Preparation method of liquid sodium bisfluorosulfonimide solution

Abstract

This invention provides a method for preparing a liquid sodium bis(fluorosulfonyl)imide solution. The method is characterized by: absorbing the hydrogen chloride gas generated in the solvent into hydrochloric acid via water; filtering the resulting reaction solution; and then subjecting it to refining processes such as degassing, concentration, and resin deacidification to obtain a high-purity sodium bis(fluorosulfonyl)imide concentrate. The sodium bis(fluorosulfonyl)imide concentrate obtained by this invention has high purity and low impurity content, making it suitable as an electrolyte salt in the production of sodium battery electrolytes. Furthermore, the method utilizes inexpensive and readily available raw materials, is simple to operate, allows for the complete recovery and reuse of byproducts, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte technology, specifically relating to a method for preparing liquid sodium difluorosulfonamide solution. Background Technology

[0002] Sodium bisfluorosulfonamide is primarily used as an important electrolyte salt in non-aqueous electrolytes for sodium batteries, requiring very high purity (typically no less than 99.5%). The content of impurities such as moisture, alkali metals, heavy metals, and other chloride ions, sulfate ions, and free acids must be strictly controlled; otherwise, it will lead to increased internal resistance, rapid capacity decay, short cycle life, and even compromised battery safety. Obtaining sodium bisfluorosulfonamide products with high purity and low levels of harmful impurities is of great significance.

[0003] Sodium-ion batteries are a type of rechargeable battery that relies primarily on the movement of sodium ions between the positive and negative electrodes to function. Compared to lithium-ion batteries, sodium-ion batteries have the following advantages: (1) Sodium salt raw materials are abundant and inexpensive; (2) Due to the properties of sodium salts, low-concentration electrolytes can be used, reducing costs; (3) Sodium ions do not form alloys with aluminum, and aluminum foil can be used as the current collector at the negative electrode, further reducing costs and weight; (4) Because sodium-ion batteries have no over-discharge characteristics, they can be discharged to zero volts.

[0004] Sodium bis(fluorosulfonyl)imide is a key high-performance electrolyte material in sodium-ion batteries and has high application value.

[0005] However, the existing methods for preparing sodium bis(fluorosulfonyl)imide have certain shortcomings. For example, the water removal process is complex, introduces many impurities during the water removal process, and has a low yield.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing liquid sodium bis(fluorosulfonyl)imide solution, thereby solving the problems of complex preparation methods, difficult impurity removal, and long process routes mentioned in the background art. By reacting bis(fluorosulfonyl)imide and sodium chloride in a non-aqueous solvent to obtain sodium bis(fluorosulfonyl)imide, the dehydration process is avoided, as well as the introduction of impurities during dehydration. This effectively controls the water content in the product and improves the yield and main content of sodium bis(fluorosulfonyl)imide.

[0008] The inventors have conducted extensive and in-depth research on the aforementioned problem and discovered that, in a method for producing sodium difluorosulfonylimide by reacting difluorosulfonylimide acid and sodium chloride in a non-aqueous organic solvent, the reaction product generated in this solvent is filtered, and the filtrate is further degassed and concentrated to easily produce a high-purity liquid sodium difluorosulfonylimide solution, thus completing this invention. Specifically, this invention provides a method for producing a liquid sodium difluorosulfonylimide solution, which involves reacting difluorosulfonylimide acid and sodium chloride in a non-aqueous organic solvent to produce a reaction product, sodium difluorosulfonylimide. The method is characterized by filtering the reaction product generated in this solvent and further degassed and concentrated the filtrate to obtain a liquid sodium difluorosulfonylimide solution. Degassed concentration refers to a method of removing acidic gases from the reaction solution by evaporating the gaseous phase contained in the solvent under reduced pressure or by introducing a carrier gas such as nitrogen or dry air. This invention discovers that by using degassing and concentration, the concentration of the solute can be increased, and acidic impurities are also removed along with the solvent, thus enabling the production of a high-purity liquid sodium difluorosulfonylimide solution. It should be noted that a lower concentration of acidic impurities in the liquid sodium difluorosulfonylimide solution is preferred. The concentration of acidic impurities in the concentrate obtained in this invention is preferably below 100 ppm by mass, more preferably below 60 ppm by mass. When the concentration of acidic impurities exceeds the above range, it will adversely affect the characteristics of sodium batteries, and is therefore not preferred. Effects of the Invention According to this invention, a high-purity liquid sodium difluorosulfonylimide solution can be easily produced by reacting difluorosulfonylimide acid and sodium chloride in a non-aqueous organic solvent, and then using the reaction product sodium difluorosulfonylimide generated in that solvent. A high-purity concentrate can be obtained by degassing and concentration without further use of a purifying agent, and in particular, it does not require complex equipment; production can be carried out using only a reaction tank, thus achieving a cost-reducing manufacturing method.

[0009] This invention provides a method for preparing a liquid sodium difluorosulfonamide solution. The resulting solution can be directly used as a material for sodium battery electrolytes. The method uses inexpensive and readily available raw materials, is simple to operate, produces few byproducts, and is suitable for industrial production.

[0010] Specifically, the preparation method of the liquid sodium difluorosulfonamide solution includes the following steps:

[0011] 1) Sodium chloride suspended in a non-aqueous solvent reacts with difluorosulfonylimide acid to produce sodium difluorosulfonylimide and hydrogen chloride gas;

[0012] 2) The above liquid sodium difluorosulfonamide solution is subjected to purification processes such as filtration, degassing, concentration, and resin deacidification to obtain a high-purity liquid sodium difluorosulfonamide solution.

[0013] Furthermore, the molar ratio of sodium chloride to difluorosulfonyl imide acid is 1 to 1.1:1.

[0014] Furthermore, the water content of the non-aqueous solvent is less than 15 ppm, and the non-aqueous solvent is at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, acetone, diethyl ether, dimethylformamide, ethylene glycol dimethyl ether, acetonitrile, and tetrahydrofuran.

[0015] Furthermore, the reaction temperature in step 1) is 50–100°C. The lower limit for the reaction temperature is 50°C, preferably 60°C, and the upper limit is 100°C, preferably 80°C. Temperatures above 100°C are not preferred as they cause coloring and side reactions. The reaction time is 6–12 hours. There are no particular restrictions on the pressure during the reaction, but since the generated components include gaseous parts, they need to be promptly removed from the reaction system.

[0016] Furthermore, in step 2), degassing is performed under reduced pressure, ranging from 0.50 to 10 kPa, to remove hydrogen chloride gas present in the resulting filtrate through degassing and concentration. Degassing and concentration are achieved by reducing the pressure of the gas phase containing volatile components volatilized from the solution, or by introducing a carrier gas such as nitrogen or dry air to expel the gas phase from the system. The degassing temperature is 20–80°C. The lower the pressure within the system, the higher the temperature, allowing for more efficient concentration. However, excessively high temperatures can cause discoloration of the resulting concentrate or a decrease in yield due to the decomposition of sodium difluorosulfonamide. Therefore, the upper limit of this temperature is 80°C, preferably 60°C. Conversely, excessively low temperatures may cause non-aqueous organic solvents to solidify, making it difficult to remove acidic impurities during solidification. Therefore, the lower limit of this temperature is 20°C, preferably 30°C. The pressure within the aforementioned system varies depending on the temperature and vapor pressure of the liquid being concentrated, and therefore cannot be generalized. Regarding the reduced pressure, it is preferable to maintain the vacuum level in the tank below 10 kPa in absolute pressure. When the maintained pressure exceeds 10 kPa, it is impossible to remove hydrogen chloride, which is an impurity, to below the desired concentration, or it requires a long time to remove the impurity to below the desired concentration, so this is not preferred. Conversely, when the maintained pressure is 5 kPa or below, the aforementioned impurities can be removed to a low concentration, so this is more preferable. When a carrier gas is introduced, it can be introduced only into the gas phase, but it is more effective to introduce it into the liquid as well as through bubbling or the like. Regarding the temperature during degassing and concentration, the lower limit is 20°C, preferably 30°C, and the upper limit is 80°C, preferably 60°C. When the temperature during degassing and concentration is below 20°C, the non-aqueous organic solvent solidifies, making it difficult to remove acidic impurities. Furthermore, when the temperature is above 80°C, it causes coloring and side reactions, making it difficult to adjust the concentration of acidic impurities in the concentrate to below 60 ppm, so this is not preferred. The concentration also depends on the initial concentration of sodium difluorosulfonyl imide; a higher concentration of sodium difluorosulfonyl imide after concentration is better, and the degassing time is 4–8 hours.

[0017] Furthermore, the resin deacidification operation temperature in step 2) is 20–60°C, and the aforementioned concentrated solution is passed through an ion exchange resin to remove acidic impurities such as hydrogen chloride. From the perspective of preventing the decomposition of sodium difluorosulfonamide, the solvent, and the ion exchange resin, this temperature is preferably 50°C. Considering the viscosity of the aforementioned concentrated solution passed through the ion exchange resin, 30°C is further preferred.

[0018] Furthermore, regarding the aforementioned ion exchange resin, the matrix structure can include styrene-divinylbenzene copolymer, styrene resin, acrylic (ester) resin, etc., and the functional groups can include -SO3H, -N(CH3)2, -N(1)(CH3)3, -N(2)(C2H4OH)(CH3)2, etc. The adsorption time is 8 to 10 hours. After completion, the insoluble matter is filtered off to obtain a liquid sodium difluorosulfonamide solution.

[0019] Furthermore, the aforementioned ion exchange resin is a hydrogen-oxygen type anion exchange resin.

[0020] Furthermore, regarding the aforementioned ion exchange resin, a fluorinated modified hydroxide-type anion exchange resin is used. Free radicals are generated by irradiating a dry-based hydroxide-type strong basic anion exchange resin, and then grafted onto triethanolamine maleate diester and 1-allyl-3-methylimidazolium tetrafluoroborate to obtain a hydroxide-type ion exchange resin with triethanolamine and tetrafluoroborate functional groups on its backbone. This resin is resistant to hydrogen fluoride corrosion, not easily broken or degraded, and its service life as an acid remover is extended.

[0021] Furthermore, regarding the aforementioned ion exchange resin, its preparation method is as follows:

[0022] S1: By weight, nitrogen gas is introduced into the reactor, and 20-30 parts of Lewis acid and 100-140 parts of dry-based quaternary ammonium salt ion exchange resin are added to 1000-1200 parts of toluene. Then, 5-10 parts of 4-amino-3-fluorobenzoyl chloride are added, and the mixture is stirred to carry out the acylation reaction. The acylation temperature is 30-60℃, and the acylation reaction time is 3-6 hours. After the reaction is completed, 3-6 parts of lithium acrylate and 2-5 parts of triethylamine are added. The reaction is carried out at 70-80℃ for 1-3 hours. The mixture is then filtered and dried. The Lewis acid can be selected from either aluminum chloride or ferric chloride.

[0023] S2: Transfer the resin to a glass exchange chamber, adding 15-30% of the resin exchange chamber volume; pass the column through a 3-5 times volume of sodium hydroxide with a mass percentage concentration of 10-20% at a flow rate of 1-3 BV / h. After the column pass is completed, vacuum dry to obtain the fluorinated resin.

[0024] Furthermore, the reactions in steps 1) and 2) are carried out in an inert gas atmosphere, wherein the inert gas is at least one of nitrogen, argon, and helium.

[0025] Technical effects:

[0026] The present invention provides a method for preparing a liquid sodium difluorosulfonyl imide solution, which, compared with the prior art, has the following significant advantages:

[0027] 1) The preparation method provided by the present invention has mild reaction conditions, high yield of the product, cheap and readily available raw materials, which can save costs significantly, and the by-products can be recycled.

[0028] 2) The preparation method provided by this invention has simple reaction steps, is easy to operate, and has simple post-reaction processing, which increases the feasibility of industrial production.

[0029] 3) The liquid sodium difluorosulfonamide solution prepared by this invention can be used as sodium salt electrolyte in sodium batteries to ensure the working performance of the battery. Detailed Implementation

[0030] This invention provides a method for preparing a liquid sodium bis(fluorosulfonyl)imide solution using inexpensive and readily available raw materials under relatively low temperature and conditions. The method includes: reacting sodium chloride and bis(fluorosulfonyl)imide acid in a non-aqueous solvent under an inert gas atmosphere to produce sodium bis(fluorosulfonyl)imide. The resulting liquid sodium bis(fluorosulfonyl)imide solution is then degassed, purified by resin deacidification, and precisely filtered to obtain a high-quality liquid sodium bis(fluorosulfonyl)imide solution.

[0031] 1. Preparation of sodium difluorosulfonamide solution

[0032] Sodium bis(fluorosulfonyl)imide is produced by reacting sodium chloride and bis(fluorosulfonyl)imide acid in a non-aqueous solvent under a nitrogen atmosphere. After degassing, resin deacidification, and precision filtration, a high-quality liquid sodium bis(fluorosulfonyl)imide solution is obtained. The reaction equation is as follows:

[0033] NaCl + HFSI → NaFSI + HCl

[0034] In some embodiments, the molar ratio of sodium chloride to difluorosulfonyl imide is 1 to 1.1:1, for example: 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1, 1.1:1.

[0035] Preferably, the sodium chloride has a purity greater than 99.5% and a water content not exceeding 50 ppm.

[0036] In some embodiments, the non-aqueous solvent is at least one selected from dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, dimethylformamide, ethylene glycol dimethyl ether, diethyl ether, acetonitrile, and tetrahydrofuran.

[0037] Preferably, the water content of the non-aqueous solvent is less than 15 ppm.

[0038] The reaction temperature is 50–100℃, and the reaction time is 6–12 h.

[0039] Non-limiting examples of the reaction temperature include: 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, etc.

[0040] Non-limiting examples of the reaction time include: 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h, 12h, etc.

[0041] 2. Purification of liquid difluorosulfonyl imide sodium solution

[0042] The above-mentioned liquid sodium difluorosulfonamide solution was subjected to purification processes such as degassing under reduced pressure and resin deacidification to obtain a high-purity liquid sodium difluorosulfonamide solution.

[0043] The degassing process employs reduced pressure, with a pressure range of 0.05–10 kPa, a degassing temperature of 20–80 °C, and a degassing time of 4–8 h.

[0044] Non-limiting examples of the degassing pressure include: 0.05 kPa, 0.5 kPa, 1 kPa, 1.5 kPa, 2 kPa, 2.5 kPa, 3 kPa, 3.5 kPa, 4 kPa, 4.5 kPa, 5 kPa, 5.5 kPa, 6 kPa, 6.5 kPa, 7 kPa, 7.5 kPa, 8 kPa, 8.5 kPa, 9 kPa, 9.5 kPa, 10 kPa, etc.

[0045] Non-limiting examples of the degassing temperature include: 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc.

[0046] Non-limiting examples of the reaction time include: 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, etc.

[0047] The resin deacidification operation temperature is 20–60℃, and the adsorption time is 8–10 hours. After completion, it is precisely filtered, and the concentration is adjusted using a non-aqueous solvent to obtain a 30% (w / w) liquid sodium bis(fluorosulfonyl)imide solution.

[0048] Non-limiting examples of the resin deacidification temperature include: 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, etc.

[0049] Non-limiting examples of the resin deacidification time include: 8h, 8.5h, 9h, 9.5h, 10h, etc.

[0050] The reaction is carried out in an inert gas atmosphere, wherein the inert gas is at least one of nitrogen, argon, and helium.

[0051] The chloride ion content in the liquid sodium difluorosulfonamide solution prepared by this invention is below 5 ppm; the concentration of free acid in the solution was tested by titration, and the acidity result was below 50 ppm. Due to the low chloride and free acid content in the solution, it can be directly used as a sodium salt electrolyte material for sodium batteries.

[0052] The following are optimized embodiments of the present invention. The present invention is not limited to the following preferred embodiments. It should be noted that any modifications and improvements made by those skilled in the art based on the inventive concept are within the scope of protection of the present invention.

[0053] Example 1

[0054] In a 500ml three-necked flask under nitrogen protection, 200ml of dimethyl carbonate and 64.28g (1.1mol) of sodium chloride were added. The mixture was stirred and the temperature was slowly raised. At 60℃, 181.14g (1mol) of bis(fluorosulfonyl)imide acid (HFSI) was slowly added dropwise over approximately 4 hours. After the addition was complete, the temperature was maintained for another 4 hours. After the reaction was complete, the vacuum pump was slowly turned on to degas the reaction flask, which took approximately 8 hours. The degassed liquid sodium(fluorosulfonyl)imide solution was then deacidified using a deacidifying resin, precisely filtered, and the concentration was adjusted with dimethyl carbonate to obtain a 30% (w / w) liquid sodium(fluorosulfonyl)imide solution.

[0055] In the deacidification process, the ion exchange resin used is a fluorinated modified hydroxide-type anion exchange resin, which is prepared as follows:

[0056] S1: Nitrogen gas is introduced into the reactor. 20g of Lewis acid and 100g of dry-based quaternary ammonium salt ion exchange resin are added to 1000g of toluene, followed by 5g of 4-amino-3-fluorobenzoyl chloride. The mixture is stirred to carry out an acylation reaction at 30℃ for 3 hours. After the reaction is complete, 3g of lithium acrylate and 2g of triethylamine are added. The reaction is carried out at 70℃ for 1 hour. The mixture is then filtered and dried. The Lewis acid can be selected from either aluminum chloride or ferric chloride.

[0057] S2: Transfer the resin to a glass exchange chamber, adding 15% of the resin exchange chamber volume; pass the column through a 10% sodium hydroxide solution (3 times its volume by mass percentage) at a flow rate of 1 BV / h. After column chromatography, vacuum dry to obtain the fluorinated resin.

[0058] The test results of this example are as follows: sodium difluorosulfonamide content 30.53%, free acid (calculated as HCl) 68 ppm, moisture (Kalfisch method) 29 ppm, alkali metal ion content (calculated as K) 1 ppm, chloride ion content 26 ppm, heavy metal ion content (calculated as Fe) 1 ppm, and insoluble matter content 80 ppm.

[0059] Example 2

[0060] In a 2000ml three-necked flask, under nitrogen protection, 1000ml of methyl ethyl carbonate, 236.68g (4.05mol) of sodium chloride, and 724.56g (4mol) of bis(fluorosulfonyl)imide acid (HFSI) were added dropwise over approximately 5 hours. After the addition, the mixture was kept at the same temperature for 5 hours. Following the reaction, while maintaining the same temperature, a vacuum pump was slowly turned on to gradually evacuate the reaction flask, maintaining a pressure of 2 kPa for approximately 9 hours. The degassed liquid sodium(fluorosulfonyl)imide solution was then deacidified using a deacidifying resin, precisely filtered, and its concentration was adjusted with methyl ethyl carbonate to obtain a 30% (w / w) liquid sodium(fluorosulfonyl)imide solution.

[0061] In the deacidification process, the ion exchange resin used is a fluorinated modified hydroxide-type anion exchange resin, which is prepared as follows:

[0062] S1: 150g of dry-based hydroxide-type strong basic anion exchange resin was subjected to ultraviolet light irradiation for 40 minutes at a wavelength of 297nm.

[0063] S2: Then immerse it in 1200g of ethanol, add 0.35g of triethanolamine maleate diester, 0.35g of 1-allyl-3-methylimidazolium tetrafluoroborate, and 1.5g of benzophenone. After stirring and mixing evenly, introduce nitrogen gas and soak at 55℃ for 2 hours.

[0064] S3: After completion, remove the resin, air dry it, place it in an ultraviolet irradiation device under nitrogen protection for grafting reaction, then remove it and soak it in a 20% sodium hydroxide solution for 20 hours. Filter the solution, wash it with water, and obtain the fluorinated modified hydroxide anion exchange resin.

[0065] The test results of this example are as follows: sodium difluorosulfonamide content 30.08%, free acid (calculated as HCl) 90 ppm, moisture (Kalfisch method) 35 ppm, alkali metal ion content (calculated as K) 1 ppm, chloride ion content 17 ppm, heavy metal ion content (calculated as Fe) 1 ppm, and insoluble matter content 102 ppm.

[0066] Example 3

[0067] In a 500ml three-necked flask, under nitrogen protection, 200ml of ethyl acetate, 30.39g (0.52mol) of sodium chloride, and 90.57g (0.5mol) of bis(fluorosulfonyl)imide acid (HFSI) were added dropwise over approximately 2 hours. After the addition, the mixture was kept at the same temperature for 4 hours. Hydrogen chloride gas was released during the reaction; this gas was absorbed using a low-concentration sodium hydroxide solution. After the reaction, while maintaining the same temperature, a vacuum pump was used to slowly evacuate the reaction flask for degassing, which lasted approximately 6 hours. The degassed liquid bis(fluorosulfonyl)imide sodium solution was then deacidified using a deacidifying resin, filtered precisely, and the concentration was adjusted with ethyl acetate to obtain a 30% (w / w) liquid bis(fluorosulfonyl)imide sodium solution.

[0068] In the deacidification process, the ion exchange resin used is a fluorinated modified hydroxide-type anion exchange resin, which is prepared as follows:

[0069] S1: Nitrogen gas is introduced into the reactor. 30g of Lewis acid and 140g of dry-based quaternary ammonium salt ion exchange resin are added to 1200g of toluene, followed by 10g of 4-amino-3-fluorobenzoyl chloride. The mixture is stirred to carry out an acylation reaction at 60℃ for 6 hours. After the reaction is completed, 6g of lithium acrylate and 5g of triethylamine are added. The reaction is carried out at 80℃ for 3 hours. The mixture is then filtered and dried. The Lewis acid can be selected from either aluminum chloride or ferric chloride.

[0070] S2: Transfer the resin to a glass exchange chamber, adding 30% of the resin exchange chamber volume; pass the column through a 5-fold volume of 20% sodium hydroxide solution at a flow rate of 3 BV / h. After column chromatography, vacuum dry to obtain the fluorinated resin.

[0071] The test results of this example are as follows: sodium difluorosulfonamide content 30.12%, free acid (calculated as HCl) 76 ppm, moisture (Kalfisch method) 25 ppm, alkali metal ion content (calculated as K) 1 ppm, chloride ion content 15 ppm, heavy metal ion content (calculated as Fe) 1 ppm, and insoluble matter content 86 ppm.

[0072] Comparative Example 1

[0073] In a 500ml three-necked flask, under nitrogen protection, 200ml of dimethyl carbonate, 58.44g (1mol) of sodium chloride, and 181.14g (1mol) of bis(fluorosulfonyl)imide acid (HFSI) were added dropwise over approximately 2 hours. After the addition, the mixture was kept at the same temperature for 2 hours. Hydrogen chloride gas was released during the reaction; this gas was absorbed using a low-concentration sodium hydroxide solution. After the reaction, while maintaining the same temperature, a vacuum pump was used to slowly evacuate the reaction flask for degassing, which lasted approximately 5 hours. The degassed liquid bis(fluorosulfonyl)imide sodium solution was then deacidified using a deacidifying resin, precisely filtered, and the concentration was adjusted with dimethyl carbonate to obtain a 30% (w / w) liquid bis(fluorosulfonyl)imide sodium solution.

[0074] In the deacidification process, the ion exchange resin used is D751 macroporous chelating styrene-based ion exchange resin.

[0075] The test results of this example are as follows: sodium difluorosulfonamide content 28.75%, free acid (calculated as HCl) 97 ppm, moisture (Kalfisch method) 33 ppm, alkali metal ion content (calculated as K) 2 ppm, chloride ion content 34 ppm, heavy metal ion content (calculated as Fe) 1 ppm, and insoluble matter content 126 ppm.

[0076] Comparative Example 2

[0077] In a 2000ml three-necked flask, under nitrogen protection, 1000ml of methyl ethyl carbonate, 233.76g (4mol) of sodium chloride, and 733.62g (4.05mol) of bis(fluorosulfonyl)imide acid (HFSI) were added dropwise over approximately 2 hours. After the addition, the mixture was kept at the same temperature for 2 hours. Hydrogen chloride gas was released during the reaction; this gas was absorbed using a low-concentration sodium hydroxide solution. After the reaction, while maintaining the same temperature, a vacuum pump was used to slowly evacuate the reaction flask to remove gas, which took approximately 5 hours. The degassed liquid bis(fluorosulfonyl)imide sodium solution was then deacidified using a deacidifying resin, precisely filtered, and the concentration was adjusted with methyl ethyl carbonate to obtain a 30% (w / w) liquid bis(fluorosulfonyl)imide sodium solution.

[0078] In the deacidification process, the ion exchange resin used is D301FC, a macroporous weakly basic anion exchange resin with a polystyrene skeleton.

[0079] The test results of this example are as follows: sodium difluorosulfonamide content 29.09%, free acid (calculated as HCl) 185 ppm, water (Kalfisch method) 29 ppm, alkali metal ion content (calculated as K) 1 ppm, chloride ion content 31 ppm, heavy metal ion content (calculated as Fe) 1 ppm, and insoluble matter content 228 ppm.

[0080] This invention is intended to cover all alternatives, modifications, and equivalents, all of which are included within the scope of the invention as defined in the claims. Those skilled in the art will recognize that many similar or equivalent methods and materials can be used to practice this invention. This invention is by no means limited to the methods and materials described herein. In the event that one or more of the incorporated documents, patents, and similar materials differ from or contradict this application (including, but not limited to, defined terminology, application of terminology, described techniques, etc.), this application shall prevail.

[0081] It should be further recognized that some features of the invention have been described in multiple independent embodiments for clarity, but may also be provided in combination in a particular embodiment; conversely, various features of the invention have been described in a single embodiment for brevity, but may also be provided individually or in any suitable sub-combination.

[0082] Unless otherwise stated, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. All patents and publications related to this invention are incorporated herein by reference in their entirety.

[0083] Unless otherwise stated, the following definitions as used in this invention shall apply. For the purposes of this invention, chemical elements and the periodic table (CAS version) are consistent with the 75th edition of the *Handbook of Chemistry and Physics*, 1994. Their entire contents are incorporated herein by reference.

[0084] The terms “comprising” or “including” are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

Claims

1. A method for preparing a liquid sodium difluorosulfonamide solution, characterized in that, The preparation method includes the following steps: 1) Sodium chloride suspended in a non-aqueous solvent reacts with difluorosulfonylimide acid to obtain a sodium difluorosulfonylimide solution; 2) The above sodium difluorosulfonamide solution is filtered, degassed, concentrated, deacidified by resin, and refined by fine filtration to obtain a high-purity sodium difluorosulfonamide concentrate. In step 2), the resin deacidification process involves passing the aforementioned concentrate through an ion exchange resin to remove acidic impurities of hydrogen chloride. The operating temperature is 20–60°C, and the adsorption time is 8–10 hours. After completion, the insoluble matter is filtered out to obtain sodium difluorosulfonamide concentrate. The ion exchange resin is a fluorinated modified hydroxide-type anion exchange resin, and its preparation method is as follows: S1: By weight, nitrogen gas is introduced into the reactor, and 20-30 parts of Lewis acid and 100-140 parts of dry-based quaternary ammonium salt ion exchange resin are added to 1000-1200 parts of toluene. Then, 5-10 parts of 4-amino-3-fluorobenzoyl chloride are added, and the mixture is stirred to carry out the acylation reaction. The acylation temperature is 30-60℃, and the acylation reaction time is 3-6 hours. After the reaction is completed, 3-6 parts of lithium acrylate and 2-5 parts of triethylamine are added. The reaction is carried out at 70-80℃ for 1-3 hours. The mixture is then filtered and dried. The Lewis acid is selected from either aluminum chloride or ferric chloride. S2: Transfer the resin to a glass exchange chamber and add 15-30% of the volume of the resin exchange chamber. Pass the column through a 3-5 times volume of sodium hydroxide with a mass percentage concentration of 10-20% at a flow rate of 1-3 BV / h. After the column is passed through, vacuum dry to obtain the fluorinated resin.

2. The method for preparing a liquid sodium difluorosulfonylimide solution according to claim 1, characterized in that, The water content of the non-aqueous solvent is less than 15 ppm, and the non-aqueous solvent is at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, dimethylformamide, ethylene glycol dimethyl ether, acetonitrile, and tetrahydrofuran.

3. The method for preparing a liquid sodium difluorosulfonamide solution according to claim 1, characterized in that, The reaction temperature in step 1) is 50–100°C, and the reaction time is 6–12 h.

4. The method for preparing a liquid sodium difluorosulfonamide solution according to claim 1, characterized in that, In step 2), degassing is performed under reduced pressure, with a pressure range of 0.50–10 kPa, a degassing temperature of 20–80 °C, and a degassing time of 4–8 h.

5. The method for preparing a liquid sodium difluorosulfonamide solution according to claim 1, characterized in that, The reactions in steps 1) and 2) are carried out in an inert gas atmosphere, wherein the inert gas is at least one of nitrogen, argon, and helium.

6. The method for preparing a liquid sodium bis(fluorosulfonyl)imide solution according to any one of claims 1 to 5, wherein the prepared sodium bis(fluorosulfonyl)imide concentrate is used in a sodium-ion battery.