Process for purifying lithium salts of bis(fluorosulfonyl)imides

Abstract

The present disclosure relates to a process for purifying the lithium salt of bis(fluorosulfonyl)imide (LiFSI), in which the purified LiFSI is extracted from crude LiFSI through supercritical fluid extraction. The present invention also relates to the purified 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. 22305584.9, filed April 21, 2022, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to a process for purifying the lithium salt of bis(fluorosulfonyl)imide (LiFSI) through supercritical fluid extraction. The present invention also relates to the purified 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 useful compounds in a variety of technical fields, such as in battery electrolytes. For these battery applications, the presence of impurities is a significant problem.

[0004] In order to reduce the contamination of metal impurities, U.S. Patent Application Publication No. 2013 / 0331609 (in the name of Nippon Soda Co., Ltd.) discloses a chlorosulfonylimide compound of the formula NH4F(HF) P (wherein p is 0-10) with a fluorinating agent. The resulting fluorosulfonylimide ammonium salt can then be subjected to a cation exchange reaction to produce another fluorosulfonylimide salt. The process is said to be industrially efficient and does not provide metal impurities.

[0005] Similarly, patent documents JP 2016124735 (in the name of Nippon Shokubai Kagaku Co., Ltd.) and JP 2016145147 (in the name of Nippon Shokubai Kagaku Co., Ltd.) disclose a method for the preparation of a chlorosulfonylimide compound and NH4F(HF) p(wherein p is 0 to 10). The fluorosulfonylimide compound may be reacted with an alkali metal compound to produce an alkali metal salt of the fluorosulfonylimide.

[0006] EP 3381923 (in the name of CLS) discloses a process for preparing lithium bis(fluorosulfonyl)imide which comprises reacting bis(chlorosulfonyl)imide with a fluorinating agent in a solvent, followed by treatment with an alkaline agent, thereby forming ammonium bis(fluorosulfonyl)imide, and then reacting the ammonium bis(fluorosulfonyl)imide with a lithium base to produce lithium bis(fluorosulfonyl)imide.

[0007] WO 2016 / 093399 (Chun Bo. Ltd.) discloses a method for preparing and purifying lithium salts of sulfonyl imides, which includes reacting chlorosulfonic acid with chlorosulfonyl isocyanate to prepare chlorosulfonylimides, then reacting the chlorosulfonylimides with ammonium fluoride to prepare fluorosulfonylimides ammonium salts, then reacting the fluorosulfonylimides ammonium salts with a lithium compound to obtain lithium sulfonylimides salts, and finally purifying the lithium sulfonylimides salts using a specific solvent.

[0008] European Patent No. 2674395 (in the name of Nippon Soda Co., Ltd.) discloses a process for producing fluorosulfonylimide ammonium salts with minimal contamination by metal impurities. The process involves reacting a specific chlorosulfonylimide ammonium salt with hydrogen fluoride. The resulting fluorosulfonylimide ammonium salt is then reacted with an alkali metal compound to obtain a fluorosulfonylimide alkali metal salt.

[0009] WO 2020 / 099527 (in the name of Solvay SA) discloses a process for producing an alkali salt of bis(fluorosulfonyl)imide, which is economically feasible on an industrial scale and results in a product of high purity, comprising reacting bis(chlorosulfonyl)imide or a salt thereof with ammonium fluoride to produce an ammonium salt of bis(fluorosulfonyl)imide, crystallizing by adding at least one precipitation solvent, isolating the ammonium salt of bis(fluorosulfonyl)imide, and reacting the crystallized ammonium salt of bis(fluorosulfonyl)imide with an alkali salt to obtain an alkali salt of bis(fluorosulfonyl)imide. Summary of the Invention

[0010] Although several methods aimed at purifying salts used in the manufacture of electrolytes for battery applications have been disclosed in the art, the Applicant has recognized that there remains a need to develop a method for purifying LiFSI salt.

[0011] Faced with the above mentioned technical problems, the Applicant has unexpectedly developed a process for producing LiFSI which is not complicated to implement in terms of equipment and reaction conditions and which is very friendly from an environmental point of view.

[0012] The process of the invention also makes it possible to obtain LiFSI in solid form in very high yields and with high purity, which can then be used in the electrolyte solution of batteries.

[0013] The preferred process for preparing LiFSI according to the invention is based on supercritical fluid extraction.

[0014] Thus, in a first objective, the present invention relates to a process for purifying the lithium salt of bis(fluorosulfonyl)imide (LiFSI), which is economically feasible on an industrial scale and results in a product of high purity. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 shows a schematic diagram of the experimental setup used in Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] 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, it is to be understood that in the relevant embodiments expressly contemplated herein, 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.

[0017] The first object of the present invention is a process for purifying the lithium salt of bis(fluorosulfonyl)imide (LiFSI), comprising: a) providing a crude composition comprising LiFSI and at least one other compound (crude LiFSI); b) contacting the crude LiFSI with at least one supercritical fluid; c) recovering a composition comprising LiFSI and at least one other compound in an amount less than the crude LiFSI; The present invention relates to a process comprising:

[0018] The term "crude composition" (hereinafter referred to as "crude LiFSI") means that the composition comprises LiFSI molecules in admixture with at least one other compound, which is an undesirable compound that adversely affects the properties of LiFSI, for example, when used as an electrolyte in battery applications. Such at least one other compound can be referred to as an "impurity." The impurities include, for example, ions, solvents, water, and / or reaction by-products. For example, crude LiFSI comprises 80-99 wt. %, preferably 85-98 wt. %, more preferably 90-97 wt. % LiFSI, the remainder being impurities removed by the process of the present invention.

[0019] Advantageously, in the process of the present invention, the crude LiFSI may be in the form of a solid, such as a powder, or a liquid, such as a slurry or solution.

[0020] As used herein, the term "contacting" refers to contacting crude LiFSI with at least one supercritical fluid. For example, such contacting is carried out 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 impurities present in the crude LiFSI, preferably greater than 80.00%, greater than 90.00%, greater than 95.00%, greater than 99.00%, greater than 99.50% or even greater than 99.90%. More preferably, all impurities are removed and the salt exhibits a purity of greater than 99.95% or even greater than 99.99%.

[0021] As used herein, the term "recovering" means that purified LiFSI, preferably in solid form, is removed or extracted from the vessel in which step b) is carried out.

[0022] 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.

[0023] According to the process of the present invention, at least one supercritical fluid is used to extract purified LiFSI salt from crude LiFSI, which has several advantages. Supercritical fluids, such as sCO2, offer many advantages because they are usually readily available, inexpensive, non-toxic, non-explosive, and not an organic solvent. Furthermore, the process of the present invention works at moderate temperatures (less than 100°C), ensuring gentle processing of the LiFSI product.

[0024] Preferably, step a) is carried out batchwise, semi-continuously or continuously.

[0025] Preferably, the at least one other compound present in the crude LiFSI is water (HO), fluoride (F - ), chloride (Cl - ), sulfate (SO4 2- ), sulfamate (NH2SO3 - ) and fluorosulfonates (FSO3 - ), more preferably selected from the group consisting of:

[0026] For example, the crude LiFSI to be purified may contain at least one of the following impurities: NH4Cl, NH4F, NH4HF2, NH4FSO3, NH4SO3NH2, NH4[N(SO3H)(SO2F)] (OFSI), and / or NH4[N(SO3H)2] (OSI).

[0027] It will be apparent to those skilled in the art that the parameters of the process according to the present invention can be appropriately selected and optimized based on, for example, the starting materials (especially the amounts of other compounds in the crude LiFSI) 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).

[0028] Preferably, step b) is carried out at a pressure P of at least 80 bar.

[0029] Preferably, step b) is carried out at a temperature T between 30°C and 90°C.

[0030] A particular advantage of the process of the present invention is the short contact time in step b), which can also advantageously be appropriately selected based on, for example, the starting material and the target yield.

[0031] 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.

[0032] In step b), the crude LiFSI is contacted with at least one supercritical fluid.

[0033] Preferably, step b) is carried out in a vessel.

[0034] As used herein, the term "vessel" refers to a vessel suitable for the process of the present invention, i.e. a vessel adapted to withstand the pressures and temperatures used in the process of the present invention and the potentially corrosive nature of the reactants and products involved in the process. The vessel as used herein may be referred to as an extraction vessel or extraction apparatus. The vessel as used herein may also be an extraction column (also referred to as a "column") or an autoclave.

[0035] According to a preferred embodiment, step b) comprises contacting the crude LiFSI of step a) with at least one supercritical fluid in a vessel.

[0036] Preferably, in step b), the crude LiFSI is contacted with one fluid in the supercritical state.

[0037] Preferably, in step b), the crude LiFSI is contacted with two or more fluids in a supercritical state. The two or more fluids may be mixed or contacted sequentially with the crude LiFSI. As an example, the crude LiFSI may be contacted with a mixture of at least two supercritical fluids.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] According to the invention, step b) can be repeated once or several times.

[0043] For example, the process 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.

[0044] In some embodiments, preferably, during extraction, the vessel used for contacting the crude LiFSI with at least one supercritical fluid in step b) is at a pressure P of at least 73 bar (7.3 MPa).

[0045] In some embodiments, preferably during extraction, the vessel used for contacting the crude LiFSI with at least one supercritical fluid in step b) is at a temperature T between 30°C and 90°C.

[0046] 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.

[0047] 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 process of the invention, very high pressures may 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).

[0048] According to one embodiment, step b) is carried out by injecting crude LiFSI into a vessel that is already pressurized.

[0049] According to one embodiment, the crude LiFSI is in a solid form, such as a powder.

[0050] According to another embodiment, the crude LiFSI is in a liquid form, such as a solution comprising LiFSI and an organic aprotic solvent.

[0051] Preferably, the organic aprotic solvent is selected in the group comprising 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 and nitrobenzene. More preferably, the solvent is selected from ethylene carbonate, propylene carbonate, butylene carbonate, tetrahydrofuran, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, isopropyl acetate and n-butyl acetate. Even more preferably, the solvent is selected from dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, isopropyl acetate and n-butyl acetate. Even more preferably, the solvent is selected from ethyl methyl carbonate and n-butyl acetate.

[0052] Crude LiFSI can be injected into the vessel, for example, via an injector or inlet valve attached to the vessel.

[0053] According to another embodiment, step b) comprises b1) introducing crude LiFSI into a vessel; b2) pressurizing the vessel to a pressure P; b3) heating the vessel to a temperature T; b4) introducing at least one supercritical fluid into the vessel; Includes.

[0054] Preferably, 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.

[0055] Preferably, the order of steps may be b1), b3), b4) and b2).

[0056] The conditions of temperature, pressure and contact time detailed above for step b) apply to steps b2) and b3) as explained above.

[0057] Preferably, step b2) is carried out at a pressure of at least 74 bar (7.4 MPa).

[0058] Preferably, step b3) is carried out at a temperature of at least 30°C.

[0059] 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 purity of the crude LiFSi.

[0060] Step b4) can be carried out batchwise, continuously or semi-continuously.

[0061] 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).

[0062] Advantageously, the supercritical fluid used in step b) may essentially comprise sCO2 or it may comprise sCO2.

[0063] 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.

[0064] The weight ratio of supercritical fluid / crude LiFSI used in the process of the present invention may vary from 1 / 1 to 400 / 1. For example, the weight ratio of supercritical fluid / crude LiFSI preferably varies from 5 / 1 to 350 / 1, such as from 20 / 1 to 300 / 1, 30 / 1 to 280 / 1, or 40 / 1 to 250 / 1.

[0065] The process of the present invention may be carried out in a batch, continuous or semi-continuous mode.

[0066] Preferably, the process is carried out in a continuous or semi-continuous mode.

[0067] Preferably, the process of the present invention includes the step of continuously or semi-continuously withdrawing the purified salt of LiFSI from the vessel.

[0068] Preferably, according to the present invention, the injection of crude LiFSI into the vessel is performed continuously or semi-continuously. In other words, according to one embodiment, crude LiFSI is injected into the vessel continuously, or alternatively, crude LiFSI is injected into the vessel semi-continuously. For example, crude LiFSI may be injected into the vessel 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 process of the present invention may include a step of continuously or semi-continuously withdrawing a salt of LiFSI from a vessel.

[0071] The purified LiFSI recovered in step c) is preferably in solid form. The purified LiFSI is preferably recovered in solid form, regardless of whether the starting crude LiFSI is in solid form or in the form of a slurry or liquid. Even more preferably, the purified LiFSI is in powder form.

[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 purified 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, such as at least one step preferably involving recycling of the supercritical fluid.

[0075] For example, the supercritical fluid may be reinjected into the process of the invention either as is or after additional purification steps.

[0076] Recycling of the supercritical fluid can be accomplished in several ways.

[0077] According to one embodiment, the supercritical fluid may be continuously recycled during the process. Preferably, it is recycled under pressure using supercritical fluid pipes.

[0078] According to another embodiment, the supercritical fluid can be recovered as a liquid phase by releasing the pressure in the vessel and then re-pressurizing it in gas form, for example by a compressor, to recycle the supercritical fluid as a supercritical fluid that can be removed in the vessel.

[0079] The process of the present invention comprises: - a container that can withstand the pressures and temperatures used, for example a pressure P of at least 73 bar (7.3 MPa) and a temperature P above 30°C; a solvent trap; - a gas tank and a supercritical gas generator; - at least one injector / inlet valve attached to said vessel; Optionally, a separation device; The method may be performed in an apparatus including:

[0080] The vessel may preferably be made from sapphire, SS316L, glass or graphite filled PTFE.

[0081] The equipment may include a separation device. Different separation devices can be used in the process of the invention. In some embodiments, separation 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 gas / solid separators. Cyclonic separators are advantageous because they can recover 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).

[0082] Preferably, the solid LiFSI is recovered at the end of the process via a fritted filter.

[0083] 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.

[0084] 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.

[0085] A second object of the present invention is the lithium salt of bis(fluorosulfonyl)imide (LiFSI) in solid form, obtainable by the process of the present invention.

[0086] Advantageously, such LiFSI salt comprises LiFSI and - Fluoride (F) in an amount of less than 100 ppm, preferably measured by ion chromatography (IC) - ), and / or - Chloride (Cl) preferably in an amount of less than 100 ppm as measured by IC - ), and / or - Sulfate (SO4) preferably in an amount less than 1,000 ppm as measured by IC 2- ), and / or - Sulfamate (NH2SO3 - ), and / or - Fluorosulfonates (FSO3 - ), and / or - Water in an amount less than 50 ppm, preferably measured by KF analysis (oven method) The present invention is characterized in that it contains:

[0087] Indeed, it is an object of the present invention to provide LiFSI salt with very low impurities. As detailed below in the experimental part, the inventors have been able to achieve LiFSI salt with a high level of purity of more than 99.90%, starting from a crude product with a purity of 98.00%. The LiFSI salt of the present invention preferably has a purity of more than 99.50%, more than 99.60%, more than 99.70%, more than 99.80%, more than 99.90%, or even more than 99.95%, as measured by Li-NMR.

[0088] The amount of impurities in the LiFSI product recovered at the end of the process according to the invention is preferably - Fluoride (F) in an amount up to 50 ppm, e.g. less than 40 ppm, less than 30 ppm, less than 25 ppm as measured by ion chromatography (IC) - ), and / or - Chloride (Cl) in an amount up to 50 ppm, e.g. less than 40 ppm, less than 30 ppm, less than 20 ppm, less than 10 ppm or less than 8 ppm as measured by IC - ), and / or - Sulfate (SO4) in an amount up to 100 ppm, e.g. less than 50 ppm, less than 30 ppm, less than 10 ppm, less than 5 ppm as measured by IC 2- ), and / or - Water in amounts up to 50 ppm as determined by KF analysis (oven method) is selected from.

[0089] Preferably, sulfate (SO4 2- ) The acid substance different from NH2SO3 - and / or FSO3 - is selected from.

[0090] Preferably, sulfate (SO4 2- ) in the amounts: - Less than 50 ppm, e.g., less than 40 ppm, less than 30 ppm, less than 20 ppm, less than 10 ppm or even less than 5 ppm sulfamate (NH2SO3 - ), and / or - Less than 50 ppm, e.g. less than 40 ppm, less than 30 ppm, less than 20 ppm, less than 10 ppm or even less than 5 ppm of fluorosulfonates (FSO3 - ).

[0091] The LiFSI salt of the present invention preferably contains at least one of the following chemical entities (as measured by ion chromatography): iron (Fe) in an amount of less than 1,000 ppm, preferably less than 500 ppm, more preferably less than 100 ppm; Chromium (Cr) in an amount of less than 1,000 ppm, preferably less than 500 ppm, more preferably less than 100 ppm; - nickel (Ni) in an amount of less than 1,000 ppm, preferably less than 500 ppm, more preferably less than 100 ppm; zinc (Zn) in an amount of less than 1,000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm; copper (Cu) in an amount of less than 1,000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm; Bismuth (Bi) in an amount of less than 1,000 ppm, preferably less than 100 ppm, more preferably less than 10 ppm; - less than 10,000 ppm, preferably less than 5,000 ppm, more preferably less than 500 ppm or even less than 100 ppm sodium (Na + ), and / or - less than 10,000 ppm, preferably less than 5,000 ppm, more preferably less than 500 ppm or even less than 100 ppm of potassium (K + ) Also includes.

[0092] The purified LiFSI salt of the present invention is characterized by containing less than 50 ppm water as measured by KF analysis (oven method). Preferably, the purified LiFSI salt contains less than 40 ppm, less than 30 ppm, less than 20 ppm, less than 10 ppm, or less than 5 ppm water.

[0093] A third object of the invention relates to a solid comprising a lithium salt of bis(fluorosulfonyl)imide (LiFSI) and at least one other substance, said at least one other substance being - water in an amount of less than 50 ppm, preferably as determined by KF analysis using the oven method, 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 an amount less than 20 ppm 2- ), and / or - Sulfates (SO4 2- ) and different acid substances is selected from.

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

[0095] A fourth object of the invention relates to the use of the solid form of the lithium salt of bis(fluorosulfonyl)imide (LiFSI) according to the invention in a battery electrolyte solution.

[0096] A fifth object of the present invention is the use of supercritical fluid extraction to purify crude lithium salt of bis(fluorosulfonyl)imide (LiFSI) containing LiFSI and impurities.

[0097] To the extent that the disclosures of any patents, patent applications, and publications incorporated herein by reference conflict with the statements in this application to the extent that any term may be unclear, the statements in this application shall control.

[0098] The invention will now be described in more detail with reference to the following examples, the purpose of which is merely illustrative and is not intended to limit the scope of the disclosure. EXAMPLES

[0099] raw materials: Crude LiFSI purchased from Provisco with the following characteristics: - Water <10ppm as determined by KF analysis (oven method) as detailed below - F determined by IC* - =1420ppm - Cl determined by IC* - <5 ppm - SO4 determined by IC* 2- =11,000ppm - NH2SO3 determined by IC* - =1,190 ppm - FSO3 determined by IC* - =7,210 ppm - Purity determined by Li-NMR = 98% *IC: Ion chromatography (DIONEX ICS-3000)

[0100] For KF analysis (oven method), 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.

[0101] Example 1 - Preparation of high purity LiFSI in powder form starting from crude LiFSI Using the equipment configuration shown in Figure 1, the experiment was conducted according to the following procedure.

[0102] 4.524 g of crude LiFSI were introduced into the vessel. The vessel was pressurized with sCO2 (temperature 45 °C, pressure 200 bar, CO2 / LiFSI solution ratio varied from 30 to 400 during the process). The outlet valve was then opened to set the flow rate of CO2 (165 g / min) at the desired level. After about 10 hours of contact in the vessel, the inlet valve between the buffer tank and the vessel was closed and the vessel and the outlet line were depressurized.

[0103] The following was obtained:

[0104] After 10 hours of extraction, a mass loss of 0.12 g (2.65 wt %) was observed. A plateau was observed at a CO2 / crude LiFSI mass ratio of 180, which corresponds to 5 hours of extraction.

[0105] The extracted powder easily flowed out of the container by gravity, in comparison, the crude LiFSI adhered loosely to the container surface.

[0106] The moisture content in the LiFSI solid product sample was less than 50 ppm as determined by KF analysis (oven method).

[0107] 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)

[0108] Li-NMR confirmed the purity to be greater than 99.9%.

Claims

1. A process for purifying lithium salts (LiFSI) of bis(fluorosulfonyl)imides, a) A step of providing a crude composition [crude LiFSI] comprising LiFSI and at least one other compound, b) A step of bringing the crude LiFSI into contact with at least one supercritical fluid, c) A step of recovering a composition comprising LiFSI and at least one other compound in an amount less than that of the crude LiFSI. A process that includes this.

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

3. - The crude LiFSI is in the form of a solid, slurry, or solution, and / or - The process according to claim 1, wherein the purified LiFSI is in solid form.

4. The process according to claim 1, wherein step b) is carried out in a vessel with a pressure P of at least 73 bar (7.3 MPa) and / or a temperature T of 30°C to 90°C.

5. The supercritical fluid is a polar solvent of which CO is 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 process according to claim 1, including the process described in claim 1.

6. - The pressure P inside the container is included in the range of 80 bar (8.0 MPa) to 500 bar (50.0 MPa), and / or - The process according to claim 5, wherein the temperature inside the container is between 35°C and 80°C.

7. The process according to claim 1, which is carried out continuously or semi-continuously.

8. The at least one other compound in the crude LiFSI is water (H ２ O), fluoride (F － ), sulfate (SO ４ ２－ ), chloride (Cl － ), sulfamate (NH ２ SO ３ － ), and fluorosulfonate (FSO ３ － ), preferably selected from the group consisting of, the process according to claim {{content}}1

9. The process according to claim 1, further comprising at least one step of recycling the supercritical fluid.

10. - A container capable of withstanding a pressure P of at least 80 bar and a temperature P exceeding 10°C, - Solvent trap and, - Gas tank and supercritical gas generator, - At least one injector / inlet valve attached to the container, - Optionally, the separation device and The process according to claim 1, performed within a device including the following:

11. A lithium salt (LiFSI) of bis(fluorosulfonyl)imide in solid form, which can be obtained by the process described in claim 1, wherein LiFSI and - Preferably an amount of fluoride (F) less than 100 ppm, as measured by ion chromatography (IC). － ), and / or - Preferably an amount of less than 100 ppm of chloride (Cl) as measured by IC. － ), and / or - Preferably an amount of less than 1,000 ppm of sulfate (SO4) as measured by IC. ４ ２－ ), and / or - Preferably an amount of less than 1,000 ppm of sulfamate (NH4) as measured by IC. ２ SO ３ － ), and / or - Preferably an amount of less than 1,000 ppm of fluorosulfonate (FSO) as measured by IC. ３ － ), and / or - A quantity of water less than 50 ppm, preferably measured by KF analysis (oven method). A lithium salt (LiFSI) of bis(fluorosulfonyl)imide characterized by containing the following.

12. Lithium salts of bis(fluorosulfonyl)imides (LiFSI), - Preferably, water and / or water in an amount of less than 50 ppm, as measured by KF analysis using the oven method. - Preferably an amount of less than 25 ppm of fluoride (F － ), and / or - Preferably an amount of less than 8 ppm of chloride (Cl － ), and / or - Preferably an amount of less than 20 ppm of sulfate (SO4). ４ ２－ ), and / or - Preferably less than 1 ppm of sulfate (SO4). ４ ２－ ) and different acidic substances A solid comprising at least one other substance selected from the following.

13. Use of the lithium salt (LiFSI) of bis(fluorosulfonyl)imide according to claim 11 or the solid according to claim 12 in a battery electrolyte solution.

14. Use of supercritical fluid extraction for purifying a crude composition of lithium bis(fluorosulfonyl)imide (crude LiFSI) containing LiFSI and at least one impurity.

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