REACTIVE DISTILLATION PROCESS FOR PREPARING FLUOROSULFONYLIMIDE SALTS

Abstract

The present invention relates to a process for preparing a fluorosulfony limide salt. More specifically. the present invention relates to a process for preparing lithium bis(fluorosulfonyl)imide (LiFSI).

Claims

1. A process for preparing a fluorosulfonylimide salt represented by the following formula (I): ##STR00004## wherein M.sup.n+ represents a metal cation or an onium cation, wherein the onium cation is not an ammonium cation, and n corresponds to the valency of the metal cation or the onium cation and is an integer of from 1 to 4; comprising the following steps: ii) reacting ammonium bis (fluorosulfonyl) imide (NH.sub.4FSI), with a compound (C) selected from the group consisting of a metal compound, an onium compound and an organic amine compound in at least one solvent S.sub.3; and iii) removing at least a part of any water being present in the reaction solution from the reaction solution; wherein the steps ii) and iii) are carried out simultaneously.

2. The process according to claim 1, wherein the NH.sub.4FSI is in the form of a solvate with at least one solvent S.sub.2.

3. The process according to claim 2, wherein the NH.sub.4FSI salt in the form of a solvate is: in a crystallized form, and/or comprises from 50 to 99 wt. %, of the NH.sub.4FSI salt, and from 1 to 50 wt. %, of at least one solvent S.sub.2.

4. The process according to claim 2, wherein said solvent S.sub.2 is selected from the group consisting of cyclic and acyclic ethers.

5. The process according to claim 1, said process comprising before step ii), a step i) of preparing a NH.sub.4FSI solvate comprising the following steps: i.sub.1) providing a crude salt of NH.sub.4FSI; i.sub.2) dissolving the crude salt of NH.sub.4FSI in at least one solvent S.sub.1; i.sub.3) crystallizing the crude salt of NH.sub.4FSI by means of at least one solvent S.sub.2; and i.sub.4) separating the NH.sub.4FSI salt from at least part of the solvents S.sub.1 and S.sub.2.

6. The process according to claim 1, wherein in step ii) the compound (C) is a lithium compound (C), selected from the group consisting of: lithium hydroxide LiOH, lithium hydroxide hydrate LiOH.Math.H.sub.2O, lithium carbonate Li.sub.2CO.sub.3, lithium hydrogen carbonate LiHCO.sub.3, lithium chloride LiCl, lithium fluoride LiF, alkoxide compounds, alkyl lithium compounds, lithium acetate CH.sub.3COOLi, and lithium oxalate Li.sub.2C.sub.2O.sub.4.

7. The process according to claim 1, wherein, in step iii), the at least a part of any water being present in the reaction solution is removed from the reaction solution by distillation.

8. The process according to claim 1, wherein, in step iii), the solvent S.sub.2 present in the NH.sub.4FSI solvate is removed from the reaction solution by distillation.

9. The process according to claim 1, wherein in step iii) the reaction temperature is of from about 0? C. to about 100? C.

10. The process according to claim 1, wherein in step iii) the reaction pressure is of from atmospheric pressure to about 0.01 mbar.

11. The process according to claim 5, wherein the solvent S.sub.1 is selected from the group consisting of acetonitrile, valeronitrile, adiponitrile, benzonitrile, methanol, ethanol, 1-propanol, 2-propanol, 2,2,2,-trifluoroethanol, n-butyl acetate, isopropyl acetate, and mixtures thereof.

12. The process according to claim 2, wherein the solvent S.sub.2 is selected from the group consisting of diethylether, diisopropylether, methyl-t-butylether, dimethoxymethane, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, 1,3-dioxane, 4-methyl-1,3-dioxane, and 1,4-dioxane, and mixtures thereof.

13. The process according to claim 1, wherein the solvent S.sub.3 is ethyl methyl carbonate (EMC) or n-butyl acetate.

14. The process according to claim 1, wherein the compound (C) of step ii) is added to the ammonium bis (fluorosulfonyl) imide (NH.sub.4FSI) over a time range of from about 0.5 hr to about 10 hr.

15. The process according to claim 1, wherein in formula (I): ##STR00005## M.sup.n+ represents Li+, and the process comprises the following steps: i) preparing a NH.sub.4FSI solvate by: i.sub.1) providing a crude salt of NH.sub.4FSI; 1.sub.2) dissolving the crude salt of NH.sub.4FSI in at least one solvent S.sub.1; i.sub.3) crystallizing the crude salt of NH.sub.4FSI by means of at least one solvent S.sub.2; and i.sub.4) separating the NH.sub.4FSI salt from at least part of the solvents S.sub.1 and S.sub.2, to obtain a NH.sub.4FSI solvate; ii) reacting the NH.sub.4FSI solvate from step i) with a lithium compound (C*) in at least one solvent S.sub.3; and iii) removing, by azeotropic distillation: at least a part of any water being present in the reaction solution from the reaction solution more than 99.0 wt. % of the water, and at least a part of the solvent S.sub.2 present in the NH.sub.4FSI solvate more than 99.0 wt. % of the solvent S.sub.2, wherein the steps ii) and iii) are carried out simultaneously.

16. The process according to claim 15, wherein: step i.sub.4) consists in separating the NH.sub.4FSI salt from both more than 99.9 wt. % of the solvent S.sub.1 and from 50 to 99 wt. % of the solvent S.sub.2; and said process comprises a step is) of drying the NH.sub.4FSI solvate obtained in step i.sub.4).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0030] According to the present invention the term about means ?10% of the specified numeric value, preferably ?5%, more preferably ?2% and even more preferably ?1%.

[0031] The present invention relates to a process for preparing a fluorosulfonylimide salt represented by the following formula (I):

##STR00002##

[0032] wherein M.sup.n+ represents a metal cation or an onium cation, wherein the onium cation is not an ammonium cation (NH.sub.4.sup.+), and n corresponds to the valency of the metal cation or the onium cation and is an integer of from 1 to 4: comprising the following steps: [0033] ii) reacting ammonium bis (fluorosulfonyl) imide (NH4FSI), preferably in a form of a solvate with at least one solvent S.sub.2, with a compound (C) selected from the group consisting of a metal compound, an onium compound and an organic amine compound in at least one solvent S.sub.3; and [0034] iii) removing at least a part of any water being present in the reaction solution from the reaction solution: wherein the steps ii) and iii) are carried out simultaneously.

[0035] Although there are no particular limitations on the metal cation, an alkali metal cation is preferable. Examples of the alkali metal cation include a lithium cation, sodium cation, potassium cation, rubidium cation and cesium cation. Of these, a lithium cation, sodium cation or potassium cation is preferable, and most preferable is a lithium cation.

[0036] Examples of the onium cation, wherein the onium cation is not an ammonium cation (NH.sub.4.sup.+), include a 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.

[0037] 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.

[0038] 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,

[0039] 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: [0040] 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,

[0041] benzyltrimethylammonium cation, benzyltributylammonium cation, benzyltriethylammonium cation, dimethyldistearylammonium cation, diallyldimethylammonium cation, 2-methoxyethoxymethyltrimethylammonium cation, and tetrakis (pentafluoroethyl) ammonium cation; [0042] 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:

[0043] primary ammonium cations such as a methylammonium cation, ethylammonium cation, butylammonium cation, hexylammonium cation, and octylammonium cation; [0044] 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: [0045] pyrrolidinium cations such as a 1-propyl-1-methylpyrrolidinium cation, 1-butyl-1-methylpyrrolidinium cation, 1-hexyl-1-methylpyrrolidinium cation, and l-octyl-1-methylpyrrolidinium cation: [0046] 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; [0047] guanidinium cations such as a guanidinium cation and a 2-ethyl-1,1,3,3-tetramethylguanidinium cation: [0048] 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.

[0049] 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.

[0050] According to the present invention, most preferably the fluorosulfonylimide salt represented by the following formula (I) is LiFSI.

[0051] According to the present invention, the process for preparing a compound according to formula (I) includes a step ii) of reacting NH.sub.4FSI (ammonium bis (fluorosulfonyl) imide) with a compound (C) selected from the group consisting of a metal compound, an onium compound and an organic amine compound in a solvent. Hereinafter this reaction is also referred to as the cation exchange reaction.

[0052] According to a preferred embodiment, the NH.sub.4FSI salt is a solvate, preferably in a crystallized form.

[0053] Preferably, said solvate comprises: [0054] 50 to 99 wt. %, of the NH.sub.4FSI salt, and [0055] 1 to 50 wt. %, of solvent S2.

[0056] Preferably, said solvent S.sub.2 is selected from the group consisting of cyclic and acyclic ethers.

[0057] Preferably, the NH.sub.4FSI solvate comprises from 51 to 98 wt. %, more preferably from 55 to 95 wt. %, or from 78 to 83 wt. % of the NH.sub.4FSI salt.

[0058] Preferably, the NH.sub.4FSI solvate comprises from 2 to 49 wt. %, more preferably from 5 to 45 wt. % or from 17 to 22 wt. % of solvent S.sub.2 as defined above.

[0059] When the NH.sub.4FSI is in the form of solvate as above defined, the process comprises before step ii), a step i) of preparing a NH.sub.4FSI solvate comprising the following steps: [0060] i1) providing a crude salt of NH.sub.4FSI: [0061] i2) dissolving the crude salt of NH.sub.4FSI in at least one solvent S.sub.1: [0062] i3) crystallizing the crude salt of NH.sub.4FSI by means of at least one solvent S2; and [0063] i.sub.4) separating the NH.sub.4FSI salt from at least part of the solvents S.sub.1 and S.sub.2, preferably by filtration.

[0064] The crude salt of NH.sub.4FSI preferably comprises 80 to 97 wt. % of the salt of NH.sub.4FSI, preferably 85-95 wt. %, more preferably 90-95 wt. %.

[0065] The solvent S.sub.1 is preferably selected from the group consisting of acetonitrile, valeronitrile, adiponitrile, benzonitrile, methanol, ethanol, 1-propanol, 2-propanol, 2,2,2,-trifluoroethanol, n-butyl acetate, isopropyl acetate, and mixtures thereof: preferably 2,2,2,-trifluoroethanol.

[0066] The solvent S.sub.2 is preferably selected from the group consisting of diethylether, diisopropylether, methyl-t-butylether, dimethoxymethane, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, 1,3-dioxane, 4-methyl-1,3-dioxane, and 1,4-dioxane, and mixtures thereof. More preferably, the solvent S2 is selected from the group consisting of: diethyl ether, diisopropyl ether, methyl t-butyl ether, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane and mixtures thereof. Even more preferably. solvent S2 is 1,3-dioxane or 1,4-dioxane.

[0067] Preferably, step i4) consists in separating the NH.sub.4FSI salt from: [0068] more than 99.9 wt. % of the solvent S.sub.1: and [0069] 50 to 99 wt. % of the solvent S.sub.2.

[0070] According to the present invention. the cation exchange reaction preferably is performed by mixing. in the presence of a solvent. NH.sub.4FSI and a compound selected from the group consisting of a metal compound. an onium compound and an organic amine compound. wherein the compound preferably is a metal compound. more preferably an alkali metal compound. even more preferably a lithium compound. still more preferably LiOHxH.sub.2O or Li.sub.2CO.sub.3 and most preferably LiOHxH.sub.2O.

[0071] There are no particular limitations on the metal compounds used in the cation exchange reaction. provided it undergoes a cation exchange reaction with NH.sub.4FSI.

[0072] Preferably. the metal compound is an alkali metal compound. More preferably. the metal compound is an alkali metal compound selected from the group consisting of LiOH, NaOH, KOH, RbOH, CSOH, LiOHxH.sub.2O, NaOHxH.sub.2O, KOHxH.sub.2O, RbOHxH.sub.2O, CsOHxH.sub.2O, Li.sub.2CO.sub.3, Na.sub.2CO.sub.3, K.sub.2CO.sub.3, Rb.sub.2CO.sub.3, Cs.sub.2CO.sub.3, LiHCO.sub.3, NaHCO.sub.3, K.sub.2CO.sub.3, RbHCO.sub.3 and CsHCO.sub.3, even more preferably the metal compound is an alkali metal compound selected from the group consisting of LiOHxH.sub.2O, NaOHxH.sub.2O, KOHxH.sub.2O, RbOHxH.sub.2O, CsOHxH.sub.2O, LizCO.sub.3, Na.sub.2CO.sub.3, K2CO.sub.3, Rb.sub.2CO; and Cs.sub.2CO.sub.3, still more preferably the metal compound is an alkali metal compound selected from the group consisting of LiOHxH.sub.2O and Li.sub.2CO.sub.3, and most preferably the metal compound is LiOHxH.sub.2O.

[0073] In case an alkali metal compound is used. the amount of the used alkali metal compound preferably is of from about 1 mol to about 10 mol, more preferably of from about 1 mol to about 5 mol, even more preferably of from about 1 mol to about 2 mol, still more preferably of from about 1 mol to about 1.5 mol and most preferably about 1.1 mol, per 1 mol of NH.sub.4FSI.

[0074] Examples of the onium compound used in the cation exchange reaction include nitrogen-based onium compounds such as imidazolium compounds, pyrazolium compounds, pyridinium compounds, pyrrolidinium compounds, piperidinium compounds, morpholinium compounds and quaternary ammonium compounds, phosphorus-based onium compounds such as quaternary phosphonium compounds and tertiary phosphine compounds, sulfur-based onium compounds such as sulfonium compounds, as well as guanidinium compounds, isouronium compounds and isothiouronium compounds. Among these compounds, organic onium compounds are preferable. Further, the onium compound preferably contains no metal elements that degrade electrolyte properties and the like.

[0075] Preferably, the onium compound is a hydroxide compound.

[0076] Specific examples of the imidazolium compounds include hydroxides such as 1,3-dimethylimidazolium hydroxide, 1-ethyl-3-methylimidazolium hydroxide, 1-butyl-3-methylimidazolium hydroxide, 1-hexyl-3-methylimidazolium hydroxide, 1-octyl-3-methylimidazolium hydroxide, 1-allyl-3-ethylimidazolium hydroxide, 1-allyl-3-butylimidazolium hydroxide, 1,3-diallylimidazolium hydroxide, 1-ethyl-2,3-dimethylimidazolium hydroxide, 1-butyl-2,3-dimethylimidazolium hydroxide and 1-hexyl-2,3-dimethylimidazolium hydroxide.

[0077] Specific examples of the pyrazolium compounds include hydroxides such as 2-ethyl-1,3,5-trimethylpyrazolium hydroxide, 2-propyl-1,3,5-trimethylpyrazolium hydroxide, 2-butyl-1,3,5-trimethylpyrazolium hydroxide and 2-hexyl-1,3,5-trimethylpyrazolium hydroxide.

[0078] Specific examples of the morpholinium compounds include 4-propyl-4-methylmorpholinium hydroxide, and 4-(2-methoxyethyl)-4-methylmorpholinium hydroxide.

[0079] Specific examples of the quaternary ammonium compounds include hydroxides such as propyltrimethylammonium hydroxide, diethyl-2-methoxyethylmethylammonium hydroxide, methyltrioctylammonium hydroxide, cyclohexyltrimethylammonium hydroxide and 2-hydroxyethyltrimethylammonium hydroxide.

[0080] Specific examples of the guanidinium compounds include guanidinium hydroxide, and 2-ethyl-1, 1,3,3-tetramethylguanidinium hydroxide.

[0081] A specific example of an isouronium compound is 2-ethyl-1,1,3,3-tetramethylisouronium hydroxide.

[0082] A specific example of an isothiouronium compound is 2-ethyl-1,1,3,3-tetramethylisothiouronium hydroxide.

[0083] In case an onium compound is used, the amount of the used onium compound is of from about 1 mol to about 10 mol, more preferably of from about 1 mol to about 5 mol, even more preferably of from about 1 mol to about 2mol, still more preferably of from about I mol to about 1.5 mol and most preferably about 1.1 mol, per 1 mol of NH.sub.4FSI.

[0084] Examples of the organic amine compound used in the cation exchange reaction include tertiary amines such as trimethylamine, triethylamine and tributylamine, cyclic amines such as 1,4-diazabicyclo [2.2.2] octane, tertiary amine salts such as trimethylamine hydrochloride, triethylamine hydrochloride, tributylamine hydrochloride, 1,4-diazabicyclo [2.2.2] octane hydrochloride, trimethylamine hydrobromide, triethylamine hydrobromide and tributylamine hydrobromide, and cyclic amine salts such as 1,4-diazabicyclo [2.2.2] octane hydrobromide.

[0085] Among these compounds, tertiary amines and cyclic amines are preferable.

[0086] In case an organic amine compound is used, the amount of the used organic amine compound is of from about 1 mol to about 10 mol, more preferably of from about 1 mol to about 5 mol, even more preferably of from about 1 mol to about 2 mol, still more preferably of from about 1 mol to about 1.5mol and most preferably about 1.1 mol, per 1 mol of NH.sub.4FSI.

[0087] Preferably, the metal compound is LiOHxH.sub.2O or Li.sub.2CO.sub.3, and the amount of the used metal compound is about 1.1 mol, per 1 mol NH.sub.4FSI, more preferably the metal compound is LiOHxH.sub.2O and the amount of the used metal compound is about 1.1 mol, per 1 mol NH.sub.4FSI.

[0088] There are no particular limitations on the temperature during the cation exchange reaction, but preferably in step ii) the reaction temperature is of from about 0? C. to about 100? C., more preferably of from about 5? C. to about 70? C. even more preferably of from about 10? C. to about 50? C. and most preferably about 15? C.

[0089] There are no particular limitations on the reaction pressure during the cation exchange reaction, but preferably in step ii) the reaction pressure is of from atmospheric pressure to about 0.01 mbar, more preferably of from about 800 mbar to about 0). 1 mbar, even more preferably of from about 600 mbar to about 1 mbar, still more preferably of from about 400 mbar to about 10 mbar, still even more preferably of from about 200 mbar to about 15 mbar, and most preferably about 30 mbar.

[0090] There are no particular limitations on the organic solvent S3 used in the cation exchange reaction. Examples of preferred solvents include aprotic solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, ?-butyrolactone, ?-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, tetrahydrofuran, 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.

[0091] The reaction time required for the cation exchange reaction varies depending on the reaction scale, but is preferably of from about 1 hr to about 48hr, and more preferably of from about 1.5 hr to about 24 hr, even more preferably of from about 1.5 hr to about 12 hr, still more preferably of from about 2 hr to about 10 hr and most preferably of from about 3 hr to about 6 hr.

[0092] Preferably, the compound of step ii) is added to the ammonium bis (fluorosulfonyl) imide (NH.sub.4FSI) over a time range of from about 0.5 hr to about 10 hr, more preferably of from about 1 hr to about 8 hr, even more preferably of from about 1 hr to about 6 hr, still more preferably of from about 1.5 hr to about 5 hr and most preferably of from about 2 hr to about 4 hr.

[0093] The reaction vessel may be made of a resin such as a fluororesin or a polyethylene resin, preferably a fluororesin.

[0094] The process according to the present invention comprises step iii) of removing at least a part of any water being present in the reaction solution from the reaction solution.

[0095] At least part of the solvent S.sub.2 present in the NH.sub.4FSI solvate may also be removed from the reaction solution during step iii).

[0096] Preferably, step iii) consists in removing, by distillation, preferably by azeotropic distillation: [0097] at least a part of any water being present in the reaction solution from the reaction solution, preferably more than 99.0 wt. % of the water, and [0098] at least a part of the solvent S.sub.2 present in the NH.sub.4FSI solvate, preferably more than 99.0 wt. % of the solvent S.sub.2 present in the NH.sub.4FSI solvate.

[0099] The water being present in the reaction solution may be formed during the reaction as a by-product or it may be introduced into the reaction solution by moist starting material. The removal of at least a part of any water being present in the reaction solution from the reaction solution may have two effects. On the one hand, the degradation of water sensitive fluorosulfonylimide salts according to formula (I) is suppressed and therefore also the degradation of the electrochemical properties of these salts is suppressed. On the other hand, if water is formed as a by-product during the cation exchange reaction, as shown in the following reaction scheme, by the removal of the water the equilibrium can be adjusted to a state that promotes the cation exchange reaction. Therefore, by the removal of at least a part of any water being present in the reaction solution from the reaction solution, both the yield of the process according to the present invention can be increased and the quality of the fluorosulfonylimide salt and its electrochemical properties can be improved.

##STR00003##

[0100] The at least part of any water being present in the reaction solution, and preferably at least part solvent S.sub.2, may be removed from the reaction solution by any method known in the art such as drying agents or distillation methods.

[0101] Preferably, the at least a part of any water being present in the reaction solution, and preferablyat least part solvent S.sub.2, is removed from the reaction solution by distillation, more preferably the at least a part of the water is removed by azeotropic distillation.

[0102] Preferably, the at least a part of any water being present in the reaction solution, and preferably at least part solvent S.sub.2, is removed by azeotropic distillation, wherein in step ii) the reaction temperature is of from about 10? C. to about 50? C. and the reaction pressure is of from about 200 mbar to about 50mbar, more preferably the at least a part of any water being present in the reaction solution is removed by azeotropic distillation, wherein in step ii) the reaction temperature is about 15? C. and the reaction pressure is about 100 mbar.

[0103] Preferably, the process according to the present invention further comprises after step iii), the following step: iv) of adding more of the solvent S.sub.3 to the reaction solution; wherein steps ii), iii) and iv) are carried out simultaneously.

[0104] In case the removal of the at least a part of any water being present in the reaction solution leads to a loss of solvent S.sub.3 from the reaction solution, more additional solvent S.sub.3 is added to the reaction solution, e.g. by a solvent dosing unit.

[0105] Preferably, in step iv) the solvent is added over time so that the molar concentration of the sulfonylimide salts in the reaction solution is kept substantially constant. In this regard, substantially constant means that the molar concentration of the sulfonylimide salts in the reaction solution do not change more than about 0.2 mol/l, preferably about 0.1 mol/l.

[0106] In general, the principal scheme of the process is shown in FIG. 1. Step ii) may be carried out in a steered reactor equipped with a distillation column using EMC (ethyl methyl carbonate) as a solvent and LiOHxH20 as a lithiation compound. Step iii) is accomplished via azeotropic distillation. A vacuum pump may be used to accomplish the azeotropic distillation. The wet solvent may be condensed in a condenser and separated from the reaction solution. Step iii) is accomplished by an EMC dosing unit and the lithiation compound is added via a solid dosing unit over time.

EXAMPLE

[0107] The present invention is described below in further detail based on an example. 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.

[0108] In a 500 ml steered tank reactor equipped with a distillation column, a condenser, a powder dosing unit and a solvent dosing unit (see FIG. 1), 3.75 mol (390 g) of EMC and 0.250 mol (49.5 g) of ammonium bis (fluorosulfonyl) imide (NH.sub.4FSI) were loaded and steered at 15? C. 0.275 mol (11.5 g) of lithium hydroxide monohydrate (LiOHxH.sub.2O) were added progressively to the reaction solution over a 3 hr time period via the solid dosing unit (see FIG. 1). While LiOHxH.sub.2O was added, the reaction temperature was kept at 15? C., the reaction pressure was reduced to lower than 30 mbar, and

[0109] EMC and water were removed by azeotropic distillation. The removed EMC and water were condensed on the overhead of the column and fresh EMC was added to the reactor to compensate the removed wet EMC and to keep the molar concentration of the fluorosulfonylimid salts constant (see FIG. 1). After the 3 hr of LiOHxH.sub.2O addition and one additional hour of reaction time, the conversion of NH.sub.4FSI was complete and the yield of LiFSI was more than 95%.