punched metal, expanded metal, and metal mesh.
  • the positive electrode may include a binder interposed between the positive electrode active material and the positive electrode current collector.
  • a binder for example, fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, and thermoplastic resins such as polypropylene, polyethylene, and polyethylene terephthalate can be used.
  • the positive electrode may contain a conductive agent or a conductive aid to improve electrical conductivity.
  • a conductive agent for example, graphite, carbon black, acetylene black, coke, etc. can be used.
  • the positive electrode can be produced, for example, by the following method. First, a paste-like positive electrode composite material containing a positive electrode active material is prepared. The positive electrode mixture may contain an organic solvent for dispersing or dissolving solid content such as the positive electrode active material, if necessary. Next, a positive electrode active material layer is formed on the surface of the positive electrode current collector by applying the positive electrode mixture onto the surface of the positive electrode current collector and drying it. After forming the positive electrode active material layer, the positive electrode active material layer may be pressed as necessary to increase the density of the positive electrode active material layer. A positive electrode can be obtained through the above steps.
  • a negative electrode of a secondary battery includes a negative electrode active material and a negative electrode current collector that holds the negative electrode active material.
  • a negative electrode active material for example, a carbon material having a graphite structure such as graphite or hard carbon, or a lithium-based oxide such as lithium titanate (Li 4 Ti 5 O 12 ) can be used.
  • a conductor similar to the above-described positive electrode current collector can be used.
  • the negative electrode may contain a binder, a conductive agent, and a conductive aid.
  • the binder, conductive agent, and conductive aid that can be used for the negative electrode are the same as those for the positive electrode.
  • the method for producing the negative electrode is the same as that for the positive electrode. That is, first, a paste-like negative electrode composite material containing a negative electrode active material is produced.
  • the negative electrode composite material may contain an organic solvent for dispersing or dissolving solid content such as the negative electrode active material, if necessary.
  • a negative electrode active material layer is formed on the surface of the negative electrode current collector by applying the negative electrode composite material onto the surface of the negative electrode current collector and drying it. After forming the negative electrode active material layer, the negative electrode active material layer may be pressed as necessary to increase the density of the negative electrode active material layer.
  • a negative electrode can be obtained through the above steps.
  • the non-aqueous electrolyte can contain an organic solvent and an electrolyte made of a lithium salt.
  • the lithium salt include LiPF 6 and the like.
  • the organic solvent can be at least one selected from the group consisting of ethylene carbonate, dimethyl carbonate, and ethylmethyl carbonate. These organic solvents have high polarity and can dissolve a large amount of electrolyte. Therefore, by using these organic solvents as a nonaqueous electrolyte, it is possible to easily increase the transfer number of charge carriers such as lithium ions in a secondary battery.
  • the positive electrode active material of this example has a composition formula of Li a Ni b Mn c W d Mg e Of (however, a to f in the above composition formula are 0.9 ⁇ a ⁇ 1.2, 0.45 ⁇ b ⁇ 0.6, 0.25 ⁇ c ⁇ 0.5, 0 ⁇ d ⁇ 0.06, 0 ⁇ e ⁇ 0.1, 1.9 ⁇ f ⁇ 2.1.) It has a composition. Further, the positive electrode active material has a layered rock salt type crystal structure that can be assigned to space group R-3m.
  • test materials S1 to S9 in this example have the compositions shown in Table 1.
  • test materials R1 to R8 in Table 1 are positive electrode active materials for comparison with test materials S1 to S9.
  • the method for producing the positive electrode active material of this example will be explained below.
  • Test material S1 200 mL of distilled water was placed in a 2 L reaction vessel, and sodium hydroxide was dissolved therein to prepare a reaction solution with a pH of 12. Separately from this reaction solution, a raw material solution in which nickel sulfate and manganese sulfate were dissolved in distilled water, and a pH adjustment solution in which a sodium hydroxide aqueous solution and aqueous ammonia were mixed were prepared.
  • reaction solution was heated to 50°C.
  • a precursor containing Ni and Mn was precipitated in the reaction solution by simultaneously dropping the raw material solution and the pH adjustment solution into the reaction solution while stirring the reaction solution while maintaining the temperature of the reaction solution.
  • a mixture was prepared by mixing the thus obtained precursor with LiOH as a Li source, WO 3 as a W source, and MgO as an Mg source. This mixture was fired in the air at a temperature of 950° C. for 5 hours, and then annealed at a temperature of 700° C. for 12 hours to obtain a bulk positive electrode active material.
  • a powdered positive electrode active material (test material S1) was obtained by crushing the lumped positive electrode active material using a mortar. Note that the symbol "M1" is written in the "Production method” column of Table 1 for the positive electrode active material produced by the method described above.
  • Test materials R1 to R3 have the same configuration as test material S1, except that at least one of W and Mg is not included.
  • the method for producing test materials R1 to R3 is the same as the method for producing test material S1, except that WO 3 and/or MgO is not added to the precursor.
  • Test materials S2 to S9 200 mL of distilled water was placed in a 2 L reaction vessel, and sodium hydroxide was dissolved therein to prepare a reaction solution with a pH of 12. Separately from this reaction solution, a first raw material solution in which ammonium tungstate is dissolved in distilled water, a second raw material solution in which nickel sulfate, manganese sulfate and magnesium sulfate are dissolved in distilled water, an aqueous sodium hydroxide solution and ammonia A pH adjusting solution was prepared by mixing with water.
  • reaction solution was heated to 50°C. Ni, Mn, W, and A precursor containing Mg was precipitated.
  • a mixture was prepared by mixing LiOH as a Li source with the precursor. This mixture was fired in the air at a temperature of 950° C. for 5 hours, and then annealed at a temperature of 700° C. for 12 hours to obtain a bulk positive electrode active material. Powdered positive electrode active materials (test materials S2 to S9) were obtained by crushing the bulk positive electrode active materials using a mortar. Note that the symbol "M2" is written in the "Production method" column of Table 1 for the positive electrode active material produced by the method described above.
  • Test materials R4 to R8 have the same configuration as test materials S2 to S9, except that at least one of W and Mg is not included.
  • the method for producing test materials R4 to R8 was the same as the method for producing test materials S2 to S9, except that WO 3 and/or MgO was not added to the precursor.
  • test materials S1 to S9 and test materials R1 to S8 were identified.
  • composition of positive electrode active material The molar ratio of each metal element in the positive electrode active material was measured by inductively coupled plasma emission spectrometry (ie, ICP-AES). The composition of each test material when the molar ratio of oxygen atoms was 2 was as shown in the "Composition of positive electrode active material" column of Table 1.
  • the crystal structure of the positive electrode active material was identified and the lattice constant was measured by powder X-ray diffraction.
  • the X-ray diffraction apparatus "SmartLab (registered trademark)" manufactured by Rigaku Co., Ltd. was used, and the characteristic X-rays irradiated were CuK ⁇ rays.
  • the scanning range of the diffraction angle 2 ⁇ was 10° to 90°, the scanning speed was 2°/min, and the sampling width was 0.02°.
  • test materials S1 to S9 and test materials R1 to R8 all had layered rock-salt crystal structures that could be assigned to space group R-3m. It had Table 1 shows the lengths of the a-axis and the c-axis in the crystal lattice of each positive electrode active material. Table 2 also shows the content of layered rock-salt crystal structure in each positive electrode active material, and the half-width w of the peak appearing in the diffraction angle range of 44.4 ⁇ 1°. The ratio w 64 /w 44 of the half width w 64 of the peak appearing in the range is shown.
  • the nonaqueous electrolyte secondary battery 1 of this example is a CR2032 type coin battery including a positive electrode 2, a negative electrode 3, a separator 4, and a nonaqueous electrolyte 5.
  • the secondary battery 1 includes a case 11 that is relatively small in height and has a cylindrical shape with a bottom, and an upper lid 12 that closes the opening of the case 11. A space is formed between the case 11 and the upper lid 12. The upper lid 12 is joined to the case 11 by caulking.
  • a positive electrode 2, a negative electrode 3, a separator 4, and a non-aqueous electrolyte 5 are housed in the space between the case 11 and the upper lid 12.
  • a rubber packing 15 is arranged between the positive electrode 2 and the separator 4.
  • a spacer 13 and a washer 14 are provided between the upper lid 12 and the positive electrode 2. Spacer 13 is arranged so as to be in contact with positive electrode 2 .
  • the washer 14 is arranged between the spacer 13 and the upper lid 12.
  • the spacer 13 of this example is a disc-shaped stainless steel plate.
  • the positive electrode 2 includes a positive electrode current collector 21 and a positive electrode active material layer 22 provided on the positive electrode current collector 21 and containing one of the positive electrode active materials shown in Table 1.
  • the positive electrode current collector 21 of this example is an aluminum foil having a disc shape with a diameter of 16 mm.
  • the negative electrode 3 is a disk-shaped metal lithium foil.
  • the separator 4 is made of polypropylene and is interposed between the positive electrode 2 and the negative electrode 3.
  • the non-aqueous electrolyte 5 is filled between at least the positive electrode 2 and the negative electrode 3 in the secondary battery 1 .
  • the non-aqueous electrolyte 5 of this example is made of an ethylene carbonate-based organic solvent containing LiPF 6 at a concentration of 1 mol/L.
  • a positive electrode composite material was obtained.
  • This positive electrode composite material was applied onto the positive electrode current collector 21 to form the positive electrode active material layer 22.
  • the thickness of the positive electrode active material layer 22 immediately after coating was approximately 220 ⁇ m.
  • the positive electrode active material layer 22 on the positive electrode current collector 21 was pressed at a pressure of about 100 MPa. Thereafter, the positive electrode 2 was obtained by punching the positive electrode active material layer 22 together with the positive electrode current collector 21 into a disk shape with a diameter of 16 mm. Further, a negative electrode 3 was produced by punching out a lithium foil into a disk shape.
  • the secondary battery was charged in constant current mode at a temperature of 25°C.
  • the current density in constant current mode was 11 mA/g, and the end-of-charge voltage was 4.5V.
  • the battery was discharged to 2.5V at a constant current with a current density of 11 mA/g, and a discharge curve at this time was obtained. Based on the discharge curve obtained in this way, the discharge capacity of the secondary battery was calculated.
  • Table 2 shows the discharge capacity of secondary batteries using each positive electrode active material.
  • the secondary battery was charged in constant current-constant voltage mode at a temperature of 25°C.
  • the current density in constant current mode was 11 mA/g.
  • the end-of-charge voltage in the constant voltage mode was set to 4.5 V, and the end-of-charge voltage was maintained by flowing an appropriate charging current for 5 hours after the voltage of the secondary battery reached the end-of-charge voltage.
  • the secondary battery was disassembled in a glove box filled with an argon atmosphere, and the positive electrode was taken out. After washing this positive electrode with dimethyl carbonate, it was dried in a glove box.
  • the positive electrode active material layer was collected from the dried positive electrode and subjected to differential scanning calorimetry analysis.
  • the conditions for differential scanning calorimetry were as follows.
  • Measurement start temperature Room temperature Measurement end temperature: 500°C Heating rate: 10°C/min
  • Table 2 shows the peak temperature of the exothermic peak appearing in the DSC curve obtained by differential scanning calorimetry and the calorific value at the exothermic peak.
  • test materials S1 to S8 have a composition represented by the above-mentioned specific compositional formula and a layered rock salt type crystal structure represented by space group R-3m. Therefore, as shown in Table 2, these test materials have excellent thermal stability and output characteristics.
  • test material R1 which has the same Ni content as test materials S1 to S8 and does not contain both W and Mg, has a higher DC resistance and inferior output characteristics than test materials S1 to S8. ing. Furthermore, the test material R1 has a larger calorific value than the test materials S1 to S8, and is inferior in thermal stability.
  • Test material R2 which has the same Ni content as test materials S1 to S8 and does not contain Mg, has a lower exothermic peak temperature than test materials S1 to S8, and may decompose at a relatively low temperature. Furthermore, test material R2 has a large calorific value and is inferior in thermal stability.
  • Test material R4 which has the same Ni content as test materials S1 to S8 and does not contain Mg, has a larger calorific value and inferior thermal stability than test materials S1 to S8.
  • Test materials R3 and R5 which have the same Ni content as test materials S1 to S8 and do not contain W, have higher DC resistance and inferior output characteristics than test materials S1 to S8.
  • test material S9 has a composition represented by the above-mentioned specific compositional formula, and has a layered rock salt type crystal structure represented by a space group R-3m. Therefore, test material S9 has excellent thermal stability and output characteristics.
  • test material R6 which has the same Ni content as the test material S9 and does not contain both W and Mg, has a higher DC resistance and inferior output characteristics than the test material S9.
  • test material R6 has a lower exothermic peak temperature than test material S9, and there is a risk that it will decompose at a relatively low temperature.
  • test material R6 has a large calorific value and is inferior in thermal stability.
  • Test material R7 which has the same Ni content as test material S9 and does not contain Mg, has a larger calorific value and inferior thermal stability than test material S9.
  • Test material R8 which has the same Ni content as test material S9 and does not contain W, has a higher DC resistance and inferior output characteristics than test material S9.

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Abstract

This positive electrode active material is constituted for use in nonaqueous electrolyte secondary batteries. The positive electrode active material has a composition represented by a composition formula LiNiMnWMgO (a-f in the composition formula satisfy the relationship 0.9<a<1.2, 0.45<b<0.6, 0.25<c<0.5, 0<d<0.06, 0<e<0.1, and 1.9<f<2.1),a b c d e fand has a layered rock-salt type crystal structure that can be attributed to a space group R-3m.

Description

正極活物質、その製造方法及び非水電解液二次電池Positive electrode active material, its manufacturing method, and non-aqueous electrolyte secondary battery
　本発明は、正極活物質、その製造方法及び非水電解液二次電池に関する。 The present invention relates to a positive electrode active material, a method for producing the same, and a non-aqueous electrolyte secondary battery.
　リチウムイオン二次電池などの非水電解液二次電池は、エネルギー密度を容易に高くすることができる。かかる特性を活かし、近年では、携帯電話及びラップトップコンピュータ等の小型電子機器や、電気自動車及びハイブリッド自動車等の大型電気駆動装置等の幅広い用途に非水電解液二次電池が用いられている。 Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries can easily increase energy density. Taking advantage of these characteristics, nonaqueous electrolyte secondary batteries have recently been used in a wide range of applications, including small electronic devices such as mobile phones and laptop computers, and large electric drive devices such as electric cars and hybrid cars.
　非水電解液二次電池の正極活物質としては、Ｌｉ（リチウム）、Ｎｉ（ニッケル）、Ｍｎ（マンガン）及びＣｏ（コバルト）を含むＬｉＮｉ0.33Ｍｎ0.33Ｃｏ0.33Ｏ2（いわゆるＮＭＣ１１１）や、Ｌｉ、Ｎｉ、Ｃｏ及びＡｌ（アルミニウム）を含むＬｉＮｉ0.8Ｃｏ0.15Ａｌ0.05Ｏ2（いわゆるＮＣＡ）などが実用化されている。しかし、これらの正極活物質よりもさらに放電容量の高い正極活物質が強く望まれている。また、これらの正極活物質は、希少元素であるＣｏを含有しているため、需給状況の変化等の種々の理由によって原料コストが上昇するリスクが比較的高い。 As positive electrode active materials for non-aqueous electrolyte secondary batteries, LiNi 0.33 Mn 0.33 Co 0.33 O 2 (so-called NMC111) containing Li (lithium), Ni (nickel), Mn (manganese) and Co (cobalt), and Li , LiNi 0.8 Co 0.15 Al 0.05 O 2 (so-called NCA) containing Ni, Co and Al (aluminum) have been put into practical use. However, there is a strong desire for a positive electrode active material that has an even higher discharge capacity than these positive electrode active materials. Furthermore, since these positive electrode active materials contain Co, which is a rare element, there is a relatively high risk that raw material costs will increase due to various reasons such as changes in the supply and demand situation.
　Ｃｏを含まない正極活物質として、例えば特許文献１には、一般式ＬｉaＮｉbＭｎ1-bＷcＯ２（但し１＜ａ＜１．２、０．５≦ｂ≦０．７、０＜ｃ≦０．０２）で表されるリチウム遷移金属複合酸化物からなる非水電解液二次電池用正極活物質が記載されている。 As a positive electrode active material that does not contain Co, for example, Patent Document 1 describes the general formula Li a Ni b Mn 1-b W c O 2 (where 1<a<1.2, 0.5≦b≦0.7, A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium-transition metal composite oxide represented by 0<c≦0.02) is described.
特開２０１２－４３６３７号公報Japanese Patent Application Publication No. 2012-43637
　非水電解液二次電池の正極と負極とが何らかの原因で短絡した場合に、ジュール熱によって非水電解液二次電池の温度が上昇することがある。また、非水電解液二次電池の温度が過度に上昇すると、正極活物質の分解を招くおそれがある。かかる観点から、特許文献１に記載された正極活物質よりもさらに高い熱的安定性を有する正極活物質が望まれている。 If the positive and negative electrodes of a non-aqueous electrolyte secondary battery are short-circuited for some reason, the temperature of the non-aqueous electrolyte secondary battery may rise due to Joule heat. Furthermore, if the temperature of the non-aqueous electrolyte secondary battery rises excessively, there is a risk that the positive electrode active material will decompose. From this point of view, a positive electrode active material having higher thermal stability than the positive electrode active material described in Patent Document 1 is desired.
　本発明は、かかる背景に鑑みてなされたものであり、原料コストを低減することができ、高い放電容量を有し、熱的安定性及び出力特性に優れた正極活物質、その製造方法及びこの正極活物質を用いた非水電解液二次電池を提供しようとするものである。 The present invention has been made in view of this background, and provides a positive electrode active material that can reduce raw material costs, has high discharge capacity, and has excellent thermal stability and output characteristics, a method for producing the same, and a positive electrode active material that can reduce raw material costs, has high discharge capacity, and has excellent thermal stability and output characteristics. The present invention aims to provide a non-aqueous electrolyte secondary battery using a positive electrode active material.
　本発明の一態様は、非水電解液二次電池に用いられる正極活物質であって、
　ＬｉaＮｉbＭｎcＷdＭｇeＯfの組成式（ただし、前記組成式におけるａ～ｆは、０．９＜ａ＜１．２、０．４５＜ｂ＜０．６、０．２５＜ｃ＜０．５、０＜ｄ＜０．０６、０＜ｅ＜０．１、１．９＜ｆ＜２．１の関係を満たす。）で表される組成を有するとともに、
　空間群Ｒ－３ｍに帰属可能な層状岩塩型結晶構造を有する、正極活物質にある。 One embodiment of the present invention is a positive electrode active material used in a non-aqueous electrolyte secondary battery, comprising:
Composition formula of Li a Ni b Mn c W d Mg e Of (however, a to f in the above composition formula are 0.9<a<1.2, 0.45<b<0.6, 0.25 <c<0.5, 0<d<0.06, 0<e<0.1, 1.9<f<2.1.)
The positive electrode active material has a layered rock salt type crystal structure that can be assigned to space group R-3m.
　本発明の他の態様は、正極と、負極と、非水電解液とを有する非水電解液二次電池であって、
　前記正極は、前記の態様の正極活物質を含む、非水電解液二次電池にある。 Another aspect of the present invention is a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolyte,
The positive electrode is in a non-aqueous electrolyte secondary battery that includes the positive electrode active material of the above embodiment.
　前記正極活物質は、前記特定の組成及び結晶構造を有している。前記正極活物質にはＣｏが含まれていないため、原料コスト上昇のリスクを低減することができる。また、前記正極活物質においては、Ｌｉ－Ｎｉ－Ｍｎ系正極活物質におけるＭｎの一部がＷ及びＭｇにより置換されている。このように、Ｌｉ－Ｎｉ－Ｍｎ系正極活物質にＷ及びＭｇを添加することにより、高い放電容量及び優れた出力特性を確保しつつ正極活物質の熱的安定性を向上させることができる。 The positive electrode active material has the specific composition and crystal structure. Since the positive electrode active material does not contain Co, the risk of an increase in raw material costs can be reduced. Further, in the positive electrode active material, a portion of Mn in the Li--Ni--Mn-based positive electrode active material is replaced with W and Mg. In this way, by adding W and Mg to the Li--Ni--Mn-based positive electrode active material, it is possible to improve the thermal stability of the positive electrode active material while ensuring high discharge capacity and excellent output characteristics.
　従って、前記正極活物質は、高い放電容量を有し、熱的安定性及び出力特性に優れているとともに、原料コストを容易に低減することができる。 Therefore, the positive electrode active material has high discharge capacity, excellent thermal stability and output characteristics, and can easily reduce raw material costs.
　また、前記の態様の非水電解液二次電池は、前記特定の正極活物質を含む正極を有している。それ故、前記非水電解液二次電池は、原料コストを容易に低減することができ、高い放電容量を有し、熱的安定性及び出力特性に優れている。 Furthermore, the non-aqueous electrolyte secondary battery of the above embodiment has a positive electrode containing the specific positive electrode active material. Therefore, the non-aqueous electrolyte secondary battery can easily reduce raw material cost, has high discharge capacity, and is excellent in thermal stability and output characteristics.
図１は、実施例における二次電池の内部構造を示す展開図である。FIG. 1 is a developed view showing the internal structure of a secondary battery in an example.
（正極活物質）
　前記正極活物質は、ＬｉaＮｉbＭｎcＷdＭｇeＯfの組成式（ただし、前記組成式におけるａ～ｆは、０．９＜ａ＜１．２、０．４５＜ｂ＜０．６、０．２５＜ｃ＜０．５、０＜ｄ＜０．０６、０＜ｅ＜０．１、１．９＜ｆ＜２．１の関係を満たす。）で表される組成を有している。 (Cathode active material)
The positive electrode active material has a composition formula of Li a Ni b Mn c W d Mg e Of (however, a to f in the composition formula are 0.9<a<1.2, 0.45<b<0 .6, 0.25<c<0.5, 0<d<0.06, 0<e<0.1, 1.9<f<2.1.) have.
　前記組成式におけるａの値、つまりＬｉ、Ｎｉ、Ｍｎ、Ｗ、Ｍｇ及びＯのモル数の合計に対するＬｉのモル比は０．９より大きく１．２より小さい。これにより、充放電時に前記特定の結晶構造が維持されやすくなり、前記正極活物質内にリチウムイオンの拡散経路を十分に形成することができる。その結果、前記正極活物質の放電容量及び出力特性を向上させることができる。 The value of a in the above compositional formula, that is, the molar ratio of Li to the total number of moles of Li, Ni, Mn, W, Mg, and O is greater than 0.9 and less than 1.2. Thereby, the specific crystal structure is easily maintained during charging and discharging, and a sufficient diffusion path for lithium ions can be formed within the positive electrode active material. As a result, the discharge capacity and output characteristics of the positive electrode active material can be improved.
　前記組成式におけるａの値が０．９以下である場合には、前記正極活物質の結晶格子において、リチウムイオンサイトが遷移金属イオンによって置換される、カチオンミキシングと呼ばれる現象が起こりやすくなる。そのため、この場合には、正極活物質中にリチウムイオンの拡散経路を十分に形成することが難しくなり、放電容量や出力特性の低下を招くおそれがある。また、前記組成式におけるａの値が１．２以上である場合には、正極活物質中に、空間群Ｃ２／ｍに帰属されるリチウム過剰層状岩塩型結晶構造が形成されやすくなり、出力特性の低下を招くおそれがある。 When the value of a in the compositional formula is 0.9 or less, a phenomenon called cation mixing, in which lithium ion sites are replaced by transition metal ions, tends to occur in the crystal lattice of the positive electrode active material. Therefore, in this case, it becomes difficult to form a sufficient diffusion path for lithium ions in the positive electrode active material, which may lead to a decrease in discharge capacity and output characteristics. Further, when the value of a in the above compositional formula is 1.2 or more, a lithium-excess layered rock salt crystal structure belonging to the space group C2/m is likely to be formed in the positive electrode active material, and the output characteristics This may lead to a decrease in
　前記組成式におけるｄの値、つまり、Ｌｉ、Ｎｉ、Ｍｎ、Ｗ、Ｍｇ及びＯのモル数の合計に対するＷのモル比は０より大きく０．０６未満である。また、前記組成式におけるｅの値、つまりＬｉ、Ｎｉ、Ｍｎ、Ｗ、Ｍｇ及びＯのモル数の合計に対するＭｇのモル比は、０を超え０．１未満である。正極活物質中にＷとＭｇとの両方を添加し、かつ、これらの元素の含有率を前記特定の範囲とすることにより、正極活物質の放電容量及び出力特性を損なうことなく、熱的安定性を向上させることができる。 The value of d in the above composition formula, that is, the molar ratio of W to the total number of moles of Li, Ni, Mn, W, Mg, and O is greater than 0 and less than 0.06. Further, the value of e in the composition formula, that is, the molar ratio of Mg to the total number of moles of Li, Ni, Mn, W, Mg, and O is greater than 0 and less than 0.1. By adding both W and Mg to the positive electrode active material and keeping the content of these elements within the specified range, thermal stability can be achieved without impairing the discharge capacity and output characteristics of the positive electrode active material. can improve sex.
　前記組成式におけるｄの値が０の場合、つまり、例えばＷ及びＭｇのうちＭｇのみを前記正極活物質に添加する場合には、放電容量及び出力特性の低下を招くおそれがある。ＷとＭｇとの併用による効果をより確実に得る観点からは、前記組成式におけるｄの値は、０．００５以上であることが好ましく、０．０１以上であることがより好ましい。 If the value of d in the compositional formula is 0, that is, if only Mg of W and Mg is added to the positive electrode active material, there is a risk that the discharge capacity and output characteristics will deteriorate. From the viewpoint of more reliably obtaining the effect of the combined use of W and Mg, the value of d in the composition formula is preferably 0.005 or more, and more preferably 0.01 or more.
　前記組成式におけるｄの値が０．０６以上の場合には、正極活物質中に、前記特定の層状岩塩型結晶構造以外の結晶構造を有する結晶相が形成されやすくなり、放電容量及び熱的安定性の低下を招くおそれがある。 When the value of d in the compositional formula is 0.06 or more, a crystalline phase having a crystal structure other than the specific layered rock salt type crystal structure is likely to be formed in the positive electrode active material, and the discharge capacity and thermal This may lead to a decrease in stability.
　また、前記組成式におけるｅの値が０の場合、つまり、例えばＷ及びＭｇのうちＷのみを前記正極活物質に添加する場合には、正極活物質の熱的安定性の低下を招くおそれがある。ＷとＭｇとの併用による効果をより確実に得る観点からは、前記組成式におけるｅの値は、０．００５以上であることが好ましく、０．０１以上であることがより好ましい。 In addition, if the value of e in the compositional formula is 0, that is, if only W out of W and Mg is added to the positive electrode active material, there is a risk that the thermal stability of the positive electrode active material will decrease. be. From the viewpoint of more reliably obtaining the effect of the combined use of W and Mg, the value of e in the composition formula is preferably 0.005 or more, and more preferably 0.01 or more.
　一方、前記組成式におけるｅの値が０．１以上の場合には、正極活物質中に、前記特定の層状岩塩型結晶構造以外の結晶構造を有する結晶相が形成されやすくなり、放電容量の低下を招くおそれがある。 On the other hand, when the value of e in the compositional formula is 0.1 or more, a crystal phase having a crystal structure other than the specific layered rock salt type crystal structure is likely to be formed in the positive electrode active material, and the discharge capacity decreases. This may lead to a decrease in
　前記組成式におけるｂ、ｃ及びｆの値、つまり、Ｌｉ、Ｎｉ、Ｍｎ、Ｗ、Ｍｇ及びＯのモル数の合計に対するＮｉ、ＭｎまたはＯのモル比は、それぞれ前記の関係を満たす範囲とする。前記組成式におけるｂ、ｃ及びｆの値が前記の関係を満たさない場合には、前記正極活物質中に前記特定の層状岩塩型結晶構造以外の結晶構造を有する結晶相が形成されやすくなり、放電容量の低下を招くおそれがある。 The values of b, c, and f in the above compositional formula, that is, the molar ratio of Ni, Mn, or O to the total number of moles of Li, Ni, Mn, W, Mg, and O, are each within a range that satisfies the above relationship. . When the values of b, c and f in the composition formula do not satisfy the above relationship, a crystal phase having a crystal structure other than the specific layered rock salt crystal structure is likely to be formed in the positive electrode active material, This may lead to a decrease in discharge capacity.
　優れた熱的安定性及び出力特性を確保しつつ、より放電容量を高める観点からは、前記組成式におけるｂの値は０．５を超え０．６未満であることが好ましい。つまり、前記正極活物質は、ＬｉaＮｉbＭｎcＷdＭｇeＯfの組成式（ただし、前記組成式におけるａ～ｆは、０．９＜ａ＜１．２、０．５＜ｂ＜０．６、０．２５＜ｃ＜０．５、０＜ｄ＜０．０６、０＜ｅ＜０．１、１．９＜ｆ＜２．１の関係を満たす。）で表される組成を有していることが好ましい。 From the viewpoint of further increasing the discharge capacity while ensuring excellent thermal stability and output characteristics, the value of b in the compositional formula is preferably greater than 0.5 and less than 0.6. In other words, the positive electrode active material has a composition formula of Li a Ni b Mn c W d Mg e Of (however, a to f in the composition formula are 0.9<a<1.2, 0.5<b <0.6, 0.25<c<0.5, 0<d<0.06, 0<e<0.1, 1.9<f<2.1.) It is preferable to have the following composition.
　同様の観点から、前記組成式におけるｃの値は０．２５を超え０．４２未満であることが好ましい。つまり、前記正極活物質は、ＬｉaＮｉbＭｎcＷdＭｇeＯfの組成式（ただし、前記組成式におけるａ～ｆは、０．９＜ａ＜１．２、０．４５＜ｂ＜０．６、０．２５＜ｃ＜０．４２、０＜ｄ＜０．０６、０＜ｅ＜０．１、１．９＜ｆ＜２．１の関係を満たす。）で表される組成を有していることが好ましい。また、前記正極活物質は、ＬｉaＮｉbＭｎcＷdＭｇeＯfの組成式（ただし、前記組成式におけるａ～ｆは、０．９＜ａ＜１．２、０．５＜ｂ＜０．６、０．２５＜ｃ＜０．４２、０＜ｄ＜０．０６、０＜ｅ＜０．１、１．９＜ｆ＜２．１の関係を満たす。）で表される組成を有していることがより好ましく、ＬｉaＮｉbＭｎcＷdＭｇeＯfの組成式（ただし、前記組成式におけるａ～ｆは、０．９＜ａ＜１．２、０．５＜ｂ＜０．６、０．２５＜ｃ＜０．４２、０．０１＜ｄ＜０．０６、０＜ｅ＜０．０８、１．９＜ｆ＜２．１の関係を満たす。）で表される組成を有していることがさらに好ましい。 From the same viewpoint, the value of c in the composition formula is preferably more than 0.25 and less than 0.42. In other words, the positive electrode active material has a composition formula of Li a Ni b Mn c W d Mg e Of (however, a to f in the above composition formula are 0.9<a<1.2, 0.45<b <0.6, 0.25<c<0.42, 0<d<0.06, 0<e<0.1, 1.9<f<2.1.) It is preferable to have the following composition. Further, the positive electrode active material has a composition formula of Li a Ni b Mn c W d Mg e Of (however, a to f in the above composition formula are 0.9<a<1.2, 0.5<b <0.6, 0.25<c<0.42, 0<d<0.06, 0<e<0.1, 1.9<f<2.1.) It is more preferable to have a composition of Li a Ni b Mn c W d Mg e Of (however, a to f in the above composition formula are 0.9<a<1.2, 0. The following relationships are satisfied: 5<b<0.6, 0.25<c<0.42, 0.01<d<0.06, 0<e<0.08, 1.9<f<2.1. ) It is more preferable to have a composition represented by:
　前記正極活物質の結晶格子におけるａ軸の長さは２．８８０Å以上２．９００Å以下であり、ｃ軸の長さは１４．２９０Å以上１４．３６０Å以下であることが好ましい。この場合には、熱的安定性及び出力特性に優れた正極活物質をより確実に得ることができる。同様の観点から、前記正極活物質は、θ－２θ法により得られるＸ線回折パターンにおける、回折角４４．４±１°の範囲に現れるピークの半値幅ｗ４４に対する回折角６４．５±１°の範囲に現れるピークの半値幅ｗ６４の比ｗ６４／ｗ４４が１．１０以上１．３０以下となる結晶構造を有していることが好ましい。 It is preferable that the a-axis length in the crystal lattice of the positive electrode active material is 2.880 Å or more and 2.900 Å or less, and the c-axis length is 14.290 Å or more and 14.360 Å or less. In this case, a positive electrode active material with excellent thermal stability and output characteristics can be obtained more reliably. From a similar point of view, the positive electrode active material has a diffraction angle of 64.5±1 with respect to a half-width w 44 of a peak appearing in a diffraction angle range of 44.4±1° in an X-ray diffraction pattern obtained by the θ-2θ method. It is preferable to have a crystal structure in which the ratio w 64 / w 44 of the half width w 64 of the peak appearing in the range of 1.10 to 1.30 is obtained.
　前記正極活物質中には、前述した効果を損なわない範囲で、前記特定の層状岩塩型結晶構造以外の結晶構造を有する結晶相が含まれていてもよい。前記特定の層状岩塩型結晶構造以外の結晶構造を有する結晶相の含有率は、２０質量％以下であることが好ましく、１５質量％以下であることがより好ましく、１０質量％以下であることがさらに好ましい。 The positive electrode active material may contain a crystal phase having a crystal structure other than the specific layered rock salt type crystal structure as long as the above-described effects are not impaired. The content of the crystalline phase having a crystal structure other than the specific layered rock salt crystal structure is preferably 20% by mass or less, more preferably 15% by mass or less, and preferably 10% by mass or less. More preferred.
　なお、前述した正極活物質中の結晶相の含有率は、粉末Ｘ線回折法により得られたＸ線回折パターンに基づいて算出することができる。より具体的には、粉末Ｘ線回折法における回折角２θの走査範囲は１０°～９０°とし、走査速度は２°／分とし、サンプリング幅は０．０２°とし、Ｘ線光源はＣｕＫα線とする。このような測定条件で得られるＸ線回折パターンに基づいてリートベルト解析を行うことにより、正極活物質中の結晶相の種類を同定するとともに各結晶相の含有率を算出することができる。 Note that the content of the crystalline phase in the positive electrode active material described above can be calculated based on the X-ray diffraction pattern obtained by powder X-ray diffraction method. More specifically, the scanning range of the diffraction angle 2θ in the powder X-ray diffraction method is 10° to 90°, the scanning speed is 2°/min, the sampling width is 0.02°, and the X-ray light source is CuKα radiation. shall be. By performing Rietveld analysis based on the X-ray diffraction pattern obtained under such measurement conditions, it is possible to identify the type of crystal phase in the positive electrode active material and to calculate the content of each crystal phase.
　前記正極活物質は、正極活物質中におけるリチウムイオンの拡散距離をより短くする観点から、通常、粉末の状態で使用される。前記正極活物質は、粒子径１０μｍ以下の粒子から構成されていることが好ましい。すなわち、前記正極活物質は、例えば、最大粒子径が１０μｍ以下となる粒径分布を有する一次粒子から構成されていてもよいし、一次粒子が凝集してなり、最大粒子径が１０μｍ以下となる粒径分布を有する二次粒子であってもよい。この場合には、正極活物質中におけるリチウムイオンの拡散距離をより短くし、非水電解液二次電池における内部抵抗をより容易に低減することができる。正極活物質中におけるリチウムイオンの拡散距離をより短くする観点からは、正極活物質は、粒子径１μｍ以下の一次粒子から構成されていることが好ましい。 The above-mentioned positive electrode active material is usually used in a powder form from the viewpoint of further shortening the diffusion distance of lithium ions in the positive electrode active material. It is preferable that the positive electrode active material is composed of particles having a particle size of 10 μm or less. That is, the positive electrode active material may be composed of primary particles having a particle size distribution such that the maximum particle size is 10 μm or less, or may be formed by agglomeration of primary particles such that the maximum particle size is 10 μm or less. The secondary particles may have a particle size distribution. In this case, the diffusion distance of lithium ions in the positive electrode active material can be made shorter, and the internal resistance in the non-aqueous electrolyte secondary battery can be more easily reduced. From the viewpoint of further shortening the diffusion distance of lithium ions in the positive electrode active material, the positive electrode active material is preferably composed of primary particles having a particle size of 1 μm or less.
　なお、前述した正極活物質の一次粒子の粒子径は、走査型電子顕微鏡（ＳＥＭ）を用いて正極活物質を観察して得られる、拡大写真に基づいて測定することができる。より具体的には、ＳＥＭで観察した拡大写真から無作為に選択した５０個以上の正極活物質の粒子について、個々の粒子に対する外接円を決定し、その直径を個々の粒子の粒子径とする。そして、これらの粒子径の最大値を正極活物質の粒子径とする。また、前述した正極活物質の二次粒子の粒子径は、レーザ散乱方式の粒度分布測定装置を用いて測定することができる。 Note that the particle diameter of the primary particles of the positive electrode active material described above can be measured based on an enlarged photograph obtained by observing the positive electrode active material using a scanning electron microscope (SEM). More specifically, for 50 or more positive electrode active material particles randomly selected from enlarged photographs observed with SEM, the circumscribed circle for each particle is determined, and the diameter is taken as the particle diameter of each particle. . The maximum value of these particle sizes is defined as the particle size of the positive electrode active material. Further, the particle diameter of the secondary particles of the positive electrode active material described above can be measured using a laser scattering type particle size distribution measuring device.
（正極活物質の製造方法）
　前記正極活物質の製造方法としては、例えば、固相法を採用することができる。具体的には、Ｌｉ源となる化合物、Ｎｉ源となる化合物、Ｍｎ源となる化合物、Ｗ源となる化合物及びＭｇ源となる化合物を含む混合物を作製した後、前記混合物を酸化性ガス雰囲気下で焼成すればよい。混合物中における各化合物の比率は、所望する正極活物質中の結晶相の組成式に応じて適宜設定すればよい。 (Method for producing positive electrode active material)
As a method for producing the positive electrode active material, for example, a solid phase method can be adopted. Specifically, after preparing a mixture containing a compound serving as a Li source, a compound serving as a Ni source, a compound serving as a Mn source, a compound serving as a W source, and a compound serving as a Mg source, the mixture is heated under an oxidizing gas atmosphere. You can bake it with The ratio of each compound in the mixture may be appropriately set according to the desired compositional formula of the crystal phase in the positive electrode active material.
　前記混合物は、粉末であることが好ましい。混合物を粉末とすることにより、混合物中において、各原料化合物を均一に分散させることができる。その結果、焼成後における焼成体の組成の偏りをより低減し、前記結晶相の含有率をより高くすることができる。 It is preferable that the mixture is a powder. By forming the mixture into powder, each raw material compound can be uniformly dispersed in the mixture. As a result, the deviation in composition of the fired body after firing can be further reduced, and the content of the crystal phase can be further increased.
　粉末状の混合物を作製するにあたっては、必要に応じて原料化合物を粉砕してもよい。粉砕方法としては、乳鉢による手粉砕、ボールミル等による機械式粉砕等が採用できる。 When producing a powdery mixture, the raw material compounds may be pulverized as necessary. As the pulverization method, manual pulverization using a mortar, mechanical pulverization using a ball mill, etc. can be adopted.
　また、粉末状の混合物を作製するにあたっては、篩などを用いて原料化合物を分級することにより、混合物の粒度調整をおこなってもよい。これらの手法によって混合物の粒度をできるだけ小さくすることにより、原料化合物をより均一に分散させることができる。その結果、焼成後における焼成体の組成の偏りをより低減し、前記結晶相の含有率をより高くすることができる。 Furthermore, when producing a powdery mixture, the particle size of the mixture may be adjusted by classifying the raw material compound using a sieve or the like. By reducing the particle size of the mixture as much as possible using these techniques, the raw material compounds can be more uniformly dispersed. As a result, the deviation in composition of the fired body after firing can be further reduced, and the content of the crystal phase can be further increased.
　混合物を作製した後、酸化性ガス雰囲気下で混合物を焼成することにより、前記特定の結晶相を含む正極活物質の焼成体を得ることができる。酸化性ガスとしては、例えば、大気等を使用することができる。焼成時の焼成温度は８００～１１００℃の範囲から適宜設定することができる。焼成時の保持時間は０．５～５０時間の範囲から適宜設定することができる。 After producing the mixture, by firing the mixture in an oxidizing gas atmosphere, a fired body of the positive electrode active material containing the specific crystal phase can be obtained. As the oxidizing gas, for example, the atmosphere can be used. The firing temperature during firing can be appropriately set within the range of 800 to 1100°C. The holding time during firing can be appropriately set within the range of 0.5 to 50 hours.
　焼成が完了した後、得られた焼成体を解砕することにより、粉末状の正極活物質を得ることができる。焼成体の解砕方法は特に限定されることはない。例えば、粉砕方法としては、乳鉢による手粉砕、ボールミル等による機械式粉砕等の種々の方法を採用することができる。また、焼成体を解砕した後、必要に応じて粉末を分級し、正極活物質の粒度を調整してもよい。 After the firing is completed, a powdered positive electrode active material can be obtained by crushing the obtained fired body. The method for crushing the fired body is not particularly limited. For example, various methods such as manual crushing using a mortar, mechanical crushing using a ball mill, etc. can be used as the crushing method. Further, after crushing the fired body, the powder may be classified as necessary to adjust the particle size of the positive electrode active material.
　また、前記正極活物質の製造方法としては、共沈法を採用してもよい。共沈法により前記正極活物質を作製する場合、例えば、アルカリ性の反応溶液と、前記正極活物質を構成する金属元素のうちＬｉを除く２種以上の金属元素のイオンを含む原料溶液と、アルカリ性のｐＨ調整溶液とを準備する。その後、反応溶液中に、前記イオンを含む原料溶液を滴下すると同時に、原料溶液を滴下した後の反応溶液のｐＨを調整するためにｐＨ調整溶液を滴下する。これにより、反応溶液中に、前述した金属元素を含む前駆体を析出させる。原料溶液中における各イオンの濃度は、所望する正極活物質中の結晶相の組成式に応じて適宜設定すればよい。 Additionally, a coprecipitation method may be employed as a method for producing the positive electrode active material. When producing the positive electrode active material by a coprecipitation method, for example, an alkaline reaction solution, a raw material solution containing ions of two or more metal elements excluding Li among the metal elements constituting the positive electrode active material, and an alkaline Prepare a pH adjustment solution. Thereafter, the raw material solution containing the ions is dropped into the reaction solution, and at the same time, a pH adjustment solution is added dropwise to adjust the pH of the reaction solution after the raw material solution has been dropped. As a result, a precursor containing the aforementioned metal element is precipitated in the reaction solution. The concentration of each ion in the raw material solution may be appropriately set according to the desired compositional formula of the crystal phase in the positive electrode active material.
　次に、前駆体に、Ｌｉ源となる化合物及び必要に応じて添加される他の原料を混合し、混合物を作製する。酸化性ガス雰囲気下で混合物を焼成することにより、前記特定の結晶相を含む正極活物質の焼成体を得ることができる。酸化性ガスとしては、例えば、大気等を使用することができる。焼成時の焼成温度は８００～１１００℃の範囲から適宜設定することができる。焼成時の保持時間は０．５～５０時間の範囲から適宜設定することができる。 Next, a compound serving as a Li source and other raw materials added as necessary are mixed with the precursor to prepare a mixture. By firing the mixture in an oxidizing gas atmosphere, a fired body of the positive electrode active material containing the specific crystal phase can be obtained. As the oxidizing gas, for example, the atmosphere can be used. The firing temperature during firing can be appropriately set within the range of 800 to 1100°C. The holding time during firing can be appropriately set within the range of 0.5 to 50 hours.
　焼成が完了した後、得られた焼成体を解砕することにより、粉末状の正極活物質を得ることができる。焼成体の解砕方法は特に限定されることはない。例えば、粉砕方法としては、乳鉢による手粉砕、ボールミル等による機械式粉砕等の種々の方法を採用することができる。また、焼成体を解砕した後、必要に応じて粉末を分級し、正極活物質の粒度を調整してもよい。 After the firing is completed, a powdered positive electrode active material can be obtained by crushing the obtained fired body. The method for crushing the fired body is not particularly limited. For example, various methods such as manual crushing using a mortar, mechanical crushing using a ball mill, etc. can be used as the crushing method. Further, after crushing the fired body, the powder may be classified as necessary to adjust the particle size of the positive electrode active material.
　前記正極活物質の製造方法においては、共沈法により前記組成のうちＬｉ以外の全ての金属元素を含む前駆体を作製し、前記前駆体と、Ｌｉを含む化合物とを混合して混合物を作製し、
　前記混合物を酸化性ガス雰囲気中で焼成することにより前記正極活物質を得ることが好ましい。 In the method for producing the positive electrode active material, a precursor containing all metal elements other than Li in the composition is produced by a coprecipitation method, and a mixture is produced by mixing the precursor and a compound containing Li. death,
It is preferable to obtain the positive electrode active material by firing the mixture in an oxidizing gas atmosphere.
　このように、共沈法によってＬｉ以外の全ての金属元素を含む前駆体を作製することにより、前駆体中における各金属元素の分布をより均一にすることができる。そして、かかる前駆体とＬｉ源となる化合物とを混合した後、混合物を焼成することにより、より均質な正極活物質を得ることができる。そして、かかる方法によれば、正極活物質の放電容量、出力特性及び熱的安定性をよりバランスよく向上させることができる。 In this way, by producing a precursor containing all metal elements other than Li by the coprecipitation method, the distribution of each metal element in the precursor can be made more uniform. Then, by mixing such a precursor and a compound serving as a Li source and then firing the mixture, a more homogeneous positive electrode active material can be obtained. According to this method, the discharge capacity, output characteristics, and thermal stability of the positive electrode active material can be improved in a better balance.
　共沈法によりＬｉ以外の全ての金属元素を含む前駆体を作製する場合、反応溶液中に滴下する原料溶液は、１種類であってもよいし、２種類以上であってもよい。しかし、原料溶液に溶解させる化合物の組み合わせによっては、原料溶液にいずれかの化合物が溶解しにくくなり、前駆体中の金属元素の比率を所望の範囲に調整しにくくなる場合がある。かかる問題をより確実に回避する観点からは、２種類以上の原料溶液を準備することが好ましい。２種類以上の原料溶液を準備することにより、各原料溶液中に、金属元素を含む化合物を容易に溶解させることができる。その結果、前駆体中の金属元素の比率をより容易に所望の範囲に調整することができる。 When producing a precursor containing all metal elements other than Li by the coprecipitation method, the number of raw material solutions dropped into the reaction solution may be one or two or more. However, depending on the combination of compounds to be dissolved in the raw material solution, some of the compounds may be difficult to dissolve in the raw material solution, making it difficult to adjust the ratio of metal elements in the precursor to a desired range. From the viewpoint of avoiding such problems more reliably, it is preferable to prepare two or more types of raw material solutions. By preparing two or more types of raw material solutions, a compound containing a metal element can be easily dissolved in each raw material solution. As a result, the ratio of metal elements in the precursor can be more easily adjusted to a desired range.
　２種類以上の原料溶液を準備する場合、例えば、いずれか１種の原料溶液中に他の原料溶液を滴下した後、この原料溶液を反応溶液に滴下してもよい。より具体的には、前記前駆体を作製する際に、アルカリ性を示す反応溶液と、Ｗを含む第１原料溶液と、前記組成のうちＬｉ及びＷ以外の金属元素を含む第２原料溶液と、を準備し、
　前記第１原料溶液を前記第２原料溶液中に滴下して混合溶液を作製し、
　その後、前記混合溶液を前記反応溶液中に滴下して前記前駆体を作製することができる。 When preparing two or more types of raw material solutions, for example, after dropping another raw material solution into any one type of raw material solution, this raw material solution may be dropped into the reaction solution. More specifically, when producing the precursor, a reaction solution exhibiting alkalinity, a first raw material solution containing W, a second raw material solution containing a metal element other than Li and W in the composition, Prepare,
Dropping the first raw material solution into the second raw material solution to create a mixed solution,
Thereafter, the mixed solution can be dropped into the reaction solution to produce the precursor.
　また、例えば、全ての原料溶液を同時に反応溶液中に滴下してもよい。より具体的には、前記前駆体を作製する際に、アルカリ性を示す反応溶液と、Ｗを含む第１原料溶液と、前記組成のうちＬｉ及びＷ以外の金属元素を含む第２原料溶液と、を準備し、
　前記第１原料溶液と前記第２原料溶液とを前記反応溶液中に同時に滴下して前記前駆体を作製することもできる。 Alternatively, for example, all the raw material solutions may be dropped into the reaction solution at the same time. More specifically, when producing the precursor, a reaction solution exhibiting alkalinity, a first raw material solution containing W, a second raw material solution containing a metal element other than Li and W in the composition, Prepare,
The precursor can also be produced by simultaneously dropping the first raw material solution and the second raw material solution into the reaction solution.
　さらに、原料溶液及び反応溶液に加えて、アルカリ性を示すｐＨ調整溶液を準備し、前記ｐＨ調整溶液を、前記第１原料溶液、前記第２原料溶液または前記混合溶液とともに前記反応溶液中に滴下して前記前駆体を作製してもよい。この場合には、原料溶液の滴下に伴う反応溶液のｐＨの変化を抑制し、所望の組成を有する前駆体をより確実に生成することができる。 Furthermore, in addition to the raw material solution and the reaction solution, a pH adjusting solution exhibiting alkalinity is prepared, and the pH adjusting solution is dropped into the reaction solution together with the first raw material solution, the second raw material solution, or the mixed solution. The precursor may be produced by In this case, changes in the pH of the reaction solution due to dropping of the raw material solution can be suppressed, and a precursor having a desired composition can be produced more reliably.
（非水電解液二次電池）
　前記正極活物質は、非水電解液二次電池に用いられ、特にリチウムイオン二次電池に好適である。二次電池は、前記正極活物質を含有する正極、負極、セパレータ、非水電解液、添加剤、及びこれらを収容するケース等を主要な構成部材として備えることができる。二次電池の形状としては、例えばコイン型、円筒型、積層型、角型等がある。 (Nonaqueous electrolyte secondary battery)
The positive electrode active material is used in nonaqueous electrolyte secondary batteries, and is particularly suitable for lithium ion secondary batteries. The secondary battery can include a positive electrode containing the positive electrode active material, a negative electrode, a separator, a non-aqueous electrolyte, an additive, a case housing these, and the like as main components. The shape of the secondary battery includes, for example, a coin shape, a cylindrical shape, a stacked type, a square shape, and the like.
　二次電池の正極は、正極活物質と、正極活物質を保持する正極集電体とを有している。正極集電体としては、例えば、銅箔、アルミニウム箔、ニッケル箔等の金属箔、ステンレス鋼メッシュ、パンチングメタル、エキスパンデッドメタル及び金属メッシュ等の種々の導体を使用することができる。 The positive electrode of the secondary battery includes a positive electrode active material and a positive electrode current collector that holds the positive electrode active material. As the positive electrode current collector, various conductors can be used, such as metal foils such as copper foil, aluminum foil, and nickel foil, stainless steel mesh, punched metal, expanded metal, and metal mesh.
　正極には、正極活物質と正極集電体との間に介在する結着剤が含まれていてもよい。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、フッ素ゴム等の含フッ素樹脂、ポリプロピレン、ポリエチレン、ポリエチレンテレフタレート等の熱可塑性樹脂を用いることができる。 The positive electrode may include a binder interposed between the positive electrode active material and the positive electrode current collector. As the binder, for example, fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, and thermoplastic resins such as polypropylene, polyethylene, and polyethylene terephthalate can be used.
　また、正極には、電気伝導性を高めるための導電剤や導電助剤が含まれていてもよい。導電剤としては、例えば黒鉛、カーボンブラック、アセチレンブラック、コークス類等を用いることができる。 Additionally, the positive electrode may contain a conductive agent or a conductive aid to improve electrical conductivity. As the conductive agent, for example, graphite, carbon black, acetylene black, coke, etc. can be used.
　正極は、例えば、以下の方法により作製することができる。まず、正極活物質を含むペースト状の正極合材を作製する。正極合材には、必要に応じて、正極活物質等の固形分を分散または溶解させるための有機溶媒が含まれていてもよい。次に、正極合材を正極集電体の表面に塗布した後、乾燥させることにより、正極集電体の表面に正極活物質層を形成する。正極活物質層を形成した後、必要に応じて正極活物質層をプレスし、正極活物質層の密度を高めてもよい。以上により正極を得ることができる。 The positive electrode can be produced, for example, by the following method. First, a paste-like positive electrode composite material containing a positive electrode active material is prepared. The positive electrode mixture may contain an organic solvent for dispersing or dissolving solid content such as the positive electrode active material, if necessary. Next, a positive electrode active material layer is formed on the surface of the positive electrode current collector by applying the positive electrode mixture onto the surface of the positive electrode current collector and drying it. After forming the positive electrode active material layer, the positive electrode active material layer may be pressed as necessary to increase the density of the positive electrode active material layer. A positive electrode can be obtained through the above steps.
　二次電池の負極は、負極活物質と、負極活物質を保持する負極集電体とを有している。負極活物質としては、例えば、グラファイトやハードカーボン等のグラファイト構造を有する炭素材料や、チタン酸リチウム（Ｌｉ4Ｔｉ5Ｏ12）等のリチウム系酸化物を用いることができる。また、負極集電体としては、前述した正極集電体と同様の導体を使用することができる。 A negative electrode of a secondary battery includes a negative electrode active material and a negative electrode current collector that holds the negative electrode active material. As the negative electrode active material, for example, a carbon material having a graphite structure such as graphite or hard carbon, or a lithium-based oxide such as lithium titanate (Li 4 Ti 5 O 12 ) can be used. Further, as the negative electrode current collector, a conductor similar to the above-described positive electrode current collector can be used.
　負極は、正極と同様に、結着剤や導電剤、導電助剤を含んでいてもよい。負極に使用し得る結着剤、導電剤及び導電助剤は、正極と同様である。 Similarly to the positive electrode, the negative electrode may contain a binder, a conductive agent, and a conductive aid. The binder, conductive agent, and conductive aid that can be used for the negative electrode are the same as those for the positive electrode.
　負極の作製方法は、正極と同様である。すなわち、まず、負極活物質を含むペースト状の負極合材を作製する。負極合材には、必要に応じて、負極活物質等の固形分を分散または溶解させるための有機溶媒が含まれていてもよい。次に、負極合材を負極集電体の表面に塗布した後、乾燥させることにより、負極集電体の表面に負極活物質層を形成する。負極活物質層を形成した後、必要に応じて負極活物質層をプレスし、負極活物質層の密度を高めてもよい。以上により負極を得ることができる。 The method for producing the negative electrode is the same as that for the positive electrode. That is, first, a paste-like negative electrode composite material containing a negative electrode active material is produced. The negative electrode composite material may contain an organic solvent for dispersing or dissolving solid content such as the negative electrode active material, if necessary. Next, a negative electrode active material layer is formed on the surface of the negative electrode current collector by applying the negative electrode composite material onto the surface of the negative electrode current collector and drying it. After forming the negative electrode active material layer, the negative electrode active material layer may be pressed as necessary to increase the density of the negative electrode active material layer. A negative electrode can be obtained through the above steps.
　非水電解液は、有機溶媒と、リチウム塩からなる電解質とを含有することができる。リチウム塩としては、例えばＬｉＰＦ6等が挙げられる。また、有機溶媒は、エチレンカーボネート、ジメチルカーボネート、及びエチルメチルカーボネートからなるグループから選ばれる少なくとも１種とすることができる。これらの有機溶媒は、極性が高く、電解質を大量に溶解することができる。そのため、これらの有機溶媒を非水電解液として使用することにより、二次電池における例えばリチウムイオン等の電荷担体の輸率を容易に高くすることができる。 The non-aqueous electrolyte can contain an organic solvent and an electrolyte made of a lithium salt. Examples of the lithium salt include LiPF 6 and the like. Further, the organic solvent can be at least one selected from the group consisting of ethylene carbonate, dimethyl carbonate, and ethylmethyl carbonate. These organic solvents have high polarity and can dissolve a large amount of electrolyte. Therefore, by using these organic solvents as a nonaqueous electrolyte, it is possible to easily increase the transfer number of charge carriers such as lithium ions in a secondary battery.
　前記正極活物質、及び前記正極活物質を備えた非水電解液二次電池の実施例を説明する。本例の正極活物質は、ＬｉaＮｉbＭｎcＷdＭｇeＯfの組成式（ただし、前記組成式におけるａ～ｆは、０．９＜ａ＜１．２、０．４５＜ｂ＜０．６、０．２５＜ｃ＜０．５、０＜ｄ＜０．０６、０＜ｅ＜０．１、１．９＜ｆ＜２．１の関係を満たす。）で表される組成を有している。また、正極活物質は、空間群Ｒ－３ｍに帰属可能な層状岩塩型結晶構造を有している。 Examples of the positive electrode active material and a non-aqueous electrolyte secondary battery provided with the positive electrode active material will be described. The positive electrode active material of this example has a composition formula of Li a Ni b Mn c W d Mg e Of (however, a to f in the above composition formula are 0.9<a<1.2, 0.45<b <0.6, 0.25<c<0.5, 0<d<0.06, 0<e<0.1, 1.9<f<2.1.) It has a composition. Further, the positive electrode active material has a layered rock salt type crystal structure that can be assigned to space group R-3m.
　本例における正極活物質（試験材Ｓ１～Ｓ９）は、具体的には、表１に示す組成を有している。なお、表１の試験材Ｒ１～Ｒ８は、試験材Ｓ１～Ｓ９との比較のための正極活物質である。本例の正極活物質の作製方法を以下に説明する。 Specifically, the positive electrode active materials (test materials S1 to S9) in this example have the compositions shown in Table 1. Note that test materials R1 to R8 in Table 1 are positive electrode active materials for comparison with test materials S1 to S9. The method for producing the positive electrode active material of this example will be explained below.
（試験材Ｓ１）
　２Ｌの反応容器に蒸留水２００ｍＬを入れ、水酸化ナトリウムを溶解させてｐＨ１２の反応溶液を調製した。この反応溶液とは別に、蒸留水に硫酸ニッケル及び硫酸マンガンを溶解させた原料溶液と、水酸化ナトリウム水溶液とアンモニア水とを混合してなるｐＨ調整溶液とを調製した。 (Test material S1)
200 mL of distilled water was placed in a 2 L reaction vessel, and sodium hydroxide was dissolved therein to prepare a reaction solution with a pH of 12. Separately from this reaction solution, a raw material solution in which nickel sulfate and manganese sulfate were dissolved in distilled water, and a pH adjustment solution in which a sodium hydroxide aqueous solution and aqueous ammonia were mixed were prepared.
　次に、反応溶液を５０℃まで加熱した。反応溶液の温度を保持した状態で、反応溶液を攪拌しながら原料溶液とｐＨ調整溶液とを反応溶液中に同時に滴下することにより、反応溶液中にＮｉ及びＭｎを含む前駆体を析出させた。 Next, the reaction solution was heated to 50°C. A precursor containing Ni and Mn was precipitated in the reaction solution by simultaneously dropping the raw material solution and the pH adjustment solution into the reaction solution while stirring the reaction solution while maintaining the temperature of the reaction solution.
　このようにして得られた前駆体に、Ｌｉ源としてのＬｉＯＨ、Ｗ源としてのＷＯ3及びＭｇ源としてのＭｇＯを混合して混合物を作製した。この混合物を大気中において９５０℃の温度で５時間焼成し、次いで、７００℃の温度で１２時間アニールすることにより、塊状の正極活物質を得た。乳鉢を用いて塊状の正極活物質を解砕することにより、粉末状の正極活物質（試験材Ｓ１）を得た。なお、前述した方法により作製された正極活物質については、表１の「作製方法」欄に記号「Ｍ１」を記載した。 A mixture was prepared by mixing the thus obtained precursor with LiOH as a Li source, WO 3 as a W source, and MgO as an Mg source. This mixture was fired in the air at a temperature of 950° C. for 5 hours, and then annealed at a temperature of 700° C. for 12 hours to obtain a bulk positive electrode active material. A powdered positive electrode active material (test material S1) was obtained by crushing the lumped positive electrode active material using a mortar. Note that the symbol "M1" is written in the "Production method" column of Table 1 for the positive electrode active material produced by the method described above.
（試験材Ｒ１～Ｒ３）
　試験材Ｒ１～Ｒ３は、Ｗ及びＭｇのうち少なくとも一方の元素が含まれていない以外は、試験材Ｓ１と同様の構成を有している。試験材Ｒ１～Ｒ３の作製方法は、前駆体にＷＯ３及び／またはＭｇＯを添加しない以外は試験材Ｓ１の作製方法と同様である。 (Test materials R1 to R3)
Test materials R1 to R3 have the same configuration as test material S1, except that at least one of W and Mg is not included. The method for producing test materials R1 to R3 is the same as the method for producing test material S1, except that WO 3 and/or MgO is not added to the precursor.
（試験材Ｓ２～Ｓ９）
　２Ｌの反応容器に蒸留水２００ｍＬを入れ、水酸化ナトリウムを溶解させてｐＨ１２の反応溶液を調製した。この反応溶液とは別に、蒸留水にタングステン酸アンモニウムを溶解させた第１原料溶液と、蒸留水に硫酸ニッケル、硫酸マンガン及び硫酸マグネシウムを溶解させた第２原料溶液と、水酸化ナトリウム水溶液とアンモニア水とを混合してなるｐＨ調整溶液とを調製した。 (Test materials S2 to S9)
200 mL of distilled water was placed in a 2 L reaction vessel, and sodium hydroxide was dissolved therein to prepare a reaction solution with a pH of 12. Separately from this reaction solution, a first raw material solution in which ammonium tungstate is dissolved in distilled water, a second raw material solution in which nickel sulfate, manganese sulfate and magnesium sulfate are dissolved in distilled water, an aqueous sodium hydroxide solution and ammonia A pH adjusting solution was prepared by mixing with water.
　次に、反応溶液を５０℃まで加熱した。反応溶液の温度を保持した状態で、反応溶液を攪拌しながら第１原料溶液、第２原料溶液及びｐＨ調整溶液を反応溶液中に同時に滴下することにより、反応溶液中にＮｉ、Ｍｎ、Ｗ及びＭｇを含む前駆体を析出させた。 Next, the reaction solution was heated to 50°C. Ni, Mn, W, and A precursor containing Mg was precipitated.
　次に、前駆体にＬｉ源としてのＬｉＯＨを混合して混合物を作製した。この混合物を大気中において９５０℃の温度で５時間焼成し、次いで、７００℃の温度で１２時間アニールすることにより、塊状の正極活物質を得た。乳鉢を用いて塊状の正極活物質を解砕することにより、粉末状の正極活物質（試験材Ｓ２～Ｓ９）を得た。なお、前述した方法により作製された正極活物質については、表１の「作製方法」欄に記号「Ｍ２」を記載した。 Next, a mixture was prepared by mixing LiOH as a Li source with the precursor. This mixture was fired in the air at a temperature of 950° C. for 5 hours, and then annealed at a temperature of 700° C. for 12 hours to obtain a bulk positive electrode active material. Powdered positive electrode active materials (test materials S2 to S9) were obtained by crushing the bulk positive electrode active materials using a mortar. Note that the symbol "M2" is written in the "Production method" column of Table 1 for the positive electrode active material produced by the method described above.
（試験材Ｒ４～Ｒ８）
　試験材Ｒ４～Ｒ８は、Ｗ及びＭｇのうち少なくとも一方の元素が含まれていない以外は、試験材Ｓ２～Ｓ９と同様の構成を有している。試験材Ｒ４～Ｒ８の作製方法は、前駆体にＷＯ３及び／またはＭｇＯを添加しない以外は試験材Ｓ２～Ｓ９の作製方法と同様である。 (Test materials R4 to R8)
Test materials R4 to R8 have the same configuration as test materials S2 to S9, except that at least one of W and Mg is not included. The method for producing test materials R4 to R8 was the same as the method for producing test materials S2 to S9, except that WO 3 and/or MgO was not added to the precursor.
　次に、試験材Ｓ１～Ｓ９及び試験材Ｒ１～Ｓ８の組成及び結晶構造の同定を行った。 Next, the compositions and crystal structures of test materials S1 to S9 and test materials R1 to S8 were identified.
・正極活物質の組成
　誘導結合プラズマ発光分析（つまり、ＩＣＰ－ＡＥＳ）により正極活物質中の各金属元素のモル比を測定した。酸素原子のモル比を２とした場合における各試験材の組成は、表１の「正極活物質の組成」欄に示す通りであった。 - Composition of positive electrode active material The molar ratio of each metal element in the positive electrode active material was measured by inductively coupled plasma emission spectrometry (ie, ICP-AES). The composition of each test material when the molar ratio of oxygen atoms was 2 was as shown in the "Composition of positive electrode active material" column of Table 1.
・正極活物質の結晶構造
　粉末Ｘ線回折により、正極活物質の結晶構造の同定及び格子定数の測定を行った。Ｘ線回折装置としては、株式会社リガク製「ＳｍａｒｔＬａｂ（登録商標）」を使用し、照射した特性Ｘ線はＣｕＫα線とした。また、回折角２θの走査範囲は１０°～９０°とし、走査速度は２°／分とし、サンプリング幅は０．０２°とした。 -Crystal structure of positive electrode active material The crystal structure of the positive electrode active material was identified and the lattice constant was measured by powder X-ray diffraction. As the X-ray diffraction apparatus, "SmartLab (registered trademark)" manufactured by Rigaku Co., Ltd. was used, and the characteristic X-rays irradiated were CuKα rays. Furthermore, the scanning range of the diffraction angle 2θ was 10° to 90°, the scanning speed was 2°/min, and the sampling width was 0.02°.
　得られたＸ線回折パターンに基づき、正極活物質の結晶構造を同定したところ、試験材Ｓ１～Ｓ９及び試験材Ｒ１～Ｒ８は、いずれも空間群Ｒ－３ｍに帰属可能な層状岩塩型結晶構造を有していた。表１に、各正極活物質の結晶格子におけるａ軸の長さ及びｃ軸の長さを示す。また、表２に、各正極活物質中の層状岩塩型結晶構造の含有率、及び回折角４４．４±１°の範囲に現れるピークの半値幅ｗ４４に対する回折角６４．５±１°の範囲に現れるピークの半値幅ｗ６４の比ｗ６４／ｗ４４を示す。 Based on the obtained X-ray diffraction patterns, we identified the crystal structures of the positive electrode active materials, and found that test materials S1 to S9 and test materials R1 to R8 all had layered rock-salt crystal structures that could be assigned to space group R-3m. It had Table 1 shows the lengths of the a-axis and the c-axis in the crystal lattice of each positive electrode active material. Table 2 also shows the content of layered rock-salt crystal structure in each positive electrode active material, and the half-width w of the peak appearing in the diffraction angle range of 44.4 ±1°. The ratio w 64 /w 44 of the half width w 64 of the peak appearing in the range is shown.
・評価用二次電池の構成及び作製方法
　次に、得られた正極活物質を用いて非水電解液二次電池（テストセル）を作製した。図１に示すごとく、本例の非水電解液二次電池１は、正極２、負極３、セパレータ４及び非水電解液５を備えたＣＲ２０３２型コイン電池である。 - Structure and manufacturing method of secondary battery for evaluation Next, a non-aqueous electrolyte secondary battery (test cell) was manufactured using the obtained positive electrode active material. As shown in FIG. 1, the nonaqueous electrolyte secondary battery 1 of this example is a CR2032 type coin battery including a positive electrode 2, a negative electrode 3, a separator 4, and a nonaqueous electrolyte 5.
　より具体的には、二次電池１は、高さの比較的小さな有底円筒形状であるケース１１と、ケース１１の開口を閉鎖する上蓋１２とを有している。ケース１１と上蓋１２との間には空間が形成されている。上蓋１２は、かしめ加工によりケース１１に接合されている。 More specifically, the secondary battery 1 includes a case 11 that is relatively small in height and has a cylindrical shape with a bottom, and an upper lid 12 that closes the opening of the case 11. A space is formed between the case 11 and the upper lid 12. The upper lid 12 is joined to the case 11 by caulking.
　ケース１１と上蓋１２との間の空間内には、正極２、負極３、セパレータ４、非水電解液５が収容されている。正極２とセパレータ４との間には、ゴム製のパッキン１５が配置されている。また、上蓋１２と正極２との間には、スペーサ１３及びワッシャ１４が設けられている。スペーサ１３は、正極２と当接するように配置されている。ワッシャ１４は、スペーサ１３と上蓋１２との間に配置されている。本例のスペーサ１３は、具体的には、円盤状のステンレス鋼板である。 A positive electrode 2, a negative electrode 3, a separator 4, and a non-aqueous electrolyte 5 are housed in the space between the case 11 and the upper lid 12. A rubber packing 15 is arranged between the positive electrode 2 and the separator 4. Further, a spacer 13 and a washer 14 are provided between the upper lid 12 and the positive electrode 2. Spacer 13 is arranged so as to be in contact with positive electrode 2 . The washer 14 is arranged between the spacer 13 and the upper lid 12. Specifically, the spacer 13 of this example is a disc-shaped stainless steel plate.
　正極２は、正極集電体２１と、表１に示した正極活物質のうちいずれかの正極活物質を含み正極集電体２１上に設けられた正極活物質層２２とを有している。本例の正極集電体２１は、具体的には、直径１６ｍｍの円盤状を呈するアルミニウム箔である。負極３は、具体的には、円盤状の金属リチウム箔である。 The positive electrode 2 includes a positive electrode current collector 21 and a positive electrode active material layer 22 provided on the positive electrode current collector 21 and containing one of the positive electrode active materials shown in Table 1. . Specifically, the positive electrode current collector 21 of this example is an aluminum foil having a disc shape with a diameter of 16 mm. Specifically, the negative electrode 3 is a disk-shaped metal lithium foil.
　セパレータ４は、ポリプロピレンからなり、正極２と負極３との間に介在している。非水電解液５は、二次電池１内における少なくとも正極２と負極３との間に充填されている。本例の非水電解液５は、具体的には濃度１ｍｏｌ／ＬのＬｉＰＦ6を含むエチレンカーボネート系の有機溶媒からなる。 The separator 4 is made of polypropylene and is interposed between the positive electrode 2 and the negative electrode 3. The non-aqueous electrolyte 5 is filled between at least the positive electrode 2 and the negative electrode 3 in the secondary battery 1 . Specifically, the non-aqueous electrolyte 5 of this example is made of an ethylene carbonate-based organic solvent containing LiPF 6 at a concentration of 1 mol/L.
　次に、二次電池１の作製方法について説明する。まず、正極活物質と、導電助剤としての黒鉛と、結着剤としてのポリフッ化ビニリデンとを、質量比において、正極活物質：導電助剤：結着剤＝８５：１０：５となるように混合し、正極合材を得た。この正極合材を正極集電体２１上に塗布し、正極活物質層２２を形成した。塗布直後の正極活物質層２２の厚みは約２２０μｍとした。 Next, a method for manufacturing the secondary battery 1 will be explained. First, the positive electrode active material, graphite as a conductive aid, and polyvinylidene fluoride as a binder are mixed in a mass ratio of positive electrode active material: conductive aid: binder = 85:10:5. A positive electrode composite material was obtained. This positive electrode composite material was applied onto the positive electrode current collector 21 to form the positive electrode active material layer 22. The thickness of the positive electrode active material layer 22 immediately after coating was approximately 220 μm.
　次いで、正極集電体２１上の正極活物質層２２を約１００ＭＰａの圧力でプレスした。その後、正極活物質層２２を正極集電体２１とともに直径１６ｍｍの円盤状に打ち抜くことにより、正極２を得た。また、リチウム箔を円盤状に打ち抜くことにより、負極３を作製した。 Next, the positive electrode active material layer 22 on the positive electrode current collector 21 was pressed at a pressure of about 100 MPa. Thereafter, the positive electrode 2 was obtained by punching the positive electrode active material layer 22 together with the positive electrode current collector 21 into a disk shape with a diameter of 16 mm. Further, a negative electrode 3 was produced by punching out a lithium foil into a disk shape.
　次いで、ケース１１内に、負極３、セパレータ４、パッキン１５、正極２、スペーサ１３及びワッシャ１４を順次重ね合わせるとともに、ケース１１内に非水電解液５を注入した。その後、上蓋１２をケース１１の開口に重ね合わせ、かしめ加工を行うことによりケース１１と上蓋１２との間の空間を密閉した。以上により、二次電池１を得た。 Next, the negative electrode 3, separator 4, packing 15, positive electrode 2, spacer 13, and washer 14 were stacked one on top of the other in the case 11, and the non-aqueous electrolyte 5 was injected into the case 11. Thereafter, the upper lid 12 was placed over the opening of the case 11 and caulked to seal the space between the case 11 and the upper lid 12. Through the above steps, a secondary battery 1 was obtained.
　次に、得られた電池を用い、放電容量測定及び出力特性の評価を行った。なお、放電容量測定及び出力特性の評価には、充放電装置（Ｂｉｏ－Ｌｏｇｉｃ社製「ＢＣＳ－８１５」）を用いた。 Next, using the obtained battery, the discharge capacity was measured and the output characteristics were evaluated. Note that a charging/discharging device (“BCS-815” manufactured by Bio-Logic) was used to measure the discharge capacity and evaluate the output characteristics.
・放電容量測定
　まず、２５℃の温度において、定電流モードで二次電池を充電した。定電流モードにおける電流密度は１１ｍＡ／ｇとし、充電終止電圧は４．５Ｖとした。充電が完了した後、１１ｍＡ／ｇの電流密度の定電流で２．５Ｖまで放電させ、このときの放電曲線を取得した。このようにして得られた放電曲線に基づいて、二次電池の放電容量を算出した。表２に各正極活物質を用いた二次電池の放電容量を示す。 - Discharge capacity measurement First, the secondary battery was charged in constant current mode at a temperature of 25°C. The current density in constant current mode was 11 mA/g, and the end-of-charge voltage was 4.5V. After charging was completed, the battery was discharged to 2.5V at a constant current with a current density of 11 mA/g, and a discharge curve at this time was obtained. Based on the discharge curve obtained in this way, the discharge capacity of the secondary battery was calculated. Table 2 shows the discharge capacity of secondary batteries using each positive electrode active material.
・出力特性の評価
　二次電池の開回路電圧（つまり、ＯＣＶ）を４．４Ｖに調整した後、放電電流が５Ｃ相当（具体的には、およそ１０ｍＡ）となるようにして二次電池を放電させ、放電中の二次電池の電圧を測定した。そして、放電開始から０．１秒後における二次電池の電圧と、１０秒後における二次電池の電圧との電位差を放電電流で除することにより、二次電池の直流抵抗を算出した。表２の「直流抵抗」欄に、このようにして算出された二次電池の直流抵抗の値を示す。 ・Evaluation of output characteristics After adjusting the open circuit voltage (that is, OCV) of the secondary battery to 4.4V, discharge the secondary battery so that the discharge current is equivalent to 5C (specifically, approximately 10mA). The voltage of the secondary battery during discharge was measured. Then, the DC resistance of the secondary battery was calculated by dividing the potential difference between the voltage of the secondary battery 0.1 seconds after the start of discharge and the voltage of the secondary battery 10 seconds after the start of discharge by the discharge current. The "DC resistance" column of Table 2 shows the value of the DC resistance of the secondary battery calculated in this way.
・熱的安定性の評価
　まず、２５℃の温度において、定電流－定電圧モードで二次電池を充電した。定電流モードにおける電流密度は１１ｍＡ／ｇとした。また、定電圧モードにおける充電終止電圧は４．５Ｖとし、二次電池の電圧が充電終止電圧に達してから５時間にわたり、適切な充電電流を流して充電終止電圧を保持した。 - Evaluation of thermal stability First, the secondary battery was charged in constant current-constant voltage mode at a temperature of 25°C. The current density in constant current mode was 11 mA/g. Further, the end-of-charge voltage in the constant voltage mode was set to 4.5 V, and the end-of-charge voltage was maintained by flowing an appropriate charging current for 5 hours after the voltage of the secondary battery reached the end-of-charge voltage.
　充電が完了した後の二次電池をアルゴン雰囲気で満たしたグローブボックス内で解体し、正極を取り出した。この正極をジメチルカーボネートで洗浄した後、グローブボックス内で乾燥させた。乾燥後の正極から正極活物質層を採取し、示差走査熱量分析を行った。なお、示差走査熱量分析の条件は以下の通りとした。 After charging was completed, the secondary battery was disassembled in a glove box filled with an argon atmosphere, and the positive electrode was taken out. After washing this positive electrode with dimethyl carbonate, it was dried in a glove box. The positive electrode active material layer was collected from the dried positive electrode and subjected to differential scanning calorimetry analysis. The conditions for differential scanning calorimetry were as follows.
　　測定開始温度：室温
　　測定終了温度：５００℃
　　昇温速度：１０℃／分 Measurement start temperature: Room temperature Measurement end temperature: 500℃
Heating rate: 10℃/min
　示差走査熱量分析により得られたＤＳＣカーブに現れる発熱ピークのピーク温度及び当該発熱ピークにおける発熱量を表２に示す。 Table 2 shows the peak temperature of the exothermic peak appearing in the DSC curve obtained by differential scanning calorimetry and the calorific value at the exothermic peak.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　表１に示したように、試験材Ｓ１～Ｓ８は、前記特定の組成式で表される組成を有するとともに、空間群Ｒ－３ｍで表される層状岩塩型結晶構造を有している。そのため、表２に示すように、これらの試験材は、優れた熱的安定性及び出力特性を有している。 As shown in Table 1, the test materials S1 to S8 have a composition represented by the above-mentioned specific compositional formula and a layered rock salt type crystal structure represented by space group R-3m. Therefore, as shown in Table 2, these test materials have excellent thermal stability and output characteristics.
　これに対し、Ｎｉの含有率が試験材Ｓ１～Ｓ８と同程度であり、Ｗ及びＭｇの両方を含まない試験材Ｒ１は、試験材Ｓ１～Ｓ８に比べて直流抵抗が高く、出力特性に劣っている。また、試験材Ｒ１は、試験材Ｓ１～Ｓ８に比べて発熱量が大きく、熱的安定性に劣っている。 On the other hand, test material R1, which has the same Ni content as test materials S1 to S8 and does not contain both W and Mg, has a higher DC resistance and inferior output characteristics than test materials S1 to S8. ing. Furthermore, the test material R1 has a larger calorific value than the test materials S1 to S8, and is inferior in thermal stability.
　Ｎｉの含有率が試験材Ｓ１～Ｓ８と同程度であり、Ｍｇを含まない試験材Ｒ２は、試験材Ｓ１～Ｓ８に比べて発熱ピーク温度が低く、比較的低い温度で分解するおそれがある。さらに、試験材Ｒ２は、発熱量が大きく、熱的安定性に劣っている。 Test material R2, which has the same Ni content as test materials S1 to S8 and does not contain Mg, has a lower exothermic peak temperature than test materials S1 to S8, and may decompose at a relatively low temperature. Furthermore, test material R2 has a large calorific value and is inferior in thermal stability.
　Ｎｉの含有率が試験材Ｓ１～Ｓ８と同程度であり、Ｍｇを含まない試験材Ｒ４は、試験材Ｓ１～Ｓ８に比べて発熱量が大きく、熱的安定性に劣っている。 Test material R4, which has the same Ni content as test materials S1 to S8 and does not contain Mg, has a larger calorific value and inferior thermal stability than test materials S1 to S8.
　Ｎｉの含有率が試験材Ｓ１～Ｓ８と同程度であり、Ｗを含まない試験材Ｒ３及び試験材Ｒ５は、試験材Ｓ１～Ｓ８に比べて直流抵抗が高く、出力特性に劣っている。 Test materials R3 and R5, which have the same Ni content as test materials S1 to S8 and do not contain W, have higher DC resistance and inferior output characteristics than test materials S1 to S8.
　また、試験材Ｓ９は、前記特定の組成式で表される組成を有するとともに、空間群Ｒ－３ｍで表される層状岩塩型結晶構造を有している。そのため、試験材Ｓ９は、優れた熱的安定性及び出力特性を有している。 Further, the test material S9 has a composition represented by the above-mentioned specific compositional formula, and has a layered rock salt type crystal structure represented by a space group R-3m. Therefore, test material S9 has excellent thermal stability and output characteristics.
　これに対し、Ｎｉの含有率が試験材Ｓ９と同程度であり、Ｗ及びＭｇの両方を含まない試験材Ｒ６は、試験材Ｓ９に比べて直流抵抗が高く、出力特性に劣っている。また、試験材Ｒ６は、試験材Ｓ９に比べて発熱ピーク温度が低く、比較的低い温度で分解するおそれがある。さらに、試験材Ｒ６は、発熱量が大きく、熱的安定性に劣っている。 On the other hand, the test material R6, which has the same Ni content as the test material S9 and does not contain both W and Mg, has a higher DC resistance and inferior output characteristics than the test material S9. In addition, test material R6 has a lower exothermic peak temperature than test material S9, and there is a risk that it will decompose at a relatively low temperature. Furthermore, test material R6 has a large calorific value and is inferior in thermal stability.
　Ｎｉの含有率が試験材Ｓ９と同程度であり、Ｍｇを含まない試験材Ｒ７は、試験材Ｓ９に比べて発熱量が大きく、熱的安定性に劣っている。 Test material R7, which has the same Ni content as test material S9 and does not contain Mg, has a larger calorific value and inferior thermal stability than test material S9.
　Ｎｉの含有率が試験材Ｓ９と同程度であり、Ｗを含まない試験材Ｒ８は、試験材Ｓ９に比べて直流抵抗が高く、出力特性に劣っている。 Test material R8, which has the same Ni content as test material S9 and does not contain W, has a higher DC resistance and inferior output characteristics than test material S9.
　以上のように、Ｎｉの含有率が同程度である試験材Ｓ１～Ｓ８と試験材Ｒ１～Ｒ５との比較、及び試験材Ｓ９と試験材Ｒ６～Ｒ８との比較から、Ｌｉ－Ｎｉ－Ｍｎ系正極活物質にＷとＭｇとの両方を添加することにより、放電容量、出力特性及び熱的安定性をバランスよく向上可能であることが理解できる。 As mentioned above, from the comparison between test materials S1 to S8 and test materials R1 to R5, which have the same Ni content, and the comparison between test material S9 and test materials R6 to R8, it was found that the Li-Ni-Mn It can be seen that by adding both W and Mg to the positive electrode active material, discharge capacity, output characteristics, and thermal stability can be improved in a well-balanced manner.
　本発明に係る正極活物質及び非水電解液二次電池の具体的な構成は、前述した実施例の構成に限定されるものではなく、本発明の趣旨を損なわない範囲で適宜変更することができる。 The specific configurations of the positive electrode active material and non-aqueous electrolyte secondary battery according to the present invention are not limited to the configurations of the embodiments described above, and may be modified as appropriate without departing from the spirit of the present invention. can.

Claims (6)

  1. 　非水電解液二次電池に用いられる正極活物質であって、
    　ＬｉaＮｉbＭｎcＷdＭｇeＯfの組成式（ただし、前記組成式におけるａ～ｆは、０．９＜ａ＜１．２、０．４５＜ｂ＜０．６、０．２５＜ｃ＜０．５、０＜ｄ＜０．０６、０＜ｅ＜０．１、１．９＜ｆ＜２．１の関係を満たす。）で表される組成を有するとともに、
    　空間群Ｒ－３ｍに帰属可能な層状岩塩型結晶構造を有する、正極活物質。     A positive electrode active material used in a nonaqueous electrolyte secondary battery,
    Composition formula of Li a Ni b Mn c W d Mg e Of (however, a to f in the above composition formula are 0.9<a<1.2, 0.45<b<0.6, 0.25 <c<0.5, 0<d<0.06, 0<e<0.1, 1.9<f<2.1).)
    A positive electrode active material having a layered rock salt crystal structure that can be assigned to space group R-3m.
  2. 　前記正極活物質の結晶格子におけるａ軸の長さが２．８８０Å以上２．９００Å以下であり、ｃ軸の長さが１４．２９０Å以上１４．３６０Å以下である、請求項１に記載の正極活物質。 The positive electrode active material according to claim 1, wherein the length of the a-axis in the crystal lattice of the positive electrode active material is 2.880 Å or more and 2.900 Å or less, and the length of the c-axis is 14.290 Å or more and 14.360 Å or less. material.
  3. 　正極と、負極と、非水電解液とを有する非水電解液二次電池であって、
    　前記正極は、請求項１または２に記載の正極活物質を含む、非水電解液二次電池。     A nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolyte,
    A non-aqueous electrolyte secondary battery, wherein the positive electrode contains the positive electrode active material according to claim 1 or 2.
  4. 　請求項１または２に記載の正極活物質の製造方法であって、
    　共沈法により前記組成のうちＬｉ以外の全ての金属元素を含む前駆体を作製し、
    　前記前駆体と、Ｌｉを含む化合物とを混合して混合物を作製し、
    　前記混合物を酸化性ガス雰囲気中で焼成することにより前記正極活物質を得る、正極活物質の製造方法。     A method for producing a positive electrode active material according to claim 1 or 2, comprising:
    Producing a precursor containing all metal elements other than Li in the composition by a coprecipitation method,
    Producing a mixture by mixing the precursor and a compound containing Li,
    A method for producing a positive electrode active material, wherein the positive electrode active material is obtained by firing the mixture in an oxidizing gas atmosphere.
  5. 　前記前駆体を作製する際に、アルカリ性を示す反応溶液と、Ｗを含む第１原料溶液と、前記組成のうちＬｉ及びＷ以外の金属元素を含む第２原料溶液と、を準備し、
    　前記第１原料溶液と前記第２原料溶液とを前記反応溶液中に同時に滴下して前記前駆体を作製する、請求項４に記載の正極活物質の製造方法。     When producing the precursor, a reaction solution exhibiting alkalinity, a first raw material solution containing W, and a second raw material solution containing a metal element other than Li and W in the composition are prepared,
    5. The method for producing a positive electrode active material according to claim 4, wherein the precursor is produced by simultaneously dropping the first raw material solution and the second raw material solution into the reaction solution.
  6. 　前記前駆体を作製する際に、さらに、アルカリ性を示すｐＨ調整溶液を準備し、
    　前記ｐＨ調整溶液を、前記第１原料溶液及び前記第２原料溶液とともに前記反応溶液中に滴下して前記前駆体を作製する、請求項５に記載の正極活物質の製造方法。     When producing the precursor, further preparing a pH adjusting solution exhibiting alkalinity,
    The method for producing a positive electrode active material according to claim 5, wherein the precursor is produced by dropping the pH adjusting solution into the reaction solution together with the first raw material solution and the second raw material solution.
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JP2005322480A (en) * 2004-05-07 2005-11-17 Nec Corp Positive pole active material for lithium secondary battery, and lithium secondary battery using it
WO2012164693A1 (en) * 2011-05-31 2012-12-06 トヨタ自動車株式会社 Lithium secondary battery
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