Battery-grade lithium sulfide and preparation method and application thereof

Abstract

The invention provides battery-grade lithium sulfide as well as a preparation method and application thereof, and relates to the technical field of battery materials. The preparation method of the battery-grade lithium sulfide comprises the following steps: S1, mixing lithium sulfate and an organic carbon source by a wet method, and performing dehydration treatment to obtain a precursor; s2, carrying out carbon thermal reduction reaction on the precursor obtained in the S1 to obtain a lithium sulfide crude product; and S3, mixing the lithium sulfide crude product obtained in the step S2 with a sulfur-containing compound to obtain a mixture, and calcining the mixture to obtain purified lithium sulfide. According to the method, the lithium sulfide crude product and the sulfur-containing compound are mixed, the content of lithium oxide and lithium sulfate impurities in the lithium sulfide crude product and the sulfur-containing compound is reduced under special segmented calcination treatment, high-purity lithium sulfide is obtained, the content of carbon is smaller than or equal to 0.07 wt%, and the content of oxygen is smaller than or equal to 0.5 wt%. The pure-phase lithium sulfide disclosed by the invention can reach battery-grade purity and can be widely applied to preparation of solid electrolyte and batteries.

Description

Technical Field

[0001] This application relates to the field of battery materials technology, specifically to a battery-grade lithium sulfide, its preparation method, and its application. Background Technology

[0002] With the rapid growth in demand for electric vehicles and renewable energy storage, traditional lithium-ion batteries are gradually facing bottlenecks in energy density, safety, and lifespan. After decades of development, traditional lithium-ion batteries are approaching their theoretical energy density limit, and the safety risks posed by the use of flammable organic electrolytes have not been completely resolved. Solid-state batteries are considered a key direction for next-generation energy storage technology. Their core feature is the complete replacement of liquid electrolytes and separators with solid electrolytes, which is expected to fundamentally solve battery safety issues and performance limitations. Lithium sulfide, as a crucial component of solid-state battery electrolytes, has its purity determining the performance of solid-state batteries, while its price constrains their development.

[0003] Currently, the main methods for synthesizing battery-grade pure lithium sulfide include solid-phase synthesis, liquid-phase synthesis, and gas-phase synthesis. Compared with other synthesis methods, such as liquid-phase methods, which have the disadvantages of flammable and explosive organic solvents causing serious environmental pollution, and gas-phase methods, which have the disadvantages of high equipment costs and high risk factors, solid-phase synthesis, specifically carbothermic reduction of lithium sulfate, is more suitable for large-scale synthesis of battery-grade pure lithium sulfide because it uses low-cost lithium sulfate and carbon sources, avoids the direct use of reactive metallic lithium, and effectively utilizes the sulfur in lithium sulfate. However, the carbothermic reaction involves complex intermediate reaction processes. The +6 valence sulfur element in lithium sulfate undergoes multiple intermediate states in the reaction until it reaches the -2 valence of lithium sulfide. Among these, the 0 valence elemental sulfur is easily sublimated and lost under high temperature conditions. When sulfur is lost, lithium element easily combines with carbon and oxygen elements to form lithium carbonate and lithium oxide impurities. Existing purification schemes usually use toxic, harmful, and explosive gases such as H2S and H2, or use alcohol-based organic solvents for complex purification operations, which increases safety risks and production costs. Therefore, developing a safe, efficient, and simple process for producing high-purity lithium sulfide is key to achieving low-cost commercial mass production of lithium sulfide using the carbothermal reduction method. Summary of the Invention

[0004] The technical problem to be solved by this application is to provide a method for preparing battery-grade lithium sulfide, which improves the purity of lithium sulfide and reduces production costs.

[0005] To address the problems of the prior art, in a first aspect, this application provides a method for preparing battery-grade lithium sulfide, comprising the following steps: S1: Lithium sulfate and an organic carbon source are wet-mixed and then dehydrated to obtain the precursor; S2: The precursor obtained in S1 is carbothermally reduced to obtain crude lithium sulfide; S3: The crude lithium sulfide product of S2 is mixed with a sulfur-containing compound to obtain a mixture, and the mixture is calcined to obtain purified lithium sulfide; The calcination described in S3 is a two-step calcination, firstly, holding at 150-250℃ for 2-5 hours, and then holding at 600-800℃ for 2-5 hours; The sulfur-containing compound mentioned in S3 is selected from one or more of elemental sulfur, thiourea, ammonium thiosulfate, ammonium hydrogen sulfide, and ammonium thiocyanate, and the mass of the sulfur-containing compound is 10% or less of the crude lithium sulfide mass.

[0006] It should be noted that: The calcination process described in S3 is a two-step calcination, with each step involving holding at a low temperature (150–250°C) and a high temperature (600–800°C) for 2–5 hours. The reaction mechanism involved is as follows: In the low-temperature region, sulfur-containing compounds (denoted as XS) react with lithium oxide impurities (such as Li2O, LiOH, and Li2CO3, all of which are calculated as Li2O) to convert lithium oxide into lithium sulfide. The chemical reaction equation is: XS + Li2O = Li2S + XO. In the high-temperature zone, the carbon from the pyrolysis of some sulfur-containing compounds completely converts the remaining lithium sulfate. The chemical reaction equation is: C + Li₂SO₄ = Li₂S + CO / CO₂.

[0007] Therefore, based on the above reaction mechanism, sulfur-containing compounds are selected to effectively suppress / convert impurity phases after the carbothermic reaction.

[0008] The sulfur compounds mentioned in this invention are one or more of elemental sulfur, thiourea, ammonium thiosulfate, ammonium hydrogen sulfide, and ammonium thiocyanate. These compounds have relatively low decomposition temperatures (<300°C), and some of their decomposition products can supplement a stable carbon source. Furthermore, all of the above materials are raw materials used on a large industrial scale, resulting in relatively low usage costs.

[0009] In some specific exemplary embodiments, in the two-step calcination mentioned in S3 of the present invention: the first-step calcination temperature can be, for example, a point value such as 150℃, 180℃, 200℃, 230℃, 250℃ or any range thereof, and the holding time can be, for example, a point value such as 2h, 3h, 4h, 5h or any range thereof; the second-step calcination temperature can be, for example, a point value such as 600℃, 630℃, 650℃, 680℃, 700℃, 720℃, 750℃, 780℃, 800℃ or any range thereof, and the holding time can be, for example, a point value such as 2h, 3h, 4h, 5h or any range thereof.

[0010] In some specific embodiments, preferably, the organic carbon source used in S1 is glucose or sucrose.

[0011] In some specific embodiments, preferably, the molar ratio of lithium sulfate to organic carbon source (based on carbon element) in S1 is 1:2.8 to 3.2. For example, it can be a point value such as 1:2.8, 1:2.9, 1:3.0, 1:3.1, 1:3.2, or any range of values.

[0012] In some specific embodiments, preferably, the temperature of the dehydration treatment in S1 is 200~300℃, and the treatment time is 3~6 h. For example, it can be a point value such as 200℃, 230℃, 250℃, 280℃, 300℃, or any range of values, and the treatment time can be a point value such as 3h, 4h, 5h, 6h, or any range of values.

[0013] In some specific embodiments, preferably, the temperature of the carbothermic reduction reaction in S2 is 700~850℃, and the holding time is 5~10h. This can be a point value such as 700℃, 730℃, 750℃, 780℃, 800℃, 830℃, 850℃, or any other range thereof, and the processing time can be a point value such as 5h, 6h, 7h, 8h, 9h, 10h, or any other range thereof.

[0014] In some specific embodiments, preferably, the content of lithium sulfate in the crude lithium sulfide in S2 is less than or equal to 4 wt%, and the content of lithium oxide is less than or equal to 7 wt%.

[0015] In some specific embodiments, preferably, the amount of sulfur-containing compound used in S3 is 5-10% of the crude lithium sulfide mass. For example, it can be a point value such as 5%, 6%, 7%, 8%, 9%, 10%, or any range of values.

[0016] In some specific embodiments, preferably, the carbothermic reduction reaction in S2 and the calcination in S3 are both carried out in a nitrogen or argon atmosphere.

[0017] Secondly, the present invention also specifically protects a battery-grade lithium sulfide prepared according to a method for preparing battery-grade lithium sulfide.

[0018] In some specific embodiments, preferably, the battery-grade lithium sulfide is a pure phase, wherein the carbon content is less than or equal to 0.07 wt% and the oxygen content is less than or equal to 0.5 wt%. For example, the carbon content can be 0.05 wt%, 0.06 wt%, 0.07 wt%, etc., with a preferred content range of 0.05~0.07 wt%; the oxygen content can be, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, etc., with a preferred content range of 0.1~0.5 wt%.

[0019] In some specific embodiments, the purified lithium sulfide obtained by the present invention is preferably subjected to grain refinement treatment, specifically by ball milling, with a preferred ball milling speed of 300~500 rpm and a ball milling time of 5~12 h, resulting in a powder particle size of D50≤10μm after ball milling.

[0020] In practical applications, the residual carbon and oxygen content of the battery-grade lithium sulfide of the present invention is determined by carbon-sulfur analysis and oxygen-nitrogen-hydrogen analysis. The test process is carried out under argon protection or dry room conditions.

[0021] Thirdly, the present invention also specifically protects the application of battery-grade lithium sulfide in the preparation of solid electrolytes.

[0022] Compared with existing preparation technologies, the technical solution of this application has the following advantages: This invention addresses the technical problem of multiphase mixing of lithium oxide compounds in carbothermic reaction systems by directionally introducing sulfur-containing compounds and combining them with a stepwise heat treatment process, achieving efficient purification of lithium sulfide (Li2S) powder. This invention uses lithium sulfate, organic carbon sources, and sulfur-containing compounds as core raw materials, which are readily available and have significant cost advantages. The preparation process is simple and efficient, with low technical requirements for production equipment, and possesses both high safety and low environmental impact, providing a feasible path for large-scale industrial production. Attached Figure Description

[0023] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0024] Figure 1 The image shows the XRD pattern of crude lithium sulfide powder from Example 1.

[0025] Figure 2 The image shows the XRD pattern of the high-purity lithium sulfide powder prepared in Example 1.

[0026] Figure 3 The image shows the SEM image of the high-purity lithium sulfide powder prepared in Example 1. Detailed Implementation

[0027] The following examples are for illustrative purposes only and are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the examples, they should be performed according to the techniques or conditions described in the literature in this field, or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased from legitimate channels.

[0028] Example 1 A method for preparing lithium sulfide includes the following steps: S1. Weigh 2 kg of lithium sulfate and glucose (calculated as carbon) at a molar ratio of 1:3, dissolve in 5 L of deionized water and stir for 5 h. After spray drying and dehydration at 250 °C for 5 h, the precursor is obtained with a particle size D. 90 ≤20μm; S2. The precursor powder in S1 is placed in a nitrogen atmosphere furnace for carbothermic reduction reaction. The reaction conditions are 800℃ for 6 hours. After the reaction is completed, crude lithium sulfide powder can be obtained. XRD analysis results showed that the crude powder contained small amounts of lithium oxide and lithium sulfate impurities, such as... Figure 1 As shown, the crude lithium sulfide contains approximately 6 wt% lithium oxide and approximately 3 wt% lithium sulfate. S3. After crushing the crude lithium sulfide powder obtained in S1, add 5% by mass of ammonium thiosulfate and 5% by mass of thiourea to the total lithium sulfide, and mix thoroughly using a powder mixer to obtain a mixed powder. The mixed powder is placed in a nitrogen atmosphere furnace and calcined in stages. The calcination process conditions are: first, the temperature is raised to 200°C and held for 3 hours, then the temperature is raised to 700°C and held for 3 hours. After calcination, purified lithium sulfide powder can be obtained.

[0029] The purified lithium sulfide powder obtained was ball-milled for further characterization and testing. The ball milling process was performed at a speed of 300 rpm for 6 hours. The purified lithium sulfide phase was pure, with no obvious other impurities. The particle size D of the refined lithium sulfide powder was [not specified]. 50 ≤10μm, the corresponding XRD and SEM are respectively Figure 2 and Figure 3 As shown.

[0030] Furthermore, the combined results of carbon and sulfur analysis and oxygen, nitrogen and hydrogen analysis (as shown in Table 1) indicate that the carbon content is 0.06 wt% and the oxygen content is 0.2 wt%.

[0031] Example 2 A method for preparing lithium sulfide includes the following steps: S1. Weigh 2 kg of lithium sulfate and glucose (calculated as carbon) at a molar ratio of 1:2.9, dissolve in 5 L of deionized water and stir for 5 h. After spray drying and dehydration at 250 °C for 5 h, the precursor is obtained with a particle size D. 90 ≤20μm; S2. The precursor powder in S1 is placed in a nitrogen atmosphere furnace for carbothermic reduction reaction. The reaction conditions are 800℃ for 6 hours. After the reaction is completed, crude lithium sulfide powder can be obtained. XRD analysis showed that the crude powder contained small amounts of lithium oxide and lithium sulfate impurities, with the crude lithium sulfide containing approximately 4% lithium oxide and 3% lithium sulfate. S3. After crushing the crude lithium sulfide powder obtained in S1, add thiourea at a mass fraction of 8% of the total lithium sulfide mass, and mix thoroughly using a powder mixer to obtain a mixed powder. The mixed powder is placed in a nitrogen atmosphere furnace and calcined in stages. The calcination process conditions are: first, the temperature is raised to 180°C and held for 3 hours, then the temperature is raised to 750°C and held for 3 hours. After calcination, purified lithium sulfide powder can be obtained.

[0032] The purified lithium sulfide powder obtained was ball-milled for further characterization and testing. The ball milling process was performed at a speed of 300 rpm for 6 hours. The purified lithium sulfide phase was pure, with no obvious other impurities. The particle size D of the refined lithium sulfide powder was [not specified]. 50 ≤10μm.

[0033] Furthermore, the combined results of carbon and sulfur analysis and oxygen, nitrogen and hydrogen analysis (Table 1) show that the carbon content is 0.05 wt% and the oxygen content is 0.1 wt%.

[0034] Example 3 A method for preparing lithium sulfide includes the following steps: S1. Weigh 2 kg of lithium sulfate and glucose (calculated as carbon) at a molar ratio of 1:3.2, dissolve in 5 L of deionized water and stir for 5 h. After spray drying and dehydration at 250 °C for 5 h, the precursor is obtained with a particle size D. 90 ≤20μm; S2. The precursor powder in S1 is placed in a nitrogen atmosphere furnace for carbothermic reduction reaction. The reaction conditions are 820℃ for 6 hours. After the reaction is completed, crude lithium sulfide powder can be obtained. XRD analysis showed that the crude powder contained small amounts of lithium oxide and lithium sulfate impurities, with the crude lithium sulfide containing approximately 7 wt% lithium oxide and 2 wt% lithium sulfate. S3. After crushing the crude lithium sulfide powder obtained in S1, add 5% by mass of sulfur powder and 5% by mass of ammonium thiocyanate to the total lithium sulfide, and mix thoroughly using a powder mixer to obtain a mixed powder. The mixed powder is placed in a nitrogen atmosphere furnace and calcined in stages. The calcination process conditions are: first, the temperature is raised to 200℃ and held for 3 hours, then the temperature is raised to 780℃ and held for 4 hours. After calcination, purified lithium sulfide powder can be obtained.

[0035] The purified lithium sulfide powder obtained was ball-milled for further characterization and testing. The ball milling process involved a rotation speed of 300 rpm and a milling time of 6 hours. The purified lithium sulfide phase was pure, with no obvious impurities, and the particle size D50 of the refined lithium sulfide powder was ≤10 μm.

[0036] Furthermore, the combined results of carbon and sulfur analysis and oxygen, nitrogen and hydrogen analysis (Table 1) show that the carbon content is 0.07 wt% and the oxygen content is 0.3 wt%.

[0037] Example 4 A method for preparing lithium sulfide includes the following steps: S1. Weigh 2 kg of lithium sulfate and glucose (calculated as carbon) at a molar ratio of 1:3.2, dissolve in 5 L of deionized water and stir for 5 h. After spray drying and dehydration at 250 °C for 5 h, the precursor is obtained with a particle size D. 90 ≤20μm; S2. The precursor powder in S1 is placed in a nitrogen atmosphere furnace for carbothermic reduction reaction. The reaction conditions are 820℃ for 6 hours. After the reaction is completed, crude lithium sulfide powder can be obtained. XRD analysis showed that the crude powder contained small amounts of lithium oxide and lithium sulfate impurities, with the crude lithium sulfide containing approximately 3 wt% lithium oxide and 4 wt% lithium sulfate. S3. After crushing the crude lithium sulfide powder obtained in S1, add 3% by mass of ammonium cyanide sulfide and 4% by mass of thiourea to the total lithium sulfide, and mix thoroughly using a powder mixer to obtain a mixed powder. The mixed powder is placed in a nitrogen atmosphere furnace and calcined in stages. The calcination process conditions are: first, the temperature is raised to 250°C and held for 3 hours, then the temperature is raised to 800°C and held for 4 hours. After calcination, purified lithium sulfide powder can be obtained.

[0038] The purified lithium sulfide powder obtained was ball-milled for further characterization and testing. The ball milling process involved a rotation speed of 500 rpm and a milling time of 4 hours. The purified lithium sulfide phase was pure, with no obvious impurities. The particle size D of the refined lithium sulfide powder was [not specified]. 50 ≤10μm, the corresponding XRD and SEM are respectively Figure 2 and Figure 3 As shown.

[0039] Furthermore, the combined results of carbon and sulfur analysis and oxygen, nitrogen and hydrogen analysis (as shown in Table 1) indicate that the carbon content is 0.07 wt% and the oxygen content is 0.5 wt%.

[0040] Comparative Example 1 A method for preparing lithium sulfide includes essentially the same steps as in Example 1, except that: in step S2, a sulfur-containing compound with the same content as in Example 1 is added for a carbothermal reduction reaction, and the subsequent distributed heat treatment purification step S3 is not required. The results of carbon-sulfur analysis and oxygen-nitrogen-hydrogen analysis are shown in Table 1 below, where the carbon content is 1.2 wt% and the oxygen content is 5.4 wt%.

[0041] Comparative Example 2 A method for preparing lithium sulfide includes steps that are basically the same as in Example 1, except that in S3, the calcination process conditions are: heating to 700℃ and holding for 5 hours, and calcination is completed in one step to obtain lithium sulfide powder. The results of carbon-sulfur analysis and oxygen-nitrogen-hydrogen analysis are shown in Table 1 below, where the carbon content is 0.08 wt% and the oxygen content is 2.2 wt%.

[0042] Comparative Example 3 A method for preparing lithium sulfide includes steps that are essentially the same as in Example 1, except that the amount of sulfur-containing compound used in S3 is 20% of the crude lithium sulfide mass. The results of carbon-sulfur analysis and oxygen-nitrogen-hydrogen analysis are shown in Table 1 below, where the carbon content is 0.16 wt% and the oxygen content is 1.2 wt%.

[0043] Result detection Figure 1 The images show the XRD patterns of crude lithium sulfide powder obtained in the examples and comparative examples. The XRD test results show that there are small amounts of lithium oxide and lithium sulfate impurities in the crude powder.

[0044] Figure 2 The image shows the XRD pattern of the high-purity lithium sulfide powder prepared in Example 1. Figure 3 The image shows a SEM image of the high-purity lithium sulfide powder prepared in Example 1. Figure 2 and Figure 3 As can be seen, the purified lithium sulfide phase is a pure phase with no obvious other impurities.

[0045] The lithium sulfide powders prepared in the above examples and comparative examples were subjected to carbon-sulfur analysis and oxygen-nitrogen-hydrogen analysis, mainly testing the residual amounts of carbon and oxygen elements. The test results are shown in Table 1 below.

[0046] The specific methods for carbon and sulfur analysis and oxygen, nitrogen, and hydrogen analysis are as follows: (1) Carbon and sulfur analysis test: The Li2S to be tested is weighed and mixed with flux (such as tin granules, used to lower the melting point and promote complete combustion), and placed in a high-temperature resistant crucible. Then it is placed in a high-frequency induction furnace and heated to 1200~1500℃ in a pure oxygen atmosphere to completely oxidize the carbon in the sample to CO2. By taking advantage of the characteristic absorption of CO2 by infrared light of a specific wavelength, and combining the calculation formula that absorbance is proportional to concentration, the carbon content in the sample can be quantitatively detected.

[0047] (2) Oxygen, nitrogen and hydrogen analysis test: The Li2S to be tested is weighed and placed in a graphite crucible. Under a high-purity helium (He) atmosphere, it is heated to 2000~3000℃ by high-frequency induction heating, and then melted and decomposed to release gas. CO / CO2 generated by the reaction of oxygen with graphite in the sample is separated by chromatographic column. Based on the same principle, the oxygen content in the sample can be quantitatively detected.

[0048] The weighing and transfer of Li2S were all carried out under an argon atmosphere.

[0049] Based on the carbon and oxygen content in the comparative examples, it can be seen that the carbon and oxygen content in Comparative Example 1 is relatively high, indicating that the addition of sulfur compounds directly in the carbothermic reaction stage did not have the effect of suppressing the impurity phase, which may be related to the decomposition or volatilization of sulfur compounds in the low-temperature stage; while the oxygen content in Comparative Example 2 is relatively high, which can be attributed to the absence of a low-temperature holding stage, resulting in the incomplete conversion of the lithium oxide impurity phase; in Comparative Example 3, the introduction of excessive sulfur compounds resulted in a certain increase in both the carbon and oxygen content in the comparative examples, which may be related to the carbon and oxygen elements in the organic carbon source of the introduced sulfur compounds.

[0050] Table 1. Results of carbon and oxygen content determination of lithium sulfide in the examples and comparative examples

[0051] (Lithium sulfide purity = 100% - carbon content - oxygen content) Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing battery-grade lithium sulfide, characterized in that, Includes the following steps: S1: Lithium sulfate and an organic carbon source are wet-mixed and then dehydrated to obtain the precursor; S2: The precursor obtained in S1 is carbothermally reduced to obtain crude lithium sulfide; S3: The crude lithium sulfide product of S2 is mixed with a sulfur-containing compound to obtain a mixture, and the mixture is calcined to obtain purified lithium sulfide; The calcination described in S3 is a two-step calcination, firstly, holding at 150-250℃ for 2-5 hours, and then holding at 600-800℃ for 2-5 hours; The sulfur-containing compound mentioned in S3 is selected from one or more of elemental sulfur, thiourea, ammonium thiosulfate, ammonium hydrogen sulfide, and ammonium thiocyanate, and the mass of the sulfur-containing compound is 10% or less of the crude lithium sulfide mass.

2. The method for preparing battery-grade lithium sulfide according to claim 1, characterized in that, The molar ratio of lithium sulfate and organic carbon source (based on carbon element) in S1 is 1:2.8~3.

2.

3. The method for preparing battery-grade lithium sulfide according to claim 2, characterized in that, The dehydration treatment described in S1 is carried out at a temperature of 200~300℃ for 3~6 hours.

4. The method for preparing battery-grade lithium sulfide according to claim 1, characterized in that, The carbothermic reduction reaction described in S2 is carried out at a temperature of 700~850℃ for 5~10h.

5. The method for preparing battery-grade lithium sulfide according to claim 4, characterized in that, The crude lithium sulfide product described in S2 has a lithium sulfate content of less than or equal to 4 wt% and a lithium oxide content of less than or equal to 7 wt%.

6. The method for preparing battery-grade lithium sulfide according to claim 1, characterized in that, The mass of the sulfur-containing compound mentioned in S3 is 5 to 10% of the mass of crude lithium sulfide.

7. The method for preparing battery-grade lithium sulfide according to any one of claims 1 to 6, characterized in that, The carbothermic reduction reaction in S2 and the calcination described in S3 are both carried out in a nitrogen or argon atmosphere.

8. A battery-grade lithium sulfide prepared by the method according to any one of claims 1 to 7.

9. The battery-grade lithium sulfide according to claim 8, characterized in that, The battery-grade lithium sulfide is a pure phase, wherein the carbon content is less than or equal to 0.07 wt% and the oxygen content is less than or equal to 0.5 wt%.

10. The use of the battery-grade lithium sulfide of claim 8 or 9 in the preparation of a solid electrolyte.

Images