Method for producing halide solid electrolyte, halide solid electrolyte, positive electrode material, and battery

Abstract

A method for producing a halide solid electrolyte according to the present disclosure comprises (A) subjecting an oxide mixture that contains a composite oxide containing Li and Ti and an oxide starting material containing Li and M to a halogenation treatment so as to obtain a halide solid electrolyte which contains Li, Ti, M, and X. Here, M represents at least one element that is selected from the group consisting of metal elements (excluding Li and Ti) and metalloid elements, and X represents at least one element that is selected from the group consisting of F, Cl, Br, and I.

Description

Method for producing halide solid electrolyte, halide solid electrolyte, positive electrode material, and battery

[0001] The present disclosure relates to a method for producing a halide solid electrolyte, a halide solid electrolyte, a positive electrode material, and a battery.

[0002] Patent Document 1 discloses a halide-based solid electrolyte material. Patent Document 2 discloses a halide-based solid electrolyte material as a solid electrolyte material that coats the surface of a positive electrode active material.

[0003] International Publication No. 2021 / 186809 International Publication No. 2021 / 187391

[0004] An object of the present disclosure is to provide a novel production method capable of stably synthesizing a halide solid electrolyte having a target composition.

[0005] The method for producing a halide solid electrolyte of the present disclosure includes: (A) performing a halogenation treatment on an oxide mixture containing a composite oxide containing Li and Ti and an oxide raw material containing Li and M to obtain a halide solid electrolyte containing Li, Ti, M, and X, wherein M is at least one element selected from the group consisting of metal elements (excluding Li and Ti) and metalloid elements, and X is at least one element selected from the group consisting of F, Cl, Br, and I.

[0006] The present disclosure provides a novel production method that can stably synthesize a halide solid electrolyte having a desired composition.

[0007] FIG. 1 is a flowchart showing an example of a method for producing a halide solid electrolyte according to a first embodiment. FIG. 2 is a flowchart showing an example of a method for producing a halide solid electrolyte according to a second embodiment. FIG. 3 is a flowchart showing a modified example of the method for producing a halide solid electrolyte according to the second embodiment. FIG. 4 is a flowchart showing an example of a method for producing a halide solid electrolyte according to a third embodiment. FIG. 5 is a cross-sectional view of a battery 1000 according to a fourth embodiment. FIG. 6A is a graph showing an X-ray diffraction pattern of a halide solid electrolyte after heat treatment and before pulverization treatment in the production method of Example 1. FIG. 6B is a graph showing X-ray diffraction patterns of the halide solid electrolyte after pulverization treatment obtained in Example 1 and the halide solid electrolyte obtained in Comparative Example 1.

[0008] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0009] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, any component that is not described in an independent claim that represents a top concept will be described as an optional component.

[0010] First Embodiment A method for producing a halide solid electrolyte according to a first embodiment will be described below.

[0011] The manufacturing method according to the first embodiment includes: (A) performing a halogenation treatment on an oxide mixture containing a composite oxide containing Li and Ti and an oxide raw material containing Li and M to obtain a halide solid electrolyte containing Li, Ti, M, and X. Here, M is at least one element selected from the group consisting of metal elements (excluding Li and Ti) and metalloid elements, and X is at least one element selected from the group consisting of F, Cl, Br, and I.

[0012] "Semi-metallic elements" are B, Si, Ge, As, Sb, and Te. "Metallic elements" are all elements included in Groups 1 to 12 of the periodic table (excluding hydrogen) and all elements included in Groups 13 to 16 of the periodic table (excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se). In other words, "metallic elements" are a group of elements that can become cations when forming inorganic compounds with halogen compounds.

[0013] According to the manufacturing method of the first embodiment, a halide solid electrolyte having a target composition can be stably synthesized. The reason for this will be explained in more detail below.

[0014] In conventional manufacturing methods for producing a Ti-containing halide solid electrolyte, titanium halides (e.g., TiX4) are typically used as the Ti source. However, titanium halides are relatively unstable substances, such as those that are easily evaporated and deliquescent. Therefore, the produced halide solid electrolyte may experience compositional variations (i.e., compositional deviations) and alterations (e.g., inclusion of moisture, etc.). As a result, conventional manufacturing methods may have difficulty consistently producing the desired halide solid electrolyte. In contrast, the manufacturing method according to the first embodiment can use a composite oxide containing Li and Ti as the Ti source. Therefore, the manufacturing method according to the first embodiment does not require the use of unstable titanium halides as raw materials in the synthesis of a Ti-containing halide solid electrolyte, and titanium halides are less likely to be produced during the synthesis process. Therefore, the production method according to the first embodiment is less likely to cause the above-mentioned compositional fluctuations and deterioration in the produced halide solid electrolyte, and can reproducibly and stably synthesize, for example, a Ti-containing halide solid electrolyte having excellent properties such as ionic conductivity. In other words, the production method according to the first embodiment can stably synthesize a halide solid electrolyte having a target composition.

[0015] In the above (A), the halogenation treatment of the oxide mixture may be carried out at a temperature of, for example, 150°C or higher. By carrying out the halogenation treatment at a temperature of 150°C or higher, the oxide mixture can be sufficiently halogenated. The temperature during the halogenation treatment may be, for example, 600°C or lower. The atmosphere for the halogenation treatment can be selected appropriately from any atmosphere suitable for the halogen-containing material used, such as air, a nitrogen atmosphere, or a reducing atmosphere.

[0016] In the above (A), the halogenation treatment of the oxide mixture may be carried out, for example, by heat treating a thermally decomposable halogen-containing material.

[0017] By performing a halogenation treatment on the oxide mixture by heat treatment of a thermally decomposable halogen-containing material, the halogenation of the oxide mixture and the solid-state reaction for synthesizing a halide solid electrolyte can occur simultaneously. Therefore, a solid electrolyte with homogeneous and excellent properties can be obtained in a short time while reducing reaction residues such as oxides. Furthermore, since the halogenation treatment is performed by heat treatment of a thermally decomposable halogen-containing material, the reactivity (halogenation property) of the oxide mixture is good and productivity is excellent. Furthermore, for example, the temperature of the halogenation reaction and the solid-state reaction of the oxide mixture, as well as the progress of these reactions, can be controlled depending on the thermal decomposition temperature of the selected halogen-containing material. Therefore, a desired halide solid electrolyte can be obtained.

[0018] When a thermally decomposable halogen-containing substance is used in the halogenation treatment of the oxide mixture, in the production method according to the first embodiment, (A) may include: (A-1) mixing the oxide mixture with the halogen-containing substance; and (A-2) heat-treating the mixture containing the oxide mixture and the halogen-containing substance obtained in (A-1) above, thereby subjecting the oxide mixture to a halogenation treatment.

[0019] In the manufacturing method according to the first embodiment, by carrying out the above (A-1) and (A-2), a heat treatment for halogenation can be carried out on a homogeneous mixture of an oxide mixture and a halogen-containing substance. Furthermore, the contact area between the oxide mixture and the halogen-containing substance can be increased. This promotes the halogenation of the oxide mixture homogeneously, thereby making it possible to obtain a homogeneous halide solid electrolyte with excellent properties.

[0020] 1 is a flowchart showing an example of a method for producing a halide solid electrolyte according to Embodiment 1. Here, as an example of the production method according to Embodiment 1, an example of a production method in which the above (A-1) and (A-2) are carried out will be described.

[0021] As shown in FIG. 1 , in one example of the manufacturing method according to the first embodiment, first, in a step corresponding to the above-mentioned (A-1), an oxide mixture and a halogen-containing substance are mixed (S11). As described above, the oxide mixture contains a composite oxide containing Li and Ti and an oxide raw material containing Li and M. The halogen-containing substance is thermally decomposable. Next, in a step corresponding to the above-mentioned (A-2), the obtained mixture containing the oxide mixture and the halogen-containing substance is heat-treated, thereby performing a halogenation treatment on the oxide mixture (S12). This results in a halide solid electrolyte containing Li, Ti, M, and X.

[0022] The oxide mixture, the halogen-containing substance, and the steps corresponding to (A-1) and (A-2) above will be specifically described below.

[0023] <Oxide Mixture> The oxide mixture contains a composite oxide containing Li and Ti, and an oxide raw material containing Li and M.

[0024] The composite oxide containing Li and Ti may contain at least Li, Ti, and O, and may further contain other cations. Using a composite oxide containing Li and Ti as a Ti source suppresses compositional fluctuations and deterioration of the halide solid electrolyte, enabling the production of a desired halide solid electrolyte with, for example, high ionic conductivity and reliability. According to the manufacturing method of the first embodiment, there is no need to use titanium oxide (e.g., TiO2) as the Ti source. Regardless of the crystal system (rutile, anatase), titanium oxide is likely to produce titanium halides (e.g., TiX4) during the halogenation process, which are prone to evaporation and deliquescence problems. This can lead to the loss of Ti components during the synthesis process or the inclusion of water due to the deliquescence of the titanium halides, resulting in deviations from the desired composition. Therefore, titanium halides can cause a decrease in the ionic conductivity and reliability of the solid electrolyte. In the manufacturing method of the first embodiment, there is no need to use titanium oxide because a composite oxide containing Li and Ti can be used as the Ti source. Therefore, it is possible to suppress the above-mentioned compositional fluctuation and deterioration of the halide solid electrolyte caused by the use of titanium oxide.

[0025] For the reasons mentioned above, it is desirable that the oxide mixture does not substantially contain TiO. Here, in this specification, "the oxide mixture does not substantially contain TiO" means that the content of TiO in the entire oxide mixture is 0.3 mass% or less.

[0026] The composite oxide may contain, for example, Li2TiO3. Li2TiO3 has excellent stability in normal air (including moisture) and also excellent stability at high temperatures up to about 800°C. By using Li2TiO3 as the composite oxide, a halide solid electrolyte containing a crystalline phase represented by Li2TiX6 can be produced.

[0027] The oxide raw material containing Li and M includes, for example, an oxide of Li and an oxide of M. By using an oxide of Li and an oxide of M as the oxide raw material, a halide solid electrolyte having a target composition can be synthesized more stably.

[0028] M may be at least one selected from the group consisting of Al, Y, Ga, Dy, Ho, Er, Tm, and Yb. M may be at least one selected from the group consisting of Al and Y. When M contains any of the above elements, a halide solid electrolyte having high ionic conductivity can be obtained.

[0029] M may contain Al. When M contains Al, a halide solid electrolyte having high ionic conductivity can be obtained. M may be Al.

[0030] As the oxide raw material, for example, metal oxides such as Li2O, Al2O3, etc. can be used. The oxide raw material may contain Li2O and Al2O3.

[0031] The oxide mixture may be, for example, in particulate form. That is, the composite oxide and the oxide raw material constituting the oxide mixture may each be in particulate form. This facilitates simultaneous halogenation (i.e., substitution of halogen element with oxygen element) from the particle surface of the oxide mixture and solid-phase reaction in the oxide mixture. Therefore, a halide can be synthesized in a short time while reducing reaction residues such as oxides. This makes it possible to obtain a homogeneous halide solid electrolyte with excellent properties. Furthermore, since the particulate oxide mixture has good reactivity, such as halogenation property and solid-phase reactivity, excellent productivity can also be achieved.

[0032] The composite oxide such as LiTiO may have an average particle size of, for example, 0.5 μm or more and 20 μm or less. However, the average particle size of the composite oxide is not limited to the above range, and any particle size and shape can be appropriately selected from the viewpoints of halogenation and solid-state reaction with the oxide raw material. For example, the smaller the particle size of the composite oxide, the lower the temperature at which the composite oxide is converted into a halide.

[0033] The average particle size of the composite oxide is the median size of the composite oxide, and means the particle size (d50) corresponding to 50% cumulative volume, determined from the particle size distribution measured on a volume basis by a laser diffraction scattering method. The same applies to the average particle sizes of the oxide raw material and the halogen-containing substance specified in this specification.

[0034] The oxide raw materials such as LiO and AlO may have an average particle size of, for example, 0.5 μm or more and 20 μm or less. As with the composite oxide, the oxide raw materials may also have any particle size and shape.

[0035] <Halogen-containing substance> The halogen-containing substance is thermally decomposable. For example, when the halide solid electrolyte to be produced contains F as the halogen element X, a fluorine-containing substance that serves as a fluorine source is used as the halogen-containing substance.

[0036] The thermal decomposition onset temperature of the halogen-containing substance used may be, for example, 100° C. or higher and 600° C. or lower. When the halogen-containing substance has a thermal decomposition onset temperature within the above temperature range, the halogen-containing substance has stability during storage and handling, such as mixing, and the obtained halide solid electrolyte can be prevented from becoming too hard.

[0037] The halogen element X may contain F or may be F. This makes it possible to obtain a halide solid electrolyte that is excellent in stability (for example, excellent in electrochemical stability and heat resistance) and has high ionic conductivity.

[0038] The halogen-containing material may be, for example, particulate. This facilitates thermal decomposition of the halogen-containing material. Therefore, by using a particulate halogen-containing material, the oxide mixture can be efficiently halogenated, and the halogen-containing material is less likely to remain in the final halide solid electrolyte. Furthermore, by using a particulate halogen-containing material, the amount of halogen can be precisely controlled. This makes it easier to synthesize a desired halide solid electrolyte. Furthermore, since only the amount of halogen-containing material necessary for halogenating the oxide mixture can be used, excess halogen gas emissions can be suppressed. This reduces the burden on the environment and also reduces the impact on corrosion of furnace materials, etc.

[0039] The halogen-containing material may have, for example, an average particle size of 0.5 μm or more and 500 μm or less, an average particle size of 0.5 μm or more and 150 μm or less, or an average particle size of 0.5 μm or more and 100 μm or less. As with the composite oxide and the oxide raw material, the halogen-containing material may have any particle size and shape.

[0040] The average particle size of the halogen-containing material may be larger than the average particle size of the oxide mixture. This results in a state in which the surface area of ​​the oxide mixture is larger than that of the halogen-containing material, i.e., the exposed surface area (i.e., the exposed area) of the oxide mixture is large. This makes it easier for halogenation to proceed from the particle surfaces of the oxide mixture, thereby producing a homogeneous halide. The average particle size of the halogen-containing material may be 5 μm or more and 100 μm or less, 5 μm or more and 20 μm or less, or 50 μm or more and 100 μm or less. The average particle size of the halogen-containing material can be appropriately adjusted taking into account the halogenation temperature or reactivity. For example, by increasing the average particle size of the halogen-containing material, the heat treatment temperature for the halogenation treatment can be increased.

[0041] The halogen-containing material may include an ammonium salt. Ammonium salts begin to thermally decompose at relatively low temperatures (e.g., about 150°C). Therefore, ammonium salts are less likely to remain as unnecessary inorganic components in the final halide solid electrolyte, and can be thermally decomposed at low temperatures to halogenate the oxide mixture. Therefore, by using ammonium salts as the halogen-containing material, it is possible to prevent unnecessary inorganic components derived from the halogen-containing material from remaining in the final halide solid electrolyte. Furthermore, energy savings in synthesis are achieved, and the temperature rise and fall times are reduced, thereby improving productivity. Furthermore, since synthesis can be performed at low temperatures, the durability of furnace materials is improved, and the running costs and replacement frequency of synthesis components are significantly reduced. Only ammonium salts may be used as the halogen-containing material.

[0042] The ammonium salt may contain NH4F. NH4F is a highly decomposable fluorine source and can effectively halogenate the oxide mixture. Therefore, NH4F can thermally decompose at a low temperature (e.g., about 150°C) and at a fast decomposition rate, thereby fluorinating the oxide mixture without leaving any residue in the solid electrolyte. Note that ammonium salts of other halogen elements, such as NH4Cl and NH4Br, are also thermally decomposable and can be similarly used as halogen sources.

[0043] The halogen-containing material may include a resin. By including a resin as the halogen-containing material, the halogen-containing material can halogenate the oxide mixture while being thermally decomposed at a relatively high temperature (e.g., about 450°C or higher and 600°C or lower). Therefore, the method including a resin as the halogen-containing material is suitable for the case where halogenation and solid-state reaction are to be carried out at a relatively high temperature (e.g., about 450°C or higher and 600°C or lower).

[0044] An example of a resin used as the halogen-containing material is a fluororesin. For example, polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) can be used. Fluororesins such as PTFE can halogenate an oxide mixture while being thermally decomposed at a relatively high temperature (e.g., about 450°C or higher and 600°C or lower). Therefore, a method using a fluororesin as the halogen-containing material is suitable when halogenation and solid-state reaction are to be carried out at a relatively high temperature (e.g., about 450°C or higher and 600°C or lower).

[0045] The halogen-containing material may contain, for example, a substance that prevents inorganic components resulting from thermal decomposition by the heat treatment in (A) from being substantially contained in the produced halide solid electrolyte, except for the halogen element. The halogen-containing material used in the halogenation treatment is required to replace the halogen element produced by thermal decomposition by the heat treatment in (A) with the oxygen element of the oxide mixture, while preventing other components from being mixed as inorganic residues in the final halide solid electrolyte. By using a substance that prevents inorganic components resulting from thermal decomposition by the heat treatment from being substantially contained in the final halide solid electrolyte, except for the halogen element, as the halogen-containing material, the mixing of inorganic residues into the halide solid electrolyte can be suppressed, allowing the desired halide solid electrolyte to be obtained. Here, in this specification, the phrase "preventing inorganic components resulting from thermal decomposition by the heat treatment from being substantially contained in the produced halide solid electrolyte, except for the halogen element" means that the content of the inorganic components in the halide solid electrolyte is, for example, 0.5 mass % or less.

[0046] The halogen-containing material may contain multiple types of halogen-containing compounds. For example, both an ammonium salt and a fluororesin can be used as the halogen-containing material. This allows for a wide range of temperature control over the temperature range in which the halogen-containing material acts as a halogen source, thereby enabling the conversion of the oxide mixture to a halide and the solid-state reaction temperature to be controlled over a wide range. This makes it easy to obtain a desired halide solid electrolyte.

[0047] The amount of the halogen-containing substance used is not particularly limited, as long as it is sufficient to halogenate the entire amount of the compound to be halogenated.For example, in the reaction of halogenating the compound to be halogenated, the molar amount of the halogen-containing substance for stoichiometrically halogenating the entire compound (i.e., stoichiometrically equivalent molar amount, in other words, the molar amount required for completely replacing the anion of the compound to be halogenated with a halogen anion such as F) is taken as 100%, and the amount of the halogen-containing substance may be, for example, 103% or more and 150% or less, 103% or more and 130% or less, or 103% or more and 110% or less.

[0048] <Regarding (A-1)> In (A-1), an oxide mixture and a halogen-containing substance are mixed. In mixing the oxide mixture and the halogen-containing substance, for example, a composite oxide containing Li and Ti, an oxide raw material containing Li and M, and a thermally decomposable halogen-containing substance are uniformly mixed. In this manner, the composite oxide, the oxide raw material, and the halogen-containing substance may be mixed simultaneously, or the composite oxide and the oxide raw material may first be uniformly mixed to obtain an oxide mixture, and then the oxide mixture and the halogen-containing substance may be mixed.

[0049] In this way, by carrying out a preliminary step of uniformly mixing the composite oxide, the oxide raw material, and the halogen-containing substance before the halogenation treatment, the oxide mixture can be uniformly converted into a halide, thereby synthesizing a homogeneous halide solid electrolyte.

[0050] For example, powders of a composite oxide, an oxide raw material, and a halogen-containing material are mixed in a desired ratio. For example, a dry mixing method is sufficient as long as the powders of the composite oxide, the oxide raw material, and the halogen-containing material are mixed uniformly. For example, the powders may be mixed uniformly by repeatedly mixing with a spatula, or by using a dry mixing device such as a mortar and pestle, a mortar and pestle, or a V-blender. Mixing may also be performed using a medium such as zirconia balls. Any mixing method may be used as long as it can uniformly mix these powders. The uniformity can be evaluated using, for example, energy dispersive X-ray spectroscopy (EDS) or an electron probe microanalyzer (EPMA). For example, the uniformity can be confirmed by observing a composition mapping image.

[0051] <Regarding (A-2)> In (A-2), the mixture containing the oxide mixture obtained in (A-1) above and a halogen-containing substance is heat-treated, thereby subjecting the oxide mixture to a halogenation treatment.

[0052] A general electric furnace may be used for the heat treatment. The heat treatment atmosphere may be selected as necessary, and the heat treatment may be performed in air, an inert gas atmosphere (e.g., nitrogen gas or argon gas), or a reducing gas (e.g., hydrogen or carbon dioxide). The synthesized halide is usually obtained as a powder, but when heat treated at or above the melting point, it may be obtained as a molten body, a sintered body, or a block-like mass in which the powder has solidified.

[0053] In the heat treatment, the uniformly mixed mixture is placed in, for example, an alumina heat-resistant container (sheath), and the mixture is fired in a firing furnace in a desired atmosphere. For example, an inert gas such as nitrogen gas is flowed into the furnace, and gases generated during halogenation (e.g., ammonium, hydrogen chloride, carbon dioxide, etc.) are discharged while the mixture is heat-treated in the atmosphere furnace at a temperature of, for example, 150°C or higher and 600°C or lower for, for example, 1 hour or higher and 40 hours or lower, to synthesize a halide solid electrolyte. In this way, by introducing and discharging gas into the firing furnace, unnecessary reaction gas components and the like are prevented from remaining in the furnace, i.e., in the halide solid electrolyte.

[0054] When introducing inert gas into the furnace, it is best to avoid direct contact of the inert gas with the sheath containing the mixture. Air may be introduced into the furnace instead of inert gas. A plate larger than the gas inlet is installed between the gas inlet and the sheath. The plate's thickness is sufficient as long as it is not damaged by the gas flow or handling. Partial shielding, such as by placing a plate such as an alumina plate against the sheath, is preferable. By shielding the space between the gas inlet and the sheath in this way, the gas flows around the shielding plate before contacting the sheath. By bypassing the gas and indirectly contacting the sheath in this way, the temperature is lower in the area directly exposed to the gas, reducing the problem of temperature distribution within the sheath. This suppresses uneven distribution of the progress (i.e., variation in progress) of the halogenation reaction of the oxide mixture and the solid-state reaction to synthesize a halide solid electrolyte.

[0055] It is advisable to install the gas inlet on the bottom side of the furnace and the exhaust port on the top side (for example, on the ceiling or above the side wall). This allows the reaction gas to be smoothly discharged outside the furnace along with the convection current (bottom to top) inside the furnace, reducing the contamination of unnecessary residual components with the halide solid electrolyte.

[0056] The gas to be introduced may be heated before being introduced into the furnace. This prevents the temperature distribution in the sheath from becoming uneven. This allows the synthesis reaction of the halide solid electrolyte to proceed uniformly, resulting in a more homogeneous halide solid electrolyte.

[0057] The heat treatment temperature is, for example, 150° C. or higher and 600° C. or lower, and may be 250° C. or higher and 550° C. or lower, as described above. The heat treatment time is, for example, 1 hour or higher and 40 hours or lower, as described above. The heat treatment temperature and time can be determined arbitrarily, taking into consideration the temperature and time required for synthesis of the halide solid electrolyte, the time required for synthesis, and the time required for discharging the reaction gas.

[0058] The furnace used for the heat treatment can be a known firing furnace (e.g., an electric furnace) or an atmospheric firing furnace. Note that in order to remove the air and moisture between the particles deep inside the sheath and completely replace it with an inert gas, the inert gas may be flowed after vacuum replacement. This reduces the effects of reactive components and moisture contained in the air. The vacuum replacement may be repeated.

[0059] The temperature distribution within the sheath during the heat treatment may be within the temperature distribution range of a commonly used firing furnace, for example, 30° C. The temperature distribution within the sheath referred to here is the difference between the maximum and minimum temperatures within the sheath.

[0060] Since this heat treatment is not intended to react easily evaporating materials such as titanium halide, it is not necessary to perform the heat treatment in a sealed state. The oxide mixture and the halogen-containing material may be placed in a sheath, and a lid (e.g., an alumina lid) may be placed on the sheath to prevent dust and foreign matter from falling in, if necessary. Therefore, unlike heat treatments in conventional manufacturing methods using halide raw materials (i.e., heat treatments for solid-phase reactions of halide raw materials), which are limited in throughput by the size of sealed heat treatment jigs, the heat treatment in the manufacturing method according to the first embodiment offers excellent productivity and workability, making it highly valuable for industrial applications. The manufacturing method according to the first embodiment thus offers excellent productivity and can produce a halide solid electrolyte with excellent ionic conductivity and stability (e.g., electrochemical stability and heat resistance). If the oxide mixture contains trace amounts of titanium oxide as an impurity, trace amounts of titanium halide (e.g., TiF) may be generated. However, since the heat treatment is performed in an open atmosphere, such trace amounts of titanium halide evaporate and disappear. Therefore, even in such a case, it is possible to obtain a titanium halide-free halide solid electrolyte having excellent characteristics and reliability.

[0061] The sheath material does not have to be alumina. Heat-resistant containers made of various dense materials (e.g., relative density of 98% or more), such as mullite or SiC, can be used for the sheath, in addition to alumina. A suitable material for the sheath may be selected in consideration of the reaction between the oxide mixture, halogen-containing material, and halide solid electrolyte contained in the sheath and the sheath. In addition to the above-mentioned sheath materials, materials that are dense, heat-resistant, and have a small heat capacity can also be used for the sheath. Various shapes, such as cylindrical, prismatic, and gourd-shaped, can be used for the sheath.

[0062] Although the heat treatment using a sagger has been described here as an example, the present invention is not limited to this. For example, a rotary furnace such as a rotary kiln may be used, or the heat treatment may be performed by spraying the mixed powder as in spray drying.

[0063] As an example of the manufacturing method according to the first embodiment, a method in which the above (A-1) and (A-2) are carried out has been described in detail. However, the step of uniformly mixing the oxide mixture and the halogen-containing substance before the halogenation treatment is not necessarily carried out. For example, the halogen-containing substance may be added to the oxide mixture, and the heat treatment may be carried out without sufficient mixing. Furthermore, although heat treatment is desirable for efficient halogenation treatment, the halogen-containing substance may be added to the oxide mixture, and then the oxide mixture may be halogenated by, for example, leaving the mixture at room temperature for a long period of time.

[0064] In the manufacturing method according to the first embodiment, an additive may be added to the oxide mixture before the halogenation treatment, as needed. For example, an additive for accelerating the halogenation reaction of the oxide mixture, an additive for accelerating the solid-state reaction of the oxide mixture, or the like may be added. Examples of such additives include an oxide containing at least one element selected from the group consisting of Nb, Ga, Zn, Mg, P, K, Na, Ca, Fe, Si, and Cu. For example, when added in trace amounts to the oxide mixture, Nb oxide and Ga oxide can lower the reaction temperature of the halogenation reaction and the solid-state reaction by, for example, about 10°C to 30°C. This can accelerate the halogenation reaction and the solid-state reaction of the oxide mixture. Nb oxide and Ga oxide may be added together, or only one of them may be added. The amount of additive added is not particularly limited and can be selected appropriately depending on the compound to be added and its purpose. For example, when Nb oxide and Ga oxide are added for the purpose of promoting the halogenation reaction and the solid-state reaction, the total amount of Nb oxide and Ga oxide added may be, for example, 0.001 mol % or more and 0.3 mol % or less with respect to the oxide mixture.

[0065] The additives such as Nb oxide and Ga oxide may be, for example, particulate. The effect of the additive may vary depending on the particle form of the additive and the state of dispersion in the oxide mixture. For Nb oxide and Ga oxide, the smaller the particle size, the greater the additive's effect, such as reaction promotion. For example, the particle size of the additive may be smaller than that of the oxide particles constituting the oxide mixture. As an example, the additive may have a particle size of 0.1 μm or less and a BET value of 100 m. 2 / g or more. Note that, if coarse particles of Nb oxide and Ga oxide are used or if they are added in excess, an extra precipitated phase other than the solid electrolyte may be generated, which may reduce ionic conductivity. Therefore, it is desirable to adjust the particle size and the amount of addition to an appropriate level. For example, it is desirable that the Nb oxide and Ga oxide have a particle size and amount such that Nb and Ga are not detected as composition phases in X-ray diffraction measurement of the finally obtained halide solid electrolyte. This allows the synthesis of a halide solid electrolyte with high ionic conductivity while achieving a reaction-accelerating effect.

[0066] The halide solid electrolyte obtained by the manufacturing method according to the first embodiment is a solid electrolyte containing Li, Ti, M, and X. When M contains Al and X contains F, the obtained halide solid electrolyte may contain, for example, a first crystalline phase represented by the following composition formula (1) and a second crystalline phase represented by the following composition formula (2). Composition formula (1): Li2TiX6 Composition formula (2): Li3MX6

[0067] When producing a halide solid electrolyte containing a first crystalline phase and a second crystalline phase, for example, Li2TiO3, which is stable in an atmospheric environment, can be used as a composite oxide containing Li and Ti. Therefore, TiO2 need not be used as a Ti source. Therefore, the generation of titanium halide is suppressed during the conversion process of the oxide mixture to a halide. As a result, a halide solid electrolyte with excellent properties can be synthesized stably and reproducibly in an atmospheric environment, with suppressed compositional fluctuations. That is, the halide solid electrolyte obtained by the production method according to the first embodiment can have the desired composition, thereby achieving a halide solid electrolyte with excellent ionic conductivity. Furthermore, because the generation of titanium halide is suppressed, synthesis in a sealed jig (e.g., a planetary ball mill or solid-state synthesis in a sealed heat-resistant container) is unnecessary. This enables synthesis with excellent productivity.

[0068] When the halide solid electrolyte obtained by the manufacturing method according to the first embodiment includes a first crystal phase and a second crystal phase, the halide solid electrolyte can be represented by the following composition formula (3): Composition formula (3): xLi2TiX6-(1-x)Li3MX6. In composition formula (3), x satisfies 0<x<1. That is, x represents the composition ratio of Li2TiX6, which is the first crystal phase, and (1-x) represents the composition ratio of Li3MX6, which is the second crystal phase. To improve ionic conductivity, x may, for example, satisfy 0.05≦x≦0.5.

[0069] In the manufacturing method according to the first embodiment, when at least one selected from the group consisting of Nb oxide and Ga oxide is used as an additive, the resulting halide solid electrolyte contains at least one selected from the group consisting of Nb and Ga. That is, in this case, the halide solid electrolyte obtained by the manufacturing method according to the first embodiment contains Li, Ti, Al, and F, and further contains at least one selected from the group consisting of Nb and Ga. This configuration results in a homogeneous halide solid electrolyte with excellent ionic conductivity. The halide solid electrolyte obtained by the manufacturing method according to the first embodiment may consist essentially of Li, Ti, Al, F, Nb, and Ga, or may consist only of Li, Ti, Al, F, Nb, and Ga. The phrase "the halide solid electrolyte is substantially composed of Li, Ti, Al, F, Nb, and Ga" means that the ratio of the total amount of substance of Li, Ti, Al, F, Nb, and Ga to the total amount of substance of all elements constituting the halide solid electrolyte is 90% or more. As an example, this ratio may be 95% or more.

[0070] The amount of oxygen as an impurity in the halide solid electrolyte obtained by the manufacturing method according to the first embodiment may be 0.5 mass% or less. The manufacturing method according to the first embodiment makes it possible to obtain a halide solid electrolyte with little oxygen contamination. The amount of oxygen as an impurity in the halide solid electrolyte may be, for example, 0.1 mass% or more.

[0071] As described above, when Nb oxide and Ga oxide are added as additives to promote the reaction of an oxide mixture, Nb and Ga may not be detected as a composition phase in X-ray diffraction measurement. Even in this case, the presence of Nb and Ga in the halide solid electrolyte can be confirmed by highly sensitive composition analysis (area analysis, etc.) such as an electron probe microanalyzer (EPMA). The total content of Nb and Ga contained in the halide solid electrolyte may be, for example, 0.0003 at. % or more and 0.15 at. % or less. The content of Nb and Ga can be determined by EPMA or the like.

[0072] When the halide solid electrolyte obtained by the manufacturing method according to the first embodiment includes the first crystalline phase and the second crystalline phase and further includes at least one element selected from the group consisting of Nb and Ga derived from the Nb oxide and Ga oxide used as additives, for example, Nb may be mainly incorporated into the first crystalline phase, i.e., Li2TiX6, and Ga may be mainly incorporated into the second crystalline phase, i.e., Li3MX6. That is, it is believed that Nb mainly acts to promote the synthesis reaction of Li2TiX6, while Ga mainly acts to promote the synthesis reaction of Li3MX6. Therefore, when the halide solid electrolyte to be manufactured is a solid electrolyte including the first crystalline phase and the second crystalline phase, co-addition of Nb oxide and Ga oxide is desirable.

[0073] The halide solid electrolyte obtained by the manufacturing method according to the first embodiment can achieve high ionic conductivity, comparable to that of a solid electrolyte manufactured using a halide raw material.

[0074] The halide solid electrolyte obtained by the manufacturing method according to the first embodiment preferably contains substantially no TiF. This configuration suppresses changes over time in the characteristics and mechanical properties of the halide solid electrolyte due to TiF evaporation and deliquescence, thereby achieving a halide solid electrolyte with excellent characteristics and reliability. Here, "the halide solid electrolyte contains substantially no TiF" means that the TiF content in the solid electrolyte is, for example, 0.5 mass% or less, preferably 0.1 mass% or less. The TiF content in the halide solid electrolyte can be determined, for example, by elemental analysis using energy dispersive X-ray spectroscopy (EDS) or electron probe microanalysis (EPMA) on the cross section of a compacted halide solid electrolyte powder or the particle surface of the solid electrolyte, and the TiF content can be determined from the area ratio of the detected TiF portion. If the oxide mixture used as the raw material for the halide solid electrolyte contains trace amounts of titanium oxide (TiO), trace amounts of TiF may be generated during the halogenation process. However, even in this case, the halogenation treatment is performed in the open state, so that TiF can be evaporated and eliminated, thereby making it possible to obtain a halide solid electrolyte that is substantially free of TiF and has excellent properties and reliability.

[0075] The halide solid electrolyte obtained by the manufacturing method according to the first embodiment preferably satisfies at least one of the following (1), (2), and (3) in an X-ray diffraction pattern obtained by X-ray diffraction measurement of the halide solid electrolyte using, for example, Cu-Kα radiation: (1) No peak derived from TiF4 is present; (2) No peak derived from LiF is present; and (3) No peak derived from AlF3 is present.

[0076] With the above-described configuration, the halide solid electrolyte obtained by the manufacturing method according to the first embodiment does not substantially contain compounds of, for example, TiF4, LiF, and / or AlF3, and therefore has excellent characteristics and reliability.

[0077] In this specification, a peak in an X-ray diffraction pattern is defined as a mountain-shaped portion having an S / N ratio (i.e., the ratio of signal S to background noise N) of 1.3 or more and a half-width of 5° or less. Therefore, the absence of a peak means that no mountain-shaped portion recognized as a peak as described above is confirmed.

[0078] For example, when the halide solid electrolyte obtained by the production method according to the first embodiment satisfies the above-mentioned configuration (1), i.e., when no peak derived from TiF is present in the X-ray diffraction pattern, no peak is present within a diffraction angle 2θ range of, for example, 24° or more and 25° or less.

[0079] The halide solid electrolyte obtained by the manufacturing method according to the first embodiment may be particulate. The halide solid electrolyte has relatively soft properties. Therefore, this configuration allows for a relatively soft particulate solid electrolyte to be realized. Therefore, a compact of such a halide solid electrolyte has high ionic conductivity, excellent stability, and can have any shape. Therefore, a compact of a halide solid electrolyte having such properties can realize a solid electrolyte layer of a battery having excellent properties and high reliability. The size and shape of the halide solid electrolyte particles can be selected appropriately depending on the application.

[0080] When the manufacturing method according to the first embodiment is compared with the manufacturing methods described in Patent Documents 1 and 2, there are the following differences.

[0081] Patent Document 1 discloses a halide-based solid electrolyte containing Li, Ti, M, and F. The "M" in the solid electrolyte described in Patent Document 1 is at least one selected from the group consisting of Al and Y. The starting materials for producing this solid electrolyte are not oxides such as composite oxides, but are all fluorides, among which TiF4. Many fluorides are unstable, and as mentioned above, titanium fluoride (TiF4) in particular is prone to evaporation even at relatively low temperatures (e.g., 50°C to 100°C) and to moisture content. Therefore, to suppress compositional fluctuations and deterioration of the fluoride raw materials, the halide solid electrolyte is synthesized by sealed ball milling in an argon atmosphere with a low dew point (e.g., −60°C or below). In contrast, the method for producing a halide solid electrolyte according to the first embodiment differs in that the halide solid electrolyte is synthesized from oxide raw materials and reaction pathways with high environmental stability. In particular, by using a composite oxide as the Ti source, a reaction path that suppresses the generation of titanium fluoride can be selected, thereby eliminating the problem of composition fluctuations caused by the evaporation and moisture absorption of the unstable Ti component. Therefore, the production method according to the first embodiment is a production method that can synthesize a halide solid electrolyte with excellent properties while also being suitable for mass production. Therefore, unlike the production method according to the first embodiment, it is clear that the solid electrolyte production method of Patent Document 1 has issues with Ti evaporation, synthesis in air, and productivity.

[0082] Patent Document 2 discloses a method for producing a halide solid electrolyte containing Li, Ti, M1, and F as part of the positive electrode material. Note that "M1" in the solid electrolyte described in Patent Document 2 is at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr. However, like the production method described in Patent Document 1, a fluoride such as TiF4 is used as a starting material. Therefore, like the production method described in Patent Document 1, it is thought to have issues such as composition deviation in the synthesis process. In contrast, as described above, the production method according to the first embodiment is a production method that can synthesize a halide solid electrolyte with excellent properties while also being suitable for mass production.

[0083] As described above, the manufacturing method according to the first embodiment uses an oxide that is stable to the environment (temperature and humidity) as a starting material, and does not require the synthesis of unstable titanium fluoride, etc. in the reaction process. Therefore, the manufacturing method according to the first embodiment is superior to the manufacturing methods described in Patent Documents 1 and 2 in that it can obtain a halide solid electrolyte with excellent properties by suppressing composition fluctuations, etc., and is also excellent in terms of mass productivity.

[0084] Second Embodiment A method for producing a halide solid electrolyte according to a second embodiment will now be described.

[0085] The production method according to the second embodiment further includes, after the step (A) in the production method according to the first embodiment, (B) subjecting the halide solid electrolyte obtained in the step (A) to a pulverization treatment.

[0086] According to the manufacturing method of the second embodiment, by carrying out the pulverization treatment (B) above, a halide solid electrolyte having excellent ionic conductivity and reliability can be obtained with a particle size suitable for the application. Furthermore, since at least a portion of the halide solid electrolyte can be made amorphous, the ionic conductivity can be improved and the softness of the halide solid electrolyte particles can be improved. By improving the softness of the halide solid electrolyte particles, the density of a compact of the halide solid electrolyte can be improved. Therefore, the halide solid electrolyte obtained by the manufacturing method of the second embodiment can form a dense compact with high ionic conductivity.

[0087] 2 is a flowchart showing an example of a method for producing a halide solid electrolyte according to Embodiment 2. Here, an example of a production method will be described in which, in the production method described in Embodiment 1, (A) is performed as (A-1) and (A-2), and (B) is performed after (A-2).

[0088] As shown in Fig. 2, first, an oxide mixture and a halogen-containing substance are mixed (S21). Next, the obtained mixture containing the oxide mixture and the halogen-containing substance is heat-treated to perform a halogenation treatment on the oxide mixture (S22). This results in a halide solid electrolyte containing Li, Ti, M, and X. Next, as a step corresponding to the above (B), the halide solid electrolyte obtained in S22 is subjected to a pulverization treatment (S23).

[0089] S21 and S22 are the same as S11 and S12 described in the first embodiment, respectively, and therefore detailed description thereof will be omitted here.

[0090] The halide solid electrolyte synthesized by the above (A) has an average particle size of, for example, about 3 μm or more and 20 μm or less. In the above (B), the halide solid electrolyte synthesized by the above (A) is pulverized to, for example, an average particle size of, for example, about 0.1 μm or more and 2 μm or less.

[0091] The pulverization process may be a dry process or a wet process using water or a solvent (e.g., ethanol, butyl acetate, etc.) as long as it can pulverize the halide to a desired particle size. For example, zirconia balls (e.g., balls with a diameter of 1 mm to 30 mm) and the halide solid electrolyte obtained in (A) above are placed in a ball mill container and pulverized for, for example, about 3 to 40 hours. The ball mill container may be, for example, a polyethylene container, a container lined with fluororesin or zirconia, or the like.

[0092] The grinding treatment in (B) above may include, for example, mechanochemical treatment. The mechanochemical treatment here is carried out to introduce distorted crystallinity or amorphousness into the crystals of the halide solid electrolyte. The distorted crystallinity or amorphousness is mainly introduced into the surface layer of the halide solid electrolyte particles. The specific means may be the same as those used in the grinding treatment described above, such as using a ball mill. However, the grinding conditions may be strengthened or the grinding time may be extended. The equipment and media used for the mechanochemical treatment may be the same as those used in the grinding treatment. Generally, grinding and mechanochemical treatment proceed simultaneously. As an example, in the case of a dry method, a ball mill container lined with zirconia is used, and zirconia balls are placed in a volume ratio of 10% to 60%. The diameter of the zirconia balls is not particularly limited, and any size may be used. As mentioned above, commercially available balls with a diameter of 1 mm to 30 mm are typically used, but balls with a smaller or larger diameter may also be used. The diameter of the balls used may be selected as desired depending on the desired particle size or degree of amorphization. Furthermore, to prevent the halide solid electrolyte from adhering to the zirconia balls or the inner wall of the zirconia container, an appropriate amount of an additive, such as ethanol, that does not adversely affect the properties of the halide solid electrolyte may be added. It is preferable that the additive be able to be removed by drying later.

[0093] The introduction of amorphousness into the halide solid electrolyte can be confirmed by the X-ray diffraction pattern obtained by X-ray diffraction measurement. The X-ray diffraction pattern can be measured by the θ-2θ method using Cu-Kα radiation (wavelengths 1.5405 Å and 1.5444 Å) as the X-ray source. Specifically, this can be confirmed by the fact that the peaks in the X-ray diffraction pattern of the halide solid electrolyte after the pulverization treatment are broadened compared to the peaks in the X-ray diffraction pattern of the halide solid electrolyte before the pulverization treatment. The broadened peaks mean that the peaks are broadened and the half-width is widened.

[0094] The introduction of distorted crystals into the halide solid electrolyte, i.e., the presence of regions with disordered crystallinity, can be observed with a transmission electron microscope (TEM) as an image consisting of regions with high order in the lattice image and regions with disordered lattice images.

[0095] The change in deformability due to amorphization can be evaluated by an evaluation method such as micro-Vickers.

[0096] As described above, since the manufacturing method according to the second embodiment includes a pulverization process, the halide solid electrolyte obtained by the manufacturing method according to the second embodiment includes, for example, an amorphous phase. This configuration makes the amorphous portion of the halide solid electrolyte even softer and more deformable. Therefore, a compact of the halide solid electrolyte can be configured into a solid electrolyte layer of any shape with higher ionic conductivity and higher stability. Therefore, a compact of the halide solid electrolyte including an amorphous phase can realize a solid electrolyte layer for a battery with excellent characteristics and high reliability.

[0097] As a modification of the manufacturing method according to the second embodiment, the halide solid electrolyte may be made into a slurry for forming a coating film simultaneously with the pulverization treatment in (B) above.

[0098] 3 is a flowchart showing a modified example of the method for producing a halide solid electrolyte according to the second embodiment. Regarding the modified example of the production method according to the second embodiment, an example of a production method will be described here, in which (A-1) and (A-2) are carried out as (A), which is an example of the production method described in the first embodiment, and (B) is carried out after (A-2).

[0099] 3 , first, an oxide mixture and a halogen-containing substance are mixed (S31). Next, the obtained mixture containing the oxide mixture and the halogen-containing substance is heat-treated to perform a halogenation treatment on the oxide mixture (S32). This results in a halide solid electrolyte containing Li, Ti, M, and X. Next, as a step corresponding to the above (B), the halide solid electrolyte obtained in S32 is subjected to a pulverization treatment and a slurry treatment (S33).

[0100] S31 and S32 are the same as S11 and S12 described in the first embodiment, respectively, and therefore detailed description thereof will be omitted here.

[0101] The pulverization process in S33 is similar to the pulverization process in S23 described as an example of the manufacturing method of the second embodiment. In a modified example of the manufacturing method of the second embodiment, a slurrying process is further performed. The slurrying process is performed, for example, by adding an organic binder, a plasticizer, etc., dispersed in an organic solvent such as tetralin to the halide solid electrolyte simultaneously with the pulverization process. An example of the organic binder is styrene butadiene block copolymer (SBS). An example of the plasticizer is bisbutyl phthalate (DBP) and butyl benzyl phthalate (BBP).

[0102] The obtained halide solid electrolyte slurry can be used for printing or coating. The thickness of the coating film may be, for example, 10 μm or more and 100 μm or less, thereby allowing, for example, a halide solid electrolyte slurry that has been pulverized to include an amorphous portion to be directly coated. In this way, an organic binder, a plasticizer, etc. may be added in the pulverization process to prepare a halide solid electrolyte slurry, and the slurry may be used to form a coating film. This allows for the formation of a halide solid electrolyte coating film with excellent properties. Such a coating film can be used, for example, in the manufacture of a coated cell.

[0103] Third Embodiment A method for producing a halide solid electrolyte according to a third embodiment will now be described.

[0104] In the manufacturing method according to the third embodiment, in the step (A) described in the first embodiment, a halogen-containing material is heat-treated to generate halogen gas, and the halogen gas is brought into contact with the oxide mixture, thereby subjecting the oxide mixture to a halogenation treatment. In the manufacturing method according to the third embodiment, the grinding treatment in the step (B) described in the second embodiment may be carried out after the step (A).

[0105] 4 is a flowchart showing an example of a method for producing a halide solid electrolyte according to the third embodiment. As shown in FIG. 4, a composite oxide containing Li and Ti is mixed with an oxide raw material containing Li and M to prepare an oxide mixture (S41). Next, the oxide mixture and a halogen-containing material are placed in a predetermined position, and the halogen-containing material is heat-treated to bring the generated halogen gas into contact with the oxide mixture (S42). This results in a halogenation treatment of the oxide mixture. Thereafter, as a step corresponding to the above-mentioned (B), the halide solid electrolyte obtained in S42 may be subjected to a pulverization treatment (S43).

[0106] According to the manufacturing method of the third embodiment, the oxide mixture can be halogenated by the generated halogen gas without directly contacting the oxide mixture with a halogen-containing material. Therefore, even if a halogen-containing material containing an inorganic component in addition to a halogen element (e.g., a material that emits fluorine gas when heated, such as CuF) is used, it is not necessary to consider inorganic residues in the halide solid electrolyte to be manufactured. This allows for a wider range of usable halogen-containing materials.

[0107] As a specific example, the oxide mixture is placed on a fine-mesh nickel mesh, and a halogen-containing material such as ammonium fluoride is placed below the nickel mesh. In this way, the oxide mixture and the halogen-containing material are placed without contacting each other. In this state, by heat-treating the halogen-containing material, halogen gas such as fluorine gas is generated, and the gas passes through the nickel mesh and comes into contact with the oxide mixture. This converts the oxide mixture to a halide. The oxide mixture and the halogen-containing material are as described in the first embodiment. Note that while the heat treatment can be performed in air, it is preferable to perform the heat treatment in a nitrogen or reducing atmosphere to prevent oxidation of the nickel mesh.

[0108] [Fourth Embodiment] A fourth embodiment will be described below. Matters described in the first, second, and third embodiments will be omitted as appropriate.

[0109] The battery according to the fourth embodiment includes a positive electrode, an electrolyte layer, and a negative electrode. The electrolyte layer is disposed between the positive electrode and the negative electrode.

[0110] At least one selected from the group consisting of the positive electrode, the electrolyte layer, and the negative electrode includes a halide solid electrolyte containing Li, Ti, Al, and F, and further containing at least one selected from the group consisting of Nb and Ga. The halide solid electrolyte can be produced by, for example, the production method according to the first, second, or third embodiment.

[0111] Hereinafter, the halide solid electrolyte contained in the battery according to the fourth embodiment, which contains Li, Ti, Al, and F and further contains at least one selected from the group consisting of Nb and Ga, will be referred to as the halide solid electrolyte according to the fourth embodiment.

[0112] As described in the first, second, or third embodiments as an example of a halide solid electrolyte that can be produced by the production method of the first, second, or third embodiments, the halide solid electrolyte according to the fourth embodiment may consist essentially of Li, Ti, Al, F, Nb, and Ga, or may consist only of Li, Ti, Al, F, Nb, and Ga. The halide solid electrolyte according to the fourth embodiment may be in a particulate form. Furthermore, the halide solid electrolyte according to the fourth embodiment may include an amorphous phase, as described in the second embodiment.

[0113] The battery according to the fourth embodiment has excellent charge / discharge characteristics because it contains the halide solid electrolyte according to the fourth embodiment.

[0114] FIG. 5 shows a cross-sectional view of a battery 1000 according to a fourth embodiment.

[0115] The battery 1000 according to the fourth embodiment includes a positive electrode 201, an electrolyte layer 202, and a negative electrode 203. The electrolyte layer 202 is provided between the positive electrode 201 and the negative electrode 203.

[0116] The positive electrode 201 may include a positive electrode material including a halide electrolyte according to the fourth embodiment. The positive electrode 201 includes a positive electrode active material 204 and a solid electrolyte 100.

[0117] The electrolyte layer 202 contains an electrolyte material.

[0118] The negative electrode 203 contains a negative electrode active material 205 and a solid electrolyte 100 .

[0119] The solid electrolyte 100 includes, for example, the halide solid electrolyte according to the fourth embodiment. The solid electrolyte 100 may be particles containing the halide solid electrolyte according to the fourth embodiment as a main component. Particles containing the halide solid electrolyte according to the fourth embodiment as a main component refer to particles in which the component contained in the largest amount by molar ratio is the halide solid electrolyte according to the fourth embodiment. The solid electrolyte 100 may be particles made of the halide solid electrolyte according to the fourth embodiment.

[0120] The positive electrode 201 contains a material capable of absorbing and releasing metal ions (e.g., lithium ions). The material is, for example, a positive electrode active material 204.

[0121] Examples of the positive electrode active material 204 include a lithium-containing transition metal oxide, a transition metal fluoride, a polyanion, a fluorinated polyanion material, a transition metal sulfide, a transition metal oxyfluoride, a transition metal oxysulfide, or a transition metal oxynitride. Examples of the lithium-containing transition metal oxide include Li(Ni,Co,Mn)O, Li(Ni,Co,Al)O, or LiCoO.

[0122] In the present disclosure, "(A, B, C)" means "at least one selected from the group consisting of A, B, and C."

[0123] The shape of the positive electrode active material 204 is not limited to a specific shape. The positive electrode active material 204 may be particles. The positive electrode active material 204 may have a median diameter of 0.1 μm or more and 100 μm or less. When the positive electrode active material 204 has a median diameter of 0.1 μm or more, the positive electrode active material 204 and the solid electrolyte 100 can be well dispersed in the positive electrode 201. This improves the charge / discharge characteristics of the battery 1000. When the positive electrode active material 204 has a median diameter of 100 μm or less, the lithium diffusion rate within the positive electrode active material 204 improves. This allows the battery 1000 to operate at a high output.

[0124] The positive electrode active material 204 may have a larger median diameter than the solid electrolyte 100. This allows the positive electrode active material 204 and the solid electrolyte 100 to be dispersed well in the positive electrode 201.

[0125] In order to improve the energy density and output of the battery 1000, in the positive electrode 201, the ratio of the volume of the positive electrode active material 204 to the sum of the volume of the positive electrode active material 204 and the volume of the solid electrolyte 100 may be 0.30 or more and 0.95 or less.

[0126] A coating layer may be formed on at least a portion of the surface of the positive electrode active material 204. The coating layer may be formed on the surface of the positive electrode active material 204, for example, before mixing with the conductive additive and the binder. Examples of coating materials included in the coating layer include a sulfide solid electrolyte, an oxide solid electrolyte, or a halide solid electrolyte. When the solid electrolyte 100 contains a sulfide solid electrolyte, the coating material may contain a halide solid electrolyte according to the fourth embodiment to suppress oxidative decomposition of the sulfide solid electrolyte. When the solid electrolyte 100 contains a halide solid electrolyte according to the fourth embodiment, the coating material may contain an oxide solid electrolyte to suppress oxidative decomposition of the solid electrolyte. Lithium niobate, which has excellent stability at high potentials, may be used as the oxide solid electrolyte. By suppressing oxidative decomposition, an increase in overvoltage of the battery 1000 can be suppressed.

[0127] As described above, when the positive electrode 201 includes a positive electrode material including the halide solid electrolyte according to the fourth embodiment, the positive electrode material may include the halide solid electrolyte according to the fourth embodiment as the solid electrolyte 100, or may include the halide solid electrolyte according to the fourth embodiment as a coating material that coats the positive electrode active material 204.

[0128] To improve the energy density and output of the battery 1000, the positive electrode 201 may have a thickness of 10 μm or more and 500 μm or less.

[0129] The electrolyte layer 202 contains an electrolyte material. The electrolyte material is, for example, a solid electrolyte. The solid electrolyte may include the halide solid electrolyte according to the fourth embodiment. The electrolyte layer 202 may be a solid electrolyte layer.

[0130] The electrolyte layer 202 may contain 50 mass % or more of the halide solid electrolyte according to the fourth embodiment. The electrolyte layer 202 may contain 70 mass % or more of the halide solid electrolyte according to the fourth embodiment. The electrolyte layer 202 may contain 90 mass % or more of the halide solid electrolyte according to the fourth embodiment. The electrolyte layer 202 may be made of only the halide solid electrolyte according to the fourth embodiment.

[0131] Hereinafter, the halide solid electrolyte according to the fourth embodiment will be referred to as a first solid electrolyte, and a solid electrolyte different from the first solid electrolyte will be referred to as a second solid electrolyte.

[0132] The electrolyte layer 202 may contain not only the first solid electrolyte but also the second solid electrolyte. The first solid electrolyte and the second solid electrolyte may be uniformly dispersed in the electrolyte layer 202. A layer made of the first solid electrolyte and a layer made of the second solid electrolyte may be stacked along the stacking direction of the battery 1000.

[0133] The battery according to the fourth embodiment may include a positive electrode 201, a second electrolyte layer, a first electrolyte layer, and a negative electrode 203, in this order. The solid electrolyte contained in the first electrolyte layer may have a lower reduction potential than the solid electrolyte contained in the second electrolyte layer. This allows the solid electrolyte contained in the second electrolyte layer to be used without being reduced. As a result, the charge / discharge efficiency of the battery 1000 can be improved. For example, when the second electrolyte layer contains the first solid electrolyte, the first electrolyte layer may contain a sulfide solid electrolyte to suppress reductive decomposition of the solid electrolyte. This allows the charge / discharge efficiency of the battery 1000 to be improved. The second electrolyte layer may contain the first solid electrolyte. The first solid electrolyte has high oxidation resistance, thereby achieving a battery with excellent charge / discharge characteristics.

[0134] The electrolyte layer 202 may consist of only the second solid electrolyte.

[0135] The electrolyte layer 202 may have a thickness of 1 μm or more and 1000 μm or less. When the electrolyte layer 202 has a thickness of 1 μm or more, the cathode 201 and the anode 203 are less likely to short-circuit. When the electrolyte layer 202 has a thickness of 1000 μm or less, the battery 1000 can operate at high power.

[0136] Examples of the second solid electrolyte are LiMgX, LiFeX, Li(Al,Ga,In)X, Li(Al,Ga,In)X, or LiI, where X is at least one selected from the group consisting of F, Cl, Br, and I.

[0137] To improve the energy density and power output of the battery 1000, the electrolyte layer 202 may have a thickness of 1 μm or more and 1000 μm or less.

[0138] The negative electrode 203 contains a material capable of absorbing and releasing metal ions (e.g., lithium ions). The material is, for example, a negative electrode active material 205.

[0139] Examples of the negative electrode active material 205 include a metal material, a carbon material, an oxide, a nitride, a tin compound, or a silicon compound. The metal material may be a simple metal or an alloy. An example of the metal material is lithium metal or a lithium alloy. Examples of the carbon material are natural graphite, coke, partially graphitized carbon, carbon fiber, spherical carbon, artificial graphite, or amorphous carbon. From the viewpoint of capacity density, suitable examples of the negative electrode active material are silicon (i.e., Si), tin (i.e., Sn), a silicon compound, or a tin compound.

[0140] The anode active material 205 may be selected taking into consideration the reduction resistance of the solid electrolyte contained in the anode 203. For example, when the anode 203 contains a first solid electrolyte, the anode active material 205 may be a material capable of absorbing and releasing lithium ions at 0.27 V or more relative to lithium. Examples of such anode active materials include titanium oxide, indium metal, or a lithium alloy. An example of titanium oxide is Li4Ti5O 12, LiTiO, or TiO. By using the above-mentioned negative electrode active material, it is possible to suppress the reductive decomposition of the first solid electrolyte contained in the negative electrode 203. As a result, it is possible to improve the charge / discharge efficiency of the battery 1000.

[0141] The shape of the negative electrode active material 205 is not limited to a specific shape. The negative electrode active material 205 may be particles. The negative electrode active material 205 may have a median diameter of 0.1 μm or more and 100 μm or less. When the negative electrode active material 205 has a median diameter of 0.1 μm or more, the negative electrode active material 205 and the solid electrolyte 100 can be well dispersed in the negative electrode 203. This improves the charge / discharge characteristics of the battery 1000. When the negative electrode active material 205 has a median diameter of 100 μm or less, the lithium diffusion rate within the negative electrode active material 205 improves. This allows the battery 1000 to operate at high power.

[0142] The negative electrode active material 205 may have a larger median diameter than the solid electrolyte 100. This allows the negative electrode active material 205 and the solid electrolyte 100 to be dispersed well in the negative electrode 203.

[0143] In order to improve the energy density and output of the battery 1000, in the negative electrode 203, the ratio of the volume of the negative electrode active material 205 to the sum of the volume of the negative electrode active material 205 and the volume of the solid electrolyte 100 may be 0.30 or more and 0.95 or less.

[0144] To improve the energy density and output of the battery 1000, the negative electrode 203 may have a thickness of 10 μm or more and 500 μm or less.

[0145] At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a second solid electrolyte for the purpose of increasing ionic conductivity, chemical stability, and electrochemical stability.

[0146] The second solid electrolyte may be a sulfide solid electrolyte.

[0147] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge0.25 P 0.75 S4, or Li 10 GeP2S 12 is.

[0148] When the electrolyte layer 202 contains the first solid electrolyte, the negative electrode 203 may contain a sulfide solid electrolyte to suppress reductive decomposition of the solid electrolyte. The electrochemically stable sulfide solid electrolyte covers the negative electrode active material, thereby preventing the first solid electrolyte from contacting the negative electrode active material. As a result, the internal resistance of the battery 1000 can be reduced.

[0149] The second solid electrolyte may be an oxide solid electrolyte.

[0150] Examples of oxide solid electrolytes include: (i) NASICON-type solid electrolytes such as LiTi2(PO4)3 or its elemental substitutions; (ii) perovskite-type solid electrolytes such as (LaLi)TiO3; (iii) Li 14 ZnGeO 16 LISICON-type solid electrolytes such as LiSiO, LiGeO or elemental substitutions thereof; (iv) LiLaZrO 12 or an element-substituted product thereof; or (v) Li3PO4 or an N-substituted product thereof.

[0151] As mentioned above, the second solid electrolyte may be a halide solid electrolyte.

[0152] Examples of halide solid electrolytes are LiMgX, LiFeX, Li(Al,Ga,In)X, Li(Al,Ga,In)X, or LiI, where X is at least one selected from the group consisting of F, Cl, Br, and I.

[0153] Other examples of halide solid electrolytes include Li a Me b Y cZ6, where a + mb + 3c = 6 and c > 0 are satisfied. Me is at least one selected from the group consisting of metal elements and metalloid elements other than Li and Y. Z is at least one selected from the group consisting of F, Cl, Br, and I. m represents the valence of Me. "Metalloid elements" are B, Si, Ge, As, Sb, and Te. "Metal elements" are all elements included in Groups 1 to 12 of the periodic table (excluding hydrogen) and all elements included in Groups 13 to 16 of the periodic table (excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se).

[0154] In order to improve the ionic conductivity of the halide solid electrolyte, Me may be at least one selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb.

[0155] The halide solid electrolyte may be Li3YCl6 or Li3YBr6.

[0156] The second solid electrolyte may be an organic polymer solid electrolyte.

[0157] An example of the organic polymer solid electrolyte is a compound of a polymer compound and a lithium salt.

[0158] The polymer compound may have an ethylene oxide structure. A polymer compound having an ethylene oxide structure can contain a large amount of lithium salt, and therefore can further increase ionic conductivity.

[0159] Examples of lithium salts include LiPF, LiBF, LiSbF, LiAsF, LiSOF, LiN(SOCF), LiN(SOCF), LiN(SOCF)(SOCF), or LiC(SOCF). One lithium salt selected from these may be used alone. Alternatively, a mixture of two or more lithium salts selected from these may be used.

[0160] At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a non-aqueous electrolyte, a gel electrolyte, or an ionic liquid to facilitate the exchange of lithium ions and improve the output characteristics of the battery.

[0161] The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.

[0162] Examples of non-aqueous solvents are cyclic carbonate ester solvents, chain carbonate ester solvents, cyclic ether solvents, chain ether solvents, cyclic ester solvents, chain ester solvents, or fluorine-containing solvents. Examples of cyclic carbonate ester solvents are ethylene carbonate, propylene carbonate, or butylene carbonate. Examples of chain carbonate ester solvents are dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate. Examples of cyclic ether solvents are tetrahydrofuran, 1,4-dioxane, or 1,3-dioxolane. Examples of chain ether solvents are 1,2-dimethoxyethane or 1,2-diethoxyethane. An example of a cyclic ester solvent is γ-butyrolactone. An example of a chain ester solvent is methyl acetate. Examples of fluorine-containing solvents are fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, or fluorodimethylene carbonate. One non-aqueous solvent selected from these may be used alone, or two or more non-aqueous solvents selected from these may be used in combination.

[0163] Examples of lithium salts include LiPF, LiBF, LiSbF, LiAsF, LiSOCF, LiN(SOCF), LiN(SOCF), LiN(SOCF)(SOCF), or LiC(SOCF). A single lithium salt selected from these may be used alone. Alternatively, a mixture of two or more lithium salts selected from these may be used. The concentration of the lithium salt is, for example, in the range of 0.5 mol / L or more and 2 mol / L or less.

[0164] The gel electrolyte may be a polymer material impregnated with a non-aqueous electrolyte, such as polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, or a polymer having an ethylene oxide bond.

[0165] Examples of cations contained in the ionic liquid are: (i) aliphatic chain quaternary salts such as tetraalkylammonium or tetraalkylphosphonium; (ii) aliphatic cyclic ammonium such as pyrrolidiniums, morpholiniums, imidazoliniums, tetrahydropyrimidiniums, piperaziniums, or piperidiniums; or (iii) nitrogen-containing heterocyclic aromatic cations such as pyridiniums or imidazoliums.

[0166] An example of an anion contained in an ionic liquid is PF6 - , BF4 - , SbF6 - , AsF6 - , SO3CF3 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , N(SO2CF3)(SO2C4F9) - , or C(SO2CF3)3 - is.

[0167] The ionic liquid may contain a lithium salt.

[0168] At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a binder to improve adhesion between particles.

[0169] Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl ester of acrylic acid, polyethyl ester of acrylic acid, polyhexyl ester of acrylic acid, polymethacrylic acid, polymethyl ester of methacrylic acid, polyethyl ester of methacrylic acid, polyhexyl ester of methacrylic acid, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, and carboxymethyl cellulose. Copolymers can also be used as binders. Examples of such binders include copolymers of two or more materials selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene. A mixture of two or more materials selected from these may be used as the binder.

[0170] At least one selected from the positive electrode 201 and the negative electrode 203 may contain a conductive additive to improve electronic conductivity.

[0171] Examples of the conductive additive include (i) graphites such as natural graphite or artificial graphite, (ii) carbon blacks such as acetylene black or ketjen black, (iii) conductive fibers such as carbon fiber or metal fiber, (iv) carbon fluoride, (v) metal powders such as aluminum, (vi) conductive whiskers such as zinc oxide or potassium titanate, (vii) conductive metal oxides such as titanium oxide, or (viii) conductive polymer compounds such as polyaniline, polypyrrole, or polythiophene. For cost reduction, the conductive additives (i) or (ii) may be used.

[0172] In addition, a separator impregnated with an electrolyte solution may be used instead of the electrolyte layer, or the exterior housing containing the positive electrode, separator portion, and negative electrode may be filled with the electrolyte solution. The electrolyte solution may be, for example, the nonaqueous electrolyte solution described above. Examples of the shape of the battery according to the fourth embodiment include a coin type, a cylindrical type, a prismatic type, a sheet type, a button type, a flat type, and a laminate type.

[0173] The battery according to the fourth embodiment may be manufactured, for example, by preparing a material for forming a positive electrode, a material for forming an electrolyte layer, and a material for forming a negative electrode, and by using a known method to fabricate a laminate in which the positive electrode, the electrolyte layer, and the negative electrode are arranged in this order.

[0174] [Other Embodiments] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0175] (Technology 1) A method for producing a halide solid electrolyte, comprising: (A) subjecting an oxide mixture containing a composite oxide containing Li and Ti and an oxide raw material containing Li and M to a halogenation treatment to obtain a halide solid electrolyte containing Li, Ti, M, and X, wherein M is at least one element selected from the group consisting of metal elements (excluding Li and Ti) and semimetal elements, and X is at least one element selected from the group consisting of F, Cl, Br, and I.

[0176] Titanium halide (TiX4) is a relatively unstable substance, being prone to evaporation and deliquescent. According to the manufacturing method of Technology 1, a composite oxide containing Li and Ti can be used as the Ti source. Therefore, according to the manufacturing method of Technology 1, it is not necessary to use the unstable titanium halide as a raw material in the synthesis of a Ti-containing halide solid electrolyte, and titanium halide is unlikely to be generated during the synthesis process. In conventional manufacturing methods, titanium halide has typically been used as the Ti source for synthesizing a Ti-containing halide solid electrolyte. Therefore, due to the instability of titanium halide, compositional fluctuations (i.e., composition deviations) and alterations (e.g., inclusion of moisture, etc.) are likely to occur during the synthesis of a Ti-containing halide solid electrolyte, resulting in fluctuations in the properties of the halide solid electrolyte. In contrast, according to the manufacturing method of Technology 1, such compositional fluctuations are unlikely to occur, and a Ti-containing halide solid electrolyte with excellent properties, such as ionic conductivity, can be reproducibly and stably synthesized. That is, according to the manufacturing method of Technology 1, a halide solid electrolyte having a desired composition can be stably synthesized.

[0177] (Technology 2) The method for producing a halide solid electrolyte according to Technology 1, wherein the halide solid electrolyte includes a first crystalline phase represented by the following composition formula (1) and a second crystalline phase represented by the following composition formula (2). Composition formula (1): Li2TiX6 Composition formula (2): Li3MX6

[0178] According to the manufacturing method of Technology 2, for example, Li2TiO3, which is stable in an atmospheric environment, can be used as a composite oxide containing Li and Ti. Therefore, it is not necessary to use TiO2 as a Ti source. Therefore, the generation of titanium halide is suppressed during the conversion process of the oxide mixture to a halide. As a result, a halide solid electrolyte with good properties can be synthesized stably in an atmospheric environment with good reproducibility. Furthermore, because the generation of titanium halide is suppressed, synthesis in a sealed jig (e.g., a planetary ball mill or solid-phase synthesis in a sealed heat-resistant container) is not necessary. This enables synthesis with excellent productivity.

[0179] (Technology 3) The method for producing a halide solid electrolyte according to Technology 1 or 2, wherein the oxide raw material contains an oxide of Li and an oxide of M.

[0180] According to the manufacturing method of Technique 3, a halide solid electrolyte having a target composition can be synthesized more stably.

[0181] (Technology 4) The method for producing a halide solid electrolyte according to any one of Technologies 1 to 3, wherein M contains Al.

[0182] According to the manufacturing method of Technique 4, a halide solid electrolyte having high ionic conductivity can be obtained.

[0183] (Technology 5) The method for producing a halide solid electrolyte according to any one of Techniques 1 to 4, wherein the X includes F.

[0184] According to the manufacturing method of Technique 5, it is possible to obtain a halide solid electrolyte having excellent stability (for example, excellent electrochemical stability and heat resistance) and high ionic conductivity.

[0185] (Technology 6) The method for producing a halide solid electrolyte according to any one of Techniques 1 to 5, wherein the oxide mixture is in a particulate form.

[0186] According to the manufacturing method of Technique 6, halogenation (i.e., substitution of halogen element with oxygen element) from the particle surface of the oxide mixture and solid-phase reaction in the oxide mixture tend to occur simultaneously. Therefore, a halide can be synthesized in a short time while reducing reaction residues such as oxides. Therefore, a solid electrolyte with homogeneous and excellent properties can be obtained. Furthermore, since the particulate oxide mixture has good reactivity (i.e., halogenation property), excellent productivity can also be achieved.

[0187] (Technology 7) The method for producing a halide solid electrolyte according to any one of Techniques 1 to 6, wherein the oxide mixture does not substantially contain TiO2.

[0188] According to the manufacturing method of Technique 7, for example, titanium halide such as titanium tetrafluoride (TiF), which is easily evaporated, is hardly generated in the process of converting the oxide mixture into a halide. Therefore, composition fluctuation and deterioration are suppressed, and a desired halide solid electrolyte can be obtained.

[0189] (Technology 8) The method for producing a halide solid electrolyte according to any one of Techniques 1 to 7, wherein in (A), the halogenation treatment of the oxide mixture is carried out by heat treating a thermally decomposable halogen-containing material.

[0190] According to the manufacturing method of Technology 8, halogenation of the oxide mixture and a solid-state reaction can occur simultaneously. Therefore, a solid electrolyte with homogeneous and excellent properties can be obtained in a short time while reducing reaction residues such as oxides. Furthermore, since the halogenation treatment is performed by heat-treating a thermally decomposable halogen-containing material, the reactivity (halogenation property) of the oxide mixture is good and productivity is excellent. Furthermore, for example, the temperatures of the halogenation reaction and solid-state reaction of the oxide mixture and the progress of these reactions can be controlled depending on the thermal decomposition temperature of the selected halogen-containing material. Therefore, a desired halide solid electrolyte can be obtained.

[0191] (Technology 9) The method for producing a halide solid electrolyte according to Technology 8, wherein the halogen-containing material is in a particulate form.

[0192] According to the manufacturing method of Technology 9, the halogen-containing material is easily thermally decomposed. Therefore, according to the manufacturing method of Technology 10, the oxide mixture can be efficiently halogenated, and the halogen-containing material is less likely to remain in the finally obtained halide solid electrolyte. Furthermore, the amount of halogen can be precisely controlled. Therefore, it is possible to synthesize a desired halide solid electrolyte. Furthermore, since only the amount of halogen-containing material necessary for halogenating the oxide mixture can be used, excess halogen gas emissions can be suppressed. This reduces the burden on the environment and also reduces the impact on corrosion of furnace materials, etc.

[0193] (Technology 10) The method for producing a halide solid electrolyte according to Technology 8 or 9, wherein (A) comprises: (A-1) mixing the oxide mixture with the halogen-containing substance; and (A-2) heat-treating the mixture containing the oxide mixture and the halogen-containing substance obtained in (A-1), thereby subjecting the oxide mixture to the halogenation treatment.

[0194] According to the manufacturing method of Technique 10, a heat treatment for halogenation can be performed on a homogeneous mixture of an oxide mixture and a halogen-containing material. Furthermore, the contact area between the oxide mixture and the halogen-containing material can be increased. Therefore, according to the manufacturing method of Technique 10, halogenation of the oxide mixture can be promoted homogeneously. As a result, a homogeneous halide solid electrolyte with excellent properties can be obtained.

[0195] (Technology 11) The method for producing a halide solid electrolyte according to Technology 8 or 9, wherein in (A), the halogen-containing material is heat-treated to generate halogen gas, and the halogen gas is brought into contact with the oxide mixture, thereby subjecting the oxide mixture to the halogenation treatment.

[0196] According to the manufacturing method of Technique 11, the oxide mixture can be halogenated by the generated halogen gas without directly contacting the oxide mixture with a halogen-containing material. Therefore, even if a halogen-containing material containing an inorganic component in addition to a halogen element is used, it is not necessary to consider inorganic residues in the halide solid electrolyte to be manufactured. Therefore, the range of usable halogen-containing materials can be expanded.

[0197] (Technology 12) The method for producing a halide solid electrolyte according to any one of Techniques 8 to 11, wherein the halogen-containing substance includes an ammonium salt.

[0198] Ammonium salts begin to thermally decompose at relatively low temperatures (e.g., about 150°C). Therefore, ammonium salts are unlikely to remain as unnecessary inorganic components in the final halide solid electrolyte, and can be thermally decomposed at low temperatures to halogenate the oxide mixture. Therefore, the manufacturing method of Technology 12 can prevent unnecessary inorganic components derived from halogen-containing materials from remaining in the final halide solid electrolyte. Furthermore, energy savings in synthesis are achieved, and the temperature rise and fall times are reduced, thereby improving productivity. Furthermore, since synthesis can be performed at low temperatures, the durability of furnace materials is improved, significantly reducing the running costs and replacement frequency of synthesis components. Conventional methods for synthesizing halide solid electrolytes by solid-phase reactions using halide raw materials require heat treatment at, for example, about 500°C to 600°C.

[0199] (Technology 13) The method for producing a halide solid electrolyte according to Technology 12, wherein the ammonium salt contains NH4F.

[0200] NH4F is a highly decomposable fluorine source and can effectively halogenate the oxide mixture. Therefore, according to the production method of Technique 13, NH4F can be thermally decomposed at a low temperature (e.g., about 150°C) and at a high decomposition rate, and can halogenate the oxide mixture without remaining in the solid electrolyte.

[0201] (Technology 14) The method for producing a halide solid electrolyte according to any one of Techniques 8 to 13, wherein the halogen-containing material includes a resin.

[0202] According to the manufacturing method of Technology 14, the oxide mixture can be halogenated while the halogen-containing material is thermally decomposed at a relatively high temperature (e.g., about 450° C. or higher and 600° C. or lower). Therefore, the manufacturing method of Technology 14 is suitable for the case where halogenation and solid-state reaction are to be carried out at a relatively high temperature (e.g., about 450° C. or higher and 600° C. or lower).

[0203] (Technology 15) The method for producing a halide solid electrolyte according to Technology 14, wherein the resin includes a fluororesin.

[0204] Fluororesins such as PTFE can halogenate the oxide mixture while being thermally decomposed at a relatively high temperature (e.g., about 450° C. or higher and 600° C. or lower). Therefore, the production method of Technique 15 is suitable for the case where halogenation and solid-state reaction are to be carried out at a relatively high temperature (e.g., about 450° C. or higher and 600° C. or lower).

[0205] (Technology 16) The method for producing a halide solid electrolyte according to any one of Techniques 8 to 11, wherein the halogen-containing material contains a substance that prevents the halide solid electrolyte from substantially containing inorganic components, except for halogen elements, that are generated by thermal decomposition by the heat treatment in (A).

[0206] The halogen-containing material is required to replace the halogen element generated by thermal decomposition by the heat treatment in (A) with the oxygen element of the oxide mixture, while preventing other components from being mixed as inorganic residues into the finally obtained halide solid electrolyte. By using a substance as the halogen-containing material that does not substantially contain inorganic components generated by thermal decomposition by the heat treatment, except for the halogen element, in the finally obtained halide solid electrolyte, the mixing of inorganic residues into the halide solid electrolyte can be suppressed, and a desired halide solid electrolyte can be obtained. Examples of halogen-containing materials that do not substantially contain inorganic components, except for the halogen element, generated by thermal decomposition by the heat treatment in the finally obtained halide solid electrolyte include substances in which inorganic components, except for the halogen element, generated by thermal decomposition by the heat treatment are gasified and discharged.

[0207] (Technology 17) The method for producing a halide solid electrolyte according to any one of Techniques 8 to 16, wherein the halogen-containing material includes a plurality of halogen-containing compounds.

[0208] According to the manufacturing method of Technique 17, for example, both an ammonium salt and a fluororesin can be used as the halogen-containing material. This allows for a wide temperature range in which the halogen-containing material acts as a halogen source. Therefore, the conversion of the oxide mixture to a halide and the solid-state reaction temperature can be controlled over a wide range. Therefore, according to the manufacturing method of Technique 17, it is easy to obtain a desired halide solid electrolyte.

[0209] (Technology 18) The method for producing a halide solid electrolyte according to any one of Techniques 1 to 17, wherein in (A), the halogenation treatment of the oxide mixture is carried out at a temperature of 150°C or higher.

[0210] The oxide mixture can be sufficiently halogenated according to the manufacturing method of Technique 18. The atmosphere for the halogenation treatment can be selected appropriately from any atmosphere suitable for the halogen-containing material used, such as air, a nitrogen atmosphere, or a reducing atmosphere.

[0211] (Technology 19) The method for producing a halide solid electrolyte according to any one of Techniques 1 to 18, further comprising, after the step (A), (B) subjecting the halide solid electrolyte obtained in the step (A) to a pulverization treatment.

[0212] According to the manufacturing method of Technology 19, a halide solid electrolyte having excellent ionic conductivity and reliability can be obtained with a particle size suitable for the application. Furthermore, since at least a portion of the halide solid electrolyte can be made amorphous, the ionic conductivity can be improved and the softness of the halide solid electrolyte particles can be improved. The improved softness of the halide solid electrolyte particles can improve the density of a compact of the halide solid electrolyte. Therefore, the halide solid electrolyte obtained by the manufacturing method of Technology 19 can form a dense compact with high ionic conductivity.

[0213] (Technology 20) A halide solid electrolyte comprising Li, Ti, Al, and F, and further comprising at least one selected from the group consisting of Nb and Ga.

[0214] This configuration makes it possible to obtain a homogeneous halide solid electrolyte with excellent ionic conductivity.

[0215] (Technology 21) The halide solid electrolyte according to Technology 20, which is substantially free of TiF4.

[0216] This configuration can suppress changes over time in the characteristics and mechanical properties of the halide solid electrolyte due to the evaporation and deliquescence of TiF4, thereby realizing a halide solid electrolyte with excellent characteristics and reliability. Note that if the oxide mixture used as the raw material for the halide solid electrolyte contains a trace amount of titanium oxide (TiO2), a trace amount of TiF4 may be generated during the halogenation process. However, even in this case, the halogenation process can be performed in an open environment, allowing the TiF4 to evaporate and disappear. This allows for the production of a halide solid electrolyte with excellent characteristics and reliability that is substantially free of TiF4.

[0217] (Technology 22) The halide solid electrolyte according to Technology 20 or 21, wherein the halide solid electrolyte is in a particulate form.

[0218] Halide solid electrolytes have relatively soft properties. Therefore, this configuration allows for the realization of a relatively soft particulate solid electrolyte. Therefore, the halide solid electrolyte compact of Technology 22 has high ionic conductivity, excellent stability, and can be formed into any shape. Furthermore, since it can be formed into any shape, the halide solid electrolyte compact of Technology 22 has excellent deformability. Therefore, the halide solid electrolyte compact of Technology 22 can realize a solid electrolyte layer of a battery with excellent properties and high reliability. The particle size and shape can be selected appropriately depending on the application.

[0219] (Technology 23) The halide solid electrolyte according to any one of Techniques 20 to 22, wherein the halide solid electrolyte includes an amorphous phase.

[0220] This configuration makes the amorphous portion of the halide solid electrolyte softer and more deformable. Therefore, the halide solid electrolyte compact can be configured into a solid electrolyte layer of any shape with higher ionic conductivity and higher stability. Therefore, the halide solid electrolyte compact of Technology 23 can realize a solid electrolyte layer of a battery with excellent characteristics and high reliability.

[0221] (Technology 24) The halide solid electrolyte according to any one of Techniques 20 to 23, wherein an X-ray diffraction pattern obtained by X-ray diffraction measurement of the halide solid electrolyte using Cu-Kα radiation satisfies at least one of the following (1), (2), and (3): (1) no peak derived from TiF4 is present; (2) no peak derived from LiF is present; and (3) no peak derived from AlF3 is present.

[0222] This configuration makes it possible to obtain a halide solid electrolyte with excellent characteristics and reliability.

[0223] (Technology 25) A positive electrode material comprising the halide solid electrolyte according to any one of Technology 20 to Technology 24.

[0224] The positive electrode material according to Technology 25 makes it possible to realize a battery having excellent charge / discharge characteristics.

[0225] (Technology 26) A battery comprising a positive electrode containing the positive electrode material according to Technology 25.

[0226] This configuration makes it possible to provide a battery with excellent charge / discharge characteristics.

[0227] (Technology 27) A battery comprising: a positive electrode; a negative electrode; and an electrolyte layer provided between the positive electrode and the negative electrode, wherein at least one selected from the group consisting of the positive electrode, the negative electrode, and the electrolyte layer contains the halide solid electrolyte according to any one of Technologies 20 to 24.

[0228] This configuration makes it possible to provide a battery with excellent charge / discharge characteristics.

[0229] While the method for producing a halide solid electrolyte and the halide solid electrolyte according to the present disclosure have been described above based on the embodiments, the present disclosure is not limited to these embodiments. As long as they do not deviate from the gist of the present disclosure, various modifications conceivable by those skilled in the art to the embodiments and other forms constructed by combining some of the components of the embodiments are also included within the scope of the present disclosure.

[0230] Furthermore, the above-described embodiments can be modified, replaced, added, omitted, and the like in various ways within the scope of the claims or their equivalents.

[0231] The present disclosure will now be described in more detail with reference to examples.

[0232] Synthesis of Halide Solid Electrolyte Example 1 As starting materials, the following were prepared: Li2TiO3 powder (average particle size: approximately 0.8 μm) as a composite oxide; Li2O powder (average particle size: 1.5 μm) and Al2O3 powder (average particle size: 0.4 μm) as oxide raw materials; NH4F powder (average particle size: approximately 35 μm) as a halogen-containing material; and Nb2O5 powder (average particle size: approximately 0.8 μm) and Ga2O3 powder (average particle size: approximately 0.6 μm) as additives.

[0233] Next, Li2TiO3 powder, Li2O powder, and Al2O3 powder were weighed out so that x = 0.25 when the synthesized halide solid electrolyte was expressed by the composition formula (3): xLi2TiX6-(1-x)Li3MX6. In this example, in the composition formula (3), X is F and M is Al. Regarding additives, Nb2O5 powder and Ga2O3 powder were weighed out so that NbF5 was 0.4 mol% and GaF3 was 0.02 mol% relative to [0.25Li2TiF6-0.75Li3AlF6]. NH4F powder was added in an amount necessary to fluorinate the raw materials. Specifically, an amount of NH4F sufficient to fluorinate all of the raw materials was used according to the reaction formula. These starting materials were weighed out in an air atmosphere.

[0234] The weighed starting materials were mixed uniformly with a pestle in an alumina mortar for about 10 minutes (a step corresponding to (A-1) above). This resulted in a mixture containing an oxide mixture, a halogen-containing substance, and an additive. The mixing of the starting materials was carried out in normal air, the same as during weighing.

[0235] Next, the mixture containing the oxide mixture, the halogen-containing material, and the additive was heat-treated (a step corresponding to (A-2) above). A high-purity (SSA-H) alumina crucible (diameter φ: 36 mm, height: 40 mm) was used for the sheath, and approximately 3 g of the above mixture was placed in the crucible. A spacer (0.5 mm thick) was placed on the outer edge of the top surface of the sheath to provide a gap to facilitate the escape of reaction gases (mainly ammonia) emitted during the heat treatment, and an alumina plate-shaped lid was placed on top to prevent foreign objects from falling. The sheath with the lid attached was then placed in the center of a firing furnace and heat-treated. In the firing furnace, the sheath was placed on a small-heat-capacity mullite cradle with a porosity of approximately 20%. A cradle measuring 10 mm in length, 10 mm in width, and 10 mm in height was used, with three cradles placed under each cradle to suspend the sheath from the bottom of the furnace. In this way, the heater (radiant) heat and inert gas were allowed to reach the bottom of the pod. After closing and sealing the furnace door, nitrogen gas was introduced as an inert gas at 1.5 L / min through the inlet at the bottom of the furnace and discharged through the exhaust port above the ceiling. The gas continued to flow until the heat treatment was completed. The heat treatment temperature was 300°C.

[0236] In this example, because oxides were used as starting materials, i.e., because the raw materials did not contain titanium halide, heat treatment could be performed in the same manner as for general oxide ceramics. For example, if titanium fluoride were heat treated without sealing as in this example, it would begin to evaporate at around 50°C to 100°C, and most (about 70%) would disappear at 200°C. For this reason, halides produced in conventional solid-phase synthesis have large compositional variations. For this reason, it is extremely effective to make the Ti component a composite oxide containing Ti in order to suppress compositional variations from the standpoints of evaporation and environmental stability.

[0237] The halide solid electrolyte obtained by the heat treatment was subjected to a pulverization treatment (a step corresponding to (B) above). In this example, a dry pulverization treatment was performed. Specifically, zirconia balls (diameter: 15 mm) and the halide solid electrolyte obtained by the heat treatment were placed in a ball mill (volume: 1 L) lined with zirconia, and pulverization was performed for 20 hours.

[0238] Comparative Example 1 A halide solid electrolyte was synthesized using a method similar to that used for the solid electrolyte material of the example described in Patent Document 1. That is, fluoride was used as a starting material, and the halide solid electrolyte of Comparative Example 1 was produced by mechanochemical synthesis. Specifically, LiF, TiF, and AlF were prepared in a molar ratio of LiF:TiF:AlF = 2.75:0.25:0.75. These materials were ground and mixed in a mortar. The resulting mixture was milled for 12 hours at 500 rpm using a planetary ball mill. In this manner, the halide solid electrolyte of Comparative Example 1 was synthesized.

[0239] <Evaluation of Halide Solid Electrolyte> The halide solid electrolyte of Example 1 synthesized as described above was evaluated for its crystalline phase, ionic conductivity, electronic conductivity, average particle size, and BET specific surface area. The crystalline phase, ionic conductivity, average particle size, and BET specific surface area were evaluated for the halide solid electrolyte both after the heat treatment and before the pulverization treatment, and after the pulverization treatment. The crystalline phase of the halide solid electrolyte of Comparative Example 1 was also evaluated. The halide solid electrolyte of Example 1 was also analyzed for trace components.

[0240] (Crystalline Phase) The crystalline phase was confirmed by powder X-ray diffraction measurement both before and after the heat treatment and grinding treatment. An X-ray diffractometer (MiniFlex 600, manufactured by RIGAKU Corporation) was used for the measurement. Cu-Kα radiation (wavelengths 1.5405 Å and 1.5444 Å) was used as the X-ray source.

[0241] FIG. 6A is a graph showing the X-ray diffraction pattern of the halide solid electrolyte after heat treatment but before pulverization in the manufacturing method of Example 1. FIG. 6B is a graph showing the X-ray diffraction pattern of the halide solid electrolyte after pulverization obtained in Example 1 and the halide solid electrolyte obtained in Comparative Example 1. As shown in FIG. 6A, Li2TiF6 corresponding to the first crystalline phase and Li3AlF6 corresponding to the second crystalline phase were confirmed in the halide solid electrolyte synthesized in Example 1. As shown in FIG. 6B, the crystallinity of the halide solid electrolyte after pulverization obtained in Example 1 was reduced by the pulverization compared to the halide solid electrolyte before pulverization, but no extra precipitated phase was observed. In contrast, as shown in FIG. 6B, the halide solid electrolyte obtained in Comparative Example 1 exhibited a compositional variation compared to the halide solid electrolyte of Example 1, and the presence of LiF and AlF3 was also confirmed.

[0242] (Ionic Conductivity) The ionic conductivity was calculated from the area, thickness, and room temperature impedance characteristics of a compacted powder sample obtained by placing a halide solid electrolyte powder in a 10 mm diameter mold and applying a pressure of approximately 3 t / cm using a uniaxial hydraulic press. The impedance measurement was performed at room temperature while applying pressure. The impedance measurement was performed at a measurement frequency of 10 Hz to 10 MHz, a measurement voltage of 1 Vrms, and no DC bias. The deviation in the electrical length of the cable and measuring jig was offset and evaluated. For the halide solid electrolyte of Example 1, the ionic conductivity before the pulverization treatment was 1.1 μS / cm, and the ionic conductivity after the pulverization treatment was 6.1 μS / cm.

[0243] (Electronic Conductivity) The electronic conductivity was calculated from DC voltage and current characteristics. The electronic conductivity of the halide solid electrolyte of Example 1 was <1.0 × 10 -9 This was a value that could be judged to have no electronic conductivity.

[0244] (Average Particle Diameter) The average particle diameter is the median diameter D50 value obtained from the volume particle size distribution measured by a laser diffraction scattering particle size distribution analyzer. Specifically, a halide solid electrolyte powder was dispersed in a 0.01 wt% aqueous solution of sodium hexametaphosphate using a homogenizer, and then the particle size distribution of the halide solid electrolyte was measured using a laser diffraction scattering particle size distribution analyzer (manufactured by Microtrac, product name: MT3100II). The D50 value (i.e., cumulative 50% particle diameter) of the measured particle size distribution was regarded as the average particle size. For the halide solid electrolyte of Example 1, the average particle diameter before pulverization was 0.83 μm, and the average particle diameter after pulverization was 0.61 μm.

[0245] (BET Specific Surface Area) The BET specific surface area was determined by a BET multipoint method using a nitrogen gas adsorption apparatus. The halide solid electrolyte of Example 1 had a BET specific surface area of ​​2.86 m before pulverization. 2 / g, and the BET specific surface area after pulverization was 3.90 m 2 / g.

[0246] (Analysis of Trace Components) Trace components contained in the halide solid electrolyte were analyzed using EPMA. Specifically, the analysis was performed as follows. A sample (powder) of the halide solid electrolyte was attached to conductive tape and fixed (the sample was fixed to a 5 mm x 5 mm area to form a solid), and the composition (quantitative) was examined by point analysis. Although not confirmed by X-ray diffraction measurement, it was confirmed that the halide solid electrolyte of Example 1 contained Nb and Ga. The Nb content was 0.07 at. %, and the Ga content was 0.004 at. %.

[0247] The evaluation results of the halide solid electrolyte obtained in Example 1 showed that the manufacturing method of the present disclosure was able to convert an oxide into a homogeneous halide, resulting in a high ionic conductivity of 6.1 μS / cm. This ionic conductivity was at a level equal to or higher than that obtained by synthesis from a fluoride raw material, and the manufacturing method of the present disclosure was able to obtain a halide solid electrolyte with excellent properties. The electronic conductivity was <1.0 × 10 -9It was confirmed that the electrolyte had no electronic conductivity (i.e., negligible electronic conductivity) and was an ionically conductive solid electrolyte.

[0248] The X-ray diffraction patterns shown in FIGS. 6A and 6B confirmed that the method of Example 1 could produce a halide solid electrolyte containing Li2TiF6 corresponding to the first crystalline phase and Li3AlF6 corresponding to the second crystalline phase. These X-ray diffraction patterns also confirmed that the halide solid electrolyte obtained in Example 1 had similar crystalline quality to the halide solid electrolyte of Comparative Example 1 synthesized by a conventional method, and that compositional variation was suppressed compared to the halide solid electrolyte of Comparative Example 1. Furthermore, for the halide solid electrolyte of Example 1, the X-ray diffraction pattern after the milling process exhibited broader peaks than the X-ray diffraction pattern before the milling process, confirming the progression of amorphization. However, no new precipitated phases were observed due to the milling process. The changes in ionic conductivity, average particle size, and BET specific surface area before and after the milling process are as described in the sections describing each evaluation item. These results show that the pulverization treatment may or may not be performed depending on the application of the halide solid electrolyte, and that the composition and crystalline phase of the halide solid electrolyte are substantially unchanged regardless of whether the pulverization treatment is performed or not, thereby maintaining excellent properties.

[0249] Furthermore, the amount of oxygen as an impurity in the halide solid electrolyte of Example 1 was 0.12 mass%, confirming that oxygen in the oxide was converted to fluorine. The oxygen amount was evaluated based on the measurement results obtained by using a melt extraction device to melt a sample (powder) of the halide solid electrolyte and measuring the gases (CO2, CO) generated by the melt extraction device. The oxygen amount in the halide solid electrolyte of Example 1 was lower than that of halide solid electrolytes obtained by a synthesis method using fluoride as a starting material. The oxygen amount in halide solid electrolytes obtained by a synthesis method using fluoride as a starting material is typically greater than 0.5 mass% and approximately 1.0 mass% or less. This is thought to be due to moisture or oxygen, etc., that was incorporated into the unstable fluoride raw material during the synthesis process, such as storage or handling, remaining after synthesis. When the fluoride raw materials were mixed and subjected to a solid-state reaction without using a sealed jig, as in the manufacturing method of the present disclosure, the Ti component evaporated as titanium fluoride due to the open condition and disappeared from the halide. This results in a change in composition, and only those with ionic conductivity of less than 1 μS / cm can be obtained. In this case, a high heat treatment temperature of 500° C. to 600° C. is also required for synthesis.

[0250] As described above, according to the manufacturing method of the present disclosure, a halide solid electrolyte containing Li, Ti, M, and X can be manufactured by a normal synthesis process (i.e., without sealing or the like, and in a synthesis environment in the atmosphere) with little compositional variation and with ionic conductivity as high as that of conventional manufacturing methods. Furthermore, whereas halide raw materials are extremely expensive, the manufacturing method of the present disclosure uses inexpensive oxide raw materials, thereby reducing the manufacturing cost of the halide solid electrolyte.

[0251] The method for producing a halide solid electrolyte according to the present disclosure can be used, for example, as a method for producing a solid electrolyte for secondary batteries such as all-solid-state batteries used in various electronic devices or automobiles.

Claims

1. A method for producing a halide solid electrolyte, comprising: (A) subjecting an oxide mixture containing a composite oxide containing Li and Ti and an oxide raw material containing Li and M to a halogenation treatment to obtain a halide solid electrolyte containing Li, Ti, M, and X, wherein M is at least one element selected from the group consisting of metal elements (excluding Li and Ti) and semimetal elements, and X is at least one element selected from the group consisting of F, Cl, Br, and I.

2. The method for producing a halide solid electrolyte according to claim 1, wherein the halide solid electrolyte includes a first crystal phase represented by the following composition formula (1) and a second crystal phase represented by the following composition formula (2). Composition formula (1): Li2TiX6 Composition formula (2): Li3MX6 3. The method for producing a halide solid electrolyte according to claim 1, wherein the oxide raw material contains an oxide of Li and an oxide of M.

4. The method for producing a halide solid electrolyte according to claim 1, wherein M contains Al.

5. The method for producing a halide solid electrolyte according to claim 1, wherein X includes F.

6. The method for producing a halide solid electrolyte according to claim 1, wherein the oxide mixture is in a particulate form.

7. The method for producing a halide solid electrolyte according to claim 1, wherein the oxide mixture is substantially free of TiO2.

8. The method for producing a halide solid electrolyte according to claim 1, wherein in (A), the halogenation treatment of the oxide mixture is carried out by heat treating a thermally decomposable halogen-containing material.

9. The method for producing a halide solid electrolyte according to claim 8, wherein the halogen-containing material is in particulate form.

10. The method for producing a halide solid electrolyte according to claim 8, wherein the (A) comprises: (A-1) mixing the oxide mixture with the halogen-containing substance; and (A-2) heat-treating the mixture containing the oxide mixture and the halogen-containing substance obtained in the (A-1) to thereby subject the oxide mixture to the halogenation treatment.

11. The method for producing a halide solid electrolyte according to claim 8, wherein in (A), the halogen-containing material is heat-treated to generate halogen gas, and the halogen gas is brought into contact with the oxide mixture, thereby subjecting the oxide mixture to the halogenation treatment.

12. The method for producing a halide solid electrolyte according to claim 8, wherein the halogen-containing substance includes an ammonium salt.

13. The method for producing a halide solid electrolyte according to claim 12, wherein the ammonium salt includes NH4F.

14. The method for producing a halide solid electrolyte according to claim 8, wherein the halogen-containing material includes a resin.

15. The method for producing a halide solid electrolyte according to claim 14, wherein the resin includes a fluororesin.

16. The method for producing a halide solid electrolyte according to claim 8, wherein the halogen-containing material includes a substance that causes inorganic components resulting from thermal decomposition by the heat treatment in (A) to be substantially not contained in the halide solid electrolyte, except for halogen elements.

17. The method for producing a halide solid electrolyte according to claim 8, wherein the halogen-containing material includes a plurality of types of halogen-containing compounds.

18. The method for producing a halide solid electrolyte according to claim 1, wherein in (A), the halogenation treatment of the oxide mixture is carried out at a temperature of 150° C. or higher.

19. The method for producing a halide solid electrolyte according to claim 1, further comprising, after the step (A), (B) subjecting the halide solid electrolyte obtained in the step (A) to a pulverization treatment.

20. A halide solid electrolyte comprising Li, Ti, Al, and F, and further comprising at least one selected from the group consisting of Nb and Ga.

21. The halide solid electrolyte according to claim 20, which is substantially free of TiF4.

22. The halide solid electrolyte according to claim 20, wherein the halide solid electrolyte is in particulate form.

23. The halide solid electrolyte according to claim 20, wherein the halide solid electrolyte includes an amorphous phase.

24. The halide solid electrolyte according to claim 20, wherein an X-ray diffraction pattern obtained by X-ray diffraction measurement of the halide solid electrolyte using Cu-Kα radiation satisfies at least one selected from the group consisting of the following (1), (2), and (3): (1) There is no peak derived from TiF4. (2) There is no peak derived from LiF. (3) There is no peak derived from AlF3.

25. A positive electrode material comprising the halide solid electrolyte of claim 20.

26. A battery comprising a positive electrode comprising the positive electrode material of claim 25.

27. A battery comprising: a positive electrode; a negative electrode; and an electrolyte layer provided between the positive electrode and the negative electrode, wherein at least one selected from the group consisting of the positive electrode, the negative electrode, and the electrolyte layer contains the halide solid electrolyte according to claim 20.

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