Electrolyte, and lithium ion battery comprising same

Abstract

The invention relates to an electrolyte for a lithium-ion battery, comprising, in percent by weight relative to the weight of the electrolyte: - between 8% and 20% lithium salt which comprises at least a mixture of LiFSI and LiPF6, - between 0.5% and 1.5% methylene methane disulfonate, - between 0.25% and 2% ethylene sulfate, - a complementary additive, the weight percentage of which does not exceed 2.5%, - a sufficient quantity of a non-aqueous organic solvent. The invention also relates to a lithium-ion battery comprising said electrolyte.

Description

DESCRIPTION ELECTROLYTE AND LITHIUM-ION ACCUMULATOR COMPRISING IT

[0001] The present invention relates to an electrolyte and a lithium-ion accumulator comprising this electrolyte.

[0002] In the context of the present invention, a lithium-ion accumulator is a device used for the electrochemical storage of energy and its restitution as needed. With reference to the English term "battery", the term "lithium-ion battery" is also used to designate this type of electric accumulator. It is an electrical generator consisting of two electrical conductors (namely the electrodes) in contact with an ionic conductor (the electrolyte) which can be in the form of liquid, gel or solid.

[0003] The principle of the lithium-ion battery is based on the reversible exchange of the lithium ion between a cathode (usually a lithiated transition metal oxide such as cobalt or manganese dioxide) and an anode (usually graphite) during the charge and discharge cycles, with very good cycling performance. The electrolyte is aprotic (usually a dissolved lithium hexafluorophosphate salt, hereinafter abbreviated as "LiPFe") to passivate the anode and avoid degrading the highly reactive electrodes.

[0004] The lithium-ion battery has the following advantages in particular: - high energy density thanks to the properties of lithium, - low self-discharge, - good cyclability.

[0005] This is why the lithium-ion accumulator is widely used for mobile applications (telephony, automotive) and in systems using renewable energies (solar, wind).

[0006] More specifically, with the increasing consumption of portable electronic devices, electric vehicles and the storage of renewable energy, the development of lithium-ion batteries with high energy density and power, safe and low cost has become essential. Research and development has therefore mainly focused on the development of new materials electrodes but also new electrolyte compositions to obtain ever more efficient lithium-ion accumulators.

[0007] Over time and with the number of charge and discharge cycles, the capacity of a lithium-ion battery tends to degrade and its internal resistance to increase, so much so that it becomes unusable.

[0008] The physicochemical phenomenon at the origin of this aging of the lithium-ion accumulator is the following: when the graphite of the electrode is in contact with the electrolyte, in particular during the èreAs the battery is charged, a layer of lithium is deposited on the electrode, naturally reducing the available quantity of lithium ions in solution in the electrolyte. This so-called "passivation" layer electrically insulates the electrode from the electrolyte, which prevents and / or restricts a further reaction of the electrode with the electrolyte. This slightly reduces the capacity of the battery and increases its internal resistance. This passivation layer thickens over time and with the number of cycles, which increases the internal resistance and accordingly reduces the capacity of the lithium-ion battery.

[0009] Thus, the alteration of the capacity, compared to its nominal value, is one of the visible effects of the aging of a lithium-ion accumulator and contributes to reducing the performance of said accumulator. In this regard, in the context of the present invention, the capacity of a lithium-ion accumulator is defined as being the quantity of charges that can be supplied by the accumulator during discharge. This is the integral of the current that can be delivered during one hour (Ah) and which allows the accumulator to go from a fully charged state to a 0% charge state. The capacity measurement is carried out by galvanostatic cycling at a constant current density.

[0010] The inventors of the present invention sought to overcome this drawback by developing a new lithium-ion battery electrolyte composition for which the retention of its capacity during charge and discharge cycles or during storage of the latter at high temperature is superior compared to that of lithium-ion batteries known from the state of the art.

[0011] In the context of the disclosure of the present invention, the following abbreviations are used: - BS for butane sultone; - CMC for carboxymethylcellulose; - DEC for diethyl carbonate; - DMC for dimethyl carbonate; - DTD for ethylene sulfate; - EC for ethylene carbonate; - EMC for ethyl and methyl carbonate; - FEC for fluoroethylene carbonate; - LCO for LiCoO2; - LiBOB for lithium bis(oxalato)borate; - LiDFOB for lithium difluoro(oxalato)borate; - LFP for LiFePO4; - LiFSI for lithium bis(fluorosulfonyl) imide; - LiPFe for lithium hexafluorophosphate; - LiTFSI for LiN(SO2CF3)2; - LMO for LiMn2O4; - MMDS for methylene methane disulfonate; - NCA for Li(Ni,Co,AI)O2; - NMC for Li(Ni,Mn,Co)O2; - NMP for N-methyl-2-pyrrolidone; - PC for propylene carbonate; - PES for prop-l-ene-l,3-sultone; - PS for 1,3-propane sultone; - PVDF for polyvinylidene fluoride; - SBR for styrene-butadiene; - TMS for trimelene sulfate; - VEC for vinylethylene carbonate; - VC for vinylene carbonate.

[0012] The first subject of the invention is an electrolyte which is characterized in that it comprises, in mass percentages expressed relative to the mass of said electrolyte: - between 8% and 20%, preferably between 11% and 16%, of lithium salt which comprises at least less a mixture of LiFSI and LiPFe, - between 0.5% and 1.5% of MMDS, - between 0.25% and 2%, preferably between 0.5% and 1.5%, of DTD, - at least one additional additive, the mass percentage of which does not exceed 5%, most preferably 2.5%, and if the additional additive is FEC, the mass percentage of FEC is less than 0.5%, preferably less than 0.25%, - Qsp of at least one non-aqueous organic solvent.

[0013] "Qsp" is the acronym for "Quantity sufficient for" to signify that the mass percentage of solvent in the electrolyte composition is such that, added to the percentages of all the other constituents of said electrolyte composition, a total of 100% is obtained.

[0014] The inventors have discovered, quite surprisingly, that the combination of MMDS and DTD in quantities such that their mass percentages are respectively between 0.5% and 1.5% and between 0.25% and 2% with at least one additional additive whose mass percentage does not exceed, quite preferably, 2.5% and if it is FEC, said mass percentage is less than 0.5%, in the composition of an electrolyte made it possible to obtain a lithium-ion accumulator whose capacity retention remains higher during cycling or during storage than that of lithium-ion accumulators known from the state of the art.

[0015] In other words, the selection of a mass content of between 0.5% and 1.5% of MMDS and between 0.25% and 2% of DTD in association with at least one additional additive at a mass content as described above in the electrolyte composition of a lithium-ion accumulator has an effect on the capacity thereof, as well as on the retention of its capacity. Indeed, this selection, in synergy with the additional additive(s), makes it possible to obtain excellent capacity retention during cycling or during storage of the lithium-ion accumulator. This is very beneficial for the performance of the lithium-ion accumulator which therefore has an increased lifetime compared to that of lithium-ion accumulators known from the state of the art.

[0016] Furthermore, the inventors have discovered, quite surprisingly, that the combination of MMDS and DTD in quantities such that their mass percentages are respectively between 0.5% and 1.5% and between 0.25% and 2% with at least less an additional additive whose mass percentage does not exceed, most preferably, 2.5% (and if it is FEC, said mass percentage is less than 0.5%) and a mixture of LiFSI and LiPFe made it possible to dissolve impurities likely to contaminate the cell. More precisely, during the manufacture of the cell, the handling of the various elements thereof is conducive to the contamination of the electrolyte by metallic impurities. These metallic impurities can cause short circuits, which in turn can cause a whole host of problems such as a loss of performance, a fire, or even an explosion. LiFSI as an additive to LiPFe makes it possible to dissolve metallic impurities, in particular stainless steel. Dissolution takes place during the cell formation stage (charge / discharge cycle of the cell to activate it).

[0017] The complementary additive may advantageously be chosen from the group consisting of PS, VC, FEC, VEC, PES, BS and TMS, taken alone or as a mixture of these.

[0018] Most preferably, the additional additive is PS and / or VC. Indeed, tests using electrolytes according to the invention comprising PS and / or VC have been very conclusive. VC passivates the graphite electrode. PS limits the generation of gas (which we wish to avoid).

[0019] As described above, the total mass percentage of the complementary additive(s) does not exceed 5% and most preferably 2.5%. If the complementary additive is FEC, the mass percentage of FEC is less than 0.5%, preferably less than 0.25%.

[0020] For additional additives other than FEC, the mass percentage of each of the additional additives may advantageously be between 0.25% and 2%, preferably between 0.5% and 1.5%. In other words: - the mass percentage of PS can be between 0.25% and 2%, preferably between 0.5% and 1.5%, - the mass percentage of VC can be between 0.25% and 2%, preferably between 0.5% and 1.5%, - the mass percentage of VEC can be between 0.25% and 2%, preferably between 0.5% and 1.5%, - the mass percentage of BS can be between 0.25% and 2%, preferably between 0.5% and 1.5%, - the mass percentage of TMS can be between 0.25% and 2%, preferably between 0.5% and 1.5%, - the mass percentage of PES can be between 0.25% and 2%, preferably between 0.5% and 1.5%.

[0021] In one embodiment of the invention, the total mass percentage of the additional additive(s) may be between 0.25% and 5%, most preferably between 0.25% and 2.5%, more preferably between 1% and 2.5%.

[0022] In a preferred embodiment of the invention, the electrolyte comprises, as complementary additives, PS and VC according to the following mass percentages: - between 0.25% and 2%, preferably between 0.5% and 1.5% of PS, - between 0.25% and 2%, preferably between 0.5% and 1.5% of VC.

[0023] In the electrolyte composition according to the invention, the lithium salt ensures the ionic conductivity of the lithium ions within the lithium-ion accumulator.

[0024] As explained above, the lithium salt comprises at least a mixture of LiFSI and LiPFe. The lithium salt may further comprise LiBF4, LiTFSI, UCIO4, LiAsFe, LiBOB and LiDFOB, taken alone or as a mixture thereof.

[0025] Preferably, the lithium salt is a mixture of LiFSI and LiPFe.

[0026] Lithium salt LiPFe offers the best compromise between electrochemical and thermal stability, ionic conductivity and passivation of the aluminum foil serving as a current collector for the positive electrode.

[0027] In one embodiment of the invention, with regard to the lithium salt, the electrolyte comprises in mass percentages expressed relative to the mass of said electrolyte: - between 1.5% and 4%, preferably between 2% and 3.5% of LiFSI, - between 8.5% and 16%, preferably between 10% and 14%, of LiPFe.

[0028] The electrolyte according to the invention may comprise one or more non-aqueous organic solvents. It allows the lithium-ion battery to function properly and optimizes the conductivity of the electrolyte.

[0029] It may for example be one or more non-aqueous organic solvents chosen from cyclic or linear chain carbonate esters. These cyclic or linear chain carbonate esters make it possible to adjust the conductivity and viscosity of the electrolyte according to the invention so as to improve the cycling and power performance of the lithium-ion battery.

[0030] More specifically, the cyclic carbonate ester may be selected from the group consisting of EC, PC, 1,2-butylene carbonate and 2,3-butylene carbonate.

[0031] The straight chain carbonate ester may be selected from the group consisting of DMC, DEC, dipropyl carbonate, dibutyl carbonate, EMC, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate and ethyl propyl carbonate.

[0032] Thus, the non-aqueous organic solvent may be selected from the group consisting of EC, PC, 1,2-butylene carbonate, 2,3-butylene carbonate, DMC, DEC, dipropyl carbonate, dibutyl carbonate, EMC, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate and ethyl propyl carbonate, taken alone or as a mixture thereof.

[0033] Preferably, the non-aqueous organic solvent is chosen from the group consisting of EC, EMC and DMC, taken alone or as a mixture thereof. These solvents allow both good ionic conductivity of the electrolyte and do not induce degradation of the electrode materials (in particular graphite), in synergy with the additional additives described above and in the mass percentages detailed above.

[0034] In one embodiment of the invention, the non-aqueous organic solvent is a mixture of solvents comprising, in mass percentages expressed relative to the total mass of said solvent: - 30% EC, - 70% EMC.

[0035] In one embodiment of the invention, the non-aqueous organic solvent is a mixture of solvents comprising, in mass percentages expressed relative to the total mass of said solvent: - 30% EC, - 40% EMC, - 30% DMC.

[0036] The non-aqueous organic solvent may further comprise at least one carboxylic acid ester to improve the conductivity of the electrolyte and reduce its viscosity.

[0037] The carboxylic acid ester may be selected from the group consisting of methyl formate, ethyl formate, propyl formate, isopropyl formate, methyl propanoate, ethyl propanoate, propyl propanoate, isopropyl propanoate, methyl acetate, ethyl acetate, propyl acetate and isopropyl acetate, taken alone or as a mixture thereof.

[0038] Preferably, the mass percentage of carboxylic acid ester expressed relative to the total mass of the electrolyte does not exceed 30%.

[0039] In a preferred embodiment of the invention, the electrolyte comprises, in mass percentages expressed relative to the mass of said electrolyte: - between 8% and 20%, preferably between 11% and 16%, of lithium salt which comprises at least a mixture of LiFSI and LiPFe, - between 0.5% and 1.5% of MMDS, - between 0.25% and 2%, preferably between 0.5% and 1.5%, of DTD, - between 0.25% and 4%, most preferably between 0.25% and 2.5%, more preferably between 0.5% and 2%, of at least one additional additive chosen from PS and VC, - Q.sp of at least one non-aqueous organic solvent chosen from EC, EMC and DMC.

[0040] In a preferred embodiment of the invention, the electrolyte comprises, in mass percentages expressed relative to the mass of said electrolyte: - between 1.5% and 4%, preferably between 2% and 3.5%, of LiFSI, - between 8.5% and 16%, preferably between 10% and 14%, of LiPFe, - between 0.5% and 1.5% of MMDS, - between 0.25% and 2%, preferably between 0.5% and 1.5%, of DTD, - between 0.25% and 4%, most preferably between 0.25% and 2.5%, more preferably between 0.5% and 2%, of at least one additional additive chosen from PS and VC, - Q.sp of at least one non-aqueous organic solvent chosen from EC, EMC and DMC.

[0041] In a preferred embodiment of the invention, the electrolyte comprises, in mass percentages expressed relative to the mass of said electrolyte: - between 1.5% and 4%, preferably between 2% and 3.5%, of LiFSI, - between 8.5% and 16%, preferably between 10% and 14%, of LiPFe, - between 0.5% and 1.5% of MMDS, - between 0.25% and 2%, preferably between 0.5% and 1.5%, of DTD, - between 0.25% and 2%, preferably between 0.5% and 1.5%, of PS, - between 0.25% and 2%, preferably between 0.5% and 1.5%, of VC, - between 10% and 50%, preferably between 20% and 40%, of EC, - between 10% and 78%, preferably between 60% and 78%, of EMC, - between 0% and 60%, preferably between 0% and 40%, of DMC.

[0042] The invention also relates to a lithium-ion accumulator comprising an electrolyte according to the invention as described above.

[0043] More specifically, the lithium-ion accumulator comprises a positive electrode, a negative electrode, a separator between the two electrodes and an electrolyte according to the invention as described above.

[0044] The positive electrode comprises a positive current collector and a layer of positive active material. The characteristics of the positive electrode are well within the reach of those skilled in the art. For example, the positive active material may be selected from the group consisting of LFP, NMC, NCA, LCO and LMO. Preferably, the positive active material is NMC.

[0045] The negative electrode comprises a negative current collector and a layer of negative active material. For example, the negative active material may be selected from the group consisting of graphite, silicon, silicon oxide, a silicon alloy, tin, a tin oxide, a tin alloy, and lithium titanate. Preferably, the negative active material is graphite.

[0046] Advantageously, the nominal voltage of the lithium-ion accumulator does not exceed 3.8 V, more preferably 3.6 V.

[0047] The invention will be better understood with the aid of the detailed description which is set out below with reference to the appended drawing representing, by way of non-limiting example, experimental data on the evolution of the capacity retention of a lithium-ion accumulator according to the invention and of a comparative lithium-ion accumulator.

[0048] [Fig. 1] Figure 1 is a graph showing the evolution of the capacity retention of lithium-ion accumulators according to the invention and comparatively as a function of the number of charge and discharge cycles of said accumulators.

[0049] [Fig. 2] Figure 2 is a graph showing the evolution of the capacity retention of lithium-ion accumulators according to the invention and comparatively depending on the number of weeks of storage at 60°C of said accumulators.

[0050] EXPERIMENTAL PART:

[0051] Experiments were carried out with an electrolyte according to the invention and a comparative electrolyte.

[0052] The electrolyte according to the invention comprised, in mass percentages expressed relative to the total mass of the electrolyte: - 12.6% LiPF6, - 3.1% LiFSI, - 0.5% MMDS, - 1% DTD, - 0.5% PS, - 0.5% VC, - 24.5% EC, - 57.3% EMC.

[0053] The comparative electrolyte included, in mass percentages expressed in relation to the total mass of the electrolyte: - 13.5% LiPF6, - 3.1% LiFSI, - 1% VC, - 1% PS - 24.4% EC, - 57% EMC.

[0054] For several years, VC and PS have been known and commonly used additives in electrolytes for lithium-ion batteries. This is why the comparative electrolyte described above is particularly interesting for comparing the performances obtained with a lithium-ion battery comprising an electrolyte according to the invention (hereinafter referred to as “lithium-ion battery according to the invention”) with those of a lithium-ion battery comprising this comparative electrolyte (hereinafter referred to as “comparative lithium-ion battery”).

[0055] The lithium-ion accumulators according to the invention and comparison were prepared according to steps 1) to 4) described just below.

[0056] More specifically, only the electrolyte preparation step differed depending on whether the lithium-ion accumulator according to the invention (i.e. step 1a) or the comparative lithium-ion accumulator (i.e. step 1b) was being prepared. In other words, steps 2) to 4) were identical for these two lithium-ion accumulators.

[0057] a) Preparation of the electrolyte according to the invention:

[0058] Under a controlled atmosphere, the EC and EMC solvents were mixed together. Then, the additives DTD, MMDS, VC and PS were added to the solvent mixture. The lithium salts LiPFe and LiFSI were dissolved in the mixture of solvents and additives. The quantities of these different constituents of the electrolyte according to the invention were chosen appropriately to obtain the electrolyte according to the invention as described above.

[0059] lb) Preparation of the comparative electrolyte:

[0060] Under controlled atmosphere, the EC and EMC solvents were mixed together. Then, the VC and PS additives were added to the solvent mixture. The lithium salts LiPFe and LiFSI were dissolved in the solvent and additive mixture. The amounts of these different components of the comparative electrolyte were chosen appropriately to obtain the comparative electrolyte as described above.

[0061] 2) Preparation of the positive electrode:

[0062] The active material NMC was mixed with a binding agent (PVDF) and a conductive agent (carbon black) according to the following mass contents expressed in relation to the total mass of the mixture of NMC, PVDF and carbon black: - 90% NMC, - 5% PVDF, - 5% carbon black.

[0063] Then, this mixture was dispersed in NMP until a homogeneous dispersion was obtained. This solution was mixed to obtain an electrode paste which was then deposited uniformly with a thickness of 200 μm on an aluminum foil, then dried at room temperature, then at 100°C for one hour and finally calendered to obtain the positive electrode.

[0064] 3) Preparation of the negative electrode:

[0065] Graphite was mixed with CMC and a binding agent (SBR) according to the following mass contents expressed relative to the total mass of the mixture of graphite, CMC and SBR: - 92% graphite, - 4% CMC, - 4% SBR.

[0066] This mixture was then dispersed in water (i.e. the solvent) so as to obtain a homogeneous dispersion. This electrode paste was then deposited uniformly with a thickness of 200 μm on a copper foil, then dried at room temperature, then at 70°C for one hour and finally calendered to obtain the negative electrode.

[0067] 4) Preparation of the lithium-ion battery:

[0068] The positive and negative electrodes and a polypropylene separator were assembled and then placed in a plastic pouch cell. The electrolyte was introduced into the pouch, which was then vacuum-sealed to obtain the lithium-ion battery.

[0069] Galvanostatic cycling aging experiments:

[0070] Galvanostatic cycling aging experiments were carried out as follows: the lithium-ion accumulators according to the invention and comparative were subjected to constant current charge and discharge cycles (approximately 1 mA / cm 2 ) at 45°C and the capacity of these accumulators was measured regularly at 25°C during the 400 charge and discharge cycles.

[0071] Table 1 below details the capacity retention C compared to its nominal value “Co” as a function of the number of charge and discharge cycles for: - the lithium-ion accumulator according to the invention (referred to as the “Invention”) and - the comparative lithium-ion accumulator (referred to as “Comparative”). [Table 1]

[0072] The graph in Figure 1 thus represents the evolution of capacity retention (ordinate axis: C / Co (%)) as a function of the number of charge and discharge cycles of the lithium-ion accumulators according to the invention and comparison.

[0073] In view of Table 1 and the graph in Figure 1, it can be seen that after 400 charge and discharge cycles, the capacity retention of the lithium-ion accumulator according to the invention is much higher than that of the comparative lithium-ion accumulator (namely 88.3% versus 83.1%).

[0074] Storage aging experiments:

[0075] Storage aging experiments were carried out as follows: the lithium-ion accumulators according to the invention and comparison were stored at 60°C and the internal resistance of these accumulators was measured regularly for 12 weeks at 25°C.

[0076] Tables 2 and 3 below detail the capacity retention C compared to its nominal value “Co” as a function of the number of weeks of storage at 60°C for: - the lithium-ion accumulator according to the invention (referred to as the “Invention”) and - the comparative lithium-ion accumulator (referred to as “Comparative”).

[0077] [Table 2]

[0078] [Table 3]

[0079] The graph in Figure 2 thus represents the evolution of capacity retention (ordinate axis: C / Co (%)) as a function of the number of weeks of storage of lithium-ion accumulators according to the invention and comparison.

[0080] In view of Tables 2 and 3, as well as the graph in Figure 2, it can be seen that after 14 weeks of storage, the capacity retention of the lithium-ion accumulator according to the invention is much higher than that of the comparative lithium-ion accumulator (namely 83.6% versus 73.3%).

[0081] These experiments demonstrate that the electrolyte according to the invention makes it possible to obtain lithium-ion accumulators with higher performance in terms of their capacity.

Claims

CLAIMS 1. Electrolyte characterized in that it comprises, in mass percentages expressed relative to the mass of said electrolyte: - between 8% and 20%, preferably between 11% and 16%, of lithium salt which comprises at least one mixture of lithium bis(fluorosulfonyl) imide (hereinafter abbreviated LiFSI) and lithium hexafluorophosphate (hereinafter abbreviated LiPFe), - between 0.5% and 1.5% of methylene methane disulfonate (hereinafter abbreviated MMDS), - between 0.25% and 2%, preferably between 0.5% and 1.5%, of ethylene sulfate (hereinafter abbreviated DTD), - at least one additional additive, the mass percentage of which does not exceed 2.5%, and if the additional additive is fluoroethylene carbonate (hereinafter abbreviated as “FEC”), the mass percentage of FEC is less than 0.5%, preferably less than 0.25%, - Qsp of at least one non-aqueous organic solvent, "Qsp" being the acronym for "Quantity sufficient for" to signify that the mass percentage of solvent in the electrolyte is such that, added to the percentages of all the other constituents of the electrolyte, a total of 100% is obtained.

2. Electrolyte according to claim 1, characterized in that the additional additive is chosen from the group consisting of 1,3-propane sultone (hereinafter abbreviated PS), vinylene carbonate (hereinafter abbreviated VC), FEC, vinylethylene carbonate, prop-l-ene-1,3-sultone, butane sultone and trimethylene sulfate, taken alone or as a mixture thereof.

3. Electrolyte according to claim 2, characterized in that the additional additive is PS and / or VC.

4. Electrolyte according to any one of claims 1 to 3, characterized in that the lithium salt further comprises IJBF4, LilX^SOzCFsh, LiCIO4, LiAsFe, lithium bis(oxalato)borate and lithium difluoro(oxalato)borate, taken alone or as a mixture thereof.

5. Electrolyte according to claim 1, characterized in that the lithium salt is a mixture of LiFSI and LiPFe.

6. Electrolyte according to any one of claims 1 to 5, characterized in that the non-aqueous organic solvent is chosen from the group consisting of carbonate ethylene carbonate (hereinafter abbreviated EC), propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, dimethyl carbonate (hereinafter abbreviated DMC), diethyl carbonate, dipropyl carbonate, dibutyl carbonate, ethyl methyl carbonate (hereinafter abbreviated EMC), methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate and ethyl propyl carbonate, taken alone or as a mixture thereof.

7. Electrolyte according to claim 6, characterized in that the non-aqueous organic solvent is chosen from the group consisting of EC, EMC and DMC, taken alone or as a mixture thereof.

8. Electrolyte according to claim 1, characterized in that the electrolyte comprises, in mass percentages expressed relative to the mass of said electrolyte: - between 8% and 20%, preferably between 11% and 16%, of lithium salt which comprises at least a mixture of LiFSI and LiPFe, - between 0.5% and 1.5% of MMDS, - between 0.25% and 2%, preferably between 0.5% and 1.5%, of DTD, - between 0.25% and 2.5%, preferably between 0.5% and 2%, of at least one additional additive chosen from PS and VC, - Q.sp of at least one non-aqueous organic solvent chosen from EC, EMC and DMC.

9. Electrolyte according to claim 1, characterized in that the electrolyte comprises, in mass percentages expressed relative to the mass of said electrolyte: - between 1.5% and 4%, preferably between 2% and 3.5%, of LiFSI, - between 8.5% and 16%, preferably between 10% and 14%, of LiPFe, - between 0.5% and 1.5% of MMDS, - between 0.25% and 2%, preferably between 0.5% and 1.5%, of DTD, - between 0.25% and 2%, preferably between 0.5% and 1.5%, of PS, - between 0.25% and 2%, preferably between 0.5% and 1.5%, of VC, - between 10% and 50%, preferably between 20% and 40%, of EC, - between 10% and 78%, preferably between 60% and 78%, of EMC, - between 0% and 60%, preferably between 0% and 40%, of DMC.

10. Lithium-ion accumulator comprising an electrolyte according to any one of claims 1 to 9.

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