Preparation method for lithium bisfluorosulfonylimide

Abstract

The present invention relates to the field of organic chemistry, and in particular relates to a preparation method for lithium bisfluorosulfonylimide. The preparation method comprises: reacting bisfluorosulfonylimide with lithium carbonate in a mixed organic solvent, and performing a post-treatment to obtain lithium bisfluorosulfonylimide. In the synthesis route of the present application, the reaction process stays at the stage of lithium bicarbonate, such that the reaction system contains very little water, and the resulting lithium bicarbonate is extremely easily recovered. Moreover, the process method of the present application is simple, and lithium bisfluorosulfonylimide with a high yield and a high quality can be prepared.

Description

A preparation method of lithium bis(fluorosulfonyl)imide salt Technical Field

[0001] The present invention relates to the field of organic chemistry, and in particular to a method for preparing a lithium salt of bis(fluorosulfonyl)imide. Background Art

[0002] Lithium-ion batteries are an important type of secondary battery, widely used in all aspects of modern production and life, due to their high operating voltage, small size, light weight, high energy, no memory effect, no pollution, low self-discharge, and long cycle life. Compared with the traditional electrolyte salt LiPF6, lithium bis(fluorosulfonyl)imide (LiFSI) has better conductivity, higher electrochemical and thermal stability, and higher resistance to hydrolysis. The addition of LiFSI can significantly increase the battery's charge and discharge cycles, and maintain the stability of highly active electrode materials such as high-nickel positive electrodes and high-voltage positive electrodes, thereby extending battery life. It also improves the flame retardancy of the electrolyte and enhances safety.

[0003] Most of the synthesis methods of LiFSI are to first synthesize bis(chlorosulfonyl)imide (HClSI), then react with MFn (M is an element of group 11-15, period 4-6) to prepare the corresponding metal or organic base bis(fluorosulfonyl)imide salt intermediate, and then react with LiOH, Li2CO3 for cation exchange reaction to obtain LiFSI (US2013331609, US2012041233, EP2415757, US2011034716). The disadvantage of these methods is that it is difficult to complete the exchange reaction after reaching an equilibrium, and the unreacted intermediate MSFI (M refers to metal cation, organic base cation) is difficult to completely separate from LiSFI to obtain high-quality products.

[0004] LiFSI is prepared by metal exchange between purified potassium bis(fluorosulfonyl)imide (KFSI) and lithium salts such as LiClO4, LiBF4, lithium bis(oxalatoborate), and LiPF6. However, the potassium ion content in the product is often very high, which affects its practical application. In particular, both LiClO4 and the generated KClO4 have a certain explosion risk (Electrochimical Acta, 2012, 66, PP.320-324, Polyhedron, 2006, 25, PP.1292-1298, CN101747242, CN101747243, CN101654229, CN105523970, CN103910346, CN104495767).

[0005] US8377406 discloses a method for preparing LiFSI by directly reacting bis(fluorosulfonyl)imide (HFSI) with lithium carbonate in an aqueous solution. However, this method also has obvious shortcomings. HFSI releases heat violently when dissolved in water, leading to HFSI decomposition. This patent uses a method of preparing an HFSI aqueous solution at ultra-low temperature (-78°C) to solve the technical problem of violent heat release when HFSI dissolves in water. However, this method increases energy consumption significantly. More importantly, LiFSI has very good water solubility and very low extraction efficiency, making it unsuitable for industrial production.

[0006] CN 104925765B also discloses the preparation of bis(fluorosulfonyl)imide (HFSI) with lithium carbonate in an organic solvent. However, this process produces water, and the product LiFSI is easily hydrolyzed in water. Therefore, SOCl2 is used to remove it, which also produces acidic waste gases such as SO2 and HCl, resulting in high waste treatment costs. Therefore, the present invention aims to provide a new method for preparing bis(fluorosulfonyl)imide lithium salt, which is simple and environmentally friendly and improves the yield and quality of bis(fluorosulfonyl)imide lithium salt.

[0007] Summary of the Invention

[0008] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a method for preparing lithium bis(fluorosulfonyl)imide, which has a simple process and can prepare lithium bis(fluorosulfonyl)imide with high yield and high quality.

[0009] To achieve the above-mentioned and other related purposes, the present invention provides a method for preparing a lithium salt of bisfluorosulfonyl imide, wherein the preparation method comprises reacting bisfluorosulfonyl imide with lithium carbonate in a mixed organic solvent, and obtaining the lithium salt of bisfluorosulfonyl imide through post-treatment, wherein the polarity of each single solvent in the mixed organic solvent is different;

[0010] The reaction equation is as follows:

[0011] In some feasible embodiments, the mixed organic solvent is a combination of solvent A and solvent B, wherein solvent A and solvent B have different polarities.

[0012] In some feasible embodiments, the molar ratio of lithium carbonate to bis(fluorosulfonyl)imide is 0.5:1 to 20:1.

[0013] In some feasible embodiments, the mass ratio of the mixed organic solvent to bis(fluorosulfonyl)imide is 0.1:1 to 20:1.

[0014] In some feasible embodiments, the reaction temperature of the reaction is -70°C to 50°C.

[0015] In some feasible embodiments, the specific reaction process is: adding bis(fluorosulfonyl)imide dropwise to a mixed organic solvent system of lithium carbonate.

[0016] In some feasible embodiments, the post-treatment includes the following steps: 1) filtering the reaction system after the reaction to obtain a filtrate; 2) adding a desiccant to the filtrate for drying; 3) after drying, filtering, concentrating and crystallizing to obtain bis(fluorosulfonyl)imide lithium salt.

[0017] The main benefits of the preparation method of the present invention are: 1) the reaction of bis(fluorosulfonyl)imide with lithium carbonate in a mixed organic solvent to produce lithium bis(fluorosulfonyl)imide and lithium bicarbonate is virtually water-free, resulting in simple post-processing and a high yield and quality of the obtained lithium bis(fluorosulfonyl)imide. 2) The lithium bicarbonate produced by the reaction can be recovered and reused through a simple process. DETAILED DESCRIPTION

[0018] The inventors of this application have discovered that reacting bis(fluorosulfonyl)imide with lithium carbonate in a mixed organic solvent controls the reaction process to lithium bicarbonate, virtually eliminating the production of water. This has led to an optimized preparation process and the production of high-yield, high-quality bis(fluorosulfonyl)imide. Furthermore, lithium bicarbonate is easily recyclable, providing an environmentally friendly process. This is the basis for the present invention.

[0019] The present invention provides a method for preparing lithium bis(fluorosulfonyl)imide (LiFSI), wherein the preparation method comprises reacting bis(fluorosulfonyl)imide (HFSI) with lithium carbonate (Li2CO3) in a mixed organic solvent, and obtaining the lithium bis(fluorosulfonyl)imide through post-treatment, wherein each single solvent in the mixed organic solvent has a different polarity;

[0020] The reaction equation is as follows:

[0021] Using the above-mentioned synthesis route, there is very little water in the reaction system, and the generated lithium bicarbonate is very easy to recycle. The control of the above-mentioned reaction process can be achieved by selecting a suitable reaction system. In certain embodiments of the present invention, the mixed organic solvent is a combination of solvent A and solvent B, wherein solvent A and solvent B have different polarities. It has been experimentally verified that LiFSI has good solubility in some solvents with higher polarity, but when a single solvent with higher polarity is used, the above-mentioned reaction is more difficult to stop at the LiHCO3 stage. LiHCO3 and HFSI will continue to react to form LiFSI, while producing carbon dioxide and water. The inventors have found that when organic solvents of different polarities are mixed as reaction solvents, the reaction of LiFSI and lithium carbonate will easily stay at the LiHCO3 stage. Of course, the inventors have also tried to use only solvents with lower polarity. LiFSI dissolves poorly in solvents with lower polarity, resulting in LiHCO3 and LiFSI being precipitated as solids together, which cannot be further separated and purified.

[0022] Specifically, solvent A is generally a polar solvent, such as a solvent containing polar groups such as hydroxyl or carboxyl groups. Preferably, solvent A is a polar aprotic solvent. More preferably, solvent A is selected from at least one of a carbonate solvent, a carboxylate solvent, an ether solvent, or a ketone solvent, wherein the C chain in the carbonate solvent, carboxylate solvent, ether solvent, or ketone solvent is selected based on its solubility for the reactants or products. Preferably, the polar organic solvent is selected from at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, methyl formate, ethyl formate, n-propyl formate, isopropyl formate, n-butyl formate, isobutyl formate, tert-butyl formate, methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, tert-butyl propionate, methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate, n-butyl butyrate, isobutyl butyrate, tert-butyl butyrate, methyl isobutyrate, ethyl isobutyrate, n-propyl isobutyrate, isopropyl isobutyrate, n-butyl isobutyrate, isobutyl isobutyrate, or tert-butyl isobutyrate.

[0023] Solvent B is generally selected from at least one of alkanes, cycloalkanes, substituted alkanes (particularly halogenated alkanes), aromatic hydrocarbons, or substituted aromatic hydrocarbons (particularly halogenated aromatic hydrocarbons). More preferably, solvent B is selected from at least one of pentane, hexane, heptane, cyclohexane, methylcyclohexane, dichloromethane (DCM), chloroform, carbon tetrachloride, dichloroethane (DCE), trichloroethane, tetrachloroethane, benzene, toluene, xylene, ethylbenzene, propylbenzene, isopropylbenzene, chlorobenzene, or dichlorobenzene.

[0024] In certain embodiments of the present invention, the molar ratio of lithium carbonate to bis(fluorosulfonyl)imide is 0.5:1 to 20:1. Alternatively, the molar ratio of lithium carbonate to bis(fluorosulfonyl)imide is 0.5:1 to 1:1, 1:1 to 2:1, 2:1 to 8:1, 8:1 to 10:1, 8:1 to 10:1, or 15:1 to 20:1. Considering the economic efficiency of the process and the yield and quality of the product, the molar ratio of lithium carbonate to bis(fluorosulfonyl)imide is preferably 3:1 to 8:1, more preferably 3:1 to 5:1.

[0025] In certain embodiments of the present invention, the mass ratio of the mixed solvent to bis(fluorosulfonyl)imide is 0.1:1 to 20:1. A reasonable mass ratio of the mixed solvent to bis(fluorosulfonyl)imide is selected based on the reaction progress, reaction efficiency, post-treatment efficiency, or product yield and quality.

[0026] Specifically, the mass ratio of solvent B to bis(fluorosulfonyl)imide is 0.5:1 to 10:1, and can be 0.5:1 to 0.8:1, 0.8:1 to 3:1, 3:1 to 8:1, or 8:1 to 10:1. Experiments have shown that maintaining a certain mass ratio of solvent B to bis(fluorosulfonyl)imide allows the reaction to proceed at the lithium bicarbonate stage.

[0027] More specifically, the mass ratio of solvent A to bis(fluorosulfonyl)imide is 0.1:1 to 10:1, and may be 0.5:1 to 1:1, 1:1 to 5:1, or 5:1 to 10:1. A preferred mass ratio of solvent A to bis(fluorosulfonyl)imide is 2:1 to 4:1. Furthermore, the mass ratio of solvent A to solvent B is 1:3 to 1:10, with a preferred mass ratio of 1:4 to 1:7. Experiments have shown that maintaining a certain mass ratio of solvent A to bis(fluorosulfonyl)imide ensures good solubility of the lithium salt of bis(fluorosulfonyl)imide.

[0028] In short, by choosing the right ratio of mixed solvents and reactants, the reaction process can be stopped at lithium bicarbonate. No water is produced in this synthetic route, so there is no need to use a desiccant to remove water during the reaction. This not only simplifies the process but also helps to improve the yield and quality of lithium bis(fluorosulfonyl)imide salt.

[0029] In certain embodiments of the present invention, the reaction temperature of the reaction is -70°C to 50°C, optionally -70°C to -50°C, -50°C to -30°C, -30°C to -15°C, -15°C to 0°C, 0°C to 20°C or 20°C to 50°C. Specifically, HFSI will release heat violently during the process of dissolving in water, and there will inevitably be a little water in the reaction solvent or the synthesis route, so maintaining a certain low temperature can improve the yield and quality of HFSI. Of course, because almost no water is produced in the synthesis route of the present application, the temperature can be controlled at -30°C to 0°C. It is worth noting that the initial temperature of the reaction system needs to be maintained, and the initial temperature is selected from -70°C to -10°C, optionally -70°C to -50°C, -50°C to -20°C or -20°C to -10°C.

[0030] In certain embodiments of the present invention, as described above, in order to avoid the violent exotherm during the dissolution of HFSI, the preferred process is to dropwise add bis(fluorosulfonyl)imide to the mixed organic solvent system of lithium carbonate, and the dropping speed is appropriately adjusted according to the system requirements.

[0031] In certain embodiments of the present invention, the reaction time is 1 to 5 hours. The reaction time can be determined by detecting the consumption of the reactants using common detection methods, and is generally maintained at 2.5 to 3.5 hours.

[0032] In certain embodiments of the present invention, the post-treatment comprises the following steps: 1) filtering the reaction system after the reaction to obtain a filtrate and a filter cake; 2) obtaining bis(fluorosulfonyl)imide lithium salt after filtration, concentration and crystallization.

[0033] Specifically, the reaction solution after the reaction is filtered, and the filtering operation is a conventional filtering method, such as suction filtration or filter press. The filtrate after filtration is concentrated and crystallized to obtain a bis(fluorosulfonyl)imide lithium salt. Specifically, after the filtration is completed, the filtrate is concentrated by means of normal pressure and / or reduced pressure, and after the concentration is completed, a poor solvent is added for crystallization, and the poor solvent is selected from an organic solvent, preferably from alkanes, cycloalkanes, halogenated alkanes, aromatic hydrocarbons, halogenated aromatic hydrocarbons, specifically selected from pentane, hexane, heptane, cyclohexane, methylcyclohexane, dichloromethane, chloroform, carbon tetrachloride, dichloroethane, trichloroethane, tetrachloroethane, benzene, toluene, xylene, ethylbenzene, propylbenzene, isopropylbenzene, chlorobenzene, dichlorobenzene. After the crystallization is completed, solid-liquid separation and drying are performed to obtain a bis(fluorosulfonyl)imide lithium salt.

[0034] In certain embodiments of the present invention, during the reaction, there may be a small amount of water present in the reaction solvent or the air humidity may introduce moisture, and the reaction may produce trace water. Therefore, step 3) is further included between the above steps 1) and 2): a desiccant is added to the filtrate in step 1) for drying, and step 2 is performed after drying. The desiccant is selected from at least one of metallic lithium, butyl lithium, lithium hydride (LiH), calcium hydride (CaH2), lithium sulfate (Li2SO4), lithium bis(fluorosulfonyl)imide (LiFSI), dichlorothionyl, phosgene, diphosgene, triphosgene, oxalyl chloride or silicon tetrachloride (SiCl4). After drying, the reaction solution is filtered again, and the filtration operation is performed by suction filtration and / or filter pressing. The filtrate obtained by this filtration is then concentrated and crystallized in step 2). A desiccant is used to keep the moisture in the filtrate below 50 ppm to ensure the yield and quality of LiFSI. The desiccant is determined based on the moisture content of the filtrate, and the mass ratio of the bis(fluorosulfonyl)imide is generally 0.001 to 0.1:1.

[0035] It is worth noting that the filter cake in step 1) is dried to obtain lithium carbonate, which can be recycled. Specifically, the reaction equation for the thermal dehydration of LiHCO3 to generate Li2CO3 is as follows: 2LiHCO3→Li2CO3+CO2+H2O

[0036] Specifically, the filter cake in step 1) is dried by gradient temperature increase to obtain lithium carbonate, and the drying temperature is 60-120°C. More specifically, the first gradient drying (60-80°C) is dried at 60°C for 5-8h, the second gradient drying (80-110°C) is dried for 1-3h, and the third gradient drying (110-120°C) is dried for 2-5h. LOD < 0.1% is the standard (LOD is loss on drying). Among them, the gradient temperature increase can make the release of CO2 more stable. If the temperature is raised to the highest level at one time, CO2 will be released in large quantities, bringing the risk of overpressure punching.

[0037] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0038] When the embodiments provide numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those generally understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, according to the understanding of the prior art by those skilled in the art and the description of the present invention, any methods, equipment, and materials of the prior art similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention may also be used to implement the present invention.

[0039] Example 1

[0040] To a 5000mL glass reaction flask, add 2250g of DCE and 450g of methyl formate, start stirring, and add 740g of Li2CO3. The system is cooled to -30±5°C, and 452.5g of HFSI is added dropwise to the kettle at this temperature. After addition, continue to maintain the temperature and stir for 3 hours, then filter to obtain 3018g of filtrate with 552ppm of filtrate moisture and 737g of filter cake. 0.5g of LiH is added to the filtrate, and the system is stirred for 2 hours until the moisture content is <50ppm, then filtered. The filtrate is desolventized, 1086g of DCE is added, stirred at room temperature for 1 hour, and filtered. The filter cake is dried to obtain 445.3g of pure LiFSI, with a yield of 95.3%. The quality of the pure LiFSI is evaluated: acid value (HF) 12ppm, chloride ion 2ppm, fluoride ion 8ppm, sulfate <1ppm, sodium 3ppm, potassium 1ppm, and moisture 23ppm. The products meet the indicators specified in the industry standard YS / T 1302-2019.

[0041] The filter cake obtained from the first filtration was 737 g, which was dried at 60° C. for 7 h, 100° C. for 2 h, and 120° C. for 3 h until LOD < 0.1%, and 638 g of lithium carbonate was recovered by dry weight with a content of 98.7%.

[0042] Example 2

[0043] A 5000mL glass reaction bottle was added with 2250g of DCM and 450g of methyl formate, and stirring was started. 630g of recycled Li2CO3 and 110g of fresh Li2CO3 were added. The system was cooled to -25°C and 452.5g of HFSI was added dropwise to the kettle at a temperature of -30±5°C. After the addition, stirring was continued for 3 hours to obtain 3036g of filtrate, 498ppm of filtrate water, and 776g of filter cake. 0.5g of CaH2 was added to the filtrate, and the mixture was stirred for 2 hours until the water content of the system was <50ppm, and then filtered. The filtrate was desolvated under reduced pressure, 1086g of DCE was added, and the mixture was stirred at room temperature for 1 hour and then filtered. The filter cake was dried to obtain 447.0g of pure LiFSI with a yield of 95.7%. The quality of pure LiFSI is evaluated as follows: acid value (HF) 15ppm, chloride ion 3ppm, fluoride ion 7ppm, sulfate <1ppm, sodium 3ppm, potassium 1ppm, and moisture 27ppm. This product meets the specifications specified in the industry standard YS / T 1302-2019.

[0044] The filter cake obtained from the first filtration was 776 g, which was dried at 60° C. for 7 h, 100° C. for 2 h, and 120° C. for 3 h until LOD < 0.1%, and 640 g of lithium carbonate was recovered by dry weight with a content of 98.5%.

[0045] Example 3

[0046] 540g of DCE and 90g of ethyl methyl carbonate were added to a 1000mL glass reaction bottle, stirring was started, 148g of Li2CO3 was added, the system was cooled to -25°C, and 90.5g of HFSI was added dropwise to the kettle at a temperature of -30±5°C. After the addition, the mixture was stirred for 3 hours and filtered to obtain 614g of filtrate, 604ppm of filtrate water, and 142g of filter cake. 2.5g of SOCl2 was added to the filtrate and stirred for 2 hours until the water content of the system was <50ppm. The reaction solution was desolvated under reduced pressure, 216g of DCE was added, stirred at room temperature for 1 hour, and filtered. After drying, the filter cake obtained 89.6g of pure LiFSI with a yield of 95.8%. The quality of the pure LiFSI was evaluated as follows: acid value (HF meter) 35ppm, chloride ion 32ppm, fluoride ion 5ppm, sulfate <1ppm, sodium 2ppm, potassium 2ppm, and water 18ppm. The products meet the indicators specified in the industry standard YS / T 1302-2019.

[0047] Example 4

[0048] To a 1000mL glass reaction flask, add 540g of DCE and 90g of dimethyl carbonate. Stirring was initiated, and 148g of LiCO was added. The system was cooled to -25°C, and at this temperature, 90.5g of HFSI was added dropwise to the kettle. Stirring was continued for 3 hours, followed by filtration to yield 609g of filtrate with 583ppm moisture and 147g of filter cake. 2.5g of SOCl2 was added to the filtrate, and the mixture was stirred for 2 hours until the moisture content was <50ppm. The reaction mixture was degassed under reduced pressure for 1 hour, and then 0.1g of LiH was added (to adjust the acid value and chloride ion content). The mixture was stirred for 2 hours, and then filtered. The filtrate was desolventized, and 216 g of DCE was added, stirred at room temperature for 1 hour, and filtered. The filter cake was dried to yield 90.3 g of pure LiFSI, a 96.6% yield. The acid value (HF) was 9 ppm, chloride ion was 8 ppm, fluoride ion was 3 ppm, sulfate ion was <1 ppm, sodium was 3 ppm, potassium was 1 ppm, and moisture was 13 ppm. This product meets the specifications specified in industry standard YS / T 1302-2019.

[0049] Example 5

[0050] To a 1000mL glass reaction flask, add 540g of DCE and 90g of butyl acetate. Stirring was initiated, and 148g of Li2CO3 was added. The system was cooled to -25°C, and 90.5g of HFSI was added dropwise to the kettle at this temperature. Stirring was continued for 3 hours, followed by filtration to yield 614g of filtrate with 604ppm moisture and 142g of filter cake. 9.5g of Li2SO4 was added to the filtrate, and the mixture was stirred for 2 hours until the moisture content was <50ppm. The filtrate was then filtered. The filtrate was desolventized, and 216g of DCE was added. Stirring was continued at room temperature for 1 hour, followed by filtration. The filter cake was dried to yield 88.4g of pure LiFSI, a 94.5% yield. The acid value (HF) was 22ppm, chloride ion 3ppm, fluoride ion 3ppm, sulfate <1ppm, sodium 4ppm, potassium 2ppm, and moisture 25ppm. This product meets the specifications specified in industry standard YS / T 1302-2019.

[0051] Example 6

[0052] 540 g of DCE and 90 g of dimethyl carbonate were added to a 1000 mL glass reaction bottle, stirred, and 300 g of Li2CO3 was added. The system was cooled to -25°C, and 90.5 g of HFSI was added dropwise to the kettle at this temperature. After the addition, the mixture was stirred for 3 hours and filtered to obtain 662 g of filtrate with a moisture content of 152 ppm and 327 g of filter cake. The filtrate was desolvated under reduced pressure, 216 g of DCE was added, stirred at room temperature for 1 hour, and filtered. The filter cake was dried to obtain 82.5 g of pure LiFSI with a yield of 88.3%. The quality of the pure LiFSI was evaluated as follows: acid value (HF) 12 ppm, chloride ion 1 ppm, fluoride ion 9 ppm, sulfate 5 ppm, sodium 4 ppm, potassium 1 ppm, and moisture 47 ppm. The product meets the indicators specified in the industry standard YS / T 1302-2019.

[0053] Example 7

[0054] 225g of DCE and 45g of methyl acetate were added to a 500mL glass reaction bottle, stirring was started, 111g of Li2CO3 was added, the system was cooled to -25°C, and 45.3g of HFSI was added dropwise to the kettle at this temperature. After the dropwise addition, stirring was continued for 3h and filtered to obtain 296g of filtrate, 257ppm of filtrate water, and 118g of filter cake. 90g of commercially available LiFSI (water ≤ 20ppm) was added to the filtrate and stirred for 1 hour before desolventizing. 330g of DCE was added and stirred at room temperature for 1 hour before filtering. After drying, 133.9g of pure LiFSI was obtained, with a conversion yield of 94.0%, acid value (HF meter) 8ppm, chloride ion 2ppm, fluoride ion 11ppm, sulfate 3ppm, sodium 2ppm, potassium 1ppm, and water 35ppm. LiFSI was added in this embodiment to make the product dissolved in the solvent easy to crystallize. The products meet the indicators specified in the industry standard YS / T 1302-2019.

[0055] Example 8

[0056] 300g of DCE and 45g of methyl acetate were added to a 500mL glass reaction bottle, stirred, and 111g of Li2CO3 was added. The system was cooled to -25°C, and 45.3g of HFSI was added dropwise to the kettle at this temperature. After the addition, the mixture was kept warm and stirred for 3 hours before filtering. The filtrate had a moisture content of 317ppm. 160g of commercially available LiFSI (moisture content ≤ 20ppm) was added to the filtrate and stirred for 1 hour before desolventizing. 500g of DCE was added and stirred at room temperature for 1 hour before filtering. The filter cake was dried to obtain 204.4g of pure LiFSI, with a yield of 95.0%, an acid value (HF meter) of 11ppm, chloride ions of 3ppm, fluoride ions of 7ppm, sulfate ions of 5ppm, sodium 2ppm, potassium 2ppm, and moisture of 26ppm. The product meets the indicators specified in the industry standard YS / T 1302-2019.

[0057] Comparative Example 1

[0058] To a 1000mL glass reaction flask, add 540g of DCE and 90g of dimethyl carbonate. Stirring was initiated, and 148g of Li2CO3 was added. The system was cooled to 0-5°C, and 90.5g of HFSI was added dropwise to the kettle at this temperature. Stirring was continued for 3 hours, followed by filtration to yield 674g of filtrate with a water content of 6600ppm and a 135g filter cake. The filtrate was desolvated under reduced pressure, and 216g of DCE was added. After stirring at room temperature for 1 hour, the system separated into two layers: a clear upper layer of liquid and a viscous lower layer of solid. Filtration was not possible.

[0059] Comparative Example 2

[0060] 540g of DCE and 90g of dimethyl carbonate were added to a 1000mL glass reaction bottle, stirred, and 148g of Li2CO3 was added. The system was cooled to -25°C and 90.5g of HFSI was added dropwise to the kettle at -30±5°C. After the addition, the mixture was stirred for 3 hours and filtered to obtain 600g of filtrate with a moisture content of 562ppm and 143g of filter cake. The filtrate was desolvated under reduced pressure, 216g of DCE was added, stirred at room temperature for 1 hour, and filtered. The filter cake was dried to obtain 87.2g of pure LiFSI with an acid value (HF) of 53ppm, chloride ion 2ppm, fluoride ion 38ppm, sulfate ion 61ppm, sodium 2ppm, potassium 1ppm, and moisture 57ppm. The moisture and sulfate content of the product were unqualified, exceeding the indicators specified in the industry standard YS / T 1302-2019.

[0061] Comparative Example 3

[0062] 450 g of dimethyl carbonate was added to a 1000 mL glass reaction bottle, stirring was started, 148 g of Li2CO3 was added, the system was cooled to -25 ° C, and 90.5 g of HFSI was added dropwise to the kettle at this temperature. After the addition was completed, the mixture was kept warm and stirred for 3 hours and then filtered to obtain 528 g of filtrate, 8210 ppm of filtrate water, and 139 g of filter cake. 34.4 g of SOCl2 was added to the filtrate and stirred for 12 hours until the system water content was <50 ppm. The reaction solution was desolventized, 216 g of DCE was added, stirred at room temperature for 1 hour, and filtered. After drying, the filter cake obtained 87.1 g of pure LiFSI with a yield of 92.2%. The quality of the pure LiFSI was evaluated as having an acid value (HF) of 174 ppm, chloride ion 144 ppm, fluoride ion 57 ppm, sulfate ion 61 ppm, sodium 2 ppm, potassium 2 ppm, and water 24 ppm. It does not meet the indicators specified in the industry standard YS / T 1302-2019.

[0063] The above examples are intended to illustrate the embodiments disclosed herein and are not to be construed as limiting the present invention. In addition, the various modifications listed herein and variations of the methods in the invention will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. Although the present invention has been specifically described in conjunction with various specific preferred embodiments of the present invention, it should be understood that the present invention should not be limited to these specific embodiments. In fact, various modifications apparent to those skilled in the art as described above to obtain the invention should be included within the scope of the present invention.

Claims

1. A method for preparing a lithium salt of bis(fluorosulfonyl)imide, characterized in that: The preparation method comprises reacting bisfluorosulfonyl imide with lithium carbonate in a mixed organic solvent, and obtaining bisfluorosulfonyl imide lithium salt through post-treatment, wherein the polarity of each single solvent in the mixed organic solvent is different; The reaction equation is as follows:

2. The method for preparing bis(fluorosulfonyl)imide lithium salt according to claim 1, characterized in that: Include at least one of the following technical features: a1. The mixed organic solvent is a combination of solvent A and solvent B, wherein solvent A and solvent B have different polarities. a2. The molar ratio of lithium carbonate to bis(fluorosulfonyl)imide is 0.5:1 to 20:1; a3, the mass ratio of the mixed organic solvent to bis(fluorosulfonyl)imide is 0.1:1 to 20:1; a4, the reaction temperature of the reaction is -70°C to 50°C; a5. The reaction time of the reaction is 1 to 5 hours; a6. The specific reaction process is: adding bis(fluorosulfonyl)imide dropwise to a mixed organic solvent system of lithium carbonate; a7. The post-treatment comprises the following steps: 1) filtering the reaction system after the reaction to obtain a filtrate and a filter cake; 2) obtaining bis(fluorosulfonyl)imide lithium salt after filtering, concentrating and crystallizing.

3. The method for preparing bis(fluorosulfonyl)imide lithium salt according to claim 2, characterized in that: It also includes at least one of the following technical features: a11. In the technical features of a1, the solvent A is selected from at least one of carbonate solvents, carboxylate solvents, ether solvents or ketone solvents; the solvent B is selected from at least one of alkanes, cycloalkanes, substituted alkanes, aromatic hydrocarbons or substituted aromatic hydrocarbons; In the technical features a12 and a1, the mass ratio of the solvent A to bis(fluorosulfonyl)imide is 0.1:1 to 10:1; preferably 0.5:1 to 8:1; more preferably 0.8:1 to 3:1; In the technical features a13 and a1, the mass ratio of the B solvent to bis(fluorosulfonyl)imide is 0.5:1 to 10:1; preferably 1:1 to 5:1, and more preferably 2:1 to 4:

1.

4. The method for preparing bis(fluorosulfonyl)imide lithium salt according to claim 3, characterized in that: The A solvent is selected from at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, methyl formate, ethyl formate, n-propyl formate, isopropyl formate, n-butyl formate, isobutyl formate, tert-butyl formate, methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, tert-butyl propionate, methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate, n-butyl butyrate, isobutyl butyrate, tert-butyl butyrate, methyl isobutyrate, ethyl isobutyrate, n-propyl isobutyrate, isopropyl isobutyrate, n-butyl isobutyrate, isobutyl isobutyrate or tert-butyl isobutyrate.

5. The method for preparing bis(fluorosulfonyl)imide lithium salt according to claim 3, characterized in that: The B solvent is selected from at least one of pentane, hexane, heptane, cyclohexane, methylcyclohexane, dichloromethane, chloroform, carbon tetrachloride, dichloroethane, trichloroethane, tetrachloroethane, benzene, toluene, xylene, ethylbenzene, propylbenzene, isopropylbenzene, chlorobenzene or dichlorobenzene.

6. The method for preparing bis(fluorosulfonyl)imide lithium salt according to claim 2, characterized in that: Also includes at least one of the following technical features: In the technical features a21 and a2, the molar ratio of lithium carbonate to bis(fluorosulfonyl)imide is 1:1 to 15:1, preferably 2:1 to 10:

1. In the technical features a41 and a4, the reaction temperature of the reaction is -50 to 20°C; more preferably -30 to 0°C.

7. The method for preparing bis(fluorosulfonyl)imide lithium salt according to claim 2, characterized in that: After step 1), the method further comprises: 3) adding a desiccant to the filtrate in step 1) for drying, and performing step 2) after drying.

8. The method for preparing bis(fluorosulfonyl)imide lithium salt according to claim 7, characterized in that: The desiccant is selected from at least one of metallic lithium, butyl lithium, lithium hydride, calcium hydride, lithium sulfate, lithium bis(fluorosulfonyl)imide salt, thionyl chloride, phosgene, diphosgene, triphosgene, oxalyl chloride or silicon tetrachloride; The mass ratio of the desiccant to the bis(fluorosulfonyl)imide is 0.001 to 0.1:

1.

9. The method for preparing bis(fluorosulfonyl)imide lithium salt according to claim 2, characterized in that: The solvent used for the crystallization is a poor solvent for lithium bis(fluorosulfonyl)imide salt; preferably, the solvent used for the crystallization is selected from at least one of alkanes, cycloalkanes, substituted alkanes, aromatic hydrocarbons or substituted aromatic hydrocarbons; more preferably, the solvent used for the crystallization is selected from at least one of pentane, hexane, heptane, cyclohexane, methylcyclohexane, dichloromethane, chloroform, carbon tetrachloride, dichloroethane, trichloroethane, tetrachloroethane, benzene, toluene, xylene, ethylbenzene, propylbenzene, isopropylbenzene, chlorobenzene or dichlorobenzene.

10. The method for preparing bis(fluorosulfonyl)imide lithium salt according to claim 2, characterized in that: The filter cake in step 1) is dried to obtain lithium carbonate; preferably, the filter cake in step 1) is dried by gradient heating to obtain lithium carbonate, and the drying temperature is 60-120°C.

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