Active material, and electrode mixture, electrode layer, and solid-state battery containing same

Abstract

The present invention addresses the problem of providing an active material with which reductions in performance during the storage of a solid-state battery can be suppressed. The active material has a core particle and a coating layer disposed on at least a part of the surface of the core particle. The coating layer contains a solid electrolyte that contains a crystal phase having an argyrodite crystal structure. The solid electrolyte contains the element lithium (Li), the element phosphorus (P), the element sulfur (S), and a halogen (X) element, and the molar ratio of the halogen (X) element to the element phosphorus (P) is less than 1.2. The solid electrolyte preferably has a molar ratio of the element sulfur (S) to the element phosphorus (P) of 4.6 or more.

Description

Active material, and electrode mixture, electrode layer, and solid-state battery containing the same

[0001] The present invention relates to an active material. The present invention also relates to an electrode mixture, an electrode layer, and a solid-state battery containing the active material.

[0002] In recent years, secondary batteries have been attracting attention as an effort to prevent global warming by reducing carbon dioxide emissions. Among these, solid-state batteries using sulfide solid electrolytes have attracted attention. Solid-state batteries using sulfide solid electrolytes have the advantage of simplifying safety devices and achieving excellent manufacturing costs and productivity because they do not use flammable organic solvents. Furthermore, this type of solid electrolyte is advantageous from the perspective of improving safety and durability, since ionic species other than lithium ions do not migrate within the electrolyte, preventing side reactions due to the migration of anions.

[0003] In order to improve the performance of solid-state batteries, Patent Document 1 proposes composite active material particles having active material particles and a lithium ion conductive oxide that coats at least a portion of the surface of the active material particles. Examples of the lithium ion conductive oxide include lithium niobate, lithium titanate, lithium lanthanum zirconate, lithium tantalate, and lithium tungstate. The document states that the use of the composite active material particles can reduce the resistance of solid-state batteries.

[0004] US2018 / 219229A1

[0005] The present inventors have conducted extensive research to further improve the performance of solid-state batteries and have found a new problem: during storage of a solid-state battery, particularly during storage in a charged state under high-temperature conditions, the solid electrolyte reacts with the active material, resulting in a deterioration in the performance of the solid-state battery. In other words, an object of the present invention is to provide an active material that can suppress the deterioration in performance of a solid-state battery during storage.

[0006] The present invention provides an active material having a core particle and a coating layer disposed on at least a portion of the surface of the core particle, wherein the coating layer contains a solid electrolyte including a crystalline phase having an argyrodite-type crystal structure, and the solid electrolyte contains lithium (Li), phosphorus (P), sulfur (S), and a halogen (X), and the molar ratio of the halogen (X) to the phosphorus (P) is less than 1.2.

[0007] The present invention will be described below based on preferred embodiments. The present invention relates to an active material for a battery. The active material of the present invention has a core particle and a coating layer disposed on the surface of the core particle. The coating layer may be disposed directly on the surface of the core particle. Alternatively, another layer may be interposed between the coating layer and the core particle. The core particle occupies the majority of the active material and is composed of an active material base material. The coating layer is disposed on the surface of the core particle and typically forms the outermost surface of the active material. The coating layer and core particle in the active material of the present invention will be described below.

[0008] [Coating Layer] The coating layer contains a solid electrolyte. The solid electrolyte preferably contains a crystalline phase having an argyrodite crystal structure. The solid electrolyte contained in the coating layer contains, in particular, lithium (Li), phosphorus (P), sulfur (S), and a halogen (X). Examples of the halogen (X) include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The halogen (X) may be one of these elements or a combination of two or more. The halogen (X) is preferably a combination of chlorine (Cl) and bromine (Br). The solid electrolyte contained in the coating layer preferably has a molar ratio of halogen (X) to phosphorus (P) of less than 1.2. A solid battery including an active material having a coating layer containing such a solid electrolyte can suppress a decrease in the recovery capacity of the solid battery and an increase in the resistance of the solid battery, even when stored in a charged state under high-temperature conditions, due to the action of the coating layer. From this viewpoint, the ratio of the coating layer to the active material of the present invention is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, and is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0009] [Method for Measuring the Ratio of Coating Layer to Active Material] The coverage can be measured, for example, by the following method. A PHI Quantes XPS device manufactured by ULVAC-PHI, Inc. is used. Specifically, the ratio of the quantitative value of elements present only in the coating portion 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 is calculated. For example, when LNMO (a spinel-type lithium transition metal composite oxide having a composition of Li: 4.1 mass%, Mn: 41.3 mass%, Ni: 13.3 mass%, Ti: 5.4 mass%) is used as the core particles and a sulfide solid electrolyte containing Li, P, S, and X elements is used as the coating portion, the coverage is calculated by (S + P + X) / (Mn + Ni + Ti + S + P + X) × 100. Similarly, for example, when NCM (LiNi ０．５ Co ０．２ Mn ０．３ O ２ When a sulfide solid electrolyte containing Li, P, S, and X elements is used as the coating portion, the coverage is calculated by (S + P + X) / (Ni + Co + Mn + S + P + X) × 100. The conditions used for the measurement are as follows: Excitation X-ray: Monochromated Al beam (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

[0010] The thickness of the coating layer is preferably within a predetermined range. Specifically, the thickness of the coating layer is preferably 1 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more. The thickness of the coating layer 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 layer within the above range, an excessive increase in the interface resistance caused by the formation of the coating layer is suppressed, and the coating layer can function as a good lithium ion conductive layer.

[0011] The thickness of the coating layer 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).

[0012] The coating layer may be absent from some portions of the surface of the core particle. In this case, the coating layer is preferably disposed on 30% or more of the entire surface area of ​​the core particle, more preferably 50% or more, and even more preferably 80% 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, the more preferable. The coating layer 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 layer disposed on the surface of the core particle does not need to be uniform.

[0013] As described above, the present inventors have found that it is advantageous to adjust the molar ratio of the X element to the P element (hereinafter also referred to as "X / P") of the solid electrolyte contained in the coating layer to a relatively low value, that is, less than 1.2. When the molar ratio X / P is in this range, the monovalent anion X decreases, and the divalent anion S occupies more of the overall composition. ２－ As a result, the ratio of Li ＋The electrostatic attraction between the active material and the solid electrolyte increases, resulting in an increase in lattice energy (stabilization of the structure). As a result, even when a solid battery using an active material with a coating layer containing this solid electrolyte is stored in a charged state under high-temperature conditions, a reaction with the solid electrolyte is unlikely to occur, which advantageously suppresses a decrease in the recovery capacity of the solid battery and an increase in the resistance of the solid battery. From this perspective, the molar ratio X / P is preferably less than 1.0, and more preferably less than 0.9. Furthermore, the molar ratio X / P may be 0.1 or more, 0.3 or more, or 0.6 or more.

[0014] The inventors have found that adjusting the molar ratio of S to P (hereinafter also referred to as "S / P") in the solid electrolyte contained in the coating layer is also advantageous. Specifically, when the molar ratio S / P is greater than 4.8, even when a solid battery using an active material with a coating layer containing a solid electrolyte is stored in a charged state under high-temperature conditions, a reaction with the solid electrolyte is less likely to occur, thereby suppressing a decrease in the recovery capacity of the solid battery and an increase in the resistance of the solid battery. From this perspective, the molar ratio S / P is preferably 5.0 or greater, and more preferably 5.1 or greater. The molar ratio S / P may be 6.8 or less, or 6.0 or less, or 5.6 or less, or 5.3 or less.

[0015] Furthermore, in the solid electrolyte contained in the coating layer, the molar ratio of Li to P (hereinafter also referred to as "Li / P") is preferably, for example, 4.0 or more, more preferably 5.0 or more, and particularly preferably 6.0 or more. On the other hand, the molar ratio Li / P is preferably, for example, 7.0 or less, more preferably 6.8 or less, and particularly preferably 6.4 or less. When the molar ratio Li / P is in this range, the argyrodite-type crystal structure, particularly the cubic argyrodite-type crystal structure, becomes more stable at around room temperature (25°C), and lithium ion vacancies can be sufficiently introduced into the structure, resulting in effectively increasing lithium ion conductivity.

[0016] The argyrodite-type crystal phase is represented by the following formula (II): ７－ｄ P.S. ６－ｄ X ｄ ...(II) The composition represented by formula (II) is the stoichiometric composition of the argyrodite-type crystal phase.

[0017] In the solid electrolyte contained in the coating layer, from the viewpoint of achieving both high ionic conductivity and suppression of the reaction between the solid electrolyte and the active material, d is preferably 0.1 or more and less than 1.2, more preferably 0.3 or more and 1.0 or less, and even more preferably 0.6 or more and 0.9 or less.

[0018] In formula (II), a part of P may be substituted with one or more elements selected from silicon (Si), germanium (Ge), tin (Sn), lead (Pb), boron (B), aluminum (Al), gallium (Ga), arsenic (As), antimony (Sb), and bismuth (Bi).

[0019] The ratio of each element contained in the coating layer can be measured using, for example, inductively coupled plasma (ICP) emission spectroscopy, energy dispersive X-ray spectroscopy (EDS), or X-ray fluorescence analysis (XRF).

[0020] The solid electrolyte contained in the coating layer is preferably a crystalline substance. This solid electrolyte preferably exhibits a diffraction peak at a specific angle in a diffraction pattern obtained by subjecting the solid electrolyte to X-ray diffraction. When an active material having a coating layer containing this solid electrolyte exhibiting a diffraction peak at a specific angle is used in a solid-state battery, even when the charged solid-state battery is stored in a high-temperature environment, reaction with the solid electrolyte is unlikely to occur, thereby achieving the advantageous effects of suppressing a decrease in the recovery capacity of the solid-state battery and suppressing an increase in the resistance of the solid-state battery.

[0021] Specifically, in an X-ray diffraction pattern measured using an X-ray diffractometer, the solid electrolyte contained in the coating layer preferably exhibits a diffraction peak A at 2θ = 15.4° ± 1°, a diffraction peak B at 2θ = 17.8° ± 1°, a diffraction peak C at 2θ = 25.3° ± 1°, and a diffraction peak D at 2θ = 29.7° ± 1°. The range of each diffraction peak may be ±0.7°, ±0.5°, or ±0.3°. To obtain the X-ray diffraction pattern, Cu-Kα is used as the radiation source. Hereinafter, in all references to X-ray diffraction patterns in this specification, Cu-Kα is used as the radiation source.

[0022] The solid electrolyte contained in the coating layer preferably has diffraction peaks observed at the angles described above, and also has a specific relationship between the intensity ratio of two specific diffraction peaks. This makes it difficult for a reaction with the solid electrolyte to occur, even when a solid battery using an active material provided with a coating layer containing this solid electrolyte is stored in a charged state under a high-temperature environment, and advantageous effects are achieved in that it is possible to suppress a decrease in the recovery capacity of the solid battery and further suppress an increase in the resistance of the solid battery. Specifically, the integrated intensity of diffraction peak A is expressed as I Ａ and the integrated intensity of the diffraction peak B is I Ｂ When I Ａ / I Ｂ The value of I is preferably 1.0 or more, more preferably 1.2 or more, and even more preferably 1.3 or more. Ａ / I Ｂ The value of is preferably 3.0 or less, more preferably 2.6 or less, even more preferably 2.5 or less, even more preferably 2.3 or less, particularly preferably 2.0 or less, and especially more preferably 1.5 or less.

[0023] In addition, for the solid electrolyte contained in the coating layer, the integrated intensity of the diffraction peak C is I Ｃ and the integrated intensity of the diffraction peak D is I Ｄ When IＣ / I Ｄ The value of I is preferably smaller than 0.90, and more preferably 0.89 or less. Ｃ / I Ｄ The value of is preferably 0.6 or more, more preferably 0.7 or more, even more preferably 0.8 or more, and even more preferably 0.85 or more.

[0024] In order to make the solid electrolyte contained in the coating layer exhibit the diffraction peaks A to D, the molar ratio of each element constituting the solid electrolyte may be adjusted, or a solid electrolyte with high crystallinity may be produced by the method described below.

[0025] As described above, the solid electrolyte contained in the coating layer is preferably a crystalline substance, and in particular, it is preferable that the solid electrolyte has an argyrodite-type crystal structure as described above, since this has excellent lithium ion conductivity. When the solid electrolyte contained in the coating layer has a crystalline phase with an argyrodite-type crystal structure, the solid electrolyte has a composition formula (I): Li ａ P.S. ｂ X ｃ (X is at least one of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I)) is preferred from the viewpoint of improving lithium ion conductivity.

[0026] When the solid electrolyte contained in the coating layer has a crystalline phase of an argyrodite-type crystal structure, the above-mentioned diffraction peak A corresponds to the 111 plane in the crystal structure. Diffraction peak B corresponds to the 020 plane in the argyrodite-type crystal structure. Diffraction peak C corresponds to the 220 plane in the argyrodite-type crystal structure. Diffraction peak D corresponds to the 311 plane in the argyrodite-type crystal structure.

[0027] The solid electrolyte contained in the coating layer preferably has high crystallinity. High crystallinity means that the solid electrolyte has few reactive sites. Therefore, when an active material having a coating layer containing this solid electrolyte is used in a solid-state battery, reactions with the solid electrolyte are unlikely to occur even when the charged solid-state battery is stored in a high-temperature environment, thereby achieving the advantageous effects of suppressing a decrease in the discharge capacity of the solid-state battery and further suppressing an increase in the resistance of the solid-state battery. The crystallinity of the solid electrolyte can be evaluated by the half-width of the X-ray diffraction peak. The smaller the half-width value, the higher the crystallinity of the solid electrolyte can be evaluated. In the solid electrolyte, the half-width of the diffraction peak D is preferably 0.16° or less, more preferably 0.15° or less, and even more preferably 0.14° or less. The reason for selecting the diffraction peak D for evaluating the half-width is that it is the most intense diffraction peak in the solid electrolyte, making it easy to calculate the half-width.

[0028] The crystallinity of the solid electrolyte can also be evaluated by the crystallite size. Specifically, the crystallite size can be calculated based on the X-ray diffraction pattern measured for the solid electrolyte. The solid electrolyte contained in the coating layer preferably has a crystallite size of 450 Å or more, more preferably 550 Å or more, and even more preferably 600 Å or more. There is no particular limit to the upper limit of the crystallite size, and it may be, for example, 2000 Å or less, 1000 Å or less, or 700 Å or less. The method for measuring the crystallite size will be explained in the examples below.

[0029] The particle diameter of the solid electrolyte contained in the coating layer is determined by the volume cumulative particle diameter at 50% by volume measured by a laser diffraction / scattering particle size distribution measurement method, from the viewpoint of successfully disposing the solid electrolyte on the surface of the core particle. ５０ When expressed as above, it is preferably 10 μm or less, more preferably 5 μm or less, even more preferably 2 μm or less, even more preferably 1 μm or less, and particularly more preferably 0.8 μm or less.

[0030] The solid electrolyte contained in the coating layer has lithium ion conductivity in a solid state, and preferably has a lithium ion conductivity of 0.5 mS / cm or more at room temperature, i.e., 25°C, more preferably 1.0 mS / cm or more, and particularly preferably 1.5 mS / cm or more.

[0031] Next, a preferred method for producing the solid electrolyte contained in the coating layer will be described. The solid electrolyte can be preferably produced by a solid-phase reaction in which a raw material composition is heated and sintered. The raw material composition is a mixture of raw material powders containing the above-mentioned elements that constitute the solid electrolyte. The raw material composition contains one or more compounds containing at least one of Li, P, S, and X.

[0032] The raw material powder may be, for example, a compound containing an Li element, a compound containing an S element, a compound containing a P element, or a compound containing an X element.

[0033] The raw material powder may contain at least two or more elements selected from Li, P, S, and X in one compound. For example, the raw material powder may be a compound containing Li and X, a compound containing P and S, a compound containing Li and S, a compound containing P and X, or a compound containing S and X. An example of the compound containing Li and X is lithium halide. An example of the compound containing P and S is diphosphorus trisulfide (P ２ S ３ ) and diphosphorus pentasulfide (P ２ S ５ As a compound containing Li and S, for example, lithium sulfide (Li ２ As a compound containing P element and X element, for example, PX ３ Ya P ２ X ５ Examples of compounds containing S and X elements include SX２ , SX ４ , SX ６ , S ２ X １０ Sulfur halides such as the following can be used.

[0034] The raw material powders are preferably subjected to a pulverization process to adjust the particle size to a predetermined size before mixing. For pulverization, a media-agitating mill such as a ball mill or a bead mill can be used. When pulverization is performed using a media-agitating mill, a slurry of the raw material powder is placed in a container, and ceramic or metal balls or beads are placed in the container. The container is rotated to cause the raw material powder to collide with the balls or beads in the container, thereby pulverizing the raw material powder. Although pulverization tends to reduce the crystallinity of the raw material powder, in this production method, it is preferable to perform pulverization so as to minimize the reduction in the crystallinity of the raw material powder to be pulverized. By performing such pulverization, a solid electrolyte with high crystallinity can be obtained, and as a result, a solid electrolyte satisfying the above-mentioned X-ray diffraction peak intensity ratio can be obtained.

[0035] After the grinding of the raw material powders is completed, the raw material powders are mixed to obtain a raw material composition. The raw material powders are preferably mixed so that the molar ratio X / P in the target solid electrolyte is smaller than 1.2, since this facilitates the production of a solid electrolyte that satisfies the above-mentioned strength ratio. From the same viewpoint, the raw material powders are preferably mixed so that the molar ratio S / P in the target solid electrolyte is larger than 4.8.

[0036] It is also preferable to use a media agitation mill to mix the raw material powders. In this case, it is preferable to mix the raw material powders in a way that minimizes the deterioration of their crystallinity. By mixing in this way, a solid electrolyte with high crystallinity can be obtained.

[0037] Next, the raw material composition is subjected to a calcination process to cause a solid-state reaction and obtain a crystalline calcined product. The calcination atmosphere can be, for example, an inert gas atmosphere such as an argon atmosphere or a nitrogen atmosphere, or a hydrogen sulfide atmosphere. From the viewpoint of adjusting the ratio of sulfur element contained in the solid electrolyte, it is preferable to use an inert gas atmosphere.

[0038] From the viewpoint of ensuring that a solid-phase reaction of the raw material composition occurs, the firing temperature is, for example, preferably 200° C. or higher, more preferably 300° C. or higher, even more preferably 350° C. or higher, and even more preferably 400° C. or higher. On the other hand, in consideration of industrial producibility and economic efficiency, the firing temperature is, for example, preferably 700° C. or lower, more preferably 600° C. or lower, and even more preferably 550° C. or lower.

[0039] The firing time is not critical, and may be any time that allows a fired product of the desired composition to be obtained. Specifically, the firing time is preferably long enough for the solid-phase reaction of the raw material composition to occur sufficiently. The firing time may be, for example, 30 minutes or more, 2 hours or more, or 3 hours or more. On the other hand, the firing time may be, for example, 10 hours or less, or 5 hours or less.

[0040] [Core Particle] The core particle is not particularly limited as long as it functions as an active material. The core particle 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 particle may be a lithium metal composite oxide represented by 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.

[0041] [Core Particle A] The core particle is preferably a particle made of a lithium transition metal composite oxide having a spinel structure containing Li, Mn, and O and one or more other elements (hereinafter, this core particle will also be referred to as "core particle A"). When the active material of the present invention containing core particle A is used as a positive electrode active material, it has an operating potential of 4.5 V or more relative to metallic Li. "Having an operating potential of 4.5 V or more relative to metallic Li" does not necessarily mean that the plateau region only has an operating potential of 4.5 V or more, but also includes cases where the plateau region also has an operating potential of 4.5 V or more. 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 more in the plateau region. For example, the active material of the present invention may also contain 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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."

[0052] 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 particles A is 0.02% by mass or more, and more preferably 0.05% by mass or more. A B element content of 0.02% by mass or more is preferable because it can maintain discharge capacity at high temperatures. Furthermore, it is preferable to contain the complex oxide phase so that the content of the B element in the core particles A is 0.80% by mass or less, and more preferably 0.60% by mass or less, more preferably 0.30% by mass or less, and particularly preferably 0.25% by mass or less. A B element content of 0.80% by mass or less is preferable because it can maintain rate characteristics.

[0053] 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 such amounts are considered to have little effect on the performance of the core particle.

[0054] Note that, when core particle A is fitted to a cubic crystal structure model of space group Fd-3m (Origin Choice 2), for example, it can be confirmed that the core particle A has a spinel structure when 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.

[0055] The primary particles of the core particles A are preferably polycrystalline rather than single crystalline. A single crystal refers to a particle in which the primary particle is composed of one 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.

[0056] [Core Particle B] The core particle is also preferably a particle 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, this core particle will also be referred to as "core particle B"). The active material of the present invention may contain other components in addition to core particle B. However, from the viewpoint of effectively obtaining the properties of core particle B, it is preferable that core particle B accounts 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).

[0057] The core particle B is 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).

[0058] 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.

[0059] "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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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, whereby it can be confirmed that the core particle B has a layered structure.

[0065] The primary particles of core particle B are preferably polycrystalline rather than single crystalline, similar to core particle A. The definitions of single crystal and polycrystalline are the same as those for core particle A.

[0066] [Core Particle C] The core particle is preferably a particle made of a lithium-excess layered rock-salt type lithium-containing composite oxide containing Li, Ma (Ma necessarily contains 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, this core particle will also be referred to as "core particle C"). The active material of the present invention may contain other components in addition to the core particle C. However, from the viewpoint of effectively obtaining the properties of the core particle C, it is preferable that the core particle C accounts for, for example, 50% by mass or more, particularly 70% by mass or more, of which 90% by mass or more, and of which 95% by mass or more (including 100% by mass) is preferred.

[0067] The core particle C is 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).

[0068] 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.

[0069] Regarding the content of Ma in the core particle, the content of Mn in Ma 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 Ma 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.

[0070] 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.

[0071] The core particles C may contain impurities. For example, SO 4 may be used as the impurity. ４ When SO is contained, it may contain 1.0 mass % or less as an impurity. ４ When elements other than those mentioned 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.

[0072] [Method for Producing Active Material] Methods for producing active materials are broadly divided into methods for producing core particles and methods for forming a coating layer on the surface of core particles. An example of a method for producing core particles is a production method comprising a raw material mixing step, a wet-pulverization step, a granulation step, a firing step, and a pulverization step. However, this production method is a preferred example, and the present invention is not limited to this production method.

[0073] The method for forming the coating layer includes the steps of preparing a coating powder and disposing a coating layer containing the coating powder on the surface of a core particle. In the step of preparing the coating powder, the above-mentioned solid electrolyte powder is prepared. The preferred particle size D of the solid electrolyte powder is ５０ As mentioned above.

[0074] In the step of disposing a coating layer containing a coating powder on the surface of a core particle, the coating powder and the core particle are dry-mixed. For example, a dry particle compositing device designed to apply compression, shear, and impact forces uniformly to each particle can be used for dry mixing. Dry mixing using a particle compositing device can firmly form a coating layer containing the coating powder on the surface of the core particle. As such a particle compositing device, for example, the NOB-MINI dry particle compositing device manufactured by Hosokawa Micron Corporation is preferably used. This device is equipped with a horizontal cylindrical mixing vessel, in which a specially shaped rotor rotates, and is designed to apply compression, shear, and impact forces uniformly to each particle. In contrast, simply mixing the core particle and the coating powder does not form a coating layer containing the coating powder on the surface of the core particle, but only a mixed powder containing the core particle and the coating powder is obtained. The powder of the core particle has a particle diameter D ５０ The particle diameter D of the core particle powder is preferably adjusted to 1 μm or more, more preferably 2 μm or more, and even more preferably 2.5 μm or more. ５０ is preferably adjusted to 20 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. By doing so, the coating layer can be successfully disposed on the surface of the core particle.

[0075] By performing the dry mixing while cooling, the coating powder is less likely to deteriorate. As a result, the battery characteristics of a solid-state battery including the obtained active material are less likely to deteriorate, which is preferable. In this case, for example, a dry mixer equipped with a water-cooling jacket can be used. The temperature of the mixture during dry mixing is preferably maintained at 10°C or higher and 50°C or lower.

[0076] The active material of the present invention thus produced is generally in the form of particles. The particle size of the active material is measured by the 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 2.5 μm or more. ５０is preferably 20.0 μm or less, more preferably 10.0 μm or less, and even more preferably 5.0 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.

[0077] In the active material of the present invention, as long as a coating layer containing the above-mentioned solid electrolyte is disposed on the outermost surface of the active material, one or more intermediate layers may be disposed between the core particle and the coating layer. The intermediate layer is preferably composed of at least one selected from the group consisting of lithium sulfate, lithium phosphate, lithium sulfide, and lithium halide. Alternatively, the intermediate layer may be LiNbO ３ , LiNbO and Li ３ NbO ４ It is preferable that the intermediate layer contains a compound such as a lithium niobium composite oxide, lithium tantalate, or lithium zirconate. These compounds can be used alone or in combination of two or more. When the intermediate layer contains these compounds, the preferred proportion of the compound is 0.1% by mass or more and 5.0% by mass or less relative to the core particles.

[0078] Examples of the lithium salt of phosphoric acid contained in the coating portion include lithium orthophosphate, lithium pyrophosphate, lithium metaphosphate, and lithium polyphosphate. Among these, from the viewpoint of more effectively suppressing the oxidation reaction of the solid electrolyte, it is preferable to use lithium pyrophosphate, and it is more preferable to use lithium metaphosphate, as the lithium salt of phosphoric acid.

[0079] In the active material of the present invention, when an intermediate layer is disposed between the core particle and the coating layer, it is preferable that the oxygen content in the coating layer be lower than that in the intermediate layer. In other words, it is preferable that there is a gradient in the oxygen content between the intermediate layer and the coating layer. By providing such a gradient, the S—O exchange reaction between the active material and the solid electrolyte is less likely to occur, thereby suppressing a deterioration in the battery characteristics of the solid-state battery.

[0080] [Electrode Mixture] The active material of the present invention can be mixed with a solid electrolyte and a conductive material to obtain an electrode mixture. In this case, the solid electrolyte can be the same as the solid electrolyte contained in the coating layer. Alternatively, it is preferable to use a different solid electrolyte having a higher ionic conductivity than the solid electrolyte contained in the coating layer. When using a different solid electrolyte, it is preferable to use a solid electrolyte having a molar ratio X / P of 1.2 or more, particularly 1.4 or more, and particularly 1.5 or more. It is also preferable to use a solid electrolyte having a molar ratio of sulfur (S) to phosphorus (P) of 4.8 or less, particularly 4.6 or less, and particularly 4.5 or less. In this way, the solid electrolyte disposed on the surface of the active material of the present invention suppresses the reaction between the active material and the solid electrolyte in the electrode, and the different solid electrolyte can increase the ionic conductivity in the electrode, thereby reducing the reaction resistance of the battery and improving the storage characteristics of the solid battery when exposed to high temperatures.

[0081] The other solid electrolyte may be one represented by the above formula (II). In this case, from the viewpoint of improving the ionic conductivity of the solid electrolyte, d is preferably 0.5 or more and less than 2.0, more preferably 1.0 or more and 1.9 or less, and even more preferably 1.4 or more and 1.7 or less.

[0082] The active material contained in the electrode mixture may be only the active material of the present invention, or may be a combination of the active material of the present invention and other active materials. Examples of other active materials include particles made of known lithium metal composite oxides. When the active material of the present invention is used in combination with other active materials, it is preferable that the active material of the present invention is contained in an amount of 50 mass % or more, particularly 70 mass % or more, based on the total active material.

[0083] The electrode mixture may be mixed with other materials such as a conductive additive, a binder, etc., as needed. The electrode mixture and the binder, etc., are mixed in a solid phase, and the mixture is formed into pellets, thereby producing an electrode layer.

[0084] [Battery] The active material 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 active material of the present invention can be suitably used for a solid-state battery, particularly a solid-state lithium battery. Among these, the active material of the present invention can be suitably used for a secondary battery, particularly a solid-state lithium secondary battery. Examples of the shape of the battery include a laminate type, a cylindrical type, a prismatic type, and a coin type.

[0085] The solid-state battery has a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located therebetween, and the positive electrode layer preferably contains the active material of the present invention. The solid-state battery can be fabricated, 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.

[0086] 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, lithium titanate, and lithium metal. 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.

[0087] In addition to the above-described embodiments, the present invention further discloses the following active materials, electrode mixtures, electrode layers, and solid-state batteries. [1] An active material comprising a core particle and a coating layer disposed on at least a portion of the surface of the core particle, wherein the coating layer contains a solid electrolyte including a crystalline phase having an argyrodite-type crystal structure, the solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X), and wherein the molar ratio of the halogen (X) to the phosphorus (P) is less than 1.2. [2] The active material according to [1], wherein the solid electrolyte has a molar ratio of sulfur (S) to the phosphorus (P) greater than 4.8. [3] The active material according to [1] or [2], wherein the core particle contains at least one selected from a lithium-containing composite oxide having a layered rock-salt structure, a lithium-containing composite oxide having a spinel structure, and a phosphate compound having an olivine structure. [4] The active material according to any one of [1] to [3], wherein a ratio of the coating layer to the active material is 0.1 mass % or more and 10 mass % or less. [5] An electrode mixture comprising the active material according to any one of [1] to [4], a solid electrolyte, and a conductive material. [6] The electrode mixture according to [5], wherein the solid electrolyte has a molar ratio of halogen (X) element to phosphorus (P) element of 1.2 or more. [7] An electrode layer comprising the electrode mixture according to [5] and a binder. [8] A solid-state 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 electrode mixture according to [5].

[0088] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0089] [Example 1] (1) Production of solid electrolyte Lithium sulfide (Li ２ S) powder, diphosphorus pentasulfide (P ２ S ５Lithium chloride (LiCl) powder, lithium bromide (LiBr) powder, and lithium fluoride (LiBr) powder were used as raw material powders. Toluene was added to each raw material powder to prepare a slurry. Each slurry was individually placed in a polyamide container and set in a Fritsch planetary ball mill P-5. Zirconia balls with a diameter of 5 mm were used as the grinding media. The ball mill was operated at 100 rpm and wet-milled for 10 hours. The toluene was removed from the ground slurry by vacuum drying at 150°C. Each ground raw material powder was obtained in this manner. Each raw material powder was weighed and mixed to obtain the composition shown in Table 1 below, and toluene was added to prepare a slurry. Each slurry was individually placed in a polyamide container and set in the planetary ball mill. Zirconia balls with a diameter of 5 mm were used as the grinding media. The ball mill was operated at 100 rpm and wet-milled for 10 hours. The toluene was removed from the mixed slurry by vacuum drying at 80°C. A raw material composition was thus obtained.

[0090] The raw material composition was fired to obtain a fired product. The firing was carried out using a tubular electric furnace. Nitrogen gas with a purity of 100% was circulated through the electric furnace during firing. The firing was carried out by raising the temperature to 500°C at 200°C / h, maintaining the temperature at 500°C for 4 hours, and then allowing it to cool to obtain a fired product.

[0091] The obtained fired product was crushed in a mortar and passed through a 250 μm sieve to obtain a crushed powder. This crushed powder was crushed in a planetary ball mill. Zirconia balls with a diameter of 5 mm were used as crushing media. The container was made of polyamide. Toluene was used as the solvent. The ball mill was operated at 100 rpm, and crushing was carried out for 3 hours. The obtained slurry was vacuum dried at 80° C. to remove the solvent. In this way, a particle size D ５０ A powder of solid electrolyte having a particle size of 3 μm was obtained.

[0092] The obtained pulverized powder was further pulverized in a planetary ball mill. Zirconia balls with a diameter of 0.8 mm were used as the pulverization media. The container was made of polyamide. Toluene containing a dispersant was used as the solvent. The ball mill was operated at 100 rpm, and pulverization was continued until the desired particle size was achieved. The obtained slurry was vacuum dried at 80°C to remove the solvent. In this way, the desired solid electrolyte was obtained.

[0093] (2) Production of Active Material As core particles, 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 used. The particle diameter D ５０ = 3.2 μm) was prepared. The solid electrolyte powder and the core particle powder were mixed using a dry particle compositing device NOB-MINI manufactured by Hosokawa Micron Corporation, and the solid electrolyte particles were attached to the surfaces of the core particles to form a coating layer containing the solid electrolyte. The amount of solid electrolyte relative to the total amount of core particles and solid electrolyte was adjusted to the value shown in Table 1. The rotation speed was set to 6000 rpm, and the coating process was carried out for 90 minutes. During mixing, the device was cooled and maintained at 30°C. In this way, active material particles were obtained.

[0094] [Example 2] Li was added to obtain the composition shown in Table 1. ２ S powder, P ２ S ５ The active material particles were obtained in the same manner as in Example 1, except that the solid electrolyte was obtained by mixing the powder and LiCl powder.

[0095] Comparative Example 1: Li was added to obtain the composition shown in Table 1. ２ S powder, P ２ S ５ The active material particles were obtained in the same manner as in Example 1, except that the solid electrolyte was obtained by mixing the powder and LiCl powder.

[0096] Comparative Example 2 The LNMO prepared in Example 1 was used as the active material particles in this comparative example.

[0097] Example 3 (1) Production of solid electrolyte Li was added to obtain the composition shown in Table 2. ２ S powder, P ２ S５ The LiCl powder and LiCl powder were mixed to obtain a solid electrolyte in the same manner as in Example 1. (2) Production of Active Material Core particles were prepared using a lithium transition metal oxide (hereinafter also referred to as "NCM622") having a layered rock salt structure and containing 7.2% Li, 36.3% Ni, 12.2% Co, and 11.3% Mn. ５０ The active material particles were obtained in the same manner as in Example 1 except for this.

[0098] [Examples 4 and 5] Li was added to obtain the composition shown in Table 2. ２ S powder, P ２ S ５ The powder, LiCl powder, and LiBr powder were mixed to obtain a solid electrolyte in the same manner as in Example 3. Except for this, active material particles were obtained in the same manner as in Example 3.

[0099] Comparative Example 3: Li was added to obtain the composition shown in Table 2. ２ S powder, P ２ S ５ The active material particles were obtained in the same manner as in Example 3, except that the solid electrolyte was obtained by mixing the powder and LiCl powder.

[0100] Comparative Example 4 NCM622 prepared in Example 3 was used as the active material particles in this comparative example.

[0101] [Evaluation] The solid electrolytes obtained in the examples and comparative examples were subjected to X-ray diffraction measurement by the following method, and the intensity ratio I Ａ / I Ｂ and I Ｃ / I Ｄ The value of was determined. The half-width of the diffraction peak D was also determined. Furthermore, the crystallite size was measured. Furthermore, the substance amount ratio of the solid electrolyte contained in the coating layer obtained in Example 4 and Comparative Example 3 was measured by ICP atomic emission spectroscopy. The substance amount ratio of the solid electrolyte was measured by dissolving the solid electrolyte in a solvent. Furthermore, solid batteries were manufactured using the active materials obtained in the Examples and Comparative Examples, and the reaction resistance and recovery capacity of the solid batteries were measured by the following methods. The results are shown in Tables 1 and 2 below.

[0102] [X-ray diffraction measurement] Measurements were performed using a Malvern Panalytical tabletop X-ray diffractometer "Aeris" without exposure to air. The measurement conditions were as follows: - Radiation source: CuKα - Tube voltage: 40 kV - Tube current: 15 mA - Measurement method: Focusing method (reflection method) - Detector: One-dimensional semiconductor detector - Incident Soller slit: Soller slit 0.02 rad - Longitudinal limiting slit: 20 mm - Receiving Soller slit: 0.02 rad - Incident slit: 1 / 2° - Receiving slit: Open - Measurement range: 2θ = 10 to 105° - Step width: 0.01° - Scan speed: 1.67° / min. The background intensity obtained from the Kapton film in the non-exposed holder was subtracted before analyzing the measurement results.

[0103] [Integrated intensity, half-width, crystallite size] The X-ray diffraction pattern obtained by X-ray diffraction measurement was read into Smart Lab Studio II and calculated by peak processing. Peak profiling was performed using a peak shape: divided pseudo-Voight function, background type: B-spline, and fitting conditions: automatic. From the obtained peak list results, the integrated intensity (Count °) and half-width FWHM (°) of the corresponding peak were read. The crystallite size (Å) was calculated from the peak at 2θ = 29.7 ° ± 1 °.

[0104] [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 powder was used as the negative electrode active material. ５．４ P.S. ４．４ C ｌ０．８ Br ０．８A sulfide solid electrolyte containing a crystalline phase having an argyrodite-type crystal structure was used. A positive electrode active material, a solid electrolyte powder, and a conductive carbon additive were mixed in a mortar at a mass ratio of 70:27:3 to prepare a positive electrode mixture powder. A negative electrode active material and a solid electrolyte powder were mixed in a mortar at a mass ratio of 1:1 to prepare a negative electrode mixture powder. 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 SUS), solid electrolyte powder was placed on top, and the cylinder was blocked with a negative electrode (made of SUS). A solid electrolyte layer was then formed by uniaxial pressing at 180 MPa. Next, the negative electrode was temporarily removed, and a 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 550 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.

[0105] [Resistance Increase Rate and Capacity Recovery Rate After Storage at 90°C] <When Core Particles are LNMO> Using the solid state batteries fabricated in Examples 1 and 2 and Comparative Examples 1 and 2, charge / discharge tests were carried out as follows. Specifically, the solid state 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. The batteries were then left to stand until the temperature of the solid state batteries reached the environmental temperature. Next, a current of 0.1 C (0.2 mA / cm ２The battery was charged at a constant current and constant potential to 5.0 V at 0.1 C, then discharged at a constant current to 3.0 V at 0.1 C, 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, and discharged at a constant current to 3.0 V at 0.1 C, and the discharge capacity was measured. The discharge capacity at this time is referred to as the initial capacity. The battery was then charged at a constant current and constant potential to 4.9 V at 0.1 C again. The battery, which had been 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 solid-state battery was removed, returned to room temperature, and then placed in an environmental test chamber at 25°C and discharged at a constant current of 0.1 C to 3.0 V. Thereafter, the battery was charged at a constant current and constant potential at 0.1 C to 4.9 V, and then discharged at a constant current of 0.1 C to 3.0 V, and the discharge capacity was measured. The discharge capacity at this time is referred to as the recovered capacity. 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) × 100. The recovered capacity relative to the initial capacity was calculated, and this value was used as the capacity recovery rate. Specifically, the capacity recovery rate was calculated using the following formula: Capacity recovery rate (%) = {(recovered capacity) / (initial capacity)} × 100

[0106] <When the core material particles are NCM> Using the solid-state batteries fabricated in Examples 3 to 5 and Comparative Examples 3 and 4, 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 left to stand until the battery temperature reached the environmental temperature. Next, a current of 0.1 C (0.3 mA / cm ２The battery was charged at a constant current and constant potential to 4.5 V at 0.1 C, then discharged at a constant current to 2.5 V at 0.1 C, 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 4.5 V at 0.1 C, and discharged at a constant current to 2.5 V at 0.1 C, and the discharge capacity was measured. The discharge capacity at this time is referred to as the initial capacity. The battery was then charged at a constant current and constant potential to 4.5 V at 0.1 C again. The battery, which had been charged at a constant current and 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 of 0.1 C to 2.5 V. Thereafter, the battery was charged at a constant current and constant potential at 0.1 C to 4.5 V, and then discharged at a constant current of 0.1 C to 2.5 V, and the discharge capacity was measured. The discharge capacity at this time is referred to as the recovery capacity. After charging until the SOC reached 50%, the resistance value after the storage test was measured by impedance measurement. Thereafter, the resistance increase rate and capacity recovery rate after storage at 90°C were calculated in the same manner as in the case where the core material particles were LNMO.

[0107]

[0108]

[0109] As is clear from the results shown in Tables 1 and 2, the solid state batteries manufactured using active materials containing the solid electrolytes obtained in the Examples in the coating layers are less likely to increase in reaction resistance and have higher recovery capacities than the solid state batteries of the Comparative Examples, even when stored in a charged state at high temperatures. Although not shown in the tables, X-ray diffraction measurements confirmed that all of the solid electrolytes obtained in the Examples contained a crystalline phase having an argyrodite-type crystal structure.

[0110] As described above in detail, the present invention provides an active material that can suppress performance degradation during storage of a solid-state battery.

Claims

1. An active material comprising a core particle and a coating layer disposed on at least a portion of the surface of the core particle, wherein the coating layer contains a solid electrolyte including a crystalline phase having an argyrodite-type crystal structure, and wherein the solid electrolyte contains lithium (Li), phosphorus (P), sulfur (S), and a halogen (X), and the molar ratio of the halogen (X) to the phosphorus (P) is less than 1.

2.

2. The active material according to claim 1, wherein the solid electrolyte has a molar ratio of sulfur (S) to phosphorus (P) greater than 4.

8.

3. The active material according to claim 1 or 2, wherein the core particles contain at least one selected from the group consisting of a lithium-containing composite oxide having a layered rock salt structure, a lithium-containing composite oxide having a spinel structure, and a phosphate compound having an olivine structure.

4. The active material according to claim 1 or 2, wherein the ratio of the coating layer to the active material is 0.1% by mass or more and 10% by mass or less.

5. An electrode mixture comprising the active material according to claim 1 or 2, a solid electrolyte, and a conductive material.

6. The electrode mixture according to claim 5, wherein the solid electrolyte has a molar ratio of halogen (X) element to phosphorus (P) element of 1.2 or more.

7. An electrode layer comprising the electrode mixture according to claim 5 and a binder.

8. A solid-state 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 electrode mixture according to claim 5.

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