Method for producing lithium bis(fluorosulfonyl)imide

Abstract

The present invention relates to a method for preparing lithium bis(fluorosulfonyl)imide, the method comprising the steps of: contacting the bis(fluorosulfonyl)imide with a lithium base in a solvent selected from carbonates, ethers, and nitriles to obtain a mixture comprising lithium bis(fluorosulfonyl)imide and water; Diafiltering the mixture through a nanofiltration membrane to obtain first a lithium bis(fluorosulfonyl)imide-enriched, water-depleted concentrate and then a lithium bis(fluorosulfonyl)imide-depleted, water-enriched permeate. The present invention also relates to a method for producing an electrolyte for a Li-ion battery.

Description

[Technical field]

[0001] The present invention relates to a process for the preparation of lithium bis(fluorosulfonyl)imide, which comprises a step of diafiltration with a nanofiltration membrane. [Background technology]

[0002] Due to their very low basicity, sulfonylimide type anions are increasingly used in the field of energy storage, either in the form of inorganic salts in batteries or in the form of organic salts in supercapacitors, or in the field of ionic liquids. The battery market is expanding in earnest and reducing the cost of battery production is a major challenge, so there is a need for cheap, large-scale processes for the synthesis of this type of anion.

[0003] In the specific field of Li-ion batteries, the salt currently most widely used is LiPF6, but this salt has many drawbacks, such as limited thermal stability, susceptibility to hydrolysis and therefore poor battery safety. 2- New salts with the group have been investigated and have demonstrated many advantages, such as good ionic conductivity and hydrolysis resistance. One of these salts, LiFSI (LiN(FSO2)2), shows very advantageous properties and is a strong candidate to replace LiPF6.

[0004] Most of the processes for producing imide salts with fluorosulfonyl groups include many steps, and by-products may be formed that have physical properties that prove to be complicated to remove and / or require expensive purification steps. Furthermore, following the lithiation reaction to obtain the desired salt, a significant amount of water may be present in the solution containing the imide salt. It is important to be able to reduce or even eliminate this amount of water.

[0005] Dehydration of organic solvents is an energy-intensive process: distillation and other thermal separation methods account for 80% of the energy consumed in industrial separations, highlighting the need for more efficient separations.

[0006] WO 2015 / 004236 relates to a method for the preparation of a dehydrated liquid mixture (having a reduced water content) intended to be used as a solvent for conductive salts (e.g. LiPF6), starting from a liquid starting mixture containing: one, two or three organic carbonates, in a total amount of 90% by weight or more based on the total amount of the liquid starting mixture, one, two or three compounds selected from the group consisting of acids with a pKa of less than 4, and a precursor which, upon hydrolysis, releases an acid with a pKa of less than 4 into the liquid starting mixture.

[0007] French Patent No. 3089214 (FR 3089214) relates to a method for preparing imide salts bearing fluorosulfonyl groups, comprising a step b) comprising a fluorination step with anhydrous HF in the presence of at least one water-immiscible organic solvent, and a step c) comprising a reaction of the composition obtained in the previous step with an aqueous composition comprising at least one lithiated base.

[0008] US 2012 / 0141868 relates to a zeolite that allows for the dehydration of non-aqueous electrolyte solutions, without the problem of sodium leaching from the zeolite during dehydration of non-aqueous electrolyte solutions for lithium batteries that use the zeolite.

[0009] US 2020 / 0148633 relates to a method for producing hydrogen bisfluoro(sulfonyl)imide, which comprises contacting a sulfonyl fluoride with hexamethyldisilazane in an organic solvent. This document also relates to a method for producing lithium bis(fluorosulfonyl)imide (LiFSI) by contacting hydrogen bis(fluorosulfonyl)imide with a lithium compound.

[0010] Japanese Patent Application No. 2002-001107 (JP 2002001107) relates to a crystalline faujasite-type zeolite having a low silica content for treating non-aqueous electrolytes, and a method for producing non-aqueous electrolytes using said zeolite.

[0011] Therefore, there is a real need to provide a method for preparing imide salts having fluorosulfonyl groups, especially lithium bis(fluorosulfonyl)imide, which can reduce energy consumption and the amount of solvent used in the process compared to existing technologies.Furthermore, there is a need to provide a method for preparing imide salts having fluorosulfonyl groups, especially lithium bis(fluorosulfonyl)imide, which can not only avoid lithiation with toxic compounds such as lithium fluoride, but also reduce the purification steps in the process.

[0012] Summary of the Invention The present invention first relates to a method for producing lithium bis(fluorosulfonyl)imide, the method comprising the steps of: contacting the bis(fluorosulfonyl)imide with a lithium base in a solvent selected from carbonates, ethers, and nitriles to obtain a mixture comprising lithium bis(fluorosulfonyl)imide and water; diafiltration of said mixture through a nanofiltration membrane to obtain first a lithium bis(fluorosulfonyl)imide-enriched, water-depleted concentrate and then a lithium bis(fluorosulfonyl)imide-depleted, water-enriched permeate. It includes.

[0013] According to some embodiments, the solvent is a carbonate, preferably selected from dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, diphenyl carbonate, methyl phenyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, vinylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, or mixtures thereof.

[0014] According to some embodiments, the lithium base is selected from lithium hydroxide, lithium carbonate, and mixtures thereof.

[0015] According to some embodiments, the nanofiltration membrane has a cutoff threshold of 80-250 Daltons, preferably 100-200 Daltons, more preferably 120-180 Daltons.

[0016] According to some embodiments, the method includes a step of pervaporation between the step of contacting the bis(fluorosulfonyl)imide with the lithium base and the step of diafiltration.

[0017] According to some embodiments, the method includes a step of azeotropic distillation between the step of contacting the bis(fluorosulfonyl)imide with the lithium base and the step of diafiltration.

[0018] According to embodiments, the lithium bis(fluorosulfonyl)imide-enriched, water-depleted concentrate has a water content of 100 ppm or less, preferably 50 ppm or less, and more preferably 20 ppm or less, by weight of the concentrate.

[0019] According to some embodiments, a solvent is added to the concentrate during the diafiltration step, which solvent is preferably the same as the solvent used in the step of contacting the bis(fluorosulfonyl)imide with the lithium base.

[0020] According to some embodiments, the diafiltration step is carried out at a pressure between 1 and 60 bar.

[0021] The present invention also relates to a method for producing an electrolyte for a Li-ion battery, the method comprising the steps of: preparing a bis(fluorosulfonyl)imide as described above; Producing an electrolyte containing lithium bis(fluorosulfonyl)imide It includes.

[0022] The present invention makes it possible to meet the above-mentioned needs. More specifically, the present invention provides a method for producing lithium bis(fluorosulfonyl)imide, which can reduce energy consumption and the amount of solvent used in the process compared to existing technologies. Furthermore, the present invention also provides a method for producing lithium bis(fluorosulfonyl)imide, which can avoid lithiation with toxic compounds such as lithium fluoride, and can also reduce the purification step of the process.

[0023] This is achieved by the method of the present invention. More specifically, the method comprises a first step of contacting a bis(fluorosulfonyl)imide with a lithium base (capable of generating water after reaction with itself) in a solvent selected from carbonates, ethers, and nitriles to form a mixture comprising a lithium bis(fluorosulfonyl)imide salt and water. The use of such a lithium base, and the fact that the water can then be effectively removed, makes it possible to avoid the use of toxic lithium salts.

[0024] A subsequent step of diafiltration with a nanofiltration membrane allows the amount of remaining water to be effectively removed without using methods that increase the energy or solvent consumption of the process.

[0025] Finally, during diafiltration, it is also possible to eliminate various impurities present in the mixture obtained after the step of contacting the bis(fluorosulfonyl)imide with the lithium base, which makes it possible to reduce or even avoid additional purification steps.

[0026] Detailed Description The present invention will be described in more detail below, but the present invention is not limited to the following description.

[0027] Lithium battery A lithium battery includes at least one electrochemical cell, and preferably includes a plurality of electrochemical cells, each of which includes a negative electrode, a positive electrode, and an electrolyte interposed between the negative and positive electrodes.

[0028] Each electrochemical cell may also include a separator impregnated with an electrolyte.

[0029] The electrochemical cells can be assembled in series and / or parallel in a battery.

[0030] The term "negative electrode" is understood to mean the electrode that acts as an anode when the battery carries electric current (i.e. when the battery is in the discharging process) and as a cathode when the battery is in the charging process.

[0031] The negative electrode typically comprises an electrochemically active material, optionally an electrically conductive material, and optionally a binder.

[0032] The term "positive electrode" is understood to mean the electrode that acts as a cathode when the battery carries electric current (i.e. when the battery is in the discharging process) and as an anode when the battery is in the charging process.

[0033] The positive electrode typically comprises an electrochemically active material, optionally an electrically conductive material, and optionally a binder.

[0034] The term "electrochemically active material" is understood to mean a material capable of reversibly inserting ions.

[0035] "Conductive material" is understood to mean a material capable of conducting electrons.

[0036] The negative electrode of the electrochemical cell may in particular comprise metallic lithium as the electrochemically active material. This metallic lithium may be in substantially pure form or in the form of an alloy. Among the lithium-based alloys that may be used, mention may be made, for example, of lithium-aluminum alloys, lithium-silica alloys, lithium-tin alloys, Li-Zn, Li3Bi, Li3Cd, and Li3SB. Mixtures of the above materials may also be used.

[0037] The negative electrode may be in the form of a film or a rod. One example of a negative electrode may include a film of active lithium produced by rolling a strip of lithium between rollers.

[0038] The positive electrode comprises an electrochemically active material, which is preferably oxide-based, preferably manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, lithium / manganese composite oxide (e.g., Li x Mn2O4, or LixMnO2), lithium / nickel composite oxides (e.g., Li x NiO2), lithium / cobalt composite oxides (e.g., Li x CoO2), lithium / nickel / cobalt composite oxides (e.g., LiNi 1-y CoyO2), lithium / nickel / cobalt / manganese composite oxides (e.g., LiNi x Mn y Co z O2, where x+y+z=1), lithium-enriched lithium / nickel / cobalt / manganese composite oxides (e.g., Li 1+x (Ni x Mn y Co z ) 1-x O2), lithium / transition metal composite oxides, lithium / manganese / nickel composite oxides with spinel structure (e.g., Li xMn 2-y Ni y O4), vanadium oxide, and mixtures thereof.

[0039] The positive electrode preferably comprises an electrochemically active material, which is a lithium / nickel / manganese / cobalt composite oxide with a high nickel content (LiNi x Mn y Co z O2, where x+y+z=1 (abbreviated as NMC, where x>y and x>z), or lithium / nickel / cobalt / aluminum composite oxide with high nickel content (LiNi x’ Co y’ Al z’ , where x'+y'+z'=1 (abbreviated as NCA), where x'>y' and x'>z'.

[0040] A specific example of these oxides is NMC532 (LiNi 0.5 Mn 0.3 Co 0.2 O2), NMC622(LiNi 0.6 Mn 0.2 Co 0.2 O2), and NMC811(LiNi 0.8 Mn 0.1 Co 0.1 O2).

[0041] The material of each electrode may also include, in addition to the electrochemically active material, a conductive material such as a carbon source, including, for example, carbon black, Ketjen® carbon, Shawinigan carbon, graphite, graphene, carbon nanotubes, carbon fibers (e.g., vapor-grown carbon fibers, or VGCF), non-powdered carbon obtained by carbonizing an organic precursor, or a combination of two or three of these. Other additives may also be present in the material of the positive electrode, such as lithium salts, or inorganic particles of the ceramic or glass type, or other compatible active materials (e.g., sulfur).

[0042] The material of each electrode may also include a binder. Non-limiting examples of binders include linear, branched and / or cross-linked polyether polymer binders (e.g., polymers based on poly(ethylene oxide) (PEO) or poly(propylene oxide) (PPO), or a mixture of the two (or EO / PO copolymers), optionally including cross-linking units), water-soluble binders (e.g., SBR (styrene / butadiene rubber), NBR (acrylonitrile / butadiene rubber), HNBR (hydrogenated NBR), CHR (epichlorohydrin rubber), ACM (acrylate rubber), or fluoropolymer-based binders (e.g., PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene)), and combinations thereof. Some binders, e.g., those that are soluble in water, may also include additives, e.g., CMC (carboxymethyl cellulose).

[0043] The separator can be a porous polymer membrane. As a non-limiting example, the separator can be made of a porous film of a polyolefin, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, or a multi-layer structure of the above copolymers.

[0044] The electrolyte comprises at least one lithium salt, and preferably comprises multiple lithium salts.

[0045] In the context of the present invention, lithium salts include lithium bis(fluorosulfonyl)imide (LiFSI).

[0046] In some embodiments, the lithium salt consists essentially of, or further consists of, lithium bis(fluorosulfonyl)imide (LiFSI).

[0047] According to other embodiments, the lithium salts also include lithium bis(fluorosulfonyl)imide (LiFSI) and one or more further salts selected from lithium 2-trifluoromethyl-4,5-dicyanoimidazolate (LiTDI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDBOB), lithium difluorophosphate (LiPO2F2), and lithium tetrafluoroborate (LiBF4).

[0048] The electrolyte solvent may be selected from ethers, esters, ketones, alcohols, nitriles, carbonates, amides, sulfamides, and sulfonamides, and mixtures thereof. The electrolyte solvent preferably comprises at least one solvent selected from carbonates, ethers, and nitriles, and more preferably the electrolyte solvent comprises at least one carbonate.

[0049] Among the ethers, mention may be made of linear or cyclic ethers, such as, for example, dimethoxyethane (DME), methyl ethers of oligoethylene glycols having 2 to 5 oxyethylene units, dioxolane, dioxane, dibutyl ether, tetrahydrofuran, and mixtures thereof.

[0050] Among these esters, mention may be made of phosphates or sulfites, such as methyl formate, methyl acetate, methyl propionate, ethyl acetate, butyl acetate, γ-butyrolactone, or mixtures thereof.

[0051] Among the ketones, particular mention may be made of cyclohexanone.

[0052] Among the alcohols, mention may be made, for example, of ethyl alcohol or isopropyl alcohol.

[0053] Examples of nitriles include acetonitrile, pyruvonitrile, propionitrile, methoxypropionitrile, dimethylaminopropionitrile, butyronitrile, isobutyronitrile, valeronitrile, pivalonitrile, isovaleronitrile, glutaronitrile, methoxyglutaronitrile, 2-methylglutaronitrile, 3-methylglutaronitrile, adiponitrile, malononitrile, 1,2,6-tricyanohexane, and mixtures thereof.

[0054] Among carbonates, for example, cyclic carbonates such as ethylene carbonate (EC) (CAS: 96-49-1), propylene carbonate (PC) (CAS: 108-32-7), butylene carbonate (BC) (CAS: 4437-85-8), dimethyl carbonate (DMC) (CAS: 616-38-6), diethyl carbonate (DEC) (CAS: 105-58-8), ethyl methyl carbonate (EMC) (CAS: 623-53-0), diphenyl carbonate (CAS: 102-09-0), Examples of suitable fluorocarbons include methyl phenyl carbonate (CAS: 13509-27-8), dipropyl carbonate (DPC) (CAS: 623-96-1), methyl propyl carbonate (MPC) (CAS: 1333-41-1), ethyl propyl carbonate (EPC), vinylene carbonate (VC) (CAS: 872-36-6), fluoroethylene carbonate (FEC) (CAS: 114435-02-8), trifluoropropylene carbonate (CAS: 167951-80-6), or mixtures thereof.

[0055] Among the amides, mention may be made of dimethylformamide and N-methylpyrrolidinone.

[0056] More preferably, the electrolyte solvent is selected from EC, EMC, a mixture of EC and EMC, a mixture of EC and DMC, a mixture of EC and DEC, a mixture of EC, DEC and PC, a mixture of EC, DMC and EMC.

[0057] Optionally, the electrolyte may include one or more polar polymers. The polar polymers preferably include monomer units derived from ethylene oxide, propylene oxide, epichlorohydrin, epifluorohydrin, trifluoroepoxypropane, acrylonitrile, methacrylonitrile, acrylic and methacrylonitrile acid esters and amides, vinylidene fluoride, N-methylpyrrolidone, and / or polycationic or polyanionic polyelectrolytes. When the electrolyte composition of the present invention includes more than one polymer, at least one of them may be crosslinked.

[0058] Further, the electrolyte may include one or more additives, which may be selected from the group consisting of fluoroethylene carbonate (FEC), vinylene carbonate, 4-vinyl-1,3-dioxolan-2-one, pyridazine, vinylpyridazine, quinoline, vinylquinoline, butadiene, sebaconitrile, alkyl disulfides, fluorotoluene, 1,4-dimethoxytetrafluorotoluene, t-butylphenol, di(t-butyl)phenol, tris(pentafluorophenyl)borane, oximes, aliphatic epoxides, halogenated biphenyls, methacrylic acid, allylethyl carbonate, vinyl acetate, divinyl adipate, propane sultone, acrylonitrile, 2-vinylpyridine, maleic anhydride, methyl cinnamate, methyl phosphonate, vinyl-containing silane compounds, and / or 2-cyanofuran.

[0059] The at least one lithium salt may be present in the electrolyte in a content ranging from 0.1% to 50% relative to the weight of the electrolyte.

[0060] process The process according to the invention makes it possible to produce lithium bis(fluorosulfonyl)imide solutions with a low water content which can be used as electrolytes in Li-ion batteries, either directly or after the addition of salts, solvents and / or additives.

[0061] The process according to the invention comprises the step of contacting a bis(fluorosulfonyl)imide with a lithium base in a solvent to obtain a mixture comprising lithium bis(fluorosulfonyl)imide and water.

[0062] The bis(fluorosulfonyl)imide used in this step can be obtained by a chlorination step from a sulfonamide of the following formula (I): (I) R-(SO2)-NH2 wherein R may be selected from a fluorine atom, a chlorine atom, or a hydroxy group.

[0063] This step may be carried out with at least one sulfur-based acid and at least one chlorinating agent.

[0064] Furthermore, this process At temperatures between 30°C and 150°C, and / or A reaction time between 1 hour and 7 days, and / or At pressures between 1bar abs and 20bar abs This can be done.

[0065] According to the present invention, the sulfur-based agent may be selected from the group consisting of chlorosulfonic acid (ClSO3H), sulfuric acid, oleum, and mixtures thereof.

[0066] According to the present invention, the chlorinating agent may be selected from the group consisting of thionyl chloride (SOCl2), oxalyl chloride (COCl)2, phosphorus pentachloride (PCl5), phosphonyl trichloride (PCl3), phosphoryl trichloride (POCl3), and mixtures thereof. The chlorinating agent is preferably thionyl chloride.

[0067] The chlorination step can be carried out in the presence of a catalyst, for example selected from tertiary amines (eg methylamine, triethylamine, or diethylmethylamine), pyridine, and 2,6-lutidine.

[0068] The molar ratio of the sulfur-based acid to the compound of formula (I) may be from 0.7 to 5, preferably from 0.9 to 5.

[0069] The molar ratio of the chlorinating agent to the compound of formula (I) may be from 2 to 10, preferably from 2 to 5.

[0070] In particular, when the sulfur-based agent is chlorosulfonic acid, the molar ratio of the latter to the compound of formula (I) is between 0.9 and 5 and / or the molar ratio of the chlorinating agent to the compound of formula (I) is between 2 and 5.

[0071] In particular, when the sulfur-based agent is sulfuric acid (or oleum), the molar ratio of sulfuric acid (or oleum) to the compound of formula (I) is 0.7-5.

[0072] In particular, when the sulfur-based agent is sulfuric acid (or fuming sulfuric acid), the molar ratio of sulfuric acid (or fuming sulfuric acid) to the compound of formula (I) is 0.9-5, and / or the molar ratio of the chlorinating agent to the compound of formula (I) is 2-10.

[0073] The chlorination step advantageously gives compounds of formula (II): (II) R-(SO2)-NH-(SO2)-Cl It becomes possible to form.

[0074] The process according to the invention may then comprise the step of fluorinating the compound of formula (II).

[0075] The step of fluorinating this compound of formula (I) can be carried out with at least one fluorinating agent, preferably in the presence of at least one organic solvent SO1.

[0076] According to one embodiment, the fluorinating agent is selected from the group consisting of HF (preferably anhydrous HF), KF, AsF3, BiF3, ZnF2, SnF2, PbF2, CuF2, and mixtures thereof, preferably the fluorinating agent is HF, more preferably anhydrous HF.

[0077] In the context of the present invention, the term "anhydrous HF" is understood to mean HF containing less than 500 ppm of water, preferably less than 300 ppm of water, and suitably less than 200 ppm of water.

[0078] The fluorination step is preferably carried out in at least one organic solvent SO1. The organic solvent SO1 preferably has a donor number between 1 and 70, advantageously between 5 and 65. The donor number of the solvent represents the -ΔH value, ΔH being the enthalpy of interaction between the solvent and antimony pentachloride (based on the method described in Journal of Solution Chemistry, vol. 13, No. 9, 1984). The organic solvent SO1 includes in particular esters, nitriles, dinitriles, ethers, diethers, amines, phosphines and mixtures thereof.

[0079] The organic solvent SO1 is preferably selected from the group consisting of methyl acetate, ethyl acetate, butyl acetate, acetonitrile, propionitrile, isobutyronitrile, glutaronitrile, dioxane, tetrahydrofuran, triethylamine, tripropylamine, diethylisopropylamine, pyridine, trimethylphosphine, triethylphosphine, diethylisopropylphosphine, and mixtures thereof. The organic solvent SO1 is in particular dioxane.

[0080] The fluorination step can be carried out at a temperature between 0° C. and the boiling point of the organic solvent SO1 (or the mixture of organic solvents SO1). The fluorination step is preferably carried out at a temperature between 5° C. and the boiling point of the organic solvent SO1 (or the mixture of organic solvents SO1), suitably at a temperature between 20° C. and the boiling point of the organic solvent SO1 (or the mixture of organic solvents SO1).

[0081] The fluorination step (preferably with anhydrous hydrofluoric acid) may be carried out at a pressure P, preferably a pressure of 0 to 16 bar abs.

[0082] The fluorination step is preferably carried out by dissolving the compound of formula (II) in an organic solvent SO1 or in a mixture of organic solvents SO1 prior to the step of reacting with a fluorinating agent, preferably anhydrous HF.

[0083] The mass ratio of the compound of formula (II) to the organic solvent SO1 or to the mixture of organic solvents SO1 is preferably between 0.001 and 10, advantageously between 0.005 and 5.

[0084] According to one embodiment, anhydrous HF is introduced into the reaction medium, preferably into the gaseous reaction medium.

[0085] The weight ratio between the fluorinating agent, preferably anhydrous HF, and the compound of formula (II) used is preferably between 1 and 10, advantageously between 1 and 5.

[0086] The step of reacting with a fluorinating agent, preferably anhydrous HF, can be carried out in closed or open medium. The fluorination step is preferably carried out in open medium, in particular with the evolution of gaseous HCl.

[0087] The fluorination reaction usually leads to the formation of HCl, most of which can be degassed from the reaction medium (as well as excess HF, in the case where the fluorinating agent is HF) for example by entrainment (stripping) with a neutral gas (e.g. nitrogen, helium, argon).

[0088] However, residual HF and / or HCl may be dissolved in the reaction medium, although in the case of HCl the amount is very small since at the operating pressures and temperatures HCl is mainly gaseous.

[0089] The composition obtained at the end of the fluorination step can be stored in an HF resistant container.

[0090] The composition obtained at the end of the fluorination step may contain HF (especially unreacted HF), bis(fluorosulfonyl)imide, a solvent SO1 (e.g., dioxane), and optionally HCl, and / or optionally heavy compounds.

[0091] The process according to the invention preferably comprises a step of distilling the solution obtained after the fluorination step.

[0092] According to one embodiment, the distillation process makes it possible to form and recover the following streams: a first stream F1 comprising HF, preferably at the top of the distillation column, optionally comprising an organic solvent SO1 and / or optionally HCl, in gaseous or liquid form, A second stream F2 comprising bis(fluorosulfonyl)imide, preferably at the bottom of the distillation column, optionally comprising heavy compounds, preferably in liquid form.

[0093] If stream F2 contains heavy compounds, it can be subjected to a further distillation step in a second distillation column to form and recover the following streams: a stream F2-1 comprising bis(fluorosulfonyl)imide, preferably at the top of the distillation column, which is free of heavy compounds and is preferably in liquid form, a stream F2-2 comprising heavy compounds and bisfluorosulfonylimides, preferably at the bottom of the distillation column, which comprises less than 10% by weight, preferably less than 7% by weight, suitably less than 5% of bis(fluorosulfonylimides) contained in the composition obtained after the fluorination step, and which is preferably in liquid form.

[0094] According to one embodiment, the step of distilling the composition obtained from the fluorination step, using two distillation columns, makes it possible to form and recover the following streams: a first stream F1 comprising HF at the top of the first distillation column, optionally also comprising an organic solvent SO1, and / or HCl, in gaseous or liquid form, a second stream F2 comprising the bis(fluorosulfonyl)imide at the bottom of the first distillation column, optionally comprising heavy compounds, preferably in liquid form, This stream F2 is subjected to a distillation process in a second distillation column to form and recover the following streams: a stream F2-1 comprising the bis(fluorosulfonyl)imide at the top of the second distillation column, the stream F2-1 being free of heavy compounds and preferably in liquid form, a stream F2-2 comprising heavy compounds and bis(fluorosulfonyl)imide at the bottom of the second distillation column, the stream F2-2 comprising less than 10% by weight of bis(fluorosulfonyl)imide in the composition obtained after the fluorination step, preferably less than 7%, and suitably less than 5%, and which is preferably in liquid form.

[0095] In the context of the present invention, the term "heavy compounds" is understood to mean organic compounds having a boiling point higher than that of bis(fluorosulfonyl)imide. Heavy compounds may result from cleavage reactions of formula (II), leading, for example, to compounds such as FSO2NH2, and / or from solvolysis reactions, leading to the formation of oligomers.

[0096] According to one embodiment, the step of distilling the composition obtained in the fluorination step makes it possible to form and recover the following streams: a first stream F'1 comprising HF, preferably at the top of the distillation column, optionally comprising an organic solvent SO1 and / or optionally HCl, in gaseous or liquid form, a second stream F'2 comprising the bis(fluorosulfonyl)imide, preferably in liquid form, preferably recovered by side-stream withdrawal, a third stream F'3 comprising heavies and bis(fluorosulfonyl)imide, preferably at the bottom of the distillation column, which comprises less than 10%, preferably less than 7%, and suitably less than 5% of bis(fluorosulfonyl)imide present in the composition obtained in the fluorination step, and which is preferably in liquid form.

[0097] To provide for side draw, the distillation column may have at least one tray.

[0098] The distillation process may be carried out in a pressure range of from 0 to 5 bar abs, preferably from 0 to 3 bar abs, suitably from 0 to 2 bar abs, advantageously from 0 to 1 bar abs.

[0099] The distillation process is at a distillation column bottom temperature in the range of 150° C. to 200° C., preferably 160° C. to 180° C., suitably 165° C. to 175° C., at a pressure of 1 bar abs, or At a distillation column bottom temperature in the range of 30° C. to 100° C., preferably 40° C. to 90° C., and suitably 40° C. to 85° C., at a pressure of 0.03 bar abs, This can be done.

[0100] The distillation process can be carried out in any conventional equipment, which can be a distillation unit including a distillation column, a boiler, and a condenser.

[0101] The distillation tower is at least one packing, for example random and / or structured packing, and / or Trays, such as perforated trays, fixed valve trays, movable valve trays, bubble cap trays, or combinations thereof may include.

[0102] The height of the distillation column usually depends on the nature of the compounds to be separated. Usually, depending on the flow rates used, the distillation column can have any type of diameter (small: up to 1 meter) or large: more than 1 meter).

[0103] The materials of the distillation column, the materials of the internal components (packing and / or trays), the materials of the boiler and / or the materials of the condenser are advantageously selected from corrosion resistant materials, taking into account the possible presence of HF and / or HCl in the composition subjected to the distillation.

[0104] The corrosion resistant material may be selected from enameled steel, nickel, titanium, chromium, graphite, silicon carbide, nickel-based alloys, cobalt-based alloys, chromium-based alloys, steel partially or completely coated with a protective fluoropolymer coating (e.g. PVDF: polyvinylidene fluoride, PTFE: polytetrafluoroethylene, PFA: copolymer of C2F4 and perfluorinated vinyl ether, FEP: copolymer of C2F4 and C3F6, ETFE: copolymer of ethylene and tetrafluoroethylene, or FKM: copolymer of hexafluoropropylene and difluoroethylene).

[0105] The nickel-based alloy is preferably an alloy containing at least 40% by weight of nickel, preferably at least 50% by weight of nickel, based on the total weight of the alloy, examples of which include Inconel®, Hastelloy® or Monel® alloys.

[0106] Streams F1 and F'1 may contain HF, HCl, and an organic solvent SO1 (especially dioxane).

[0107] According to one embodiment, stream F1 comprises 2 to 70% by weight of HF, preferably 5 to 60% by weight of HF, relative to the total weight of stream F1, and 30 to 98% by weight of SO1, preferably 40 to 95% by weight of SO1, relative to the total weight of stream F1.

[0108] According to one embodiment, stream F'1 comprises 2 to 70% by weight of HF, preferably 5 to 60% by weight of HF, relative to the total weight of stream F1, and 30 to 98% by weight of SO1, preferably 40 to 95% by weight of SO1, relative to the total weight of stream F1.

[0109] According to one embodiment, stream F2 comprises from 50 to 100% by weight of bis(fluorosulfonyl)imide, preferably from 70 to 99% by weight of bis(fluorosulfonyl)imide, relative to the total weight of stream F2.

[0110] According to one embodiment, stream F'2 comprises from 50 to 100% by weight of bis(fluorosulfonyl)imide, preferably from 70 to 99% by weight of bis(fluorosulfonyl)imide, relative to the total weight of stream F'2.

[0111] According to one embodiment, stream F2-1 comprises from 50 to 100% by weight of bis(fluorosulfonyl)imide, preferably from 70 to 99% by weight of bis(fluorosulfonyl)imide, relative to the total weight of stream F2-1.

[0112] Thus, the streams comprising the bis(fluorosulfonyl)imide (or the solutions resulting from the fluorination step), such as streams F2, F'2 and / or F-1 described above, are contacted with a lithium base.

[0113] The lithium base may include at least one lithium atom and at least one oxygen atom. Thus, the base may generate water after reacting with the bis(fluorosulfonyl)imide. The base may include or be selected from, for example, lithium hydroxide (LiOH), lithium carbonate (Li2CO3), and mixtures thereof.

[0114] Preferably, the lithium base does not include lithium fluoride.

[0115] The molar ratio of the lithium base to the bis(fluorosulfonyl)imide can be from 0.9 to 1.1, preferably from 1 to 1.05.

[0116] The contacting is carried out in a solvent selected from carbonates, ethers, and nitriles.

[0117] Among the ethers, linear or cyclic ethers such as dimethoxyethane (DME), methyl ether of oligoethylene glycol having 2 to 5 oxyethylene units, dioxolane, dioxane, dibutyl ether, tetrahydrofuran, and mixtures thereof can be mentioned.

[0118] Examples of nitriles include acetonitrile, pyruvonitrile, propionitrile, methoxypropionitrile, dimethylaminopropionitrile, butyronitrile, isobutyronitrile, valeronitrile, pivalonitrile, isovaleronitrile, glutaronitrile, methoxyglutaronitrile, 2-methylglutaronitrile, 3-methylglutaronitrile, adiponitrile, malononitrile, 1,2,6-tricyanohexane, and mixtures thereof. A preferred nitrile is acetonitrile.

[0119] Carbonates, for example cyclic carbonates, include, for example, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, diphenyl carbonate, methyl phenyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, vinylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, or mixtures thereof.

[0120] The solvent used to contact the lithium base with the bis(fluorosulfonyl)imide is preferably a carbonate, more preferably dimethyl carbonate.

[0121] The mass ratio of bis(fluorosulfonyl)imide to the solvent is 10% to 60%, preferably 30% to 40%.

[0122] This step can be carried out by adding the bis(fluorosulfonyl)imide and the lithium base to a solvent. For example, the bis(fluorosulfonyl)imide can be added to a dispersion of the lithium base in the solvent.

[0123] Furthermore, the contacting step may be carried out at a temperature of 0 to 50°C.

[0124] This process thus makes it possible to obtain a mixture comprising lithium bis(fluorosulfonyl)imide and water, which may have a water content of less than or equal to 2%, preferably less than or equal to 3%, preferably less than or equal to 4%, relative to the weight of the mixture.

[0125] The mixture may also include one or more impurities, which may include, for example, lithium fluoride (LiF), lithium sulfate (Li2SO4), and / or lithium chloride (LiCl).

[0126] A filtration step can optionally be performed after the contacting step.

[0127] According to some embodiments, the method according to the invention comprises a step of pervaporating the mixture obtained above. This step makes it possible to reduce the water content in the mixture. Thus, after the end of the step, the mixture containing lithium bis(fluorosulfonyl)imide has a water content of less than 500 ppm, preferably less than 400 ppm, relative to the weight of the mixture. For example, this content can be 100-150 ppm, or 150-200 ppm, or 200-250 ppm, or 250-300 ppm, or 300-350 ppm, or 350-400 ppm, or 400-450 ppm, or 450-500 ppm, relative to the weight of the mixture.

[0128] Additionally or alternatively, the process according to the invention may comprise a step of azeotropic distillation of the mixture previously obtained. This distillation step may be carried out, for example, by evaporation (batch evaporation or falling film evaporation or wiped-film evaporation) or in the presence of a distillation column, preferably at a pressure of 0.01 to 1013 mbar and at a temperature preferably below 100° C., preferably below 50° C. This step also makes it possible to reduce the water content in the mixture. Thus, after the end of this step, the mixture comprising lithium bis(fluorosulfonyl)imide may have a water content of less than or equal to 500 ppm, preferably less than or equal to 400 ppm, relative to the weight of the mixture. For example, this content may be from 100 to 150 ppm, or from 150 to 200 ppm, or from 200 to 250 ppm, or from 250 to 300 ppm, or from 300 to 350 ppm, or from 350 to 400 ppm, or from 400 to 450 ppm, or from 450 to 500 ppm, based on the weight of the mixture.

[0129] Alternatively or in addition to one of the above steps, the process according to the invention comprises a step of diafiltration of the mixture, where the term "mixture" is understood to mean either the mixture obtained after the step of contacting the lithium base with the bis(fluorosulfonyl)imide, or the mixture obtained after pervaporation, or the mixture obtained after the azeotropic distillation step.

[0130] Diafiltration is performed with a nanofiltration membrane.

[0131] According to some embodiments, the nanofiltration membrane may have a cutoff threshold of 80-250 Daltons, preferably 100-200 Daltons, and more preferably 120-180 Daltons.

[0132] The presence of the nanofiltration membrane makes it possible to retain the lithium bis(fluorosulfonyl)imide while allowing water, solvent and various impurities to pass through, so that at the end of this process, first a concentrate is obtained that is enriched in lithium bis(fluorosulfonyl)imide and depleted in water (and impurities), and then a permeate that is depleted in lithium bis(fluorosulfonyl)imide and enriched in water (and impurities).

[0133] According to some embodiments, the diafiltration step is carried out at a pressure between 1 and 60 bar.

[0134] According to some embodiments, the diafiltration step is carried out at a temperature between 5 and 60°C.

[0135] Preferably, a solvent can be added to the concentrate during the diafiltration step. Thus, preferably, the content of lithium bis(fluorosulfonyl)imide in the concentrate is substantially equal to the content of lithium bis(fluorosulfonyl)imide in the mixture entering the diafiltration. Preferably, this solvent is the same as the solvent used in the step of contacting the bis(fluorosulfonyl)imide with the lithium base. Alternatively, this solvent is different from the solvent used in the step of contacting the bis(fluorosulfonyl)imide with the lithium base. In this case, this solvent can be selected from the carbonates, ethers, and nitriles detailed above. The added solvent is preferably water-free or contains a water content of, for example, 50 ppm or less, or 20 ppm or less. Alternatively, a solvent can be added to the mixture before the diafiltration step to perform dilution. In this case, the concentrate can be concentrated to remove some of the solvent.

[0136] During the diafiltration step, the amount of solvent used may be 1 to 20 times the volume of the mixture obtained after the step of contacting the lithium base with the bisfluorosulfonylimide. More specifically, if the process includes a pervaporation or azeotropic distillation step (before diafiltration), the amount of solvent used during the diafiltration step may be 1 to 10 times, preferably 2 to 3 times, the volume of the mixture obtained after the step of contacting the lithium base with the bisfluorosulfonylimide. On the other hand, if the process does not include a pervaporation or azeotropic distillation step, the amount of solvent used during the diafiltration step may be 5 to 20 times, preferably 6 to 8 times, the volume of the mixture obtained after the step of contacting the lithium base with the bisfluorosulfonylimide.

[0137] According to a preferred embodiment, the concentrate obtained after the diafiltration step comprises a water content of less than or equal to 100 ppm, preferably less than or equal to 50 ppm, more preferably less than or equal to 20 ppm, relative to the weight of the concentrate, which may for example be between 1 and 10 ppm, or between 10 and 20 ppm, or between 20 and 30 ppm, or between 30 and 40 ppm, or between 40 and 50 ppm, or between 50 and 60 ppm, or between 60 and 70 ppm, or between 70 and 80 ppm, or between 80 and 90 ppm, or between 90 and 100 ppm, relative to the weight of the concentrate.

[0138] Furthermore, the concentrate obtained after the diafiltration step may have an impurity content of less than 100 ppm lithium fluoride and / or less than 10 ppm lithium chloride and / or less than 50 ppm lithium sulfate.

[0139] Thus, the concentrate may have a lithium bis(fluorosulfonyl)imide content of 10 to 60% by weight, preferably 30 to 40% by weight.

[0140] use The present invention also relates to the use of the lithium bis(fluorosulfonyl)imide obtainable by the process according to the invention in the aforementioned Li-ion batteries, in particular in the electrolyte of Li-ion batteries.

[0141] In particular, such batteries are Li-ion batteries in mobile devices (e.g. mobile phones, cameras, tablets or laptop computers), Li-ion batteries in electric vehicles or Li-ion batteries for storing renewable energy (e.g. photovoltaic or wind energy).

[0142] According to some embodiments, the concentrate obtained after the diafiltration step can be directly used as an electrolyte in a Li-ion battery.

[0143] According to another preferred embodiment, the concentrate obtained after the diafiltration step can be used as an electrolyte in a Li-ion battery after adding one or more components, such as further lithium salts, further solvents and / or additives, as described above.

Claims

1. 1. A method for producing lithium bis(fluorosulfonyl)imide, comprising the steps of: contacting the bis(fluorosulfonyl)imide with a lithium base in a solvent selected from carbonates, ethers, and nitriles to obtain a mixture comprising lithium bis(fluorosulfonyl)imide and water; diafiltration of said mixture through a nanofiltration membrane to obtain first a lithium bis(fluorosulfonyl)imide-enriched, water-depleted concentrate and then a lithium bis(fluorosulfonyl)imide-depleted, water-enriched permeate. A method comprising:

2. 2. The method of claim 1, wherein the solvent is a carbonate, preferably selected from dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, diphenyl carbonate, methyl phenyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, vinylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, or mixtures thereof.

3. 3. The method of claim 1 or 2, wherein the lithium base is selected from lithium hydroxide, lithium carbonate, and mixtures thereof.

4. The method according to any one of claims 1 to 3, wherein the nanofilter membrane has a cut-off threshold of 80 to 250 Daltons, preferably 100 to 200 Daltons, more preferably 100 to 200 Daltons.

5. 5. The method according to claim 1, further comprising a step of pervaporation between the step of contacting the bis(fluorosulfonyl)imide with the lithium base and the step of diafiltration.

6. 6. The process according to claim 1, comprising a step of azeotropic distillation between the step of contacting the bis(fluorosulfonyl)imide with the lithium base and the step of diafiltration.

7. 7. The process according to any one of claims 1 to 6, wherein the water content of the lithium bis(fluorosulfonyl)imide-enriched, water-depleted concentrate is 100 ppm or less, preferably 50 ppm or less, more preferably 20 ppm or less, based on the weight of the concentrate.

8. 8. The method according to claim 1, wherein a solvent is added to the concentrate during the diafiltration step, said solvent being preferably the same as that used in the step of contacting the bis(fluorosulfonyl)imide with the lithium base.

9. The method according to any one of claims 1 to 8, wherein the diafiltration step is carried out at a pressure of from 1 to 60 bar.

10. 1. A method for producing an electrolyte for a Li-ion battery, comprising: Producing lithium bis(fluorosulfonyl)imide as claimed in any one of claims 1 to 9; Producing an electrolyte containing lithium bis(fluorosulfonyl)imide A method comprising:

Images