Patent Description:
Bis(fluoro sulfonyl)imide and salts thereof, in particular the lithium salt of bis(fluoro sulfonyl)imide (LiFSI), are useful compounds in a variety of technical fields, including in battery electrolytes.

Several methods for the manufacture of LiFSI have been described in the art. Among the various technologies described, the majority uses a fluorination reaction with a fluorinating agent in a solvent.

Many efforts have also been taken in the art to improve the manufacturing methods of the intermediate compounds leading to LiFSI, in particular with regard to purity, yield and cost reduction.

<CIT>) discloses a process for the preparation of a bis(sulphonato)imide salt of formula:.

(III)     (SO<NUM>-)- N- - (SO<NUM>-) 3C+.

wherein C+ represents a monovalent cation, the process comprising the reaction of amido-sulphoric acid of formula:.

wherein X represents a halon atom, and comprising a reaction with a base which is a salt formed with cation C+. According to an embodiment of such a process, the reaction between compounds of formula (I) and (II) is conducted in the presence of a first base, to provide a bis(sulphonyl)imide of formula:.

which is then reacted with a second base, which is a salt formed with cation C+ to provide the compound of formula (III) above.

The compound of formula (III) thus obtained is further purified in water or other polar solvents, such as alcohols.

<CIT>discloses an ionic complex that is said to contribute to the high-temperature durability of a nonaqueous electrolyte battery. This patent document discloses among the others compounds of formula:
<CHM>
and
<CHM>
wherein
X<NUM> and X<NUM> are independently a fluorine atom, or a group selected from alkyl, alkenyl, aryl, etc., and M<NUM> and M<NUM> being a proton, a metal cation or an onium cation.

<CIT>further discloses ionic complexes containing - among the others - compounds of formula:
<CHM>
and
<CHM>
wherein each of Z<NUM>, Z<NUM> and Z<NUM> can be a fluorine atom and B+, C+ and D+ are each a proton, a metal ion or an onium ion.

The importance of the purity of the electrolyte compositions comprising bis(fluorosulfonyl)imide is known in the art.

For example, <CIT>) discloses a liquid conductive material characterized by diminished turbidity and a method for producing and purifying such conductive material. More in particular, the production and purification method is characterized by filtering a solution containing the (fluoro sulfonyl)imide salt using a filter comprising at least one material selected from cellulose, polyester resin, silicon dioxide material and activated carbon.

<CIT>) discloses a process for the purification of an ionic electrolyte comprising at least one alkali metal salt, the process having at least one stage in which particles of at least one calcium salt are brought into contact. The process makes it possible to obtain electrolytes characterized in particular by a particularly low water content. Example <NUM> discloses a solution of LiFSI in ethylene carbonate and gamma-butyrolactone, having a water content of <NUM> ppm and a yellowish color, while after purification, the water content is reduced to <NUM> ppm and the color of the solution is light.

) discloses an electrolyte comprising an ionic compound and a free acid with less than <NUM> ppm (by mass). Said electrolyte is manufactured by mixing the ionic compound and a hydrocarbon-based solvent and/or a carbonate-based solvent, followed by distilling some or all of the solvent off; and/or a step of contacting with a molecular sieve. The examples start from compositions wherein a lithium bis (fluoro sulfonyl) imide was placed in ethylene carbonate / ethyl methyl carbonate, then a molecular sieve step was performed and the solution was then stored for <NUM> months in an environment of <NUM> temperature.

) discloses an electrolyte solution for a secondary battery comprising a combination of a small amount of stabilizer and a particular sulfate-based additive and/or a sulfonate additive, said solution retaining an initial (immediately after the preparation of the electrolyte solution) color or transparency for a long time in a temperature range from low temperature to high temperature.

<CIT>) discloses that the cycle performance and the high-temperature storage performance of the high-voltage lithium ion battery can be improved by adding the <NUM>,<NUM>,<NUM>-hexane trinitrile into the electrolyte, and the chromaticity of the electrolyte containing the substance can be controlled by controlling the chromaticity of the <NUM>,<NUM>,<NUM>-hexane trinitrile, so that the chromaticity requirements for production and storage of the electrolyte of the lithium ion battery can be met.

<CIT>) discloses a method of removing trace impurities from lithium bis(tri-fluoro sulfon)imide, which comprises: (<NUM>) adding a good solvent to a mixture of lithium bis(tri-fluoro sulfon)imide salt and an inert solvent to provide a first filtrate after filtration; (<NUM>) adding a degermination agent to said filtrate to form a mixed solution to provide a second filtrate after filtration; and (<NUM>) distilling said second filtrate under reduced pressure to provide a product of lithium bis(tri-fluoro sulfon)imide salt. The index of the finished product of bis(fluoro sulfone)imide lithium salt complies with a combination of one or more of the following: ion chromatography content greater than or equal to <NUM> percent, wherein sulfate impurity anions less than or equal to <NUM> ppm, fluoride impurity anions are less than or equal to <NUM> ppm, sulfamic acid content anions are less than or equal to <NUM> ppm, fluorosulfonic acid impurity anions less than or equal to <NUM> ppm, acidic impurities less than or equal to <NUM> ppm, the turbidity of <NUM> percent dimethyl carbonate solution is less than or equal to <NUM>/L and chromaticity less than or equal to <NUM> Hazen.

The Applicant is aware that despite all the attempts in the art, there is still the need for a composition comprising an alkali metal salt of bis(fluoro sulfonyl) imide showing improved electrical properties when used in battery applications, said composition being also easy to prepare at industrial scale.

In particular, the Applicant faced the problem of providing a composition, having a lower content of impurities compared to compositions known in the art. Indeed, contrary to the methods proposed in the art, the Applicant faced the problem of providing a composition that can be prepared via a method that is the least expensive when implemented at industrial scale, in particular by limiting or avoiding the use of peculiar compounds in the manufacturing method, which decrease the need for additional purification steps.

The Applicant has surprisingly found a composition comprising an alkali metal salt of bis(fluoro sulfonyl)imide, which is characterized by a specific amount of certain compounds. Also and to the best of the Applicant knowledge, such formulation is characterized by the presence of a specific compound that has never been disclosed in the art as an ingredient in a bis(fluoro sulfonyl) imide composition. Advantageously, the formulation of the present invention is characterized by good electrical properties when compared to compositions currently available on the market.

The composition according to the present invention can be advantageously used as electrolyte in battery applications.

In a first aspect, the present invention relates to a composition [composition (COMP)] comprising:.

in an amount up to <NUM> ppm as measured by ionic chromatography.

Preferably, said composition (COMP) comprises said at least one alkali metal salt of FSO<NUM>- in an amount from <NUM> ppm to <NUM> ppm, preferably from <NUM> ppm to <NUM> ppm, more preferable from <NUM> ppm to <NUM> ppm and even more preferably from <NUM> ppm to <NUM> ppm.

Preferably, said composition (COMP) comprises said compound of formula (I) or the alkali metal salt thereof in an amount from <NUM> ppm to <NUM> ppm, preferably from <NUM> ppm to <NUM> ppm, more preferably from <NUM> ppm to <NUM> ppm and even more preferably from below <NUM> ppm to <NUM> ppm.

Preferably, said composition (COMP) comprises said compound (II) in an amount from <NUM> ppm to <NUM> ppm, more preferably from <NUM> ppm to <NUM> ppm, more preferable from <NUM> ppm to <NUM> ppm and even more preferably from <NUM> ppm to <NUM> ppm. As will be further explained in the experimental section, the amounts disclosed herein above for compound (II) are measured by ionic chromatography and calculated based on SO<NUM><NUM>- response factor.

For sake of clarity, it should be understood that compounds (I) and (II) exist as represented above or in their deprotonated forms.

For example, compound (I) exists as follows:
<CHM>
and/or
<CHM>.

Similarly, compound (II) exists as follows:
<CHM>
and/or
<CHM>.

Preferably, said alkali metal in each of the FSI-salt, in FSO<NUM>- is selected from lithium, sodium and potassium.

Preferably, each of said salt of compound of formula (I) and of compound of formula (II) is a salt with an alkali metal. Said alkali metal is preferably selected from lithium, sodium and potassium.

Preferably, said composition (COMP) is a liquid composition.

According to this embodiment, composition (COMP) further comprises at least one solvent [solvent (S1)].

Preferably, said at least one solvent (S1) is selected in the group comprising, more preferably consisting of: ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, dimethoxymethane, <NUM>,<NUM>-dimethoxyethane, tetrahydrofuran, <NUM>-methyltetrahydrofuran, <NUM>,<NUM>-dioxane, <NUM>-methyl-<NUM>,<NUM>- dioxolane, methyl formate, methyl acetate, methyl propionate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, sulfolane, <NUM>-methylsulfolane, dimethylsulfoxide, N,N-dimethylformamide, N-methyl oxazolidinone, acetonitrile, valeronitrile, benzonitrile, ethyl acetate, isopropyl acetate, n-butyl acetate, nitromethane and nitrobenzene.

Even more preferably, said solvent (S1) is selected from 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. Advantageously, said solvent (S1) is selected from ethyl methyl carbonate and n-butyl acetate.

More preferably, said composition (COMP) comprises from <NUM> to <NUM> wt. %, even more preferably from <NUM> to <NUM> wt. % and still more preferably from <NUM> to <NUM> wt. % of said at least one alkali metal salt of bis(fluoro sulfonyl)imide based on the total weight of said liquid composition.

Advantageously, composition (COMP) according to the present invention is further characterized by a low moisture content.

Preferably, composition (COMP) has a moisture content equal to or less than <NUM> ppm, as measured by Karl-Fisher titration.

Advantageously, composition (COMP) according to the present invention is further characterized by a low content of alcohol.

Preferably, composition (COMP) has a total alcohol content equal to or less than <NUM> ppm, as measured by head-space gas chromatography (HS-GC-FID).

Advantageously, all raw materials used to manufacture composition (COMP), including all reactants, preferably show very high purity.

Preferably, the content of metal components, such as Na, K, Ca, Mg, Fe, Cu, Cr, Ni, Zn, in such raw materials and reactants is below <NUM> ppm, more preferably below <NUM> ppm, or below <NUM> ppm.

The method for manufacturing composition (COMP) according to the present invention is not limited.

For example, according to an embodiment, composition (COMP) may be manufactured via a method comprising the following steps:.

The steps (a) to (d) can be carried out in a batch, semi-batch or continuous mode.

Preferably, the HCSI is in the form of a solid or in its molten state. More preferably, when the HCSI is provided in its molten state, before step (a), a step of pre-heating the HCSI at a temperature of at least <NUM> is performed. Advantageously, said preheating step is performed at a temperature higher than <NUM>. More preferably, said preheating step is performed at a temperature lower than <NUM>.

As used above and within the present invention, the expression "ammonium fluoride" includes NH<NUM>F and HF adducts of ammonium fluoride, for example NH<NUM>F(HF)n, wherein n is <NUM> to <NUM>, preferably <NUM> to <NUM>, more preferably NH<NUM>F. HF or NH<NUM>F(HF)<NUM>. The fluorinating agent may be commercially available, or produced by a known method.

Preferably, the ammonium fluoride is in the form of a solid.

According to a preferred embodiment, ammonium fluoride is anhydrous. More preferably, the moisture content is <NUM> ppm or less.

The amount of ammonium fluoride used is preferably between <NUM> and <NUM> equivalents, per <NUM> mol of the bis(chlorosulfonyl)imide or the salt thereof.

Preferably, the solvent of step (a) is selected from aprotic organic solvents.

More preferably, said solvent is selected in the group comprising:.

According to a preferred embodiment, the organic solvent for step (a) is selected from the group consisting of ethyl acetate, isopropyl acetate, butyl acetate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, valeronitrile and acetonitrile.

According to a preferred embodiment, the organic solvent is anhydrous.

Step (a) is preferably carried out at a temperature of between <NUM> and <NUM>, preferably between <NUM> and <NUM> and more preferably between <NUM> and <NUM>.

Preferably, step (a) is carried out at atmospheric pressure. However, the reaction can be performed below or above atmospheric pressure.

The order in which the reactants are added is not limited. According to a preferred embodiment, the ammonium fluoride is first added to the organic solvent. Then, the bis(chlorosulfonyl)imide or a salt thereof may be added to the reaction medium.

The method for manufacturing the starting HCSI or a salt thereof is not limited.

For example, HCSI can be prepared by reacting chlorosulfonyl isocyanate and chlorosulfonic acid.

Preferably, HCSI is prepared under heating, more preferably at a temperature in the range from <NUM> to <NUM>.

HCSI thus obtained can be directly used in the method according to the present invention. Alternatively, HCSI thus obtained can be purified before being used in the method according to the present invention. For example, such purification can be performed by distillation.

Preferably, the anti-solvent used in step (c) is selected in the group comprising, more preferably consisting of: dichloromethane, <NUM>,<NUM>-dichloro- ethane, chloroform, carbon tetrachloride, <NUM>,<NUM>,<NUM>,<NUM>-tetrachloroethane, chloro- benzene, dichlorobenzene, trichlorobenzene, diethyl ether, diisopropyl ether, methyl t-butyl ether, pentane, hexane, heptane. Dichloromethane is particularly preferred.

Preferably, said at least one alkali metal salt in the salification agent used in step (d) is selected from lithium, sodium and potassium.

When the salification agent comprises lithium as the alkali metal salt, then the agent is preferably selected from the group consisting of lithium chloride (LiCl), lithium fluoride (LiF), lithium carbonate (Li<NUM>CO<NUM>), lithium sulfate (Li<NUM>SO<NUM>), lithium carboxylate (Lin(RCO<NUM>)n), Li<NUM>SiO<NUM>, Li<NUM>B<NUM>O<NUM> and mixtures thereof.

Preferably, the solvent of step (d) is selected from aprotic organic solvents. More preferably, said solvent is selected in the group comprising the solvents detailed above for step (a).

According to a preferred embodiment, the organic solvent for step (d) is selected from the group consisting of ethyl acetate, isopropyl acetate, butyl acetate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, valeronitrile and acetonitrile.

Step (d) is preferably carried out at a temperature of between -<NUM> and <NUM>, preferably between -<NUM> and <NUM> and more preferably between -<NUM> and <NUM>.

Preferably, step (d) is carried out at atmospheric pressure. However, the reaction can be performed below or above atmospheric pressure.

In a further object, the present invention relates to the use of said composition (COMP) as a non-aqueous electrolyte solution in a battery.

The present invention will be now described in more detail with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the disclosure.

Ionic chromatography (IC). The anionic impurities were determined by IC using a Dionex ICS-<NUM> system with conductivity detection, with the following components:.

The amounts of F-, Cl-, FSO<NUM>- (or LiFSOs) in LiFSI solutions were measured quantitatively after calibration using commercial standard solutions (F-, Cl-) or commercial samples of KFSOs.

The amounts of compounds (I) and (II) were calculated based on SO<NUM><NUM>-response factor.

The alcohol content was determined by GC (Agilent 6890N network GC system) equipped with FID detector and Headspace injector, with Split/splitless injection system.

The <NUM>F-NMR purity of LiFSI was determined using the Area% method on a Bruker advance NMR <NUM> equipment.

The moisture content of final LiFSI solutions was determined under an inert atmosphere by means of a KF Titrator, such as Mettler C30S device.

Synthesis of HCSI. Into a glass-lined <NUM><NUM> vessel equipped with baffles, a mechanically stirred shaft, a glass-lined DN300 distillation column and heat exchanger, pressure and temperature sensors and liquid and gas glass-lined inlets and outlets, a PTFE-venting, PTFE-gaskets and receiving glass-lined tanks, the whole system being connected to an alkali scrubber, were reacted chlorosulfonyl isocyanate (<NUM>) and chlorosulfonic acid (<NUM>) by heating progressively to <NUM>-<NUM>, then up to <NUM>-<NUM> over <NUM> until gas evolution stopped. The reaction mixture was distilled in order to isolate a pure HCSI fraction (<NUM>).

Synthesis of ammonium-FSI. Into a PFA-coated <NUM><NUM> vessel equipped with PFA-lined baffles, a mechanically stirred PFA-coated shaft, a PTFE-lined connectors and heat exchanger, the whole system being connected to an alkali scrubber, ethyl methyl carbonate (<NUM>) and anhydrous ammonium fluoride (<NUM>) were introduced. The suspension was homogenized before the HCSI (<NUM>) obtained as disclosed above was introduced progressively, while maintaining the mixture's temperature below <NUM>. After complete addition, the suspension was heated at <NUM> for <NUM> and cooled to room temperature (RT). The resulting slurry was filtered and the cake washed with additional ethyl methyl carbonate (<NUM>). The resulting filtrate (<NUM>) was transferred to a separate <NUM><NUM> steel vessel equipped with a mechanically stirred shaft, baffles, liquid and gas inlets and outlets and a distillation equipment. The filtrate was mixed with water (<NUM>) and <NUM>% aqueous ammonia (<NUM>) and stirred at RT for <NUM>. Then, wet ethyl methyl carbonate was distilled off, and the resulting concentrate (<NUM>) was filtered and transferred into a glass-lined <NUM><NUM> vessel equipped with baffles, a mechanically stirred shaft and a heat exchanger. The filtered concentrate was precipitated by controlled addition of dichloromethane (<NUM>). The resulting slurry was filtered onto a stainless steel <NUM><NUM> filter, the cake washed with additional dichloromethane (<NUM>). Crude ammonium bis(fluoro sulfonyl)imide was isolated as a wet solid and further dried to provide a crude dry product (<NUM>). The crude NH<NUM>FSI was partitioned in <NUM> batches and each batch was separately purified. Each batch was dissolved at <NUM> wt. % in trifluoroethanol at <NUM>-<NUM> into a <NUM><NUM> steel vessel equipped with baffles, a mechanically stirred shaft, a heat exchanger, pressure and temperature sensors and liquid and gas inlets and outlets, a PTFE-venting, PTFE-gaskets and receiving tanks, the whole system being connected to an organic vapors management system. After complete dissolution, <NUM>,<NUM>-Dioxane was added over <NUM>. After complete <NUM>,<NUM>-Dioxane addition, the suspension was cooled to <NUM> over <NUM> and maintained at RT for <NUM>. The resulting slurry was filtered, and the white solid thus obtained was washed with TFE/Dioxane (<NUM>/<NUM> w/w). This protocol was repeated until the impurity profile reached the intermediate required specifications.

Synthesis of LiFSI. Lithiation was performed into a glass-lined <NUM><NUM> vessel equipped with baffles, a mechanically stirred shaft, and a heat exchanger, as follows. A <NUM> wt% solution (based on NH<NUM>FSI) of NH<NUM>FSI. Dioxane in ethyl methyl carbonate was prepared, filtered, then was subjected to a first lithiation step by adding at <NUM> eq of LiOH. H<NUM>O at atmospheric pressure (Patm) and <NUM> to the solution. This mixture was stirred at Patm over <NUM> at <NUM>. A second step of ammonia removal was then performed until the NH<NUM>+ residual content was <<NUM> ppm, and the residual <NUM>,<NUM>-dioxane content was < <NUM> ppm. All the <NUM> batches were subsequently filtered and the resulting filtrates were submitted to distillation.

Three batches were obtained, each containing <NUM> wt. % LiFSI in EMC, which were characterized by NMR, GC Head-space, ionic chromatography, KF, ICP, turbidimetry, colorimetry and pH. The results are reported in Table <NUM> as average.

The LiFSI solution employed in example <NUM> is prepared according to the method described in Example <NUM> and Example <NUM> of patent application published as <CIT> (in the name of Solvay SA).

Three batches were obtained, each containing <NUM> wt. % LiFSI in EMC, which were characterized by NMR, GC Head-space, ionic chromatography, KF, ICP, and pH. The results are reported in Table <NUM> as average.

Each of the compositions comprising EMC and LiFSI prepared as described above in Example <NUM> and Comparative Example <NUM> were used for preparing the formulations suitable to be tested in pouch cells.

Three batches of Formulation A according to the invention were prepared. Two batches of Formulation B of comparison were prepared. The Formulations A and the Formulations B comprised the ingredients shown below:.

A commercial solution of LiFSI <NUM> wt. % in EMC (considered a benchmark in this technical field) was used as a further comparison.

The pouch cells were as follows: NCM622/graphite from UTP (<NUM>. 2V, <NUM> mAh). Test temperature was <NUM>. Charge: 1C / <NUM>. 2V (CC-CV). Discharge: 1C / <NUM>.

The cells were tested for discharge capacity and thickness change. The results are summarized in the following tables.

As shown in Table <NUM>, the formulations according to the present invention showed a higher initial discharge capacity than the benchmark and after <NUM> cycles, they maintained a retention capacity comparable to the benchmark. Differently, as shown in Table <NUM>, compared to the benchmark, the formulations according to the present invention had a lower thickness change during storage test at <NUM> (which is due to a diminished gas evolution and degradation within the pouch cell).

Claim 1:
A composition [composition (COMP)] comprising:
- at least one alkali metal salt of bis(fluoro sulfonyl)imide [FSI-salt];
- at least one alkali metal salt of FSO<NUM>- in an amount up to <NUM> ppm, as measured by ionic chromatography;
- at least one compound of formula (I) or a salt thereof as represented in the following formulae, in an amount up to <NUM> ppm, as measured by ionic chromatography:
<CHM>
and
- at least one compound of formula (II) or a salt thereof as represented in the following formulae, in an amount up to <NUM> ppm as measured by ionic chromatography:
<CHM>