Lithium-ion battery positive electrode active material, lithium-ion battery positive electrode, lithium-ion battery, all-solid-state lithium-ion battery positive electrode active material, all-solid-state lithium-ion battery positive electrode, all-solid-state lithium-ion battery, method for manufacturing lithium-ion battery positive electrode active material, and method for manufacturing all-solid-state lithium-ion battery positive electrode active material

Abstract

A lithium-ion battery positive electrode active material represented by the composition indicated in formula (1) LiaNibCocMndTaeOf (in formula (1), 1.0 ≤ a ≤ 1.07, 0.8 ≤ b ≤ 0.9, b + c + d + e = 1, 1.8 ≤ f ≤ 2.2, and 0.001 ≤ e / (b + c + d + e) ≤ 0.005),　wherein: the magnitudes of a coefficient of variation CV1, which is the value obtained by dividing the standard deviation of the average concentration of the Ta element inside primary particles obtained by transmission electron microscopy (TEM)–energy dispersive X-ray spectroscopy (EDX) analysis by the average concentration of the Ta element, and a coefficient of variation CV2, which is the value obtained by dividing the standard deviation of the average concentration of the Ta element at the grain boundaries of primary particles obtained by TEM-EDX analysis by the average concentration of the Ta element at the grain boundaries of primary particles, are such that CV2 > CV1; and the average concentration of the Ta element at the grain boundaries obtained by TEM-EDX analysis is higher than the concentration of the Ta element in the lithium-ion battery positive electrode active material analyzed by ICP.

Description

Positive electrode active material for lithium-ion batteries, positive electrode for lithium-ion batteries, lithium-ion batteries, positive electrode active material for all-solid-state lithium-ion batteries, positive electrode for all-solid-state lithium-ion batteries, all-solid-state lithium-ion batteries, method for manufacturing positive electrode active material for lithium-ion batteries, and method for manufacturing positive electrode active material for all-solid-state lithium-ion batteries

[0001] The present invention relates to a positive electrode active material for lithium-ion batteries, a positive electrode for lithium-ion batteries, a lithium-ion battery, a positive electrode active material for all-solid-state lithium-ion batteries, a positive electrode for all-solid-state lithium-ion batteries, an all-solid-state lithium-ion battery, a method for producing a positive electrode active material for lithium-ion batteries, and a method for producing a positive electrode active material for all-solid-state lithium-ion batteries.

[0002] In recent years, with the rapid proliferation of information-related devices and communication equipment such as personal computers, video cameras, and mobile phones, the development of batteries used as their power sources has become increasingly important. Among these batteries, lithium-ion secondary batteries have attracted attention due to their high energy density. In addition to liquid-type lithium-ion secondary batteries that use an electrolyte, there are also all-solid-state lithium-ion batteries, which use a solid electrolyte and have been gaining attention in recent years.

[0003] In the 1990s and 2000s, LiCoO2 was the most commonly used positive electrode active material for lithium-ion secondary batteries. However, to address challenges such as increased power consumption due to the sophistication of electronic devices and the need for longer driving ranges with the rise of EVs, positive electrode active materials such as NCM523 and NCM622, which have a Ni ratio of 50% or more, have been used since the 2010s. While these positive electrode active materials offer an excellent balance of power output and durability, further improvements in power output and durability are required for use in automotive applications. To overcome the challenge of particularly high durability, methods have been employed to modify the surface of positive electrode active materials with elements that have high affinity for oxygen, such as Zr, W, Nb, and Ta, or to dope them.

[0004] In Patent Documents 1 and 2, it is disclosed that in the manufacturing process of the positive electrode active material, by equalizing the concentrations at grain boundaries and within grains of elements such as W, Al, Ti, Zr, Nb, Ta, and Mo, battery characteristics such as cycle characteristics, thermal stability, and rate characteristics are improved.

[0005] Japanese Patent No. 6378246 Japanese Unexamined Patent Application Publication No. 2021 - 048070

[0006] In Patent Documents 1 and 2, in the manufacturing process of the positive electrode active material, different elements are added at the stage of preparing the precursor by the crystallization method. The concentration variation between grain boundaries and within grains of the added elements affects the characteristics of the battery using the positive electrode active material. However, in the conventional manufacturing method, the control of the concentration variation between grain boundaries and within grains of the added elements is determined at the stage of preparing the precursor, and it is difficult to control in the firing process of the raw material obtained by mixing the subsequent precursor with the Li source. As a result, it becomes difficult to control the concentration variation between grain boundaries and within grains of the added elements in a desired manner, and there is a risk that the battery characteristics deteriorate.

[0007] The present invention has been made to solve the above problems, and an object thereof is to provide a positive electrode active material for a lithium - ion battery having good battery characteristics, a positive electrode for a lithium - ion battery using the same, a lithium - ion battery, and a method for manufacturing a positive electrode active material for a lithium - ion battery. Another object is to provide a positive electrode active material for an all - solid - state lithium - ion battery having good battery characteristics, a positive electrode for an all - solid - state lithium - ion battery using the same, an all - solid - state lithium - ion battery, and a method for manufacturing a positive electrode active material for an all - solid - state lithium - ion battery.

[0008] The present invention completed based on the above findings is defined as follows. 1. A positive electrode active material for a lithium - ion battery represented by the composition shown in the following formula (1), Li a Ni b Co c Mn d Ta e O f(1) (In the formula (1), 1.0 ≤ a ≤ 1.07, 0.8 ≤ b ≤ 0.9, b + c + d + e = 1, 1.8 ≤ f ≤ 2.2, 0.001 ≤ e / (b + c + d + e) ≤ 0.005.) The coefficient of variation CV1, which is the value obtained by dividing the standard deviation of the average Ta element concentration inside the primary particles obtained by transmission electron microscope (TEM)-energy dispersive X-ray spectroscopy (EDX) analysis by the average Ta element concentration, and the coefficient of variation CV2, which is the value obtained by dividing the standard deviation of the average Ta element concentration at the grain boundaries of the primary particles obtained by the TEM-EDX analysis by the average Ta element concentration at the grain boundaries of the primary particles, are such that CV2 > CV1. The average Ta element concentration at the grain boundaries obtained by the TEM-EDX analysis is higher than the Ta element concentration of the positive electrode active material for lithium-ion batteries analyzed by ICP. A positive electrode active material for lithium-ion batteries. The 2.50% cumulative volume particle size D50 is 5 to 8 μm, and the positive electrode active material for lithium-ion batteries according to 1 above. 3. A positive electrode for a lithium-ion battery, comprising the positive electrode active material for a lithium-ion battery according to 1 or 2 above. 4. A lithium-ion battery, comprising the positive electrode for a lithium-ion battery and a negative electrode according to 3 above. 5. The positive electrode active material for a lithium-ion battery according to 1 or 2 above, and a coating layer made of an oxide of Li and Nb provided on the surface of the positive electrode active material particles of the positive electrode active material for a lithium-ion battery. A positive electrode active material for an all-solid-state lithium-ion battery. 6. The positive electrode active material for an all-solid-state lithium-ion battery according to 5 above, wherein the content of Nb in the positive electrode active material for an all-solid-state lithium-ion battery is 0.5 to 0.8% by mass. 7. A positive electrode for an all-solid-state lithium-ion battery, comprising the positive electrode active material for an all-solid-state lithium-ion battery according to 6 above. 8. An all-solid-state lithium-ion battery, comprising the positive electrode and a negative electrode for an all-solid-state lithium-ion battery according to 7 above. 9. A step of preparing a precursor of a positive electrode active material for a lithium-ion battery represented by the composition shown in the following formula (2), Ni b Co c Mn d(OH)2 (2) (In formula (2) above, 0.8 ≤ b ≤ 0.9, 0.07 ≤ c ≤ 0.15, and b + c + d = 1.) A method for producing a positive electrode active material for a lithium-ion battery, comprising the steps of: mixing an oxide of Ta having a 50% cumulative volume particle size D50 of 1.0 μm or less with a precursor of the positive electrode active material for a lithium-ion battery to obtain a mixture; and dry mixing the mixture with a lithium source and firing at 700°C or higher for 4 hours or more. 10. The method for producing a positive electrode active material for a lithium-ion battery according to 9 above, wherein the oxide of Ta has a D50 of 0.3 to 1.0 μm. 11. The method for producing a positive electrode active material for a lithium-ion battery according to 9 above, wherein in the step of firing the mixture, the mixture is dry mixed with a lithium source and fired at 700 to 800°C for 4 to 12 hours. 12. A method for producing a positive electrode active material for an all-solid-state lithium-ion battery, comprising the steps of: preparing a positive electrode active material for a lithium-ion battery produced by any of the methods described in 9 to 11 above; and forming a coating layer on the surface of the positive electrode active material particles of the positive electrode active material for a lithium-ion battery using an aqueous solution containing Li and Nb with a rolling fluidized bed coating apparatus. 13. The method for producing a positive electrode active material for an all-solid-state lithium-ion battery according to 12 above, wherein the aqueous solution containing Li and Nb is an aqueous solution containing (1) one of lithium hydroxide monohydrate, lithium carbonate, and lithium nitrate as a lithium source; (2) one of niobium hydroxide, niobium oxalate, and niobium ammonium oxalate as a niobium source; and (3) one of pure water, hydrogen peroxide solution, and ammonia solution.

[0009] According to the present invention, it is possible to provide a positive electrode active material for lithium-ion batteries having good battery characteristics, a positive electrode for lithium-ion batteries using the same, a lithium-ion battery, and a method for manufacturing a positive electrode active material for lithium-ion batteries. Furthermore, it is possible to provide a positive electrode active material for all-solid-state lithium-ion batteries having good battery characteristics, a positive electrode for all-solid-state lithium-ion batteries using the same, an all-solid-state lithium-ion battery, and a method for manufacturing a positive electrode active material for all-solid-state lithium-ion batteries.

[0010] It is a schematic diagram of an all-solid-state lithium-ion battery according to an embodiment of the present invention. It is a TEM image showing the measurement location of the Ta element concentration inside the primary particles by TEM-EDX analysis of the positive electrode active material according to Example 1. It is a TEM image showing the measurement location of the Ta element concentration at the grain boundaries of the primary particles by TEM-EDX analysis of the positive electrode active material according to Example 1.

[0011] Next, modes for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments, and it should be understood that design changes, improvements, etc. can be appropriately added based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention.

[0012] (Positive electrode active material for lithium-ion battery) In the present invention, when simply referred to as "positive electrode active material for lithium-ion battery", it includes both positive electrode active materials for liquid-based lithium-ion batteries using electrolytic solutions and positive electrode active materials for all-solid-state lithium-ion batteries with solid electrolytes. The positive electrode active material for lithium-ion battery according to an embodiment of the present invention is represented by the composition shown in the following formula (1). Li a Ni b Co c Mn d Ta e O f (1) (In the above formula (1), 1.0 ≤ a ≤ 1.07, 0.8 ≤ b ≤ 0.9, b + c + d + e = 1, 1.8 ≤ f ≤ 2.2, 0.001 ≤ e / (b + c + d + e) ≤ 0.005.)

[0013] The positive electrode active material for lithium-ion battery according to an embodiment of the present invention has a controlled lithium composition a of 1.0 ≤ a ≤ 1.07 in the above formula (1). Since a representing the lithium composition is 1.0 or more, reduction of nickel due to lithium deficiency can be suppressed. Also, since a representing the lithium composition is 1.07 or less, residual alkali components such as lithium carbonate and lithium hydroxide present on the surface of the positive electrode active material particles, which can be resistance components when made into a battery, can be suppressed.

[0014] In the positive electrode active material for lithium-ion batteries according to the embodiment of the present invention, the sum of b, which represents the nickel composition, c, which represents the cobalt composition, d, which represents the manganese composition, and e, which represents the Ta composition, in formula (1) above is controlled to b + c + d + e = 1, that is, 0.1 ≤ c + d + e ≤ 0.2. As a result, cycle characteristics are improved and the expansion and contraction behavior of the crystal lattice due to lithium insertion and deinsertion during charging and discharging can be reduced. When c + d + e is 0.1 or greater, the above-mentioned effects of improved cycle characteristics and reduced expansion and contraction behavior are more easily obtained, and when c + d + e is 0.2 or less, the decrease in initial discharge capacity is suppressed.

[0015] The positive electrode active material for a lithium-ion battery according to an embodiment of the present invention has the form of secondary particles formed by the aggregation of a plurality of primary particles. The shape of the primary particles constituting the secondary particles is not particularly limited and may be various shapes such as substantially spherical, substantially elliptical, substantially plate-shaped, or substantially needle-shaped. Furthermore, the form in which the plurality of primary particles aggregate is not particularly limited and may be various forms such as aggregation in random directions or aggregation radially and substantially evenly from the center to form substantially spherical or substantially elliptical secondary particles. In the embodiment of the present invention, primary particles refer to regions in which grain boundaries are observed in part or all of the surrounding area when a cross-section of the positive electrode active material is observed with a transmission electron microscope (TEM).

[0016] In the embodiment of the present invention, the positive electrode active material for a lithium-ion battery satisfies the following condition in formula (1): 0.001 ≤ e / (b+c+d+e) ≤ 0.005. That is, the positive electrode active material for a lithium-ion battery contains Ta. This element, by solid-solubilating into the positive electrode active material, has the effect of reducing the expansion and contraction behavior of the crystal lattice due to the insertion and removal of lithium during charging and discharging. For this reason, if the composition ratio of Ta, e / (b+c+d+e), is 0.001 or higher, the cycle characteristics are improved. On the other hand, this element does not contribute to charge compensation during charging and discharging. For this reason, if the composition ratio of Ta, e / (b+c+d+e), is 0.005 or lower, it has the effect of suppressing the decrease in discharge capacity. Preferably, the value is 0.004 ≤ e / (b+c+d+e) ≤ 0.005.

[0017] In the positive electrode active material for lithium-ion batteries according to the embodiment of the present invention, the coefficient of variation CV1, which is the value obtained by dividing the standard deviation of the average concentration of Ta elements inside primary particles obtained by transmission electron microscopy (TEM)-energy dispersive X-ray spectroscopy (EDX) analysis by the average concentration of Ta elements inside the primary particles, and the coefficient of variation CV2, which is the value obtained by dividing the standard deviation of the average concentration of Ta elements at the grain boundaries of primary particles obtained by the TEM-EDX analysis by the average concentration of Ta elements at the grain boundaries of primary particles, are such that CV2 > CV1. Here, the average concentration of Ta elements inside primary particles and at grain boundaries is measured and calculated as follows. First, as a sample pretreatment, the positive electrode active material particles are processed using an ion milling device or a focused ion beam (FIB) device to expose the cross-section of secondary particles. Next, using a JEOL atomic-resolution analytical electron microscope (JEM-ARM300F2), electron beam irradiation is performed at five points each inside and at the grain boundaries of any given primary particle, observed at a field of view of 100,000x magnification, under the conditions of an acceleration voltage of 300 kV and an irradiation current of 1.0 nA. Energy-dispersive X-ray spectroscopy (EDX) analysis is then performed, and the concentrations of each element, Ni, Mn, Co, and Ta, can be determined from the counts of characteristic X-rays generated at each energy. The average Ta concentration at the five points inside and at the grain boundaries of the primary particle, when the sum of the elemental concentrations of Ni, Mn, Co, and Ta calculated in this way is set to 100, is defined as the average Ta element concentration inside the primary particle and the average Ta element concentration at the grain boundaries of the primary particle. Note that the "inside the primary particle" is measured at the central part of the primary particle, at a distance of 20 nm or more from the nearest "grain boundary". Furthermore, in the measurement of Ta concentrations at five points within the primary particle and at the grain boundaries using TEM-EDX as described above, if the Ta concentration falls below the detection limit, the average concentration of the remaining measurement points after excluding the data below the detection limit is taken as the average concentration of Ta elements within the primary particle and the average concentration of Ta elements at the grain boundaries of the primary particle.

[0018] In the embodiment of the present invention, when the above-mentioned CV2 > CV1 is satisfied, the heterogeneous element Ta is segregated at the grain boundaries of the primary particles, and the battery characteristics such as discharge capacity and rate characteristics of the lithium-ion battery using this positive electrode active material for lithium-ion batteries are improved.

[0019] In the embodiment of the present invention, the average concentration of Ta elements at grain boundaries obtained by TEM-EDX analysis of the positive electrode active material for lithium-ion batteries is higher than the concentration of Ta elements of the positive electrode active material for lithium-ion batteries analyzed by ICP. Here, ICP analysis is a compositional analysis performed using an ICP (inductively coupled plasma) emission spectrometer (ICP-OES), and can be performed, for example, using the ICP (inductively coupled plasma) emission spectrometer (ICP-OES) "PS7800" manufactured by Hitachi High-Tech Corporation.

[0020] As described above, in the positive electrode active material for lithium-ion batteries according to the embodiment of the present invention, the average concentration of Ta element at the grain boundaries obtained by TEM-EDX analysis is higher than the concentration of Ta element in the positive electrode active material for lithium-ion batteries analyzed by ICP. Therefore, Ta, which is a different element, is segregated at the grain boundaries of the primary particles, and the battery characteristics such as discharge capacity and rate characteristics of the lithium-ion battery using this positive electrode active material for lithium-ion batteries are improved.

[0021] The 50% cumulative volume particle size D50 of the positive electrode active material for lithium-ion batteries according to the embodiment of the present invention is preferably 5 to 8 μm. Here, the 50% cumulative volume particle size D50 is the volume particle size at 50% accumulation in the volume-based cumulative particle size distribution curve. If the 50% cumulative volume particle size D50 of the positive electrode active material for lithium-ion batteries is 5 μm or more, the specific surface area can be suppressed and the amount of coating of Li and Nb oxides can be suppressed. If the 50% cumulative volume particle size D50 of the positive electrode active material for lithium-ion batteries is 8 μm or less, it can be suppressed that the specific surface area becomes excessively small. The 50% cumulative volume particle size D50 of the positive electrode active material for lithium-ion batteries is more preferably 5 to 6 μm. The above 50% cumulative volume particle size D50 can be measured, for example, as follows. Specifically, first, 100 mg of positive electrode active material powder is dispersed by irradiating it with 40 W of ultrasound for 60 seconds at a flow rate of 50% using a Microtrac MT3300EXII laser diffraction particle size distribution analyzer, and then the particle size distribution is measured to obtain a volume-based cumulative particle size distribution curve. Next, in the obtained cumulative particle size distribution curve, the volume particle size at 50% accumulation is defined as the 50% cumulative volume particle size D50 of the positive electrode active material powder. The water-soluble solvent used for measurement is filtered, with a solvent refractive index of 1.333, particle permeability conditions of permeability, particle refractive index of 1.81, and shape of non-spherical particle. The measurement range is 0.021 to 2000 μm, and the measurement time is 30 seconds.

[0022] (Positive electrode active material for all-solid-state lithium-ion batteries) The positive electrode active material for all-solid-state lithium-ion batteries according to an embodiment of the present invention includes a positive electrode active material for lithium-ion batteries and a coating layer made of an oxide of Li and Nb provided on the surface of the positive electrode active material particles of the positive electrode active material for lithium-ion batteries. The oxide of Li and Nb constituting the coating layer may include lithium niobate (LiNbO3) or LiNbO3.

[0023] The positive electrode active material for a lithium-ion battery according to an embodiment of the present invention is represented by the composition shown in the following formula (1), similar to the positive electrode active material for a lithium-ion battery according to the embodiment of the present invention described above. Li a Ni b Co c Mnd Ta e O f (1) (In equation (1) above, 1.0 ≤ a ≤ 1.07, 0.8 ≤ b ≤ 0.9, b + c + d + e = 1, 1.8 ≤ f ≤ 2.2, and 0.001 ≤ e / (b + c + d + e) ​​≤ 0.005.)

[0024] In the positive electrode active material for an all-solid-state lithium-ion battery according to the embodiment of the present invention, the coefficient of variation CV1, which is the value obtained by dividing the standard deviation of the average concentration of Ta elements inside primary particles obtained by transmission electron microscopy (TEM)-energy dispersive X-ray spectroscopy (EDX) analysis by the average concentration of Ta elements inside the primary particles, and the coefficient of variation CV2, which is the value obtained by dividing the standard deviation of the average concentration of Ta elements at the grain boundaries of primary particles obtained by the TEM-EDX analysis by the average concentration of Ta elements at the grain boundaries of primary particles, are such that CV2 > CV1, meaning that the average concentration of Ta elements at the grain boundaries obtained by TEM-EDX analysis is higher than the concentration of Ta elements in the positive electrode active material for an all-solid-state lithium-ion battery analyzed by ICP. Similar to the positive electrode active material for a lithium-ion battery according to the embodiment of the present invention described above, this configuration improves the battery characteristics of the lithium-ion battery, such as discharge capacity and rate characteristics.

[0025] The Nb content in the positive electrode active material for all-solid-state lithium-ion batteries is preferably 0.5 to 0.8% by mass. When the Nb content is 0.5% by mass or more, it coats the entire surface of the active material, suppressing the increase in resistance due to the interfacial reaction between the solid electrolyte and the positive electrode active material when exposed to a high potential during charging. When the Nb content is 0.8% by mass or less, the coating layer is formed as thinly as possible, shortening the movement of Li ions within the coating layer during charging and discharging, and reducing diffusion transfer resistance. The Nb content in the positive electrode active material for all-solid-state lithium-ion batteries is more preferably 0.6 to 0.7% by mass.

[0026] The thickness of the coating layer is preferably 10 nm or less, and more preferably 6 nm or less. A coating layer thickness of 6 nm or less allows for better avoidance of adverse effects such as inhibition of Li ion migration. The lower limit of the coating layer thickness is not particularly limited, but is typically 4 nm or more, and preferably 5 nm or more. The thickness of the coating layer can be measured by elemental mapping analysis and line analysis using a scanning transmission electron microscope (STEM).

[0027] (Method for producing positive electrode active material for lithium-ion batteries) Next, a method for producing positive electrode active material for lithium-ion batteries according to an embodiment of the present invention will be described in detail. The method for producing positive electrode active material for lithium-ion batteries according to an embodiment of the present invention first involves preparing a precursor of positive electrode active material for lithium-ion batteries represented by the composition shown in the following formula (2). Ni b Co c Mn d (OH)2 (2) (In equation (2) above, 0.8 ≤ b ≤ 0.9, 0.07 ≤ c ≤ 0.15, and b + c + d = 1.)

[0028] As a method for producing a precursor of positive electrode active material for lithium-ion batteries, first, an aqueous solution containing (a) a nickel salt, (b) a cobalt salt, (c) a manganese salt, and (d) a basic aqueous solution containing ammonia and a basic aqueous solution of an alkali metal is prepared. (a) Nickel salts include nickel sulfate, nickel nitrate, or nickel hydrochloride. (b) Cobalt salts include cobalt sulfate, cobalt nitrate, or cobalt hydrochloride. (c) Manganese salts include manganese sulfate, manganese nitrate, or manganese hydrochloride. (d) Basic aqueous solutions containing ammonia include aqueous solutions of ammonia, ammonium sulfate, ammonium carbonate, ammonium hydrochloride, etc. The basic aqueous solution of the alkali metal may be an aqueous solution of sodium hydroxide, potassium hydroxide, carbonate, etc. Furthermore, as the aqueous solution of the carbonate, for example, an aqueous solution using a carbonate salt such as an aqueous solution of sodium carbonate, an aqueous solution of potassium carbonate, an aqueous solution of sodium bicarbonate, or an aqueous solution of potassium bicarbonate may be used.

[0029] Furthermore, the composition of the aqueous solution can be appropriately adjusted depending on the composition of the precursor to be produced, but it is preferable that it is (a) an aqueous solution containing 45 to 110 g / L of nickel ions, (b) an aqueous solution containing 4 to 20 g / L of cobalt ions, (c) an aqueous solution containing 1 to 4 g / L of manganese ions, (d) an aqueous ammonia solution of 10 to 28% by mass, and a basic aqueous solution with an alkali metal concentration of 10 to 30% by mass.

[0030] Next, an aqueous solution containing (a) nickel salt, (b) cobalt salt, (c) manganese salt, and (d) a basic aqueous solution containing ammonia and a basic aqueous solution of an alkali metal is used as the reaction solution, and a coprecipitation reaction is carried out while controlling the pH of the reaction solution to 10.8 to 11.4, the ammonium ion concentration to 10 to 22 g / L, and the liquid temperature to 55 to 65°C. At this time, the chemical solutions may be supplied to the reaction vessel from three tanks: a tank containing a mixed aqueous solution of nickel salt, cobalt salt, and manganese salt, a tank containing a basic aqueous solution containing ammonia, and a tank containing a basic aqueous solution of an alkali metal. In this way, a precursor for the positive electrode active material for lithium-ion batteries represented by formula (2) above can be produced.

[0031] Next, a mixture is obtained by wet or dry mixing a hydroxide precursor of lithium-ion battery positive electrode active material with an oxide of Ta having a 50% cumulative volume particle size D50 of 1.0 μm or less. The amount of Ta oxide to be mixed can be appropriately adjusted depending on the target composition of the lithium-ion battery positive electrode active material. Ta2O5 and the like can be used as the Ta oxide. For wet mixing, the hydroxide precursor of lithium-ion battery positive electrode active material and the Ta oxide are added to an aqueous solvent, and a slurry is prepared by mechanical means, after which the slurry is allowed to dry while standing. For dry mixing, the mixture can be mixed using a Nobilta manufactured by Hosokawa Micron Corporation or an Intensive Mixer manufactured by Nippon Eirich Co., Ltd., which can mix the hydroxide precursor of lithium-ion battery positive electrode active material and the added Ta oxide while applying shear force.

[0032] As described above, by preparing a slurry by mixing a Ta oxide with a 50% cumulative volume particle size D50 of 1.0 μm or less with the precursor of the lithium-ion battery positive electrode active material before mixing it with a lithium source, the adhesion rate of the oxide of the foreign element (Ta) to the surface of the precursor of the lithium-ion battery positive electrode active material is improved. Furthermore, by adding a foreign element using this method, even with the addition of a small amount of element, it is possible to improve the cycle characteristics (capacity retention rate) and reduce the DC resistance of the lithium-ion battery using the manufactured positive electrode active material. The 50% cumulative volume particle size D50 of the Ta oxide particles to be mixed is preferably 0.3 to 1.0 μm, and more preferably 0.3 to 0.5 μm.

[0033] Next, a lithium source is dry-mixed with the lithium-ion battery positive electrode active material precursor and Ta oxide mixture obtained as described above to form a lithium mixture. The amount of lithium source to be mixed can be appropriately adjusted depending on the target composition of the lithium-ion battery positive electrode active material. Lithium hydroxide is an example of a lithium source. The mixing method involves adjusting the mixing ratio of each raw material and dry-mixing using a Henschel mixer, automatic mortar and pestle, or V-type mixer.

[0034] Next, the lithium mixture obtained as described above is calcined at 700°C or higher for 4 hours or more. By calcining the lithium mixture at a temperature of 700°C or higher and for a long period of 4 hours or more in one go, the solid solution rate of the dissimilar element (Ta) into the positive electrode active material for lithium-ion batteries is improved, and the strength of the positive electrode active material particles is improved. As a result, the occurrence of particle cracking in the subsequent lithium composite oxide coating process is suppressed, and it becomes possible to coat the material well with an oxide containing Li and Nb, improving the output characteristics and durability of the all-solid-state lithium-ion battery. The calcination temperature is preferably 700 to 800°C, and the calcination time is preferably 4 to 12 hours. The calcination atmosphere is preferably an oxygen atmosphere.

[0035] Increasing the amount of Ta oxide added, and / or increasing the firing time, and / or increasing the firing temperature, improves the solid solubility of the foreign element (Ta) in the positive electrode active material, allowing Ta to diffuse more into the primary particles of the positive electrode active material. On the other hand, decreasing the amount of Ta oxide added, and / or shortening the firing time, and / or lowering the firing temperature, suppresses the diffusion of Ta into the primary particles of the positive electrode active material and allows it to segregate at the grain boundaries. By this method, it is possible to control the concentration variation between the grain boundaries and inside the primary particles. In other words, the magnitude of the coefficient of variation CV1, which is the value obtained by dividing the standard deviation of the average concentration of Ta elements inside the primary particles obtained by the TEM-EDX analysis by the average concentration of Ta elements, and the magnitude of the coefficient of variation CV2, which is the value obtained by dividing the standard deviation of the average concentration of Ta elements at the grain boundaries of the primary particles obtained by the TEM-EDX analysis by the average concentration of Ta elements at the grain boundaries of the primary particles, can be controlled so that CV2 > CV1, and the average concentration of Ta elements at the grain boundaries obtained by the TEM-EDX analysis can be made higher than the concentration of Ta elements in the positive electrode active material for lithium-ion batteries analyzed by ICP.

[0036] Subsequently, if necessary, the calcined body can be crushed using, for example, a pulverizer to obtain powder for the positive electrode active material of lithium-ion batteries.

[0037] (Method for manufacturing positive electrode active material for all-solid-state lithium-ion batteries) The method for manufacturing positive electrode active material for all-solid-state lithium-ion batteries according to an embodiment of the present invention involves first coating the surface of the positive electrode active material particles of the lithium-ion battery positive electrode active material manufactured by the above-described method with an aqueous solution (coating solution) containing Li and Nb. Examples of the coating solution include (1) one of lithium hydroxide monohydrate, lithium carbonate, and lithium nitrate as a lithium source, (2) one of niobium hydroxide, niobium oxalate, and niobium ammonium oxalate as a niobium source, and (3) an aqueous solution containing one of pure water, hydrogen peroxide solution, and ammonia solution. Furthermore, a coating apparatus having a rolling fluidized bed (rolling fluidized bed coating apparatus) is used as the coating method. By using a rolling fluidized bed coating apparatus, uniform coating can be achieved while controlling the thickness.

[0038] (Positive electrode for lithium-ion battery and lithium-ion battery) The positive electrode for a lithium-ion battery according to an embodiment of the present invention has a structure in which a positive electrode composite material, prepared by mixing the positive electrode active material for a lithium-ion battery having the above-described configuration, a conductive additive, and a binder, is provided on one or both sides of a current collector. Furthermore, the lithium-ion battery according to an embodiment of the present invention comprises a positive electrode for a lithium-ion battery having such a configuration and a known negative electrode for a lithium-ion battery.

[0039] Examples of conductive additives include carbon-based conductive additives (graphite and carbon black (acetylene black, Ketjen black, furnace black, channel black, and thermal lamp black), etc.), and mixtures thereof. These conductive additives may be used individually or in combination of two or more. These conductive additives may also be formed by coating a particulate ceramic material or resin material with a conductive material (preferably a metallic conductive additive from the above-mentioned list) by plating or the like. The shape (form) of the conductive additive is not limited to particle form, but may be in a form other than particle form, and may be in a form that has been put into practical use as a so-called filler-type conductive additive, such as carbon nanofibers or carbon nanotubes.

[0040] Examples of binders include substances commonly used in positive electrode composites for lithium-ion batteries, but it is preferable that they be copolymers having a structure derived from vinylidene fluoride, polyvinylidene fluoride (PVDF), copolymers or homopolymers having a structure derived from tetrafluoroethylene (TEF), or copolymers or homopolymers having a structure derived from hexafluoropropylene (HFP). Specifically, examples include PVDF-HFP, PVDF-HFP-TEF, PVDF-TEF, TEF-HFP, etc.

[0041] The positive electrode mixture is prepared by mixing a positive electrode active material for lithium-ion batteries, a conductive additive, and a binder in a solvent to form a positive electrode mixture slurry. This slurry is then applied to one or both sides of a current collector, and after drying and other processes, it is placed on the current collector to form the positive electrode active material layer.

[0042] As the solvent for the cathode mixture slurry, known organic solvents, such as hydrocarbon organic solvents, amide compounds, lactam compounds, urea compounds, organosulfur compounds, and cyclic organophosphorus compounds, can be used as single solvents or as mixed solvents. As hydrocarbon organic solvents, saturated hydrocarbons, unsaturated hydrocarbons, or aromatic hydrocarbons can be used. Examples of saturated hydrocarbons include hexane, pentane, 2-ethylhexane, heptane, decane, and cyclohexane. Examples of unsaturated hydrocarbons include hexene, heptene, and cyclohexene. Examples of aromatic hydrocarbons include toluene, xylene, decalin, and 1,2,3,4-tetrahydronaphthalene. Of these, toluene and xylene are particularly preferred.

[0043] Materials that constitute the current collector include metallic materials such as copper, aluminum, titanium, stainless steel, nickel and their alloys, as well as calcined carbon, conductive polymer materials, and conductive glass. Among these, aluminum is more preferred from the viewpoint of weight reduction, corrosion resistance, and high conductivity. Furthermore, the current collector is preferably a resin current collector made of a conductive polymer material. The shape of the current collector is not particularly limited and may be a sheet-shaped current collector made of the above material, or a deposited layer made of fine particles composed of the above material. The thickness of the current collector is not particularly limited, but is preferably 50 to 500 μm. As the conductive polymer material that constitutes the resin current collector, for example, a conductive polymer or a resin to which a conductive additive is added as needed can be used.

[0044] From the viewpoint of battery performance, the thickness of the positive electrode for lithium-ion batteries is preferably 150 to 600 μm, and more preferably 200 to 450 μm.

[0045] A lithium-ion battery using a lithium-ion battery positive electrode is obtained by combining it with a negative electrode (the opposite electrode), housing it in a cell container with a separator, injecting electrolyte, and sealing the cell container. Alternatively, a bipolar electrode can be fabricated by forming a positive electrode on one side of a current collector and a negative electrode on the other side, stacking the bipolar electrode with a separator and housing it in a cell container, injecting electrolyte, and sealing the cell container.

[0046] Examples of negative electrodes include those containing a negative electrode active material, conductive additives, and current collectors. Known negative electrode active materials for lithium-ion batteries can be used as the negative electrode active material, including carbon-based materials (graphite, non-graphitizable carbon, amorphous carbon, resin-fired bodies (e.g., phenolic resin and furan resin fired and carbonized), cokes (e.g., pitch coke, needle coke, and petroleum coke), and carbon fibers), silicon-based materials (silicon, silicon oxide (SiO₂)). xExamples include silicon-carbon composites (carbon particles coated with silicon and / or silicon carbide, silicon particles or silicon oxide particles coated with carbon and / or silicon carbide, and silicon carbide, etc.), silicon alloys (silicon-aluminum alloy, silicon-lithium alloy, silicon-nickel alloy, silicon-iron alloy, silicon-titanium alloy, silicon-manganese alloy, silicon-copper alloy, and silicon-tin alloy, etc.), conductive polymers (e.g., polyacetylene and polypyrrole), metals (tin, aluminum, zirconium, and titanium, etc.), metal oxides (titanium oxide and lithium-titanium oxide, etc.), metal alloys (e.g., lithium-tin alloy, lithium-aluminum alloy, and lithium-aluminum-manganese alloy, etc.), and mixtures of these with carbon-based materials. Furthermore, conductive additives similar to those used for the positive electrode can be suitably used.

[0047] The current collector can be the same as the current collector that constitutes the positive electrode described above, and is preferably made of copper from the viewpoint of weight reduction, corrosion resistance, and high conductivity. A resin current collector may also be used, and one similar to the current collector that constitutes the positive electrode described above can be suitably used. The thickness of the current collector is not particularly limited, but is preferably 10 to 60 μm.

[0048] Examples of separators include known separators for lithium-ion batteries such as porous films made of polyethylene or polypropylene, laminated films of porous polyethylene film and porous polypropylene, nonwoven fabrics made of synthetic fibers (polyester fibers and aramid fibers, etc.) or glass fibers, and those on which ceramic fine particles such as silica, alumina, and titania are attached to the surface.

[0049] (Positive electrode for all-solid-state lithium-ion battery and all-solid-state lithium-ion battery) A positive electrode can be formed using a positive electrode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention, and an all-solid-state lithium-ion battery can be manufactured by forming the positive electrode with the positive electrode as the positive electrode layer, and including the positive electrode layer, a solid electrolyte layer, and a negative electrode layer. The solid electrolyte layer and the negative electrode layer constituting the all-solid-state lithium-ion battery according to an embodiment of the present invention are not particularly limited and can be formed from known materials, and can have known configurations as shown in Figure 1.

[0050] The positive electrode layer of the all-solid-state lithium-ion battery can be made by forming a positive electrode composite material in layers, which is obtained by mixing the positive electrode active material for all-solid-state lithium-ion batteries according to the present invention with a solid electrolyte. The content of the positive electrode active material in the positive electrode layer is preferably 50% by mass or more and 99% by mass or less, and more preferably 60% by mass or more and 90% by mass or less.

[0051] The positive electrode composite may further contain a conductive additive. A carbon-based material can be used as the conductive additive. Examples of carbon-based materials include carbon black such as Ketjenblack, acetylene black, Denka black, thermal black, and channel black, as well as graphite, carbon fiber, activated carbon, and the like.

[0052] The average thickness of the positive electrode layer of an all-solid-state lithium-ion battery is not particularly limited and can be designed appropriately depending on the purpose. The average thickness of the positive electrode layer of an all-solid-state lithium-ion battery may be, for example, 1 μm to 100 μm, or 1 μm to 10 μm.

[0053] The method for forming the positive electrode layer of an all-solid-state lithium-ion battery is not particularly limited and can be appropriately selected depending on the purpose. Examples of methods for forming the positive electrode layer of an all-solid-state lithium-ion battery include a method of compression molding the positive electrode active material for the all-solid-state lithium-ion battery.

[0054] The negative electrode layer of an all-solid-state lithium-ion battery may be formed by creating layers of known negative electrode active materials for all-solid-state lithium-ion batteries. Alternatively, the negative electrode layer may be formed by creating layers of a negative electrode composite material which is a mixture of known negative electrode active materials for all-solid-state lithium-ion batteries and a solid electrolyte. The content of the negative electrode active material in the negative electrode layer is preferably, for example, 10% by mass or more and 99% by mass or less, and more preferably 20% by mass or more and 90% by mass or less.

[0055] The negative electrode layer, like the positive electrode layer, may contain a conductive additive. The conductive additive can be the same material as the material described for the positive electrode layer. As the negative electrode active material, for example, carbon-based materials can be used, specifically artificial graphite, graphite carbon fiber, resin-calcined carbon, pyrolysis vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-calcined carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, and non-graphitizable carbon, or mixtures thereof. Furthermore, as the negative electrode material, for example, metallic lithium, metallic indium, metallic aluminum, metallic silicon, or alloys combined with other elements or compounds can be used.

[0056] The average thickness of the negative electrode layer of an all-solid-state lithium-ion battery is not particularly limited and can be appropriately selected depending on the purpose. The average thickness of the negative electrode layer of an all-solid-state lithium-ion battery may be, for example, 1 μm to 100 μm, or 1 μm to 10 μm.

[0057] The method for forming the negative electrode layer of an all-solid-state lithium-ion battery is not particularly limited and can be appropriately selected depending on the purpose. Examples of methods for forming the negative electrode layer of an all-solid-state lithium-ion battery include a method of compression molding of negative electrode active material particles and a method of vapor deposition of negative electrode active material.

[0058] A known solid electrolyte for all-solid-state lithium-ion batteries can be used as the solid electrolyte. Sulfide-based solid electrolytes, etc., can be used.

[0059] Examples of sulfide-based solid electrolytes include LiI-Li2S-P2S5, LiI-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2, LiPO4-Li2S-SiS, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li3PS4, and Li2S-P2S5.

[0060] The average thickness of the solid electrolyte layer in an all-solid-state lithium-ion battery is not particularly limited and can be designed appropriately depending on the purpose. The average thickness of the solid electrolyte layer in an all-solid-state lithium-ion battery may be, for example, 50 μm to 500 μm, or 50 μm to 100 μm.

[0061] The method for forming the solid electrolyte layer of an all-solid-state lithium-ion battery is not particularly limited and can be appropriately selected depending on the purpose. Examples of methods for forming the solid electrolyte layer of an all-solid-state lithium-ion battery include sputtering using a target material for the solid electrolyte, or compression molding of the solid electrolyte.

[0062] Other components constituting the all-solid-state lithium-ion battery are not particularly limited and can be appropriately selected depending on the purpose, and examples include a positive electrode current collector, a negative electrode current collector, and a battery case.

[0063] The size and structure of the positive electrode current collector are not particularly limited and can be appropriately selected according to the purpose. Examples of materials for the positive electrode current collector include die steel, stainless steel, aluminum, aluminum alloy, titanium alloy, copper, gold, and nickel. Examples of shapes for the positive electrode current collector include foil, plate, and mesh. The average thickness of the positive electrode current collector may be, for example, 10 μm to 500 μm, or 50 μm to 100 μm.

[0064] The size and structure of the negative electrode current collector are not particularly limited and can be appropriately selected according to the purpose. Examples of materials for the negative electrode current collector include die steel, gold, indium, nickel, copper, and stainless steel. Examples of shapes for the negative electrode current collector include foil, plate, and mesh. The average thickness of the negative electrode current collector may be, for example, 10 μm to 500 μm, or 50 μm to 100 μm.

[0065] The battery case is not particularly limited and can be appropriately selected depending on the purpose, for example, known laminate films that can be used with conventional all-solid-state lithium-ion batteries. Examples of laminate films include resin laminate films and films in which metal has been vapor-deposited onto a resin laminate film. The shape of the battery is not particularly limited and can be appropriately selected depending on the purpose, for example, cylindrical, rectangular, button-shaped, coin-shaped, and flat-shaped batteries.

[0066] The following examples are provided to better understand the present invention and its advantages, but the present invention is not limited to these examples.

[0067] (Example 1) First, the composition formula: Ni 0.82 Co 0.15 Mn 0.03 A precursor for the positive electrode active material for lithium-ion batteries, represented by (OH)2, was prepared. Next, the precursor for the positive electrode active material for lithium-ion batteries, having a 50% cumulative volume particle size D50 of 5.6 μm, and Ta2O5, a heterogeneous element with a 50% cumulative volume particle size D50 of 0.32 μm, were added to an aqueous solvent in an amount of 0.1 mol%. These were mixed by mechanical means (wet mixing) to prepare a slurry, and then the slurry was allowed to stand and dried to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed in a Henschel mixer (dry mixing) to form a lithium mixture. Next, the lithium mixture obtained as described above was calcined at 700°C for 12 hours in an oxygen atmosphere to produce positive electrode active material particles. Next, a coating layer was formed on the positive electrode active material particles according to the following procedure. First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water was prepared as a coating solution, with Li content and Nb content of 0.15 mol / L, respectively. Next, using this coating solution, the surface of the prepared positive electrode active material particles was coated with an oxide precursor containing Li and Nb using a rolling fluidized bed coating apparatus, and heat treatment was performed at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer on its surface.

[0068] (Example 2) First, the composition formula: Ni0.82 Co 0.15 Mn 0.03 A precursor for the positive electrode active material for lithium-ion batteries, represented by (OH)2, was prepared. Next, the precursor for the positive electrode active material for lithium-ion batteries, having a 50% cumulative volume particle size D50 of 5.6 μm, and Ta2O5, a heterogeneous element with a 50% cumulative volume particle size D50 of 0.31 μm, were added to an aqueous solvent in an amount of 0.2 mol%. These were mixed by mechanical means (wet mixing) to prepare a slurry, and then the slurry was allowed to stand and dried to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed in a Henschel mixer (dry mixing) to form a lithium mixture. Next, the lithium mixture obtained as described above was calcined at 700°C for 12 hours in an oxygen atmosphere to produce positive electrode active material particles. Next, a coating layer was formed on the positive electrode active material particles according to the following procedure. First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water was prepared as a coating solution, with Li content and Nb content of 0.15 mol / L, respectively. Next, using this coating solution, the surface of the prepared positive electrode active material particles was coated with an oxide precursor containing Li and Nb using a rolling fluidized bed coating apparatus, and heat treatment was performed at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer on its surface.

[0069] (Example 3) First, the composition formula: Ni 0.82 Co 0.15 Mn 0.03A precursor for the positive electrode active material for lithium-ion batteries, represented by (OH)2, was prepared. Next, the precursor for the positive electrode active material for lithium-ion batteries, having a 50% cumulative volume particle size D50 of 5.6 μm, and Ta2O5, a heterogeneous element with a 50% cumulative volume particle size D50 of 0.32 μm, were added to an aqueous solvent in an amount of 0.3 mol%. These were mixed by mechanical means (wet mixing) to prepare a slurry, and then the slurry was allowed to stand and dried to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed in a Henschel mixer (dry mixing) to form a lithium mixture. Next, the lithium mixture obtained as described above was calcined at 700°C for 12 hours in an oxygen atmosphere to produce positive electrode active material particles. Next, a coating layer was formed on the positive electrode active material particles according to the following procedure. First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water was prepared as a coating solution, with Li content and Nb content of 0.15 mol / L, respectively. Next, using this coating solution, the surface of the prepared positive electrode active material particles was coated with an oxide precursor containing Li and Nb using a rolling fluidized bed coating apparatus, and heat treatment was performed at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer on its surface.

[0070] (Example 4) First, the composition formula: Ni 0.82 Co 0.15 Mn 0.03A precursor for the positive electrode active material for lithium-ion batteries, represented by (OH)2, was prepared. Next, the precursor for the positive electrode active material for lithium-ion batteries, having a 50% cumulative volume particle size D50 of 5.6 μm, and Ta2O5, a heterogeneous element with a 50% cumulative volume particle size D50 of 0.31 μm, were added to an aqueous solvent in an amount of 0.4 mol%. These were mixed mechanically (wet mixing) to prepare a slurry, and then the slurry was allowed to stand and dried to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed in a Henschel mixer (dry mixing) to form a lithium mixture. Next, the lithium mixture obtained as described above was calcined at 700°C for 12 hours in an oxygen atmosphere to produce positive electrode active material particles. Next, a coating layer was formed on the positive electrode active material particles according to the following procedure. First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water was prepared as a coating solution, with Li content and Nb content of 0.15 mol / L, respectively. Next, using this coating solution, the surface of the prepared positive electrode active material particles was coated with an oxide precursor containing Li and Nb using a rolling fluidized bed coating apparatus, and heat treatment was performed at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer on its surface.

[0071] (Example 5) First, the composition formula: Ni 0.82 Co 0.15 Mn 0.03A precursor for the positive electrode active material for lithium-ion batteries, represented by (OH)2, was prepared. Next, the precursor for the positive electrode active material for lithium-ion batteries, having a 50% cumulative volume particle size D50 of 5.6 μm, and Ta2O5, a heterogeneous element with a 50% cumulative volume particle size D50 of 0.30 μm, were added to an aqueous solvent in an amount of 0.5 mol%. These were mixed by mechanical means (wet mixing) to prepare a slurry, and then the slurry was dried while standing to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed in a Henschel mixer (dry mixing) to form a lithium mixture. Next, the lithium mixture obtained as described above was calcined at 700°C for 12 hours in an oxygen atmosphere to produce positive electrode active material particles. Next, a coating layer was formed on the positive electrode active material particles according to the following procedure. First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water was prepared as a coating solution, with Li content and Nb content of 0.15 mol / L, respectively. Next, using this coating solution, the surface of the prepared positive electrode active material particles was coated with an oxide precursor containing Li and Nb using a rolling fluidized bed coating apparatus, and heat treatment was performed at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer on its surface.

[0072] (Example 6) First, composition formula: Ni 0.82 Co 0.15 Mn 0.03A precursor for the lithium-ion battery positive electrode active material, represented by (OH)2, was prepared. Next, the precursor for the lithium-ion battery positive electrode active material, having a 50% cumulative volume particle size D50 of 5.6 μm, and Ta2O5, a heterogeneous element with a 50% cumulative volume particle size D50 of 0.31 μm, were added to an aqueous solvent in an amount of 0.2 mol%. These were mixed by mechanical means (wet mixing) to prepare a slurry, and then the slurry was dried while standing to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed in a Henschel mixer (dry mixing) to form a lithium mixture. Next, the lithium mixture obtained as described above was calcined at 710°C for 12 hours in an oxygen atmosphere to produce positive electrode active material particles. Next, a coating layer was formed on the positive electrode active material particles according to the following procedure. First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water was prepared as a coating solution, with Li content and Nb content of 0.15 mol / L, respectively. Next, using this coating solution, the surface of the prepared positive electrode active material particles was coated with an oxide precursor containing Li and Nb using a rolling fluidized bed coating apparatus, and heat treatment was performed at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer on its surface.

[0073] (Example 7) First, composition formula: Ni 0.82 Co 0.15 Mn 0.03A precursor for the positive electrode active material for lithium-ion batteries, represented by (OH)2, was prepared. Next, the precursor for the positive electrode active material for lithium-ion batteries, having a 50% cumulative volume particle size D50 of 5.6 μm, and Ta2O5, a heterogeneous element with a 50% cumulative volume particle size D50 of 0.31 μm, were added to an aqueous solvent in an amount of 0.4 mol%. These were mixed by mechanical means (wet mixing) to prepare a slurry, and then the slurry was allowed to stand and dried to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed in a Henschel mixer (dry mixing) to form a lithium mixture. Next, the lithium mixture obtained as described above was calcined at 710°C for 12 hours in an oxygen atmosphere to produce positive electrode active material particles. Next, a coating layer was formed on the positive electrode active material particles according to the following procedure. First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water was prepared as a coating solution, with Li content and Nb content of 0.15 mol / L, respectively. Next, using this coating solution, the surface of the prepared positive electrode active material particles was coated with an oxide precursor containing Li and Nb using a rolling fluidized bed coating apparatus, and heat treatment was performed at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer on its surface.

[0074] (Example 8) First, composition formula: Ni 0.82 Co 0.15 Mn 0.03A precursor for the lithium-ion battery positive electrode active material, represented by (OH)2, was prepared. Next, the precursor for the lithium-ion battery positive electrode active material, having a 50% cumulative volume particle size D50 of 5.6 μm, and Ta2O5, a heterogeneous element with a 50% cumulative volume particle size D50 of 0.31 μm, were added to an aqueous solvent in an amount of 0.2 mol%. These were mixed mechanically (wet mixing) to prepare a slurry, and then the slurry was allowed to stand and dried to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed in a Henschel mixer (dry mixing) to form a lithium mixture. Next, the lithium mixture obtained as described above was calcined at 720°C for 12 hours in an oxygen atmosphere to produce positive electrode active material particles. Next, a coating layer was formed on the positive electrode active material particles according to the following procedure. First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water was prepared as a coating solution, with Li content and Nb content of 0.15 mol / L, respectively. Next, using this coating solution, the surface of the prepared positive electrode active material particles was coated with an oxide precursor containing Li and Nb using a rolling fluidized bed coating apparatus, and heat treatment was performed at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer on its surface.

[0075] (Example 9) First, the composition formula: Ni 0.82 Co 0.15 Mn 0.03A precursor for the positive electrode active material for lithium-ion batteries, represented by (OH)2, was prepared. Next, the precursor for the positive electrode active material for lithium-ion batteries, having a 50% cumulative volume particle size D50 of 5.6 μm, and Ta2O5, a heterogeneous element with a 50% cumulative volume particle size D50 of 0.32 μm, were added to an aqueous solvent in an amount of 0.3 mol%. These were mixed by mechanical means (wet mixing) to prepare a slurry, and then the slurry was allowed to stand and dried to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed in a Henschel mixer (dry mixing) to form a lithium mixture. Next, the lithium mixture obtained as described above was calcined at 720°C for 12 hours in an oxygen atmosphere to produce positive electrode active material particles. Next, a coating layer was formed on the positive electrode active material particles according to the following procedure. First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water was prepared as a coating solution, with Li content and Nb content of 0.15 mol / L, respectively. Next, using this coating solution, the surface of the prepared positive electrode active material particles was coated with an oxide precursor containing Li and Nb using a rolling fluidized bed coating apparatus, and heat treatment was performed at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer on its surface.

[0076] (Example 10) First, composition formula: Ni 0.82 Co 0.15 Mn 0.03A precursor for the positive electrode active material for lithium-ion batteries, represented by (OH)2, was prepared. Next, the precursor for the positive electrode active material for lithium-ion batteries, having a 50% cumulative volume particle size D50 of 5.6 μm, and Ta2O5, a heterogeneous element with a 50% cumulative volume particle size D50 of 0.30 μm, were added to an aqueous solvent in an amount of 0.5 mol%. These were mixed by mechanical means (wet mixing) to prepare a slurry, and then the slurry was allowed to stand and dried to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed in a Henschel mixer (dry mixing) to form a lithium mixture. Next, the lithium mixture obtained as described above was calcined at 720°C for 12 hours in an oxygen atmosphere to produce positive electrode active material particles. Next, a coating layer was formed on the positive electrode active material particles according to the following procedure. First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water was prepared as a coating solution, with Li content and Nb content of 0.15 mol / L, respectively. Next, using this coating solution, the surface of the prepared positive electrode active material particles was coated with an oxide precursor containing Li and Nb using a rolling fluidized bed coating apparatus, and heat treatment was performed at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer on its surface.

[0077] (Comparative Example 1) First, the composition formula: Ni 0.82 Co 0.15 Mn 0.03A precursor for the positive electrode active material for lithium-ion batteries, represented by (OH)2, was prepared. Next, the precursor for the positive electrode active material for lithium-ion batteries, having a 50% cumulative volume particle size D50 of 5.6 μm, and Ta2O5, a heterogeneous element with a 50% cumulative volume particle size D50 of 0.32 μm, were added to an aqueous solvent in an amount of 0.1 mol%. These were mixed by mechanical means (wet mixing) to prepare a slurry, and then the slurry was allowed to stand and dried to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed in a Henschel mixer (dry mixing) to form a lithium mixture. Next, the lithium mixture obtained as described above was calcined at 710°C for 12 hours in an oxygen atmosphere to produce positive electrode active material particles. Next, a coating layer was formed on the positive electrode active material particles according to the following procedure. First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water was prepared as a coating solution, with Li content and Nb content of 0.15 mol / L, respectively. Next, using this coating solution, the surface of the prepared positive electrode active material particles was coated with an oxide precursor containing Li and Nb using a rolling fluidized bed coating apparatus, and heat treatment was performed at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer on its surface.

[0078] (Comparative Example 2) First, the composition formula: Ni 0.82 Co 0.15 Mn 0.03A precursor for the positive electrode active material for lithium-ion batteries, represented by (OH)2, was prepared. Next, the precursor for the positive electrode active material for lithium-ion batteries, having a 50% cumulative volume particle size D50 of 5.6 μm, and Ta2O5, a heterogeneous element with a 50% cumulative volume particle size D50 of 0.32 μm, were added to an aqueous solvent in an amount of 0.3 mol%. This mixture was then mixed mechanically (wet mixing) to prepare a slurry, and the slurry was then dried while standing to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed in a Henschel mixer (dry mixing) to form a lithium mixture. Next, the lithium mixture obtained as described above was calcined at 710°C for 12 hours in an oxygen atmosphere to produce positive electrode active material particles. Next, a coating layer was formed on the positive electrode active material particles using the following procedure. First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water was prepared as a coating solution, with Li content and Nb content of 0.15 mol / L, respectively. Next, using this coating solution, the surface of the prepared positive electrode active material particles was coated with an oxide precursor containing Li and Nb using a rolling fluidized bed coating apparatus, and heat treatment was performed at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer on its surface.

[0079] (Comparative Example 3) First, the composition formula: Ni 0.82 Co 0.15 Mn 0.03A precursor for the positive electrode active material for lithium-ion batteries, represented by (OH)2, was prepared. Next, the precursor for the positive electrode active material for lithium-ion batteries, having a 50% cumulative volume particle size D50 of 5.6 μm, and Ta2O5, a heterogeneous element with a 50% cumulative volume particle size D50 of 0.30 μm, were added to an aqueous solvent in an amount of 0.5 mol%. These were mixed by mechanical means (wet mixing) to prepare a slurry, and then the slurry was allowed to stand and dried to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed in a Henschel mixer (dry mixing) to form a lithium mixture. Next, the lithium mixture obtained as described above was calcined at 710°C for 12 hours in an oxygen atmosphere to produce positive electrode active material particles. Next, a coating layer was formed on the positive electrode active material particles according to the following procedure. First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water was prepared as a coating solution, with Li content and Nb content of 0.15 mol / L, respectively. Next, using this coating solution, the surface of the prepared positive electrode active material particles was coated with an oxide precursor containing Li and Nb using a rolling fluidized bed coating apparatus, and heat treatment was performed at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer on its surface.

[0080] (Comparative Example 4) First, the composition formula: Ni 0.82 Co 0.15 Mn 0.03A precursor for the positive electrode active material for lithium-ion batteries, represented by (OH)2, was prepared. Next, the precursor for the positive electrode active material for lithium-ion batteries, having a 50% cumulative volume particle size D50 of 5.6 μm, and Ta2O5, a heterogeneous element with a 50% cumulative volume particle size D50 of 0.31 μm, were added to an aqueous solvent in an amount of 0.4 mol%. These were mixed mechanically (wet mixing) to prepare a slurry, and then the slurry was allowed to stand and dried to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed in a Henschel mixer (dry mixing) to form a lithium mixture. Next, the lithium mixture obtained as described above was calcined at 720°C for 12 hours in an oxygen atmosphere to produce positive electrode active material particles. Next, a coating layer was formed on the positive electrode active material particles according to the following procedure. First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water was prepared as a coating solution, with Li content and Nb content of 0.15 mol / L, respectively. Next, using this coating solution, the surface of the prepared positive electrode active material particles was coated with an oxide precursor containing Li and Nb using a rolling fluidized bed coating apparatus, and heat treatment was performed at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer on its surface. The above manufacturing conditions are shown in Table 1.

[0081] <Composition of Cathode Active Materials for All-Solid-State Lithium-Ion Batteries> 0.2 g of each sample (powder) of the obtained cathode active material for all-solid-state lithium-ion batteries was weighed out, decomposed by alkaline fusion, and then compositional analysis was performed using Hitachi High-Tech Corporation's ICP (Inductively Coupled Plasma) Atomic Emission Spectrometer (ICP-OES) "PS7800". The oxygen content was determined by subtracting the impurity concentration and residual alkali amount, in addition to the analytical values ​​of Li and metal components, from the total amount of the analytical sample, and thus the "O" in equation (1) was determined. f The value of f was calculated. The evaluation results are shown in Table 2.

[0082] <TEM-EDX Analysis> For each sample (powder) of positive electrode active material for all-solid-state lithium-ion batteries obtained, the average concentration of element Ta in the interior of primary particles and at grain boundaries was measured and calculated as follows. First, as a sample pretreatment, the sample particles were processed using a focused ion beam (FIB) to expose the cross-section of secondary particles. Next, using an atomic resolution analytical electron microscope (JEM-ARM300F2) manufactured by JEOL Ltd., electron beam irradiation was performed at five arbitrary points each in the interior of primary particles and at grain boundaries, observed in a 100,000x field of view, under the conditions of an acceleration voltage of 300 kV and an irradiation current of 1.0 nA. Energy-dispersive X-ray spectroscopy (EDX) analysis was performed, and the concentration of each element was determined from the count number of characteristic X-rays generated at each energy for the active material components Ni, Mn, Co, and Ta. Here, for the "interior of primary particles" mentioned above, measurements were taken at the central part of the primary particle, at a distance of 20 nm or more from the nearest "grain boundary". The average of the Ta concentrations at five points inside the primary particle and at the grain boundaries, with the sum of the elemental concentrations of Ni, Mn, Co, and Ta calculated in this manner set to 100, was defined as the average Ta concentration inside the primary particle and the average Ta concentration at the grain boundaries of the primary particle. Furthermore, in the measurement of the Ta concentration at five points inside the primary particle and at the grain boundaries using TEM-EDX as described above, if the Ta concentration fell below the detection limit, the average of the concentrations at the remaining measurement points (four or three points) after excluding the data below the detection limit was defined as the average Ta concentration inside the primary particle and the average Ta concentration at the grain boundaries of the primary particle. Specifically, for the primary particle interior in Example 1 and the primary particle interior and grain boundaries in Example 2, the average of the Ta concentrations at four points was used, while for the grain boundaries and primary particle interior in Comparative Example 1, the average of the Ta concentrations at three points was used. The coefficient of variation CV1, obtained by dividing the standard deviation of the average concentration of Ta elements inside the primary particles obtained by the TEM-EDX analysis by the average concentration of Ta elements inside the primary particles, and the coefficient of variation CV2, obtained by dividing the standard deviation of the average concentration of Ta elements at the grain boundaries of the primary particles obtained by the TEM-EDX analysis by the average concentration of Ta elements at the grain boundaries of the primary particles, were calculated, and the magnitudes of CV1 and CV2 were compared. In addition, the magnitudes of the average concentration of Ta elements at the grain boundaries obtained by the TEM-EDX analysis and the concentration of Ta elements in the positive electrode active material for lithium-ion batteries analyzed by the ICP described above were compared.The evaluation results are shown in Table 3. In Table 3, "○" indicates that CV2 > CV1 is satisfied, and "×" indicates that it is not satisfied. Also in Table 3, "○" indicates that the average concentration of Ta elements at grain boundaries obtained from TEM-EDX analysis is greater than the concentration of Ta elements in the lithium-ion battery positive electrode active material analyzed by ICP as described above, i.e., "TEM-EDX grain boundary Ta average concentration" > "ICP Ta composition analysis concentration" is satisfied, and "×" indicates that it is not satisfied.

[0083] Figure 2 is a TEM image showing the measurement locations of the Ta element concentration inside primary particles by TEM-EDX analysis of the positive electrode active material according to Example 1. In Figure 2, it can be seen that the five measurement locations are set inside the primary particles. Figure 3 is a TEM image showing the measurement locations of the Ta element concentration at the grain boundaries of primary particles by TEM-EDX analysis of the positive electrode active material according to Example 1. In Figure 3, it can be seen that the five measurement locations are set at the grain boundaries of primary particles.

[0084] (Battery Characteristics) <Method for Manufacturing All-Solid-State Lithium-Ion Batteries> The positive electrode active material for all-solid-state lithium-ion batteries obtained in Examples 1 to 10 and Comparative Examples 1 to 4, sulfide-based solid electrolyte (75Li2S-25P2S5), acetylene black, and binder were mixed in this order in a mass ratio of 60:35:5:1.5. Anisole was added as a solvent so that the solid content of the slurry was 65% by mass, and the mixture was mixed in a Mazelstar for 400 seconds to obtain a positive electrode mixture slurry, which was then coated onto the surface of a 0.03 mm thick aluminum foil, which served as the positive electrode current collector. At this time, the positive electrode mixture slurry was coated onto the surface of the positive electrode current collector by using an applicator with a gap of 400 μm and moving the applicator at a moving speed of 15 mm / s. Next, a positive electrode composite slurry was coated onto the surface of a positive electrode current collector, and the solvent was removed by drying the current collector on a hot plate at 100°C for 30 minutes to form a positive electrode composite layer on the surface of the current collector. Next, the aforementioned positive electrode composite layer was placed on top of a sulfide-based solid electrolyte of the same composition as the sulfide-based solid electrolyte used in the preparation of the positive electrode composite layer, and pressed at 333 MPa to create a laminate of solid electrolyte layer / positive electrode composite layer / positive electrode current collector. Next, a metallic Li-In alloy was pressed onto the negative electrode side of the solid electrolyte layer at 37 MPa to form the negative electrode layer. The laminate thus prepared was placed in a SUS304 battery test cell and confined under pressure to create an all-solid-state secondary battery. The all-solid-state secondary battery with confined pressure was then placed in a sealed container to block out air.

[0085] <Evaluation of Initial Discharge Capacity> The discharge capacity of the all-solid-state lithium-ion battery was evaluated by measuring the impedance and resistance after the initial charge at 0.1C at 55°C, and then discharging at 0.1C. The evaluation results are shown in Table 3.

[0086] <Evaluation of Rate Characteristics> The rate characteristics (%) of the all-solid-state lithium-ion battery were evaluated by first measuring the initial capacity obtained at a discharge rate of 0.1C (55°C, upper charge voltage limit: 3.7V, lower discharge voltage limit: 2.5V vs Li-In), and then measuring the high-rate capacity obtained at a discharge rate of 0.5C (55°C, upper charge voltage limit: 3.7V, lower discharge voltage limit: 2.5V vs Li-In). The ratio of (high-rate capacity) / (initial capacity) was expressed as a percentage. The evaluation results are shown in Table 3.

[0087]

[0088]

[0089]

[0090] (Evaluation Results) According to the above test results, Examples 1 to 10 are all positive electrode active materials for lithium-ion batteries represented by the composition shown in the following formula (1), Li a Ni b Co c Mn d Ta e O f (1) (In formula (1) above, 1.0 ≤ a ≤ 1.07, 0.8 ≤ b ≤ 0.9, b + c + d + e = 1, 1.8 ≤ f ≤ 2.2, and 0.001 ≤ e / (b + c + d + e) ​​≤ 0.005.) The coefficient of variation CV1, which is the value obtained by dividing the standard deviation of the average concentration of Ta elements inside the primary particles obtained by TEM-EDX analysis by the average concentration of Ta elements, and the coefficient of variation CV2, which is the value obtained by dividing the standard deviation of the average concentration of Ta elements at the grain boundaries of the primary particles obtained by TEM-EDX analysis by the average concentration of Ta elements at the grain boundaries of the primary particles, satisfy the condition CV2 > CV1, and the average concentration of Ta elements at the grain boundaries obtained by TEM-EDX analysis was higher than the concentration of Ta elements in the positive electrode active material for lithium-ion batteries analyzed by ICP. For this reason, the battery characteristics were good in all of Examples 1 to 10.

[0091] Comparative Examples 1 to 4 all failed to satisfy the condition CV2 > CV1, and therefore their battery characteristics were inferior to those of Examples 1 to 10.

[0092] According to one embodiment of the present invention, it is possible to provide a positive electrode active material for lithium-ion batteries having good battery characteristics, a positive electrode for lithium-ion batteries using the same, a lithium-ion battery, and a method for manufacturing the positive electrode active material for lithium-ion batteries, a positive electrode active material for all-solid-state lithium-ion batteries having good battery characteristics, a positive electrode for all-solid-state lithium-ion batteries using the same, an all-solid-state lithium-ion battery, and a method for manufacturing the positive electrode active material for all-solid-state lithium-ion batteries. This could lead to the widespread use of non-fossil energy, reduce the use of fossil energy such as oil and gas which currently account for a large portion of energy production, and potentially contribute to mitigating global warming. Furthermore, since the main materials used are substances with low environmental impact such as lithium, carbon, manganese, nickel, and cobalt, and harmful substances such as cadmium, lead, and mercury are not used, it is possible to reduce the environmental impact. Therefore, one embodiment of the present invention has the potential to contribute to the United Nations-led Sustainable Development Goals (SDGs), specifically Goal 7, "Ensure access to affordable, reliable, sustainable, and modern energy for all," Goal 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation," and Goal 12, "Ensure sustainable consumption and production patterns."

Claims

1. A positive electrode active material for lithium-ion batteries represented by the composition shown in the following formula (1), Li a Ni b Co c Mn d Ta e O f (1) (In formula (1) above, 1.0 ≤ a ≤ 1.07, 0.8 ≤ b ≤ 0.9, b + c + d + e = 1, 1.8 ≤ f ≤ 2.2, and 0.001 ≤ e / (b + c + d + e) ​​≤ 0.005.) The coefficient of variation CV1 is the value obtained by dividing the standard deviation of the average concentration of Ta elements inside primary particles obtained by transmission electron microscopy (TEM)-energy dispersive X-ray spectroscopy (EDX) analysis by the average concentration of Ta elements, and the coefficient of variation CV2 is the value obtained by dividing the standard deviation of the average concentration of Ta elements at the grain boundaries of primary particles obtained by the TEM-EDX analysis by the average concentration of Ta elements at the grain boundaries of primary particles, wherein CV2 > CV1, and the average concentration of Ta elements at the grain boundaries obtained by the TEM-EDX analysis is higher than the concentration of Ta elements in the lithium-ion battery positive electrode active material analyzed by ICP.

2. The positive electrode active material for a lithium-ion battery according to claim 1, wherein the 50% cumulative volume particle size D50 is 5 to 8 μm.

3. A positive electrode for a lithium-ion battery comprising the positive electrode active material for a lithium-ion battery described in claim 1 or 2.

4. A lithium-ion battery comprising a positive electrode and a negative electrode for a lithium-ion battery as described in claim 3.

5. A positive electrode active material for a lithium-ion battery, comprising: a positive electrode active material for a lithium-ion battery according to claim 1 or 2; and a coating layer made of an oxide of Li and Nb provided on the surface of the positive electrode active material particles of the positive electrode active material for a lithium-ion battery.

6. The positive electrode active material for a lithium-ion battery according to claim 5, wherein the Nb content in the positive electrode active material for a lithium-ion battery is 0.5 to 0.8% by mass.

7. A positive electrode for an all-solid-state lithium-ion battery, comprising the positive electrode active material for an all-solid-state lithium-ion battery described in claim 6.

8. An all-solid-state lithium-ion battery comprising a positive electrode and a negative electrode for an all-solid-state lithium-ion battery as described in claim 7.

9. A step of preparing a precursor of a positive electrode active material for a lithium ion battery represented by the composition shown in the following formula (2), Ni b Co c Mn d (OH)2 (2) (In the formula (2), 0.8 ≦ b ≦ 0.9, 0.07 ≦ c ≦ 0.15, and b + c + d = 1.) A step of mixing an oxide of Ta having a 50% cumulative volume particle size D50 of 1.0 μm or less with the precursor of the positive electrode active material for the lithium ion battery to obtain a mixture, and a step of dry-mixing the mixture with a lithium source and firing at 700° C. or higher for 4 hours or longer. A method for producing a positive electrode active material for a lithium ion battery.

10. The method for producing a positive electrode active material for a lithium-ion battery according to claim 9, wherein the oxide of Ta has a D50 of 0.3 to 1.0 μm.

11. The method for producing a positive electrode active material for a lithium-ion battery according to claim 9, wherein in the step of firing the mixture, the mixture is dry-mixed with a lithium source and fired at 700 to 800°C for 4 to 12 hours.

12. A method for producing a positive electrode active material for an all-solid-state lithium-ion battery, comprising the steps of: preparing a positive electrode active material for a lithium-ion battery produced by the method described in any one of claims 9 to 11; and forming a coating layer on the surface of the positive electrode active material particles of the positive electrode active material for a lithium-ion battery using an aqueous solution containing Li and Nb, with a rolling fluidized bed coating apparatus.

13. The method for producing a positive electrode active material for an all-solid-state lithium-ion battery according to claim 12, wherein the aqueous solution containing Li and Nb is an aqueous solution containing (1) one of lithium hydroxide monohydrate, lithium carbonate, and lithium nitrate as a lithium source, (2) one of niobium hydroxide, niobium oxalate, and niobium ammonium oxalate as a niobium source, and (3) one of pure water, hydrogen peroxide solution, and ammonia solution.

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