Preparation method of lithium bis (fluorosulfonyl) imide

Abstract

The invention discloses a preparation method of lithium bis (fluorosulfonyl) imide, which comprises the following steps: by taking sulfuryl fluoride and formamide as raw materials, adding an organic solvent and organic alkali into the formamide, and introducing sulfuryl to react, thereby obtaining bis (fluorosulfonyl) imide acid organic alkali salt; the preparation method comprises the following steps: dissolving the imidodisulfuryl fluoride acid organic alkali salt in an organic solvent, adding a lithium source for lithiation reaction, then filtering and concentrating, adding a poor solvent for crystallization and separation to obtain a lithium imidodisulfuryl fluoride crude product, and finally refining the lithium imidodisulfuryl fluoride crude product to obtain the lithium imidodisulfuryl fluoride. Formamide and sulfuryl fluoride serve as raw materials, lithium bis (fluorosulfonyl) imide can be synthesized through a two-step method, and the method is easy and convenient to operate, mild in reaction condition, easy to purify, high in yield and purity and suitable for industrial production.

Description

Technical Field

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

[0002] Lithium bis(fluorosulfonyl)imide is a new type of electrolyte lithium salt. With its excellent performance and broad application prospects, it is gradually becoming an important research direction in the field of lithium battery electrolytes. Compared with the traditional lithium salt lithium hexafluorophosphate, its anion radius is larger, it is easier to dissociate lithium ions, and can improve the conductivity of the electrolyte; its application in the electrolyte of rechargeable lithium batteries can effectively reduce the resistance of the interface layer formed on the electrode surface at high and low temperatures, reduce the capacity loss of the battery during storage, and thus improve the electrochemical performance of the battery; it can also significantly improve the battery's cycle life, rate performance and safety, which is consistent with the future development direction of lithium batteries. With the reduction of production costs and the maturity of technology, lithium bis(fluorosulfonyl)imide is expected to achieve more extensive commercial applications in the next few years, making an important contribution to the improvement of lithium battery performance.

[0003] The current mainstream method for preparing lithium bis(fluorosulfonyl)imide can be divided into a three-step method and a two-step method (sulfuryl fluoride method) according to the synthesis steps. The three-step synthesis process can be divided into three main steps: synthesis (chlorination), fluorination, and lithiation of bis(chlorosulfonyl)imide and subsequent filtration and washing; the two-step method (sulfuryl fluoride method) skips the chlorination process and directly obtains bis(fluorosulfonyl)imide acid using sulfuryl fluoride and amine source as raw materials, and then prepares lithium bis(fluorosulfonyl)imide through a lithiation process of alkaline lithium or lithium halide.

[0004] CN115140716A uses sulfuryl fluoride and liquid ammonia to react to obtain bisfluorosulfonyl imide acid organic alkali salt, and then prepares bisfluorosulfonyl imide lithium through lithiation reaction. This method uses liquid ammonia as an amine source, has a high reaction risk coefficient, large environmental pollution, and is prone to equipment corrosion. CN115448268A discloses the use of sulfuryl fluoride and ammonium fluoride to react to obtain bisfluorosulfonyl imide acid organic alkali salt, and then prepares bisfluorosulfonyl imide lithium through lithiation reaction. This method uses lithium fluoride as a lithium source, and there is a problem that the reaction is difficult to be carried out thoroughly. At the same time, hydrogen fluoride is generated during the reaction process, and the product purification is difficult. CN116902930A uses sulfuryl fluoride and lithium nitride to directly prepare bisfluorosulfonyl imide lithium, and the process flow is simplified, but a large amount of lithium fluoride will be generated during the reaction, which increases the difficulty of product purification, and is prone to cause the impurity content in the product to exceed the standard, affecting the further application of the product. Summary of the invention

[0005] The invention provides a method for preparing lithium bis(fluorosulfonyl)imide. Formamide and sulfuryl fluoride are used as raw materials to synthesize lithium bis(fluorosulfonyl)imide through a two-step method. The method is simple to operate, the product is easy to purify, the yield and purity are high, and the method is suitable for industrial production.

[0006] The technical solution of the present invention is to provide a method for preparing lithium bis(fluorosulfonyl)imide, comprising the following steps: S1, using sulfuryl fluoride and formamide as raw materials, adding an organic solvent and an organic base to formamide, introducing sulfuryl to react, and preparing a bis(fluorosulfonyl)imide acid organic base salt; The organic base salt of the bis(fluorosulfonyl)imide acid obtained in S2 and S1 is dissolved in an organic solvent, a lithium source is added to carry out a lithiation reaction, and then filtered and concentrated, and a poor solvent is added to crystallize to separate and obtain a crude lithium bis(fluorosulfonyl)imide. The crude lithium bis(fluorosulfonyl)imide is finally refined to obtain lithium bis(fluorosulfonyl)imide.

[0007] In the optional scheme, the molar ratio of formamide to the organic base and sulfuryl fluoride is 1:3~5:2~3.

[0008] In the optional scheme, the reaction temperature in S1 is 0~60°C, the reaction pressure is controlled at 0.15~0.6 Mpa, and the reaction time is 6~18 hours.

[0009] In an optional embodiment, the organic base is one or more of triethylamine, N,N-diisopropylethylamine, tri-n-propylamine, pyridine, tetrahydropyrrole, and 1,8-diazabicyclo[5.4.0]undec-7-ene.

[0010] In an optional embodiment, the organic solvent in S1 and S2 is one or more of acetone, ethyl acetate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl ether, isopropyl ether, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, acetonitrile, glutaronitrile, 1,4-dioxane, and tetrahydrofuran.

[0011] In an optional scheme, the lithium sources in S2 are lithium oxide and lithium hydroxide, and the molar ratio between the two is 1: 0.3~2.4.

[0012] In an optional solution, the amount of lithium source added is 1 to 2.7 times the amount of the bis(fluorosulfonyl)imide acid organic base salt substance.

[0013] In the optional scheme, the reaction temperature in S2 is 0~45°C and the reaction time is 12~48 hours.

[0014] In an optional solution, the poor solvent is one or more of n-hexane, n-heptane, cyclohexane, petroleum ether, dichloromethane, dichloroethane, chloroform, toluene and xylene; in S2, the poor solvent is added under a protective atmosphere for crystallization.

[0015] In an optional scheme, during purification, the crude lithium bis(fluorosulfonyl)imide is dissolved in an organic solvent, filtered, the filtrate is concentrated, and a poor solvent is added for crystallization to obtain lithium bis(fluorosulfonyl)imide.

[0016] The present invention has the following beneficial effects: 1. The present invention uses formamide and sulfuryl fluoride as raw materials, the reaction process is mild and controllable, the operation is simple and safe, and lithium bis(fluorosulfonyl)imide can be obtained through two-step reaction, the chlorination process is omitted, and there is no need to use strong acidic and highly corrosive raw materials such as chlorosulfonic acid, aminosulfonic acid, and dichlorothionyl, thereby avoiding the generation of waste gases such as hydrogen chloride and sulfur dioxide, and reducing environmental protection and equipment investment costs.

[0017] 2. In the lithiation process of the present invention, lithium oxide and lithium hydroxide are used as lithium sources. Lithium oxide can provide lithium and also serve as a dehydrating agent, thereby avoiding the need for dehydration treatment with thionyl chloride and the introduction of other impurities, thereby helping to improve the purity of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Attached Figure 1 The lithium bis(fluorosulfonyl)imide prepared in Example 1 19 F-NMR spectrum. DETAILED DESCRIPTION

[0019] The present invention is described in detail below in conjunction with specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and a specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0020] The experimental methods in the following examples are conventional methods unless otherwise specified. The raw materials, reagents, etc. used in the following examples are commercially available products unless otherwise specified.

[0021] Example 1 100 g of formamide, 500 g of acetonitrile, and 800 g of triethylamine were added to a reactor equipped with a mechanical stirrer, the reactor temperature was controlled to be 10°C, sulfuryl fluoride gas was slowly introduced into the reactor, and the reactor pressure was controlled to be 0.5 Mpa. When the reactor pressure dropped to 0.15 Mpa, sulfuryl fluoride gas was continued to be introduced to 0.5 Mpa until the pressure of the reaction system remained stable or decreased very slowly for a long time, indicating that sulfuryl fluoride no longer participated in the reaction process, and stirring was immediately stopped. The reaction time was 15 hours, and the total mass of sulfuryl fluoride gas introduced was 532 g. After the reactor was depressurized, the reaction solution was filtered to remove the generated triethylamine hydrofluoride, and the filtrate was further concentrated to remove acetonitrile and excess triethylamine to obtain bis(fluorosulfonyl)imide acid triethylamine salt.

[0022] The above-mentioned bis(fluorosulfonyl)imide acid triethylamine salt and 1000 g of ethyl acetate were placed in a reaction bottle. After stirring, 54 g of lithium hydroxide and 68 g of lithium oxide were slowly added to the reaction system, and the temperature of the reaction system was maintained at 0-5°C. After the addition was completed, the reaction was continued to stir at 20°C for 24 hours. After the reaction was completed, the reaction solution was filtered, and the main components of the filter cake were lithium hydroxide and unreacted lithium oxide, which were recycled; the filtrate was concentrated by vacuum pump under reduced pressure, and 1000 g of 1,2-dichloroethane was added to the concentrated solution under nitrogen atmosphere, and stirred for crystallization for 3 hours. After the crystallization was completed, it was filtered, and the filter cake was washed 3 times with 1,2-dichloroethane, and vacuum dried to obtain 406.9 g of crude bis(fluorosulfonyl)imide lithium.

[0023] The obtained crude lithium bis(fluorosulfonyl)imide was placed in a reaction bottle, and 1200 g of a mixed solvent of ethanol:n-hexane in a volume ratio of 1:1.5 was added. After sufficient stirring until the crude product was completely dissolved, the mixture was filtered. The filtrate was concentrated under reduced pressure by a vacuum pump. Under a nitrogen atmosphere, 1000 g of 1,2-dichloroethane was added to the concentrated solution, and the mixture was stirred and crystallized for 3 hours. After the crystallization was completed, the mixture was filtered. The filter cake was vacuum dried to obtain 382.8 g of white lithium bis(fluorosulfonyl)imide powder. The total reaction yield was 92.17%, and the product purity was 99.96%.

[0024] The lithium bis(fluorosulfonyl)imide prepared in this example 19 F-NMR spectrum is shown in Figure 1 It can be seen that the chemical shift of the prepared lithium bis(fluorosulfonyl)imide is the same as that reported in the literature (such as CN 104495767 A), and there is no impurity peak signal.

[0025] Example 2 Add 100 g formamide, 500 g acetonitrile, and 1020 g N, N-diisopropylethylamine to a reactor equipped with a mechanical stirrer, control the reactor temperature to 10°C, slowly introduce sulfuryl fluoride gas into the reactor, and control the reactor pressure to 0.5 Mpa. When the reactor pressure drops to 0.15 Mpa, continue to introduce sulfuryl fluoride gas to 0.5 Mpa until the pressure of the reaction system remains stable or decreases very slowly for a long time, indicating that sulfuryl fluoride no longer participates in the reaction process, and then stop stirring. The reaction time is 18 hours, and the total mass of sulfuryl fluoride gas introduced is 635 g. After the reactor is depressurized, filter the reaction solution to remove the generated N, N-diisopropylethylamine hydrofluoride, and further concentrate the filtrate to remove acetonitrile and excess N, N-diisopropylethylamine to obtain bis(fluorosulfonyl)imide acid N, N-diisopropylethylamine salt.

[0026] The above-mentioned bis(fluorosulfonyl)imide acid N,N-diisopropylethylamine salt and 1000 g of ethyl acetate were placed in a reaction bottle. After stirring, 54 g of lithium hydroxide and 68 g of lithium oxide were slowly added to the reaction system, and the temperature of the reaction system was maintained at 0-5°C. After the addition was completed, the reaction was continued to stir at 20°C for 36 hours. After the reaction was completed, the reaction solution was filtered, and the main components of the filter cake were lithium hydroxide and unreacted lithium oxide, which were recycled; the filtrate was concentrated by vacuum pump under reduced pressure, and 1000 g of dichloromethane was added to the concentrated solution under nitrogen atmosphere, stirred and crystallized for 3 hours. After the crystallization was completed, it was filtered, the filter cake was washed with dichloromethane 3 times, and vacuum dried to obtain 408.1 g of crude bis(fluorosulfonyl)imide lithium.

[0027] The obtained crude lithium bis(fluorosulfonyl)imide was placed in a reaction bottle, and 1200 g of a mixed solvent of ethanol:n-hexane in a volume ratio of 1:1.5 was added. After sufficient stirring until the crude product was completely dissolved, the mixture was filtered, and the filtrate was concentrated under reduced pressure by a vacuum pump. Under a nitrogen atmosphere, 1000 g of dichloromethane was added to the concentrated solution, and the mixture was stirred and crystallized for 3 hours. After the crystallization was completed, the mixture was filtered, and the filter cake was vacuum dried to obtain 385.2 g of white lithium bis(fluorosulfonyl)imide powder. The total reaction yield was 92.74%, and the product purity was 99.95%.

[0028] Example 3 Add 100 g of formamide, 600 g of N,N-dimethylformamide, and 900 g of triethylamine to a reactor equipped with mechanical stirring, control the reactor temperature to 20°C, slowly introduce sulfuryl fluoride gas into the reactor, and control the reactor pressure to 0.6 Mpa. When the reactor pressure drops to 0.15 Mpa, continue to introduce sulfuryl fluoride gas to 0.6 Mpa until the pressure of the reaction system remains stable or decreases very slowly for a long time, indicating that sulfuryl fluoride no longer participates in the reaction process, and then stop stirring. The reaction time is 12 hours, and the total mass of sulfuryl fluoride gas introduced is 498 g. After the reactor is depressurized, filter the reaction solution to remove the generated triethylamine hydrofluoride, and further concentrate the filtrate to remove N,N-dimethylformamide and excess triethylamine to obtain bisfluorosulfonyl imide acid triethylamine salt.

[0029] The above-mentioned bis(fluorosulfonyl)imide acid triethylamine salt and 1000 g of ethyl acetate were placed in a reaction bottle. After stirring, 49 g of lithium hydroxide and 75 g of lithium oxide were slowly added to the reaction system, and the temperature of the reaction system was maintained at 0-5°C. After the addition was completed, the reaction was continued to stir at 25°C for 30 hours. After the reaction was completed, the reaction solution was filtered, and the main components of the filter cake were lithium hydroxide and unreacted lithium oxide, which were recycled; the filtrate was concentrated by vacuum pump under reduced pressure, and 1000 g of n-hexane was added to the concentrated solution under nitrogen atmosphere for stirring and crystallization for 3 hours. After the crystallization was completed, it was filtered, the filter cake was washed 3 times with n-hexane, and vacuum dried to obtain 402.6 g of crude bis(fluorosulfonyl)imide lithium.

[0030] The obtained crude lithium bis(fluorosulfonyl)imide was placed in a reaction bottle, and 1200 g of a mixed solvent of ethanol: dichloromethane in a volume ratio of 1:1.5 was added. After sufficient stirring until the crude product was completely dissolved, the mixture was filtered, and the filtrate was concentrated under reduced pressure by a vacuum pump. Under a nitrogen atmosphere, 1000 g of n-hexane was added to the concentrated solution, and the mixture was stirred and crystallized for 3 hours. After the crystallization was completed, the mixture was filtered, and the filter cake was vacuum dried to obtain 379.4 g of white lithium bis(fluorosulfonyl)imide powder. The total reaction yield was 91.35%, and the product purity was 99.98%.

[0031] Example 4 Add 100 g of formamide, 500 g of acetone, and 900 g of triethylamine to a reactor equipped with mechanical stirring, control the reactor temperature to 20°C, slowly introduce sulfuryl fluoride gas into the reactor, and control the reactor pressure to 0.6 Mpa. When the reactor pressure drops to 0.15 Mpa, continue to introduce sulfuryl fluoride gas to 0.6 Mpa until the pressure of the reaction system remains stable or decreases very slowly for a long time, indicating that sulfuryl fluoride no longer participates in the reaction process, and then stop stirring. The reaction time is 15 hours, and the total mass of sulfuryl fluoride gas introduced is 546 g. After the reactor is depressurized, filter the reaction solution to remove the generated triethylamine hydrofluoride, and further concentrate the filtrate to remove acetone and excess triethylamine to obtain bisfluorosulfonyl imide acid triethylamine salt.

[0032] The above-mentioned bis(fluorosulfonyl)imide acid triethylamine salt and 1200 g of diethyl carbonate were placed in a reaction bottle. After stirring, 43 g of lithium hydroxide and 82 g of lithium oxide were slowly added to the reaction system, and the temperature of the reaction system was maintained at 0-5°C. After the addition was completed, the reaction was continued to stir at 10°C for 28 hours. After the reaction was completed, the reaction solution was filtered, and the main components of the filter cake were lithium hydroxide and unreacted lithium oxide, which were recycled; the filtrate was concentrated by vacuum pump under reduced pressure, and 1000 g of n-heptane was added to the concentrated solution under nitrogen atmosphere for stirring and crystallization for 3 hours. After the crystallization was completed, it was filtered, the filter cake was washed 3 times with n-heptane, and vacuum dried to obtain 406.8 g of crude bis(fluorosulfonyl)imide lithium.

[0033] The obtained crude lithium bis(fluorosulfonyl)imide was placed in a reaction bottle, and 1200 g of a mixed solvent of ethanol:cyclohexane in a volume ratio of 1:1.5 was added. After sufficient stirring until the crude product was completely dissolved, the mixture was filtered, and the filtrate was concentrated under reduced pressure by a vacuum pump. Under a nitrogen atmosphere, 1000 g of n-heptane was added to the concentrated solution, and the mixture was stirred and crystallized for 3 hours. After the crystallization was completed, the mixture was filtered, and the filter cake was vacuum dried to obtain 388.5 g of white lithium bis(fluorosulfonyl)imide powder. The total reaction yield was 93.54%, and the product purity was 99.95%.

[0034] Example 5 To a reactor equipped with a mechanical stirrer, 100 g of formamide, 600 g of tetrahydrofuran, and 1200 g of 1,8-diazabicyclo[5.4.0]undec-7-ene were added, the temperature of the reactor was controlled at 0°C, sulfuryl fluoride gas was slowly introduced into the reactor, and the pressure of the reactor was controlled at 0.5 MPa. When the pressure of the reactor dropped to 0.15 MPa, sulfuryl fluoride gas was continued to be introduced to 0.5 MPa until the pressure of the reaction system remained stable for a long time or decreased very slowly, indicating that sulfuryl fluoride no longer participated in the reaction process, and stirring was immediately stopped. The reaction time was 16 hours, and the total mass of sulfuryl fluoride gas introduced was 589 g. After the pressure of the reactor is released, the reaction liquid is filtered to remove the generated 1,8-diazabicyclo[5.4.0]undec-7-ene hydrofluoride. The filtrate is further concentrated to remove tetrahydrofuran and excess 1,8-diazabicyclo[5.4.0]undec-7-ene to obtain bis(fluorosulfonylimide) acid 1,8-diazabicyclo[5.4.0]undec-7-ene salt.

[0035] The above-mentioned 1,8-diazabicyclo[5.4.0]undec-7-ene salt of bis(fluorosulfonyl)imide and 1200 g of ethyl methyl carbonate were placed in a reaction bottle. After stirring, 54 g of lithium hydroxide and 68 g of lithium oxide were slowly added to the reaction system, and the temperature of the reaction system was maintained at 0-5°C. After the addition was completed, the reaction was continued to stir at 30°C for 32 hours. After the reaction was completed, the reaction solution was filtered, and the main components of the filter cake were lithium hydroxide and unreacted lithium oxide, which were recycled; the filtrate was concentrated by vacuum pump under reduced pressure, and 1000 g of petroleum ether was added to the concentrated solution under nitrogen atmosphere for stirring and crystallization for 3 hours. After the crystallization was completed, it was filtered, the filter cake was washed with petroleum ether 3 times, and vacuum dried to obtain 404.9 g of crude lithium bis(fluorosulfonyl)imide.

[0036] The obtained crude lithium bis(fluorosulfonyl)imide was placed in a reaction bottle, and 1800 g of a mixed solvent of ethanol:toluene in a volume ratio of 1:2 was added. After sufficient stirring until the crude product was completely dissolved, the mixture was filtered, and the filtrate was concentrated under reduced pressure by a vacuum pump. Under a nitrogen atmosphere, 1000 g of petroleum ether was added to the concentrated solution, and the mixture was stirred and crystallized for 3 hours. After the crystallization was completed, the mixture was filtered, and the filter cake was vacuum dried to obtain 381.6 g of white lithium bis(fluorosulfonyl)imide powder. The total reaction yield was 91.88%, and the product purity was 99.97%.

[0037] Example 6 100 g of formamide, 600 g of ether, and 800 g of triethylamine were added to a reactor equipped with mechanical stirring, the reactor temperature was controlled to 30°C, sulfuryl fluoride gas was slowly introduced into the reactor, and the reactor pressure was controlled to 0.5 Mpa. When the reactor pressure dropped to 0.15 Mpa, sulfuryl fluoride gas was continued to be introduced to 0.5 Mpa until the pressure of the reaction system remained stable or decreased very slowly for a long time, indicating that sulfuryl fluoride no longer participated in the reaction process, and stirring was immediately stopped. The reaction time was 12 hours, and the total mass of sulfuryl fluoride gas introduced was 543 g. After the reactor was depressurized, the reaction solution was filtered to remove the generated triethylamine hydrofluoride, and the filtrate was further concentrated to remove ether and excess triethylamine to obtain bisfluorosulfonyl imide acid triethylamine salt.

[0038] The above-mentioned bis(fluorosulfonyl)imide acid triethylamine salt and 1200 g of acetonitrile were placed in a reaction bottle. After stirring, 49 g of lithium hydroxide and 75 g of lithium oxide were slowly added to the reaction system, and the temperature of the reaction system was maintained at 0-5°C. After the addition was completed, the reaction was continued to stir at 20°C for 45 hours. After the reaction was completed, the reaction solution was filtered, and the main components of the filter cake were lithium hydroxide and unreacted lithium oxide, which were recycled; the filtrate was concentrated by vacuum pump under reduced pressure, and 1000 g of dichloromethane was added to the concentrated solution under nitrogen atmosphere, stirred and crystallized for 3 hours. After the crystallization was completed, it was filtered, the filter cake was washed 3 times with dichloromethane, and vacuum dried to obtain 408.5 g of crude bis(fluorosulfonyl)imide lithium.

[0039] The obtained crude lithium bis(fluorosulfonyl)imide was placed in a reaction bottle, and 1200 g of a mixed solvent of ether:n-hexane in a volume ratio of 1:1.5 was added. After sufficient stirring until the crude product was completely dissolved, the mixture was filtered, and the filtrate was concentrated under reduced pressure by a vacuum pump. Under a nitrogen atmosphere, 1000 g of dichloromethane was added to the concentrated solution, and the mixture was stirred and crystallized for 3 hours. After the crystallization was completed, the mixture was filtered, and the filter cake was vacuum dried to obtain 383.7 g of white lithium bis(fluorosulfonyl)imide powder. The total reaction yield was 92.38%, and the product purity was 99.96%.

[0040] Example 7 100 g of formamide, 600 g of tetrahydrofuran, and 800 g of triethylamine were added to a reactor equipped with mechanical stirring, the reactor temperature was controlled to 30°C, sulfuryl fluoride gas was slowly introduced into the reactor, and the reactor pressure was controlled to 0.6 Mpa. When the reactor pressure dropped to 0.15 Mpa, sulfuryl fluoride gas was continued to be introduced to 0.6 Mpa until the pressure of the reaction system remained stable or decreased very slowly for a long time, indicating that sulfuryl fluoride no longer participated in the reaction process, and stirring was immediately stopped. The reaction time was 9 hours, and the total mass of sulfuryl fluoride gas introduced was 487 g. After the reactor was depressurized, the reaction solution was filtered to remove the generated triethylamine hydrofluoride, and the filtrate was further concentrated to remove tetrahydrofuran and excess triethylamine to obtain bisfluorosulfonyl imide acid triethylamine salt.

[0041] The above-mentioned bis(fluorosulfonyl)imide acid triethylamine salt and 1200 g of dimethyl carbonate were placed in a reaction bottle. After stirring, 54 g of lithium hydroxide and 68 g of lithium oxide were slowly added to the reaction system, and the temperature of the reaction system was maintained at 0-5°C. After the addition was completed, the reaction was continued to stir at 20°C for 36 hours. After the reaction was completed, the reaction solution was filtered, and the main components of the filter cake were lithium hydroxide and unreacted lithium oxide, which were recycled; the filtrate was concentrated by vacuum pump under reduced pressure, and 1000 g of n-hexane was added to the concentrated solution under nitrogen atmosphere for stirring and crystallization for 3 hours. After the crystallization was completed, it was filtered, the filter cake was washed 3 times with n-hexane, and vacuum dried to obtain 407.1 g of crude bis(fluorosulfonyl)imide lithium.

[0042] The obtained crude lithium bis(fluorosulfonyl)imide was placed in a reaction bottle, and 1200 g of a mixed solvent of ethyl acetate: dichloromethane in a volume ratio of 1:1.5 was added. After sufficient stirring until the crude product was completely dissolved, the mixture was filtered, and the filtrate was concentrated under reduced pressure by a vacuum pump. Under a nitrogen atmosphere, 1000 g of n-hexane was added to the concentrated solution, and the mixture was stirred and crystallized for 3 hours. After the crystallization was completed, the mixture was filtered, and the filter cake was vacuum dried to obtain 377.8 g of white lithium bis(fluorosulfonyl)imide powder. The total reaction yield was 90.96%, and the product purity was 99.98%.

[0043] Comparative Example 1 The formamide was replaced by acetamide, and the remaining experimental steps were the same as those in Example 1. The experimental results showed that the total yield of the reaction was only 30.65%, and the product purity was 98.71%.

[0044] Comparative Example 2 The lithium source of the reaction was adjusted from lithium oxide and lithium hydroxide to lithium carbonate, and the remaining experimental steps were the same as in Example 1. The experimental results showed that the total yield of the reaction was 60.33% and the product purity was 99.82%.

[0045] The above embodiments describe the preferred implementation of the present invention, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing lithium bis(fluorosulfonyl)imide, characterized in that: The following steps are involved: S1, using sulfuryl fluoride and formamide as raw materials, adding an organic solvent and an organic base to formamide, introducing sulfuryl to react, and preparing a bis(fluorosulfonyl)imide acid organic base salt; The organic base salt of the bis(fluorosulfonyl)imide acid obtained in S2 and S1 is dissolved in an organic solvent, a lithium source is added to carry out a lithiation reaction, and then filtered and concentrated, and a poor solvent is added to crystallize to separate and obtain a crude lithium bis(fluorosulfonyl)imide. The crude lithium bis(fluorosulfonyl)imide is finally refined to obtain lithium bis(fluorosulfonyl)imide.

2. The preparation method according to claim 1, characterized in that: The molar ratio of formamide to the organic base and sulfuryl fluoride is 1:3~5:2~3.

3. The preparation method according to claim 1, characterized in that: In S1, the reaction temperature is 0-60°C, the reaction pressure is controlled at 0.15-0.6 MPa, and the reaction time is 6-18 hours.

4. The preparation method according to claim 1, characterized in that: The organic base is one or more of triethylamine, N,N-diisopropylethylamine, tri-n-propylamine, pyridine, tetrahydropyrrole, and 1,8-diazabicyclo[5.4.0]undec-7-ene.

5. The preparation method according to claim 1, characterized in that: The organic solvent in S1 and S2 is one or more of acetone, ethyl acetate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl ether, isopropyl ether, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, acetonitrile, glutaronitrile, 1,4-dioxane, and tetrahydrofuran.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The lithium sources in S2 are lithium oxide and lithium hydroxide, and the molar ratio between the two is 1: 0.3~2.

4.

7. The preparation method according to claim 6, characterized in that: The amount of the lithium source added is 1 to 2.7 times the amount of the bis(fluorosulfonyl)imide acid organic base salt substance.

8. The preparation method according to claim 1, characterized in that: The reaction temperature in S2 is 0-45°C, and the reaction time is 12-48 hours.

9. The preparation method according to claim 1, characterized in that: The poor solvent is one or more of n-hexane, n-heptane, cyclohexane, petroleum ether, dichloromethane, dichloroethane, chloroform, toluene and xylene; in S2, the poor solvent is added under a protective atmosphere to perform crystallization.

10. The preparation method according to claim 1, characterized in that: During purification, the crude lithium bis(fluorosulfonyl)imide is dissolved in an organic solvent, filtered, the filtrate is concentrated, and a poor solvent is added for crystallization to obtain lithium bis(fluorosulfonyl)imide.

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