Positive-electrode active material for all-solid-state lithium ion secondary batteries, and all-solid-state lithium ion secondary battery

Abstract

A purpose of the present invention is to provide a positive-electrode active material having a high discharge capacity in all-solid-state lithium ion secondary batteries.　The positive-electrode active material for all-solid-state lithium ion secondary batteries comprises a lithium transition metal composite oxide composed of secondary particles each comprising a plurality of aggregated primary particles and a coating layer that covers the surfaces of the secondary particles, wherein the lithium transition metal composite oxide includes lithium and nickel and optionally contains cobalt and element M (element M being an additive element other than lithium, nickel, cobalt, and oxygen) and the coating layer includes a compound at least containing lithium and tungsten. The surfaces of the secondary particles have a degree of coverage with tungsten, P (%), determined through XPS analysis and a calculation with (equation 1), of 30-95%.　(Equation 1): P=(W / (W+Ni+Co+M))×100 (%)

Description

Positive electrode active material for all-solid-state lithium-ion secondary battery, and all-solid-state lithium-ion secondary battery

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

[0002] In recent years, with the widespread use of electric vehicles, there has been a strong demand for the development of small, lightweight secondary batteries with high energy density. One such secondary battery is the lithium-ion secondary battery. A lithium-ion secondary battery comprises a positive electrode, a negative electrode, and an electrolyte. The active materials used for the negative and positive electrodes are materials capable of desorbing and inserting lithium.

[0003] Currently, in general lithium-ion secondary batteries, the positive electrode active material is LiCoO ２ , LiNiO ２ , LiMn ２ O ４ The negative electrode active material is lithium metal, lithium alloy, metal oxide, carbon, or the like, and the electrolyte is LiClO in an organic solvent such as ethylene carbonate, dimethyl carbonate, or ethyl methyl carbonate. ４ , LiPF ６ An electrolyte solution in which a Li salt such as the above is dissolved as a supporting salt is used.

[0004] Among the components of the lithium-ion secondary battery, the electrolyte in particular is a factor that limits battery performance, such as high-speed charging, safety, and lifespan, due to its chemical properties such as heat resistance and potential window. Therefore, research and development is currently being actively conducted on all-solid-state lithium-ion secondary batteries (hereinafter simply referred to as "all-solid-state batteries") that improve battery performance by using a solid electrolyte instead of an electrolyte.

[0005] In the course of this research and development, for example, Patent Document 1 proposes that, among solid electrolytes, sulfide-based solid electrolytes have high lithium ion conductivity and are preferable for use in all-solid-state batteries. However, as disclosed in Non-Patent Document 1, when a sulfide-based solid electrolyte comes into contact with a positive electrode active material that is an oxide, a reaction occurs at the contact interface between the solid electrolyte and the positive electrode active material during charge and discharge, and a high-resistance layer is formed at the interface, hindering the operation of the battery.

[0006] For example, Patent Document 2 proposes providing a lithium ion conductive oxide coating layer on the surface of the positive electrode active material in order to suppress the formation of this high resistance layer.

[0007] JP 2014-056661 A International Publication No. 2007 / 004590

[0008] Narumi Ohta et al., “LiNbO3-coated LiCoO2 as cathode material for all solid-state lithium secondary batteries”, Electrochemistry Communications 9 (2007) 1486-1490

[0009] For example, in the example of Patent Document 2, among lithium ion conductive oxides, LiNbO ３ However, the charge-discharge capacity of the all-solid-state battery is still low compared to that of a lithium-ion secondary battery that uses an electrolytic solution as the electrolyte, and further increase in charge-discharge capacity is desired.

[0010] In view of the above problems, an object of the present invention is to provide a positive electrode active material having a coating layer for an all-solid-state lithium ion secondary battery, which has a higher discharge capacity.

[0011] In order to solve the above-mentioned problems, the present inventors have conducted extensive research into positive electrode active materials for all-solid-state batteries having a coating layer that suppresses interfacial reactions between the solid electrolyte and the positive electrode active material, and have found that the charge / discharge capacity of all-solid-state batteries can be increased by coating the surfaces of secondary particles of the positive electrode active material with a compound consisting of at least lithium and tungsten in a specific ratio.

[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, the positive electrode active material having a lithium transition metal composite oxide composed of secondary particles formed by aggregation of a plurality of primary particles, and a coating layer coating the surfaces of the secondary particles, wherein the lithium transition metal composite oxide contains lithium, nickel, and optionally cobalt, and an element M (wherein the element M is an additive element other than lithium, nickel, cobalt, and oxygen), the coating layer contains a compound containing at least lithium and tungsten, and the coverage P (%) of the secondary particle surfaces with tungsten, calculated by the following (Equation 1), is 30% or more and 95% or less.

[0013] P = (W / (W + Ni + Co + M)) × 100 (%) ... (Equation 1) W: Amount of substance of tungsten quantified by X-ray photoelectron spectroscopy (XPS analysis) Ni: Amount of substance of nickel quantified by X-ray photoelectron spectroscopy (XPS analysis) Co: Amount of substance of cobalt quantified by X-ray photoelectron spectroscopy (XPS analysis) M: Amount of substance of element M (excluding tungsten) quantified by X-ray photoelectron spectroscopy (XPS analysis)

[0014] The lithium transition metal composite oxide is preferably represented by the following formula (2).

[0015] Li ａ Ni １－ｘ－ｙ Co ｘ M ｙ O ２＋ｚ... (Formula 2) where M is one or more elements selected from Mg, Ca, Sr, Ba, Al, Ti, V, Cr, Mn, Fe, Cu, Zr, Nb, Mo, W, Ta, Si, P, and B, and satisfies 0.9≦a≦1.2, 0.01≦x≦0.5, 0.01≦y≦0.5, 0.02≦x+y<1.0, and −0.1≦z≦0.1.

[0016] In addition, it is preferable that the lithium transition metal composite oxide has a compound containing tungsten present between primary particles inside the secondary particles. It is also preferable that the coverage P is 60% or more and 95% or less. It is also preferable that the coverage P is 80% or more and 95% or less. It is also preferable that the lithium transition metal composite oxide has a volume average particle diameter Mv of 1 μm or more and 10 μm or less. It is also preferable that the content of tungsten contained in the positive electrode active material is 0.1 mass% or more and 6 mass% or less with respect to the total amount of the positive electrode active material. It is also preferable that the pore volume of the positive electrode active material is 0.001 cm or more. ３ / g or more 0.008cm ３ / g or less, and the average pore diameter of the positive electrode active material is preferably 1 nm or more and 10 nm or less.

[0017] In a second aspect of the present invention, there is provided an all-solid-state lithium-ion secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte, each containing the above-mentioned positive electrode active material for an all-solid-state lithium-ion secondary battery.

[0018] According to the present invention, it is possible to provide a positive electrode active material having a coating layer for an all-solid-state lithium ion secondary battery, which has a higher discharge capacity.

[0019] Fig. 1 is a schematic diagram showing an example of a positive electrode active material according to the present embodiment, and Fig. 2 is an explanatory diagram of a cross-sectional configuration of an evaluation battery used for battery evaluation.

[0020] An embodiment of the present invention will be described below with reference to the drawings. In the drawings, some components are emphasized or simplified to make each component easier to understand, and the actual structure, shape, scale, etc. may differ. Furthermore, the present invention is not limited to the following embodiment, and various modifications and substitutions can be made to the following embodiment without departing from the scope of the present invention.

[0021] 1. Cathode Active Material for All-Solid-State Lithium-Ion Secondary Battery One configuration example of the cathode active material for an all-solid-state lithium-ion secondary battery according to this embodiment (hereinafter also simply referred to as "cathode active material") will be described.

[0022] Fig. 1 is a diagram schematically illustrating an example of a positive electrode active material according to this embodiment. As shown in Fig. 1, the positive electrode active material 10 includes a lithium transition metal composite oxide 1 and a coating layer 2 that coats the surface of the lithium transition metal composite oxide 1. Each of the components will be described below.

[0023] (1) Lithium Transition Metal Composite Oxide The lithium transition metal composite oxide 1 is composed of secondary particles formed by aggregation of a plurality of primary particles. The lithium transition metal composite oxide 1 may contain lithium, a transition metal, and oxygen and may have a layered rock salt crystal structure.

[0024] (Composition) The lithium transition metal composite oxide 1 is a compound containing lithium, a transition metal, and oxygen, and preferably contains nickel as the transition metal, and more preferably contains nickel and cobalt. The lithium transition metal composite oxide 1 preferably has a composition represented by the following general formula (1):

[0025] General formula (1): Li ａ Ni １－ｘ－ｙ Co ｘ M ｙ O ２＋ｚ

[0026] In the general formula (1), M is one or more elements selected from Mg, Ca, Sr, Ba, Al, Ti, V, Cr, Mn, Fe, Cu, Zr, Nb, Mo, W, Ta, Si, P, and B, and satisfies the following conditions: 0.9≦a≦1.2, 0.01≦x≦0.5, 0.01≦y≦0.5, 0.02≦x+y<1, and −0.1≦z≦0.1.

[0027] In the general formula (1), the value of a, which indicates the lithium content, is 0.9 to 1.2, and may be 0.95 to 1.2, more preferably 1.0 to 1.1. When the value of a is within the above range, the output characteristics and capacity characteristics of a secondary battery using the positive electrode active material 10 can be improved. Specifically, by setting the value of a to 0.9 or more, the internal resistance of a secondary battery using the positive electrode active material 10 can be suppressed and the output characteristics can be improved. Furthermore, by setting the value of a to 1.2 or less, the initial discharge capacity of a secondary battery using the positive electrode active material 10 can be maintained high.

[0028] In the general formula (1), (1-x-y), which represents the nickel content, is greater than 0 and not greater than 0.98, and may be 0.3 or greater and 0.98 or less, or 0.5 or greater and 0.98 or less. The lower limit of the nickel content may be 0.6 or greater, 0.7 or greater, or 0.8 or greater. 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.

[0029] In the general formula (1), x, which represents the cobalt content, is 0.01 to 0.5, or may be 0.01 to 0.3, or may be 0.05 to 0.2. When the cobalt content is within the above range, the charge-discharge cycle characteristics and output characteristics can be improved.

[0030] In the general formula (1), the element M is one or more elements selected from Mg, Ca, Sr, Ba, Al, Ti, V, Cr, Mn, Fe, Cu, Zr, Nb, Mo, W, Ta, Si, P, and B. The element M preferably contains at least one element selected from Al and Mn, and preferably contains Al. The element M can be appropriately selected depending on the application and required performance of the secondary battery constructed using the positive electrode active material 10.

[0031] In the substance amount ratio, y, which indicates the content ratio of element M, is 0<y≦0.5, preferably 0<y≦0.3, and may be 0<y≦0.2. For example, when element M includes Al, the range of Al (y1) may be, for example, 0<y≦0.1, or 0<y≦0.05.

[0032] (Crystal Structure) The lithium transition metal composite oxide 1 preferably has a layered rock salt crystal structure. When the lithium transition metal composite oxide 1 has a layered rock salt crystal structure, it can have a high battery capacity in a secondary battery. The crystal structure of the lithium transition metal composite oxide 1 can be confirmed by powder X-ray diffraction (XRD) measurement. Specifically, it is preferable that peaks attributable to a layered rock salt crystal structure with an "R-3m" structure (a crystal structure belonging to the space group R-3m) are detected from the diffraction pattern obtained when powder X-ray diffraction (XRD) measurement of the lithium transition metal composite oxide 1 is performed. In particular, it is more preferable that only peaks attributable to a layered rock salt crystal structure with an "R-3m" structure are detected from the diffraction pattern.

[0033] (Particle Structure) The lithium transition metal composite oxide 1 is composed of secondary particles formed by agglomeration of multiple primary particles. The structure of the secondary particles of the lithium transition metal composite oxide 1 is not particularly limited, but is preferably a solid structure in which the primary particles are densely arranged. For example, the porosity (ratio of the void area inside the secondary particles to the cross-sectional area of ​​the secondary particles) of the lithium transition metal composite oxide 1 may be less than 15%, 10% or less, 5% or less, or 2% or less. The lower limit of the porosity is not particularly limited, but is, for example, 0.1% or more.

[0034] The porosity can be measured by observing an arbitrary cross section of the lithium transition metal composite oxide 1 (a cross section of a secondary particle having a cross-sectional major axis of ±20% of the volume average particle diameter Mv) using a scanning electron microscope and performing image analysis. For example, a plurality of particles of the lithium transition metal composite oxide 1 are embedded in a resin or the like, and the particles are made into a state in which their cross sections can be observed by cross-section polishing or the like. Then, using image analysis software such as WinRoof 6.1.1, voids within the secondary particles (areas where no primary particles are present) are measured as black, and dense areas within the outlines of the secondary particles (areas where primary particles are present) are measured as white. The porosity can be determined by calculating the area of ​​[black areas / (black areas + white areas)] for any 20 or more particles.

[0035] (Volume Average Particle Diameter) When measured using a laser diffraction / scattering particle size distribution analyzer, the volume average particle diameter Mv of the lithium transition metal composite oxide 1 is preferably 1 μm or more and 10 μm or less, more preferably 2 μm or more and 7 μm or less, and even more preferably 3 μm or more and 5 μm or less. This is because, when the volume average particle diameter of the lithium transition metal composite oxide particles is 1 μm or more and 10 μm or less, a secondary battery using a positive electrode active material 10 containing the lithium transition metal composite oxide 1 as a positive electrode can have a sufficiently large battery capacity per volume. Furthermore, the lower limit of the volume average particle diameter Mv may be 2 μm or more, or may be 3 μm or more. Furthermore, the volume average particle diameter Mv may be within a range between any one of the above upper and lower limits, or within a range between any two of the above upper limits.

[0036] (2) Coating Layer The positive electrode active material 10 has a coating layer 2 on the surface of the lithium transition metal composite oxide 1. By having the coating layer 2 on the surface of the lithium transition metal composite oxide 1, in a secondary battery having a positive electrode containing the positive electrode active material 10, it is possible to suppress mutual reaction between the positive electrode active material 10 and a solid electrolyte.

[0037] The coating layer 2 includes a compound containing lithium and tungsten, and may be formed from, for example, a compound consisting of lithium, tungsten, and oxygen. Examples of the compound containing lithium and tungsten include Li ２ WO ４ , 7Li ２ WO ４ ・4H ２ O, Li ４ WO ５ Lithium having a rock salt structure (space group: Fm-3m) ４ WO ５ The type of compound containing lithium and tungsten can be confirmed from the diffraction pattern of X-ray diffraction (XDR). Specifically, from the diffraction pattern obtained when powder X-ray diffraction (XRD) measurement of the positive electrode active material 10 is performed, Li having an "R-3" structure can be identified. ２ WO ４ Peaks assigned to "P-43m" structure, 7Li ２ WO ４ ・4H２ Peaks attributed to O and Li having the "Fm-3m" structure ４ WO ５ Preferably, at least one of the peaks assigned to

[0038] The coating layer 2 refers to a portion (region) in the surface region (surface layer) of the positive electrode active material 10 where the concentration of tungsten (W element) is higher than that of the lithium transition metal composite oxide 1 (central region), which is the coated material. The coating layer 2 and the lithium transition metal composite oxide 1 may or may not have a clear boundary line. For example, the coating layer 2 may be partially dissolved in the lithium transition metal composite oxide 1.

[0039] (Tungsten Coverage) The tungsten coverage P can be calculated from semi-quantitative analysis by X-ray photoelectron spectroscopy (XPS) using the following formula 1. The tungsten coverage P indicates the extent of the coverage area of ​​the coating layer 2 relative to the secondary particle surface of the lithium transition metal composite oxide (the coverage of the coating layer containing lithium and tungsten relative to the secondary particle surface).

[0040] P=(W / (W+Ni+Co+M))×100...(Formula 1)

[0041] In the above formula (1), W represents the amount of substance of tungsten as determined by XPS analysis, Ni represents the amount of substance of nickel as determined by XPS analysis, Co represents the amount of substance of cobalt as determined by XPS analysis, and M represents the amount of substance of element M (excluding tungsten) as determined by XPS analysis.

[0042] The XPS analysis is a value obtained from the intensity (area) ratio of peaks derived from each metal element in the XPS spectrum obtained when lithium transition metal composite oxide 1 is measured by X-ray photoelectron spectroscopy (XPS) using an X-ray photoelectron spectrometer (Versa Probe II, manufactured by ULVAC-PHI) with a monochromated Al-Kα X-ray source, an X-ray beam width of 100 μm, and an output of 25 W. XPS analysis has the characteristic of being able to selectively obtain information from a surface of 1 nm or more and 5 nm or less of the object to be measured, and therefore, the composition ratio of the surface layer of the material (within the range of 1 to 5 nm from the surface) can be determined.

[0043] The tungsten coverage P is 30% or more, preferably 60% or more, and more preferably 80% or more. By setting the tungsten coverage P of the coating layer within this range, a high discharge capacity is obtained, and the effects of preventing both the interfacial reaction between the lithium transition metal composite oxide and the solid electrolyte and the interfacial mixing between the lithium transition metal composite oxide and the coating layer are exhibited, thereby suppressing deterioration during cycling.

[0044] The upper limit of the tungsten coverage is not particularly limited, and may be 100% or less, or may be 100% or less, or may be 95% or less. Furthermore, when using the manufacturing method described below, a positive electrode active material 10 having a high discharge capacity can be obtained even if the tungsten coverage is 90% or less. Furthermore, when the tungsten coverage is 30% or more and 95% or less, the positive electrode active material for an all-solid-state lithium-ion secondary battery can have a high discharge capacity.

[0045] (Tungsten Content) The tungsten content in the positive electrode active material 10 is not particularly limited and can be adjusted as appropriate to satisfy the above coverage rate. The tungsten content may be, for example, 0.1% by mass or more and 6% by mass or less, more than 1% by mass or less and 5% by mass or less, or 1.5% by mass or more and 4% by mass or less, relative to the total amount of the positive electrode active material 10. When the tungsten content is within the above range, a uniform coating layer can be formed over the entire surface of the lithium transition metal composite oxide 1. Furthermore, tungsten may exist as a tungsten-containing compound between primary particles inside the secondary particles. Furthermore, the lower limit of the tungsten content may be 2% by mass or more, or 2.5% by mass or more. Furthermore, the upper limit of the tungsten content may be 3% by mass or less.

[0046] (Average Thickness of Coating Layer) The average thickness of the coating layer is, for example, preferably 2 nm to 20 nm, more preferably 2 nm to 15 nm, and even more preferably 5 nm to 15 nm. The average thickness of the coating layer may be 10 nm or more.

[0047] The average thickness of the coating layer 2 can be calculated by measuring the layer uniformly formed on the surface of the lithium transition metal composite oxide 1 through observation with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), or by analysis with a spectrometer attached to such an SEM or TEM, such as an energy dispersive X-ray spectrometer (EDS) or 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 measured at multiple sites. Alternatively, the average thickness of the coating layer 2 can be simply calculated from the specific surface area, coverage, and tungsten content of the lithium transition metal composite oxide 1.

[0048] (3) Positive Electrode Active Material The positive electrode active material 10 has the above-described lithium transition metal composite oxide 1 and the coating layer 2, and is preferably composed only of particles of the lithium transition metal composite oxide 1 and the coating layer 2. In addition, the positive electrode active material 10 preferably has the following properties.

[0049] (Water Content) Impurities may be mixed into the positive electrode active material 10 during the manufacturing process. Examples of impurities include water. Water is an impurity that may increase in the positive electrode active material 10 due to treatment using water or an aqueous solution in the coating process. Water may cause hydrolysis and deterioration of the solid electrolyte and affect the initial discharge capacity, so it is preferable that the water content be controlled within a predetermined range.

[0050] The cathode active material 10 preferably has a water content (water content) of 0.08% by mass or less relative to the total amount of the cathode active material 10. By setting the water content to 0.08% by mass or less, the hydrolysis reaction of the solid electrolyte can be more reliably suppressed in a solid secondary battery using the cathode active material 10. Furthermore, when the solid electrolyte is hydrolyzed, hydrogen sulfide is generated, causing deterioration and a decrease in lithium ion conductivity. However, by setting the water content of the cathode active material 10 to 0.08% by mass or less, the hydrolysis reaction of the solid electrolyte can be more reliably suppressed, thereby suppressing such deterioration.

[0051] The moisture content of the positive electrode active material 10 can be evaluated by, for example, the Karl Fischer method at a heating temperature of 300° C. The lower limit of the moisture content of the positive electrode active material 10 is not particularly limited, but is, for example, 0.001 mass % or more.

[0052] (Specific Surface Area) The specific surface area of ​​the positive electrode active material 10 is not particularly limited and may be, for example, 0.3 m ２ / g or more 2.0m ２ / g or less, and ２ / g or more 1.0m ２ / g or less. When the specific surface area is in the above range, the output characteristics are good. The specific surface area can be measured by the nitrogen adsorption BET method. The specific surface area of ​​the positive electrode active material 10 may be, for example, 0.8 m ２ / g or less.

[0053] (Pore Volume and Average Pore Diameter) The pore volume diameter of the positive electrode active material 10 is not particularly limited, but may be, for example, 0.001 cm ３ / g or more 0.008cm ３ / g or less, and ３ / g or more 0.004cm ３ / g or less. When the pore volume is within the above range, the added tungsten can be sufficiently infiltrated not only into the surface but also into the interior of the secondary particles, forming a uniform coating layer on the surface of the secondary particles and forming a compound containing tungsten inside the secondary particles. In all-solid-state lithium-ion secondary batteries, the solid electrolyte does not penetrate into the interior of the secondary particles of the positive electrode active material, so lithium ions cannot diffuse through the voids inside the secondary particles. When the pore volume is within the above range, the proportion of voids is small, which is thought to reduce the resistance of the battery.

[0054] The average pore size (diameter) of the positive electrode active material 10 may be, for example, 1 nm or more and 10 nm or less, or 1 nm or more and 4 nm or less. When the average pore size is within the above range, the added tungsten can be efficiently infiltrated into the surface and interior of the secondary particles. The pore volume size and average pore size can be measured using the Barrett-Joyner-Halenda (BJH) method.

[0055] 2. Manufacturing Method of Cathode Active Material for All-Solid-State Lithium-Ion Secondary Battery The manufacturing method of the cathode active material 10 is not particularly limited as long as it can produce a cathode active material having the above-described properties. For example, the above-described cathode active material 10 can be manufactured with high productivity by using the manufacturing method described below.

[0056] The method for producing the positive electrode active material 10 includes, for example, a dispersion step (S10) of dispersing a lithium transition metal composite oxide (base material) in pure water or an LiOH aqueous solution to obtain a positive electrode active material slurry, a separation step (S20) of dehydrating the positive electrode active material slurry to obtain a washed cake, a mixing step (S30) of mixing the washed cake with a compound (powder) containing tungsten to obtain a mixture, and a drying step (S40) of drying the mixture.

[0057] [Dispersion Step (S10)] The dispersion step (S10) is a step of mixing a lithium transition metal composite oxide (base material) with water or an aqueous solution to obtain a positive electrode active material slurry. The dispersion step (S10) removes impurities (such as excess lithium and sulfate) present on the surfaces of the primary particles of the lithium transition metal composite oxide (base material) and at the grain boundaries between the primary particles. Furthermore, wetting the entire surface of the lithium transition metal composite oxide (base material) with water or an aqueous solution promotes adhesion of a tungsten-containing compound, which is added in a later step, to the surfaces and interiors of the secondary particles, thereby forming a more uniform coating layer 2.

[0058] The lithium transition metal composite oxide used as the base material may be one obtained by a known technique. For example, the lithium transition metal composite oxide (base material) can be obtained by mixing a nickel composite hydroxide obtained by coprecipitating (crystallizing) metal elements (other than lithium) that constitute the lithium transition metal composite oxide, or a nickel composite oxide obtained by further heat-treating this nickel composite hydroxide (hereinafter, these are also collectively referred to as "precursor") with a lithium compound, and then calcining the resulting lithium mixture.

[0059] The lithium transition metal composite oxide (base material, before coating) may have the same composition as the lithium transition metal composite oxide 1 contained in the positive electrode active material 10. The lithium transition metal composite oxide (base material) may have a BET specific surface area after the dispersion step (S10) (and before coating) larger than the BET specific surface area before the dispersion step (S10), for example, 1.0 m ２ / g or more 2.0m ２ The pore volume of the lithium transition metal composite oxide (base material) after the dispersion step (S10) (and before coating) may be larger than the pore volume before the dispersion step (S10). For example, the pore volume after the dispersion step (S10) may be 0.005 cm ３ / g or more 0.01cm ３ The average pore size after the dispersion step (S10) may be 1 nm or more and 10 nm or less.

[0060] The dispersion step may be performed by a known method and under known conditions, as long as the dispersion step is performed within a range in which excessive lithium is not eluted from the surface of the lithium transition metal composite oxide (base material) and the battery characteristics are not deteriorated. For example, the slurry concentration of the positive electrode active material can be appropriately adjusted within a range of 500 g / L or more and 2500 g / L or less.

[0061] The water or aqueous solution used in the dispersion step (S10) is not particularly limited, but it is preferable to use an aqueous solution containing Li, and it is preferable to use an aqueous lithium hydroxide solution. By using an aqueous lithium hydroxide solution, a sufficient amount of lithium can be supplied to the surfaces of the secondary particles of the lithium transition metal composite oxide (base material) and to the interiors of the secondary particles (voids between primary particles and incomplete grain boundaries) that are connected to the outer surfaces of the secondary particles, thereby promoting the reaction with the tungsten compound in the drying step (S40) and efficiently removing other impurities. The concentration of the aqueous lithium hydroxide solution can be appropriately adjusted, for example, within a range of 0.5 g / L to 35 g / L in terms of lithium weight.

[0062] [Solid-Liquid Separation Step (S20)] The solid-liquid separation step (S20) is a step of dehydrating the positive electrode active material slurry to obtain a washed cake. The slurry is subjected to solid-liquid separation to obtain a washed cake containing the lithium nickel composite oxide. The method for dehydrating the positive electrode active material slurry is not particularly limited, and for example, dehydration is performed by solid-liquid separation using a suction filter, a centrifuge, a filter press, or the like.

[0063] The moisture content of the washed cake may be, for example, in the range of 2% by mass to 15% by mass.

[0064] [Mixing Step (S30)] The mixing step (S30) is a step of mixing the washed cake with a powder of a tungsten compound to obtain a mixture. The mixing step (S30) allows the tungsten compound to penetrate into the surface of the lithium transition metal composite oxide (base material) and into the interior of the base material, which is permeable to water or an aqueous solution. As a result, tungsten can be uniformly dispersed on the surfaces of the secondary particles and inside the secondary particles (in the voids between the primary particles and at the interfaces) in the lithium transition metal composite oxide 1.

[0065] [Drying Step (S40)] The drying step (S40) is a step of drying the mixture obtained in the mixing step (S30). The drying step (S40) forms a compound containing tungsten and lithium from W supplied from the tungsten compound and Li supplied from the aqueous solution of the cathode active material slurry or Li eluted from the lithium transition metal composite oxide (base material), thereby obtaining a cathode active material 10 in which a coating layer 2 is uniformly formed on the surface of secondary particles of the lithium transition metal composite oxide 1. The obtained cathode active material 10 may have a smaller specific surface area and / or pore volume than the lithium transition metal composite oxide (base material) after the dispersion step (S10) and before the mixing step (S30).

[0066] The drying conditions may be any conditions that can sufficiently reduce the moisture content in the mixture, and for example, the drying temperature may be 80° C. or higher and 110° C. or lower. After the drying step (S40), a heat treatment step may be carried out at a temperature higher than that of the drying step.

[0067] 3. All-Solid-State Lithium-Ion Secondary Battery The all-solid-state lithium-ion secondary battery according to this embodiment (hereinafter also referred to as "all-solid-state battery") includes a positive electrode, a negative electrode, and a solid electrolyte, and contains a positive electrode active material 10 in the positive electrode. The positive electrode may contain a positive electrode active material other than the above-described positive electrode active material 10, for example, it may contain a single primary particle, or it may be a mixture of a single primary particle and a secondary particle. The positive electrode may also contain a positive electrode active material having a different composition or particle size from the above-described positive electrode active material 10. Hereinafter, each component of the all-solid-state battery according to this embodiment will be described.

[0068] The embodiments described below are merely examples, and the all-solid-state battery can be implemented in various forms, including the following embodiments, with various modifications and improvements based on the knowledge of those skilled in the art. Furthermore, the use of the all-solid-state battery is not particularly limited.

[0069] (Positive electrode) The positive electrode can be formed by molding the positive electrode mixture. The positive electrode can be processed appropriately depending on the battery to be used. For example, the positive electrode can be subjected to a pressure compression treatment using a press or the like to increase the electrode density.

[0070] The above-mentioned positive electrode mixture can be formed by mixing the above-mentioned positive electrode active material in powder form with a solid electrolyte.

[0071] The solid electrolyte is added to the electrode to provide it with suitable ionic conductivity. The material of the solid electrolyte is not particularly limited, but for example, Li ３ P.S. ４ , Li ７ P ３ S １１ , Li １０ GeP ２ S １２ Sulfide-based solid electrolytes such as Li ７ La ３ Zr ２ O １２ , Li ０．３４ La ０．５１ TiO ２．９４ An oxide-based solid electrolyte such as SiO 2 or a polymer-based electrolyte such as PEO can be used.

[0072] A binder and a conductive additive may also be added to the positive electrode mixture.

[0073] The binder serves to bind the positive electrode active material together. The binder used in the positive electrode mixture is not particularly limited, but may be one or more selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose-based resin, polyacrylic acid, and the like.

[0074] The conductive material is added to the electrode to provide it with appropriate conductivity. The material of the conductive material is not particularly limited, but examples thereof include graphite such as natural graphite, artificial graphite, and expanded graphite, and carbon black materials such as acetylene black and Ketjenblack (registered trademark).

[0075] The mixing ratio of each material 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.

[0076] However, the method for producing the positive electrode is not limited to the above-mentioned example, and other methods may be used.

[0077] (Negative Electrode) The negative electrode can be formed by molding metals (lithium metal, indium metal, lithium-indium alloy, lithium-aluminum alloy, Si or an alloy containing Si, etc.) or a negative electrode mixture. Although the components and their formulation of the negative electrode mixture differ, it is formed substantially in the same manner as the positive electrode described above, and various treatments are performed as necessary, as with the positive electrode. The negative electrode mixture can be prepared by mixing a negative electrode active material with a solid electrolyte. For example, an occlusion material capable of occluding and desorbing lithium ions can be used as the negative electrode active material. The occlusion material is not particularly limited, but can be one or more selected from, for example, natural graphite, artificial graphite, baked organic compounds such as phenolic resins, and powdered carbon materials such as coke. When such an occlusion material is used as the negative electrode active material, a sulfide electrolyte such as Li3PS4 can be used as the solid electrolyte, as with the positive electrode.

[0078] (Solid electrolyte) The solid electrolyte is Li ＋ The solid electrolyte is a solid having ion conductivity. As the solid electrolyte, one selected from oxides, sulfides, polymers, etc. can be used alone or in combination of two or more.

[0079] The oxide-based solid electrolyte is not particularly limited, and any oxide-based solid electrolyte containing oxygen (O) and having lithium ion conductivity and electronic insulation properties can be used.

[0080] Examples of oxide-based solid electrolytes include lithium phosphate (Li ３ P.O. ４ ), Li ３ P.O. ４ NX, LiBO ２ NX, LiNbO ３ , LiTaO ３ , Li ２ SiO ３ , Li ４ SiO ４ -Li ３ P.O. ４ , Li ４ SiO４ -Li ３ VO ４ , Li ２ Alumni ２ O ３ -P ２ O ５ , Li ２ O—SiO ２ , Li ２ Alumni ２ O ３ -ZnO, Li １＋Ｘ Al Ｘ Ti ２－Ｘ (P.O. ４ ) ３ (0≦X≦1), Li １＋Ｘ Al Ｘ Ge ２－Ｘ (P.O. ４ ) ３ (0≦X≦1), LiTi ２ (P.O. ４ ) ３ , Li ３ XLa ２／３－Ｘ TiO ３ (0≦X≦2 / 3), Li ５ La ３ Ta ２ O １２ , Li ７ La ３ Zr ２ O １２ , Li ６ BaLa ２ Ta ２ O １２ , Li ３．６ Si ０．６ P ０．４ O ４ etc.

[0081] The sulfide-based solid electrolyte is not particularly limited, and any sulfide-based solid electrolyte containing sulfur (S) and having lithium ion conductivity and electronic insulation can be used. ２ S-P ２ S ５ , Li ２ S-SiS ２ , LiI-Li ２ S-SiS ２ , LiI-Li ２ S-P ２ S５ , LiI-Li ２ S-B ２ S ３ , Li ３ P.O. ４ -Li ２ S-Si ２ S., Li. ３ P.O. ４ -Li ２ S-SiS ２ , LiPO ４ -Li ２ S-SiS, LiI-Li ２ S-P ２ O ５ , LiI-Li ３ P.O. ４ -P ２ S ５ etc.

[0082] In addition, inorganic solid electrolytes other than those mentioned above may be used. For example, Li ３ N, LiI, Li ３ N-LiI-LiOH or the like may also be used.

[0083] The polymer solid electrolyte is not particularly limited as long as it is a polymer compound that exhibits ion conductivity, and examples thereof include polyethylene oxide, polypropylene oxide, and copolymers thereof. The organic solid electrolyte may also contain a supporting salt (lithium salt). When using a solid electrolyte, the solid electrolyte may also be mixed into the positive electrode material to ensure contact between the electrolyte and the positive electrode active material.

[0084] (Shape and configuration of all-solid-state battery) Next, examples of the arrangement and configuration of components of the all-solid-state battery according to this embodiment will be described. An all-solid-state battery configured with the above-described positive electrode, negative electrode, and solid electrolyte can be formed into various shapes, such as a coin shape or a stacked shape, as long as a certain pressure can be applied. Regardless of the shape, the positive electrode and negative electrode can be stacked via the solid electrolyte. Then, the positive electrode current collector and the positive electrode terminal connected to the outside, and the negative electrode current collector and the negative electrode terminal connected to the outside can be connected using a current collecting lead or the like, and the battery can be sealed in a battery case to form an all-solid-state battery.

[0085] (Characteristics of All-Solid-State Battery) The all-solid-state battery according to this embodiment using the positive electrode active material 10 can have a charge / discharge capacity equivalent to that of a lithium-ion secondary battery using an electrolyte solution. For example, when the positive electrode active material 10 according to this embodiment is used in the positive electrode to construct the test battery shown in Fig. 2, the initial discharge capacity measured under the conditions of the example may be 110% or more, 130% or more, 150% or more, or 170% or more of the initial discharge capacity of a lithium transition metal composite oxide produced under the same conditions except that no coating layer is formed.

[0086] The secondary battery of this embodiment is not particularly limited in its application, and can be suitably used for applications requiring various power sources. Furthermore, since the secondary battery of this embodiment has a charge / discharge capacity equivalent to that of a lithium-ion battery using an electrolyte solution and can be miniaturized, it can also be suitably used as a power source for electric vehicles, which are subject to space restrictions.

[0087] The present invention will be specifically described below using examples and comparative examples.

[0088] [Example 1] 1. Lithium Transition Metal Composite Oxide A lithium transition metal composite oxide having the following physical properties was prepared using a known method. (a) Chemical Composition The chemical composition of the lithium transition metal composite oxide was quantitatively analyzed using an ICP optical emission spectrometer (725ES, manufactured by VARIAN), and the ratio of the amounts of Li, Ni, Co, and Al was Li:Ni:Co:Al = 1.03:0.80:0.15:0.05. (b) Crystal Structure The crystal structure of the lithium transition metal composite oxide was measured using XRD (X'Pert, PROMRD, manufactured by PANALYTICAL), and was found to be a layered rock salt structure attributed to the R-3m structure. (c) Specific Surface Area The BET specific surface area of ​​the lithium transition metal composite oxide was measured using a fully automatic BET specific surface area measurement device (Maxsorb, manufactured by Mountec Co., Ltd.), and was found to be 0.60 m ２(d) Volume Average Particle Diameter The volume average particle diameter of the lithium transition metal composite oxide was measured using a laser diffraction scattering particle size distribution measuring device (Microtrac HRA, manufactured by Nikkiso Co., Ltd.) and was found to be 5.1 μm.

[0089] 2. Covering layer formation Li １．０３ Ni ０．８０ Co ０．１５ Al ０．０５ O ２ The lithium transition metal composite oxide powder was subjected to the following coating process to produce a positive electrode active material.

[0090] The lithium transition metal composite oxide was dispersed in an aqueous LiOH solution to form a positive electrode active material slurry, which was then dehydrated to obtain a positive electrode active material cake (water content: 5.8% by mass). ３ The mixture was mixed with the above, then vacuum dried and sieved to obtain a positive electrode active material. The obtained positive electrode active material was evaluated by the following method.

[0091] 3. Evaluation of the Positive Electrode Active Material (a) Composition The composition was analyzed using an ICP optical emission spectrometer (VARIAN, 725ES). This analysis revealed that the positive electrode active material contained 1.7 wt% W. The moisture content of the positive electrode active material was measured by the Karl Fischer method at a heating temperature of 300°C, and was found to be 0.08% by mass.

[0092] (b) Evaluation of Coverage (Surface Analysis) The positive electrode active material was measured using XPS (Versa Probe II, manufactured by ULVAC-PHI), and the amount of material (at%) on the positive electrode active material surface was obtained from the semi-quantitative values ​​calculated from the peak areas of the obtained Ni = 2p3 / 2 spectrum, Co = 2p3 / 2 spectrum, Al = 2p spectrum, W = 4f7 / 2 spectrum, and Nb = 3d5 / 2 spectrum. The W coverage, which is the ratio of W present on the surface to the sum of Ni, Co, Al, and W, was (W) / (Ni + Co + Al + W) × 100 = 33%. The Nb coverage, which is the ratio of Nb present on the surface to the sum of Ni, Co, Al, and Nb, was (Nb) / (Ni + Co + Al + Nb) × 100 = 0%.

[0093] The crystal structure of the positive electrode active material was measured using an XRD (D8 DISCOVER Vario-1, manufactured by Bruker Japan). As a result, a peak attributed to a lithium transition metal composite oxide (R-3m) and a peak attributed to Li ２ WO ４ , 7Li ２ WO ４ ・4H ２ O and Li ４ WO ５ A peak attributed to was detected.

[0094] (c) Thickness of Coating Layer The thickness of the coating layer was calculated from the amount of W contained in the positive electrode active material, the coverage of W, and the BET specific surface area of ​​the positive electrode active material. The BET specific surface area was measured using a fully automatic BET specific surface area measuring device (Macsorb, manufactured by Mountec Co., Ltd.).

[0095] (d) Pore volume and average pore diameter The pore volume and average pore diameter were calculated by the Barrett-Joyner-Halenda (BJH) method from a nitrogen adsorption isotherm measured using an independent four-station specific surface area / pore size distribution analyzer (QUADRASORB SI, manufactured by Quantachrome Instruments). In the BJH method, the pore shape is assumed to be cylindrical, and the pore size distribution is obtained from the relationship between the pore diameter at which capillary condensation occurs and the relative pressure of nitrogen (Kelvin equation).

[0096] 4. Preparation of All-Solid-State Battery (Test Battery) For battery evaluation of the positive electrode active material, a battery (hereinafter referred to as "test battery") having the structure shown in Figure 2 was used. As shown in Figure 2, the test battery SBA is composed of a case including a negative electrode can NC and a positive electrode can PC, and a compacted powder cell C housed in the case.

[0097] The case includes a hollow negative can NC with one open end and a positive can PC that is placed in the opening of the negative can NC. When the positive can PC is placed in the opening of the negative can NC, a space is formed between the positive can and the negative can NC to house the compacted cell C. The positive can PC is fixed to the negative can NC with a thumbscrew SW and a nut N.

[0098] The negative electrode can NC has a negative terminal, and the positive electrode can PC has a positive terminal. The case is provided with an insulating sleeve ISV, which fixes the negative electrode can NC and the positive electrode can PC so that they are kept out of contact with each other.

[0099] A pressure screw PSW is provided at one closed end of the negative electrode can NC, and after the positive electrode can PC is fixed to the negative electrode can NC, the pressure screw PSW is tightened toward the storage space of the compacted cell C, thereby maintaining the compacted cell C in a pressurized state through a hemispherical washer W. A screw-in plug P is provided at the end of the negative electrode can NC where the pressure screw PSW is located. 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, which seal the gap between the negative electrode can NC and the positive electrode can PC and maintain an airtight seal inside the case.

[0100] The green cell C is a pellet composed of a positive electrode layer PL, a solid electrolyte layer SEL, and a negative electrode layer NL, stacked in this order. The positive electrode layer PL contacts the inner surface of the positive electrode can PC through the lower current collector LCC, and the negative electrode layer NL contacts the inner surface of the negative electrode can NC through the upper current collector UCC, a hemispherical washer W, and a pressure screw PSW. The lower current collector LCC, green cell C, and upper current collector UCC are protected by a sleeve SV to prevent electrical contact between the positive electrode layer PL and the negative electrode layer NL.

[0101] The test battery SBA was prepared as follows.

[0102] First, 60 mg of the positive electrode active material and the solid electrolyte Li ３ P.S. ４ Next, a molding die capable of producing a pellet with a diameter of 10 mm was prepared, and (1) 60 mg of the solid electrolyte was placed in the mold and pressed at 10 MPa. Then, (2) 15 mg of the positive electrode mixture was added and pressed at 360 MPa to obtain a two-layer pellet consisting of a firmly bonded positive electrode layer PL and a solid electrolyte layer.

[0103] The lower current collector LCC, the pellet with the positive electrode layer PL facing downward, the indium foil (negative electrode layer NL), and the upper current collector UCC were stacked in this order from the bottom to form the electrode (compacted powder cell C). The electrode (compacted powder cell C) was then sealed in a case, and the pressure screw PSW was tightened with a torque of 5 to 7 N m to apply a restraining force. The test battery was fabricated in a glove box with an Ar atmosphere and a dew point controlled at -80°C.

[0104] 5. Evaluation of Solid Secondary Battery The charge / discharge capacity of the test battery was measured under the following conditions.

[0105] The test battery SBA was placed in a constant temperature bath at 25 ° C., and after the open circuit voltage OCV (Open Circuit Voltage) stabilized, the battery was charged to a cutoff voltage of 4.3 V (vs. Li + / Li) so that the current value per 1 g of active material was 19 mA / g, and then the current value per 1 g of active material was 1.9 mA / g. Charging was continued at 4.3 V (vs. Li + / Li). After a 1-hour pause, the battery was discharged to a cutoff voltage of 3.0 V (vs. Li + / Li) so that the current value per 1 g of active material was 19 mA / g. Charging was continued at 3.0 V (vs. Li + / Li) until the current per 1 g of active material was 1.9 mA / g.

[0106] The evaluation results are shown in Table 1. The discharge capacities shown in Table 1 are relative ratios with the discharge capacity of Comparative Example 1 as the reference (100%), and a discharge capacity relative ratio exceeding 100% indicates an increase in discharge capacity compared to the uncoated product of Comparative Example 1. The discharge capacity relative ratio of Example 1 was 111%. Furthermore, analysis of the cross section of the positive electrode active material of Example 1 confirmed the presence of a compound containing tungsten between the primary particles inside the secondary particles. Furthermore, the porosity of the positive electrode active material of Example 1 was 5% or less.

[0107] [Example 2] WO of Example 1 ３ Positive electrode active materials were prepared and evaluated under the same conditions except for the amount of addition. The results were W coverage = 61%, Nb coverage = 0%, and the discharge capacity relative ratio to Comparative Example 1 was 139%. The results are shown in Table 1.

[0108] [Example 3] WO of Example 1 ３Positive electrode active materials were prepared and evaluated under the same conditions except for the amount of addition. The results were W coverage = 89%, Nb coverage = 0%, and the discharge capacity relative ratio to Comparative Example 1 was 174%. The results are shown in Table 1.

[0109] [Example 4] WO of Example 1 ３ Positive electrode active materials were prepared and evaluated under the same conditions except for the amount of addition. The results were W coverage = 91%, Nb coverage = 0%, and the discharge capacity relative ratio to Comparative Example 1 was 151%. The results are shown in Table 1.

[0110] [Comparative Example 1] A positive electrode active material was prepared and evaluated under the same conditions as in Example 1, except that the coating layer formation step was omitted. As a result, the W coverage rate was 0% and the Nb coverage rate was 0%. The discharge capacity of Comparative Example 1 was set to 100%, which serves as the reference for relative ratios. The results are shown in Table 1.

[0111] [Comparative Example 2] WO of Example 1 ３ All were prepared in the same manner except for changing the amounts added. As a result, the W coverage was 13%, the Nb coverage was 0%, and the discharge capacity relative ratio to Comparative Example 1 was 74%. The results are shown in Table 1.

[0112] [Comparative Example 3] A positive electrode active material was produced and evaluated under the same conditions as in Example 1, except that the process for forming the coating layer (containing tungsten) was changed and a coating layer (containing niobium) was formed using the following process. As a result, the W coverage was 0%, the Nb coverage was 83%, and the discharge capacity relative ratio to Comparative Example 1 was 124%. The results are shown in Table 1.

[0113] (Niobium Coating Step) 500 g of lithium transition metal composite oxide powder was weighed and fluidized in a tumbling fluidized granulation coating apparatus (MP-01, manufactured by Powrex Corporation), and a mixed aqueous solution adjusted to a Li / Nb ratio of 1.0 was sprayed into a fluidization tank. The temperature of the air supplied to the fluidization tank was controlled to 120°C, and a coating process was carried out slowly over 4 hours to form a coating layer on the surface of the powder. The resulting powder was recovered and then heat-treated in an oxygen atmosphere at 300°C for 2 hours to produce a lithium transition metal composite oxide having a coating layer composed of Li and Nb from which moisture had been completely removed.

[0114] [Comparative Example 4] In the step of forming the coating layer of Example 1, WO ３ A positive electrode active material was prepared under the same conditions except that it was dried without mixing any of the above. The results were that the W coverage was 0%, the Nb coverage was 0%, and the discharge capacity relative ratio to Comparative Example 1 was 16%. The results are shown in Table 1.

[0115]

[0116] [Evaluation Results] The positive electrode active materials of the Examples exhibited significantly improved initial discharge capacities compared to the positive electrode active materials of Comparative Examples 1 and 4, which had no coating layer, and Comparative Example 2, which had a low W coverage.

[0117] Furthermore, the positive electrode active materials of Examples 2 to 4 (W coverage 61 to 91%) were shown to have a higher initial discharge capacity than the positive electrode active material of Comparative Example 3 (Nb coverage 83%) coated with a compound containing lithium and niobium.

[0118] Furthermore, in Comparative Example 4, in which a tungsten compound was not mixed into the positive electrode active material slurry in the coating layer formation step, the initial discharge capacity was significantly reduced compared to Comparative Example 1, in which the coating layer formation step was not performed.

[0119] According to the present invention, it is possible to provide a positive electrode active material that can be suitably used for the positive electrode of an all-solid-state lithium ion secondary battery that requires a high battery capacity.

[0120] The technical scope of the present invention is not limited to the aspects described in the above-mentioned embodiments. One or more of the requirements described in the above-mentioned embodiments may be omitted. Furthermore, the requirements described in the above-mentioned embodiments may be combined as appropriate. Furthermore, to the extent permitted by law, the disclosures of Japanese Patent Application No. 2023-132647 and all documents cited in the above-mentioned embodiments are incorporated by reference into this specification.

[0121] DESCRIPTION OF SYMBOLS 1...Lithium transition metal composite oxide 2...Coating layer 10...Positive electrode active material SBA...Test battery PC...Positive electrode can NC...Anode can ISV...Insulating sleeve C...Powder compact cell PL...Positive electrode layer NL...Anode layer SEL...Solid electrolyte layer LCC...Lower current collector UCC...Upper current collector P...Plug PSW...Pressure 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: a lithium transition metal composite oxide composed of secondary particles formed by agglomeration of a plurality of primary particles; and a coating layer coating the surfaces of the secondary particles, wherein the lithium transition metal composite oxide contains lithium, nickel, and optionally cobalt, and an element M (wherein the element M is an additive element other than lithium, nickel, cobalt, and oxygen), the coating layer contains a compound containing at least lithium and tungsten, and a coverage rate P (%) of the secondary particle surface with tungsten calculated by the following (Equation 1) is 30% or more and 95% or less. P = (W / (W+Ni+Co+M)) x 100 (%) ... (Formula 1) W: Amount of tungsten quantified by X-ray photoelectron spectroscopy (XPS analysis) Ni: Amount of nickel quantified by X-ray photoelectron spectroscopy (XPS analysis) Co: Amount of cobalt quantified by X-ray photoelectron spectroscopy (XPS analysis) M: Amount of element M (excluding tungsten) quantified by X-ray photoelectron spectroscopy (XPS analysis) 2. The positive electrode active material for an all-solid-state lithium ion secondary battery according to claim 1, wherein the lithium transition metal composite oxide is represented by the following formula 2: Li ａ Ni １－ｘ－ｙ Co ｘ M ｙ O ２＋ｚ ... (Formula 2) where M is one or more elements selected from Mg, Ca, Sr, Ba, Al, Ti, V, Cr, Mn, Fe, Cu, Zr, Nb, Mo, W, Ta, Si, P, and B, and satisfies 0.9≦a≦1.2, 0.01≦x≦0.5, 0.01≦y≦0.5, 0.02≦x+y<1.0, and −0.1≦z≦0.

1.

3. The positive electrode active material for an all-solid-state lithium-ion secondary battery according to claim 1 or 2, wherein the lithium transition metal composite oxide has a compound containing tungsten present between primary particles inside the secondary particles.

4. The positive electrode active material for an all-solid-state lithium ion secondary battery according to claim 1 or 2, wherein the coverage rate P is 60% or more and 95% or less.

5. The positive electrode active material for an all-solid-state lithium ion secondary battery according to claim 1 or 2, wherein the coverage rate P is 80% or more and 95% or less.

6. The positive electrode active material for an all-solid-state lithium ion secondary battery according to claim 1 or 2, wherein the lithium transition metal composite oxide has a volume average particle diameter Mv of 1 μm or more and 10 μm or less.

7. The positive electrode active material for an all-solid-state lithium-ion secondary battery according to claim 1 or 2, wherein the content of tungsten in the positive electrode active material is 0.1 mass % or more and 6 mass % or less with respect to the total amount of the positive electrode active material.

8. The pore volume of the positive electrode active material is 0.001 cm ３ / g or more 0.008cm ３ 3. The positive electrode active material for an all-solid-state lithium ion secondary battery according to claim 1, wherein the average pore size of the positive electrode active material is 1 nm or more and 10 nm or less.

9. An all-solid-state lithium ion secondary battery comprising a positive electrode containing the positive electrode active material for an all-solid-state lithium ion secondary battery according to claim 1 or 2, a negative electrode, and a solid electrolyte.

Images