Preparation method of high-purity lithium fluoride and bis (trifluoromethanesulfonyl) lithium imide

Abstract

The invention provides a preparation method of high-purity lithium fluoride and bis (trifluoromethanesulfonyl) lithium imide, which comprises the following steps: S1, dissolving solid lithium carbonate in ultrapure water, introducing carbon dioxide into the ultrapure water, and fully reacting; filtering to obtain a pure lithium bicarbonate solution; s2, in a stirring state, dropwise adding water-containing hydrofluoric acid into the aqueous solution in the step S1 for reaction to obtain lithium fluoride, continuously stirring for 2-3 hours, and standing for 4-8 hours; and S3, filtering the lithium fluoride precipitate in the step S2, separating out a lithium fluoride solid, and finally drying to obtain the high-purity lithium fluoride. S4, enabling trifluoromethylsulfonyl fluoride, ammonia gas and lithium fluoride to react in an organic solvent through a stirring device, and directly filtering after the reaction is finished; and S5, distilling the filtrate under a stirring condition, and removing the organic solvent to obtain bis (trifluoromethanesulfonyl) lithium imide. According to the method, the quality of the lithium fluoride is ensured, and the bis (trifluoromethanesulfonyl) imide lithium product prepared from the lithium fluoride is high in purity and high in yield.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery electrolyte salt preparation, and in particular to a preparation method of high-purity lithium fluoride and lithium bis(trifluoromethanesulfonyl)imide. Background Art

[0002] As the national new energy industry chain ushers in rapid development, especially the new energy vehicle industry, it is inseparable from high-performance power batteries and the electrolyte salts in the batteries.

[0003] Lithium-ion batteries are the most representative of power batteries. The electrolyte salts related to lithium-ion batteries are key materials that determine the excellent performance of batteries. Currently known electrolyte lithium salts include lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalatoborate, lithium bis(oxalatoborate), lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, etc. Among the many electrolyte salts, lithium bis(trifluoromethanesulfonyl)imide has good comprehensive properties, including electrochemical stability, high conductivity and high and low temperature performance.

[0004] Currently known methods for synthesizing lithium bis(trifluoromethanesulfonyl)imide include the following three methods:

[0005] (1) Bis(trifluoromethanesulfonyl)imidic acid reacts with lithium carbonate to generate lithium bis(trifluoromethanesulfonyl)imide. The cost of the imidic acid used in this method is relatively high. At the same time, if the imidic acid remains during the reaction process and cannot be discharged in time during the solution drying process, the product will change color and the pH, color, turbidity and other indicators will be unqualified.

[0006] (2) Bis(trifluoromethanesulfonyl)imidic acid reacts with lithium hydroxide to generate lithium bis(trifluoromethanesulfonyl)imide. This method produces a large amount of by-product water, which makes it difficult to remove the water and increases the process cost.

[0007] (3) CN116425128A discloses a method for preparing anhydrous lithium bis(trifluoromethanesulfonyl)imide, wherein an organic base salt or an inorganic base salt of bis(trifluoromethanesulfonyl)imide is subjected to a double decomposition reaction with a lithium reagent to generate lithium bis(trifluoromethanesulfonyl)imide; however, since the double decomposition reaction cannot be completely converted, a certain amount of bis(trifluoromethanesulfonyl)imide salt which is difficult to separate will remain, resulting in a low yield and purity of the final product. Summary of the invention

[0008] The purpose of the present invention is to solve the shortcomings of the prior art, such as high cost, low yield and purity of the final product, and to propose a method for preparing high-purity lithium fluoride and lithium bis(trifluoromethanesulfonyl)imide.

[0009] The technical solution of the present invention:

[0010] A method for preparing high-purity lithium fluoride and lithium bis(trifluoromethanesulfonyl)imide prepared therefrom, comprising the following steps:

[0011] S1, dissolving solid lithium carbonate in ultrapure water, introducing carbon dioxide into the water for reaction, stirring to allow the water to react fully; then filtering to obtain a pure lithium bicarbonate solution;

[0012] S2. Under stirring, add aqueous hydrofluoric acid to the lithium bicarbonate solution described in step S1 to react to obtain lithium fluoride, continue stirring for 2 to 3 hours, and let stand for 4 to 8 hours;

[0013] S3, filtering the lithium fluoride precipitate in step S2, separating the lithium fluoride solid, and finally drying the lithium fluoride solid to obtain high-purity lithium fluoride.

[0014] Preferably, the purity of the solid lithium carbonate in S1 is greater than or equal to 95%, the concentration of lithium carbonate dissolved in ultrapure water is controlled between 10% and 30% by weight, and the speed of carbon dioxide introduction is 30 to 50 Nm 3 / h, reaction temperature is 25-40°C, reaction time is 1.5-3.5h, and stirring speed is maintained at 10-100Hz.

[0015] Preferably, the mass percentage of aqueous hydrofluoric acid in S2 is 30% to 40%, the reaction temperature is 40 to 60° C., the reaction is carried out at a molar ratio of lithium bicarbonate to hydrogen fluoride of 1.0:1.0 to 1.5, the reaction time is 1.5 to 3.5 hours, and the synthesis endpoint pH is controlled at 2 to 3.

[0016] Preferably, the drying temperature in S3 is controlled at 150-200° C., the drying time is controlled at 24-36 hours, and the moisture content of the high-purity lithium fluoride is controlled below 100 ppm.

[0017] A method for preparing lithium bis(trifluoromethanesulfonyl)imide comprises the following steps:

[0018] S4, trifluoromethylsulfonyl fluoride, ammonia and high-purity lithium fluoride are stirred in an organic solvent by a stirring device for reaction, and filtered directly after the reaction is completed;

[0019] The present invention prepares high-purity lithium fluoride by direct synthesis, and then uses the synthesized high-purity lithium fluoride to prepare lithium bis(trifluoromethanesulfonyl)imide by a one-step reaction, and the reaction equation is as follows:

[0020]

[0021] In step S4, the trifluoromethylsulfonyl fluoride, ammonia and lithium fluoride react in one step to obtain the target product, lithium bis(trifluoromethylsulfonyl)imide / organic solvent solution, and generate LiHF2 at the same time. LiHF2 is poorly soluble in organic solvents, and a simple solid-liquid separation can be used later;

[0022] The reaction process is simple, the reaction efficiency is high, and the time required is short. By using synthesized high-purity lithium fluoride as a raw material, the time cost and raw material cost of preparing lithium bis(trifluoromethanesulfonyl)imide are significantly reduced.

[0023] S5. The filtrate is heated and distilled under stirring conditions, and the organic solvent is collected to obtain lithium bis(trifluoromethanesulfonyl)imide.

[0024] In step S5, the lithium bis(trifluoromethanesulfonyl)imide / organic solvent solution is subjected to simple distillation to discharge the organic solvent in the form of gas, and lithium bis(trifluoromethanesulfonyl)imide powder is obtained at the same time, which reduces the subsequent water removal process and simplifies the process route.

[0025] Preferably, the organic solvent in step S4 is one of acetonitrile, dichloromethane, 1,1-dichloroethylene, 1,2-dichloroethylene, 1,1,1-trichloroethylene, 1,1,2-trichloroethylene, 1,1,1,2-tetrachloroethylene and 1,1,2,2-tetrachloroethylene; the amount of the organic solvent is 1 to 3 times the theoretical yield mass of lithium bis(trifluoromethanesulfonyl)imide; preferably 2 times.

[0026] The molar ratio of trifluoromethylsulfonyl fluoride, ammonia and high-purity lithium fluoride is (2-3):1:(4-6), preferably 2:1:4, 3:1:4, 3:1:4, 3:1:4, 3:1:6, 3:1:6. Preferably, lithium fluoride is appropriately excessive to allow trifluoromethylsulfonyl fluoride and ammonia to react completely, and lithium fluoride and LiHF2 are subsequently removed by filtration to improve the purity of the product.

[0027] Preferably, the stirring device comprises a stirring rod, the bottom of which is provided with two radial impellers of the same shape as the bottom of the reaction container at 90 degrees to each other, and the middle of the stirring rod is provided with multi-layer axial impellers. Preferably, there are four groups of multi-layer axial impellers, so that the material is continuously lifted upward and rotated.

[0028] The stirring device uses two radial impellers that are 90 degrees apart and have a shape that is completely similar or identical to the bottom of the container. The lowest point of the impeller is only 15 to 25 mm from the bottom of the container. After the stirring is turned on, the bottom materials can be continuously rotated and raised, which is conducive to full contact between the materials, promotes the reaction, and improves the reaction yield. Since the stirring diameter is close to the container diameter, the wall sticking phenomenon is prevented, and the materials at the bottom of the container are easier to rise, making the reaction more complete and improving the product yield.

[0029] A downward-flowing multi-layer axial impeller is arranged below the liquid level in the center of the container and in the middle of the tank liquid level, so that the material in the center of the container flows downward and reacts with the material at the bottom, which not only accelerates the reaction rate but also improves the reaction yield.

[0030] Preferably, the reaction temperature in step S4 is 0 to 90°C, preferably 5°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 90°C; the reaction time is 1 to 12h, preferably 1h, 3h, 5h, 6h, 7h, 8h; the reaction pressure is 0.01 to 1.0MPa, preferably 0.01MPa, 0.06MPa, 0.08MPa, 0.1MPa, 0.5MPa, 0.6MPa, 0.7MPa, 0.8MPa; and the stirring speed is 10 to 100Hz, preferably 20Hz, 30Hz, 40Hz or 80Hz.

[0031] Preferably, the heating temperature of the heating distillation described in step S5 is 60-200°C, preferably 80°C, 100°C, 140°C, 160°C or 180°C; the pressure is -0.01 to -0.1MPa, preferably -0.01MPa, -0.02MPa, -0.03MPa, -0.04MPa, -0.05MPa, -0.06MPa, -0.07MPa, -0.08MPa, -0.09MPa; the stirring speed is 10-100Hz, preferably 30Hz, 40Hz, 50Hz or 80Hz.

[0032] Preferably, the stirring speed in step S4 is 20 to 50 Hz;

[0033] Step S5: the stirring speed is 30-50 Hz;

[0034] The organic solvent collected in step S5 is recycled to the reaction in step S4.

[0035] The beneficial effects of the present invention are:

[0036] The invention prepares high-purity lithium fluoride by a direct synthesis method, and uses the prepared high-purity lithium fluoride as a raw material to prepare lithium bis(trifluoromethanesulfonyl)imide by a one-step method, using trifluoromethanesulfonyl fluoride, ammonia and lithium fluoride as raw materials, and lithium fluoride is excessive in the reaction process, which is conducive to the complete reaction of trifluoromethanesulfonyl fluoride and ammonia; the reaction process adopts a stirring device, and the radial flow of the combined impeller and the axial flow upward along the four walls and downward in the center of the container and the organized flow of the feed liquid in the entire container are ensured, so that the uniformity of the material in the reaction container is improved.

[0037] At the same time, the presence of the organic solvent makes the product soluble in the organic solvent while the byproduct LiHF2 and excess lithium fluoride exist in solid form, and good separation of the byproduct and the product can be achieved by filtration. The organic solvent can be removed by subsequent simple evaporation and concentration, and can be recycled.

[0038] The preparation method of the invention is simple and highly operable, the prepared lithium bis(trifluoromethanesulfonyl)imide has high purity and yield, is easy to mass produce, and has low safety risk. The obtained product can meet the electrolyte salt requirements of lithium ion batteries and has good market demand and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the structure of the stirring device of the present invention.

[0040] Figure 2 It is a schematic diagram of the axial impeller structure of the present invention.

[0041] In the accompanying drawings, 1- stirring rod, 2- radial impeller, 3- axial impeller. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0043] like Figure 1-2 As shown, the stirring device used in the embodiment of the present invention includes a stirring rod 1, at the bottom of which are arranged two radial impellers 2 with an angle of 90 degrees to each other and the same shape as the bottom of the reaction container, and in the middle of which are arranged multiple layers of axial impellers 3.

[0044] Example 1

[0045] Add 100 g of high-purity lithium carbonate (purity: 99.5%) and 1000 g of high-purity water into the reactor, stir at 50 Hz and 30 Nm 3 / h of gas flow into carbon dioxide for carbonization reaction, the reactor is controlled to react at 30°C for 1.5h, and then filtered to obtain a pure lithium bicarbonate solution.

[0046] Aqueous hydrofluoric acid (40%) was added dropwise to the pure lithium carbonate solution at a rate of 100 L / h. The reaction temperature was controlled at 45°C for 2 h and the end point pH was controlled at 2.7 to obtain lithium fluoride slurry, which was then filtered to obtain high-purity lithium fluoride ointment.

[0047] The high-purity lithium fluoride paste enters the belt vacuum dryer, the drying temperature is 160℃, the drying time is 30h, and the water content of lithium fluoride is controlled at 95ppm. The dried high-purity lithium fluoride is put into the synthesis high-pressure reactor through screw conveyor.

[0048] Trifluoromethylsulfonyl fluoride, ammonia, lithium fluoride and 1,1,2,2-tetrachloroethylene were added to a closed high-pressure reactor at a molar ratio of 2:1:4:1.8, and reacted for 12 hours at 0°C, 0.01MPa and 10Hz using a combined stirring device. The obtained product was filtered to remove solid impurities. The obtained filtrate was then transferred to a drying kettle and dried at 60°C, -0.01MPa and 10Hz. After reduced pressure drying, lithium bis(trifluoromethanesulfonyl)imide was obtained with a yield of 79.4%, a content of 99.6%, a chromaticity of 5 Hazen, chloride ions of 8.5ppm, fluoride ions of 18ppm, SO4 2- ions 8.2ppm.

[0049] Example 2

[0050] Add 200g of high-purity lithium carbonate (purity: 99.5%) and 1000g of high-purity water into the reactor, stir at 60Hz and 40Nm 3 / h of gas flow into carbon dioxide for carbonization reaction, the reactor is controlled to react at 30°C for 2.0h, and then filtered to obtain a pure lithium bicarbonate solution.

[0051] Aqueous hydrofluoric acid (40%) was added dropwise to the pure lithium carbonate solution at a rate of 100 L / h. The reaction temperature was controlled at 45°C for 2 h and the end point pH was controlled at 2.8 to obtain lithium fluoride slurry, which was then filtered to obtain high-purity lithium fluoride ointment.

[0052] The high-purity lithium fluoride paste enters the belt vacuum dryer, the drying temperature is 160℃, the drying time is 30h, and the water content of lithium fluoride is controlled at 95ppm. The dried high-purity lithium fluoride is put into the synthesis high-pressure reactor through screw conveyor.

[0053] Trifluoromethylsulfonyl fluoride, ammonia, lithium fluoride and 1,1,2,2-tetrachloroethylene were added to a closed high-pressure reactor in a molar ratio of 3:1:6:5.4, and reacted for 3 hours at 90°C, 1.0MPa and 100Hz using a combined stirring device. The obtained product was filtered to remove solid impurities. The obtained filtrate was then transferred to a drying kettle and dried at 200°C, -0.1MPa and 100Hz. After reduced pressure drying, lithium bis(trifluoromethanesulfonyl)imide was obtained with a yield of 80.4%, a content of 99.7%, a chromaticity of 10 Hazen, a chloride ion of 5.5ppm, a fluoride ion of 20ppm, and SO4 2- ions 4.2ppm.

[0054] Example 3

[0055] Add 100 g of high-purity lithium carbonate (purity: 99.5%) and 1000 g of high-purity water into the reactor, stir at 50 Hz and 30 Nm3 / h of gas flow into carbon dioxide for carbonization reaction, the reactor is controlled to react at 30°C for 3.0h, and then filtered to obtain a pure lithium bicarbonate solution.

[0056] Aqueous hydrofluoric acid (40%) was added dropwise to the pure lithium carbonate solution at a rate of 200 L / h. The reaction temperature was controlled at 50°C for 2 h and the end point pH was controlled at 3.0 to obtain lithium fluoride slurry, which was then filtered to obtain high-purity lithium fluoride ointment.

[0057] The high-purity lithium fluoride paste enters the belt vacuum dryer, the drying temperature is 160℃, the drying time is 30h, and the water content of lithium fluoride is controlled at 95ppm. The dried high-purity lithium fluoride is put into the synthesis high-pressure reactor through screw conveyor.

[0058] Trifluoromethylsulfonyl fluoride, ammonia, lithium fluoride and 1,1,2,2-tetrachloroethylene were added to a closed high-pressure reactor in a molar ratio of 2.3:1:5:3.7, and reacted for 4 hours at 50°C, 0.4MPa and 25Hz using a combined stirring device, and the obtained product was filtered to remove solid impurities. The obtained filtrate was then transferred to a drying kettle and dried at 150°C, -0.05MPa and 35Hz. After reduced pressure drying, lithium bis(trifluoromethanesulfonyl)imide was obtained with a yield of 87.2%, a content of 99.8%, a chromaticity of 5Hazen, a chloride ion of 2.2ppm, a fluoride ion of 13ppm, and SO4 2- ions 2.2ppm.

[0059] Example 4

[0060] Add 300g of high-purity lithium carbonate (purity: 99.5%) and 2500g of high-purity water into the reactor, stir at 80Hz and 30Nm 3 / h of gas flow into carbon dioxide for carbonization reaction, the reactor is controlled to react at 30°C for 1.5h, and then filtered to obtain a pure lithium bicarbonate solution.

[0061] Aqueous hydrofluoric acid (40%) was added dropwise to the pure lithium carbonate solution at a rate of 100 L / h. The reaction temperature was controlled at 45°C for 2 h and the end point pH was controlled at 2.7 to obtain lithium fluoride slurry, which was then filtered to obtain high-purity lithium fluoride ointment.

[0062] The high-purity lithium fluoride paste enters the belt vacuum dryer, the drying temperature is 160℃, the drying time is 35h, and the water content of lithium fluoride is controlled to 85ppm. The dried high-purity lithium fluoride is put into the synthesis autoclave through screw conveyor.

[0063] Trifluoromethylsulfonyl fluoride, ammonia, lithium fluoride and 1,1,2,2-tetrachloroethylene were added to a closed high-pressure reactor at a molar ratio of 2.3:1:5:3.8, and reacted for 6 hours at 60°C, 0.4MPa and 25Hz using a combined stirring device. The obtained product was filtered to remove solid impurities. The obtained filtrate was then transferred to a drying kettle and dried at 160°C, -0.09MPa and 40Hz. After reduced pressure drying, lithium bis(trifluoromethanesulfonyl)imide was obtained with a yield of 89.1%, a content of 99.9%, a chromaticity of 5Hazen, a chloride ion of 0.8ppm, a fluoride ion of 12ppm, and SO4 2- ions 1.8ppm.

[0064] Example 5

[0065] Add 100 g of high-purity lithium carbonate (purity: 99.5%) and 1000 g of high-purity water into the reactor, stir at 50 Hz and 30 Nm 3 / h of gas flow into carbon dioxide for carbonization reaction, the reactor is controlled to react at 30°C for 1.5h, and then filtered to obtain a pure lithium bicarbonate solution.

[0066] Aqueous hydrofluoric acid (40%) was added dropwise to the pure lithium carbonate solution at a rate of 100 L / h. The reaction temperature was controlled at 45°C for 2 h and the end point pH was controlled at 2.7 to obtain lithium fluoride slurry, which was then filtered to obtain high-purity lithium fluoride ointment.

[0067] The high-purity lithium fluoride paste enters the belt vacuum dryer, the drying temperature is 160℃, the drying time is 30h, and the water content of lithium fluoride is controlled at 95ppm. The dried high-purity lithium fluoride is put into the synthesis high-pressure reactor through screw conveyor.

[0068] Trifluoromethylsulfonyl fluoride, ammonia, lithium fluoride and acetonitrile were added into a closed high-pressure reactor in a molar ratio of 2.1:1:5.2:15, respectively, and reacted for 6 hours at 40°C, 0.6MPa and 30Hz using a combined stirring device, and then the obtained product was filtered to remove solid impurities. The obtained filtrate was then transferred to a drying kettle, dried at 180°C, -0.09MPa and 40Hz, and lithium bis(trifluoromethanesulfonyl)imide was obtained after reduced pressure drying, with a yield of 87.1%, a content of 99.8%, a chromaticity of 5Hazen, a chloride ion of 1.8ppm, a fluoride ion of 16ppm, and SO4 2- ions 3.5ppm.

[0069] The following is a comparative example to illustrate the advantages of the present invention.

[0070] Comparative Example 1

[0071] Add 300g of high-purity lithium carbonate (purity: 99.5%) and 2500g of high-purity water into the reactor, stir at 80Hz and 30Nm 3 / h of gas flow into carbon dioxide for carbonization reaction, the reactor is controlled to react at 30°C for 1.5h, and then filtered to obtain a pure lithium bicarbonate solution.

[0072] Aqueous hydrofluoric acid (40%) was added dropwise to the pure lithium carbonate solution at a rate of 100 L / h. The reaction temperature was controlled at 45°C for 2 h and the end point pH was controlled at 2.7 to obtain lithium fluoride slurry, which was then filtered to obtain high-purity lithium fluoride ointment.

[0073] The high-purity lithium fluoride paste enters the belt vacuum dryer, the drying temperature is 160℃, the drying time is 35h, and the water content of lithium fluoride is controlled to 85ppm. The dried high-purity lithium fluoride is put into the synthesis autoclave through screw conveyor.

[0074] Trifluoromethylsulfonyl fluoride, ammonia, lithium fluoride and 1,1,2,2-tetrachloroethylene were added to a closed high-pressure reactor in a molar ratio of 2.3:1:5:3.8, and reacted for 6 hours at 60°C, 0.4MPa and 25Hz using a frame stirring device, and the obtained product was filtered to remove solid impurities. The obtained filtrate was then transferred to a drying kettle and dried at 160°C, -0.09MPa and 40Hz. After reduced pressure drying, lithium bis(trifluoromethanesulfonyl)imide was obtained with a yield of 76.1%, a content of 98.9%, a chromaticity of 5Hazen, a chloride ion of 10ppm, a fluoride ion of 400ppm, and SO4 2- Ions 18ppm.

[0075] Comparative Example 2

[0076] Add 100 g of high-purity lithium carbonate (purity: 99.5%) and 1000 g of high-purity water into the reactor, stir at 50 Hz, introduce carbon dioxide at a gas flow of 30 Nm3 / h for carbonization reaction, control the reactor to react at 30°C for 3.0 h, and then filter to obtain a pure lithium bicarbonate solution.

[0077] Aqueous hydrofluoric acid (40%) was added dropwise to the pure lithium carbonate solution at a rate of 200 L / h. The reaction temperature was controlled at 50°C for 2 h and the end point pH was controlled at 3.0 to obtain lithium fluoride slurry, which was then filtered to obtain high-purity lithium fluoride ointment.

[0078] The high-purity lithium fluoride paste enters the belt vacuum dryer, the drying temperature is 160℃, the drying time is 30h, and the water content of lithium fluoride is controlled at 95ppm. The dried high-purity lithium fluoride is put into the synthesis high-pressure reactor through screw conveyor.

[0079] Trifluoromethylsulfonyl fluoride, ammonia, and lithium fluoride were added to a closed high-pressure reactor at a molar ratio of 2.3:1:5, and reacted for 6 hours at 60°C, 0.4MPa, and 25Hz using a combined stirring device. The obtained product was dissolved in a certain amount of 1,1,2,2-tetrachloroethylene solvent, and then filtered to remove solid impurities. The obtained filtrate was then transferred to a drying kettle and dried at 160°C, -0.09MPa, and 40Hz. After reduced pressure drying, lithium bis(trifluoromethanesulfonyl)imide was obtained with a yield of 75.2%, a content of 98.7%, a chromaticity of 5Hazen, a chloride ion of 5.2ppm, a fluoride ion of 50ppm, and SO4 2- ions 8.2ppm.

[0080] According to the comparison between the above embodiment and the comparative example, it can be seen that the lithium bis(trifluoromethanesulfonyl)imide product obtained in the embodiment of the present invention has high yield and high purity, and the residual impurities (especially chloride ions and sulfate ions) of the product are relatively low.

[0081] The present invention has been described above by way of the above-mentioned embodiments to illustrate the method for preparing lithium bis(trifluoromethanesulfonyl)imide of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field within the technical scope disclosed by the present invention can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing high-purity lithium fluoride, characterized in that: The following steps are involved: S1, dissolving solid lithium carbonate in ultrapure water, introducing carbon dioxide into the water for reaction, stirring to allow the water to react fully; then filtering to obtain a pure lithium bicarbonate solution; S2. Under stirring, add aqueous hydrofluoric acid to the lithium bicarbonate solution described in step S1 to react to obtain lithium fluoride, continue stirring for 2 to 3 hours, and let stand for 4 to 8 hours; S3, filtering the lithium fluoride precipitate in step S2, separating the lithium fluoride solid, and finally drying the lithium fluoride solid to obtain high-purity lithium fluoride.

2. A method for preparing high-purity lithium fluoride according to claim 1, characterized in that: The purity of the solid lithium carbonate in S1 is greater than or equal to 95%, the lithium carbonate is dissolved in ultrapure water and the concentration is controlled between 10% and 30% by weight, and the speed of carbon dioxide introduction is 30 to 50 Nm 3 / h, reaction temperature is 25-40°C, reaction time is 1.5-3.5h, and stirring speed is maintained at 10-100Hz.

3. A method for preparing high-purity lithium fluoride according to claim 1, characterized in that: The mass percentage of aqueous hydrofluoric acid in the S2 is 30% to 40%, the reaction temperature is 40 to 60° C., the reaction is carried out at a molar ratio of lithium bicarbonate to hydrogen fluoride of 1.0:1.0 to 1.5, the reaction time is 1.5 to 3.5 hours, and the synthesis endpoint pH is controlled at 2 to 3.

4. A method for preparing high-purity lithium fluoride according to claim 1, characterized in that: In S3, the drying temperature is controlled at 150-200° C., the drying time is controlled at 24-36 hours, and the moisture content of the high-purity lithium fluoride is controlled below 100 ppm.

5. A method for preparing lithium bis(trifluoromethanesulfonyl)imide, wherein the high-purity lithium fluoride prepared by the method for preparing high-purity lithium fluoride according to any one of claims 1 to 4 is prepared, characterized in that: The following steps are involved: S4, trifluoromethylsulfonyl fluoride, ammonia and high-purity lithium fluoride are stirred in an organic solvent by a stirring device for reaction, and filtered directly after the reaction is completed; S5. The filtrate is heated and distilled under stirring conditions, and the organic solvent is collected to obtain lithium bis(trifluoromethanesulfonyl)imide.

6. The method for preparing lithium bis(trifluoromethanesulfonyl)imide according to claim 5, characterized in that: The organic solvent in step S4 is one of acetonitrile, dichloromethane, 1,1-dichloroethylene, 1,2-dichloroethylene, 1,1,1-trichloroethylene, 1,1,2-trichloroethylene, 1,1,1,2-tetrachloroethylene and 1,1,2,2-tetrachloroethylene; the amount of the organic solvent is 1 to 3 times the theoretical yield mass of lithium bis(trifluoromethanesulfonyl)imide; The molar ratio of trifluoromethylsulfonyl fluoride, ammonia gas and high-purity lithium fluoride is (2-3):1:(4-6).

7. The method for preparing lithium bis(trifluoromethanesulfonyl)imide according to claim 5, characterized in that: The stirring device comprises a stirring rod (1), the bottom of which is provided with two radial impellers (2) which are 90 degrees apart and have the same shape as the bottom of the reaction container, and the middle of which is provided with a multi-layer axial impeller (3).

8. The method for preparing lithium bis(trifluoromethanesulfonyl)imide according to claim 5, characterized in that: The reaction temperature in step S4 is 0-90° C., the reaction time is 1-12 h, the reaction pressure is 0.01-1.0 MPa, and the stirring speed is 10-100 Hz.

9. The method for preparing lithium bis(trifluoromethanesulfonyl)imide according to claim 8, characterized in that: The heating temperature of the heating distillation described in step S5 is 60 to 200° C., the pressure is -0.01 to -0.1 MPa, and the stirring speed is 10 to 100 Hz.

10. The method for preparing lithium bis(trifluoromethanesulfonyl)imide according to claim 9, characterized in that: Step S4: the stirring speed is 20-50 Hz; Step S5: the stirring speed is 30-50 Hz; The organic solvent collected in step S5 is recycled to the reaction in step S4.

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