Solid electrolyte, method for producing solid electrolyte, positive electrode material, and battery

Abstract

A solid electrolyte according to the present disclosure includes a first crystal phase that is represented by following compositional formula (1): Li3AlF6, and that has a crystal structure of an orthorhombic crystal system. A method for producing a solid electrolyte according to the present disclosure includes: (A) mixing a raw material containing at least one selected from the group consisting of oxides of Li, carbonates of Li, and hydroxides of Li, and at least one selected from the group consisting of oxides of Al, carbonates of Al, and hydroxides of Al; and subjecting the mixed raw material to a fluorination treatment.

Description

Solid electrolyte, method for producing solid electrolyte, positive electrode material, and battery

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

[0002] Patent Document 1 discloses a lithium ion battery having a solid electrolyte layer containing Li3AlF6.

[0003] International Publication No. 2018 / 123479

[0004] An object of the present disclosure is to provide a new, highly useful solid electrolyte material.

[0005] The solid electrolyte of the present disclosure includes a first crystalline phase represented by the following composition formula (1) and having an orthorhombic crystal structure:

[0006] The present disclosure provides a new, highly useful solid electrolyte material.

[0007] FIG. 1 is a flowchart showing an example of a method for producing a solid electrolyte according to a second embodiment. FIG. 2 is a flowchart showing an example of a method for producing a solid electrolyte according to a third embodiment. FIG. 3 is a flowchart showing a modified example of the method for producing a solid electrolyte according to the third embodiment. FIG. 4 is a flowchart showing an example of a method for producing a solid electrolyte according to a fourth embodiment. FIG. 5 is a flowchart showing an example of a method for producing a solid electrolyte according to a fifth embodiment. FIG. 6 is a flowchart showing a modified example of the method for producing a solid electrolyte according to the fifth embodiment. FIG. 7 is a cross-sectional view of a battery 1000 according to a sixth embodiment. FIG. 8A is a graph showing an X-ray diffraction pattern of a solid electrolyte after heat treatment and before pulverization in the production method of Example 1, and an X-ray diffraction pattern of a solid electrolyte obtained in Comparative Example 1. FIG. 8B is a graph showing an X-ray diffraction pattern of a solid electrolyte after pulverization obtained in Example 1.

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

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

[0010] [First Embodiment] A solid electrolyte according to a first embodiment of the present disclosure includes a first crystalline phase represented by the following composition formula (1) and having an orthorhombic crystal structure.

[0011] The solid electrolyte according to the first embodiment is a novel, highly useful solid electrolyte. A solid electrolyte including a first crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure can exhibit high ionic conductivity and excellent stability. A solid electrolyte having such a configuration can be synthesized, for example, at low temperatures (e.g., 150°C or higher and 700°C or lower), and is therefore less likely to be exposed to high temperatures for long periods during production. This prevents the solid electrolyte from being sintered excessively during production, resulting in excessive hardness, or excessive grain growth of the solid electrolyte. Therefore, the solid electrolyte according to the first embodiment is soft, has excellent deformability, and can be provided as fine particles. Such a fine-particle solid electrolyte with excellent deformability is likely to form an interface where particles adhere to each other when compacted, facilitating high density and thin layer formation, and can also be expected to exhibit improved ionic conductivity. Therefore, the solid electrolyte according to the first embodiment is a highly useful solid electrolyte, for example, when used in a solid electrolyte layer of a battery, enabling 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 by using the solid electrolyte according to the first embodiment. The hardness of the solid electrolyte can be comparatively evaluated by a technique such as micro-Vickers measurement using particles or a compressed powder.

[0012] The solid electrolyte according to the first embodiment may be particulate. 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 assume any desired shape. A compact of a solid electrolyte having these 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.

[0013] The solid electrolyte according to the first embodiment includes particles having a particle diameter of 1 μm or less, for example. By including such particles in the solid electrolyte according to the first embodiment, when the solid electrolyte is used in a solid electrolyte layer, the solid electrolyte layer can be made even thinner, or the solid electrolyte can be more suitably used in a coating layer for active material particles. A solid electrolyte having such a configuration realizes a battery with higher performance.

[0014] The solid electrolyte according to the first embodiment contains particles having a particle diameter of, for example, 0.3 μm or more. When the solid electrolyte according to the first embodiment contains such particles, the ionic conductivity can be improved.

[0015] The solid electrolyte according to the first embodiment may have an average particle size of 1 μm or less. When a solid electrolyte having such an average particle size is used in, for example, a solid electrolyte layer of a battery, the solid electrolyte layer can be made even thinner, or it can be more suitably used in a coating layer for active material particles. Therefore, by having an average particle size of 1 μm or less, the solid electrolyte according to the first embodiment can realize a battery with higher performance. The solid electrolyte according to the first embodiment may have an average particle size of, for example, 0.1 μm or more.

[0016] The average particle size of the solid electrolyte is a median size, which means a particle size (d50) corresponding to 50% cumulative volume, determined from a particle size distribution measured on a volume basis by a laser diffraction scattering method. The same applies to the average particle sizes of the raw materials and fluorine-containing substances specified in this specification.

[0017] The solid electrolyte according to the first embodiment may include particles having an aspect ratio of 2.0 or more. Here, the aspect ratio of the solid electrolyte particles is the ratio (long axis length / short axis length) of the longest diameter (i.e., the long axis length) of the solid electrolyte particles to the shortest diameter (i.e., the short axis length) of the solid electrolyte particles.

[0018] By including elongated particles having an aspect ratio of 2.0 or more, the solid electrolyte according to the first embodiment can improve ionic conductivity. Furthermore, when a slurry containing a solid electrolyte containing particles having such an aspect ratio is prepared and the slurry is used for printing or coating, the particles of the solid electrolyte are likely to be oriented and aligned along the printed or coated surface. Therefore, when a solid electrolyte containing particles having an aspect ratio of 2.0 or more is used in a solid electrolyte layer of a battery, the solid electrolyte layer can be further thinned. Therefore, a solid electrolyte containing particles having an aspect ratio of 2.0 or more can realize a small battery with a high capacity density. Furthermore, when a solid electrolyte having such a configuration is used in a solid electrolyte layer of a battery, the resistance component of the solid electrolyte layer is reduced, resulting in a high-performance battery.

[0019] The particles of the solid electrolyte according to the first embodiment may have an aspect ratio of, for example, 6.0 or less.

[0020] The solid electrolyte according to the first embodiment may have an average aspect ratio of 2.0 or more. The solid electrolyte according to the first embodiment may have an average aspect ratio of 3.0 or less.

[0021] Here, the aspect ratio of the solid electrolyte particles can be determined from an SEM image of the solid electrolyte obtained by a scanning electron microscope (SEM). That is, the shortest and longest diameters of the particles are identified from the SEM image of the solid electrolyte particles, and the aspect ratio of each particle is calculated. The average aspect ratio can be determined by determining the aspect ratios of 50 particles randomly extracted from the SEM image of the solid electrolyte and calculating the average value.

[0022] The solid electrolyte according to the first embodiment may include particles having a free surface. This configuration allows the solid electrolyte according to the first embodiment to have excellent stability against the atmosphere. Here, in the present disclosure, the free surface of the solid electrolyte refers to the surface of the solid electrolyte in the synthesized state (i.e., a highly stable surface), and does not include a highly reactive active surface inside the solid electrolyte that is exposed by pulverization or the like.

[0023] The solid electrolyte according to the first embodiment may be a Li3AlF6 solid solution that is represented by composition formula (1): Li3AlF6 and includes a first crystalline phase having an orthorhombic crystal structure.

[0024] The solid electrolyte according to the first embodiment may further include a second crystalline phase represented by composition formula (1): LiAlF and having a monoclinic crystal structure. This configuration allows for a softer, more deformable solid electrolyte. Such a softer, more deformable solid electrolyte is more likely to form an interface where particles adhere to each other when compacted, making it easier to achieve higher density and thinner layers, and further improving ionic conductivity. Therefore, when used in a solid electrolyte layer and a coating layer for active material particles in a battery, a solid electrolyte further including the second crystalline phase can form a high-quality solid electrolyte layer and coating layer with reduced defects such as voids. Therefore, the solid electrolyte according to the first embodiment can realize a battery with higher performance and excellent reliability. The solid electrolyte according to the first embodiment may be a LiAlF solid solution including a first crystalline phase and a second crystalline phase.

[0025] The solid electrolyte according to the first embodiment may include first particles that include a first crystalline phase but do not include a second crystalline phase, and second particles that include the second crystalline phase. In this case, the second particles are softer than the first particles. Here, in the present disclosure, the hardness of the first particles and the second particles can be comparatively evaluated by, for example, micro-Vickers measurement of these particles or a compact of these particles.

[0026] The ionic conductivity of the first crystalline phase tends to be higher than that of the second crystalline phase. For example, a solid electrolyte composed of the first crystalline phase can achieve an ionic conductivity of, for example, more than 3 μS / cm in a compact. On the other hand, the ionic conductivity of a solid electrolyte composed of the second crystalline phase is, for example, 1 μS / cm or more and 2 μS / cm or less in a compact.

[0027] The solid electrolyte according to the first embodiment includes the first particles and the second particles, thereby further improving softness and deformability. Thus, a softer, more deformable solid electrolyte is more likely to form an interface where particles adhere to each other when compacted, which makes it easier to achieve higher density and thinner layers, and further improves ionic conductivity. Furthermore, thermal shock resistance, such as in thermal cycling, is also improved. Therefore, by having such a configuration, when used in a battery, the solid electrolyte according to the first embodiment can realize a battery with higher performance and excellent reliability.

[0028] The solid electrolyte according to the first embodiment may include an amorphous phase. This configuration makes the amorphous portion of the solid electrolyte softer, more deformable, and improves the bonding between particles. Therefore, the compact of the solid electrolyte according to the first embodiment can form a solid electrolyte layer having higher ionic conductivity and higher stability in any shape. Therefore, when the solid electrolyte according to the first embodiment includes 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 having excellent characteristics and high reliability. As a result, a battery with high performance and high reliability is realized.

[0029] The solid electrolyte according to the first embodiment may further contain at least one selected from the group consisting of Ti, Si, Cu, and Ga as a minor component. In other words, in this case, the solid electrolyte obtained by the manufacturing method according to the first embodiment is represented by composition formula (1): LiAlF, contains a crystalline phase having an orthorhombic crystal structure, and further contains at least one selected from the group consisting of Ti, Si, Cu, and Ga. This configuration allows for the production of a homogeneous solid electrolyte with excellent ionic conductivity.

[0030] The above-mentioned elements (i.e., at least one selected from the group consisting of Ti, Si, Cu, and Ga) contained as minor components may be derived from a substance added as an additive to promote the reaction of raw materials when synthesizing the solid electrolyte according to the first embodiment. Furthermore, in X-ray diffraction measurement of the solid electrolyte according to the first embodiment, Ti, Si, Cu, and Ga may not be detected as a composition phase. Even in this case, the presence of Ti, Si, Cu, and Ga 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 Ti, Si, Cu, and Ga contained in the solid electrolyte may be, for example, 0.0003 at. % or more and 0.15 at. % or less. The content of Ti, Si, Cu, and Ga can be determined by EPMA or the like.

[0031] When the solid electrolyte according to the first embodiment is compared with the solid electrolyte described in Patent Document 1, the following differences are observed.

[0032] Patent Document 1 discloses LiAlF as an example of a second solid electrolyte, which is a minor component contained in the solid electrolyte layer of a lithium-ion battery. Although Patent Document 1 does not disclose a crystal structure, it is believed to have been synthesized by a known method, since it does not disclose a synthesis method or the like. That is, the LiAlF disclosed in Patent Document 1 is believed to have a monoclinic crystal structure. Furthermore, based on the description in Patent Document 1, it is not believed that the LiAlF disclosed in Patent Document 1 is amorphous. Therefore, the LiAlF disclosed as the second solid electrolyte in Patent Document 1 is not LiAlF having an orthorhombic crystal structure like the solid electrolyte according to the first embodiment, and naturally, it is difficult to obtain high ionic conductivity like the solid electrolyte according to the first embodiment. Furthermore, the LiAlF disclosed as the second solid electrolyte in Patent Document 1 is believed to be soft and highly deformable, and when compacted, it is likely to form an interface where particles are closely attached to each other, and is not highly useful for densifying and thinning the solid electrolyte according to the first embodiment.

[0033] Second Embodiment A method for producing a solid electrolyte according to a second embodiment will now be described.

[0034] The solid electrolyte produced by the production method according to the second embodiment is the solid electrolyte according to the first embodiment. That is, the production method according to the second embodiment is a method for producing a solid electrolyte that is represented by composition formula (1): LiAlF and includes a first crystalline phase having an orthorhombic crystal structure.

[0035] The manufacturing method according to the second embodiment includes: (A) mixing raw materials containing 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 Al, a carbonate of Al, and a hydroxide of Al, and subjecting the mixed raw materials to a fluorination treatment.

[0036] The manufacturing method according to the second embodiment uses relatively stable oxides, carbonates, and hydroxides as raw materials and simultaneously fluorinates the raw materials and causes a solid-state reaction. This allows for the synthesis of a solid electrolyte containing a first crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure. Furthermore, this manufacturing method allows for the synthesis of a solid electrolyte containing a first crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure at low temperatures (e.g., temperatures of approximately 150°C to 700°C) that cannot be achieved by solid-state reactions using fluoride raw materials. Furthermore, this manufacturing method allows for the accurate production of a solid electrolyte having a desired composition by controlling the ratio of each component of the raw materials. Therefore, the manufacturing method according to the second embodiment allows for the stable, low-cost, easy-to-produce, and highly reproducible production of a solid electrolyte containing a crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure.

[0037] For example, when LiAlF having an orthorhombic crystal structure synthesized by the manufacturing method according to the second embodiment is compressed under a certain pressure, the density of the compressed powder is, for example, 1.92 g / cm 3 1.98g / cm or more 3 The following can be shown: This is the density of the green compact that can be realized by using fluoride as a raw material and compacting LiAlF having a monoclinic crystal structure obtained by solid-phase synthesis from fluoride at the same pressure. 3 1.94g / cm or more 3 Compared to or of the same order as or greater than:

[0038] 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.

[0039] By fluorinating the raw material through heat treatment of a thermally decomposable fluorine-containing material, the fluorination of the raw material and the solid-state reaction for synthesizing the solid electrolyte simultaneously occur, allowing for the synthesis of a solid electrolyte containing a first crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure. This allows for the production of a homogeneous solid electrolyte with excellent properties while reducing reaction residues such as oxides. Furthermore, the temperatures of the fluorination reaction and solid-state reaction of the raw material, as well as the progress of these reactions, can be controlled, for example, depending on the thermal decomposition temperature of the selected fluorine-containing material. This allows for the execution of a fluorination process suitable for various raw materials.

[0040] When a thermally decomposable fluorine-containing substance is used in the fluorination treatment of the raw materials, in the production method according to the second 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.

[0041] In the production method according to the second 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 substance. Furthermore, the contact area between the raw material and the fluorine-containing substance can be increased. This promotes homogeneous fluorination of the raw material, thereby enabling a homogeneous solid electrolyte with excellent properties to be obtained with good productivity.

[0042] 1 is a flowchart showing an example of a method for producing a solid electrolyte according to Embodiment 2. Here, as an example of the production method according to Embodiment 2, an example of a production method in which the above (A-1) and (A-2) are carried out will be described.

[0043] As shown in FIG. 1 , in one example of the manufacturing method according to the second 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 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 Al oxide, Al carbonate, and Al hydroxide. 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 first crystalline phase represented by composition formula (1): Li3AlF6 and having an orthorhombic crystal structure.

[0044] The raw materials, the fluorine-containing material, and the steps corresponding to (A-1) and (A-2) above will be specifically described below.

[0045] <Raw Materials> The raw materials include 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 Al, a carbonate of Al, and a hydroxide of Al.

[0046] 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 with homogeneous and excellent properties. Furthermore, particulate raw materials have good reactivity, such as fluoridability and solid-phase reactivity, and therefore excellent productivity can be achieved. Furthermore, since the raw material is particulate, the raw material can be easily mixed homogeneously with the fluorine-containing material, so the fluorination of the raw material proceeds homogeneously, and a solid electrolyte with excellent properties can be synthesized.

[0047] In order to synthesize Li3AlF6 having a fine and orthorhombic crystal structure, it is suitable to use small particles as the Al source contained in the raw material. For example, at least one selected from the group consisting of Al oxide, Al carbonate, and Al hydroxide used as the Al source may have an average particle diameter of, for example, 0.06 μm or more and 1.0 μm or less. Furthermore, at least one selected from the group consisting of Al oxide, Al carbonate, and Al hydroxide used as the Al source may have a BET specific surface area of, for example, 3 m 2 / g or more and 30m 2 / g or less. An Al source having such a BET specific surface area is suitable for fluorination treatment. Therefore, by using an Al source having such a configuration as a raw material, a fluorination reaction and a solid-state reaction are likely to occur simultaneously.

[0048] The average particle size of the Li source contained in the raw material is not particularly limited, but may be, for example, 1 μm or more and 20 μm or less. An appropriately large Li source can be selected in consideration of the stability and properties of the solid electrolyte to be synthesized and handling in the production process.

[0049] The raw materials may be pulverized into individual substances in advance. The reactivity of the raw materials can be increased by reducing the particle size of the raw materials or by exposing the fractured surfaces of the particles through the pulverization process. The fractured surfaces of the particles are more active than the unfractured surfaces. The introduction of the pulverization process to the raw materials may be appropriately adjusted in terms of the stability and properties of the synthesis of the solid electrolyte. The raw materials may also be a mixture of pulverized powder and unpulverized powder. The pulverized powder may be included as part of the raw materials. The fractured surfaces of the pulverized powder of the raw materials can be observed from a state different from the free surface by SEM observation of the powder.

[0050] The raw material as a whole may have an average particle size of, for example, 0.1 μm or more and 20 μm or less, or may have 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 may be 0.5 μm or more and 20 μm or less. The raw material may be further refined and may have an average particle size of, for example, 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 an average particle size of, for example, 0.1 μm or more and 1.0 μm or less. However, the average particle size of the raw material is not limited to the above range, and any particle size and shape can be appropriately selected from the viewpoints of fluorination and solid-state reaction. For example, the smaller the particle size of the raw material, the lower the temperature for conversion to fluoride can be.

[0051] <Fluorine-containing substance> The fluorine-containing substance is thermally decomposable.

[0052] 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.

[0053] 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.

[0054] 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 raw material, the fluorine-containing material may have any particle size and shape.

[0055] 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, 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.

[0056] 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 unlikely 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, the above-described manufacturing method is effective for fluorinating raw materials at low temperatures (e.g., about 150 to 200°C). This prevents the solid electrolyte from being sintered and hardened, or from undergoing excessive grain growth. Therefore, a softer, more deformable, fine-grained solid electrolyte containing a first crystalline phase represented by the composition formula (1): Li3AlF6 and having an orthorhombic crystal structure can be obtained. This allows the solid electrolyte obtained by the above-described manufacturing method to be easily densified and thin-layered. For example, when the solid electrolyte obtained by the above manufacturing method is used in a solid electrolyte layer of a battery, it can achieve a thinner solid electrolyte layer and higher 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 above manufacturing method realizes a higher-performance battery. It is possible to prevent unnecessary inorganic components derived from fluorine-containing materials from remaining in the final solid electrolyte. When a fluoride raw material is subjected to a solid-state reaction, for example, at a low temperature of 150°C or higher and 700°C or lower, it is difficult to produce a solid electrolyte containing a crystalline phase represented by composition formula (1): Li3AlF6. A temperature exceeding 700°C (e.g., a temperature of about 750°C to 800°C) is required. Therefore, when a fluoride raw material is subjected to a solid-state reaction, it is difficult to obtain a solid electrolyte that is soft and fine and contains a crystalline phase represented by composition formula (1): Li3AlF6.

[0057] 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.

[0058] 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 400°C or higher and 600°C or lower). Therefore, a method including a resin as the fluorine-containing material is suitable for the case where fluorination and solid-state reaction are to be performed at a relatively high temperature (e.g., about 400°C or higher and 600°C or lower).

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] <Regarding (A-1)> In (A-1), the raw material and the fluorine-containing substance are mixed.

[0064] Prior to the fluorination treatment, a first preliminary step may be performed in which the raw materials are uniformly mixed. Furthermore, a second preliminary step may be performed in which the mixed raw materials and a fluorine-containing substance are uniformly mixed. These first and second preliminary steps allow the raw materials to be uniformly converted into fluoride. This allows a homogeneous solid electrolyte to be synthesized.

[0065] In the first preliminary step, the raw materials may be pulverized. As described above, the reactivity of the raw materials can be increased by pulverizing the mixed powder of the raw materials to reduce the particle size of the raw materials or by exposing the fracture surfaces of the particles through the pulverization process. Furthermore, the pulverization process of the raw materials can improve the mixability of the raw materials, and further the mixability of the raw materials with the fluorine-containing substance. Furthermore, the particle shape of the solid electrolyte to be produced can be controlled, for example, to achieve fine particle size of the solid electrolyte. Examples of the average particle size of the raw materials are as described above.

[0066] The mixing in the first preliminary step can be either dry or wet, as long as the raw materials are homogenized. In wet mixing, a known dispersant can be used to achieve uniform mixing and increase the processing volume (i.e., increase the solid content of the slurry). Examples of known dispersants include ammonium polycarboxylate dispersants and nonionic surfactants. The pulverization process results in fine particles and exposes the active surfaces of the broken particles, improving the reactivity of the raw materials in the subsequent fluorination process. This allows for homogenization of synthesis and reaction at low temperatures. Therefore, a soft, highly deformable solid electrolyte containing a crystalline phase represented by the composition formula (1): Li3AlF6 and having an orthorhombic crystal structure can be easily produced.

[0067] In the second preliminary step, a pulverization treatment may be performed to adjust the particle size of the fluorine-containing material. By finely pulverizing the mixed powder containing the raw material and the fluorine-containing material, the synthesis temperature of the solid electrolyte can be lowered, for example, by about 10°C 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.

[0068] In the second preliminary step, it is sufficient that the raw material and fluorine-containing material powders are mixed 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 means 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.

[0069] <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.

[0070] 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.

[0071] In the heat treatment, the homogeneously mixed mixture is placed in a heat-resistant alumina container (sheath) and fired in a furnace under an appropriate atmosphere. For example, an inert gas such as nitrogen gas is flowed into the furnace, and the mixture is heat-treated in the furnace for a period of time ranging from 150°C to 700°C, for example, between 1 hour and 40 hours, while evacuating gases generated during fluorination (e.g., ammonium, hydrogen chloride, carbon dioxide, etc.). This process synthesizes a solid electrolyte containing a first crystalline phase represented by the composition formula (1): LiAlF and having an orthorhombic crystal structure. By introducing and evacuating gas into the furnace, unnecessary reactive gas components are prevented from remaining in the furnace, i.e., the solid electrolyte.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] The heat treatment temperature is, for example, 150°C or higher and 700°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. According to the production method of the second embodiment, a solid electrolyte represented by composition formula (1): LiAlF can be synthesized at a lower temperature than conventional synthesis methods that involve solid-state reactions of fluorides. Therefore, according to the production method of the second embodiment, a solid electrolyte composed of soft, fine particles can be obtained, compared to solid electrolytes synthesized by conventional methods. This production method allows for the production of a solid electrolyte that can be formed into a dense, compacted powder body with excellent ionic conductivity.

[0076] The heat treatment temperature and heat treatment time can be determined arbitrarily in consideration of the properties of the raw materials (e.g., crystal system and powder characteristics, etc.), the properties of the solid electrolyte to be synthesized (e.g., crystal system and powder characteristics, etc.), the temperature required for synthesizing the solid electrolyte containing a first crystal phase that is represented by composition formula (1): LiAlF and has an orthorhombic crystal structure, the time required for synthesis, the time required for the synthesis, and the discharge time of the reaction gas.

[0077] The heat treatment conditions for the fluorination treatment of raw materials in the manufacturing method according to the second embodiment allow the synthesis of a solid electrolyte containing a first crystalline phase represented by composition formula (1): Li3AlF6 and having an orthorhombic crystalline structure, which is difficult to achieve using conventional synthesis methods that involve solid-state reactions of fluorides. Depending on the fluorination conditions, a second crystalline phase represented by composition formula (1): Li3AlF6 and having a monoclinic crystalline structure can also be produced. Although this depends on the particle size of the raw materials and the fluorine-containing material, for example, a solid electrolyte containing a monoclinic second crystalline phase can be synthesized at a lower temperature (e.g., 150°C or higher and 200°C or lower). By pulverizing the raw materials and the fluorine-containing material, the temperature at which these crystal systems change occurs can be lowered, for example, to a range of 10°C or higher and 50°C or lower. Because the second crystalline phase is produced by a lower heat treatment temperature, sintering and grain growth during synthesis are suppressed for solid electrolytes containing both the first and second crystalline phases. Therefore, a solid electrolyte further containing the second crystalline phase by carrying out the heat treatment at a low temperature can be obtained as a softer powder.

[0078] 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.

[0079] 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.

[0080] As described above, since the fluorination treatment can be performed at a relatively low temperature, the raw materials used as raw materials are less likely to evaporate due to the temperature during the fluorination treatment. Therefore, the fluorination treatment does not need to be performed in a sealed container. The mixture of raw materials and fluorine-containing material 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, and then the heat treatment may be performed. Therefore, the heat treatment in the manufacturing method according to the second embodiment has excellent productivity and workability, and is extremely valuable industrially. According to the manufacturing method according to the second embodiment, a solid electrolyte having excellent ionic conductivity and stability (e.g., electrochemical stability and heat resistance), represented by composition formula (1): LiAlF, and including a first crystalline phase having an orthorhombic crystalline structure, can be obtained by this highly productive manufacturing method.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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 third 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.

[0085] In the manufacturing method according to the second 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. Examples of such additives include compounds (e.g., oxides) containing at least one element selected from the group consisting of Ti, Si, Cu, Ga, Zn, Mg, Nb, P, K, Na, Ca, and Fe. For example, when added in trace amounts to the raw materials, Ti oxide, Si oxide, Cu oxide, and Ga oxide can lower the reaction temperature of the fluorination reaction and solid-state reaction by, for example, about 10 to 20°C, or 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 Ti oxide, Si oxide, Cu oxide, and Ga oxide may be added together, or only one selected from the group consisting of Ti oxide, Si oxide, Cu oxide, and Ga oxide may be added. For example, when Ti oxide, Si oxide, Cu oxide, and Ga oxide are added for the purpose of promoting the fluorination reaction and the solid-state reaction, the total amount of Ti oxide, Si oxide, Cu oxide, and Ga oxide added may be, for example, 0.001 mol % or more and 0.3 mol % or less with respect to the raw material.

[0086] Additives such as Ti oxide, Si oxide, Cu oxide, and Ga oxide may be, for example, particulate. The effect of the additive may vary depending on the particle form of the additive and the state of dispersion in the raw material. For Ti oxide, Si oxide, Cu oxide, and Ga oxide, generally, the smaller the particle size, the greater the additive's effect, such as reaction promotion. For example, the particle diameter of the additive may be smaller than that of the raw material particles. As an example, the additive may have a particle diameter of 0.1 μm or less and a BET specific surface area of ​​100 m. 2 / g or more. Note that using coarse particles or adding excessive amounts of Ti oxide, Si oxide, Cu oxide, and Ga 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. The Ti, Si, Cu, and Ga elements derived from the Ti oxide, Si oxide, Cu oxide, and Ga oxide added as additives act, for example, as fluoride conversion aids and solid-phase reaction aids, and are incorporated into the solid electrolyte. For example, it is desirable to adjust the particle size and amount of Ti oxide, Si oxide, Cu oxide, and Ga oxide so that Ti, Si, Cu, and Ga are not detected as composition phases in X-ray diffraction measurement of the final solid electrolyte. This allows for the synthesis of a solid electrolyte with high ionic conductivity while achieving a reaction-accelerating effect.

[0087] In the manufacturing method according to the second embodiment, when at least one selected from the group consisting of Ti oxide, Si oxide, Cu oxide, and Ga oxide is used as the additive, the resulting solid electrolyte contains at least one selected from the group consisting of Ti, Si, Cu, and Ga. That is, in this case, the solid electrolyte obtained by the manufacturing method according to the second embodiment contains a first crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure, and further contains at least one selected from the group consisting of Ti, Si, Cu, and Ga. This configuration allows for the production of a homogeneous solid electrolyte with excellent ionic conductivity.

[0088] The amount of oxygen as an impurity in the solid electrolyte obtained by the manufacturing method according to the second embodiment may be 0.5 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 mass % or more.

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

[0090] The production method according to the third 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 third 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 and amorphization of the surface) suitable for the application. Furthermore, since at least a portion of the solid electrolyte can be amorphized, the ionic conductivity and the softness of the solid electrolyte particles can be improved. The improved softness of the solid electrolyte particles can increase the density of the solid electrolyte powder compact. Therefore, the solid electrolyte obtained by the manufacturing method of the third 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 Embodiment 3. Here, an example of the production method described in Embodiment 2 will be described, in which (A) is a production method in which (A-1) and (A-2) are performed as (A), 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 first crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure. 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 second embodiment, respectively, and therefore detailed description thereof will be omitted here.

[0095] The solid electrolyte pulverized in (B) 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, it is useful for solid electrolyte layers, composite components of active material layers, and coating layers for active material particles. This realizes high performance and high reliability of batteries.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] The change in deformability due to amorphization can be evaluated by an evaluation method such as micro-Vickers.

[0101] 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.

[0102] As a modification of the manufacturing method according to the third embodiment, the solid electrolyte may be made into a slurry for forming a coating film simultaneously with the pulverization treatment in (B) above.

[0103] 3 is a flowchart showing a modified example of the method for producing a solid electrolyte according to the third embodiment. Regarding the modified example of the production method according to the third embodiment, an example of the production method described in the second embodiment will be described here, in which (A) is the production method in which (A-1) and (A-2) are performed as the above (A), and (B) is performed after (A-2).

[0104] As shown in Fig. 3, first, raw materials and a fluorine-containing material are mixed (S31). Next, the resulting mixture containing the raw materials and the fluorine-containing material is heat-treated to fluorinate the raw materials (S32). This results in a solid electrolyte containing a first crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure. 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).

[0105] S31 and S32 are the same as S11 and S12 described in the second embodiment, respectively, and therefore detailed description thereof will be omitted here.

[0106] The pulverization process in S33 is the same as the pulverization process in S23 described as an example of the manufacturing method of the third embodiment. In a modified example of the manufacturing method of the third 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).

[0107] 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.

[0108] Fourth Embodiment A method for producing a solid electrolyte according to a fourth embodiment will now be described.

[0109] In the production method according to the fourth embodiment, in the step (A) described in the second 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 fourth embodiment, the grinding treatment in the step (B) described in the third embodiment may be carried out after the step (A).

[0110] 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 , raw materials are prepared (S41). The raw materials include 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 Al oxide, Al carbonate, and Al hydroxide, and are prepared by mixing these. Additives for promoting the fluorination reaction of the raw materials, additives for promoting the solid-state reaction of the raw materials, etc. are added to the raw materials during raw material preparation. That is, for example, at least one selected from the group consisting of Ti oxide, Si oxide, Cu oxide, and Ga oxide may be added to the raw materials.

[0111] Next, the raw material and the fluorine-containing material are placed at 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 fluorination treatment of the raw material is carried out. Thereafter, as a step corresponding to the above (B), the solid electrolyte obtained in S42 may be subjected to a pulverization treatment (S43).

[0112] According to the manufacturing method of the fourth 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 an inorganic component 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] Fifth Embodiment A method for producing a solid electrolyte according to a fifth embodiment will now be described.

[0115] The production method according to the fifth embodiment is a method of obtaining a solid electrolyte including both the first crystal phase and the second crystal phase by mixing LiAlF having a monoclinic crystal structure with a solid electrolyte including a first crystal phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure, which solid electrolyte is obtained by the production method of any one of the second to fourth embodiments.

[0116] 5 is a flowchart showing an example of a method for producing a solid electrolyte according to the fifth embodiment. Here, an example is described in which a solid electrolyte containing a first crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure is synthesized by the production method according to the second embodiment.

[0117] As shown in FIG. 5 , raw materials and a fluorine-containing material are mixed (S51). Next, the resulting mixture containing the raw materials and the fluorine-containing material is heat-treated to fluorinate the raw materials, synthesizing a solid electrolyte containing a first crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure (S52). Next, LiAlF having a monoclinic crystal structure is mixed with the solid electrolyte containing the first crystalline phase (S53). A pulverization treatment may be performed on each of the solid electrolyte containing the first crystalline phase (i.e., LiAlF having an orthorhombic crystal structure) and the LiAlF having a monoclinic crystal structure before the mixing in S53, or the mixture may be pulverized during the mixing in S53. The pulverization treatment here may be the same as that described in the manufacturing method according to the third embodiment.

[0118] Li3AlF6 having a monoclinic crystal structure may be synthesized by adjusting the heat treatment temperature during the fluorination treatment in the manufacturing methods of the second to fourth embodiments, for example. That is, in the manufacturing methods of the second to fourth embodiments, a solid electrolyte having a high content of Li3AlF6 having a monoclinic crystal structure (i.e., the second crystal phase) may be synthesized by lowering the heat treatment temperature during the fluorination treatment, and the obtained solid electrolyte may be used as Li3AlF6 having a monoclinic crystal structure.

[0119] FIG. 6 is a flowchart showing a modified example of the method for producing a solid electrolyte according to the fifth embodiment. In this example, LiAlF having a monoclinic crystal structure is synthesized using the production method according to the second embodiment. First, a first raw material and a first fluorine-containing material are mixed (S61). This first raw material is a raw material for synthesizing a solid electrolyte containing a first crystal phase, and corresponds to the raw material described in the second embodiment. The first fluorine-containing material corresponds to the fluorine-containing material described in the second embodiment. Next, the obtained first mixture containing the first raw material and the first fluorine-containing material is heat-treated to fluorinate the first raw material, thereby synthesizing a solid electrolyte containing a first crystal phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure (S62). Meanwhile, a raw material for LiAlF having a monoclinic crystal structure (hereinafter referred to as the second raw material) is prepared, which contains 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 Al oxide, Al carbonate, and Al hydroxide. The raw material described in the second embodiment may be used as the second raw material. The second raw material is mixed with a second fluorine-containing material (S63). The second fluorine-containing material may be the fluorine-containing material described in the second embodiment. The obtained second mixture containing the second raw material and the second fluorine-containing material is heat-treated to fluorinate the second raw material, synthesizing LiAlF having a monoclinic crystal structure and a solid electrolyte containing a high proportion of LiAlF having a monoclinic crystal structure (i.e., the second crystal phase) (S64). Next, LiAlF having a monoclinic crystal structure is mixed with the solid electrolyte containing the first crystal phase (S65). The pulverization treatment may be performed on each of the solid electrolyte containing the first crystal phase (i.e., LiAlF having an orthorhombic crystal structure) and LiAlF having a monoclinic crystal structure before mixing S65, or the pulverization treatment may be performed on the mixture when mixing S65. The pulverization treatment here may be the same as that described in the manufacturing method according to the third embodiment.

[0120] According to the above-described manufacturing method, a solid electrolyte including a first crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystalline structure, and a second crystalline phase represented by composition formula (1): LiAlF and having a monoclinic crystalline structure can be manufactured by adjusting the content ratio of the first crystalline phase to the second crystalline phase. This allows the ionic conductivity, powder characteristics, and processability to be individually adjusted, thereby enabling a wide range of adjustments to the properties of the solid electrolyte.

[0121] Here, as an example of the manufacturing method of the fifth embodiment, a method of mixing Li3AlF6 having an orthorhombic crystal structure and Li3AlF6 having a monoclinic crystal structure has been described. However, the manufacturing method of the fifth embodiment is not limited to this method, and two or more solid electrolytes having different content ratios of a first crystal phase having an orthorhombic crystal structure and a second crystal phase having a monoclinic crystal structure may be mixed. Furthermore, instead of mixing solid electrolytes having different content ratios of the first crystal phase and the second crystal phase, multiple combinations of solid electrolytes having different manufacturing conditions, such as different compositions or contents of subcomponents or different pulverized particle sizes, may be mixed.

[0122] Sixth Embodiment A sixth embodiment will be described below. Matters described in the first, second, third, fourth, and fifth embodiments will be omitted as appropriate.

[0123] The battery according to the sixth 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.

[0124] At least one selected from the group consisting of the positive electrode, the electrolyte layer, and the negative electrode contains the solid electrolyte according to the first embodiment, i.e., the solid electrolyte is represented by composition formula (1): LiAlF and includes a first crystalline phase having an orthorhombic crystal structure.

[0125] The battery according to the sixth embodiment contains the solid electrolyte material according to the first embodiment, and therefore has excellent charge / discharge characteristics.

[0126] FIG. 7 shows a cross-sectional view of a battery 1000 according to a sixth embodiment.

[0127] The battery 1000 according to the sixth 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.

[0128] The positive electrode 201 may include a positive electrode material including the solid electrolyte according to the first embodiment. The positive electrode 201 includes a positive electrode active material 204 and a solid electrolyte 100.

[0129] The electrolyte layer 202 contains an electrolyte material.

[0130] The negative electrode 203 contains a negative electrode active material 205 and a solid electrolyte 100 .

[0131] The solid electrolyte 100 includes, for example, the solid electrolyte according to the first embodiment. The solid electrolyte 100 may be particles containing the solid electrolyte according to the first embodiment as a main component. Particles containing the solid electrolyte according to the first 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 first embodiment. The solid electrolyte 100 may be particles made of the solid electrolyte according to the first embodiment.

[0132] 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.

[0133] 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.

[0134] In the present disclosure, "(A, B, C)" means "at least one selected from the group consisting of A, B, and C."

[0135] 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.

[0136] 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.

[0137] 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.

[0138] A coating layer may be formed on at least a portion of the surface of the positive electrode active material 204. The coating layer may be formed on the surface of the positive electrode active material 204, for example, before mixing with the conductive additive and the binder. Examples of coating materials included in the coating layer include a sulfide solid electrolyte, an oxide solid electrolyte, or a halide solid electrolyte. When the solid electrolyte 100 contains a sulfide solid electrolyte, the coating material may contain the solid electrolyte according to the first embodiment to suppress oxidative decomposition of the sulfide solid electrolyte. When the solid electrolyte 100 contains the solid electrolyte according to the first 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.

[0139] As described above, when the positive electrode 201 includes a positive electrode material including the solid electrolyte according to the first embodiment, the positive electrode material may include the solid electrolyte according to the first embodiment as the solid electrolyte 100, or may include the solid electrolyte as a coating material that coats the positive electrode active material 204.

[0140] 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.

[0141] 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 first embodiment. The electrolyte layer 202 may be a solid electrolyte layer.

[0142] The electrolyte layer 202 may contain 50 mass % or more of the solid electrolyte according to the first embodiment. The electrolyte layer 202 may contain 70 mass % or more of the solid electrolyte according to the first embodiment. The electrolyte layer 202 may contain 90 mass % or more of the solid electrolyte according to the first embodiment. The electrolyte layer 202 may be made of only the solid electrolyte according to the first embodiment.

[0143] Hereinafter, the solid electrolyte according to the first 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.

[0144] 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.

[0145] The battery according to the sixth 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.

[0146] The electrolyte layer 202 may consist of only the second solid electrolyte.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] The shape of the negative electrode active material 205 is not limited to a specific shape. The negative electrode active material 205 may be particles. The negative electrode active material 205 may have a median diameter of 0.1 μm or more and 100 μm or less. When the negative electrode active material 205 has a median diameter of 0.1 μm or more, the negative electrode active material 205 and the solid electrolyte 100 can be well dispersed in the negative electrode 203. This improves the charge / discharge characteristics of the battery 1000. When the negative electrode active material 205 has a median diameter of 100 μm or less, the lithium diffusion rate within the negative electrode active material 205 improves. This allows the battery 1000 to operate at high power.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] The second solid electrolyte may be a sulfide solid electrolyte.

[0159] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75 S4, or Li 10 GeP2S 12 is.

[0160] 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.

[0161] The second solid electrolyte may be an oxide solid electrolyte.

[0162] 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) LiLaZrO12 or an element-substituted product thereof; or (v) Li3PO4 or an N-substituted product thereof.

[0163] As mentioned above, the second solid electrolyte may be a halide solid electrolyte.

[0164] 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.

[0165] Other examples of halide solid electrolytes include Li a Me b Y c Z6, 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).

[0166] 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.

[0167] The halide solid electrolyte may be Li3YCl6 or Li3YBr6.

[0168] The second solid electrolyte may be an organic polymer solid electrolyte.

[0169] An example of the organic polymer solid electrolyte is a compound of a polymer compound and a lithium salt.

[0170] 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.

[0171] 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.

[0172] 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.

[0173] The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] Examples of cations contained in the ionic liquid are: (i) aliphatic chain quaternary salts such as tetraalkylammonium or tetraalkylphosphonium; (ii) aliphatic cyclic ammoniums such as pyrrolidiniums, morpholiniums, imidazoliniums, tetrahydropyrimidiniums, piperaziniums, or piperidiniums; or (iii) nitrogen-containing heterocyclic aromatic cations such as pyridiniums or imidazoliums.

[0178] 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.

[0179] The ionic liquid may contain a lithium salt.

[0180] 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.

[0181] Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl ester of acrylic acid, polyethyl ester of acrylic acid, polyhexyl ester of acrylic acid, polymethacrylic acid, polymethyl ester of methacrylic acid, polyethyl ester of methacrylic acid, polyhexyl ester of methacrylic acid, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, and carboxymethyl cellulose. Copolymers can also be used as binders. Examples of such binders include copolymers of two or more materials selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene. A mixture of two or more materials selected from these may be used as the binder.

[0182] At least one selected from the positive electrode 201 and the negative electrode 203 may contain a conductive additive to improve electronic conductivity.

[0183] 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. To reduce costs, the conductive additives (i) or (ii) above may be used.

[0184] 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 sixth embodiment include a coin type, a cylindrical type, a prismatic type, a sheet type, a button type, a flat type, and a laminate type.

[0185] The battery according to the sixth 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.

[0186] [Other Embodiments] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0187] (Technology 1) A solid electrolyte including a first crystalline phase represented by the following composition formula (1) and having an orthorhombic crystal structure. Composition formula (1): Li3AlF6

[0188] A solid electrolyte having the above configuration is a highly useful new solid electrolyte. For example, a solid electrolyte having the above configuration can have high ionic conductivity and excellent stability. For example, a solid electrolyte having the above configuration can be synthesized at low temperatures (e.g., about 150°C or higher and 700°C or lower), and therefore is less likely to be exposed to high temperatures for long periods during production. This prevents the solid electrolyte from being sintered too hard during production, or from undergoing excessive grain growth. Therefore, a solid electrolyte having the above configuration can be provided as, for example, soft, highly deformable, and fine particles. Such a fine-particle solid electrolyte with excellent deformability is likely to form an interface where particles are in close contact with 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 forms a surface (junction interface) where the contact points between the particles expand. 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 exhibit improved ionic conductivity. Therefore, the solid electrolyte according to Technology 1 is a highly useful solid electrolyte that, for example, when used in a solid electrolyte layer of a battery, can realize a thin solid electrolyte layer, and can be suitably used as a coating layer for active material particles. Therefore, the solid electrolyte according to Technology 1 realizes a high-performance battery.

[0189] (Technology 2) The solid electrolyte according to Technology 1, wherein the solid electrolyte contains particles having a particle diameter of 1 μm or less.

[0190] The solid electrolyte having the above-described structure, when used in a solid electrolyte layer of a battery, can further reduce the thickness of the solid electrolyte layer, and can be more suitably used in a coating layer of active material particles. Therefore, the solid electrolyte of Technology 2 can realize a battery with higher performance.

[0191] (Technology 3) The solid electrolyte according to Technology 2, wherein the solid electrolyte has an average particle size of 1 μm or less.

[0192] The solid electrolyte having the above-described structure, when used in a solid electrolyte layer of a battery, can further reduce the thickness of the solid electrolyte layer, and can be more suitably used in a coating layer of active material particles. Therefore, the solid electrolyte of Technology 3 can realize a battery with higher performance.

[0193] (Technology 4) The solid electrolyte according to any one of Technologies 1 to 3, wherein the solid electrolyte contains particles having a particle diameter of 0.3 μm or more.

[0194] With the above-described configuration, the ionic conductivity can be improved in the solid electrolyte containing the first crystalline phase having an orthorhombic crystal structure.

[0195] (Technology 5) The solid electrolyte according to any one of Technologies 1 to 4, wherein the solid electrolyte contains particles having an aspect ratio of 2.0 or more.

[0196] The above configuration can improve ionic conductivity in a solid electrolyte containing a first crystalline phase having an orthorhombic crystal structure. Furthermore, when a slurry containing the solid electrolyte according to Technology 5 is printed or coated, the particles of the solid electrolyte are likely to be oriented and aligned along the printed or coated surface. Therefore, when the solid electrolyte according to Technology 5 is used in a solid electrolyte layer of a battery, the solid electrolyte layer can be further thinned and densified. This reduces the resistance of the solid electrolyte layer. Therefore, the solid electrolyte according to Technology 5 can realize a small battery with a high capacity density. Furthermore, when the solid electrolyte according to Technology 5 is used in a solid electrolyte layer of a battery, the resistance component of the solid electrolyte layer is reduced, resulting in a high-performance battery.

[0197] (Technology 6) The solid electrolyte according to any one of Technologies 1 to 5, wherein the solid electrolyte includes particles having a free surface.

[0198] With the above-described configuration, it is possible to realize a solid electrolyte that is excellent in stability against, for example, the atmosphere.

[0199] (Technology 7) The solid electrolyte according to any one of Technologies 1 to 6, wherein the solid electrolyte further contains a second crystalline phase represented by the composition formula (1) and having a monoclinic crystal structure.

[0200] The above-described configuration allows for the production of a softer, more deformable solid electrolyte. When a softer, more deformable solid electrolyte is compacted, it is more likely to form an interface where particles adhere to each other, which makes it easier to achieve a higher density and a thinner layer. Furthermore, further improvements in ionic conductivity can be expected. Therefore, when the solid electrolyte of Technology 7 is used in a battery, it can realize a battery with higher performance and excellent reliability.

[0201] (Technology 8) The solid electrolyte according to Technology 7, wherein the solid electrolyte includes: first particles that include the first crystalline phase and do not include the second crystalline phase; and second particles that include the second crystalline phase, and the second particles are softer than the first particles.

[0202] The above-described configuration allows for the production of a softer, more deformable solid electrolyte. When a softer, more deformable solid electrolyte is compacted, it is more likely to form an interface where particles adhere to each other, making it easier to achieve higher density and thinner layers. Further, improved ionic conductivity can be expected. Furthermore, thermal shock resistance, such as in thermal cycling, is also improved. Therefore, when the solid electrolyte of Technology 8 is used in a battery, it can realize a battery with higher performance and superior reliability.

[0203] (Technology 9) The solid electrolyte according to any one of Technologies 1 to 8, wherein the solid electrolyte further includes an amorphous phase.

[0204] With the above configuration, the amorphous portion of the solid electrolyte becomes softer, exhibiting better deformability and improved inter-particle bonding. Therefore, the compacted solid electrolyte can be configured to form a solid electrolyte layer of any shape with higher ionic conductivity and higher stability. Therefore, the compacted solid electrolyte of Technology 9 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 9 realizes a battery with high performance and high reliability.

[0205] (Technology 10) The solid electrolyte according to any one of Techniques 1 to 9, wherein the solid electrolyte further contains at least one selected from the group consisting of Ti, Si, Cu, and Ga as a minor component.

[0206] With the above-mentioned structure, a homogeneous solid electrolyte having excellent ionic conductivity can be obtained.

[0207] (Technology 11) A method for producing the solid electrolyte according to any one of Technologies 1 to 10, comprising: (A) mixing raw materials containing 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 Al, a carbonate of Al, and a hydroxide of Al, and subjecting the mixed raw materials to a fluorination treatment.

[0208] The above-described manufacturing method uses relatively stable oxides, carbonates, and hydroxides as raw materials and simultaneously induces fluorination of the raw materials and a solid-state reaction. This allows for the synthesis of a solid electrolyte having a first crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure. Furthermore, this manufacturing method allows for the synthesis of a solid electrolyte having a first crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure at low temperatures (e.g., temperatures between 150°C and 700°C) that cannot be achieved by solid-state reactions using fluoride raw materials. Furthermore, this manufacturing method allows for the production of a solid electrolyte having a precise desired composition by controlling the ratio of each component of the raw materials. Therefore, a solid electrolyte having a crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure can be produced stably, at low cost, easily, and with good reproducibility.

[0209] (Technology 12) The method for producing a solid electrolyte according to Technology 11, wherein in (A), the fluorination treatment of the raw material is carried out by heat treating a thermally decomposable fluorine-containing material.

[0210] According to the above-described manufacturing method, fluorination of raw materials and solid-state reaction can be simultaneously performed to synthesize a solid electrolyte containing a first crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure. Therefore, a solid electrolyte with homogeneous and excellent properties can be obtained in a short time while reducing reaction residues such as oxides. Furthermore, the temperatures and reaction rates of the fluorination reaction and solid-state reaction of the raw materials can be controlled by selecting fluorine-containing materials with different thermal decomposition temperatures and adjusting the particle size of the raw materials. Therefore, fluorination treatment suitable for various raw materials can be performed.

[0211] (Technology 13) The method for producing a solid electrolyte according to Technology 12, wherein the fluorine-containing material is in a particulate form.

[0212] According to the above-described manufacturing method, 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 above-described manufacturing method, 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, the amount of fluorine can be precisely controlled. 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.

[0213] (Technology 14) The method for producing a solid electrolyte according to Technology 12 or 13, 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.

[0214] According to the above-described manufacturing method, a homogeneous mixture of the raw material and the fluorine-containing material can be subjected to a heat treatment for fluorination. Furthermore, the contact area between the raw material and the fluorine-containing material can be increased. Therefore, according to the above-described manufacturing method, 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.

[0215] (Technology 15) The method for producing a solid electrolyte according to any one of Techniques 12 to 14, 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.

[0216] According to the above-described manufacturing method, 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 in addition to 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.

[0217] (Technology 16) The method for producing a solid electrolyte according to any one of Techniques 12 to 15, wherein the fluorine-containing substance includes ammonium fluoride.

[0218] Ammonium fluoride begins to thermally decompose at relatively low temperatures (e.g., about 150°C). Therefore, ammonium salts are unlikely to remain as unnecessary inorganic components in the final solid electrolyte, and can be thermally decomposed at low temperatures to fluorinate the raw material. Therefore, the above-described manufacturing method is effective for fluorinating raw materials containing fluorine at low temperatures (e.g., about 150 to 200°C). This method can prevent 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 facilitates the densification and thinning of the powder compact. For example, when the solid electrolyte obtained by the above-described manufacturing method is 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 manufactured by the above-described manufacturing method can realize a higher-performance battery. This method can prevent unnecessary inorganic components derived from fluorine-containing materials from remaining in the final solid electrolyte. Furthermore, it saves energy during synthesis and reduces the time required for heating and cooling, thereby improving productivity. Furthermore, since synthesis can be performed at low temperatures, the durability of furnace materials is improved, significantly reducing the running costs and replacement frequency of synthesis components.

[0219] (Technology 17) The method for producing a solid electrolyte according to any one of Techniques 12 to 16, wherein the fluorine-containing material includes a resin.

[0220] According to the above-described manufacturing method, the raw material can be fluorinated while the fluorine-containing material is thermally decomposed at a relatively high temperature (e.g., about 400° C. or higher and 600° C. or lower). Therefore, the above-described manufacturing method 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).

[0221] (Technology 18) The method for producing a solid electrolyte according to Technology 17, wherein the resin is a fluororesin.

[0222] 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).

[0223] (Technology 19) The method for producing a solid electrolyte according to any one of Techniques 12 to 18, wherein the fluorine-containing material contains a substance that causes the solid electrolyte to substantially not contain inorganic components, except for elemental fluorine, that are generated by thermal decomposition by the heat treatment in (A).

[0224] The fluorine-containing material is required to replace the fluorine element generated by thermal decomposition by the heat treatment in (A) above with the oxygen element of the raw material, while preventing other components from being mixed as inorganic residues into the final solid electrolyte, which is represented by composition formula (1): LiAlF and includes a first crystalline phase having an orthorhombic crystal structure. By using a substance 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, 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 substance in which the inorganic components, except for the fluorine element, generated by thermal decomposition by the heat treatment are gasified and discharged.

[0225] (Technology 20) The method for producing a solid electrolyte according to any one of Techniques 12 to 19, wherein the fluorine-containing material includes a plurality of kinds of fluorine-containing compounds.

[0226] According to the above-described manufacturing method, for example, both ammonium fluoride and a fluororesin can be used as the fluorine-containing material. This allows for a wide temperature range in which the fluorine-containing material acts as a fluorine source. Therefore, the conversion of the raw material to a fluoride and the solid-state reaction temperature can be controlled over a wide range. Therefore, according to the above-described manufacturing method, the desired solid electrolyte can be easily synthesized.

[0227] (Technology 21) The method for producing a solid electrolyte according to any one of Techniques 11 to 20, further comprising, after the step (A), (B) subjecting the solid electrolyte obtained in the step (A) to a pulverization treatment.

[0228] According to the above manufacturing method, a solid electrolyte can be obtained with powder properties (e.g., particle shape, amorphization of the surface, etc.) suitable for the application. According to the above manufacturing method, at least a portion of the solid electrolyte can be amorphized, thereby improving ionic conductivity and improving the softness of the solid electrolyte particles. By improving the softness of the solid electrolyte particles, the density of a compact of the solid electrolyte can be improved. Therefore, the solid electrolyte obtained by the manufacturing method of Technology 17 can form a dense compact with high ionic conductivity.

[0229] (Technology 22) A positive electrode material comprising the solid electrolyte according to any one of Technology 1 to Technology 10.

[0230] The positive electrode material according to Technology 22 can realize a high-performance battery having excellent charge / discharge characteristics.

[0231] (Technology 23) A battery comprising a positive electrode containing the positive electrode material according to Technology 22.

[0232] This configuration makes it possible to provide a battery with excellent charge / discharge characteristics.

[0233] (Technology 24) 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 any one of Technologies 1 to 10.

[0234] This configuration makes it possible to provide a high-performance battery having excellent charge / discharge characteristics.

[0235] While the solid electrolyte and the manufacturing method thereof 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 a person skilled in the art to the embodiments and other forms constructed by combining some of the components of the embodiments are also included in the scope of the present disclosure.

[0236] 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.

[0237] The present disclosure will now be described in more detail with reference to examples.

[0238] <Synthesis of Solid Electrolyte> (Example 1) Li2CO3 (average particle size: about 1.5 μm) and Al2O3 (average particle size: 0.3 μm) were prepared as raw materials, NH4F (average particle size: about 120 μm) was used as a fluorine-containing substance, and TiO2 (average particle size: about 0.5 μm, rutile type), SiO2 (average particle size: about 0.3 μm), CuO (average particle size: about 1.2 μm), and Ga2O3 (average particle size: about 0.8 μm) were used as additives.

[0239] Li2CO3 and Al2O3 were weighed out so that Li3AlO3 would be synthesized. Furthermore, the additives were weighed out so that the TiO2 powder, SiO2 powder, CuO powder, and Ga2O3 powder would be 0.01 mol%, 0.005 mol%, and 0.005 mol%, respectively, relative to the Li3AlO3 to be synthesized. These raw materials and additives were weighed out in the air.

[0240] The raw material 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 for approximately 10 minutes using a mortar and pestle, and then passed through a #32 mesh sieve to obtain a raw material powder containing the raw materials and additives. The average particle size of the resulting raw material powder was approximately 0.46 μm.

[0241] Next, NH4F powder, which is a fluorine-containing material, was mixed with the raw material powder. The amount of NH4F powder needed to fluorinate the raw material was added. Specifically, the amount of NH4F used was enough to fluorinate all of the raw material according to the reaction formula.

[0242] The mixture of raw material powders and NH4F powder was mixed uniformly with a pestle in an alumina mortar for about 10 minutes (a step corresponding to (A-1) above). This resulted in a mixture containing raw materials, additives, and a fluorine-containing substance. Note that mixing of these substances was carried out in normal air, the same as when they were weighed.

[0243] 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 320°C.

[0244] The solid electrolyte of this example was synthesized by using carbonate and oxide as raw materials and fluorinating the mixture, which resulted in the fluorination of each component constituting the raw materials and a solid-state reaction. Since the manufacturing method of this example does not produce evaporative components, the reaction in a sealed container is not necessary, and the solid electrolyte could be heat-treated (fired) without causing compositional fluctuations, with a structure similar to that of general oxide ceramics.

[0245] 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 36 hours.

[0246] Comparative Example 1: Fluoride was used as a raw material, and the solid electrolyte of Comparative Example 1 was prepared by mechanochemical synthesis. Specifically, LiF and AlF were prepared in a molar ratio of LiF:AlF = 3:1. 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.

[0247] <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, and the particle shape was also observed using an SEM. The crystalline phase, ionic conductivity, average particle size, and BET specific surface area were evaluated for both the solid electrolyte after heat treatment and before pulverization, and the solid electrolyte after pulverization. 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.

[0248] (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.

[0249] FIG. 8A is a graph showing the X-ray diffraction pattern of the solid electrolyte after heat treatment and before pulverization in the manufacturing method of Example 1, and the X-ray diffraction pattern of the solid electrolyte obtained in Comparative Example 1. FIG. 8B is a graph showing the X-ray diffraction pattern of the solid electrolyte after pulverization obtained in Example 1. As shown in FIG. 8A, the XRD pattern of Li3AlF6 having an orthorhombic crystal structure was confirmed in the solid electrolyte after fluorination obtained in Example 1. Note that only the orthorhombic crystal phase (first crystal phase) of Li3AlF6 was confirmed from the XRD pattern of the solid electrolyte after fluorination obtained in Example 1, and no other precipitated phases, such as compositions related to additives, were detected. In the solid electrolyte after further pulverization of this fluorinated solid electrolyte, the progression of amorphization can be confirmed from the X-ray diffraction pattern shown in FIG. 8B. Note that, although the crystallinity of the pulverized solid electrolyte was reduced by the pulverization compared to the solid electrolyte before pulverization, no additional precipitated phases were observed. The solid electrolyte obtained in Comparative Example 1 was Li3AlF6 having a monoclinic crystal structure.

[0250] (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. The electrical length deviations 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 0.93 μS / cm, and the ionic conductivity after the pulverization treatment was 3.8 μS / cm. For the solid electrolyte obtained in Comparative Example 1, the ionic conductivity after the pulverization treatment was 1.2 μS / cm.

[0251] (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.

[0252] (Average particle size) The average particle size 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 size) of the measured particle size distribution was considered to be the average particle size. For the solid electrolyte of Example 1, the average particle size before pulverization was 0.7 μm, and the average particle size after pulverization was 0.62 μm.

[0253] (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 3.2 m 2 / g, and the BET specific surface area after pulverization was 4.1 m 2 / g.

[0254] (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 and solidified within a 5 mm x 5 mm area), 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 Ti, Si, Cu, and Ga. The Ti content was 0.003 at. %, the Si content was 0.005 at. %, the Cu content was 0.002 at. %, and the Ga content was 0.002 at. %.

[0255] (Observation of Particle Shape) The particle shape was observed using an SEM image of the solid electrolyte obtained in Example 1. The solid electrolyte particles confirmed from the SEM image had an elongated shape. It was also confirmed that the particle diameter (major axis) was 0.3 μm or more and 1 μm or less, and that the particles contained particles with an aspect ratio of 2.0 or more.

[0256] The evaluation results of the solid electrolyte obtained in Example 1 showed that the manufacturing method of the present disclosure and the solid electrolyte manufactured by the manufacturing method had a high ionic conductivity of 3.8 μS / cm. This ionic conductivity is higher than the ionic conductivity (approximately 1 μS / cm) of Li3AlF6, which has a monoclinic crystal structure and is synthesized by a solid-state reaction from a fluoride raw material, and it was confirmed that the solid electrolyte of the present disclosure is a useful one with excellent properties. In addition, the electronic conductivity was <1.0 × 10 -9 It was confirmed that the electrolyte had no electronic conductivity (i.e., negligible electronic conductivity) and was an ionically conductive solid electrolyte.

[0257] The X-ray diffraction pattern shown in FIG. 8A confirmed the presence of a first crystalline phase represented by composition formula (1): LiAlF and having an orthorhombic crystal structure for the solid electrolyte of Example 1. Furthermore, the X-ray diffraction pattern shown in FIG. 8B confirmed that the X-ray diffraction pattern for the solid electrolyte of Example 1 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 descriptions for each evaluation item. These results demonstrate that the pulverization treatment 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.

[0258] As described above, the solid electrolyte and manufacturing method thereof disclosed herein can realize a highly useful solid electrolyte that is difficult to synthesize using conventional manufacturing methods and has higher ionic conductivity than LiAlF having a monoclinic crystal structure synthesized using conventional manufacturing methods, and that is soft and has excellent deformability. Furthermore, while the fluoride raw materials used in conventional manufacturing methods are extremely expensive, the manufacturing method disclosed herein uses inexpensive raw materials such as oxides, thereby reducing the manufacturing cost of the solid electrolyte. Therefore, the manufacturing method disclosed herein has great industrial utility.

[0259] 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 solid electrolyte comprising a first crystal phase represented by the following composition formula (1) and having a rectangular crystal structure. Composition formula (1): Li3AlF6 2. The solid electrolyte according to claim 1, wherein the solid electrolyte contains particles having a particle diameter of 1 μm or less.

3. The solid electrolyte according to claim 2, wherein the average particle size of the solid electrolyte is 1 μm or less.

4. The solid electrolyte according to claim 1, wherein the solid electrolyte contains particles having a particle diameter of 0.3 μm or more.

5. The solid electrolyte according to claim 1, wherein the solid electrolyte contains particles having an aspect ratio of 2.0 or more.

6. The solid electrolyte according to claim 1, wherein the solid electrolyte comprises particles having a free surface.

7. The solid electrolyte according to claim 1, further comprising a second crystal phase represented by the composition formula (1) and having a monoclinic crystal structure.

8. The solid electrolyte according to claim 7, comprising: first particles including the first crystal phase and not including the second crystal phase; and second particles including the second crystal phase, the second particles being softer than the first particles.

9. The solid electrolyte according to claim 1, further comprising an amorphous phase.

10. The solid electrolyte according to claim 1, further comprising at least one selected from the group consisting of Ti, Si, Cu, and Ga as a minor component.

11. A method for producing the solid electrolyte according to any one of claims 1 to 10, comprising: (A) mixing raw materials containing 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 Al, a carbonate of Al, and a hydroxide of Al, and subjecting the mixed raw materials to a fluorination treatment.

12. The method for producing a solid electrolyte according to claim 11, wherein in (A), the fluorination treatment of the raw material is carried out by heat treating a thermally decomposable fluorine-containing material.

13. The method for producing a solid electrolyte according to claim 12, wherein the fluorine-containing material is in particulate form.

14. The method for producing a solid electrolyte according to claim 12, 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.

15. The method for producing a solid electrolyte according to claim 12, 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.

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

17. The method for producing a solid electrolyte according to claim 12, wherein the fluorine-containing material includes a resin.

18. The method for producing a solid electrolyte according to claim 17, wherein the resin is a fluororesin.

19. The method for producing a solid electrolyte according to claim 12, 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).

20. The method for producing a solid electrolyte according to claim 12, wherein the fluorine-containing material includes a plurality of types of fluorine-containing compounds.

21. The method for producing a solid electrolyte according to claim 11, further comprising, after the step (A), (B) subjecting the solid electrolyte obtained in the step (A) to a pulverization treatment.

22. A positive electrode material comprising the solid electrolyte of claim 1.

23. A battery comprising a positive electrode comprising the positive electrode material of claim 22.

24. 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 1.

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