DESC:FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION:

“PROCESS FOR THE PREPARATION OF LITHIUM BIS(FLUOROSULFONYL) IMIDE”

2.APPLICANT(S):
Name Nationality Address
GUJARAT FLUOROCHEMICALS LIMITED INDIAN INOX Towers, 17, Sector -16A, Noida- 201301, Uttar Pradesh, India
GFCL EV PRODUCTS LIMITED INDIAN Survey No. 16/3, 26, 27, Ranjitnagar, Tal. Ghoghamba, Panchmahals-389380, Gujarat, India

3. PREAMBLE TO THE DESCRIPTION:

The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION:

The present invention relates to a process for the preparation of lithium bis(fluorosulfonyl)imide. More particularly, the present invention relates to a process for preparation of lithium bis(fluorosulfonyl)imide (LiFSI) having high yield and high purity, which is cost-effective and industrially scalable.

BACKGROUND OF THE INVENTION:
Lithium bis(fluorosulfonyl)imide (LiFSI) is having a chemical structure of Formula-I as given below:

Formula-I

Lithium bis(fluorosulfonyl)imide (LiFSI) is chemically also known as lithium bis(fluorosulfonyl)amide or lithium bis(fluorosulfonyl)imido or lithium imidodisulfuryl fluoride. Lithium bis(fluorosulfonyl)imide is a white, powdery lithium salt often used as the source of lithium in high-performance electrolytes for lithium-ion batteries. In comparison to lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI) has marked advantages including a higher ionic conductivity in organic solvents and improved thermal stability. In addition, LiFSI has advantages in better stability against hydrolysis, lower aluminium corrosion with stability up to 4.7 V, higher transference number, and generally higher columbic efficiency for lithium metal anode cycling. Because of these advantages, many of the ground-breaking works to improve electrolytes use lithium bis(fluorosulfonyl)imide. Lithium bis(fluorosulfonyl)imide is shown to produce a LiF-rich solid-electrolyte interphase on Li metal surfaces, which promotes cycling with high coulombic efficiencies.

Lithium bis(fluorosulfonyl)imide hereinafter may be referred to as LiFSI. Various processes for the preparation of LiFSI are known in the prior art.

Michot et al. in US patent number 6254797 (hereinafter the US ‘797) describes a reaction between fluorosulfonic acid and urea, but uses a strongly acidic raw material and is very difficult to handle. Therefore, the process for preparing lithium bis(fluorosulfonyl)imide as disclosed in US ‘797 is unsuitable for large-scale industrial production.

Cernik et al. in US patent number 7253317 (hereinafter the US ‘317) describes the synthesis of HFSI from bis(chlorosulfonyl)imide or HCSI, using potassium fluoride (KF) and other monovalent fluorides. This process is relatively slow (22 hours), typically requires volatile organic solvents (nitromethane) and yields a product with high potassium content for use in batteries. In addition, the reaction can form dangerous nitrous vapours in the reactor. Therefore, the process for preparing lithium bis(fluorosulfonyl)imide as disclosed in US ‘317 is unsuitable for large-scale industrial production.

Michot in his US patent number 7919629 (herein after US ‘629) describes the difficulty of synthesizing HFSI, stating in part “It thus appears that the use of bis(fluorosulfonyl)imide is particularly complex to implement. Therefore, the process for preparing lithium bis(fluorosulfonyl)imide as disclosed in US ‘629 is unsuitable for large-scale industrial production.

Electrochemical Society Transactions, 2009, 24, pp. 91-98; and Polyhedron, 2006, 25, pp. 1292-1298 describes lithium salt of HFSI was synthesized by the metathesis reaction of potassium salt of HFSI (i.e., KFSI) with lithium perchlorate (LiClO4). This reaction also produces potassium perchlorate (KClO4), which is an explosive compound. HFSI has also been synthesized from KFSI using perchloric acid. This reaction also produces KClO4. These processes are not suitable for commercial-scale synthesis due to the explosive nature of perchloric acid, lithium perchlorate, and potassium perchlorate.

Further, the conventional methods for the synthesis and purification of lithium bis(fluorosulfonyl)imide are associated with many problems at a commercial scale production such as the process being cumbersome and long, the product conversion rate is low, and the consumption of raw and auxiliary materials is large and difficult to recycle, thereby making the process uneconomic.

Therefore, there is a need for a relatively safer and/or less costly method for producing high-purity and high-yield LiFSI.

OBJECTS OF THE INVENTION:
An object of the present invention is to provide a process for the preparation of lithium bis(fluorosulfonyl)imide with a higher yield and a higher purity.

Another object of the present invention is to provide a process for the preparation of lithium bis(fluorosulfonyl)imide by using cheap and readily available reagents.

Another object of the present invention is to provide a simple, efficient and economical process for the preparation of lithium bis(fluorosulfonyl)imide.

Other objects and advantages of the present invention will be more apparent from the following description, which is not intended to limit the scope of the present invention.

SUMMARY OF THE INVENTION:
The present invention relates to an improved process for the preparation of lithium bis(fluorosulfonyl)imide, which is simple, environmental, economic and commercially viable.

The first aspect of the present invention relates to a process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI), comprising the steps of:
reacting hydrogen fluoride with a mixture of sulfur dioxide and chlorine in the presence of a catalyst at a temperature in the range of 75 °C to 300 °C in a continuous vapour phase fixed bed reactor to obtain sulfuryl fluoride;

reacting the sufuryl fluoride of step a) with a solution of bis(trimethylsilyl)amine (HMDS) in a polar aprotic solvent at temperature ranging between 70 – 100 °C for time duration ranging between 12 to 20 hours to obtain pure hydrogen bis(fluorosulfonyl)imide (HFSI);

adding a solution of lithiation reagent in an organic solvent with step (b) HFSI under continuous stirring for time duration ranging between 5 to 10 hours to obtain a LiFSI; and

optionally, purifying LiFSI of step (c) to get highly pure LiFSI with purity of exceeding 99.80% w/w.

Another aspect of the present invention relates to a process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI) according to first aspect, wherein step a) for the preparation of sulfuryl fluoride alternatively comprising a process by reacting sulfuryl chloride with anhydrous hydrogen fluoride or metal fluoride (MF) at a temperature ranging between 50 °C to 150 °C to get sulfuryl fluoride.

Another aspect of the present invention relates to a process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI) according to first aspect, wherein step b) by-product generated as fluoro trimethyl silane is recycled by treating with ammonia gas to obtain HMDS of purity exceeding 99.0% (by GC).

Another aspect of the present invention relates to a process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI), comprising the steps of:
reacting sulfuryl chloride with anhydrous hydrogen fluoride or metal fluoride (MF) at a temperature ranging between 50 °C to 90 °C to obtain a to obtain selectively sulfuryl chloride fluoride;

reacting sulfuryl chloride fluoride with ammonium source to obtain sulfamoyl fluoride;

reacting sulfamoyl fluoride with sulfuryl chloride fluoride in the presence of base in polar aprotic solvent to obtain hydrogen bis(fluorosulfonyl)imide (HFSI);

reacting with lithiation reagent in an organic solvent with step (c) HFSI under continuous stirring at a temperature ranging between 15 °C to 30 °C for time duration ranging between 5 to 10 hours to obtain LiFSI; and

optionally, purifying LiFSI of step (d) to get highly pure LiFSI with purity of exceeding 99.80% w/w.

DETAILED DESCRIPTION:
The present invention relates a process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI).

Embodiments are provided so as to thoroughly and fully convey the scope of the present invention to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present invention. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present invention. In some embodiments, known processes or well-known apparatus or structures, and well-known techniques are not described in detail.

The terminology used, in the present invention, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present invention. As used in the present invention, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure are not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.

The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present invention.

The current lithium-ion batteries still suffer from various drawbacks such as lithium-ion batteries have relatively low energy densities which is required in high power applications such as electrical vehicles (EVs), hybrid electrical vehicles (HEVs), grid energy storage, and the like.

Further, the conventional methods for the synthesis and purification of LiFSI are associated with many problems at a commercial scale production such as the process is cumbersome and long, the product conversion rate is low, and the consumption of raw and auxiliary materials is large and difficult to recycle, thereby making the process uneconomic.

The present invention envisages a simple, efficient and economic process for the preparation of lithium bis(fluorosulfonyl)imide.

In a first embodiment of the present invention, the process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI), comprising the steps of:
reacting hydrogen fluoride with a mixture of sulfur dioxide and chlorine in the presence of a catalyst at a temperature in the range of 75 °C to 300 °C in a continuous vapour phase fixed bed reactor to obtain sulfuryl fluoride;

reacting the sufuryl fluoride of step a) with a solution of bis(trimethylsilyl)amine (HMDS) in a polar aprotic solvent at temperature ranging between 70 – 100 °C for time duration ranging between 12 to 20 hours to obtain pure hydrogen bis(fluorosulfonyl)imide (HFSI);

adding a solution of lithiation reagent in an organic solvent with step (b) HFSI under continuous stirring for time duration ranging between 5 to 10 hours to obtain a LiFSI; and

optionally, purifying LiFSI of step (c) to get highly pure LiFSI with purity of exceeding 99.80% w/w.

In accordance with the first embodiment of the present invention step (a), the catalyst can include, but is not limited to, granulated charcoal or zeolite or alumina beads. Other known suitable catalysts can also be used. In an embodiment, the diameter of the granulated charcoal is in the range of 2 mm to 5 mm.

In first embodiment, the step (a) process comprising, by charging vapours of hydrogen fluoride, sulfur dioxide and chlorine mixture in a reactor containing a catalyst and heating gradually to a temperature in the range of 75 °C to 150 °C and further maintaining at a temperature in the range of 150 °C to 300 °C in a continuous vapour phase fixed bed reactor to obtain a gaseous product of sulfuryl fluoride.

In accordance with the present invention, the reactor should be HF resistant reactor. In an embodiment, the reactor is a jacketed reactor through which heating and cooling fluids are passed for maintaining the appropriate temperature of the reactor during the reaction.

Typically, hydrogen chloride (HCl) gas is formed during the reaction of hydrogen fluoride with a mixture of sulfur dioxide and chlorine. The HCl gas so formed and the unreacted chlorine (if any) can be scrubbed by passing the gaseous product mixture through a chamber typically containing alkaline scrubber.

In accordance with the first embodiment of the present invention step (b), the gaseous product of sulfuryl fluoride can be added to the reactor containing bis(trimethylsilyl)amine solution. In another embodiment, bis(trimethylsilyl)amine solution can be added to the reactor containing the gaseous product mixture comprising sulfuryl fluoride.

In first embodiment, the step (b) process comprising, either of any sequences of adding gaseous product of sulfuryl fluoride and the solution of bis(trimethylsilyl)amine and blending for a time period in the range of 12 hours to 20 hours to obtain a hydrogen bis(fluorosulfonyl)imide (HFSI); preferably 13 hours to 14 hours.

In first embodiment, the step (b) process using polar aprotic solvent for preparing a solution of bis(trimethylsilyl)amine (HMDS) are selected from propionitrile, 1,4-dioxane, xylene, monochlorobenzene, dichlorobenzene, orthodichlorobenzene or mixture of thereof.
In accordance with the first embodiment of the present invention step (c), the lithiation solution can be prepared as mixing lithiation reagent in suitable solvent.

The lithiation reagent can include, but is not limited to, lithium fluoride, lithium hydroxide and lithium carbonate or hydrates thereof. Other known suitable lithiation reagents can also be used.

The solvent is not limited to organic, inorganic or mixture of thereof can also be used. In another embodiment of the present invention, the lithiation solution can be prepared in the organic solvent selected from ethers, carbonates, esters and alcohols. In another embodiment of the present invention, the lithiation solution can be prepared in water. In still another embodiment of the present invention, the lithiation solution can be prepared in a mixture of water and the organic solvent.

In first embodiment, the step (c) process comprising, cooling the reactor comprising the HFSI and adding a solution of lithiation reagent and stirring for a time period in the range of 5 hours to 10 hours to obtain a resultant solution and evaporating the fluid medium to obtain a lithium bis(fluorosulfonyl)imide (LiFSI). Optionally, which is further purified by crystallization to obtain battery grade lithium bis(fluorosulfonyl)imide (LiFSI).

In accordance with the first embodiment of the present invention step (c) or (d), the yield of LiFSI can be greater than 90% and the purity can be greater than 99%.

In another embodiment of the present invention, the process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI) according to first ambodiment, wherein step (a) for preparing sulfuryl fluoride alternatively comprising a process by reacting sulfuryl chloride with anhydrous hydrogen fluoride or metal fluoride (MF) at a temperature ranging between 50 °C to 150 °C to get sulfuryl fluoride.

In accordance with the another embodiment of the present invention, the metal fluoride (MF) can include, but is not limited to, sodium, potassium, calcium, zinc, Caesium, lithium.
In another embodiment of the present invention, the process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI) according to first embodiment, wherein step (b) by-product generated as fluoro trimethyl silane is recycled by treating with ammonia gas to obtain HMDS of purity exceeding 99.0% (by GC).

In a second embodiment of the present invention, the process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI), comprising the steps of:
reacting sulfuryl chloride with anhydrous hydrogen fluoride or metal fluoride (MF) at a temperature ranging between 50 °C to 90 °C to obtain a to obtain selectively sulfuryl chloride fluoride;

reacting sulfuryl chloride fluoride with ammonium source to obtain sulfamoyl fluoride;

reacting sulfamoyl fluoride with sulfuryl chloride fluoride in the presence of base in polar aprotic solvent to obtain hydrogen bis(fluorosulfonyl)imide (HFSI);

reacting with lithiation reagent in an organic solvent with step (c) HFSI under continuous stirring at a temperature ranging between 15 °C to 30 °C for time duration ranging between 5 to 10 hours to obtain LiFSI; and

optionally, purifying LiFSI of step (d) to get highly pure LiFSI with purity of exceeding 99.80% w/w.

In accordance with the second embodiment of the present invention step (a), the metal fluoride (MF) can include, but is not limited to, sodium, potassium, calcium, zinc, lithium.
In accordance with the second embodiment of the present invention step (b), the ammonium source can include, but is not limited to, ammonia gas, ammonium hydroxide or HMDS.

In accordance with the second embodiment of the present invention step (b), the sulfuryl chloride fluoride can be added to the reactor containing ammonium source. In another embodiment, ammonium source can be added to the reactor containing the sulfuryl chloride fluoride.

In second embodiment, the step (b) process comprising, adding a predetermined amount of aqueous ammonium source to the reactor comprising the sulfuryl chloride fluoride and carrying out the reaction at a temperature in the range of 30 °C to 50 °C for a time period in the range of 5 hours to 10 hours to obtain a product mixture comprising sulfamoyl fluoride.

In accordance with the second embodiment of the present invention step (c), the base can include, but is not limited to, ammonia or an organic bases selected from trimethyl amine and triethyl amine.

In accordance with the second embodiment of the present invention step (c), the polar aprotic solvent is selected from propionitrile, 1,4-dioxane, xylene, monochlorobenzene, dichlorobenzene, orthodichlorobenzene or mixture of thereof.

In second embodiment the step (c) process comprising, adding sulfuryl chloride fluoride to the reactor comprising the product mixture comprising sulfamoyl fluoride followed by adding a predetermined amount of base and stirring at a temperature in the range of 30 °C to 50 °C for a time period in the range of 5 hours to 10 hours to obtain a product mixture comprising hydrogen bis(fluorosulfonyl)imide (HFSI).

In accordance with the second embodiment of the present invention step (d), the lithiation solution can be prepared as dissolved lithiation reagent in suitable solvent.

The lithiation reagent can include, but is not limited to, lithium fluoride, lithium hydroxide, lithium carbonate or hydrates thereof. Other known suitable lithiation reagents can also be used.

The solvent is not limited to organic, inorganic or mixture of thereof can also be used. In another embodiment of the present invention, the lithiation solution can be prepared in the organic solvent selected from ethers, carbonates, esters and alcohols. In another embodiment of the present invention, the lithiation solution can be prepared in water. In still another embodiment of the present invention, the lithiation solution can be prepared in a mixture of water and the organic solvent.

In second embodiment, the step (d) process comprising, cooling the reactor comprising the product mixture of hydrogen bis(fluorosulfonyl)imide (HFSI) and adding a solution of a lithiation reagent and stirring for a time period in the range of 5 hours to 10 hours to obtain a resultant solution and evaporating water to obtain a lithium bis(fluorosulfonyl)imide (LiFSI). Optionally, which is purified by crystallization to obtain battery grade lithium bis(fluorosulfonyl)imide (LiFSI).

In accordance with the second embodiment of the present invention, the yield of LiFSI can be greater than 95% and the purity can be greater than 99%.

The present invention provides a simple, efficient and economic process for the preparation of LiFSI with a comparatively higher better yield and better purity.

TECHNICAL ADVANCEMENTS AND ECONOMICAL SIGNIFICANCE
The present invention described herein above has several technical advantages including, but not limited to, the realization of a process for the preparation of lithium bis(fluorosulfonyl)imide, that:
employs cheap and easily available reagents;
is simple, efficient and environment friendly; and
is feasible on a large/commercial scale.

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the invention. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the invention as it existed anywhere before the priority date of this application.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the invention, unless there is a statement in the specification specific to the contrary.

While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the invention. These and other changes in the preferred embodiment as well as other illustrative of the invention and not as a limitation.

EXAMPLE(S):
Example-01: Preparation of SO2F2
In the fixed bed vapour phase reactor of size 1m long and 0.0254 m diameter, activated carbon (250 g) was charged and calcinated by passing nitrogen at a temperature from 250 °C to 330 °C for 12h. The mixture of SO2, Cl2, and HF (molar ratio of 1:1.1:4.5 with respect to SO2:Cl2: HF) was passed through the preheater at a temperature of 160 to 180 °C followed by a fixed bed reactor divided into four number of temperature zone set in a succeeding order of 160 °C, 200 °C, 240 °C & 280 °C. The reactants were passed through bed reactor over a contact period of 30 to 35 seconds. Resulting the reaction product(s) were obtained and analysed by gas chromatography (TCD detector). The product rate for SO2F2-mixture with unreacted HF was 85 g/h giving a 91.8 % of SO2F2 selectivity. The obtained crude SO2F2 was further purified by pressure distillation with an isolated yield-85.3 % having purity of 99.1 % analysed by GC (TCD).

Example-02: Preparation of SO2F2
Charged anhydrous sulfolane (3000 mL) and anhydrous potassium fluoride (861 g) in 5L Hastelloy autoclave at room temperature. Heated the reaction mixture at 100 ? and slowly pump sulfuryl chloride (600 g) into the autoclave and stirred for 3 hours at 100-150 °C. The reaction mass was cooled to ambient temperature. The obtained pressure containing crude product mixture (448 g) from the autoclave was collected under cooling at -55 to -30 ? in an appropriate Hastelloy bomb with 96.3 % yield having 92.1% GC-TCD purity. The crude product mixture of sulfuryl fluoride (SO2F2) was purified by pressure distillation to afford 422.4 g (yield - 90.8 % w/w) having purity of 99.8 % analysed by GC-TCD.

Example-03: Preparation of hydrogen bis(fluorosulfonyl)imide (HFSI)
Charged anhydrous propionitrile (600 mL) at room temperature in 2L Hastelloy autoclave and. Further, charged sulfuryl fluoride (306 g) and hexamethyldisilane (161.4 g) slowly into the autoclave. The reaction mixture was heated to 90-95°C and maintained for 11-13h. Unreacted sulfuryl fluoride and the by-product trimethylfluorosilane (TMSF) were recovered through pressure distillation. After completion of reaction, the reaction mixture was distilled under vacuum to obtained hydrogen bis(fluorosulfonyl)imide (172.3 g; yield - 95.2 % w/w) having purity 99.92 % analysed by HPLC-ELSD

Example-04: Preparation of LiFSI
Charged propionitrile (300 ml) and lithium hydroxide monohydrate (1.01 mol eq.) to a three-neck flask at room temperature. The reaction mixture was cooled to 10° C. Added dropwise HFSI (100 g) to above reaction mixture at less than 15 °C. The reaction mixture was stirred for 6 hours at 15-30 °C. The reaction mixture was filtered to remove unreacted LiOH.H2O, and the filtrate was concentrated to get a crude product. The obtained crude product was purified by toluene (2 volumes) followed by isolation to get pure material (94.8 g) with yield - 91.8 % w/w having purity of 99.92 %.

Example-05: Recovery of Bis(trimethylsilyl)amine (HMDS) from Trimethylfluorosiliane (TMSF)
Charged trimethylfluorosilane (180 g) in to the Hastelloy autoclave and NH3 gas was purged. The reaction mixture was heated at 40-50 °C and maintained for 2 hours under pressure (1-2 kg/cm2). The reaction mixture was cooled to below 10 °C followed by addition of water to dissolve ammonium fluoride (by-product). The resulting reaction mixture was allowed to separate. The organic layer contains crude Bis(trimethylsilyl)amine (HMDS) which was further purified by distillation to get pure HMDS (145.69 g) with yield - 95% having purity of 99.45 %.

Example-06: Preparation of SO2ClF
Charged sulfuryl chloride (2000 g) and anhydrous HF (1482.7 g) into the autoclave via the deep pipe at 0 to 10 ?. The reaction mixture was gradually heated to 75-90°C for 12h and a pressure maintained at 10 bar throughout the reaction. The mixture of SO2ClF and HF was obtained after completion of the reaction. The obtained mixture was purified by pressure distillation and collected pure SO2ClF (yield 90.4% and purity of 98.3 %) in a pressure vessel and stored at -30 to 0 °C. The extremely volatile material of SO2ClF (bp: 7°C) was confirmed by 19F-NMR: 30 ?ppm.

Example-07: Preparation of FSO2NH2
Charged SO2ClF (450 g) and NH3 gas (162 g) into the autoclave at -10 to 0 ?. The mixture was slowly heated to 35-45 ? and maintained for 6 hours. After completion of the reaction, the reaction mixture was cooled to ambient temperature. The obtained pressure gases mixture was collected into a scrubber. The obtained reaction mass was filtered to get yellow oily material of sulfamoyl fluoride (354g) with yield - 94.2% w/w and having purity of 98.2% analysed by GC. The isolated material was confirmed by GCMS: m/z 100.

Example-08: Preparation of HFSI
Charged sulfamoyl fluoride (200 g), propionitrile (2 volumes), ClSO2F (1.01 mol eq.) followed by an NH3 gas (1.01 mol eq.) into the autoclave at -10 to 0 ?. The reaction mixture was stirred for 4h at 40-50 ?. Cool the reaction mass at ambient temperature. The remaining gases were collected into a scrubber. The reaction mass was filtered and filtrate was distilled under reduced pressure to obtain HFSI (342g) with yield - 93.6% w/w having the purity 99.92 %. The isolated material was confirmed by 19F-NMR: 56 ?ppm.

Example-09: Preparation of LiFSI
Charged dimethyl carbonate (3 volumes) and lithium hydroxide monohydrate (1.01 mol eq.) to a three-neck flask at room temperature. The reaction mixture was cooled to 10° C. Added dropwise HFSI (200 g) to above reaction mixture at less than 15 °C. The reaction mixture was stirred for 6 hours at 15-30 °C. The reaction mixture was filtered to remove unreacted LiOH.H2O, and the filtrate was concentrated to get a crude product. Dichloroethane was added into the obtained crude product while stirring and the reaction mixture was concentrated to get white precipitate, filtered and dried to obtain pure LiFSI (190.5g) with yield - 92.2% w/w and having purity of 98.30%.

Example-10: Purification of crude LiFSI
Charged dichloromethane (300 ml) and crude LiFSI (100g) having purity of 98.15 % to a three-neck flask at room temperature. The reaction mixture was heated to 35-40 °C and stirred for 1 hour. Cool the reaction mass at 0 °C to get a precipitated product, which was filtered-off to get pure material (97.2 g) having purity of 99.96 %.

Various modifications of the embodiments, in addition to those described herein the examples, will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims. Each reference, including all patent, patent applications, and publications, cited in the present application is incorporated herein by reference in its entirety.
,CLAIMS:WE CLAIM:

A process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI), comprising the steps of:
reacting hydrogen fluoride with a mixture of sulfur dioxide and chlorine in the presence of a catalyst at a temperature in the range of 75 °C to 300 °C in a continuous vapour phase fixed bed reactor to obtain sulfuryl fluoride;

reacting the sufuryl fluoride of step a) with a solution of bis(trimethylsilyl)amine (HMDS) in a polar aprotic solvent at temperature ranging between 70 – 100 °C for time duration ranging between 12 to 20 hours to obtain pure hydrogen bis(fluorosulfonyl)imide (HFSI);

adding a solution of lithiation reagent in an organic solvent with step (b) HFSI under continuous stirring for time duration ranging between 5 to 10 hours to obtain a LiFSI; and

optionally, purifying LiFSI of step (c) to get highly pure LiFSI with purity of exceeding 99.80% w/w.

The process as claimed in claim 1, wherein the catalyst in step (a) is selected from granulated charcoal or zeolite or alumina beads.

A process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI) according to claim-1, wherein step a) for preparing sulfuryl fluoride alternatively comprising a process by reacting sulfuryl chloride with anhydrous hydrogen fluoride or metal fluoride (MF) at a temperature ranging between 50 °C to 150 °C to get sulfuryl fluoride.

A process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI) according to claim-1, wherein step b) using polar aprotic solvent for preparing a solution of bis(trimethylsilyl)amine (HMDS) are selected from propionitrile, 1,4-dioxane, xylene, monochlorobenzene, dichlorobenzene, orthodichlorobenzene or mixture of thereof.

A process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI) according to claim-1, wherein step b) by-product generated as fluoro trimethyl silane is recycled by treating with ammonia gas to obtain HMDS of purity exceeding 99.0% (by GC).

A process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI), comprising the steps of:
reacting sulfuryl chloride with anhydrous hydrogen fluoride or metal fluoride (MF) at a temperature ranging between 50 °C to 90 °C to obtain a to obtain selectively sulfuryl chloride fluoride;

reacting sulfuryl chloride fluoride with ammonium source to obtain sulfamoyl fluoride;

reacting sulfamoyl fluoride with sulfuryl chloride fluoride in the presence of base in polar aprotic solvent to obtain hydrogen bis(fluorosulfonyl)imide (HFSI);

reacting with lithiation reagent in an organic solvent with step (c) HFSI under continuous stirring at a temperature ranging between 15 °C to 30 °C for time duration ranging between 5 to 10 hours to obtain LiFSI; and

optionally, purifying LiFSI of step (d) to get highly pure LiFSI with purity of exceeding 99.80% w/w.

The process as claimed in claim 6, wherein the ammonium source in step (b) is selected from ammonia gas, ammonium hydroxide or HMDS.

The process as claimed in claim 6, wherein the polar aprotic solvent in step (c) is selected from propionitrile, 1,4-dioxane, xylene, monochlorobenzene, dichlorobenzene, orthodichlorobenzene or mixture of thereof.

The process as claimed in claim 6, wherein the base in step (c) is selected from ammonia, trimethyl amine, triethyl amine or mixture(s) thereof.

The process as claimed in claim 1 to 6, wherein the lithiation reagent is selected from lithium fluoride, lithium hydroxide, lithium carbonate or hydrates thereof.