Method for reducing sodium bis (fluorosulfonyl) imide solvent residue and improving crystal particle uniformity

Abstract

The invention belongs to the technical field of lithium battery materials, and particularly relates to a method for reducing the residual of a sodium bis (fluorosulfonyl) imide solvent and improving the uniformity of crystal particles. The method comprises the steps of 1) NaFSI synthesis, 2) recrystallization, 3) post-treatment and the like. According to the invention, the particle size distribution of NaFSI can be effectively controlled by combining real-time monitoring and temperature adjustment of the online particle size detector. In addition, the crystallization process is controlled through temperature, so that the crystals reach a stable state, solvent residues are reduced, post-treatment is easier, the solvent removal time is shortened, or the process is simplified. Through the gradient slow cooling process, stable NaFSI crystals are generated in the crystallization process, reagents are effectively prevented from being contained in the NaFSI crystals, the post-treatment solvent residual time is shortened, and material partial decomposition caused by long-time heating and drying is avoided. According to the invention, the particle size distribution is controlled, so that the NaFSI crystal particles are obviously increased.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery material technology, specifically relating to a method for reducing sodium difluorosulfonyl imide solvent residue and improving crystal particle uniformity. Background Technology

[0002] In recent years, the rapid development of lithium batteries has accelerated the rapid consumption of lithium resources, raising people's awareness of potential risks. As a result, sodium batteries have been widely studied as a supplement to lithium batteries. Due to the certain similarities between the two, the research results of lithium batteries have been applied to sodium batteries to a certain extent.

[0003] Sodium bis(fluorosulfonyl)imide (NaFSI) is an important component of lithium-ion battery electrolytes. Compared with traditional sodium hexafluorophosphate, NaFSI exhibits superior chemical stability and lower viscosity, thus improving the electrochemical performance of sodium batteries. Currently, the synthesis of NaFSI largely follows the synthesis route of lithium bis(fluorosulfonyl)imide (LiFSI). However, due to the differences in the properties of sodium and lithium, the previous LiFSI process often resulted in high solvent residue and a wide particle size distribution in NaFSI, severely impacting its quality.

[0004] To address the problems encountered in NaFSI preparation, it is necessary to make referential adjustments to the LiFSI process. A method is proposed to reduce NaFSI solvent residue and improve its particle uniformity in order to obtain high-quality NaFSI.

[0005] Existing technologies also disclose methods for preparing sodium difluorosulfonyl imide, such as CN115893335B, a method for preparing sodium difluorosulfonyl imide, and CN118026111A, a method for preparing high-purity sodium difluorosulfonyl imide. However, existing technologies focus on optimizing the NaFSI preparation method, without specifically optimizing the recrystallization process. They simply follow the general recrystallization method to reduce impurities in the crude salt. After recrystallization, a long period of vacuum drying is required to remove reagents and reduce solvent residues to obtain the NaFSI product.

[0006] In addition, the existing technology also has the following problems:

[0007] 1) Recrystallization using conventional methods can improve the purity of the product, but the pure product has a wide particle size distribution and varies in size, which affects its transfer, handling and dissolution process.

[0008] 2) Using conventional recrystallization methods, NaFSI often has a high level of solvent residue after recrystallization, requiring a long or complex drying process to remove the residual solvent.

[0009] Based on this, the present invention can effectively control the problem of uneven particle size in the product by controlling the recrystallization temperature and using an online particle size analyzer. At the same time, the present invention also controls the crystallization process by temperature, allowing the crystals to reach a stable state, reducing solvent residue, simplifying post-processing, reducing solvent removal time, or simplifying the process.

[0010] The abbreviations appearing in this application are as follows: HFSI is difluorosulfonyl imide acid (purity 99.5%), LiFSI is lithium difluorosulfonyl imide, NaFSI is sodium difluorosulfonyl imide, DMC is dimethyl carbonate, EDC is dichloroethane, and DEC is diethyl carbonate. Summary of the Invention

[0011] Based on the problems existing in the prior art, this invention proposes a method to reduce sodium difluorosulfonyl imide solvent residue and improve the uniformity of crystal particles. By combining real-time monitoring with online particle size analyzer and temperature adjustment, the particle size distribution of NaFSI can be effectively controlled.

[0012] In addition, the present invention controls the crystallization process by temperature, allowing the crystals to reach a stable state, reducing solvent residue, making post-processing easier, reducing solvent removal time, or simplifying the process.

[0013] To achieve the above objectives, the present invention adopts the following technical solution:

[0014] A method for reducing sodium difluorosulfonamide solvent residue and improving crystal particle uniformity includes the following steps:

[0015] 1) NaFSI Synthesis

[0016] Sodium salt is first dispersed in organic solvent one to form a dispersion, and the temperature of the dispersion is controlled at 5-10℃. HFSI is added to the dispersion, and the reaction is carried out for 5-10 hours. When the acidity of the reaction system is detected to be below 200ppm, the reaction is stopped. The reaction solution is filtered, the solid crude salt is collected, washed, and purged under an inert atmosphere for 8-14 hours to obtain crude NaFSI.

[0017] 2) Recrystallization

[0018] Dissolve crude NaFSI salt in a good solvent and stir for 0.5-2 hours. After the solution is completely clear, filter to remove insoluble matter and obtain a clear solution.

[0019] The clarified liquid was transferred to a four-necked flask, and the flask necks were connected to an online particle size analyzer and the outlet of a peristaltic pump, respectively. The inlet of the peristaltic pump was then connected to a single-necked bottle containing the antisolvent. The other two ports of the four-necked flask were connected to a condenser and a mechanical stirrer, respectively. The entire connected system was placed in an oil bath and heated while stirring. At the same time, the peristaltic pump added the antisolvent to the four-necked flask. The particle size of the precipitated NaFSI crystals was monitored by the online particle size analyzer, and the crystallization solution was obtained.

[0020] 3) Post-processing

[0021] The crystallization solution was filtered, and the surface of the NaFSI crystals was dried under an inert atmosphere. The dried NaFSI crystals were then transferred to a single-necked flask and dried under negative pressure in a rotary evaporator to obtain the final product.

[0022] Furthermore, in step 1), the sodium salt is any one of sodium carbonate, sodium sulfate, or sodium chloride.

[0023] Furthermore, in step 1), the organic solvent is any one of carbon tetrachloride, dichloromethane, dichloroethane, and chloroform.

[0024] Furthermore, in step 1), the mass ratio of sodium salt to organic solvent is 1:(8-10).

[0025] Furthermore, in step 1), the molar ratio of HFSI to sodium salt is 1:(1.0 to 3.0).

[0026] Furthermore, in step 1), the HFSI is added at a rate of 2-5 ml / min.

[0027] Furthermore, in step 2), the good solvent is one or more of DMC, DEC, and acetonitrile.

[0028] Furthermore, in step 2), the amount of good solvent used is 2-4 times the mass of NaFSI.

[0029] Furthermore, in step 2), the antisolvent is one or both of carbon tetrachloride and EDC.

[0030] Furthermore, in step 2), the initial reaction temperature in the oil bath is 60-70℃.

[0031] Furthermore, in step 2), the amount of antisolvent used is 5-8 times the mass of NaFSI.

[0032] Furthermore, in step 2), the stirring speed of the mechanical stirring device is 100-200 r / min.

[0033] Furthermore, in step 2), the peristaltic pump is used to add water at a rate of 2-6 ml / min.

[0034] Furthermore, in step 2), during the process of monitoring the NaFSI crystal particle size using an online particle size analyzer, when the particle size distribution width (Span) exceeds 0.25, the temperature is increased by 5-10℃ to dissolve some crystal defect particles, maintaining the particle size distribution width within 0.25. After all the antisolvent is added, the temperature is maintained for 0.5-1h to allow the particle size and particle size distribution to stabilize. As seed crystals for later crystallization, the temperature is gradually decreased by 5-10℃, and then the temperature is restored by 3-5℃. After restoration, the system is maintained for 0.5-1h, and then the next gradual temperature decrease is carried out until the crystallization temperature drops to 15-20℃.

[0035] Furthermore, in step 3), the pressure during negative pressure drying is 100-200 Pa, the rotary evaporation temperature is 70-80℃, and the rotary evaporation time is 0.5-1 h.

[0036] Furthermore, the inert atmosphere is an atmosphere formed by nitrogen or argon.

[0037] Compared with the prior art, the advantages of the present invention are:

[0038] 1. This invention effectively controls the particle size distribution of NaFSI by combining real-time monitoring with temperature adjustment using an online particle size analyzer.

[0039] 2. This invention uses a gradual cooling process to generate stable NaFSI crystals during crystallization, effectively preventing reagents from being contained within the crystals, reducing solvent residue time in later processing, and avoiding partial decomposition of the material caused by prolonged heating and drying.

[0040] 3. By controlling the particle size distribution, the NaFSI crystal particles of this invention are significantly increased. Detailed Implementation

[0041] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. However, those skilled in the art should understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Unless otherwise specified, the experimental methods in the following examples are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise specified, the raw materials and reagents used are all commercially available products.

[0043] In the following examples, room temperature or normal temperature refers to 25±5℃.

[0044] The mechanical stirring devices used in the following embodiments can all be conventional equipment in the prior art, and their structure is not the inventive point of this invention, so they will not be described in detail.

[0045] Example 1

[0046] A method for reducing sodium difluorosulfonamide solvent residue and improving crystal particle uniformity includes the following steps:

[0047] 1) NaFSI Synthesis

[0048] Weigh 73g of sodium carbonate into a three-necked flask, add 653g of carbon tetrachloride, and disperse the sodium carbonate in the carbon tetrachloride using mechanical stirring. Maintain the system temperature at 6℃ using a circulating cold bath. Then add 250g of HFSI at a rate of 4ml / min. After reacting for 8 hours, stop the reaction. At this point, the acidity of the system drops to 180ppm. Filter off the reaction solution, collect the solid crude salt, wash it with carbon tetrachloride, and purge it with nitrogen for 10 hours to obtain crude NaFSI.

[0049] 2) Recrystallization

[0050] Dissolve 200g of crude NaFSI from step 1) in 400g of DMC and stir mechanically for 0.5h. After the solution is completely clear, filter the solution using a positive pressure filter to remove insoluble matter and obtain a clear NaFSI solution. Transfer the clear NaFSI solution to a 2500ml four-necked flask and test it with an online particle size analyzer (model: Mettler ParticleTrack). The G400 detector was connected to a four-necked flask and the probe was inserted into the solution. Mechanical stirrers, condensers, and the outlet of a peristaltic pump were connected to the other three necks of the four-necked flask. At the same time, the inlet of the peristaltic pump was connected to a single-necked bottle containing the antisolvent (carbon tetrachloride). The total amount of carbon tetrachloride in the single-necked bottle was 1200g. The entire connected system was placed in an oil bath with an initial temperature of 60℃ and a mechanical stirring speed of 150r / min. After the solution temperature stabilized, the peristaltic pump pumped carbon tetrachloride into the four-necked flask at a rate of 4ml / min. During this process, recrystallization of NaFSI was achieved. Meanwhile, an online particle size analyzer monitored the particle size of the NaFSI crystals precipitated in the solution in real time.

[0051] Monitoring with an online particle size analyzer revealed that when approximately 700g of carbon tetrachloride was added, the recrystallized crystal particle size distribution was 0.29 (D50 = 158μm). Increasing the temperature to 70℃ reduced the particle size distribution to 0.22 (D50 = 176μm), controlling the particle size distribution within 0.25. Continued addition of carbon tetrachloride, with temperature adjustments to control the particle size, resulted in a particle size distribution of 0.24 (D50 = 182μm) after complete addition of carbon tetrachloride and adjustment of the oil bath temperature to 75℃, while maintaining stable stirring. After 0.5 h, the temperature was lowered to 65 °C using an oil bath program at 10 °C / h, then restored to 5 °C after 5 min, and stabilized for 0.5 h. At this point, the crystal size distribution width was 0.29 (D50 was 191 μm). Similar operations were performed using this temperature control program (i.e., after stabilizing and stirring for 0.5 h, the temperature was lowered by 10 °C using an oil bath program at 10 °C / h, then restored to 5 °C after 5 min) until the system temperature dropped to 20 °C. The final crystal size distribution width was 0.41 (D50 was 284 μm), and a crystallization solution was obtained.

[0052] 3) Post-processing

[0053] The crystallization solution from step 2) was filtered in a positive pressure filter and purged with nitrogen for 0.5 h to dry the surface of the NaFSI crystals. A sample was taken to measure the solvent residue, and the remaining sample was transferred to a 250 ml single-necked bottle. The residual reagent was removed under negative pressure in a rotary evaporator. The pressure inside the rotary evaporator was reduced to 135 Pa and the temperature was 70 °C. The evaporation was carried out for 0.5 h to obtain the final product.

[0054] Sampling and testing are conducted to assess the quality of the finished product and the solvent residue in the samples.

[0055] Table 1. Indicators after recrystallization with NaFSI and nitrogen purging

[0056]

[0057] Table 2 NaFSI index after negative pressure drying (step 3)

[0058]

[0059] Example 2

[0060] A method for reducing sodium difluorosulfonamide solvent residue and improving crystal particle uniformity includes the following steps:

[0061] 1) NaFSI Synthesis

[0062] Weigh 81g of sodium carbonate and place it in a three-necked flask. Add 776g of dichloroethane and disperse the sodium carbonate in the dichloroethane using mechanical stirring. Maintain the system temperature at 8°C using a circulating cold bath. Then, add 231g of HFSI at a rate of 3ml / min. After reacting for 8 hours, stop the reaction. At this point, the acidity of the system drops to 160ppm. Filter out the reaction solution, collect the solid crude salt, wash it with dichloroethane, and purge it with nitrogen for 9 hours to obtain crude NaFSI.

[0063] 2) Recrystallization

[0064] Dissolve 180g of crude NaFSI from step 1) in 450g of DEC and stir mechanically for 0.5h. After the solution is completely clear, filter the solution using a positive pressure filter to remove insoluble matter and obtain the clear NaFSI solution at the bottom. Transfer the clear NaFSI solution to a 2500ml four-necked flask and test it with an online particle size analyzer (model: Mettler ParticleTrack). The G400 detector was connected to a four-necked flask and the probe was inserted into the solution. Mechanical stirrers, condensers, and the outlet of a peristaltic pump were connected to the other three necks of the four-necked flask. At the same time, the inlet of the peristaltic pump was connected to a single-necked bottle containing the antisolvent (dichloroethane). The total amount of dichloroethane in the single-necked bottle was 1260g. The entire connected system was placed in an oil bath with an initial temperature of 60℃ and a mechanical stirring speed of 160r / min. After the solution temperature stabilized, the peristaltic pump pumped dichloroethane into the four-necked flask at a rate of 3ml / min. During this process, recrystallization of NaFSI was achieved. Meanwhile, an online particle size analyzer monitored the particle size of the NaFSI crystals precipitated in the solution in real time.

[0065] Monitoring with an online particle size analyzer revealed that when approximately 750g of dichloroethane was added, the recrystallized crystal particle size distribution was 0.27 (D50 = 161μm). Increasing the temperature to 70℃ reduced the particle size distribution to 0.22 (D50 = 176μm), controlling the particle size distribution within 0.25. Further addition of dichloroethane, with temperature adjustments to control the particle size, resulted in a final particle size distribution of 0.21 (D50 = 191μm) after complete addition of the dichloroethane and adjustment of the oil bath temperature to 72℃. Stirring was then maintained at this temperature. After 0.5 h, the temperature was lowered to 62 °C using an oil bath program at 10 °C / h, then restored to 5 °C after 5 min, and stabilized for 0.5 h. At this point, the crystal size distribution width was 0.26 (D50 was 207 μm). Similar operations were performed using this temperature control program (i.e., after stabilizing and stirring for 0.5 h, the temperature was lowered by 10 °C using an oil bath program at 10 °C / h, then restored to 5 °C after 5 min) until the system temperature dropped to 22 °C. The final crystal size distribution width was 0.39 (D50 was 311 μm), and a crystallization solution was obtained.

[0066] 3) Post-processing

[0067] The crystallization solution from step 2) was filtered in a positive pressure filter and purged with nitrogen for 0.5 h to dry the surface of the NaFSI crystals. A sample was taken to measure the solvent residue, and the remaining sample was transferred to a 250 ml single-necked bottle. The residual reagent was removed under negative pressure in a rotary evaporator. The pressure inside the rotary evaporator was reduced to 146 Pa and the temperature was 70 °C. The evaporation was carried out for 0.5 h to obtain the final product.

[0068] Sampling and testing are conducted to assess the quality of the finished product and the solvent residue in the samples.

[0069] Table 3. Indicators after recrystallization with NaFSI and nitrogen purging

[0070]

[0071] Table 4. NaFSI index after negative pressure drying (step 3)

[0072]

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for reducing sodium difluorosulfonyl imide solvent residue and improving crystal particle uniformity, characterized in that, Includes the following steps: 1) NaFSI Synthesis Sodium salt is first dispersed in organic solvent one to form a dispersion, and the temperature of the dispersion is controlled at 5-10℃. HFSI is added to the dispersion, and the reaction is carried out for 5-10 hours. When the acidity of the reaction system is detected to be below 200ppm, the reaction is stopped. The reaction solution is filtered, the solid crude salt is collected, washed, and purged under an inert atmosphere for 8-14 hours to obtain crude NaFSI. 2) Recrystallization Dissolve crude NaFSI salt in a good solvent and stir for 0.5-2 hours. After the solution is completely clear, filter to remove insoluble matter and obtain a clear solution. The clarified liquid was transferred to a four-necked flask, and the mouth of the four-necked flask was connected to an online particle size analyzer and the outlet of a peristaltic pump, respectively. The inlet of the peristaltic pump was then connected to a single-necked bottle containing the antisolvent. The other two ports of the four-necked flask were connected to a condenser and a mechanical stirrer, respectively. The entire connected system was placed in an oil bath, and the heating process was controlled while stirring. At the same time, the antisolvent was added to the four-necked flask using a peristaltic pump. The particle size of the precipitated NaFSI crystals was monitored by the online particle size analyzer, and the crystallization solution was obtained. 3) Post-processing The crystallization solution was filtered, and the surface of the NaFSI crystals was dried under an inert atmosphere. The dried NaFSI crystals were then transferred to a single-necked flask and dried under negative pressure in a rotary evaporator to obtain the final product.

2. The method as described in claim 1, characterized in that, In step 1), the sodium salt is any one of sodium carbonate, sodium sulfate, or sodium chloride.

3. The method as described in claim 1, characterized in that, In step 1), the organic solvent is any one of carbon tetrachloride, dichloromethane, dichloroethane, and chloroform.

4. The method as described in claim 1, characterized in that, In step 1), the mass ratio of sodium salt to organic solvent is 1:(8~10). In step 1), the molar ratio of HFSI to sodium salt is 1:(1.0~3.0).

5. The method as described in claim 1, characterized in that, In step 2), the good solvent is one or more of DMC, DEC, and acetonitrile; In step 2), the amount of good solvent used is 2-4 times the mass of NaFSI.

6. The method as described in claim 1, characterized in that, In step 2), the antisolvent is one or both of carbon tetrachloride and EDC; In step 2), the amount of antisolvent used is 5-8 times the mass of NaFSI.

7. The method as described in claim 1, characterized in that, Step 2) The initial reaction temperature in the oil bath is 60-70℃.

8. The method as described in claim 1, characterized in that, In step 2), during the process of monitoring the NaFSI crystal particle size using an online particle size analyzer, when the particle size distribution width exceeds 0.25, the temperature is increased by 5-10℃ to dissolve some crystal defect particles, maintaining the particle size distribution width within 0.

25. After all the antisolvent is added, the temperature is maintained for 0.5-1h to allow the particle size and particle size distribution to stabilize. As seed crystals for later crystallization, the temperature is gradually decreased by 5-10℃, and then the temperature is restored by 3-5℃. After restoration, the system is maintained for 0.5-1h, and then the next temperature gradient is performed until the crystallization temperature drops to 15-20℃.

9. In the method of claim 1, in step 3), the pressure during negative pressure drying is 100-200 Pa, the rotary evaporation temperature is 70-80℃, and the rotary evaporation time is 0.5-1 h.

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