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 represented by compositional formula (1) below: Li3AlF6 and having an orthorhombic crystal structure. A method for producing a solid electrolyte according to the present disclosure includes (A) mixing a starting material including at least one selected from the group consisting of oxides of Li, carbonates of Li, and hydroxides of Li with at least one selected from the group consisting of oxides of Al, carbonates of Al, and hydroxides of Al, and subjecting the mixed starting material to a fluorination treatment.

Description

Technical Field

[0001] This disclosure relates to solid electrolytes, methods for manufacturing solid electrolytes, cathode materials, and batteries. Background Technology

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

[0003] Existing technical documents Patent documents Patent Document 1: International Publication No. 2018 / 123479 Summary of the Invention

[0004] The problem that the invention aims to solve The purpose of this disclosure is to provide new solid electrolyte materials with high utility.

[0005] Methods for solving problems The solid electrolyte disclosed herein comprises a first crystal phase represented by the following compositional formula (1) and having a crystal structure of orthorhombic crystal system (also known as orthorhombic crystal system).

[0006] Composition formula (1): Li3AlF6 Invention Effects This disclosure provides new solid electrolyte materials with high usefulness. Attached Figure Description

[0007] Figure 1 This is a flowchart illustrating an example of a method for manufacturing a solid electrolyte according to the second embodiment.

[0008] Figure 2 This is a flowchart illustrating an example of a method for manufacturing a solid electrolyte according to the third embodiment.

[0009] Figure 3 This is a flowchart illustrating a variation of the method for manufacturing a solid electrolyte according to the third embodiment.

[0010] Figure 4 This is a flowchart illustrating an example of a method for manufacturing a solid electrolyte according to the fourth embodiment.

[0011] Figure 5 This is a flowchart illustrating an example of a method for manufacturing a solid electrolyte according to the fifth embodiment.

[0012] Figure 6 This is a flowchart illustrating a variation of the method for manufacturing a solid electrolyte according to the fifth embodiment.

[0013] Figure 7 A cross-sectional view of the battery 1000 according to the sixth embodiment is shown.

[0014] Figure 8A This 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.

[0015] Figure 8B This is a graph showing the X-ray diffraction pattern of the solid electrolyte after pulverization obtained in Example 1. Detailed Implementation

[0016] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0017] The embodiments described below are either general or specific examples. The numerical values, shapes, materials, and constituent elements shown in the following embodiments are examples and are not intended to limit this disclosure. In addition, the constituent elements in the following embodiments that are not described in the independent claims representing the highest concept are described as optional constituent elements.

[0018] [First Implementation Method] The solid electrolyte in the first embodiment of this disclosure comprises a first crystal phase represented by the following compositional formula (1) and having an orthorhombic crystal system.

[0019] Composition formula (1): Li3AlF6 The solid electrolyte of the first embodiment is a novel solid electrolyte with high utility. The solid electrolyte, comprising a first crystal phase represented by the formula (1): Li3AlF6 and having an orthorhombic crystal system, possesses high ionic conductivity and excellent stability. Solid electrolytes with such a structure can be synthesized, for example, at low temperatures (e.g., above 150°C and below 700°C), thus avoiding prolonged exposure to high temperatures during manufacturing. Consequently, the solid electrolyte does not become excessively hardened during manufacturing, nor does excessive grain growth occur. Therefore, the solid electrolyte of the first embodiment is soft and has excellent deformability, and can be provided as fine particles. Such finely deformable solid electrolyte particles easily form interfaces where particles are closely packed together when formed into powder, enabling high density and easy thinning, further promising improved ionic conductivity. Therefore, the solid electrolyte of the first embodiment, for example, in the case of a solid electrolyte layer for a battery, allows for thinning of the solid electrolyte layer, or is suitable for use as a coating layer for active material particles, making it a highly useful solid electrolyte. Therefore, a high-performance battery can be achieved using the solid electrolyte according to the first embodiment. It should be noted that the hardness of the solid electrolyte can be evaluated, for example, by methods such as micro-Vickers hardness testing of particles or pressed powders.

[0020] The solid electrolyte in the first embodiment can be in particle form. Based on this configuration, a relatively soft, particle-shaped solid electrolyte can be achieved. Therefore, the pressed powder of such a solid electrolyte exhibits high ionic conductivity, excellent stability, and can be shaped in any manner. Thus, the pressed powder of a solid electrolyte with these characteristics can be used to create a solid electrolyte layer or a coating layer of active material particles for a battery with excellent properties and high reliability. Therefore, based on the solid electrolyte obtained by the manufacturing method of the first embodiment, a high-performance and highly reliable battery can be achieved. It should be noted that the size and shape of the solid electrolyte particles can be appropriately selected according to the application.

[0021] The solid electrolyte of the first embodiment, for example, contains particles with a particle size of 1 μm or less. By including such particles in the solid electrolyte of the first embodiment, when the solid electrolyte is used as a solid electrolyte layer, it is possible to further thin the solid electrolyte layer, or to more appropriately use it as a coating layer for active material particles. Based on a solid electrolyte having such a configuration, a battery with higher performance can be achieved.

[0022] The solid electrolyte of the first embodiment, for example, contains particles with a particle size of 0.3 μm or more. By including such particles in the solid electrolyte of the first embodiment, ionic conductivity can be improved.

[0023] The average particle size of the solid electrolyte in the first embodiment can be 1 μm or less. A solid electrolyte having such an average particle size, for example, in the case of a solid electrolyte layer used in a battery, allows for further thinning of the solid electrolyte layer, or it can be more appropriately used as a coating layer for active material particles. Therefore, by having an average particle size of 1 μm or less, the solid electrolyte of the first embodiment can achieve a battery with higher performance. The average particle size of the solid electrolyte in the first embodiment can, for example, be 0.1 μm or more.

[0024] It should be noted that the average particle size of the solid electrolyte is the median particle size, which refers to the particle size (d50) equivalent to 50% of the volume cumulative size, determined by the particle size distribution measured on a volume basis using laser diffraction scattering. The same applies to the average particle size of the raw materials and fluorine-containing substances specifically specified in this specification.

[0025] The solid electrolyte of the first embodiment may contain particles with an aspect ratio of 2.0 or greater. Here, the aspect ratio of the solid electrolyte particles refers to the ratio of the longest diameter (i.e., the length of the major axis) of the solid electrolyte particles to the shortest diameter (i.e., the length of the minor axis) of the solid electrolyte particles (length of the major axis / length of the minor axis).

[0026] By including particles with elongated shapes having an aspect ratio of 2.0 or higher, the solid electrolyte of the first embodiment can improve ionic conductivity. Furthermore, when a slurry containing a solid electrolyte with particles having such an aspect ratio is prepared and then used for printing or coating, the solid electrolyte particles easily align along the printing or coating surface. Therefore, when a solid electrolyte containing particles with an aspect ratio of 2.0 or higher is used in the solid electrolyte layer of a battery, further thinning of the solid electrolyte layer is possible. Thus, based on a solid electrolyte containing particles with an aspect ratio of 2.0 or higher, a small battery with high capacity density can be achieved. Additionally, when a solid electrolyte with this configuration is used in the solid electrolyte layer of a battery, the resistivity of the solid electrolyte layer is reduced, thereby enabling a high-performance battery.

[0027] The particles of the solid electrolyte in the first embodiment may, for example, have an aspect ratio of 6.0 or less.

[0028] The average aspect ratio of the solid electrolyte in the first embodiment can be 2.0 or higher. Alternatively, the average aspect ratio of the solid electrolyte in the first embodiment can be 3.0 or lower.

[0029] Here, the aspect ratio of the solid electrolyte particles can be determined from SEM images of the solid electrolyte obtained by scanning electron microscopy (SEM). Specifically, the shortest and longest diameters of the particles are determined from the SEM images, and the aspect ratio of each particle is calculated. The average aspect ratio can be obtained by calculating the aspect ratios of 50 randomly selected particles from the SEM images of the solid electrolyte and then averaging them.

[0030] The solid electrolyte of the first embodiment may contain particles with free surfaces. With this configuration, the solid electrolyte of the first embodiment can exhibit excellent atmospheric stability. Here, in this disclosure, the free surface of the solid electrolyte refers to the surface of the solid electrolyte in its synthetic state (i.e., a highly stable surface), excluding the reactive active surface inside the solid electrolyte exposed by crushing or the like.

[0031] The solid electrolyte of the first embodiment may be a Li3AlF6 solid solution containing a first crystal phase represented by the formula (1): Li3AlF6 and having an orthorhombic crystal system.

[0032] The solid electrolyte of the first embodiment may further include a second crystalline phase represented by the formula (1): Li3AlF6 and having a monoclinic crystal structure. With this configuration, a softer, more deformable solid electrolyte can be obtained. This makes it easier to form a tightly packed interface between particles when the solid electrolyte is pressed into powder, enabling higher density and easier thinning, and further improvement in ionic conductivity can be expected. Therefore, when the solid electrolyte further includes the second crystalline phase, it can form a high-quality solid electrolyte layer and coating layer that suppresses defects such as voids when used as a solid electrolyte layer and active material particle coating layer in a battery. Therefore, the solid electrolyte of the first embodiment can achieve a battery with higher performance and better reliability. The solid electrolyte of the first embodiment may be a Li3AlF6 solid solution containing both a first and a second crystalline phase.

[0033] The solid electrolyte of the first embodiment may comprise a first particle containing a first crystalline phase but not a second crystalline phase, and a second particle containing a second crystalline phase. In this case, the second particle is softer than the first particle. Here, in this disclosure, the hardness of the first and second particles can be compared and evaluated by, for example, a micro Vickers hardness test on these particles or a pressed powder of these particles.

[0034] It should be noted that the ionic conductivity tends to be higher in the first crystalline phase than in the second crystalline phase. For example, solid electrolytes composed of the first crystalline phase can achieve ionic conductivity exceeding 3 μS / cm in pressed powder. On the other hand, the ionic conductivity of solid electrolytes composed of the second crystalline phase in pressed powder is, for example, about 1 μS / cm or more and about 2 μS / cm or less.

[0035] The solid electrolyte of the first embodiment, comprising a first particle and a second particle, further enhances flexibility and deformability. This makes it easier to form a tightly packed interface between particles during powder preparation, enabling higher density and easier thinning, and further improving ionic conductivity. Furthermore, thermal shock resistance, such as during thermal cycling, is also improved. Therefore, with this configuration, the solid electrolyte of the first embodiment, when used in batteries, enables batteries with higher performance and superior reliability.

[0036] The solid electrolyte of the first embodiment may contain an amorphous phase. According to this configuration, the amorphous portion of the solid electrolyte becomes more flexible, exhibits better deformability, and improves interparticle bonding. Therefore, the pressed powder of the solid electrolyte of the first embodiment can be formed into a solid electrolyte layer with higher ionic conductivity and higher stability in any shape. Thus, when the solid electrolyte of the first embodiment contains an amorphous phase, the pressed powder of this solid electrolyte can achieve a solid electrolyte layer or active material particle coating layer for a battery with excellent characteristics and high reliability. As a result, a high-performance and highly reliable battery can be achieved.

[0037] The solid electrolyte of the first embodiment may further include at least one selected from Ti, Si, Cu, and Ga as a secondary component. That is, in this case, the solid electrolyte obtained by the manufacturing method of the first embodiment includes a crystal phase represented by the compositional formula (1): Li3AlF6 and having an orthorhombic crystal structure, and also includes at least one selected from Ti, Si, Cu, and Ga. With this configuration, a homogeneous solid electrolyte with excellent ionic conductivity can be obtained.

[0038] The aforementioned elements (i.e., at least one selected from Ti, Si, Cu, and Ga) included as byproducts may, for example, come from substances added as additives to promote the reaction of the raw materials during the synthesis of the solid electrolyte of the first embodiment. Furthermore, in X-ray diffraction measurements of the solid electrolyte of the first embodiment, Ti, Si, Cu, and Ga are sometimes not detected as a composite phase. In such cases, the presence of Ti, Si, Cu, and Ga in the solid electrolyte can be confirmed by highly sensitive compositional analysis (surface analysis, etc.) such as electron probe microanalysis (EPMA). The total content of Ti, Si, Cu, and Ga in the solid electrolyte may, for example, be 0.0003 atomic% or more and 0.15 atomic% or less. The content of Ti, Si, Cu, and Ga can be determined using EPMA, etc.

[0039] When comparing the solid electrolyte of the first embodiment with the solid electrolyte described in Patent Document 1, the following differences exist.

[0040] In Patent Document 1, Li3AlF6 is disclosed as an example of a second solid electrolyte, a byproduct included in the solid electrolyte layer of a lithium-ion battery. Patent Document 1 does not describe a crystal structure, nor does it describe a synthesis method, therefore it is assumed to be synthesized using a known method. That is, it is believed that the Li3AlF6 disclosed in Patent Document 1 has a monoclinic crystal structure. Furthermore, according to Patent Document 1, the Li3AlF6 disclosed in Patent Document 1 is not considered amorphous. Therefore, the Li3AlF6 disclosed as a second solid electrolyte in Patent Document 1 is not the orthorhombic crystal structure of the solid electrolyte of the first embodiment, and thus it is difficult to obtain the high ionic conductivity of the solid electrolyte of the first embodiment. Additionally, the Li3AlF6 disclosed as a second solid electrolyte in Patent Document 1 is not as soft and deformable as the solid electrolyte of the first embodiment, nor does it easily form a dense particle interface when pressed into powder, making it more suitable for high-density and thin-layer production.

[0041] [Second Implementation] The manufacturing method of the solid electrolyte in the second embodiment will be described below.

[0042] The solid electrolyte manufactured by the manufacturing method of the second embodiment is the solid electrolyte of the first embodiment. That is, the manufacturing method of the second embodiment is a method for manufacturing a solid electrolyte comprising a first crystal phase represented by the compositional formula (1): Li3AlF6 and having an orthorhombic crystal system.

[0043] The manufacturing method of the second embodiment includes: (A) mixing a raw material containing at least one selected from Li oxide, Li carbonate and Li hydroxide with at least one selected from Al oxide, Al carbonate and Al hydroxide, and subjecting the mixed raw material to fluorination treatment.

[0044] The manufacturing method of the second embodiment uses relatively stable oxides, carbonates, and hydroxides as raw materials, allowing the fluorination of the raw materials and the solid-phase reaction to occur simultaneously. Therefore, it is possible to synthesize a solid electrolyte containing a first crystalline phase with an orthorhombic crystal structure represented by the compositional formula (1): Li3AlF6. Furthermore, according to this manufacturing method, a solid electrolyte containing a first crystalline phase with an orthorhombic crystal structure represented by the compositional formula (1): Li3AlF6 can be synthesized at low temperatures (e.g., around 150°C to 700°C) that cannot be synthesized in the solid-phase reaction using fluoride raw materials. Additionally, according to this manufacturing method, by controlling the ratio of each component of the raw materials, a solid electrolyte with the desired composition can be accurately manufactured. Therefore, according to the manufacturing method of the second embodiment, a solid electrolyte containing a crystalline phase with an orthorhombic crystal structure represented by the compositional formula (1): Li3AlF6 can be stably, cost-effectively, easily, and reproducibly manufactured.

[0045] For example, when Li3AlF6 with an orthorhombic crystal structure synthesized by the manufacturing method of the second embodiment is pressed into powder under a certain pressure, the density of the pressed powder can be shown to be 1.92 g / cm³. 3 Above and 1.98 g / cm 3 The following is related to the density of the pressed powder, which is 1.81 g / cm³. 3 Above and 1.94 g / cm 3 Compared to the following, which are considered to be of the same or greater extent, the density of the pressed powder is 1.81 g / cm³. 3 Above and 1.94 g / cm 3 The following can be achieved by using fluorides as raw materials to press Li3AlF6, which has a monoclinic crystal structure and is obtained by solid-state synthesis of fluorides, into powder under the same pressure.

[0046] In (A) above, the fluorination treatment of the raw material can be carried out, for example, by heat treatment of a fluorinated substance that is thermally decomposable.

[0047] By heat-treating the raw materials using thermally decomposable fluorinated substances, the fluorination of the raw materials and the solid-phase reaction for synthesizing the solid electrolyte can occur simultaneously, enabling the synthesis of a solid electrolyte containing a first crystalline phase with an orthorhombic crystal structure represented by the formula (1): Li3AlF6. Therefore, a homogeneous solid electrolyte with excellent properties can be obtained while reducing reaction residues such as oxides in a short time. Furthermore, the temperatures of the fluorination reaction and the solid-phase reaction, as well as the conduction of these reactions, can be controlled, for example, based on the selected thermal decomposition temperature of the fluorinated substance. Therefore, fluorination treatment suitable for various raw materials can be performed.

[0048] When a thermally decomposable fluorinated substance is used in the fluorination treatment of the raw material, in the manufacturing method of the second embodiment, step (A) above may also include: (A-1) Mix the above raw materials and the above fluorine-containing substance; and (A-2) By heat-treating the mixture containing the above raw material and the above fluorinated substance obtained in (A-1) above, the raw material is fluorinated to obtain a solid electrolyte.

[0049] In the manufacturing method of the second embodiment, by performing steps (A-1) and (A-2) as described above, a homogeneous mixture of raw materials and fluorinated substances can be subjected to heat treatment for fluorination. Furthermore, the contact area between the raw materials and the fluorinated substances can be increased. As a result, the fluorination of the raw materials is homogenized and promoted, thus enabling the efficient production of homogeneous solid electrolytes with excellent properties.

[0050] Figure 1 This is a flowchart illustrating an example of a method for manufacturing a solid electrolyte according to the second embodiment. Here, as an example of a manufacturing method according to the second embodiment, an example of implementing the manufacturing methods described above (A-1) and (A-2) will be described.

[0051] like Figure 1 As shown, in one example of the manufacturing method of the second embodiment, firstly, as a step equivalent to (A-1) above, the raw material and the fluorinated substance are mixed (S11). As described above, the raw material contains at least one selected from Li oxide, Li carbonate, and Li hydroxide, and at least one selected from Al oxide, Al carbonate, and Al hydroxide. The fluorinated substance is thermally decomposable. Next, as a step equivalent to (A-2) above, the obtained mixture containing the raw material and the fluorinated substance is heat-treated to fluorinate the raw material (S12). Thus, a solid electrolyte containing a first crystal phase represented by the compositional formula (1): Li3AlF6 and having an orthorhombic crystal system is obtained.

[0052] The following is a detailed description of each process corresponding to the above-mentioned raw materials, the above-mentioned fluorinated substances, and (A-1) and (A-2).

[0053] <Ingredients> The raw materials comprise at least one selected from Li oxides, Li carbonates and Li hydroxides, and at least one selected from Al oxides, Al carbonates and Al hydroxides.

[0054] Fluorination of the raw material occurs from the surface, so the raw material can be, for example, in particulate form. This facilitates simultaneous fluorination from the particle surface of the raw material (i.e., the substitution of oxygen with fluorine) and solid-phase reactions within the raw material. Therefore, fluorides can be synthesized quickly while minimizing reaction residues such as oxides. Consequently, a homogeneous solid electrolyte with excellent properties can be obtained. Furthermore, the particulate form of the raw material exhibits good reactivity, including good fluorination properties and solid-phase reactivity, thus enabling excellent productivity. Additionally, by making the raw material particulate, it is easy to mix uniformly with fluorine-containing substances, resulting in uniform fluorination and the synthesis of a solid electrolyte with excellent properties.

[0055] To synthesize Li3AlF6 with a fine, orthorhombic crystal structure, small particles are suitable as the Al source contained in the raw material. For example, the average particle size of at least one selected from Al oxides, Al carbonates, and Al hydroxides used as the Al source can be, for example, 0.06 μm or more and 1.0 μm or less. Furthermore, the BET specific surface area of ​​at least one selected from Al oxides, Al carbonates, and Al hydroxides used as the Al source can be, for example, 3 m². 2 / g or more and 30m 2 / g or less. Al sources with such a BET specific surface area are suitable for fluorination treatment. Therefore, by using an Al source with such a structure as a raw material, fluorination and solid-phase reactions can easily occur simultaneously.

[0056] The average particle size of the Li source contained in the raw material is not particularly limited; for example, it can be greater than 1 μm and less than 20 μm. Considering the stability, properties, and operability of the solid electrolyte for the purpose of synthesis, an appropriately large Li source can be selected.

[0057] The raw materials can be pre-crushed into individual substances. Reactivity can be improved by reducing the particle size or exposing the fracture surfaces of the particles through crushing. It should be noted that the fracture surfaces of particles are more reactive than unfractured surfaces. The incorporation of crushing treatment into the raw materials can be appropriately adjusted from the perspective of the stability and properties of solid electrolyte synthesis. Alternatively, the raw materials can be a mixture of crushed and uncrushed powders. A portion of the raw materials can also contain crushed powder. It should be noted that the fracture surfaces of the crushed powder can be observed through SEM of the powder, revealing a state different from the free surface.

[0058] The raw material can have an average particle size of, for example, 0.1 μm or more and 20 μm or less, or an average particle size of 0.5 μm or more and 20 μm or less. The average particle size of the composite oxide contained in the raw material can also be, for example, 0.1 μm or more and 20 μm or less, or 0.5 μm or more and 20 μm or less. The raw material can be further refined, for example, having an average particle size of 0.1 μm or more and 1.0 μm or less. The average particle size of the composite oxide contained in the raw material can also be, 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 ranges; from the viewpoint of fluorination and solid-phase reactions, any particle size and shape can be appropriately selected. For example, the smaller the particle size of the raw material, the lower the temperature of the conversion to fluoride can be.

[0059] <Fluoride-containing substances> Fluorine-containing substances are thermally decomposable.

[0060] The thermal decomposition start temperature of the fluorinated material used can be, for example, above 100°C and below 600°C. By ensuring that the fluorinated material has a thermal decomposition start temperature within the above temperature range, the fluorinated material exhibits stability during storage and mixing operations, and the resulting solid electrolyte can be prevented from becoming too hard.

[0061] Fluorine-containing substances can be in particulate form, for example. Therefore, these substances are prone to thermal decomposition. However, by using particulate fluorine-containing substances, the raw materials can be fluorinated efficiently, and fluorine residues are less likely to remain in the final solid electrolyte. Furthermore, the fluorination reaction can be controlled by the particle shape of the fluorine-containing substance. For example, by making the fluorine-containing substance particles finer, the fluorination temperature can be lowered, or the fluorination rate can be increased. Additionally, by mixing the raw materials with the fluorine-containing substance, the powder can be fluorinated uniformly throughout. Furthermore, precise control of the fluorine content is possible. Therefore, the desired solid electrolyte can be synthesized. Moreover, since only the amount of fluorine-containing substance required for the fluorination of the raw materials can be used, unlike the case where fluorine gas is introduced into the furnace, excess fluorine gas emissions can be suppressed. Therefore, the environmental impact is reduced, and consequently, the corrosive effect on furnace materials is also reduced.

[0062] Fluorine-containing substances can 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. Similar to the raw materials, fluorine-containing substances can also have any particle size and shape.

[0063] The average particle size of the fluorinated substance can be larger than that of the raw material. This results in a larger volume of the mixture of raw material and fluorinated substance, creating a fluffy state. In other words, the exposed surface area of ​​the raw material is large, reducing the contact points between the raw material particles. The fluorine in the fluorinated substance reacts with the raw material particles in a gaseous state after thermal decomposition. Therefore, fluorination is easily achieved from the surface of the raw material particles, resulting in a homogeneous fluoride solid electrolyte. Furthermore, because the contact points between the raw material particles are discontinuous (i.e., the contact points between the raw material particles are reduced), the necking between particles during the fluorination and solid-phase reactions is broken after the fluorinated substance decomposes and disappears. Therefore, it is possible to synthesize a solid electrolyte with fine particles. The average particle size of the fluorinated substance can be 5 μm or more and 150 μm or less, or 5 μm or more and 100 μm or less, or 5 μm or more and 20 μm or less, or 50 μm or more and 100 μm or less, or 80 μm or more and 150 μm or less. The average particle size of fluorinated materials can be appropriately adjusted by considering the fluorination temperature or reactivity. For example, by increasing the average particle size of the fluorinated material, the heat treatment temperature used for fluorination can be increased.

[0064] Fluorine-containing materials may include ammonium fluoride (NH4F). Ammonium fluoride begins to decompose thermally at relatively low temperatures (e.g., about 150°C). Therefore, ammonium fluoride salts are less likely to remain as unwanted inorganic components in the final solid electrolyte, and the raw material can be fluorinated by thermal decomposition at low temperatures. Therefore, the above-described manufacturing method is effective for fluorinating raw materials containing fluorine at low temperatures (e.g., around 150~200°C). Thus, according to the above-described manufacturing method, it is possible to suppress the hardening of the manufactured solid electrolyte due to sintering or excessive grain growth of the solid electrolyte. Therefore, a solid electrolyte containing a first crystal phase with a crystal structure represented by the compositional formula (1): Li3AlF6 and having an orthorhombic crystal system, comprising finer particles with better flexibility and deformability, can be obtained. Thus, the solid electrolyte obtained by the above-described manufacturing method can be easily densified and thinned into powder form. For example, when the solid electrolyte obtained by the above manufacturing method is used as a solid electrolyte layer in a battery, it is possible to further thin the solid electrolyte layer and increase its ionic conductivity, or to make it suitable as a coating layer for active material particles to achieve high ionic conductivity of the electrode. Therefore, a battery with higher performance can be achieved based on the solid electrolyte manufactured by the above manufacturing method. Unwanted inorganic components from fluorine-containing substances can be suppressed from remaining in the final solid electrolyte. It should be noted that when fluoride raw materials are subjected to a solid-phase reaction, for example, at a low temperature of about 150°C to about 700°C, it is difficult to generate a solid electrolyte containing a crystalline phase represented by the compositional formula (1): Li3AlF6, and a temperature of at least 700°C (for example, about 750°C to 800°C) is required. Therefore, when fluoride raw materials are subjected to a solid-phase reaction, it is difficult to obtain a soft and fine solid electrolyte containing a crystalline phase represented by the compositional formula (1): Li3AlF6.

[0065] Furthermore, by using ammonium fluoride as the fluorine-containing material, energy efficiency in the synthesis process can be achieved, and heating and cooling times are reduced, thus increasing productivity. Additionally, since solid electrolytes can be synthesized at low temperatures, the durability of the furnace materials is improved, and the operating costs and replacement frequency of the synthesis components are significantly reduced. As the fluorine-containing material, only ammonium salts can be used.

[0066] Fluorinated substances can include resins. By including resins as fluorinated substances, the fluorinated substances can undergo thermal decomposition at relatively high temperatures (e.g., above about 400°C and below 600°C) while fluorinating the raw materials. Therefore, methods that include resins as fluorinated substances are suitable for situations where fluorination and solid-phase reactions need to be performed at relatively high temperatures (e.g., above about 400°C and below 600°C).

[0067] Examples of resins used as fluorinated materials are fluoropolymers. For example, polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) can be used. Fluoropolymers such as PTFE and PVDF can fluorinate the raw material while undergoing thermal decomposition at relatively high temperatures (e.g., above approximately 400°C and below 600°C). Therefore, methods using fluoropolymers as fluorinated materials are suitable for situations where fluorination and solid-phase reactions need to be performed at relatively high temperatures. For example, in the case of PVDF, fluorination above 400°C is suitable, and in the case of PTFE, fluorination above 500°C is suitable.

[0068] The fluorinated material may include, for example, a substance that substantially eliminates all inorganic components other than fluorine produced by thermal decomposition through heat treatment as described in (A) above. For the fluorinated material used in the fluorination process, it is required that while the fluorine produced by thermal decomposition through heat treatment as described in (A) above replaces the oxygen in the raw material, other components are not mixed into the final solid electrolyte as inorganic residues. By using a fluorinated material that substantially eliminates all inorganic components other than fluorine produced by thermal decomposition through heat treatment in the final solid electrolyte, the mixing of inorganic residues into the solid electrolyte can be suppressed, resulting in the desired solid electrolyte. Here, in this specification, "substantially eliminating all inorganic components other than fluorine produced by thermal decomposition through heat treatment in the manufactured solid electrolyte" means that the content of the aforementioned inorganic components in the solid electrolyte is, for example, 0.5% by mass or less.

[0069] Fluorine-containing substances can include a variety of fluorine-containing compounds. For example, by using multiple fluorine-containing compounds with different thermal decomposabilities or different particle sizes, the fluorination of the raw materials can be appropriately carried out. For example, ammonium fluoride and fluoropolymers can both be used as fluorine-containing substances. Therefore, a wider temperature range can be controlled for the fluorine-containing substances to function as fluorine sources, thus allowing for wider control of the conversion of the raw materials to fluorides and the solid-phase reaction temperature. Consequently, the desired solid electrolyte can be readily obtained.

[0070] The amount of fluorinated material used is not particularly limited, as long as it is sufficient to fluorinate the total amount of the compound to be fluorinated. For example, in a reaction that fluorinates a compound, when the molar amount of fluorinated material used to fluorinate the compound stoichiometrically (i.e., the stoichiometric equivalent molar amount, in other words, the molar amount required to completely replace the anion of the compound to be fluorinated with F anions) is set to 100%, the amount of fluorinated material can 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.

[0071] <About (A-1)> In (A-1), the raw materials and fluorine-containing substances are mixed.

[0072] Before fluorination, a first preparatory step can be performed to uniformly mix the raw materials. A second preparatory step can be performed to uniformly mix the mixed raw materials with a fluorine-containing substance. Through these first and second preparatory steps, a uniform conversion from the raw materials to the fluoride can be achieved. This allows the synthesis of a homogeneous solid electrolyte.

[0073] In the first preparatory step, the raw materials can be pulverized. As described above, by pulverizing the mixed powder of the raw materials to reduce the particle size, or by exposing the fracture surfaces of the particles through pulverization, the reactivity of the raw materials can be improved. Furthermore, pulverization improves the mixability of the raw materials and their compatibility with fluorine-containing substances. Moreover, it allows for control over the particle shape of the manufactured solid electrolyte, for example, enabling the micronization of the solid electrolyte. Examples of the average particle size of the raw materials are described above.

[0074] The mixing in the first preparatory step only needs to homogenize the raw materials, so it can be either dry mixing or wet mixing. In wet mixing, known general dispersants can be used to achieve uniform mixing and increased throughput (i.e., increased solid content of the slurry). Examples of known dispersants include ammonium polycarboxylate dispersants and nonionic surfactants. It should be noted that by using a pulverizing process to micronize and expose the active surfaces that break into particles, the reactivity of the raw materials in the subsequent fluorination process is improved. Therefore, it is possible to achieve homogenization of synthesis and reaction at low temperatures. Therefore, it is possible to easily produce a soft and highly deformable solid electrolyte containing a crystal phase represented by the formula (1): Li3AlF6 and having an orthorhombic crystal structure.

[0075] In the second preparative step, a pulverization process can be performed to adjust the particle size of the fluorinated material. By micronizing the mixed powder containing the raw material and the fluorinated material, the synthesis temperature of the solid electrolyte can be reduced, for example, by about 10°C to 50°C. Therefore, sintering and grain growth of the solid electrolyte can be further suppressed, resulting in a softer and finer solid electrolyte.

[0076] In the second preparatory step, it is sufficient to mix the raw materials and the fluorine-containing powder in a way that makes them homogeneous. For example, they can be mixed uniformly by repeatedly mixing with a scraper, or by using a dry mixing machine such as a mortar and pestle, a grinder, or a V-type mixer. Alternatively, they can be mixed using a medium such as zirconia balls, and pulverized as needed. Any mixing method can be used as long as the powders can be mixed uniformly. The uniformity can be evaluated, for example, using energy dispersive X-ray spectrophotometry (EDS) or electron probe microanalysis (EPMA). For example, uniformity can be confirmed by observing the composition mapping image.

[0077] <About (A-2)> In (A-2), the raw material is fluorinated by heat treatment of the mixture containing the raw material and the fluorine-containing substance obtained in (A-1) above.

[0078] In heat treatment, a conventional electric furnace can also be used. The heat treatment atmosphere can be selected according to the needs, and heat treatment can be carried out in the atmosphere, inert gas atmospheres (such as nitrogen or argon), or reducing gas atmospheres (such as hydrogen or carbon dioxide). Synthesized fluorides are usually obtained in powder form, but when heat treatment is carried out above the melting point, they are sometimes obtained in the form of melt, sintered body, or blocky form of powder.

[0079] In terms of heat treatment, for example, the above-mentioned uniformly mixed mixture is placed in a heat-resistant container (boiler) made of alumina, and the mixture is calcined in a calcining furnace under any atmosphere. For example, while introducing inert gases such as nitrogen into the furnace and venting gases generated during fluorination (such as ammonium, hydrogen chloride, carbon dioxide, etc.), heat treatment is carried out in an atmosphere furnace at a temperature of, for example, 150°C or higher and 700°C or lower for a time of, for example, 1 hour or more and 40 hours or less, to synthesize a solid electrolyte containing a first crystal phase with a crystal structure represented by the compositional formula (1): Li3AlF6 and having an orthorhombic crystal system. In this way, by introducing and venting the gas into the calcining furnace, unwanted reactive gas components, etc., are not left in the furnace, i.e., in the solid electrolyte.

[0080] The preferred method for introducing inert gases into the furnace is to prevent them from directly contacting the flask containing the mixture. Alternatively, atmospheric air can be introduced into the furnace instead of inert gases. A plate larger than the gas inlet is placed between the gas inlet and the flask. The plate's thickness is sufficient to prevent damage from gas flow or operation. More preferably, it provides partial shielding, for example, by using a plate such as an upright alumina plate. In this way, by shielding the gas inlet from the flask, the gas bypasses the shielding plate and comes into contact with the flask. By indirectly contacting the flask through this circuitous route, the problem of lower temperatures at the point of direct gas contact and a larger temperature distribution within the flask is reduced. Therefore, for the synthesis reaction of solid electrolytes from the fluorination reaction and solid-phase reaction of the raw materials, the uneven distribution of the reaction state (i.e., deviation of the reaction state) can be suppressed.

[0081] Preferably, the gas inlet is located on the bottom side of the furnace, and the exhaust port is located on the top side (e.g., the top side of the ceiling or the top side wall). This allows the reaction gases to be smoothly discharged from the furnace through convection (from bottom to top) within the furnace, thus reducing the possibility of unwanted residual components mixing into the solid electrolyte.

[0082] Alternatively, the introduced gas can be heated before being introduced into the furnace. This suppresses the uneven temperature distribution within the furnace. Consequently, the synthesis reaction of the solid electrolyte proceeds more uniformly, resulting in a more homogeneous solid electrolyte.

[0083] 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. When the heat treatment temperature is lowered and the treatment time is shortened, sintering and grain growth of the solid electrolyte do not occur, thus a solid electrolyte composed of soft, fine particles can be obtained. According to the manufacturing method of the second embodiment, a solid electrolyte represented by the compositional formula (1): Li3AlF6 can be synthesized at a lower temperature than conventional synthesis methods that involve solid-phase reactions of fluorides. Therefore, according to the manufacturing method of the second embodiment, a solid electrolyte composed of soft, fine particles can be obtained compared to solid electrolytes synthesized using conventional methods. By manufacturing in this way, a solid electrolyte that can form a dense powder with excellent ionic conductivity can be obtained.

[0084] It should be noted that the heat treatment temperature and heat treatment time can be arbitrarily determined by taking into account the properties of the raw materials (e.g., crystal system and powder characteristics), the properties of the solid electrolyte for synthesis (e.g., crystal system and powder characteristics), the temperature required for synthesis of the solid electrolyte containing the first crystal phase represented by the formula (1): Li3AlF6 and having an orthorhombic crystal system, the time required for synthesis, and the time for the removal of reaction gases.

[0085] According to the heat treatment conditions for the fluorination treatment of the raw materials in the manufacturing method of the second embodiment, a solid electrolyte containing a first crystalline phase with an orthorhombic crystal structure, which is difficult to achieve in conventional synthesis methods that involve solid-phase reactions of fluorides, can be synthesized. Here, depending on the fluorination conditions, a second crystalline phase with a monoclinic crystal structure, represented by the formula (1): Li3AlF6, can also be generated. Although it also depends on the particle size of the raw materials and the fluorinated material, as an example, a solid electrolyte containing a monoclinic second crystalline phase can be synthesized at a lower temperature (e.g., above 150°C and below 200°C). It should be noted that by micronizing the raw materials and the fluorinated material, the temperature at which their crystal system changes is lowered, for example, to a range of above 10°C and below 50°C. It should be noted that since the second crystalline phase is generated in a lower temperature heat treatment, sintering and grain growth during synthesis of a solid electrolyte containing a second crystalline phase in addition to the first crystalline phase are suppressed. Therefore, solid electrolytes that further contain a second crystalline phase by heat treatment at low temperatures can be obtained in the form of a softer powder.

[0086] The furnace used in heat treatment can be a known firing furnace (e.g., an electric furnace) or an atmosphere firing furnace. It should be noted that, in order to remove atmospheric and moisture deposits deep within the firing pan and completely replace them with inert gases, inert gases can be circulated after vacuum replacement. This reduces the influence of reactive components and moisture contained in the atmosphere. Vacuum replacement can be repeated.

[0087] The temperature distribution within the firing pan during heat treatment can be within the temperature distribution range of a commonly used firing furnace, for example, within 30°C. Furthermore, the temperature distribution within the firing pan referred to here is the difference between the highest and lowest temperatures within the firing pan.

[0088] It should be noted that, as described above, fluorination can be carried out at a relatively low temperature, so the material used as a raw material is less likely to evaporate due to the temperature during fluorination. Therefore, fluorination does not require heat treatment in a sealed environment. The mixture of raw material and fluorinated substance can be placed in a cauldron and, as needed, placed under a cover (e.g., an alumina cover) to prevent debris and foreign matter from falling in, and then heat treated. Therefore, the heat treatment in the manufacturing method of the second embodiment has extremely high productivity and operability, and has great industrial value. According to the manufacturing method of the second embodiment, a solid electrolyte containing a first crystal phase with a crystal structure represented by the compositional formula (1): Li3AlF6 and having an orthorhombic crystal system can be obtained through such a highly productive manufacturing method.

[0089] Furthermore, the material of the beaker does not have to be alumina. Besides alumina, heat-resistant containers made of various dense materials (e.g., relative density above 98%) such as mullite and SiC can also be used. From the perspective of the raw materials contained in the beaker, the fluorine-containing substances, and the reaction between the solid electrolyte and the beaker, a suitable material can be selected. In addition to the materials mentioned above, dense materials with heat resistance and low heat capacity can also be used as the beaker material. The shape of the beaker can be various, such as cylindrical, prismatic, or gourd-shaped.

[0090] Furthermore, examples of using a firing pan in heat treatment are given here, but the method is not limited to this. For example, a rotary kiln or other rotary furnace can be used, or the mixed powder can be heat-treated by spraying, such as in spray drying.

[0091] It should be noted that, as an example of the manufacturing method of the first embodiment, the methods described in (A-1) and (A-2) above have been explained in detail. However, the step of uniformly mixing the raw materials and the fluorinated substance before fluorination may not be necessary. For example, the fluorinated substance can be added to the raw materials, and heat treatment can be performed without sufficient mixing. In addition, heat treatment is preferred for effective fluorination, but for example, the raw materials can be fluorinated by adding the fluorinated substance and then leaving them at room temperature for a long time.

[0092] The surface of the solid electrolyte synthesized through fluorination, which is not subsequently subjected to pulverization as described in the third embodiment described later, is a free surface. This free surface is not the reactive active surface exposed after pulverization, thus exhibiting high surface stability. Such a solid electrolyte is stable, particularly exhibiting excellent environmental resistance (storage characteristics). Therefore, pulverization can be performed after long-term storage, and the pulverization step after fluorination can be omitted or added as appropriate, depending on the application and requirements.

[0093] In the manufacturing method of the second embodiment, additives can be added to the raw materials as needed before the fluorination treatment. For example, additives that promote the fluorination reaction of the raw materials or additives that promote the solid-phase reaction of the raw materials can be added. Examples of such additives include compounds (e.g., oxides) containing at least one element selected from Ti, Si, Cu, Ga, Zn, Mg, Nb, P, K, Na, Ca, and Fe. For example, by adding trace amounts of Ti oxide, Si oxide, Cu oxide, and Ga oxide to the raw materials, the reaction temperature of the fluorination reaction and the solid-phase reaction can be lowered, for example, by about 10°C to 20°C, or the reactivity of the fluorination reaction and the solid-phase reaction can be improved. This promotes the fluorination reaction and the solid-phase reaction of the raw materials. Two or more of the elements selected from Ti oxide, Si oxide, Cu oxide, and Ga oxide can be added together, or only one of the elements selected from Ti oxide, Si oxide, Cu oxide, and Ga oxide can be added. For example, when Ti oxide, Si oxide, Cu oxide and Ga oxide are added for the purpose of promoting fluorination reaction and solid-phase reaction, the total amount of Ti oxide, Si oxide, Cu oxide and Ga oxide added relative to the raw materials may be more than 0.001 mol% and less than 0.3 mol%.

[0094] Additives such as Ti oxide, Si oxide, Cu oxide, and Ga oxide can be in particulate form. The effect of an additive sometimes varies depending on its particle morphology and dispersion relative to the raw material. Generally, for Ti oxide, Si oxide, Cu oxide, and Ga oxide, smaller particle sizes result in greater reaction-promoting effects. For example, the particle size of the additive can be smaller than that of the raw material. As an example, the additive can have a particle size of less than 0.1 μm and a BET specific surface area of ​​100 m². 2 Fine particles of 1 g or more are preferred. However, if coarse particles or excessive amounts of Ti oxides, Si oxides, Cu oxides, and Ga oxides are used, excess precipitated phases outside the solid electrolyte may form, reducing ionic conductivity. Therefore, it is preferable to adjust the particle size and amount of addition to an appropriate level. Ti, Si, Cu, and Ga from Ti oxides, Si oxides, Cu oxides, and Ga oxides added as additives act as promoters for fluoride conversion and solid-phase reactions, and are incorporated into the solid electrolyte. For example, the particle size and amount of Ti oxides, Si oxides, Cu oxides, and Ga oxides are preferably set such that Ti, Si, Cu, and Ga are not detected as a composite phase in X-ray diffraction analysis of the final solid electrolyte. This allows for the synthesis of a solid electrolyte with high ionic conductivity while achieving a reaction-promoting effect.

[0095] In the manufacturing method of the second embodiment, when at least one selected from Ti oxide, Si oxide, Cu oxide, and Ga oxide is used as an additive, the resulting solid electrolyte contains at least one selected from Ti, Si, Cu, and Ga. That is, in this case, the solid electrolyte obtained by the manufacturing method of the second embodiment contains a first crystal phase represented by the formula (1): Li3AlF6 and having an orthorhombic crystal structure, and also contains at least one selected from Ti, Si, Cu, and Ga. With this configuration, a homogeneous solid electrolyte with excellent ionic conductivity can be obtained.

[0096] The oxygen content as an impurity in the solid electrolyte obtained by the manufacturing method of the second embodiment can be 0.5% by mass or less. According to the manufacturing method of the first embodiment, a solid electrolyte with low oxygen contamination can be obtained. For example, the oxygen content as an impurity in the solid electrolyte can be 0.1% by mass or more.

[0097] [Third Implementation Method] The method for manufacturing the solid electrolyte in the third embodiment will now be described.

[0098] The manufacturing method of the third embodiment further includes, after step (A) of the manufacturing method of the first embodiment, (B) pulverizing the solid electrolyte obtained in step (A).

[0099] According to the manufacturing method of the third embodiment, by performing the pulverization process described in (B) above, a solid electrolyte with excellent ionic conductivity and reliability can be obtained with powder characteristics suitable for its application (e.g., particle shape and surface amorphization). Furthermore, since at least a portion of the solid electrolyte can be amorphized, ionic conductivity or the softness of the solid electrolyte particles can be improved. By improving the softness of the solid electrolyte particles, the density of the pressed solid electrolyte powder can be increased. Therefore, the solid electrolyte obtained by the manufacturing method of the third embodiment can form a dense pressed powder with high ionic conductivity.

[0100] Figure 2 This is a flowchart illustrating an example of a method for manufacturing a solid electrolyte according to the third embodiment. Here, an example of a manufacturing method described in the second embodiment will be described, namely, an example in which the manufacturing method described above (A-2) is performed after the manufacturing method described above (A-2) in which the above (A-1) and above (A-2) are performed.

[0101] like Figure 2As shown, firstly, the raw material and the fluorine-containing substance are mixed (S21). Next, the raw material is subjected to fluorination treatment by heat treatment of the obtained mixture containing the raw material and the fluorine-containing substance (S22). As a result, a solid electrolyte containing a first crystal phase represented by the composition formula (1): Li3AlF6 and having an orthorhombic crystal system is obtained. Next, as a step equivalent to (B) above, the solid electrolyte obtained in S22 is subjected to a pulverization process (S23).

[0102] S21 and S22 are the same as S11 and S12 described in the second embodiment, so detailed descriptions are omitted here.

[0103] The pulverized solid electrolyte in (B) above, for example, contains BET with a specific surface area of ​​2.0 m². 2 / g or more and 30m 2 The solid electrolyte contains particles smaller than 1 g. Such a solid electrolyte exhibits excellent ionic conductivity and consequently excellent atmospheric stability. Furthermore, it is flexible, deformable, and can be pulverized. Therefore, it is useful for the composition of composite materials for solid electrolyte layers and active material layers, as well as for the coating of active material particles. This leads to the achievement of high-performance and high-reliability batteries.

[0104] The pulverization process only needs to be able to finely break down the fluoride into the desired particle size. It can be dry or wet, using water or a solvent (e.g., ethanol, butyl acetate, etc.). For example, zirconium oxide 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 carried out for approximately 4 to 80 hours. The ball mill container can be, for example, a container made of polyethylene, or a container lined with fluororesin or zirconium oxide.

[0105] The pulverization process described in (B) above may include, for example, mechanochemical treatment. This mechanochemical treatment is performed to introduce deformed crystals or amorphous material into the solid electrolyte. The deformed crystals or amorphous material are primarily introduced into the surface layer of the solid electrolyte particles. Specific methods can be the same as the pulverization process described above, such as using a ball mill. However, pulverization conditions can be intensified or the time extended. The apparatus and media used for mechanochemical treatment can be the same as those used for pulverization; generally, pulverization and mechanochemical treatment are performed simultaneously. As an example, in a dry process, a ball mill container lined with zirconia is used, and zirconia balls are placed in a volume ratio of 10% to 60%, performing mechanochemical grinding simultaneously with pulverization. The diameter of the zirconia balls is not particularly limited, and any size can be used. Typically, as mentioned above, commercially available balls with diameters of 1 mm to 30 mm are used; smaller or larger diameters are also possible. The diameter of the balls used can be arbitrarily selected depending on the target particle size or the degree of amorphization. In addition, to prevent solid electrolyte from adhering to the inner wall of the zirconia spheres or zirconia container, an appropriate amount of additives such as ethanol that do not adversely affect the properties of the solid electrolyte can be added. Preferably, the additives are those that can be removed by drying afterward.

[0106] The introduction of amorphous properties into a solid electrolyte can be confirmed using X-ray diffraction (XRD) patterns. XRD patterns can be determined using Cu-Kα rays (wavelengths 1.5405 Å and 1.5444 Å) as the X-ray source via the θ-2θ method. Specifically, this can be confirmed by the broadening of peaks in the XRD pattern of the pulverized solid electrolyte compared to the peaks in the solid electrolyte before pulverization. Peak broadening refers to the expansion of the peak width at half maximum (WWHM).

[0107] The presence of deformed crystals, i.e., regions of disordered crystallization, in solid electrolytes can be observed using transmission electron microscopy (TEM) in the form of images formed by regions of high regularity in the lattice pattern and regions of disordered lattice pattern.

[0108] In addition, changes in deformability caused by amorphization can be evaluated using methods such as microVickers hardness.

[0109] As described above, the manufacturing method of the second embodiment includes a pulverization process, therefore the solid electrolyte obtained by the manufacturing method of the second embodiment contains, for example, an amorphous phase. According to this configuration, the amorphous portion of the solid electrolyte becomes softer and exhibits superior deformability. Therefore, the pressed powder of the solid electrolyte can be formed into a solid electrolyte layer with higher ionic conductivity and higher stability in any shape. Thus, the pressed powder of the solid electrolyte containing the amorphous phase can realize a solid electrolyte layer for a battery with excellent characteristics and high reliability.

[0110] As a variation of the manufacturing method of the third embodiment, during the pulverization process described above (B), the solid electrolyte can be slurried at the same time as the pulverization process to form a coating film.

[0111] Figure 3 This is a flowchart illustrating a variation of the manufacturing method of the solid electrolyte according to the third embodiment. Regarding the variation of the manufacturing method of the third embodiment, an example of the manufacturing method described in the second embodiment will also be described here, namely, an example in which the manufacturing method described above (A-2) is performed after the manufacturing method described above (A-2) in the manufacturing method described above (A-1) and (A-2) described above (A).

[0112] like Figure 3 As shown, firstly, the raw material and the fluorine-containing substance are mixed (S31). Next, the raw material is subjected to fluorination treatment by heat treatment of the obtained mixture containing the raw material and the fluorine-containing substance (S32). As a result, a solid electrolyte containing a first crystal phase represented by the composition formula (1): Li3AlF6 and having an orthorhombic crystal system is obtained. Next, as a step equivalent to (B) above, the solid electrolyte obtained in S32 is subjected to pulverization treatment, and at the same time, slurry treatment is performed (S33).

[0113] S31 and S32 are the same as S11 and S12 described in the second embodiment, so detailed descriptions are omitted here.

[0114] In S33, the pulverization process is the same as the pulverization process in S23, which is described as an example of the manufacturing method of the third embodiment. In a variation of the manufacturing method of the third embodiment, a slurry-forming process is further performed. The slurry-forming process is performed, for example, by adding a solid electrolyte while pulverizing, in a state where an organic binder and plasticizer are dispersedly contained in an organic solvent such as tetrahydronaphthalene. Examples of organic binders include styrene-butadiene block copolymer (SBS). Examples of plasticizers include dibutyl phthalate (DBP) and butyl benzyl phthalate (BBP).

[0115] 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, thus, for example, it is possible to directly coat a slurry of solid electrolyte containing amorphous components that has been pulverized. In this way, organic binders and plasticizers can be added during the pulverization process to prepare a solid electrolyte slurry, and the coating film can be formed using this slurry. As a result, a solid electrolyte coating film with excellent properties can be formed. Such a coating film can be used, for example, in the manufacture of coated batteries.

[0116] [Fourth Implementation Method] The manufacturing method of the solid electrolyte in the fourth embodiment will be described below.

[0117] The manufacturing method of the fourth embodiment, as described in (A) of the second embodiment, involves generating fluorine gas by heat treatment of a fluorine-containing substance, and then contacting the fluorine gas with the raw material to perform fluorination treatment on the raw material. In the manufacturing method of the fourth embodiment, the pulverization process described in (B) of the third embodiment can be performed after (A).

[0118] Figure 4 This is a flowchart illustrating an example of a method for manufacturing a solid electrolyte according to the third embodiment. (Example) Figure 4 As shown, the raw material is prepared (S41). The raw material comprises at least one selected from Li oxide, Li carbonate, and Li hydroxide, and at least one selected from Al oxide, Al carbonate, and Al hydroxide, and is prepared by mixing them. Additives for promoting the fluorination reaction of the raw material, additives for promoting the solid-phase reaction of the raw material, etc., are added to the raw material during its preparation. That is, for example, at least one selected from Ti oxide, Si oxide, Cu oxide, and Ga oxide can be added to the raw material.

[0119] Next, the raw materials and the fluorinated substance are placed in a designated position, and the fluorinated substance is heat-treated to bring the generated fluorine gas into contact with the raw materials (S42). This performs fluorination treatment on the raw materials. Then, as a step equivalent to (B) above, the solid electrolyte obtained in S42 can be pulverized (S43).

[0120] According to the manufacturing method of the fourth embodiment, the raw material can be fluorinated using the generated fluorine gas without direct contact between the raw material and the fluorine-containing substance. Therefore, even if a fluorine-containing substance containing inorganic components other than fluorine (such as CuF2, a substance that is released as fluorine gas upon heating) is used, inorganic residues in the manufactured solid electrolyte can be disregarded. Thus, the range of usable fluorine-containing substances can be expanded.

[0121] As a specific example, the raw material is placed on, for example, a fine-mesh nickel mesh, and a fluorine-containing substance such as ammonium fluoride is placed below the nickel mesh. This ensures that the raw material and the fluorine-containing substance are not in contact with each other. In this state, the fluorine-containing substance is heat-treated to generate fluorine gas, which passes through the nickel mesh and comes into contact with the raw material. Thus, the raw material is converted into a fluoride. The raw material and the fluorine-containing substance are as described in the first embodiment. It should be noted that the heat treatment can also be performed in the atmosphere, but to prevent oxidation of the nickel mesh, heat treatment in a nitrogen atmosphere or a reducing atmosphere is preferred.

[0122] [Fifth Implementation] The method for manufacturing the solid electrolyte in the fifth embodiment will now be described.

[0123] The manufacturing method of the fifth embodiment is to mix Li3AlF6 having a monoclinic crystal structure into a solid electrolyte containing a first crystal phase represented by the crystal structure of orthorhombic crystal system, obtained by the manufacturing method of any one of the second to fourth embodiments, thereby obtaining a solid electrolyte containing both the first crystal phase and the second crystal phase.

[0124] Figure 5 This is a flowchart illustrating an example of a method for manufacturing a solid electrolyte according to the fifth embodiment. Here, an example of synthesizing a solid electrolyte comprising a first crystal phase represented by the compositional formula (1): Li3AlF6 and having an orthorhombic crystal system by the manufacturing method of the second embodiment will be described.

[0125] like Figure 5 As shown, the raw materials and the fluorine-containing substance are mixed (S51). Next, the raw materials are subjected to fluorination treatment by heat treatment of the obtained mixture containing the raw materials and the fluorine-containing substance, thereby synthesizing a solid electrolyte containing a first crystal phase represented by the compositional formula (1): Li3AlF6 and having an orthorhombic crystal structure (S52). Next, Li3AlF6 having a monoclinic crystal structure is mixed into the solid electrolyte containing the first crystal phase (S53). The pulverization process can be performed on the solid electrolyte containing the first crystal phase (i.e., Li3AlF6 having an orthorhombic crystal structure) and the Li3AlF6 having a monoclinic crystal structure separately before mixing in S53, or the mixture can be pulverized during mixing in S53. Here, the pulverization process described in the manufacturing method of the third embodiment can be performed.

[0126] Li3AlF6 having a monoclinic crystal structure can be synthesized, for example, by adjusting the heat treatment temperature during fluorination in the manufacturing methods of the second to fourth embodiments. That is, in the manufacturing methods of the second to fourth embodiments, by setting the heat treatment temperature during fluorination to a lower temperature, a solid electrolyte containing a high proportion of Li3AlF6 (i.e., the second crystal phase) with a monoclinic crystal structure is synthesized, and the resulting solid electrolyte can be used as Li3AlF6 with a monoclinic crystal structure.

[0127] Figure 6 This is a flowchart illustrating a variation of the method for manufacturing a solid electrolyte according to the fifth embodiment. In this example, Li3AlF6 having a monoclinic crystal structure is synthesized using the manufacturing method of the second embodiment. First, a first raw material and a first fluorinated substance are mixed (S61). The first raw material is a raw material used to synthesize a solid electrolyte containing a first crystalline phase, and is equivalent to the raw material described in the second embodiment. In addition, the first fluorinated substance is equivalent to the fluorinated substance described in the second embodiment. Next, the first raw material is subjected to fluorination treatment by heat treatment of the obtained first mixture containing the first raw material and the first fluorinated substance, thereby synthesizing a solid electrolyte containing a first crystalline phase represented by the compositional formula (1): Li3AlF6 and having an orthorhombic crystal structure (S62). On the other hand, as a raw material for Li3AlF6 having a monoclinic crystal structure (hereinafter referred to as the second raw material), a raw material containing at least one selected from Li oxides, Li carbonates and Li hydroxides and at least one selected from Al oxides, Al carbonates and Al hydroxides is prepared. As the second raw material, the raw material described in the second embodiment can be used. The second raw material is mixed with the second fluorinated substance (S63). The second fluorinated substance can be the fluorinated substance described in the second embodiment. By heat-treating the obtained second mixture containing the second raw material and the second fluorinated substance, the second raw material is fluorinated, and a solid electrolyte containing a large proportion of Li3AlF6 (i.e., the second crystal phase) with a monoclinic crystal system is synthesized as Li3AlF6 (i.e., the second crystal phase) with a monoclinic crystal system (S64). Next, Li3AlF6 with a monoclinic crystal system is mixed into the solid electrolyte containing the first crystal phase (S65). The pulverization process can be performed on the solid electrolyte containing the first crystal phase (i.e., Li3AlF6 with an orthorhombic crystal system) and the Li3AlF6 with a monoclinic crystal system separately before mixing in S65, or the mixture can be pulverized during mixing in S65. For the pulverization process here, the pulverization process described in the manufacturing method of the third embodiment can be performed.

[0128] According to the manufacturing method described above, a solid electrolyte comprising a first crystal phase having an orthorhombic crystal structure represented by the formula (1): Li3AlF6 and a second crystal phase having a monoclinic crystal structure can be manufactured by adjusting the content ratio of the first and second crystal phases. Therefore, ionic conductivity, powder characteristics, and processability can be adjusted individually, thus allowing for a wider range of adjustments to the properties of the solid electrolyte.

[0129] It should be noted that, as an example of the manufacturing method of the fifth embodiment, a method of mixing Li3AlF6 having an orthorhombic crystal structure with Li3AlF6 having a monoclinic crystal structure has been described. However, the manufacturing method of the fifth embodiment is not limited to this method, and it is also possible to mix two or more solid electrolytes having an orthorhombic crystal structure and a second crystal phase having a monoclinic crystal structure in different proportions. Alternatively, instead of mixing solid electrolytes having different proportions of the first and second crystal phases, it is also possible to combine and mix solid electrolytes with different compositions or contents of by-components, solid electrolytes with different particle sizes, and other solid electrolytes with different manufacturing conditions.

[0130] [Sixth Implementation Method] The sixth embodiment will be described below. Items described in the first, second, third, fourth, and fifth embodiments will be appropriately omitted.

[0131] 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.

[0132] The solid electrolyte of the first embodiment is selected from at least one of the positive electrode, the electrolyte layer and the negative electrode, that is, the solid electrolyte contains a first crystal phase represented by the formula (1): Li3AlF6 and having an orthorhombic crystal system.

[0133] The battery of the sixth embodiment has excellent charge and discharge characteristics because it contains the solid electrolyte material of the first embodiment.

[0134] Figure 7 A cross-sectional view showing the battery 1000 according to the sixth embodiment.

[0135] The battery 1000 of the sixth embodiment includes a positive electrode 201, an electrolyte layer 202, and a negative electrode 203. The electrolyte layer 202 is disposed between the positive electrode 201 and the negative electrode 203.

[0136] The positive electrode 201 may contain a positive electrode material containing the solid electrolyte of the first embodiment. The positive electrode 201 contains a positive electrode active material 204 and a solid electrolyte 100.

[0137] Electrolyte layer 202 contains electrolyte material.

[0138] The negative electrode 203 contains negative electrode active material 205 and solid electrolyte 100.

[0139] Solid electrolyte 100 may include, for example, the solid electrolyte of the first embodiment. Solid electrolyte 100 may be particles containing the solid electrolyte of the first embodiment as a main component. Particles containing the solid electrolyte of the first embodiment as a main component refer to particles in which the solid electrolyte of the first embodiment is the most abundant component in terms of molar ratio. Solid electrolyte 100 may be particles composed of the solid electrolyte of the first embodiment.

[0140] The positive electrode 201 contains a material capable of inserting and deintercalating metal ions (e.g., lithium ions). This material is, for example, positive electrode active material 204.

[0141] Examples of positive electrode active material 204 include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, transition metal sulfides, transition metal fluorides, transition metal oxysulfides, or transition metal oxynitrides. Examples of lithium-containing transition metal oxides include Li(Ni, Co, Mn)O2, Li(Ni, Co, Al)O2, or LiCoO2.

[0142] In this disclosure, “(A, B, C)” means “at least one selected from A, B and C”.

[0143] The shape of the positive electrode active material 204 is not limited to a specific shape. The positive electrode active material 204 can be particles. The positive electrode active material 204 can have a median particle size of 0.1 μm or more and 100 μm or less. When the positive electrode active material 204 has a median particle size 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. As a result, the charge and discharge characteristics of the battery 1000 are improved. When the positive electrode active material 204 has a median particle size of 100 μm or less, the lithium diffusion rate within the positive electrode active material 204 is increased. As a result, the battery 1000 can operate at high output.

[0144] The positive electrode active material 204 can have a larger median particle size than the solid electrolyte 100. Therefore, the positive electrode active material 204 and the solid electrolyte 100 can be well dispersed in the positive electrode 201.

[0145] 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 total volume of the positive electrode active material 204 and the solid electrolyte 100 can be 0.30 or more and 0.95 or less.

[0146] A coating layer can be formed on at least a portion of the surface of the positive electrode active material 204. The coating layer can be formed on the surface of the positive electrode active material 204, for example, before being mixed with a conductive additive and a binder. Examples of coating materials included in the coating layer are sulfide solid electrolytes, oxide solid electrolytes, or halide solid electrolytes. When the solid electrolyte 100 contains a sulfide solid electrolyte, the coating material can contain the solid electrolyte of the first embodiment to suppress the oxidative decomposition of the sulfide solid electrolyte. When the solid electrolyte 100 contains the solid electrolyte of the first embodiment, the coating material can contain an oxide solid electrolyte to suppress the oxidative decomposition of the solid electrolyte. Lithium niobate, which has excellent stability at high potentials, can be used as the oxide solid electrolyte. By suppressing oxidative decomposition, the overvoltage rise of the battery 1000 can be suppressed.

[0147] As described above, when the positive electrode 201 contains a positive electrode material containing the solid electrolyte of the first embodiment, the positive electrode material may contain the solid electrolyte of the first embodiment as a solid electrolyte 100, or it may contain it as a coating material for the coated positive electrode active material 204.

[0148] To improve the energy density and output of the battery 1000, the positive electrode 201 can have a thickness of more than 10 μm and less than 500 μm.

[0149] Electrolyte layer 202 contains an electrolyte material. This electrolyte material is, for example, a solid electrolyte. The solid electrolyte may include the solid electrolyte of the first embodiment. Electrolyte layer 202 may be a solid electrolyte layer.

[0150] The electrolyte layer 202 may contain 50% by mass or more of the solid electrolyte of the first embodiment. The electrolyte layer 202 may contain 70% by mass or more of the solid electrolyte of the first embodiment. The electrolyte layer 202 may contain 90% by mass or more of the solid electrolyte of the first embodiment. The electrolyte layer 202 may also be composed solely of the solid electrolyte of the first embodiment.

[0151] Hereinafter, the solid electrolyte of the first embodiment will be referred to as the first solid electrolyte. The solid electrolyte that is different from the first solid electrolyte will be referred to as the second solid electrolyte.

[0152] The electrolyte layer 202 may contain not only a first solid electrolyte but also a second solid electrolyte. The first and second solid electrolytes can be uniformly dispersed within the electrolyte layer 202. The layers composed of the first solid electrolyte and the layers composed of the second solid electrolyte can be stacked along the stacking direction of the battery 1000.

[0153] The battery of the sixth embodiment may sequentially include a positive electrode 201, a second electrolyte layer, a first electrolyte layer, and a negative electrode 203. Here, 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. Therefore, the solid electrolyte contained in the second electrolyte layer can be used without reduction. As a result, the charge / discharge efficiency of the battery 1000 can be improved. For example, when the second electrolyte layer contains a first solid electrolyte, in order to suppress the reductive decomposition of this solid electrolyte, the first electrolyte layer may contain a sulfide solid electrolyte. This can improve the charge / discharge efficiency of the battery 1000. The second electrolyte layer may contain a first solid electrolyte. Since the first solid electrolyte has high oxidation resistance, a battery with excellent charge / discharge characteristics can be achieved.

[0154] The electrolyte layer 202 may also consist of only the second solid electrolyte.

[0155] The electrolyte layer 202 can have a thickness of 1 μm or more but less than 1000 μm. When the electrolyte layer 202 has a thickness of 1 μm or more, the positive electrode 201 and the negative electrode 203 become less prone to short circuits. When the electrolyte layer 202 has a thickness of less than 1000 μm, the battery 1000 can operate at high output.

[0156] Examples of the second solid electrolyte are Li₂MgX₄, Li₂FeX₄, Li(Al,Ga,In)X₄, Li₃(Al,Ga,In)X₆, or LiI. Here, X is at least one selected from F, Cl, Br, and I.

[0157] To improve the energy density and output of the battery 1000, the electrolyte layer 202 can have a thickness of more than 1 μm and less than 1000 μm.

[0158] The negative electrode 203 contains a material capable of intercalating and deintercalating metal ions (e.g., lithium ions). This material is, for example, the negative electrode active material 205.

[0159] Examples of negative electrode active materials 205 include metallic materials, carbon materials, oxides, nitrides, tin compounds, and silicon compounds. Metallic materials can be elemental metals or alloys. Examples of metallic materials include lithium metal or lithium alloys. Examples of carbon materials include natural graphite, coke, graphitized carbon, carbon fibers, spherical carbon, artificial graphite, or amorphous carbon. From the viewpoint of capacity density, preferred examples of negative electrode active materials are silicon (i.e., Si), tin (i.e., Sn), silicon compounds, or tin compounds.

[0160] The negative electrode active material 205 can be selected considering the reduction resistance of the solid electrolyte contained in the negative electrode 203. For example, if the negative electrode 203 contains a first solid electrolyte, the negative electrode active material 205 can be a material capable of inserting and deintercalating lithium ions at a voltage greater than 0.27V relative to lithium. Examples of such negative electrode active materials are titanium oxides, indium metal, or lithium alloys. An example of titanium oxide is Li4Ti5O. 12 LiTi₂O₄ or TiO₂. By using the above-mentioned negative electrode active material, the reduction and decomposition of the first solid electrolyte contained in the negative electrode 203 can be suppressed. As a result, the charge and discharge efficiency of the battery 1000 can be improved.

[0161] The shape of the negative electrode active material 205 is not limited to a specific shape. The negative electrode active material 205 can be particles. The negative electrode active material 205 can have a median particle size of 0.1 μm or more and 100 μm or less. When the negative electrode active material 205 has a median particle size 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. As a result, the charge and discharge characteristics of the battery 1000 are improved. When the negative electrode active material 205 has a median particle size of 100 μm or less, the lithium diffusion rate within the negative electrode active material 205 is increased. As a result, the battery 1000 can operate at high output.

[0162] The negative electrode active material 205 can have a larger median particle size than the solid electrolyte 100. Therefore, the negative electrode active material 205 and the solid electrolyte 100 can be well dispersed in the negative electrode 203.

[0163] 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 total volume of the negative electrode active material 205 and the solid electrolyte 100 can be greater than 0.30 and less than 0.95.

[0164] To improve the energy density and output of the battery 1000, the negative electrode 203 can have a thickness of more than 10 μm and less than 500 μm.

[0165] For the purpose of improving ionic conductivity, chemical stability and electrochemical stability, at least one of the cathode 201, electrolyte layer 202 and anode 203 may contain a second solid electrolyte.

[0166] The second solid electrolyte can be a sulfide solid electrolyte.

[0167] Examples of sulfide solid electrolytes include Li₂S-P₂S₅, Li₂S-SiS₂, Li₂S-B₂S₃, Li₂S-GeS₂, and Li₂S-P₂S₅. 3.25 Ge 0.25 P0.75 S4 or Li 10 GeP2S 12 .

[0168] When the electrolyte layer 202 contains a first solid electrolyte, the negative electrode 203 may contain a sulfide solid electrolyte to suppress the reductive decomposition of the solid electrolyte. By covering the negative electrode active material with an electrochemically stable sulfide solid electrolyte, contact between the first solid electrolyte and the negative electrode active material can be suppressed. As a result, the internal resistance of the battery 1000 can be reduced.

[0169] The second solid electrolyte can be an oxide solid electrolyte.

[0170] Examples of oxide solid electrolytes are: (i) Sodium superionic conductor (NASICON) type solid electrolytes such as LiTi2(PO4)3 or its elemental substitutes; (ii)Perovskite-type solid electrolytes such as (LaLi)TiO3; (iii)Li 14 ZnGe4O 16 LISICON-type solid electrolytes such as Li4SiO4, LiGeO4, or their elemental substitutions; (iv)Li7La3Zr2O 12 Garnet-type solid electrolytes, such as those containing elemental substitutions; or (v)Li3PO4 or its N-substituted derivatives.

[0171] As mentioned above, the second solid electrolyte can be a halide solid electrolyte.

[0172] Examples of halide solid electrolytes are Li₂MgX₄, Li₂FeX₄, Li(Al,Ga,In)X₄, Li₃(Al,Ga,In)X₆, or LiI. Here, X is at least one selected from F, Cl, Br, and I.

[0173] Another example of a halide solid electrolyte is Li a Me b Y cZ6 represents the compound. Here, a + mb + 3c = 6 and c > 0 are satisfied. Me is at least one of the metallic elements and metalloids selected from those other than Li and Y. Z is at least one of F, Cl, Br, and I. m represents the valence of Me. "Metalloids" refers to B, Si, Ge, As, Sb, and Te. "Metallic elements" refers to all elements contained in Groups 1 to 12 of the periodic table (except hydrogen) and all elements contained in Groups 13 to 16 of the periodic table (except B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se).

[0174] To improve the ionic conductivity of halide solid electrolytes, Me can be at least one selected from Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb.

[0175] The halide solid electrolyte can be Li3YCl6 or Li3YBr6.

[0176] The second solid electrolyte can be an organic polymer solid electrolyte.

[0177] Examples of organic polymer solid electrolytes are compounds of polymers and lithium salts.

[0178] Polymers can possess an ethylene oxide structure. Polymers with an ethylene oxide structure can contain a large amount of lithium salt, thus further improving ionic conductivity.

[0179] Examples of lithium salts are LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3F3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), or LiC(SO2CF3)3. One lithium salt selected from these can be used alone. Alternatively, a mixture of two or more lithium salts selected from these can be used.

[0180] In order to facilitate the acceptance and donation of lithium ions and improve the output characteristics of the battery, at least one of the positive electrode 201, electrolyte layer 202 and negative electrode 203 may contain a non-aqueous electrolyte, a gel electrolyte or an ionic liquid.

[0181] The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.

[0182] Examples of non-aqueous solvents include cyclic carbonate solvents, chain carbonate solvents, cyclic ether solvents, chain ether solvents, cyclic ester solvents, chain ester solvents, and fluorinated solvents. Examples of cyclic carbonate solvents include ethylene carbonate, propylene carbonate, or butyl carbonate. Examples of chain carbonate solvents include dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate. Examples of cyclic ether solvents include tetrahydrofuran, 1,4-dioxane, or 1,3-dioxolane. Examples of chain ether solvents include 1,2-dimethoxyethane or 1,2-diethoxyethane. Examples of cyclic ester solvents include γ-butyrolactone. Examples of chain ester solvents include methyl acetate. Examples of fluorinated solvents include fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, ethyl fluorocarbonate, or dimethyl fluorocarbonate. One of these non-aqueous solvents may be used alone. Alternatively, a combination of two or more of these non-aqueous solvents may be used.

[0183] Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), or LiC(SO2CF3)3. One lithium salt selected from these can be used alone. Alternatively, a mixture of two or more lithium salts selected from these can 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.

[0184] As a gel electrolyte, a polymeric material impregnated with a non-aqueous electrolyte can be used. Examples of polymeric materials include polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, or polymers containing ethylene oxide bonds.

[0185] Examples of cations contained in ionic liquids are: (i) Aliphatic chain quaternary salts such as tetraalkylammonium or tetraalkylphosphonium; (ii) Aliphatic cyclic ammonium compounds such as pyrrolidinemonium, morpholinium, imidazolinemonium, tetrahydropyrimidinemonium, piperazinemonium, or piperidinemonium; or (iii) Nitrogen-containing heterocyclic aromatic cations such as pyridinium or imidazoline.

[0186] An example of anion contained in ionic liquids is PF6. - BF4 - SbF6 - AsF6 - SO3CF3 - N(SO2CF3)2 - N(SO2C2F5)2 - N(SO2CF3)(SO2C4F9) - Or C(SO2CF3)3- .

[0187] Ionic liquids can contain lithium salts.

[0188] To improve the adhesion between particles, at least one of the positive electrode 201, electrolyte layer 202 and negative electrode 203 may contain a binder.

[0189] Examples of adhesives include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aromatic polyamide resins, polyamides, polyimides, polyamide-imides, polyacrylonitrile, polyacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, or carboxymethyl cellulose. Copolymers can also be used as adhesives. Examples of such adhesives are copolymers selected from two or more materials chosen from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ethers, vinylidene fluoride, trifluorochloroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene. Mixtures selected from two or more of these materials can be used as adhesives.

[0190] To improve electronic conductivity, at least one of the positive electrode 201 and the negative electrode 203 may contain a conductive additive.

[0191] Examples of conductive additives are: (i) Graphite, such as natural or artificial graphite; (ii) Carbon blacks such as acetylene black or Ketjen black; (iii) Conductive fibers such as carbon fiber or metal fiber; (iv) Fluorinated carbon; (v) Metal powders such as aluminum; (vi) Conductive whiskers such as zinc oxide or potassium titanate; (vii) Conductive metal oxides such as titanium dioxide; or (viii) Conductive polymers such as polyaniline, polypyrrole or polythiophene.

[0192] To reduce costs, the conductive additives described in (i) or (ii) above can be used.

[0193] It should be noted that a separator impregnated with electrolyte can be used instead of the electrolyte layer, or the outer packaging containing the positive electrode, separator, and negative electrode can be filled with electrolyte. The electrolyte can be, for example, the non-aqueous electrolyte described above. Examples of the battery shape in the sixth embodiment include coin type, cylindrical type, square type, sheet type, button type, flat type, or stacked type.

[0194] The battery of the sixth embodiment can be manufactured, for example, by preparing materials for forming a positive electrode, materials for forming an electrolyte layer, and materials for forming a negative electrode, and then using a known method to make a laminate in which a positive electrode, an electrolyte layer, and a negative electrode are sequentially arranged.

[0195] [Other Implementation Methods] (Postscript) The following technology has been disclosed through the above description of the embodiments.

[0196] (Technology 1) A solid electrolyte comprising a first crystalline phase represented by the following compositional formula (1) and having an orthorhombic crystal system.

[0197] Composition formula (1): Li3AlF6 The solid electrolyte with the above-described structure is a novel solid electrolyte with high utility. For example, the solid electrolyte with the above-described structure can possess high ionic conductivity and excellent stability. For example, the solid electrolyte with the above-described structure can be synthesized at low temperatures (e.g., around 150°C to 700°C), so it is not easily exposed to high temperatures for extended periods during manufacturing. As a result, the solid electrolyte does not become excessively hardened due to over-sintering during manufacturing, or the grain growth of the solid electrolyte does not proceed excessively. Therefore, the solid electrolyte with the above-described structure is, for example, soft and highly deformable, and can be provided in the form of fine particles. Such a solid electrolyte with highly deformable fine particles easily forms a dense interface between particles when it is made into a powder. More specifically, the contact between particles that are difficult to deform is a point contact, while the contact between particles that are easily deformable is a surface (bonding interface) formed by expanding the contact points between particles. As a result, voids are reduced, and densification is achieved. Therefore, the solid electrolyte with the above-described structure can be made into high-density sheets and is easy to produce thin layers, and further improvements in ionic conductivity can be expected. Therefore, the solid electrolyte of Technology 1, for example, in the case of a solid electrolyte layer used in a battery, can achieve a thin layer of the solid electrolyte layer, or can be suitable for use as a coating layer for active material particles, making it a highly useful solid electrolyte. Therefore, according to the solid electrolyte of Technology 1, a high-performance battery can be realized.

[0198] (Technology 2) According to the solid electrolyte of technology 1, the solid electrolyte contains particles with a particle size of less than 1 μm.

[0199] The solid electrolyte having the above-described structure, for example in the case of a solid electrolyte layer used in a battery, allows for further thinning of the solid electrolyte layer, or it can be more appropriately used as a coating layer for active material particles. Therefore, according to the solid electrolyte of Technology 2, a battery with higher performance can be achieved.

[0200] (Technology 3) According to the solid electrolyte of technology 2, the average particle size of the solid electrolyte is less than 1 μm.

[0201] The solid electrolyte having the above-described structure, for example in the case of a solid electrolyte layer used in a battery, allows for further thinning of the solid electrolyte layer, or allows for more suitable use as a coating layer for active material particles. Therefore, according to the solid electrolyte of Technology 3, a battery with higher performance can be achieved.

[0202] (Technology 4) The solid electrolyte according to any one of techniques 1 to 3, wherein the solid electrolyte comprises particles with a particle size of 0.3 μm or more.

[0203] Based on the above configuration, ionic conductivity can be improved in a solid electrolyte containing a first crystal phase with an orthorhombic crystal system.

[0204] (Technology 5) The solid electrolyte according to any one of techniques 1 to 4, wherein the solid electrolyte comprises particles with an aspect ratio of 2.0 or greater.

[0205] According to the above configuration, ionic conductivity can be improved in a solid electrolyte containing a first crystal phase with an orthorhombic crystal structure. Furthermore, when a paste containing the solid electrolyte of technique 5 is printed or coated, the particles of the solid electrolyte readily align along the printed or coated surface. Therefore, when the solid electrolyte of technique 5 is used in the solid electrolyte layer of a battery, the solid electrolyte layer can be further thinned, and the solid electrolyte layer can also be densified. This reduces the resistance of the solid electrolyte layer. Therefore, according to the solid electrolyte of technique 5, a small battery with high capacity density can be realized. Furthermore, when the solid electrolyte of technique 5 is used in the solid electrolyte layer of a battery, the resistivity of the solid electrolyte layer is reduced, thus resulting in a high-performance battery.

[0206] (Technology 6) The solid electrolyte according to any one of techniques 1 to 5, wherein the solid electrolyte comprises particles having free surfaces.

[0207] With the above configuration, a solid electrolyte with excellent atmospheric stability can be achieved, for example.

[0208] (Technology 7) The solid electrolyte according to any one of techniques 1 to 6, wherein the solid electrolyte further comprises a second crystal phase represented by the compositional formula (1) and having a monoclinic crystal structure.

[0209] The above-described structure yields a more flexible and deformable solid electrolyte. This more flexible and deformable solid electrolyte makes it easier to form tightly bonded interfaces between particles during powder preparation, enabling higher density and easier thinning, and further improving ionic conductivity. Therefore, the solid electrolyte of Technology 7, when used in batteries, can achieve batteries with higher performance and superior reliability.

[0210] (Technology 8) According to the solid electrolyte of technique 7, the solid electrolyte comprises: The first particle contains the first crystalline phase but does not contain the second crystalline phase; and The second particle, which contains the second crystalline phase. The second particle is softer than the first particle.

[0211] The above-described structure allows for the production of a more flexible and deformable solid electrolyte. This flexibility and deformability facilitate the formation of tightly packed interfaces between particles during powder preparation, enabling higher density and easier thinning, and further improving ionic conductivity. Furthermore, thermal shock resistance, such as during thermal cycling, is also enhanced. Therefore, when used in batteries, the solid electrolyte of Technology 8 enables the development of batteries with higher performance and superior reliability.

[0212] (Technology 9) The solid electrolyte according to any one of techniques 1 to 8, wherein the solid electrolyte further comprises an amorphous phase.

[0213] Based on the above composition, the amorphous portion of the solid electrolyte becomes softer, exhibits better deformability, and improves interparticle bonding. Therefore, the pressed powder of the solid electrolyte can be formed into a solid electrolyte layer with higher ionic conductivity and greater stability in any shape. Thus, the pressed powder of the solid electrolyte of Technology 9 can realize a solid electrolyte layer or active material particle coating layer for a battery with excellent characteristics and high reliability. As a result, according to the solid electrolyte of Technology 9, a high-performance and highly reliable battery can be achieved.

[0214] (Technology 10) The solid electrolyte according to any one of techniques 1 to 9, wherein the solid electrolyte further comprises at least one selected from Ti, Si, Cu and Ga as a secondary component.

[0215] With the above configuration, a homogeneous solid electrolyte with excellent ionic conductivity can be obtained.

[0216] (Technology 11) A method for manufacturing a solid electrolyte, which is a method for manufacturing a solid electrolyte as described in any one of techniques 1 to 10, comprising: (A) mixing a raw material containing at least one selected from Li oxide, Li carbonate and Li hydroxide with at least one selected from Al oxide, Al carbonate and Al hydroxide, and subjecting the mixed raw material to fluorination treatment.

[0217] The above-described manufacturing method uses relatively stable oxides, carbonates, and hydroxides as raw materials, allowing the fluorination of the raw materials and the solid-phase reaction to occur simultaneously. Therefore, it is possible to synthesize a solid electrolyte containing a first crystalline phase with an orthorhombic crystal structure represented by the formula (1): Li3AlF6. Furthermore, according to this manufacturing method, a solid electrolyte containing a first crystalline phase with an orthorhombic crystal structure represented by the formula (1): Li3AlF6 can be synthesized at low temperatures (e.g., around 150°C to 700°C) that cannot be synthesized in the solid-phase reaction using fluoride raw materials. Moreover, according to this manufacturing method, by controlling the ratio of each component of the raw materials, a solid electrolyte with the desired composition can be accurately manufactured. Therefore, it is possible to stably, cost-effectively, easily, and reproducibly manufacture a solid electrolyte containing a crystalline phase with an orthorhombic crystal structure represented by the formula (1): Li3AlF6.

[0218] (Technology 12) According to the method for manufacturing a solid electrolyte as described in Technique 11, in step (A), the fluorination treatment of the raw material is carried out by heat treatment of a fluorine-containing substance that is thermally decomposable.

[0219] According to the above manufacturing method, the fluorination and solid-phase reaction of the raw materials can occur simultaneously to synthesize a solid electrolyte containing a first crystalline phase with an orthorhombic crystal structure represented by the formula (1): Li3AlF6. Therefore, a homogeneous solid electrolyte with excellent properties can be obtained while reducing reaction residues such as oxides in a short time. Furthermore, by selecting fluorinated substances with different thermal decomposition temperatures and adjusting the particle size of the raw materials, the temperatures and reaction rates of the fluorination and solid-phase reactions of the raw materials can be controlled. Therefore, fluorination treatment suitable for various raw materials can be performed.

[0220] (Technology 13) According to the method for manufacturing a solid electrolyte as described in Technique 12, the fluorine-containing substance is in particulate form.

[0221] According to the manufacturing method described above, fluorinated substances are easily thermally decomposed, and the contact area between the raw material and the fluorinated substance is increased. Therefore, the manufacturing method described above allows for efficient fluorination of the raw material and minimizes the possibility of fluorinated substances remaining in the final solid electrolyte. Furthermore, the fluorination reaction can be controlled by the particle shape of the fluorinated substance. For example, by refining the particles of the fluorinated substance, the fluorination temperature can be lowered, or the fluorination rate can be increased. Additionally, by mixing the raw material with the fluorinated substance, the powder can be fluorinated uniformly throughout. Furthermore, precise control of the fluorine content is possible. Therefore, the desired solid electrolyte can be synthesized. Moreover, since only the amount of fluorinated substance required for the fluorination of the raw material can be used, unlike the case where fluorine gas is introduced into the furnace, the emission of excess fluorine gas can be suppressed. Therefore, the environmental impact is reduced, and consequently, the corrosive effect on furnace materials is also reduced.

[0222] (Technology 14) The method for manufacturing a solid electrolyte according to technique 12 or 13, wherein step (A) comprises: (A-1) Mix the raw material and the fluorine-containing substance; and (A-2) The raw material is fluorinated by heat treatment of the mixture containing the raw material and the fluorine-containing substance obtained in (A-1) to obtain the solid electrolyte.

[0223] According to the above manufacturing method, a homogeneous mixture of raw materials and fluorinated substances can be subjected to heat treatment for fluorination. Furthermore, the contact area between the raw materials and the fluorinated substances can be increased. Therefore, according to the above manufacturing method, the fluorination of the raw materials can be uniformly promoted. Thus, a homogeneous solid electrolyte with excellent properties can be obtained with high productivity.

[0224] (Technology 15) According to any one of Artificial Intelligence 12 to 14, in the method for manufacturing a solid electrolyte, in step (A), fluorine gas is generated by heat treatment of the fluorine-containing substance, and the fluorine gas is brought into contact with the raw material to fluorinate the raw material, thereby obtaining the solid electrolyte.

[0225] According to the manufacturing method described above, the raw materials can be fluorinated using the generated fluorine gas without direct contact between the raw materials and the fluorine-containing substances. Therefore, even if fluorine-containing substances containing inorganic components in addition to fluorine are used, inorganic residues in the manufactured solid electrolyte can be disregarded. Thus, the range of usable fluorine-containing substances can be expanded.

[0226] (Technology 16) The method for manufacturing a solid electrolyte according to any one of techniques 12 to 15, wherein the fluorine-containing substance comprises ammonium fluoride.

[0227] Ammonium fluoride begins to thermally decompose at a relatively low temperature (e.g., about 150°C). Therefore, ammonium salts are less likely to remain as unwanted inorganic components in the final solid electrolyte, and the raw material can be fluorinated by thermal decomposition at low temperatures. Thus, the above-described manufacturing method is effective for fluorinating fluorinated materials at low temperatures (e.g., around 150-200°C). Consequently, according to the above-described manufacturing method, it is possible to suppress the hardening of the manufactured solid electrolyte due to sintering or excessive grain growth of the solid electrolyte. Therefore, a softer, more deformable microparticle-like solid electrolyte can be obtained. Thus, the solid electrolyte obtained by the above-described manufacturing method can easily achieve densification and thinning of the powder. For example, when the solid electrolyte obtained by the above-described manufacturing method is used as a solid electrolyte layer in a battery, the solid electrolyte layer can be further thinned and its ionic conductivity increased, or it can be suitable for use as a coating layer for active material particles to achieve high ionic conductivity of the electrode. Therefore, according to the solid electrolyte manufactured by the above-described manufacturing method, a higher performance battery can be achieved. It can suppress unwanted inorganic components from fluorine-containing substances from remaining in the final solid electrolyte. Furthermore, it enables energy-efficient synthesis, reduces heating and cooling times, and thus increases productivity. In addition, because synthesis can be performed at low temperatures, the durability of the furnace material is improved, and the operating costs and replacement frequency of the synthesis components are significantly reduced.

[0228] (Technology 17) A method for manufacturing a solid electrolyte according to any one of techniques 12 to 16, wherein the fluorinated substance comprises a resin.

[0229] According to the manufacturing method described above, fluorinated materials can be thermally decomposed at relatively high temperatures (e.g., above about 400°C and below 600°C) while fluorinating the raw materials. Therefore, the manufacturing method described above is suitable for situations where it is desired to perform fluorination of raw materials and solid-phase reactions at relatively high temperatures (e.g., above about 400°C and below 600°C).

[0230] (Technology 18) According to the method for manufacturing a solid electrolyte of technology 17, the resin is a fluororesin.

[0231] Fluoropolymers such as PTFE and PVDF can fluorinate raw materials while undergoing thermal decomposition at relatively high temperatures (e.g., above about 400°C and below 600°C). Therefore, the manufacturing method of Technique 14 is suitable for situations where it is desired to perform fluorination of raw materials and solid-phase reaction at relatively high temperatures (e.g., above about 400°C and below 600°C).

[0232] (Technology 19) A method for manufacturing a solid electrolyte according to any one of techniques 12 to 18, wherein the fluorine-containing substance comprises a substance that substantially does not contain inorganic components other than fluorine elements produced by thermal decomposition via heat treatment in (A).

[0233] For fluorine-containing substances, it is required that while the fluorine element produced by thermal decomposition through heat treatment in (A) above replaces the oxygen element in the raw material, other components are not mixed in as inorganic residues into the final solid electrolyte represented by the composition formula (1): Li3AlF6 and containing a first crystal phase with an orthorhombic crystal system. As a fluorine-containing substance, a substance that substantially does not contain inorganic components other than fluorine element produced by thermal decomposition through heat treatment is used in the final solid electrolyte, thereby suppressing the mixing of inorganic residues into the solid electrolyte by replacing only fluorine element with oxygen. As a result, a high-purity solid electrolyte with the desired composition can be obtained. It should be noted that the fluorine-containing substance that substantially does not contain inorganic components other than fluorine element produced by thermal decomposition through heat treatment in the final solid electrolyte can be, for example, a substance in which inorganic components other than fluorine element produced by thermal decomposition through heat treatment are released as gas.

[0234] (Technology 20) The method for manufacturing a solid electrolyte according to any one of techniques 12 to 19, wherein the fluorine-containing substance comprises a variety of fluorine-containing compounds.

[0235] According to the manufacturing method described above, ammonium fluoride and fluoropolymers can be used as fluorinated substances, for example. This allows for wider control over the temperature range at which the fluorinated substance functions as a fluorine source. Consequently, the conversion of the raw materials to fluoride and the solid-phase reaction temperature can be controlled over a wider range. Therefore, the synthesis of the desired solid electrolyte becomes easier according to the manufacturing method described above.

[0236] (Technology 21) The method for manufacturing a solid electrolyte according to any one of techniques 11 to 20, wherein, after step (A), the method further includes: (B) pulverizing the solid electrolyte obtained in step (A).

[0237] According to the manufacturing method described above, a solid electrolyte can be obtained with powder characteristics suitable for its application (e.g., particle shape and surface amorphization). According to the manufacturing method described above, at least a portion of the solid electrolyte can be amorphized, thereby improving ionic conductivity or increasing the softness of the solid electrolyte particles. By increasing the softness of the solid electrolyte particles, the density of the pressed powder of the solid electrolyte can be increased. Therefore, the solid electrolyte obtained according to the manufacturing method of technique 17 can form a dense pressed powder with high ionic conductivity.

[0238] (Technology 22) A positive electrode material comprising the solid electrolyte described in any one of techniques 1 to 10.

[0239] According to the cathode material of Technology 22, a high-performance battery with excellent charge and discharge characteristics can be realized.

[0240] (Technology 23) A battery having a positive electrode comprising the positive electrode material described in Technique 22.

[0241] This configuration enables the provision of batteries with excellent charge and discharge characteristics and other structural capabilities.

[0242] (Technology 24) A battery comprising: a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode. The positive electrode, the negative electrode, and the electrolyte layer are selected from at least one of the solid electrolytes described in any one of techniques 1 to 10.

[0243] This configuration enables the provision of high-performance batteries with excellent charge and discharge characteristics.

[0244] The solid electrolyte and its manufacturing method involved in this disclosure have been described above based on the embodiments, but this disclosure is not limited to these embodiments. Various modifications to the embodiments that can be conceived by those skilled in the art, as well as other ways of constructing by combining some of the constituent elements of the embodiments, are also included within the scope of this disclosure, as long as they do not depart from the spirit of this disclosure.

[0245] Furthermore, the above-described embodiments can be modified, substituted, added, omitted, etc., within the scope of the claims or their equivalents.

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

[0247] Synthesis of Solid Electrolytes (Example 1) The following materials were prepared as raw materials: Li2CO3 (average particle size: approximately 1.5 μm) and Al2O3 (average particle size: 0.3 μm); NH4F (average particle size: approximately 120 μm) as a fluorine-containing substance; and TiO2 (average particle size: approximately 0.5 μm, rutile type), SiO2 (average particle size: approximately 0.3 μm), CuO (average particle size: approximately 1.2 μm) and Ga2O3 (average particle size: approximately 0.8 μm) as additives.

[0248] Li₂CO₃ and Al₂O₃ were weighed in accordance with the method used for synthesizing Li₃AlO₃. Furthermore, regarding additives, each powder was weighed to achieve the following percentages relative to the synthesized Li₃AlO₃: TiO₂ 0.01 mol%, SiO₂ 0.005 mol%, CuO 0.001 mol%, and Ga₂O₃ 0.005 mol%. The weighing of these raw materials and additives was carried out under atmospheric conditions.

[0249] The raw materials and additives powders weighed as described above are mixed. 30g of the resulting mixed powder, 600g of φ5mm zirconia balls, and 200mL of ethanol are placed in a 600mL ball mill and mixed and pulverized for 20 hours to prepare a slurry. The resulting slurry is dried in a hot air dryer at approximately 50-60°C under atmospheric pressure for 20 hours. The dried powder is then pulverized using a mortar and pestle for approximately 10 minutes and passed through a #32 mesh sieve to obtain a raw material powder containing the raw materials and additives. The average particle size of the obtained raw material powder is approximately 0.46μm.

[0250] Next, NH4F powder, which is a fluorinated substance, is mixed with the raw material powder. The amount (ratio) of NH4F powder added is required for the fluorination of the raw material. Specifically, an amount of NH4F sufficient to fluorinate all the raw materials according to the reaction formula is used.

[0251] Using an alumina mortar, the mixture of raw material powder and NH4F powder is mixed with a mortar and pestle for approximately 10 minutes to achieve homogeneity (equivalent to step (A-1) above). This yields a mixture containing the raw material, additives, and fluorine-containing substances. It should be noted that the mixing of these substances is carried out in normal atmospheric conditions, as was done during weighing.

[0252] Next, the resulting mixture is heat-treated (equivalent to step (A-2) above). For the cauldron, a high-purity (SSA-H) alumina crucible (diameter φ: 36 mm, height: 40 mm) is used, and approximately 3 g of the mixture is added to the crucible. To facilitate the escape of the reaction gases (mainly ammonia and CO2) during heat treatment, spacers (0.5 mm thick) are placed on the outer edge of the upper surface of the cauldron, and an alumina plate-shaped cover is placed to prevent foreign matter from falling. The cauldron with the cover thus placed is then placed in the center of the firing furnace for heat treatment. In the firing furnace, the cauldron is placed on a small heat-capacity mullite block with a porosity of approximately 20%. Using blocks 10 mm long, 10 mm wide, and 10 mm high, three blocks are placed under one cauldron, causing the cauldron to float from the bottom of the furnace. This operation allows the heater (radiant) heat and inert gases to also circulate around to the bottom of the cauldron. After the furnace door is closed and sealed, nitrogen, as an inert gas, flows in at a rate of 2 L / min from the inlet at the bottom of the furnace and exits from the exhaust port on the upper side of the roof, allowing the gas to flow continuously until the heat treatment is completed. The heat treatment temperature is 320℃.

[0253] The solid electrolyte of this embodiment is synthesized by using carbonates and oxides in the raw materials, fluorinating the mixture, thereby fluorinating each component of the raw materials, and then carrying out a solid-phase reaction. In the manufacturing method of this embodiment, since no evaporation components are generated, a reaction in a closed container is not required, and heat treatment (firing) can be performed without compositional changes, with the same structure as general oxide ceramics.

[0254] The solid electrolyte obtained by the above heat treatment was subjected to a pulverization process (equivalent to step (B) above). In this embodiment, dry pulverization was performed. Specifically, zirconia balls (diameter: 15 mm) and the solid electrolyte obtained by the above heat treatment were placed in a ball mill (volume: 1 L) lined with zirconia and pulverized for 36 hours.

[0255] (Comparative Example 1) The solid electrolyte of Comparative Example 1 was prepared by mechanochemical synthesis using fluorides as raw materials. Specifically, LiF and AlF3 were prepared with a molar ratio of LiF:AlF3 = 3:1. These materials were mixed as powder in a mortar for approximately 5 minutes under an Ar atmosphere (glove box). 10 g of the resulting mixture was then added together with 400 g of φ5 mm zirconia balls into a 500 mL planetary ball mill and sealed. Mechanochemical milling was performed at 500 rpm for 20 h. This operation synthesized the solid electrolyte of Comparative Example 1.

[0256] Evaluation of Solid Electrolytes For the solid electrolyte of Example 1 synthesized as described above, its crystal phase, ionic conductivity, electronic conductivity, average particle size, and BET specific surface area were evaluated, and particle shape was also observed using SEM. It should be noted that the crystal phase, ionic conductivity, average particle size, and BET specific surface area were evaluated for both the solid electrolyte before and after heat treatment and pulverization treatment. Furthermore, the crystal phase of the solid electrolyte of Comparative Example 1 was also evaluated. Additionally, trace component analysis was performed on the solid electrolyte of Example 1.

[0257] (Crystal phase) The crystal phase was determined by powder X-ray diffraction, both before and after heat treatment and before pulverization. The determination was performed using an X-ray diffractometer (RIGAKU MiniFlex 600). Cu-Kα rays (wavelengths 1.5405 Å and 1.5444 Å) were used as the X-ray source.

[0258] Figure 8A This is a graph showing the X-ray diffraction pattern of the solid electrolyte obtained in the manufacturing method of Example 1, after heat treatment and before pulverization, and the X-ray diffraction pattern of the solid electrolyte obtained in Comparative Example 1. Figure 8B This is a graph showing the X-ray diffraction pattern of the solid electrolyte after pulverization obtained in Example 1. (As shown) Figure 8A As shown, the XRD pattern of Li3AlF6 with an orthorhombic crystal structure can be confirmed in the fluorinated solid electrolyte obtained in Example 1. It should be noted that, based on the XRD pattern of the fluorinated solid electrolyte obtained in Example 1, only the orthorhombic crystal phase of Li3AlF6 (the first crystal phase) was confirmed; no other precipitated phases, such as those related to additives, were detected. In the solid electrolyte obtained after further pulverizing this fluorinated solid electrolyte, the amorphization process can be determined by… Figure 8B The X-ray diffraction pattern shown confirms this. It should be noted that although the crystallinity of the pulverized solid electrolyte decreased due to the pulverization process compared to the solid electrolyte before pulverization, no excess precipitated phase was observed. The solid electrolyte obtained in Comparative Example 1 was Li3AlF6 with a monoclinic crystal structure.

[0259] (ionic conductivity) Regarding ionic conductivity, the solid electrolyte powder was placed in a mold with a diameter of 10 mm, and a pressure of approximately 3 t / cm was applied using a uniaxial hydraulic press. The ionic conductivity was calculated from the area, thickness, and impedance characteristics at room temperature of the resulting pressed powder sample. Impedance measurements were performed at room temperature under pressure. Furthermore, impedance measurements were performed at a measurement frequency of 10 Hz to 10 MHz, a measurement voltage of 1 Vrms, and without DC bias. Deviations in the electrical lengths of the cable and measuring fixture were evaluated after compensation. For the solid electrolyte of Example 1, the ionic conductivity before pulverization was 0.93 μS / cm, and the ionic conductivity after pulverization was 3.8 μS / cm. For the solid electrolyte obtained in Comparative Example 1, the ionic conductivity after pulverization was 1.2 μS / cm.

[0260] (Electron conductivity) Electronic conductivity was calculated from DC voltage and current characteristics. The electronic conductivity of the solid electrolyte in Example 1 was <1.0 × 10⁻⁶. -9 μS / cm is a value that can be used to determine whether a substance has no electronic conductivity.

[0261] (Average particle size) The average particle size is the median particle size D50 obtained from the volumetric particle size distribution measured by a laser diffraction scattering particle size distribution measuring device. Specifically, the solid electrolyte powder was dispersed in a 0.01% by weight sodium hexametaphosphate aqueous solution using a homogenizer, and then the particle size distribution of the solid electrolyte was measured using a laser diffraction scattering particle size distribution measuring device (Microtrac, trade name: MT3100II). The D50 value of the measured particle size distribution (i.e., the cumulative 50% particle size) was taken as 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.

[0262] (BET specific surface area) The BET specific surface area was determined using a nitrogen adsorption apparatus via the BET multi-point method. For the solid electrolyte in Example 1, the BET specific surface area before pulverization was 3.2 m². 2 / g, the specific surface area of ​​BET after pulverization is 4.1m². 2 / g.

[0263] (Analysis of trace components) The trace components in the solid electrolyte were analyzed by EPMA. Specifically, the analysis was performed as follows: A sample (powder) of the solid electrolyte was attached and fixed to a conductive tape (the sample was fixed in a 5 mm × 5 mm area to become a solid), and the composition was investigated (quantitatively) by point analysis. Although not confirmed by X-ray diffraction, Ti, Si, Cu, and Ga were confirmed to be present in the solid electrolyte of Example 1. The content of Ti was 0.003 atomic%, Si was 0.005 atomic%, Cu was 0.002 atomic%, and Ga was 0.002 atomic%.

[0264] (Observation of particle shape) Using SEM images of the solid electrolyte obtained in Example 1, the particle shape was observed. The SEM images confirmed that the solid electrolyte particles had elongated shapes. In addition, particles with a length (long axis) of 0.3 μm or more and 1 μm or less and an aspect ratio of 2.0 or more were also confirmed.

[0265] Based on the evaluation results of the solid electrolyte obtained in Example 1, it is evident that the solid electrolyte manufactured by the method of this disclosure exhibits a high ionic conductivity of 3.8 μS / cm. This ionic conductivity is higher than that of Li3AlF6, which has a monoclinic crystal structure and is synthesized from fluoride raw materials via a solid-state reaction (approximately 1 μS / cm), confirming that the solid electrolyte of this disclosure is a useful solid electrolyte with excellent properties. It should be noted that the electronic conductivity is <1.0 × 10⁻⁶. -9 μS / cm, confirmed as an ionicly conductive solid electrolyte with no electronic conductivity (i.e., negligible level of electronic conductivity).

[0266] according to Figure 8A The X-ray diffraction pattern shown confirms, for the solid electrolyte of Example 1, a first crystal phase with a crystal structure represented by the compositional formula (1): Li3AlF6 and having an orthorhombic crystal system. Furthermore, according to... Figure 8B The X-ray diffraction pattern shown, for the solid electrolyte of Example 1, indicates that the X-ray diffraction pattern after pulverization treatment shows a broadening of peaks compared to the pattern before pulverization treatment, confirming the progress of amorphization. However, no new precipitates were generated by the pulverization treatment. The changes in ionic conductivity, average particle size, and BET specific surface area before and after pulverization treatment are as described in the description section regarding each evaluation item. From these results, it can be seen that pulverization treatment can be performed or not, depending on the intended use of the solid electrolyte. Regardless of whether pulverization treatment is performed, the composition and crystal phase of the solid electrolyte remain almost unchanged, thus maintaining excellent properties.

[0267] As described above, the solid electrolyte and its manufacturing method disclosed herein enable the production of a highly useful solid electrolyte that is difficult to synthesize using conventional methods and exhibits higher ionic conductivity, softness, and excellent deformability than Li3AlF6 with a monoclinic crystal structure synthesized using conventional methods. Furthermore, the fluoride raw materials used in conventional manufacturing methods are extremely expensive, while the manufacturing method of this disclosure uses inexpensive raw materials such as oxides, thus reducing the manufacturing cost of the solid electrolyte. Therefore, the manufacturing method of this disclosure has significant industrial applicability.

[0268] Industrial applicability The method for manufacturing the solid electrolyte disclosed herein can be used, for example, as a method for manufacturing solid electrolytes for secondary batteries such as all-solid batteries used in various electronic devices or automobiles.

Claims

1. A solid electrolyte comprising a first crystalline phase having an orthorhombic crystal structure represented by the following formula (1), Composition formula (1): Li3AlF6.

2. The solid electrolyte according to claim 1, wherein, The solid electrolyte contains particles with a diameter of less than 1 μm.

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

4. The solid electrolyte according to claim 1, wherein, The solid electrolyte contains particles with a diameter of 0.3 μm or larger.

5. The solid electrolyte according to claim 1, wherein, The solid electrolyte contains particles with an aspect ratio of 2.0 or greater.

6. The solid electrolyte according to claim 1, wherein, The solid electrolyte contains particles with free surfaces.

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

8. The solid electrolyte according to claim 7, wherein, The solid electrolyte comprises: The first particle contains the first crystalline phase but does not contain the second crystalline phase; and The second particle, which contains the second crystalline phase. The second particle is softer than the first particle.

9. The solid electrolyte according to claim 1, wherein, The solid electrolyte also contains an amorphous phase.

10. The solid electrolyte according to claim 1, wherein, The solid electrolyte also contains at least one selected from Ti, Si, Cu and Ga as a secondary component.

11. A method for manufacturing a solid electrolyte, comprising the method of manufacturing the solid electrolyte according to any one of claims 1 to 10, comprising: (A) A raw material comprising at least one selected from Li oxides, Li carbonates and Li hydroxides is mixed with at least one selected from Al oxides, Al carbonates and Al hydroxides, and the mixed raw material is subjected to fluorination treatment.

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

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

14. The method for manufacturing a solid electrolyte according to claim 12, wherein, The (A) includes: (A-1) Mix the raw material and the fluorine-containing substance; and (A-2) The raw material is fluorinated by heat treatment of the mixture containing the raw material and the fluorine-containing substance obtained in (A-1) to obtain the solid electrolyte.

15. The method for manufacturing a solid electrolyte according to claim 12, wherein, In step (A), fluorine gas is generated by heat treatment of the fluorine-containing substance, and the fluorine gas is brought into contact with the raw material to fluorinate the raw material, thereby obtaining the solid electrolyte.

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

17. The method for manufacturing a solid electrolyte according to claim 12, wherein, The fluorinated substance includes resin.

18. The method for manufacturing a solid electrolyte according to claim 17, wherein, The resin is a fluoropolymer.

19. The method for manufacturing a solid electrolyte according to claim 12, wherein, The fluorine-containing substance further includes a substance that makes the solid electrolyte substantially free of inorganic components other than fluorine produced by thermal decomposition via heat treatment in (A).

20. The method for manufacturing a solid electrolyte according to claim 12, wherein, The fluorine-containing substances include a variety of fluorine-containing compounds.

21. The method for manufacturing a solid electrolyte according to claim 11, wherein, Following (A), the process further includes (B) pulverizing the solid electrolyte obtained in (A).

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

23. A battery having 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 disposed between the positive electrode and the negative electrode. in, The solid electrolyte of claim 1 is selected from at least one of the positive electrode, the negative electrode and the electrolyte layer.

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