Process

Abstract

A process for the at least partial conversion of a bisfluorsulfonimide (HFSI) to a metal bisfluorsulfonimide (MHFSI), comprising: feeding a composition comprising a metai bicarbonate, a solvent and a composition comprising bisfluorsulfonimide into a reactor to form an admixture thereof; and allowing the metal bicarbonate and bisfluorsulfonimide to react together.

Description

[0001]PROCESS Field of the invention The present invention relates to a process for the production of a metal salt of bisfluorsulfonimide. This process is particularly useful in the production of lithium bisfluorsulfonimide. Background of the invention Lithium salts (such as Lithium bisfluorsulfonimide (LiFSI)) are used in batteries, such as commercial secondary batteries, an application that exploits its high solubility in non-aqueous, polar solvents. LiFSI is used as an electrolyte in Lithium-ion batteries. Currently lithium bicarbonate production occurs by conversion of bisfluorsulfonimide (HFSI) to LiFSI by reaction with lithium carbonate (Li2CO3). However, this syntheses of LiFSI require multiple filtration steps to isolate the product from the reactants. This is largely due to the use of insoluble lithium source Li2CO3). This reduces the potential final yield of the product. Thus there is a need for an improved method of producing lithium bicarbonate. Summary of the invention According to a first aspect of the present invention there is provided a process for the at least partial conversion of a bisfluorsulfonimide (HFSI) to a metal bisfluorsulfonimide (MHFSI), comprising: feeding a composition comprising a metal bicarbonate, a solvent and a composition comprising bisfluorsulfonimide into a reactor to form an admixture thereof; and allowing the metal bicarbonate and bisfluorsulfonimide to react together. Generally the conversion of the bisfluorsulfonimide (HFSI) to the metal bisfluorsulfonimide (MHFSI) is at least partial. Preferably the conversion is or approaches 100%. Any unconverted bisfluorsulfonimide (HFSI) is preferably recycled back into the reaction via a recycling and / or purification step. Optionally the process comprises a stage wherein the bisfluorsulfonimide is prepared. Preferably the bisfluorsulfonimide is prepared by reaction of a bischlorosulfonimide with a fluorinating agent (preferably comprising HF). Thus according to a second aspect of the present invention there is provided a process for the preparation of a metal bisfluorsulfonimide (MHFSI), comprising: a) at least partial conversion of a bischlorosulfonimide to a bisfluorsulfonimide (HFSI), comprising: feeding a composition comprising a bischlorosulfonimide and fluorinating agent into a reactor to form an admixture thereof; and allowing the bischlorosulfonimide and fluorinating agent to react together; and b) at least partial conversion of the bisfluorsulfonimide (HFSI) to a metal bisfluorsulfonimide (M HFSI), comprising: feeding a composition comprising a metal bicarbonate, a solvent and a composition comprising bisfluorsulfonimide into a reactor to form an admixture thereof; and allowing the metal bicarbonate and bisfluorsulfonimide to react together. Generally the conversion of the bisfluorsulfonimide (HFSI) to the metal bisfluorsulfonimide (MHFSI) is at least partial. Preferably the conversion is or approaches 100%. Any unconverted bisfluorsulfonimide (HFSI) is preferably recycled back into the reaction via a recycling and / or purification step. Elements of each aspect of the invention shall be described below. It will be understood that the elements shall apply equally to either / both aspects mutatits mutandis. Preferably the metal bicarbonate and solvent form a solution / suspension. Most preferably the metal bicarbonate and solvent form a solution. Most preferably the metal bicarbonate is or comprises lithium bicarbonate. Most preferably the solvent for the metal bicarbonate is or comprises water. The process of the invention has been found to be advantageous in that it allows the production of a metal bisfluorsulfonimide easily and cost-effectively. The process is extremely straightforward. It does not require the intermediate filtration steps that are associated with some prior art process. The removal of same, limits the loss of metal bisfluorsulfonimide during this process. Additionally the whole efficiency of the metalation (lithiation) reaction has been found to be increased. This is suspected to be due to the metal (lithium) bicarbonate being (preferably) fully solubilised. Preferably in the bisfluorsulfonimide preparation portion of the process the bischlorosulfonimide is added to the reactor in the form of a suspension / solution. Preferably acetonitrile is used as the solvent in the suspension / solution (can any other solvent be used??). Preferably the concentration of bischlorosulfonimide is about 33wt%. Preferably the fluorinating agent comprises HF. Preferably an excess of fluorinating agent is used to perform the fluorination. Preferably the reactor is released during the reaction. Following the reaction the reactor is preferably vented with an inert gas (such as nitrogen) to remove the HCl formed in the reaction. Given the aggressive nature of most fluorinating agents (and particularly HF) the bisfluorsulfonimide preparation portion of the process is preferably performed in a reactor formed or at least coated in a corrosion resistant material such as Hastelloy (any other materials??). Following the reaction the product is transferred into the metalation portion of the process. In the metalation portion of the process preferably the bisfluorosulfonimide solution is added to the metal bicarbonate solution / suspension. The metal bicarbonate solution is preferably at a concentration of 0.5 - 0.8 M. The two agents are allowed to react. The product metal bisfluorsulfonimide is preferably extracted from the reaction product admixture with a solvent. A preferred solvent is ethyl acetate. The invention is illustrated with reference to the following non-limiting Examples. Example 1 – Preparation of LiFSI Step 1 – Bisfluorsulfonimide Preparation Bischlorosulfonimide (HClSI) (25 g) and acetonitrile (50 mL) were sealed in a 450 mL Hastelloy autoclave in a nitrogen purged glovebox. The autoclave was transferred to a reactor stand and pressure tested to 30 bar with nitrogen gas. Having passed the pressure test, the nitrogen was vented and HF (10 g) was transferred into the autoclave. The mixture was stirred at 10 °C for 16 hours. After 16 hours the HCl formed and the excess HF were purged out of the reactor with a stream of nitrogen gas. The solution was transferred to a fluoropolymer container. Step 2 - Preparation of LiFSI The mixture obtained in Step 1 was added dropwise to a solution of LiHCO3in deionised water (1 L, 0.5 - 0.8 M). The aqueous solution of LiFSI formed was concentrated to 200 mL of liquid. The LiFSI was extracted with three portions of 200ml of ethyl acetate. The organic layer was concentrated by solvent extraction to yield a solution of LiFSI in ethyl acetate.

Claims

Claims 1. A process for the at least partial conversion of a bisfluorsulfonimide (HFSI) to a metal bisfluorsulfonimide (MHFSI), comprising: feeding a composition comprising a metal bicarbonate, a solvent and a composition comprising bisfluorsulfonimide into a reactor to form an admixture thereof; and allowing the metal bicarbonate and bisfluorsulfonimide to react together.

2. A process for the preparation of a metal bisfluorsulfonimide (M HFSI), comprising a) at least partial conversion of a bischlorosulfonimide to a bisfluorsulfonimide (HFSI), comprising: feeding a composition comprising a bischlorosulfonimide and fluorinating agent into a reactor to form an admixture thereof; and allowing the bischlorosulfonimide and fluorinating agent to react together; and b) at least partial conversion of the bisfluorsulfonimide (HFSI) to a metal bisfluorsulfonimide (MHFSI), comprising: feeding a composition comprising a metal bicarbonate, a solvent and a composition comprising bisfluorsulfonimide into a reactor to form an admixture thereof; and allowing the metal bicarbonate and bisfluorsulfonimide to react together.

3. A process according to claim 1 or 2, wherein the metal bicarbonate and solvent form a solution.

4. A process according to claim 1, 2 or 3, wherein the metal bicarbonate is or comprises lithium bicarbonate.

5. A process according to any one of claims 1 to 4, wherein the solvent for the metal bicarbonate comprises water.

6. A process according to any one of claims 2 to 5, wherein the bischlorosulfonimide is added to the reactor in the form of a suspension / solution.

7. A process according to claim 6, wherein acetonitrile is used as the solvent in the suspension / solution (can any other solvent be used??).

8. A process according to any one of claims 2 to 7, wherein the fluorinating agent comprises HF.

9. A process according to any one of claims 1 to 8, wherein in the metalation portion of the process the bisfluorosulfonimide solution is added to the metal bicarbonate solution / suspension.

10. A process according to any one of claims 1 to 8, wherein the product metal bisfluorsulfonimide is extracted from the reaction product admixture with a solvent.

11. A metal bisfluorsulfonimide produced by a process according to any one of claims 1 to 10.

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