Coated particles and methods for making the same

Abstract

The coated particle of the present invention has a core particle and a coating layer disposed on at least a part of the surface of the core particle. The core particle contains a spinel-type composite oxide containing a lithium element and a manganese element. The coating layer contains an oxide of a lanthanum element and a zirconium element. The content of the lanthanum element is preferably 0.01 mass% or more and 1.0 mass% or less when the coated particle is taken as 100 mass%. The content of the zirconium element is preferably 0.01 mass% or more and 1.0 mass% or less when the coated particle is taken as 100 mass%.

Description

Technical Field

[0001] This invention relates to coated particles and their manufacturing methods. Background Technology

[0002] In recent years, secondary batteries have attracted attention as a countermeasure to prevent global warming by reducing carbon dioxide emissions. Among secondary batteries, lithium-ion batteries, which have high energy density and high voltage, are widely used.

[0003] Lithium manganese oxides (LiMnO2, LiMn2O4, etc.) are known as active materials in the positive electrode of such batteries. When batteries with a positive electrode containing manganese active materials are repeatedly charged and discharged, there is a problem that manganese elements dissolve into the electrolyte, leading to a decrease in battery performance.

[0004] To address the aforementioned issues, for example, Patent Document 1 discloses a lithium-manganese based cathode active material, which has a coating containing tungsten and boron formed on the surface of lithium manganese oxide. This document describes that, based on this cathode active material, the leaching of manganese can be suppressed.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: US2020 / 0119341A1 Summary of the Invention

[0008] In recent years, there has been an urgent need to further improve the performance of lithium-ion secondary batteries. However, the technology described in Patent Document 1 cannot adequately suppress the leaching of manganese, thus failing to achieve excellent battery performance.

[0009] Therefore, the objective of this invention is to provide particles that are useful for suppressing the leaching of manganese and obtaining excellent battery performance.

[0010] The present invention solves the aforementioned 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.

[0011] The aforementioned nuclear particles contain spinel-type composite oxides containing lithium and manganese.

[0012] The aforementioned coating layer contains oxides of lanthanum and zirconium.

[0013] In addition, the present invention provides a method for manufacturing coated particles, wherein a core particle containing a spinel-type composite oxide comprising lithium and manganese is rolled while an aqueous liquid comprising lanthanum and zirconium is applied to the core particle.

[0014] The aforementioned core particles, to which the aforementioned aqueous liquid has been applied, are heated in an oxidizing atmosphere to form a coating layer containing oxides of lanthanum and zirconium on the surface of the core particles. Detailed Implementation

[0015] The present invention will now be described based on its preferred embodiments. The coated particles of the present invention are suitable for use as active materials in batteries and have 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 performance degradation of the core particle. Hereinafter, the core particle and the coating layer in the coated particles will be described separately.

[0016] [Nuclear particles]

[0017] The core particles make up the majority of the coated particles and become the parent material of the coated particles.

[0018] The core particles may, for example, comprise lithium metal composite oxides. Preferably, the lithium metal composite oxide is a spinel-type composite oxide comprising lithium (Li), manganese (Mn), and oxygen (O). This spinel-type composite oxide can be represented, for example, by the general formula LiMn₂O₄.

[0019] The nucleus may contain elements other than lithium (Li), manganese (Mn), and oxygen (O). There may be one or more of these other elements. When there are two or more other elements, at least one element is preferably selected from the group consisting of Ni, Co, and Fe (hereinafter referred to as "M"). 1 Element”). M 1 The element is a substitutional element that primarily contributes to achieving an operating potential above 3.0V with a metallic Li reference potentiometer. Another preferred element is M, which is a combination of one 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 Element. M 2 The element is a substitutional element that primarily contributes to stabilizing the crystal structure and thus improving its properties. By selecting M from the above elements... 2 The element can improve capacity retention. The M contained in the structure... 1 Elements and M 2 Elements are different kinds of elements.

[0020] As a preferred composition example of the core particles, particles comprising a spinel-type lithium-manganese composite oxide, wherein the spinel-type lithium-manganese composite oxide has a spinel-type LiMn2O 4-δ Part of the Mn site in the solution is made of Li and M 1 Elements and other M2 Crystal structures formed by elemental substitution. Furthermore, equation (1) can be cited as an example: Li 1+x (M) 1 y M 2 z Mn 2-x-y-z )O 4-δ Formula (2): General formula [Li 1+x (Ni) y M 3 z Mn 2-x-y-z )O 4-δ The spinel-type lithium-manganese composite oxide shown in equation (2) is an example of such a composite oxide. 3 The elements, as described above, are preferably selected from one or more combinations of 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.

[0021] In formula (1), it is preferred 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 preferred 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. Furthermore, "4-δ" indicates that oxygen vacancies may be included, and δ is preferably 0 or more and 0.2 or less.

[0022] Examples of spinel-type composite oxides include LiMn2O4 and Li4Mn5O4, which are lithium manganese oxides. 12 (Li) 1.333 Mn 1.667 O4), Li2Mn4O9 (Li 0.889 Mn 1.778 O4), LiNi as a lithium manganese nickel oxide x Mn 2-x O4 (where x represents a number greater than 0 and less than 2), etc.

[0023] The types and contents of metallic elements contained in spinel-type composite oxides can be analyzed, for example, by ICP emission spectroscopy.

[0024] From the perspective of improving capacity retention, a BET specific surface area of ​​0.1 m² is preferred in nuclear particles. 2 / g or more and 10m 2 / g or less. From the viewpoint of making this advantage more significant, the BET specific surface area of ​​the core particles is, for example, further preferably 0.2m². 2 / g or more, and preferably 0.3m 2 / g or more. On the other hand, the BET specific surface area of ​​the nuclei is, for example, more preferably 5m². 2 / g or less, and preferably 3m 2 / g or less, and more preferably 2m 2 / g or less.

[0025] The method for determining the BET specific surface area is described in the examples described later.

[0026] It should be noted that other descriptions of nuclear particles are the same as those described in WO2017 / 150504A1. This publication is incorporated herein by reference as part of this specification.

[0027] It should be noted that the particle size of the core particles is appropriately selected based on the particle size of the target coated particles.

[0028] [Covering layer]

[0029] The coating layer is disposed on the surface of the nucleus particle, covering the surface of the nucleus particle. The coating layer either completely covers the surface of the nucleus particle or partially covers the surface, leaving a portion of the surface exposed. Considering the purpose of this coating layer configuration to prevent performance degradation of the nucleus particle, it is preferable that the coating layer completely covers the surface of the nucleus particle, with the surface of the nucleus particle being minimized from being exposed. The configuration of the coating layer will be described later.

[0030] The coating layer is disposed on the surface of the core particle to suppress the leaching of manganese (Mn) during use of the battery in which the coated particles of the present invention are assembled, so as not to degrade the performance of the core particle. For this purpose, the coating layer is composed of an oxide containing lanthanum (La) and zirconium (Zr) (hereinafter also referred to as "coated oxide").

[0031] The inventors discovered that if a battery with a positive electrode containing a spinel-type composite oxide containing Mn is repeatedly charged and discharged, Mn dissolves out, resulting in a tendency for the battery's performance, such as its recovery capacity, to decrease. To address this problem, the inventors discovered that it is effective to provide a coating layer containing a coating oxide on the surface of core particles formed from a spinel-type composite oxide containing lithium (Li), manganese (Mn), and oxygen (O), thus completing the present invention.

[0032] Based on the above viewpoints, in the coated particles of the present invention, when the coated particles are set to 100% by mass, 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.

[0033] Furthermore, in the coated particles of the present invention, from the viewpoint of not impairing the basic performance of the active substance, when the coated particles are set to 100% by mass, 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.

[0034] The content of La in the coated particles of the present invention can be determined by ICP emission spectroscopy analysis of the solution in which the coated particles are dissolved. The coated particles can be dissolved using, for example, hydrochloric acid and nitric acid. Specific determination methods are described in the examples described later.

[0035] From the same point of view as described above, in the coated particles of the present invention, when the coated particles are set to 100% by mass, 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.

[0036] Furthermore, in the coated particles of the present invention, from the viewpoint of not impairing the basic performance of the active substance, when the coated particles are set to 100% by mass, 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.

[0037] The Zr content in the coated particles of the present invention can be determined by ICP emission spectroscopy analysis of a solution containing the coated particles. The coated particles can be dissolved using, for example, hydrochloric acid and nitric acid. Specific determination methods are described in the examples described later.

[0038] The coated particles of the present invention, when used as active materials in either batteries containing solid electrolytes or batteries containing liquid electrolytes, can effectively suppress battery performance degradation through the coating layer. Preferred methods for forming coating layers with such advantages will be described later.

[0039] Preferably, the coating layer contains elements other than La and Zr. Specifically, from the viewpoint of suppressing the leaching of Mn during the use of the battery assembled with the coated particles of the present invention and more effectively suppressing the performance degradation of the battery, the coating layer preferably also contains tantalum (Ta).

[0040] From this perspective, in the coated particles of the present invention, when the coated particles are set to 100% by mass, the content of Ta element is preferably 0.01% by mass or more, more preferably 0.015% by mass or more, further 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.

[0041] Furthermore, in the coated particles of the present invention, from the viewpoint of not impairing the basic performance of the active substance, when the coated particles are set to 100% by mass, the content of Ta 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.

[0042] The Ta content in the coated particles of the present invention can be determined by ICP emission spectroscopy analysis of a solution containing the coated particles. The coated particles can be dissolved using, for example, hydrochloric acid and nitric acid. Specific determination methods are described in the examples described later.

[0043] In the coated particles of the present invention, when the coating layer contains Ta, there are no particular restrictions on the state in which Ta exists. Ta can exist, for example, in an oxide state. Alternatively, Ta can exist together with La and Zr in a composite oxide state.

[0044] From the viewpoint of suppressing the leaching of Mn elements during the use of batteries assembled with the coated particles of the present invention and more effectively suppressing the performance degradation of the battery, it is also preferable that the coating layer further contains lithium (Li) elements.

[0045] There is no particular limitation on the Li content in the coated particles of this invention. It can be appropriately set according to the types of elements contained in the core particles and the coating layer.

[0046] The Li content in the coated particles of the present invention can be determined by ICP emission spectroscopy analysis of the solution containing the coated particles. The coated particles can be dissolved using, for example, hydrochloric acid and nitric acid. Specific determination methods are described below.

[0047] In the coated particles of the present invention, when the coating layer contains Li, there are no particular restrictions on the state in which the Li element exists. For example, the Li element can exist in an oxide state. Alternatively, the Li element can exist together with La and Zr elements in a composite oxide state.

[0048] Furthermore, from the viewpoint of suppressing the leaching of Mn elements during the use of batteries assembled with the coated particles of the present invention and more effectively suppressing the performance degradation of the battery, it is also preferable that the coating layer further includes aluminum (Al) elements.

[0049] In the coated particles of the present invention, when the coating layer contains Al, there are no particular restrictions on the state in which the Al element exists. For example, the Al element can exist in an oxide state. Alternatively, the Al element can exist together with La and Zr elements in a composite oxide state.

[0050] Whether the coating layer contains elements can be confirmed by the following methods.

[0051] Specifically, ICP emission spectroscopy was used to analyze solutions containing the surface of the coated particles dissolved in a solvent and solutions containing the remaining particles after the surface has been removed. The coated particles can be dissolved using, for example, hydrochloric acid or nitric acid. If an element is present in a solution containing the dissolved particle surface at a higher concentration than the element present in a solution containing the remaining particles, it can be concluded that that element is contained within the coating layer.

[0052] In the coated particles of the present invention, as described above, from the viewpoint of suppressing the dissolution of Mn element during the use of the battery in which the coated particles are assembled, and more effectively suppressing the performance degradation of the battery, it is preferable that the La and Zr elements contained in the coating layer exist in the state of oxides. In the coated particles, the oxide containing La and the oxide containing Zr can exist separately, or they can exist in the form of a composite oxide containing La and Zr. There are no particular restrictions on the state of other elements besides La and Zr, such as Ta, Li, and Al. When La and Zr exist in the form of a composite oxide, from the viewpoint of making the above-mentioned effects more significant, it is preferable that all three elements are contained in the composite oxide.

[0053] Regarding the aforementioned state of existence, as a preferred composition example of the La and Zr elements in the coating layer, an oxide having a garnet-type crystal structure can be cited. This oxide can, for example, be of the general formula Li7La3Zr2O. 12 This can be represented as: Alternatively, an example could be Li7La3Zr2O with a garnet-type structure. 12 A portion of the Zr sites in the M 4 Oxides with crystal structures formed by elemental substitution, and oxides having a portion of the Li sites replaced with M 5 Oxides with crystal structures formed by elemental substitution. Such oxides can be obtained from equation (3): Li 7-x La3Zr 2-x M 4 x O 12 Equation (4): Li 7-x-3y M 5 y La3Zr 2-x M 4 x O 12 Indicated. M in equations (3) and (4) 4 The element is preferably selected from one or more combinations of Ta and Nb. M in equation (4) 5The element is preferably selected from one or more combinations of Al, Ga and Mg.

[0054] In equations (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.

[0055] Examples of oxides with a garnet-type crystal structure include Li, which is an oxide of lithium lanthanum zirconium tantalum. 6.75 La3Zr 1.75 Ta 0.25 O 12 、Li7La3Zr 1.75 Ta 0.25 O 12 Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Li 6.6 La3Zr 1.6 Ta 0.4 O 12 Li as a lithium aluminum lanthanum zirconium tantalum oxide 6.27 Al 0.16 La3Zr 1.75 Ta 0.25 O 12 wait.

[0056] In the coated particles of the present invention, from the viewpoint of suppressing the leaching of Mn element during the use of the battery in which the coated particles are assembled, and more effectively suppressing the performance degradation of the battery, 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 making this advantage more significant, the average thickness is, for example, further preferably 2 nm or more, and even more preferably 2.5 nm or more. On the other hand, the average thickness is, for example, further preferably 20 nm or less, and even more preferably 10 nm or less.

[0057] In the coated particles of the present invention, when the coating layer is formed using the rolling fluidized bed coating method described later, the "average thickness of the coating layer" can be calculated. Specifically, it is calculated by dividing the amount of feed liquid coated by the coating layer (g) by the estimated density of the feed liquid in the coating layer (g / cm³). 3 ), calculate the volume of the coating layer (cm³) 3 Then, based on the specific surface area and mass of the nuclear particles, it is assumed that they are uniformly coated and the thickness is calculated.

[0058] [Coated Particles]

[0059] The shape of the coated particles in this invention is not particularly limited; for example, granular particles can be used. The size of the coated particles in this invention is defined as the volumetric particle size D at a cumulative volume percentage of 50% obtained by laser diffraction scattering particle size distribution determination method. 50 This indicates that, for example, a particle size of 5 μm or more is preferred, more preferably 8 μm or more, and even more preferably 10 μm or more. This is because it suppresses excessive aggregation of particles, resulting in good dispersibility. On the other hand, the aforementioned cumulative particle size D... 50 For example, a particle size of 30 μm or less is preferred, more preferably 20 μm or less, and particularly preferably 15 μm or less. This is because it ensures sufficient contact between the coated particles and between the coated particles and the solid electrolyte particles.

[0060] Volumetric cumulative particle size D 50 The particle size distribution was determined using the following method. An automated sample feeder (Microtrac SDC, manufactured by Microtrac BEL Corp.) was used to measure the particle size distribution. The coated powder was placed in a solvent containing 0.1% hexametaphosphate in 20% ethanol. After irradiation with 40W ultrasound at a flow rate of 40% for 90 seconds, the particle size distribution was measured using a Microtrac BEL Corp. laser diffraction particle size distribution analyzer (MT3000II). The volumetric cumulative particle size (D) was determined from the obtained volumetric baseline particle size distribution spectrum. 50 .

[0061] Make the cumulative particle size D measured 50 The water-soluble solvent was passed through a 60 μm filter. The solvent refractive index was set to 1.33, the particle transmittance condition was set to "transmittance", the measurement range was set to above 0.243 μm and below 704.0 μm, and the measurement time was set to 30 seconds. The average of the two measurements was taken as the volumetric cumulative particle size D. 50 .

[0062] In the coated particles of the present invention, as described above, it is preferable that the coating layer completely covers the surface of the core particle. Furthermore, the coating layer preferably covers the surface of the core particle relatively uniformly. By configuring the coating layer in this way, the leaching of Mn element during use of the battery assembled with the coated particles can be effectively suppressed. As a result, the performance degradation of the battery can be more effectively suppressed.

[0063] The configuration of the coating layer can be determined, for example, based on the increase rate of the BET specific surface area before and after coating the core particle. When the surface of the core particle is uniformly coated, the smoothness of the surface increases, and therefore the increase rate does not become excessively large. On the other hand, when the surface of the core particle is unevenly coated, the smoothness of the surface decreases due to the creation of coated and uncoated areas and the thickness variation of the coating layer, thus increasing the increase rate. Therefore, in the coated particles of the present invention, the configuration of the coating layer is determined by the increase rate of the BET specific surface area.

[0064] Specifically, when the BET specific surface area of ​​the nuclear particle is set as S1 (m 2 / g), the BET specific surface area of ​​the coated particles is set as S2 (m 2 From the viewpoint of effectively suppressing the leaching of Mn element during the use of batteries assembled with coated particles and more effectively suppressing the degradation of battery performance, the specific surface area increase rate, defined as (S2-S1) / S1×100, is preferably 10% or less. From this viewpoint, the specific surface area increase rate is further preferably 8% or less, and even more preferably 5% or less.

[0065] Regarding the BET specific surface area of ​​the coated particles themselves, from the viewpoint of suppressing the dissolution of Mn and improving power characteristics, a surface area of ​​0.1 m² is preferred. 2 / g or more and 10m 2 / g or less. From the viewpoint of making this advantage more significant, the BET specific surface area is, for example, further preferably 0.2m². 2 / g or more, and preferably 0.3m 2 / g or more. On the other hand, the BET specific surface area is, for example, more preferably 5m². 2 / g or less, and preferably 3m 2 / g or less, and more preferably 2m 2 / g or less.

[0066] The method for determining the BET specific surface area is described in the examples described later.

[0067] According to the coated particles of the present invention, the leaching of Mn element during use of a battery in which the coated particles are assembled can be suppressed. The degree of leaching suppression can be defined by the following values. Specifically, when the amount of Mn element leached when 1 g of core particles is dispersed in 10 mL of an organic solvent containing lithium salt and placed at 85°C for 144 hours is defined as D1 (g), and the amount of Mn element leached when 1 g of coated particles is dispersed in 10 mL of an organic solvent containing lithium salt and placed at 85°C for 144 hours is defined as D2 (g), if the value of D2 / D1 is 0.8 or less, it can be determined that the leaching of Mn element can be sufficiently suppressed. From this viewpoint, the value of D2 / D1 is further preferably 0.7 or less, and even more preferably 0.6 or less. As the lithium salt-containing organic solvent that can be used to determine the value of D2 / D1, it is desirable to use the same solvent as the electrolyte used in a typical liquid battery.

[0068] The detailed method for determining the value of D2 / D1 is described in the examples described later.

[0069] [Manufacturing method of coated particles]

[0070] Next, a preferred method for manufacturing the coated particles of the present invention will be described.

[0071] This manufacturing method includes a step of coating the surface of the core particles with a coating layer containing oxides of lanthanum and zirconium. For this purpose, for example, a feed liquid containing lanthanum and zirconium feedstock is brought into contact with the powder of the core particles, allowing the feed liquid to adhere to the surface of the core particles, and then the core particles are fired to form a coating layer on the surface of the core particles. In particular, to form a thin and uniform coating layer on the surface of the core particles or to composite the elements contained in the coating layer, an aqueous liquid or dispersion, described later, can be used as the feed liquid; the use of an aqueous liquid is particularly advantageous.

[0072] When forming a coating layer on the surface of the nucleus particle, if the aforementioned aqueous solution is used, it can be prepared, for example, by mixing an aqueous solution of lanthanic acid with an aqueous solution of zirconic acid. If the aforementioned aqueous solution contains Ta, Li, and / or Al elements, it can be prepared by mixing an aqueous solution of tantalic acid, an aqueous solution of lithium acetate, and / or an aqueous solution of aluminic acid with the aqueous solution of lanthanic acid and the aqueous solution of zirconic acid. Alternatively, an aqueous solution of zirconium can be used instead of the aqueous solution of zirconic acid. The mixing of these aqueous solutions can be performed sequentially or simultaneously.

[0073] When forming a coating layer on the surface of a nuclear particle, if the aforementioned dispersion is used, the dispersion can be prepared by mixing a liquid obtained by the following method. This mixing of liquids can be performed sequentially or simultaneously.

[0074] Liquids containing La can be obtained by dissolving commercially available lanthanum compounds in pure water. It should be noted that examples of such lanthanum compounds include lanthanum acetate (·n hydrate) and lanthanum ethylenediaminetetraacetic acid complex.

[0075] Liquids containing Zr can be obtained by dissolving commercially available zirconium compounds in pure water. It should be noted that examples of such zirconium compounds include zirconium acetate (·n hydrate) and ammonium zirconium carbonate.

[0076] A liquid containing Ta can be obtained, for example, by the following method. Specifically, first, hydrogen peroxide is added to an aqueous solution of tantalum fluoride, and neutralized with ammonia or the like, thereby obtaining a precipitate of tantalum hydroxide. The fluorine content can be reduced by repeatedly washing with ammonia. Furthermore, by adding an alkaline aqueous solution containing Li to the aforementioned tantalum hydroxide precipitate, a liquid containing Ta can be obtained.

[0077] In the case of lithium, a water-soluble solution can be used. This solution can be obtained by dissolving a commercially available lithium compound in pure water. It should be noted that examples of such lithium compounds include lithium hydroxide, lithium carbonate, lithium acetate, trilithium citrate, and lithium lactate.

[0078] In the case of Al, a water-soluble solution can be used. This solution can be obtained by dissolving a commercially available aluminum compound in pure water. It should be noted that examples of such aluminum compounds include aluminum acetate, aluminum lactate, and aluminum ethylenediaminetetraacetate complexes. A solution can also be obtained by adding an acid or strong base to aluminum hydroxide.

[0079] The coating method for attaching a feed solution containing lanthanum and zirconium feedstock to the surface of the nucleus particles is not particularly limited, and either wet coating or dry coating methods can be used. Examples of wet coating methods include fluidized bed coating, electrolytic plating, and adhesion coating where the feed solution is dried after attachment. Examples of fluidized bed coating methods include rolling fluidized bed coating. In adhesion coating methods, the feed solution can be attached by immersing the nucleus particles in the feed solution or by spraying the feed solution onto the surface of the nucleus particles. Alternatively, in adhesion coating methods, the nucleus particles can be broken up after the feed solution is dried. Examples of dry coating methods include physical vapor deposition (PVD) and chemical vapor deposition (CVD), as well as solution plating. Examples of PVD methods include vacuum vapor deposition, sputtering coating, and ion plating. Of these coating methods, it is advantageous to use one of the group consisting of rolling fluidized bed coating and adhesion coating. By using this method, a thin and uniform coating layer can be smoothly formed over the entire surface area of ​​the core particle.

[0080] When the aforementioned aqueous liquid is applied by a rolling fluidized bed coating method, the target coated particles can be appropriately obtained by sequentially performing the following steps: applying an aqueous liquid containing La and Zr while rolling a core particle containing a spinel-type composite oxide containing Li and Mn elements; and heating the core particle to which the aforementioned aqueous liquid has been applied under an oxidizing atmosphere to form a coating layer containing La and Zr elements on the surface of the core particle.

[0081] In performing the above method, examples of devices for rolling the core particles include the rolling fluidized bed coating apparatus (Multiplex: MP) manufactured by Powrex Corp. and the SPIR-A-FLOW manufactured by FREUND CORPORATION. When using these devices to roll the core particles while applying an aqueous liquid containing La and Zr elements, devices such as the rolling fluidized bed coating apparatus (Multiplex: MP) manufactured by Powrex Corp. and the SPIR-A-FLOW manufactured by FREUND CORPORATION can be used. By applying the aforementioned aqueous liquid to the core particles using such devices, unlike the previously used impregnation method, the aqueous liquid can be applied more uniformly to the surface of the core particles. In this case, by adjusting the amount of the aforementioned aqueous liquid adhering to the core particles and the spraying speed, the thickness of the coating layer in the target coated particles can be adjusted.

[0082] When the feed solution containing lanthanum and zirconium feedstock is either the aforementioned aqueous solution or the aforementioned dispersion, from the viewpoint of easily and uniformly coating the surface of the core particles, it is preferable that the feed solution has higher dispersibility.

[0083] As a highly dispersible state, the maximum transmittance of the aforementioned raw material liquid in the wavelength range of 400nm~760nm can be above 70%T.

[0084] It should be noted that the maximum transmittance of the aforementioned raw material liquid in the wavelength range of 400nm to 760nm can be above 72%T, above 74%T, above 76%T, above 78%T, above 80%T, above 85%T, above 90%T, above 95%T, above 97%T, above 98%T, above 99%T, or even 100%T.

[0085] In addition, the transmittance of the aforementioned raw material liquid at any one or more of the wavelengths of 400nm, 600nm and 750nm can be above 70%T.

[0086] The transmittance of the aforementioned raw material liquid at any one or more wavelengths of 400nm, 600nm, and 750nm can be 72%T or higher, 74%T or higher, 76%T or higher, 78%T or higher, 80%T or higher, 85%T or higher, 90%T or higher, 95%T or higher, 97%T or higher, 98%T or higher, 99%T or higher, or 100%T.

[0087] Therefore, the minimum transmittance of the aforementioned raw material liquid in the wavelength range of 400nm to 760nm can be above 70%T.

[0088] The minimum transmittance in the wavelength range of 400nm to 760nm can be above 72%T, above 74%T, above 76%T, above 78%T, or above 80%T.

[0089] As a highly dispersible state, the particle size (cumulative particle size D) of the aforementioned raw material liquid obtained by dynamic light scattering method is... 50 It can be below 3000nm.

[0090] In addition, the particle size (cumulative particle size D) of the aforementioned feed liquid was obtained by dynamic light scattering method. 50 () can be below 1000nm, below 500nm, below 300nm, below 100nm, below 50nm, below 30nm, below 10nm, below 5nm, or below 1nm.

[0091] After applying the aqueous liquid or dispersion containing La and Zr elements obtained above to the surface of the core particles, the core particles are sintered. Sintering can form a thin and uniform coating layer. Even without sintering, La and Zr elements can be present on the surface of the core particles, but in this case, the surface of the coated particles may become uneven, making it difficult for lithium ions to be inserted / extracted smoothly.

[0092] The firing atmosphere is preferably set to an oxidizing atmosphere as described above. Using the atmosphere is convenient, but it is not limited to this.

[0093] From the perspective of ensuring the successful formation of the coating layer, the firing 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.

[0094] When the firing temperature is within the above range, the firing time is preferably 5 minutes or more and 50 hours or less.

[0095] After the core particles are sintered, the resulting particles can be crushed and graded as needed. This allows for adjustment to achieve a target cumulative particle size D. 50 .

[0096] [Electrode Mixture]

[0097] The coated particles obtained in this way can be used, for example, in the form of an electrode mixture containing the coated particles and an electrolyte. The electrolyte can be either a solid electrolyte or a liquid electrolyte. When using a solid electrolyte, with the solid component as a whole set at 100% by mass, the content of the coated particles in the aforementioned electrode mixture can be 30% by mass or more, 40% by mass or more, or 50% by mass or more. Furthermore, the content of the coated particles can be, for example, 98% by mass or less, 90% by mass or less, or 85% by mass or less. By keeping the content of the coated particles within the aforementioned range, the function as an electrode can be fully utilized.

[0098] The electrolyte that can be used in this invention can be the same as the electrolyte used in general liquid batteries. For example, organic electrolytes, polymeric solid electrolytes, molten salts, etc. can be used. Regarding organic electrolytes, examples of solvents include esters such as propylene carbonate, ethylene carbonate, butyl 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, methyl acetate, etc., and one or more of these mixed solvents can be mentioned. In addition, examples of lithium salts that are soluble in organic solvents include lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate (hereinafter referred to as "LiPF6"), lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium halides, and lithium aluminate.

[0099] The solid electrolyte used in this invention can be the same as that used in general solid-state batteries. Examples include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes, with sulfide solid electrolytes being preferred. The sulfide solid electrolyte can be, for example, a material containing lithium (Li) and sulfur (S) elements and possessing lithium-ion conductivity, or it can be a material containing lithium (Li), phosphorus (P), and sulfur (S) elements and possessing lithium-ion conductivity. The sulfide solid electrolyte can be any of crystalline materials, glass ceramics, or glass. The sulfide solid electrolyte can have a sulfide-germanium ore-type crystal phase. Examples of such sulfide solid electrolytes include Li₂S-P₂S₅, Li₂S-P₂S₅-LiX ("X" represents one or more halogens), Li₂S-P₂S₅-P₂O₅, Li₂S-Li₃PO₄-P₂S₅, Li₃PS₄, Li₄P₂S₆, and Li₂S-P₂S₅. 10 GeP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, Li7P3S 11 Li 3.25 P 0.95 S4, Li a PS b X c (X is at least one halogen. a represents a number of 3.0 or more and 6.0 or less. b represents a number of 3.5 or more and 4.8 or less. c represents a number of 0.1 or more and 3.0 or less.) Compounds as shown. In addition, sulfide solid electrolytes described in WO2013 / 099834A1 and WO2015 / 001818A1 may be cited as examples. These publications are incorporated herein by reference as part of this specification.

[0100] The coated particles contained in the electrode mixture may be solely the coated particles of the present invention, or they may be a combination of the coated particles of the present invention and other active substances. Examples of other active substances include particles formed from known lithium metal composite oxides. When using the coated particles of the present invention in combination with other active substances, it is preferable to contain 50% by mass or more, and particularly preferably 70% by mass or more of the coated particles of the present invention, relative to the total active substance.

[0101] When the electrode mixture contains a solid electrolyte, it may also contain other materials such as conductive additives and binders, as needed. A paste is prepared by mixing the electrode mixture with a solvent, coated onto a current collector such as aluminum foil, and then dried to create an electrode layer, such as a positive electrode layer. Alternatively, in the case of a powder-pressed battery instead of a coated battery, active materials, solid electrolytes, and conductive additives can be mixed in a solid-state mixture, shaped into granules, and used to create the electrode layer.

[0102] [Battery]

[0103] The coated particles of the present invention can be suitably used as the positive electrode active material of a battery. The aforementioned battery can be a primary battery or a secondary battery. The battery of the present invention, for example, may have a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the aforementioned positive electrode layer and the aforementioned negative electrode layer and containing an electrolyte. Furthermore, the aforementioned positive electrode layer contains the coated particles of the present invention.

[0104] The coated particles of this invention can be suitably used in solid-state batteries, particularly solid-state lithium batteries. They can also be suitably used in secondary batteries, especially solid-state lithium-ion secondary batteries. Examples of battery shapes include laminated, cylindrical, square, and coin-shaped types.

[0105] Solid-state batteries preferably have a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between them, and the positive electrode layer contains the coated particles described in this invention. Solid-state batteries can be manufactured, for example, by sequentially stacking the positive electrode layer, the solid electrolyte layer, and the negative electrode layer and then pressing them together. The term "solid-state battery" includes not only solid-state batteries that completely do not contain liquid or gel-like substances as electrolytes, but also, for example, those containing 50% or less, 30% or less, or 10% or less of liquid or gel-like substances as electrolytes.

[0106] As the negative electrode active material used in the aforementioned negative electrode layer, materials that absorb, store, and release lithium ions can be used, such as carbon materials, silicon, silicon oxide compounds like Si-O, tin compounds, lithium titanate, and other known materials. Examples of the aforementioned carbon materials include materials sintered from organic polymers such as polyacrylonitrile, phenolic resin, phenolic varnish resin, and cellulose; artificial graphite; and natural graphite. The aforementioned negative electrode layer, in addition to using such a negative electrode active material, can be fabricated in the same manner as the positive electrode layer.

[0107] The present invention has been described above based on its preferred embodiments, but the present invention is not limited to the above embodiments.

[0108] Regarding the aforementioned embodiments, the following coated particles and their manufacturing method are further disclosed.

[0109] [1] A coated particle having a core particle and a coating layer disposed on at least a portion of the surface of the core particle.

[0110] The aforementioned core particles contain spinel-type composite oxides containing lithium and manganese.

[0111] The aforementioned coating layer contains oxides of lanthanum and zirconium.

[0112] [2] According to the coated particles described in [1], wherein,

[0113] When the aforementioned coated particles are set to 100% by mass, the lanthanum content is 0.01% by mass or more and 1.0% by mass or less.

[0114] When the aforementioned coated particles are set to 100% by mass, the zirconium content is 0.01% by mass or more and 1.0% by mass or less.

[0115] [3] According to the coated particles described in [1] or [2], wherein,

[0116] The aforementioned coating also contains tantalum.

[0117] When the aforementioned coated particles are set to 100% by mass, the tantalum content is 0.01% by mass or more and 1.0% by mass or less.

[0118] [4] The coated particles according to any one of [1] to [3], wherein the aforementioned coating layer further comprises lithium.

[0119] [5] The coated particles according to any one of [1] to [4], wherein the aforementioned coating layer further comprises aluminum.

[0120] [6] The coated particles according to any one of [1] to [5], wherein the average thickness of the aforementioned coating layer is 1 nm or more and 80 nm or less.

[0121] [7] The coated particles according to any one of [1] to [6] have a BET specific surface area of ​​0.1 m². 2 / g or more and 10m 2 / g or less.

[0122] [8] The coated particles according to any one of [1] to [7], wherein the BET specific surface area of ​​the aforementioned core particles is set as S1 (m 2 / g), the BET specific surface area of ​​the aforementioned coated particles is set as S2 (m 2 When the surface area increases by (S2-S1) / S1×100, the value is less than 10%.

[0123] [9] The coated particles according to any one of [1] to [8], wherein,

[0124] The amount of manganese dissolved when 1g of the aforementioned core particles are dispersed in 10mL of organic solvent containing lithium salt and placed at 85°C for 144 hours is defined as D1(g).

[0125] When 1g of the aforementioned coated particles is dispersed in 10mL of organic solvent containing lithium salt and left at 85°C for 144 hours, the amount of manganese dissolved is defined as D2(g).

[0126] The value of D2 / D1 is below 0.8.

[0127]

[10] A lithium-ion secondary battery comprising, as any one of [1] to [9], coated particles as positive electrode active material.

[0128]

[11] A method for manufacturing coated particles, wherein,

[0129] While rotating a core particle containing a spinel-type composite oxide containing lithium and manganese, an aqueous solution containing lanthanum and zirconium is applied to the core particle.

[0130] The aforementioned core particles, to which the aforementioned aqueous liquid has been applied, are heated in an oxidizing atmosphere to form a coating layer containing oxides of lanthanum and zirconium on the surface of the core particles.

[0131] Example

[0132] The present invention will now be described in more detail through examples. However, the scope of the present invention is not limited to these examples. Unless otherwise stated, "%" and "parts" refer to "mass %" and "parts by mass," respectively.

[0133] [Example 1]

[0134] (1) Preparation of nuclei

[0135] Spinel-type lithium manganese composite oxide LiMn2O4 was prepared as the core particle.

[0136] (2) Formation of the coating layer

[0137] The raw materials were weighed to prepare an aqueous solution with the coating layer having the composition shown in Table 1 below. Specifically, in a polypropylene container, 3.8 mL of 0.5 mol / L lanthanic acid aqueous solution prepared by Nippon Yttrium Co., Ltd., 3.5 mL of 0.3 mol / L zirconic acid aqueous solution prepared by Mitsui Mining Co., Ltd., 0.6 mL of 0.26 mol / L tantalic acid aqueous solution prepared by Mitsui Mining Co., Ltd., and 5 mL of 0.76 mol / L lithium acetate aqueous solution were mixed to obtain an aqueous solution.

[0138] Next, 12 mL of aqueous solution was applied to 100 g of nuclear particles using a rolling flow method. The amount of aqueous solution applied was set to a coating thickness of 5 nm (calculated value).

[0139] Then, the nuclear particles coated with the aforementioned aqueous liquid were calcined at 700°C for 12 hours in an atmospheric atmosphere, followed by crushing and grading to obtain the target coated particles.

[0140] [Example 2]

[0141] In Example 1, 0.7 mL of a 1.6 mol / L zirconium aqueous solution was used instead of a zirconic acid aqueous solution. Additionally, the amount of aqueous solution applied was changed to a coating thickness of 3 nm (calculated). Otherwise, coated particles were obtained in the same manner as in Example 1.

[0142] [Example 3]

[0143] In Example 1, the amount of lithium acetate aqueous solution was changed to 6.3 mL. Additionally, the amount of aqueous solution adhering was changed to a coating thickness of 3 nm (calculated). Otherwise, coated particles were obtained in the same manner as in Example 1.

[0144] [Example 4]

[0145] In Example 1, an aqueous solution was prepared using 0.3 mL of a 0.39 mol aluminic acid aqueous solution. The amount of lithium acetate aqueous solution was also changed to match the composition shown in Table 1. The amount of aqueous solution adhering was changed to a coating thickness of 3 nm (calculated). Otherwise, coated particles were obtained in the same manner as in Example 1.

[0146] [Example 5]

[0147] In Example 2, an aqueous solution was further prepared using 0.3 mL of a 0.39 mol aqueous solution of aluminic acid. Otherwise, coated particles were obtained in the same manner as in Example 2.

[0148] [Comparative Example 1]

[0149] The core particles used as raw materials for the coated particles in Example 1 were themselves used as coated particles.

[0150] [evaluate]

[0151] For the coated particles obtained in the examples and comparative examples, the amounts of lanthanum, zirconium, and tantalum were determined by the following method.

[0152] In addition, for the coated particles obtained in the examples and comparative examples, the cumulative volumetric particle size D was measured using the method described above. 50 .

[0153] In addition, the BET specific surface area of ​​the coated particles obtained in the examples and comparative examples was determined by the following method.

[0154] In addition, the values ​​of D2 / D1 were determined for the coated particles obtained in the examples and comparative examples, as well as the core particles used in the examples and comparative examples, by the following method.

[0155] Furthermore, a lithium-ion secondary battery using the coated particles obtained in the examples and comparative examples as the positive electrode active material was fabricated, and the recovery capacity and cycle retention rate of the battery were measured.

[0156] The results are shown in Table 1 below.

[0157] [Amounts of lanthanum, zirconium, and tantalum]

[0158] The amounts of lanthanum, zirconium, and tantalum were determined using an ICP-AES analyzer (model: PS3520-DD2) manufactured by Hitachi High-Tech Science Corporation.

[0159] [BET specific surface area]

[0160] Macsorb, manufactured by MOUNTECH Co., Ltd., was used for determination by the BET 1-point method.

[0161] [Value of D2 / D1]

[0162] Disperse 1g of the nucleus particles in 10mL of organic solvent containing lithium salt. Incubate the liquid at 85°C for 144 hours, and determine the amount of manganese dissolved, D1 (g). Let D1 be the concentration of manganese in the liquid.

[0163] Next, 1 g of coated particles were dispersed in 10 mL of organic solvent containing lithium salt. The liquid was placed at 85 °C for 144 hours, and the amount of manganese dissolved in the liquid, D2 (g), was determined. D2 is set as the concentration of manganese in the liquid.

[0164] Organic solvents containing lithium salts refer to organic solvents in which LiPF6 is dissolved in a solvent with a mixing ratio of ethylene carbonate (EC) / dimethyl carbonate (DMC) of 3 / 7 to achieve a concentration of 1 mol / L.

[0165] Based on the obtained D1 and D2, calculate the value of D2 / D1.

[0166] [Restore Capacity]

[0167] 89 parts of the coated particles, 5 parts of acetylene black, and 6 parts of polyvinylidene fluoride (PVDF) obtained in the examples and comparative examples were weighed and mixed. 100 parts of 1-methyl-2-pyrrolidone (NMP) were added, and a positive electrode slurry was prepared using a planetary stirring / degassing apparatus (manufactured by KURABOINDUSTRIES LTD. MAZERUSTAR KK-50S). At this time, PVDF was pre-dissolved in NMP, and the coated particles and acetylene black were added and dry-thickened to prepare a positive electrode slurry (solids concentration of 50%).

[0168] The positive electrode slurry was coated onto the aluminum foil (serving as the current collector) using a coating machine at a conveying speed of 20 cm / min. The foil was then heated to 70°C for 2 minutes and dried to 120°C for 2 minutes using the same coating machine to form a positive electrode slurry layer, resulting in an aluminum foil with the positive electrode slurry layer. Next, the aluminum foil with the positive electrode slurry layer was punched into a rectangle of 50 mm × 100 mm, then compacted using a roller press at a pressing rate of 3 t / cm, and punched into a circle with a diameter of 16 mm. Finally, under vacuum, the foil was heated from room temperature to 200°C and dried at 200°C for 6 hours to produce the positive electrode (electrode weight per unit area: 15 mg / cm²). 2 ).

[0169] The negative electrode is made by coating natural spherical graphite onto copper foil, which serves as a current collector, and then punching it into a 14mmΦ circle.

[0170] TOMCELL (registered trademark), a battery cell for electrochemical evaluation, is fabricated by placing positive and negative electrodes on each side of a separator made of borosilicate glass fiber impregnated with electrolyte. The electrolyte is prepared by dissolving LiPF6 in a solvent prepared by mixing ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7 at a concentration of 1 mol / L.

[0171] For this battery, at 25°C, the current is 0.15 mA / cm. 2 (Equivalent to 0.1C) Charging is equivalent to reducing the discharge capacity to 10% of 100%, creating an open circuit for 9 hours (hereinafter referred to as "SOC 10%)". Then, charging to SOC 60%, creating an open circuit for 24 hours, followed by constant current charging to 4.2V. After reaching 4.2V, constant voltage charging is then performed until 0.015mA / cm is achieved. 2 (Equivalent to 0.01C). Then, at 0.15 mA / cm... 2 (Equivalent to 0.1C) Perform constant current discharge until 3.0V for initial activation. It should be noted that the rate at which the initial discharge capacity of the fabricated battery cell is fully discharged within 1 hour is defined as 1C.

[0172] After initial activation, the capacitor is charged at a constant current of 0.2C until it reaches 4.2V. After reaching 4.2V, it is charged at a constant voltage until it reaches 0.01C. Then, it is discharged at a constant current of 0.2C until it reaches 3.0V, which is taken as the initial discharge capacity.

[0173] Then, charge the battery at a constant current of 0.2C until it reaches 4.2V. After reaching 4.2V, charge it at a constant voltage until it reaches 0.01C. Then, place the battery in an environment of 60°C for 7 days, and then discharge it at a constant current of 0.2C until it reaches 3.0V. Then, charge the battery at a constant current of 0.2C until it reaches 4.2V. After reaching 4.2V, charge it at a constant voltage until it reaches 0.01C. Then, discharge the battery at a constant current of 0.2C until it reaches 3.0V. This discharge capacity after storage is recorded.

[0174] Calculate the ratio of the discharge capacity after placement to the initial discharge capacity, and use this value as the recovery capacity.

[0175] [Cycle Maintenance Rate]

[0176] Prepare the same battery used in the recovery capacity determination described above, and determine the cycle retention rate of the battery according to the following steps.

[0177] The capacitor was charged at a constant current of 0.5C until it reached 4.2V. After reaching 4.2V, it was charged at a constant voltage until it reached 0.01C, and then discharged at a constant current of 0.5C until it reached 3.0V. This charge-discharge cycle was performed 50 times. The cycle maintenance rate was calculated as the percentage (%) of the discharge capacity of the 50th cycle divided by the discharge capacity of the 1st cycle.

[0178] [Table 1]

[0179]

[0180] As can be clearly seen from the results shown in Table 1, the batteries made using the coated particles obtained in each embodiment can suppress Mn dissolution even after repeated charge and discharge, have high recovery capacity, and high cycle retention rate.

[0181] Industrial availability

[0182] According to the present invention, there is a method for manufacturing coated particles that are useful for inhibiting the leaching of manganese and obtaining active materials with excellent battery performance.

[0183] This invention excels in providing coated particles and a method for manufacturing the same, which are useful for producing active materials with battery performance superior to that of the prior art. Furthermore, this invention excels in providing coated particles and a method for manufacturing the same, which are useful as active materials for batteries capable of achieving high capacity recovery after storage at high temperatures. Thus, the generation of defective products, such as those that fail to achieve sufficient capacity recovery after storage at high temperatures, can be suppressed. From this viewpoint, according to the invention, defective product waste can be reduced, and the energy costs associated with waste disposal can also be decreased. For these reasons, according to the invention, advantages in the sustainable management and efficiency of natural resources, as well as decarbonization (carbon neutralization), are achieved.

Claims

1. A coated particle having a core particle and a coating layer disposed on at least a portion of the surface of the core particle. The core particles contain spinel-type composite oxides containing lithium and manganese. The coating layer contains oxides of lanthanum and zirconium.

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

3. The coated particles according to claim 1 or 2, wherein, The coating layer also contains tantalum. When the coated particles are set to 100% by mass, the tantalum content is 0.01% by mass or more and 1.0% by mass or less.

4. The coated particles according to claim 1 or 2, wherein, The coating layer also contains lithium.

5. The coated particles according to claim 1 or 2, wherein, The coating layer also contains aluminum.

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

7. The coated particles according to claim 1 or 2, having a BET specific surface area of ​​0.1 m². 2 / g or more and 10m 2 / g or less.

8. The coated particles according to claim 1 or 2, wherein, The BET specific surface area of ​​the nuclear particle is set as S1 (m 2 / g), the BET specific surface area of ​​the coated particles is set as S2 (m 2 When the surface area increases by (S2-S1) / S1×100, the value is less than 10%.

9. The coated particles according to claim 1 or 2, wherein, The amount of manganese dissolved when 1g of the core particles are dispersed in 10mL of organic solvent containing lithium salt and placed at 85°C for 144 hours is defined as D1(g). When 1g of the coated particles is dispersed in 10mL of organic solvent containing lithium salt and left at 85°C for 144 hours, the amount of manganese dissolved is defined as D2 (g). The value of D2 / D1 is below 0.

8.

10. A lithium-ion secondary battery comprising the coated particles as described in claim 1 or 2 as the positive electrode active material.

11. A method for manufacturing coated particles, wherein, While rotating a core particle containing a spinel-type composite oxide containing lithium and manganese, an aqueous solution containing lanthanum and zirconium is applied to the core particle. The core particles to which the aqueous liquid has been applied are heated in an oxidizing atmosphere to form a coating layer on the surface of the core particles containing oxides of lanthanum and zirconium.

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