Positive electrode active material for all-solid-state lithium-ion secondary battery and method for manufacturing same

Abstract

An object of the present application is to provide a positive electrode active material having higher battery capacity when used as a positive electrode active material of a full solid battery. A positive electrode active material for a full solid lithium ion secondary battery, having particles of a lithium-nickel composite oxide and a coating layer coating the surface of the particles, wherein the particles of the lithium-nickel composite oxide have a crystal structure belonging to space group R-3m, the particles of the lithium-nickel composite oxide contain at least Li, Ni, an element M, and Nb, the mass ratio of each element is represented by Li:Ni:M:Nb=a:(1-x-y):x:y (0.98≤a≤1.15, 0

Description

TECHNICAL FIELD

[0001] The present application relates to a positive electrode active material for a full solid lithium ion secondary battery and a method for producing the same. BACKGROUND

[0002] In recent years, with the improvement of environmental awareness, the conversion from gasoline vehicles to hybrid vehicles and electric vehicles is being promoted, and in particular, the development of small and lightweight secondary batteries with high energy, which are essential for the popularization of electric vehicles, is strongly desired. As such a secondary battery, there is a lithium ion secondary battery.

[0003] Currently, in general lithium ion secondary batteries, a lithium transition metal complex oxide such as LiCoO2, LiNiO2, LiMn2O4 is used as a positive electrode active material, and lithium metal, lithium alloy, metal oxide, carbon, etc. are used as a negative electrode active material.

[0004] In addition, in the case of using a non-aqueous electrolyte as an electrolyte, for example, an electrolyte obtained by dissolving LiClO4, LiPF6, etc. as a supporting salt in an organic solvent such as ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, etc. is used.

[0005] Among the constituent elements of a lithium ion secondary battery, in particular, a non-aqueous electrolyte becomes a major cause of limiting battery performance such as high-speed charging, thermal stability, and life due to chemical properties such as heat resistance and potential window. Therefore, a full solid lithium ion secondary battery (hereinafter, also referred to as "full solid battery") in which the above battery performance is improved by using a solid electrolyte instead of a non-aqueous electrolyte as an electrolyte is currently being actively researched and developed.

[0006] For example, it is described in Patent Literature 1 that among solid electrolytes, a sulfide solid electrolyte has high lithium ion conductivity at the time of charge and discharge, and is suitable for use in a full solid battery. However, for example, as disclosed in Non-Patent Literature 1, if a sulfide solid electrolyte comes into contact with a positive electrode active material which is an oxide, a reaction occurs at the interface between the solid electrolyte and the positive electrode active material during charge and discharge, and a high resistance phase is generated at the interface, hindering the operation of the full solid battery. This is because, in the contact interface, the concentration of conduction ions changes due to the difference in electrochemical potential, thereby forming a space charge layer, becoming an ion conductivity different from the bulk, and the resistance becomes high.

[0007] Therefore, for example, in Patent Literature 2, in order to prevent the contact of the solid electrolyte with the positive electrode active material (oxide) and suppress the generation of a high resistance phase, a technology of providing a coating layer composed of LiNbO3 on the surface of the positive electrode active material is proposed.

[0008] PRIOR ART DOCUMENTS

[0009] PATENT LITERATURE

[0010] Patent Literature 1: Japanese Patent Application Publication No. 2014-056661

[0011] Patent Literature 2: Japanese Patent Application Publication No. 2010-170715

[0012] Patent Literature 3: Japanese Patent Application Publication No. 2011-116580

[0013] Non Patent Literature

[0014] Non Patent Literature 1: Narumi Ohta et al., "LiNbO3-coated LiCoO2 as cathode material for all solid-state lithium secondary batteries", Electrochemistry Communications 9 (2007) 1486-1490. SUMMARY

[0015] PROBLEMS TO BE SOLVED BY THE INVENTION

[0016] However, in order to increase the energy density of lithium ion secondary batteries, it is preferable to use a cathode active material having a large charge-discharge capacity, such as LiNiO2, LiNi 0.80 Co 0.15 Al 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, and the like, which have a high Ni ratio. Thus, the inventors have studied the possibility of using a cathode active material having a high Ni ratio in an all-solid-state lithium ion secondary battery. As a result, the inventors have found that, in the case of using a solid electrolyte, it is possible to design a battery in which cells are connected in series, and thus, although the energy density of the entire battery is increased, the energy density obtained from a cathode active material having a high Ni ratio does not reach the expected energy density or battery capacity, as compared to the case of using a non-aqueous electrolyte.

[0017] In view of the above problems, an object of the present application is to provide a cathode active material that has a higher battery capacity in the case of using a cathode active material having a high Ni ratio as a cathode active material for an all-solid-state battery.

[0018] METHOD FOR SOLVING THE PROBLEM

[0019] The first aspect of the present application provides a positive electrode active material for a full-solid-state lithium ion secondary battery, which has particles of a lithium-nickel composite oxide and a coating layer that coats the surface of the particles, wherein the particles of the lithium-nickel composite oxide have a crystal structure belonging to space group R-3m, the particles of the lithium-nickel composite oxide contain at least Li, Ni, an element M, and Nb, the mass ratio of each element is represented by Li:Ni:M:Nb=a:(1-x-y):x:y (0.98≤a≤1.15, 0

[0020] In addition, it is preferable that the particles of the lithium-nickel composite oxide contain secondary particles composed of a plurality of primary particles, and that the secondary particles have a porous structure having a plurality of void portions in which the primary particles are not present, and that the specific surface area measured by the nitrogen adsorption BET method is 0.3 m 2 / g or more and 2.0 m 2 / g or less. In addition, it is preferable that at least a part of the niobium contained in the particles of the lithium-nickel composite oxide is concentrated at the interface of the primary particles. In addition, it is preferable that, in a cumulative volume distribution curve of the particle size distribution, the particle diameter (D50) of the particles of the lithium-nickel composite oxide corresponding to a cumulative volume rate of 50% is 7 μm or less. In addition, the average thickness of the coating layer is preferably 1 nm or more and 15 nm or less.

[0021] The second aspect of the present application provides a method for producing the above-mentioned positive electrode active material for a full-solid-state lithium ion secondary battery, which includes: a mixing step of mixing a nickel composite compound, a niobium compound, and a lithium compound to obtain a mixture; a calcination step of calcining the mixture to obtain particles of a lithium-nickel composite oxide; and a coating step of causing a coating liquid containing at least one element selected from the group consisting of Al, Si, Ti, V, Ga, Ge, Zr, Nb, Mo, Ta, and W to adhere to the surface of the particles of the lithium-nickel composite oxide to form a coating layer.

[0022] Further, preferably, the nickel composite compound includes a nickel composite oxide, and the manufacturing method includes an oxidizing calcination step of oxidizing calcining the nickel composite hydroxide adjusted by the crystallization reaction to obtain the nickel composite oxide. Further, preferably, the manufacturing method includes a heat treatment step of heat treating the lithium nickel composite oxide particle on which the coating layer is formed at 300°C or higher after the coating step.

[0023] Effects of Invention

[0024] When the positive electrode active material of the present application is used as a positive electrode active material of a full solid battery, the capacity of the battery is improved. Further, the manufacturing method of the present application can manufacture the positive electrode active material at high productivity. BRIEF DESCRIPTION OF DRAWINGS

[0025] [ Figure 1 ] Figure 1 is a schematic view showing an example of the positive electrode active material of the present embodiment.

[0026] [ Figure 2 ] Figure 2 is a view showing an example of the manufacturing method of the positive electrode active material of the present embodiment.

[0027] [ Figure 3 ] Figure 3 is a view showing an example of the manufacturing method of the nickel composite compound of the present embodiment.

[0028] [ Figure 4 ] Figure 4 is an explanatory view of a cross-sectional configuration of an evaluation battery used in battery evaluation. DETAILED DESCRIPTION

[0029] Hereinafter, an embodiment of the present application will be described with reference to the accompanying drawings. Note that, in the drawings, in order to easily understand each structure, a part is sometimes emphasized or simplified to be represented, and the actual structure or shape, scale, and the like are different. Further, the present application is not limited to the following embodiment, and various modifications and substitutions can be applied to the following embodiment without departing from the scope of the present application.

[0030] 1. Positive electrode active material for full solid lithium ion secondary battery

[0031] First, one configuration example of the positive electrode active material for full solid lithium ion secondary battery (hereinafter, also referred to as "positive electrode active material") of the present embodiment will be described.

[0032] Figure 1 is a view schematically showing an example of the positive electrode active material of the present embodiment. As shown in the view, the positive electrode active material of the present embodiment includes a lithium nickel composite oxide particle 1 on which a coating layer 2 is formed. Figure 1As shown, the positive electrode active material 10 has particles 1 of a lithium-nickel composite oxide and a coating layer 2 that coats the surfaces of the particles 1. Hereinafter, each constituent element will be described.

[0033] (1) Particles of lithium-nickel composite oxide

[0034] The particles 1 of the lithium-nickel composite oxide have a crystal structure belonging to the space group R-3m, and are a composite oxide containing at least lithium (Li), nickel (Ni), an element M, and Nb.

[0035] (Composition)

[0036] In the case where the molar ratio of each element contained in the particles 1 of the lithium-nickel composite oxide is represented by Li:Ni:M:Nb = a:(1-x-y):x:y, 0.98 ≤ a ≤ 1.15, 0 < x ≤ 0.5, 0 < y ≤ 0.03, and 0 < x+y ≤ 0.5 are satisfied. In the above molar ratio, it is preferable that 0.98 ≤ a ≤ 1.15, 0 < x ≤ 0.3, 0 < y ≤ 0.02, and 0 < x+y ≤ 0.4 are satisfied.

[0037] In the above molar ratio, a representing the content ratio of Li is 0.98 ≤ a ≤ 1.15, can be 0.98 ≤ a ≤ 1.10, can be 0.98 ≤ a ≤ 1.06, or can be 0.98 ≤ a ≤ 1.03. In the case where a is less than 0.98, Li is deficient in the positive electrode active material, and this easily leads to a decrease in capacity as a battery material. When a exceeds 1.15, the crystal structure of the particles 1 of the lithium-nickel composite oxide excessively grows, the primary particles become coarse, and cracks in the particles 1 easily occur, and thus the durability is easily impaired.

[0038] In the above molar ratio, (1-x-y) representing the content ratio of Ni is 0.5 or more and less than 1.0. In addition, the lower limit of the content ratio of Ni is preferably 0.6 or more, can be 0.7 or more, or can be 0.8 or more. The higher the content ratio of (1-x-y) is, the lower the voltage required for charging is, and as a result, the battery capacity is higher. When (1-x-y) is less than 0.5, the battery capacity is lower.

[0039] In the above molar ratio, the element M is preferably at least one selected from the group consisting of Co, Al, Mn, Zr, Si, Zn, and Ti. In addition, the element M preferably contains at least one element selected from cobalt (Co), aluminum (Al), and manganese (Mn). The element M can be appropriately selected depending on the use of the secondary battery constituted using the positive electrode active material 10, and the required performance.

[0040] In the above mass ratio, x representing the content ratio of the element M is 0 < x < 0.5, preferably 0 < x < 0.3, and can also be 0 < x < 0.2. For example, in the case where the element M contains Co and Co is contained within the above range, high battery capacity is obtained, and the cycle characteristics are excellent. In addition, the element M can also contain Co and Al. The range of Co can be, for example, 0 < x < 0.3, or 0 < x < 0.2. The range of Al can be, for example, 0 < x < 0.1, or 0 < x < 0.07.

[0041] In the above mass ratio, y representing the content ratio of Nb is 0 < y < 0.03, preferably 0 < y < 0.02. In the case where y is within the above range, in the all-solid-state battery, high battery capacity can be obtained. When y exceeds 0.03, LiNb3O8 having low activity is sometimes generated, causing a decrease in battery capacity. In addition, for example, in the case where y is 0.001 < y < 0.01, higher battery capacity can be obtained.

[0042] In addition, the niobium contained in the lithium-nickel composite oxide particle 1 can be solid-solved in the interior of the primary particles, or can exist at the interface of the primary particles. At least a part of the niobium is preferably concentrated at the interface of the primary particles. The detailed reason is not clear, but for example, it is assumed that by concentrating the niobium at the interface of the primary particles, the effect of reducing the potential barrier of the movement of Li ions within the secondary particles, and increasing the battery capacity is obtained. In addition, it is considered that by concentrating at least a part of the niobium at the interface of the primary particles, it is easy to adjust the amount of eluted lithium described later to a specific range.

[0043] (Crystal structure)

[0044] The lithium-nickel composite oxide particle 1 has a crystal structure belonging to the space group R-3m. In the case where the lithium-nickel composite oxide particle 1 has a crystal structure belonging to the space group R-3m, in the secondary battery, an increase in internal resistance can be suppressed.

[0045] The crystal structure of the lithium-nickel composite oxide particle 1 can be confirmed by powder X-ray diffraction (XRD) measurement. That is, it is preferable to detect the peaks of the layered rock salt type crystal structure (crystal structure belonging to the space group R-3m) belonging to the "R-3m" structure from the diffraction pattern obtained when powder X-ray diffraction (XRD) measurement of the lithium-nickel composite oxide particle 1 is performed. In particular, it is more preferable to detect only the peaks of the layered rock salt type crystal structure belonging to the "R-3m" structure from the above diffraction pattern.

[0046] Note that the lithium-nickel composite oxide particle 1 can be a single phase of a lithium-nickel composite oxide having a crystal structure of "R-3m" structure, but can not be a single phase. In the case of not being a single phase and mixing other compounds (e.g., impurities, etc.), the intensity of a heterogeneous phase peak other than the "R-3m" structure layered rock salt type structure is preferably not more than the peak intensity attributed to the "R-3m" structure layered rock salt type structure.

[0047] (crystallite diameter)

[0048] The crystallite diameter of the lithium-nickel composite oxide particle 1 is preferably 140 nm or less, and more preferably 40 nm or more and 140 nm or less. In addition, the range including the upper limit of the crystallite diameter can be 130 nm or less. In addition, the range including the lower limit of the crystallite diameter can be 50 nm or more. Note that the crystallite diameter can be calculated by the Scherrer method using a peak attributed to (003) of the above-described XRD diffraction pattern. When the crystallite diameter of the lithium-nickel composite oxide particle 1 exceeds 140 nm, the solid-state diffusion distance within the crystal sometimes becomes long, and the battery capacity decreases. In addition, when the crystallite diameter of the lithium-nickel composite oxide particle 1 is less than 40 nm, the crystal structure becomes unstable, and the battery capacity easily decreases.

[0049] (eluted lithium ion amount)

[0050] For the lithium-nickel composite oxide particle 1, the eluted lithium ion amount calculated by neutralization titration with respect to the total amount of the particle 1 is 0.30% by mass or more and 1.00% by mass or less, and is preferably 0.30% by mass or more and 0.70% by mass or less. Note that the eluted lithium ion amount can be calculated by a neutralization titration method using hydrochloric acid to calculate the amount of lithium ions eluted into water when the lithium-nickel composite oxide particle 1 is dispersed in water. As the neutralization titration method, Warder method, Winkler method can be used.

[0051] When the eluted lithium ion amount of the lithium-nickel composite oxide particle 1 is less than 0.30% by mass, the battery capacity sometimes decreases. The detailed reason is not clear, but it is considered that one of the reasons is that, for example, by containing a specific amount of eluted lithium ions on the surface of the lithium-nickel composite oxide particle 1, direct contact between the lithium-nickel composite oxide particle 1 and the solid electrolyte in the all-solid battery is suppressed, and the generation of a high-resistance phase is suppressed.

[0052] Note that, in the case where the lithium-nickel composite oxide particle 1 contains niobium, the amount of eluted lithium ions increases compared to the lithium-nickel composite oxide not containing niobium. Therefore, for example, by adjusting the niobium content to the above range and adjusting the amount of eluted lithium to 0.3% by mass or more using the manufacturing method described later, a positive electrode active material having a high discharge capacity can be obtained. However, in the case where the amount of eluted lithium ions of the lithium-nickel composite oxide particle 1 exceeds 1.00% by mass, the discharge capacity decreases.

[0053] (Microcrystalline diameter and amount of eluted lithium ions)

[0054] Further, the lithium-nickel composite oxide particle 1 preferably has a microcrystalline diameter of 140 nm or less and an amount of eluted lithium ions of 0.30% by mass or more.

[0055] That is, in the case of the lithium-nickel composite oxide particle 1, even if the microcrystalline diameter is 140 nm or less, in the case where the amount of eluted lithium ions is less than 0.30% by mass, the battery capacity sometimes decreases. The detailed reason is not clear, but for example, it is assumed as follows.

[0056] The lithium-nickel composite oxide particle 1 includes secondary particles composed of a plurality of primary particles. It is considered that the microcrystalline particle diameter of the lithium-nickel composite oxide particle 1 is positively correlated with the size of the primary particles that constitute the secondary particles, and the smaller the microcrystalline particle diameter, the more the particle interfaces of the primary particles exist. In addition, the eluted lithium ions mainly exist at the particle interfaces of the primary particles. Therefore, in the case where the microcrystalline diameter is small and the interfaces of the primary particles exist in a large amount, if the eluted lithium ions existing at the interfaces (surfaces) of the primary particles excessively decrease, voids are formed at the interfaces of the primary particles. In the case where a large amount of voids exist at the interfaces of the primary particles, the positive electrode active material is easily broken during the electrode production process of the all-solid battery, and the contact interface of the lithium-nickel composite oxide particle and the solid electrolyte increases. Moreover, it is considered that, due to the side reaction that occurs at the increased contact interface, the generated phase hinders the charge and discharge of the electrolyte and the positive electrode active material, and thus the resistance of the battery becomes high and the battery capacity decreases.

[0057] On the other hand, in the case where the microcrystalline diameter of the lithium-nickel composite oxide particle 1 exceeds 140 nm, even if the amount of eluted lithium ions is 0.30% by mass or more, the battery capacity decreases, and thus it is not preferable. It is considered that this is because, by the primary particles becoming coarse, the crystal boundaries between the primary particles decrease, and thus the eluted lithium ions are scattered in bulk at the surface of the secondary particles, and the existence of the eluted lithium ions themselves becomes a resistance phase. Note that, the microcrystalline diameter and the amount of eluted lithium can be adjusted to the above range, for example, by using the manufacturing method of the positive electrode active material described later.

[0058] (Particle structure)

[0059] The lithium-nickel composite oxide particle 1 contains secondary particles formed by aggregation of a plurality of primary particles. In addition, the lithium-nickel composite oxide particle 1 can contain only primary particles, or a mixture of primary particles and secondary particles.

[0060] When observed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), or the like, the average particle diameter of the secondary particles is preferably 3.0 μm or more and 7.0 μm or less. In addition, the secondary particles are preferably formed by aggregation of a large number of primary particles having a particle diameter of 0.1 μm or more and 2.0 μm or less. In addition, in the case of containing only primary particles, the primary particles preferably have a particle diameter of 1.0 μm or more and 7.0 μm or less. Note that the average particle diameter of each particle can be obtained, for example, by calculating the average value of the diameters of the equivalent circles of 20 or more particles.

[0061] (Average particle diameter D50)

[0062] In the cumulative volume distribution curve of the particle size distribution, the particle diameter corresponding to the cumulative volume rate of 50% (D50, hereinafter also referred to as "average particle diameter D50") of the lithium-nickel composite oxide particle 1 is preferably 7 μm or less, more preferably 2 μm or more and 7 μm or less, and further preferably 3 μm or more and 7 μm or less. Note that the average particle diameter (D50) can be measured using a particle size distribution meter of the laser diffraction scattering type.

[0063] In the case where the average particle diameter D50 of the lithium-nickel composite oxide particle 1 is 7 μm or less, in a secondary battery in which the positive electrode active material 10 is used for a positive electrode, the battery capacity per unit battery capacity can be sufficiently increased, and excellent battery characteristics such as thermal stability, high output power, and the like can be obtained. On the other hand, in the case where the average particle diameter D50 is 2 μm or less, aggregation is easy when the coating layer 2 is imparted, and thus is not preferable.

[0064] (Width of particle size distribution)

[0065] The [(d90-d10) / volume average particle diameter Mv] as an index of the width of the particle size distribution of the particle 1 of the lithium-nickel composite oxide is not particularly limited, and can be 0.7 or less, 0.6 or less, or 0.55 or less from the viewpoint of uniformizing the particle diameter. In the case where the particle diameter is relatively uniform, the coating layer 2 is easily uniformly coated on the surface of the particle 1 of the lithium-nickel composite oxide, and a good output characteristic can be obtained in the secondary battery. Note that the lower limit of the [(d90-d10) / volume average particle diameter Mv] is not particularly limited, and is, for example, 0.3 or more. In addition, the [(d90-d10) / volume average particle diameter Mv] can be 0.7 or more from the viewpoint of packing, and the coating layer 2 can be relatively uniformly coated by using the manufacturing method of the positive electrode active material described later.

[0066] Note that d10 refers to the particle diameter at which the number of particles under each particle diameter is accumulated from the side of small particle diameter, and the cumulative volume becomes 10% of the total volume of all particles, and d90 refers to the particle diameter at which the number of particles is similarly accumulated, and the cumulative volume becomes 90% of the total volume of all particles. In addition, d10, d90, and the volume average particle diameter Mv can be calculated from the volume cumulative value measured by a laser diffraction scattering particle size analyzer, like the average particle diameter D50.

[0067] (Specific surface area)

[0068] The specific surface area of the particle 1 of the lithium-nickel composite oxide is not particularly limited, and can be, for example, 0.3 m 2 / g or more and 2.0 m 2 / g or less, or 0.3 m 2 / g or more and 1.0 m 2 / g or less. In the case where the specific surface area is in the above range, the output characteristic is good. Note that the specific surface area can be measured by the nitrogen adsorption BET method.

[0069] (2) Coating layer

[0070] The positive electrode active material 10 has the coating layer 2 on the surface of the particle 1 of the lithium-nickel composite oxide. By having the coating layer 2 on the surface of the particle 1, the mutual reaction of the positive electrode active material 10 and the solid electrolyte can be suppressed in the secondary battery having a positive electrode including the positive electrode active material 10.

[0071] The coating layer 2 is composed of a composite oxide containing lithium (Li) and one or more elements selected from the group consisting of Al, Si, Ti, V, Ga, Ge, Zr, Nb, Mo, Ta, and W. Note that the constituent elements of the coating layer 2 other than lithium (Li) and oxygen (O) can be one or more than two. The coating layer 2 can be, for example, a composite oxide composed of Li and Ti or a composite oxide composed of Li and Nb.

[0072] (Content of constituent elements of coating layer)

[0073] The amount of coating of the coating layer 2 is not particularly limited and can be adjusted depending on the specific surface area (m 2 / g) of the lithium-nickel composite oxide particle 1 to be coated. The coating layer 2 is more preferably, for example, contained at a ratio of 30 pmol or more and 600 pmol or less per 1 m 2 of the specific surface area of the lithium-nickel composite oxide particle 1.

[0074] The content of the constituent elements (other than Li and O) of the coating layer 2 per 1 m 2 of the specific surface area of the lithium-nickel composite oxide particle 1 is 30 pmol or more, the coating layer 2 can be uniformly arranged on the entire surface of the lithium-nickel composite oxide particle 1.

[0075] In addition, by providing the coating layer 2, it is possible to suppress the reaction of the lithium-nickel composite oxide particle 1 with the solid electrolyte, but at the same time, the internal resistance of the secondary battery can also increase. The content of the constituent elements (other than Li and O) of the coating layer 2 per 1 m 2 of the specific surface area of the lithium-nickel composite oxide particle 1 is 600 pmol or less, it is possible to suppress the coating layer 2 from becoming an obstacle to the reaction of the insertion / detachment of lithium into / from the lithium-nickel composite oxide particle 1, and it is possible to reduce the internal resistance.

[0076] In the coating layer 2, the evaluation and calculation method of the content of the constituent elements (excluding Li and O) of the coating layer 2 is not particularly limited and can be calculated, for example, as follows.

[0077] First, the content of the constituent elements (other than Li and O) of the coating layer 2 in 1 g of the positive electrode active material is measured by a method such as chemical analysis. As a method of chemical analysis, measurement is performed by ICP (Inductively Coupled Plasma) emission spectrometry or the like.

[0078] On the other hand, the specific surface area of the lithium-nickel composite oxide particle 1 before being coated with the coating layer 2 is measured by a nitrogen adsorption BET method or the like.

[0079] Next, by dividing the content of the constituent elements of the coating layer 2 (except Li and O) in the positive electrode active material 1 g by the specific surface area (m 2 / g) of the lithium nickel composite oxide particle 1, the content of the constituent elements of the coating layer 2 (except Li and O) per 1 m 2 of the surface of the lithium nickel composite oxide particle 1 can be obtained.

[0080] Note that, in the case where the lithium nickel composite oxide particle 1 contains the constituent elements of the coating layer 2 (except Li and O), the difference between the content of the constituent elements of the coating layer 2 (except Li and O) before and after the coating can be used as the content of the constituent elements of the coating layer 2 (except Li and O) used in the coating.

[0081] (Average thickness of coating layer)

[0082] The average thickness of the coating layer is preferably, for example, 2 nm or more and 20 nm or less, more preferably 2 nm or more and 15 nm or less, and further preferably 5 nm or more and 15 nm or less.

[0083] Note that the average thickness of the coating layer 2 can be calculated by observing with a scanning electron microscope (SEM), a transmission electron microscope (TEM), or the like, or analyzing with a spectrometer such as an energy dispersive X-ray spectrometer (EDS) or electron energy loss spectroscopy (EELS) attached to them, measuring the layer formed uniformly on the surface of the lithium nickel composite oxide particle 1, and the like. Note that, in the case where the thickness of the coating layer 2 has a variation depending on the measurement site, the thickness of the coating layer 2 refers to the average value when a plurality of sites are measured.

[0084] (Disposition of coating layer)

[0085] In addition, the coating layer 2 is preferably present in contact with the surface of the lithium nickel composite oxide particle 1. Whether the coating layer 2 is present in contact with the surface of the particle 1 can be determined by whether a compound containing the constituent elements of the coating layer 2 is present free from the surface of the lithium nickel composite oxide particle 1. In the case where the coating layer 2 is present free from the surface of the lithium nickel composite oxide particle 1, it does not contribute to the battery capacity electrochemically, and thus becomes a main cause of the decrease in the battery capacity per unit weight.

[0086] Note that the coated layer 2 can not have a clear boundary line with the surface of the lithium-nickel composite oxide particle 1. For example, in a case where the lithium-nickel composite oxide particle 1 before coating does not contain the elements constituting the coated layer 2 (except for Li and O), the coated layer 2 refers to a region in which the elements constituting the coated layer 2 (except for Li and O) are detected, and can also include a region in which both the elements constituting the coated layer 2 (except for Li and O) and the elements constituting the lithium-nickel composite oxide particle 1 are detected. In addition, in a case where the lithium-nickel composite oxide particle 1 before coating contains the elements constituting the coated layer 2 (except for Li and O), it refers to a region on the surface side of the particle constituting the positive electrode active material 10, and is a region (part) in which the concentration of the elements constituting the coated layer 2 (except for Li and O) is higher than that in the central portion of the lithium-nickel composite oxide particle 1.

[0087] In addition, the elements constituting the coated layer 2 (except for Li and O) can be partially solid-solved from the surface of the lithium-nickel composite oxide particle to the inside. For example, when a heat treatment process (S40) is performed after the coating process (S30), the coated layer elements of the coated layer can be diffused into the lithium-nickel composite oxide depending on the conditions at that time.

[0088] For example, in a case where Ti and / or Nb is contained in the coated layer 2, Ti and / or Nb are solid-solved from the surface of the lithium-nickel composite oxide particle 1 to the inside, whereby the coated layer 2 not only prevents the solid electrolyte from directly contacting the lithium-nickel composite oxide particle 1, reducing the chance of reaction, but also produces an effect of reducing the reactivity of the surface layer of the lithium-nickel composite oxide particle 1 with the solid electrolyte. Note that in the positive electrode active material 10, the degree of solid-solution is preferably adjusted so as to be able to sufficiently exert the effect of improving the cycle characteristics.

[0089] 2. Method for manufacturing positive electrode active material for all-solid-state lithium-ion secondary battery

[0090] Next, a method for manufacturing a positive electrode active material for an all-solid-state lithium-ion secondary battery (hereinafter, also referred to as "positive electrode active material") according to the present embodiment will be described. By using the manufacturing method according to the present embodiment, the above-described positive electrode active material 10 can be manufactured at high productivity.

[0091] Figure 2 、 Figure 3 is a view showing an example of the method for manufacturing a positive electrode active material according to the present embodiment. As shown in FIG. 8, the method for manufacturing a positive electrode active material according to the present embodiment includes a lithium-nickel composite oxide particle preparation process (S10), a coating process (S30), and a heat treatment process (S40). Figure 2As shown, the manufacturing method of the positive electrode active material of the present embodiment includes: a mixing step (S10) of mixing a nickel composite compound, a niobium compound, and a lithium compound to obtain a mixture; a calcining step (S20) of calcining the mixture to obtain particles of a lithium-nickel composite oxide; and a coating step (S30) of causing a coating liquid to adhere to the surface of the particles of the lithium-nickel composite oxide to form a coating layer. Further, after the coating step (S30), a heat treatment step (S40) of heat-treating the particles of the lithium-nickel composite oxide on which the coating layer is formed at 300°C or higher can be included.

[0092] In addition, the nickel composite compound can be a nickel composite oxide obtained by oxidizing and calcining a nickel composite hydroxide adjusted through a crystallization reaction. For example, as shown in Figure 3 As shown, the nickel composite compound can be manufactured by a method including a crystallization step (S1) and an oxidizing and calcining step (S2). Hereinafter, each step will be described in detail. Note that the following description is an example of the manufacturing method and does not limit the manufacturing method.

[0093] (Crystallization step: S1)

[0094] In the crystallization step (S1), a nickel composite hydroxide, which is a precursor of a lithium-nickel composite oxide, is prepared through a crystallization reaction.

[0095] For example, a raw material aqueous solution is prepared using water-soluble compounds (metal compounds) of each element in such a manner that the mass ratio of each element is equal to the mass ratio of each element contained in the target lithium-nickel composite oxide particles, the prepared raw material aqueous solution is supplied to a reaction tank together with an alkali aqueous solution and an ammonium ion supplier, a neutralization crystallization reaction is performed, and a nickel composite hydroxide is obtained.

[0096] The raw material of each element can be manufactured by, for example, dissolving each raw material of each element in water to prepare a mixed aqueous solution. Alternatively, a separate raw material aqueous solution can be prepared for each raw material of each element. Note that when there is a disadvantage in preparing the raw material aqueous solution in the form of a mixed aqueous solution, it is preferable to prepare a separate raw material aqueous solution for each raw material. For example, when the liquid properties of the aqueous solution of each raw material are divided into acidic and basic, it is preferable to prepare a separate raw material aqueous solution for each raw material.

[0097] The metal compound used as the raw material of each element can be water-soluble, and a sulfate, a chloride, a nitrate, or the like can be used, but from the viewpoint of cost, a cheap sulfate is preferable. Note that when a suitable metal compound of each element M or the like is not found to be water-soluble, it can be added in the oxidizing and calcining step (S2) and the mixing step (S10) described later, instead of being added to the mixed aqueous solution of the raw materials.

[0098] The aqueous alkali metal solution is not particularly limited, and one or more selected from the group consisting of sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, and potassium carbonate can be preferably used.

[0099] The ammonium ion supplier is not particularly limited, and one or more selected from the group consisting of aqueous ammonia, aqueous ammonium carbonate, aqueous ammonium chloride, and aqueous ammonium sulfate can be preferably used.

[0100] The shape of the reaction tank is not particularly limited, and a cylindrical container having a baffle inside, a stirrer, and a temperature regulator are preferably provided. The stirrer preferably has a motor, a shaft, and stirring blades. The temperature regulator is preferably in a form in which a heating medium is circulated outside the cylindrical container to heat or cool the cylindrical container.

[0101] In the neutralization crystallization reaction of the raw material aqueous solution, the aqueous alkali metal solution, and the ammonium ion supplier in the reaction tank, the pH and the ammonia concentration are preferably maintained at fixed values.

[0102] The pH of the aqueous solution in the reaction tank is preferably adjusted to 11.0 or more and 12.2 or less based on a liquid temperature of 25°C. For example, when preparing a nickel composite hydroxide, impurities sometimes mix into the nickel composite hydroxide due to anions that constitute metal compounds contained in the raw material aqueous solution used. However, by setting the value of the pH of the initial aqueous solution (in the reaction tank) to 11.0 or more, the mixing of impurities due to anions can be suppressed. In addition, by setting the pH of the initial aqueous solution to 12.2 or less, the obtained nickel composite hydroxide can be suppressed from being particulated, and a composite hydroxide having a particle size suitable for charge-discharge reactions can be obtained.

[0103] The ammonia concentration of the aqueous solution in the reaction tank is preferably adjusted to 5 g / L or more and 20 g / L or less. In the case where the ammonia concentration is set to 5 g / L or more, Ni in the raw material aqueous solution (mixed aqueous solution) becomes an ammonium complex, and the precipitation rate from the liquid phase to the solid phase as a hydroxide decreases, and thus the sphericity of the particles of the obtained nickel composite hydroxide improves. On the other hand, in the case where the ammonia concentration is set to 20 g / L or less, the solubility of nickel that forms an ammonium complex can be suppressed from excessively increasing, and the mass of the obtained nickel composite hydroxide can be more reliably made to be the target mass. In addition, excessive consumption of ammonia can be suppressed, which is preferable in industry.

[0104] The atmosphere in the reaction tank is preferably a non-oxidizing atmosphere, such as an atmosphere in which the oxygen concentration is 1% by volume or less. In the case where the atmosphere in the reaction tank is set to a non-oxidizing atmosphere, the raw material compounds and the like can be suppressed from being oxidized. For example, cobalt and manganese that are oxidized can be prevented from being precipitated as fine particles and the like.

[0105] The temperature in the reaction tank in the crystallization step (S1) is preferably maintained at 40°C or higher and 60°C or lower, more preferably 45°C or higher, and further preferably 55°C or lower.

[0106] The temperature in the reaction tank increases due to the reaction heat and the stirring Joule heat, and thus by making the temperature in the reaction tank 40°C or higher, no additional energy is consumed in the cooling. Also, by making the temperature in the reaction tank 60°C or lower, evaporation and loss of ammonia from the initial aqueous solution and the reaction aqueous solution can be suppressed, and the target ammonia concentration can be easily maintained.

[0107] The particles (powder) of the lithium-nickel composite oxide are preferably particles having a narrow width of particle size distribution and uniform particle diameter. To produce such particles, particles having a uniform particle diameter are required in the nickel composite hydroxide as a precursor thereof. As a method of obtaining such particles, Patent Literature 3, for example, can be exemplified.

[0108] (Oxidative calcination step: S2)

[0109] The oxidative calcination step (S2) can also be performed after the precursor crystallization step (S1). In the oxidative calcination step (S2), the nickel composite hydroxide obtained in the precursor crystallization step (S1) is subjected to oxidative calcination, and a nickel composite oxide is obtained. In the oxidative calcination step (S2), heat treatment is performed in an oxygen-containing atmosphere, and then cooled to room temperature, whereby a nickel composite oxide can be obtained.

[0110] The calcination conditions in the oxidative calcination step (S2) are not particularly limited, and for example, it is preferable to calcine in an oxygen-containing atmosphere, an air atmosphere, at a temperature of 500°C or higher and 700°C or lower, for 1 hour or longer and 12 hours or less. When the calcination temperature is set to 500°C or higher, the nickel composite hydroxide can be completely converted into a nickel composite oxide. Also, by making the calcination temperature 700°C or lower, the specific surface area of the nickel composite oxide can be suppressed from becoming too small, and is preferable.

[0111] By making the calcination time 1 hour or longer, the temperature in the calcination vessel can be made uniform, and the reaction can be made to proceed uniformly, and thus is preferable. Also, even if calcination is performed for a time longer than 12 hours, no great change is seen in the obtained nickel composite oxide, and thus from the viewpoint of energy efficiency, the calcination time is preferably set to 12 hours or less.

[0112] The oxygen concentration in the oxygen-containing atmosphere at the time of calcination is preferably the oxygen concentration of air or higher, that is, 20% by volume or higher. Since an oxygen atmosphere can also be provided, the upper limit of the oxygen concentration of the oxygen-containing atmosphere can be set to 100% by volume.

[0113] Note that, for example, in a case where the compound containing the element M cannot be co-precipitated in the crystallization step (S1), the compound containing the element M can be added in the same manner as the target mass ratio and subjected to calcination with respect to the nickel composite hydroxide supplied to the oxidative calcination step S2, for example. The compound containing the element M added is not particularly limited, and oxides, hydroxides, carbonates, or mixtures thereof, or the like can be used, for example.

[0114] In addition, in a case where slight sintering is observed in the nickel composite oxide obtained after the oxidative calcination step (S2) ends, a crushing treatment can also be applied. Note that, in the oxidative calcination step (S2), as long as at least a part of the nickel composite hydroxide is converted into a nickel composite oxide, it is not necessary to convert all of the nickel composite hydroxide into an oxide.

[0115] (Mixing step: S10)

[0116] The mixing step (S10) is a step of obtaining a lithium mixture by mixing a nickel composite compound, a niobium compound, and a lithium compound.

[0117] In the production method of the present embodiment, in the mixing step (S10), niobium is added in solid phase by mixing the niobium compound. The solid phase addition of niobium is an addition method that does not require a chemical solution or the like, and is thus an addition method that is low in environmental load and excellent in productivity, as compared to the method of co-precipitating or coating niobium in the crystallization step known in the past.

[0118] The nickel composite compound is preferably at least one of a nickel composite hydroxide and a nickel composite oxide, and is more preferably a nickel composite oxide. In addition, the nickel composite compound is preferably obtained by a method including the crystallization step (S1) and / or the oxidative calcination step (S2) described above.

[0119] The niobium compound can use niobic acid, niobium oxide, niobium nitrate, niobium pentachloride, or the like, for example. Among them, from the viewpoints of easiness of obtaining and avoidance of impurities mixed into the lithium nickel composite oxide to be fired, niobium hydroxide or niobium oxide is preferred.

[0120] When niobium is added in the solid phase, depending on the particle diameter of the added niobium compound, the reactivity can sometimes change. The particle size distribution of the niobium compound preferably has a cumulative volume distribution curve in which the particle diameter corresponding to a cumulative volume rate of 90% (D90) is 0.1 μm or more and 20 μm or less, more preferably 0.1 μm or more and 10 μm or less, and further preferably 0.1 μm or more and 5 μm or less. When the D90 of the niobium compound is less than 0.1 μm, there is a problem in that the handling of the powder becomes very difficult. When the D90 of the niobium compound is more than 20 μm, the reactivity during firing decreases, the diffusion of niobium into the particles of the lithium-nickel composite oxide is insufficient, and sometimes the thermal stability cannot be ensured. In addition, when the D90 of the niobium is too large, the formation of the coating layer 2 can become non-uniform. Note that the particle diameter of the niobium compound can be appropriately adjusted within the above range to obtain a positive electrode active material having desired properties.

[0121] The D90 of the niobium compound can be adjusted to the above range by pulverizing the raw niobium compound using a pulverizer such as a ball mill, a planetary ball mill, a jet mill, a bead mill, or a pin mill. Alternatively, classification can be performed using a dry classifier or a sieve classifier as needed. Note that the D90 of the niobium compound can be measured by a laser scattering / diffraction method.

[0122] The niobium compound is mixed in an amount such that the target niobium content is obtained with respect to the total of the atomic numbers of Ni and the element M contained in the nickel composite compound. The content of niobium does not change before and after the firing step, and thus the niobium compound corresponding to the niobium addition amount of the positive electrode active material is added.

[0123] There is no particular limitation on the lithium compound, and for example, lithium hydroxide, lithium nitrate, or lithium carbonate, or a mixture thereof can be used. From the viewpoint of a low melting point and high reactivity, it is preferable to use lithium hydroxide as the lithium compound.

[0124] The lithium compound can be mixed, for example, in an amount such that the content of lithium is 95 atomic% or more and 115 atomic% or less with respect to the total (Me) of Ni, the element M, and Nb, can be mixed in an amount such that the content of lithium is 98 atomic% or more and 115 atomic% or less, and can be mixed in an amount such that the content of lithium is 98 atomic% or more and 110 atomic% or less.

[0125] (Firing step: S20)

[0126] The firing step (S20) is a step of firing the obtained lithium mixture to obtain the particles 1 of the lithium-nickel composite oxide. The firing conditions are not particularly limited, and for example, it is preferable to fire at a temperature of 700°C or more and 800°C or less in an oxygen-containing atmosphere for 1 hour or more and 24 hours or less. After firing, the lithium-nickel composite oxide particles 1 can be obtained by cooling to room temperature.

[0127] In the case where the firing temperature is set to 700°C or higher, the crystal structure of the lithium nickel composite oxide particle 1 can be sufficiently grown. In the case where the firing temperature is set to 800°C or lower, the mixing of Ni atoms into the Li sites in the obtained lithium nickel composite oxide particle 1 can be suppressed.

[0128] By setting the firing time to 1 hour or more, the temperature in the firing vessel can be made uniform, and the reaction can be made to proceed uniformly, and thus is preferable. In addition, even if firing is performed for a time longer than 24 hours, no great change is observed in the obtained lithium nickel composite oxide, and thus from the viewpoint of energy efficiency, the firing time is preferably 24 hours or less, can be 12 hours or less, can be 10 hours or less, or can be 6 hours or less.

[0129] In addition, as the oxygen-containing atmosphere, an atmosphere containing 80% by volume or more of oxygen is preferable. This is because, by setting the oxygen concentration in the atmosphere to 80% by volume or more, the mixing of Ni atoms into the Li sites in the obtained lithium nickel composite oxide can be particularly suppressed, and thus is preferable. Since an oxygen atmosphere can also be provided, the upper limit value of the oxygen concentration of the oxygen-containing atmosphere can be set to 100% by volume.

[0130] Note that, in the case where slight sintering is observed in the obtained lithium nickel composite oxide particle 1 after the firing process (S20), a crushing process can also be applied.

[0131] (Coating process: S30)

[0132] The coating process (S30) is a process of causing the coating liquid to adhere to the surface of the obtained lithium nickel composite oxide particle 1 to form a coating layer 2.

[0133] Regarding the formation of the coating layer 2, for example, the lithium nickel composite oxide particle 1 is mixed with the coating liquid and dried, and the coating layer 2 is formed on the surface of the lithium nickel composite oxide particle 1. In addition, as described later, a heat treatment process (S40) can also be performed in an oxygen-containing atmosphere after coating. Hereinafter, one example of the coating process (S30) will be described.

[0134] First, the coating liquid is prepared in a prescribed amount (coating agent preparation step). The coating agent can be prepared in accordance with the content of the constituent elements (except Li and O) of the coating layer 2 per unit specific surface area (m 2 / g) of the lithium nickel composite oxide particle 1 obtained in the firing process (S20).

[0135] The coating liquid contains at least one element selected from the group consisting of Al, Si, Ti, V, Ga, Ge, Zr, Nb, Mo, Ta, and W. For example, the coating liquid can be prepared by dissolving a raw compound containing the constituent elements of the coating layer 2 (except Li and O) as a target in a solvent.

[0136] As the raw compound, for example, one or more selected from the group consisting of alcoholates, and chelates using a complex having a carbonyl group, a peroxide group, and the like can be cited.

[0137] From the viewpoint of uniform coating, the coating liquid can be prepared by dissolving a compound containing the constituent elements of the coating layer 2 in a solvent, for example, and can be a compound containing the constituent elements of the coating layer 2 having a low melting point and dissolving in a heat treatment at a low temperature, as long as it is in a liquid state at the time of adhering to the surface of the lithium-nickel composite oxide particle 1. The coating liquid can contain Li or can not contain Li. In the case where the coating liquid does not contain Li, Li present in the lithium-nickel composite oxide particle 1 reacts with the compound containing the above-mentioned constituent elements in the coating liquid in the coating step (S30) and / or the heat treatment step (S40), and the coating layer 2 can be formed.

[0138] It is to be noted that the coating liquid can contain Li or can not contain Li. In the case where the coating liquid does not contain Li, Li present in the lithium-nickel composite oxide particle 1 reacts with the compound containing the above-mentioned constituent elements in the coating liquid in the coating step (S30) and / or the heat treatment step (S40), and the coating layer 2 can be formed.

[0139] Next, the coating liquid is adhered to the surface of the lithium-nickel composite oxide particle 1. The adhesion of the coating liquid can be performed by mixing the lithium-nickel composite oxide particle 1 with the coating liquid, for example (mixture preparation step). The mixing can be performed using a general mixer. In addition, drying can be performed after the mixing (drying step).

[0140] In addition, from the viewpoint of forming a coating layer 2 that is more uniform and has a specific thickness, it is preferable to perform the mixture preparation step and the drying step in parallel, and it is preferable to use a rotary flow coating device.

[0141] The coating liquid shrinks due to drying, and therefore, when only the mixture preparation step and the drying step are performed once, respectively, a gap can be generated in the formed coating layer 2, and the function of protecting the contact between the lithium-nickel composite oxide particle 1 and the solid electrolyte can not be sufficiently exerted. However, in the case of using a rotary flow coating device, since the coating liquid is sprayed to the lithium-nickel composite oxide particle 1 flowing by using a heated gas stream in the device, the mixture preparation step and the drying step are repeatedly performed in parallel, a uniform coating layer without a gap is obtained, and therefore, it is preferable.

[0142] In the drying step, drying is preferably performed at a temperature at which the coating agent and the like can be sufficiently removed. For example, in the case of using a rotary flow coating device, the supply air temperature can be set to 80°C or higher and less than 300°C. In addition, after the coating treatment, additional drying can be performed using a stationary-type drying machine.

[0143] The atmosphere in the drying step is not particularly limited, and in order to prevent the lithium-nickel composite oxide particles 1 from reacting with moisture in the atmosphere, a non-reactive atmosphere such as air, nitrogen, and argon supplied from a compressor provided with a dryer is preferable.

[0144] (Heat treatment step: S40)

[0145] Further, as needed, after the coating step (S30), a heat treatment step (S40) of heat-treating the lithium-nickel composite oxide particles 1 on which the coating layer 2 is formed on the surface at 300°C or higher can be provided. By the heat treatment step (S40), the binding of the coating layer 2 to the lithium-nickel composite oxide particles 1 can be made more robust.

[0146] The heat treatment conditions in the heat treatment step (S40) are not particularly limited, and heat treatment at a temperature of 300°C or higher and 600°C or lower for 1 hour or longer and 5 hours or shorter in an oxygen-containing atmosphere is preferable. The oxygen-containing atmosphere can be, for example, an air atmosphere.

[0147] The oxygen concentration in the oxygen-containing atmosphere in the heat treatment step (S40) is preferably the oxygen concentration of an air atmosphere or higher, that is, the oxygen concentration is 20% by volume or higher. By setting the oxygen-containing atmosphere at the time of heat treatment to be the oxygen concentration of an air atmosphere or higher, the production of oxygen defects in the interior of the obtained positive electrode active material 10 can be further suppressed. The oxygen-containing atmosphere can be an oxygen atmosphere, and the upper limit of the oxygen concentration of the oxygen-containing atmosphere is 100% by volume.

[0148] In the case where the heat treatment temperature is 300°C or higher, the impurities contained in the coating liquid can be further suppressed from remaining in the interior of the positive electrode active material 10. In addition, in the case where the heat treatment temperature is 600°C or lower, the components of the coating layer 2 can be suppressed from excessively diffusing, and the morphology of the coating layer 2 can be maintained.

[0149] In the case where the heat treatment time is 1 hour or longer, the impurities contained in the coating liquid can be further suppressed from remaining in the interior of the positive electrode active material 10. In addition, even in the case where the heat treatment time is longer than 5 hours, no great change is observed in the obtained positive electrode active material 10. Therefore, from the viewpoint of energy efficiency, the heat treatment time is preferably 5 hours or shorter.

[0150] After the heat treatment step (S40), cooling to room temperature can be performed, and a positive electrode active material having the lithium-nickel composite oxide particles 1 and the coating layer 2 on the surface thereof as final products can be obtained.

[0151] Note that the heat treatment step (S40) can not be performed. That is, the coated positive electrode active material 10 can be manufactured by performing only the coating step (S30). This is because the coating layer can be uniformly and firmly formed on the surface of the lithium-nickel composite oxide particles even if the heat treatment step (S40) is not performed. Even if the heat treatment step is not performed, drying can be preferably performed as needed in order to reduce, remove, or the like, the solvent, moisture, or the like, of the coating agent.

[0152] In a case where slight sintering is observed in the positive electrode active material 10 obtained after the coating step (S30) and / or the heat treatment step (S40), a crushing treatment can be further performed.

[0153] (3) All-solid-state lithium ion secondary battery

[0154] The all-solid-state lithium ion secondary battery (hereinafter, also referred to as "all-solid-state battery") of the present embodiment includes the positive electrode active material described above in the positive electrode. Hereinafter, the all-solid-state battery of the present embodiment will be described for each of the constituent elements.

[0155] Note that the embodiments described below are merely examples, and the all-solid-state battery can be implemented in a manner in which various modifications and improvements are made based on the knowledge of those skilled in the art, using the embodiments described below as a representative. In addition, the all-solid-state battery is not particularly limited in its use.

[0156] (Positive electrode)

[0157] The positive electrode can be formed by molding a positive electrode mixture. Note that the positive electrode can be appropriately processed according to the battery to be used. For example, in order to increase the density of the electrode, pressure compression processing or the like based on pressing or the like can be performed.

[0158] The positive electrode mixture described above can be formed by mixing the positive electrode active material described above and the solid electrolyte in a powder form.

[0159] The solid electrolyte is added in order to impart appropriate ionic conductivity to the electrode.

[0160] The material of the solid electrolyte is not particularly limited, and for example, Li3PS4, Li7P3S 11 , Li 10 GeP2S 12 , and the like sulfide-based solid electrolytes, Li7La3Zr2O 12 , Li 0.34 La 0.51 TiO 2.94 , and the like oxide-based solid electrolytes, PEO, and the like polymer-based electrolytes can be used.

[0161] Note that a binder and a conductive aid can also be added to the positive electrode mixture.

[0162] The binder functions to hold the positive electrode active material. The binder used in the positive electrode mixture is not particularly limited, and for example, one or more selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose-based resin, polyacrylic acid, and the like can be used.

[0163] The conductive material is added in order to impart appropriate conductivity to the electrode. The material of the conductive material is not particularly limited, and for example, graphite such as natural graphite, artificial graphite, and expanded graphite, carbon black-based materials such as acetylene black and Ketjen black (registered trademark).

[0164] In addition, the mixing ratio of each substance in the positive electrode mixture is not particularly limited. For example, the content of the positive electrode active material of the positive electrode mixture can be set to 50 parts by mass or more and 90 parts by mass or less, and the content of the solid electrolyte can be set to 10 parts by mass or more and 50 parts by mass or less.

[0165] However, the method of producing the positive electrode is not limited to the above-described example, and can be produced by another method.

[0166] (Negative electrode)

[0167] The negative electrode can be formed by molding a negative electrode mixture.

[0168] As for the negative electrode, although the components constituting the negative electrode mixture, the combination thereof, and the like are different, the negative electrode is substantially formed by the same method as the positive electrode described above, and various treatments are performed as needed in the same manner as the positive electrode.

[0169] The negative electrode mixture can be produced by mixing a negative electrode active material and a solid electrolyte. As the negative electrode active material, for example, a storage material capable of occluding and releasing lithium ions can be used.

[0170] The storage material is not particularly limited, and for example, one or more selected from the group consisting of powdery bodies of natural graphite, artificial graphite, organic compound sintered bodies such as phenol resin, and carbonaceous substances such as coke can be used. In the case where the negative electrode active material uses this storage material, as with the positive electrode, as the solid electrolyte, Li3PS4or the like can be used.

[0171] In addition, the negative electrode can also be, for example, a sheet-shaped member composed of a metal such as lithium or indium containing a metal alloyed with lithium.

[0172] (Solid electrolyte)

[0173] The solid electrolyte is a material having Li +A solid having ion conductivity. As the solid electrolyte, one selected from sulfides, oxides, polymers, and the like can be used alone, or two or more kinds can be used in combination.

[0174] As the sulfide-based solid electrolyte, there is no particular limitation, and a substance containing sulfur (S) and having lithium ion conductivity and electronic insulation can be used. As the sulfide-based solid electrolyte, for example, Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2, LiPO4-Li2S-SiS, LiI-Li2S-P2O5, LiI-Li3PO4-P2O5, and the like can be given.

[0175] As the oxide-based solid electrolyte, there is no particular limitation, and a substance containing oxygen (O) and having lithium ion conductivity and electronic insulation can be used.

[0176] As the oxide-based solid electrolyte, for example, lithium phosphate (Li3PO4), Li3PO4NX, LiBO2NX, LiNbO3, LiTaO3, Li2SiO3, Li4SiO4-Li3PO4, Li4SiO4-Li3VO4, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3-ZnO, Li 1+X Al X Ti 2-X (PO4)3(0≤X≤1), Li 1+X Al X Ge 2-X (PO4)3(0≤X≤1), LiTi2(PO4)3, Li3XLa 2 / 3-X TiO3(0≤X≤2 / 3), Li5La3Ta2O 12 , Li7La3Zr2O 12 , Li6BaLa2Ta2O 12 , Li 3.6 Si 0.6 P 0.4 O4, and the like.

[0177] Note that, as the inorganic solid electrolyte, a substance other than the above can be used, and for example, Li3N, LiI, Li3N-LiI-LiOH, and the like can be used.

[0178] As the polymer-based solid electrolyte, there is no particular limitation as long as it is a high molecular compound showing ionic conductivity, and for example, polyethylene oxide, polypropylene oxide, a copolymer thereof, or the like can be used. In addition, the organic solid electrolyte can contain a supporting salt (lithium salt). Note that in the case of using a solid electrolyte, in order to ensure contact of the electrolyte with the positive electrode active material, the solid electrolyte can also be mixed in the positive electrode material.

[0179] (Shape and configuration of all-solid battery)

[0180] Next, an example of the configuration and arrangement of the components of the all-solid battery according to the present embodiment will be described.

[0181] The all-solid battery composed of the above-described positive electrode, negative electrode, and solid electrolyte can be manufactured in various shapes such as a coin shape, a stacked shape, or the like. In the case of adopting any shape, the positive electrode and the negative electrode can be stacked with the solid electrolyte interposed therebetween. Furthermore, the positive electrode current collector and the negative electrode current collector can be connected to the positive electrode terminal and the negative electrode terminal leading to the outside, respectively, using a current collecting lead or the like, and the all-solid battery can be manufactured by sealing in a battery case.

[0182] (Properties of all-solid battery)

[0183] The all-solid battery according to one embodiment of the present application using the above-described positive electrode active material exhibits a high capacity.

[0184] Specifically, it is preferable to use the positive electrode active material according to the present embodiment for the positive electrode to configure Figure 4 The test battery shown in Table 1 was used, and the current density was set to 0.2 mA / cm 2 , and charged to a cutoff voltage of 4.3 V (vs. Li), and after stopping for 1 hour, the discharge capacity at the time of discharging to a cutoff voltage of 2.5 V (vs. Li) was 130 mAh / g or more.

[0185] Examples

[0186] Hereinafter, the present application will be specifically described using examples and comparative examples.

[0187] [Example 1]

[0188] 1. Manufacture of lithium-nickel composite oxide

[0189] The manufacture of the lithium-nickel composite oxide was performed by the following procedure.

[0190] (a) Crystallization step

[0191] 10 L of pure water was added to a reaction tank having a content volume of 60 L, and the temperature in the tank was maintained at 50°C while stirring. At this time, the inside of the reaction tank was set to a nitrogen atmosphere having an oxygen concentration of 1% by volume or less.

[0192] An initial aqueous solution was prepared by adding 25 mass% sodium hydroxide aqueous solution and 25 mass% ammonia water to the reaction tank in such a manner that the pH value based on the liquid temperature of 25°C was 12.8 and the ammonia concentration of the solution in the reaction tank was 15 g / L.

[0193] A 25-L 2.0 mol / L nickel-cobalt mixed aqueous solution was prepared by simultaneously dissolving nickel sulfate and cobalt sulfate in pure water in such a manner that the mass ratio of nickel to cobalt was Ni:Co = 0.84:0.16. In addition, a 0.37 mol / L aluminum sulfate aqueous solution was prepared in 5 L.

[0194] The nickel-cobalt mixed aqueous solution was added dropwise at 109 mL / min with respect to the initial aqueous solution in the reaction tank to prepare a reaction aqueous solution. At this time, 25 mass% ammonia water and 25 mass% sodium hydroxide aqueous solution were also added dropwise to the initial aqueous solution at a certain rate to control the pH value of the reaction aqueous solution to be 12.8 based on the liquid temperature of 25°C.

[0195] Next, sulfuric acid was added dropwise to the reaction tank to adjust the pH of the reaction aqueous solution to 11.5. This operation was intended to lower the speed of precipitation of the complex hydroxide of Ni, Co, and Al from the liquid phase to the solid phase in the subsequent precursor crystallization process by lowering the pH, thereby improving the uniformity of the particle size distribution and the sphericity of the particles.

[0196] After the pH control, the nickel-cobalt mixed aqueous solution was added dropwise at 109.2 mL / min with respect to the reaction aqueous solution in the reaction tank to further add the aluminum sulfate aqueous solution at 24.8 mL / min with respect to 5.9 L. At this time, 25 mass% ammonia water and 25 mass% sodium hydroxide aqueous solution were also added dropwise to the initial aqueous solution at a certain rate to control the pH value of the reaction aqueous solution to be 11.5 based on the liquid temperature of 25°C and the ammonia concentration to be maintained at 15 g / L.

[0197] After the addition of the entire amount of the nickel-cobalt mixed aqueous solution and the aluminum sulfate aqueous solution, the pH of the reaction aqueous solution in the reaction tank was increased to 13.0 based on the liquid temperature of 25°C. This operation was intended to precipitate the nickel ions that had been complexed with ammonia and dissolved in the liquid phase on the hydroxide to obtain the target chemical composition.

[0198] Then, the reaction aqueous solution was subjected to solid-liquid separation using a Buchner funnel, a filter tank, and a vacuum filter. Further, the obtained solid phase was dispersed in 20 L of pure water at 40°C and subjected to solid-liquid separation twice to remove water-soluble impurities such as sodium sulfate from the nickel complex hydroxide.

[0199] The solid phase in the form of a filter cake after the solid-liquid separation of the washed slurry was dried in a fixed-type drier at 120°C for 24 hours under an air atmosphere, and a sieve having a mesh size of 100 μm was used to obtain a powder of the nickel composite hydroxide.

[0200] (b) Oxidation calcination step

[0201] The composite hydroxide prepared was calcined in an atmosphere calcination furnace (BM-50100M, SILICONIT Co., Ltd.) under an air atmosphere having an oxygen concentration of 20 vol% at 600°C for 2 hours, and then cooled to room temperature to obtain a nickel composite oxide.

[0202] (c) Mixing step

[0203] To the nickel composite oxide was added niobium oxide (Nb2O3xH2O) powder manufactured by Kishida Chemical Co., Ltd. so that the mass of Nb was 0.1% relative to the total mass of Ni, Co, and Al contained in the nickel composite oxide, and lithium hydroxide monohydrate weighed so that the mass of Li was 103% relative to the total mass of Ni, Co, Al, and Nb was added, and mixed using a turbo mixer (T2F, DALTON Co., Ltd.) to obtain a lithium mixture.

[0204] (d) Calcination step

[0205] The lithium mixture obtained was calcined in an atmosphere calcination furnace (BM-50100M, SILICONIT Co., Ltd.) in an oxygen-containing atmosphere having an oxygen concentration of 90 vol% or more at 750°C for 5 hours, and then cooled to room temperature. Thus, particles of a lithium nickel composite oxide were obtained.

[0206] 2. Evaluation of particles of lithium nickel composite oxide

[0207] The lithium nickel composite oxide obtained was evaluated as follows.

[0208] (a) Composition

[0209] The mass ratio of Li, Ni, Co, Al, and Nb of the lithium nickel composite oxide was confirmed to be Li:Ni:Co:Al:Nb = 1.04:0.815:0.150:0.034:0.001 by analysis using an ICP emission spectrometer (725ES, VARIAN Co., Ltd.).

[0210] (b) Crystal structure

[0211] The crystal structure of the lithium-nickel composite oxide particles was measured using XRD (PANALYTICAL, X'Pert, PROMRD), and the results confirmed that a crystal structure of a layered rock salt type in which peaks attributed to R-3m structure were detected in the diffraction pattern.

[0212] In addition, the half-value width of the (003) plane attributed peak in the diffraction pattern was measured, and when the size of the microcrystal was calculated using the Scherrer method, it was confirmed to be 123.4 nm.

[0213] (c) Measurement of the amount of dissolved lithium ions

[0214] The amount of dissolved lithium ions in the lithium-nickel composite oxide was calculated by titration. 2.0 g of the lithium-nickel composite oxide was dispersed in 125 ml of pure water, and 2 mL of a 10% barium chloride solution was further added. While stirring, neutralization titration was performed using 1 mol / L hydrochloric acid, and the amount of 1 mol / L hydrochloric acid required to reach the inflection point of the resulting titration curve near pH 4 was converted to the amount of Li resulting from the dissolved lithium ions. As a result, the amount of dissolved lithium ions in the lithium-nickel composite oxide was 0.31 wt%.

[0215] (d) Specific surface area

[0216] The BET specific surface area of the lithium-nickel composite oxide was measured using a full-automatic BET specific surface area measuring device (Mountech, Macsorb), and it was confirmed to be 0.49 m 2 / g.

[0217] (e) Particle size distribution

[0218] The particle size distribution of the lithium-nickel composite oxide was measured using a laser diffraction scattering type particle size distribution measuring device (Nikkiso Co., Ltd., Microtrac HRA). According to the results, the average particle size D50 on a volume basis was 5.4 μm, and the deviation index ((D90-D10) / MV) calculated from D10, D90, and MV was 0.44.

[0219] 3. Coating of the lithium-nickel composite oxide

[0220] The obtained lithium-nickel composite oxide was subjected to the following coating process.

[0221] To the solution obtained by adding isopropyl alcohol (IPA) 30 ml, titanium tetrabutoxide (Ti-BuOH) 1.8 g, and stirring, a solution to which IPA 20 ml and acetylacetone 0.9 g were added was added dropwise while heating and stirring at 60°C. This is because a high concentration of acetylacetone and Ti solution was not directly added. Then, a solution obtained by adding 0.54 g of pure water to 10 ml of IPA was added to the above-mentioned solution after cooling. Finally, IPA 65 ml was added to the obtained solution, and the coating solution was adjusted.

[0222] Using the coating liquid described above, 500 g of the lithium nickel composite oxide was subjected to a coating treatment using a rotational flow coating device (MP-01, Powrex).

[0223] With respect to 500 g of the lithium nickel composite oxide, air heated to 120°C was made to flow in the chamber at a flow rate of 0.3 m 3 / h, and the lithium nickel composite oxide was sprayed with the coating liquid at 1.7 ml / min.

[0224] After the coating liquid was completely sprayed, the lithium nickel composite oxide was recovered from the chamber, and heat-treated at 400°C for 10 hours under oxygen flow using an atmosphere firing furnace (BM-50100M, SILICONIT Co., Ltd.). Then, the lithium nickel composite oxide particles (positive electrode active material) having a coating layer (containing Li and Ti) were obtained by cooling to room temperature.

[0225] 4. Evaluation of the lithium nickel composite oxide particles having a coating layer

[0226] (a) Composition

[0227] Through analysis using an ICP emission spectrometer (725ES, VARIAN Co., Ltd.), it was confirmed that the coated lithium nickel composite oxide contained 0.88 wt% of Ti, and the amount of Ti per unit area of the base material was 370 μmol / m 2 .

[0228] (b) Thickness of the coating layer

[0229] The coated lithium nickel composite oxide was observed using a TEM (JEM-ARM200F, JEOL) after being thinned using a low-temperature ion microtome (IB-09060CIS, JEOL), and as a result, it was confirmed that the thickness of the coating layer was 11 nm.

[0230] 5. Production of a full solid secondary battery

[0231] In the evaluation of the capacity of the obtained positive electrode active material, a battery having the structure shown in FIG. 1 (hereinafter, referred to as "test battery") was used. Figure 4

[0232] (Structure of the test battery)

[0233] As shown in FIG. 1, the test battery SBA was provided with a case having a negative electrode can NC and a positive electrode can PC, and a powder cell C housed in the case. Figure 4

[0234] ​​The housing has a hollow negative electrode container NC with one open end and a positive electrode container PC disposed at the opening of the negative electrode container NC. A space for accommodating the compressed powder unit C is formed between the positive electrode container PC and the negative electrode container NC. The positive electrode container PC is fixed to the negative electrode container NC, for example, by a wing screw SW. The negative electrode container NC has a negative terminal, and the positive electrode container PC has a positive terminal. The housing also has an insulating sleeve ISV. The negative electrode container NC and the positive electrode container PC are fixed in a non-contact manner by means of the insulating sleeve ISV.

[0235] A pressure screw PSW is provided at the closed end of the negative electrode container NC. After the positive electrode container PC is fixed to the negative electrode container NC, the pressure screw PSW is screwed into the receiving space of the powder pressing unit C, thereby maintaining the powder pressing unit C under pressure through the hemispherical washer W. Additionally, a screw-in plug P is provided at the end of the negative electrode container NC where the pressure screw PSW is located. O-rings OL are provided between the negative electrode container NC and the positive electrode container PC, and between the negative electrode container NC and the plug P, sealing the gap between the negative electrode container NC and the positive electrode container PC and maintaining the airtightness of the housing.

[0236] The powder compaction unit C is a granular structure formed by stacking the positive electrode layer PL, the solid electrolyte layer SEL, and the negative electrode layer NL in this order. The positive electrode layer PL is in contact with the inner surface of the positive electrode container PC through the lower current collector LCC. The negative electrode layer NL is in contact with the inner surface of the negative electrode container NC through the upper current collector UCC, the hemispherical washer W, and the pressure screw PSW. The lower current collector LCC, the powder compaction unit C, and the upper current collector UCC are protected by the sleeve SV to prevent the positive electrode layer PL and the negative electrode layer NL from making electrical contact.

[0237] (Evaluation of battery manufacturing)

[0238] The experimental battery SBA was fabricated as follows.

[0239] First, 80 mg of the synthesized solid electrolyte was pressurized to 25 MPa using a particle forming apparatus to obtain... Solid electrolyte particles were then prepared. Next, 70 mg of positive electrode active material and 30 mg of solid electrolyte were mixed in a mortar. 15 mg of the solid electrolyte particles and the mixture of positive electrode active material and solid electrolyte were placed in a particle forming apparatus and pressurized at 360 MPa to form a positive electrode layer on the solid electrolyte particles. From bottom to top, the lower current collector LCC, particles with the positive electrode layer PL facing down, indium (In) foil (negative electrode layer NL), and upper current collector UCC were stacked sequentially and pressurized at 9 kN to form the electrode (pressed powder unit C). The electrode (pressed powder unit C) was sealed into a housing and tightened with a torque of 6–7 N·m using a pressure screw. The test battery SBA was fabricated in a glove box with an Ar atmosphere where the dew point was controlled to -80°C.

[0240] 6. Evaluation of the all-solid secondary battery

[0241] The charge-discharge capacity indicating the performance of the fabricated test battery was evaluated as follows.

[0242] (a) Initial discharge capacity

[0243] The initial discharge capacity was evaluated by fabricating a test battery using an indium foil as a negative electrode, leaving it for about 24 hours, stabilizing the open circuit voltage (OCV), setting the current density with respect to the positive electrode to 0.2 mA / cm 2 , charging to the cut-off voltage 3.7 V (vs. Li-In), stopping for 1 hour, and measuring the discharge capacity at the time of discharging to the cut-off voltage 1.9 V (vs. Li-In) (initial discharge capacity). The measurement result was 134 mAh / g.

[0244] [Example 2]

[0245] Except that the Nb addition amount in the lithium nickel composite oxide synthesis process of Example 1 was set to 0.8%, a coated lithium nickel composite oxide was synthesized under the same conditions as Example 1. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0246] [Example 3]

[0247] Except that the Nb addition amount in the lithium nickel composite oxide synthesis process of Example 1 was set to 1.2%, a coated lithium nickel composite oxide was synthesized under the same conditions as Example 1. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0248] [Example 4]

[0249] Except that the Nb addition amount in the lithium nickel composite oxide synthesis process of Example 1 was set to 3%, a coated lithium nickel composite oxide was synthesized under the same conditions as Example 1. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0250] [Example 5]

[0251] Except that the firing time in the lithium nickel composite oxide synthesis process of Example 2 was set to 12 h, a coated lithium nickel composite oxide was synthesized under the same conditions as Example 2. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0252] [Example 6]

[0253] Except that the firing time in the lithium nickel composite oxide synthesis process of Example 3 was set to 12 h, a coated lithium nickel composite oxide was synthesized under the same conditions as Example 3. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0254] [Example 7]

[0255] The lithium nickel composite oxide obtained in Example 2 was coated with lithium niobate in a coating step, and heat-treated under the following conditions, and otherwise, a coated lithium nickel composite oxide was synthesized under the same conditions as in Example 2. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0256] After the coating liquid was entirely sprayed, the lithium nickel composite oxide was recovered from the chamber, and heat-treated at 350°C for 1 hour under atmospheric pressure using an atmosphere firing furnace (BM-50100M manufactured by SILICONIT Co., Ltd.). Then, it was cooled to room temperature, and particles of the lithium nickel composite oxide having a coating layer (containing Li and Nb) (positive electrode active material) were obtained.

[0257] [Example 8]

[0258] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 6, except that the proportion a of Li in the lithium nickel composite oxide synthesis step of Example 6 was set to 1.00. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0259] [Example 9]

[0260] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 6, except that the proportion a of Li in the lithium nickel composite oxide synthesis step of Example 6 was set to 1.09. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0261] [Example 10]

[0262] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 6, except that the proportion (1-x-y) of Ni in the lithium nickel composite oxide synthesis step of Example 6 was set to 0.85, and the proportion (x 1 ) of Co was set to 0.116. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0263] [Example 11]

[0264] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 6, except that the proportion (1-x-y) of Ni in the lithium nickel composite oxide synthesis step of Example 6 was set to 0.744, and the proportion (x 1 ) of Co was set to 0.222. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0265] [Comparative Example 1]

[0266] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 1 except that no Nb was added in the lithium nickel composite oxide synthesis process of Example 1. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0267] [Comparative Example 2]

[0268] A coated lithium nickel composite oxide was synthesized under the same conditions as in Comparative Example 1 except that the firing temperature in the lithium nickel composite oxide synthesis process of Comparative Example 1 was set to 735°C. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0269] [Comparative Example 3]

[0270] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 1 except that the amount of Nb added in the lithium nickel composite oxide synthesis process of Example 1 was 5 atomic%. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0271] [Comparative Example 4]

[0272] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 2 except that no coating of the particles of the lithium nickel composite oxide of Example 2 was performed. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0273] [Comparative Example 5]

[0274] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 6 except that the proportion a of Li in the lithium nickel composite oxide synthesis process of Example 6 was set to 1.18. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0275] [Table 1]

[0276]

[0277] [Table 2]

[0278]

[0279] [Results of Evaluation]

[0280] The discharge capacity in the all-solid battery was significantly improved in the positive electrode active material of the embodiment compared to the positive electrode active material of Comparative Example 1 not containing Nb. In particular, in Example 2 (Nb: 0.8 atom%), the discharge capacity was significantly improved. In addition, in the positive electrode active materials of Examples 1 and 2 with a firing time of 5 hours and the positive electrode active materials of Examples 4 and 5 with a firing time of 12 hours, the characteristics of the positive electrode active material such as the crystallite diameter and the specific surface area, and the battery characteristics (initial discharge capacity) were also the same degree, showing that a positive electrode active material with high battery characteristics can be obtained even with a firing time of 5 hours. In addition, in Example 7 in which the coating layer contains Nb, the same as in Examples 1 to 6 in which the coating layer contains Ti, a high discharge capacity was shown.

[0281] In addition, in Example 8 in which the proportion of Li (a) is 1.00 and Example 9 in which the proportion of Li (a) is 1.09, a high discharge capacity equivalent to that of Example 6 (a: 1.04) was also shown. In addition, according to Example 10 (proportion of Ni: 0.850) and Example 11 (proportion of Ni: 0.744) in which the proportion of Ni (1-x-y) differs from Example 6 (proportion of Ni: 0.806), the higher the proportion of Ni, the higher the discharge capacity.

[0282] On the other hand, in the positive electrode active material of Comparative Example 2 not containing Nb the same as in Comparative Example 1, even if the firing temperature (735°C) was changed, an improvement in the discharge capacity was not seen, and instead, the discharge capacity decreased.

[0283] In addition, in the positive electrode active material of Comparative Example 3 in which the amount of added Nb exceeds 3 atom%, the discharge capacity in the all-solid battery also decreased compared to Comparative Examples 1 and 2 in which no Nb was added.

[0284] In addition, in the positive electrode active material of Comparative Example 4 manufactured under the same conditions as in Example 1 except that no coating layer was provided, the discharge capacity in the all-solid battery was very low. This is thought to be because there was no coating layer on the surface of the particles of the lithium-nickel composite oxide, and therefore the interfacial resistance between the positive electrode active material and the solid electrolyte increased. In addition, in Comparative Example 5 (a: 1.18) in which the proportion of Li (a) was too high, the amount of dissolved lithium was large, and the discharge capacity decreased.

[0285] Industrial Applicability

[0286] According to the present application, a positive electrode active material that can be suitably used for the positive electrode of an all-solid lithium ion secondary battery that requires high battery capacity, and a method for manufacturing the same, can be provided.

[0287] Furthermore, the technical scope of the present application is not limited to the modes described in the above-described embodiments and the like. One or more of the components described in the above-described embodiments and the like are sometimes omitted. In addition, the components described in the above-described embodiments and the like can be appropriately combined. In addition, to the extent permitted by law, the disclosure of all documents cited in the above-described embodiments and the like is incorporated herein by reference as part of the description of the present application. In addition, to the extent permitted by law, the content of Japanese Patent Application No. 2020-129024 is incorporated herein by reference as part of the description of the present application.

[0288] Symbol explanation

[0289] 1… particle of lithium-nickel composite oxide; 2… coating layer; 10… positive electrode active material; SBA… test battery; PC… positive electrode can; NC… negative electrode can; ISV… insulation sleeve; C… pressed powder unit; PL… positive electrode layer; NL… negative electrode layer; SEL… solid electrolyte layer; LCC… lower current collector; UCC… upper current collector; P… plug; PSW… press screw; W… semispherical washer; OL… O-ring; SV sleeve; SW… screw; N… nut.

Claims

1. A positive electrode active material for a full-solid-state lithium ion secondary battery, comprising particles of a lithium-nickel composite oxide and a coating layer that coats a surface of the particles, the particles of the lithium-nickel composite oxide have a crystal structure belonging to a space group R-3m, the particles of the lithium-nickel composite oxide contain at least Li, Ni, an element M, and Nb, a mass ratio of each element is represented by Li:Ni:M:Nb = a:(1-x-y):x:y, 0.98 ≤ a ≤ 1.15, 0 < x ≤ 0.5, 0 < y ≤ 0.03, 0 < x+y ≤ 0.5, the element M is at least one selected from the group consisting of Co, Al, Mn, Zr, Si, Zn, and Ti, a crystallite diameter of the particles of the lithium-nickel composite oxide calculated from a diffraction peak belonging to a (003) plane measured by XRD is 140 nm or less, an amount of eluted lithium ions of the particles of the lithium-nickel composite oxide calculated by neutralization titration is 0.30% by mass or more and 1.00% by mass or less with respect to a total amount of the particles of the lithium-nickel composite oxide, the coating layer is composed of a composite oxide containing Li and at least one element selected from the group consisting of Al, Si, Ti, V, Ga, Ge, Zr, Nb, Mo, Ta, and W.

2. The positive electrode active material for a full-solid-state lithium-ion secondary battery according to claim 1, wherein The lithium-nickel composite oxide particle contains secondary particles composed of a plurality of primary particles, has a porous structure in the secondary particles, has a plurality of void portions in which the primary particles are not present in the porous structure, and has a specific surface area of 0.3 m 2 / g or more and 2.0 m 2 / g or less, as measured by the nitrogen adsorption BET method.

3. The positive electrode active material for a full-solid-state lithium-ion secondary battery according to claim 2, wherein At least a part of niobium contained in the particles of the lithium-nickel composite oxide is concentrated at an interface of the primary particles.

4. The positive electrode active material for a all-solid-state lithium-ion secondary battery according to any one of claims 1 to 3, wherein, In a cumulative volume distribution curve of a particle size distribution, a particle diameter corresponding to a cumulative volume rate of 50%, that is, D50 of the particles of the lithium-nickel composite oxide is 7 μm or less.

5. The positive electrode active material for a full-solid-state lithium-ion secondary battery according to any one of claims 1 to 3, wherein An average thickness of the coating layer is 2 nm or more and 15 nm or less.

6. A method for producing the positive electrode active material for a full-solid-state lithium ion secondary battery according to any one of claims 1 to 5, comprising: a mixing step of mixing a nickel composite compound, a niobium compound, and a lithium compound to obtain a mixture, a calcination step of calcining the mixture to obtain the particles of the lithium-nickel composite oxide, and a coating step of causing a coating liquid containing at least one element selected from the group consisting of Al, Si, Ti, V, Ga, Ge, Zr, Nb, Mo, Ta, and W to adhere to a surface of the particles of the lithium-nickel composite oxide to form the coating layer.

7. The method for producing a positive electrode active material for a full-solid-state lithium-ion secondary battery according to claim 6, wherein the nickel composite compound contains a nickel composite oxide, the method for producing the positive electrode active material for a full-solid-state lithium ion secondary battery comprises: an oxidative calcination step of performing oxidative calcination on a nickel composite hydroxide adjusted by a crystallization reaction to obtain the nickel composite oxide.

8. The method for producing a positive electrode active material for a full-solid-state lithium-ion secondary battery according to claim 6 or 7, wherein after the coating step, a heat treatment step of performing heat treatment on the particles of the lithium-nickel composite oxide on which the coating layer is formed on a surface at 300°C or higher.

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