Coated particles and method for manufacturing same

Abstract

The present invention addresses the problem of providing: coated particles that are useful as an active material of a battery, with which it is possible to suppress gas generation when exposed to a high voltage; and a method for manufacturing the same. Coated particles according to the present invention each have a core particle and a coating layer that is disposed on at least a part of the surface of the core particle. The core particle contains a spinel-type composite oxide that contains a lithium element, a manganese element, and a nickel element. The coating layer contains a phosphorus element. The content of the phosphorus element is 0.01 mass% to 1.0 mass% inclusive when the coated particles are each taken as 100 mass%. By means of XPS measurement, a peak is found at an energy value that is derived from a P-O bond of phosphoric acid.

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 LiMn １．５ Ni ０．５ O ４ Known lithium manganese nickel-based oxides include the following: Batteries equipped with a positive electrode containing an active material having such lithium manganese nickel-based oxides have a problem in that battery performance deteriorates when stored in a high-temperature environment.

[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 has a high capacity retention rate and a low resistance increase rate after multiple charge-discharge cycles.

[0004] US2020 / 083524A1

[0005] In recent years, there has been a demand for further improvements in the performance of lithium-ion secondary batteries. However, the technology described in Patent Document 1 cannot achieve better battery performance, for example, it cannot suppress gas generation in a battery when the positive electrode active material is exposed to a high potential. Therefore, an object of the present invention is to provide particles useful for an active material that can achieve better battery performance than conventional techniques.

[0006] The present invention solves the above-mentioned problems by providing coated particles comprising a core particle and a coating layer disposed on at least a part of the surface of the core particle, wherein the core particle contains a spinel-type composite oxide containing lithium, manganese, and nickel, and the coating layer contains phosphorus, the phosphorus content being 0.01% by mass or more and 1.0% by mass or less when the coated particle is taken as 100% by mass, and wherein a peak is observed at an energy value derived from a P—O bond of phosphoric acid by XPS measurement.

[0007] The present invention also provides a method for producing coated particles, which comprises applying an aqueous liquid containing phosphorus to core particles containing a spinel-type composite oxide containing lithium, manganese, and nickel 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 a compound in which phosphorus is bonded to oxygen on the surface of the core particles.

[0008] 1 is an XPS spectrum of phosphorus element for the coated particles obtained in Example 1. FIG. 2 is an XPS spectrum of manganese element for the coated particles obtained in Example 1.

[0009] 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 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.

[0010] [Core Particle] The core particle occupies the majority of the coated particle and serves as the base material for the active material. 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), nickel (Ni), and oxygen (O). This spinel-type composite oxide is, for example, a compound represented by the general formula LiNi Ｘ Mn ２－Ｘ O ４ (where x is a number greater than 0 and less than 2).

[0011] The core particle may contain elements other than lithium (Li), manganese (Mn), nickel (Ni), and oxygen (O). The other elements may be one type or two or more types. The other elements are preferably M elements consisting of one or a combination of two or more elements selected from the group consisting of Na, Mg, B, Al, P, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce. The M element is a substitution element that mainly contributes to stabilizing the crystal structure and improving the characteristics. By selecting the M element from the above-mentioned elements, it is possible to improve the capacity retention rate.

[0012] A preferred composition example of the core particle is a spinel-type LiNi Ｘ Mn ２－Ｘ O ４－δ In addition, examples of the lithium manganese-containing spinel composite oxide include those having a crystal structure in which a part of the Mn site in the formula (1): Li, Ni, and another M element are substituted. ｘ (Ni ｙ M ｚ Mn ２－ｘ－ｙ－ｚ ) O ４－δ As described above, the M element in formula (1) is preferably one or a combination of two or more selected from the group consisting of Na, Mg, B, Al, P, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce.

[0013] 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. Furthermore, "4-δ" indicates that oxygen vacancies may be contained, and δ is preferably 0 or more and 0.2 or less.

[0014] The type and content of the metal elements contained in the spinel-type composite oxide can be analyzed, for example, by ICP atomic emission spectroscopy. Other details of the core particle are similar to those described in, for example, WO 2017 / 150504 A1. 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 target active material 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 entire surface of the core particle, or partially covers the surface of the core particle so that a portion 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 entire surface of the core particle so that the surface of the core particle is not exposed as much as possible.

[0017] The coating layer is disposed on the surface of the core particle for the purpose of preventing a decrease in the performance of the core particle during use of a battery incorporating the coated particle of the present invention. For this purpose, the coating layer contains phosphorus (P).

[0018] The present inventors have found that when a battery equipped with a positive electrode containing a spinel-type composite oxide containing Mn is charged and exposed to a high potential, gases such as hydrogen gas and carbon dioxide gas tend to be generated. The hydrogen gas is believed to be generated due to the Mn contained in the core particles. The carbon dioxide gas is believed to be generated due to the carbon contained in the electrolyte. In response to the above-mentioned problems, the present inventors have discovered that providing a coating layer containing P on the surface of core particles made of a spinel-type composite oxide containing lithium (Li), manganese (Mn), nickel (Ni), and oxygen (O) is effective, leading to the completion of the present invention. In particular, it has been found that when the coating layer contains oxygen (O) in addition to P, gas generation from a battery exposed to a high potential is further suppressed. Providing a coating layer containing P on the surface of core particles is also advantageous in that it improves the characteristics of a battery containing the coated particles of the present invention as an active material when discharged at a high rate.

[0019] From the above viewpoints, in the coated particles of the present invention, the content of the P element is preferably 0.01% by mass or more, more preferably 0.015% by mass or more, and even more preferably 0.017% 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 the P element is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, even more preferably 0.3% by mass or less, and even more preferably 0.12% by mass or less, when the coated particles are taken as 100% by mass. The content of the P 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. Specific measurement methods will be described in the Examples below.

[0020] In the coated particles of the present invention, there are no particular limitations on the state of the P element contained in the coating layer. When the coating layer contains an O element in addition to the P element, it is preferable that the P element be present in a state bonded to the O element, from the viewpoint of more effectively suppressing gas generation from a battery exposed to a high potential. From this viewpoint, it is more preferable that the P element be present in the form of phosphoric acid. The presence of the P element in the coating layer in the form of phosphoric acid can be confirmed by observing a peak at the energy value derived from the P-O bond of phosphoric acid in XPS (X-ray photoelectron spectroscopy). The energy value (P2p) derived from the P-O bond of phosphoric acid is observed in the range of approximately 133 eV to 134 eV. Details of the XPS measurement method will be explained in the Examples below. As used herein, the term "phosphoric acid" refers, depending on the context, to orthophosphoric acid, condensed phosphoric acids such as pyrophosphoric acid and metaphosphoric acid, and also to alkali metal salts, alkaline earth metal salts, ammonium salts, and salts of organic nitrogen compounds such as amines, or to each of the individual phosphoric acids.

[0021] In relation to the XPS measurement described above, in the coated particles of the present invention, when the intensity (counts / s) of the peak observed at the energy value derived from the oxide of manganese in the XPS measurement is X1, and the intensity (counts / s) of the peak observed at the energy value derived from the P—O bond of phosphoric acid is X2, it is preferable that the value of X2 / X1 is 0.006 or more from the viewpoint of the gas generation suppression effect of a battery incorporating the coated particles of the present invention. From the viewpoint of making this advantage even more pronounced, the value of X2 / X1 is more preferably 0.007 or more, and even more preferably 0.01 or more. Furthermore, from the viewpoint of suppressing an increase in the electrode resistance of a battery incorporating the coated particles of the present invention, the value of X2 / X1 is preferably 0.1 or less, more preferably 0.05 or less, and even more preferably 0.03 or less.

[0022] Examples of the "manganese oxides" include MnO, MnO ２ , Mn ２ O ３ and Mn ３ O ４ and the like. The bond energy values ​​(Mn2p1) derived from these manganese oxides are observed in the range of approximately 653 eV to 655 eV. When multiple peaks derived from manganese oxides are observed in the XPS spectrum, the intensity of the peak with the highest intensity is taken as the value of X1. Similarly, when multiple peaks derived from the P—O bond of phosphoric acid are observed in the XPS spectrum, the intensity of the peak with the highest intensity is taken as the value of X2.

[0023] The coated particles of the present invention, whether used in a battery containing a solid electrolyte or a battery containing an electrolyte solution as the active material, effectively suppress gas generation from the battery due to the action of the coating layer. Furthermore, high-rate discharge can be performed satisfactorily. A preferred method for forming a coating layer having such advantages will be described later.

[0024] In the coated particles of the present invention, it is preferable that the coating layer contains tantalum (Ta) in addition to P and O elements, from the viewpoint of even more effectively suppressing gas generation from batteries exposed to high potential. From this viewpoint, in the coated particles of the present invention, the content of Ta element is preferably 10 ppm or more, more preferably 100 ppm or more, and even more preferably 200 ppm or more, when the coated particles are taken as 100 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 element is preferably 3000 ppm or less, more preferably 2900 ppm or less, more preferably 2800 ppm or less, and even more preferably 2300 ppm or less, when the coated particles are taken as 100 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. Note that, in this specification, "ppm" refers to a value based on mass.

[0025] In the coated particle of the present invention, when the coating layer contains Ta, there is no particular limitation on the state in which the Ta element is present. For example, the Ta element may be present in the form of an oxide. Alternatively, the Ta element may be present together with the P element in the form of a composite oxide.

[0026] In the coated particles of the present invention, it is also preferable that the coating layer further contains lithium (Li) element, from the viewpoint of even more effectively suppressing gas generation from a battery exposed to a high potential. In the coated particles of the present invention, when the coating layer contains Li element, there are no particular restrictions on the state of existence of the Li element. The Li element may exist, for example, in the form of an oxide. Alternatively, the Li element may exist, for example, in the form of a phosphate. In the coating layer, the Li element may be in a mixed state or a complex state with a compound containing P element. For example, when the compound containing P element is phosphoric acid, the Li element may exist in the form of a mixed oxide with phosphoric acid, a complex oxide with phosphoric acid, or a lithium phosphate salt.

[0027] In the coated particles of the present invention, the surface of the core particle is coated with a coating layer, so that in a battery containing the coated particles, the Mn element contained in the core particle is less likely to leach out. This is advantageous from the viewpoint of further suppressing gas generation from the battery and improving rate characteristics during discharge. From this viewpoint, when the amount of eluted Mn element when 1 g of the core particle is dispersed in 10 mL of an organic solvent containing a lithium salt and left at 85 ° C for 144 hours is defined as D1 (g), and the amount of eluted Mn element when 1 g of the coated particle is dispersed in 10 mL of an organic solvent containing a lithium salt and left at 85 ° C for 144 hours is defined as D2 (g), the value of D2 / D1 is preferably 0.8 or less, more preferably 0.6 or less, and even more preferably 0.4 or less. The lithium salt used in measuring the elution amounts D1 and D2 of the Mn element is LiPF ６ The organic solvent used to dissolve this lithium salt is a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3:7. The amount of dissolved Mn element is determined by ICP emission spectroscopy.

[0028] [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 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more, because excessive aggregation of particles is suppressed and dispersibility is improved. ５０ is preferably 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. ５０is 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.

[0029] The coated particles of the present invention have a BET specific surface area of ​​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 2m ２ The BET specific surface area is measured by a BET single-point method using a Macsorb manufactured by Mountech Co., Ltd.

[0030] [Method for Producing Coated Particles] Next, a preferred method for producing the coated particles of the present invention will be described. This method includes a step of coating the surfaces of core particles with a coating layer containing a phosphorus element. For this purpose, for example, a raw material liquid containing a phosphorus source is contacted with core particle powder to deposit the raw material liquid on the surfaces of the core particles, and the core particles are then fired to form a coating layer on the surfaces of the core particles. From the viewpoint of forming a uniform and thin coating layer on the surfaces of the core particles and facilitating the complexation of the P element with the optional Ta element, it is advantageous to use an aqueous liquid containing the P element, as described below. The coating method for depositing the raw material liquid containing a phosphorus source on the surfaces 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, electroplating coating, and an adhesion coating method in which the deposited raw material liquid is dried. Examples of fluidized bed coating methods include tumbling fluidized bed coating. In the adhesion coating method, the raw material liquid can be deposited by, for example, immersing the core particles in the raw material liquid or spraying the raw material liquid onto the surfaces 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. Among these coating methods, it is advantageous to use tumbling fluidized bed coating or adhesion coating. It is particularly advantageous to use tumbling fluidized bed coating. By using this method, a thin and uniform coating layer can be successfully formed over the entire surface of the core particles.

[0031] When the tumbling fluidized bed coating method is used, specifically, the following steps are carried out in this order to suitably obtain the desired coated particles: applying an aqueous liquid containing a P element to core particles containing a spinel-type composite oxide containing Li, Mn, and Ni while the core particles are tumbling; and heating the core particles to which the aqueous liquid has been applied in an oxidizing atmosphere to form a coating layer containing a compound in which a P element is bonded to an O element on the surface of the core particles.

[0032] When carrying out the above-mentioned method, 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 as the apparatus used to roll the core particles and to apply the aqueous liquid containing the P element while rolling the core particles using the apparatus. In this case, the thickness of the coating layer on the intended coated particles can be adjusted by adjusting the amount of the aqueous liquid attached to the core particles.

[0033] The aqueous liquid containing P preferably has a phosphorus content of 0.01% by mass or more and 10% by mass or less in terms of P atoms, in order to successfully form the desired coating layer. From this viewpoint, the phosphorus content is more preferably 0.01% by mass or more and 5% by mass or less, and even more preferably 0.05% by mass or more and 2% by mass or less in terms of P atoms.

[0034] The aqueous liquid containing P may further contain Li and / or Ta. The tantalum content in the aqueous liquid is preferably 0.01% by mass or more and 30% by mass or less, more preferably 0.5% by mass or more and 25% by mass or less, and even more preferably 1% by mass or more and 20% by mass or less, calculated as Ta atoms.

[0035] When the aqueous liquid containing P element further contains Li element and Ta element, from the viewpoint of being able to successfully form the target coating layer, the molar ratio Li / P of Li element to P element is preferably 0.01 or more and 5 or less, more preferably 0.01 or more and 2 or less, and even more preferably 0.05 or more and 2 or less. From the same viewpoint, the molar ratio Ta / P of Ta element to P element is preferably 0.01 or more and 10 or less, more preferably 0.05 or more and 5 or less, and even more preferably 0.1 or more and 3 or less.

[0036] The aqueous liquid containing P can be prepared, for example, through the following steps. Specifically, hydrogen peroxide is first added to a tantalum fluoride aqueous solution and neutralized with ammonia water or the like to obtain a tantalum hydroxide precipitate. The fluorine content can be reduced by repeatedly washing with ammonia water. Furthermore, the aqueous liquid containing P can be prepared through a reaction step in which an alkaline aqueous solution containing Li is added to the tantalum hydroxide precipitate to produce a tantalum compound aqueous solution, and a mixing step in which the tantalum compound aqueous solution is mixed with a phosphorus compound or a phosphorus compound solution. Furthermore, in the mixing step in which the tantalum compound aqueous solution and the phosphorus compound are mixed, an alkaline compound or an alkaline compound aqueous solution containing Li can be optionally added to prepare the aqueous liquid containing P. In the mixing step, it is preferable to mix the phosphorus compound or the phosphorus compound solution with the Li element to produce a phosphorus compound mixed solution with the tantalum compound aqueous solution. In this case, an alkaline compound containing Li (e.g., lithium hydroxide) or an alkaline compound aqueous solution may be added. Examples of the phosphorus compound that can be used include phosphoric acids such as orthophosphoric acid, metaphosphoric acid, and pyrophosphoric acid; phosphonic acids such as phosphorous acid and hypophosphorous acid; and phosphinic acid. From the viewpoint of increasing the pH of the aqueous liquid containing P, it is preferable to use pyrophosphoric acid as the phosphorus compound. The aqueous liquid containing P may further contain an alcohol-based solvent or a surfactant. The surfactant may contain, for example, one or more surfactants selected from nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants. Specific examples of nonionic surfactants include ester / ether types, ester types, ether types, and fluorine-based surfactants.

[0037] The aqueous liquid containing the P element is preferably in a state of higher dispersibility from the viewpoint of facilitating uniform application to the surface of a substrate. The highly dispersible state of the aqueous liquid containing the P element may be such that the maximum light transmittance in the wavelength region of 400 nm to 760 nm is 70% T or more. The maximum light transmittance in the wavelength region of 400 nm to 760 nm of the aqueous liquid containing the P element 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 even 100% T.

[0038] The aqueous liquid containing the phosphorus element 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 aqueous liquid containing the phosphorus element 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.

[0039] Furthermore, the aqueous liquid containing the P element may have a minimum light transmittance in a wavelength region of 400 nm to 760 nm of 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.

[0040] As a state of high dispersibility, the particle diameter (particle diameter D ５０ The particle diameter (particle diameter D) of the particles of the aqueous liquid containing the P element by dynamic light scattering may be 3000 nm or less. 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.

[0041] After applying the aqueous liquid containing P element to the surface of the core particles as described above, the core particles are fired. A thin, uniform coating layer can be formed by firing. It is possible to have phosphorus element present on the surface of the core particles without firing, 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 firing atmosphere is preferably an oxidizing atmosphere. Air is conveniently used as the oxidizing atmosphere, but this is not limited to this. 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, in order to successfully form a coating layer. When the firing temperature is within the above range, the firing time is preferably 5 minutes to 50 hours.

[0042] [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 30% by mass or more, 40% by mass or more, or 50% by mass or more of the coated particles, with the total solid content being 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.

[0043] 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 the organic electrolyte solution include solvents such as esters such as propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and γ-butyrolactone (hereinafter 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 "LiPF ). ６ "), lithium salts such as lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium halides, and lithium chloroaluminate.

[0044] 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), Li２ 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.

[0045] The active material 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 material.

[0046] 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.

[0047] [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 electrolyte solution disposed between the positive electrode layer and the negative electrode layer. The positive electrode layer contains the coated particles of the present invention. An example of such a battery is a lithium ion secondary battery comprising the coated particles of the present invention as a positive electrode active material. 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, rectangular, and coin shapes.

[0048] 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.

[0049] 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.

[0050] In addition to the above-described embodiments, the present invention further discloses the following coated particles, methods for producing the same, and lithium-ion secondary batteries. [1] A coated particle 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, manganese, and nickel, and the coating layer contains phosphorus, the phosphorus content of which 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 wherein a peak is observed in an energy value derived from a P-O bond of phosphoric acid by XPS measurement. [2] The coated particle according to [1], wherein the coating layer further contains tantalum, the tantalum content of which is 10 ppm by mass or more and 3000 ppm by mass or less when the coated particle is taken as 100% by mass. [3] The coated particles according to [1] or [2], wherein, when X1 is the intensity of a peak observed at an energy value derived from an oxide of manganese in XPS measurement, and X2 is the intensity of a peak observed at an energy value derived from a P—O bond of phosphoric acid, the value of X2 / X1 is 0.006 or more. [4] The coated particles according to any one of [1] to [3], wherein, when 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, the value of D2 / D1 is 0.8 or less. [5] A method for producing coated particles, comprising applying an aqueous liquid containing phosphorus to core particles containing a spinel-type composite oxide containing lithium, manganese, and nickel 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 a compound in which phosphorus is bonded to oxygen on the surfaces of the core particles. [6] The method according to [5], wherein the aqueous liquid further contains lithium, and the molar ratio of lithium to phosphorus in the aqueous liquid is 0.01 or more and 5.0 or less. [7] The method according to [5] or [6], wherein the aqueous liquid further contains tantalum.[8] The method according to [7], wherein the molar ratio of tantalum to phosphorus in the aqueous solution is 0.01 or more and 10.0 or less. [9] A lithium ion secondary battery comprising the coated particles according to any one of [1] to [4] as a positive electrode active material.

[0051] 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.

[0052] Example 1 (1) Preparation of core particles Spinel-type lithium nickel manganese composite oxide LiNi ０．５ Mn １．５ O ４ were prepared as core particles. (2) Formation of coating layer An aqueous liquid containing P element was applied to the core particles by a tumbling fluidized bed coating method. The amount of the aqueous liquid containing P element applied was set to an amount that would result in a coating layer thickness of 6 nm (calculated value). 40 g of a phosphorus compound mixed solution was used as the aqueous liquid containing P element. The Li / P molar ratio in the aqueous liquid containing P element was 1.8. Next, the core particles with the aqueous solution applied were fired at 750°C for 3 hours in an air atmosphere to obtain the desired coated particles. The aqueous liquid containing P element was prepared by the following procedure.

[0053] [Preparation of aqueous solution containing phosphorus element] 4.5 g of pyrophosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: diphosphoric acid (containing phosphoric acid), CAS number: 2466-09-3) and 419.1 g of pure water were placed in a polypropylene container, and 76.4 g of a 5% aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds. The 5% aqueous solution of lithium hydroxide monohydrate was prepared by adding 15 g of LiOH.H ２ O was mixed with 285 g of purified water.

[0054] Example 2 The spinel-type lithium nickel manganese composite oxide used in Example 1 was used as the core particle. An aqueous liquid containing P element was adhered to the core particle by a tumbling fluidized bed coating method. The amount of the aqueous liquid containing P element adhered was an amount that resulted in a coating layer thickness of 3 nm (calculated value). The Li / P molar ratio in the aqueous liquid containing P element was 1.8, and the Ta / P molar ratio was 0.4. The aqueous liquid containing P element was prepared by the following procedure. Except for the above, coated particles were obtained in the same manner as in Example 1.

[0055] [Preparation of aqueous solution containing phosphorus element] 2.9 g of pyrophosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: diphosphoric acid (containing phosphoric acid), CAS number: 2466-09-3) and 499.4 g of pure water were placed in a polypropylene container, and 38.4 g of a 5% aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds. The 5% aqueous solution of lithium hydroxide monohydrate was prepared by adding 15 g of LiOH.H ２ The phosphorus compound mixed solution was obtained by mixing 285 g of tantalum compound aqueous solution with 0. 59.3 g of a tantalum compound aqueous solution (described later) was added to the phosphorus compound mixed solution, and the mixture was stirred and mixed for 30 minutes to obtain an aqueous solution containing P. The tantalum compound aqueous solution was obtained as follows.

[0056] First, 137.9 g of tantalum hydroxide (Ta ２ O ５ A tantalum fluoride aqueous solution (Ta 66%) was dissolved in 120 g of a 55% hydrofluoric acid aqueous solution, and 849 g of pure water was added to the solution. ２ O ５ To 1,000 g of this tantalum fluoride aqueous solution, 36.1 g of hydrogen peroxide (H ２ O ２ (H ２ O ２ The aqueous solution was stirred for 5 minutes (a molar ratio of 1.0 to 1.0), and 1,036.1 g of this aqueous solution was added to aqueous ammonia (NH ３ (NH ３ / Ta molar ratio = 245, NH ３A reaction solution (pH 11) was obtained, with a fluoride ion / HF molar ratio of 30.6. This reaction solution was a slurry of a tantalum acid compound hydrate, in other words, a slurry containing a tantalum hydroxide precipitate. Next, this reaction solution was decanted using a centrifuge and washed until the amount of liberated fluoride ions was 100 mg / L or less, thereby obtaining a tantalum hydroxide precipitate from which the fluoride ions had been removed. At this time, ammonia water was used as the washing liquid. The tantalum hydroxide precipitate from which the fluoride ions had been removed was further diluted with pure water to obtain a tantalum-containing precipitate slurry. The tantalum-containing precipitate slurry diluted with pure water and a 5% aqueous solution of lithium hydroxide monohydrate were added to pure water at 70°C to 80°C and mixed to obtain an aqueous tantalum compound solution. The tantalum content in the aqueous tantalum compound solution was 4.06%, and the lithium content was 0.14%.

[0057] [Example 3] The core particles were the same spinel-type lithium nickel manganese composite oxide as used in Example 1. The aqueous liquid containing P had a Li / P molar ratio of 1.5 and a Ta / P molar ratio of 0.2. Except for these, the coated particles were obtained in the same manner as in Example 2.

[0058] [Example 4] The core particles were the same spinel-type lithium nickel manganese composite oxide as used in Example 1. The aqueous liquid containing P had a Li / P molar ratio of 1.8 and a Ta / P molar ratio of 0.1. Except for these, coated particles were obtained in the same manner as in Example 2.

[0059] [Example 5] As the core particles, a spinel-type lithium nickel manganese composite oxide LiNi different from the spinel-type lithium nickel manganese composite oxide used in Example 1 was used. ０．５ Mn １．５ O ４ The aqueous liquid containing P element had a Li / P molar ratio of 1.5 and a Ta / P molar ratio of 0.1. Except for these, the coated particles were obtained in the same manner as in Example 2.

[0060] [Example 6] As the core particles, a spinel-type lithium nickel manganese composite oxide LiNi different from the spinel-type lithium nickel manganese composite oxide used in Example 1 was used. ０．５ Mn １．５ O ４ The aqueous solution containing P element was used in which the Li / P molar ratio was 1.5 and the Ta / P molar ratio was 0.2. Except for these, the coated particles were obtained in the same manner as in Example 2.

[0061] [Example 7] As the core particles, a spinel-type lithium nickel manganese composite oxide LiNi different from the spinel-type lithium nickel manganese composite oxide used in Example 1 was used. ０．５ Mn １．５ O ４ The aqueous solution containing P element was used in which the Li / P molar ratio was 1.4 and the Ta / P molar ratio was 0.4. Except for these, the coated particles were obtained in the same manner as in Example 2.

[0062] Example 8 As the core particles, a spinel-type lithium nickel manganese composite oxide LiNi different from the spinel-type lithium nickel manganese composite oxide used in Example 1 was used. ０．５ Mn １．５ O ４ The aqueous liquid containing P element had a Li / P molar ratio of 0.8 and a Ta / P molar ratio of 1.6. Except for these, the coated particles were obtained in the same manner as in Example 2.

[0063] [Example 9] As the core particles, a spinel-type lithium nickel manganese composite oxide LiNi different from the spinel-type lithium nickel manganese composite oxide used in Example 1 was used. ０．５ Mn １．５ O ４ The aqueous liquid containing P element had a Li / P molar ratio of 0.8 and a Ta / P molar ratio of 1.6. The baking temperature was changed to 300°C. Except for these, the coated particles were obtained in the same manner as in Example 2.

[0064] [Example 10] As the core particles, a spinel-type lithium nickel manganese composite oxide LiNi different from the spinel-type lithium nickel manganese composite oxide used in Example 1 was used. ０．５ Mn １．５ O ４ The aqueous liquid used had a Li / P molar ratio of 1.5 and a Ta / P molar ratio of 0.2. The aqueous liquid was adhered to the core particles by a stirring coating method. Specifically, 100 g of core particles were used. An aqueous solution containing P element was used in an amount such that the thickness of the coating layer would be 3 nm (calculated value). A predetermined amount of pure water was also used. These were placed in a beaker, and a stirrer was added, followed by stirring the contents of the beaker with a stirrer for 30 minutes. The core particles were then recovered and dried overnight in a vacuum dryer at 80°C. Thereafter, the core particles with the aqueous liquid adhered thereto were fired at 750°C for 3 hours in an air atmosphere. Except for these points, the coated particles were obtained in the same manner as in Example 2.

[0065] Comparative Example 1 The core particles used as the raw material for the coated particles in Example 1 were used as the active material particles.

[0066] Comparative Example 2 The core particles used as the raw material for the coated particles in Example 5 were used as the active material particles.

[0067] [Evaluation] The particle size distribution D ５０ The specific surface area (BET) and specific surface area (SES) of the coated particles obtained in the Examples and Comparative Examples were measured by the methods described above. The amounts of phosphorus and tantalum were measured by the following methods for the coated particles obtained in the Examples and Comparative Examples. XPS and Mn elution amounts were measured for the coated particles obtained in the Examples and Comparative Examples by the following methods. XPS spectra of P and Mn for the coated particles of Example 1 are shown in Figures 1 and 2, respectively. 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 initial capacity, discharge rate characteristics, and gas generation amount of the batteries were measured. These results are shown in Table 1 below.

[0068] [Amounts of Phosphorus and Tantalum] Measurements were made using an ICP-AES analyzer (model: PS3520-DD2) manufactured by Hitachi High-Tech Science Corporation.

[0069] [XPS Measurement] The surfaces of the coated particles were analyzed using a PHI Quantes XPS device manufactured by ULVAC-PHI, Inc. The conditions used for the measurement were as follows: Excitation X-ray: Monomer Al-Kα ray (1486.6 eV) Output: 50 W Acceleration voltage: 20 kV X-ray irradiation diameter: 200 μmφ Measurement area: 1000 μm × 300 μm Pass energy: 26.0 eV Energy step: 0.1 eV

[0070] XPS data analysis was performed using data analysis software (ULVAC-PHI, Inc., "Multipack Ver. 9.9"). Shirley was used as the background mode. Charging correction was performed by setting the binding energy of the hydrocarbon (C-H) peak in the C1s spectrum to 284.8 eV. The orbitals used for calculation were determined for each element as follows: Li: 1s C: 1s O: 1s P: 2p Mn: 2p1 Furthermore, each peak intensity X1 and X2 was calculated using the following method. The binding energy of the highest peak in the XPS spectrum of Mn was used as the base point, and the average value of the intensity 5 eV before and after this base point was used as the background value. X1 was calculated by subtracting the background value from the highest peak intensity value. Similarly, the binding energy of the highest peak in the XPS spectrum of P was used as the base point, and the average value of the intensity 2 eV before and after this base point was used as the background value. X2 was calculated by subtracting the background intensity from the highest peak intensity.

[0071] [Mn elution amount] When 1 g of core particles was dispersed in 10 mL of an organic solvent containing a lithium salt and left at 85° C. for 144 hours, the elution amount of manganese element was defined as D1 (g), and when 1 g of coated particles was dispersed in 10 mL of an organic solvent containing a lithium salt and left at 85° C. for 144 hours, the elution amount of manganese element was defined as D2 (g). The value of D2 / D1 was determined as the elution amount of Mn. The organic solvent containing the lithium salt was a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3 / 7, and LiPF ６ The organic solvent used was one in which the compound was dissolved to a concentration of 1 mol / L.

[0072] [Initial Capacity] 90 parts of the coated particles obtained in the Examples and Comparative Examples, 6 parts of acetylene black, and 4 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 (solid content concentration 50%) 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 content concentration 50%).

[0073] 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 using the coater to maintain 70°C for 2 minutes, 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 12 mg / cm). ２ The negative electrode was a circular metal Li with a diameter of 19 mm and a thickness of 0.5 mm. The electrolyte was a solution of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) mixed in a volume ratio of 3 / 7, in which LiPF ６The electrolyte solution was dissolved to a concentration of 1 mol / L. A separator made of porous polypropylene film was impregnated with the electrolyte solution. A positive electrode and a negative electrode were placed on each side of the separator to prepare a TOMCELL (registered trademark) cell for electrochemical evaluation.

[0074] This battery was placed in an environmental test chamber set at 25°C and tested at 0.15 mA / cm ２ (equivalent to 0.1C) to 4.99V, and then charge at a constant current of 0.03mA / cm ２ The battery was then charged at a constant voltage until the current reached 0.15 mA / cm (equivalent to 0.02 C). ２ The battery was discharged at a constant current (equivalent to 0.1 C) to 3.0 V. The series of charge and discharge cycles was repeated three times, and the discharge capacity of the third cycle was taken as the initial capacity. The rate at which the initial discharge capacity of the fabricated cell was completely discharged in one hour was defined as 1 C.

[0075] [Rate characteristics] A battery similar to the battery used to measure the initial capacity described above was fabricated and subjected to a first charge / discharge cycle under the same conditions as those used to measure the initial capacity. Four more charge / discharge cycles were performed. The charge conditions were the same as the first cycle. The discharge conditions were 0.1 C for the second cycle, 0.5 C for the third cycle, 1.0 C for the fourth cycle, and 3.0 C for the fifth cycle. The ratio of the fifth discharge capacity to the first discharge capacity was calculated, and this value was taken as the rate characteristic.

[0076] [Gas Generation Amount] (1) Fabrication of Laminated Battery The aluminum foil with the positive electrode mixture layer obtained in the manufacturing process of the battery used to measure the initial capacity was punched out to a size of 50 mm x 100 mm and then pressed and consolidated using a roll press. The press linear pressure was 1.5 t / cm. After press consolidation, the aluminum foil with the positive electrode mixture layer was punched out to a 40 mm x 30 mm square. The punched aluminum foil with the positive electrode mixture layer was heated from room temperature to 200°C in a vacuum state and heated and dried by holding at 200°C for 6 hours. This produced a positive electrode (electrode basis weight 12 mg / cm ２ The lithium titanate was applied to an aluminum foil current collector to produce a negative electrode sheet, which was then cut into a size of 31 mm x 42 mm to obtain a negative electrode (electrode basis weight 11 mg / cm ２A laminated battery was fabricated by disposing a positive electrode and a negative electrode on each side of a separator (porous polypropylene film) impregnated with an electrolyte solution. The electrolyte solution was a carbonate-based mixed solvent containing LiPF at a concentration of 1 mol / L. ６ was prepared by dissolving

[0077] (2) Measurement of Gas Generation Amount The resulting laminated battery was charged and discharged four times at 25°C at 0.2C between 1.5V and 3.45V. A float test was then conducted at 60°C, and the amount of gas generated during the test was measured. The float test was conducted at a charging voltage of 3.45V and 0.1C for 144 hours, followed by constant current discharge at 0.1C to 1.5V. The volume of the laminated cell was then measured using the Archimedes method. The amount of gas generated was calculated by subtracting the volume of the cell immediately after fabrication from the volume of the cell after the float test. The relative amounts of gas generated for Examples 1 to 4 relative to the amount of gas generated for Comparative Example 1 were calculated.

[0078] [Cycle Retention Rate] (1) Preparation of Tomcell-Type Battery The aluminum foil with the positive electrode mixture layer obtained in the manufacturing process of the battery used to measure the initial capacity was punched out to a size of 50 mm x 100 mm and then pressed and consolidated using a roll press. The press linear pressure was 1.5 t / cm. After press consolidation, the aluminum foil with the positive electrode mixture layer was punched out to a size of 13 mmφ. The punched aluminum foil with the positive electrode mixture layer was heated from room temperature to 200°C in a vacuum state and heated and dried by holding at 200°C for 6 hours. This produced a positive electrode (electrode basis weight 12 mg / cm ２ The lithium titanate was applied to an aluminum foil current collector to produce a negative electrode sheet, which was then cut into a size of 14 mmφ to obtain a negative electrode (electrode capacity 1.8 mAh / cm ２ A positive electrode and a negative electrode were placed on each side of a separator (porous polypropylene film) impregnated with an electrolyte solution to prepare a TOMCELL (registered trademark) cell for electrochemical evaluation. The electrolyte solution was a carbonate-based mixed solvent containing LiPF 5 at a concentration of 1 mol / L. ６The resulting battery was charged and discharged three times at 0.1 C between 1.5 V and 3.45 V at 25°C. It was then charged at a constant current of 1 C to 3.45 V in an environmental test chamber set at 45°C. It was subsequently discharged at a constant current of 1 C to 3.0 V. This cycle of charging and discharging was repeated 100 times, and the value obtained by dividing the discharge capacity at the 100th time by the discharge capacity at the 5th time was defined as the cycle retention rate.

[0079]

[0080] As is clear from the results shown in Table 1, the batteries produced using the coated particles obtained in each Example exhibited initial capacities comparable to those of the batteries produced using the active materials of the Comparative Examples, while exhibiting improved discharge rate characteristics and suppressing the amount of gas generated by float charging.

[0081] The present invention is advantageous in that it relates to coated particles useful as active materials for batteries that can suppress gas generation when exposed to high potential compared to conventional techniques, and a method for producing the same. For example, it can suppress the generation of defective batteries that become unusable due to gas generation when exposed to high potential. From this perspective, it is possible to reduce the amount of waste from defective products and also reduce the energy costs associated with waste disposal. For these reasons, the present invention leads to the sustainable management and efficient use of natural resources, as well as the achievement of decarbonization (carbon neutrality).

Claims

1. 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, manganese, and nickel, and the coating layer contains phosphorus, the phosphorus content being 0.01% by mass or more and 1.0% by mass or less when the coated particle is taken as 100% by mass, and wherein a peak is observed at an energy value derived from the P-O bond of phosphoric acid by XPS measurement.

2. The coated particle according to claim 1, wherein the coating layer further contains elemental tantalum, and the content of elemental tantalum is 10 ppm or more and 3000 ppm or less by mass when the coated particle is taken as 100 mass %.

3. The coated particle according to claim 1 or 2, wherein the value of X2 / X1 is 0.006 or more, where X1 is the intensity of the peak observed at the energy value derived from the oxide of manganese in XPS measurement, and X2 is the intensity of the peak observed at the energy value derived from the P-O bond of phosphoric acid.

4. 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 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 at 85°C for 144 hours.

5. A method for producing coated particles, comprising: applying an aqueous liquid containing phosphorus to core particles containing a spinel-type composite oxide containing lithium, manganese, and nickel 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 a compound in which phosphorus is bonded to oxygen on the surface of the core particles.

6. The method according to claim 5, wherein the aqueous liquid further contains lithium element, and the molar ratio of lithium element to phosphorus element in the aqueous liquid is 0.01 or more and 5.0 or less.

7. The manufacturing method according to claim 5 or 6, wherein the aqueous liquid further contains elemental tantalum.

8. The method according to claim 7, wherein the molar ratio of tantalum to phosphorus in the aqueous solution is 0.01 or more and 10.0 or less.

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

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