Electrolyte composition for lithium-ion electrochemical element

Abstract

An electrolyte comprising: - a solvent mixture including methyl propionate, at least one cyclic carbonate and / or at least one linear carbonate, - vinylene carbonate or ethylene monofluorocarbonate or a mixture thereof, ethylene sulfate and lithium difluorophosphate, - one or more lithium salts other than lithium difluorophosphate. Methyl propionate, ethylene sulfate and lithium difluorophosphate interact to limit the growth of the passivation layer on the surface of the negative electrode and thus limit the increase in the internal resistance of the electrochemical element. Abbreviated figure: Figure 1

Description

Title of the invention: Electrolyte composition for lithium-ion electrochemical element. Technical field

[0001] The present exposition belongs to the technical field of electrolyte compositions for lithium-ion type electrochemical elements. Background

[0002] Lithium-ion electrochemical elements are known in 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 bundle. The bundle is impregnated with an organic electrolyte, often a liquid, generally composed of a mixture of alkyl carbonates in which a lithium salt is dissolved, for example, lithium hexafluorophosphate (LiPF6).

[0003] Lithium-ion electrochemical cells age more rapidly when exposed to temperatures above ambient temperature (20-25°C). The temperature increase promotes the growth of a passivation layer on the surface of the negative electrode. While this passivation layer does protect the negative electrode from corrosion by the electrolyte, it also contributes to increasing the irreversible capacitance of the cell. Furthermore, it is resistive, and its growth tends to increase the internal resistance of the cell, consequently reducing its power performance. This performance degradation is even more pronounced when the cell is discharged under high currents and at low temperatures.

[0004] We therefore sought to reduce the aging rate of a lithium-ion electrochemical element when it is exposed to a temperature above ambient temperature.

[0005] US patent documents 2023 / 0187696 and WO 2024 / 04578 explain that LiPF6 is sensitive to heat and traces of moisture present in the element's container. Under the influence of heat and moisture, LiPF6 decomposes into HF and phosphorus pentafluoride PF5. PF5 reacts with the electrolyte solvents and the

[0006]

[0007] decomposes. This results in a decrease in the element's performance. These two documents propose additives capable of preventing the decomposition reaction of the electrolyte solvents by PF5. US 2023 / 0187696 describes in its example 1 an electrolyte comprising: - LiPF6 as a lithium salt, - a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) as organic solvents, - a first additive of formula A [Chem.l]

[0008]

[0009] Formula A - a second additive which is vinyl and ethylene carbonate (VEC), - vinylene carbonate (VC), - a third additive which is 1,3-propane sultone, - a fourth additive which is ethylene sulfate. WO 2024 / 04578 describes the use of an additive of formula B: [Chem.2]

[0010] Formula B where Ri, R2, Ri, and R4 are independently chosen from a hydrogen atom (H) and an alkyl group, and R5 is a halogen atom. Example 1 in this document describes an electrolyte containing LiPF6, a solvent mixture consisting of diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and ethylene carbonate (EC) in a mass ratio of 20:50:30. Additives are added at a rate of 1% vinylene carbonate (VC), 2% ethylene sulfate, 2% lithium difluorophosphate, and 20 ppm of additive formula B. Document EP-A-3 703 174 describes an electrolyte comprising: - at least one tetrafluorinated or hexafluorinated lithium salt, - lithium bis(fluorosulfonyl)imidide salt LiFSI, - vinylene carbonate, - ethylene sulfate (ESA, also abbreviated as DTD), - lithium difluorophosphate, - at least one organic solvent selected from the group consisting of cyclic or linear carbonates, cyclic or linear esters, cyclic or linear ethers, and a mixture thereof, the ratio of the mass of ethylene sulfate to the mass of vinylene carbonate before addition to the solvent being strictly less than 1, The mass percentage of lithium difluorophosphate representing less than 1% of the mass of the assembly consisting of said at least one tetrafluorinated or hexafluorinated lithium salt, lithium bis(fluorosulfonyl)imidide salt, and said at least one organic solvent. An element comprising such an electrolyte exhibits stable performance even when used at a temperature of 85°C.

[0011] New means of extending the life of a lithium-ion electrochemical element when it is exposed for several days to a temperature above ambient temperature, in particular by limiting the growth of internal resistance of the electrochemical elements during cycling or storage of these elements. Summary

[0012] To this end, an electrolyte composition has been discovered that reduces the growth rate of the passivation layer. This electrolyte composition comprises: - a mixture of solvents comprising methyl propionate, at least one cyclic carbonate and / or at least one linear carbonate, - vinylene carbonate or ethylene monofluorocarbonate or a mixture thereof, ethylene sulfate and lithium difluorophosphate, - one or more lithium salts other than lithium difluorophosphate.

[0013] The invention is based on the discovery of an interaction between methyl propionate and the two additives, which are ethylene sulfate and lithium difluorophosphate. Methyl propionate, ethylene sulfate, and lithium difluorophosphate interact to limit the growth of the passivation layer at the negative electrode, even when the element is subjected to accelerated aging conditions, such as exposure to a temperature above ambient, for example close to 45°C, whether the element is stored or used in cycling.

[0014] According to one embodiment, the volume of methyl propionate in the solvent mixture is greater than or equal to the volume of cyclic carbonate.

[0015] According to one embodiment, the volume of methyl propionate is greater than or equal to the volume of linear carbonate.

[0016] According to one embodiment, methyl propionate represents from 30% to 90% of the volume of the solvent mixture.

[0017] According to one embodiment, the mass percentage of vinylene carbonate represents from 0.5 to 5% of the total mass of the mixture of solvents and said one or more lithium salts.

[0018] According to one embodiment, the mass percentage of ethylene sulfate represents from 0.1 to 3% of the total mass of the mixture of solvents and said one or more lithium salts.

[0019] According to one embodiment, the mass percentage of lithium difluorophosphate represents from 0.1 to 3% of the total mass of the mixture of solvents and said one or more lithium salts.

[0020] According to one embodiment, methyl propionate represents 30 to 60% of the total volume of solvents, said at least one cyclic carbonate represents 20 to 35% of the total volume of solvents, and said at least one linear carbonate represents 20 to 35% of the total volume of solvents.

[0021] According to one embodiment, the electrolyte consists of: - methyl propionate, ethylene carbonate and dimethyl carbonate, - vinylene carbonate and / or ethylene monofluorocarbonate or a mixture thereof, ethylene sulfate and lithium difluorophosphate, - lithium hexafluorophosphate.

[0022] The invention also relates to an electrochemical element comprising: - an electrolyte as described above, - at least one positive electrode comprising a first positive active material chosen from: a) a lithium iron phosphate of formula LixFei yMyP04 (LFP), where 0.8 <x<l,2 ; 0<y<0,6 et M est choisi dans le groupe consistant en Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Mn, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S et des mélanges de ceux-ci ; b) a lithium manganese phosphate of formula LixMni yMyP04 (LMP), where 0.8 <x<l,2 ; 0<y<0,6 et M est choisi dans le groupe consistant en Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Fe, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S et des mélanges de ceux-ci ; c) a lithium manganese and iron phosphate of formula: LixMni y zFeyMzPO4(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 et des mélanges de ceux-ci ; d) a lithium vanadium fluorophosphate of formula Lil+xVPO4F (LVPF) where 0 <x<0,15, ou l’un de ses dérivés de formule Lil+xVl-yMyPO4Fz (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, et Zr, ou un mélange de plusieurs composés des groupes a) à d).

[0023] According to one embodiment, the first positive active ingredient is mixed with a second positive active ingredient selected from: e) a lithium oxide of nickel, manganese and cobalt of formula Liw(NixMnyCozMt)O2(NMC) where 0.9 <w<l,l ; 0<x<l ; 0<y<l ; 0<z<l ; 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 ; f) a lithium oxide of nickel, cobalt and aluminium of formula Liw(NixCoyAlzMt)O2(NCA) where 0.9 <w<l,l ; 0<x<l ; 0<y<l ; 0<z<l ; 0<t<l ; M étant choisi dans le groupe constitué de Al, 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 ; g) a compound of formula Lii+xMi_xO2_yFy with 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 ; h) a lithium nickel manganese oxide (NMX) of formula Lia(Nii_x y zMnxCoyMz)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 ; i) un oxyde lithié de nickel et de manganèse de formule Liw(NixMnyCozMt)O2 où 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. j) a lithium oxide of nickel and manganese of formula LixMn2.y.zM'yM"zO4.ô 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<ô<l, ou un mélange de plusieurs composés des groupes e) à j).

[0024] According to one embodiment, the first positive active material is a compound of group c), the second positive active material is a compound of group e), the first positive active material representing from 50 to 99% of the total mass of the first positive active material and the second positive active material, the second positive active material representing from 1 to 50% of the total mass of the first positive active material and the second positive active material.

[0025] According to one embodiment, the first positive active ingredient represents from 65 to 95% of the total mass of the first positive active ingredient and the second positive active ingredient, the second positive active substance represents from 5 to 35% of the total mass of the first positive active substance and the second positive active substance.

[0026] Finally, the invention also relates to the use of the electrolyte as described above, in an electrochemical element to improve the storage or cycling life of the element at a temperature greater than or equal to 25°C. Brief description of the figure

[0027] [Fig. 1] represents the variation of the internal resistance of an element during aging at 45°C for two electrolyte compositions, one which is the electrolyte composition A outside the invention, the other which is the electrolyte composition B according to the invention. Detailed description of the implementation methods Electrolyte:

[0028] The electrolyte contains a mixture of solvents which may contain one or more saturated or unsaturated cyclic carbonates. Examples of saturated carbonates include ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butylene carbonate (BC), and mixtures thereof. Examples of unsaturated carbonates include vinylene carbonate (VC). FEC and VC may be used either as solvents or as additives if present in small amounts. A "small amount" is defined as a mass proportion of less than 10% relative to the mass of the solvent mixture and the lithium salt(s). Preferred cyclic carbonates are EC, PC, FEC, and VC.

[0029] The solvent mixture may contain one or more linear carbonates. Examples of linear carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dipropyl carbonate (DPC), and mixtures thereof. Preferred linear carbonates are DMC and DEC.

[0030] The solvent mixture may contain one or more cyclic carbonates, saturated or unsaturated, and one or more linear carbonates.

[0031] The volume proportion of methyl propionate in the solvent mixture may be greater than the volume proportion of the cyclic carbonate(s).

[0032] The volume proportion of methyl propionate in the solvent mixture may be greater than the volume proportion of the linear carbonate(s).

[0033] The volume proportion of methyl propionate in the solvent mixture may be greater than the sum of the volume proportions of the cyclic carbonate(s) and the linear carbonate(s).

[0034] The volume proportion of methyl propionate in the solvent mixture may be greater than or equal to 30% or greater than or equal to 40% or greater than or equal to at 50% or greater than or equal to 60% or greater than or equal to 70% or greater than or equal to 80%.

[0035] The volume proportion of methyl propionate in the solvent mixture may be less than or equal to 90% or less than or equal to 80% or less than or equal to 70% or less than or equal to 60% or less than or equal to 50% or less than or equal to 40%.

[0036] A preferred range of the volume percentage of methyl propionate is from 30 to 50%.

[0037] A preferred mixture of solvents consists of EC, DMC and MP.

[0038] Preferably, the electrolyte composition does not contain any esters other than methyl propionate. Preferably, the electrolyte composition does not contain any solvents other than the cyclic or linear carbonate(s) and methyl propionate.

[0039] The electrolyte composition contains at least one lithium salt, other than lithium difluorophosphate. This lithium salt can be chosen from lithium perchlorate LiClO4, lithium hexafluorophosphate LiPF6, lithium tetrafluoroborate LiBF4, lithium hexafluoroarsenate LiAsF6, lithium hexafluoroantimonate LiSbF6, lithium trifluoromethanesulfonate LiCF3SO3, lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI), lithium bis(trifluoromethanesulfonyl)imidide LiN(CF3SO2)2 (LiTFSI), lithium trifluoromethanesulfonemethide LiC(CF3SO2)3 (LiTFSM), lithium bisperfluoroethylsulfonylimidide LiN(C2F5SO2)2 (LiBETI), lithium 4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI), lithium bis(oxalato)borate (LiBOB), the lithium difluoro(oxalato)borate (LIDFOB), lithium tris(pentafluoroethyl)trifluorophosphate LiPF3(CF2CF3)3 (LiFAP) and mixtures thereof.

[0040] The concentration of the lithium salt or the total concentration of lithium salts generally ranges from 0.5 to 1.5 mol.L 1 or from 1 to 1.5 mol.L *. Preferably, it is approximately equal to 1 mol.L *.

[0041] Preferably, lithium hexafluorophosphate LiPF6 is chosen, whether or not associated with lithium bis(fluorosulfonyl)imidide Li(FSO2)2N (LiFSI). If LiFSI is associated with LiPF6, the percentage of lithium ions from LiFSI can represent 10 to 90%, 20 to 80%, or 30 to 70% of the total number of lithium ions in the electrolyte.

[0042] Vinylene carbonate VC or ethylene monofluorocarbonate FEC, ethylene sulfate ES A and lithium difluorophosphate LiPO2F2 are preferably used as additives and added to the solvent mixture already supplemented with one or more lithium salts.

[0043] The mass percentage of VC or FEC may range from 0.5 to 5%, or from 1 to 4%, or from 2 to 3% relative to the total mass of the solvent mixture and said one or more lithium salts. In the case where VC and FEC are used together, the sum of the mass percentages of VC and FEC falls within these ranges.

[0044] The mass percentage of ESA can range from 0.1 to 3% or from 0.2 to 2% or from 0.5 to 1.5% of the total mass of the mixture of solvents and said one or more lithium salts.

[0045] The mass percentage of LiPO2F2 can range from 0.1 to 3% or from 0.2 to 2% or from 0.5 to 1.5% or from 0.1 to 1% of the total mass of the mixture of solvents and said one or more lithium salts.

[0046] Preferably, the electrolyte does not contain any additives other than VC and / or FEC, ESA and LiPO2F2. Preferred electrolyte compositions:

[0047] A preferred electrolyte composition includes: - a solvent mixture consisting of EC / DMC / MP in the following volume proportions: 20-35% / 20-35% / 30-60%, - VC in a mass proportion ranging from 2 to 4%, - ESA in a mass proportion ranging from 0.5 to 2% - LiPO2F2 in a mass proportion ranging from 0.1 to 1%.

[0048] A preferred electrolyte composition includes: - a solvent mixture consisting of EC / DMC / MP in the following volume proportions: 25-35% / 25-35% / 30-50%, - VC in a mass proportion ranging from 2.5 to 3.5%, - ESA in a mass proportion ranging from 0.5 to 1.5% - LiPO2F2 in a mass proportion ranging from 0.2 to 0.8%.

[0049] A preferred electrolyte composition includes: - a solvent mixture consisting of EC / DMC / MP in the following volume proportions: 30% / 30% / 40%, - VC in a mass proportion of 3%, - ESA in a mass proportion of 1%, - LiPO2F2 in a mass proportion of 0.5%. Positive active material and positive electrode:

[0050] The positive active material is not particularly limited. It may be a lithium phosphate of at least one transition metal or a lamellar lithium oxide of at least one transition metal or a mixture of the phosphate and the lamellar oxide.

[0051] The lithium phosphate of at least one transition metal may be chosen from compounds of the following groups: a) a lithium iron phosphate of formula LixFei yMyPO4 (LFP), where 0.8 <x<l,2 ; 0<y<0,6 et M est choisi dans le groupe consistant en Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Mn, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S et des mélanges de ceux-ci ; b) a lithium manganese phosphate of formula LixMni yMyPO4 (LMP), where 0.8 <x<l,2 ; 0<y<0,6 et M est choisi dans le groupe consistant en Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Fe, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S et des mélanges de ceux-ci ; c) a lithium manganese and iron phosphate of formula: LixMni y zFeyMzPO4(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 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 of lithium manganese and iron phosphate are LiMnOj8FeOj2PO4, LiMnOj7FeOj3PO4, LiMn2 / 3FeI / 3PO4 and LiMnOj5FeOj5PO4; d) a lithium vanadium fluorophosphate of formula Lil+xVPO4F (LVPF) where 0 <x<0,15, ou l’un de ses dérivés de formule Lil+xVl-yMyPO4Fz (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 et Zr, ou un mélange de plusieurs composés des groupes a) à d). The lithium phosphate type compound(s), in particular the lithium manganese and iron phosphate type compound(s) (LMFP) and the lithium iron phosphate type compound(s) (LFP), may be coated with a layer of carbon and / or carbon nanotubes, in particular to increase their electronic conductivity and / or ionic diffusivity.

[0052] The lamellar lithium oxide of at least one transition metal may be chosen from compounds of the following groups: e) a lithium oxide of nickel, manganese and cobalt of formula Liw(NixMnyCozMt)O2(NMC) where 0.9 <w<l,l ; 0<x<l ; 0<y<l ; 0<z<l ; 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 ; Examples of compounds in group e) are LiNii / 3Mni / 3Coi / 3O2, LiNio,5Mnoj3Coo>2O2, LiNio>6MnOj2Cooj2O2 and LiNio^MnojCoojO^ f) a lithium oxide of nickel, cobalt and aluminium of formula Liw(NixCoyAlzMt)O2(NCA) where 0.9 <w<l,l ; 0<x<l ; 0<y<l ; 0<z<l ; 0<t<l ; M étant choisi dans le groupe constitué de Al, 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 ; According to one embodiment, 0.5 <x ou 0,6<x ou 0,7<x ou 0,8<x. According to one embodiment, x<0.9 or x<0.8. According to one embodiment, 0.5 <x<0,9. Examples of compounds of group f) are LiNio>84Coojo8Alojo802, LiNio,85COo,loAlo,0502, LiNioj87COo>06Alo,0702 and LiNioj89COo>06Alo,0502. g) a compound of the formula Lii+xMi_xO2_yFy 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 ; h) a nickel and manganese lithiated oxide (NMX) of the formula Lia(Nii-xyzMnxCoyMz)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 ; i) a lithium oxide of nickel and manganese of formula Liw(NixMnyCozMt)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. According to one embodiment 0.5 <x<0,9. j) a lithium oxide of nickel and manganese of formula LixMn2.y.zM'yM"zO4.ô 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<ô<l, ou un mélange de plusieurs composés des groupes e) à j).

[0053] The composition of positive active material may comprise a first active material consisting of one or more of the compounds of groups a) to d) and a second active material consisting of one or more of the compounds of groups e) to j).

[0054] The composition of the positive active ingredient may include: - 50 to 99% or 65 to 95% or 75 to 90% by mass of the first active substance, - 1 to 50% or 5 to 35% or 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.

[0055] According to one embodiment, one or more of the compounds of group a) is or are associated with one or more compounds of one of the groups e), f), h) and i). Preferably, one or more of the compounds of group a) is associated with one or more compounds of group f), i.e. one or more LFP type compounds is or are associated with one or more NCA type compounds.

[0056] According to one embodiment, one or more of the compounds of group c) is or are associated with one or more compounds of one of the groups e), f), h) and i). Preferably, one or more of the compounds of group c) is associated with one or more compounds of group e), i.e. one or more LMFP type compounds is or are associated with one or more NMC type compounds.

[0057] According to one embodiment, the positive active ingredient composition comprises: - 50 to 99% or 65 to 95% or 75 to 90% or 75 to 85% by mass of an LMFP type compound, - 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.

[0058] 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.

[0059] 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 mainly of aluminum, optionally coated with a conductive material, such as carbon. It can be made of steel or stainless steel. Its thickness can be in the range of 6 to 30 µm, 5 to 20 µm, or 10 to 15 µm, preferably 10 to 15 µm.

[0060] 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 on 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 active ingredients, - 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.

[0061] The binder can be chosen from poly(vinylidene fluoride) (PVDF) and its copolymers, polytetrafluoroethylene (PTFE) and its copolymers, the Polyacrylonitrile (PAN), poly(methyl or butyl methacrylate), poly(vinyl chloride) (PVC), poly(vinyl formalin), polyester, sequenced polyetheramides, acrylic acid polymers, methacrylic acid polymers, acrylamide polymers, itaconic acid polymers, sulfonic acid polymers, elastomers, and cellulosic compounds such as carboxymethylcellulose (CMC). Elastomers suitable as binders include 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).

[0062] The electronically conductive material is generally chosen from graphite, carbon black, acetylene black, soot, graphene, carbon fibers, carbon nanotubes or a mixture thereof. Negative active material and negative electrode:

[0063] The negative electrode may include a negative active material capable of inserting lithium into its structure. This may be graphite, coke, carbon black, or vitreous carbon. It may also be tin, silicon, carbon-silicon compounds, carbon-tin compounds, or carbon-tin-silicon compounds. It may also be titanium oxides, such as Li4Ti5O12. Preferably, it is graphite.

[0064] 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.

[0065] The binder(s) may be chosen from the same list as that described in relation to the positive electrode, without necessarily being the same as those of the positive electrode. Similarly, the electronically conductive material(s) may be chosen from the same list as that described in relation to the positive electrode, without necessarily being the same as those of the positive electrode.

[0066] By varying the amount of solvent incorporated into the mixture, the viscosity of the ink can be varied before it is deposited on 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 potential of the operation of the chosen negative active material with respect to the Li+ / Li couple. It is made of copper in the case of a graphite-based active material. The thickness of the current collector 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 materials, the proportions of whose various constituents are typically: - 85 to 98% or 90 to 98% by mass of one or more negative active ingredients, - 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:

[0067] A separator is generally interposed between a negative electrode and a positive electrode to prevent potential short circuits. It prevents electrical contact between a negative electrode and a positive electrode but nevertheless allows the transport of ions between these two electrodes. The separator material can be chosen from the following materials: a polyolefin, for example polypropylene and polyethylene, a polyester, glass fibers bonded together by 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 is made of a combination of three layers which are polypropylene PP / polyethylene PE / polypropylene PP.

[0068] A preferred electrochemical element comprises: - 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 graphite as the active material, - an electrolyte consisting of methyl propionate, ethylene carbonate, dimethyl carbonate, vinylene carbonate, ethylene sulfate, lithium difluorophosphate and LiPF6, in the proportions or percentages as described above.

[0069] The electrochemical element is manufactured in a conventional manner. It can be in prismatic, cylindrical, pocket or button format. Examples

[0070] Two electrolytes were prepared. Their compositions are detailed in Table 1.

[0071] [Tables 1] Composition A (comparative) Composition B Solvents EC / PC / EMC / DMC 10 / 20 / 25 / 45 (% vol.) EC / DMC / MP 30 / 30 / 40 (% vol.) Lithium salt LiPF61 mol / L LiPF61 mol / L Additives VC3% VC3% FEC 1% - - ES A 1% - LiPO2F2 0.5% Increase in internal element strength after 170 days of accelerated aging at 45°C +32% +2% Element capacity retention after 170 days of accelerated aging at 45°C 91% 93%

[0072] Composition B differs from composition A by the presence of methyl propionate in the solvent mixture and the presence of ethylene sulfate and lithium difluorophosphate among the additives.

[0073] Two electrochemical elements A and B, comprising electrolytes A and B, were prepared. Their positive electrodes are identical. These electrodes comprise, as active materials, a mixture consisting by mass of 80% of a lithium manganese iron phosphate (LMFP) and 20% of a lithium nickel manganese cobalt oxide (NMC), which is a compound of group e) in which x > 0.5. Their negative electrodes are identical and comprise graphite as an active material.

[0074] The electrochemical elements A and B underwent an accelerated aging test which consisted of placing them in a thermostatically controlled chamber at a temperature of 45°C. Periodically, the elements were removed from the chamber and their internal resistance was measured. The internal resistance measurement was performed for a state of charge fixed at 50% and during a 30-second discharge test at 3C. The variation in the internal resistance of the elements during 200 days of storage is shown in [Fig. 1]. It can be noted that the internal resistance of element A increases much more rapidly than that of element B. The percentage of initial capacity retention of element B is greater than that of element A. This test therefore highlights the beneficial effect of combining propionate with ethylene sulfate and lithium difluorophosphate on limiting the growth of the passivation layer.

Claims

Demands

1. Electrolyte comprising: - a mixture of solvents including methyl propionate, at least one cyclic carbonate and / or at least one linear carbonate, - vinylene carbonate or ethylene monofluorocarbonate or a mixture thereof, ethylene sulfate and lithium difluorophosphate, - one or more lithium salts other than lithium difluorophosphate, - methyl propionate representing from 30 to 60% of the total volume of solvents, - said at least one cyclic carbonate representing from 20 to 35% of the total volume of solvents, - said at least one linear carbonate representing from 20 to 35% of the total volume of solvents.

2. Electrolyte according to claim 1, wherein the volume of methyl propionate in the solvent mixture is greater than or equal to the volume of cyclic carbonate.

3. Electrolyte according to claim 1 or 2, wherein the volume of methyl propionate is greater than or equal to the volume of linear carbonate.

4. Electrolyte according to any one of the preceding claims, wherein the mass percentage of vinylene carbonate represents from 0.5 to 5% of the total mass of the mixture of solvents and said one or more lithium salts.

5. Electrolyte according to any one of the preceding claims, wherein the mass percentage of ethylene sulfate represents from 0.1 to 3% of the total mass of the mixture of solvents and said one or more lithium salts.

6. Electrolyte according to any one of the preceding claims, wherein the mass percentage of lithium difluorophosphate represents from 0.1 to 3% of the total mass of the mixture of solvents and said one or more lithium salts.

7. Electrolyte according to any one of the preceding claims, consisting of: - methyl propionate, ethylene carbonate and dimethyl carbonate, - vinylene carbonate and / or ethylene monofluorocarbonate or a mixture of these, ethylene sulfate and lithium difluorophosphate, - lithium hexafluorophosphate.

8. Electrochemical element comprising: - an electrolyte according to any one of the preceding claims, - at least one positive electrode comprising a first positive active material selected from: a) a lithium iron phosphate of formula LixFei yMyPO4 (LFP), where 0.8 <x<l,2 ; 0<y<0,6 et M est choisi dans le groupe consistant en Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Mn, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S et des mélanges de ceux-ci ; b) un phosphate lithié de manganèse de formule LixMni yMyPO4 (LMP), où 0,8<x<l,2 ; 0<y<0,6 et M est choisi dans le groupe consistant en Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Fe, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S et des mélanges de ceux-ci ; c) un phosphate lithié de manganèse et de fer de formule : LixMnb y zFeyMzP04(LMFP) où 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 et des mélanges de ceux-ci ;d) a lithium vanadium fluorophosphate of formula Lil+xVP04F (LVPF) where 0 <x<0,15, ou l’un de ses dérivés de formule Lil+xVl-yMyPO4Fz (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, et Zr, ou un mélange de plusieurs composés des groupes a) à d).;

9. Electrochemical element according to claim 8, wherein the first positive active material is mixed with a second positive active material selected from: e) a lithium oxide of nickel, manganese and cobalt of formula Liw(NixMnyCozMt)O2(NMC) where 0.9 <w<l,l ; 0<x<l ; 0<y<l ; 0<z<l ; 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 ; f) un oxyde lithié de nickel, cobalt et aluminium de formule

10.

11. Liw(NixCoyAlzMt)O2(NCA) where 0.9 <w<l,l ; 0<x<l ; 0<y<l ; 0<z<l ; 0<t< 1 ; M étant choisi dans le groupe constitué de Al, 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 ; g) a compound of formula Lii+xMi_xO2 yFy with 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 ; h) a lithium nickel manganese oxide (NMX) of formula Lia(Nii_x_y_zMnxCoyMz)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 ; i) a lithium oxide of nickel and manganese of formula Liw(NixMnyCozMt)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 ; j) a lithium nickel manganese oxide of formula LixMn2 y_zM'yM"zO4_ô 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<ô<l, or a mixture of several compounds from groups e) to j). Electrochemical element according to any one of claims 8 to 9, in which the first positive active substance is a compound from group c), the second positive active substance is a compound from group e), the first positive active substance representing from 50 to 99% of the total mass of the first positive active substance and the second positive active substance, the second positive active substance representing from 1 to 50% of the total mass of the first positive active substance and the second positive active substance. Element according to claim 10, in which The first positive active ingredient represents 65 to 95% of the total mass of the first and second positive active ingredients. the second positive active substance represents from 5 to 35% of the total mass of the first positive active substance and the second positive active substance.

12. Use of the electrolyte according to any one of claims 1 to 7, in an electrochemical element to improve the storage or cycling life of the element at a temperature greater than or equal to 25 °C.