Electrolyte composition for a lithium-ion electrochemical element

Abstract

The invention relates to an electrolyte comprising: - 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 sulphate and lithium difluorophosphate; - one or more lithium salts other than lithium difluorophosphate; the methyl propionate, ethylene sulphate and lithium difluorophosphate interact to limit the growth of the passivation layer on the surface of the negative electrode and thereby limit the increase in the internal resistance of the electrochemical element.

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 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 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 room 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 electrolyte corrosion, it also contributes to increasing the cell's irreversible capacitance. Furthermore, it is resistive, and its growth tends to increase the cell's internal resistance, consequently reducing its power output. 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 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 and decomposes the electrolyte solvents, resulting in decreased element performance. These two documents propose additives capable of preventing the decomposition reaction of the electrolyte solvents by PF5.

[0006] 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 1] A - 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.

[0007] WO 2024 / 04578 describes the use of an additive of formula B: [Chem 2] B where R1, R2, R3, 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 the additive of formula B.

[0008] Document EP-A-3703174 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 whole 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 containing such an electrolyte exhibits stable performance even when used at a temperature of 85°C.

[0009] We are looking for new ways to extend the lifespan of an electrochemical element lithium-ion when exposed for several days to a temperature above ambient temperature, notably by limiting the growth of internal resistance of electrochemical elements during cycling or storage. Summary

[0010] To this end, an electrolyte composition has been discovered that reduces the growth rate of the passivation layer. This electrolyte composition includes: - 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.

[0011] The invention is based on the discovery of an interaction between methyl propionate and two additives, namely 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 temperatures above ambient, for example close to 45°C, whether the element is stored or used in cycling.

[0012] According to one embodiment, the volume of methyl propionate in the solvent mixture is greater than or equal to the volume of cyclic carbonate.

[0013] According to one embodiment, the volume of methyl propionate is greater than or equal to the volume of linear carbonate.

[0014] According to one embodiment, methyl propionate represents from 30% to 90% of the volume of the solvent mixture.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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 selected from: a) a lithium iron phosphate of formula LixFe1-yMyPO4 (LFP), where 0.8 ≤ x ≤ 1.2; 0 ≤ y ≤ 0.6 and M is selected from the group consisting of Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Mn, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S and mixtures thereof; b) a lithium manganese phosphate of formula Li x Mn 1-y M yPO4(LMP), where 0.8 ≤ x ≤ 1.2; 0 ≤ y ≤ 0.6 and M is chosen from the group consisting of Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Fe, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S and mixtures thereof; c) a lithium manganese and iron phosphate of formula: LixMn1-y-zFeyMzPO4 (LMFP) where 0.8 ≤ x ≤ 1.2; 0.5 ≤ 1-yz < 1; 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 mé- langes de ceux-ci ; d) un fluorophosphate lithié de vanadium de formule Li1+xVPO4F (LVPF) où 0≤x≤0,15, ou l’un de ses dérivés de formule Li 1+x V 1-y M y PO4F z (LVMPF) where 0≤x≤0.15, 0 <y≤0,5, 0,8≤z≤1,2 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).

[0021] 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≤1.1 ; 0 <x<1 ; 0<y<1 ; 0<z<1 ; 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 ; f) un oxyde lithié de nickel, cobalt et aluminium de formule Liw(NixCoyAlzMt)O2 (NCA) où 0,9≤w≤1,1 ; 0<x<1 ; 0<y<1 ; 0<z<1 ; 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) un composé de formule Li 1+x M 1-x O 2-y F yof cubic crystal structure where 0 ≤ x ≤ 0.5 and 0 ≤ y ≤ 1 and M represents an element chosen from the group consisting of 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 and Sm and mixtures thereof; h) a lithium nickel manganese oxide (NMX) of formula Lia(Ni1-xy-zMnxCoyMz)O2 with 0.9 ≤ a ≤ 1.1; 0.60 ≤ 1-xyz < 0.80; 0 <x<1 ; 0≤y≤0,02 ; 0≤z<1 ; 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 Li w (Neither x Mn y Co z M t )O2 where 1.1 <w≤1,6 ; 0<x<1 ; 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 mé- langes de ceux-ci. j) un oxyde lithié de nickel et de manganèse de formule LixMn2-y-zM'yM''zO4-δ 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≤δ≤1, or a mixture of several compounds from groups e) to j).

[0022] According to one embodiment, the first positive active substance is a compound of group c), the second positive active substance is a compound of 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.

[0023] According to one embodiment, the first positive active substance represents from 65 to 95% of the total mass of the first positive active substance and the second positive active substance, 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.

[0024] Finally, the invention also relates to the use of the electrolyte as described above in an electrochemical element to improve the storage or cycling lifespan of the element at a temperature of 25°C or higher. Brief description of the figure

[0025] [Fig. 1] shows the variation in the internal resistance of an element during aging at 45°C for two electrolyte compositions, one being electrolyte composition A outside the scope of the invention, the other being electrolyte composition B according to the invention. Detailed description of embodiments Electrolyte:

[0026] The electrolyte contains a solvent mixture that may include 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 in small amounts. A small amount is defined as a mass proportion of less than 10% of the total mass of the solvent mixture and the lithium salt(s). Preferred cyclic carbonates are EC, PC, FEC, and VC.

[0027] The solvent mixture may contain one or more linear carbonates. Examples of linear carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (EMC), dipropyl carbonate (DPC), and mixtures thereof. DMC and DEC are preferred linear carbonates.

[0028] The solvent mixture may contain one or more cyclic carbonates, saturated or unsaturated, and one or more linear carbonates.

[0029] The volume proportion of methyl propionate in the solvent mixture may be greater than the volume proportion of the cyclic carbonate(s).

[0030] The volume proportion of methyl propionate in the solvent mixture may be greater than the volume proportion of the linear carbonate(s).

[0031] 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).

[0032] 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 50% or greater than or equal to 60% or greater than or equal to 70% or greater than or equal to 80%.

[0033] 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%.

[0034] A preferred range for the volume percentage of methyl propionate is from 30 to 50%.

[0035] A preferred solvent mixture consists of EC, DMC and MP.

[0036] Preferably, the electrolyte composition contains no esters other than methyl propionate. Preferably, the electrolyte composition contains no solvents other than cyclic or linear carbonate(s) and methyl propionate.

[0037] The electrolyte composition contains at least one lithium salt, other than lithium difluorophosphate. This lithium salt may be chosen from lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), or lithium tetrafluoroborate (LiBF6). 4,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), lithium difluoro(oxalato)borate (LIDFOB), lithium tris(pentafluoroethyl)trifluorophosphate LiPF3(CF2CF3)3 (LiFAP) and mixtures thereof.

[0038] The concentration of 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 -1 Preferably, it is approximately equal to 1 mol.L -1 .

[0039] Lithium hexafluorophosphate (LiPF6) is preferred, with or without lithium bis(fluorosulfonyl)imidide (Li(FSO2)2N, or LiFSI). If LiFSI is combined with LiPF6, the percentage of lithium ions from LiFSI can represent 10 to 90%, 20 to 80%, or 30 to 70% of the total lithium ions in the electrolyte.

[0040] Vinylene carbonate VC or ethylene monofluorocarbonate FEC, ethylene sulfate ESA and lithium difluorophosphate LiPO2F2 are preferably used as additives and added to the solvent mixture already supplemented with one or more lithium salts.

[0041] The mass percentage of VC or FEC can 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 lithium salt(s). When VC and FEC are used together, the sum of the mass percentages of VC and FEC falls within these ranges.

[0042] 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.

[0043] 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.

[0044] Preferably, the electrolyte contains no additives other than VC and / or FEC, ESA, and LiPO2F2. Preferred electrolyte compositions:

[0045] A preferred electrolyte composition includes: - a solvent mixture consisting of EC / DMC / MP in the following volume proportion ranges: 20-35% / 20-35% / 30-60%, - VC in a mass proportion of 2 to 4%, - ESA in a mass proportion of 0.5 to 2%, - LiPO2F2 in a mass proportion of 0.1 to 1%.

[0046] A preferred electrolyte composition includes: - a solvent mixture consisting of EC / DMC / MP in the following volume proportion ranges: 25-35% / 25-35% / 30-50%, - VC in a mass proportion of 2.5 to 3.5%, - ESA in a mass proportion of 0.5 to 1.5%, - LiPO2F2 in a mass proportion of 0.2 to 0.8%.

[0047] 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:

[0048] The active ingredient is not particularly limited. It can 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.

[0049] The lithium phosphate of at least one transition metal may be chosen from compounds in the following groups: a) a lithium iron phosphate of formula LixFe1-yMyPO4 (LFP), where 0.8 ≤ x ≤ 1.2; 0 ≤ y ≤ 0.6 and M is chosen from the group consisting of Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Mn, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S and mixtures thereof; b) a lithium manganese phosphate of formula Li x Mn 1-y M yPO4(LMP), where 0.8 ≤ x ≤ 1.2; 0 ≤ y ≤ 0.6 and M is chosen from the group consisting of Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Fe, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S and mixtures thereof; c) a lithium manganese and iron phosphate of formula: LixMn1-y-zFeyMzPO4 (LMFP) where 0.8 ≤ x ≤ 1.2; 0.5 ≤ 1-yz < 1; 0 <y+z≤0,5 ; 0<y≤0,50 et 0≤z≤0,2 et M est choisi dans le groupe consisting of Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S and mixtures thereof; In one embodiment, 0.7≤1-yz≤0.9 or 0.75≤1-yz≤0.9; In another embodiment, 0.15≤y≤0.25; Typical formulas of lithium manganese and iron phosphate are LiMn0.8Fe0.2PO4, LiMn0.7Fe0.3PO4, LiMn2 / 3Fe1 / 3PO4 and LiMn0.5Fe0.5PO4; d) a lithium vanadium fluorophosphate of formula Li1+xVPO4F (LVPF) where 0≤x≤0.15, or one of its derivatives of formula Li 1+x V 1-y M y PO4F z(LVMPF) where 0≤x≤0.15, 0 <y≤0,5, 0,8≤z≤1,2 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). Le ou les composé(s) de type phosphate lithié, notamment le ou les composé(s) de type phos- phate lithié de manganèse et de fer (LMFP) et le ou les composé(s) de type phosphate lithié de fer (LFP), peuvent être revêtus d’une couche de carbone et / ou de nanotubes de carbone, notam- ment afin d’accroitre leur conductivité électronique et / ou leur diffusivité ionique.

[0050] 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≤1.1 ; 0 <x<1 ; 0<y<1 ; 0<z<1 ; 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 ; Des exemples de composés du groupe e) sont LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, LiNi 0,5 Mn 0,3 Co 0,2 O2, LiNi0.6Mn0.2Co0.2O2 and LiNi0.8Mn0.1Co0.1O2. f) a lithium oxide of nickel, cobalt and aluminum of formula Li w (Neither x Co y Al z M t)O2(NCA) where 0.9 ≤ w ≤ 1.1 ; 0 <x<1 ; 0<y<1 ; 0<z<1 ; 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 ; Selon un mode de réalisation, 0,5≤x ou 0,6≤x ou 0,7≤x ou 0,8≤x. Selon un mode de réalisation, x≤0,9 ou x≤0,8. Selon un mode de réalisation, 0,5≤x≤0,9. Des exemples de composés du groupe f) sont LiNi0,84Co0,08Al0,08O2, LiNi0,85Co0,10Al0,05O2, LiNi0,87Co0,06Al0,07O2 et LiNi0,89Co0,06Al0,05O2. g) un composé de formule Li 1+x M 1-x O 2-y F y of cubic crystal structure where 0≤x≤0.5 and 0≤y≤1 and M represents an element chosen from the group consisting of 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 and Sm and mixtures thereof; h) a lithium nickel manganese oxide (NMX) of formula Li a (Neither 1-x-y-z Mn x Co y M z)O2with 0.9≤a≤1.1; 0.60≤1-xyz<0.80; 0 <x<1 ; 0≤y≤0,02 ; 0≤z<1 ; 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<1 ; 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 and mixtures thereof. According to an embodiment 0.5≤x≤0.9. j) a lithium nickel and manganese oxide of formula LixMn2-y-zM'yM''zO4-δ 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≤δ≤1, or a mixture of several compounds from groups e) to j).

[0051] The composition of positive active material may include a first active material consisting of one or more of the compounds from groups a) to d) and a second active material consisting of one or more of the compounds from groups e) to j).

[0052] The composition of positive active material may include: - 50 to 99% or 65 to 95% or 75 to 90% by mass of the first active material, - 1 to 50% or 5 to 35% or 10 to 25% by mass of the second active material, the percentages being expressed in relation to the total mass of the first positive active material and the second positive active material.

[0053] 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.

[0054] 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.

[0055] According to one embodiment, the positive active material composition comprises: - 50 to 99% or 65 to 95% or 75 to 90% or 75 to 85% by mass of an LMFP type compound, - 1 to 50% or 5 to 35% or 10 to 25% or 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.

[0056] 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.

[0057] 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, possibly coated with a conductive material, such as carbon. It can be made of of steel or stainless steel. Its thickness can be in the range of 6 to 30 µm or 5 to 20 µm or 10 to 15 µm, preferably 10 to 15 µm.

[0058] An ink is prepared by dispersing one or more active ingredients 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 ingredients in proportions of the various constituents that 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, - 0.1 to 10% or 2 to 5% by mass of one or more electronically conductive materials.

[0059] 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), carboxymethyl cellulose (CMC), styrene-butadiene (SBR), butadiene-acrylonitrile (NBR), hydrogenated butadiene-acrylonitrile (HNBR) and polyvinyl alcohol (PVA).

[0060] 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:

[0061] The negative electrode may include a negative active material capable of incorporating lithium into its structure. This material 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. Titanium oxides, such as Li4Ti5O12, may also be used. Preferably, it is graphite.

[0062] 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 mixture of solvents. The solvent(s) may be organic or aqueous. Preferably, it is N-methylpyrrolidone.

[0063] 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 of the positive electrode. Similarly, The electronic 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.

[0064] 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 material. 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 materials, the proportions of the various constituents of which are typically: - 85 to 98% or 90 to 98% by mass of one or more negative active materials, - 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:

[0065] A separator is generally placed between a negative and a positive electrode to prevent potential short circuits. It prevents electrical contact between a negative and a positive electrode but nevertheless allows the transport of ions between them. The separator material can be chosen from the following: 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.

[0066] 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.

[0067] The electrochemical element is manufactured conventionally. It can be prismatic, cylindrical, pocket-shaped, or button-shaped. Examples

[0068] Two electrolytes were prepared. Their compositions are detailed in Table 1.

[0069] Table 1 Composition A Composition B (comparative) Solvents EC / PC / EMC / DMC EC / DMC / MP 10 / 20 / 25 / 45 (% vol.) 30 / 30 / 40 (% vol.) Lithium salt LiPF61 mol.L -1 LiPF61 mol.L -1 Additives VC 3% VC 3% FEC 1% - - ESA 1% - LiPO2F20.5% Increase in internal resistance of the element after 170 days of accelerated aging at 45°C +32% +2% Capacity retention of the element after 170 days of accelerated aging at 45°C

[0070] 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.

[0071] Two electrochemical elements A and B, comprising electrolytes A and B respectively, were prepared. Their positive electrodes are identical. These electrodes comprise, as active materials, a mixture consisting by mass of 80% lithium manganese iron phosphate (LMFP) and 20% 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.

[0072] Electrochemical elements A and B underwent an accelerated aging test, which consisted of placing them in a temperature-controlled chamber at 45°C. Periodically, the elements were removed from the chamber and their internal resistance was measured. The internal resistance measurement was performed at a fixed 50% state of charge and during a 30-second discharge test at 3°C. The change in internal resistance of the elements during 200 days of storage is shown in Figure 1. It can be observed 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 provided by the association of propionate with ethylene sulfate and lithium difluorophosphate on limiting the growth of the passivation layer.

Claims

Claims

1. 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.

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 claims 1 to 3, wherein methyl propionate constitutes from 30% to 90% of the volume of the solvent mixture.

5. 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 solvent mixture and said one or more lithium salts.

6. 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 solvent mixture and said one or more lithium salts.

7. 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 solvent mixture and said one or more lithium salts.

8. An electrolyte according to any one of the preceding claims, wherein: - methyl propionate represents from 30 to 60% of the total volume of solvents, - said at least one cyclic carbonate represents from 20 to 35% of the total volume of solvents, - said at least one linear carbonate represents from 20 to 35% of the total volume of solvents.

9. An 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 thereof. ethylene sulfate and lithium difluorophosphate, - lithium hexafluorophosphate.

10. 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 LixFe1-yMyPO4 (LFP), where 0.8≤x≤1.2; 0≤y≤0.6 and M is selected from the group consisting of Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Mn, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S and mixtures thereof; b) a lithium manganese phosphate of formula LixMn1-yMyPO4 (LMP), where 0.8≤x≤1.2; 0 ≤ y ≤ 0.6 and M is chosen from the group consisting of Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Fe, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S and mixtures thereof; c) a lithium manganese and iron phosphate of formula: LixMn1-y-zFeyMzPO4 (LMFP) where 0.8 ≤ x ≤ 1.2; 0.5 ≤ 1 - yz < 1; 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) un fluorophosphate lithié de vanadium de formule Li; 1+x VPO4F (LVPF) where 0≤x≤0.15, or one of its derivatives with the formula Li1+xV1-yMyPO4Fz (LVMPF) where 0≤x≤0.15, 0 <y≤0,5, 0,8≤z≤1,2 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). [Revendication 11] Elément électrochimique selon la revendication 10, dans lequel la première matière active positive est mélangée à une seconde matière active positive choisie parmi : e) un oxyde lithié de nickel, manganèse et cobalt de formule Li w (Neither x Mn y Co z M t)O2(NMC) where 0.9 ≤ w ≤ 1.1 ; 0 <x<1 ; 0<y<1 ; 0<z<1 ; 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 ; f) un oxyde lithié de nickel, cobalt et aluminium de formule Li w (Neither x Co y Al z M t )O2(NCA) where 0.9 ≤ w ≤ 1.1 ; 0 <x<1 ; 0<y<1 ; 0<z<1 ; 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) un composé de formule Li 1+x M 1-x O 2-y F y of cubic crystal structure where 0≤x≤0.5 and 0≤y≤1 and M represents an element chosen from the group consisting of 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 and Sm and mixtures thereof; h) a lithium nickel manganese oxide (NMX) of formula Li a(Neither 1-x-y-z Mn x Co y M z )O2with 0.9≤a≤1.1; 0.60≤1-xyz<0.80; 0 <x<1 ; 0≤y≤0,02 ; 0≤z<1 ; 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<1 ; 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 and mixtures thereof; j) a lithium oxide of nickel and manganese of formula Li x Mn 2-y-z M' y M'' z O 4-δwhere 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≤δ≤1, or a mixture of several compounds from groups e) to j).

12. Electrochemical element according to any one of claims 10 to 11, wherein 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.

13. An element according to claim 12, wherein the first positive active material represents from 65 to 95% of the total mass of the first and second positive active materials, and the second positive active material represents from 5 to 35% of the total mass of the first and second positive active materials.

14. Use of the electrolyte according to any one of claims 1 to 9 in an electrochemical element to improve the storage or cycling life of the element at a temperature of 25°C or higher.

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