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

Abstract

This active material has a core material particle and a coating part arranged on the surface of the core material particle. The coating part includes a compound A and a sulfide solid electrolyte. The compound A is at least one selected from the group consisting of lithium sulfate, a lithium salt of phosphoric acid, lithium sulfide, and lithium halide. The value of the mass of the sulfide solid electrolyte with respect to the mass of the compound A is 1 or less. It is preferable that the compound A contains lithium sulfate and a lithium salt of phosphoric acid. It is also preferable that the compound A contains lithium halide.

Description

Active material and its manufacturing method, electrode mixture, electrode, and battery

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

[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] However, solid-state batteries have a problem in that their storage characteristics are easily affected by the storage environment, and further improvement in storage characteristics is desired. However, the composite active materials described in Patent Documents 1 and 2 were not able to sufficiently improve the storage characteristics of solid-state batteries. 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 provides an active material having core particles and a coating portion disposed on the surface of the core particles, the coating portion including a compound A and a sulfide solid electrolyte, the compound A being at least one selected from the group consisting of lithium sulfate, a lithium salt of phosphoric acid, lithium sulfide, and a lithium halide, and the ratio of the mass of the sulfide solid electrolyte to the mass of the compound A being 1 or less.

[0007] The present invention also provides a method for producing an active material, comprising: a step of dry-mixing core particles with a compound A to obtain an active material intermediate in which a first layer containing compound A is disposed on the surface of the core particles; and a step of dry-mixing the active material intermediate with a sulfide solid electrolyte to obtain the active material in which a second layer containing the sulfide solid electrolyte is disposed on the surface of the first layer, wherein compound A is at least one selected from the group consisting of lithium sulfate, a lithium salt of phosphoric acid, lithium sulfide, and a lithium halide.

[0008] The present invention will be described below based on preferred embodiments. In this specification, the term "value of B relative to A" refers to the ratio B / A of A and B. The present invention relates to a battery active material, for example, an active material for a lithium-ion battery, and a method for producing the same. The active material of the present invention comprises core particles and a coating portion disposed on the surface of the core particles. The core particles occupy the majority of the active material and are composed of an active material matrix. The coating portion, as described below, contains a specific lithium compound (hereinafter also referred to as "compound A") and a sulfide solid electrolyte. Details of compound A will be described later. The active material of the present invention, in which a coating portion composed of a specific compound is disposed on the surface of the core particles, can improve the storage characteristics of solid-state batteries, whose storage characteristics are susceptible to the storage environment. In particular, the active material of the present invention can suppress the increase in resistance and decrease in capacity of solid-state batteries, which become significant when stored in a high-temperature and / or high-voltage (charged) environment. The inventors speculate that the reason for this is as follows. In an electrode comprising the active material of the present invention and a solid electrolyte, the coating portion of the active material contains Compound A, thereby suppressing deterioration of the solid electrolyte. This makes it possible to suppress an increase in resistance and a decrease in capacity of the solid-state battery due to deterioration of the solid electrolyte. Furthermore, the coating portion of the active material of the present invention contains a sulfide solid electrolyte, thereby increasing the interfacial contact area of ​​the active material and making lithium ion transport smoother. This makes it less likely that an increase in resistance and a decrease in capacity will occur in the solid-state battery.

[0009] The sulfide solid electrolyte contained in the coating portion of the active material of the present invention and the solid electrolyte used in combination with the active material of the present invention when producing an electrode may be the same type or different types.

[0010] [Compound A] Compound A contained in the coating portion is at least one selected from the group consisting of lithium sulfate, lithium salt of phosphate, lithium sulfide, and lithium halide. The present inventors believe that by including compound A in the coating portion, as described above, it is possible to suppress the deterioration of the solid electrolyte used in combination with the active material of the present invention to prepare an electrode. The reason for this is presumed to be as follows. The deterioration of a solid electrolyte generally progresses through a decomposition reaction or an oxidation reaction. The decomposition reaction referred to here is, for example, a reaction in which a compound having the composition formula Li ６ P.S. ５ The solid electrolyte represented by X (X is a halogen atom) is Li ３ P.S. ４ and LiX and Li ２ S, and is typically a reaction without the involvement of oxygen atoms. On the other hand, an oxidation reaction refers to a reaction in which oxygen atoms contained in core particles migrate to the solid electrolyte, oxidizing the solid electrolyte. Lithium sulfide and lithium halide are typical decomposition products produced by the decomposition reaction of a solid electrolyte. Therefore, by including lithium sulfide or lithium halide in the coating portion, the reverse reaction of the decomposition reaction of the solid electrolyte (i.e., the solid electrolyte production reaction) becomes more likely to proceed when the battery is stored, and the decomposition reaction of the solid electrolyte is apparently suppressed. Furthermore, by including lithium sulfate or a lithium salt of phosphoric acid in compound A, the oxidation reaction of the solid electrolyte is suppressed. Lithium sulfate and a lithium salt of phosphoric acid are reactants produced when the solid electrolyte is oxidized. Therefore, the present inventors believe that by including lithium sulfate and lithium phosphate in the coating portion, the reverse reaction of the oxidation reaction of the solid electrolyte becomes more likely to proceed when the battery is stored, and the oxidation reaction of the solid electrolyte is apparently suppressed.

[0011] 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 or lithium metaphosphate as the lithium salt of phosphoric acid, and it is more preferable to use lithium metaphosphate.

[0012] Examples of the lithium halide contained in the coating portion include LiF, LiCl, LiBr, and LiI, and one of these can be used alone or two or more can be used in combination. From the viewpoint of more reliably obtaining the above-mentioned effects, the lithium halide is preferably a decomposition product of the solid electrolyte. In other words, it is preferable that the lithium halide contains the same type of halogen element as the solid electrolyte. For example, when the solid electrolyte contains a chlorine element, the lithium halide preferably contains LiCl. Furthermore, when the sulfide solid electrolyte contained in the coating portion contains a halogen element, it is also preferable that the lithium halide contains the same type of halogen element as the sulfide solid electrolyte contained in the coating portion.

[0013] When compound A contains lithium sulfate, the mass thereof is preferably 5% or more, more preferably 15% or more, and even more preferably 30% or more of the mass of compound A. Furthermore, the mass of lithium sulfate is preferably 95% or less, more preferably 85% or less, and even more preferably 70% or less of the mass of compound A. When compound A contains a lithium phosphate salt, the mass thereof is preferably 5% or more, more preferably 15% or more, and even more preferably 30% or more of the mass of compound A. Furthermore, the mass of the lithium phosphate salt is preferably 95% or less, more preferably 85% or less, even more preferably 70% or less, still more preferably 60% or less, and particularly preferably 55% or less of the mass of compound A.

[0014] When compound A contains lithium sulfide, its mass is preferably 0.01% or more, more preferably 0.05% or more, and even more preferably 0.10% or more of the mass of compound A. Furthermore, the mass of lithium sulfide is preferably 10.00% or less, more preferably 5.00% or less, and even more preferably 3.00% or less of the mass of compound A. When compound A contains lithium halide, its mass is preferably 0.01% or more, more preferably 0.05% or more, and even more preferably 0.10% or more of the mass of compound A. Furthermore, the mass of lithium halide is preferably 10.00% or less, more preferably 5.00% or less, and even more preferably 3.00% or less of the mass of compound A.

[0015] From the viewpoint of more reliably suppressing deterioration due to oxidation of the solid electrolyte, it is preferable that Compound A contains lithium sulfate and a lithium salt of phosphoric acid. In this case, the content of the lithium salt of phosphoric acid per 100 parts by mass of lithium sulfate is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more. Furthermore, the content of the lithium salt of phosphoric acid per 100 parts by mass of lithium sulfate is preferably 1,000 parts by mass or less, more preferably 500 parts by mass or less, and even more preferably 300 parts by mass or less.

[0016] From the same viewpoint, compound A preferably contains lithium halide, and more preferably contains lithium sulfate, a lithium salt of phosphoric acid, and a lithium halide. When compound A contains lithium sulfate, a lithium salt of phosphoric acid, and a lithium halide, the content of the lithium salt of phosphoric acid per 100 parts by mass of lithium sulfate is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more. Furthermore, the content of the lithium salt of phosphoric acid per 100 parts by mass of lithium sulfate is preferably 1,000 parts by mass or less, more preferably 500 parts by mass or less, and even more preferably 300 parts by mass or less.

[0017] When compound A contains lithium sulfate, a lithium phosphate salt, and a lithium halide, the content of the lithium halide relative to 100 parts by mass of lithium sulfate is preferably 0.01 parts by mass or more, more preferably 0.10 parts by mass or more, and even more preferably 0.50 parts by mass or more, and the content of the lithium halide relative to 100 parts by mass of lithium sulfate is preferably 20.00 parts by mass or less, more preferably 10.00 parts by mass or less, and even more preferably 5.00 parts by mass or less.

[0018] From the viewpoint of making the above-mentioned advantages of compound A more pronounced, the mass of compound A contained in the active material of the present invention is preferably 0.01% or more, more preferably 0.50% or more, and even more preferably 1.00% or more of the mass of the core material particles. From the same viewpoint, the mass of compound A contained in the active material of the present invention is preferably 30.00% or less, more preferably 20.00% or less, and even more preferably 10.00% or less of the mass of the core material particles.

[0019] [Sulfide Solid Electrolyte] The sulfide solid electrolyte contained in the coating portion preferably has lithium ion conductivity. Specific examples of the sulfide solid electrolyte include Li ２ S-P ２ S ５ , Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ -LiCl-LiBr, Li ２ S-P ２ S ５ -LiCl-LiI, Li ２ S-P ２ S ５ -LiBr-LiI, Li ２ S-P ２ S ５ -Li ２O, Li ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-SiS ２ , Li ２ S-SiS ２ - LiI, Li ２ S-SiS ２ - LiBr, Li ２ S-SiS ２ -LiCl, Li ２ S-SiS ２ -B ２ S ３ - LiI, Li ２ S-SiS ２ -P ２ S ５ - LiI, Li ２ S-B ２ S ３ , Li ２ S-P ２ S ５ -Z ｍ S ｎ (m and n are each independently a positive number, and Z represents one or more of Ge, Zn, and Ga), Li ２ S-GeS ２ , Li ２ S-SiS ２ -Li ３ P.O. ４ , Li ２ S-SiS ２ -Li ｘ MO ｙ (x and y are each independently a positive number, and M represents one or more of P, Si, Ge, B, Al, Ga, and In.), Li １０ GeP ２ S １２ The following can be mentioned:

[0020] The sulfide solid electrolyte may be crystalline or amorphous, such as glass ceramics. When the sulfide solid electrolyte is a crystalline material, it preferably contains a crystalline phase having an argyrodite-type crystal structure. This is because sulfide solid electrolytes containing a crystalline phase having an argyrodite-type crystal structure have excellent lithium ion conductivity.

[0021] The argyrodite crystal structure has the chemical formula: Ag ８ GeS ６ This is a crystalline structure possessed by a group of compounds derived from minerals represented by the formula: Whether or not a sulfide solid electrolyte has a crystalline phase with an argyrodite-type crystalline structure can be confirmed by measurement using XRD, etc. For example, in a diffraction pattern measured by XRD using CuKα1 radiation, a crystalline phase with an argyrodite-type crystalline structure exhibits characteristic diffraction peaks at 2θ = 25.5° ± 1.0°, 30.0° ± 1.0°, and 30.9° ± 1.0°. Furthermore, depending on the element species constituting the surface portion, in addition to the diffraction peaks described above, characteristic diffraction peaks may also be observed at 2θ = 15.3° ± 1.0°, 18.0° ± 1.0°, 44.3° ± 1.0°, 47.2° ± 1.0°, 51.7° ± 1.0°, 58.3° ± 1.0°, 60.7° ± 1.0°, 61.5° ± 1.0°, 70.4° ± 1.0°, and 72.6° ± 1.0°. To identify the diffraction peaks derived from the argyrodite-type crystal structure, for example, data from PDF No. 00-034-0688 is used.

[0022] From the viewpoint of further improving the performance of a battery including the active material of the present invention, the sulfide solid electrolyte preferably contains lithium (Li), phosphorus (P), sulfur (S), and a halogen (X). In this case, the sulfide solid electrolyte preferably contains a compound represented by the 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 preferable from the viewpoint of improving lithium ion conductivity between the composite active materials.

[0023] In composition formula (I), a, which represents the molar ratio of Li element, is preferably 3.0 or more and 6.5 or less, more preferably 4.0 or more and 5.9 or less, and even more preferably 5.0 or more and 5.6 or less. It is preferable that a is in this range because the cubic argyrodite-type crystal structure is stable at around room temperature (25°C) and sufficient lithium ion vacancies can be introduced into the structure, thereby enhancing the lithium ion conductivity.

[0024] In composition formula (I), b is preferably 3.5 or more and 5.5 or less, more preferably 4.0 or more and 4.9 or less, and even more preferably 4.2 or more and 4.7 or less, from the viewpoint of stabilizing the argyrodite-type crystal structure at around room temperature (25°C) and increasing the lithium ion conductivity.

[0025] In composition formula (I), c is preferably 0.1 or more and 2.5 or less, more preferably 1.1 or more and 2.0 or less, and even more preferably 1.4 or more and 1.8 or less.

[0026] The sulfide solid electrolyte has the composition formula (II): Li ７－ｄ P.S. ６－ｄ X ｄ The composition represented by composition formula (II) is a stoichiometric composition of an argyrodite-type crystal phase. In composition formula (II), X has the same meaning as in composition formula (I).

[0027] In composition formula (II), d is preferably 0.4 or more and 2.2 or less, more preferably 0.8 or more and 2.0 or less, and even more preferably 1.2 or more and 1.8 or less.

[0028] The sulfide solid electrolyte has the composition formula (III): Li ７－ｄ－２ｅ P.S. ６－ｄ－ｅ X ｄ The argyrodite-type crystalline phase having the composition represented by the composition formula (III) may be, for example, a mixture of an argyrodite-type crystalline phase having the composition represented by the composition formula (II) and P ２ S ５ It is produced by reaction with diphosphorus pentasulfide.

[0029] In the composition formula (III), e is the Li from the stoichiometric composition represented by the composition formula (II). ２ e is a value indicating the deviation of the S component. e is preferably −0.9 or more and (−d+2) or less, more preferably −0.6 or more and (−d+1.6) or less, and even more preferably −0.3 or more and (−d+1.0) or less.

[0030] In the composition formula (I), (II) or (III), a part of P may be substituted with at least one or more elements selected from Si, Ge, Sn, Pb, B, Al, Ga, As, Sb and Bi. In this case, the composition formula (I) is Li ａ (P １－ｙ M ｙ ) S ｂ X ｃ The composition formula (II) is Li ７－ｄ (P １－ｙ M ｙ ) S ６－ｄ X ｄ The composition formula (III) is Li ７－ｄ－２ｅ (P １－ｙ M ｙ ) S ６－ｄ－ｅ X ｄ M is one or more elements selected from Si, Ge, Sn, Pb, B, Al, Ga, As, Sb, and Bi. y is preferably 0.01 or more and 0.70 or less, more preferably 0.02 or more and 0.40 or less, and even more preferably 0.05 or more and 0.20 or less.

[0031] In the sulfide solid electrolyte, the atomic ratio X / P of halogen (X) elements to phosphorus (P) elements in the sulfide solid electrolyte is, for example, preferably greater than 1.0, more preferably 1.1 or greater, even more preferably 1.2 or greater, and even more preferably 1.4 or greater. Meanwhile, the atomic ratio X / P is, for example, preferably 2.5 or less, more preferably 2.3 or less, and even more preferably 2.2 or less. By having the atomic ratio X / P within the above range, lithium ion conductivity between the composite active materials is further improved. For example, this can be measured by inductively coupled plasma atomic emission spectroscopy (ICP atomic emission spectroscopy) or SEM-EDS analysis.

[0032] In particular, when the halogen (X) element includes at least chlorine (Cl) and bromine (Br), the value of the total atomic number of chlorine (Cl) and bromine (Br) elements relative to phosphorus (P) element (Cl + Br) / P is, for example, preferably greater than 1.0, more preferably 1.1 or greater, even more preferably 1.2 or greater, and even more preferably 1.4 or greater. Meanwhile, the atomic ratio (Cl + Br) / P is, for example, preferably 2.5 or less, more preferably 2.3 or less, and even more preferably 2.0 or less. Having the atomic ratio (Cl + Br) / P within the above range further improves the lithium ion conductivity between the composite active materials, which is preferable. For example, this can be measured by elemental analysis using inductively coupled plasma atomic emission spectroscopy (ICP atomic emission spectroscopy) or an EDS-equipped scanning electron microscope (SEM-EDS).

[0033] The sulfide solid electrolyte is particularly preferably a sulfide solid electrolyte represented by the composition formula (IV) Li ７－ｄ P.S. ６－ｄ Cl ｄ１ Br ｄ２ In the composition formula (IV), the total molar ratio d (= d1 + d2) of Cl and Br preferably satisfies 1.0 < d ≦ 1.9. It is preferable that the total molar ratio d (= d1 + d2) of Cl and Br is greater than 1.0 and less than 1.9, from the viewpoint of further enhancing lithium ion conductivity. In particular, it is preferable that d is 1.9 or less, from the viewpoint of controlling the formation of heterophases and suppressing a decrease in ion conductivity. From this viewpoint, it is preferable that d in the composition formula (IV) is greater than 1.0 and less than 1.9, and more preferably 1.2 or more or 1.8 or less, and even more preferably 1.4 or more or 1.7 or less.

[0034] In the composition formula, the molar ratio of Br to Cl (d2 / d1) is, for example, preferably 0.1 to 10.0, more preferably 0.3 to 5.0, and even more preferably 0.5 to 3.0. By having d2 / d1 within the above range, lithium ion conductivity can be further improved.

[0035] In the composition formula, d1, which indicates the molar ratio of Cl, preferably satisfies, for example, 0.3 to 1.5, more preferably 0.4 to 1.2, and even more preferably 0.6 to 1.0. When d1 is equal to or greater than the lower limit, lithium ion conductivity can be further improved. On the other hand, when d1 is equal to or less than the upper limit, the sulfide solid electrolyte can be easily obtained.

[0036] In the composition formula, d2, which indicates the molar ratio of Br, preferably satisfies, for example, 0.3 to 1.5, more preferably 0.4 to 1.2, and even more preferably 0.6 to 1.0. When d2 is equal to or greater than the lower limit, the sulfide solid electrolyte is easily obtained. On the other hand, when d2 is equal to or less than the upper limit, lithium ion conductivity can be further increased.

[0037] In any case where the sulfide solid electrolyte is represented by any of the composition formulas (I), (II), (III), and (IV), it is preferable that the halogen (X) element contains bromine (Br), since this further improves the lithium ion conductivity between the composite active materials.

[0038] From the viewpoint of smoother lithium ion transport, the mass of the sulfide solid electrolyte contained in the active material of the present invention is preferably 0.1% or more, more preferably 0.5% or more, and even more preferably 1.0% or more of the mass of the core particles. Furthermore, from the viewpoint of ensuring the electronic conductivity of the active material and improving the storage characteristics of a battery containing the active material, the mass of the sulfide solid electrolyte contained in the active material of the present invention is preferably 50.0% or less of the mass of the core particles, more preferably 40.0% or less, even more preferably 30.0% or less, even more preferably 20.0% or less, even more preferably 10.0% or less, and particularly preferably 4.5% or less. In particular, when the active material does not contain conductive carbon as described below, the mass of the solid electrolyte contained in the active material is preferably 4.5% or less of the mass of the core particles.

[0039] [Coating Portion] The coating portion of the active material of the present invention may have a single-layer structure or a multi-layer structure. When the coating portion has a single-layer structure, the compound A, sulfide solid electrolyte, and other components constituting the coating portion may be uniformly mixed. An example of a coating portion having a multi-layer structure is an embodiment in which the coating portion has a first layer disposed on the surface of the core particle and a second layer disposed on the surface of the first layer. In this case, it is preferable that no other layer is disposed outside the second layer. Furthermore, when there is a region on the surface of the core particle where the first layer is not present, the second layer may be disposed on the surface of the first layer as well as in the region on the surface of the core particle where the first layer is not present. It is preferable that the first layer and the second layer satisfy at least one of the following (i) and (ii): (i) The first layer contains compound A, and the second layer contains a sulfide solid electrolyte. (ii) The first layer contains a sulfide solid electrolyte, and the second layer contains compound A.

[0040] When the first layer and the second layer satisfy the condition (i), it is preferable that the first layer does not contain a sulfide solid electrolyte. Also, it is preferable that the second layer does not contain compound A. When the first layer and the second layer satisfy the condition (ii), it is preferable that the first layer does not contain compound A. Also, it is preferable that the second layer does not contain a sulfide solid electrolyte. From the viewpoint of making the transport of lithium ions smoother by the sulfide solid electrolyte, it is preferable that at least a part of the sulfide solid electrolyte is located on the outermost surface of the active material. Therefore, when the coating portion has a multilayer structure, it is preferable that the first layer and the second layer satisfy the condition (i).

[0041] Whether the coating portion has a single-layer structure or a multilayer structure, the mass of the coating portion is preferably 0.1% or more of the mass of the core material particle, more preferably 0.2% or more, and even more preferably 0.5% or more. Furthermore, the mass of the coating portion is preferably 50.0% or less of the mass of the core material particle, more preferably 40.0% or less, and even more preferably 30.0% or less. By having the mass of the coating portion within the above range, in an electrode containing an active material and a solid electrolyte, the reaction between the active material and the solid electrolyte can be suppressed, and lithium ion transport can be made smoother. Furthermore, the energy density of the electrode can be increased.

[0042] Whether the coating portion has a single-layer structure or a multilayer structure, the coverage of the core particle by the coating portion is preferably 40% or more, more preferably 70% or more, and even more preferably 85% or more, from the viewpoint of further improving the storage characteristics of the battery. The upper limit of the coverage is not particularly limited, but can be, for example, 99% or less, particularly 95% or less. The "coverage" refers to the area ratio of the region on the surface of the core particle where the coating portion is disposed. The presence of the coating portion on the surface of the core particle 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, as well as by Auger electron spectroscopy (AES) or X-ray diffraction (XRD). The thickness of the coating portion disposed on the surface of the core particle does not need to be uniform. The coverage can be measured by observing the active material using XPS. Details of the measurement method will be explained in the examples below.

[0043] The coating portion of the active material of the present invention may contain conductive carbon in addition to compound A and the sulfide solid electrolyte. When the coating portion contains conductive carbon, the storage characteristics of the battery can be further improved. This is thought to be because the conductive carbon improves the electronic conductivity of the coating portion. Suitable conductive carbons include, for example, carbon black, acetylene black, and carbon nanotubes. When the coating portion contains conductive carbon, the mass of the conductive carbon is preferably 0.01% or more of the mass of the core particles, more preferably 0.05% or more, and even more preferably 0.10% or more. Furthermore, the mass of the conductive carbon is preferably 10.00% or less of the mass of the core particles, more preferably 5.00% or less, even more preferably 2.00% or less, and even more preferably 1.50% or less.

[0044] The conductive carbon may be present in the entire coating portion or in a part of the coating portion. From the viewpoint of making the effect of the conductive carbon in improving the battery storage characteristics more pronounced, when the coating portion has a multilayer structure consisting of a first layer and a second layer, the conductive carbon is preferably contained in the second layer, and more preferably contained only in the second layer (i.e., the first layer does not contain conductive carbon). From the same viewpoint, when the first layer and the second layer satisfy the above (i), the content of the conductive carbon contained in the second layer is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 2.0% by mass or more, relative to the sulfide solid electrolyte. Furthermore, the content of the conductive carbon contained in the second layer is preferably 30.0% by mass or less, more preferably 25.0% by mass or less, and even more preferably 20.0% by mass or less, relative to the sulfide solid electrolyte. From the same viewpoint, when the first layer and the second layer satisfy the above (ii), the content of the conductive carbon in the second layer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1.0% by mass or more, relative to compound A. Furthermore, the content of the conductive carbon in the second layer is preferably 400.0% by mass or less, more preferably 200.0% by mass or less, and even more preferably 100.0% by mass or less, relative to compound A.

[0045] As preferred embodiments that can particularly improve the storage characteristics of the battery, the following embodiments (A) and (B) can be mentioned: (A) The value W2 / W1, where W2 is the mass of the sulfide solid electrolyte and W1 is the mass of the compound A, is equal to or less than 1. (B) The coating portion contains conductive carbon in addition to the compound A and the sulfide solid electrolyte.

[0046] The reason why the storage characteristics of the battery are improved in the active material of the embodiment (A) is thought to be because the coating can suppress the decomposition reaction and / or oxidation reaction of the electrolyte in contact with the active material. Another reason for the improved storage characteristics of the battery is thought to be that the sulfide solid electrolyte in the coating is deformed, suppressing the generation of voids between particles in an electrode containing the active material of the present invention, thereby more reliably establishing a Li ion conduction path (hereinafter also referred to as "Li ion path"). From the viewpoint of further improving the storage characteristics of the battery, W2 / W1 is preferably 1.00 or less, more preferably 0.60 or less. Furthermore, from the viewpoint of improving the reaction uniformity of the active material by establishing a Li ion path, W2 / W1 is preferably 0.01 or more, more preferably 0.05 or more, even more preferably 0.10 or more, even more preferably 0.20 or more, and particularly preferably 0.25 or more.

[0047] In the embodiment (B), from the viewpoint of further improving the storage characteristics of the battery, it is preferable that the value W2 / W1, where W2 is the mass of the sulfide solid electrolyte relative to W1 is 0.50 or greater. The reason why the storage characteristics of the battery are improved by setting W2 / W1 to 0.50 or greater is thought to be that the sulfide solid electrolyte contained in the coating portion improves the contact between the active material and the electrolyte, more reliably establishing Li-ion paths and further improving the reaction uniformity of the active material. From the viewpoint of further improving the storage characteristics of the battery, in this embodiment, W2 / W1 is more preferably 0.70 or greater, even more preferably 0.90 or greater, even more preferably 1.20 or greater, even more preferably 1.50 or greater, and particularly preferably 2.00 or greater. Furthermore, from the viewpoint of improving the energy density of the electrode, W2 / W1 is preferably 7.00 or less, more preferably 5.00 or less, even more preferably 3.00 or less, and even more preferably 2.65 or less.

[0048] W2 / W1 can be measured by combining XRD measurement with ICP optical emission spectroscopy. Furthermore, it can also be measured by combining XPS. Details of the measurement method will be described in the examples below.

[0049] The coating may contain components other than the above-mentioned compound A, sulfide solid electrolyte, and conductive carbon. However, from the viewpoint of improving the storage characteristics of the battery at high temperatures, the coating may contain LiNbO ３ , LiNbO, 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.

[0050] [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.) The core particles may be one of these, or may be a combination of two or more of these. However, the core particles are not limited to these.

[0051] [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.

[0052] 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.

[0053] 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.

[0054] The metal element M1 is a substitution element that mainly contributes to the development of 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 core material particle A may contain at least one of these elements, and it is particularly preferable that the core material particle A contains at least one of Ni and Co.

[0055] 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.

[0056] An example of the composition of the core particle A is a compound represented by the formula (2): Li ｘ (M1 ｙ M2 ｚ Mn ２－ｙ－ｚ ) O ４－δ Examples include a spinel-type lithium-manganese-containing composite oxide represented by the formula (2): The metal element M1 and the metal element M2 in the formula (2) are as described above.

[0057] In the formula (2), "x" is preferably 1.00 or more, more preferably 1.01 or more, and even more preferably 1.02 or more. In the formula (2), "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.

[0058] Another example of the composition of the core particle A is a compound represented by the formula (3): Li ｘ (Ni ｙ M3 ｚ Mn ３－ｘ－ｙ－ｚ ) O ４－δ Examples of suitable lithium-manganese-containing spinel oxides include those represented by the formula (3). In formula (3), "x" is preferably 1.00 or more, more preferably 1.01 or more, and even more preferably 1.02 or more. In formula (3), "x" is preferably 1.20 or less, more preferably 1.10 or less, and even more preferably 1.08 or less. In formula (3), "y" is preferably 0.20 or more, more preferably 0.30 or more, and even more preferably 0.35 or more. In formula (3), "y" is preferably 0.70 or less, more preferably 0.60 or less, and even more preferably 0.55 or less.

[0059] In the formula (3), 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 above-mentioned elements. The "z" indicating 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.

[0060] In addition, "4-δ" in the above formulas (2) and (3) 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.

[0061] 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."

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] [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 core particles B. However, from the viewpoint of effectively obtaining the properties of core particles B, it is preferable that core particles B account for, for example, 80% by mass or more of the core particles, particularly 90% by mass or more, and of these, 95% by mass or more (including 100% by mass).

[0067] The core particles B are represented by the formula (4): 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 located between Groups 3 and 11 of the periodic table and typical metal elements from Periods 1 to 3 of the periodic table).

[0068] Formula (4): Li １＋ｘ M １－ｘ O ２ In the formula (4), "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.

[0069] "M" in the formula (4) 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.

[0070] 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.

[0071] When "M" in the formula (4) 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.

[0072] In the above formula (4), 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] [Core Particles C] The core particles are preferably particles made of a lithium-excess layered rock-salt type lithium transition metal 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).

[0077] 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 element selected from Ni and Co; and Mb contains at least one element selected from Al, Mg, Ti, Fe, and Nb).

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] The active material of the present invention can be mixed with a solid electrolyte to obtain an electrode mixture. The solid electrolyte can be the same as the solid electrolyte used in general solid-state batteries. Examples include sulfur-containing solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes. Among these, sulfur-containing solid electrolytes are preferred. The sulfur-containing solid electrolyte can be any of the various sulfide solid electrolytes exemplified as the sulfide solid electrolyte contained in the coating portion of the active material of the present invention. The solid electrolyte used in combination with the active material to prepare the electrode mixture and the sulfide solid electrolyte contained in the coating portion of the active material may be the same type or different types. From the perspective of further enhancing the effects of the present invention, it is preferable that the two are the same type. The electrode mixture may contain a conductive material in addition to the active material and solid electrolyte. Examples of the conductive material include conductive carbons such as carbon black and acetylene black.

[0084] The electrode mixture is mixed with a solvent and a binder to form a paste, which is then applied to a current collector such as aluminum foil and dried to form an electrode (positive electrode layer and / or negative electrode layer). The electrode thus produced contains the electrode mixture and the binder.

[0085] [Method for Producing Active Material] Next, a suitable method for producing the active material of the present invention will be described using as an example a method for producing an active material having a coating portion consisting of a first layer disposed on the surface of a core particle and a second layer disposed on the surface of the first layer. This production method includes the following steps: a step of preparing core particles (core particle preparation step); a step of dry-mixing core particles with compound A to obtain an active material intermediate in which a first layer containing compound A is disposed on the surface of the core particle (first layer formation step); and a step of dry-mixing the active material intermediate with a sulfide solid electrolyte to obtain the active material in which a second layer containing the sulfide solid electrolyte is disposed on the surface of the first layer (second layer formation step).

[0086] [Core particle preparation process] The core particles can be produced by a production method including a raw material mixing process, a wet grinding process, a granulation process, a firing process, a heat treatment process, a washing / drying process, and a grinding process. However, this production method is a preferred example, and the present invention is not limited to this production method. In addition, commercially available core particles can also be used.

[0087] [First Layer Formation Step] Once the core particles are prepared, the core particles and compound A are dry-mixed to form a first layer containing compound A on the surface of the core particles, thereby obtaining an active material intermediate. Details of compound A are as described above. The dry mixing of the core particles and compound A is preferably carried out under conditions in which shear force, compression force, and / or impact force is applied. By employing such a dry mixing method, a strong coating portion can be formed on the surface of the core particles. For example, a dry particle composite device (Nobilta (registered trademark) manufactured by Hosokawa Micron Corporation) can be used for dry mixing.

[0088] [Second Layer Formation Step] The second layer can be formed in the same manner as the first layer. That is, the active material intermediate and the sulfide solid electrolyte are dry-mixed to form a second layer containing the sulfide solid electrolyte on the surface of the first layer, thereby obtaining the active material. Details of the sulfide solid electrolyte are as described above. The dry mixing in this step is preferably carried out under a state in which shear force, compression force, and / or impact force is applied, as in the dry mixing in the first layer formation step.

[0089] When the first layer formation step or the second layer formation step is performed by dry mixing, the temperature may rise due to the generation of frictional heat, which may cause deterioration of the components constituting the coating portion. From the viewpoint of reducing the temperature rise caused by dry mixing and suppressing the deterioration of the components constituting the coating portion, it is preferable to perform at least one of the dry mixing of the compound A and the core particles (first layer formation step) and the dry mixing of the sulfide solid electrolyte and the active material intermediate (second layer formation step) while cooling, and it is more preferable to perform both while cooling. Suppressing the deterioration of the components constituting the coating portion is preferable because it can further improve the storage characteristics of the battery. When dry mixing is performed while cooling, 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.

[0090] When the first layer constituting the coating portion contains a component other than compound A, the core material particles, compound A, and the other component may be dry-mixed. The order of mixing is not limited, and for example, the core material particles, compound A, and the other component may be dry-mixed simultaneously, or compound A and the other component may be mixed to obtain a mixed powder, and then the mixed powder and the core material particles may be dry-mixed. This also applies when the second layer contains a component other than the sulfide solid electrolyte (e.g., conductive carbon).

[0091] Conventionally, when a coating portion is formed on a core particle, the core particle is typically contacted 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 portion 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 portion containing a compound is formed on a core particle, these challenges can be overcome by performing dry mixing as described above. Furthermore, dry mixing tends to result in a close relationship between the input ratio of each raw material powder and the composition ratio of each component in the resulting active material, making it easier to produce an active material with a desired composition. In contrast, wet mixing tends to result in a discrepancy between the input ratio of each raw material powder and the composition ratio of each component in the resulting active material.

[0092] Although the present invention has been described above based on the preferred embodiments, the present invention is not limited to the above embodiments.

[0093] The above-described embodiments of the present invention encompass the following technical concepts. [1] An active material having core particles and a coating portion disposed on the surface of the core particles, the coating portion including a compound A and a sulfide solid electrolyte, the compound A being at least one selected from the group consisting of lithium sulfate, a lithium salt of phosphate, lithium sulfide, and a lithium halide, and the ratio of the mass of the sulfide solid electrolyte to the mass of the compound A being 1 or less. [2] An active material having core particles and a coating portion disposed on the surface of the core particles, the coating portion including a compound A, a sulfide solid electrolyte, and conductive carbon, the compound A being at least one selected from the group consisting of lithium sulfate, a lithium salt of phosphate, lithium sulfide, and a lithium halide. [3] The active material according to [2], wherein the ratio of the mass of the sulfide solid electrolyte to the mass of the compound A is 0.50 or more. [4] The active material according to any one of [1] to [3], wherein the compound A includes lithium sulfate and a lithium salt of phosphate. [5] The active material according to any one of [1] to [4], wherein compound A contains lithium halide. [6] The active material according to any one of [1] to [5], wherein the coverage rate with the coating portion is 40% or more and 99% or less. [7] The active material according to any one of [1] to [6], wherein the mass of the coating portion is 0.5% or more and 30.0% or less of the mass of the core particle. [8] The active material according to any one of [1] to [7], wherein the sulfide solid electrolyte contains a crystalline phase having an argyrodite-type crystal structure. [9] The active material according to any one of [1] to [8], wherein the core particle contains 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.

[10] The active material according to any one of [1] to [9], wherein the coating portion has a multilayer structure including a first layer disposed on a surface of the core particle and a second layer disposed on the surface of the first layer, the first layer including compound A, and the second layer including the sulfide solid electrolyte.

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

[10] and a solid electrolyte.

[12] An electrode including 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 contains the active material according to any one of [1] to

[10] .

[14] A method for producing an active material, comprising: dry-mixing core particles with a compound A to obtain an active material intermediate having a first layer containing compound A disposed on the surface of the core particles; and dry-mixing the active material intermediate with a sulfide solid electrolyte to obtain the active material having a second layer containing the sulfide solid electrolyte disposed on the surface of the first layer, wherein compound A is at least one selected from the group consisting of lithium sulfate, a lithium salt of phosphoric acid, lithium sulfide, and a lithium halide.

[15] The method according to

[14] , wherein the dry-mixing of compound A with the core particles and the dry-mixing of the sulfide solid electrolyte with the active material intermediate are both carried out while cooling.

[0094] 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, "%" means "% by mass."

[0095] In the following examples and comparative examples, the following materials were used as the active material. As the 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 used, or a lithium transition metal composite oxide (hereinafter also referred to as "NCM") having a layered rock salt structure and a composition of Li: 7.2%, Ni: 36.3%, Co: 12.2%, and Mn: 11.3% was used. As compound A, lithium sulfate (Li ２ SO ４ ), lithium metaphosphate (LiPO ３ ), and lithium chloride (LiCl) were used. The sulfide solid electrolyte was ５．８ P.S. ４．８ Cl １．２ or a sulfide solid electrolyte represented by the composition formula Li ５．４ P.S. ４．４ Cl ０．８ Br ０．８A sulfide solid electrolyte represented by the formula (hereinafter also referred to as "sulfide solid electrolyte B") was used. VGCF (registered trademark) manufactured by Resonac Corporation was used as the conductive carbon.

[0096] <Method for Producing Sulfide Solid Electrolyte> The sulfide solid electrolyte A was produced by the following method. ５．８ P.S. ４．８ Cl １．２ So that Li ２ S powder and P ２ S ５ The powder and LiCl powder were weighed and pulverized and mixed in a ball mill for 3 hours to prepare a mixed powder. This mixed powder was filled into a carbon container, heated at a temperature increase / decrease rate of 200°C / h in a tubular electric furnace while circulating nitrogen gas at 1.0 L / min, and fired at 500°C for 4 hours to obtain a fired body. This fired body was pulverized and sieved using a sieve with a mesh size of 53 μm to obtain a raw material powder for molding the surface portion. Weighing, mixing, setting in the electric furnace, removal from the electric furnace, pulverization, and sieving were all carried out in a glove box purged with sufficiently dried Ar gas (dew point -60°C or less). Sulfide solid electrolyte B has a composition of Li ５．４ P.S. ４．４ Cl ０．８ Br ０．８ So that Li ２ S powder and P ２ S ５ The sulfide solid electrolyte A was produced in the same manner as in the sulfide solid electrolyte A, except that the sulfide solid electrolyte B, the LiCl powder, and the LiBr powder were each weighed and pulverized and mixed in a ball mill for 3 hours to prepare a mixed powder.

[0097] Examples 1 to 4 First Layer Formation Step Core particles and Compound A in the amounts shown in Table 1 were dry-mixed using a NOB-MINI dry particle compositer manufactured by Hosokawa Micron Corporation to obtain an active material intermediate. Mixing was carried out for 70 minutes at a rotor rotation speed of 7,500 rpm. During mixing, the apparatus was cooled and maintained at 25°C or below.

[0098] <Second Layer Formation Step> Next, the sulfide solid electrolyte and conductive carbon in the amounts shown in Table 1 were charged into the same device containing the active material intermediate, and these were dry-mixed to obtain an active material. Mixing was carried out for 90 minutes with the rotor rotation speed set to 6000 rpm. During mixing, the device was cooled and maintained at 25°C or below. The amounts of Compound A, sulfide solid electrolyte, and conductive carbon listed in Table 1 are percentages relative to the mass of the core particles.

[0099] Comparative Example 1 An active material was obtained in the same manner as in Example 1, except that the second layer forming step was not carried out.

[0100] Comparative Example 2 An active material was obtained in the same manner as in Example 3, except that no conductive carbon was used.

[0101] [Evaluation 1] For the active materials obtained in the examples and comparative examples, the mass and coverage of Compound A and the sulfide solid electrolyte were measured. The results are shown in Table 1. In Table 1, "-" indicates that no measurement was performed.

[0102] [Measured Values ​​of Compound A and Sulfide Solid Electrolyte Amounts] First, the active materials obtained in the Examples and Comparative Examples were measured by XRD to determine the mass ratio of lithium chloride to the sulfide solid electrolyte. Next, the active materials obtained in the Examples and Comparative Examples were dissolved by an alkali fusion method, and quantitative analysis of the elements contained in the resulting solution was performed using inductively coupled plasma atomic emission spectroscopy (ICP-AES). The masses of lithium chloride and the sulfide solid electrolyte were determined from the amount of halogen in the solution, the mass ratio of lithium chloride to the sulfide solid electrolyte in the coating portion, and the composition formula of the sulfide solid electrolyte used. The mass of Compound A was measured as follows. First, the mass of S element contained in Compound A was calculated by subtracting the mass of S element contained in the sulfide solid electrolyte, calculated based on the previously calculated mass of the sulfide solid electrolyte, from the mass of S element contained in the solution. Similarly, the mass of the P element contained in the compound A was calculated by subtracting the mass of the P element contained in the sulfide solid electrolyte, which was calculated based on the previously measured mass of the sulfide solid electrolyte, from the mass of the P element contained in the solution. Then, from the masses of the S element and P element contained in the compound A and the composition formula of the compound A, Li ２ SO ４ and LiPO ３ The mass of Li was calculated. ２ SO ４ and LiPO ３The mass of the compound A was calculated by adding the mass of the compound A and the mass of LiCl calculated previously. The measured values ​​of the amount of compound A and the amount of sulfide solid electrolyte shown in Table 1 are percentages relative to the mass of the core particles. [Covering Ratio] The covering ratio was measured using a PHI Quantes XPS device manufactured by ULVAC-PHI, Inc. Specifically, the ratio of the quantitative value of the element present only in the coating portion to the sum of the quantitative value of the element present only in the coating portion and the quantitative value of the element present only in the core particles was calculated. For example, when LNMO was used as the core particles and lithium sulfate, lithium metaphosphate, and sulfide solid electrolyte A were used as the coating portion, the covering ratio was calculated by (S + P + Cl) / (Mn + Ni + Ti + S + P + Cl) × 100. Similarly, for example, when NCM was used as the core particles and lithium sulfate, lithium metaphosphate, and sulfide solid electrolyte B were used as the coating portion, the coating ratio was calculated by (S + P + Br) / (Ni + Co + Mn + S + P + Br) × 100. The conditions used for the measurement were 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

[0103] Solid-state batteries were manufactured using the active materials obtained in the examples and comparative examples by the following method, and the resistance increase rate and capacity recovery rate after storage at 90° C., which are used to evaluate storage characteristics, were measured. The results are shown in Table 1 below.

[0104] [Fabrication of Solid-State Battery] 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. ５．４ PPS 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 stainless steel), solid electrolyte powder was placed on top, and the cylinder was blocked with a negative electrode (made of stainless steel). A solid electrolyte layer was then formed by uniaxial pressing at 10 MPa. Next, the negative electrode was temporarily removed, and a negative electrode mixture powder was placed on the solid electrolyte layer and 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.

[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 Example 1, a charge-discharge test was 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> A charge / discharge test was carried out as follows using the solid-state batteries produced in Examples 3 and 4 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 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 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

[0107]

[0108] As is clear from Table 1, when comparing the active materials of Example 1 and Comparative Example 1, which have the same core particles, it is found that the active material of Example 1, which has a second layer containing a sulfide solid electrolyte, has a lower resistance increase rate and a higher capacity recovery rate. Furthermore, when comparing Example 3 and Comparative Example 2, it is found that the resistance increase rate and capacity recovery rate can be improved by including conductive carbon in the coating portion.

[0109] According to the present invention, an active material capable of improving the storage characteristics of a battery is provided.

Claims

1. An active material having core particles and a coating portion disposed on the surface of the core particles, the coating portion including compound A and a sulfide solid electrolyte, compound A being at least one selected from the group consisting of lithium sulfate, lithium salt of phosphoric acid, lithium sulfide, and lithium halide, and the ratio of the mass of compound A to the mass of the sulfide solid electrolyte is 1 or less.

2. An active material having core particles and a coating portion disposed on the surface of the core particles, the coating portion including compound A, a sulfide solid electrolyte, and conductive carbon, and compound A being at least one selected from the group consisting of lithium sulfate, lithium salt of phosphoric acid, lithium sulfide, and lithium halide.

3. The active material according to claim 2, wherein the ratio of the mass of the sulfide solid electrolyte to the mass of compound A is 0.50 or more.

4. The active material of claim 1 or 2, wherein compound A comprises lithium sulfate and a lithium salt of phosphoric acid.

5. The active material according to claim 1 or 2, wherein compound A comprises a lithium halide.

6. The active material according to claim 1 or 2, wherein the coverage by the coating portion is 40% or more and 99% or less.

7. The active material according to claim 1 or 2, wherein the mass of the coating portion is 0.1% or more and 50.0% or less of the mass of the core particle.

8. The active material according to claim 1 or 2, wherein the sulfide solid electrolyte contains a crystalline phase having an argyrodite-type crystalline structure.

9. The active material according to claim 1 or 2, 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.

10. The active material according to claim 1 or 2, wherein the coating portion has a multilayer structure including a first layer disposed on the surface of the core particle and a second layer disposed on the surface of the first layer, the first layer including compound A, and the second layer including the sulfide solid electrolyte.

11. An electrode mixture comprising the active material according to claim 1 or 2 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 claim 1 or 2.

14. A method for producing an active material, comprising: a step of dry-mixing core particles with compound A to obtain an active material intermediate in which a first layer containing compound A is disposed on the surface of the core particles; and a step of dry-mixing the active material intermediate with a sulfide solid electrolyte to obtain the active material in which a second layer containing the sulfide solid electrolyte is disposed on the surface of the first layer, wherein compound A is at least one selected from the group consisting of lithium sulfate, lithium salt of phosphoric acid, lithium sulfide, and lithium halide.

15. The manufacturing method according to claim 14, wherein the dry mixing of compound A with the core particles and the dry mixing of the sulfide solid electrolyte with the active material intermediate are both carried out while cooling.

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