Method for synthesizing liquid bis (fluorosulfonyl) imide salt

Abstract

The invention relates to a method for synthesizing liquid bis (fluorosulfonyl) imide salt, which comprises the following steps: 1) adding metal salt and a proper amount of organic solvent into a dissolving tank, dropwise adding bis (fluorosulfonyl) imide acid under a stirring condition, continuously stirring and reacting for 2-5 hours after dropwise adding, and controlling the temperature to be less than or equal to 10 DEG C in the dropwise adding and reacting processes; 2) obtaining a solution system A after the reaction, and adding carbonate for stirring reaction to remove acid; then adding molecular sieve powder and an adsorbent to further remove impurities; and finally, performing membrane filtration. The method is simple in technological process and low in cost, the solvent is easy to recover, and the prepared product is low in chloride ion content (smaller than or equal to 5 ppm), high in free acid content (smaller than or equal to 30 ppm) and high in moisture content (smaller than or equal to 20 ppm), does not contain insoluble substances and can be directly used as a battery additive.

Description

Technical Field

[0001] The invention belongs to the technical field of electrolytes, and in particular relates to a method for synthesizing liquid bis(fluorosulfonyl)imide salt. Background Art

[0002] New energy materials are the foundation and forerunner of the development of the new energy and new energy vehicle industries. "One generation of materials, one generation of technology, one generation of equipment" is becoming a consensus, and "materials first" has become a hallmark of the times. Developing new lithium salts that enhance the chemical stability of LiPF6 as functional additives to improve battery high-temperature cycling stability, including extending cycle life, enhancing rate capability, and improving safety, has been a recent technological development in optimizing electrolyte performance. Bis(fluorosulfonyl)imide salts, added as a primary salt or additive to LiPF6 electrolytes, significantly improve the chemical stability of the electrolyte by inhibiting the formation of hydrogen fluoride and blocking the slow, continuous decomposition of LiPF6. Furthermore, by increasing the electrolyte's conductivity and leveraging its unique SEI film-forming ability, they not only enhance battery cycling performance, but also effectively improve low-temperature discharge performance and capacity retention after high-temperature storage, while also inhibiting swelling. Bis(fluorosulfonyl)imide salts are increasing in proportion in new battery electrolytes, gradually evolving from additives to primary salts. They can meet the demands of high energy density and fast charging, becoming a key material for next-generation batteries.

[0003] At present, the bis(fluorosulfonyl)imide salts sold on the market are all crystalline salts. The synthesis process is relatively complicated and faces the characteristics of large solvent consumption, difficult solvent recovery, long process, and easy deterioration of the product. Liquid salt preparation can be produced continuously, reducing the steps of crystallization and drying, and improving production capacity utilization. At the same time, downstream electrolyte manufacturers have shown that liquid salt can be directly used in electrolyte preparation, eliminating the crystal dissolution and filtration steps and reducing production costs. However, the cost of preparing liquid salt with crystalline salt is obviously higher, so it is necessary to invent a method for directly synthesizing liquid salt, which can simplify the process and significantly reduce production costs.

[0004] Chinese patent application CN118164443A discloses a method for preparing a liquid sodium bis(fluorosulfonyl)imide solution. The method involves reacting sodium chloride suspended in a non-aqueous solvent with bis(fluorosulfonyl)imide acid to produce a sodium bis(fluorosulfonyl)imide solution. The resulting sodium bis(fluorosulfonyl)imide concentrate is then subjected to purification steps such as filtration, degassing, concentration, resin deacidification, and fine filtration to yield a high-purity sodium bis(fluorosulfonyl)imide concentrate. This method, which uses resin deacidification, suffers from complex procedures, high costs, and the solvent's susceptibility to oxidation and deterioration, making it difficult to recycle. Furthermore, the product contains high chloride ion content (15-26 ppm), free acid content (68-90 ppm), moisture content (above 25 ppm), and insoluble matter content (above 80 ppm), making it unsuitable for direct use as an electrolyte salt or electrolyte additive. This led to the development of the present application. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the prior art by providing a method for synthesizing a liquid bis(fluorosulfonyl)imide salt. This method features a simple process flow, low cost, and easily recyclable solvents. Furthermore, the resulting product has a low chloride ion content (≤5 ppm), a high free acid content (≤30 ppm), a high moisture content (≤20 ppm or greater), and is free of insoluble matter, making it suitable for direct use as a battery additive.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A method for synthesizing a liquid bis(fluorosulfonyl)imide salt comprises the following steps: 1) Add metal salt and appropriate amount of organic solvent to the dissolution tank, add bis(fluorosulfonyl)imidic acid dropwise under stirring, and continue stirring and reacting for 2-5 hours after the addition is completed. The temperature should be controlled at ≤10°C during the addition and reaction process; 2) After the reaction is completed, solution system A is obtained, and carbonate is added to the stirred reaction to remove the acid; then molecular sieve powder and adsorbent are added to further remove impurities, and finally the solution is filtered through a membrane to obtain the solution.

[0007] Specifically, the metal in step 1) is one or more of lithium, sodium, potassium, and magnesium. For example, metal salts include, but are not limited to, lithium salts, sodium salts, potassium salts, and magnesium salts. The metal salts are selected from one or more of metal halides, metal hydrides, and metal organic salts. The metal salts themselves do not contain water of crystallization and do not generate water upon reaction with bis(fluorosulfonyl)imidic acid.

[0008] Furthermore, the metal salt can be selected from one or more of lithium fluoride, lithium chloride, lithium bromide, lithium hydride, lithium benzoate, lithium terephthalate, lithium phenoxide, lithium p-methylphenoxide, lithium fumarate, sodium fluoride, sodium chloride, sodium bromide, sodium hydride, sodium benzoate, sodium terephthalate, sodium phenoxide, sodium p-methylphenoxide, sodium fumarate, potassium fluoride, potassium chloride, potassium bromide, potassium hydride, potassium benzoate, potassium terephthalate, potassium phenoxide, potassium p-methylphenoxide, potassium fumarate, magnesium fluoride, magnesium chloride, magnesium bromide, magnesium hydride, magnesium benzoate, magnesium terephthalate, magnesium phenoxide, magnesium p-methylphenoxide, magnesium fumarate, etc. These metal salts react with purified bis(fluorosulfonyl)imidic acid without generating water. The bis(fluorosulfonyl)imidic acid salts generated under anhydrous conditions disperse and dissolve well in benign solvents, forming liquid salts with extremely high reaction and conversion rates. Furthermore, generated gases such as hydrogen fluoride, hydrogen chloride, hydrogen bromide, and hydrogen are easily removed, while generated organic acids are insoluble in benign solvents and can be removed by filtration. The reaction equation for the lithium-containing compound with bis(fluorosulfonyl)imidic acid is as follows.

[0009] NH(SO2F)2+LiH→LiN(SO2F)2+H2↑ NH(SO2F)2+LiCl→LiN(SO2F)2+HCl↑ NH(SO2F)2+LiF→LiN(SO2F)2+HF↑ NH(SO2F)2+LiBr→LiN(SO2F)2+HBr↑ NH(SO2F)2+CH3COOLi→LiN(SO2F)2+CH3COOH NH(SO2F)2+C6H5COOLi→LiN(SO2F)2+C6H5COOH 2NH(SO2F)2+C8H4O4·2Li→2LiN(SO2F)2+C8H6O4 NH(SO2F)2+C6H5LiO→LiN(SO2F)2+C6H6O NH(SO2F)2+C7H7LiO→LiN(SO2F)2+C7H8O 2NH(SO2F)2+C4H2Li2O4→2LiN(SO2F)2+C4H4O4 The organic solvent is selected based on the electrolyte formulation requirements. Specifically, the organic solvent in step 1) is typically dimethyl carbonate or ethyl methyl carbonate. After adding the metal salt to the dissolution tank, introduce an appropriate amount of organic solvent. The amount of organic solvent added should ensure that the mass concentration of the bis(fluorosulfonyl)imide salt in the liquid salt is 29% to 31%. Then, slowly add the bis(fluorosulfonyl)imide acid dropwise while stirring at a speed of 200 to 500 rpm. During the addition, maintain the temperature ≤10°C.

[0010] Furthermore, if an inorganic salt such as a metal halide or metal hydride is used in step 1), gas will be generated. Nitrogen should be purged for 2-5 hours after the addition of the bis(fluorosulfonyl)imidate acid is completed, with a nitrogen flow rate of 150-300 m³ / h. If an organic metal salt is used, nitrogen is not required.

[0011] The one-step synthesis of the liquid salt in the present invention requires that the bisfluorosulfonyl imide acid, metal salt, and organic solvent are all high-purity chemicals. This ensures product purity after the liquid salt is formed, minimizes impurity content, and reduces subsequent steps. Therefore, the bisfluorosulfonyl imide acid must be purified. Furthermore, the bisfluorosulfonyl imide acid in step 1) can be purified by vacuum distillation, normal pressure or vacuum distillation, and CO2 supercritical extraction to remove impurities, achieving a purity of 99.8% or greater. Furthermore, the fluorosulfonate content is ≤500 ppm, the chloride content is ≤2 ppm, the fluoride content is ≤2 ppm, the sulfate content is ≤1000 ppm, and the sulfamate content is ≤200 ppm.

[0012] Specifically, in step 2), add 0.1‰ to 0.5‰ of carbonate by mass of solution system A and stir the reaction for 1.5-3 hours to remove the acid. It is preferred to use a filter membrane for filtration before deacidification. After the reaction is completed, the liquid salt is tested for moisture and acidity, and if a halide salt is used, the content of anions such as F, Cl, and Br needs to be tested. Because anhydrous raw materials are selected, the liquid salt is basically anhydrous after synthesis, and the acidity is controlled at ≤200ppm. If a metal halide salt is used, the generated anions such as F, Cl, and Br are controlled at ≤10ppm. At this time, add 0.1‰ to 0.5‰ of carbonate and stir the reaction for 1.5-3 hours to remove the acid. After filtration, the acidity of the solution is tested to control it to 20-50ppm.

[0013] Furthermore, in step 2), the amount of molecular sieve powder added is 0.5‰ to 2‰ of the mass of solution system A, and the amount of adsorbent added is 0.5‰ to 2‰ of the mass of solution system A; the adsorbent is selected from nano γ-Al2O3, chitosan with acetylation degree >95%, or hydrotalcite intercalation material.

[0014] Furthermore, the impurity removal process in step 2) is carried out at a low temperature of -10°C to 10°C, and the reaction is stirred for 1 to 4 hours.

[0015] Furthermore, in step 2), the pore size of the filter membrane used for the membrane filtration is 0.1 μm to 0.5 μm.

[0016] According to the moisture and acidity indexes of the liquid salt, 0.5‰ to 2‰ of molecular sieve powder is added to remove trace amounts of water and acid. Due to its high specific surface area, the molecular sieve powder can also adsorb some anions. However, if the anion indexes such as fluorosulfonate, chloride, fluoride, sulfate, and aminosulfonate are still high, 0.5‰ to 2‰ of adsorbent can be added for anion adsorption. The above impurity removal process is carried out at a low temperature of -10℃ to 10℃, and the reaction is stirred for 1 to 4 hours. After the reaction is completed, membrane filtration is performed, and the pore size of the filter membrane is 0.1μm to 0.5μm. The filtrate is the qualified liquid salt, and the amount of filter residue is very small. After accumulating a certain amount, it is compressed into sheets and calcined to make building materials.

[0017] The choice of molecular sieve powder depends on the type of liquid salt being prepared. For example, for lithium bis(fluorosulfonyl)imide liquid salt, lithium molecular sieve powder is selected; for sodium bis(fluorosulfonyl)imide liquid salt, sodium molecular sieve powder is selected. Adsorbents generally include nano-metal oxide powders with large surface areas, such as nano-γ-Al2O3, chitosan with an acetylation degree greater than 95%, or hydrotalcite-type intercalation materials (LDHs).

[0018] Compared with the prior art, the advantages and beneficial effects of the method of the present invention are as follows: The present invention provides a method for directly synthesizing a bisfluorosulfonyl imide salt and removing impurities to prepare a qualified liquid salt. The method not only solves the problems of a long preparation process of a crystalline salt product and difficulty in recovering the solvent, but also provides a one-step continuous process for preparing the liquid salt, thus overcoming the shortcomings of the prior art.

[0019] The advantages of the present invention are mild reaction process conditions, continuous operation, a liquid bis(fluorosulfonyl)imide salt yield of over 98.5%, a short process flow, and no poor solvents are used during the process, eliminating recovery and purification issues, and greatly reducing recovery energy consumption. The present invention can effectively remove impurities such as moisture, acidity, and anions from liquid salt by adding a trace amount of powdered impurity removal reagent. Because it is a powdered adsorbent, compared to spherical adsorbents such as molecular sieves and resins, it can significantly improve the external diffusion rate and adsorption efficiency of anions by shortening the diffusion path and increasing the specific surface area. While reducing the dosage, it can also shorten the reaction time of the impurity removal process. According to measurements, the liquid salt obtained by this method has high purity and low impurity ions. The prepared product has a low chloride ion content (≤5 ppm), a high free acid content (≤30 ppm), a high moisture content (≤20 ppm or more), and no insoluble matter. It can be directly used as a battery additive and fully meets the purity requirements of downstream products. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described in detail below in conjunction with the embodiments, but the protection scope of the present invention is not limited thereto.

[0021] Example 1 A one-step process for synthesizing liquid bis(fluorosulfonyl)imide salts comprises the following steps: 1) Add 93.8kg of anhydrous lithium chloride metal salt into the dissolution tank (test indicators: main content 99.9%, water 50ppm, Na 100ppm, K 30ppm, Ca 25ppm, Fe1ppm, SO4 2- 10ppm), then inject 948.6kg of ethyl methyl carbonate (the organic solvent), and start stirring at 200r / min. Weigh 400kg of bis(fluorosulfonyl)imidic acid and slowly add it dropwise to the dissolution tank. As the reaction proceeds, adjust the stirring speed continuously. In the later stages, when the reaction rate is low, increase the stirring speed by 20 revolutions per minute, reaching a maximum speed of 500r / min. The bis(fluorosulfonyl)imidic acid is added dropwise at a rate of 3.33kg / min. After the addition is complete over approximately 2 hours, start nitrogen bubbling at a flow rate of 150m³ / h to remove the generated hydrogen chloride gas. Nitrogen bubbling lasts for 3 hours. The temperature is maintained at 10°C throughout the reaction.

[0022] 2) After the synthesis, Solution A was obtained. The mass of the solution was weighed to 1342.7 kg. The liquid brine content was 16 ppm, the acidity was 195 ppm, and the chloride ion content was 5 ppm. At this point, 484 g of lithium carbonate was added and stirred for 2 hours to remove the acid. After filtration, the solution was tested for moisture content of 85 ppm, and the acidity was controlled at 34 ppm.

[0023] 3) Based on the water content and acidity of the liquid salt, 0.8‰ of the weight of Solution A's lithium molecular sieve powder (activated 13X molecular sieve powder, obtained by grinding commercially available 13X molecular sieve into a powder) and 1‰ of the weight of Solution A's adsorbent (γ-Al₂O₃) were added to remove impurities. The impurity removal process was carried out at 0°C, with stirring for 4 hours. After the reaction, the mixture was filtered using a 0.1μm pore size membrane. The filtrate was tested, and the residue was collected.

[0024] 1342.5 kg of liquid salt was obtained, with a concentration of 30.5% and a yield of 99.08%. The liquid salt was tested and its various indicators are shown below. The liquid salt composition is: bis(fluorosulfonyl)imide salt (approximately 30%) + solvent (approximately 70%).

[0025] Example 2 A one-step process for synthesizing liquid bis(fluorosulfonyl)imide salts comprises the following steps: 1) Add 165 kg of lithium fumarate (test indicators: 99.9% main content, 30 ppm water) to a dissolving tank. Then, inject 1038 kg of ethyl methyl carbonate (organic solvent). Start stirring at 200 rpm. Weigh 424.2 kg of bis(fluorosulfonyl)imidic acid and slowly add it dropwise to the dissolving tank. Adjust the stirring speed continuously as the reaction proceeds. In the later stages, when the reaction rate is low, increase the stirring speed by 20 rpm, to a maximum of 500 rpm. Add the bis(fluorosulfonyl)imidic acid dropwise at a rate of 1.67 kg / min. After the addition is complete in approximately 4 hours, continue stirring for 2 hours. Maintain the temperature at 10°C throughout the reaction.

[0026] 2) After the synthesis, Solution A was obtained. The mass of the solution was weighed to 1627.2 kg. After filtration through a 0.5 μm membrane, the filtrate showed a liquid brine content of 105 ppm and an acidity of 201 ppm. The residue, totaling 150.9 kg, consisted of the generated fumaric acid and excess unreacted lithium fumarate. At this point, 482 g of lithium carbonate was added and stirred for 2 hours to remove the acid. After filtration, the solution was tested for moisture content of 195 ppm, and the acidity was controlled at 30 ppm.

[0027] 3) Based on the water content and acidity of the liquid salt, 1‰ of lithium molecular sieve powder (13X activated molecular sieve powder) and 0.5‰ of an adsorbent (food-grade chitosan with an acetylation degree >95%, purchased from Zhengzhou Mingze Biotechnology Co., Ltd.) were added to remove impurities. The impurity removal process was carried out at -10°C with stirring for 4 hours. After completion of the reaction, the mixture was filtered through a 0.45μm pore size membrane. The filtrate was tested, and the residue was collected.

[0028] 1439.9 kg of liquid salt was obtained with a concentration of 30.0% and a yield of 98.56%. The various indicators of the liquid salt were tested as shown below.

[0029] Example 3 A one-step process for synthesizing liquid bis(fluorosulfonyl)imide salts comprises the following steps: 1) Add 17.68 kg of lithium hydride (test index: main content 99.9%) to the dissolution tank, then inject 950.6 kg of dimethyl carbonate (organic solvent). Start stirring at 200 r / min. Weigh 400 kg of bis(fluorosulfonyl)imidic acid and slowly add it dropwise to the dissolution tank. As the reaction proceeds, adjust the stirring speed continuously. In the later stages, when the reaction rate is low, increase the stirring speed by 20 revolutions per minute, to a maximum of 500 r / min. Add the bis(fluorosulfonyl)imidic acid dropwise at a rate of 0.83 kg / min. After the addition is complete in approximately 8 hours, start nitrogen bubbling at a rate of 200 m³ / h to remove the generated hydrogen. The nitrogen bubbling time is 2 hours. Maintain the temperature at 5°C throughout the reaction.

[0030] 2) After the synthesis, solution system A was obtained. The mass of the solution was weighed to 1335.3 kg. After filtration through a 0.45 μm membrane, the filtrate was tested for liquid brine content of 25 ppm and acidity of 186 ppm. At this point, 459 g of lithium carbonate was added and stirred for 2 hours to remove acid. After filtration, the solution was tested for water content of 65 ppm, and the acidity was controlled at 39 ppm.

[0031] 3) Based on the water content and acidity of the liquid salt, 0.5‰ of the weight of Solution A was added with lithium molecular sieve powder (13X molecular sieve activated powder) and 0.5‰ of the weight of Solution A adsorbent (hydrotalcite-based intercalation material, LDHs, AR magnesium-aluminum hydrotalcite, purchased from the Quzhou Resource and Chemical Innovation Institute). The mixture was calcined at 500°C for 4 hours to remove impurities. The impurity removal process was carried out at -5°C with stirring for 4 hours. After the reaction, the mixture was filtered using a 0.1μm pore size membrane. The filtrate was tested, and the residue was collected.

[0032] 1335.0 kg of liquid salt was obtained with a concentration of 30.5% and a yield of 98.53%. The various indicators of the liquid salt were tested as shown below.

[0033] Example 4 A one-step process for synthesizing liquid bis(fluorosulfonyl)imide salts comprises the following steps: 1) Add 92.8kg of high-purity sodium fluoride into the dissolution tank (test indicators: main content 99.95%, water 150 ppm, Mg5ppm, Ca 5ppm, Fe 10ppm, SO4 2- 15ppm, Cl - 5ppm), then inject 1059kg of dimethyl carbonate (an organic solvent) and start stirring at 200r / min. Weigh 400kg of bis(fluorosulfonyl)imidic acid and slowly add it dropwise to the dissolution tank. As the reaction proceeds, adjust the stirring speed continuously. In the later stages, when the reaction rate is low, increase the stirring speed by 20 revolutions per minute, reaching a maximum of 500r / min. Add the bis(fluorosulfonyl)imidic acid at a rate of 3.33kg / min. After the addition is complete in approximately 2 hours, start nitrogen bubbling at a flow rate of 300m³ / h to remove the generated hydrogen fluoride gas. Nitrogen bubbling lasts for 5 hours. Maintain the temperature at 5°C throughout the reaction.

[0034] 2) After the synthesis, Solution A was obtained. The mass of the solution was weighed to 1465.2 kg, and the liquid brine was 15 ppm and the acidity was 175 ppm. At this point, 679 g of sodium carbonate was added and stirred for 2 hours to remove the acid. After filtration, the solution was tested for moisture at 65 ppm, and the acidity was controlled at 28 ppm.

[0035] 3) Based on the water content and acidity of the liquid salt, 0.5‰ of the weight of Solution A's sodium molecular sieve powder (JLPH5 activated powder, obtained by grinding commercially available JLPH5 hydrogen production molecular sieve into a powder) and 1‰ of the weight of Solution A's adsorbent (γ-Al2O3) were added to remove impurities. The impurity removal process was carried out at 10°C, with stirring for 4 hours. After the reaction, the mixture was filtered through a membrane with a pore size of 0.1μm. The filtrate was tested, and the residue was collected.

[0036] 1464.9 kg of liquid salt was obtained with a concentration of 30.2% and a yield of 98.61%. The various indicators of the liquid salt were tested as shown below.

[0037] Example 5 A one-step process for synthesizing liquid bis(fluorosulfonyl)imide salts comprises the following steps: 1) Add 318.2kg of sodium benzoate into the dissolving tank (test indicators: main content 99.9%, moisture 100ppm, Cl - 30ppm, Fe5ppm, SO4 2- 10ppm), then inject 1088kg of dimethyl carbonate (an organic solvent) and start stirring at 200 rpm. Weigh 400kg of bis(fluorosulfonyl)imidic acid and slowly add it dropwise to the dissolution tank. Adjust the stirring speed as the reaction proceeds. In the later stages, when the reaction rate is low, increase the stirring speed by 20 rpm, reaching a maximum of 500 rpm. Add the bis(fluorosulfonyl)imidic acid at a rate of 3.33kg / min. After the entire addition is complete over approximately 2 hours, continue stirring for another 2 hours. Maintain the temperature at 5°C throughout the reaction.

[0038] 2) After the synthesis, Solution A was obtained. The mass of the solution was weighed to 1806.2 kg. Filtered through a 0.45 μm membrane, the filtrate showed a liquid brine content of 45 ppm and an acidity of 146 ppm. The residue, totaling 324.0 kg, was the generated benzoic acid, which was returned to the synthesis of sodium benzoate. At this point, 573 g of sodium carbonate was added to the solution and stirred for 2 hours to remove the acid. After filtration, the solution was tested for moisture content of 82 ppm and acidity of 49 ppm.

[0039] 3) Based on the water content and acidity of the liquid salt, 2‰ of the weight of Solution A was added with sodium molecular sieve powder (JLPH5 activated powder) and 1‰ of the weight of Solution A with an adsorbent (γ-Al₂O₃) to remove impurities. This process was carried out at 5°C with stirring for 4 hours. After the reaction, the mixture was filtered using a 0.1μm pore size membrane. The filtrate was tested, and the residue was collected.

[0040] 1482.2 kg of liquid salt was obtained with a concentration of 29.8% and a yield of 98.45%. The various indicators of the liquid salt were tested as shown below.

[0041] Example 6 A one-step process for synthesizing liquid bis(fluorosulfonyl)imide salts comprises the following steps: 1) Add 263kg of anhydrous potassium bromide into the dissolving tank (test indicators: main content 99.9%, water 95 ppm, Cl - 10ppm, Fe 5ppm, SO4 2-10ppm), then inject 1132kg of ethyl methyl carbonate (the organic solvent), and start stirring at 200r / min. Weigh 400kg of bis(fluorosulfonyl)imidic acid and slowly add it dropwise to the dissolution tank. As the reaction proceeds, adjust the stirring speed continuously. In the later stages, when the reaction rate is low, increase the stirring speed by 20 revolutions per minute, reaching a maximum of 500r / min. Add the bis(fluorosulfonyl)imidic acid at a rate of 3.33kg / min. After the addition is complete in approximately 2 hours, continue stirring while starting nitrogen bubbling at a rate of 200m³ / h to carry away the generated hydrogen bromide gas. Nitrogen bubbling lasts for 5 hours. Maintain the temperature at 0°C throughout the reaction.

[0042] 2) After the synthesis, solution system A was obtained. The mass of the solution was weighed to 1582.0 kg. After filtration through a 0.45 μm membrane, the filtrate was tested for liquid brine content of 55 ppm and acidity of 246 ppm. At this point, 1343 g of potassium carbonate was added and stirred for 2 hours to remove acid. After filtration, the solution was tested for moisture content of 115 ppm, and the acidity was controlled at 21 ppm.

[0043] 3) Based on the water content and acidity of the liquid salt, 2‰ of the weight of Solution A's sodium molecular sieve powder (JLPH5 activated powder) and 1‰ of the weight of Solution A's adsorbent (hydrotalcite-based intercalation material, LDHs, calcined at 500°C for 4 hours) were added to remove impurities. The impurity removal process was carried out at 10°C, with stirring for 4 hours. After the reaction, the mixture was filtered using a 0.1μm pore size membrane. The filtrate was tested, and the residue was collected.

[0044] 1581.9 kg of liquid salt was obtained with a concentration of 30.1% and a yield of 98.38%. The various indicators of the liquid salt were tested as shown below.

[0045] Example 7 A one-step process for synthesizing liquid bis(fluorosulfonyl)imide salts comprises the following steps: 1) Add 207.7 kg of anhydrous magnesium terephthalate (test indicators: main content 99.9%, water 50 ppm) to a dissolving tank. Then, inject 1024 kg of dimethyl carbonate (organic solvent). Start stirring at 200 rpm. Weigh 400 kg of bis(fluorosulfonyl)imidic acid and slowly add it dropwise to the dissolving tank. As the reaction proceeds, adjust the stirring speed continuously. In the later stages, when the reaction rate is low, increase the stirring speed by 20 rpm, to a maximum of 500 rpm. Add the bis(fluorosulfonyl)imidic acid dropwise at a rate of 3.33 kg / min. After the entire addition is complete in approximately 2 hours, continue stirring for 2 hours. Maintain the temperature at 10°C throughout the reaction.

[0046] 2) After the synthesis, Solution A was obtained. The mass of the solution was weighed to 1631.7 kg. Filtered through a 0.45 μm membrane, the filtrate showed a liquid brine content of 35 ppm and an acidity of 162 ppm. The residue, totaling 224.4 kg, was the generated terephthalic acid. The terephthalic acid was returned to the synthesis of magnesium terephthalate. At this point, 478 g of magnesium carbonate was added to the solution and stirred for 2 hours to remove the acid. After filtration, the solution was tested for moisture content of 78 ppm and acidity of 42 ppm.

[0047] 3) Based on the water content and acidity of the liquid salt, 0.8‰ of sodium molecular sieve powder (JLPH5 activated powder) and 1‰ of adsorbent (γ-Al₂O₃) were added to remove impurities. The impurity removal process was carried out at 5°C with stirring for 4 hours. After the reaction, the mixture was filtered using a 0.1μm pore size membrane. The filtrate was tested and the residue collected.

[0048] 1407.3 kg of liquid salt was obtained with a concentration of 29.6% and a yield of 98.18%. The various indicators of the liquid salt were tested as follows: Comparative Example A comparative example of a one-step process for synthesizing a liquid bis(fluorosulfonyl)imide salt is provided, specifically comprising the following steps: 1) Add 500 kg of crude salt of lithium bis(fluorosulfonyl)imide to the dissolution tank (the crude salt has the following test indicators: moisture: 800 ppm, acidity: 250 ppm, chloride ion: 49 ppm, insoluble matter: 1%), then add dimethyl carbonate (a non-polar organic solvent) at a mass ratio of 1:0.6. Then add lithium carbonate (5‰ by mass of the crude salt), maintain the temperature at 25±5°C, and stir thoroughly to dissolve for 4 hours.

[0049] 2) The fully dissolved mixture was filtered, and the turbidity of the filtrate was controlled to be ≤10 NTU to obtain 795 kg of clear and transparent liquid salt solution.

[0050] 3) The liquid salt solution from step 2) was mixed with dichloromethane in a mass ratio of 1:20. The reactor was stirred for 5 h, centrifuged for 3 h, purged with nitrogen for 10 h, and dried at 30°C for 10 h to obtain 470.25 kg of finished crystalline salt.

[0051] 4) 470.25 kg of the finished crystalline salt was dissolved in 1097.25 kg of ethyl methyl carbonate solvent and stirred for reaction for 4 hours. After filtration, the filtrate had a mass of 1567.2 kg. Lithium molecular sieve powder (13X molecular sieve activated powder) with a weight of 0.5‰ of the liquid salt was used for dewatering to obtain 1567.1 kg of liquid salt with a concentration of 29.9% and a yield of 94.75%. The various indicators of the liquid salt were tested as shown below.

[0052] From the results of the above embodiments and comparative examples, compared with the existing comparative examples, the product prepared by this process has high purity, high yield, lower moisture and acidity, and provides a high-yield, high-purity, low-cost method for the preparation of liquid bis(fluorosulfonyl)imide salts.

Claims

1. A method for synthesizing a liquid bis(fluorosulfonyl)imide salt, characterized in that: The steps include: 1) Add metal salt and appropriate amount of organic solvent to the dissolution tank, add bis(fluorosulfonyl)imidic acid dropwise under stirring, and continue stirring and reacting for 2-5 hours after the addition is completed. The temperature should be controlled at ≤10°C during the addition and reaction process; 2) After the reaction is completed, solution system A is obtained, and carbonate is added to the stirred reaction to remove the acid; then molecular sieve powder and adsorbent are added to further remove impurities, and finally the solution is filtered through a membrane to obtain the solution.

2. The method for synthesizing the liquid bis(fluorosulfonyl)imide salt according to claim 1, wherein: In step 1), the metal is one or more of lithium, sodium, potassium, and magnesium; and the metal salt is one or more of metal halides, metal hydrides, and metal organic salts.

3. The method for synthesizing the liquid bis(fluorosulfonyl)imide salt according to claim 2, wherein: The metal salt is one or more of lithium fluoride, lithium chloride, lithium bromide, lithium hydride, lithium benzoate, lithium terephthalate, lithium phenoxide, lithium p-methylphenoxide, lithium fumarate, sodium fluoride, sodium chloride, sodium bromide, sodium hydride, sodium benzoate, sodium terephthalate, sodium phenoxide, sodium p-methylphenoxide, sodium fumarate, potassium fluoride, potassium chloride, potassium bromide, potassium hydride, potassium benzoate, potassium terephthalate, potassium phenoxide, potassium p-methylphenoxide, potassium fumarate, magnesium fluoride, magnesium chloride, magnesium bromide, magnesium hydride, magnesium benzoate, magnesium terephthalate, magnesium phenoxide, magnesium p-methylphenoxide, and magnesium fumarate.

4. The method for synthesizing the liquid bis(fluorosulfonyl)imide salt according to claim 2, wherein: In step 1), when the metal salt is a metal halide or metal hydride, nitrogen gas needs to be passed through for 2-5 hours after the reaction is completed, with a nitrogen flow rate of 150-300 m³ / h.

5. The method for synthesizing the liquid bis(fluorosulfonyl)imide salt according to claim 1, wherein: The organic solvent in step 1) is dimethyl carbonate or ethyl methyl carbonate.

6. The method for synthesizing the liquid bis(fluorosulfonyl)imide salt according to claim 1, wherein: The bisfluorosulfonyl imide acid in step 1) is subjected to impurity removal by vacuum distillation, atmospheric distillation, vacuum distillation, or CO2 supercritical extraction, so that the purity of the bisfluorosulfonyl imide acid reaches more than 99.8%, and the fluorosulfonate ion is ≤500ppm, the chloride ion is ≤2ppm, the fluoride ion is ≤2ppm, the sulfate ion is ≤1000ppm, and the aminosulfonate ion is ≤200ppm.

7. The method for synthesizing the liquid bis(fluorosulfonyl)imide salt according to claim 1, wherein: In step 2), 0.1‰ to 0.5‰ of carbonate is added to the solution system A by weight, and the mixture is stirred for 1.5-3 hours to remove the acid.

8. The method for synthesizing the liquid bis(fluorosulfonyl)imide salt according to claim 1, wherein: In step 2), the amount of molecular sieve powder added is 0.5‰ to 2‰ of the mass of solution system A, and the amount of adsorbent added is 0.5‰ to 2‰ of the mass of solution system A; the adsorbent is selected from nano γ-Al2O3, chitosan with acetylation degree greater than 95%, or hydrotalcite intercalation material.

9. The method for synthesizing the liquid bis(fluorosulfonyl)imide salt according to claim 1, wherein: In step 2), the impurity removal process is carried out at a low temperature of -10°C to 10°C, and the reaction is stirred for 1 to 4 hours.

10. The method for synthesizing liquid bis(fluorosulfonyl)imide salt according to claim 1, wherein: Step 2) The pore size of the filter membrane used for membrane filtration is 0.1μm to 0.5μm.

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