Method for manufacturing positive electrode active material particles

Abstract

To provide a method for producing positive electrode active material particles having a core-shell structure and excellent uniformity of coating layer thickness. [Solution] A method for producing positive electrode active material particles, comprising the steps of (i) mixing a specific 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 specific hydrolyzing agent to the mixed solution 2 to hydrolyze and dehydrate the alkoxide monomer and / or oligomer, causing them to precipitate 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 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

[Technical Field]

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

[0002] In recent years, lithium-ion rechargeable 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 rechargeable batteries are required to have high safety standards and further performance improvements. To further improve the safety of lithium-ion secondary batteries, development is underway on all-solid-state batteries, which replace the flammable liquid electrolyte with a solid electrolyte. To enhance 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, which allows 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 cathode active material with a core-shell structure has been proposed, in which the surface of the composite oxide core particles is coated with a lithium-ion conductive shell that does not react with the solid electrolyte. Patent Document 1 discloses a method for coating the surface of core particles of a composite oxide by spraying an alcohol solution mixed with an alkoxide onto the surface of the core particles using a spray-drying method, and then evaporating the alcohol solution to dryness in a heat treatment step. Patent Document 2 discloses a method for coating the surface of core particles while suppressing the occurrence of areas with high concentrations of the shell constituent material by intermittently dropping an aqueous solution containing dissolved shell constituent materials onto a dispersion containing dispersed core particles of a composite oxide, thereby causing the shell to precipitate on the surface of the core particles due to differences in solubility. Patent Document 3 discloses a method for coating the surface of a core particle by adding water to an alcohol solution mixed with an alkoxide, hydrolyzing it, and then dehydrating and condensing it to form fine particles of the material constituting the shell, and then depositing these fine particles onto the surface of the core particle of a 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 the mixture. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2010-129190 [Patent Document 2] Japanese Patent Publication No. 2014-238957 [Patent Document 3] Japanese Patent Publication No. 2016-072072 [Patent Document 4] Special Publication No. 2023-540135 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, in the manufacturing method shown in Patent Document 1, the core grain is produced by spray drying. When forming a shell by attaching an alkoxide to the subsurface, unreacted alkoxide may react. At this time, the coating state of the shell is likely to vary depending on the attachment state of the alkoxide on the surface of the core particles. In the manufacturing method shown in Patent Document 2, the constituent material of the shell does not precipitate uniformly on the surface of the core particles, and there may be variations in the film thickness of the shell between the 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 constituent material of the shell, portions that are not coated with the shell are likely to occur. In the manufacturing method shown in Patent Document 4, the condensate of the alkoxide that is the shell does not precipitate uniformly on the surface of the core particles, and there may be variations in the film thickness of the shell between the core particles. As described above, the 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. When the film thickness of the coating layer is not uniform, it becomes impossible to control the film thickness to an appropriate value, so a resistance layer is likely to be formed at the interface between the positive electrode active material and the solid electrolyte, and the output may decrease.

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

Means for Solving the Problems

[0008] This disclosure includes a step (i) of mixing an alkoxide monomer and / or its oligomer and an organic solvent to obtain a mixed liquid 1, a step (ii) of mixing the mixed liquid 1 and core particles formed of a composite oxide to obtain a mixed liquid 2, and, a step (iii) of adding a hydrolyzing agent while stirring the mixed liquid 2, hydrolyzing and dehydrating and condensing the alkoxide monomer and / or oligomer contained in the mixed liquid 2, and depositing it on the surface of the core particles to obtain a mixed liquid 3 in which positive electrode active material particles having a core-shell structure are dispersed, having these in this order, the alkoxide monomer and / or its oligomer being, Lithium alkoxide monomers and / or their oligomers, It comprises at least one alkoxide monomer and / or its oligomer selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, The hydrolyzing agent comprises at least one hydrolyzing agent selected from the group consisting of water, acidic aqueous solutions, and alkaline aqueous solutions. In step (ii) above, 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, which is contained in the mixture 2, is A (mol). In step (iii) above, when the total amount of water in the hydrolyzing agent contained in the mixture 3 is B (mol), The present invention relates to a method for producing positive electrode active material particles, characterized in that A and B satisfy the following formula (1). B / A ≥ 3.0 (1) [Effects of the Invention]

[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. [Modes for carrying out the invention]

[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 combined in any way. Furthermore, in this disclosure, any statement 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 selections may be made 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 mentioned above, the coating condition of the coating layer can significantly affect battery performance. If the coating layer thickness 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 resistance increases in areas with thicker thickness, leading to a decrease in lithium ion conductivity. Therefore, when using positive electrode active material particles with uneven coating layer thickness, the charge and discharge characteristics of the battery may deteriorate. The inventors of the present invention conducted intensive studies to solve the above problems and found that by preparing a mixed solution in which core particles of an alkoxide, an organic solvent, and a metal composite oxide are dispersed, and then adding a hydrolyzing agent in an amount satisfying formula (1) while stirring, hydrolysis occurs, and the surface of the core particles is coated while dehydration condensation is carried out, thereby improving the uniformity of the film thickness of the coating layer and solving the above problems.

[0013] <Embodiment> The embodiment relates to a method for producing positive electrode active material particles. The method for manufacturing positive electrode active material particles is: (i) A step of mixing an alkoxide monomer and / or its oligomer with an organic solvent to obtain a mixed solution 1. (ii) A step of mixing the aforementioned mixture 1 with core particles formed of a composite oxide to obtain a mixture 2, and (iii) A step in which a hydrolyzing agent is added to the mixture 2 while stirring, the alkoxide monomer and / or oligomer contained in the mixture 2 is hydrolyzed, dehydrated and condensed, and precipitated 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. It has them in this order, The alkoxide monomer and / or its oligomer, Lithium alkoxide monomers and / or their oligomers, It comprises at least one alkoxide monomer and / or its oligomer selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, The hydrolyzing agent comprises at least one hydrolyzing agent selected from the group consisting of water, acidic aqueous solutions, and alkaline aqueous solutions. In step (ii) above, 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, which is contained in the mixture 2, is A (mol). The present invention relates to a method for producing positive electrode active material particles, characterized in that, in step (iii) above, when the total amount of water in the hydrolyzing agent contained in the mixed liquid 3 is B (mol), 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, in step (ii), core particles formed of a composite oxide are added to the mixture 1. As a result, a mixed solution (mixture 2) can be obtained in which core particles formed from alkoxide monomers and / or their oligomers, an organic solvent, and a complex oxide are uniformly dispersed. Then, in step (iii), an amount of hydrolyzing agent satisfying formula (1) is added while stirring to hydrolyze the alkoxide monomers and / or their oligomers, causing dehydration condensation and precipitation 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 materials 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 in 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 that includes steps (i) to (iii) above, and involves adding a large amount of hydrolyzing agent, the surface of the core particles 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. At least one selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten is preferably 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 includes 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 thin. As a result, the precipitated condensate adheres easily to the core particle surface. Therefore, it is thought that the uniformity of the shell film thickness can be further improved. The above alcohol may be used alone, or two or more alcohols may be used in mixture form. The organic solvent preferably 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. In addition, 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 that are mixed, and in terms of mass, for example, 1.95 to 10.4 g or 2.34 to 9.10 g.

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

[0024] Adding a step of preparing alkoxide monomers and / or their oligomers is preferable because it allows the shell of the core-shell structure cathode active material particles obtained in step (iii) to be made atomically uniform in composition. 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 the mixture at, for example, 50-95°C for 1-12 hours while continuing to stir, to obtain a mixed solution 1.

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

[0026] Examples of the core particles formed of the composite oxide include at least one selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. In addition, in "Li(NiCoMn)O2" and "Li(NiCoAl)O2", "(NiCoMn)" and "(NiCoAl)" indicate that the total of the composition ratios in the parentheses is 1. As long as the total is 1, the individual component amounts are arbitrary. Li(NiCoMn)O2 may include, for example, Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2, Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, etc.

[0027] Li(NiCoMn)O2 is preferred for the core particles. A commercially available product of Li(NiCoMn)O2 may be used. For example, LiNi 0.8 Co 0.1 Mn 0.1 O2 (PO5038 (trade name) manufactured by MSE S upplies) may be mentioned. From the perspective of material dispersion, it is preferable to mix the mixed solution 2 and the core particles while continuing stirring. The amounts of the mixed solution 2 and the core particles may be controlled so as to be the amount of the desired coating layer.

[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 comprises at least one hydrolyzing agent selected from the group consisting of water (H2O), acidic aqueous solutions, and alkaline aqueous solutions.

[0029] In step (ii), 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, is A (mol). Also, in step (iii), the total amount of water in the hydrolyzing agent contained in the mixture 3 is B (mol). At this time, A and B satisfy the following formula (1). B / A ≥ 3.0 (1)

[0030] The B / A ratio 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. The B / A ratio is preferably 3.0 to 90.0, more preferably 5.0 to 90.0, more preferably 5.0 to 70.0, more preferably 6.0 to 70.0, more preferably 6.0 to 60.0, and even more preferably 10.0 to 60.0. By keeping the B / A ratio within the above range, the amount of hydrolyzing agent can be set to a sufficient amount 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 alkoxy monomer and / or its oligomer up to step (iii). For example, it is preferable not to substantially add a hydrolyzing agent up to step (iii). "Substantially omitting hydrolysants" means intentionally omitting hydrolysants, and trace amounts of hydrolysants that inevitably become 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 hydrolysants 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 using 2-propanol, methanol, or ethanol with a purity of 99.9%, the frequency of contact between water and alkoxide can be extremely low, so it is considered that no hydrolytic effect will occur.

[0032] The following describes a method for further improving the uniformity of the shell thickness 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 place 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 performing step (iii) as described above, the uniformity of the shell film thickness 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] The stirring flow rate Q(m) of the stirring means3 It is preferable that the relationship between the time ( / 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 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 for 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 × 10⁻⁶ -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 make it possible to suppress the entrainment of bubbles generated at the liquid surface, thus 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 × 10 -2 It is more preferable that the following conditions be met: 1.50 × 10 -2 The above 1.80 × 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 (m³) 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×ρ×n3 ×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]. 3 This shows the rotational speed of the impeller [rps], and d is the blade diameter [m]. The discharge flow rate Nq and power rate 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-blade paddle impeller, and a propeller impeller, the discharge flow rate Nq and power rate Np can be calculated using the following formulas, respectively. Discharge flow rate: Nq=0.1×S Power constant: Np=Cosα×S However, S is the maximum area [m²] when the impeller is projected onto a vertical plane. 2 This indicates the angle between the bottom of the impeller and the horizontal plane in contact with the bottom of the impeller [rad]. If there are multiple impellers, calculate S for each impeller and sum the values. α represents 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 apparatus used in step (iii) is not particularly limited, but for example, one can be used that has a rotating stirring blade as a stirring means, a stirring shaft, a stirring motor, and a stirring vessel. Examples of stirring means that satisfy the above formula (1) include Fullzone blades (manufactured by Kobe Steel Pantech Co., Ltd.), Maxblend blades (manufactured by Sumitomo Heavy Industries, Ltd.), Sunmeler blades (manufactured by Mitsubishi Heavy Industries, Ltd.), Hi-F mixer blades (manufactured by Soken Chemical Co., Ltd.), and Bendleaf blades (manufactured by Hakko Sangyo Co., Ltd.). If the density of mixture 3 is 1.0, the Q / P ratio for a full-zone wing is 1.65 × 10⁻⁶. -2 This results in a four-paddle wing (1.00 x 10 -2 ), propeller wing (7.69 × 10 -3 ), and 12 disc turbine blades (6.87 × 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 of the following methods may be used: single addition, divided addition such as adding in two parts, or continuous addition. From the viewpoint of making a large change in the concentration of the hydrolyzing agent, it is preferable to add the hydrolyzing agent in a single addition.

[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 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 through 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 when recovered by evaporation solidification.

[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 1-100 μm, 2-50 μm, 3-20 μm, and 5-15 μm.

[0043] Preferably, the process further includes a step of adding a chelating agent to the mixture 1 between step (i) and step (ii). In other words, it is preferable that the mixture 1 contains a chelating agent. Adding a chelating agent to the mixture 1 can suppress the hydrolysis and dehydration condensation of the alkoxide monomer and / or its oligomer in steps (i) and (ii). Therefore, it is preferable because it makes it easier to keep the alkoxide monomer and / or its oligomer in a state where they do 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, preventing the formation of fine particles, and the hydrolysis and dehydration condensation reaction can be initiated when the 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. [Examples]

[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 manufacturing of positive electrode active material particles 1> [Preparation of Mixture 1] In a container equipped with a full-zone impeller for stirring, 100 ml of 2-propanol (ultra-dehydrated) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added. While stirring, 260.0 mg of LiOC2H5 (manufactured by Kojunsei Kagaku Co., Ltd.) and 1.25 ml of Nb(OC2H5)5 (manufactured by Kojunsei Kagaku Co., Ltd.) were added. The mixture was then refluxed at 85°C overnight. This was designated as mixture 1.

[0048] [Preparation of Mixture 2] To the above mixture 1, while continuing to stir, LiNi is added as core particles containing a composite oxide. 0.8 Co 0.1 Mn 0.1 30g of O2 (PO5038, manufactured by MSE Supplies) was added to obtain mixture 2.

[0049] Next, 4.5 ml of H2O was added to the mixture 2 all at once as a hydrolyzing agent while continuing to stir, and stirring was continued overnight to hydrolyze the alkoxide monomers, causing dehydration condensation and deposition on the core particle surface to form a coating layer. Subsequently, the material 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] [Uniformity of film thickness] The film thickness uniformity of the positive electrode active material particles was evaluated using cross-sectional images obtained with a transmission electron microscope (TEM). Cross-sectional observation of positive electrode active material particles is performed using the following method. The specific procedure for observing the cross-section of the positive electrode active material particles is as follows: First, the powder of the positive electrode active material particles is processed using a focused ion / electron beam processing system "Helios G4UC" (manufactured by FI Japan) under acceleration voltages of 30kV (sampling) and 8kV (finishing) to cut out a thin section sample with a thickness of 100nm. Cross-sectional observation and elemental mapping using EDS were performed on the excised samples. The mapping images allow for the identification of atoms contained in the core particles and shell.

[0051] The observation conditions are as follows: Equipment used (TEM): JEM-2800 manufactured by JEOL Ltd. Equipment used (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 Observation 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: 40.0 μm Detection signal: STEM-DF

[0052] Based on the obtained cross-sectional mapping image, line analysis is performed on the elements contained in the coating layer in the direction normal to the particles. The conditions for line analysis are as follows: STEM magnification: 1,000,000x Line length: 100nm Points: 100 The full width at half maximum (FWHM) of the obtained X-ray intensity peak is taken as the thickness of the coating layer at the relevant location. Perform a similar line analysis at 20 locations on a single cross-sectional image. Ensure that the analysis points are spaced equally apart. Of the 20 thickness measurements mentioned above, the standard deviation of the locations where a thickness of 0.5 nm or more was observed is defined as the standard deviation of film thickness for one sample. A similar analysis is performed on 50 cross-sectional images, and the average standard deviation of film thickness is 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 film thickness uniformity of the positive electrode active material particles, and the evaluation was performed based on the following evaluation criteria. 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 less than or equal to 1.0. C: The average standard deviation of the film thickness is greater than 1.0 and less than or equal to 1.5. D: The average standard deviation of the film thickness is greater than 1.5. If the evaluation rank is C or higher, it is considered that the film thickness uniformity is good.

[0053] <Manufacturing examples of positive electrode active material particles 2-6> In the example of producing positive electrode active material particle 1, positive electrode active material particles 2 to 6 were obtained in the same manner, except that the type of stirring blade was changed as shown in Table 2, and the amounts of Li alkoxide LiOC2H5, Nb alkoxide Nb(OC2H5)5, and hydrolyzing agent (H2O) were 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] <Manufacturing examples of positive electrode active material particles 7-8> In the example of producing positive electrode active material particle 1, positive electrode active material particles 7 and 8 were obtained in the same manner, 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 and 8 are shown in Table 3.

[0055] <Example of manufacturing of positive electrode active material particles 9> In the example of producing positive electrode active material particles 1, positive electrode active material particles 9 were obtained in the same manner, except that the type of organic solvent was 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 of positive electrode active material particles 10> In the example of manufacturing positive electrode active material particles 9, positive electrode active material particles 10 are obtained in the same manner except that Nb(OC2H5)5 is changed to Al(OC4H9)3. The evaluation results regarding the film thickness uniformity of positive electrode active material particles 10 are shown in Table 3.

[0057] <Example of manufacturing of positive electrode active material particles 11> In the example of manufacturing positive electrode active material particles 9, positive electrode active material particles 11 are obtained in the same manner except that Nb(OC2H5)5 is replaced with Ti(OC4H9)4. The evaluation results regarding the film thickness uniformity of the positive electrode active material particles 11 are shown in Table 3.

[0058] <Example of manufacturing of positive electrode active material particles 12> Add 2 ml of 2-propanol to a container equipped with a propeller blade as a stirring device, and while stirring, add 130.0 mg of LiOC2H5, 0.70 ml of Nb(OC2H5)5, and 0.52 ml of acetylacetone. Then reflux at 80°C for 1 hour. After refluxing, the mixture was cooled to room temperature, and a mixture of 9.5 ml of 2-propanol and 0.3 ml of H2O was added all at once while continuing to stir. The mixture was kept at 24°C for 5 hours to allow hydrolysis and dehydration condensation to occur. By doing so, a dispersion of fine particles containing shell particles is obtained. 85.0 ml of 2-propanol is added to the aforementioned fine particle dispersion, and then 30 g of PO5038 manufactured by MSE Supplies is added as core particles, and shell particles are deposited on the surface of the core particles to form a coating layer. Subsequently, the material 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 12 having a core-shell structure. The evaluation results regarding the film thickness uniformity of the positive electrode active material particles 12 are shown in Table 3.

[0059] <Example of manufacturing of positive electrode active material particles 13> To 1.00 kg of ethanol, 8.16 g of LiOC2H5 and 39.2 ml of Nb(OC2H5)5 are added and stirred to obtain a coating material composition. The raw material composition is applied to the surface of MSE Supplies' PO5038 using a coating apparatus with a rolling fluidized bed. At this time, the ratio of the coating raw material composition to the core particles is adjusted so that 0.0525 mg of the coating raw material composition is present per 1 g of core particles. Then, a sintering treatment is performed at 350°C to obtain positive electrode active material particles 13. The evaluation results regarding the film thickness uniformity of the positive electrode active material particles 13 are shown in Table 3.

[0060] <Example of manufacturing of positive electrode active material particles 14> In a container equipped with a propeller blade as a stirring device, 18 ml of H2O and 6 ml of 30% by mass hydrogen peroxide solution are added, and while stirring, 0.60 g of niobic acid (Nb2O5·6.1H2O (Nb2O5 content 70.8%)) and 1.2 g of 28% by mass aqueous ammonia solution are added. Then, 0.14 g of LiOH·H2O is added to obtain a mixed solution A in which the lithium compound and peroxoniob complex are dissolved. Mixture B is obtained by adding 180 ml of 2-propanol to a container equipped with a propeller blade as a stirring device, and then adding 30 g of PO5038 manufactured by MSE Supplies as core particles, and stirring. The temperature of the above 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 then 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 manufacturing of positive electrode active material particles 15> In the example of producing positive electrode active material particles 1, the type of stirring blade is changed as shown in Table 2, the type of organic solvent is changed to ethanol (super-dehydrated) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), the amounts of Li alkoxide LiOC2H5, Nb alkoxide Nb(OC2H5)5 and hydrolyzing agent (H2O) are changed as shown in Table 1, and the hydrolyzing agent is added while stirring is stopped in step (iii), and stirring is resumed. The same procedure is followed to obtain positive electrode active material particles 15. The evaluation results regarding the film thickness uniformity of positive electrode active material particles 15 are shown in Table 3.

[0062] <Example of manufacturing of positive electrode active material particles 16> In the example of producing positive electrode active material particles 1, positive electrode active material particles 16 were obtained in the same manner except that the type of organic solvent was changed to ethanol (super-dehydrated) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and the amount of hydrolyzing agent (H2O) added was changed as shown in Table 1. The evaluation results regarding the film thickness uniformity of 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. [Table 1]

[0064] [Table 2]

[0065] [Table 3] 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 made by the following method. (Method 1) (i) A step of mixing an alkoxide monomer and / or its oligomer with an organic solvent to obtain a mixed solution 1. (ii) A step of mixing the aforementioned mixture 1 with core particles formed of a composite oxide to obtain a mixture 2, and (iii) A step in which a hydrolyzing agent is added to the mixture 2 while stirring, the alkoxide monomer and / or oligomer contained in the mixture 2 is hydrolyzed, dehydrated and condensed, and precipitated 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. It has them in this order, The alkoxide monomer and / or its oligomer, Lithium alkoxide monomers and / or their oligomers, It comprises at least one alkoxide monomer and / or its oligomer selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, The hydrolyzing agent comprises at least one hydrolyzing agent selected from the group consisting of water, acidic aqueous solutions, and alkaline aqueous solutions. In step (ii) above, 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, which is contained in the mixture 2, is A (mol). In step (iii) above, when the total amount of water in the hydrolyzing agent contained in the mixture 3 is B (mol), A method for producing positive electrode active material particles, characterized in that A and B satisfy the following formula (1). B / A ≥ 3.0 (1) (Method 2) Step (iii) is to place the mixed liquid 2 into a container having a stirring means, and add the hydrolyzing agent while stirring with the stirring means, The process involves 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. A method for producing positive electrode active material particles as described in Method 1. (Method 3) The stirring means is a rotating stirring blade, The stirring flow rate Q(m) of the stirring blade is calculated from the following formula (3). 3 A method for producing positive electrode active material particles according to Method 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, and ρ is the density of the mixed liquid 3 [kg / m³]. 3 ] indicates the rotational speed of the impeller [rps], and d indicates the blade diameter [m] of the impeller. (Method 4) The alkoxide monomer and / or its oligomer, Lithium alkoxide monomers and / or their oligomers, Niobium alkoxide monomers and / or their oligomers, A method for producing positive electrode active material particles according to any one of methods 1 to 3, including the method described above. (Method 5) The aforementioned composite oxide Lithium and, At least one selected from the group consisting of manganese, cobalt, nickel, aluminum, iron, and phosphorus, A method for producing positive electrode active material particles according to any one of methods 1 to 4, wherein the composite oxide contains a composite oxide. (Method 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.

Claims

1. (i) A step of mixing an alkoxide monomer and / or its oligomer with an organic solvent to obtain a mixed solution 1. (ii) A step of mixing the aforementioned mixture 1 with core particles formed of a composite oxide to obtain a mixture 2, and (iii) A step in which a hydrolyzing agent is added to the mixture 2 while stirring, the alkoxide monomer and / or oligomer contained in the mixture 2 is hydrolyzed, dehydrated and condensed, and precipitated on the surface of the core particles to obtain a mixture 3 in which positive electrode active material particles of a core-shell structure are dispersed. It has them in this order, The alkoxide monomer and / or its oligomer, Lithium alkoxide monomers and / or their oligomers, It comprises at least one alkoxide monomer and / or its oligomer selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, The hydrolyzing agent comprises at least one hydrolyzing agent selected from the group consisting of water, acidic aqueous solutions, and alkaline aqueous solutions. In step (ii) above, 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, which is contained in the mixture 2, is A (mol). In step (iii) above, when the total amount of water in the hydrolyzing agent contained in the mixed liquid 3 is B (mol), A method for producing positive electrode active material particles, characterized in that A and B satisfy the following formula (1). B / A≧3.0 (1)

2. Step (iii) is to place the mixed liquid 2 into a container having a stirring means, and add the hydrolyzing agent while stirring with the stirring means, The process involves 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. A method for producing positive electrode active material particles according to claim 1.

3. The stirring means is a rotating stirring blade, The stirring flow rate Q (m) of the stirring blade is calculated from the following formula (3). ３ The 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(κW)=NL×ρ×. 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. The alkoxide monomer and / or its oligomer, Lithium alkoxide monomers and / or their oligomers, Niobium alkoxide monomers and / or their oligomers, A method for producing positive electrode active material particles according to any one of claims 1 to 3, including

5. The aforementioned composite oxide Lithium and, At least one selected from the group consisting of manganese, cobalt, nickel, aluminum, iron, and phosphorus, A method for producing positive electrode active material particles according to any one of claims 1 to 3, wherein the composite oxide contains a composite oxide.

6. A method for producing positive electrode active material particles according to any one of claims 1 to 3, 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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