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

Abstract

Provided is a positive electrode active material for all-solid-state lithium ion batteries that includes positive electrode active material particles and a coating layer provided to the positive electrode active material particle surfaces, wherein the positive electrode active material particles are represented by the composition indicated in formula (1): LiaNibCocMndMeOf (in formula (1), 1.0 ≤ a ≤ 1.10, 0.58 ≤ b ≤ 0.62, b+c+d+e=1, 0.0035 ≤ e / (b+c+d) ≤ 0.055, 1.8 ≤ f ≤ 2.2, and M is at least one selected from Zr, Ta, and W), the coating layer contains Li, Nb, and Ti, and in ICP emission spectrometry, the Ti content contained in the positive electrode active material for all-solid-state lithium ion batteries is 10 to 30 mass ppm and the mass ratio Ti / Nb of Ti and Nb in the positive electrode active material for all-solid-state lithium ion batteries is 0.0020 to 0.0040.

Description

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

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

[0002] Currently used lithium-ion secondary batteries use organic electrolytes, but these electrolytes are flammable, and the risk of fire during charging is difficult to completely eliminate no matter how hard we try. For these reasons, active development is underway for all-solid-state lithium-ion secondary batteries, which use a solid electrolyte.

[0003] Conventional solid electrolytes have poor lithium ion conductivity, making battery design difficult. However, in recent years, solid electrolytes with good conductivity have been discovered, and many inventions have been made to apply these to all-solid-state lithium ion secondary batteries.

[0004] However, all-solid-state lithium-ion secondary batteries have a problem in that a high-resistance layer is formed due to an interfacial reaction between the positive electrode and the solid electrolyte, resulting in a decrease in output. A method for suppressing the formation of this high-resistance layer is known in which the surface of the positive electrode active material is coated with a Li composite oxide. A typical Li composite oxide for coating the surface of the positive electrode active material is LiNbO, which exhibits high ionic conductivity (Patent Document 1).

[0005] Patent No. 6293338

[0006] LiNbO3 is amorphous and has a -6 The Li composite oxide has a high ionic conductivity of about 10 S / cm. -4 ~10 -3 S / cm, and the Li ion diffusion in the coating layer is the rate-limiting process for the entire battery. For this reason, there is still room for development of a positive electrode active material for all-solid-state lithium-ion batteries that will provide good battery characteristics when used in such batteries.

[0007] 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 an all-solid-state lithium-ion battery, which exhibits good battery characteristics when used in the all-solid-state lithium-ion battery, a cathode for the all-solid-state lithium-ion battery, an all-solid-state lithium-ion battery, and a method for producing the cathode active material for the all-solid-state lithium-ion battery.

[0008] The present invention, which was completed based on the above findings, is defined as follows: 1. A cathode active material for an all-solid-state lithium ion battery, comprising cathode active material particles and a coating layer provided on the surface of the cathode active material particles, wherein the cathode active material particles are represented by the composition shown in the following formula (1): Li a Ni b Co c Mn d M e O f (1) (in formula (1), 1.0≦a≦1.10, 0.58≦b≦0.62, b+c+d+e=1, 0.0035≦e / (b+c+d)≦0.055, 1.8≦f≦2.2, and M is at least one selected from Zr, Ta, and W), the coating layer contains Li, Nb, and Ti, and the content of Ti contained in the all-solid-state lithium-ion battery positive electrode active material is 10 to 30 ppm by mass, as determined by ICP atomic emission spectroscopy, and the mass ratio of Ti to Nb in the all-solid-state lithium-ion battery positive electrode active material, Ti / Nb, is 0.0020 to 0.0040. 3. The cathode active material for an all-solid-state lithium-ion battery according to 1 above, wherein Ti is detected for up to 50 seconds from the start of analysis when ion sputtering is performed with a sputtering rate set to 0.25 nm / second in a TOF-SIMS analysis of the surface of the cathode active material for an all-solid-state lithium-ion battery. 4. A cathode active material for an all-solid-state lithium-ion battery according to 1 or 2 above, having a 50% cumulative volume particle size D50 of 4 to 7 μm. 5. 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 1 to 3 above. 6. An all-solid-state lithium-ion battery comprising the cathode and anode for an all-solid-state lithium-ion battery according to 4 above. 7. A method for producing a cathode active material for an all-solid-state lithium-ion battery, the method comprising the steps of: preparing a precursor of a cathode active material for an all-solid-state lithium-ion battery represented by the composition shown in formula (2) below; andb Co c Mn d (OH)2 (2) (In formula (2), 0.58≦b≦0.62, 0.19≦c≦0.21, and b+c+d=1.) A method for producing a cathode active material for an all-solid-state lithium ion battery, 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 cathode active material for an all-solid-state lithium ion battery to obtain a mixture; dry-mixing the mixture with a lithium source and firing at 800° C. or higher for 10 hours or more to obtain cathode active material particles; and coating the surfaces of the cathode active material particles with a coating liquid containing Li, Nb, and Ti, and then performing heat treatment at 300° C. or lower, to form a coating layer containing Li, Nb, and Ti on the surfaces of the cathode active material particles. 7. The method for producing a positive electrode active material for an all-solid-state lithium-ion battery according to 6, wherein the coating liquid containing Li, Nb, and Ti is an aqueous solution obtained by mixing an aqueous solution of peroxo complexes of Li and Nb, each having a Li content and a Nb content of 0.1 to 0.2 mol / L, with an aqueous solution of peroxo complexes of Ti, each having a Ti content of 0.002 to 0.01 mol / L, in a mass ratio of the aqueous solution of peroxo complexes of Li and Nb:the aqueous solution of peroxo complexes of Ti=30:1 to 30:5.

[0009] According to the present invention, it is possible to provide a cathode active material for an all-solid-state lithium ion battery, a cathode for an all-solid-state lithium ion battery, an all-solid-state lithium ion battery, and a method for producing a cathode active material for an all-solid-state lithium ion battery, which provide good battery characteristics when used in the all-solid-state lithium ion battery.

[0010] FIG. 1 is a schematic diagram of an all-solid-state lithium ion battery according to an embodiment of the present invention. FIG. 2 is a graph of the spectral distribution obtained by TOF-SIMS analysis in Example 1. FIG. 3 is a graph of the spectral distribution obtained by TOF-SIMS analysis in Example 2. FIG. 4 is a graph of the spectral distribution obtained by TOF-SIMS analysis in Example 3. FIG. 5 is a graph of the spectral distribution obtained by TOF-SIMS analysis in Comparative Example 1. FIG. 6 is a graph of the spectral distribution obtained by TOF-SIMS analysis in Comparative Example 2. FIG. 7 is a graph of the spectral distribution obtained by TOF-SIMS analysis in Comparative Example 3.

[0011] 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.

[0012] (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 positive electrode active material particles and a coating layer provided on the surface of the positive electrode active material particles. The positive electrode active material particles are 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≦1.10, 0.58≦b≦0.62, b+c+d+e=1, 0.0035≦e / (b+c+d)≦0.055, 1.8≦f≦2.2, and M is at least one selected from Zr, Ta, and W.)

[0013] In the positive electrode active material particles of the positive electrode active material for an all-solid-state lithium-ion battery, in the above formula (1), a, which indicates the lithium composition, is controlled to be 1.0≦a≦1.10. 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 1.10 or less, residual alkaline components such as lithium carbonate and lithium hydroxide present on the surface of the positive electrode active material particles, which can become resistance components when formed into a battery, can be suppressed.

[0014] In the positive electrode active material particles of the positive electrode active material for an all-solid-state lithium-ion battery, b, which indicates the nickel composition in the above formula (1), is controlled to satisfy 0.58≦b≦0.62. Since b, which indicates the nickel composition, is 0.58 or more, a good battery capacity of the all-solid-state lithium-ion battery can be obtained.

[0015] In the positive electrode active material particles of the all-solid-state lithium-ion battery positive electrode active material, the sum of b representing the nickel composition, c representing the cobalt composition, d representing the manganese composition, and e representing the composition of the additive element M 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 extraction of lithium during charge and discharge. If c + d + e is less than 0.38, it becomes difficult to obtain the effects of the above-mentioned cycle characteristics and expansion and contraction behavior, and if c + d + e exceeds 0.42, the amounts of cobalt and manganese added may be too large, resulting in a significant decrease in initial discharge capacity or being disadvantageous in terms of cost.

[0016] The positive electrode active material particles of the positive electrode active material for all-solid-state lithium-ion batteries have the above formula (1) where e / (b+c+d) satisfies 0.0035≦e / (b+c+d)≦0.055, and M is at least one element selected from Zr, Ta, and W. That is, the positive electrode active material particles of the positive electrode active material for all-solid-state lithium-ion batteries contain 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), is 0.0035 or higher, 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), is 0.055 or lower, the effect of suppressing a decrease in discharge capacity is achieved. Furthermore, preferably, 0.04≦e / (b+c+d)≦0.05.

[0017] The coating layer provided on the surface of the positive electrode active material particles of the positive electrode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention contains Li, Nb, and Ti. The coating layer is preferably in the form of lithium niobate (LiNbO3) containing a trace amount of Ti. The effect of containing a trace amount of Ti in the lithium niobate (LiNbO3) of the coating layer will be described. The inclusion of Ti in the coating layer, which exists as a tetravalent ion with a lower valence than Nb, which exists as a pentavalent ion, results in the formation of holes within the coating layer. During charge and discharge, lithium ions migrate solely through interstitial diffusion in conventional lithium niobate coating layers. However, when a trace amount of Ti is included, Li ions can also migrate by vacancy diffusion via the formed holes. This facilitates Li ion migration, improving rate performance and reducing diffusion resistance within the coating layer.

[0018] In inductively coupled plasma (ICP) emission spectroscopy, the Ti content in the positive electrode active material for an all-solid-state lithium-ion battery is controlled to 10 to 30 ppm by mass. When the Ti content is 10 ppm by mass or more, the rate characteristics of an all-solid-state lithium-ion battery using the positive electrode active material are improved and the diffusion resistance can be reduced. When the Ti content is more than 30 ppm by mass, the rate characteristics and diffusion resistance may deteriorate. The Ti content in the positive electrode active material for an all-solid-state lithium-ion battery is preferably 10 to 20 ppm by mass, and more preferably 10 to 15 ppm by mass.

[0019] In ICP atomic emission spectroscopy, the mass ratio Ti / Nb of Ti to Nb in the positive electrode active material for an all-solid-state lithium-ion battery is controlled to 0.0020 to 0.0040. When the mass ratio Ti / Nb of Ti to Nb is 0.0020 or more, holes are formed in the coating layer containing lithium niobate, improving the rate characteristics of an all-solid-state lithium-ion battery using the positive electrode active material and reducing the diffusion resistance. When the mass ratio Ti / Nb of Ti to Nb is greater than 0.0040, more holes are formed in the lithium niobate coating layer, deteriorating the rate characteristics and the diffusion resistance. In ICP atomic emission spectroscopy, the mass ratio Ti / Nb of Ti to Nb in the positive electrode active material for an all-solid-state lithium-ion battery is preferably 0.0020 to 0.0035, and more preferably 0.0020 to 0.0025.

[0020] The above-mentioned ICP optical emission spectroscopy can be measured, for example, by weighing out 0.2 g of the positive electrode active material (powder), decomposing it by an alkali fusion method, and then performing composition analysis using an ICP (inductively coupled plasma) optical emission spectroscopy analyzer (ICP-OES) "PS7800" manufactured by Hitachi High-Tech Corporation.

[0021] Furthermore, the Ti content obtained by analyzing the positive electrode active material by ICP optical emission spectrometry can be determined by, for example, analyzing the Ti data detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS), which indicates that the Ti content is the Ti content contained in the coating layer on the surface of the positive electrode active material particles. Specifically, in TOF-SIMS analysis of the surface of a positive electrode active material for an all-solid-state lithium ion battery, when ion sputtering is performed with a sputtering rate set to 0.25 nm / sec, if Ti is detected within 50 seconds from the start of the analysis, it can be determined that Ti is contained in the coating layer. For example, TOF-SIMS analysis of the surface of the positive electrode active material was performed using a TOF-SIMS analyzer (TOF-SIMS 4S manufactured by ION-TOF). Specifically, Bi was used as the primary ion. 3+ , Cs to sputter ions +TOF-SIMS analysis was performed in high mass resolution mode (negative) with a sputtering rate of 0.25 nm / sec (SiO2 equivalent). The sputtering area was 300 μm × 300 μm, and the measurement area was 150 μm × 150 μm. The coating layer was 6 to 10 nm thick, and if Ti was detected in the TOF-SIMS analysis within approximately 50 seconds from the start of analysis, during which the thickness of the coating layer was sputtered, it was determined that Ti was present in the coating layer. Here, when Ti is contained in the positive electrode active material particles, as in the TOF-SIMS Ni results shown in Figures 2 to 4 below, the graphs show an increasing trend for 50 seconds after the start of sputtering. When Ti is contained in the coating layer, as in the TOF-SIMS Ti and Nb results shown in Figures 2 to 4 below, the graphs show a peak at the start of sputtering and a decreasing trend thereafter. When the coating layer does not contain Ti, the result of ICP analysis is below the lower limit of quantification.

[0022] 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).

[0023] The positive electrode active material for an all-solid-state lithium-ion battery 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 aggregated is also not particularly limited and may be 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 approximately uniformly radially from the center to form substantially spherical or substantially elliptical secondary particles.

[0024] The 50% cumulative volume particle size D50 of the positive electrode active material for an all-solid-state lithium-ion battery is preferably 4 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 positive electrode active material for an all-solid-state lithium-ion battery is 4 μm or more, the specific surface area can be reduced and the coating amounts of Li, Nb, and Ti can be reduced. When the 50% cumulative volume particle size D50 of the positive electrode active material for an all-solid-state lithium-ion battery is 7 μm or less, the specific surface area can be prevented from becoming excessively small. The 50% cumulative volume particle size D50 of the positive electrode active material for an all-solid-state lithium-ion battery is more preferably 5 to 6 μm.

[0025] The 50% cumulative volume particle size D50 of the positive electrode active material for an all-solid-state lithium-ion battery can be measured, for example, as follows. 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% cumulative was taken as the 50% cumulative volume particle size D50 of the positive electrode active material powder. The aqueous solvent used in the measurement was passed through a filter, with a solvent refractive index of 1.333, particle permeability conditions of permeable, particle refractive index of 1.81, and shape of aspherical. The measurement range was 0.021 to 2000 μm, and the measurement time was 30 seconds.

[0026] (Method for producing a cathode active material for an all-solid-state lithium-ion battery) Next, a method for producing a cathode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention will be described in detail. In the method for producing a cathode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention, first, a precursor of a cathode active material for an all-solid-state 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, 0.19≦c≦0.21, and b+c+d=1.)

[0027] A method for producing a precursor of a positive electrode active material for an all-solid-state lithium-ion battery first involves preparing aqueous solutions 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.

[0028] 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 %.

[0029] 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.

[0030] Next, the precursor of the positive electrode active material for an all-solid-state 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 appropriately adjusted depending on the target composition of the positive electrode active material for an all-solid-state 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. The wet mixing method is not particularly limited, but examples include adding the precursor of the positive electrode active material for an all-solid-state lithium-ion battery and at least one oxide selected from Zr oxide, Ta oxide, and W oxide to an aqueous solvent, mixing them by mechanical means to prepare a slurry, and then drying the slurry while standing, or drying the slurry by spray drying, to obtain a mixture.

[0031] As described above, by wet-mixing Zr oxide, Ta oxide, and W oxide with the precursor of the all-solid-state lithium-ion battery cathode active material before mixing with the lithium source, the adhesion rate of the oxides of the different elements (Zr, Ta, W) to the surface of the precursor of the all-solid-state lithium-ion battery cathode active material is improved. Furthermore, by controlling the D50 of the particles of Zr oxide, Ta oxide, and W oxide to be mixed to 1 μm or less, the adhesion rate of the oxides of the different elements (Zr, Ta, W) to the surface of the precursor of the all-solid-state lithium-ion battery cathode active material is improved. Improving the adhesion rate of the different elements (Zr, Ta, W) to the surface of the precursor of the all-solid-state lithium-ion battery cathode active material can prevent the oxides of the different elements (Zr, Ta, W) from adhering to the surface of the particles of the all-solid-state lithium-ion battery cathode active material and remaining as independent particles. The D50 of the particles of Zr oxide, Ta oxide and W oxide to be mixed is preferably 0.3 to 1.0 μm, more preferably 0.3 to 0.5 μm.

[0032] Next, the mixture of the precursor of the positive electrode active material for an all-solid-state lithium-ion battery obtained as described above and at least one of Zr oxide, Ta oxide, and W oxide is dry-mixed with a lithium source 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 an all-solid-state lithium-ion battery. 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.

[0033] Next, the lithium mixture obtained as described above is fired at 800°C or higher for 10 hours or more. By firing the lithium mixture at a temperature of 800°C or higher for a long period of time, such as 10 hours or more, the solid solution rate of the different elements (Zr, Ta, W) in the positive electrode active material for an all-solid-state lithium-ion battery is improved. This also prevents oxides of the different elements (Zr, Ta, W) from adhering to the surface of the positive electrode active material particles for an all-solid-state lithium-ion battery and remaining as independent particles. The firing temperature is preferably 820 to 880°C, and the firing time is preferably 10 to 12 hours. The firing atmosphere is preferably an oxygen atmosphere.

[0034] Thereafter, if necessary, the fired body can be pulverized using, for example, a pulverizer to obtain positive electrode active material particles.

[0035] Next, the surfaces of the positive electrode active material particles are coated with an aqueous solution (coating liquid) containing Li, Nb, and Ti. In this case, the coating liquid is preferably an aqueous solution obtained by mixing an aqueous solution of Li and Nb peroxo complexes, each having a Li content and a Nb content of 0.1 to 0.2 mol / L, with an aqueous solution of Ti peroxo complexes, each having a Ti content of 0.002 to 0.01 mol / L, in a mass ratio of the aqueous solution of Li and Nb peroxo complexes:the aqueous solution of Ti peroxo complexes = 30:1 to 30:5.

[0036] The coating method is not particularly limited as long as it is a method that can apply a coating liquid to the surface of the positive electrode active material particles. For example, a method using a coating device having a tumbling fluidized bed or a method using spray drying may be used.

[0037] After the surfaces of the positive electrode active material particles are coated with the aqueous solution (coating solution) containing Li, Nb, and Ti, a heat treatment is performed at 300° C. or less. The heat treatment is preferably performed at 200 to 300° C. for 1 to 5 hours. In this manner, a positive electrode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention can be obtained, in which a coating layer containing Li, Nb, and Ti is formed on the surfaces of the positive electrode active material particles.

[0038] (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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] The negative electrode layer (negative electrode) of the all-solid-state lithium-ion battery may be a layer of a known metal foil for all-solid-state lithium-ion batteries or a layer of a negative electrode active material. 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.

[0044] The negative electrode layer may be made of, for example, a metal such as lithium metal, indium metal, or silicon, or an alloy of the metal combined with other elements or compounds, or graphite, silicon oxide, or a composite material thereof.

[0045] 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.

[0046] 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 inserting a metal foil and a method of compression molding negative electrode active material particles.

[0047] The solid electrolyte may be a known solid electrolyte for all-solid-state lithium ion batteries, such as a sulfide-based solid electrolyte.

[0048] 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.

[0049] 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.

[0050] The solid electrolyte layer of the all-solid-state lithium ion battery can be formed by compression molding the solid electrolyte.

[0051] 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.

[0052] 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, and aluminum alloys. Examples of the shape of the positive electrode current collector include foil and plate. The average thickness of the positive electrode current collector may be, for example, 10 μm to 500 μm, or 50 μm to 100 μm.

[0053] 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, indium, copper, and stainless steel. Examples of the shape of the negative electrode current collector include foil and plate. The average thickness of the negative electrode current collector may be, for example, 10 μm to 500 μm, or 50 μm to 100 μm.

[0054] 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. 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, square, button, coin, and flat types.

[0055] 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.

[0056] (Example 1) First, the composition formula: Ni 0.598 Co 0.198 Mn 0.199 A precursor of a positive electrode active material for an all-solid-state lithium-ion battery represented by (OH)2 was prepared. Next, a precursor of a positive electrode active material for an all-solid-state lithium-ion battery having a D50 of 6.2 μm and ZrO2 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. Next, as a coating liquid, an aqueous solution (a Li-Nb-Ti peroxo complex aqueous solution) was prepared by mixing an aqueous Li and Nb peroxo complex aqueous solution, each having a Li content and a Nb content of 0.15 mol / L, with an aqueous Ti peroxo complex aqueous solution, each having a Ti content of 0.011 mol / L, in a mass ratio of the aqueous Li and Nb peroxo complex aqueous solution:the aqueous Ti peroxo complex aqueous solution = 18: 1. Next, using this coating liquid, the surfaces of the prepared positive electrode active material particles were coated with an oxide precursor containing Li, Nb, and Ti in a tumbling fluidized bed coating apparatus, and the coated particles were heat-treated at 230°C in an oxygen atmosphere to produce a positive electrode active material having a coating layer formed on the surface.

[0057] (Example 2) First, the composition formula: Ni 0.598 Co 0.198 Mn 0.199 A precursor of a cathode active material for an all-solid-state lithium-ion battery represented by (OH)2 was prepared. Next, a precursor of a cathode active material for an all-solid-state lithium-ion battery having a D50 of 6.2 μm and WO3 having a D50 of 0.29 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 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 cathode active material particles. Next, as a coating liquid, an aqueous solution (a Li-Nb-Ti peroxo complex aqueous solution) was prepared by mixing an aqueous Li and Nb peroxo complex aqueous solution, each having a Li content and a Nb content of 0.15 mol / L, with an aqueous Ti peroxo complex aqueous solution, each having a Ti content of 0.011 mol / L, in a mass ratio of the aqueous Li and Nb peroxo complex aqueous solution:the aqueous Ti peroxo complex aqueous solution = 18: 1. Next, using this coating liquid, the surfaces of the prepared positive electrode active material particles were coated with an oxide precursor containing Li, Nb, and Ti in a tumbling fluidized bed coating apparatus, and the coated particles were heat-treated at 230°C in an oxygen atmosphere to produce a positive electrode active material having a coating layer formed on the surface.

[0058] (Example 3) First, the composition formula: Ni 0.598 Co 0.198 Mn 0.199A precursor of a cathode active material for an all-solid-state lithium-ion battery represented by (OH) was prepared. Next, a precursor of a cathode active material for an all-solid-state lithium-ion battery having a D50 of 6.2 μm and TaO having a D50 of 0.31 μm were added to an aqueous solvent in a charged amount of 0.25 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 cathode active material particles. Next, as a coating liquid, an aqueous solution (a Li-Nb-Ti peroxo complex aqueous solution) was prepared by mixing an aqueous Li and Nb peroxo complex aqueous solution, each having a Li content and a Nb content of 0.15 mol / L, with an aqueous Ti peroxo complex aqueous solution, each having a Ti content of 0.011 mol / L, in a mass ratio of the aqueous Li and Nb peroxo complex aqueous solution:the aqueous Ti peroxo complex aqueous solution = 18: 1. Next, using this coating liquid, the surfaces of the prepared positive electrode active material particles were coated with an oxide precursor containing Li, Nb, and Ti in a tumbling fluidized bed coating apparatus, and the coated particles were heat-treated at 230°C in an oxygen atmosphere to produce a positive electrode active material having a coating layer formed on the surface.

[0059] (Comparative Example 1) First, the composition formula: Ni 0.598 Co 0.198 Mn 0.199A precursor of a cathode active material for an all-solid-state lithium-ion battery represented by (OH)2 was prepared. Next, a precursor of a cathode active material for an all-solid-state lithium-ion battery having a D50 of 6.2 μm and ZrO2 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 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 cathode active material particles. Next, an aqueous solution of a Li and Nb peroxo complex (Li-Nb peroxo complex aqueous solution) having a Li content and a Nb content of 0.15 mol / L, respectively, was prepared as a coating liquid. Next, using the coating liquid, the surfaces of the prepared positive electrode active material particles were coated with an oxide precursor containing Li and Nb using a tumbling fluidized bed coating device, and heat treatment was performed at 250°C in an oxygen atmosphere to prepare a positive electrode active material having a coating layer on the surface.

[0060] (Comparative Example 2) First, the composition formula: Ni 0.598 Co 0.198 Mn 0.199A precursor of a cathode active material for an all-solid-state lithium-ion battery represented by (OH)2 was prepared. Next, a precursor of a cathode active material for an all-solid-state lithium-ion battery having a D50 of 6.2 μm and WO3 having a D50 of 0.29 μm were added to an aqueous solvent in a charge 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 cathode active material particles. Next, an aqueous solution of a Li and Nb peroxo complex (Li-Nb peroxo complex aqueous solution) having a Li content and a Nb content of 0.15 mol / L, respectively, was prepared as a coating liquid. Next, using the coating liquid, the surfaces of the prepared positive electrode active material particles were coated with an oxide precursor containing Li and Nb using a tumbling fluidized bed coating device, and heat treatment was performed at 250°C in an oxygen atmosphere to prepare a positive electrode active material having a coating layer on the surface.

[0061] (Comparative Example 3) First, the composition formula: Ni 0.598 Co 0.198 Mn 0.199A precursor of a cathode active material for an all-solid-state lithium-ion battery represented by (OH)2 was prepared. Next, a precursor of a cathode active material for an all-solid-state lithium-ion battery having a D50 of 6.2 μm and Ta2O5 having a D50 of 0.31 μm were added to an aqueous solvent in a charge amount of 0.25 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 cathode active material particles. Next, a Li-Nb peroxo complex aqueous solution (Li-Nb peroxo complex aqueous solution) with a Li content and a Nb content of 0.15 mol / L each was prepared as a coating liquid. Next, using the coating liquid, the surfaces of the prepared positive electrode active material particles were coated with an oxide precursor containing Li and Nb using a tumbling fluidized bed coating device, and heat treatment was performed at 250°C in an oxygen atmosphere to prepare a positive electrode active material having a coating layer on its surface.

[0062] (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, and thus the "O" in formula (1) was calculated. f " was calculated.

[0063] (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.

[0064] (TOF-SIMS Analysis) TOF-SIMS analysis of the surface of the positive electrode active material was carried out using a TOF-SIMS analyzer (TOF-SIMS 4S manufactured by ION-TOF). 3+ , Cs to sputter ions + TOF-SIMS analysis was performed in high mass resolution mode (negative) at a sputtering rate of 0.25 nm / sec (SiO2 equivalent) using a SiO2 sensor. The sputtering area was 300 μm × 300 μm, and the measurement area was 150 μm × 150 μm. The coating layer had a thickness of 6 to 10 nm, and if Ti is detected in the TOF-SIMS analysis within approximately 50 seconds from the start of analysis, during which the coating layer's thickness is sputtered, it is determined that Ti is present in the coating layer. Figures 2 to 7 show graphs of the spectral distribution obtained by the TOF-SIMS analysis of Examples 1 to 3 and Comparative Examples 1 to 3. The vertical axis of the graphs in Figures 2 to 7 represents ion intensity, and the horizontal axis represents the elapsed time from the start of analysis (sputtering time [seconds]). According to the graphs of the spectral distribution obtained by the TOF-SIMS analysis of Examples 1 to 3 in Figures 2 to 4, Ti (Ti +) was detected, and it is determined that Ti is present in the coating layer. According to the graphs of spectral distribution obtained by TOF-SIMS analysis of Comparative Examples 1 to 3 in Figures 5 to 7, it can be determined that the amount of Ti detected during the approximately 50 seconds from the start of analysis until the thickness of the coating layer is sputtered is an amount that can be recognized as noise and therefore is not significantly detected, and as a result, it can be determined that Ti is not present in the coating layer. Note that in the graphs of spectral distribution obtained by TOF-SIMS analysis in Figures 2 to 7, it can be determined that Ti (Ti + ), Li (LiCs + ), Nb(Nb + ) was also detected, and it is judged that Nb is also present in the coating layer. 2+ ), Li(LiCs + ), Ni(NiCs + ) was distributed at a constant amount after about 50 seconds had passed since the start of the analysis, and was found to be uniformly present in the depth direction within the positive electrode active material particles.

[0065] (ICP Optical Emission Spectroscopy) 0.2 g of the positive electrode active material (powder) was weighed out and decomposed by an alkali fusion method, and then a composition analysis was performed using an ICP (inductively coupled plasma) optical emission spectrometer (ICP-OES) "PS7800" manufactured by Hitachi High-Technologies Corporation. The Ti and Nb contents in the positive electrode active material were evaluated.

[0066] (Battery Characteristics) <Method of Manufacturing All-Solid-State Lithium-Ion Battery> The positive electrode active material obtained in Examples 1 to 3 and Comparative Examples 1 to 3, 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.

[0067] <Evaluation of 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.

[0068] <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.

[0069] <Evaluation of Resistance> The resistance of the all-solid-state lithium ion battery was evaluated as the initial resistance of the all-solid-state cell by measuring AC impedance from 0.1 Hz to 1 MHz and analyzing the obtained Cole-Cole plot.

[0070] <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 manufacturing conditions and test results are shown in Tables 1 to 3.

[0071]

[0072]

[0073]

[0074] (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. Li a Ni b Co c Mn d M e O f (1) (In the formula (1), 1.0≦a≦1.10, 0.58≦b≦0.62, b+c+d+e=1, 0.0035≦e / (b+c+d)≦0.055, 1.8≦f≦2.2, and M is at least one selected from Zr, Ta, and W.) In addition, in all of the positive electrode active materials of Examples 1 to 3, the coating layer contained Li, Nb, and Ti, and in ICP atomic emission spectroscopy analysis, the content of Ti contained in the positive electrode active material was 10 to 30 ppm by mass, and the mass ratio of Ti to Nb in the positive electrode active material for an all-solid-state lithium-ion battery, Ti / Nb, was 0.0020 to 0.0040. Therefore, for all of Examples 1 to 3, the initial discharge capacity, rate characteristics, all-solid-state cell initial resistance, and 20-cycle capacity retention rate all showed good results.

[0075] The positive electrode active materials of Comparative Examples 1 to 3 did not contain Ti in the coating layer, and all of them had high initial resistance in the all-solid-state cells. Furthermore, Comparative Example 1 also had poor rate characteristics.

Claims

1. A positive electrode active material for an all-solid-state lithium-ion battery, comprising positive electrode active material particles and a coating layer provided on the surface of the positive electrode active material particles, wherein the positive electrode active material particles are 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 ≦ 1.10, 0.58 ≦ b ≦ 0.62, b + c + d + e = 1, 0.0035 ≦ e / (b + c + d) ≦ 0.055, 1.8 ≦ f ≦ 2.2, and M is at least one selected from Zr, Ta, and W.) The coating layer contains Li, Nb, and Ti. In inductively coupled plasma optical emission spectrometry, the content of Ti contained in the positive electrode active material for the all-solid-state lithium-ion battery is 10 to 30 mass ppm, and the mass ratio Ti / Nb of Ti to Nb in the positive electrode active material for the all-solid-state lithium-ion battery is 0.0020 to 0.0040. A positive electrode active material for an all-solid-state lithium-ion battery.

2. The positive electrode active material for an all-solid-state lithium ion battery according to claim 1, wherein in the TOF-SIMS analysis of the surface of the positive electrode active material for an all-solid-state lithium ion battery, when ion sputtering is performed with the sputtering rate set to 0.25 nm / second, Ti is detected within 50 seconds from the start of the analysis.

3. The positive electrode active material for an all-solid-state lithium ion battery according to claim 1, wherein the 50% cumulative volume particle size D50 is 4 to 7 μm.

4. 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 1 to 3.

5. An all-solid-state lithium ion battery, comprising the positive electrode for an all-solid-state lithium ion battery according to claim 4 and a negative electrode.

6. A step of preparing a precursor of a cathode active material for an all-solid-state lithium-ion battery represented by the composition shown in the following formula (2); Ni b Co c Mn d (OH)2 (2) (In the formula (2), 0.58 ≦ b ≦ 0.62, 0.19 ≦ c ≦ 0.21, and b + c + d = 1.) A step of wet-mixing at least one selected from oxides of Zr, oxides of Ta, and oxides of W, having a 50% cumulative volume particle size D50 of 1 μm or less, with the precursor of the cathode active material for the all-solid-state lithium-ion battery to obtain a mixture; A step of dry-mixing the mixture with a lithium source and firing at 800° C. or higher for 10 hours or more to obtain cathode active material particles; A step of forming a coating layer containing Li, Nb, and Ti on the surface of the cathode active material particles by coating the surface of the cathode active material particles with a coating solution containing Li, Nb, and Ti and performing heat treatment at 300° C. or lower. A method for producing a cathode active material for an all-solid-state lithium-ion battery, comprising the steps.

7. The method for producing a positive electrode active material for an all-solid-state lithium ion battery according to claim 6, wherein the coating liquid containing Li, Nb, and Ti is an aqueous solution of a peroxo complex of Li and Nb having an Li content and an Nb content of 0.1 to 0.2 mol / L, respectively, and an aqueous solution of a peroxo complex of Ti having a Ti content of 0.002 to 0.01 mol / L, and the mass ratio is such that the aqueous solution of the peroxo complex of Li and Nb: the aqueous solution of the peroxo complex of Ti = 30:1 to 30:5.

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