WO2019229376A2

WO2019229376A2 - Process for purifying lithium bis(fluorosulfonyl)imide salt

Info

Publication number: WO2019229376A2
Application number: PCT/FR2019/051257
Authority: WO
Inventors: Grégory Schmidt
Original assignee: Arkema France
Priority date: 2018-06-01
Filing date: 2019-05-28
Publication date: 2019-12-05
Also published as: WO2019229376A3; FR3081724A1

Abstract

The present invention relates to a process for purifying a lithium bis(fluorosulfonyl)imide salt in a solution in an organic solvent SO1. The present invention likewise relates to a composition based on lithium bis(fluorosulfonyl)imide salt.

Description

Process for purifying the bis (fluorosulfonyl) imide lithium salt

FIELD OF THE INVENTION

The present invention relates to a process for purifying a bis (fluorosulfonyl) imide lithium salt.

The invention also relates to a process for manufacturing a lithium salt of bis (fluorosulfonyl) imide, purified by the purification method according to the invention.

TECHNICAL BACKGROUND

Anions of sulfonylimide type, by their very low basicity, are increasingly used in the field of energy storage in the form of inorganic salts in batteries, or organic salts in supercapacitors or in the field of liquids ionic. As the battery market is booming and the reduction of battery manufacturing costs becomes a major issue, a large-scale and low-cost synthesis process for this type of anion is necessary.

In the specific field of Li-ion batteries, the salt currently most used is LiPF ₆ but this salt shows numerous disadvantages such as limited thermal stability, sensitivity to hydrolysis and therefore lower battery safety. . Recently, new salts having the FSO ₂ group have been studied and have demonstrated many advantages such as better ionic conductivity and resistance to hydrolysis. One of these salts, LiFSI (LiN (FSO ₂ ) ₂ ) has shown very interesting properties that make it a good candidate to replace LiPF ₆ .

The identification and quantification of impurities in salts and / or electrolytes, and the understanding of their impacts on battery performance become paramount. For example, impurities having a mobile proton, due to their interference with electrochemical reactions, lead to lower overall performance and stability of the Li-ion batteries. The application of Li-ion batteries requires having products of high purity (minimum of impurities).

Various methods of purification of LiFSI are known. However, these processes have several drawbacks: risk of hydrolysis of LiFSI to sulphates, numerous steps, low yield, etc.

There is therefore a need for a process for purifying the bis (fluorosulfonyl) imide lithium salt to overcome, at least in part, at least one of the aforementioned drawbacks. DESCRIPTION OF THE INVENTION

Purification process

The present invention relates to a process for purifying a bis (fluorosulfonyl) imide lithium salt in solution in an SOI organic solvent, said process comprising the following steps:

a) liquid-liquid extraction of the bis (fluorosulfonyl) imide lithium salt of the SOI organic solvent by contact with deionized water, and recovery of an aqueous solution of said bis (fluorosulfonyl) imide lithium salt;

b) optional concentration of said aqueous solution;

(c) one of the following steps (c1) or (c2):

- c1)

i) liquid-liquid extraction of the bis (fluorosulfonyl) imide lithium salt from said aqueous solution, by contact with an organic solvent SO 2, and recovery of an organic solution of said bis (fluorosulfonyl) imide lithium salt;

ii) contacting said organic phase with at least one organic solvent S03, said organic solvent SO3 being immiscible with water; iii) decanting and recovering an organic solution of said bis (fluorosulfonyl) imide lithium salt;

or

- c2) liquid-liquid extraction of the lithium salt of bis (fluorosulfonyl) imide of said aqueous solution, by contact with at least one organic solvent SO 2 and at least one organic solvent SO 3, said organic solvent SO 3 being immiscible with the water, and recovering an organic solution of said bis (fluorosulfonyl) imide lithium salt;

d) concentration of said organic solution of bis (fluorosulfonyl) imide lithium salt, and

e) possible crystallization of the bis (fluorosulfonyl) imide lithium salt,

the process being characterized in that the organic solvent S02 and the organic solvent S03 are different.

In the context of the invention, the terms "lithium salt of bis (fluorosulfonyl) imide", "lithium bis (sulfonyl) imide", "LiFSI", "LiN (FSO ₂ ) _2" are used in an equivalent manner, " bis (sulfonyl) imide lithium, or lithium bis (fluorosulfonyl) imide.

In the context of the invention, the term "ppm" or "part per million" means ppm by weight. In the context of the invention, the terms "deionized water" and "demineralized water" are used equivalently.

The initial solution of bis (fluorosulfonyl) imide lithium salt can come from any synthesis of the bis (fluorosulfonyl) imide lithium salt, comprising in particular the following steps:

i) synthesis of bis (chlorosulfonyl) imide;

ii) fluorination of bis (chlorosulfonyl) imide to bis (fluorosulfonyl) imide;

iii) preparation of an alkaline or alkaline earth salt of bis (fluorosulfonyl) imide by neutralization of bis (fluorosulfonyl) imide;

iv) cation exchange to obtain the lithium salt of bis (fluorosulfonyl) imide.

At the end of these steps, the lithium salt of bis (fluorosulfonyl) imide is preferably obtained in solution in an organic solvent (corresponding in particular to the SOI solvent), at a mass concentration of between 5% and 50% by weight. relative to the total mass of the solution.

Such a method is for example described in the document WO 2015/158979.

The initial solution of bis (fluorosulfonyl) imide lithium salt can be obtained by dissolving the solid bis (fluorosulfonyl) imide lithium salt in an SOI organic solvent, said solid bis (fluorosulfonyl) imide lithium salt being have been obtained by any synthesis followed by a possible stage of evaporation of solvent (s).

According to one embodiment, the aforementioned SOI organic solvent is selected from the group consisting of esters, nitriles, ethers, chlorinated solvents, aromatic solvents, and mixtures thereof. Preferably, the solvent SOI is chosen from dichloromethane, ethyl acetate, butyl acetate, tetrahydrofuran, acetonitrile, diethyl ether, and mixtures thereof. Preferably, the organic solvent SOI is butyl acetate.

The mass content of lithium salt of bis (fluorosulfonyl) imide in the organic solvent SOI may be between 5% and 50% by weight relative to the total mass of the solution.

Step a)

The above-mentioned step a) comprises in particular the addition of deionized water to the solution of the lithium salt of bis (fluorosulfonyl) imide in the above-mentioned organic solvent SOI, to allow the dissolution of said lithium salt of bis (fluorosulfonyl) imide, and extracting said salt in water (aqueous phase).

The extraction can be carried out by any known extraction means. The extraction typically allows the separation of an aqueous phase (aqueous solution of said salt in this case) and an organic phase. According to the invention, step a) may be repeated at least once, preferably repeated one to 10 times, preferably repeated one to five times, and advantageously repeated three times.

In a first extraction, the deionized water mass ratio: initial solution is greater than or equal to 1: 10, preferably greater than or equal to 1: 9, and advantageously greater than or equal to 1: 8.

In a second extraction, the mass ratio deionized water: initial solution is greater than or equal to 1: 10, preferably greater than or equal to 1: 9, and preferably greater than or equal to 1: 8.

In a third extraction, the mass ratio deionized water: initial solution is greater than or equal to 1: 10, preferably greater than or equal to 1: 9 and advantageously greater than or equal to 1: 8.

In a fourth extraction, the mass ratio deionized water: initial solution is greater than or equal to 1: 10, preferably greater than or equal to 1: 9 and advantageously greater than or equal to 1: 8.

Preferably, step a) is such that the mass of deionized water used is greater than or equal to one-third, preferably greater than or equal to half, of the mass of the initial solution of said salt in the SOI organic solvent ( in the case of a single extraction, or for the first extraction only if step a) is repeated at least once).

In the case of multiple extractions (repetition of step a)), the extracted aqueous phases are combined together to form a single aqueous solution of said LiFSI.

According to one embodiment, the mass content of LiFSI in the aqueous solution is between 5% and 35%, preferably between 10% and 25%, relative to the total weight of said aqueous solution.

Step a) advantageously makes it possible to obtain an aqueous phase and an organic phase, which are separated. Step b) is thus advantageously carried out on the aqueous solution extracted in step a) (single aqueous phase or aqueous phases combined in case of repetition of step a)).

The aforementioned purification method may comprise a concentration step of the aqueous solution containing LiFSI.

This concentration step advantageously leads to an aqueous solution comprising a mass content of LiFSI of between 20% and 80%, in particular between 25% and 80%, preferably between 25% and 70%, and advantageously between 30% and 65%. relative to the total mass of the solution. The concentration step may be carried out by any means known to those skilled in the art. It may for example be carried out in an evaporator or a stirred reactor provided with a double jacket.

Preferably, the concentration step b) is carried out in an evaporator under reduced pressure, at a pressure of less than 50 mbar abs (preferably less than 30 mbar abs), and in particular at a temperature of between 25 ° C. and 60 ° C. C., preferably between 25 ° C. and 50 ° C., preferably between 25 ° C. and 40 ° C., for example at 40 ° C.

Preferably, the purification method according to the invention comprises step b). After concentration b) of the aqueous solution obtained at the end of step a), an aqueous solution of concentrated LiFSI is advantageously obtained.

Step c

According to one embodiment, the aforementioned purification process comprises the following steps:

b) optional concentration of said aqueous solution;

d)

ii) contacting said organic phase with at least one organic solvent SO 3, said organic solvent SO 3 being immiscible with water;

iii) decanting and recovering an organic solution of said bis (fluorosulfonyl) imide lithium salt;

e) possible crystallization of the lithium salt of bis (fluorosulfonyl) imide.

According to one embodiment, the aforementioned purification process comprising the following steps:

b) optional concentration of said aqueous solution; c2) liquid-liquid extraction of the bis (fluorosulfonyl) imide lithium salt from said aqueous solution, by contacting with at least one organic solvent SO 2 and at least one organic solvent SO 3, said organic solvent SO 3 being immiscible with water and recovering an organic solution of said bis (fluorosulfonyl) imide lithium salt;

c) concentration of said organic solution of bis (fluorosulfonyl) imide lithium salt, and

d) possible crystallization of the lithium salt of bis (fluorosulfonyl) imide.

Step c1) or c2) can be carried out on the aqueous solution of the bis (fluorosulfonyl) imide lithium salt obtained at the end of step a) or of step b) (concentrated aqueous solution).

The SO 2 extraction solvent of the LiFSI salt dissolved in deionized water is advantageously:

A good LiFSI solvent, that is to say that the LiFSI may have a solubility greater than or equal to 10% by weight relative to the total weight of the sum LiFSI and solvent; and or

• immiscible with water.

According to one embodiment, the organic solvent S02 has a dielectric constant greater than 4.

The measurement of the dielectric constant can for example be done as described in the thesis entitled "Characterization of dielectric and magnetic layers of multilayer structures by resonant cavity microwave" Radwan Dib submitted August 26, 2015 (https: //tel.archives- open.fr/tel-01 187109).

The organic solvent S02 is an organic solvent advantageously forming an azeotrope with water.

According to one embodiment, the organic solvent SO 2 is selected from the group consisting of esters, alcohols, ketones, ethers, chlorinated solvents, aromatic solvents, and mixtures thereof. For example, mention may be made of methyl t-butyl ether, cyclopentyl methyl ether, ethyl acetate, propyl acetate, butyl acetate, dichloromethane, diethyl ether, 2-butanone, diisopropyl ether, and mixtures thereof. Preferably, the solvent SO 2 is selected from methyl-t-butyl ether, cyclopentyl methyl ether, ethyl acetate, propyl acetate, butyl acetate, and mixtures thereof.

Preferably, the organic solvent SO 2 is butyl acetate.

Preferably, the organic solvent SO 3 is miscible with the solvent SOI.

In the context of the invention, and unless otherwise stated, a solvent "immiscible with water" is a solvent of which less than 0.5% by weight is miscible in water, preferably less than 0.1% by weight, advantageously less than 0.05% by weight, at a temperature of 25 ° C and at atmospheric pressure. The weight percentage means that it is the weight ratio of the solvent / weight (solvent + water).

In the context of the invention, and unless otherwise stated, a solvent A "miscible with a solvent B" is a solvent A of which more than 5% by weight is miscible in the solvent B, preferably more than 10% by weight. , advantageously more than 15% by weight, at a temperature of 25 ° C and at atmospheric pressure. The weight percentage refers to the weight ratio of the solvent A / weight (solvent A + solvent B).

The miscibilities mentioned refer to "pure substances", namely solvents or water as such, for example without the presence of components such as LiFSI.

According to one embodiment, the organic solvent S03 has a dielectric constant strictly greater than 1 and less than 4.

Preferably, the organic solvent SO 3 is selected from the group consisting of esters, alcohols, ketones, ethers, chlorinated solvents, alkanes, cycloalkanes, aromatic solvents, and mixtures thereof. For example, there may be mentioned methyl-t-butyl ether, cyclopentyl methyl ether, ethyl acetate, propyl acetate, butyl acetate, tetrachloromethane, chloroform, cyclohexane, 1,2 dichloromethane, dichloromethane, diethyl ether, n-butanol, 2-butanone, heptane, hexane, pentane, toluene, trichlorethylene, diisopropyl ether, and mixtures thereof. Preferably, the solvent SO 3 is chosen from methyl-t-butyl ether, butyl acetate, tetrachloromethane, chloroform, cyclohexane, 1,2-dichloroethane, dichloromethane, diethyl ether and 2-butanone. heptane, hexane, pentane, toluene, trichlorethylene, diisopropyl ether, and mixtures thereof. More preferably, the solvent SO 3 is selected from tetrachloromethane, chloroform, cyclohexane, 1,2-dichloroethane, dichloromethane, heptane, hexane, pentane, toluene, trichlorethylene, and mixtures thereof. Advantageously, the organic solvent SO 3 is cyclohexane.

LiFSI is advantageously insoluble in the SO 3 extraction solvent, that is, less than 5% by weight of LiFSI is soluble in the SO 3 solvent, preferably less than 3% by weight, and advantageously less than 5% by weight. 2% by weight relative to the total mass of the solvent SO3 and LiFSI.

Step c1

Preferably, the contacting in step i) corresponds to the addition of the organic solvent SO 2 in the aqueous solution obtained in the previous step of the purification process. The extraction can be carried out by any known extraction means. The extraction typically allows the separation of an organic phase (organic solution of said salt in this case noted 01) and an aqueous phase.

According to the invention, step i) can be repeated at least once, preferably repeated one to 10 times, preferably repeated one to five times, and advantageously repeated twice.

For each extraction, the mass quantity of organic solvent S02 used can vary between 1/10 and 1 times the mass of the aqueous solution. Preferably, the mass ratio organic solvent SO 2 / water, during an extraction of step i), varies from 1/8 to 1/1, the number of extractions varying in particular from 2 to 10.

In case of multiple extractions (repetition of step i)), the extracted aqueous phases are combined together to form a single organic solution of said LiFSI.

According to one embodiment, the mass content of LiFSI in solution in the organic phase is between 5% and 35%, preferably between 10% and 25% by weight relative to the total mass of the solution.

The aforementioned step ii) is advantageously carried out on the organic solution extracted in step i) denoted 01 (single organic phase or combined organic phases in case of repetition of step i)).

The volume ratio of organic solvent SO 3 / organic solvent SO 2 may range from 1/10 to 1/1, preferably from 1/8 to 1/1, preferably from 1/6 to 1/1 and advantageously from 1/5 to 1/1. 1.

Preferably, the contacting ii) comprises the addition of the organic solvent SO 3 in the organic solution (noted 01) obtained in the preceding step i).

Preferably, the process comprises an intermediate step between step ii) and step iii) of stirring the reaction medium.

The decantation step iii) advantageously leads to at least one organic phase (denoted O 2) and to an aqueous phase, the organic phase being isolated and recovered. The organic phase O 2 advantageously comprises a mixture of the organic solvent SO 2 and the organic solvent SO 3, and LiFSI.

Advantageously, steps i), ii) and iii) of step c1) are consecutive without any intermediate step between each of them.

Step c2

The aqueous solution of LiFSI is brought into contact with at least one organic solvent SO 2 and at least one organic solvent SO 3 can be done by adding said organic solvents SO 2 and SO 3 in the aqueous solution obtained in the preceding step of the purification process. It may be a simultaneous addition of the organic solvents SO2 and SO3, or a successive addition of the solvent SO2 (respectively SO3) and of the solvent SO3 (respectively SO2).

The extraction can be carried out by any known extraction means. The extraction typically allows the separation of an organic phase (organic solution of said salt in this case denoted 03) and an aqueous phase.

According to the invention, the extraction can be repeated at least once, preferably repeated one to 10 times, preferably repeated one to five times, and advantageously repeated twice.

For each extraction:

the mass quantity of organic solvent S02 used can vary between 1/10 and 1 time, preferably between 1/8 and 1 time, advantageously between 1/5 and 1 times the mass of the aqueous solution; and or

the mass quantity of organic solvent S03 used can vary between 1/10 and 1 time, preferably between 1/8 and 1 time, advantageously between 1/6 and 1 times the mass of the aqueous solution; and or

the volume ratio of organic solvent SO 3 / organic solvent SO 2 can range from 1/5 to 2/1, preferably from 1/4 to 2/1, preferably from 1/4 to 1/1 and advantageously from 1/3 to 1 / 1.

In case of multiple extractions (repetition of step c2)), the extracted organic phases are combined together to form a single organic solution of said LiFSI.

According to one embodiment, the mass content of LiFSI in solution in the organic phase (denoted 03) is between 5% and 35%, preferably between 10% and 25% by weight relative to the total mass of the solution.

Step d

The aforementioned purification process comprises a step d) of concentration of the organic solution of the LiFSI salt obtained in the preceding step.

The organic solution may be the organic solution obtained at the end of step c1) (organic phase O2) or the organic solution obtained at the end of step c2) (organic phase O3).

The concentration step may be carried out by any concentration means known to those skilled in the art. It can be a concentration carried out in an evaporator.

The concentration step may be carried out at a temperature below 100 ° C, preferably between 25 ° C and 60 ° C, preferably between 250 ° and 50 ° C; and / or at a pressure of less than 50 mbar abs, preferably less than 30 mbar abs.

The concentration step can be carried out in two stages, namely to understand: a first concentration step carried out in an evaporator under reduced pressure; and

a second concentration step carried out in a short-path thin-film evaporator, preferably under the following conditions:

- temperature between 30 ° C and 95 ° C, preferably between 30 ° C and 90 ° C, preferably between 40 ° C and 85 ° C;

pressure between 10 ^-3 mbar abs and 5 mbar abs;

- residence time less than or equal to 15 min, preferably less than or equal to 10 min, and preferably less than or equal to 5 min.

In the context of the invention, and unless otherwise stated, "residence time" means the time that elapses between the entry of the solution into the evaporator and the outlet of the first drop of the solution.

The aforementioned short-path thin-film evaporators are also known as "Wiped film short path" (WFSP). They are typically so called because the vapors generated during evaporation make a "short trip" (short distance) before being condensed to the condenser. Among the short-path thin film evaporators, there may be mentioned evaporators marketed by the companies Buss SMS Ganzler ex Luwa AG, UIC Gmbh or VTA Process.

Step e

According to one embodiment, the purification process further comprises a step e) of crystallization of the lithium salt of bis (fluorosulfonyl) imide obtained at the end of step d) mentioned above.

The crystallization step may be carried out by any means known to those skilled in the art.

Preferably, the crystallization step e) of LiFSI is carried out at low temperature, especially at a temperature of less than or equal to 25 ° C.

Preferably, the crystallization step e) of LiFSI is carried out in an organic solvent ("crystallization solvent") chosen from chlorinated solvents, such as, for example, dichloromethane, from alkanes such as pentane, hexane, cyclohexane and heptane. and aromatic solvents, such as, for example, toluene, in particular at a temperature of less than or equal to 25 ° C. Preferably, the crystallized LiFSI at the end of step e) is recovered by filtration.

Preferably, the crystallized LiFSI at the end of the recrystallization step is recovered by filtration.

The process according to the invention advantageously leads to a high purity LiFSI, and in particular comprising a reduced content of both water and chlorides. Indeed, the use of an immiscible solvent with water advantageously allows to decant water initially dissolved in the SOI organic solvent, as well as the solubilized impurities in the water.

Process for preparing LiFSI

The invention also relates to a process for preparing a bis (fluorosulfonyl) imide lithium salt which comprises the following steps i) to v):

i) synthesis of bis (chlorosulfonyl) imide;

ii) fluorination of bis (chlorosulfonyl) imide to bis (fluorosulfonyl) imide;

iii) preparation of the alkaline or alkaline earth salt of bis (fluorosulfonyl) imide by neutralization of bis (fluorosulfonyl) imide;

iv) cation exchange to obtain a bis (fluorosulfonyl) imide lithium salt. v) purification method mentioned above.

In particular, the present invention relates to a process for preparing a bis (fluorosulfonyl) imide lithium salt comprising the following steps:

i) synthesis of bis (chlorosulfonyl) imide from sulfamic acid;

ii) fluorination of bis (chlorosulfonyl) imide to bis (fluorosulfonyl) imide;

iii) preparation of the alkaline or alkaline earth salt of bis (fluorosulfonyl) imide by neutralization of bis (fluorosulfonyl) imide, in particular with the aid of an aqueous solution of a base chosen from alkali metal or alkaline carbonates; earthy, and the hydroxides of alkali or alkaline earth metals; iv) cation exchange to obtain a bis (fluorosulfonyl) imide lithium salt; v) purification method according to the invention mentioned above, comprising the steps a) to e) as described above.

LiFSI composition and uses

The present invention also relates to a composition C comprising:

at least 99.80%, preferably at least 99.85%, advantageously at least 99.90%, and preferably at least 99.95% by weight, still more preferably at least 99.99% by weight of sodium salt; bis (fluorosulfonyl) imide lithium (LiFSI) relative to the total weight of composition C; and

organic solvent S03 having a content strictly greater than 0 ppm and less than or equal to 2000 ppm, preferably from 0.1 ppm to 1500 ppm, preferably from 0.1 ppm to 1000 ppm, and advantageously from 1 ppm at 500 ppm by weight relative to the total weight of composition C, the organic solvent SO 3 being preferably cyclohexane; and

less than 20 ppm, preferably less than 19 ppm, preferably less than 15 ppm, and preferably less than 10 ppm of chlorides relative to the total weight of the composition C.

The content of organic solvent SO 2 and of organic solvent SO 3 can be carried out by proton NMR.

Preferably, the composition C comprises:

less than 100 ppm, less than 60 ppm, preferably less than 50 ppm of water relative to the total mass of composition C; and or

less than 100 ppm of sulphate, preferably less than 90 ppm, preferably less than 80 ppm, still more preferably less than 50 ppm, advantageously less than 30 ppm, and for example less than 20 ppm; and or

less than 5000 ppm, preferably from 0.1 ppm to 4000 ppm, preferentially from 0.1 ppm to 3500 ppm, and advantageously from 1 ppm to 2500 ppm, still more advantageously from 1 ppm to 2000 ppm , for example from 1 ppm to 1500 ppm of organic solvent SO 2 as defined above relative to the total weight of the composition C.

Preferably, the composition C comprises:

less than 500 ppm, preferably from 0.1 ppm to 250 ppm, preferentially from 0.1 to 200 ppm of water relative to the total weight of composition C; and or

less than 5000 ppm, preferably from 0.1 ppm to 4000 ppm, preferably from 0.1 ppm to 3500 ppm, advantageously from 1 ppm to 2500 ppm, still more advantageously from 1 to 2000 ppm, example of 1 to 1500 ppm of organic solvent S02 as defined above relative to the total weight of the composition C.

According to one embodiment, the composition C is such that the chloride content is strictly greater than 0 relative to the total weight of the composition C.

According to one embodiment, the composition C is such that the sum of the mass contents of chlorides and water is less than or equal to 100 ppm, preferably less than or equal to 100 ppm. or equal to 80 ppm, advantageously less than or equal to 60 ppm, for example less than or equal to 50 ppm, relative to the total weight of the composition C.

According to one embodiment, the composition C is such that the sum of the mass contents of chlorides, water and sulphates is less than or equal to 100 ppm, preferably less than or equal to 80 ppm, advantageously less than or equal to 60 ppm , for example less than or equal to 50 ppm, relative to the total weight of the composition C.

According to one embodiment, the composition C comprises a mass content of acetic acid of less than or equal to 400 ppm, preferably less than or equal to 350 ppm, preferably less than or equal to 300 ppm, advantageously less than or equal to 250 ppm, and even more advantageously less than or equal to 200 ppm, for example less than or equal to 150 ppm. Even more preferably, the acetic acid content in the composition is less than or equal to 100 ppm, and in particular less than or equal to 50 ppm, relative to the total weight of the composition C.

According to one embodiment, the mass content of acetic acid in the composition C is greater than or equal to 0.1 ppm, preferably greater than or equal to 1 ppm, advantageously greater than or equal to 10 ppm relative to the total weight of the composition C.

According to one embodiment, the mass content of acetic acid in composition C ranges from 0.1 ppm to 300 ppm, preferably from 0.1 ppm to 200 ppm, advantageously from 0.1 ppm to 150 ppm, even more advantageously from 0.1 ppm to 100 ppm relative to the total weight of composition C.

Composition C may also comprise:

a Na ⁺ content less than or equal to 200 ppm, preferably less than or equal to 100 ppm, advantageously less than or equal to 50 ppm, even more advantageously less than or equal to 20 ppm by weight relative to the total weight of said composition C ; and or

a content of FSO ₃ Li less than or equal to 500 ppm, preferably less than or equal to 300 ppm, advantageously less than or equal to 200 ppm, even more advantageously less than or equal to 100 ppm, and in particular less than or equal to 20 ppm by weight relative to the total weight of said composition C; and or

a content of FSO2NH2 less than or equal to 200 ppm, preferably less than or equal to 100 ppm, advantageously less than or equal to 50 ppm, even more advantageously less than or equal to 20 ppm, and in particular less than or equal to 10 ppm by weight relative to the total weight of said composition C. Preferably, the composition C is characterized in that the sum of the total contents of acetic acid and of organic solvent SO 2 as defined above, for example butyl acetate, is less than or equal to 5 200 ppm, preferably lower or equal to 3700 ppm, advantageously less than or equal to 2700 ppm relative to the total weight of the composition C. In particular, the composition is such that:

0.1 ppm <[acetic acid] + [SO2] <2200 ppm, and preferentially:

0.1 ppm <[acetic acid] + [SO2] <2100 ppm.

The composition C may also comprise a butanol content less than or equal to 500 ppm, preferably less than or equal to 300 ppm, preferably less than or equal to 200 ppm, advantageously less than or equal to 100 ppm, in particular less than or equal to 50 ppm relative to the total weight of the composition C.

The composition C may also comprise a content of crystallization solvent, preferably chosen from chlorinated solvents and aromatic solvents, less than or equal to 1000 ppm, preferably less than or equal to 800 ppm, preferably less than or equal to 500 ppm, advantageously less than or equal to 200 ppm, in particular less than or equal to 100 ppm relative to the total weight of the composition C.

The "crystallization solvent" is preferably dichloromethane or toluene.

Preferably, the composition C is characterized in that the sum of the total contents of acetic acid and water is less than or equal to 700 ppm, preferably less than or equal to 450 ppm, advantageously less than or equal to 300 ppm relative to the weight total composition C. In particular, the composition C is such that:

0.1 ppm <[acetic acid] + [water] <200 ppm, and preferentially:

0.1 ppm <[acetic acid] + [water] <150 ppm

The present invention also relates to the use of the above-mentioned composition C in batteries, in particular Li-ion batteries, in particular in electrolytes of Li-ion batteries.

In particular, the composition C according to the invention can be used in Li-ion batteries of mobile devices (for example mobile phones, cameras, tablets or laptops), or electric vehicles, or storage vehicles. renewable energy (such as photovoltaic or wind energy). Composition C according to the invention advantageously has at least one of the following advantages:

- decrease the risk of short circuit, ignition or explosion of the battery;

- longer battery life;

- Reduction or elimination of corrosion of the constituents of the battery, such as the AI collector.

In the context of the invention, "between x and y" or "ranging from x to y" means an interval in which the terminals x and y are included. For example, the temperature "between 30 and 100 ° C" includes in particular the values 30 ° C and 100 ° C.

All the embodiments described above can be combined with each other. In particular, each embodiment of any step of the method of the invention may be combined with another particular embodiment.

EXPERIMENTAL PART

The anion analysis conditions in ion chromatography (Cl) are as follows: Thermo ICS 5000 DUAL Apparatus

AS16-HC column

Flow rate 1 ml / min

Isocratic KOH eluent at 20 mmol / l

Conductivity detection

ASRS suppressor 4 mm with 50 mA of imposed current.

Injection of 25 mI of LiFSI solutions at 5g / l and 10g / l according to the required sensitivity per anionic species present.

Calibration of each anionic species with five synthetic solutions ranging from 0.1 mg / l to 25 mg / l.

Comparative Example 1:

An initial solution of LiFSI in butyl acetate of 3400 g (ES = 33.42%) containing 480 ppm of Cl ions is washed a first time with a mass of demineralized water corresponding to half the mass of the initial solution (1700 g). The resulting organic phase is washed a second time with a mass of demineralized water corresponding to one third of the mass of the initial solution (1100 g). The resulting organic phase is washed a third time with a mass of demineralized water corresponding to one quarter of the mass of the initial solution (840 g). The aqueous phases are combined to form a single aqueous phase and then concentrated to a solids content of 36.48%. The aqueous phase (2060 g) is re-extracted four times with an amount of butyl acetate (515 g) corresponding to one quarter of the mass of the aqueous solution.

The following table shows the amount of residual chlorides in each of the reextractions.

Table 1

Example 2 (Invention)

An initial solution of LiFSI in butyl acetate (328 g) (dry extract = 39.6%) containing 423 ppm of Cl ions is washed a first time with a mass of demineralized water corresponding to half of the mass of the initial solution (162 g). The resulting organic phase is washed a second time with a mass of demineralized water corresponding to one third of the mass of the initial solution (109 g). The resulting organic phase is washed a third time with a mass of demineralized water corresponding to one quarter of the mass of the initial solution (82 g). The aqueous phases are combined to form a single aqueous phase and then concentrated to a solids content of 41.20%. The aqueous phase (280 g) is re-extracted four times with an amount of butyl acetate (70 g) and toluene (35 g) corresponding to one quarter of the mass of the aqueous solution.

The following Table 2 shows the amount of residual chlorides in each of the organic phases resulting from the stripping.

Table 2

The amount of residual chlorides in the organic phases is advantageously lower in Example 2 than in Comparative Example 1. Example 3 (comparative):

Purification of an aqueous LiFSI solution with a 36.5% solids content containing 440 ppm of chloride. The aqueous LiFSI solution was from a solution of LiFSI in butyl acetate which was subjected to liquid-liquid extraction with deionized water.

2060 g of the aqueous LiFSI solution with a 36.5% solids content containing 440 ppm of chloride are extracted in a glass separating funnel four times with successively 515 g, 515 g, 515 g and 515 g of sodium acetate. butyl. The organic phases obtained are analyzed independently of each other by ion chromatography. The analysis by ion chromatography shows 130 ppm of chlorides in the organic phase 1, 49 ppm of chlorides in the organic phase 2, 40 ppm of chlorides in the organic phase 3 and 26 ppm of chlorides in the organic phase 4.

Example 4 (according to the invention):

Purification of an aqueous solution of LiFSI with a solids content of 39.2% containing 565 ppm of chlorides. The aqueous LiFSI solution was from a solution of LiFSI in butyl acetate which was subjected to liquid-liquid extraction with deionized water.

2405 g of the aqueous LiFSI solution with a dry extract of 39.2% containing 565 ppm of chlorides are extracted in a glass separating funnel four times with successively 600 g, 600 g, 600 g and 600 g of sodium acetate. butyl. In each of the organic phases obtained, 300 g of cyclohexane are added thereto. After decantation, each of the organic phases is analyzed by ion chromatography. The analysis by ion chromatography shows 5 ppm of chlorides in the organic phase 1.3 ppm of chlorides in the organic phase 2, 1 ppm of chlorides in the organic phase 3 and 1 ppm of chlorides in the organic phase 4.

Claims

1. A process for purifying a bis (fluorosulfonyl) imide lithium salt dissolved in an SOI organic solvent, said process comprising the following steps: a) liquid-liquid extraction of the SOI organic solvent bis (fluorosulfonyl) imide lithium salt by contacting with deionized water, and recovering an aqueous solution of said bis (fluorosulfonyl) imide lithium salt;

b) optional concentration of said aqueous solution;

(c) one of the following steps (c1) or (c2):

- c1)

e) possible crystallization of the bis (fluorosulfonyl) imide lithium salt,

2. The process according to claim 1, wherein the mass content of lithium salt of bis (fluorosulfonyl) imide in the aqueous solution of step a) is between 5% and 35%, preferably between 10% and 25%. %, based on the total mass of said aqueous solution.

3. Method according to any one of claims 1 or 2, wherein the mass content of lithium salt of bis (fluorosulfonyl) imide in the organic solvent SOI is between 5% and 50% by weight relative to the total mass. of the solution.

4. Process according to any one of claims 1 to 3, wherein the organic solvent S02 has a dielectric constant greater than 4.

The process according to any one of claims 1 to 4, wherein the SO 2 organic solvent is selected from the group consisting of esters, alcohols, ketones, ethers, chlorinated solvents, aromatic solvents, and mixtures thereof. the organic solvent S02 being preferably selected from methyl-t-butyl ether, cyclopentylmethyl ether, ethyl acetate, propyl acetate, butyl acetate, and mixtures thereof, said organic solvent S02 being advantageously butyl acetate.

6. Process according to any one of claims 1 to 5, wherein the organic solvent S03:

is miscible with the solvent SOI; and or

has a dielectric constant strictly greater than 1 and less than 4.

7. Process according to any one of claims 1 to 6, wherein the organic solvent SO 3 is selected from the group consisting of esters, alcohols, ketones, ethers, chlorinated solvents, alkanes, cycloalkanes, solvents. aromatic, and mixtures thereof, said organic solvent SO3 being preferably selected from methyl-t-butyl ether, cyclopentylmethyl ether, ethyl acetate, propyl acetate, butyl acetate, tetrachloromethane, chloroform, cyclohexane, 1,2-dichloroethane, dichloromethane, diethyl ether, 2-butanone, heptane, hexane, pentane, toluene, trichlorethylene, diisopropyl ether, and mixtures thereof.

8. Process according to any one of Claims 1 to 7, in which the organic solvent SO 3 is chosen from tetrachloromethane, chloroform, cyclohexane, 1,2-dichloroethane, dichloromethane, heptane and hexane. pentane, toluene, trichlorethylene, and mixtures thereof, said organic solvent SO 3 being preferably cyclohexane.

9. Method according to any one of claims 1 to 8, characterized in that in step c1), the volume ratio organic solvent S03 / organic solvent S02 is 1/10 to 1/1, preferably 1/8 at 1/1, preferably 1/6 to 1/1, and advantageously 1/5 to 1/1.

10. Process according to any one of claims 1 to 9, characterized in step c2), bringing the aqueous solution of bis (fluorosulfonyl) imide lithium salt into contact with at least one organic solvent SO 2 and at least one an organic solvent S03 comprises the simultaneous addition of the organic solvents SO2 and SO3, or the successive addition of the solvent SO2 (respectively SO3) and of the solvent SO3 (respectively SO2).

1 1. Process according to any one of claims 1 to 10, characterized in that in step c2):

12. Method according to any one of claims 1 to 1 1, characterized in that the concentration step d) is carried out in two stages, and comprises:

a first concentration step carried out in an evaporator under reduced pressure; and

pressure between 10 ^-3 mbar abs and 5 mbar abs;

A process for preparing a bis (fluorosulfonyl) imide lithium salt which comprises the following steps i) to v):

i) synthesis of bis (chlorosulfonyl) imide;

ii) fluorination of bis (chlorosulfonyl) imide to bis (fluorosulfonyl) imide;

iv) cation exchange to obtain a bis (fluorosulfonyl) imide lithium salt. v) purification process as defined according to any one of the claims

1 to 12.

14. Composition C comprising:

at least 99.80%, preferably at least 99.85%, advantageously at least 99.90%, and preferably at least 99.95% by weight, still more preferably at least 99.99% by weight of sodium salt; bis (fluorosulfonyl) imide lithium based on the total weight of composition C; and

15. Composition C according to claim 14, comprising:

less than 5000 ppm, preferably from 0.1 ppm to 4000 ppm, preferentially from 0.1 ppm to 3500 ppm, and advantageously from 1 ppm to 2500 ppm of organic solvent SO 2 as defined in one of any of claims 3 or 4 relative to the total weight of the composition C.

16. Composition C according to any one of claims 14 or 15, characterized in that the sum of the mass contents of chlorides and water is less than or equal to 100 ppm, preferably less than or equal to 80 ppm, advantageously less or equal to 60 ppm, for example less than or equal to 50 ppm, relative to the total weight of the composition C.

17. Composition C according to any one of claims 14 to 16, characterized in that the sum of the mass contents of chlorides, water and sulphates is less than or equal to 100 ppm, preferably less than or equal to 80 ppm, advantageously less than or equal to 60 ppm, for example less than or equal to 50 ppm, relative to the total weight of the composition C.

18. Composition C according to any one of claims 14 to 17, characterized in that the mass content of acetic acid is less than or equal to 400 ppm, preferably less than or equal to 350 ppm, preferably less than or equal to 300 ppm, advantageously less than or equal to 250 ppm, even more advantageously less than or equal to 200 ppm, for example less than or equal to 150 ppm.

19. Composition C according to any one of claims 14 to 18, characterized in that it comprises:

a content of FSO2NH2 less than or equal to 200 ppm, preferably less than or equal to 100 ppm, advantageously less than or equal to 50 ppm, even more advantageously less than or equal to 20 ppm, and in particular less than or equal to 10 ppm by weight relative to the total weight of said composition C.

20. Composition C according to any one of claims 14 to 19, characterized in that the sum of the total contents of acetic acid and water is less than or equal to 700 ppm, preferably less than or equal to 450 ppm, advantageously less or equal to 300 ppm relative to the total weight of the composition C.