Electrolyte with high lifsi concentration

Abstract

The invention relates to an electrolyte composition comprising: - 5 to 70% by weight of lithium bis(fluorosulfonyl)imide salt; - 20 to 85% by weight of at least one organic solvent. The present invention also relates to electrochemical cells and batteries using such an electrolyte composition.

Description

[0001] High concentration LiFSI electrolyte

[0002] Field of invention

[0003] The present invention relates to an electrolyte composition comprising a lithium bis(fluorosulfonyl)imide salt. The present invention also relates to an electrochemical cell comprising said composition and a battery comprising said electrochemical cell.

[0004] Technical background

[0005] Lithium (Li) batteries, such as lithium-ion (Li-ion) batteries, are commonly used in electric vehicles and mobile and portable devices.

[0006] A Li-ion battery consists of at least one negative electrode (anode), one positive electrode (cathode), an electrolyte, and preferably a separator. The electrolyte is usually a lithium salt dissolved in a solvent, which is usually a mixture of organic solvents, in order to achieve a good compromise between the viscosity and dielectric constant of the electrolyte.

[0007] The Li-ion battery market requires the development of higher-power batteries. This involves increasing the nominal voltage of Li-ion batteries. Li-ion batteries using high-voltage cathodes (typically >4.5V) such as LMNO represent a considerable challenge for increasing the battery's energy density. The key then is to find electrolytes that are stable at high voltages and compatible with the aluminum current collector, which guarantee the battery's lifespan. Furthermore, to achieve the target voltages, high-purity electrolytes are required.

[0008] In the field of Li-ion batteries, the currently most widely used salt is LiPFe. This salt has many disadvantages such as limited thermal stability, sensitivity to hydrolysis and therefore lower battery safety. New sulfonylimide lithium salts have been developed to try to improve battery performance, including LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) and LiFSI (lithium bis(fluorosulfonyl)imide). These salts exhibit little or no spontaneous decomposition and are more stable against hydrolysis than LiPFe. However, LiTFSI has the disadvantage of being corrosive to aluminum current collectors.

[0009] The passivation layers formed during the first charge / discharge cycles of a battery are essential for its 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 (SEI), which is the inorganic and polymeric layer that forms at the anode / electrolyte and cathode / electrolyte interfaces. The stability of these interfaces is an important issue for improving battery lifespan.

[0010] Document WO2018 / 150131 relates to a lithium bis(fluorosulfonyl)imide salt, characterized in that, after dissolving in water to form an aqueous solution, said aqueous solution has a pH of between 4 and 8, in particular at a temperature of 25°C, and its uses in Li-ion batteries.

[0011] The article by C. Luo et al, Electrochimica Acta 419 of 2022 (p.140353) studies the corrosion of LiFSI on aluminum and stainless steel. The proposed solution is to use a concentrated electrolyte solution in the presence of a fluorinated diluent (LHCE).

[0012] The article by B. Aktekin et al, Applied Energy Material 2022, 5, 1 (p.585-595) describes an electrolyte with a high concentration of LiFSI (2-6M) in ethylene carbonate.

[0013] JP2019220450 claims an electrolyte that suppresses aluminum corrosion in a Li-ion battery. The solution is a concentration greater than 2 mol / kg of lithium salt including LiFSI in an oxygenated solvent (typically methyl 3-methoxypropionate and triethylene glycol dimethyl ether).

[0014] Document CN104300176 claims an electrolyte containing LiPF6 and LiFSI in the presence of corrosion inhibitors such as LiBOB.

[0015] There is a real need to provide electrolytes that can be used at high charge cut-off voltages, particularly above 4.5 V, without affecting the lifespan and electronic performance of Li-ion batteries. There is also a real need to provide higher-performance electrolytes that are free from aluminum corrosion over a long period of time and at temperatures that can exceed 40 °C.

[0016] Summary of the invention

[0017] The invention relates firstly to an electrolyte composition comprising:

[0018] - 5 to 70% by weight of lithium bis(fluorosulfonyl)imide salt;

[0019] - 20 to 85% by weight of at least one organic solvent.

[0020] According to a preferred embodiment, the organic solvent is chosen from ethers; carbonic acid esters or organic carbonates; cyclic carbonates, carboxylic acid esters; lactones; phosphoric acid esters; nitriles; amides; lactams; nitro compounds; sulfones; sulfoxides; ionic liquids with FSI (bis(fluorosulfonyl)imide) anion with a cation of ammonium, imidazolium, pyrrolidinium, piperidinium, phosphonium, sulfonium or oxonium type; fluorinated solvents, and mixtures thereof, and preferably is chosen from sulfones, sulfoxides, nitriles, ionic liquids, fluorinated ethers and fluorinated carbonates, and mixtures thereof.

[0021] The solvent is preferably sulfolane.

[0022] According to another preferred embodiment, the electrolyte composition comprises from 10 to 60% by weight, preferably from 15 to 50% by weight, more preferably from 20 to 40% by weight, of LiFSI relative to the total weight of the electrolyte composition.

[0023] In a preferred embodiment, the electrolyte composition comprises from 30 to 85% by weight, preferably from 40 to 85% by weight, more preferably from 50 to 80% by weight, even more preferably from 60 to 75% by weight, of solvent relative to the total weight of the electrolyte composition.

[0024] In a preferred embodiment, the electrolyte composition further comprises dissolved aluminum salts so as to have a concentration by weight of aluminum relative to the weight of the electrolyte composition of between 0.5 and 10000 ppm by weight, preferably between 0.5 and 9000 ppm, preferably between 0.5 and 8000 ppm, preferably between 0.5 and 7000 ppm, preferably between 0.5 and 6000 ppm, preferably between 0.5 and 5000 ppm, preferably between 0.5 and 4000 ppm, preferably between 0.5 and 3000 ppm, preferably between 0.5 and 2000 ppm, preferably between 0.5 and 1000 ppm, preferably between 0.5 and 900 ppm, preferably between 0.5 and 800 ppm, preferably between 0.5 and 700 ppm, preferably between 0.5 and 600 ppm, preferably between 0.5 and 500 ppm, preferably between 0.5 and 400 ppm, preferably between 0.5 and 300 ppm, preferably between 0.5 and 200 ppm, preferably between 0.5 and 100 ppm, preferably between 0.5 and 90 ppm, preferably between 0.5 and 80 ppm,preferably between 0.5 and 70 ppm, preferably between 0.5 and 60 ppm, preferably between 0.5 and 50 ppm, preferably between 0.5 and 40 ppm, preferably between 0.5 and 30 ppm, preferably between 0.5 and 20 ppm, preferably between 0.5 and 10 ppm.,

[0025] According to a preferred embodiment, the electrolyte composition exhibits in cyclic voltammetry a positive current difference between the forward scan and the reverse scan over the range of 4.2 to 5 Volts during the 1 er cycle.

[0026] According to a preferred embodiment, the electrolyte composition has a pH greater than or equal to 3.5, measured at a temperature of 25°C after dilution at a mass ratio of 1:1 in distilled water having a pH of 6.5.

[0027] According to another aspect the invention relates to an electrochemical cell comprising a negative electrode, a positive electrode and the electrolyte composition defined above, in which preferably the negative electrode is graphite and the positive electrode is an LNMO electrode.

[0028] According to a preferred embodiment, the electrochemical cell comprises an aluminum current collector electrode support, which is preferably associated with the positive electrode.

[0029] According to another aspect, the present invention relates to a battery comprising at least one electrochemical cell as defined above.

[0030] In a preferred embodiment, the battery has a charge cutoff voltage greater than or equal to 4.5 V.

[0031] According to another aspect, the invention relates to the use of the electrolyte composition defined above in a Li-ion battery, preferably in a Li-ion battery of a portable electronic device, for example a mobile phone or a laptop, a Li-ion battery of an electric vehicle, or a Li-ion battery for storing renewable energy, for example, photovoltaic or wind.

[0032] In a preferred embodiment, the Li-ion battery has a charge cutoff voltage greater than or equal to 4.5 V.

[0033] According to another aspect, the invention relates to the use of the electrolyte composition as defined above for increasing the lifetime of a Li-ion battery and / or for improving the electronic performance of a Li-ion battery, preferably having a charge cut-off voltage greater than or equal to 4.5 V.

[0034] The present invention makes it possible to meet the need expressed above. More particularly, it provides new electrolytes for Li-ion batteries, which preferably offer improved performance, in particular in terms of SEI quality, coulombic efficiency and / or lifetime and which can be used at high charge cut-off voltages, in particular above 4.5 V, for example LMNO cathode and in particular graphite / LMNO cell, without affecting the lifetime and electronic performance of the Li-ion batteries. The electrolytes of the present invention advantageously make it possible to avoid corrosion of aluminum up to voltages of 5 V and form an SEI on a graphite anode.

[0035] The high concentration of lithium salt in the electrolyte solvent is advantageous especially for high voltage applications (typically above 4.5 V). This high concentration prevents the dissolution of transition metals in the electrolyte and thus extends the battery life.

[0036] This is achieved by the electrolyte composition according to the invention. More particularly, the fact that the electrolyte composition according to the invention has a lithium bis(fluorosulfonyl)imide salt content greater than or equal to 5% by weight makes it possible to reduce the oxidation of the electrolyte solvents and therefore to increase the stability and lifetime of the battery, in particular at potentials greater than 4.5 V.

[0037] Description of figures

[0038] [Fig.1] represents the voltammetry curves obtained with electrolytes 1 and 2 according to the examples. The arrows indicate the direction of scanning.

[0039] [Fig.2] represents the capacity retention and coulombic efficiency of 3 LNMO / graphite button cells with electrolytes 1 and 2 according to the examples.

[0040] [Fig.3] represents the surface of aluminum after 200 voltammetry test cycles at 60 °C with electrolytes 1 (b) and 2(a) according to the examples. Detailed description

[0041] The invention is now described in more detail and in a non-limiting manner in the following description.

[0042] In the context of the invention, and unless otherwise stated, the term "charge cut-off voltage" means the upper voltage limit of a battery considered to be fully charged. The cut-off voltage is usually chosen in order to obtain the maximum capacity of the battery.

[0043] Electrolyte composition

[0044] The present invention relates to an electrolyte composition comprising a lithium bis(fluorosulfonyl)imide salt (LiFSI). In the context of the invention, the terms "lithium bis(fluorosulfonyl)imide salt", "lithium bis(sulfonyl)imide", "LiFSI", "LiN(FSC>2)2", "lithium bis(sulfonyl)imide", or "lithium bis(fluorosulfonyl)imide" are used equivalently.

[0045] The electrolyte composition has a lithium bis(fluorosulfonyl)imide salt content of 5 to 70% by weight relative to the total weight of the electrolyte composition. The LiFSI content in the electrolyte can be determined by NMR. This content can be 10 to 60% by weight, preferably 15 to 50% by weight, more preferably 20 to 40% by weight, relative to the total weight of the electrolyte composition.

[0046] The electrolyte composition according to the invention is preferably non-aqueous or essentially non-aqueous. In the context of the present invention, the term "essentially non-aqueous" means a water content in the electrolyte composition of less than or equal to 50 ppm of water, preferably less than or equal to 20 ppm of water.

[0047] The electrolyte composition has an organic solvent content of 20 to 85% by weight relative to the total weight of the electrolyte composition.

[0048] The organic solvents may be chosen from ethers; carbonic acid esters or organic carbonates; cyclic carbonates, carboxylic acid esters; lactones; phosphoric acid esters; nitriles; amides; lactams; nitro compounds; sulfones; sulfoxides; ionic liquids with FSI (bis(fluorosulfonyl)imide) anion with a cation of ammonium, imidazolium, pyrrolidinium, piperidinium, phosphonium, sulfonium or oxonium type; fluorinated solvents. The ethers may in particular be chosen from ethylene glycol dimethyl ether (1,2-dimethoxyethane), ethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2,6-dimethyltetrahydrofuran, tetrahydropyran, 1,4-dioxane and 1,3-dioxolane.

[0049] The carbonic acid esters or organic carbonates may be selected from dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), diphenyl carbonate and methyl phenyl carbonate.

[0050] The cyclic carbonates can be selected from ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, vinylene carbonate (VC) and vinyl ethylene carbonate (VEC).

[0051] The carboxylic acid esters may be selected from methyl formate, methyl acetate, methyl propionate, ethyl acetate, propyl acetate, butyl acetate, amyl acetate, vinyl acetate, divinyl adipate, methyl benzoate and ethyl benzoate.

[0052] The lactones can be selected from γ-butyrolactone, γ-valerolactone and 5-valerolactone.

[0053] The phosphoric acid esters may be selected from trimethyl phosphate, dimethyl ethyl phosphate, diethyl methyl phosphate and triethyl phosphate.

[0054] The nitriles may be selected from acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, sebaconitrile, 2-methylglutaronitrile, valeronitrile, butyronitrile, isobutyronitrile, benzonitrile and tolunitrile.

[0055] The amides may be chosen from N-methylformamide, N-ethylformamide, N,N-dimethylformamide, N,N dimethylacetamide.

[0056] The lactams may be selected from N-methylpyrrolidone, N-butylpyrrolidone and N-vinylpyrrolidone.

[0057] The nitrated compound can for example be nitromethane.

[0058] The sulfones may be selected from dimethylsulfone, ethylmethylsulfone, diethylsulfone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane and sulfolene.

[0059] The sulfoxides may be chosen from dimethyl sulfoxide, methyl ethyl sulfoxide and diethyl sulfoxide.

[0060] The ionic liquids can be chosen from EMIM-FSI (1 -Ethyl-3- methylimidazolium bis (fluorosulfonyl) imide), BMIM-FSI (1 -Butyl-3- methylimidazolium bis (trifluoromethylsulfonyl) imide), PYR14-FSI (1 -Butyl-1 - methylpyrrolidinium bis (fluorosulfonyl) imide), PYR13-FSI (1 -Propyl-3 methylpyrrolidinium bis(fluorosulfonyl)imide), PIP14-FSI (1 -butyl-1 methylpiperidinium bis(fluorosulfonyl)imide), PIP13-FSI (1 -methyl-1 propylpiperidinium bis(fluorosulfonyl)imide), P1444-FSI (Methyl(tri-n butyl)phosphonium bis(fluorosulfonyl)imide), P1222-FSI (Methyl(tri-n ethyl)phosphoium bis(fluorosulfoyl)imide).

[0061] The fluorinated solvents may be chosen from fluorinated ethers, fluorinated esters, fluorinated orthoformates, fluorinated carbonates, fluorinated phosphates, fluorinated phosphites or fluorinated sulfates. Non-exhaustively, 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, 1,1,2.2,-tetrafluoroethyl-2,2.2-trifluoroethyl ether, methoxynonafluorobutane, ethoxynonafluorobutane, 1,2-(1,1,2,2-Tetrafluoroethoxy)-ethane, 2,2,3,3-tetrafluoro-1,4-dimethoxubutane, 2-(2-ethoxyethyl)-1,1,1,- trifluoroethane, 2-(2-(2,2-difluoroethoxy)ethoxy)-1,1-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 (F1 EC), 4,5-difluoro- 1 ,3- dioxolan-2-one (F2EC), ethyl-(1 -fluoroethyl)carbonate (F1 DEC), 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, propyl-trifluoroethyl carbonate, fluorotoluene and 1,4-dimethoxytetrafluorotoluene.,

[0062] Solvents can be used alone or in combination. Sulphones, sulfoxides, nitriles, ionic liquids, fluorinated ethers, and fluorinated carbonates are preferred. Among ionic liquids, the pyrrolidinium, piperidinium, and phosphonium families are preferred.

[0063] Sulphones, and especially sulfolane, are more preferred.

[0064] The organic solvent content in the electrolyte composition according to the invention is preferably between 30 and 85% by weight relative to the total weight of the electrolyte composition, preferably between 40 and 85% by weight, more preferably between 50 and 80% by weight, even more preferably between 60 and 75% by weight, relative to the total weight of the electrolyte composition.

[0065] The electrolyte composition according to the invention may optionally comprise one or more additives. Said additives may in particular be chosen from lithium salts other than LiFSI, organic compounds comprising silicon, organic compounds comprising boron, anhydrides and compounds comprising aluminium.

[0066] Additional lithium salts other than LiFSI may be selected from LiPFe (lithium hexafluorophosphate), LiTDI (lithium 2-trifluoromethyl-4,5-dicyanoimidazolate), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorophosphate (UPO2F2), lithium bis(oxalato)borate (LiB(C2CU)2), lithium difluoro(oxalato)borate (LiF2B(C2CU)2), lithium tetrafluorate (UBF4), lithium nitrate (LiNOs), lithium perchlorate (UCIO4), lithium fluoride (LiF) and lithium fluorosulfonate (FSOsLi).

[0067] The organic compounds comprising silicon may in particular be chosen from diphenylsilanediol, dimethoxyphenylsilane, tetrakis(trimethylsilyl)silane, trimethylsilyl acetate, trimethylsilyl trifluoroacetate, trimethylsilyl trifluoromethanesulfonate, bistrimethylsilyl sulfate and tert-butyl-dimethylsilyl trifluoromethanesulfonate.

[0068] The organic compounds comprising phosphorus may in particular be chosen from tris(trimethylsylilyl)phosphate, tris(hexafluoroisopropyl)phosphate, ethyl polyphosphate, bis(2,2,2)trifluoroethyl phosphonate, trimethyl phosphite and tris(trimethylsylilyl)phosphite (TMSPi).

[0069] The organic compounds comprising sulfur may in particular be chosen from propane sultone (PS), prop-1-ene-1,3-sultone (PES), methylene methane disulfonate (MMDS), ethylene sulfite, 1,4-butanesultone and methyl methanesulfonate. The organic compounds comprising boron may in particular be chosen from trimethyl borate, triethyl borate, triisopropyl borate; tributyl borate, tris-2,2,2-trifluoroethyl borate, tris-trimethylsilyl borate, tris(pentafluorophenyl)borane, trimethoxyboroxine, triisopropylboroxine and triphenylboroxine.

[0070] The anhydrides may be selected from maleic anhydride, succinic anhydride, glutaric anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride and phenylsuccinic anhydride.

[0071] The compounds comprising aluminum, preferably in the salt form, may be chosen from aluminum tris-bis(fluorosulfonyl)imide (AI(FSI)3=AI[(N(SO2F)2]3), aluminum tris-bis(trifluoromethanesulfonyl)imide (AI(TFSI)3=AI[(N(SC>2CF3)2]3), aluminum acetate, aluminum acetylacetonate, aluminum carbonate, aluminum nitrate, aluminum chlorate, aluminum alkyls such as triethylaluminum and aluminum alcoholates such as aluminum triethylate, preferably AI(FSI)s.

[0072] The additive content in the electrolyte composition may be 0 to 10% by weight, preferably 0 to 5% by weight, relative to the total weight of the electrolyte composition.

[0073] Preferably, the electrolyte composition of the invention comprises aluminum salts dissolved so as to have a concentration by weight of aluminum in the electrolyte composition of between 0.5 and 10000 ppm, preferably between 0.5 and 9000 ppm, preferably between 0.5 and 8000 ppm, preferably between 0.5 and 7000 ppm, preferably between 0.5 and 6000 ppm, preferably between 0.5 and 5000 ppm, preferably between 0.5 and 4000 ppm, preferably between 0.5 and 3000 ppm, preferably between 0.5 and 2000 ppm, preferably between 0.5 and 1000 ppm, preferably between 0.5 and 900 ppm, preferably between 0.5 and 800 ppm, preferably between 0.5 and 700 ppm, preferably between 0.5 and 600 ppm, preferably between 0.5 and 500 ppm, preferably between 0.5 and 400 ppm, preferably between 0.5 and 300 ppm, preferably between 0.5 and 200 ppm, preferably between 0.5 and 100 ppm, preferably between 0.5 and 90 ppm, preferably between 0.5 and 80 ppm, preferably between 0.5 and 70 ppm,preferably between 0.5 and 60 ppm, preferably between 0.5 and 50 ppm, preferably between 0.5 and 40 ppm, preferably between 0.5 and 30 ppm, preferably between 0.5 and 20 ppm, preferably between 0.5 and 10 ppm. The aluminum content in the electrolyte composition can be determined by any method known to those skilled in the art and in particular by ICP-MS (inductively coupled plasma mass spectrometry), ICP-AES (inductively coupled plasma optical emission spectrometry) or X-ray fluorescence spectrometry, preferably by ICP-MS.,

[0074] In a particular embodiment, the electrolyte composition according to the invention exhibits in cyclic voltammetry a positive current difference between the forward sweep and the reverse sweep over the range of 4.2 to 5V during the first cycle. The cyclic voltammetry is carried out in a cell of three polypropylene Swagelook electrodes comprising an aluminum working electrode, optionally a lithium metal reference electrode, a lithium metal counter electrode and the electrolyte composition. The cyclic voltammetry is carried out under the following conditions:

[0075] - 3 to 5V sweep vs Li + / Li ;

[0076] - 1 mV / s scanning speed

[0077] - Temperature of 60°C.

[0078] A positive current difference between the forward and reverse sweeps over the range 4.2 to 5 V means that for any potential value Ei chosen between 4.2 and 5 V the forward sweep current IA(EI) is greater than the reverse sweep current IR(EI), i.e. lA(Ei)-lR(Ei)>0.

[0079] Advantageously, an electrolyte composition exhibiting such a voltammetry curve characteristic makes it possible to avoid corrosion of the aluminum, in particular making it possible to improve the lifespan and coulombic efficiency of a high voltage cell.

[0080] In a particular embodiment, which can be combined with the preferences and other embodiments of the invention, the electrolyte composition according to the invention has a pH greater than or equal to 3.5, measured at a temperature of 25°C after dilution at a mass ratio of 1:1 in distilled water having a pH of 6.5. The pH may be greater than or equal to 4, and preferably from 4 to 8. Said pH may be from 3.5 to 4; or from 4 to 4.5; or from 4.5 to 5; or from 5 to 5.5; or from 5.5 to 6; or from 6 to 6.5; or from 6.5 to 7; or from 7 to 7.5; or from 7.5 to 8; or from 8 to 8.5; or from 8.5 to 9; or from 9 to 9.5; or from 9.5 to 10; or from 10 to 10.5; or from 10.5 to 11; or from 11 to 11.5; or from 11.5 to 12; or from 12 to 12.5; or from 12.5 to 13; or from 13 to 13.5; or from 13.5; or from 13.5 to 14.

[0081] The pH can be measured by any method known to those skilled in the art. For example, the pH can be measured using a glass electrode, the potential of which can vary depending on the concentration of hydrogen ions according to the Nernst equation. This potential can be measured relative to a reference electrode using a high-impedance potentiometer, commonly called a pH meter. As a pH meter, the pHM210 model from Radiometer can, for example, be used. The pH meter can be previously calibrated using three buffer solutions (for example, at pH=4.0, 7.0 and 10.0). The aqueous solution can be stirred during the pH measurement. The pH measurement is preferably carried out within one hour of dilution in distilled water.

[0082] The fact that the aqueous solution (prepared by dissolving lithium bis(fluorosulfonyl)imide salt in distilled water) has a pH greater than or equal to 3.5 advantageously allows the stability of the electrolyte of high salt concentration to be maintained at high voltage (greater than 4.5 V).

[0083] The electrolyte composition may be prepared by mixing the LiFSI salt, the organic solvent(s), and optionally one or more additives. Preferably, the desired amount of lithium salts is dissolved in the organic solvent(s), and then any additives are added.

[0084] Preparation of lithium bis(fluorosulfonyl)imide salt

[0085] LiFSI can be obtained by any method known to those skilled in the art and in particular according to the method described in WO2018 / 104674.

[0086] The invention relates either to the electrolyte initially charged in the battery or to the electrolyte formed in situ during operation of the battery.

[0087] Electrochemical cell and battery

[0088] The present invention also relates to the use of the above electrolyte composition in Li-ion batteries, in particular with a high voltage cathode (greater than or equal to 4.5 V), in particular in Li-ion batteries of portable electronic devices, for example mobile phones or laptops, of electric vehicles, of renewable energy storage, for example photovoltaic or wind energy.

[0089] The present invention relates to the use of the electrolyte composition according to the invention for increasing the lifetime of a Li-ion battery and / or improving the electronic performance (coulombic efficiency) of a Li-ion battery. More particularly, the present invention relates to the use of the electrolyte composition according to the invention for forming a stable SEI on graphite making it possible to increase the coulombic efficiency and the lifetime of the Li-ion battery. By "increasing the lifetime of the Li-ion battery" is meant the increase in the number of cycles making it possible to retain at least 80% of the initial capacity of the battery.

[0090] By "improving the electronic performance (coulombic efficiency) of a Li-ion battery" is meant the improvement of the capacity for high charge or discharge current, in particular at low temperature and / or after storage at high temperature.

[0091] By "Stable SEI on graphite" is meant obtaining a stable delithiation capacity over 5 cycles, i.e. not changing by plus or minus 5%, and equal to at least 90% of the theoretical capacity of the active material. The delithiation capacity is obtained during discharge in a Li / graphite half-cell cycling at constant current at C / 10 in charge and discharge between 0.01 and 1 V. This capacity can be obtained by any method known to those skilled in the art and for example by means of a CR2016 button cell assembly, comprising a stainless steel spring, a 1 mm diameter stainless steel shim, a 14 mm diameter lithium metal pellet, a 16 mm diameter fiberglass separator impregnated with 10OpiL of electrolyte, and a 12 mm diameter graphite pellet.

[0092] The invention also relates to an electrochemical cell comprising an electrolyte composition as described above. The electrochemical cell also comprises a negative electrode (or anode) and a positive electrode (or cathode). Preferably, the positive electrode (or cathode) operates at high voltage (greater than or equal to 4.5 V).

[0093] The electrochemical cell may also include a separator, in which the electrolyte is impregnated.

[0094] By "negative electrode" we mean the electrode which acts as an anode when the cell is delivering current (i.e. when it is discharging) and which acts as cathode when the cell is charging.

[0095] The negative electrode typically comprises an electrochemically active material, optionally an electronically conductive material, and optionally a binder.

[0096] The term "positive electrode" refers to the electrode that acts as the cathode when the cell is delivering current (i.e., when it is discharging) and acts as the anode when the cell is charging. The positive electrode typically comprises an electrochemically active material, possibly an electronically conductive material, and possibly a binder.

[0097] An "electrochemically active material" means a material capable of reversibly inserting ions.

[0098] An "electronically conductive material" means a material capable of conducting electrons.

[0099] 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 Li4TisOi2 type or titanium oxide TiO2, silicon or an alloy of lithium and silicon, a tin oxide, a lithium intermetallic compound, or one of their mixtures.

[0100] When the negative electrode comprises lithium, it may be in the form of a metallic lithium film or an alloy comprising lithium. Examples of lithium-based alloys that may be used include lithium-aluminum alloys, lithium-silica alloys, lithium-tin alloys, Li-Zn, LisBi, LisCd and LisSB. An example of a negative electrode may comprise a live lithium film prepared by rolling a lithium foil between rollers.

[0101] Preferably, the negative electrode is made of graphite.

[0102] The positive electrode comprises an electrochemically active material of lithium oxide type having:

[0103] - a lamellar structure of formula UMO2 where M is a metal which may in particular be nickel, cobalt, manganese, aluminum, magnesium, titanium, chromium or a combination;

[0104] - a spinel structure of formula UM2O4 where M is a metal such as manganese or a combination of manganese with nickel, cobalt, copper, iron, chromium, in particular of formula LiNio,5-xMni,5+x04 with x between 0 and 0.5 for example LiNii / 2Mns / 2O4 (LNMO);

[0105] - a spinel structure of formula UMO4 where M is a combination of manganese with cobalt, iron, chromium, nickel;

[0106] - an olivine structure of formula LiMPCU where M is a metal such as nickel, cobalt, manganese or a combination of iron, nickel, manganese, cobalt;

[0107] - a Lii type formula + xMi-xC>2 where M is a metal such as nickel, cobalt, manganese, aluminum, magnesium, titanium, chromium or a combination of these metals;

[0108] - a structure of type LiMVCU where M is a metal such as nickel; - a formula of type Ü2MPO4F where M is a metal such as cobalt; or

[0109] - a formula of the type LisM2(PO4)3 where M is a metal such as nickel, cobalt, manganese, iron, vanadium or a combination of these metals.

[0110] Such positive electrodes are notably described in the document Li, Wangda, Song, Bohang, & Manthiram, Arumugam, High-voltage positive electrode materials for lithium-ion batteries, Chemical Society Reviews, 2017, 46(10).

[0111] Preferably, the positive electrode is LNMO.

[0112] Alternatively, or additionally, the positive electrode may comprise sulfur, IJ2S, O2, and / or UO2 as an electrochemically active material.

[0113] 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 thereof. 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).

[0114] 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 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).

[0115] The metal supports of the electrodes serving as current collectors are generally made of aluminum for the cathode and copper for the anode. The metal supports can be surface-treated and have a conductive primer. The conductive primer can contain carbonaceous materials, metallic materials, and polymer materials as described in the review by H. Jeong et al., Chemical Engineering Journal 446, 2022, 136860. The supports can also be carbon fiber woven or nonwoven.

[0116] The separator must have a low thickness, sufficient mechanical and temperature resistance, good electrochemical resistance to the voltages to which it is exposed, optimal affinity for the electrolyte and more generally allow excellent ionic conductivity. The separator may be made of a porous film (substrate). Examples of porous substrates useful in the invention as a separator include, but are not limited to, polyolefins, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, poly(phenylene oxide), poly(phenylene sulfide), polyethylene naphthalene or mixtures thereof.Non-limiting examples of polyolefin separators include ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, or multilayer structures of the above polymers.

[0117] Alternatively, the separator may be made of glass fibers. Nonwoven materials made of natural and synthetic materials may also be used as the substrate of the separator. The porous substrate generally has a thickness of 1 to 50 µm, and are typically membranes obtained by extrusion and stretching (wet or dry processes) or cast nonwovens. The porous substrate preferably has a porosity of between 5% and 95%. The average pore size (diameter) is preferably between 0.001 and 50 µm, more preferably between 0.01 and 10 µm.

[0118] The separator may comprise a coating. This coating may optionally be disposed on one or both sides of a porous support. In this case, the coating is used to coat the support of a separator, on at least one side, in the form of a monolayer or multilayers. Said coating may be a fluoropolymer alone or in a mixture with an acrylic polymer. Preferably, the fluoropolymer comprises monomeric units derived from vinylidene fluoride. The separator coating may contain inorganic particles that serve to form micropores in the coating (the interstices between inorganic particles). The addition of inorganic particles may also contribute to heat resistance or improve wettability.According to one embodiment, said inorganic particles are chosen from the group consisting of: BaTiO3, Pb(Zr,Ti)O3, Pb1 -x LaxZryO3 (0 <x<1 , 0<y<1 ), PbMg3Nb2 / 3)3, PbTiO3, hafnie (HfO (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, Y2O3, bohémite (y- AIO(OH)), AI2O3, TiO2, SiC, ZrO2, silicate de bore, BaSO4, nano-argiles, ou leurs mélanges.

[0119] 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.

[0120] Preferably, the battery according to the invention has a charge cut-off value greater than or equal to 4.3 V, more preferably greater than or equal to 4.5 V.

[0121] The following examples illustrate the invention without limiting it.

[0122] Example 1

[0123] Electrolyte 1 is prepared by dissolving 2.9 g of LiFSI in 7.8 g of sulfolane.

[0124] The voltammetry curve of this electrolyte is obtained by producing a Swagelok type cell in polypropylene filled with electrolyte 1, and comprising an aluminum working electrode and a lithium metal counter electrode.

[0125] The conditions for cyclic voltammetry are as follows:

[0126] • 3 to 5V sweep vs Li+ / Li

[0127] • 1 mV / s scan speed

[0128] • Temperature of 60°C

[0129] The voltammetry curve is shown in Figure 1.

[0130] Example 2 (comparative)

[0131] Electrolyte 2 is prepared by dissolving 0.76g of LiPF6, 0.1g of LiFSI and 0.06g of LiBOB in 1.98g of ethyl carbonate (EC), 3.54g of ethyl methyl carbonate (EMC) and 0.11g of fluoroethylene carbonate (FEC).

[0132] The voltammetry curve of this electrolyte is obtained by making a Swagelok type cell in polypropylene filled with electrolyte 2, and comprising an aluminum working electrode, a lithium metal counter electrode.

[0133] The conditions for cyclic voltammetry are as follows:

[0134] • 3 to 5V sweep vs Li+ / Li

[0135] • 1 mV / s scan speed

[0136] • Temperature of 60°C

[0137] The voltammetry curve is shown in Figure 1.

[0138] Figure 1 shows that electrolyte 1 according to the invention has, over the potential range of 4.2 to 5 V, a forward sweep current greater than the return sweep current, unlike electrolyte 2.

[0139] Figure 3 shows that electrolyte 1 according to the invention does not corrode aluminum (b) unlike electrolyte 2 for which corrosion marks appear on the aluminum (a).

[0140] Example 3: Study of the lifespan of a battery with electrolyte 1 and electrolyte 2

[0141] Button cells are prepared to evaluate the impact of the electrolyte on the battery life. The button cells are composed of a CR2032 case made of 316L stainless steel. The interior of the button cell is composed of the lower case surrounded by a polypropylene gasket, a 316L stainless steel spring, a 1 mm thick 316L stainless steel shim, a graphite anode cut into a 14 mm diameter disc, a Whatman fiberglass separator impregnated with 100 μL of electrolyte 1 or 2, an LNMO cathode cut into a 12 mm disc, an aluminum foil that completely covers the upper case.

[0142] The LNMO cathode is prepared by dispersing in a Thinky mixer 93% by weight of active material (LNMO TBM129, Haldor Topsoe), 4% by weight of carbon black (C65, Imerys) and 3% by weight of PVDF binder (Kynar® HSV1810, Arkema) in the NMP solvent (N-methylpyrrolidone) to obtain 60% dry extract. The ink thus obtained is coated on an aluminum collector using a 270pm height doctor blade, at a speed of 0.2m / min, then dried for 12 hours at 90 °C in an oven.

[0143] The active material weight of the cathode is 13.5 mg / cm 2 .

[0144] The electrode is calendered to obtain a porosity of 30%.

[0145] The graphite anode comes from the supplier NEI (reference BE-150E).

[0146] The active material weight of the anode is 6.2 mg / cm 2 .

[0147] The electrodes and separator are vacuum dried for 12 hours at 60°C before cell assembly, which is carried out in an anhydrous room at a dew point of -40°C. LNMO / graphite button cells are tested on a VMP3 potentiostat (Biology). The test program consists of 2 formation cycles at C / 10 (charge or discharge cycle in 10 hours) (charge in CCCV (Constant current phase applied until the potential reaches 4.85V, followed by a phase with constant potential applied until the current drops below C / 10), discharge in CC (constant current) between 3.5V and 4.85V, followed by 400 cycles with a charge at C / 5 (charge or discharge cycle in 5 hours) in CCCV and a discharge in CC at 1 C, between 3.5V and 4.85V.

[0148] The evolution of the capacity and coulombic efficiency of 3 batteries containing electrolyte 1 and 3 batteries containing electrolyte 2 is presented in figure 2.

[0149] The implementation of electrolyte 1 results in an improvement in battery life and coulombic efficiency, particularly linked to the absence of corrosion of the aluminum collector, compared to electrolyte 2.

Claims

Claims 1. Electrolyte composition comprising: - 5 to 70% by weight of lithium bis(fluorosulfonyl)imide salt; - 20 to 85% by weight of at least one organic solvent.

2. Electrolyte composition according to claim 1, in which the organic solvent is chosen from ethers; carbonic acid esters or organic carbonates; cyclic carbonates, carboxylic acid esters; lactones; phosphoric acid esters; nitriles; amides; lactams; nitro compounds; sulfones; sulfoxides; ionic liquids with FSI (bis(fluorosulfonyl)imide) anion with a cation of ammonium, imidazolium, pyrrolidinium, piperidinium, phosphonium, sulfonium or oxonium type; fluorinated solvents, and mixtures thereof, and preferably is chosen from sulfones, sulfoxides, nitriles, ionic liquids, fluorinated ethers and fluorinated carbonates, and mixtures thereof.

3. An electrolyte composition according to claim 1 or 2, wherein the solvent is sulfolane.

4. Electrolyte composition according to one of claims 1 to 3, comprising from 10 to 60% by weight, preferably from 15 to 50% by weight, more preferably from 20 to 40% by weight, of Li FSI relative to the total weight of the electrolyte composition.

5. Electrolyte composition according to one of claims 1 to 4, comprising from 30 to 85% by weight, preferably from 40 to 85% by weight, more preferably from 50 to 80% by weight, even more preferably from 60 to 75% by weight, of solvent relative to the total weight of the electrolyte composition.

6. Electrolyte composition according to one of claims 1 to 5, further comprising aluminum salts dissolved so as to have a concentration by weight of aluminum relative to the weight of the electrolyte composition between 0.5 and 10000 ppm by weight, preferably between 0.5 and 9000 ppm, preferably between 0.5 and 8000 ppm, preferably between 0.5 and 7000 ppm, preferably between 0.5 and 6000 ppm, preferably between 0.5 and 5000 ppm, preferably between 0.5 and 4000 ppm, preferably between 0.5 and 3000 ppm, preferably between 0.5 and 2000 ppm, preferably between 0.5 and 1000 ppm, preferably between 0.5 and 900 ppm, preferably between 0.5 and 800 ppm, preferably between 0.5 and 700 ppm, preferably between 0.5 and 600 ppm, preferably between 0.5 and 500 ppm, preferably between 0.5 and 400 ppm, preferably between 0.5 and 300 ppm, preferably between 0.5 and 200 ppm, preferably between 0.5 and 100 ppm, preferably between 0.5 and 90 ppm, preferably between 0.5 and 80 ppm, preferably between 0.5 and 70 ppm, preferably between 0.5 and 60 ppm, preferably between 0.5 and 50 ppm, preferably between 0.5 and 40 ppm, preferably between 0.5 and 30 ppm, preferably between 0,5 and 20 ppm, preferably between 0.5 and 10 ppm., 7. Electrolyte composition according to any one of claims 1 to 6 exhibiting in cyclic voltammetry a positive current difference between the forward scan and the return scan over the range of 4.2 to 5 Volts during the 1 er cycle.

8. Electrolyte composition according to any one of claims 1 to 7, characterized in that it has a pH greater than or equal to 3.5, measured at a temperature of 25°C after dilution at a mass ratio of 1:1 in distilled water having a pH of 6.

5.

9. Electrochemical cell comprising a negative electrode, a positive electrode and the electrolyte composition according to one of claims 1 to 8, in which preferably the negative electrode is graphite and the positive electrode is an LNMO electrode.

10. Electrochemical cell according to claim 9, comprising an aluminum current collector electrode support, which is preferably associated with the positive electrode.

11. Battery comprising at least one electrochemical cell according to claim 9 or 10.

12. Battery according to claim 11, having a charge cut-off voltage greater than or equal to 4.5 V.

13. Use of the electrolyte composition according to one of claims 1 to 8, in a Li-ion battery, preferably in a Li-ion battery of a portable electronic device, for example a mobile phone or a laptop, a Li-ion battery of an electric vehicle, or a Li-ion battery for storing renewable energy, for example, photovoltaic or wind.

14. Use according to claim 13, in a Li-ion battery having a charge cut-off voltage greater than or equal to 4.5 V.

15. Use of the electrolyte composition according to one of claims 1 to 8, for increasing the lifetime of a Li-ion battery and / or for improving the electronic performance of a Li-ion battery, preferably having a charge cut-off voltage greater than or equal to 4.5 V.

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