Solid electrolyte, electrode material, and battery

Abstract

A solid electrolyte according to the present disclosure contains Li, Al, and F, and contains, as a main phase, a first phase that is a monoclinic Li3AlF6 phase. In an XRD pattern obtained by powder X-ray diffraction, the full width at half maximum of a peak having the strongest intensity among peaks belonging to the first phase is greater than 1.0° and not greater than 3.0°, and the BET specific surface area is 50 m2 / g to 350 m2 / g inclusive. A battery 1000 according to the present disclosure is provided with a positive electrode 201, a negative electrode 203, and an electrolyte layer 202 that is arranged between the positive electrode 201 and the negative electrode 203. At least one selected from the group consisting of the positive electrode 201, the negative electrode 203, and the electrolyte layer 202 contains the solid electrolyte according to the present disclosure.

Description

Solid electrolyte, electrode material, and battery

[0001] The present disclosure relates to a solid electrolyte, an electrode material, and a battery.

[0002] Patent Document 1 discloses a solid electrolyte containing Li, Ti, M, and F. Here, M is at least one selected from the group consisting of Al and Y.

[0003] International Publication No. 2021 / 186809

[0004] The present disclosure provides a highly useful solid electrolyte.

[0005] The solid electrolyte of the present disclosure is a solid electrolyte containing Li, Al, and F, wherein the solid electrolyte mainly contains a first phase which is a monoclinic Li3AlF6 phase, and in the XRD pattern obtained by powder X-ray diffraction of the solid electrolyte, the half-value width of the peak with the highest intensity among the peaks belonging to the first phase is greater than 1.0° and 3.0° or less, and the BET specific surface area is 50 m 2 / g or more and 350 m 2 / g or less.

[0006] According to the present disclosure, a highly useful solid electrolyte can be provided.

[0007] FIG. 1 is a cross-sectional view showing a schematic configuration of a coated active material 100 in which an electrode active material is coated with the solid electrolyte according to the second embodiment, which is an example of an electrode material according to the second embodiment. FIG. 2 shows a cross-sectional view of a battery 1000 according to the third embodiment. FIG. 3 is a diagram showing XRD patterns of fluoride solid electrolytes obtained by heat treatment of starting material powders of sample numbers 1, 2, 8, and 10. FIG. 4 is a diagram showing XRD patterns of the solid electrolytes after the crystallinity reduction treatment of sample numbers 1, 2, 8, and 10.

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

[0009] The embodiments described below all show comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement positions of the components, connection forms, etc. shown in the following embodiments are just examples and are not intended to limit the present disclosure. Among the components in the following embodiments, the components not described in the independent claims indicating the most general concept are described as optional components.

[0010] [First Embodiment] The solid electrolyte according to the first embodiment of the present disclosure is a solid electrolyte containing Li, Al, and F. The solid electrolyte according to the first embodiment mainly contains a low-crystalline monoclinic Li3AlF6 phase. The BET specific surface area of the solid electrolyte according to the first embodiment is 50 m 2 / g or more and 350 m 2 / g or less.

[0011] In the present disclosure, that the solid electrolyte contains a low-crystalline monoclinic Li3AlF6 phase means that in the XRD pattern obtained by powder X-ray diffraction (XRD) of the solid electrolyte powder, the full width at half maximum (FWHM) of the peak with the highest intensity among the peaks belonging to the monoclinic Li3AlF6 phase (the strongest peak) is greater than 1.0° and 3.0° or less. Thus, due to its low crystallinity, the FWHM of the peak showing the low-crystalline monoclinic Li3AlF6 phase shows a large value within the above numerical range. That is, in the XRD pattern obtained by powder X-ray diffraction of the solid electrolyte according to the first embodiment, the FWHM of the peak with the highest intensity among the peaks belonging to the monoclinic Li3AlF6 phase is greater than 1.0° and 3.0° or less. Hereinafter, the "low-crystalline monoclinic Li3AlF6 phase" may be referred to as the "first phase". The peak with the highest intensity among the peaks belonging to the first phase exists, for example, in the range of diffraction angle 2θ of 20.0° or more and 24.0° or less.

[0012] The solid electrolyte according to the first embodiment can have improved ionic conductivity by including a first phase as the main phase. Furthermore, the solid electrolyte according to the first embodiment can be made denser by compression due to the improved softness resulting from the low crystallinity of the first phase. This density increase by compression can form a dense, high-density solid electrolyte (a high-density compacted powder), which in turn can improve the ionic conductivity of the solid electrolyte according to the first embodiment. Thus, according to the first embodiment, a solid electrolyte consisting of fine particles with excellent ionic conductivity can be provided. For example, the solid electrolyte according to the first embodiment has a high ionic conductivity of 2.8 μS / cm or more.

[0013] As described above, the solid electrolyte according to the first embodiment has high ionic conductivity and improved softness, making it useful in batteries and energy storage devices, such as for use as a solid electrolyte layer in compacted powder or as a coating layer for electrode active material particles. This enables the provision of high-performance batteries and energy storage devices with excellent charge-discharge characteristics and reliability.

[0014] Low-crystallinity monoclinic Li3AlF6 phases can be formed, for example, by applying external stress to a powder containing a monoclinic Li3AlF6 phase, such as through mechanochemical processing like grinding, thereby straining the crystals. Solid electrolytes containing monoclinic Li3AlF6 phases can be synthesized by converting starting materials such as oxides containing Li and Al into fluorides and undergoing solid-phase reactions at relatively low temperatures (e.g., below 300°C).

[0015] In this disclosure, the statement that the solid electrolyte according to the first embodiment contains the first phase as the main phase means that, in the solid electrolyte according to the first embodiment, the first phase (a low-crystallinity monoclinic Li3AlF6 phase) is present in the largest amount by mass. The mass proportion in the solid electrolyte can be determined by XRD and Rietveld analysis of the solid electrolyte according to the first embodiment.

[0016] The BET specific surface area of ​​the solid electrolyte according to the first embodiment is 60 m². 2 / g or more 350m 2 It may be less than / g, and 60m 2Greater than / g and less than 350 m 2 It may be / g or less, and 60 m 2 Greater than / g and less than 300 m 2 It may be / g or less, and 63 m 2 / g or more and 294 m 2 It may be / g or less. The BET specific surface area of the solid electrolyte according to the first embodiment is 90 m 2 / g or more and 350 m 2 It may be / g or less, and 100 m 2 / g or more and 300 m 2 It may be / g or less, and 180 m 2 / g or more and 300 m 2 It may be / g or less. According to the above configuration, the ionic conductivity of the solid electrolyte can be further improved. In some cases, the BET specific surface area of the solid electrolyte according to the first embodiment is 50 m 2 / g or more and 180 m 2 It may be / g or less, and 50 m 2 / g or more and 150 m 2 It may be / g or less, and 60 m 2 / g or more and 100 m 2 It may be / g or less, and 60 m 2 Greater than / g and less than 100 m 2 It may be / g or less.

[0017] The solid electrolyte according to the first embodiment may be in particle form. The solid electrolyte according to the first embodiment, which is fine particles having the above BET specific surface area, can be used as a pressure-formed body, for example, as a solid electrolyte layer of an all-solid-state battery, and thus can contribute to the thinning, miniaturization, and high energy density of the all-solid-state battery. In addition, the solid electrolyte according to the first embodiment can be used as a component for improving ionic conductivity and reliability by being dispersed and included as a particulate additive component in another solid electrolyte or the like. For example, it is also possible to use the solid electrolyte according to the first embodiment as a coating material for particles of an electrode active material.

[0018] The proportion of the first phase on the particle surface may be greater than the proportion of the first phase inside the particle. When the low-crystallinity first phase is present in large quantities on the particle surface, the particle surface becomes softer. Therefore, when forming a compacted powder by compressing the solid electrolyte according to the first embodiment, friction between particles in the compact is reduced, making it easier to densify. Thus, a high-performance solid electrolyte can be obtained that has high ionic conductivity and can form a high-density compacted powder.

[0019] In this disclosure, the monoclinic Li3AlF6 phase includes phases having a monoclinic Li3AlF6 structure in which at least one element selected from the group consisting of Li, Al, and F is substituted with another element, and also phases having a non-stoichiometric composition. The same applies to other phases (crystalline phases) in this disclosure.

[0020] The ratio of the amount of substance of F to the total amount of substance of all elements constituting the solid electrolyte according to the first embodiment (i.e., mole fraction) may be 55.0% or more and 68.0% or less, 58.0% or more and 67.0% or less, or 58.0% or more and 66.0% or less. With this configuration, the purity of the first phase is increased by suppressing the formation of unnecessary precipitated phases. This makes it possible to further improve the ionic conductivity of the solid electrolyte. The ratio of the amount of substance of F may be 60.0% or more and 67.0% or less, 60.0% or more and 66.0% or less, or 60.0% or more and 65.0% or less. This makes it possible to obtain a solid electrolyte with a higher ionic conductivity (for example, 6.0 μS / cm or more) by further increasing the purity of the first phase.

[0021] In the first phase, some of the Al sites may be substituted with M1. Here, M1 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements. By substituting some of the Al sites with M1, a monoclinic Li3AlF6 phase is more easily formed stably at low temperatures (e.g., below approximately 280°C). The monoclinic Li3AlF6 phase synthesized by heat treatment at such low temperatures is easily pulverized because sintering has not progressed. Therefore, a solid electrolyte with fine particles and excellent ionic conductivity can be obtained.

[0022] M1 may contain at least one selected from the group consisting of Ti, Si, Zr, and Sn. This facilitates the stable synthesis of the monoclinic Li3AlF6 phase at lower temperatures. Consequently, it becomes easier to pulverize and promotes a reduction in crystallinity, i.e., partial amorphousness, thereby enabling the production of a solid electrolyte consisting of fine particles with excellent ionic conductivity. M1 may be at least one selected from the group consisting of Ti, Si, Zr, and Sn, or it may be Ti. This also enables the production of a solid electrolyte consisting of fine particles with excellent ionic conductivity. Such solid electrolytes are useful as solid electrolyte layers in batteries, coating layers for electrode active materials, and electrode materials. Furthermore, Ti-containing raw materials are available in many grades and brands with specific powder properties as industrial raw materials, are widely distributed, and are readily available at low cost. Therefore, such solid electrolytes have high supply and quality stability and are suitable for industrial use.

[0023] The amount of substitution by M1 may be 0 at% to 20 at%, 0 at% to 15 at%, 0 at% to 10 at%, greater than 0 at% and 10 at%, or 1 at% to 10 at%. This makes it easier to stably synthesize the monoclinic Li3AlF6 phase at a low temperature (for example, about 230°C), making it easier to pulverize and reducing the crystallinity of the monoclinic Li3AlF6 phase, i.e., promoting partial amorphousization. Thus, a solid electrolyte can be obtained that is a fine particle with excellent ionic conductivity and a BET specific surface area that satisfies the numerical range of this disclosure. As described above, by not having an excess amount of M1, the decrease in ionic conductivity and the appearance of unnecessary precipitated phases can be reduced.

[0024] Furthermore, M1 may be composed of multiple elements. For example, M1 may be Ti and Zr, or Ti and Si. Partial substitution of Al in M1 promotes halogenation at low temperatures (e.g., 250°C to 270°C). This allows for a reduction in the synthesis temperature of the monoclinic Li3AlF6 phase, thereby adjusting its ionic conductivity and atmospheric stability. Additionally, the lower temperature softens the monoclinic Li3AlF6 phase, making it easier to pulverize and reducing its crystallinity, i.e., promoting partial amorphous formation.

[0025] The solid electrolyte according to the first embodiment may further include a second phase which is a Li2M2F6 phase, where M2 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements. This allows the solid electrolyte to have higher ionic conductivity (e.g., 6.0 μS / cm or higher).

[0026] The second phase is, for example, a tetragonal Li2M2F6 phase. The second phase has a lower melting point (approximately 600°C to 650°C) than the monoclinic Li3AlF6 phase and is softer compared to the monoclinic Li3AlF6 phase. Therefore, the inclusion of the second phase in the solid electrolyte improves the binding action between powders, thereby improving the reliability and ionic conductivity of the solid electrolyte. The second phase, like the first phase, has excellent atmospheric stability. Therefore, the inclusion of the second phase in the solid electrolyte improves the ionic conductivity and atmospheric stability of the solid electrolyte.

[0027] The second phase may be a low-crystallinity Li2M2F6 phase, or a low-crystallinity tetragonal Li2M2F6 phase; that is, the solid electrolyte according to the first embodiment may further contain a low-crystallinity Li2M2F6 phase.

[0028] In this disclosure, the solid electrolyte being said to contain a low-crystallinity Li2M2F6 phase means that in the XRD pattern obtained by powder XRD of the solid electrolyte, the full width at half maximum of the strongest peak belonging to the Li2M2F6 phase is greater than 1.0° and less than or equal to 3.0°.

[0029] M2 may be Ti. That is, the solid electrolyte according to the first embodiment may further contain a low-crystallinity Li2TiF6 phase. This may allow the solid electrolyte to have higher ionic conductivity (e.g., 6.0 μS / cm or higher). Also, the compacted powder of the solid electrolyte may have a higher density (e.g., 1.8 g / cm³). 3 It is possible to have the above.

[0030] The proportion of the second phase in the solid electrolyte is, for example, 1% to 40% by mass ratio to the first phase, from the viewpoint of improving properties. The second phase may also be, for example, 25% by mass ratio to the first phase. This makes it possible to increase the ionic conductivity of the solid electrolyte.

[0031] The solid electrolyte according to the first embodiment may further contain a third phase, which is an orthorhombic Li3AlF6 phase. Since the orthorhombic phase is a crystalline phase synthesized at a much higher temperature than the monoclinic phase, the third phase has higher mechanical strength than the monoclinic Li3AlF6 phase. Furthermore, the orthorhombic phase is stable at high temperatures. Therefore, by including the third phase as a secondary phase in coexistence with the first phase, a solid electrolyte can be obtained that is a fine particle with excellent ionic conductivity, improved high-temperature stability, and enhanced mechanical strength.

[0032] The third phase may be a low-crystallinity orthorhombic Li3AlF6 phase; that is, the solid electrolyte according to the first embodiment may further contain a low-crystallinity orthorhombic Li3AlF6 phase.

[0033] In this disclosure, the solid electrolyte being said to contain a low-crystallinity orthorhombic Li3AlF6 phase means that, in the XRD pattern obtained by powder XRD of the solid electrolyte, the full width at half maximum of the strongest peak belonging to the orthorhombic Li3AlF6 phase is greater than 1.0° and less than or equal to 3.0°.

[0034] In the third phase, some of the Al sites may be substituted with M3. Here, M3 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements. By substituting some of the Al sites with M3, the third phase, which is a high-temperature stable phase of Li3AlF6, becomes easier to synthesize stably. This makes it easier to obtain a solid electrolyte with excellent ionic conductivity and high-temperature durability.

[0035] M3 may contain at least one selected from the group consisting of Ti, Si, Zr, and Sn. This makes it possible to obtain a solid electrolyte containing a third phase while exhibiting high ionic conductivity of, for example, 2.8 μS / cm or more. M3 may be at least one selected from the group consisting of Ti, Si, Zr, and Sn, or it may be Ti. This makes it possible for the solid electrolyte to have even higher ionic conductivity of, for example, 6.0 μS / cm or more and high temperature durability.

[0036] The amount of substitution with M3 may be between 0 at% and 30 at%, or between 0 at% and 30 at%. This makes it easier to stably and reproducibly generate the third phase. As a result, it becomes easier to obtain a solid electrolyte of stable quality with excellent ionic conductivity and high-temperature durability. As described above, by not having an excess amount of M3, the decrease in ionic conductivity can be reduced.

[0037] The amount of substitution of M3 may be greater than the amount of substitution of M1. This results in high ionic conductivity (e.g., 6.0 μS / cm or more) and excellent high-temperature stability, and fine (e.g., BET specific surface area of ​​60 m²) 2 / g or more 300m 2 A solid electrolyte is obtained that is in the form of particles (less than / g).

[0038] The crystallinity of the first phase may be lower than that of the third phase. That is, the first phase may have lower crystallinity than the third phase, i.e., partial amorphousness has progressed. With such a configuration, high ionic conductivity (e.g., 6.0 μS / cm or higher) can be achieved. In addition, the density of the compacted solid electrolyte is increased due to the improved softness, resulting in densification and suppression of structural defects such as fine cracks or voids. Therefore, a solid electrolyte with excellent ionic conductivity and reliability can be obtained, possessing excellent charge-discharge characteristics and enabling the realization of highly reliable batteries and energy storage devices. The crystallinity of each phase can be compared by comparing the full width at half maximum (FWHM) of the strongest peaks belonging to each phase in the powder XRD. A larger FWHM indicates lower crystallinity. That is, in the XRD pattern of the solid electrolyte according to the first embodiment, the FWHM of the strongest peak belonging to the monoclinic Li3AlF6 phase may be larger than the FWHM of the strongest peak belonging to the orthorhombic Li3AlF6 phase. In XRD patterns, if the strongest peaks of each phase overlap, making it difficult to compare the full width at half maximum (FWHM), it is also possible to compare crystallinity by comparing the FWHM of the strongest peaks in the diffraction patterns calculated by Rietveld analysis. Alternatively, the crystallinity of each phase can be compared by observing the lattice image within the particle using a transmission electron microscope (TEM) or scanning transmission electron microscope (STEM) to confirm the distribution of crystallinity within the particle.

[0039] If the solid electrolyte includes a second phase in addition to the first phase, M1 and M2 may contain common elements or may be the same element. If the solid electrolyte includes a third phase in addition to the first phase, M1 and M3 may contain common elements or may be the same element. If the solid electrolyte includes a second phase and a third phase in addition to the first phase, M1, M2, and M3 may contain common elements. With such a configuration, the affinity between the first phase, the second phase, and the third phase can be improved, for example, the thermal expansion characteristics can be improved. This improves the thermal cycling and thermal shock performance and improves the reliability of the solid electrolyte. M1, M2, and M3 may be the same element.

[0040] The composition of each phase in a solid electrolyte can be evaluated (particle by particle) by, for example, radio frequency inductively coupled plasma (ICP) emission spectroscopy and combustion ion chromatography (CIC), or by composition mapping analysis using electron probe microanalyzer (EPMA) or energy dispersive X-ray spectroscopy (EDS). For example, the Li, Al, and Ti content can be measured by ICP emission spectroscopy, and the F content can be measured by CIC.

[0041] In the solid electrolyte according to the first embodiment, the mass proportion of the first phase may be greater than the mass proportion of the second phase, and the mass proportion of the second phase may be greater than the mass proportion of the third phase. That is, the solid electrolyte according to the first embodiment may contain the first phase as the component with the highest mass (main phase), and further contain the second and third phases in that order by mass as secondary phases. In this way, by containing a large amount of the first phase, which is a highly ionically conductive monoclinic phase that is formed at relatively low temperatures, and further containing a crystalline phase such as orthorhombic, which has excellent high-temperature durability, as a secondary phase, it becomes easier to pulverize, and the deterioration of properties due to frictional heat between powder particles during the formation of the solid electrolyte compact (during pressing) can be suppressed. Therefore, a solid electrolyte with excellent properties such as ionic conductivity and reliability can be obtained.

[0042] The solid electrolyte does not have to contain a second phase, nor does it have to contain a third phase, nor does it have to contain both a second and a third phase.

[0043] The first phase in the solid electrolyte according to the first embodiment may be 50% by mass or more, 60% by mass or more, 70% by mass or more, or even 80% by mass or more. The first phase in the solid electrolyte according to the first embodiment may be, for example, 100% by mass or less, or less than 100% by mass.

[0044] An example of a method for producing a solid electrolyte according to the first embodiment will be described.

[0045] The solid electrolyte according to the first embodiment can be obtained, for example, by reducing the crystallinity of a solid electrolyte containing a monoclinic Li3AlF6 phase as the main phase, that is, by partially amorphizing it.

[0046] The method for producing a solid electrolyte according to this disclosure includes, for example, halogenating (converting to a fluoride) a starting material containing Li and Al, synthesizing a solid electrolyte containing a monoclinic Li3AlF6 phase as the main phase, and reducing the crystallinity of the monoclinic Li3AlF6 phase. The starting material contains at least one selected from the group consisting of oxides, carbonates, and hydroxides. The starting material may consist of only at least one selected from the group consisting of oxides, carbonates, and hydroxides. The starting material may contain Li, Al, and Ti.

[0047] The method for producing a solid electrolyte according to this disclosure, by including halogenation of the above-mentioned starting materials, enables the synthesis of a solid electrolyte mainly composed of a monoclinic Li3AlF6 phase at a low temperature (e.g., 300°C or below). The solid electrolyte mainly composed of a monoclinic Li3AlF6 phase synthesized here is a solid electrolyte mainly composed of a monoclinic Li3AlF6 phase before the reduction of crystallinity (i.e., not low crystallinity). Hereinafter, in order to distinguish it from the solid electrolyte according to the first embodiment, the solid electrolyte mainly composed of a monoclinic Li3AlF6 phase obtained in the production method of this disclosure before the reduction of crystallinity may be referred to as a "fluoride solid electrolyte". Note that the halogenation temperature may vary depending on the particle size, particle surface area, and atmosphere.

[0048] Fluoride solid electrolytes obtained by heat treatment at low temperatures are hard and not sintered, making them easy to pulverize. Therefore, they are suitable as solid electrolytes with excellent ionic conductivity and high density in compacted form, and as fine particles (for example, with a BET specific surface area of ​​50 m²) for thinning of the active material layer and solid electrolyte layer, or as a coating layer covering the surface of the electrode active material. 2 / g or more 350m 2It is possible to obtain a solid electrolyte with a purity of less than / g. Furthermore, because it is easy to finely grind, contamination from impurities from the grinding medium (e.g., zirconia balls or alumina balls) is reduced, so a solid electrolyte with high purity can be obtained.

[0049] The above starting materials and a halogen-containing substance for halogenation may be mixed to simultaneously induce a solid-phase reaction and halogenation. That is, halogenation of the starting materials and synthesis of a fluoride solid electrolyte containing a monoclinic Li3AlF6 phase as the main phase may be carried out simultaneously. Halogenation of the starting materials may include contacting the starting materials with a halogen gas. This allows for a homogeneous halogenation treatment of the starting materials. Therefore, reaction unevenness is suppressed, and a fluoride solid electrolyte with excellent properties can be obtained. The halogen gas can be obtained, for example, by heat-treating a thermally decomposable halogen-containing compound. Halogenation of the starting materials may also be carried out by mixing the starting materials with a thermally decomposable halogen-containing compound and heat-treating it. With the above configuration, halogenation of the starting materials and the solid-phase reaction can be carried out simultaneously, and desired halogenation control, such as adjustment of the degree of halogenation (synthesis of halogenated oxides, etc.) and control of the amount of F, becomes possible, and a monoclinic Li3AlF6 phase can be stably produced, resulting in a useful solid electrolyte with excellent ionic conductivity.

[0050] The thermal decomposition temperature of the halogen-containing compound may be 300°C or lower. The formation of the monoclinic Li3AlF6 phase is suitable for treatment at 200°C to 300°C (preferably 250°C to 300°C), and it can be stabilized and formed by solid-phase reactions at these temperatures. Because the thermal decomposition temperature of the halogen-containing compound is 300°C or lower, the monoclinic Li3AlF6 phase can be synthesized by heat treatment of the starting materials and halogen-containing compounds at the low temperatures described above. Furthermore, the fluoride solid electrolyte produced by the low-temperature heat treatment is easily pulverized, and the reduction in the crystallinity of the monoclinic Li3AlF6 phase proceeds easily. Therefore, fine particles (for example, with a BET specific surface area of ​​50 m²) that have excellent ionic conductivity and can form dense compacts are desirable. 2 / g or more 350m 2A solid electrolyte with a value of less than or equal to 1 / g can be obtained.

[0051] In the method for producing a solid electrolyte according to the present disclosure, halogenation of the starting material and synthesis of a solid electrolyte containing a monoclinic Li3AlF6 phase as the main phase may be carried out by heat-treating the starting material and the halogen-containing compound at a temperature of 200°C to 450°C. The temperature of the heat treatment may be 200°C to 400°C, 200°C to 350°C, or 200°C to 300°C.

[0052] The halogen-containing compound may also contain ammonium fluoride (NH4F). NH4F has a low thermal decomposition temperature (below 200°C), allowing halogenation and solid-phase reactions to occur at low temperatures.

[0053] The halogen-containing compound may be in particulate form. This allows for homogeneous mixing with the starting material and subsequent heat treatment under good contact conditions to achieve halogenation, resulting in uniform halogenation of the mixed powder. Consequently, reaction unevenness is suppressed, and a monoclinic Li3AlF6 phase with excellent properties can be stably produced.

[0054] The average particle size of the halogen-containing compound may be between 5 μm and 100 μm. This facilitates homogeneous dispersion of the halogen-containing compound when mixed with the starting materials. As a result, reaction unevenness is suppressed, and a monoclinic Li3AlF6 phase with excellent properties can be stably produced.

[0055] Depending on the heat treatment temperature conditions, an orthorhombic Li3AlF6 phase can be included as a secondary phase. Alternatively, the orthorhombic Li3AlF6 phase can be synthesized separately and then included as a secondary phase in a fluoride solid electrolyte containing a monoclinic Li3AlF6 phase.

[0056] Furthermore, depending on the mixing ratio of the starting materials, for example, Li2M2F6 phase can be included as a secondary phase.

[0057] Specific examples of halogenating starting materials and synthesizing fluoride solid electrolytes are as follows. For example, by mixing simple oxides of Al (Al2O3), Li carbonate (Li2CO3), and Li-containing complex oxides (Li2TiO3) as starting material powders with a halogen-containing compound such as a halide (NH4F), and then heat-treating the mixture, halogenation, decarbonate removal from lithium carbonate, and solid-phase reactions are carried out simultaneously. In this way, a solid electrolyte (fluoride solid electrolyte) containing a monoclinic Li3AlF6 phase as the main phase is synthesized.

[0058] Reducing the crystallinity of the monoclinic Li3AlF6 phase is achieved by straining the crystal. Reducing the crystallinity of the monoclinic Li3AlF6 phase can be achieved, for example, by amorphousizing a portion of the fluoride solid electrolyte. Reducing crystallinity includes mechanochemical treatment. The synthesized fluoride solid electrolyte may be subjected to grinding (mechanochemical treatment). This grinding treatment can amorphous at least a portion of the fluoride solid electrolyte, resulting in a solid electrolyte containing a low-crystallinity monoclinic Li3AlF6 phase as the main phase and exhibiting excellent ionic conductivity.

[0059] The grinding process may be dry or wet, using water or a solvent (e.g., ethanol, butyl acetate, etc.). From the viewpoint of uniformly reducing the crystallinity of the particle surface, wet grinding with high uniform fluidity may be used. For example, zirconia balls (e.g., φ1 mm to 20 mm) and the synthesized fluoride solid electrolyte may be placed in a ball mill container and ground for, for example, 1 to 40 hours. As a result, at least a portion of the fluoride solid electrolyte can be amorphous, and the crystallinity of the monoclinic Li3AlF6 phase can be reduced.

[0060] The repeated collisions between the particle surface of the fluoride solid electrolyte and the grinding medium or the ball mill wall cause mechanochemical action, leading to amorphization of each crystalline phase from the particle surface. Therefore, the crystallinity of the particle surface tends to be more amorphous than that of the particle interior. Also, when multiple powders with different hardnesses are ground simultaneously, amorphization generally progresses more in the softer particles than in the harder particles. The hardness referred to here is the hardness that can be compared and evaluated using micro-Vickers. For example, when monoclinic Li3AlF6 phase and tetragonal Li2TiF6 phase are ground and amorphized more rapidly in the Li2TiF6 phase, which has a lower melting point and is softer, than in the Li3AlF6 (monoclinic) phase. Therefore, the particle size and crystallinity can be such that monoclinic Li3AlF6 phase > Li2TiF6 phase, respectively. For example, after wet grinding, the average particle size of each phase can be approximately 0.08 μm for the monoclinic Li3AlF6 phase, approximately 0.04 μm for the Li2TiF6 phase, and approximately 0.07 μm for both phases combined. The average particle size of each phase can be calculated from the area of ​​each crystalline phase particle when identified and made into a perfect circle using, for example, EPMA. The above trend is also observed between the monoclinic Li3AlF6 phase and the orthorhombic Li3AlF6 phase, which is a harder, high-temperature stable phase than the monoclinic Li3AlF6 phase. Therefore, when both phases are included and simultaneously subjected to mechanochemical treatment, the grinding and amorphization of the monoclinic Li3AlF6 phase, which has a lower melting point and is softer, proceeds more rapidly than that of the orthorhombic Li3AlF6 phase, resulting in a particle size and crystallinity relationship where orthorhombic Li3AlF6 phase > monoclinic Li3AlF6 phase.

[0061] In addition to the monoclinic Li3AlF6 phase, a fluoride solid electrolyte containing at least one selected from the group consisting of Li2M2F6 phase and orthorhombic Li3AlF6 phase as a secondary phase may be partially amorphous by simultaneously mechanochemical treatment as described above. Alternatively, the monoclinic Li3AlF6 phase and the Li2M2F6 phase and orthorhombic Li3AlF6 phase may be partially amorphous by individually grinding them before mixing them. This allows for adjustment of the properties of the solid electrolyte over a wide range.

[0062] There are the following differences between the solid electrolyte according to the first embodiment and the solid electrolyte described in Patent Document 1. Patent Document 1 discloses a solid electrolyte containing Li, Ti, M, and F. However, while Patent Document 1 describes the halide used as a starting material for the synthesis of the solid electrolyte, it does not disclose the resulting compound. Furthermore, Patent Document 1 synthesizes the solid electrolyte by mechanochemical treatment of the starting material, which is a halide. Thus, the synthesis method also differs from that of this disclosure. According to the inventor's research, the monoclinic Li3AlF6 phase is a crystalline phase that is produced only when a starting material, which is at least one selected from the group consisting of oxides, carbonates, and hydroxides, is halogenated at a relatively low temperature and subjected to a solid-phase reaction. Therefore, the synthesis method of the solid electrolyte described in Patent Document 1 differs from the synthesis method in this disclosure, and thus the solid electrolyte described in Patent Document 1 is a different compound from the fluoride solid electrolyte and solid electrolyte of this disclosure. Furthermore, Patent Document 1 does not disclose the relative amounts of crystalline phase content in solid electrolytes, their specific solid solution compositions (for example, substitutions of Al sites by M1, M2, and M3 and the amounts of substitution), nor the F content in monoclinic Li3AlF6. These are also technologies that have been revealed by this study to be factors that significantly affect ionic conductivity and reliability.

[0063] [Second Embodiment] The second embodiment will now be described. Matters described in the first embodiment will be omitted as appropriate.

[0064] The electrode material according to the second embodiment includes the solid electrolyte and electrode active material according to the first embodiment. This makes it possible to realize a high-performance battery with improved charge / discharge characteristics and reliability.

[0065] In the electrode material according to the second embodiment, the solid electrolyte according to the first embodiment may be included as a solid electrolyte mixed with the electrode active material, or as a coating material that coats the particles of the electrode active material.

[0066] Figure 1 is a cross-sectional view showing a schematic configuration of a coated active material 100, an example of an electrode material according to the second embodiment, in which the electrode active material is coated with a solid electrolyte according to the first embodiment. The coated active material 100 includes an electrode active material 110 and a coating layer 120. The shape of the electrode active material 110 is, for example, particulate. The coating layer 120 contains a solid electrolyte according to the first embodiment and covers at least a portion of the surface of the electrode active material 110. The coating layer 120 has excellent ionic conductivity due to the solid electrolyte according to the first embodiment. Furthermore, due to the soft nature of the solid electrolyte according to the first embodiment, the coating layer 120 can cover the surface of the electrode active material 110 in accordance with the irregularities of the particle surface. In such a coated active material 100, the coating layer 120 can reduce the interfacial resistance between the particles of the electrode active material 110 and the electrolyte, thereby improving the charge / discharge characteristics and reliability of the battery performance.

[0067] The electrode active material 110 may be a positive electrode active material. Examples of positive electrode active materials included in the electrode material according to the second embodiment are lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanion materials, transition metal sulfides, transition metal oxyfluorides, transition metal oxysulfides, or transition metal oxynitrides. Examples of lithium-containing transition metal oxides are Li(Ni,Co,Mn)O2, Li(Ni,Co,Al)O2, or LiCoO2.

[0068] [Third Embodiment] The third embodiment will now be described. Matters described in the first embodiment will be omitted as appropriate.

[0069] The battery according to the third embodiment comprises a positive electrode, an electrolyte layer, and a negative electrode. The electrolyte layer is located between the positive electrode and the negative electrode.

[0070] At least one selected from the group consisting of a positive electrode, an electrolyte layer, and a negative electrode contains a solid electrolyte according to the first embodiment.

[0071] The battery according to the third embodiment contains the solid electrolyte according to the first embodiment, resulting in a high-performance battery with improved charge / discharge characteristics and reliability.

[0072] Figure 2 shows a cross-sectional view of the battery 1000 according to the third embodiment.

[0073] The battery 1000 according to the third embodiment comprises a positive electrode 201, an electrolyte layer 202, and a negative electrode 203. The electrolyte layer 202 is provided between the positive electrode 201 and the negative electrode 203.

[0074] The positive electrode 201 contains a positive electrode active material 204 and a solid electrolyte 200.

[0075] The electrolyte layer 202 contains an electrolyte material.

[0076] The negative electrode 203 contains a negative electrode active material 205 and a solid electrolyte 200.

[0077] The solid electrolyte 200 may, for example, include the solid electrolyte according to the first embodiment. That is, in this case, the positive electrode 201 and the negative electrode 203 correspond to electrodes containing the electrode material according to the second embodiment. With such a configuration, a high-performance battery with improved charge / discharge characteristics and reliability can be provided. The solid electrolyte 200 in the positive electrode 201 may include the solid electrolyte according to the first embodiment, while the negative electrode 203 may not include the solid electrolyte according to the first embodiment.

[0078] The positive electrode 201 contains a material capable of intercalating and releasing metal ions (e.g., lithium ions). This material is, for example, the positive electrode active material 204.

[0079] Examples of positive electrode active material 204 include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanion materials, transition metal sulfides, transition metal oxyfluorides, 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.

[0080] In this disclosure, "(A, B, C)" means "at least one selected from the group consisting of A, B, and C."

[0081] The shape of the positive electrode active material 204 is not limited to a specific shape. The positive electrode active material 204 may be particles. The positive electrode active material 204 may have a median diameter of 0.1 μm or more and 100 μm or less. When the positive electrode active material 204 has a median diameter of 0.1 μm or more, the positive electrode active material 204 and the solid electrolyte 200 can be well dispersed in the positive electrode 201. This improves the charge and discharge characteristics of the battery 1000. When the positive electrode active material 204 has a median diameter of 100 μm or less, the lithium diffusion rate within the positive electrode active material 204 is improved. This allows the battery 1000 to operate at high power.

[0082] The positive electrode active material 204 may have a larger median diameter than the solid electrolyte 200. This allows the positive electrode active material 204 and the solid electrolyte 200 to be well dispersed in the positive electrode 201.

[0083] In order to improve the energy density and output of the battery 1000, the ratio of the volume of the positive electrode active material 204 to the sum of the volume of the positive electrode active material 204 and the volume of the solid electrolyte 200 in the positive electrode 201 may be 0.30 or more and 0.95 or less.

[0084] A coating layer may 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 mixing with the conductive additive and binder. Examples of coating materials included in the coating layer are sulfide solid electrolytes, oxide solid electrolytes, or halide solid electrolytes. If the solid electrolyte 200 contains a sulfide solid electrolyte, the coating material may contain a solid electrolyte according to the first embodiment in order to suppress the oxidative decomposition of the sulfide solid electrolyte. By having the positive electrode 201 with such a configuration, a high-performance battery with improved charge-discharge characteristics and reliability can be provided.

[0085] When the solid electrolyte 200 contains the solid electrolyte according to the first embodiment, the coating material may contain an oxide solid electrolyte in order to suppress the oxidative decomposition of the solid electrolyte. As the oxide solid electrolyte, lithium niobate, which has excellent stability at high potentials, may be used. By suppressing oxidative decomposition, the overvoltage rise of the battery 1000 can be suppressed. By including the solid electrolyte according to the first embodiment as a mixture in this way, the soft nature of the solid electrolyte forms an interface that contacts the surface irregularities of the positive electrode active material 204 particles. This increases the contact area between the positive electrode active material 204 particles and the solid electrolyte, and an ion path is formed, so that the positive electrode 201 has excellent ionic conductivity and reliability. As a result, a battery with excellent charge / discharge characteristics and reliability can be constructed.

[0086] As described above, when the positive electrode 201 includes an electrode material containing a solid electrolyte according to the first embodiment, the positive electrode 201 may include the solid electrolyte according to the first embodiment as a solid electrolyte 200, or it may include it as a coating material that covers the positive electrode active material 204.

[0087] To improve the energy density and output of the battery 1000, the positive electrode 201 may have a thickness of 10 μm or more and 500 μm or less.

[0088] The electrolyte layer 202 contains an electrolyte material. This electrolyte material is, for example, a solid electrolyte. This solid electrolyte may include the solid electrolyte according to the first embodiment. The electrolyte layer 202 may be a solid electrolyte layer. As a result, the solid electrolyte layer has high ionic conductivity, and the softness of the solid electrolyte according to the first embodiment ensures strong bonding with the electrode layer. Therefore, a battery with excellent charge / discharge characteristics and reliability can be constructed.

[0089] The electrolyte layer 202 may contain 50% by mass or more of the solid electrolyte according to the first embodiment. The electrolyte layer 202 may contain 70% by mass or more of the solid electrolyte according to the first embodiment. The electrolyte layer 202 may contain 90% by mass or more of the solid electrolyte according to the first embodiment. The electrolyte layer 202 may consist only of the solid electrolyte according to the first embodiment.

[0090] Hereinafter, the solid electrolyte according to the first embodiment will be referred to as the first solid electrolyte. A solid electrolyte different from the first solid electrolyte will be referred to as the second solid electrolyte.

[0091] The electrolyte layer 202 may contain not only a first solid electrolyte but also a second solid electrolyte. In the electrolyte layer 202, the first solid electrolyte and the second solid electrolyte may be uniformly dispersed. The layer consisting of the first solid electrolyte and the layer consisting of the second solid electrolyte may be stacked along the stacking direction of the battery 1000.

[0092] The battery according to the third embodiment may comprise a positive electrode 201, a second electrolyte layer, a first electrolyte layer, and a negative electrode 203 in this order. 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. This allows the solid electrolyte contained in the second electrolyte layer to be used without reduction. As a result, the charge and discharge efficiency of the battery 1000 can be improved. For example, if the second electrolyte layer contains the first solid electrolyte, the first electrolyte layer may contain a sulfide solid electrolyte to suppress the reductive decomposition of the halide solid electrolyte contained in the first solid electrolyte. This improves the charge and discharge efficiency of the battery 1000. The second electrolyte layer may contain the first solid electrolyte. Since the first solid electrolyte has high oxidation resistance, a battery with excellent charge and discharge characteristics can be realized.

[0093] The electrolyte layer 202 may consist only of the second solid electrolyte.

[0094] The electrolyte layer 202 may have a thickness of 1 μm or more and 1000 μm or less. If the electrolyte layer 202 has a thickness of 1 μm or more, the positive electrode 201 and the negative electrode 203 are less likely to short-circuit. If the electrolyte layer 202 has a thickness of 1000 μm or less, the battery 1000 can operate at high output.

[0095] Examples of solid electrolytes that constitute the second solid electrolyte are Li2MgX14, Li2FeX14, Li(Al,Ga,In)X14, Li3(Al,Ga,In)X16, or LiI. Here, X1 is at least one selected from the group consisting of F, Cl, Br, and I.

[0096] To improve the energy density and output of the battery 1000, the electrolyte layer 202 may have a thickness of 1 μm or more and 1000 μm or less.

[0097] The negative electrode 203 contains a material capable of intercalating and releasing metal ions (e.g., lithium ions). This material is, for example, the negative electrode active material 205.

[0098] Examples of negative electrode active materials 205 include metallic materials, carbon materials, oxides, nitrides, tin compounds, or silicon compounds. Metallic materials may be elemental metals or alloys. Examples of metallic materials include lithium metal or lithium alloys. Examples of carbon materials include natural graphite, coke, carbon in the process of graphitization, carbon fibers, spheroidal 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.

[0099] The negative electrode active material 205 may 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 may be a material capable of intercalating and releasing lithium ions at a voltage of 0.27 V or higher relative to lithium. Examples of such negative electrode active materials are titanium oxide, indium metal, or lithium alloy. An example of titanium oxide is Li4Ti5O 12 The material is either LiTi2O4 or TiO2. By using the above-mentioned negative electrode active material, the reductive decomposition of the halide solid electrolyte contained in 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.

[0100] The shape of the negative electrode active material 205 is not limited to a specific shape. The negative electrode active material 205 may be particles. The negative electrode active material 205 may have a median diameter of 0.1 μm or more and 100 μm or less. When the negative electrode active material 205 has a median diameter of 0.1 μm or more, the negative electrode active material 205 and the solid electrolyte 200 can be well dispersed in the negative electrode 203. This improves the charge and discharge characteristics of the battery 1000. When the negative electrode active material 205 has a median diameter of 100 μm or less, the lithium diffusion rate within the negative electrode active material 205 is improved. This allows the battery 1000 to operate at high power.

[0101] The negative electrode active material 205 may have a larger median diameter than the solid electrolyte 200. This allows the negative electrode active material 205 and the solid electrolyte 200 to be well dispersed in the negative electrode 203.

[0102] In order to improve the energy density and output of the battery 1000, the ratio of the volume of the negative electrode active material 205 to the sum of the volume of the negative electrode active material 205 and the volume of the solid electrolyte 200 in the negative electrode 203 may be 0.30 or more and 0.95 or less.

[0103] To improve the energy density and output of the battery 1000, the negative electrode 203 may have a thickness of 10 μm or more and 500 μm or less.

[0104] At least one selected from the group consisting of a positive electrode 201, an electrolyte layer 202, and a negative electrode 203 may contain a second solid electrolyte for the purpose of enhancing ionic conductivity, chemical stability, and electrochemical stability.

[0105] The second solid electrolyte may contain a sulfide solid electrolyte.

[0106] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75 S4, or Li 10 GeP2S 12 That is the case.

[0107] If 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 halide solid electrolyte contained in the first 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.

[0108] The second solid electrolyte may contain an oxide solid electrolyte.

[0109] Examples of oxide solid electrolytes include: (i) NASICON-type solid electrolytes such as LiTi2(PO4)3 or its elemental substitutions; (ii) perovskite-type solid electrolytes such as (LaLi)TiO3; (iii) Li 14 ZnGe4O 16 , LISICON-type solid electrolytes such as Li4SiO4, LiGeO4 or their elementally substituted counterparts, (iv)Li7La3Zr2O 12 (v) Li3PO4 or its N-substituted counterparts, which are garnet-type solid electrolytes.

[0110] As described above, the second solid electrolyte may contain a halide solid electrolyte different from the halide solid electrolyte contained in the first solid electrolyte. Examples of halide solid electrolytes different from the halide solid electrolyte contained in the first solid electrolyte are Li2MgX24, Li2FeX24, Li(Al,Ga,In)X24, Li3(Al,Ga,In)X26, or LiI. Here, X2 is at least one selected from the group consisting of F, Cl, Br, and I.

[0111] Other examples of halogenated solid electrolytes different from the halogenated solid electrolytes contained in the first solid electrolyte include Li p Me q Y rThis is a compound represented by Z6. Here, p + mq + 3r = 6 and c > 0 are satisfied. Me is at least one selected from the group consisting of metallic elements other than Li and Y and metalloid elements. Z is at least one selected from the group consisting of F, Cl, Br, and I. m represents the valence of Me. "Metalloid elements" are B, Si, Ge, As, Sb, and Te. "Metallic elements" are all elements in groups 1 to 12 of the periodic table (except hydrogen), and all elements in groups 13 to 16 of the periodic table (except B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se).

[0112] To improve the ionic conductivity of the above-mentioned halide solid electrolyte, Me may be at least one selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb.

[0113] The halide solid electrolyte, which is different from the halide solid electrolyte contained in the first solid electrolyte, may be Li3YCl6 or Li3YBr6.

[0114] The second solid electrolyte may be an organic polymer solid electrolyte.

[0115] Examples of organic polymer solid electrolytes include polymer compounds and lithium salt compounds.

[0116] Polymer compounds may have an ethylene oxide structure. Polymer compounds having an ethylene oxide structure can contain a large amount of lithium salt, and therefore their ionic conductivity can be further increased.

[0117] Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3F3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), or LiC(SO2CF3)3. One lithium salt selected from these may be used alone, or a mixture of two or more lithium salts selected from these may be used.

[0118] At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a non-aqueous electrolyte, a gel electrolyte, or an ionic liquid to facilitate the transfer of lithium ions and improve the output characteristics of the battery.

[0119] The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.

[0120] Examples of non-aqueous solvents include cyclic carbonate solvents, linear carbonate solvents, cyclic ether solvents, linear ether solvents, cyclic ester solvents, linear ester solvents, or fluorinated solvents. Examples of cyclic carbonate solvents are ethylene carbonate, propylene carbonate, or butylene carbonate. Examples of linear carbonate solvents are dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate. Examples of cyclic ether solvents are tetrahydrofuran, 1,4-dioxane, or 1,3-dioxolane. Examples of linear ether solvents are 1,2-dimethoxyethane or 1,2-diethoxyethane. An example of a cyclic ester solvent is γ-butyrolactone. An example of a linear ester solvent is methyl acetate. Examples of fluorinated solvents are fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, or fluorodimethylene carbonate. One non-aqueous solvent selected from these may be used alone, or a combination of two or more non-aqueous solvents selected from these may be used.

[0121] 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 may be used alone, or a mixture of two or more lithium salts selected from these may be used. The concentration of the lithium salt is, for example, in the range of 0.5 mol / L or more and 2 mol / L or less.

[0122] Polymer materials impregnated with a non-aqueous electrolyte can be used as the gel electrolyte. Examples of polymer materials include polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, or polymers having ethylene oxide bonds.

[0123] Examples of cations contained in ionic liquids include: (i) aliphatic quaternary salts such as tetraalkylammonium or tetraalkylphosphonium; (ii) aliphatic cyclic ammonium compounds such as pyrrolidinium, morpholinium, imidazolinium, tetrahydropyrimidinium, piperadinium, or piperidinium; or (iii) nitrogen-containing heterocyclic aromatic cations such as pyridinium or imidazolium.

[0124] An example of anion contained in an ionic liquid is PF6. - BF4 - SbF6 - AsF6 - SO3CF3 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , N(SO2CF3)(SO2C4F9) - , or C(SO2CF3)3 - That is the case.

[0125] The ionic liquid may contain lithium salts.

[0126] At least one selected from the group consisting of a positive electrode 201, an electrolyte layer 202, and a negative electrode 203 may contain a binder to improve the adhesion between particles.

[0127] Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, or carboxymethylcellulose. Copolymers can also be used as binders. Examples of such binders are copolymers of two or more materials selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene. Mixtures of two or more materials selected from these may also be used as binders.

[0128] At least one of the positive electrode 201 and the negative electrode 203 may contain a conductive additive to improve electronic conductivity.

[0129] Examples of conductive additives include: (i) graphites such as natural or artificial graphite; (ii) carbon blacks such as acetylene black or Ketjen black; (iii) conductive fibers such as carbon fibers or metal fibers; (iv) carbon fluoride; (v) metal powders such as aluminum; (vi) conductive whiskers such as zinc oxide or potassium titanate; (vii) conductive metal oxides such as titanium oxide; or (viiii) conductive polymer compounds such as polyaniline, polypyrrole, or polythiophene. For cost reduction, conductive additives of (i) or (ii) above may be used.

[0130] Furthermore, a separator impregnated with an electrolyte may be used instead of the electrolyte layer, and the casing containing the positive electrode, separator, and negative electrode may be filled with an electrolyte. The electrolyte may be, for example, the non-aqueous electrolyte described above. Examples of battery shapes according to the third embodiment include coin-type, cylindrical, prismatic, sheet-type, button-type, flat-type, or stacked type.

[0131] The battery according to the third embodiment may be manufactured, for example, by preparing a material for forming a positive electrode, a material for forming an electrolyte layer, and a material for forming a negative electrode, and then fabricating a laminate in which the positive electrode, electrolyte layer, and negative electrode are arranged in this order by a known method.

[0132] [Other Embodiments] (Note) The above description of embodiments discloses the following technologies.

[0133] (Technology 1) A solid electrolyte comprising Li, Al, and F, wherein the solid electrolyte mainly comprises a first phase which is a monoclinic Li3AlF6 phase, and in the XRD pattern obtained by powder X-ray diffraction of the solid electrolyte, the full width at half maximum of the peak with the strongest intensity among the peaks belonging to the first phase is greater than 1.0° and less than or equal to 3.0°, and the BET specific surface area is 50 m². 2 / g or more 350m 2 A solid electrolyte with a concentration of less than or equal to / g.

[0134] The solid electrolyte of Technology 1 exhibits excellent ionic conductivity. According to Technology 1, a useful solid electrolyte can be provided.

[0135] By using a low-crystallinity monoclinic Li3AlF6 phase as the main phase, the ionic conductivity of the solid electrolyte can be improved. Furthermore, the solid electrolyte of Technology 1 can be made denser by compression due to the improved softness resulting from the low crystallinity of the first phase. This density increase by compression allows for the formation of a dense compact, thus further enhancing the ionic conductivity of the solid electrolyte of Technology 1. Thus, Technology 1 provides a particulate solid electrolyte with excellent ionic conductivity.

[0136] (Technology 2) The solid electrolyte according to Technology 1, wherein the solid electrolyte is particulate, and the proportion of the first phase on the surface of the particles is greater than the proportion of the first phase inside the particles.

[0137] With the above configuration, the particle surface of the solid electrolyte becomes softer. This reduces friction between particles, making it easier to densify the compacted solid electrolyte. Therefore, according to Technology 2, a high-performance solid electrolyte can be realized that has high ionic conductivity and can form a dense compacted powder.

[0138] (Technology 3) The solid electrolyte according to Technology 1 or 2, wherein the ratio of the amount of substance of F to the total amount of substance of all elements constituting the solid electrolyte is 58.0% or more and 67.0% or less.

[0139] According to technique 3, the purity of the first phase is increased. This allows for a further improvement in the ionic conductivity of the solid electrolyte.

[0140] (Technical 4) The solid electrolyte according to Technical 3, wherein the above ratio is 60.0% or more and 67.0% or less.

[0141] According to technique 4, the purity of the first phase is further increased. This allows for a further improvement in the ionic conductivity of the solid electrolyte.

[0142] (Technical 5) The solid electrolyte according to any one of Technical 1 to 4, wherein in the first phase, a portion of the Al sites is substituted with M1, and M1 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements.

[0143] With the above configuration, a monoclinic Li3AlF6 phase is easily formed stably at low temperatures (for example, about 280°C). The monoclinic Li3AlF6 phase formed by low-temperature heat treatment is easily pulverized because sintering has not progressed. Therefore, according to Technology 5, a solid electrolyte consisting of fine particles with excellent ionic conductivity can be realized.

[0144] (Technical 6) The solid electrolyte according to Technical 5, wherein M1 comprises at least one selected from the group consisting of Ti, Si, Zr, and Sn.

[0145] With the above configuration, a solid electrolyte consisting of fine particles with excellent ionic conductivity can be realized.

[0146] (Technical 7) The solid electrolyte according to Technical 5 or 6, wherein M1 is Ti.

[0147] With the above configuration, a solid electrolyte consisting of fine particles with excellent ionic conductivity can be realized.

[0148] (Technical 8) The solid electrolyte according to any one of Technical 5 to 7, wherein the amount of substitution by M1 is greater than 0 at% and 10 at% or less.

[0149] With the above configuration, the monoclinic Li3AlF6 phase is more easily and stably formed at low temperatures (for example, about 230°C). Therefore, according to Technology 8, a solid electrolyte consisting of fine particles with excellent ionic conductivity can be realized.

[0150] (Technical 9) The solid electrolyte according to any one of Technical 1 to 8, further comprising a second phase which is a Li2M2F6 phase, wherein M2 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements.

[0151] With the above configuration, a solid electrolyte with superior ionic conductivity can be realized.

[0152] (Technical 10) A solid electrolyte as described in Technical 9, wherein M2 is Ti.

[0153] With the above configuration, a solid electrolyte with superior ionic conductivity can be realized.

[0154] (Technical 11) A solid electrolyte according to any one of Technical 1 to 10, further comprising a third phase which is an orthorhombic Li3AlF6 phase.

[0155] Since the orthorhombic Li3AlF6 phase is synthesized at a considerably higher temperature than the monoclinic Li3AlF6 phase, the third phase has higher mechanical strength than the first phase. Furthermore, the orthorhombic phase is stable at high temperatures. Therefore, according to Technology 11, it is possible to realize a solid electrolyte that is a fine particle with excellent ionic conductivity, as well as improved high-temperature stability and mechanical strength.

[0156] (Technical 12) The solid electrolyte according to Technical 11, wherein the crystallinity of the first phase is lower than that of the third phase.

[0157] The above configuration improves ionic conductivity. Furthermore, the improved softness allows for the formation of a denser compacted powder, thereby suppressing structural defects such as fine cracks or voids. Therefore, according to Technology 12, a solid electrolyte with excellent ionic conductivity and reliability can be realized.

[0158] (Technical 13) The solid electrolyte according to Technical 11 or 12, wherein in the third phase, a portion of the Al sites are replaced by M3, and M3 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements.

[0159] With the above configuration, a solid electrolyte with excellent ionic conductivity and high-temperature durability can be realized.

[0160] (Technical 14) The solid electrolyte according to Technical 13, wherein M3 comprises at least one selected from the group consisting of Ti, Si, Zr, and Sn.

[0161] With the above configuration, a solid electrolyte with excellent ionic conductivity and high-temperature durability can be realized.

[0162] (Technical 15) The solid electrolyte according to Technical 13 or 14, wherein M3 is Ti.

[0163] With the above configuration, a solid electrolyte with excellent ionic conductivity and high-temperature durability can be realized.

[0164] (Technical 16) The solid electrolyte according to any one of Technical 13 to 15, wherein the amount of substitution by M3 is greater than 0 at% and 30 at% or less.

[0165] With the above configuration, a solid electrolyte with excellent ionic conductivity and high-temperature durability, and stable quality can be realized.

[0166] (Technical 17) The solid electrolyte according to any one of Technical 13 to 16, wherein in the first phase, a portion of the Al site is substituted with M1, where M1 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements, and the amount of substitution of M3 is greater than the amount of substitution of M1.

[0167] With the above configuration, a solid electrolyte with excellent ionic conductivity and high-temperature durability can be realized.

[0168] (Technical 18) A solid electrolyte according to any one of Technical 1 to 17, further comprising a second phase which is a Li2M2F6 phase and a third phase which is an orthorhombic Li3AlF6 phase, wherein in the first phase, a portion of the Al sites is substituted with M1, and in the third phase, a portion of the Al sites is substituted with M3, where M1 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements, M2 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements, and M3 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements, and M1, M2, and M3 include a common element.

[0169] With the above configuration, the affinity between the first, second, and third phases can be improved. This enhances the thermal cycling and thermal shock performance, and improves the reliability of the solid electrolyte.

[0170] (Technical 19) A solid electrolyte according to any one of Technical 1 to 18, further comprising a second phase which is a Li2M2F6 phase and a third phase which is an orthorhombic Li3AlF6 phase, wherein M2 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements, the mass proportion of the first phase is greater than the mass proportion of the second phase, and the mass proportion of the second phase is greater than the mass proportion of the third phase.

[0171] With the above configuration, a solid electrolyte with excellent ionic conductivity and reliability can be realized.

[0172] (Technical 20) A method for producing a solid electrolyte, comprising: halogenating a starting material containing Li and Al; synthesizing a solid electrolyte containing a monoclinic Li3AlF6 phase as the main phase; and reducing the crystallinity of the monoclinic Li3AlF6 phase, wherein the starting material comprises at least one selected from the group consisting of oxides, carbonates, and hydroxides.

[0173] According to the manufacturing method of Technology 20, a monoclinic Li3AlF6 phase can be produced at a relatively low temperature. Furthermore, since the monoclinic Li3AlF6 phase obtained by heat treatment at a low temperature is hard and not sintered, it is easy to finely grind, and the crystallinity of the monoclinic Li3AlF6 phase can be easily reduced. Therefore, a highly useful solid electrolyte can be obtained that has excellent ionic conductivity and can form a dense compacted powder. In addition, because the monoclinic Li3AlF6 phase is easily finely ground, the inclusion of impurities from the grinding medium is reduced, so a solid electrolyte with high purity can be obtained.

[0174] (Technical 21) The method for producing a solid electrolyte according to Technical 20, wherein the halogenation includes contacting the starting material with a halogen gas.

[0175] With the above configuration, homogeneous halogenation treatment can be performed on the starting material. Therefore, according to technology 21, a monoclinic Li3AlF6 phase with suppressed reaction unevenness can be produced.

[0176] (Technical 22) The halogen gas is obtained by heat-treating a pyrolytic halogen-containing compound, as described in Technical 21, for the method of producing a solid electrolyte.

[0177] With the above configuration, halogenation of the starting material and solid-phase reaction can be carried out simultaneously.

[0178] (Technical 23) The method for producing a solid electrolyte according to Technical 22, wherein the thermal decomposition temperature of the halogen-containing compound is 300°C or lower.

[0179] With the above configuration, halogenation and solid-phase reactions can be carried out at low temperatures of 300°C or less. This allows for the stable production of a monoclinic Li3AlF6 phase.

[0180] (Technical 24) A method for producing a solid electrolyte according to Technical 22 or 23, wherein the halogen-containing compound is in particulate form.

[0181] With the above configuration, the starting materials can be mixed uniformly and then heat-treated under good contact conditions to perform halogenation, enabling homogeneous halogenation (conversion to fluoride) of the mixed powder. Therefore, reaction unevenness is suppressed, and a monoclinic Li3AlF6 phase can be stably produced.

[0182] (Technical 25) A method for producing a solid electrolyte according to any one of Technical 22 to 24, wherein the average particle size of the halogen-containing compound is 5 μm or more and 100 μm or less.

[0183] With the above configuration, halogen-containing compounds are more easily dispersed homogeneously when mixed with the starting materials. Therefore, reaction unevenness is suppressed, and a monoclinic Li3AlF6 phase can be stably produced.

[0184] (Technical 26) A method for producing a solid electrolyte according to any one of Technical 22 to 25, wherein the halogen-containing compound includes NH4F.

[0185] Because NH4F has a low thermal decomposition temperature (below 200°C), halogenation and solid-phase reactions can be carried out at low temperatures. This allows for the stable production of a monoclinic Li3AlF6 phase.

[0186] (Technical 27) A method for producing a solid electrolyte according to any one of Technical 21 to 26, wherein reducing the crystallinity includes a mechanochemical treatment.

[0187] With the above configuration, a highly useful solid electrolyte with excellent ionic conductivity can be obtained.

[0188] (Technical 28) An electrode material comprising a solid electrolyte and an electrode active material as described in any one of Technical 1 to 19.

[0189] According to the electrode material of Technology 28, it is possible to provide a high-performance battery with improved charge / discharge characteristics and reliability.

[0190] (Technical 29) The electrode material according to Technical 28, wherein at least a portion of the surface of the electrode active material is coated with the solid electrolyte.

[0191] According to the electrode material of Technology 29, it is possible to provide a high-performance battery with improved charge / discharge characteristics and reliability.

[0192] (Technical 30) A battery comprising a positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode, wherein at least one selected from the group consisting of the positive electrode, the negative electrode, and the electrolyte layer contains a solid electrolyte as described in any one of Technical 1 to 20.

[0193] The above configuration makes it possible to provide a high-performance battery with improved charge / discharge characteristics and reliability.

[0194] The solid electrolytes, electrode materials, and batteries relating to this disclosure have been described above based on embodiments, but this disclosure is not limited to these embodiments. Without departing from the spirit of this disclosure, various modifications to the embodiments that a person skilled in the art could conceive, and other forms constructed by combining some of the components of the embodiments, are also included in the scope of this disclosure.

[0195] Furthermore, the above embodiments may be modified, replaced, added, omitted, etc., within the scope of the claims or their equivalents.

[0196] The present disclosure will be described in more detail below with reference to the examples.

[0197] (Sample No. 1) <Synthesis of Fluoride Solid Electrolytes> As starting materials, Li2CO3 powder (average particle size: approximately 1.2 μm), γ-Al2O3 powder (average particle size: approximately 0.01 μm), Li2TiO3 (average particle size: approximately 0.5 μm), and NH4F powder (average particle size: approximately 42 μm), a halogen-containing compound for halogenation, were prepared.

[0198] Next, as the initial composition, a fluoride solid electrolyte with the composition formula: aLi3Al 1-x M1 x F6-bLi2TiF6-cLi3Al 1-y M3 yEach starting material (Li2TiO3, Li2CO3, Al2O3, NH4F) was weighed in an air atmosphere so that the molar composition ratios satisfy a, b, c, x, and y shown in Table 1 when expressed as F6 (a + b + c = 1.0). These starting material powders were mixed in an air atmosphere, as in the weighing process, using an alumina mortar and pestle for approximately 10 minutes until homogeneous, to obtain a mixture containing Li2CO3, Al2O3, Li2TiO3, and NH4F in predetermined ratios.

[0199] Approximately 3 g of the resulting mixture was placed into a high-purity (SSA-H) alumina crucible (diameter φ: 36 mm, height: 40 mm). To allow the reaction gases (mainly ammonia and CO2) emitted during heat treatment to escape easily, a spacer (thickness: 0.5 mm) was placed on the outer edge of the top surface of the pod, and an alumina plate-shaped lid was placed on top to prevent foreign matter from falling in. Next, the pod was placed on a mullite crucible with a low heat capacity and a porosity of approximately 20% in the center of the firing furnace and heat-treated. The crucible used was 15 mm long, 15 mm wide, and 15 mm high, with three crucibles placed under one pod, lifting the pod off the bottom of the furnace. In this way, heater (radiant) heat and inert gases were allowed to circulate around the bottom of the pod as well. After closing and sealing the furnace door, nitrogen gas was introduced at a rate of 5 L / min through the inlet at the bottom of the furnace and discharged through the exhaust vent at the top of the ceiling. The gas flow continued until the heat treatment was complete. The heat treatment was carried out at 300°C.

[0200] The fluoride solid electrolyte obtained by the above heat treatment has an average particle size of approximately 1.7 μm and a BET specific surface area of ​​1.4 m². 2 The particles were in particulate form at a density of 1 / g. The particle size distribution of the fluoride solid electrolyte was measured using a laser diffraction scattering particle size distribution analyzer (Microtrac, product name: MT3100II), and the D50 value (i.e., cumulative 50% particle size) of the obtained volume particle size distribution was taken as the average particle size.

[0201] The crystalline phase of the obtained fluoride solid electrolyte was evaluated by powder X-ray diffraction (XRD). For example, the fluoride solid electrolyte of sample number 1 consisted only of the monoclinic Li3AlF6 phase. Therefore, the fluoride solid electrolyte of sample number 1 had the monoclinic Li3AlF6 phase as its main phase. Figure 3 shows the XRD pattern of the fluoride solid electrolyte obtained by heat treatment of the starting material powder of sample number 1.

[0202] Furthermore, the crystalline phases were quantitatively evaluated using multiphase analysis in Rietveld analysis of powder XRD, and the relative magnitudes of the content of each phase were assessed.

[0203] <Crystallization Reduction Treatment> Next, the fluoride solid electrolyte powder synthesized by the above method was pulverized, and the crystallinity was reduced by making a portion of the fluoride solid electrolyte (specifically, the particle surface) amorphous. Specifically, a commercially available polyethylene ball mill and a zirconia grinding medium (φ1.0 mm) were used, and wet grinding treatment (mechanochemical treatment) with ethanol was performed. The grinding time for each sample number was adjusted between 4 hours and 40 hours so that the BET specific surface area of ​​the final obtained solid electrolyte would be the value shown in Table 2.

[0204] The slurry obtained by the above grinding process was subjected to primary drying in an explosion-proof dryer under hot air (approximately 70°C for 10 hours) to dry the solvent, and then the temperature was increased for secondary drying (180°C for 10 hours). This yielded the final solid electrolyte.

[0205] As described above, the solid electrolyte of sample number 1 was obtained.

[0206] (Sample No. 2) The solid electrolyte for Sample No. 2 was obtained in the same manner as for Sample No. 1, except that the heat treatment temperature of the mixture was changed to 650°C.

[0207] (Sample No. 3) The solid electrolyte of Sample No. 3 was obtained in the same manner as Sample No. 1, except that the powder of the fluoride solid electrolyte was not subjected to mechanochemical treatment (i.e., crystallinity reduction treatment). In other words, the solid electrolyte of Sample No. 3 was the fluoride solid electrolyte obtained by heat treatment of the mixture in Sample No. 1.

[0208] (Sample numbers 4 to 16) Solid electrolytes for samples 4 to 16 were obtained in the same manner as for sample number 1, except that the mixing ratio of the starting materials was changed to satisfy a, b, c, x, and y shown in Table 1, the heat treatment temperature was changed to the fluorination temperature shown in Table 1, and whether or not crystallinity reduction treatment was performed was as shown in Table 1.

[0209] (Sample numbers 17 to 22) In the mixture of starting material powders used in the synthesis of the fluoride solid electrolyte of sample number 10, the amount of NH4F powder, a halogen-containing compound, was changed to the ratio shown in Table 3 relative to the stoichiometric ratio (i.e., the amount of NH4F used in sample number 10) to obtain the mixed powder. The amount of NH4F shown in Table 3 is the ratio calculated by the formula: (amount of NH4F in each sample number) / (amount of NH4F in sample number 10). In other words, the amount of starting material and NH4F powder mixed in sample number 18 was the same as the amount of these mixed in sample number 10.

[0210] The resulting mixture was heat-treated at 300°C using the same procedure as for sample number 1 to obtain a fluoride solid electrolyte.

[0211] The synthesized fluoride solid electrolyte powder was subjected to amorphization in the same manner as in the procedure for sample number 1. This yielded solid electrolytes for samples 17 to 22.

[0212] <Evaluation of Solid Electrolytes> For the solid electrolytes prepared as described above, samples 1 to 22 were evaluated for their crystalline phase, ionic conductivity, BET specific surface area, and compacted powder density. For samples 17 to 22, the ratio of F element (F amount α) in each constituent element contained in the solid electrolyte was also evaluated.

[0213] (Crystalline Phase) The crystalline phase was confirmed by powder X-ray diffraction measurement both after heat treatment and before crystallinity reduction treatment (before grinding) and after crystallinity reduction treatment (after grinding). An X-ray diffractometer (RIGAKU, MiniFlex 600) was used for the measurements. Cu-Kα rays (wavelengths 1.5405 Å and 1.5444 Å) were used as the X-ray source. Figure 3 shows the XRD patterns of the fluoride solid electrolytes obtained by heat treatment of the starting material powders of sample numbers 1, 2, 8, and 10 before crystallinity reduction treatment. Figure 4 shows the XRD patterns of the solid electrolytes of sample numbers 1, 2, 8, and 10 after crystallinity reduction treatment. In Figures 3 and 4, the monoclinic Li3AlF6 phase is denoted as "Li3AlF6(m)", and the orthorhombic Li3AlF6 phase is denoted as "Li3AlF6(o)". Tables 2 and 3 show the types of crystalline phases detected in the measurement, their relative mass levels, and the full width at half maximum of the peaks belonging to the monoclinic Li3AlF6 phase in the XRD pattern of the solid electrolyte after crystallinity reduction treatment. In Tables 2 and 3, the monoclinic Li3AlF6 phase is denoted as "LAF(m)", the Li2TiF6 phase as "LTF", and the orthorhombic Li3AlF6 phase as "LAF(o)".

[0214] (BET specific surface area) The BET specific surface area was determined by the BET multipoint method using a nitrogen gas adsorption apparatus. The BET specific surface area of ​​the solid electrolyte after pulverization is shown in Tables 2 and 3.

[0215] (Ionic Conductivity) Ionic conductivity was calculated from the area, thickness, and impedance characteristics at room temperature of a compacted powder sample obtained by placing solid electrolyte powder in a 10 mm diameter mold and applying a pressure of approximately 3 t / cm using a single-axis hydraulic press. Impedance measurements were performed at room temperature while the pressure was applied. Impedance measurements were performed at a measurement frequency of 10 Hz to 10 MHz, a measurement voltage of 1 Vrms, and without DC bias. The deviation in the electrical length of the cable and measurement jig was evaluated with an offset.

[0216] (Amount of F α) The content of Li, Al, and Ti in the solid electrolyte was evaluated using an ICP emission spectrometer, and the content of F was evaluated using combustion ion chromatography (CIC). From the above, the amount of F α, which is the ratio (%) of the amount of F when the total amount of each constituent element is taken as 100%, was determined. Note that the content of Li, Al, and Ti in samples 17 to 22 was constant, the same as in sample 10.

[0217]

[0218]

[0219]

[0220] The evaluation results for solid electrolytes of sample numbers 1 to 16 are shown in Tables 1 and 2. The evaluation results for solid electrolytes of sample numbers 17 to 22 are shown in Table 3. In Tables 1 and 2, the sample numbers are marked with an asterisk (*), indicating that these samples do not satisfy the constituent requirements of the solid electrolytes of this disclosure. Specifically, the solid electrolytes of sample numbers 2, 13, and 14 do not have a low-crystallinity monoclinic Li3AlF6 phase as their main phase, and the solid electrolytes of sample numbers 3 and 14 do not contain a low-crystallinity monoclinic Li3AlF6 phase.

[0221] Based on the evaluation of the crystalline phase, it was confirmed that the solid electrolyte of sample number 1 consists solely of the monoclinic Li3AlF6 phase. Furthermore, the full width at half maximum of the strongest peak of the monoclinic Li3AlF6 phase in the XRD pattern of the solid electrolyte of sample number 1 was 1.9°, indicating that it mainly contained a low-crystallinity monoclinic Li3AlF6 phase.

[0222] XRD confirmed that the solid electrolytes in samples 4 through 12 and 15 through 22 also contained a low-crystallinity monoclinic Li3AlF6 phase as the main phase.

[0223] As shown in Figure 3, XRD confirmed that the solid electrolyte of sample number 2 was primarily composed of an orthorhombic Li3AlF6 phase. The solid electrolyte of sample number 3 was primarily composed of a monoclinic Li3AlF6 phase, but the full width at half maximum of the strongest peak identified by XRD was 0.4°. Therefore, the solid electrolyte of sample number 3 did not contain a low-crystallinity monoclinic Li3AlF6 phase. The solid electrolytes of samples number 13 and 14 contained a monoclinic Li3AlF6 phase, but the orthorhombic Li3AlF6 phase was the dominant phase. Furthermore, the solid electrolyte of sample number 14 did not contain a low-crystallinity monoclinic Li3AlF6 phase.

[0224] From the results for sample numbers 1, 4 to 12, 15, and 16, when the main phase is a low-crystallinity monoclinic Li3AlF6 phase, the solid electrolyte has a BET specific surface area of ​​63 m². 2 / g to 294m 2 Despite being fine particles with a density of 1.80 g / cm, they exhibit high ionic conductivity of 2.8 μS / cm or higher, and 1.80 g / cm². 3 The samples exhibited the above-mentioned high compaction density. In contrast, sample number 3, which was not subjected to crystallinity reduction treatment, had an ionic conductivity of 0.001 μS / cm, which was more than three orders of magnitude lower than sample number 1, despite its main phase being a monoclinic Li3AlF6 phase, and its compaction density was 1.78 g / cm³. 3 It was low. Sample No. 2 had a BET specific surface area (65 m²) similar to that of Sample No. 1. 2 Although the particle size was adjusted to ( / g), both the ionic conductivity and compacted powder density were lower than those of other sample numbers with monoclinic Li3AlF6 phase as the main phase. From the above, it can be concluded that the monoclinic Li3AlF6 phase with reduced crystallinity is 50m 2 / g or more 350m 2 It can be seen that the fine particles have a BET specific surface area of ​​less than / g, have excellent ionic conductivity, and can form a compacted powder with high density.

[0225] Furthermore, as shown in samples 8 and 9, when a Li2TiF6 phase was included as a secondary phase in addition to the low-crystallinity monoclinic Li3AlF6 phase, even higher ionic conductivity was observed. This is thought to be due to the densification of the solid electrolyte by the binding action between the soft Li2TiF6 phase particles in the particulate solid electrolyte. The Li2TiF6 phase belonged to the tetragonal crystal structure. Also, as shown in samples 10 to 12, when a hard orthorhombic Li3AlF6 phase with a high melting point was further included as a secondary phase, very high ionic conductivity of 6.4 μS / cm to 6.7 μS / cm was observed. In contrast to these, when the orthorhombic Li3AlF6 phase was the main phase, as in samples 13 and 14, the ionic conductivity decreased. Furthermore, sample 14, which did not undergo crystallinity reduction treatment and had high crystallinity, showed a very low ionic conductivity of 0.002 μS / cm. The solid electrolytes in samples 13 and 14 also had a compacted powder density of 1.80 g / cm³. 3 It was less than and therefore low.

[0226] Furthermore, from samples 4 to 12, 15, and 16, the synthesis of solid electrolytes by heat treatment (halogenation treatment) at less than 300°C facilitates fine pulverization, resulting in 90 m 2 / g to 300m 2 It can be seen that a large BET specific surface area and high ionic conductivity tend to be obtained with a high ratio of 1 / g. In particular, when the Li2TiF6 phase is included as a secondary phase, synthesis by heat treatment at 270°C or lower tends to yield excellent ionic conductivity and a large BET specific surface area. Specifically, from samples 5 and 6, and 10 to 12, it can be seen that the lower the heat treatment (halogenation treatment) temperature, the easier it is to finely grind the material and the larger the BET specific surface area tends to be obtained, and this trend is consistent across the same compositions.

[0227] M1 substitution at the Al site in monoclinic Li3AlF6 phase and M3 substitution at the Al site in orthorhombic Li3AlF6 phase are effective in lowering the heat treatment temperature (halogenation temperature), and this effect makes it possible to obtain particulate solid electrolytes with excellent ionic conductivity.

[0228] In samples 17 to 22, the crystalline phase after heat treatment was composed of a monoclinic Li3AlF6 phase as the main phase, and a secondary phase consisting of a Li2TiF6 phase and an orthorhombic Li3AlF6 phase, similar to sample 10, and was partially amorphous after grinding. As shown in Table 3, the amount of F α tended to change in correspondence with the amount of NH4F used for conversion to fluoride. In other words, it was found that the F content of the solid electrolyte is affected by the amount of halogen-containing compound mixed with the starting material. The inventors found that the ionic conductivity of a solid electrolyte containing a low-crystallinity monoclinic Li3AlF6 phase as the main phase depends on the F content. As shown in samples 18 to 21, when the amount of F α was in the range of approximately 60% to 67%, which is the stoichiometric ratio or a certain excess of the stoichiometric ratio, even higher ionic conductivity of 6.0 μS / cm or more was obtained. Therefore, the reason why higher ionic conductivity can be obtained within the range of F amount α of the present invention is thought to be due to the suppression of excess impurity phases generated in trace amounts during the conversion synthesis to fluoride (synthesis of fluoride solid electrolyte). Furthermore, since the BET specific surface area of ​​the solid electrolytes from samples 17 to 22 was adjusted to the same level, their powder properties can all be considered equivalent.

[0229] As described above, the first phase is a low-crystallinity monoclinic Li3AlF6 phase, and the BET specific surface area is 50 m². 2 / g or more 350m 2 Solid electrolytes with a concentration of less than / g were confirmed to have excellent ionic conductivity. By using such solid electrolytes, batteries and energy storage devices with superior performance and high reliability can be realized.

[0230] The solid electrolyte relating to this disclosure can be used, for example, as a solid electrolyte in lithium-ion batteries used in various electronic devices or automobiles.

Claims

1. A solid electrolyte comprising Li, Al, and F, wherein the solid electrolyte mainly comprises a first phase which is a monoclinic Li3AlF6 phase, and in the XRD pattern obtained by powder X-ray diffraction of the solid electrolyte, the full width at half maximum of the peak with the strongest intensity among the peaks belonging to the first phase is greater than 1.0° and less than or equal to 3.0°, and the BET specific surface area is 50 m². 2 / g or more 350m 2 A solid electrolyte with a concentration of less than or equal to / g.

2. The solid electrolyte according to claim 1, wherein the solid electrolyte is particulate, and the proportion of the first phase on the surface of the particles is greater than the proportion of the first phase inside the particles.

3. The solid electrolyte according to claim 1, wherein the ratio of the amount of substance of F to the total amount of substance of all elements constituting the solid electrolyte is 58.0% or more and 67.0% or less.

4. The solid electrolyte according to claim 3, wherein the aforementioned ratio is 60.0% or more and 67.0% or less.

5. The solid electrolyte according to claim 1, wherein in the first phase, a portion of the Al sites are substituted with M1, where M1 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements.

6. The solid electrolyte according to claim 5, wherein M1 comprises at least one selected from the group consisting of Ti, Si, Zr, and Sn.

7. The solid electrolyte according to claim 5, wherein M1 is Ti.

8. The solid electrolyte according to claim 5, wherein the amount of substitution by M1 is greater than 0 at% and 10 at% or less.

9. The solid electrolyte according to claim 1, further comprising a second phase which is a Li2M2F6 phase, wherein M2 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements.

10. The solid electrolyte according to claim 9, wherein M2 is Ti.

11. The solid electrolyte according to claim 1, further comprising a third phase which is an orthorhombic Li3AlF6 phase.

12. The solid electrolyte according to claim 11, wherein the crystallinity of the first phase is lower than that of the third phase.

13. The solid electrolyte according to claim 11, wherein in the third phase, a portion of the Al sites are substituted with M3, where M3 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements.

14. The solid electrolyte according to claim 13, wherein M3 comprises at least one selected from the group consisting of Ti, Si, Zr, and Sn.

15. The solid electrolyte according to claim 13, wherein M3 is Ti.

16. The solid electrolyte according to claim 13, wherein the amount of substitution by M3 is greater than 0 at% and 30 at% or less.

17. The solid electrolyte according to claim 13, wherein in the first phase, a portion of the Al site is substituted with M1, where M1 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements, and the amount of substitution of M3 is greater than the amount of substitution of M1.

18. A solid electrolyte according to claim 1, further comprising a second phase which is a Li2M2F6 phase and a third phase which is an orthorhombic Li3AlF6 phase, wherein in the first phase, a portion of the Al sites is substituted with M1, and in the third phase, a portion of the Al sites is substituted with M3, where M1 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements, M2 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements, and M3 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements, and M1, M2, and M3 include a common element.

19. The solid electrolyte according to claim 1, further comprising a second phase which is a Li2M2F6 phase and a third phase which is an orthorhombic Li3AlF6 phase, wherein M2 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements, the mass proportion of the first phase is greater than the mass proportion of the second phase, and the mass proportion of the second phase is greater than the mass proportion of the third phase.

20. A method for producing a solid electrolyte, comprising: halogenating a starting material containing Li and Al; synthesizing a solid electrolyte containing a monoclinic Li3AlF6 phase as the main phase; and reducing the crystallinity of the monoclinic Li3AlF6 phase, wherein the starting material contains at least one selected from the group consisting of oxides, carbonates, and hydroxides.

21. The method for producing a solid electrolyte according to claim 20, wherein the halogenation includes contacting the starting material with a halogen gas.

22. The method for producing a solid electrolyte according to claim 21, wherein the halogen gas is obtained by heat-treating a pyrolytic halogen-containing compound.

23. The method for producing a solid electrolyte according to claim 22, wherein the thermal decomposition temperature of the halogen-containing compound is 300°C or lower.

24. The method for producing a solid electrolyte according to claim 22, wherein the halogen-containing compound is in particulate form.

25. The method for producing a solid electrolyte according to claim 24, wherein the average particle size of the halogen-containing compound is 5 μm or more and 100 μm or less.

26. The method for producing a solid electrolyte according to claim 22, wherein the halogen-containing compound includes NH4F.

27. The method for producing a solid electrolyte according to claim 20, wherein reducing the crystallinity includes a mechanochemical treatment.

28. An electrode material comprising the solid electrolyte and electrode active material according to claim 1.

29. The electrode material according to claim 28, wherein at least a portion of the surface of the electrode active material is coated with the solid electrolyte.

30. A battery comprising a positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode, wherein at least one selected from the group consisting of the positive electrode, the negative electrode, and the electrolyte layer contains the solid electrolyte described in claim 1.

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