Positive electrode active material for lithium secondary batteries, method for manufacturing the same, 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] This invention relates to a positive electrode active material for lithium secondary batteries, a method for producing the same, and a lithium secondary battery using the positive electrode active material. [Background technology]

[0002] In recent years, as home appliances have become increasingly portable and cordless, lithium-ion secondary batteries have been put into practical use as power sources for small electronic devices such as laptop computers, mobile phones, and video cameras. 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 on lithium-based composite oxides has been actively pursued, and many proposals have been made to date.

[0003] However, with the increasing size and performance of electronic devices, further improvements in various battery characteristics are needed.

[0004] The applicant has previously proposed various positive electrode active materials for lithium secondary batteries that can produce lithium secondary batteries with excellent cycle characteristics even under high voltage. For example, in Patent Document 1, the applicant proposed a positive electrode active material for lithium secondary batteries that, when used as the positive electrode active material for a lithium secondary battery, can produce a lithium secondary battery with excellent cycle characteristics, a high energy capacity retention rate, and a small decrease in average operating voltage. Furthermore, in Patent Document 2, for example, the applicant proposed a positive electrode active material for lithium secondary batteries that, when used as the positive electrode active material for a lithium secondary battery, can produce a lithium secondary battery with excellent cycle characteristics, a small decrease in average operating voltage, a high average operating voltage maintenance 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 Publication No. 2020-064711 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, in response to the recent demands for improved battery characteristics, the conventional technologies described above have not yet achieved a high level of performance across various aspects of batteries.

[0007] In particular, batteries used in electric bicycles, electric vehicles, robots, drones, and backup power supplies are expected to operate at high voltage and high output.

[0008] Therefore, it was desirable to improve the cycle characteristics at temperatures of around 25°C and high voltage, as well as to have low impedance. Furthermore, in addition to the above battery performance, it was also desired to improve the cycle characteristics at high temperatures of around 45-60°C and high voltage.

[0009] Accordingly, the present invention aims 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 manufacturing the same, and a lithium secondary battery that exhibits excellent cycle characteristics under high voltage and can reduce impedance. Furthermore, the object of the present invention is to provide a positive electrode active material for lithium secondary batteries that, in addition to the above-mentioned battery performance, has excellent cycle characteristics under high temperature and high voltage conditions, an industrially advantageous method for producing the same, and a lithium secondary battery that, in addition to the above-mentioned battery performance, has excellent cycle characteristics under high temperature and high voltage conditions. [Means for solving the problem]

[0010] In view of the above circumstances, the inventors have conducted extensive research and have discovered that by using a mixture of aluminum-containing lithium cobalt composite oxide particles, in which aluminum is solid-dissolved within the lithium cobalt composite oxide particles, and inorganic fluoride particles, which are compounds containing MgF2, Al, and F, as the positive electrode active material for a lithium secondary battery, a lithium secondary battery with excellent cycle characteristics under high voltage and low impedance can be obtained, thus completing the present invention.

[0011] In other words, the present invention (1) consists 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 contain aluminum in a solid solution within at least the aluminum-containing lithium cobalt composite oxide particles, and the inorganic fluoride particles are compounds containing MgF2 and Al and F.

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

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

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

[0015] Further, in the present invention (5), 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 terms of atoms of MgF₂ to the number of moles of F in terms of atoms of the compound containing Al and F (number of moles of F in terms of atoms of MgF₂ / number of moles of F in terms of atoms of the compound containing Al and F) is 0.033 to 33, and it provides a positive electrode active material for a lithium secondary battery according to any one of (1) to (4).

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

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

[0018] Further, in the present invention (8), it is a fired product of a mixture of aluminum-containing lithium cobalt composite oxide particles and inorganic fluoride particles, where the aluminum-containing lithium cobalt composite oxide particles are those in which aluminum is dissolved and present at least inside the aluminum-containing lithium cobalt composite oxide particles, and the inorganic fluoride particles are MgF₂ and AlF₃, and it provides a positive electrode active material for a lithium secondary battery.

[0019] Further, in the present invention (9), 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, and it provides a positive electrode active material for a lithium secondary battery according to (8).

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

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

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

[0023] Furthermore, the present invention (13) provides a positive electrode active material for lithium secondary batteries, which is characterized by having a c-axis lattice constant of 14.055 to 14.070 Å, as described in any of (8) to (12).

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

[0025] Furthermore, the present invention (15) includes a first mixing step of mixing a lithium compound, a cobalt compound, and an aluminum compound as raw materials to obtain a first mixture, A first calcination step involves calcining the first mixture to obtain aluminum-containing lithium cobalt composite oxide particles in which aluminum is solid-dissolved at least inside the particles as a first calcined product, A second mixing step involves mixing the first calcined product obtained in the first calcination step with inorganic fluoride particles to obtain a second mixture. The process includes a second firing step in which the second mixture is fired to obtain a positive electrode active material for lithium secondary batteries as a second fired product, The present invention provides a method for producing a positive electrode active material for lithium secondary batteries, characterized in that the inorganic fluoride particles are MgF2 and AlF3.

[0026] Furthermore, the present invention (16) provides a method for producing a positive electrode active material for a lithium secondary battery according to (15), characterized in that in the first mixing step, the aluminum compound is mixed such that the amount of Al in the first mixture relative to Co is 0.05 to 5.0 mol% on an atomic basis ((Al / Co) × 100).

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

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

[0029] Furthermore, in the present invention (19), in the second mixing step, the inorganic fluoride particles are added in the second mixture in an amount of 0.05 to 0.05 in terms of the molar percentage of F on an atomic basis relative to Co ((F / Co) × 100). 5.0 The present invention provides a method for producing a positive electrode active material for lithium secondary batteries according to any of (15) to (18), characterized by mixing in a manner that results in a molar percentage.

[0030] Furthermore, the present invention (20) provides a method for producing a positive electrode active material for a lithium secondary battery, which is the second calcined product, characterized in that the lattice constant of the c axis of the positive electrode active material for a lithium secondary battery is 14.055 to 14.070 Å, as described in (15) to (19).

[0031] Furthermore, the present invention (21) provides a lithium secondary battery characterized in that any of the lithium secondary battery positive electrode active materials (1) to (14) are 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 manufacturing 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, in addition to the above-mentioned battery performance, a positive electrode active material for lithium secondary batteries that is excellent in cycle characteristics under high temperature and high voltage conditions, an industrially advantageous method for manufacturing the same, and a lithium secondary battery that is excellent in cycle characteristics under high temperature and high voltage conditions in addition to the above-mentioned battery performance can be provided. [Brief explanation of the drawing]

[0033] [Figure 1] X-ray diffraction pattern of the aluminum-containing lithium-cobalt composite oxide obtained in the first firing step of Example 1. [Modes for carrying out the invention]

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

[0035] The positive electrode active material for lithium secondary batteries according to the first embodiment of the present invention (hereinafter also referred to as the positive electrode active material (1) for lithium secondary batteries of the present invention) consists of 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 solid solution at least within the aluminum-containing lithium cobalt composite oxide particles, and the inorganic fluoride particles are compounds containing MgF2 and Al and F. Furthermore, the aluminum-containing lithium-cobalt composite oxide particles relating to the positive electrode active material (1) for lithium secondary batteries of the present invention will also be referred to as aluminum-containing lithium-cobalt composite oxide particles (1).

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

[0037] The aluminum-containing lithium-cobalt composite oxide that forms the aluminum-containing lithium-cobalt composite oxide particles (1) in 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 in which aluminum is added as an additive element to the lithium-cobalt composite oxide. In the aluminum-containing lithium-cobalt composite oxide particles (1) in the positive electrode active material (1) for lithium secondary batteries of the present invention, Al is present in solid solution at least inside the aluminum-containing lithium-cobalt composite oxide particles. Furthermore, in the aluminum-containing lithium-cobalt composite oxide particles (1) in the positive electrode active material (1) for lithium secondary batteries of the present invention, since Al is present in solid solution at least inside the aluminum-containing lithium-cobalt composite oxide particles (1), the crystal structure of the lithium-cobalt composite oxide particles themselves is stabilized even under high voltage, so that the decrease in charge / discharge capacity is suppressed, the cycle characteristics at high voltage are improved, and more preferably the cycle characteristics at high voltage and high temperature are also improved.

[0038] In the aluminum-containing lithium-cobalt composite oxide particles (1) of the positive electrode active material (1) for lithium secondary batteries of the present invention, the presence of Al in 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 rays with the particles (1) as a source, diffraction peaks caused by the raw material aluminum compound and / or Al2O3 are substantially not detected, indicating that the particles are single-phase aluminum-containing lithium-cobalt composite oxide particles. Furthermore, the statement that diffraction peaks caused by the raw materials, aluminum compounds and Al2O3, are substantially undetectable means that the diffraction peaks caused by the aluminum compounds and Al2O3 are below the detection limit of the analytical instrument. Furthermore, as will be discussed later, the presence of Al as a solid solution within the aluminum-containing lithium cobalt composite oxide particles (1) can be inferred from the fact that the lattice constant of the c axis of the lithium cobalt composite oxide (1), which contains Al as a solid solution within the particles, is larger than that of pure lithium cobalt composite oxide particles that do not contain Al as a solid solution within the particles.

[0039] In the aluminum-containing lithium-cobalt composite oxide (1) of the positive electrode active material (1) for lithium secondary batteries of the present invention, Al may be present only inside the composite oxide particles, or it 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 it may be present on the surface of the composite oxide particles. Furthermore, in the positive electrode 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 in solid solution at least inside the composite oxide particles, in order to stabilize the structure of the composite oxide. Note that Al being present in solid solution at least inside the composite oxide particles means that Al is present only inside the particles, or that it is present both inside and on the surface of the particles.

[0040] In the aluminum-containing lithium-cobalt composite oxide particles (1) of the positive electrode active material (1) for lithium secondary batteries of the present invention, the molar ratio of Li to Co (Li / Co) on an atomic basis is preferably 0.90 to 1.20, and particularly preferably 0.95 to 1.15. By having the molar ratio of Li to Co (Li / Co) in the aluminum-containing lithium-cobalt composite oxide particles (1) within the above range, the capacity per unit volume of the positive electrode active material for lithium secondary batteries can be improved.

[0041] In the aluminum-containing lithium-cobalt composite oxide particles (1) of the positive electrode active material (1) for lithium secondary batteries of the present invention, the molar percentage ((Al / Co) × 100) of Al relative to Co is preferably 0.05 to 5.0 mol%, and particularly preferably 0.5 to 2.0 mol%. By having the molar percentage ((Al / Co) × 100) of Al relative to Co in the aluminum-containing lithium-cobalt composite oxide particles (1) within the above range, it is possible to improve the cycle characteristics at high voltage, cycle characteristics at high voltage and high temperature, and high-temperature storage characteristics while suppressing a decrease in the charge-discharge capacity of the positive electrode active material for lithium secondary batteries.

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

[0043] The aluminum-containing lithium-cobalt composite oxide particles (1) of the positive electrode active material (1) for lithium secondary batteries of the present invention preferably contain at least one of Ca and Sr as the M element, and particularly preferably contain at least one of Ca and Sr and one or more selected from Mg, Zr, Nb, B and W, in order to further improve battery characteristics. Furthermore, the aluminum-containing lithium-cobalt composite oxide particles (1) of the positive electrode active material (1) for lithium secondary batteries of the present invention preferably contain at least one or two or more selected from Ca, Mg, Sr and Zr as the M element. Furthermore, the aluminum-containing lithium-cobalt composite oxide particles (1) of the positive electrode active material (1) for lithium secondary batteries 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) for the positive electrode active material (1) of the present invention contain element M, the molar percentage ((M / Co) × 100) of element M relative to Co atoms in the aluminum-containing lithium-cobalt composite oxide particles (1) is preferably 0.01 to 2.0 mol%, and particularly preferably 0.05 to 1.0 mol%. When the aluminum-containing lithium-cobalt composite oxide particles (1) contain element M, having the molar percentage ((M / Co) × 100) of element M relative to Co in the aluminum-containing lithium-cobalt composite oxide particles (1) within the above range makes it possible to improve battery characteristics without impairing the charge-discharge capacity of the positive electrode active material for lithium-cobalt secondary batteries. Note that when the aluminum-containing lithium-cobalt composite oxide contains two or more types of element M, the number of moles of element M relative to Co that forms the basis for calculating the above molar percentage refers to the sum of the number of moles of each element M.

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

[0046] If element M is present on the particle surface of aluminum-containing lithium-cobalt composite oxide particles (1), element M may exist in the form of an oxide, composite oxide, sulfate, phosphate, etc.

[0047] The average particle size of the aluminum-containing lithium-cobalt composite oxide particles (1) in the positive electrode active material (1) for lithium secondary batteries of the present invention is the particle size at 50% of the volume integrated in the particle size distribution measured by laser diffraction-scattering (D50), which is preferably 0.5 to 30 μm, and particularly preferably 3 to 25 μm. Furthermore, the BET specific surface area of ​​the aluminum-containing lithium-cobalt composite oxide particles (1) is preferably 0.05 to 5.0 m². 2 / g, particularly preferably 0.15~1.0m 2 The value is / g. By having the average particle diameter or BET specific surface area of ​​the aluminum-containing lithium cobalt composite oxide particles (1) within the above range, the preparation and coating of the positive electrode mixture become easier, and an electrode with high packing performance can be obtained.

[0048] One of the features of the inorganic fluoride particles in the positive electrode active material (1) for lithium secondary batteries of the present invention is that they are a combination of MgF2 and a compound containing Al and F. Hereafter, compounds containing MgF2, 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] In the positive electrode active material (1) for lithium secondary batteries of the present invention, the content of inorganic fluoride particles is preferably 0.05 to 5.0 mol%, and particularly preferably 0.1 to 2.0 mol%, in terms of the molar percentage ((F / Co) × 100) of F relative to Co in the aluminum-containing lithium-cobalt composite oxide particles (1). By having the molar percentage ((F / Co) × 100) of F relative to Co in the aluminum-containing lithium-cobalt composite oxide particles (1) within the above range, the effect of improving the cycle characteristics at high voltages while suppressing the decrease in the charge and 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 Al-F compound is such that the ratio of the number of moles of F in MgF2 to the number of moles of F in the Al-F compound (number of moles of F in MgF2 / number of moles of F in the Al-F compound) 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 to the number of moles of F in the Al-F compound (number of moles of F in MgF2 / number of moles of F in the Al-F compound) within the above range is preferable in terms of achieving both initial discharge capacity and impedance.

[0051] The inorganic fluoride particles may be present on the surface of the aluminum-containing lithium-cobalt composite oxide particles (1), or they may be present in a simple mixed state with the aluminum-containing lithium-cobalt composite oxide particles (1), or both. In other words, the positive electrode active material for lithium secondary batteries of the present invention may consist of 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 it may be a simple mixture of aluminum-containing lithium-cobalt composite oxide particles (1) and inorganic fluoride particles, or it may be a mixture of both forms. When the inorganic fluoride particles are present on the surface of the aluminum-containing lithium-cobalt composite oxide particles (1), it is preferable that the inorganic fluoride particles are partially present on the surface of the aluminum-containing lithium-cobalt composite oxide particles (1) in order to prevent the deintercalation and insertion of lithium on the surface of the aluminum-containing lithium-cobalt composite oxide.

[0052] The average particle size of the inorganic fluoride particles is the particle size at 50% of the volume integrated in the particle size distribution measured by laser diffraction and scattering (D50), which is preferably 0.01 to 30 μm, and particularly preferably 0.1 to 20 μm. Having the average particle size of the inorganic fluoride particles within the above range makes it less likely for problems to occur in the mixing process when preparing the positive electrode mixture and in the coating process when 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 lithium secondary batteries of the present invention is the particle size at 50% of the volume integrated in the particle size distribution measured by laser diffraction-scattering (D50), which is preferably 0.5 to 30 μm, and particularly preferably 3 to 25 μm. Furthermore, the BET specific surface area of ​​the positive electrode active material (1) for lithium secondary batteries of the present invention is preferably 0.05 to 5.0 m². 2 / g, particularly preferably 0.15~1.0m 2The average particle size or BET specific surface area of ​​the lithium secondary battery positive electrode active material (1) of the present invention is within the above range, which makes it less likely for problems to occur in the kneading process when preparing the positive electrode mixture and in the coating process when applying the obtained positive electrode mixture to the positive electrode current collector.

[0054] The inventors speculate that the Al contained in LiCoO2 as a solid solution affects the crystal structure of pure LiCoO2. Specifically, while the c-axis lattice constant of pure LiCoO2 without Al solid solution inside the particles is 14.050~14.055 Å, the positive electrode active material (1) for lithium secondary batteries of the present invention has a larger c-axis lattice constant compared to that of pure LiCoO2. The 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 lithium secondary batteries of the present invention is preferably 14.055 to 14.070 Å, and particularly preferably 14.055 to 14.065 Å. By having the c-axis lattice constant within the above range, the collapse of the crystal structure due to charging and discharging can be reduced, and the cycle characteristics can be improved.

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

[0057] The first mixing step is, for example, 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 involved in the first mixing step is not particularly limited as long as it is a lithium compound that is normally used as a raw material for the production of lithium cobalt complex oxides, and examples include lithium oxides, hydroxides, carbonates, nitrates, sulfates, and organic acid salts.

[0059] The cobalt compound involved 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 the production of lithium cobalt-based complex oxides, and examples include cobalt oxides, oxyhydroxides, hydroxides, carbonates, nitrates, sulfates, and organic acid salts.

[0060] The aluminum compound used in the first mixing step is not particularly limited, as long as it is an aluminum compound used as a raw material for producing lithium cobalt composite oxide with added aluminum elements, and examples include aluminum oxides, hydroxides, carbonates, nitrates, sulfates, and organic acid salts. Of these, aluminum hydroxide is preferred as the aluminum compound.

[0061] In the first mixing step, the lithium compound and the cobalt compound are mixed such that the molar ratio of Li to Co in the first mixture (Li / Co), on an atomic basis, is preferably 0.90 to 1.20, particularly preferably 0.95 to 1.15, and even more preferably 1.03 to 1.06. Having the mixing ratio of the lithium compound and cobalt compound within this range makes it easier to obtain a single phase of lithium-cobalt composite oxide containing aluminum in X-ray diffraction analysis.

[0062] In the first mixing step, the aluminum compound is mixed such that the molar percentage ((Al / Co) × 100) of Al relative to Co in the first mixture is preferably 0.05 to 5.0 mol%, and particularly preferably 0.5 to 2.0 mol%. By having the aluminum compound mixed within the above range, it is possible to improve the cycle characteristics at high voltage, cycle characteristics at high voltage and high temperature, and high-temperature storage characteristics without impairing the inherent charge and discharge capacity of the lithium cobalt composite oxide.

[0063] In the first mixing step, a compound containing element M may be added to the first mixture for the purpose of improving its performance or physical properties.

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

[0065] In the first mixing step, when mixing a compound containing element M, the mixing ratio of the compound containing element M is such that the molar percentage ((M / Co) × 100) of element M relative to the Co atoms in the first mixture is preferably 0.01 to 2.0 mol%, and particularly preferably 0.05 to 1.0 mol%. By having the mixing ratio of the compound containing element M within the above range, it is possible to improve the battery characteristics without impairing the charge and discharge capacity of the positive electrode active material for lithium secondary batteries.

[0066] In the first mixing step, a method for mixing the lithium compound, cobalt compound, aluminum compound, and a compound containing element M, which may be used as needed, can be described by using a coffee mill, ribbon mixer, Henschel mixer, super mixer, Nauter mixer, etc.

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

[0068] In the first firing step, the firing temperature for firing the first mixture to react the raw materials is 800 to 1150°C, preferably 850 to 1100°C. By having the firing temperature within the above range, the generation of unreacted cobalt oxide or overheating decomposition products of lithium cobalt composite oxide, which are factors that cause a decrease in the volume of aluminum-containing lithium cobalt composite oxide, can be reduced.

[0069] In the first firing process, the firing time for firing the first mixture to react the raw materials is 1 to 30 hours, preferably 5 to 20 hours. Furthermore, the firing atmosphere in the first firing process is preferably an oxidizing atmosphere such as air or oxygen gas.

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

[0071] In the second mixing step, the amount of inorganic fluoride particles to be mixed is preferably 0.05 to 5.0 mol%, and particularly preferably 0.1 to 2.0 mol%, in terms of the molar percentage ((F / Co) × 100) of F relative to Co in the first calcined product, aluminum-containing lithium-cobalt composite oxide particles (2). By having the amount of inorganic fluoride particles within the above range, the effect of improving the cycle characteristics at high voltages while suppressing the decrease in the charge and 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 first calcined product, aluminum-containing lithium-cobalt composite oxide particles (2), carbon dioxide gas is generated by decomposition products during charging and discharging, which can easily cause malfunctions and increase impedance. In the method for producing a positive electrode active material for lithium secondary batteries of the present invention, it is thought that the carbonate reacts when inorganic fluoride particles are mixed and calcined, and unreacted lithium carbonate can be removed. Therefore, it is presumed that the impedance can be lowered.

[0072] The inorganic fluoride particles in the second mixing step are MgF2 and AlF3. The mixing ratio of MgF2 to AlF3 is 0.05 to 50 in molar ratio (MgF2 / AlF3), 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 preferable in terms of achieving both initial discharge capacity and impedance.

[0073] In the second mixing step, a method for mixing aluminum-containing lithium-cobalt composite oxide particles with inorganic fluoride particles can be, for example, a coffee mill, ribbon mixer, Henschel mixer, super mixer, Nauter mixer, ball mill, bead mill, etc.

[0074] The second firing process involves firing the second mixture obtained in the second mixing process to obtain a positive electrode active material for lithium secondary batteries as a second fired product.

[0075] In the second firing process, the firing temperature for 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. By having the firing temperature within the above range, moisture can be sufficiently removed, making it less likely for characteristic deterioration such as a decrease in charge / discharge capacity and a decrease in cycle characteristics to occur.

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

[0077] In the first or second step, firing may be performed multiple times as needed, and after firing, the fired material may be crushed or classified as needed.

[0078] The positive electrode active material for lithium secondary batteries according to the second embodiment of the present invention (hereinafter also referred to as the positive electrode active material (2) for lithium secondary batteries of the present invention) is a calcined 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) are characterized in that aluminum is present in solid solution within at least the aluminum-containing lithium cobalt composite oxide particles (3), and the inorganic fluoride particles are MgF2 and AlF3. Furthermore, in the positive electrode active material (2) for lithium secondary batteries of the present invention, aluminum-containing lithium cobalt composite oxide particles before being calcined as a mixture with inorganic fluoride particles, that is, aluminum-containing lithium cobalt composite oxide particles that are calcined in the presence of inorganic fluoride particles as raw materials, are also referred to as aluminum-containing lithium cobalt composite oxide particles (3).

[0079] The aluminum-containing lithium-cobalt composite oxide particles (3) of the positive electrode active material (2) for lithium secondary batteries of the present invention are such that aluminum is present in solid solution within at least 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 in solid solution within at least the aluminum-containing lithium-cobalt composite oxide particles (3), but aluminum-containing lithium-cobalt composite oxide particles (2) obtained by performing the first mixing step and first firing step according to the method for producing the positive electrode active material for lithium secondary batteries of the present invention are preferred.

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

[0081] Furthermore, the positive electrode active material (2) for lithium secondary batteries of the present invention is a calcined product of a mixture of aluminum-containing lithium cobalt composite oxide particles (3) and inorganic fluoride particles. In other words, the positive electrode active material (2) for lithium secondary batteries of the present invention is a calcined product obtained by mixing aluminum-containing lithium cobalt composite oxide particles (3) and inorganic fluoride particles and calcining the resulting mixture.

[0082] In the positive electrode active material (2) for lithium secondary batteries of the present invention, the calcined product of a mixture of aluminum-containing lithium cobalt composite oxide particles (3) and inorganic fluoride particles is a product obtained by calcining a mixture of aluminum-containing lithium cobalt composite oxide particles (3) and inorganic fluoride particles at a calcination temperature of 200 to 1100°C, preferably 500 to 1000°C, particularly preferably 500 to 700°C, for a calcination time of 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, when a mixture of aluminum-containing lithium cobalt composite oxide particles (3) and inorganic fluoride particles, namely MgF2 and AlF3, is calcined, the F in the inorganic fluoride particles in the mixture exists in the form of a compound containing MgF2, Al, and F. In other words, the positive electrode active material (2) for lithium secondary batteries of the present invention 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, and can be said to be a positive electrode active material for lithium secondary batteries. 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) of the positive electrode active material (2) for lithium secondary batteries of the present invention, the molar ratio of Li to Co on an atomic basis (Li / Co) is preferably 0.90 to 1.20, and particularly preferably 0.95 to 1.15. By having the molar ratio of Li to Co on an atomic basis (Li / Co) in the aluminum-containing lithium-cobalt composite oxide particles (3) within the above range, the capacity per unit 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) of the positive electrode active material (2) for lithium secondary batteries of the present invention, the molar percentage ((Al / Co) × 100) of Al relative to Co is preferably 0.05 to 5.0 mol%, and particularly preferably 0.5 to 2.0 mol%. By having the molar percentage ((Al / Co) × 100) of Al relative to Co in the aluminum-containing lithium-cobalt composite oxide particles (3) within the above range, it is possible to improve the cycle characteristics at high voltage, cycle characteristics at high voltage and high temperature, and high-temperature storage characteristics while suppressing a decrease in the charge-discharge capacity of the positive electrode active material for lithium secondary batteries.

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

[0087] The aluminum-containing lithium-cobalt composite oxide particles (3) of the positive electrode active material (2) for lithium secondary batteries of the present invention preferably contain at least one of Ca and Sr as the M element, and particularly preferably contain at least one of Ca and Sr and one or more selected from Mg, Zr, Nb, B and W, in order to further improve battery characteristics. Furthermore, the aluminum-containing lithium-cobalt composite oxide particles (3) of the positive electrode active material (2) for lithium secondary batteries of the present invention preferably contain at least one or two or more selected from Ca, Mg, Sr and Zr as the M element. Furthermore, the aluminum-containing lithium-cobalt composite oxide particles (3) of the positive electrode active material (2) for lithium secondary batteries 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) of the positive electrode active material (2) for lithium secondary batteries of the present invention contain element M, the molar percentage ((M / Co) × 100) of element M relative to Co atoms in the aluminum-containing lithium-cobalt composite oxide particles (3) is preferably 0.01 to 2.0 mol%, and particularly preferably 0.05 to 1.0 mol%. When the aluminum-containing lithium-cobalt composite oxide particles (3) contain element M, having the molar percentage ((M / Co) × 100) of element M relative to Co in the aluminum-containing lithium-cobalt composite oxide particles (3) within the above range makes it possible to improve battery characteristics without impairing the charge-discharge capacity of the positive electrode active material for lithium secondary batteries. Note that when the aluminum-containing lithium-cobalt composite oxide particles (3) contain two or more types of element M, the number of moles of element M relative to Co that forms the basis for calculating the above molar percentage refers to the sum of the number of moles of each element M.

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

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

[0091] The aluminum-containing lithium-cobalt composite oxide particles (3) related to the positive electrode active material (2) for lithium secondary batteries of the present invention are granular materials of the above-mentioned aluminum-containing lithium-cobalt composite oxide. The average particle diameter of the aluminum-containing lithium-cobalt composite oxide particles (3) is the particle diameter at 50% of the volume integrated in the particle size distribution measured by laser diffraction-scattering (D50), which is preferably 0.5 to 30 μm, and particularly preferably 3 to 25 μm. Furthermore, the BET specific surface area of ​​the aluminum-containing lithium-cobalt composite oxide particles (3) is preferably 0.05 to 5.0 m². 2 / g, particularly preferably 0.15~1.0m 2 The value is / g. By having the average particle diameter or BET specific surface area of ​​the aluminum-containing lithium cobalt composite oxide particles (3) within the above range, the preparation and coating of the positive electrode mixture become easier, and an electrode with high packing performance 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 in the mixture of aluminum-containing lithium cobalt composite oxide particles (3) and inorganic fluoride particles is preferably 0.05 to 5.0 mol%, and particularly preferably 0.1 to 2.0 mol%, in terms of the molar percentage ((F / Co) × 100) of F relative to Co in the aluminum-containing lithium cobalt composite oxide particles (3). By having the molar percentage ((F / Co) × 100) of F relative to Co in the aluminum-containing lithium cobalt composite oxide particles (3) within the above range, the effect of improving the cycle characteristics at high voltages while suppressing the decrease in the charge and 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 is 0.05 to 50 in molar ratio (MgF2 / AlF3), preferably 0.1 to 10, and particularly preferably 0.7 to 5. By having the mixing ratio of MgF2 to AlF3 (molar ratio of MgF2 / AlF3) within the above range, it is possible to achieve both initial discharge capacity and impedance.

[0094] The average particle size of the inorganic fluoride particles in the positive electrode active material (2) for lithium secondary batteries of the present invention is the particle size at 50% of the volume integrated in the particle size distribution measured by laser diffraction-scattering (D50), which is preferably 0.01 to 30 μm, and particularly preferably 0.1 to 20 μm. Having the average particle size of the inorganic fluoride particles within the above range makes it less likely for problems to occur in the kneading process when preparing the positive electrode mixture and in the coating process when applying the obtained positive electrode mixture to the positive electrode current collector.

[0095] The average particle size of the positive electrode active material (2) for lithium secondary batteries of the present invention is the particle size at 50% of the volume integrated in the particle size distribution measured by laser diffraction-scattering (D50), which is preferably 0.5 to 30 μm, and particularly preferably 3 to 25 μm. Furthermore, the BET specific surface area of ​​the positive electrode active material (2) for lithium secondary batteries of the present invention is preferably 0.05 to 5.0 m². 2 / g, particularly preferably 0.15~1.0m 2 The average particle size or BET specific surface area of ​​the positive electrode active material (2) for lithium secondary batteries of the present invention is within the above range, which makes it less likely for problems to occur in the mixing process when preparing the positive electrode mixture and in the coating process when applying the obtained positive electrode mixture to the positive electrode current collector.

[0096] The c-axis lattice constant of the positive electrode active material (2) for lithium secondary batteries of the present invention is preferably 14.055 to 14.070 Å, and particularly preferably 14.055 to 14.065 Å. By having the c-axis lattice constant within the above range, the collapse of the crystal structure due to charging and discharging can be reduced, and the cycle characteristics can be improved.

[0097] In the second firing step of the method for producing a positive electrode active material for lithium secondary batteries of the present invention, a mixture of aluminum-containing lithium cobalt composite oxide particles and inorganic fluoride particles, which is the first firing product, is fired. However, 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 (2) for lithium secondary batteries of the present invention, the magnitude of the c-axis lattice constant is due to 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 lithium secondary battery positive electrode active material 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 coating and drying a positive electrode mixture on a positive electrode current collector. The positive electrode mixture consists of a positive electrode active material, a conductive agent, a binder, and fillers added as needed.

[0101] The lithium secondary battery of the present invention has the positive electrode of the present invention uniformly coated on the positive electrode. As a result, the lithium secondary battery of the present invention has high battery performance, and is particularly excellent in cycle characteristics under high voltage, cycle characteristics under high voltage and high temperature, and high temperature storage characteristics, and also 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 preferably 70 to 100% by mass, more preferably 90 to 98% by 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 battery in which it is constructed. Examples include stainless steel, nickel, aluminum, titanium, calcined carbon, and aluminum or stainless steel with carbon, nickel, titanium, or silver surface treatments. The surfaces of these materials may be oxidized before use, or the surface of the current collector may be made uneven by surface treatment. Examples of the form of the current collector include foil, film, sheet, net, punched material, lath, porous material, foam, fiber group, and molded nonwoven fabric. The thickness of the current collector is not particularly limited, but it 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-conducting material that does not undergo chemical changes in the constructed battery. Examples include graphite such as natural graphite and artificial graphite, carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, or conductive materials such as polyphenylene derivatives. Examples of natural graphite include scaly graphite, flake graphite, and earthy graphite. These can be used individually or in combination of two or more. The blending ratio of the conductive agent is 1 to 50% by mass, preferably 2 to 30% by mass, in the positive electrode mixture.

[0105] Examples of the binder for the lithium secondary battery of the present invention include, for example, starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluorine rubber, 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 product, ethylene-methacrylic acid copolymer or its (Na + ) ion crosslinked product, ethylene-methyl acrylate copolymer or its (Na + ) ion crosslinked product, ethylene-methyl methacrylate copolymer or its (Na + ) ion crosslinked product, polysaccharides such as polyethylene oxide, thermoplastic resins, polymers having rubber elasticity, etc. 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 add a compound such as an isocyanate group to deactivate the functional group. The blending ratio of the binder is 1 to 50% by mass, preferably 2 to 15% by mass in the positive electrode mixture.

[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, but for example, olefin polymers such as polypropylene and polyethylene, glass, carbon fibers, etc. are used. The amount of filler added is not particularly limited, but 0 to 30% by mass in the positive electrode mixture is preferred.

[0107] The negative electrode in the lithium secondary battery of the present invention is formed by coating and drying a negative electrode material on a negative electrode current collector. The negative electrode current collector in 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, but examples include stainless steel, nickel, copper, titanium, aluminum, calcined carbon, copper or stainless steel with surface treatment of carbon, nickel, titanium, or silver, and aluminum-cadmium alloy. Furthermore, the surface of these materials may be oxidized before use, or the surface of the current collector may be made uneven by surface treatment. Examples of the form of the current collector include foil, film, sheet, net, punched material, lath, porous material, foam, fiber group, and molded nonwoven fabric. The thickness of the current collector is not particularly limited, but it is preferably 1 to 500 μm.

[0108] The negative electrode material for the lithium secondary battery of the present invention is not particularly limited, but examples include carbonaceous materials, metal composite oxides, lithium metal, lithium alloys, silicon alloys, tin alloys, metal oxides, conductive polymers, chalcogen compounds, Li-Co-Ni materials, and Li4Ti5O 12 , lithium niobate, silicon dioxide (SiO x Examples include (0.5 ≤ x ≤ 1.6). Examples of carbonaceous materials include non-graphitizable carbon materials and graphite-based carbon materials. Examples of metal composite oxides include Sn p (M1) 1-p (M2) q O r(In the formula, 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, and 1 ≤ r ≤ 8 are satisfied.), Li t Fe2O3(0 ≤ t ≤ 1), Li t Compounds such as WO2(0 ≤ t ≤ 1) can be mentioned. 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 according to 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, glass fibers, or sheets and non-woven fabrics made of polyethylene, etc. are used due to their organic 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. 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 non-aqueous electrolyte containing a lithium salt for the lithium secondary battery of the present invention consists of a non-aqueous electrolyte and a lithium salt. As the non-aqueous electrolyte for the lithium secondary battery of the present invention, a non-aqueous electrolyte, an organic solid electrolyte, or an inorganic solid electrolyte can be used. 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, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, diethyl ether, 1,3-propanesalton, methyl propionate, and ethyl propionate.

[0111] Examples of organic solid electrolytes 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 ionic dissociation groups such as polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polyhexafluoropropylene, and mixtures of polymers containing ionic dissociation groups and the above non-aqueous electrolyte.

[0112] As the inorganic solid electrolyte for the lithium secondary battery of the present invention, lithium nitrides, halides, oxyacid 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 that dissolve 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] Furthermore, the following compounds can be added to the non-aqueous electrolyte to improve discharge, charge characteristics, and flame retardancy. Examples include pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone and N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, polyethylene glycol, pyrrole, 2-methoxyethanol, aluminum trichloride, monomers of conductive polymer electrode active materials, triethylenephosphonamide, trialkylphosphine, morpholine, aryl compounds having a carbonyl group, hexamethylphosphoric triamide and 4-alkylmorpholine, bicyclic tertiary amines, oils, phosphonium salts and tertiary sulfonium salts, phosphazene, carbonate esters, etc. In addition, halogen-containing solvents, such as carbon tetrachloride and trifluorinated ethylene, can be added to the electrolyte to make it non-flammable. Furthermore, carbon dioxide can be added to the electrolyte to make it suitable for high-temperature storage.

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

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

[0118] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. (X-ray diffraction analysis) In this example, measurements were performed 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 grinder to obtain a first mixture in which the molar ratio of Li to Co (Li / Co) was 1.040 and the molar percentage of Al to Co ((Al / Co) × 100) was 1.0 mol%. (First firing process) Next, the resulting first mixture was fired in an alumina bowl at 900°C for 5 hours. X-ray diffraction analysis of the fired product revealed that it was a single-phase LiCoO2, confirming that Al was contained as a solid solution inside the lithium cobalt composite oxide particles (see Figure 1). After the firing process was completed, the fired product was crushed and classified to obtain aluminum-containing lithium cobalt composite oxide particles containing 1.0 mol% Al relative to Co. (Second mixing process) Next, the obtained aluminum-containing lithium cobalt composite oxide particles, MgF2 (average particle size D50 = 0.9 μm), and AlF3 (average particle size D50 = 2.2 μm) were weighed and mixed in a coffee grinder to obtain a second mixture in which the molar percentage of F relative to Co ((F / Co) × 100) was 0.9 mol%, and the content of MgF2 relative to AlF3 was 3 in molar ratio (MgF2 / AlF3). (Second firing process) Next, the resulting second mixture was fired in an alumina pot at 600°C for 5 hours. After the firing process was completed, the fired product was crushed and classified to obtain a positive electrode active material sample.

[0120] (Examples 2-7) A fired product was obtained by following the same procedure as in Example 1, through the first mixing step and first firing step shown in Table 1. X-ray diffraction analysis of the fired product revealed that it was a single-phase LiCoO2, confirming that Al was contained in solid solution inside the lithium cobalt composite oxide particles. Next, the calcined product was crushed and classified to obtain an aluminum-containing lithium-cobalt composite oxide. Then, a positive electrode active material sample was obtained by going through a second mixing step and a second calcination step in the same manner as in Example 1.

[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 grinder to obtain a first mixture with a molar ratio of Li to Co (Li / Co) of 1.040. (First firing process) Next, the resulting first mixture was fired in an alumina bowl at 900°C for 5 hours. X-ray diffraction analysis of the fired product revealed that it was a single-phase LiCoO2. After the firing process was completed, the fired product was crushed and classified to obtain lithium cobalt composite oxide particles. (Second mixing process) Next, the obtained lithium cobalt composite oxide particles, MgF2 (average particle size 0.9 μm), and AlF3 (average particle size 2.2 μm) were weighed and mixed in a coffee grinder to obtain a second mixture in which the molar percentage of F relative to Co ((F / Co) × 100) was 0.9 mol%, and the content of MgF2 relative to AlF3 was 3 in molar ratio (MgF2 / AlF3). (Second firing process) Next, the resulting second mixture was fired in an alumina pot at 600°C for 5 hours. After the firing process 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 grinder to obtain a first mixture in which the molar ratio of Li to Co (Li / Co) was 1.040 and the molar percentage of Al to Co ((Al / Co) × 100) was 1.0 mol%. (First firing process) Next, the resulting first mixture was fired in an alumina bowl at 900°C for 5 hours. X-ray diffraction analysis of the fired product revealed that it was a single-phase LiCoO2. After the firing process 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 first mixture in which the molar ratio of Li to Co (Li / Co) was 1.043, the molar percentage of Ti to Co ((Ti / Co) × 100) was 1.0 mol%, and the molar percentage of Ca to Co ((Ca / Co) × 100) was 0.06 mol%. (First firing process) Next, the resulting first mixture was fired in an alumina pot at 1070°C for 5 hours. After the firing process was completed, the fired product was crushed and classified to obtain lithium cobalt composite oxide particles containing 1.0 mol% Ti relative to Co and 0.06 mol% Ca relative to Co. (Second mixing process) Next, the obtained lithium cobalt composite oxide particles, MgF2 (average particle size 0.9 μm), and AlF3 (average particle size 2.2 μm) were weighed and mixed in a coffee grinder to obtain a second mixture in which the molar percentage of F relative to Co ((F / Co) × 100) was 0.85 mol%, and the content of MgF2 relative to AlF3 was 0.625 in molar ratio (MgF2 / AlF3). (Second firing process) Next, the resulting second mixture was fired in an alumina pot at 600°C for 5 hours. After the firing process 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 1-7, Comparative Examples 1 and 2, and Reference Example 1. The results are shown in Tables 1 and 2.

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

[0126] [Table 1]

[0127] [Table 2]

[0128] In Table 2, for the values ​​marked with *, the molar percentage of Ti relative to Co is 1.0 mol%, and the molar percentage of Ca relative to Co is 0.06%.

[0129] Tables 1 and 2 show that when comparing the positive electrode active material sample that does not contain Al in solid solution (Comparative Example 1) with the positive electrode active material samples that contain Al in solid solution (Examples 1-4), the c-axis lattice constant is larger for the positive electrode active material that contains Al in 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). This shows that the c-axis lattice constant increases as the Al content relative to Co increases.

[0130] Next, battery performance tests were conducted as follows.

[0131] <Manufacturing of lithium secondary batteries> 95% by mass of the positive electrode active material obtained in Examples 1-7, Comparative Examples 1 and 2, and Reference Example 1, 2.5% by mass of graphite powder, and 2.5% by mass of polyvinylidene fluoride were mixed to form a positive electrode material, which was then dispersed in N-methyl-2-pyrrolidinone to prepare a kneaded paste. The kneaded paste was applied to aluminum foil, dried, pressed, and punched out into a 15 mm diameter disc to obtain a positive electrode plate. Using this positive electrode plate, a coin-type lithium secondary battery was manufactured using various components such as a separator, negative electrode, positive electrode, current collector plate, mounting bracket, external terminals, and electrolyte. Of these, metallic lithium foil was used for the negative electrode, and the electrolyte was a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a ratio of 2.5:6:1.5, in which 1 mole of LiPF6 and 1% by weight of vinylene carbonate were dissolved.

[0132] <Battery performance evaluation> The following battery performance characteristics (cycle characteristics under high voltage, cycle characteristics under high voltage and high temperature, and impedance) were evaluated for the fabricated coin-type lithium secondary battery. 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 4.6V at 0.5C over 2 hours, and then constant current / constant voltage charging (CCCV charging) was performed, maintaining the voltage at 4.6V for 3 hours. After that, a constant current discharge (CC discharge) was performed at 0.2C to 2.7V. These operations 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 In the cycle characteristic evaluation, the discharge capacity of the first cycle was defined as the initial discharge capacity under high voltage (initial discharge capacity at 25°C (4.6V)). (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 weight of active material) at cycle 1 and cycle 20 in the cycle characteristic evaluation using the following formula. Capacity retention rate (%) = (Discharge capacity at 20th cycle / Discharge capacity at 1st cycle) × 100 (2) Evaluation of cycle characteristics under high voltage and high temperature (2-1) Test conditions First, the battery was charged at 0.5C to 4.55V over 2 hours, and then constant current / constant voltage charging (CCCV charging) was performed, maintaining the voltage at 4.55V for 3 hours. After that, a constant current discharge (CC discharge) was performed at 0.2C to 2.7V, and these operations constituted one cycle. 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 In the evaluation of high-temperature cycle characteristics, the discharge capacity of the first cycle was defined 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 from the discharge capacity (per weight of active material) at the 1st cycle and 50th cycle in the high-temperature cycle characteristic evaluation using the following formula. Capacity retention rate under high voltage and high temperature (%) = (Discharge capacity at 50 cycles / Discharge capacity at 1 cycle) × 100 (3) Impedance After fully charging a coin-type lithium secondary battery to 100% (State of Charge), AC impedance measurements were performed using an impedance measuring device within a frequency range of 0.02 Hz to 20 kHz, with no voltage applied to the open-circuit circuit. The resistance value was then determined from the Cole-Cole plot obtained from the AC impedance measurements.

[0133] [Table 3]

[0134] [Table 4]

[0135] [Table 5]

Claims

1. It consists of a mixture of aluminum-containing lithium cobalt composite oxide particles and inorganic fluoride particles. The aluminum-containing lithium cobalt composite oxide particles are such that aluminum is present in solid solution within at least the aluminum-containing lithium cobalt composite oxide particles, and the inorganic fluoride particles are MgF 2 and a compound containing Al and F, and the aforementioned MgF 2 The mixing ratio of the Al and F compound is such that the MgF is equal to the number of moles of F in the Al and F compound on an atomic basis. 2 The ratio of the number of moles of F on an atomic basis (MgF 2 The ratio of moles of F (on an atomic basis) to the number of moles of F in a compound containing Al and F (on an atomic basis) must be between 1 and 10. A positive electrode active material for lithium secondary batteries characterized by the following.

2. The aforementioned compound containing AlF 3 and / or LiAlF 4 The positive electrode active material for lithium secondary batteries according to claim 1, characterized in that it is the positive electrode active material described in claim 1.

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

4. The positive electrode active material for lithium secondary batteries according to claim 1 or 2, characterized in that the content of the inorganic fluoride particles is 0.05 to 5.0 mol% in terms of the atomic molar percentage of F relative to Co in the aluminum-containing lithium cobalt composite oxide particles ((F / Co) × 100).

5. The positive electrode active material for lithium secondary batteries according to claim 1 or 2, characterized in that the lattice constant of the c axis is 14.055 to 14.070 Å.

6. The positive electrode active material for lithium secondary batteries according to claim 1 or 2, characterized in that the aluminum-containing lithium cobalt composite oxide particles contain one or more elements selected from the group consisting of Ca, Mg, Sr, Zr, Nb, B, and W as the M element.

7. It is a calcined product of a mixture of aluminum-containing lithium cobalt composite oxide particles and inorganic fluoride particles. The aluminum-containing lithium cobalt composite oxide particles are those in which aluminum is at least dissolved in the interior of the aluminum-containing lithium cobalt composite oxide particles, and the inorganic fluoride particles are MgF 2 and AlF 3 . The mixing ratio of MgF 2 in the mixture of the aluminum-containing lithium cobalt composite oxide particles and the inorganic fluoride particles is 0.7 to 5 in terms of molar ratio (MgF 3 / AlF 2 / AlF 3 ), A positive electrode active material for lithium secondary batteries characterized by the following.

8. The positive electrode active material for a lithium secondary battery according to claim 7, characterized in that the aluminum-containing lithium cobalt composite oxide particles are a calcined product of a mixture of a lithium compound, a cobalt compound, and an aluminum compound.

9. The positive electrode active material for lithium secondary batteries according to claim 7 or 8, characterized in that the Al content of the aluminum-containing lithium cobalt composite oxide particles is 0.05 to 5.0 mol% in terms of the atomic molar percentage of Al relative to Co in the aluminum-containing lithium cobalt composite oxide particles ((Al / Co) × 100).

10. The positive electrode active material for a lithium secondary battery according to claim 7 or 8, characterized in that the amount of inorganic fluoride particles 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 the atomic molar percentage of F relative to Co in the aluminum-containing lithium cobalt composite oxide particles ((F / Co) × 100).

11. The positive electrode active material for lithium secondary batteries according to claim 7 or 8, characterized in that the lattice constant of the c axis is 14.055 to 14.070 Å.

12. The positive electrode active material for lithium secondary batteries according to claim 7 or 8, characterized in that the aluminum-containing lithium cobalt composite oxide particles contain one or more elements selected from the group consisting of Ca, Mg, Sr, Zr, Nb, B, and W as the M element.

13. A first mixing step involves mixing the raw materials, a lithium compound, a cobalt compound, and an aluminum compound, to obtain a first mixture. A first calcination step involves calcining the first mixture to obtain aluminum-containing lithium cobalt composite oxide particles in which aluminum is solid-dissolved at least inside the particles as a first calcined product, A second mixing step involves mixing the first calcined product obtained in the first calcination step with inorganic fluoride particles to obtain a second mixture. A second firing step involves firing the second mixture to obtain a positive electrode active material for lithium secondary batteries as a second fired product, It has, The inorganic fluoride particles are MgF 2 and AlF 3 The MgF 2 The mixing ratio of the above AlF 3 Molar ratio (MgF 2 / AlF 3 ) The value should be between 0.7 and 5. A method for producing a positive electrode active material for lithium secondary batteries, characterized by the above.

14. The method for producing a positive electrode active material for a lithium secondary battery according to claim 13, characterized in that, in the first mixing step, the aluminum compound is mixed in such a way that the amount of Al in the first mixture, on an atomic basis, is 0.05 to 5.0 mol% ((Al / Co) × 100) relative to Co, is 0.05 to 5.0 mol%.

15. The method for producing a positive electrode active material for a lithium secondary battery according to claim 13 or 14, characterized in that the first calcined product contains one or more elements selected from the group consisting of Ca, Mg, Sr, Zr, Nb, B, and W as the M element.

16. A method for producing a positive electrode active material for a lithium secondary battery according to claim 13 or 14, characterized in that the firing temperature in the first firing step is 800 to 1150°C.

17. The method for producing a positive electrode active material for a lithium secondary battery according to claim 13 or 14, characterized in that in the second mixing step, the inorganic fluoride particles are mixed in such a way that the amount of F relative to Co in the second mixture is 0.05 to 5.0 mol% on an atomic basis ((F / Co) × 100).

18. The method for producing a positive electrode active material for a lithium secondary battery according to claim 13 or 14, characterized in that the lattice constant of the c axis of the positive electrode active material for a lithium secondary battery, which is the second calcined product, is 14.055 to 14.070 Å.

19. A lithium secondary battery characterized in that the positive electrode active material for lithium secondary batteries described in claim 1 or 7 is used as the positive electrode active material.

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