WO2025120887A1 - 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 - Google Patents

Abstract

Provided are: a lithium-ion battery positive-electrode active material having good battery characteristics; a lithium-ion battery positive electrode using the same; a lithium ion battery; and a method for manufacturing a lithium-ion battery positive-electrode active material. Also provided are: an all-solid lithium-ion battery positive-electrode active material having good battery characteristics; an all-solid lithium-ion battery positive electrode using the same; an all-solid lithium-ion battery; and a method for manufacturing an all-solid lithium-ion battery positive-electrode active material.　The present invention provides a lithium-ion battery positive-electrode active material represented by the composition indicated in formula (1): Li_aNi_bCo_cMn_dM_eO_f (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, and M is at least one element selected from Zr, Ta, and W), wherein the lithium-ion battery positive-electrode active material has a particle strength of 100 MPa or greater, a crystallite size of a (003) plane of 650 Å or less, and a 50% cumulative volume particle size D50 of 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

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.

In recent years, with the 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 power sources for these devices has become important. Among these batteries, lithium-ion secondary batteries have attracted attention due to their high energy density. In addition to liquid-based lithium-ion secondary batteries that use an electrolyte, there are also all-solid-state lithium-ion batteries that use a solid electrolyte, which have been attracting attention in recent years.

In the 1990s and 2000s, the most commonly used positive electrode active material for lithium-ion secondary batteries was LiCoO ₂ , but in order to solve problems such as high power consumption due to the high functionality of electronic devices and long driving distance due to 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 instead since the 2010s. These positive electrode active materials are materials with an excellent balance of output and durability characteristics, but for use in automobile applications, etc., further high output and high durability are required. Until now, in order to overcome the problem of high durability in particular, a method of surface modification or doping of the positive electrode active material with elements with high affinity for oxygen, such as Zr, W, Nb, and Ta, has been adopted.

Patent Document 1 discloses a positive electrode active material that is a lithium-nickel-cobalt-manganese composite oxide that contains tungsten and niobium. It also states that this configuration makes it possible to provide a positive electrode active material that has excellent output characteristics and generates little gas, and a battery that uses the same.

Patent Document 2 discloses a method for producing a lithium-containing composite oxide, which is characterized in that when a transition metal hydroxide, essential for which Ni and Mn are present, is mixed with a lithium source and sintered 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 the crystal structure model of the space group P-3m1 in the X-ray diffraction pattern is used. It also discloses that such a configuration can provide a method for producing a lithium-containing composite oxide that can improve the performance of lithium ion secondary batteries, such as the cycle characteristics and rate characteristics.

JP 2009-140787 A JP 2016-44120 A

In order to increase the crystallinity of positive electrode active materials such as NCM523 and NCM622, the sintering temperature must be set higher than that of high-nickel positive electrode active materials such as NCM811. As a result, the primary particles of the active material after sintering become larger, which causes the problem of reduced particle strength. In particular, with low-strength particles, there is a problem that the particles break when coating with Li composite oxide, which is essential for positive electrode active materials for all-solid-state lithium-ion batteries, using a device with a mechanism that fluidizes powder, such as a rolling fluidized bed coating device. If cracks occur in the particles during coating, they will break during the press when making the electrode, and the Li composite oxide will not be coated on the broken surface. When assembled into a battery, they will come into contact with the solid electrolyte and form a high-resistance layer, causing performance degradation.

The present invention has been made to solve the above problems, and aims 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. It also aims 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.

The present invention, which has been completed based on the above findings, is defined in the following items 1 to 11.
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 Of} (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.)
A positive electrode active material for a lithium ion battery, having a particle strength of 100 MPa or more, a crystallite size of the (003) plane of 650 Å or less, and a 50% cumulative volumetric particle size D50 of 5 to 7 μm.
2. A positive electrode for a lithium ion battery, comprising the positive electrode active material for a lithium ion battery according to 1 above.
3. A lithium ion battery comprising the positive electrode and the negative electrode for a lithium ion battery according to 2 above.
4. 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 Of} (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.)
a coating layer made of an oxide of Li and Nb provided on a surface of a positive electrode active material particle of the positive electrode active material for a lithium ion battery;
The positive electrode active material for an all-solid-state lithium ion battery comprises: a particle circularity of 0.94 to 0.96; a specific surface area of 0.6 m ² /g or less; a particle strength of 100 MPa or more; and a crystallite size of the (003) plane of 650 Å or less.
5. 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 4 above.
6. An all-solid-state lithium ion battery comprising the positive electrode and the negative electrode for the all-solid-state lithium ion battery according to 5 above.
7. 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 Mnd} (OH) ₂ (2)
(In the formula (2), 0.58≦b≦0.62, 0.18≦c≦0.22, and b+c+d=1.)
A step of wet-mixing 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, with the precursor of the positive electrode active material for lithium ion batteries to obtain a mixture;
dry mixing the mixture with a lithium source and calcining at 820° C. or higher for 4 hours or more;
The method for producing a positive electrode active material for a lithium ion battery includes the steps of:
8. The method for producing a positive electrode active material for a lithium ion battery according to 7 above, wherein the Zr oxide, the Ta oxide and the W oxide have a D50 of 0.3 to 1.0 μm.
9. The method for producing a positive electrode active material for a lithium ion battery according to 7 or 8, wherein in the step of calcining the mixture, the mixture is mixed with a lithium source in a dry state and calcined at 820 to 860° C. for 6 to 12 hours.
10. A step of preparing a positive electrode active material for a lithium ion battery produced by any one of the methods described in 7 to 9 above;
forming a coating layer made of an oxide of Li and Nb on the surface of the positive electrode active material particles of the lithium ion battery positive electrode active material by using an aqueous solution containing Li and Nb with a tumbling fluidized bed apparatus;
The method for producing a positive electrode active material for an all-solid-state lithium ion battery includes the steps of:
11. The method for producing a positive electrode active material for an all-solid-state lithium-ion battery according to 10 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.

The present invention can 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. It can also 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.

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

Next, the form 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 embodiment, and it should be understood that appropriate design changes, improvements, etc. may be made based on the ordinary knowledge of those skilled in the art within the scope of the spirit of the present invention.

(Positive electrode active material for lithium ion batteries)
In the present invention, when simply referring to a "positive electrode active material for lithium ion batteries", this includes both a liquid-based positive electrode active material for lithium ion batteries using an electrolyte solution and a positive electrode active material for all-solid-state lithium ion batteries in which the electrolyte is a solid.
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).
Li _a Ni _b Co _c Mn _d M _{e Of} (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.)

In the positive electrode active material for lithium ion batteries 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, it is possible to suppress the reduction of nickel due to lithium deficiency. In addition, because a, which indicates the lithium composition, is 1.07 or less, it is possible to suppress 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 formed into a battery.

In the positive electrode active material for lithium ion batteries according to an embodiment of the present invention, the sum of b, which indicates a nickel composition, c, which indicates a cobalt composition, d, which indicates a manganese composition, and e, which indicates a composition of at least one selected from Zr, Ta, and W, in the above formula (1) is controlled to be 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 desorption of lithium during charging and discharging. 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.

The positive electrode active material for lithium ion batteries according to the embodiment of the present invention has a form in which a majority of the secondary particles are formed by agglomeration of multiple primary particles, and may also have a form in which some primary particles are not agglomerated as secondary particles. The shapes of the primary particles constituting the secondary particles and the primary particles existing alone are not particularly limited, and may have various shapes, such as, for example, a roughly spherical, roughly elliptical, roughly plate-like, roughly needle-like, etc. The form in which multiple primary particles are agglomerated is also not particularly limited, and may have various forms, such as a form in which the primary particles are agglomerated in random directions, or a form in which the primary particles are agglomerated almost evenly radially from the center to form roughly spherical or roughly elliptical secondary particles.

In the positive electrode active material for lithium ion batteries 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 selected from Zr, Ta, and W. That is, the positive electrode active material for lithium ion batteries contains at least one element selected from Zr, Ta, and W. The element is dissolved in the positive electrode active material, and has the effect of reducing the expansion and contraction behavior of the crystal lattice due to the insertion and removal of lithium accompanying charging and discharging. Therefore, when the composition ratio of the element, e/(b+c+d+e), is 0.0035 or more, the cycle characteristics are improved. On the other hand, the element does not contribute to charge compensation during charging and discharging. Therefore, when the composition ratio of the element, e/(b+c+d+e), is 0.0055 or less, the effect of suppressing the decrease in discharge capacity is achieved. In addition, preferably, 0.004≦e/(b+c+d+e)≦0.005.

The positive electrode active material for lithium ion batteries according to an embodiment of the present invention has a particle strength of 100 MPa or more. Because the positive electrode active material for lithium ion batteries according to an embodiment of the present invention has such high particle strength, particle cracking during the lithium ion conductive oxide coating process during the manufacture of the positive electrode active material for all-solid-state batteries is suppressed, improving battery characteristics such as output characteristics and durability in all-solid-state batteries. The particle strength is preferably 110 MPa or more, more preferably 120 MPa or more, and even more preferably 130 MPa or more.

The particle strength of the positive electrode active material for lithium-ion batteries can be measured using a micro-compression tester MCT-211 manufactured by Shimadzu Corporation as follows. That is, the dispersed powder sample is placed on the 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 20μm diameter indenter is pressed against the sample at a loading speed of 0.532mN/sec, and the strength at break is measured at N=11-14, with the average value being the particle strength. In measuring particle strength, the MCT-211 applies a load to the sample and draws a curve with the load on the vertical axis and the displacement on the horizontal axis. When the sample "breaks", a horizontal line is drawn on the curve, where the load is a constant on the horizontal axis, and the software built into the MCT-211 determines the starting point of this horizontal line as the "strength at break".

The positive electrode active material for lithium ion batteries according to an embodiment of the present invention 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 removed from the positive electrode active material during charging and discharging, and reduces cracks due to accumulation of strain at the primary particle interface, resulting in improved cycle characteristics. The crystallite size of the (003) plane is preferably 600 Å or less, and more preferably 550 Å or less.

The crystallite size of the (003) plane of the positive electrode active material for lithium-ion batteries can be measured using an X-ray diffraction device: Smart-Lab manufactured by Rigaku Corporation, with a CuKα X-ray source, a tube voltage of 40 kV, a tube current of 30 mA, 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. The (003) plane diffraction peak near 2θ = 18.7° can be determined using the XRD analysis software PDXL2, and this can be used as the crystallite size.

The 50% cumulative volume particle size D50 of the positive electrode active material for lithium ion batteries according to an 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. 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 reduced and the amount of coating of Li and Nb oxides can be reduced. If the 50% cumulative volume particle size D50 of the positive electrode active material for lithium ion batteries is 7 μm or less, the specific surface area can be prevented from becoming excessively small. It is more preferable that the 50% cumulative volume particle size D50 of the positive electrode active material for lithium ion batteries is 5 to 6 μm. The above 50% cumulative volume particle size D50 can be measured, for example, as follows. That is, first, 100 mg of the powder of the positive electrode active material is dispersed by irradiating 40 W of ultrasound for 60 seconds at a flow rate of 50% using a laser diffraction type particle size distribution measuring device "MT3300EXII" manufactured by Microtrac, and then the particle size distribution is measured to obtain a cumulative particle size distribution curve based on volume. Next, in the obtained cumulative particle size distribution curve, the volume particle size at 50% accumulation is taken as the 50% cumulative volume particle size D50 of the powder of the positive electrode active material. Note that the water-soluble solvent used in the measurement is passed through a filter, the solvent refractive index is 1.333, the particle permeability conditions are transparent, the particle refractive index is 1.81, the shape is aspherical, the measurement range is 0.021 to 2000 μm, and the measurement time is 30 seconds.

(Positive electrode active material for all-solid-state lithium-ion batteries)
The positive electrode active material for an all-solid-state lithium-ion battery according to the embodiment of the present invention includes a positive electrode active material for a lithium-ion battery 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. The oxide of Li and Nb constituting the coating layer may include lithium niobate ( _LiNbO3 ) or may be _LiNbO3 .

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), similarly 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 Mn _d M _{e Of} (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.)

The positive electrode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention has a particle strength of 100 MPa or more. The particle strength is preferably 110 MPa or more, more preferably 120 MPa or more, and even more preferably 130 MPa or more.

The positive electrode active material for all-solid-state lithium-ion batteries according to an embodiment of the present invention has a crystallite size of 650 Å or less on 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 removed from the positive electrode active material during charging and discharging, and reduces cracks due to accumulation of strain at the primary particle interface, resulting in improved cycle characteristics. The crystallite size of the (003) plane is preferably 600 Å or less, and more preferably 550 Å or less.

The positive electrode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention has a particle circularity of 0.94 to 0.96. Circularity is an index that indicates how close the shape of a particle is to a sphere, and for example, the circularity of a truly spherical particle is at its upper limit of 1.00. If the circularity of the positive electrode active material is 0.88 or more, the contact area between the solid electrolyte and the positive electrode active material becomes large, and the conductivity of Li ions between the positive electrode active material and the solid electrolyte becomes good. This makes it possible to produce a high-capacity all-solid-state lithium-ion battery. The circularity is preferably 0.95 to 0.96.

The circularity of the positive electrode active material can be measured by a particle image analyzer: Morphologi G3 manufactured by Malvern. Specifically, the particle image analyzer measures the circularity by filtering the 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 introduction line is connected to the dispersion unit, and the sample is dispersed on the glass plate by spraying nitrogen gas. Particle images of the dispersed sample on the glass plate are continuously photographed and analyzed. Then, the circularity is calculated from the projected area and perimeter of each photographed particle (18,000 or more) using the following formula 3. The average circularity refers to the average circularity of all the measured positive electrode active material particles.

Circularity=4πS/L2 (Equation 3)
(In the above formula, S is the projected area of the particle, L is the perimeter of the projected image of the particle, and π is the circular constant.)

The specific surface area of the positive electrode active material for an all-solid-state lithium-ion battery is 0.6 m ² /g or less. When the specific surface area is 0.6 m ² /g or less, it 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, and the effect of improving the output characteristics and the cycle characteristics is obtained. The specific surface area is preferably 0.4 to 0.5 m ² /g.

The specific surface area of the positive electrode active material for all-solid-state lithium-ion batteries 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, and then heat-treated in a nitrogen gas atmosphere at 40°C for 20 minutes to degas it. After that, the glass cell containing the degassed sample (powder) is set in a Quantachrome specific surface area measuring device: Monosorb Model MS-21, 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.

The Nb content in the positive electrode active material for all-solid-state lithium-ion batteries is preferably 0.5 to 0.8 mass%. If the Nb content is 0.5 mass% or more, the entire surface of the active material is coated with Nb, 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. If the Nb content is 0.8 mass% or less, the coating layer is formed as thin as possible, shortening the movement of Li ions within the coating layer during charging and discharging, thereby reducing the diffusion movement 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 mass%.

The thickness of the coating layer is preferably 10 nm or less, and more preferably 6 nm or less. If the thickness of the coating layer is 6 nm or less, adverse effects such as inhibition of the movement of Li ions 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, 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).

(Method for producing positive electrode active material for lithium ion batteries)
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 the 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 Mnd} (OH) ₂ (2)
(In the formula (2), 0.58≦b≦0.62, 0.18≦c≦0.22, and b+c+d=1.)

In the method for producing a precursor of a positive electrode active material for a lithium ion battery, 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) Examples of the nickel salt include nickel sulfate, nickel nitrate, or nickel hydrochloride. (b) Examples of the cobalt salt include cobalt sulfate, cobalt nitrate, or cobalt hydrochloride. (c) Examples of the manganese salt include manganese sulfate, manganese nitrate, or manganese hydrochloride. (d) Examples of the basic aqueous solution containing ammonia include aqueous solutions of ammonia, ammonium sulfate, ammonium carbonate, and ammonium hydrochloride. 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 an aqueous solution using a salt of a carbonate group, such as an aqueous solution of sodium carbonate, an aqueous solution of potassium carbonate, an aqueous solution of sodium hydrogen carbonate, or an aqueous solution of potassium hydrogen carbonate.

The composition of the aqueous solution can be adjusted as appropriate depending on the composition of the precursor to be produced, but it is preferable that the aqueous solution 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, or (d) a basic aqueous solution containing 10 to 28 mass% ammonia and a basic aqueous solution with an alkali metal concentration of 10 to 30 mass%.

Next, an aqueous solution containing the above-mentioned (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 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 liquid temperature to 55 to 65°C. At this time, chemical solutions may be sent to the reaction tank 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 of the positive electrode active material represented by the above formula (2) can be produced.

Next, 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, is mixed in a wet manner with the precursor of the positive electrode active material for lithium ion batteries to obtain a mixture. The total amount of at least one oxide selected from Zr oxide, Ta oxide, and W oxide to be mixed can be appropriately adjusted depending on the composition of the target positive electrode active material for lithium ion batteries. ZrO ₂ can be used as the oxide of Zr, Ta ₂ O ₅ can be used as the oxide of Ta, and WO ₂ or WO ₃ can be used as the oxide of W. In the wet mixing, the precursor of the positive electrode active material for lithium ion batteries 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.

As described above, by preparing a slurry by wet mixing Zr oxide, Ta oxide, and W oxide, each having a 50% cumulative volume particle size D50 of 1 μm or less, with a precursor of a positive electrode active material for a lithium ion battery before mixing with a lithium source, the adhesion rate of the oxides of different elements (Zr, Ta, W) to the surface of the precursor of the positive electrode active material for a lithium ion battery is improved. Furthermore, by adding different elements using this method, it is possible to improve the cycle characteristics (capacity retention rate) of a lithium ion battery using the manufactured positive electrode active material and reduce the DC resistance even with a small amount of element addition. 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.

Next, a lithium source is dry-mixed with the mixture of the precursor of the positive electrode active material for lithium ion batteries obtained as described above and at least one of an oxide of Zr, an oxide of Ta, and an oxide of W 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 positive electrode active material for lithium ion batteries. 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, an automatic mortar, a V-type mixer, or the like.

Then, the lithium mixture obtained as described above is baked at 820°C or higher for 4 hours or more. In this way, the lithium mixture is baked at a temperature of 820°C or higher for a long period of time of 4 hours or more at once, which improves the solid solution rate of the different elements (Zr, Ta, W) inside the positive electrode active material for lithium ion batteries, and improves the strength of the positive electrode active material particles. This suppresses the occurrence of particle cracking in the subsequent lithium composite oxide coating process, making it possible to coat the oxide containing Li and Nb well, and improving the output characteristics and durability of the all-solid-state battery. The baking temperature is preferably 820 to 860°C, and the baking time is preferably 6 to 12 hours. The baking atmosphere is preferably an oxygen atmosphere.

If necessary, the fired body can then be pulverized, for example, using a pulverizer to obtain a powder of the positive electrode active material for lithium ion batteries.

(Method for producing positive electrode active material for all-solid-state lithium-ion battery)
In the manufacturing method of the positive electrode active material for all-solid-state lithium-ion batteries according to the embodiment of the present invention, first, an aqueous solution (coating solution) containing Li and Nb is coated on the surface of the positive electrode active material particles of the positive electrode active material for lithium-ion batteries manufactured by the manufacturing method of the positive electrode active material for lithium-ion batteries described above. At this time, the coating solution may be, for example, (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) an aqueous solution containing any one of pure water, hydrogen peroxide, and ammonia water. In addition, a coating device (rolling fluidized bed device) having a rolling fluidized bed is used as the coating method. By using the rolling fluidized bed device, it is possible to coat uniformly while controlling the thickness.

(Positive electrode for lithium ion batteries and lithium ion batteries)
The positive electrode for a 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 a lithium ion battery having the above-mentioned configuration, a conductive auxiliary material, 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 a lithium ion battery having such a configuration and a known negative electrode for a lithium ion battery.

The conductive assistant may be a carbon-based conductive assistant (graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, and thermal lamp black), etc.), or a mixture thereof. These conductive assistants may be used alone or in combination of two or more. These conductive assistants may also be particulate ceramic materials or resin materials coated with a conductive material (preferably a metal one of the conductive assistants listed above) by plating or the like. The shape (form) of the conductive assistant is not limited to a particulate form, and may be a form other than a particulate form, such as carbon nanofibers or carbon nanotubes, which are so-called filler-based conductive assistants.

Binders include substances that are 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.

The positive electrode mixture is made 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, which is then applied to one or both sides of a current collector and, after drying, etc., placed on the current collector to form a positive electrode active material layer.

　As the solvent for the positive electrode composite slurry, known organic solvents such as hydrocarbon organic solvents, amide compounds, lactam compounds, urea compounds, organic sulfur compounds, cyclic organic phosphorus compounds, etc. can be used as a single solvent or as a mixed solvent. As the hydrocarbon organic solvent, 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.

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 weight reduction, corrosion resistance, and high conductivity. 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 deposition 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 that can be used to constitute the resin current collector include conductive polymers and resins to which conductive materials have been added as necessary.

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.

A lithium-ion battery using a lithium-ion battery positive electrode can be produced by combining a negative electrode as a counter electrode, storing it together with a separator in a cell container, injecting an electrolyte, and sealing the cell container. It can also be produced by forming a positive electrode on one side of a current collector and a negative electrode on the other side to create a bipolar electrode, stacking the bipolar electrode with a separator, storing it in a cell container, injecting an electrolyte, and sealing the cell container.

The negative electrode may include a negative electrode active material, a conductive assistant, a current collector, etc. As the negative electrode active material, a known negative electrode active material for lithium ion batteries may be used, and may include carbon-based materials (graphite, non-graphitizable carbon, amorphous carbon, resin baked bodies (e.g., phenolic resins, furan resins, etc. baked and carbonized), cokes (e.g., pitch coke, needle coke, petroleum coke, etc.), and carbon fibers, etc.), 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.), metal alloys (e.g., lithium-tin alloys, lithium-aluminum alloys, and lithium-aluminum-manganese alloys, etc.), and mixtures of these with carbon-based materials, etc. can be mentioned. In addition, the conductive auxiliary material can be suitably used as the conductive auxiliary material of the positive electrode described above.

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 it is preferable to use a current collector similar to the current collector constituting the positive electrode described above. The thickness of the current collector is not particularly limited, but is preferably 10 to 60 μm.

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, aramid fibers, etc.) or glass fibers, and those with ceramic particles such as silica, alumina, or titania attached to their surfaces.

(Positive electrode for all-solid-state lithium-ion battery and all-solid-state lithium-ion battery)
A positive electrode is formed by the positive electrode active material for an all-solid-state lithium ion battery according to the embodiment of the present invention, and the positive electrode is used as a positive electrode layer, and an all-solid-state lithium ion battery including the positive electrode layer, a solid electrolyte layer, and a negative electrode layer can be produced. The solid electrolyte layer and the negative electrode layer constituting the all-solid-state lithium ion battery according to the embodiment of the present invention are not particularly limited and can be formed of known materials and can have a known configuration as shown in FIG.

The positive electrode layer of the all-solid-state lithium-ion battery can be a layer of a positive electrode composite material formed by mixing a positive electrode active material for all-solid-state lithium-ion batteries 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 preferably, for example, 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.

The positive electrode mixture may further contain a conductive additive. A carbon material can be used as the conductive additive. Examples of the carbon material that can be used include carbon black such as ketjen black, acetylene black, denka black, thermal black, and channel black, graphite, carbon fiber, and activated carbon.

The average thickness of the positive electrode layer of the all-solid-state lithium-ion battery is not particularly limited and can be designed appropriately according to 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.

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. For example, a method for forming the positive electrode layer of the all-solid-state lithium-ion battery can be mentioned, such as a method of compression molding a positive electrode active material for the all-solid-state lithium-ion battery.

The negative electrode layer (negative electrode) 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. The negative electrode layer may also be a layer of a negative electrode composite material 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.

The negative electrode layer may contain a conductive auxiliary material, as in the positive electrode layer. The conductive auxiliary material may be the same material as that described for the positive electrode layer. The negative electrode active material may be, for example, a carbon material, specifically, artificial graphite, graphite carbon fiber, resin-sintered carbon, pyrolytic vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-sintered carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, non-graphitizable carbon, or a mixture thereof. The negative electrode material may be, for example, a metal itself, such as metallic lithium, metallic indium, metallic aluminum, or metallic silicon, or an alloy in combination with other elements or compounds.

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.

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 negative electrode active material particles and a method of vapor-depositing negative electrode active material.

The solid electrolyte may be a known solid electrolyte for all-solid-state lithium-ion batteries. A sulfide-based solid electrolyte, etc. may be used as the solid electrolyte.

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 .}

The average thickness of the solid electrolyte layer of the all-solid-state lithium-ion battery is not particularly limited and can be designed appropriately according to 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.

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.

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

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 the material for the positive electrode current collector include die steel, stainless steel, aluminum, aluminum alloys, titanium alloys, copper, gold, and nickel.
The positive electrode current collector may be in the form of, for example, a foil, a plate, or a 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.

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 the material for the negative electrode current collector include die steel, gold, indium, nickel, copper, and stainless steel.
The negative electrode current collector may be in the form of, for example, a foil, a plate, or a 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.

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 batteries, etc. Examples of the laminate film include a resin laminate film and a film in which a metal is vapor-deposited on a resin laminate film.
The shape of the battery is not particularly limited and can be appropriately selected depending on the purpose. Examples of the shape of the battery include cylindrical, square, button, coin, and flat types.

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

Example 1
First, a precursor of a positive electrode active material for a lithium ion battery represented by the composition formula: Ni _0.598 Co _0.198 Mn _0.199 (OH) ₂ was prepared.
Next, a precursor of a positive electrode active material for a lithium ion battery having a D50 of 6.2 μm and _ZrO2 having a D50 of 0.34 μm as a different element were added to the aqueous solvent in an amount of 0.5 mol%, and this was mixed (wet mixed) by a mechanical means to prepare a slurry. Next, the slurry was left to stand and dried to obtain a mixture.
Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed (dry mixed) in a Henschel mixer to form a lithium mixture.
Next, the lithium mixture obtained as described above was baked in an oxygen atmosphere at 850° C. for 12 hours to prepare positive electrode active material particles.

Example 2
First, a precursor of a positive electrode active material for a lithium ion battery represented by the composition formula: Ni _0.598 Co _0.198 Mn _0.199 (OH) ₂ was prepared.
Next, a precursor of a positive electrode active material for a lithium ion battery having a D50 of 6.2 μm and _WO3 having a D50 of 0.29 μm as a different element were added to the aqueous solvent in an amount of 0.5 mol%, and this was mixed (wet mixed) by a mechanical means to prepare a slurry. Next, the slurry was left to stand and dried to obtain a mixture.
Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed (dry mixed) in a Henschel mixer to form a lithium mixture.
Next, the lithium mixture obtained as described above was baked in an oxygen atmosphere at 850° C. for 12 hours to prepare positive electrode active material particles.

Example 3
First, a precursor of a positive electrode active material for a lithium ion battery represented by the composition formula: Ni _0.598 Co _0.198 Mn _0.199 (OH) ₂ was prepared.
Next, a precursor of a positive electrode active material for a lithium ion battery having a D50 of 6.2 μm and _Ta2O5 having a D50 of 0.31 _μm as a different element were added to the aqueous solvent in an amount of 0.5 mol%, and this was mixed (wet mixed) by mechanical means to prepare a slurry. The slurry was then left to stand and dried to obtain a mixture.
Next, lithium carbonate (lithium source) was added to the obtained mixture and mixed (dry mixed) in a Henschel mixer to form a lithium mixture.
Next, the lithium mixture obtained as described above was baked in an oxygen atmosphere at 850° C. for 12 hours to prepare positive electrode active material particles.

(Comparative Example 1)
First, a precursor of a positive electrode active material for a lithium ion battery represented by the composition formula: Ni _0.601 Co _0.199 Mn _0.200 (OH) ₂ was prepared.
Next, a precursor of a positive electrode active material for a lithium ion battery having a D50 of 6.2 μm was mixed (wet mixed) with the aqueous solvent by mechanical means to prepare a slurry, and then the slurry was left to stand and dried.
Next, lithium carbonate (lithium source) was added to the obtained dried body and mixed (dry mixed) in a Henschel mixer to form a lithium mixture.
Next, the lithium mixture obtained as described above was fired at 850° C. for 8 hours in an oxygen atmosphere to produce positive electrode active material particles.

Example 4
A coating layer was formed on the positive electrode active material particles prepared in Example 1 by the following procedure.
First, an aqueous solution containing lithium hydroxide, niobium hydroxide, and pure water, each having a Li content and a Nb content of 0.15 mol/L, was prepared as a coating liquid. Next, the surfaces of the produced positive electrode active material particles were coated with an oxide precursor containing Li and Nb using the coating liquid by a tumbling fluidized bed coating device, 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 having a coating layer on the surface.

Example 5
A coating layer was formed on the positive electrode active material particles prepared in Example 2 by the following procedure.
First, an aqueous solution containing lithium carbonate, niobium hydroxide, and pure water, each having a Li content and a Nb content of 0.15 mol/L, was prepared as a coating liquid. Next, the surfaces of the produced positive electrode active material particles were coated with an oxide precursor containing Li and Nb using the coating liquid by a tumbling fluidized bed coating device, 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 having a coating layer on the surface.

Example 6
A coating layer was formed on the positive electrode active material particles prepared in Example 3 by the following procedure.
First, an aqueous solution containing lithium carbonate, niobium hydroxide, and pure water, each having a Li content and a Nb content of 0.15 mol/L, was prepared as a coating liquid. Next, the surfaces of the produced positive electrode active material particles were coated with an oxide precursor containing Li and Nb using the coating liquid by a tumbling fluidized bed coating device, 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 having a coating layer on the surface.

(Comparative Example 2)
A coating layer was formed on the positive electrode active material particles prepared in Comparative Example 1 by the following procedure.
First, an aqueous solution containing lithium carbonate, niobium hydroxide, and pure water, each having a Li content and a Nb content of 0.15 mol/L, was prepared as a coating liquid. Next, the surfaces of the produced positive electrode active material particles were coated with an oxide precursor containing Li and Nb using the coating liquid by a tumbling fluidized bed coating device, 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 having a coating layer on the surface.

<Composition of Positive Electrode Active Material>
0.2 g of each of the obtained positive electrode active material samples (powder) 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 analysis values of Li and metal components, as well as the impurity concentration and the amount of residual alkali, from the total amount of the analyzed sample, and f in "O _f " in formula (1) was calculated from this.

<50% cumulative volume particle size D50>
100 mg of each sample (powder) of the obtained positive electrode active material was dispersed by irradiating 40 W ultrasonic waves for 60 seconds at a flow rate of 50% using a laser diffraction type particle size distribution measuring device "MT3300EXII" manufactured by Microtrac, and then the particle size distribution was measured to obtain a cumulative particle size distribution curve based on volume. 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 powder of the positive electrode active material. In addition, the water-soluble solvent at the time of 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 aspheric, the measurement range was 0.021 to 2000 μm, and the measurement time was 30 seconds.

<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 filled with nitrogen gas in the glass cell, and then heat-treated in a nitrogen gas atmosphere at 40° C. for 20 minutes to degas. Thereafter, the glass cell containing the degassed sample (powder) was set in a specific surface area measuring device manufactured by Quantachrome: Monosorb Model MS-21, and the specific surface area X was measured by the BET method (one-point method) while flowing a He: 70 at %-N2: 30 at % mixed gas as an adsorption gas. The specific surface area was also measured for the sample before and after coating with the coating layer.

<Circularity>
The circularity was measured by a particle image analyzer manufactured by Malvern: Morphologi G3. Specifically, the circularity was measured by filtering the 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 set in a dispersion unit after the sample was put into a sample cartridge. A nitrogen gas introduction 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 photographed and analyzed. Then, the circularity was calculated from the projected area and perimeter of each photographed particle (18,000 or more) using the following formula 3. The average value of the circularity refers to the average of the circularity of all the particles of the measured positive electrode active material. The circularity was measured before and after the coating layer of the sample was coated.

Circularity=4πS/L2 (Equation 3)
(In the above formula, S is the projected area of the particle, L is the perimeter of the projected image of the particle, and π is the circular constant.)

<Particle strength>
The particle strength was measured as follows using a microcompression tester: MCT-211 manufactured by Shimadzu Corporation: That is, the dispersed sample was placed on a sample stage, and a microscope was used to aim at the center of a single secondary particle having an average particle diameter of D50, and an indenter having a diameter of 20 μm was pressed against the sample at a load rate of 0.532 mN/sec, and the strength at the time of breakage was measured at N=11 to 14, and the average value was taken as the particle strength.

<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 an X-ray source of CuKα, a tube voltage of 40 kV, a tube current of 30 mA, 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 ° was obtained, and this was taken as the crystallite size.

<Initial discharge capacity, capacity retention rate over 20 cycles>
The positive electrode active material, the conductive assistant, and the 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 the conductive assistant were mixed to form a slurry, which was applied to an Al foil, dried, and pressed to form a positive electrode. Next, a 2032-type coin cell for evaluation was prepared with Li as the counter electrode, and 1M-LiPF ₆ was dissolved in EC-DMC (1:1) as the electrolyte. 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.

<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[%].

(Battery characteristics)
<How to make an 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 (75Li ₂ S-25P ₂ S ₅ ), acetylene black, and a 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 mass%, and the mixture was mixed with Mazerustar for 400 seconds to form a positive electrode mixture slurry, which was then applied to the surface of an aluminum foil having a thickness of 0.03 mm, which was a positive electrode current collector. At this time, the positive electrode mixture slurry was applied to the surface of the positive electrode current collector by moving the applicator at a moving speed of 15 mm/s using an applicator with a gap of 400 μm.
Next, the positive electrode current collector with the positive electrode mixture slurry applied on its surface was dried on a hot plate at 100° C. for 30 minutes to remove the solvent, thereby forming a positive electrode mixture layer on the surface of the positive electrode current collector.
Next, the above-mentioned positive electrode composite layer was placed on a sulfide-based solid electrolyte having the same composition as the sulfide-based solid electrolyte used in producing the positive electrode composite layer, and pressed at 333 MPa to produce a laminate of solid electrolyte layer/positive electrode composite layer/positive electrode current collector.
Next, a metal Li-In alloy was pressed at 37 MPa onto the negative electrode side of the solid electrolyte layer to form a negative electrode layer. The laminate thus produced was placed in a battery test cell made of SUS304 and subjected to a confining pressure to produce an all-solid-state secondary battery. The all-solid-state secondary battery produced by applying the confining pressure was then placed in a sealed container to block the air.

<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 the initial charge at 0.1 C at 55° C., and then discharging at 0.1 C.

<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.

<Evaluation of Capacity Retention Rate over 20 Cycles>
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.

<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 performing AC impedance measurement from 0.1 Hz to 1 MHz and analyzing the obtained Cole-Cole plot.
The above production conditions and test results are shown in Tables 1 to 3.

(Evaluation Results)
The positive electrode active materials of Examples 1 to 3 all had the composition represented by the following formula (1): In addition, 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 lithium ion batteries.
Li _a Ni _b Co _c Mn _d M _{e Of} (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.)
Moreover, all of the positive electrode active materials of Examples 1 to 3 had a particle strength of 100 MPa or more, 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.
In addition, all of the positive electrode active materials of Examples 4 to 6 had a coating layer consisting 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, the specific surface area was 0.6 ^m2 /g or less, the particle strength was 100 MPa or more, and the crystallite size of the (003) plane was 650 Å or less.
Therefore, in Examples 4 to 6 in which a coating layer was provided on Examples 1 to 3, the initial discharge capacity, the 20 cycle capacity retention rate, the initial DC resistance, the DC resistance after 20 cycles, and the resistance increase rate after 20 cycles all showed good results.

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

Claims (11)

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 Of} (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.)
A positive electrode active material for a lithium ion battery, having a particle strength of 100 MPa or more, a crystallite size of the (003) plane of 650 Å or less, and a 50% cumulative volumetric particle size D50 of 5 to 7 μm. A positive electrode for a lithium ion battery comprising the positive electrode active material for a lithium ion battery according to claim 1. A lithium ion battery comprising the positive electrode and negative electrode for a lithium ion battery according to claim 2. 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 Of} (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.)
a coating layer made of an oxide of Li and Nb provided on a surface of a positive electrode active material particle of the positive electrode active material for a lithium ion battery;
The positive electrode active material for an all-solid-state lithium ion battery comprises: a particle circularity of 0.94 to 0.96; a specific surface area of 0.6 m ² /g or less; a particle strength of 100 MPa or more; and a crystallite size of the (003) plane of 650 Å or less. 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 claim 4. 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 5. 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 Mnd} (OH) ₂ (2)
(In the formula (2), 0.58≦b≦0.62, 0.18≦c≦0.22, and b+c+d=1.)
A step of wet-mixing 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, with the precursor of the positive electrode active material for lithium ion batteries to obtain a mixture;
dry mixing the mixture with a lithium source and calcining at 820° C. or higher for 4 hours or more;
The method for producing a positive electrode active material for a lithium ion battery includes the steps of: The method for producing a positive electrode active material for a lithium ion battery according to claim 7, wherein the D50 of the Zr oxide, Ta oxide and W oxide is 0.3 to 1.0 μm. The method for producing a positive electrode active material for a lithium ion battery according to claim 7, 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. A step of preparing a positive electrode active material for a lithium ion battery produced by the method according to any one of claims 7 to 9;
forming a coating layer made of an oxide of Li and Nb on the surface of the positive electrode active material particles of the lithium ion battery positive electrode active material by using an aqueous solution containing Li and Nb with a tumbling fluidized bed apparatus;
The method for producing a positive electrode active material for an all-solid-state lithium ion battery includes the steps of: The method for producing a positive electrode active material for an all-solid-state lithium-ion battery according to claim 10, 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, and ammonia water.

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