Preparation method of sodium bis (fluorosulfonyl) imide

Abstract

The invention relates to a preparation method of bis (fluorosulfonyl) imide sodium, which comprises the following steps: in a weak polar solvent, bis (chlorosulfonyl) imide acid and sodium hydrogenfluoride are subjected to a fluorination reaction under microwave-induced catalysis to generate bis (fluorosulfonyl) imide sodium, and the weak polar solvent is an ester solvent. According to the invention, sodium hydrogen fluoride is used as a fluorination reagent and a sodium modification reagent, bis (chlorosulfonyl) imidic acid can be directly converted into bis (chlorosulfonyl) imidic acid sodium, synthesis steps and emission of three wastes are reduced, the production efficiency is improved, and the production cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of sodium ion batteries, and in particular to a method for preparing sodium bis(fluorosulfonyl)imide. Background Art

[0002] Sodium bis(fluorosulfonyl)imide (NaFSI for short) is a sodium salt electrolyte with moderate conductivity. Compared with sodium hexafluorophosphate (NaPF6), it has higher hydrolysis stability, thermal stability and electrochemical stability, which is beneficial to improving battery cycle performance and high and low temperature performance. These advantages make NaFSI the most promising sodium salt electrolyte / additive in energy storage batteries.

[0003] The preparation methods of NaFSI mainly include chlorosulfonic acid method, ionic liquid method and cation exchange method. Among them, the chlorosulfonic acid method is the mainstream preparation process of NaFSI, which uses chlorosulfonic acid as raw material.

[0004] Patent CN103935970A discloses a method for preparing a bisfluorosulfonyl imide salt, firstly, chlorosulfonic acid reacts with aminosulfonic acid and dichlorothionyl to prepare bischlorosulfonyl imide acid (HCSI); then fluorination is performed to prepare bisfluorosulfonyl imide acid (HFSI); finally, NaFSI is prepared by reacting with a sodium reagent. Patent CN104671224A discloses a method for preparing NaFSI by fluorinating sodium bischlorosulfonyl imide (NaCSI) using a fluorination reagent, wherein NaCSI needs to be prepared from chlorosulfonic acid as a raw material to prepare HCSI, and then obtained by sodiumization. The preparation of NaFSI from NaCSI involves fluorine-chlorine exchange, and the product may have a problem of excessive chloride ion content. The above chlorosulfonic acid methods all have problems such as many reaction steps, long time consumption, high cost and low product quality.

[0005] The ionic liquid method has many side reactions and poor reproducibility, and the reaction involving ammonia is highly exothermic, causing the pressure in the reactor to increase rapidly and posing the risk of explosion. The cation exchange method has problems such as expensive raw materials and high levels of impurities such as other cations in the product. Summary of the invention

[0006] In order to solve the above technical problems, the present invention proposes a method for preparing sodium bis(fluorosulfonyl)imide which has high production efficiency, less three wastes, low energy consumption, high yield and is suitable for industrial production.

[0007] The objective of the present invention is achieved through the following technical solutions:

[0008] A method for preparing sodium bis(fluorosulfonyl)imide, the method comprising: in a weak polar solvent, bis(chlorosulfonyl)imide acid and sodium bifluoride (NaHF2) are subjected to a fluorination reaction under microwave-induced catalysis to generate sodium bis(fluorosulfonyl)imide, wherein the weak polar solvent is an ester solvent. The present invention adopts NaHF2 as a fluorination agent and a sodiumation agent, and can directly convert HCSI into NaFSI, thereby reducing the synthesis steps. NaHF2 reacts with HCSI under conventional heating conditions. Although the sodiumation reaction is relatively easy, the time required for the fluorination reaction is relatively long, and there are many fluorination side reactions, and the by-products include sodium fluorosulfonate, sodium aminosulfonate and other unknown impurities. The present invention utilizes microwave-induced catalytic fluorination reaction, which can greatly shorten the reaction time, improve the selectivity of the fluorination reaction and reduce the occurrence of side reactions, including decomposition caused by HCSI staying in the reaction system for too long, the generation of unknown impurities, etc., and fully improve the yield and quality of the product. In addition, the preparation method of the present invention does not require a phase transfer catalyst, which can further reduce costs and avoid catalyst residues.

[0009] The microwave power of the present invention is 0-800W, and the microwave time is 0.5-12h; preferably, the microwave power is 200-400W, and the microwave time is 1-8h; more preferably, the microwave power is 200-300W, and the microwave time is 1-2h.

[0010] Specifically, the preparation method of the present invention comprises the following steps: first, sodium bifluoride is fully mixed with a weak polar solvent, then bischlorosulfonyl imide acid is added to the reaction system, and a fluorination reaction is carried out under microwave induced catalysis for 1 to 2 hours to obtain a reaction solution containing sodium bisfluorosulfonyl imide; then, the reaction solution is post-treated to obtain a high-purity sodium bisfluorosulfonyl imide product. Furthermore, the post-treatment step specifically comprises filtering the reaction solution to obtain a clarified solution, adding a poor solvent after concentration to stir and crystallize, filtering and drying to obtain a high-purity sodium bisfluorosulfonyl imide product.

[0011] Due to the strong polar solvents such as DMF, DMSO and other commonly used solvents for fluorination reactions, the microwave-induced catalysis will be affected in the reaction process of the present invention, so that the reaction rate of the reaction of the present invention is no different from that of conventional heating at the same reaction temperature. Non-polar solvents such as n-hexane are poor solvents and are not suitable as reaction solvents in this reaction system. Therefore, the present invention chooses to replace the commonly used strong polar solvents with weak polar solvents to further effectively promote the increase in reaction rate. Specifically, the weak polar solvent is an ester solvent; preferably, the weak polar solvent is a carbonate solvent; more preferably, the weak polar solvent is selected from at least one of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

[0012] The microwave-induced catalytic reaction of the present invention can be carried out at room temperature without heating.

[0013] The equivalent ratio of NaHF2 to HCSI is 4:1 to 1:1, preferably 3:1 to 1.5:1, and more preferably 2:1 to 1.5:1.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. The present invention adopts NaHF2 as a fluorination agent and a sodiumation agent, which can directly convert HCSI into NaFSI, reduce the synthesis steps and the discharge of three wastes, improve production efficiency, and reduce production costs;

[0016] 2. The present invention utilizes microwave to induce catalytic fluorination reaction, which can greatly shorten the reaction time, improve the selectivity of the reaction and reduce the occurrence of side reactions, thereby fully improving the yield and quality of the product; and the method of the present invention does not require a phase transfer catalyst, which can further reduce costs and avoid catalyst residues;

[0017] 3. In the present invention, a weak polar solvent is used to replace the strong polar solvent commonly used in the fluorination reaction, which effectively promotes the improvement of the reaction rate. DETAILED DESCRIPTION

[0018] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements and equivalents within the scope of the claims.

[0019] Example 1

[0020] 9.3g sodium bifluoride (0.15mol) and 50g dimethyl carbonate were mixed in a reaction vessel, and 21.4g bis(chlorosulfonyl)imide acid (0.1mol) was slowly added dropwise under stirring. After the addition was complete, a microwave reactor (250W) was turned on and the reaction was refluxed for 2h. After the reaction was completed, the reaction solution was filtered to remove NaHF2 to obtain a clear solution. After the solution was concentrated, 30g dichloromethane was added to stir and crystallize, filtered and dried to obtain 19.4g of high-purity sodium bis(fluorosulfonyl)imide.

[0021] After testing and calculation, the yield of the NaFSI product is 95.6% and the purity is 99.96%.

[0022] Example 2

[0023] The operation of Example 2 is the same as that of Example 1, except that the dimethyl carbonate is replaced by ethyl methyl carbonate, and other operations remain unchanged to obtain 19.3 g of high-purity NaFSI product.

[0024] After testing and calculation, the yield of the NaFSI product is 95.1% and the purity is 99.94%.

[0025] Example 3

[0026] The operation of Example 3 is the same as that of Example 1, except that dimethyl carbonate is replaced by ethyl acetate, and other operations remain unchanged to obtain 18.3 g of high-purity NaFSI product.

[0027] After testing and calculation, the yield of the NaFSI product is 90.1% and the purity is 99.95%.

[0028] Example 4

[0029] The operation of Example 5 is the same as that of Example 1, except that the microwave power is 200 W, and other operations remain unchanged, to obtain 18.9 g of high-purity NaFSI product.

[0030] After testing and calculation, the yield of the NaFSI product is 93.1% and the purity is 99.97%.

[0031] Example 5

[0032] The operation of Example 6 is the same as that of Example 1, except that the microwave power is 300 W, and other operations remain unchanged, to obtain 19.2 g of high-purity NaFSI product.

[0033] After testing and calculation, the yield of the NaFSI product is 94.6% and the purity is 99.95%.

[0034] Example 6

[0035] The operation of Example 7 is the same as that of Example 1, except that the amount of sodium bifluoride used is 18.6 g (0.3 mol), and other operations remain unchanged, to obtain 19.5 g of high-purity NaFSI product.

[0036] After testing and calculation, the yield of the NaFSI product is 96.1% and the purity is 99.91%.

[0037] Example 7

[0038] The operation of Example 8 is the same as that of Example 1, except that the reaction time is 1 h, and other operations remain unchanged, to obtain 18.6 g of high-purity NaFSI product.

[0039] After testing and calculation, the yield of the NaFSI product is 91.6% and the purity is 99.90%.

[0040] Comparative Example 1

[0041] 9.3g sodium bifluoride (0.15mol) and 50g dimethyl carbonate were mixed in a reaction container, and 21.4g bis(chlorosulfonyl)imide acid HCSI (0.1mol) was slowly added dropwise under stirring. After the addition was completed, the oil bath was turned on for heating and the reaction was refluxed for 2h. After the reaction was completed, the reaction solution was filtered to remove NaHF2 to obtain a clear solution. After the solution was concentrated, 30g dichloromethane was added to stir and crystallize, and the solution was filtered and dried to obtain 10.8g of high-purity sodium bis(fluorosulfonyl)imide.

[0042] After testing and calculation, the yield of the NaFSI product is 53.2% and the purity is 99.30%.

[0043] Comparative Example 2

[0044] The operation of Comparative Example 2 is the same as that of Comparative Example 1, except that the reaction solvent is DMF, and other operations remain unchanged to obtain 10.1 g of high-purity NaFSI product.

[0045] After testing and calculation, the yield of the NaFSI product is 49.8% and the purity is 99.23%.

[0046] Comparative Example 3

[0047] The operation of Comparative Example 3 is the same as that of Comparative Example 1, except that the reaction solvent is ethyl acetate, and other operations remain unchanged to obtain 9.8 g of high-purity NaFSI product.

[0048] After testing and calculation, the yield of the NaFSI product is 48.3% and the purity is 99.09%.

[0049] Comparative Example 4

[0050] The operation of Comparative Example 4 is the same as that of Comparative Example 1, except that the reaction time is 24 h, and other operations remain unchanged to obtain 9.8 g of high-purity NaFSI product.

[0051] After testing and calculation, the yield of the NaFSI product is 83.3% and the purity is 95.47%.

[0052] Comparative Example 5

[0053] The operation of Comparative Example 1 is the same as that of Example 1, except that the reaction solvent is DMF, and other operations remain unchanged to obtain 10.7 g of high-purity NaFSI product.

[0054] After testing and calculation, the yield of the NaFSI product is 52.7% and the purity is 99.13%.

[0055] From the data of Examples 1 to 7 and Comparative Examples 1 to 5, it can be seen that compared with conventional heating, the use of microwave-induced catalysis in the present invention can fully improve the yield and quality of the product; and the use of small polar solvents such as esters as reaction solvents has a much higher product yield than large polar solvents such as DMF. Conventional heating to prepare NaFSI products can improve the yield by extending the reaction time, but because the reactants and products stay in the reaction system for too long, they are prone to decomposition or generate other unknown impurities, which greatly reduces the quality of the product. The purity of the electrolyte usually needs to be at least 99.9%, which cannot meet the quality requirements of sodium salt electrolyte products.

Claims

1. A method for preparing sodium bis(fluorosulfonyl)imide, characterized in that: In a weak polar solvent, bischlorosulfonyl imide acid and sodium bifluoride undergo fluorination reaction under microwave-induced catalysis to generate sodium bisfluorosulfonyl imide, wherein the weak polar solvent is an ester solvent.

2. The method for preparing sodium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The microwave power is 0-800W, and the microwave time is 0.5-12h.

3. The method for preparing sodium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The microwave power is 200-400W, and the microwave time is 1-8h.

4. The method for preparing sodium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The microwave power is 200-300W, and the microwave time is 1-2h.

5. The method for preparing sodium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The preparation method comprises the following steps: firstly, fully mixing sodium bifluoride and a weak polar solvent, then adding bischlorosulfonyl imide acid into the reaction system, and performing a fluorination reaction under microwave-induced catalysis for 1 to 2 hours to obtain a reaction solution containing sodium bisfluorosulfonyl imide; and then post-treating the reaction solution to obtain a high-purity sodium bisfluorosulfonyl imide product.

6. The method for preparing sodium bis(fluorosulfonyl)imide according to claim 5, characterized in that: The post-treatment step specifically includes filtering the reaction solution to obtain a clarified solution, concentrating the solution, adding a poor solvent, stirring and crystallizing, filtering and drying to obtain a high-purity sodium bis(fluorosulfonyl)imide product.

7. The method for preparing sodium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The weakly polar solvent is a carbonate solvent.

8. The method for preparing sodium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The weak polar solvent is selected from at least one of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

9. The method for preparing sodium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The equivalent ratio of sodium bifluoride to bischlorosulfonyl imide acid is 4:1 to 1:

1.

10. The method for preparing sodium bis(fluorosulfonyl)imide according to claim 5, characterized in that: The equivalent ratio of sodium bifluoride to bischlorosulfonyl imide acid is 3:1 to 1.5:1.