A method for preparing high-purity lithium bis(fluorosulfonyl)imide liquid salt

Abstract

This invention relates to the field of organic chemistry and provides a method for preparing high-purity lithium difluorosulfonylimide liquid salt. The steps include: mixing difluorosulfonylimide with lithium fluoride and reacting, followed by a first filtration to obtain crude lithium difluorosulfonylimide salt; dissolving the crude lithium difluorosulfonylimide salt in a good solvent, adding an acid-removing agent, and then performing a second filtration to obtain lithium difluorosulfonylimide liquid salt; wherein the good solvent is a carbonate solvent; in this invention, difluorosulfonylimide is both a raw material and a reaction solvent, reacting with lithium fluoride at a certain temperature to generate lithium difluorosulfonylimide salt; after the reaction is completed, the crude lithium difluorosulfonylimide salt is obtained by a first filtration; the filtrate obtained after the first filtration of the reaction solution is unreacted difluorosulfonylimide, which can be reused; the preparation method of this invention produces less waste, is economical and environmentally friendly, has a simple process, high yield, and good product quality, and is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of organic chemistry, and more particularly to a method for preparing high-purity lithium difluorosulfonylimide liquid salt. Background Technology

[0002] Lithium-ion batteries are an important type of rechargeable battery. Due to their high operating voltage, small size, light weight, high energy density, lack of memory effect, lack of pollution, low self-discharge, and long cycle life, they have been widely used in all aspects of modern production and daily life. Lithium bisfluorosulfonyl imide (LiFSI) possesses better conductivity, higher electrochemical and thermal stability, and greater resistance to hydrolysis compared to the traditional electrolyte salt LiPF6. Adding LiFSI can significantly increase the number of charge-discharge cycles and stabilize highly active electrode materials such as high-nickel and high-voltage cathodes, thereby extending battery life. It also improves the flame-retardant properties of the electrolyte and enhances safety.

[0003] Most methods for synthesizing LiFSI involve first synthesizing bischlorosulfonamide (HClSI), then reacting it with MFn to prepare the corresponding metal or organic base bischlorosulfonamide salt intermediate, and then performing a cation exchange reaction with LiOH or Li2CO3 to obtain LiFSI. The disadvantage of these methods is that once the exchange reaction reaches an equilibrium, it is difficult to complete the process, and the unreacted intermediate MSFI is difficult to completely separate from LiFSI to obtain a high-quality product.

[0004] LiFSI is prepared by metal exchange of purified potassium bis(fluorosulfonyl)imide (KFSI) with lithium salts such as LiClO4, LiBF4, lithium bis(oxalato)borate, and LiPF6. The product often has a high potassium ion content, which affects its practical application. In particular, both LiClO4 and the generated KClO4 pose a certain explosion risk.

[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 significant drawbacks. HFSI releases heat violently when dissolved in water, leading to its decomposition. This patent uses an ultra-low temperature (-78°C) method to prepare an aqueous solution of HFSI to solve the technical problem of the violent heat release when HFSI dissolves in water. However, this method increases energy consumption significantly. More importantly, LiFSI has very good water solubility, resulting in very low extraction efficiency, making it unsuitable for industrial production.

[0006] Therefore, there is an urgent need for a simple preparation method that can improve the yield and quality of lithium difluorosulfonylimide. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing high-purity lithium bis(fluorosulfonyl)imide liquid salt.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing high-purity lithium difluorosulfonylimide liquid salt is provided, comprising the following steps: mixing difluorosulfonylimide with lithium fluoride and reacting them, followed by a first filtration treatment to obtain crude lithium difluorosulfonylimide salt; dissolving the crude lithium difluorosulfonylimide salt in a good solvent, adding an acid remover, and then performing a second filtration treatment to obtain lithium difluorosulfonylimide liquid salt;

[0010] The benign solvent is a carbonate solvent;

[0011] The deacidifying agent is an alkaline reagent;

[0012] The equation for the reaction is as follows:

[0013]

[0014] Preferably, the mass ratio of the bis(fluorosulfonyl)imide to the lithium fluoride is (15-50):1.

[0015] Preferably, the reaction temperature is 80℃-150℃; the reaction time is 1h-8h.

[0016] Preferably, the carbonate solvent includes at least one of dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate.

[0017] Preferably, the mass ratio of the benign solvent to the crude bis(fluorosulfonyl)imide lithium salt is (1-5):1.

[0018] Preferably, the deacidifying agent includes at least one of an inorganic alkali or an organic alkali.

[0019] More preferably, the inorganic base includes at least one of lithium hydride, calcium hydride, or ammonia; and the organic base includes at least one of butyllithium, triethylamine, tripropylamine, tributylamine, or diisopropylethylamine.

[0020] Preferably, the material used in the second filtration process includes at least one of the following: vinylidene fluoride resin membrane, polytetrafluoroethylene pleated filter element, or ceramic membrane.

[0021] More preferably, the pore size of the material is 1nm-1000nm.

[0022] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0023] In this invention, bis(fluorosulfonyl)imide serves as both a raw material and a reaction solvent, reacting with lithium fluoride at a certain temperature to generate lithium bis(fluorosulfonyl)imide salt. After the reaction is complete, a first filtration process yields crude lithium bis(fluorosulfonyl)imide salt. The filtrate obtained after the first filtration process is unreacted bis(fluorosulfonyl)imide, which can be reused. The byproduct hydrogen fluoride that overflows during the reaction can react with lithium carbonate to prepare lithium fluoride, thereby achieving the recovery and reuse of the byproduct. The preparation method of this invention produces less waste, is economical and environmentally friendly, has a simple process, high yield, and good product quality, making it suitable for industrial production. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0026] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0027] Example 1

[0028] This embodiment provides a method for preparing high-purity lithium bis(fluorosulfonyl)imide liquid salt. The steps include: mixing 750g of bis(fluorosulfonyl)imide (HFSI) and 30g of lithium fluoride (LiF) in a reaction vessel and reacting at 110°C for 5 hours; the hydrogen fluoride (HF) tail gas generated during the reaction is introduced into a PFA reaction vessel containing sufficient Li2CO3 and deionized water through a PFA resin tube; after the reaction is completed, the reaction vessel is cooled to room temperature and subjected to a first filtration treatment to obtain 540.2g of filtrate and 215.9g of crude lithium bis(fluorosulfonyl)imide salt (LiFSI), with an acid value (based on HF) of 476ppm; when the pH of the PFA reaction vessel system is 6-7, the material in the PFA reaction vessel is filtered and dried to obtain recovered LiF;

[0029] 490g of ethyl methyl carbonate (EMC) with a moisture content of less than 5ppm was placed in a reactor, and 210g of crude LiFSI and 0.04g of lithium hydride (LiH) were added. After stirring at room temperature for 1 hour, the mixture was filtered a second time using a ceramic membrane with a pore size of 50nm to obtain the LiFSI solution. The concentration of the LiFSI solution was 29.8%, the acid value (HF) was 12ppm, the moisture content was 8ppm, the chloride ion concentration was less than 1ppm, the fluoride ion concentration was 5ppm, the sulfate ion concentration was less than 1ppm, the sodium concentration was 2ppm, and the potassium concentration was 1ppm.

[0030] Example 2

[0031] This embodiment provides another method for preparing high-purity lithium bis(fluorosulfonyl)imide liquid salt. The steps include: mixing 520g of HFSI, 230g of HFSI and 30g of LiF from the filtrate described in Example 1 in a reaction vessel, and reacting at 120°C for 4 hours. The HF tail gas generated during the reaction is introduced into a PFA reaction vessel containing sufficient Li2CO3 and deionized water through a PFA resin tube. After the reaction is completed, the reaction vessel is cooled to room temperature and subjected to a first filtration treatment to obtain 538.4g of filtrate and 217.9g of crude LiFSI, with an acid value (based on HF) of 506ppm.

[0032] 490g of dimethyl carbonate (DMC) with a moisture content of less than 5ppm was placed in a reactor, and 210g of crude LiFSI and 0.51g of triethylamine were added. After stirring at room temperature for 1 hour, the mixture was filtered a second time using a vinylidene fluoride resin membrane with a pore size of 450nm to obtain the LiFSI solution. The concentration of the LiFSI solution was 30.0%, the acid value (HF) was 9ppm, the moisture content was 11ppm, the chloride ion concentration was less than 1ppm, the fluoride ion concentration was 12ppm, the sulfate ion concentration was less than 1ppm, the sodium concentration was 1ppm, and the potassium concentration was 1ppm.

[0033] Example 3

[0034] This embodiment provides another method for preparing high-purity lithium bis(fluorosulfonyl)imide liquid salt. The steps include: mixing 750g of HFSI with 30g of the recovered LiF described in the embodiment in a reaction vessel and reacting at 120°C for 4h; the HF tail gas generated during the reaction is introduced into a PFA reaction vessel containing sufficient Li2CO3 and deionized water through a PFA resin tube; after the reaction is completed, the reaction vessel is cooled to room temperature and subjected to a first filtration treatment to obtain 539.0g of filtrate and 216.1g of crude LiFSI, with an acid value (based on HF) of 480ppm;

[0035] 490g of diethyl carbonate (DEC) with a moisture content of less than 5ppm was placed in a reactor, and 210g of crude LiFSI and 0.11g of calcium hydride (CaH2) were added. After stirring at room temperature for 1 hour, the mixture was filtered a second time using a polytetrafluoroethylene pleated filter with a pore size of 200nm to obtain the LiFSI solution. The concentration of the LiFSI solution was 29.8%, the acid value (HF value) was 5ppm, the moisture content was 15ppm, the chloride ion concentration was less than 1ppm, the fluoride ion concentration was 3ppm, the sulfate ion concentration was less than 1ppm, the sodium concentration was 3ppm, and the potassium concentration was 1ppm.

[0036] In summary, in this invention, bis(fluorosulfonyl)imide serves as both a raw material and a reaction solvent, reacting with lithium fluoride at a certain temperature to generate lithium bis(fluorosulfonyl)imide salt. After the reaction is complete, a first filtration process yields crude lithium bis(fluorosulfonyl)imide salt. The filtrate obtained after the first filtration process is unreacted bis(fluorosulfonyl)imide, which can be reused. The byproduct hydrogen fluoride that overflows during the reaction can react with lithium carbonate to prepare lithium fluoride, thereby achieving the recovery and reuse of the byproduct. The preparation method of this invention generates less waste, is economical and environmentally friendly, has a simple process, high yield, and good product quality, making it suitable for industrial production.

[0037] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for preparing high purity lithium bisfluorosulfonylimide liquid salt, characterized by the steps of include: Difluorosulfonyl imide was mixed with lithium fluoride and reacted, followed by a first filtration process to obtain crude difluorosulfonyl imide lithium salt. The crude difluorosulfonylimide lithium salt is dissolved in a good solvent, treated with an acid remover, and then filtered a second time to obtain liquid difluorosulfonylimide lithium salt. The benign solvent is a carbonate solvent; The deacidifying agent is an alkaline reagent; The mass ratio of the bis(fluorosulfonyl)imide to the lithium fluoride is (15-50):1; The reaction temperature is 80℃-150℃; the reaction time is 1h-8h; In this process, the difluorosulfonamide serves as both a raw material and a reaction solvent.

2. The preparation method according to claim 1, characterized in that, The carbonate solvents include at least one of dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the benign solvent to the crude lithium difluorosulfonylimide salt is (1-5):

1.

4. The preparation method according to claim 1, characterized in that, The deacidifying agent includes at least one of inorganic or organic bases.

5. The preparation method according to claim 4, characterized in that, The inorganic base includes at least one of lithium hydride, calcium hydride, or ammonia; the organic base includes at least one of butyllithium, triethylamine, tripropylamine, tributylamine, or diisopropylethylamine.

6. The preparation method according to claim 1, characterized in that, The materials used in the second filtration process include at least one of the following: vinylidene fluoride resin membrane, polytetrafluoroethylene pleated filter element, or ceramic membrane.

7. The preparation method according to claim 6, characterized in that, The pore size of the material is 1nm-1000nm.

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