Preparation method of sodium bisfluorosulfonimide and product thereof

Abstract

The application provides a preparation method of sodium bisfluorosulfonimide and a product thereof, and belongs to the technical field of sodium ion battery additive preparation. The preparation method of the sodium bisfluorosulfonimide comprises the following steps: 1) in a water-free and oxygen-free environment, organic solvent containing bisfluorosulfonimide is added dropwise into organic solvent containing sodium fluoride to perform reaction, and a mixed solution containing sodium bisfluorosulfonimide is obtained; 2) the mixed solution containing sodium bisfluorosulfonimide is mixed with dichloromethane, and crystallization and filtration are sequentially performed, and the filtrate is a sodium bisfluorosulfonimide crude product; 3) the sodium bisfluorosulfonimide crude product is dissolved by using an organic solvent and then filtered to obtain a filtrate; and 4) the pH of the filtrate is adjusted to 7-8 by using hexamethyldisilazane, and liquid sodium bisfluorosulfonimide is obtained. The sodium bisfluorosulfonimide prepared by the method has high purity, low acid value and low water content.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion battery additive preparation, and particularly relates to a preparation method of sodium bisfluorosulfonylimide and a product obtained by the method. BACKGROUND

[0002] As an important component of sodium ion batteries, the performance of electrolyte sodium salt affects the specific energy, safety performance, cycle performance, rate performance and battery cost of the battery. NaFSI is used as an electrolyte sodium salt for sodium ion batteries, and is stable in film formation, which is attributed to the gradual decomposition of the FSI - anion group, which can form an ultra-thin SEI film rich in inorganic and gradient distribution, such as NaF, NaSON and Na2S, and further reduces the Na + The activation energy for transmission in the SEI film can significantly improve the rate performance of the sodium battery system.

[0003] NaFSI, as a new type of sodium salt additive for sodium ion batteries, is non-toxic, has high chemical stability, is less sensitive to water than NaPF6 (is very sensitive to water and is easy to produce highly corrosive HF, which can damage the SEI film), has a large volume difference between the anion and the cation, has low electrolyte viscosity, has better kinetic performance, has low film formation resistance, is friendly to the rate performance of the battery, has low viscosity, and is particularly low in dependence on the relatively high price of fluorine element, and has low synthesis cost. Therefore, NaFSI is a new type of sodium electrolyte salt with better performance.

[0004] In the prior art, sodium bisfluorosulfonylimide is generally prepared by reacting bisfluorosulfonylimide acid with sodium salt. This reaction does not introduce other cations, but produces acidic by-products, resulting in a high acid value of the product. The solvent evaporation process can cause the color and turbidity to rise, affecting the performance of the battery. In patent CN115818593A, liquid bisfluorosulfonylimide is reacted with sodium fluoride, the generated product is mixed with an organic solvent to obtain a sodium bisfluorosulfonylimide solution, and then the sodium bisfluorosulfonylimide solution is reacted with sodium carbonate to remove the by-product HF mixed in the sodium bisfluorosulfonylimide. However, hydrogen fluoride is more acidic than carbonic acid, and sodium bicarbonate can react with all substances that are more acidic than carbonic acid to generate carbon dioxide. In the patent, sodium carbonate is used to remove acid, which is unstable in a strong acidic solvent environment and can still generate water and carbon dioxide, introducing water and promoting the hydrolysis of the product NaFSI, thereby affecting the performance of the battery. SUMMARY

[0005] The application provides a preparation method of sodium bisfluorosulfonylimide and a product obtained by the method. The sodium bisfluorosulfonylimide prepared by the method has high purity, low acid value and low water content.

[0006] In order to achieve the above object, the present application provides a preparation method of sodium bisfluorosulfonimide, comprising the following steps:

[0007] 1) in anhydrous and anaerobic environment, drop the organic solvent containing bisfluorosulfonimide into the organic solvent containing sodium fluoride to react, to obtain a mixed solution containing sodium bisfluorosulfonimide;

[0008] 2) mix the mixed solution containing sodium bisfluorosulfonimide with dichloromethane, and sequentially perform crystallization and filtration, and the filtrate is a crude product of sodium bisfluorosulfonimide;

[0009] 3) dissolve the crude product of sodium bisfluorosulfonimide with an organic solvent, and then perform filtration to obtain a filtrate;

[0010] 4) adjust the pH of the filtrate to 7-8 with hexamethyldisilazane to obtain liquid sodium bisfluorosulfonimide.

[0011] Preferably, in step 1), the mass ratio of bisfluorosulfonimide to the organic solvent in the organic solvent containing bisfluorosulfonimide is 1:1-3.45, and the mass ratio of sodium fluoride to the organic solvent in the organic solvent containing sodium fluoride is 1:6-20.59.

[0012] Preferably, in step 1), the molar ratio of bisfluorosulfonimide to sodium fluoride is 1:1-1.05.

[0013] Preferably, in step 1), the reaction temperature is 20-35℃, and the reaction time is 1.5-5h.

[0014] Preferably, in step 2), before mixing the mixed solution containing sodium bisfluorosulfonimide with dichloromethane, filtration and rotary evaporation of the filtrate are sequentially performed.

[0015] Preferably, the rotary evaporation temperature is 45-55℃, and the rotary evaporation is stopped when the mass of the initial liquid is reduced to 20%-30%.

[0016] Preferably, in step 1), the organic solvent includes one or more of dimethyl carbonate, diethyl carbonate, vinyl carbonate and propylene carbonate.

[0017] Preferably, in step 3), the organic solvent includes one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, vinyl carbonate and propylene carbonate.

[0018] Preferably, in step 2), the amount of dichloromethane added is 15-25 times the mass of bisfluorosulfonimide.

[0019] Preferably, in step 4), after obtaining liquid sodium bisfluorosulfonimide, rotary evaporation and crystallization are further performed to obtain solid sodium bisfluorosulfonimide.

[0020] The application also provides the sodium bisfluorosulfonimide prepared by the method, wherein the purity of the sodium bisfluorosulfonimide is greater than 99.9%, the acid value is less than or equal to 20 ppm, the moisture content is less than or equal to 20 ppm, the fluoride ion content is less than or equal to 20 ppm, the chloride ion content is less than or equal to 10 ppm, and the sulfate ion content is less than or equal to 10 ppm.

[0021] Compared with the prior art, the application has the advantages and positive effects that:

[0022] The application provides a preparation method of sodium bisfluorosulfonimide. The sodium bisfluorosulfonimide is prepared from bisfluorosulfonimide and sodium fluoride as raw materials, which are dissolved in an organic solvent and reacted in a non-aqueous liquid phase reaction system. The solid-liquid reaction is sufficient, the yield is high, and no by-product water affecting the product properties is generated in the reaction. Dichloromethane, a poor solvent, is used to wash the residual acid on the surface of the crystallized solid and dilute the acidity of the concentrated liquid. A large amount of acid in the organic system is removed in the liquid phase by solid-liquid separation, and then the neutralization agent (hexamethyldisilazane) is used to fine-tune the NaFSI liquid salt to achieve neutrality. The acid value of the liquid salt NaFSI is further reduced, and the residual fluoride and chloride ions are also reduced. The introduction of the neutralization agent will not react with the reaction system to produce other by-products (and a small amount of hexamethyldisilazane will be added to improve the cycle performance of the sodium ion battery), and no water is introduced and generated in the whole process, which will not cause the hydrolysis of the product NaFSI. Therefore, the obtained sodium bisfluorosulfonimide has high purity, and the acid value and moisture content are small. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The chromatogram of the sodium bisfluorosulfonimide before pH adjustment in Example 1;

[0024] Figure 2 The chromatogram of the sodium bisfluorosulfonimide after pH adjustment in Example 1;

[0025] Figure 3 The chromatogram of the sodium bisfluorosulfonimide prepared in Comparative Example 6. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the application will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the application.

[0027] The application provides a preparation method of sodium bisfluorosulfonimide, which comprises the following steps:

[0028] 1) in anhydrous and anaerobic environment, organic solvent containing bisfluorosulfonylimide is added dropwise into organic solvent containing sodium fluoride to react, to obtain mixed solution containing sodium bisfluorosulfonylimide;

[0029] 2) the mixed solution containing sodium bisfluorosulfonylimide is mixed with dichloromethane, and is sequentially subjected to crystallization, filtration, and the filtrate is sodium bisfluorosulfonylimide crude product;

[0030] 3) the sodium bisfluorosulfonylimide crude product is dissolved in organic solvent and filtered, to obtain filtrate;

[0031] 4) the pH of the filtrate is adjusted to 7-8 by using hexamethyldisilazane, to obtain liquid sodium bisfluorosulfonylimide.

[0032] In the present application, in anhydrous and anaerobic environment, organic solvent containing bisfluorosulfonylimide is added dropwise into organic solvent containing sodium fluoride to react, to obtain mixed solution containing sodium bisfluorosulfonylimide. In the present application, both sodium fluoride and organic solvent are preferably subjected to water removal before use. In the present application, sodium fluoride is preferably subjected to water removal by rotary evaporation; and organic solvent is preferably subjected to water removal by molecular sieve. In the present application, the content of chloride in the bisfluorosulfonylimide is preferably <200 ppm, and the content of sulfate is preferably <200 ppm.

[0033] In the present application, the mass ratio of bisfluorosulfonylimide to organic solvent in the organic solvent containing bisfluorosulfonylimide is preferably 1:1-3.45; and the mass ratio of sodium fluoride to organic solvent in the organic solvent containing sodium fluoride is 1:6-20.59. In the prior art, in order to enable the reactants to fully contact each other, to improve the reaction rate, yield and purity, when the reaction is carried out in an organic system, a high amount of organic solvent is generally used to dissolve and dilute the raw materials. However, a high amount of organic solvent leads to high cost. The method provided by the present application can reduce the amount of organic solvent without affecting the quality of the final product, so that the concentration of sodium bisfluorosulfonylimide in the obtained mixed solution containing sodium bisfluorosulfonylimide can reach 30% at most. It can be understood that: if the concentration of the system is too high (the amount of organic solvent is too small), the amount of by-products will increase, which will affect the quality of the final product and even make it impossible to obtain the final product. However, if the amount of organic solvent is too large, the cost will be increased. The amount of organic solvent defined in the present application is the best range considering the cost and product quality. At the same time, the inventors have accidentally found that using methyl ethyl carbonate as the organic solvent cannot obtain the target product, which may be because methyl ethyl carbonate has reacted with the raw materials.

[0034] In the present application, the organic solvent preferably includes one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate and propylene carbonate, and more preferably dimethyl carbonate or diethyl carbonate.

[0035] In the present application, the molar ratio of the bisfluorosulfonylimide to sodium fluoride is preferably 1:1.01-1.05. In the present application, the use amount of bisfluorosulfonylimide and sodium fluoride is limited in the above range, the use amount of sodium fluoride is slightly excessive, which promotes the forward movement of the reaction, makes the bisfluorosulfonylimide react completely as much as possible, improves the reaction conversion rate, reduces the acid value of the system, and is beneficial to the next step of removing acid. However, if the use amount of sodium fluoride is too much, which is higher than the range limited in the present application, not only will cause waste of sodium fluoride, but also will bring certain trouble to the subsequent removal, and affect the purity. It can be understood that: the use amount of bisfluorosulfonylimide and sodium fluoride in the range limited in the present application can achieve the best effect.

[0036] In the present application, the temperature of the reaction is preferably 20-35℃, and the time is preferably 1.5h-5h.

[0037] After obtaining the mixed solution containing sodium bisfluorosulfonylimide, the present application mixes the mixed solution containing sodium bisfluorosulfonylimide with dichloromethane, and then performs crystallization and filtration in sequence, and the filtrate is a crude product of sodium bisfluorosulfonylimide. In the present application, before mixing the mixed solution containing sodium bisfluorosulfonylimide with dichloromethane, filtration and rotary evaporation of the filtrate are also performed in sequence. In the present application, the filtration can remove unreacted sodium fluoride. The rotary evaporation of the filtrate not only can reduce the organic solvent, thereby improving the subsequent reaction process, but also can take away part of hydrogen fluoride in the process of reducing the organic solvent, thereby reducing the acid value. In the present application, the temperature of the rotary evaporation is preferably 45-55℃, and the rotary evaporation is stopped when the mass of the initial liquid is reduced to 20%-30%. In the present application, the introduction of the poor solvent dichloromethane promotes the crystallization of NaFSI crystals in the concentrated solution, which not only removes the residual acid on the surface of the crystals, but also dilutes the acid value in the concentrated solution. Finally, the free acid and part of the free fluorine, chlorine and sulfate ions are taken away in the form of solid-liquid separation in the liquid phase system, thereby reducing the acid value in the solid. In the present application, the use amount of dichloromethane is preferably 15-25 times of the mass of bisfluorosulfonylimide, and more preferably 22 times. If the use amount of dichloromethane is too small, the acid reduction effect is not obvious, and if the use amount of dichloromethane is too much, the cost will be increased, thereby reducing the economic benefit. It can be understood that: the use amount of dichloromethane limited in the present application is the best range considering the acid reduction effect and economic benefit.

[0038] After obtaining the crude product of sodium bisfluorosulfonylimide, the present application dissolves the crude product of sodium bisfluorosulfonylimide with an organic solvent, and then performs filtration to obtain a filtrate. In the present application, the organic solvent preferably includes one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate and propylene carbonate.

[0039] After the filtrate is obtained, the pH of the filtrate is adjusted to 7-8 by using hexamethyldisilazane to obtain liquid sodium bisfluorosulfonylimide. In the present application, since the concentration of HF in the system at this stage is already low, after adjusting the pH, stirring is preferably performed, the reaction time can be prolonged, so that the hexamethyldisilazane is completely reacted with HF, and the acid is removed as completely as possible. In the present application, the pH is adjusted by using hexamethyldisilazane, and hexamethyldisilazane reacts with hydrofluoric acid and hydrogen chloride in the crude liquid sodium bisfluorosulfonylimide to generate corresponding ammonia or ammonium fluoride and trimethylfluorosilane (boiling point 16℃), ammonia or ammonium chloride and trimethylchlorosilane, which are removed in the form of gas or by filtration, thereby reducing the acidity and the concentration of fluoride ions and chloride ions in the liquid salt, so as to obtain a product with low acid value and high purity. The reaction formula is specifically as follows:

[0040] C6H 19 NSi2+HF→NH3↑+(CH3)3SiF↑

[0041] C6H 19 NSi2+HCl→NH3↑+C3H9ClSi

[0042] In the present application, in order to further remove impurities, after adjusting the pH and stirring, filtration is preferably further performed.

[0043] The present application also provides sodium bisfluorosulfonylimide prepared by the method described in any one of the above, the purity of the sodium bisfluorosulfonylimide is greater than 99.9%, the acid value is ≤20ppm, the water content is ≤20ppm, the fluoride ion content is ≤20ppm, the chloride ion content is ≤10ppm, and the sulfate ion content is ≤10ppm. The sodium bisfluorosulfonylimide provided by the present application has high purity, low acid value, and low water content, and is suitable for use in sodium ion batteries additives with high quality requirements. When used as an additive, the sodium bisfluorosulfonylimide is dissolved in an organic solvent and then added, so the method used in the present application directly obtains liquid sodium bisfluorosulfonylimide (i.e., containing part of the organic solvent). If solid sodium bisfluorosulfonylimide is needed, the liquid sodium bisfluorosulfonylimide is subjected to rotary evaporation and crystallization, and the solvent is removed.

[0044] In order to further illustrate the present application, the technical solutions provided by the present application are described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the present application.

[0045] Example 1

[0046] (1) Raw material preparation: Bisfluorosulfonylimide (chloride ion content 185 ppm, sulfate ion content 178 ppm); NaF (water content 20 ppm) dried by rotary evaporation; dimethyl carbonate (water content 14 ppm) dried by molecular sieve

[0047] (2) In the glove box, 29 g of HFSI was added dropwise into a round-bottom flask containing 29 g of DMC solution to obtain an HFSI / DMC solution; 41 g of DMC was added into a polytetrafluoroethylene container, a magnetic stirrer was added, magnetic stirring was started at 600 rpm, 6.8 g of NaF was added, and stirring was performed for 1 h to obtain a NaF / DMC solution;

[0048] (3) The HFSI / DMC solution was transferred into a constant-pressure dropping funnel, and the HFSI / DMC solution was added dropwise into the NaF / DMC solution (the dropwise rate was controlled to be completed in 20 min); reaction was performed at room temperature for 3 h, magnetic stirring was performed during the reaction (at a rate of 600 rpm) to obtain a mixed solution containing sodium bisfluorosulfonylimide;

[0049] (4) The mixed solution containing sodium bisfluorosulfonylimide was subjected to negative pressure suction filtration by using a G5 sand core funnel, and unreacted NaF was filtered out;

[0050] (5) The filtrate was subjected to rotary evaporation, and the temperature was increased to 50°C at a rate of 0.5°C / min from room temperature, and finally constant rotary evaporation was performed at 50°C; the rotary evaporation time was 1 h, and a yellowish thick concentrated solution was obtained in a round-bottom rotary evaporation flask;

[0051] (6) The yellowish concentrated solution in the rotary evaporation flask was washed and crystallized by using 450 g of dichloromethane, and magnetic stirring was performed for 10 h (at a rotation speed of 260 rpm);

[0052] (7) The solution was subjected to negative pressure filtration by using a G5 sand core funnel, and was washed with dichloromethane three times (50 g of dichloromethane was used each time);

[0053] (8) The filter cake was dissolved by using 75 g of dimethyl carbonate, and magnetic stirring was performed for 3 h (at a rotation speed of 500 rpm);

[0054] (9) Filtration was performed by using a G5 sand core funnel, and the filtrate was subjected to chromatographic analysis, as shown in Table 1. Figure 1

[0055] (10) The filtrate obtained in step (9) was adjusted to a pH of 7-8 by using hexamethyldisilazane (the original solution had a pH of 6), and magnetic stirring was performed at 300 rpm for 8 h after the adjustment;

[0056] (11) Filtration was performed by using a G5 sand core funnel, the filtrate was transferred into a polytetrafluoroethylene bottle, and the concentration of the obtained liquid salt NaFSI was calculated to be 30.1%. The filtrate was subjected to chromatographic analysis, as shown in Table 1. The obtained liquid salt NaFSI had a purity of 99.9% and a water content of 0.1%. Figure 2 Figure 1 ​​and 2 It can be seen that the addition of hexamethyldisilazane reduces the content of fluorine, chlorine, sulfate ions in NaFSI and does not produce other by-products.

[0057] Example 2

[0058] (1) Raw material preparation: Bisfluorosulfonylimide (chloride ion content 185 ppm, sulfate ion content 178 ppm); NaF dried by rotary evaporation (water content 20 ppm); dimethyl carbonate after water removal by molecular sieve (water content 14 ppm)

[0059] (2) In the glove box, 29g of HFSI was added dropwise into a round-bottom flask containing 100g of DMC solution to obtain an HFSI / DMC solution; 140g of DMC was added into a polytetrafluoroethylene container, a magnetic stirrer was added, the magnetic stirring was started at 600 rpm, 7.0g of NaF was added, and stirring was performed for 1h to obtain a NaF / DMC solution;

[0060] (3) The HFSI / DMC solution was transferred to a constant-pressure dropping funnel, and the HFSI / DMC solution was added dropwise into the NaF / DMC solution (the drop rate was controlled to be completed in 20min); the reaction was performed at room temperature for 1.5h, and magnetic stirring was performed at a speed of 600 rpm during the reaction to obtain a mixed solution containing sodium bisfluorosulfonylimide;

[0061] (4) The mixed solution containing sodium bisfluorosulfonylimide was subjected to negative pressure suction filtration with a G5 sand core funnel to filter out the unreacted NaF;

[0062] (5) The filtrate was subjected to rotary evaporation, and the temperature was increased from room temperature to 50℃ at a rate of 0.5℃ / min, and finally constant at 50℃, and the rotary evaporation time was 1.5h, and a light yellow thick concentrated solution was obtained in a round-bottom rotary evaporation flask;

[0063] (6) The yellow concentrated solution in the rotary evaporation flask was washed with 650g of dichloromethane to crystallize, and magnetic stirring was performed for 10h (at a speed of 260rpm);

[0064] (7) The solution was subjected to negative pressure filtration with a G5 sand core funnel, and washed with dichloromethane three times, each time 50g;

[0065] (8) The filter cake was dissolved with 71g of dimethyl carbonate, and magnetic stirring was performed for 3h (at a speed of 500rpm);

[0066] (9) Filtration was performed with a G5 sand core funnel, and the filtrate was collected;

[0067] (10) The filtrate obtained in step (9) was adjusted to a pH of 7-8 with hexamethyldisilazane, and magnetic stirring was performed at 300rpm for 6h;

[0068] (11) Filter with G5 sand core funnel, and transfer the filtrate into a polytetrafluoroethylene bottle; calculate the concentration of the obtained liquid salt NaFSI, which is 30.08%.

[0069] Example 3

[0070] The parameters are different, and the organic solvent is diethyl carbonate (DEC).

[0071] (1) Raw material preparation: difluorosulfonyl imide (chloride content 185 ppm, sulfate content 178 ppm); NaF dried by rotary evaporation (water content 20 ppm); diethyl carbonate dried by molecular sieve (water content 15 ppm)

[0072] (2) In the glove box, add 29 g of diethyl carbonate (DEC) solution to a round-bottom flask, and drop 29 g of HFSI to obtain an HFSI / DEC solution; add 41 g of DEC to a polytetrafluoroethylene container, add a magnetic stirrer, start magnetic stirring at 600 rpm, add 6.8 g of NaF, and stir for 1 h to obtain a NaF / DEC solution;

[0073] (3) Transfer the HFSI / DEC solution to a constant-pressure dropping funnel, and drop the HFSI / DEC solution into the NaF / DEC solution (control the dropping speed to complete in 20 min); react at room temperature for 5 h, and perform magnetic stirring (speed 600 rpm) during the reaction process to obtain a mixed solution containing sodium difluorosulfonyl imide;

[0074] (4) Use a G5 sand core funnel to perform negative pressure suction filtration on the mixed solution containing sodium difluorosulfonyl imide, and filter out the unreacted NaF;

[0075] (5) Perform rotary evaporation on the filtrate, and heat from room temperature to 55°C at a rate of 0.5°C / min, finally constant at 55°C, rotary evaporation time 55 min, and obtain a yellow concentrated liquid in a round-bottom rotary evaporation flask;

[0076] (6) Wash the yellow concentrated liquid in the rotary evaporation flask with 450 g of dichloromethane to crystallize, and perform magnetic stirring for 10 h (speed 260 rpm);

[0077] (7) Perform negative pressure filtration on the solution with a G5 sand core funnel, and wash with dichloromethane three times, each time 50 g;

[0078] (8) Dissolve the filter cake with 71 g of dimethyl carbonate, and perform magnetic stirring for 3 h (speed 500 rpm);

[0079] (9) Filter with a G5 sand core funnel, and collect the filtrate;

[0080] (10) The filtrate obtained in step (9) was adjusted to pH 7-8 with hexamethyldisilazane, and was stirred at 300 rpm for 8 h after adjustment;

[0081] (11) Filtration was performed using a G5 sand core funnel, and the filtrate had a pH of 6-7; the filtrate was transferred to a polytetrafluoroethylene bottle; and the concentration of the obtained liquid salt NaFSI was calculated to be 29.95%.

[0082] Example 4

[0083] The parameters were different, and the organic solvent was a mixture of dimethyl carbonate (DMC) and diethyl carbonate (DEC) mixed in a mass ratio of 1:1.

[0084] (1) Raw material preparation: bisfluorosulfonylimide (chloride content 185 ppm, sulfate content 178 ppm); NaF dried by rotary evaporation (water content 20 ppm); dimethyl carbonate (water content 14 ppm) after molecular sieve dehydration; diethyl carbonate (water content 15 ppm);

[0085] (2) In the glove box, 29 g of HFSI was added dropwise to a round-bottom flask containing 29 g of dimethyl carbonate / diethyl carbonate (DMC / DEC) solution to obtain an HFSI / (DMC / DEC) solution; 41 g of (DMC / DEC) was added to a polytetrafluoroethylene container, a magnetic stirrer was added, magnetic stirring was started at 600 rpm, 6.8 g of NaF was added, and stirring was performed for 1 h to obtain a NaF / (DMC / DEC) solution;

[0086] (3) The HFSI / (DMC / DEC) solution was transferred to a constant-pressure dropping funnel, and the HFSI / (DMC / DEC) solution was added dropwise to the NaF / (DMC / DEC) solution (the dropwise rate was controlled to be completed in 20 min); the reaction was performed at room temperature for 3 h, and magnetic stirring was performed at a rate of 600 rpm during the reaction to obtain a mixed solution containing sodium bisfluorosulfonylimide;

[0087] (4) The mixed solution containing sodium bisfluorosulfonylimide was subjected to negative pressure suction filtration using a G5 sand core funnel, and unreacted NaF was filtered out;

[0088] (5) The filtrate was subjected to rotary evaporation, and was heated from room temperature to 45°C at a rate of 0.5°C / min, and finally constant at 45°C, and the rotary evaporation time was 1 h, and a yellow thick concentrated liquid was obtained in a round-bottom rotary evaporation flask;

[0089] (6) The yellow concentrated liquid in the rotary evaporation flask was washed with 450 g of dichloromethane to crystallize, and was stirred magnetically for 10 h (at a speed of 260 rpm);

[0090] (7) The solution was subjected to negative pressure filtration using a G5 sand core funnel, and was washed with dichloromethane three times, 50 g each time;

[0091] (8) Dissolve the filter cake with 71 g of dimethyl carbonate and magnetically stir for 3 h (500 rpm);

[0092] (9) Filter with a G5 sand core funnel and collect the filtrate;

[0093] (10) Adjust the pH of the filtrate obtained in step (9) to 7-8 with hexamethyldisilazane and magnetically stir at 300 rpm for 8 h after adjustment;

[0094] (11) Filter with a G5 sand core funnel and transfer to a polytetrafluoroethylene bottle; calculate the concentration of the obtained liquid salt NaFSI, which is 29.86%.

[0095] Comparative Example 1

[0096] The difference from Example 1 is only that hexamethyldisilazane is used to adjust the pH.

[0097] (1) Raw material preparation: bisfluorosulfonylimide (chloride ion content 185 ppm, sulfate ion content 178 ppm); NaF dried by rotary evaporation (water content 20 ppm); dimethyl carbonate dried by molecular sieves (water content 14 ppm)

[0098] (2) In the glove box, add 29 g of HFSI to the round-bottom flask containing 29 g of DMC solution to obtain an HFSI / DMC solution; add 41 g of DMC to a polytetrafluoroethylene container, add a magnetic stirrer, start magnetic stirring at 600 rpm, add 6.8 g of NaF, and stir for 1 h to obtain a NaF / DMC solution;

[0099] (3) Transfer the HFSI / DMC solution to a constant-pressure dropping funnel and add the HFSI / DMC solution to the NaF / DMC solution (control the drop rate to complete in 20 min); react at room temperature for 3 h, and magnetically stir (speed 600 rpm) during the reaction to obtain a mixed solution containing sodium bisfluorosulfonylimide;

[0100] (4) Use a G5 sand core funnel to perform negative pressure suction filtration on the mixed solution containing sodium bisfluorosulfonylimide to filter out unreacted NaF;

[0101] (5) Rotary evaporate the filtrate, warm from room temperature to 50°C at a rate of 0.5°C / min, and finally constant at 50°C rotary evaporation, rotary evaporation time 1 h, to obtain a yellowish thick concentrated liquid in a round-bottom rotary evaporation flask;

[0102] (6) Wash the yellow concentrated liquid in the rotary evaporation flask with 450 g of dichloromethane to crystallize, and magnetically stir for 10 h (rotation speed 260 rpm);

[0103] (7) The solution was filtered under negative pressure using a G5 sand core funnel and washed three times with 50 g of dichloromethane each time;

[0104] (8) The filter cake was dissolved with 75 g of dimethyl carbonate and magnetically stirred for 3 h (at a speed of 500 rpm);

[0105] (9) The filtrate was filtered using a G5 sand core funnel;

[0106] (10) The filtrate obtained in step (9) was adjusted to a pH of 7-8 using heptamethyldisilazane, and after adjustment, magnetically stirred at 300 rpm for 8 h;

[0107] (11) The filtrate was filtered using a G5 sand core funnel and transferred to a polytetrafluoroethylene bottle, and the concentration of the obtained liquid salt NaFSI was calculated to be 28.69%.

[0108] Comparative Example 2

[0109] The difference from Example 1 is only that the pH was not adjusted using heptamethyldisilazane, and the specific operation is as follows:

[0110] (1) Raw material preparation: bisfluorosulfonylimide (chloride ion content 185 ppm, sulfate ion content 178 ppm); NaF dried by rotary evaporation (water content 20 ppm); dimethyl carbonate after water removal by molecular sieves (water content 14 ppm)

[0111] (2) In the glove box, 29 g of HFSI was added dropwise into a round-bottom flask containing 29 g of DMC solution to obtain an HFSI / DMC solution; 41 g of DMC was added to a polytetrafluoroethylene container, a magnetic stirrer was added, the magnetic stirring was started at 600 rpm, 6.8 g of NaF was added, and stirring was performed for 1 h to obtain a NaF / DMC solution;

[0112] (3) The HFSI / DMC solution was transferred to a constant pressure dropping funnel, and the HFSI / DMC solution was added dropwise into the NaF / DMC solution (the dropwise speed was controlled to be completed in 20 min); the reaction was performed at room temperature for 3 h, and magnetic stirring was performed during the reaction (at a speed of 600 rpm) to obtain a mixed solution containing sodium bisfluorosulfonylimide;

[0113] (4) The mixed solution containing sodium bisfluorosulfonylimide was filtered under negative pressure using a G5 sand core funnel, and unreacted NaF was filtered out;

[0114] (5) The filtrate was rotary evaporated from room temperature to 50°C at a rate of 0.5°C / min, and finally constant at 50°C rotary evaporation, the rotary evaporation time was 1 h, and a light yellow viscous concentrated liquid was obtained in a round-bottom rotary evaporation flask;

[0115] (6) The yellow concentrated solution in the rotary evaporation flask was washed with 450 g of dichloromethane to crystallize, and was magnetically stirred for 10 h (rotation speed 260 rpm);

[0116] (7) The solution was filtered under negative pressure using a G5 sand core funnel, and was washed with dichloromethane three times, each time 50 g;

[0117] (8) The filter cake was dissolved with 75 g of dimethyl carbonate, and was magnetically stirred for 3 h (rotation speed 500 rpm);

[0118] (9) Filtration was performed using a G5 sand core funnel, and the filtrate was collected;

[0119] (10) The filtrate obtained in step (9) was filtered using a G5 sand core funnel, and the filtrate was transferred to a polytetrafluoroethylene bottle; the concentration of the obtained liquid salt NaFSI was calculated to be 25.03%.

[0120] Comparative Example 3

[0121] The difference from Example 1 is only that the poor solvent in step (6) is different, and dichloroethane is used for crystallization.

[0122] (1) Raw material preparation: bisfluorosulfonylimide (chloride ion content 185 ppm, sulfate ion content 178 ppm); NaF dried by rotary evaporation (water content 20 ppm); dimethyl carbonate after water removal by molecular sieves (water content 14 ppm)

[0123] (2) In the glove box, 29 g of HFSI was added dropwise into a round-bottom flask containing 29 g of DMC solution to obtain an HFSI / DMC solution; 41 g of DMC was added into a polytetrafluoroethylene container, a magnetic stirrer was started at 600 rpm, 6.8 g of NaF was added, and stirring was performed for 1 h to obtain a NaF / DMC solution;

[0124] (3) The HFSI / DMC solution was transferred to a constant pressure dropping funnel, and the HFSI / DMC solution was added dropwise into the NaF / DMC solution (the dropwise speed was controlled to be completed in 20 min); reaction was performed at room temperature for 3 h, and magnetic stirring was performed during the reaction (speed 600 rpm) to obtain a mixed solution containing sodium bisfluorosulfonylimide;

[0125] (4) The mixed solution containing sodium bisfluorosulfonylimide was filtered under negative pressure using a G5 sand core funnel, and unreacted NaF was filtered out;

[0126] (5) The filtrate was rotary evaporated, and was heated from room temperature to 50°C at a rate of 0.5°C / min, and finally constant at 50°C, and the rotary evaporation time was 1 h, and a yellowish viscous concentrated solution was obtained in a round-bottom rotary evaporation flask;

[0127] (6) The yellow concentrated solution in the rotary evaporation flask was washed with 450 g of dichloroethane to crystallize, and was magnetically stirred for 10 h (rotation speed 260 rpm);

[0128] (7) The solution was filtered under negative pressure using a G5 sand core funnel, and was washed with 50 g of dichloroethane three times;

[0129] (8) The filter cake was dissolved with 75 g of dimethyl carbonate, and was magnetically stirred for 3 h (rotation speed 500 rpm);

[0130] (9) Filtration was performed using a G5 sand core funnel, and the filtrate was collected;

[0131] (10) The filtrate obtained in step (9) was adjusted to a pH of 7-8 using hexamethyldisilazane, and was magnetically stirred at 300 rpm for 8 h after adjustment;

[0132] (11) Filtration was performed using a G5 sand core funnel, and the obtained liquid salt NaFSI was transferred to a polytetrafluoroethylene bottle, and the concentration was calculated to be 27.86%.

[0133] Comparative Example 4

[0134] The difference from Example 1 is only that in step (2), the amount of NaF is different, specifically:

[0135] 29 g of HFSI was added dropwise to a round-bottom flask containing 29 g of DMC solution to obtain an HFSI / DMC solution; 41 g of DMC was added to a polytetrafluoroethylene container, a magnetic stirrer was added, magnetic stirring was started at 600 rpm, 5 g of NaF was added, and stirring was performed for 1 h to obtain a NaF / DMC solution; the remaining operation processes were the same to obtain sodium bisfluorosulfonylimide, and finally the liquid salt NaFSI was obtained to calculate the concentration, which was 22.05%.

[0136] Comparative Example 5

[0137] The difference from Example 1 is only that in step (2), the amount of NaF is different, specifically:

[0138] 29 g of HFSI was added dropwise to a round-bottom flask containing 29 g of DMC solution to obtain an HFSI / DMC solution; 41 g of DMC was added to a polytetrafluoroethylene container, a magnetic stirrer was added, magnetic stirring was started at 600 rpm, 5 g of NaF was added, and stirring was performed for 1 h to obtain a NaF / DMC solution; the remaining operation processes were the same to obtain sodium bisfluorosulfonylimide, and finally the liquid salt NaFSI was obtained to calculate the concentration, which was 22.05%.

[0139] Comparative Example 6

[0140] (1) Raw material preparation: bisfluorosulfonylimide (chloride content 185 ppm, sulfate content 178 ppm); NaF (water content 20 ppm) dried by rotary evaporation; dimethyl carbonate (water content 14 ppm) dried by molecular sieve

[0141] (2) In the glove box, 29 g of HFSI was added dropwise into a round-bottom flask containing 29 g of DMC solution to obtain an HFSI / DMC solution; 41 g of DMC was added into a polytetrafluoroethylene container, a magnetic stirrer was added, magnetic stirring was started at 600 rpm, 6.8 g of NaF was added, and stirring was performed for 1 h to obtain a NaF / DMC solution;

[0142] (3) The HFSI / DMC solution was transferred into a constant-pressure dropping funnel, and the HFSI / DMC solution was added dropwise into the NaF / DMC solution (the drop rate was controlled to be completed in 20 min); the reaction was performed at room temperature for 3 h, and magnetic stirring was performed during the reaction (at a rate of 600 rpm) to obtain a mixed solution containing sodium bisfluorosulfonylimide;

[0143] (4) Sodium carbonate was added to the sodium bisfluorosulfonylimide solution obtained in step (3) to perform a reaction, the mass ratio of the sodium bisfluorosulfonylimide solution to the sodium carbonate was 100:5, the reaction temperature was -5°C, and the reaction time was 8 h; after the reaction was completed, the product was filtered to remove sodium bicarbonate to obtain liquid salt sodium bisfluorosulfonylimide. The concentration of the obtained liquid salt NaFSI was calculated to be 20.32%. The liquid salt sodium bisfluorosulfonylimide was subjected to chromatographic analysis, and the results are shown in Table 1. Figure 3 Figure 3 It can be seen that peaks appear at multiple positions in the liquid salt sodium bisfluorosulfonylimide, indicating that the product has many impurities.

[0144] Performance test

[0145] The NaFSI prepared in Examples 1-4 and Comparative Examples 1-6 was detected, and the specific results are shown in Table 1.

[0146] Table 1

[0147]

[0148] The above only describes the preferred embodiments of the present application, and it should be noted that those of ordinary skill in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the protection scope of the present application.​

Claims

1. A method for producing sodium bisfluorosulfonimide, characterized by, The method comprises the following steps: 1) in anhydrous and anaerobic environment, organic solvent containing difluorosulfurylimine is added dropwise into organic solvent containing sodium fluoride to react, obtaining mixed solution containing sodium difluorosulfurylimine; 2) the mixed solution containing sodium difluorosulfurylimine is mixed with dichloromethane, and crystallization, filtration are carried out in sequence, and the filtrate is sodium difluorosulfurylimine crude product; 3) the sodium difluorosulfurylimine crude product is dissolved by using organic solvent, and then filtered, obtaining filtrate; 4) the pH of the filtrate is adjusted to 7-8 by using hexamethyldisilazane, obtaining liquid sodium difluorosulfurylimine; The purity of the sodium difluorosulfurylimine is greater than 99.9%, the acid value is less than or equal to 20 ppm, the moisture content is less than or equal to 20 ppm, the fluoride ion content is less than or equal to 20 ppm, the chloride ion content is less than or equal to 10 ppm, and the sulfate ion content is less than or equal to 10 ppm; The organic solvent in step 1) comprises one or more of dimethyl carbonate, diethyl carbonate, vinyl carbonate and propylene carbonate; After obtaining the liquid sodium difluorosulfurylimine in step 4), rotary evaporation and crystallization are further included to obtain solid sodium difluorosulfurylimine.

2. The production method according to claim 1, characterized by, In step 1), the mass ratio of difluorosulfurylimine to organic solvent in the organic solvent containing difluorosulfurylimine is 1:1-3.45, and the mass ratio of sodium fluoride to organic solvent in the organic solvent containing sodium fluoride is 1:6-20.

59.

3. The preparation method according to claim 1, characterized in that, In step 1), the molar ratio of difluorosulfurylimine to sodium fluoride is 1:1-1.

05.

4. The method of claim 1, wherein, In step 1), the temperature of the reaction is 20-35 DEG C, and the time is 1.5-5 h.

5. The preparation method according to claim 1, characterized in that, In step 2), before the mixed solution containing sodium difluorosulfurylimine is mixed with dichloromethane, filtration and rotary evaporation of the filtrate are further carried out in sequence.

6. The preparation method according to claim 5, characterized in that, The temperature of the rotary evaporation is 45-55 DEG C, and the rotary evaporation is stopped when the mass of the initial liquid is 20%-30%.

7. The preparation method according to claim 1, characterized in that, The organic solvent in step 3) comprises one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, vinyl carbonate and propylene carbonate.

8. The method of claim 1, wherein, In step 2), the addition amount of dichloromethane is 15-25 times of the mass of difluorosulfurylimine.

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