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, - a complementary additive, the weight percentage of which does not exceed 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, - good cyclability, - low self-discharge.

[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 at low cost has become essential. Research and development have therefore mainly focused on the development of new electrode materials 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 passivation layer 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 increase in the internal resistance of the lithium-ion battery during charge and discharge cycles or during its storage in a charged state is one of the problems which contributes to reducing the performance of said lithium-ion battery.

[0010] The inventors of the present invention sought to overcome this drawback by developing a new lithium-ion battery electrolyte composition for which the increase in internal resistance during charge and discharge cycles or during storage is significantly reduced compared to 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 LiCoOz; - 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 a mixture of LiFSI and LiPFe, - between 0.5% and 1.5% of MMDS, - at least one additional additive, the mass percentage of which does not exceed 5%, preferably 2.5%, and if the additional additive is FEC or DTD, the percentage mass in FEC or DTD 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 discovered, quite surprisingly, that the combination of MMDS in a quantity such that its mass percentage is between 0.5% and 1.5% with at least one additional additive whose mass percentage does not exceed 5% and if it is FEC or DTD, said mass percentage is less than 0.5%, in the composition of an electrolyte made it possible to obtain a lithium-ion accumulator whose internal resistance increases very moderately during cycling or storage, and this in comparison with the lithium-ion accumulators known from the state of the art.

[0015] In other words, the selection of a mass percentage of between 0.5% and 1.5% of MMDS 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 internal resistance thereof, or more precisely on the control of the internal resistance. Indeed, this selection in synergy with the additional additive(s) makes it possible to moderate the increase in internal resistance during cycling or storage of the lithium-ion accumulator. This is very beneficial for the performance of the lithium-ion accumulator which therefore has an increased lifespan and power performance compared to that of lithium-ion accumulators known from the state of the art.

[0016] The presence of additional additives in the electrolyte according to the invention allows the formation of passivation layers at the electrodes which are low in resistance and sufficiently protective, such that they make it possible to limit the increase in internal resistance over time, i.e. during cycling and during storage of the accumulator, in particular in the charged state and / or at a temperature above ambient temperature.

[0017] Furthermore, the inventors have discovered, quite surprisingly, that the combination of MMDS in an amount such that its mass percentage is between 0.5% and 1.5% with at least one additional additive whose mass percentage does not exceed 5% (and if it is FEC, said mass percentage is less than 0.5%) and a mixture of LiFSI and LiPFe makes 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 loss of performance, fire, or even an explosion. LiFSI as an additive to LiPFe makes it possible to dissolve metallic impurities, in particular stainless steel.Dissolution occurs during the cell formation stage (charge / discharge cycle of the cell to activate it).

[0018] The complementary additive may advantageously be chosen from the group consisting of PS, VC, FEC, VEC, PES, BS, TMS and DTD, taken alone or as a mixture thereof.

[0019] 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).

[0020] As described above, the total mass percentage of the complementary additive(s) does not exceed 5%, preferably 2.5%. If the complementary additive is FEC or DTD, the mass percentage of FEC or DTD is less than 0.5%, preferably less than 0.25%.

[0021] For additional additives other than FEC and DTD, 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%.

[0022] In one embodiment of the invention, the total mass percentage of the additional additive(s) may be between 0.25% and 5%, preferably between 1% and 2.5%.

[0023] 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.

[0024] In the electrolyte composition according to the invention, the lithium salt ensures the ionic conductivity of the lithium ions within the lithium-ion accumulator.

[0025] 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.

[0026] Preferably, the lithium salt is a mixture of LiFSI and LiPFe.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] In one embodiment of the invention, the non-aqueous organic solvent is a mixture comprising, in mass percentages expressed relative to the total mass of said solvent: - 30% EC, - 70% EMC.

[0036] In one embodiment of the invention, the non-aqueous organic solvent is a mixture comprising, in mass percentages expressed relative to the total mass of said solvent: - 30% EC, - 40% EMC, - 30% DMC.

[0037] 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.

[0038] 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.

[0039] Preferably, the mass percentage of carboxylic acid ester expressed relative to the total mass of the electrolyte does not exceed 30%.

[0040] 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 4%, 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 4%, preferably between 0.5% and 2%, of at least one additive complementary chosen from PS and VC, - Q.sp of at least one non-aqueous organic solvent chosen from EC, EMC and DMC.

[0042] 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 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 79%, preferably between 60% and 79%, of EMC, - between 0% and 60%, preferably between 0% and 40%, of DMC.

[0043] The invention also relates to a lithium-ion accumulator comprising an electrolyte according to the invention as described above.

[0044] 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.

[0045] The positive electrode comprises a positive current collector and a layer of positive active material. 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.

[0046] 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.

[0047] Advantageously, the nominal voltage of the lithium-ion accumulator does not exceed 3.8 V, more preferably 3.6 V.

[0048] 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 internal resistance of a lithium-ion accumulator according to the invention and of a comparative lithium-ion accumulator.

[0049] [Fig. 1] Figure 1 is a graph of the evolution of the internal resistance of lithium-ion accumulators according to the invention and comparative as a function of the number of charge and discharge cycles of said accumulators.

[0050] [Fig. 2] Figure 2 is a graph of the evolution of the internal resistance of lithium-ion accumulators according to the invention and comparative as a function of the number of weeks of storage of said accumulators.

[0051] EXPERIMENTAL PART:

[0052] Experiments were carried out with an electrolyte according to the invention and a comparative electrolyte.

[0053] 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, - 1% MMDS, - 0.5% PS, - 1% VC, - 24.6% EC, - 57.3% EMC.

[0054] 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.

[0055] For several years, VC and PS have been known and commonly used additives in electrolytes for lithium-ion batteries. Therefore, the electrolyte comparative described above is particularly interesting for comparing the performances obtained with a lithium-ion accumulator comprising an electrolyte according to the invention (hereinafter referred to as “lithium-ion accumulator according to the invention”) with those of a lithium-ion accumulator comprising this comparative electrolyte (hereinafter referred to as “comparative lithium-ion accumulator”).

[0056] The lithium-ion accumulators according to the invention and comparison were prepared according to steps 1) to 4) described just below.

[0057] 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.

[0058] a) Preparation of the electrolyte according to the invention:

[0059] Under a controlled atmosphere, the EC and EMC solvents were mixed together. Then, the MMDS, VC and PS additives 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.

[0060] lb) Preparation of the comparative electrolyte:

[0061] 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.

[0062] 2) Preparation of the positive electrode:

[0063] The active material NMC was mixed with a binding agent (PVDF) and a conductive agent (carbon black) according to the following mass percentages expressed relative to the total mass of the mixture of NMC, PVDF and carbon black: - 90% NMC, - 5% PVDF, - 5% carbon black.

[0064] 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.

[0065] 3) Preparation of the negative electrode:

[0066] Graphite was mixed with CMC and a binding agent (SBR) according to the following mass percentages expressed relative to the total mass of the mixture of graphite, CMC and SBR: - 92% graphite, - 4% CMC, - 4% SBR.

[0067] 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.

[0068] 4) Preparation of the lithium-ion battery:

[0069] The positive and negative electrodes and a polypropylene separator were assembled and then placed in a cell, a plastic bag also known as a "pouch cell". The electrolyte was introduced into the pouch, which was then vacuum-sealed to obtain the lithium-ion battery.

[0070] Galvanostatic cycling aging experiments:

[0071] 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 internal resistance of these accumulators was measured regularly at 25°C during the 400 charge and discharge cycles.

[0072] Table 1 below details, according to 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 (designated “Comparative”), the internal resistance whose value R is expressed as a percentage in relation to that of the initial internal resistance called “Ro” set at 100%.

[0073] [Table 1]

[0074] The graph in Figure 1 thus represents the evolution of the internal resistance (the value R of which is expressed as a percentage relative to that of the initial internal resistance known as “Ro” set at 100% - ordinate axis: R / Ro (%)) as a function of the number of charge and discharge cycles of the lithium-ion accumulators according to the invention and comparative.

[0075] In view of Table 1 and the graph in Figure 1, it can be seen that after 400 charge and discharge cycles, the increase in the internal resistance of the lithium-ion accumulator according to the invention is much lower than that of the comparative lithium-ion accumulator (namely 108.5% versus almost 159.9%).

[0076] Storage aging experiments:

[0077] 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 regularly measured for 12 weeks at 25°C.

[0078] Tables 2 and 3 below detail, based on the number of weeks of storage for: - the lithium-ion accumulator according to the invention (referred to as the “Invention”) and - the comparative lithium-ion accumulator (designated “Comparative”), the internal resistance whose value R is expressed as a percentage in relation to that of the initial internal resistance called “Ro” set at 100%.

[0079] [Table 2]

[0080] [Table 3]

[0081] The graph in Figure 2 thus represents the evolution of the internal resistance (the value R of which is expressed as a percentage relative to that of the initial internal resistance known as “Ro” set at 100% - ordinate axis: R / Ro (%)) as a function of the number of weeks of storage of the lithium-ion accumulators according to the invention and comparison.

[0082] In view of Tables 2 and 3, as well as the graph in Figure 2, it can be seen that after 20 weeks of storage, the increase in the internal resistance of the lithium-ion accumulator according to the invention is much lower than that of the comparative lithium-ion accumulator (namely 131.7% versus 186.1%).

[0083] 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 internal resistance.

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), - 0.5% and 1.5% of methylene methane disulfonate (hereinafter abbreviated MMDS), - at least one additional additive, the mass percentage of which does not exceed 5%, preferably 2.5%, and if the additional additive is fluoroethylene carbonate (hereinafter abbreviated as “FEC”) or ethylene sulfate (hereinafter abbreviated as “DTD”), the mass percentage of FEC or DTD 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, trimethylene sulfate and DTD, 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 ethylene carbonate (hereinafter abbreviated EC), propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, dimethyl carbonate (hereinafter abbreviated DMC), carbonate 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 4%, 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 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 79%, preferably between 60% and 79%, 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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