LOW SULFAMATE ION ELECTROLYTE

Abstract

The invention relates to an electrolyte comprising: an ionic liquid comprising: a bis(fluorosulfonyl)imide anion, and at least one phosphonium cation of formula (PR1R2R3R4)+, in which each group R1, R2, R3 and R4 independently represents a linear or branched, saturated or unsaturated alkyl group comprising from 1 to 14 carbon atoms, or an alkyl-aryl group comprising from 7 to 14 carbon atoms, or an aryl group comprising from 6 to 10 carbon atoms, the groups R1, R2, R3 and R4 optionally comprising one or more heteroatoms; and a lithium bis(fluorosulfonyl)imide salt; in which the sulfamate ion content is from 0.1 to 3000 ppm by weight. No figure.

Description

Title of the invention: ELECTROLYTE WITH LOW SULFAMATE ION CONTENT Field of invention

[0001] The present invention relates to an electrolyte containing a lithium bis(fluorosulfonyl)imide (LiFSI) salt and an ionic liquid which comprises a bis(fluorosulfonyl)imide (FSI) anion and a phosphonium cation, and having a low sulfamate ion content; as well as to a method for preparing this electrolyte, an electrochemical cell containing this electrolyte, and a battery containing such an electrochemical cell. Technical background

[0002] Lithium (Li) batteries, such as lithium-ion batteries, are commonly used in electric vehicles and mobile and portable devices.

[0003] A lithium-ion battery comprises at least one negative electrode (anode), one positive electrode (cathode), an electrolyte and preferably a separator. The electrolyte consists of a lithium salt dissolved in a solvent which is generally a mixture of organic solvents, in order to have a good compromise between the viscosity and the dielectric constant of the electrolyte.

[0004] Additives can be added to improve the stability of the electrolyte salts or passivation layers. Indeed, the passivation layers formed during the first charge-discharge cycles of a battery are essential for the battery's lifespan. Examples of passivation layers include the passivation of aluminum, which is generally the current collector used at the cathode, and the solid-electrolyte interface (or "Solid Electrolyte Interface" in English, or SEI), which is the layer that is both inorganic and polymeric and forms at the anode / electrolyte and cathode / electrolyte interfaces. The stability of these interfaces is an important issue for improving the lifespan of batteries.

[0005] Another major challenge is improving the overall safety of batteries, particularly for electric vehicle applications. Indeed, the flammability of solvents used in electrolytes is a problem. Different solutions exist to avoid the flammability of the electrolyte, such as the use of fluorinated solvents or ionic liquids.

[0006] The use of fluorinated solvents has the disadvantage of reducing the ionic conductivity of the electrolyte. Ionic liquids do not have this disadvantage, but the use of large quantities of ionic liquid is necessary to make the electrolyte non-flammable. Under these conditions, it is essential to use ionic liquids. presenting good electrochemical stability to obtain batteries with a sufficient lifespan.

[0007] Furthermore, lithium-ion batteries with silicon or silicon-graphite anodes have a significant theoretical capacity (up to 10 times greater than that of graphite). However, the significant volume variations during the insertion and removal of lithium (up to 300%) impose significant constraints on the electrodes and expose the silicon particles to incessant regeneration of the SEI and continuous decomposition of the electrolyte.

[0008] Documents EP 2162942, EP 2549577, WO 2018 / 172696, WO 2019 / 113406, US 10,446,875, EP 3503268 and the article by G. Girard et al. in Phys. Chem. Chem. Phys. 2015, 17, 8706-8713 describe various ionic liquids containing an anion such as FSI and their use in batteries. Document WO 2016 / 049391 describes ionic liquids in other applications.

[0009] It is known to manufacture an ionic liquid containing the FSI anion from potassium bis(fluorosulfonyl)imide (KFSI), as taught in WO 99 / 40025, US 2009 / 0270286, WO 2018 / 172696 and US 2021 / 0194059.

[0010] Document WO 2020 / 241161 describes an electrolyte containing a sulfonylimide compound and an amidosulfuric acid compound.

[0011] Document WO 2019 / 229359 describes a process for manufacturing salts such as LiFSI from bis(fluorosulfonyl)imide (HFSI).

[0012] Document EP 3954651 describes an aqueous composition of LiFSI.

[0013] The article by K. Arano et al. in Journal of The Electrochemical Society, 2020,167(12), 120520 focuses on the electrochemical behavior of silicon in two ionic liquids, including a phosphonium ionic liquid.

[0014] The article by K. Arano et al. in ACS Applied Materials & Interfaces, 2021,13(24), 28281-28294 describes the characterization of the SEI on a silicon anode as a function of the cation of the ionic liquid and the concentration of LiFSI in the electrolyte.

[0015] There is a need to provide a higher performing electrolyte, particularly when used in an electrochemical cell having a silicon-containing anode, producing a more stable SEI and improving battery life. Summary of the Invention

[0016] The invention relates firstly to an electrolyte comprising: • an ionic liquid comprising: • a bis(fluorosulfonyl)imide anion, • and at least one phosphonium cation of formula (PR*R2R3R4) +, in which each group R1, R2, R3 and R4 independently represents a linear or branched, saturated alkyl group or unsaturated, comprising from 1 to 14 carbon atoms, or an alkyl-aryl group comprising from 7 to 14 carbon atoms, or an aryl group comprising from 6 to 10 carbon atoms, the groups R1, R2, R3 and R4 optionally being able to comprise one or more heteroatoms; and • a lithium bis(fluorosulfonyl)imide salt;

[0017] wherein the sulfamate ion content is 0.1 to 3000 ppm by weight.

[0018] In embodiments, the phosphonium cation may be selected from tetraethylphosphonium, tetrabutylphosphonium, trimethyl(propyl)phosphonium, trimethyl(hexyl)phosphonium, trimethyl(2-methylpropyl)phosphonium, triethyl(methyl)phosphonium, triethyl(butyl)phosphonium, triethyl(pentyl)phosphonium, triethyl(hexyl)phosphonium, tributyl(methyl)phosphonium, tri(2-methylpropyl)(methyl)phosphonium, trihexyl(dodecyl)phosphonium, trihexyl(tetradecyl)phosphonium, dimethyldipropylphosphonium, diethyl(methyl)(2-methylpropyl)phosphonium, tributyl-6-hepten-1-ylphosphonium, tetraphenylphosphonium, triphenyl(methyl)phosphonium, trimethyl(methoxymethyl)phosphonium, triethyl(methoxymethyl)-phosphonium, triethyl(2-methoxyethyl)-phosphonium, triethyl[(methylthio)methyl]-phosphonium, triethyl[2-(methylthio)ethyl]-phosphonium, triethyl[2-(ethylthio)ethyl]-phosphonium,tributyl[(methylthio)methyl]-phosphonium, tributyl[2-(methylthio)ethyl]-phosphonium and tributyl[2-(ethylthio)ethyl]-phosphonium. ,

[0019] In embodiments, the sulfamate ion content may be 1 to 1000 ppm, preferably 10 to 300 ppm, by weight.

[0020] In embodiments, the ionic liquid may be present in a weight content of 1 to 90%, preferably 20 to 80%.

[0021] In embodiments, the electrolyte may comprise at least one organic solvent.

[0022] In embodiments, the lithium bis(fluorosulfonyl)imide salt may be present at a concentration of 0.1 to 6 M, preferably 0.2 to 4 M, relative to the total of the ionic liquid and any organic solvents present.

[0023] The invention also relates to a method for preparing an electrolyte as described above, comprising a step of mixing the lithium bis(fluorosulfonyl)imide salt with the ionic liquid.

[0024] In embodiments, the ionic liquid is prepared by: • provision of the bis(fluorosulfonyl)imide compound; and • reaction of bis(fluorosulfonyl)imide with a precursor of the phosphonium cation.

[0025] In embodiments, the bis(fluorosulfonyl)imide has a sulfamic acid content of 1 to 5000 ppm, preferably 500 to 2500 ppm by weight.

[0026] In embodiments, the precursor of the phosphonium cation is a halide of the phosphonium cation, preferably a chloride or bromide of the phosphonium cation.

[0027] In embodiments, the reaction is carried out: • without organic solvent and possibly in the presence of water; and / or • with a molar ratio of bis(fluorosulfonyl)imide / precursor of the onium cation of 0.9 to 1.1, preferably of 1 to 1.05, more preferably of 1 to 1.01; and / or • at a temperature of 10 to 100°C, preferably 20 to 30°C.

[0028] In embodiments, the method comprises the following step: • purification of the reaction mixture after the reaction, preferably by washing, decantation and / or drying.

[0029] The invention also relates to an electrochemical cell comprising a negative electrode, a positive electrode and an electrolyte, in which the electrolyte is as described above.

[0030] In embodiments, the negative electrode comprises an electrochemically active material which comprises silicon, in a mass content which is preferably greater than or equal to 10%, more preferably greater than or equal to 20%.

[0031] The invention also relates to a battery comprising at least one electrochemical cell as described above.

[0032] The present invention makes it possible to meet the need expressed above. More particularly, it provides a more efficient electrolyte, in particular when used in an electrochemical cell having an anode containing silicon, producing a more stable SEI and improving the battery life. This is obtained by combining the LiFSI salt with a phosphonium-FSI type ionic liquid, with a sulfamate ion content in a range of 0.1 to 3000 ppm by weight.

[0033] Advantageously, the ionic liquid can be produced by a relatively inexpensive method. Advantageously, the ionic liquid is produced without carrying out an ion exchange from a reagent such as KFSI or LiFSI, which is expensive and likely to give rise to contamination by cations such as K+ or Li+ . Advantageously, the method for purifying the ionic liquid is simplified compared to the prior art.

[0034] Advantageously, the electrolyte of the invention makes it possible to improve the coulombic efficiency after the formation of the SEI and makes it possible to increase the lifetime of the battery (i.e. to increase the number of cycles making it possible to conserve at least less than 80% of the initial battery capacity) - and this, in particular in the presence of an anode comprising silicon.

[0035] Advantageously, a battery incorporating this electrolyte has increased safety (due to low flammability) and exhibits good performance even at high charging and discharging rates. Detailed description

[0036] The invention is now described in more detail and in a non-limiting manner in the following description.

[0037] Unless otherwise indicated, all percentages and proportions are mass percentages and proportions and all ratios between two quantities are mass ratios. Ionic liquid

[0038] The ionic liquid which is present in the electrolyte of the invention comprises a bis(fluorosulfonyl)imide anion or FSI, of formula N(SO2F)2) and a phosphonium cation of formula (PR'R^R4)*.

[0039] An ionic liquid is a salt having a melting temperature below 100°C and preferably below room temperature (i.e. at a temperature ranging from 15 to 35°C). Thus, by "ionic liquid" is meant a salt, i.e. an ionic compound comprising at least one anion and one cation, present in a liquid form at a temperature of 100°C. An ionic liquid comprises only ionic species (cations and anions), with the exception of the possible presence of non-ionic impurities.

[0040] Thus, the ionic liquid comprises at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight, more preferably at least 99% by weight, even more preferably at least 99.5% by weight, even more preferably greater than or equal to 99.9% by weight, of FSI anion and phosphonium cation.

[0041] In some embodiments, several phosphonium cations may be present, but preferably, only one phosphonium cation is present. In the present text, any reference to the phosphonium cation in the singular must be understood as a reference to all phosphonium cations, when several are present.

[0042] In embodiments, the ionic liquid may comprise one or more other anions and / or one or more other cations.

[0043] In embodiments, the ionic liquid may comprise, in addition to the flag FSI, at least one other anion selected from F, Cf, Br, I, NO3, M(R*)4, A(R*)6, R2O2, [R2ONZ'], [R2YOCZ2Z3], 4,5-dicyano-1,2,3-triazolate, 3,5- bis(RF)-l,2,4-triazolate, tricyanomethanide, pentacyanocyclopentadienide, pentakis(trifluoromethyl)cyclopentadienide; in which: • M is B, Al, Ga or Bi; • A is P, As or Sb; • R1 is a halogen; • R2 represents H, F, an alkyl, alkenyl, aryl, arylalkyl, alkylaryl, arylalkenyl, alkenylaryl, dialkylamino, alkoxy or thioalkoxy group, each having from 1 to 18 carbon atoms and being unsubstituted or substituted by one or more oxa, thia, or aza substituents, and in which one or more hydrogen atoms are optionally replaced by a halogen in a proportion of 0 to 100%, and which may optionally be part of a polymer chain; • Y representing C, SO, S=NCN, S=C(CN)2, POR2, P(NCN)R2, P(C(CN)2)R2, an alkyl, alkenyl, aryl, arylalkyl, alkylaryl, arylalkenyl, alkenylaryl group having from 1 to 18 carbon atoms and optionally substituted by one or more oxa, thia or aza substituents; a dialkylamino group N(R*)2; • Z1 to Z3 independently represent R2, R2YO or CN, this group optionally being part of a polymer chain; • RF is a perfluorinated or partially fluorinated alkyl chain containing from 1 to 8 carbon atoms, or a phenyl, substituted phenyl, pyridyl or substituted pyridyl group.

[0044] In the general formula of the phosphonium cation (PR'R^R4)4^, each group (R1, R2, R3 and R4) independently represents a linear or branched, saturated or unsaturated alkyl group comprising from 1 to 14 carbon atoms, or an alkyl-aryl group comprising from 7 to 14 carbon atoms, or an aryl group comprising from 6 to 10 carbon atoms, the groups R1, R2, R3 and R4 optionally being able to comprise one or more heteroatoms.

[0045] The preferred alkyl groups are groups containing from 1 to 12 carbon atoms, in particular from 1 to 6 carbon atoms.

[0046] The heteroatoms, when present, may be chosen in particular from O, N, S, P and Si, and preferably from O and S.

[0047] The groups R1, R2, R3 and R4 may in particular be chosen from the group consisting of the groups methyl, ethyl, propyl, 2-methylpropyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, phenyl, methoxymethyl, 2-methoxyethyl, ethoxymethyl, 2-ethoxyethyl, methylthiomethyl, 2-methylthioethyl, ethylthiomethyl, 2-ethylthioethyl, and alkenyl, especially heptenyl.

[0048] In some embodiments, at least two groups among R1, R2, R3 and R4 are identical.

[0049] In certain embodiments, at least three groups among R1, R2, R3 and R4 are identical. Preferably, the at least three identical groups are chosen from alkyl groups comprising from 1 to 6 carbon atoms and phenyl groups.

[0050] Preferred phosphonium cations are: tetraethylphosphonium, tetrabutylphosphonium, trimethyl(propyl)phosphonium, trimethyl(hexyl)phosphonium, trimethyl(2-methylpropyl)phosphonium, triethyl(methyl)phosphonium, triethyl(butyl)phosphonium, triethyl(pentyl)phosphonium, triethyl(hexyl)phosphonium, tributyl(methyl)phosphonium, tri(2-methylpropyl)(methyl)phosphonium, trihexyl(dodecyl)phosphonium, trihexyl(tetradecyl)phosphonium, dimethyldipropylphosphonium, diethyl(methyl)(2-methylpropyl)phosphonium, tributyl-6-hepten-1-ylphosphonium, tetraphenylphosphonium, triphenyl(methyl)phosphonium, trimethyl(methoxymethyl)phosphonium, triethyl(methoxymethyl)-phosphonium, triethyl(2-methoxyethyl)-phosphonium, triethyl[(methylthio)methyl]-phosphonium, triethyl[2-(methylthio)ethyl]-phosphonium, triethyl[2-(ethylthio)ethyl]-phosphonium, tributyl[(methylthio)methyl]-phosphonium,tributyl[2-(methylthio)ethyl]-phosphonium and tributyl[2-(ethylthio)ethyl]-phosphonium. , Electrolyte

[0051] The electrolyte of the invention comprises the ionic liquid described above and a LiFSI salt. This electrolyte may optionally further comprise one or more additional lithium salts, one or more organic solvents, one or more polar polymers and / or one or more additives. In certain embodiments, the electrolyte consists essentially of, or even consists of, the ionic liquid, the LiFSI salt, the additional lithium salt(s) (optionally), the organic solvent(s) (optionally) and the additive(s) (optionally).

[0052] Advantageously, the ionic liquid is present in the electrolyte in an amount of 1 to 90% by weight, preferably 20 to 80% by weight, more preferably 40 to 80% by weight, relative to the total weight of the electrolyte. In embodiments, the electrolyte may comprise 1 to 10%, or 10 to 20%, or 20 to 30%, or 30 to 40%, or 40 to 50%, or 50 to 60%, or 60 to 70%, or 70 to 80%, or 80 to 90%, by weight, of ionic liquid (relative to the total weight of the electrolyte).

[0053] The LiFSI salt is present in the electrolyte at a concentration of 0.1 to 6 M, preferably 0.2 to 4 M, relative to the total of the ionic liquid and organic solvents (when present). In embodiments, the concentration of LiFSI salt in the electrolyte may be 0.1 to 0.2 M, or 0.2 to 0.5 M, or 0.5 to 1 M, or 1 to 2 M, or 2 to 3 M, or 3 to 4 M, or 4 to 5 M, or 5 to 6 M.

[0054] The organic solvent(s) are preferably aprotic solvents.

[0055] The organic solvent(s) may be chosen from the non-exhaustive list following: ethers, carbonic acid esters, cyclic carbonate esters, aliphatic carboxylic acid esters, aromatic carboxylic acid esters, cyclic esters, fluorinated solvents (including fluorinated ethers, fluorinated esters, fluorinated orthoformates, fluorinated carbonates, fluorinated phosphates, fluorinated phosphites and fluorinated sulfates), phosphoric acid esters, nitriles, amides, sulfur compounds, alcohols, sulfoxides and mixtures thereof.

[0056] Among the ethers, mention may be made of linear or cyclic ethers, such as, for example, ethylene glycol dimethyl ether (1,2-dimethoxyethane or DME), ethylene glycol diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2,6-dimethyltetrahydrofuran, tetrahydropyran, a crown ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,4-dioxane and 1,3-dioxolane.

[0057] Among the carbonic acid esters, mention may be made of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, diphenyl carbonate and methyl phenyl carbonate.

[0058] Among the cyclic carbonate esters, mention may be made of ethylene carbonate, propylene carbonate, ethylene 2,3-dimethylcarbonate, butylene carbonate, vinylene carbonate and ethylene 2-vinylcarbonate.

[0059] Among the aliphatic carboxylic acid esters, mention may be made of methyl formate, methyl acetate, methyl propionate, ethyl acetate, propyl acetate, butyl acetate and amyl acetate.

[0060] Among the aromatic carboxylic acid esters, mention may be made of methyl benzoate and ethyl benzoate.

[0061] Among the cyclic esters, mention may be made of γ-butyrolactone, γ-valerolactone and δ-valerolactone.

[0062] Among the fluorinated solvents, mention may be made of 1,1,2,2-tetrafluoroethyl-methyl ether, 1,1,2,2-tetrafluoroethyl-ethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, hexafluoroisopropyl-methyl ether, 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl-methyl ether, 1,1,2,3,3,3-hexafluoropropyl-methyl ether, 1,1,2,3,3,3-hexafluoropropyl-ethyl ether, 1,1,1,3,3,3-hexafluoro-2-(2,2,2-trifluoroethoxy)propane, bis(2,2,2- trifluoroethyl) ether, l,l,2,2,-tetrafluoroethyl-2,2,2-trifluoroethyl ether, methoxynonafluorobutane, ethoxynonafluorobutane, l,2-(l,l,2,2-tetrafluoroethoxy)-ethane, 2,2,3,3-tetrafluoro-l,4-dimethoxybutane, 2-(2-ethoxyethyl)-1,1,1,-trifluoroethane, 2-(2-(2,2-difluoroethoxy)ethoxy)-l,l-difluoroethane, 2-(2-(2,2-difluoroethoxy)ethoxy)-1,1,1 -trifluoroethane,-1,1,1 -trifluoro-2-(2-(2-trifluoroethoxy)ethoxy) ethane, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, 2,2-difluoroethyl propionate, 3,3-difluoropropyl acetate, 3,3-difluoropropyl propionate, ethyl 4,4-difluorobutanoate, difluoroethyl formate, trifluoroethyl formate, 2,2,2-trifluoroethyl orthoformate, 4-fluoro-1,3-dioxolan-2-one (F1EC), 4,5-difluoro-1,3-dioxolan-2-one (F2EC), ethyl-(1-fluoroethyl)carbonate (F1DEC), 1-fluoroethyl (2,2,2-trifluoroethyl)carbonate (F4DEC), bis(2,2,2-trifluoroethyl)carbonate (BFEC), 2,2,2-trifluoroethyl-methyl carbonate (F3EMC), trifluoropropylene carbonate, monofluoro dimethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, 2,2-difluoroethyl methyl carbonate, trifluoroethyl ethyl carbonate, methyl hexafluoro-i-propyl carbonate, ethyl hexafluoro-i-propyl carbonate, bis(trifluoroethyl) carbonate and propyl trifluoroethyl carbonate.

[0063] Among the phosphoric acid esters, mention may be made of trimethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate and triethyl phosphate.

[0064] Among the nitriles, mention may be made of acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, 2-methylglutaronitrile, valeronitrile, butyronitrile and isobutyronitrile; as well as aromatic nitriles such as benzonitrile and tolunitrile, nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1,H)-pyrimidinone and 3-methyl-2-oxazolidinone.

[0065] Among the amides, mention may be made of N-methylformamide, N-ethylformamide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidinone and N-vinylpyrrolidone.

[0066] Among the sulfur compounds, mention may be made of dimethylsulfone, ethylmethylsulfone, diethylsulfone, sulfolane, 3-methylsulfolane and 2,4-dimethylsulfolane.

[0067] Among the alcohols, mention may be made of ethylene glycol, propylene glycol, ethylene glycol monomethyl ether and ethylene glycol monoethyl ether.

[0068] Among the sulfoxides, mention may be made of dimethyl sulfoxide, methyl ethyl sulfoxide and diethyl sulfoxide.

[0069] All of these solvents cited individually can be used alone or in combination.

[0070] The content of organic solvent(s) in the electrolyte may be from 10 to 99% by weight.

[0071] As indicated above, the electrolyte may also optionally comprise one or more additional lithium salts, other than LiFSI. As non-limiting examples, the additional lithium salt(s) may be selected from LiPF6 (lithium hexafluorophosphate), LiTDI (lithium 2-trifluoromethyl-4,5-dicyanoimidazolate), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide (LiFTFSI), LiPOF2, lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiB(C2O4)2), lithium difluoro(oxalato)borate (LiF2B(C2O4)2), lithium difluoro(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, lithium tris(oxalato)phosphate, LiBF4, LiNO3 and LiC104.

[0072] The total content of additional lithium salt(s) in the electrolyte is preferably less than or equal to 1.5M, preferably less than or equal to 0.5M. This content may in particular be from 0.05M to 1.5M, or from 0.1M to 1M, or from 0.2M to 0.5M.

[0073] The electrolyte may optionally comprise one or more polar polymers. A 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 polyelectrolytes of polycation or polyanion type. When the electrolyte comprises more than one polymer, at least one of these may be crosslinked.

[0074] The electrolyte may optionally comprise one or more additives. The additive(s) may be selected from the group consisting of nitrogen compounds such as, for example, pentafluorophenyl isocyanate (PFPS) or dimethylacrylamide (DMAA), 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, borane compounds such as tris(pentafluorophenyl)borane or lithium fluoromalonato(difluoro)borate, oximes, aliphatic epoxides, halogenated biphenyls, methacrylic acids, allyl ethyl carbonate, vinyl acetate, divinyl adipate, compounds sulfur compounds such as propanesultone (PS), prop-1-ene 1,3 sultone (PES), ethylene sulfite, butanesultone, methyl methanesulfonate, sulfolene, or 1,3-propanediocyclic sulfate, acrylonitrile, 2-vinylpyridine, maleic anhydride, methyl cinnamate, anhydrides such as succinic anhydride, phosphonates, silane compounds such as monomethoxy trimethyl silane, dimethoxy dimethyl silane, trimethoxy methyl silane (TMMS), vinyl, tris(2-methoxyethoxy) silane (VTMS), or other vinyl-containing silane compounds, and / or 2-cyanofuran.

[0075] The total content of additive(s) in the electrolyte is preferably less than or equal to 10% by weight relative to the total weight of the electrolyte composition, preferably less than or equal to 5%. This content may in particular be from 0.1 to 10%, or from 0.2 to 5%, or from 0.5 to 2%, by weight.

[0076] The electrolyte may have a sulfamate ion (NH2SO3) content of less than or equal to 3000 ppm; less than or equal to 2000 ppm; less than or equal to 1000 ppm; less than or equal to 500 ppm; less than or equal to 300 ppm; less than or equal to 200 ppm; less than or equal to 100 ppm; less than or equal to 50 ppm; less than or equal to 20 ppm (by weight).

[0077] The electrolyte may in particular comprise a sulfamate ion content of 0.1 to 3000 ppm, preferably of 0.5 to 2000 ppm, more preferably of 1 to 1000 ppm, more preferably of 10 to 300 ppm (by weight).

[0078] The electrolyte according to the invention may in particular comprise a sulfamate ion content of 0.1 to 10 ppm; 10 to 50 ppm, 50 to 100 ppm; 100 to 200 ppm; 200 to 300 ppm; 300 to 500 ppm; 500 to 1000 ppm; 1000 to 2000 ppm; 2000 to 3000 ppm (by weight).

[0079] The sulfamate ion content indicated above can allow optimal performance of the electrolyte to be obtained.

[0080] Advantageously, the electrolyte comprises F ions, in an amount less than or equal to 500 ppm, preferably less than or equal to 200 ppm, preferably less than or equal to 100 ppm, in some cases less than or equal to 50 ppm or 20 ppm by weight. The F ions may be essentially absent or be present in an amount greater than or equal to 0.1 ppm, 1 ppm, 2 ppm, 5 ppm or 10 ppm by weight. For example, the F ions may be present in an amount of 0.1 to 500 ppm, or 1 to 200 ppm, or 2 to 100 ppm, or 5 to 50 ppm, or 10 to 20 ppm, by weight.

[0081] Advantageously, the electrolyte comprises Cf ions, in an amount less than or equal to 500 ppm, preferably less than or equal to 200 ppm, preferably less than or equal to 100 ppm, in some cases less than or equal to 50 ppm or 20 ppm by weight. The Cf ions may be essentially absent or be present in an amount greater than or equal to 0.1 ppm, 1 ppm, 2 ppm, 5 ppm or 10 ppm by weight. For example, the Cf ions may be present in an amount of 0.1 to 500 ppm, or 1 to 200 ppm, or 2 to 100 ppm, or 5 to 50 ppm, or 10 to 20 ppm, by weight.

[0082] Advantageously, the electrolyte comprises SO42 ions, in an amount less than or equal to 500 ppm, preferably less than or equal to 200 ppm, preferably less than or equal to 100 ppm, in some cases less than or equal to 50 ppm or 20 ppm by weight. The SO42 ions may be essentially absent or be present in an amount greater than or equal to 0.1 ppm, 1 ppm, 2 ppm, 5 ppm or 10 ppm by weight. For example, the SO42 ions may be present in an amount of 0.1 to 500 ppm, or 1 to 200 ppm, or 2 to 100 ppm, or 5 to 50 ppm, or 10 to 20 ppm, by weight.

[0083] Advantageously, the electrolyte comprises Na+ ions, in an amount less than or equal to 100 ppm, preferably less than or equal to 50 ppm, preferably less than or equal to 20 ppm, in some cases less than or equal to 10 ppm or 5 ppm by weight. The Na+ ions may be essentially absent or be present in an amount greater than or equal to 0.1 ppm by weight. For example, the Na+ ions may be present in an amount of 0.1 to 100 ppm, or 0.1 to 50 ppm, or 0.1 to 20 ppm, or 0.1 to 10 ppm, or 0.1 to 5 ppm, by weight.

[0084] Advantageously, the electrolyte comprises K+ ions, in an amount less than or equal to 100 ppm, preferably less than or equal to 50 ppm, preferably less than or equal to 20 ppm, in some cases less than or equal to 10 ppm or 5 ppm by weight. The K+ ions may be essentially absent or be present in an amount greater than or equal to 0.1 ppm by weight. For example, the K+ ions may be present in an amount of 0.1 to 100 ppm, or 0.2 to 50 ppm, or 0.3 to 20 ppm, or 0.4 to 10 ppm, or 0.5 to 5 ppm, by weight.

[0085] Advantageously, the electrolyte comprises alkali and alkaline earth ions (excluding Li+ ions), in a total amount of less than or equal to 100 ppm, preferably less than or equal to 50 ppm, preferably less than or equal to 20 ppm, in some cases less than or equal to 10 ppm or 5 ppm by weight. The alkali and alkaline earth ions (excluding Li+ ions) may be substantially absent or be present in an amount greater than or equal to 0.1 ppm by weight. For example, the alkali and alkaline earth ions (excluding Li+ ions) may be present in a total amount of 0.1 to 100 ppm, or 0.2 to 50 ppm, or 0.3 to 20 ppm, or 0.4 to 10 ppm, or 0.5 to 5 ppm, by weight.

[0086] The ion content in the electrolyte can be analyzed by ion chromatography and / or inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma atomic emission spectrometry (ICP-AES) and / or X-ray fluorescence spectrometry (XRF).

[0087] The electrolyte may have a total water content of less than or equal to 3% by weight, preferably less than or equal to 2%, or 1%, or 1000 ppm, or 500 ppm or 200 ppm by weight. The electrolyte may have a total water content of greater than or equal to 0.1 ppm, preferably greater than or equal to 1 ppm, or 5 ppm, or 10 ppm, by weight. The electrolyte may have a total water content of 0.1 ppm to 3%, preferably 1 ppm to 1000 ppm, or 5 ppm to 500 ppm, or 10 ppm to 200 ppm by weight. Preparation of the electrolyte

[0088] The electrolyte can be prepared by mixing the LiFSI salt with the ionic liquid and with the other optional constituents (organic solvents, additional salts, additives).

[0089] In this mixing, the ionic liquid may be incorporated in an amount of 1 to 90% by weight, preferably 20 to 80% by weight, more preferably 40 to 80% by weight, relative to all of the constituents. In embodiments, the ionic liquid may be incorporated in an amount of 1 to 10%, or 10 to 20%, or 20 to 30%, or 30 to 40%, or 40 to 50%, or 50 to 60%, or 60 to 70%, or 70 to 80%, or 80 to 90%, by weight (relative to all of the constituents).

[0090] In this mixing, the LiFSI salt may be incorporated at a concentration of 0.1 to 6 M, preferably 0.2 to 4 M, relative to the total of the ionic liquid and organic solvents (when present). In embodiments, the LiFSI salt may be incorporated at a concentration of 0.1 to 0.2 M, or 0.2 to 0.5 M, or 0.5 to 1 M, or 1 to 2 M, or 2 to 3 M, or 3 to 4 M, or 4 to 5 M, or 5 to 6 M, relative to the total of the ionic liquid and organic solvents (when present).

[0091] During this mixing, the additional lithium salt(s) may be incorporated in a content less than or equal to 10% by weight relative to all of the constituents, preferably less than or equal to 5%. This content may in particular be from 0.1 to 10%, or from 0.2 to 5%, or from 0.5 to 2%, by weight.

[0092] During this mixing, the additive(s) may be incorporated in a content less than or equal to 10% by weight relative to all of the constituents, preferably less than or equal to 5%. This content may in particular be from 0.1 to 10%, or from 0.2 to 5%, or from 0.5 to 2%, by weight.

[0093] The ionic liquid can be prepared by the following method: • optionally, prior synthesis of the bis(fluorosulfonyl)imide compound or HFSI, of formula NH(SO2F)2; • reaction of HFSI with a phosphonium cation precursor to obtain a reaction mixture comprising the bis(fluorosulfonyl)imide anion; • optionally, purification of the reaction mixture.

[0094] HFSI can be synthesized in particular by fluorination of a chlorinated compound, of formula NH(SO2R)(SO2R') with R and R' independently representing an atom of halogen (F or Cl), at least one of the two being a chlorine atom. Preferably, the chlorinated compound is (bis(chlorosulfonyl)imide).

[0095] The fluorination is carried out by contacting the chlorinated compound with a fluorinating agent, which is preferably selected from the group consisting of HF (preferably anhydrous HF), KF, AsF3, BiF3, ZnF2, SnF2, PbF2, CuF2, and mixtures thereof, the fluorinating agent being more preferably HF, and even more preferably anhydrous HF. By "anhydrous HF" is meant HF containing less than 500 ppm of water, preferably less than 300 ppm of water, more preferably less than 200 ppm of water.

[0096] The fluorination is preferably carried out in at least one organic solvent SOL. The organic solvent SOI preferably has a donor number between 1 and 70 and advantageously between 5 and 65. The donor index of a solvent represents the value -AH, AH 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 SOI, mention may in particular be made of esters, nitriles, dinitriles, ethers, diethers, amines, phosphines, and mixtures thereof.

[0097] Preferably, the organic SOI solvent 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 SOI solvent is dioxane.

[0098] The fluorination can be carried out at a temperature between 0°C and the boiling temperature of the organic SOI solvent (or of the mixture of organic SOI solvents). Preferably, step b) is carried out at a temperature between 5°C and the boiling temperature of the organic SOI solvent (or of the mixture of organic SOI solvents), preferably between 20°C and the boiling temperature of the organic SOI solvent (or of the mixture of organic SOI solvents).

[0099] Fluorination, preferably with anhydrous hydrofluoric acid, can be carried out at a pressure between 0 and 16 bar abs.

[0100] Fluorination is preferably carried out by dissolving the chlorinated compound in the SOI organic solvent, or the SOI organic solvent mixture, prior to reaction with the fluorinating agent (preferably anhydrous HF).

[0101] The mass ratio between the chlorinated compound and the organic SOI solvent, or the mixture of organic SOI solvents, is preferably between 0.001 and 10, and advantageously between 0.005 and 5.

[0102] According to one embodiment, the anhydrous HF is introduced into the reaction medium, preferably in gaseous form.

[0103] The molar ratio between the fluorinating agent, preferably anhydrous HF, and the chlorinated compound is preferably between 1 and 10, and advantageously between 1 and 5.

[0104] The reaction with the fluorinating agent, preferably anhydrous HF, can be carried out in a closed medium or in an open medium, preferably in an open medium.

[0105] 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).

[0106] 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 the HCl is mainly in gas form.

[0107] The product obtained at the end of the fluorination reaction can be stored in a container resistant to HF.

[0108] The product obtained at the end of the fluorination reaction may comprise HF (in particular unreacted HF), the chlorinated compound, the SOI solvent (such as, for example, dioxane), and optionally HCl, and / or optionally heavy compounds.

[0109] After the reaction, the HFSI can be purified, in particular by one or more distillation steps.

[0110] According to one embodiment, the distillation makes it possible to form and recover: • a first stream Fl comprising HF, optionally the organic solvent SOI and / or optionally HCl, preferably at the top of the distillation column, said stream Fl being gaseous or liquid; • a second stream F2 comprising HFSI, and possibly heavy compounds, preferably at the bottom of the distillation column, said stream F2 preferably being liquid.

[0111] When stream F2 comprises 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 HFSI 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 HFSI, preferably at the bottom of the distillation column, said stream F2-2 containing less than 10% by weight of HFSI contained in the composition obtained in step b), preferably less than 7% by weight, and preferentially less than 5% by weight, said stream F2-2 preferably being liquid.

[0112] By "heavy compounds" is meant organic compounds having a boiling point higher than that of HFSI. They can result from cleavage reactions of the chlorinated compound leading for example to compounds such as FSO2NH2, and / or from solvent degradation reactions leading to the formation of oligomers.

[0113] According to one embodiment, the distillation step makes it possible to form and recover: • a first stream F' 1 comprising HF, optionally the organic solvent SOI 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 the HFSI, preferably recovered by lateral withdrawal, said stream F'2 preferably being liquid; • a third stream F'3 comprising heavy compounds and HFSI, preferably at the bottom of the distillation column, said stream F'3 containing less than 10% by weight of HFSI contained in the composition obtained in step b), preferably less than 7% by weight, and preferentially less than 5% by weight, said stream F'3 preferably being liquid.

[0114] To carry out the side withdrawal, the distillation column may contain at least one tray.

[0115] 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.

[0116] The distillation step can be carried out in any conventional device. It can be a distillation device comprising a distillation column, a boiler and a condenser. The distillation column can comprise at least one packing such as for example a bulk packing and / or a structured packing, and / or trays such as for example perforated trays, trays with fixed valves, trays with movable valves, trays with caps, or combinations thereof.

[0117] At the end of the purification, the HFSI can be recovered with high purity. The use of high purity HFSI advantageously makes it possible to prepare a high purity ionic liquid, avoiding complex subsequent purification steps.

[0118] The product collected (and / or used for the reaction with the phosphonium cation precursor) thus preferably comprises at least 95% by weight of HFSI, more preferably at least 98% by weight, at least 99% by weight, at least 99.5% by weight or even at least 99.8% by weight of HFSI.

[0119] The product collected (and / or used for the reaction with the phosphonium cation precursor) preferably has a sulfamic acid content of less than or equal to 5000 ppm, preferably less than or equal to 4000 ppm, less than or equal to 3000 ppm, less than or equal to 2500 ppm, or even less than or equal to 2000 ppm, by weight. In some cases, the sulfamic acid may be essentially absent, or present in a content of at least 1 ppm by weight. The sulfamic acid content may be in particular 1 to 5000 ppm, 10 to 4000 ppm, 100 to 3000 ppm, 500 to 2500 ppm by weight. It may be for example 1 to 10 ppm, 10 to 50 ppm, 50 to 100 ppm, 100 to 200 ppm, 200 to 500 ppm, 500 to 1000 ppm, 1000 to 2000 ppm, 2000 to 3000 ppm, 3000 to 4000 ppm or 4000 to 5000 ppm by weight. The sulfamic acid content may be determined by ion chromatography (expressed as NH2SO3).

[0120] For ion chromatography measurements, it is possible to use the “ICS 5000” device from THERMO. It has two analytical channels, one of which is dedicated to the analysis of anions, and is made up of: • an ultra-pure water supply (18.2 Mohm) via a double piston pump; • an automatic eluent generator (EGC); • a valve with injection loop (volume = 25 microliters); • a pre-column (AG19, T=35°C) and a separation column (AS 19, T=20°C); • a suppressor (AERS 62 mA); • a conductivity meter for peak detection.

[0121] The eluent used may be a KOH solution at a concentration of 25 mmol / L and may have a flow rate of 1 mL / min.

[0122] By “phosphonium cation precursor” is meant any compound capable of reacting with HFSI to give the FSI anion associated with the phosphonium cation.

[0123] In particular, the phosphonium cation precursor may be a phosphonium cation halide, i.e., the compound AX, in which A represents a halogen atom and X+ represents the phosphonium cation. Preferably, the precursor is a chloride or a bromide (A is Cl or Br).

[0124] In this case, the reaction with HFSI produces, in addition to the ionic liquid composed of the FSI anion and the phosphonium cation, a co-product of formula HA (preferably HCl or HBr).

[0125] The reaction is preferably carried out in the absence (or essentially in the absence) of organic solvent and optionally in the presence of water. The mass ratio of water to the precursor of the phosphonium cation may be, for example, from 1:2 to 5:1, preferably from 1:1 to 4:1, more preferably from 3:2 to 3:1.

[0126] The molar ratio of HFSI placed in the presence of the phosphonium cation precursor is preferably from 0.9 to 1.1, more preferably from 1 to 1.05, more preferably from 1 to 1.01.

[0127] The temperature of the reaction medium is preferably from 10 to 100°C, more preferably from 20 to 30°C.

[0128] In embodiments, the phosphonium cation precursor is melt cast onto the HFSI and maintained at a desired temperature.

[0129] In other embodiments, the HFSI is added molten to the phosphonium cation precursor made in liquid form by the addition of water. The mass ratio of water to the phosphonium cation precursor may be, for example, from 0.02 to 6, preferably from 0.5 to 5, preferably from 1 to 4, more preferably from 1.5 to 3.

[0130] Water may in particular be present in the reaction medium in an amount of 1% to 90%, preferably 2 to 80%, more preferably 5 to 70%, or 10 to 60%, by weight, relative to the total weight of the precursor of the phosphonium cation and of the HFSI.

[0131] The progress of the reaction can be followed by the release of co-product, in particular of formula HA.

[0132] The ionic liquid is thus obtained with a high yield, preferably greater than or equal to 70%.

[0133] After the reaction, the reaction medium containing the ionic liquid can be purified, for example, by washing, decanting (or any other aqueous phase separation), and drying operations, at atmospheric pressure or preferably under vacuum. It is also possible to provide a decolorization step, for example by contacting with activated carbon. However, in preferred embodiments, no decolorization step is provided.

[0134] When the bleaching is carried out, it can be carried out by bringing the ionic liquid into contact with activated carbon, with a mass ratio of activated carbon relative to the ionic liquid advantageously from 0.05 to 0.5, preferably from 0.1 to 0.5. The activated carbon can for example have a specific surface area greater than 300 m2 / g, or even greater than 1000 m2 / g, measured by the BET method by nitrogen adsorption. The duration of the contacting can be in particular from 1 to 72 h, preferably from 5 to 48 h. The temperature during the contacting can range from 10°C up to the boiling temperature of any solvent possibly present with the ionic liquid; or it can be a temperature higher than the melting temperature of the ionic liquid in the absence of solvent.At the end of the decolorization step, the activated carbon can be separated from the decolorized ionic liquid for example by filtration, for example using a polytetrafluoroethylene or poly(vinylidene fluoride) membrane or a cellulose membrane, or a filter medium (silica, alumina, diatom).

[0135] The washing may be aqueous, i.e. a step of bringing the ionic liquid into contact with an aqueous solution (water containing one or more dissolved species), or preferably with demineralized water.

[0136] The ionic liquid undergoing the aqueous wash(s) may be previously dissolved in a water-insoluble polar organic solvent. Preferably, the water-insoluble polar organic solvent is selected from the group consisting of butyl acetate, ethyl acetate, tert-butyl acetate, butyronitrile, isobutyronitrile, glutaronitrile, diethyl ether, cyclopentyl methyl ether, tetrahydrofuran, methyl isobutyl ketone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate and propylene carbonate.

[0137] Preferably, however, no organic solvent is used at this stage.

[0138] The aqueous wash(s) reduce and remove impurities present in the ionic liquid, such as chloride ions, fluoride ions, sulfate ions, sulfamate ions and others.

[0139] During each aqueous wash, the mass ratio of the aqueous washing solution, preferably demineralized water, to the ionic liquid is preferably from 0.01 to 5, for example from 0.01 to 0.05, or from 0.05 to 0.1, or from 0.1 to 0.5 or from 0.5 to 1, or from 1 to 2, or from 2 to 5. A ratio of 1 to 0.5 may be preferred.

[0140] The duration of contact of the ionic liquid with the aqueous washing solution may vary from 1 second to 24 h. In particular, it may be from 1 second to 1 min, or from 1 min to 10 min, or from 10 min to 30 min, or from 30 min to 1 h, or from 1 h to 2 h, or from 2 h to 3 h, or from 3 h to 4 h, or from 4 h to 5 h, or from 5 h to 6 h, or from 6 h to 12 h, or from 12 h to 24 h. For the shortest contact times, it is possible to use a static mixer.

[0141] The washing may be followed by decantation to separate the aqueous phase from the organic phase. The organic phase is enriched in the ionic liquid and depleted in impurities (e.g. depleted in chloride, fluoride, sulfate, sulfamate ions, etc.), i.e. in the organic phase the ratio of molar concentrations of ionic liquid to impurities (in particular chloride, fluoride, sulfate, sulfamate ions) is higher than that of the initial ionic liquid. The aqueous phase is enriched in impurities (e.g. enriched in chloride, fluoride, sulfate, sulfamate ions), i.e. in the aqueous phase the ratio of molar concentrations of ionic liquid to impurities (in particular chloride, fluoride, sulfate, sulfamate ions) is lower than that of the initial ionic liquid. The aqueous phase may then be removed.

[0142] Several aqueous washes may be carried out, in particular from two to eleven aqueous washes (e.g., two, or three, or four, or five, or ten washes). When several washes are carried out, each may independently be such that described above. Preferably, the subsequent washing is carried out on the organic phase obtained, after decantation, at the end of the previous washing.

[0143] At the end of this or these steps, the solvent of the organic phase, if present, can be removed, for example by evaporation of the solvent, preferably under reduced pressure. A purified ionic liquid is thus obtained.

[0144] The product obtained can be characterized by nuclear magnetic resonance, by Karl Fisher type analysis for its water content and by ion chromatography for its anion and cation content. Electrochemical cell and battery

[0145] The electrolyte described above may be introduced into an electrochemical cell. The electrochemical cell comprises a negative electrode (or anode) and a positive electrode (or cathode). The electrochemical cell may also comprise a separator, in which the electrolyte is impregnated.

[0146] By "negative electrode" is meant the electrode which acts as an anode, when the cell delivers current (i.e. when it is in the process of discharging) and which acts as a cathode when the cell is in the process of charging.

[0147] The negative electrode typically comprises an electrochemically active material, optionally an electronically conductive material, and optionally a binder.

[0148] By "positive electrode" is meant the electrode which acts as cathode, when the cell delivers current (i.e. when it is in the process of discharging) and which acts as an anode when the cell is in the process of charging.

[0149] The positive electrode typically comprises an electrochemically active material, optionally an electronically conductive material, and optionally a binder.

[0150] The term “electrochemically active material” means a material capable of reversibly inserting ions.

[0151] The term “electronic conductive material” means a material capable of conducting electrons.

[0152] The negative electrode of the electrochemical cell may in particular comprise, as electrochemically active material, graphite, lithium, a lithium alloy, a lithium titanate of the Li4Ti50i2 type or titanium oxide TiO2, silicon or an alloy of lithium and silicon, a tin oxide, an intermetallic lithium compound, or one of their mixtures.

[0153] When the negative electrode comprises lithium, this may be in the form of a metallic lithium film or an alloy comprising lithium. Among the lithium-based alloys that may be used, examples that may be mentioned are lithium-aluminium alloys, lithium-silica alloys, lithium-tin alloys, Li-Zn, Li3Bi, Li3Cd and Li3SB. An example of a negative electrode may include a live lithium film prepared by rolling a lithium foil between rollers.

[0154] The negative electrode can simply consist of a current collector (for example made of copper); the lithium metal, which then constitutes the active material of the electrode, is deposited on the collector during charging.

[0155] Preferably, the negative electrode comprises, as electrochemically active material, silicon, optionally mixed with graphite. The proportion of silicon, by mass, in the electrochemically active material, may be greater than or equal to 10%, preferably greater than or equal to 20%. This proportion may in particular be 10 to 100%, or 20 to 99%, or 30 to 98%, or 50 to 95%. This electrochemically active material may be micro or nano structured, for example in the form of nanoparticles, porous or non-porous microparticles, nanowires, or even nanotubes. The surface of the silicon particles may comprise Si-C or SiOx bonds (0 <x<2).

[0156] The positive electrode comprises an electrochemically active material of the oxide type. It is preferably a lithium-iron-phosphate (LixFePO4 with 0 <x<l), ou d’un oxyde composite lithium-nickel-manganèse-cobalt à haut taux de nickel (LiNixMny CozO2 avec x+y+z = 1, en abrégé NMC, avec x> y and x>z), or a lithium-nickel-cobalt-aluminium composite oxide with a high nickel content (LiNixCoyAlz- with x'+y'+z'=l, abbreviated NCA, with x'>y' and x'>z').

[0157] Particular examples of these oxides are NMC532 (LiNi0.5Mn03Co0.2O2), NMC622 (LiNi0.6Mn0.2Co0.2O2) and NMC811 (LiNi0.8Mn0.1Co0.102).

[0158] Mixtures of these oxides can be used. The oxide material described above may optionally be combined with another oxide such as, for example: manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, lithium-manganese composite oxides (e.g., LixMn2O4 or LixMnO2), lithium-nickel composite oxides (e.g., LixNiO2), lithium-cobalt composite oxides (e.g., LixCoO2), lithium-nickel-cobalt composite oxides (e.g., LiNii yCoyO2), lithium-transition metal composite oxides, lithium-manganese-nickel composite oxides with a spinel structure (e.g., LixMn2 yNiyO4), vanadium oxides, NMC and NCA oxides that are not high in nickel, and mixtures thereof.

[0159] Preferably, the high nickel NMC or NCA oxide represents at least 50% by weight, preferably at least 75% by weight, more preferably at least 90% by weight, and more preferably essentially all of the oxide material present in the positive electrode as electrochemically active material.

[0160] Alternatively, or additionally, the positive electrode may comprise sulfur, Li2S, O2, and / or LiO2 as the electrochemically active material.

[0161] 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 of the ceramic or glass type, or other compatible active materials (e.g., sulfur).

[0162] The material of each electrode may also comprise 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 copolymer), 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 an additive such as CMC (carboxymethylcellulose) or alginate.

[0163] Preferably, the negative electrode comprises a binder chosen from polyacrylic acids, carboxymethylcellulose, an alginate and PVDF.

[0164] 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. Alternatively, the separator may be made of glass fibers.

[0165] The invention also relates to a battery comprising at least one, and preferably several, electrochemical cells as described above. The electrochemical cells may be assembled in series and / or in parallel in the battery.

[0166] The battery can be integrated into a portable electronic device, for example a mobile phone or a laptop, into an electric vehicle, into a renewable energy storage device, for example photovoltaic or wind.

Claims

Claims

1. Electrolyte comprising: • an ionic liquid comprising: • a bis(fluorosulfonyl)imide anion, • and at least one phosphonium cation of formula (PR*R2R3R4)h ', in which each group R1, R2, R3 and R4 independently represents a linear or branched, saturated or unsaturated alkyl group comprising from 1 to 14 carbon atoms, or an alkyl-aryl group comprising from 7 to 14 carbon atoms, or an aryl group comprising from 6 to 10 carbon atoms, the groups R1, R2, R3 and R4 optionally being able to comprise one or more heteroatoms; and • a lithium bis(fluorosulfonyl)imide salt; wherein the sulfamate ion content is 0.1 to 3000 ppm by weight.

2. The electrolyte of claim 1, wherein the phosphonium cation is selected from tetraethylphosphonium, tetrabutylphosphonium, trimethyl(propyl)phosphonium, trimethyl(hexyl)phosphonium, trimethyl(2-methylpropyl)phosphonium, triethyl(methyl)phosphonium, triethyl(butyl)phosphonium, triethyl(pentyl)phosphonium, triethyl(hexyl)phosphonium, tributyl(methyl)phosphonium, tri(2-methylpropyl)(methyl)phosphonium, trihexyl(dodecyl)phosphonium, trihexyl(tetradecyl)phosphonium, dimethyldipropylphosphonium, diethyl(methyl)(2-methylpropyl)phosphonium, tributyl-6-hepten-1-ylphosphonium, tetraphenylphosphonium, triphenyl(methyl)phosphonium, trimethyl(methoxymethyl)phosphonium, triethyl(methoxymethyl)-phosphonium, triethyl(2-methoxyethyl)-phosphonium, triethyl[(methylthio)methyl]-phosphonium, triethyl[2-(methylthio)ethyl]-phosphonium, triethyl[2-(ethylthio)ethyl]-phosphonium,tributyl[(methylthio)methyl]-phosphonium, tributyl[2-(methylthio)ethyl]-phosphonium and tributyl[2-(ethylthio)ethyl]-phosphonium.

3. Electrolyte according to one of claims 1 to 2, wherein the sulfamate ion content is 1 to 1000 ppm, preferably 10 to 300 ppm, by weight.

4. Electrolyte according to one of claims 1 to 3, wherein the ionic liquid is present in a weight content of 1 to 90%, preferably 20 to 80%.

5. Electrolyte according to one of claims 1 to 4, comprising at least one organic solvent.

6. Electrolyte according to one of claims 1 to 5, in which the lithium bis(fluorosulfonyl)imide salt is present at a concentration of 0.1 to 6 M, preferably 0.2 to 4 M, relative to the total of the ionic liquid and the organic solvents possibly present.

7. A method of preparing an electrolyte according to one of claims 1 to 6, comprising a step of mixing the lithium bis(fluorosulfonyl)imide salt with the ionic liquid.

8. A method according to claim 7, wherein the ionic liquid is prepared by: • providing the bis(fluorosulfonyl)imide compound; and • reacting the bis(fluorosulfonyl)imide with a precursor of the phosphonium cation.

9. The method of claim 8, wherein the bis(fluorosulfonyl) imide has a sulfamic acid content of 1 to 5000 ppm, preferably 500 to 2500 ppm by weight.

10. A method according to claim 8 or 9, wherein the precursor of the phosphonium cation is a halide of the phosphonium cation, preferably a chloride or bromide of the phosphonium cation.

11. Process according to one of claims 8 to 10, in which the reaction is carried out: • without organic solvent and optionally in the presence of water; and / or • with a molar ratio of bis(fluorosulfonyl)imide / precursor of the phosphonium cation of 0.9 to 1.1, preferably of 1 to 1.05, more preferably of 1 to 1.01; and / or • at a temperature of 10 to 100°C, preferably 20 to 30°C.

12. Method according to one of claims 8 to 11, comprising the following step: • purification of the reaction mixture after the reaction, preferably by washing, decantation and / or drying.

13. An electrochemical cell comprising a negative electrode, a positive electrode and an electrolyte, wherein the electrolyte is according to one of claims 1 to 6.

14. An electrochemical cell according to claim 13, wherein the negative electrode comprises an electrochemically active material which comprises silicon, in a mass content which is preferably greater than or equal to 10%, more preferably greater than or equal to 20%.

15. Battery comprising at least one electrochemical cell according to claim 13 or 14.