WO2024110725A1

WO2024110725A1 - Electrolyte with high local concentration of lifsi

Info

Publication number: WO2024110725A1
Application number: PCT/FR2023/051825
Authority: WO
Inventors: Jean-Luc Couturier; Marie BICHON
Original assignee: Arkema France
Priority date: 2022-11-23
Filing date: 2023-11-20
Publication date: 2024-05-30
Also published as: FR3142293A1

Abstract

The invention relates to an electrolyte composition comprising: - a lithium bis(fluorosulfonyl)imide salt; - at least one non-fluorinated organic solvent; - at least one diluent which is a halogenated compound of formula (I): wherein each of the groups R1, R2 and R3 is, independently, of empirical formula CxR'(2x+1)-yHy, each R' being, independently, selected from F and Cl, each x being a number from 1 to 6 and each y being a number from 0 to 2x+1; the lithium bis(fluorosulfonyl)imide salt concentration being greater than or equal to 2 M with respect to the non-fluorinated organic solvent(s).

Description

Electrolyte with high local concentration in LiFSI

Field of the invention

The present invention relates to an electrolyte composition comprising a lithium bis(fluorosulfonyl)imide salt. The present invention also relates to an electrochemical cell comprising said composition and a battery comprising said electrochemical cell.

Technical background

Lithium (Li) batteries, such as lithium-ion (Li-ion) batteries, are commonly used in electric vehicles and mobile and portable devices.

A Li-ion battery comprises at least one negative electrode (anode), one positive electrode (cathode), an electrolyte and preferably a separator. The electrolyte generally consists of a lithium salt dissolved in a solvent which is generally a mixture of organic solvents, in order to have a good compromise between the viscosity and the dielectric constant of the electrolyte.

The Li-ion battery market requires the development of higher power batteries. This involves increasing the nominal voltage of Li-ion batteries. To achieve the targeted voltages, high purity electrolytes are necessary.

In the field of Li-ion batteries, the salt currently most used is LiPFe. This salt has many disadvantages such as limited thermal stability, susceptibility to hydrolysis and therefore lower battery safety.

New sulfonylimide type lithium salts have been developed in an attempt to improve battery performance, including LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) and LiFSI (lithium bis(fluorosulfonyl)imide). These salts show little or no spontaneous decomposition, and are more stable to hydrolysis than LiPFe. However, LiTFSI has the disadvantage of being corrosive to aluminum current collectors.

The passivation layers formed during the first charge/discharge cycles of a battery are essential for its lifespan. As passivation layers, we can in particular cite the passivation of aluminum which is generally the current collector used at the cathode, and the solid-electrolyte interface (or “Solid Electrolyte Interface” in English, or SEI) which is the both inorganic and polymeric layer which forms at the anode/electrolyte and cathode/electrolyte interfaces. The stability of these interfaces is an important issue for improving battery life.

LiFSI salt generally gives rise to SEIs of unsatisfactory quality. In addition, its use at high concentration leads to difficulties with excessive viscosity, and therefore poor wettability of the separator and the electrodes.

It is known to prepare an electrolyte with a high local concentration of lithium salt. Such an electrolyte relies on the use of a solvent in combination with a diluent (or bad solvent), which makes it possible to obtain clumps of salt at high concentration in the solvent, which are distributed in the diluent.

Document US 10,367,232 describes electrolytes comprising a lithium salt, a solvent and a diluent in which the lithium salt is relatively poorly soluble. The salt can be present for example in a concentration of at least 3 M relative to the solvent. The diluent is chosen from 1,1,2,2-tetrafluoroethyl-2,2,2,3-tetrafluoropropyl ether (TTE), bis (2,2,2-trifluoroethyl) ether (BTFE), 1,1 ,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), methoxynonafluorobutane (MOFB) and ethoxynonafluorobutane (EOFB).

Document US 2020/0328475 relates to an electrolyte with a high local salt concentration, comprising a solvent and a diluent chosen from a fluorinated glyme and a fluorinated ether. Regarding fluorinated ether, two examples are provided: TTE and BTFE.

The article Review - Localized High-Concentration Electrolytes for Lithium Batteries, by Cao et al. (J. Electrochem. Soc. 168:010522, 2021) contains a general presentation of electrolytes at high local salt concentration. TTE and BTFE are listed as diluents.

Document WO 2022/150414 describes certain fluorinated ethers and their use for cooling electronic devices by immersion. The document also mentions in a very general way the possibility of using this family of compounds as solvents or additives in electrolytes. There is a need to provide new electrolytes for Li-ion batteries, preferably offering improved performance, particularly in terms of SEI quality, coulombic efficiency and/or lifespan.

Summary of the invention

The invention firstly relates to an electrolyte composition comprising:

- a lithium bis(fluorosulfonyl)imide salt;

- at least one non-fluorinated organic solvent;

- at least one diluent which is a halogenated compound of formula (I):

in which each of the groups Ri, R2 and R3 is independently of the crude formula CxR'(2x+i)- _y H _y , each R' being chosen independently from F and Cl, each x being a number from 1 to 6 and each y being a number from 0 to 2x+1; the concentration of lithium bis(fluorosulfonyl)imide salt being greater than or equal to 2 M relative to the non-fluorinated organic solvent(s).

In variations, the non-fluorinated organic solvent is selected from aliphatic carboxylic acid esters, carboxylic acid esters, ethers and mixtures thereof, and preferably is selected from carbonic acid esters and mixtures thereof.

In variations, all of the R' substituents in the halogen compound are fluorine atoms.

In variations, the concentration of lithium bis(fluorosulfonyl)imide salt is greater than or equal to 3 M relative to the non-fluorinated organic solvent(s).

In variations, the diluent(s) on the one hand and the non-fluorinated organic solvent(s) on the other hand are in a volume ratio of 10:90 to 50:50.

The invention also relates to an electrochemical cell comprising a negative electrode, a positive electrode and the electrolyte composition as described above. The invention also relates to a battery comprising at least one electrochemical cell as described above.

In variations, this battery has a charge cut-off voltage greater than or equal to 4.3V.

The invention also relates to the use of the electrolyte composition as described above, in a Li-ion battery, preferably in a Li-ion battery of a portable electronic device, for example a mobile telephone or a computer portable, a Li-ion battery for an electric vehicle, or a Li-ion battery for renewable energy storage, for example, photovoltaic or wind power.

In variations, use is in a Li-ion battery having a charge cut-off voltage greater than or equal to 4.3 V.

The invention also relates to the use of the electrolyte composition as described above, to increase the lifespan of a Li-ion battery and/or to improve the electronic performance of a Li-ion battery, preferably having a charge cut-off voltage greater than or equal to 4.3 V.

The present invention makes it possible to meet the need expressed above. More particularly, it provides new electrolytes for Li-ion batteries, which preferably offer improved performance, particularly in terms of SEI quality, coulombic efficiency and/or lifespan.

The high concentration of lithium salt in the electrolyte solvent is advantageous particularly for high voltage applications (typically above 4.3 V). This high concentration prevents the dissolution of transition metals in the electrolyte and thus extends the life of the battery. In addition, LiFSI salt is more compatible than other salts with the Li metal anode.

The use of the diluent makes it possible to reduce the viscosity of the composition and to improve the wettability of the composition with respect to the separator and the electrodes. The diluents as claimed are stable over a wide electrochemical window and allow the advantages of concentrated LiFSI solutions to be retained, particularly at high voltage. Furthermore, the invention makes it possible to obtain improved SEI, whether on graphite, silicon or lithium metal anode, which improves the performance of the battery in terms of coulombic efficiency and battery life. .

The use of a compound of formula (I) as a diluent offers electrochemical stability advantages. The branched structure of the compound formula (I) makes it possible to obtain a particularly favorable viscosity compared to the compositions of the state of the art.

detailed

The invention is now described in more detail and in a non-limiting manner in the description which follows.

Electrolvte composition

The present invention relates to an electrolyte composition comprising a lithium bis(fluorosulfonyl)imide (LiFSI) salt. In the context of the invention, the terms “lithium bis(fluorosulfonyl)imide”, “lithium bis(sulfonyl)imide”, “LiFSI”, “lithium bis(sulfonyl)imide”, “LiFSI”, are used equivalently.

“LiN(FSO2)2”, “. lithium bis(sulfonyl)imide”, or “lithium bis(fluorosulfonyl)imide”.

The electrolyte composition further comprises a non-fluorinated organic solvent (i.e. a solvent which does not contain the element fluorine). In the context of this application, the organic solvent is not, and does not include, a compound of formula (I) as defined in this application.

Examples of non-fluorinated organic solvents include:

- ethers, such as ethylene glycol dimethyl ether (1,2-dimethoxyethane), ethylene glycol diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2,6-dimethyltetrahydrofuran, tetrahydropyran, a crown ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,4-dioxane and 1,3-dioxolane, as well as mixtures thereof;

- non-cyclic carbonic acid esters (or carbonates) such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, diphenyl carbonate and methyl phenyl carbonate as well as their mixtures;

- cyclic carbonic acid esters (or carbonates) such as ethylene carbonate, propylene carbonate, ethylene 2,3-dimethylcarbonate, butylene carbonate, vinylene carbonate and ethylene 2-vinylcarbonate as well as their mixtures;

- non-cyclic aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate, ethyl acetate, propyl acetate, butyl acetate and acetate amyl as well as their mixtures; - aromatic carboxylic acid esters such as methyl benzoate and ethyl benzoate as well as their mixtures;

- cyclic carboxylic acid esters such as y-butyrolactone, y-valerolactone and 5-valerolactone as well as their mixtures;

- phosphoric acid esters such as trimethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate and triethyl phosphate as well as their mixtures;

- non-aromatic nitriles such as acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, 2-methylglutaron itrile, valeronitrile, butyronitrile and isobutyron itrile as well as their mixtures;

- aromatic nitriles such as benzonitrile and tolunitrile as well as their mixtures;

- amides such as N-methylformamide, N-ethylformamide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidinone, N-methylpyrrolidone and N-vinylpyrrolidone as well as their mixtures;

- sulfur compounds such as dimethylsulfone, ethylmethylsulfone, diethylsulfone, sulfolane, 3-methylsulfolane and 2,4-dimethylsulfolane as well as their mixtures;

- alcohols such as ethylene glycol, propylene glycol, ethylene glycol monomethyl ether and ethylene glycol monoethyl ether as well as their mixtures;

- sulfoxides such as dimethyl sulfoxide, methyl ethyl sulfoxide and diethyl sulfoxide as well as their mixtures;

- nitromethane;

- 1,3-dimethyl-2-imidazolidinone;

- 1,3-dimethyl-3,4,5,6-tetrahydro-2(1,H)-pyrimidinone;

- 3-methyl-2-oxazolidinone.

Solvents from more than one of the above categories can be used in combination.

Alternatively, a single non-fluorinated organic solvent is used.

Carbonic acid esters, aliphatic carboxylic acid esters, carboxylic acid esters and ethers are preferred.

Carbonic acid esters are even more preferred. For example, a mixture of ethylene carbonate/ethyl and methyl carbonate can be used, in particular in a volume ratio of approximately 3/7, for the non-fluorinated organic solvent.

The electrolyte composition further comprises at least one diluent. The diluent comprises one or more halogenated compounds of formula (I):

R ₁

Rn. in which each of the groups Ri, R2 and R3 is independently of the crude formula CxR'(2x+i)- _y H _y , each R' being chosen independently from F and Cl, each x being a number from 1 to 6 and each y being a number from 0 to 2x+1.

By “halogenated compound” we mean that the compound comprises at least one R’ substituent (Cl or F), preferably several.

Preferably, the halogenated compound is a fluorinated compound, that is to say it comprises at least one R'=F substituent.

Preferably, the total number of R' groups in the compound of formula (I) is greater than or equal to 2, or 3, or 4, or 5, or more particularly preferably 6.

Preferably, the compound of formula (I) contains from 0 to 2 Cl substituents. More preferably, the compound of formula (I) contains from 0 to 1 Cl substituent. Even more preferably, the compound of formula (I) is devoid of any chlorine atoms (i.e. each R' is a fluorine atom).

In certain embodiments, the compound of formula (I) satisfies one or more of the following conditions:

(i) If Ri and R2 are CF3, then R3 is different from CF3 and CH2F.

(ii) The total number of F atoms in the compound of formula (I) is from 7 to 15.

(iii) If the total number of R' groups in the compound of formula (I) is greater than or equal to 8, then the molar ratio of R' to H in the O-CH2-R3 group is greater than or equal to 1, 5; and if the total number of R' groups in the compound of formula (I) is greater than or equal to 13, then the molar ratio of R' on H in the O-CH2-R3 group is greater than or equal to 2.

(iv) The compound includes 0 or 1 chlorine atom.

(v) R3 includes at least one CF3 with x greater than or equal to 2.

(vi) If the total number of F in the compound of formula (I) is greater than or equal to 8, then the molar ratio of F to H in the O-CH2-R3 group is greater than or equal to 1.5; and if the total number of F groups in the compound of formula (I) is greater than or equal to 13, then the molar ratio of F to H in the O-CH2-R3 group is greater than or equal to 2.

In some embodiments, all three conditions (ii) to (iv) are satisfied.

In some embodiments, all four conditions (i) to (iv) are satisfied.

In some embodiments, all five conditions (i) to (v) are satisfied.

In some embodiments, all three conditions (i), (ii) and (vi) are satisfied.

In some embodiments, all four conditions (i), (ii), (v) and (vi) are satisfied.

In some embodiments, all five conditions (i), (ii), (iv), (v) and (vi) are satisfied.

In certain embodiments, if the total number of R' groups in the compound of formula (I) is greater than or equal to 13, then the molar ratio of R' to H in the O-CH2-R3 group is greater than or equal at 2.5; preferably is greater than or equal to 3; more preferably is greater than or equal to 3.5.

In certain embodiments, if the total number of F groups in the compound of formula (I) is greater than or equal to 13, then the molar ratio of F to H in the O-CH2-R3 group is greater than or equal to 2 .5; preferably is greater than or equal to 3; more preferably is greater than or equal to 3.5.

In certain embodiments, x=1 for Ri and for R2.

In certain embodiments, Ri is CF3 and/or R2 is CF3, preferably Ri and R2 are each CF3.

In certain embodiments, R3 is a perhalogenated group (y=0), preferably a perfluorinated group (y=0, each R' represents F). In certain embodiments, the compound of formula (I) is 1,1,1,3,3,3-hexafluoro-2-(2,2,2-trifluoroethoxy)propane of formula (II):

In certain embodiments, the compound of formula (I) is the compound of formula (III):

In certain embodiments, the compound of formula (I) is the compound of formula (IV):

F ₃ C

In certain embodiments, the compound of formula (I) is the compound of formula (V):

CH — O— CH — CF2CF2CF2CFg

FgC

In certain embodiments, the compound of formula (I) is the compound of formula (VI):

In certain embodiments, the compound of formula (I) is the compound of formula (VII):

In certain embodiments, the compound of formula (I) is 2-(2,2-difluoroethoxy)-1,1,1,3,3,3-hexafluoropropane; 1,1,1,3,3,3-hexafluoro-2-(2,2,2-trifluoroethoxy)propane; 1,1,1,3,3,3-hexafluoro-2-(2,2,3,3-tetrafluoropropoxy)propane; 1,1,1,2,2,4,4,5,5,5-decafluoro-3-(2,2,2-trifluoroethoxy)pentane; 1,1,2,2,3,3,4,4-octafluoro-5-[2,2,2-trifluoro-1-(trifluoromethyl)ethoxy]pentane; or 1,1,1,2,2,3,3,5,5,6,6,6-dodecafluoro-4-(2,2,2-trifluoroethoxy)hexane. Alternatively, in some embodiments, the composition does not include one of these compounds, or does not include any of these compounds.

In some embodiments, a single compound of formula (I) is used as a diluent. Alternatively, several compounds of formula (I) may be present in combination.

The concentration of LiFSI is greater than or equal to 2 M (2 mol/L) relative to the total volume of non-fluorinated organic solvent(s). Preferably, this concentration is greater than or equal to 2.5 M, or 3 M, or 3.5 M, or 4 M.

The electrolyte composition may have a LiFSI content greater than or equal to 30% by weight relative to the total weight of the electrolyte composition. The LiFSI content in the electrolyte can be determined by NMR. This content can be 30 to 35%; or 35 to 40%; or 40 to 45%; or 45 to 50%; or 50 to 55%; or 55 to 60%; or 60 to 65%; or 65 to 70%; or 70 to 75%; or 75 to 80%; or 80 to 85%; or 85 to 90%; or 90 to 95%; or greater than 95% by weight relative to the total weight of the electrolyte composition.

Non-fluorinated organic diluents and solvents may be present in a volume ratio (total volume of diluent(s) to total volume of non-fluorinated organic solvent(s)) of 10:90 to 50:50. This volume ratio can be from 10:90 to 20:80, or from 20:80 to 30:70, or from 30:70 to 40:60, or from 40:60 to 50:50.

The electrolyte composition according to the invention may optionally comprise one or more additional lithium salts, different from LiFSI. By way of non-limiting examples, the additional lithium salt (or lithium salts) may be chosen from LiPFe (lithium hexafluorophosphate), LiTDI (lithium 2-trifluoromethyl-4,5-dicyano-imidazolate), THE lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), I POF2, lithium difluorophosphate (ÜPO2F2), lithium bis(oxalato)borate (LiB(C2O4)2), lithium difluoro(oxalato)borate (LiF2B( C2C>4)2), LiBF4, LiNOs, LiCICU.

The content of additional lithium salts in the electrolyte composition according to the invention may be from 0 to 5% by weight relative to the total weight of the electrolyte composition.

According to certain embodiments, the electrolyte composition according to the invention may comprise one or more polar polymers. The polar polymer preferably comprises monomer units derived from ethylene oxide, propylene oxide, epichlorohydrin, epifluorohydrin, trifluoroepoxypropane, acrylonitrile, methacrylonitrile, acid esters and amides. acrylic and methacrylic, vinylidene fluoride, N-methylpyrrolidone and/or polyelectrolytes of the polycation or polyanion type. When the present electrolyte composition comprises more than one polymer, at least one thereof may be crosslinked.

The content of polar polymers in the electrolyte composition according to the invention may for example be from 0.1 to 60% by weight relative to the total weight of the electrolyte composition.

In some embodiments, the electrolyte composition may include one or more additives.

The content of additives in the electrolyte composition according to the invention may be 0 to 5% by weight relative to the total weight of the electrolyte composition.

The additive(s) may be chosen from the group consisting of fluoroethylene carbonate (FEC), vinylene carbonate, 4-vinyl-1,3-dioxolan-2-one, pyridazine, vinyl pyridazine, quinoline, vinyl quinoline, butadiene, sebaconitrile, alkyldisulfides, fluorotoluene, 1,4-dimethoxytetrafluorotoluene, t-butylphenol, di-t-butylphenol, tris(pentafluorophenyl)borane, oximes, epoxides aliphatics, halogenated biphenyls, metacrylic acids, allyl ethyl carbonate, vinyl acetate, divinyl adipate, propanesultone, acrylonitrile, 2-vinylpyridine, maleic anhydride, methyl cinnamate, ionic liquids, anhydrides such as for example succinic anhydride, phosphonates, vinyl-containing silane compounds, and/or 2-cyanofuran.

Preferably, the electrolyte composition has a viscosity of 0.1 to 100 cP, more preferably 1 to 30 cP, at a temperature of 25°C. The viscosity can for example be measured with a Brookfield Metek DV2T viscometer by applying a shear of 20 s ^-1 .

The electrolyte composition can be prepared by mixing the LiFSI salt, the non-fluorinated organic solvent(s), the diluent(s), as well as optionally other compounds present, in particular additional lithium salt(s), additive(s). s) and polar polymer(s). Preferably, the desired quantity of lithium salts is dissolved in the non-fluorinated organic solvent(s), then the other compounds are added, in particular additive(s) and diluent(s).

Electrochemical cell and battery

The present invention also relates to the use of the above electrolyte composition in Li-ion batteries, in particular in Li-ion batteries of portable electronic devices, for example mobile phones or laptop computers, vehicles electrical, renewable energy storage for example photovoltaic or wind turbines.

The present invention relates to the use of the electrolyte composition according to the invention to increase the lifespan of a Li-ion battery and/or improve the electronic performance (coulombic efficiency) of a Li-ion battery.

By “increased lifespan of the Li-ion battery” we mean the increase in the number of cycles allowing at least 80% of the initial capacity of the battery to be retained.

By “improvement of the electronic performance (coulombic efficiency) of a Li-ion battery” we mean the improvement of the capacity at high charge or discharge current, in particular at low temperature and/or after storage at high temperature.

The invention also relates to an electrochemical cell comprising an electrolyte composition as described above. The electrochemical cell also includes a negative electrode (or anode) and a positive electrode (or cathode).

The electrochemical cell can also include a separator, in which the electrolyte is impregnated.

By "negative electrode", we mean the electrode which acts as an anode, when the cell delivers current (that is to say when it is in the discharge process) and which acts as cathode when the cell is charging. The negative electrode typically comprises an electrochemically active material, optionally an electronic conductive material, and optionally a binder.

By "positive electrode", we mean the electrode which acts as a cathode, when the cell delivers current (that is to say when it is in the discharge process) and which acts as an anode when the cell is charging.

The positive electrode typically comprises an electrochemically active material, optionally an electronic conductive material, and optionally a binder.

The term “electrochemically active material” means a material capable of reversibly inserting ions.

The term “electronic conductive material” means a material capable of conducting electrons.

The negative electrode of the electrochemical cell may in particular comprise, as electrochemically active material, graphite, lithium, a lithium alloy, a lithium titanate of the Li4TisOi2 type or titanium oxide TiO2, silicon or an alloy of lithium and silicon, a tin oxide, an intermetallic lithium compound, or a mixture thereof.

When the negative electrode comprises lithium, this may be in the form of a film of metallic lithium or of an alloy comprising lithium. Among the lithium-based alloys likely to be used, we can for example cite lithium-aluminum alloys, lithium-silica alloys, lithium-tin alloys, Li-Zn, LisBi, LisCd and LisSB. An example of a negative electrode may include a live lithium film prepared by rolling a lithium strip between rollers.

The positive electrode includes an electrochemically active oxide material. It is preferably a lithium-iron-phosphate (LixFePC with 0<x<1), or a lithium-nickel-manganese-cobalt composite oxide with a high nickel content (LiNi _x Mn _y Co _z O2 with x+y+z = 1, abbreviated NMC, with x>y and x>z), or a lithium-nickel-cobalt-aluminum composite oxide with a high nickel content (LiNixCoyAlz' with x'+y'+z'=1 , abbreviated NCA, with x'>y' and x'>z').

Particular examples of these oxides are NMC532 (LiNio,sMno,3Coo,202), NMC622 (LiNio,eMno,2Coo,202) and NMC811 (LiNio,8Mno,iCoo,i02).

Mixtures of these oxides can be used. The oxide material described above can where appropriate be combined with another oxide such as for example: manganese dioxide (MnC), iron oxide, iron oxide copper, nickel oxide, lithium-manganese composite oxides (for example Li _x Mn2O4 or LixMnC), lithium-nickel composition oxides (for example Li _x NiG>2), lithium-cobalt composite oxides (for example LixCoC ), lithium-nickel-cobalt composite oxides (e.g. LiNii-yCoyC), lithium and transition metal composite oxides, lithium-manganese-nickel composite oxides with spinel structure (e.g. Li _x Mn ₂ -yNiyO4 ), vanadium oxides, NMC and NCA oxides which do not contain a high nickel content, and mixtures thereof.

Preferably, the NMC or NCA oxide with a high nickel content represents at least 50% by weight, preferably at least 75% by weight, more preferably at least 90% by weight, and more preferably essentially all, of the oxide material present in the positive electrode as an electrochemically active material.

Alternatively, or additionally, the positive electrode may include sulfur, I_i2S, O2, and/or I O2 as an electrochemically active material.

The material of each electrode may also comprise, in addition to the electrochemically active material, an electronic conductive material such as a carbon source, including, for example, carbon black, Ketjen® carbon, Shawinigan carbon, graphite, graphene, carbon nanotubes, carbon fibers (for example gas-phase carbon fibers or VGCF), non-powdery carbon obtained by carbonization of an organic precursor, or a combination of two or more of these. Other additives may also be present in the material of the positive electrode, such as lithium salts or inorganic particles such as ceramic or glass, or other compatible active materials (for example, sulfur).

The material of each electrode may also include a binder. Non-limiting examples of binders include linear, branched and/or cross-linked polyether polymer binders (for example, polymers based on poly(ethylene oxide) (PEO), or poly(propylene oxide) (PPO) or a mixture of the two (or an EO/PO copolymer), and optionally comprising crosslinkable units), water-soluble binders (such as SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), HNBR (hydrogenated NBR), CHR (epichlorohydrin rubber), ACM (acrylate rubber)), or fluoropolymer type binders (such as PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), and their combinations. Some binders, such as those soluble in water, may also include an additive such as CMC (carboxymethylcellulose).

The separator may be a porous polymer film. By way of non-limiting example, the separator may consist of a porous polyolefin film such as ethylene homopolymers, propylene homopolymers, ethylene/butene copolymers, ethylene/hexene copolymers, ethylene/methacrylate copolymers, or multilayer structures of the above polymers. Alternatively, the separator can be made of fiberglass.

The invention also relates to a battery comprising at least one, and preferably several, electrochemical cells as described above. The electrochemical cells can be assembled in series and/or parallel in the battery.

By “cut-off voltage” we mean the upper voltage limit of a battery considered to be fully charged. The cut-off voltage is usually chosen in order to obtain the maximum capacity of the battery.

Preferably, the battery according to the invention has a charge cut-off voltage greater than or equal to 4.3 V, more preferably greater than or equal to 4.5 V.

Claims

Claims Electrolyte composition comprising:

- a lithium bis(fluorosulfonyl)imide salt;

- at least one non-fluorinated organic solvent;

- at least one diluent which is a halogenated compound of formula (I):

in which each of the groups Ri, R2 and R3 is independently of the crude formula CxR'(2x+i)- _y H _y , each R' being chosen independently from F and Cl, each x being a number from 1 to 6 and each y being a number from 0 to 2x+1; the concentration of lithium bis(fluorosulfonyl)imide salt being greater than or equal to 2 M relative to the non-fluorinated organic solvent(s). Electrolyte composition according to claim 1, in which the non-fluorinated organic solvent is chosen from aliphatic carboxylic acid esters, carboxylic acid esters, ethers and mixtures thereof, and preferably is chosen from esters of carbonic acid and their mixtures. An electrolyte composition according to claim 1 or 2, wherein all of the R' substituents in the halogenated compound are fluorine atoms. Electrolyte composition according to one of claims 1 to 3, in which the concentration of lithium bis(fluorosulfonyl)imide salt is greater than or equal to 3 M relative to the non-organic solvent(s). fluorinated(s). Electrolyte composition according to one of claims 1 to 4, in which the diluent(s) on the one hand and the non-fluorinated organic solvent(s) on the other hand are in a volume ratio of 10:90 to 50:50. Electrochemical cell comprising a negative electrode, a positive electrode and the electrolyte composition according to one of claims 1 to 5. Battery comprising at least one electrochemical cell according to claim 6. Battery according to claim 7, having a cut-off voltage of charge greater than or equal to 4.3 V. Use of the electrolyte composition according to one of claims 1 to 5, in a Li-ion battery, preferably in a Li-ion battery of a portable electronic device, for example a mobile phone or a laptop computer, a Li-ion battery for an electric vehicle, or a Li-ion battery for renewable energy storage, for example, photovoltaic or wind power. Use according to claim 9, in a Li-ion battery having a charge cut-off voltage greater than or equal to 4.3 V. Use of the electrolyte composition according to one of claims 1 to 5, to increase the duration of life of a Li-ion battery and/or to improve the electronic performance of a Li-ion battery, preferably having a charge cut-off voltage greater than or equal to 4.3 V.