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

Abstract

This positive electrode active material for a lithium-ion battery is represented by a composition indicated in formula (1): LiaNibCocMndMeOf (In formula (1), the following relationships hold: 1.0 ≤ a ≤ 1.07, 0.58 ≤ b ≤ 0.62, b + c + d + e = 1, 1.8 ≤ f ≤ 2.2, 0.0035 ≤ e / (b + c + d + e) ≤ 0.0055, where M is at least one element selected from Zr, Ta, and W.)　In the positive electrode active material for a lithium-ion battery, the value when the difference between a particle intensity maximum value (A) and a particle intensity minimum value (B) is divided by the average value (M) of the particle intensity: {((A)-(B)) / (M)} is 0.42 or less, the crystallite size of the (003) plane is 650 Å or less, and the 50% cumulative volume particle size D50 is 5-7 µm.

Description

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

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

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as their power sources has become important. Among these batteries, lithium-ion secondary batteries have attracted attention from the viewpoint of their high energy density. In addition to liquid-type lithium-ion secondary batteries that use an electrolyte solution, lithium-ion secondary batteries also include all-solid-state lithium-ion batteries that use a solid electrolyte, which have been attracting attention in recent years.

[0003] In the 1990s and 2000s, the most commonly used cathode active material for lithium-ion secondary batteries was LiCoO2. However, to address issues such as increased power consumption due to the increasing functionality of electronic devices and longer driving ranges due to the rise of electric vehicles (EVs), cathode active materials with a Ni ratio of 50% or more, such as NCM523 and NCM622, have been used since the 2010s. These cathode active materials offer an excellent balance of output and durability, but for use in automotive applications, even higher output and durability are required. To overcome the challenge of achieving high durability, methods have been used to surface-modify or dope cathode active materials with elements with high oxygen affinity, such as Zr, W, Nb, and Ta.

[0004] Patent Document 1 discloses a positive electrode active material that is a lithium-nickel-cobalt-manganese composite oxide containing tungsten and niobium, and states that such a configuration makes it possible to provide a positive electrode active material that has excellent output characteristics and generates little gas, and a battery using the same.

[0005] Patent Document 2 discloses a method for producing a lithium-containing composite oxide, characterized in that when a transition metal hydroxide containing Ni and Mn as essential components is mixed with a lithium source and calcined to produce a lithium-containing composite oxide, a transition metal hydroxide having a crystallite diameter of 35 nm or less in the (100) plane in a crystal structure model of space group P-3m1 in an X-ray diffraction pattern is used. It also describes that such a configuration can provide a method for producing a lithium-containing composite oxide that can improve the performance of a lithium ion secondary battery, such as cycle characteristics and rate characteristics.

[0006] JP 2009-140787 A JP 2016-44120 A

[0007] To enhance crystallinity, cathode active materials such as NCM523 and NCM622 require a higher sintering temperature than high-nickel cathode active materials such as NCM811. As a result, the primary particles of the sintered active material may become larger, potentially resulting in reduced particle strength. Furthermore, particularly for low-strength particles, coating with Li composite oxide, essential for cathode active materials for all-solid-state lithium-ion batteries, using a powder-fluidized coating device, such as a tumbling fluidized bed coating device, can result in cracking of the particles during coating. For this reason, the inventors of this disclosure have previously investigated the particle strength of cathode active materials. However, large variations in particle strength of the manufactured cathode active materials can result in variations in capacity retention and potentially degraded battery characteristics.

[0008] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a cathode active material for a lithium ion battery having good battery characteristics, a lithium ion battery cathode using the same, a lithium ion battery, and a method for manufacturing the cathode active material for a lithium ion battery. Another object of the present invention is to provide a cathode active material for an all-solid-state lithium ion battery having good battery characteristics, a cathode for an all-solid-state lithium ion battery using the same, an all-solid-state lithium ion battery, and a method for manufacturing the cathode active material for an all-solid-state lithium ion battery.

[0009] The present invention, which was 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), wherein Li a Ni b Co c Mn d M e O f (1) (In the formula (1), 1.0≦a≦1.07, 0.58≦b≦0.62, b+c+d+e=1, 1.8≦f≦2.2, 0.0035≦e / (b+c+d+e)≦0.0055, and M is at least one element selected from Zr, Ta, and W.) A positive electrode active material for a lithium ion battery, in which the value obtained by dividing the difference between the maximum particle strength (A) and the minimum particle strength (B) by the average particle strength (M): {((A)−(B)) / (M)} is 0.42 or less. 2. The positive electrode active material for a lithium ion battery according to 1 above, in which the crystallite size of the (003) plane is 650 Å or less. 3. The positive electrode active material for a lithium ion battery according to 1 or 2 above, in which the 50% cumulative volume particle size D50 is 5 to 7 μm. 4. A positive electrode for a lithium ion battery, comprising the positive electrode active material for a lithium ion battery according to any one of paragraphs 1 to 3. 5. A lithium ion battery, comprising the positive electrode and negative electrode for a lithium ion battery according to paragraph 4. 6. A positive electrode active material for a lithium ion battery represented by the composition shown in formula (1) below, and Li a Ni b Co c Mn d M e O f(1) (in formula (1), 1.0≦a≦1.07, 0.58≦b≦0.62, b+c+d+e=1, 1.8≦f≦2.2, 0.0035≦e / (b+c+d+e)≦0.0055, and M is at least one selected from Zr, Ta, and W), and a coating layer made of an oxide of Li and Nb provided on the surface of the cathode active material particles of the cathode active material for a lithium ion battery, wherein the value obtained by dividing the difference between the maximum particle strength (A) and the minimum particle strength (B) by the average particle strength (M): {((A)−(B)) / (M)} is 0.42 or less. 7. The cathode active material for an all-solid-state lithium ion battery according to 6 above, wherein the circularity of the particles is 0.94 to 0.96. 8. Specific surface area is 0.6m 2 / g or less. 9. The cathode active material for an all-solid-state lithium ion battery according to any one of 6 to 8 above, wherein the crystallite size of the (003) plane is 650 Å or less. 10. A cathode for an all-solid-state lithium ion battery, comprising the cathode active material for an all-solid-state lithium ion battery according to any one of 6 to 9 above. 11. An all-solid-state lithium ion battery, comprising the cathode and anode for an all-solid-state lithium ion battery according to 10 above. 12. A process for preparing a precursor of a cathode active material for a lithium ion battery, the precursor being represented by the composition shown in the following formula (2): b Co c Mn d(OH)2 (2) (in formula (2), 0.58≦b≦0.62, 0.18≦c≦0.22, and b+c+d=1). The method for producing a lithium ion battery positive electrode active material according to any one of items 1 to 3, comprising: wet-mixing at least one oxide selected from Zr oxide, Ta oxide, and W oxide, each oxide having a 50% cumulative volume particle size D50 of 1 μm or less, with a precursor of the lithium ion battery positive electrode active material to obtain a mixture; and dry-mixing the mixture with a lithium source, and firing the mixture at 820° C. or higher for 4 hours or more. 13. The method for producing a lithium ion battery positive electrode active material according to item 12, wherein the Zr oxide, Ta oxide, and W oxide have a D50 of 0.3 to 1.0 μm. 14. 14. A method for producing a cathode active material for a lithium ion battery according to 12 or 13 above, wherein in the step of firing the mixture, the mixture is dry-mixed with a lithium source and fired at 820 to 860° C. for 6 to 12 hours. 15. A method for producing a cathode active material for an all-solid-state lithium ion battery, comprising the steps of: preparing a cathode active material for a lithium ion battery produced by the method according to any one of 12 to 14 above; and forming a coating layer made of an oxide of Li and Nb on surfaces of cathode active material particles of the cathode active material for a lithium ion battery using an aqueous solution containing Li and Nb by a tumbling fluidized bed coating apparatus. 16. 16. The method for producing a positive electrode active material for an all-solid-state lithium-ion battery according to 15 above, wherein the aqueous solution containing Li and Nb is an aqueous solution containing: (1) any one of lithium hydroxide monohydrate, lithium carbonate, and lithium nitrate as a lithium source; (2) any one of niobium hydroxide, niobium oxalate, and ammonium niobium oxalate as a niobium source; and (3) any one of pure water, hydrogen peroxide water, and ammonia water.

[0010] The present invention can 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 the positive electrode active material for a lithium ion battery. It can also 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 the positive electrode active material for an all-solid-state lithium ion battery.

[0011] FIG. 1 is a schematic diagram of an all-solid-state lithium-ion battery according to an embodiment of the present invention.

[0012] Next, embodiments of the present invention will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes and improvements may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0013] (Positive electrode active material for lithium ion battery) In the present invention, when simply referring to a "positive electrode active material for lithium ion battery", it includes both a liquid-based positive electrode active material for lithium ion battery using an electrolyte solution and a positive electrode active material for all-solid-state lithium ion battery in which the electrolyte is solid. The positive electrode active material for lithium ion battery according to the embodiment of the present invention is represented by the composition shown in the following formula (1). Li a Ni b Co c Mn d M e O f (1) (In the formula (1), 1.0≦a≦1.07, 0.58≦b≦0.62, b+c+d+e=1, 1.8≦f≦2.2, 0.0035≦e / (b+c+d+e)≦0.0055, and M is at least one selected from Zr, Ta, and W.)

[0014] In the positive electrode active material for a lithium ion battery according to an embodiment of the present invention, in the above formula (1), a, which indicates the lithium composition, is controlled to be 1.0≦a≦1.07. Because a, which indicates the lithium composition, is 1.0 or more, reduction of nickel due to lithium deficiency can be suppressed. Furthermore, because a, which indicates the lithium composition, is 1.07 or less, residual alkaline components, such as lithium carbonate and lithium hydroxide, present on the surface of the positive electrode active material particles, which may become resistance components when the battery is formed, can be suppressed.

[0015] In the positive electrode active material for a lithium-ion battery according to an embodiment of the present invention, the sum of b, which represents a nickel composition, c, which represents a cobalt composition, d, which represents a manganese composition, and e, which represents a composition of at least one element selected from Zr, Ta, and W, in the above formula (1) is controlled to satisfy b+c+d+e=1, i.e., 0.38≦c+d+e≦0.42, thereby improving cycle characteristics and reducing the expansion and contraction behavior of the crystal lattice due to the insertion and extraction of lithium during charge and discharge. When c+d+e is 0.38 or more, the effects of the above cycle characteristics and expansion and contraction behavior are easily obtained, and when c+d+e is 0.42 or less, the decrease in initial discharge capacity is suppressed.

[0016] The positive electrode active material for a lithium ion battery according to the embodiment of the present invention may be in the form of secondary particles formed by agglomeration of a plurality of primary particles, with some primary particles not agglomerated as secondary particles. The shapes of the primary particles constituting the secondary particles and the primary particles present alone are not particularly limited, and may be various shapes, such as substantially spherical, substantially elliptical, substantially plate-like, or substantially needle-like. The form in which the plurality of primary particles are agglomerated is also not particularly limited, and may be various forms, such as agglomeration in random directions or agglomeration approximately uniformly radially from the center to form substantially spherical or substantially elliptical secondary particles.

[0017] In the positive electrode active material for a lithium ion battery according to an embodiment of the present invention, in the above formula (1), 0.0035≦e / (b+c+d+e)≦0.0055, and M is at least one element selected from Zr, Ta, and W. That is, the positive electrode active material for a lithium ion battery contains at least one element selected from Zr, Ta, and W. This element, when solid-dissolved within the positive electrode active material, has the effect of reducing the expansion and contraction behavior of the crystal lattice due to lithium insertion and extraction during charge and discharge. Therefore, when the composition ratio of this element, e / (b+c+d+e), is 0.0035 or more, cycle characteristics are improved. On the other hand, this element does not contribute to charge compensation during charge and discharge. Therefore, when the composition ratio of this element, e / (b+c+d+e), is 0.0055 or less, the effect of suppressing a decrease in discharge capacity is achieved. Preferably, 0.004≦e / (b+c+d+e)≦0.005.

[0018] In the positive electrode active material for lithium ion batteries according to an embodiment of the present invention, the difference between the maximum particle strength (A) and the minimum particle strength (B) divided by the average particle strength (M) is {((A)-(B)) / (M)}, which is 0.42 or less. This configuration reduces cracking of the positive electrode active material due to pressing during electrode fabrication, thereby reducing the difference between the maximum and minimum 20-cycle capacity retention rates of the lithium ion battery to 1.0% or less, stabilizing the capacity retention rate of the lithium ion battery and improving battery characteristics. The above {((A)-(B)) / (M)}, which relates to the particle strength of the positive electrode active material for lithium ion batteries according to an embodiment of the present invention, is preferably 0.40 or less, more preferably 0.35 or less, and even more preferably 0.30 or less.

[0019] The positive electrode active material for a lithium ion battery according to an embodiment of the present invention preferably has an average particle strength (M) of 100 MPa or more. When the positive electrode active material for a lithium ion battery according to an embodiment of the present invention has such a high particle strength, particle cracking is suppressed in the lithium ion conductive oxide coating step during the production of the positive electrode active material for an all-solid-state lithium ion battery, and the battery characteristics, such as output characteristics, and durability of the all-solid-state lithium ion battery are improved. The average particle strength (M) is more preferably 110 MPa or more, and even more preferably 120 MPa or more.

[0020] The particle strength of the positive electrode active material for lithium-ion batteries can be measured using a microcompression tester (MCT-211) manufactured by Shimadzu Corporation as follows. That is, the dispersed powder sample is placed on a sample stage, and a microscope is used to aim at the center of a single secondary particle with an average particle diameter of D50. A 20 μm diameter indenter is pressed at a loading rate of 0.532 mN / sec, and the strength at break is measured. In measuring particle strength, a load is applied to the sample using the MCT-211, and a curve is drawn with the load on the vertical axis and the displacement on the horizontal axis. When "breakage" occurs, a horizontal line is drawn on the curve at a constant load on the horizontal axis, and the starting point of this horizontal line is determined by the software built into the MCT-211 as the "strength at breakage." Furthermore, when measured in this manner, the "maximum particle strength (A)," "minimum particle strength (B)," and "average particle strength (M)" of the positive electrode active material for a lithium ion battery according to the embodiment of the present invention respectively mean the maximum, minimum, and average values ​​among the above particle strength measurements carried out with N=11 to 14.

[0021] The positive electrode active material for a lithium ion battery according to an embodiment of the present invention preferably has a crystallite size of 650 Å or less in the (003) plane. When the crystallite size of the (003) plane is 650 Å or less, the positive electrode active material has fine primary particles, which reduces the volume expansion and contraction rate when lithium ions are inserted and extracted from the positive electrode active material during charge and discharge. This reduces cracking due to strain accumulation at the primary particle interface, resulting in improved cycle characteristics. The crystallite size of the (003) plane is more preferably 600 Å or less, and even more preferably 550 Å or less.

[0022] The crystallite size of the (003) plane of the positive electrode active material for lithium-ion batteries was measured using an X-ray diffractometer manufactured by Rigaku Corporation: Smart-Lab, with a CuKα X-ray source, a tube voltage of 40 kV, a tube current of 30 mA, and a scan speed of 7.5 degrees / min in the range of 2θ = 10 ° to 80 °, a step width of 0.01 degrees, a slit width of 1 / 4 ° on the incident side, and a slit width of 10 mm on the receiving side. Using the XRD analysis software PDXL2, the (003) plane diffraction peak near 2θ = 18.7 ° can be determined, and this can be used as the crystallite size.

[0023] The 50% cumulative volume particle size D50 of the lithium-ion battery positive electrode active material according to the embodiment of the present invention is preferably 5 to 7 μm. Here, the 50% cumulative volume particle size D50 is the volume particle size at 50% accumulation in a volume-based cumulative particle size distribution curve. When the 50% cumulative volume particle size D50 of the lithium-ion battery positive electrode active material is 5 μm or more, the specific surface area can be reduced, and the amount of Li and Nb oxide coating can be reduced. When the 50% cumulative volume particle size D50 of the lithium-ion battery positive electrode active material is 7 μm or less, an excessive decrease in the specific surface area can be prevented. The 50% cumulative volume particle size D50 of the lithium-ion battery positive electrode active material is more preferably 5 to 6 μm. The 50% cumulative volume particle size D50 can be measured, for example, as follows. That is, first, 100 mg of the positive electrode active material powder was dispersed using a Microtrac laser diffraction particle size distribution analyzer "MT3300EXII" at a 50% flow rate by irradiating it with 40 W ultrasonic waves for 60 seconds, and then the particle size distribution was 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 was taken as the 50% cumulative volume particle size D50 of the positive electrode active material powder. Note that the aqueous solvent used in the measurement was passed through a filter, the solvent refractive index was 1.333, the particle permeability conditions were transmission, the particle refractive index was 1.81, the shape was aspherical, the measurement range was 0.021 to 2000 μm, and the measurement time was 30 seconds.

[0024] (Positive electrode active material for all-solid-state lithium-ion battery) The positive electrode active material for all-solid-state lithium-ion battery 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 may be LiNbO3.

[0025] The positive electrode active material for a lithium ion battery of the all-solid-state lithium ion battery according to the 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. a Ni b Co c Mn d M e O f (1) (In the formula (1), 1.0≦a≦1.07, 0.58≦b≦0.62, b+c+d+e=1, 1.8≦f≦2.2, 0.0035≦e / (b+c+d+e)≦0.0055, and M is at least one selected from Zr, Ta, and W.)

[0026] In the cathode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention, the difference between the maximum particle strength (A) and the minimum particle strength (B) divided by the average particle strength (M) ({(A)-(B)) / (M)}) is 0.42 or less. This configuration reduces cracking of the cathode active material due to pressing during electrode fabrication. Cracked portions may impede the movement of Li ions during charge and discharge. Therefore, by suppressing cracking of the cathode active material, the difference between the maximum and minimum 20-cycle capacity retention rates of the all-solid-state lithium-ion battery is reduced to 1.0% or less, thereby stabilizing the capacity retention rate of the all-solid-state lithium-ion battery and improving battery characteristics. The above {(A)-(B)) / (M)} ratio for the particle strength of the cathode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention is preferably 0.40 or less, more preferably 0.35 or less, and even more preferably 0.30 or less.

[0027] The positive electrode active material for an all-solid-state lithium-ion battery according to the embodiment of the present invention preferably has an average particle strength (M) of 100 MPa or more, more preferably 110 MPa or more, and even more preferably 120 MPa or more.

[0028] In the positive electrode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention, the crystallite size of the (003) plane is preferably 650 Å or less. When the crystallite size of the (003) plane is 650 Å or less, the positive electrode active material has fine primary particles, which reduces the volume expansion and contraction rate when lithium ions are inserted and extracted from the positive electrode active material during charge and discharge. This reduces cracking due to strain accumulation at the primary particle interface, resulting in improved cycle characteristics. The crystallite size of the (003) plane is more preferably 600 Å or less, and even more preferably 550 Å or less.

[0029] The positive electrode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention preferably has a particle circularity of 0.94 to 0.96. Circularity is an index that indicates how close a particle shape is to a sphere; for example, the circularity of a truly spherical particle is 1.00, which is the upper limit. When the circularity of the positive electrode active material is 0.94 or more, the contact area between the solid electrolyte and the positive electrode active material increases, improving the conductivity of Li ions between the positive electrode active material and the solid electrolyte. This makes it possible to fabricate a high-capacity all-solid-state lithium-ion battery. The circularity is more preferably 0.95 to 0.96.

[0030] The circularity of the positive electrode active material can be measured using a particle image analyzer, Morphologi G3, manufactured by Malvern. Specifically, the particle image analyzer measures the circularity by filtering optical images of more than 20,000 particles using a parameter of "solidity = 0.93." The particle image analyzer first loads the sample (positive electrode active material) into a sample cartridge and then sets it in the dispersion unit. A nitrogen gas inlet line is connected to the dispersion unit, and the sample is dispersed onto a glass plate by spraying nitrogen gas. Particle images of the dispersed sample on the glass plate are continuously captured and analyzed. The circularity is then calculated using the following formula 1 from the projected area and perimeter of each of the captured particles (more than 18,000 particles). The average circularity refers to the average circularity of all measured positive electrode active material particles.

[0031] Circularity = 4πS / L 2 ... (Equation 1) (In the above equation, S is the projected area of ​​the particle, L is the perimeter of the projected image of the particle, and π is the ratio of the circumference of the particle to its circumference.)

[0032] The specific surface area of ​​the positive electrode active material for all-solid-state lithium-ion batteries is 0.6 m 2 / g or less. 2 / g or less indicates that the coating layer is in a densified state, and the generation of a high resistance layer due to a reaction with the solid electrolyte is suppressed, resulting in the effects of improving the output characteristics and the cycle characteristics. 2 / g is more preferred.

[0033] The specific surface area of ​​the positive electrode active material for an all-solid-state lithium-ion battery can be measured by the following method. That is, first, 1.0 g of the positive electrode active material (powder) is weighed into a glass cell, set in a degassing device, and the glass cell is filled with nitrogen gas. After that, the cell is heat-treated in a nitrogen gas atmosphere at 40°C for 20 minutes to degas the sample. Thereafter, the glass cell containing the degassed sample (powder) is set in a specific surface area measuring device (Monosorb Model MS-21) manufactured by Quantachrome, and the specific surface area X is measured by the BET method (single-point method) while flowing a He:70 at%-N2:30 at% mixed gas as the adsorption gas.

[0034] The Nb content in the positive electrode active material for an all-solid-state lithium-ion battery is preferably 0.5 to 0.8% by mass. When the Nb content is 0.5% by mass or more, the entire surface of the active material is coated with Nb, suppressing an increase in resistance due to an 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 thin as possible, shortening the movement of Li ions within the coating layer during charge and discharge, thereby reducing diffusion resistance. The Nb content in the positive electrode active material for an all-solid-state lithium-ion battery is more preferably 0.6 to 0.7% by mass.

[0035] The thickness of the coating layer is preferably 10 nm or less, more preferably 6 nm or less. When the thickness of the coating layer is 6 nm or less, adverse effects such as inhibition of Li ion migration can be better avoided. The lower limit of the thickness of the coating layer is not particularly limited, but is typically 4 nm or more, 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).

[0036] (Method for producing a positive electrode active material for a lithium ion battery) Next, a method for producing a positive electrode active material for a lithium ion battery according to an embodiment of the present invention will be described in detail. In the method for producing a positive electrode active material for a lithium ion battery according to an embodiment of the present invention, first, a precursor of a positive electrode active material for a lithium ion battery represented by the composition shown in the following formula (2) is prepared. Ni b Co c Mn d(OH)2 (2) (wherein, in the formula (2), 0.58≦b≦0.62, 0.18≦c≦0.22, and b+c+d=1.)

[0037] A method for producing a precursor of a positive electrode active material for a lithium-ion battery first involves preparing 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. (a) Examples of the nickel salt include nickel sulfate, nickel nitrate, or nickel chloride. (b) Examples of the cobalt salt include cobalt sulfate, cobalt nitrate, or cobalt chloride. (c) Examples of the manganese salt include manganese sulfate, manganese nitrate, or manganese chloride. (d) Examples of the basic aqueous solution containing ammonia include aqueous solutions of ammonia, ammonium sulfate, ammonium carbonate, or ammonium chloride. The basic aqueous solution of an alkali metal may be an aqueous solution of sodium hydroxide, potassium hydroxide, or a carbonate. Examples of the carbonate aqueous solution include aqueous solutions of carbonate salts such as sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate.

[0038] The composition of the aqueous solution can be adjusted appropriately depending on the composition of the precursor to be produced, but is preferably (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, or (d) a basic aqueous solution containing 10 to 28 mass % of ammonia water and an alkali metal concentration of 10 to 30 mass %.

[0039] Next, an aqueous solution containing the above-mentioned (a) nickel salt, (b) cobalt salt, (c) manganese salt, and (d) ammonia and an alkali metal basic aqueous solution is used as a 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 solution temperature to 55 to 65°C. At this time, chemical solutions may be sent 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 ammonia-containing basic aqueous solution, and a tank containing an alkali metal basic aqueous solution. In this way, a precursor of the positive electrode active material represented by the above formula (2) can be produced.

[0040] Next, the precursor of the positive electrode active material for a lithium ion battery is wet-mixed with at least one oxide selected from Zr oxide, Ta oxide, and W oxide, each having a 50% cumulative volume particle size D50 of 1 μm or less, to obtain a mixture. The total amount of the at least one oxide selected from Zr oxide, Ta oxide, and W oxide to be mixed can be adjusted appropriately depending on the target composition of the positive electrode active material for a lithium ion battery. ZrO2 can be used as the Zr oxide, Ta2O5 can be used as the Ta oxide, and WO2 or WO3 can be used as the W oxide. In this wet-mixing, the precursor of the positive electrode active material for a lithium ion battery and at least one oxide selected from Zr oxide, Ta oxide, and W oxide are added to an aqueous solvent, and the mixture is mixed by mechanical means to prepare a slurry.

[0041] As described above, Zr oxide, Ta oxide, and W oxide, each having a 50% cumulative volume particle size D50 of 1 μm or less, are wet mixed with a precursor of a positive electrode active material for a lithium ion battery before mixing with a lithium source to prepare a slurry. This improves the adhesion rate of the oxides of the different elements (Zr, Ta, and W) to the surface of the precursor of the positive electrode active material for a lithium ion battery. Furthermore, by adding different elements using this method, even small amounts of the elements can improve the cycle characteristics (capacity retention rate) of lithium ion batteries using the resulting positive electrode active material and reduce DC resistance. The D50 of the particles of Zr oxide, Ta oxide, and W oxide to be mixed is preferably 0.3 to 1.0 μm, and more preferably 0.3 to 0.5 μm.

[0042] Next, a lithium source is dry-mixed with the mixture of the precursor of the lithium-ion battery positive electrode active material obtained as described above and at least one of Zr oxide, Ta oxide, and W oxide to form a lithium mixture. The amount of the lithium source to be mixed can be appropriately adjusted depending on the target composition of the lithium-ion battery positive electrode active material. An example of the lithium source is lithium hydroxide. As a mixing method, the mixing ratio of each raw material is adjusted and dry-mixed using a Henschel mixer, automatic mortar, V-type mixer, or the like.

[0043] Next, the lithium mixture obtained as described above is fired at 820°C or higher for 4 hours or more. By firing the lithium mixture at a temperature of 820°C or higher for a long period of time, such as 4 hours or more, the solid solution rate of the different elements (Zr, Ta, W) inside the positive electrode active material for lithium ion batteries is improved, and the strength of the positive electrode active material particles is improved. Therefore, the occurrence of particle cracking in the subsequent lithium composite oxide coating process is suppressed, enabling good coating of oxides containing Li and Nb, thereby improving the output characteristics and durability of the all-solid-state lithium ion battery. The firing temperature is preferably 820 to 860°C, and the firing time is preferably 6 to 12 hours. The firing atmosphere is preferably an oxygen atmosphere.

[0044] Increasing the amounts of Zr oxide, Ta oxide, and W oxide added and / or lengthening the firing time and / or increasing the firing temperature can reduce the difference between the maximum particle strength (A) and the minimum particle strength (B). On the other hand, decreasing the amounts of Zr oxide, Ta oxide, and W oxide added and / or shortening the firing time and / or lowering the firing temperature can increase the difference between the maximum particle strength (A) and the minimum particle strength (B).

[0045] Thereafter, if necessary, the fired body can be pulverized using, for example, a pulverizer to obtain a powder of the positive electrode active material for a lithium ion battery.

[0046] (Method of Manufacturing a Cathode Active Material for an All-Solid-State Lithium-Ion Battery) In the method of manufacturing a cathode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention, first, an aqueous solution (coating liquid) containing Li and Nb is coated on the surface of cathode active material particles of the lithium-ion battery cathode active material manufactured by the above-described method of manufacturing a cathode active material for a lithium-ion battery. Examples of the coating liquid include: (1) a lithium source containing one of lithium hydroxide monohydrate, lithium carbonate, and lithium nitrate; (2) a niobium source containing one of niobium hydroxide, niobium oxalate, and ammonium niobium oxalate; and (3) an aqueous solution containing one of pure water, hydrogen peroxide, and aqueous ammonia. The coating method uses a coating apparatus having a tumbling fluidized bed (tumbling fluidized bed coating apparatus). Using the tumbling fluidized bed coating apparatus allows for uniform coating while controlling the thickness.

[0047] (Positive electrode for lithium ion battery and lithium ion battery) The positive electrode for lithium ion battery according to the embodiment of the present invention has a structure in which a positive electrode composite prepared by mixing the positive electrode active material for 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. The lithium ion battery according to the embodiment of the present invention includes a positive electrode for lithium ion battery having such a configuration and a known negative electrode for lithium ion battery.

[0048] Examples of the conductive additive include carbon-based conductive additives (graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, and thermal lamp black), and mixtures thereof. These conductive additives may be used alone or in combination of two or more. These conductive additives may also be particulate ceramic materials or resin materials coated with a conductive material (preferably a metal one of the above-mentioned conductive additives) by plating or the like. The shape (form) of the conductive additive is not limited to particulate form, and may be a form other than particulate form, or may be a form that is put into practical use as a so-called filler-based conductive additive, such as carbon nanofibers or carbon nanotubes.

[0049] Examples of binders include substances commonly used in positive electrode composites for lithium ion batteries, but copolymers having a structure derived from vinylidene fluoride, polyvinylidene fluoride (PVDF), copolymers or homopolymers having a structure derived from tetrafluoroethylene (TEF), and copolymers or homopolymers having a structure derived from hexafluoropropylene (HFP) are preferred. Specific examples include PVDF-HFP, PVDF-HFP-TEF, PVDF-TEF, and TEF-HFP.

[0050] The positive electrode mixture is prepared by mixing a positive electrode active material for a lithium ion battery, a conductive additive, and a binder in a solvent to form a positive electrode mixture slurry, which is then applied to one or both sides of a current collector and, after drying or the like, provided on the current collector to form a positive electrode active material layer.

[0051] As the solvent for the positive electrode mixture slurry, known organic solvents such as hydrocarbon organic solvents, amide compounds, lactam compounds, urea compounds, organic sulfur compounds, and cyclic organic phosphorus compounds can be used alone or as a mixed solvent. Examples of hydrocarbon organic solvents that can be used include saturated hydrocarbons, unsaturated hydrocarbons, and aromatic hydrocarbons. 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.

[0052] Materials constituting the current collector include metal materials such as copper, aluminum, titanium, stainless steel, nickel, and alloys thereof, as well as baked carbon, conductive polymer materials, conductive glass, etc. Among these, aluminum is more preferable from the viewpoints of lightweight, 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-like current collector made of the above material, or a sediment 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. Examples of conductive polymer materials constituting the resin current collector include conductive polymers and resins to which a conductive additive is added as needed.

[0053] From the viewpoint of battery performance, the thickness of the positive electrode for a lithium ion battery is preferably 150 to 600 μm, and more preferably 200 to 450 μm.

[0054] Lithium-ion batteries using a lithium-ion battery positive electrode are produced by combining a counter electrode with a negative electrode, placing them together with a separator in a cell container, injecting an electrolyte, and sealing the cell container. Alternatively, a bipolar electrode can be produced by forming a positive electrode on one side of a current collector and a negative electrode on the other, stacking the bipolar electrode with a separator, placing it in a cell container, injecting an electrolyte, and sealing the cell container.

[0055] The negative electrode may include a negative electrode active material, a conductive additive, a current collector, etc. As the negative electrode active material, known negative electrode active materials for lithium ion batteries can be used, and examples thereof include carbon-based materials (graphite, non-graphitizable carbon, amorphous carbon, burned resins (e.g., phenolic resins, furan resins, etc., which are burned and carbonized), cokes (e.g., pitch coke, needle coke, petroleum coke, etc.), and carbon fibers), silicon-based materials (silicon, silicon oxide (SiO x ), silicon-carbon composites (carbon particles whose surfaces are coated with silicon and / or silicon carbide, silicon particles or silicon oxide particles whose surfaces are coated with carbon and / or silicon carbide, and silicon carbide, etc.) and silicon alloys (silicon-aluminum alloys, silicon-lithium alloys, silicon-nickel alloys, silicon-iron alloys, silicon-titanium alloys, silicon-manganese alloys, silicon-copper alloys, silicon-tin alloys, etc.), conductive polymers (e.g., polyacetylene and polypyrrole), metals (tin, aluminum, zirconium, titanium, etc.), metal oxides (titanium oxide and lithium-titanium oxide, etc.) and metal alloys (e.g., lithium-tin alloys, lithium-aluminum alloys, lithium-aluminum-manganese alloys, etc.), and mixtures of these with carbon-based materials, etc. Examples of the conductive additive include the same conductive additives as those used in the positive electrode described above.

[0056] The current collector may be the same as the current collector constituting the positive electrode described above, and is preferably copper from the viewpoints of weight reduction, corrosion resistance, and high conductivity. A resin current collector may also be used, and the same current collector as the current collector constituting 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.

[0057] Examples of the separator 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, aramid fibers, etc.) or glass fibers, and those having ceramic fine particles such as silica, alumina, or titania attached to the surface thereof.

[0058] (Positive electrode for all-solid-state lithium-ion battery and all-solid-state lithium-ion battery) A positive electrode is formed using the positive electrode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention, and the positive electrode is used as a positive electrode layer, thereby producing an all-solid-state lithium-ion battery 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 a known configuration as shown in FIG.

[0059] The positive electrode layer of the all-solid-state lithium-ion battery can be a layer of a positive electrode mixture obtained by mixing the positive electrode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention with a solid electrolyte. The content of the positive electrode active material in the positive electrode layer is, for example, 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.

[0060] The positive electrode mixture may further contain a conductive additive, such as a carbon material. Examples of the conductive additive include carbon black (e.g., ketjen black, acetylene black, denka black, thermal black, channel black, etc.), graphite, carbon fiber, and activated carbon.

[0061] The average thickness of the positive electrode layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately designed depending on the purpose. The average thickness of the positive electrode layer of the all-solid-state lithium ion battery may be, for example, 1 μm to 100 μm, or 1 μm to 10 μm.

[0062] The method for forming the positive electrode layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately selected depending on the purpose. Examples of the method for forming the positive electrode layer of the all-solid-state lithium ion battery include a method of compression molding a positive electrode active material for an all-solid-state lithium ion battery.

[0063] The negative electrode layer of the all-solid-state lithium-ion battery may be a layer of a known negative electrode active material for all-solid-state lithium-ion batteries. Alternatively, the negative electrode layer may be a layer of a negative electrode composite obtained by mixing a known negative electrode active material for all-solid-state lithium-ion batteries with a solid electrolyte. The content of the negative electrode active material in the negative electrode layer is, for example, preferably 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.

[0064] The negative electrode layer, like the positive electrode layer, may contain a conductive additive. The conductive additive may be the same material as described for the positive electrode layer. Examples of the negative electrode active material include carbon materials, specifically, artificial graphite, graphite carbon fiber, resin-fired carbon, pyrolytic vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-fired carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, and non-graphitizable carbon, or mixtures thereof. Examples of the negative electrode material include metals such as lithium metal, indium metal, aluminum metal, and silicon metal, or alloys of these metals combined with other elements or compounds.

[0065] The average thickness of the negative electrode layer of the 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 the all-solid-state lithium ion battery may be, for example, 1 μm to 100 μm, or 1 μm to 10 μm.

[0066] The method for forming the negative electrode layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately selected depending on the purpose. Examples of the method for forming the negative electrode layer of the all-solid-state lithium ion battery include a method of compression molding negative electrode active material particles and a method of vapor-depositing a negative electrode active material.

[0067] The solid electrolyte may be a known solid electrolyte for all-solid-state lithium ion batteries, such as a sulfide-based solid electrolyte.

[0068] 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.

[0069] The average thickness of the solid electrolyte layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately designed depending on the purpose. The average thickness of the solid electrolyte layer of the all-solid-state lithium ion battery may be, for example, 50 μm to 500 μm, or 50 μm to 100 μm.

[0070] The method for forming the solid electrolyte layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately selected depending on the purpose. Examples of the method for forming the solid electrolyte layer of the all-solid-state lithium ion battery include sputtering using a target material for the solid electrolyte and compression molding of the solid electrolyte.

[0071] Other components constituting the all-solid-state lithium-ion battery are not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include a positive electrode current collector, a negative electrode current collector, and a battery case.

[0072] The size and structure of the positive electrode current collector are not particularly limited and can be appropriately selected depending on the purpose. Examples of materials for the positive electrode current collector include die steel, stainless steel, aluminum, aluminum alloys, titanium alloys, copper, gold, and nickel. Examples of the shape of 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.

[0073] The size and structure of the negative electrode current collector are not particularly limited and can be appropriately selected depending on the purpose. Examples of materials for the negative electrode current collector include die steel, gold, indium, nickel, copper, and stainless steel. Examples of the shape of 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.

[0074] The battery case is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include known laminate films that can be used in conventional all-solid-state lithium-ion batteries. Examples of laminate films include resin laminate films and films in which metal is vapor-deposited on resin laminate films. The shape of the battery is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include cylindrical, rectangular, button, coin, and flat types.

[0075] The following examples are provided to provide a better understanding of the present invention and its advantages, but the present invention is not limited to these examples.

[0076] (Example 1) First, the composition formula: Ni 0.598 Co 0.198 Mn 0.199 A precursor of a lithium-ion battery positive electrode active material represented by (OH)2 was prepared. Next, a precursor of a lithium-ion battery positive electrode active material having a D50 of 6.2 μm and ZrO2 as a different element having a D50 of 0.34 μm were added to an aqueous solvent in a charged amount of 0.5 mol%, and the mixture was mixed (wet mixed) by mechanical means to prepare a slurry. The slurry was then allowed to stand and dried to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed (dry mixed) using a Henschel mixer to form a lithium mixture. Next, the lithium mixture obtained as described above was fired in an oxygen atmosphere at 850 °C for 12 hours to produce positive electrode active material particles.

[0077] (Example 2) First, the composition formula: Ni 0.598 Co0.198 Mn 0.199 A precursor of a lithium-ion battery positive electrode active material represented by (OH)2 was prepared. Next, a precursor of a lithium-ion battery positive electrode active material having a D50 of 6.2 μm and WO3 having a D50 of 0.29 μm as a different element were added to an aqueous solvent in a charged amount of 0.5 mol%, and the mixture was mixed (wet mixed) by mechanical means to prepare a slurry. The slurry was then allowed to stand and dried to obtain a mixture. Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed (dry mixed) using a Henschel mixer to form a lithium mixture. Next, the lithium mixture obtained as described above was fired in an oxygen atmosphere at 850 °C for 12 hours to produce positive electrode active material particles.

[0078] (Example 3) First, the composition formula: Ni 0.598 Co 0.198 Mn 0.199 A precursor of a lithium-ion battery positive electrode active material represented by (OH)2 was prepared. Next, a precursor of a lithium-ion battery positive electrode active material having a D50 of 6.2 μm and Ta2O5 having a D50 of 0.31 μm as a different element were added to an aqueous solvent in a charged amount of 0.5 mol%, and the mixture was mixed (wet mixed) by mechanical means to prepare a slurry. The slurry was then allowed to stand and dried to obtain a mixture. Next, lithium carbonate (lithium source) was added to the resulting mixture and mixed (dry mixed) using a Henschel mixer to form a lithium mixture. Next, the lithium mixture obtained as described above was fired in an oxygen atmosphere at 850 °C for 12 hours to produce positive electrode active material particles.

[0079] (Comparative Example 1) First, the composition formula: Ni 0.601 Co 0.199 Mn 0.200A precursor of a lithium-ion battery positive electrode active material represented by (OH)2 was prepared. Next, a precursor of a lithium-ion battery positive electrode active material having a D50 of 6.2 μm was mixed with an aqueous solvent by mechanical means (wet mixing) to prepare a slurry, and then the slurry was allowed to stand and dried. Next, lithium carbonate (lithium source) was added to the obtained dried product and mixed (dry mixing) using a Henschel mixer to form a lithium mixture. Next, the lithium mixture obtained as described above was fired in an oxygen atmosphere at 850°C for 8 hours to produce positive electrode active material particles.

[0080] Example 4 A coating layer was formed on the positive electrode active material particles produced in Example 1 by the following procedure. First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water, with a Li content and a Nb content of 0.15 mol / L, was prepared as a coating liquid. Next, using the coating liquid, the surfaces of the produced positive electrode active material particles were coated with an oxide precursor containing Li and Nb using a tumbling fluidized bed coating device, and the coated particles were heat-treated at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery having a coating layer on the surface.

[0081] Example 5 A coating layer was formed on the positive electrode active material particles produced in Example 2 by the following procedure. First, an aqueous solution containing lithium carbonate, niobium hydroxide, and pure water, with a Li content and an Nb content of 0.15 mol / L, was prepared as a coating liquid. Next, using the coating liquid, the surfaces of the produced positive electrode active material particles were coated with an oxide precursor containing Li and Nb using a tumbling fluidized bed coating device, and the coated particles were heat-treated at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery having a coating layer on the surface.

[0082] Example 6 A coating layer was formed on the positive electrode active material particles produced in Example 3 by the following procedure. First, an aqueous solution containing lithium carbonate, niobium hydroxide, and pure water, with a Li content and a Nb content of 0.15 mol / L, was prepared as a coating liquid. Next, using the coating liquid, the surfaces of the produced positive electrode active material particles were coated with an oxide precursor containing Li and Nb using a tumbling fluidized bed coating device, and the coated particles were heat-treated at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery having a coating layer on the surface.

[0083] Comparative Example 2 A coating layer was formed on the positive electrode active material particles produced in Comparative Example 1 by the following procedure. First, an aqueous solution containing lithium carbonate, niobium hydroxide, and pure water, with a Li content and a Nb content of 0.15 mol / L, was prepared as a coating liquid. Next, using the coating liquid, the surfaces of the produced positive electrode active material particles were coated with an oxide precursor containing Li and Nb using a tumbling fluidized bed coating device, and the coated particles were heat-treated at 250°C in an oxygen atmosphere to produce a positive electrode active material for an all-solid-state lithium-ion battery having a coating layer on the surface.

[0084] <Composition of Positive Electrode Active Material> 0.2 g of each obtained sample (powder) of the positive electrode active material was weighed out and decomposed by an alkali fusion method, and then the composition was analyzed using an ICP (inductively coupled plasma) optical emission spectrometer (ICP-OES) "PS7800" manufactured by Hitachi High-Tech Corporation. The oxygen content was determined by subtracting the analytical values ​​of Li and metal components, as well as the impurity concentration and residual alkali amount, from the total amount of the analyzed sample. f " was calculated.

[0085] <50% cumulative volume particle size D50> 100 mg of each obtained positive electrode active material sample (powder) was dispersed by irradiating 40 W ultrasonic waves for 60 seconds at a flow rate of 50% using a Microtrac laser diffraction particle size distribution analyzer "MT3300EXII". The particle size distribution was measured and a volume-based cumulative particle size distribution curve was obtained. Next, in the obtained cumulative particle size distribution curve, the volume particle size at 50% accumulation was taken as the 50% cumulative volume particle size D50 of the positive electrode active material powder. Note that the water-soluble solvent used in the measurement was passed through a filter, the solvent refractive index was 1.333, the particle permeability conditions were transmission, the particle refractive index was 1.81, the shape was aspherical, the measurement range was 0.021 to 2000 μm, and the measurement time was 30 seconds.

[0086] <Specific Surface Area> The specific surface area was measured by the following method. That is, first, 1.0 g of the sample (powder) was weighed into a glass cell, set in a degassing device, and the glass cell was filled with nitrogen gas. After that, the cell was heat-treated in a nitrogen gas atmosphere at 40°C for 20 minutes to degas the sample. Thereafter, the glass cell containing the degassed sample (powder) was set in a specific surface area measuring device (Monosorb Model MS-21) manufactured by Quantachrome, and the specific surface area X was measured by the BET method (single-point method) while flowing a He:70 at%-N2:30 at% mixed gas as the adsorption gas. The specific surface area was also measured for the sample before and after coating with the coating layer.

[0087] <Circularity> The circularity was measured using a particle image analyzer, Morphologi G3, manufactured by Malvern. Specifically, the circularity was measured by filtering optical images of more than 20,000 particles acquired by the particle image analyzer using a parameter of "solidity = 0.93." The particle image analyzer was first loaded with a sample into a sample cartridge and then set in a dispersion unit. A nitrogen gas inlet line was connected to the dispersion unit, and the sample was dispersed on a glass plate by spraying nitrogen gas. Particle images of the dispersed sample on the glass plate were continuously captured and analyzed. Then, the circularity was calculated using the following formula 1 from the projected area and perimeter of each photographed particle (more than 18,000 particles). The average circularity refers to the average circularity of all measured positive electrode active material particles. The circularity was measured for both the sample before and after coating with the coating layer.

[0088] Circularity = 4πS / L 2 ... (Equation 1) (In the above equation, S is the projected area of ​​the particle, L is the perimeter of the projected image of the particle, and π is the ratio of the circumference of the particle to its circumference.)

[0089] <Particle Strength> Particle strength was measured using a microcompression tester MCT-211 manufactured by Shimadzu Corporation as follows. That is, the dispersed powder sample was placed on a sample stage, and a 20 μm diameter indenter was pressed against the center of a single secondary particle with an average particle diameter of D50 using a microscope at a loading rate of 0.532 mN / sec, and the strength at the time of fracture was measured. The particle strength measurements were carried out for N = 11 to 14, and the maximum, minimum, and average values ​​were designated as "maximum particle strength (A)," "minimum particle strength (B)," and "average particle strength (M)," respectively.

[0090] <Crystallite Size> The crystallite size of the (003) plane of the positive electrode active material for lithium ion batteries was measured using an X-ray diffractometer: Smart-Lab manufactured by Rigaku Corporation, with a CuKα X-ray source, a tube voltage of 40 kV, and a tube current of 30 mA, with a scan speed of 7.5 degrees / min in the range of 2θ = 10 ° to 80 °, a step width of 0.01 degrees, a slit width of 1 / 4 ° on the incident side, and a slit width of 10 mm on the receiving side. Using XRD analysis software PDXL2, the (003) plane diffraction peak near 2θ = 18.7 ° was determined, and this was taken as the crystallite size.

[0091] <Initial Discharge Capacity, 20-Cycle Capacity Retention Rate> The positive electrode active material, conductive additive, and binder were weighed in a ratio of 90:5:5 mol%. Next, the binder was dissolved in an organic solvent (N-methylpyrrolidone), and the positive electrode active material and conductive additive were mixed to form a slurry. The slurry was then applied to an Al foil, dried, and pressed to form a positive electrode. Subsequently, a 2032-type coin cell for evaluation was fabricated using a Li counter electrode. Using an electrolyte solution of 1M LiPF6 dissolved in EC-DMC (1:1), the initial capacity (25°C, upper charge voltage limit: 4.3 V, lower discharge voltage limit: 3.0 V) obtained at a discharge rate of 0.1 C and the 55°C high-temperature cycle characteristics after 20 cycles at a charge / discharge rate of 1 C were measured, and the 20-cycle capacity retention rate (%) was calculated. This measurement was performed with N = 3, and the average 20-cycle capacity retention rate (%) and the difference between the maximum and minimum values ​​were calculated.

[0092] <DC Resistance> In the above coin cell evaluation, the initial DC resistance and the DC resistance after 20 cycles were calculated by dividing the voltage change ΔV 2 seconds after the start of discharge by the current value, and the resistance increase rate after 20 cycles was calculated using the formula ((DC resistance after 20 cycles−initial DC resistance) / (initial DC resistance))×100[%].

[0093] (Battery Characteristics) <Method of Manufacturing All-Solid-State Lithium-Ion Battery> The positive electrode active material for all-solid-state lithium-ion batteries obtained in Examples 4 to 6 and Comparative Example 2, a sulfide-based solid electrolyte (75Li2S-25P2S5), acetylene black, and a binder were mixed in this order in a mass ratio of 60:35:5:1.5, and anisole was added as a solvent so that the solid content of the slurry was 65% by mass. The mixture was mixed for 400 seconds with a Mazerustar to form a positive electrode composite slurry, which was then applied to the surface of a 0.03 mm thick aluminum foil positive electrode current collector. At this time, the positive electrode composite slurry was applied to the surface of the positive electrode current collector by moving the applicator at a movement speed of 15 mm / s using an applicator with a gap of 400 μm. Next, the positive electrode current collector with the positive electrode composite slurry coated on its surface was dried at 100 ° C. for 30 minutes on a hot plate to remove the solvent, forming a positive electrode composite layer on the surface of the positive electrode current collector. Next, the above-described positive electrode composite layer was placed on a sulfide-based solid electrolyte having 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 prepare a solid electrolyte layer / positive electrode composite layer / positive electrode current collector laminate. Next, a metal Li—In alloy was pressed onto the negative electrode side of the solid electrolyte layer at 37 MPa to form a negative electrode layer. The laminate thus prepared was placed in a battery test cell made of SUS304 and subjected to a confining pressure to form an all-solid-state secondary battery. The all-solid-state secondary battery prepared by applying the confining pressure was then placed in a sealed container to block the atmosphere.

[0094] <Evaluation of Initial Discharge Capacity> The discharge capacity of the all-solid-state lithium ion battery was evaluated by measuring the impedance to determine the resistance after initial charging at 0.1 C at 55° C., and then discharging at 0.1 C.

[0095] <Evaluation of Rate Characteristics> The rate characteristics (%) of the all-solid-state lithium-ion battery were evaluated by measuring the initial capacity (55°C, upper limit charge voltage: 3.7 V, lower limit discharge voltage: 2.5 V vs. Li-In) obtained at a discharge rate of 0.1 C, and then measuring the high-rate capacity (55°C, upper limit charge voltage: 3.7 V, lower limit discharge voltage: 2.5 V vs. Li-In) obtained at a discharge rate of 0.5 C, and the ratio of (high-rate capacity) / (initial capacity) was expressed as a percentage.

[0096] <Evaluation of 20-cycle capacity retention rate> The capacity retention rate of the all-solid-state lithium-ion battery was evaluated as the 20-cycle capacity retention rate by dividing the discharge capacity after 20 cycles by the initial discharge capacity obtained at a discharge current of 0.5 C at 55° C. The measurement was performed with N = 11 to 14, and the average value of the 20-cycle capacity retention rate (%) and the difference between the maximum and minimum values ​​were calculated.

[0097] <Evaluation of Initial Resistance of All-Solid-State Cell> The resistance of the all-solid-state lithium-ion battery was evaluated as the resistance after the first charge by measuring AC impedance from 0.1 Hz to 1 MHz and analyzing the obtained Cole-Cole plot. The manufacturing conditions and test results are shown in Tables 1 to 5.

[0098]

[0099]

[0100]

[0101]

[0102]

[0103] (Evaluation Results) The positive electrode active materials of Examples 1 to 3 all had the composition of the following formula (1). Note that the "Li / Me ratio" in Table 2 indicates the composition ratio of Li to the total of Ni, Co, Mn, and M in the positive electrode active material for a lithium ion battery. Li a Ni b Co c Mn d M e O f(1) (In the formula (1), 1.0≦a≦1.07, 0.58≦b≦0.62, b+c+d+e=1, 1.8≦f≦2.2, 0.0035≦e / (b+c+d+e)≦0.0055, and M is at least one element selected from Zr, Ta, and W.) In addition, the positive electrode active materials of Examples 1 to 3 all had a value obtained by dividing the difference between the maximum particle strength (A) and the minimum particle strength (B) by the average particle strength (M): {((A)−(B)) / (M)} of 0.42 or less, a crystallite size of the (003) plane of 650 Å or less, and a 50% cumulative volume particle size D50 of 5 to 7 μm. The positive electrode active materials of Examples 4 to 6 all had a coating layer made of an oxide of Li and Nb provided on the surface of the positive electrode active material particles, and the particle circularity was 0.94 to 0.96 and the specific surface area was 0.6 m 2 / g or less, the value obtained by dividing the difference between the maximum particle strength (A) and the minimum particle strength (B) by the average particle strength (M): {((A)-(B)) / (M)} was 0.42 or less, and the crystallite size of the (003) plane was 650 Å or less. Therefore, for Examples 4 to 6 in which a coating layer was provided on Examples 1 to 3, all of the initial discharge capacity, stability of the 20-cycle capacity retention rate, initial DC resistance, DC resistance after 20 cycles, and resistance increase rate after 20 cycles all showed good results.

[0104] The positive electrode active material of Comparative Example 1 did not contain any of Zr, Ta, and W in its composition, and Comparative Example 2, in which a coating layer was provided, was poor in rate characteristics, stability of 20-cycle capacity retention rate, and initial resistance of the all-solid-state cell.

[0105] According to one embodiment of the present invention, it is possible to provide a cathode active material for a lithium ion battery having good battery characteristics, a cathode for a lithium ion battery using the same, a lithium ion battery, and a method for manufacturing the cathode active material for a lithium ion battery, a cathode active material for an all-solid-state lithium ion battery having good battery characteristics, a cathode for an all-solid-state lithium ion battery using the same, an all-solid-state lithium ion battery, and a method for manufacturing the cathode active material for an all-solid-state lithium ion battery, which may lead to the spread of non-fossil energy, reduce the use of fossil energy such as oil and gas, which currently accounts for a large portion of energy generation, and contribute to the suppression of global warming. Furthermore, since the main materials used are environmentally friendly substances such as lithium, carbon, manganese, nickel, and cobalt, and toxic substances such as cadmium, lead, and mercury are not used, there is a possibility that the environmental burden may be reduced. For this reason, one embodiment of the present invention may contribute to Goal 7 of the United Nations-led Sustainable Development Goals (SDGs), which is to "Ensure access to affordable, reliable, sustainable and modern energy for all," Goal 9, which is to "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation," and Goal 12, which is to "Ensure sustainable consumption and production patterns."

Claims

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 M e O f (1) (in said formula (1), 1.0≦a≦1.07, 0.58≦b≦0.62, b+c+d+e=1, 1.8≦f≦2.2, 0.0035≦e / (b+c+d+e)≦0.0055, and M is at least one selected from Zr, Ta, and W.) A positive electrode active material for a lithium ion battery, wherein a value obtained by dividing a difference between a maximum particle strength (A) and a minimum particle strength (B) by an average particle strength (M): {((A)−(B)) / (M)} is 0.42 or less.

2. The positive electrode active material for a lithium ion battery according to claim 1, wherein the crystallite size of the (003) plane is 650 Å or less.

3. 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 7 μm.

4. A positive electrode for a lithium ion battery, comprising the positive electrode active material for a lithium ion battery according to any one of claims 1 to 3.

5. A lithium ion battery comprising the positive electrode and negative electrode for a lithium ion battery according to claim 4.

6. A positive electrode active material for a lithium ion battery represented by the composition shown in the following formula (1), and Li a Ni b Co c Mn d M e O f (1) (in formula (1), 1.0≦a≦1.07, 0.58≦b≦0.62, b+c+d+e=1, 1.8≦f≦2.2, 0.0035≦e / (b+c+d+e)≦0.0055, and M is at least one selected from Zr, Ta, and W), and a coating layer made of an oxide of Li and Nb provided on a surface of a cathode active material particle of the cathode active material for a lithium ion battery, wherein a value obtained by dividing a difference between a maximum value (A) of particle strength and a minimum value (B) of particle strength by an average value (M) of particle strength: {((A)−(B)) / (M)} is 0.42 or less.

7. The positive electrode active material for an all-solid-state lithium-ion battery according to claim 6, wherein the circularity of the particles is 0.94 to 0.

96.

8. Specific surface area is 0.6 m 2 The positive electrode active material for an all-solid-state lithium ion battery according to claim 6, wherein the SiO2 content is 0.01g or less.

9. The positive electrode active material for an all-solid-state lithium-ion battery according to claim 6, wherein the crystallite size of the (003) plane is 650 Å or less.

10. 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 any one of claims 6 to 9.

11. An all-solid-state lithium ion battery comprising the positive electrode and negative electrode for the all-solid-state lithium ion battery according to claim 10.

12. 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); b Co c Mn d (OH)2 (2) (in formula (2), 0.58≦b≦0.62, 0.18≦c≦0.22, and b+c+d=1). The method for producing a positive electrode active material for a lithium ion battery according to claim 1, comprising: a step of wet-mixing at least one oxide selected from the group consisting of an oxide of Zr, an oxide of Ta, and an oxide of W, each oxide having a 50% cumulative volume particle size D50 of 1 μm or less, with the precursor of the positive electrode active material for a lithium ion battery to obtain a mixture; and a step of dry-mixing the mixture with a lithium source and firing the mixture at 820° C. or higher for 4 hours or more.

13. The method for producing a positive electrode active material for a lithium ion battery according to claim 12, wherein the Zr oxide, Ta oxide, and W oxide have a D50 of 0.3 to 1.0 μm.

14. The method for producing a positive electrode active material for a lithium ion battery according to claim 12, wherein in the step of calcining the mixture, the mixture is dry-mixed with a lithium source and calcined at 820 to 860°C for 6 to 12 hours.

15. 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 defined in any one of claims 12 to 14; and forming a coating layer made of an oxide of Li and Nb on the surfaces 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 in a tumbling fluidized bed coating apparatus.

16. The method for producing a positive electrode active material for an all-solid-state lithium-ion battery according to claim 15, 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 ammonium niobium oxalate as a niobium source; and (3) one of pure water, hydrogen peroxide water, and ammonia water.

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