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) converting a first composition that contains Li, Ti, and O into a first halide that contains Li, Ti, and X1; and (B) synthesizing a halide solid electrolyte that contains Li, Ti, M, X1, and X2 using the first halide obtained in (A) and a second halide that contains Li, M, and X2. Here, M represents at least one element that is selected from the group consisting of metal elements (excluding Li) and metalloid elements, X1 represents at least one element that is selected from the group consisting of F, Cl, Br, and I, and X2 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) converting a first composition containing Li, Ti, and O into a first halide containing Li, Ti, and X1; and (B) synthesizing a halide solid electrolyte containing Li, Ti, M, X1, and X2 using the first halide obtained in (A) and a second halide containing Li, M, and X2, wherein M is at least one element selected from the group consisting of metal elements (excluding Li) and metalloid elements, X1 is at least one element selected from the group consisting of F, Cl, Br, and I, and X2 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) converting a first composition containing Li, Ti, and O into a first halide containing Li, Ti, and X1; and (B) synthesizing a halide solid electrolyte containing Li, Ti, M, X1, and X2 using the first halide obtained in (A) and a second halide containing Li, M, and X2. Here, M is at least one element selected from the group consisting of metal elements (excluding Li) and metalloid elements, X1 is at least one element selected from the group consisting of F, Cl, Br, and I, and X2 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 deterioration (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 first composition containing Li, Ti, and O 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 synthesizing 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] The step (A) may include converting a second composition containing Li, M, and O into the second halide. In this case, in the step (B), a halide solid electrolyte is synthesized using the first halide and the second halide obtained in the step (A).

[0016] In the above (A), the halogenation treatment for converting the first composition and the second composition into the first halide and the second halide, respectively, 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 first composition and the second composition can be sufficiently halogenated. The temperature during the halogenation treatment may be, for example, 600°C or lower. The atmosphere for the halogenation treatment may be, for example, air, a nitrogen atmosphere, a reducing atmosphere, or any other atmosphere suitable for the halogen-containing material used.

[0017] In the above (A), the conversion of the first composition to the first halide may be carried out, for example, by heat-treating a thermally decomposable first halogen-containing material. Furthermore, in the above (A), the conversion of the second composition to the second halide may be carried out, for example, by heat-treating a thermally decomposable second halogen-containing material. The first halogen-containing material and the second halogen-containing material may be the same substance or different substances.

[0018] According to the above-described manufacturing method, the halogenation of the first composition and the second composition can be carried out efficiently and in a short time. Furthermore, because halogenation can be carried out in a short heat treatment, a solid electrolyte with homogeneous and excellent properties can be obtained while reducing reaction residues such as oxides. Furthermore, by heat treating the thermally decomposable first halogen-containing material and the second halogen-containing material, the first composition is converted to the first halide and the second composition is converted to the second halide, respectively. Therefore, the reactivity (halogenation property) of the first composition and the second composition is excellent, and productivity is also excellent. Furthermore, for example, the temperature of the halogenation reaction of the first composition and the progress of the reaction can be controlled depending on the thermal decomposition temperature of the substance selected as the first halogen-containing material. Furthermore, for example, the temperature of the halogenation reaction of the second composition and the progress of the reaction can be controlled depending on the thermal decomposition temperature of the substance selected as the second halogen-containing material. Therefore, processing suitable for various halide solid electrolytes can be performed.

[0019] When a first halogen-containing substance is used to convert the first composition to the first halide, in the production method according to the first embodiment, (A) above may include: (A-1) mixing the first composition with the first halogen-containing substance; and (A-2) converting the first composition to the first halide by heat-treating the mixture containing the first composition and the first halogen-containing substance obtained in (A-1) above.

[0020] In the production 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 the first composition and the first halogen-containing substance. Furthermore, the contact area between the first composition and the first halogen-containing substance can be increased. Therefore, the halogenation of the first composition can be promoted uniformly. Therefore, a homogeneous halide solid electrolyte with excellent properties can be obtained.

[0021] When a second halogen-containing substance is used to convert the second composition to the second halide, in the production method according to the first embodiment, (A) above may include: (A-3) mixing the second composition with the second halogen-containing substance; and (A-4) converting the second composition to the second halide by heat-treating the mixture containing the second composition and the second halogen-containing substance obtained in (A-3) above.

[0022] In the production method according to the first embodiment, by carrying out the above (A-3) and (A-4), a heat treatment for halogenation can be carried out on a homogeneous mixture of the second composition and the second halogen-containing substance. Furthermore, the contact area between the second composition and the second halogen-containing substance can be increased. Therefore, the halogenation of the second composition can be promoted homogeneously. Therefore, a homogeneous halide solid electrolyte with excellent properties can be obtained.

[0023] 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), (A-2), (A-3), and (A-4) are carried out will be described.

[0024] As shown in FIG. 1 , in one example of the manufacturing method according to the first embodiment, first, a first composition and a first halogen-containing substance are mixed (S11) in a step corresponding to the above (A-1), and then a second composition and a second halogen-containing substance are mixed (S12) in a step corresponding to the above (A-3). As described above, the first composition contains Li, Ti, and O. The second composition contains Li, M, and O. The first halogen-containing substance and the second halogen-containing substance are thermally decomposable. Next, in a step corresponding to the above (A-2), the first mixture containing the first composition and the first halogen-containing substance obtained in (A-1) is heat-treated to convert the first composition into a first halide (S13). Furthermore, in a step corresponding to the above (A-4), the second mixture containing the second composition and the second halogen-containing substance obtained in (A-3) is heat-treated to convert the second composition into a second halide (S14). Next, in a step corresponding to the above (B), a halide solid electrolyte containing Li, Ti, M, X1, and X2 is synthesized using the first halide and the second halide (S15).

[0025] The first composition, the second composition, the first halogen-containing substance, and the second halogen-containing substance will be specifically described below.Furthermore, the steps corresponding to (A-1), (A-2), (A-3), and (A-4) above, as well as (B) above will be specifically described.

[0026] <First Composition> The first composition contains Li, Ti, and O.

[0027] The first composition may contain metal oxides, hydroxides, and carbonates containing Li or Ti. The first composition may contain, for example, lithium oxide (e.g., LiO) and titanium oxide (e.g., TiO). The first composition may also contain a composite oxide containing Li and Ti, such as LiTiO.

[0028] The first composition may be, for example, a composition that produces a complex fluoride containing Li and Ti. The composition ratio of metal oxides, hydroxides, carbonates, or the like, of the components that make up the first composition may be adjusted, for example, so that the molar ratio of Li to Ti is a desired ratio. The composition ratio of the first composition may be adjusted, for example, so that a complex fluoride containing Li and Ti is produced. As an example, the composition ratio may be adjusted to satisfy Li:Ti=2:1 (molar ratio).

[0029] Titanium oxide (e.g., TiO2) can be used as the Ti source. As described above, the first composition may be a composition that produces a complex fluoride containing Li and Ti. For example, if the first composition has a composition of Li2O+TiO2 (Li:Ti=2:1 (molar ratio)), it can be converted into a first halide, such as Li2TiF6, by halogenation treatment. This can suppress the production of TiF4 even when TiO2 is used as the starting material. The crystal system of titanium oxide is not particularly limited, and both rutile and anatase can be used.

[0030] The shape of each component constituting the first composition, such as Li2O and TiO2, is not particularly limited. Each component constituting the first composition may be, for example, particulate. This facilitates simultaneous halogenation (i.e., substitution of halogen element with oxygen element) from the particle surface of the component constituting the first composition and solid-phase reaction in the component constituting the first composition. Therefore, a homogeneous first halide can be synthesized in a short time while reducing reaction residues such as oxides. Furthermore, when each component constituting the first composition is particulate, reactivity such as halogenation and solid-phase reactivity is good, thereby achieving excellent productivity.

[0031] Each component constituting the first composition may have, for example, an average particle size of 0.5 μm or more and 20 μm or less. However, the average particle size of each component constituting the first composition is not limited to the above range, and any particle size and shape can be appropriately selected from the viewpoints of the halogenation reaction and the solid-state reaction. For example, the smaller the particle size of each component constituting the first composition, the lower the temperature for conversion to the first halide can be.

[0032] The average particle size of each component constituting the first composition is the median size of each component, 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 each component constituting the second composition, the first halogen-containing substance, and the second halogen-containing substance specified in this specification.

[0033] <Second Composition> The second composition contains Li, M, and O.

[0034] Metal oxides, hydroxides, and carbonates containing Li or M can be used as components constituting the second composition. The second composition includes, for example, lithium oxide (e.g., LiO) and an oxide of M. The second composition may also include a complex oxide containing Li and M, such as a complex oxide containing Li and Al.

[0035] 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.

[0036] M may contain Al. When M contains Al, a halide solid electrolyte having high ionic conductivity can be obtained. M may be Al.

[0037] The second composition may be, for example, a composition that produces a complex fluoride containing Li and M. The composition ratio of metal oxides, hydroxides, carbonates, etc., of the components that make up the second composition may be adjusted so that the molar ratio of Li to M is a desired ratio. For example, when M is Al, the composition ratio of the second composition may be adjusted so that a complex fluoride containing Li and Al is produced. As an example, the composition ratio may be set to satisfy Li:Al=3:1 (molar ratio). For example, when the second composition is 3LiO 1 / 2 + AlO 3 / 2 When the halide has a composition of Li:Al=3:1 (molar ratio), it can be converted into a second halide represented by, for example, LiAlF by halogenation treatment. This can prevent unstable precipitated phases such as titanium halides (e.g., TiX), which are prone to problems of evaporation and deliquescence, from forming in the halide solid electrolyte. This makes it possible to obtain a halide solid electrolyte with excellent ionic conductivity and stability.

[0038] The shape of each component constituting the second composition, such as Li2O and Al2O3, is not particularly limited. Each component constituting the second composition may be, for example, particulate. This facilitates simultaneous halogenation (i.e., substitution of halogen element with oxygen element) from the particle surface of the component constituting the second composition and solid-phase reaction in the component constituting the second composition. Therefore, a homogeneous second halide can be synthesized in a short time while reducing reaction residues such as oxides. Furthermore, when each component constituting the second composition is particulate, reactivity such as halogenation and solid-phase reactivity is good, thereby achieving excellent productivity.

[0039] Each component constituting the second composition 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 each component constituting the second composition is not limited to the above range, and any particle size and shape can be appropriately selected from the viewpoints of the halogenation reaction and the solid-state reaction. For example, the smaller the particle size of each component constituting the second composition, the lower the temperature for conversion to the second halide can be.

[0040] <First Halogen-Containing Substance and Second Halogen-Containing Substance> The first halogen-containing substance and the second halogen-containing substance are thermally decomposable. For example, when the first halide contains F as the halogen element X1, a fluorine-containing substance that serves as a fluorine source is used as the first halogen-containing substance. When the second halide contains F as the halogen element X2, a fluorine-containing substance that serves as a fluorine source is used as the second halogen-containing substance.

[0041] Hereinafter, the first halogen-containing substance and the second halogen-containing substance may be collectively referred to simply as "halogen-containing substance." Furthermore, the halogen element X1 and the halogen element X2 may be collectively referred to simply as "halogen element X."

[0042] 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.

[0043] 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.

[0044] 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 components constituting the first composition and the second composition can be efficiently halogenated, and the halogen-containing material is less likely to remain in the finally obtained halide solid electrolyte. Furthermore, by using a particulate halogen-containing material, the amount of halogen can be precisely controlled. Therefore, the synthesis of a desired halide solid electrolyte is made easier. Furthermore, since the halogen-containing material can be used in only the amount necessary to halogenate the components constituting the first composition and the second composition, 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.

[0045] 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.

[0046] The average particle size of the halogen-containing substance may be larger than the average particle size of the components constituting the first composition and the second composition. This results in a state in which the surface area of ​​the components constituting the first composition and the second composition is larger than that of the halogen-containing substance, i.e., the surface exposed area (i.e., the exposed area) of the components constituting the first composition and the second composition is large. Therefore, halogenation easily proceeds from the particle surface of the components constituting the first composition and the second composition, thereby obtaining a homogeneous halide. The average particle size of the halogen-containing substance 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 substance can be appropriately adjusted taking into account the halogenation temperature or reactivity. For example, by increasing the average particle size of the halogen-containing substance, the heat treatment temperature for the halogenation treatment can be increased.

[0047] 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 components constituting the first composition and the second composition. 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.

[0048] The ammonium salt may include NH4F. NH4F is a highly decomposable fluorine source and can effectively halogenate the components constituting the first composition and the second composition. Therefore, NH4F can thermally decompose at a low temperature (e.g., about 150°C) and at a fast decomposition rate, thereby fluorinating the components constituting the first composition and the second composition without remaining 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.

[0049] The halogen-containing substance may include a resin. By including a resin as the halogen-containing substance, the halogen-containing substance can halogenate the components constituting the first composition and the second composition 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 substance is suitable when it is desired to carry out the halogenation and solid-state reaction at a relatively high temperature (e.g., about 450°C or higher and 600°C or lower).

[0050] 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 the components constituting the first composition and the second composition while being thermally decomposed at a relatively high temperature (e.g., about 450°C or higher and 600°C or lower). Therefore, a method including a fluororesin as the halogen-containing material is suitable when the 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).

[0051] The halogen-containing material may contain, for example, a substance that, except for the halogen element, does not substantially contain inorganic components resulting from thermal decomposition by the heat treatment in (A) above in the halide solid electrolyte produced. The halogen-containing material used in the halogenation treatment is required to replace the oxygen element in the components constituting the first composition and the second composition, while preventing other components from being mixed as inorganic residues into the halide solid electrolyte finally obtained by thermal decomposition by the heat treatment. By using a substance that, except for the halogen element, does not substantially contain inorganic components resulting from thermal decomposition by the heat treatment in the halide solid electrolyte finally obtained, the mixing of inorganic residues into the halide solid electrolyte can be suppressed, and the desired halide solid electrolyte can be obtained. Here, in this specification, "the halogen-containing material is substantially free of inorganic components" means that the content of inorganic components in the entire halogen-containing material is 0.5 mass% or less.

[0052] 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 temperature range in which the halogen-containing material acts as a halogen source, thereby enabling the conversion of the components constituting the first composition and the second composition to halides and the solid-state reaction temperature to be controlled over a wide range. This makes it easy to obtain a desired halide solid electrolyte.

[0053] 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.

[0054] <Regarding (A-1)> In (A-1), the first composition and the first halogen-containing substance are mixed together. For example, the components constituting the first composition and the first halogen-containing substance are mixed uniformly.

[0055] In this way, by performing a preliminary step of uniformly mixing the first composition and the first halogen-containing substance before the halogenation treatment, the first composition can be uniformly converted into the first halide, thereby synthesizing a homogeneous first halide solid electrolyte.

[0056] For example, the components constituting the first composition and the powder of the first halogen-containing substance are mixed in a desired ratio. For example, dry mixing is sufficient as long as these powders are uniform. For example, they 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 these powders can be mixed uniformly. 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.

[0057] <Regarding (A-2)> In (A-2), a first mixture containing the first composition obtained in (A-1) above and a first halogen-containing substance is heat-treated to convert the first composition into the first halide.

[0058] 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.

[0059] 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.

[0060] When introducing the inert gas into the furnace, it is preferable to prevent the inert gas from directly hitting the sheath containing the mixture. Instead of inert gas, air may be introduced into the furnace. 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. For example, 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 hit by the gas, reducing the problem of large temperature distribution within the sheath. This suppresses uneven distribution of the progress (i.e., variation in progress) of the halogenation reaction of the first composition and the solid-state reaction to synthesize a halide solid electrolyte.

[0061] 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.

[0062] 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 first halide to proceed uniformly, resulting in a more uniform halide solid electrolyte.

[0063] The heat treatment temperature is, for example, 150°C or higher and 600°C or lower, as described above, or may be 250°C or higher and 600°C or lower, or 250°C or higher and 550°C or lower. The heat treatment time is, for example, 1 hour or higher and 40 hours or lower, as described above. Lowering the heat treatment temperature prevents sintering, allowing for the production of soft halide particles. This makes it possible to obtain a dense green compact (a solid electrolyte with good ionic conductivity). 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 exhausting the reaction gas.

[0064] 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.

[0065] 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.

[0066] Since this heat treatment is not intended to react easily evaporating materials such as titanium halide, the heat treatment does not need to be performed in a sealed state. The mixture of the first composition and the first 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, before the heat treatment. Therefore, unlike heat treatments in conventional manufacturing methods using halide raw materials (i.e., heat treatments for solid-state 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 useful industrially. The manufacturing method according to the first embodiment thus offers excellent productivity, allowing for the production of halide solid electrolytes with excellent ionic conductivity and stability (e.g., electrochemical stability and heat resistance). Even if trace amounts of titanium halide (e.g., TiF) are generated as impurities, the trace amounts of titanium halide evaporate and disappear because the heat treatment is performed in an open atmosphere. Therefore, even in such a case, it is possible to obtain a titanium halide-free halide solid electrolyte having excellent characteristics and reliability.

[0067] 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 from the viewpoint of the reaction between the sheath and the first composition, first halogen-containing substance, and first halide contained in 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 a cylindrical shape, a prismatic shape, or a gourd shape, can be used for the sheath.

[0068] 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.

[0069] As an example of the production 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 first composition and the first halogen-containing substance before the treatment of converting the first composition to the first halide does not necessarily have to be carried out. For example, the first halogen-containing substance may be added to the first composition, and heat treatment may be carried out without sufficient mixing. Furthermore, while heat treatment is desirable for efficient halogenation treatment, the first composition may also be converted to the first halide by, for example, adding the halogen-containing substance to the first composition and then leaving it at room temperature for a long period of time.

[0070] In the manufacturing method according to the first embodiment, an additive may be added to the first composition as needed before the halogenation treatment that converts the first composition into the first halide. For example, an additive for accelerating the halogenation reaction of the first composition, an additive for accelerating the solid-state reaction of the first composition, etc. may be added. Examples of such additives include an oxide containing at least one element selected from the group consisting of K, Fe, Nb, Ga, Zn, Mg, P, Na, Ca, Si, and Cu. For example, when added in trace amounts to the first composition, K oxide and Fe oxide can lower the reaction temperature of the halogenation reaction and the solid-state reaction by, for example, about 10°C to 20°C. This can accelerate the halogenation reaction and the solid-state reaction of the first composition. K oxide and Fe oxide may be added together, or either one may be added alone. 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 K oxide and Fe oxide are added for the purpose of promoting the halogenation reaction and solid-state reaction of the first composition, the total amount of K oxide and Fe oxide added may be adjusted so that the total content of K and Fe contained in the finally obtained halide solid electrolyte is, for example, in the range of 0.0003 at. % or more and 0.10 at. % or less.

[0071] The additives such as K oxide and Fe 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 first composition. For K oxide, Fe oxide, etc., generally, the smaller the particle size, the greater the additive's effect, such as reaction promotion effect. For example, the particle size of the additive may be smaller than the particles of the components constituting the first composition. As an example, the additive may have a particle size of 0.1 μm or less and a BET specific surface area of ​​100 m 2 / g or more. Note that, if coarse particles of K oxide and Fe 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 K oxide and Fe 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.

[0072] Regarding (A-3): In (A-3), the second composition and the second halogen-containing substance are mixed together. For example, the components constituting the second composition and the second halogen-containing substance are mixed uniformly.

[0073] In this way, by performing a preliminary step of uniformly mixing the second composition and the second halogen-containing substance before the halogenation treatment, the second composition can be uniformly converted into the second halide, thereby synthesizing a homogeneous second halide solid electrolyte.

[0074] The specific steps carried out in (A-3) are the same as those described above in (A-1), so detailed description will be omitted here.

[0075] <Regarding (A-4)> In (A-4), the second mixture containing the second composition obtained in (A-4) above and the second halogen-containing substance is heat-treated to convert the twelfth composition into a second halide.

[0076] The heat treatment carried out in (A-4) and the additives therefor are the same as those described in (A-2) above, and therefore detailed description thereof will be omitted here.

[0077] <Regarding (B)> In (B), a halide solid electrolyte containing Li, Ti, M, X1, and X2 is synthesized using the first halide obtained in (A) above (for example, (A-1) to (A-4)) and a second halide containing Li, M, and X2.

[0078] (B) includes, for example, mixing a first halide and a second halide. This method allows the content ratio of the first halide and the second halide to be controlled and then mixed to homogenize them. Therefore, a halide solid electrolyte having a desired composition and excellent ionic conductivity and stability can be obtained.

[0079] For example, a solid electrolyte with high ionic conductivity and stability can be obtained by mixing Li2TiF6 as the first halide and Li3AlF6 as the second halide. For example, Li2TiF6 may be contained in Li3AlF6 up to about 60 mol%. By forming an aggregate of particles with different properties (i.e., an aggregate of the first halide and the second halide), local stress concentrations are dispersed and absorbed by the composite structure, improving mechanical properties (e.g., bending resistance and thermal shock resistance).

[0080] The first halide and the second halide may be mixed by weighing out predetermined amounts of each and mixing them uniformly in a dry manner, for example, by a mixing method such as that described above in (A-1) or (A-3).

[0081] The step (B) may include heat-treating the first halide and the second halide. According to this method, the first halide and the second halide are reacted while controlling the content ratio of the first halide and the second halide to a desired value, thereby obtaining a halide solid electrolyte having a desired composition and excellent ionic conductivity and stability.

[0082] The above heat treatment can, for example, replace a portion of the Al in the LiAlF crystal with Ti, resulting in even higher ionic conductivity. The replacement of Al with Ti can be confirmed by evaluating the amount of Ti substitution using Rietveld analysis using powder XRD. The above heat treatment can be performed using the same sagger and firing furnace as in the heat treatment (A-2) or (A-4) described above, and the reaction between the first halide and the second halide can be controlled by controlling the temperature, time, and atmosphere.

[0083] 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 the first halide contains Li2TiX16 and the second halide contains Li3MX26, 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): Li2TiX16 Composition formula (2): Li3MX26

[0084] When a halide solid electrolyte containing the first and second crystalline phases is produced, the generation of unstable halides (e.g., titanium halide) that are easily evaporated is suppressed, and therefore a halide solid electrolyte with good properties can be obtained stably and reproducibly in an atmospheric environment.

[0085] 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): xLi2TiX16-(1-x)Li3MX26 Here, in composition formula (3), x satisfies 0<x<1. That is, x represents the composition ratio of Li2TiX16, which is the first crystal phase, and (1-x) represents the composition ratio of Li3MX26, which is the second crystal phase. To improve ionic conductivity, x may, for example, satisfy 0.05≦x≦0.5.

[0086] In the manufacturing method according to the first embodiment, when at least one selected from the group consisting of K oxide and Fe oxide is used as an additive, the resulting halide solid electrolyte contains at least one selected from the group consisting of K and Fe. That is, in this case, the halide solid electrolyte obtained by the manufacturing method according to the first embodiment contains, for example, Li, Ti, Al, and F and further contains at least one selected from the group consisting of K and Fe. 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, K, and Fe, or may consist only of Li, Ti, Al, F, K, and Fe. The phrase "the halide solid electrolyte consists essentially of Li, Ti, Al, F, K, and Fe" means that the ratio of the total amount of substance of Li, Ti, Al, F, K, and Fe to the total amount of substance of all elements constituting the halide solid electrolyte is 90% or more. As an example, the ratio may be 95% or more.

[0087] 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.

[0088] As described above, when K oxide and Fe oxide are added as additives to promote the reaction of the first composition and the second composition, K and Fe may not be detected as a composition phase in X-ray diffraction measurement. Even in this case, the presence of K and Fe 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 K and Fe contained in the halide solid electrolyte may be, for example, 0.0003 at. % or more and 0.10 at. % or less. The content of K and Fe can be determined by EPMA or the like.

[0089] When the halide solid electrolyte obtained by the production 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 K and Fe derived from the K oxide and Fe oxide used as additives, for example, Fe may be mainly incorporated into the first crystalline phase, i.e., Li2TiX16, and K may be mainly incorporated into the second crystalline phase, i.e., Li3MX26. That is, it is believed that Fe mainly acts to promote the synthesis reaction of Li2TiX16, while K mainly acts to promote the reaction of Li3MX26. Therefore, when the halide solid electrolyte to be produced is a solid electrolyte including the first crystalline phase and the second crystalline phase, co-addition of K oxide and Fe oxide is desirable.

[0090] 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.

[0091] 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. Even if a trace amount of TiF is generated during the halogenation process of the first composition, the TiF can be evaporated and eliminated by performing the halogenation process in an open environment. Therefore, it is possible to obtain a halide solid electrolyte that is substantially free of TiF4 and has excellent characteristics and reliability.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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 do not include oxides such as composite oxides; instead, all fluorides are used, including 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 highly environmentally stable raw materials (e.g., O-containing raw materials, e.g., oxides) and a reaction pathway. In particular, the production method includes a reaction pathway that suppresses the generation of titanium halides such as titanium fluoride (e.g., a pathway that converts a titanium-containing composition into a stable halide), and homogenization can eliminate 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 and is also 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.

[0099] 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.

[0100] As described above, the manufacturing method according to the first embodiment uses raw materials that are stable to the environment (temperature and humidity), and does not require the synthesis of unstable titanium fluoride, etc., during 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.

[0101] Second Embodiment A method for producing a halide solid electrolyte according to a second embodiment will now be described.

[0102] In the production method according to the second embodiment, the step (B) in the production method according to the first embodiment includes mechanochemically treating the first halide and the second halide.

[0103] According to the manufacturing method of the second embodiment, it is possible to react the first halide with the second halide and to amorphize a portion of the synthesized halide solid electrolyte. Therefore, it is possible to obtain a halide solid electrolyte having a desired composition with excellent ionic conductivity and stability. Furthermore, it is possible to microparticulate the synthesized halide solid electrolyte, thereby obtaining a halide solid electrolyte useful for a solid electrolyte layer of a battery, a coating layer for an active material, and the like. Therefore, it is possible to realize a battery with excellent performance and reliability.

[0104] 2 is a flowchart showing an example of a method for producing a halide solid electrolyte according to the second embodiment. Here, an example of a production method will be described in which, as an example of the production method described in the first embodiment, the above-mentioned (A) is a production method in which the above-mentioned (A-1) to (A-4) are carried out, and the above-mentioned (B) includes a mechanochemical treatment.

[0105] As shown in FIG. 2, first, a first composition and a first halogen-containing substance are mixed (S21) in a step corresponding to the above (A-1), and then a second composition and a second halogen-containing substance are mixed (S22) in a step corresponding to the above (A-3). Next, in a step corresponding to the above (A-2), the first mixture containing the first composition and the first halogen-containing substance obtained in (A-1) is heat-treated to convert the first composition into a first halide (S23). Furthermore, in a step corresponding to the above (A-4), the second mixture containing the second composition and the second halogen-containing substance obtained in (A-3) is heat-treated to convert the second composition into a second halide (S24). Next, in a step corresponding to the above (B), the first halide and the second halide are subjected to mechanochemical treatment to synthesize a halide solid electrolyte containing Li, Ti, M, X1, and X2 (S25).

[0106] S21 to S24 are the same as S11 to S14 described in the first embodiment, respectively, and therefore detailed description thereof will be omitted here.

[0107] The first halide and the second halide have an average particle size of, for example, about 3 μm or more and 20 μm or less. In the above (B), the first halide and the second halide are pulverized so that the average particle size is, for example, about 0.1 μm or more and 2 μm or less.

[0108] 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.

[0109] The mechanochemical treatment in (B) above, for example, introduces distorted crystallinity or amorphousness into halide crystals. The distorted crystallinity or amorphousness is primarily introduced into the surface layer of the halide particles. The specific means may be similar to 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 extended. The equipment and media used for the mechanochemical treatment may be similar to those used in the grinding treatment. Generally, grinding and mechanochemical treatment proceed simultaneously. For example, in the case of a dry method, a ball mill vessel 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 can be used. As described above, commercially available balls with a diameter of 1 mm to 30 mm are typically used, but balls with smaller or larger diameters may also be used. The diameter of the balls used may be selected arbitrarily depending on the desired particle size or degree of amorphization. To prevent halide from adhering to the zirconia balls or the inner wall of the zirconia container, an appropriate amount of 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 can be removed by drying later.

[0110] The introduction of amorphousness into the halide 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.

[0111] 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.

[0112] The change in deformability due to amorphization can be evaluated by an evaluation method such as micro-Vickers.

[0113] As described above, since the manufacturing method according to the second embodiment includes a mechanochemical treatment, 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 formed 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.

[0114] 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 mechanochemical treatment during the pulverization treatment of (B) above.

[0115] 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, this example is a production method in which the above-mentioned (A-1) to (A-4) are carried out as the above-mentioned (A), which is an example of the production method described in the first embodiment, and in which the halide solid electrolyte is slurried for forming a coating film during the above-mentioned (B) pulverization treatment and mechanochemical treatment are simultaneously performed.

[0116] As shown in FIG. 3, first, a first composition and a first halogen-containing substance are mixed (S31) in a step corresponding to the above (A-1), and then a second composition and a second halogen-containing substance are mixed (S32) in a step corresponding to the above (A-3). Next, in a step corresponding to the above (A-2), the first mixture containing the first composition and the first halogen-containing substance obtained in (A-1) is heat-treated to convert the first composition into a first halide (S33). Furthermore, in a step corresponding to the above (A-4), the second mixture containing the second composition and the second halogen-containing substance obtained in (A-3) is heat-treated to convert the second composition into a second halide (S34). Next, in a step corresponding to the above (B), the first halide and the second halide are subjected to mechanochemical treatment and simultaneously formed into a slurry (S35).

[0117] S31 to S34 are the same as S11 to S14 described in the first embodiment, respectively, and therefore detailed description thereof will be omitted here.

[0118] The mechanochemical treatment in S35 is similar to the pulverization treatment in S25 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 treatment is further performed. The slurrying treatment is performed, for example, by adding an organic binder and a plasticizer dispersed in an organic solvent such as tetralin to the halide solid electrolyte simultaneously with the pulverization treatment. 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).

[0119] 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.

[0120] Third Embodiment A method for producing a halide solid electrolyte according to a third embodiment will now be described.

[0121] In the manufacturing method according to the third embodiment, in (A) described in the first embodiment, a first halogen-containing material is heat-treated to generate a first halogen gas, and the first composition is converted to the first halide by contacting the first halogen gas with the first composition. In addition, in (A) described in the first embodiment, a second halogen-containing material is heat-treated to generate a second halogen gas, and the second composition is converted to the second halide by contacting the second halogen gas with the second composition. In the manufacturing method according to the third embodiment, the mechanochemical treatment (B) described in the second embodiment may be performed after (A).

[0122] 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 first composition is placed at a predetermined position, a first halogen-containing material is heat-treated, and the generated halogen gas is brought into contact with the first composition (S41). This results in a halogenation treatment of the first composition. Furthermore, a second composition is placed at a predetermined position, and a second halogen-containing material is heat-treated, and the generated halogen gas is brought into contact with the second composition (S42). Thereafter, as a step corresponding to (B) above, the first halide and second halide obtained in S41 and S42 are mixed (S43).

[0123] According to the manufacturing method of the third embodiment, the first composition can be halogenated by the generated halogen gas without directly contacting the first composition with the first 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 resulting halide solid electrolyte. This allows for a wider range of usable first halogen-containing materials. Furthermore, the second composition can be halogenated by the generated halogen gas without directly contacting the second composition with the second 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 resulting halide solid electrolyte. This allows for a wider range of usable second halogen-containing materials.

[0124] As a specific example, the first composition is placed on a fine-mesh nickel mesh, and a first halogen-containing material, such as ammonium fluoride, is placed below the nickel mesh. In this manner, the first composition and the halogen-containing material are placed without contacting each other. In this state, heat-treating the first halogen-containing material generates a halogen gas, such as fluorine gas, which passes through the nickel mesh and comes into contact with the first composition. This converts the first composition to the first halide. The first composition and the halide are as described in the first embodiment. 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. The halogenation of the second composition is also performed in a similar manner.

[0125] [Fourth Embodiment] A fourth embodiment will be described below. Matters described in the first, second, and third embodiments will be omitted as appropriate.

[0126] 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.

[0127] 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 K and Fe. The halide solid electrolyte can be produced by, for example, the production method according to the first, second, or third embodiment.

[0128] 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 K and Fe, will be referred to as the halide solid electrolyte according to the fourth embodiment.

[0129] 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, K, and Fe, or may consist only of Li, Ti, Al, F, K, and Fe. 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.

[0130] The battery according to the fourth embodiment has excellent charge / discharge characteristics because it contains the halide solid electrolyte according to the fourth embodiment.

[0131] Figure 5 shows a cross-sectional view of a battery 1000 according to the fourth embodiment.

[0132] 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.

[0133] The positive electrode 201 may include a positive electrode material including the halide solid electrolyte according to the fourth embodiment. The positive electrode 201 includes a positive electrode active material 204 and a solid electrolyte 100.

[0134] The electrolyte layer 202 contains an electrolyte material.

[0135] The negative electrode 203 contains a negative electrode active material 205 and a solid electrolyte 100 .

[0136] 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.

[0137] 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.

[0138] 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.

[0139] In the present disclosure, "(A, B, C)" means "at least one selected from the group consisting of A, B, and C."

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] The electrolyte layer 202 may consist of only the second solid electrolyte.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] The second solid electrolyte may be a sulfide solid electrolyte.

[0164] 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.

[0165] 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. By covering the negative electrode active material with the electrochemically stable sulfide solid electrolyte, contact between the first solid electrolyte and the negative electrode active material can be suppressed. As a result, the internal resistance of the battery 1000 can be reduced.

[0166] The second solid electrolyte may be an oxide solid electrolyte.

[0167] 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.

[0168] As mentioned above, the second solid electrolyte may be a halide solid electrolyte.

[0169] 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.

[0170] 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).

[0171] 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.

[0172] The halide solid electrolyte may be Li3YCl6 or Li3YBr6.

[0173] The second solid electrolyte may be an organic polymer solid electrolyte.

[0174] An example of the organic polymer solid electrolyte is a compound of a polymer compound and a lithium salt.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.

[0179] 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.

[0180] An example of a lithium salt is LiPF 6 , LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), or LiC(SO2CF3)3. 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. 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.

[0181] 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.

[0182] 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.

[0183] 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.

[0184] The ionic liquid may contain a lithium salt.

[0185] 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.

[0186] 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.

[0187] At least one selected from the positive electrode 201 and the negative electrode 203 may contain a conductive additive to improve electronic conductivity.

[0188] 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.

[0189] 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.

[0190] 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.

[0191] [Other Embodiments] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0192] (Technology 1) A method for producing a halide solid electrolyte, comprising: (A) converting a first composition containing Li, Ti, and O into a first halide containing Li, Ti, and X1; and (B) synthesizing a halide solid electrolyte containing Li, Ti, M, X1, and X2 using the first halide obtained in (A) and a second halide containing Li, M, and X2, wherein M is at least one element selected from the group consisting of metal elements (excluding Li) and metalloid elements, X1 is at least one selected from the group consisting of F, Cl, Br, and I, and X2 is at least one selected from the group consisting of F, Cl, Br, and I.

[0193] Titanium halide (TiX4) is a relatively unstable substance, e.g., easily evaporates and exhibits deliquescent properties. According to the manufacturing method of Technology 1, a first composition containing Li, Ti, and O 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 variations in the properties of the halide solid electrolyte. In contrast, according to the manufacturing method of Technology 1, such compositional fluctuations and the like 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 Technique 1, a halide solid electrolyte having a target composition can be stably synthesized.

[0194] (Technology 2) The method for producing a halide solid electrolyte according to Technology 1, wherein the step (A) includes converting a second composition containing Li, M, and O into the second halide, and the step (B) synthesizes the halide solid electrolyte using the first halide and the second halide obtained in the step (A).

[0195] According to the manufacturing method of Technique 2, a halide solid electrolyte having a target composition can be stably synthesized.

[0196] (Technology 3) The method for producing a halide solid electrolyte according to Technology 1 or 2, wherein the step (B) includes mixing the first halide and the second halide.

[0197] According to the manufacturing method of Technique 3, the content ratio of the first halide and the second halide can be controlled and then homogenized by mixing them, thereby obtaining a halide solid electrolyte having a desired composition with excellent ionic conductivity and stability.

[0198] (Technology 4) The method for producing a halide solid electrolyte according to any one of Techniques 1 to 3, wherein the step (B) includes heat treating the first halide and the second halide.

[0199] According to the manufacturing method of Technology 4, the first halide and the second halide are reacted while being controlled to a desired content ratio, whereby a halide solid electrolyte having a target composition and excellent ionic conductivity and stability can be obtained.

[0200] (Technology 5) The method for producing a halide solid electrolyte according to any one of Technologies 1 to 4, wherein (B) includes mechanochemically treating the first halide and the second halide.

[0201] According to the manufacturing method of Technology 5, it is possible to react the first halide with the second halide and to make a portion of the synthesized halide solid electrolyte amorphous. Therefore, it is possible to obtain a halide solid electrolyte having a desired composition with excellent ionic conductivity and stability. Furthermore, it is possible to obtain a halide solid electrolyte useful for a solid electrolyte layer of a battery, a coating layer for an active material, etc., because the synthesized halide solid electrolyte can be microparticulated. Therefore, it is possible to realize a battery with excellent performance and reliability.

[0202] (Technology 6) The method for producing a halide solid electrolyte according to any one of Techniques 1 to 5, wherein the first halide contains Li2TiX16, the second halide contains Li3MX26, and the halide solid electrolyte contains 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): Li2TiX16 Composition formula (2): Li3MX26

[0203] According to the manufacturing method of Technique 6, the generation of unstable halides (e.g., titanium halide) that are easily evaporated is suppressed, and therefore a halide solid electrolyte with good properties can be obtained stably in an atmospheric environment with good reproducibility.

[0204] (Technology 7) The method for producing a halide solid electrolyte according to any one of Techniques 1 to 6, wherein M contains Al.

[0205] According to the manufacturing method of Technique 7, a halide solid electrolyte having high ionic conductivity can be obtained.

[0206] (Technology 8) The method for producing a halide solid electrolyte according to any one of Techniques 1 to 7, wherein at least one selected from the group consisting of X1 and X2 contains F.

[0207] According to the manufacturing method of Technique 8, it is possible to obtain a halide solid electrolyte having excellent stability (for example, excellent electrochemical stability and heat resistance) and high ionic conductivity.

[0208] (Technology 9) The method for producing a halide solid electrolyte according to Technology 2, wherein in (A), at least one selected from the group consisting of the following (I) and (II) is carried out: (I) The conversion of the first composition to the first halide is carried out by heat-treating a thermally decomposable first halogen-containing material; and (II) The conversion of the second composition to the second halide is carried out by heat-treating a thermally decomposable second halogen-containing material.

[0209] According to the manufacturing method of Technology 9, halogenation of at least one selected from the group consisting of the first composition and the second composition can be carried out efficiently and in a short time. Furthermore, because halogenation can be carried out with a short heat treatment, a solid electrolyte with homogeneous and excellent properties can be obtained while reducing reaction residues such as oxides. Furthermore, because the first composition is converted into the first halide by heat treating a thermally decomposable first halogen-containing material, the reactivity (halogenation property) of the first composition is good and productivity is excellent. Similarly, because the second composition is converted into the first halide by heat treating a thermally decomposable second halogen-containing material, the reactivity (halogenation property) of the second composition is good and productivity is excellent. Furthermore, for example, the temperature of the halogenation reaction of the first composition and the progress of the reaction can be controlled depending on the thermal decomposition temperature of the substance selected as the first halogen-containing material. Similarly, the temperature of the halogenation reaction of the second composition and the progress of the reaction can be controlled depending on the thermal decomposition temperature of the substance selected as the second halogen-containing material. Therefore, processing suitable for various halide solid electrolytes can be performed.

[0210] (Technology 10) The method for producing a halide solid electrolyte according to Technology 9, wherein at least one selected from the group consisting of the first halogen-containing substance and the second halogen-containing substance is in a particulate form.

[0211] According to the manufacturing method of Technology 10, at least one selected from the group consisting of the first halogen-containing substance and the second halogen-containing substance is easily thermally decomposed, thereby increasing the contact area between the first halogen-containing substance and the first composition and / or the contact area between the second halogen-containing substance and the second composition. Therefore, according to the manufacturing method of Technology 10, the first composition and / or the second composition can be efficiently halogenated, and the first halogen-containing substance and / or the second halogen-containing substance are less likely to remain in the final halide solid electrolyte. Furthermore, precise control of the halogen content is possible. This enables the synthesis of a desired halide solid electrolyte. Furthermore, since the first halogen-containing substance can be used in only the amount necessary for halogenating the first composition, excess halogen gas emissions can be suppressed. Similarly, since the second halogen-containing substance can be used in only the amount necessary for halogenating the second composition, excess halogen gas emissions can be suppressed. This reduces the environmental impact and also reduces the impact on corrosion of furnace materials, etc.

[0212] (Technology 11) When (I) is performed in (A), (A) comprises: (A-1) mixing the first composition with the first halogen-containing substance; and (A-2) converting the first composition to the first halide by heat-treating the mixture containing the first composition and the first halogen-containing substance obtained in (A-1). When (II) is performed in (A), (A) comprises: (A-3) mixing the second composition with the second halogen-containing substance; and (A-4) converting the second composition to the second halide by heat-treating the mixture containing the second composition and the second halogen-containing substance obtained in (A-3). The method for producing a halide solid electrolyte according to Technology 9 or 10.

[0213] According to the manufacturing method of Technology 11, a homogeneous mixture of the first composition and the first halogen-containing substance can be subjected to a heat treatment for halogenation. Similarly, a homogeneous mixture of the second composition and the second halogen-containing substance can be subjected to a heat treatment for halogenation. Furthermore, the contact area between the first composition and the first halogen-containing substance can be increased. Similarly, the contact area between the second composition and the second halogen-containing substance can be increased. Therefore, according to the manufacturing method of Technology 11, the halogenation of the first composition and / or the second composition can be promoted uniformly. Therefore, a homogeneous halide solid electrolyte with excellent properties can be obtained.

[0214] (Technology 12) The method for producing a halide solid electrolyte according to any one of Techniques 9 to 11, wherein, when (I) is carried out in (A), in (A), a first halogen gas is generated by heat-treating the first halogen-containing material, and the first composition is converted to the first halide by contacting the first halogen gas with the first composition; and when (II) is carried out in (A), in (A), a second halogen gas is generated by heat-treating the second halogen-containing material, and the second composition is converted to the second halide by contacting the second halogen gas with the second composition.

[0215] According to the manufacturing method of Technology 12, the first composition can be halogenated by the generated halogen gas without directly contacting the first composition with the first halogen-containing material. Similarly, the second composition can be halogenated by the generated halogen gas without directly contacting the second composition with the second 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 resulting halide solid electrolyte. This allows for a wider range of usable first halogen-containing materials and / or second halogen-containing materials.

[0216] (Technology 13) The method for producing a halide solid electrolyte according to any one of Techniques 9 to 12, wherein at least one selected from the group consisting of the first halogen-containing substance and the second halogen-containing substance contains an ammonium salt.

[0217] 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 first composition and / or the second composition. Therefore, the manufacturing method of Technology 13 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, 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.

[0218] (Technology 14) The method for producing a halide solid electrolyte according to Technology 13, wherein the ammonium salt contains NH4F.

[0219] The manufacturing method of Technology 14 is effective in halogenating the first composition and / or the second composition at a low temperature (e.g., 150°C to 200°C). This makes it difficult for the first halide to sinter and become too hard, resulting in a soft first halide. Similarly, it makes it difficult for the second halide to sinter and become too hard, resulting in a soft second halide. Therefore, the manufacturing method of Technology 14 can produce a halide solid electrolyte useful for battery solid electrolyte layers, active material coating layers, etc. This allows for the realization of batteries with excellent performance and reliability. Furthermore, NH4F is a highly decomposable fluorine source and can effectively halogenate the first composition and / or the second composition. Therefore, the manufacturing method of Technology 14 allows for the halogenation of the first composition and / or the second composition while NH4F thermally decomposes at a low temperature (e.g., about 150°C to 200°C) and at a fast decomposition rate, without leaving any residue in the first halide and / or the second halide.

[0220] (Technology 15) The method for producing a halide solid electrolyte according to any one of Techniques 9 to 14, wherein at least one selected from the group consisting of the first halogen-containing substance and the second halogen-containing substance includes a resin.

[0221] According to the manufacturing method of technique 15, the first halogen-containing compound can halogenate the first composition while being thermally decomposed at a relatively high temperature (e.g., about 450°C or higher and 600°C or lower). Similarly, the second halogen-containing compound can halogenate the second composition while being thermally decomposed at a relatively high temperature (e.g., about 450°C or higher and 600°C or lower).

[0222] (Technology 16) The method for producing a halide solid electrolyte according to Technology 15, wherein the resin includes a fluororesin.

[0223] A fluororesin such as PTFE can halogenate the first composition and / or the second composition while being thermally decomposed at a relatively high temperature (for example, about 450° C. or higher and 600° C. or lower).

[0224] (Technology 17) The method for producing a halide solid electrolyte according to any one of Techniques 9 to 16, wherein at least one selected from the group consisting of the first halogen-containing substance and the second halogen-containing substance contains a substance that prevents inorganic components, generated by thermal decomposition by the heat treatment in (A), from being substantially contained in the halide solid electrolyte, except for halogen elements.

[0225] The first halogen-containing substance 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. Similarly, the second halogen-containing substance 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 selected from the group consisting of the first halogen-containing substance and the second halogen-containing substance 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. An example of a halogen-containing substance 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 is a substance in which inorganic components generated by thermal decomposition by the heat treatment, except for the halogen element, are gasified and discharged.

[0226] (Technology 18) The method for producing a halide solid electrolyte according to any one of Techniques 9 to 17, wherein at least one selected from the group consisting of the first halogen-containing substance and the second halogen-containing substance contains a plurality of halogen-containing compounds.

[0227] According to the manufacturing method of Technology 18, for example, both an ammonium salt and a fluororesin can be used as the first halogen-containing substance and / or the second halogen-containing substance. This allows for a wide temperature range in which the first halogen-containing substance and / or the second halogen-containing substance act as a halogen source. Therefore, the conversion temperature of the first composition to the first halide can be controlled over a wide range. Similarly, the conversion temperature of the second composition to the second halide can be controlled over a wide range. Therefore, according to the manufacturing method of Technology 18, it is easy to obtain a desired halide solid electrolyte.

[0228] (Technology 19) A halide solid electrolyte comprising Li, Ti, Al, and F, and further comprising at least one selected from the group consisting of K and Fe.

[0229] This configuration makes it possible to obtain a homogeneous halide solid electrolyte with excellent ionic conductivity.

[0230] (Technology 20) The halide solid electrolyte according to Technology 19, which is substantially free of TiF4.

[0231] This configuration can suppress changes over time in the characteristics and mechanical properties of the halide solid electrolyte caused by the evaporation and deliquescence of TiF, thereby realizing a halide solid electrolyte with excellent characteristics and reliability. Even if a trace amount of TiF is generated during the halogenation process of the first composition, the TiF can be evaporated and eliminated by performing the halogenation treatment in an open state. Therefore, a halide solid electrolyte with excellent characteristics and reliability that is substantially free of TiF can be obtained.

[0232] (Technology 21) The halide solid electrolyte according to Technology 19 or 20, wherein the halide solid electrolyte is in a particulate form.

[0233] 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 21 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 21 has excellent deformability. Therefore, the halide solid electrolyte compact of Technology 21 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.

[0234] (Technology 22) The halide solid electrolyte according to any one of Techniques 19 to 21, wherein the halide solid electrolyte includes an amorphous phase.

[0235] 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 22 can realize a solid electrolyte layer of a battery with excellent characteristics and high reliability.

[0236] (Technology 23) The halide solid electrolyte according to any one of Techniques 19 to 22, 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.

[0237] This configuration makes it possible to obtain a halide solid electrolyte with excellent characteristics and reliability.

[0238] (Technology 24) A positive electrode material comprising the halide solid electrolyte according to any one of Technology 19 to Technology 23.

[0239] The cathode material according to Technology 24 makes it possible to realize a battery with excellent charge / discharge characteristics.

[0240] (Technology 25) A battery comprising a positive electrode containing the positive electrode material according to Technology 24.

[0241] This configuration makes it possible to provide a battery with excellent charge / discharge characteristics.

[0242] (Technology 26) 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 19 to 23.

[0243] This configuration makes it possible to provide a battery with excellent charge / discharge characteristics.

[0244] 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.

[0245] 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.

[0246] The present disclosure will now be described in more detail with reference to examples.

[0247] <Synthesis of Halide Solid Electrolyte> (Example 1) As starting materials, LiO powder (average particle size: about 1.5 μm) as a constituent of the first composition and the second composition, TiO powder (average particle size: about 0.8 μm, anatase type) as a constituent of the first composition, AlO powder (average particle size: 0.4 μm) as a constituent of the second composition, NHF powder (average particle size: about 35 μm) as a first halogen-containing substance and a second halogen-containing substance, and KO powder (average particle size: about 0.7 μm) and FeO powder (average particle size: about 0.6 μm) as additives were prepared.

[0248] Next, when the synthesized halide solid electrolyte was expressed by the composition formula (3): xLiTiX16-(1-x)LiMX26, LiO powder, TiO2 powder, and AlO3 powder were weighed out so that x = 0.25. In this example, in composition formula (3), X is F and M is Al. Regarding additives, KO powder and FeO3 powder were weighed out so that KF was 0.3 mol% and FeF3 was 0.01 mol% relative to [0.25LiTiF6-0.75LiAlF6]. These starting materials were weighed out in an air atmosphere. The K and Fe components were incorporated into the first and second compositions at a molar ratio of 25:75, respectively, based on the above contents. NH4F powder was added in the amount necessary for fluorinating the first and second compositions. Specifically, an amount of NH4F was used that would fluorinate both the first composition and the second composition in the reaction formula.

[0249] The first composition was composed of LiO powder and TiO powder. The second composition was composed of LiO powder and AlO powder. KO and FeO were added to the first composition and the first halogen-containing material (NHF) so as to achieve the molar ratio described above. The mixture was mixed uniformly with a pestle in an alumina mortar for approximately 10 minutes (a step corresponding to (A-1) above). KO and FeO were added to the second composition and the second halogen-containing material (NHF) so as to achieve the molar ratio described above. The mixture was mixed uniformly with a pestle in an alumina mortar for approximately 10 minutes (a step corresponding to (A-3) above). The starting materials were mixed in normal air, the same as when they were weighed. As a result, a first mixture containing the first composition, the halogen-containing material, and the additive, and a second mixture containing the second composition, the halogen-containing material, and the additive, were obtained.

[0250] Next, two sheaths were prepared. High-purity (SSA-H) alumina crucibles (diameter φ: 36 mm, height: 40 mm) were used for the sheaths. 3 g of the first mixture was placed in one crucible, and 3 g of the second mixture was placed in the other crucible, and each was heat-treated (steps corresponding to (A-2) and (A-4) above). 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 gas (mainly ammonia) emitted during heat treatment, and an alumina plate-shaped lid was placed on top to prevent foreign matter 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%. Three 10mm long, 10mm wide, and 10mm high tubings were used, with three tubings placed under each tubing, floating the tubing above the bottom of the furnace. This allowed the heater (radiant) heat and inert gas to reach the bottom of the tubing. After closing and sealing the furnace door, nitrogen gas was introduced as an inert gas at 2L / min through the inlet at the bottom of the furnace and discharged through the exhaust port above the ceiling. The gas flow continued until the heat treatment was completed. The heat treatment temperature was 300°C.

[0251] In this example, the first and second compositions, each composed of an oxide, were fluorinated, and a solid-phase reaction occurred while oxygen in each composition was replaced with fluorine, synthesizing the first and second halides. In this example, oxides were used as starting materials, meaning that titanium halide was not contained in the materials. Furthermore, the method of this example made it difficult to generate titanium halide during the synthesis process. Therefore, since no volatile components such as titanium halide were included, this example did not require a sealed container reaction, and 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 around 50°C to 100°C, and most (approximately 70%) would disappear by 200°C. Therefore, halides produced in conventional solid-phase synthesis have large compositional variations. Separating the first and second compositions and halogenating each, as in this example, is extremely effective in suppressing compositional variations.

[0252] Next, the first halide and the second halide were mixed in a molar ratio of 25:75, and the mixture was dry-mixed in a mortar for about 10 minutes to homogenize it, followed by a pulverization process (a step corresponding to (B) above). The pulverization process included a mechanochemical treatment. Specifically, a ball mill (volume: 1 L) lined with zirconia was loaded with zirconia balls (diameter: 15 mm), the first halide, and the second halide, and the mixture was pulverized for 20 hours. This resulted in the production of the halide solid electrolyte of Example 1.

[0253] 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.

[0254] <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 first halide and the second halide were mixed and homogenized and before and after the pulverization treatment. The halide solid electrolyte of Comparative Example 1 was also evaluated for its crystalline phase. The halide solid electrolyte of Example 1 was also analyzed for trace components.

[0255] (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.

[0256] FIG. 6A is a graph showing the X-ray diffraction pattern of the halide solid electrolyte obtained after mixing and homogenizing the first halide and the second halide in the manufacturing method of Example 1 and before the pulverization treatment. FIG. 6B is a graph showing the X-ray diffraction patterns of the halide solid electrolyte obtained in Example 1 after the pulverization treatment and the halide solid electrolyte obtained in Comparative Example 1. As shown in FIG. 6A, the halide solid electrolyte synthesized in Example 1 contained Li2TiF6 corresponding to the first crystalline phase and Li3AlF6 corresponding to the second crystalline phase. As shown in FIG. 6B, the halide solid electrolyte obtained in Example 1 after the pulverization treatment was confirmed to have the same crystalline quality as the halide solid electrolyte of Comparative Example 1 obtained by mechanochemical synthesis using fluoride as the starting material. Furthermore, no extraneous precipitated phase was observed in the halide solid electrolyte of Example 1.

[0257] (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 the measurement jig was offset and evaluated. For the halide solid electrolyte of Example 1, the ionic conductivity before the pulverization treatment was 0.81 μS / cm, and the ionic conductivity after the pulverization treatment was 5.7 μS / cm.

[0258] (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 -9This was a value that could be judged to have no electronic conductivity.

[0259] (Average Particle Diameter) The average particle diameter is the median diameter D50 value obtained from the volume particle size distribution measured using 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 the particle size distribution of the halide solid electrolyte was then 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 considered to be the average particle size. For the halide solid electrolyte of Example 1, the average particle diameter before pulverization was 0.88 μm, and the average particle diameter after pulverization was 0.65 μm.

[0260] (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 ​​2.63 m before pulverization. 2 / g, and the BET specific surface area after pulverization was 3.65 m 2 / g.

[0261] (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 K content was 0.03 at. %, and the Fe content was 0.003 at. %.

[0262] 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 5.7 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 -9 It was confirmed that the electrolyte had no electronic conductivity (i.e., negligible electronic conductivity) and was an ionically conductive solid electrolyte.

[0263] 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.

[0264] Furthermore, the amount of oxygen as an impurity in the halide solid electrolyte of Example 1 was 0.10 mass%, confirming that the 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 is 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 are 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 evaporates as titanium fluoride due to the open environment and disappears from the halide. As a result, the composition varies, and only a material having a lower ionic conductivity than that of Example 1 is obtained. In this case, a high heat treatment temperature of 500°C to 600°C is also required for synthesis.

[0265] 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.

[0266] 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) converting a first composition containing Li, Ti, and O into a first halide containing Li, Ti, and X1; and (B) synthesizing a halide solid electrolyte containing Li, Ti, M, X1, and X2 using the first halide obtained in (A) and a second halide containing Li, M, and X2. Here, M is at least one element selected from the group consisting of metal elements (excluding Li) and semimetal elements, X1 is at least one selected from the group consisting of F, Cl, Br, and I, and X2 is at least one 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 step (A) includes converting a second composition containing Li, M, and O into the second halide, and in the step (B), synthesizing the halide solid electrolyte using the first halide and the second halide obtained in the step (A).

3. The method for producing a halide solid electrolyte according to claim 1, wherein (B) includes mixing the first halide and the second halide.

4. The method for producing a halide solid electrolyte according to claim 1, wherein (B) includes heat treating the first halide and the second halide.

5. The method for producing a halide solid electrolyte according to claim 1, wherein (B) includes mechanochemically treating the first halide and the second halide.

6. The method for producing a halide solid electrolyte according to claim 1, wherein the first halide contains Li2TiX16, the second halide contains Li3MX26, and the halide solid electrolyte contains 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): Li2TiX16 Composition formula (2): Li3MX26 7. The method for producing a halide solid electrolyte according to claim 1, wherein M includes Al.

8. The method for producing a halide solid electrolyte according to claim 1, wherein at least one selected from the group consisting of X1 and X2 contains F.

9. The method for producing a halide solid electrolyte according to claim 2, wherein in (A), at least one selected from the group consisting of the following (I) and (II) is carried out: (I) the conversion of the first composition to the first halide is carried out by heat-treating a thermally decomposable first halogen-containing material; (II) the conversion of the second composition to the second halide is carried out by heat-treating a thermally decomposable second halogen-containing material.

10. The method for producing a halide solid electrolyte according to claim 9, wherein at least one selected from the group consisting of the first halogen-containing substance and the second halogen-containing substance is in particulate form.

11. The method for producing a halide solid electrolyte according to claim 9, wherein, when (I) is carried out in (A), (A) comprises: (A-1) mixing the first composition with the first halogen-containing substance; and (A-2) converting the first composition to the first halide by heat-treating the mixture containing the first composition and the first halogen-containing substance obtained in (A-1); and, when (II) is carried out in (A), (A) comprises: (A-3) mixing the second composition with the second halogen-containing substance; and (A-4) converting the second composition to the second halide by heat-treating the mixture containing the second composition and the second halogen-containing substance obtained in (A-3).

12. The method for producing a halide solid electrolyte according to claim 9, wherein, when (I) is carried out in (A), in (A), a first halogen gas is generated by heat-treating the first halogen-containing material, and the first composition is converted to the first halide by contacting the first halogen gas with the first composition; and when (II) is carried out in (A), in (A), a second halogen gas is generated by heat-treating the second halogen-containing material, and the second composition is converted to the second halide by contacting the second halogen gas with the second composition.

13. The method for producing a halide solid electrolyte according to claim 9, wherein at least one selected from the group consisting of the first halogen-containing substance and the second halogen-containing substance contains an ammonium salt.

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

15. The method for producing a halide solid electrolyte according to claim 9, wherein at least one selected from the group consisting of the first halogen-containing substance and the second halogen-containing substance includes a resin.

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

17. A method for producing a halide solid electrolyte as described in claim 9, wherein at least one selected from the group consisting of the first halogen-containing substance and the second halogen-containing substance contains a substance that causes the halide solid electrolyte to substantially not contain inorganic components, except for halogen elements, produced by thermal decomposition by the heat treatment in (A).

18. The method for producing a halide solid electrolyte according to claim 9, wherein at least one selected from the group consisting of the first halogen-containing substance and the second halogen-containing substance contains a plurality of types of halogen-containing compounds.

19. A halide solid electrolyte comprising Li, Ti, Al, and F, and further comprising at least one selected from the group consisting of K and Fe.

20. The halide solid electrolyte according to claim 19, which is substantially free of TiF4.

21. The halide solid electrolyte according to claim 19, wherein the halide solid electrolyte is in particulate form.

22. The halide solid electrolyte according to claim 19, wherein the halide solid electrolyte includes an amorphous phase.

23. The halide solid electrolyte according to claim 19, 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) No peak derived from TiF4 exists. (2) No peak derived from LiF exists. (3) No peak derived from AlF3 exists.

24. A positive electrode material comprising the halide solid electrolyte of claim 19.

25. A battery comprising a positive electrode comprising the positive electrode material of claim 24.

26. 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 19.

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