Coated particle and method for manufacturing same

Abstract

Coated particles according to the present invention each have a core particle and a coating layer disposed on at least a portion of the surface of the core particle. The core particle contains a spinel-type composite oxide including elemental lithium and elemental manganese. The coating layer contains an oxide of elemental zirconium and elemental lanthanum. The elemental lanthanum content is preferably 0.01-1.0 mass% when the mass of the coated particles is defined as 100 mass%. The elemental zirconium content is preferably 0.01-1.0 mass% when the mass of the coated particles is defined as 100 mass%.

Description

Coated particles and their manufacturing method

[0001] The present invention relates to coated particles and a method for producing the same.

[0002] In recent years, secondary batteries have been attracting attention as an effort to prevent global warming by reducing carbon dioxide emissions. Among secondary batteries, lithium ion secondary batteries, which have high energy density and high voltage, are widely used. One of the active materials contained in the positive electrode of such batteries is lithium manganese oxide (LiMnO ２ , LiMn ２ O ４ Batteries equipped with a positive electrode containing a manganese-containing active material have a problem in that when they are repeatedly charged and discharged, the manganese element dissolves into the electrolyte, causing a decrease in battery performance.

[0003] To solve the above-mentioned problems, for example, Patent Document 1 describes a lithium-manganese-based positive electrode active material in which a coating layer containing tungsten, boron, etc. is formed on the surface of a lithium-manganese oxide. The document also describes that this positive electrode active material can suppress the elution of manganese element.

[0004] US2020 / 0119341A1

[0005] In recent years, there has been a demand for further improvement in the performance of lithium-ion secondary batteries. However, the technology described in Patent Document 1 cannot sufficiently suppress the elution of manganese element, and therefore, excellent battery performance cannot be obtained. Therefore, an object of the present invention is to provide particles useful for active materials that can suppress the elution of manganese element and obtain excellent battery performance.

[0006] The present invention solves the above-mentioned problems by providing coated particles having a core particle and a coating layer disposed on at least a portion of the surface of the core particle, wherein the core particle contains a spinel-type composite oxide containing lithium and manganese, and the coating layer contains an oxide of lanthanum and zirconium.

[0007] The present invention also provides a method for producing coated particles, which comprises applying an aqueous liquid containing lanthanum and zirconium to core particles containing a spinel-type composite oxide containing lithium and manganese while rolling the core particles, and heating the core particles to which the aqueous liquid has been applied in an oxidizing atmosphere to form a coating layer containing an oxide of lanthanum and zirconium on the surface of the core particles.

[0008] The present invention will be described below based on preferred embodiments. The coated particle of the present invention is suitable for use as an active material in a battery and comprises a core particle and a coating layer. The coating layer is disposed on at least a portion of the surface of the core particle. The coating layer is disposed on the surface of the core particle for the purpose of preventing a decrease in performance of the core particle. The core particle and the coating layer of the coated particle will be described below.

[0009] [Core Particle] The core particle occupies the majority of the coated particle and serves as the base material of the coated particle. The core particle may contain, for example, a lithium metal composite oxide. The lithium metal composite oxide preferably contains a spinel-type composite oxide containing lithium (Li), manganese (Mn), and oxygen (O). This spinel-type composite oxide is, for example, a spinel-type composite oxide represented by the general formula LiMn ２ O ４ It can be expressed as:

[0010] The core particle may contain elements other than lithium (Li), manganese (Mn), and oxygen (O). The other elements may be one type or two or more types. When the other elements are two or more types, at least one type of element is one type selected from the group consisting of Ni, Co, and Fe (hereinafter, referred to as "M １ It is preferable that M is an element. １ The element is a substitution element that mainly contributes to the development of an operating potential of 3.0 V or more relative to the metallic Li reference potential. The other element is M, which is one element or a combination of two or more elements selected from the group consisting of Na, Mg, Al, P, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce. ２ It is preferably an element.２ The elements are mainly substitution elements that contribute to stabilizing the crystal structure and improving the properties. ２ By selecting the element from the above-mentioned elements, it is possible to improve the capacity retention rate. １ Elements and M ２ The elements are different elemental species.

[0011] A preferred composition example of the core particle is a spinel-type LiMn ２ O ４－δ A part of the Mn site in １ Elements and other M ２ In addition, examples of the lithium manganese-containing spinel composite oxide include those having a crystal structure in which the lithium manganese-containing composite oxide is substituted with the element represented by the formula (1): Li １＋ｘ (M １ ｙ M ２ ｚ Mn ２－ｘ－ｙ－ｚ ) O ４－δ and formula (2): general formula [Li １＋ｘ (Ni ｙ M ３ ｚ Mn ２－ｘ－ｙ－ｚ ) O ４－δ In the formula (2), M is a spinel-type lithium-manganese-containing composite oxide represented by the formula (2). ３ As described above, the element is preferably one or a combination of two or more selected from the group consisting of Na, Mg, Al, P, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce.

[0012] In formula (1), it is preferable that "x" is 0.001 or more and 0.2 or less, "y" is 0.20 or more and 1.20 or less, and "z" is 0.001 or more and 0.400 or less. In formula (2), it is preferable that "x" is 0.001 or more and 0.2 or less, "y" is 0.20 or more and 0.70 or less, and "z" is 0 or more and 0.5 or less. In addition, "4-δ" indicates that oxygen vacancies may be contained, and δ is preferably 0 or more and 0.2 or less.

[0013] Examples of spinel-type composite oxides include lithium manganese oxide, LiMn ２ O ４ , Li ４ Mn ５ O １２ (Li １．３３３ Mn １．６６７ O ４ ), Li ２ Mn ４ O ９ (Li ０．８８９ Mn １．７７８ O ４ ) and lithium manganese nickel oxide, LiNi ｘ Mn ２－ｘ O ４ (x is a number greater than 0 and less than 2) The type and content of the metal element contained in the spinel-type composite oxide can be analyzed by, for example, ICP emission spectroscopy.

[0014] The core particles have a BET specific surface area of ​​0.1 m ２ / g or more 10m ２ From the viewpoint of improving the capacity retention rate, it is preferable that the BET specific surface area of ​​the core particles is, for example, 0.2 m / g or less. ２ / g or more, and more preferably 0.3m ２ On the other hand, the BET specific surface area of ​​the core particles is preferably 5 m / g or more. ２ / g or less is more preferable, ２ / g or less is more preferable, and 2m ２ / g or less is even more preferable. The method for measuring the BET specific surface area will be explained in the Examples below. Other details regarding the core particles are the same as those described in, for example, WO2017 / 150504A1. This publication is incorporated herein by reference.

[0015] The particle size of the core particles is appropriately selected depending on the particle size of the desired coated particles.

[0016] [Coating Layer] The coating layer is disposed on the surface of the core particle, covering the surface of the core particle. The coating layer covers the surface of the core particle evenly, or partially covers the surface of the core particle so that a part of the surface of the core particle is exposed. Considering the purpose of disposing the coating layer, which is to prevent a decrease in the performance of the core particle, it is preferable that the coating layer covers the surface of the core particle evenly, and that the surface of the core particle is not exposed as much as possible. The manner in which the coating layer is disposed will be described later.

[0017] The coating layer is disposed on the surface of the core particle for the purpose of suppressing the elution of manganese (Mn) element during use of a battery incorporating the coated particle of the present invention and preventing a decrease in the performance of the core particle. For this purpose, the coating layer is composed of oxides of lanthanum (La) element and zirconium (Zr) element (hereinafter also referred to as "coating oxide").

[0018] The present inventors have found that repeated charge and discharge of a battery equipped with a positive electrode containing a spinel-type composite oxide containing Mn element causes the Mn element to dissolve, which tends to reduce the performance of the battery, for example, its recovery capacity. To address this issue, the present inventors have found that providing a coating layer containing a coating oxide on the surface of core particles made of a spinel-type composite oxide containing lithium (Li), manganese (Mn), and oxygen (O) is effective, and have completed the present invention.

[0019] From the above viewpoints, in the coated particles of the present invention, the content of La element is preferably 0.01% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more, when the coated particles are taken as 100% by mass. Furthermore, in the coated particles of the present invention, from the viewpoint of not impairing the basic performance as an active material, the content of La element is preferably 1.0% by mass or less, more preferably 0.7% by mass or less, and even more preferably 0.5% by mass or less, when the coated particles are taken as 100% by mass. The content of La element contained in the coated particles of the present invention can be measured by ICP atomic emission spectroscopy of a solution in which the coated particles are dissolved. For example, hydrochloric acid and nitric acid can be used to dissolve the coated particles. Specific measurement methods will be described in the examples below.

[0020] From the same viewpoint as above, in the coated particles of the present invention, the content of Zr element is preferably 0.01% by mass or more, more preferably 0.04% by mass or more, and even more preferably 0.1% by mass or more, when the coated particles are taken as 100% by mass. Furthermore, in the coated particles of the present invention, from the viewpoint of not impairing the basic performance as an active material, the content of Zr element is preferably 1.0% by mass or less, more preferably 0.7% by mass or less, and even more preferably 0.3% by mass or less, when the coated particles are taken as 100% by mass. The content of Zr element contained in the coated particles of the present invention can be measured by ICP atomic emission spectroscopy of a solution in which the coated particles are dissolved. For example, hydrochloric acid and nitric acid can be used to dissolve the coated particles. Specific measurement methods will be described in the examples below.

[0021] The coated particles of the present invention effectively suppress deterioration of battery performance due to the action of the coating layer, whether the coated particles are used as the active material in a battery containing a solid electrolyte or in a battery containing an electrolytic solution. A preferred method for forming a coating layer having such advantages will be described later.

[0022] The coating layer preferably contains elements other than La and Zr. Specifically, it is preferable that the coating layer further contains tantalum (Ta) from the viewpoint of suppressing the elution of Mn during use of a battery incorporating the coated particles of the present invention and more effectively suppressing deterioration in battery performance. From this viewpoint, in the coated particles of the present invention, the content of Ta is preferably 0.01% by mass or more, more preferably 0.015% by mass or more, even more preferably 0.02% by mass or more, even more preferably 0.025% by mass or more, and even more preferably 0.03% by mass or more, when the coated particles are taken as 100% by mass. Furthermore, in the coated particles of the present invention, from the viewpoint of not impairing the basic performance as an active material, the content of Ta is preferably 1.0% by mass or less, more preferably 0.7% by mass or less, and even more preferably 0.3% by mass or less, when the coated particles are taken as 100% by mass. The content of Ta element contained in the coated particles of the present invention can be measured by ICP atomic emission spectroscopy of a solution in which the coated particles are dissolved. For example, hydrochloric acid and nitric acid can be used to dissolve the coated particles. Specific measurement methods will be described in the examples below.

[0023] In the coated particle of the present invention, when the coating layer contains Ta, there is no particular limitation on the state of Ta. For example, Ta may exist in the form of an oxide. Alternatively, Ta may exist in the form of a composite oxide together with La and Zr.

[0024] It is also preferable that the coating layer further contains lithium (Li) element, from the viewpoint of suppressing the elution of Mn element during use of a battery incorporating the coated particles of the present invention and more effectively suppressing deterioration in battery performance. There are no particular restrictions on the content of Li element in the coated particles of the present invention. It can be set appropriately depending on the types of elements contained in the core particle and the coating layer. The content of Li element contained in the coated particles of the present invention can be measured by ICP atomic emission spectroscopy of a solution in which the coated particles are dissolved. For example, hydrochloric acid and nitric acid can be used to dissolve the coated particles. A specific measurement method is as follows.

[0025] In the coated particle of the present invention, when the coating layer contains elemental Li, there are no particular limitations on the state of existence of the elemental Li. For example, the elemental Li may exist in the form of an oxide. Alternatively, the elemental Li may exist in the form of a composite oxide together with elements La and Zr.

[0026] It is also preferable that the coating layer further contains aluminum (Al) element, from the viewpoint of suppressing the elution of Mn element during use of a battery incorporating the coated particles of the present invention and more effectively suppressing deterioration of battery performance.

[0027] In the coated particles of the present invention, when the coating layer contains Al, there are no particular limitations on the state of existence of the Al element. For example, the Al element may exist in the form of an oxide. Alternatively, the Al element may exist in the form of a composite oxide together with La and Zr elements.

[0028] Whether or not an element is contained in the coating layer can be confirmed by the following method. Specifically, a solution in which the particle surfaces of the coated particles are dissolved in a solvent and a solution in which the remaining particles after removing the particle surfaces are dissolved in a solvent are each analyzed by ICP atomic emission spectroscopy. For example, hydrochloric acid and nitric acid can be used to dissolve the coated particles. If the content of any element in the solution in which the particle surfaces are dissolved is greater than the content of the element in the solution in which the remaining particles are dissolved, it can be concluded that the element is contained in the coating layer.

[0029] As described above, in the coated particles of the present invention, it is preferable that the La and Zr elements contained in the coating layer are present in the form of oxides, from the viewpoint of suppressing the elution of the Mn element during use of a battery incorporating the coated particles and more effectively suppressing deterioration in battery performance. In the coated particles, an oxide containing the La element and an oxide containing the Zr element may exist separately, or they may exist as a composite oxide containing the La element and the Zr element. There are no particular restrictions on the state of existence of elements other than the La element and the Zr element, such as the Ta element, the Li element, and the Al element. When the La element and the Zr element exist as a composite oxide, it is preferable that all three elements exist in a state contained in the composite oxide, from the viewpoint of making the above-mentioned effects more pronounced.

[0030] Regarding the above-mentioned state of existence, a preferred composition example of the La element and Zr element in the coating layer is, for example, an oxide having a garnet-type crystal structure. This oxide is, for example, an oxide having a general formula Li ７ La ３ Zr ２ O １２ Alternatively, garnet-type Li ７ La ３ Zr ２ O １２ In this case, some of the Zr sites are replaced by M ４ An oxide having a crystal structure in which a part of the Li site is replaced with M ５ The oxides having a crystal structure formed by substitution with an element can also be mentioned. Such oxides are represented by the formula (3): Li ７―ｘ La ３ Zr ２－ｘ M ４ ｘ O １２ and formula (4): Li ７―ｘ－３ｙ M ５ ｙ La ３ Zr ２－ｘ M ４ ｘ O １２ M in formula (3) and formula (4) can be expressed as ４ The element is preferably one or a combination of two or more selected from the group consisting of Ta and Nb. ５ The element is preferably one or a combination of two or more elements selected from the group consisting of Al, Ga, and Mg.

[0031] In formulas (3) and (4), "x" is preferably 0.01 or more and 1.9 or less, more preferably 0.1 or more and 1.0 or less, and even more preferably 0.2 or more and 0.5 or less. "y" is preferably 0.01 or more and 1.0 or less, more preferably 0.1 or more and 0.7 or less, and even more preferably 0.1 or more and 0.5 or less.

[0032] An example of an oxide having a garnet-type crystal structure is lithium lanthanum zirconium tantalum oxide, Li ６．７５La ３ Zr １．７５ Ta ０．２５ O １２ , Li ７ La ３ Zr １．７５ Ta ０．２５ O １２、 Li ６．５ La ３ Zr １．５ Ta ０．５ O １２、 Li ６．６ La ３ Zr １．６ Ta ０．４ O １２ and Lithium Aluminum Lanthanum Zirconium Tantalum Oxide, Li ６．２７ Al ０．１６ La ３ Zr １．７５ Ta ０．２５ O １２ Examples include:

[0033] In the coated particles of the present invention, it is preferable that the average thickness of the coating layer is 1 nm or more and 80 nm or less, from the viewpoint of suppressing the elution of Mn element during use of a battery incorporating the coated particles and more effectively suppressing deterioration in battery performance. From the viewpoint of making this advantage more pronounced, the average thickness is, for example, more preferably 2 nm or more, and even more preferably 2.5 nm or more. On the other hand, the average thickness is, for example, more preferably 20 nm or less, and even more preferably 10 nm or less. In the case of the coated particles of the present invention, when the coating layer is formed using the tumbling fluidized bed coating method described below, the "average thickness of the coating layer" can be calculated. Specifically, the coating amount (g) of the raw material solution for the coating layer is multiplied by the estimated density (g / cm) of the raw material solution for the coating layer. ３ ) to obtain the volume (cm ３ ) is calculated, and then the thickness is calculated based on the specific surface area and mass of the core particles, assuming that they are uniformly coated.

[0034] [Coated Particles] The shape of the coated particles of the present invention is not particularly limited, but may be, for example, particulate. The size of the coated particles of the present invention is determined by the volume cumulative particle size D at 50% cumulative volume as measured by a laser diffraction / scattering particle size distribution measurement method.５０ The volume cumulative particle diameter D is preferably 5 μm or more, more preferably 8 μm or more, and even more preferably 10 μm or more, because excessive aggregation of particles is suppressed and dispersibility is improved. ５０ is preferably, for example, 30 μm or less, more preferably 20 μm or less, and particularly preferably 15 μm or less, because this ensures sufficient contact between the coated particles and between the coated particles and the solid electrolyte particles.

[0035] Volume cumulative particle size D ５０ is measured by the following method: Using an automatic sample feeder for a laser diffraction particle size distribution analyzer ("Microtrac SDC" manufactured by Microtrac Bell Co., Ltd.), the powder of the coated particles is introduced into a solvent in which 20% by mass of ethanol solvent is mixed with 0.1% by mass of hexametaphosphoric acid, and the powder is irradiated with 40 W ultrasonic waves at a flow rate of 40% for 90 seconds, and then the particle size distribution is measured using a laser diffraction particle size distribution analyzer "MT3000II" manufactured by Microtrac Bell Co., Ltd., and the volume cumulative particle size D is calculated from the obtained volume-based particle size distribution chart. ５０ The volume cumulative particle diameter D is measured. ５０ The aqueous solvent used for measuring the particle diameter was passed through a 60 μm filter, the "solvent refractive index" was set to 1.33, the particle permeability condition was set to "permeation", the measurement range was set to 0.243 μm or more and 704.0 μm or less, and the measurement time was set to 30 seconds. The average value of two measurements was taken as the volume cumulative particle diameter D ５０ It was decided.

[0036] In the coated particles of the present invention, as described above, it is preferable that the coating layer uniformly coats the surface of the core particle. In addition, it is preferable that the coating layer coats the surface of the core particle relatively uniformly. By disposing the coating layer in this manner, it is possible to effectively suppress the elution of Mn element during use of a battery incorporating the coated particle. As a result, it is possible to more effectively suppress deterioration of battery performance. The arrangement of the coating layer can be defined, for example, by the rate of increase in the BET specific surface area of ​​the core particle before and after coating. When the surface of the core particle is coated relatively uniformly, the smoothness of the surface is high, so the rate of increase is not excessively large. On the other hand, when the surface of the core particle is coated unevenly, the smoothness of the surface is reduced due to the occurrence of coated and uncoated regions or uneven thickness of the coating layer, resulting in a large rate of increase. Therefore, in the coated particles of the present invention, the arrangement of the coating layer is defined by the rate of increase in the BET specific surface area.

[0037] Specifically, the BET specific surface area of ​​the core particle is S1 (m ２ / g), and the BET specific surface area of ​​the coated particles is S2 (m ２ / g), the specific surface area increase rate defined as (S2-S1) / S1 x 100 is preferably 10% or less, from the viewpoint of effectively suppressing the elution of Mn element during use of a battery incorporating the coated particles and more effectively suppressing the deterioration of battery performance. From this viewpoint, the specific surface area increase rate is more preferably 8% or less, and even more preferably 5% or less.

[0038] The BET specific surface area of ​​the coated particles is 0.1 m ２ / g or more 10m ２ From the viewpoint of suppressing the elution of Mn element and output characteristics, it is preferable that the BET specific surface area is, for example, 0.2 m / g or less. ２ / g or more, and more preferably 0.3m ２ On the other hand, the BET specific surface area is, for example, 5 m ２ / g or less is more preferable, ２ / g or less is more preferable, and 2m２ The method for measuring the BET specific surface area will be explained in the examples below.

[0039] The coated particles of the present invention can suppress the elution of Mn elements during use of a battery incorporating the coated particles. The degree of suppression of this elution can be defined by the following value. Specifically, when 1 g of core particles is dispersed in 10 mL of an organic solvent containing a lithium salt and left at 85°C for 144 hours, the amount of eluted Mn elements is defined as D1 (g), and when 1 g of coated particles is dispersed in 10 mL of an organic solvent containing a lithium salt and left at 85°C for 144 hours, the amount of eluted Mn elements is defined as D2 (g). If the value of D2 / D1 is 0.8 or less, it can be determined that the elution of Mn elements has been sufficiently suppressed. From this perspective, the value of D2 / D1 is more preferably 0.7 or less, and even more preferably 0.6 or less. It is desirable to use the same organic solvent containing a lithium salt that can be used to measure the value of D2 / D1 as the electrolyte used in a typical liquid-phase battery. A detailed method for measuring the value of D2 / D1 will be described in the Examples below.

[0040] [Method for producing coated particles] Next, a preferred method for producing the coated particles of the present invention will be described. This production method includes a step of coating the surfaces of core particles with a coating layer containing oxides of La and Zr. For this purpose, for example, a raw material liquid containing a lanthanum raw material and a zirconium raw material is brought into contact with a powder of core particles to adhere the raw material liquid to the surfaces of the core particles, and then the core particles are fired to form a coating layer on the surfaces of the core particles. In particular, to form a thin and uniform coating layer on the surfaces of the core particles or to compound the elements contained in the coating layer, for example, an aqueous liquid or dispersion liquid described below can be used as the raw material liquid, and it is particularly advantageous to use an aqueous liquid described below.

[0041] When the aqueous liquid is used to form a coating layer on the surface of the core particles, the aqueous liquid can be prepared, for example, by mixing an aqueous lanthanum acid solution with an aqueous zirconium acid solution. When the aqueous liquid contains Ta, Li, and / or Al, the aqueous liquid can be prepared by mixing an aqueous lanthanum acid solution and an aqueous zirconium acid solution with an aqueous tantalum acid solution, an aqueous lithium acetate solution, and / or an aqueous aluminum acid solution. Alternatively, an aqueous zirconium solution can be used instead of the aqueous zirconium acid solution. These aqueous solutions can be mixed sequentially or all at once.

[0042] When the dispersion is used to form a coating layer on the surface of core particles, the dispersion can be prepared by mixing liquids obtained by the following method. The liquids can be mixed sequentially or all at once. A liquid containing La element can be obtained by dissolving a commercially available lanthanum compound in pure water. Examples of the lanthanum compound include lanthanum acetate (n-hydrate) and lanthanum ethylenediaminetetraacetate complex.

[0043] The solution containing Zr element can be obtained by dissolving a commercially available zirconium compound, such as zirconium acetate (n-hydrate) or ammonium zirconium carbonate, in pure water.

[0044] A solution containing Ta element can be obtained, for example, by the following method. Specifically, first, hydrogen peroxide is added to a tantalum fluoride aqueous solution, and the solution is neutralized with ammonia water or the like to obtain a precipitate of tantalum hydroxide. The amount of fluorine can be reduced by repeatedly washing with ammonia water. Furthermore, a solution containing Ta element can be obtained by adding an alkaline aqueous solution containing Li element to the tantalum hydroxide precipitate.

[0045] In the case of elemental Li, an aqueous solution can be used. The solution can be obtained by dissolving a commercially available lithium compound in pure water. Examples of the lithium compound include lithium hydroxide, lithium carbonate, lithium acetate, trilithium citrate, and lithium lactate.

[0046] In the case of elemental Al, a water-soluble solution can be used. The solution can be obtained by dissolving a commercially available aluminum compound in pure water. Examples of the aluminum compound include aluminum acetate, aluminum lactate, and ethylenediaminetetraacetic acid aluminum complex. A solution can also be obtained by adding an acid or a strong base to aluminum hydroxide.

[0047] The coating method for adhering the raw material liquid containing the lanthanum raw material and the zirconium raw material to the surface of the core particles is not particularly limited, and either a wet coating method or a dry coating method may be employed. Examples of wet coating methods include fluidized bed coating, electrolytic plating coating, and an adhesion coating method in which the raw material liquid is applied and then dried. Examples of fluidized bed coating methods include tumbling fluidized bed coating. In the adhesion coating method, the raw material liquid can be applied by, for example, immersing the core particles in the raw material liquid or spraying the raw material liquid onto the surface of the core particles. In the adhesion coating method, the core particles may be crushed after drying the raw material liquid. Examples of dry coating methods include vapor deposition coating methods such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), as well as melt plating. Examples of PVD methods include vacuum deposition, sputtering coating, and ion plating. Of these coating methods, it is advantageous to use one selected from the group consisting of tumbling fluidized bed coating and adhesion coating. By using this method, a thin and uniform coating layer can be successfully formed over the entire surface of the core particle.

[0048] When the aqueous liquid is applied by the tumbling fluidized bed coating method, the desired coated particles can be suitably obtained by carrying out the following steps in this order: applying an aqueous liquid containing La and Zr elements to core particles containing a spinel-type composite oxide containing Li and Mn elements while rolling the core particles; and heating the core particles to which the aqueous liquid has been applied in an oxidizing atmosphere to form a coating layer containing an oxide of La and Zr elements on the surface of the core particles.

[0049] When carrying out the above-mentioned method, examples of the apparatus used to roll the core particles include a tumbling fluidized bed coating apparatus (Multiplex: MP) manufactured by Powrex Corporation and a Spiraflow manufactured by Freund Corporation. To apply an aqueous liquid containing La and Zr elements to the core particles while rolling them using these apparatuses, an apparatus such as a tumbling fluidized bed coating apparatus (Multiplex: MP) manufactured by Powrex Corporation or a Spiraflow manufactured by Freund Corporation can be used. By applying the aqueous liquid to the core particles using such an apparatus, the aqueous liquid can be applied relatively uniformly to the surfaces of the core particles, unlike the immersion method that has been previously adopted. In this case, the thickness of the coating layer on the desired coated particles can be adjusted by adjusting the amount of the aqueous liquid attached to the core particles and the spray speed.

[0050] Whether the raw material liquid containing the lanthanum raw material and the zirconium raw material is the aqueous liquid or the dispersion liquid, it is preferable that the raw material liquid be in a state of high dispersibility from the viewpoint of facilitating uniform application to the surfaces of the core particles. The high dispersibility state may be such that the maximum light transmittance of the raw material liquid in the wavelength region of 400 nm to 760 nm is 70% T or more. The maximum light transmittance of the raw material liquid in the wavelength region of 400 nm to 760 nm may be 72% T or more, 74% T, 76% T or more, 78% T or more, 80% T or more, 85% T or more, 90% T or more, 95% T or more, 97% T or more, 98% T or more, 99% T or more, or 100% T.

[0051] The source liquid may have a light transmittance of 70% T or more at one or more of the wavelengths of 400 nm, 600 nm, and 750 nm. The source liquid may have a light transmittance of 72% T or more, 74% T, 76% T or more, 78% T or more, 80% T or more, 85% T or more, 90% T or more, 95% T or more, 97% T or more, 98% T or more, 99% T or more, or 100% T.

[0052] Furthermore, the minimum light transmittance of the raw material liquid in a wavelength region of 400 nm to 760 nm may be 70% T or more. The minimum light transmittance in the wavelength region of 400 nm to 760 nm may be 72% T or more, 74% T or more, 76% T or more, 78% T or more, or 80% T or more.

[0053] As a state of high dispersibility, the particle diameter (volume cumulative particle diameter D ５０ The particle diameter (volume cumulative particle diameter D ５０ ) may be 1000 nm or less, 500 nm or less, 300 nm or less, 100 nm or less, 50 nm or less, 30 nm or less, 10 nm or less, 5 nm or less, or 1 nm or less.

[0054] The aqueous liquid or dispersion containing the La and Zr elements obtained as described above is applied to the surface of the core particles, and then the core particles are calcined. A thin, uniform coating layer can be formed by calcination. It is possible to have the La and Zr elements present on the surface of the core particles without calcination, but in that case, the surface of the coated particles will be uneven, which may hinder smooth insertion and desorption of lithium ions. As described above, the calcination atmosphere is preferably an oxidizing atmosphere. Air is conveniently used as the oxidizing atmosphere, but this is not limited thereto. The calcination temperature is preferably 300°C or higher and 1000°C or lower, more preferably 500°C or higher and 900°C or lower, and even more preferably 600°C or higher and 800°C or lower, in order to successfully form a coating layer. When the calcination temperature is within the above-mentioned range, the calcination time is preferably 5 minutes to 50 hours.

[0055] After the core particles are fired, the resulting particles may be crushed and classified as needed. ５０ can be adjusted to have

[0056] [Electrode Mixture] The coated particles of the present invention obtained in this manner can be used, for example, in the form of an electrode mixture containing the coated particles and an electrolyte. The electrolyte may be either solid or liquid. When a solid electrolyte is used as the electrolyte, the electrode mixture may contain the coated particles in an amount of 30% by mass or more, 40% by mass or more, or 50% by mass or more, when the total solid content is taken as 100% by mass. Furthermore, the content of the coated particles may be, for example, 98% by mass or less, 90% by mass or less, or 85% by mass or less. When the content of the coated particles is within the above range, the electrode can fully function.

[0057] The electrolyte solution that can be used in the present invention can be the same as that used in general liquid-phase batteries. For example, an organic electrolyte solution, a polymer solid electrolyte, a molten salt, etc. can be used. Examples of organic electrolyte solutions include solvents such as esters such as propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and γ-butyrolactone (hereinafter referred to as "GBL"); substituted tetrahydrofurans such as tetrahydrofuran and 2-methyltetrahydrofuran; ethers such as dioxolane, diethyl ether, dimethoxyethane, diethoxyethane, and methoxyethoxyethane; dimethyl sulfoxide, sulfolane, methyl sulfolane, acetonitrile, methyl formate, and methyl acetate; and solvents containing one or more of these solvents. Examples of electrolyte salts that dissolve in organic solvents include lithium perchlorate, lithium fluoroborate, and lithium hexafluorophosphate (hereinafter referred to as "LiPF ). ６ "), lithium salts such as lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium halides, and lithium chloroaluminate.

[0058] The solid electrolyte that can be used in the present invention can be the same as the solid electrolyte used in general solid state batteries. For example, sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, etc. can be mentioned, among which sulfide solid electrolytes are preferred. The sulfide solid electrolyte may, for example, contain lithium (Li) element and sulfur (S) element and have lithium ion conductivity, or may contain lithium (Li) element, phosphorus (P) element and sulfur (S) element and have lithium ion conductivity. The sulfide solid electrolyte may be any of a crystalline material, glass ceramics, and glass. The sulfide solid electrolyte may have a crystalline phase with an argyrodite structure. Examples of such sulfide solid electrolytes include Li ２ S-P ２ S ５ , Li ２ S-P ２ S ５-LiX (where "X" represents one or more halogen elements), Li ２ S-P ２ S ５ -P ２ O ５ , Li ２ S-Li ３ P.O. ４ -P ２ S ５ , Li ３ P.S. ４ , Li ４ P ２ S ６ , Li １０ GeP ２ S １２ , Li ３．２５ Ge ０．２５ P ０．７５ S ４ , Li ７ P ３ S １１ , Li ３．２５ P ０．９５ S ４ , Li ａ P.S. ｂ X ｃ (X is at least one halogen element; a is a number of 3.0 or more and 6.0 or less; b is a number of 3.5 or more and 4.8 or less; c is a number of 0.1 or more and 3.0 or less). Other examples include sulfide solid electrolytes described in WO2013 / 099834A1 and WO2015 / 001818A1. These publications are incorporated herein by reference.

[0059] The coated particles contained in the electrode mixture may be only the coated particles of the present invention, or may be a combination of the coated particles of the present invention with other active materials. Examples of other active materials include particles made of known lithium metal composite oxides. When the coated particles of the present invention are used in combination with other active materials, it is preferable that the coated particles of the present invention account for 50% by mass or more, particularly 70% by mass or more, of the total active materials.

[0060] When the electrode mixture contains a solid electrolyte, the electrode mixture may contain other materials such as a conductive additive or a binder as necessary. An electrode layer such as a positive electrode layer can be produced by mixing the electrode mixture with a solvent to produce a paste, and then applying the paste to a current collector such as aluminum foil and drying it. Furthermore, in the case of a compacted battery, rather than a coated battery, the active material, solid electrolyte, and conductive additive materials can be mixed in a solid phase and molded into pellets to produce an electrode layer.

[0061] [Battery] The coated particles of the present invention can be suitably used as a positive electrode active material for a battery. The battery may be a primary battery or a secondary battery. The battery of the present invention may have, for example, a positive electrode layer, a negative electrode layer, and an electrolyte layer containing an electrolytic solution disposed between the positive electrode layer and the negative electrode layer. The positive electrode layer contains the coated particles of the present invention. The coated particles of the present invention can be suitably used in solid-state batteries, particularly solid-state lithium batteries. Among these, they can be suitably used in secondary batteries, particularly solid-state lithium-ion secondary batteries. Examples of the shape of the battery include laminate, cylindrical, prismatic, and coin shapes.

[0062] The solid-state battery has a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located therebetween, and it is preferable that the positive electrode layer contains the coated particles of the present invention described above. The solid-state battery can be produced, for example, by stacking the positive electrode layer, the solid electrolyte layer, and the negative electrode layer in this order and pressure-molding them. The term "solid-state battery" includes not only solid-state batteries that do not contain any liquid or gel-like substance as an electrolyte, but also batteries that contain, for example, 50% by mass or less, 30% by mass or less, or 10% by mass or less of a liquid or gel-like substance as an electrolyte.

[0063] The negative electrode active material used in the negative electrode layer can be a material that absorbs and releases lithium ions, such as a known material, including carbon materials, silicon, silicon oxide compounds such as Si—O, tin compounds, and lithium titanate. Examples of the carbon material include sintered organic polymer compounds such as polyacrylonitrile, phenolic resin, phenolic novolac resin, and cellulose, as well as artificial graphite and natural graphite. The negative electrode layer can be prepared in the same manner as the positive electrode layer, except that such a negative electrode active material is used.

[0064] Although the present invention has been described above based on the preferred embodiments, the present invention is not limited to the above embodiments.

[0065] In relation to the above-described embodiment, the following coated particles and methods for producing the same are further disclosed: [1] Coated particles having a core particle and a coating layer disposed on at least a portion of the surface of the core particle, the core particle containing a spinel-type composite oxide containing lithium and manganese, and the coating layer containing an oxide of lanthanum and zirconium.

[0066] [2] The coated particle according to [1], wherein the content of elemental lanthanum is 0.01% by mass or more and 1.0% by mass or less, when the coated particle is taken as 100% by mass, and the content of elemental zirconium is 0.01% by mass or more and 1.0% by mass or less, when the coated particle is taken as 100% by mass. [3] The coated particle according to [1] or [2], wherein the coating layer further contains elemental tantalum, and the content of elemental tantalum is 0.01% by mass or more and 1.0% by mass or less, when the coated particle is taken as 100% by mass. [4] The coated particle according to any one of [1] to [3], wherein the coating layer further contains elemental lithium. [5] The coated particle according to any one of [1] to [4], wherein the coating layer further contains elemental aluminum. [6] The coated particle according to any one of [1] to [5], wherein the average thickness of the coating layer is 1 nm or more and 80 nm or less.

[0067] [7] BET specific surface area is 0.1 m ２ / g or more 10m ２ [8] The coated particles according to any one of [1] to [6], wherein the BET specific surface area of ​​the core particle is S1 (m ２ / g), and the BET specific surface area of ​​the coated particles is S2 (m ２

[0013] The coated particles according to any one of [1] to [7], wherein when the specific surface area of ​​the core particles is 100% or less, the specific surface area increase rate defined by (S2-S1) / S1×100 is 10% or less when the specific surface area of ​​the core particles is 100% or less and the specific surface area increase rate defined by (S2-S1) / S1×100 is 10% or less when the specific surface area of ​​the core particles is 100% or less and the specific surface area of ​​the core particles is 100% or less when the specific surface area of ​​the core particles is 100% or less. [9] The coated particles according to any one of [1] to [8], wherein the specific surface area increase rate defined by (S2-S1) / S1×100 is 10% or less when the specific surface area of ​​the core particles is 100% or less and the specific surface area of ​​the core particles is 100% or less when the specific surface area of ​​the core particles is 100% or less and the specific surface area of ​​the core particles is 100% or less when the specific surface area of ​​the core particles is 100% or less.

[0014] The coated particles according to any one of [1] to [9], wherein the specific surface area increase rate defined by (S2-S1) / S1×100 is 10% or less when the specific surface area of ​​the core particles is 100% or less and the specific surface area of ​​the core particles is 100% or less when the specific surface area of ​​the core particles is 100% or less.

[0015] The coated particles according to any one of [1] to [9], wherein the specific surface area increase rate defined by (S2-S1) / S1×100 is 10% or less when the specific surface area of ​​the core particles is 100% or less and the specific surface area of ​​the core particles is 100% or less when the specific surface area of ​​the core particles is 100% or less

[11] A method for producing coated particles, comprising: applying an aqueous liquid containing lanthanum and zirconium to core particles containing a spinel-type composite oxide containing lithium and manganese while rolling the core particles; and heating the core particles to which the aqueous liquid has been applied in an oxidizing atmosphere to form a coating layer containing an oxide of lanthanum and zirconium on the surface of the core particles.

[0068] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" and "parts" mean "% by mass" and "parts by mass", respectively.

[0069] Example 1 (1) Preparation of core particles Spinel-type lithium manganese composite oxide LiMn ２ O ４ was prepared as the core particles.

[0070] (2) Formation of Coating Layer An aqueous liquid was prepared by weighing raw materials so that the coating layer would have the composition shown in Table 1 below. Specifically, 3.8 mL of a 0.5 mol / L lanthanum acid aqueous solution manufactured by Nippon Yttrium Co., Ltd., 3.5 mL of a 0.3 mol / L zirconium acid aqueous solution manufactured by Mitsui Mining & Smelting Co., Ltd., 0.6 mL of a 0.26 mol tantalum acid aqueous solution manufactured by Mitsui Mining & Smelting Co., Ltd., and 5 mL of a 0.76 mol lithium acetate aqueous solution were mixed in a polypropylene container to obtain an aqueous liquid. Next, 12 mL of the aqueous liquid was applied to 100 g of core particles by a tumbling flow method. The amount of aqueous liquid applied was set to an amount that would result in a coating layer thickness of 5 nm (calculated value). The core particles to which the aqueous liquid had been applied were then calcined at 700 °C for 12 hours in an air atmosphere, crushed, and classified to obtain the desired coated particles.

[0071] [Example 2] In Example 1, 0.7 mL of a 1.6 mol / L aqueous zirconium solution was used instead of the aqueous zirconate solution. In addition, the amount of aqueous liquid applied was changed to an amount that would result in a coating layer thickness of 3 nm (calculated value). Other than this, coated particles were obtained in the same manner as in Example 1.

[0072] [Example 3] In Example 1, the amount of the lithium acetate aqueous solution was changed to 6.3 mL. In addition, the amount of the aqueous liquid applied was changed to an amount that would result in a coating layer thickness of 3 nm (calculated value). Other than this, coated particles were obtained in the same manner as in Example 1.

[0073] Example 4 In Example 1, 0.3 mL of a 0.39 mol aqueous aluminum acid solution was further used to prepare an aqueous liquid. The amount of the lithium acetate aqueous solution was changed so that the composition was as shown in Table 1. The amount of the aqueous liquid applied was changed so that the thickness of the coating layer was 3 nm (calculated value). Covered particles were obtained in the same manner as in Example 1 except for this.

[0074] Example 5 Covered particles were obtained in the same manner as in Example 2, except that 0.3 mL of a 0.39 mol aqueous aluminum acid solution was further used to prepare an aqueous liquid.

[0075] Comparative Example 1 The core particles used as the raw material for the coated particles in Example 1 were used as the coated particles.

[0076] [Evaluation] The amounts of lanthanum, zirconium, and tantalum were measured for the coated particles obtained in the Examples and Comparative Examples by the following methods. ５０ was measured by the method described above. Furthermore, the BET specific surface area of ​​the coated particles obtained in the Examples and Comparative Examples was measured by the following method. Furthermore, the D2 / D1 values ​​of the coated particles obtained in the Examples and Comparative Examples and the core particles used in the Examples and Comparative Examples were measured by the following method. Furthermore, lithium ion secondary batteries were fabricated using the coated particles obtained in the Examples and Comparative Examples as the positive electrode active material, and the recovered capacity and cycle retention rate of the batteries were measured. These results are shown in Table 1 below.

[0077] [Amounts of lanthanum, zirconium and tantalum] The amounts of lanthanum, zirconium and tantalum were measured using an ICP-AES analyzer (model: PS3520-DD2) manufactured by Hitachi High-Tech Science Corporation.

[0078] [BET Specific Surface Area] Measurement was carried out by the BET single-point method using a Macsorb manufactured by Mountech Co., Ltd.

[0079] [D2 / D1 Value] 1 g of core particles was dispersed in 10 mL of an organic solvent containing a lithium salt. This solution was left standing at 85°C for 144 hours, and the amount D1 (g) of elemental manganese eluted in the solution was measured. D1 was defined as the concentration of elemental manganese in the solution. Next, 1 g of coated particles was dispersed in 10 mL of an organic solvent containing a lithium salt. This solution was left standing at 85°C for 144 hours, and the amount D2 (g) of elemental manganese eluted in the solution was measured. D2 was defined as the concentration of elemental manganese in the solution. The organic solvent containing a lithium salt was a solvent in which ethylene carbonate (EC) / dimethyl carbonate (DMC) were mixed at a mixing ratio of 3 / 7, and LiPF ６ The organic solvent was dissolved so that the concentration of D2 was 1 mol / L. Based on the obtained D1 and D2, the value of D2 / D1 was calculated.

[0080] [Recovery Capacity] 89 parts of the coated particles obtained in the Examples and Comparative Examples, 5 parts of acetylene black, and 6 parts of polyvinylidene fluoride (PVDF) were weighed and mixed, and 100 parts of 1-methyl-2-pyrrolidone (NMP) was added thereto, and a positive electrode mixture slurry was prepared using a planetary stirring and degassing device (Kurabo Industries, Ltd., Mazerustar KK-50S). At this time, PVDF was previously dissolved in NMP, and the coated particles and acetylene black were added and kneaded to prepare a positive electrode mixture slurry (solid concentration 50%).

[0081] This positive electrode mixture slurry was applied to an aluminum foil current collector at a conveying speed of 20 cm / min using a coater, and then heated to 70°C for 2 minutes using the coater, followed by drying at 120°C for 2 minutes to form a positive electrode mixture layer, thereby obtaining an aluminum foil with a positive electrode mixture layer. Next, this aluminum foil with a positive electrode mixture layer was punched out into a rectangular electrode having a size of 50 mm x 100 mm, and then pressed and densified using a roll press at a linear pressure of 3 t / cm, and then punched out into a circle having a diameter of 16 mm. Next, in a vacuum state, the aluminum foil was heated from room temperature to 200°C, and heated and dried at 200°C for 6 hours to obtain a positive electrode (electrode basis weight 15 mg / cm). ２ )

[0082] A negative electrode sheet was produced by applying natural spherical graphite to a copper foil current collector, and this was then punched out into a 14 mm diameter circle to form the negative electrode. A TOMCELL (registered trademark) electrochemical evaluation cell was produced by placing the positive and negative electrodes on either side of a separator made of borosilicate glass fiber impregnated with an electrolyte. The electrolyte was a 3:7 volume mixture of ethylene carbonate and dimethyl carbonate, to which LiPF was added to achieve a concentration of 1 mol / L. ６ was prepared by dissolving

[0083] When this battery was discharged at 25°C and the discharge capacity was taken as 100%, the capacity equivalent to 10% was 0.15 mA / cm ２ (equivalent to 0.1 C) and left open circuit for 9 hours (hereinafter referred to as "SOC 10%)." After that, the battery was charged to an SOC of 60% and left open circuit for 24 hours, after which it was charged at a constant current of 0.015 mA / cm ２The battery was then charged at a constant voltage until the current reached 0.15 mA / cm (equivalent to 0.01 C). ２ Initial activation was performed by constant current discharge at 0.2C (equivalent to 0.1C) to 3.0V. The rate at which the initial discharge capacity of the prepared cell is completely discharged in 1 hour is defined as 1C. After initial activation in this manner, the cell was charged at a constant current of 0.2C to 4.2V, and once 4.2V was reached, constant voltage charging was performed to 0.01C. Next, constant current discharge was performed at 0.2C to 3.0V, and the initial discharge capacity was determined. Subsequently, constant current charging was performed at 0.2C to 4.2V, and once 4.2V was reached, constant voltage charging was performed to 0.01C. The battery was then left in a 60°C environment for 7 days, after which constant current discharge was performed at 0.2C to 3.0V. Subsequently, constant current charging was performed at 0.2C to 4.2V, and once 4.2V was reached, constant voltage charging was performed to 0.01C. Subsequently, constant current discharge was performed at 0.2C to 3.0V, and the discharge capacity after storage was determined. The ratio of the discharge capacity after standing to the initial discharge capacity was calculated, and this value was taken as the recovered capacity.

[0084] [Cycle Retention Rate] A battery similar to the battery used for measuring the recovered capacity described above was fabricated, and the cycle retention rate of the battery was measured by the following procedure. The battery was charged at a constant current of 0.5 C to 4.2 V, and once 4.2 V had been reached, it was charged at a constant voltage of 0.01 C, and then discharged at a constant current of 0.5 C to 3.0 V. This charge / discharge cycle was repeated 50 times. The discharge capacity at the 50th cycle was divided by the discharge capacity at the first cycle to obtain a percentage (%), which was used as the cycle retention rate.

[0085]

[0086] As is clear from the results shown in Table 1, the batteries fabricated using the coated particles obtained in each Example suppressed Mn elution even after repeated charge and discharge, had high recovered capacity values, and also had high cycle retention rates.

[0087] According to the present invention, it is possible to provide coated particles useful as active materials that can suppress the elution of manganese element and obtain excellent battery performance, and a method for producing the same.

[0088] The present invention is advantageous in that it provides coated particles useful as active materials that can achieve better battery performance than conventional techniques, and a method for producing the same. The present invention is also advantageous in that it provides coated particles useful as active materials for batteries that can achieve high recovery capacity after storage in a high-temperature environment, and a method for producing the same. This can reduce the occurrence of defective products that cannot achieve sufficient recovery capacity after storage in a high-temperature environment, for example. From this perspective, the present invention can reduce waste of defective products and also reduce energy costs associated with waste disposal. These advantages lead to the sustainable management and efficient benefits of natural resources, as well as the achievement of decarbonization (carbon neutrality).

Claims

1. Coated particles comprising a core particle and a coating layer disposed on at least a portion of the surface of the core particle, wherein the core particle contains a spinel-type composite oxide containing lithium and manganese, and the coating layer contains an oxide of lanthanum and zirconium.

2. The coated particles according to claim 1, wherein the lanthanum element content is 0.01% by mass or more and 1.0% by mass or less when the coated particles are taken as 100% by mass, and the zirconium element content is 0.01% by mass or more and 1.0% by mass or less when the coated particles are taken as 100% by mass.

3. The coated particle according to claim 1 or 2, wherein the coating layer further contains elemental tantalum, and the content of elemental tantalum is 0.01% by mass or more and 1.0% by mass or less when the coated particle is taken as 100% by mass.

4. The coated particle according to claim 1 or 2, wherein the coating layer further contains lithium element.

5. The coated particle according to claim 1 or 2, wherein the coating layer further contains aluminum element.

6. The coated particle according to claim 1 or 2, wherein the average thickness of the coating layer is 1 nm or more and 80 nm or less.

7. BET specific surface area is 0.1m ２ / g or more 10m ２ The coated particles according to claim 1 or 2, wherein the surface roughness is 1 / g or less.

8. The BET specific surface area of ​​the core particles is S1 (m ２ / g), and the BET specific surface area of ​​the coated particles is S2 (m ２ 3. The coated particles according to claim 1, wherein when the specific surface area of ​​the coated particles is 100% or less, the specific surface area increase rate defined as (S2-S1) / S1×100 is 10% or less.

9. The coated particles according to claim 1 or 2, wherein the value of D2 / D1 is 0.8 or less, where D1 (g) is the amount of eluted manganese element when 1 g of the core particles is dispersed in 10 mL of an organic solvent containing a lithium salt and left to stand at 85°C for 144 hours, and D2 (g) is the amount of eluted manganese element when 1 g of the coated particles is dispersed in 10 mL of an organic solvent containing a lithium salt and left to stand at 85°C for 144 hours.

10. A lithium ion secondary battery comprising the coated particles according to claim 1 or 2 as a positive electrode active material.

11. A method for producing coated particles, comprising: applying an aqueous liquid containing lanthanum and zirconium to core particles containing a spinel-type composite oxide containing lithium and manganese while rolling the core particles; and heating the core particles to which the aqueous liquid has been applied in an oxidizing atmosphere to form a coating layer containing an oxide of lanthanum and zirconium on the surface of the core particles.

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