Synthesis method of nanoscale lithium sulfide

Abstract

The invention provides a synthesis method of nanoscale lithium sulfide, and relates to the technical field of lithium sulfide synthesis. The synthesis method provided by the invention comprises the following steps: stirring and dissolving a lithium sulfide raw material in an alcohol solvent, and separating to obtain a lithium sulfide alcohol solution; evaporating, crystallizing and drying the lithium sulfide alcohol solution to obtain lithium sulfide crystals; and mixing the lithium sulfide crystals with a sulfur source, and firing at 550-850 DEG C to obtain the nanoscale lithium sulfide. The nanoscale lithium sulfide is directly synthesized in one step through a solid-phase sintering method, the operation method is simple, the cost is low, and large-scale industrial production can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium sulfide synthesis, and particularly to a method for synthesizing nanoscale lithium sulfide. Background Art

[0002] Since the advent of lithium-ion batteries, due to their characteristics such as high cycle life and high energy density, they have been widely used in portable electronic devices such as cameras, laptops, mobile phones, and power tools. In recent years, with the update and iteration of lithium-ion batteries, they have even been applied to the field of new energy vehicles. However, with the rapid development of the new energy vehicle industry, problems such as the vehicle's cruising range, charging time, and safety have become key factors restricting its further development. Therefore, it is particularly important to develop the next-generation battery technology with high energy density. Lithium-sulfur batteries and all-solid-state batteries are considered to be one of the most promising directions in future battery technologies due to their high energy density. As the active cathode material of lithium-sulfur batteries and the key raw material for synthesizing solid electrolytes, lithium sulfide has broad market demand and application prospects and has received extensive attention.

[0003] It is reported that as the cathode material of lithium-sulfur batteries, the purity of lithium sulfide needs to reach more than 99.9%, which helps to reduce the adverse effects of impurities on battery performance, reduce the capacity attenuation of the battery, and extend the cycle life. In addition, the particle size of lithium sulfide should reach the nanoscale. Nanoscale lithium sulfide has a larger specific surface area, which is conducive to the contact between the electrolyte and the electrode, can effectively promote the intercalation and deintercalation processes of lithium ions, thereby improving the lithium ion transport rate and the charge-discharge performance of the battery. For the currently much-concerned sulfide-based all-solid-state batteries, the ionic conductivity of lithium sulfide in the solid electrolyte plays a crucial role and is one of the key factors determining the performance of all-solid-state batteries. Therefore, the quality requirements for lithium sulfide materials are extremely high, especially the influence of its purity and particle size on battery performance is particularly significant.

[0004] Existing methods for preparing lithium sulfide have some deficiencies. Many methods cannot prepare lithium sulfide products with high purity, and there is a lot of moisture in the reaction process, resulting in easy agglomeration of the products and larger particle sizes. In addition, the production process is complex, the requirements for equipment are high, and it is difficult to achieve large-scale production. Currently, the preparation of nanoscale lithium sulfide mainly relies on wet ball milling technology. This method not only has high requirements for equipment, a cumbersome operation process, but also the obtained lithium sulfide has low purity and high cost. Therefore, there is an urgent need to provide a solution to improve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for synthesizing nanoscale lithium sulfide.

[0006] A method for synthesizing nanoscale lithium sulfide provided by the present invention includes: stirring and dissolving a lithium sulfide raw material in an alcohol solvent and then separating to obtain a lithium sulfide alcohol solution; performing evaporation crystallization on the lithium sulfide alcohol solution and drying to obtain lithium sulfide crystals; mixing the lithium sulfide crystals with a sulfur source and firing at 550°C - 850°C to obtain nanoscale lithium sulfide.

[0007] Optionally, the alcohol solvent includes one of ethanol, methanol, ethylene glycol, propylene glycol, isopropanol, and n-butanol.

[0008] Optionally, the lithium sulfide raw material includes industrially produced lithium sulfide products and lithium sulfide products containing impurities.

[0009] Optionally, evaporation crystallization is performed on the lithium sulfide alcohol solution at 100°C - 150°C.

[0010] Optionally, evaporation crystallization is performed on the lithium sulfide alcohol solution in an ultrasonic environment.

[0011] Optionally, evaporation crystallization is performed on the lithium sulfide alcohol solution in an evaporation reaction kettle, a continuous oscillating baffle crystallizer, a vertical conical crystallizer, or a rotary evaporator.

[0012] Optionally, drying is performed at 200°C - 350°C after evaporation crystallization.

[0013] Optionally, drying is performed under vacuum or in an inert atmosphere.

[0014] Optionally, drying is performed for 5h - 10h after evaporation crystallization.

[0015] Optionally, evaporation crystallization is followed by evaporation to constant weight.

[0016] Optionally, the sulfur source includes one of sulfur, thiol compounds, thiophenol compounds, thioether compounds, thiacarboxylic acid compounds, thioamide compounds, and thiocyanate compounds.

[0017] Optionally, the thiol compounds include isobutanethiol, ethanedithiol, or dodecanethiol.

[0018] Optionally, the thiophenol compounds include tolyl mercaptan or naphthyl mercaptan.

[0019] Optionally, the thioether compounds include dibenzyl sulfide or diethyl sulfide.

[0020] Optionally, the thiacarboxylic acid compounds include thiobenzoic acid.

[0021] Optionally, the thioamide compounds include thiourea or thioacetamide.

[0022] Optionally, the thiocyanate compounds include ammonium thiocyanate.

[0023] Optionally, the lithium sulfide crystals are mixed with a sulfur source in a powder grinder, a high-speed mixer, a ball mill or a roller mill.

[0024] Optionally, the mass ratio of lithium sulfide to the sulfur source is 100:(5 - 30).

[0025] Optionally, the lithium sulfide crystals and the sulfur source are mixed and ground to a particle size of 50 nm - 1000 nm.

[0026] Optionally, after mixing, the temperature is raised to 550°C - 850°C at a rate of 2°C / min - 20°C / min for firing.

[0027] Optionally, after mixing, it is fired at 550°C - 850°C for 2 h - 5 h.

[0028] Optionally, after firing at 550°C - 850°C, it is cooled to room temperature to obtain nanoscale lithium sulfide.

[0029] Optionally, the particle size of the nanoscale lithium sulfide is 200 nm - 800 nm.

[0030] Optionally, the firing is carried out in an inert gas at 550°C - 850°C.

[0031] Optionally, the inert gas includes nitrogen, helium or argon.

[0032] Optionally, the flow rate of the inert gas is 2 mL / s - 8 mL / s.

[0033] Optionally, the firing is carried out in an inert gas at 550°C - 850°C and 0.8 atm. - 1.5 atm.

[0034] Optionally, the firing is carried out in a vacuum environment at 550°C - 850°C, and the vacuum degree of the vacuum environment is greater than 0.08 MPa.

[0035] The synthesis method of nanoscale lithium sulfide provided by the present invention has at least one of the following beneficial technical effects compared with the prior art: 1. The nanoscale lithium sulfide is directly synthesized in one step by the solid-phase sintering method, with simple operation method, low cost, and can be mass-produced industrially; 2. By dissolving the lithium sulfide raw material in an alcohol solvent, not only can the lithium sulfide be purified, but also more uniform nucleation sites can be formed during the evaporation drying and recrystallization processes, thereby promoting the precipitation of more fine lithium sulfide crystals; 3. By adding lithium sulfide, the formation of organolithium compounds during the sintering process can be effectively inhibited, impurities can be effectively avoided, and the purity of the lithium sulfide nanoparticles can be ensured. Description of the Drawings

[0036] Figure 1Flow chart of a method for synthesizing nanoscale lithium sulfide provided by the present invention; Figure 2 X-ray diffraction patterns of lithium sulfide in Examples 1 to 3 of the present invention; Figure 3 SEM image of the nanoscale lithium sulfide prepared in Example 1 of the present invention; Figure 4 SEM image of the nanoscale lithium sulfide prepared in Example 2 of the present invention; Figure 5 SEM image of the nanoscale lithium sulfide prepared in Example 3 of the present invention; Figure 6 X-ray diffraction pattern of the nanoscale lithium sulfide prepared in Comparative Example 1 of the present invention; Figure 7 X-ray diffraction pattern of the nanoscale lithium sulfide prepared in Comparative Example 2 of the present invention; Figure 8 X-ray diffraction pattern of the nanoscale lithium sulfide prepared in Comparative Example 3 of the present invention; Figure 9 Appearance comparison diagrams of Example 1, Comparative Examples 1 to 3 of the present invention. Detailed implementation manners

[0037] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein shall have the ordinary meanings understood by those of ordinary skill in the art to which the present invention belongs.

[0038] See Figure 1 , the present invention provides a method for synthesizing nanoscale lithium sulfide, including the following steps: S1. Stir and dissolve the lithium sulfide raw material in an alcohol solvent, and then separate to obtain a lithium sulfide alcohol solution; S2. Perform evaporation crystallization on the lithium sulfide alcohol solution and then dry it to obtain lithium sulfide crystals; S3. Mix the lithium sulfide crystals with a sulfur source and sinter at 550°C - 850°C to obtain nanoscale lithium sulfide.

[0039] In fact, for the synthesis method provided by the present invention, by utilizing the good solubility of the alcohol solvent in lithium sulfide, the lithium sulfide substance in the lithium sulfide raw material can be purified. At the same time, solid lithium sulfide crystals are obtained through evaporation crystallization, and nanoscale sulfide substances are obtained through a one-time sintering process after sufficient mixing with the sulfur source.

[0040] Actually, the alcohol solvent used in step S1 includes one of ethanol, methanol, ethylene glycol, propylene glycol, isopropanol, and n-butanol. Through the dissolution of the alcohol solvent, the insoluble substances in the lithium sulfide raw material can be separated, and at the same time, a pure lithium sulfide alcohol solution can be obtained. Specifically, when stirring and separating, in order to improve the dissolution rate of the lithium sulfide raw material, common dissolution-promoting means in the art can be adopted, such as stirring, oscillation, heating, etc.

[0041] In some embodiments, the lithium sulfide raw material used in step S1 includes industrially produced lithium sulfide products or lithium sulfide products containing impurities. In fact, the method provided by the present invention can not only purify the lithium sulfide product, but also reduce the particle size of the lithium sulfide product. For example, micron-sized lithium sulfide can be transformed into nano-sized lithium sulfide. Specifically, when the lithium sulfide raw material is a lithium sulfide product containing impurities, the impurities may be lithium compounds such as lithium carbonate, lithium sulfate, lithium hydroxide, and lithium oxide.

[0042] In some embodiments, it is necessary for the alcohol solvent used in step S1 to be able to dissolve the lithium sulfide in the lithium sulfide raw material. In fact, when the impurities in the lithium sulfide raw material are insoluble in the alcohol solvent, an excessive amount of alcohol solvent can be added to improve the purification efficiency and reduce the concentration of lithium sulfide in the alcohol solution to obtain fine lithium sulfide crystal precipitation. In some embodiments, after stirring and dissolving the lithium sulfide raw material in the alcohol solvent in step S1, common solid-liquid separation means such as suction filtration and filtration can be used to separate the lithium sulfide alcohol solution.

[0043] Actually, when performing step S2, the lithium sulfide alcohol solution can be evaporated and crystallized at a temperature below 150°C. Thereby, not only can the precipitation of lithium sulfide crystals be promoted, but also the growth of crystals can be inhibited, so that a large number of lithium sulfide particles with small sizes and uniform distribution can be accumulated during the evaporation process. Specifically, in order to balance the evaporation crystallization rate and the crystal morphology, the evaporation crystallization can be carried out at 100°C - 150°C.

[0044] In some embodiments, when performing step S2, ultrasonic treatment can be applied during the evaporation crystallization process, so that the lithium sulfide alcohol solution is evaporated and crystallized under an ultrasonic environment. In fact, through ultrasonic treatment, the ultrasonic cavitation effect can be effectively utilized to further reduce the nucleation size, promote the formation of more nucleation sites, and inhibit the in-situ growth of crystals.

[0045] Specifically, when performing step S2 industrially, the lithium sulfide alcohol solution can be evaporated and crystallized in an evaporation reaction kettle, a continuous oscillating baffle crystallizer, a vertical conical crystallizer, or a rotary evaporator. In fact, the existing evaporation equipment in industry can be used to evaporate and crystallize the lithium sulfide alcohol solution, and at the same time, the obtained alcohol solvent can be recycled and reused.

[0046] Actually, after evaporation crystallization and drying in step S2, the cleanliness and dryness of lithium sulfide crystallization can be further improved, effectively avoiding the formation of organolithium compounds during subsequent sintering and enhancing the purity of nanoscale lithium sulfide products. Specifically, drying can be carried out at 200°C - 350°C for 5h - 10h until constant weight. In addition, drying treatment can also be carried out under vacuum or inert atmosphere.

[0047] Actually, after adding the sulfur source in step S3, during the heating and sintering process, the sulfur source melts and covers the surface of lithium sulfide crystallization, which can not only effectively inhibit the further growth of lithium sulfide crystallization but also effectively inhibit the formation of organolithium compounds, avoiding the generation of impurities during high-temperature sintering. Specifically, in step S3, the mass ratio of lithium sulfide to the sulfur source is 100:(5 - 30).

[0048] Specifically, the sulfur source used includes one of sulfur, thiol compounds, thiophenol compounds, thioether compounds, thiocarboxylic acid compounds, thioamide compounds, and thiocyanic acid compounds. Further, the thiol compounds include isobutanethiol, ethanedithiol, or dodecanethiol; the thiophenol compounds include tolyl mercaptan or naphthyl mercaptan; the thioether compounds include dibenzyl sulfide or diethyl sulfide; the thiocarboxylic acid compounds include thiobenzoic acid; the thioamide compounds include thiourea or thioacetamide; and the thiocyanic acid compounds include ammonium thiocyanate.

[0049] In some embodiments, when performing step S3, the lithium sulfide crystallization and the sulfur source can be mixed, which is beneficial to improving the dispersion uniformity of the sulfur source and further beneficial to the melting of the sulfur source and the coverage of the lithium sulfide crystallization during high-temperature sintering. Specifically, the lithium sulfide crystallization and the sulfur source can be ground and mixed in equipment such as a powder mill, high-speed mixer, ball mill, or roller mill to a particle size of 50nm - 1000nm.

[0050] Actually, in step S3, the mixed lithium sulfide crystallization and sulfur source are heated to 550°C - 850°C at a rate of 2°C / min - 20°C / min for firing for 2h - 5h and then cooled to room temperature to obtain nanoscale lithium sulfide of 200nm - 800nm. In some embodiments, firing can be carried out in an inert gas (including nitrogen, helium, or argon) at 550°C - 850°C and 0.8atm. - 1.5atm., and the flow rate of the inert gas can also be controlled at 2mL / s - 8mL / s. In some embodiments, firing can also be carried out in a vacuum environment (vacuum degree greater than 0.08MPa) at 550°C - 850°C.

[0051] Example 1 This Example 1 provides a method for synthesizing nanoscale lithium sulfide, including the following steps: S1. Add 100 g of deteriorated lithium sulfide raw material containing impurities (the impurities are lithium carbonate, lithium sulfate, lithium hydroxide, and lithium oxide) into 5000 mL of anhydrous ethanol, stir and dissolve, and filter and separate to obtain a lithium sulfide alcohol solution; S2, performing rotary evaporation concentration and crystallization on the lithium sulfide alcohol solution at 120° C. and recovering anhydrous ethanol, transferring the obtained crystals to a vacuum oven at 250° C. and keeping the temperature for 8 hours, and cooling the oven to room temperature to obtain lithium sulfide crystals; S3. The lithium sulfide crystals and sulfur element with a mass fraction of 30% are fully mixed in a mixer and loaded into a crucible. The mixture is heated to 600°C at a rate of 10°C / min in an argon flow at a flow rate of 5 mL / s and sintered for 2 hours. The mixture is then cooled to room temperature to obtain lithium sulfide with a primary particle size of 500 nm.

[0052] Example 2 This embodiment 2 provides a method for synthesizing nanoscale lithium sulfide, comprising the following steps: S0, 278.6g of lithium sulfate monohydrate and 261.4g of glucose were mixed uniformly in a mixer at a speed of 28000rpm and then loaded into an alumina crucible, and the crucible was transferred to a tubular furnace in an argon atmosphere, heated to 850°C at a rate of 5°C / min and calcined at a constant temperature for 5h, and then cooled to room temperature with the furnace, and the crucible was transferred to a glove box with a water and oxygen content of less than 0.1ppm to grind the material in the crucible to obtain a lithium sulfide raw material; S1. Add the lithium sulfide raw material into 5000 mL of anhydrous ethanol, stir and dissolve, and then filter and separate to obtain a lithium sulfide alcohol solution; S2, performing rotary evaporation concentration and crystallization on the lithium sulfide alcohol solution at 120° C. and recovering anhydrous ethanol, transferring the obtained crystals to a vacuum oven at 250° C. and keeping the temperature for 8 hours, and cooling the oven to room temperature to obtain lithium sulfide crystals; S3. The lithium sulfide crystals and sulfur element with a mass fraction of 30% are fully mixed in a mixer and loaded into a crucible. The mixture is heated to 600°C at a rate of 10°C / min in a vacuum environment and sintered for 2 hours. The mixture is then cooled to room temperature to obtain lithium sulfide with a primary particle size of 200 nm.

[0053] Example 3 This embodiment 3 provides a method for synthesizing nanoscale lithium sulfide, comprising the following steps: S0, 300 g of anhydrous lithium sulfate powder with an average particle size of 0.1 μm was loaded into an alumina boat, and the temperature was raised to 780° C. at a rate of 10° C. / min in a mixed atmosphere of hydrogen and carbon monoxide and kept warm for 5 hours, then cooled to room temperature with the furnace, and the alumina boat was transferred to a glove box with a water and oxygen content of less than 0.1 ppm to grind the material in the crucible to obtain a lithium sulfide raw material; S1. Add the lithium sulfide raw material into 5000 mL of anhydrous methanol, stir and dissolve, and then filter and separate to obtain a lithium sulfide alcohol solution; S2, performing rotary evaporation concentration and crystallization on the lithium sulfide alcohol solution at 120° C. and recovering anhydrous methanol, transferring the obtained crystals to a vacuum oven at 250° C. and keeping the temperature for 8 hours, and cooling the oven to room temperature to obtain lithium sulfide crystals; S3. The lithium sulfide crystals and 10% by mass thiourea are fully mixed in a mixer and loaded into a crucible. The mixture is heated to 600°C at a rate of 10°C / min in a vacuum environment and sintered for 2 hours. The mixture is then cooled to room temperature to obtain lithium sulfide with a primary particle size of 800 nm.

[0054] Comparative Example 1 Comparative Example 1 provides a method for synthesizing nano-scale lithium sulfide, which is different from Example 1 in that in step S2, the temperature is kept in a vacuum oven at 350°C for 8 hours.

[0055] Comparative Example 2 This comparative example 2 provides a method for synthesizing nano-scale lithium sulfide, which is different from that of example 1 in that the amount of sulfur added in step S3 is 10%.

[0056] Comparative Example 3 Comparative Example 3 provides a method for synthesizing nano-scale lithium sulfide, which is different from Example 1 in that the crystals obtained in step S2 are not dried.

[0057] Structural characterization The nanoscale lithium sulfide obtained in Examples 1 to 3 was characterized by XRD. Figure 2 As shown, SEM characterization was performed as Figures 3 to 5 As shown. Figure 2 It can be seen that compared with the lithium sulfide standard card (77-2145), the nanoscale lithium sulfide prepared in Examples 1 to 3 is a pure lithium sulfide phase, while Figures 3 to 5 It can be seen that the lithium sulfide synthesized in Examples 1 to 3 has a nanoscale structure.

[0058] The nanoscale lithium sulfide in Comparative Examples 1 to 3 was characterized by XRD as follows: Figures 6 to 8 As shown, the appearance of the nanoscale lithium sulfide obtained in Example 1 and Comparative Examples 1 to 3 is compared. Figure 9 shown.

[0059] from Figure 6 and Figure 9It can be seen that in the lithium sulfide prepared in Comparative Example 1, there is a lithium carbonate impurity phase, the product agglomerates and is brownish-yellow. This is because after increasing the drying temperature, ethanol reacts with lithium sulfide to form lithium hydroxide, and during the firing process, lithium hydroxide reacts with sulfur to form lithium carbonate. At the same time, the volatilization of internal ethanol makes it difficult to ensure the growth of lithium sulfide in the expected direction during the subsequent firing process, resulting in agglomeration and making it difficult to obtain high-purity nanoscale sulfides.

[0060] It can be seen from Figure 7 and Figure 9 that the lithium sulfide prepared in Comparative Example 2 is similar to that in Comparative Example 1, both having a lithium carbonate impurity phase, the product agglomerating and being brownish-gray. This is because the decrease in the addition amount of sulfur fails to effectively inhibit the reaction between ethanol and lithium sulfide, resulting in the appearance of an organolithium impurity phase, and lithium carbonate is formed after calcination.

[0061] It can be seen from Figure 8 and Figure 9 that in the lithium sulfide prepared in Comparative Example 3, due to the failure to perform deep ethanol removal, ethanol cannot be quickly discharged during the heating process, resulting in carburization, and the product is blackish-gray, making it difficult to obtain high-purity nanoscale lithium sulfide.

[0062] Although the embodiments of the present invention have been described in detail above, it is obvious to those skilled in the art that various modifications and changes can be made to these embodiments. However, it should be understood that such modifications and changes are all within the scope and spirit of the present invention described in the claims. Moreover, the present invention described herein can have other embodiments and can be implemented or realized in various ways.

Claims

1. A method for synthesizing nanoscale lithium sulfide, characterized in that: include: The lithium sulfide raw material is stirred and dissolved in an alcohol solvent and then separated to obtain a lithium sulfide alcohol solution; The lithium sulfide alcohol solution is evaporated and crystallized and then dried to obtain lithium sulfide crystals; The lithium sulfide crystals are mixed with a sulfur source and then fired at 550°C-850°C to obtain nano-scale lithium sulfide.

2. The synthesis method according to claim 1, characterized in that The alcohol solvent includes one of ethanol, methanol, ethylene glycol, propylene glycol, isopropanol and n-butanol; and / or the lithium sulfide raw material includes industrially produced lithium sulfide products and lithium sulfide products containing impurities.

3. The synthesis method according to claim 1, characterized in that The lithium sulfide alcohol solution is evaporated and crystallized at 100° C.-150° C.; and / or, the lithium sulfide alcohol solution is evaporated and crystallized in an ultrasonic environment; and / or, the lithium sulfide alcohol solution is evaporated and crystallized in an evaporation reactor, a continuous oscillating baffle crystallizer, a vertical conical crystallizer or a rotary evaporator.

4. The synthesis method according to claim 1, characterized in that After evaporation and crystallization, drying is performed at 200°C-350°C; and / or, drying is performed under vacuum or inert atmosphere; and / or, drying is performed for 5h-10h after evaporation and crystallization; and / or, evaporation and crystallization is evaporated to constant weight.

5. The synthesis method according to claim 1, characterized in that The sulfur source includes one of elemental sulfur, thiol compounds, thiophenol compounds, thioether compounds, thiocarboxylic acid compounds, thioamide compounds, and thiocyanate compounds.

6. The synthesis method according to claim 5, characterized in that The thiol compound includes isobutyl thiolate, ethanedithiol or dodecanethiol; and / or, the thiophenol compound includes toluene thiophenol or naphthiophenol; and / or, the thioether compound includes dibenzyl sulfide or diethyl sulfide; and / or, the thiocarboxylic acid compound includes thiobenzoic acid; and / or, the thioamide compound includes thiourea or thioacetamide; and / or, the thiocyanate compound includes ammonium thiocyanate.

7. The synthesis method according to claim 1, characterized in that The lithium sulfide crystals and the sulfur source are mixed in a powder mill, a high-speed mixer, a ball mill or a roller mill; and / or, the mass ratio of lithium sulfide to the sulfur source is 100:(5-30); and / or, the lithium sulfide crystals and the sulfur source are mixed and ground to a particle size of 50nm-1000nm.

8. The synthesis method according to claim 1, characterized in that After mixing, the temperature is raised to 550°C-850°C at a rate of 2°C / min-20°C / min for firing; and / or, after mixing, the mixture is fired at 550°C-850°C for 2h-5h; and / or, after firing at 550°C-850°C, the mixture is cooled to room temperature to obtain nano-scale lithium sulfide; and / or, the particle size of the nano-scale lithium sulfide is 200nm-800nm.

9. The synthesis method according to claim 1, characterized in that The firing is carried out in an inert gas at 550°C-850°C; wherein: the inert gas includes nitrogen, helium or argon, and / or, the flow rate of the inert gas is 2mL / s-8mL / s; and / or, the firing is carried out in an inert gas at 550°C-850°C and 0.8atm.-1.5atm.

10. The synthesis method according to claim 1, characterized in that The firing is carried out in a vacuum environment at 550° C.-850° C., and the vacuum degree of the vacuum environment is greater than 0.08 MPa.

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