Active material and method for producing same, and electrode mixture, electrode, and battery including same

Abstract

An active material according to the present invention comprises core material particles and a coating part disposed on the surface of the core material particles. The coating part contains at least one of lithium sulfide and lithium halide. It is preferable that the coating part furthermore contains at least one of lithium sulfate and a lithium salt of phosphoric acid. The lithium salt of phosphoric acid is preferably lithium metaphosphate. The total amount of lithium halide and lithium sulfide is preferably 0.01-0.80 parts by mass with respect to 100 parts by mass of the core material particles. The lithium halide is preferably lithium chloride, lithium bromide, or lithium iodide. The coverage of the coating part is preferably 30-100%.

Description

Active material and its manufacturing method, and electrode mixture, electrode, and battery containing the same

[0001] The present invention relates to an active material and a method for producing the same, as well as an electrode mixture, an electrode, and a battery containing the same.

[0002] In recent years, CO ２ Secondary batteries have been attracting attention as an approach to preventing global warming by reducing CO2 emissions. Various technologies for forming a coating layer on the surface of an active material are known to improve various performances of secondary batteries.

[0003] For example, Patent Documents 1 and 2 describe coating the surface of an active material with a lithium ion conductive oxide. These documents state that this coating can prevent a high-resistance layer from being formed between the active material and the solid electrolyte, thereby improving the output characteristics of, for example, an all-solid-state lithium battery.

[0004] US Patent Application Publication No. 2009 / 0081554 US Patent Application Publication No. 2018 / 0219229

[0005] In recent years, among secondary batteries, solid-state batteries have been expected to be put into practical use as batteries that combine safety and high energy density. However, solid-state batteries have issues with storage characteristics, and changes in battery characteristics can occur. This tendency is particularly pronounced under high temperatures and high voltages. As mentioned above, the technologies described in Patent Documents 1 and 2 are aimed at improving the output characteristics of batteries, but storage characteristics have not been considered. Therefore, an object of the present invention is to provide an active material that can improve the storage characteristics of batteries.

[0006] The present invention solves the above-mentioned problems by providing an active material having core particles and a coating portion disposed on the surface of the core particles, wherein the coating portion contains at least one of lithium sulfide and lithium halide.

[0007] The present invention also provides a method for producing an active material, which comprises mixing lithium sulfate or a lithium salt of phosphate with lithium sulfide or a lithium halide to obtain a mixed powder for coating, and dry-mixing a mixture containing the mixed powder for coating and core particles to dispose a coating portion containing the mixed powder for coating on the surface of the core particles.

[0008] The present invention will be described below based on preferred embodiments. In this specification, "the value of B relative to A" means the ratio B / A of A and B. The present invention relates to an active material for a battery, for example, an active material for a lithium ion battery, and a method for producing the same. The active material of the present invention has core particles and a coating portion disposed on the surface of the core particles. The core particles are composed of an active material matrix, which is a portion that accounts for the majority of the active material. The coating portion, core particles, and active material will each be described below.

[0009] [Coating portion] The coating portion contains at least one of lithium sulfide and lithium halide. As a result of extensive research by the present inventors to improve the storage characteristics of a battery, it was found that the storage characteristics of a battery can be improved by forming a coating portion containing a specific compound on the surface of the active material base material. This is presumably due to the suppression of the reaction between the active material and the solid electrolyte. Furthermore, while this reaction is particularly pronounced under high temperatures and / or high voltages, it was found that the active material of the present invention can improve the storage characteristics of a battery even in such environments.

[0010] Examples of the lithium halide contained in the coating portion include lithium fluoride, lithium chloride, lithium bromide, and lithium iodide. The lithium halides can be used alone or in combination. The lithium halide can be selected, for example, depending on the type of halogen in the solid electrolyte used together with the active material. From the viewpoint of improving the storage characteristics of the battery, the lithium halide is preferably at least one of lithium chloride, lithium bromide, and lithium iodide, and more preferably lithium chloride.

[0011] When the coating portion contains at least one of the lithium sulfide and the lithium halide, the storage characteristics of a battery using an active material having the coating portion are improved. From the viewpoint of making this effect significant, the coating portion preferably contains at least a lithium halide, and more preferably contains both lithium sulfide and a lithium halide.

[0012] From the viewpoint of suppressing the reaction between the active material and the solid electrolyte and improving the storage characteristics of the battery, the total amount of lithium halide and lithium sulfide is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.08 parts by mass or more, relative to 100 parts by mass of the core particles. Furthermore, from the viewpoint of ensuring the battery capacity and the ionic conductivity and electronic conductivity within the battery, the total amount of lithium halide and lithium sulfide is preferably 0.80 parts by mass or less, more preferably 0.60 parts by mass or less, and even more preferably 0.50 parts by mass or less, relative to 100 parts by mass of the core particles.

[0013] The reason why the storage characteristics of the battery containing the active material of the present invention are improved is believed to be as follows: When the solid electrolyte decomposes, various decomposition products are generated, causing changes in the battery characteristics. For example, when the solid electrolyte is Li ６ P.S. ５ In the case of a material having a composition represented by X (X represents a halogen element), a decomposition reaction represented by the following formula (1) can occur. This reaction is an equilibrium reaction.

[0014]

[0015] In this way, Li ６ P.S. ５ The decomposition reaction of X gives LiX and Li ２ S may be generated. This decomposition reaction can also occur on the surface of the active material where the solid electrolyte is present. Therefore, by preliminarily disposing the decomposition product on the surface of the active material, the equilibrium reaction represented by formula (1) can be shifted to the left. As a result, it is presumed that the decomposition of the solid electrolyte can be suppressed. This is thought to suppress the reaction between the active material and the solid electrolyte, thereby improving the storage characteristics of the battery.

[0016] The coating portion preferably further contains at least one of lithium sulfate and a lithium salt of phosphoric acid. Examples of lithium salts of phosphoric acid include lithium salts of orthophosphoric acid, and lithium salts of pyrophosphoric acid, metaphosphoric acid, and polyphosphoric acid, which are condensates of orthophosphoric acid. The lithium salts of phosphoric acid can be used alone or in combination of two or more. When the coating portion contains at least one of lithium sulfate and a lithium salt of phosphoric acid, the initial resistance of the solid-state battery can be reduced and the storage characteristics can be improved. From the viewpoint of making such effects significant, the lithium salt of phosphoric acid is preferably lithium metaphosphate. From the same viewpoint, the coating portion preferably contains both lithium sulfate and a lithium salt of phosphoric acid, and particularly preferably contains both lithium sulfate and lithium metaphosphate.

[0017] From the viewpoint of reducing the initial resistance of the solid-state battery and improving the storage characteristics, the total amount of lithium sulfate and the lithium salt of phosphate is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more, and even more preferably 4.0 parts by mass or more, per 100 parts by mass of the core particles. Furthermore, from the viewpoint of ensuring the battery capacity and the ionic conductivity and electronic conductivity within the battery, the total amount of lithium sulfate and the lithium salt of phosphate is preferably 10.0 parts by mass or less, more preferably 9.0 parts by mass or less, and even more preferably 7.0 parts by mass or less, per 100 parts by mass of the core particles.

[0018] In order to set the proportions of lithium sulfide, lithium halide, lithium sulfate and lithium salt of phosphate within the above ranges, it is preferable to adjust the blending of the coating mixed powder in the production method described below.

[0019] The aforementioned lithium sulfide, lithium halide, lithium sulfate, and lithium salt of phosphate (hereinafter, these are also collectively referred to simply as "lithium compounds for coating") are present on the surface of the core particles in the form of (I) particles, (II) aggregated particles formed by aggregation of particles, or (III) a layer. "Present in the form of a layer" means a state in which the aforementioned compounds are present with a certain thickness. In this specification, any of the above embodiments (I) to (III) is encompassed by "a coating portion containing lithium sulfide, lithium halide, lithium sulfate, and lithium salt of phosphate is formed."

[0020] In the active material, the content of the coating lithium compound is preferably within a predetermined range. Specifically, from the viewpoint of suppressing the reaction between the active material and the solid electrolyte and improving the storage characteristics of the battery, the amount of the coating lithium compound is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more, and even more preferably 4.0 parts by mass or more, relative to 100 parts by mass of the core particles. Furthermore, from the viewpoint of ensuring the battery capacity and the ionic conductivity and electronic conductivity within the battery, the amount of the coating lithium compound is preferably 10.0 parts by mass or less, more preferably 9.0 parts by mass or less, and even more preferably 7.0 parts by mass or less, relative to 100 parts by mass of the core particles.

[0021] The state of the lithium compound for coating depends on the method for forming the coating portion. Depending on the method for forming the coating portion, the lithium compound for coating may be present in a mixed state in the coating portion (this state is also referred to as a "single layer"). Alternatively, the coating portion may be formed by stacking a layer containing primarily one compound and a layer containing primarily another compound (this state is also referred to as a "multilayer"). Regardless of whether the coating portion is single-layer or multilayer, it is preferable that lithium sulfide or lithium halide be present in a predetermined region in the thickness direction. As described above, when a solid electrolyte decomposes, various decomposition products are generated. The inventors' research has revealed that, in particular, by positioning lithium sulfide or lithium halide in a position where it can come into contact with the solid electrolyte, decomposition of the solid electrolyte can be suppressed. From the viewpoint of making this effect more pronounced, it is preferable that lithium sulfide or lithium halide be present on the surface of the coating portion. Specifically, when the coating portion is single-layer, it is preferable that lithium sulfide or lithium halide be present on the surface of the coating portion. Alternatively, when the coating portion has multiple layers, it is preferable that lithium sulfide or lithium halide is present in the outermost layer of the coating portion, and lithium sulfate and a lithium salt of phosphoric acid are present in layers further inward than the outermost layer.

[0022] The coating portion may further contain other compounds in addition to the coating lithium compound. The other compounds may be used singly or in combination of two or more. When the coating portion contains other compounds, the suitable amount of the other compounds is 0.1 to 5.0 parts by mass per 100 parts by mass of the core particles. However, from the viewpoint of improving the storage characteristics of the battery at high temperatures, the coating portion may contain LiNbO ３ , LiNbO, and Li ３ NbO ４ Lithium niobium composite oxides such as LiTaO ３ It is preferable that the material does not contain compounds with low heat resistance such as lithium tantalum composite oxides.

[0023] Even when the coating portion contains other compounds, as described above, it is preferable that at least lithium sulfide or lithium halide is present on the surface of the coating portion. Specifically, when the coating portion is a single layer, it is preferable that at least lithium sulfide or lithium halide is present on the surface of the coating portion. Alternatively, when the coating portion is a multilayer, it is preferable that at least lithium sulfide or lithium halide is present in the outermost layer of the coating portion, and that lithium sulfate, a lithium salt of phosphate, and other compounds are present in layers more inward than the outermost layer.

[0024] In order to make the compound in the coating portion exist in the above-mentioned state, it is preferable to change the order in which the coating mixed powder is arranged on the surface of the core particle in the manufacturing method described below.

[0025] The proportions of the lithium coating compound and other compounds contained in the coating portion, the total amount of the lithium coating compound and / or any compounds in the lithium coating compound per 100 parts by mass of the core particles, and the state of existence of these compounds can be measured by elemental analysis using ICP atomic emission spectroscopy. If necessary, measurements of X-ray absorption fine structure (XAFS), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) can also be combined.

[0026] The thickness of the coating portion is preferably within a predetermined range. Specifically, the thickness of the coating portion is preferably 1 nm or more, more preferably 3 nm or more, even more preferably 5 nm or more, even more preferably 10 nm or more, particularly preferably 20 nm or more, and especially preferably 30 nm or more. Furthermore, the thickness of the coating portion is preferably 100 nm or less, more preferably 80 nm or less, and even more preferably 60 nm or less. By setting the thickness of the coating portion within the above range, excessive increase in interface resistance due to the formation of the coating portion is suppressed, and the coating portion can function as a good lithium ion conductive layer.

[0027] The thickness of the coating portion can be measured by, for example, X-ray photoelectron spectroscopy (XPS). If necessary, it can also be measured by observation using a scanning transmission electron microscope (STEM) in combination with Auger electron spectroscopy (AES).

[0028] There may be some areas on the surface of the core particle where the coating portion is not present. In this case, it is preferable that the coating portion is disposed on 30% or more of the entire surface area of ​​the core particle, preferably 40% or more, and more preferably 50% or more (this value is also referred to as the "coverage rate"). From the viewpoint of suppressing the reaction between the active material and the solid electrolyte and improving the storage characteristics of the battery, the higher the coverage rate by the coating portion, the more preferable. The coating portion may be disposed on 100% or less of the entire surface area of ​​the core particle. The coverage rate can be confirmed, for example, by observing the surface of the core particle using X-ray photoelectron spectroscopy (XPS) in combination with, if necessary, a scanning transmission electron microscope (STEM) and energy dispersive X-ray analysis (EDS), as described above, in addition to Auger electron spectroscopy (AES). The thickness of the coating portion disposed on the surface of the core particle does not need to be uniform.

[0029] [Core Particles] The core particles are not particularly limited as long as they function as an active material. The core particles may contain, for example, a lithium metal composite oxide. As the lithium metal composite oxide, a known lithium metal composite oxide can be used. For example, the core particles may be formed of a material having the general formula LiM ２ O ４ (M represents a metal element), a lithium transition metal composite oxide having a spinel structure represented by the general formula LiMO ２ (M represents a metal element), a lithium transition metal composite oxide having a layered rock salt structure represented by the general formula LiMPO ４ (M represents a metal element). Alternatively, it may be a combination of two or more of these. However, it is not limited to these.

[0030] [Core Particle A] The core particles are preferably particles made of a lithium transition metal composite oxide having a spinel structure containing Li, Mn, and O and one or more other elements (hereinafter, these core particles will also be referred to as "core particles A"). When the active material of the present invention containing core particles A is used as a positive electrode active material, it has an operating potential of 4.5 V or higher relative to metallic Li. "Having an operating potential of 4.5 V or higher relative to metallic Li" does not necessarily mean that the active material has only an operating potential of 4.5 V or higher in the plateau region, but also includes cases where the active material has a partial operating potential of 4.5 V or higher. Therefore, the present invention is not limited to a positive electrode active material consisting solely of a 5 V-class positive electrode active material having an operating potential of 4.5 V or higher in the plateau region. For example, the active material of the present invention may also include a positive electrode active material having an operating potential of less than 4.5 V in the plateau region. Specifically, it is preferable that the 5V-class positive electrode active material occupies, for example, 30% by mass or more, preferably 50% by mass or more, and particularly preferably 80% by mass or more (including 100% by mass) of the positive electrode active material.

[0031] As described above, the core particle A is preferably a particle made of a spinel-type composite oxide containing Li, Mn, and O and two or more other elements. At least one of the "two or more other elements" is preferably a metal element M1 selected from the group consisting of Ni, Co, and Fe, and the other element is preferably a metal element M2 consisting of one or a combination of two or more selected from the group consisting of Na, Mg, Al, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce.

[0032] A preferred composition example of the core particle A is LiMn ２ O ４－δ Examples of the lithium-manganese-containing spinel composite oxide include those having a crystal structure in which a part of the Mn sites in the formula (I) is substituted with Li, a metal element M1, and another metal element M2.

[0033] The metal element M1 is a substitution element that mainly contributes to realizing an operating potential of 4.5 V or more relative to the metallic Li reference potential, and examples thereof include Ni, Co, and Fe. The active material A may contain at least one of these elements, and it is particularly preferable that the active material A contains at least one element selected from Ni and Co.

[0034] The metal element M2 is a substitution element that mainly contributes to stabilizing the crystal structure and improving characteristics. Examples of substitution elements that contribute to improving the capacity retention rate include Na, Mg, Al, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce. Among these, Na, Mg, Al, K, Ca, Ti, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, Ta, and W are preferred. The metal element M2 may be one or a combination of two or more of the above-mentioned elements. The metal element M2 preferably contains at least one of the above-mentioned elements, and may also contain a metal element other than the above-mentioned elements. The metal element M2 contained in the structure is a different element species from the metal element M1.

[0035] An example of the composition of the core particle A is a compound represented by the formula (1): Li ｘ (M1 ｙ M2 ｚ Mn ２－ｙ－ｚ ) O ４－δ The metal element M1 and the metal element M2 in the formula (1) are as described above.

[0036] In the formula (1), "x" is preferably 1.00 or more, more preferably 1.01 or more, and even more preferably 1.02 or more. In the formula (1), "x" is preferably 1.20 or less, more preferably 1.10 or less, and even more preferably 1.08 or less. "y" indicating the content of the metal element M1 is preferably 0.20 or more, more preferably 0.30 or more, and even more preferably 0.35 or more. "y" indicating the content of the metal element M1 is preferably 1.20 or less, more preferably 1.10 or less, and even more preferably 1.05 or less. "z" indicating the content of the metal element M2 is preferably 0.001 or more, more preferably 0.002 or more, more preferably 0.005 or more, and even more preferably 0.100 or more. Setting "z" to 0.100 or more can more effectively improve cycle characteristics. Furthermore, "z", which indicates the content of the metal element M2, is preferably, for example, 0.400 or less, and more preferably 0.300 or less.

[0037] Another example of the composition of the core particle A is a compound represented by the formula (2): Li ｘ (Ni ｙ M3 ｚ Mn ３－ｘ－ｙ－ｚ ) O ４－δ Examples of suitable lithium-manganese-containing spinel composite oxides include those represented by the formula (2). In formula (2), "x" is preferably 1.00 or more, more preferably 1.01 or more, and even more preferably 1.02 or more. In formula (2), "x" is preferably 1.20 or less, more preferably 1.10 or less, and even more preferably 1.08 or less. In formula (2), "y" is preferably 0.20 or more, more preferably 0.30 or more, and even more preferably 0.35 or more. In formula (2), "y" is preferably 0.70 or less, more preferably 0.60 or less, and even more preferably 0.55 or less.

[0038] In the formula (2), examples of the metal element M3 include Na, Mg, Al, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce. Of these, Na, Mg, Al, K, Ca, Ti, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, Ta, and W are preferred. The metal element M3 may be one or a combination of two or more of the aforementioned elements. "z," which indicates the molar ratio of the metal element M3, is preferably greater than 0, more preferably greater than 0.01, even more preferably 0.05 or greater, and even more preferably 0.10 or greater. By setting "z" to be equal to or greater than this lower limit, the cycle characteristics can be more effectively improved. Furthermore, "z" indicating the molar ratio of the metal element M3 is preferably, for example, 0.50 or less, more preferably 0.45 or less, even more preferably 0.40 or less, and even more preferably 0.35 or less.

[0039] In addition, "4-δ" in the above formulas (1) and (2) indicates that oxygen vacancies may be present. Furthermore, a portion of the oxygen may be substituted with fluorine or other elements. In this case, δ is preferably 0 or more. Furthermore, δ is preferably, for example, 0.20 or less, more preferably 0.10 or less, and even more preferably 0.05 or less.

[0040] The core particle A may contain B (boron). The state of B may include a composite oxide phase containing Ni, Mn, and B in addition to a spinel crystal phase. Examples of the composite oxide phase containing Ni, Mn, and B include Ni, Mn, and B. ５ MnO ４ (BO ３ ) ２ The crystal phase of Ni can be mentioned. ５ MnO ４ (BO ３ ) ２ The presence of the crystalline phase can be confirmed by comparing the diffraction pattern obtained by X-ray diffraction (XRD) with PDF (Powder Diffraction File) number "01-079-1029."

[0041] Regarding the content of the complex oxide phase containing Ni, Mn, and B, it is preferable to contain the complex oxide phase so that the content of the B element in the core particle A is 0.02 mass% or more, and more preferably 0.05 mass% or more. A B element content of 0.02 mass% or more is preferable because it allows the discharge capacity at high temperatures to be maintained. Furthermore, it is preferable to contain the complex oxide phase so that the content of the B element in the core particle A is 0.80 mass% or less, and more preferably 0.60 mass% or less, more preferably 0.30 mass% or less, and particularly preferably 0.25 mass% or less. A B element content of 0.80 mass% or less is preferable because it allows the rate characteristics to be maintained.

[0042] The core particle A may contain components other than the above-mentioned Li, Mn, metal element M1, metal element M2, metal element M3, O, and B. In particular, the other elements may be contained in an amount of 0.5 mass% or less, because this amount is considered to have little effect on the performance of the core particle.

[0043] It should be noted that when the core particle A is fitted to a cubic crystal structure model of the space group Fd-3m (Origin Choice 2), for example, the ranges of Rwp and S, which indicate the degree of agreement between the observed intensity and the calculated intensity, are Rwp<10 or S<2.5, and thus it can be confirmed that the core particle A has a spinel structure.

[0044] The primary particles of the core particles A may be either single crystal or polycrystalline, but are preferably polycrystalline. A single crystal refers to a particle in which the primary particle is composed of a single crystallite, and a polycrystalline refers to a particle in which multiple crystallites exist within the primary particle. Whether the core particles are polycrystalline or not can be confirmed by observing the cross section of the primary particle using electron backscatter diffraction (EBSD). In the case of a polycrystalline particle, it can be confirmed that crystals with multiple orientations exist within the primary particle.

[0045] [Core Particles B] The core particles are also preferably particles made of a lithium transition metal composite oxide having a layered rock salt structure, containing Li, an M element (M includes at least one or a combination of two or more elements selected from the group consisting of Ni, Co, Mn, and Al), and O (hereinafter, these core particles will also be referred to as "core particles B"). The active material of the present invention may contain other components in addition to the core particles B. However, from the viewpoint of effectively obtaining the properties of the core particles B, it is preferable that the core particles B account for, for example, 80% by mass or more, preferably 90% by mass or more, and of these, 95% by mass or more (including 100% by mass).

[0046] The core particles B are represented by the formula (3): Li １＋ｘ M １－ｘ O ２ (wherein M is a combination of one or more elements selected from the group consisting of Ni, Co, Mn, and Al, or includes a combination of one or more elements selected from the group consisting of Ni, Co, Mn, and Al and a combination of one or more elements selected from the group consisting of transition metal elements present in Groups 3 to 11 of the periodic table and typical metal elements from Periods 1 to 3 of the periodic table).

[0047] Formula (3): Li １＋ｘ M １－ｘ O ２ In the formula (3), "1+x" is, for example, 0.95 or more, preferably 0.97 or more, and more preferably 0.98 or more. １＋ｘ M １－ｘ O ２ In the above formula, "1+x" is preferably, for example, 1.09 or less, more preferably 1.07 or less, and even more preferably 1.05 or less.

[0048] "M" in the formula (3) may contain the three elements Mn, Co, and Ni. For example, it may be composed of only the three elements Mn, Co, and Ni, or may contain one or more of the other elements in addition to the three elements, or may have another configuration.

[0049] Examples of the transition metal elements present among the elements of Groups 3 to 11 of the periodic table and the typical metal elements of the first to third periods of the periodic table include Al, V, Fe, Ti, Mg, Cr, Ga, In, Cu, Zn, Nb, Zr, Mo, W, Ta, and Re, and among these, V, Fe, Ti, Mg, Cr, Ga, Cu, Zn, Nb, Zr, Mo, W, and Ta are preferred.

[0050] When "M" in the formula (3) contains the three elements Mn, Co, and Ni, the molar ratios of Mn, Co, and Ni are preferably Mn:Co:Ni = greater than 0.00 and not greater than 0.45: greater than 0.00 and not greater than 0.40: 0.30 or greater and less than 1.00, and more preferably Mn:Co:Ni = 0.01 or greater and not greater than 0.45: 0.01 or greater and not greater than 0.40: 0.30 or greater and not greater than 0.95, and particularly preferably Mn:Co:Ni = 0.05 or greater and not greater than 0.40: 0.03 or greater and not greater than 0.40: 0.30 or greater and not greater than 0.85, and even more preferably Mn:Co:Ni = 0.05 or greater and not greater than 0.40: 0.03 or greater and not greater than 0.40: 0.30 or greater and not greater than 0.75.

[0051] In the above formula (3), the atomic ratio of the oxygen amount is written as "2" for convenience, but may have some degree of non-stoichiometry. That is, the atomic ratio of the oxygen amount may be "2-δ", where "-δ" indicates oxygen deficiency. In this case, δ is preferably 0 or more. Furthermore, δ is preferably, for example, 0.20 or less, more preferably 0.10 or less, and even more preferably 0.05 or less.

[0052] The core particles B may contain impurities. For example, the core particles B may contain 0.17% by mass or less of each impurity element. This is because such amounts are thought to have little effect on the properties of the core particles B.

[0053] When the core particle B is fitted to a hexagonal crystal structure model of space group R-3m, for example, the ranges of Rwp and S, which indicate the degree of agreement between the observed intensity and the calculated intensity, are Rwp<10 or S<2.5, and thus it can be confirmed that the core particle B has a layered structure.

[0054] The primary particles of the core particles B may be single crystals or polycrystals, similar to the core particles A, but are preferably polycrystals. The definitions of single crystals and polycrystals are the same as those for the core particles A.

[0055] [Core Particles C] The core particles are preferably particles made of a lithium-excess layered rock salt type lithium-containing composite oxide containing Li, Ma (Ma must contain Mn and also contains at least one selected from Ni and Co), Mb (Mb contains at least one selected from Al, Mg, Ti, Fe, and Nb), and O (hereinafter, these core particles will also be referred to as "core particles C"). The active material of the present invention may contain other components in addition to the core particles C. However, from the viewpoint of effectively obtaining the properties of the core particles C, it is preferable that the core particles C account for, for example, 50% by mass or more, particularly 70% by mass or more, particularly 90% by mass or more, and of these, 95% by mass or more (including 100% by mass).

[0056] The core particles C are represented by the formula (5): Li １＋ｘ Ma １－ｘ－ｙ Mb ｙ O ２ (wherein Ma necessarily contains Mn and also contains at least one selected from Ni and Co; and Mb contains at least one selected from Al, Mg, Ti, Fe, and Nb).

[0057] In the formula (5), "x" is, for example, preferably 0.10 or more, more preferably 0.11 or more, and even more preferably 0.12 or more. In the formula (5), "x" is, for example, preferably 0.33 or less, more preferably 0.32 or less, and even more preferably 0.31 or less. In the formula (5), "y" is, for example, preferably 0.000 or more, more preferably 0.005 or more, and even more preferably 0.010 or more. In the formula (5), "y" is, for example, preferably 0.300 or less, more preferably 0.295 or less, and even more preferably 0.290 or less.

[0058] Regarding the content of Mn in the core particles, the content of Mn in Mn is, for example, preferably 30% by mass or more, more preferably 31% by mass or more, and even more preferably 32% by mass or more, and the content of Mn in Mn is, for example, preferably 80% by mass or less, more preferably 79% by mass or less, and even more preferably 78% by mass or less.

[0059] In the above formula (5), the atomic ratio of the oxygen amount is written as "2" for convenience, but may have some degree of non-stoichiometry. That is, the atomic ratio of the oxygen amount may be "2-δ", where "-δ" indicates oxygen deficiency. In this case, δ is preferably 0 or more. Furthermore, δ is preferably, for example, 0.20 or less, more preferably 0.10 or less, and even more preferably 0.05 or less.

[0060] The core particles C may contain impurities. For example, SO ４ When SO is contained, it may contain 1.0 mass % or less as an impurity. ４ When elements other than the above are contained, they may be contained in an amount of 0.5 mass % or less, because it is believed that such an amount will have almost no effect on the properties of the core particles C.

[0061] [Active Material] The active material of the present invention is generally in the form of particles. The particle size of the active material is measured by a volume cumulative particle size D at 50% cumulative volume by a laser diffraction / scattering particle size distribution measurement method. ５０ The particle diameter D of the active material is preferably 1.0 μm or more, more preferably 2.0 μm or more, and even more preferably 3.0 μm or more. ５０ is preferably 20.0 μm or less, more preferably 15.0 μm or less, and even more preferably 10.0 μm or less. ５０ By setting the value of the resistance of the active material to within the above range, the resistance when lithium ions diffuse into the particles of the active material can be reduced, and as a result, the charge / discharge characteristics can be improved.

[0062] The active material of the present invention preferably has a moisture content (ppm by mass) up to 250°C measured by the Karl Fischer method of not more than a predetermined value. Specifically, the moisture content is preferably 1000 ppm or less, more preferably 800 ppm or less, and even more preferably 500 ppm or less. The moisture content of the active material (i.e., the amount of moisture contained in the active material) is preferably as low as possible in terms of reducing structural deterioration of the active material due to reaction with lithium and reducing reaction with the electrolyte during battery operation, but may be 100 ppm or more, 300 ppm or more, or 400 ppm or more. To minimize the amount of moisture contained in the active material, the active material may be dried, for example, at a temperature of 300°C or the like, under vacuum and in an inert atmosphere.

[0063] The procedure for measuring the moisture content by the Karl Fischer method is as follows. That is, using a Karl Fischer moisture meter capable of coulometric titration, the measurement sample is heated to 110°C, the released moisture content (ppm by mass) is measured, and then the measurement sample is heated to 250°C, the released moisture content (ppm by mass) is measured, and the sum of these values ​​is taken as the moisture content. The measurement is carried out in an argon atmosphere. As the Karl Fischer moisture meter, which is the measuring device, for example, an 860 KF Thermoprep (manufactured by Metrohm) and an 899 Coulometer (manufactured by Metrohm) are used.

[0064] The active material of the present invention can be used in a battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer. Specifically, the active material of the present invention can be used in the positive electrode layer or the negative electrode layer, and it is particularly preferable that the positive electrode layer contains the active material of the present invention. The active material of the present invention is also preferably used in a solid-state battery containing a solid electrolyte. In a solid-state battery, the effects of the present invention can be achieved by the presence of a contact portion between the active material of the present invention and the solid electrolyte. 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.

[0065] The active material of the present invention can be mixed with a solid electrolyte and a conductive material to obtain an electrode mixture. The electrode mixture thus obtained contains an active material and a solid electrolyte. The solid electrolyte can be the same as the solid electrolyte used in general solid-state batteries. Examples include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes. Among these, it is preferable to use a sulfide solid electrolyte containing sulfur (S). The sulfide solid electrolyte may be, for example, one containing lithium (Li) and S and having lithium ion conductivity, or one containing Li, phosphorus (P), and S and having 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, for example, Li, ２ S-P ２ S ５ , Li ２ S-P ２ S ５ -LiX (where "X" represents one or more halogen elements), Li ２ S-P ２ S ５ -P ２ O ５ , Li ２ S-Li ３ P.O. ４ -P ２ S ５ , Li ３ P.S. ４ , Li ４ P ２ S ６ , Li １０ GeP ２ S １２ , Li ３．２５ Ge ０．２５ P ０．７５ S ４ , Li ７ P ３ S １１ , Li ３．２５ P ０．９５ S ４ , Li ７－ｘ P.S. ６－ｘ X ｘ(a solid electrolyte having a crystalline phase of an argyrodite structure, "X" represents one or more halogen elements, and 0.2<x<2.0 or 0.2<x<1.8), and 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.) Examples of the conductive material that can be used include electron-conductive carbonaceous materials such as carbon black and acetylene black.

[0066] An electrode (positive electrode layer and / or negative electrode layer) can be produced by mixing an electrode mixture with a solvent and a binder to produce a paste, and then applying the paste to a current collector such as aluminum foil and drying it. The electrode produced in this manner contains the electrode mixture and the binder.

[0067] [Method for Manufacturing Active Material] Methods for manufacturing active materials are broadly divided into methods for manufacturing core particles and methods for forming coating portions on the surfaces of core particles. One example of a method for manufacturing core particles is a manufacturing method comprising a raw material mixing step, a wet grinding step, a granulation step, a firing step, a heat treatment step, a washing / drying step, and a grinding step. However, this manufacturing method is a preferred example, and the present invention is not limited to this manufacturing method.

[0068] The method for forming the coating portion is appropriately selected depending on the type of compound that constitutes the coating portion. When the coating portion contains, for example, the aforementioned lithium compound, the formation method includes a step of obtaining a coating mixture powder and a step of disposing the coating portion containing the coating mixture powder on the surface of the core particle.

[0069] The coating mixed powder is obtained by mixing the aforementioned lithium compounds, which are raw material powders. As the raw material powder, at least one of lithium sulfide and lithium halide, and, if necessary, at least one of lithium sulfate and lithium salt of phosphate, can be prepared. If necessary, raw material powders of the other compounds can also be prepared. The raw material powders may be appropriately selected depending on the composition of the desired coating portion. For example, lithium sulfate or lithium salt of phosphate can be mixed with lithium sulfide or lithium halide. The order in which the raw material powders are mixed is not particularly limited, and the raw material powders may be mixed together or sequentially.

[0070] The mixing may be carried out dry or wet, and there are no particular limitations on the mixing method. It is preferable to mix the raw material powders using grinding media, from the viewpoint of uniformly mixing the raw material powders and successfully disposing the coating portion containing the aforementioned compound on the entire surface of the core particle in the process described below. Such grinding can be carried out using known devices, such as a planetary ball mill or a vibrating ball mill. Regardless of the device used, the diameter of the grinding media is preferably 0.1 mm or more and 50.0 mm or less. The material of the grinding media is generally zirconia, alumina, or the like. The operating time and rotation speed of the device may be appropriately adjusted depending on the raw material powder used.

[0071] Once the coating mixture powder is obtained, the coating mixture powder is subjected to a drying treatment, if necessary. By removing moisture from the coating mixture powder in advance, it is possible to successfully arrange the coating portion containing the above-mentioned compound on the surface of the core particle in the process described below. The temperature and time of the drying treatment are not particularly limited as long as it is possible to remove a certain amount of moisture from the coating mixture powder. For example, it is preferable to dry the coating mixture powder at a temperature of 100°C or higher and 250°C or lower for 1 hour or higher and 24 hours or lower under vacuum.

[0072] The coating mixture powder and the core particles are then mixed to obtain a mixture, which is then dry-mixed. This allows a coating portion containing the coating mixture powder to be disposed on the surface of the core particles. In particular, dry-mixing the mixture while cooling the mixture reduces the deterioration of the coating mixture powder. When dry-mixing is performed, the temperature may rise due to the generation of frictional heat, which may cause the coating mixture powder to deteriorate. Dry-mixing while suppressing the temperature rise due to the generation of frictional heat, i.e., while cooling, is preferred because it reduces the deterioration of the coating mixture powder. As a result, the resulting active material is advantageous in that it reduces the initial resistance of the solid-state battery and effectively improves its storage characteristics. When dry-mixing is performed while cooling, a dry mixer equipped with a water-cooling jacket, for example, can be used. The temperature of the mixture during dry-mixing is preferably maintained between 10°C and 50°C.

[0073] To control the placement of the compounds in the coating, dry mixing may be performed multiple times. For example, a first coating mixed powder containing a compound to be placed on the surface of the coating and a second coating mixed powder containing a compound to be placed in a region other than the surface may be prepared, and the core particles and the second coating mixed powder may be dry mixed, followed by further dry mixing with the first coating mixed powder. Alternatively, the active material may be obtained by a single dry mixing. Specifically, the core particles (which may be in powder form or in another form) and the raw material powder to be included in the coating may be dry mixed simultaneously. In either case, performing dry mixing while cooling is preferable, as this reduces the initial resistance of the solid-state battery and effectively improves its storage characteristics.

[0074] Conventionally, when a coating containing a compound is formed on the surface of a core particle, the core particle is typically brought into contact with a solution containing the compound. This method aims to uniformly coat the surface of the core particle with the compound. However, conventional methods have the drawback of requiring additional drying and heat treatment steps after the coating is formed. In addition, the chemical structure of the compound may change, particularly during the heat treatment step. After extensive research, the present inventors have found that when a coating containing a compound is formed on the surface of a core particle, these drawbacks can be resolved by performing dry mixing as described above. Furthermore, dry mixing tends to result in a close relationship between the ratio of the raw material powders added and the composition ratio of each component in the resulting active material, making it easier to produce an active material with the desired composition. In contrast, wet mixing tends to result in a discrepancy between the ratio of the raw material powders added and the composition ratio of each component in the resulting active material.

[0075] In relation to the above-described embodiments, the following active materials and methods for producing the same, as well as electrode mixtures, electrodes, and batteries containing the same are further disclosed. [1] An active material having core particles and a coating portion disposed on the surface of the core particles, the coating portion containing at least one of lithium sulfide and lithium halide. [2] The active material according to [1], wherein the coating portion further contains at least one of lithium sulfate and a lithium salt of phosphoric acid. [3] The active material according to [2], wherein the lithium salt of phosphoric acid is lithium metaphosphate. [4] The active material according to any one of [1] to [3], wherein the total amount of the lithium halide and lithium sulfide is 0.01 parts by mass or more and 0.80 parts by mass or less per 100 parts by mass of the core particles. [5] The active material according to any one of [1] to [4], wherein the lithium halide is lithium chloride, lithium bromide, or lithium iodide.

[0076] [6] The active material according to any one of [1] to [5], wherein the coverage rate of the coating portion is 30% or more and 100% or less. [7] The active material according to any one of [1] to [6], wherein the thickness of the coating portion is 1 nm or more and 100 nm or less. [8] The active material according to any one of [1] to [7], wherein the core particles contain at least one selected from a lithium transition metal composite oxide having a spinel structure, a lithium transition metal composite oxide having a layered rock salt structure, and a phosphate compound having an olivine structure. [9] The active material according to any one of [1] to [8], wherein the moisture regain up to 250°C measured by the Karl Fischer method is 1000 ppm or less.

[10] The active material according to any one of [1] to [9], wherein the active material is used for a solid-state battery.

[0077]

[11] An electrode mixture comprising the active material according to any one of [1] to

[10] and a solid electrolyte.

[12] An electrode comprising the electrode mixture according to

[11] and a binder.

[13] A battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer comprises the active material according to any one of [1] to

[10] .

[14] A method for producing an active material, comprising: mixing lithium sulfate or a lithium salt of phosphoric acid with lithium sulfide or a lithium halide to obtain a coating mixed powder; and dry-mixing a mixture containing the coating mixed powder and core particles to arrange a coating portion containing the coating mixed powder on the surface of the core particles.

[15] The production method according to

[14] , wherein the mixture is dry-mixed while being cooled.

[0078] 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".

[0079] Example 1 (1) Preparation of Core Particles A spinel-type lithium transition metal composite oxide (hereinafter also referred to as "LNMO") having a composition of Li: 4.1%, Mn: 41.3%, Ni: 13.3%, and Ti: 5.4% was prepared as core particles.

[0080] (2) Formation of the coating portion As raw material powder, lithium chloride (LiCl), lithium sulfate (Li ２ SO ４ ) and lithium metaphosphate (LiPO ３ ) were prepared. These raw material powders were mixed to obtain the composition shown in Table 1, to obtain a coating mixture. Mixing was performed using a planetary ball mill (grinding media diameter 5.0 mm) at 600 rpm for 90 minutes. The obtained coating mixture was vacuum dried at 200°C for 24 hours. The coating mixture and core particles were mixed using a NOB-MINI dry particle composite device manufactured by Hosokawa Micron Corporation, and the coating mixture was attached to the surface of the core particles to form a coating portion containing the coating mixture. The amounts of the core particles and the coating mixture were adjusted to the values ​​shown in Table 1. The device was cooled and maintained at 30°C during mixing. In this manner, active material particles were obtained.

[0081] Examples 2 and 3 In Example 1, the composition of the raw material powder was changed to the values ​​shown in Table 1. Active material particles were obtained in the same manner as in Example 1 except for this.

[0082] Example 4 In Example 1, the composition of the raw material powder and the amounts of the core particles and coating mixed powder were changed to the values ​​shown in Table 1. Active material particles were obtained in the same manner as in Example 1 except for this.

[0083] [Example 5] In step (1) of Example 1, a lithium transition metal composite oxide (hereinafter also referred to as "NCM") having a composition of Li: 7.2%, Ni: 36.3%, Co: 12.2%, and Mn: 11.3% was prepared as core particles. In addition, the composition of the raw material powder was changed to the values ​​shown in Table 1. Other than this, active material particles were obtained in the same manner as in Example 1.

[0084] Comparative Example 1 Lithium sulfate and lithium metaphosphate were prepared as raw material powders. These raw material powders were mixed to obtain the composition shown in Table 1, thereby obtaining a mixed powder for coating. Active material particles were obtained in the same manner as in Example 1 except for this.

[0085] Comparative Example 2 Lithium sulfate and lithium metaphosphate were prepared as raw material powders. These raw material powders were mixed to obtain the composition shown in Table 1, thereby obtaining a mixed powder for coating. Active material particles were obtained in the same manner as in Example 5 except for this.

[0086] [Evaluation 1] The active materials obtained in the examples and comparative examples were evaluated for the coverage, thickness and particle size D of the coating portion. ５０ was measured by the following method. Furthermore, the moisture content was measured by the method described above. Note that for Example 4 and Comparative Example 2, the coverage rate and thickness of the coated portion were not measured. The results are shown in Table 1 below. Note that "-" in Table 1 indicates that there was no measurement data.

[0087] [Coating Ratio] The coating ratio was measured using a PHI Quantes XPS device manufactured by ULVAC-PHI, Inc. Specifically, the quantitative value of elements present only in the coating portion was calculated relative to the sum of the quantitative value of elements present only in the coating portion and the quantitative value of elements present only in the core particles. For example, when LNMO was used as the core particles and lithium chloride, lithium sulfate, and lithium metaphosphate were used as the coating portion, the coating ratio was calculated by (S + P + Cl) / (Mn + Ni + Ti + S + P + Cl) × 100. Similarly, when NCM was used as the core particles and lithium chloride, lithium sulfate, and lithium metaphosphate were used as the coating portion, the coating ratio was calculated by (S + P + Cl) / (Ni + Co + Mn + S + P + Cl) × 100. The conditions used for the measurement were as follows. Excitation X-ray: Monochromated Al ray (1486.7 eV) Output: 50 W Acceleration voltage: 15 kV X-ray irradiation diameter: 200 μmφ Measurement area: 1000 μm × 300 μm Take of angle: 45° Pass energy: 26.0 eV Energy step: 0.1 eV

[0088] [Thickness of the coating portion] The thickness was measured using a PHI Quantes XPS device used to measure the coverage. Specifically, Ar ion sputtering was performed, and XPS measurement was performed to obtain a depth profile. When the area of ​​the peak derived from the element specific to the coating portion, which is not the main element constituting the core particle, was reduced by half compared to before sputtering, the thickness of the SiO２ The converted sputtering depth was taken as the thickness of the coated portion. The conditions used for the measurement were the same as those used for measuring the coverage.

[0089] [Particle size D ５０ ] Particle size D of active material ５０ The measurement was carried out by the following procedure. Specifically, an automatic sample feeder for a laser diffraction particle size distribution measurement device ("Microtrac SDC" manufactured by Microtrac-Bell Corporation) was used to put the active material into a mixed solution of water / ethanol (mass ratio 80 / 20), and the measurement sample was irradiated with 30 W ultrasonic waves for 360 seconds. Thereafter, the particle size distribution was measured using a laser diffraction particle size distribution measurement device "MT3300EXII" manufactured by Microtrac-Bell Corporation, and the particle size at which the cumulative volume was 50% by volume was determined from the obtained volume-based particle size distribution chart. ５０ It was decided.

[0090] [Evaluation 2] Using the active materials obtained in the examples and comparative examples, solid state batteries were manufactured by the following method, and the resistance increase rate after storage at 90°C, which is an evaluation of storage characteristics, was measured. The results are shown in Table 1 below.

[0091] [Fabrication of Solid-State Batteries] The active materials obtained in the Examples and Comparative Examples were used as the positive electrode active material, and graphite (Gr) powder was used as the negative electrode active material. A sulfide solid electrolyte with an argyrodite structure was used as the solid electrolyte powder. The positive electrode mixture powder was prepared by mixing the positive electrode active material, solid electrolyte powder, and a carbon-based conductive additive in a mortar at a mass ratio of 70:27:3. The negative electrode mixture powder was prepared by mixing the negative electrode active material and solid electrolyte powder in a mortar at a mass ratio of 1:1. The lower opening of a polypropylene cylinder (opening diameter 10.5 mm, height 18 mm) with an open top and bottom was blocked with a positive electrode (made of stainless steel), and the solid electrolyte powder was placed on top of it. The cylinder was then blocked with a negative electrode (made of stainless steel), and a solid electrolyte layer was formed by uniaxial pressing at 10 MPa. Next, the negative electrode was temporarily removed, and the negative electrode mixture powder was placed on the solid electrolyte layer, which was then blocked again with the negative electrode. Thereafter, the cylinder was turned upside down, the positive electrode was temporarily removed, a positive electrode mixture powder was placed on the solid electrolyte layer, and the positive electrode was again sealed, followed by uniaxial pressing at 60 MPa to produce a solid battery having a three-layer structure of the positive electrode mixture, the solid electrolyte layer, and the negative electrode mixture.

[0092] [Resistance Increase Rate After Storage at 90°C] <When Core Particles are LNMO> Using the solid-state batteries fabricated in Examples 1 to 4 and Comparative Example 1, charge / discharge tests were carried out as follows. Specifically, the batteries were placed in an environmental tester set so that the environmental temperature for charging and discharging the batteries was 25°C, and the batteries were prepared for charging and discharging, and were left to stand until the battery temperature reached the environmental temperature. Next, a current of 0.1 C (0.2 mA / cm ２) to 5.0 V, followed by constant current discharge at 0.1 C to 3.0 V, and this cycle was repeated three times. The battery was then charged to a state of charge (SOC) of 50%, and the resistance before the storage test was measured by impedance measurement. The battery was then charged at a constant current and constant potential to 4.9 V at 0.1 C, discharged at a constant current to 3.0 V at 0.1 C, and then charged at a constant current and constant potential to 4.9 V at 0.1 C again. The battery charged at a constant current and constant potential to 4.9 V at 0.1 C was placed in a thermostatic chamber at 90 ° C and stored for 168 hours. After 168 hours, the battery was removed, returned to room temperature, and then placed in an environmental test chamber at 25 ° C and discharged at a constant current to 3.0 V at 0.1 C. The battery was then charged at a constant current and constant potential to 4.9 V at 0.1 C, and discharged at a constant current to 3.0 V at 0.1 C. After charging until the SOC reached 50%, the resistance value after the storage test was measured by impedance measurement. The resistance increase rate after storage at 90°C was calculated using the following formula: (Resistance increase rate after storage at 90°C) = {(Resistance value after storage test) - (Resistance value before storage test)} / (Resistance value before storage test).

[0093] <When the core material particles are NCM> A charge / discharge test was carried out as follows using the solid-state batteries produced in Example 5 and Comparative Example 2. Specifically, the batteries were placed in an environmental tester set to an environmental temperature of 25°C for charging and discharging the batteries, and were left to stand until the battery temperature reached the environmental temperature. Next, a current of 0.1 C (0.3 mA / cm ２) to 4.5 V, followed by a constant current constant potential charge at 0.1 C to 2.5 V, and this cycle was repeated three times. The battery was then charged to a state of charge (SOC) of 50%, and the resistance before the storage test was measured by impedance measurement. The battery was then charged at a constant current constant potential to 4.5 V at 0.1 C, discharged at a constant current to 2.5 V at 0.1 C, and then charged at a constant current constant potential to 4.5 V at 0.1 C again. The battery charged at a constant current constant potential to 4.5 V at 0.1 C was placed in a thermostatic chamber at 90 ° C and stored for 168 hours. After 168 hours, the battery was removed, returned to room temperature, and then placed in an environmental test chamber at 25 ° C and discharged at a constant current to 2.5 V at 0.1 C. The battery was then charged at a constant current constant potential to 4.5 V at 0.1 C, and discharged at a constant current to 2.5 V at 0.1 C. After charging until the SOC reached 50%, the resistance value after the storage test was measured by impedance measurement. The resistance increase rate after storage at 90°C was calculated using the following formula: (Resistance increase rate after storage at 90°C) = {(Resistance value after storage test) - (Resistance value before storage test)} / (Resistance value before storage test).

[0094]

[0095] As is clear from the results shown in Table 1, the solid state batteries obtained using the active materials of Examples 1 to 4 exhibited lower resistance increase rates after storage at 90°C than the solid state battery obtained using the active material of Comparative Example 1. Similarly, the solid state battery obtained using the active material of Example 5 exhibited lower resistance increase rates after storage at 90°C than the solid state battery obtained using the active material of Comparative Example 2. From the above, it can be seen that the active materials obtained in each Example improve the storage characteristics of solid state batteries.

[0096] According to the present invention, an active material capable of improving the storage characteristics of a battery and a method for producing the same are provided.

Claims

1. An active material having a core particle and a coating portion disposed on the surface of the core particle, the coating portion containing at least one of lithium sulfide and lithium halide.

2. The active material according to claim 1, wherein the coating further contains at least one of lithium sulfate and a lithium salt of phosphoric acid.

3. The active material of claim 2, wherein the lithium salt of phosphoric acid is lithium metaphosphate.

4. The active material according to claim 1, wherein the total amount of the lithium halide and lithium sulfide is 0.01 parts by mass or more and 0.80 parts by mass or less per 100 parts by mass of the core particles.

5. The active material of claim 1, wherein the lithium halide is lithium chloride, lithium bromide, or lithium iodide.

6. The active material according to claim 1, wherein the coverage by the coating portion is 30% or more and 100% or less.

7. The active material according to claim 1, wherein the thickness of the coating portion is 1 nm or more and 100 nm or less.

8. The active material according to claim 1, wherein the core particles contain at least one selected from the group consisting of lithium transition metal composite oxides having a spinel structure, lithium transition metal composite oxides having a layered rock salt structure, and phosphate compounds having an olivine structure.

9. The active material according to claim 1, which has a moisture content of 1000 ppm or less at temperatures up to 250° C. as measured by the Karl Fischer method.

10. The active material according to claim 1, which is used in a solid-state battery.

11. An electrode mixture comprising the active material according to any one of claims 1 to 10 and a solid electrolyte.

12. An electrode comprising the electrode mixture according to claim 11 and a binder.

13. A battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer contains the active material according to any one of claims 1 to 10.

14. A method for producing an active material, comprising: mixing lithium sulfate or a lithium salt of phosphate with lithium sulfide or a lithium halide to obtain a coating mixture; dry-mixing a mixture containing the coating mixture and core particles to form a coating portion containing the coating mixture on the surface of the core particles.

15. The method of claim 14, wherein the mixture is dry mixed while cooling.

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