Solid electrolytes, electrode materials, and batteries

Abstract

Useful solid electrolytes can be obtained. [Solution] The solid electrolyte of this disclosure is a solid electrolyte containing Li, Al, and F, and mainly comprises a first phase which is an orthorhombic Li3AlF6 phase, and in the XRD pattern obtained by powder X-ray diffraction, the full width at half maximum of the strongest peak 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 5 m². 2 / g or more 65m 2 The amount is less than or equal to / g. The battery 1000 of the present disclosure comprises a positive electrode 201, a negative electrode 203, and an electrolyte layer 202 provided between the positive electrode 201 and the negative electrode 203, wherein 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 of the present disclosure.

Description

Technical Field

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

Background Art

[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.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

Means for Solving the Problems

[0005] The solid electrolyte of the present disclosure is a solid electrolyte containing Li, Al, and F, the solid electrolyte contains, as a main phase, a first phase which is a cubic Li3AlF6 phase, in the XRD pattern obtained by powder X-ray diffraction of the solid electrolyte, the full width at half maximum of the peak belonging to the first phase with the highest intensity is greater than 1.0° and 3.0° or less, the BET specific surface area is 5 m 2 / g or more and 65 m 2 [ / g or less.

Effects of the Invention

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

Brief Description of the Drawings

[0007] [Figure 1] Figure 1 is a cross-sectional view showing a schematic configuration of a coated active material 100, which is 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. [Figure 2] Figure 2 shows a cross-sectional view of the battery 1000 according to the third embodiment. [Figure 3] Figure 3 shows the XRD patterns of fluoride solid electrolytes obtained by heat treatment of the starting material powders of samples 1, 2, 8, and 10. [Figure 4] Figure 4 shows the XRD patterns of solid electrolytes after crystallinity reduction treatment for samples 1, 2, 8, and 10. [Modes for carrying out the invention]

[0008] The embodiments of this disclosure will be described in detail below with reference to the drawings.

[0009] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement positions of components, and connection configurations shown in the following embodiments are examples only and are not intended to limit this disclosure. Furthermore, among the components in the following embodiments, those not described in the independent claim representing the highest-level concept will be described as optional components.

[0010] [First Embodiment] The solid electrolyte according to the first embodiment of this disclosure is a solid electrolyte comprising Li, Al, and F. The solid electrolyte according to the first embodiment mainly comprises a low-crystallinity orthorhombic Li3AlF6 phase. The BET specific surface area of ​​the solid electrolyte according to the first embodiment is 5 m². 2 / g or more 65m 2 It is less than / g.

[0011] In this disclosure, the solid electrolyte being described as containing a low-crystallinity orthorhombic Li3AlF6 phase means that, in the XRD pattern obtained by powder X-ray diffraction (XRD) of the solid electrolyte, the full width at half maximum (FWHM) of the strongest peak (most intense peak) belonging to the orthorhombic Li3AlF6 phase is greater than 1.0° and less than or equal to 3.0°. Thus, the FWHM of the peaks indicating the low-crystallinity orthorhombic Li3AlF6 phase is large due to its low crystallinity, as shown in the above numerical range. That is, in the solid electrolyte according to the first embodiment, the FWHM of the strongest peak belonging to the orthorhombic Li3AlF6 phase in the XRD pattern obtained by XRD is greater than 1.0° and less than or equal to 3.0°. Hereinafter, the "low-crystallinity orthorhombic Li3AlF6 phase" may be referred to as the "first phase." The strongest peak belonging to the first phase is located in the diffraction angle range 2θ, for example, between 20.0° and 24.0°.

[0012] The solid electrolyte according to the first embodiment can improve ionic conductivity by including a first phase as the main phase. Furthermore, the solid electrolyte according to the first embodiment possesses sufficient softness to allow for high density by compression due to the low crystallinity of its first phase. This high density by compression can form a dense, high-density solid electrolyte, i.e., a high-density compacted powder, which also enhances the ionic conductivity of the solid electrolyte according to the first embodiment. Thus, the first embodiment can provide solid electrolyte particles with excellent ionic conductivity. For example, the solid electrolyte according to the first embodiment has a high ionic conductivity of 2.6 μS / cm or higher. In addition, the orthorhombic Li3AlF6 phase has high mechanical strength. This can improve the reliability of batteries and energy storage devices using the solid electrolyte according to the first embodiment, such as flexural resistance and impact resistance.

[0013] The solid electrolyte according to the first embodiment has high ionic conductivity as described above, and is useful for batteries and energy storage devices, such as being used as the solid electrolyte layer of the compacted powder or as the coating layer of electrode active material particles, and can provide high-performance batteries and energy storage devices with excellent charge-discharge characteristics and reliability.

[0014] The low-crystalline orthorhombic Li3AlF6 phase can be formed, for example, by applying external stress to the powder, such as mechanical chemical treatment like grinding, to distort the crystals in a solid electrolyte containing the orthorhombic Li3AlF6 phase. The solid electrolyte containing the orthorhombic Li3AlF6 phase can be synthesized by converting and solid-state reacting starting materials such as oxides containing Li and Al into fluorides at a temperature of, for example, 500 °C or higher and 650 °C or lower. Here, in the synthesis at the above temperature, for example, sintering proceeds to form secondary particles and grain growth occurs in the orthorhombic Li3AlF6 phase. Therefore, particles with a BET specific surface area of 5 m 2 / g or more and 65 m 2 / g or less contain some amorphous components to have low crystallinity while exhibiting high ionic conductivity.

[0015] In the present disclosure, 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, that is, the low-crystalline orthorhombic Li3AlF6 phase, is contained the most in terms of mass basis. The mass ratio in the solid electrolyte can be determined by XRD of the solid electrolyte according to the first embodiment and its Rietveld analysis.

[0016] The BET specific surface area of the solid electrolyte according to the first embodiment may be 10 m 2 / g or more and 65 m 2 / g or less, or may be 5 m 2 / g or more and 60 m 2 / g or less. The BET specific surface area of the solid electrolyte according to the first embodiment may be 10 m 2 / g or more and 60 m 2 / g or less, or may be 11 m 2 / g or more and 60 m2 It may be less than / g, 19m 2 / g or more 60m 2 It may be less than / g, 20m 2 / g or more 60m 2 It may be less than / g, 30m 2 / g or more 60m 2 It may be less than / g.

[0017] The solid electrolyte according to the first embodiment may be in particulate form. The solid electrolyte according to the first embodiment, which is fine particles having the above-mentioned BET specific surface area, can be used as a compacted powder, for example, as the solid electrolyte layer of an all-solid-state battery, thereby contributing to the thinning, miniaturization, and high energy density of all-solid-state batteries. Furthermore, the solid electrolyte according to the first embodiment can also be dispersed and included in another solid electrolyte as a particulate additive component to be used as a component for improving ionic conductivity and reliability. For example, the solid electrolyte according to the first embodiment can also be used as a coating material for electrode active material particles.

[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 orthorhombic Li3AlF6 phase includes phases having an orthorhombic 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, or 57.0% or more and 67.0% 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 58.0% or more and 67.0% or less, 59.0% or more and 67.0% or less, 59.8% or more and 66.5% or less, or 60.0% or more and 66.5% or less. This makes it possible to obtain a solid electrolyte having an even higher ionic conductivity, for example, an ionic conductivity of 4.0 μS / cm or more.

[0021] In the first phase, a portion of the Al site 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 a portion of the Al site with M1, the orthorhombic Li3AlF6 phase is more easily formed stably at relatively high temperatures, for example, between approximately 500°C and 650°C. As a result, a solid electrolyte with 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 improves reactivity, lowering the reaction temperature, and allowing for stable acquisition of the orthorhombic Li3AlF6 phase even at temperatures between 470°C and 620°C. Therefore, reaction variability is reduced, and the homogeneity of the orthorhombic Li3AlF6 phase is increased. This reduces property variability during large-scale synthesis and improves reproducibility. In addition, it reduces the residue of anions such as oxygen contained in the starting materials in the solid electrolyte. This results in solid electrolyte particles with superior ionic conductivity. Furthermore, the reduction in reaction temperature also has the effect of suppressing the progress of sintering, which suppresses the growth of secondary particles in the orthorhombic Li3AlF6 phase, making it easier to pulverize and promoting a reduction in crystallinity, i.e., partial amorphousness. Therefore, ionic conductivity can be further improved. M1 may be at least one selected from the group consisting of Ti, Si, Zr, and Sn, and may be Ti. This allows for the acquisition of a solid electrolyte with superior ionic conductivity. Such solid electrolytes are useful as solid electrolyte layers in batteries, coating layers for electrode active materials, and electrode materials. Furthermore, raw materials containing Ti are available in many grades and powder types as industrial raw materials, are widely distributed, and are readily available at low cost. Therefore, such solid electrolytes offer high supply and quality stability, making them suitable for industrial use.

[0023] The amount of substitution by M1 may be between 0 at% and 30 at%, greater than 0% and 30 at%, or between 1 at% and 30 at%. This makes it easier to synthesize the orthorhombic Li3AlF6 phase more stably. Reaction variability is reduced, the homogeneity of the orthorhombic Li3AlF6 phase is increased, and a solid electrolyte with excellent ionic conductivity can be obtained. 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 improves reactivity and promotes fluorination by lowering the reaction temperature. As a result, reaction variability is reduced and the homogeneity of the orthorhombic Li3AlF6 phase is increased. In addition, the residue of anions such as oxygen contained in the starting materials can be reduced in the solid electrolyte. This results in solid electrolyte particles with superior ionic conductivity and atmospheric stability. Moreover, since the effect of suppressing the progress of sintering is obtained by lowering the reaction temperature, secondary particle growth of the orthorhombic Li3AlF6 phase is suppressed, making it easier to pulverize and reducing crystallinity, i.e., promoting partial amorphousness.

[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 a higher ionic conductivity, for example, 3.0 μS / cm or more.

[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 orthorhombic Li3AlF6 phase and is softer compared to the orthorhombic 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. Also, the compacted powder of the solid electrolyte may have a higher density (e.g., 1.88 g / cm³). 3 (The above) It is possible to hold it.

[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, 20% by mass ratio to the first phase. This can 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 a monoclinic Li3AlF6 phase. The monoclinic phase is softer because it is a crystalline phase that is synthesized at a lower temperature than the orthorhombic phase. Therefore, by including the third phase as a secondary phase in coexistence with the first phase, it is possible to achieve high ionic conductivity of, for example, 3.0 μS / cm or more, and even 4.0 μS / cm or more, as well as excellent density, for example, 1.89 g / cm³. 3 This makes it possible to realize solid electrolytes exhibiting even higher compacted powder densities.

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

[0033] In this disclosure, the statement that a solid electrolyte contains a low-crystallinity monoclinic 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 monoclinic Li3AlF6 phase is greater than 1.0° and less than or equal to 3.0°.

[0034] In the third phase, a portion of the Al site 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. Substitution of a portion of the Al site with M3 facilitates the synthesis of the third phase, which is a low-temperature stable phase of Li3AlF6. This makes it easier to obtain a solid electrolyte with excellent ionic conductivity.

[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. Therefore, a solid electrolyte with excellent ionic conductivity and density can be realized. 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 and density, for example, 3.0 μS / cm or more.

[0036] The amount of substitution with M3 may be between 0 at% and 10 at%, or between 0 at% and 10 at%. This facilitates the stable and reproducible formation of the third phase. As a result, it becomes easier to obtain a solid electrolyte of stable quality with excellent ionic conductivity and density. 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 M1 may be greater than the amount of substitution of M3. This results in a solid electrolyte particle with high ionic conductivity and excellent high-temperature stability.

[0038] The crystallinity of the third phase may be lower than that of the first phase. That is, the third phase may have lower crystallinity than the first phase, i.e., partial amorphous formation has progressed. With such a configuration, high ionic conductivity 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. This enables the realization of batteries and energy storage devices with excellent charge-discharge characteristics and high reliability. 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 properties 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 phase and the third phase 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 orthorhombic crystal that is formed at a relatively high temperature and undergoes grain growth through sintering, and further containing a crystalline phase such as a monoclinic crystal with excellent softness as a secondary phase, it is possible to obtain particles with high ionic conductivity while suppressing the deterioration of properties due to frictional heat between powders during the formation of the compacted solid electrolyte (during pressing). 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 an orthorhombic 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 an orthorhombic Li3AlF6 phase as the main phase, and reducing the crystallinity of the orthorhombic 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] By including halogenation of the above starting materials, a solid electrolyte mainly composed of an orthorhombic Li3AlF6 phase can be synthesized by a reaction at a temperature of, for example, 500°C to 650°C. The solid electrolyte mainly composed of an orthorhombic Li3AlF6 phase synthesized here is a solid electrolyte mainly composed of an orthorhombic 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 an orthorhombic Li3AlF6 phase obtained in the manufacturing 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] The orthorhombic Li3AlF6 phase synthesized at the temperatures mentioned above has undergone a certain degree of sintering, with a BET specific surface area of, for example, 0.1 m². 2 / g to 4.0m 2 Secondary particles with a BET specific surface area of ​​5 m² are formed by the normal grinding process. 2 / g to 65m 2 / g, and even 10m 2 / g to 60m 2A solid electrolyte with a specific surface area of ​​1 / g, including amorphous material, i.e., low crystalline particulate matter, is easily obtained. Therefore, a solid electrolyte with excellent ionic conductivity and mechanical strength can be obtained, and particles suitable for thinning the active material layer and solid electrolyte layer, or for coating layers that cover the surface of electrode active materials, can be obtained. Furthermore, because the BET specific surface area is as described above, excessive grinding is avoided, so contamination from impurities from the grinding medium (e.g., zirconia balls or alumina balls) is reduced, and 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 an orthorhombic 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 adjusting the degree of halogenation (e.g., synthesis of halogenated oxides) and controlling the amount of F, becomes possible, allowing for the stable production of an orthorhombic Li3AlF6 phase, and as a result, a useful solid electrolyte with excellent ionic conductivity can be obtained.

[0050] The thermal decomposition temperature of the halogen-containing compound may be 300°C or lower. This allows the starting material to be converted to fluoride before sintering has progressed. As a result, the starting material can be homogeneously converted to fluoride, and a homogeneous orthorhombic Li3AlF6 phase can be obtained. Therefore, a solid electrolyte with excellent ionic conductivity can be obtained. However, if sintering progresses and the material grows into dense secondary particles, fluorine may not reach the interior of the particles, and conversion to fluoride may not be possible.

[0051] In the method for producing a solid electrolyte according to this disclosure, halogenation of the starting material and synthesis of a solid electrolyte containing an orthorhombic 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 480°C to 650°C. The temperature of the heat treatment may be 500°C to 650°C, 500°C to 600°C, 510°C to 600°C, or 520°C to 600°C.

[0052] The halogen-containing compound may also contain ammonium fluoride (NH4F). Because NH4F has a low thermal decomposition temperature (below 200°C), the starting material can be converted to fluoride before sintering has progressed. Therefore, the starting material can be homogeneously converted to fluoride, and a homogeneous orthorhombic Li3AlF6 phase can be obtained. Consequently, a solid electrolyte with excellent ionic conductivity can be obtained.

[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 stably produced orthorhombic Li3AlF6 phase with excellent properties can be generated.

[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 inconsistencies are suppressed, and a stably produced orthorhombic Li3AlF6 phase with excellent properties can be obtained.

[0055] Depending on the heat treatment temperature conditions, a monoclinic Li3AlF6 phase can be included as a secondary phase. For example, heat treatment at 500°C to 550°C can result in the inclusion of a monoclinic Li3AlF6 phase as a secondary phase. Alternatively, the monoclinic Li3AlF6 phase can be synthesized separately (e.g., by fluoridation and solid-state reaction at 250°C to 350°C) and then incorporated as a secondary phase into a fluoride solid electrolyte containing an orthorhombic Li3AlF6 phase.

[0056] Furthermore, depending on the mixing ratio of the starting materials, for example, the 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 an orthorhombic Li3AlF6 phase as the main phase is synthesized.

[0058] Reducing the crystallinity of the orthorhombic Li3AlF6 phase is achieved by straining the crystal. Reducing the crystallinity of the orthorhombic 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 orthorhombic 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 orthorhombic Li3AlF6 phase can be reduced.

[0060] Mechanochemical reactions caused by repeated collisions between the particle surface of the fluoride solid electrolyte and the grinding medium or the ball mill wall lead 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. Here, hardness refers to hardness that can be compared and evaluated using micro-Vickers. For example, when orthorhombic 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 orthorhombic Li3AlF6 phase. Therefore, the particle size and crystallinity can be such that orthorhombic Li3AlF6 phase > Li2TiF6 phase. For example, after wet grinding, the average particle size of each phase can be approximately 0.26 μm for the orthorhombic Li3AlF6 phase, approximately 0.15 μm for the Li2TiF6 phase, and approximately 0.19 μm for both phases combined. The average particle size of each phase can be calculated from the area when the particles of each crystalline phase are identified and made into perfect circles, for example, by EPMA. The above trend is also observed between the orthorhombic Li3AlF6 phase and the monoclinic Li3AlF6 phase, which is a softer, lower-temperature stable phase than the orthorhombic Li3AlF6 phase. Therefore, when both phases are included and treated simultaneously with mechanochemicals, 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 of orthorhombic Li3AlF6 phase > monoclinic Li3AlF6 phase.

[0061] In addition to the orthorhombic Li3AlF6 phase, a fluoride solid electrolyte containing at least one selected from the group consisting of Li2M2F6 phase and monoclinic Li3AlF6 phase as a secondary phase may be partially amorphous by simultaneously mechanochemical treatment as described above. Alternatively, the orthorhombic Li3AlF6 phase, Li2TiM2F6 phase, and monoclinic 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] The solid electrolyte according to the first embodiment and the solid electrolyte described in Patent Document 1 have the following differences. Patent Document 1 discloses a solid electrolyte containing Li, Ti, M, and F. However, while Patent Document 1 describes the halides used as starting materials 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 orthorhombic 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 by heat treatment and a solid-phase reaction is carried out. 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. Patent Document 1 also does not describe the effect of the low-crystallinity orthorhombic Li3AlF6 phase on high ionic conductivity. 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 their substitution amounts), or the F content in solid electrolytes. 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 low crystallinity of the solid electrolyte according to the first embodiment, and the soft properties provided by the monoclinic Li3AlF6 phase, 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. In this disclosure, "(A,B,C)" means "at least one selected from the group consisting of A, B, and C."

[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. Such a configuration can provide a high-performance battery with improved charge / discharge characteristics and reliability. 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, if 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 as a coating material that covers the positive electrode active material 204.

[0087] To improve the energy density and output of 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-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-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-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 are metallic materials, carbon materials, oxides, nitrides, tin compounds, or silicon compounds. Metallic materials may be elemental metals or alloys. Examples of metallic materials are lithium metal or lithium alloys. Examples of carbon materials are 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 negative electrode active material is either LiTi2O4 or TiO2. By using the above 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 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 are: (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 or a garnet-type solid electrolyte such as an elemental substitution thereof, (v) Li3PO4 or its N-substituted derivatives, That is the case.

[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 through 12 of the periodic table (except hydrogen), and all elements in groups 13 through 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 halogen solid electrolyte, which is different from the halogen 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. 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] As the gel electrolyte, polymer materials impregnated with a non-aqueous electrolyte can be used. 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 are: (i) aliphatic chain quaternary salts such as tetraalkylammonium or tetraalkylphosphonium, (ii) Aliphatic cyclic ammonium compounds such as pyrrolidiniums, morpholiniums, imidazoliniums, tetrahydropyrimidiniums, piperadiniums, or piperidiniums, (iii) Nitrogen-containing heterocyclic aromatic cations such as pyridinium or imidazolium That is the case.

[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, vinylylidene 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 are: (i) Graphites such as natural graphite or artificial graphite, (ii) Carbon blacks such as acetylene black or Ketjen black, (iii) Conductive fibers such as carbon 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 (viii) Conductive polymer compounds such as polyaniline, polypyrrole, or polythiophene, Therefore, to reduce costs, the conductive additives described in (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 inside of the casing housing 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 that 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, The solid electrolyte contains a first phase, which is an orthorhombic Li3AlF6 phase, as its main phase. 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°. BET specific surface area 5m 2 / g or more 65m 2 It is less than or equal to / g. solid electrolyte.

[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 orthorhombic Li3AlF6 phase as the main phase, the ionic conductivity of the solid electrolyte can be improved. Furthermore, the solid electrolyte of Technology 1 possesses sufficient flexibility to be compressed to a high density due to the low crystallinity of the first phase. This compression to a high density can form a dense, high-density solid electrolyte, i.e., a high-density compacted powder, which also enhances the ionic conductivity of the solid electrolyte. Moreover, the orthorhombic Li3AlF6 phase has high mechanical strength. Thus, Technology 1 can provide a solid electrolyte with excellent ionic conductivity, and furthermore, can realize highly reliable batteries and energy storage devices.

[0136] (Technology 2) The solid electrolyte according to Technology 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 57.0% or more and 67.0% or less.

[0137] According to Technique 2, the purity of the first phase is increased. This allows for further improvement of the ionic conductivity of the solid electrolyte.

[0138] (Technology 3) A solid electrolyte as described in Technology 2, wherein the aforementioned ratio is 59.0% or more and 67.0% or less.

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

[0140] (Technology 4) It is particulate, A solid electrolyte according to any one of the art 1 to 3, wherein the proportion of the first phase on the particle surface is greater than the proportion of the first phase inside the particle.

[0141] 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 4, a high-performance solid electrolyte can be realized that has high ionic conductivity and can form a dense compacted powder.

[0142] (Technology 5) The solid electrolyte according to any one of the Art 1 to 4, wherein in the first phase, a portion of the Al sites are 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, for example, the orthorhombic Li3AlF6 phase can be stably formed at temperatures between approximately 500°C and 650°C. Therefore, a solid electrolyte with excellent ionic conductivity can be realized.

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

[0145] With the above configuration, the reactivity is improved, which lowers the reaction temperature, allowing for the stable acquisition of an orthorhombic Li3AlF6 phase even at temperatures between 470°C and 620°C. This reduces reaction variability and increases the homogeneity of the orthorhombic Li3AlF6 phase, resulting in solid electrolyte particles with superior ionic conductivity. Furthermore, it reduces property variability during large-scale synthesis, improving reproducibility. In addition, the lower reaction temperature suppresses the progression of sintering, inhibiting the growth of secondary particles in the orthorhombic Li3AlF6 phase. This makes the orthorhombic Li3AlF6 phase easier to pulverize, and can also promote a reduction in the crystallinity of the orthorhombic Li3AlF6 phase, i.e., partial amorphous formation. Therefore, according to Technology 6, the ionic conductivity of the solid electrolyte can be further improved.

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

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

[0148] (Technology 8) A solid electrolyte according to any one of the techniques 5 to 7, wherein the amount of substitution by M1 is greater than 0 at% and 30 at% or less.

[0149] With the above configuration, the orthorhombic Li3AlF6 phase can be synthesized more stably. Therefore, according to Technique 8, a solid electrolyte with excellent ionic conductivity can be realized.

[0150] (Technology 9) A solid electrolyte according to any one of the Art 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] (Technology 10) M2 is Ti, a solid electrolyte as described in Technology 9.

[0153] With the above configuration, a solid electrolyte can be realized that has superior ionic conductivity and can form a compacted powder with high density.

[0154] (Technology 11) A solid electrolyte according to any one of the arts 1 to 10, further comprising a third phase which is a monoclinic Li3AlF6 phase.

[0155] The monoclinic phase is softer because it is synthesized at a lower temperature than the orthorhombic phase. Therefore, by incorporating a third phase as a secondary phase in coexistence with the first phase, it is possible to realize a solid electrolyte that has superior ionic conductivity and can form a compacted powder with higher density.

[0156] (Technology 12) The solid electrolyte according to Art 11, wherein the crystallinity of the third phase is lower than that of the first 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] (Technology 13) The solid electrolyte according to Art 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, the third phase, which is the low-temperature stable phase of Li3AlF6, is easily synthesized. This makes it possible to realize a solid electrolyte with excellent ionic conductivity.

[0160] (Technology 14) The solid electrolyte according to Art 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 density can be realized.

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

[0163] With the above configuration, a solid electrolyte with even better ionic conductivity and density can be realized.

[0164] (Technology 16) The solid electrolyte according to any one of the technical specifications 13 to 15, wherein the amount of substitution by M3 is greater than 0 at% and 10 at% or less.

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

[0166] (Technology 17) In the first phase, a portion of the Al site is replaced by M1. Here, M1 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements. The amount of substitution of M1 is greater than the amount of substitution of M3. A solid electrolyte as described in any one of the technical items 13 to 16.

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

[0168] (Technology 18) It further comprises a second phase which is the Li2M2F6 phase, and a third phase which is the monoclinic Li3AlF6 phase. In the first phase, a portion of the Al site is replaced by M1. In the third phase, a portion of the Al site is replaced by M3. Here, M1 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements. The aforementioned M2 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements. The aforementioned M3 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements. The aforementioned M1, M2, and M3 contain a common element, A solid electrolyte as described in any one of the technical items 1 to 17.

[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] (Technology 19) It further comprises a second phase which is the Li2M2F6 phase, and a third phase which is the monoclinic Li3AlF6 phase. Here, M2 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements. The mass ratio of the first phase is greater than the mass ratio of the second phase. The mass ratio of the second phase is greater than the mass ratio of the third phase. A solid electrolyte as described in any one of the technical items 1 to 18.

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

[0172] (Technology 20) The process involves halogenating a starting material containing Li and Al, To synthesize a solid electrolyte containing the orthorhombic Li3AlF6 phase as the main phase, To reduce the crystallinity of the orthorhombic Li3AlF6 phase, Includes, The aforementioned starting material comprises at least one selected from the group consisting of oxides, carbonates, and hydroxides. A method for producing solid electrolytes.

[0173] According to the manufacturing method of Technology 20, for example, a solid electrolyte mainly composed of an orthorhombic Li3AlF6 phase can be produced by a reaction at a temperature of 500°C to 650°C. The orthorhombic Li3AlF6 phase synthesized at the above temperature has undergone a certain degree of sintering, and has a BET specific surface area of, for example, 0.1 m². 2 / g to 4.0m 2 Secondary particles with a BET specific surface area of ​​5 m² are formed by the normal grinding process. 2 / g to 65m 2 A low-crystalline, particulate solid electrolyte with a density of / g is easily obtained. As a result, a highly useful solid electrolyte with excellent ionic conductivity and mechanical strength can be obtained.

[0174] (Technology 21) The method for producing a solid electrolyte according to Technical Reference 20, wherein the halogenation process 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, an orthorhombic Li3AlF6 phase with suppressed reaction unevenness can be produced.

[0176] (Technology 22) The halogen gas is obtained by heat-treating a pyrolytic halogen-containing compound, as described in Technical Reference 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] (Technology 23) The method for producing a solid electrolyte according to Technology 22, wherein the thermal decomposition temperature of the halogen-containing compound is 300°C or lower.

[0179] With the above configuration, the starting material can be converted to fluoride before sintering has progressed. Therefore, the starting material can be homogeneously converted to fluoride, and a homogeneous orthorhombic Li3AlF6 phase can be obtained. Consequently, a solid electrolyte with excellent ionic conductivity can be obtained.

[0180] (Technology 24) A method for producing a solid electrolyte according to Art 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 the orthorhombic Li3AlF6 phase can be stably produced.

[0182] (Technology 25) A method for producing a solid electrolyte according to any one of the Art 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 the orthorhombic Li3AlF6 phase can be stably produced.

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

[0185] Since NH4F has a low thermal decomposition temperature of 200°C or less, the starting material can be converted to fluoride before sintering has progressed. Therefore, the starting material can be homogeneously converted to fluoride, and a homogeneous orthorhombic Li3AlF6 phase can be obtained. Consequently, a solid electrolyte with excellent ionic conductivity can be obtained.

[0186] (Technology 27) The method for producing a solid electrolyte according to any one of the Art 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] (Technology 28) Solid electrolytes as described in any one of the Technical Articles 1 to 19, and electrode active material, including, electrode material.

[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] (Technology 29) The electrode material according to Technology 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 based on Technology 29, it is possible to provide a high-performance battery with improved charge / discharge characteristics and reliability.

[0192] (Technology 30) positive electrode, Negative electrode, and An electrolyte layer provided between the positive electrode and the negative electrode, Equipped with, 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 the Art 1 to 20. battery.

[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, or omitted in various ways within the scope of the claims or their equivalents. [Examples]

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

[0197] (Sample number 1) <Synthesis of fluoride solid electrolytes> As starting materials, we prepared Li2CO3 powder (average particle size: approximately 1.1 μm), γ-Al2O3 powder (average particle size: approximately 0.01 μm), Li2TiO3 (average particle size: approximately 0.4 μm), and NH4F powder (average particle size: approximately 44 μm), a halogen-containing compound for halogenation.

[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 y Each 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 3g of the obtained mixture was placed into a high-purity (SSA-H) alumina crucible (diameter φ: 36mm, height: 40mm). To allow the reaction gases (mainly ammonia and CO2) emitted during heat treatment to escape easily, a spacer (thickness: 0.5mm) 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 sack with a low heat capacity and a porosity of approximately 20% in the central part of the firing furnace and heat-treated. A sack measuring 15mm in length, 15mm in width, and 15mm in height was used, with three sacks 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 the furnace door to seal it, nitrogen gas was introduced at 5L / min through the inlet at the bottom of the furnace and discharged through the exhaust port at the top of the ceiling, and the gas flow continued until the heat treatment was completed. The heat treatment was performed at 550°C.

[0200] The fluoride solid electrolyte obtained by the above heat treatment has an average particle size of approximately 2.7 μm and a BET specific surface area of ​​1.0 m². 2The particles were in particulate form at a density of / 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 orthorhombic Li3AlF6 phase. Therefore, the fluoride solid electrolyte of sample number 1 had the orthorhombic 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 amorphousizing a portion of the fluoride solid electrolyte (specifically, the particle surface). Specifically, a commercially available polyethylene ball mill and zirconia grinding medium (φ1.0 mm) were used, and wet grinding (mechanochemical treatment) with ethanol was performed. The grinding time for each sample number was adjusted between 4 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 number 2) The solid electrolyte for sample number 2 was obtained in the same manner as for sample number 1, except that the heat treatment temperature of the mixture was changed to 250°C.

[0207] (Sample number 3) The solid electrolyte of sample number 3 was obtained in the same manner as sample number 1, except that the fluoride solid electrolyte powder was not subjected to mechanochemical treatment (i.e., crystallinity reduction treatment). In other words, the solid electrolyte of sample number 3 was the fluoride solid electrolyte obtained in sample number 1 by heat treatment of the mixture.

[0208] (Sample numbers 4 to 15) Solid electrolytes for samples 4 to 15 were obtained in the same manner as for sample 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 16 to 21) In the synthesis of the fluoride solid electrolyte of sample number 11, the amount of NH4F powder, a halogen-containing compound, was changed in the mixing of the starting material powders to the ratio shown in Table 3 relative to the stoichiometric ratio (i.e., the amount of NH4F used in sample number 11) to obtain the mixture. 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 11). In other words, the amount of starting material and NH4F powder mixed in sample number 17 was the same as the amount of these mixed in sample number 11.

[0210] The resulting mixture was heat-treated at 500°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 amorphous formation in the same manner as in the procedure for sample number 1. This yielded solid electrolytes for samples 16 to 21.

[0212] <Evaluation of solid electrolytes> For the solid electrolytes prepared as described above (sample numbers 1 to 21), the crystalline phase, ionic conductivity, BET specific surface area, and compacted powder density were evaluated. For samples 16 to 21, the fluorine element ratio (fluorine amount α) of each constituent element contained in the solid electrolyte was also evaluated.

[0213] (crystalline phase) The crystalline phase was confirmed by powder X-ray diffraction measurements both after heat treatment and before crystallinity reduction treatment (before grinding) and after crystallinity reduction treatment (after grinding). An X-ray diffractometer (RIGAKU, MiniFlex600) 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 after crystallinity reduction treatment of sample numbers 1, 2, 8, and 10. In Figures 3 and 4, the orthorhombic crystal system Li3AlF6 phase is referred to as "Li3AlF6(o)", and the monoclinic crystal system Li3AlF6 phase is referred to as "Li3AlF6(m)". 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 strongest peaks belonging to the orthorhombic Li3AlF6 phase in the XRD pattern of the solid electrolyte after crystallinity reduction treatment. In Tables 2 and 3, the orthorhombic Li3AlF6 phase is denoted as "LAF(о)", the Li2TiF6 phase as "LTF", and the monoclinic Li3AlF6 phase as "LAF(m)".

[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 areas of the solid electrolyte after pulverization are 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 still 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] (F amount α) The Li, Al, and Ti content in the solid electrolyte was evaluated using ICP emission spectrometry, and the F content was evaluated using combustion ion chromatography (CIC). From these results, the F content α, which is the ratio (%) of the amount of F to the total amount of each constituent element (with the sum of the amounts of each element being 100%), was determined. The Li, Al, and Ti content in samples 16 to 21 were constant values, the same as in sample 11.

[0217] [Table 1]

[0218] [Table 2]

[0219] [Table 3]

[0220] The evaluation results for solid electrolytes of sample numbers 1 to 15 are shown in Tables 1 and 2. The evaluation results for solid electrolytes of sample numbers 16 to 21 are shown in Table 3. In Tables 1 and 2, sample numbers marked with an asterisk (*) are samples that do not satisfy the constituent requirements of the solid electrolyte in this disclosure. Specifically, the solid electrolytes of sample numbers 2 and 13 do not have a low-crystallinity orthorhombic Li3AlF6 phase as the main phase, and the solid electrolytes of sample numbers 3 and 14 do not contain a low-crystallinity orthorhombic 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 orthorhombic Li3AlF6 phase. Furthermore, the full width at half maximum of the strongest peak of the orthorhombic Li3AlF6 phase in the XRD pattern of the solid electrolyte of sample number 1 was 2.7°, indicating that it mainly contained a low-crystallinity orthorhombic Li3AlF6 phase.

[0222] XRD analysis confirmed that the solid electrolytes in samples 4, 5 through 12, and 15 through 21 also contained a low-crystallinity orthorhombic Li3AlF6 phase as the main phase.

[0223] As shown in Figure 2, XRD confirmed that the monoclinic Li3AlF6 phase was the dominant phase of the solid electrolyte of sample number 2. The solid electrolyte of sample number 3 had an orthorhombic Li3AlF6 phase as its dominant phase, but the full width at half maximum of the strongest peak confirmed by XRD was 0.5°. Therefore, the solid electrolyte of sample number 3 did not contain a low-crystallinity orthorhombic Li3AlF6 phase. The solid electrolytes of samples number 13 and 14 contained an orthorhombic Li3AlF6 phase, but the monoclinic Li3AlF6 phase was the dominant phase. Furthermore, the solid electrolyte of sample number 14 did not contain a low-crystallinity orthorhombic Li3AlF6 phase.

[0224] From the results for sample numbers 1, 4-12, and 15, when the main phase is a low-crystallinity orthorhombic Li3AlF6 phase, the solid electrolyte has a BET specific surface area of ​​12 m². 2 / g to 60m 2Particles with a density of / g, high ionic conductivity of 3.0 μS / cm or higher, and 1.80 g / cm². 3 These samples exhibited a high compaction density. In contrast, sample number 3, which did not undergo crystallinity reduction treatment, had an ionic conductivity of 0.001 μS / cm, more than three orders of magnitude lower than sample number 1, despite its main phase being an orthorhombic Li3AlF6 phase, and a compaction density of 1.74 g / cm³. 3 It was low. Sample No. 2 had a BET specific surface area (11m²) similar to that of Sample No. 1. 2 Although the particle size was adjusted to 5m / g, the ionic conductivity was lower than that of other sample numbers whose main phase was orthorhombic Li3AlF6. From the above, it can be concluded that the orthorhombic Li3AlF6 phase with reduced crystallinity is 5m 2 / g or more 65m 2 Less than / g, preferably 10mg 2 / g or more 60m 2 It is understood that the particulate matter has a BET specific surface area of ​​less than / g and exhibits excellent ionic conductivity.

[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 orthorhombic Li3AlF6 phase, an even higher ionic conductivity of 4.0 μS / cm or higher was observed, along with a high compact density. This is thought to be due to the densification of the solid electrolyte by the binding action between the particles of the soft Li2TiF6 phase in the particulate solid electrolyte. The Li2TiF6 phase belonged to the tetragonal crystal structure. Also, as shown in samples 10 to 12, when a monoclinic Li3AlF6 phase, which is synthesized at a lower temperature and is softer, was further included as a secondary phase, a high ionic conductivity of 4.0 μS / cm or higher was observed. In contrast to these, when the monoclinic 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 0.001 μS / cm.

[0226] As shown in Sample Nos. 11, 12, and 15, the substitution of M1 at the Al site in the cubic Li3AlF6 phase and the substitution of M3 at the Al site in the monoclinic Li3AlF6 phase are effective in lowering the heat treatment temperature (halogenation temperature). Even when the fluorination temperature was lowered to 510 °C or lower, a high ionic conductivity of 4.0 μS / cm or more and a high green compact density were obtained. This is presumably due to the activation of reactivity.

[0227] In Sample Nos. 16 to 21, the crystal phases after heat treatment were all composed of the cubic Li3AlF6 phase as the main phase and the Li2TiF6 phase and the monoclinic Li3AlF6 phase as the secondary phases, similar to Sample No. 11, and were partially amorphous after the pulverization treatment. As shown in Table 3, the F content α tended to change corresponding to the amount of NH4F used for the conversion to fluoride. That is, it was found that the F content of the solid electrolyte is affected by the amount of halogen-containing compound mixed in the starting materials. The inventors found that the ionic conductivity of a solid electrolyte containing a low-crystalline cubic Li3AlF6 phase as the main phase depends on the F content. As shown in Sample Nos. 18 to 20, when the F content α is in the range of 60.0% to 66.5%, which is a value in a somewhat excessive region compared to the stoichiometric ratio, a higher ionic conductivity of 4.1 μS / cm or more was obtained. Therefore, the reason for obtaining a higher ionic conductivity at the F content α within the scope of the present invention is considered to be due to the suppression of the formation of unnecessary impurity phases generated in trace amounts during the conversion synthesis to fluoride, that is, the synthesis of the fluoride solid electrolyte. Note that since the BET specific surface areas of the solid electrolytes of Sample Nos. 16 to 21 were adjusted to the same level, all of these powder properties can be regarded as equivalent.

[0228] [[ID=捌]]As described above, it was confirmed that a solid electrolyte containing, as the main phase, a first phase which is a low-crystalline cubic Li3AlF6 phase and having a BET specific surface area of 5 m 2 / g or more and 65 m 2 / g or less is excellent in ionic conductivity. By using such a solid electrolyte of the present disclosure, a battery and a power storage device with excellent performance and high reliability can be realized.

Industrial Applicability

[0229] The solid electrolyte according to the present disclosure can be used as a solid electrolyte used in, for example, lithium-ion batteries used in various electronic devices or automobiles and the like.

Explanation of reference numerals

[0230] 100 Coated active material 110 Electrode active material 120 Coating layer 200 Solid electrolyte 201 Positive electrode 202 Electrolyte layer 203 Negative electrode 204 Positive electrode active material 205 Negative electrode active material 1000 Battery

Claims

1. A solid electrolyte comprising Li, Al, and F, The solid electrolyte is an orthorhombic Li 3 AlF 6 The first aspect, which is a phase, is included as the main phase. 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°. BET specific surface area is 5 m 2 / g or more 65m 2 It is less than or equal to / g. solid electrolyte.

2. The ratio of the amount of substance of F to the total amount of substance of all elements constituting the solid electrolyte is 57.0% or more and 67.0% or less. The solid electrolyte according to claim 1.

3. The aforementioned percentage is between 59.0% and 67.0%. The solid electrolyte according to claim 2.

4. It is particulate, The proportion of the first phase on the particle surface is greater than the proportion of the first phase inside the particle. The solid electrolyte according to claim 1.

5. In the first phase, a portion of the Al site is replaced by M1. Here, M1 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements. The solid electrolyte according to claim 1.

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

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

8. The amount of substitution by M1 is greater than 0 at% and less than or equal to 30 at%. The solid electrolyte according to claim 5.

9. Li 2 M2F 6 It further includes the second phase, which is a phase, Here, M2 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements. The solid electrolyte according to claim 1.

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

11. Monoclinic Li 3 AlF 6 It further includes the third phase, The solid electrolyte according to claim 1.

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

13. In the third phase, a portion of the Al site is replaced by M3. Here, M3 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements. The solid electrolyte according to claim 11.

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

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

16. The amount of substitution by M3 is greater than 0 at% and less than or equal to 10 at%. The solid electrolyte according to claim 13.

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

18. Li 2 M2F 6 a second phase that is a phase, and monoclinic Li 3 AlF 6 further includes a third phase that is a phase In the first phase, a portion of the Al site is replaced by M1. In the third phase, a portion of the Al site is replaced by M3. Here, M1 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements. The aforementioned M2 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements. The aforementioned M3 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements. The aforementioned M1, M2, and M3 contain a common element, The solid electrolyte according to claim 1.

19. Li 2 M2F 6 The second phase, which is the phase of the monoclinic Li 3 AlF 6 It further includes the third phase, which is a phase, Here, M2 is at least one element selected from the group consisting of tetravalent metallic elements and tetravalent metalloid elements. The mass ratio of the first phase is greater than the mass ratio of the second phase. The mass ratio of the second phase is greater than the mass ratio of the third phase. The solid electrolyte according to claim 1.

20. The process of halogenating starting materials containing Li and Al, Orthorhombic Li 3 AlF 6 Synthesizing a solid electrolyte containing a phase as the main phase, The orthorhombic Li 3 AlF 6 To reduce the crystallinity of the phase, Includes, The aforementioned starting material comprises at least one selected from the group consisting of oxides, carbonates, and hydroxides. A method for producing solid electrolytes.

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

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

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

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

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

26. The halogen-containing compound is NH 4 Including F, A method for producing a solid electrolyte according to claim 22.

27. Reducing the aforementioned crystallinity includes, A method for producing a solid electrolyte according to claim 20.

28. The solid electrolyte according to claim 1, and electrode active material, including, electrode material.

29. At least a portion of the surface of the electrode active material is covered with the solid electrolyte. The electrode material according to claim 28.

30. positive electrode, Negative electrode, and An electrolyte layer provided between the positive electrode and the negative electrode, Equipped with, 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. battery.

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