Positive Electrode Active Material for All-Solid-State Lithium-Ion Secondary Battery and Method for Producing the Same

Abstract

The purpose of the present invention is to provide a positive electrode active material that exhibits a higher battery capacity in use as a positive electrode active material in an all-solid-state battery.　The positive electrode active material for all-solid-state lithium ion secondary batteries has lithium nickel composite oxide particles and a coating layer that coats the surface of the particles. The lithium nickel composite oxide particles have a crystal structure belonging to space group R-3m; contain at least Li, Ni, an element M, and Nb wherein the amount of substance ratio for the individual elements is given 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, and the element M is at least one selected from the group consisting of Co, Al, Mn, Zr, Si, Zn, and Ti); have a crystallite diameter of not more than 140 nm; and have an amount of lithium ion elution of 0.30-1.00 mass%. The coating layer is a composite oxide that contains Li and at least one element selected from the group consisting of Al, Si, Ti, V, Ga, Ge, Zr, Nb, Mo, Ta, and W.

Description

Technical Field

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

Background Art

[0002] In recent years, with the increasing environmental awareness, the shift from gasoline vehicles to hybrid vehicles and electric vehicles has been progressing. In particular, the development of a small and lightweight secondary battery with high energy, which is 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 a general lithium ion secondary battery, lithium transition metal composite oxides such as LiCoO2, LiNiO2, and LiMn2O4 are used as the positive electrode active material, and lithium metal, lithium alloy, metal oxide, carbon, etc. are used as the negative electrode active material.

[0004] When a non-aqueous electrolyte is used as the electrolyte, for example, an electrolyte in which a Li salt such as LiClO4 or LiPF6 is dissolved as a supporting salt in an organic solvent such as ethylene carbonate, dimethyl carbonate, or ethyl methyl carbonate is used.

[0005] Among the components of a lithium ion secondary battery, in particular, the non-aqueous electrolyte is a factor that limits battery performance such as fast charging, thermal stability, and life due to chemical characteristics such as heat resistance and potential window. Therefore, research and development are currently being actively conducted on an all-solid-state lithium ion secondary battery (hereinafter also referred to as "all-solid-state battery") in which the above battery performance is improved by using a solid electrolyte instead of the non-aqueous electrolyte.

[0006] For example, in Patent Document 1, among solid electrolytes, sulfide solid electrolytes are described as having high lithium ion conductivity during charge and discharge and being preferable for use in all-solid-state batteries. However, as disclosed in Non-Patent Document 1, for example, when a sulfide solid electrolyte comes into contact with a cathode active material that is an oxide, a reaction occurs at the interface between the solid electrolyte and the cathode active material during charge and discharge, a high-resistance phase is generated at the interface, and the operation of the all-solid-state battery is inhibited. This is because a space charge layer is formed due to a change in the conductive ion concentration caused by a difference in electrochemical potential at the contact interface, resulting in an ion conductivity different from that of the bulk and an increase in resistance.

[0007] Therefore, for example, in Patent Document 2, a technique has been proposed in which a coating layer made of LiNbO3 is provided on the surface of the cathode active material in order to prevent contact between the solid electrolyte and the cathode active material (oxide) and suppress the generation of a high-resistance phase.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0009]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] By the way, for increasing the energy density of a lithium-ion secondary battery, it is preferable to use a positive electrode active material having a high Ni ratio such as LiNiO2, LiNi 0.80 Co 0.15 Al 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2 or the like. Therefore, the inventors examined the applicability of a positive electrode active material having a high Ni ratio to an all-solid-state lithium-ion secondary battery. As a result, the inventors found that when using a solid electrolyte, since it is possible to design a battery in which cells are connected in series, although the energy density of the entire battery is improved compared to the case of using a non-aqueous electrolyte, the energy density obtained from the positive electrode active material having a high Ni ratio does not reach the expected energy density or battery capacity.

[0011] In view of the above problems, an object of the present invention is to provide a positive electrode active material having a higher battery capacity when using a positive electrode active material having a high Ni ratio as the positive electrode active material of an all-solid-state battery.

Means for Solving the Problems

[0012] In a first aspect of the present invention, there is provided a positive electrode active material for an all-solid-state lithium-ion secondary battery, which has particles of a lithium nickel composite oxide and a coating layer covering the surface of the particles. The particles of the lithium nickel composite oxide have a crystal structure belonging to the space group R-3m, contain at least Li, Ni, element M and Nb, and the molar ratio of each element is 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, and element M is at least one selected from the group consisting of Co, Al, Mn, Zr, Si, Zn and Ti). The crystallite size calculated by the Scherrer method from the diffraction peak attributed to the (003) plane measured by XRD is 140 nm or less, and the amount of eluted lithium ions determined by neutralization titration is 0.30 mass% or more and 1.00 mass% or less with respect to the total amount of the particles of the lithium nickel composite oxide. The coating layer is 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.

[0013] Further, the particles of the lithium nickel composite oxide include secondary particles formed by aggregation of a plurality of primary particles, have a porous structure having a plurality of void portions where no primary particles exist in the secondary particles, and 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. Further, at least a part of the niobium contained in the particles of the lithium nickel composite oxide is preferably segregated at the primary particle interface. Further, the particles of the lithium nickel composite oxide preferably have a particle size (D50) corresponding to an integrated volume ratio of 50% in the integrated volume distribution curve of the particle size distribution of 7 μm or less. Further, the average thickness of the coating layer is preferably 1 nm or more and 15 nm or less.

[0014] In a second aspect of the present invention, there is provided a method for manufacturing a positive electrode active material for an all-solid-state lithium-ion secondary battery, comprising: a mixing step of mixing a nickel composite compound, a niobium compound, and a lithium compound to obtain a mixture; a firing step of firing the mixture to obtain particles of a lithium nickel composite oxide; and a coating step of attaching 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 the surface of the particles of the lithium nickel composite oxide to form a coating layer.

[0015] Further, the nickel composite compound preferably includes a nickel composite oxide and includes an oxidation roasting step of obtaining the nickel composite oxide by oxidizing and roasting a nickel composite hydroxide adjusted by a crystallization reaction. Further, preferably, after the coating step, there is a heat treatment step of heat-treating the particles of the lithium nickel composite oxide having a coating layer formed on the surface at 300°C or higher.

Advantages of the Invention

[0016] When the positive electrode active material of the present invention is used as a positive electrode active material of an all-solid-state battery, the battery capacity is improved. Further, the manufacturing method of the present invention can produce this positive electrode active material with high productivity.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, for the sake of clarity, some parts are emphasized or some parts are simplified, and the actual structure, shape, scale, etc. may be different. Also, the present invention is not limited to the following embodiments, and various modifications and substitutions can be made to the following embodiments without departing from the scope of the present invention.

[0019] 1. Cathode active material for all-solid-state lithium-ion secondary battery First, a configuration example of the cathode active material for an all-solid-state lithium-ion secondary battery according to the present embodiment (hereinafter also referred to as the "cathode active material") will be described.

[0020] FIG. 1 is a diagram schematically showing an example of the cathode active material according to the present embodiment. As shown in FIG. 1, the cathode active material 10 has particles 1 of a lithium nickel composite oxide and a coating layer 2 covering the surface of the particles 1. Hereinafter, each component will be described.

[0021] (1) Particles of lithium nickel composite oxide 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), element M, and Nb.

[0022] (Composition) When the molar ratio of the amounts of substances of each element contained in the particles 1 of the lithium nickel composite oxide is expressed as 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 are satisfied. Also, in the above molar ratio, it is preferable to satisfy 0.98 ≦ a ≦ 1.15, 0 < x ≦ 0.3, 0 < y ≦ 0.02, 0 < x + y ≦ 0.4.

[0023] In the above substance mass ratio, a representing the Li content ratio satisfies 0.98 ≦ a ≦ 1.15, and it may also satisfy 0.98 ≦ a ≦ 1.10, 0.98 ≦ a ≦ 1.06, or 0.98 ≦ a ≦ 1.03. When a is less than 0.98, Li is deficient in the positive electrode active material, which 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 grows excessively, the primary particles become coarse, and cracks in the particles 1 are likely to occur, thus easily impairing the durability.

[0024] In the above substance mass ratio, (1 - x - y) representing the Ni content ratio is 0.5 or more and less than 1.0. Also, the range including the lower limit of the Ni content ratio is preferably 0.6 or more, and it may also be 0.7 or more, or 0.8 or more. The higher the content ratio of (1 - x - y), the lower the voltage required for charging, and as a result, the higher the battery capacity. When (1 - x - y) is less than 0.5, the battery capacity becomes low.

[0025] In the above substance mass ratio, element M is preferably at least one selected from the group consisting of Co, Al, Mn, Zr, Si, Zn, and Ti. Also, element M preferably contains at least one element selected from cobalt (Co), aluminum (Al), and manganese (Mn). Element M can be appropriately selected according to the application and required performance of the secondary battery constituted by using the positive electrode active material 10.

[0026] In the above substance mass ratio, x representing the content ratio of element M satisfies 0 < x ≦ 0.5, preferably 0 < x ≦ 0.3, and it may also be 0 < x ≦ 0.2. For example, when element M contains Co and Co is within the above range, it has a high battery capacity and excellent cycle characteristics. Also, element M may contain Co and Al. The range of Co may be, for example, 0 < x ≦ 0.3 or 0 < x ≦ 0.2. The range of Al may be, for example, 0 < x ≦ 0.1 or 0 < x ≦ 0.07.

[0027] In the above substance mass ratio, y representing the content ratio of Nb satisfies 0 < y ≤ 0.03, preferably 0 < y ≤ 0.02. When y is within the above range, a high battery capacity can be achieved in the all-solid-state battery. When y exceeds 0.03, low-active LiNb3O8 may be generated, causing a decrease in battery capacity. Further, for example, when 0.001 ≤ y ≤ 0.01, a higher battery capacity can be achieved.

[0028] Also, the niobium contained in the particles 1 of the lithium nickel composite oxide may be solid-solved inside the primary particles or may be present at the interface of the primary particles. At least a part of the niobium preferably segregates at the interface of the primary particles. Although the details of the reason are unclear, for example, it is assumed that when niobium segregates at the interface of the primary particles, it has the effect of reducing the barrier to Li-ion movement in the secondary particles and improving the battery capacity. Further, it is considered that when at least a part of the niobium segregates at the interface of the primary particles, it becomes easy to adjust the amount of eluted lithium described later within a specific range.

[0029] (Crystal structure) The particles 1 of the lithium nickel composite oxide have a crystal structure belonging to the space group R-3m. When the particles 1 of the lithium nickel composite oxide have a crystal structure belonging to the space group R-3m, an increase in internal resistance can be suppressed in the secondary battery.

[0030] The crystal structure of the particles 1 of the lithium nickel composite oxide can be confirmed by powder X-ray diffraction (XRD) measurement. That is, from the diffraction pattern obtained when performing powder X-ray diffraction (XRD) measurement on the particles 1 of the lithium nickel composite oxide, it is preferable that peaks attributed to the layered rock salt-type crystal structure of the "R-3m" structure (crystal structure belonging to the space group R-3m) are detected. In particular, it is more preferable that only peaks attributed to the layered rock salt-type crystal structure of the "R-3m" structure are detected from the above diffraction pattern.

[0031] The particles 1 of the lithium nickel composite oxide may be a single-phase lithium nickel composite oxide having a crystal structure of the "R-3m" structure, or may not be a single phase. When it is not a single layer and other compounds (e.g., impurities, etc.) are mixed in, the intensity of the heterogeneous peak other than the layered rock salt structure of the "R-3m" structure is preferably not higher than the peak intensity attributed to the layered rock salt structure of the "R-3m" structure.

[0032] (Crystallite size) The particles 1 of the lithium nickel composite oxide preferably have a crystallite size of 140 nm or less, more preferably 40 nm or more and 140 nm or less. Also, the range including the upper limit of the crystallite size may be 130 nm or less. Also, the range including the lower limit of the crystallite size may be 50 nm or more. The crystallite size can be calculated by the Scherrer method using the peak attributed to (003) of the above XRD diffraction pattern. When the crystallite size of the particles 1 of the lithium nickel composite oxide exceeds 140 nm, the solid diffusion distance within the crystal may become long and the battery capacity may decrease. Also, when the crystallite size of the particles 1 of the lithium nickel composite oxide is less than 40 nm, the crystal structure becomes unstable and the battery capacity is likely to decrease.

[0033] (Amount of eluted lithium ions) For the particles 1 of the lithium nickel composite oxide, the amount of eluted lithium ions determined by neutralization titration is 0.30 mass% or more and 1.00 mass% or less, preferably 0.30 mass% or more and 0.70 mass% or less, based on the total amount of the particles 1. The amount of eluted lithium ions can be determined by a neutralization titration method using hydrochloric acid for the amount of lithium ions eluted into water when the particles 1 of the lithium nickel composite oxide are dispersed in water. As the neutralization titration method, the Warder method or the Winkler method can be used.

[0034] When the amount of eluted lithium ions in the particles 1 of the lithium nickel composite oxide is less than 0.30% by mass, the battery capacity may decrease. Although the details of this reason are unclear, for example, it is considered that one of the reasons is that a specific amount of eluted lithium ions is contained on the surface of the particles 1 of the lithium nickel composite oxide, which suppresses the direct contact between the particles 1 of the lithium nickel composite oxide and the solid electrolyte in the all-solid-state battery and suppresses the formation of a high-resistance phase.

[0035] In addition, when the particles 1 of the lithium nickel composite oxide contain niobium, the amount of eluted lithium ions increases compared to the lithium nickel composite oxide not containing niobium. Therefore, for example, by using the manufacturing method described later, adjusting the niobium content to be within the above range and adjusting the amount of eluted lithium to be 0.3% by mass or more, a positive electrode active material having a high discharge capacity can be obtained. However, when the amount of eluted lithium ions in the particles 1 of the lithium nickel composite oxide exceeds 1.00% by mass, the discharge capacity decreases.

[0036] (Crystallite size and amount of eluted lithium ions) Furthermore, the particles 1 of the lithium nickel composite oxide preferably have a crystallite size of 140 nm or less and an amount of eluted lithium ions of 0.30% by mass or more.

[0037] That is, even if the crystallite size of the particles 1 of the lithium nickel composite oxide is 140 nm or less, when the amount of eluted lithium ions is less than 0.30% by mass, the battery capacity may decrease. Although the details of this reason are unclear, for example, it is speculated as follows.

[0038] The particles 1 of the lithium nickel composite oxide contain secondary particles formed by aggregation of a plurality of primary particles. The crystallite size of the particles 1 of the lithium nickel composite oxide is positively correlated with the size of the primary particles constituting the secondary particles, and it is considered that the smaller the crystallite size, the more particle interfaces exist between the primary particles. Also, the eluted lithium ions mainly exist at the particle interfaces between the primary particles. Therefore, when the crystallite size is small and there are many interfaces of the primary particles, if the eluted lithium ions existing at the interfaces (surfaces) of the primary particles decrease too much, voids will be formed at the interfaces of the primary particles. When there are many voids at the interfaces of the primary particles, the positive electrode active material is likely to crack during the electrode fabrication process of the all-solid-state battery, and the contact interface between the particles of the lithium nickel composite oxide and the solid electrolyte increases. And it is considered that due to the side reactions occurring at this increased contact interface, the generated phase hinders the charge transfer between the electrolyte and the positive electrode active material, resulting in an increase in the battery resistance and a decrease in the battery capacity.

[0039] On the other hand, when the crystallite size of the particles 1 of the lithium nickel composite oxide exceeds 140 nm, even if the amount of eluted lithium ions is 0.30 mass% or more, the battery capacity decreases, which is not preferable. This is presumably because as the primary particles coarsen, the grain boundaries between the primary particles decrease, so that the eluted lithium ions become scattered in lumps on the surface of the secondary particles, and the existence of these eluted lithium ions itself becomes a resistive phase. Note that the crystallite size and the amount of eluted lithium can be adjusted within the above ranges, for example, by using the method for manufacturing the positive electrode active material described later.

[0040] (Particle Structure) The particles 1 of the lithium nickel composite oxide contain secondary particles formed by aggregation of a plurality of primary particles. Also, the particles 1 of the lithium nickel composite oxide may contain single primary particles or may be a mixture of single primary particles and secondary particles.

[0041] When observed with a scanning electron microscope (SEM), a transmission electron microscope (TEM), etc., it is preferable that the average particle size of the secondary particles is 3.0 μm or more and 7.0 μm or less. Further, it is preferable that these secondary particles are formed by aggregation of a large number of primary particles having a particle size of 0.1 μm or more and 2.0 μm or less. Further, when including single primary particles, the primary particles preferably have a particle size of 1.0 μm or more and 7.0 μm or less. Note that the average particle size of each particle can be obtained, for example, by calculating the average of the equivalent circle diameters of the areas of 20 or more particles.

[0042] (Average particle size D50) For the particles 1 of the lithium nickel composite oxide, it is preferable that the particle size (D50, hereinafter also referred to as "average particle size D50") corresponding to an integrated volume ratio of 50% in the integrated volume distribution curve of the particle size distribution is 7 μm or less, more preferably 2 μm or more and 7 μm or less, and still more preferably 3 μm or more and 7 μm or less. Note that the average particle size (D50) can be measured with a laser diffraction / scattering particle size distribution analyzer.

[0043] When the average particle size D50 of the particles 1 of the lithium nickel composite oxide is 7 μm or less, in a secondary battery using the positive electrode active material 10 as the positive electrode, the battery capacity per battery capacity can be made sufficiently large, and excellent battery characteristics such as thermal stability and high output can be obtained. On the other hand, when the average particle size D50 is 2 μm or less, it is not preferable because it tends to aggregate when applying the coating layer 2.

[0044] (Spread of particle size distribution) The index [(d90 - d10) / volume average particle size Mv] indicating the spread of the particle size distribution of the particles 1 of the lithium nickel composite oxide is not particularly limited. However, from the perspective of making the particle size uniform, it may be 0.7 or less, may be 0.6 or less, or may be 0.55 or less. When the particle size is relatively uniform, it becomes easy to uniformly coat the surface of the particles 1 of the lithium nickel composite oxide with the coating layer 2, and good output characteristics can be obtained in the secondary battery. The lower limit of [(d90 - d10) / volume average particle size Mv] is not particularly limited, but for example, it is 0.3 or more. Also, [(d90 - d10) / volume average particle size Mv] may be 0.7 or more from the perspective of fillability, and by using the method for manufacturing the positive electrode active material described later, the coating layer 2 can be coated relatively uniformly.

[0045] Note that d10 means the particle size at which the cumulative volume of the particles at each particle size from the smaller side of the particle size becomes 10% of the total volume of all the particles, and d90 means the particle size at which the cumulative volume becomes 90% of the total volume of all the particles in the same way by accumulating the particle numbers. Also, d10, d90, and the volume average particle size Mv can be obtained from the volume integration value measured by a laser diffraction / scattering particle size analyzer in the same manner as the average particle size D50.

[0046] (Specific surface area) The specific surface area of the particles 1 of the lithium nickel composite oxide is not particularly limited. For example, it may be 0.3 m 2 / g or more and 2.0 m 2 / g or less, or may be 0.3 m 2 / g or more and 1.0 m 2 / g or less. When the specific surface area is within the above range, the output characteristics are good. The specific surface area can be measured by the nitrogen adsorption BET method.

[0047] (2) Coating layer The positive electrode active material 10 includes a coating layer 2 on the surface of the particles 1 of the lithium nickel composite oxide. By having the coating layer 2 on the surface of the particles 1, in a secondary battery including a positive electrode containing the positive electrode active material 10, the mutual reaction between the positive electrode active material 10 and the solid electrolyte can be suppressed.

[0048] The coating layer 2 is a composite oxide containing lithium (Li) and at least one element 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 excluding lithium (Li) and oxygen (O) may be one type or two or more types. The coating layer 2 may be, for example, a composite oxide composed of Li and Ti, or a composite oxide composed of Li and Nb.

[0049] (Content of constituent elements of the coating layer) The coating amount of the coating layer 2 is not particularly limited, but it can be adjusted according to the specific surface area (m 2 / g) of the particles 1 of the lithium nickel composite oxide to be coated. The coating layer 2 preferably contains the constituent elements (excluding Li and O) of the coating layer 2 at a ratio of, for example, 30 μmol or more and 600 μmol or less, more preferably 50 μmol or more and 400 μmol or less, per 1 m 2 of the surface area of the particles 1 of the lithium nickel composite oxide.

[0050] When the content of the constituent elements (excluding Li and O) of the coating layer 2 per 1 m 2 of the surface area of the particles 1 of the lithium nickel composite oxide is 30 μmol or more, the coating layer 2 can be uniformly disposed on the entire surface of the particles 1 of the lithium nickel composite oxide.

[0051] Also, by providing the coating layer 2, the reaction between the particles 1 of the lithium nickel composite oxide and the solid electrolyte can be suppressed, but at the same time, there is a possibility that the internal resistance of the secondary battery may increase. When the content of the constituent elements (excluding Li and O) of the coating layer 2 per 1 m 2 of the surface area of the particles 1 of the lithium nickel composite oxide is 600 μmol or less, it is possible to suppress the coating layer 2 from becoming an obstacle to the intercalation / deintercalation reaction of lithium into / from the particles 1 of the lithium nickel composite oxide and reduce the internal resistance.

[0052] In the coating layer 2, the method for evaluating and calculating the content of the constituent elements (excluding Li and O) of the coating layer 2 is not particularly limited, but can be determined, for example, as follows.

[0053] First, measure the content of the constituent elements (excluding Li and O) of the coating layer 2 in 1 g of the positive electrode active material by a method such as chemical analysis. As the method of chemical analysis, measurement is performed by ICP (Inductively Coupled Plasma) emission spectrometry or the like.

[0054] On the other hand, measure the specific surface area of the particles 1 of the lithium nickel composite oxide before coating the coating layer 2 by the nitrogen adsorption BET method or the like.

[0055] Next, divide the content of the constituent elements (excluding Li and O) of the coating layer 2 in 1 g of the positive electrode active material by the specific surface area (m 2 / g) of the particles 1 of the lithium nickel composite oxide to obtain the content of the constituent elements (excluding Li and O) of the coating layer 2 per 1 m 2 of the surface area of the particles 1 of the lithium nickel composite oxide.

[0056] When the particles 1 of the lithium nickel composite oxide contain the constituent elements (excluding Li and O) of the coating layer 2, the difference in the content of the constituent elements (excluding Li and O) of the coating layer 2 before and after coating can be used as the content of the constituent elements (excluding Li and O) of the coating layer 2 used for coating.

[0057] (Average thickness of the coating layer) 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 even more preferably 5 nm or more and 15 nm or less.

[0058] The average thickness of the coating layer 2 can be calculated by measuring the layer uniformly formed on the surface of the lithium nickel composite oxide particle 1 through observation with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) or by analysis with an associated spectrometer such as an energy dispersive X-ray spectrometer (EDS) or an electron energy loss spectroscopy (EELS). When the thickness of the coating layer 2 varies depending on the measurement site, the thickness of the coating layer 2 refers to the average value when multiple sites are measured.

[0059] (Arrangement of coating layer) Moreover, the coating layer 2 is preferably present adjacent to the surface of the lithium nickel composite oxide particle 1. Whether the coating layer 2 is present adjacent to the surface of the particle 1 can be determined by whether a compound containing the constituent elements of the coating layer 2 is present in a state separated from the surface of the lithium nickel composite oxide particle 1. When the coating layer 2 is separated from the surface of the lithium nickel composite oxide particle 1, it does not electrochemically contribute to the battery capacity, and therefore becomes a factor in reducing the battery capacity per weight.

[0060] It is not necessary that there is a clear boundary between the coating layer 2 and the surface of the lithium nickel composite oxide particle 1. For example, when the lithium nickel composite oxide particle 1 before coating does not contain the constituent elements of the coating layer 2 (excluding Li and O), the coating layer 2 refers to a region where the constituent elements of the coating layer 2 (excluding Li and O) are detected, and may include a region where both the constituent elements of the coating layer 2 (excluding Li and O) and the elements of the lithium nickel composite oxide particle 1 are detected. When the lithium nickel composite oxide particle 1 before coating contains the constituent elements of the coating layer 2 (excluding Li and O), it refers to a region (site) on the surface side of the particle constituting the positive electrode active material 10, where the concentration of the constituent elements of the coating layer 2 (excluding Li and O) is higher than that of the central part of the lithium nickel composite oxide particle 1.

[0061] Further, the constituent elements of the coating layer 2 (excluding Li and O) may be partially dissolved from the surface to the inside of the particles of the lithium nickel composite oxide. For example, a heat treatment step (S40) may be performed after the coating step (S30), and depending on the conditions at that time, the constituent elements of the coating layer can be diffused into the lithium nickel composite oxide.

[0062] For example, when the coating layer 2 contains Ti and / or Nb, by dissolving Ti and / or Nb from the surface to the inside of the particles 1 of the lithium nickel composite oxide, the coating layer 2 not only prevents the solid electrolyte from directly contacting the particles 1 of the lithium nickel composite oxide and reduces the chance of reaction, but also has the effect of reducing the reactivity between the surface layer of the particles 1 of the lithium nickel composite oxide and the solid electrolyte. In the positive electrode active material 10, it is preferable to adjust the degree of solid solution so that the effect of improving the cycle characteristics can be fully exerted.

[0063] 2. Method for manufacturing a positive electrode active material for an all-solid-state lithium-ion secondary battery 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 of the present embodiment, the above positive electrode active material 10 can be manufactured with high productivity.

[0064] FIG. 2 and FIG. 3 are diagrams showing an example of a method for manufacturing a positive electrode active material according to the present embodiment. As shown in FIG. 2, the method for manufacturing a positive electrode active material according to 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 firing step (S20) of firing the mixture to obtain particles of a lithium nickel composite oxide, and a coating step (S30) of attaching a coating liquid 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 having a coating layer formed on the surface at 300°C or higher may be provided.

[0065] Alternatively, the nickel composite compound may be a nickel composite oxide obtained by oxidizing and roasting a nickel composite hydroxide adjusted by a crystallization reaction. For example, as shown in FIG. 3, the nickel composite compound can be produced by a method including a crystallization step (S1) and an oxidation roasting step (S2). Details will be described below for each step. Note that the following description is an example of the production method and does not limit the production method.

[0066] (Crystallization step: S1) In the crystallization step (S1), a nickel composite hydroxide, which is a precursor of a lithium nickel composite oxide, is prepared by a crystallization reaction.

[0067] For example, using water-soluble compounds of each element (metal compounds), a raw material aqueous solution is prepared so that the molar ratio of each element is equal to the molar ratio of each element contained in the particles of the target lithium nickel composite oxide. The prepared raw material aqueous solution, an alkali metal aqueous solution, and an ammonium ion donor are both fed into a reaction tank, and a neutralization crystallization reaction is carried out to obtain a nickel composite hydroxide.

[0068] The raw materials of each element may be dissolved in water simultaneously to produce a mixed aqueous solution as the raw material aqueous solution. Alternatively, individual aqueous solutions may be prepared for each raw material of each element to produce individual raw material aqueous solutions. If there are inconveniences in preparing the raw material aqueous solution as a mixed aqueous solution, it is preferable to adjust individual raw material aqueous solutions for each raw material. For example, when the liquid properties of the aqueous solutions of each raw material are divided into acidic and basic, it is preferable to adjust individual raw material aqueous solutions for each raw material.

[0069] The metal compound used as the raw material of each element only needs to be water-soluble, and sulfates, chlorides, nitrates, etc. can be used. From the perspective of cost, inexpensive sulfates are preferred. If a suitable water-soluble metal compound cannot be found for element M or the like, it may be added in the subsequent oxidation roasting step (S2) or mixing step (S10) without adding it to the mixed aqueous solution of the raw materials.

[0070] The aqueous alkali metal solution is not particularly limited, but one or more selected from the group consisting of sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, potassium hydroxide, and potassium carbonate can be preferably used.

[0071] The ammonium ion donor is not particularly limited, but one or more selected from aqueous ammonia, aqueous ammonium carbonate solution, aqueous ammonium chloride solution, and aqueous ammonium sulfate solution can be preferably used.

[0072] The shape of the reaction tank is not particularly limited, but a cylindrical container equipped with a baffle plate inside and equipped with a stirrer and a temperature controller is preferred. The stirrer preferably includes a motor, a shaft, and stirring blades. The temperature controller is preferably of a type that circulates a heat medium outside the cylindrical container to heat or cool the cylindrical container.

[0073] In the neutralization crystallization reaction of the raw material aqueous solution, the aqueous alkali metal solution, and the ammonium ion donor in the reaction tank, it is preferable to maintain the pH and ammonia concentration at constant values.

[0074] The pH of the aqueous solution in the reaction tank is preferably adjusted to be 11.0 or more and 12.2 or less based on a liquid temperature of 25°C. For example, when preparing nickel composite hydroxide, impurities caused by anions constituting the metal compound contained in the used raw material aqueous solution may be mixed into the nickel composite hydroxide. However, by setting the pH value of the initial aqueous solution (inside the reaction tank) to 11.0 or more, it is possible to suppress the mixing of impurities caused by anions. Also, by setting the pH of the initial aqueous solution to 12.2 or less, it is possible to suppress the micronization of the obtained nickel composite hydroxide and obtain a composite hydroxide with a particle size suitable for the charge-discharge reaction.

[0075] 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. When the ammonia concentration is 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, so the sphericity of the particles of the obtained nickel composite hydroxide increases. On the other hand, when the ammonia concentration is 20 g / L or less, the solubility of nickel forming the ammonium complex is suppressed from rising excessively, and the molar ratio of the obtained nickel composite hydroxide can be more surely set to the target molar ratio. In addition, excessive consumption of ammonia can be suppressed, which is industrially preferable.

[0076] The atmosphere in the reaction tank is preferably a non-oxidizing atmosphere, for example, an atmosphere with an oxygen concentration of 1% by volume or less. When the atmosphere in the reaction tank is a non-oxidizing atmosphere, oxidation of raw material compounds and the like can be suppressed. For example, precipitation of oxidized cobalt or manganese as fine particles can be prevented.

[0077] The temperature in the reaction tank in the crystallization step (S1) is preferably maintained at 40°C or more and 60°C or less, more preferably 45°C or more, and still more preferably 55°C or less.

[0078] Since the temperature of the reaction tank rises due to the reaction heat and the Joule heat of stirring, by setting the temperature in the reaction tank to 40°C or more, unnecessary energy consumption for cooling is not incurred. Also, by setting the temperature in the reaction tank to 60°C or less, evaporation of ammonia from the initial aqueous solution and the reaction aqueous solution can be suppressed, and it becomes easier to maintain the target ammonia concentration.

[0079] The particles (powder) of the lithium nickel composite oxide preferably have a narrow spread in particle size distribution and uniform particle diameters. In order to produce such particles, it is necessary to obtain particles with uniform particle diameters in the nickel composite hydroxide that is the precursor thereof. Specific examples of methods for obtaining such particles include Patent Document 3.

[0080] (Oxidative roasting step: S2) After the precursor crystallization step (S1), an oxidation roasting step (S2) may be performed. In the oxidation roasting step (S2), the nickel composite hydroxide obtained in the precursor crystallization step (S1) is oxidation roasted to obtain a nickel composite oxide. In the oxidation roasting 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.

[0081] The roasting conditions in the oxidation roasting step (S2) are not particularly limited. For example, it is preferably roasted at a temperature of 500°C or higher and 700°C or lower for 1 hour or more and 12 hours or less in an oxygen-containing atmosphere or an air atmosphere. When the roasting temperature is 500°C or higher, the nickel composite hydroxide can be completely converted into a nickel composite oxide. Also, by setting the roasting temperature to 700°C or lower, it is possible to suppress the specific surface area of the nickel composite oxide from becoming excessively small, which is preferable.

[0082] By setting the roasting time to 1 hour or more, the temperature inside the firing container can be made uniform, and the reaction can proceed uniformly, which is preferable. Also, even if roasting is performed for a time longer than 12 hours, no significant change is observed in the obtained nickel composite oxide. Therefore, from the viewpoint of energy efficiency, the roasting time is preferably 12 hours or less.

[0083] The oxygen concentration in the oxygen-containing atmosphere during roasting is preferably equal to or higher than the oxygen concentration in air, that is, the oxygen concentration is 20% by volume or more. Since an oxygen atmosphere can also be used, the upper limit value of the oxygen concentration in the oxygen-containing atmosphere can be 100% by volume.

[0084] In addition, for example, when the compound containing element M cannot be coprecipitated in the crystallization step (S1), for example, for the nickel composite hydroxide to be subjected to the oxidation roasting step S2, a compound containing element M may be added so as to have the same molar ratio as the target substance and then fired. The compound containing element M to be added is not particularly limited. For example, an oxide, a hydroxide, a carbonate, or a mixture thereof can be used.

[0085] Also, after the completion of the oxidative roasting step (S2), if slight sintering is observed in the obtained nickel composite oxide, a crushing treatment may be applied. In the oxidative roasting step (S2), at least a part of the nickel composite hydroxide may be converted into the nickel composite oxide, and it is not necessary to convert all of the nickel composite hydroxide into the oxide.

[0086] (Mixing step: S10) The mixing step (S10) is a step of mixing a nickel composite compound, a niobium compound, and a lithium compound to obtain a lithium mixture.

[0087] In the manufacturing method according to the present embodiment, in the mixing step (S10), niobium is added in a solid phase by mixing the niobium compound. The solid-phase addition of niobium is an addition method with a low environmental load and excellent productivity because it does not require a chemical solution or the like as compared with the method of coprecipitating or coating niobium in a conventionally known crystallization step.

[0088] The nickel composite compound is preferably at least one of a nickel composite hydroxide and a nickel composite oxide, and more preferably a nickel composite oxide. Further, the nickel composite compound is preferably obtained by a method including the above crystallization step (S1) and / or oxidative roasting step (S2).

[0089] As the niobium compound, for example, niobic acid, niobium oxide, niobium nitrate, niobium pentachloride, etc. can be used. Among these, niobium hydroxide or niobium oxide is preferable from the viewpoints of easy availability and avoiding contamination of impurities into the fired lithium nickel composite oxide.

[0090] When adding niobium in the solid phase, the reactivity may change depending on the particle size of the niobium compound to be added. In the cumulative volume distribution curve of the particle size distribution of the niobium compound, the particle size (D90) corresponding to a cumulative volume ratio of 90% is preferably 0.1 μm or more and 20 μm or less, more preferably 0.1 μm or more and 10 μm or less, and even more 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 that it becomes very difficult to handle the powder. When the D90 of the niobium compound is greater than 20 μm, the reactivity during firing may decrease and the diffusion of niobium into the particles of the lithium nickel composite oxide may be insufficient, and it may not be possible to ensure thermal stability. In addition, when the D90 of niobium is too large, there is a possibility that the formation of the coating layer 2 becomes non-uniform. The particle size of the niobium compound can be appropriately adjusted within the above particle size range so that a positive electrode active material having desired characteristics can be obtained.

[0091] The D90 of the niobium compound can be adjusted to the above range by pulverizing the raw material niobium compound using a pulverizer such as a ball mill, a planetary ball mill, a jet mill, a bead mill, or a pin mill. Further, if necessary, it may be classified by a dry classifier or a sieve. The D90 of the niobium compound can be measured by the laser scattering diffraction method.

[0092] The niobium compound is mixed in an amount having the target niobium content with respect to the total number of atoms of Ni and element M contained in the nickel composite compound. Since the niobium content does not change before and after the firing step, a niobium compound corresponding to the niobium addition amount of the positive electrode active material is added.

[0093] The lithium compound is not particularly limited, and for example, lithium hydroxide, lithium nitrate, or lithium carbonate, or a mixture thereof can be used. From the viewpoint of low melting point and high reactivity, it is preferable to use lithium hydroxide as the lithium compound.

[0094] The lithium compound may be mixed, for example, in an amount such that the lithium content is 95 atomic % or more and 115 atomic % or less, 98 atomic % or more and 115 atomic % or less, or 98 atomic % or more and 110 atomic % or less, relative to the total of Ni, element M, and Nb (Me).

[0095] (Firing step: S20) The firing step (S20) is a step of firing the obtained lithium mixture to obtain particles 1 of a lithium nickel composite oxide. The firing conditions are not particularly limited, but for example, it is preferably fired at a temperature of 700°C or higher and 800°C or lower for 1 hour or more and 24 hours or less in an oxygen-containing atmosphere. Further, after firing, it may be cooled to room temperature to obtain particles 1 of a lithium nickel composite oxide.

[0096] When the firing temperature is 700°C or higher, the crystal structure of particles 1 of the lithium nickel composite oxide can be sufficiently grown. Further, when the firing temperature is 800°C or lower, the mixing of Ni atoms into the Li sites in particles 1 of the obtained lithium nickel composite oxide can be suppressed.

[0097] The firing time is preferably 1 hour or more because the temperature inside the firing container can be made uniform and the reaction can proceed uniformly. Further, even if firing is performed for a time longer than 24 hours, no significant change is observed in the obtained lithium nickel composite oxide. Therefore, from the viewpoint of energy efficiency, the firing time is preferably 24 hours or less, and may be 12 hours or less, 10 hours or less, or 6 hours or less.

[0098] Further, 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, which is preferable. Since an oxygen atmosphere can also be used, the upper limit value of the oxygen concentration in the oxygen-containing atmosphere can be 100% by volume.

[0099] In addition, if slight sintering is observed in the particles 1 of the obtained lithium nickel composite oxide after the firing step (S20), a crushing treatment may be applied.

[0100] (Coating step: S30) The coating step (S30) is a step of forming a coating layer 2 by adhering a coating solution to the surface of the obtained particles 1 of the lithium nickel composite oxide.

[0101] The formation of the coating layer 2 is performed, for example, by mixing the particles 1 of the lithium nickel composite oxide and the coating solution, followed by drying to form the coating layer 2 on the surface of the particles 1 of the lithium nickel composite oxide. Further, as will be described later, after coating, a heat treatment step (S40) may optionally be performed in an oxygen-containing atmosphere. Hereinafter, an example of the coating step (S30) will be described.

[0102] First, a predetermined amount of the coating solution is prepared (coating agent preparation step). The coating agent can be prepared according to the content of the constituent elements (excluding Li and O) of the coating layer 2 per specific surface area (m 2 / g) of the particles 1 of the lithium nickel composite oxide obtained in the firing step (S20).

[0103] The coating solution 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 solution can be prepared by dissolving a raw material compound containing the constituent elements (excluding Li and O) of the target coating layer 2 in a solvent.

[0104] Examples of the raw material compound include one or more selected from the group consisting of alkoxides and chelates using complexes having a carbonyl group, a peroxide group, etc.

[0105] From the perspective of uniform coating, the coating liquid only needs to be in a liquid state when it is attached to the surface of the particles 1 of the lithium nickel composite oxide. For example, it may be prepared by dissolving a compound containing the constituent elements of the coating layer 2 in a solvent and may be in a liquid state at room temperature, or may be a compound containing the constituent elements of the coating layer 2 with a low melting point that dissolves by heat treatment at a low temperature.

[0106] Note that the coating liquid may or may not contain Li. When the coating liquid does not contain Li, in the coating step (S30) and / or the heat treatment step (S40), Li present in the particles 1 of the lithium nickel composite oxide reacts with the compound containing the above-mentioned constituent elements in the coating liquid to form the coating layer 2.

[0107] Next, the coating liquid is attached to the surface of the particles 1 of the lithium nickel composite oxide. The attachment of the coating liquid may be performed, for example, by mixing the particles 1 of the lithium nickel composite oxide and the coating liquid (mixture preparation step). A general mixer can be used for mixing. Also, drying may be performed after mixing (drying step).

[0108] Also, from the perspective of forming a more uniform coating layer 2 with a specific thickness, it is preferable to proceed with the mixture preparation step and the drying step in parallel, and it is preferable to use a tumbling fluidized coating device.

[0109] Since the coating liquid shrinks due to drying, if the mixture preparation step and the drying step are each passed through only once, gaps will form in the formed coating layer 2, and the function of protecting the contact between the particles 1 of the lithium nickel composite oxide and the solid electrolyte may not be fully achieved. However, when using a tumbling fluidized coating device, the coating liquid is sprayed onto the particles 1 of the lithium nickel composite oxide flowing by the heated air flow in the device, so the mixture preparation step and the drying step are repeated in parallel, and a uniform coating layer without gaps can be obtained, which is preferable.

[0110] In the drying step, it is preferable to perform drying at a temperature sufficient to sufficiently remove the solvent of the coating agent. For example, when using a tumbling fluidized coating apparatus, the air supply temperature may be set to 80°C or higher and lower than 300°C. Further, after the coating treatment, additional drying may be performed using a stationary dryer separately.

[0111] The atmosphere in the drying step is not particularly limited, but in order to prevent the particles 1 of the lithium nickel composite oxide from reacting with moisture in the atmosphere, an inert atmosphere such as air, nitrogen, and argon gas supplied from a compressor equipped with a dryer is preferable.

[0112] (Heat treatment step: S40) Furthermore, if necessary, after the coating step (S30), a heat treatment step (S40) may be provided in which the particles 1 of the lithium nickel composite oxide having the coating layer 2 formed on the surface are heat-treated at 300°C or higher. By the heat treatment step (S40), the bond between the coating layer 2 and the particles 1 of the lithium nickel composite oxide can be made stronger.

[0113] The heat treatment conditions of the heat treatment step (S40) are not particularly limited, but it is preferable to perform heat treatment at a temperature of 300°C or higher and 600°C or lower for 1 hour or more and 5 hours or less in an oxygen-containing atmosphere. The oxygen-containing atmosphere may be, for example, an air atmosphere.

[0114] The oxygen concentration in the oxygen-containing atmosphere of the heat treatment step (S40) is preferably equal to or higher than the oxygen concentration in the air atmosphere, that is, the oxygen concentration is 20% by volume or higher. By setting the oxygen-containing atmosphere during heat treatment to be equal to or higher than the oxygen concentration in the air atmosphere, it is possible to further suppress the occurrence of oxygen defects inside the obtained positive electrode active material 10. The oxygen-containing atmosphere may be an oxygen atmosphere, and the upper limit value of the oxygen concentration in the oxygen-containing atmosphere is 100% by volume.

[0115] When the heat treatment temperature is 300°C or higher, it is possible to further suppress the remaining of impurities contained in the coating liquid inside the positive electrode active material 10. Further, when the heat treatment temperature is 600°C or lower, it is possible to suppress the excessive diffusion of the components of the coating layer 2 and maintain the form of the coating layer 2.

[0116] When the heat treatment time is 1 hour or longer, it is possible to further suppress the remaining of impurities contained in the coating liquid inside the positive electrode active material 10. Further, even when the heat treatment time is longer than 5 hours, no significant 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.

[0117] After the heat treatment step (S40), it is cooled to room temperature, and a positive electrode active material having lithium nickel composite oxide particles 1 as the final product and a coating layer 2 on the surface thereof can be obtained.

[0118] Note that the heat treatment step (S40) may not be performed. That is, only up to the coating step (S30) may be performed to produce the positive electrode active material 10. This is because even when the heat treatment step (S40) is not performed, a coating layer can be formed uniformly and firmly on the surface of the lithium nickel composite oxide particles. Even when the heat treatment step is not performed, it is preferable to perform drying as necessary to reduce and remove the solvent of the coating agent, moisture, etc.

[0119] When slight sintering is observed in the positive electrode active material 10 obtained after the coating step (S30) and / or the heat treatment step (S40), further pulverization treatment may be performed.

[0120] (3) All-solid-state lithium-ion secondary battery The all-solid-state lithium-ion secondary battery (hereinafter, also referred to as "all-solid-state battery") according to the present embodiment includes a positive electrode, a negative electrode, and a solid electrolyte, and contains the above positive electrode active material in the positive electrode. Hereinafter, each component of the all-solid-state battery according to the present embodiment will be described.

[0121] Note that the embodiments described below are merely examples, and all-solid-state batteries can be implemented in various modified forms based on the knowledge of those skilled in the art, including the following embodiments. Also, the applications of all-solid-state batteries are not particularly limited.

[0122] (Positive electrode) The positive electrode can be formed by molding a positive electrode mixture. Note that the positive electrode is appropriately processed according to the battery to be used. For example, pressure compression treatment such as pressing can be performed to increase the electrode density.

[0123] The above-mentioned positive electrode mixture can be formed by mixing the aforementioned positive electrode active material in powder form and a solid electrolyte.

[0124] The solid electrolyte is added to impart appropriate ionic conductivity to the electrode. The material of the solid electrolyte is not particularly limited. For example, sulfide-based solid electrolytes such as Li3PS4, Li7P3S 11 , Li 10 GeP2S 12 and the like, oxide-based solid electrolytes such as Li7La3Zr2O 12 , Li 0.34 La 0.51 TiO 2.94 and the like, or polymer-based electrolytes such as PEO can be used.

[0125] Note that a binder and a conductive aid can also be added to the positive electrode mixture.

[0126] The binder serves to connect and hold the positive electrode active material. The binder used for such a positive electrode mixture is not particularly limited, and for example, one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose-based resin, polyacrylic acid, etc. can be used.

[0127] The conductive material is added 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, or carbon black-based materials such as acetylene black and Ketjenblack (registered trademark) can be used.

[0128] Also, 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 in the positive electrode mixture can be 50 parts by mass or more and 90 parts by mass or less, and the content of the solid electrolyte can be 10 parts by mass or more and 50 parts by mass or less.

[0129] However, the method for producing the positive electrode is not limited to the above-exemplified ones, and other methods may also be used.

[0130] (Negative electrode) The negative electrode can be formed by molding the negative electrode mixture. Although the components constituting the negative electrode mixture and its formulation are different, the negative electrode is formed by substantially the same method as the above-described positive electrode, and various treatments are performed as necessary in the same manner as the positive electrode.

[0131] The negative electrode mixture can be prepared by mixing a negative electrode active material and a solid electrolyte. As the negative electrode active material, for example, an occluding material capable of occluding and desorbing lithium ions can be employed.

[0132] The occluding material is not particularly limited, and for example, one or more selected from organic compound fired bodies such as natural graphite, artificial graphite, and phenolic resin, and powdery substances of carbon materials such as coke can be used. When such an occluding material is employed as the negative electrode active material, a sulfide electrolyte such as Li3PS4 can be used as the solid electrolyte, similar to the positive electrode.

[0133] Also, the negative electrode can be a sheet-like member made of a material containing a metal that alloys with lithium, such as metallic lithium or indium.

[0134] (Solid electrolyte) The solid electrolyte is Li+ It is a solid with ionic conductivity. As the solid electrolyte, one selected from sulfides, oxides, polymers, etc. can be used alone, or two or more thereof can be mixed and used.

[0135] The sulfide-based solid electrolyte is not particularly limited, and any material that contains sulfur (S) and has lithium ion conductivity and electron insulation can be used. Examples of the sulfide-based solid electrolyte include 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-P2S5, etc.

[0136] The oxide-based solid electrolyte is not particularly limited, and any material that contains oxygen (O) and has lithium ion conductivity and electron insulation can be used.

[0137] Examples of the oxide-based solid electrolyte include 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, etc.

[0138] In addition, as the inorganic solid electrolyte, those other than the above may be used. For example, Li3N, LiI, Li3N-LiI-LiOH, etc. may be used.

[0139] The polymer solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity. For example, polyethylene oxide, polypropylene oxide, copolymers thereof, etc. can be used. Further, the organic solid electrolyte may contain a supporting salt (lithium salt). When using a solid electrolyte, in order to ensure contact between the electrolyte and the positive electrode active material, the solid electrolyte may also be mixed into the positive electrode material.

[0140] (Shape and Configuration of All-Solid-State Battery) Next, an example of the arrangement and configuration of the members of the all-solid-state battery according to this embodiment will be described. The all-solid-state battery composed of the above positive electrode, negative electrode, and solid electrolyte can be made into various shapes such as coin shape and laminated shape. In any case of the shape, the positive electrode and the negative electrode can be laminated via the solid electrolyte. Then, the positive electrode current collector and the positive electrode terminal communicating with the outside, and between the negative electrode current collector and the negative electrode terminal communicating with the outside are connected using a current collecting lead or the like, and sealed in a battery case to form an all-solid-state battery.

[0141] (Characteristics of All-Solid-State Battery) The all-solid-state battery according to an embodiment of the present invention using the above positive electrode active material exhibits high capacity. Specifically, using the positive electrode active material of this embodiment as the positive electrode, a test battery shown in FIG. 4 is configured, and the current density is 0.2 mA / cm 2 When charging up to a cut-off voltage of 4.3 V (vs. Li) and discharging to a cut-off voltage of 2.5 V (vs. Li) after a 1-hour rest, the initial discharge capacity, which is the discharge capacity in this case, is preferably 130 mAh / g or more.

Examples

[0142] Hereinafter, the present invention will be specifically described using examples and comparative examples.

[0143] [Example 1] 1. Production of Lithium Nickel Composite Oxide The lithium nickel composite oxide was produced by the following steps.

[0144] (a) Crystallization step 10 L of pure water was placed in a reaction tank with an internal volume of 60 L and stirred while maintaining the temperature inside the tank at 50°C. At this time, the inside of the reaction tank was set to a nitrogen atmosphere with an oxygen concentration of 1% by volume or less. An appropriate amount of 25% by mass aqueous sodium hydroxide solution and 25% by mass aqueous ammonia solution were added to this reaction tank to prepare an initial aqueous solution such that the pH value based on a liquid temperature of 25°C was 12.8 and the ammonia concentration in the solution inside the reaction tank was 15 g / L.

[0145] At the same time, nickel sulfate and cobalt sulfate were dissolved in pure water so that the molar ratio of nickel to cobalt was Ni:Co = 0.84:0.16, and 25 L of a 2.0 mol / L nickel-cobalt mixed aqueous solution was prepared. Also, 5 L of a 0.37 mol / L aluminum sulfate aqueous solution was prepared.

[0146] 66 mL of the nickel-cobalt mixed aqueous solution was dropped into the initial aqueous solution in the reaction tank at a rate of 109 mL / min to obtain a reaction aqueous solution. At this time, 25% by mass aqueous ammonia solution and 25% by mass aqueous sodium hydroxide solution were also dropped into the initial aqueous solution at a constant rate, and the pH value based on a liquid temperature of 25°C of the reaction aqueous solution was controlled to be maintained at 12.8.

[0147] Subsequently, sulfuric acid was dropped into the reaction tank to adjust the pH of the reaction aqueous solution to 11.5. This operation was intended to lower the pH and thereby reduce the rate at which the composite hydroxide of Ni, Co, and Al precipitates from the liquid phase to the solid phase in the subsequent precursor crystallization step, improving the uniformity of the resulting particle size distribution and the sphericity of the particles.

[0148] After pH control, 26.2 L of an aqueous nickel-cobalt mixed solution was dropped into the reaction aqueous solution in the reaction tank at a rate of 109.2 mL / min, and at the same time, 5.9 L of an aqueous aluminum sulfate solution was dropped at a rate of 24.8 mL / min. At this time, 25% by mass ammonia water and 25% by mass sodium hydroxide aqueous solution were also dropped into the initial aqueous solution at a constant rate, and the pH value of the reaction aqueous solution was controlled to be 11.5 based on a liquid temperature of 25 °C, and the ammonia concentration was maintained at 15 g / L.

[0149] After dropping all of the aqueous nickel-cobalt mixed solution and the aqueous aluminum sulfate solution, the pH of the reaction aqueous solution in the reaction tank was raised until it reached 13.0 based on a liquid temperature of 25 °C. This operation is intended to precipitate nickel ions complexed with ammonia and dissolved in the liquid phase onto the hydroxide to obtain the target chemical composition.

[0150] Thereafter, the reaction aqueous solution was subjected to solid-liquid separation using a Buchner funnel, a filtration tank, and a vacuum pump vacuum filter. Further, the operation of dispersing the obtained solid phase in 20 L of pure water at 40 °C and performing solid-liquid separation was repeated twice to remove water-soluble impurities such as sodium sulfate from the nickel composite hydroxide. After the solid-liquid separation of the washed cake-like solid phase, it was dried in an air atmosphere at 120 °C for 24 hours in a stationary dryer, and then sieved through a sieve with a mesh size of 100 μm to obtain a powdery nickel composite hydroxide.

[0151] (b) Oxidative roasting process Using an atmosphere firing furnace (manufactured by Siliconit Co., Ltd., BM-50100M), the prepared composite hydroxide was fired at 600 °C for 2 hours in an air atmosphere with an oxygen concentration of 20% by volume, and then cooled to room temperature to obtain a nickel composite oxide.

[0152] (c) Mixing process To a nickel composite oxide, niobic acid (Nb2O3·xH2O) powder manufactured by Mitsuwa Chemical Co., Ltd. was added such that the amount of substance of Nb was 0.1% with respect to the total amount of substance of Ni, Co, and Al contained in this nickel composite oxide. Lithium hydroxide monohydrate was weighed out such that the amount of substance of Li was 103% with respect to the total amount of substance of Ni, Co, Al, and Nb, and they were mixed using a Turbler shaker mixer (manufactured by Dalton Co., Ltd., T2F) to obtain a lithium mixture.

[0153] (d) Firing process Using an atmospheric firing furnace (manufactured by Siliconit Co., Ltd., BM-50100M), the obtained lithium mixture was fired at 750 °C for 5 hours in an oxygen-containing atmosphere with an oxygen concentration of 90% by volume or more, and then cooled to room temperature. Thereby, particles of lithium nickel composite oxide were obtained.

[0154] 2. Evaluation of particles of lithium nickel composite oxide The following evaluations were performed on the obtained lithium nickel composite oxide.

[0155] (a) Composition By analysis using an ICP emission spectrometer (manufactured by VARIAN, 725ES), it was confirmed that the lithium nickel composite oxide had a molar ratio of Li, Ni, Co, Al, and Nb of Li:Ni:Co:Al:Nb = 1.04:0.815:0.150:0.034:0.001.

[0156] (b) Crystal structure When the crystal structure of the particles of lithium nickel composite oxide was measured using XRD (manufactured by PANALYTICAL, X‘Pert, PROMRD), it was confirmed that the diffraction pattern had a layered rock salt-type crystal structure in which peaks attributed to the R-3m structure were detected. Also, the half-width of the peak attributed to the (003) plane in the diffraction pattern was measured, and when the crystallite size was calculated using the Scherrer method, it was confirmed that it was 123.4 nm.

[0157] (c) Measurement of eluted lithium ion amount The amount of eluted lithium ions in the lithium nickel composite oxide was determined 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. Neutralization titration was carried out with 1 mol / L hydrochloric acid while stirring, and the amount of 1 mol / L hydrochloric acid required up to the inflection point near pH 4 of the obtained titration curve was converted as the Li amount due to the eluted lithium ions. As a result, the amount of eluted lithium ions in the lithium nickel composite oxide was 0.31 wt%.

[0158] (d) Specific surface area The BET specific surface area of the lithium nickel composite oxide was measured using a fully automatic BET specific surface area measuring device (manufactured by Mountech Co., Ltd., Macsorb), and it was confirmed to be 0.49 m 2 / g.

[0159] (e) Particle size distribution The particle size distribution of the lithium nickel composite oxide was measured using a laser diffraction scattering type particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., Microtrac HRA). From the results, it was confirmed that the volume-based average particle size D50 was 5.4 μm, and the variation index ((D90 - D10) / MV) calculated from D10, D90, and MV was 0.44.

[0160] 3. Coating of the lithium nickel composite oxide The following coating process was carried out on the obtained lithium nickel composite oxide. A solution obtained by adding 30 ml of isopropyl alcohol (IPA) and 1.8 g of titanium tetrabutoxide (Ti-BuOH) and stirring was added dropwise while heating and stirring at 60 °C to a solution obtained by adding 20 ml of IPA and 0.9 g of acetylacetone. This is because a high concentration of acetylacetone is used and the Ti solution is not added directly. Then, a solution obtained by adding 0.54 g of pure water to 10 ml of IPA was added to the aforementioned cooled solution. Finally, 65 ml of IPA was added to the obtained solution to prepare a coating solution.

[0161] Using the above coating solution, a coating treatment was performed on 500 g of lithium nickel composite oxide using a rolling fluid coating apparatus (MP-01, Paulech).

[0162] 500 g of lithium nickel composite oxide was fluidized in the chamber with air at a flow rate of 0.3 m 3 / h heated to 120°C, and the coating solution was sprayed onto this lithium nickel composite oxide at a rate of 1.7 ml / min.

[0163] After spraying the entire amount of the coating solution, the lithium nickel composite oxide was recovered from the chamber and heat-treated at 400°C for 10 hours under oxygen flow using an atmospheric firing furnace (manufactured by Siliconit Co., Ltd., BM-50100M). Then, it was cooled to room temperature to obtain particles (cathode active material) of lithium nickel composite oxide having a coating layer (containing Li and Ti).

[0164] 4. Evaluation of Particles of Lithium Nickel Composite Oxide with Coating Layer (a) Composition Analysis using an ICP emission spectrometer (725ES manufactured by Varian) 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 as confirmed.

[0165] (b) Thickness of Coating Layer As a result of observing the coated lithium nickel composite oxide thinned with a cryo ion slicer (JEOL, IB-09060CIS) using a TEM (JEOL, JEM-ARM200F), it was confirmed that the thickness of the coating layer was 11 nm.

[0166] 5. Fabrication of All-Solid-State Secondary Battery For the evaluation of the capacity of the obtained cathode active material, a battery with the structure shown in Figure 4 (hereinafter referred to as the "test battery") was used.

[0167] (Configuration of Test Battery) As shown in Fig. 4, the test battery SBA includes a case having a negative electrode can NC and a positive electrode can PC, and a pressed powder cell C accommodated in the case.

[0168] The case has a hollow negative electrode can NC with one end opened and a positive electrode can PC disposed at the opening of the negative electrode can NC. Also, a space for accommodating the pressed powder cell C is formed between the positive electrode can PC and the negative electrode can NC. The positive electrode can PC is fixed to the negative electrode can NC, for example, with a butterfly screw SW. Further, the negative electrode can NC has a terminal for the negative electrode, and the positive electrode can PC has a terminal for the positive electrode. Also, the case has an insulating sleeve ISV. The insulating sleeve ISV is fixed so as to maintain a non-contact state between the negative electrode can NC and the positive electrode can PC.

[0169] A pressure screw PSW is provided at the closed end of the negative electrode can NC. After fixing the positive electrode can PC to the negative electrode can NC, the pressure screw PSW is tightened toward the accommodation space of the pressed powder cell C to hold the pressed powder cell C in a pressurized state through the hemispherical washer W. Also, a screwed plug P is provided at the end of the negative electrode can NC where the pressure screw PSW is present. O-rings OL are provided between the negative electrode can NC and the positive electrode can PC, and between the negative electrode can NC and the plug P to seal the gap between the negative electrode can NC and the positive electrode can PC and maintain the airtightness inside the case.

[0170] The pressed powder cell C is a pellet in which a positive electrode layer PL, a solid electrolyte layer SEL, and a negative electrode layer NL are laminated in this order. The positive electrode layer PL contacts the inner surface of the positive electrode can PC through the lower current collector LCC. The negative electrode layer NL contacts the inner surface of the negative electrode can NC through the upper current collector UCC, the hemispherical washer W, and the pressure screw PSW. The lower current collector LCC, the pressed powder cell C, and the upper current collector UCC are protected by a sleeve SV so that the positive electrode layer PL and the negative electrode layer NL do not contact electrically.

[0171] (Fabrication of the evaluation battery) The test battery SBA was fabricated as follows

[0172] First, 80 mg of the synthesized solid electrolyte was pressed at 25 MPa using a pellet former to obtain a solid electrolyte pellet with a diameter of 10 mm. Next, 70 mg of the positive electrode active material and 30 mg of the solid electrolyte were mixed in a mortar. 15 mg of the mixture of the solid electrolyte pellet and the positive electrode active material + solid electrolyte was set in the pellet former and pressed at 360 MPa to form a positive electrode layer on the solid electrolyte pellet. In order from the bottom, a lower current collector LCC, a pellet with the positive electrode layer PL arranged downward, an indium (In) foil (negative electrode layer NL), and an upper current collector UCC were laminated in this order and pressed at 9 kN to construct an electrode (compressed powder cell C). The electrode (compressed powder cell C) was enclosed in a case, and the pressure screw was tightened with a torque of 6 to 7 N·m. The test battery SBA was fabricated in a glove box with an Ar atmosphere where the dew point was controlled at -80°C.

[0173] 6. Evaluation of All-Solid-State Secondary Battery The charge-discharge capacity indicating the performance of the fabricated test battery was evaluated as follows.

[0174] (a) Initial discharge capacity The initial discharge capacity was measured by fabricating a test battery using indium foil as the negative electrode, leaving it standing for about 24 hours after fabrication, charging the current density with respect to the positive electrode to 0.2 mA / cm 2 until the cut-off voltage of 3.7 V (vs. Li-In), resting for 1 hour, and then discharging until the cut-off voltage of 1.9 V (vs. Li-In). The measured result was 134 mAh / g.

[0175] [Example 2] 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 step of Example 1 was 0.8%. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0176] [Example 3] 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 step of Example 1 was changed to 1.2%. The production conditions are shown in Table 1, and the results are shown in Table 2.

[0177] [Example 4] 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 step of Example 1 was changed to 3%. The production conditions are shown in Table 1, and the results are shown in Table 2.

[0178] [Example 5] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 2, except that the firing time in the lithium nickel composite oxide synthesis step of Example 2 was changed to 12 h. The production conditions are shown in Table 1, and the results are shown in Table 2.

[0179] [Example 6] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 3, except that the firing time in the lithium nickel composite oxide synthesis step of Example 3 was changed to 12 h. The production conditions are shown in Table 1, and the results are shown in Table 2.

[0180] [Example 7] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 2, except that lithium niobate was coated in the coating step on the lithium nickel composite oxide obtained in Example 2 and heat treatment was performed under the following conditions. The production conditions are shown in Table 1, and the results are shown in Table 2.

[0181] After spraying all of the coating solution, 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 (manufactured by Siliconit Co., Ltd., BM-50100M). Then, it was cooled to room temperature to obtain particles (cathode active material) of a lithium nickel composite oxide having a coating layer (containing Li and Nb).

[0182] [Example 8] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 6, except that the ratio a of Li in the lithium nickel composite oxide synthesis step of Example 6 was set to 1.00. The production conditions are shown in Table 1, and the results are shown in Table 2.

[0183] [Example 9] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 6, except that the ratio a of Li in the lithium nickel composite oxide synthesis step of Example 6 was set to 1.09. The production conditions are shown in Table 1, and the results are shown in Table 2.

[0184] [Example 10] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 6, except that the ratio (1 - x - y) of Ni and the ratio x of Co in the lithium nickel composite oxide synthesis step of Example 6 were set to 0.85 and 0.116, respectively. The production conditions are shown in Table 1, and the results are shown in Table 2. 1

[0185] [Example 11] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 6, except that the ratio (1 - x - y) of Ni and the ratio x of Co in the lithium nickel composite oxide synthesis step of Example 6 were set to 0.744 and 0.222, respectively. The production conditions are shown in Table 1, and the results are shown in Table 2. 1

[0186] [Comparative Example 1] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 1, except that Nb was not added in the lithium nickel composite oxide synthesis step of Example 1. The production conditions are shown in Table 1, and the results are shown in Table 2.

[0187] [Comparative Example 2] 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 step of Comparative Example 1 was set to 735°C. The production conditions are shown in Table 1, and the results are shown in Table 2.

[0188] [Comparative Example 3] ​​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 step of Example 1 was 5 atomic %. The production conditions are shown in Table 1, and the results are shown in Table 2.

[0189] [Comparative Example 4] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 2, except that the coating of the particles of the lithium nickel composite oxide of Example 2 was not performed. The production conditions are shown in Table 1, and the results are shown in Table 2.

[0190] [Comparative Example 5] A coated lithium nickel composite oxide was synthesized under the same conditions as in Example 6, except that the ratio a of Li in the lithium nickel composite oxide synthesis step of Example 6 was 1.18. The production conditions are shown in Table 1, and the results are shown in Table 2.

[0191]

Table 1

[0192]

Table 2

[0193] [Evaluation Results] In the positive electrode active material of the example, the discharge capacity in the all-solid-state battery was significantly improved as compared with the positive electrode active material of Comparative Example 1 that does not contain Nb. In particular, in Example 2 (Nb: 0.8 atomic %), the discharge capacity was significantly improved. Also, 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 size and specific surface area, and the battery characteristics (initial discharge capacity) were also comparable, indicating that a positive electrode active material having high battery characteristics can be obtained even with a firing time of 5 hours. Also, it was shown that Example 7 in which the coating layer contains Nb also has a high discharge capacity, similar to Examples 1 to 6 in which the coating layer contains Ti.

[0194] Also, in Example 8 where the proportion (a) of Li is 1.00 and Example 9 where the proportion (a) of Li is 1.09, it was shown that they have a high discharge capacity equivalent to that of Example 6 (a: 1.04). Also, from Example 6 (proportion of Ni: 0.806), Example 10 (proportion of Ni: 0.850) and Example 11 (proportion of Ni: 0.744) where the proportion (1 - x - y) of Ni is different, it is clear that the higher the proportion of Ni, the higher the discharge capacity.

[0195] On the other hand, in the positive electrode active material of Comparative Example 2 that does not contain Nb, similar to Comparative Example 1, even when the firing temperature (735 °C) was changed, no improvement in the discharge capacity was observed, and instead it decreased.

[0196] Also, in the positive electrode active material of Comparative Example 3 where the addition amount of Nb exceeds 3 atomic%, the discharge capacity in the all-solid-state battery decreased compared to Comparative Examples 1 and 2 that do not add Nb.

[0197] Also, in the positive electrode active material of Comparative Example 4 produced under the same conditions as Example 1 except that it does not have a coating layer, the discharge capacity in the all-solid-state battery was very low. This is presumably because there is no coating layer on the surface of the particles of the lithium nickel composite oxide, so the resistance increased at the interface between the positive electrode active material and the solid electrolyte. Also, in Comparative Example 5 where the proportion (a) of Li is too high (a: 1.18), the amount of eluted lithium was large and the discharge capacity decreased.

Industrial Applicability

[0198] According to the present invention, it is possible to provide a positive electrode active material suitably used for the positive electrode of an all-solid-state lithium-ion secondary battery that requires a high battery capacity, and a method for manufacturing the same.

[0199] Note that the technical scope of the present invention is not limited to the aspects described in the above embodiments and the like. One or more of the requirements described in the above embodiments and the like may be omitted. Further, the requirements described in the above embodiments and the like can be combined as appropriate. Also, to the extent permitted by law, the disclosures of all the documents cited in the above embodiments and the like are incorporated by reference to form part of the description herein. Also, to the extent permitted by law, the content of Japanese Patent Application No. 2020-129024 is incorporated by reference to form part of the description herein.

Explanation of Reference Numerals

[0200] 1…Particles 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…Insulating sleeve C…Pressed powder cell PL…Positive electrode layer NL…Negative electrode layer SEL…Solid electrolyte layer LCC…Lower current collector UCC…Upper current collector P…Plug PSW…Pressing screw W…Hemispherical washer OL…O-ring SV…Sleeve SW…Screw N…Nut

Claims

1. A positive electrode active material for an all-solid-state lithium-ion secondary battery, comprising particles of a lithium nickel composite oxide and a coating layer covering the surface of the particles, wherein the particles of the lithium nickel composite oxide have a crystal structure belonging to the space group R-3m, contain at least Li, Ni, element M and Nb, the molar ratio of each element is 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, wherein the element M is at least one selected from the group consisting of Co, Al, Mn, Zr, Si, Zn and Ti), the crystallite size calculated by the Scherrer method from the diffraction peak attributed to the (003) plane measured by XRD is 140 nm or less, the amount of eluted lithium ions determined by neutralization titration is 0.30% by mass or more and 1.00% by mass or less based on the total amount of the particles of the lithium nickel composite oxide, the coating layer is 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, a positive electrode active material for an all-solid-state lithium-ion secondary battery.

2. the particles of the lithium nickel composite oxide include secondary particles formed by aggregation of a plurality of primary particles, and have a porous structure having a plurality of void portions in the secondary particles where the primary particles do not exist, 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, a positive electrode active material for an all-solid-state lithium-ion secondary battery according to Claim 1.

3. At least a part of the niobium contained in the particles of the lithium nickel composite oxide segregates at the interface of the primary particles, a positive electrode active material for an all-solid-state lithium-ion secondary battery according to Claim 2.

4. The particles of the lithium nickel composite oxide have a particle size (D50) corresponding to an integrated volume ratio of 50% in the integrated volume distribution curve of the particle size distribution of 7 μm or less, a positive electrode active material for an all-solid-state lithium-ion secondary battery according to any one of Claims 1 to 3.

5. The average thickness of the coating layer is 2 nm or more and 15 nm or less, a positive electrode active material for an all-solid-state lithium-ion secondary battery according to any one of Claims 1 to 4.

6. A mixing step of mixing a nickel composite compound, a niobium compound and a lithium compound to obtain a mixture, a firing step of firing the mixture to obtain the particles of the lithium nickel composite oxide, A coating step of adhering 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 the surface of the particles of the lithium nickel composite oxide to form the coating layer; The method for producing a positive electrode active material for an all-solid-state lithium-ion secondary battery according to any one of claims 1 to 5.

7. The nickel composite compound includes a nickel composite oxide, The method for producing a positive electrode active material for an all-solid-state lithium-ion secondary battery according to claim 6, comprising an oxidation roasting step of obtaining the nickel composite oxide by oxidizing and roasting a nickel composite hydroxide adjusted by a crystallization reaction.

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

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