DESC:FIELD OF THE INVENTION:
The present invention relates to a process for the preparation and purification of lithium bis(fluorosulfonyl)imide (LiFSI). More particularly, the present invention relates to a process for the preparation of battery-grade lithium bis(fluorosulfonyl)imide (LiFSI) having high purity with reduced content of moisture, metal and anionic impurities, 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:

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. There are several processes known in the art for the preparation and purification of LiFSI, however, they suffer from various drawbacks due to which producing battery grade LiFSI becomes challenging. For use as an electrolyte additive in lithium-ion batteries, purity is a very critical parameter. The electrolyte must have high purity of the order of >99.9%. Additionally, the content of moisture, free metal as well as anionic impurities must also be controlled to ppm levels. However, many commercial processes that are used for synthesizing LiFSI lead to the formation of impurities such as Lithium fluoride (LiF), Lithium chloride (LiCl), Lithium sulfate (Li2SO4) etc. that are difficult to remove.
The US patent number US9079780B2 (US’780) and Chinese patent number CN103664712B (CN’712) disclose the preparation of alkali metal salt of fluorosulfonyl imide with metal hydroxide in a water solution. US’780 demonstrated a method of extraction of LiFSI from an aqueous solution with the help of an organic solvent. However, said process claimed a low yield (~73%) and the process was not found to be commercially viable. On the other hand, CN’712 discloses a process of LiFSI isolation involving spray drying at ~125 ? to 200 ?, but the purity of LiFSI along with the critical impurities present in the isolated product have not been disclosed therein.
The US patent number US 10734664 discloses the various impurities of chloride, fluoride, sulfate and metals isolated from the crude HFSI by crystallization in chlorinated hydrocarbon solvent/s. However, there is no disclosure of the isolated yield of HFSI.
Accordingly, there exists a need in the art to develop a cost-effective and commercially viable process for the preparation and purification of LiFSI that can overcome the aforementioned drawbacks and provide a high-quality, pure battery- grade LiFSI.
OBJECT OF THE INVENTION:
The main objective of the present invention is to provide a simple, cost-effective and an efficient process for the preparation of pure lithium bis(fluorosulfonyl)imide (LiFSI).
Another objective of the present invention is to provide a process for the preparation of pure lithium bis(fluorosulfonyl)imide (LiFSI) which can prevent the degradation of LiFSI during isolation.
Another one objective of the present invention is to provide a process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI) with high yield and purity.
Another objective of the present invention to provide an industrially viable process for the preparation of lithium bis(fluorosulfonyl)imide (LiFSI) that can consistently provide high quality product with reduced amounts of metal and anionic impurities.
One more objective of the present invention is to provide a method for purifying lithium bis(fluorosulfonyl)imide (LiFSI) which can provide a product of >99.9% purity.
SUMMARY OF THE INVENTION:
Various embodiments of the present invention relate to a process for the preparation and purification of lithium bis(fluorosulfonyl)imide (LiFSI).
In accordance with an aspect of the invention, a process for preparing lithium bis(fluorosulfonyl)imide (LiFSI) of Formula (I) has been provided. The process comprises the steps of reacting bis(fluorosulfonyl)imide (HFSI) of Formula (II) with a lithiation reagent in the presence of a solvent at a temperature of 0-30 °C. The reaction mixture obtained is then subjected to filtration followed by concentration of the filtrate to yield the crude product.

In accordance with another aspect of the invention, a process for purification of lithium bis(fluorosulfonyl)imide (LiFSI) of Formula (I) is provided. The process comprises subjecting the crude product to co-distillation with a chlorinated hydrocarbon solvent followed by the dissolution of the solid LiFSI in anhydrous carbonate solvent. The insoluble impurities are then removed through micron filtration and the filtrate is concentrated to obtain a concentrated reaction mass which is then subjected to crystallization to obtain pure LiFSI.
In accordance with another aspect of the invention, a process for the preparation of pure lithium bis(fluorosulfonyl)imide, comprising the steps of:
a) reacting bis(fluorosulfonyl)imide with lithiation reagent in the presence of C1-4 alcoholic solvent at temperature ranging between 0 °C to 30 °C;
b) performing the azeotropic distillation of step (a) reaction mass using the alcoholic solvent under vacuum ranging between 10 to 100 torr at a temperature below 50°C, up to the residual mass B comprising, moisture content less than 0.50% and alcohol content less than 20%;
c) dissolving the residual mass B of step (b) in an organic carbonate solvent;
d) filtering the insoluble in an inert atmosphere to get a solution of lithium bis(fluorosulfonyl)imide;
e) performing activated carbon treatment of step (d) solution to isolate residual mass E, wherein the residual mass E comprises carbonate solvent content less than 20%;
f) mixing the residual mass E of step (e) with chlorinated hydrocarbon solvent at temperature below 30 °C and maintained under stirring for 10 to 30 hours; and
g) isolating pure lithium bis(fluorosulfonyl)imide crystals in an inert atmosphere, wherein pure lithium bis(fluorosulfonyl)imide crystals comprises:
i. purity at least 99.95% (w/w);
ii. the moisture content less than 50 ppm;
iii. total anionic impurities less than 50 ppm;
iv. APHA value less than 20;
v. any individual metal impurities less than 1 ppm except Na and K;
vi. individual Na or K impurity less than 10 ppm;
vii. total insoluble impurities less than 50 ppm; and
viii. any acid impurity less than 50 ppm.
DETAILED DESCRIPTION OF THE INVENTION:
Various embodiments of the present invention relates to a process for the preparation of pure lithium bis(fluorosulfonyl)imide (LiFSI).
Discussed below are some representative embodiments of the present invention. The invention in its broader aspects is not limited to the specific details and representative methods. An illustrative example is described in this section in connection with the embodiments and methods provided.
It is to be noted that, as used in the specification, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. It should also be noted that the term "‘or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
The expression of various quantities in terms of “%” or “% w/w” means the percentage by weight of the total solution or composition unless otherwise specified. The term “ppm” refers to “parts per million.”
The present invention, in all its aspects, is described in detail as follows:
Described herein is an improved process for preparation and purification of lithium bis(fluorosulfonyl)imide (LiFSI, CAS RN 171611-11-3) that provides the product with high yield and purity while ensuring consistent production of high quality, battery- grade LiFSI. The process of preparation of lithium bis(fluorosulfonyl)imide comprises the steps of a) reacting bis(fluorosulfonyl)imide (HFSI) with a lithiation reagent in the presence of a solvent at a temperature of 0-30 °C; and b) subjecting the reaction mixture to filtration followed by concentration of the filtrate to yield the crude product. The reaction is depicted in the scheme below:

Preferably, step (a) of the reaction process is carried out under a nitrogen atmosphere.
Solvent
The term “solvent” refers to a substance that helps in dissolution of a solute resulting in a solution. The solvents are used at various stages during the process of synthesis and purification of LiFSI such as lithiation reaction, distillation, crystallization etc. In accordance with an embodiment, the solvent used in the lithiation reaction is selected from the class of esters, ethers, alcohols, carbonates, halogenated hydrocarbons, nitriles, ketones, such as n-butyl acetate, ethyl acetate, 1,4-dioxane, dimethoxyethane, 2-methoxy ethanol, methanol, ethyl alcohol, isopropanol, n-butanol, n-propyl alcohol, t-butyl alcohol, trifluoroethanol, hexafluoro isopropanol, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dichloroethane, carbon tetrachloride, acetonitrile and acetone or combinations thereof. Water can also be used as a solvent for said reaction. Preferably, the solvent for said reaction is selected from alcohols and carbonates such as n-butanol, n-propyl alcohol, isopropanol, ethyl alcohol, t-butyl alcohol, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and water. The amount of the reaction solvent used is 2-4 times of the mass of the bis(fluorosulfonyl)imide (HFSI).
Lithiation reagent
The lithiation reagent refers to the lithium containing compound used to affect the lithiation reaction. The lithiation reagent useful for the reaction of the present invention is one or more selected from Lithium hydroxide (LiOH) and/or hydrates like Lithium hydroxide monohydrate (LiOH.H2O), Lithium carbonate (Li2CO3), Lithium methoxide (LiOMe), Lithium isopropoxide (LiOi-Pr), Lithium hydride (LiH), Lithium oxide (Li2O) and Lithium fluoride (LiF).
In accordance with an embodiment, the crude product that is obtained after the reaction of bis(fluorosulfonyl)imide (HFSI) with lithium hydroxide monohydrate (LiOH.H2O) followed by filtration and concentration to obtain the solid yield of 85-97% with a purity of > 99%. Also, the moisture content is below 0.05% and the water insoluble substance is less than or equal to 0.005%. In a preferred embodiment, the crude product obtained after the lithiation reaction step, subjected to filtration to remove the excess of lithiation reagent. The filtrate obtained is then concentrated under a vacuum of 2-100 Torr at a temperature of 15 to 60 ?. The concentration is performed at basic pH between 7-8 so as to prevent degradation of the crude material; the pH being maintained by using inorganic bases such as ammonia, LiHCO3 and Li2CO3 or combinations thereof. The concentrate is then subjected to a purification process to yield pure LiFSI.
The present invention also discloses a process for the purification of lithium bis(fluorosulfonyl)imide (LiFSI) comprising the steps of:
a. subjecting the crude product to co-distillation with a chlorinated hydrocarbon solvent;
b. dissolving the solid LiFSI in anhydrous carbonate solvent;
c. removing the insoluble impurities through micron filtration followed by concentration of the filtrate; and
d. subjecting the concentrated mass to crystallization to obtain pure LiFSI.
In accordance with an embodiment, the chlorinated hydrocarbon solvent used is selected from dichloromethane, 1,2-dichloroethane, carbon tetrachloride, chloroform, trichloroethanes, tetrachloroethylene or mixture(s) thereof.
Further, the anhydrous carbonate solvent used for dissolution of the solid LiFSI is one or more selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate, propylene carbonate, butylene carbonate, and ethyl methyl carbonate (EMC) or mixture(s) thereof.
Insoluble impurities such as chloride (Cl-), fluoride (F-) and sulfate (SO42-) are removed through micron filtration. In an alternative embodiment, the LiFSI is treated with 0.1 to 0.5% w/w lithium carbonate (Li2CO3) before subjecting it to micron filtration to significantly reduce said Cl-, F- and SO42- impurities. The filtrate obtained is then concentrated under reduced pressure (50-100 Torr) at a temperature of below 50 °C to obtain a concentrated reaction mass. The solvent is also recovered during said step. In another embodiment, Ammonia/ Li2CO3 may be introduced into the concentrated reaction mass to stabilize the reaction process, prevent degradation of LiFSI while ensuring that a high-quality product is obtained. The product obtained is then further distilled and crystallized to yield pure LiFSI having a purity of greater than or equal to 99.9%. The crystallization is performed using an organic solvent. Preferably, the organic solvent is one or more selected from n-hexane, n-heptane, cyclohexane, dichloromethane, dichloroethane, toluene, xylene, chlorobenzene, and dichlorobenzene.
In accordance with an embodiment, the micron filtration is carried out using a filter with pore size of 0.1 to 0.7 microns, preferably of 0.1 to 0.5 microns.
In accordance with another embodiment, a process for the preparation of pure lithium bis(fluorosulfonyl)imide, comprising the steps of:
a) reacting bis(fluorosulfonyl)imide with lithiation reagent in the presence of C1-4 alcoholic solvent at temperature ranging between 0 °C to 30 °C;
b) performing the azeotropic distillation of step (a) reaction mass using the alcoholic solvent under vacuum ranging between 10 - 100 torr at a temperature below 50°C, up to the residual mass B comprising, moisture content less than 0.50% and alcohol content less than 20%;
c) dissolving the residual mass B of step (b) in an organic carbonate solvent;
d) filtering the insoluble in an inert atmosphere to get a solution of lithium bis(fluorosulfonyl)imide;
e) performing activated carbon treatment of step (d) solution to isolate residual mass E, wherein the residual mass E comprises carbonate solvent content less than 20%;
f) mixing the residual mass E of step (e) with chlorinated hydrocarbon solvent at temperature below 30°C and maintained under stirring for 10 to 30 hours; and
g) isolating pure lithium bis(fluorosulfonyl)imide crystals in an inert atmosphere, wherein pure lithium bis(fluorosulfonyl)imide crystals comprises:
i. purity at least 99.95% (w/w);
ii. the moisture content less than 50 ppm;
iii. total anionic impurities less than 50 ppm;
iv. APHA value less than 20;
v. any individual metal impurities less than 1 ppm except Na and K;
vi. individual Na or K impurity less than 10 ppm;
vii. total insoluble impurities less than 50 ppm; and
viii. any acid impurity less than 50 ppm.
The present invention saltification process used C1-4 alcoholic solvent was selected from methanol, ethanol, propanol, isopropanol, butanol, isobutanol or mixture(s) thereof.
Further, in step (c) the organic carbonate solvent can be selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate, propylene carbonate, butylene carbonate, and ethyl methyl carbonate (EMC) or mixture(s) thereof.
In the step (e), activated carbon treatment is performed with acid washed activated carbon, which is selected from granule or powder form, or coconut shell activated carbon and/or coal-based activated carbon. Isolation of the product was performed in chlorinated hydrocarbon solvent, the chlorinated hydrocarbon solvent was selected from dichloromethane, 1,2-dichloroethane, carbon tetrachloride, chloroform, trichloroethanes, tetrachloroethylene or mixture(s) thereof.
In accordance with an embodiment, the reaction mass B is obtained after the reaction of bis(fluorosulfonyl)imide (HFSI) with lithium carbonate (Li2CO3) followed by azeotropic distillation using isopropyl alcoholic solvent and distillation can be performed continuously under vacuum range between 10 to 100 torr at a temperature below 50°C. Further residual mass B is maintain to the alcohol solvent content should be less than 20% of the reaction mass B and the moisture content up to less than 0.50 %; Preferably, the alcohol content should be less than 15% of the reaction mass B and the moisture content up to less than 0.30 %. The purpose of azeotropic distillation is to maintain the moisture content level in the reaction mass B comprising lithium bis(fluorosulfonyl)imide.
In accordance with an embodiment, the residual mass B obtained in step (b) is dissolved in dimethyl carbonate under an inert atmosphere at a temperature of 25 to 30 ? to obtain a dimethyl carbonate solution of residual mass B comprising lithium bis(fluorosulfonyl)imide.
The above solution obtained in step (c) is subjected to filtration using micron filtration to remove the excess of lithiation reagent.
After filtration, the solution obtained in above step (d) is treated with acid washed activated carbon, filtered through micron filtration and the obtained filtrate was concentrated under a vacuum of 2 to 100 Torr at a temperature of 15 to 60 ? till generation of residual mass E, which comprises: carbonate solvent content less than 20% and total anionic impurity less than 50 ppm. In this filtration insoluble impurities such as chloride (Cl-), fluoride (F-) and sulfate (SO42-) are removed through micron filtration. The purpose of carbon treatment and micron filtration is to maintain the anionic impurity (i.e., chloride (Cl-), fluoride (F-) and sulfate (SO42-)) level in the residual mass E comprising lithium bis(fluorosulfonyl)imide.
The obtained residual mass E was treated with dichloromethane at temperature ranging between 25 to 35 ? under starring for 10 to 30 hours. Appears the precipitated white crystals, filtered and dried at 25 to 50 ? under a vacuum of 2 to 100 Torr to get pure crystals of lithium bis(fluorosulfonyl)imide. The pure lithium bis(fluorosulfonyl)imide crystals obtained in step (g) comprises:
i. purity at least 99.95% (w/w);
ii. the moisture content less than 50 ppm;
iii. total anionic impurities less than 50 ppm;
iv. APHA value less than 20;
v. any individual metal impurities less than 1 ppm except Na and K;
vi. individual Na or K impurity less than 10 ppm;
vii. total insoluble impurities less than 50 ppm; and
viii. any acid impurity less than 50 ppm.
The present invention is more particularly described in the following examples that are intended as illustration only, since numerous modifications and variations within the scope of the present invention will be apparent to those skilled in the art. Unless otherwise noted, all parts, percentages, and ratios reported in the following examples are on a weight basis, and all reagents used in the examples were obtained or are available from the chemical suppliers.
The following examples illustrate the basic methodology and versatility of the present invention.
EXAMPLES:
Example 1
To the 1000 mL of the reaction vessel, 320g of dimethyl carbonate, and 32.11g of lithium hydroxide monohydrate (LiOH.H2O) were added under nitrogen while ensuring the temperature remained between 20-30°C. Subsequently, 100g of bis(fluorosulfonyl)imide (HFSI) was slowly introduced with stirring at 20-25 ?. The exhaust gas was absorbed by the scrubber. The reaction was allowed to proceed for 6 hours under the same conditions, with monitoring via 19F-NMR. Filtration was employed to remove any insoluble material, followed by concentration of the filtrate. The concentrated mass was treated with dichloromethane, followed by co-distillation to yield a solid product. The resultant solid lithium bis(fluorosulfonyl)imide (LiFSI) precipitate was separated through filtration, and the wet cake obtained was then dissolved in anhydrous dimethyl carbonate. Insoluble impurities such as chloride, fluoride, and sulfate were removed through micron filtration (0.45µ) at room temperature, and the filtrate was subsequently concentrated below 50°C. The addition of dichloromethane to the concentrated mass yielded pure crystalline LiFSI, which was dried below 50°C under reduced pressure, resulting in 88g (85%) of pure LiFSI. The final product obtained was a white solid powder with a melting point ranging from 125 to 137°C. Moisture content, determined via Karl Fisher titration was 20 ppm. The purity was 99.6%, as measured by Ion Chromatography (DIONEX IC). Anion impurities were detected by IC: F- = 48 ppm, Cl-= 4 ppm, and SO42- = 40 ppm.
The total concentration of metal impurities was 18 ppm through ICP analysis.
Example 2
To the 1000 mL of the reaction flask, 320g of dimethyl carbonate, 5g of water, and 29.81g of lithium hydroxide monohydrate (LiOH.H2O) were added under nitrogen, and 100g of HFSI was added dropwise with stirring at 20-25 ?. After stirring for 4 hours under the same conditions, with monitoring via 19F-NMR. Upon completion of the reaction, filtration was employed to remove insoluble material, followed by a concentration of the filtrate below 50 °C to obtain concentrated mass. The concentrate was treated with dichloromethane and co-distilled to get a solid product. The resultant wet cake comprising lithium bis(fluorosulfonyl)imide (LiFSI) was subsequently dissolved in anhydrous ethyl methyl carbonate and insoluble impurities were eliminated through micron filtration, followed by concentration of the filtrate at temperatures below 50 ?. Dichloromethane was added to the concentrated mass to obtain pure crystalline LiFSI, which was filtered and dried below 50 ? under reduced pressure yielding 92g (89%) of pure LiFSI. The product obtained was a white solid powder with a melting point of 125-135 °C.
Ion Chromatography (DIONEX IC) analysis revealed that the purity of LiFSI was 99.95% and the anion concentrations were, F- = 21 ppm, Cl- = 3 ppm, SO42- = 12 ppm. Moisture content, determined via Karl Fisher titration was 8 ppm. Subsequent analysis by ICP for metal content showed all individual metal concentrations such as Fe, Pb, Ca, Zn, B, Ba, Cd, Hg, Cr, Mg, Mn, As, Ni, Cu, Al were <2 ppm and Na, K was <10 ppm.
Example 3
In a reaction flask containing 1000 mL, 320g of dimethyl carbonate, 10g of water, and 27.52g of lithium hydroxide monohydrate (LiOH.H2O) were introduced under a nitrogen atmosphere. Subsequently, 100g of HFSI was added dropwise with stirring at 20-25 ?. The stirring continued for 4 hours under the same conditions, with monitoring via 19F-NMR. Upon completion of the reaction, filtration was carried out to remove the insoluble material. The filtrate was then concentrated below 50 °C to obtain a concentrated mass. This concentrated mass was treated with dichloromethane and co-distilled to yield a solid product. The resulting wet cake, comprising lithium bis(fluorosulfonyl)imide (LiFSI), was dissolved in anhydrous diethyl carbonate. Insoluble impurities were removed through micron filtration, followed by further concentration of the filtrate at temperatures below 50 ?. Dichloromethane was added to the concentrated mass to isolate pure crystalline LiFSI, which was filtered and dried below 50 ? under reduced pressure, resulting in 90g (88%) of pure LiFSI. The product obtained was a white solid powder with a melting point of 127-135 °C.
Ion Chromatography (DIONEX IC) analysis revealed the purity of LiFSI was 99.96% and the anion contents were F- = 18 ppm, Cl- = 3 ppm, SO42- = 13 ppm. The total concentration of metal impurities was found 16 ppm through ICP analysis.
Example 4
To the 1000 mL of the reaction vessel, 320g of dimethyl carbonate and 29.81g of lithium hydroxide monohydrate (LiOH.H2O) were added under nitrogen while ensuring the temperature remained between 20-30°C. Subsequently, 100g of Bis(fluorosulfonyl)imide (HFSI) was slowly introduced with stirring at 20-25 ?. The exhaust gas was absorbed by the scrubber. The reaction was allowed to proceed for 6 hours under the same conditions, with monitoring via 19F-NMR. Filtration was employed to remove any insoluble material, followed by concentration of the filtrate. Subsequently, the reaction mass was then purged with ammonia until its pH reached 7-8. After adjustment of pH, the concentrated mass was treated with dichloromethane, followed by co-distillation to yield a solid product. The resultant solid lithium bis(fluorosulfonyl)imide (LiFSI) precipitate was separated through filtration, and the wet cake obtained was then dissolved in anhydrous dimethyl carbonate. Insoluble impurities such as chloride, fluoride, and sulfate were removed through micron filtration (0.45µ) at room temperature, and the filtrate was subsequently concentrated below 50°C. The addition of dichloromethane to the concentrated mass yielded pure crystalline LiFSI, which was dried below 50°C under reduced pressure, resulting in 94g (91%) of pure LiFSI. The final product obtained was a white solid powder with a melting point ranging from 127 to 136°C.
The purity was 99.97%, as measured by Ion Chromatography (DIONEX IC). Anion impurities were detected by IC: F- = 14 ppm, Cl- = 3 ppm, SO42- = 12 ppm.
Example 5
In a 500 mL reaction vessel, 100g of deionized water was introduced and cooled to approximately 15 ?. Slowly, 100g of HFSI was added while controlling the reaction temperature below 20 ?, all under a nitrogen atmosphere with continuous stirring. Subsequently, 240 g 10% lithium hydroxide monohydrate solution in water was added gradually over the course of an hour, ensuring the temperature remained between 20-30 ?, still under a nitrogen atmosphere and with stirring. The reaction mixture was then maintained at the same temperature for a duration of 2 hours under the same conditions, with monitoring via 19F-NMR. The reaction mass underwent vacuum distillation below 50 °C to get concentrated reaction mass. Then, the reaction mass was then treated with ammonia until its pH reached 7-8. Subsequently, the concentrated mass was treated with dichloromethane, followed by co-distillation to yield a solid product. The resultant solid lithium bis(fluorosulfonyl)imide (LiFSI) precipitate was separated through filtration, and the wet cake obtained was then dissolved in diethyl carbonate. Insoluble impurities such as chloride, fluoride, and sulfate were removed through micron filtration (0.45µ) at room temperature, and the filtrate was subsequently concentrated below 50°C. The addition of dichloromethane to the concentrated mass yielded pure crystalline LiFSI, which was dried below 50°C under reduced pressure, resulting in 87g (84%) of pure LiFSI. The final product obtained was a white solid powder with a melting point ranging from 129 to 137°C.
Ion Chromatography (DIONEX IC) analysis revealed the purity of LiFSI was 99.95% and the anion contents were F- = 90 ppm, Cl- = 3 ppm, SO42- = 122 ppm. Moisture content, determined via Karl Fisher titration was 15 ppm. Subsequent analysis by ICP for metal content showed all individual metal concentrations such as Fe, Pb, Ca, Zn, B, Ba, Cd, Hg, Cr, Mg, Mn, As, Ni, Cu, Al were <2 ppm and Na, K was <10 ppm.
Example 6
In a 500 mL reaction vessel, 100g of deionized water was introduced and cooled to approximately 15 ?. Slowly, 100g of HFSI was added while controlling the reaction temperature below 20 ?, all under a nitrogen atmosphere with continuous stirring. Subsequently, 240 g 10% lithium hydroxide monohydrate solution in water was added gradually over the course of an hour, ensuring the temperature remained between 20-30 ?, still under a nitrogen atmosphere and with stirring. The reaction mixture was then maintained at the same temperature for a duration of 2 hours under the same conditions, with monitoring via 19F-NMR. The reaction mass underwent vacuum distillation below 50 °C to get concentrated reaction mass. Subsequently, the reaction mass was then treated with lithium carbonate until its pH reached 7-8. Afterward, the concentrated mass was treated with dichloromethane, followed by co-distillation to yield a solid product. The resultant solid lithium bis(fluorosulfonyl)imide (LiFSI) precipitate was separated through filtration, and the wet cake obtained was then dissolved in anhydrous ethyl methyl carbonate. Insoluble impurities such as chloride, fluoride, and sulfate were removed through micron filtration (0.45µ) at room temperature, and the filtrate was subsequently concentrated below 50°C. The addition of dichloromethane to the concentrated mass yielded pure crystalline LiFSI, which was dried below 50°C under reduced pressure, resulting in 89g (86%) of pure LiFSI. The final product obtained was a white solid powder with a melting point ranging from 128 to 135°C.
Ion Chromatography (DIONEX IC) analysis revealed the purity of LiFSI was 99.96% and the anion contents were F- = 38 ppm, Cl- = 7 ppm, SO42- = 99 ppm.
Example 7
To the 1000 mL of the reaction vessel, 300g of Isopropyl alcohol and 22.44g lithium carbonate (Li2CO3) were added under nitrogen while ensuring the temperature remained between 20-30°C. Subsequently, 100g of Bis(fluorosulfonyl)imide (HFSI) was slowly introduced with stirring at 20-25 ?. The exhaust gas was absorbed by the scrubber. The reaction was allowed to proceed for 4 hours under the same conditions, with monitoring via 19F-NMR. Filtration was employed to remove any insoluble material, followed by concentration of the filtrate. The concentrated mass was treated with dichloromethane, followed by co-distillation to yield a solid product. The resultant solid lithium bis(fluorosulfonyl)imide (LiFSI) precipitate was separated through filtration, and the wet cake obtained was then dissolved in anhydrous dimethyl carbonate. Insoluble impurities such as chloride, fluoride, and sulfate were removed through micron filtration (0.45µ) at room temperature, and the filtrate was subsequently concentrated below 50°C. The addition of dichloromethane to the concentrated mass yielded pure crystalline LiFSI, which was dried below 50°C under reduced pressure, resulting in 96g (93%) of pure LiFSI. The final product obtained was a white solid powder with a melting point ranging from 125 to 137°C.
Moisture content, determined via Karl Fisher titration was found 6 ppm. The purity was 99.98%, as measured by Ion chromatography (DIONEX IC). Anion impurities were detected by IC: F- = 13 ppm, Cl- = 2 ppm, SO42- = 11 ppm. Additionally, the total concentration of metal impurities was 8 ppm through ICP analysis.
Example 8
To the 1000 mL of the reaction vessel, 300g of n-butyl alcohol and 22.44g lithium carbonate (Li2CO3) were added under nitrogen while ensuring the temperature remained between 20-30°C. Subsequently, 100g of bis(fluorosulfonyl)imide (HFSI) was slowly introduced with stirring at 20-25 ?. The exhaust gas was absorbed by the scrubber. The reaction was allowed to proceed for 4 hours under the same conditions, with monitoring via 19F-NMR. Filtration was employed to remove any insoluble material, followed by concentration of the filtrate. The concentrated mass was treated with dichloromethane, followed by co-distillation to yield a solid product. The resultant solid lithium bis(fluorosulfonyl)imide (LiFSI) precipitate was separated through filtration, and the wet cake obtained was then dissolved in anhydrous diethyl carbonate. Insoluble impurities such as chloride, fluoride, and sulfate were removed through micron filtration (0.45µ) at room temperature, and the filtrate was subsequently concentrated below 50°C. The addition of dichloromethane to the concentrated mass yielded pure crystalline LiFSI, which was dried below 50°C under reduced pressure, resulting in 97g (94%) of pure LiFSI. The final product obtained was a white solid powder with a melting point ranging from 125 to 137°C.
The purity was 99.97%, as measured by Ion Chromatography (DIONEX IC). Anion impurities were detected by IC: F- = 14 ppm, Cl- = 2 ppm, SO42- = 12 ppm.
Example 9
To the 1000 mL of the reaction vessel, 320g of dimethyl carbonate, 5g of water, and 22.44g of lithium carbonate (Li2CO3) were added under nitrogen while ensuring the temperature remained between 20-30°C. Subsequently, 100g of Bis(fluorosulfonyl)imide (HFSI) was slowly introduced with stirring at 20-25 ?. The exhaust gas was absorbed by the scrubber. The reaction was allowed to proceed for 6 hours under the same conditions, with monitoring via 19F-NMR. Filtration was employed to remove any insoluble material, followed by concentration of the filtrate. Subsequently, the reaction mass was then treated with Li2CO3 until its pH reaches 7-8. Subsequently, the concentrated mass was treated with dichloromethane, followed by co-distillation to yield a solid product. The resultant solid lithium bis(fluorosulfonyl)imide (LiFSI) precipitate was separated through filtration, and the wet cake obtained was then dissolved in anhydrous dimethyl carbonate. Insoluble impurities such as chloride, fluoride, and sulfate were removed through micron filtration (0.45µ) at room temperature, and the filtrate was subsequently concentrated below 50°C. The addition of dichloromethane to the concentrated mass yielded pure crystalline LiFSI, which was dried below 50°C under reduced pressure, resulting in 97g (94%) of pure LiFSI. The final product obtained was a white solid powder with a melting point ranging from 125 to 135°C.
Moisture content, determined via Karl Fisher titration was 15 ppm. The purity was 99.6%, as measured by Ion Chromatography (DIONEX IC). Anion impurities were detected by IC: F- = 13 ppm, Cl- = 5 ppm, and SO42- = 27 ppm. The total concentration of metal impurities was 15 ppm through ICP analysis.
Example 10
To the 1000 mL of the reaction vessel, 300g of Isopropyl alcohol and 22.44g lithium carbonate (Li2CO3) were added under nitrogen while ensuring the temperature remained between 20-30°C. Subsequently, 100g of bis(fluorosulfonyl)imide (HFSI) was slowly introduced with stirring at 20-25 ?. The exhaust gas was absorbed by the scrubber. The reaction was allowed to proceed for 4 hours under the same conditions, with monitoring via 19F-NMR. Filtration was employed to remove any insoluble material, followed by concentration of the filtrate. The concentrated mass was treated with isopropyl alcohol, followed by co-distillation to yield a solid product. The resultant solid lithium bis(fluorosulfonyl)imide (LiFSI) precipitate was separated through filtration below 10?, and the wet cake obtained was then dissolved in anhydrous ethyl methyl carbonate. Insoluble impurities such as chloride, fluoride, and sulfate were removed through micron filtration (0.45µ) at room temperature, and the filtrate was subsequently concentrated below 50°C. The addition of dichloromethane to the concentrated mass yielded pure crystalline LiFSI, which was dried below 50°C under reduced pressure, resulting in 98.5g (95%) of pure LiFSI. The final product obtained was a white solid powder with a melting point ranging from 125 to 137°C.
The purity was 99.96%, as measured by Ion Chromatography (DIONEX IC). Anion impurities were detected by IC: F- = 8 ppm, Cl- = 2 ppm, SO42- = 12 ppm. The total concentration of metal impurities such as Fe, Pb, Ca, Zn, B, Ba, Cd, Hg, Cr, Mg, Mn, As, Ni, Cu, Al was 8 ppm and Na, K was <10 ppm through ICP analysis.
Example 11
To the 1000 mL of the reaction vessel, 300 g of n-butyl alcohol and 22.44g lithium carbonate (Li2CO3) were added under nitrogen while ensuring the temperature remained between 20-30°C. Subsequently, 100g of Bis(fluorosulfonyl)imide (HFSI) was slowly introduced with stirring at 20-25 ?. The exhaust gas was absorbed by the scrubber. The reaction was allowed to proceed for 4 hours under the same conditions, with monitoring via 19F-NMR. Filtration was employed to remove any insoluble material, followed by concentration of the filtrate. The concentrated mass was treated with n-butyl alcohol, followed by co-distillation to yield a solid product. The resultant solid lithium bis(fluorosulfonyl)imide (LiFSI) precipitate was separated through filtration, and the wet cake obtained was then dissolved in anhydrous ethyl methyl carbonate. Insoluble impurities such as chloride, fluoride, and sulfate were removed through micron filtration (0.45µ) at room temperature, and the filtrate was subsequently concentrated below 50°C. The addition of dichloromethane to the concentrated mass yielded pure crystalline LiFSI, which was dried below 50 °C under reduced pressure, resulting in 97g (94%) of pure LiFSI. The final product obtained was a white solid powder with a melting point ranging from 125 to 135 °C.
Moisture content, determined via Karl Fisher titration was 5 ppm. The purity was 99.98%, as measured by Ion Chromatography (DIONEX IC). Anion impurities were detected by IC: F- = 9 ppm, Cl- = 3 ppm, SO42- = 16 ppm.
Example 12:
To the 1000 mL of the reaction vessel was charged with isopropyl alcohol (600 mL) at 25-30°C. The above mass was cooled to 15-20°C and lithium carbonate (44.87 g) was charged under stirring. Hydrogen bis(fluorosulfonyl)imide (HFSI, 200 g) was charged under stirring over 1 hour at 15-20°C. The mixture was then stirred at 25-30°C for 8 hours. After completion of the reaction, isopropyl alcohol was recovered via vacuum distillation (10-100 torr, <50°C) over 4 hours, followed by azeotropic distillation with fresh isopropyl alcohol until moisture was <0.5%. The obtained crude mass underwent vacuum degassing (10-5 torr, 50°C) for 3-4 hours, reducing isopropyl alcohol content to <20%. Dimethyl carbonate (400 mL) was charged to the above crude mass and stirred for 1 hour at 25-30?, filtered through a micron filtration to remove impurities. The obtained filtrate was treated with acid-washed activated charcoal (10 g) for 8 hours at 25-30°C, filtered and obtained filtrate was distilled under vacuum (10-100 Torr, <50°C) to remove dimethyl carbonate. The obtained crude mass underwent vacuum degassing (5-10 torr, 50°C) for 3-4 hours, reducing dimethyl carbonate content to 10-16%. After cooling, methylene dichloride (400 mL) was added under stirring and maintained for 24 hours at 25-30 °C. The obtained crystallized material was filtered off, washed with methylene dichloride, and vacuum-dried (1-2 torr, <50 °C) for 12 hours, yielding dry LiFSI powder (187 g). The dry LiFSI solid as a white powder was stored in an HDPE bottle under nitrogen, exhibiting a bulk density of 1.0517 g/cm³ and a melting point of 128-132°C. Ion Chromatography (DIONEX IC) analysis revealed the purity of LiFSI was 99.98% and the anion contents were F- = 3 ppm, Cl- = 1 ppm, SO42- = 6 ppm. Moisture content, determined via Karl Fisher titration was 11 ppm. Subsequent analysis by ICP for metal content showed all individual metal concentrations such as Mg = 0.17 ppm, Al = 0.13 ppm, Ca = 0.14 ppm, Cr = 0.15 ppm, Fe = 0.46 ppm, Ni = 0.1 ppm, Cu = 0.02 ppm, Cd = 0.001 ppm, Pb = 0.04 ppm, Na = 2.9 ppm and K = 1.6 ppm.
The residual filtrate from the above crystallization was further treated according process mentioned above to get another 12 g of dry LiFSI powder as a second crop.
Example 13:
To the 1000 mL of the reaction vessel was charged with ethyl alcohol (600 mL) at 25-30°C. The above mass was cooled to 15-20°C and lithium carbonate (44.87 g) was charged under stirring. Hydrogen bis(fluorosulfonyl)imide (HFSI, 200 g) was charged under stirring over 1 hour at 15-20°C. The mixture was then stirred at 25-30°C for 8 hours. After completion of the reaction, ethyl alcohol was recovered via vacuum distillation (10-100 torr, <50°C) over 5 hours, followed by azeotropic distillation with fresh ethyl alcohol until moisture was <0.5%. The obtained crude mass underwent vacuum degassing (5-10 torr, 50°C) for 3 hours, reducing ethyl alcohol content to <20%. Dimethyl carbonate (400 mL) was charged to the above crude mass and stirred for 1 hour at 25-30 ?, filtered through a micron filtration to remove impurities. The obtained filtrate was treated with acid-washed activated charcoal (10 g) for 8 hours at 25-30 °C, filtered and obtained filtrate was distilled under vacuum (10-100 torr, <50°C) to remove dimethyl carbonate. The obtained crude mass underwent vacuum degassing (5-10 torr, 50°C) for 3-4 hours, reducing dimethyl carbonate content to 10-16%. After cooling, methylene dichloride (400 mL) was added under stirring and maintained for 24 hours at 25-30°C. The crystallized material was filtered off, washed with methylene dichloride, and vacuum-dried (1-2 torr, <50 °C) for 12 hours, yielding dry LiFSI powder (183 g). The dry LiFSI solid as a white powder was stored in an HDPE bottle under nitrogen, exhibiting a bulk density of 1.0512 g/cm³ and a melting point of 129-132°C. Ion Chromatography (DIONEX IC) analysis revealed the purity of LiFSI was 99.96% and the anion contents were F- = 8 ppm, Cl- = 4 ppm, SO42- = 7 ppm. Moisture content, determined via Karl Fisher titration was 19 ppm. Subsequent analysis by ICP for metal content showed all individual metal concentrations such as Mg = 0.17 ppm, Al = 0.14 ppm, Ca = 0.14 ppm, Cr = 0.04 ppm, Fe = 0.52 ppm, Ni = 0.05 ppm, Cu = 0.02 ppm, Cd = 0.001 ppm, Pb = 0.01 ppm, Na = 6.10 ppm and K = 2.19 ppm.
The residual filtrate from the above crystallization was further treated according process mentioned above to get another 10 g of dry LiFSI powder as a second crop.
Example 14:
To the 1000 mL of the reaction vessel was charged with n-butyl alcohol (600 mL) at 25-30°C. The above mass was cooled to 15-20°C and lithium carbonate (44.87 g) was charged under stirring. Hydrogen bis(fluorosulfonyl)imide (HFSI, 200 g) was charged under stirring over 1 hour at 15-20°C. The mixture was then stirred at 25-30°C for 8 hours. After completion of the reaction, n-butyl alcohol was recovered via vacuum distillation (10-100 torr, <50°C) over 6 hours, followed by azeotropic distillation with fresh n-butyl alcohol until moisture was <0.5%. The obtained crude mass underwent vacuum degassing (10-5 torr, 50°C) for 6 hours, reducing n-butyl alcohol content to <20%. Dimethyl carbonate (400 mL) was charged to the above crude mass and stirred for 1 hour at 25-30?, filtered through a micron filtration to remove impurities. The obtained filtrate was treated with acid-washed activated charcoal (10 g) for 8 hours at 25-30°C, filtered and obtained filtrate was vacuum distilled (10-100 torr, <50°C) to remove dimethyl carbonate. The obtained crude mass underwent vacuum degassing (5-10 torr, 50°C) for 3-4 hours, reducing dimethyl carbonate content to 10-16%. After cooling, methylene dichloride (400 mL) was added under stirring and maintained for 24 hours at 25-30°C. The crystallized material was filtered off, washed with methylene dichloride, and vacuum-dried (1-2 torr, <50°C) for 12 hours, yielding dry LiFSI powder (186 g). The dry LiFSI solid as a white powder was stored in an HDPE bottle under nitrogen, exhibiting a bulk density of 1.0496 g/cm³ and a melting point of 130-132°C. Ion Chromatography (DIONEX IC) analysis revealed the purity of LiFSI was 99.95% and the anion contents were F- = 7 ppm, Cl- = 3 ppm, SO42- = 8 ppm. Moisture content, determined via Karl Fisher titration was 14 ppm. Subsequent analysis by ICP for metal content showed all individual metal concentrations such as Mg = 0.09 ppm, Al = 0.11 ppm, Ca = 0.15 ppm, Cr = 0.04 ppm, Fe = 0.27 ppm, Ni = 0.08 ppm, Cu = 0.03 ppm, Cd = 0.001 ppm, Pb = 0.03 ppm, Na = 2.1 ppm and K = 1.5 ppm.
The residual filtrate from the above crystallization was further treated according process mentioned above to get another 9 g of dry LiFSI powder as a second crop.
Example 15:
To the 1000 mL of the reaction vessel was charged with isopropyl alcohol (600 mL) at 25-30°C. The above mass was cooled to 15-20°C and lithium carbonate (44.87 g) was charged under stirring. Hydrogen bis(fluorosulfonyl)imide (HFSI, 200 g) was charged under stirring over 1 hour at 15-20°C. The mixture was then stirred at 25-30°C for 8 hours. After completion of the reaction, isopropyl alcohol was recovered via vacuum distillation (10-100 torr, <50°C) over 4 hours, followed by azeotropic distillation with fresh isopropyl alcohol until moisture was <0.5%. The obtained crude mass underwent vacuum degassing (5-10 torr, 50°C) for 3-4 hours, reducing isopropyl alcohol content to <20%. Ethyl methyl carbonate (400 mL) was charged to the above crude mass and stirred for 1 hour at 25-30?, filtered through a micron filtration to remove impurities. The obtained filtrate was treated with acid-washed activated charcoal (10 g) for 8 hours at 25-30°C, filtered and obtained filtrate was vacuum distilled (10-100 torr, <50°C) to remove ethyl methyl carbonate. The obtained crude mass underwent vacuum degassing (10-5 torr, 50°C) for 4-5 hours, reducing ethyl methyl carbonate content to 10-16%. After cooling, methylene dichloride (400 mL) was added under stirring and maintained for 24 hours at 25-30°C. The crystallized material was filtered off, washed with methylene dichloride, and vacuum-dried (1-2 torr, <50°C) for 12 hours, yielding dry LiFSI powder (184 g). The dry LiFSI solid as a white powder was stored in an HDPE bottle under nitrogen, exhibiting a bulk density of 1.0521 g/cm³ and a melting point of 128-132 °C. Ion Chromatography (DIONEX IC) analysis revealed the purity of LiFSI was 99.96% and the anion contents were F- = 6 ppm, Cl- = 4 ppm, SO42- = 9 ppm. Moisture content, determined via Karl Fisher titration was 25 ppm. Subsequent analysis by ICP for metal content showed all individual metal concentrations such as Mg = 0.16 ppm, Al = 0.12 ppm, Ca = 0.13 ppm, Cr = 0.14 ppm, Fe = 0.53 ppm, Ni = 0.1 ppm, Cu = 0.03 ppm, Cd = 0.001 ppm, Pb = 0.03 ppm, Na = 2.1 ppm and K = 1.8 ppm. The residual filtrate from the above crystallization was further treated according process mentioned above to get another 11 g of dry LiFSI powder as a second crop.
Example 16:
To the 1000 mL of the reaction vessel was charged with isopropyl alcohol (600 mL) at 25-30°C. The above mass was cooled to 15-20°C and lithium carbonate (44.87 g) was charged under stirring. Hydrogen bis(fluorosulfonyl)imide (HFSI, 200 g) was charged under stirring over 1 hour at 15-20°C. The mixture was then stirred at 25-30°C for 8 hours. After completion of the reaction, isopropyl alcohol was recovered via vacuum distillation (10-100 torr, <50°C) over 4 hours, followed by azeotropic distillation with fresh isopropyl alcohol until moisture was <0.5%. The obtained residue mass underwent vacuum degassing (5-10 torr, 50°C) for 3-4 hours, reducing isopropyl alcohol content to <20%. Ethyl methyl carbonate (400 mL) was charged to the above crude mass and stirred for 1 hour at 25-30?, filtered through a micron filtration set-up to remove impurities. The obtained filtrate was treated with acid-washed activated charcoal (10 g) for 8 hours at 25-30°C, filtered and obtained filtrate was vacuum distilled (100-10 torr, <50°C) to remove ethyl methyl carbonate. The obtained mass underwent vacuum degassing (5-10 torr, 50°C) for 4-5 hours, reducing ethyl methyl carbonate content to 10-16%. After cooling, ethylene dichloride (400 mL) was added under stirring and maintained for 24 hours at 25-30°C. The crystallized material was filtered off, washed with ethylene dichloride, and vacuum-dried (1-2 torr, <50°C) for 15 hours, yielding dry LiFSI powder (186 g). The dry LiFSI solid as a white powder was stored in an HDPE bottle under nitrogen, exhibiting a bulk density of 1.0498 g/cm³ and a melting point of 128-132°C. Ion Chromatography (DIONEX IC) analysis revealed the purity of LiFSI was 99.96% and the anion contents were F- = 4 ppm, Cl- = 4 ppm, SO42- = 8 ppm. Moisture content, determined via Karl Fisher titration was 24 ppm. Subsequent analysis by ICP for metal content showed all individual metal concentrations such as Mg = 0.11 ppm, Al = 0.15 ppm, Ca = 0.09 ppm, Cr = 0.07 ppm, Fe = 0.17 ppm, Ni = 0.09 ppm, Cu = 0.02 ppm, Cd = 0.001 ppm, Pb = 0.04 ppm, Na = 4.1 ppm and K = 1.7 ppm. The residual filtrate from the above crystallization was further treated according process mentioned above to get another 8 g of dry LiFSI powder as a second crop.

Example 17:
To the 1000 mL of the reaction vessel was charged with isopropyl alcohol (600 mL) at 25-30°C. The above mass was cooled to 15-20°C and lithium carbonate (44.87 g) was charged under stirring. Hydrogen bis(fluorosulfonyl)imide (HFSI, 200 g) was charged under stirring over 1 hour at 15-20°C. The mixture was then stirred at 25-30°C for 8 hours. After completion of the reaction, isopropyl alcohol was recovered via vacuum distillation (10-100 torr, <50°C) over 4 hours, followed by azeotropic distillation with fresh isopropyl alcohol until moisture was <0.5%. The obtained crude mass underwent vacuum degassing (5-10 torr, 50°C) for 3-4 hours, reducing isopropyl alcohol content to <20%. Diethyl carbonate (400 mL) was charged to the above crude mass and stirred for 1 hour at 25-30?, filtered through a micron filtration to remove impurities. The obtained filtrate was treated with acid-washed activated charcoal (10 g) for 8 hours at 25-30°C, filtered and obtained filtrate was vacuum distilled (10-100 torr, <50°C) to remove diethyl carbonate. The obtained crude mass underwent vacuum degassing (5-10 torr, 50°C) for 4-5 hours, reducing diethyl carbonate content to 10-16%. After cooling, ethylene dichloride (400 mL) was added under stirring and maintained for 24 hours at 25-30°C. The crystallized material was filtered off, washed with ethylene dichloride, and vacuum-dried (1-2 torr, <50°C) for 12 hours, yielding dry LiFSI powder (182 g). The dry LiFSI solid as a white powder was stored in an HDPE bottle under nitrogen, exhibiting a bulk density of 1.0498 g/cm³ and a melting point of 128-132°C. Ion Chromatography (DIONEX IC) analysis revealed the purity of LiFSI was 99.95% and the anion contents were F- = 6 ppm, Cl- = 4 ppm, SO42- = 5 ppm. Moisture content, determined via Karl Fisher titration was 26 ppm. Subsequent analysis by ICP for metal content showed all individual metal concentrations such as Mg = 0.14 ppm, Al = 0.12 ppm, Ca = 0.11 ppm, Cr = 0.08 ppm, Fe = 0.24 ppm, Ni = 0.07 ppm, Cu = 0.03 ppm, Cd = 0.001 ppm, Pb = 0.02 ppm, Na = 3.2 ppm and K = 1.43 ppm. The residual filtrate from the above crystallization was further treated according process mentioned above to get another 11 g of dry LiFSI powder as a second crop.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore, to be considered in all respects as illustrative and not restrictive.
The process of preparation of lithium bis(fluorosulfonyl)imide (LiFSI) as described in the various embodiments above offers several advantages, including:
a) high purity of the product of the order of > 99.9%;
b) consistent production of high quality LiFSI;
c) improved yield of the product;
d) lesser degradation of LiFSI during isolation;
e) anionic impurities (Cl-, F- and SO42-) less than 50 ppm; and
f) moisture content less than 50 ppm. ,CLAIMS:WE CLAIM:
1. A process for the preparation of pure lithium bis(fluorosulfonyl)imide, comprising the steps of:
a) reacting bis(fluorosulfonyl)imide with lithiation reagent in the presence of C1-4 alcoholic solvent at temperature ranging between 0 °C to 30 °C;
b) performing the azeotropic distillation of step (a) reaction mass using the alcoholic solvent under vacuum ranging between 10 to 100 torr at a temperature below 50°C, up to the residual mass B comprising, moisture content less than 0.50% and alcohol content less than 20%;
c) dissolving the residual mass B of step (b) in an organic carbonate solvent;
d) filtering the insoluble in an inert atmosphere to get a solution of lithium bis(fluorosulfonyl)imide;
e) performing activated carbon treatment of step (d) solution to isolate residual mass E, wherein the residual mass E comprises carbonate solvent content less than 20%;
f) mixing the residual mass E of step (e) with chlorinated hydrocarbon solvent at temperature below 30 °C and maintain under stirring for 10 to 30 hours; and
g) isolating pure lithium bis(fluorosulfonyl)imide crystals in an inert atmosphere.

2. The process as claimed in claim 1, wherein the lithiation reagent in step (a) is selected from Lithium hydroxide (LiOH) and/or hydrates like Lithium hydroxide monohydrate (LiOH.H2O), Lithium carbonate (Li2CO3), Lithium methoxide (LiOMe), Lithium isopropoxide (LiOi-Pr), Lithium hydride (LiH), Lithium oxide (Li2O) and Lithium fluoride (LiF).

3. The process as claimed in claim 1, wherein the C1-4 alcoholic solvent in step (a) is selected from methanol, ethanol, propanol, isopropanol, butanol, isobutanol or mixture(s) thereof.

4. The process as claimed in claim 1, wherein the organic carbonate solvent in step (c) is selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate, propylene carbonate, butylene carbonate, and ethyl methyl carbonate (EMC) or mixture(s) thereof.

5. The process as claimed in claim 1, wherein the activated carbon in step (e) is acid washed activated carbon, which is selected from granule or powder form, or coconut shell activated carbon and/or coal-based activated carbon.

6. The process as claimed in claim 1, wherein the chlorinated hydrocarbon solvent in step (f) is selected from dichloromethane, 1,2-dichloroethane, carbon tetrachloride, chloroform, trichloroethanes, tetrachloroethylene or mixture(s) thereof.

7. The process as claimed in claim 1, wherein the pure lithium bis(fluorosulfonyl)imide crystals obtained in step (g) comprises:
i. purity at least 99.95% (w/w);
ii. the moisture content less than 50 ppm;
iii. total anionic impurities less than 50 ppm;
iv. APHA value less than 20;
v. any individual metal impurities less than 1 ppm except Na and K;
vi. individual Na or K impurity less than 10 ppm;
vii. total insoluble impurities less than 50 ppm; and
viii. any acid impurity less than 50 ppm.