Preparation method for synthesizing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide, preparation method of solid electrolyte and solid-state battery

Abstract

The invention provides a preparation method for synthesizing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide, a preparation method for a solid electrolyte and a solid-state battery, and the preparation method for synthesizing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide comprises the following steps: dissolving an industrial-grade lithium hydroxide raw material, and sequentially carrying out oxidation, filtration, washing and drying to obtain lithium sulfide; sodium sulfide and a flocculating agent are added for precipitation and filtration, then sodium carbonate and barium nitrate are sequentially added for impurity removal and filtration, and a lithium hydroxide purified solution is obtained; reacting the sodium sulfide solid with dilute sulphuric acid to obtain hydrogen sulfide gas; hydrogen sulfide gas is introduced into the lithium hydroxide purification liquid for a reaction, and lithium sulfide slurry is obtained; evaporating, concentrating and crystallizing the lithium sulfide slurry, and centrifugally separating; and carrying out vacuum calcination on the crystal, and crushing to obtain lithium sulfide powder. Through oxidative conversion, chemical precipitation and crystallization purification, efficient and deep removal of impurities is realized, the problems that raw material components are complex and difficult to separate are solved, and the purity of lithium sulfide is improved.

Description

Technical Field

[0001] This disclosure relates to the field of lithium battery material production, and in particular to a method for preparing industrial-grade lithium hydroxide and sodium sulfide to synthesize lithium sulfide, a method for preparing solid electrolyte, and a solid battery. Background Technology

[0002] Lithium sulfide is an important inorganic chalcogenide compound with excellent ionic conductivity and chemical stability, showing broad application prospects in many fields. In the field of solid-state batteries, lithium sulfide is a key precursor for preparing high-performance sulfide solid electrolytes. Its purity directly affects the ionic conductivity, interfacial stability, and ultimately the cycle life and safety of the battery. With the rapid development of the new energy industry, especially solid-state battery technology, the demand for high-purity lithium sulfide is increasing, and the purity requirements are becoming increasingly stringent, typically needing to reach 99.95% or higher.

[0003] Lithium sulfide is produced by reacting lithium hydroxide or lithium carbonate with hydrogen sulfide gas. The raw materials are relatively readily available, but the purity of the lithium hydroxide or lithium carbonate used is critical. Industrial-grade lithium hydroxide is obtained through lithium ore extraction and brine lake lithium extraction processes. However, if industrial-grade lithium hydroxide is used, the raw material contains impurities such as iron, calcium, magnesium, silicon, potassium, sodium, and sulfate, resulting in a complex and unstable composition that may contain multiple types of impurities. Single or simple purification methods are insufficient to address this complexity, leading to lithium sulfide products with purity levels that fail to meet the requirements of high-end battery applications.

[0004] For example, CN202511622940.9 discloses a method for preparing and applying micronized lithium sulfide. Lithium hydroxide is heated to a purification temperature under vacuum and held at that temperature to obtain molten lithium hydroxide. The molten lithium hydroxide is then transferred to a reaction apparatus, and a mixed gas containing hydrogen sulfide is continuously introduced into the molten lithium hydroxide through the bottom gas inlet. The reaction is carried out with stirring at 470-650°C. After the reaction is complete, the reaction product is discharged into a high-temperature centrifuge and centrifuged at 500-600°C. The resulting lithium hydroxide melt is returned to the reaction apparatus, and the precipitate obtained from centrifugation is the micronized lithium sulfide. This method removes water of crystallization, organic residues, and low-boiling-point impurities from lithium hydroxide, but it cannot purify impurities such as iron, calcium, magnesium, silicon, potassium, sodium, and sulfate contained in industrial-grade raw materials. Furthermore, the high-temperature centrifugal separation of the lithium hydroxide melt and lithium sulfide cannot separate impurities such as iron, calcium, magnesium, silicon, potassium, sodium, and sulfate, thus affecting the purity of the obtained lithium sulfide. Summary of the Invention

[0005] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide a method for preparing industrial-grade lithium sulfide by synthesizing lithium sulfide from sodium sulfide with efficient and deep removal of impurities, a method for preparing solid electrolyte, and a solid battery.

[0006] The purpose of this disclosure is achieved through the following technical solution: A method for preparing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide includes the following steps: Industrial-grade lithium hydroxide raw material is added to deionized water to obtain a lithium hydroxide solution; An aqueous solution of hydrogen peroxide was added to the lithium hydroxide solution for oxidation to obtain an oxidized premixed solution. Sodium sulfide and flocculant are added to the oxidative premixed solution for precipitation and then filtered to obtain a purified filtrate. Sodium carbonate and barium nitrate are added sequentially to the impurity-removing filtrate for impurity removal and then filtered to obtain a lithium hydroxide purified solution. Sodium sulfide solid is reacted with dilute sulfuric acid under heating conditions to obtain hydrogen sulfide gas; The lithium hydroxide purification solution is heated under an inert atmosphere, and the hydrogen sulfide gas is introduced into the lithium hydroxide purification solution to react and obtain lithium sulfide slurry. The lithium sulfide slurry was evaporated, concentrated, and crystallized under an inert atmosphere. After centrifugation, lithium sulfide crystals and mother liquor were obtained. The lithium sulfide crystals are calcined under vacuum to obtain lithium sulfide material, which is then pulverized to obtain lithium sulfide powder.

[0007] In one embodiment, the purity of the industrial-grade lithium hydroxide raw material is greater than 98%, and the concentration of the lithium hydroxide solution is 10wt%-20wt%.

[0008] In one embodiment, after adding the hydrogen peroxide solution, the oxidation time is 30-60 minutes.

[0009] In one embodiment, sodium sulfide solid is reacted with dilute sulfuric acid under heating conditions to obtain hydrogen sulfide gas. The concentration of the dilute sulfuric acid is 20wt%-35wt%, wherein the molar ratio of sodium sulfide to sulfuric acid is 1:1.03 to 1:1.15, and the heating temperature is less than 60°C.

[0010] In one embodiment, the lithium hydroxide purification solution is heated under an inert atmosphere, and hydrogen sulfide gas is introduced into the lithium hydroxide purification solution to react and obtain a lithium sulfide slurry. The temperature is raised to 103°C-110°C, the hydrogen sulfide is introduced at a rate of 0.3L / min-2L / min, and the lithium hydroxide purification solution is stirred and reacted for 5-8 hours.

[0011] In one embodiment, the molar ratio of lithium hydroxide to hydrogen sulfide in the lithium hydroxide solution and hydrogen sulfide gas is from 2:1.02 to 2:1.04.

[0012] In one embodiment, the vacuum calcination temperature is 180℃-400℃, the calcination time is 6h-10h, and the vacuum degree of the vacuum calcination is ≤30Pa.

[0013] In one embodiment, the lithium sulfide slurry is evaporated, concentrated, and crystallized under an inert atmosphere. After centrifugation, lithium sulfide crystals and mother liquor are obtained. The evaporation and concentration temperature is 105-115°C, and the crystallization temperature is 58°C-65°C.

[0014] A sulfide solid electrolyte is prepared by using the method described in any of the above embodiments to synthesize lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide to obtain lithium sulfide powder, and then reacting the lithium sulfide powder with phosphide or halide raw materials to synthesize the sulfide solid electrolyte.

[0015] A solid-state battery comprising the sulfide solid electrolyte described in any of the above embodiments.

[0016] Compared with the prior art, this disclosure has at least the following advantages: The above-described method for synthesizing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide utilizes hydrogen peroxide solution to alter the valence and form of iron, followed by efficient removal through flocculation. This solves the problem of iron impurities introducing color and causing electrochemical interference. The addition of sodium sulfide for precipitation removes trace amounts of heavy metal ions such as lead, copper, and cadmium, significantly reducing the content of harmful heavy metal impurities. Further targeted precipitation with sodium carbonate and barium nitrate avoids precipitation competition, removing alkaline earth metal ions such as calcium, magnesium, and barium, as well as sulfate ions, preventing impurities from forming insoluble substances or affecting electrochemical performance in lithium sulfide. This pre-precipitation process further enhances the effectiveness of the method. The precipitation step removes impurities with significantly different chemical properties from lithium ions, avoiding competitive co-precipitation or encapsulation during the concentration and crystallization process, thus ensuring the selectivity of the crystallization process. Utilizing the physical differences in the solubility of Li2S, sodium salts, and potassium salts in the same solvent with temperature, alkali metal impurities such as sodium and potassium are further separated. Through oxidation conversion, chemical precipitation, and crystallization purification, efficient and deep removal of impurities is achieved. This solves the problem of complex and unstable raw material composition leading to large fluctuations in product purity and difficulty in consistently meeting battery-grade application requirements, reduces production costs, and overcomes the dependence on high-purity raw materials. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating the steps of a method for synthesizing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide. Figure 2 This is another step in the preparation method of lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide. Detailed Implementation

[0019] To facilitate understanding of this disclosure, a more complete description will be given below with reference to the accompanying drawings, which illustrate preferred embodiments of the present disclosure. However, this disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure.

[0020] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] To better understand the technical solutions and beneficial effects of this disclosure, the following detailed description is provided in conjunction with specific embodiments: Please see Figure 1 and Figure 2 The present invention provides a method for preparing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide, comprising the following steps: S101, industrial-grade lithium hydroxide raw material is added to deionized water to obtain a lithium hydroxide solution. It is understood that industrial-grade lithium hydroxide raw material is obtained through lithium ore extraction and salt lake lithium extraction processes. This raw material contains impurities such as iron, calcium, magnesium, silicon, potassium, sodium, and sulfate. Using deionized water to dissolve the industrial-grade lithium hydroxide raw material avoids introducing new impurities.

[0023] S103, hydrogen peroxide solution is added to the lithium hydroxide solution for oxidation to obtain an oxidized premixed solution. It is understood that the oxidizing property of hydrogen peroxide solution is used to oxidize any ferrous ions (Fe2+) that may be present in the solution. 2+ Oxidized to Fe 3+ ions, Fe 3+ The ions will subsequently form Fe(OH)3 precipitate with extremely low solubility and thus be removed.

[0024] S105, sodium sulfide and flocculant are added to the oxidizing premixed solution for precipitation and then filtered to obtain a purified filtrate. It is understood that the sodium sulfide contains S... 2- The ions can react with other trace heavy metal ions, such as Pb, that may be present in the solution. 2+ Cu 2+ ...to form insoluble sulfide precipitates, further purifying the solution. Simultaneously, S... 2- It may also be related to some Ca 2+ Mg 2+Plasma has a certain co-precipitation effect; flocculants can cause the tiny Fe(OH)3 precipitates and sulfide precipitates generated above to aggregate and grow into larger flocs, which facilitates subsequent filtration and separation.

[0025] S107, sodium carbonate and barium nitrate are added sequentially to the impurity-removing filtrate for impurity removal and then filtered to obtain a purified lithium hydroxide solution. It is understood that sodium carbonate provides CO3. 2- , with Ca in the solution 2+ Mg 2+ The plasma reaction produces a sparingly soluble carbonate precipitate, and barium nitrate is used to remove sulfate (SO4). 2- Impurities. Ba 2+ With SO4 2- It forms a barium sulfate (BaSO4) precipitate, which has extremely low solubility and can completely remove SO4. 2- Sodium carbonate is added first to precipitate most of the impurity cations, preventing them from reacting with the subsequently added Ba. 2+ A competitive precipitate is formed, and then barium nitrate is added to specifically remove sulfate ions, ensuring that Ba... 2+ Highly efficient and specific removal of sulfate SO4 2- In alkaline solutions, silicon exists as soluble silicate ions. Amorphous Fe(OH)3 colloidal precipitates, with their large specific surface area and strong adsorption capacity, carry a positive charge. Negatively charged silicate ions are strongly adsorbed onto their surface through electrostatic attraction. Furthermore, silicate ions can undergo ligand exchange reactions with the hydroxyl groups on the Fe(OH)3 surface, forming stable Fe-O-Si bonds, thus being chemically fixed on the surface or inside the iron precipitate. Silicate ions and carbonate ions have similar geometric structures and charges. During the growth of crystals such as CaCO3, SiO3... 2- It can partially replace CO3 2- It enters the crystal lattice or forms a co-precipitate on its surface in the form of CaSiO3, thereby precipitating and filtering out soluble silicon impurities through physical adsorption and chemical co-precipitation.

[0026] S109 involves reacting solid sodium sulfide with dilute sulfuric acid under heating conditions to obtain hydrogen sulfide gas. It is understandable that using solid Na₂S and dilute sulfuric acid as raw materials to obtain high-purity H₂S gas reduces the possibility of introducing additional impurities due to the gas's own impurity. Dilute sulfuric acid reacts more smoothly than concentrated sulfuric acid, making it easier to control the gas generation rate. Heating further effectively increases the reaction rate and ensures a continuous gas supply.

[0027] S111, the lithium hydroxide purification solution is heated under an inert atmosphere, and hydrogen sulfide gas is introduced into the lithium hydroxide purification solution to react and obtain a lithium sulfide slurry. It is understood that the inert atmosphere prevents gases such as oxygen and carbon dioxide in the air from reacting with hydrogen sulfide, lithium hydroxide, or the generated lithium sulfide, avoiding the introduction of new impurities and preventing the oxidation of the lithium sulfide product. Heating promotes the reaction, and the generated lithium sulfide forms a slurry in the solution.

[0028] S113, the lithium sulfide slurry is concentrated and crystallized under an inert atmosphere, and then centrifuged to obtain lithium sulfide crystals and mother liquor. It is understood that the sodium salt includes industrial-grade lithium hydroxide, sodium sulfide containing trace amounts of Na+ impurities, sodium sulfide (Na2S) and sodium carbonate (Na2CO3) added in the purification step, and sulfate impurities generated in the reaction that react with Na+ to form Na2SO4; the potassium salt includes industrial-grade lithium hydroxide, sodium sulfide containing trace amounts of K+. + Impurities, and CO3 in the process 2- SO4 2- Anions combine to form potassium salts; barium nitrate is added during the purification process, which reacts with SO4 in the solution. 2- The reaction produces BaSO4 precipitate, which is removed by filtration, leaving trace amounts of Ba. 2+ With CO3 2- The reaction produces a precipitate, which is removed by filtration to avoid Ba. 2+ Lithium sulfide remains in the solution; therefore, lithium sulfide slurry contains lithium sulfide, trace amounts of sodium salts (Na2SO4, Na2CO3), and trace amounts of potassium salts (Na2SO4, Na2CO3). The solubility of lithium sulfide in water varies greatly with temperature. Crystallization within this temperature range can yield Li2S crystals with high purity and uniform particle size. Concentration increases the concentration of Li2S and promotes crystallization. Potassium, sodium, and barium ions, due to the difference in solubility of their sulfides or hydroxides in water compared to lithium sulfide, are mainly retained in the mother liquor. Centrifugation separates them from the Li2S crystals, achieving deep purification.

[0029] S115, the lithium sulfide crystal is subjected to vacuum calcination to obtain lithium sulfide material, and the lithium sulfide material is pulverized to obtain lithium sulfide powder. It is understood that vacuum calcination removes residual moisture, adsorbed small amounts of mother liquor, and volatile impurities from the Li2S crystal, thereby obtaining lithium sulfide powder.

[0030] The above-described method for synthesizing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide utilizes hydrogen peroxide solution to alter the valence and form of iron, followed by efficient removal through flocculation. This solves the problem of iron impurities introducing color and causing electrochemical interference. The addition of sodium sulfide for precipitation removes trace amounts of heavy metal ions such as lead, copper, and cadmium, significantly reducing the content of harmful heavy metal impurities. Further targeted precipitation with sodium carbonate and barium nitrate avoids precipitation competition, removing alkaline earth metal ions such as calcium, magnesium, and barium, as well as sulfate ions, preventing impurities from forming insoluble substances or affecting electrochemical performance in lithium sulfide. This pre-precipitation process further enhances the effectiveness of the method. The precipitation step removes impurities with significantly different chemical properties from lithium ions, avoiding competitive co-precipitation or encapsulation during the concentration and crystallization process, thus ensuring the selectivity of the crystallization process. Utilizing the physical differences in the solubility of Li2S, sodium salts, and potassium salts in the same solvent with temperature, alkali metal impurities such as sodium and potassium are further separated. Through oxidation conversion, chemical precipitation, and crystallization purification, efficient and deep removal of impurities is achieved. This solves the problem of complex and unstable raw material composition leading to large fluctuations in product purity and difficulty in consistently meeting battery-grade application requirements, reduces production costs, and overcomes the dependence on high-purity raw materials.

[0031] In one embodiment, the purity of the industrial-grade lithium hydroxide raw material is greater than 98%, and the concentration of the lithium hydroxide solution is 10wt%-20wt%. In this embodiment, by using industrial-grade lithium hydroxide raw material with a purity greater than 98%, a clear impurity treatment baseline is set for the multi-stage purification system while ensuring cost control. When the concentration of the lithium hydroxide solution is less than 10wt%, the batch throughput is reduced, leading to increased energy consumption. When the concentration of the lithium hydroxide solution is greater than 20wt%, it is easy to cause supersaturation of impurity ions, forming fine precipitates or co-precipitations during the impurity removal process, affecting the purification effect and filtration efficiency. When the concentration of the lithium hydroxide solution is 10wt%-20wt%, the efficiency of subsequent reactions is ensured, and the co-precipitation or dissolution difficulties of impurities caused by excessively high concentrations are avoided, thereby balancing process efficiency and impurity removal effect.

[0032] In one embodiment, after adding the hydrogen peroxide solution, the oxidation time is 30-60 minutes. In this embodiment, by controlling the oxidation time, sufficient contact and diffusion between reactant molecules are ensured, thus guaranteeing the presence of Fe in the raw materials. 2+ To be converted to Fe at the maximum extent 3+ This allows excess hydrogen peroxide solution to decompose spontaneously in the aqueous environment after oxidation, reducing the amount of H2O2 entering the subsequent sodium sulfide precipitation step. Specifically, the concentration of hydrogen peroxide solution is 30 wt%, and the Fe content in the lithium hydroxide solution is... 2+ The content is 100ppm-500ppm, and the amount of hydrogen peroxide solution added is equal to the Fe content in the solution. 2+ Completely oxidized to Fe3 + The required amount is 1.3-1.8 times the theoretical amount, and the amount of hydrogen peroxide solution added is 0.7 L / m³ of lithium hydroxide solution. 3 Up to 1.0L / m 3 .

[0033] Further, in one embodiment, sodium carbonate and barium nitrate are sequentially added to the impurity-removing filtrate for impurity removal and then filtered to obtain a purified lithium hydroxide solution. The pH of the purified lithium hydroxide solution is 12.5-13.5. In this embodiment, under a high-pH, strongly alkaline environment, Ca... 2+ Mg 2+ Carbonate precipitation, and Fe 3+ The precipitation reaction of hydroxide precipitates is more thorough, avoiding the potential increase in the solubility of amphoteric hydroxides or carbonates, which could lead to the re-dissolution of trace impurities and affect the purification effect. The lithium hydroxide purification solution reacts with acidic gas H2S. The LiOH solution with a pH of 12.5-13.5 provides a strong alkaline driving force and sufficient reactant concentration for the absorption of H2S, ensuring that H2S is quickly and completely absorbed and converted into Li2S, thereby improving the reaction rate and conversion rate.

[0034] It is understandable that a 10wt%-20wt% LiOH solution has a pH of around 14, and the final purified solution has a pH of 12.5-13.5. During the impurity removal process, the oxidation by hydrogen peroxide and the addition of sodium carbonate and barium nitrate may slightly affect the pH. Although the pH drops slightly, it must still be maintained within this extremely alkaline range. By precisely controlling the amount of impurity removal reagents added, it is necessary to avoid adding too much, which would introduce new impurities or significantly change the pH of the system, or adding too little, which would result in incomplete impurity removal. The pH value is monitored online to determine whether the impurity removal step is completed and whether the purified solution is qualified, so as to achieve stable and repeatable production of high-purity products.

[0035] Furthermore, in one embodiment, the amount of sodium sulfide added is 0.5 kg / m³. 3 -3.0kg / m 3 The amount of sodium carbonate added is 2.0 kg / m³. 3 -8.0kg / m 3 The amount of barium nitrate added is 1.5 kg / m³. 3 -5.0kg / m 3The flocculant is added at a concentration of 10 ppm to 50 ppm. In this embodiment, sodium sulfide acts as the main precipitant, reacting with heavy metal ions in the solution to form insoluble metal sulfide precipitates; sodium carbonate precipitates alkaline earth metal ions such as calcium and magnesium in the solution, forming carbonate precipitates, and can adjust the pH of the solution, promoting the co-precipitation of impurities; barium nitrate is used to remove sulfate ions in the solution, forming barium sulfate precipitates with extremely low solubility; the flocculant is polyacrylamide, which causes the fine, dispersed precipitate particles generated by the reaction to rapidly aggregate into large, dense flocs, thereby significantly accelerating the settling speed and significantly improving the efficiency of subsequent filtration processes and the clarity of the filtrate; the sodium sulfide addition amount is 0.5 kg / m³. 3 -3.0kg / m 3 For heavy metal ions of 10ppm-50ppm, the excess coefficient is 1.2-2.0 to ensure Pb 2+ Cu 2+ After complete sedimentation, the flocculant is polyacrylamide, with an addition amount of 10-50 PPM to meet the flocculation requirements of the preceding sedimentation particles; the addition amount of sodium carbonate is 2.0 kg / m³. 3 -8.0kg / m 3 For 500ppm-1000ppm Ca 2+ 300ppm-800ppm Mg 2 + An excess of 1.1-1.5 will produce CaCO3 and MgCO3 precipitates; the amount of barium nitrate added is 1.5 kg / m³. 3 -5.0kg / m 3 For SO4 at 500ppm-1500ppm 2- The excess coefficient is 1.05-1.3 to ensure Ba 2+ With SO4 2- Complete formation of BaSO4 precipitate; the above range is calculated based on the common fluctuation range of impurities in industrial-grade raw materials. In actual applications, it is necessary to make fine adjustments based on the test results of raw material impurities. The core is to ensure that the target impurities are completely precipitated and to avoid the accumulation of new impurities due to excessive reagent.

[0036] In one embodiment, sodium sulfide solid is reacted with dilute sulfuric acid under heating conditions to obtain hydrogen sulfide gas. The concentration of the dilute sulfuric acid is 20wt%-35wt%, wherein the molar ratio of sodium sulfide to sulfuric acid is 1:1.03 to 1:1.15, and the heating temperature is less than 60°C. In this embodiment, a moderately active 20wt%-35wt% dilute sulfuric acid is used to ensure effective and continuous gas production from the reaction of dilute sulfuric acid and sodium sulfide. This avoids the risks of violent reactions, local overheating, and increased side reactions that may occur with concentrated sulfuric acid, thus ensuring the stability and purity of gas generation. The molar ratio of sodium sulfide to sulfuric acid is controlled between 1:1.03 and 1:1.15, with a slight excess of sulfuric acid. This ensures that the relatively expensive sodium sulfide raw material is completely consumed, improving raw material utilization and driving the reaction to proceed fully. At the same time, it avoids the burden and waste of subsequent gas processing due to excessive acid. The reaction temperature is controlled below 60°C, which effectively suppresses the solubility of hydrogen sulfide gas in water, facilitating its efficient precipitation and collection. Low-temperature operation significantly reduces the thermal motion speed of hydrogen sulfide molecules, reducing the risk of diffusion and escape. At the same time, it prevents side reactions that occur at high temperatures, thereby maintaining gas purity. The reaction of solid sodium sulfide with dilute sulfuric acid under heating conditions, through the coordinated control of key parameters such as reactant concentration, ratio, and temperature, optimizes the preparation process of hydrogen sulfide gas.

[0037] Furthermore, in one embodiment, after preparing hydrogen sulfide gas, before heating the lithium hydroxide purification solution under an inert atmosphere and introducing the hydrogen sulfide gas into the lithium hydroxide purification solution to react and obtain lithium sulfide slurry, the following steps are also included: The hydrogen sulfide gas is washed with an alkaline solution.

[0038] In this embodiment, hydrogen sulfide gas is obtained from high-purity raw materials. However, during the generation and transportation process, trace amounts of volatile acidic impurities may still be entrained or generated, such as sulfur dioxide that may be generated during the reaction, or hydrogen chloride gas introduced from the raw materials. By passing the hydrogen sulfide gas through an alkaline detergent, the acidic impurities are efficiently neutralized. The alkaline detergent is a dilute solution of sodium hydroxide or potassium hydroxide. When the gas passes through the alkaline solution, the small amount of water mist, fine dust, and other soluble impurities it carries are also captured and removed, further purifying and drying the gas. The hydrogen sulfide gas washed with the alkaline solution is then passed into a deeply purified lithium hydroxide solution to prevent exogenous impurities from being introduced into the final synthesis system, ensuring the purity of the hydrogen sulfide gas. Specifically, the washing process is carried out in a buffer bottle, where the alkaline solution is a 5%-10% NaOH solution. The hydrogen sulfide gas passes through the buffer bottle in a bubbling manner to ensure sufficient contact between the hydrogen sulfide gas and the alkaline solution.

[0039] In one embodiment, the molar ratio of lithium hydroxide to hydrogen sulfide in the lithium hydroxide solution and hydrogen sulfide gas is 2:1.02 to 2:1.04. In this embodiment, a slight excess of H2S gas ensures that the relatively more valuable lithium resource, LiOH, can be completely consumed and converted. Simultaneously, the excess H2S gas acts as a driving force, propelling the reaction equilibrium towards Li2S formation, thereby increasing the lithium yield and preventing LiOH residue due to insufficient H2S supply. The excess H2S is strictly limited to a low range of 2%-4% to avoid the burden of hazardous H2S tail gas treatment and safety analysis, and to avoid the risk of introducing additional sulfur impurities from excess H2S dissolved in the reaction solution.

[0040] In one embodiment, the lithium hydroxide purification solution is heated under an inert atmosphere, and hydrogen sulfide gas is introduced into the lithium hydroxide purification solution to react and obtain a lithium sulfide slurry. The temperature is raised to 103°C-110°C, the hydrogen sulfide is introduced at a rate of 0.3L / min-2L / min, and the lithium hydroxide purification solution is stirred and reacted for 5-8 hours. In this embodiment, the reaction temperature is 103℃-110℃, which causes the water to reach a slightly boiling state. The intense convection enhances the mass transfer process between the gas and liquid phases, allowing the introduced hydrogen sulfide gas to quickly contact the lithium hydroxide solution. At the same time, the high temperature significantly increases the activation energy of the reactant molecules, thereby accelerating the reaction rate. The reaction process is 2LiOH + H2S → Li2S + 2H2O. Under slightly boiling conditions, the water generated in the reaction continuously evaporates partially, reducing the water content of the product and thus driving the chemical equilibrium towards lithium sulfide. The solubility of hydrogen sulfide gas in the liquid decreases with increasing temperature. After the reaction, very little unreacted dissolved hydrogen sulfide remains in the solution, avoiding pH imbalance or the formation of polysulfides and other byproducts caused by residual hydrogen sulfide.

[0041] Understandably, by introducing hydrogen sulfide gas at a rate of 0.3 L / min to 2 L / min in conjunction with a slight boiling state, and under stirring conditions, hydrogen sulfide and lithium hydroxide undergo a neutralization reaction, thus ensuring the homogeneity of the reactants and avoiding excessively high or low local concentrations, allowing the reaction to proceed smoothly. By matching the reaction time with the slight boiling evaporation and gas flow rate, the introduced H2S gas reacts fully with LiOH, ensuring complete conversion of the raw materials. While ensuring complete reaction, this avoids excessively long reaction times that would lead to increased energy consumption and extended production cycles.

[0042] Furthermore, in one embodiment, when the lithium hydroxide purification solution is heated under an inert atmosphere and the hydrogen sulfide gas is introduced into the lithium hydroxide purification solution to react, the purity of the inert gas is greater than 99.99%, and the positive pressure of the inert atmosphere is maintained at 110 kPa to 150 kPa. In this embodiment, the purity of the inert atmosphere is greater than 99.99%, and the total content of key impurities such as O2, H2O, and CO2 is controlled below 100 ppm to avoid the negative impact of impurity accumulation on the electrochemical performance of the lithium sulfide product. The inert gas prevents the oxidation of H2S to elemental sulfur or sulfate by isolating oxygen, preventing the oxidation of LiOH or the product Li2S, and avoiding the introduction of oxygen impurities. It also isolates carbon dioxide to prevent it from reacting with the strongly alkaline LiOH to form Li2CO3. High-purity lithium sulfide is extremely sensitive to oxygen, water vapor, and carbon dioxide. By introducing an inert atmosphere to remove air first, the most important source of pollution is fundamentally isolated from the reaction environment, ensuring the chemical stability of Li2S during synthesis and subsequent processing. Specifically, the inert atmosphere includes one of the following gases: nitrogen, helium, and argon.

[0043] It is understandable that maintaining an inert atmosphere positive pressure of 110 kPa to 150 kPa, approximately 1.1 to 1.5 times atmospheric pressure, effectively suppresses the escape and vaporization of the gaseous reactant H2S, shifting the chemical equilibrium towards the formation of solid Li2S. This thermodynamically suppresses the hydrolysis side reaction of Li2S. Appropriately increasing the pressure also increases the solubility of H2S gas in the liquid phase, enhancing gas-liquid mass transfer and allowing H2S to be absorbed more quickly and thoroughly and participate in the reaction. Maintaining the internal system pressure slightly higher than the external atmospheric pressure effectively prevents backflow of outside air into the reaction system due to minor leaks. The pressure control of 110 kPa-150 kPa is directly related to the reaction temperature of 103℃-110℃. This ensures that the saturated vapor pressure of water at this temperature is close to or slightly above atmospheric pressure. The setting of a slight positive pressure is precisely to allow the reaction liquid to boil steadily at temperatures above 100°C. Through a high-purity inert atmosphere and a slight positive pressure reaction environment, the reaction of deeply purified lithium hydroxide solution and hydrogen sulfide gas is carried out specifically and efficiently to obtain high-quality lithium sulfide slurry.

[0044] In one embodiment, the vacuum calcination temperature is 180℃-400℃, the calcination time is 6h-10h, and the vacuum degree of the vacuum calcination is ≤30Pa. In this embodiment, the vacuum calcination temperature is greater than 180℃ to ensure sufficient heat energy is provided to overcome the adsorption or binding forces of water molecules and volatile impurities, allowing them to diffuse and escape. Lithium sulfide's thermal stability decreases at high temperatures; the vacuum calcination temperature is less than 400℃ to prevent lithium sulfide from decomposing or oxidizing, thus ensuring the thermal stability of lithium sulfide and avoiding decomposition or lattice defects due to excessive heating. Vacuum calcination uses a vacuum degree of less than 30 Pa. Under vacuum conditions, the boiling point of water and the saturated vapor pressure of other volatiles are significantly reduced. At temperatures far below atmospheric pressure boiling points, moisture is efficiently evaporated and removed, achieving a deep drying effect at low temperatures and avoiding potential side reactions caused by high temperatures. Furthermore, the vacuum environment creates a protective atmosphere with low oxygen partial pressure, reducing the risk of oxidation of lithium sulfide at higher calcination temperatures. The calcination time is 6-10 hours, allowing heat to be transferred from the surface of the material to the center, and for the volatiles adsorbed inside to diffuse to the surface and be removed by the vacuum system, thus achieving uniform and thorough dehydration and impurity removal of the lithium sulfide material.

[0045] Furthermore, in one embodiment, after evaporating and concentrating the lithium sulfide slurry under an inert atmosphere and crystallizing it, and obtaining lithium sulfide crystals and mother liquor by centrifugation, the process further includes recycling the mother liquor, comprising the following steps: After adding Ca(OH)2 suspension to the mother liquor and stirring gently, the mixture is filtered to obtain the first filtrate. The first filtrate is evaporated and crystallized to precipitate impurity salt crystals, thereby obtaining a concentrated alkaline solution; The concentrated alkaline solution is selectively electrodialyzed using a cation-selective membrane to obtain a concentrated recovery solution. The concentrated recovery liquid is then diverted and recovered.

[0046] When the nitrate ion concentration of the concentrated recovery solution is less than 10 g / L, the concentrated recovery solution is recovered to S107, and the concentrated recovery solution and barium nitrate are added together to the impurity removal filtrate.

[0047] When the nitrate ion concentration of the concentrated recovery solution is greater than 50 g / L, the concentrated recovery solution is evaporated, cooled, and crystallized to separate and obtain industrial-grade lithium nitrate.

[0048] The concentrated lithium hydroxide is then transferred to the lithium hydroxide solution for recycling. In this embodiment, a Ca(OH)₂ suspension is added to the mother liquor, and the Ca(OH)₂ reacts with any trace amounts of SO₄²⁻ that may remain in the mother liquor. 2- CO3 2- and S2O3 2-The reaction precipitates the anions to prevent them from reacting with Na+ during the concentration process. + Li + This process avoids the formation of difficult-to-treat complex salts or membrane fouling, eliminates the interference of sulfur in the recycled solution on upstream processes, and increases pH by OH⁻ while introducing Ca. 2+ It can promote trace amounts of Ba 2+ The formation of Ba(OH)₂ precipitate or co-precipitation with CaSO₄ in a solid solution resolves the issue of self-introduced impurities from the preceding barium nitrate purification step. Through evaporation and crystallization, the NaOH concentration increases dramatically, eventually crystallizing out in large quantities. Due to the difference in solubility between LiOH and NaOH, more LiOH remains in the liquid phase. The crystallization of impurities mainly consists of NaOH crystals and small amounts of sodium carbonate and sodium sulfate crystals, ensuring that most sodium ions are filtered out in solid form. The main cation in the concentrated alkali solution is Li₂. + and Ca 2+ After passing through a cation-selective membrane, Ca 2+ The nitrate is almost completely retained to obtain a high-purity, concentrated LiOH solution with extremely low calcium and sodium content; the nitrate concentration is used to separate the components, avoiding the problem of the components circulating and accumulating in the system and affecting the purity of the final lithium sulfide; and at high concentrations, the nitrate is recovered as industrial-grade lithium nitrate. The recovery step is connected to the crystallization centrifugation process, and the process is continuous and closed, avoiding pollution and resource waste caused by the discharge of mother liquor, and not introducing new pollution sources.

[0049] In one embodiment, the lithium sulfide slurry is evaporated, concentrated, and crystallized under an inert atmosphere. After centrifugation, lithium sulfide crystals and mother liquor are obtained. The evaporation and concentration temperature is 105-115°C, and the crystallization temperature is 58°C-65°C. In this embodiment, an evaporation and concentration temperature greater than 105°C ensures a stable micro-boiling state during the evaporation process at atmospheric pressure, enhancing heat and mass transfer and resulting in uniform and efficient water evaporation. Lithium sulfide exhibits a certain tendency to hydrolyze in high-temperature aqueous solutions; an evaporation and concentration temperature below 115°C suppresses the hydrolysis side reactions that may be exacerbated by overheating, reducing the risk of hydrogen sulfide gas and lithium hydroxide impurities generated by hydrolysis. Simultaneously, under the protection of an inert atmosphere, the evaporation and concentration temperature is far below the temperature at which lithium sulfide undergoes significant oxidation, ensuring the chemical stability of lithium sulfide.

[0050] It is understandable that sodium salts include industrial-grade lithium hydroxide and sodium sulfide containing trace amounts of Na+ impurities, sodium sulfide (Na2S) and sodium carbonate (Na2CO3) added during the purification process, and sulfate impurities generated in the reaction that react with Na+ to form Na2SO4; potassium salts include industrial-grade lithium hydroxide and sodium sulfide containing trace amounts of K. + Impurities, and CO3 in the process 2- SO4 2- Anions combine to form potassium salts; barium nitrate is added during the purification process, which reacts with SO4 in the solution.2- The reaction produces BaSO4 precipitate, which has extremely low solubility (≈2.4 × 10⁻⁶). -4 (g / 100g water), and almost unaffected by temperature changes, removed by filtration, trace amounts of Ba. 2+ With CO3 2- The reaction produces BaCO3 precipitate, which has extremely low solubility (≈2.2 × 10⁻⁶). -3 (g / 100g water), and almost unaffected by temperature changes, it is removed through filtration to avoid Ba. 2+ Residual substances remain in the solution; therefore, the lithium sulfide slurry contains lithium sulfide, trace amounts of sodium salts (Na2SO4, Na2CO3), and trace amounts of potassium salts (Na2SO4, Na2CO3). The solubility trends of each compound are shown in Table 1 below: Table 1. Solubility Trends of Compounds in Lithium Sulfide Slurry It is understandable that when the crystallization temperature is above 58℃, Li₂S is already in a supersaturated state, while for Na… + K + The solution, far from saturated with impurity salts, allows Li₂S to precipitate preferentially and in large quantities, while leaving most of the sodium and potassium impurity ions in the mother liquor. Simultaneously, because the temperature is above the maximum solubility inflection point of Na₂SO₄ (32.4℃), Na₂SO₄ is prevented from precipitating due to a reverse change in solubility during cooling. When the crystallization temperature is below 65℃, sufficient supersaturation and crystallization yield of Li₂S are ensured, while suppressing the increase in impurity ion activity and co-crystallization tendency that may occur due to excessively high temperatures. Based on the difference in solubility between lithium sulfide and the main coexisting impurities in water, the solubility of Li₂S is significantly reduced, driving a large amount of Li₂S to crystallize preferentially from the supersaturated solution, thus achieving a high yield. Since the solubility of alkali metal impurities such as sodium and potassium is relatively high and less affected by temperature, most remain in the mother liquor. By precisely controlling this crystallization temperature and supplementing it with sufficient crystallization time, the final and efficient separation of Li₂S product from alkali metal impurities, which are most difficult to remove by chemical precipitation, is achieved.

[0051] Furthermore, in one embodiment, a trace amount of sodium sulfide inhibitor is precisely added to the lithium sulfide slurry before the evaporation and concentration begins. In this embodiment, for the reversible hydrolysis reaction Li₂S + H₂O ⇌ 2LiOH + H₂S, the reactant S is increased. 2-The concentration of sodium sulfide can shift the chemical equilibrium towards the reverse reaction to produce Li₂S. Choosing sodium sulfide as an inhibitor avoids introducing additional non-sulfur lithium sources into the system, eliminating the potential risk of introducing free LiOH and causing crystal contamination or affecting purity during subsequent crystallization, thus ensuring the purity of the inhibitor's action pathway. By adding trace amounts of sodium sulfide, the sulfur concentration of the system is increased before the start of evaporation and concentration. 2- The concentration of sodium sulfide inhibitor directly and effectively suppresses the hydrolysis tendency of Li2S at high temperatures from a thermodynamic perspective. Specifically, the amount of sodium sulfide inhibitor added is 0.01 wt% to 0.5 wt% based on the theoretical Li2S content in the lithium sulfide slurry, and the addition is precisely controlled by a metering pump. Under the condition of maintaining an inert atmosphere, the sodium sulfide inhibitor is uniformly added to the lithium sulfide slurry in the form of solution or solid powder, and thoroughly stirred. The introduced sodium ions are inherent impurities that are already present in the process system and are intended to be removed. By strictly controlling the amount of inhibitor added, the incremental amount of sodium ions introduced is negligible compared to the total amount of sodium ions already present in the raw materials and previous steps, and it avoids affecting the sodium content control of the final product within the sodium removal capacity range of the subsequent crystallization and separation steps.

[0052] Furthermore, in one embodiment, the evaporated lithium sulfide slurry is subjected to online pH monitoring, wherein the pH value of the slurry is maintained at 12.0-13.0, and the H2S concentration in the gas phase space at the top of the evaporator is less than 10 ppm. If the pH value of the slurry is detected to be continuously lower than 12.0, a trace amount of sodium sulfide solution with a concentration of 0.1 wt%-0.5 wt% is pulsedly added to the evaporation system through a metering pump until the pH value recovers to above 12.0. In this embodiment, online monitoring of slurry pH and gas phase H2S concentration constitutes a dual-confirmation monitoring system for the hydrolysis reaction. The pH value reflects the shift in liquid phase chemical equilibrium and serves as a trend warning indicator. The H2S concentration directly reflects the escape amount of gaseous products and serves as a result confirmation and safety indicator. The pulsed addition of trace amounts of sodium sulfide solution achieves precise dosage control of minute flow rates and rapid response adjustment capabilities, avoiding over-addition or system disturbances that may occur with continuous addition, ensuring the fineness and stability of the adjustment. Through dynamic control, it is ensured that the evaporation and concentration process is always in a state of deep inhibition of hydrolysis, thereby minimizing Li2S loss and impurity generation caused by hydrolysis.

[0053] In one embodiment, the method for preparing lithium sulfide by synthesizing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide yields lithium sulfide powder with a purity greater than 99.95%. The impurities in the lithium sulfide powder mainly include elements or ions such as Fe, Ca, Mg, K, Na, Ba, SiO2, and sulfate.

[0054] In one embodiment, the contents of Fe, Ca, Mg, K, Na, Ba, and SiO2 in the lithium sulfide powder are all less than 0.005 wt%, and the content of sulfate is less than 0.008 wt%. In this embodiment, the method for synthesizing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide incorporates specialized, efficient, and multiple removal or control steps for each key impurity present. Through precise impurity control design combined with a fully inert atmosphere protection, high-purity lithium sulfide powder with a purity greater than 99.95% and extremely low impurity content is stably obtained.

[0055] In one embodiment, the method for preparing lithium sulfide by synthesizing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide uses a lithium sulfide production device to prepare lithium sulfide powder. The lithium sulfide production device includes a lithium hydroxide unit, a hydrogen sulfide unit, a lithium sulfide synthesis unit, a deep purification unit, and a post-processing unit. The lithium hydroxide unit is used to dissolve industrial-grade lithium hydroxide raw materials and perform precipitation and impurity removal to obtain purified lithium hydroxide liquid. The hydrogen sulfide chamber unit is used to synthesize hydrogen sulfide gas. The lithium sulfide synthesis unit is used to react hydrogen sulfide gas with impurity-removed hydrogen hydroxide to obtain lithium sulfide slurry. The deep purification unit is used to evaporate and concentrate the lithium sulfide material to obtain lithium sulfide crystals. The post-processing unit is used to vacuum calcine the lithium sulfide crystals to obtain lithium sulfide powder. In this embodiment, the device ensures the high purity and consistency of the purified solution through a tiered impurity removal design and online monitoring in the lithium hydroxide unit. The lithium sulfide synthesis unit and the deep purification unit utilize an inert atmosphere and precise temperature control throughout the process, completely isolating air pollution and achieving ultimate separation of alkali metal impurities. The high-vacuum calcination in the post-treatment unit further removes volatiles, ultimately resulting in extremely high purity lithium sulfide powder with key impurities such as heavy metals, alkali metals, and sulfate levels all below the threshold requirements for battery material applications. Each unit module is equipped with specialized sensors and actuators, such as pH meters, pressure sensors, temperature controllers, and mass flow meters, to monitor and automatically adjust key process parameters such as concentration, pH, temperature, pressure, ventilation rate, and vacuum level in real time. This highly proceduralizes the entire conversion process from industrial-grade raw materials to high-purity products, significantly reducing human error and ensuring high consistency and stability of product quality across different production batches.

[0056] In one embodiment, the lithium hydroxide purification unit includes a dissolving tank, a hydrogen peroxide solution storage tank, a flocculant storage tank, a sodium sulfide storage tank, a sodium carbonate storage tank, a barium nitrate storage tank, and a filter press assembly. The hydrogen peroxide solution storage tank, the flocculant storage tank, the sodium sulfide storage tank, the sodium carbonate storage tank, and the barium nitrate storage tank are all connected to the inlet of the dissolving tank. The filter press assembly is used to filter the lithium hydroxide solution in the dissolving tank and separate precipitates. The hydrogen sulfide preparation unit includes a hydrogen sulfide reactor, a sodium sulfide silo, and a dilute sulfuric acid metering tank. The sodium sulfide silo and the dilute sulfuric acid metering tank are both connected to the hydrogen sulfide reactor. The lithium sulfide synthesis unit includes a lithium sulfide reactor, the gas inlet of which is connected to the gas outlet of the sulfidation chamber reactor, the liquid inlet of which is connected to the liquid outlet of the dissolving tank, and the lithium sulfide reactor is provided with an inert atmosphere gas inlet. The deep purification unit includes a concentrator and a centrifugal separator connected in sequence. The concentrator is used to evaporate and concentrate lithium sulfide slurry, and the centrifugal separator is used to separate Li2S crystals from mother liquor. The post-processing unit includes a vacuum calcination furnace and a pulverizer / classifier arranged sequentially. The vacuum calcination furnace is used to calcine and remove impurities from the lithium sulfide crystals, and the pulverizer / classifier is used to pulverize the lithium sulfide material to obtain lithium sulfide powder. In this embodiment, key materials are transported between closed units via pipelines from the dissolving tank to the lithium sulfide reactor and then to the concentrator, reducing the exposure risk and loss caused by material transfer. The direct connection between the hydrogen sulfide reactor and the lithium sulfide reactor adopts an online generation and immediate consumption mode, avoiding the risks of large-scale storage and transportation of H2S. The dissolving tank integrates a multi-channel precise metering feeding system, adding various impurity removal reagents sequentially and quantitatively, ensuring that the complex multi-step purification reaction is completed efficiently and orderly within the container. The close cooperation between the filter press assembly and the dissolving tank enables efficient solid-liquid separation after each round of precipitation reaction. The inert atmosphere inlet of the lithium sulfide reactor is equipped with a high-purity gas source and pressure regulation system to maintain a high-purity inert atmosphere and a slightly positive pressure reaction environment.

[0057] This application also provides a sulfide solid electrolyte, which is prepared by using the method described in any of the above embodiments to synthesize lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide to obtain lithium sulfide powder. The lithium sulfide powder is then reacted with phosphide or halide raw materials to synthesize the sulfide solid electrolyte. In this embodiment, heavy metals and alkaline earth metals are removed through multi-stage chemical precipitation, alkali metals Na and K are deeply removed through crystallization separation, and low oxygen and low water content of lithium sulfide is ensured through full inert protection and vacuum calcination, resulting in high-purity lithium sulfide powder. The sulfide solid electrolyte synthesized from high-purity lithium sulfide has extremely low impurity content, which reduces the hindrance of ion migration by lattice defects, improves the conductivity of lithium ions, reduces side reactions caused by impurities, and improves electrochemical stability.

[0058] A solid-state battery includes a sulfide solid electrolyte as described in any of the above embodiments. In this embodiment, the ultra-high purity of the lithium sulfide precursor results in a solid electrolyte with a complete lattice and few defects, exhibiting extremely high lithium-ion conductivity. The extremely low impurity content significantly reduces side reactions and passivation layer growth at the electrode or electrolyte interface during battery cycling, resulting in a battery with lower interfacial impedance, better coulombic efficiency, and longer cycle life.

[0059] Compared with the prior art, this disclosure has at least the following advantages: The above-described method for synthesizing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide utilizes hydrogen peroxide solution to alter the valence and form of iron, followed by efficient removal through flocculation. This solves the problem of iron impurities introducing color and causing electrochemical interference. The addition of sodium sulfide for precipitation removes trace amounts of heavy metal ions such as lead, copper, and cadmium, significantly reducing the content of harmful heavy metal impurities. Further targeted precipitation with sodium carbonate and barium nitrate avoids precipitation competition, removing alkaline earth metal ions such as calcium, magnesium, and barium, as well as sulfate ions, preventing impurities from forming insoluble substances in lithium sulfide or affecting electrochemical performance. This method also incorporates a pre-treatment process... The precipitation step removes impurities with significantly different chemical properties from lithium ions, avoiding competitive co-precipitation or encapsulation during the concentration and crystallization process, thus ensuring the selectivity of the crystallization process. Utilizing the physical difference in the solubility of sodium and potassium Li2S salts in the same solvent with temperature, alkali metal impurities such as sodium and potassium are further separated. Through oxidation conversion, chemical precipitation, and crystallization purification, efficient and deep removal of impurities is achieved. This solves the problem of complex and unstable raw material composition leading to large fluctuations in product purity and difficulty in consistently meeting the requirements of battery-grade applications, reduces production costs, and overcomes the dependence on high-purity raw materials.

[0060] The following are some specific examples. When %, it refers to a percentage by weight. It should be noted that the following examples do not exhaustively list all possible scenarios, and unless otherwise specified, the materials used in the following examples are commercially available.

[0061] Example 1 Take 100 kg of industrial-grade lithium hydroxide (98.5% purity) and add deionized water to prepare a 15 wt% lithium hydroxide solution. Add 1.5 times the theoretical volume of hydrogen peroxide (30 wt%) to the solution to oxidize Fe2+, and stir for 45 minutes. Then add an appropriate amount of sodium sulfide (industrial-grade, 98.2% purity), stir for 30 minutes, then add a small amount of polyacrylamide flocculant, stir for 8 minutes, and filter using a plate and frame filter press. Add sodium carbonate to the filtrate, stir for 40 minutes, then add barium nitrate, stir for 40 minutes, and filter again. Detect impurities in the purified solution. Detect impurities in the purified lithium hydroxide solution.

[0062] Industrial grade sodium sulfide (98.2% purity) solid was mixed with 25 wt% dilute sulfuric acid at a molar ratio of 1:1.08 and reacted at 50°C to generate hydrogen sulfide gas. The gas was then preliminarily washed in a water washing tower before being put into use.

[0063] The purified lithium hydroxide solution was pumped into a 500L stainless steel reactor. High-purity nitrogen (99.999% purity) was introduced three times to replace the air inside the reactor, and a slight positive pressure was maintained. The temperature was raised to 105℃, and the prepared hydrogen sulfide gas was introduced at a rate of 1.0 L / min. The molar ratio of lithium hydroxide to hydrogen sulfide was controlled at 2:1.03. The reaction was continued for 6 hours to obtain a lithium sulfide slurry.

[0064] The lithium sulfide slurry was transferred to a nitrogen-protected concentrator and concentrated by evaporation at 110°C. After concentration, the solution was transferred to a crystallization vessel and cooled to 60°C for crystallization. After crystallization, Li₂S crystals were obtained by centrifugation. The impurity content in the crystals was then analyzed.

[0065] The Li₂S crystals obtained by centrifugation were placed in a vacuum calcination furnace, the vacuum degree was set to 20 Pa, the temperature was raised to 300 °C, and calcined for 8 hours. After naturally cooling to room temperature, the crystals were crushed and sieved (200 mesh) to obtain a white powdery high-purity lithium sulfide product.

[0066] Example 2 Take 100 kg of industrial-grade lithium hydroxide (98.5% purity) and add deionized water to prepare a 20 wt% lithium hydroxide solution. Add 1.3 times the theoretical volume of hydrogen peroxide (30 wt%) to the solution to oxidize Fe2+, and stir for 30 minutes. Then add an appropriate amount of sodium sulfide (industrial-grade, 98.2% purity), stir for 45 minutes, add a small amount of polyacrylamide flocculant, stir for 5 minutes, and then filter using a plate and frame filter press. Add sodium carbonate to the filtrate, stir for 60 minutes, then add barium nitrate, stir for 60 minutes, filter again, and test the impurities in the purified lithium hydroxide solution.

[0067] Industrial grade sodium sulfide (98.2% purity) solid was mixed with 20 wt% dilute sulfuric acid at a molar ratio of 1:1.03 and reacted at 50°C to generate hydrogen sulfide gas. The gas was then preliminarily washed in a water washing tower before being put into use.

[0068] The purified lithium hydroxide solution was pumped into a 500L stainless steel reactor. High-purity helium (99.999% purity) was introduced three times to replace the air inside the reactor, and then a slight positive pressure of nitrogen was maintained. The temperature was raised to 110℃, and the prepared hydrogen sulfide gas was introduced at a rate of 0.3 L / min. The molar ratio of lithium hydroxide to hydrogen sulfide was controlled at 2:1.02. The reaction was continued for 6 hours to obtain a lithium sulfide slurry.

[0069] The lithium sulfide slurry was transferred to a nitrogen-protected concentrator and concentrated by evaporation at 105°C. After concentration, the solution was transferred to a crystallization vessel and cooled to 65°C for crystallization. After crystallization, Li₂S crystals were obtained by centrifugation. The impurity content in the crystals was then analyzed.

[0070] The Li₂S crystals obtained by centrifugation were placed in a vacuum calcination furnace, the vacuum degree was set to 25 Pa, the temperature was raised to 400℃, and calcined for 6 hours. After naturally cooling to room temperature, the crystals were crushed and sieved (200 mesh) to obtain a white powdery high-purity lithium sulfide product.

[0071] Example 3 Take 100 kg of industrial-grade lithium hydroxide (98.5% purity) and add deionized water to prepare a 10 wt% lithium hydroxide solution. Add 1.8 times the theoretical volume of hydrogen peroxide (30 wt%) to the solution to oxidize Fe2+, and stir for 60 minutes. Then add an appropriate amount of sodium sulfide (industrial-grade, 98.2% purity), stir for 60 minutes, add a small amount of polyacrylamide flocculant, stir for 10 minutes, and then filter using a plate and frame filter press. Add sodium carbonate to the filtrate, stir for 30 minutes, then add barium nitrate, stir for 30 minutes, filter again, and test the impurities in the purified lithium hydroxide solution.

[0072] Industrial grade sodium sulfide (98.2% purity) solid was mixed with 35 wt% dilute sulfuric acid at a molar ratio of 1:1.15 and reacted at 40°C to generate hydrogen sulfide gas. The gas was then preliminarily washed in a water washing tower before being put into use.

[0073] The purified lithium hydroxide solution was pumped into a 500L stainless steel reactor. High-purity argon gas (99.999% purity) was introduced three times to replace the air inside the reactor, and then a slight positive pressure of nitrogen was maintained. The temperature was raised to 103℃, and the prepared hydrogen sulfide gas was introduced at a rate of 2.0 L / min. The molar ratio of lithium hydroxide to hydrogen sulfide was controlled at 2:1.04. The reaction was continued for 8 hours to obtain a lithium sulfide slurry.

[0074] The lithium sulfide slurry was transferred to a nitrogen-protected concentrator and concentrated by evaporation at 115°C. After concentration, the solution was transferred to a crystallization vessel and cooled to 58°C for crystallization. After crystallization, Li₂S crystals were obtained by centrifugation. The impurity content in the crystals was then analyzed.

[0075] The Li2S crystals obtained by centrifugation were placed in a vacuum calcination furnace, the vacuum degree was set to 15 Pa, the temperature was raised to 180℃, and calcined for 10 hours. After naturally cooling to room temperature, the crystals were crushed and sieved (200 mesh) to obtain a white powdery high-purity lithium sulfide product.

[0076] Table 2. Test Table of Impurity Content in Lithium Hydroxide Purification Solution Table 3. Content Test Table of Lithium Sulfide Crystals It should be noted that Fe was detected using inductively coupled plasma mass spectrometry (ICP-MS). 3+ Ca 2+ M 2+ K + Na + Ba 2 + SiO2, SO4 2- Impurities.

[0077] As can be seen from Tables 1 and 2 above, the Fe in the lithium hydroxide purification solution in Examples 1-3 3+ Ca 2+ Mg 2+ All were below the requirement of 0.005 wt%, SO4 2- All impurities were below the requirement of 0.008 wt%, indicating that the multi-stage impurity removal process of this patent (hydrogen peroxide oxidation + sodium sulfide precipitation + sodium carbonate + barium nitrate impurity removal) can efficiently and deeply remove the core impurities in industrial-grade lithium hydroxide, laying a key foundation for the subsequent preparation of high-purity lithium sulfide. Furthermore, the small fluctuation in impurity content among the various embodiments proves that the impurity removal process is highly stable and adaptable to the impurity fluctuation characteristics of industrial-grade raw materials.

[0078] In Examples 1-3, the lithium sulfide crystals all had a lithium sulfide (Li₂S) content greater than 99.95%, indicating that after the entire process of "impurity removal-synthesis-crystallization-calcination," the product purity fully meets the basic purity requirements (target ≥ 99.95%) for lithium sulfide precursors in solid-state batteries, and the impurity ions (Fe) are also significantly reduced. 3+ Ca 2+ Na + The content of impurities (such as sulfide solid electrolyte) is controlled below 0.005 wt%, thus avoiding the negative impact of impurities on the ionic conductivity of the subsequent sulfide solid electrolyte and the cycle life of the battery.

[0079] Compared to Examples 1-3, Example 2 had a crystallization temperature of 65°C and a crystallization time of 100 min, with Na... + K + The highest content was found in Example 1, where the crystallization temperature was 60°C and the crystallization time was 120 min. (Na) + K + The content is moderate; the crystallization temperature in Example 3 is 58°C; Na + K + The lowest content indicates that the crystallization temperature affects alkali metal impurities (Na). + K +The separation efficiency of Li2S is higher in the range of 58℃-65℃. The lower the crystallization temperature and the longer the holding time, the better it is to use the difference in solubility between Li2S and sodium / potassium salts to separate impurities and finally obtain lithium sulfide crystals with lower impurity content. However, it is necessary to balance crystallization efficiency and energy consumption cost.

[0080] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the disclosed patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for preparing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide, characterized in that, Includes the following steps: Industrial-grade lithium hydroxide raw material is added to deionized water to obtain a lithium hydroxide solution; An aqueous solution of hydrogen peroxide was added to the lithium hydroxide solution for oxidation to obtain an oxidized premixed solution. Sodium sulfide and flocculant are added to the oxidative premixed solution for precipitation and then filtered to obtain a purified filtrate. Sodium carbonate and barium nitrate are added sequentially to the impurity-removing filtrate for impurity removal and then filtered to obtain a lithium hydroxide purified solution. Sodium sulfide solid is reacted with dilute sulfuric acid under heating conditions to obtain hydrogen sulfide gas; The lithium hydroxide purification solution is heated under an inert atmosphere, and the hydrogen sulfide gas is introduced into the lithium hydroxide purification solution to react and obtain lithium sulfide slurry. The lithium sulfide slurry was evaporated, concentrated, and crystallized under an inert atmosphere. After centrifugation, lithium sulfide crystals and mother liquor were obtained. The lithium sulfide crystals are calcined under vacuum to obtain lithium sulfide material, which is then pulverized to obtain lithium sulfide powder.

2. The method for preparing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide according to claim 1, characterized in that, The purity of the industrial-grade lithium hydroxide raw material is greater than 98%, and the concentration of the lithium hydroxide solution is 10wt%-20wt%.

3. The method for preparing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide according to claim 1, characterized in that, After adding the hydrogen peroxide solution, the oxidation time is 30-60 minutes.

4. The method for preparing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide according to claim 1, characterized in that, Sodium sulfide solid is reacted with dilute sulfuric acid under heating conditions to obtain hydrogen sulfide gas. The concentration of the dilute sulfuric acid is 20wt%-35wt%, and the molar ratio of sodium sulfide to sulfuric acid is 1:1.03 to 1:1.

15. The heating temperature is less than 60°C.

5. The method for preparing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide according to claim 1, characterized in that, Under an inert atmosphere, the lithium hydroxide purification solution is heated to 103℃-110℃, and hydrogen sulfide gas is introduced into the lithium hydroxide purification solution to react and obtain lithium sulfide slurry. The hydrogen sulfide is introduced at a rate of 0.3L / min-2L / min, and the lithium hydroxide purification solution is stirred and reacted for 5h-8h.

6. The method for preparing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide according to claim 5, characterized in that, In the lithium hydroxide solution and hydrogen sulfide gas, the molar ratio of lithium hydroxide to hydrogen sulfide is 2:1.02 to 2:1.

04.

7. The method for preparing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide according to claim 1, characterized in that, The vacuum calcination temperature is 180℃-400℃, the calcination time is 6h-10h, and the vacuum degree of the vacuum calcination is ≤30Pa.

8. The method for preparing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide according to claim 1, characterized in that, The lithium sulfide slurry was evaporated, concentrated, and crystallized under an inert atmosphere. After centrifugation, lithium sulfide crystals and mother liquor were obtained. The evaporation and concentration temperature was 105-115℃, and the crystallization temperature was 58℃-65℃.

9. A sulfide solid electrolyte, characterized in that, Lithium sulfide powder is obtained by synthesizing lithium sulfide from industrial-grade lithium hydroxide and sodium sulfide according to any one of claims 1-8. The lithium sulfide powder is then reacted with phosphide or halide raw materials to synthesize a sulfide solid electrolyte.

10. A solid-state battery, characterized in that, Includes the sulfide solid electrolyte as described in claim 9.

Images