Electrolyte composition for a lithium-ion electrochemical element

Abstract

The invention relates to a lithium-ion electrochemical element comprising: a) a positive electrode comprising a lithium phosphate of at least one transition metal operating at a potential greater than or equal to 3.6 V vs. Li+ / Li; b) a negative electrode; c) an electrolyte comprising: - one or more solvents, one being methyl propionate, - one or more diluents selected from a fluorinated alkyl ether, fluorobenzene, 1,2-difluorobenzene and isomers thereof, 1,2,3-trifluorobenzene and isomers thereof, 1,2,3,4-tetrafluorobenzene and isomers thereof, pentafluorobenzene, hexafluorobenzene, 2-fluorotoluene and isomers thereof and a mixture thereof, the volume proportion of the one or more diluents representing from 50 to 80% of the total volume of the one or more solvents and the one or more diluents, - lithium bis(fluorosulfonyl)imide, - a negative-electrode passivation additive selected from ethylene monofluorocarbonate and / or vinylene carbonate.

Description

Description Title of the invention: Electrolyte composition for lithium-ion electrochemical element technical field

[0001] This presentation falls within the technical field of electrolyte compositions for lithium-ion type electrochemical elements. Background

[0002] Lithium-ion electrochemical elements are known from the prior art. They are commonly used in many fields such as automotive, telecommunications, electronic devices, and aerospace. Their operating principle is based on the reversible exchange of lithium ions between the active material of a positive electrode (cathode), most often a lithium oxide of a transition metal or a lithium phosphate of a transition metal, and the active material of a negative electrode (anode), for example, graphite. The negative and positive electrodes are separated by a separator. The assembly formed by the negative electrode, the positive electrode, and the separator constitutes an electrochemical beam.The electrochemical beam is impregnated with an organic electrolyte, often liquid, usually composed of a mixture of cyclic or linear alkyl carbonates in which a lithium salt is dissolved, for example lithium hexafluorophosphate LiPFe.

[0003] Lithium-ion electrochemical elements experience a more rapid loss of capacity when exposed to temperatures above room temperature (20-25°C). One cause of this loss is the presence of secondary reactions at the interfaces between the positive electrode(s) and the electrolyte, and between the negative electrode(s) and the electrolyte. The formation of passivation layers on the electrode surfaces, known as SEI (Solid Electrolyte Interphase) at the negative electrode and CEI (Cathode Electrolyte Interphase) at the positive electrode, helps to limit these secondary reactions and thus reduce the capacity loss during cycling. These passivation layers form spontaneously when the positive and negative electrodes come into contact with the electrolyte. They are primarily composed of the electrolyte's redox products.Their composition and therefore their stability over time depend both on the nature of the materials of the positive and negative electrodes and on the composition of the electrolyte.

[0004] We therefore sought to improve the cycling lifetime of an electrochemical element by modifying the composition of the electrolyte in order to create more stable and less soluble passivation layers over time.

[0005] Document WO 2024 / 011322 describes a lithium-ion electrochemical element comprising: - a linear ester and / or a cyclic ester as solvent(s), - a thinner, and - an alkali metal salt. Summary

[0006] An electrolyte composition has been discovered that improves the cycling lifetime of a lithium-ion cell. The electrolyte composition according to the invention comprises: - one or more solvents, one of which is methyl propionate (MP), - one or more diluents selected from a fluorinated alkyl ether, fluorobenzene, 1,2-di-fluorobenzene and its isomers, 1,2,3-trifluorobenzene and its isomers, 1,2,3,4-tetrafluorobenzene and its isomers, pentafluorobenzene, hexafluorobenzene, 2-fluorotoluene and its isomers and a mixture thereof, the volume proportion of said one or more diluents representing from 50 to 80% of the total volume of said one or more solvents and said one or more diluents, - lithium bis(fluorosulfonyl)imide Li(FSÛ2)2N (LiFSI), - a negative electrode passivation additive selected from ethylene monofluorocarbonate (FEC), vinylene carbonate (VC) and a mixture thereof.

[0007] The association of methyl propionate, said one or more diluents as stated above, lithium bis(fluorosulfonyl)imidide and the passivation additive allows an improvement in the cycling life of the element compared with an electrochemical element containing a conventional electrolyte consisting of a mixture of one or more cyclic alkyl carbonate(s) with one or more linear alkyl carbonate(s) in which LiPFe is dissolved.

[0008] It has been observed that the electrolyte according to the invention can be used in a lithium-ion element comprising a positive electrode based on a lithium phosphate of at least one transition metal operating at an average potential greater than or equal to 3.6 V vs. Li + / Li. The electrolyte exhibits satisfactory oxidation resistance, even under the high potential conditions imposed by the nature of the active material of the positive electrode.

[0009] The invention therefore relates to a lithium-ion electrochemical element comprising: a) at least one positive electrode comprising a first positive active material which is a lithium phosphate of at least one transition metal operating at an average potential greater than or equal to 3.6 V vs. Li + / Li ; b) at least one negative electrode comprising a negative active material; c) the electrolyte as described above.

[0010] According to one embodiment, lithium bis(fluorosulfonyl)imidide Li(FSÛ2)2N (LiFSI) is the only salt of the electrolyte.

[0011] According to one embodiment, the electrolyte consists of: - a solvent which is methyl propionate and in one or more diluents selected from a fluorinated alkyl ether, fluorobenzene, 1,2-difluorobenzene and its isomers, 1,2,3-trifluorobenzene and its isomers, 1,2,3,4-tetrafluorobenzene and its isomers, pentafluorobenzene, hexafluorobenzene, 2-fluorotoluene and its isomers and a mixture thereof, the volume proportion of said one or more diluents representing from 50 to 80% of the total volume of methyl propionate and said one or more diluents, - lithium bis(fluorosulfonyl)imide Li(FSÛ2)2N (LiFSI), - a negative electrode passivation additive selected from ethylene monofluorocarbonate (FEC), vinylene carbonate (VC) and a mixture thereof.

[0012] According to one embodiment, the fluorinated alkyl ether is the ether of 1,1,2,2-tetrafluoroethyl and 2,2,3,3-tetrafluoropropyl.

[0013] According to one embodiment, the electrolyte consists of: i) methyl propionate and 1,1,2,2-tetrafluoroethyl and 2,2,3,3-tetrafluoropropyl ether, ii) lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI), and iii) vinylene carbonate.

[0014] According to one embodiment, the electrolyte consists of: i) methyl propionate and fluorobenzene, ii) lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI), and iii) vinylene carbonate.

[0015] In one embodiment, the electrolyte consists of: i) methyl propionate and 1,2-difluorobenzene, ii) lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI), and iii) vinylene carbonate. In one embodiment, the volume proportion of fluorinated alkyl ether in the electrolyte ranges from 65% to 75% of the total volume of said one or more solvents and said one or more diluents.

[0016] According to one embodiment, in the electrolyte, the volume proportion of fluorobenzene ranges from 65 to 75% of the total volume of said one or more solvents and said one or more diluents.

[0017] According to one embodiment, in the electrolyte, the volume proportion of 1,2-difluorobenzene ranges from 65 to 75% of the total volume of said one or more solvents and said one or more diluents.

[0018] According to one embodiment, in the electrolyte, the mass of the passivation additive represents 1 to 4% of the total mass of said one or more solvents, said one or more diluents and lithium bis(fluorosulfonyl)imidide Li(FSO2)2N.

[0019] According to one embodiment, the concentration of lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI) ranges from 0.8 to 1.5 mol. 1 .

[0020] According to one embodiment, the first positive active ingredient is chosen from: i) a lithium manganese and iron phosphate of formula: Li x Mni-y-zFe y MzPO4 (LMFP) where 0.8 <x<l,2 ; 0,5<l-y-z<l; 0<y+z<0,5 ; 0<y<0,50 et 0<z<0,2 et M est choisi dans le groupe constitué de Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S, Hf, Bi, Se et des mélanges de ceux-ci ; ii) un fluorophosphate lithié de vanadium de formule Lii+xVPCUF (LVPF) où 0<x<0,15, ou l’un de ses dérivés de formule Lii+xVi-yMyPCUFz (LVMPF) où 0<x<0,15, 0<y<0,5, 0,8<z<l,2 et M est choisi dans le groupe consistant en Ti, Al, Y, Cr, Cu, Mg, Mn, Fe, Co, Ni, Zr et des mélanges de ceux-ci, ou un mélange de plusieurs composés des groupes i) et ii).

[0021] According to one embodiment, the first positive active ingredient is mixed with a second positive active ingredient chosen from: iii) a lithium oxide of nickel, manganese and cobalt of formula The w (NixMn y CozMt)O2 (NMC) where 0.9 <w<l,l ; 0<x<l,l ; 0<y<l,l ; 0<z<l,l ; 0<t<l, 1 ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; iv) un oxyde lithié de nickel, cobalt et aluminium de formule The w (NixCoyAl z Mt)O2 (NCA) where 0.9 <w<l,l ; 0<x<l,l ; 0<y<l, 1 ; 0<z<l,l ; 0<t<l,l ; M étant choisi dans le groupe constitué de B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; v) un composé de formule Lii+xMi-xCL-yFy de structure cristalline cubique où 0<x<0,5 et 0<y<l et M représente un élément choisi dans le groupe constitué de Na, K, Mg, Ca, B, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Y, Zr, Nb, Mo, Ru, Ag, Sn, Sb, Ta, W, Bi, La, Pr, Eu, Nd et Sm et des mélanges de ceux-ci ; vi) un oxyde lithié de nickel et de manganèse (NMX) de formule Lia(Nii-xy-zMnxCo y Mz)O2 with 0.9 <a<l,l ; 0,60<l-x-y-z<0,80 ; 0<x<l ; 0<y<0,02 ; 0<z<l ; et M étant choisi dans le groupe consistant en Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ga, Ta, Nd, Pr, La et des mélanges de ceux-ci ; vii) un oxyde lithié de nickel et de manganèse de formule Li w (NixMn y Co z Mt)O2 where 1, 1 <W<1,6 ; 0<x<l ; 0,50<y<0,80 ; 0<z<0,02 ; 0<t<l ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; viii) un oxyde lithié de nickel, de manganèse, de cobalt et d’aluminium (NMC A) de formule Li w (NixCoyAl z MntMs)O2 where 0.9 <w<l,l ; 0<x<l,l ; 0<y<l, 1 ; 0<z<l,l ; 0<t<l,l ; 0<s<l, 1, M étant au moins un élément choisi dans le groupe constitué de B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ga, Ta, Nd, Pr et La ; ix) un oxyde lithié de manganèse de formule LixMn2-y-zM'yM" z O4-5 where M' and M" are chosen from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo; M' and M" being different from each other, and 1 <X<1,4 ; 0<y<0,6 ; 0<z<0,2 ; 0<5<l, ou un mélange de plusieurs composés des groupes iii) à ix).

[0022] According to one embodiment, the first positive active substance represents from 30 to 99% of the total mass of positive active substances, and the second positive active substance represents from 1 to 70% of the total mass of positive active substances.

[0023] According to one embodiment, the first positive active substance is a compound of group i) and the second positive active substance is a compound of group iii).

[0024] According to one embodiment, the negative active material is selected from carbon, preferably graphite, silicon, a carbon-silicon composite Si-C, silicon oxides SiOx with 0 <x<2 et un mélange de ceux-ci.

[0025] Finally, the invention relates to the use of an electrolyte consisting of: - a solvent which is methyl propionate and in one or more diluents chosen from a fluorinated alkyl ether, fluorobenzene, 1,2-difluorobenzene and its isomers, 1,2,3-trifluorobenzene and its isomers, 1,2,3,4-tetrafluorobenzene and its isomers, pentafluorobenzene, F hexafluorobenzene, 2-fluorotoluene and its isomers and a mixture thereof, the volume proportion of said one or more diluents representing from 50 to 80% of the total volume of methyl propionate and said one or more diluents, - lithium bis(fluorosulfonyl)imide Li(FSÛ2)2N (LiFSI), - a passivation additive for a negative electrode of a lithium-ion electrochemical element, the passivation additive being selected from ethylene monofluorocarbonate (FEC), vinylene carbonate (VC) and a mixture thereof, in a lithium-ion electrochemical element to improve its cycling life. Brief description of the figures

[0026] [Fig. 1] represents the percentage of capacity discharged by elements A and B, expressed relative to their initial capacity during a cycle conducted at a temperature of 30°C and including charges and discharges at the C / 2 regime.

[0027] [Fig. 2] represents the percentage of capacity discharged by elements C, D and E, expressed relative to their initial capacity during a cycle conducted at a temperature of 30°C and including charges and discharges at the C / 2 regime.

[0028] [Fig. 3] represents the percentage of capacity discharged by the Al elements at Dl, expressed relative to their initial capacity during a cycle conducted at a temperature of 30°C and including charges and discharges at the C / 2 regime. Detailed description of the implementation methods Electrolyte:

[0029] The electrolyte contains methyl propionate (MP), which is a linear ester. The low viscosity of methyl propionate allows for good performance of the element at low temperatures. Methyl propionate can be combined with one or more solvents. These can be chosen from: - saturated cyclic alkyl carbonates other than ethylene monofluorocarbonate (FEC), - unsaturated cyclic alkyl carbonates other than vinylene carbonate (VC), - saturated or unsaturated linear alkyl carbonates, - linear esters other than methyl propionate, - cyclic esters, - linear ethers other than fluorinated alkyl ethers, and - cyclic ethers.

[0030] Methyl propionate can be associated with one or more cyclic alkyl carbonates, saturated or unsaturated, and / or with one or more linear alkyl carbonates, saturated or unsaturated.

[0031] Examples of saturated cyclic alkyl carbonates include ethylene carbonate EC, propylene carbonate PC, butylene carbonate BC and mixtures thereof.

[0032] Examples of saturated linear alkyl carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dipropyl carbonate (DPC), and mixtures thereof. DMC and DEC are the preferred saturated linear alkyl carbonates.

[0033] Preferably, the electrolyte contains neither saturated nor unsaturated cyclic alkyl carbonate, nor saturated or unsaturated linear alkyl carbonate.

[0034] Methyl propionate can be associated with one or more linear esters and / or one or more cyclic esters. The term "linear ester" refers to a compound with the general formula RC(=O)OR' in which the R and R' groups each independently represent an alkyl group, the compound not containing an oxygen atom between the alkyl group R and the carbonyl group -C(=O). Examples of linear esters other than methyl propionate include methyl acetate, ethyl acetate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and mixtures thereof.

[0035] Preferably, the electrolyte does not contain any esters other than methyl propionate.

[0036] Methyl propionate can be associated with one or more linear ethers other than fluorinated alkyl ethers and / or with one or more cyclic ethers. Examples of linear ethers include dimethoxyethane, propyl ethyl ether, dimethyl ether (DME), diethyl ether (DEE), and mixtures thereof. Examples of cyclic ethers include tetrahydrofuran (THF) and 1,3-dioxolane.

[0037] Preferably, the electrolyte does not contain any ether(s) other than fluorinated alkyl ether(s).

[0038] The electrolyte contains one or more diluents selected from the group consisting of a fluorinated alkyl ether, (mono)fluorobenzene, a mixture of at least one fluorinated alkyl ether and fluorobenzene, 1,2-difluorobenzene (DFB) and its isomers, 1,2,3-trifluorobenzene and its isomers, 1,2,3,4-tetrafluorobenzene and its isomers, pentafluorobenzene, hexafluorobenzene, 2-fluorotoluene and its isomers, and mixtures thereof, the volume proportion of said one or more diluents representing from 50 to 80% of the total volume of said one or more solvents and said one or more diluents. It is known to those skilled in the art that isomers are chemical compounds that have the same molecular formula but different structural formulas. The isomers of 1,2-difluorobenzene are 1,3-difluorobenzene and 1,4-difluorobenzene. The isomers of 1,2,3-trifluorobenzene are 1,2,4-trifluorobenzene and 1,3,5-trifluorobenzene.The isomers of 1,2,3,4-tetrafluorobenzene are 1,2,3,5-tetrafluorobenzene and 1,2,4,5-tetrafluorobenzene. The isomers of 2-fluorotoluene are 3-fluorotoluene and 4-fluorotoluene.

[0039] Unlike a solvent, as defined in the present invention, a diluent is a molecule that cannot dissolve the lithium salt into an anion and a cation, and therefore does not create a solvation sphere around the anion and cation that would result from the dissolution of the salt if it were to occur. The use of fluorinated alkyl ether is advantageous because it minimizes the viscosity of the electrolyte. The fluorinated alkyl ether may be selected from the group consisting of 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl ether and 2,2,2-trifluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, di-fluoromethyl ether and 2,2,3,3-tetrafluoropropyl ether, 2,2,3,3-tetrafluoropropyl ether and 1,1,2,3,3,3-hexafluoroisopropyl ether, 2,2,3,3,4,4,5,5-octafropentyl ether and 1,1,2,2-tetrafluoroethyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether and mixtures of these- ci. Preferably, this is 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl (TTE).

[0040] Preferred diluents are 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl (TTE), fluorobenzene and 1,2-difluorobenzene, especially 1,2-difluorobenzene.

[0041] According to one embodiment, the electrolyte contains no ether other than 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl (TTE).

[0042] According to one embodiment, the electrolyte contains no other diluent than the fluorinated alkyl ether(s) or fluorobenzene.

[0043] According to one embodiment, the electrolyte contains no diluent other than 1,2-difluorobenzene and its isomers. The volume proportion of methyl propionate may range from 20 to 50%, or from 25 to 40%, or from 30 to 35%, or from 20 to 30%, expressed as a percentage of the total volume of said solvent(s) and said diluent(s). A preferred range is from 25 to 35%.

[0044] The volume proportion of said diluent(s) may range from 50 to 80%, or from 60 to 75%, or from 65 to 70%, or from 70 to 80%, expressed as a percentage of the total volume of said solvent(s) and said diluent(s). A preferred range is from 65 to 75%. If several diluents are used together, the sum of the volume proportions of each diluent must fall within these ranges.

[0045] The electrolyte contains a negative electrode passivation additive selected from ethylene monofluorocarbonate (EFC), vinylene carbonate (VC), and a mixture thereof. The mass percentage of VC or FEC may range from 0.5 to 5%, 1 to 4%, or 2 to 3%, expressed as a percentage of the total mass of the mixture of one or more solvents, one or more diluents, and lithium salt(s). When VC and FEC are used together, the sum of the mass percentages of VC and FEC falls within these ranges.

[0046] Preferably, the electrolyte does not contain any other negative electrode passivation additives other than VC and / or FEC.

[0047] According to one embodiment, the electrolyte composition contains no solvent other than methyl propionate and no diluent other than 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl (TTE).

[0048] According to one embodiment, the electrolyte composition contains no solvent other than methyl propionate and no diluent other than fluorobenzene.

[0049] According to one embodiment, the electrolyte composition contains no solvent other than methyl propionate and no diluent other than 1,2-difluorobenzene.

[0050] The electrolyte composition contains one or more lithium salts, one of which is lithium bis(fluorosulfonyl)imidide Li(FSÛ2)2N (LiFSI). The combined use of a passivation additive with LiFSI results in the formation of a thin and stable passivation layer, thereby improving the cycling lifespan of the element.

[0051] Imidide salts can be associated with LiFSI. Examples include lithium bis(trifluoromethanesulfonyl)imidide LiN(CF3SÛ2)2 (LiTFSI) and lithium bisperfluoroethylsulfonylimidide LiN(C2F5SO2)2 (LiBETI).

[0052] Other lithium salts besides imidides may also be present. They can be selected among lithium hexafluorophosphate LiPFe, lithium perchlorate LiClCU, lithium tetrafluoroborate IÛBF4, lithium hexafluoroarsenate LiAsFe, lithium hexafluoroantimonate LiSbFe, lithium trifluoromethanesulfonate LiCFsSCh, lithium trifluoromethanesulfonemethide LiC(CF3SO2)3 (LiTFSM), lithium 4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LIDFOB), lithium tris(pentafluoroethyl)trifluorophosphate LiPF3(CF2CF3)3 (Li-FAP) and mixtures thereof.

[0053] The percentage of lithium ions from LiFSI can represent 50 to 100%, 60 to 90%, or 70 to 80% of the total number of lithium ions in the electrolyte. In a preferred embodiment, the only salt in the electrolyte is lithium bis(fluorosulfonyl)imidide, Li(FSO2)2N (LiFSI). In another preferred embodiment, the electrolyte does not contain LiPF6.

[0054] The total concentration of lithium salts generally ranges from 0.5 to 3 mol.L' 1 or from 0.8 to 2 mol. 1 or 1 to 1.5 mol. 1 . Preferred electrolyte compositions:

[0055] A preferred electrolyte composition consists of: - methyl propionate in volume proportions of 25-45% / 25-40% / 25-35%, - one or more of the diluents mentioned above in the volume proportions of 55-75% / 60-75% / 65-75%, the volume proportions being expressed in relation to the total volume of methyl propionate and said one or more diluents, - lithium bis(fluorosulfonyl)imide Li(FSÛ2)2N (LiFSI), - 1 to 4% by mass of a negative electrode passivation additive chosen from ethylene monofluorocarbonate (FEC), vinylene carbonate (VC) and a mixture thereof, the mass percentage of passivation additive being expressed in relation to the total mass of methyl propionate, said one or more diluents and lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI).

[0056] A preferred electrolyte composition consists of: - methyl propionate in volume proportions of 25-45% / 25-40% / 25-35%, - 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl ether (TTE) in volume proportions of 55-75% / 60-75% / 65-75%, the proportions being expressed relative to the total volume of methyl propionate and 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl ether (TTE), - lithium bis(fluorosulfonyl)imide Li(FSÛ2)2N (LiFSI), - 1 to 4% by mass of a negative electrode passivation additive chosen from ethylene monofluorocarbonate (FEC), vinylene carbonate (VC) and a mixture thereof, the mass percentage being expressed in relation to the total mass of methyl propionate, 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl ether (TTE) and lithium bis(fluorosulfonyl)imidide Li(FSÛ2)2N (LiFSI).

[0057] A preferred electrolyte composition consists of: - methyl propionate in a volume proportion of 25-35%, - of 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl ether (TTE) in a volume proportion of 65-75%, the volume proportions being expressed in relation to the total volume of methyl propionate and 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl ether (TTE), - lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI), - 1 to 4% by mass of vinylene carbonate (VC), the mass percentage being expressed in relation to the total mass of methyl propionate, 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl ether (TTE) and lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI).

[0058] A preferred electrolyte composition consists of: - methyl propionate in volume proportions of 25-45% / 25-40% / 25-35%, - fluorobenzene in volume proportions of 55-75% / 60-75% / 65-75%, the proportions being expressed relative to the total volume of methyl propionate and fluorobenzene, - lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI), - 1 to 4% by mass of a negative electrode passivation additive chosen from ethylene monofluorocarbonate (FEC), vinylene carbonate (VC) and a mixture thereof, the mass percentage being expressed relative to the total mass of methyl propionate, fluorobenzene and lithium bis(fluorosulfonyl)imidide Li(FSÛ2)2N (LiFSI).

[0059] A preferred electrolyte composition consists of: - methyl propionate in a volume proportion of 25-35%, - fluorobenzene in a volume proportion of 65-75%, the volume proportions being expressed relative to the total volume of methyl propionate and fluorobenzene, - lithium bis(fluorosulfonyl)imide Li(FSÛ2)2N (LiFSI), - 1 to 4% by mass of vinylene carbonate (VC), the mass percentage being expressed in relation to the total mass of methyl propionate, fluorobenzene and lithium bis(fluorosulfonyl)imidide Li(FSÛ2)2N (LiFSI).

[0060] A preferred electrolyte composition consists of: - methyl propionate in volume proportions of 25-45% / 25-40% / 25-35%, - 1,2-difluorobenzene in volume proportions of 55-75% / 60-75% / 65-75%, the proportions being expressed relative to the total volume of methyl propionate and 1,2-difluorobenzene, - lithium bis(fluorosulfonyl)imide Li(FSÛ2)2N (LiFSI), - 1 to 4% by mass of a negative electrode passivation additive chosen from ethylene monofluorocarbonate (FEC), vinylene carbonate (VC) and a mixture thereof, the mass percentage being expressed relative to the total mass of methyl propionate, 1,2-difluorobenzene and lithium bis(fluorosulfonyl)imidide Li(FSÛ2)2N (LiFSI).

[0061] A preferred electrolyte composition consists of: - methyl propionate in a volume proportion of 25-35%, - 1,2-Difluorobenzene in a volume proportion of 65-75%, the volume proportions being expressed relative to the total volume of methyl propionate and 1,2-difluorobenzene, - lithium bis(fluorosulfonyl)imide Li(FSÛ2)2N (LiFSI), - 1 to 4% by mass of vinylene carbonate (VC), the mass percentage being expressed in relation to the total mass of methyl propionate, 1,2-difluorobenzene and lithium bis(fluorosulfonyl)imidide Li(FSÛ2)2N (LiFSI). Positive active material and positive electrode:

[0062] The positive electrode comprises a first positive active material which is a lithium phosphate of at least one transition metal operating at an average potential greater than or equal to 3.6 V vs. Li + / Li. The lithium phosphate of at least one transition metal may be chosen from compounds of the following groups: i) a lithium phosphate of manganese and iron of formula: Li x Mni-y-zFe y MzPO4 (LMFP) where 0.8 <x<l,2 ; 0,5<l-y-z<l; 0<y+z<0,5 ; 0<y<0,50 et 0<z<0,2 et M est choisi dans le groupe constitué de Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S, Hf, Bi, Se et des mélanges de ceux-ci. In one embodiment, 0.7 <l-y-z<0,9 ou 0,75<l-y-z<0,9 ; In one embodiment, 0.15 <y<0,25 ; Typical formulas for lithium manganese and iron phosphate are LiMno.8Feo.2PO4, LiMno.7Feo.3PO4, LiMn2 / 3Fei / 3PO4 and LiMno.5Feo.5PO4. ii) a lithium vanadium fluorophosphate with the formula Lii+ X VPO4F (LVPF) where 0 <x<0,15, ou l’un de ses dérivés de formule Lii +x Vi-yMyPO4F z (LVMPF) where 0 <x<0,15, 0<y<0,5, 0,8<z<l,2 et M est choisi dans le groupe consistant en Ti, Al, Y, Cr, Cu, Mg, Mn, Fe, Co, Ni, Zr et des mélanges de ceux-ci, ou un mélange de plusieurs composés des groupes i) à ii).

[0063] Transition metal phosphates of the formula LiMPÛ4, where M denotes one or more transition metals and Fe, Ni, or Co is the major element, do not exhibit an average potential greater than or equal to 3.6 V vs. Li + / Li.

[0064] The lithium phosphate of at least one transition metal can be coated with a layer of carbon and / or carbon nanotubes, in particular to increase its electronic conductivity and / or ionic diffusivity.

[0065] The first positive active ingredient may be combined with a second positive active ingredient which is a lamellar lithiasis oxide of at least one transition metal which may be chosen from: iii) a lithiasis oxide of nickel, manganese and cobalt of formula Li w (Neither x Mn y Co z Mt)O2 (NMC) where 0.9 <w<l,l ; 0<x<l,l ; 0<y<l,l ; 0<z<l,l ; 0<t<l, 1 ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; iv) un oxyde lithié de nickel, cobalt et aluminium de formule Li w (Neither x CoyAl zMt)O2 (NCA) where 0.9 <w<l,l ; 0<x<l,l ; 0<y<l, 1 ; 0<z<l,l ; 0<t<l,l ; M étant choisi dans le groupe constitué de B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; (v) a compound of formula Lii +x Mid- x O2-yF y of cubic crystal structure where 0 <x<0,5 et 0<y<l et M représente un élément choisi dans le groupe constitué de Na, K, Mg, Ca, B, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Y, Zr, Nb, Mo, Ru, Ag, Sn, Sb, Ta, W, Bi, La, Pr, Eu, Nd et Sm et des mélanges de ceux-ci ; vi) un oxyde lithié de nickel et de manganèse (NMX) de formule Lia(Nii- x -y-zMn x CoyM z)O2 with 0.9 <a<l,l ; 0,60<l-x-y-z<0,80 ; 0<x<l ; 0<y<0,02 ; 0<z<l ; et M étant choisi dans le groupe consistant en Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ga, Ta, Nd, Pr, La et des mélanges de ceux-ci ; vii) un oxyde lithié de nickel et de manganèse de formule Li w (Neither x Mn y Co z Mt)O2 where 1, 1 <W<1,6 ; 0<x<l ; 0,50<y<0,80 ; 0<z<0,02 ; 0<t< 1 ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; viii) un oxyde lithié de nickel, de manganèse, de cobalt et d’aluminium (NMCA) de formule Li w (Neither x CoyAl zMntMs)O2 where 0.9 <w<l,l ; 0<x<l,l ; 0<y<l, 1 ; 0<z<l,l ; 0<t<l,l ; 0<s<l, 1, M étant au moins un élément choisi dans le groupe constitué de B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ga, Ta, Nd, Pr et La, avec plus particulièrement 0,83 < x. ix) un oxyde lithié de manganèse de formule Li x Mn2-y-zM'yM" z O4-5 where M' and M" are chosen from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo; M' and M" being different from each other, and 1 <X<1,4 ; 0<y<0,6 ; 0<z<0,2 ; 0<5<l, ou un mélange de plusieurs composés des groupes iii) à ix).

[0066] The composition of positive active matter may include a first active matter consisting of one or more of the compounds of groups i) to ii) and a second active matter consisting of one or more of the compounds of groups iii) to ix).

[0067] The composition of the active ingredient may include: - from 30 to 99% or from 40 to 99% or 50 to 99% or from 65 to 95% or from 75 to 90% by mass of the first active ingredient, - from 1 to 70% or from 1 to 60% or from 1 to 50% or from 5 to 35% or from 10 to 25% by mass of the second active substance, the percentages being expressed in relation to the total mass of the first positive active substance and the second positive active substance.

[0068] According to one embodiment, one or more of the compounds of group i) (LMFP) is or are associated with one or more compounds of group iii) (NMC).

[0069] According to one embodiment, the composition of the positive active ingredient comprises: - from 30 to 99% or 50 to 99% or from 65 to 95% or from 75 to 90% or from 75 to 85% by mass of an LMFP type compound, - from 1 to 70% or from 1 to 50% or from 5 to 35% or from 10 to 25% or from 15 to 25% by mass of an NMC type compound, the percentages being expressed in relation to the total mass of the LMFP type compound and the NMC type compound.

[0070] The positive electrode includes a current collector, at least one of whose faces is coated with a layer of a composition of positive active materials, which includes one or more active materials and optionally one or more binders and one or more electronically conductive materials.

[0071] The positive current collector is a current-conducting support that can take the form of a grid, foam, or metal strip. The metal strip can be solid or perforated. It can be made of aluminum or an alloy consisting primarily of aluminum, possibly coated with a conductive material such as carbon. It can also be made of steel or stainless steel. Its thickness can range from 6 to 30 µm, 5 to 20 µm, or 10 to 15 µm, preferably from 10 to 15 µm.

[0072] An ink is prepared by dispersing one or more positive active substances in a solvent or a mixture of several solvents. Optionally, a binder and an electronically conductive material are added to the dispersion. By varying the amount of solvent incorporated into the mixture, the viscosity of the ink can be varied before it is deposited onto a face of the current collector. The ink-coated current collector is dried and then laminated to adjust its thickness. After evaporation of the solvent(s), a layer is obtained composed of one or more active substances, the proportions of whose various constituents are typically: - 80 to 98% or 90 to 95% by mass of one or more positive active substances, - 1 to 10% or 2 to 5% by mass of one or more binders, - from 0.1 to 10% or from 2 to 5% by mass of one or more electronically conductive materials.

[0073] The binder can be selected from poly(vinylidene fluoride) (PVDF) and its copolymers, polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl or butyl methacrylate), poly(vinyl chloride) (PVC), poly(vinyl formalin), polyester, sequenced polyetheramides, polymers of acrylic acid, methacrylic acid, acrylamide, itaconic acid, sulfonic acid, elastomers, and cellulosic compounds such as carboxymethylcellulose (CMC). Elastomers suitable as binders can be selected from styrene-butadiene (SBR), butadiene-acrylonitrile (NBR), and hydrogenated butadiene-acrylonitrile (HNBR).Preferably, said at least one binder is an aqueous dispersible binder, such as polytetrafluoroethylene (PTFE), carboxymethylcellulose (CMC), styrene-butadiene (SBR), butadiene-acrylonitrile (NBR), hydrogenated butadiene-acrylonitrile (HNBR) and polyvinyl alcohol (PVA).

[0074] The electronic conductive material is usually chosen from graphite, carbon black, acetylene black, soot, graphene, carbon fibers, carbon nanotubes or a mixture of these. Negative active material and negative electrode:

[0075] The negative electrode may contain an active material capable of incorporating lithium into its structure. This may include graphite, coke, carbon black, and vitreous carbon. It may also include tin, silicon, carbon-silicon compounds such as Si-C composites, carbon-tin compounds, or carbon-tin compounds. and silicon, silicon oxides SiO x with 0 <x<2. Il peut aussi s’agir d’oxydes de titane, tels que Li^isOn. De préférence, il s’agit de graphite ou de composite Si-C.

[0076] Preferably, the negative active material is not lithium or a lithium-based alloy.

[0077] To obtain the negative active ingredient composition, an ink is prepared by dispersing one or more negative active ingredients, and optionally one or more binders and one or more electronically conductive compounds, in a solvent or a mixture of solvents. The solvent(s) may be organic or aqueous. Preferably, it is N-methylpyrrolidone.

[0078] The binder(s) can be chosen from the same list as that described in relation to the positive electrode, without necessarily being the same as those used for the positive electrode. Similarly, the electronically conductive material(s) can be chosen from the same list as that described in relation to the positive electrode, without necessarily being the same as those used for the positive electrode.

[0079] By varying the amount of solvent incorporated into the mixture, the viscosity of the ink can be varied before it is deposited onto a face of a current collector. The negative current collector is a current-conducting support that can take the form of a grid, foam, or foil. The metal foil can be solid or perforated and can be made of copper or a copper-based alloy, or aluminum or an aluminum-based alloy, depending on the operating potential of the chosen negative active material with respect to the Li couple. + / Li. It is made of copper in the case of a graphite-based active ingredient. The current collector thickness can range from 3 to 25 µm, or from 3 to 10 µm, preferably from 5 to 8 µm. The ink-coated current collector is dried and then laminated to adjust its thickness. After evaporation of the solvent(s), a layer is obtained composed of one or more active ingredients, the proportions of which are typically: - 85 to 98% or 90 to 98% by mass of one or more negatively charged active substances, - 1 to 10% or 1 to 5% by mass of one or more binders, - 0 to 5% by mass or 1 to 5% of one or more electronically conductive materials. Separator:

[0080] A separator is generally placed between a negative and a positive electrode to prevent potential short circuits. It prevents electrical contact between the negative and positive electrodes but still allows ion transport between them. The separator material can be chosen from the following: a polyolefin, for example, polypropylene and polyethylene; a polyester; glass fibers bonded together with a polymer; polyimide; polyamide; polyaramid; polyamideimide; and cellulose. The polyester can be chosen from polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). Advantageously, the polyester, polypropylene, or polyethylene contains or is coated with a material chosen from the group consisting of a metal oxide, a carbide, a nitride, a boride, a silicide, and a sulfide. This material can be SiO2 or Al2O3. The separator can be coated with an organic coating, for example, comprising an acrylate or PVDF or P(VdF-HFP). A preferred separator is made of polyethylene or consists of a combination of three layers: polypropylene PP / polyethylene PE / polypropylene PP.

[0081] A first preferred electrochemical element includes: - at least one positive electrode comprising a mixture of an LMFP-type compound and an NMC-type compound, in the mass proportions described above, - at least one negative electrode comprising a mixture of graphite and a Si-C composite, - an electrolyte consisting of a solvent which is methyl propionate, a diluent which is 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl (TTE) in a volume proportion of 50 to 80% of the total volume of methyl propionate and TTE, LiFSI and vinylene carbonate, in the proportions or percentages as described above.

[0082] A second preferred electrochemical element includes: - at least one positive electrode comprising a mixture of an LMFP-type compound and an NMC-type compound, in the mass proportions described above, - at least one negative electrode whose active material is made of graphite, - an electrolyte consisting of a solvent which is methyl propionate, a diluent which is 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl (TTE) in a volume proportion of 50 to 80% of the total volume of methyl propionate and TTE, LiFSI and vinylene carbonate, in the proportions or percentages as described above.

[0083] A third preferred electrochemical element includes: - at least one positive electrode comprising a mixture of an LMFP-type compound and an NMC-type compound, in the mass proportions described above, - at least one negative electrode whose active material is made of graphite, - an electrolyte consisting of a solvent which is methyl propionate, a diluent which is fluorobenzene in a volume proportion of 50 to 80% of the total volume of methyl propionate and fluorobenzene, LiFSI and vinylene carbonate, in the proportions or percentages as described above.

[0084] A preferred electrochemical element includes: - at least one positive electrode comprising a mixture of an LMFP-type compound and an NMC-type compound, in the mass proportions described above, - at least one negative electrode whose active material is made of graphite, - an electrolyte consisting of a solvent which is methyl propionate, a diluent which is 1,2-difluorobenzene in a volume proportion of 50 to 80% of the total volume of methyl propionate and 1,2-difluorobenzene, LiFSI and vinylene carbonate, in the proportions or percentages as described above.

[0085] The electrochemical element is manufactured using conventional methods. It can be prismatic, cylindrical, pocket-shaped, or button-shaped. Examples

[0086] Electrochemical elements of pouch type A to E were prepared. Their components are detailed in Table 1.

[0087] Table 1

[0088] Elements A and C are comparative. Their electrolyte comprises a mixture of two solvents, EC and EMC, but no diluent. Elements B, D, and E are according to the invention. Their electrolyte comprises a mixture of a solvent and a diluent, which is either 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl (TTE) or fluorobenzene (FB).

[0089] Cells A through E underwent cycling at 30°C, during which they were subjected to charge and discharge cycles at a rate of C / 2, where C is the cell's nominal capacity. The capacity discharged by each cell in each cycle was compared to its initial capacity. The change in the percentage of capacity discharged by cells A and B relative to their initial capacity is shown in Figure 1. It can be observed that the capacity discharged by cell B is greater than that discharged by cell A over the entire cycling period. This test highlights the effect of replacing the EC / EMC mixture with the MP / TTE mixture and the replacement of LiPFe with LiFSI on increasing the cell's cycling lifetime. Similarly, the change in the percentage of capacity discharged by cells C, D, and E relative to their initial capacity is shown in Figure 2.It can be noted that the discharged capacities of cells D and E are greater than that discharged by cell C over the entire cycling period. This test highlights the effect of replacing the EC / EMC mixture with the MP / TTE or MP / FB mixture and replacing LiPFe with LiFSI on increasing the cell's cycling lifetime.

[0090] Di-Al pouch-type electrochemical elements were prepared. The active material of the positive electrode is the same for all elements: a mixture of LMFP and NMC in mass proportions of 40 / 60% w / w. The active material of the negative electrode is also the same for all elements: graphite. The electrolyte compositions of these elements are detailed in Table 2.

[0091] Table 2 * Example outside of invention TTE: 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl ether FB: fluorobenzene DFB: difluorobenzene

[0092] The Al elements with DI underwent cycling at 30°C, including charges and discharges at the C / 2 regime. The IC regime corresponds to the current applied to charge / discharge the electrochemical element to the cutoff voltage within one hour. The capacitance discharged by each element in each cycle was compared to its initial capacitance. The change in the percentage of capacitance discharged by the Al elements with DI relative to their initial capacitance is shown in Figure 3. The capacitance retention after 200 cycles is shown in Table 2. It can be noted that: - the element DI whose electrolyte includes 1,2-difluorobenzene as a diluent has a longer cycling lifetime than the element Al whose electrolyte includes a mixture of cyclic carbonates EC, PC and linear carbonates DMC, EMC. - Element DI exhibits a longer cycling lifetime than elements B1 and Cl, whose electrolyte contains methyl propionate (MP) and, as diluents, 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl ether, and fluorobenzene, respectively. This test demonstrates the superiority of 1,2-difluorobenzene over these two other diluents.

Claims

Demands

1. Lithium-ion electrochemical element comprising: a) at least one positive electrode comprising a first positive active material which is a lithium phosphate of at least one transition metal operating at an average potential greater than or equal to 3.6 V vs. Li + / Li; b) at least one negative electrode comprising a negatively active material; c) an electrolyte comprising: - one or more solvents, one of which is methyl propionate (MP), - one or more diluents selected from a fluorinated alkyl ether, fluorobenzene, 1,2-difluorobenzene and its isomers, 1,2,3-trifluorobenzene and its isomers, 1,2,3,4-tetrafluorobenzene and its isomers, pentafluorobenzene, hexafluorobenzene, 2-fluorotoluene and its isomers and a mixture thereof, the volume proportion of said one or more diluents representing from 50 to 80% of the total volume of said one or more solvents and said one or more diluents, - lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI), - a negative electrode passivation additive selected from ethylene monofluorocarbonate (FEC), vinylene carbonate (VC), and a mixture thereof. Claim 2] Lithium-ion electrochemical element according to claim 1, wherein lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI) is the sole salt of the electrolyte. Claim 3] Lithium-ion electrochemical element according to claim 1 or 2, wherein the electrolyte consists of: - a solvent which is methyl propionate and in one or more diluents selected from a fluorinated alkyl ether, fluorobenzene, 1,2-difluorobenzene and its isomers, 1,2,3-trifluorobenzene and its isomers, 1,2,3,4-tetrafluorobenzene and its isomers, pentafluorobenzene, hexafluorobenzene, 2-fluorotoluene and its isomers and a mixture thereof, the volume proportion of said one or more diluents representing from 50 to 80% of the total volume of methyl propionate and said one or more diluents, - lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI), - a negative electrode passivation additive selected from ethylene monofluorocarbonate (FEC), vinylene carbonate (VC) and a mixture thereof. Claim 4] Lithium-ion electrochemical element according to any one of the preceding claims, wherein the fluorinated alkyl ether is the ether of 1,1,2,2-tetrafluoroethyl and 2,2,3,3-tetrafluoropropy 1 e.

5. Electrochemical element according to any one of claims 1 to 3, wherein the diluent is 1,2-difluorobenzene.

6. Lithium-ion electrochemical element according to claim 3 or 4, wherein the electrolyte consists of: i) methyl propionate and 1,1,2,2-tetrafluoroethyl ether and 2,2,3,3-tetrafluoropropyl ether, ii) lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI), and iii) vinylene carbonate.

7. Lithium-ion electrochemical element according to claim 3, wherein the electrolyte consists of: i) methyl propionate and fluorobenzene, ii) lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI), and iii) vinylene carbonate. Claim 8] Lithium-ion electrochemical element according to claim 5, wherein the electrolyte consists of: i) methyl propionate and 1,2-difluorobenzene, ii) lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI), and iii) vinylene carbonate.Claim 9] Lithium-ion electrochemical element according to any one of claims 1 to 7, wherein in the electrolyte, the volume proportion of said one or more diluents is from 65 to 75% of the total volume of said one or more solvents and said one or more diluents. Claim 10] Lithium-ion electrochemical element according to any one of the preceding claims, wherein in the electrolyte, the mass of the passivation additive represents from 1 to 4% of the total mass of said one or more solvents, said one or more diluents, and lithium bis(fluorosulfonyl)imidide Li(FSO2)2N. Claim 11] Lithium-ion electrochemical element according to any one of the preceding claims, wherein the concentration of lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI) is from 0.8 to 1.5 mol.L'. 1Claim 12] Lithium-ion electrochemical element according to any one of the preceding claims, wherein the first positive active material is selected from: i) a lithium manganese iron phosphate of formula: Li x Mni-y-zFe y MzPO4 (LMFP) where 0.8 <x<l,2 ; 0,5<l-y-z<l; 0<y+z<0,5 ; 0<y<0,50 et 0<z<0,2 et M est choisi dans le groupe constitué de Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S, Hf, Bi, Se et des mélanges de ceux-ci ; ii) un fluorophosphate lithié de vanadium de formule Lii+xVPCLF (LVPF) où 0<x<0,15, ou l’un de ses dérivés de formule Lii+xVi-yMyPCUFz (LVMPF) où 0<x<0,15, 0<y<0,5, 0,8<z<l,2 et M est choisi dans le groupe consistant en Ti, Al, Y, Cr, Cu, Mg, Mn, Fe, Co, Ni, Zr et des mélanges de ceux-ci, ou un mélange de plusieurs composés des groupes i) et ii).

13. Lithium-ion electrochemical element according to claim 12, wherein the first positive active material is mixed with a second positive active material selected from: iii) a lithium oxide of nickel, manganese, and cobalt of formula Li w (NixMn y CozMt)O2 (NMC) where 0.9 <w<l,l ; 0<x<l,l ; 0<y<l,l ; 0<z<l,l ; 0 <t<l, 1 ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; iv) un oxyde lithié de nickel, cobalt et aluminium de formule Liw(Ni x Co y Al zMt)O2 (NCA) where 0.9 <w<l,l ; 0<x<l,l ; 0<y<l,l ; 0<z<l,l ; 0<t<l,l ; M étant choisi dans le groupe constitué de B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; v) un composé de formule Lii+xMi-xCL-yFy de structure cristalline cubique où 0<x<0,5 et 0<y<l et M représente un élément choisi dans le groupe constitué de Na, K, Mg, Ca, B, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Y, Zr, Nb, Mo, Ru, Ag, Sn, Sb, Ta, W, Bi, La, Pr, Eu, Nd et Sm et des mélanges de ceux-ci ; vi) un oxyde lithié de nickel et de manganèse (NMX) de formule Lia(Nii-xy-zMnxCo y Mz)O2 with 0.9 <a<l,l ; 0,60<l-x-y-z<0,80 ; 0<x<l ; 0<y<0,02 ; 0 <z<l ; et M étant choisi dans le groupe consistant en Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ga, Ta, Nd, Pr, La et des mélanges de ceux-ci ; vii) un oxyde lithié de nickel et de manganèse de formule Liw(NixMn y Co zMt)O2 where 1, 1 <W<1,6 ; 0<x<l ; 0,50<y<0,80 ; 0<z<0,02 ; 0<t<l ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; viii) un oxyde lithié de nickel, de manganèse, de cobalt et d’aluminium (NMC A) de formule Liw(NixCo y Al z MntMs)O2 where 0.9 <w<l,l ; 0<x<l,l ; 0<y<l, 1 ; 0<z<l,l ; 0 <t<l, 1 ; 0<s<l, 1, M étant au moins un élément choisi dans le groupe constitué de B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, Sr, Ce, Ga, Ta, Nd, Pr et La . ix) un oxyde lithié de manganèse de formule LixMn2-y-zM'yM" zO4-5 where M' and M" are chosen from the group consisting of Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo; M' and M" being different from each other, and 1 <X<1,4 ; 0<y<0,6 ; 0<z<0,2 ; 0<5<l, ou un mélange de plusieurs composés des groupes iii) à ix). Revendication 14] Elément électrochimique lithium-ion selon la revendication 13, dans lequel la première matière active positive représente de 30 à 99% de la masse totale des matières actives positives et la seconde matière active positive représente de 1 à 70% de la masse totale des matières actives positives. Revendication 15] Elément électrochimique lithium-ion selon l’une des revendications 12 à 14, dans lequel la première matière active positive est un composé du groupe i) et la seconde matière active positive est un composé du groupe iii).Claim 16] Lithium-ion electrochemical element according to any one of the preceding claims, wherein the negative active material is selected from carbon, preferably from. graphite, silicon, a carbon-silicon composite (Si-C), silicon oxides (SiO₂) x with 0 <x<2 et un mélange de ceux-ci.

17. Use of an electrolyte consisting of: - a solvent which is methyl propionate and in one or more diluents selected from a fluorinated alkyl ether, fluorobenzene, 1,2-difluorobenzene and its isomers, 1,2,3-trifluorobenzene and its isomers, 1,2,3,4-tetrafluorobenzene and its isomers, pentafluorobenzene, hexafluorobenzene, 2-fluorotoluene and its isomers and a mixture thereof, the volume proportion of said one or more diluents representing from 50 to 80% of the total volume of methyl propionate and said one or more diluents, - lithium bis(fluorosulfonyl)imide Li(FSÛ2)2N (LiFSI), - a passivation additive for a negative electrode of a lithium-ion electrochemical element, the passivation additive being selected from ethylene monofluorocarbonate (FEC), vinylene carbonate (VC) and a mixture thereof, in a lithium-ion electrochemical element to improve its cycling life.

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