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

Abstract

The purpose of the present invention is to provide: a positive electrode active material for an all-solid-state lithium ion secondary battery, said positive electrode active material having high battery capacity; and a method for producing the positive electrode active material. The positive electrode active material for an all-solid-state lithium ion secondary battery has particles of a lithium-nickel composite oxide and a coating layer that coats the surfaces of the particles, the particles of the lithium-nickel composite oxide have a crystal structure belonging to space group R-3m, the particles of the lithium-nickel composite oxide contain at least Li, Ni, and elements M and Nb, and the mass ratio of the elements is Li: Ni: M: Nb = a: (1-x-y): x: y (0.98 < = a < = 1.15, 0 lt; x is less than or equal to 0.5, 0lt; y is less than or equal to 0.03, 0lt; x + y < = 0.5), the crystallite diameter is 140 nm or less, the amount of eluted lithium ions is 0.30-1.00 mass%, and the coating layer is composed of a composite oxide containing Li and at least one element selected from the group consisting of Al and the like.

Description

[0001] This application is a divisional application of Chinese patent application filed on July 29, 2021, with application number 202180059735.X and invention title "Positive electrode active material for all-solid-state lithium-ion secondary batteries and manufacturing method thereof". Technical Field

[0002] This invention relates to the positive electrode active material for all-solid-state lithium-ion secondary batteries and its manufacturing method. Background Technology

[0003] In recent years, with increasing environmental awareness, there is a growing trend of shifting from gasoline vehicles to hybrid and electric vehicles. There is a strong desire to develop small, lightweight, high-energy-density secondary batteries essential for the widespread adoption of electric vehicles. Lithium-ion batteries are one such secondary battery.

[0004] 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.

[0005] In addition, when using non-aqueous electrolytes as electrolytes, for example, electrolytes obtained by dissolving Li salts such as LiClO4 and LiPF6 in organic solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate as supporting salts.

[0006] Among the components of lithium-ion secondary batteries, non-aqueous electrolytes, in particular, are the main factors limiting battery performance, such as high-speed charging, thermal stability, and battery life, due to their chemical properties, including heat resistance and potential window. Therefore, research and development are actively underway for all-solid-state lithium-ion secondary batteries (hereinafter also referred to as "all-solid-state batteries") that improve these battery performance by using a solid electrolyte instead of a non-aqueous electrolyte.

[0007] For example, Patent Document 1 describes that sulfide solid electrolytes have high lithium-ion conductivity during charge and discharge, making them suitable for all-solid-state batteries. However, as disclosed in Non-Patent Document 1, if the sulfide 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 charge and discharge, forming a high-resistivity phase at the interface and hindering the operation of the all-solid-state battery. This is because, at the contact interface, the concentration of conductive ions varies with the electrochemical potential, thereby forming a space charge layer with a different ionic conductivity than the bulk layer, resulting in higher resistance.

[0008] Therefore, for example, in Patent Document 2, in order to prevent the solid electrolyte from contacting the positive electrode active material (oxide) and to suppress the formation of a high-resistivity phase, a technique is proposed to set a coating layer composed of LiNbO3 on the surface of the positive electrode active material.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2014-056661

[0012] Patent Document 2: Japanese Patent Application Publication No. 2010-170715

[0013] Patent Document 3: Japanese Patent Application Publication No. 2011-116580

[0014] Non-patent literature

[0015] Non-patent literature 1: Narumi Ohta et al., “LiCoO2 with LiNbO3-coated LiCoO2 as cathode material for all solid-state lithium secondary batteries”, Electrochemistry Communications 9 (2007) 1486-1490. Summary of the Invention

[0016] The problem that the invention aims to solve

[0017] However, to achieve high energy density in lithium-ion secondary batteries, it is preferable to use LiNiO2 and LiNiO2 with large charge / discharge capacity. 0.80 Co 0.15 Al 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2 and other positive electrode active materials with high Ni ratios were used. Therefore, the inventors investigated the application possibilities of positive electrode active materials with high Ni ratios in all-solid-state lithium-ion secondary batteries. As a result, the inventors discovered that, when using a solid electrolyte, it is possible to design a battery composed of cells connected in series. Therefore, compared to the use of non-aqueous electrolytes, although the overall energy density of the battery is improved, the energy density obtained from positive electrode active materials with high Ni ratios still does not reach the expected energy density or battery capacity.

[0018] In view of the above problems, an object of the present invention is to provide a positive electrode active material which has a higher battery capacity when a positive electrode active material having a high Ni ratio is used as the positive electrode active material of a all-solid-state battery.

[0019] Method for solving the problem

[0020] A first aspect of the present invention provides a positive electrode active material for an all-solid-state lithium ion secondary battery, which has particles of a lithium nickel composite oxide and a coating layer covering the surface of the particles. The particles of the lithium nickel composite oxide have a crystal structure belonging to the space group R-3m. The particles of the lithium nickel composite oxide contain at least Li, Ni, element M and Nb. The molar ratio of each element is expressed as Li:Ni:M:Nb = a:(1-x-y):x:y (0.98 ≤ a ≤ 1.15, 0 < x ≤ 0.5, 0 < y ≤ 0.03, 0 < x + y ≤ 0.5, and element M is at least one selected from the group consisting of Co, Al, Mn, Zr, Si, Zn and Ti). The crystallite diameter calculated from the diffraction peak attributed to the (003) plane measured by XRD by the Scherrer method is 140 nm or less. The amount of eluted lithium ions determined by neutral titration is 0.30 mass% or more and 1.00 mass% or less with respect to the total amount of the particles of the lithium nickel composite oxide. The coating layer is composed of a composite oxide containing Li and at least one element selected from the group consisting of Al, Si, Ti, V, Ga, Ge, Zr, Nb, Mo, Ta and W.

[0021] In addition, it is preferable that the particles of the lithium nickel composite oxide contain secondary particles formed by aggregation of a plurality of primary particles, have a porous structure in which there are a plurality of void portions in the secondary particles where the primary particles do not exist, and the specific surface area measured by the nitrogen adsorption BET method is 0.3 m 2 / g or more and 2.0 m 2 / g or less. In addition, it is preferable that at least a part of the niobium contained in the particles of the lithium nickel composite oxide is concentrated at the primary particle interface. In addition, preferably, in the cumulative volume distribution curve of the particle size distribution, the particle diameter (D50) corresponding to the cumulative volume rate of 50% of the particles of the lithium nickel composite oxide is 7 μm or less. The average thickness of the coating layer is preferably 1 nm or more and 15 nm or less.

[0022] A second aspect of the present invention provides a method for manufacturing the above-mentioned positive electrode active material for all-solid-state lithium-ion secondary batteries, comprising: a mixing step, wherein a nickel composite compound, a niobium compound and a lithium compound are mixed to obtain a mixture; a calcination step, wherein the mixture is calcined to obtain lithium-nickel composite oxide particles; and a coating step, wherein a coating liquid comprising at least one element selected from the group consisting of Al, Si, Ti, V, Ga, Ge, Zr, Nb, Mo, Ta and W is attached to the surface of the lithium-nickel composite oxide particles to form a coating layer.

[0023] Furthermore, preferably, the nickel composite compound comprises a nickel composite oxide, and the above-described manufacturing method includes an oxidation calcination step of oxidizing and calcining a nickel composite hydroxide that has been adjusted by a crystallization reaction to obtain a nickel composite oxide. Additionally, preferably, after the coating step, a heat treatment step is performed on the lithium-nickel composite oxide particles with the coating layer formed on their surface, heat-treating them at 300°C or higher.

[0024] Invention Effects

[0025] When the positive electrode active material of the present invention is used as the positive electrode active material in an all-solid-state battery, the battery capacity is increased. Furthermore, the manufacturing method of the present invention enables the high-efficiency production of this positive electrode active material. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating an example of the positive electrode active material of this embodiment.

[0027] Figure 2 This is a diagram illustrating an example of a method for manufacturing the positive electrode active material according to this embodiment.

[0028] Figure 3 This is a diagram illustrating an example of a method for manufacturing the nickel composite compound according to this embodiment.

[0029] Figure 4 This is an explanatory diagram showing the cross-section of an evaluation battery used in battery evaluation.

[0030] Symbol Explanation

[0031] 1…Particles of lithium-nickel 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…Plug; PSW…Pressure screw; W…Hemispherical washer; OL…O-ring; SV sleeve; SW…Screw; N…Nut. Detailed Implementation

[0032] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. It should be noted that in the drawings, in order to facilitate understanding of each structure, sometimes a part is emphasized or a part is simplified for representation, and the actual structure, shape, scale, etc. are different. In addition, the present invention is not limited to the following embodiments, and various modifications and substitutions can be made to the following embodiments without departing from the scope of the present invention.

[0033] 1. Positive electrode active material for all-solid-state lithium-ion secondary battery

[0034] First, a constitutional example of the positive electrode active material for the all-solid-state lithium-ion secondary battery of the present embodiment (hereinafter, also referred to as "positive electrode active material") will be described.

[0035] Figure 1 is a diagram schematically showing an example of the positive electrode active material of the present embodiment. As Figure 1 shown, the positive electrode active material 10 has particles 1 of a lithium nickel composite oxide and a coating layer 2 covering the surface of the particles 1. Hereinafter, each component will be described.

[0036] (1) Particles of lithium nickel composite oxide

[0037] The particles 1 of the lithium nickel composite oxide have a crystal structure belonging to the space group R-3m and are a composite oxide containing at least lithium (Li), nickel (Ni), element M, and Nb.

[0038] (Composition)

[0039] When the molar ratio of the amounts of substances of the respective elements contained in the particles 1 of the lithium nickel composite oxide is represented by Li:Ni:M:Nb = a:(1-x-y):x:y, 0.98 ≤ a ≤ 1.15, 0 < x ≤ 0.5, 0 < y ≤ 0.03, and 0 < x + y ≤ 0.5 are satisfied. In addition, in the above molar ratio of the amounts of substances, it is preferably 0.98 ≤ a ≤ 1.15, 0 < x ≤ 0.3, 0 < y ≤ 0.02, and 0 < x + y ≤ 0.4.

[0040] In the above molar ratio of the amounts of substances, a representing the content ratio of Li is 0.98 ≤ a ≤ 1.15, it can be 0.98 ≤ a ≤ 1.10, it can be 0.98 ≤ a ≤ 1.06, and it can also be 0.98 ≤ a ≤ 1.03. When a is less than 0.98, Li is lacking in the positive electrode active material, which easily leads to a decrease in the capacity as a battery material. When a exceeds 1.15, the crystal structure of the particles 1 of the lithium nickel composite oxide grows excessively, the primary particles become coarser, and cracks in the particles 1 are likely to occur, so the durability is easily impaired.

[0041] In the above molar ratio, (1 - x - y) representing the content ratio of Ni is 0.5 or more and less than 1.0. Additionally, the lower limit range of the content ratio of Ni is preferably 0.6 or more, can be 0.7 or more, and can also be 0.8 or more. The higher the content ratio of (1 - x - y), the lower the voltage required for charging, and as a result, the higher the battery capacity. When (1 - x - y) is less than 0.5, the battery capacity becomes low.

[0042] In the above molar ratio, element M is preferably at least one selected from the group consisting of Co, Al, Mn, Zr, Si, Zn, and Ti. Additionally, element M preferably contains at least one element selected from cobalt (Co), aluminum (Al), and manganese (Mn). Element M can be appropriately selected according to the use and required performance of the secondary battery constituted by the positive electrode active material 10.

[0043] In the above molar ratio, x representing the content ratio of element M is 0 < x ≤ 0.5, preferably 0 < x ≤ 0.3, and can also be 0 < x ≤ 0.2. For example, when element M contains Co and Co is within the above range, it has a high battery capacity and excellent cycle characteristics. Additionally, element M can also contain Co and Al. The range of Co can be, for example, 0 < x ≤ 0.3, and can also be 0 < x ≤ 0.2. The range of Al can be, for example, 0 < x ≤ 0.1, and can also be 0 < x ≤ 0.07.

[0044] In the above molar ratio, y representing the content ratio of Nb is 0 < y ≤ 0.03, preferably 0 < y ≤ 0.02. When y is within the above range, in a all - solid - state battery, it can have a high battery capacity. When y exceeds 0.03, sometimes LiNb3O8 with low activity is generated, resulting in a decrease in battery capacity. Additionally, for example, when 0.001 ≤ y ≤ 0.01, it can have an even higher battery capacity.

[0045] Additionally, the niobium contained in the particles 1 of the lithium nickel composite oxide can be dissolved in the interior of the primary particles or can exist at the interface of the primary particles. At least a part of the niobium is preferably concentrated at the interface of the primary particles. The detailed reason is not yet clear, but for example, it is conceivable that by concentrating niobium at the above primary particle interface, it has the effect of reducing the potential barrier for the movement of Li ions in the secondary particles and increasing the battery capacity. Additionally, it is considered that by concentrating at least a part of the niobium at the interface of the primary particles, it is easy to adjust the amount of dissolved lithium described later to a specific range.

[0046] (Crystal structure)

[0047] The lithium-nickel composite oxide particle 1 has a crystal structure belonging to space group R-3m. When the lithium-nickel composite oxide particle 1 has a crystal structure belonging to space group R-3m, the increase in internal resistance can be suppressed in a secondary battery.

[0048] The crystal structure of the lithium-nickel composite oxide particles 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 powder XRD determination of the lithium-nickel composite oxide particles 1. More preferably, it is preferable to detect only peaks belonging to the layered rock salt type crystal structure of the "R-3m" structure from the aforementioned diffraction pattern.

[0049] It should be noted that the lithium-nickel composite oxide particle 1 can be a single phase of lithium-nickel composite oxide with a crystal structure of "R-3m", but it may not be a single phase. In the case that it is not a single phase and is mixed with other compounds (such as impurities), the intensity of the heterogeneous peaks other than the layered rock salt type structure of "R-3m" structure is preferably no greater than the peak intensity of the layered rock salt type structure belonging to the "R-3m" structure.

[0050] (Crystal diameter)

[0051] The crystallite diameter of the lithium nickel composite oxide particles 1 is preferably 140 nm or less, more preferably 40 nm or more and 140 nm or less. Furthermore, the upper limit of the crystallite diameter can be 130 nm or less. The lower limit of the crystallite diameter can be 50 nm or more. It should be noted that the crystallite diameter can be calculated using the Scherrer method using the peak at (003) of the XRD diffraction pattern described above. When the crystallite diameter of the lithium nickel composite oxide particles 1 exceeds 140 nm, the solid-state diffusion distance within the crystal sometimes increases, leading to a decrease in battery capacity. Furthermore, when the crystallite diameter of the lithium nickel composite oxide particles 1 is less than 40 nm, the crystal structure becomes unstable, and the battery capacity is easily reduced.

[0052] (Amount of lithium ions dissolved)

[0053] For lithium-nickel composite oxide particles 1, the amount of lithium ions dissolved by neutralization titration relative to the total amount of particles 1 is 0.30% by mass or more and 1.00% by mass or less, preferably 0.30% by mass or more and 0.70% by mass or less. It should be noted that the amount of lithium ions dissolved can be determined by neutralization titration using hydrochloric acid, which shows the amount of lithium ions dissolved in water when the lithium-nickel composite oxide particles 1 are dispersed in water. The Warder method or the Winkler method can be used as the neutralization titration method.

[0054] When the amount of dissolved lithium ions in lithium nickel composite oxide particles 1 is less than 0.30% by mass, the battery capacity sometimes decreases. The detailed reasons are not yet clear, but one of the reasons is believed to be that, for example, by containing a specific amount of dissolved lithium ions on the surface of lithium nickel composite oxide particles 1, the direct contact between lithium nickel composite oxide particles 1 and the solid electrolyte is suppressed in all-solid-state batteries, thereby suppressing the formation of a high-resistivity phase.

[0055] It should be noted that when the lithium-nickel composite oxide particles 1 contain niobium, the amount of dissolved lithium ions increases compared to lithium-nickel composite oxides without niobium. Therefore, for example, by using the manufacturing method described later to adjust the niobium content to the above-mentioned range and adjust the amount of dissolved lithium to 0.3% by mass or more, a positive electrode active material with high discharge capacity can be obtained. However, when the amount of dissolved lithium ions in the lithium-nickel composite oxide particles 1 exceeds 1.00% by mass, the discharge capacity decreases.

[0056] (Crystal diameter and amount of dissolved lithium ions)

[0057] Furthermore, the particle 1 of the lithium-nickel composite oxide preferably has a crystallite diameter of less than 140 nm and a dissolved lithium ion content of more than 0.30% by mass.

[0058] That is, for lithium-nickel composite oxide particles 1, even if the crystallite diameter is below 140 nm, the battery capacity may still decrease when the amount of dissolved lithium ions is less than 0.30% by mass. The detailed reasons are not yet clear, but for example, the following speculations are made.

[0059] The lithium-nickel composite oxide particles 1 contain secondary particles composed of multiple primary particles aggregated together. It is believed that the crystallite size of lithium-nickel composite oxide particles 1 is positively correlated with the size of the primary particles constituting the secondary particles; the smaller the crystallite size, the more particle interfaces exist between primary particles. Furthermore, dissolved lithium ions mainly exist at the particle interfaces between primary particles. Therefore, with small crystallite diameters and a large number of primary particle interfaces, if the amount of dissolved lithium ions at the primary particle interfaces (surfaces) is excessively reduced, voids will form at the primary particle interfaces. With a large number of voids at the primary particle interfaces, the positive electrode active material is prone to breakage during the electrode fabrication process of all-solid-state batteries, increasing the contact interface between the lithium-nickel composite oxide particles and the solid electrolyte. Moreover, it is believed that due to the side reactions occurring at this increased contact interface, the generated phase hinders the charge transfer between the electrolyte and the positive electrode active material, thus increasing the battery resistance and reducing the battery capacity.

[0060] On the other hand, when the crystallite diameter of the lithium-nickel composite oxide particles 1 exceeds 140 nm, the battery capacity decreases even if the amount of dissolved lithium ions is 0.30% by mass or more, which is therefore undesirable. This is believed to be because, by coarsening the primary particles, the grain boundaries between primary particles are reduced, resulting in the dissolved lithium ions being distributed in a blocky manner on the surface of the secondary particles. The presence of these dissolved lithium ions themselves constitutes a resistive phase. It should be noted that the crystallite diameter and the amount of dissolved lithium can be adjusted to the above range, for example, by using the manufacturing method of the positive electrode active material described later.

[0061] (Particle structure)

[0062] The lithium-nickel composite oxide particles 1 comprise secondary particles formed by the aggregation of multiple primary particles. Alternatively, the lithium-nickel composite oxide particles 1 may comprise a single primary particle or a mixture of a single primary particle and secondary particles.

[0063] When observed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), the average particle size of the secondary particles is preferably 3.0 μm or more and 7.0 μm or less. Furthermore, these secondary particles are preferably formed by the aggregation of a large number of primary particles with a particle size of 0.1 μm or more and 2.0 μm or less. Additionally, when individual primary particles are included, the primary particles preferably have a particle size of 1.0 μm or more and 7.0 μm or less. It should be noted that the average particle size can be obtained, for example, by calculating the average of the area equivalent circle diameters of 20 or more particles.

[0064] (Average particle size D50)

[0065] In the cumulative volume distribution curve of particle size distribution, the particle size (D50, hereinafter also referred to as "average particle size D50") of the lithium nickel composite oxide particles 1 at 50% of the cumulative volume fraction is preferably 7 μm or less, more preferably 2 μm or more and 7 μm or less, and even more preferably 3 μm or more and 7 μm or less. It should be noted that the average particle size (D50) can be measured using a laser diffraction scattering particle size analyzer.

[0066] When the average particle size D50 of the lithium nickel composite oxide particles 1 is 7 μm or less, the battery capacity per unit cell can be significantly increased in a secondary battery using the positive electrode active material 10 as the positive electrode, and excellent battery characteristics such as thermal stability and high output power can be obtained. On the other hand, when the average particle size D50 is 2 μm or less, it tends to agglomerate when the coating layer 2 is applied, which is therefore not preferred.

[0067] (Width of particle size distribution)

[0068] The value of [(d90-d10) / volume average particle size Mv], which is an indicator of the width of the particle size distribution of the lithium nickel composite oxide particles 1, is not particularly limited. From the viewpoint of uniform particle size, it can be 0.7 or less, 0.6 or less, or 0.55 or less. When the particle size is relatively uniform, it is easy to uniformly coat the coating layer 2 onto the surface of the lithium nickel composite oxide particles 1, resulting in good output characteristics in a secondary battery. It should be noted that the lower limit of [(d90-d10) / volume average particle size Mv] is not particularly limited, for example, it can be 0.3 or more. In addition, from the viewpoint of filling, [(d90-d10) / volume average particle size Mv] can be 0.7 or more, and by using the manufacturing method of the positive electrode active material described later, the coating layer 2 can be coated relatively uniformly.

[0069] It should be noted that d10 refers to the particle size at which the accumulated number of particles of each size, starting from the smallest particle size side, is 10% of the total volume of all particles. Similarly, d90 refers to the particle size at which the accumulated number of particles is 90% of the total volume of all particles. Furthermore, d10, d90, and the volume average particle size Mv, like the average particle size D50, can be determined from the accumulated volume values ​​measured using a laser diffraction scattering particle size analyzer.

[0070] (Specific surface area)

[0071] The specific surface area of ​​lithium-nickel composite oxide particles 1 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 Below / g. With a specific surface area 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.

[0072] (2) Covering layer

[0073] The positive electrode active material 10 has a coating layer 2 on the surface of the lithium nickel composite oxide particles 1. By having a coating layer 2 on the surface of the particles 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.

[0074] The coating layer 2 is composed of a composite oxide containing lithium (Li) and one or more elements selected from the group consisting of Al, Si, Ti, V, Ga, Ge, Zr, Nb, Mo, Ta, and W. It should be noted that the constituent elements of the coating layer 2, excluding lithium (Li) and oxygen (O), can be one or more. For example, the coating layer 2 can be a composite oxide composed of Li and Ti, or a composite oxide composed of Li and Nb.

[0075] (The content of constituent elements of the coating layer)

[0076] The amount of coating layer 2 is not particularly limited and can be determined based on the specific surface area (m²) of the lithium nickel composite oxide particles 1 being coated. 2 The coating amount is adjusted by ( / g). Coating layer 2 is more preferably composed of lithium nickel composite oxide particles 1 per 1m³. 2 The surface area preferably contains the constituent elements (other than Li and O) of the coating layer 2 in a proportion of 30 μmol or more and 600 μmol or less, more preferably 50 μmol or more and 400 μmol or less.

[0077] The per 1m of lithium nickel composite oxide particles 1 2 When the content of the constituent elements (excluding Li and O) of the coating layer 2 is 30 μmol or more, the coating layer 2 can be uniformly disposed on the surface of the lithium nickel composite oxide particles 1.

[0078] Furthermore, by setting the coating layer 2, the reaction between the lithium nickel composite oxide particles 1 and the solid electrolyte can be suppressed, but at the same time, the internal resistance of the secondary battery may also increase. The lithium nickel composite oxide particles 1 per 1m 2 When the content of the constituent elements (other than Li and O) of the coating layer 2 is less than 600 μmol, it can suppress the barrier to the intercalation / deintercalation reaction of the coating layer 2 into the lithium-to-lithium nickel composite oxide particles 1, and reduce the internal resistance.

[0079] In the coating layer 2, there are no particular limitations on the evaluation and calculation methods for the content of the constituent elements (excluding Li and O) of the coating layer 2. For example, it can be calculated as follows.

[0080] First, the content of constituent elements (excluding Li and O) in the coating layer 2 of 1g of positive electrode active material was determined by chemical analysis and other methods. The chemical analysis method used was ICP (Inductively Coupled Plasma) luminescence spectrophotometry.

[0081] On the other hand, the specific surface area of ​​the lithium-nickel composite oxide particles 1 before the coating layer 2 was determined by nitrogen adsorption BET method and other methods.

[0082] Next, the content of the constituent elements (excluding Li and O) of the coating layer 2 in 1g of positive electrode active material is divided by the specific surface area (m²) of the lithium nickel composite oxide particles 1. 2 / g), which can be used to calculate the particle size per 1m of lithium-nickel composite oxide 1. 2 The content of constituent elements (other than Li and O) of the surface area of ​​the coating layer 2.

[0083] It should be noted that when the particles 1 of the lithium nickel composite oxide contain the constituent elements of the coating layer 2 (other than Li and O), the difference in the content of the constituent elements of the coating layer 2 (other than Li and O) before and after coating can be used as the content of the constituent elements of the coating layer 2 (other than Li and O) used in the coating.

[0084] (Average thickness of the coating layer)

[0085] The average thickness of the coating 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.

[0086] It should be noted that the average thickness of coating layer 2 can be calculated as follows: It can be determined by observing with a scanning electron microscope (SEM), transmission electron microscope (TEM), or by analyzing with a spectrometer such as an energy dispersive X-ray spectrometer (EDS) or electron energy loss spectrometer (EELS) attached to these instruments, measuring the layer uniformly formed on the surface of the lithium-nickel composite oxide particles 1, and thus calculating the thickness. It should be noted that, in cases where the thickness of coating layer 2 may vary depending on the measurement location, the thickness of coating layer 2 refers to the average value obtained from measuring multiple locations.

[0087] (Configuration of the coating layer)

[0088] Furthermore, the coating layer 2 preferably exists adjacent to the surface of the lithium nickel composite oxide particles 1. Whether the coating layer 2 exists adjacent to the surface of the particles 1 can be determined by whether the compound containing the constituent elements of the coating layer 2 is freely present from the surface of the lithium nickel composite oxide particles 1. When the coating layer 2 is free from the surface of the lithium nickel composite oxide particles 1, it does not contribute to the battery capacity electrochemically, and therefore becomes the main reason for the reduction in battery capacity per unit weight.

[0089] It should be noted that the surface of the coating layer 2 and the lithium nickel composite oxide particles 1 may not have a clear boundary line. For example, if the lithium nickel composite oxide particles 1 before coating do not contain the constituent elements of the coating layer 2 (other than Li and O), the coating layer 2 refers to the region where the constituent elements of the coating layer 2 (other than Li and O) are detected, or it may include the region where both the constituent elements of the coating layer 2 (other than Li and O) and the elements constituting the lithium nickel composite oxide particles 1 are detected. Furthermore, if the lithium nickel composite oxide particles 1 before coating contain the constituent elements of the coating layer 2 (other than Li and O), it refers to the surface region of the particles constituting the positive electrode active material 10, which is the region (site) where the concentration of the constituent elements of the coating layer 2 (other than Li and O) is higher than that of the central portion of the lithium nickel composite oxide particles 1.

[0090] Furthermore, the constituent elements of the coating layer 2 (other than Li and O) can be partially dissolved from the surface of the lithium nickel composite oxide particles into the interior. For example, when performing a heat treatment process (S40) after the coating process (S30), depending on the conditions at that time, the constituent elements of the coating layer can diffuse into the lithium nickel composite oxide.

[0091] For example, when the coating layer 2 contains Ti and / or Nb, Ti and / or Nb dissolve from the surface of the lithium nickel composite oxide particles 1 into the interior. Thus, the coating layer 2 not only prevents direct contact between the solid electrolyte and the lithium nickel composite oxide particles 1, reducing the chance of reaction, but also reduces the reactivity of the surface layer of the lithium nickel composite oxide particles 1 with the solid electrolyte. It should be noted that in the positive electrode active material 10, in order to fully utilize the improvement effect on cycle performance, it is preferable to adjust the degree of solid solution.

[0092] 2. Method for manufacturing positive electrode active material for all-solid-state lithium-ion secondary batteries

[0093] Next, the manufacturing method 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. By using the manufacturing method of this embodiment, the above-mentioned positive electrode active material 10 can be manufactured with high productivity.

[0094] Figure 2 , Figure 3 This diagram illustrates an example of a method for manufacturing the positive electrode active material according to this embodiment. Figure 2As shown, the method for manufacturing the positive electrode active material in this embodiment includes: a mixing step (S10), in which a nickel composite compound, a niobium compound, and a lithium compound are mixed to obtain a mixture; a calcination step (S20), in which the mixture is calcined to obtain lithium-nickel composite oxide particles; and a coating step (S30), in which a coating liquid is attached to the surface of the lithium-nickel composite oxide particles to form a coating layer. Furthermore, after the coating step (S30), a heat treatment step (S40) can be performed to heat-treat the lithium-nickel composite oxide particles with the coating layer formed on their surface at a temperature of 300°C or higher.

[0095] Furthermore, for nickel composite compounds, the nickel composite compound can be a nickel composite oxide obtained by oxidative calcination of a nickel composite hydroxide that has been modified through a crystallization reaction. For example, such as Figure 3 As shown, nickel composite compounds can be manufactured by a method comprising a crystallization step (S1) and an oxidation calcination step (S2). Each step is described in detail below. It should be noted that the following description is an example of a manufacturing method and does not limit the manufacturing method.

[0096] (Crystallization process: S1)

[0097] In the crystallization process (S1), nickel composite hydroxide, which serves as a precursor for lithium-nickel composite oxides, is prepared by a crystallization reaction.

[0098] For example, a water-soluble compound of each element (metal compound) is used to prepare a raw material aqueous solution in such a way that the mass ratio of each element is equal to the mass ratio of each element contained in the target lithium nickel composite oxide particles. The prepared raw material aqueous solution is then supplied to a reaction tank together with an alkali metal aqueous solution and an ammonium ion donor to carry out a neutralization crystallization reaction, thereby obtaining a nickel composite hydroxide.

[0099] The raw materials of each element can be dissolved simultaneously in water to form a mixed aqueous solution to produce a raw material aqueous solution. Alternatively, a separate aqueous solution can be prepared for each raw material of each element to produce a separate raw material aqueous solution. It should be noted that when there are adverse effects when preparing a raw material aqueous solution in the form of a mixed aqueous solution, it is preferable to prepare a separate raw material aqueous solution for each raw material. For example, if the aqueous solutions of each raw material are acidic and alkaline, it is preferable to prepare a separate raw material aqueous solution for each raw material.

[0100] The metal compounds used as raw materials for each element only need to be water-soluble. Sulfates, chlorides, nitrates, etc., can be used, but from a cost point of view, inexpensive sulfates are preferred. It should be noted that if no suitable water-soluble metal compound is found for element M, etc., it may be omitted from the mixed aqueous solution of the raw materials and added in the oxidation roasting process (S2) and mixing process (S10) described later.

[0101] There are no particular limitations on the aqueous solution of alkali metals, but it is preferable to use one or more of the following: sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, and potassium carbonate.

[0102] There are no particular limitations on the ammonium ion donor, but one or more selected from ammonia water, ammonium carbonate aqueous solution, ammonium chloride aqueous solution, and ammonium sulfate aqueous solution can be preferred.

[0103] The shape of the reaction vessel is not particularly limited, but it is preferably a cylindrical container with internal baffles, in which a stirrer and a temperature controller are installed. The stirrer preferably includes a motor, a shaft, and stirring blades. The temperature controller is preferably a type that circulates a hot medium around the outside of the cylindrical container to heat or cool it.

[0104] In the neutralization crystallization reaction of the raw material aqueous solution, alkali metal aqueous solution and ammonium ion donor in the reaction tank, it is preferable to maintain the pH and ammonia concentration at a fixed value.

[0105] The pH of the aqueous solution in the reaction tank is preferably adjusted to be 11.0 or higher and 12.2 or lower, based on a liquid temperature of 25°C. For example, in the preparation of nickel composite hydroxides, impurities sometimes enter the nickel composite hydroxides due to anions of metal compounds contained in the aqueous solution of the raw materials used. However, by setting the pH of the initial aqueous solution (in the reaction tank) to 11.0 or higher, the introduction of impurities caused by anions can be suppressed. In addition, by setting the pH of the initial aqueous solution to 12.2 or lower, the microparticle formation of the obtained nickel composite hydroxide can be suppressed, resulting in a composite hydroxide with a particle size suitable for charge-discharge reactions.

[0106] The ammonia concentration in the aqueous solution within the reaction tank is preferably adjusted to be 5 g / L or higher and 20 g / L or lower. When the ammonia concentration is set to 5 g / L or higher, Ni in the raw material aqueous solution (mixed aqueous solution) will form an ammonium complex, reducing the rate at which it precipitates from the liquid phase to the solid phase as hydroxide, thus improving the sphericity of the obtained nickel composite hydroxide particles. On the other hand, when the ammonia concentration is set to 20 g / L or lower, excessive increase in the solubility of nickel forming the ammonium complex can be suppressed, allowing for more reliable determination of the target molar ratio of the obtained nickel composite hydroxide. Furthermore, excessive ammonia consumption can be suppressed, which is preferable for industrial applications.

[0107] The atmosphere inside the reaction vessel is preferably a non-oxidizing atmosphere, such as an atmosphere with an oxygen concentration of 1% by volume or less. Setting the atmosphere inside the reaction vessel to a non-oxidizing atmosphere can suppress the oxidation of raw material compounds. For example, it can prevent oxidized cobalt and manganese from precipitating as particulate matter.

[0108] The temperature in the reaction tank during the crystallization process (S1) is preferably maintained at 40°C or higher and 60°C or lower, more preferably at 45°C or higher, and even more preferably at 55°C or lower.

[0109] The temperature of the reaction tank rises due to the heat of reaction and the Joule heat from stirring. Therefore, by maintaining the temperature inside the reaction tank above 40°C, no additional energy is consumed during cooling. Furthermore, by maintaining the temperature inside the reaction tank below 60°C, the evaporation and loss of ammonia from the initial aqueous solution and the reaction aqueous solution can be suppressed, making it easier to maintain the target ammonia concentration.

[0110] The particles (powders) of lithium-nickel composite oxides are preferably particles with a narrow particle size distribution and uniform particle size. To produce such particles, it is necessary to obtain particles with uniform particle size in the nickel composite hydroxide that serves as a precursor. Specifically, methods for obtaining such particles can be exemplified by Patent Document 3, etc.

[0111] (Oxidative roasting process: S2)

[0112] Alternatively, an oxidation roasting step (S2) can be performed after the precursor crystallization step (S1). In the oxidation roasting step (S2), the nickel composite hydroxide obtained in the precursor crystallization step (S1) is oxidized and roasted to obtain a nickel composite oxide. In the oxidation roasting step (S2), heat treatment is performed in an oxygen-containing atmosphere, and then cooled to room temperature, thereby obtaining the nickel composite oxide.

[0113] The calcination conditions in the oxidation calcination process (S2) are not particularly limited. For example, calcination in an oxygen-containing atmosphere or an air atmosphere at a temperature of 500°C to 700°C for 1 hour to 12 hours is preferred. Setting the calcination temperature to 500°C or higher allows for the complete conversion of nickel composite hydroxides into nickel composite oxides. Furthermore, setting the calcination temperature to 700°C or lower helps to prevent the specific surface area of ​​the nickel composite oxides from becoming too small, which is preferable.

[0114] By calcining for more than 1 hour, the temperature inside the calcination vessel can be made uniform, and the reaction can proceed uniformly, which is therefore preferred. In addition, even if calcination is carried out for a longer time than 12 hours, no significant changes are observed in the obtained nickel composite oxide. Therefore, from the viewpoint of energy efficiency, the calcination time is preferably set to less than 12 hours.

[0115] The oxygen concentration in the oxygen-containing atmosphere during roasting is preferably higher than that of air, i.e., 20% by volume or higher. Since an oxygen atmosphere can also be used, the upper limit of the oxygen concentration in the oxygen-containing atmosphere can be set to 100% by volume.

[0116] It should be noted that, for example, if the compound containing element M cannot be co-precipitated in the crystallization step (S1), the compound containing element M can be added relative to the nickel composite hydroxide supplied to the oxidative roasting step (S2) in the same mass ratio as the target substance, and then roasted. There are no particular limitations on the compound containing the added element M; for example, oxides, hydroxides, carbonates, or mixtures thereof can be used.

[0117] Additionally, if slight sintering is observed in the obtained nickel composite oxide after the oxidation roasting process (S2), a crushing process can be applied. It should be noted that in the oxidation roasting process (S2), it is sufficient for at least a portion of the nickel composite hydroxide to be converted into nickel composite oxide; it is not necessary to convert all of the nickel composite hydroxide into oxide.

[0118] (Mixing process: S10)

[0119] The mixing process (S10) is a process of mixing nickel composite compound, niobium compound and lithium compound to obtain lithium mixture.

[0120] In the manufacturing method of this embodiment, niobium is added in the solid phase by mixing a niobium compound in the mixing step (S10). Compared with conventional crystallization processes for co-precipitating or coating niobium, solid-phase addition of niobium does not require reagents, making it an addition method with low environmental impact and excellent productivity.

[0121] The nickel composite compound is preferably at least one of nickel composite hydroxide and nickel composite oxide, more preferably nickel composite oxide. Furthermore, the nickel composite compound is preferably obtained by a method comprising the above-described crystallization step (S1) and / or oxidative calcination step (S2).

[0122] Niobium compounds such as niobic acid, niobium oxide, niobium nitrate, and niobium pentachloride can be used. Among these, niobium hydroxide or niobium oxide is preferred from the viewpoint of ease of acquisition and avoiding the introduction of impurities into the calcined lithium-nickel composite oxide.

[0123] When niobium is added in the solid phase, the reactivity can vary depending on the particle size of the added niobium compound. The particle size (D90) corresponding to 90% of the cumulative volume fraction in the cumulative volume distribution curve of the niobium compound is preferably 0.1 μm or more and 20 μm or less, more preferably 0.1 μm or more and 10 μm or less, and even more preferably 0.1 μm or more and 5 μm or less. When the D90 of the niobium compound is less than 0.1 μm, powder processing becomes very difficult. When the D90 of the niobium compound is greater than 20 μm, the reactivity during calcination decreases, and the diffusion of niobium into the lithium-nickel composite oxide particles is insufficient, sometimes failing to ensure thermal stability. Furthermore, if the D90 of niobium is too large, the formation of the coating layer 2 may become uneven. It should be noted that the particle size of the niobium compound can be appropriately adjusted within the above-mentioned particle size range to obtain a positive electrode active material with the desired properties.

[0124] The D90 of niobium compounds can be adjusted to the aforementioned range by pulverizing the raw niobium compound using a ball mill, planetary ball mill, spray mill, bead mill, or needle mill. Alternatively, dry classifiers or sieves can be used for classification as needed. It should be noted that the D90 of niobium compounds can be determined by laser scattering diffraction.

[0125] The niobium compound is mixed in an amount that achieves the target niobium content relative to the total number of Ni and element M atoms contained in the nickel composite compound. The niobium content remains unchanged before and after the calcination process; therefore, the amount of niobium compound added is equivalent to the amount of niobium added to the positive electrode active material.

[0126] There are no particular limitations on the lithium compound used; for example, lithium hydroxide, lithium nitrate, or lithium carbonate, or mixtures thereof, can be used. From the viewpoint of low melting point and high reactivity, lithium hydroxide is preferred as the lithium compound.

[0127] Lithium compounds, for example, can be mixed in amounts with a lithium content of 95 atomic percent or more and 115 atomic percent or less, or 98 atomic percent or more and 115 atomic percent or less, or 98 atomic percent or more and 110 atomic percent or less, relative to the sum of Ni, element M and Nb (Me).

[0128] (Firing process: S20)

[0129] The firing process (S20) is a process of firing the obtained lithium mixture to obtain lithium-nickel composite oxide particles 1. The firing conditions are not particularly limited; for example, it is preferable to fire in an oxygen-containing atmosphere at a temperature of 700°C or higher and 800°C or lower for 1 hour or more and 24 hours or less. Alternatively, after firing, the mixture can be cooled to room temperature to obtain lithium-nickel composite oxide particles 1.

[0130] When the firing temperature is set to 700°C or higher, the crystal structure of the lithium-nickel composite oxide particles 1 can be sufficiently grown. Furthermore, when the firing temperature is set to 800°C or lower, the incorporation of Ni atoms into the Li sites of the obtained lithium-nickel composite oxide particles 1 can be suppressed.

[0131] By setting the firing time to 1 hour or more, the temperature inside the firing vessel can be made uniform, and the reaction can proceed uniformly, which is therefore preferred. In addition, even if the firing time is longer than 24 hours, no significant changes are observed in the resulting lithium-nickel composite oxide. Therefore, from the viewpoint of energy efficiency, the firing time is preferably 24 hours or less, and can be 12 hours or less, 10 hours or less, or 6 hours or less.

[0132] Furthermore, as an oxygen-containing atmosphere, an atmosphere containing 80% by volume or more of oxygen is preferred. This is because by making the oxygen concentration in the atmosphere 80% by volume or more, the mixing of Ni atoms into Li sites in the resulting lithium-nickel composite oxide can be particularly suppressed, and therefore is preferred. Since an oxygen atmosphere can also be used, the upper limit of the oxygen concentration in the oxygen-containing atmosphere can be set to 100% by volume.

[0133] It should be noted that if slight sintering is observed in the particles 1 of the obtained lithium-nickel composite oxide after the sintering process (S20), a crushing process can also be applied.

[0134] (Coating process: S30)

[0135] The coating process (S30) is a process in which the coating liquid is attached to the surface of the obtained lithium nickel composite oxide particles 1 to form a coating layer 2.

[0136] Regarding the formation of the coating layer 2, for example, lithium nickel composite oxide particles 1 are mixed with a coating solution and dried to form the coating layer 2 on the surface of the lithium nickel composite oxide particles 1. Alternatively, as described later, a heat treatment process (S40) can be arbitrarily performed in an oxygen-containing atmosphere after coating. An example of the coating process (S30) will be described below.

[0137] First, a coating liquid is prepared in a specified amount (coating agent preparation step). The coating agent can be determined based on the specific surface area per unit area (m²) of the lithium-nickel composite oxide particles 1 obtained in the calcination process (S20). 2 The coating layer 2 is prepared by determining the content of constituent elements (excluding Li and O) of the coating layer 2 ( / g).

[0138] The coating solution contains at least one element selected from the group consisting of Al, Si, Ti, V, Ga, Ge, Zr, Nb, Mo, Ta, and W. For example, the coating solution can be prepared by dissolving a raw material compound containing the constituent elements of the target coating layer 2 (other than Li and O) in a solvent.

[0139] As a raw material compound, examples include one or more compounds selected from the group consisting of alkoxides and chelates containing complexes having carbonyl groups, peroxide groups, etc.

[0140] From the perspective of uniform coating, the coating liquid only needs to be liquid at the moment it is attached to the surface of the lithium nickel composite oxide particles 1. For example, it can be prepared by dissolving a compound containing the constituent elements of the coating layer 2 in a solvent and being liquid at room temperature. Alternatively, it can be a compound containing the constituent elements of the coating layer 2 with a low melting point and being dissolved in a low-temperature heat treatment.

[0141] It should be noted that the coating solution may or may not contain Li. In the case that the coating solution does not contain Li, in the coating process (S30) and / or the heat treatment process (S40), the Li present in the lithium nickel composite oxide particles 1 reacts with the compound containing the above-mentioned constituent elements in the coating solution to form the coating layer 2.

[0142] Next, a coating solution is applied to the surface of the lithium nickel composite oxide particles 1. The application of the coating solution can be achieved, for example, by mixing the lithium nickel composite oxide particles 1 with the coating solution (mixture preparation step). A conventional mixer can be used for mixing. Alternatively, drying can be performed after mixing (drying step).

[0143] Furthermore, from the viewpoint of forming a more uniform coating layer 2 with a specific thickness, it is preferable to perform the mixture preparation step and the drying step in parallel, and it is preferable to use a rotary flow coating device.

[0144] The coating liquid shrinks during drying, so if the mixture preparation step and drying step are performed only once, gaps may sometimes form in the formed coating layer 2, failing to fully protect the lithium nickel composite oxide particles 1 from contact with the solid electrolyte. However, when using a rotary flow coating apparatus, since the coating liquid is sprayed onto the lithium nickel composite oxide particles 1 flowing with a heated airflow in the apparatus, the mixture preparation step and drying step are performed in parallel and repeatedly, resulting in a uniform coating layer without gaps, which is therefore preferable.

[0145] In the drying step, it is preferable to perform drying at a temperature sufficient to remove solvents and other contaminants from the coating agent. For example, when using a rotary flow coating apparatus, the supply gas temperature can be set to 80°C or higher and less than 300°C. Additionally, after the coating process, further drying can be performed using a stationary dryer.

[0146] The atmosphere for the drying step is not particularly limited. However, in order to prevent the lithium nickel composite oxide particles 1 from reacting with moisture in the atmosphere, it is preferable to use an inactive atmosphere such as air, nitrogen, or argon supplied from a compressor equipped with a dryer.

[0147] (Heat treatment process: S40)

[0148] Furthermore, if necessary, after the coating process (S30), a heat treatment process (S40) can be performed to heat-treat the lithium nickel composite oxide particles 1 on which the coating layer 2 is formed at a temperature of 300°C or higher. Through the heat treatment process (S40), the bonding between the coating layer 2 and the lithium nickel composite oxide particles 1 can be made stronger.

[0149] The heat treatment conditions for the heat treatment process (S40) are not particularly limited, but it is preferable to perform the heat treatment in an oxygen-containing atmosphere at a temperature of 300°C or higher and 600°C or lower for 1 hour or more and 5 hours or less. The oxygen-containing atmosphere may be, for example, an air atmosphere.

[0150] The oxygen concentration in the oxygen-containing atmosphere during the heat treatment process (S40) is preferably higher than or equal to the oxygen concentration of an air atmosphere, i.e., an oxygen concentration of 20% by volume or higher. By setting the oxygen-containing atmosphere during heat treatment to have an oxygen concentration higher than or equal to that of an air atmosphere, the generation of oxygen defects inside the obtained positive electrode active material 10 can be further suppressed. The oxygen-containing atmosphere can be an oxygen atmosphere, and the upper limit of the oxygen concentration of the oxygen-containing atmosphere is 100% by volume.

[0151] When the heat treatment temperature is above 300°C, it is possible to further suppress the residue of impurities contained in the coating liquid inside the positive electrode active material 10. In addition, when the heat treatment temperature is below 600°C, it is possible to suppress excessive diffusion of the components of the coating layer 2 and maintain the morphology of the coating layer 2.

[0152] When the heat treatment time is 1 hour or more, it can further suppress the residue of impurities contained in the coating liquid inside the positive electrode active material 10. Furthermore, even when the heat treatment time is longer than 5 hours, no significant changes are observed in the obtained positive electrode active material 10. Therefore, from the viewpoint of energy efficiency, the heat treatment time is preferably 5 hours or less.

[0153] After the heat treatment process (S40), the material is cooled to room temperature to obtain a positive electrode active material having a lithium nickel composite oxide particle 1 as the final product and a coating layer 2 on its surface.

[0154] It should be noted that the heat treatment step (S40) may be omitted. That is, the positive electrode active material 10 can be manufactured by proceeding to the coating step (S30). This is because, even without the heat treatment step (S40), a coating layer can be uniformly and firmly formed on the surface of the lithium nickel composite oxide particles. Even without the heat treatment step, drying is preferable as needed to reduce or remove solvents, moisture, etc., from the coating agent.

[0155] If slight sintering is observed in the positive electrode active material 10 obtained after the coating process (S30) and / or heat treatment process (S40), further crushing processing can be performed.

[0156] (3) All-solid-state lithium-ion secondary battery

[0157] The all-solid-state lithium-ion secondary battery of this embodiment (hereinafter also referred to as "all-solid-state battery") includes a positive electrode, a negative electrode, and a solid electrolyte, wherein the positive electrode contains the aforementioned positive electrode active material. Hereinafter, the all-solid-state battery of this embodiment will be described separately for each component.

[0158] It should be noted that the embodiments described below are merely illustrative, and all-solid-state batteries can be implemented in various ways with modifications and improvements based on the knowledge of those skilled in the art, as exemplified by the following embodiments. Furthermore, there are no particular limitations on the applications of all-solid-state batteries.

[0159] (positive electrode)

[0160] 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, pressure compression processing or similar methods can be performed.

[0161] The aforementioned positive electrode mixture can be formed by mixing the aforementioned positive electrode active material in powder form with a solid electrolyte.

[0162] Solid electrolytes are added to impart appropriate ionic conductivity to the electrodes.

[0163] 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 oxides and polymer electrolytes such as PEO.

[0164] It should be noted that binders and conductive additives can also be added to the positive electrode mixture.

[0165] The binder plays a role in maintaining the positive electrode active material. 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.

[0166] 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.

[0167] 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.

[0168] However, the method of producing the positive electrode is not limited to the method exemplified above, and other methods can also be used.

[0169] (negative electrode)

[0170] The negative electrode can be formed by molding the negative electrode compound.

[0171] Regarding the negative electrode, although the components and their combination of the negative electrode mixture are different, it is essentially formed in the same way as the positive electrode and is treated in various ways as needed, just like the positive electrode.

[0172] Negative electrode additives can be prepared by mixing a negative electrode active material with a solid electrolyte. For example, an absorbent material capable of absorbing and desorbing lithium ions can be used as the negative electrode active material.

[0173] The absorbent material is not particularly limited; for example, one or more materials selected from natural graphite, artificial graphite, sintered organic compounds such as phenolic resin, and powdered carbonaceous materials such as coke can be used. When this absorbent material is used as the negative electrode active material, Li3PS4 or similar materials can be used as the solid electrolyte, similar to the positive electrode.

[0174] Alternatively, the negative electrode can also be a sheet-like component made of a substance containing a metal alloyed with lithium, such as lithium metal or indium.

[0175] (Solid electrolyte)

[0176] Solid electrolytes are those containing Li +A solid with ion conductivity. As a solid electrolyte, it can be used alone, selected from sulfides, oxides, polymers, etc., or in combination of two or more.

[0177] 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-P₂O₅.

[0178] 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.

[0179] 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, Li3XLa 2 / 3-X TiO3(0≤X≤2 / 3), Li5La3Ta2O 12 Li7La3Zr2O 12 Li6BaLa2Ta2O 12 Li 3.6 Si 0.6 P 0.4 O4, etc.

[0180] 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.

[0181] As a polymer-based solid electrolyte, there are no particular limitations as long as it is a polymeric compound exhibiting ion conductivity; for example, polyethylene oxide, polypropylene oxide, and their copolymers can be used. Furthermore, organic solid electrolytes can contain supporting salts (lithium salts). It should be noted that, in the case of 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.

[0182] (The shape and structure of all-solid-state batteries)

[0183] Next, examples of the configuration and structure of the components of the all-solid-state battery according to this embodiment will be described.

[0184] All-solid-state batteries, composed of the aforementioned positive electrode, negative electrode, and solid electrolyte, can be manufactured in various shapes, such as coin-shaped or stacked. Regardless of the shape, the positive and negative electrodes can be stacked with the solid electrolyte in between. Furthermore, current-collecting leads or the like can be used to connect the positive current collector to the external positive terminal and the negative current collector to the external negative terminal, sealing the battery within a casing to create an all-solid-state battery.

[0185] (Characteristics of all-solid-state batteries)

[0186] An all-solid-state battery of one embodiment of the present invention, which uses the above-described positive electrode active material, exhibits high capacity.

[0187] Specifically, it is preferable to use the positive electrode active material of this embodiment in the positive electrode to form a positive electrode. Figure 4 The test battery shown was used with a current density of 0.2 mA / cm². 2 After charging to the cutoff voltage of 4.3V (vs. Li) and stopping for 1 hour, the discharge capacity when discharging to the cutoff voltage of 2.5V (vs. Li), i.e. the initial discharge capacity, is more than 130mAh / g.

[0188] Example

[0189] The present invention will now be specifically described using examples and comparative examples.

[0190] [Example 1]

[0191] 1. Manufacturing of lithium-nickel composite oxides

[0192] The following steps are used to manufacture lithium-nickel composite oxides.

[0193] (a) Crystallization process

[0194] Add 10L of pure water to a 60L reaction vessel, and maintain the temperature inside the vessel at 50℃ while stirring. At this time, the reaction vessel is set to a nitrogen atmosphere with an oxygen concentration of less than 1% by volume.

[0195] An appropriate amount of 25% sodium hydroxide aqueous solution and 25% ammonia solution were added to the reaction tank to prepare an initial aqueous solution with a pH of 12.8 based on a liquid temperature of 25℃ and an ammonia concentration of 15 g / L in the reaction tank.

[0196] Nickel sulfate and cobalt sulfate were simultaneously dissolved in pure water at a nickel:cobalt mass ratio of Ni:Co = 0.84:0.16 to prepare 25 L of a 2.0 mol / L nickel-cobalt mixed aqueous solution. Separately, 5 L of a 0.37 mol / L aluminum sulfate aqueous solution was prepared.

[0197] Relative to the initial aqueous solution in the reaction tank, 66 mL of a nickel-cobalt mixed aqueous solution was added dropwise at a rate of 109 mL / min to prepare the reaction aqueous solution. At this time, 25% by mass ammonia and 25% by mass sodium hydroxide aqueous solutions were also added dropwise to the initial aqueous solution at a certain rate, and the pH value was maintained at 12.8 based on the temperature of the reaction aqueous solution at 25°C.

[0198] Next, sulfuric acid is added dropwise to the reaction vessel to adjust the pH of the aqueous reaction solution to 11.5. This operation aims to reduce the rate at which the Ni, Co, and Al composite hydroxide precipitates from the liquid phase to the solid phase in the subsequent precursor crystallization process by lowering the pH, thereby improving the uniformity of the particle size distribution and the sphericity of the particles.

[0199] After pH control, 26.2 L of a nickel-cobalt mixed aqueous solution was added dropwise at a rate of 109.2 mL / min relative to the reaction aqueous solution in the reaction tank, followed simultaneously by 5.9 L of an aluminum sulfate aqueous solution at a rate of 24.8 mL / min. At this time, 25% (w / w) ammonia and 25% (w / w) sodium hydroxide aqueous solutions were also added dropwise to the initial aqueous solution at a certain rate. The pH of the reaction aqueous solution was controlled at 11.5 based on a liquid temperature of 25°C, and the ammonia concentration was maintained at 15 g / L.

[0200] After adding the complete amount of the nickel-cobalt mixed aqueous solution and the aluminum sulfate aqueous solution, the pH of the reaction solution in the reaction tank was raised to 13.0 based on a liquid temperature of 25°C. This operation aims to precipitate the nickel ions that have undergone ammonia complexation and dissolved in the liquid phase onto the hydroxide to obtain the target chemical composition.

[0201] Then, the reaction aqueous solution was subjected to solid-liquid separation using a Buchner funnel, a filter tank, and a vacuum filter with a vacuum pump. Subsequently, the solid phase was dispersed in 20 L of pure water at 40 °C and the solid-liquid separation process was repeated twice to remove water-soluble impurities such as sodium sulfate from the nickel complex hydroxide.

[0202] After the solid-liquid separation was completed, the filter cake-like solid phase was dried in an air atmosphere at 120°C for 24 hours. Then, a powdered nickel composite hydroxide was obtained by using a 100μm mesh sieve.

[0203] (b) Oxidative roasting process

[0204] Using an atmosphere firing furnace (manufactured by SILICONIT, BM-50100M), the prepared composite hydroxide was fired at 600°C for 2 hours in an air atmosphere with an oxygen concentration of 20% by volume, and then cooled to room temperature to obtain nickel composite oxide.

[0205] (c) Mixing process

[0206] Niobic acid (Nb₂O₃·xH₂O) powder manufactured by Mitsuwa Chemical Co., Ltd. was added to a nickel composite oxide such that the mass of Nb was 0.1% relative to the total mass of Ni, Co, and Al contained in the nickel composite oxide. Lithium hydroxide monohydrate, weighed in such a way that the mass of Li was 103% relative to the total mass of Ni, Co, Al, and Nb, was added. The mixture was then mixed using a turbine mixer (manufactured by DALTON Co., Ltd., T2F) to obtain a lithium mixture.

[0207] (d) Firing process

[0208] The obtained lithium mixture was calcined at 750°C for 5 hours in an oxygen-containing atmosphere with an oxygen concentration of 90% by volume or higher using an atmosphere calcination furnace (SILICONIT, BM-50100M). After that, it was cooled to room temperature. As a result, lithium-nickel composite oxide particles were obtained.

[0209] 2. Evaluation of lithium-nickel composite oxide particles

[0210] The obtained lithium-nickel composite oxide was evaluated as follows.

[0211] (a) Composition

[0212] Analysis using an ICP emission spectrophotometer (VARIAN, 725ES) confirmed that the molar ratio of Li, Ni, Co, Al, and Nb in the lithium-nickel composite oxide was Li:Ni:Co:Al:Nb = 1.04:0.815:0.150:0.034:0.001.

[0213] (b) Crystal structure

[0214] The crystal structure of the lithium-nickel composite oxide particles was determined using XRD (PANALYTICAL, X'Pert, PROMRD), and the results confirmed that it was a layered rock salt type crystal structure with peaks belonging to the R-3m structure detected in the diffraction pattern.

[0215] In addition, when the half-width of the peak belonging to the (003) plane in the diffraction pattern was measured and the size of the microcrystal was calculated using the Scherrer method, it was confirmed to be 123.4 nm.

[0216] (c) Determination of dissolved lithium ions

[0217] The amount of lithium ions dissolved in the lithium-nickel composite oxide was determined by titration. 2.0 g of the lithium-nickel composite oxide was dispersed in 125 mL of pure water, and 2 mL of a 10% barium chloride solution was added. While stirring, the solution was neutralized and titrated with 1 mol / L hydrochloric acid. The amount of 1 mol / L hydrochloric acid required to reach the inflection point near pH 4 of the titration curve was converted into the amount of Li due to the dissolved lithium ions. The result showed that the amount of lithium ions dissolved in the lithium-nickel composite oxide was 0.31 wt%.

[0218] (d) Specific surface area

[0219] The BET specific surface area of ​​the lithium-nickel composite oxide was determined using a fully automated BET specific surface area measuring device (Mountech Corporation, Macsorb). The result was confirmed to be 0.49 m². 2 / g.

[0220] (e) Particle size distribution

[0221] The particle size distribution of lithium-nickel composite oxides was determined using a laser diffraction scattering particle size distribution measuring device (Microtrac HRA, manufactured by Nikkiso Corporation). Based on the results, the average particle size D50 on a volume basis was confirmed to be 5.4 μm, and the deviation index ((D90-D10) / MV) calculated from D10, D90, and MV was 0.44.

[0222] 3. Coating of lithium-nickel composite oxides

[0223] The obtained lithium-nickel composite oxide is subjected to the following coating process.

[0224] In a solution obtained by adding 30 ml of isopropanol (IPA) and 1.8 g of tetrabutoxytitanium (Ti-BuOH) and stirring, a solution containing 20 ml of IPA and 0.9 g of acetylacetone was added dropwise while heating and stirring at 60°C. This was done to avoid directly adding a high concentration of acetylacetone and Ti solution. Then, a solution obtained by adding 0.54 g of pure water to 10 ml of IPA was added to the cooled solution above. Finally, 65 ml of IPA was added to the resulting solution to adjust the coating solution.

[0225] Using the above-mentioned coating liquid, 500g of lithium-nickel composite oxide was coated using a rotary flow coating device (MP-01, Powrex).

[0226] For 500g of lithium-nickel composite oxide, the flow rate is 0.3m / s² when heated to 120°C. 3 Air flows through the chamber at a rate of 1 h, and the coating liquid is sprayed onto the lithium-nickel composite oxide at a rate of 1.7 ml / min.

[0227] After the coating liquid is completely sprayed, the lithium-nickel composite oxide is recovered from the chamber and heat-treated at 400°C for 10 hours in an atmosphere sintering furnace (manufactured by SILICONIT, BM-50100M) under oxygen flow. Then, it is cooled to room temperature to obtain lithium-nickel composite oxide particles (positive electrode active material) with a coating layer (containing Li and Ti).

[0228] 4. Evaluation of coated lithium-nickel composite oxide particles

[0229] (a) Composition

[0230] Analysis using an ICP-based spectrophotometer (VARIAN 725ES) confirmed that the coated lithium-nickel composite oxide contained 0.88 wt% Ti, with a Ti content of 370 μmol / m² per unit area of ​​the substrate. 2 .

[0231] (b) Thickness of the coating

[0232] The coated lithium-nickel composite oxide, which was thinned using a low-temperature ion slicer (JEOL, IB-09060CIS) and observed by TEM (JEOL, JEM-ARM200F), was confirmed to have a coating thickness of 11 nm.

[0233] 5. Fabrication of all-solid-state secondary batteries

[0234] In evaluating the capacity of the obtained positive electrode active material, the following methods were used: Figure 4 The battery shown (hereinafter referred to as the "experimental battery").

[0235] (Composition of the experimental battery)

[0236] like Figure 4 As shown, the test battery SBA has a housing with a negative electrode container NC and a positive electrode container PC, and a powder pressing unit C housed in the housing.

[0237] The housing has a hollow negative electrode container NC with one open end and a positive electrode container PC disposed at the opening of the negative electrode container NC. A space for accommodating the compressed powder unit C is formed between the positive electrode container PC and the negative electrode container NC. The positive electrode container PC is fixed to the negative electrode container NC, for example, by a wing screw SW. The negative electrode container NC has a negative terminal, and the positive electrode container PC has a positive terminal. The housing also has an insulating sleeve ISV. The negative electrode container NC and the positive electrode container PC are fixed in a non-contact manner by means of the insulating sleeve ISV.

[0238] A pressure screw PSW is provided at the closed end of the negative electrode container NC. After the positive electrode container PC is fixed to the negative electrode container NC, the pressure screw PSW is screwed into the receiving space of the powder pressing unit C, thereby maintaining the powder pressing unit C under pressure through the hemispherical washer W. Additionally, a screw-in plug P is provided at the end of the negative electrode container NC where the pressure screw PSW is located. O-rings OL are provided between the negative electrode container NC and the positive electrode container PC, and between the negative electrode container NC and the plug P, sealing the gap between the negative electrode container NC and the positive electrode container PC and maintaining the airtightness of the housing.

[0239] The powder compaction unit C is a granular structure formed by stacking the positive electrode layer PL, the solid electrolyte layer SEL, and the negative electrode layer NL in this order. The positive electrode layer PL is in contact with the inner surface of the positive electrode container PC through the lower current collector LCC. The negative electrode layer NL is in contact with the inner surface of the negative electrode container NC through the upper current collector UCC, the hemispherical washer W, and the pressure screw PSW. The lower current collector LCC, the powder compaction unit C, and the upper current collector UCC are protected by the sleeve SV to prevent the positive electrode layer PL and the negative electrode layer NL from making electrical contact.

[0240] (Evaluation of battery manufacturing)

[0241] The experimental battery SBA was fabricated as follows.

[0242] First, 80 mg of the synthesized solid electrolyte was pressurized at 25 MPa using a particle forming apparatus to obtain solid electrolyte particles with a diameter of 10 mm. Next, 70 mg of positive electrode active material and 30 mg of solid electrolyte were mixed in a mortar. 15 mg of the solid electrolyte particles and the mixture of positive electrode active material and solid electrolyte were placed in the particle forming apparatus and pressurized at 360 MPa to form a positive electrode layer on the solid electrolyte particles. From bottom to top, the lower current collector LCC, particles with the positive electrode layer PL facing downwards, indium (In) foil (negative electrode layer NL), and the upper current collector UCC were stacked sequentially and pressurized at 9 kN to form the electrode (pressed powder unit C). The electrode (pressed powder unit C) was sealed into a casing and tightened with a torque of 6–7 N·m using a pressure screw. The experimental battery SBA was fabricated in a glove box with an Ar atmosphere where the dew point was controlled to -80°C.

[0243] 6. Evaluation of all-solid-state secondary batteries

[0244] The charge-discharge capacity, which represents the performance of the experimental battery, is evaluated as follows.

[0245] (a) Initial discharge capacity

[0246] The initial discharge capacity was evaluated as follows: After the test battery with indium foil as the negative electrode was fabricated and left for approximately 24 hours, and the open circuit voltage (OCV) stabilized, the current density relative to the positive electrode was set to 0.2 mA / cm². 2 The battery was charged to a cutoff voltage of 3.7V (vs. Li-In), and after a 1-hour pause, the discharge capacity (initial discharge capacity) was measured when the battery was discharged to a cutoff voltage of 1.9V (vs. Li-In). The result was 134 mAh / g.

[0247] [Example 2]

[0248] Except that the Nb addition amount in the lithium-nickel composite oxide synthesis process of Example 1 was set to 0.8%, coated lithium-nickel composite oxides were synthesized under the same conditions as in Example 1. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0249] [Example 3]

[0250] Except that the Nb addition amount in the lithium-nickel composite oxide synthesis process of Example 1 was 1.2%, the coated lithium-nickel composite oxide was synthesized under the same conditions as in Example 1. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0251] [Example 4]

[0252] Except that the Nb addition amount in the lithium-nickel composite oxide synthesis process of Example 1 was 3%, the coated lithium-nickel composite oxide was synthesized under the same conditions as in Example 1. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0253] [Example 5]

[0254] Except that the firing time in the lithium-nickel composite oxide synthesis process of Example 2 was set to 12 hours, the coated lithium-nickel composite oxide was synthesized under the same conditions as in Example 2. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0255] [Example 6]

[0256] Except that the firing time in the lithium-nickel composite oxide synthesis process of Example 3 was set to 12 hours, the coated lithium-nickel composite oxide was synthesized under the same conditions as in Example 3. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0257] [Example 7]

[0258] For the lithium-nickel composite oxide obtained in Example 2, lithium niobate was coated in the coating process, and heat treatment was performed under the following conditions. Otherwise, the coated lithium-nickel composite oxide was synthesized under the same conditions as in Example 2. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0259] After the coating liquid is completely sprayed, the lithium-nickel composite oxide is recovered from the chamber and heat-treated at atmospheric pressure and 350°C for 1 hour using an atmosphere sintering furnace (manufactured by SILICONIT, BM-50100M). Then, it is cooled to room temperature to obtain lithium-nickel composite oxide particles (positive electrode active material) with a coating layer (containing Li and Nb).

[0260] [Example 8]

[0261] Except that the proportion a of Li in the lithium-nickel composite oxide synthesis process of Example 6 was set to 1.00, the coated lithium-nickel composite oxide was synthesized under the same conditions as in Example 6. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0262] [Example 9]

[0263] Except that the proportion of Li (a) in the lithium-nickel composite oxide synthesis process of Example 6 was set to 1.09, the coated lithium-nickel composite oxide was synthesized under the same conditions as in Example 6. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0264] [Example 10]

[0265] Except that the proportion of Ni (1-xy) in the lithium-nickel composite oxide synthesis process of Example 6 is set to 0.85 and the proportion of Co (xy) is set to 0.85. 1 Except for a value of 0.116, coated lithium-nickel composite oxides were synthesized under the same conditions as in Example 6. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0266] [Example 11]

[0267] Except that the proportion of Ni (1-xy) in the lithium-nickel composite oxide synthesis process of Example 6 is set to 0.744 and the proportion of Co (xy) is set to 0.744. 1 Except for a value of 0.222, coated lithium-nickel composite oxides were synthesized under the same conditions as in Example 6. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0268] [Comparative Example 1]

[0269] Except that Nb was not added in the lithium-nickel composite oxide synthesis process of Example 1, the coated lithium-nickel composite oxide was synthesized under the same conditions as in Example 1. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0270] [Comparative Example 2]

[0271] Except that the firing temperature in the lithium-nickel composite oxide synthesis process of Comparative Example 1 was set to 735°C, the coated lithium-nickel composite oxide was synthesized under the same conditions as Comparative Example 1. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0272] [Comparative Example 3]

[0273] Except that the Nb addition amount in the lithium-nickel composite oxide synthesis process of Example 1 was 5 atomic%, the coated lithium-nickel composite oxide was synthesized under the same conditions as in Example 1. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0274] [Comparative Example 4]

[0275] Except that the lithium-nickel composite oxide particles of Example 2 were not coated, coated lithium-nickel composite oxides were synthesized under the same conditions as in Example 2. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0276] [Comparative Example 5]

[0277] Except that the proportion a of Li in the lithium-nickel composite oxide synthesis process of Example 6 was set to 1.18, the coated lithium-nickel composite oxide was synthesized under the same conditions as in Example 6. The manufacturing conditions are shown in Table 1, and the results are shown in Table 2.

[0278] [Table 1]

[0279]

[0280] [Table 2]

[0281]

[0282] [Evaluation Results]

[0283] Compared to the positive electrode active material of Comparative Example 1, which does not contain Nb, the discharge capacity in the all-solid-state battery of the examples is significantly improved. Particularly in Example 2 (Nb: 0.8 atomic%), the discharge capacity is significantly improved. Furthermore, in the positive electrode active materials of Examples 1 and 2 with a firing time of 5 hours and the positive electrode active materials of Examples 4 and 5 with a firing time of 12 hours, the characteristics of the positive electrode active material, such as crystallite diameter and specific surface area, and the battery characteristics (initial discharge capacity) are also similar, demonstrating that a positive electrode active material with high battery characteristics can be obtained even with a firing time of 5 hours. In Example 7, where the coating layer contains Nb, a high discharge capacity is also observed, similar to Examples 1-6 where the coating layer contains Ti.

[0284] Furthermore, in Example 8, where the Li ratio (a) was 1.00, and in Example 9, where the Li ratio (a) was 1.09, the same high discharge capacity as in Example 6 (a: 1.04) was also observed. Additionally, based on Examples 10 (Ni ratio: 0.850) and 11 (Ni ratio: 0.744), where the Ni ratio (1-xy) differed from that of Example 6 (Ni ratio: 0.806), it was found that a higher Ni ratio resulted in a higher discharge capacity.

[0285] On the other hand, in the positive electrode active material of Comparative Example 2, which is Nb-free like Comparative Example 1, even with a change in firing temperature (735°C), no increase in discharge capacity was observed; instead, it decreased.

[0286] Furthermore, in the positive electrode active material of Comparative Example 3, where the amount of Nb added exceeded 3 atomic%, the discharge capacity in the all-solid-state battery was also reduced compared to Comparative Examples 1 and 2, where no Nb was added.

[0287] Furthermore, apart from lacking a coating layer, the discharge capacity of the positive electrode active material in Comparative Example 4, manufactured under the same conditions as Example 1, was very low in the all-solid-state battery. This is believed to be because the lack of a coating layer on the surface of the lithium-nickel composite oxide particles led to an increase in the interfacial resistance between the positive electrode active material and the solid electrolyte. Additionally, in Comparative Example 5 (a: 1.18), where the Li ratio (a) was too high, a large amount of lithium was dissolved, resulting in a decrease in discharge capacity.

[0288] Industrial availability

[0289] 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 and a method thereof are provided.

[0290] Furthermore, the technical scope of the present invention is not limited to the embodiments described above. Sometimes, one or more elements described in the embodiments above are omitted. Also, the elements described in the embodiments above can be appropriately combined. Furthermore, wherever permitted by law, all disclosures of the documents cited in the embodiments above are incorporated into the text. Furthermore, wherever permitted by law, the contents of Japanese Patent Application No. 2020-129024 are incorporated into the text.

Claims

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

2. The positive electrode active material for an all-solid-state lithium-ion secondary battery according to claim 1, wherein, The lithium-nickel composite oxide particles comprise secondary particles formed by the aggregation of multiple primary particles. These secondary particles possess a porous structure with multiple voids where the primary particles are absent, and the specific surface area, measured by the nitrogen adsorption BET method, is 0.3 m². 2 / g or more and 2.0m 2 / g or less.

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

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

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

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

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

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

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