A method for preparing a high-purity bisfluorosulfonylimide salt solution

Abstract

The application discloses a preparation method of a high-purity bistrifluorosulfonylimide salt solution, which comprises the following steps: mixing bistrifluorosulfonylimide acid and inorganic alkali in an ester solvent and performing reaction; after the reaction is completed, solid-liquid separation is performed to remove insoluble substances in the reaction liquid, so that a bistrifluorosulfonylimide salt crude solution is obtained; the bistrifluorosulfonylimide salt crude solution is subjected to rectification and purification, and the moisture content is reduced to below 20 ppm; the bistrifluorosulfonylimide salt solution after rectification is filtered by using a filter membrane; and the inorganic alkali is at least one of lithium, sodium or potassium hydroxide, carbonate or bicarbonate. According to the integrated process route of "reaction-solid-liquid separation-rectification-filtration", the bistrifluorosulfonylimide salt is prepared, and deep purification is completed at the same time, so that the liquid salt product with high purity, low moisture content and high yield is obtained in one step, the process flow is significantly simplified, and the problems of solvent waste and impurity introduction in the traditional purification method are avoided.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte additive technology, specifically relating to a method for preparing a high-purity bis(fluorosulfonyl)imide salt solution. Background Technology

[0002] Difluorosulfonyl imide salts are important fluorine-containing compounds used in the preparation of electrolyte materials for lithium-ion batteries, sodium-ion batteries, and supercapacitors. Potassium difluorosulfonyl imide, as a novel electrolyte material, can suppress lithium dendrite growth in lithium-ion batteries, exhibiting high ionic conductivity and good chemical stability. Sodium difluorosulfonyl imide is mainly used in sodium-ion battery electrolytes and is one of the core candidate materials for high-performance electrolyte salts, possessing high ionic conductivity, good thermal and electrochemical stability, and fast-charging potential. In particular, lithium difluorosulfonyl imide, primarily used as a high-performance lithium-ion battery electrolyte salt, can improve conductivity, low-temperature performance, and high-temperature cycle stability, partially replacing or compounding with lithium hexafluorophosphate. Therefore, developing efficient, low-cost, and high-purity difluorosulfonyl imide salt solution preparation processes has significant industrial value.

[0003] Currently, the conventional method for preparing bis(fluorosulfonyl)imide salt solution is as follows: first, a crude bis(fluorosulfonyl)imide salt is prepared, then a solid product is obtained through recrystallization, and finally, the solution is obtained by dissolving the product in a solvent. This process involves multiple lengthy steps such as crystallization, filtration, drying, and redissolution, which not only results in a large waste of solvent but also leads to low production efficiency and increases the cost of industrial production.

[0004] To address the aforementioned issues, researchers have proposed improved solutions. Patent CN113277487B, concerning the preparation of liquid salt, emphasizes that no water is produced during the reaction; however, this method generates a large amount of corrosive exhaust gas, making industrial production difficult. Patent CN120136051A uses molecular sieves for water removal, but this method has limited effectiveness in reducing moisture content to below 20 ppm and may introduce other metal ion impurities (such as potassium ions), making it difficult to meet the application requirements of high-purity electrolytes.

[0005] In view of the various problems existing in the preparation process of bis(fluorosulfonyl)imide salt solution, there is an urgent need to develop a new preparation process for bis(fluorosulfonyl)imide salt solution to achieve the direct preparation of liquid salt products with high purity, low moisture and low impurities, so as to meet the industrial application requirements of battery electrolytes. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a method for preparing a high-purity bis(fluorosulfonyl)imide salt solution. This invention utilizes an integrated process route of "reaction-solid-liquid separation-distillation-filtration" to simultaneously prepare the bis(fluorosulfonyl)imide salt and achieve deep purification, obtaining a high-purity, low-moisture, and high-yield liquid salt product in one step. This significantly simplifies the process and avoids the problems of solvent waste and impurity introduction in traditional purification methods.

[0007] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution: This invention provides a method for preparing a high-purity difluorosulfonyl imide salt solution, comprising the following steps: S1: Mix difluorosulfonylimide acid with an inorganic base in an ester solvent and react. S2: After the reaction is completed, solid-liquid separation is performed to remove insoluble matter from the reaction solution, and a crude solution of difluorosulfonyl imide salt with a water content of 1wt%~5wt% is obtained. S3: The crude solution of difluorosulfonylimide salt is purified by distillation to reduce the water content to below 20 ppm; S4: Filter the difluorosulfonyl imide salt solution after distillation using a filter membrane; The inorganic base is selected from at least one of lithium, sodium or potassium hydroxides, carbonates or bicarbonates.

[0008] Preferably, the ester solvent is at least one of methyl ethyl carbonate, diethyl carbonate, and propylene carbonate.

[0009] Preferably, the molar amount of the inorganic base is 0.5 to 5 times that of the difluorosulfonyl imide acid.

[0010] Preferably, the reaction temperature in step S1 is -25℃ to 20℃, and the reaction time is 2 to 6 hours.

[0011] Preferably, the temperature for distillation purification in step S3 is 30℃~50℃.

[0012] Preferably, the distillation and purification time in step S3 is 40 to 80 hours.

[0013] Preferably, the reflux ratio for distillation purification in step S3 is 1:1 to 10:1.

[0014] Preferably, the filter membrane in step S4 is a polytetrafluoroethylene filter membrane with a pore size of 0.1~0.5 micrometers.

[0015] Preferably, the distillation column used in step S3 is greater than 1 meter in height and is filled with packing material, which is made of metal, glass or ceramic, and the shape of the packing material is a triangular helix, a Pall ring or a θ ring.

[0016] Furthermore, the preparation method of this high-purity difluorosulfonyl imide salt solution includes the following specific steps: At room temperature, an inorganic base is added to an ester solvent in one step to prepare a mixture. The temperature is controlled at -10℃ to 10℃, and difluorosulfonyl imide acid is slowly added dropwise. After the addition is complete, the reaction is carried out at this temperature for 2 to 3 hours. After the reaction is completed, insoluble matter is removed by solid-liquid separation under a protective atmosphere. The resulting filtrate is placed in a distillation apparatus and distilled under a protective atmosphere at a temperature of 35℃~40℃, an absolute vacuum of ≤1000Pa, a reflux ratio of 5:1~10:1, and for 48~72 hours to reduce the water content to below 20ppm. Under a protective atmosphere, the distilled liquid salt was filtered through a polytetrafluoroethylene filter membrane with a pore size of 0.2-0.5 micrometers to obtain a difluorosulfonamide salt solution.

[0017] The beneficial effects of this invention are as follows: This invention achieves efficient preparation and deep purification of bis(fluorosulfonyl)imide salt solutions through a synergistic mechanism of an integrated "reaction-solid-liquid separation-distillation-filtration" process. First, in an ester solvent, bis(fluorosulfonyl)imide acid reacts with an inorganic base via neutralization to generate the target salt. During this reaction, water and insoluble byproducts (unreacted inorganic base, salts, etc.) are dispersed in the system. If distillation is performed directly, these insoluble substances will clog the distillation column packing, reduce separation efficiency, and may even act as nucleation sites, inducing product decomposition or catalyzing side reactions between the ester solvent and residual acid. Therefore, these substances must be removed beforehand through solid-liquid separation, while controlling the water content of the crude solution after this step to 1wt%~5wt% to achieve an optimal balance between distillation load and separation efficiency. Subsequently, based on the boiling point difference between bis(fluorosulfonyl)imide salt and water, the water content is reduced to below 20ppm through distillation. No solid-phase dehydrating agent is introduced during this process, eliminating the introduction of metal ion impurities at the source. After distillation, a precision filter membrane is used to remove submicron-sized particles and mechanical impurities that may be introduced during distillation and pipeline transportation, ensuring the final product's cleanliness. Thus, the solid-liquid separation process ensures the cleanliness of the distillation feed, the distillation process removes water and volatile impurities, and the filtration process intercepts particulate matter. These three processes work synergistically to achieve comprehensive control from chemical reaction to final product cleanliness. The entire process eliminates the need to separate the salt from the solvent system, avoiding product loss during recrystallization and eliminating the need for chemical dehydrators or molecular sieves, thus preventing the introduction of additional impurities. This allows for the direct production of high-purity liquid salt products suitable for battery electrolytes in a single step.

[0018] In summary, this invention achieves deep purification while preparing difluorosulfonamide salt through an integrated process route of "reaction-solid-liquid separation-distillation-filtration". It can obtain liquid salt products with high purity, low moisture content and high yield in one step, which significantly simplifies the process and avoids the problems of solvent waste and impurity introduction in traditional purification methods. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] This invention provides a method for preparing a high-purity difluorosulfonylimide salt solution, comprising the following steps: mixing difluorosulfonylimide acid with an inorganic base in an ester solvent for reaction; after the reaction, performing solid-liquid separation to remove insoluble matter in the reaction solution to obtain a crude difluorosulfonylimide salt solution with a water content of 1wt%~5wt%; subsequently, purifying the crude solution by distillation to reduce the water content to below 20ppm; after distillation, filtering with a filter membrane to finally obtain a high-purity difluorosulfonylimide salt solution.

[0021] In the method of this invention, the inorganic base used is selected from at least one of lithium, sodium, or potassium hydroxides, carbonates, or bicarbonates. Exemplarily, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, lithium bicarbonate, sodium bicarbonate, or potassium bicarbonate can be used. These bases can be used alone or in any combination. The molar amount of the inorganic base is typically 0.5 to 5 times that of bis(fluorosulfonyl)imide acid, preferably 1 to 3 times, and more preferably 1 to 1.5 times. It is understood that if the amount of base used is too low, the reaction of bis(fluorosulfonyl)imide acid will be incomplete, affecting the yield and the acid value of the product; if the amount used is too high, excessive metal ions will be introduced, increasing the burden of subsequent purification and potentially generating more side reactions.

[0022] The ester solvent used in this invention can be any type of ester organic solvent known in the art. Preferably, the ester solvent is selected from at least one of methyl ethyl carbonate, diethyl carbonate, or propylene carbonate, and more preferably methyl ethyl carbonate. The water content of the solvent is preferably as low as possible, typically below 500 ppm, and more preferably below 200 ppm, to reduce the hydrolysis of bis(fluorosulfonyl)imide in trace amounts of water and further reduce the generation of impurities. The mass concentration of the prepared bis(fluorosulfonyl)imide salt solution can be adjusted according to the actual application requirements. For example, the mass concentration is 1-55%, and more preferably 1-40%.

[0023] In step S1, the reaction temperature is typically controlled at a low temperature, exemplarily -25°C to 20°C, preferably -10°C to 15°C, and more preferably -10°C to 10°C. Low-temperature reaction has the following advantages: First, the neutralization reaction of difluorosulfonylimide acid with an inorganic base is exothermic; using low-temperature conditions effectively controls the reaction rate, prevents local overheating, and thus avoids product decomposition or discoloration at high temperatures. Second, difluorosulfonylimide acid has strong acidity and may undergo side reactions (such as transesterification or decomposition) with ester solvents at higher temperatures; the low-temperature environment significantly reduces the probability of such side reactions, ensuring product purity. Third, the water generated during the reaction has a weaker hydrolytic effect on the product at low temperatures, which helps reduce the formation of acidic impurities and provides a good foundation for obtaining a crude solution with low moisture and low acid value in subsequent distillation processes. The reaction time is typically 2 to 6 hours. For example, in a typical operation, an inorganic base can be added to an ester solvent at room temperature to prepare a mixture. Then, the temperature is controlled to -10°C to 10°C, and difluorosulfonyl imide acid is slowly added dropwise. After the addition is complete, the reaction continues at this low temperature for 2 to 3 hours.

[0024] After the reaction, the resulting reaction solution undergoes solid-liquid separation to remove insoluble matter. It is understood that the reaction system contains unreacted inorganic bases and insoluble salts, which, if directly introduced into the distillation process, may clog the distillation column packing, reduce separation efficiency, or even act as nucleation sites to induce product decomposition or catalyze side reactions between ester solvents and residual acids. Therefore, pre-removal of insoluble matter through solid-liquid separation is a crucial step to ensure subsequent distillation efficiency and product purity. For example, solid-liquid separation can be achieved through filtration, such as using medium-speed qualitative filter paper under a protective atmosphere. After solid-liquid separation, a crude solution of difluorosulfonamide salt with a moisture content of 1wt%–5wt% is obtained. This moisture range optimizes the balance between the distillation process load and separation efficiency, avoiding excessively high moisture content that leads to prolonged distillation time, and also avoiding the risk of salt precipitation that may result from excessively low moisture content.

[0025] The crude solution is purified by distillation. The distillation operation is based on the boiling point difference between the difluorosulfonyl imide salt and water, and the azeotropic properties of the ester solvent, aiming to reduce the water content to below 20 ppm. The distillation temperature is typically controlled between 30°C and 50°C, preferably between 35°C and 40°C. Using a relatively mild distillation temperature has the following advantages: firstly, it avoids side reactions (such as transesterification, decomposition, or discoloration) between the ester solvent and the salt or residual acid caused by high temperatures, ensuring the product is colorless and transparent; secondly, it achieves deep dehydration by extending the distillation time under low-temperature conditions, reflecting the technical approach of low-temperature long-time distillation. The distillation time is typically 40–80 hours, preferably 48–72 hours, ensuring sufficient dehydration while maintaining production efficiency. The reflux ratio is controlled between 1:1 and 10:1, preferably 5:1 to 10:1. A higher reflux ratio is beneficial for improving separation efficiency and ensuring that water is fully separated. The distillation process is typically carried out under a protective atmosphere to avoid contact with moisture in the air. Inert gases such as nitrogen or argon can be used as the protective gas, and the absolute vacuum is controlled below 1000 Pa. The distillation column used is greater than 1 meter in height and filled with packing material, which can be metal, glass, or ceramic, preferably 316L stainless steel. The packing shape can be triangular spiral, Pall rings, or θ rings, with an exemplary size of 2.5 mm × 2.5 mm.

[0026] After distillation, the resulting distillate salt is filtered through a membrane to remove submicron particles and mechanical impurities that may have been introduced during distillation and pipeline transport. The preferred membrane is a polytetrafluoroethylene (PTFE) membrane, which utilizes its hydrophobic properties to prevent the introduction of moisture. Furthermore, PTFE itself does not introduce metal ions, avoiding secondary contamination. The pore size of the membrane is typically 0.1–0.5 micrometers, preferably 0.2–0.5 micrometers, a range that effectively traps various types of fine particles. The filtration process is also performed under a protective atmosphere to ensure that the product does not come into contact with moisture in the air during filtration.

[0027] In the process of this invention, "solid-liquid separation" ensures the cleanliness of the distillation feed and controls the distillation load; "distillation" removes water and volatile impurities; and "precision filtration" intercepts particulate matter. These three processes work synergistically to achieve comprehensive control over the cleanliness of the chemical reaction, solvent medium, and final product. The entire process eliminates the need to separate the salt from the solvent system, avoiding product loss during recrystallization. Furthermore, it eliminates the need for chemical dehydrating agents or molecular sieves, completely preventing the introduction of additional impurities. The final difluorosulfonyl imide salt solution product achieves a purity of over 99.9%, with moisture content reduced to below 20 ppm. Acid value and other impurity ions (such as fluoride, chloride, and sulfate ions) can be controlled below 10 ppm, with a yield exceeding 95%. It can be directly used for preparing battery electrolytes.

[0028] Example 1

[0029] At room temperature, in a glove box, add 400g of methyl ethyl carbonate to a three-necked flask, then add 41g of potassium carbonate all at once. Then control the temperature to -10℃ to 10℃ and stir thoroughly for 30 minutes. Then slowly add 90g of difluorosulfonyl imide acid dropwise using a constant pressure dropping funnel over a period of 1 hour. The internal temperature of the reaction should not exceed 10℃. After the addition is complete, keep the temperature for 2 hours. Take a sample to measure the moisture content and acid value. The reaction is complete when the acid value is below 50ppm. The reaction solution was filtered in a glove box using medium-speed qualitative filter paper to remove the residue. The filtrate was then placed in a three-necked distillation flask. The entire distillation apparatus must be purged with nitrogen as a protective gas to prevent contact with moisture in the air. The oil bath heating temperature was set to 40°C, the absolute vacuum to below 1000 Pa, and the reflux ratio to 5:1~10:1. Distillation was carried out for 72 hours. The moisture content was tested to be 8 ppm. The solution was then filtered in a glove box using a 0.45-micron polytetrafluoroethylene (PTFE) filter membrane to obtain 106.6 g of qualified product (acid value and other impurity ions were all below 10 ppm). The product purity was above 99.92%, and the yield was 96.6%, which met the product requirements.

[0030] Example 2

[0031] At room temperature, in a glove box, add 400g of methyl ethyl carbonate to a three-necked flask, then add 50g of sodium bicarbonate all at once. Then control the temperature to -10℃ to 10℃ and stir thoroughly for 30 minutes. Then slowly add 90g of difluorosulfonyl imide acid dropwise using a constant pressure dropping funnel over a period of 1 hour. The internal temperature of the reaction should not exceed 10℃. After the addition is complete, keep the temperature for 2 hours. Take a sample to measure the moisture content and acid value. The reaction is complete when the acid value is below 50ppm. The reaction solution was filtered in a glove box using medium-speed qualitative filter paper to remove the residue. The filtrate was then placed in a three-necked distillation flask. The entire distillation apparatus must be purged with nitrogen as a protective gas to prevent contact with moisture in the air. The oil bath heating temperature was set to 38°C, the absolute vacuum to below 1000 Pa, and the reflux ratio to 5:1~10:1. Distillation was carried out for 65 hours until the moisture content decreased to 15 ppm. The solution was then filtered in a glove box using a 0.45-micron polytetrafluoroethylene (PTFE) filter membrane to obtain 96 g of qualified product (acid value and other impurity ions were all below 10 ppm). The product purity was 99.91%, and the yield was 95.1%, which met the product requirements.

[0032] Example 3

[0033] At room temperature, in a glove box, add 400g of methyl ethyl carbonate to a three-necked flask, then add 14g of lithium hydroxide all at once. Then control the temperature to -10℃~10℃ and stir thoroughly for 30 minutes. Then slowly add 90g of difluorosulfonyl imide acid dropwise using a constant pressure dropping funnel over a period of 1 hour. The internal temperature of the reaction should not exceed 10℃. After the addition is complete, keep the temperature for 2 hours. Take a sample to measure the moisture content and acid value. The reaction is complete when the acid value is below 50ppm. The reaction solution was filtered in a glove box using medium-speed qualitative filter paper to remove the residue. The filtrate was then placed in a three-necked distillation flask. The entire distillation apparatus must be purged with nitrogen as a protective gas to prevent contact with moisture in the air. The oil bath heating temperature was set to 40°C, the absolute vacuum to below 1000 Pa, and the reflux ratio to 5:1~10:1. The distillation time was 71 hours. The moisture content was tested to be 18 ppm. The solution was then filtered in a glove box using a 0.45-micron polytetrafluoroethylene (PTFE) filter membrane to obtain 90 g of qualified product (acid value and other impurity ions were all below 10 ppm). The product purity was 99.93%, and the yield was 96.25%, which met the product requirements.

[0034] Comparative Example 1 At room temperature, in a glove box, add 400g of methyl ethyl carbonate to a three-necked flask, then add 30g of sodium carbonate all at once. Then control the temperature to -10℃ to 10℃ and stir thoroughly for 30 minutes. Then slowly add 90g of difluorosulfonyl imide acid dropwise using a constant pressure dropping funnel over a period of 1 hour. The internal temperature of the reaction should not exceed 10℃. After the addition is complete, keep the temperature for 2 hours. Take a sample to measure the moisture content and acid value. The reaction is complete when the acid value is below 50ppm. The reaction solution was filtered in a glove box using medium-speed qualitative filter paper to remove the residue. The filtrate was then placed in a three-necked distillation flask. The entire distillation apparatus was purged with nitrogen as a protective gas to prevent contact with moisture in the air. The oil bath heating temperature was set to 60°C, the absolute vacuum to below 1000 Pa, and the reflux ratio to 5:1~10:1. The distillation time was 72 hours. The moisture content was tested to be 8 ppm. The solution was then filtered in a glove box using a 0.45-micron polytetrafluoroethylene (PTFE) membrane. 98 g of the product was obtained, with a purity of 75.69%, which did not meet the requirements for electrolyte products.

[0035] The reason for the low purity of the product is that difluorosulfonyl imide acid is a strong organic acid, which cannot coexist with methyl ethyl carbonate at high temperatures. The two will react, leading to an increase in side reactions and a decrease in product purity.

[0036] Comparative Example 2 At room temperature, in a glove box, add 400g of methyl ethyl carbonate to a three-necked flask, then add 30g of potassium hydroxide all at once. Then control the temperature to -10℃~10℃ and stir thoroughly for 30 minutes. Then slowly add 90g of difluorosulfonyl imide acid dropwise using a constant pressure dropping funnel over a period of 1 hour. The internal temperature of the reaction should not exceed 10℃. After the addition is complete, keep the temperature for 2 hours. Take a sample to measure the moisture content and acid value. The reaction is complete when the acid value is below 50ppm. The reaction solution was filtered in a glove box using medium-speed qualitative filter paper to remove the residue. The filtrate was placed in a three-necked distillation flask, 15g of activated molecular sieve was added, and the mixture was allowed to stand for 72 hours. After dehydration, the water content was 53ppm, and the product purity was 99.92%. The potassium ion content was 38ppm according to ICP testing, which exceeded the standard and did not meet the requirements for electrolyte products.

[0037] Analysis of the reasons for excessive potassium ions in the product suggests that the molecular sieve may contain potassium ions, which were introduced during the dehydration process, leading to product defects.

[0038] Comparative Example 3 At room temperature, in a glove box, add 400g of methyl ethyl carbonate to a three-necked flask, then add 30g of potassium hydroxide all at once. Then control the temperature to -10℃~10℃ and stir thoroughly for 30 minutes. Then slowly add 90g of difluorosulfonyl imide acid dropwise using a constant pressure dropping funnel over a period of 1 hour. The internal temperature of the reaction should not exceed 10℃. After the addition is complete, keep the temperature for 2 hours. Take a sample to measure the moisture content and acid value. The reaction is complete when the acid value is below 50ppm. The reaction solution was filtered in a glove box using medium-speed qualitative filter paper to remove the residue. The filtrate was then placed in a three-necked distillation flask. The entire distillation apparatus was purged with nitrogen as a protective gas to prevent contact with moisture in the air. The oil bath heating temperature was set to 60°C, the absolute vacuum to below 1000 Pa, and the reflux ratio to 5:1~10:1. Distillation was carried out for 100 hours, and the moisture content was tested to be 5.6 ppm. The solution was then filtered in a glove box using a 0.45-micron polytetrafluoroethylene (PTFE) filter membrane. 101g of product was obtained, with a purity of 99.78%. The liquid salt was yellowish and the color did not meet the requirements for electrolyte products.

[0039] Comparative Example 4 At room temperature, in a glove box, add 400g of methyl ethyl carbonate to a three-necked flask, then add 41g of potassium carbonate all at once. Then control the temperature to -10℃~10℃ and stir thoroughly for 30 minutes. Then slowly add 90g of difluorosulfonyl imide acid dropwise using a constant pressure dropping funnel over a period of 1 hour. The internal temperature of the reaction should not exceed 10℃. After the addition is complete, keep the temperature for 2 hours. Take a sample to measure the moisture content and acid value. The reaction is considered complete when the acid value is below 50ppm. The reaction solution was placed directly (without filtration) into a three-necked distillation flask. The entire distillation apparatus was purged with nitrogen as a protective gas to prevent contact with moisture in the air. The oil bath heating temperature was set to 40°C, the absolute vacuum to be below 1000Pa, the reflux ratio to be 5:1 to 10:1, and the distillation time was 72 hours. During the distillation process, the distillation column gradually became clogged, and the distillation efficiency decreased significantly. After the distillation was completed, the moisture content was measured to be 25 ppm. After filtration with a 0.45-micron polytetrafluoroethylene filter membrane in a glove box, 102 g of product was obtained, with a product purity of 97.32%, a moisture content of 25 ppm, and an acid value of 18 ppm, which did not meet the requirements for electrolyte products (moisture content > 20 ppm).

[0040] The reason why the product's moisture content and purity are substandard is that there is unreacted potassium carbonate and insoluble salts from the reaction byproducts in the reaction solution. When directly fed into the distillation column, these insoluble substances clog the distillation column packing, reducing the separation efficiency. At the same time, the insoluble substances act as nucleation sites during the distillation process, inducing partial decomposition of the product and catalyzing the side reaction between the ester solvent and the residual acid, making it difficult to effectively remove moisture and reducing the product purity.

[0041] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0042] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a high-purity difluorosulfonyl imide salt solution, characterized in that, Includes the following steps: S1: Mix difluorosulfonylimide acid with an inorganic base in an ester solvent and react. S2: After the reaction is completed, solid-liquid separation is performed to remove insoluble matter from the reaction solution, and a crude solution of difluorosulfonyl imide salt with a water content of 1wt%~5wt% is obtained. S3: The crude solution of difluorosulfonylimide salt is purified by distillation to reduce the water content to below 20 ppm; S4: Filter the difluorosulfonyl imide salt solution after distillation using a filter membrane; The inorganic base is selected from at least one of lithium, sodium or potassium hydroxides, carbonates or bicarbonates.

2. The method for preparing the high-purity difluorosulfonyl imide salt solution according to claim 1, characterized in that, The ester solvent is at least one of methyl ethyl carbonate, diethyl carbonate, and propylene carbonate.

3. The method for preparing the high-purity difluorosulfonyl imide salt solution according to claim 1, characterized in that, The molar amount of the inorganic base is 0.5 to 5 times that of the difluorosulfonyl imide acid.

4. The method for preparing the high-purity difluorosulfonyl imide salt solution according to claim 1, characterized in that, The reaction temperature in step S1 is -25℃ to 20℃, and the reaction time is 2 to 6 hours.

5. The method for preparing the high-purity difluorosulfonyl imide salt solution according to claim 1, characterized in that, The distillation and purification temperature in step S3 is 30℃~50℃.

6. The method for preparing the high-purity difluorosulfonyl imide salt solution according to claim 1, characterized in that, The distillation and purification time in step S3 is 40-80 hours.

7. The method for preparing the high-purity bis(fluorosulfonyl)imide salt solution according to claim 1, characterized in that, In step S3, the reflux ratio for distillation purification is 1:1 to 10:

1.

8. The method for preparing the high-purity bis(fluorosulfonyl)imide salt solution according to claim 1, characterized in that, The filter membrane in step S4 is a polytetrafluoroethylene filter membrane with a pore size of 0.1~0.5 micrometers.

9. The method for preparing the high-purity difluorosulfonyl imide salt solution according to claim 1, characterized in that, In step S3, the distillation column used for distillation is greater than 1 meter in height and is filled with packing material, which is made of metal, glass or ceramic, and the shape of the packing material is a triangular helix, Pall ring or θ ring.

10. The method for preparing the high-purity difluorosulfonyl imide salt solution according to claim 1, characterized in that, The specific steps include the following: At room temperature, an inorganic base is added to an ester solvent in one step to prepare a mixture. The temperature is controlled at -10℃ to 10℃, and difluorosulfonyl imide acid is slowly added dropwise. After the addition is complete, the reaction is carried out at this temperature for 2 to 3 hours. After the reaction is completed, insoluble matter is removed by solid-liquid separation under a protective atmosphere. The resulting filtrate is placed in a distillation apparatus and distilled under a protective atmosphere at a temperature of 35℃~40℃, an absolute vacuum of ≤1000Pa, a reflux ratio of 5:1~10:1, and a distillation time of 48~72 hours to reduce the water content to below 20ppm. Under a protective atmosphere, the distilled liquid salt was filtered through a polytetrafluoroethylene filter membrane with a pore size of 0.2-0.5 micrometers to obtain a difluorosulfonamide salt solution.