A method for preparing lithium bisfluorosulfonylimide by mild fluorination of ammonium fluoride

Abstract

The application belongs to the technical field of new energy battery electrolyte, and discloses a method for preparing lithium bisfluorosulfonylimide by mildly fluorinating ammonium fluoride, which solves the defects of the existing LiFSI preparation process, such as complex process route, high reaction risk, uncontrollable exothermic feeding, low product purity and yield, and high difficulty in industrial implementation. In the constant temperature interval, the ammonium fluoride suspension is added to the dichlorosulfonylimide by using the intermittent gradient non-equal feeding mode, and then the dichlorosulfonylimide is deeply fluorinated by heating to prepare the ammonium bisfluorosulfonylimide salt. The ammonium bisfluorosulfonylimide salt is acidified by a strong acid, filtered and separated to obtain the bisfluorosulfonylimide solution. The bisfluorosulfonylimide solution is reacted with a lithium source, filtered and separated, concentrated and crystallized, and purified to obtain the lithium bisfluorosulfonylimide. The preparation method has mild reaction conditions, low fluorination process risk coefficient, low equipment requirement, rapid and complete acidification process, and the whole process is green and environmentally friendly. The prepared lithium bisfluorosulfonylimide has high yield and high purity, and is suitable for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of new energy battery electrolyte technology, and particularly relates to a method for lithium difluorosulfonylimide. Background Technology

[0002] The physicochemical and electrochemical properties of lithium-ion battery electrolytes directly determine their ion transport capacity, thermal stability, and interfacial compatibility. Traditional commercial lithium salt LiPF6 suffers from poor thermal stability, is prone to hydrolysis to generate acidic impurities that cause electrode corrosion, and exhibits poor low-temperature ionic conductivity. Lithium bisfluorosulfonylimide (LiFSI), as a new generation of alkali metal electrolyte salt, possesses a unique anionic structure that significantly promotes lithium-ion dissociation, resulting in an ionic conductivity more than 30% higher than LiPF6. Its electrochemical window reaches 4.5 V (vs. Li⁺ / Li), enabling it to be matched with high-voltage cathode materials and breaking through the voltage limitations of traditional batteries. Simultaneously, its decomposition temperature exceeds 200℃, exhibiting excellent hydrolysis resistance and electrode compatibility, effectively improving the battery's high-temperature storage stability and low-temperature discharge performance. Lithium bisfluorosulfonylimide (LiFSI) is a preferred material for replacing traditional lithium salts and overcoming the technical challenges of high-performance battery electrolytes, possessing significant application value and industrialization prospects in the fields of power batteries and energy storage batteries.

[0003] In recent years, research on the "two-step method" for LiFSI has gradually increased, as it has lower costs and a shorter reaction pathway. For example, CN116040592A uses ClSO₂N=C=O and FSO₃H as raw materials, and under SbCl₅ catalysis, anhydrous HF is passed through to obtain HFSI, which is then dissolved in anhydrous petroleum ether, and Li₂ is added. 0.51 Sn 0.49 After the reaction, the product was filtered, distilled under reduced pressure, and dried under vacuum to obtain LiFSI crystals with a purity of 99.9% and a yield of 93.1%. CN114604832A describes the direct synthesis of HFSI using FSO2N=C=O and FSO3H, followed by reaction with a lithiation reagent to synthesize LiFSI. CN115818591A describes the synthesis of lithium difluorosulfonyl imide using sulfuryl fluoride, an ammonia source, and an organic base. Current research on two-step methods focuses on the "fluorination-salt formation" field, most of which require high pressure / Lewis acid catalysts and introduce additional metal impurities. Furthermore, the multiple reaction sites result in the generation of numerous intermediates, raising issues of product purity and thermal runaway. These problems prevent the method from meeting the purity, safety, and cost requirements of LiFSI for power batteries, and it remains some distance from large-scale industrial production.

[0004] Currently, the industrial process mainly employs a three-step method: chlorination-fluorination-lithiation. For example, in Shenzhen Xinzhoubang's patent CN103935970A and Kangpeng Chemical's patent CN104925765A, dichlorosulfonylimide is synthesized using aminosulfonic acid, chlorosulfonic acid, and thionyl chloride as raw materials. It is then fluorinated with hydrogen fluoride to obtain difluorosulfonylimide. Lithium hydroxide, lithium fluoride, or lithium carbonate are used as the lithium source to obtain crude difluorosulfonylimide lithium. The product is then dehydrated by adding thionyl chloride, followed by solid-liquid separation. The solid product is further purified by pulping. The three-step fluorination route using HF gas requires high-performance fluorination equipment (must be Monel alloy, Hastelloy alloy, PTFE-lined / Hastelloy-lined equipment, etc.), significantly increasing industrial costs. Furthermore, the fluorination process generates a large amount of waste gas, increasing post-treatment costs.

[0005] In recent years, there have been reports both domestically and internationally on the preparation of LiFSI by fluorinating bis(chlorosulfonyl)imide with metal fluorides. Nippon Soda Corporation's patent CN103391896A utilizes solid ammonium fluoride as a fluorinating agent to react with bis(chlorosulfonyl)imide, generating bis(chlorosulfonyl)imide ammonium salt NH4FSI, with a reaction yield of 95%. However, this process has significant limitations. The subsequent lithiation process has a narrow applicability range, only allowing the use of strongly alkaline lithium hydroxide as a replacement source to prepare LiFSI. The strongly alkaline system easily induces side reactions, leading to increased impurity content in the product. Simultaneously, the raw material and post-processing costs are relatively high, resulting in high industrial production costs. Furthermore, traditional processes often use a one-time direct addition of solid ammonium fluoride, which easily leads to problems such as excessively high local material concentrations and concentrated exothermic reactions. This can easily cause thermal decomposition of the bis(chlorosulfonyl)imide raw material, increasing by-products, reducing product color and purity, and resulting in poor controllability of the reaction process.

[0006] Patent CN120964738A also uses solid ammonium fluoride to fluorinate and prepare NH4FSI solution, which is then acidified by a strongly acidic ion exchange column and concentrated under reduced pressure to obtain HFSI, which is then exchanged with a lithium source to prepare LiFSI. This process has drawbacks such as a long ion exchange cycle, limited exchange capacity, and incomplete ion exchange, which easily leads to intermediate residues and seriously affects the yield and purity of the final LiFSI product.

[0007] In summary, existing processes for preparing LiFSI by ammonium fluoride fluorination generally suffer from problems such as harsh reaction conditions, crude feed methods, difficulty in controlling exothermic reactions, limited subsequent conversion routes, long process cycles, difficulty in impurity control, high equipment requirements, and poor adaptability to large-scale industrial applications. Therefore, there is an urgent need to develop a LiFSI preparation process with mild reaction conditions, easy process control, low safety risk, simple equipment structure, fast reaction rate, environmental friendliness, excellent product yield and purity, and suitability for large-scale industrial applications. Summary of the Invention

[0008] To address the shortcomings of existing LiFSI preparation processes, such as complex routes, high reaction risks, uncontrollable exothermic reactions during feed, low product purity and yield, and difficulties in industrial implementation, this invention proposes a method for preparing lithium bis(fluorosulfonyl)imide via mild fluorination with ammonium fluoride. This process prepares high-purity lithium bis(fluorosulfonyl)imide through a multi-step reaction, allowing for step-by-step reaction control, gradual optimization of reaction conditions, and reduction of side reaction risks, thus improving yield. Combined with multi-step purification steps, this significantly enhances product purity, enabling the high-yield and high-purity preparation of lithium bis(fluorosulfonyl)imide.

[0009] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0010] A method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride, comprising the following steps:

[0011] (1) Dichlorosulfonamide was synthesized from aminosulfonic acid, chlorosulfonic acid, and thionyl chloride. The reaction equation is as follows:

[0012] .

[0013] (2) Then, using an intermittent gradient non-equal feeding mode in the isothermal zone, ammonium fluoride suspension was added to dichlorosulfonylimide, followed by heating to deeply fluorinate dichlorosulfonylimide to prepare dichlorosulfonylimide ammonium salt. The reaction equation is as follows:

[0014] .

[0015] (3) The ammonium bis(fluorosulfonyl)imide salt obtained in step (2) is acidified with strong acid and separated by filtration to obtain a bis(fluorosulfonyl)imide solution. The reaction equation is as follows:

[0016] .

[0017] (4) The bis(fluorosulfonyl)imide solution obtained in step (3) reacts with a lithium source, and after filtration, separation, concentration and crystallization, crude bis(fluorosulfonyl)imide lithium is obtained.

[0018] (5) The crude lithium difluorosulfonylimide obtained in step (4) is purified to obtain (high-purity) lithium difluorosulfonylimide. The specific purification steps are as follows: the crude lithium difluorosulfonylimide is added to the first solvent (the mass ratio of the crude lithium difluorosulfonylimide to the first solvent is 1:(10-20)) and stirred at room temperature. The upper solid is filtered to remove excess acid in the acid system. Then the solid is fully dissolved in the second solvent (the mass ratio of the crude lithium difluorosulfonylimide to the second solvent is 1:(10-20)), the insoluble matter is removed by filtration, and the solution is concentrated under reduced pressure to obtain a concentrated lithium difluorosulfonylimide solution. The concentrated lithium difluorosulfonylimide solution is slowly added dropwise to the third solvent (the mass ratio of the concentrated lithium difluorosulfonylimide solution to the third solvent is 1:(10-20)) for back precipitation (temperature is 0-20℃). The precipitate is allowed to stand and precipitate. After separation and vacuum drying, high-purity lithium difluorosulfonylimide is obtained.

[0019] Furthermore, in step (1) above, the molar ratio of aminosulfonic acid, chlorosulfonic acid and thionyl chloride is 1:(1-1.1):(2.7-3), and the reaction conditions are 120℃-125℃ for 16-18 h to obtain the product.

[0020] In step (2) above, the molar ratio of ammonium fluoride to dichlorosulfonamide in the ammonium fluoride suspension is (3-8):1. The solvent in the ammonium fluoride suspension is at least one of dimethyl carbonate, diethyl carbonate, butyl acetate, ethyl acetate, N,N-dimethylformamide, diethyl ether, and methyl tert-butyl ether, and the mass ratio of ammonium fluoride to solvent is 1:20-30.

[0021] In step (2) above, the temperature in the isothermal range is 50±5℃. The intermittent gradient non-equal feeding mode refers to: first, adding 10%-20% of the required total mass of ammonium fluoride in the ammonium fluoride suspension, and waiting for the system to stabilize; then adding 60%-80% of the required total mass of ammonium fluoride in the ammonium fluoride suspension, and after the system stabilizes, adding the remaining ammonium fluoride suspension (10%-20% of the required total mass of ammonium fluoride). The temperature for deep fluorination is 60-100℃, and the time is 2-12 h.

[0022] In step (3) above, the strong acid is at least one of fluorosulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, trifluoroacetic acid and concentrated sulfuric acid, and the molar ratio of difluorosulfonylimide ammonium salt to the strong acid is 1:(1-3); the acidification temperature is -10~10℃, and the reaction time is 10-120 min.

[0023] In step (4) above, the anion in the lithium source is one of hydroxide ions, carbonate ions, bicarbonate ions and tetrafluoroborate ions, and the molar ratio of lithium source to difluorosulfonamide is (0.5-2):1.

[0024] In step (5) above, the first solvent and the third solvent are at least one of dichloromethane, dichloroethane, petroleum ether, n-hexane, toluene, xylene, chlorobenzene and dichlorobenzene; the second solvent is at least one of acetonitrile, propionitrile, isopropionitrile, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, butyl acetate, diethyl ether, propyl ether, methyl tert-butyl ether, tetrahydrofuran, N,N-dimethylformamide and N,N-dimethylacetamide.

[0025] The lithium bis(fluorosulfonyl)imide prepared by the above preparation method of the present invention has a yield of ≥97% and a purity of ≥99%, wherein the free acid content is ≤30 ppm, the moisture content is ≤50 ppm, the chloride ion content is ≤10 ppm, the fluoride ion content is ≤20 ppm, the impurity metal ion content is ≤5 ppm, and the DMC insoluble matter content is ≤30 ppm.

[0026] The beneficial effects of this invention are:

[0027] (1) This invention provides a method for preparing high-purity LiFSI with mild process conditions, simple operation, high safety, high product purity and yield, and is suitable for large-scale mass production. This invention is based on a three-step process route of chlorination-fluorination-lithiation, and selects ammonium fluoride as a fluorinating agent, which is safe and stable, has mild reaction conditions, and does not require high-pressure special equipment. Instead of the traditional one-time solid feeding method, the ammonium fluoride is prepared into an anhydrous suspension. An intermittent gradient non-equal feeding mode is adopted in a constant temperature range of 50±5℃. The feeding strategy follows the principle of first adding a small amount of material, then adding a large amount of material in the middle, and finally adding a small amount of material to finish the process. After all the ammonium fluoride suspension has been added, the temperature is raised for deep fluorination to avoid local overheating that could cause raw material decomposition and by-product generation.

[0028] (2) The present invention uses a non-ion exchange efficient acidification process to prepare HFSI from the fluorinated NH4FSI intermediate, which avoids the disadvantages of long cycle and incomplete exchange in traditional ion exchange; and adds a fine purification process for crude LiFSI, which solves the problems of limited lithium source, high impurities and long cycle in the existing route from the source of the process, and finally achieves stable preparation of high yield and high purity LiFSI. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 For NH4FSI 19 F NMR spectrum.

[0031] Figure 2 For HFSI 19 F NMR spectrum.

[0032] Figure 3 For LiFSI 19 F NMR spectrum. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride in this embodiment includes the following steps:

[0036] (1) Add 0.5 mol aminosulfonic acid and 1.35 mol thionyl chloride to the reaction vessel, stir for 20 min and then heat to 80℃. Start adding 0.55 mol chlorosulfonic acid (the molar ratio of aminosulfonic acid, chlorosulfonic acid and thionyl chloride is 1:1.1:2.7). After all the addition is complete, heat to 125℃ and react for 18 h. Immediately after the reaction is completed, distillation is carried out to separate the impurity components. Collect the fraction at 90℃ to obtain pure dichlorosulfonylimide.

[0037] (2) First, 33 g of ammonium fluoride (0.9 mol) was dispersed in 660 g of dimethyl carbonate to prepare an ammonium fluoride suspension. Then, under nitrogen protection, 0.3 mol of dichlorosulfonyl imide was added to the reaction flask. Subsequently, within a constant temperature range of 50±5℃, the above ammonium fluoride suspension was added to the reaction flask system using an intermittent gradient non-equal feeding mode (the non-equal feeding ratios for the early, middle, and late stages were 10%, 80%, and 10%, respectively (all referring to the percentage of the required mass of ammonium fluoride to the total mass of ammonium fluoride at each stage)). After the feeding was completed, the temperature was raised to 80℃ for deep fluorination for 6 h to obtain a dichlorosulfonyl imide ammonium solution. This solution did not need to be concentrated and was directly used for the next acidification step. The dichlorosulfonyl imide ammonium 19 F NMR spectrum as shown Figure 1 As shown.

[0038] (3) Cool the ammonium bis(fluorosulfonyl)imide solution obtained in step (2) to 0°C, slowly add fluorosulfonic acid (molar ratio of ammonium bis(fluorosulfonyl)imide to fluorosulfonic acid is 1:1) for 30 min, filter the byproduct ammonium fluorosulfonate salt at low temperature to obtain a bis(fluorosulfonyl)imide solution, and proceed directly to the next lithiation step without concentration. The bis(fluorosulfonyl)imide...19 F NMR spectrum as shown Figure 2 As shown.

[0039] (4) Add lithium carbonate to the bis(fluorosulfonyl)imide solution obtained in step (3) (the molar ratio of bis(fluorosulfonyl)imide to lithium carbonate is 0.55:1), react at 10°C for 3 h, and after the reaction, filter, concentrate and crystallize to obtain crude bis(fluorosulfonyl)imide.

[0040] (5) Lithium difluorosulfonylimide was purified through a series of processes to obtain high-purity lithium difluorosulfonylimide. 10 g of crude lithium difluorosulfonylimide was added to 150 g of dichloroethane and stirred at room temperature. The supernatant was filtered to remove excess acid from the acid system. Then, 9.8 g of the solid was fully dissolved in 150 g of diethyl ether, filtered to remove insoluble matter, and concentrated under reduced pressure to obtain a concentrated lithium difluorosulfonylimide solution. The above concentrated lithium difluorosulfonylimide solution was slowly added dropwise to petroleum ether (the mass ratio of the concentrated lithium difluorosulfonylimide solution to petroleum ether was 1:20) for back precipitation. After standing to precipitate, the precipitate was separated and dried under vacuum to obtain high-purity lithium difluorosulfonylimide. The lithium difluorosulfonylimide... 19 F NMR spectrum as shown Figure 3 As shown.

[0041] Example 2

[0042] The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride in this embodiment includes the following steps:

[0043] (1) Add 0.5 mol aminosulfonic acid and 1.5 mol thionyl chloride to the reaction vessel, stir for 20 min and then heat to 80℃. Start adding 0.5 mol chlorosulfonic acid (the molar ratio of aminosulfonic acid, chlorosulfonic acid and thionyl chloride is 1:1:3). After all the chlorosulfonic acid is added, heat to 120℃ and react for 16 h. Immediately after the reaction is completed, distillation is carried out to separate the impurity components. Collect the fraction at 90℃ to obtain pure dichlorosulfonylimide.

[0044] (2) First, 44 g of ammonium fluoride (1.2 mol) was dispersed in 880 g of ethyl acetate to prepare an ammonium fluoride suspension. Then, under nitrogen protection, 0.3 mol of dichlorosulfonylimide was added to the reaction flask. Subsequently, within a constant temperature range of 50±5℃, the above ammonium fluoride suspension was added to the reaction flask system using an intermittent gradient non-equal feeding mode (the non-equal feeding ratios for the early, middle, and late stages were 15%, 75%, and 10%, respectively, all referring to the percentage of the required mass of ammonium fluoride to the total mass of ammonium fluoride at each stage)). After the feeding was completed, the temperature was raised to 60℃ for deep fluorination for 6 h to obtain a dichlorosulfonylimide ammonium solution. This solution did not need to be concentrated and was directly used for the next acidification step.

[0045] (3) Cool the ammonium difluorosulfonamide solution obtained in step (2) to 0°C, slowly add trifluoromethanesulfonic acid (the molar ratio of ammonium difluorosulfonamide to trifluoromethanesulfonic acid is 1:1) and acidify for 20 min. Filter the byproduct ammonium trifluoromethanesulfonate at low temperature to obtain the difluorosulfonamide solution. No concentration is required to proceed directly to the next lithiation step.

[0046] (4) Add lithium carbonate to the bis(fluorosulfonyl)imide solution obtained in step (3) (the molar ratio of bis(fluorosulfonyl)imide to lithium carbonate is 0.55:1), react at 10°C for 3 h, and after the reaction, filter, concentrate and crystallize to obtain crude bis(fluorosulfonyl)imide.

[0047] (5) Lithium difluorosulfonylimide was purified through a series of processes to obtain high-purity lithium difluorosulfonylimide. 10 g of crude lithium difluorosulfonylimide was added to 150 g of dichloromethane and stirred at room temperature. The supernatant was filtered to remove excess acid from the acid system. The solid was then fully dissolved in methyl tert-butyl ether (the mass of methyl tert-butyl ether was 20 times that of crude lithium difluorosulfonylimide). The insoluble matter was removed by filtration and the solution was concentrated under reduced pressure to obtain a concentrated lithium difluorosulfonylimide solution. The concentrated lithium difluorosulfonylimide solution was slowly added dropwise to toluene (the mass ratio of the concentrated lithium difluorosulfonylimide solution to toluene was 1:20) for back precipitation. The precipitate was allowed to stand and then separated and dried under vacuum to obtain high-purity lithium difluorosulfonylimide.

[0048] Example 3

[0049] The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride in this embodiment includes the following steps:

[0050] (1) Add 0.5 mol aminosulfonic acid and 1.5 mol thionyl chloride to the reaction vessel, stir for 20 min and then heat to 80℃. Start adding 0.5 mol chlorosulfonic acid (the molar ratio of aminosulfonic acid, chlorosulfonic acid and thionyl chloride is 1:1:3). After all the chlorosulfonic acid is added, heat to 125℃ and react for 18 h. After the reaction is completed, immediately carry out distillation to separate the impurity components and collect the fraction at 90℃ to obtain pure dichlorosulfonylimide.

[0051] (2) First, 44 g of ammonium fluoride (1.2 mol) was dispersed in 880 g of butyl acetate to prepare an ammonium fluoride suspension. Then, under nitrogen protection, 0.3 mol of dichlorosulfonylimide was added to the reaction flask. Subsequently, within a constant temperature range of 50±5℃, the above ammonium fluoride suspension was added to the reaction flask system using an intermittent gradient non-equal feeding mode (the non-equal feeding ratios for the early, middle, and late stages were 20%, 70%, and 10%, respectively, all referring to the percentage of the required mass of ammonium fluoride to the total mass of ammonium fluoride at each stage)). After the feeding was completed, the temperature was raised to 60℃ for deep fluorination for 6 h to obtain a dichlorosulfonylimide ammonium solution. This solution did not need to be concentrated and was directly used for the next acidification step.

[0052] (3) Cool the ammonium difluorosulfonamide solution obtained in step (2) to 0°C, slowly add concentrated sulfuric acid (molar ratio of ammonium difluorosulfonamide to concentrated sulfuric acid is 1:1.1) for 60 min, filter the by-product at low temperature to obtain the difluorosulfonamide solution, and proceed directly to the next lithiation step without concentration.

[0053] (4) Add lithium hydroxide to the bis(fluorosulfonyl)imide solution obtained in step (3) (the molar ratio of bis(fluorosulfonyl)imide to lithium hydroxide is 0.55:1), react at 10°C for 3 h, and after the reaction, filter, concentrate and crystallize to obtain crude bis(fluorosulfonyl)imide.

[0054] (5) Lithium difluorosulfonylimide was purified through a series of processes to obtain high-purity lithium difluorosulfonylimide. 10 g of crude lithium difluorosulfonylimide was added to 150 g of chlorobenzene and stirred at room temperature. The supernatant was filtered to remove excess acid from the acid system. The solid was then fully dissolved in acetonitrile (the mass of acetonitrile was 15 times that of crude lithium difluorosulfonylimide). The insoluble matter was removed by filtration and the solution was concentrated under reduced pressure to obtain a concentrated lithium difluorosulfonylimide solution. The concentrated lithium difluorosulfonylimide solution was slowly added dropwise to n-hexane (the mass ratio of the concentrated lithium difluorosulfonylimide solution to n-hexane was 1:20) for back precipitation. The precipitate was allowed to stand and then separated and dried under vacuum to obtain high-purity lithium difluorosulfonylimide.

[0055] Example 4

[0056] The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride in this embodiment includes the following steps:

[0057] (1) Add 0.5 mol aminosulfonic acid and 1.5 mol thionyl chloride to the reaction vessel, stir for 20 min and then heat to 80℃. Start adding 0.5 mol chlorosulfonic acid (the molar ratio of aminosulfonic acid, chlorosulfonic acid and thionyl chloride is 1:1:3). After all the chlorosulfonic acid is added, heat to 125℃ and react for 18 h. After the reaction is completed, immediately carry out distillation to separate the impurity components and collect the fraction at 90℃ to obtain pure dichlorosulfonylimide.

[0058] (2) First, 55 g of ammonium fluoride (1.5 mol) was dispersed in 1375 g of N,N-dimethylformamide to prepare an ammonium fluoride suspension. Then, under nitrogen protection, 0.3 mol of dichlorosulfonylimide was added to the reaction flask. Subsequently, within a constant temperature range of 50±5℃, the above ammonium fluoride suspension was added to the reaction flask system using an intermittent gradient non-equal feeding mode (the non-equal feeding ratios for the early, middle, and late stages were 10%, 70%, and 20%, respectively (all referring to the percentage of the required mass of ammonium fluoride to the total mass of ammonium fluoride at each stage)). After the feeding was completed, the temperature was raised to 90℃ for deep fluorination for 6 h to obtain a dichlorosulfonylimide ammonium solution. This solution did not need to be concentrated and was directly used for the next acidification step.

[0059] (3) Cool the ammonium difluorosulfonamide solution obtained in step (2) to 0°C, slowly add trifluoromethanesulfonic acid (the molar ratio of ammonium difluorosulfonamide to trifluoromethanesulfonic acid is 1:1.2) for 60 min, filter the by-product ammonium salt at low temperature to obtain the difluorosulfonamide solution, and proceed directly to the next lithiation step without concentration.

[0060] (4) Add lithium carbonate to the bis(fluorosulfonyl)imide solution obtained in step (3) (the molar ratio of bis(fluorosulfonyl)imide to lithium carbonate is 0.55:1), react at 10°C for 3 h, and after the reaction, filter, concentrate and crystallize to obtain crude bis(fluorosulfonyl)imide.

[0061] (5) Lithium difluorosulfonylimide was purified through a series of processes to obtain high-purity lithium difluorosulfonylimide. 10 g of crude lithium difluorosulfonylimide was added to 150 g of dichloromethane and stirred at room temperature. The supernatant was filtered to remove excess acid from the acid system. The solid was then fully dissolved in methyl tert-butyl ether (the mass of methyl tert-butyl ether was 15 times that of crude lithium difluorosulfonylimide). The insoluble matter was removed by filtration and the solution was concentrated under reduced pressure to obtain a concentrated lithium difluorosulfonylimide solution. The concentrated lithium difluorosulfonylimide solution was slowly added dropwise to toluene (the mass ratio of the concentrated lithium difluorosulfonylimide solution to toluene was 1:20) for back precipitation. The precipitate was allowed to stand and then separated and dried under vacuum to obtain high-purity lithium difluorosulfonylimide.

[0062] Example 5

[0063] The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride in this embodiment includes the following steps:

[0064] (1) Add 0.5 mol aminosulfonic acid and 1.5 mol thionyl chloride to the reaction vessel, stir for 20 min and then heat to 80℃. Start adding 0.5 mol chlorosulfonic acid (the molar ratio of aminosulfonic acid, chlorosulfonic acid and thionyl chloride is 1:1:3). After all the chlorosulfonic acid is added, heat to 125℃ and react for 18 h. After the reaction is completed, immediately carry out distillation to separate the impurity components and collect the fraction at 90℃ to obtain pure dichlorosulfonylimide.

[0065] (2) First, 55 g of ammonium fluoride (1.5 mol) was dispersed in 1100 g of methyl tert-butyl ether to prepare an ammonium fluoride suspension. Then, under nitrogen protection, 0.3 mol of dichlorosulfonyl imide was added to the reaction flask. Subsequently, within a constant temperature range of 50±5℃, the above ammonium fluoride suspension was added to the reaction flask system using an intermittent gradient non-equal feeding mode (the non-equal feeding ratios for the early, middle, and late stages were 10%, 80%, and 10%, respectively (all referring to the percentage of the required mass of ammonium fluoride to the total mass of ammonium fluoride at each stage)). After the feeding was completed, the temperature was raised to 95℃ for deep fluorination for 6 h to obtain a dichlorosulfonyl imide ammonium solution. This solution did not need to be concentrated and was directly used for the next acidification step.

[0066] (3) Cool the ammonium difluorosulfonamide solution obtained in step (2) to 0°C, slowly add trifluoromethanesulfonic acid (the molar ratio of ammonium difluorosulfonamide to trifluoromethanesulfonic acid is 1:1.05) for 30 min, filter the by-product ammonium salt at low temperature to obtain the difluorosulfonamide solution, and proceed directly to the next lithiation step without concentration.

[0067] (4) Add lithium carbonate to the bis(fluorosulfonyl)imide solution obtained in step (3) (the molar ratio of bis(fluorosulfonyl)imide to lithium carbonate is 0.55:1), react at 10°C for 3 h, and after the reaction, filter, concentrate and crystallize to obtain crude bis(fluorosulfonyl)imide.

[0068] (5) Lithium difluorosulfonylimide was purified through a series of processes to obtain high-purity lithium difluorosulfonylimide. 10 g of crude lithium difluorosulfonylimide was added to 150 g of dichloromethane and stirred at room temperature. The supernatant was filtered to remove excess acid from the acid system. The solid was then fully dissolved in methyl tert-butyl ether (the mass of methyl tert-butyl ether was 15 times that of crude lithium difluorosulfonylimide). The insoluble matter was removed by filtration and the solution was concentrated under reduced pressure to obtain a concentrated lithium difluorosulfonylimide solution. The concentrated lithium difluorosulfonylimide solution was slowly added dropwise to toluene (the mass ratio of the concentrated lithium difluorosulfonylimide solution to toluene was 1:20) for back precipitation. The precipitate was allowed to stand and then separated and dried under vacuum to obtain high-purity lithium difluorosulfonylimide.

[0069] Example 6

[0070] The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride in this embodiment includes the following steps:

[0071] (1) Add 0.5 mol aminosulfonic acid and 1.5 mol thionyl chloride to the reaction vessel, stir for 20 min and then raise the temperature to 80℃. Start adding 0.5 mol chlorosulfonic acid (the molar ratio of aminosulfonic acid, chlorosulfonic acid and thionyl chloride is 1:1:3). After all the chlorosulfonic acid is added, raise the temperature to 122℃ and the reaction time is 17 h. After the reaction is completed, immediately carry out distillation to separate the impurity components and collect the fraction at 90℃ to obtain pure dichlorosulfonylimide.

[0072] (2) First, 59 g of ammonium fluoride (1.6 mol) was dispersed in 1770 g of ethyl acetate to prepare an ammonium fluoride suspension. Then, under nitrogen protection, 0.2 mol of dichlorosulfonylimide was added to the reaction flask. Subsequently, within a constant temperature range of 50±5℃, the above ammonium fluoride suspension was added to the reaction flask system using an intermittent gradient non-equal feeding mode (the non-equal feeding ratios for the early, middle, and late stages were 15%, 75%, and 10%, respectively (all referring to the percentage of the required mass of ammonium fluoride to the total mass of ammonium fluoride at each stage)). After the feeding was completed, the temperature was raised to 100℃ for deep fluorination for 2 h to obtain a dichlorosulfonylimide ammonium solution. This solution did not need to be concentrated and was directly used for the next acidification step.

[0073] (3) Cool the ammonium difluorosulfonamide solution obtained in step (2) to 10°C, slowly add trifluoromethanesulfonic acid (the molar ratio of ammonium difluorosulfonamide to trifluoromethanesulfonic acid is 1:3) and acidify for 10 min. Filter the byproduct ammonium trifluoromethanesulfonate at low temperature to obtain the difluorosulfonamide solution. No concentration is required to proceed directly to the next lithiation step.

[0074] (4) Add lithium carbonate to the bis(fluorosulfonyl)imide solution obtained in step (3) (the molar ratio of bis(fluorosulfonyl)imide to lithium carbonate is 2:1), react at 10°C for 3 h, and after the reaction, filter, concentrate and crystallize to obtain crude bis(fluorosulfonyl)imide.

[0075] (5) Lithium difluorosulfonylimide was purified through a series of processes to obtain high-purity lithium difluorosulfonylimide. 10 g of crude lithium difluorosulfonylimide was added to 200 g of dichloromethane and stirred at room temperature. The supernatant was filtered to remove excess acid from the acid system. The solid was then fully dissolved in methyl tert-butyl ether (the mass of methyl tert-butyl ether was 20 times that of crude lithium difluorosulfonylimide). The insoluble matter was removed by filtration and the solution was concentrated under reduced pressure to obtain a concentrated lithium difluorosulfonylimide solution. The concentrated lithium difluorosulfonylimide solution was slowly added dropwise to toluene (the mass ratio of the concentrated lithium difluorosulfonylimide solution to toluene was 1:15) for back precipitation. After standing to precipitate, the precipitate was separated and dried under vacuum to obtain high-purity lithium difluorosulfonylimide.

[0076] Example 7

[0077] The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride in this embodiment includes the following steps:

[0078] (1) Add 0.5 mol aminosulfonic acid and 1.5 mol thionyl chloride to the reaction vessel, stir for 20 min and then heat to 80℃. Start adding 0.5 mol chlorosulfonic acid (the molar ratio of aminosulfonic acid, chlorosulfonic acid and thionyl chloride is 1:1:3). After all the chlorosulfonic acid is added, heat to 120℃ and react for 16 h. Immediately after the reaction is completed, distillation is carried out to separate the impurity components. Collect the fraction at 90℃ to obtain pure dichlorosulfonylimide.

[0079] (2) First, 44 g of ammonium fluoride (1.2 mol) was dispersed in 880 g of ethyl acetate to prepare an ammonium fluoride suspension. Then, under nitrogen protection, 0.3 mol of dichlorosulfonylimide was added to the reaction flask. Subsequently, within a constant temperature range of 50±5℃, the above ammonium fluoride suspension was added to the reaction flask system using an intermittent gradient non-equal feeding mode (the non-equal feeding ratios for the early, middle, and late stages were 15%, 75%, and 10%, respectively (all referring to the percentage of the required mass of ammonium fluoride to the total mass of ammonium fluoride at each stage)). After the feeding was completed, the temperature was raised to 60℃ for deep fluorination for 12 h to obtain a dichlorosulfonylimide ammonium solution. This solution did not need to be concentrated and was directly used for the next acidification step.

[0080] (3) Cool the ammonium difluorosulfonamide solution obtained in step (2) to -10°C, slowly add trifluoromethanesulfonic acid (the molar ratio of ammonium difluorosulfonamide to trifluoromethanesulfonic acid is 1:2) and acidify for 120 min. Filter the byproduct ammonium trifluoromethanesulfonate at low temperature to obtain the difluorosulfonamide solution. No concentration is required to proceed directly to the next lithiation step.

[0081] (4) Add lithium carbonate to the bis(fluorosulfonyl)imide solution obtained in step (3) (the molar ratio of bis(fluorosulfonyl)imide to lithium carbonate is 1:0.5), react at 10°C for 3 h, and after the reaction, filter, concentrate and crystallize to obtain crude bis(fluorosulfonyl)imide.

[0082] (5) Lithium difluorosulfonylimide was purified through a series of processes to obtain high-purity lithium difluorosulfonylimide. 10 g of crude lithium difluorosulfonylimide was added to 100 g of dichloromethane and stirred at room temperature. The supernatant was filtered to remove excess acid from the acid system. The solid was then fully dissolved in methyl tert-butyl ether (the mass of methyl tert-butyl ether was 20 times that of crude lithium difluorosulfonylimide). The insoluble matter was removed by filtration and the solution was concentrated under reduced pressure to obtain a concentrated lithium difluorosulfonylimide solution. The concentrated lithium difluorosulfonylimide solution was slowly added dropwise to toluene (the mass ratio of the concentrated lithium difluorosulfonylimide solution to toluene was 1:15) for back precipitation. The precipitate was allowed to stand and then separated and dried under vacuum to obtain high-purity lithium difluorosulfonylimide.

[0083] Comparative Example 1

[0084] The preparation method of lithium bis(fluorosulfonyl)imide in this comparative example differs from that in Example 5 in that it involves a single-stage addition of the feed, and the steps are as follows:

[0085] (1) Add 0.5 mol aminosulfonic acid and 1.5 mol thionyl chloride to the reaction vessel, stir for 20 min and then heat to 80℃. Start adding 0.5 mol chlorosulfonic acid (the molar ratio of aminosulfonic acid, chlorosulfonic acid and thionyl chloride is 1:1:3). After all the chlorosulfonic acid is added, heat to 125℃ and react for 18 h. After the reaction is completed, immediately carry out distillation to separate the impurity components and collect the fraction at 90℃ to obtain pure dichlorosulfonylimide.

[0086] (2) First, 55 g of ammonium fluoride (1.5 mol) was dispersed in 1100 g of methyl tert-butyl ether to prepare an ammonium fluoride suspension. Then, under nitrogen protection, 0.3 mol of dichlorosulfonyl imide was added to the reaction flask. Subsequently, the above ammonium fluoride suspension was added to the reaction flask system all at once within a constant temperature range of 50±5℃. After the addition was completed, the temperature was raised to 95℃ for deep fluorination for 6 h to obtain a dichlorosulfonyl imide ammonium solution. This solution did not need to be concentrated and was directly used for the next acidification step.

[0087] (3) Cool the ammonium difluorosulfonamide solution obtained in step (2) to 0°C, slowly add trifluoromethanesulfonic acid (the molar ratio of ammonium difluorosulfonamide to trifluoromethanesulfonic acid is 1:1.05) for 30 min, filter the by-product ammonium salt at low temperature to obtain the difluorosulfonamide solution, and proceed directly to the next lithiation step without concentration.

[0088] (4) Add lithium carbonate to the bis(fluorosulfonyl)imide solution obtained in step (3) (the molar ratio of bis(fluorosulfonyl)imide to lithium carbonate is 0.55:1), react at 10°C for 3 h, and after the reaction, filter, concentrate and crystallize to obtain crude bis(fluorosulfonyl)imide.

[0089] (5) Lithium difluorosulfonylimide was purified through a series of processes to obtain high-purity lithium difluorosulfonylimide. 10 g of crude lithium difluorosulfonylimide was added to 150 g of dichloromethane and stirred at room temperature. The supernatant was filtered to remove excess acid from the acid system. The solid was then fully dissolved in methyl tert-butyl ether (the mass of methyl tert-butyl ether was 15 times that of crude lithium difluorosulfonylimide). The insoluble matter was removed by filtration and the solution was concentrated under reduced pressure to obtain a concentrated lithium difluorosulfonylimide solution. The concentrated lithium difluorosulfonylimide solution was slowly added dropwise to toluene (the mass ratio of the concentrated lithium difluorosulfonylimide solution to toluene was 1:20) for back precipitation. The precipitate was allowed to stand and then separated and dried under vacuum to obtain lithium difluorosulfonylimide.

[0090] Comparative Example 2

[0091] The preparation method of lithium bis(fluorosulfonyl)imide in this comparative example differs from that in Example 5 in that acidification with a cation exchange resin is used, and the steps are as follows:

[0092] (1) Add 0.5 mol aminosulfonic acid and 1.5 mol thionyl chloride to the reaction vessel, stir for 20 min and then heat to 80℃. Start adding 0.5 mol chlorosulfonic acid (the molar ratio of aminosulfonic acid, chlorosulfonic acid and thionyl chloride is 1:1:3). After all the chlorosulfonic acid is added, heat to 125℃ and react for 18 h. After the reaction is completed, immediately carry out distillation to separate the impurity components and collect the fraction at 90℃ to obtain pure dichlorosulfonylimide.

[0093] (2) First, 55 g of ammonium fluoride (1.5 mol) was dispersed in 1100 g of methyl tert-butyl ether to prepare an ammonium fluoride suspension. Then, under nitrogen protection, 0.3 mol of dichlorosulfonyl imide was added to the reaction flask. Subsequently, within a constant temperature range of 50±5℃, the above ammonium fluoride suspension was added to the reaction flask system using an intermittent gradient non-equal feeding mode (the non-equal feeding ratios for the early, middle, and late stages were 10%, 80%, and 10%, respectively (all referring to the percentage of the required mass of ammonium fluoride to the total mass of ammonium fluoride at each stage)). After the feeding was completed, the temperature was raised to 95℃ for deep fluorination for 6 h to obtain a dichlorosulfonyl imide ammonium solution. This solution did not need to be concentrated and was directly used for the next acidification step.

[0094] (3) The ammonium bis(fluorosulfonyl)imide solution obtained in step (2) is acidified with a strong acid cation exchange resin to obtain a bis(fluorosulfonyl)imide solution. The flow rate is controlled at 15 mL / min. The pH of the effluent is ≈7 and the exchange is completed to obtain the bis(fluorosulfonyl)imide solution.

[0095] (4) Add lithium carbonate to the bis(fluorosulfonyl)imide solution obtained in step (3) (the molar ratio of bis(fluorosulfonyl)imide to lithium carbonate is 0.55:1), react at 10°C for 3 h, and after the reaction, filter, concentrate and crystallize to obtain crude bis(fluorosulfonyl)imide.

[0096] (5) Lithium difluorosulfonylimide was purified through a series of processes to obtain high-purity lithium difluorosulfonylimide. 10 g of crude lithium difluorosulfonylimide was added to 150 g of dichloromethane and stirred at room temperature. The supernatant was filtered to remove excess acid from the acid system. The solid was then fully dissolved in methyl tert-butyl ether (the mass of methyl tert-butyl ether was 15 times that of crude lithium difluorosulfonylimide). The insoluble matter was removed by filtration and the solution was concentrated under reduced pressure to obtain a concentrated lithium difluorosulfonylimide solution. The concentrated lithium difluorosulfonylimide solution was slowly added dropwise to toluene (the mass ratio of the concentrated lithium difluorosulfonylimide solution to toluene was 1:20) for back precipitation. The precipitate was allowed to stand and then separated and dried under vacuum to obtain lithium difluorosulfonylimide.

[0097] The total yield and purity of lithium bis(fluorosulfonyl)imide prepared in Examples 1-5 and Comparative Examples 1-2 are shown in Table 1.

[0098] Table 1

[0099]

[0100] As shown in Table 1, the overall product yield of Examples 1-5 was ≥97%. Among them, the highest product content (≥99.5%) and overall yield (≥99.1%) were achieved after optimizing the amount of ammonium fluoride added, reaction time, type and amount of strong acid, type and amount of lithium source, and purification solvent during the purification process. Specifically, under the same feed amount, Comparative Example 1 had a larger amount of ammonium fluoride suspension added at once, and since the reaction was a solid-liquid reaction, excessive ammonium fluoride added at once would cause some NH4FSI to be encapsulated by the ammonium fluoride, resulting in product loss during subsequent filtration. The acidification time of Comparative Example 2 was 20 h, which was relatively long.

[0101] The impurity metal ions, anions, and moisture content in lithium difluorosulfonamide were determined by ICP-MS, IC, and Karl Fischer moisture analyzers, respectively. The free acid and DMC insoluble content in lithium difluorosulfonamide were determined by self-testing according to the method specified in GB / T19282-2014. The results are shown in Table 2.

[0102] Table 2

[0103]

[0104] As shown in Table 2, the products in Examples 1-5 had free acid content ≤30ppm, moisture content ≤50ppm, chloride ion content ≤10ppm, fluoride ion content ≤20ppm, and DMC insoluble content ≤30ppm. In comparison, the products in Example 4, using DMF as a solvent and acidification with trifluoromethanesulfonic acid, showed a significant increase in impurities. The moisture content and DMC insoluble content in Comparative Example 1 were significantly higher, indicating a clear limitation.

[0105] Therefore, by changing the synthesis and purification conditions, the yield, product content, and purity of lithium bis(fluorosulfonyl)imide can be significantly improved. Furthermore, this process route offers mild conditions, easy reaction control, low risk, rapid reaction facilitating large-scale application, and high yield and purity of lithium bis(fluorosulfonyl)imide, meeting the market demand for high-purity bis(fluorosulfonyl)imide.

[0106] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride, characterized in that, The steps are as follows: (1) In the constant temperature range, an intermittent gradient non-equal feeding mode was used to add ammonium fluoride suspension to dichlorosulfonimide, and then the temperature was raised to deeply fluorinate dichlorosulfonimide to prepare dichlorosulfonimide ammonium salt. (2) The difluorosulfonamide ammonium salt obtained in step (1) is acidified with strong acid and separated by filtration to obtain a difluorosulfonamide solution; (3) The difluorosulfonylimide solution obtained in step (2) reacts with a lithium source, and after filtration, separation, concentration and crystallization, crude difluorosulfonylimide lithium is obtained; then it is purified to obtain difluorosulfonylimide lithium.

2. The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride according to claim 1, characterized in that, The preparation method of dichlorosulfonamide in step (1) is as follows: it is prepared by reacting aminosulfonic acid, chlorosulfonic acid and thionyl chloride as raw materials.

3. The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride according to claim 1, characterized in that, In step (1), the molar ratio of dichlorosulfonamide to ammonium fluoride in the ammonium fluoride suspension is 1:(3-8).

4. The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride according to claim 3, characterized in that, In step (1), the solvent in the ammonium fluoride suspension is at least one of dimethyl carbonate, diethyl carbonate, butyl acetate, ethyl acetate, N,N-dimethylformamide, diethyl ether, and methyl tert-butyl ether.

5. The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride according to claim 4, characterized in that, In step (1), the temperature of the constant temperature range is 50±5℃. The intermittent gradient non-equal feeding mode refers to: first, adding 10%-20% of the mass of ammonium fluoride in the ammonium fluoride suspension, and waiting for the system to stabilize; then adding 60%-80% of the mass of ammonium fluoride in the ammonium fluoride suspension, and after the system stabilizes, adding the remaining 10%-20% of the total mass of ammonium fluoride in the ammonium fluoride suspension.

6. The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride according to claim 5, characterized in that, In step (1), the temperature for deep fluorination is 60-100℃ and the time is 2-12 h.

7. The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride according to claim 6, characterized in that, In step (2), the strong acid is at least one of fluorosulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid and concentrated sulfuric acid, and the molar ratio of difluorosulfonylimide ammonium salt to the strong acid is 1:(1-3); the acidification temperature is -10~10℃, and the reaction time is 10-120 min.

8. The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride according to claim 7, characterized in that, In step (3), the anion in the lithium source is one of hydroxide ions, carbonate ions, bicarbonate ions and tetrafluoroborate ions, and the molar ratio of lithium source to difluorosulfonamide is (0.5-2):

1.

9. The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride according to claim 8, characterized in that, In step (3), the purification steps are as follows: add the first solvent to the crude lithium difluorosulfonylimide and slurry at room temperature, filter to obtain the solid; then dissolve the solid in the second solvent, filter to remove insoluble matter, concentrate under reduced pressure to obtain lithium difluorosulfonylimide concentrate; add the lithium difluorosulfonylimide concentrate to the third solvent for back precipitation, let it stand to precipitate, separate and vacuum dry to obtain lithium difluorosulfonylimide.

10. The method for preparing lithium bis(fluorosulfonyl)imide by mild fluorination with ammonium fluoride according to claim 9, characterized in that, The first solvent and the third solvent are at least one of dichloromethane, dichloroethane, petroleum ether, n-hexane, toluene, xylene, chlorobenzene, and dichlorobenzene; the second solvent is at least one of acetonitrile, propionitrile, isopropionitrile, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, butyl acetate, diethyl ether, propyl ether, methyl tert-butyl ether, tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide.

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