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

Abstract

The purpose of the present invention is to provide a positive electrode active material having a high discharge capacity in an all-solid-state lithium ion secondary battery. A positive electrode active material for an all-solid-state lithium ion secondary battery, the positive electrode active material comprising a lithium transition metal composite oxide comprising secondary particles in which a plurality of primary particles are aggregated, and a coating layer that coats the surfaces of the secondary particles, the lithium transition metal composite oxide containing lithium, nickel, and any cobalt and element M (wherein M represents an integer of 1-3). 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 coating rate P (%) of tungsten on the surfaces of the secondary particles, calculated from the following formula (1) using XPS analysis, is 30-95% (inclusive). P = (W / (W + Ni + Co + M)) * 100 (%) (Formula 1).

Description

Technical Field

[0001] This invention relates to positive electrode active materials for all-solid-state lithium-ion secondary batteries and all-solid-state lithium-ion secondary batteries. Background Technology

[0002] In recent years, with the popularization of electric vehicles, there has been a strong demand for the development of small and lightweight secondary batteries with high energy density. Lithium-ion secondary batteries are one such example. Lithium-ion secondary batteries have a positive electrode, a negative electrode, and an electrolyte. The active materials for the negative and positive electrodes are materials capable of lithium ion insertion and extraction.

[0003] Currently, in typical lithium-ion secondary batteries, the positive electrode active material uses lithium transition metal composite oxides such as LiCoO2, LiNiO2, and LiMn2O4, while the negative electrode active material uses lithium metal, lithium alloys, metal oxides, carbon, etc. As electrolytes, the electrolytes use Li salts such as LiClO4 and LiPF6 dissolved in organic solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate as supporting salts.

[0004] Among the components of lithium-ion secondary batteries, the electrolyte, in particular, is a major factor limiting battery performance, including high-speed charging, safety, and lifespan, due to its chemical properties such as heat resistance and potential window. Therefore, research and development are actively underway for all-solid-state lithium-ion secondary batteries (hereinafter referred to as "all-solid-state batteries"), which improve battery performance by using a solid electrolyte instead of a liquid electrolyte.

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

[0006] For example, in Patent Document 2, in order to suppress the formation of the high-resistivity layer, it is proposed to provide a lithium-ion conductive oxide coating on the surface of the positive electrode active material.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2014-056661

[0010] Patent Document 2: International Publication No. 2007 / 004590

[0011] Non-patent literature

[0012] Non-patent document 1: Narumi Ohta et al., "LiNbO3-coated LiCoO2 as cathode material for all solid-state lithium secondary batteries", Electrochemistry Communications 9 (2007), 1486-1490 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] For example, in an embodiment of Patent Document 2, it is disclosed that by providing a coating layer composed of LiNbO3, a lithium-ion conductive oxide, on the surface of the positive electrode active material, the formation of a high-resistivity layer can be suppressed, thereby increasing the discharge capacity of the all-solid-state battery. However, compared with lithium-ion secondary batteries that use electrolyte as the electrolyte, its charge-discharge capacity is still low, and further increases in charge-discharge capacity are desired.

[0015] In view of the above problems, the object of the present invention is to provide a positive electrode active material with higher discharge capacity as a positive electrode active material for all-solid-state lithium-ion secondary batteries with a coating.

[0016] Methods for solving problems

[0017] To address the aforementioned issues, the inventors conducted in-depth research on positive electrode active materials for all-solid-state batteries, which have a coating layer that inhibits interfacial reactions between the solid electrolyte and the positive electrode active material. The results showed that by coating the secondary particle surface of the positive electrode active material with a compound containing at least lithium and tungsten in a specific ratio, the charge and discharge capacity of the all-solid-state battery can be increased.

[0018] In a first aspect of the present invention, a positive electrode active material for an all-solid-state lithium-ion secondary battery is provided, comprising a lithium transition metal composite oxide composed of secondary particles formed by the aggregation of multiple primary particles and a coating layer on the surface of the secondary particles, wherein the lithium transition metal composite oxide contains lithium, nickel and any cobalt and element M (wherein element M is an added element other than lithium, nickel, cobalt and oxygen), and the coating layer contains a compound containing at least lithium and tungsten, and the tungsten coverage rate P (%) on the surface of the secondary particles calculated by the following formula 1 is 30% or more and 95% or less.

[0019] P=(W / (W+Ni+Co+M))×100(%)…(Formula 1)

[0020] W: The amount of tungsten quantified by X-ray photoelectron spectrophotometry (XPS analysis).

[0021] Ni: The amount of nickel quantified by X-ray photoelectron spectrophotometry (XPS analysis).

[0022] Co: The amount of cobalt quantified by X-ray photoelectron spectrophotometry (XPS analysis).

[0023] M: The amount of element M (excluding tungsten) quantified by X-ray photoelectron spectrophotometry (XPS analysis).

[0024] Furthermore, the aforementioned lithium transition metal composite oxide is preferably represented by the following Formula 2.

[0025] Li a Ni 1-x-y Co x M y O 2+z …(Equation 2)

[0026] Wherein, 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, satisfying 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.

[0027] Furthermore, the lithium transition metal composite oxide preferably contains a tungsten-containing compound between the primary particles within the secondary particles. The coating percentage P is preferably 60% or more and 95% or less. The volume average particle size Mv of the lithium transition metal composite oxide is preferably 1 μm or more and 10 μm or less. The tungsten content in the positive electrode active material is preferably 0.1% by mass or more and 6% by mass or less relative to the total amount of the positive electrode active material. The pore volume of the positive electrode active material is preferably 0.001 cm³. 3 / g or more and 0.008cm 3 The average pore size of the positive electrode active material is above 1 nm and below 10 nm.

[0028] In a second aspect of the present invention, an all-solid-state lithium-ion secondary battery is provided, comprising a positive electrode, a negative electrode, and a solid electrolyte containing the aforementioned positive electrode active material for all-solid-state lithium-ion secondary batteries.

[0029] Invention Effects

[0030] According to the present invention, a positive electrode active material with higher discharge capacity can be provided as a positive electrode active material for an all-solid-state lithium-ion secondary battery with a coating. Attached Figure Description

[0031] [Figure 1 ] Figure 1 This is a schematic diagram illustrating an example of the positive electrode active material of this embodiment.

[0032] [ Figure 2 ] Figure 2 This is an explanatory diagram showing the cross-section of an evaluation battery used for battery evaluation. Detailed Implementation

[0033] Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings. It should be noted that, in the drawings, for ease of understanding of the various components, some parts are emphasized or simplified, and sometimes the actual structure or shape, scale, etc., may differ. Furthermore, the present invention is not limited to the following embodiment, and various modifications and substitutions can be applied to the following embodiment without departing from the scope of the present invention.

[0034] 1. Positive electrode active material for all-solid-state lithium-ion secondary batteries

[0035] An example of the configuration of the positive electrode active material (hereinafter also referred to as "positive electrode active material") for an all-solid-state lithium-ion secondary battery according to this embodiment will be described.

[0036] Figure 1 This is a schematic diagram illustrating an example of the positive electrode active material of this embodiment. Figure 1 As shown, the positive electrode active material 10 has a lithium transition metal composite oxide 1 and a coating layer 2 covering the surface of the lithium transition metal composite oxide 1. The constituent elements will be described below.

[0037] (1) Lithium transition metal composite oxide

[0038] Lithium transition metal composite oxide 1 is composed of secondary particles formed by the aggregation of multiple primary particles. In addition, lithium transition metal composite oxide 1 may contain lithium, transition metal and oxygen, and has a layered rock salt-type crystal structure.

[0039] (composition)

[0040] Lithium transition metal composite oxide 1 is a compound containing lithium, a transition metal, and oxygen. As the transition metal, nickel is preferred, and nickel and cobalt are more preferred. In addition, lithium transition metal composite oxide 1 preferably has a composition shown in the following general formula (1).

[0041] General formula (1): Li a Ni 1-x-y Co x M y O 2+z

[0042] In the above 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, satisfying 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.

[0043] In the above general formula (1), the value of 'a', which represents the lithium content, is 0.9 or more and 1.2 or less, can be 0.95 or more and 1.2 or less, and more preferably 1.0 or more and 1.1 or less. When the value of 'a' is within the above range, the output characteristics and capacity characteristics of the 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 the secondary battery using the positive electrode active material 10 can be suppressed, and the output characteristics can be improved. In addition, by setting the value of 'a' to 1.2 or less, the initial discharge capacity of the secondary battery using the positive electrode active material 10 can be maintained at a high level.

[0044] In the above general formula (1), (1-xy) representing the nickel content is greater than 0 and less than 0.98, can be greater than 0.3 and less than 0.98, or greater than 0.5 and less than 0.98. Furthermore, the lower limit of the nickel content can be greater than 0.6, greater than 0.7, or greater than 0.8. The higher the content ratio of (1-xy), the lower the voltage required for charging, resulting in a higher battery capacity.

[0045] In the above general formula (1), x, representing the cobalt content, is 0.01 or more and 0.5 or less, or it can be 0.01 or more and 0.3 or less, or it can be 0.05 or more and 0.2 or less. When the cobalt content is within the above range, the charge-discharge cycle characteristics and output characteristics can be improved.

[0046] In the above general formula (1), 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. Furthermore, element M preferably includes at least one element selected from Al and Mn, and more preferably includes Al. Element M can be appropriately selected according to the application of the secondary battery constructed using the positive electrode active material 10 and the required performance.

[0047] In the above mass ratio, y, representing the content ratio of element M, is 0 < y ≤ 0.5, preferably 0 < y ≤ 0.3, and can also be 0 < y ≤ 0.2. For example, when element M includes Al, the range of Al (y1) can be, for example, 0 < y1 ≤ 0.1 or 0 < y1 ≤ 0.05.

[0048] (Crystal Structure)

[0049] The lithium transition metal composite oxide 1 preferably has a layered rock-salt type crystal structure. When the lithium transition metal composite oxide 1 has a layered rock-salt type crystal structure, it can achieve 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). Specifically, it is preferable to detect peaks belonging to the layered rock-salt type crystal structure (crystal structure belonging to space group R-3m) based on the diffraction pattern obtained during the powder X-ray diffraction (XRD) measurement of the lithium transition metal composite oxide 1. More preferably, it is preferable to detect only peaks belonging to the layered rock-salt type crystal structure of the "R-3m" structure based on the aforementioned diffraction pattern.

[0050] (Particle structure)

[0051] The lithium transition metal composite oxide 1 is composed of secondary particles formed by the aggregation of multiple primary particles. Furthermore, the structure of the secondary particles in the lithium transition metal composite oxide 1 is not particularly limited, but a solid structure with closely spaced primary particles is preferred. For example, the porosity (the area of ​​voids within the secondary particles relative to the cross-sectional area of ​​the secondary particles) of the lithium transition metal composite oxide 1 can be less than 15%, less than 10%, less than 5%, or less than 2%. The lower limit of the porosity is not particularly limited, but for example, it can be 0.1% or more.

[0052] It should be noted that the porosity can be determined by observing any cross-section of lithium transition metal composite oxide 1 (the cross-section of secondary particles with a cross-sectional major axis of volume average particle size Mv ± 20%) using a scanning electron microscope and performing image analysis. For example, after embedding multiple lithium transition metal composite oxide 1 particles in resin or the like, and achieving a state where the cross-section of the particles can be observed through cross-section polishing or other processes, the porosity can be determined using image analysis software such as WinRoof 6.1.1, where the void portion (the part without primary particles) within the secondary particles is measured as black, and the dense portion (the part containing primary particles) within the outline of the secondary particles is measured as white. For any 20 or more particles, the area of ​​[black portion / (black portion + white portion)] can be calculated, thereby determining the porosity.

[0053] (Volume average particle size)

[0054] When measuring the volume average particle size Mv of the lithium transition metal composite oxide 1 using a laser diffraction scattering particle size analyzer, it 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. When the volume average particle size of the lithium transition metal composite oxide is 1 μm or more and 10 μm or less, this allows for a substantial increase in the battery capacity per unit volume when the positive electrode active material 10 containing the lithium transition metal composite oxide 1 is used as the positive electrode in a secondary battery. Furthermore, the lower limit of the volume average particle size Mv can be 2 μm or more, or 3 μm or more. Additionally, the volume average particle size Mv can be within the range of any one of the upper and lower limits, or within the range of any two of the upper limits.

[0055] (2) Covering layer

[0056] The positive electrode active material 10 has a coating layer 2 on the surface of the lithium transition metal composite oxide 1. By having a coating layer 2 on the surface of the lithium transition metal composite oxide 1, the interaction between the positive electrode active material 10 and the solid electrolyte can be suppressed in a secondary battery having a positive electrode containing the positive electrode active material 10.

[0057] The coating layer 2 contains a compound containing lithium and tungsten, and can be formed, for example, from a compound containing lithium, tungsten, and oxygen. Examples of compounds containing lithium and tungsten include Li₂WO₄, 7Li₂WO₄·4H₂O, and Li₄WO₅, and Li₄WO₅ with a rock salt structure (space group: Fm-3m) may also be included. The type of compound containing lithium and tungsten can be determined from the diffraction pattern obtained by X-ray diffraction (XDR). Specifically, it is preferable to detect at least one of the peaks belonging to Li₂WO₄ with an "R-3" structure, the peak belonging to 7Li₂WO₄·4H₂O with a "P-43m" structure, and the peak belonging to Li₄WO₅ with an "Fm-3m" structure, based on the diffraction pattern obtained during powder X-ray diffraction (XRD) determination of the positive electrode active material 10.

[0058] It should be noted that the coating layer 2 refers to the region (area) on the surface side 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) used as the coating 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.

[0059] (Tungsten coverage)

[0060] The tungsten coverage P can be calculated using Equation 1 below, based on semi-quantitative analysis using X-ray photoelectron spectroscopy (XPS). It should be noted that the tungsten coverage P represents the extent to which the coating layer 2 covers the secondary particle surface of the lithium transition metal composite oxide (the coverage of the lithium and tungsten-containing coating layer on the secondary particle surface).

[0061] P=(W / (W+Ni+Co+M))×100···(Formula 1)

[0062] In the above (Equation 1), W represents the amount of tungsten quantified by XPS analysis, Ni represents the amount of nickel quantified by XPS analysis, Co represents the amount of cobalt quantified by XPS analysis, and M represents the amount of element M (excluding tungsten) quantified by XPS analysis.

[0063] It should be noted that XPS analysis, for example, involves using an X-ray photoelectron spectrometer (ULVAC-PHI, VersaProbe II) with a monochromatic Al-Kα X-ray source, an X-ray beam width of 100 μm, and an output of 25 W. The value is determined by the ratio of the intensity (area) of the peaks from each metal element in the obtained XPS spectrum when measuring lithium transition metal composite oxide 1 using X-ray photoelectron spectrometry (XPS). XPS analysis selectively obtains information from the surface of the measured object up to 1 nm and down to 5 nm, thus revealing the composition of the material's surface layer (1–5 nm from the surface).

[0064] The tungsten coating percentage P is 30% or more, preferably 60% or more, and more preferably 80% or more. By making the tungsten coating percentage P of the coating layer within the above range, it has a high discharge capacity and can prevent the interfacial reaction between lithium transition metal composite oxide and solid electrolyte, as well as prevent the mixing of lithium transition metal composite oxide and coating layer at the interface, thereby suppressing degradation during cycling.

[0065] There is no particular upper limit to the tungsten coating percentage; it can be 100% or less, or even 95% or less. Furthermore, using the manufacturing method described later, even with a tungsten coating percentage of 90% or less, a positive electrode active material 10 with high discharge capacity can be obtained. Additionally, when the tungsten coating percentage is 30% or more and 95% or less, it can exhibit high discharge capacity as a positive electrode active material for all-solid-state lithium-ion secondary batteries.

[0066] (Tungsten content)

[0067] The tungsten content in the positive electrode active material 10 is not particularly limited and can be appropriately adjusted to meet the aforementioned coating rate. For example, the tungsten content relative to the total amount of the positive electrode active material 10 can be 0.1% by mass or more and 6% by mass or less, greater than 1% by mass or 5% by mass or less, or 1.5% by mass or more and 4% by mass or less. When the tungsten content is within the above range, a coating layer can be uniformly formed on the entire surface of the lithium transition metal composite oxide 1. Alternatively, tungsten can also exist in the form of a tungsten-containing compound between primary particles within secondary particles. Furthermore, the lower limit of the tungsten content can be 2% by mass or more, or 2.5% by mass or more. Furthermore, the upper limit of the tungsten content can be 3% by mass or less.

[0068] (Average thickness of the coating layer)

[0069] The average thickness of the coating layer is preferably 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. Alternatively, the average thickness of the coating layer may be 10 nm or more.

[0070] It should be noted that the average thickness of the coating layer 2 can be calculated by observing it using a scanning electron microscope (SEM), transmission electron microscope (TEM), or by analyzing it using spectrometers such as energy dispersive X-ray spectrometer (EDS) or electron energy loss spectroscopy (EELS), measuring the uniformly formed layer on the surface of the lithium transition metal composite oxide 1. It should also be noted that, in cases where the thickness of the coating layer 2 varies depending on the measurement location, the thickness of the coating layer 2 refers to the average value when measuring multiple locations. Furthermore, the average thickness of the coating layer 2 can also be easily calculated based on the specific surface area, coating ratio, and tungsten content of the lithium transition metal composite oxide 1.

[0071] (3) Positive electrode active material

[0072] The positive electrode active material 10 has the above-mentioned lithium transition metal composite oxide 1 and coating layer 2, and preferably consists only of particles of lithium transition metal composite oxide 1 and coating layer 2. In addition, the positive electrode active material 10 preferably has the following characteristics.

[0073] (Moisture content)

[0074] Sometimes impurities may be introduced during the manufacturing process. Moisture is an example of such an impurity. Moisture is an impurity that can increase in the positive electrode active material 10 through the use of water or aqueous solutions during the coating process. Moisture can cause hydrolysis and degradation of the solid electrolyte, potentially affecting the initial discharge capacity; therefore, it is preferable to control it within a predetermined range.

[0075] The water content (moisture content) in the positive electrode active material 10 is preferably 0.08% by mass or less relative to the total amount of the positive electrode 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 the solid-state secondary battery using the positive electrode active material 10. Furthermore, the hydrolysis of the solid electrolyte produces hydrogen sulfide, leading to degradation and a decrease in lithium-ion conductivity. However, by keeping the water content of the positive electrode active material 10 to 0.08% by mass or less, the hydrolysis reaction of the solid electrolyte can be more reliably suppressed, thus preventing this degradation.

[0076] The moisture content of the positive electrode active material 10 can be evaluated, for example, by using the Karl Fischer method with a heating temperature of 300°C. It should be noted that there is no particular lower limit to the moisture content of the positive electrode active material 10, for example, it can be 0.001% by mass or more.

[0077] (Specific surface area)

[0078] Furthermore, the specific surface area of ​​the positive electrode active material 10 is not particularly limited; for example, it can be 0.3 m². 2 / g or more and 2.0m 2 Below / g, it can also be 0.3m. 2 / g or more and 1.0m 2 / g or less. When the specific surface area is within the above range, the output characteristics are good. It should be noted that the specific surface area can be determined by the nitrogen adsorption BET method. Additionally, the specific surface area of ​​the positive electrode active material 10 can be, for example, 0.8 m². 2 / g or less.

[0079] (pore volume and average pore diameter)

[0080] The pore volume of the positive electrode active material 10 is not particularly limited; for example, it can be 0.001 cm³. 3 / g or more and 0.008cm 3 Below / g, it can also be 0.001cm 3 / g or more and 0.004cm 3 / g or less. When the pore volume is within the above range, the added tungsten can not only fully penetrate the surface of the secondary particles but also fully penetrate into the interior, forming a uniform coating layer on the surface of the secondary particles and a tungsten-containing compound within the secondary particles. In all-solid-state lithium-ion secondary batteries, since the solid electrolyte does not enter the interior of the secondary particles of the positive electrode active material, lithium ions cannot diffuse in the voids within the secondary particles. It is believed that when the pore volume is within the above range, the proportion of voids is small, thus reducing the battery resistance.

[0081] Furthermore, the average pore size (diameter) of the positive electrode active material 10 can 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 efficiently penetrate to the surface and interior of the secondary particles. It should be noted that the pore volume and average pore size can be determined using the Barrett-Joyner-Halenda (BJH) method.

[0082] 2. Manufacturing method of positive electrode active material for all-solid-state lithium-ion secondary batteries

[0083] The manufacturing method of the positive electrode active material 10 is not particularly limited as long as it can produce a positive electrode active material with the above-mentioned characteristics. For example, the positive electrode active material 10 can be manufactured with high productivity by using the following manufacturing method.

[0084] The method for manufacturing the positive electrode active material 10 includes, for example, a dispersion step (S10) in which lithium transition metal composite oxide (master material) is dispersed in pure water or LiOH aqueous solution to obtain a positive electrode active material slurry, a separation step (S20) in which the positive electrode active material slurry is dehydrated to obtain a cleaning filter cake, a mixing step (S30) in which the cleaning filter cake is mixed with a tungsten-containing compound (powder) to obtain a mixture, and a drying step (S40) in which the mixture is dried.

[0085] [Dispersion process (S10)]

[0086] The dispersion step (S10) is a process of mixing lithium transition metal composite oxide (base material) with water or an aqueous solution to obtain a positive electrode active material slurry. Through the dispersion step (S10), impurities (residual lithium, sulfate, etc.) present on the surface of the primary particles and at the grain boundaries between the primary particles are removed, and the entire surface of the lithium transition metal composite oxide (base material) is wetted with water or an aqueous solution. This promotes the adhesion of tungsten-containing compounds added in subsequent steps to the surface and interior of the secondary particles, forming a more uniform coating layer 2.

[0087] The lithium transition metal composite oxide used as the base material can be a material obtained using known techniques. For example, the lithium transition metal composite oxide (base material) can be obtained by mixing a nickel composite hydroxide obtained by co-precipitating (crystallizing) the metal elements (other than lithium) constituting the lithium transition metal composite oxide, or by further heat-treating the nickel composite hydroxide (hereinafter also collectively referred to as the "precursor") with a lithium compound, and then firing the resulting lithium mixture.

[0088] Furthermore, the lithium transition metal composite oxide (base material, before coating) can be a material with the same composition as the lithium transition metal composite oxide 1 contained in the positive electrode active material 10. Additionally, the BET specific surface area of ​​the lithium transition metal composite oxide (base material) after the dispersion step (S10) (and before coating) can be greater than the BET specific surface area before the dispersion step (S10), for example, it can be 1.0 m². 2 / g or more and 2.0m 2 / g or less. Furthermore, the pore volume of the lithium transition metal composite oxide (base material) after the dispersion process (S10) (but before coating) can be greater than the pore volume before the dispersion process (S10). For example, the pore volume after the dispersion process (S10) can be 0.005 cm³. 3 / g or more and 0.01cm 3 / g or less. In addition, the average pore size after the dispersion process (S10) can be 1nm or more and 10nm or less.

[0089] The dispersion process can be carried out using known methods and conditions, as long as it allows for excessive dissolution of lithium from the surface of the lithium transition metal composite oxide (matrix) without deterioration of battery characteristics. For example, the slurry concentration of the positive electrode active material can be appropriately adjusted within the range of 500 g / L or higher and 2500 g / L or lower.

[0090] There are no particular restrictions on the water or aqueous solution used in the dispersion step (S10), but an aqueous solution containing Li is preferred, and a lithium hydroxide aqueous solution is even more preferred. By using a lithium hydroxide aqueous solution, a sufficient amount of lithium can be supplied to the surface of the secondary particles of the lithium transition metal composite oxide (base material) and to the interior of the secondary particles (voids between primary particles, imperfect grain boundaries) that communicate with the outer surface of the secondary particles. This promotes the reaction with the tungsten compound in the drying step (S40) and efficiently removes other impurities. The concentration of the lithium hydroxide aqueous solution can be appropriately adjusted, for example, within a range of 0.5 g / L or more and 35 g / L or less based on the weight of lithium.

[0091] [Solid-liquid separation process (S20)]

[0092] The solid-liquid separation process (S20) is a process of dehydrating the positive electrode active material slurry to obtain a cleaned filter cake. It involves separating the solid and liquid components of the slurry to obtain a cleaned filter cake containing the aforementioned lithium-nickel composite oxide. There are no particular limitations on the method for dehydrating the positive electrode active material slurry; for example, a suction filter, centrifuge, or filter press can be used for solid-liquid separation to achieve dehydration.

[0093] The water content for washing the filter cake can be, for example, between 2% and 15% by mass.

[0094] [Mixing process (S30)]

[0095] The mixing process (S30) is a process of mixing the washed filter cake with tungsten compound powder to obtain a mixture. Through the mixing process (S30), the tungsten compound penetrates into the surface of the lithium transition metal composite oxide (base material) and into the interior of the base material that water or aqueous solution can penetrate, thereby enabling tungsten to be uniformly dispersed in the lithium transition metal composite oxide 1 on the surface and inside of the secondary particles (the gaps and interfaces between primary particles).

[0096] [Drying process (S40)]

[0097] The drying process (S40) is a process of drying the mixture obtained by the mixing process (S30). Through the drying process (S40), a compound containing tungsten and lithium is formed from W supplied from a tungsten compound and Li supplied from an aqueous solution of the positive electrode active material slurry or Li dissolved from the lithium transition metal composite oxide (base material). This allows for the formation of a positive electrode active material 10 with a coating layer 2 uniformly formed on the surface of the secondary particles of the lithium transition metal composite oxide 1. Furthermore, compared to the lithium transition metal composite oxide (base material) after the dispersion process (S10) and before the mixing process (S30), the obtained positive electrode active material 10 can have a smaller specific surface area and / or pore volume.

[0098] The drying conditions only need to be sufficient to reduce the moisture content in the mixture; for example, the drying temperature can be above 80°C and below 110°C. It should be noted that a heat treatment process at a higher temperature than the drying process can also be performed after the drying process (S40).

[0099] 3. All-solid-state lithium-ion secondary battery

[0100] The all-solid-state lithium-ion secondary battery (hereinafter also referred to as "all-solid-state battery") of this embodiment includes a positive electrode, a negative electrode, and a solid electrolyte. The positive electrode includes a positive electrode active material 10. It should be noted that the positive electrode may also include a positive electrode active material other than the positive electrode active material 10 described above. For example, it may include a single primary particle or a mixture of a single primary particle and a secondary particle. In addition, the positive electrode may also include a positive electrode active material having a different composition and particle size than the positive electrode active material 10 described above. Hereinafter, each component of the all-solid-state battery of this embodiment will be described separately.

[0101] It should be noted that the embodiments described below are merely illustrative, and all-solid-state batteries can be implemented based on the following embodiments with various modifications and improvements made based on the knowledge of those skilled in the art. Furthermore, there are no particular limitations on the applications of all-solid-state batteries.

[0102] (positive electrode)

[0103] The positive electrode can be formed by molding a positive electrode compound. It should be noted that the positive electrode can be appropriately processed depending on the battery used. For example, to increase electrode density, it can also be subjected to pressure compression treatment, such as pressing.

[0104] The aforementioned positive electrode mixture can be formed by mixing the aforementioned positive electrode active material, which will become a powder, with a solid electrolyte.

[0105] Solid electrolytes are added to impart appropriate ionic conductivity to the electrodes.

[0106] The material of this solid electrolyte is not particularly limited; for example, Li3PS4 or Li7P3S can be used. 11 Li 10 GeP2S 12 Sulfide-based solid electrolytes, Li7La3Zr2O 12 Li 0.34 La 0.51 TiO 2.94 Solid electrolytes such as oxide-based electrolytes and polymer-based electrolytes such as PEO.

[0107] It should be noted that binders and conductive additives can also be added to the positive electrode mixture.

[0108] The binder serves to bind the positive electrode active material together. There are no particular limitations on the binder used in this positive electrode mixture; for example, one or more can be selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resins, polyacrylic acid, etc.

[0109] Conductive materials are added to impart appropriate conductivity to electrodes. There are no particular limitations on the materials used; for example, natural graphite, artificial graphite, expanded graphite, and carbon black materials such as acetylene black and Ketjen black (registered trademark) can be used.

[0110] Furthermore, there is no particular limitation on the mixing ratio of the various substances in the positive electrode mixture. For example, the content of the positive electrode active material in the positive electrode mixture can be set to 50 parts by mass or more and 90 parts by mass or less, and the content of the solid electrolyte can be set to 10 parts by mass or more and 50 parts by mass or less.

[0111] However, the method for producing the positive electrode is not limited to the method exemplified above, and other methods can also be used.

[0112] (negative electrode)

[0113] The negative electrode can be formed by molding a metal (lithium metal, indium metal, lithium-indium alloy, lithium-aluminum alloy, Si or Si-containing alloy, etc.) or a negative electrode compound. Although the components and their combinations in the negative electrode compound may differ, they can be formed by essentially the same method as the positive electrode described above, and can be processed in various ways as needed, just like the positive electrode. The negative electrode compound can be prepared by mixing a negative electrode active material with a solid electrolyte. As the negative electrode active material, for example, an absorbent material capable of absorbing and desorbing lithium ions can be used. There are no particular limitations on the absorbent material; for example, one or more can be selected from sintered organic compounds such as natural graphite, artificial graphite, phenolic resin, and powders of carbonaceous materials such as coke. When this absorbent material is used as the negative electrode active material, a sulfide electrolyte such as Li3PS4 can be used as the solid electrolyte, just like the positive electrode.

[0114] (Solid electrolyte)

[0115] Solid electrolytes are those with Li + A solid with ion conductivity. As a solid electrolyte, it can be used alone, selected from oxides, sulfides, polymers, etc., or in combination of two or more.

[0116] As an oxide-based solid electrolyte, there are no particular limitations; any substance containing oxygen (O) and possessing lithium-ion conductivity and electronic insulation can be used.

[0117] Examples of oxide-based solid electrolytes include lithium phosphate (Li3PO4), Li3PO4NX, LiBO2NX, LiNbO3, LiTaO3, Li2SiO3, Li4SiO4-Li3PO4, Li4SiO4-Li3VO4, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3-ZnO, and 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, Li 3X La 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.

[0118] There are no particular limitations on the type of sulfide-based solid electrolyte; any substance containing sulfur (S) and possessing lithium-ion conductivity and electronic insulation properties can be used. Examples of sulfide-based solid electrolytes 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, and LiI-Li₃PO₄-P₂S₅.

[0119] It should be noted that, as an inorganic solid electrolyte, substances other than those mentioned above can be used, such as Li3N, LiI, Li3N-LiI-LiOH, etc.

[0120] As a polymer-based solid electrolyte, there are no particular limitations on the type of polymer compound exhibiting ion conductivity; for example, polyethylene oxide, polypropylene oxide, and their copolymers can be used. Furthermore, organic solid electrolytes can also contain supporting salts (lithium salts). It should be noted that when using solid electrolytes, to ensure contact between the electrolyte and the positive electrode active material, the solid electrolyte can also be mixed into the positive electrode material.

[0121] (The shape and structure of all-solid-state batteries)

[0122] Next, examples of the configuration and structure of the components of the all-solid-state battery according to this embodiment will be described.

[0123] The all-solid-state battery, composed of the aforementioned positive electrode, negative electrode, and solid electrolyte, can be formed into various shapes, such as coin-shaped or stacked, to which a certain pressure can be applied. Regardless of the shape, the positive and negative electrodes can be stacked with the solid electrolyte in between. Then, current-collecting leads or the like can be used to connect the positive current collector to the positive terminal leading to the outside, and the negative current collector to the negative terminal leading to the outside, and the battery can be sealed within a battery casing to form an all-solid-state battery.

[0124] (Characteristics of all-solid-state batteries)

[0125] The all-solid-state battery of this embodiment, which uses the positive electrode active material 10, can have a charge / discharge capacity equivalent to that of a lithium-ion secondary battery using an electrolyte. For example, when the positive electrode active material 10 of this embodiment is used as the positive electrode to construct... Figure 2In the case of the test battery shown, the initial discharge capacity measured under the conditions of the embodiment can be 110% or more, 130% or more, 150% or more, or 170% or more, relative to the initial discharge capacity of a lithium transition metal composite oxide manufactured under the same conditions except that no coating is formed.

[0126] It should be noted that the application of the secondary battery in this embodiment is not particularly limited, and it can be suitable for applications requiring various power sources. Furthermore, since the secondary battery of this embodiment has a charge / discharge capacity equivalent to that of lithium-ion batteries using electrolyte, it can be miniaturized, and therefore is also suitable for use as a power source for electric vehicles where installation space is limited.

[0127] Example

[0128] The present invention will now be described in detail using examples and comparative examples.

[0129] [Example 1]

[0130] 1. Lithium transition metal composite oxides

[0131] Lithium transition metal composite oxides with the following properties were prepared using known methods.

[0132] (a) Chemical composition

[0133] The chemical composition of the lithium transition metal composite oxide was quantitatively analyzed using an ICP-based luminescence spectrophotometer (VARIAN, 725ES). The molar ratio of Li, Ni, Co, and Al was Li:Ni:Co:Al = 1.03:0.80:0.15:0.05.

[0134] (b) Crystal structure

[0135] The crystal structure of the lithium transition metal complex oxide was determined using XRD (Panelytical, X'Pert, PROMRD), and the result was a layered rock salt structure belonging to the R-3m structure.

[0136] (c) Specific surface area

[0137] The BET specific surface area of ​​the lithium transition metal composite oxide was determined using a fully automated BET specific surface area measuring device (Macsorb, Mountech Co., Ltd.), and the result was 0.60 m². 2 / g.

[0138] (d) Volume average particle size

[0139] The volume average particle size of lithium transition metal composite oxides was determined using a laser diffraction scattering particle size distribution measuring device (manufactured by Nikkiso Corporation, Microtrac HRA), and the result was 5.1 μm.

[0140] 2. Formation of the covering layer

[0141] By Li 1.03 Ni 0.80 Co 0.15 Al 0.05 The following coating process is performed on O2 lithium transition metal composite oxide powder to manufacture positive electrode active material.

[0142] A lithium transition metal composite oxide was dispersed in an aqueous LiOH solution to prepare a slurry of positive electrode active material. This slurry was then dehydrated to obtain a filter cake of positive electrode active material (moisture content: 5.8% by mass). The filter cake was mixed with WO3, vacuum dried, and sieved to obtain the positive electrode active material. The obtained positive electrode active material was evaluated using the following methods.

[0143] 3. Evaluation of positive electrode active material

[0144] (a) Composition

[0145] The composition was analyzed using an ICP-based luminescence spectrophotometer (VARIAN, 725ES). This analysis revealed that the positive electrode active material contains 1.7 wt% W. Furthermore, the water content of the positive electrode active material was determined using the Karl Fischer method at a heating temperature of 300°C, and the result showed a water content of 0.08% by mass.

[0146] (b) Evaluation of Coverage Rate (Surface Analysis)

[0147] The active material of the cathode was determined by XPS (Ulvac-PHI, Versa Probe II). The surface mass (at%) of the active material was calculated from the peak areas of the obtained Ni=2p³ / ², Co=2p³ / ², Al=2p, W=4f⁷ / ², and Nb=3d⁵ / ² spectra. The W coverage rate, i.e., the ratio of W present on the surface to the sum of Ni, Co, Al, and W, is (W) / (Ni+Co+Al+W)×100 = 33%. The Nb coverage rate, i.e., the ratio of Nb present on the surface to the sum of Ni, Co, Al, and Nb, is (Nb) / (Ni+Co+Al+Nb)×100 = 0%.

[0148] In addition, the crystal structure of the positive electrode active material was determined by XRD (Bruker Japan, D8 DISCOVER Vario-1). The results showed that peaks belonging to lithium transition metal complex oxide (R-3m) and peaks belonging to Li2WO4, 7Li2WO4·4H2O and Li4WO5 were detected.

[0149] (c) Thickness of the coating

[0150] The thickness of the coating layer was calculated from the amount of W contained in the positive electrode active material, the W coating rate, and the BET specific surface area of ​​the positive electrode active material. The BET specific surface area was measured using a fully automated BET specific surface area measuring device (Macsorb, manufactured by Mounttech Co., Ltd.).

[0151] (d) Pore volume and average pore diameter

[0152] The micropore volume and average micropore diameter were calculated from nitrogen adsorption isotherms measured using the Barrett-Joyner-Halenda (BJH) method with an independent four-station specific surface area / micropore distribution measuring apparatus (Quantachrome Instruments, QUADRASORB SI). In the BJH method, the micropore shape is assumed to be cylindrical, and the micropore size distribution is obtained using the relationship between the micropore size that causes capillary condensation and the relative pressure of nitrogen (Kelvin equation).

[0153] 4. Fabrication of all-solid-state batteries (experimental batteries)

[0154] In battery evaluation of positive electrode active materials, the use of materials with... Figure 2 The battery shown (hereinafter referred to as the "experimental battery"). For example... Figure 2 As shown, the test battery SBA consists of a housing with a negative electrode container NC and a positive electrode container PC, and a powder pressing unit C housed within the housing.

[0155] The housing comprises a hollow negative electrode container NC with an opening at one end and a positive electrode container PC disposed at the opening of the negative electrode container NC. If the positive electrode container PC is disposed at the opening of the negative electrode container NC, a space for accommodating the compressed powder unit C is formed between the positive electrode container and the negative electrode container NC. The positive electrode container PC is fixed to the negative electrode container NC by a wing screw SW and a nut N.

[0156] The negative electrode container NC has a negative terminal, and the positive electrode container PC has a positive terminal. The housing has an insulating sleeve ISV, which is used to fix the negative electrode container NC and the positive electrode container PC in a non-contact manner.

[0157] A pressure screw PSW is located at the sealed end of the negative electrode container NC. After the positive electrode container PC is fixed to the negative electrode container NC, the pressure screw PSW is tightened toward the storage space of the powder pressing unit C, thereby maintaining the powder pressing unit C under pressure through the hemispherical washer W. A screw-in pin P is located at the end of the negative electrode container NC where the pressure screw PSW is located. O-rings OL are located between the negative electrode container NC and the positive electrode container PC, and between the negative electrode container NC and the pin P, sealing the gap between the negative electrode container NC and the positive electrode container PC and maintaining the airtightness of the housing.

[0158] The powder pressing unit C consists of small pellets arranged in this order, comprising a positive electrode layer PL, a solid electrolyte layer SEL, and a negative electrode layer NL. The positive electrode layer PL contacts the inner surface of the positive electrode tank PC through the lower current collector LCC, while the negative electrode layer NL contacts the inner surface of the negative electrode tank NC through the upper current collector UCC, the hemispherical washer W, and the pressure screw PSW. The lower current collector LCC, the powder pressing unit C, and the upper current collector UCC are protected by the sleeve SV to prevent electrical contact between the positive electrode layer PL and the negative electrode layer NL.

[0159] The SBA used in the above experiment was fabricated as follows.

[0160] First, a positive electrode mixture was prepared by mixing 60 mg of positive electrode active material and 40 mg of solid electrolyte Li3PS4 in a mortar. Next, a molding die capable of making small balls with a diameter of 10 mm was prepared. (1) 60 mg of solid electrolyte was added and the mixture was molded under pressure at 10 MPa. (2) 15 mg of positive electrode mixture was added and the mixture was pressurized at 360 MPa. This yielded a two-layer ball consisting of a firmly bonded positive electrode layer PL and a solid electrolyte layer.

[0161] Starting from the bottom, the lower current collector LCC, a small ball with the positive electrode layer PL facing downwards, an indium foil (negative electrode layer NL), and the upper current collector UCC are stacked sequentially to form the electrode (powder-pressed unit C). After the electrode (powder-pressed unit C) is sealed into the housing, the pressure screw PSW is tightened with a torque of 5~7 N·m to apply a restraining force. The test battery was fabricated in a glove box with an Ar atmosphere where the dew point was controlled to -80°C.

[0162] 5. Evaluation of Solid-State Secondary Batteries

[0163] The charge and discharge capacity of the test battery was determined under the following conditions.

[0164] The test battery SBA was placed in a constant temperature bath at 25°C. After the open circuit voltage (OCV) stabilized, it was charged at a current of 19 mA / g per gram of active material until the cutoff voltage of 4.3V (vs. Li+ / Li). Then, it was charged at 4.3V (vs. Li+ / Li) until the current of 1.9 mA / g per gram of active material was reached. After a 1-hour rest period, it was discharged at a current of 19 mA / g per gram of active material until the cutoff voltage of 3.0V (vs. Li+ / Li). Then, it was charged at 3.0V (vs. Li+ / Li) until the current of 1.9 mA / g per gram of active material was reached.

[0165] The above evaluation results are shown in Table 1. It should be noted that the discharge capacity shown in Table 1 is a relative comparison with the discharge capacity of Comparative Example 1 (100%). A discharge capacity relative comparison exceeding 100% indicates an increase in discharge capacity compared to Comparative Example 1, which was an uncoated sample. The discharge capacity relative comparison for Example 1 is 111%. Furthermore, analysis of the cross-section of the positive electrode active material of Example 1 confirmed the presence of tungsten-containing compounds between primary particles within the secondary particles. Additionally, the porosity of the positive electrode active material of Example 1 is less than 5%.

[0166] [Example 2]

[0167] Except for changing the amount of WO3 added in Example 1, the positive electrode active material was prepared and evaluated under the same conditions. The results showed that the W coating was 61%, the Nb coating was 0%, and the discharge capacity was 139% relative to Comparative Example 1. The results are shown in Table 1.

[0168] [Example 3]

[0169] Except for changing the amount of WO3 added in Example 1, the positive electrode active material was prepared and evaluated under the same conditions. The results showed that the W coverage was 89%, the Nb coverage was 0%, and the discharge capacity was 174% relative to Comparative Example 1. The results are shown in Table 1.

[0170] [Example 4]

[0171] Except for changing the amount of WO3 added in Example 1, the positive electrode active material was prepared and evaluated under the same conditions. The results showed that the W coverage was 911%, the Nb coverage was 0%, and the discharge capacity was 151% relative to Comparative Example 1. The results are shown in Table 1.

[0172] [Comparative Example 1]

[0173] Except for omitting the coating formation process of Example 1, all positive electrode active materials were prepared and evaluated under the same conditions. The results showed that the W coating rate was 0% and the Nb coating rate was 0%. It should be noted that the discharge capacity of Comparative Example 1 was set as 100% of the relative baseline. The results are shown in Table 1.

[0174] [Comparative Example 2]

[0175] Except for changing the amount of WO3 added in Example 1, all were prepared in the same manner. As a result, the W coverage was 13%, the Nb coverage was 0%, and the discharge capacity was 74% relative to Comparative Example 1. The results are shown in Table 1.

[0176] [Comparative Example 3]

[0177] The coating (containing tungsten) formation process of Example 1 was modified, and the coating (containing niobium) was formed in the following processes. Otherwise, the positive electrode active material was fabricated and evaluated under the same conditions. The results showed that the W coating rate was 0%, the Nb coating rate was 83%, and the discharge capacity was 124% higher than that of Comparative Example 1. The results are shown in Table 1.

[0178] (Niobium coating process)

[0179] 500g of lithium transition metal composite oxide powder was weighed and flowed in a rolling flow granulation coating apparatus (POWREX, MP-01). A mixed aqueous solution prepared with a Li / Nb ratio of 1.0 was sprayed into the flow tank, and the temperature of the air supplied to the flow tank was controlled at 120°C. The coating process was carried out slowly for 4 hours, thereby forming a coating layer on the surface of the powder. The resulting powder was then recycled and heat-treated at 300°C for 2 hours in an oxygen atmosphere, thereby producing a lithium transition metal composite oxide with a coating layer composed of Li and Nb that had been completely dehydrated.

[0180] [Comparative Example 4]

[0181] In the coating formation process of Example 1, WO3 was not mixed and the material was directly dried. Otherwise, the positive electrode active material was prepared and evaluated under the same conditions. The results showed that the W coating rate was 0%, the Nb coating rate was 0%, and the discharge capacity was 16% relative to Comparative Example 1. The results are shown in Table 1.

[0182] [Table 1]

[0183]

[0184] [Evaluation Results]

[0185] In the positive electrode active materials of the embodiments, the initial discharge capacity was significantly improved compared with the positive electrode active materials of Comparative Examples 1 and 4 which did not have a coating layer and Comparative Example 2 which had a low coating rate.

[0186] Furthermore, the positive electrode active materials (W coverage 61-91%) in Examples 2 to 4 also showed higher initial discharge capacity compared to the positive electrode active material (Nb coverage 83%) in Comparative Example 3, which was coated with a compound containing lithium and niobium.

[0187] In addition, in Comparative Example 4, where no tungsten compound was mixed in the positive electrode active material slurry during the coating formation process, the initial discharge capacity was significantly reduced compared to Comparative Example 1, which did not undergo the coating formation process.

[0188] According to the present invention, a positive electrode active material suitable for use in the positive electrode of an all-solid-state lithium-ion secondary battery requiring high battery capacity can be provided.

[0189] It should be noted that the technical scope of the present invention is not limited to the methods described in the above embodiments, etc. Sometimes, one or more of the elements described in the above embodiments, etc. are omitted. In addition, the elements described in the above embodiments, etc., can be appropriately combined. Furthermore, to the extent permitted by law, the disclosure of Japanese Patent Application No. 2023-132647 and all documents cited in the above embodiments, etc., are incorporated as part of the text.

[0190] Explanation of reference numerals in the attached figures

[0191] 1…Lithium transition metal composite oxide, 2…Coating layer, 10…Positive electrode active material, SBA…Experimental battery, PC…Positive electrode container, NC…Negative electrode container, ISV…Insulating sleeve, C…Powder pressing unit, PL…Positive electrode layer, NL…Negative electrode layer, SEL…Solid electrolyte layer, LCC…Lower current collector, UCC…Upper current collector, P…Pin, PSW…Pressure screw, W…Hemispherical washer, OL…O-ring, SV…Sleeve, SW…Screw, N…Nut.

Claims

1. A positive electrode active material for all-solid-state lithium-ion secondary batteries, which has the following characteristics: Lithium transition metal composite oxides, which are composed of secondary particles formed by the aggregation of multiple primary particles, and A coating layer that covers the surface of the secondary particles; The lithium transition metal composite oxide contains lithium, nickel, and any cobalt and element M, wherein, Element M is an added element other than lithium, nickel, cobalt, and oxygen. The coating layer contains a compound containing at least lithium and tungsten. The tungsten coverage P on the surface of the secondary particles, calculated by Equation 1 below, is 30% or more and 95% or less. P=(W / (W+Ni+Co+M))×100(%)…(Formula 1) W: The amount of tungsten measured by X-ray photoelectron spectrophotometry (XPS). Ni: The amount of nickel quantified by X-ray photoelectron spectrophotometry (XPS). Co: The amount of cobalt quantified by X-ray photoelectron spectrophotometry (XPS). M: The amount of element M quantified by X-ray photoelectron spectrophotometry (XPS), where element M does not include tungsten.

2. The positive electrode active material for all-solid-state lithium-ion secondary batteries 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) Wherein, 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 all-solid-state lithium-ion secondary batteries according to claim 1 or 2, wherein, The lithium transition metal composite oxide contains tungsten-containing compounds between the primary particles within the secondary particles.

4. The positive electrode active material for all-solid-state lithium-ion secondary batteries according to claim 1 or 2, wherein, The coverage rate P is above 60% and below 95%.

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 above 80% and below 95%.

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

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

8. The positive electrode active material for an all-solid-state lithium-ion secondary battery according to claim 1 or 2, wherein, The pore volume of the positive electrode active material is 0.001 cm³. 3 / g or more and 0.008cm 3 The positive electrode active material has an average pore size of 1 nm or more and 10 nm or less per g.

9. A fully solid-state lithium-ion secondary battery, comprising a positive electrode, a negative electrode, and a solid electrolyte. The positive electrode comprises the positive electrode active material for all-solid-state lithium-ion secondary batteries as described in claim 1 or 2.

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