Process for the preparation of lithium bis(fluorosulfonyl) imide

Description

Field of invention

[0001] The present invention relates to a process for preparing lithium bis(fluorosulfonyl)imide comprising a diafiltration step on a nanofiltration membrane. Technical background

[0002] Sulfonylimide anions, due to their very low basicity, are increasingly used in the field of energy storage in the form of inorganic salts in batteries, or organic salts in supercapacitors or in the field of ionic liquids. With the battery market booming and reducing battery manufacturing costs becoming a major challenge, a large-scale and low-cost synthesis process for this type of anion is required.

[0003] In the specific field of Li-ion batteries, the currently most used salt is LiPF 6 but this salt shows many disadvantages such as limited thermal stability, sensitivity to hydrolysis and therefore lower battery safety. Recently, new salts possessing the FSO 2-< group have been studied and have demonstrated many advantages such as better ionic conductivity and resistance to hydrolysis. One of these salts, LiFSI (LiN(FSO 2 ) 2 ) has shown very interesting properties that make it a good candidate to replace LiPF 6 .

[0004] Most processes for preparing imide salts containing a fluorosulfonyl group involve many steps, resulting in the formation of side products with physical properties such that their removal can be complex and / or require costly purification steps. In addition, following the lithiation reaction to obtain the desired salt, a significant amount of water may be present in the solution comprising 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 for industrial separations, highlighting the need for more efficient separation.

[0006] WO 2015 / 004236 relates to a process for producing a dehydrated liquid mixture for use as a solvent for conductive salts (e.g. LiPF 6 ) in which the water content is reduced, from a starting liquid mixture comprising one, two, three or more organic carbonates in a total amount of 90% by weight or more, based on the total amount of the starting liquid mixture and one, two or more compounds selected from the group consisting of acids with a pKa less than 4 and precursors releasing acids with a pKa less than 4 into the starting liquid mixture by hydrolysis.

[0007] Document FR 3089214 relates to a process for preparing imide salts containing a fluorosulfonyl group, the process comprising a step b) comprising a fluorination step with anhydrous HF, in the presence of at least one water-immiscible organic solvent; a step comprising the 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 enabling dehydration treatment of a non-aqueous electrolytic solution without posing a problem of elution of sodium from the zeolite during dehydration of a non-aqueous electrolytic solution for a lithium battery using a zeolite.

[0009] US 2020 / 0148633 relates to a process for preparing hydrogen bis(fluorosulfonyl)imide comprising contacting sulfonyl fluoride with hexamethyldisilazane in an organic solvent. This document also relates to a process for preparing lithium bis(fluorosulfonyl)imide (LiFSI) by contacting hydrogen bis(fluorosulfonyl)imide with a lithium compound.

[0010] JP 2002001107 relates to a low-silica crystalline faujasite-type zeolite for treating a non-aqueous electrolyte and a method for manufacturing the non-aqueous electrolyte using the zeolite.

[0011] Document CN110436424 A describes a method for preparing lithium bis(fluorosulfonyl)imide comprising contacting the bis(fluorosulfonyl)imide with a lithium base (e.g. lithium hydroxide or lithium carbonate) in a solvent such as dimethyl carbonate, methyl ethyl carbonate, acetonitrile, ethylene glycol dimethyl ether.

[0012] Document JP2014201453 A discloses a process for synthesizing an alkali metal bis(fluorosulfonyl)imide, in particular lithium, in the presence of a solvent selected, inter alia, from carbonates, ethers and nitriles

[0013] There is therefore a real need to provide a process for preparing imide salts containing a fluorosulfonyl group, in particular lithium bis(fluorosulfonyl)imide, which makes it possible to reduce energy consumption but also the quantity of solvent used during the process, compared to existing techniques. In addition, there is a need to provide a process for preparing imide salts containing a fluorosulfonyl group, in particular lithium bis(fluorosulfonyl)imide, which not only makes it possible to avoid lithiation by toxic compounds, such as lithium fluoride, but also to reduce the purification steps of the process. Summary of the invention

[0014] The invention firstly relates to a process for preparing lithium bis(fluorosulfonyl)imide, comprising the following steps: bringing bis(fluorosulfonyl)imide into contact with a lithium base in a solvent chosen from carbonates, ethers and nitriles to obtain a mixture comprising lithium bis(fluorosulfonyl)imide and water; diafiltration of the mixture on a nanofiltration membrane so as to obtain on the one hand a concentrate enriched in lithium bis(fluorosulfonyl)imide and depleted in water and on the other hand a permeate depleted in lithium bis(fluorosulfonyl)imide and enriched in water.

[0015] In 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.

[0016] According to some embodiments, the lithium base is selected from lithium hydroxide, lithium carbonate, and mixtures thereof.

[0017] According to certain embodiments, the nanofiltration membrane has a cutoff threshold of 80 to 250 Daltons, preferably 100 to 200 Daltons and more preferably 120 to 180 Daltons.

[0018] According to certain embodiments, the method comprises a pervaporation step between the step of contacting the bis(fluorosulfonyl)imide with a lithium base and the diafiltration step.

[0019] According to certain embodiments, the method comprises an azeotropic distillation step between the step of contacting the bis(fluorosulfonyl)imide with a lithium base and the diafiltration step.

[0020] According to certain embodiments, the lithium bis(fluorosulfonyl)imide enriched and water-depleted concentrate comprises a water content equal to or less than 100 ppm, preferably equal to or less than 50 ppm, and more preferably equal to or less than 20 ppm relative to the weight of the concentrate.

[0021] According to certain embodiments, solvent is added during the diafiltration step to the concentrate, the solvent preferably being the same as the solvent used in the step of contacting the bis(fluorosulfonyl)imide with a lithium base.

[0022] According to some embodiments, the diafiltration step is carried out at a pressure of 1 to 60 bar.

[0023] The invention also relates to a method for preparing a Li-ion battery electrolyte comprising: the preparation of lithium bis(fluorosulfonyl)imide as described above; the preparation of an electrolyte comprising lithium bis(fluorosulfonyl)imide.

[0024] The present invention makes it possible to meet the need expressed above). More particularly, it provides a process for preparing lithium bis(fluorosulfonyl)imide, which makes it possible to reduce energy consumption but also the quantity of solvent used during the process, compared to existing techniques. In addition, the present invention also provides a process for preparing lithium bis(fluorosulfonyl)imide, which not only makes it possible to avoid lithiation by toxic compounds, such as lithium fluoride, but also to reduce the purification steps of the process.

[0025] This is accomplished by the method of the present invention. More particularly, this method comprises a first step of contacting the bis(fluorosulfonyl)imide with a lithium base (capable of generating water after its reaction with the bis(fluorosulfonyl)imide) in a solvent selected from carbonates, ethers and nitriles, to form a mixture comprising the lithium bis(fluorosulfonyl)imide salt and water. The use of such a lithium base, as well as the fact that the water can be efficiently removed thereafter, makes it possible to avoid the use of toxic lithium salts.

[0026] Then, the diafiltration step on a nanofiltration membrane makes it possible to efficiently remove the remaining amount of water without using methods that increase the energy consumption of the process, nor the consumption of solvent.

[0027] Finally, during this diafiltration step, various impurities present in the mixture obtained after the step of bringing the bis(fluorosulfonyl)imide into contact with the lithium base can also be eliminated, which makes it possible to reduce or even avoid additional purification steps. Detailed description

[0028] The invention is now described in more detail and in a non-limiting manner in the following description. Lithium battery

[0029] A lithium battery comprises at least one electrochemical cell, and preferably a plurality of electrochemical cells. Each electrochemical cell comprises a negative electrode, a positive electrode and an electrolyte interposed between the negative electrode and the positive electrode.

[0030] Each electrochemical cell may also include a separator, in which the electrolyte is impregnated.

[0031] Electrochemical cells can be assembled in series and / or in parallel in the battery.

[0032] By " negative electrode ", we mean the electrode which acts as anode, when the battery delivers current (that is to say when it is in the process of discharging) and which acts as cathode when the battery is in the process of charging.

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

[0034] By " positive electrode ", we mean the electrode which acts as cathode, when the battery delivers current (that is to say when it is in the process of discharging) and which acts as an anode when the battery is in the process of charging.

[0035] The positive electrode typically comprises an electrochemically active material, optionally an electronically conductive material, and optionally a binder.

[0036] By "we mean electrochemically active material » a material capable of reversibly inserting ions.

[0037] By "we mean electronically conductive material » a material capable of conducting electrons.

[0038] The negative electrode of the electrochemical cell may in particular comprise, as electrochemically active material, metallic lithium. This metallic lithium may be in essentially pure form, or in the form of an alloy. Among the lithium-based alloys that may be used, we may cite, for example, lithium-aluminium alloys, lithium-silica alloys, lithium-tin alloys, Li-Zn, Li 3 Bi, Li 3 Cd and Li 3 SB. Mixtures of the above materials may also be used.

[0039] The negative electrode may be in the form of a film or a rod. An example of a negative electrode may include a live lithium film prepared by rolling, between rollers, a lithium foil.

[0040] The positive electrode comprises an electrochemically active material, preferably of the oxide type, and preferably selected from manganese dioxide (MnO 2 ), iron oxide, copper oxide, nickel oxide, lithium-manganese composite oxides (e.g. Li x Mn 2 O 4 or Li x MnO 2 ), lithium-nickel composite oxides (e.g. Li x NiO 2 ), lithium-cobalt composite oxides (e.g. Li x CoO 2 ), lithium-nickel-cobalt composite oxides (e.g. LiNi 1-y Co y O 2 ), lithium-nickel-cobalt-manganese composite oxides (e.g. LiNi x Mn y Co z O 2 with 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 O 2 ), lithium and transition metal composite oxides, lithium-manganese-nickel composite oxides of spinel structure (e.g. Li x Mn 2-y Ni y O 4 ), vanadium oxides, and mixtures thereof.

[0041] Preferably, the positive electrode comprises an electrochemically active material which is a high nickel lithium-nickel-manganese-cobalt composite oxide (LiNi x Mn y Co z O 2 with x+y+z = 1, abbreviated NMC, with x>y and x>z), or a high nickel lithium-nickel-cobalt-aluminum composite oxide (LiNi x' Co y' Al z' with x'+y'+z'=1, abbreviated NCA, with x'>y' and x'>z').

[0042] Particular examples of these oxides are NMC532 (LiNi 0.5 Mn 0.3 Co 0.2 O 2 ), NMC622 (LiNi 0.6 Mn 0.2 Co 0.2 O 2 ) and NMC811 (LiNi 0.8 Mn 0.1 CO 0.1 O 2 ).

[0043] The material of each electrode may also comprise, in addition to the electrochemically active material, an electronically conductive material such as a carbon source, including, for example, carbon black, Ketjen® carbon, Shawinigan carbon, graphite, graphene, carbon nanotubes, carbon fibers (e.g., gas-formed carbon fibers or VGCF), non-powdery carbon obtained by carbonization of an organic precursor, or a combination of two or more of these. Other additives may also be present in the material of the positive electrode, such as lithium salts or inorganic particles such as ceramic or glass, or other compatible active materials (e.g., sulfur).

[0044] The material of each electrode may also include a binder. Non-limiting examples of binders include linear, branched and / or crosslinked polyether polymer binders (e.g., polymers based on poly(ethylene oxide) (PEO), or poly(propylene oxide) (PPO) or a mixture of both (or an EO / PO co-polymer), and optionally including crosslinkable units), water-soluble binders (such as SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), HNBR (hydrogenated NBR), CHR (epichlorohydrin rubber), ACM (acrylate rubber)), or fluoropolymer binders (such as PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), and combinations thereof. Some binders, such as water-soluble ones, may also include a additive such as CMC (carboxymethylcellulose).

[0045] The separator may be a porous polymer film. By way of non-limiting example, the separator may be made of a porous polyolefin film such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, or multilayer structures of the above polymers.

[0046] The electrolyte comprises at least one lithium salt and preferably comprises a plurality of lithium salts.

[0047] In the context of the invention, the lithium salt comprises lithium bis(fluorosulfonyl)imide (LiFSI).

[0048] In some embodiments, the lithium salt consists essentially of, or consists of, lithium bis(fluorosulfonyl)imide (LiFSI).

[0049] In other embodiments, the lithium salt comprises lithium bis(fluorosulfonyl)imide and one or more additional 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 (LiPO 2 F 2 ), and lithium tetrafluoroborate (LiBF 4 ).

[0050] The electrolyte solvent may be selected from ethers, esters, ketones, alcohols, nitriles, carbonates, amides, sulfamides and sulfonamides and mixtures thereof. Preferably, the electrolyte solvent comprises at least one solvent selected from carbonates, ethers and nitriles, and more preferably, the electrolyte solvent comprises at least one carbonate.

[0051] Among the ethers, we can cite linear or cyclic ethers, such as for example dimethoxyethane (DME), methyl ethers of oligoethylene glycols of 2 to 5 oxyethylene units, dioxolane, dioxane, dibutyl ether, tetrahydrofuran, and their mixtures.

[0052] Examples of esters include phosphoric acid esters or sulfite esters. Examples include methyl formate, methyl acetate, methyl propionate, ethyl acetate, butyl acetate, gamma butyrolactone, or mixtures thereof.

[0053] Among the ketones, we can notably cite cyclohexanone.

[0054] Examples of alcohols include ethyl alcohol and isopropyl alcohol.

[0055] 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.

[0056] Examples of carbonates include 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), methyl ethyl carbonate (EMC) (CAS: 623-53-0), diphenyl carbonate (CAS 102-09-0), 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.

[0057] Among the amides, we can cite dimethylformamide, N-methylpyrrolidinone.

[0058] More preferably, the electrolyte solvent is selected from EC, EMC, mixtures of EC and EMC, mixtures of EC and DMC, mixtures of EC and DEC, mixtures of EC and DEC, PC, mixtures of EC, DMC and EMC.

[0059] Optionally, the electrolyte may comprise one or more polar polymers. The polar polymer preferably comprises monomer units derived from ethylene oxide, propylene oxide, epichlorohydrin, epifluorohydrin, trifluoroepoxypropane, acrylonitrile, methacrylonitrile, esters and amides of acrylic and methacrylic acid, vinylidene fluoride, N-methylpyrrolidone and / or polycation or polyanion type polyelectrolytes. When the present electrolyte composition comprises more than one polymer, at least one of these may be crosslinked.

[0060] Additionally, the electrolyte may include one or more additives. The additive(s) may be selected from the group consisting of fluoroethylene carbonate (FEC), vinylene carbonate, 4-vinyl-1,3-dioxolan-2-one, pyridazine, vinyl pyridazine, quinoline, vinyl quinoline, butadiene, sebaconitrile, alkyl disulfides, fluorotoluene, 1,4-dimethoxytetrafluorotoluene, t-butylphenol, di-t-butylphenol, tris(pentafluorophenyl)borane, oximes, aliphatic epoxides, halogenated biphenyls, methacrylic acids, allyl ethyl carbonate, vinyl acetate, divinyl adipate, propanesultone, acrylonitrile, 2-vinylpyridine, maleic anhydride, cinnamate, methyl, phosphonates, vinyl-containing silane compounds, and / or 2-cyanofuran.

[0061] The at least one lithium salt may be present in the electrolyte at a content of 0.1 to 50% relative to the weight of the electrolyte. Process

[0062] The process according to the invention makes it possible to prepare a lithium bis(fluorosulfonyl)imide solution having a low water content and which can be used as a Li-ion battery electrolyte either directly or after addition of salts, solvents and / or additives.

[0063] The method according to the invention comprises a step of bringing the bis(fluorosulfonyl)imide into contact with a lithium base in a solvent, to form a mixture comprising the lithium bis(fluorosulfonyl)imide and water.

[0064] The bis(fluorosulfonyl)imide used in this step can be obtained from a sulfonamide of the following formula (I) by a chlorination step: (I) R-(SO 2 )-NH 2 in which R can be chosen from a fluorine atom, a chlorine atom or a hydroxy group.

[0065] This step can be carried out with at least one sulfur acid and at least one chlorinating agent.

[0066] In addition, this step can be carried out: at a temperature between 30°C and 150°C; and / or with a reaction time between 1 hour and 7 days; and / or at a pressure between 1 bar abs and 20 bar abs.

[0067] According to the invention, the sulfur-containing agent can be chosen from the group consisting of chlorosulfonic acid (ClSO 3 H), sulfuric acid, oleum, and mixtures thereof.

[0068] According to the invention, the chlorinating agent may be chosen from the group consisting of thionyl chloride (SOCl 2 ), oxalyl chloride (COCl) 2 , phosphorus pentachloride (PCl 5 ), phosphonyl trichloride (PCl 3 ), phosphoryl trichloride (POCl 3 ), and mixtures thereof. Preferably, the chlorinating agent is thionyl chloride.

[0069] The chlorination step may be carried out in the presence of a catalyst, such as for example chosen from a tertiary amine (such as methylamine, triethylamine, or diethylmethylamine); pyridine; and 2,6-lutidine.

[0070] The molar ratio between the sulfur acid and the compound of formula (I) may be between 0.7 and 5, preferably between 0.9 and 5.

[0071] The molar ratio between the chlorinating agent and the compound of formula (I) may be between 2 and 10, preferably between 2 and 5.

[0072] In particular, when the sulfur-containing agent is chlorosulfonic acid, the molar ratio between the latter and the compound of formula (I) is between 0.9 and 5, and / or the molar ratio between the chlorinating agent and the compound of formula (I) is between 2 and 5.

[0073] In particular, when the sulfur-containing agent is sulfuric acid (or oleum), the molar ratio between sulfuric acid (or oleum) and the compound of formula (I) is between 0.7 and 5.

[0074] In particular, when the sulfur-containing agent is sulfuric acid (or oleum), the molar ratio between sulfuric acid (or oleum) and the compound of formula (I) is between 0.9 and 5, and / or the molar ratio between the chlorinating agent and the compound of formula (I) is between 2 and 10.

[0075] The chlorination step advantageously makes it possible to form a compound of formula (II): (II) R-(SO 2 )-NH-(SO 2 )-Cl

[0076] The process according to the invention can then comprise a step of fluorination of the compound of formula (II).

[0077] The fluorination of this compound of formula (I) can be carried out with at least one fluorinating agent and preferably in the presence of at least one organic solvent SO1.

[0078] According to one embodiment, the fluorinating agent is chosen from the group consisting of HF (preferably anhydrous HF), KF, AsF 3 , BiF 3 , ZnF 2 , SnF 2 , PbF 2 , CuF 2 , and mixtures thereof, the fluorinating agent preferably being HF, and even more preferably anhydrous HF.

[0079] In the context of the invention, by " Anhydrous HF ", means HF containing less than 500 ppm of water, preferably less than 300 ppm of water, and most preferably less than 200 ppm of water.

[0080] The fluorination step is preferably carried out in at least one organic solvent SO1. The organic solvent SO1 preferably has a donor number of between 1 and 70 and advantageously of between 5 and 65. The donor number of a solvent represents the value -ΔH, ΔH being the enthalpy of the interaction between the solvent and antimony pentachloride (according to the method described in Journal of Solution Chemistry, vol. 13, no. 9, 1984). As organic solvent SO1, mention may in particular be made of esters, nitriles, dinitriles, ethers, diethers, amines, phosphines, and mixtures thereof.

[0081] Preferably, the organic solvent SO1 is 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. In particular, the organic solvent SO1 is dioxane.

[0082] The fluorination step can be carried out at a temperature between 0°C and the boiling temperature of the organic solvent SO1 (or of the mixture of organic solvents SO1). Preferably, the fluorination step is carried out at a temperature between 5°C and the boiling temperature of the organic solvent SO1 (or of the mixture of organic solvents SO1), preferably between 20°C and the boiling temperature of the organic solvent SO1 (or of the mixture of organic solvents SO1).

[0083] The fluorination step, preferably with anhydrous hydrofluoric acid, can be carried out at a pressure P, preferably between 0 and 16 bar abs.

[0084] This fluorination step is preferably carried out by dissolving the compound of formula (II) in the organic solvent SO1, or the mixture of organic solvents SO1, prior to the reaction step with the fluorinating agent, preferably with anhydrous HF.

[0085] The mass ratio between the compound of formula (II) and the organic solvent SO1, or the mixture of organic solvents SO1, is preferably between 0.001 and 10, and advantageously between 0.005 and 5.

[0086] According to one embodiment, anhydrous HF is introduced into the reaction medium, preferably in gaseous form.

[0087] The molar ratio between the fluorinating agent, preferably anhydrous HF, and the compound of formula (II) used is preferably between 1 and 10, and advantageously between 1 and 5.

[0088] The reaction step with the fluorinating agent, preferably anhydrous HF, can be carried out in a closed environment or in an open environment, preferably the fluorination step is carried out in an open environment with in particular the release of HCl in gas form.

[0089] The fluorination reaction typically leads to the formation of HCl, the majority of which can be degassed from the reaction medium (as can excess HF if the fluorinating agent is HF), for example by stripping with a neutral gas (such as nitrogen, helium or argon).

[0090] However, residual HF and / or HCl may be dissolved in the reaction medium. In the case of HCl, the quantities are very small because at working pressures and temperatures, HCl is mainly in gas form.

[0091] The composition obtained at the end of the fluorination step can be stored in an HF-resistant container.

[0092] The composition obtained in the fluorination step may comprise HF (in particular unreacted HF), bis(fluorosulfonyl)imide, solvent SO1 (such as dioxane), and optionally HCl, and / or optionally heavy compounds.

[0093] The process according to the invention may preferably comprise a step of distillation of the solution obtained after the fluorination step.

[0094] According to one embodiment, the distillation step makes it possible to form and recover: a first stream F1 comprising HF, optionally the organic solvent SO1 and / or optionally HCl, preferably at the top of the distillation column, said stream F1 being gaseous or liquid; a second stream F2 comprising bis(fluorosulfonyl)imide, and optionally heavy compounds, preferably at the bottom of the distillation column, said stream F2 preferably being liquid.

[0095] When stream F2 includes heavy compounds, it can be subjected to an additional distillation step in a second distillation column, to form and recover: a stream F2-1 comprising the bis(fluorosulfonyl)imide free of heavy compounds, preferably at the top of the distillation column, said stream F2-1 preferably being liquid, a stream F2-2 comprising the heavy compounds and the bis(fluorosulfonyl)imide, preferably at the bottom of the distillation column, said stream F2-2 containing less than 10% by weight of the bis(fluorosulfonyl)imide contained in the composition obtained after the fluorination step, preferably less than 7% by weight, and preferentially less than 5% by weight, said stream F2-2 preferably being liquid.

[0096] According to one embodiment, the step of distillation of the composition obtained in the fluorination step makes it possible to form and recover, thanks to the use of two distillation columns: a first stream F1 comprising HF, optionally the organic solvent SO1 and / or optionally HCl at the top of the first distillation column, said stream F1 being gaseous or liquid; a second stream F2 comprising bis(fluorosulfonyl)imide, and optionally heavy compounds at the bottom of the first distillation column, said stream F2 preferably being liquid;said stream F2 being subjected to a distillation step in a second distillation column, to form and recover: a stream F2-1 comprising the bis(fluorosulfonyl)imide free of heavy compounds at the top of the second distillation column, said stream F2-1 preferably being liquid, a stream F2-2 comprising the heavy compounds and the bis(fluorosulfonyl)imide, at the bottom of the second distillation column, said stream F2-2 containing less than 10% by weight of the bis(fluorosulfonyl)imide contained in the composition obtained in the fluorination step, preferably less than 7% by weight, and preferentially less than 5% by weight, said stream F2-2 preferably being liquid. ;

[0097] In the context of the invention, the term “ heavy compounds", organic compounds having a boiling point higher than that of bis(fluorosulfonyl)imide. They can result from cleavage reactions of the compound of formula (II) leading for example to compounds such as FSO 2 NH 2 , and / or from solvent degradation reactions leading to the formation of oligomers.

[0098] According to one embodiment, the step of distillation of the composition obtained in the fluorination step makes it possible to form and recover: a first stream F'1 comprising HF, optionally the organic solvent SO1 and / or optionally HCl, preferably at the top of the distillation column, said stream F'1 being gaseous or liquid; a second stream F'2 comprising bis(fluorosulfonyl)imide, preferably recovered by side withdrawal, said stream F'2 preferably being liquid; a third stream F'3 comprising heavy metals and bis(fluorosulfonyl)imide preferably at the bottom of the distillation column, said stream F'3 containing less than 10% by weight of the bis(fluorosulfonyl)imide contained in the composition obtained in the fluorination step, preferably less than 7% by weight, and preferentially less than 5% by weight, said stream F'3 preferably being liquid.

[0099] To carry out side withdrawal, the distillation column may contain at least one tray.

[0100] The distillation step can be carried out at a pressure ranging from 0 to 5 bar abs, preferably from 0 to 3 bar abs, preferentially from 0 to 2 bar abs, and advantageously from 0 to 1 bar abs.

[0101] The distillation step can be carried out: at a temperature at the bottom of the distillation column ranging from 150°C to 200°C, preferably from 160°C to 180°C, and preferentially from 165°C to 175°C, at a pressure of 1 bar abs; or at a temperature at the bottom of the distillation column ranging from 30°C to 100°C, preferably from 40°C to 90°C, and preferentially from 40°C to 85°C, at a pressure of 0.03 bar abs.

[0102] The distillation step can be carried out in any conventional device. This can be a distillation device comprising a distillation column, a boiler and a condenser.

[0103] The distillation column may include: at least one filling such as for example a loose filling and / or a structured filling, and / or trays such as for example perforated trays, trays with fixed flaps, trays with movable flaps, trays with caps, or combinations thereof.

[0104] The height of the distillation column typically depends on the nature of the compounds to be separated. Typically, depending on the flow rates used, the distillation column can have any diameter: small (less than or equal to 1 meter) or high (greater than 1 meter).

[0105] The material of the distillation column, its internal components (packing and / or trays), the boiler, and / or the condenser is advantageously chosen from corrosion-resistant materials, due to the potential presence of HF and / or HCl in the composition subjected to distillation.

[0106] Corrosion-resistant materials may be selected from enameled steels, nickel, titanium, chromium, graphite, silicon carbides, nickel-based alloys, cobalt-based alloys, chromium-based alloys, steels partially or fully coated with a protective coating of fluoropolymer (such as, for example, PVDF: polyvinylidene fluoride, PTFE: polytetrafluoroethylene, PFA: copolymer of C 2 F 4 and perfluorinated vinyl ether, FEP: copolymer of C 2 F 4 and C 3 F 6 , ETFE: copolymer of ethylene and tetrafluoroethylene, or FKM: copolymer of hexafluoropropylene and difluoroethylene).

[0107] Nickel-based alloys are preferably alloys comprising at least 40% by weight of nickel, preferably at least 50% by weight of nickel relative to the total weight of the alloy. Examples include Inconel ®<, Hastelloy ®<, or Monel ®< alloys.

[0108] Streams F1 and F'1 may include HF, HCl, organic solvent SO1 (especially dioxane).

[0109] According to one embodiment, the stream F1 comprises from 2 to 70% by weight of HF, preferably from 5 to 60% by weight of HF relative to the total weight of the stream F1, and from 30% to 98% by weight of organic solvent SO1, preferably from 40% to 95% by weight of SO1, relative to the total weight of the stream F1.

[0110] According to one embodiment, the stream F'1 comprises from 2 to 70% by weight of HF, preferably from 5 to 60% by weight of HF relative to the total weight of the stream F'1, and from 30% to 98% by weight of organic solvent SO1, preferably from 40% to 95% by weight of SO1, relative to the total weight of the stream F'1.

[0111] According to one embodiment, the flux 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 the flux F2.

[0112] According to one embodiment, the flux 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 the flux F'2.

[0113] According to one embodiment, the flux 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 the flux F2-1.

[0114] Thus, the flow comprising the bis(fluorosulfonyl)imide (or the solution resulting from the fluorination step), for example one of the flows F2, F'2 and / or F2-1 described above, is brought into contact with a lithium base.

[0115] The lithium base may comprise at least one lithium atom and at least one oxygen atom. Thus, this base is capable of generating water after its reaction with the bis(fluorosulfonyl)imide. This base may for example comprise or be chosen from lithium hydroxide (LiOH), lithium carbonate (Li 2 CO 3 ), and mixtures thereof.

[0116] Preferably, the lithium base does not comprise lithium fluoride.

[0117] The molar ratio of lithium base to bis(fluorosulfonyl)imide may be 0.9 to 1.1 and preferably 1 to 1.05.

[0118] This contact is carried out in a solvent. The solvent is chosen from carbonates, ethers and nitriles.

[0119] Among the ethers, we can cite linear or cyclic ethers, such as for example dimethoxyethane (DME), methyl ethers of oligoethylene glycols of 2 to 5 oxyethylene units, dioxolane, dioxane, dibutyl ether, tetrahydrofuran, and their mixtures.

[0120] 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.

[0121] Among the carbonates, mention may be made, for example, of cyclic carbonates such as, for example, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, diphenyl carbonate, methyl phenyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, vinylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate or mixtures thereof.

[0122] Preferably, the solvent used for bringing the lithium base into contact with the bis(fluorosulfonyl)imide is a carbonate, and more preferably dimethyl carbonate.

[0123] The mass ratio of bis(fluorosulfonyl)imide to solvent can be 10 to 60%, and preferably 30 to 40%.

[0124] This step can be performed by adding the bis(fluorosulfonyl)imide and lithium base into the solvent. For example, the bis(fluorosulfonyl)imide can be added into a dispersion of the lithium base in the solvent.

[0125] Furthermore, the contacting step can be carried out at a temperature of 0 to 50°C.

[0126] Thus, this step makes it possible to obtain a mixture comprising lithium bis(fluorosulfonyl)imide and water. This mixture may have a water content equal to or greater than 2%, preferably equal to or greater than 3%, preferably equal to or greater than 4% relative to the weight of the mixture.

[0127] This mixture may also include one or more impurities. These impurities may include, for example, lithium fluoride (LiF), lithium sulfate (Li 2 SO 4 ), and / or lithium chloride (LiCl).

[0128] A filtration step can optionally be carried out after the contacting step.

[0129] According to certain embodiments, the method according to the invention comprises a step of pervaporation of the mixture obtained above. This step makes it possible to reduce the water content in the mixture. Thus, at 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, and preferably less than or equal to 400 ppm relative to the weight of the mixture. For example, this content may be 100 to 150 ppm; or 150 to 200 ppm; or 200 to 250 ppm; or 250 to 300 ppm; or 300 to 350 ppm; or 350 to 400 ppm; or 400 to 450 ppm; or 450 to 500 ppm relative to the weight of the mixture.

[0130] Additionally or alternatively, the process according to the invention may comprise a step of azeotropic distillation of the mixture obtained above. This distillation may for example be carried out by evaporation (batch evaporation, or falling film evaporation, or scraped film evaporation) or in the presence of a distillation column, preferably at a pressure of between 0.01 and 1013 mbar and at a temperature preferably lower than 100°C, and more preferably lower than 50°C. This step also makes it possible to reduce the water content in the mixture. Thus, at 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, and preferably less than or equal to 400 ppm relative to the weight of the mixture.For example, this content may be 100 to 150 ppm; or 150 to 200 ppm; or 200 to 250 ppm; or 250 to 300 ppm; or 300 to 350 ppm; or 350 to 400 ppm; or 400 to 450 ppm; or 450 to 500 ppm relative to the weight of the mixture.

[0131] Alternatively or in addition to one of the steps described above, the method according to the invention comprises a step of diafiltration of the mixture. By " blend » here we mean either the mixture obtained after the step of bringing the lithium base into contact with the bis(fluorosulfonyl)imide, or the mixture obtained after the pervaporation step, or the mixture obtained after the azeotropic distillation step.

[0132] Diafiltration is performed on a nanofiltration membrane.

[0133] According to certain embodiments, the nanofiltration membrane may have a cutoff threshold of 80 to 250 Daltons, preferably 100 to 200 Daltons and more preferably 120 to 180 Daltons.

[0134] The presence of the nanofiltration membrane allows on one side to retain the lithium bis(fluorosulfonyl)imide and on the other side to allow water, the solvent and the various impurities to pass through. Thus, at the end of this step we obtain on one side a concentrate enriched in lithium bis(fluorosulfonyl)imide and depleted in water (and impurities) and on the other side a permeate depleted in lithium bis(fluorosulfonyl)imide and enriched in water (and impurities).

[0135] According to certain embodiments, the diafiltration step is carried out at a pressure of 1 to 60 bar.

[0136] According to certain embodiments, the diafiltration step is carried out at a temperature of 5 to 60°C.

[0137] Preferably, during the diafiltration step, solvent may be added to the concentrate. Thus, preferably, the lithium bis(fluorosulfonyl)imide content in the concentrate is essentially equal to the lithium bis(fluorosulfonyl)imide content in the diafiltration inlet mixture. 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, the solvent may be chosen from carbonates, ethers and nitriles as detailed above. Preferably, the added solvent is free of water or has a water content of less than or equal to 50 ppm, or less than or equal to 20 ppm for example.Alternatively, solvent can be added to the mixture before the diafiltration step to effect dilution. In this case, the concentrate can then be concentrated to remove some of the solvent.

[0138] 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 bringing the lithium base into contact with the bis(fluorosulfonyl)imide. More particularly, in the case where the process comprises a pervaporation or azeotropic distillation step (before the diafiltration step), the amount of solvent used during the diafiltration step may be 1 to 10 times, and preferably 2 to 3 times, the volume of the mixture obtained after the step of bringing the lithium base into contact with the bis(fluorosulfonyl)imide. On the other hand, in the case where the process does not include a pervaporation or azeotropic distillation step, the quantity of solvent used during the diafiltration step can be 5 to 20 times, and preferably 6 to 8 times the volume of the mixture obtained after the step of bringing the lithium base into contact with the bis(fluorosulfonyl)imide.

[0139] According to certain preferred embodiments, the concentrate obtained after the diafiltration step comprises a water content equal to or less than 100 ppm, preferably equal to or less than 50 ppm, and more preferably equal to or less than 20 ppm relative to the weight of the concentrate. This content may be for example 1 to 10 ppm; or 10 to 20 ppm; or 20 to 30 ppm; or 30 to 40 ppm; or 40 to 50 ppm; or 50 to 60 ppm; or 60 to 70 ppm; or 70 to 80 ppm; or 80 to 90 ppm; or 90 to 100 ppm relative to the weight of the concentrate.

[0140] In addition, the concentrate obtained after the diafiltration step may comprise an impurity content equal to or less than 100 ppm of lithium fluoride, and / or equal to or less than 10 ppm of lithium chloride, and / or equal to or less than 50 ppm of lithium sulfate.

[0141] Thus, the concentrate may have a lithium bis(fluorosulfonyl)imide content of 10 to 60% by weight, and preferably 30 to 40% by weight. Use

[0142] The present invention also relates to the use of lithium bis(fluorosulfonyl)imide obtained by the process according to the invention, in Li-ion batteries as described above, in particular in Li-ion battery electrolytes.

[0143] In particular, these may be Li-ion batteries from portable devices (e.g. mobile phones, cameras, tablets or laptops), or electric vehicles, or renewable energy storage (such as photovoltaic or wind).

[0144] According to certain embodiments, the concentrate obtained after the diafiltration step can be directly used as a Li-ion battery electrolyte.

[0145] According to other preferred embodiments, the concentrate obtained after the diafiltration step can be used as a Li-ion battery electrolyte after the addition of one or more components such as additional lithium salts, additional solvents and / or additives. These components are as detailed above.

Claims

1. A process for preparing lithium bis(fluorosulfonyl)imide, comprising the following steps of: - contacting of 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 the mixture on a nanofiltration membrane so as to obtain, firstly, a concentrate enriched in lithium bis(fluorosulfonyl)imide and depleted in water and, secondly, a permeate depleted in lithium bis(fluorosulfonyl)imide and enriched in water.

2. The process as claimed in 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. The process as claimed in either of claims 1 and 2, wherein the lithium base is selected from lithium hydroxide, lithium carbonate, and mixtures thereof.

4. The process as claimed in either of claims 1 and 3, wherein the nanofiltration membrane has a cutoff threshold of 80 to 250 dalton, preferably 100 to 200 dalton, and more preferably 120 to 180 dalton.

5. The process as claimed in one of claims 1 to 4, comprising a step of pervaporation between the step of contacting bis(fluorosulfonyl)imide with a lithium base and the diafiltration step.

6. The process as claimed in one of claims 1 to 5, comprising a step of azeotropic distillation between the step of contacting bis(fluorosulfonyl)imide with a lithium base and the diafiltration step.

7. The process as claimed in one of claims 1 to 6, wherein the concentrate enriched in lithium bis(fluorosulfonyl)imide and depleted in water comprises a content of water of equal to or less than 100 ppm, preferably equal to or less than 50 ppm, and more preferably equal to or less than 20 ppm, relative to the weight of the concentrate.

8. The process as claimed in one of claims 1 to 7, wherein solvent is added during the diafiltration step to the concentrate, the solvent preferably being the same as the solvent used in the step of contacting bis(fluorosulfonyl)imide with a lithium base.

9. The process as claimed in one of claims 1 to 8, wherein the diafiltration step is effected at a pressure from 1 to 60 bar.

10. A process for preparing an Li-ion battery electrolyte, comprising: - preparing lithium bis(fluorosulfonyl)imide as claimed in one of claims 1 to 9; - preparing an electrolyte comprising lithium bis(fluorosulfonyl)imide.