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

Abstract

A method for producing a solid electrolyte according to the present disclosure includes: (A) subjecting a starting material that contains a composite oxide containing Li and Ti to a fluorination treatment so as to obtain a solid electrolyte which contains a crystal phase that is represented by composition formula (1) Li2TiF6.　The solid electrolyte according to the present disclosure contains a crystal phase that is represented by composition formula (1) Li2TiF6, and does not substantially contain TiF4.

Description

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

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

[0002] Patent Document 1 discloses a method for producing a halide solid electrolyte such as a solid electrolyte represented by the composition LiYBrCl. Non-Patent Document 1 discloses a solid electrolyte represented by the composition LiYF and a method for producing the same.

[0003] International Publication No. 2020 / 136956

[0004] Thermochimica Acta 265 (1995) 189-195

[0005] 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.

[0006] The method for producing a solid electrolyte according to the present disclosure includes: (A) subjecting a raw material containing a composite oxide containing Li and Ti to a fluorination treatment to obtain a solid electrolyte containing a crystalline phase represented by the following composition formula (1): Composition formula (1): Li2TiF6

[0007] The present disclosure provides a novel production method that can stably synthesize a halide solid electrolyte having a desired composition.

[0008] FIG. 1 is a flowchart showing an example of a method for producing a solid electrolyte according to a first embodiment. FIG. 2 is a flowchart showing an example of a method for producing a solid electrolyte according to a second embodiment. FIG. 3 is a flowchart showing a modified example of the method for producing a solid electrolyte according to the second embodiment. FIG. 4 is a flowchart showing an example of a method for producing a solid electrolyte according to a third embodiment. FIG. 5 is a cross-sectional view of a battery 1000 according to a fourth embodiment. Graphs showing an X-ray diffraction pattern of a solid electrolyte after heat treatment (i.e., after fluorination) and before pulverization in the production method of Example 1 ((a) after fluorination), an X-ray diffraction pattern of a solid electrolyte after pulverization obtained in Example 1 ((b) after pulverization), and an X-ray diffraction pattern of a solid electrolyte obtained in Comparative Example 1 ((c) Comparative Example 1).

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0010] 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.

[0011] First Embodiment A method for producing a solid electrolyte according to a first embodiment will be described below.

[0012] The manufacturing method according to the first embodiment includes: (A) subjecting a raw material containing a composite oxide containing Li and Ti to a fluorination treatment to obtain a solid electrolyte containing a crystalline phase represented by the following composition formula (1): Composition formula (1): Li2TiF6

[0013] According to the manufacturing method of the first embodiment, a 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 solid electrolyte, titanium fluoride (e.g., TiF) is typically used as the Ti source. However, titanium fluoride is a relatively unstable substance, easily evaporating and exhibiting deliquescent properties. Therefore, the resulting solid electrolyte may experience compositional variations (i.e., compositional deviations) and alterations (e.g., inclusion of moisture, etc.). As a result, conventional manufacturing methods may have difficulty consistently producing the desired solid electrolyte. In contrast, the manufacturing method according to the first embodiment allows for the use of a composite oxide containing Li and Ti as the Ti source. Therefore, the manufacturing method according to the first embodiment can synthesize a solid electrolyte containing a crystalline phase represented by composition formula (1): LiTiF without using the unstable and expensive titanium fluoride as a raw material. Therefore, the manufacturing method according to the first embodiment is less likely to cause the aforementioned compositional variations and alterations in the resulting solid electrolyte, and can reproducibly and stably synthesize a solid electrolyte having the desired composition while suppressing the formation of secondary phases. Furthermore, according to the manufacturing method of the first embodiment, fluorides can be produced at lower temperatures than in conventional manufacturing methods that involve solid-phase reactions of fluoride raw materials, and therefore the raw materials and the produced solid electrolyte are less likely to be exposed to high temperatures. This prevents the produced solid electrolyte from sintering and becoming hard, and prevents excessive grain growth of the solid electrolyte, resulting in a soft, fine-particle solid electrolyte with excellent deformability. Such a fine-particle solid electrolyte with excellent deformability is likely to form an interface where particles adhere to each other when compacted, making it easier to increase density and form a thin layer, and can also be expected to have improved ionic conductivity. The hardness of the obtained solid electrolyte can be comparatively evaluated, for example, by a technique such as micro-Vickers measurement of particles or a compact.

[0015] For example, when Li2TiF6 synthesized by the manufacturing method according to the first embodiment is made into a powder compact at a certain pressure, the density of the powder compact is, for example, 2.15 g / cm 3 2.18g / cm or more 3The following can be shown: This shows that the density of the green compact can be achieved by using fluoride as a raw material and compacting Li2TiF6 obtained by solid-phase synthesis from fluoride at the same pressure. 3 2.13g / cm or more 3 Greater than:

[0016] Therefore, according to the manufacturing method of the first embodiment, a useful solid electrolyte can be obtained that, for example, when used in a solid electrolyte layer of a battery, can realize a thin solid electrolyte layer, or can be suitably used as a coating layer for active material particles. Therefore, the solid electrolyte manufactured by the manufacturing method of the first embodiment realizes a high-performance battery.

[0017] In the above (A), the fluorination treatment of the raw material may be carried out, for example, by heat treating a thermally decomposable fluorine-containing material.

[0018] By heat-treating a thermally decomposable fluorine-containing material to fluorinate a raw material containing a composite oxide containing Li and Ti, fluorination of the raw material and a solid-state reaction for synthesizing a solid electrolyte can occur simultaneously. Therefore, a solid electrolyte with homogeneous and excellent properties can be obtained in a short time while reducing reaction residues such as oxides. Furthermore, since the fluorination is performed by heat-treating a thermally decomposable fluorine-containing material, the reactivity (fluoridability) of the composite oxide contained in the raw material is good, and productivity is also excellent. Furthermore, for example, the temperature of the fluorination reaction and solid-state reaction of the raw material, as well as the progress of these reactions, can be controlled depending on the thermal decomposition temperature of the selected fluorine-containing material. Therefore, a desired solid electrolyte can be obtained.

[0019] When a thermally decomposable fluorine-containing substance is used in the fluorination treatment of the raw materials, in the production method according to the first embodiment, (A) above may include: (A-1) mixing the raw materials with the fluorine-containing substance; and (A-2) heat-treating the mixture containing the raw materials and the fluorine-containing substance obtained in (A-1) above, thereby fluorinating the raw materials to obtain a solid electrolyte.

[0020] In the production method according to the first embodiment, by carrying out the steps (A-1) and (A-2), a heat treatment for fluorination can be carried out on a homogeneous mixture of the raw material and the fluorine-containing material. Furthermore, the contact area between the raw material and the fluorine-containing material can be increased. This promotes homogeneous fluorination of the raw material, thereby enabling the production of a homogeneous solid electrolyte with excellent properties.

[0021] 1 is a flowchart showing an example of a method for producing a solid electrolyte according to Embodiment 1. Here, as an example of the production method according to Embodiment 1, an example of a production method in which the above (A-1) and (A-2) are carried out will be described.

[0022] As shown in FIG. 1, in one example of the manufacturing method according to the first embodiment, first, in a step corresponding to the above-mentioned (A-1), raw materials and a fluorine-containing substance are mixed (S11). As described above, the raw materials include a composite oxide containing Li and Ti. The fluorine-containing substance is thermally decomposable. Next, in a step corresponding to the above-mentioned (A-2), the obtained mixture containing the raw materials and the fluorine-containing substance is heat-treated to fluorinate the raw materials (S12). This results in a solid electrolyte containing a crystalline phase represented by composition formula (1): LiTiF.

[0023] The raw materials, the fluorine-containing material, and the steps corresponding to (A-1) and (A-2) above will be specifically described below.

[0024] <Raw Materials> The raw materials include a composite oxide containing Li and Ti.

[0025] By using a composite oxide containing Li and Ti as the Ti source, compositional fluctuations and alterations of the solid electrolyte to be produced can be suppressed, thereby enabling the production of a desired solid electrolyte with, for example, high ionic conductivity and reliability. According to the manufacturing method of the first embodiment, there is no need to use titanium oxide (e.g., TiO2) as the Ti source. Regardless of the crystal system (rutile, anatase), titanium oxide is likely to produce titanium fluoride (e.g., TiF4) during the fluorination process, which is prone to problems of evaporation and deliquescence. Therefore, the loss of Ti components during the synthesis process or the inclusion of water due to the deliquescence of titanium fluoride can lead to deviations from the desired composition. Therefore, titanium fluoride can sometimes cause a decrease in the ionic conductivity and reliability of the solid electrolyte. According to the manufacturing method of the first embodiment, since a composite oxide containing Li and Ti can be used as the Ti source, there is no need to use titanium oxide. Therefore, the compositional fluctuations and alterations of the solid electrolyte caused by the use of titanium oxide can be suppressed, allowing the stable production of a solid electrolyte with high ionic conductivity.

[0026] For the reasons mentioned above, it is desirable that the raw materials are substantially free of TiO. In this specification, "the raw materials are substantially free of TiO" means that the TiO content in the entire raw materials is 0.3 mass% or less.

[0027] The composite oxide containing Li and Ti is represented by, for example, the following composition formula (2): x Ti y O z

[0028] Here, in the composition formula (2), the following conditions are satisfied: 1.95≦x≦2.05, 0.95≦y≦1.05, and 2.95≦z≦3.05.

[0029] The above composition formula (2) Li x Ti y O z The composite oxide represented by the composition formula (2) Li is an oxide that is stable in the atmospheric environment. x Ti y Oz By using the composite oxide represented by the formula (1), a solid electrolyte containing a crystalline phase represented by the formula Li2TiF6 can be synthesized stably in an atmospheric environment with good reproducibility and good characteristics.

[0030] The composite oxide containing Li and Ti may be LiTiO. By using LiTiO as the composite oxide, a solid electrolyte containing a crystalline phase represented by composition formula (1): LiTiF can be produced stably and reproducibly in an air environment with good properties, and more efficiently.

[0031] Since the fluorination of the raw material proceeds from the surface, the raw material may be, for example, particulate. This facilitates simultaneous fluorination from the particle surface of the raw material (i.e., substitution of elemental fluorine with elemental oxygen) and solid-phase reaction in the raw material. Therefore, fluorides can be synthesized in a short time while reducing reaction residues such as oxides. This makes it possible to obtain a solid electrolyte that is homogeneous and has excellent properties. Furthermore, particulate raw materials have good reactivity, such as fluoridability and solid-phase reactivity, and therefore, excellent productivity can be achieved.

[0032] The composite oxide contained in the raw material may be in the form of particles, and the BET specific surface area of ​​the composite oxide is 1.0 m 2 / g or more and 30m 2 / g or less. A composite oxide having such a BET specific surface area is suitable for fluorination treatment. Therefore, by using a composite oxide having such a configuration as a raw material, fluorination (i.e., substitution of elemental fluorine with elemental oxygen) from the particle surface of the composite oxide and a solid-phase reaction tend to occur simultaneously. Therefore, it is possible to synthesize, for example, a fluoride having composition formula (1): Li2TiF6 in a short time while reducing reaction residues such as oxides. As a result, a solid electrolyte containing a crystalline phase represented by composition formula (1): Li2TiF6 can be synthesized in large quantities at low cost.

[0033] In order to more efficiently proceed with the fluorination treatment and more efficiently prepare a solid electrolyte, the BET specific surface area of ​​the composite oxide is 1.5 m 2 / g or more and 30m 2 / g or less, and 1.5m 2 / g or more and 10m 2 / g or less, and 2 / g or more and 10m 2 / g or less. For example, when the raw materials are wet-mixed, if it is difficult to disperse the composite oxide due to its large BET specific surface area, a dispersant may be used. In this case, the dispersant may be any known dispersant that can be used in producing a solid electrolyte.

[0034] The raw material may have, for example, an average particle size of 0.1 μm or more and 20 μm or less, or an average particle size of 0.5 μm or more and 20 μm or less. The average particle size of the complex oxide contained in the raw material may also be, for example, 0.1 μm or more and 20 μm or less, or 0.5 μm or more and 20 μm or less. The raw material may be further refined and may have, for example, an average particle size of 0.1 μm or more and 1.0 μm or less. The average particle size of the complex oxide contained in the raw material may also have, for example, an average particle size of 0.1 μm or more and 1.0 μm or less. However, the average particle sizes of the raw material and the complex oxide are not limited to the above ranges, and any particle size and shape can be appropriately selected from the viewpoints of fluorination and solid-phase reaction. For example, the smaller the particle sizes of the raw material and the complex oxide, the lower the temperature for conversion to fluoride can be.

[0035] The average particle diameters of the raw materials and the composite oxides are median diameters, which refer to particle diameters (d50) corresponding to 50% cumulative volume, determined from particle size distributions measured on a volume basis by a laser diffraction scattering method. The same applies to the average particle diameters of fluorine-containing materials specified in this specification.

[0036] The composite oxide can be, for example, a precursor of the crystalline phase represented by composition formula (1): Li2TiF6 contained in the target solid electrolyte produced by the production method according to the first embodiment. For example, in order to obtain a single phase of Li2TiF6, it is desirable that the composite oxide be a single phase of Li2TiO3, since it can be converted to a fluoride without precipitating any extraneous phases. For example, if XRD measurement of the composite oxide confirms that it is a single phase of Li2TiO3, then fluorination of the composite oxide can be performed to obtain a single phase of Li2TiF6 without producing TiF4.

[0037] The composite oxide used as the raw material may be synthesized in the production method according to the first embodiment.

[0038] For example, in the manufacturing method according to the first embodiment, (A) may include synthesizing the composite oxide using at least one selected from the group consisting of Li oxide, Li carbonate, and Li hydroxide, and at least one selected from the group consisting of Ti oxide, Ti carbonate, and Ti hydroxide. This manufacturing method allows the composite oxide to be synthesized using Li and Ti sources as raw materials that are more stable against air and moisture and less expensive than LiF and TiF. The composite oxide thus synthesized can be fluorinated to produce a crystalline phase represented by composition formula (1): LiTiF with high reproducibility and high quality. Furthermore, this manufacturing method can also reproducibly produce, for example, high-quality LiTiO controlled to a single phase. Therefore, this manufacturing method allows the synthesis of a solid electrolyte with excellent properties in an air environment with high reproducibility.

[0039] Hereinafter, with regard to the raw materials used in the synthesis of the above-mentioned composite oxides, at least one selected from the group consisting of Li oxide, Li carbonate, and Li hydroxide will be referred to as a Li raw material, and at least one selected from the group consisting of Ti oxide, Ti carbonate, and Ti hydroxide will be referred to as a Ti raw material.

[0040] The Li and Ti raw materials used in the synthesis of the composite oxide are, for example, particulate. The particle size and shape of the Li and Ti raw materials are arbitrary and are not particularly limited. To produce a composite oxide such as Li2TiO3 using a general oxide synthesis process, for example, the average particle size of the Li and Ti raw materials may be 0.1 μm or more and 20 μm or less for ease of handling. The particles of the Li and Ti raw materials may be spherical, elliptical, or aggregates of fine particles. Note that the general oxide synthesis process refers to a manufacturing process for ordinary ceramic materials. The synthesis of the composite oxide may be performed, for example, by a general solid-phase method.

[0041] The mixing of raw materials for synthesizing the composite oxide may be performed by dry mixing or wet mixing, and any mixing method capable of homogenizing the raw materials may be used. In wet mixing, a known general dispersant (such as an ammonium polycarboxylate or a nonionic surfactant) may be used to mix powders with small particle sizes, to achieve uniform mixing, and to increase the processing volume (i.e., to increase the solid content of the slurry). This allows the dispersion of fine powders (for example, powders with a BET specific surface area of ​​30 m) to be dispersed. 2 This makes it easy to handle even if the powder is in a powder form (about 1 / g), and enables uniform fluorination in the subsequent fluorination treatment.

[0042] The synthesized composite oxide may be pulverized after solid-phase synthesis, for example. The pulverization process can reduce the particle size of the composite oxide and expose the fractured surfaces of the particles pulverized by the pulverization process. The fractured surfaces of the particles are more active than the unfractured surfaces. Therefore, the reactivity of the composite oxide (i.e., reactivity in solid-phase reactions and fluorination reactions) can be increased by the pulverization process. Therefore, by pulverizing the composite oxide, the composite oxide can be converted into a highly reactive precursor material, thereby lowering the temperature for synthesizing the solid electrolyte and further achieving uniformity in the reaction. Therefore, the introduction of the pulverization process on the composite oxide may be appropriately adjusted in terms of the stability and characteristics of the synthesis of the composite oxide. The composite oxide may also be a mixture of pulverized powder and unpulverized powder. The fractured surface of the pulverized powder of the composite oxide can be observed from a different state from the free surface by scanning electron microscopy (SEM) of the composite oxide powder. The composite oxide used as the raw material can be an appropriate one, taking into consideration the stability and properties of the composite oxide and handling in the production process.

[0043] <Fluorine-containing substance> The fluorine-containing substance is thermally decomposable.

[0044] The thermal decomposition onset temperature of the fluorine-containing material used may be, for example, 100° C. or higher and 600° C. or lower. When the fluorine-containing material has a thermal decomposition onset temperature within the above temperature range, the fluorine-containing material has stability during storage and handling, such as mixing, and the obtained solid electrolyte can be prevented from becoming too hard.

[0045] The fluorine-containing material may be, for example, particulate. This facilitates thermal decomposition of the fluorine-containing material. Therefore, by using a particulate fluorine-containing material, the raw materials can be fluorinated efficiently and the fluorine-containing material is less likely to remain in the final solid electrolyte. Furthermore, the fluorination reaction can be controlled by the particle shape of the fluorine-containing material. For example, by making the particles of the fluorine-containing material finer, the fluorination temperature can be lowered and the fluorination rate can be increased. Furthermore, by mixing the raw materials and the fluorine-containing material, uniform fluorination of the entire powder is possible. Furthermore, precise control of the amount of fluorine is possible. Therefore, the desired solid electrolyte can be synthesized. Furthermore, since only the amount of fluorine-containing material required for fluorination of the raw materials can be used, unlike when fluorine gas is introduced into the furnace, excess fluorine gas emissions can be suppressed. This reduces the environmental impact and also reduces the impact on corrosion of furnace materials, etc.

[0046] The fluorine-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, the fluorine-containing material may have any particle size and shape.

[0047] The average particle size of the fluorine-containing material may be larger than the average particle size of the raw material. This results in a bulky, fluffy mixture of the raw material and the fluorine-containing material. This means that the surface exposed area (i.e., the exposed area) of the raw material is large, reducing the contact points between the raw material particles. The fluorine in the fluorine-containing material reacts with the raw material particles in a pyrolyzed gaseous state. This facilitates fluorination from the raw material particle surface, resulting in a homogeneous fluoride solid electrolyte. Furthermore, since the contact points between the raw material particles become discontinuous (i.e., the contact points between the raw material particles are reduced), after the fluorine-containing material decomposes and disappears, the necking between particles during the fluorination reaction and solid-state reaction is disrupted. Therefore, a solid electrolyte with fine particles can be synthesized. The average particle size of the fluorine-containing material may be 5 μm or more and 150 μm or less, 5 μm or more and 100 μm or less, 5 μm or more and 20 μm or less, 50 μm or more and 100 μm or less, 50 μm or more and 20 μm or less, or 80 μm or more and 150 μm or less. The average particle size of the fluorine-containing material can be appropriately adjusted taking into account the fluorination temperature or reactivity. For example, by increasing the average particle size of the fluorine-containing material, the heat treatment temperature for the fluorination treatment can be increased.

[0048] The fluorine-containing material may include ammonium fluoride (NH4F). Ammonium fluoride begins to thermally decompose at relatively low temperatures (e.g., about 150°C). Therefore, ammonium fluoride salt is less likely to remain as an unnecessary inorganic component in the final solid electrolyte, and can be thermally decomposed at low temperatures to fluorinate the raw material. Therefore, by using ammonium fluoride as the fluorine-containing material, it is possible to prevent unnecessary inorganic components from remaining in the final solid electrolyte. Furthermore, because ammonium fluoride can fluorinate the raw material at low temperatures (e.g., about 150°C), it is possible to synthesize a solid electrolyte without promoting grain growth and sintering. Therefore, a softer, finer solid electrolyte can be obtained compared to solid electrolytes obtained by solid-phase reaction from fluoride raw materials. Therefore, in the manufacturing method according to embodiment 1, by fluorinating the raw material using a fluorine-containing material, a solid electrolyte can be produced that can achieve a densified and thin-layered compact. When used in a solid electrolyte layer of a battery, the resulting solid electrolyte layer can be made thinner and have higher ionic conductivity. It can also be used as a coating layer for active material particles to achieve higher ionic conductivity of the electrode. Therefore, using the solid electrolyte produced by the production method of embodiment 1, a high-performance battery with improved conductivity and reliability can be obtained. Note that when a fluoride raw material is subjected to a solid-state reaction, it is difficult to produce a solid electrolyte containing a crystalline phase represented by composition formula (1): Li2TiF6 at low temperatures, for example, between 150°C and 600°C. A temperature exceeding 600°C (e.g., a temperature between 600°C and 800°C) is required. Therefore, when a fluoride raw material is subjected to a solid-state reaction, it is difficult to obtain a soft, fine solid electrolyte.

[0049] Furthermore, by using ammonium fluoride as the fluorine-containing material, energy saving in synthesis is achieved and the temperature rise and fall time is shortened, thereby improving productivity. Furthermore, since the solid electrolyte can be synthesized at low temperatures, the durability of the furnace material is improved and the running cost and replacement frequency of the synthesis components are significantly reduced. Only ammonium salt may be used as the fluorine-containing material.

[0050] The fluorine-containing material may include a resin. By including a resin as the fluorine-containing material, the fluorine-containing material can fluorinate the raw material 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 resin as the fluorine-containing material is suitable for performing the fluorination and solid-state reaction at a relatively high temperature (e.g., about 450°C or higher and 600°C or lower).

[0051] An example of a resin used as the fluorine-containing material is a fluororesin. For example, polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) can be used. Fluororesins such as PTFE and PVDF can fluorinate raw materials while being thermally decomposed at relatively high temperatures (e.g., about 400°C or higher and 600°C or lower). Therefore, a method using a fluororesin as the fluorine-containing material is suitable when fluorination and solid-state reaction are to be carried out at relatively high temperatures. For example, PVDF is suitable for fluorination at 400°C or higher, and PTFE is suitable for fluorination at 500°C or higher.

[0052] The fluorine-containing material may contain, for example, a substance that prevents inorganic components resulting from thermal decomposition by the heat treatment in (A) from being substantially contained in the solid electrolyte to be produced, except for elemental fluorine. The fluorine-containing material used in the fluorination treatment is required to replace the elemental fluorine produced by thermal decomposition by the heat treatment in (A) with elemental oxygen from the raw material, while preventing other components from being mixed as inorganic residues into the final solid electrolyte. By using a substance that prevents inorganic components resulting from thermal decomposition by the heat treatment from being substantially contained in the final solid electrolyte to be produced, except for elemental fluorine, as the fluorine-containing material, the mixing of inorganic residues into the solid electrolyte can be suppressed, and a desired solid electrolyte can be produced. Here, in this specification, the phrase "preventing inorganic components resulting from thermal decomposition by the heat treatment from being substantially contained in the solid electrolyte to be produced, except for elemental fluorine" means that the content of the inorganic components in the solid electrolyte is, for example, 0.5 mass % or less.

[0053] The fluorine-containing material may contain multiple types of fluorine-containing compounds. For example, by using multiple types of fluorine-containing compounds with different thermal decomposition properties or multiple types of fluorine-containing compounds with different particle sizes, the raw material can be appropriately fluorinated. For example, both ammonium fluoride and a fluororesin may be used as the fluorine-containing material. This allows the temperature range in which the fluorine-containing material acts as a fluorine source to be widely controlled, thereby allowing the conversion of the raw material to fluoride and the solid-state reaction temperature to be controlled over a wide range. This makes it easy to obtain a desired solid electrolyte.

[0054] The amount of the fluorine-containing material used is not particularly limited, as long as it is an amount sufficient to fluorinate the entire amount of the compound to be fluorinated.For example, when the molar amount of the fluorine-containing material for stoichiometrically fluorinating the entire compound in the reaction of fluorinating the compound to be fluorinated (i.e., a stoichiometrically equivalent molar amount, in other words, a molar amount necessary to completely replace the anion of the compound to be fluorinated with F anion) is taken as 100%, the amount of the fluorine-containing material 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.

[0055] <Regarding (A-1)> In (A-1), a raw material and a fluorine-containing substance are mixed. In mixing the raw material and the fluorine-containing substance, for example, a raw material containing a composite oxide containing Li and Ti and a thermally decomposable fluorine-containing substance are uniformly mixed.

[0056] In this way, by carrying out a preliminary step of uniformly mixing the raw material and the fluorine-containing substance before the fluorination treatment, the raw material can be uniformly converted into a fluoride, thereby synthesizing a homogeneous solid electrolyte.

[0057] In this preliminary step, a pulverization treatment may be performed to adjust the particle size of the fluorine-containing material. By pulverizing the mixed powder, the synthesis temperature of the solid electrolyte can be lowered, for example, by about 10 to 50°C. Therefore, sintering and grain growth of the solid electrolyte can be further suppressed, and a softer and finer solid electrolyte can be obtained.

[0058] For example, a raw material powder containing a composite oxide containing Li and Ti and a powder of a fluorine-containing material are mixed in a desired ratio. For example, it is sufficient to mix the raw material powder and the fluorine-containing material powder uniformly. 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. They may also be mixed using a medium such as zirconia balls and then pulverized as necessary. 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.

[0059] <Regarding (A-2)> In (A-2), the mixture containing the raw material obtained in (A-1) above and a fluorine-containing substance is heat-treated, thereby subjecting the raw material to a fluorination treatment.

[0060] 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 fluoride 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-shaped mass in which the powder has solidified.

[0061] In the heat treatment, the uniformly mixed mixture is placed in a heat-resistant alumina container (sheath), and the mixture is fired in a furnace under any atmosphere. For example, an inert gas such as nitrogen gas is flowed into the furnace, and gases generated during fluorination (e.g., ammonium, hydrogen chloride, carbon dioxide, etc.) are discharged. The mixture is then heat-treated in the furnace at a temperature of, for example, 200°C to 600°C for, for example, 1 hour to 40 hours, to synthesize a solid electrolyte containing a crystalline phase represented by composition formula (1): LiTiF. By introducing and discharging gas into the furnace in this way, unnecessary reactive gas components and the like are prevented from remaining in the furnace, i.e., in the solid electrolyte.

[0062] When introducing inert gas into the furnace, it is best to avoid direct contact of the inert gas with the sheath containing the mixture. Air may be introduced into the furnace instead of inert gas. A plate larger than the gas inlet is installed between the gas inlet and the sheath. The plate's thickness is sufficient as long as it is not damaged by the gas flow or handling. Partial shielding, such as by placing a plate such as an alumina plate against the sheath, is preferable. By shielding the space between the gas inlet and the sheath in this way, the gas flows around the shielding plate before contacting the sheath. By bypassing the gas and indirectly contacting the sheath in this way, the temperature is lower in the areas directly exposed to the gas, reducing the problem of temperature distribution within the sheath. This suppresses unevenness (i.e., variability) in the progress of the raw material fluorination reaction and the solid-state reaction to synthesize the solid electrolyte.

[0063] 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 (from bottom to top) inside the furnace, reducing the contamination of the solid electrolyte with unwanted residual components.

[0064] 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 solid electrolyte synthesis reaction to proceed uniformly, resulting in a more homogeneous solid electrolyte.

[0065] The heat treatment temperature is, for example, 200°C or higher and 600°C or lower, as described above. The heat treatment time is, for example, 1 hour or higher and 40 hours or lower, as described above. Lowering the heat treatment temperature and shortening the treatment time prevents sintering and grain growth of the solid electrolyte, resulting in a solid electrolyte composed of soft, fine particles. This manufacturing process allows for the production of a solid electrolyte capable of forming a dense, compacted powder with excellent ionic conductivity. The heat treatment temperature and time can be determined arbitrarily, taking into consideration the properties of the raw materials (e.g., crystal system and powder characteristics), the properties of the solid electrolyte to be synthesized (e.g., crystal system and powder characteristics), the temperature and time required to synthesize a solid electrolyte containing a crystalline phase represented by composition formula (1): LiTiF, the time required for synthesis, and the time required for exhausting the reaction gas.

[0066] 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.

[0067] 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.

[0068] Since this heat treatment is not intended to react easily volatile materials such as titanium fluoride, it is not necessary to perform the heat treatment in a sealed container. The mixture of raw materials and fluorine-containing materials may be placed in a sheath, and if necessary, a lid (e.g., an alumina lid) may be placed on the sheath to prevent dust and foreign matter from falling in. Therefore, unlike conventional heat treatments using fluoride raw materials (i.e., heat treatments for solid-phase reactions of fluoride raw materials) that are limited in throughput by the size of sealed heat treatment jigs, the heat treatment in the manufacturing method according to the first embodiment offers excellent productivity and workability, making it highly valuable for industrial applications. The manufacturing method according to the first embodiment, with its excellent productivity, can produce a solid electrolyte containing a crystalline phase represented by the composition formula (1): Li2TiF6, which has excellent ionic conductivity and stability (e.g., electrochemical stability and heat resistance). Note that if the raw materials contain trace amounts of titanium oxide as impurities, trace amounts of titanium fluoride (e.g., TiF4) may be generated. However, when the heat treatment is performed in an open atmosphere, such a small amount of titanium fluoride evaporates and disappears, so even in such a case, a titanium fluoride-free solid electrolyte with excellent properties and reliability can be obtained.

[0069] 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 raw materials, fluorine-containing material, and solid electrolyte 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 as the sheath material. Various shapes, such as cylindrical, prismatic, and gourd-shaped, can be used for the sheath.

[0070] 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.

[0071] As an example of the manufacturing method according to the first embodiment, a method in which the above (A-1) and (A-2) are carried out has been described in detail, but the step of uniformly mixing the raw material and the fluorine-containing material before the fluorination treatment does not necessarily have to be carried out. For example, the fluorine-containing material may be added to the raw material and heat-treated without sufficient mixing. Furthermore, while heat treatment is desirable for efficient fluorination treatment, the raw material may be fluorinated by, for example, adding the fluorine-containing material to the raw material and then leaving it at room temperature for a long period of time.

[0072] The surface of a solid electrolyte synthesized by fluorination treatment and not subsequently subjected to a pulverization treatment, as in the manufacturing method according to the second embodiment described below, is a free surface. This free surface is not a highly reactive active surface that is exposed after pulverization, and therefore has high surface stability. Such a solid electrolyte is stable and has particularly excellent environmental resistance (storage characteristics). Therefore, depending on the application and needs, such as performing a pulverization treatment after long-term storage, the pulverization step after fluorination can be omitted or added as appropriate.

[0073] In the manufacturing method according to the first embodiment, additives may be added to the raw materials as needed before the fluorination treatment. For example, additives for accelerating the fluorination reaction of the raw materials, additives for accelerating the solid-state reaction of the raw materials, etc. may be added. When a composite oxide containing Li and Ti used as a raw material is synthesized using the manufacturing method according to the first embodiment, the additives may be added when the composite oxide containing Li and Ti used as a raw material is synthesized. Examples of such additives include oxides containing at least one element selected from the group consisting of Zn, Mg, Nb, P, Ga, K, Na, Ca, Fe, Si, and Cu. For example, when added in trace amounts to the raw materials, Zn oxide, Mg oxide, Nb oxide, and P oxide can lower the reaction temperature of the fluorination reaction and solid-state reaction by, for example, about 10 to 20°C, or can improve the reactivity of the fluorination reaction and solid-state reaction. This can accelerate the fluorination reaction and solid-state reaction of the raw materials. Two or more selected from the group consisting of Zn oxide, Mg oxide, Nb oxide, and P oxide may be added together, or only one selected from the group consisting of Zn oxide, Mg oxide, Nb oxide, and P oxide may be added. P can also be diluted with an aqueous phosphoric acid solution and added. This allows for accurate addition of trace amounts, and in the case of wet mixing, P can also be uniformly dispersed. The amount of additive added is not particularly limited and can be appropriately selected depending on the compound to be added and its purpose. For example, when Zn oxide, Mg oxide, Nb oxide, and P oxide are added for the purpose of promoting the fluorination reaction and the solid-state reaction, the total amount of Zn oxide, Mg oxide, Nb oxide, and P oxide added may be, for example, 0.001 mol % or more and 0.3 mol % or less relative to the raw material.

[0074] Additives such as Zn oxide, Mg oxide, Nb oxide, and P oxide may be in particulate form, for example. The effect of the additive may vary depending on the particle form of the additive and the state of dispersion in the raw material. For Zn oxide, Mg oxide, Nb oxide, and P oxide, the smaller the particle size, the greater the additive's effect, such as reaction promotion. For example, the particle size of the additive may be smaller than that of the composite oxide particles constituting the raw material. As an example, the additive may have a particle size of 0.1 μm or less and a BET value of 100 m. 2 / g or more. Note that using coarse particles or adding excessive amounts of Zn oxide, Mg oxide, Nb oxide, and P oxide may generate extra precipitated phases other than the solid electrolyte, reducing ionic conductivity. Therefore, it is desirable to adjust the particle size and amount to an appropriate level. Zn, Mg, Nb, and P derived from the Zn oxide, Mg oxide, Nb oxide, and P oxide added as additives act, for example, as auxiliary agents for conversion to fluorides and solid-state reactions, and are incorporated into the solid electrolyte. For example, it is desirable to adjust the particle size and amount of Zn oxide, Mg oxide, Nb oxide, and P oxide so that Zn, Mg, Nb, and P are not detected as composition phases in X-ray diffraction measurement of the final solid electrolyte. This allows the synthesis of a solid electrolyte with high ionic conductivity while achieving a reaction-accelerating effect.

[0075] In the manufacturing method according to the first embodiment, when at least one selected from the group consisting of Zn oxide, Mg oxide, Nb oxide, and P oxide is used as the additive, the resulting solid electrolyte contains at least one selected from the group consisting of Zn, Mg, Nb, and P. That is, in this case, the solid electrolyte obtained by the manufacturing method according to the first embodiment contains a crystalline phase represented by composition formula (1): LiTiF, and further contains at least one selected from the group consisting of Zn, Mg, Nb, and P. This configuration allows for the production of a homogeneous solid electrolyte with excellent ionic conductivity.

[0076] The amount of oxygen as an impurity in the solid electrolyte obtained by the manufacturing method according to the first embodiment may be 0.5% by mass or less. The manufacturing method according to the first embodiment makes it possible to obtain a solid electrolyte with little oxygen contamination. The amount of oxygen as an impurity in the solid electrolyte may be, for example, 0.1% by mass or more.

[0077] As described above, when at least one selected from the group consisting of Zn oxide, Mg oxide, Nb oxide, and P oxide is added as an additive to promote the reaction of raw materials, Zn, Mg, Nb, and P may not be detected as a composition phase in X-ray diffraction measurement. Even in this case, the presence of Zn, Mg, Nb, and P in the solid electrolyte can be confirmed by highly sensitive composition analysis (area analysis, etc.) such as an electron probe microanalyzer (EPMA). The total content of Zn, Mg, Nb, and P contained in the solid electrolyte may be, for example, 0.0003 at. % or more and 0.3 at. % or less. The content of Zn, Mg, Nb, and P can be determined using EPMA or the like.

[0078] The solid electrolyte obtained by the manufacturing method according to the first embodiment preferably does not substantially contain TiF4.

[0079] The solid electrolyte obtained by the manufacturing method according to the first embodiment may be a solid electrolyte containing a crystalline phase represented by composition formula (1): LiTiF, but substantially free of TiF. Here, "solid electrolyte substantially free of TiF" means that the TiF content in the solid electrolyte is, for example, 0.5% by mass or less, preferably 0.1% by mass or less. The TiF content in the 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 powder of a halogenated solid electrolyte or the particle surface of the solid electrolyte, and the TiF content can be determined from the area ratio of the detected TiF portion. This configuration can suppress changes over time in the characteristics and mechanical properties of the solid electrolyte due to evaporation and deliquescence of TiF, thereby achieving a solid electrolyte with excellent ionic conductivity and reliability. If the raw materials for the solid electrolyte contain a small amount of titanium oxide (TiO), a small amount of TiF may be generated during the fluorination process. However, even in this case, the fluorination process is performed in an open atmosphere, allowing the TiF to evaporate and disappear. This allows for the production of a solid electrolyte that is substantially free of TiF and has excellent properties and reliability.

[0080] The solid electrolyte obtained by the manufacturing method according to the first embodiment may be substantially free of TiF and may be composed of a single crystalline phase represented by composition formula (1): Li2TiF6. The fact that the solid electrolyte obtained by the manufacturing method according to the first embodiment is composed of a single crystalline phase represented by composition formula (1): Li2TiF6 can be confirmed by an 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 presence of only peaks derived from Li2TiF6 in the X-ray diffraction pattern, and the absence of peaks derived from other crystalline phases. Here, in the present disclosure, a peak in an X-ray diffraction pattern is defined as the angle showing the maximum intensity of a mountain-shaped portion having an S / N ratio (i.e., the ratio of signal S to background noise N) of 1.3 or greater and a half-width of 10° or less. The half-width is the maximum intensity of the X-ray diffraction peak. MAX When the intensity is I MAX A peak whose half-width exceeds 5° is considered to be non-existent.

[0081] As described above, when at least one selected from the group consisting of Zn oxide, Mg oxide, Nb oxide, and P oxide is used as an additive in the production method according to the first embodiment, the resulting solid electrolyte contains a crystalline phase represented by composition formula (1): LiTiF, and further contains at least one selected from the group consisting of Zn, Mg, Nb, and P. It is desirable that such a solid electrolyte also be substantially free of TiF.

[0082] The solid electrolyte obtained by the manufacturing method according to the first embodiment may be in a particulate form. This configuration allows for the realization of a relatively soft, particulate solid electrolyte. A compact of such a solid electrolyte has high ionic conductivity, excellent stability, and can have any desired shape. A compact of a solid electrolyte having such properties can thus be used to form a solid electrolyte layer or a coating layer of active material particles in a battery with excellent properties and high reliability. The solid electrolyte obtained by the manufacturing method according to the first embodiment thus allows for the realization of a high-performance, highly reliable battery. The size and shape of the solid electrolyte particles can be appropriately selected depending on the application.

[0083] The solid electrolyte obtained by the manufacturing method according to the first embodiment includes a crystalline phase represented by composition formula (1): Li2TiF6. This crystalline phase includes, for example, a first crystalline phase belonging to a tetragonal system. This configuration allows for a solid electrolyte having high ionic conductivity. Furthermore, since the solid electrolyte can be heat-resistant at approximately 250°C to 300°C, a highly reliable battery can be obtained. The solid electrolyte obtained by the manufacturing method according to the first embodiment may further include a second crystalline phase having a crystal system different from that of the first crystalline phase.

[0084] The solid electrolyte obtained by the manufacturing method according to the first embodiment may contain an amorphous phase. This configuration makes the amorphous portion of the solid electrolyte softer, more deformable, and improves the bonding between particles. Therefore, a compact of the solid electrolyte can be formed into a solid electrolyte layer of any shape with higher ionic conductivity and higher stability. Therefore, when the solid electrolyte contains an amorphous phase, the compact of the solid electrolyte can realize a solid electrolyte layer or a coating layer of active material particles for a battery with excellent characteristics and high reliability. As a result, a battery with high performance and high reliability is realized.

[0085] Comparing the manufacturing method according to the first embodiment with the manufacturing methods described in Patent Document 1 and Non-Patent Document 1, there are the following differences.

[0086] Patent Document 1 discloses a halide solid electrolyte such as LiYBrCl and a method for producing the same. This halide solid electrolyte, such as LiYBrCl, is synthesized from raw materials containing a simple oxide YO and further containing NHCl and LiBr. Unlike the method using a composite oxide, such as the method for producing a solid electrolyte according to the first embodiment, the method disclosed in Patent Document 1 uses a simple oxide (i.e., an oxide containing one type of cation) and multiple simple halides (i.e., halides containing one type of cation) to synthesize a halide containing multiple cations. The halogenation conditions (i.e., halogenation behavior) differ for each simple oxide and simple halide. In other words, the reaction involves a collection of substances with different halogenation conditions. This results in a complex reaction path, which tends to leave intermediate products generated during the reaction, making it difficult to obtain a solid electrolyte with the desired composition.

[0087] Furthermore, Non-Patent Document 1 discloses a solid electrolyte represented by the composition LiYF4 and a method for producing the same. LiYF4 is synthesized by a solid-state reaction using Li2CO3, YO3, and NH4F. Li2CO3 and YO3 have different halogenation behaviors, and this method also has the same problems as the method described in Patent Document 1.

[0088] The method for producing a solid electrolyte according to the first embodiment solves the above-mentioned problems of the production methods described in Patent Document 1 and Non-Patent Document 1, and is a synthesis method that uses a precursor oxide containing multiple cations (e.g., Li2TiO3) as a raw material and converts the precursor oxide into a fluoride. Therefore, the production method according to the first embodiment is clearly different from the production methods disclosed in Patent Document 1 and Non-Patent Document 1, and can stably synthesize a halide solid electrolyte having a target composition.

[0089] Second Embodiment A method for producing a solid electrolyte according to a second embodiment will now be described.

[0090] The production method according to the second embodiment further includes, after the step (A) in the production method according to the first embodiment, the step (B) of subjecting the solid electrolyte obtained in the step (A) to a pulverization treatment.

[0091] According to the manufacturing method of the second embodiment, by carrying out the pulverization treatment (B) above, a solid electrolyte having excellent ionic conductivity and reliability can be obtained with powder characteristics (e.g., particle shape, particle size, etc.) suitable for the application. Furthermore, since at least a portion of the solid electrolyte can be made amorphous, it is possible to improve the ionic conductivity and the softness of the solid electrolyte particles. By improving the softness of the solid electrolyte particles, it is possible to improve the density of the solid electrolyte powder compact. Therefore, the solid electrolyte obtained by the manufacturing method of the second embodiment can form a dense powder compact with high ionic conductivity.

[0092] 2 is a flowchart showing an example of a method for producing a solid electrolyte according to the second embodiment. Here, an example of a production method will be described in which, in the production method described in the first embodiment, (A) is performed as (A-1) and (A-2), and (B) is performed after (A-2).

[0093] As shown in Fig. 2, first, raw materials and a fluorine-containing substance are mixed (S21). Next, the resulting mixture containing the raw materials and the fluorine-containing substance is heat-treated to fluorinate the raw materials (S22). This results in a solid electrolyte containing a crystalline phase represented by composition formula (1): LiTiF. Next, as a step corresponding to (B) above, the solid electrolyte obtained in S22 is subjected to a pulverization treatment (S23).

[0094] S21 and S22 are the same as S11 and S12 described in the first embodiment, respectively, and therefore detailed description thereof will be omitted here.

[0095] The solid electrolyte synthesized by the above (A) has an average particle size of, for example, about 3 μm or more and 20 μm or less. In the above (B), the solid electrolyte synthesized by the above (A) is pulverized to, for example, an average particle size of, for example, about 0.1 μm or more and 2 μm or less.

[0096] The solid electrolyte pulverized in (A) above has a BET specific surface area of, for example, 2.0 m 2 / g or more 30m 2 / g or less. Such a solid electrolyte has excellent ionic conductivity, excellent stability in the atmosphere, and is soft and therefore deformable, and can be pulverized. Therefore, since it has , it is useful for a solid electrolyte layer, a composite component of an active material layer, and a coating layer of active material particles. Therefore, it realizes high performance and high reliability of a battery. The solid electrolyte pulverized in (B) above has, for example, a BET specific surface area of ​​4.0 m 2 / g or more 150m 2 It contains fine particles of less than 1 / g.

[0097] 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 fluoride to a desired particle size. For example, zirconia balls (e.g., balls with a diameter of 1 mm to 30 mm) and the solid electrolyte obtained in (A) above are placed in a ball mill container, and pulverization is performed for, for example, about 4 hours to 80 hours. The ball mill container may be, for example, a polyethylene container, or a container lined with fluororesin or zirconia.

[0098] The pulverization treatment in (B) above may include, for example, mechanochemical treatment. The mechanochemical treatment here is carried out to introduce distorted crystallinity or amorphousness into the crystals of the solid electrolyte. The distorted crystallinity or amorphousness is mainly introduced into the surface layer of the solid electrolyte particles. The specific means may be the same as those used in the pulverization treatment described above, for example, a ball mill. However, the pulverization conditions may be strengthened or the pulverization time may be extended. The equipment and media used for the mechanochemical treatment may be the same as those used in the pulverization treatment. Generally, pulverization and mechanochemical treatment proceed simultaneously. As an example, in the case of a dry method, a ball mill container lined with zirconia is used, and zirconia balls are placed in a volume ratio of 10% to 60% of the container, and pulverization and mechanochemical milling are performed simultaneously. The diameter of the zirconia balls is not particularly limited, and any size can be used. As mentioned above, commercially available balls with a diameter of 1 mm to 30 mm are usually used, but balls with a smaller or larger diameter may also be used. The diameter of the balls used may be selected as desired depending on the desired particle size or degree of amorphization. Furthermore, to prevent the solid electrolyte from adhering to the zirconia balls or the inner wall of the zirconia container, an appropriate amount of an additive, such as ethanol, that does not adversely affect the properties of the solid electrolyte may be added. It is preferable that the additive can be removed by drying later.

[0099] The introduction of amorphousness into the solid electrolyte can be confirmed by the X-ray diffraction pattern obtained by X-ray diffraction measurement. The X-ray diffraction pattern can be measured by the θ-2θ method using Cu-Kα radiation (wavelengths 1.5405 Å and 1.5444 Å) as the X-ray source. Specifically, this can be confirmed by the fact that the peaks in the X-ray diffraction pattern of the solid electrolyte after the pulverization treatment are broadened compared to the peaks in the X-ray diffraction pattern of the solid electrolyte before the pulverization treatment. The broadened peaks mean that the peaks are broadened and the half-width is widened.

[0100] The introduction of distorted crystals into the 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.

[0101] The change in deformability due to amorphization can be evaluated by an evaluation method such as micro-Vickers.

[0102] As described above, since the manufacturing method according to the second embodiment includes a pulverization process, the 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 solid electrolyte softer and more deformable. Therefore, a compact of the 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 solid electrolyte including an amorphous phase can realize a solid electrolyte layer of a battery with excellent characteristics and high reliability.

[0103] As a modification of the manufacturing method according to the second embodiment, the solid electrolyte may be made into a slurry for forming a coating film simultaneously with the pulverization treatment in (B) above.

[0104] 3 is a flowchart showing a modified example of the method for producing a solid electrolyte according to the second embodiment. Regarding the modified example of the production method according to the second embodiment, an example of a production method will be described here, in which (A-1) and (A-2) are carried out as (A), which is an example of the production method described in the first embodiment, and (B) is carried out after (A-2).

[0105] As shown in Fig. 3, first, raw materials and a fluorine-containing substance are mixed (S31). Next, the resulting mixture containing the raw materials and the fluorine-containing substance is heat-treated to fluorinate the raw materials (S32). This results in a solid electrolyte containing a crystalline phase represented by composition formula (1): LiTiF. Next, as a step corresponding to (B) above, the solid electrolyte obtained in S32 is subjected to a pulverization treatment and a slurry treatment (S33).

[0106] S31 and S32 are the same as S11 and S12 described in the first embodiment, respectively, and therefore detailed description thereof will be omitted here.

[0107] The pulverization process in S33 is the same as the pulverization process in S23 described as an example of the manufacturing method of the second embodiment. In a modified example of the manufacturing method of the second embodiment, a slurrying process is further performed. The slurrying process is performed, for example, by adding an organic binder, a plasticizer, etc., dispersed in an organic solvent such as tetralin to the solid electrolyte simultaneously with the pulverization process. An example of the organic binder is styrene butadiene block copolymer (SBS). An example of the plasticizer is bisbutyl phthalate (DBP) and butyl benzyl phthalate (BBP).

[0108] The obtained solid electrolyte slurry can be used for printing or coating. The thickness of the coating film can be, for example, 10 μm or more and 100 μm or less, which allows, for example, a solid electrolyte slurry that has been pulverized to contain amorphous portions to be directly coated. In this way, an organic binder, a plasticizer, etc. may be added in the pulverization process to prepare a solid electrolyte slurry, and the slurry may be used to form a coating film. This allows the formation of a solid electrolyte coating film with excellent properties. Such a coating film can be used, for example, in the manufacture of a coated cell.

[0109] Third Embodiment A method for producing a solid electrolyte according to a third embodiment will now be described.

[0110] In the production method according to the third embodiment, in the step (A) described in the first embodiment, a fluorine-containing material is heat-treated to generate fluorine gas, and the raw material is brought into contact with the fluorine gas, thereby subjecting the raw material to a fluorination treatment. In the production method according to the third embodiment, the grinding treatment in the step (B) described in the second embodiment may be carried out after the step (A).

[0111] 4 is a flowchart showing an example of a method for producing a solid electrolyte according to the third embodiment. As shown in FIG. 4, a raw material containing a composite oxide containing Li and Ti is prepared (S41). Next, the raw material and a fluorine-containing material are placed in a predetermined position, and the fluorine-containing material is heat-treated to bring the generated fluorine gas into contact with the raw material (S42). This results in a fluorination treatment of the raw material. Thereafter, as a step corresponding to (B) above, the solid electrolyte obtained in S42 may be subjected to a pulverization treatment (S43).

[0112] According to the manufacturing method of the third embodiment, the raw materials can be fluorinated by the generated fluorine gas without directly contacting the raw materials with the fluorine-containing material. Therefore, even if a fluorine-containing material containing inorganic components in addition to elemental fluorine (e.g., a substance that is emitted as fluorine gas when heated, such as CuF) is used, it is not necessary to consider inorganic residues in the produced solid electrolyte. This allows for a wider range of usable fluorine-containing materials.

[0113] As a specific example, the raw material is placed on a fine-mesh nickel mesh, and a fluorine-containing material such as ammonium fluoride is placed below the nickel mesh. In this way, the raw material and the fluorine-containing material are placed without contacting each other. In this state, heat treatment of the fluorine-containing material generates fluorine gas, which passes through the nickel mesh and comes into contact with the raw material. This converts the raw material to a fluoride. The raw material and the fluorine-containing material are as described in the first embodiment. Note that while 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.

[0114] [Fourth Embodiment] A fourth embodiment will be described below. Matters described in the first, second, and third embodiments will be omitted as appropriate.

[0115] 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.

[0116] At least one selected from the group consisting of the positive electrode, the electrolyte layer, and the negative electrode includes a solid electrolyte containing a crystalline phase represented by composition formula (1): Li2TiF6 and substantially no TiF4, or a solid electrolyte containing a crystalline phase represented by composition formula (1): Li2TiF6 and further containing at least one element selected from the group consisting of Zn, Mg, Nb, and P. The solid electrolyte can be produced by, for example, the production method according to the first, second, or third embodiment.

[0117] Hereinafter, a solid electrolyte included in the battery according to the fourth embodiment, which includes a crystalline phase represented by composition formula (1): Li2TiF6 and is substantially free of TiF4, or a solid electrolyte which includes a crystalline phase represented by composition formula (1): Li2TiF6 and further includes at least one element selected from the group consisting of Zn, Mg, Nb, and P, will be referred to as a solid electrolyte according to the fourth embodiment.

[0118] The solid electrolyte according to the fourth embodiment is described in the first, second, or third embodiment as an example of a solid electrolyte that can be manufactured by, for example, the manufacturing method according to the first, second, or third embodiment. The solid electrolyte according to the fourth embodiment may be in a particulate form. Furthermore, the solid electrolyte according to the fourth embodiment may include an amorphous phase, as described in the second embodiment.

[0119] The battery according to the fourth embodiment has excellent charge / discharge characteristics because it contains the solid electrolyte according to the fourth embodiment.

[0120] FIG. 5 shows a cross-sectional view of a battery 1000 according to a fourth embodiment.

[0121] 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.

[0122] The positive electrode 201 may include a positive electrode material including a halide electrolyte according to the fourth embodiment. The positive electrode 201 includes a positive electrode active material 204 and a solid electrolyte 100.

[0123] The electrolyte layer 202 contains an electrolyte material.

[0124] The negative electrode 203 contains a negative electrode active material 205 and a solid electrolyte 100 .

[0125] The solid electrolyte 100 includes, for example, the solid electrolyte according to the fourth embodiment. The solid electrolyte 100 may be particles containing the solid electrolyte according to the fourth embodiment as a main component. Particles containing the 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 solid electrolyte according to the fourth embodiment. The solid electrolyte 100 may be particles made of the solid electrolyte according to the fourth embodiment.

[0126] 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.

[0127] 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.

[0128] In the present disclosure, "(A, B, C)" means "at least one selected from the group consisting of A, B, and C."

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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 solid electrolyte. When the solid electrolyte 100 contains a sulfide solid electrolyte, the coating material may contain the solid electrolyte according to the fourth embodiment to suppress oxidative decomposition of the sulfide solid electrolyte. When the solid electrolyte 100 contains the 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.

[0133] As described above, when the positive electrode 201 includes a positive electrode material including the solid electrolyte according to the fourth embodiment, the positive electrode material may include the solid electrolyte according to the fourth embodiment as the solid electrolyte 100, or may include the solid electrolyte according to the fourth embodiment as a coating material that coats the positive electrode active material 204.

[0134] 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.

[0135] The electrolyte layer 202 contains an electrolyte material. The electrolyte material is, for example, a solid electrolyte. The solid electrolyte may include the solid electrolyte according to the fourth embodiment. The electrolyte layer 202 may be a solid electrolyte layer.

[0136] The electrolyte layer 202 may contain 50 mass % or more of the solid electrolyte according to the fourth embodiment. The electrolyte layer 202 may contain 70 mass % or more of the solid electrolyte according to the fourth embodiment. The electrolyte layer 202 may contain 90 mass % or more of the solid electrolyte according to the fourth embodiment. The electrolyte layer 202 may be made of only the solid electrolyte according to the fourth embodiment.

[0137] Hereinafter, the 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.

[0138] 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.

[0139] 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.

[0140] The electrolyte layer 202 may consist of only the second solid electrolyte.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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 a high output.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] The second solid electrolyte may be a sulfide solid electrolyte.

[0153] 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.

[0154] When the electrolyte layer 202 contains the first solid electrolyte, the negative electrode 203 may contain a sulfide solid electrolyte to suppress reductive decomposition of the solid electrolyte. The electrochemically stable sulfide solid electrolyte covers the negative electrode active material, thereby preventing the first solid electrolyte from contacting the negative electrode active material. As a result, the internal resistance of the battery 1000 can be reduced.

[0155] The second solid electrolyte may be an oxide solid electrolyte.

[0156] 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.

[0157] As mentioned above, the second solid electrolyte may be a halide solid electrolyte.

[0158] 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.

[0159] 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).

[0160] 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.

[0161] The halide solid electrolyte is Li3YCl 6 Or it may be Li3YBr6.

[0162] The second solid electrolyte may be an organic polymer solid electrolyte.

[0163] An example of the organic polymer solid electrolyte is a compound of a polymer compound and a lithium salt.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.

[0168] 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.

[0169] Examples of lithium salts include LiPF, LiBF, LiSbF, LiAsF, LiSOCF, LiN(SOCF), LiN(SOCF), LiN(SOCF)(SOCF), or LiC(SOCF). A single lithium salt selected from these may be used alone. Alternatively, a mixture of two or more lithium salts selected from these may be used. The concentration of the lithium salt is, for example, in the range of 0.5 mol / L or more and 2 mol / L or less.

[0170] 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.

[0171] 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.

[0172] 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.

[0173] The ionic liquid may contain a lithium salt.

[0174] 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.

[0175] 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. Mixtures of two or more materials selected from these may also be used as binders.

[0176] At least one selected from the positive electrode 201 and the negative electrode 203 may contain a conductive additive to improve electronic conductivity.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] [Other Embodiments] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0181] (Technology 1) A method for producing a solid electrolyte, comprising: (A) subjecting a raw material containing a composite oxide containing Li and Ti to a fluorination treatment to obtain a solid electrolyte containing a crystalline phase represented by the following composition formula (1): Composition formula (1): Li2TiF6

[0182] Titanium fluoride (TiF4) is a relatively unstable substance, due to its tendency to evaporate and its deliquescent nature. Furthermore, titanium fluoride is a very expensive substance. According to the manufacturing method of Technology 1, a composite oxide containing Li and Ti can be used as the Ti source. Therefore, according to the manufacturing method of Technology 1, a solid electrolyte containing a crystalline phase represented by the composition formula (1): Li2TiF6 can be reproducibly and stably synthesized without using the unstable and expensive titanium fluoride as a raw material. Furthermore, according to the manufacturing method of Technology 1, a dry room with a controlled dew point is not required. Therefore, according to the manufacturing method of Technology 1, for example, a solid electrolyte with excellent properties such as ionic conductivity can be reproducibly and stably produced at low cost, with reduced compositional variation (i.e., composition deviation), alteration (e.g., inclusion of moisture, etc.), and secondary phase formation. Furthermore, according to the manufacturing method of Technology 1, fluorides are produced at lower temperatures than in conventional manufacturing methods, and therefore the raw materials and the produced solid electrolyte are less likely to be exposed to high temperatures. This prevents the solid electrolyte from sintering and becoming hard, and prevents excessive grain growth of the solid electrolyte, resulting in a soft, highly deformable, fine-particle solid electrolyte. Such a highly deformable, fine-particle solid electrolyte is likely to form an interface where particles adhere to each other when compacted. More specifically, contact between particles that are difficult to deform forms a point contact, whereas contact between particles that are easy to deform expands the contact points between the particles to form a surface (junction interface). This reduces voids and achieves densification. Therefore, a solid electrolyte having the above configuration can be easily densified and thinned, and can also be expected to have improved ionic conductivity. Therefore, a useful solid electrolyte can be obtained that, for example, can be used in a solid electrolyte layer of a battery, allowing the solid electrolyte layer to be thinned or can be suitably used as a coating layer for active material particles. Therefore, a high-performance battery can be realized using a solid electrolyte manufactured by the manufacturing method of Technology 1.

[0183] (Technology 2) The composite oxide is represented by the following composition formula (2): Composition formula (2): Li x Ti y O z2. The method for producing a solid electrolyte according to claim 1, wherein in the composition formula (2), the following conditions are satisfied: 1.95≦x≦2.05, 0.95≦y≦1.05, and 2.95≦z≦3.05.

[0184] According to the manufacturing method of Technique 2, for example, an oxide that is stable in an atmospheric environment can be used as a composite oxide containing Li and Ti, and therefore, a solid electrolyte with good properties can be synthesized stably in an atmospheric environment with good reproducibility.

[0185] (Technology 3) The method for producing a solid electrolyte according to Technology 2, wherein the composite oxide is Li2TiO3.

[0186] According to the manufacturing method of Technology 3, for example, Li2TiO3, which is stable in an atmospheric environment, can be used as a composite oxide containing Li and Ti. Furthermore, by fluorinating Li2TiO3, a crystalline phase represented by composition formula (1): Li2TiF6 can be produced with high reproducibility and high quality. Therefore, according to the manufacturing method of Technology 3, a solid electrolyte with good properties can be synthesized stably and reproducibly in an atmospheric environment.

[0187] (Technology 4) The method for producing a solid electrolyte according to any one of Technologies 1 to 3, wherein (A) comprises synthesizing the composite oxide using at least one selected from the group consisting of an oxide of Li, a carbonate of Li, and a hydroxide of Li, and at least one selected from the group consisting of an oxide of Ti, a carbonate of Ti, and a hydroxide of Ti.

[0188] According to the manufacturing method of Technology 4, a composite oxide (i.e., a composite oxide containing Li and Ti) can be synthesized as a raw material using a Li source and a Ti source that are more stable against air and moisture and less expensive than LiF and TiF. The composite oxide synthesized in this manner can be fluorinated to produce a crystalline phase represented by composition formula (1): Li2TiF6 with good reproducibility and high quality. Furthermore, according to the manufacturing method of Technology 4, for example, high-quality Li2TiO3 controlled to a single phase can also be obtained with good reproducibility. Therefore, according to the manufacturing method of Technology 4, a solid electrolyte with good properties can be synthesized stably and reproducibly in an air environment.

[0189] (Technology 5) The composite oxide is in a particulate form, and the BET specific surface area of ​​the composite oxide is 1.0 m 2 / g or more and 30m 2 / g or less.

[0190] The composite oxide having the above structure is suitable for fluorination treatment. Therefore, according to the manufacturing method of Technique 5, a solid electrolyte containing a crystalline phase represented by composition formula (1): Li2TiF6 can be synthesized in large quantities at low cost.

[0191] (Technology 6) The method for producing a solid electrolyte according to any one of Technologies 1 to 5, wherein the raw material does not substantially contain TiO2.

[0192] According to the manufacturing method of Technology 6, for example, titanium tetrafluoride (TiF), which is easily evaporated and has deliquescent properties, is less likely to be produced in the process of converting the raw material into a fluoride. Therefore, composition fluctuation and deterioration of the produced solid electrolyte are suppressed, and a solid electrolyte with high ionic conductivity can be stably produced.

[0193] (Technology 7) The method for producing a solid electrolyte according to any one of Techniques 1 to 6, wherein in (A), the fluorination treatment of the raw material is carried out by heat treating a thermally decomposable fluorine-containing material.

[0194] According to the manufacturing method of Technology 7, a solid electrolyte containing a crystalline phase represented by the composition formula (1): Li2TiF6 can be synthesized by simultaneously fluorinating a raw material containing a composite oxide containing Li and Ti and carrying out a solid-state reaction. This allows for a uniform solid electrolyte with excellent properties to be obtained in a short time while reducing reaction residues such as oxides. Furthermore, since the fluorination process is performed by heat-treating a thermally decomposable fluorine-containing material, the reactivity (fluoridability) of the composite oxide contained in the raw material is good, resulting in excellent productivity. Furthermore, the temperatures and reaction rates of the fluorination and solid-state reactions of the raw material can be controlled by selecting fluorine-containing materials with different thermal decomposition temperatures and adjusting the particle size of the raw material. This allows for a fluorination process suitable for various raw materials.

[0195] (Technology 8) The method for producing a solid electrolyte according to Technology 7, wherein the temperature of the heat treatment is 200°C or higher and 600°C or lower.

[0196] Conventional manufacturing methods that use fluorides (e.g., LiF and TiF) as starting materials and synthesize solid electrolyte materials through solid-state reactions require heat treatment at high temperatures (e.g., 600°C or higher and 800°C or lower). In contrast, the manufacturing method of Technology 8 allows for the synthesis of a solid electrolyte containing a crystalline phase represented by composition formula (1): LiTiF at a lower temperature than conventional manufacturing methods. Furthermore, the manufacturing method of Technology 8 further suppresses the solid electrolyte from being sintered and becoming hard, or from undergoing excessive grain growth. Therefore, a softer, finely particulate solid electrolyte with better deformability can be obtained. This makes it easier to achieve densification and thinning of the powder compact with the solid electrolyte obtained by the manufacturing method of Technology 8. For example, when used in a solid electrolyte layer of a battery, the solid electrolyte layer can be further thinned and have high ionic conductivity, or it can be suitably used in a coating layer of active material particles to achieve high ionic conductivity of the electrode. Therefore, the solid electrolyte produced by the production method of Technique 8 realizes a battery with higher performance.

[0197] (Technology 9) The method for producing a solid electrolyte according to Technology 7 or 8, wherein the fluorine-containing material is in a particulate form.

[0198] According to the manufacturing method of Technology 9, the fluorine-containing material is easily thermally decomposed, and the contact area between the raw material and the fluorine-containing material is increased. Therefore, according to the manufacturing method of Technology 9, the raw material can be efficiently fluorinated, and the fluorine-containing material is less likely to remain in the final solid electrolyte. Furthermore, the fluorination reaction can be controlled by the particle shape of the fluorine-containing material. For example, by reducing the particle size of the fluorine-containing material, the fluorination temperature can be lowered and the fluorination rate can be increased. Furthermore, by mixing the raw material and the fluorine-containing material, uniform fluorination of the entire powder is possible. Furthermore, precise control of the amount of fluorine is possible. Therefore, the desired solid electrolyte can be synthesized. Furthermore, since only the amount of fluorine-containing material required for fluorination of the raw material can be used, unlike when fluorine gas is introduced into the furnace, excess fluorine gas emissions can be suppressed. This reduces the environmental impact and also reduces the impact on corrosion of furnace materials, etc.

[0199] (Technology 10) The method for producing a solid electrolyte according to any one of Techniques 7 to 9, wherein (A) comprises: (A-1) mixing the raw material with the fluorine-containing substance; and (A-2) heat-treating the mixture containing the raw material and the fluorine-containing substance obtained in (A-1) to fluorinate the raw material, thereby obtaining the solid electrolyte.

[0200] According to the manufacturing method of Technique 10, a heat treatment for fluorination can be performed on a homogeneous mixture of the raw material and the fluorine-containing material. Furthermore, the contact area between the raw material and the fluorine-containing material can be increased. Therefore, according to the manufacturing method of Technique 10, the fluorination of the raw material can be uniformly promoted. Therefore, a solid electrolyte having homogeneous and excellent properties can be obtained with good productivity.

[0201] (Technology 11) The method for producing a solid electrolyte according to any one of Techniques 7 to 9, wherein in (A), the fluorine-containing material is heat-treated to generate fluorine gas, and the raw material is fluorinated by bringing the fluorine gas into contact with the raw material, thereby obtaining the solid electrolyte.

[0202] According to the manufacturing method of Technique 11, the raw material can be fluorinated by the generated fluorine gas without directly contacting the raw material with the fluorine-containing material. Therefore, even if a fluorine-containing material containing inorganic components other than elemental fluorine is used, it is not necessary to consider inorganic residues in the produced solid electrolyte. Therefore, the range of usable fluorine-containing materials can be expanded.

[0203] (Technology 12) The method for producing a solid electrolyte according to any one of Techniques 7 to 11, wherein the fluorine-containing substance includes ammonium fluoride.

[0204] Ammonium fluoride begins to thermally decompose at a relatively low temperature (e.g., about 150°C). Therefore, the ammonium salt is unlikely to remain as an unnecessary inorganic component in the final solid electrolyte, and can be thermally decomposed at a low temperature to fluorinate the raw material. Therefore, according to the manufacturing method of Technology 12, the fluorine-containing substance effectively fluorinates the raw material at a low temperature (e.g., about 150 to 200°C). This further prevents the solid electrolyte from being sintered and becoming hard, or from undergoing excessive grain growth. Therefore, a softer, fine-particle solid electrolyte with better deformability can be obtained. This makes it easier to achieve densification and thinning of the powder compact. For example, when the solid electrolyte obtained by the manufacturing method of Technology 12 is used in a solid electrolyte layer of a battery, it can further thin the solid electrolyte layer and increase its ionic conductivity. It can also be used suitably as a coating layer for active material particles to increase the ionic conductivity of an electrode. Therefore, the solid electrolyte produced by the production method of Technology 12 realizes a battery with higher performance. It is possible to prevent unnecessary inorganic components derived from fluorine-containing materials from remaining in the final solid electrolyte. Furthermore, energy saving in the synthesis is achieved, and the temperature rise and fall time is also 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.

[0205] (Technology 13) The method for producing a solid electrolyte according to any one of Techniques 7 to 12, wherein the fluorine-containing material includes a resin.

[0206] According to the production method of technique 13, the raw material can be fluorinated while the fluorine-containing material is thermally decomposed at a relatively high temperature (e.g., about 450° C. or higher and 600° C. or lower). Therefore, the production method of technique 13 is suitable for the case where the fluorination of the raw material and the 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).

[0207] (Technology 14) The method for producing a solid electrolyte according to Technology 13, wherein the resin is a fluororesin.

[0208] Fluororesins such as PTFE and PVDF can fluorinate the raw material while pyrolyzing them at a relatively high temperature (e.g., about 400° C. or higher and 600° C. or lower). Therefore, the production method of Technique 14 is suitable for cases where the fluorination of the raw material and the solid-state reaction are to be carried out at a relatively high temperature (e.g., about 400° C. or higher and 600° C. or lower).

[0209] (Technology 15) The method for producing a solid electrolyte according to any one of Techniques 7 to 14, wherein the fluorine-containing material contains a substance that prevents the solid electrolyte from substantially containing inorganic components, except for elemental fluorine, that are generated by thermal decomposition by the heat treatment in (A).

[0210] The fluorine-containing material is required to replace the fluorine element generated by thermal decomposition by the heat treatment in (A) with the oxygen element of the raw material, while preventing other components from being mixed as inorganic residues into the final solid electrolyte containing a crystalline phase represented by composition formula (1): LiTiF. By using a material that does not substantially contain inorganic components, except for the fluorine element, generated by thermal decomposition by the heat treatment in the final solid electrolyte, only the fluorine element is substituted for oxygen in the oxide, thereby preventing the inorganic residue from being mixed into the solid electrolyte. As a result, a high-purity solid electrolyte having a desired composition can be obtained. An example of a fluorine-containing material that does not substantially contain inorganic components, except for the fluorine element, generated by thermal decomposition by the heat treatment in the final solid electrolyte is a material in which inorganic components, except for the fluorine element, generated by thermal decomposition by the heat treatment are gasified and discharged.

[0211] (Technology 16) The method for producing a solid electrolyte according to any one of Techniques 7 to 16, wherein the fluorine-containing material includes a plurality of kinds of fluorine-containing compounds.

[0212] According to the manufacturing method of Technique 16, for example, both ammonium fluoride and fluororesin can be used as the fluorine-containing material. This makes it possible to widely control the temperature range in which the fluorine-containing material acts as a fluorine source. Therefore, the conversion of the raw material to fluoride and the solid-state reaction temperature can be controlled over a wide range. Therefore, according to the manufacturing method of Technique 16, it is easy to obtain a desired solid electrolyte.

[0213] (Technology 17) The method for producing a solid electrolyte according to any one of Techniques 1 to 16, further comprising, after (A), (B) subjecting the solid electrolyte obtained in (A) to a pulverization treatment.

[0214] According to the manufacturing method of Technology 17, a solid electrolyte can be obtained with powder properties (e.g., particle shape, particle size, etc.) suitable for the application. Furthermore, since at least a portion of the solid electrolyte can be made amorphous, it is possible to improve ionic conductivity and improve the softness of the solid electrolyte particles. By improving the softness of the solid electrolyte particles, it is possible to improve the density of a compacted powder of the solid electrolyte. Therefore, the solid electrolyte obtained by the manufacturing method of Technology 17 can form a dense compacted powder with high ionic conductivity.

[0215] (Technology 18) A solid electrolyte comprising a crystalline phase represented by the following composition formula (1), and substantially not containing TiF4. Composition formula (1): Li2TiF6

[0216] This configuration allows a solid electrolyte with excellent ionic conductivity to be obtained. Furthermore, since the solid electrolyte according to Technology 18 is substantially free of TiF, it is possible to suppress changes over time in the characteristics and mechanical properties of the solid electrolyte caused by evaporation and deliquescence of TiF. Therefore, a solid electrolyte with excellent characteristics and reliability can be realized. Even if a trace amount of TiF is contained in the raw material, the TiF can be evaporated and eliminated by heat treatment for fluorination. Therefore, a solid electrolyte with excellent characteristics and reliability that is substantially free of TiF can be obtained.

[0217] (Technology 19) A solid electrolyte comprising a crystalline phase represented by the following composition formula (1), and further comprising at least one selected from the group consisting of Zn, Mg, Nb, and P. Composition formula (1): Li2TiF6

[0218] This configuration makes it possible to obtain a homogeneous solid electrolyte with excellent ionic conductivity.

[0219] (Technology 20) The solid electrolyte according to Technology 18 or 19, which is substantially free of TiF4.

[0220] This configuration can suppress changes over time in the characteristics and mechanical properties of the solid electrolyte caused by evaporation and deliquescence of TiF4. Therefore, a solid electrolyte with excellent characteristics and reliability can be realized. Even if the raw material contains a trace amount of TiF4, the TiF4 can be evaporated and eliminated by the heat treatment for the fluorination treatment. Therefore, a solid electrolyte with excellent characteristics and reliability that is substantially free of TiF4 can be obtained.

[0221] (Technology 21) The solid electrolyte according to any one of Techniques 18 to 20, wherein the solid electrolyte is in a particulate form.

[0222] This configuration provides a soft solid electrolyte that is easy to form an interface. Therefore, the compact of the solid electrolyte 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 compact of the solid electrolyte of Technology 21 has excellent deformability. Therefore, the compact of the solid electrolyte of Technology 22 can realize a solid electrolyte layer or a coating layer of active material particles in a battery with excellent characteristics and high reliability. As a result, the solid electrolyte of Technology 21 realizes a high-performance, highly reliable battery. The size and shape of the solid electrolyte particles can be selected appropriately depending on the application.

[0223] (Technology 22) The solid electrolyte according to any one of Technologies 18 to 21, wherein the crystalline phase includes a first crystalline phase belonging to a tetragonal system.

[0224] This structure allows for the production of a solid electrolyte with high ionic conductivity. In addition, the solid electrolyte can be heat-resistant up to approximately 250°C to 300°C, resulting in a highly reliable battery.

[0225] (Technology 23) The solid electrolyte according to any one of Technologies 18 to 22, wherein the solid electrolyte includes an amorphous phase.

[0226] This configuration makes the amorphous portion of the solid electrolyte softer, more deformable, and improves the bonding between particles. Therefore, the solid electrolyte compact can be configured to form a solid electrolyte layer with higher ionic conductivity and higher stability in any shape. Therefore, the solid electrolyte compact of Technology 24 can realize a solid electrolyte layer or a coating layer of active material particles in a battery with excellent characteristics and high reliability. As a result, the solid electrolyte of Technology 24 realizes a battery with high performance and high reliability.

[0227] While the method for producing a solid electrolyte and the 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.

[0228] 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.

[0229] The present disclosure will now be described in more detail with reference to examples.

[0230] Synthesis of Solid Electrolyte Example 1 First, Li2TiO3, a composite oxide used as a raw material, was synthesized. As starting materials for synthesizing Li2TiO3, Li2O powder (average particle size: approximately 1.5 μm) and TiO2 powder (average particle size: approximately 0.3 μm, rutile type) were prepared so as to have the composition ratio of Li2TiO3. Furthermore, ZnO (average particle size: approximately 1.5 μm), MgO (average particle size: 2.2 μm), Nb2O5 (average particle size: approximately 1.6 μm), and PO5 (average particle size: approximately 2.4 μm) were prepared as additives. Each additive powder was weighed so that the ZnO, MgO, Nb2O5, and PO5 contents were 0.02 mol%, 0.004 mol%, 0.15 mol%, and 0.03 mol% of the Li2TiO3 to be synthesized. The starting materials and additives were weighed in an air atmosphere.

[0231] The starting materials and additive powders weighed as described above were mixed. 30 g of the resulting mixed powder, 600 g of 5 mm diameter zirconia balls, and 200 mL of ethanol were placed in a 600 mL ball mill and mixed and ground for 20 hours to produce a slurry. The resulting slurry was dried for 20 hours under atmospheric pressure using a hot air dryer at approximately 50 to 60°C. The dried powder was crushed using a mortar and pestle for approximately 10 minutes and then passed through a #32 mesh sieve to obtain a raw material powder containing Li2TiO3. The average particle size of the resulting raw material powder was approximately 0.8 μm. The raw material powder also contained the above-mentioned additives.

[0232] Next, NH4F powder (average particle size: approximately 120 μm), which is a fluorine-containing material, was prepared and mixed with the raw material powder prepared by the above method. The NH4F powder was added in an amount necessary to fluorinate the raw material. Specifically, an amount of NH4F was used that would fluorinate all of the raw material according to the reaction formula.

[0233] The mixture of raw material powder and NH4F powder was mixed in an alumina mortar with a pestle for about 10 minutes until uniform (this step corresponds to (A-1) above). This resulted in a mixture containing the composite oxide Li2TiO3, the additives, and a fluorine-containing substance. The mixing of these substances was carried out in normal air, the same as when they were weighed.

[0234] Next, the resulting mixture was heat-treated (a step corresponding to (A-2) above). A high-purity (SSA-H) alumina crucible (diameter φ: 36 mm, height: 40 mm) was used for the sheath, and approximately 3 g of the above mixture was placed into the crucible. A spacer (0.5 mm thick) was placed on the outer edge of the top surface of the sheath to provide a gap to facilitate the escape of reactive gases (mainly ammonia and CO2) emitted during heat treatment, and an alumina plate-shaped lid was placed on top to prevent foreign objects from falling. The sheath with the lid attached was then placed in the center of a firing furnace and heat-treated. In the firing furnace, the sheath was placed on a small-heat-capacity mullite cradle with a porosity of approximately 20%. Cradles measuring 10 mm in length, 10 mm in width, and 10 mm in height were used, with three cradles placed under each cradle, suspending the sheath from the furnace bottom. In this way, the heater (radiant) heat and inert gas were able to reach the bottom of the sheath. After the furnace door was closed and sealed, nitrogen gas was introduced as an inert gas at a rate of 2 L / min through an inlet at the bottom of the furnace and discharged through an exhaust port above the ceiling. The gas flow continued until the heat treatment was completed. The heat treatment temperature was 700°C.

[0235] In this example, because an oxide was used as the starting material, i.e., the raw material did not contain titanium fluoride, heat treatment could be performed in the same manner as with general oxide ceramics. For example, if titanium fluoride is heat treated without sealing as in this example, it will begin to evaporate at around 50°C to 100°C, and most (about 70%) will disappear at 200°C. For this reason, fluorides produced in normal solid-phase synthesis will have large compositional variations. For this reason, making the Ti component a composite oxide containing Ti is extremely effective in suppressing compositional variations from the standpoint of evaporation and environmental stability.

[0236] The solid electrolyte obtained by the heat treatment was subjected to a pulverization treatment (a step corresponding to (B) above). In this example, a dry pulverization treatment was performed. Specifically, zirconia balls (diameter: 15 mm) and the solid electrolyte obtained by the heat treatment were placed in a ball mill (volume: 1 L) lined with zirconia, and pulverized for 20 hours.

[0237] Comparative Example 1: A fluoride was used as a starting material, and the solid electrolyte of Comparative Example 1 was prepared by mechanochemical synthesis. Specifically, LiF and TiF were prepared in a molar ratio of LiF:TiF = 2:1. These materials were mixed in a mortar for approximately 5 minutes in an Ar atmosphere (glove box). 10 g of the resulting mixture was placed in a 500 mL planetary ball mill together with 400 g of 5 mm diameter zirconia balls, sealed, and subjected to mechanochemical milling at 500 rpm for 20 hours. In this manner, the solid electrolyte of Comparative Example 1 was synthesized.

[0238] <Evaluation of Solid Electrolyte> The 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 both the solid electrolyte after the heat treatment and before the pulverization treatment, and the solid electrolyte after the pulverization treatment. The crystalline phase of the solid electrolyte of Comparative Example 1 was also evaluated. The solid electrolyte of Example 1 was also analyzed for trace components.

[0239] (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.

[0240] FIG. 6 is a graph showing the X-ray diffraction pattern ((a) after fluorination) of the solid electrolyte after heat treatment (i.e., after fluorination) and before pulverization in the manufacturing method of Example 1, the X-ray diffraction pattern ((b) after pulverization) of the solid electrolyte after pulverization obtained in Example 1, and the X-ray diffraction pattern ((c) Comparative Example 1) of the solid electrolyte obtained in Comparative Example 1. As shown in FIG. 6, an XRD pattern of a tetragonal Li2TiF6 single phase was confirmed in the solid electrolyte after fluorination. In the solid electrolyte after this fluorination solid electrolyte was further pulverized, the progress of amorphization could be confirmed from the X-ray diffraction pattern. Note that, although the crystallinity of the solid electrolyte before and after pulverization was reduced by the pulverization compared to the solid electrolyte before pulverization, no unnecessary precipitated phase was observed. In the solid electrolyte obtained in Comparative Example 1, a peak was confirmed in the X-ray diffraction pattern at a diffraction angle 2θ of approximately 12°, confirming a compositional variation compared to the solid electrolyte of Example 1. It is also apparent that the solid electrolyte of Comparative Example 1 became hard due to the progress of sintering, and therefore did not become amorphous, i.e., the peaks in the X-ray diffraction pattern did not broaden.

[0241] (Ionic Conductivity) The ionic conductivity was calculated from the area, thickness, and room temperature impedance characteristics of a powder compact obtained by placing solid electrolyte powder in a 10 mm diameter mold and applying a pressure of approximately 3 t / cm using a uniaxial hydraulic press. Impedance measurements were performed at room temperature while applying pressure. The impedance measurements were performed at a measurement frequency of 10 Hz to 10 MHz, a measurement voltage of 1 Vrms, and no DC bias. Deviations in the electrical length of the cable and measuring jig were offset and evaluated. For the solid electrolyte of Example 1, the ionic conductivity before the pulverization treatment was 0.87 μS / cm, and the ionic conductivity after the pulverization treatment was 1.6 μS / cm.

[0242] (Electronic Conductivity) The electronic conductivity was calculated from DC voltage and current characteristics. The electronic conductivity of the solid electrolyte of Example 1 was <1.0 × 10 -9 This was a value that could be judged to have no electronic conductivity.

[0243] (Average Particle Diameter) The average particle diameter is the value of the median diameter D50 obtained from the volume particle size distribution measured by a laser diffraction scattering particle size distribution analyzer. Specifically, solid electrolyte powder was dispersed in a 0.01 wt% aqueous solution of sodium hexametaphosphate using a homogenizer, and then the particle size distribution of the solid electrolyte was measured using a laser diffraction scattering particle size distribution analyzer (manufactured by Microtrac, product name: MT3100II). The value of D50 (i.e., cumulative 50% particle diameter) of the measured particle size distribution was considered to be the average particle size. For the solid electrolyte of Example 1, the average particle diameter before pulverization was 0.74 μm, and the average particle diameter after pulverization was 0.61 μm.

[0244] (BET Specific Surface Area) The BET specific surface area was determined by a BET multipoint method using a nitrogen gas adsorption apparatus. The BET specific surface area of ​​the solid electrolyte of Example 1 before the pulverization treatment was 2.7 m 2 / g, and the BET specific surface area after pulverization was 3.6 m 2 / g.

[0245] (Analysis of Trace Components) Trace components contained in the solid electrolyte were analyzed using EPMA. Specifically, the analysis was performed as follows. A sample (powder) of the solid electrolyte was attached and fixed to conductive tape (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 solid electrolyte of Example 1 contained Zn, Mg, Nb, and P. The Zn content was 0.02 at. %, the Mg content was 0.003 at. %, the Nb content was 0.2 at. %, and the P content was 0.06 at. %.

[0246] From the evaluation results of the solid electrolyte obtained in Example 1, it was found that the manufacturing method of the present disclosure was able to convert an oxide into a homogeneous fluoride, resulting in a high ionic conductivity of 1.6 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 solid electrolyte with excellent properties. The electronic conductivity was <1.0 × 10 -9It was confirmed that the electrolyte had no electronic conductivity (i.e., negligible electronic conductivity) and was an ionically conductive solid electrolyte.

[0247] The X-ray diffraction pattern shown in FIG. 6 confirmed the presence of a crystalline phase represented by composition formula (1): Li2TiF6 according to the method of Example 1. Furthermore, these X-ray diffraction patterns confirmed that the solid electrolyte obtained in Example 1 had similar crystalline quality to the solid electrolyte of Comparative Example 1 synthesized by a conventional method, and that compositional variation was suppressed compared to the solid electrolyte of Comparative Example 1. Furthermore, for the solid electrolyte of Example 1, the X-ray diffraction pattern after the pulverization treatment exhibited broader peaks than the X-ray diffraction pattern before the pulverization treatment, confirming the progression of amorphization. However, no new precipitated phases were observed due to the pulverization treatment. The changes in ionic conductivity, average particle size, and BET specific surface area before and after the pulverization treatment are as described in the explanations for each evaluation item. These results demonstrate that pulverization may or may not be performed depending on the application of the solid electrolyte, and that the composition and crystalline phase of the solid electrolyte remain largely unchanged regardless of the pulverization treatment, thereby maintaining excellent properties.

[0248] Furthermore, the amount of oxygen as an impurity in the solid electrolyte of Example 1 was 0.12 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 solid electrolyte sample (powder) and measuring the gases (CO2, CO) generated by the melt extraction device. The oxygen amount of the solid electrolyte of Example 1 was lower than that of solid electrolytes obtained by synthesis methods using fluoride as a starting material. The oxygen amount of solid electrolytes obtained by synthesis methods using fluoride as a starting material is typically greater than 0.5 mass% and approximately 1.0 mass% or less. This is thought to be due to moisture or oxygen, etc., that was incorporated into the unstable fluoride raw material during the synthesis process, such as storage or handling, remaining after synthesis. When the fluoride raw materials were mixed and subjected to a solid-state reaction without using a sealed jig, as in the manufacturing method of the present disclosure, the Ti component evaporated as titanium fluoride due to the open condition and disappeared from the fluoride. This resulted in composition fluctuations, resulting in a product with a lower ionic conductivity than that of Example 1. In this case, the heat treatment temperature for synthesis must be as high as about 600°C.

[0249] As described above, according to the manufacturing method of the present disclosure, a solid electrolyte containing a crystalline phase represented by composition formula (1): LiTiF can be produced by a conventional synthesis process (i.e., without sealing or the like, and in an atmospheric synthesis environment) with little compositional variation, etc., and with high ionic conductivity comparable to that of conventional manufacturing methods, as well as softness and excellent deformability. Furthermore, while fluoride raw materials are extremely expensive, the manufacturing method of the present disclosure uses inexpensive oxide raw materials, thereby reducing the manufacturing cost of the solid electrolyte. Therefore, the manufacturing method of the present disclosure has great industrial utility value.

[0250] The method for producing a 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 solid electrolyte, comprising: (A) subjecting a raw material containing a composite oxide containing Li and Ti to a fluorination treatment to obtain a solid electrolyte containing a crystalline phase represented by the following composition formula (1). Composition formula (1): Li2TiF6 2. The composite oxide is represented by the following composition formula (2): x Ti y O z 2. The method for producing a solid electrolyte according to claim 1, wherein the following conditions are satisfied in the composition formula (2): 1.95≦x≦2.05, 0.95≦y≦1.05, and 2.95≦z≦3.

05.

3. The method for producing a solid electrolyte according to claim 2, wherein the composite oxide is Li2TiO3.

4. The method for producing a solid electrolyte according to claim 1, wherein (A) comprises synthesizing the composite oxide using at least one selected from the group consisting of an oxide of Li, a carbonate of Li, and a hydroxide of Li, and at least one selected from the group consisting of an oxide of Ti, a carbonate of Ti, and a hydroxide of Ti.

5. The composite oxide is in the form of particles, and the BET specific surface area of ​​the composite oxide is 1.0 m 2 / g or more and 30m 2 The method for producing a solid electrolyte according to claim 1, wherein the Mo content is 1 / g or less.

6. The method for producing a solid electrolyte according to claim 1, wherein the raw material is substantially free of TiO2.

7. The method for producing a solid electrolyte according to claim 1, wherein in (A), the fluorination treatment of the raw material is carried out by heat treating a thermally decomposable fluorine-containing material.

8. The method for producing a solid electrolyte according to claim 7, wherein the temperature of the heat treatment is 200°C or higher and 600°C or lower.

9. The method for producing a solid electrolyte according to claim 7, wherein the fluorine-containing material is in particulate form.

10. The method for producing a solid electrolyte according to claim 7, wherein the (A) comprises: (A-1) mixing the raw material with the fluorine-containing substance; and (A-2) heat-treating the mixture containing the raw material and the fluorine-containing substance obtained in the (A-1) to fluorinate the raw material to obtain the solid electrolyte.

11. The method for producing a solid electrolyte according to claim 7, wherein in (A), fluorine gas is generated by heat-treating the fluorine-containing material, and the raw material is fluorinated by contacting the fluorine gas with the raw material to obtain the solid electrolyte.

12. The method for producing a solid electrolyte according to claim 7, wherein the fluorine-containing substance includes ammonium fluoride.

13. The method for producing a solid electrolyte according to claim 7, wherein the fluorine-containing material includes a resin.

14. The method for producing a solid electrolyte according to claim 13, wherein the resin is a fluororesin.

15. The method for producing a solid electrolyte according to claim 7, wherein the fluorine-containing material includes a substance that causes the solid electrolyte to substantially not contain inorganic components, other than elemental fluorine, that are generated by thermal decomposition through the heat treatment in (A).

16. The method for producing a solid electrolyte according to claim 7, wherein the fluorine-containing material includes a plurality of types of fluorine-containing compounds.

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

18. A solid electrolyte comprising a crystalline phase represented by the following composition formula (1) and substantially not containing TiF4. Composition formula (1): Li2TiF6 19. A solid electrolyte comprising a crystalline phase represented by the following composition formula (1), and further comprising at least one selected from the group consisting of Zn, Mg, Nb, and P. Composition formula (1): Li2TiF6 20. The solid electrolyte of claim 19, which is substantially free of TiF4.

21. The solid electrolyte according to claim 18 or 19, wherein the solid electrolyte is in particulate form.

22. The solid electrolyte according to claim 18 or 19, wherein the crystal phase includes a first crystal phase belonging to a tetragonal system.

23. The solid electrolyte according to claim 18 or 19, wherein the solid electrolyte includes an amorphous phase.

24. A positive electrode material comprising the solid electrolyte according to claim 18 or 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 solid electrolyte according to claim 18 or 19.

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