Method for preparing lithium salts of bis(fluorosulfonyl)imides in solid form

Abstract

The present disclosure relates to a method for preparing a solid form of a lithium salt of bis(fluorosulfonyl)imide (LiFSI), wherein the solid form of LiFSI salt is extracted from a solution comprising at least one solvent through supercritical fluid extraction. The present invention also relates to the solid form of LiFSI obtained therefrom and the use of such LiFSI in an electrolyte for a battery.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to the earlier European Patent Application Publication No. 22305583.1, filed April 21, 2022, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to a method for preparing the lithium salt of bis(fluorosulfonyl)imide (LiFSI) in solid form. The present invention also relates to the solid form of LiFSI obtained therefrom and the use of such LiFSI in an electrolyte for a battery. [Background technology]

[0003] Bis(fluorosulfonyl)imides and their salts, particularly the lithium salt of bis(fluorosulfonyl)imide (LiFSI), are compounds that are useful in various technical fields, such as battery electrolytes.

[0004] The preparation of LiFSI has been described in the literature, and among the various techniques described, most use a fluorination reaction using a fluorinating agent in a solvent.

[0005] For example, WO 2017 / 090877 (in the name of CLS) describes a method for preparing LiFSI, which includes the steps of (1) reacting bis(chlorosulfonyl)imide with a fluorinating agent in a solvent, followed by treatment with an alkaline agent, thereby producing ammonium bis(fluorosulfonyl)imide, and (2) reacting ammonium bis(fluorosulfonyl)imide with a lithium base. The solvent used in step (1) is selected from the group consisting of alkyl ketones, such as acetone, methyl ethyl ketone, and methyl isopropyl ketone; alcohols, such as methanol, absolute ethanol, 1-propanol, and isopropanol; alkyl nitriles, such as acetonitrile and propionitrile; and ethers, such as tetrahydrofuran and dialkoxyalkanes. The solvent is then removed by distillation and concentration under reduced pressure.

[0006] WO 2012 / 117961 (in the name of Nippon Soda Co., Ltd.) describes a method for preparing fluorosulfonylimide salts. According to Examples 1 and 2, ammonium di(fluorosulfonyl)imide is prepared from di(chlorosulfonyl)imide in acetonitrile. The solvent is then removed by vacuum distillation.

[0007] JP 2016-145147 A (in the name of Nippon Shokubai Co., Ltd.) relates to a method for obtaining a fluorosulfonylimide compound represented by formula (1) by reacting a compound represented by formula (2) with a compound represented by composition formula (3) in a stoichiometric amount of 1 to 3 equivalents per mole of the compound in the presence of a solvent in an amount of 0 to 4 times the mass of the compound. [ka] In the formula, R 1 is C 1~6 is a fluoroalkyl group, R 6 is halogen or C 1~6 Fluoroalkyl group, Cat1 + and Cat2 + is a monovalent group, and p is an integer from 1 to 10.

[0008] JP 2014-201453 A (in the name of Nippon Shokubai Co., Ltd.) describes a method for producing an alkali metal salt of a fluorosulfonylimide, comprising the steps of synthesizing an alkali metal salt of a fluorosulfonylimide in the presence of a reaction solvent containing at least one solvent selected from the group consisting of carbonate-based solvents, aliphatic ether-based solvents, ester-based solvents, amide-based solvents, nitro-based solvents, sulfur-based solvents, and nitrile-based solvents, and then concentrating the alkali metal salt solution of a fluorosulfonylimide by distilling off the reaction solvent in the presence of the reaction solvent and at least one poor solvent for the alkali metal salt of a fluorosulfonylimide selected from the group consisting of aromatic hydrocarbon-based solvents, aliphatic hydrocarbon-based solvents, and aromatic ether-based solvents, and the concentration step comprises the step of mixing the poor solvent with a reaction solution containing the reaction solvent and the alkali metal salt of a fluorosulfonylimide.

[0009] Supercritical fluid extraction has been used for recycling purposes. In particular, US Patent Publication No. 2003 / 0186110 (in the name of ECO BAT INDIANA LLC, ONTO TECH LLC), China Patent No. 105406146 (in the name of HARBIN INST TECHNOLOGY) and China Patent No. 110534835 (in the name of University of Changzhou) disclose a method of removing electrolyte from energy storage devices (e.g., lithium batteries) using supercritical fluids.

[0010] Supercritical fluid extraction has also been described for the extraction of bis(fluorosulfonyl)imide (HFSI) from a reaction mixture containing an acid. In particular, WO 2021 / 082450 (in the name of GUANGZHOU LIWEN TECH CO LTD) discloses a method for purifying HFSI from a reaction mixture containing a strong acid (e.g., concentrated sulfuric acid, phosphoric acid) and an FSI salt (e.g., NaFSI, KFSI or LiFSI, among others) using supercritical extraction, in particular supercritical CO2 fluid. CN 111517293 (in the name of SHANGHAI INST ORGANIC CHEMISTRY CAS) also describes the following steps: [ka] (wherein X is an alkali metal; R 1 and R 2 are independently F or C1-12 alkyl all substituted with F. This application describes a method for preparing HFSI using a supercritical fluid, comprising: Summary of the Invention

[0011] As described in the literature, the preparation of LIFSI by fluorination is carried out in a solvent, e.g. an organic solvent, to disperse the reactive species and allow them to react.

[0012] However, such solvents need to be removed after the reaction in order to obtain a product of as high purity as possible that can be used for battery applications.

[0013] The applicant recognizes that the process of preparing a solid form of LiFSI based on LiFSI in solution is complex, in particular the amount of residual solvent must be as low as possible to make it sufficiently suitable for use as a battery electrolyte.

[0014] The Applicant therefore faced the task of developing a new method for the production of LiFSI, making it possible to overcome the complexities of the methods known so far.

[0015] Unexpectedly, the applicant has developed a method for producing LiFSI that is not complicated to implement in terms of equipment and reaction conditions, and is very environmentally friendly.

[0016] The process of the invention also makes it possible to obtain LiFSI in solid form with very high yields and high purity, which can then be used in the electrolyte solution of batteries.

[0017] An advantageous method for preparing LiFSI in solid form according to the invention is based on supercritical fluid extraction.

[0018] Therefore, a first object of the present invention relates to a method for preparing LiFSI in solid form from a solution comprising at least one solvent and a LiFSI salt, such method being based on the use of a supercritical fluid. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 shows a schematic diagram of the experimental setup used in Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] In this application: - the expression "included in..." is to be understood as including the limiting values, - any description, even if made in relation to a particular embodiment, is applicable and interchangeable with other embodiments of the invention; - when an element or component is said to be included in and / or selected from a list of enumerated elements or components, in the relevant embodiments expressly contemplated herein, it is to be understood that the element or component may be any one of the individual enumerated elements or components, or may also be selected from the group consisting of any two or more of the explicitly enumerated elements or components, and that any element or component enumerated in a list of elements or components may be omitted from such list; - Any recitation herein of numerical ranges by endpoints includes all numbers subsumed within the recited range, as well as the endpoints of the range and equivalents thereof.

[0021] The first object of the present invention is a method for preparing the lithium salt of bis(fluorosulfonyl)imide (LiFSI) in solid form, comprising the steps of: a) providing a solution comprising LiFSI and at least one solvent (LiFSI solution); b) contacting the LiFSI solution with at least one supercritical fluid; c) recovering the LiFSI in solid form; The present invention relates to a method comprising the steps of:

[0022] As used herein, the term "contacting" means that a solution is contacted with at least one supercritical fluid, for example in a vessel, under specified conditions of pressure and temperature, for a period of time sufficient for the fluid to remove at least a portion of the solvent present in the solution, preferably greater than 80.0%, greater than 90.0%, greater than 95.0%, greater than 99.0%, greater than 99.5%, or even greater than 99.9% of the solvent.

[0023] As used herein, the term "recovering" means removing or extracting LiFSI in solid form from the vessel in which step b) is carried out.

[0024] In this specification, the expression "supercritical fluid" means a gas (or a mixture of at least two gases) in the supercritical state. Depending on the gas used in step b), the pressure and temperature used in the vessel in which the contact of the solution with the supercritical fluid takes place are appropriately selected. More precisely, in order to be in the supercritical state, the gas used in step b) is kept above its critical temperature and critical pressure.

[0025] As used herein, the term "vessel" refers to a vessel suitable for the process of the invention, i.e. a vessel adapted to withstand the pressures and temperatures used in the process and the potentially corrosive nature of the reactants and products involved in the process. As will be explained in more detail below, the vessel used herein may in particular be an extraction column (also called "column") or an autoclave.

[0026] According to the method of the present invention, at least one supercritical fluid is used to extract LiFSI salt from the solution, which has several advantages. Supercritical fluids, such as sCO2, have distinct advantages, being usually readily available, inexpensive, non-toxic, non-explosive, and not an organic solvent. Moreover, the method of the present invention works at moderate temperatures (less than 100°C), thus ensuring gentle processing of the LiFSI product. The method of the present invention also allows easy separation of the solvent and the extract in solid form.

[0027] Preferably, step a) is carried out batchwise, semi-continuously or continuously.

[0028] As disclosed above, the LiFSI solution comprises at least one solvent. Preferably, the LiFSI solution comprises one solvent. Alternatively, the LiFSI solution comprises two or more solvents, for example a mixture of two or three solvents.

[0029] Preferably, the solvent is selected from the group comprising, more preferably consisting of, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, dimethoxymethane, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, 4-methyl-1,3-dioxolane, methyl formate, methyl acetate, methyl propionate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, sulfolane, 3-methyl sulfolane, dimethyl sulfoxide, N,N-dimethylformamide, N-methyloxazolidinone, acetonitrile, valeronitrile, benzonitrile, ethyl acetate, isopropyl acetate, n-butyl acetate, nitromethane, nitrobenzene, trifluoroethanol and mixtures thereof.

[0030] More preferred solvents include ethylene carbonate, propylene carbonate, butylene carbonate, tetrahydrofuran, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, isopropyl acetate, and n-butyl acetate. More preferred solvents include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, isopropyl acetate, and n-butyl acetate. More preferred solvents include ethyl methyl carbonate and n-butyl acetate. The most preferred solvent is ethyl methyl carbonate.

[0031] In some embodiments, the LiFSI solution comprises 5-70 wt % LiFSI, based on the total weight of the LiFSI solution.

[0032] The LiFSI solution preferably contains 10-60 wt.%, for example 15-50 wt.%, 20-40 wt.%, or 25-35 wt.% LiFSI. As an example, the solution contains 30±2 wt.% LiFSI based on the total weight of the LiFSI solution.

[0033] The weight ratio of supercritical fluid / LiFSI solution used in the method of the present invention may vary from 1 / 1 to 4000 / 1. For example, the weight ratio of supercritical fluid / LiFSI solution preferably varies from 10 / 1 to 3500 / 1.

[0034] It will be clear to the skilled person that the parameters of the process according to the invention can be appropriately selected and optimized based on, for example, the starting materials (especially the purity of the product) and the scale at which the process is carried out (e.g. whether the process is carried out on an industrial scale or on a laboratory scale).

[0035] Preferably, step b) is carried out in a vessel at a pressure P of at least 73 bar (7.3 MPa).

[0036] Preferably, step b) is carried out at a temperature T between 30°C and 90°C.

[0037] Step b) may preferably be carried out in a vessel capable of withstanding high pressure.

[0038] According to this embodiment, step b) comprises contacting the solution of step a) with at least one supercritical fluid in a vessel.

[0039] A particular advantage of the method of the present invention is the short contact time in step b), which can also be advantageously selected appropriately based on, for example, the starting material and the target yield.

[0040] Preferably, the contact time in step b) varies from a few seconds, for example from 5 seconds to 24 hours, more preferably from 1 minute to 12 hours, for example from 5 minutes to 10 hours or from 10 minutes to 5 hours.

[0041] Preferably, step b) is carried out by injecting the supercritical fluid into the bottom of the container, which advantageously improves mixing of the LiFSI solution with the supercritical fluid.

[0042] Preferably, during step b), the LiFSI solution is contacted with one fluid in the supercritical state.

[0043] Preferably, during step b) the LiFSI solution is contacted with two or more fluids in the supercritical state. The two or more fluids may be mixed or may be contacted with the solution sequentially. As an example, the LiFSI solution may be contacted with a mixture of at least two supercritical fluids.

[0044] Additionally, in accordance with the present invention, at least one other component, also referred to herein as a modifier, may be mixed with the supercritical fluid.

[0045] Advantageously, said at least one other component is chosen from polar solvents having a solubility in the supercritical fluid of less than 10% by weight, based on the total weight of the supercritical fluid and the other components.

[0046] More preferably, when used, the at least one other component is in an amount in the range of 0.1 to 10% by weight, such as 0.5 to 8% by weight or 1 to 6% by weight, based on the total weight of the supercritical fluid and other components.

[0047] Preferably, said at least one other component is selected from polar solvents, more preferably in the group comprising alcohol, toluene, dimethylsulfoxide (DMSO), acetonitrile, etc. According to a preferred embodiment, said polar solvent is an alcohol. More preferably, said alcohol is ethanol.

[0048] According to the invention, step b) can be repeated two or more times.

[0049] For example, the method according to the invention comprises a first step b) and a second step b'), wherein in each of said steps b) and b') the same or different supercritical fluids or a mixture of at least two supercritical fluids are used.

[0050] In some embodiments, preferably the vessel used for contacting the LiFSI solution with the at least one supercritical fluid in step b) is at a pressure P of at least 73 bar (7.3 MPa).

[0051] In some embodiments, preferably the vessel used for contacting the LiFSI solution with the at least one supercritical fluid in step b) is at a temperature T between 30° C. and 90° C. during extraction.

[0052] Preferably, the temperature T inside the container may vary between 37°C and 75°C, for example between 38°C and 70°C or between 40°C and 65°C.

[0053] Preferably, the pressure P in the vessel may be at least 80 bar (8.0 MPa), at least 100 bar (10.0 MPa), at least 130 bar (13.0 MPa) or at least 150 bar (15.0 MPa). In the method of the invention, even much higher pressures can be used. For example, the pressure P in the vessel may be up to 200 bar (20.0 MPa) or 300 bar (30.0 MPa). The pressure in the vessel is usually less than 500 bar (50.0 MPa), for example less than 450 bar (45.0 MPa), less than 400 bar (40.0 MPa) or even less than 350 bar (35.0 MPa).

[0054] According to one embodiment, step b) is carried out by injecting the LiFSI solution into an already pressurized vessel, which may be injected, for example, via an injector or an inlet valve attached to the vessel.

[0055] According to another embodiment, step b) comprises b1) introducing a LiFSI solution into a vessel; b2) pressurizing the vessel to a pressure P; and b3) heating the vessel to a temperature T; and b4) introducing at least one supercritical fluid into the vessel; Includes.

[0056] According to one embodiment, step b2) may be performed before step b3), or step b3) may be performed before step b2), or steps b2) and b3) may be performed simultaneously.

[0057] According to one embodiment, the order can also be: b1), b3), b4), b2).

[0058] The conditions of temperature, pressure and contact time detailed above for step b) apply to steps b2) and b3) as explained above.

[0059] Preferably, step b2) is carried out at a pressure of at least 74 bar (7.4 MPa).

[0060] Preferably, step b3) is carried out at a temperature of at least 30°C.

[0061] The flow rate for introducing the supercritical fluid into the vessel in step b4) is not particularly limited, and can be determined by those skilled in the art based on the equipment used, the amount and concentration of the LiFSi solution.

[0062] Step b4) can be carried out batchwise, continuously or semi-continuously.

[0063] Preferably, the supercritical fluid used in step b) comprises supercritical carbon dioxide (sCO2), which is a fluid state of carbon dioxide maintained above its critical temperature (31.0°C) and critical pressure (7.3773 MPa).

[0064] Advantageously, the supercritical fluid used in step b) essentially comprises sCO2 or it comprises sCO2.

[0065] According to one embodiment, the sCO2 is mixed with up to 10% ethanol by weight, for example, 0.1-8% ethanol by weight, the weight percentage being based on the total weight of the supercritical fluid and ethanol.

[0066] The process of the present invention may be carried out in a batch, continuous or semi-continuous mode.

[0067] According to one embodiment, the process is carried out in a continuous or semi-continuous manner.

[0068] For example, according to the present invention, the injection of the LiFSI solution into the container can be continuous or semi-continuous. In other words, according to one embodiment, the LiFSI solution is continuously injected into the container, or alternatively, the LiFSI solution is semi-continuously injected into the container. For example, the LiFSI solution can be injected into the container for a certain period of time (e.g., 30 to 120 seconds, e.g., 60 seconds), after which the injection is stopped for another certain period of time, which may be equal to, less than, or greater than the injection time.

[0069] For example, in accordance with the present invention, the supercritical fluid may be introduced into the vessel continuously or semi-continuously.

[0070] For example, the method of the present invention may include the step of continuously or semi-continuously withdrawing the salt of LiFSI from the vessel.

[0071] The solid form of LiFSI recovered in step c) is preferably in the form of a powder.

[0072] In step c), LiFSi in solid form can be recovered at the end of step b) or while step b) is in progress.

[0073] According to a particular embodiment of step c), the solid LiFSI enters the separation device together with the supercritical fluid. The pressure is released and the supercritical fluid becomes a gas. Such gas is preferably recycled, as described in more detail below.

[0074] The process of the present invention may further comprise additional steps, for example at least one step involving solvent recycling and / or supercritical fluid recycling.

[0075] Advantageously, the process of the present invention includes solvent recycling and supercritical fluid recycling.

[0076] For example, the supercritical fluid may be reinjected into the process of the invention either as is or after an additional purification step.

[0077] For example, the recycled solvent may be reused in another process, such as an upstream process for preparing LiFSI salt.

[0078] Recycling of the solvent and / or supercritical fluid can be accomplished in a number of ways.

[0079] According to one embodiment, the supercritical fluid may be recycled continuously during the process. Preferably, it is recycled under pressure using a supercritical fluid pipe.

[0080] According to another embodiment, the supercritical fluid can be recovered in the liquid phase by releasing the pressure in the vessel and then recompressing it in gaseous form, for example by a compressor, for recycling as a supercritical fluid that can be removed in the vessel.

[0081] The method of the present invention comprises the steps of: - a container that can withstand the pressures and temperatures used, for example a pressure P of at least 73 bar and / or a temperature P of more than 30°C, a solvent trap; - a gas tank and a supercritical gas generator; Optionally, a solution tank; - at least one injector / inlet valve attached to the vessel; Optionally, a separation device; The method may be performed in an apparatus including:

[0082] The vessel may preferably be made from sapphire, SS316L, glass or graphite filled PTFE.

[0083] The vessel may in particular be a column or an autoclave.

[0084] The equipment may include a separation device. Different separation devices can be used in the method of the invention. In some embodiments, the separation of liquid and gas / fluid can be performed by conventional filtration (also called "dead-end filtration") or cross filtration (also called tangential filtration), as disclosed, for example, in US Patent Application Publication No. 2007 / 0021570 (in the name of Solvay SA.). Alternatively, cyclonic separators can be used, such as those that function as liquid / solid or gas / solid separators. Cyclonic separators are advantageous because they allow the recovery of solids that may clog the filter medium. Several hybrid devices based on this principle exist. In particular, reference can be made to US Patent No. 7,410,620 (in the name of North Carolina State University).

[0085] Preferably, the solid LiFSI is recovered at the end of the process via a fritted filter.

[0086] For example, the frit filter may be made of stainless steel. Preferably, the frit filter has at least one of the following characteristics: - a pore size of 1 to 6 μm, preferably 2 to 4 μm, a diameter between 1 and 20 mm, preferably between 5 and 15 mm, more preferably about 10 mm, and / or - a thickness of 0.1 to 5 mm, preferably 0.7 to 3.5 mm, more preferably 1.5 to 2.5 mm.

[0087] If the device comprises one or more filters, the filters may in particular be located at the bottom or at the top of the vessel.

[0088] A second object of the invention relates to the lithium salt of bis(fluorosulfonyl)imide (LiFSI) in solid form which can be obtained by the process of the invention.

[0089] Advantageously, such LiFSI salts are characterized by containing less than 50 ppm of solvent as measured by Li NMR.

[0090] The amount of solvent in LiFSI in solid form, such as powder form, is preferably less than 40 ppm, less than 30 ppm, less than 20 ppm, less than 10 ppm, or even less than 5 ppm.

[0091] The LiFSI salts of the present invention also preferably exhibit at least one of the following chemical contents (as measured by ion chromatography): - less than 10,000 ppm, preferably less than 5,000 ppm, more preferably less than 1,000 ppm, more preferably less than 500 ppm, more preferably less than 100 ppm, more preferably less than 50 ppm, more preferably less than 20 ppm fluoride (F - ) content, and / or - less than 30,000 ppm, preferably less than 10,000 ppm, more preferably less than 5,000 ppm, even more preferably less than 1,000 ppm, even more preferably less than 100 ppm, more preferably less than 50 ppm, even more preferably less than 20 ppm sulfate (SO 2- ) content, and / or - less than 10,000 ppm, preferably less than 5,000 ppm, more preferably less than 1,000 ppm, more preferably less than 500 ppm, more preferably less than 100 ppm, more preferably less than 50 ppm, more preferably less than 20 ppm, more preferably less than 8 ppm chloride (Cl - ) content, and / or an iron (Fe) content of less than 1,000 ppm, preferably less than 800 ppm, more preferably less than 500 ppm, and / or a chromium (Cr) content of less than 1,000 ppm, preferably less than 800 ppm, more preferably less than 500 ppm, and / or a nickel (Ni) content of less than 1,000 ppm, preferably less than 800 ppm, more preferably less than 500 ppm, and / or a zinc (Zn) content of less than 1,000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm, and / or a copper (Cu) content of less than 1,000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm, and / or a bismuth (Bi) content of less than 1000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm, and / or a sodium (Na+) content of less than 10,000 ppm, preferably less than 5,000 ppm, more preferably less than 500 ppm, and / or - less than 10,000 ppm, preferably less than 5,000 ppm, more preferably less than 500 ppm potassium (K + ) content.

[0092] According to a third object, the present invention relates to a powder comprising a lithium salt of bis(fluorosulfonyl)imide (LiFSI) and at least one other substance, said at least one other substance being selected from: a solvent, preferably in an amount of less than 50 ppm as measured by Li NMR, and / or - water, preferably in an amount of less than 50 ppm as measured by KF, and / or - Fluoride (F) preferably in an amount less than 25 ppm - ), and / or - Chloride (Cl) preferably in an amount less than 8 ppm - ), and / or - Sulfates (SO4) preferably in amounts less than 20 ppm 2- ), and / or - Acidic substances, preferably in amounts less than 1 ppm.

[0093] Preferably, the solvent as described herein above is the same as the solvent used in the LiFSI solution provided in step (a).

[0094] Preferably, the acidic substance is NH2SO3 - and / or FSO3 - is selected from.

[0095] Advantageously, said powder as defined above is obtainable by the method according to the invention.

[0096] A fourth object of the present invention relates to the use of the lithium salt of a bis(fluorosulfonyl)imide (LiFSI) of the present invention in a battery electrolyte solution.

[0097] A fifth object of the present invention relates to the use of supercritical fluid extraction to prepare a solid form of the lithium salt of bis(fluorosulfonyl)imide (LiFSI) from a solution comprising LiFSI and at least one solvent.

[0098] To the extent that the disclosures of any patents, patent applications, and publications incorporated herein by reference conflict with the statements of this application to the extent that a term may be unclear, this statement shall control.

[0099] The present invention will now be described in more detail with reference to the following examples, the purposes of which are illustrative only and are not intended to limit the scope of the disclosure. EXAMPLES

[0100] Example 1 – Preparation of LiFSI solution A LiFSI solution was prepared as follows. The process was carried out in a 1 L reactor under N2 equipped with a means of stirring, a double jacket for heat regulation, a condenser, a means of pressure regulation, and a means of adding liquids or gases. 577.18 g of ethyl methyl carbonate (EMC) was charged at room temperature and 145.77 g of anhydrous NH4F was suspended in it. 190.52 g of bis(chlorosulfonyl)imide of formula (Cl-SO2)2-NH(HCSI) was gradually added over 1 hour, and the mixture was heated to less than 75 degrees with stirring for 18-20 hours. The mixture was cooled to room temperature and 0.945 g of 25% NH4(aq) (aqueous ammonia) was added. The resulting mixture was stirred at room temperature for 2 hours and then filtered.

[0101] The product was then concentrated to 866.18 g, and 247.5 g of the concentrated solution was transferred to a glass reactor. 371.3 g of dichloromethane was slowly added over 1 h. The precipitated NH4FSI was filtered, washed with dichloromethane, and dried in a vacuum oven to give 144.5 g of NH4FSI as a white solid.

[0102] 110.12 g of crystallized NH4FSI was dissolved in 902.7 g of EMC. 23.37 g of 25 wt % aqueous LiOH·H2O was added. The resulting two-phase mixture was stirred at room temperature for 1 h and then decanted. The organic phase was collected and concentrated under reduced pressure (10 -1 The mixture was placed in a thin film evaporator at 60° C. under 10 bar.

[0103] A 30 wt % LiFSI solution in EMC was obtained.

[0104] Example 2 - Preparation of LiFSI in powder form starting from the LiFSI solution of Example 1 Using the equipment configuration shown in Figure 1, the experiment was carried out as follows.

[0105] 8.907 g of LiFSI solution (2.67 g of LiFSI) obtained according to the procedure of Example 1 were introduced into the vessel. The vessel was pressurized with sCO2 (temperature 45 °C; pressure 200 bar). The outlet valve was then opened at the desired level to set the flow rate of CO2. After about 90 minutes of contact in the vessel (sCO2 / LiFSI solution ratio 3-80), the inlet valve between the buffer tank and the vessel was closed and the vessel and the outlet line were depressurized.

[0106] result: 2.27 g of LiFSI salt (white, dry) was isolated from the extractor, so the extraction yield was about 85%.

[0107] The water content was measured according to Karl Fischer analysis (oven method) as follows: Samples were prepared by an automatic oven sample processor (Metrohm); sample weight 0.1 g, carrier gas = N2, oven temperature = 160°C. Titration was performed using a mixture of methanol and NHF (1:1 v / v). The polarization current for potentiometric measurement of the reaction end point was 10 μA, and the titration end point voltage was 50 mV.

[0108] The moisture content of the LiFSI solid product sample was less than 50 ppm.

[0109] No major impurities were detected by ion chromatography (DIONEX ICS-3000). - F - <20 ppm - Cl - <5 ppm - SO4 2- <15 ppm - NH2SO 3- n / d (not detected) - FSO3 - n / d (not detected)

[0110] Li-NMR confirmed the purity to be greater than 99.9%.

Claims

1. 1. A process for preparing the lithium salt of bis(fluorosulfonyl)imide (LiFSI) in solid form, comprising the steps of: a) providing a solution comprising LiFSI and at least one solvent (LiFSI solution); b) contacting the LiFSI solution with at least one supercritical fluid; c) recovering the LiFSI in solid form; The method includes:

2. 2. The method according to claim 1, wherein the at least one supercritical fluid in step b) is selected from one fluid in the supercritical state or a mixture of at least two fluids in the supercritical state.

3. 3. The method of claim 1 or 2, wherein the LiFSI solution comprises a solvent preferably selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, dimethoxymethane, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, 4-methyl-1,3-dioxolane, methyl formate, methyl acetate, methyl propionate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, sulfolane, 3-methylsulfolane, dimethylsulfoxide, N,N-dimethylformamide, N-methyloxazolidinone, acetonitrile, valeronitrile, benzonitrile, ethyl acetate, isopropyl acetate, n-butyl acetate, nitromethane, nitrobenzene, trifluoroethanol and mixtures thereof.

4. 4. The method of claim 1, wherein the LiFSI solution comprises 5-70 wt. % LiFSI, based on the total weight of the LiFSI solution.

5. The method according to any one of claims 1 to 4, wherein the LiFSI in solid form is in the form of a powder.

6. The method according to any one of claims 1 to 5, wherein step b) is carried out in a vessel at a pressure P of at least 73 bar (7.3 MPa) and / or a temperature T of 30°C to 90°C.

7. The supercritical fluid is a CO2 solution optionally mixed with at least one polar solvent having a solubility in the supercritical fluid of less than 10% by weight, based on the total weight of the supercritical fluid and the at least one polar solvent. ２ The method according to any one of claims 1 to 6, comprising:

8. the pressure P in the container is comprised between 80 bar and 500 bar, and / or The method according to claim 7, wherein the temperature in the container is comprised between 35°C and 80°C.

9. The process according to any one of claims 1 to 8, which is carried out continuously or semi-continuously.

10. The method according to any one of claims 1 to 9, further comprising at least one step of recycling the solvent and / or recycling the supercritical fluid.

11. a container capable of withstanding a pressure P of at least 80 bar and a temperature P above 10° C.; a solvent trap; - a gas tank and a supercritical gas generator; Optionally, a solution tank; at least one injector / inlet valve attached to said container; - optionally a separation device; The method according to any one of claims 1 to 10, carried out in an apparatus comprising:

12. A solid form of the lithium salt of bis(fluorosulfonyl)imide (LiFSI) obtainable by the process according to any one of claims 1 to 11, characterized in that it contains LiFSI and a solvent in an amount of less than 50 ppm as measured by Li NMR.

13. A powder comprising the lithium salt of bis(fluorosulfonyl)imide (LiFSI) and at least one other substance, the at least one other substance being a solvent, preferably in an amount of less than 50 ppm as measured by Li NMR, and / or water, preferably in an amount of less than 50 ppm as measured by KF, and / or - Fluoride (F) in an amount preferably less than 25 ppm as measured by ion chromatography (IC) － ), and / or - Chloride (Cl) preferably in an amount of less than 8 ppm as measured by IC － ), and / or - Sulfates (SO ) preferably in an amount of less than 20 ppm as measured by IC ４ ２－ ), and / or - Acidic substances in an amount preferably less than 1 ppm as measured by IC A powder selected from the group consisting of

14. 14. Use of the solid form of the lithium salt of bis(fluorosulfonyl)imide (LiFSI) according to claim 12 or the powder according to claim 13 in a battery electrolyte solution.

15. The use of supercritical fluid extraction to prepare a solid form of the lithium salt of bis(fluorosulfonyl)imide (LiFSI) from a solution comprising LiFSI and at least one solvent.

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