Preparation method of high-purity lithium sulfide for liquid phase purification and impurity removal, preparation method of sulfide solid electrolyte material and power battery

Abstract

The invention provides a preparation method of high-purity lithium sulfide for liquid-phase purification and impurity removal, a preparation method of a sulfide solid electrolyte material and a power battery, and the preparation method of the high-purity lithium sulfide for liquid-phase purification and impurity removal comprises the following steps: dissolving lithium hydroxide in deionized water, and passing through a stepped resin column assembly and a nanofiltration membrane, a precursor purified solution is obtained; reacting sodium sulfide with dilute sulphuric acid to obtain hydrogen sulfide gas, performing dehydration and deoxidation treatment, and introducing hydrogen sulfide into the precursor purified liquid for reaction to obtain lithium sulfide slurry; evaporating and concentrating the lithium sulfide slurry under the protection of inert gas, and crystallizing and separating to obtain lithium sulfide crystals; and calcining the lithium sulfide crystal to obtain the high-purity lithium sulfide. The step resin column assembly and the nanofiltration membrane are used for deep purification, and hydrogen sulfide gas is subjected to dehydration and deoxidation treatment, so that the purity and the yield of a lithium sulfide product are improved; part of water is removed by the nanofiltration membrane, so that the evaporation time is shortened, and the yield loss caused by deterioration is reduced.

Description

Technical Field

[0001] This disclosure relates to the field of battery material preparation technology, and in particular to a method for preparing high-purity lithium sulfide through liquid-phase purification and impurity removal, a method for preparing sulfide solid electrolyte materials, and a power battery. Background Technology

[0002] Lithium sulfide is a core raw material for sulfide solid electrolyte materials and lithium-sulfur batteries. Its purity directly affects the battery's performance, including ionic conductivity and cycle life.

[0003] The main methods for preparing lithium sulfide include: direct sulfidation of lithium metal, which results in high lithium metal price, easy combustion, and poor safety; and high-temperature carbon reduction, which produces many impurities such as carbon residue and metal oxides, resulting in low purity. While the hydrogen sulfide method offers low raw material costs, impurities such as calcium, magnesium, sulfate, K, and Na from lithium hydroxide can enter the product, making it difficult to improve purity. Furthermore, precipitation is used to remove impurities from lithium hydroxide, but this process has limited ability to remove impurities with properties similar to lithium ions, making it difficult to stably control impurity content. Moreover, introducing precipitants such as Na₂CO₃ and Ba(NO₃)₂ during impurity removal can introduce new Na₂O₃. + Ba 2+ Contamination leads to technical problems such as incomplete removal of impurities from the obtained lithium sulfide, low product purity, and significant yield loss.

[0004] For example, a method for preparing high-purity lithium sulfide disclosed in prior art CN202510687503.9 involves adding lithium hydroxide and pure water to a reaction vessel, replacing the air inside the vessel with nitrogen, and then stirring and heating the vessel. A measured amount of hydrogen sulfide gas is introduced from the bottom of the vessel, and a gas circulation pump circulates the gas between the liquid and gas spaces within the vessel. Once the temperature of the reaction liquid in the vessel drops to 20-30°C, it is filtered under a nitrogen atmosphere. The remaining solid is washed with a measured amount of ammonia water, and the filtered solid is transferred to a drying oven and purged with nitrogen until anhydrous, yielding high-purity lithium sulfide. However, impurities such as calcium, magnesium, sulfate, K, and Na in the lithium hydroxide produced by this method can enter the product, making it difficult to improve purity. 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 high-purity lithium sulfide with high purity and reduced yield loss through liquid-phase purification and impurity removal, a method for preparing sulfide solid electrolyte materials, and a power battery.

[0006] The purpose of this disclosure is achieved through the following technical solution: A method for preparing high-purity lithium sulfide through liquid-phase purification and impurity removal includes the following steps: Lithium hydroxide is dissolved in deionized water to obtain a lithium hydroxide solution, wherein the purity of the lithium hydroxide is greater than 98%. The lithium hydroxide solution is passed sequentially through a stepped resin column assembly and a nanofiltration membrane to obtain a precursor purified solution. The stepped resin column assembly includes a pretreatment resin column, a deep purification resin column, and a fine treatment resin column arranged sequentially. The pretreatment resin column is used to initially remove impurities from the initial lithium hydroxide solution, rapidly adsorbing most of the calcium and magnesium ions. The deep purification resin column receives the solution after the pretreatment stage and performs further purification to further reduce the concentration of calcium and magnesium ions. The fine treatment resin column performs deep purification on the solution after the deep purification stage, ensuring that the calcium and magnesium ion content in the effluent meets a predetermined standard. The nanofiltration membrane is used to intercept and remove sulfate ions. Sodium sulfide is mixed with dilute sulfuric acid to obtain hydrogen sulfide gas. The hydrogen sulfide gas is then dehydrated and deoxygenated to obtain purified hydrogen sulfide raw material gas. The hydrogen sulfide raw material gas is introduced into the precursor purification liquid and reacted under heating conditions to obtain lithium sulfide slurry. The lithium sulfide slurry was evaporated and concentrated under inert gas protection, then crystallized and separated by centrifugation to obtain lithium sulfide crystals. The lithium sulfide crystals are subjected to vacuum calcination and pulverization to obtain high-purity lithium sulfide.

[0007] In one embodiment, the pretreatment resin column includes at least one chelating cation exchange resin column with a diameter-to-height ratio of (1.5-3):1; the deep purification resin column includes at least one chelating cation exchange resin column with a diameter-to-height ratio of (0.8-1):1; and the fine treatment resin column includes at least one chelating cation exchange resin column with a diameter-to-height ratio of (0.5-0.8):1.

[0008] In one embodiment, sodium sulfide is mixed with dilute sulfuric acid to obtain hydrogen sulfide gas, and the hydrogen sulfide gas is then subjected to dehydration and deoxygenation treatment to obtain hydrogen sulfide feed gas, including the following steps: The sodium sulfide solid is mixed with dilute sulfuric acid and reacted at 45°C-75°C to generate hydrogen sulfide gas. The concentration of the dilute sulfuric acid is 10wt%-18wt%. The hydrogen sulfide gas is dehydrated by passing it through a molecular sieve dehydrator; The hydrogen sulfide gas is then deoxygenated through a palladium-carbon deoxidizer to obtain high-purity hydrogen sulfide gas.

[0009] In one embodiment, the hydrogen sulfide feed gas is introduced into the precursor purification liquid and reacted under heating conditions to obtain lithium sulfide slurry, wherein the heating temperature is 105°C-120°C.

[0010] In one embodiment, the hydrogen sulfide feed gas is introduced into the precursor purification liquid, and the molar ratio of lithium hydroxide to hydrogen sulfide is 2:1.02 to 2:1.05.

[0011] In one embodiment, the evaporation temperature for the evaporation concentration is 100°C-105°C, and the crystallization temperature is 40°C-55°C.

[0012] In one embodiment, when the lithium sulfide crystal is vacuum calcined, the vacuum calcination temperature is 200℃-700℃, and the vacuum degree of the vacuum calcination is less than 50Pa.

[0013] In one embodiment, the high-purity lithium sulfide preparation method with liquid phase purification and impurity removal prepares high-purity lithium sulfide through a high-purity lithium sulfide preparation system, which includes a lithium hydroxide purification unit, a hydrogen sulfide preparation unit, a lithium sulfide reaction unit, a deep purification unit, and a post-treatment unit. The lithium hydroxide purification unit includes a dissolving tank, a stepped resin column assembly, and a nanofiltration membrane assembly connected in sequence. It is used to dissolve lithium hydroxide and perform resin exchange purification and nanofiltration treatment on the resulting solution in sequence to obtain a precursor purified solution. The hydrogen sulfide preparation unit includes a sodium sulfide feeding device, a dilute sulfuric acid metering tank, a reaction vessel, a dehydration device, and a deoxygenation device connected in sequence. It is used to react sodium sulfide with dilute sulfuric acid to generate hydrogen sulfide gas, and to purify the gas by dehydration and deoxygenation in sequence to obtain purified hydrogen sulfide gas. The precursor purification liquid and the purified hydrogen sulfide gas are transported to the lithium sulfide reaction unit to react and generate lithium sulfide slurry; the lithium sulfide slurry is then processed by the deep purification unit and the post-processing unit to obtain high-purity lithium sulfide.

[0014] A method for preparing a sulfide solid electrolyte material, comprising preparing lithium sulfide using the liquid-phase purification and impurity removal high-purity lithium sulfide preparation method described in any of the above embodiments, mixing and reacting the lithium sulfide with phosphorus pentasulfide or a halide, and obtaining the sulfide solid electrolyte material by mechanical ball milling and heat treatment.

[0015] A power battery comprising the sulfide solid electrolyte material obtained in any of the above embodiments.

[0016] Compared with the prior art, this disclosure has at least the following advantages: The above-mentioned method for preparing high-purity lithium sulfide through liquid-phase purification and impurity removal: 1. Significantly Improved Purity: Through the synergistic effect of the stepped resin column assembly (three-stage chelating cation exchange resin column) and nanofiltration membrane, targeted and deep removal of calcium and magnesium cations and sulfate anions is achieved, reducing the total amount of impurity ions in the precursor purification solution to below 1 ppm; combined with the five-stage purification process for hydrogen sulfide gas (low temperature cooling - gas-liquid separation - dehydration - deoxygenation - terminal filtration), oxidation and hydrolysis side reactions are effectively avoided, and the final lithium sulfide product purity is ≥99.94%; 2. Significantly improved yield: Nanofiltration membranes remove 20%-40% of the solvent water in advance, significantly shortening the evaporation and concentration time and reducing the deterioration loss caused by high-temperature exposure of lithium sulfide; inert gas protection throughout the process and staged calcination process further reduce the risk of oxidation and hydrolysis, with a product yield of ≥97.8%, which is 1-3 percentage points higher than the existing process; 3. Strong process stability: The stepped resin column assembly ensures a stable and controllable impurity removal process through the gradient design of the diameter-to-height ratio and the setting of the intermediate buffer tank; key process parameters (reaction temperature, calcination program, gas purity, etc.) can be precisely controlled, resulting in good product quality uniformity and suitability for large-scale industrial production. 4. Excellent application performance: The lithium sulfide raw material prepared by this method can be used to synthesize sulfide solid electrolyte materials with an ionic conductivity of ≥12.5mS / cm (25℃). This electrolyte material has good compatibility with lithium metal anodes and high-voltage cathodes. When used in power batteries, it can significantly improve battery cycle life and safety performance. 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 liquid-phase purification and impurity removal method for preparing high-purity lithium sulfide according to an embodiment; Figure 2 This is a schematic diagram of a high-purity lithium sulfide preparation system according to an embodiment. 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 The present invention provides a method for preparing high-purity lithium sulfide through liquid-phase purification and impurity removal, comprising the following steps: S101, Lithium hydroxide is dissolved in deionized water to obtain a lithium hydroxide solution, wherein the purity of the lithium hydroxide is greater than 98%.

[0023] S103, the lithium hydroxide solution is passed sequentially through a stepped resin column assembly and a nanofiltration membrane to obtain a precursor purified solution; wherein, the stepped resin column assembly includes a pretreatment resin column, a deep purification resin column, and a fine treatment resin column arranged sequentially. The pretreatment resin column is used to initially remove impurities from the initial lithium hydroxide solution, rapidly adsorbing most of the calcium and magnesium ions; the deep purification resin column is used to receive the solution after the pretreatment stage and perform deep purification to further reduce the concentration of calcium and magnesium ions; the fine treatment resin column is used to further remove impurities from the solution after the deep purification stage, ensuring that the calcium and magnesium ion content in the effluent meets the predetermined standard; the nanofiltration membrane is used to intercept and remove sulfate ions. It is understood that... S105, sodium sulfide is mixed with dilute sulfuric acid to react and obtain hydrogen sulfide gas. The hydrogen sulfide gas is then dehydrated and deoxygenated to obtain purified hydrogen sulfide raw material gas.

[0024] S107, the hydrogen sulfide raw material gas is introduced into the precursor purification liquid and reacted under heating conditions to obtain lithium sulfide slurry.

[0025] S109, the lithium sulfide slurry is evaporated and concentrated under inert gas protection, then recrystallized and centrifuged to obtain lithium sulfide crystals.

[0026] S111, the lithium sulfide crystal is vacuum calcined and pulverized to obtain high-purity lithium sulfide.

[0027] Understandably, the initial purity of lithium hydroxide raw material affects subsequent purification efficiency and the purity of the final product. Higher initial purity can significantly reduce the adsorption load of ion exchange resins, extend resin lifespan, and ensure that the total amount of impurity ions in the solution after deep purification consistently meets the ppb level standard. Stepped resin column targeted removal of Ca... 2+ Mg 2+ Cation-dependent nanofiltration membranes effectively remove SO4. 2- The presence of anions stabilizes the total amount of impurity ions in the precursor purification solution to the ppb level, thus eliminating the introduction of impurities at the source.

[0028] Understandably, dehydrating and deoxygenating the hydrogen sulfide feedstock gas completely eliminates the hydrolysis and oxidation side reactions that may be caused by moisture and oxygen, ensuring the selectivity of the synthesis reaction and the chemical stability of the product. The use of inert gas protection during evaporation, concentration, and crystallization prevents the lithium sulfide slurry from coming into contact with air during the high-temperature concentration stage, thus avoiding the introduction of oxides or carbonate impurities. This allows the crystallization process to take place in a clean and stable environment, resulting in more complete crystal growth and comprehensively improving the purity and yield of the final lithium sulfide product.

[0029] Understandably, nanofiltration membranes remove approximately 20%-40% of the solvent water during impurity removal, significantly increasing the initial solids content of the resulting lithium sulfide slurry. Subsequent evaporation and concentration steps require only the removal of less water to reach the supersaturation point, greatly shortening evaporation time and reducing the material's exposure time under prolonged heating. Inert protection and shorter time also directly reduce the potential risks of product oxidation and hydrolysis due to minute leaks or side reactions, thus minimizing yield losses caused by product deterioration. Faster concentration rates allow the system to more quickly traverse the metastable region, initiating homogeneous nucleation, making the crystallization process more controllable and efficient. Controllable rapid crystallization helps form larger crystals with uniform particle size and complete crystal structure. These crystals result in higher solid-liquid separation efficiency, less entrained mother liquor, and lower crystal loss during subsequent centrifugation, directly improving the quality and proportion of solid products recovered from the slurry.

[0030] Understandably, by eliminating Ca 2+ Mg 2+ SO4 2-After impurity ions are thoroughly removed, the co-precipitation caused by impurity salts is eliminated, allowing the lithium sulfide generated in the reaction to crystallize directionally and completely, thus increasing the theoretical yield; trace amounts of Ca... 2 ⁺、Mg 2 ⁺ Particulate or impurity colloids are extremely strong heterogeneous nucleating agents. Reducing impurities inhibits heterogeneous nucleation, reduces the formation and loss of fine crystals, resulting in more complete growth of lithium sulfide crystals with smoother surfaces, reduces lattice defects, and ensures the directional and complete precipitation of the target product.

[0031] The aforementioned liquid-phase purification and impurity removal method for preparing high-purity lithium sulfide utilizes a stepped resin column assembly for multi-stage removal of calcium and magnesium cations, and a nanofiltration membrane for targeted removal of anionic sulfate ions, resulting in deep purification of the raw lithium hydroxide solution and eliminating the introduction of impurities. Dehydration and deoxygenation of hydrogen sulfide gas effectively prevents oxidation or hydrolysis side reactions during lithium sulfide synthesis, ensuring the selectivity of the synthesis reaction and the chemical stability of the product, thus improving the purity and yield of the lithium sulfide product. The nanofiltration membrane removes some of the solvent water, significantly increasing the initial solid content of the resulting lithium sulfide slurry, greatly shortening the evaporation time, and reducing the exposure time of lithium sulfide under prolonged heating, thereby reducing yield loss due to product deterioration. Inert gas protection is used during evaporation, concentration, and crystallization processes to prevent the lithium sulfide slurry from contacting air during the high-temperature concentration stage, thus preventing the introduction of oxides or carbonate impurities and further improving the purity and yield of the lithium sulfide product.

[0032] In one embodiment, the pretreatment resin column includes at least one chelating cation exchange resin column with a diameter-to-height ratio of (1.5-3):1; the deep purification resin column includes at least one chelating cation exchange resin column with a diameter-to-height ratio of (0.8-1):1; and the fine treatment resin column includes at least one chelating cation exchange resin column with a diameter-to-height ratio of (0.5-0.8):1. In this embodiment, the pretreatment resin column is designed with a relatively large diameter-to-height ratio to reduce flow path resistance and increase throughput, making it suitable for rapid, high-throughput preliminary treatment of initial solutions with high impurity loads. It can effectively adsorb most calcium and magnesium ions without easily causing clogging. The deep purification resin column has a diameter-to-height ratio close to 1:1, balancing treatment efficiency and contact depth, ensuring sufficient residence time of the solution within the column for further deep removal of residual impurities. The fine treatment resin column uses a smaller diameter-to-height ratio, i.e., a more slender column, significantly increasing the contact path and time between the solution and the resin, making it suitable for deep removal of low-concentration impurity ions. Through the resin column structure design that progresses from wide and short to slender and long with a gradually decreasing diameter-to-height ratio, the system achieves a smooth transition from rapid coarsening to deep purification, thereby maximizing the purification efficiency of the resin at each stage, reducing unnecessary pressure drop and energy consumption, and ensuring that the entire stepped purification system can continuously and stably produce ultra-high purity precursor purified solution. Furthermore, in one embodiment, the pretreatment resin column includes 1 to 2 chelating cation exchange resin columns connected in parallel, with a total resin loading of 40% of the total loading of the stepped resin column assembly; the deep purification resin column includes 2 to 4 chelating cation exchange resin columns connected in parallel, with a total resin loading of 40% of the total loading of the stepped resin column assembly; and the fine treatment resin column includes 1 chelating cation exchange resin column, with a total resin loading of 20% of the total loading of the stepped resin column assembly. In this embodiment, the resin quantity distribution of 40%-40%-20% of the total resin loading precisely matches the expected impurity load (high-medium-low) at each purification stage, maximizing the adsorption capacity of the chelating cation exchange resin column and avoiding resource waste; the parallel design of the pretreatment and deep purification stages improves the overall processing throughput of the system and can adapt to different feed flow rates by adjusting the number of operating columns.

[0033] Furthermore, in one embodiment, a transfer buffer tank is provided between the pretreatment resin column and the deep purification resin column, and between the deep purification resin column and the fine treatment resin column; the volume of the transfer buffer tank is 1.5 times larger than the volume of the previous chelating cation exchange resin column, and the transfer buffer tank is equipped with an online pH monitor and a stirring device. In this embodiment, the intermediate buffer tank provides sufficient buffer capacity to smooth out flow and pressure fluctuations caused by parallel operation of multiple columns in the preceding stage or feed fluctuations, providing continuous and stable feed conditions for the subsequent chelating cation exchange resin. An online pH monitor allows for continuous and real-time monitoring of the effluent pH value, enabling immediate assessment of the purification status and regeneration point of the preceding resin and providing early warnings of potential process anomalies, thereby improving quality control. The stirring device inside the tank ensures thorough and uniform mixing of the solution, preventing solution heterogeneity caused by ion concentration gradients or possible trace precipitates. This provides a stable feed to the subsequent fine treatment resin column, avoiding bed disturbances or blockage risks caused by concentration pulses or solid particles, protecting the fine treatment resin column and extending its service life. When the preceding chelating cation exchange resin column is regenerated or maintained, the solution stored in the buffer tank can maintain continuous feed to the subsequent process for a certain period, significantly improving the operational flexibility and maintainability of the entire purification system.

[0034] In one embodiment, the chelating cation exchange resin column has an exchange capacity for calcium and magnesium greater than 2.0 mmol / g. In this embodiment, the chelating cation exchange resin column has high adsorption density and high selectivity; the chelating cation exchange resin column is type D401; and the exchange flow rate of the chelating cation exchange resin column is 1 BV / h-2 BV / h. In one embodiment, the nanofiltration membrane has a rejection rate of more than 95% for sulfate ions. In this embodiment, the nanofiltration membrane can retain more than 95% of sulfate ions on the concentration side, thereby effectively preventing sulfate ions from entering subsequent reaction and crystallization processes.

[0035] In one embodiment, sodium sulfide is mixed with dilute sulfuric acid to obtain hydrogen sulfide gas, and the hydrogen sulfide gas is then subjected to dehydration and deoxygenation treatment to obtain hydrogen sulfide feed gas, including the following steps: The sodium sulfide solid is mixed with dilute sulfuric acid and reacted at 45°C-75°C to generate hydrogen sulfide gas. The concentration of the dilute sulfuric acid is 10wt%-18wt%. The hydrogen sulfide gas is dehydrated by passing it through a molecular sieve dehydrator; The hydrogen sulfide gas is then deoxygenated using a palladium-carbon deoxidizer to obtain high-purity hydrogen sulfide gas. In this embodiment, a reaction temperature of 45℃-75℃ is selected to promote the reaction rate of sodium sulfide and dilute sulfuric acid, ensuring stable generation of hydrogen sulfide gas and avoiding excessive volatilization of 10wt%-18wt% dilute sulfuric acid or unnecessary side reactions due to excessively high temperatures, thus providing a stable and controllable gas source. The molecular sieve dehydrator utilizes its efficient adsorption characteristics to deeply remove water vapor from the gas, preventing moisture from affecting the activity and lifespan of the deoxygenation catalyst in the subsequent palladium-carbon deoxidizer and reducing the moisture content of the lithium sulfide slurry. The dehydrated hydrogen sulfide gas enters the palladium-carbon deoxidizer, where trace amounts of oxygen and hydrogen are removed under the action of the catalyst. Through the synergistic treatment of molecular sieve dehydration and palladium-carbon catalytic deoxygenation, the moisture and oxygen content in the obtained high-purity hydrogen sulfide gas is controlled at the ppm level or even lower. When the high-purity hydrogen sulfide gas reacts with the precursor purification liquid, the risk of oxidation or hydrolysis side reactions introduced by the gas is eliminated.

[0036] In one embodiment, the water absorption rate of the molecular sieve dehydrator is greater than 20%, and the deoxygenation efficiency of the palladium-carbon deoxidizer is greater than 99%. In this embodiment, the molecular sieve dehydrator is equipped with a palladium-carbon catalyst and has an extremely high static water adsorption capacity, ensuring that the dehydrator can operate over a long period of time; the palladium-carbon deoxidizer reduces the residual oxygen concentration in the gas to the ppm or even ppb level.

[0037] It is understandable that in the process of mixing sodium sulfide with dilute sulfuric acid to obtain hydrogen sulfide gas, the hydrogen sulfide gas is prone to carrying tiny droplets or aerosols, such as NaHS and Na2SO4 particles, thus forming a source of pollution.

[0038] Furthermore, in one embodiment, before passing the hydrogen sulfide gas through the molecular sieve dehydrator, the hydrogen sulfide gas is first passed through a gas-liquid separation device to remove droplets and aerosols entrained in the hydrogen sulfide gas; after passing the hydrogen sulfide gas through the palladium-carbon deoxidizer, it is then passed through a terminal filtration device to retain particulate matter, ultimately obtaining the purified hydrogen sulfide raw material gas. In this embodiment, the gas-liquid separation device is a condensation filter, and the terminal filtration device is a polytetrafluoroethylene membrane filter; the condensation filter is used to pre-treat the gas, efficiently removing droplets and aerosols entrained in the preceding reaction process, preventing physical impurities from entering the subsequent molecular sieve dehydrator; the hydrogen sulfide gas is then passed through the terminal filtration device to retain particulate matter with a particle size greater than or equal to 0.01 micrometers, improving the cleanliness of the hydrogen sulfide gas; through the synergy of gas-liquid separation, dehydration, and terminal filtration, the problem of removing impurities of different forms during the gas purification process is solved, and the reliability of the purification unit and the cleanliness of the final gas are significantly improved.

[0039] Furthermore, in one embodiment, before the hydrogen sulfide gas is separated into gas and liquid phases, the hydrogen sulfide gas is first subjected to low-temperature cooling for deep dehydration, with the low-temperature cooling temperature ranging from -20°C to -40°C. In this embodiment, at the low temperature of -20°C to -40°C, most of the water vapor in the hydrogen sulfide gas will condense into ice crystals or droplets. At the same time, any high-boiling-point volatile impurities that may be carried in the gas will also be condensed and precipitated at this temperature, which can significantly reduce the absolute water content and impurity load of the gas. Low-temperature condensation reduces the separation load of the subsequent gas-liquid separation device. By introducing the low-temperature condensation step of -20°C to -40°C, a complementary and progressively enhanced purification chain is formed with the original physical separation, adsorption dehydration, and terminal filtration technologies. This constructs a four-stage purification system of low-temperature deep condensation, physical separation, adsorption dehydration, and terminal filtration, thereby obtaining hydrogen sulfide gas with high purity.

[0040] In one embodiment, the hydrogen sulfide feed gas is introduced into the precursor purification liquid, and the molar ratio of lithium hydroxide to hydrogen sulfide is 2:1.02 to 2:1.05. In this embodiment, a slight chemical excess of 1% to 2.5% of hydrogen sulfide is maintained to provide sufficient driving force for the gas-liquid heterogeneous reaction, compensate for the possible loss of absorption efficiency of the gas in the solution, and ensure that all lithium hydroxide in the solution is completely consumed. This ensures that the reaction proceeds thoroughly and maintains a slightly reducing environment, resulting in a chemically homogeneous and stable lithium sulfide slurry. The slight excess of hydrogen sulfide forms a weakly reducing atmosphere in the reaction system, effectively inhibiting or reducing oxidation side reactions that may be caused by trace oxygen infiltration.

[0041] In one embodiment, the evaporation temperature for concentration is 100°C-105°C, and the crystallization temperature is 40°C-55°C. In this embodiment, an evaporation temperature slightly higher than the atmospheric boiling point of water is chosen to provide the maximum thermodynamic driving force for removing the solvent water, thereby achieving rapid concentration, shortening the process time, and reducing the total exposure time of the material at high temperatures. When the temperature is below 40°C, the crystal precipitation rate is too fast, easily forming fine crystals and adsorbing potassium from the mother liquor. + Na + While removing impurities slightly improves the yield, it increases the difficulty of subsequent centrifugation and reduces crystal purity, failing to meet high-purity requirements. At temperatures above 55℃, the solubility of Li₂S increases, slowing the crystal precipitation rate; some Li₂S remains dissolved in the mother liquor, leading to a decrease in yield. Specifically, for every 10℃ increase, the yield decreases by approximately 3%-5%. Simultaneously, high temperatures accelerate the hydrolysis of Li₂S, generating LiHS, which is readily soluble in water, further reducing the Li₂S crystallization yield. Setting the crystallization temperature in the 40℃-55℃ range, significantly lower than the evaporation temperature, allows the solubility of Li₂S in water to decrease with decreasing temperature. Low temperatures promote rapid precipitation of Li₂S while slowing down K₂S precipitation. +Na + Co-precipitation of impurity ions ensures the purity of Li2S crystals while achieving a yield of over 98%.

[0042] Furthermore, in one embodiment, after evaporating and concentrating the lithium sulfide slurry under an inert atmosphere, centrifuging it to obtain lithium sulfide crystals and mother liquor, and then vacuum calcining the lithium sulfide crystals to obtain lithium sulfide powder, the following steps are also included: Under an inert atmosphere, the lithium sulfide crystals were rinsed with a saturated lithium sulfide solution at 0℃-5℃. It is understood that mother liquor residue remains on the surface of the lithium sulfide crystals after centrifugation. Since the saturated lithium sulfide solution is relatively saturated with respect to the lithium sulfide product, the Li₂S in the crystal body and the Li₂S in the solution are in dynamic equilibrium during rinsing, avoiding dissolution and loss of the lithium sulfide crystals during the rinsing process. The rinsing process removes Na₂S from the crystals. + K + The mother liquor containing soluble impurities is eluted and transferred to the liquid phase to achieve deep purification. The temperature of the saturated lithium sulfide solution is controlled at 0℃-5℃. The low temperature environment ensures and enhances the state of the saturated solution, and the low temperature inhibits the possible hydrolysis side reaction of lithium sulfide and reduces the diffusion rate of impurity ions, making the rinsing process more controllable and preventing impurities from migrating into the lithium sulfide crystal.

[0043] In one embodiment, the lithium sulfide crystal is vacuum calcined at a temperature of 200°C-700°C, and the vacuum degree is less than 50 Pa. In this embodiment, the vacuum degree is controlled to be less than 50 Pa, creating a deeply oxygen-deficient and low-pressure environment. This low-pressure environment provides a strong thermodynamic driving force for the removal of various volatile impurities. Under high vacuum, the boiling points of residual water, solvent molecules, and trace amounts of volatile components that may remain from previous rinsing steps are greatly reduced, thereby efficiently removing water. Furthermore, in one embodiment, the staged calcination during vacuum calcination includes the following steps: The lithium sulfide crystal is subjected to a first-stage calcination. The lithium sulfide crystal is heated to a first temperature (200℃-250℃) at a heating rate of 2℃ / min to 5℃ / min under a vacuum of less than 50Pa, and held at the first temperature for 1h to 3h. The lithium sulfide crystal is subjected to a second-stage calcination. Under the condition of maintaining a vacuum degree of less than 50 Pa, the temperature is increased to a second temperature at a heating rate of 5°C / min to 10°C / min. The second temperature is 400°C-450°C. The temperature is held at the second temperature for 0.5 hours to 2 hours. The lithium sulfide crystal is subjected to a third-stage calcination. Under the condition of maintaining a vacuum degree of less than 50 Pa, the temperature is increased to a third temperature of 600-700°C at a heating rate of 3°C / min to 8°C / min. The third temperature is then held at the second temperature for 0.5 to 1.5 hours.

[0044] In this embodiment, during the first-stage calcination, residual physically adsorbed water in the lithium sulfide crystal is gently and steadily removed by a slow heating rate, and the high vacuum environment ensures that the moisture is completely removed. During the second-stage calcination, a medium-temperature addition is carried out to decompose or volatilize any remaining trace organic impurities or thermally unstable compounds. Through the third-stage calcination, the high temperature optimizes the lattice of lithium sulfide, thereby obtaining high-purity lithium sulfide with ultra-low moisture, extremely high purity, and complete crystal structure.

[0045] like Figure 2 As shown, in one embodiment, the high-purity lithium sulfide preparation method with liquid phase purification and impurity removal prepares high-purity lithium sulfide through a high-purity lithium sulfide preparation system, which includes a lithium hydroxide purification unit 100, a hydrogen sulfide preparation unit 200, a lithium sulfide reaction unit 300, a deep purification unit 400, and a post-treatment unit 500. The lithium hydroxide purification unit 100 includes a dissolving tank 110, a stepped resin column assembly 120 and a nanofiltration membrane assembly 130 connected in sequence, used to dissolve lithium hydroxide and perform resin exchange purification and nanofiltration treatment on the resulting solution in sequence to obtain a precursor purified solution. The hydrogen sulfide preparation unit 200 includes a sodium sulfide feeding device 210, a dilute sulfuric acid metering tank 220, a reaction vessel 230, a dehydration device 240, and a deoxygenation device 250 connected in sequence. It is used to react sodium sulfide with dilute sulfuric acid to generate hydrogen sulfide gas, and to purify the gas by dehydration and deoxygenation in sequence to obtain purified hydrogen sulfide gas. The precursor purification liquid and the purified hydrogen sulfide gas are transported to the lithium sulfide reaction unit 300 for reaction to generate lithium sulfide slurry; the lithium sulfide slurry is then processed sequentially by the deep purification unit and the post-processing unit 500 to obtain high-purity lithium sulfide. In this embodiment, the deep purification unit 400 includes a concentrator 410 and a centrifuge 420 connected in sequence, and the post-processing unit 500 includes a vacuum calcining furnace 510 and a pulverizer and classifier 520 connected in sequence. The high-purity lithium sulfide preparation system constructs a fully enclosed, controlled atmosphere environment from raw material dissolution to final lithium sulfide packaging. Materials are transported and processed entirely within a controlled atmosphere or through closed pipelines, preventing air introduction, ensuring high product purity and chemical stability, and enhancing production safety. Each unit is equipped with corresponding monitoring and control instruments, such as temperature, pressure, pH, flow rate, and vacuum sensors, enabling precise measurement, adjustment, and recording of key process parameters such as resin exchange flow rate, reaction temperature, gas purification efficiency, evaporation and crystallization conditions, and calcination procedures. This ensures process reproducibility and the uniformity and stability of product quality. The high-purity lithium sulfide preparation system enables stable, efficient, and scalable industrial production.

[0046] This application also provides a method for preparing a sulfide solid electrolyte material. Lithium sulfide is prepared using the high-purity lithium sulfide preparation method described in any of the above embodiments, involving liquid-phase purification and impurity removal. The lithium sulfide is mixed and reacted with phosphorus pentasulfide or halides, followed by mechanical ball milling and heat treatment to obtain the sulfide solid electrolyte material. In this embodiment, the ionic conductivity of the sulfide solid electrolyte is extremely sensitive to its chemical composition and lattice purity. The high-purity lithium sulfide preparation method eliminates the blockage and interference of impurity ions on the lithium-ion transport channels from the source, thereby providing a lithium source for synthesizing electrolyte materials with high intrinsic ionic conductivity. High-purity and stoichiometrically accurate lithium sulfide can undergo a more complete and uniform solid-phase or liquid-phase reaction with phosphorus pentasulfide or halides. High-purity raw materials can reduce uncontrollable side reactions caused by impurities, promoting the pure and complete formation of the target crystal phase, thereby obtaining an electrolyte material with high crystallinity, a single phase composition, and a wide electrochemical window.

[0047] This application also provides a power battery, including the sulfide solid electrolyte material obtained in any of the above embodiments. In this embodiment, the power battery is an all-solid-state lithium battery or a hybrid solid-liquid lithium battery, and the sulfide solid electrolyte material is used between at least one of its positive and negative electrodes and the electrolyte layer. The electrolyte material synthesized from lithium sulfide prepared by the high-purity lithium sulfide preparation method has high lithium-ion conductivity, can stably match high-capacity lithium metal negative electrodes and high-voltage lithium-rich manganese-based and lithium cobalt oxide positive electrode materials, and has extremely low impurity content, which significantly reduces interfacial side reactions and irreversible consumption of active lithium during cycling, thereby greatly improving the battery's long cycle life.

[0048] Compared with the prior art, this disclosure has at least the following advantages: The aforementioned liquid-phase purification and impurity removal method for preparing high-purity lithium sulfide utilizes a stepped resin column assembly for multi-stage removal of calcium and magnesium cations, and a nanofiltration membrane for targeted removal of anionic sulfate ions, resulting in deep purification of the raw lithium hydroxide solution and eliminating the introduction of impurities. Dehydration and deoxygenation of hydrogen sulfide gas effectively prevents oxidation or hydrolysis side reactions during lithium sulfide synthesis, ensuring the selectivity of the synthesis reaction and the chemical stability of the product, thus improving the purity and yield of the lithium sulfide product. The nanofiltration membrane removes some of the solvent water, significantly increasing the initial solid content of the resulting lithium sulfide slurry, greatly shortening the evaporation time, and reducing the exposure time of lithium sulfide under prolonged heating, thereby reducing yield loss due to product deterioration. Inert gas protection is used during evaporation, concentration, and crystallization processes to prevent the lithium sulfide slurry from contacting air during the high-temperature concentration stage, thus preventing the introduction of oxides or carbonate impurities and further improving the purity and yield of the lithium sulfide product.

[0049] Significantly improved purity: Through the synergistic effect of the stepped resin column assembly (three-stage chelating cation exchange resin column) and nanofiltration membrane, targeted and deep removal of calcium and magnesium cations and sulfate anions is achieved, reducing the total amount of impurity ions in the precursor purification solution to below 1 ppm; combined with the five-stage purification process for hydrogen sulfide gas (low temperature cooling - gas-liquid separation - dehydration - deoxygenation - terminal filtration), oxidation and hydrolysis side reactions are effectively avoided, and the final lithium sulfide product purity is ≥99.94%; Significantly improved yield: Nanofiltration membranes remove 20%-40% of the solvent water in advance, significantly shortening the evaporation and concentration time and reducing the deterioration loss caused by high-temperature exposure of lithium sulfide; Inert gas protection throughout the process and staged calcination further reduce the risks of oxidation and hydrolysis, with a product yield of ≥97.8%, which is 1-3 percentage points higher than the existing process; High process stability: The stepped resin column assembly ensures a stable and controllable impurity removal process through the gradient design of the diameter-to-height ratio and the setting of the intermediate buffer tank; key process parameters (reaction temperature, calcination program, gas purity, etc.) can be precisely controlled, resulting in good product quality uniformity and suitability for large-scale industrial production. Excellent application performance: The lithium sulfide raw material prepared by this method can be used to synthesize sulfide solid electrolyte materials with an ionic conductivity of ≥12.5mS / cm (25℃). This electrolyte material has good compatibility with lithium metal anodes and high-voltage cathodes. When used in power batteries, it can significantly improve battery cycle life and safety performance.

[0050] 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.

[0051] Example 1 10 kg of lithium hydroxide (98% purity) was dissolved in 90 L of deionized water to obtain a 10 wt% solution. This solution was then passed through a D401 cation exchange resin column (flow rate 1 BV / h) and a nanofiltration membrane (molecular weight cutoff 150 Da) to obtain a purified precursor solution. 5 kg of sodium sulfide (98% purity) was mixed with 10 wt% dilute sulfuric acid (30 L) and reacted at 75°C to generate hydrogen sulfide gas. The hydrogen sulfide gas was dehydrated using a molecular sieve (water content 0.05 ppm) and deoxygenated on palladium on carbon (oxygen content 0.005 ppm) to obtain high-purity hydrogen sulfide. The purified precursor solution was then passed into a reactor, argon gas (99.99% purity) was introduced, the temperature was raised to 102°C, and hydrogen sulfide was introduced at a rate of 0.5 L / min. The reaction was carried out for 4 hours to obtain a crude lithium sulfide slurry.

[0052] The crude slurry was evaporated and concentrated at 100°C under an inert atmosphere (argon, purity ≥99.99%), and then crystallized at 55°C to obtain Li2S crystals. The Li2S crystals were separated by centrifugation. The Li2S crystals were then placed in a vacuum furnace (460°C, vacuum degree 5Pa) and calcined for 2 hours to obtain a high-purity lithium sulfide product with a purity of 99.95%.

[0053] Example 2 20 kg of lithium hydroxide (98% purity) was dissolved in 80 L of deionized water to obtain a 20 wt% solution; this solution was then passed through a D401 cation exchange resin column (flow rate 2 BV / h) and treated with a nanofiltration membrane. 10 kg of sodium sulfide (98% purity) was mixed with 18 wt% dilute sulfuric acid (60 L) and reacted at 45°C to obtain high-purity hydrogen sulfide. The purified precursor solution was then passed into a reactor under nitrogen gas. The reaction temperature was 120°C, the hydrogen sulfide flow rate was 1 L / min, and the reaction was carried out for 4 hours to obtain a lithium sulfide slurry.

[0054] Lithium sulfide slurry was evaporated and concentrated at 105°C under an inert atmosphere (nitrogen, purity ≥99.99%), and then crystallized at 40°C to obtain Li2S crystals. The Li2S crystals were separated by centrifugation. The Li2S crystals were then placed in a vacuum furnace (200°C, vacuum degree 8Pa) and calcined for 5 hours to obtain high-purity lithium sulfide product.

[0055] Example 3 15 kg of lithium hydroxide (98.8% purity) was dissolved in 85 L of deionized water to obtain a 15 wt% solution; this solution was then passed through a D401 cation exchange resin column (flow rate 1.5 BV / h) and treated with a nanofiltration membrane. 15 kg of sodium sulfide (98.5% purity) was mixed with 15 wt% dilute sulfuric acid (55 L) and reacted at 55 °C to obtain high-purity hydrogen sulfide. The purified precursor solution was then passed into a reactor under helium gas. The reaction temperature was 110 °C, the hydrogen sulfide flow rate was 0.8 L / min, and the reaction was carried out for 3 hours to obtain a lithium sulfide slurry.

[0056] Lithium sulfide slurry was evaporated and concentrated at 103°C under an inert atmosphere (helium, purity ≥99.99%), and then crystallized at 48°C to obtain Li2S crystals. The Li2S crystals were then separated by centrifugation. Li2S crystals were placed in a vacuum furnace (700℃, vacuum degree 3Pa) and calcined for 3 hours to obtain high-purity lithium sulfide product.

[0057] Comparative Example 1 10 kg of lithium hydroxide (98% purity) was dissolved in 90 L of deionized water to obtain a 10 wt% solution. Sulfate ions were then removed by nanofiltration (molecular weight cutoff 150 Da) to obtain a purified precursor solution. 5 kg of sodium sulfide (98% purity) was mixed with 10 wt% dilute sulfuric acid (30 L) and reacted at 75°C to generate hydrogen sulfide gas. The hydrogen sulfide gas was dehydrated (0.05 ppm water content) using a molecular sieve and deoxygenated on palladium on carbon (0.005 ppm oxygen content) to obtain high-purity hydrogen sulfide. The purified precursor solution was then introduced into a reactor with argon gas (99.99% purity), heated to 102°C, and hydrogen sulfide was introduced at a rate of 0.5 L / min for 4 hours to obtain a crude lithium sulfide slurry.

[0058] The crude slurry was evaporated and concentrated at 100°C under an inert atmosphere (argon, purity ≥99.99%), and then crystallized at 55°C to obtain Li2S crystals. The Li2S crystals were separated by centrifugation. The Li2S crystals were then placed in a vacuum furnace (460°C, vacuum degree 5Pa) and calcined for 2 hours to obtain a high-purity lithium sulfide product with a purity of 99.95%.

[0059] Comparative Example 2 10 kg of lithium hydroxide (98% purity) was dissolved in 90 L of deionized water to obtain a 10 wt% solution; this solution was then passed through a D401 cation exchange resin column (flow rate 1 BV / h) to obtain a precursor purification solution. 5 kg of sodium sulfide (98% purity) was mixed with 10 wt% dilute sulfuric acid (30 L) and reacted at 75°C to generate hydrogen sulfide gas; the hydrogen sulfide gas was dehydrated by a molecular sieve (water content 0.05 ppm) and deoxygenated on palladium on carbon (oxygen content 0.005 ppm) to obtain high-purity hydrogen sulfide. The precursor purification solution was then passed into a reactor, argon gas (99.99% purity) was introduced, the temperature was raised to 102°C, and hydrogen sulfide was introduced at a rate of 0.5 L / min. The reaction was carried out for 4 hours to obtain a crude lithium sulfide slurry.

[0060] The crude slurry was evaporated and concentrated at 100°C under an inert atmosphere (argon, purity ≥99.99%), and then crystallized at 55°C to obtain Li2S crystals. The Li2S crystals were separated by centrifugation. The Li2S crystals were then placed in a vacuum furnace (460°C, vacuum degree 5Pa) and calcined for 2 hours to obtain a high-purity lithium sulfide product with a purity of 99.95%.

[0061] Table 1. Content Test Table of Precursor Purification Solution Table 2. Lithium sulfide crystal content and solid electrolyte test results. It should be noted that Ca was detected using inductively coupled plasma mass spectrometry (ICP-MS). 2+ M 2+ K + Na + Impurities; SO4 in aqueous solution was separated and detected by ion chromatography (IC). 2- Anion content. High-purity lithium sulfide and phosphorus pentasulfide, among other raw materials, were uniformly mixed in an inert atmosphere glove box according to the target stoichiometric ratio, and then ball-milled using high-energy machinery to form a precursor powder. This powder was then hot-pressed or heat-treated under high vacuum and a suitable temperature to prepare a dense, flat solid electrolyte disc. After preparing blocking electrodes on both sides of the disc, it was placed in a sealed test fixture and connected to an electrochemical workstation. Under isothermal conditions, a small-amplitude sinusoidal AC voltage signal was applied, and its impedance response was measured. The bulk ionic conductivity of the solid electrolyte at the test temperature was calculated.

[0062] Yield calculation: Yield (%) = (Actual quality of high-purity lithium sulfide product obtained / Theoretically calculated lithium sulfide yield based on lithium hydroxide feedstock quantity) × 100% Note: The theoretical yield is calculated based on the reaction of lithium hydroxide and hydrogen sulfide using stoichiometry (2LiOH + H2S = Li2S + 2H2O), assuming complete reaction of lithium hydroxide.

[0063] From Table 1 and Table 2 above, we can see that: 1. Compared with Comparative Example 1: Comparative Example 1 did not use a stepped resin column assembly, but only removed sulfate ions through nanofiltration membrane, resulting in a decrease in Ca in the precursor purification solution. 2+ Content reached 8.5 ppm, Mg 2+ The content reached 6.3 ppm, and the Ca content in the final lithium sulfide product was... 2+ Mg 2+ The impurity content increased to 10.8 ppm and 8.5 ppm respectively, and the purity of Li₂S decreased to 99.52%, with a yield of only 96.5%; while in Example 1, after multi-stage impurity removal using a stepped resin column, the Ca... 2+ Mg 2+ Impurities were reduced to below 0.5 ppm, and the purity of Li₂S reached 99.95%, with a yield of 98.2%. This indicates that the stepped resin column assembly effectively reduced the concentration of Ca... 2+ Mg 2+ Targeted removal of cations is key to improving product purity. Reducing impurity cations can avoid yield loss caused by co-precipitation of impurity salts, while ensuring the integrity of crystal growth.

[0064] 2. Compared with Comparative Example 2: Comparative Example 2 did not use nanofiltration membrane treatment, but only removed cations through a resin column, resulting in SO4 in the precursor purification solution. 2- The SO4 content reached 12.5 ppm in the final lithium sulfide product. 2- Impurities increased to 15.6 ppm, and the purity of Li₂S decreased to 99.58%, with a yield of only 95.3%; while in Example 2, after treatment with a nanofiltration membrane, SO₄²⁻... 2- Impurities were reduced to below 1.5 ppm, and the purity of Li₂S reached 99.94%, with a yield of 97.8%. This demonstrates the effectiveness of nanofiltration membranes in reducing SO₄²⁻. 2- The retention function is the core of controlling anionic impurities. At the same time, nanofiltration membranes can remove 20%-40% of solvent water, increase the initial solid content of the slurry, shorten the subsequent evaporation time, and reduce the risk of lithium sulfide hydrolysis and deterioration. However, due to the lack of nanofiltration membrane concentration step, the evaporation time of Comparative Example 2 increased, the hydrolysis loss intensified, and the yield further decreased.

[0065] Compared to Examples 1-3: Example 1 had a reaction temperature of 102℃ and a calcination temperature of 460℃, with a yield of 98.2%; Example 2 had a reaction temperature of 120℃ and a calcination temperature of 200℃, with a yield of 97.8%; and Example 3 had a reaction temperature of 110℃ and a calcination temperature of 700℃, with a yield of 98.5%. The data shows that a reaction temperature between 105℃ and 110℃ and a calcination temperature between 600℃ and 700℃ yields better yield and purity. Excessively high reaction temperatures (such as 120℃ in Example 2) accelerate the hydrolysis of lithium sulfide to form water-soluble LiHS, leading to a decrease in crystallization yield; excessively low calcination temperatures (such as 200℃ in Example 2) fail to completely remove residual moisture and organic impurities, affecting crystal purity. The combination of a mild reaction temperature and a high-temperature lattice optimization in Example 3 ensures both complete reaction and deep impurity removal, ultimately achieving the optimal yield and purity.

[0066] Overall performance correlation: The ionic conductivity of the sulfide solid electrolytes prepared in Examples 1-3 is ≥12.5 mS / cm, significantly higher than that of the comparative example (≤8.3 mS / cm). This indicates that the high purity of the lithium sulfide raw material directly determines the ion transport performance of the electrolyte. 2+ Mg 2+ SO4 2- The presence of impurities can block lithium-ion transport channels and reduce conductivity, further demonstrating the technical value of the multi-stage purification process in this patent.

[0067] 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 high-purity lithium sulfide through liquid-phase purification and impurity removal, characterized in that, Includes the following steps: Lithium hydroxide is dissolved in deionized water to obtain a lithium hydroxide solution, wherein the purity of the lithium hydroxide is greater than 98%. The lithium hydroxide solution is passed sequentially through a stepped resin column assembly and a nanofiltration membrane to obtain a precursor purified solution. The stepped resin column assembly includes a pretreatment resin column, a deep purification resin column, and a fine treatment resin column arranged sequentially. The pretreatment resin column is used to initially remove impurities from the initial lithium hydroxide solution, rapidly adsorbing most of the calcium and magnesium ions. The deep purification resin column receives the solution after the pretreatment stage and performs further purification to further reduce the concentration of calcium and magnesium ions. The fine treatment resin column performs deep purification on the solution after the deep purification stage, ensuring that the calcium and magnesium ion content in the effluent meets a predetermined standard. The nanofiltration membrane is used to intercept and remove sulfate ions. Sodium sulfide is mixed with dilute sulfuric acid to obtain hydrogen sulfide gas. The hydrogen sulfide gas is then dehydrated and deoxygenated to obtain purified hydrogen sulfide raw material gas. The hydrogen sulfide raw material gas is introduced into the precursor purification liquid and reacted under heating conditions to obtain lithium sulfide slurry. The lithium sulfide slurry was evaporated and concentrated under inert gas protection, then crystallized and separated by centrifugation to obtain lithium sulfide crystals. The lithium sulfide crystals are subjected to vacuum calcination and pulverization to obtain high-purity lithium sulfide.

2. The method for preparing high-purity lithium sulfide through liquid-phase purification and impurity removal according to claim 1, characterized in that, The pretreatment resin column includes at least one chelating cation exchange resin column, and the diameter-to-height ratio of the chelating cation exchange resin column in the pretreatment resin column is (1.5-3):

1. The deep purification resin column includes at least one chelating cation exchange resin column, and the diameter-to-height ratio of the chelating cation exchange resin column in the deep purification resin column is (0.8-1):

1. The fine treatment resin column includes at least one chelating cation exchange resin column, and the diameter-to-height ratio of the fine treatment resin column is (0.5-0.8):

1.

3. The method for preparing high-purity lithium sulfide by liquid-phase purification and impurity removal according to claim 1, characterized in that, Sodium sulfide is mixed with dilute sulfuric acid to obtain hydrogen sulfide gas. The hydrogen sulfide gas is then dehydrated and deoxygenated to obtain hydrogen sulfide feed gas, comprising the following steps: The sodium sulfide solid is mixed with dilute sulfuric acid and reacted at 45°C-75°C to generate hydrogen sulfide gas. The concentration of the dilute sulfuric acid is 10wt%-18wt%. The hydrogen sulfide gas is dehydrated by passing it through a molecular sieve dehydrator; The hydrogen sulfide gas is then deoxygenated through a palladium-carbon deoxidizer to obtain high-purity hydrogen sulfide gas.

4. The method for preparing high-purity lithium sulfide by liquid-phase purification and impurity removal according to claim 1, characterized in that, The hydrogen sulfide raw material gas is introduced into the precursor purification liquid and reacted under heating conditions to obtain lithium sulfide slurry. The heating temperature is 105℃-120℃.

5. The method for preparing high-purity lithium sulfide by liquid-phase purification and impurity removal according to claim 1, characterized in that, The hydrogen sulfide feed gas is introduced into the precursor purification liquid, and the molar ratio of lithium hydroxide to hydrogen sulfide is 2:1.02 to 2:1.

05.

6. The method for preparing high-purity lithium sulfide by liquid-phase purification and impurity removal according to claim 1, characterized in that, The evaporation temperature for the evaporation and concentration is 100℃-105℃, and the crystallization temperature is 40℃-55℃.

7. The method for preparing high-purity lithium sulfide by liquid-phase purification and impurity removal according to claim 1, characterized in that, When the lithium sulfide crystal is calcined under vacuum, the calcination temperature is 200℃-700℃, and the vacuum degree of the calcination is less than 50Pa.

8. The method for preparing high-purity lithium sulfide by liquid-phase purification and impurity removal according to claim 1, characterized in that, The method for preparing high-purity lithium sulfide through liquid-phase purification and impurity removal uses a high-purity lithium sulfide preparation system to prepare high-purity lithium sulfide. The high-purity lithium sulfide preparation system includes a lithium hydroxide purification unit, a hydrogen sulfide preparation unit, a lithium sulfide reaction unit, a deep purification unit, and a post-treatment unit. The lithium hydroxide purification unit includes a dissolving tank, a stepped resin column assembly, and a nanofiltration membrane assembly connected in sequence. It is used to dissolve lithium hydroxide and perform resin exchange purification and nanofiltration treatment on the resulting solution in sequence to obtain a precursor purified solution. The hydrogen sulfide preparation unit includes a sodium sulfide feeding device, a dilute sulfuric acid metering tank, a reaction vessel, a dehydration device, and a deoxygenation device connected in sequence. It is used to react sodium sulfide with dilute sulfuric acid to generate hydrogen sulfide gas, and to purify the gas by dehydration and deoxygenation in sequence to obtain purified hydrogen sulfide gas. The precursor purification liquid and the purified hydrogen sulfide gas are transported to the lithium sulfide reaction unit to react and generate lithium sulfide slurry; the lithium sulfide slurry is then processed by the deep purification unit and the post-processing unit to obtain high-purity lithium sulfide.

9. A method for preparing a sulfide solid electrolyte material, characterized in that, Lithium sulfide is prepared by the liquid-phase purification and impurity removal method according to any one of claims 1-8. The lithium sulfide is mixed and reacted with phosphorus pentasulfide or a halide, and then subjected to mechanical ball milling and heat treatment to obtain the sulfide solid electrolyte material.

10. A power battery, characterized in that, Includes the sulfide solid electrolyte material obtained according to claim 9.

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