Cross-reference to related patent applications

This application claims priority filed on 23 December 2021 in EUROPE with Nr 21306917.2, the whole content of this application being incorporated herein by reference for all purposes.

Field of the invention

The present invention relates to a process for removing at least a part of any water being present in a solution, wherein the solution comprises bis(fluorosulfonyl)imide or a salt thereof and one or more organic solvents. Furthermore, the present invention relates to the use of one or more specific compounds in a process for removing at least a part of any water being present in a solution, wherein the solution comprises bis(fluorosulfonyl)imide or a salt thereof and one or more organic solvents. Moreover, the present invention relates to a solution obtainable by the process of the present invention and to a solution comprising bis(fluorosulfonyl)imide or a salt thereof, one or more organic solvents, a water content of less than 800 ppm and specific impurities.

Technical Background

Bis(fluoro sulfonyl)imide and salts thereof, in particular the lithium salt of bis(fluorosulfonyl)imide (LiFSI), are useful compounds in a variety of technical fields, notably for battery electrolytes. Bis(fluoro sulfonyl)imide and salts thereof are sensible to water.

In particular, LiFSI is known to react with any remaining water to form unwanted species, such as FSO ₃ Li, FSO ₂ NH ₂ and derivatives. These side- products (or impurities) severely degrade the quality and the electrochemical properties of the LiFSI product.

The production of bis(fluoro sulfonyl)imide (FSI) and salts thereof is described in the literature. One of the possible intermediates leading to FSI salts of interest is ammonium bis(fluorosulfonyl)imide (NH ₄ FSI).

For example, WO 2017/090877 A1 (CLS) describes a method for producing lithium bis(fluorosulfonyl)imide comprising the steps:

(1) reacting bis(chlorosulfonyl)imide with a fluorinating reagent in a solvent, followed by treatment with an alkaline reagent, thereby producing NH4FSI; and

(2) reacting the NH4FSI with a lithium base, also called lithiation of NH4FSI.

The usual method to eliminate water formed during the lithiation step involves one or more distillation steps implying heating the reaction media in order to eliminate volatile species. This step can cause undesired side-products formation, which is deleterious for the quality of the final product.

KR 2021-0063797 (LT Material Co., Ltd.) dislcoses a method for manufacturing an alkali metal salt of bis(fluoro sulfonyl) imide, which comprises moisture removal.

Summary of the invention

The Applicant faced the problem of providing a method for removing at least a part of the residual water present in a solution of bis(fluoro sulfonyl)imide (FSI) and salts thereof, notably a lithium salt of bis(fluoro sulfonyl)imide (LiFSI), wherein such method avoids the formation of undesired side-products.

Thus, an object of the present invention is to provide a process for removing at least a part of any water being present in a solution, preferably substantially all of the water present in a solution, the solution comprising a bis(fluoro sulfonyl)imide (FSI) or a salt thereof and one or more organic solvents, wherein the step of removing at least a part of any water may be efficiently performed at a relatively low temperature and wherein the solution can be easily and efficiently purified subsequently under mild conditions.

Moreover, the present invention provides an efficient process to remove at least a part of any water being present in a highly diluted solution comprising a bis(fluoro sulfonyl)imide (FSI) or a salt thereof and one or more organic solvents.

In addition, the present invention provides an above-described process, wherein after the step of removing at least a part of any water being present in the solution, the impurities (or side-products) formed during the process of the present invention can be removed easily and efficiently from the solution under mild conditions.

Finally, it is a problem of the invention to provide a solution obtainable by the process of the present invention and a solution comprising bis(fluoro sulfonyl)imide or a salt thereof, one or more organic solvents, a water content of less than 800 ppm and further comprising a relatively low amount of impurities formed during the process of the present invention.

The present invention relates to a process for removing at least a part of any water being present in a solution [solution (S _start )], wherein said solution (S _start ) comprises: a) bis(fluoro sulfonyl)imide or a salt thereof according to the following formula (I):

(I) wherein

M ⁿ⁺ represents a metal cation or an onium cation, and n corresponds to the valency of the metal cation or the onium cation and is an integer of from 1 to 4, b) one or more organic solvents, and c) water in an amount higher than 800 pmm based on the total weight of said solution, as measured by Karl-Fischer titration; and wherein the process comprises the following step: i) adding to solution (S _start ) one or more compounds [compound (D)] selected from the group consisting of: trimethyl orthoformate, triethyl orthoformate, tri-n-propyl orthoformate, tri-iso-propyl orthoformate, tri-n-butyl orthoformate, 2-methoxy-1,3-dioxolane, 2-ethoxy-1 ,3-dioxolane, dimethoxy(ethoxy)ethane, diethoxy(methoxy)ethane, trimethyl orthoacetate, triethyl orthoacetate, tri-n-propyl orthoacetate, tri-iso-propyl orthoacetate, tri-n- butyl orthoacetate, trimethyl orthopropionate, triethyl orthopropionate, tri-n- propyl orthopropionate, tri-iso-propyl orthopropionate, tri-n-butyl orthopropionate, trimethyl orthobutyrate, triethyl orthobutyrate, tri-n-propyl orthobutyrate, tri-iso-propyl orthobutyrate, tri-n-butyl orthobutyrate, trimethyl orthopentanoate, triethyl orthopentanoate, tri-n-propyl orthopentanoate, tri-iso- propyl orthopentanoate, tri-n-butyl orthopentanoate and mixtures thereof; thus obtaining a solution [solution (SF)] comprising: a) bis(fluoro sulfonyl)imide or a salt thereof according to the following formula (I) as defined above, b) one or more organic solvents, and c*) water in an amount of less than 800 pmm based on the total weight of said solution, as measured by Karl-Fischer titration.

In addition, the present invention relates to the use of compound (D) selected from the group consisting of: trimethyl orthoformate, triethyl orthoformate, tri-n-propyl orthoformate, tri-iso-propyl orthoformate, tri-n-butyl orthoformate, 2-methoxy-1,3-dioxolane, 2-ethoxy-1 ,3-dioxolane, dimethoxy(ethoxy)ethane, diethoxy(methoxy)ethane, trimethyl orthoacetate, triethyl orthoacetate, tri-n-propyl orthoacetate, tri-iso-propyl orthoacetate, tri-n- butyl orthoacetate, trimethyl orthopropionate, triethyl orthopropionate, tri-n- propyl orthopropionate, tri-iso-propyl orthopropionate, tri-n-butyl orthopropionate, trimethyl orthobutyrate, triethyl orthobutyrate, tri-n-propyl orthobutyrate, tri-iso-propyl orthobutyrate, tri-n-butyl orthobutyrate, trimethyl orthopentanoate, triethyl orthopentanoate, tri-n-propyl orthopentanoate, tri-iso- propyl orthopentanoate, tri-n-butyl orthopentanoate and mixtures thereof; in a process for removing at least a part of any water being present in a solution (S _start ) as defined above.

Additionally, the present invention relates to a solution [solution (SF)] comprising: a) bis(fluoro sulfonyl)imide or a salt thereof according to the following formula (I):

(I) wherein

M ⁿ⁺ represents a metal cation or an onium cation, and n corresponds to the valency of the metal cation or the onium cation and is an integer of from 1 to 4; b) one or more organic solvents; c) a water content of less than 800 ppm based on the total weight of said solution, as measured by Karl-Fischer titration; and optionally d) one or more impurities which originate from the reaction of water with compound (D) selected from the group consisting of: trimethyl orthoformate, triethyl orthoformate, tri-n-propyl orthoformate, tri-iso-propyl orthoformate, tri-n- butyl orthoformate, 2-methoxy-1 ,3-dioxolane, 2-ethoxy-1,3-dioxolane, dimethoxy(ethoxy)ethane, diethoxy(methoxy)ethane, trimethyl orthoacetate, triethyl orthoacetate, tri-n-propyl orthoacetate, tri-iso-propyl orthoacetate, tri-n- butyl orthoacetate, trimethyl orthopropionate, triethyl orthopropionate, tri-n- propyl orthopropionate, tri-iso-propyl orthopropionate, tri-n-butyl orthopropionate, trimethyl orthobutyrate, triethyl orthobutyrate, tri-n-propyl orthobutyrate, tri-iso-propyl orthobutyrate, tri-n-butyl orthobutyrate, trimethyl orthopentanoate, triethyl orthopentanoate, tri-n-propyl orthopentanoate, tri-iso- propyl orthopentanoate, tri-n-butyl orthopentanoate, and mixtures thereof.

Advantagesoulsy, such solution (SF) is obtainable by the process according to the present invention as defined herein.

The present invention is based on the recognition that the process for removing at least a part of any water being present in a solution according to the present invention is advantageously performed at relatively low temperatures.

In addition, the purification of the solution (S _start ), to remove the side- products (or impurities) formed during the process of the present invention, from the solution as defined above, can be performed under mild conditions.

Furthermore, the process according to the present invention can be used to efficiently remove at least a part of any water from highly diluted solutions, wherein the solution comprises a relatively low amount of the bis(fluoro sulfonyl)imide or a salt thereof.

As used in the present description and in the following claims, the expression “highly diluted solution” is intended to indicate a solution comprising more than 800 ppm of water based on the total weight of said solution, as measured by Karl-Fischer titration.

Moreover, the present invention is based on the recognition that the process according to the present invention and the use of the compounds as defined herein in the process according to the present invention are highly efficient for removing water from solutions comprising LiFSI and one or more organic solvents.

Finally, the solutions obtainable by the process of the present invention comprise a relatively low water content and a low amount of impurities, and therefore highly purified bis(fluoro sulfonyl)imide or salts thereof can easily and efficiently be obtained from these solutions.

Detailed description of the invention

According to the present invention the term “about” means ±10% of the specified numeric value, preferably ±5% and most preferably ±2%.

As used within the present description and in the following claims, the expression “compound (D)” is intended to indicate both the singular and the plural form, in other words both “one compound (D)” and “one or more compounds (D)”, unless otherwise specified.

As used within the present description and in the following claims, the expression “removing at least a part of any water being present in a solution” means, that the water content of the solution obtained by the process of the present invention as defined herein, is less than about 800 ppm, preferably less than about 600 ppm, more preferably less than about 500 ppm, even more preferably less than about 250 ppm, still more preferably less than about 100 ppm, even still more preferably less than about 50 ppm, even still more preferably less than about 10ppm, most preferably less than about 1 ppm.

Preferably, in the salt according to formula (I), M ⁿ⁺ represents a metal cation. Although there are no particular limitations on the metal cation, an alkali metal cation is preferable. Examples of the alkali metal cation include Li, Na, K, Rb, Cs. Amongst these, Li, Na or K are preferable, and most preferable is Li or Na.

Examples of the onium cation include a ammonium cation, phosphonium cation, oxonium cation, sulfonium cation, fluoronium cation, chloronium cation, bromonium cation, iodonium cation, selenonium cation, telluronium cation, arsonium cation, stibonium cation, bismutonium cation; iminium cation, diazenium cation, nitronium cation, diazonium cation, nitrosonium cation, hydrazonium cation, diazenium dication, diazonium dication, imidazolium cation, pyridinium cation, quaternary ammonium cation, tertiary ammonium cation, secondary ammonium cation, primary ammonium cation, piperidinium cation, pyrrolidinium cation, morpholinium cation, pyrazolium cation, guanidinium cation, isouronium cation and isothiouronium cation.

The onium cation is preferably an onium cation having an organic group, namely an organic onium cation. Examples of the organic group include saturated and unsaturated hydrocarbon groups. The saturated or unsaturated hydrocarbon group may be linear, branched or cyclic. The number of carbon atoms that constitute the saturated or unsaturated hydrocarbon group is preferably from 1 to 18, and more preferably from 1 to 8. The atoms or atom groupings that constitute the organic group preferably include a hydrogen atom, fluorine atom, amino group, imino group, amide group, ether group, hydroxyl group, ester group, carboxyl group, carbamoyl group, cyano group, sulfone group, sulfide group, nitrogen atom, oxygen atom or sulfur atom; and more preferably include a hydrogen atom, fluorine atom, ether group, hydroxyl group, cyano group or sulfone group. The organic group may have only one of these atoms or atom groupings, or may have two or more of the atoms or atom groupings. When two or more organic groups are bonded, bonds may be formed between the main structures of the organic groups, between the main structures of the organic groups and an aforementioned atom grouping, or between atom groupings described above.

Examples of the onium cation having an organic group include imidazolium cations such as a 1,3-dimethylimidazolium cation, 1-ethyl-3- methylimidazolium cation, 1-propyl-3-methylimidazolium cation, 1-butyl-3- methylimidazolium cation, 1-pentyl-3-methylimidazolium cation, 1-hexyl-3- methylimidazolium cation, 1-heptyl-3-methylimidazolium cation, 1-octyl-3- methylimidazolium cation, 1-decyl-3-methylimidazolium cation, 1 -tetradecyl-3- methylimidazolium cation, 1-hexadecyl-3-methylimidazolium cation, 1- octadecyl-3-methylimidazolium cation, 1-allyl-3-ethylimidazolium cation, 1-allyl- 3-butylimidazolium cation, 1 ,3-diallylimidazolium cation, 1-ethyl-2,3- dimethylimidazolium cation, 1-butyl-2,3-dimethylimidazolium cation, 1-hexyl-2,3- methylimidazolium cation, and 1 -hexadecyl-2, 3-methylimidazolium cation; pyridinium cations such as a 1 -ethylpyridinium cation, 1 -butylpyridinium cation, 1 -hexylpyridinium cation, 1 -octylpyridinium cation, 1-ethyl-3-methylpyridinium cation, 1-ethyl-3-hydroxymethylpyridinium cation, 1-butyl-3-methylpyridinium cation, 1-butyl-4-methylpyridinium cation, 1-octyl-4-methylpyridinium cation, 1- butyl-3,4-dimethylpyridinium cation, and 1-butyl-3,5-dimethylpyridinium cation; quaternary ammonium cations such as a tetramethylammonium cation, tetraethylammonium cation, tetrapropylammonium cation, tetrabutylammonium cation, tetraheptylammonium cation, tetrahexylammonium cation, tetraoctylammonium cation, triethylmethylammonium cation, propyltrimethylammonium cation, diethyl-2-methoxyethylmethylammonium cation, methyltrioctylammonium cation, cyclohexyltrimethylammonium cation, 2- hydroxyethyltrimethylammonium cation, trimethylphenylammonium cation, benzyltrimethylammonium cation, benzyltributylammonium cation, benzyltriethylammonium cation, dimethyldistearylammonium cation, diallyldimethylammonium cation, 2-methoxyethoxymethyltrimethylammonium cation, and tetrakis(pentafluoroethyl)ammonium cation; tertiary ammonium cations such as a trimethylammonium cation, triethylammonium cation, tributylammonium cation, diethylmethylammonium cation, dimethylethylammonium cation, dibutylmethylammonium cation, and 4- aza-1-azoniabicyclo[2.2.2]octane cation; secondary ammonium cations such as a dimethylammonium cation, diethylammonium cation, and dibutylammonium cation; primary ammonium cations such as a methylammonium cation, ethylammonium cation, butylammonium cation, hexylammonium cation, and octylammonium cation; organic ammonium cations such as an N-methoxytrimethylammonium cation, N-ethoxytrimethylammonium cation, and N-propoxytrimethylammonium cation; piperidinium cations such as a 1-propyl-1-methylpiperidinium cation and 1-(2- methoxyethyl)-1-methylpiperidinium cation; pyrrolidinium cations such as a 1-propyl-1-methylpyrrolidinium cation, 1-butyl-1 - methylpyrrolidinium cation, 1-hexyl-1-methylpyrrolidinium cation, and 1-octyl-1- methylpyrrolidinium cation; morpholinium cations such as a 4-propyl-4-methylmorpholinium cation and 4-(2- methoxyethyl)-4-methylmorpholinium cation; pyrazolium cations such as a 2-ethyl-1 ,3,5-trimethylpyrazolium cation, 2-propyl- 1 ,3,5-trimethylpyrazolium cation, 2-butyl-1,3,5-trimethylpyrazolium cation, and

2-hexyl-1 ,3,5-trimethylpyrazolium cation; guanidinium cations such as a guanidinium cation and a 2-ethyl-1, 1,3,3- tetramethylguanidinium cation; sulfonium cations such as a trimethylsulfonium cation; phosphonium cations such as a trihexyltetradecylphosphonium cation; isouronium cations such as a 2-ethyl-1 ,1 ,3,3-tetramethylisouronium cation; and isothiouronium cations such as a 2-ethyl-1 ,1 ,3,3-tetramethylisothiouronium cation.

Among these, the onium cation preferably contains no metal elements that degrade electrolyte properties and the like. Specifically, imidazolium cations such as a 1,3-dimethylimidazolium cation, 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, 1-octyl-

3-methylimidazolium cation, 1-allyl-3-ethylimidazolium cation, 1-allyl-3- butylimidazolium cation, 1 ,3-diallylimidazolium cation, 1-ethyl-2,3- dimethylimidazolium cation, 1-butyl-2,3-dimethylimidazolium cation, and 1- hexyl-2,3-dimethylimidazolium cation; and organic ammonium cations such as a propyltrimethylammonium cation, diethyl-2-methoxyethylmethylammonium cation, methyltrioctylammonium cation, cyclohexyltrimethylammonium cation, 2- hydroxyethyltrimethylammonium cation, trimethylammonium cation, triethylammonium cation, tributylammonium cation, and 4-aza-1- azoniabicyclo[2.2.2]octane cation are preferable.

Preferably, in the salt of formula (I), M ⁿ⁺ represents a metal cation or an onium cation, wherein the onium cation is not an ammonium cation (NH ₄ ⁺ ).

According to the present invention, most preferably the salt according to formula (I) is LiFSI or NaFSI. Preferably, in the process according to the present invention, solution (S _start ) or solution (SF) comprises from about 1 wt.% to about 60 wt.% of bis(fluoro sulfonyl)imide or of the salt according to formula (I) with respect to the total weight of the solution. More preferably solution (S _start ) or solution (SF) comprises from about 5 wt.% about 50 wt.%, even more preferably of from about 5 wt.% to about 45 wt.%, still more preferably of from about 7.5 wt.% to about 45 wt.%, even still more preferably of from about 10 wt.% to about 45 wt.%, even still more preferably of from about 10 wt.% to about 40 wt.%, even still more preferably of from about 20 wt.% to about 40 wt.%, most preferably about 30 wt.% with respect to the total weight of the solution.

There are no particular limitations on the one or more organic solvents used in the process according to the present invention.

Preferably, the solution (S _start ) comprises one organic solvent or more. For example, it may include from 2 to 5 organic solvents, from 2 to 4 organic solvents, from 2 to 3 organic solvents, or 2 organic solvents.

Examples of preferred solvents include aprotic solvents. More preferred aprotic solvents are: ethylene carbonate, propylene carbonate, butylene carbonate, y-butyrolactone, y-valerolactone, dimethoxymethane, 1,2- dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, 4- methyl-1,3-dioxolane, methyl formate, methyl acetate, methyl propionate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, sulfolane, 3- methylsulfolane, dimethylsulfoxide, N,N-dimethylformamide, N-methyl oxazolidinone, acetonitrile, valeronitrile, benzonitrile, ethyl acetate, isopropyl acetate, n-butyl acetate, nitromethane and nitrobenzene. More preferred solvents include ethylene carbonate, propylene carbonate, butylene carbonate, tetra hydrofuran, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, isopropyl acetate and n-butyl acetate, even more preferred solvents include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, isopropyl acetate and n-butyl acetate. Still more preferred solvents include ethyl methyl carbonate and n-butyl acetate. The most preferred solvent is ethyl methyl carbonate.

Solution (S _start ) to be treated with the process according to the present invention may contain water as an impurity. In addition, if the salt according to formula (I) is synthesized in the one or more organic solvent, during the synthesis of the salt, water may be formed as a by-product, which contaminates the solution. The water content of the solution according to the present invention as defined herein may be determined by any known method suitable known in the art. For example, the water content may be determined by elemental analysis or Karl-Fisher titration. If the water is formed during the synthesis of the fluorosulfonylimide salt the amount of the formed water can be calculated based on the amount of the used starting materials.

Preferably, in step i) of the process according to the present invention, the amount of the added compound (D) is from about 1.0 to about 7.5 equivalents with respect to the amount of the water present in the solution, more preferably of from about 1.0 to about 5.0 equivalents, even more preferably of from about 1.0 to about 4.0 equivalents, still more preferably of from about 1.0 to about 3.0 equivalents, even still more preferably of from about 1.0 to about 2.5 equivalents, even still more preferably of from about 1.0 to about 2.0 equivalents, most preferably of from about 1.0 to about 1.5 equivalents with respect to the amount of the water present in the solution. In step i) of the process according to the present invention, compound (D) isselected from the group consisting of: trimethyl orthoformate, triethyl orthoformate, tri-n-propyl orthoformate, tri-iso-propyl orthoformate, tri-n-butyl orthoformate, 2-methoxy-1,3-dioxolane, 2-ethoxy-1 ,3-dioxolane, dimethoxy(ethoxy)ethane, diethoxy(methoxy)ethane, trimethyl orthoacetate, triethyl orthoacetate, tri-n-propyl orthoacetate, tri-iso-propyl orthoacetate, tri-n- butyl orthoacetate, trimethyl orthopropionate, triethyl orthopropionate, tri-n- propyl orthopropionate, tri-iso-propyl orthopropionate, tri-n-butyl orthopropionate, trimethyl orthobutyrate, triethyl orthobutyrate, tri-n-propyl orthobutyrate, tri-iso-propyl orthobutyrate, tri-n-butyl orthobutyrate, trimethyl orthopentanoate, triethyl orthopentanoate, tri-n-propyl orthopentanoate, tri-iso- propyl orthopentanoate, tri-n-butyl orthopentanoate and mixtures thereof.

Preferably, compound (D) is selected from the group consisting of: trimethyl orthoformate, triethyl orthoformate, tri-n-propyl orthoformate, tri-iso- propyl orthoformate, 2-methoxy-1,3-dioxolane, dimethoxy(ethoxy)ethane, trimethyl orthoacetate, triethyl orthoacetate, tri-n-propyl orthoacetate, tri-iso- propyl orthoacetate, trimethyl orthopropionate, triethyl orthopropionate, tri-n- propyl orthopropionate, tri-iso-propyl orthopropionate, trimethyl orthobutyrate, triethyl orthobutyrate, tri-n-propyl orthobutyrate, tri-iso-propyl orthobutyrate, trimethyl orthopentanoate, triethyl orthopentanoate, tri-n-propyl orthopentanoate, tri-iso-propyl orthopentanoate and mixtures thereof. More preferably, compound (D) isselected from the group consisting of: trimethyl orthoformate, triethyl orthoformate, 2-methoxy-1,3-dioxolane, trimethyl orthoacetate, triethyl orthoacetate, trimethyl orthopropionate, triethyl orthopropionate, trimethyl orthobutyrate, triethyl orthobutyrate and mixtures thereof. Even more preferably, compound (D) is selected from the group consisting of: trimethyl orthoformate, triethyl orthoformate, trimethyl orthoacetate, triethyl orthoacetate, trimethyl orthopropionate, triethyl orthopropionate and mixtures thereof. Still more preferably, compound (D) is selected from the group consisting of: trimethyl orthoformate, triethyl orthoformate, trimethyl orthoacetate, triethyl orthoacetate and mixtures thereof. Most preferably, such compound (D) is trimethyl orthoformate.

Preferably, in step i) of the process according to the present invention, compound (D) is added to the solution under stirring.

Preferably, in step i) of the process according to the present invention, compound (D) is added to the solution in a one-time addition, sequentially or in a continuous way, for example drop-wise.

In case compound (D) is added to the solution sequentially or in a continuous way, preferably compound (D) are added over a period of time of from about 4 minutes to about 110 minutes, more preferably over a time period of from about 4 minutes to about 80 minutes, even more preferably of from about 4 minutes to about 50 minutes, still more preferably of from about 8 minutes to about 50 minutes, even still more preferably of from about 8 minutes to about 40 minutes, even still more preferably of from about 13 minutes to about 40 minutes, even still more preferably of from about 13 minutes to about 35 minutes, even still more preferably of from about 15 minutes to about 30 minutes, most preferably about 25 minutes.

Preferably, step i) of the process according to the present invention, is carried out a temperature of from about 0°C to about 80°C, more preferably of from about 5°C to about 80°C, even more preferably of from about 5°C to about 70°C, still more preferably of from about 5°C to about 60°C, even still more preferably of from about 5°C to about 50°C, even still more preferably of from about 7.5°C to about 45°C, even still more preferably of from about 10°C to about 40°C, even still more preferably of from about 15°C to about 35°C, even still more preferably of from about 20°C to about 30°C. Most preferably step i) is carried out at a temperature of about 29°C.

Preferably, step i) of the process according to the present invention is carried out in a time of from about 5 minutes to about 120 minutes, more preferably of from about 5 minutes to about 90 minutes, even more preferably of from about 5 minutes to about 60 minutes, still more preferably of from about 10 minutes to about 60 minutes, even still more preferably of from about 10 minutes to about 45 minutes, even still more preferably of from about 15 minutes to about 45 minutes, even still more preferably of from about 15 minutes to about 40 minutes, even still more preferably of from about 20 minutes to about 35 minutes, most preferably about 30 minutes.

Preferably, the process according to the present invention further comprises before step i), a step 0) of:

0) preparing the bis(fluoro sulfonyl)imide or a salt thereof according to formula (I) as defined above in the one or more organic solvents.

According to a preferred embodiment, in the process according to the present invention, the salt of formula (I) is selected from ammonium bis(fluoro sulfonyl)imide, sodium bis(fluoro sulfonyl)imide or lithium bis(fluoro sulfonyl)imide, and the process further comprises step 0*) of:

0*) preparing an ammonium bis(fluoro sulfonyl)imide, a sodium bis(fluoro sulfonyl)imide or a lithium bis(fluoro sulfonyl)imide in the one or more organic solvents.

Preferably, in the process according to the present invention, steps 0) and i) are carried out simultaneously. More preferably, steps 0*) and i) are carried out simultaneously.

Preferably, the process according to the present invention, further comprises, after said step i), a step ii) of: ii) removing one or more impurities from the solution obtained in step i), wherein the one or more impurities originate from the reaction of water with the compound (D).

Step ii) is carried out to remove the impurities (or side-products) formed during step i) of the process of the present invention.

For example, trimethyl orthoformate reacts with water to form 1 equivalent of methyl formate and 2 equivalents of methanol. Triethyl orthoformate reacts with water to form 1 equivalent of ethyl formate and 2 equivalents of ethanol.

It has been surprisingly found that these impurities can be easily removed from the solutions as defined herein, using a distillation process under relatively low temperature.

Specifically, it has been surprisingly found that these impurities can be removed from solutions comprising LiFSI and one or more organic solvents as defined herein, using a distillation process under relatively low temperature.

Preferably, in the process according to the present invention, step ii) comprises, more preferably consists of, step iia) of removing one or more impurities from the solution obtained in step i) via distillation, wherein the one or more impurities originate from the reaction of water with compound (D).

Preferably, step iia) is carried out at a temperature below about 90°C, more preferably at a temperature below about 80°C, even more preferably at a temperature below about 75°C, still more preferably at a temperature below about 70°C, even still more preferably at a temperature below about 60°C, even still more preferably at a temperature below about 50°C, most preferably at a temperature below about 40°C.

Preferably, step iia) is carried out at a pressure of from about 10mbar to about 900mbar, more preferably of from about 10mbar to about 800mbar, even more preferably of from about 10mbar to about 600mbar, still more preferably of from about 10mbar to about 400mbar, even still more preferably of from about 10mbar to about 200mbar, even still more preferably of from about 20mbar to about 150mbar, most preferably of from about 30mbar to about 150mbar.

Moreover, it has been surprisingly found that some of compounds (D) listed above form insoluble side-products upon reaction with water. These side- products can be easily and efficiently removed from the solution via a filtration step.

Preferably, in the process according to the present invention, step ii) comprises, more preferably consists of, step iib) of removing one or more impurities from the solution obtained in step i) via filtration, wherein the one or more impurities originate from the reaction of water with compound (D).

Preferably, in step iib), the filtration is carried out at atmospheric pressure, under pressure or under vacuum, by any means known by the person skilled in the art. Mesh size of the filtration medium may be preferably of 2 micrometer or below, more preferably of 0.45 micrometer or below, and even more preferably of 0.22 micrometer or below. A PTFE membrane can especially be used.

Preferably, the process according to the present invention further comprises, after step ii), a step iii) of carrying out an azeotropic distillation on the solution obtained in step ii).

Furthermore, the present invention relates to the use of compound (D) selected from the group consisting of: trimethyl orthoformate, triethyl orthoformate, tri-n-propyl orthoformate, tri-iso-propyl orthoformate, tri-n-butyl orthoformate, 2-methoxy-1,3-dioxolane, 2-ethoxy-1 ,3-dioxolane, dimethoxy(ethoxy)ethane, diethoxy(methoxy)ethane, trimethyl orthoacetate, triethyl orthoacetate, tri-n-propyl orthoacetate, tri-iso-propyl orthoacetate, tri-n- butyl orthoacetate, trimethyl orthopropionate, triethyl orthopropionate, tri-n- propyl orthopropionate, tri-iso-propyl orthopropionate, tri-n-butyl orthopropionate, trimethyl orthobutyrate, triethyl orthobutyrate, tri-n-propyl orthobutyrate, tri-iso-propyl orthobutyrate, tri-n-butyl orthobutyrate, trimethyl orthopentanoate, triethyl orthopentanoate, tri-n-propyl orthopentanoate, tri-iso- propyl orthopentanoate, tri-n-butyl orthopentanoate and mixtures thereof; in a process for removing at least a part of any water being present in a solution [solution (S _start )], wherein the solution (S _start ) comprises: a) a fluorosulfonylimide salt according to the following formula (I): wherein M ⁿ⁺ represents a metal cation or an onium cation, and n corresponds to the valency of the metal cation or the onium cation and is an integer of from 1 to 4; b) one or more organic solvents; and c) water in an amount higher than 800 ppm based on the total weight of said solution, as measured by Karl-Fischer titration.

Preferably, in the process according to the present invention, the salt according to formula (I) is ammonium bis(fluoro sulfonyl)imide, NaFSI or LiFSI.

Additionally, the present invention relates to a solution [solution (SF)] comprising: a) bis(fluoro sulfonyl)imide or a salt thereof according to the following formula (I):

(I) wherein

M ⁿ⁺ represents a metal cation or an onium cation, and n corresponds to the valency of the metal cation or the onium cation and is an integer of from 1 to 4; b) one or more organic solvents; c) water in an amount of less than 800 ppm based on the total weight of said solution, as measured by Karl-Fischer titration.

Preferably, said solution (SF) is obtainable by the process according to the present invention.

Said solution (SF) preferably comprises water in an amount of less than about 600 ppm, more preferably less than about 500 ppm, even more preferably less than about 250 ppm, still more preferably less than about 100 ppm, even still more preferably less than about 50 ppm, even still more preferably less than about 10 ppm, most preferably less than about 1 ppm, based on the total weight of said solution, as measured by Karl-Fischer titration.

Optionally, said solution (SF) further comprises

(d) one or more impurities which originate from the reaction of water with one or more compounds selected from the group consisting of: trimethyl orthoformate, triethyl orthoformate, tri-n-propyl orthoformate, tri-iso-propyl orthoformate, tri-n-butyl orthoformate, 2-methoxy-1 ,3-dioxolane, 2-ethoxy-1,3- dioxolane, dimethoxy(ethoxy)ethane, diethoxy(methoxy)ethane, trimethyl orthoacetate, triethyl orthoacetate, tri-n-propyl orthoacetate, tri-iso-propyl orthoacetate, tri-n-butyl orthoacetate, trimethyl orthopropionate, triethyl orthopropionate, tri-n-propyl orthopropionate, tri-iso-propyl orthopropionate, tri- n-butyl orthopropionate, trimethyl orthobutyrate, triethyl orthobutyrate, tri-n- propyl orthobutyrate, tri-iso-propyl orthobutyrate, tri-n-butyl orthobutyrate, trimethyl orthopentanoate, triethyl orthopentanoate, tri-n-propyl orthopentanoate, tri-iso-propyl orthopentanoate, tri-n-butyl orthopentanoate, and mixtures thereof. The one or more impurities which originate from the reaction of water with compound (D) as listed above are impurities such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, methyl formate, ethyl formate, n-propyl formate, iso-propyl formate, n-butyl formate, 2-hydroxyethyl formate (or ethylene glycol formate), formyl acetate, methyl acetate, ethyl acetate, iso-propyl acetate, n-butyl acetate, formyl propionate, methyl propionate, ethyl propionate, iso-propyl propionate, n- butyl propionate, formyl butyrate, methyl butyrate, ethyl butyrate, iso-propyl butyrate, n-butyl butyrate, formyl pentanoate, methyl pentanoate, ethyl pentanoate, iso-propyl pentanoate, n-butyl pentanoate.

Preferably, said solution (SF) comprises the one or more impurities which originate from the reaction of water with compound (D) in an amount of at least about 1 ppm and less than about 100 ppm, more preferably at least about 1 ppm and less than about 90 ppm, even more preferably at least about 1 ppm and less than about 80 ppm, still more preferably at least about 1 ppm and less than about 70 ppm, even still more preferably at least about 1 ppm and less than about 50 ppm, even still more preferably at least about 1 ppm and less than about 25 ppm, even still more preferably at least about 1 ppm and less than about 20 ppm, even still more preferably at least about 1 ppm and less than about 15 ppm, most preferably at least about 1 ppm and less than about 10 ppm.

Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

Examples

The present invention is described below in further detail based on the examples. However, the present invention is in no way limited by the following example, and appropriate changes can, of course, be made while still conforming with the purport of the present invention, and such changes are all deemed to be included within the technical scope of the present invention.

All the Examples were carried out in a glove bag.

Example 1

To a solution comprising 30 wt.% of LiFSI in ethyl methyl carbonate, having a water content of 5000 ppm, 1.5 equivalents of trimethyl orthoformate were added to the solution maintained at a temperature of about 29°C. After 30 minutes, the water content, as measured with Karl-Fisher titration method, was below 1 ppm.

Example 2

To a solution comprising 30 wt.% of LiFSI in ethyl methyl carbonate, having a water content of 5000 ppm, 1.0 equivalents of trimethyl orthoformate were added to the solution maintained at a temperature of about 29°C. After 30 minutes, the water content, as measured with Karl-Fisher titration method, was below 8.5 ppm. Comparative Example 1

To a solution comprising 30 wt.% of LiFSI in ethyl methyl carbonate, having a water content of 5000 ppm, 1.0 equivalents of tetraethyl orthosilicate were added to the solution maintained at a temperature of about 29°C. After 30 minutes, the water content, as measured with Karl-Fisher titration method, was below 4600 ppm.

Example 4

The obtained solution from example 2 was subjected to a distillation process to remove methanol and methyl formate generated during the process.

The distillation was carried out as follows.

Tools:

-500mL 3 neck R.B.F, glass distill head with condenser and a glass receiver.

-Glass lined thermometer in boiler and distillation head connected to a recorder and computer

-Heat by heating block (< 40°C)

-Mini chiller connected to a condenser (-15°C)

-Glass cold trap (-15°C) and vacuum pump (100mbar to 50mbar)

-Ar tube line connected to distillation unit

-a glove bag

-optionally an Oldershow column.

Methodology:

The distillation was carried out using a glass unit in a glove bag under nitrogen atmosphere. The distillation is carried out under full reflux.

After the distillation process, the final solution was analyzed using ¹ H- NMR and Karl-Fisher titration methodology. It was found that by using an Oldershow column, 100% of the methyl formate and of from 80.9% to 87.1% of the methanol were removed from the solution.

In case no Oldershow column was used, 99% of the methyl formate and 26% of the methanol were removed from the solution.

The water content of the final solutions was about 8 ppm.