Solid electrolyte material, its manufacturing method and battery

Abstract

To provide solid electrolyte material enabling reduction of a value of resistance of a battery.SOLUTION: Solid electrolyte material is provided, including: sulfide that has a composition including lithium, phosphorus, and sulfur and has an argyrodite type crystal structure; lithium phosphate; and sulfate ions. In the solid electrolyte material, a content of sulfate ions is equal to or more than 0.5 mass%. When the solid electrolyte material is measured by a θ-2θ method using CuKα rays having wavelengths of 0.15405nm and 0.15444nm as X-ray sources in an X-ray diffraction pattern, a first peak is observed in a range of a value of a diffraction angle 2θ being equal to or more than 21° and less than 23°and a second peak is observed in a range of the value of the diffraction angle 2θ being equal to or more than 25°and less than 27°, wherein a ratio of intensity of the first peak to that of the second peal is equal to or more than 0.03 and less than 0.15.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] There is a demand for safer all-solid-state lithium-ion secondary batteries that use solid electrolytes. Examples of solid electrolytes include oxide-based solid electrolytes containing lithium, metal elements, and oxygen, sulfide-based solid electrolytes containing lithium, phosphorus, and sulfur, and halogen-based solid electrolytes containing lithium, metal elements, and halogen. Among these, sulfides with an argyrodite structure have attracted attention as sulfide-based solid electrolytes due to their high ionic conductivity and low manufacturing costs.

[0003] For example, Patent Document 1 proposes a solid electrolyte material that has a peak corresponding to Li7PS6 and a peak corresponding to Li3PO4 in X-ray diffraction measurement, and that has high Li-ion conductivity and high thermal stability. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-33858 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of one aspect of the present disclosure is to provide a solid electrolyte material that can reduce the resistance value in a battery and a method for producing the same. [Means for solving the problem]

[0006] The first aspect is a method for producing a solid electrolyte material, comprising obtaining a mixture containing a lithium-containing compound, a phosphorus- and sulfur-containing compound, a metal sulfate, and a metal phosphate, and heat-treating the mixture to obtain a heat-treated product containing sulfate ions and lithium phosphate. The lithium-containing compound in the production method includes at least one selected from the group consisting of lithium sulfide, lithium oxide, and lithium carbonate. The mixture in the production method has a metal phosphate content of less than 15.0 mass%.

[0007] A second aspect of the present invention is a solid electrolyte material comprising a sulfide having an argyrodite-type crystal structure containing lithium, phosphorus, and sulfur, lithium phosphate, and sulfate ions. The solid electrolyte material has a sulfate ion content of 0.5% by mass or more. When measured by the θ-2θ method using CuKα radiation with wavelengths of 0.15405 nm and 0.15444 nm as an X-ray diffraction source, the solid electrolyte material exhibits an X-ray diffraction pattern in which a first peak is observed in a diffraction angle 2θ range of 21° to less than 23°, and a second peak is observed in a diffraction angle 2θ range of 25° to less than 27°, with the ratio of the intensity of the first peak to the intensity of the second peak being 0.03 to less than 0.15. [Effects of the Invention]

[0008] According to one aspect of the present disclosure, it is possible to provide a solid electrolyte material that can reduce the resistance value in a battery and a method for producing the same. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of a battery 1000. FIG. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a measurement cell for evaluating battery characteristics. [Figure 3] 1 shows X-ray diffraction (XRD) patterns of solid electrolyte materials according to Example 1 and Comparative Example 1. [Figure 4] 1 shows XRD patterns of solid electrolyte materials according to Examples 2, 3, and 4. [Figure 5]1 shows XRD patterns of solid electrolyte materials according to Comparative Examples 2, 3, and 4. DETAILED DESCRIPTION OF THE INVENTION

[0010] In this specification, the term "process" refers not only to an independent process, but also to a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. Furthermore, the content of each component in a composition refers to the total amount of the multiple substances present in the composition, unless otherwise specified, when multiple substances corresponding to each component are present in the composition. Furthermore, the upper and lower limits of the numerical ranges described in this specification can be arbitrarily selected and combined. Hereinafter, embodiments of the present invention will be described in detail. However, the embodiments described below are intended to exemplify a solid electrolyte material, a manufacturing method thereof, and a battery for embodying the technical concept of the present invention, and the present invention is not limited to the solid electrolyte material, manufacturing method thereof, and battery described below.

[0011] Method for manufacturing solid electrolyte material The method for producing a solid electrolyte material includes a preparation step of obtaining a mixture containing a lithium-containing compound, a phosphorus- and sulfur-containing compound, a metal sulfate, and a metal phosphate, and a heat-treatment step of heat-treating the prepared mixture to obtain a heat-treated product containing sulfate ions and lithium phosphate. The lithium-containing compound contained in the mixture includes at least one selected from the group consisting of lithium sulfide, lithium oxide, and lithium carbonate. The content of the metal phosphate in the mixture is less than 15.0 mass%.

[0012] When a solid electrolyte material containing a sulfide having an argyrodite-type crystal structure is produced, adding a predetermined amount of a metal sulfate in addition to a metal phosphate reduces the resistance of a battery constructed using the produced solid electrolyte material. This can be attributed to, for example, the presence of predetermined amounts of sulfate ions and lithium phosphate in the solid electrolyte material, which improves the conductivity of lithium ions.

[0013] Preparation process In the preparation step, a mixture containing a lithium-containing compound, a phosphorus- and sulfur-containing compound, a metal sulfate, and a metal phosphate is obtained. The mixture may further contain a chlorine-containing compound. The mixture may be, for example, a raw material composition for a solid electrolyte material.

[0014] Examples of the lithium-containing compound include lithium sulfide (e.g., LiS), lithium oxide (e.g., LiO), and lithium carbonate (e.g., LiCO), and the like may contain at least one selected from the group consisting of these, and preferably may contain at least lithium sulfide.

[0015] The content of the lithium-containing compound in the mixture may be, for example, 3 to 7 moles, preferably 3.1 to 5 moles, more preferably 3.3 to 4.3 moles, per mole of the phosphorus- and sulfur-containing compound. Here, the content of the lithium-containing compound does not include metal sulfates, metal phosphates, and chlorine-containing compounds, which will be described later.

[0016] The compound containing phosphorus and sulfur may be, for example, a compound having a phosphorus-sulfur bond. Examples of the compound containing phosphorus and sulfur include diphosphorus trisulfide (e.g., P2S3) and diphosphorus pentasulfide (e.g., P2S5), and the like. The compound may contain at least one selected from the group consisting of these compounds, and preferably contains at least diphosphorus pentasulfide.

[0017] The metal sulfate may be, for example, an alkali metal sulfate. Examples of the metal sulfate include lithium sulfate (e.g., LiSO), sodium sulfate (NaSO), etc., and the metal sulfate may contain at least one selected from the group consisting of these, and preferably contains at least lithium sulfate.

[0018] The content of the metal sulfate in the mixture may be, for example, 1.0% by mass or less, preferably 0.7% by mass or less, 0.6% by mass or less, or 0.55% by mass or less, based on the mixture. The lower limit of the content of the metal sulfate may be, for example, 0.01% by mass or more, preferably 0.1% by mass or more, 0.2% by mass or more, or 0.4% by mass or more, based on the mixture. When the content of the metal sulfate is within the above range, the lithium ion conductivity of the produced solid electrolyte material tends to be further improved, the battery resistance is further reduced, and the battery characteristics tend to be further improved.

[0019] The metal phosphate may be, for example, an alkali metal phosphate. Examples of the metal phosphate include lithium phosphate (e.g., Li3PO4), sodium phosphate (Na3PO4), etc., and the metal phosphate may contain at least one selected from the group consisting of these, and preferably contains at least lithium phosphate.

[0020] The content of the metal phosphate in the mixture may be, for example, 15.0% by mass or less, preferably 10.0% by mass or less, 7.0% by mass or less, 5.0% by mass or less, or 3.0% by mass or less, based on the mixture. The lower limit of the content of the metal phosphate may be, for example, 0.1% by mass or more, preferably 0.5% by mass or more, or 1.0% by mass or more, based on the mixture. When the content of the metal phosphate is within the above range, the battery resistance of the produced solid electrolyte material tends to be further reduced.

[0021] The chlorine-containing compound may be, for example, a metal chloride, preferably an alkali metal chloride. Examples of alkali metals include lithium (Li), sodium (Na), potassium (K), and rubidium (Rb). Specific examples of the chlorine-containing compound include lithium chloride (e.g., LiCl), sodium chloride (e.g., NaCl), and potassium chloride (e.g., KCl). The compound may contain at least one selected from the group consisting of these compounds, and preferably contains at least lithium chloride.

[0022] The content of the chlorine-containing compound in the mixture may be, for example, 0 to 3.9 moles, preferably 1 to 3.7 moles, more preferably 2.9 to 3.5 moles, per mole of the phosphorus- and sulfur-containing compound. When the content of the chlorine-containing compound in the mixture is within the above range, the effect of reducing internal resistance, which will be described later, tends to be greater.

[0023] A portion of the chlorine-containing compound may be replaced with a bromine-containing compound. The bromine-containing compound may be, for example, a metal bromide, preferably an alkali metal bromide. Examples of alkali metals include lithium (Li), sodium (Na), potassium (K), and rubidium (Rb). Specific examples of the bromine-containing compound include lithium bromide (e.g., LiBr), sodium bromide (e.g., NaBr), and potassium bromide (e.g., KBr). The bromine-containing compound may contain at least one selected from the group consisting of these, and preferably contains at least lithium bromide. When a portion of the chlorine-containing compound is replaced with a bromine-containing compound, the content of the bromine-containing compound may be greater than 0 moles and less than 1 mole, preferably 0.5 moles or less, and more preferably 0.1 moles or less, per mole of the chlorine-containing compound. The lower limit of the content of the bromine-containing compound relative to the chlorine-containing compound may be, for example, 0.001 moles or more. Furthermore, when a portion of the chlorine-containing compound is substituted with a bromine-containing compound, the total amount of the chlorine-containing compound and the bromine-containing compound may be 0 mole or more and 3.9 moles or less, preferably 1 mole or more and 3.7 moles or less, and more preferably 2.9 moles or more and 3.5 moles or less, relative to 1 mole of the phosphorus- and sulfur-containing compound.

[0024] In the mixture, a part of the chlorine-containing compound may be replaced by a compound containing a halogen atom other than chlorine and bromine. Examples of the halogen atom contained in the compound containing a halogen atom other than chlorine and bromine include fluorine and iodine, and at least one of these may be contained. The compound containing a halogen atom other than chlorine and bromine may contain, for example, a metal halide, preferably an alkali metal halide, or at least a lithium halide.

[0025] When the mixture contains a compound containing a halogen atom other than chlorine and bromine, the content of the compound containing a halogen atom other than chlorine and bromine in the mixture may be, for example, greater than 0 mol and 0.1 mol or less, and preferably greater than 0 mol and 0.05 mol or less, per 1 mol of the compound containing chlorine.

[0026] The mixture can be prepared by weighing out and mixing the lithium-containing compound, the phosphorus- and sulfur-containing compound, the metal sulfate, the metal phosphate, and, if necessary, the chlorine-containing compound so as to obtain desired contents. For example, the total molar ratio of the lithium-containing compound and the chlorine-containing compound to the phosphorus- and sulfur-containing compound in the mixture may be, for example, 3 or more and 8 or less, preferably 5 or more and 7.8 or less, and more preferably 6 or more and 7.5 or less.

[0027] Examples of the method for mixing the raw materials include a mixing method capable of applying mechanical stress, such as a high-speed shear mixer, a ball mill, a bead mill, a vibration mill, or a planetary ball mill.

[0028] Heat Treatment Process In the heat treatment step, the prepared mixture is heat-treated to obtain a heat-treated product containing sulfate ions and lithium phosphate. The heat-treated product may contain a sulfide having an argyrodite-type crystal structure that contains lithium, phosphorus, and sulfur in its composition, and the sulfide having the argyrodite-type crystal structure may contain a crystalline phase. When the sulfide contains a crystalline phase, it may contain a crystalline phase having a composition represented by Li7PS6.

[0029] The heat treatment temperature of the mixture may be, for example, 400°C or higher, preferably 450°C or higher, or 500°C or higher. The upper limit of the heat treatment temperature may be, for example, 1000°C or lower, preferably 800°C or lower, or 600°C or lower. The heat treatment time may be, for example, 1 hour or longer and 20 hours or shorter, preferably 5 hours or longer and 15 hours or shorter. The heat treatment atmosphere may be, for example, an inert gas atmosphere such as nitrogen gas or a rare gas, or the heat treatment may be performed under reduced pressure.

[0030] solid electrolyte material The solid electrolyte material contains lithium, phosphorus, and sulfur in its composition, and includes a sulfide having an argyrodite-type crystal structure, lithium phosphate, and sulfate ions. When the X-ray diffraction pattern of the solid electrolyte material is measured by the θ-2θ method using CuKα radiation with wavelengths of 0.15405 nm and 0.15444 nm as an X-ray source, a first peak is observed in a diffraction angle 2θ range of 21° or more and less than 23°, and a second peak is observed in a diffraction angle 2θ range of 25° or more and less than 27°. Furthermore, the ratio of the intensity of the first peak to the intensity of the second peak may be, for example, 0.03 or more and less than 0.15. The content of sulfate ions contained in the solid electrolyte material may be, for example, 0.5% by mass or more relative to the solid electrolyte material.

[0031] The inclusion of lithium phosphate and sulfate ions in a solid electrolyte material, in addition to sulfides having an argyrodite-type crystal structure, improves lithium ion conductivity. Furthermore, when used in a battery, the internal resistance is reduced, resulting in superior battery performance. This can be explained, for example, as follows: When sulfides having an argyrodite-type crystal structure are used as a solid electrolyte, the presence of lithium phosphate, which has a higher lithium concentration than sulfides having an argyrodite-type crystal structure, on the particle surface of the solid electrolyte improves lithium ion diffusibility and battery resistance. Furthermore, the argyrodite-type crystal structure is composed of a Li2S-Li3PS4-Li2S structure. When lithium sulfate is present nearby, some of the lithium sulfate is thought to replace Li3PS4 and form a solid solution. This causes lithium deficiency in the solid electrolyte, creating vacant lithium sites, which is thought to facilitate lithium migration within the solid electrolyte. Furthermore, when a solid electrolyte material contains lithium chloride, some of the lithium chloride is thought to replace Li2S and form a solid solution, resulting in lithium deficiency and creating vacant lithium sites. It is believed that the replacement of the Li2S and Li3PS4 units in this way synergistically improves lithium ion conductivity.

[0032] The solid electrolyte material includes a sulfide containing lithium, phosphorus, and sulfur and having an argyrodite-type crystal structure. The sulfide constituting the solid electrolyte material may include, for example, a crystalline phase having a composition represented by Li7PS6. The presence of the crystalline phase having a composition represented by Li7PS6 in the sulfide can be confirmed, for example, by X-ray diffraction (XRD) measurement. Specifically, when XRD measurement of the solid electrolyte material is performed using CuKα radiation with wavelengths of 0.15405 nm and 0.15444 nm as an X-ray source by the theta-2theta method, peaks corresponding to the crystalline phase having a composition represented by Li7PS6 typically appear at 2θ=25.7°, 30.2°, 31.6°, 45.3°, 48.2°, and 52.7°.

[0033] The lithium content in the sulfide composition may be, for example, 4 to 7 moles, preferably 5 to 6 moles, per mole of phosphorus. The sulfur content in the sulfide composition may be, for example, 3 to 6 moles, preferably 4 to 5 moles, per mole of phosphorus.

[0034] The sulfide having an argyrodite-type crystal structure may contain a halogen in its composition. The inclusion of a halogen tends to further improve lithium ion conductivity. Examples of halogen include chlorine, bromine, iodine, etc., and the sulfide may contain at least one selected from the group consisting of these, may contain either chlorine or bromine, or may contain at least chlorine. The inclusion of chlorine tends to result in a sulfide solid electrolyte with higher chemical stability.

[0035] When the sulfide having an argyrodite-type crystal structure contains a halogen in its composition, the content of the halogen in the sulfide composition may be, for example, more than 0 mol and not more than 2 mol per mol of phosphorus, preferably 1 mol or more and 2 mol or less, and more preferably 1.4 mol or more and 1.8 mol or less. When the halogen contained in the composition of the sulfide having an argyrodite-type crystal structure is within the above range, the lithium ion conductivity of the sulfide tends to be more easily improved.

[0036] The solid electrolyte material contains lithium phosphate in addition to sulfides having an argyrodite-type crystal structure. The presence of lithium phosphate in the solid electrolyte material can be evaluated using an X-ray diffraction pattern. Specifically, when XRD measurement of the solid electrolyte material is performed using the θ-2θ method with CuKα radiation at wavelengths of 0.15405 nm and 0.15444 nm as an X-ray source, peaks corresponding to lithium phosphate (e.g., Li3PO4) typically appear at 2θ = 22.3°, 23.2°, 24.8°, 33.9°, and 36.6°.

[0037] A solid electrolyte material containing lithium phosphate in addition to a sulfide having an argyrodite-type crystal structure may have, in an X-ray diffraction pattern using CuKα radiation as an X-ray source, a first peak corresponding to lithium phosphate (e.g., Li3PO4) and a second peak corresponding to a crystalline phase having a composition represented by Li7PS6. The first peak may have a diffraction angle 2θ value of 21° or more and less than 23°, for example, about 22.3°. The second peak may have a diffraction angle 2θ value of 25° or more and less than 27°, for example, about 25.7°.

[0038] The lithium phosphate content of the solid electrolyte material can be evaluated, for example, using an X-ray diffraction pattern. Specifically, it can be evaluated by the ratio of the intensity of the first peak to the intensity of the second peak (hereinafter simply referred to as the "peak intensity ratio"). The solid electrolyte material may have a ratio of the intensity of the first peak to the intensity of the second peak of, for example, 0.03 or more and less than 0.15, preferably 0.04 or more or 0.045 or more, and preferably 0.10 or less or 0.06 or less. When the peak intensity ratio corresponding to the lithium phosphate content is within the above range, the battery resistance tends to be further reduced.

[0039] The solid electrolyte material contains sulfate ions. The content of sulfate ions contained in the solid electrolyte material may be, for example, 0.5% by mass or more, and preferably 0.54% by mass or more, relative to the solid electrolyte material. The upper limit of the content of sulfate ions may be, for example, 1.0% by mass or less, and preferably 0.8% by mass or less, relative to the solid electrolyte material. When sulfate ions are present in a content within the above range, lithium ion conductivity is further improved, battery resistance is further reduced, and battery characteristics tend to be further improved.

[0040] The content of sulfate ions contained in the solid electrolyte material is measured by high-frequency inductively coupled plasma atomic emission spectroscopy (ICP atomic emission spectroscopy).

[0041] The composition of the solid electrolyte material may be, for example, a lithium atom composition ratio of 4 to 7 moles, preferably 5 to 6 moles, per mole of phosphorus. The sulfur atom composition ratio may be, for example, 3 to 6 moles, preferably 4 to 5 moles, per mole of phosphorus. The oxygen atom composition ratio may be, for example, 0 to 4 moles, preferably 0.1 to 2.0 moles, per mole of phosphorus. The halogen atom composition ratio may be, for example, 0 to less than 2 moles, preferably 1.4 to 1.8 moles, per mole of phosphorus.

[0042] The solid electrolyte material may have a composition represented by the following formula (I), for example. Li r PS s O t X u (I) In formula (I), r, s, t, and u are 4≦r≦7, 3≦s≦6, 0≦t≦4, and 0≦u<2, respectively, and X may be at least one selected from the group consisting of F, Cl, Br, and I. Preferably, 5≦r≦6, 4≦s≦5, 0.1≦t≦2, and 1.4≦u≦1.8 may be satisfied, and X may be at least one of Br and Cl.

[0043] battery The battery is configured to include an electrolyte containing the above-described solid electrolyte material, a positive electrode, and a negative electrode. The electrolyte may form an electrolyte layer disposed between the positive electrode and the negative electrode. An example of the battery configuration will now be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of a battery 1000. The battery 1000 includes a positive electrode 201, a negative electrode 203, and an electrolyte layer 202 disposed between the positive electrode 201 and the negative electrode 203. The positive electrode 201 includes a positive electrode active material layer containing a positive electrode active material 204. The positive electrode active material layer constituting the positive electrode 201 may contain, in addition to the positive electrode active material 204, a conductive additive, the solid electrolyte material 100, and the like. The positive electrode 201 may also include a current collector and a lead connected to the current collector. The negative electrode 203 includes a negative electrode active material layer containing a negative electrode active material 205. The negative electrode active material layer constituting the negative electrode 203 may contain, in addition to the negative electrode active material 205, a conductive additive, the solid electrolyte material 100, and the like. The negative electrode 203 may include a current collector and a lead connected to the current collector. The electrolyte layer 202 includes a solid electrolyte material. An example of the battery is a lithium ion battery, which may be an all-solid-state secondary battery.

[0044] The lithium-ion battery in this specification includes a lithium-ion secondary battery using a lithium transition metal composite oxide in the positive electrode and a lithium-sulfur battery using a material that absorbs and releases lithium in the negative electrode. Specific examples of lithium transition metal composite oxides can be found in, for example, paragraph 0066 of WO 2017 / 141735 (paragraphs 0152 to 0156 of U.S. Patent Publication No. 2018 / 0309167). Furthermore, examples of materials that absorb and release lithium can be found in, for example, paragraph 0058 of WO 2015 / 056564 (paragraph 0070 of U.S. Patent Publication No. 2016 / 0254529).

[0045] For example, a lithium-transition metal composite oxide is used for the positive electrode active material 204, and examples thereof include transition metal oxides having a layered rock salt structure and transition metal oxides having a spinel structure, as described in the above-mentioned publications. In addition to lithium-containing transition metal phosphate compounds, lithium-containing transition metal halide phosphate compounds, and lithium-containing transition metal silicate compounds, transition metal fluorides, transition metal sulfides, transition metal oxyfluorides, transition metal oxysulfides, and transition metal oxynitrides can also be used for the positive electrode active material 204. In the case of a lithium-sulfur battery, elemental sulfur can be used as the positive electrode active material.

[0046] The average particle size of the positive electrode active material 204 may be, for example, 0.1 μm or more and 30 μm or less. When the average particle size of the positive electrode active material 204 is 30 μm or less, lithium diffusion within the positive electrode active material 204 is not too slow, which may facilitate high-power operation of the battery. The thickness of the positive electrode active material layer may be, for example, 10 μm or more and 500 μm or less. When the thickness of the positive electrode active material layer is 10 μm or more, it may be easier to ensure sufficient battery energy density. Furthermore, when the thickness of the positive electrode active material layer is 500 μm or less, it may facilitate high-power operation.

[0047] The average particle size of the positive electrode active material 204 may be larger than the average particle size of the solid electrolyte material 100. This allows the positive electrode active material 204 and the solid electrolyte material to be well dispersed in the positive electrode active material layer.

[0048] The volume ratio of the positive electrode active material 204 to the total volume of the positive electrode active material 204 and the solid electrolyte material 100 contained in the positive electrode active material layer may be, for example, 30% or more and 95% or less. When the volume ratio is 30% or more, the energy density of the battery can be sufficiently ensured. Furthermore, when the volume ratio is 95% or less, high-power operation may be facilitated.

[0049] The electrolyte layer 202 may be a solid electrolyte layer containing the above-mentioned solid electrolyte material. The thickness of the solid electrolyte layer may be, for example, 1 μm or more and 100 μm or less. If the thickness of the solid electrolyte layer is 1 μm or more, short-circuiting between the positive electrode 201 and the negative electrode 203 can be suppressed. Furthermore, if the thickness of the solid electrolyte layer is 100 μm or less, high-power operation may be facilitated.

[0050] The negative electrode active material 205 is composed of a material having the property of being able to absorb and release metal ions such as lithium ions. Specific examples of the negative electrode active material 205 include metal materials, carbon materials, and the like. The metal material may be a simple metal or an alloy. Examples of metal materials include lithium metal and lithium alloys. Examples of carbon materials include natural graphite, coke, partially graphitized carbon, carbon fiber, spherical carbon, artificial graphite, and amorphous carbon.

[0051] The average particle size of the negative electrode active material 205 may be, for example, 0.1 μm or more and 100 μm or less. When the average particle size of the negative electrode active material 205 is 0.1 μm or more, it is possible that the negative electrode active material 205 and the solid electrolyte material 100 can form a good dispersion state in the negative electrode active material layer. This can prevent a deterioration in the charge / discharge characteristics of the battery. Furthermore, when the average particle size of the negative electrode active material 205 is 100 μm or less, lithium diffusion within the negative electrode active material 205 does not become too slow, which may make it easier for the battery to operate at high power.

[0052] The average particle size of the negative electrode active material 205 may be larger than the average particle size of the solid electrolyte material 100. This allows the negative electrode active material 205 and the solid electrolyte material to be well dispersed in the negative electrode active material layer.

[0053] The volume ratio of the negative electrode active material 205 to the total volume of the negative electrode active material 205 and the solid electrolyte material 100 contained in the negative electrode active material layer may be, for example, 30% or more and 95% or less. When the volume ratio is 30% or more, the energy density of the battery can be sufficiently ensured. Furthermore, when the volume ratio is 95% or less, high-power operation may be facilitated.

[0054] At least one of the positive electrode 201 and the negative electrode 203 may contain a conductive additive as needed. The conductive additive is used to reduce the electrical resistance of the battery. Examples of the conductive additive include graphites such as natural graphite and artificial graphite, and carbons such as acetylene black and ketjen black. [Example]

[0055] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0056] Example 1 In a dry atmosphere with a dew point of -50°C or less, the raw materials Li2S, P2S5, LiCl, Li2SO4, and Li3PO4 were weighed out so that the molar ratio of Li2S:P2S5:LiCl:Li2SO4:Li3PO4 = 3.74:1:3.28:0.03:0.05. These were pulverized and mixed in an absolute mill to obtain a mixture. The obtained mixture was filled into a crucible and placed in a sealed quartz container. A carbon packing was placed in the sealed container and tightened with a torque of 3.4 Nm. The sealed container was heat-treated at 500°C for 8 hours in a nitrogen atmosphere to obtain a powder of the solid electrolyte material of Example 1. The solid electrolyte material of Example 1 was made of Li 5.5 PS 4.2 O 0.1 Cl 1.7 The Li2SO4 content (mass %) in the mixture is shown in Table 1.

[0057] Example 2 A powder of the solid electrolyte material of Example 2 was obtained in the same manner as in Example 1, except that the raw materials in the mixture were weighed so that the molar ratio of Li2S:P2S5:LiCl:Li2SO4:Li3PO4 was 3.76:1:3.43:0.03:0.14. 5.5 PS 4.0 O 0.5 Cl 1.6 The composition was as follows:

[0058] Example 3 A powder of the solid electrolyte material of Example 3 was obtained in the same manner as in Example 1, except that the raw materials in the mixture were weighed so that the molar ratio of Li2S:P2S5:LiCl:Li2SO4:Li3PO4 was 3.90:1:3.68:0.025:0.25. 5.4 PS 3.6 O 0.9 Cl 1.6 The composition was as follows:

[0059] Example 4 A powder of the solid electrolyte material of Example 4 was obtained in the same manner as in Example 1, except that the raw materials in the mixture were weighed so that the molar ratio of Li2S:P2S5:LiCl:Li2SO4:Li3PO4 was 3.65:1:3.43:0.04:0.14. 5.2 PS 3.9 O 0.6 Cl 1.6 The composition was as follows:

[0060] Comparative Example 1 A powder of the solid electrolyte material of Comparative Example 1 was obtained in the same manner as in Example 1, except that the raw materials in the mixture were weighed so that the molar ratio of Li2S:P2S5:LiCl was 3.8:1:3.2. 5.4 PS 4.4 Cl 1.6 The composition was as follows:

[0061] Comparative Example 2 A powder of the solid electrolyte material of Comparative Example 2 was obtained in the same manner as in Example 1, except that the raw materials in the mixture were weighed so that the molar ratio of Li2S:P2S5:LiCl:Li2SO4 was 3.84:1:3.22:0.03. 5.3 PS 4.35 O 0.05 Cl 1.6 The composition was as follows:

[0062] Comparative Example 3 A powder of the solid electrolyte material of Comparative Example 3 was obtained in the same manner as in Example 1, except that the raw materials in the mixture were weighed so that the molar ratio of Li2S:P2S5:LiCl:Li3PO4 was 3.92:1:3.23:0.30. 5.2 PS 3.9 O 0.5 Cl 1.4 The composition was as follows:

[0063] Comparative Example 4 A powder of the solid electrolyte material of Comparative Example 4 was obtained in the same manner as in Example 1, except that the raw materials in the mixture were weighed out so that the molar ratio of Li2S:P2S5:LiCl:Li2SO4:Li3PO4 was 3.85:1:3.99:0.03:0.5. 5.0 PS 3.1 O 1.4 Cl 1.4 The composition was as follows:

[0064] evaluation Crystal structure analysis The crystal structure of the solid electrolyte material was analyzed by measuring the X-ray diffraction pattern of a sample packed in a sealed cell at a dew point of -50°C using an X-ray diffractometer (Rigaku Corporation, SmartLab). The X-ray source used was CuKα radiation with wavelengths of 0.15405 nm and 0.15444 nm.

[0065] In the obtained X-ray diffraction pattern, the peak at 2θ = 22.3° was selected as the first peak corresponding to Li3PO4, and the peak at 2θ = 25.7° was selected as the second peak corresponding to Li7PS6, and the ratio of the intensity of the first peak to the intensity of the second peak (peak intensity ratio) was calculated. The results are shown in Table 1.

[0066] The XRD patterns of the solid electrolyte materials obtained in Example 1 and Comparative Example 1 are shown in Figure 3. As shown in Figure 3, peaks corresponding to Li7PS6 (2θ = 25.7°, 30.2°, 31.6°, 45.3°, 48.2°, 52.7°) were confirmed in the solid electrolyte materials of Example 1 and Comparative Example 1. Furthermore, peaks corresponding to Li3PO4 (2θ = 22.3°, 23.2°, 24.8°, 33.9°, 36.6°) were confirmed in the solid electrolyte material of Example 1.

[0067] Figure 4 shows the XRD patterns of the solid electrolyte materials obtained in Examples 2, 3, and 4. As shown in Figure 4, the solid electrolyte materials of Examples 2, 3, and 4 had peaks corresponding to Li7PS6 (2θ = 25.7°, 30.2°, 31.6°, 45.3°, 48.2°, 52.7°) and peaks corresponding to Li3PO4 (2θ = 22.3°, 23.2°, 24.8°, 33.9°, 36.6°).

[0068] Figure 5 shows the XRD patterns of the solid electrolyte materials obtained in Comparative Examples 2, 3, and 4. As shown in Figure 5, peaks corresponding to Li7PS6 (2θ = 25.7°, 30.2°, 31.6°, 45.3°, 48.2°, 52.7°) were confirmed in the solid electrolyte materials of Comparative Examples 2, 3, and 4, and peaks corresponding to Li3PO4 (2θ = 22.3°, 23.2°, 24.8°, 33.9°, 36.6°) were further confirmed in the XRD patterns of the solid electrolyte materials obtained in Comparative Examples 3 and 4.

[0069] Sulfate ion content The powders of the solid electrolyte materials obtained in the examples and comparative examples were treated with zinc acetate to remove sulfur as zinc sulfide, and then analyzed for sulfate ions (SO4 2- The results are shown in Table 1.

[0070] Battery characteristic evaluation Charge / discharge characteristics The solid electrolyte materials obtained in the examples and comparative examples were pressed and compacted at 310 MPa using the jig shown in Figure 2 in a dry atmosphere with a dew point of -50°C or lower. The upper punch 303 was then removed, and a mixture of the cathode material, the solid electrolyte material, and a conductive additive was packed inside, followed by a pressure of 310 MPa. The lower punch 302 was then removed, and a Li negative electrode was packed inside, followed by a pressure of 310 MPa to fabricate a battery. The fabricated battery was connected to a potentiometer, and the charge and discharge capacities were measured. The efficiency (%) was calculated by dividing the discharge capacity by the measured charge capacity. The results are shown in Table 1.

[0071] Battery resistance The battery resistance (Ω) of the battery prepared above was measured at frequencies ranging from 20 Hz to 120 MHz using an impedance measuring device (Keysight Impedance Analyzer E4990A). The results are shown in Table 1.

[0072] [Table 1]

[0073] As shown in Table 1, the batteries fabricated using the solid electrolyte materials of Examples 1 to 4 had reduced battery resistance. [Explanation of symbols]

[0074] 1000 batteries 100 Solid electrolyte materials 201 Positive electrode 202 Electrolyte layer 203 Negative electrode 204 Cathode active material 205 Anode active material 300 Pressure molding die 301 Frame type 302 Punch bottom 303 Punch top

Claims

1. obtaining a mixture comprising a lithium-containing compound, a phosphorus- and sulfur-containing compound, a metal sulfate, and a metal phosphate; and heat-treating the mixture to obtain a heat-treated product containing sulfate ions and lithium phosphate, the lithium-containing compound includes at least one selected from the group consisting of lithium sulfide, lithium oxide, and lithium carbonate, the mixture has a content of the metal phosphate of less than 15.0 mass%, The solid electrolyte material has a composition represented by the following formula (I): Li r PS s O t X u (I) (In formula (I), r, s, t, and u satisfy the following conditions: 5≦r≦6, 4≦s≦5, 0.1≦t≦2, and 1.4≦u≦1.8, respectively. X is at least one of Cl and Br.)

2. The method of claim 1 , wherein the mixture further comprises a compound containing chlorine.

3. 3. The method according to claim 1, wherein the compound containing phosphorus and sulfur contains at least one of diphosphorus trisulfide and diphosphorus pentasulfide.

4. 3. The method according to claim 2, wherein the lithium-containing compound comprises lithium sulfide, the phosphorus and sulfur-containing compound comprises diphosphorus pentasulfide, the chlorine-containing compound comprises lithium chloride, the metal sulfate comprises lithium sulfate, and the metal phosphate comprises lithium phosphate.

5. The method according to claim 1 , wherein the mixture contains the metal sulfate in an amount of 1.0 mass % or less.

6. The method according to claim 1 , wherein the mixture contains the metal sulfate in an amount of 0.7 mass % or less.

7. The method according to claim 1 , wherein the mixture contains the metal phosphate in an amount of 10.0 mass % or less.

8. The method according to any one of claims 1 to 7, wherein the heat treatment of the mixture is carried out at a temperature of 400°C or higher.

9. The composition includes a sulfide having an argyrodite-type crystal structure and containing lithium, phosphorus, and sulfur, lithium phosphate, and sulfate ions; The content of the sulfate ions is 0.5% by mass or more, In an X-ray diffraction pattern, when measured by the θ-2θ method using CuKα rays having wavelengths of 0.15405 nm and 0.15444 nm as an X-ray source, a first peak is observed in a diffraction angle 2θ value range of 21° or more and less than 23°, and a second peak is observed in a diffraction angle 2θ value range of 25° or more and less than 27°, and the ratio of the intensity of the first peak to the intensity of the second peak is 0.03 or more and less than 0.15, and the solid electrolyte material has a composition represented by the following formula (I): Li r PS s O t X u (I) (In formula (I), r, s, t, and u satisfy the following conditions: 5≦r≦6, 4≦s≦5, 0.1≦t≦2, and 1.4≦u≦1.8, respectively. X is at least one of Cl and Br.)

10. The solid electrolyte material according to claim 9 , wherein the content of the sulfate ions is 1.0 mass % or less.

11. The solid electrolyte material according to claim 9 or 10, wherein the sulfide further contains chlorine.

12. A battery comprising a solid electrolyte containing the solid electrolyte material according to claim 9 , a positive electrode, and a negative electrode.

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