Preparation method of battery-grade lithium salt

Abstract

The invention provides a preparation method of battery-grade lithium salt, and relates to the technical field of new energy materials. Starting from battery-grade lithium sulfate, part of lithium sulfate is reduced under hydrogen to obtain battery-grade lithium sulfide; part of lithium sulfate reacts with sodium carbonate to obtain battery-grade lithium carbonate, the battery-grade lithium carbonate reacts with hydrochloric acid to obtain lithium chloride, lithium chloride is electrolyzed to obtain metal lithium, and the metal lithium reacts with sulfur, is reduced and is converted into battery-grade lithium sulfide; part of lithium sulfate reacts with sodium hydroxide to obtain battery-grade lithium hydroxide, and then the battery-grade lithium hydroxide reacts with hydrogenation tail gas to obtain battery-grade lithium sulfide. Further, the battery-grade lithium sulfide can be obtained from the lithium-containing ore through the steps of calcination, sulfuric acid leaching, purification and the like. Through conversion and adjustment among different lithium salts, the cost of the lithium sulfide can be adjusted according to different conditions, and low-cost and large-scale mass production of the lithium sulfide is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of new energy materials and relates to a method for preparing battery-grade lithium salt. Background Art

[0002] All-solid-state lithium-ion batteries have high safety performance and excellent electrochemical performance due to the use of non-flammable solid electrolytes. Sulfide solid-state batteries are one of them. They have the characteristics of high ionic conductivity and low Young's modulus, and are one of the key research and development routes for all-solid-state lithium-ion batteries. Metallic lithium and lithium sulfide (Li2S) are the key raw materials for sulfide solid-state batteries, but the high price of lithium sulfide currently limits its widespread application in the market and hinders the rapid development of all-solid-state batteries. Therefore, exploring low-cost large-scale synthesis of battery-grade lithium sulfide has become one of the key factors in the industrialization of all-solid-state batteries.

[0003] At present, the main industrial production method of Li2S is carbon thermal reduction (Li2SO4+2C→Li2S+2CO2), which has many by-products and emits CO2. Other synthesis methods include double decomposition (2LiCl+Na2S→Li2S+2NaCl), solid phase reaction (2LiOH+H2S→Li2S+H2O or Li2CO3+H2S→Li2S+H2O+CO2), etc. Double decomposition reaction and gas-solid phase reaction are not thorough, the product purity cannot meet the requirements, and double decomposition reaction requires a large amount of organic solvents, which pollutes the environment. High temperature reaction has high requirements for reaction equipment and has certain safety risks.

[0004] Therefore, it is necessary to further study and improve the preparation process of battery-grade lithium salts to achieve large-scale mass production of Li2S at a low cost. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for preparing battery-grade lithium salt.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a battery-grade lithium salt comprises the following steps:

[0008] S1, providing battery-grade lithium sulfate, adding 10-60 wt % of the battery-grade lithium sulfate into sodium carbonate solution to precipitate lithium to obtain battery-grade lithium carbonate and lithium precipitation mother liquor; adding 10-30 wt % of the battery-grade lithium sulfate into alkaline solution, cooling and separating salt, evaporating and crystallizing to obtain battery-grade lithium hydroxide;

[0009] S2, the battery-grade lithium sulfate remaining in step S1 is reduced and purified using hydrogen to obtain battery-grade lithium sulfide and hydrogenation tail gas;

[0010] S3, the battery-grade lithium carbonate in step S1 is reacted with hydrochloric acid to obtain battery-grade lithium chloride, and the battery-grade lithium chloride is electrolyzed to obtain metallic lithium and chlorine;

[0011] S4. The battery-grade lithium hydroxide described in step S1 and the hydrogenated tail gas described in step S2 react to obtain battery-grade lithium sulfide.

[0012] Preferably, the preparation method of the battery-grade lithium sulfate described in step S1 is: roasting and leaching lithium-containing ore to obtain a lithium sulfate solution; the lithium sulfate solution is purified and concentrated, and then partially crystallized, dried, and crushed to obtain the battery-grade lithium sulfate.

[0013] More preferably, the purification is carried out by one or a combination of two or more of precipitation, filtration, resin adsorption and extraction methods; and the sum of the calcium and magnesium contents in the purified solution does not exceed 10 mg / L.

[0014] Preferably, the lithium precipitation mother liquor in step S1 is treated to obtain a sulfuric acid solution and an alkaline solution;

[0015] The sulfuric acid solution is used for the leaching in the method for preparing the battery-grade lithium sulfate;

[0016] The alkaline solution is used as the alkaline solution described in step S1.

[0017] More preferably, the treatment is carried out using a bipolar membrane electrodialysis method.

[0018] Preferably, the volume content of hydrogen sulfide in the hydrogenated tail gas in step S2 is 1-20%.

[0019] Preferably, the chlorine and hydrogen in step S3 react to obtain hydrogen chloride, and the hydrogen chloride is used as a raw material for the hydrochloric acid in step S3.

[0020] Preferably, in step S3, the metallic lithium and sulfur are reacted and then reduced with hydrogen to obtain battery-grade lithium sulfide.

[0021] More preferably, the reaction of metallic lithium and sulfur is carried out in an atmosphere containing a reducing gas.

[0022] Preferably, the purity of the hydrogen is not less than 99.99%, and the content of oxidizing gas, the content of water vapor, or the sum of the content of oxidizing gas and water vapor in the hydrogen does not exceed 20 ppm alone.

[0023] The beneficial effects of the present invention are:

[0024] (1) For battery-grade lithium salts, the present invention starts with battery-grade lithium sulfate, prepares battery-grade lithium carbonate, battery-grade lithium hydroxide, and metallic lithium respectively, and then converts them into battery-grade lithium sulfide respectively, thereby meeting the demand of sulfide solid-state batteries for sulfide electrolytes.

[0025] (2) The battery-grade lithium sulfate of the present invention starts from lithium-containing ore, opens up the lithium-containing ore-lithium sulfate-lithium carbonate-lithium chloride-metal lithium-lithium sulfide industry chain, provides sufficient raw materials for sulfide all-solid-state batteries, and can dynamically adjust the type and output of battery-grade lithium salts according to market demand, which is conducive to reducing the cost of sulfide electrolytes and realizing large-scale production.

[0026] (3) Auxiliary materials can be recycled, further reducing costs and increasing the self-sufficiency rate of raw materials. Sulfuric acid and alkali solution can be recycled after treatment, and the auxiliary material hydrochloric acid is obtained by the reaction of chlorine and hydrogen produced by electrolysis and recycled.

[0027] (4) Hydrogen has low impurity content and high purity. It is used in lithium sulfate hydrogenation, lithium polysulfide reduction, preparation of hydrochloric acid and other steps. It can improve the reaction rate while fully ensuring the quality of products such as lithium sulfide and hydrochloric acid. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further illustrated and described below through specific implementation methods.

[0029] In order to further optimize the preparation process of battery-grade lithium salt and obtain battery-grade lithium sulfide that can be mass-produced at a lower cost, the present invention provides a method for preparing battery-grade lithium salt, comprising the following steps:

[0030] S1, providing battery-grade lithium sulfate, adding 10-60 wt% of battery-grade lithium sulfate into sodium carbonate solution to precipitate lithium to obtain battery-grade lithium carbonate and lithium precipitation mother liquor; adding 10-30 wt% of battery-grade lithium sulfate into alkaline solution, cooling and separating salt, evaporating and crystallizing to obtain battery-grade lithium hydroxide;

[0031] S2, the battery-grade lithium sulfate remaining in step S1 is reduced and purified using hydrogen to obtain battery-grade lithium sulfide and hydrogenation tail gas;

[0032] S3, the battery-grade lithium carbonate obtained in step S1 is reacted with hydrochloric acid to obtain battery-grade lithium chloride, and the battery-grade lithium chloride is electrolyzed to obtain metallic lithium and chlorine;

[0033] S4. The battery-grade lithium hydroxide obtained in step S1 is reacted with the hydrogenated tail gas in step S2 to obtain battery-grade lithium sulfide.

[0034] The invention starts with battery-grade lithium sulfate, which is reacted with sodium carbonate to obtain lithium carbonate, reacted with alkali solution to obtain lithium hydroxide, and reduced with hydrogen to obtain lithium sulfide, thereby obtaining different battery-grade lithium salts (lithium sulfate, lithium carbonate, lithium sulfide, lithium hydroxide); the battery-grade lithium carbonate is reacted with hydrochloric acid to obtain lithium chloride, which is subjected to electrolysis to obtain metallic lithium; the lithium hydroxide reacts with hydrogen sulfide in hydrogenation tail gas to obtain battery-grade lithium sulfide, thereby further converting the battery-grade lithium hydroxide into battery-grade lithium sulfide.

[0035] For the lithium precipitate in the above step S1, lithium sulfate and sodium carbonate can be soluble in water, and the solubility of the generated lithium carbonate in water is low, so lithium carbonate can be precipitated. In order to better obtain a lithium carbonate precipitate with higher purity, the concentration of lithium sulfate can be 0.5-2mol / L, sodium carbonate is slightly excessive relative to lithium sulfate (sodium carbonate can be 1.1-1.2 times of lithium sulfate), and the pH of the solution system can be>10 to reduce the solubility of lithium carbonate. The precipitated lithium carbonate is dried to obtain battery-grade lithium carbonate, and the purity can reach 99.5% and above. The remaining solution is the lithium precipitate mother liquor, containing sodium sulfate, a small amount of lithium carbonate and sodium carbonate, etc.

[0036] For the lithium hydroxide and sulfate obtained by the reaction of lithium sulfate and alkali solution (such as sodium hydroxide, or lithium hydroxide and potassium hydroxide) in the above step S1, the solubility of lithium hydroxide in water at room temperature is low, but as the temperature decreases, the solubility increases; the solubility of sulfate (such as sodium sulfate) in water is high, but as the temperature decreases, the solubility decreases. Therefore, the difference in solubility of lithium hydroxide and sulfate can be increased by cooling (such as cooling to 0-5°C), and the sulfate precipitates, while lithium hydroxide remains in the solution. After separation, the lithium hydroxide solution is heated and evaporated to remove part of the water and crystallize to obtain high-purity lithium hydroxide (or lithium hydroxide monohydrate is obtained, and lithium hydroxide is obtained after heating and decomposition), and the purity can reach 99.5% or more.

[0037] In some embodiments, the preparation method of battery-grade lithium sulfate in step S1 is: roasting and leaching lithium-containing ore to obtain lithium sulfate solution; the lithium sulfate solution is purified and concentrated, and then partially crystallized, dried, and crushed to obtain battery-grade lithium sulfate. The battery-grade lithium sulfate of the present invention starts from lithium-containing ore, fully utilizes lithium-containing ore resources, and helps to reduce the cost of battery-grade lithium salts and lithium sulfide. After the lithium-containing ore is roasted and leached with sulfuric acid solution, a lithium sulfate solution can be directly obtained, and then after purification, concentration and other steps, lithium sulfate crystallizes and precipitates, and battery-grade lithium sulfate can be obtained. Lithium-containing ores may include spodumene, lithium mica, etc. Taking spodumene as an example, spodumene is calcined at 950-1260°C for 1-5h, and then reacted with sulfuric acid in an acidification kiln for leaching and filtration to obtain a lithium sulfate solution. The lithium sulfate solution at this time contains impurities such as Fe, Al, Mg, and Ca. These impurities can be removed through a purification process, and then through concentration, crystallization, drying, and crushing steps to obtain battery-grade lithium sulfate with a purity of 99.9% or above. The particle size can be obtained by crushing using different crushing processes according to different needs. For example, the D50 particle size can be 1-1000μm.

[0038] In some embodiments, purification is a combination of one or two or more of precipitation, filtration, resin adsorption and extraction methods; after the above purification process, impurities such as Fe, Al, Mg, Ca contained in the lithium sulfate solution can be basically removed, and the sum of the contents of calcium and magnesium in the purified solution does not exceed 10 mg / L, which can ensure the quality of battery-grade lithium sulfate and subsequent lithium carbonate, lithium hydroxide, and lithium sulfide. The above purification process can adopt a purification method, such as precipitation, or filtration, or resin adsorption (such as using anion and cation exchange resins), or extraction, or a combination of two purification processes, such as precipitation + resin adsorption, filtration + extraction, filtration + resin adsorption, etc. Taking the precipitation + resin adsorption process as an example, the pH of the lithium sulfate solution is adjusted to 10-11 so that most of the Mg, Ca ions, etc. are separated in the form of precipitation, and then sodium phosphate is added to further precipitate the remaining Mg and Ca ions, and the content of Mg and Ca ions is as low as 10ppm or less, and then anion exchange resin is used to remove anionic impurities such as phosphate, and cation exchange resin is used to remove cationic impurities such as sodium ions. The sum of the contents of calcium and magnesium in the purified lithium sulfate solution can be 1 mg / L, 3 mg / L, 4 mg / L, 5 mg / L, 7 mg / L, 8 mg / L, 10 mg / L, etc.

[0039] In some embodiments, the lithium precipitation mother liquor in step S1 is treated to obtain a sulfuric acid solution and an alkaline solution; the lithium precipitation mother liquor contains a relatively high concentration of sodium sulfate, or a partial or small amount of lithium sulfate, and after treatment, a sulfuric acid solution and an alkaline solution (sodium hydroxide solution or a mixed solution of sodium hydroxide and lithium hydroxide) can be obtained respectively, and the treatment can be carried out by a bipolar membrane electrodialysis method.

[0040] The sulfuric acid solution is used for leaching in the preparation method of the battery-grade lithium sulfate; the concentration of the sulfuric acid solution can be 5-22wt%; the alkaline solution is used as the alkaline solution in step S1. The above scheme can realize the recovery of lithium precipitation mother liquor and the recycling of sulfuric acid solution and alkaline solution, which is more conducive to environmental protection, recycling of raw materials and reducing the cost of raw materials. The concentration of the alkaline solution can be 3.5-15wt%.

[0041] In some embodiments, the volume content of hydrogen sulfide in the hydrogenation tail gas in step S2 is 1-20%. Battery-grade lithium sulfate is reduced under hydrogen to obtain lithium sulfide, but since excess hydrogen will further promote the conversion of lithium sulfide into lithium hydrosulfide and hydrogen sulfide, some hydrogen sulfide will be produced. Therefore, the hydrogenation tail gas contains hydrogen sulfide. For example, the volume content of hydrogen sulfide in the hydrogenation tail gas can be any value of 1%, 1.5%, 2%, 3%, 5%, 6%, 8%, 10%, 12%, 15%, 17%, 18%, 20%, etc., without special restrictions. Further, the volume content of hydrogen sulfide in the hydrogenation tail gas can be 1.5-12%. The specific process of hydrogenation reduction of battery-grade lithium sulfate can be as follows: in a reduction reactor, the reduction temperature is 500-950°C, the reaction time is 2-100h, and 36-80% of the product battery-grade lithium sulfide is thermally circulated to the inlet of the reduction reactor. The partial product cyclic reduction method can decompose the lithium hydrosulfide obtained by partial over-reduction into lithium sulfide again in the thermal cycle process, thereby increasing the content of lithium sulfide in the reduction product, and the remaining small amount of by-product lithium hydrosulfide (not exceeding 5%) can be purified by thermal decomposition (300-500°C) and converted into lithium sulfide. Since the lithium sulfate hydrogenation reduction process will produce water, the end point of the hydrogenation reduction reaction can be determined by testing the water content in the hydrogenation tail gas produced.

[0042] In some embodiments, chlorine and hydrogen react in step S3 to obtain hydrogen chloride, which is used as the raw material of hydrochloric acid in step S3. By adopting this method, the chlorine produced by electrolysis can be recycled and reused, and used as one of the reaction raw materials. In addition, the hydrochloric acid has high purity and few impurities, which avoids the introduction of impurities in the lithium salt, and can obtain high-concentration hydrochloric acid, such as the hydrochloric acid concentration of 35wt%. The reaction of chlorine and hydrogen can be carried out in a three-in-one reactor, such as a reaction temperature of 215°C, a reaction pressure of 0.012MPa, and a hydrogen-chlorine molar ratio of 1.02:1. For the reaction of battery-grade lithium carbonate and hydrochloric acid, there are no special restrictions on the reaction conditions. For example, the reaction temperature can be 15°C and the reaction time can be 1h. There are no special restrictions on the electrolysis conditions of battery-grade lithium chloride. For example, the electrolysis voltage can be 3V and the electrolysis current can be 15A / cm 2 .

[0043] In some embodiments, in step S3, the reaction of metallic lithium and sulfur is followed by hydrogen reduction to obtain battery-grade lithium sulfide. The reaction of metallic lithium and sulfur can be carried out at room temperature or under heating, such as the reaction of metallic lithium and sulfur by ball milling at room temperature, or the reaction of metallic lithium and sulfur vapor, but the reaction will produce lithium polysulfide as a by-product. The by-product lithium polysulfide can be reduced with hydrogen to obtain lithium sulfide, so that the purity of the product lithium sulfide is higher. For specific technology, reference can be made to the prior art CN119176525A.

[0044] In some embodiments, the reaction of metallic lithium and sulfur is carried out in an atmosphere of an inert gas, such as argon or helium, wherein the volume content of nitrogen in the inert gas does not exceed 0.1%, or further, does not exceed 0.05%.

[0045] In some embodiments, the purity of hydrogen is not less than 99.99%, and the content of hydrogen oxidizing gas, water vapor or the sum of the content of oxidizing gas and water vapor does not exceed 20ppm alone. Oxidizing gas (such as oxygen) and water vapor can react with metallic lithium, or excessive content will affect the hydrogen reduction effect and ultimately affect the purity of lithium sulfide. In the present invention, there is no particular restriction on the source of hydrogen, such as it can be obtained by electrolysis of water, and it can be further purified so that the purity of hydrogen reaches 99.99% or more. The source of electricity for electrolysis of water can be wind power generation, photovoltaic power generation, hydropower generation, etc., or it can be obtained by chemical energy conversion, such as from energy storage batteries.

[0046] In the above step S4, battery-grade lithium hydroxide and hydrogenation tail gas react to obtain battery-grade lithium sulfide, and a multi-stage absorption method can be used, such as secondary absorption, tertiary absorption, etc. Taking secondary absorption as an example, the primary absorption liquid after the first absorption is a mixed liquid containing lithium sulfide and lithium hydrosulfide, and the secondary absorption liquid after the second absorption is a mixed liquid containing lithium hydroxide and lithium sulfide. The primary absorption liquid and the secondary absorption liquid can be processed separately to obtain battery-grade lithium sulfide, or part of the secondary absorption liquid can be added to the primary absorption liquid so that the lithium hydrosulfide in the primary absorption liquid is converted into lithium sulfide, and solid-liquid separation is performed by cooling, and high-purity lithium sulfide is obtained by collecting the solid.

[0047] The technical solution of the present invention is further described and illustrated according to various embodiments below. Unless otherwise specified, the parts described in the following embodiments are parts by weight.

[0048] Example 1

[0049] Spodumene (lithium oxide content 5.5wt%) was transformed and roasted at 950℃ for 5h, and then leached with sulfuric acid solution to obtain a crude lithium sulfate solution. Sodium hydroxide solution was added to the crude lithium sulfate solution to adjust the pH to 11 and precipitate, the precipitate was separated and the primary filtrate was collected, and then an appropriate amount of sodium phosphate was added according to the content of Mg and Ca ions in the primary filtrate for precipitation, and the precipitate was separated again and the secondary filtrate was collected. The secondary filtrate was then passed through an anion exchange resin and a cation exchange resin respectively to obtain a purified solution, and the sum of the content of calcium and magnesium ions in the purified solution was measured to be 7mg / L. The purified solution was heated and concentrated, cooled to precipitate crystals, and the crystals were collected and dried and then crushed to a D50 particle size of 120μm to obtain battery-grade lithium sulfate with a measured purity of 99.9%.

[0050] The above-mentioned lithium sulfate of 50 weight % is added in sodium carbonate solution and continues to stir and dissolve, and solution pH is 12, and the concentration of lithium sulfate is 1mol / L, and the mole number of sodium carbonate is 1.1 times of the mole number of lithium sulfate, collects precipitation and is dried, obtains lithium carbonate, and records purity is 99.7%. The remaining solution after separation and precipitation is a lithium sinking mother liquor. The lithium sinking mother liquor adopts the method for bipolar membrane electrodialysis to process, obtains sulfuric acid and alkaline solution. Sulfuric acid is used for the leaching after the above-mentioned spodumene roasting, and alkaline solution (sodium hydroxide solution) is used for the following reaction with lithium sulfate.

[0051] 20 wt% of the above lithium sulfate was added to a 5 wt% sodium hydroxide solution, stirred and dissolved, pH 13, cooled to 0°C, sodium sulfate was precipitated and separated, the remaining filtrate was heated to 90°C, water was evaporated and concentrated to crystallize monohydrated lithium hydroxide. The monohydrated lithium hydroxide was heated to 160°C and thermally decomposed to obtain lithium hydroxide, the purity of which was measured to be 99.6%.

[0052] The remaining lithium sulfate is added to the reduction reactor and reacted at 920°C for 3 hours in a high-purity hydrogen atmosphere without generating any water vapor. During the reduction reaction, 72% of the reduction product is continuously heat-circulated to the reactor inlet and enters the reduction reactor again for reduction. The obtained reduction product, lithium sulfide, contains 4.2wt% lithium hydrosulfide, and the volume fraction of hydrogen sulfide gas in the generated hydrogenation tail gas is 1.5%. The reduction product is then thermally decomposed at 400°C and a high-purity hydrogen atmosphere for 1 hour to obtain lithium sulfide, with a measured purity of ≥99.9%.

[0053] The lithium hydroxide is dispersed in water to prepare a saturated lithium hydroxide solution. The hydrogenation tail gas is subjected to a two-stage absorption method, wherein the primary absorption liquid is a mixed liquid containing lithium sulfide and lithium hydrosulfide, and the secondary absorption liquid is a mixed liquid containing lithium hydroxide and lithium sulfide. Part of the secondary absorption liquid is added to the primary absorption liquid to convert the lithium hydrosulfide in the primary absorption liquid into lithium sulfide, and then the temperature is lowered to no more than 3°C, and the precipitated solid is collected, which is lithium sulfide, and the purity is measured to be ≥99.9%.

[0054] The lithium carbonate was added to 20 wt% hydrochloric acid, and the pH of the solution was 6.3 after dissolution. Lithium chloride was obtained after removing water. The lithium chloride was electrolyzed (electrolysis voltage 3 V, current 15 A / cm 2 ), obtaining metallic lithium and chlorine, the purity of metallic lithium being 99.9%. Chlorine and high-purity hydrogen react in a three-in-one reactor to obtain high-purity hydrogen chloride, which is dissolved in pure water to generate hydrochloric acid for the above reaction with lithium carbonate.

[0055] The above-mentioned metallic lithium and sulfur react and then undergo a reduction reaction to prepare battery-grade hydrogen sulfide, according to the method of Example 1 in the prior art CN119176525A.

[0056] In this embodiment, high-purity hydrogen can be obtained by electrolyzing water and then separated by membrane. The purity of high-purity hydrogen is ≥99.99%, and the sum of oxygen and water vapor content is 10.3ppm.

[0057] This embodiment starts with spodumene and can mass produce battery-grade lithium sulfide, thereby reducing the cost of lithium sulfide. According to the raw materials, the cost of obtaining 1 kg of lithium sulfide by the method of this embodiment is more than 25% lower than that of the method of the prior art CN119176525A.

[0058] Example 2

[0059] The difference between this embodiment and embodiment 1 is that the weight proportion of lithium sulfate reacted with sodium carbonate is 30%, and the weight proportion of lithium sulfate reacted with sodium hydroxide is 10%. The other steps remain unchanged.

[0060] Example 3

[0061] The difference between this embodiment and embodiment 1 is that the weight proportion of lithium sulfate reacted with sodium carbonate is 10%, and the weight proportion of lithium sulfate reacted with sodium hydroxide is 30%. The other steps remain unchanged.

[0062] Example 4

[0063] The difference between this embodiment and embodiment 1 is that the weight proportion of lithium sulfate reacted with sodium carbonate is 60%, and the weight proportion of lithium sulfate reacted with sodium hydroxide is 10%. The other steps remain unchanged.

[0064] In the above four embodiments, the cost of lithium sulfide is from low to high: Example 3, Example 2, Example 1 and Example 4, but they are all more than 20% lower than the method of the prior art CN119176525A, and the method is more flexible and can be adjusted according to the different costs, market supply and demand of lithium salts, and it has opened up the lithium-containing ore-lithium sulfate-lithium carbonate-lithium chloride-metal lithium-lithium sulfide industry chain, providing sufficient raw materials for sulfide all-solid-state batteries.

[0065] As described above, the basic principles, main features and advantages of the present invention are shown and described. Those skilled in the art should understand that the present invention is not limited by the above embodiments, which are only preferred embodiments of the present invention and cannot be used to limit the scope of the present invention. That is, equivalent changes and modifications made according to the scope of the present invention and the content of the specification should still be within the scope of the present invention. The scope of protection required by the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for preparing a battery-grade lithium salt, characterized in that: The following steps are involved: S1, providing battery-grade lithium sulfate, adding 10-60 wt % of the battery-grade lithium sulfate into sodium carbonate solution to precipitate lithium to obtain battery-grade lithium carbonate and lithium precipitation mother liquor; adding 10-30 wt % of the battery-grade lithium sulfate into alkaline solution, cooling and separating salt, evaporating and crystallizing to obtain battery-grade lithium hydroxide; S2, the battery-grade lithium sulfate remaining in step S1 is reduced and purified using hydrogen to obtain battery-grade lithium sulfide and hydrogenation tail gas; S3, the battery-grade lithium carbonate in step S1 is reacted with hydrochloric acid to obtain battery-grade lithium chloride, and the battery-grade lithium chloride is electrolyzed to obtain metallic lithium and chlorine; S4. The battery-grade lithium hydroxide described in step S1 and the hydrogenated tail gas described in step S2 react to obtain battery-grade lithium sulfide.

2. The method for preparing battery-grade lithium salt according to claim 1, characterized in that: The preparation method of the battery-grade lithium sulfate described in step S1 is: roasting and leaching lithium-containing ore to obtain a lithium sulfate solution; the lithium sulfate solution is purified and concentrated, and then partially crystallized, dried, and crushed to obtain the battery-grade lithium sulfate.

3. The method for preparing battery-grade lithium salt according to claim 2, characterized in that: The purification is carried out by using one or a combination of two or more of precipitation, filtration, resin adsorption and extraction methods; the sum of the contents of calcium and magnesium in the purified solution does not exceed 10 mg / L.

4. The method for preparing battery-grade lithium salt according to claim 1, characterized in that: The lithium precipitation mother liquor in step S1 is treated to obtain sulfuric acid solution and alkaline solution; The sulfuric acid solution is used for the leaching as claimed in claim 2; The alkaline solution is used as the alkaline solution described in step S1.

5. The method for preparing battery-grade lithium salt according to claim 4, characterized in that: The treatment is carried out by using a bipolar membrane electrodialysis method.

6. The method for preparing battery-grade lithium salt according to claim 1, characterized in that: The volume content of hydrogen sulfide in the hydrogenated tail gas in step S2 is 1-20%.

7. The method for preparing battery-grade lithium salt according to claim 1, characterized in that: In step S3, the chlorine and hydrogen react to obtain hydrogen chloride, which is used as the raw material of the hydrochloric acid in step S3.

8. The method for preparing battery-grade lithium salt according to claim 1, characterized in that: In step S3, the metallic lithium and sulfur react and then are reduced by hydrogen to obtain battery-grade lithium sulfide.

9. The method for preparing battery-grade lithium salt according to claim 8, characterized in that: The reaction of metallic lithium and sulfur is carried out under an inert gas atmosphere.

10. The method for preparing battery-grade lithium salt according to any one of claims 1 to 9, characterized in that: The purity of the hydrogen is not less than 99.99%, and the content of oxidizing gas, the content of water vapor, or the sum of the content of oxidizing gas and water vapor in the hydrogen does not exceed 20 ppm alone.