A method for preparing sodium bisfluorosulfonimide

Abstract

The application belongs to the field of preparation of sodium bisfluorosulfonimide, and particularly relates to a preparation method of sodium bisfluorosulfonimide. The preparation method of sodium bisfluorosulfonimide adopts sodium nitride as a sodium source and sulfuric fluoride gas to react in a saturated alkane nonpolar solvent system, so as to obtain sodium bisfluorosulfonimide solid and sodium fluoride solid, and through post-treatment, high-purity sodium bisfluorosulfonimide with low anion content and high-purity sodium fluoride by-product are obtained. The process is simple and environmentally friendly, and has no three wastes, and the product has high yield and purity.

Description

Technical Field

[0001] This invention belongs to the field of sodium bisfluorosulfonamide preparation technology, and particularly relates to a method for preparing sodium bisfluorosulfonamide. Background Technology

[0002] Alkali metal ion rechargeable batteries occupy an important position in the field of electrochemical energy storage. Sodium is abundant in the Earth's crust and inexpensive. Sodium-ion batteries are superior to lithium-ion batteries in terms of safety and cost, thus having broad application prospects in the power and energy storage fields. It is one of the potential energy storage technologies to replace lithium-ion batteries and is expected to alleviate the problem of lithium resource shortages limiting the electrochemical energy storage field. Currently known sodium electrolyte salts include sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium difluorooxalateborate, and sodium bis(oxalateborate), etc. Among them, sodium bis(fluorosulfonyl)imide has high conductivity, excellent stability, and high and low temperature performance, making it highly valuable for applications.

[0003] Currently, the preparation methods for sodium bis(fluorosulfonyl)imide mainly involve the following steps: 1. Chlorination: preparing bis(fluorosulfonyl)imide acid; 2. Fluorination: obtaining bis(fluorosulfonyl)imide acid through fluorination; 3. Sodium formation: obtaining sodium salt through a sodium formation reaction, followed by recrystallization to obtain high-purity sodium salt that meets battery requirements. The problems with this route are a long process, numerous byproducts, severe environmental pollution, and high cost. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing sodium bis(fluorosulfonyl)imide, which is simple, environmentally friendly, produces less waste, and yields high product purity.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing sodium difluorosulfonamide includes the following steps: S1. Sodium nitride is dispersed in a saturated alkane nonpolar solvent and cooled. Saturated alkane nonpolar solvents have no active hydrogen and no electrophilic point, and are somewhat inert, which can effectively physically disperse sodium nitride. Moreover, sodium bis(fluorosulfonyl)imide solid is prepared in this solvent. During solid-liquid separation, the solvent carries away free anions, which is the key to reducing the anion content in refined sodium bis(fluorosulfonyl)imide and thus preparing high-purity sodium bis(fluorosulfonyl)imide. Then, sulfuryl fluoride gas is introduced to react and a slurry is obtained. The slurry is then separated into solid and liquid phases. S2. The solid obtained in step S1 is dissolved in an organic solvent for a secondary solid-liquid separation; this step is used to separate the two solid products in step S1. Sodium difluorosulfonamide is dissolved in the organic solvent, while the sodium fluoride byproduct remains undissolved and is still a solid. S3. The liquid obtained in step S2 is concentrated under vacuum to obtain a concentrated solution. Then, a solvent is added and the mixture is stirred for 6-12 hours to obtain a crystallization slurry. The slurry is filtered, washed, and dried under nitrogen protection at 35℃-100℃ for 8-12 hours to obtain high-purity sodium difluorosulfonamide powder.

[0006] Furthermore, the saturated alkane nonpolar solvent is at least one of cyclohexane, methylcyclohexane, n-hexane, n-heptane, and isooctane; the mass ratio of the saturated alkane nonpolar solvent to sodium nitride is (6-12):1; after sodium nitride is dispersed in the saturated alkane nonpolar solvent, the dispersion is cooled to -20℃ to -10℃.

[0007] Furthermore, in step S1, the molar ratio of thioyl fluoride to sodium nitride is 2.5–4:1, the reaction temperature is 0–10°C, and the reaction time is 12–48 h.

[0008] Furthermore, in step S2, the organic solvent is an ester solvent and / or an ether solvent, and the filter cake obtained by the secondary solid-liquid separation filtration is dried at 80-120℃ for 4-8 hours to obtain sodium fluoride powder, and the mass ratio of organic solvent to solid is 1.0-3.0:1.

[0009] Furthermore, the ester solvent is at least one of dimethyl carbonate, diethyl carbonate, and ethyl acetate; the ether solvent is at least one of diethyl ether, tetrahydrofuran, methyl tert-butyl ether, and isopropyl ether.

[0010] Furthermore, in step S3, the solvent is at least one of alkanes, chlorinated hydrocarbons, toluene, xylene, dichloroethylene, and anisole. The amount of solvent used is 6 to 10 times the theoretical mass of sodium salt. The solvent can reduce the solubility of sodium difluorosulfonamide in organic solvents, facilitating the precipitation of the product. The crystal product obtained by this method has high purity, and the product particle size is easy to control, while also having low energy consumption.

[0011] Furthermore, the alkane is at least one selected from cyclohexane, methylcyclohexane, n-hexane, n-heptane, and isooctane; the chlorinated hydrocarbon is at least one selected from dichloromethane, dichloroethane, carbon tetrachloride, and chloroform.

[0012] The reaction mechanism is as follows: Na3N + 2SO2F2 = NaN(SO2F)2 + 2NaF The advantages of this invention are as follows: The preparation method of sodium difluorosulfonylimide of this invention uses a saturated alkane nonpolar solvent that does not dissolve the target product sodium difluorosulfonylimide as a dispersant in the reaction system, and reacts with sodium nitride as a sodium source and sulfuryl fluoride gas to obtain solid sodium difluorosulfonylimide and solid sodium fluoride. The solid-liquid separation solvent carries away the free anions, and then a benign solvent dissolves NaFSI but does not dissolve NaF, thus separating NaFSI and the by-product NaF. This process is simple and environmentally friendly, with virtually no waste. All solvents used can be recycled, and there is no waste liquid. The by-product sodium fluoride is a high-purity product with no solid waste, and the product yield and purity are high. Detailed Implementation

[0013] Example 1 The preparation method of sodium difluorosulfonamide in this embodiment includes the following steps: (1) Disperse 41.5g of sodium nitride in 312g of methylcyclohexane solvent, cool to -20℃, then introduce 127.5g of sulfuryl fluoride gas, and then heat to 5℃ for 24h to obtain a slurry system, and then filter it; (2) The solid obtained in step (1) was fully dissolved in 210g of diethyl carbonate solvent. After being fully dissolved, solid-liquid separation was performed. The resulting filter cake was dried at 100℃ for 4h to obtain 40.5g of powder. XRD analysis showed that it was pure sodium fluoride. Atomic absorption analysis of sodium element yielded a purity of 99.85% and a yield of 96.35%.

[0014] (3) The clarified filtrate obtained from step (2) was concentrated at 60℃ and -0.098 MPa to obtain a concentrated slurry. The volume of the concentrated slurry was 50% of the original volume of the clarified filtrate. Then, 640g of dichloromethane was added, stirred and crystallized for 10h, filtered, and the slurry was washed three times with dichloromethane, each time with 1 times the mass of the filter cake. The powder obtained from the filtration was dried in nitrogen at 80℃ for 12h to obtain 97.5g of powder with a yield of 96%. The main impurities were solvent residues: diethyl carbonate residue was 120 ppm, dichloromethane residue was 24 ppm, and 19F NMR analysis showed 51.7 ppm (solvent: deuterated acetonitrile, internal standard: CCl3F). The purity was 99.96%. Ion chromatography was used to detect the anion content of the obtained sodium difluorosulfonamide, which showed 54.8 ppm of aminosulfonate, 5.1 ppm of sulfate, ND of chloride (ND means not detected, the same applies below), and 3.4 ppm of fluoride.

[0015] Example 2 The preparation method of sodium difluorosulfonamide in this embodiment includes the following steps: (1) Disperse 83g of sodium nitride in 830g of cyclohexane solvent, cool to -20℃, then introduce 408g of sulfuryl fluoride gas, and then heat to 10℃ for 48h to obtain a slurry system, and then filter it; (2) The solid obtained in step (1) was fully dissolved in 570g of dimethyl carbonate solvent. After being fully dissolved, solid-liquid separation was performed. The resulting filter cake was dried at 120℃ for 4h to obtain 83.3g of powder. XRD analysis showed that it was pure sodium fluoride. Atomic absorption analysis of sodium element yielded a purity of 99.94% and a yield of 99.17%.

[0016] (3) The clarified filtrate obtained by filtration in step (2) was concentrated at 50℃ and -0.098 MPa to obtain a concentrated slurry. The volume of the concentrated slurry was 40% of the original volume of the clarified filtrate. Then, 2000g of dichloromethane was added, stirred and crystallized for 12h, filtered, and washed three times with dichloromethane, each time with 1 times the mass of the filter cake. The obtained powder was dried under nitrogen at 60℃ for 8h to obtain 198.9g of powder with a yield of 98%. The main impurities were solvent residues: dimethyl carbonate residue was 343ppm, dichloromethane residue was 50ppm, and the 19F NMR test showed 51.8ppm (solvent deuterated acetonitrile, internal standard CCl3F). The purity was 99.94%. The anion content of the obtained sodium difluorosulfonamide was detected by ion chromatography. The aminosulfonate content was 61.1ppm, the sulfate content was 3.8ppm, the chloride content was ND, and the fluoride content was 7.2ppm.

[0017] Example 3 The preparation method of sodium difluorosulfonamide in this embodiment includes the following steps: (1) Disperse 41.5g of sodium nitride in 415g of n-hexane solvent, cool to -20℃, then introduce 153g of sulfuryl fluoride gas, and then heat to 10℃ for 36h to obtain a slurry system, and then filter it; (2) The solid obtained in step (1) was fully dissolved in 350g of diethyl ether solvent. After being fully dissolved, solid-liquid separation was performed. The resulting filter cake was dried at 40℃ for 10h to obtain 40.9g of powder. XRD analysis showed that it was pure sodium fluoride. Atomic absorption analysis of sodium element yielded a purity of 99.91% and a yield of 97.38%.

[0018] (3) The clarified filtrate obtained by filtration in step (2) was concentrated at 30°C and -0.098 MPa to obtain a concentrated slurry. The volume of the concentrated slurry was 40% of the original volume of the clarified filtrate. Then, 1015 g of dichloromethane was added, stirred and crystallized for 12 h, filtered, and the slurry was washed three times with dichloromethane, each time with 1 times the mass of the filter cake. The obtained powder was dried under nitrogen at 35°C for 10 h to obtain 99.9 g of powder, with a yield of 98.5%. The main impurities were solvent residues: ether residues were 80 ppm, dichloromethane residues were 35 ppm, and the 19F NMR test showed 51.8 ppm (solvent deuterated acetonitrile, internal standard CCl3F). The purity was 99.97%. The anion content of the obtained sodium difluorosulfonamide was detected by ion chromatography. The aminosulfonate content was 32.2 ppm, the sulfate content was 3.7 ppm, the chloride content was ND, and the fluoride content was 2.7 ppm.

[0019] Comparative Example The preparation method of lithium bis(fluorosulfonyl)imide includes the following steps: 17.5 g of lithium nitride was dispersed in 300 g of diethyl ether solvent, cooled to -20 °C, and then 127.5 g of sulfuryl fluoride gas was introduced. The mixture was then heated to 25 °C and reacted for 24 h to obtain a slurry system. The slurry was then filtered, and the filter cake was dried at 100 °C for 6 h to obtain 25.4 g of powder. XRD analysis showed that the powder was pure phase lithium fluoride, and atomic absorption spectrometry showed that the purity of lithium was 99.95% and the yield was 97.69%.

[0020] The clarified filtrate obtained by filtration was concentrated at 30℃ and -0.098 MPa to obtain a concentrated slurry, the volume of which was 40% of the original volume of the clarified filtrate. Then, 580 g of dichloromethane was added, and the mixture was stirred and crystallized for 12 h. After filtration, the mixture was washed three times with dichloromethane, each time with one times the mass of the filter cake. The obtained powder was dried under nitrogen at 35℃ for 8 h to obtain 88.8 g of powder, with a yield of 95%. The 19F NMR test showed a purity of 51.6 ppm (solvent deuterated acetonitrile, internal standard CCl3F), with a purity of 99.95%. Ion chromatography was used to detect the anion content of the obtained sodium difluorosulfonamide, which showed an aminosulfonate content of 121.5 ppm, a sulfate content of 17.2 ppm, a chloride content of ND, and a fluoride content of 12.1 ppm.

[0021] The purity and yield of sodium bis(fluorosulfonyl)imide / lithium in Examples 1-3 and the comparative examples were tested and recorded in Table 1.

[0022] Table 1. Summary of purity and yield of sodium bis(fluorosulfonyl)imide / lithium in Examples 1-3 and Comparative Examples. The comparative example is the preparation of lithium bis(fluorosulfonyl)imide from lithium nitride. The main difference is that the refined salt prepared by directly preparing a salt solution in a good solvent and then undergoing post-treatment has a higher anion content than the refined salt prepared by first preparing a solid salt in a poor solvent and then undergoing post-treatment in this application. This is because sodium nitride is not stable in good solvents (it reacts with ester solvents) or cannot be stable for a long time (ether bonds break in ether solvents to generate alcohol impurities). Therefore, the reaction system of the comparative example cannot be used for the preparation of sodium bis(fluorosulfonyl)imide.

Claims

1. A method for preparing sodium difluorosulfonyl imide, characterized in that, Includes the following steps: S1. Disperse sodium nitride in a saturated alkane nonpolar solvent, then introduce sulfuryl fluoride gas to react and obtain a slurry, and then separate the solid and liquid components of the slurry; S2. Dissolve the solid obtained in step S1 in an organic solvent to perform a secondary solid-liquid separation; S3. The liquid obtained in step S2 is stirred and crystallized under the action of a solvent to obtain a crystallization slurry. The crystallization slurry is filtered, washed and dried to obtain sodium difluorosulfonamide powder.

2. The method as described in claim 1, characterized in that: The saturated alkane nonpolar solvent is at least one of cyclohexane, methylcyclohexane, n-hexane, n-heptane, and isooctane; the mass ratio of the saturated alkane nonpolar solvent to sodium nitride is (6-12):1; after sodium nitride is dispersed in the saturated alkane nonpolar solvent, the dispersion is cooled to -20℃ to -10℃.

3. The method as described in claim 1, characterized in that: In step S1, the molar ratio of thioyl fluoride to sodium nitride is 2.5–4:1, the reaction temperature is 0–10℃, and the reaction time is 12–48 h.

4. The method as described in claim 1, characterized in that: In step S2, the organic solvent is an ester solvent and / or an ether solvent. The filter cake obtained by the secondary solid-liquid separation filtration is dried at 80-120℃ for 4-8 hours to obtain sodium fluoride powder, and the mass ratio of organic solvent to solid is 1.0-3.0:

1.

5. The method as described in claim 4, characterized in that: The ester solvent is at least one of dimethyl carbonate, diethyl carbonate, and ethyl acetate; the ether solvent is at least one of diethyl ether, tetrahydrofuran, methyl tert-butyl ether, and isopropyl ether.

6. The method as described in claim 1, characterized in that: In step S3, the solvent is at least one of alkanes, chlorinated hydrocarbons, toluene, xylene, dichloroethylene, and anisole, and the amount of solvent used is 6 to 10 times the theoretical mass of sodium salt.

7. The method as described in claim 6, characterized in that: The alkane is at least one of cyclohexane, methylcyclohexane, n-hexane, n-heptane, and isooctane; the chlorinated hydrocarbon is at least one of dichloromethane, dichloroethane, carbon tetrachloride, and chloroform.

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