A bifluorosulfimide alkali metal salt, a preparation method and application thereof

Abstract

The application belongs to the technical field of chemical synthesis, discloses a kind of bifsulfurylimide alkali metal salt and its preparation method and application, to solve the technical problem of low purity and high water content of bifsulfurylimide alkali metal salt.The steps are as follows:alkali metal compound is reacted with monohydric hydroxyl-containing phosphate ester in mixed solvent, and phosphonate alkali metal salt is obtained by vacuum distillation, after water removal, the phosphonate alkali metal salt is reacted with bifsulfurylimide acid in organic solvent, and bifsulfurylimide alkali metal salt is precipitated, and bifsulfurylimide alkali metal salt is obtained by suction filtration, washing and drying.The application has mild reaction conditions, simple operation, less pollution, high yield and purity, the synthesized phosphonate alkali metal salt can be dried at high temperature, and water is not generated during the second step reaction, so the prepared bifsulfurylimide lithium and other alkali metal salt have low water content, and are suitable for electrolyte materials in lithium ion battery, sodium ion battery and other new energy devices.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of chemical synthesis, and particularly relates to a bisfluorosulfonylimide alkali metal salt, a preparation method and application thereof. BACKGROUND

[0002] The bisfluorosulfonylimide alkali metal salt is an important fluorine-containing compound. In particular, lithium bisfluorosulfonylimide can be applied to the electrolyte of a lithium ion battery. Compared with the commonly used lithium hexafluorophosphate, the lithium bisfluorosulfonylimide has higher conductivity, thermal stability and safety, and can improve the low-temperature discharge and high-temperature energy storage performance of the lithium battery. Similarly, sodium bisfluorosulfonylimide can be applied to the electrolyte of a sodium ion battery. Therefore, lithium bisfluorosulfonylimide and other bisfluorosulfonylimide alkali metal salts have high application prospects as electrolyte materials.

[0003] The lithium bisfluorosulfonylimide needs to meet strict requirements such as high purity and anhydrousness as a battery electrolyte material. In particular, after water is introduced, it is difficult to completely remove the water by heating, drying and decomposing. There are mainly the following methods for preparing lithium bisfluorosulfonylimide. Chinese patent CN101747242A discloses a preparation method of bis(fluorosulfonyl)imide and (perfluoroalkylsulfonyl fluorosulfonyl)imide alkali metal salt. The method has the following steps: 1) sulfonamide is reacted with thionyl chloride and chlorosulfonic acid to obtain bischlorosulfonylimide; 2) bischlorosulfonylimide is reacted with antimony trifluoride to obtain bisfluorosulfonylimide; 3) bisfluorosulfonylimide is reacted with one of potassium carbonate, rubidium carbonate or cesium carbonate to obtain the corresponding bisfluorosulfonylimide salt; and 4) finally, lithium perchlorate or sodium perchlorate is reacted to obtain lithium bisfluorosulfonylimide or sodium bisfluorosulfonylimide. The method has a long process flow, consumes a large amount of raw materials and solvents, and has many impurities in the product. Chinese patent CN103935970A discloses a preparation method of bisfluorosulfonylimide and alkali metal salt thereof. Hydrogen fluoride is used as a fluorination reagent and reaction solvent to react with bischlorosulfonylimide and alkali metal halide to obtain bisfluorosulfonylimide alkali metal salt. The patent uses hydrogen fluoride for fluorination, and generates hydrogen chloride gas. The reaction of fluoride salt and bisfluorosulfonylimide also generates hydrogen fluoride, which has high requirements for equipment. The reaction with alkali metal halide has low ion exchange degree. Chinese patent CN114180542A discloses a preparation method of lithium bisfluorosulfonylimide salt. Bischlorosulfonylimide is first reacted with hydrogen fluoride to obtain bisfluorosulfonylimide, and then bisfluorosulfonylimide is reacted with lithium carbonate to obtain lithium bisfluorosulfonylimide. The method is essentially an acid-base neutralization reaction, and generates lithium bisfluorosulfonylimide and water. When water exists in the system, it will cause partial hydrolysis of the product, resulting in high water content, high fluoride ion and high sulfate ion in the product. Patent CN110697668A proposes a preparation method of high-purity bisfluorosulfonylimide salt. Bisfluorosulfonylimide is reacted with M + nX n-After the reaction of (n≥2) in a non-aqueous solvent, a high-quality and high-yield bisfluorosulfonylimide salt can be obtained by a post-treatment method. However, when n=1, water or acid dissolved in the reaction system is generated, resulting in a decrease in the purity and yield of the product. Therefore, it is crucial to propose a preparation method of a bisfluorosulfonylimide alkali metal salt with high purity and low water content. SUMMARY

[0004] In order to obtain a battery-grade bisfluorosulfonylimide alkali metal salt, that is, to solve the technical problems of low purity and high water content of the bisfluorosulfonylimide alkali metal salt, the present application proposes a bisfluorosulfonylimide alkali metal salt, a preparation method and application thereof, and achieves the purpose of efficiently preparing high-purity bisfluorosulfonylimide lithium and other bisfluorosulfonylimide alkali metal salts.

[0005] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0006] A preparation method of a bisfluorosulfonylimide alkali metal salt, the steps are as follows:

[0007] (1) reacting an alkali metal compound with a phosphate ester in a mixed solvent, vacuum distillation, and if the phosphate ester is excessive, filtering and drying to obtain an alkali metal phosphate salt; (2) reacting the alkali metal phosphate salt obtained in step (1) with bisfluorosulfonylimide in an organic solvent to generate bisfluorosulfonylimide alkali metal salt, which is precipitated, and then the precipitate is filtered, washed and vacuum dried to obtain the bisfluorosulfonylimide alkali metal salt.

[0008] The chemical formula of the alkali metal compound in step (1) is M + n X n- , wherein M is any one of Li, Na, K, Rb and Cs, X is CO3 or OH, and n is 1 or 2.

[0009] The phosphate ester is one of 2-ethylhexyl phosphate mono-2-ethylhexyl ester (A), di(2-ethylhexyl) phosphate ester (B), dibutyl phosphate (C) and dibenzyl phosphate (D), and the structural formula is as follows:

[0010]

[0011] The mixed solvent in step (1) is water and ethanol mixed at a mass ratio of 1:(0.1-1). When there is no ethanol in the solvent, the system is very viscous and stirring cannot proceed normally. After adding ethanol, a homogeneous reaction is formed and the reaction efficiency is improved. Preferably, water and ethanol are mixed at a mass ratio of 1:(0.1-0.5).

[0012] The mass ratio of the phosphate ester to the mixed solvent is 1:(5-20), and the molar ratio of the phosphate ester to the alkali metal in the alkali metal compound is 1:(0.9-1).

[0013] The temperature of the reaction in step (1) is room temperature (20℃), and the time is 2-8h.

[0014] The reduced pressure distillation in step (1) is carried out at 50-70℃ under a pressure of 20-50mbar, and the process is continued with the supplement of ethanol; water and ethanol form an azeotrope, which is more conducive to the removal of water.

[0015] The phosphate alkali metal salt obtained in step (1) has high stability and can be dried at 60℃ under reduced pressure or dried at 100℃ under normal pressure to remove water.

[0016] The organic solvent in step (2) is a non-polar organic solvent, which is one or more of dichloromethane, trichloromethane, tetrachloromethane, dichloroethane, trichloroethane, tetrachloroethane, dichloropropane, trichloropropane, and tetrachloropropane.

[0017] Preferably, dichloromethane or dichloroethane is selected, and the water content is less than 50ppm, preferably, the water content is less than 20ppm.

[0018] The mass ratio of the phosphate alkali metal salt to the organic solvent is 1:(5-20).

[0019] The molar ratio of the phosphate alkali metal salt to the bisfluorosulfonylimide is (0.95-1):1, and the bisfluorosulfonylimide is slightly excessive, which ensures the complete reaction of the phosphate alkali metal salt, and the excessive bisfluorosulfonylimide is easily removed by washing.

[0020] The temperature of the reaction in step (2) is -10-30℃, and the time is 4-12h.

[0021] The reaction, suction filtration, washing, and drying in step (2) are all protected by nitrogen, and the suction filtration, washing, and vacuum drying are all carried out at room temperature.

[0022] The bisfluorosulfonylimide alkali metal salt is extremely hygroscopic, and is immediately stored in N2 after obtaining the product to avoid hygroscopic decomposition.

[0023] The bisfluorosulfonylimide alkali metal salt prepared by the above preparation method has a structural formula as shown in formula I:

[0024]

[0025] The bisfluorosulfonylimide alkali metal salt is applied in a battery electrolyte.

[0026] The present application has the following beneficial effects:

[0027] (1) The preparation method of the present application has mild reaction conditions, simple operation, does not produce hydrogen fluoride acid, and has no special requirements for equipment. Moreover, the preparation process of the phosphate ester alkali metal salt used in the preparation process is simple and low in cost.

[0028] (2) The preparation method of the present application has high purity and low water content of the prepared bisfluorosulfonylimide metal salt. Although water is involved in the first step, the prepared phosphate ester alkali metal salt is stable, and water can be removed. Water is not introduced in the second step, and water is not generated, which is beneficial to obtain anhydrous product and ensure that the product does not hydrolyze. The method is suitable for the synthesis of bisfluorosulfonylimide alkali metal salt, and bisfluorosulfonylimide lithium and other bisfluorosulfonylimide alkali metal salts with a purity greater than 99% can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0030] Figure 1 ESI-MS spectrum of the product obtained in Example 1 of the present application.

[0031] Figure 2 ESI-MS spectrum of the product obtained in Example 1 of the present application. 19 F-NMR spectrum. DETAILED DESCRIPTION

[0032] The technical solutions of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0033] The purity of the drug used in the embodiments of the present application is higher than 99%, the water content of the organic solvent is less than 20 ppm, and the content of chloride ions in the bisfluorosulfonylimide is less than 20 ppm.

[0034] Example 1

[0035] The preparation method of a bisfluorosulfonylimide alkali metal salt in this embodiment is as follows:

[0036] (1) Weigh 12 g (0.5 mol) of LiOH into a flask, add 1532 g of mixed solvent (m 水 :m 乙醇(0.5 mol) 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester was added dropwise, the reaction was stirred at room temperature for 4 h, distilled at 60 °C under reduced pressure, and water was continuously added with ethanol until a solid powder was obtained. The solid was dried at 100 °C to constant weight, and the dried solid was ground into powder to obtain 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester lithium 150.6 g.

[0037] (2) 89 g (0.285 mol) of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester lithium was weighed into a three-necked flask, 712 g of dichloromethane was added, and the flask was placed in a 0 °C low-temperature reaction instrument. 54.3 g (0.3 mol) of bisfluorosulfonyl imide was added dropwise to the flask with a constant-pressure dropping funnel, and the reaction was carried out under N2atmosphere for 6 h. Filtration gave a solid powder, which was washed with 100 g of dichloromethane for 3-5 times and then filtered to obtain a solid. After the filtration and washing process was repeated three times, the solid was dried at room temperature under vacuum to obtain bisfluorosulfonyl imide lithium product 52.5 g, with a yield of 98.6%.

[0038] The ESI-MS spectrum thereof is shown in Figure 1 , 19 The F-NMR spectrum is shown in Figure 2 . The data are as follows: HRMS (ESI): calcd for N(SO2F)2 - 179.9242, found 179.9232; 19 F NMR (564 MHz, Acetone-d6): 53.13 (s, 1F).

[0039] Example 2

[0040] A method for preparing a bisfluorosulfonyl imide alkali metal salt according to the present embodiment is as follows:

[0041] (1) 20 g (0.5 mol) of NaOH was weighed into a flask, 1289.6 g of a mixed solvent (m 水 : m 乙醇 = 1:0.3) was added, and 161.2 g (0.5 mol) of bis(2-ethylhexyl) phosphate was added dropwise. The reaction was stirred at room temperature for 6 h, distilled at 60 °C under reduced pressure, and water was continuously added with ethanol until a solid was obtained. The solid was dried at 100 °C to constant weight, and the dried solid was ground into powder to obtain sodium bis(2-ethylhexyl) phosphate 168.8 g.

[0042] (2) Weigh 98.2 g (0.285 mol) of sodium bis(2-ethylhexyl) phosphate into a three-necked flask, add 785 g of dichloromethane, and place it in a 5°C low-temperature reactor. Add 54.3 g (0.3 mol) of bisfluorosulfonimide drop by drop into the flask using a constant-pressure dropping funnel, and react for 8 h under N2 atmosphere. Filter to obtain a solid, wash it with 100 g of dichloromethane, and then filter to obtain a solid powder. Wash the solid powder with dichloromethane for three times, and then dry the obtained solid powder at room temperature under vacuum to obtain 56.4 g of sodium bisfluorosulfonimide product, with a yield of 97.4%.

[0043] Example 3

[0044] The preparation method of the alkali metal salt of bisfluorosulfonimide in this example is as follows:

[0045] (1) Weigh 25.2 g (0.45 mol) of KOH into a flask, add 2178 g of mixed solvent (m water:m ethanol = 1:0.5), and add 105.1 g (0.5 mol) of dibutyl phosphate drop by drop. Stir at room temperature for 8 h, distill under reduced pressure at 60°C, continuously add ethanol to remove water, and finally obtain a mixture of oil and solid. Filter, and dry the solid at 100°C to constant weight. Grind the dried solid into powder to obtain 106.1 g of potassium dibutyl phosphate.

[0046] (2) Weigh 59.9 g (0.285 mol) of potassium dibutyl phosphate into a three-necked flask, add 561.6 g of dichloromethane, and place it in a 10°C low-temperature reactor. Add 54.3 g (0.3 mol) of bisfluorosulfonimide drop by drop into the flask using a constant-pressure dropping funnel, and react for 4 h under N2 atmosphere. Filter to obtain a solid powder, wash it with 100 g of dichloromethane, and then filter to obtain a solid. Wash the solid with dichloromethane for three times, and then dry the obtained solid at room temperature under vacuum to obtain 61.4 g of potassium bisfluorosulfonimide product, with a yield of 98.3%.

[0047] Example 4

[0048] The preparation method of the alkali metal salt of bisfluorosulfonimide in this example is as follows:

[0049] (1) Weigh 81.5 g (0.25 mol) of Cs2CO3 into a flask, add 1391 g of mixed solvent (m water:m ethanol = 1:0.5), and add 139.1 g (0.5 mol) of dibenzyl phosphate drop by drop. Stir at room temperature for 6 h, distill under reduced pressure at 60°C, continuously add ethanol to remove water, and finally obtain a solid. Dry the solid at 100°C to constant weight. Grind the dried solid into powder to obtain 202.2 g of cesium dibenzyl phosphate.

[0050] (2) Weigh 123 g (0.3 mol) of cesium dibenzyl phosphate into a three-necked flask, add 561.6 g of dichloromethane, and place in a 20 °C water bath. Add 54.3 g (0.3 mol) of bisfluorosulfonimide dropwise into the flask using a constant pressure dropping funnel, and react for 4 h under N2 atmosphere. Filter to obtain a solid, wash with 100 g of dichloromethane, and filter to obtain a solid. Repeat the filtering and washing process three times, and vacuum dry the obtained solid at room temperature to obtain 92.6 g of bisfluorosulfonimide cesium product, with a yield of 98.7%.

[0051] Example 5

[0052] The preparation method of the bisfluorosulfonimide alkali metal salt in this example is as follows:

[0053] (1) Weigh 18.5 g (0.25 mol) of Li2CO3 into a flask, add 1532 g of a mixed solvent (m water:m ethanol = 1:0.2), and add 153.2 g (0.5 mol) of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester dropwise. Stir at room temperature for 4 h, distill at 60 °C under reduced pressure, continuously add ethanol to remove water until a solid is obtained, and dry the solid at 100 °C until the weight is constant. Grind the dried solid into powder to obtain 152.5 g of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester lithium.

[0054] (2) Weigh 89 g (0.285 mol) of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester lithium into a three-necked flask, add 712 g of dichloroethane, and place in a 0 °C low-temperature reactor. Add 54.3 g (0.3 mol) of bisfluorosulfonimide dropwise into the flask using a constant pressure dropping funnel, and react for 6 h under N2 atmosphere. Filter to obtain a solid, wash with 100 g of dichloroethane, and filter to obtain a solid. Repeat the filtering and washing process three times, and vacuum dry the obtained solid at room temperature to obtain 52.8 g of bisfluorosulfonimide lithium product, with a yield of 99%.

[0055] Example 6

[0056] The preparation method of the bisfluorosulfonimide alkali metal salt in this example is as follows:

[0057] (1) Weigh 12 g (0.5 mol) of LiOH into a flask, add 766 g of a mixed solvent (m 水 :m 乙醇 = 1:0.1), and add 153.2 g (0.5 mol) of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester dropwise. Stir at room temperature for 2 h, distill at 50 °C under reduced pressure, continuously add ethanol to remove water until a solid powder is obtained, and dry the solid at 100 °C until the weight is constant. Grind the dried solid into powder to obtain 150.4 g of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester lithium.

[0058] (2) Weigh 89 g (0.285 mol) of 2-ethylhexyl phosphinic acid mono-2-ethylhexyl lithium into a three-necked flask, add 445 g of dichloromethane, place it in a -10°C low-temperature reaction instrument, and add 54.3 g (0.3 mol) of bisfluorosulfonyl imide drop by drop into the flask using a constant-pressure dropping funnel. React for 12 h under N2 atmosphere, filter to obtain solid powder, and then filter to obtain solid after washing with 100 g of dichloromethane for 3-5 times. Repeat the filtering and washing process for three times, and then vacuum dry the solid at room temperature to obtain 51.4 g of bisfluorosulfonyl imide lithium product with a yield of 96.5%.

[0059] Example 7

[0060] The preparation method of a bisfluorosulfonyl imide alkali metal salt in this example is as follows:

[0061] (1) Weigh 12 g (0.5 mol) of LiOH into a flask, add 3064 g of mixed solvent (m 水 :m 乙醇 = 1:0.5), and add 153.2 g (0.5 mol) of 2-ethylhexyl phosphinic acid mono-2-ethylhexyl ester drop by drop. Stir and react at room temperature for 4 h, distill at 70°C under reduced pressure, and continuously add ethanol to remove water until solid powder is obtained. Dry the solid at 100°C to constant weight, grind the dried solid into powder, and obtain 152.1 g of 2-ethylhexyl phosphinic acid mono-2-ethylhexyl lithium.

[0062] (2) Weigh 89 g (0.285 mol) of 2-ethylhexyl phosphinic acid mono-2-ethylhexyl lithium into a three-necked flask, add 890 g of dichloromethane, place it in a 30°C water bath, and add 54.3 g (0.3 mol) of bisfluorosulfonyl imide drop by drop into the flask using a constant-pressure dropping funnel. React for 4 h under N2 atmosphere, filter to obtain solid powder, and then filter to obtain solid after washing with 100 g of dichloromethane for 3-5 times. Repeat the filtering and washing process for three times, and then vacuum dry the solid at room temperature to obtain 50.4 g of bisfluorosulfonyl imide lithium product with a yield of 94.6%.

[0063] Test Example

[0064] The products prepared in Examples 1-5 are tested for relevant indicators according to the industry standard YS / T 1302-2019. The purity is calculated by the difference method, that is, 100% minus the impurity content. The moisture content is tested by Karl Fischer moisture meter, the impurity anion content is tested by ion chromatography, the metal cation content is tested by ICP-OES, the free acid content is tested by NaOH titration method, and the insoluble content is tested by gravimetric method. When testing bisfluorosulfonyl imide sodium and bisfluorosulfonyl imide potassium according to the standard, Na + and K +The content of the bismethylene sulfoneimide alkali metal salt was determined, and the test results are shown in Table 1.

[0065] Table 1 Test results

[0066]

[0067]

[0068] As shown in Table 1, the purity of the bismethylene sulfoneimide alkali metal salt prepared by Examples 1-5 is all higher than 99.9%, and each index reaches the industry standard of battery electrolyte.

[0069] The above description is merely preferred embodiments of the present application, but not to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A process for the preparation of a bisfluorosulfonimide alkali metal salt, characterized in that, The steps are as follows: (1) Dissolve the alkali metal compound in the mixed solvent, and add the monohydroxyl-containing phosphate ester under stirring. After the reaction is completed, the phosphate ester alkali metal salt is obtained by removing the solvent and drying; The mixed solvent is prepared by mixing water and ethanol in a mass ratio of 1: (0.1-1); the monohydroxyl-containing phosphate ester is any one of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, di(2-ethylhexyl)phosphonate, dibutyl phosphate, and dibenzyl phosphate; the mass ratio of the phosphate ester to the mixed solvent is 1: (5-20); the molar ratio of the phosphate ester to the alkali metal in the alkali metal compound is 1: (0.9-1); the reaction temperature is room temperature, and the reaction time is 2-8 h; (2) The phosphate ester alkali metal salt obtained in step (1) is added to an organic solvent, and difluorosulfurylimide acid is added. After the reaction and post-treatment, the difluorosulfurylimide alkali metal salt is obtained; the molar ratio of the phosphate ester alkali metal salt to difluorosulfurylimide is (0.95-1):

1.

2. The method for producing a bifluorosulfonimide alkali metal salt according to claim 1, characterized by, The chemical formula of the alkali metal compound in step (1) is M + n X n- n is 1 or 2.

3. The method for producing a bifluorosulfimide alkali metal salt according to claim 2, characterized by, The M + n X n- M is any one of Li, Na, K, Rb and Cs, and X is CO3 or OH.

4. The process for the preparation of a bifluorosulfimide alkali metal salt according to claim 3, characterized in that, The organic solvent in step (2) is one or more of dichloromethane, trichloromethane, tetrachloromethane, dichloroethane, trichloroethane, tetrachloroethane, dichloropropane, trichloropropane, and tetrachloropropane.

5. The process for the preparation of a bifluorosulfimine alkali metal salt according to claim 4, characterized in that, The mass ratio of the phosphate ester alkali metal salt to the organic solvent in step (2) is 1: (5-20).

6. The process for the preparation of a bifluorosulfone imide alkali metal salt according to claim 5, characterized in that, The reaction temperature in step (2) is -10-30℃, and the reaction time is 4-12 h. The post-treatment process includes: suction filtration, washing, and vacuum drying.

7. The difluorosulfurylimide alkali metal salt prepared by the preparation method of claim 6.

8. The application of the difluorosulfurylimide alkali metal salt of claim 7 in battery electrolyte materials.

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