Method for producing positive electrode active material particles

Abstract

Provided is a method for producing positive electrode active material particles having a core-shell structure and excellent film thickness uniformity of a coating layer. The method for producing positive electrode active material particles is characterized by including, in the following order: a step (i) for mixing a specific alkoxide monomer and / or an oligomer thereof with an organic solvent to obtain a mixed solution 1; a step (ii) for mixing the mixed solution 1 with core particles formed of a composite oxide to obtain a mixed solution 2; and a step (iii) for adding a specific hydrolyzing agent to the mixed solution 2 to hydrolyze and dehydrate-condense the alkoxide monomer and / or oligomer and deposit the resultant on the surface of the core particles, thereby obtaining a mixed solution 3 in which positive electrode active material particles having a core–shell structure are dispersed, wherein, when the total amount of alkoxy groups contained in the specific alkoxide monomer in the mixed solution 2 is A (mol) and the total amount of water in the hydrolyzing agent in the mixed solution 3 is B (mol), A and B satisfy a specific relationship.

Description

Method for manufacturing positive electrode active material particles

[0001] This disclosure relates to a method for producing positive electrode active material particles that can be used in lithium-ion secondary batteries.

[0002] In recent years, lithium-ion secondary batteries have been used in a wide range of applications, from small electronic devices such as smartphones and laptops to large devices such as electric vehicles. Therefore, lithium-ion secondary batteries require high safety and further performance improvements. To further enhance the safety of lithium-ion secondary batteries, development is underway on all-solid-state batteries, which change the electrolyte from a flammable liquid to a solid electrolyte. To improve the charge-discharge characteristics of all-solid-state batteries, it is generally important to increase the interface between the solid electrolyte and the electrode active material, and to increase the mobility of lithium ions at the interface.

[0003] Electrode active materials include positive electrode active materials and negative electrode active materials. The positive electrode active material uses a metal oxide that can insert and remove lithium ions. Solid electrolytes include sulfide-based and oxide-based types. Sulfide-based electrolytes are softer than oxide-based electrolytes, allowing for a larger interface with the electrode active material. However, at the interface between the positive electrode active material and the solid electrolyte, the composite oxide contained in the positive electrode active material may react with the solid electrolyte. As a result, the resistance generated when lithium ions move at the interface between the positive electrode active material and the solid electrolyte (hereinafter referred to as "interfacial resistance") increases, which can lead to a decrease in output power.

[0004] To address these challenges, a positive electrode active material with a core-shell structure has been proposed, in which the surface of the core particles of a composite oxide is coated with a lithium-ion conductive shell that does not react with the solid electrolyte. Patent Document 1 discloses a method of coating the core particle surface by spraying an alcohol solution mixed with an alkoxide onto the surface of the core particles of a composite oxide using a spray-drying method, and then evaporating the alcohol solution to dryness in a heat treatment step. Patent Document 2 discloses a method of coating the core particle surface by intermittently dropping an aqueous solution in which the constituent material of the shell is dissolved onto a dispersion of core particles of a composite oxide, thereby precipitating the shell on the core particle surface due to differences in solubility, while suppressing the occurrence of areas with high concentrations of the constituent material of the shell. Patent Document 3 discloses a method of coating the core particle surface by adding water to an alcohol solution mixed with an alkoxide, hydrolyzing and dehydrating to form fine particles of the material constituting the shell, and then depositing these fine particles onto the surface of the core particles of the composite oxide. Patent Document 4 discloses a method for coating the surface of core particles by adding a positive electrode active material to an alcohol solution containing an alkoxide, stirring the mixture, and then adding a small amount of water to hydrolyze and dehydrate it.

[0005] Japanese Patent Publication No. 2010-129190, Japanese Patent Publication No. 2014-238957, Japanese Patent Publication No. 2016-072072, Japanese Patent Publication No. 2023-540135

[0006] However, in the manufacturing method shown in Patent Document 1, unreacted alkoxide may react when the alkoxide is deposited on the core particle surface by the spray-drying method to form a shell. In this case, the state of shell coating tends to vary depending on the state of alkoxide deposition on the core particle surface. In the manufacturing method shown in Patent Document 2, the shell constituent material does not precipitate uniformly on the core particle surface, which can cause variations in shell thickness between core particles. In the manufacturing method shown in Patent Document 3, since the surface of the core particles is coated with fine particles of the shell constituent material, areas that are not covered by the shell are likely to occur. In the manufacturing method shown in Patent Document 4, the alkoxide condensate, which is the shell, does not precipitate uniformly on the core particle surface, which can cause variations in shell thickness between core particles. As described above, the present inventors have found that there is room for improvement in the uniformity of the coating layer in the method of coating the surface of the positive electrode active material. If the thickness of the coating layer is not uniform, it becomes impossible to control the thickness to an appropriate level, which can easily lead to the formation of a resistive layer at the interface between the positive electrode active material and the solid electrolyte, resulting in a decrease in output.

[0007] This disclosure solves the above-mentioned problems in the production of positive electrode active material particles with a core-shell structure, and provides a method for producing positive electrode active material particles with excellent uniformity of coating layer thickness.

[0008] This disclosure comprises, in this order, steps (i) of mixing an alkoxide monomer and / or its oligomer with an organic solvent to obtain a mixture 1, (ii) of mixing the mixture 1 with core particles formed of a composite oxide to obtain a mixture 2, and (iii) of adding a hydrolyzing agent to the mixture 2 while stirring to hydrolyze the alkoxide monomer and / or oligomer contained in the mixture 2, dehydrate and condense it, and precipitate it on the surface of the core particles to obtain a mixture 3 in which positive electrode active material particles with a core-shell structure are dispersed, wherein the alkoxide monomer and / or its oligomer comprises a lithium alkoxide monomer and / or its oligomer and at least one alkoxide monomer and / or its oligomer selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, and the hydrolyzing agent comprises at least one hydrolyzing agent selected from the group consisting of water, acidic aqueous solution, and alkaline aqueous solution. The present invention relates to a method for producing positive electrode active material particles, characterized in that, in step (ii), the total amount of alkoxy groups contained in at least one alkoxy monomer selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten in the mixed liquid 2 is A (mol), and in step (iii), the total amount of water in the hydrolyzing agent contained in the mixed liquid 3 is B (mol), and A and B satisfy the following formula (1): B / A ≥ 3.0 (1)

[0009] According to this disclosure, a method for producing positive electrode active material particles having a core-shell structure and excellent uniformity of coating layer thickness is provided.

[0010] In this disclosure, descriptions of numerical ranges such as "XX or greater and YY or less" or "XX to YY" mean a numerical range that includes the lower and upper limits, unless otherwise specified. When numerical ranges are described in steps, the upper and lower limits of each numerical range can be any combination. In addition, in this disclosure, a description such as "at least one selected from the group consisting of XX, YY, and ZZ" means any of the following: XX, YY, ZZ, a combination of XX and YY, a combination of XX and ZZ, a combination of YY and ZZ, or a combination of XX, YY, and ZZ. Note that if XX is a group, multiple values ​​may be selected from XX, and the same applies to YY and ZZ.

[0011] The embodiments of this disclosure will be described in more detail below, but this disclosure is not limited to these embodiments.

[0012] As described above, the coating state of the coating layer can significantly affect the performance of the battery. If the thickness of the coating layer is uneven, the effect of suppressing side reactions between the positive electrode active material and the solid electrolyte is reduced in areas with thin thickness, while the resistance increases in areas with thick thickness, thus reducing the conductivity of lithium ions. Therefore, when positive electrode active material particles with uneven coating layer thickness are used, the charge and discharge characteristics of the battery may deteriorate. The inventors of this invention have conducted diligent studies to solve the above problems and have found that by preparing a mixed solution in which core particles of alkoxide, organic solvent, and metal composite oxide are dispersed, and then adding an amount of hydrolyzing agent satisfying formula (1) while stirring, hydrolysis occurs, and the surface of the core particles is coated while dehydration condensation occurs, thereby improving the uniformity of the coating layer thickness and solving the above problems.

[0013] <Embodiment> The embodiment relates to a method for producing positive electrode active material particles. A method for producing positive electrode active material particles comprises, in this order: (i) mixing an alkoxide monomer and / or its oligomer with an organic solvent to obtain a mixed solution 1; (ii) mixing the mixed solution 1 with core particles formed of a composite oxide to obtain a mixed solution 2; and (iii) adding a hydrolyzing agent to the mixed solution 2 while stirring to hydrolyze the alkoxide monomer and / or oligomer contained in the mixed solution 2, causing dehydration condensation and deposition on the surface of the core particles to obtain a mixed solution 3 in which positive electrode active material particles with a core-shell structure are dispersed; wherein the alkoxide monomer and / or its oligomer comprises a lithium alkoxide monomer and / or its oligomer and at least one alkoxide monomer and / or its oligomer selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten; and the hydrolyzing agent comprises at least one hydrolyzing agent selected from the group consisting of water, acidic aqueous solution, and alkaline aqueous solution. The present invention relates to a method for producing positive electrode active material particles, characterized in that, in step (ii), the total amount of alkoxy groups contained in at least one alkoxy monomer selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten in the mixed liquid 2 is A (mol), and in step (iii), the total amount of water in the hydrolyzing agent contained in the mixed liquid 3 is B (mol), and A and B satisfy the following formula (1): B / A ≥ 3.0 (1)

[0014] The inventors believe that the effects of this disclosure can be obtained by the above manufacturing method as follows: In the above manufacturing method, core particles formed of a composite oxide are added to the mixture 1 in step (ii), so a mixture (mixture 2) can be obtained in which alkoxide monomers and / or their oligomers, an organic solvent, and core particles formed of a composite oxide are uniformly dispersed. Thereafter, in step (iii), an amount of hydrolyzing agent satisfying formula (1) is added while stirring to hydrolyze the alkoxide monomers and / or their oligomers, cause dehydration condensation, and precipitate on the surface of the core particles to form a coating layer.

[0015] As described above, the mixture 2 obtained in step (ii) contains a uniform dispersion of alkoxide monomer and / or its oligomer, an organic solvent, and core particles. Subsequently, in step (iii), hydrolysis and dehydration condensation can be initiated from a state in which the core particles and the alkoxide monomer and / or its oligomer, which are the material for the coating layer, are uniformly dispersed. Furthermore, the fact that the total amount A (mol) of alkoxy groups and the total amount B (mol) of water satisfy formula (1) indicates that the amount of hydrolyzing agent is sufficient to uniformly hydrolyze and dehydrate the alkoxide monomer and / or its oligomer. By adding the amount of hydrolyzing agent that satisfies formula (1) while stirring, the uniformity of the reaction within the system can be further improved. As a result, condensates derived from the alkoxide monomer and / or its oligomer precipitate uniformly on the surface of the core particles, and a coating layer (shell) with a uniform thickness can be formed on the surface of the core particles. In addition, the variation in the probability that core particles are coated with the shell is reduced among the particles.

[0016] In other words, by a manufacturing method including steps (i) to (iii) above, which involves adding a large amount of hydrolyzing agent, the core particle surface can be uniformly coated with condensates derived from alkoxide monomers and / or their oligomers while suppressing variations in the coating state between core particles. As a result, positive electrode active material particles having a core-shell structure and excellent film thickness uniformity can be obtained.

[0017] Step (i) is a step of mixing a lithium alkoxide monomer and / or its oligomer with at least one alkoxide monomer and / or its oligomer selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, and an organic solvent to obtain a mixture 1. The at least one selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten preferably includes niobium, and more preferably niobium.

[0018] In other words, it is preferable that the alkoxide monomer and / or its oligomer includes lithium alkoxide monomer and / or its oligomer and niobium alkoxide monomer and / or its oligomer. It is preferable that the shell constituent material contains a condensate of the alkoxide monomer and / or its oligomer, as this can further reduce the interfacial resistance when lithium ions move at the interface between the positive electrode active material particles and the solid electrolyte particles.

[0019] The alkoxide monomer and / or its oligomer is preferably an alkoxide monomer. That is, step (i) is preferably a mixture of lithium alkoxide, at least one alkoxide selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, and an organic solvent. The number of carbon atoms in the alkoxy group in the alkoxide is, for example, 1 to 6, preferably 1 to 3, and more preferably 1 or 2.

[0020] Known organic solvents can be used. Preferably, the organic solvent contains at least one organic solvent selected from the group consisting of ethanol, 2-propanol, 1-butanol, and toluene. Because these organic solvents have low dielectric constants, the electrical double layer of the condensate derived from the alkoxide monomer and / or its oligomer obtained in step (iii) can be made thinner. As a result, the precipitated condensate is more likely to adhere to the core particle surface, which is thought to further improve the uniformity of the shell film thickness. The alcohols may be used alone or as a mixture of two or more alcohols. Preferably, the organic solvent contains 2-propanol or ethanol. The purity of the organic solvent is preferably 99.9% or higher, and more preferably 99.99% or higher.

[0021] In step (i), the amount of lithium alkoxide monomer and / or its oligomer may be, for example, 50.0 to 500.0 mg or 100.0 to 300.0 mg per 100 ml of organic solvent. In step (ii), the amount may be, for example, 300 to 1500 mg or 400 to 1300 mg per 100 g of the core particles described later that are mixed.

[0022] In step (i), the amount of at least one alkoxide monomer and / or its oligomer selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten is, for example, 0.10 to 2.00 ml or 0.20 to 1.50 ml per 100 ml of organic solvent, and in terms of mass, for example, 0.13 to 2.60 g or 0.26 to 1.95 g. Also, in step (ii), the amount is, for example, 1.50 to 8.00 ml or 1.80 to 7.00 ml per 100 g of the core particles described later to be mixed, and in terms of mass, for example, 1.95 to 10.4 g or 2.34 to 9.10 g.

[0023] In step (i), a step of preparing an alkoxide monomer and / or its oligomer by heating under reflux in a nitrogen atmosphere may be added. That is, step (i) may include a step of preparing an alkoxide monomer and / or its oligomer by heating under reflux in a nitrogen atmosphere, and a step of mixing the prepared alkoxide monomer and / or its oligomer, an organic solvent, to obtain a mixed solution 1.

[0024] By adding a step of preparing an alkoxide monomer and / or its oligomer, it is preferable because the shell of the core-shell structured cathode active material particles obtained in step (iii) can be made uniform in composition at the atomic level. For example, it is preferable to add an alkoxide monomer and / or its oligomer and an organic solvent to a container having a stirring blade, and reflux at, for example, 50 to 95 °C for 1 to 12 h while continuing stirring to obtain a mixed solution 1.

[0025] Step (ii) is a step of mixing the mixed solution 1 and core particles formed of a composite oxide to obtain a mixed solution 2. The core particles formed of a composite oxide preferably contain lithium and are composed of a composite oxide containing at least one selected from the group consisting of manganese, cobalt, nickel, aluminum, iron, and phosphorus. That is, it is preferable that the composite oxide is a composite oxide containing lithium and at least one selected from the group consisting of manganese, cobalt, nickel, aluminum, iron, and phosphorus.

[0026] The core particles formed of a composite oxide are, for example, LiCoO ２ , LiNiO ２ , LiMnO ２ , LiMn ２ O ４ , Li(NiCoMn)O ２ , Li(NiCoAl)O ２ and LiFePO ４ etc. at least one selected from the group consisting of. Note that "Li(NiCoMn)O ２ " and "Li(NiCoAl)O ２In the above, "(NiCoMn)" and "(NiCoAl)" indicate that the sum of the composition ratios in parentheses is 1. As long as the sum is 1, the amounts of individual components are arbitrary. Li(NiCoMn)O ２ For example, Li(Ni １／３ Co １／３ Mn １／３ ) O ２ , Li(Ni ０．５ Co ０．２ Mn ０．３ ) O ２ , Li(Ni ０．８ Co ０．１ Mn ０．１ ) O ２ It may include the following:

[0027] The core particle is Li(NiCoMn)O ２ Li(NiCoMn)O is preferred. ２ Commercially available products can be used, for example, LiNi ０．８ Co ０．１ Mn ０．１ O ２ (Example is PO5038 (product name) manufactured by MSE Supplies). From the viewpoint of material dispersion, it is preferable to mix the mixture 2 and the core particles while continuing to stir. The amount of mixture 2 and the amount of core particles should be controlled so that the desired amount of coating layer is achieved.

[0028] Step (iii) is a step in which a hydrolyzing agent is added to the mixture 2 while stirring, hydrolyzing the alkoxide monomer and / or its oligomer in the mixture 2, causing dehydration condensation, and precipitating the condensate on the surface of the core particles to obtain positive electrode active material particles with a core-shell structure. The hydrolyzing agent is water (H ２ It contains at least one hydrolyzing agent selected from the group consisting of acidic aqueous solutions and alkaline aqueous solutions.

[0029] In step (ii), let A (mol) be the total amount of alkoxy groups contained in the alkoxy monomer selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, which is contained in the mixture 2. Also, in step (iii), let B (mol) be the total amount of water in the hydrolyzing agent contained in the mixture 3. At this time, A and B satisfy the following formula (1): B / A ≥ 3.0 (1)

[0030] B / A is preferably 5.0 or higher, more preferably 6.0 or higher, and even more preferably 10.0 or higher. There is no particular upper limit, but for example, 90.0 or lower is preferred, 70.0 or lower is more preferred, and 60.0 or lower is even more preferred. B / A is preferably 3.0 or higher and 90.0 or lower, more preferably 5.0 or higher and 90.0 or lower, more preferably 5.0 or higher and 70.0 or lower, more preferably 6.0 or higher and 70.0 or lower, more preferably 6.0 or higher and 60.0 or lower, and even more preferably 10.0 or higher and 60.0 or lower. By having B / A within the above range, the amount of hydrolyzing agent can be set to an amount sufficient to uniformly hydrolyze and dehydrate the alkoxide monomer and / or its oligomer. As a result, the reaction uniformity within the system can be further improved.

[0031] From the viewpoint of further improving the uniformity of the coating layer thickness, it is preferable not to hydrolyze the alkoxide monomer and / or its oligomer until step (iii). For example, it is preferable not to substantially add a hydrolyzing agent until step (iii). "Substantially adding a hydrolyzing agent" means intentionally not adding a hydrolyzing agent, and trace amounts of hydrolyzing agents that are inevitably mixed in small amounts during the production of positive electrode active material particles are acceptable. For example, trace amounts of water that are inevitably contained in organic solvents, or amounts of water that are too small to exert a hydrolytic effect, are acceptable. For example, the content ratio of the hydrolyzing agent in mixture 1 and mixture 2 is 0.5% by mass or less, preferably 0.2% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.05% by mass or less. For example, when 2-propanol, methanol, or ethanol with a purity of 99.9% is used, the frequency of contact between water and alkoxide can be extremely reduced, so it is considered that no hydrolytic effect will occur.

[0032] The following describes a method for further improving the uniformity of the film thickness of the shell of the positive electrode active material particles. From the viewpoint of material dispersion, it is preferable to carry out step (iii) while continuing stirring. Specifically, in step (iii), it is preferable to put the mixed liquid 2 into a container having a stirring means, add the hydrolyzing agent while stirring with the stirring means, hydrolyze the alkoxide monomer and / or its oligomer, and precipitate the dehydrated condensed product on the surface of the core particles. By carrying out step (iii) as described above, the uniformity of the film thickness of the shell can be further improved.

[0033] By stirring the mixture 2 and the hydrolyzing agent in a container equipped with a stirring mechanism, the hydrolysis and dehydration condensation reaction can be carried out with a uniform concentration of the hydrolyzing agent, making it possible to precipitate alkoxide-derived condensates more uniformly. As a result, the uniformity of the shell film thickness can be further improved.

[0034] Agitation flow rate Q (m) of the agitation means ３ It is preferable that the relationship between the temperature ( / sec) and the power P (kW) required for stirring satisfies the following equation (2): 1.20 × 10－２ ≤Q / P ≤2.00 × 10 －２ (2) The stirring flow rate Q and the power P can be calculated using the formulas described later. The stirring means is preferably a rotating impeller. That is, it is preferable that the relationship between the stirring flow rate Q of the rotating impeller and the power P required for stirring satisfies the above formula (2).

[0035] In step (iii), the larger the stirring flow rate Q is relative to the power P of the stirring means, the less power is required to stir the mixture 2 and the hydrolyzing agent. This is preferable because it allows hydrolysis and dehydration condensation to be carried out while maintaining a uniform concentration of the hydrolyzing agent, thereby improving the uniformity of the film thickness of the formed coating layer.

[0036] In other words, the Q / P value is 1.20 × 10 －２ As a result, the uniformity of the film thickness of the formed coating layer can be further improved. Also, the Q / P value is 2.00 × 10 －２ The following conditions suppress the entrainment of bubbles generated at the liquid surface, making it easier to maintain a uniform concentration of the hydrolyzing agent and further improving the uniformity of the coating layer thickness. The Q / P value is 1.30 × 10⁻⁶. －２ The above 1.80 x 10 －２ It is more preferable that the following conditions be met: 1.50 × 10 －２ The above 1.80 x 10 －２ The following is even more preferable:

[0037] The power P (kW) of the stirring means is calculated from the following formula (4), and the stirring flow rate Q (m ３ The power ( / sec) is calculated from the following formula (3). The power P and stirring flow rate Q can be calculated from the parameters defined as follows: Stirring flow rate: Q [m ３ / sec]=Nq×n×d ３ (3) Power: P [kW] = Np x ρ x n ３ ×d ５ (4) In equations (3) and (4), Nq is the discharge flow rate, Np is the power, and ρ is the density of the mixed liquid 3 [kg / m³]. ３This shows the rotational speed of the impeller [rps], and d is the blade diameter [m]. The discharge flow rate Nq and power constant Np are unique values ​​that differ for each impeller and are determined by the shape and size of the impeller. For example, in the case of a full-zone impeller, a four-paddle impeller, and a propeller impeller, the discharge flow rate Nq and power constant Np can be calculated using the following formulas: Discharge flow rate: Nq = 0.1 × S Power constant: Np = Cosα × S Where S is the maximum area [m] when the impeller is projected onto a vertical plane. ２ This indicates the minimum angle [rad] between the bottom of the impeller and the horizontal plane in contact with the bottom of the impeller.

[0038] The stirring device used in step (iii) is not particularly limited, but for example, one having a rotating stirring blade as a stirring means, a stirring shaft, a stirring motor, and a stirring container can be used. Examples of stirring means that satisfy the above formula (1) include Fullzone blade (manufactured by Kobe Steel Pantech Co., Ltd.), Maxblend blade (manufactured by Sumitomo Heavy Industries, Ltd.), Sunmerer blade (manufactured by Mitsubishi Heavy Industries, Ltd.), Hi-F mixer blade (manufactured by Soken Chemical Co., Ltd.), and Bendleaf blade (manufactured by Hakko Sangyo Co., Ltd.). When the density of the mixed liquid 3 is 1.0, the Q / P for the Fullzone blade is 1.65 × 10⁻⁶. －２ This results in a four-paddle wing (1.00 x 10 －２ ), propeller blade (7.69 x 10 －３ ), and 12 disc turbine blades (6.87 x 10 －３ The value is greater than ). For this reason, it is preferable to use a full-zone blade as a stirring means.

[0039] In step (iii), the method of adding the hydrolyzing agent is not particularly limited, and any method of addition may be used, such as adding it all at once, adding it in two parts, or adding it continuously. From the viewpoint of making a large change in the concentration of the hydrolyzing agent, it is preferable to add the hydrolyzing agent all at once.

[0040] From the viewpoint of further improving the uniformity of the coating layer thickness, after adding the hydrolyzing agent, the reaction is preferably carried out for, for example, 1 to 48 hours or 2 to 24 hours while continuing to stir. Through this reaction, the alkoxide monomer and / or its oligomer are hydrolyzed and precipitated on the core particle surface while undergoing dehydration condensation to form a coating layer, thereby obtaining positive electrode active material particles.

[0041] The method for recovering the positive electrode active material particles with formed shells is not particularly limited, and known methods can be used. For example, positive electrode active material particles can be recovered by evaporation solidification or solid-liquid separation. That is, step (iii) may include a step of obtaining positive electrode active material particles with a core-shell structure by removing the positive electrode active material particles as solid matter by solid-liquid separation. By performing solid-liquid separation, aggregation of positive electrode active material particles can be suppressed more effectively than by recovery by evaporation to dryness.

[0042] Furthermore, the obtained positive electrode active material particles may be dried and sintered at approximately 200°C to 800°C for the purpose of removing residual carbon and controlling the crystal structure of the coating layer. The particle size of the positive electrode active material particles is not particularly limited and can be set according to the application. Examples of volume-based median diameters (D50) of the positive electrode active material particles include 1 to 100 μm, 2 to 50 μm, 3 to 20 μm, and 5 to 15 μm.

[0043] It is preferable to further include a step of adding a chelating agent to the mixture 1 between step (i) and step (ii). That is, it is preferable that the mixture 1 contains a chelating agent. By adding a chelating agent to the mixture 1, it is possible to suppress the hydrolysis and dehydration condensation of the alkoxy monomer and / or its oligomer in steps (i) and (ii). Therefore, it is preferable because it is easier to keep the alkoxy monomer and / or its oligomer in a state where it does not undergo hydrolysis and dehydration condensation until step (iii).

[0044] In particular, lithium alkoxide monomers and / or their oligomers, and at least one alkoxide monomer and / or its oligomer selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, have a rapid hydrolysis rate and readily react with moisture in the air to form hydroxides. By adding a chelating agent, the stability of the alkoxide monomer and / or its oligomer can be increased, making it easier to suppress hydrolysis in steps (i) and (ii). As a result, the hydrolysis and dehydration condensation of the alkoxide in steps (i) and (ii) is suppressed to form fine particles, and the hydrolysis and dehydration condensation reaction can be initiated when a hydrolyzing agent is added in step (iii), thereby further improving the uniformity of the film thickness of the formed shell.

[0045] Examples of chelating agents that can be used include amines such as triethanolamine, methyldiethanolamine, and ethyldiethanolamine; glycols such as diethylene glycol and dipropylene glycol; ketones such as ethyl acetoethyl; or diketones such as acetylacetone.

[0046] The present disclosure will be described in detail below with reference to examples and comparative examples, but the present disclosure is not limited to these examples.

[0047] Examples relating to the positive electrode active material particles of this disclosure will be described below. <Example of production of positive electrode active material particles 1> [Preparation of mixed solution 1] 100 ml of 2-propanol (super dehydrated) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) is added to a container having a full-zone blade as a stirring device, and LiOC is added while stirring. ２ H ５ 260.0 mg of (manufactured by High Purity Chemicals Co., Ltd.) and Nb(OC ２ H ５ ) ５ 1.25 ml of (manufactured by High Purity Chemicals Co., Ltd.) was added. Then, it was refluxed at 85°C overnight. This was designated as mixture 1.

[0048] [Preparation of Mixture 2] While continuing to stir, LiNi is added to the Mixture 1 as core particles containing a composite oxide. ０．８ Co ０．１Mn ０．１ O ２ 30g of (PO5038, manufactured by MSE Supplies) was added to obtain mixture 2.

[0049] Next, while continuing to stir, H is added to the mixture 2 as a hydrolyzing agent. ２ 4.5 ml of O was added all at once, and stirring was continued overnight to hydrolyze the alkoxide monomer, causing dehydration condensation and deposition on the core particle surface to form a coating layer. Subsequently, it was recovered by filtration, vacuum dried at 80°C for 4 hours, and sintered at 350°C for 1 hour to obtain positive electrode active material particles 1 having a core-shell structure. The evaluation performed on the obtained positive electrode active material particles 1 is described below.

[0050] [Film Thickness Uniformity] The film thickness uniformity of the positive electrode active material particles was evaluated using cross-sectional observation images obtained by a transmission electron microscope (TEM). Cross-sectional observation of the positive electrode active material particles was performed by the following method. Specifically, the cross-section of the positive electrode active material particles was observed as follows. First, the powder of the positive electrode active material particles was processed using a focused ion / electron beam processing system "Helios G4UC" (manufactured by FE-I Japan Co., Ltd.) under acceleration voltage conditions of 30 kV (sampling) and 8 kV (finishing) to cut out a thin section sample with a thickness of 100 nm. Cross-sectional observation and elemental mapping by EDS were performed on the cut-out sample using a transmission electron microscope. The atoms contained in the core particles and shells can be identified from the mapping image.

[0051] The observation conditions are as follows: TEM (TEM): JEOL JEM-2800; EDS detector (EDS detector): JEOL JED-2300T; Dry SD100GV detector (detection element area: 100 mm²) ２ Equipment used (EDS analyzer): Thermo Fisher Scientific NORAN System 7 Acceleration voltage: 200kV Magnification: 500,000x Probe size: 1.0mm STEM image size: 1024 pixels x 1024 pixels EDS mapping size: 256 pixels x 256 pixels Number of frames: 1000 Aperture size: 40.0μm Detection signal: STEM-DF

[0052] From the obtained cross-sectional mapping image, line analysis was performed in the direction normal to the particles for the elements contained in the coating layer. The conditions for line analysis were as follows: STEM magnification: 1,000,000x Line length: 100 nm Number of points: 100 The full width at half maximum of the obtained X-ray intensity peak was taken as the thickness of the coating layer at the corresponding location. The same line analysis was performed at 20 locations for one cross-sectional image. In this case, the locations to be analyzed were spaced equally apart. Of the above 20 thicknesses, the standard deviation of the locations where a thickness of 0.5 nm or more was observed was taken as the standard deviation of the film thickness for one sample. The same analysis was performed on cross-sectional images of 50 fields of view, and the average standard deviation of the film thickness was calculated using the locations where a thickness of 0.5 nm or more was observed. The above average standard deviation was used as an indicator of the uniformity of the film thickness of the positive electrode active material particles, and evaluation was performed based on the evaluation criteria below. The evaluation results are shown in Table 3. A: The average standard deviation of the film thickness is 0.5 or less. B: The average standard deviation of the film thickness is greater than 0.5 and 1.0 or less. C: The average standard deviation of the film thickness is greater than 1.0 and 1.5 or less. D: The average standard deviation of the film thickness is greater than 1.5. If the evaluation rank is C or higher, the film thickness uniformity is considered to be good.

[0053] <Production Examples of Positive Electrode Active Material Particles 2-6> In the production example of positive electrode active material particle 1, the type of stirring blade was changed as shown in Table 2, and Li alkoxide LiOC ２ H ５ Nb alkoxide Nb(OC ２ H ５ ) ５ and hydrolyzing agent (H ２ Positive electrode active material particles 2 to 6 are obtained in the same manner, except that the amount of O) added is changed as shown in Table 1. The evaluation results regarding the film thickness uniformity of positive electrode active material particles 2 to 6 are shown in Table 3.

[0054] <Production Examples of Positive Electrode Active Material Particles 7-8> Positive electrode active material particles 7-8 were obtained in the same manner as in the production example of positive electrode active material particle 1, except that the type of organic solvent was changed to methanol (super dehydrated) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and the type of stirring blade was changed as shown in Table 2. The evaluation results regarding the film thickness uniformity of positive electrode active material particles 7-8 are shown in Table 3.

[0055] <Example of manufacturing positive electrode active material particles 9> Positive electrode active material particles 9 are obtained in the same manner as in the manufacturing example of positive electrode active material particles 1, except that the type of organic solvent is changed to methanol (super dehydrated) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). The evaluation results regarding the film thickness uniformity of positive electrode active material particles 9 are shown in Table 3.

[0056] <Example of manufacturing positive electrode active material particles 10> In the example of manufacturing positive electrode active material particles 9, Nb(OC ２ H ５ ) ５ Al(OC) ４ H ９ ) ３ The positive electrode active material particles 10 are obtained in the same manner, except for the change to [specific component]. The evaluation results regarding the film thickness uniformity of the positive electrode active material particles 10 are shown in Table 3.

[0057] <Example of manufacturing positive electrode active material particles 11> In the example of manufacturing positive electrode active material particles 9, Nb(OC ２ H ５ ) ５ Ti(OC ４ H ９ ) ４ The positive electrode active material particles 11 are obtained in the same manner, except for the change to [specific component]. The evaluation results regarding the film thickness uniformity of the positive electrode active material particles 11 are shown in Table 3.

[0058] <Example of production of positive electrode active material particles 12> Add 2 ml of 2-propanol to a container with propeller blades as a stirring device, and while stirring, add LiOC ２ H ５ 130.0 mg of Nb(OC) ２ H ５ ) ５ Add 0.70 ml of and 0.52 ml of acetylacetone. Then reflux at 80°C for 1 hour. After reflux, cool to room temperature and continue stirring while adding 9.5 ml of 2-propanol and H ２A mixed solution with 0.3 ml of O was added in one batch. It was held at 24 °C for 5 hours, and by hydrolysis and dehydration condensation, a particulate dispersion in which fine particles of the shell were dispersed was obtained. To the said particulate dispersion, 85.0 ml of 2-propanol was added, and further, 30 g of PO5038 manufactured by MSE Supplies was introduced as core particles, and fine particles of the shell were deposited on the surface of the core particles to form a coating layer. Thereafter, it was recovered by filtration, vacuum dried at 80 °C for 4 hours, and sintered at 350 °C for 1 hour to obtain cathode active material particles 12 having a core-shell structure. The evaluation results regarding the film thickness uniformity of the cathode active material particles 12 are shown in Table 3.

[0059] <Production Example of Cathode Active Material Particles 13> To 1.00 kg of ethanol, 8.16 g of LiOC ２ H ５ and 39.2 ml of Nb(OC ２ H ５ ) ５ were added and stirred to obtain a coating raw material composition. The raw material composition was applied onto the surface of PO5038 manufactured by MSE Supplies using a coating apparatus with a rolling fluidized bed. At this time, the ratio of the coating raw material composition to the core particles was adjusted so that the coating raw material composition would be 0.0525 mg with respect to 1 g of the core particles. Thereafter, a sintering treatment was performed at 350 °C to obtain cathode active material particles 13. The evaluation results regarding the film thickness uniformity of the cathode active material particles 13 are shown in Table 3.

[0060] <Production Example of Cathode Active Material Particles 14> In a container having a propeller blade as a stirring device, 18 ml of H ２ O and 6 ml of hydrogen peroxide solution with a concentration of 30 mass% were added, and while stirring, 0.60 g of niobic acid (Nb ２ O ５ ·6.1H ２ O (Nb ２ O ５ content rate 70.8%)) and 1.2 g of ammonia water with a concentration of 28 mass% were added. Thereafter, LiOH·H ２0.14 g of O is added to obtain a mixture A containing a dissolved lithium compound and peroxoniob complex. 180 ml of 2-propanol is added to a container with propeller blades as a stirring device, and then 30 g of PO5038 manufactured by MSE Supplies is added as core particles. Mixture B is obtained by stirring. The temperature of mixture B is set to 40°C, and stirring is continued at a rotation speed of 600 rpm to prevent the core particles from settling. Mixture A is continuously added over 120 minutes under a nitrogen atmosphere. After the reaction is complete, the mixture is recovered by filtration, vacuum dried at 80°C for 4 hours, and sintered at 350°C for 1 hour to obtain positive electrode active material particles 14 having a core-shell structure. The evaluation results regarding the film thickness uniformity of the positive electrode active material particles 14 are shown in Table 3.

[0061] <Example of production of positive electrode active material particles 15> In the example of production of positive electrode active material particles 1, the type of stirring blade is changed as shown in Table 2, and the type of organic solvent is changed to ethanol (super dehydrated) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), Li alkoxide LiOC ２ H ５ Nb alkoxide Nb(OC ２ H ５ ) ５ and hydrolyzing agent (H ２ The positive electrode active material particles 15 are obtained in the same manner, except that the amount of O) added is changed as shown in Table 1, and the hydrolyzing agent is added while stirring is stopped in step (iii), and then stirring is resumed. The evaluation results regarding the uniformity of the film thickness of the positive electrode active material particles 15 are shown in Table 3.

[0062] <Example of manufacturing positive electrode active material particles 16> In the example of manufacturing positive electrode active material particles 1, the type of organic solvent was changed to ethanol (super dehydrated) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and the hydrolyzing agent (H ２ The positive electrode active material particles 16 are obtained in the same manner, except that the amount of O) added is changed as shown in Table 1. The evaluation results regarding the film thickness uniformity of the positive electrode active material particles 16 are shown in Table 3.

[0063] The film thickness uniformity was evaluated using the method described above, with positive electrode active material particles 1 to 11 designated as Examples 1 to 11, and positive electrode active material particles 12 to 16 designated as Comparative Examples 1 to 5.

[0064]

[0065] In the table, the numbers listed in the "Evaluation of Film Thickness Uniformity" column indicate the average standard deviation of the film thickness.

[0066] This disclosure is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are attached to make the scope of this disclosure public. This application claims priority based on Japanese Patent Application No. 2024-228808 filed on 25 December 2024 and Japanese Patent Application No. 2025-141402 filed on 27 August 2025, the contents of which are incorporated herein by reference.

Claims

1. The process comprises the steps of (i) mixing an alkoxide monomer and / or its oligomer with an organic solvent to obtain a mixed solution 1, (ii) mixing the mixed solution 1 with core particles formed of a composite oxide to obtain a mixed solution 2, and (iii) adding a hydrolyzing agent while stirring the mixed solution 2 to hydrolyze the alkoxide monomer and / or oligomer contained in the mixed solution 2, causing dehydration condensation and deposition on the surface of the core particles to obtain a mixed solution 3 in which positive electrode active material particles with a core-shell structure are dispersed, wherein the alkoxide monomer and / or its oligomer comprises a lithium alkoxide monomer and / or its oligomer and at least one alkoxide monomer and / or its oligomer selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, and the hydrolyzing agent comprises at least one hydrolyzing agent selected from the group consisting of water, acidic aqueous solution, and alkaline aqueous solution. A method for producing positive electrode active material particles, characterized in that, in step (ii), the total amount of alkoxy groups contained in at least one alkoxy monomer selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten in the mixed liquid 2 is A (mol), and in step (iii), the total amount of water in the hydrolyzing agent contained in the mixed liquid 3 is B (mol), and A and B satisfy the following formula (1). B / A ≥ 3.0 (1) 2. The method for producing positive electrode active material particles according to claim 1, wherein step (iii) is a step of placing the mixed liquid 2 into a container having a stirring means, adding the hydrolyzing agent while stirring with the stirring means, hydrolyzing the alkoxide monomer and / or oligomer, dehydrating and condensing it, and precipitating it on the surface of the core particles to obtain positive electrode active material particles with a core-shell structure.

3. The stirring means is a rotating impeller, and the stirring flow rate Q (m³) of the impeller is calculated from the following formula (3). ３ A method for producing positive electrode active material particles according to claim 2, wherein the relationship between ( / sec) and the power P (kW) required for stirring the stirring blade, calculated from the following formula (4), satisfies the following formula (2). 1.20 × 10 －２ ≤Q / P ≤ 2.00 × 10 －２ (2) Q(m ３ / sec)=Nq×n×d ３ (3) P (kW) = Np×ρ×n ３ ×d ５ (4) (In equations (3) and (4), Nq represents the discharge flow rate, Np represents the power rate, and ρ is the density of the mixed liquid 3 [kg / m³]. ３ ] indicates the rotational speed of the stirring blade [rps], and d indicates the blade diameter [m] of the stirring blade.

4. A method for producing positive electrode active material particles according to any one of claims 1 to 3, wherein the alkoxide monomer and / or its oligomer comprises a lithium alkoxide monomer and / or its oligomer, and a niobium alkoxide monomer and / or its oligomer.

5. A method for producing positive electrode active material particles according to any one of claims 1 to 4, wherein the composite oxide is a composite oxide comprising lithium and at least one selected from the group consisting of manganese, cobalt, nickel, aluminum, iron, and phosphorus.

6. A method for producing positive electrode active material particles according to any one of claims 1 to 5, wherein the organic solvent comprises at least one organic solvent selected from the group consisting of ethanol, 2-propanol, 1-butanol, and toluene.

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