Method for preparing high-purity lithium sulfide based on solution double decomposition method

Abstract

The invention discloses a method for preparing high-purity lithium sulfide based on a solution double decomposition method, and belongs to the technical field of battery materials, and the method comprises the following steps: adding lithium chloride and sodium sulfide into ethanol, mixing, and reacting in the mixing process to generate lithium sulfide; performing solid-liquid separation on the reaction system to obtain a solid product; washing the solid product with tetrahydrofuran and drying; and continuously introducing inert gas into the heat treatment chamber to purge a solid product in the heat treatment chamber, carrying out heat treatment on the solid product under the conditions of 200-300 DEG C and 10-1000 Pa, and removing complex impurities in the solid product to obtain the high-purity lithium sulfide. Compared with the prior art, the method has the advantages that the Li2S.EtOH impurity in the lithium sulfide is removed, the lithium carbonate impurity generated by the reaction of the impurity at high temperature is reduced, and the risk of electrolyte and battery performance is further reduced.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to a method for preparing high-purity lithium sulfide based on solution metathesis. Background Technology

[0002] High-purity lithium sulfide (Li₂S) is a key lithium source material for preparing sulfide solid electrolytes, and its purity and properties directly affect the performance of solid-state batteries. Existing lithium sulfide preparation processes, such as the lithium sulfide preparation process disclosed in patent document CN114455549B, typically involve adding lithium and sulfur compounds to an ethanol solvent, reacting thoroughly, centrifuging the suspension to collect the precipitate, washing with dimethyl sulfoxide to remove lithium chloride impurities, washing with tetrahydrofuran to remove sodium chloride impurities, and then heat-treating the material at 700°C to eliminate lattice defects caused by rapid precipitation, transforming the metastable crystalline phase of lithium sulfide into a stable crystalline phase, thus ensuring the long-term stability of the electrolyte's electrochemical performance.

[0003] However, this preparation process overlooks the fact that lithium sulfide and ethanol form a complex (Li₂S·EtOH). During the high-temperature heat treatment in the lithium sulfide preparation process and the high-temperature heat treatment in the lithium sulfide electrolyte preparation process (Li₂S, P₂S₅, LiCl solid-state reaction to generate the cubic crystalline phase Li₆PS₅Cl with fast ion conductivity), this complex thermally decomposes to generate water and carbon dioxide, ultimately forming lithium carbonate impurities. Lithium carbonate has strong thermal stability and is the most difficult and persistent impurity to remove in sulfide electrolytes. It forms a passivation layer at the electrolyte-electrode interface, reducing the ionic conductivity of the electrolyte and increasing the battery interface impedance.

[0004] Therefore, how to remove Li2S·EtOH impurities from lithium sulfide and reduce the risk of these impurities generating lithium carbonate impurities at high temperatures, thereby affecting the electrolyte and battery performance, has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing high-purity lithium sulfide based on solution metathesis, so as to solve the above-mentioned technical problems.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing high-purity lithium sulfide based on solution metathesis includes the following steps: S100, a lithium compound and a sulfur compound are added to ethanol and mixed to obtain a first mixture, wherein the lithium compound is lithium chloride and / or its hydrate, and the sulfur compound is sodium sulfide and / or its hydrate, and during the mixing process, the lithium compound and the sulfur compound react to generate lithium sulfide; S200, the first mixture is subjected to solid-liquid separation to obtain a solid product; S300, washing the solid product; the process for washing the solid product is S320, washing the solid product with tetrahydrofuran. S400, the solid product after drying and washing; S500, the dried solid product is placed in a heat treatment chamber, and inert gas is continuously introduced into the heat treatment chamber to purge the solid product. The solid product is heat-treated under a first preset temperature and a first preset pressure to remove complex impurities from the solid product and obtain high-purity lithium sulfide. The first preset temperature is 200-300℃ and the first preset pressure is 10-1000Pa.

[0007] Preferably, in S100, the lithium compound is lithium chloride, and the sulfur compound is sodium sulfide nonahydrate.

[0008] Preferably, the molar ratio of the lithium compound to the sulfur compound is (2-2.3):1.

[0009] Preferably, in step S100, solid lithium compounds and sulfur compounds are added to liquid ethanol at a liquid-to-solid ratio of 10-30 mL / g, and the mixture is stirred for 20-40 minutes to obtain a first mixture.

[0010] Preferably, in step S200, the process for solid-liquid separation of the first mixture is as follows: Centrifuge the first mixture at 7000-9000 rpm for 8-15 minutes and collect the centrifuged precipitate as a solid product.

[0011] Preferably, in step S400, the process for drying the solid product is as follows: The solid product is subjected to reduced pressure rotary evaporation to remove residual solvent.

[0012] Preferably, in step S400, the solid product is subjected to reduced pressure rotary evaporation treatment at a second preset temperature and a second preset pressure, at a second preset rotation speed and for a second preset duration, to remove residual solvent from the solid product. The second preset temperature is 40-60°C, the second preset pressure is 0.09-0.1 MPa lower than the standard atmospheric pressure, the second preset rotation speed is 80-120 rpm, and the second preset duration is 20-40 minutes.

[0013] Preferably, in S500, the solid product is heat-treated in an inert gas environment at a first preset temperature and a first preset pressure for a first preset time to obtain high-purity lithium sulfide, wherein the first preset time is 100-150 minutes.

[0014] Preferably, in S500, the first preset pressure is 50-300 Pa.

[0015] Lithium ions (Li) are obtained from the weak dissociation of lithium sulfide. + The oxygen combines with the hydroxyl groups (-OH) of 1-2 ethanol molecules, and the lone pair of electrons of oxygen is transferred to the empty orbitals of lithium, forming a semi-coordinate bond such as a lithium bond, thus forming [Li(EtOH)]. X ] + • [LiS] - Such a semi-coordinate structure or its polymeric structure is hereinafter referred to as the Li₂S·EtOH complex. The solid product obtained by this invention through low-temperature (200-300℃) and low-pressure (10-1000Pa) thermal treatment has low lithium bond energies. The low-temperature thermal treatment at 200-300℃ can break these weak interactions, disintegrate the complex, and allow ethanol to evaporate and desorb in its intact molecular form, restoring the complex to its lithium sulfide compound structure. The product after thermal treatment can be directly used as the high-purity lithium sulfide, or it can undergo necessary post-processing. At this point, the Li₂S·EtOH complex impurities in the lithium sulfide have been sufficiently removed. The temperature of the lithium sulfide preparation process or the post-processing process for preparing the electrolyte can be arbitrarily adjusted according to actual needs, without the formation of lithium carbonate impurities due to the reaction of the complex at high temperatures, which would adversely affect the ionic conductivity performance of the electrolyte and battery.

[0016] In summary, compared with the prior art, the present invention can remove Li2S·EtOH impurities from lithium sulfide, reducing the risk that these impurities will generate lithium carbonate impurities at high temperatures, thereby affecting the electrolyte and battery performance. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings: Figure 1 A process flow diagram for preparing high-purity lithium sulfide based on solution metathesis method provided in this application; Figure 2 The image shows the XRD analysis results of the high-purity lithium sulfide prepared in Example 1. Figure 3 The images show the EDS analysis results and SEM images of the high-purity lithium sulfide prepared in Example 1. Figure 4 The graph shows the ionic conductivity test results of the electrolyte prepared using high-purity lithium sulfide in Example 1 and the commercially available electrolyte. Figure 5 The image shows the XRD analysis results of lithium sulfide prepared in Comparative Example 1. Figure 6 The image shows the EDS analysis results of lithium sulfide prepared in Comparative Example 1. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0019] This invention provides a method for preparing high-purity lithium sulfide based on solution metathesis, comprising the following steps: S100, a lithium compound and a sulfur compound are added to ethanol and mixed to obtain a first mixture, wherein the lithium compound is lithium chloride and / or its hydrate, and the sulfur compound is sodium sulfide and / or its hydrate, and during the mixing process, the lithium compound and the sulfur compound react to generate lithium sulfide; S200, the first mixture is subjected to solid-liquid separation to obtain a solid product; S300, washing the solid product; the process for washing the solid product is S320, washing the solid product with tetrahydrofuran. S400, the solid product after drying and washing; S500, the dried solid product is placed in a heat treatment chamber, and inert gas is continuously introduced into the heat treatment chamber to purge the solid product. The solid product is heat-treated under a first preset temperature and a first preset pressure to remove complex impurities from the solid product and obtain high-purity lithium sulfide. The first preset temperature is 200-300℃ and the first preset pressure is 10-1000Pa.

[0020] Lithium ions (Li) are obtained from the weak dissociation of lithium sulfide. + The oxygen combines with the hydroxyl groups (-OH) of 1-2 ethanol molecules, and the lone pair of electrons of oxygen is transferred to the empty orbitals of lithium, forming a semi-coordinate bond such as a lithium bond, thus forming [Li(EtOH)]. X ] + • [LiS] -Such a semi-coordinate structure or its polymeric structure is hereinafter referred to as the Li₂S·EtOH complex. The solid product obtained by this invention through low-temperature (200-300℃) and low-pressure (10-1000Pa) thermal treatment has low lithium bond energies. The low-temperature thermal treatment at 200-300℃ can break these weak interactions, disintegrate the complex, and allow ethanol to evaporate and desorb in its intact molecular form, restoring the complex to its lithium sulfide compound structure. The product after thermal treatment can be directly used as the high-purity lithium sulfide, or it can undergo necessary post-processing. At this point, the Li₂S·EtOH complex impurities in the lithium sulfide have been sufficiently removed. The temperature of the lithium sulfide preparation process or the post-processing process for preparing the electrolyte can be arbitrarily adjusted according to actual needs, without the formation of lithium carbonate impurities due to the reaction of the complex at high temperatures, which would adversely affect the ionic conductivity performance of the electrolyte and battery.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. Advantages in reaction conditions and intrinsic safety. Compared to the traditional carbothermal reduction method requiring temperatures above 800°C, this invention conducts the reaction in a liquid phase environment at room temperature to low temperatures, optimizing reaction rate and solubility differences, and significantly reducing temperature requirements. This method avoids problems such as grain agglomeration and growth, as well as the formation of stubborn impurities like lithium carbonate, caused by high temperatures, ensuring the nanoscale microstructure of the product. Furthermore, compared to processes using metallic lithium or hydrogen sulfide, the lithium chloride, sodium sulfide, and anhydrous ethanol raw materials used in this invention are all conventional chemicals, completely eliminating highly reactive, flammable, and highly toxic hazardous materials, significantly reducing the danger of the production process, equipment complexity, and overall cost.

[0022] 2. Advantages in product purity and impurity control. Existing metathesis methods for preparing lithium sulfide suffer from two major technical drawbacks: the difficulty in completely separating the byproduct NaCl and the tendency of Li2S to form stable complexes with solvents. This invention achieves a breakthrough by combining tetrahydrofuran washing with a specific low-temperature heat treatment process, thus solving these technical defects and enabling the product purity to consistently reach and exceed 99.5%, meeting the stringent requirements of high-end solid-state electrolytes for raw material purity.

[0023] 3. Advantages in product performance and downstream applications. The lithium sulfide product prepared by this invention not only has high purity but also features uniform particle size and good crystallinity. Its nanoscale particle size (40-50 nm) is beneficial for forming a dense and uniform microstructure during subsequent preparation of solid-state electrolytes. Electrochemical tests show that the Li6PS5Cl electrolyte synthesized using it as a raw material has excellent room-temperature ionic conductivity, proving that the lithium sulfide and the electrolyte prepared by this invention have excellent electrochemical performance and can provide reliable material support for the downstream manufacturing of high-performance solid-state batteries.

[0024] 4. Advantages in terms of process economy and environmental benefits. The entire process of this invention is short and the conditions are mild. Compared with the high-energy-consuming high-temperature method and the high-cost organic lithium method, the overall production cost of this invention is more competitive in the market, and the emissions of waste are less. It is an environmentally friendly green process with great potential for large-scale industrial application.

[0025] This application does not specify whether additional post-processing steps are required for the preparation of lithium sulfide. The solid product after heat treatment at 200-300℃ can be directly used as the high-purity lithium sulfide obtained. Alternatively, after heat treatment at 200-300℃, a second heat treatment at 500-800℃ can be performed to eliminate lattice defects, with the aim of improving the electrochemical performance of the material and enhancing the performance of the electrolyte and battery.

[0026] This application does not specifically limit whether a washing step of the solid product is added, or whether other detergents are used to wash the solid product. Washing can be done with only tetrahydrofuran, or with water washing followed by tetrahydrofuran washing, and so on. Figure 3 The process can be optimized by using water washing + dimethyl sulfoxide washing (using solubility difference to remove excess lithium chloride impurities in solid products) + tetrahydrofuran washing in the washing step. The principle is to improve the electrochemical performance of the material and the performance of the electrolyte and battery.

[0027] In one possible implementation, S100, the lithium compound is lithium chloride, the sulfur compound is sodium sulfide nonahydrate, and the molar ratio of the lithium compound to the sulfur compound is (2-2.3):1, preferably 2:1, 2.05:1, 2.1:1 or 2.2:1.

[0028] In one possible implementation, S100, solid lithium compounds and sulfur compounds are added to liquid ethanol, with a liquid-to-solid ratio (total volume of ethanol / total mass of lithium compounds and sulfur compounds) of 10-30 mL / g, preferably 20 mL / g, and the mixture is stirred for 20-40 minutes, preferably 30 minutes, at a stirring speed of 300-1000 rpm, preferably 600 rpm, to obtain a first mixture.

[0029] Preferably, in step S200, the process for solid-liquid separation of the first mixture is as follows: The first mixture is centrifuged at 7000-9000 rpm (preferably 8000 rpm) for 8-15 minutes (preferably 10 or 12 minutes). After centrifugation, the supernatant is removed, and the centrifuged precipitate is a solid product.

[0030] In one possible implementation, S400, the step of drying the solid product specifically involves subjecting the solid product to vacuum rotary evaporation to remove residual solvent.

[0031] Preferably, in step S400, under a second preset temperature and pressure, and at a second preset rotation speed for a second preset duration, the solid product is subjected to reduced-pressure rotary evaporation to remove residual ethanol. The second preset temperature is 40-60°C, preferably 50°C; the second preset pressure is 0.09-0.1 MPa below standard atmospheric pressure, preferably 0.095 MPa below standard atmospheric pressure, i.e., the gauge pressure reading is -0.095 MPa; the second preset rotation speed is 80-120 rpm, preferably 100 rpm; and the second preset duration is 20-40 minutes, preferably 30 minutes.

[0032] In one possible implementation, step S300, washing the solid product, specifically involves: S310, wash the solid product with water; S320, the solid product is washed with tetrahydrofuran.

[0033] The specific operating steps are as follows: The solid product is subjected to at least one (preferably three) water washing treatment. The water washing process is as follows: water is added to the solid product until the final volume fraction of water (in the total solid-liquid system) is 0.5%-2%, and the mixture is micro-mixed or allowed to stand to obtain the first material. The first material is centrifuged, and the supernatant after centrifugation is removed. The centrifuged precipitate is used as the solid product after water washing. The solid product is subjected to at least one (preferably three) tetrahydrofuran washing treatment. The tetrahydrofuran washing treatment process is as follows: add tetrahydrofuran solution to the solid product, with a solid-liquid ratio of 20 mL / g, mix thoroughly to obtain a second material, centrifuge the second material, remove the supernatant after centrifugation, and the resulting centrifuged precipitate is used as the solid product after tetrahydrofuran washing.

[0034] In one possible implementation, S500, the process of introducing an inert gas into the heat treatment chamber to heat treat the solid product therein specifically includes: S510, the solid product is placed in a tube furnace, with the inner cavity of the tube furnace serving as the heat treatment chamber. Then, throughout S500, an inert gas (preferably argon) is continuously introduced into the heat treatment chamber to purge it, ensuring the chamber environment remains inert. The chamber pressure is then adjusted to the first preset pressure, and the temperature is increased to the first preset temperature at a rate of 1-5°C / min, maintaining the chamber pressure at the first preset pressure throughout the heating process. The inert gas flow rate is 100-200 sccm, the flow velocity is 1-3 cm / s, and the appropriate inner diameter of the tube furnace can be selected, preferably 20-30 mm. The preferred heating rate is 2°C / min. S520, heat treatment of solid product is performed by holding the product at a first preset temperature and a first preset pressure for a first preset time, wherein the first preset time is 100-150 minutes. S530 was cooled at a rate of 1-5℃ / min, and the solid product was taken out after cooling as the high-purity lithium sulfide prepared.

[0035] To better illustrate the present invention, the following embodiments and comparative examples are provided.

[0036] Example 1 Step 1: Raw Material Preparation and Pretreatment. In a glove box (moisture and oxygen content both below 0.1 ppm), accurately weigh lithium chloride (LiCl, purity ≥98.0%) and sodium sulfide nonahydrate (Na₂S·9H₂O, purity ≥98.0%) powder using an analytical balance. The molar ratio of lithium chloride to NaS is controlled at LiCl:NaS = 2.2:1. This 10% excess LiCl serves to drive the metathesis reaction (2LiCl + NaS → LiS↓ + 2NaCl) to the right to proceed completely, maximizing the yield of Li₂S using the principle of chemical equilibrium shift, and ensuring that Na₂S is completely consumed without residue.

[0037] Step Two: Liquid-Phase Metathesis Reaction. The weighed raw materials were placed in a reaction vessel lined with polytetrafluoroethylene (PTFE), and an appropriate amount of anhydrous ethanol was added as a solvent, maintaining a liquid-to-solid ratio of 20 mL / g. The reaction vessel was then sealed and magnetically stirred at 600 rpm for 30 minutes at room temperature (25°C). This step aims to provide a homogeneous liquid environment for the Li... + With S 2- It can fully contact and undergo ion exchange reaction, and take advantage of the low solubility of Li2S in ethanol to precipitate it from the solution, thereby achieving simultaneous reaction and initial separation.

[0038] Step 3: Solid-liquid separation. After the reaction is complete, transfer all materials in the reactor to a high-speed centrifuge and centrifuge at 8000 rpm for 10 minutes to separate the generated Li₂S solid precipitate from the ethanol mother liquor containing the byproduct NaCl and excess LiCl. After centrifugation, remove the supernatant and collect the solid precipitate at the bottom as the aforementioned solid product.

[0039] Step 4: Washing the solid product with tetrahydrofuran. NaCl has good solubility in tetrahydrofuran, while Li₂S has extremely low solubility in it. Three washes are performed using tetrahydrofuran (THF) solvent to further dissolve and remove NaCl impurities coated or mixed in with Li₂S. The solid-liquid ratio of tetrahydrofuran to solid product is 20 mL / g for each wash. After thorough mixing, the mixture is centrifuged at 8000 rpm for 10 minutes. The supernatant is removed, and the solid precipitate at the bottom is collected as the washed solid product.

[0040] Step 5: Drying the solid product. Transfer the obtained solid product to a rotary evaporator and evaporate it under vacuum for 30 minutes at a water bath temperature of 50°C (gauge pressure reading -0.095MPa). The solvent (tetrahydrofuran) is recovered and removed.

[0041] Step Six: Heat Treatment under an Inert Atmosphere. Transfer the dried solid product to a tube furnace and continuously purge with high-purity argon gas (the purging flow rate is constant at 100 sccm; the exhaust flow rate varies with the target pressure, as long as the pressure can be controlled to ensure the solid product is in an inert gas environment; the inert gas is not static, and the gas near the solid product is constantly changing). Reduce the pressure to 180 Pa at a rate of 800 Pa / min. Increase the temperature to 250 °C at a rate of 2 °C / min, maintaining the pressure at 180 Pa during the heating process. Hold at 250 °C and 180 Pa for 120 minutes to break the lithium bonds in the complex (e.g., Li₂S·EtOH or Li₂S·THF complex), causing irreversible dissociation of lithium sulfide and ethanol / tetrahydrofuran. Because the heat treatment temperature is lower than its thermal decomposition temperature but higher than its boiling point, ethanol and tetrahydrofuran are directly discharged as gases from the solid product and carried away by high-purity argon gas continuously flowing through the solid production area, thus ensuring the high purity of the final product. The product is cooled to room temperature at a rate of 2°C / min, the exhaust flow rate is reduced, and the pressure is increased to atmospheric pressure at a rate of 800 Pa / min. The heat-treated solid product and container are then rapidly transferred to a glove box, where the final solid product (white powder) is collected as the high-purity lithium sulfide prepared in Example 1.

[0042] The high-purity lithium sulfide prepared in Example 1 was subjected to XRD phase analysis, and its spectrum is shown below. Figure 2 As shown. Figure 2 Only the characteristic peaks of the cubic phase of Li₂S are shown, with no diffraction peaks from other impurities. The average grain size is calculated to be approximately 45 nm using the Scherrer formula. Chemical titration analysis using the iodometric method yielded a product purity of 99.7%.

[0043] The high-purity lithium sulfide prepared in Example 1 was analyzed by SEM and EDS, and the results are as follows: Figure 3 As shown. By Figure 3The SEM images show that the particles in the sample have a uniform microstructure. It should be noted that due to limitations in its working principle, EDS has extremely low sensitivity to ultralight elements (such as Li and H), and typically cannot detect the Li peak; therefore, this should not be interpreted as the absence of lithium in the sample. Figure 3 The EDS results show that the elemental composition of the sample is mainly O and S (the strong oxygen signal is due to oxidation caused by contact with air during centrifugation, washing, and removal of the material from the tube furnace), while the Na and Cl signals are extremely weak. The C peak is relatively weak compared to Comparative Example 1 (see Comparative Example 1). Figure 6 The decrease in the concentration of organic solvent residues (the aforementioned complexes) in the product indicates that these residues have been removed.

[0044] Furthermore, Li6PS5Cl electrolyte was prepared using the high-purity lithium sulfide obtained in Example 1, and the ionic conductivity of the electrolyte was measured by electrochemical impedance spectroscopy. Figure 4 (As shown in red), the ionic conductivity of a commercially available similar material (Li6PS5Cl electrolyte) was measured as follows: Figure 4 (Black) As shown. The results indicate that the ionic conductivity of this electrolyte at room temperature is 3.86 mS·cm. -1 The ionic conductivity is 2.81 mS·cm, higher than that of commercially available similar materials (Li6PS5Cl electrolyte). -1 This indicates that heat treatment removes the Li2S·EtOH and Li2S·THF complexes from high-purity lithium sulfide without generating lithium carbonate impurities due to these complexes, thus ensuring the ionic conductivity of the electrolyte.

[0045] Comparative Example 1 The preparation process of Comparative Example 1 is basically the same as that of Example 1, except that after obtaining the solid product through solid-liquid separation in step three of Comparative Example 1, step four (washing the solid product with hydrogen furan) is not performed. Instead, step five (drying the solid product) is performed directly. After drying, the heat treatment in step six is ​​not performed. Instead, the dried solid product is used directly as the lithium sulfide obtained.

[0046] Apart from the differences mentioned above, all other operations in Comparative Example 1 are the same as in Example 1.

[0047] The lithium sulfide prepared in Comparative Example 1 was subjected to XRD phase analysis, and the results are as follows: Figure 5 As shown. Since the diffraction peaks of NaCl and Li₂S are very close, EDS elemental analysis was also performed on the sample, as shown below. Figure 6 As shown. Analysis Figure 5 , 6 It can be seen that the lithium sulfide prepared in Comparative Example 1 contains elements such as C, Na, and Cl in addition to Li₂S, indicating the presence of sodium chloride impurities, and possibly lithium chloride, Li₂S·EtOH complexes, and Li₂S·THF complexes. It should be noted that... The weak signal of sulfur (S) with only one peak is due to the presence of solvent complexes and other impurities in the system, which form a capping layer on the surface of lithium sulfide grains. When the electron beam penetrates the capping layer to excite S atoms, some of the characteristic X-ray energy released by the S transition is absorbed and scattered by the capping layer, ultimately reducing the number of characteristic X-rays of S reaching the detector and weakening the signal intensity, which is lower than the actual value of S in the sample.

[0048] Example 2 The preparation process of Example 2 is basically the same as that of Example 1. The difference is that the heat treatment temperature (first preset temperature) in step six of Example 2 is set to 300°C and the heat treatment time (first preset duration) is shortened to 60 minutes.

[0049] The high-purity lithium sulfide prepared in Example 2 was analyzed by chemical titration using the iodometric method, and the purity of the product was found to be above 99.6%.

[0050] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-purity lithium sulfide based on solution metathesis, characterized in that, Includes the following steps: S100, a lithium compound and a sulfur compound are added to ethanol and mixed to obtain a first mixture, wherein the lithium compound is lithium chloride and / or its hydrate, and the sulfur compound is sodium sulfide and / or its hydrate, and during the mixing process, the lithium compound and the sulfur compound react to generate lithium sulfide; S200, the first mixture is subjected to solid-liquid separation to obtain a solid product; S300, Wash the solid product. The process for washing the solid product is as follows: S320, Wash the solid product with tetrahydrofuran. S400, the solid product after drying and washing; S500, the dried solid product is placed in a heat treatment chamber, and inert gas is continuously introduced into the heat treatment chamber to purge the solid product. The solid product is heat-treated under a first preset temperature and a first preset pressure to remove complex impurities from the solid product and obtain high-purity lithium sulfide. The first preset temperature is 200-300℃ and the first preset pressure is 10-1000Pa.

2. The method for preparing high-purity lithium sulfide based on solution metathesis according to claim 1, characterized in that, S100, wherein the lithium compound is lithium chloride and the sulfur compound is sodium sulfide nonahydrate.

3. The method for preparing high-purity lithium sulfide based on solution metathesis according to claim 1, characterized in that, The molar ratio of the lithium compound to the sulfur compound is (2-2.3):

1.

4. The method for preparing high-purity lithium sulfide based on solution metathesis according to claim 1, characterized in that, S100: Solid lithium compounds and sulfur compounds are added to liquid ethanol at a liquid-to-solid ratio of 10-30 mL / g and stirred for 20-40 minutes to obtain the first mixture.

5. The method for preparing high-purity lithium sulfide based on solution metathesis according to claim 1, characterized in that, S200, the process for solid-liquid separation of the first mixture is as follows: Centrifuge the first mixture at 7000-9000 rpm for 8-15 minutes and collect the centrifuged precipitate as a solid product.

6. The method for preparing high-purity lithium sulfide based on solution metathesis according to claim 1, characterized in that, S400, the process for drying the solid product is as follows: The solid product is subjected to reduced pressure rotary evaporation to remove residual solvent.

7. The method for preparing high-purity lithium sulfide based on solution metathesis according to claim 6, characterized in that, S400, at a second preset temperature and a second preset pressure, the solid product is subjected to reduced pressure rotary evaporation treatment at a second preset speed for a second preset time to remove residual solvent from the solid product. The second preset temperature is 40-60℃, the second preset pressure is 0.09-0.1MPa lower than the standard atmospheric pressure, the second preset speed is 80-120rpm, and the second preset time is 20-40 minutes.

8. The method for preparing high-purity lithium sulfide based on solution metathesis according to claim 1, characterized in that, S500, in an inert gas environment, heat-treats a solid product at a first preset temperature and a first preset pressure for a first preset time to obtain high-purity lithium sulfide, wherein the first preset time is 100-150 minutes.

9. The method for preparing high-purity lithium sulfide based on solution metathesis according to claim 1, characterized in that, S500, the first preset pressure is 50-300Pa.

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