Coated particles and method for manufacturing same

Abstract

The present invention addresses the problem of providing: coated particles useful as an active material for batteries capable of realizing high recovery capacity after storage under high-temperature conditions; and a method for producing the same. These coated particles each comprise 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 including elemental lithium and elemental manganese. The coating layer contains elemental phosphorus. The content of the elemental phosphorus is 0.01 to 1.0 mass% when the coated particles are taken to be 100 mass%. A peak is observed at an energy value corresponding to the P–O bond of phosphoric acid as determined by XPS measurement.

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 ２ O ４ and LiMn １．５ Ni ０．５ O ４ Known lithium manganese oxides include the following: Batteries equipped with a positive electrode containing an active material having lithium manganese oxide 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 does not provide better battery performance, such as a high recovery capacity after storage in a high-temperature environment. Therefore, an object of the present invention is to provide particles useful for active materials that can provide better battery performance than conventional technologies.

[0006] The present invention has solved 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 and manganese, 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.

[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 and manganese while rolling the core particles, and heating the core particles to which the aqueous liquid has been applied in an oxidizing atmosphere to form a coating layer containing 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), and oxygen (O). This spinel-type composite oxide is, for example, a spinel-type composite oxide represented by the general formula LiMn ２ O ４ It can be expressed as:

[0011] The core particle may contain elements other than lithium (Li), manganese (Mn), and oxygen (O). The other elements may be one type or two or more types. When the other elements are two or more types, at least one type of element is one type selected from the group consisting of Ni, Co, and Fe (hereinafter, referred to as "M １ It is preferable that M is an element. １ The element is a substitution element that mainly contributes to the development of an operating potential of 3.0 V or more relative to the metallic Li reference potential. The other element is M, which is one element or a combination of two or more elements selected from the group consisting of Na, Mg, Al, P, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce. ２ It is preferably an element. ２ The elements are mainly substitution elements that contribute to stabilizing the crystal structure and improving the properties. ２ By selecting the element from the above-mentioned elements, it is possible to improve the capacity retention rate. １ Elements and M ２ The elements are different elemental species.

[0012] A preferred composition example of the core particle is a spinel-type LiMn ２ O ４－δ A part of the Mn site in １ Elements and other M ２ In addition, examples of the lithium manganese oxide include spinel-type lithium manganese composite oxides having a crystal structure in which the lithium manganese oxide is substituted with the element represented by the formula (1): Li ｘ (M １ ｙ M ２ ｚ Mn ２－ｘ－ｙ－ｚ ) O ４－δ and formula (2): general formula [Li ｘ (Ni ｙ M ３ ｚ Mn ２－ｘ－ｙ－ｚ ) O ４－δ The spinel-type lithium manganese composite oxide represented by the formula (2) is ３As described above, the element is preferably one or a combination of two or more selected from the group consisting of Na, Mg, Al, P, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce.

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

[0014] Examples of spinel-type composite oxides include lithium manganese oxide, LiMn ２ O ４ , Li ４ Mn ５ O １２ (Li １．３３３ Mn １．６６７ O ４ ), Li ２ Mn ４ O ９ (Li ０．８８９ Mn １．７７８ O ４ ) and lithium manganese nickel oxide, LiNi ｘ Mn ２－ｘ O ４ (where x is a number greater than 0 and less than 2). The type and content of the metal element contained in the spinel-type composite oxide can be analyzed, for example, by ICP atomic emission spectroscopy. Other descriptions of the core particle are the same as those described in, for example, WO2017 / 150504A1. This publication is incorporated herein by reference.

[0015] The particle size of the core particles is appropriately selected depending on the particle size of the 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 core particle is configured to contain 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 stored in a high-temperature environment, the performance of the battery, for example, its recovery capacity, tends to decrease. To address this issue, 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), and oxygen (O) is effective, leading to the completion of the present invention. In particular, they have found that when the coating layer contains oxygen (O) in addition to P, the performance degradation of the battery stored in a high-temperature environment is further suppressed.

[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 0.02% 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 existence 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 performance degradation of batteries stored in high-temperature environments. 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 in the XPS measurement at the energy value derived from the oxide of manganese is designated as X1, and the intensity (counts / s) of the peak observed at the energy value derived from the P—O bond of phosphoric acid is designated as X2, it is preferable from the viewpoint of the recovery capacity of a battery incorporating the coated particles of the present invention that the value of X2 / X1 is 0.005 or more. From the viewpoint of making this advantage even more pronounced, the value of X2 / X1 is more preferably 0.006 or more, even 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, even more preferably 0.05 or less, and even more preferably 0.03 or less.

[0022] Examples of the "manganese oxides" include MnO, MnO ２ , Mn２ 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 effectively suppress deterioration of battery performance due to the action of the coating layer, whether the coated particles are used as the active material in a battery containing a solid electrolyte or in a battery containing an electrolytic solution. A preferred method for forming a coating layer having such advantages will be described later.

[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, from the viewpoint of more effectively suppressing performance degradation of batteries stored in high-temperature environments. From this viewpoint, in the coated particles of the present invention, the content of Ta 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% by mass. Furthermore, in the coated particles of the present invention, from the viewpoint of not impairing the basic performance as an active material, the content of Ta is preferably 3000 ppm or less, more preferably 2900 ppm or less, more preferably 2800 ppm or less, even more preferably 2000 ppm or less, and even more preferably 1000 ppm or less, when the coated particles are taken as 100% by mass. The content of Ta 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. In this specification, the term "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 more effectively suppressing the deterioration of battery performance when stored in a high-temperature environment. 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] [Method for Producing Coated Particles] Next, a preferred method for producing the coated particles of the present invention will be described. This production method includes a step of coating the surfaces of core particles with a coating layer containing a phosphorus element. For this purpose, for example, a raw material liquid containing a phosphorus source is contacted with core particle powder to adhere the raw material liquid to 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 compounding 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 adhering the raw material liquid containing a phosphorus source to 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 raw material liquid is applied and then dried. Examples of fluidized bed coating methods include tumbling fluidized bed coating. In the adhesion coating method, the raw material liquid can be adhered by, for example, immersing the core particles in the raw material liquid or spray-coating 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.

[0028] When the tumbling fluidized bed coating method is used, specifically, the following steps are carried out in this order: applying an aqueous liquid containing a P element to core particles containing a spinel-type composite oxide containing Li and Mn elements while rolling the core particles; and heating the core particles to which the aqueous liquid has been applied in an oxidizing atmosphere to form a coating layer containing a compound in which a P element is bonded to an O element on the surface of the core particles. This allows the desired coated particles to be obtained favorably.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] When the aqueous liquid containing P element further contains Li element and Ta element, from the viewpoint of successfully forming the target coating layer, the molar ratio Li / P of Li element to P element is preferably 0.01 or more and 5.0 or less, more preferably 0.01 or more and 2.0 or less, and even more preferably 0.05 or more and 2.0 or less. From the same viewpoint, the molar ratio Ta / P of Ta element to P element is preferably 0.01 or more and 10.0 or less, more preferably 0.05 or more and 5.0 or less, and even more preferably 0.1 or more and 3.0 or less.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] [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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] [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.

[0045] 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.

[0046] 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.

[0047] 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 and manganese, 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 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 being 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 the value of X2 / X1 is 0.005 or more, where 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. [4] A method for producing coated particles, comprising: applying an aqueous liquid containing phosphorus to core particles containing a spinel-type composite oxide containing lithium and manganese while rolling the core particles; and heating the core particles to which the aqueous liquid has been applied in an oxidizing atmosphere to form a coating layer containing a compound in which phosphorus is bonded to oxygen on the surfaces of the core particles. [5] The method according to [4], 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. [6] The method according to [4] or [5], wherein the aqueous liquid further contains tantalum. [7] The manufacturing method according to [6], wherein the molar ratio of tantalum to phosphorus in the aqueous liquid is 0.01 or more and 10 or less. [8] A lithium ion secondary battery comprising the coated particles according to any one of [1] to [3] as a positive electrode active material.

[0048] 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.

[0049] Example 1 (1) Preparation of core particles Spinel-type lithium manganese composite oxide LiMn ２ O ４ was prepared as the core particle.

[0050] (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 3 nm (calculated value). Next, the core particles with the aqueous liquid applied were fired at 750°C for 3 hours in an air atmosphere to obtain the desired coated particles. 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.

[0051] [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.

[0052] 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 O2 content 35%) was added (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 (NH３ (NH ３ / Ta molar ratio = 245, NH ３ A 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%.

[0053] [Example 2] The aqueous liquid 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 this, the coated particles were obtained in the same manner as in Example 1.

[0054] Example 3 Instead of the aqueous liquid containing P element used in Example 1, 40 g of the following aqueous liquid containing P element was used. The Li / P molar ratio in the aqueous liquid containing P element was 1.8. The amount of the aqueous liquid containing P element attached was an amount that resulted in a coating layer thickness of 6 nm (calculated value). Except for this, coated particles were obtained in the same manner as in Example 1.

[0055] [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.

[0056] [Example 4] The aqueous liquid used in Example 1 was used, and the amount of the aqueous liquid containing P element attached was adjusted to an amount that would result in a coating layer thickness of 5 nm (calculated value). Covered particles were obtained in the same manner as in Example 1.

[0057] Example 5: Instead of the aqueous liquid containing P element used in Example 1, an aqueous liquid having a Li / P molar ratio of 1.8 and a Ta / P molar ratio of 0.1 was used. The aqueous liquid was adhered to 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 was 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 calcined at 750°C for 3 hours in an air atmosphere to obtain the desired coated particles.

[0058] 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.

[0059] [Evaluation] The amounts of phosphorus and tantalum were measured for the coated particles obtained in the Examples and Comparative Examples using the following method. Furthermore, XPS measurements were performed for the coated particles obtained in the Examples and Comparative Examples using the following method. The 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 recovered capacity and cycle retention rate of the batteries were measured. These results are shown in Table 1 below.

[0060] [Amounts of Phosphorus and Tantalum] Measurements were made using an ICP-AES analyzer (model: PS3520-DD2) manufactured by Hitachi High-Tech Science Corporation.

[0061] [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

[0062] 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.

[0063] [Recovery Capacity] 89 parts of the coated particles obtained in the Examples and Comparative Examples, 5 parts of acetylene black, and 6 parts of polyvinylidene fluoride (PVDF) were weighed and mixed, and 100 parts of 1-methyl-2-pyrrolidone (NMP) was added thereto, and a positive electrode mixture slurry (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%).

[0064] This positive electrode mixture slurry was applied to an aluminum foil current collector at a conveying speed of 20 cm / min using a coater, and then heated to 70°C for 2 minutes using the coater, followed by drying at 120°C for 2 minutes to form a positive electrode mixture layer, thereby obtaining an aluminum foil with a positive electrode mixture layer. Next, this aluminum foil with a positive electrode mixture layer was punched out to an electrode 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 to 13 mmΦ. 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, resulting in a positive electrode (electrode basis weight 15 mg / cm). ２ )

[0065] A negative electrode sheet was produced by applying natural spherical graphite to a copper foil current collector, and this was then punched out to a diameter of 14 mm to form a negative electrode. A TOMCELL (registered trademark) electrochemical evaluation cell was produced by placing the positive and negative electrodes on either side of a separator made of borosilicate glass fiber impregnated with an electrolyte. The electrolyte was a 3:7 volume mixture of ethylene carbonate and dimethyl carbonate, to which LiPF was added to achieve a concentration of 1 mol / L. ６ was prepared by dissolving

[0066] When the discharge capacity of this battery is 100% at 25°C, the capacity equivalent to 10% is 0.15 mA / cm ２ (equivalent to 0.1 C) and left open circuit for 9 hours (hereinafter referred to as "SOC 10%)." After that, the battery was charged to an SOC of 60% and left open circuit for 24 hours, after which it was charged at a constant current of 0.015 mA / cm ２ The battery was then charged at a constant voltage until the current reached 0.15 mA / cm (equivalent to 0.01 C). ２Initial activation was performed by constant current discharge at 0.2C (equivalent to 0.1C) to 3.0V. The rate at which the initial discharge capacity of the prepared cell was completely discharged in 1 hour is defined as 1C. After initial activation in this manner, the cell was charged at a constant current of 0.2C to 4.2V, and once 4.2V was reached, constant voltage charging was performed to 0.01C. A constant current discharge was then performed at 0.2C to 3.0V, and the initial discharge capacity was determined. A constant current charge was then performed at 0.2C to 4.2V, and once 4.2V was reached, constant voltage charging was performed to 0.01C. The battery was then left in a 60°C environment for 7 days, after which a constant current discharge was performed at 0.2C to 3.0V. A constant current charge was then performed at 0.2C to 4.2V, and once 4.2V was reached, constant voltage charging was performed to 0.01C. A constant current discharge was then performed at 0.2C to 3.0V, and the discharge capacity after storage was determined. The ratio of the discharge capacity after storage to the initial discharge capacity was calculated, and this value was determined as the recovery capacity.

[0067] [Cycle Retention Rate] A battery similar to the battery used for measuring the recovered capacity described above was fabricated, and the cycle retention rate of the battery was measured by the following procedure. The battery was charged at a constant current of 0.5 C to 4.2 V, and once 4.2 V had been reached, it was charged at a constant voltage of 0.01 C, and then discharged at a constant current of 0.5 C to 3.0 V. This charge / discharge cycle was repeated 50 times. The discharge capacity at the 50th cycle was divided by the discharge capacity at the first cycle to obtain a percentage (%), which was used as the cycle retention rate.

[0068]

[0069] As is clear from the results shown in Table 1, the batteries manufactured using the coated particles obtained in each example have high recovered capacity values ​​and high cycle retention rates even after storage in a high-temperature environment.

[0070] According to the present invention, coated particles useful as active materials for batteries capable of achieving high recovered capacity after storage in a high-temperature environment, and a method for producing the same, can be provided. The present invention is advantageous in that it relates to coated particles useful as active materials capable of achieving better battery performance than conventional techniques, and a method for producing the same. The present invention is also advantageous in that it relates to coated particles useful as active materials for batteries capable of achieving high recovered capacity after storage in a high-temperature environment, and a method for producing the same. Therefore, for example, the generation of defective batteries that cannot achieve sufficient recovered capacity after storage in a high-temperature environment can be suppressed. From this perspective, it is possible to reduce waste of defective products and cut 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 and manganese, 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 in XPS measurement at an energy value derived from the P-O bond of phosphoric acid.

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

5. The method according to claim 4, 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.

6. The manufacturing method according to claim 4 or 5, wherein the aqueous liquid further contains elemental tantalum.

7. The method according to claim 6, wherein the molar ratio of tantalum to phosphorus in said aqueous solution is 0.01 or more and 10 or less.

8. 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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