Preparation method of low-solvent-residue lithium bis (fluorosulfonyl) imide
By using fluoronitrile organic solvents and adsorption filter aids in the lithium battery electrolyte, adjusting pH and adding crystal form inducers to form high-purity sheet hexagonal lithium difluorosulfonimide, the solvent residue problem is solved. , simplifies the drying process and realizes the preparation of low-soluble residue lithium battery electrolyte, which is suitable for the industrial production of high-end lithium-ion electrolytes.
Patent Information
- Application Number
- CN202411215359.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-23
- Publication Date
- 2025-01-03
AI Technical Summary
The prior art is difficult to effectively reduce the solvent residue of lithium difluorosulfonimide in lithium battery electrolyte, resulting in limited development of high-quality lithium battery electrolyte, and the drying process is complicated and energy consumption is high, making it difficult to achieve extremely low solvent residue. .
Fluoronitrile organic solvent is used as a good solvent for dissolving lithium difluorosulfonimide, adjusting the pH of the system to a weak acidic environment, adding adsorption filter aids and crystal form inducers, and then flakes are formed by decompression distillation and vacuum drying. The edge crystal reduces solvent cross-clustering and adsorption, and simplifies the drying process.
It realizes crystal preparation with higher purity, reduces solvent residue, simplifies the drying process, has the advantage of green energy saving, and is suitable for the preparation of high-end lithium-ion electrolytes.
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Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of new lithium battery materials, and specifically is a method for preparing low-residual bis(fluorosulfonyl)imide lithium. Background Art
[0002] The electrolyte lithium salt in lithium-ion batteries has a crucial impact on the performance of the battery. In lithium-ion battery electrolytes, lithium bis(fluorosulfonyl)imide (LiFSI) is a new type of electrolyte lithium salt with high electrochemical stability and thermal stability, and can cooperate well with lithium metal electrodes and graphite electrodes. It also has good environmental performance, low temperature performance and safety performance. Therefore, it is the lithium battery electrolyte lithium salt with the most industrialization prospects.
[0003] According to literature reports, one of the main reasons that currently affect the performance of lithium battery electrolytes is that the impurities brought in by LiFSI undergo redox side reactions at the negative electrode of the battery, especially the solvent molecules used in the LiFSI crystallization process have poor oxidation resistance. Due to the lattice structure entrapment and high-energy adsorption on the surface, the LiFSI crystallization process causes the product's solvent residue to be as high as 2000ppm or more, and this impurity content cannot be fed back in the LiFSI purity data detected by conventional ion chromatographs. Due to the strong interaction between LiFSI and solvent molecules, it is also difficult to give accurate content through rapid detection methods such as gas chromatography. The quantitative H-NMR method can give a more accurate content, but the detection cost is high and the time cycle is long, so it is ignored by industry product indicators. In short, due to the limitations of the current process research and development level and detection methods, the real low-residue lithium bis(fluorosulfonyl)imide is still lacking in the market, which directly affects the development of high-quality lithium battery electrolytes.
[0004] Patent CN113562710B discloses a method for reducing the residual solvent in lithium bis(fluorosulfonyl)imide salt. The essential principle of the method is to add a third type of solvent with stronger interaction force with LiFSI to reduce the binding force between the two solvents of the original crystallization system and LiFSI, and then match a long drying process to achieve the reduction of residual solvent. The problems of this method are: (1) the use of three solvents makes solvent recovery difficult; (2) the drying process is complicated, the cycle is long (more than 21 hours), and the energy consumption is high; (3) it is impossible to avoid the solvent molecules trapped in the lattice structure from the source of crystallization, and it is difficult to achieve extremely low solvent residue. Therefore, the method of this patent is difficult to be used as a reliable method for industrial preparation of low-residue lithium bis(fluorosulfonyl)imide.
[0005] Therefore, there is an urgent need in the art for a method for preparing low-residual lithium bis(fluorosulfonyl)imide to solve the problem of solvent inclusion or adsorption during the crystallization process of LiFSI and to meet the market demand for high-end lithium-ion electrolytes. Summary of the invention
[0006] To solve the above problems, the present invention aims to provide a method for preparing low-residual bis(fluorosulfonyl)imide lithium.
[0007] In order to achieve the above object, the present invention is implemented through the following technical solutions: A method for preparing low-residual bis(fluorosulfonyl)imide lithium comprises the following steps: 1) dissolving crude lithium bis(fluorosulfonyl)imide in a fluoronitrile organic solvent to obtain a crude lithium bis(fluorosulfonyl)imide solution, adding the obtained crude lithium bis(fluorosulfonyl)imide solution to a pretreatment kettle, introducing high-purity carbon dioxide gas into the pretreatment kettle under stirring to adjust the pH of the system to 5.0-5.5, stopping the aeration to obtain a mixed solution; 2) adding an adsorption filter aid to the mixed solution obtained in step 1), stirring for 0.5 to 1 hour, and then filtering through a precision filter to obtain a filtrate; 3) The filtrate obtained in step 2) is transferred to a crystallizer, and vacuum distilled at 10-70° C. and 0.5-20 kPa. As the fluoronitrile organic solvent is evaporated, a poor solvent is added to the solution to keep the mass in the crystallizer constant. When the viscosity of the solution in the crystallizer reaches 300 centipoise, a crystal form inducing agent is added to the solution; wherein the poor solvent is a benzene, alkane or chlorinated alkane solvent; 4) Continue to distill under reduced pressure until the content of fluoronitrile organic solvent in the system is less than 0.5%, end the crystallization, filter, transfer the obtained filter cake to a vacuum dryer, and dry to obtain low-residue lithium bis(fluorosulfonyl)imide.
[0008] The fluoronitrile organic solvent in step 1) is fluoroacetonitrile, difluoroacetonitrile, 3,3,3-trifluoropropionitrile or 2,3,3,3-tetrafluoropropionitrile.
[0009] The mass concentration of the crude lithium bis(fluorosulfonyl)imide solution in step 1) is 30-60%, and the water content is less than 3000 ppm.
[0010] The adsorption filter aid in step 2) is molecular sieve, activated carbon or activated clay; the added amount is 0.1-5% of the mass of the mixed solution.
[0011] The precision filter described in step 2) is a filtering device with a filtration accuracy of <0.1um.
[0012] The poor solvent in step 3) is chlorobenzene, dichlorobenzene, n-hexane, dichloromethane or tetrachloroethane.
[0013] The crystal form inducing agent in step 3) is prepared by mixing lithium bis(fluorosulfonyl)imide and a poor solvent into a slurry, adding a fluoronitrile organic solvent, and stirring for 30 minutes; wherein the mass ratio of lithium bis(fluorosulfonyl)imide, fluoronitrile organic solvent and poor solvent is 100:1~5:95~99, and the total mass of the fluoronitrile organic solvent and the poor solvent is the same as the mass of lithium bis(fluorosulfonyl)imide; the microscopic morphology of the lithium bis(fluorosulfonyl)imide is a thin flaky hexagonal crystal; the amount of the crystal form inducing agent added is 0.1~5% of the mass of the solution in the crystallizer.
[0014] The drying parameters of the vacuum dryer in step 4) are drying at 0.1-0.5 kPa and 30-50° C. for 2-10 hours.
[0015] Preferably, the adsorption filter aid in step 2) is a molecular sieve; the added amount is 0.5-2% of the mass of the mixed solution; and the precision filter is a two-stage series ceramic membrane filtration device.
[0016] Preferably, the amount of the crystal form inducing agent added in step 3) is 0.5-2% of the mass of the solution in the crystallizer.
[0017] Compared with the prior art, the present invention has the following advantages: The method for preparing low residual bis(fluorosulfonyl)imide lithium of the present invention adopts fluorine-containing nitrile solvents as good solvents for dissolving bis(fluorosulfonyl)imide lithium. Such solvents have weak solvation energy with LiFSI, which is beneficial to reducing the structural entrapment of solvent molecules in the crystallization process of LiFSI. A weakly acidic environment is provided for crystallization by adjusting the pH value of the system, and the weak acidity contributes to a better crystal structure and lower residual solution. The addition of an adsorption filter aid is to enhance the filtering effect and adsorb and remove nano-scale solid impurities.
[0018] The method for preparing low-residue bis(fluorosulfonyl)imide lithium of the present invention adopts bis(fluorosulfonyl)imide with flake morphology. Lithium imide is used as seed crystal, and the SEM image of the seed crystal used is as follows Figure 1 As shown, the surface activity of the crystal is adjusted by etching the surface with a mixed solvent. Suitable surface activity can induce the crystallization process to form products with specific morphology (shape and size). Research data show that the products with flaky hexagonal morphology prepared by the present invention have lower solvent entrapment characteristics.
[0019] The method for preparing low-residue lithium bis(fluorosulfonyl)imide of the present invention can achieve higher purity crystal preparation in the crystallization process, solve the problems of solvent entrapment and adsorption from the source, so that lower drying parameters can be used to complete the drying process, which has the advantage of being green and energy-saving. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1This is a SEM image of lithium bis(fluorosulfonyl)imide seed crystals used in the preparation process of the crystal form inducing agent of the present invention; Figure 2 This is a SEM image of low-residue lithium bis(fluorosulfonyl)imide prepared in Example 1 of the present invention. DETAILED DESCRIPTION
[0021] In order to better understand the technical solution of the present invention, the above content of the present invention is further described in detail below through specific implementation methods in the form of embodiments, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples. All technologies realized based on the above content of the present invention belong to the scope of the present invention.
[0022] Example 1: Dissolve crude lithium bis(fluorosulfonyl)imide in fluoroacetonitrile to obtain 1000 kg of crude lithium bis(fluorosulfonyl)imide solution with a mass concentration of 45%. Add the crude lithium bis(fluorosulfonyl)imide solution to a pretreatment kettle, introduce high-purity carbon dioxide gas into the pretreatment kettle under stirring to adjust the pH of the system to 5.25, stop aeration, and obtain a mixed solution. Add 1 kg of molecular sieve to the obtained mixed solution, stir for 0.5 h, and then pass through a ceramic membrane filter with a pore size of 0.1 um to obtain a filtrate. Transfer the obtained filtrate to a crystallizer, and perform vacuum distillation at 30°C and 2 kPa. As the fluoroacetonitrile is removed, the mixture is stirred for 0.5 h. Distill it out, add chlorobenzene to the solution to keep the mass in the crystallizer constant, and when the viscosity of the solution in the crystallizer reaches 300 centipoise, add a crystal inducer to the solution; the crystal inducer is prepared by mixing 5.0kg of flaky lithium bis(fluorosulfonyl)imide with 4.875kg of chlorobenzene to form a slurry, and then adding 0.125kg of fluoroacetonitrile and stirring for 30 minutes; continue to distill under reduced pressure until the fluoroacetonitrile content in the system is less than 0.5%, end the crystallization, filter, and transfer the obtained filter cake to a vacuum dryer, and dry it at 0.2kPa and 40°C for 4 hours to obtain low-residue lithium bis(fluorosulfonyl)imide. Its SEM picture is as follows Figure 2 As shown, from Figure 2 It can be seen that the product prepared by the method of the present invention has a flake-like hexagonal morphology.
[0023] Example 2: Dissolve crude lithium bis(fluorosulfonyl)imide in difluoroacetonitrile to obtain 1500 kg of crude lithium bis(fluorosulfonyl)imide solution with a mass concentration of 50%. Add the crude lithium bis(fluorosulfonyl)imide solution to a pretreatment kettle, introduce high-purity carbon dioxide gas into the pretreatment kettle under stirring to adjust the pH of the system to 5.35, stop aeration, and obtain a mixed solution. Add 15 kg of activated carbon to the obtained mixed solution, stir for 0.75 h, and then pass through a ceramic membrane filter with a pore size of 0.1 um to obtain a filtrate. Transfer the obtained filtrate to a crystallizer, and perform vacuum distillation at 40°C and 5 kPa. As difluoroacetonitrile is removed, the mixture is stirred for 0.75 h. The mixture was evaporated, and dichlorobenzene was added to the solution to keep the mass in the crystallizer constant. When the viscosity of the solution in the crystallizer reached 300 centipoise, a crystal inducer was added to the solution; wherein the crystal inducer was prepared by mixing 7.5 kg of lithium bis(fluorosulfonyl)imide with a flake morphology with 7.125 kg of dichlorobenzene to form a slurry, and then adding 0.375 kg of difluoroacetonitrile and stirring for 30 minutes; the reduced pressure distillation was continued until the content of difluoroacetonitrile in the system was less than 0.5%, the crystallization was terminated, and the filter cake was transferred to a vacuum dryer and dried at 0.3 kPa and 45° C. for 6 hours to obtain low-residue lithium bis(fluorosulfonyl)imide.
[0024] Example 3: Dissolve crude lithium bis(fluorosulfonyl)imide in 3,3,3-trifluoropropionitrile to obtain 2000 kg of crude lithium bis(fluorosulfonyl)imide solution with a mass concentration of 55%. Add the crude lithium bis(fluorosulfonyl)imide solution to a pretreatment kettle, introduce high-purity carbon dioxide gas into the pretreatment kettle under stirring to adjust the pH of the system to 5.45, stop aeration, and obtain a mixed solution. Add 40 kg of activated clay to the obtained mixed solution, stir for 0.5 h, and then pass it through a ceramic membrane with a pore size of 0.1 μm. The obtained filtrate is transferred to a crystallizer, and vacuum distilled at 50°C and 10 kPa. As 3,3,3-trifluoropropionitrile is evaporated, n-hexane is added to the solution to keep the mass in the crystallizer constant. When the viscosity of the solution in the crystallizer reaches 300 centipoise, a crystal form inducer is added to the solution. The crystal form inducer is prepared by mixing 10 kg of flaky lithium bis(fluorosulfonyl)imide with 9.75 kg of n-hexane to form a slurry, and then adding 0.25 kg of 3,3,3-trifluoropropionitrile and stirring for 30 min. The vacuum distillation is continued until the content of 3,3,3-trifluoropropionitrile in the system is less than 0.5%, the crystallization is terminated, and the filter cake is transferred to a vacuum dryer and dried at 0.4 kPa and 50°C for 8 h to obtain low-residue lithium bis(fluorosulfonyl)imide.
[0025] Example 4: Dissolve crude lithium bis(fluorosulfonyl)imide in 2,3,3,3-tetrafluoropropionitrile to obtain 2500 kg of a crude lithium bis(fluorosulfonyl)imide solution having a mass concentration of 60%. Add the crude lithium bis(fluorosulfonyl)imide solution to a pretreatment kettle, introduce high-purity carbon dioxide gas into the pretreatment kettle under stirring to adjust the pH of the system to 5.5, stop aeration, and obtain a mixed solution. Add 12.5 kg of molecular sieve to the obtained mixed solution, stir for 0.5 h, and then pass through a ceramic membrane filter with a pore size of 0.1 μm to obtain to obtain a filtrate; the obtained filtrate is transferred to a crystallizer, and vacuum distillation is performed at 70° C. and 20 kPa. As 2,3,3,3-tetrafluoropropionitrile is evaporated, carbon tetrachloride is added to the solution to keep the mass in the crystallizer constant. When the viscosity of the solution in the crystallizer reaches 300 centipoise, a crystal form inducer is added to the solution; wherein the crystal form inducer is prepared by mixing 12.5 kg of flaky lithium bis(fluorosulfonyl)imide with 12.1875 kg of carbon tetrachloride to form a slurry, and then adding 0.3125 kg of 2,3,3,3-tetrafluoropropionitrile and stirring for 30 minutes; vacuum distillation is continued until the content of 2,3,3,3-tetrafluoropropionitrile in the system is less than 0.5%, crystallization is terminated, filtration is performed, and the obtained filter cake is transferred to a vacuum dryer, and dried at 0.5 kPa and 50° C. for 10 hours to obtain low-residue lithium bis(fluorosulfonyl)imide.
[0026] Example 5: Dissolve crude lithium bis(fluorosulfonyl)imide in fluoroacetonitrile to obtain 3000 kg of a crude lithium bis(fluorosulfonyl)imide solution having a mass concentration of 30%. Add the crude lithium bis(fluorosulfonyl)imide solution to a pretreatment kettle, introduce high-purity carbon dioxide gas into the pretreatment kettle under stirring to adjust the pH of the system to 5, stop aeration, and obtain a mixed solution. Add 150 kg of activated carbon to the obtained mixed solution, stir for 1 hour, and then pass through a ceramic membrane filter with a pore size of 0.1 μm to obtain a filtrate. Transfer the obtained filtrate to a crystallizer, and perform vacuum distillation at 10°C and 0.5 kPa. As the fluoroacetonitrile is evaporated, , and at the same time, dichloromethane is added to the solution to keep the mass in the crystallizer constant. When the viscosity of the solution in the crystallizer reaches 300 centipoise, a crystal form inducer is added to the solution; wherein the crystal form inducer is prepared by mixing 15 kg of flaky lithium bis(fluorosulfonyl)imide with 14.85 kg of dichloromethane to form a slurry, and then adding 0.15 kg of fluoroacetonitrile and stirring for 30 minutes; continuing to distill under reduced pressure until the fluoroacetonitrile content in the system is less than 0.5%, ending the crystallization, filtering, and transferring the obtained filter cake to a vacuum dryer, and drying at 0.1 kPa and 30°C for 2 hours to obtain low-residue lithium bis(fluorosulfonyl)imide.
[0027] The low-residue lithium bis(fluorosulfonyl)imide prepared in Examples 1 to 5 were respectively subjected to solvent residue detection and aqueous solution turbidity detection, and the detection results are shown in Table 1.
[0028] Table 1 Test results of products prepared in Examples 1 to 5 Detection indicators Example 1 Example 2 Example 3 Example 4 Example 5 Fluoronitrile organic solvents / ppm 8.5 16.2 10.1 8.9 15.3 Poor solvent / ppm 15.6 30.1 20.5 17.2 26.8 10% aqueous solution turbidity / NTU 1.1 3.2 2.2 1.5 2.9 It can be seen from the results in Table 1 that in the low residual bis(fluorosulfonyl)imide lithium prepared by the method for preparing low residual bis(fluorosulfonyl)imide lithium of the present invention, the residual fluoronitrile organic solvent is less than 17 ppm, the residual poor solvent is less than 31 ppm, and the turbidity of the aqueous solution is low.
[0029] Although the above describes the specific implementation methods of the present invention, it does not limit the scope of protection of the present invention. Based on the technical solution of the present invention, various modifications or variations that can be made by those skilled in the art without creative work are still within the scope of protection of the present invention.
Claims
1. A method for preparing low-residue lithium bis(fluorosulfonyl)imide, characterized in that: The following steps are involved: 1) dissolving crude lithium bis(fluorosulfonyl)imide in a fluoronitrile organic solvent to obtain a crude lithium bis(fluorosulfonyl)imide solution, adding the obtained crude lithium bis(fluorosulfonyl)imide solution to a pretreatment kettle, introducing high-purity carbon dioxide gas into the pretreatment kettle under stirring to adjust the pH of the system to 5.0-5.5, stopping the aeration to obtain a mixed solution; 2) adding an adsorption filter aid to the mixed solution obtained in step 1), stirring for 0.5 to 1 hour, and then filtering through a precision filter to obtain a filtrate; 3) The filtrate obtained in step 2) is transferred to a crystallizer, and vacuum distilled at 10-70° C. and 0.5-20 kPa. As the fluoronitrile organic solvent is evaporated, a poor solvent is added to the solution to keep the mass in the crystallizer constant. When the viscosity of the solution in the crystallizer reaches 300 centipoise, a crystal form inducing agent is added to the solution; wherein the poor solvent is a benzene, alkane or chlorinated alkane solvent; 4) Continue to distill under reduced pressure until the content of fluoronitrile organic solvent in the system is less than 0.5%, end the crystallization, filter, transfer the obtained filter cake to a vacuum dryer, and dry to obtain low-residue lithium bis(fluorosulfonyl)imide.
2. The method for preparing low-residue lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The fluoronitrile organic solvent in step 1) is fluoroacetonitrile, difluoroacetonitrile, 3,3,3-trifluoropropionitrile or 2,3,3,3-tetrafluoropropionitrile.
3. The method for preparing low-residue lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The mass concentration of the crude lithium bis(fluorosulfonyl)imide solution in step 1) is 30-60%, and the water content is less than 3000 ppm.
4. The method for preparing low-residue lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The adsorption filter aid in step 2) is molecular sieve, activated carbon or activated clay; the added amount is 0.1-5% of the mass of the mixed solution.
5. The method for preparing low-residue lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The precision filter described in step 2) is a filtering device with a filtering accuracy of <0.1um.
6. The method for preparing low-residue lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The poor solvent in step 3) is chlorobenzene, dichlorobenzene, n-hexane, dichloromethane or tetrachloroethane.
7. The method for preparing low-residue lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The crystal form inducing agent in step 3) is prepared by mixing lithium bis(fluorosulfonyl)imide and a poor solvent into a slurry, adding a fluoronitrile organic solvent, and stirring for 30 minutes; wherein the mass ratio of lithium bis(fluorosulfonyl)imide, fluoronitrile organic solvent and poor solvent is 100:1~5:95~99, and the total mass of the fluoronitrile organic solvent and the poor solvent is the same as the mass of lithium bis(fluorosulfonyl)imide; the microscopic morphology of the lithium bis(fluorosulfonyl)imide is a thin flaky hexagonal crystal; the amount of the crystal form inducing agent added is 0.1~5% of the mass of the solution in the crystallizer.
8. The method for preparing low-residue lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The drying parameters of the vacuum dryer in step 4) are drying at 0.1-0.5 kPa and 30-50° C. for 2-10 hours.
9. The method for preparing low-residue lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: In step 2), the adsorption filter aid is a molecular sieve; the added amount is 0.5-2% of the mass of the mixed solution; and the precision filter is a two-stage series ceramic membrane filtration device.
10. The method for preparing low-residue lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The amount of the crystal form inducing agent added in step 3) is 0.5-2% of the mass of the solution in the crystallizer.