Positive electrode active material for lithium secondary battery, manufacturing method thereof, and lithium secondary battery

Abstract

To provide a positive electrode active material for a lithium secondary battery, which has excellent cycle characteristics under high voltage and can reduce impedance.SOLUTION: A positive electrode active material for a lithium secondary battery is composed of a mixture of aluminum-containing lithium cobalt composite oxide particles and inorganic fluoride particles, and the aluminum-containing lithium cobalt composite oxide particles have aluminum present in a solid solution at least inside the aluminum-containing lithium cobalt composite oxide particles, and the inorganic fluoride particles are compounds containing MgF2, Al, and F.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery using the positive electrode active material for a lithium secondary battery. [Background technology]

[0002] In recent years, with the rapid advancement of portable and cordless home appliances, lithium-ion secondary batteries have been put to practical use as power sources for small electronic devices such as laptop computers, mobile phones, video cameras, etc. Since Mizushima et al. reported in 1980 that lithium cobalt oxide is useful as a positive electrode active material for lithium-ion secondary batteries, research and development into lithium-based composite oxides has been actively carried out, and many proposals have been made to date.

[0003] However, as electronic devices become larger and more sophisticated, further improvements in various battery properties are required.

[0004] The present applicant has previously proposed various positive electrode active materials for lithium secondary batteries that can provide lithium secondary batteries with excellent cycle characteristics even under high voltage. For example, in Patent Document 1, a mixture of lithium-cobalt composite oxide particles and inorganic fluoride particles is used as the positive electrode active material for lithium secondary batteries, thereby providing lithium secondary batteries with excellent cycle characteristics, a high energy capacity retention rate, and a small decrease in average operating voltage. Furthermore, in Patent Document 2, a mixture of titanium-containing lithium-cobalt composite oxide particles and inorganic fluoride particles is used as the positive electrode active material for lithium secondary batteries, thereby providing lithium secondary batteries with excellent cycle characteristics, a small decrease in average operating voltage, a high average operating voltage retention rate, and a high energy density retention rate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-064712 [Patent Document 2] Japanese Patent Application Publication No. 2020-064711 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in response to the recent demand for improved battery characteristics, the above-mentioned conventional techniques have not yet achieved a high level of performance in various battery performance areas.

[0007] In particular, batteries used in electric bicycles, electric vehicles, robots, drones, backup power sources, etc. are expected to be used at high voltages and with high power output.

[0008] Therefore, it has been desired to improve the cycle characteristics at high voltages at temperatures of about 25° C. and to have low impedance.Furthermore, in addition to the above battery performance, it has been desired to improve the cycle characteristics at high voltages at temperatures of about 45 to 60° C.

[0009] Therefore, an object of the present invention is to provide a positive electrode active material for a lithium secondary battery that, when used as a positive electrode active material for a lithium secondary battery, exhibits excellent cycle characteristics under high voltage and can reduce impedance, an industrially advantageous method for producing the same, and a lithium secondary battery that exhibits excellent cycle characteristics under high voltage and can reduce impedance. do. Another object of the present invention is to provide a positive electrode active material for a lithium secondary battery that has excellent cycle characteristics at high temperatures and high voltages in addition to the above-mentioned battery performance, an industrially advantageous method for producing the same, and a lithium secondary battery that has excellent cycle characteristics at high temperatures and high voltages in addition to the above-mentioned battery performance. [Means for solving the problem]

[0010] The present inventors have conducted extensive research in light of the above-mentioned circumstances, and as a result have found that by using a mixture of aluminum-containing lithium-cobalt composite oxide particles, in which aluminum is contained in the form of a solid solution inside the lithium-cobalt composite oxide particles as aluminum-containing lithium-cobalt composite oxide particles, and inorganic fluoride particles that are a compound containing MgF and Al and F, as a positive electrode active material for a lithium secondary battery, a lithium secondary battery can be obtained that has excellent cycle characteristics under high voltage and low impedance, and have completed the present invention.

[0011] That is, the present invention (1) comprises a mixture of aluminum-containing lithium-cobalt composite oxide particles and inorganic fluoride particles, The present invention provides a positive electrode active material for a lithium secondary battery, characterized in that the aluminum-containing lithium-cobalt composite oxide particles have aluminum present as a solid solution at least inside the aluminum-containing lithium-cobalt composite oxide particles, and the inorganic fluoride particles are MgF2 and a compound containing Al and F.

[0012] The present invention (2) also provides a positive electrode active material for a lithium secondary battery according to (1), characterized in that the compound containing Al and F is AlF3 and / or LiAlF4.

[0013] The present invention (3) also provides a positive electrode active material for a lithium secondary battery according to (1) or (2), characterized in that the content of Al in the aluminum-containing lithium-cobalt composite oxide particles is 0.05 to 5.0 mol % in terms of atomic molar percentage of Al relative to Co in the aluminum-containing lithium-cobalt composite oxide particles ((Al / Co) × 100).

[0014] The present invention (4) also provides a positive electrode active material for a lithium secondary battery according to any one of (1) to (3), characterized in that the content of the inorganic fluoride particles is 0.05 to 5.0 mol % in terms of atomic molar percentage of F relative to Co in the aluminum-containing lithium-cobalt composite oxide particles ((F / Co) × 100).

[0015] The present invention (5) also provides a positive electrode active material for a lithium secondary battery according to any one of (1) to (4), characterized in that the mixing ratio of the MgF2 and the compound containing Al and F is such that the ratio of the number of moles of F in atomic terms in the MgF2 to the number of moles of F in atomic terms in the compound containing Al and F (number of moles of F in atomic terms in MgF2 / number of moles of F in atomic terms in the compound containing Al and F) is 0.033 to 33.

[0016] The present invention (6) also provides a positive electrode active material for a lithium secondary battery according to any one of (1) to (5), characterized in that the c-axis lattice constant is 14.055 to 14.070 Å.

[0017] The present invention (7) also provides a positive electrode active material for a lithium secondary battery according to any one of (1) to (6), characterized in that the aluminum-containing lithium-cobalt composite oxide particles contain, as the M element, one or more elements selected from the group consisting of Ca, Mg, Sr, Zr, Nb, B, and W.

[0018] The present invention (8) is a fired product of a mixture of aluminum-containing lithium-cobalt composite oxide particles and inorganic fluoride particles, The present invention provides a positive electrode active material for a lithium secondary battery, characterized in that the aluminum-containing lithium-cobalt composite oxide particles have aluminum present as a solid solution at least inside the aluminum-containing lithium-cobalt composite oxide particles, and the inorganic fluoride particles are MgF2 and AlF3.

[0019] The present invention (9) also provides a positive electrode active material for a lithium secondary battery according to (8), characterized in that the aluminum-containing lithium-cobalt composite oxide particles are a fired product of a mixture of a lithium compound, a cobalt compound, and an aluminum compound.

[0020] The present invention (10) also provides a positive electrode active material for a lithium secondary battery according to (8) or (9), characterized in that the content of Al in the aluminum-containing lithium-cobalt composite oxide particles is 0.05 to 5.0 mol % in terms of atomic mol % of Al relative to Co in the aluminum-containing lithium-cobalt composite oxide particles ((Al / Co) × 100).

[0021] The present invention (11) also provides a positive electrode active material for a lithium secondary battery according to any one of (8) to (10), characterized in that the amount of the inorganic fluoride particles mixed in the mixture of the aluminum-containing lithium cobalt composite oxide particles and the inorganic fluoride particles is 0.05 to 5.0 mol % in terms of atomic molar percentage of F relative to Co in the aluminum-containing lithium cobalt composite oxide particles ((F / Co) × 100).

[0022] The present invention (12) also provides a positive electrode active material for a lithium secondary battery according to any one of (8) to (11), characterized in that the mixing ratio of the MgF2 in the mixture of the aluminum-containing lithium-cobalt composite oxide particles and inorganic fluoride particles is 0.05 to 50 in terms of molar ratio (MgF2 / AlF3) to the AlF3.

[0023] The present invention (13) also provides a positive electrode active material for a lithium secondary battery according to any one of (8) to (12), characterized in that the c-axis lattice constant is 14.055 to 14.070 Å.

[0024] The present invention (14) also provides a positive electrode active material for a lithium secondary battery according to any one of (8) to (13), characterized in that the aluminum-containing lithium-cobalt composite oxide particles contain, as the M element, one or more elements selected from the group consisting of Ca, Mg, Sr, Zr, Nb, B, and W.

[0025] The present invention (15) also provides a method for producing a sintered product, comprising: a first mixing step of mixing raw materials, a lithium compound, a cobalt compound, and an aluminum compound, to obtain a first mixture; a first firing step of firing the first mixture to obtain, as a first fired product, aluminum-containing lithium-cobalt composite oxide particles in which aluminum is present as a solid solution at least inside the particles; a second mixing step of mixing the first fired product obtained in the first firing step with inorganic fluoride particles to obtain a second mixture; a second firing step of firing the second mixture to obtain a positive electrode active material for a lithium secondary battery as a second fired product, The present invention provides a method for producing a positive electrode active material for a lithium secondary battery, characterized in that the inorganic fluoride particles are MgF2 and AlF3.

[0026] Further, the present invention (16) is characterized in that in the first mixing step, the aluminum compound is mixed with The present invention provides a method for producing a positive electrode active material for a lithium secondary battery according to (15), characterized in that Al is mixed with Co in the first mixture so that the molar percentage of Al relative to Co in atomic terms ((Al / Co) × 100) is 0.05 to 5.0 molar percentage.

[0027] The present invention (17) also provides the method for producing a positive electrode active material for a lithium secondary battery according to (15) or (16), characterized in that the first fired product contains, as the M element, one or more selected from the group consisting of Ca, Mg, Sr, Zr, Nb, B, and W.

[0028] The present invention (18) also provides a method for producing a positive electrode active material for a lithium secondary battery according to any one of (15) to (17), characterized in that in the first firing step, the firing temperature is 800 to 1150°C.

[0029] The present invention (19) also provides the method for producing a positive electrode active material for a lithium secondary battery according to any one of (15) to (18), characterized in that in the second mixing step, the inorganic fluoride particles are mixed so that the molar percentage of F relative to Co in the second mixture, calculated as atoms ((F / Co) × 100), is 0.05 to 2.0 mol %.

[0030] The present invention (20) also provides a method for producing a positive electrode active material for a lithium secondary battery according to any one of (15) to (19), characterized in that the c-axis lattice constant of the positive electrode active material for a lithium secondary battery, which is the second fired product, is 14.055 to 14.070 Å.

[0031] The present invention (21) also provides a lithium secondary battery characterized in that any one of the positive electrode active materials for lithium secondary batteries (1) to (14) is used as the positive electrode active material. [Effects of the Invention]

[0032] According to the present invention, it is possible to provide a positive electrode active material for lithium secondary batteries that, when used as a positive electrode active material for lithium secondary batteries, exhibits excellent cycle characteristics under high voltage and can reduce impedance; an industrially advantageous method for producing the same; and a lithium secondary battery that exhibits excellent cycle characteristics under high voltage and can reduce impedance. Furthermore, according to the present invention, it is possible to provide a positive electrode active material for a lithium secondary battery that has excellent cycle characteristics at high temperatures and high voltages in addition to the above-mentioned battery performance, an industrially advantageous method for producing the same, and a lithium secondary battery that has excellent cycle characteristics at high temperatures and high voltages in addition to the above-mentioned battery performance. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is an X-ray diffraction diagram of the aluminum-containing lithium-cobalt composite oxide obtained in the first firing step of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0034] The present invention will be described below based on preferred embodiments.

[0035] The positive electrode active material for a lithium secondary battery according to the first embodiment of the present invention (hereinafter also referred to as the positive electrode active material for a lithium secondary battery (1) of the present invention) comprises a mixture of aluminum-containing lithium-cobalt composite oxide particles (1) and inorganic fluoride particles, The aluminum-containing lithium-cobalt composite oxide particles (1) are characterized in that aluminum is present in the form of a solid solution at least inside the aluminum-containing lithium-cobalt composite oxide particles, and the inorganic fluoride particles are MgF2 and a compound containing Al and F. The aluminum-containing lithium-cobalt composite oxide particles according to the positive electrode active material (1) for a lithium secondary battery of the present invention are also referred to as aluminum-containing lithium-cobalt composite oxide particles (1).

[0036] The positive electrode active material (1) for a lithium secondary battery of the present invention basically comprises a mixture of aluminum-containing lithium-cobalt composite oxide particles (1) and inorganic fluoride particles.

[0037] The aluminum-containing lithium-cobalt composite oxide forming the aluminum-containing lithium-cobalt composite oxide particles (1) according to the positive electrode active material (1) for lithium secondary batteries of the present invention is a composite oxide containing at least lithium, cobalt, and aluminum, and is a composite oxide obtained by adding aluminum as an additive element to the lithium-cobalt composite oxide. In the aluminum-containing lithium-cobalt composite oxide particles (1) according to the positive electrode active material (1) for lithium secondary batteries of the present invention, Al is present as a solid solution at least inside the aluminum-containing lithium-cobalt composite oxide particles. In the aluminum-containing lithium-cobalt composite oxide particles (1) according to the positive electrode active material (1) for lithium secondary batteries of the present invention, Al is present as a solid solution at least inside the aluminum-containing lithium-cobalt composite oxide particles (1), which stabilizes the crystal structure of the lithium-cobalt composite oxide particles themselves even under high voltage. This prevents a decrease in charge / discharge capacity and improves cycle characteristics at high voltages, and more preferably improves cycle characteristics at high voltages and high temperatures.

[0038] In the aluminum-containing lithium-cobalt composite oxide particles (1) according to the positive electrode active material (1) for a lithium secondary battery of the present invention, the presence of Al in the form of a solid solution inside the aluminum-containing lithium-cobalt composite oxide particles (1) means that when the aluminum-containing lithium-cobalt composite oxide particles (1) are subjected to X-ray diffraction analysis using CuKα radiation as a radiation source, the aluminum-containing lithium-cobalt composite oxide particles (1) are single-phase aluminum-containing lithium-cobalt composite oxide particles in which diffraction peaks attributable to the raw material aluminum compound and / or AlO are substantially not detected. The phrase "diffraction peaks attributable to the aluminum compound and Al2O3 in the raw material are not substantially detected" means that the diffraction peaks attributable to the aluminum compound and Al2O3 are below the detection limit of the analytical device. As will be described later, the presence of Al in the form of solid solution inside the aluminum-containing lithium-cobalt composite oxide particles (1) can also be inferred from the fact that the lithium-cobalt composite oxide (1) containing Al in the form of solid solution inside the particles has a larger c-axis lattice constant than pure lithium-cobalt composite oxide particles not containing Al in the form of solid solution inside the particles.

[0039] In the aluminum-containing lithium-cobalt composite oxide (1) according to the cathode active material (1) for lithium secondary batteries of the present invention, Al may be present only inside the composite oxide particles, or may be present both inside and on the surface of the composite oxide particles. In the present invention, Al may be present inside the composite oxide particles or on the surface of the composite oxide particles. In the cathode active material (1) for lithium secondary batteries of the present invention, it is preferable that the aluminum-containing lithium-cobalt composite oxide particles (1) have Al present as a solid solution at least inside the composite oxide particles, in order to stabilize the structure of the composite oxide. The phrase "Al present as a solid solution at least inside the composite oxide particles" refers to cases where Al is present only inside the particles or both inside and on the particle surface.

[0040] In the aluminum-containing lithium-cobalt composite oxide particles (1) relating to the positive electrode active material for lithium secondary batteries (1) of the present invention, the molar ratio of Li to Co in terms of atoms (Li / Co) is preferably 0.90 to 1.20, particularly preferably 0.95 to 1.15. When the molar ratio of Li to Co in terms of atoms (Li / Co) in the aluminum-containing lithium-cobalt composite oxide particles (1) is within the above range, the positive electrode active material for lithium secondary batteries per volume The capacity can be improved.

[0041] In the aluminum-containing lithium-cobalt composite oxide particles (1) according to the positive electrode active material (1) for lithium secondary batteries of the present invention, the molar percentage of Al relative to Co, calculated as an atom ((Al / Co) × 100), is preferably 0.05 to 5.0 molar percentages, particularly preferably 0.5 to 2.0 molar percentages. When the molar percentage of Al relative to Co, calculated as an atom ((Al / Co) × 100), in the aluminum-containing lithium-cobalt composite oxide particles (1) is within the above range, the positive electrode active material for lithium secondary batteries can have improved cycle characteristics at high voltage, cycle characteristics at high voltage and high temperature, and high-temperature storage characteristics, while suppressing a decrease in charge / discharge capacity.

[0042] The aluminum-containing lithium-cobalt composite oxide particles (1) according to the positive electrode active material (1) for a lithium secondary battery of the present invention contain Al as an essential additive element for the lithium-cobalt composite oxide, but may contain an element M, if necessary, for the purpose of improving performance or physical properties. The element M is one or more metal elements selected from Ca, Mg, Sr, Zr, Nb, B, and W.

[0043] The aluminum-containing lithium-cobalt composite oxide particles (1) according to the cathode active material (1) for a lithium secondary battery of the present invention preferably contain at least one of Ca and Sr as the M element, in order to further improve battery characteristics, and particularly preferably contain at least one of Ca and Sr and one or more selected from Mg, Zr, Nb, B, and W. The aluminum-containing lithium-cobalt composite oxide particles (1) according to the cathode active material (1) for a lithium secondary battery of the present invention preferably contain at least one or two or more selected from Ca, Mg, Sr, and Zr as the M element. The aluminum-containing lithium-cobalt composite oxide particles (1) according to the cathode active material (1) for a lithium secondary battery of the present invention preferably contain Mg, Sr, and Zr as the M element.

[0044] When the aluminum-containing lithium-cobalt composite oxide particles (1) according to the present invention for the positive electrode active material for lithium secondary batteries contain an M element, the molar percentage of the M element relative to the Co atoms in the aluminum-containing lithium-cobalt composite oxide particles (1) ((M / Co) × 100) in atomic terms is preferably 0.01 to 2.0 mol %, particularly preferably 0.05 to 1.0 mol %. When the aluminum-containing lithium-cobalt composite oxide particles (1) contain an M element, the molar percentage of the M element relative to the Co atoms in the aluminum-containing lithium-cobalt composite oxide particles (1) ((M / Co) × 100) in atomic terms within the above range can improve the battery characteristics without impairing the charge / discharge capacity of the positive electrode active material for lithium secondary batteries. When the aluminum-containing lithium-cobalt composite oxide contains two or more M elements, the molar number of the M element in atomic terms, which is the basis for calculating the molar percentage, refers to the sum of the molar numbers of the individual M elements.

[0045] The M element may be present inside the aluminum-containing lithium-cobalt-based composite oxide particles (1), or may be present on the particle surface of the aluminum-containing lithium-cobalt-based composite oxide particles (1), or may be present both inside and on the particle surface of the aluminum-containing lithium-cobalt-based composite oxide particles (1).

[0046] When the M element is present on the particle surface of the aluminum-containing lithium-cobalt-based composite oxide particles (1), the M element may be present in the form of an oxide, composite oxide, sulfate, phosphate, or the like.

[0047] The average particle diameter of the aluminum-containing lithium-cobalt composite oxide particles (1) according to the positive electrode active material (1) for a lithium secondary battery of the present invention is preferably 0.5 to 30 μm, particularly preferably 0.5 to 30 μm, in terms of the particle diameter at 50% by volume (D50) in the particle size distribution measured by a laser diffraction / scattering method. The BET specific surface area of the aluminum-containing lithium cobalt composite oxide particles (1) is preferably 0.05 to 5.0 m 2 / g, particularly preferably 0.15 to 1.0 m 2 When the average particle size or BET specific surface area of the aluminum-containing lithium-cobalt composite oxide particles (1) is within the above range, the preparation and coating properties of the positive electrode mixture become easy, and furthermore, an electrode with high packing properties can be obtained.

[0048] One of the features of the inorganic fluoride particles according to the positive electrode active material (1) for a lithium secondary battery of the present invention is that they contain MgF2 and a compound containing Al and F in combination. Hereinafter, MgF2 and compounds containing Al and F may be collectively referred to as "inorganic fluorides" or "inorganic fluoride particles." Examples of compounds containing Al and F include AlF3 and / or LiAlF4.

[0049] The content of the inorganic fluoride particles in the positive electrode active material for lithium secondary batteries (1) of the present invention is, in atomic molar percentage ((F / Co) × 100) of F relative to Co in the aluminum-containing lithium-cobalt composite oxide particles (1), preferably 0.05 to 5.0 molar percentage, particularly preferably 0.1 to 2.0 molar percentage. When the atomic molar percentage ((F / Co) × 100) of F relative to Co in the aluminum-containing lithium-cobalt composite oxide particles (1) is within the above range, the effect of improving the cycle characteristics at high voltages while suppressing a decrease in the charge / discharge capacity of the positive electrode active material for lithium secondary batteries is enhanced, and the impedance of the positive electrode active material for lithium secondary batteries can be reduced.

[0050] The mixing ratio of MgF2 and the compound containing Al and F, expressed as the ratio of the number of moles of F in MgF2 in atomic terms to the number of moles of F in the compound containing Al and F (number of moles of F in MgF2 in atomic terms / number of moles of F in the compound containing Al and F) is 0.033 to 33, preferably 0.1 to 20, and particularly preferably 1 to 10. Having the ratio of the number of moles of F in MgF2 in atomic terms to the number of moles of F in the compound containing Al and F (number of moles of F in MgF2 in atomic terms / number of moles of F in the compound containing Al and F) in the above range is preferred in terms of achieving both initial discharge capacity and impedance.

[0051] The inorganic fluoride particles may be present on the particle surface of the aluminum-containing lithium-cobalt composite oxide particles (1), or may be present in a simple mixture with the aluminum-containing lithium-cobalt composite oxide particles (1), or both. That is, the positive electrode active material for a lithium secondary battery of the present invention may consist of the aluminum-containing lithium-cobalt composite oxide particles (1) and inorganic fluoride particles present on the surface of the aluminum-containing lithium-cobalt composite oxide particles (1), or may be a simple mixture of the aluminum-containing lithium-cobalt composite oxide particles (1) and inorganic fluoride particles, or may be a mixture of both forms. Note that when the inorganic fluoride particles are present on the particle surface of the aluminum-containing lithium-cobalt composite oxide particles (1), it is preferable that the inorganic fluoride particles are present only partially on the surface of the aluminum-containing lithium-cobalt composite oxide particles (1), since this does not inhibit lithium intercalation and deintercalation on the surface of the aluminum-containing lithium-cobalt composite oxide.

[0052] The inorganic fluoride particles have an average particle size of preferably 0.01 to 30 μm, particularly preferably 0.1 to 20 μm, as the particle size at 50% volume (D50) in the particle size distribution measured by a laser diffraction / scattering method. When the average particle size of the inorganic fluoride particles is within the above range, problems are less likely to occur in the kneading step for preparing the positive electrode mixture and in the coating step for applying the obtained positive electrode mixture to the positive electrode current collector.

[0053] The average particle size of the positive electrode active material (1) for a lithium secondary battery of the present invention is the particle size at 50% of the volume (D50) in the particle size distribution measured by a laser diffraction / scattering method, and is preferably 0. The BET specific surface area of the positive electrode active material (1) for a lithium secondary battery of the present invention is preferably 0.05 to 5.0 m 2 / g, particularly preferably 0.15 to 1.0 m 2When the average particle size or BET specific surface area of the positive electrode active material (1) for a lithium secondary battery of the present invention is within the above range, problems are unlikely to occur in the kneading step for preparing the positive electrode mixture and in the coating step for coating the obtained positive electrode mixture on a positive electrode current collector.

[0054] The present inventors speculate that the Al contained in LiCoO2 as a solid solution affects the crystal structure of pure LiCoO2. That is, the c-axis lattice constant of pure LiCoO2 without Al dissolved inside the particles is 14.050 to 14.055 Å, whereas the c-axis lattice constant of the positive electrode active material for lithium secondary batteries (1) of the present invention is larger than that of pure LiCoO2. The present inventors speculate that this is due to the influence of Al present as a solid solution in the lithium-cobalt composite oxide.

[0055] The c-axis lattice constant of the positive electrode active material (1) for a lithium secondary battery of the present invention is preferably 14.055 to 14.070 Å, particularly preferably 14.055 to 14.065 Å. When the c-axis lattice constant is in the above range, collapse of the crystal structure due to charge and discharge can be reduced, and cycle characteristics can be improved.

[0056] The method for producing a positive electrode active material for a lithium secondary battery of the present invention includes a first mixing step of mixing raw materials, that is, a lithium compound, a cobalt compound, and an aluminum compound, to obtain a first mixture; a first firing step of firing the first mixture to obtain, as a first fired product, aluminum-containing lithium-cobalt composite oxide particles (2) in which aluminum is present as a solid solution at least inside the particles; a second mixing step of mixing the first fired product obtained in the first firing step with inorganic fluoride particles to obtain a second mixture; a second firing step of firing the second mixture to obtain a positive electrode active material for a lithium secondary battery as a second fired product, The inorganic fluoride particles are MgF2 and AlF3. In the method for producing a positive electrode active material for a lithium secondary battery of the present invention, the aluminum-containing lithium-cobalt composite oxide particles before being mixed with inorganic fluoride particles and fired, i.e., the aluminum-containing lithium-cobalt composite oxide particles as the raw material when being mixed with inorganic fluoride particles and fired, are also referred to as aluminum-containing lithium-cobalt composite oxide particles (2).

[0057] The first mixing step is, for example, a step of mixing a lithium compound, a cobalt compound, and an aluminum compound to obtain a first mixture containing the lithium compound, the cobalt compound, and the aluminum compound.

[0058] The lithium compound to be used in the first mixing step is not particularly limited as long as it is a lithium compound that is usually used as a raw material for producing a lithium-cobalt composite oxide, and examples thereof include oxides, hydroxides, carbonates, nitrates, sulfates, and organic acid salts of lithium.

[0059] The cobalt compound used in the first mixing step is not particularly limited as long as it is a cobalt compound that is normally used as a raw material for producing a lithium-cobalt-based composite oxide, and examples thereof include oxides, oxyhydroxides, hydroxides, carbonates, nitrates, sulfates, and organic acid salts of cobalt.

[0060] The aluminum compound in the first mixing step is particularly an aluminum compound used as a raw material for producing lithium-cobalt composite oxide to which aluminum element is added. Examples of the aluminum compound include, but are not limited to, aluminum oxide, hydroxide, carbonate, nitrate, sulfate, and organic acid salts, etc. Among these, aluminum hydroxide is preferred as the aluminum compound.

[0061] In the first mixing step, the lithium compound and the cobalt compound are mixed so that the molar ratio of Li to Co in the first mixture (Li / Co) in atomic terms is preferably 0.90 to 1.20, particularly preferably 0.95 to 1.15, and even more preferably 1.03 to 1.06. When the mixing ratio of the lithium compound and the cobalt compound is within the above range, a single phase lithium-cobalt composite oxide containing aluminum is easily obtained in X-ray diffraction analysis.

[0062] In the first mixing step, the aluminum compound is mixed so that the molar percentage of Al relative to Co in the first mixture ((Al / Co)×100) in atomic terms is preferably 0.05 to 5.0 mol %, and particularly preferably 0.5 to 2.0 mol %. When the mixing ratio of the aluminum compound is within the above range, the high-voltage cycle characteristics, high-voltage and high-temperature cycle characteristics, and high-temperature storage characteristics can be improved without impairing the inherent charge / discharge capacity of the lithium-cobalt composite oxide.

[0063] In the first mixing step, a compound containing an M element can be mixed into the first mixture for the purpose of improving performance or physical properties.

[0064] The M element is one or more metal elements selected from Ca, Mg, Sr, Zr, Nb, B, and W. Examples of compounds containing the M element include oxides, hydroxides, carbonates, nitrates, and organic acid salts containing the M element. Compounds containing two or more M elements may also be used as the compound containing the M element.

[0065] When a compound containing M element is mixed in the first mixing step, the compound containing M element is mixed so that the atomic molar percentage of M element relative to Co atoms in the first mixture ((M / Co)×100) is preferably 0.01 to 2.0 molar percent, and particularly preferably 0.05 to 1.0 molar percent. When the mixing ratio of the compound containing M element is within the above range, the battery characteristics can be improved without impairing the charge / discharge capacity of the positive electrode active material for lithium secondary batteries.

[0066] In the first mixing step, examples of a method for mixing the lithium compound, the cobalt compound, the aluminum compound, and the compound containing the M element that is used as needed include mixing methods using a coffee mill, a ribbon mixer, a Henschel mixer, a Super mixer, a Nauta mixer, or the like.

[0067] The first firing step is a step of firing the first mixture obtained by the first mixing step to obtain aluminum-containing lithium-cobalt composite oxide particles (2) in which aluminum is present in the form of a solid solution inside the particles as a first fired product.

[0068] In the first firing step, the firing temperature when firing the first mixture to react the raw materials is 800 to 1150° C., preferably 850 to 1100° C. When the firing temperature is within the above range, it is possible to reduce the production of unreacted cobalt oxide or overheat decomposition products of lithium-cobalt composite oxide, which are a cause of a decrease in capacity of the aluminum-containing lithium-cobalt composite oxide.

[0069] In the first firing step, the firing time when the first mixture is fired to react the raw materials is 1 to 30 hours, preferably 5 to 20 hours. The atmosphere is preferably an oxidizing atmosphere such as air or oxygen gas.

[0070] The second mixing step is a step of mixing the aluminum-containing lithium-cobalt composite oxide particles (2), which are the first fired product, with inorganic fluoride particles to obtain a second mixture containing the aluminum-containing lithium-cobalt composite oxide particles (2) and the inorganic fluoride particles.

[0071] In the second mixing step, the inorganic fluoride particles are mixed in such an amount that the molar percentage of F relative to Co in the aluminum-containing lithium-cobalt composite oxide particles (2) (first calcined product) is preferably 0.05 to 5.0 mol %, particularly preferably 0.1 to 2.0 mol %, expressed in atomic terms as F relative to Co ((F / Co) × 100). By mixing the inorganic fluoride particles in the above range, the effect of improving the cycle characteristics at high voltage while suppressing a decrease in the charge / discharge capacity of the positive electrode active material for lithium secondary batteries is enhanced, and the impedance of the positive electrode active material for lithium secondary batteries can be reduced. For example, if unreacted lithium carbonate remains on the surface of the aluminum-containing lithium-cobalt composite oxide particles (2) (first calcined product), carbon dioxide gas is generated by decomposition during charge / discharge, which can easily cause problems and increase the impedance. In the method for producing a positive electrode active material for lithium secondary batteries of the present invention, mixing inorganic fluoride particles and calcining the mixture is thought to cause the carbonate radicals to react, thereby removing the unreacted lithium carbonate. It is therefore presumed that the impedance can be reduced.

[0072] The inorganic fluoride particles in the second mixing step are MgF2 and AlF3. The mixing ratio of MgF2 to AlF3, in terms of molar ratio (MgF2 / AlF3), is 0.05 to 50, preferably 0.1 to 10, and particularly preferably 0.7 to 5. Having the mixing ratio of MgF2 to AlF3 (MgF2 / AlF3 molar ratio) within the above range is preferred in terms of achieving both good initial discharge capacity and good impedance.

[0073] In the second mixing step, examples of the method for mixing the aluminum-containing lithium-cobalt composite oxide particles and the inorganic fluoride particles include mixing methods using a coffee mill, a ribbon mixer, a Henschel mixer, a super mixer, a Nauta mixer, a ball mill, a bead mill, or the like.

[0074] The second firing step is a step of firing the second mixture obtained in the second mixing step to obtain a positive electrode active material for a lithium secondary battery as a second fired product.

[0075] In the second firing step, the firing temperature when firing the second mixture to react the raw materials is 200 to 1100° C., preferably 500 to 1000° C., and particularly preferably 500 to 700° C. When the firing temperature is within the above range, moisture can be sufficiently removed, and deterioration of characteristics such as a decrease in charge / discharge capacity and a decrease in cycle characteristics can be prevented.

[0076] In the second calcination step, the calcination time for calcining the second mixture to react the raw materials is 1 to 10 hours, preferably 2 to 7 hours. The calcination atmosphere in the second calcination step is preferably an oxidizing atmosphere such as air or oxygen gas.

[0077] In the first step or the second step, firing may be carried out multiple times as necessary, and after firing, the fired product may be pulverized or classified as necessary.

[0078] A positive electrode active material for a lithium secondary battery according to a second embodiment of the present invention (hereinafter also referred to as a positive electrode active material for a lithium secondary battery (2) of the present invention) is a fired product of a mixture of aluminum-containing lithium-cobalt composite oxide particles (3) and inorganic fluoride particles, The aluminum-containing lithium-cobalt composite oxide particles (3) contain little aluminum. The inorganic fluoride particles are present as a solid solution at least inside the aluminum-containing lithium cobalt composite oxide particles (3), and the inorganic fluoride particles are MgF2 and AlF3. In the positive electrode active material (2) for a lithium secondary battery of the present invention, the aluminum-containing lithium-cobalt composite oxide particles before being fired as a mixture with inorganic fluoride particles, i.e., the raw aluminum-containing lithium-cobalt composite oxide particles that are fired in the presence of inorganic fluoride particles, are also referred to as aluminum-containing lithium-cobalt composite oxide particles (3).

[0079] The aluminum-containing lithium-cobalt composite oxide particles (3) according to the positive electrode active material (2) for a lithium secondary battery of the present invention have aluminum present as a solid solution at least inside the aluminum-containing lithium-cobalt composite oxide particles (3). The aluminum-containing lithium-cobalt composite oxide particles (3) are not particularly limited as long as aluminum is present as a solid solution at least inside the aluminum-containing lithium-cobalt composite oxide particles, but aluminum-containing lithium-cobalt composite oxide particles (2) obtained by carrying out the first mixing step and the first firing step according to the method for producing a positive electrode active material for a lithium secondary battery of the present invention are preferred.

[0080] The inorganic fluoride particles according to the positive electrode active material (2) for a lithium secondary battery of the present invention are MgF2 and AlF3.

[0081] The positive electrode active material (2) for lithium secondary batteries of the present invention is a fired product of a mixture of aluminum-containing lithium-cobalt composite oxide particles (3) and inorganic fluoride particles. That is, the positive electrode active material (2) for lithium secondary batteries of the present invention is a fired product obtained by mixing the aluminum-containing lithium-cobalt composite oxide particles (3) with inorganic fluoride particles and firing the resulting mixture.

[0082] In the positive electrode active material (2) for a lithium secondary battery of the present invention, the fired product of the mixture of the aluminum-containing lithium-cobalt composite oxide particles (3) and inorganic fluoride particles is a product obtained by firing the mixture of the aluminum-containing lithium-cobalt composite oxide particles (3) and inorganic fluoride particles at a firing temperature of 200 to 1100°C, preferably 500 to 1000°C, particularly preferably 500 to 700°C, for 1 to 10 hours, preferably 2 to 7 hours, in an oxidizing atmosphere such as air or oxygen gas.

[0083] Furthermore, in the positive electrode active material (2) for lithium secondary batteries of the present invention, a mixture of aluminum-containing lithium-cobalt composite oxide particles (3) and inorganic fluoride particles MgF2 and AlF3 is calcined, so that the F in the inorganic fluoride particles in the mixture exists in the form of MgF2 and a compound containing Al and F. In other words, the positive electrode active material (2) for lithium secondary batteries of the present invention can also be said to be a positive electrode active material for lithium secondary batteries that is a mixture of aluminum-containing lithium-cobalt composite oxide particles (3) and inorganic fluoride particles, and the inorganic fluoride particles are a compound containing MgF2, Al, and F. The inventors speculate that the compound containing Al and F is AlF3 and / or LiAlF4.

[0084] In the aluminum-containing lithium-cobalt composite oxide particles (3) according to the positive electrode active material for lithium secondary batteries (2) of the present invention, the molar ratio of Li to Co (Li / Co) in terms of atoms is preferably 0.90 to 1.20, particularly preferably 0.95 to 1.15. When the molar ratio of Li to Co (Li / Co) in terms of atoms in the aluminum-containing lithium-cobalt composite oxide particles (3) is within the above range, the capacity per volume of the positive electrode active material for lithium secondary batteries can be improved.

[0085] In the aluminum-containing lithium-cobalt composite oxide particles (3) according to the positive electrode active material (2) for lithium secondary batteries of the present invention, the molar percentage of Al relative to Co, calculated as an atomic percentage ((Al / Co) × 100), is preferably 0.05 to 5.0 molar percentages, particularly preferably 0.5 to 2.0 molar percentages. When the molar percentage of Al relative to Co, calculated as an atomic percentage ((Al / Co) × 100), in the aluminum-containing lithium-cobalt composite oxide particles (3) is within the above range, the positive electrode active material for lithium secondary batteries can have improved cycle characteristics at high voltage, cycle characteristics at high voltage and high temperature, and high-temperature storage characteristics, while suppressing a decrease in charge / discharge capacity.

[0086] The aluminum-containing lithium-cobalt composite oxide particles (3) according to the positive electrode active material (2) for a lithium secondary battery of the present invention contain Al as an essential additive element for the lithium-cobalt composite oxide, but may contain an element M, if necessary, for the purpose of improving performance or physical properties. The element M is one or more metal elements selected from Ca, Mg, Sr, Zr, Nb, B, and W.

[0087] The aluminum-containing lithium-cobalt composite oxide particles (3) according to the cathode active material (2) for a lithium secondary battery of the present invention preferably contain at least one of Ca and Sr as the M element, in order to further improve battery characteristics, and particularly preferably contain at least one of Ca and Sr and one or more selected from Mg, Zr, Nb, B, and W. The aluminum-containing lithium-cobalt composite oxide particles (3) according to the cathode active material (2) for a lithium secondary battery of the present invention preferably contain at least one or two or more selected from Ca, Mg, Sr, and Zr as the M element. The aluminum-containing lithium-cobalt composite oxide particles (3) according to the cathode active material (2) for a lithium secondary battery of the present invention preferably contain Mg, Sr, and Zr as the M element.

[0088] When the aluminum-containing lithium-cobalt composite oxide particles (3) according to the present invention's positive electrode active material (2) for lithium secondary batteries contain an M element, the atomic molar percentage ((M / Co) × 100) of the M element relative to the Co atoms in the aluminum-containing lithium-cobalt composite oxide particles (3) is preferably 0.01 to 2.0 mol %, particularly preferably 0.05 to 1.0 mol %. When the aluminum-containing lithium-cobalt composite oxide particles (3) contain an M element, the atomic molar percentage ((M / Co) × 100) of the M element relative to the Co atoms in the aluminum-containing lithium-cobalt composite oxide particles (3) within the above range can improve the battery characteristics without impairing the charge / discharge capacity of the positive electrode active material for lithium secondary batteries. When the aluminum-containing lithium-cobalt composite oxide particles (3) contain two or more M elements, the number of moles of the M element in atomic terms, which is the basis for calculating the above molar percentage, refers to the sum of the number of moles of each M element.

[0089] The M element may be present inside the aluminum-containing lithium-cobalt-based composite oxide particles (3), or may be present on the particle surface of the aluminum-containing lithium-cobalt-based composite oxide particles (3), or may be present both inside and on the particle surface of the aluminum-containing lithium-cobalt-based composite oxide particles (3).

[0090] When the M element is present on the particle surface of the aluminum-containing lithium-cobalt-based composite oxide particles (3), the M element may be present in the form of an oxide, composite oxide, sulfate, phosphate, or the like.

[0091] The aluminum-containing lithium-cobalt composite oxide particles (3) according to the positive electrode active material (2) for a lithium secondary battery of the present invention are granular products of the aluminum-containing lithium-cobalt composite oxide. The average particle size of the aluminum-containing lithium-cobalt composite oxide particles (3) is preferably 0.5 to 30 μm, particularly preferably 3 to 25 μm, as a particle size at 50% volume (D50) in the particle size distribution measured by a laser diffraction / scattering method. The BET specific surface area of the lithium-cobalt composite oxide particles (3) is preferably 0.05 to 5.0 m 2 / g, particularly preferably 0.15 to 1.0 m 2 When the average particle size or BET specific surface area of the aluminum-containing lithium-cobalt composite oxide particles (3) is within the above range, the preparation and coating properties of the positive electrode mixture become easy, and furthermore, an electrode with high packing properties can be obtained.

[0092] In the positive electrode active material (2) for lithium secondary batteries of the present invention, the amount of inorganic fluoride particles mixed in the mixture of aluminum-containing lithium-cobalt composite oxide particles (3) and inorganic fluoride particles is, in atomic equivalent mole % of F relative to Co in the aluminum-containing lithium-cobalt composite oxide particles (3) ((F / Co) × 100), preferably 0.05 to 5.0 mole %, particularly preferably 0.1 to 2.0 mole %. When the atomic equivalent mole % of F relative to Co in the aluminum-containing lithium-cobalt composite oxide particles (3) ((F / Co) × 100) is within the above range, the effect of improving cycle characteristics at high voltages while suppressing a decrease in charge / discharge capacity of the positive electrode active material for lithium secondary batteries is enhanced, and the impedance of the positive electrode active material for lithium secondary batteries can be reduced.

[0093] The mixing ratio of MgF2 to AlF3, in terms of molar ratio (MgF2 / AlF3), is 0.05 to 50, preferably 0.1 to 10, and particularly preferably 0.7 to 5. When the mixing ratio of MgF2 to AlF3 (MgF2 / AlF3 molar ratio) is within the above range, it is possible to achieve both a good initial discharge capacity and a good impedance.

[0094] The inorganic fluoride particles according to the positive electrode active material (2) for a lithium secondary battery of the present invention preferably have an average particle size of 0.01 to 30 μm, particularly preferably 0.1 to 20 μm, as the particle size at 50% cumulative volume (D50) in the particle size distribution measured by a laser diffraction / scattering method. When the average particle size of the inorganic fluoride particles is within the above range, problems are less likely to occur in the kneading step for preparing the positive electrode mixture and in the coating step for applying the obtained positive electrode mixture to a positive electrode current collector.

[0095] The positive electrode active material (2) for a lithium secondary battery of the present invention has an average particle size, expressed as a particle size at 50% volume (D50) in a particle size distribution measured by a laser diffraction / scattering method, of preferably 0.5 to 30 μm, particularly preferably 3 to 25 μm. The BET specific surface area of the positive electrode active material (2) for a lithium secondary battery of the present invention is preferably 0.05 to 5.0 m. 2 / g, particularly preferably 0.15 to 1.0 m 2 When the average particle size or BET specific surface area of the positive electrode active material (2) for a lithium secondary battery of the present invention is within the above range, problems are unlikely to occur in the kneading step for preparing the positive electrode mixture and in the coating step for coating the obtained positive electrode mixture on a positive electrode current collector.

[0096] The c-axis lattice constant of the positive electrode active material (2) for a lithium secondary battery of the present invention is preferably 14.055 to 14.070 Å, particularly preferably 14.055 to 14.065 Å. When the c-axis lattice constant is in the above range, collapse of the crystal structure due to charge and discharge can be reduced, and cycle characteristics can be improved.

[0097] In the second firing step of the method for producing a positive electrode active material for a lithium secondary battery of the present invention, the mixture of aluminum-containing lithium-cobalt composite oxide particles and inorganic fluoride particles, which is the first fired product, is fired, but the firing in this second firing step does not affect the magnitude of the c-axis lattice constant of the aluminum-containing lithium-cobalt composite oxide particles. Therefore, in the positive electrode active material for a lithium secondary battery (2) of the present invention, the magnitude of the c-axis lattice constant is derived from the aluminum-containing lithium-cobalt composite oxide particles in the mixture of aluminum-containing lithium-cobalt composite oxide particles and inorganic fluoride particles.

[0098] The lithium secondary battery of the present invention uses the positive electrode active material for lithium secondary batteries of the present invention as the positive electrode active material.

[0099] The lithium secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt.

[0100] The positive electrode of the lithium secondary battery of the present invention is formed, for example, by applying a positive electrode mixture to a positive electrode current collector and drying the mixture, etc. The positive electrode mixture comprises a positive electrode active material, a conductive agent, a binder, and optionally a filler.

[0101] The lithium secondary battery of the present invention has a positive electrode uniformly coated with the positive electrode active material for lithium secondary batteries of the present invention, and therefore has high battery performance, particularly excellent cycle characteristics at high voltage, cycle characteristics at high voltage and high temperature, and high-temperature storage characteristics, and further has low impedance.

[0102] The content of the positive electrode active material contained in the positive electrode mixture for the lithium secondary battery of the present invention is desirably 70 to 100 mass %, and preferably 90 to 98 mass %.

[0103] The positive electrode current collector for the lithium secondary battery of the present invention is not particularly limited as long as it is an electron conductor that does not undergo chemical changes in the constructed battery. Examples include stainless steel, nickel, aluminum, titanium, calcined carbon, and aluminum or stainless steel surfaces that have been surface-treated with carbon, nickel, titanium, or silver. These materials may be used after oxidizing their surfaces, or the current collector surface may be roughened by surface treatment. Examples of the current collector form include foil, film, sheet, net, punched material, lath, porous material, foam, fiber group, and nonwoven fabric molded body. The thickness of the current collector is not particularly limited, but is preferably 1 to 500 μm.

[0104] The conductive agent for the lithium secondary battery of the present invention is not particularly limited as long as it is an electron-conductive material that does not undergo chemical changes in the constructed battery. Examples include graphite (e.g., natural graphite and artificial graphite); carbon black (e.g., carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black); conductive fibers (e.g., carbon fiber and metal fiber); metal powders (e.g., carbon fluoride, aluminum, and nickel powder); conductive whiskers (e.g., zinc oxide and potassium titanate); conductive metal oxides (e.g., titanium oxide); and conductive materials such as polyphenylene derivatives. Examples of natural graphite include scaly graphite, flake graphite, and amorphous graphite. These can be used alone or in combination. The conductive agent is incorporated in an amount of 1 to 50% by mass, preferably 2 to 30% by mass, of the positive electrode mixture.

[0105] Examples of the binder for the lithium secondary battery of the present invention include starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer or its (Na +) ion crosslinked body, ethylene-methacrylic acid copolymer or its (Na + ) ion crosslinked body, ethylene-methyl acrylate copolymer or its (Na + ) ion crosslinked body, ethylene-methyl methacrylate copolymer or its (Na + Examples of suitable binders include ionic crosslinkers, polysaccharides such as polyethylene oxide, thermoplastic resins, and polymers with rubber elasticity, and these can be used alone or in combination of two or more. When using a compound containing a functional group that reacts with lithium, such as a polysaccharide, it is preferable to deactivate the functional group by adding a compound such as an isocyanate group. The blending ratio of the binder in the positive electrode mixture is 1 to 50 mass %, preferably 2 to 15 mass %.

[0106] The filler in the lithium secondary battery of the present invention suppresses volume expansion of the positive electrode in the positive electrode mixture and is added as needed. Any fibrous material that does not undergo chemical changes in the constructed battery can be used as the filler, and examples of such materials include fibers of olefin polymers such as polypropylene and polyethylene, glass, and carbon. The amount of filler added is not particularly limited, but is preferably 0 to 30 mass % in the positive electrode mixture.

[0107] The negative electrode of the lithium secondary battery of the present invention is formed by applying a negative electrode material to a negative electrode current collector and drying it. The negative electrode current collector of the lithium secondary battery of the present invention is not particularly limited as long as it is an electron conductor that does not undergo chemical changes in the constructed battery. Examples of the negative electrode current collector include stainless steel, nickel, copper, titanium, aluminum, calcined carbon, copper or stainless steel surfaces surface-treated with carbon, nickel, titanium, or silver, and aluminum-cadmium alloys. These materials may also be used after oxidizing their surfaces, or the current collector surface may be roughened by surface treatment. Examples of the current collector form include foils, films, sheets, nets, punched materials, laths, porous materials, foamed materials, fiber clusters, and nonwoven fabric molded bodies. The thickness of the current collector is not particularly limited, but is preferably 1 to 500 μm.

[0108] As the negative electrode material for the lithium secondary battery of the present invention, there is no particular limitation, and examples thereof include carbonaceous materials, metal composite oxides, lithium metal, lithium alloys, silicon-based alloys, tin-based alloys, metal oxides, conductive polymers, chalcogen compounds, Li-Co-Ni-based materials, Li4Ti5O 12 , lithium niobate, silicon oxide (SiO x : 0.5 ≦ x ≦ 1.6), etc. Examples of the carbonaceous material include graphitizable carbon materials, graphite-based carbon materials, etc. Examples of the metal composite oxide include Sn p (M1) 1-p (M2) q O r (wherein, M1 represents one or more elements selected from Mn, Fe, Pb, and Ge, M2 represents one or more elements selected from Al, B, P, Si, Group 1, Group 2, Group 3 of the periodic table, and halogen elements, 0 < p ≦ 1, 1 ≦ q ≦ 3, 1 ≦ r ≦ 8 are shown.), Li t Fe2O3 (0 ≦ t ≦ 1), Li t WO2 (0 ≦ t ≦ 1), and other compounds. Examples of the metal oxide include GeO, GeO2, SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, Bi2O3, Bi2O4, Bi2O5, etc. Examples of the conductive polymer include polyacetylene, poly-p-phenylene, etc.

[0109] As the separator for the lithium secondary battery of the present invention, an insulating thin film having a large ion permeability and a predetermined mechanical strength is used. Olefin-based polymers such as polypropylene, or sheets or non-woven fabrics made of glass fiber or polyethylene, etc. are used due to their solvent resistance and hydrophobicity. The pore diameter of the separator may generally be within a range useful for batteries, for example, 0.01 to 10 μm. The thickness of the separator may generally be within a range for general batteries, for example, 5 to 300 μm. In addition, when a solid electrolyte such as a polymer is used as the electrolyte described later, the solid electrolyte may also serve as the separator.

[0110] The lithium salt-containing non-aqueous electrolyte of the lithium secondary battery of the present invention comprises a non-aqueous electrolyte and a lithium salt. The non-aqueous electrolyte of the lithium secondary battery of the present invention may be a non-aqueous electrolytic solution, an organic solid electrolyte, or an inorganic solid electrolyte. Examples of non-aqueous electrolytes include solvents obtained by mixing one or more aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, diethyl ether, 1,3-propane sultone, methyl propionate, and ethyl propionate.

[0111] Examples of the organic solid electrolyte for the lithium secondary battery of the present invention include polyethylene derivatives, polyethylene oxide derivatives or polymers containing the same, polypropylene oxide derivatives or polymers containing the same, phosphate ester polymers, polymers containing ionically dissociable groups such as polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polyhexafluoropropylene, and mixtures of polymers containing ionically dissociable groups with the above-mentioned nonaqueous electrolyte solutions.

[0112] As the inorganic solid electrolyte for the lithium secondary battery of the present invention, lithium nitrides, halides, oxygen acid salts, sulfides, etc. can be used. For example, Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, P2S5, Li2S or Li2S-P2S5, Li2S-SiS2, Li2S-GeS2, Li2S-Ga2S3, Li2S-B2S3, Li2S-P2S5-X, Li2S-SiS2-X, Li2S-GeS2-X, Li2S-Ga2S3-X, Li2S-B2S3-X, (where X is at least one or more selected from LiI, B2S3, or Al2S3), etc. can be mentioned.

[0113] Furthermore, when the inorganic solid electrolyte is amorphous (glass), compounds containing oxygen such as lithium phosphate (Li3PO4), lithium oxide (Li2O), lithium sulfate (Li2SO4), phosphorus oxide (P2O5), lithium borate (Li3BO3), etc., and compounds containing nitrogen such as Li3PO4-uN2u / 3 (u is 0 < u < 4), Li4SiO4-uN2u / 3 (u is 0 < u < 4), Li4GeO4-uN2u / 3 (u is 0 < u < 4), Li3BO3-uN2u / 3 (u is 0 < u < 3), etc. can be contained in the inorganic solid electrolyte. By adding this compound containing oxygen or compound containing nitrogen, the gaps in the formed amorphous skeleton can be widened, the hindrance to the movement of lithium ions can be reduced, and furthermore, the ionic conductivity can be improved.

[0114] As the lithium salt for the lithium secondary battery of the present invention, those dissolved in the above non-aqueous electrolyte are used. For example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 、LiPF6、LiCF3SO3、LiCF3CO2、LiAsF6、LiSbF6、LiB 10 Cl 10 、LiAlCl4、CH3SO3Li、CF3SO3Li、(CF3SO2)2NLi、 lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, salts mixed with one or more of imides, etc. can be mentioned.

[0115] The non-aqueous electrolyte contains the following compounds for the purpose of improving the discharge and charge characteristics and flame retardancy: Examples of suitable additives include pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones and N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, polyethylene glycol, pyrrole, 2-methoxyethanol, aluminum trichloride, monomers of conductive polymer electrode active materials, triethylenephosphonamide, trialkylphosphine, morpholine, aryl compounds with carbonyl groups, hexamethylphosphoric triamide and 4-alkylmorpholine, bicyclic tertiary amines, oils, phosphonium salts and tertiary sulfonium salts, phosphazenes, and carbonate esters. Furthermore, halogen-containing solvents, such as carbon tetrachloride and ethylene trifluoride, can be added to the electrolyte to make it nonflammable. Carbon dioxide can also be added to the electrolyte to improve its suitability for high-temperature storage.

[0116] The lithium secondary battery of the present invention is a lithium secondary battery that has a high capacity per volume, excellent safety and cycle characteristics, a high energy density retention rate, and a small decrease in average operating voltage, and the shape of the battery may be any shape, such as button, sheet, cylinder, prismatic, or coin shape.

[0117] The uses of the lithium secondary battery of the present invention are not particularly limited, and examples thereof include electronic devices such as notebook computers, laptop personal computers, pocket word processors, mobile phones, cordless handsets, portable CD players, radios, liquid crystal televisions, backup power supplies, electric shavers, memory cards, video camcorders, automobiles, electric vehicles, game devices, robots, drones, and power tools. [Example]

[0118] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. (X-ray diffraction analysis) In the examples, measurements were carried out using an X-ray diffractometer (Ultima IV manufactured by Rigaku Corporation) under the following measurement conditions. Source: CuKα Tube voltage: 40kV Tube current: 40mA Scanning speed: 4.0° / sec

[0119] Example 1 (First mixing process) Tricobalt tetroxide (average particle size 2.1 μm), lithium carbonate (average particle size 5.7 μm), and aluminum hydroxide (average particle size 1.6 μm) were weighed and mixed in a coffee mill to obtain a first mixture having a molar ratio of Li to Co (Li / Co) of 1.040 and a molar percentage of Al to Co ((Al / Co) × 100) of 1.0 mol%. (First firing process) Next, the obtained first mixture was fired in an alumina pot at 900°C for 5 hours. X-ray diffraction analysis of the fired product revealed that it was single-phase LiCoO2, confirming that Al was contained in the lithium-cobalt composite oxide particles as a solid solution (see Figure 1). After the firing was completed, the fired product was pulverized and classified to obtain aluminum-containing lithium cobalt composite oxide particles containing 1.0 mol % of Al relative to Co. (Second mixing process) Next, the obtained aluminum-containing lithium-cobalt composite oxide particles, MgF2 (average particle diameter D50 = 0.9 μm), and AlF3 (average particle diameter D50 = 2.2 μm), were weighed and mixed in a coffee mill to obtain a second mixture in which the molar percentage of F relative to Co ((F / Co) x 100) was 0.9 molar percent and the content of MgF2 relative to AlF3 was 3 in terms of the molar ratio (MgF2 / AlF3). (Second firing process) The resulting second mixture was then fired in an alumina pot at 600° C. for 5 hours. After the firing was completed, the fired product was crushed and classified to obtain a positive electrode active material sample.

[0120] Examples 2 to 7 A fired product was obtained through the first mixing step and the first firing step shown in Table 1 by the same operations as in Example 1. X-ray diffraction analysis of the fired product revealed that it was single-phase LiCoO, confirming that Al was contained in the lithium-cobalt composite oxide particles as a solid solution. The fired product was then crushed and classified to obtain an aluminum-containing lithium-cobalt composite oxide, which was then subjected to a second mixing step and a second firing step in the same manner as in Example 1 to obtain a positive electrode active material sample.

[0121] (Comparative Example 1) (First mixing process) Tricobalt tetroxide (average particle size 2.1 μm) and lithium carbonate (average particle size 5.7 μm) were weighed and mixed in a coffee mill to obtain a first mixture having a molar ratio of Li to Co (Li / Co) of 1.040. (First firing process) The resulting first mixture was then calcined in an alumina pot at 900°C for 5 hours. X-ray diffraction analysis of the calcined product revealed that it was single-phase LiCoO2. After the firing was completed, the fired product was pulverized and classified to obtain lithium-cobalt composite oxide particles. (Second Mixing Step) Next, the obtained lithium-cobalt composite oxide particles, MgF2 (average particle diameter 0.9 μm), and AlF3 (average particle diameter 2.2 μm) were weighed and mixed in a coffee mill to obtain a second mixture in which the molar percentage of F relative to Co ((F / Co) × 100) was 0.9 molar%, and the molar ratio of MgF2 to AlF3 (MgF2 / AlF3) was 3. (Second firing process) The resulting second mixture was then fired in an alumina pot at 600° C. for 5 hours. After the firing was completed, the fired product was crushed and classified to obtain a positive electrode active material sample.

[0122] (Comparative Example 2) (First mixing process) Tricobalt tetroxide (average particle size 2.1 μm), lithium carbonate (average particle size 5.7 μm), and aluminum hydroxide (average particle size 1.6 μm) were weighed and mixed in a coffee mill to obtain a first mixture having a molar ratio of Li to Co (Li / Co) of 1.040 and a molar percentage of Al to Co ((Al / Co) × 100) of 1.0 mol%. (First firing process) The resulting first mixture was then calcined in an alumina pot at 900°C for 5 hours. X-ray diffraction analysis of the calcined product revealed that it was single-phase LiCoO2. After the firing was completed, the fired product was crushed and classified to obtain a positive electrode active material sample.

[0123] (Reference example 1) (First mixing process) Tricobalt tetroxide (average particle size 2.1 μm), lithium carbonate (average particle size 5.7 μm), titanium dioxide (average particle size 0.4 μm), and calcium sulfate (average particle size 7.3 μm) were weighed and mixed in a household mixer to obtain a mixture with a Li to Co molar ratio (Li / Co) of 1.043, a Ti to Co molar ratio ((Ti / Co) × 100) of 1.0 molar%, and A first mixture was obtained in which the molar percentage of Ca relative to Co ((Ca / Co)×100) was 0.06 molar percentage. (First firing process) The resulting first mixture was then fired in an alumina pot at 1070°C for 5 hours. After the firing was completed, the fired product was pulverized and classified to obtain lithium cobalt composite oxide particles containing 1.0 mol % of Ti relative to Co and 0.06 mol % of Ca relative to Co. (Second mixing process) Next, the obtained lithium-cobalt composite oxide particles, MgF2 (average particle diameter 0.9 μm), and AlF3 (average particle diameter 2.2 μm) were weighed and mixed in a coffee mill to obtain a second mixture in which the molar percentage of F relative to Co ((F / Co) × 100) was 0.85 molar%, and the molar ratio of MgF2 to AlF3 (MgF2 / AlF3) was 0.625. (Second firing process) The resulting second mixture was then fired in an alumina pot at 600° C. for 5 hours. After the firing was completed, the fired product was crushed and classified to obtain a positive electrode active material sample.

[0124] The following physical properties (average particle size, BET specific surface area, and c-axis lattice constant) were measured for the positive electrode active material samples obtained in Examples 1 to 7, Comparative Examples 1 and 2, and Reference Example 1. The results are shown in Tables 1 and 2.

[0125] (1) Average particle size The average particle size was determined from the particle size at 50% volume (D50) in the particle size distribution measured by laser diffraction / scattering method. (2) BET specific surface area The BET specific surface area was measured by the BET method. (3) c-axis lattice constant The c-axis lattice constant was measured by Rietveld analysis using a diffraction pattern measured by X-ray diffraction (XRD).

[0126] [Table 1]

[0127] [Table 2]

[0128] In Table 2, * indicates that the mole percent of Ti relative to Co is 1.0 mole percent, and the mole percent of Ca relative to Co is 1.0 mole percent. The mole percentage of is 0.06%.

[0129] From Tables 1 and 2, when comparing the positive electrode active material sample (Comparative Example 1) that does not contain Al as a solid solution with the positive electrode active material samples (Examples 1 to 4) that contain Al as a solid solution, it can be seen that the c-axis lattice constant is larger in the positive electrode active material that contains Al as a solid solution. Furthermore, the Al content relative to Co was 0.5 mol % in Example 2 (c-axis lattice constant: 14.055 Å), 0.75 mol % in Example 4 (c-axis lattice constant: 14.056 Å), 1.0 mol % in Example 1 (c-axis lattice constant: 14.059 Å), and 2.0 mol % in Example 3 (c-axis lattice constant: 14.060 Å), and it can be seen that the c-axis lattice constant increases as the Al content relative to Co increases.

[0130] Next, a battery performance test was carried out as follows.

[0131] <Fabrication of lithium secondary batteries> A positive electrode agent was prepared by mixing 95% by mass of the positive electrode active materials obtained in Examples 1 to 7, Comparative Examples 1 and 2, and Reference Example 1, 2.5% by mass of graphite powder, and 2.5% by mass of polyvinylidene fluoride, and this was dispersed in N-methyl-2-pyrrolidinone to prepare a kneaded paste. After coating the foil, it was dried, pressed, and punched into a disk with a diameter of 15 mm to obtain a positive electrode plate. Using this positive electrode plate, a coin-type lithium secondary battery was fabricated using components such as a separator, negative electrode, positive electrode, current collector, mounting hardware, external terminals, and electrolyte. Metallic lithium foil was used for the negative electrode, and the electrolyte was a 1-liter mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a ratio of 2.5:6:1.5, in which 1 mol of LiPF6 and 1 wt% of vinylene carbonate were dissolved.

[0132] <Battery performance evaluation> The coin-type lithium secondary batteries thus fabricated were evaluated for the following battery performance (cycle characteristics under high voltage, cycle characteristics under high voltage and high temperature, and impedance). The results are shown in Tables 3, 4, and 5. (1) Evaluation of cycle characteristics under high voltage (1-1) Test conditions First, the battery was charged to 4.6 V at 0.5 C over two hours, and then held at 4.6 V for three hours (constant current / constant voltage charging (CCCV charging)). This was followed by a constant current discharge (CC discharge) at 0.2 C down to 2.7 V. This cycle constituted one cycle, and the discharge capacity was measured after each cycle. This cycle was repeated 20 times at 25°C. (1-2) Initial discharge capacity under high voltage The discharge capacity at the first cycle in the cycle characteristic evaluation was taken as the initial discharge capacity under high voltage (initial discharge capacity at 25° C. (4.6 V)). (1-3) Capacity retention rate under high voltage The capacity retention rate under high voltage (25°C capacity retention rate (4.6V)) was calculated from the discharge capacity (per active material weight) at the 1st and 20th cycles in the cycle characteristic evaluation using the following formula. Capacity retention rate (%) = (discharge capacity at 20th cycle / discharge capacity at 1st cycle) x 100 (2) Evaluation of cycle characteristics under high voltage and high temperature (2-1) Test conditions First, the battery was charged to 4.55 V at 0.5 C over two hours, and then held at 4.55 V for three hours (constant current / constant voltage charging (CCCV charging)). This was followed by a constant current discharge (CC discharge) at 0.2 C down to 2.7 V. This cycle constituted one cycle, and the discharge capacity was measured after each cycle. This cycle was repeated 50 times at 45°C. (2-2) Initial discharge capacity under high voltage and high temperature The discharge capacity at the first cycle in the high-temperature cycle characteristic evaluation was taken as the initial discharge capacity under high voltage and high temperature conditions (initial discharge capacity at 45°C (4.55V)). (2-3) Capacity retention rate under high voltage and high temperature The capacity retention rate under high voltage and high temperature (45°C capacity retention rate (4.55V)) was calculated using the following formula from the discharge capacities (per weight of active material) at the 1st and 50th cycles in the high-temperature cycle characteristic evaluation. Capacity retention rate under high voltage and high temperature (%) = (discharge capacity at 50th cycle / discharge capacity at 1st cycle) x 100 (3) Impedance After the coin-type lithium secondary battery was brought to SOC 100%, i.e., fully charged, the applied voltage was 0 V to the open circuit circuit, i.e., no voltage was applied, and AC impedance measurements were performed using an impedance measuring device in the frequency measurement range of 0.02 Hz to 20 kHz. Then, the resistance value was calculated from the Cole-Cole plot obtained by the AC impedance measurement.

[0133] [Table 3]

[0134] [Table 4]

[0135] [Table 5]

Claims

1. The aluminum-containing lithium-cobalt composite oxide particles and the inorganic fluoride particles are mixed together. The aluminum-containing lithium-cobalt composite oxide particles have aluminum present in the form of a solid solution at least inside the aluminum-containing lithium-cobalt composite oxide particles, and the inorganic fluoride particles are MgF ２ and a compound containing Al and F; A positive electrode active material for a lithium secondary battery, characterized by:

2. The compound containing Al and F is AlF ３ and / or LiAlF ４ 2. The positive electrode active material for a lithium secondary battery according to claim 1,

3. 3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the aluminum-containing lithium-cobalt composite oxide particles have an Al content of 0.05 to 5.0 mol % in terms of atomic mol % of Al relative to Co in the aluminum-containing lithium-cobalt composite oxide particles ((Al / Co)×100).

4. 3. The positive electrode active material for lithium secondary batteries according to claim 1, wherein the content of the inorganic fluoride particles is 0.05 to 5.0 mol % in terms of atomic mol % of F relative to Co in the aluminum-containing lithium-cobalt composite oxide particles ((F / Co) × 100).

5. The MgF ２ and the mixing ratio of the compound containing Al and F is the number of moles of F in the compound containing Al and F converted into atoms of the compound containing Al and F. ２ The ratio of the number of moles of F in atomic terms (MgF ２ 3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the ratio (moles of F in terms of atoms of Al / moles of F in terms of atoms of the compound containing Al and F) is 0.033 to 33.

6. 3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the c-axis lattice constant is 14.055 to 14.070 Å.

7. 3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the aluminum-containing lithium-cobalt composite oxide particles contain, as an M element, one or more elements selected from the group consisting of Ca, Mg, Sr, Zr, Nb, B, and W.

8. A fired product of a mixture of aluminum-containing lithium-cobalt composite oxide particles and inorganic fluoride particles, The aluminum-containing lithium-cobalt composite oxide particles have aluminum present in the form of a solid solution at least inside the aluminum-containing lithium-cobalt composite oxide particles, and the inorganic fluoride particles are MgF ２ and AlF ３ That is, A positive electrode active material for a lithium secondary battery, characterized by:

9. 9. The positive electrode active material for a lithium secondary battery according to claim 8, wherein the aluminum-containing lithium-cobalt composite oxide particles are a fired product of a mixture of a lithium compound, a cobalt compound, and an aluminum compound.

10. 10. The positive electrode active material for a lithium secondary battery according to claim 8, wherein the aluminum-containing lithium-cobalt composite oxide particles have an Al content of 0.05 to 5.0 mol % in terms of atomic mol % of Al relative to Co in the aluminum-containing lithium-cobalt composite oxide particles ((Al / Co)×100).

11. 10. The positive electrode active material for lithium secondary batteries according to claim 8, wherein the amount of the inorganic fluoride particles mixed in the mixture of the aluminum-containing lithium cobalt composite oxide particles and the inorganic fluoride particles is 0.05 to 5.0 mol % in terms of atomic mol % of F relative to Co in the aluminum-containing lithium cobalt composite oxide particles ((F / Co)×100).

12. The MgF in the mixture of the aluminum-containing lithium cobalt composite oxide particles and inorganic fluoride particles ２ The mixing ratio of AlF ３ Molar ratio (MgF ２ / AlF ３ 10. The positive electrode active material for a lithium secondary battery according to claim 8, wherein the ρ is 0.05 to 50.

13. 10. The positive electrode active material for a lithium secondary battery according to claim 8, wherein the c-axis lattice constant is 14.055 to 14.070 Å.

14. 10. The positive electrode active material for a lithium secondary battery according to claim 8, wherein the aluminum-containing lithium-cobalt composite oxide particles contain, as an M element, one or more elements selected from the group consisting of Ca, Mg, Sr, Zr, Nb, B, and W.

15. a first mixing step of mixing raw materials, i.e., a lithium compound, a cobalt compound, and an aluminum compound, to obtain a first mixture; a first firing step of firing the first mixture to obtain, as a first fired product, aluminum-containing lithium-cobalt composite oxide particles in which aluminum is present as a solid solution at least inside the particles; a second mixing step of mixing the first fired product obtained in the first firing step with inorganic fluoride particles to obtain a second mixture; a second firing step of firing the second mixture to obtain a positive electrode active material for a lithium secondary battery as a second fired product; and The inorganic fluoride particles are MgF ２ and AlF ３ That is, A method for producing a positive electrode active material for a lithium secondary battery, characterized by:

16. 16. The method for producing a positive electrode active material for a lithium secondary battery according to claim 15, wherein in the first mixing step, the aluminum compound is mixed so that the content of Al relative to Co in the first mixture is 0.05 to 5.0 mol % in atomic terms ((Al / Co)×100).

17. 17. The method for producing a positive electrode active material for a lithium secondary battery according to claim 15 or 16, wherein the first fired product contains, as an M element, one or more elements selected from the group consisting of Ca, Mg, Sr, Zr, Nb, B, and W.

18. 17. The method for producing a positive electrode active material for a lithium secondary battery according to claim 15, wherein the firing temperature in the first firing step is 800 to 1150°C.

19. 17. The method for producing a positive electrode active material for a lithium secondary battery according to claim 15 or 16, wherein in the second mixing step, the inorganic fluoride particles are mixed so that the molar percentage of F relative to Co in the second mixture, in terms of atoms ((F / Co)×100), is 0.05 to 2.0 mol %.

20. 17. The lithium secondary battery according to claim 15, wherein the positive electrode active material for a lithium secondary battery, which is the second fired product, has a c-axis lattice constant of 14.055 to 14.070 Å. A method for producing a positive electrode active material for a battery.

21. A lithium secondary battery, comprising the positive electrode active material for lithium secondary batteries according to claim 1 or 8 as a positive electrode active material.

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