Lithium secondary battery with enhanced energy density

Abstract

The present invention relates to a lithium secondary battery comprising a) a positive electrode comprising a nickel-rich lithium transition metal oxide as a positive electroactive material, b) a negative electrode, and c) a liquid electrolyte comprising at least one lithium salt dissolved in a solvent mixture comprising from 5.0 to 80.0% by volume (vol%) of at least one fluorinated acyclic carboxylic acid ester, vol% being based on the total volume of the solvent mixture, and to an electronic device, a transportation device or a telecommunication device comprising a lithium secondary battery of the present invention.

Description

LITHIUM SECONDARY BATTERY WITH ENHANCED ENERGY DENSITYCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to European patent application No.23207496.3 filed on November 2, 2023, the whole content of this application being incorporated herein by reference for all purposes.TECHNICAL FIELD

[0002] The present invention relates to a lithium secondary battery comprising a) a positive electrode comprising a nickel-rich lithium transition metal oxide as a positive electroactive material, b) a negative electrode, and c) a liquid electrolyte comprising at least one lithium salt dissolved in a solvent mixture comprising from 5.0 to 80.0% by volume (vol%) of at least one fluorinated acyclic carboxylic acid ester, vol% being based on the total volume of the solvent mixture. The present invention also relates to an electronic device, a transportation device or a telecommunication device comprising a lithium secondary battery of the present invention.BACKGROUND OF THE INVENTION

[0003] Lithium-ion batteries have retained dominant position in the market of rechargeable energy storage devices for decades, thanks to many benefits such as light-weight, reasonable energy density and good cycle life.

[0004] In this regard, however, higher energy density has been continuously required pursuant to the development of high power applications such as electrical vehicles (EVs), hybrid electrical vehicles, grid energy storages, etc. and these requirements keep increasing according to the strong demand from the industry.

[0005] The energy density is defined by capacity multiplied by voltage. Accordingly, the energy density can be increased by increasing capacity and / or voltage. Voltage of a lithium secondary battery is decided by the potential difference between the positive electrode and the negative electrode, among which the positive electroactive materials, serving as the main provider of lithium ions, determines the energy capacity of a lithium secondary battery.

[0006] LiCoO2 (LCO, hereinafter) has kept the dominant position as a positive electroactive material for a lithium secondary battery, thanks to its high capacity and high density, as well as relatively easy processing for the manufacture. However, LCO also has drawbacks, mainly due to the scarcity of Co resources and its high cost. Accordingly, it becomes necessary to find an alternative, preferably the one with higher energy capacity to meet the ever increasing demand from the industry.

[0007] Among various positive electroactive materials such as lithium oxide compounds with layered structures, notably ternary positive electroactive materials, such as LiNixCoyMni-x-yO2 (NCM, hereinafter) and LiNixCoyAli-x-yO2 (NCA, hereinafter); those with spinel structure such as LiMn2O4 and Lii+xMn2- yO4; and those with olivine-type structures such as LiFePCM, the positive electroactive materials having high content of Ni and hence providing desired specific capacity have been highlighted as promising candidates to satisfy the needs. However, this comes with a downside, i.e. the adverse impact on the thermal stability and long-term cycling performance. This results from the residual lithiums forming on the surface of a Ni-rich compound over time when exposed to air, which becomes detrimental to the electrode making as well as cyclability.

[0008] In parallel, increasing the cut-off voltage have been also tried to improve the energy density. In this regard, at the cut-off voltage higher than about 4.2 V, the electrolyte system is often deteriorated because the components of the electrolyte, such as a solvent, a conducting salt, and an additive, especially a film-forming additive which is believed to form a protective layer (often called “solid electrolyte interphase (SEI)”) on a surface of the electrode(s) on initial charging, cannot endure such high voltage. On the contrary, the battery which can be operated at higher voltage (for instance, up to 5.0 V) is desired in the art, and accordingly the development of liquid electrolytes suitable for the high- voltage batteries, and / or the components for such a liquid electrolyte has been consistently required in the art. In terms of the cut-off voltage, such high- voltage batteries have a charge cut-off voltage of at least 4.3 V.

[0009] However, notably at such a high voltage, the positive electroactive materials having high content of Ni rapidly decrease its capacity because of the sidereactions occurring between the positive electroactive materials and the liquid electrolyte, and subsequently encounter collateral difficulties in view of thermal stability. This is because the high voltage accelerates the gas formation such as O2, CO, and CO2 that eventually results in the safety concerns, including but not limited to large volume change, microcracks accompanying surface modification of the positive electrode, etc.

[0010] In response to the above challenges, C. Liao et. al. proposed several approaches such as element doping, surface coating, single-crystal fabrication, structural design change, and use of multifunctional electrolyte additives in “Challenges and modification strategies of Ni-rich cathode materials operating at high voltage (Nanomaterials, 2022, 12, 1888)”. In the meantime, the decrease of the electrical conductivity was also observed as the content of Ni increases such that use of well-dispersed carbon nanotubes (CNTs) as a conductive additive in a cathode fabricated with LiNiO.8Coo.1Mno.1O2 (NMC811 , hereinafter), while controlling the solid content within the positive electrode, was proposed by J. H. Choi et. al. in “Improved electrochemical performance using well-dispersed carbon nanotubes as conductive additive in the Ni-rich positive electrode of lithium-ion batteries (Electrochemistry Communications 146 (2023) 107419)”.

[0011] CN111883839A (Envision Power Tech Jiangsu Co. Ltd.) discloses a high- voltage non-aqueous electrolyte comprising a lithium salt, a non-aqueous organic solvent, a first additive particularly defined and a second additive, wherein the lithium salt comprises lithium hexafluorophosphate and an auxiliary lithium salt comprising lithium difluorophosphate, lithium difluorooxalato phosphate and lithium tetrafluoroborate, and the second additive comprises fluoroethylene carbonate and / or 1 ,3-propene sultone, to mitigate the side reactions occurring on the surface of cathode under high voltage. In this regard, CN’839A defines high voltage as being 5.5 V or less.

[0012] Organic carbonates have been conventionally used as liquid electrolytes for lithium secondary batteries, for instance acyclic carbonates, such as ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate, and cyclic carbonates, such as ethylene carbonate or propylene carbonate. However, these organic carbonates relatively easily decompose at certain voltage, e.g.above 4.3V. Typically, driving the electrodes to higher / extreme voltage or exposing the cells to higher temperatures accelerates undesired reactions between liquid electrolytes and highly reactive electrodes that may result in reduced cycle life and capacity reduction. In a worst case scenario, a thermal runaway may occur, which accompanies fire / flame, followed by cell rupture / explosion and eventually by cell disintegration. Notably, such safety concerns are mainly because of the use of organic carbonates having relatively low boiling point and high flammability.

[0013] Accordingly, various approaches have been made to overcome the limitations of commonly used liquid electrolytes based on the organic carbonates, which becomes more crucial in case the positive electroactive material has high Ni content, and there still exist outstanding needs for a liquid electrolyte optimal for a lithium secondary battery comprising a positive electroactive material having high content of Ni, in particular at normal voltage, which nonetheless may exhibit high energy density.SUMMARY OF THE INVENTION

[0014] A first object of the present invention is a lithium secondary battery comprising: a) a positive electrode comprising, as a positive electroactive material, a lithium transition metal oxide represented by the following formula (I)LiNii-x-y-zMnxCoyAlzO2 (I) wherein x>0; y>0; z>0; 0<x+y+z<0.40; and Ni, Mn, Co, and / or Al are optionally doped with at least one metal selected from the group consisting of Sc, Ti, V, Cr, Fe, Cu, Zn, Mg, Al, Sn, B, Ga, Sr, Ca, In, Si, Zr, La, P, Nb, and Ge, respectively; b) a negative electrode; and c) a liquid electrolyte comprising at least one lithium salt dissolved in a solvent mixture comprising at least one fluorinated acyclic carboxylic acid ester represented by the formula (II)R1-C(O)O-R2(II) wherein R1and R2represent an alkyl group respectively; the sum of carbon atoms in R1and R2is from 2 to 7; R1does not contain fluorine, and R2contains fluorine; andwherein the fluorinated acyclic carboxylic acid ester is in an amount of from 5.0 to 80.0% by volume (vol%), based on the total volume of the solvent mixture.

[0015] The other object of the present invention is an electronic device, a transportation device, or a telecommunication device comprising a lithium secondary battery of the present invention.

[0016] It was surprisingly found by the inventors that a liquid electrolyte comprising at least one lithium salt dissolved in a solvent mixture comprising at least one fluorinated acyclic carboxylic acid ester in an amount of from 5.0 to 80.0 vol%, based on the total volume of the solvent mixture according to the present invention may deliver a particularly advantageous combination of properties, when used in a lithium secondary battery comprising a positive electroactive material having high content of Ni at normal voltage.DETAILED DESCRIPTION OF THE INVENTION

[0017] Ratios, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. In the context of the present invention, the term ‘percent by weight’ (wt%) indicates the content of a specific component in a mixture, calculated as the ratio between the weight of the component and the total weight of the mixture, and the term ‘percent by volume’ (vol%) indicates the content of a specific component in a mixture, calculated as the ratio between the volume of the component and the total volume of the mixture.

[0018] It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention as claimed. Accordingly, various changes and modifications described herein will be apparent to those skilled in the art. Moreover, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

[0019] The present invention provides a lithium secondary battery comprising:a) a positive electrode comprising, as a positive electroactive material, a lithium transition metal oxide represented by the following formula (I)LiNii-x-y-zMnxCoyAlzO2 (I) wherein x>0; y>0; z>0; 0<x+y+z<0.40; and Ni, Mn, Co, and / or Al are optionally doped with at least one metal selected from the group consisting of Sc, Ti, V, Cr, Fe, Cu, Zn, Mg, Al, Sn, B, Ga, Sr, Ca, In, Si, Zr, La, P, Nb, and Ge, respectively; b) a negative electrode; and c) a liquid electrolyte comprising at least one lithium salt dissolved in a solvent mixture comprising at least one fluorinated acyclic carboxylic acid ester represented by the formula (II)R1-C(O)O-R2(II) wherein R1and R2represent an alkyl group respectively; the sum of carbon atoms in R1and R2is from 2 to 7; R1does not contain fluorine, and R2contains fluorine; and wherein the fluorinated acyclic carboxylic acid ester is in an amount of from 5.0 to 80.0% by volume (vol%), based on the total volume of the solvent mixture.

[0020] In the present invention, the term “positive electrode” is intended to denote, in particular, the electrode of an electrochemical cell, where reduction occurs during discharging, while the term “negative electrode” is intended to denote, in particular, the electrode of an electrochemical cell, where oxidation occurs during discharging.

[0021] In the present invention, the term “electroactive material” is intended to denote a material that is able to incorporate or insert into its structure and substantially release therefrom lithium ions during the charging and discharging phases in a battery.

[0022] An electrode in a lithium secondary battery is referred to as either an anode or cathode. The anode is defined as the electrode where electrons leave the cell and oxidation occurs, and the cathode as the electrode where electrons enter the cell and reduction occurs. Each electrode may become either an anode or a cathode depending on the direction of electric current through acell. A bipolar electrode is an electrode that functions as an anode of one cell and as an cathode of another cell. When a cell is being charged, the anode becomes the positive electrode and the cathode becomes the negative electrode, while when a cell is being discharged, the anode becomes the negative electrode and the cathode becomes the positive electrode.

[0023] In the present invention, the term “cut-off voltage” is intended to denote a prescribed lower-limit voltage at which the discharging is considered complete. The cut-off voltage is usually chosen so that the maximum useful capacity of the battery is achieved. The cut-off voltage is different from one battery to the other and highly dependent on the type of batteries.

[0024] In the present invention, the term “normal voltage” is intended to denote the voltage in the range of from 2.5 to 4.3 V, while the term “high voltage” is intended to denote the voltage exceeding 4.3 V.

[0025] In the present invention, a positive electrode comprises, as a positive electroactive material, a lithium transition metal oxide represented by the following formula (I)LiNii-x-y-zMnxCoyAlzO2 (I) wherein x>0; y>0; z>0; 0<x+y+z<0.40; and Ni, Mn, Co, and / or Al are optionally doped with at least one metal selected from the group consisting of Sc, Ti, V, Cr, Fe, Cu, Zn, Mg, Al, Sn, B, Ga, Sr, Ca, In, Si, Zr, La, P, Nb, and Ge, respectively.

[0026] The positive electrode according to the present invention corresponds to a Ni-rich or high-Ni positive electrode comprising a positive electroactive material having high content of Ni. In the present invention, “Ni-rich” or “high- Ni” is intended to denote that the content of Ni within a positive electroactive material is high, wherein x+y+z is at most 0.40 in LiNii-x-y-zMnxCoyAlzO2.

[0027] In a particular embodiment, 0.05<x+y+z<0.30.

[0028] In a more particular embodiment, 0.08<x+y+z<0.25.

[0029] In another more particular embodiment, 0.12<x+y+z<0.20.

[0030] In one embodiment, the positive electroactive material is selected from the group consisting of LiNio.8Mno.1Coo.1O2 and LiNi0.9Mn0.05Co0.05O2.

[0031] In the other embodiment, the positive electroactive material is selected from the group consisting of LiNi0.92Mn0.04Co0.03AI0.01O2, LiNi0.9Mn0.045Co0.045AI0.01O2, LiNi0.89Co0.08AI0.03O2, LiNi0.88Co0.09AI0.03O2, and LiNio .815C00.15AI0.035O2.

[0032] In some embodiments, b) the negative electrode comprises, as a negative electroactive material, metallic lithium or a composite material of at least a carbon material and at least a silicon material.

[0033] The carbon material should be able to absorb and desorb lithium ions. Non- limitative examples of the carbon material include graphite, amorphous carbon, diamond-like carbon, or a complex thereof. Carbon materials typically commercialized for a negative electroactive material are mesocarbon microbead (MCMB), mesophase-pitch-based carbon fiber (MCF) and massive artificial graphite (MAG). Carbon materials may preferably consist of between 2.0 and 99.0 wt%, more preferably between 2.0 and 97.0 wt%, based on the total weight of the negative electroactive material. Carbon materials may consist of between 2.0 and 30.0 wt%, or between 30.0 and 50.0 wt%, or between 50.0 and 97.0 wt% of the negative electroactive material.

[0034] The silicon material should be able to absorb and desorb lithium ion and / or should be able to alloy with lithium. The silicon material may be metallic silicon (“Si”) or silicon oxide (“SiOa”, 0<a<2), or mixtures thereof. Metallic silicon may preferably consist of between 3.0 and 90.0 wt%, more preferably between 3.0 and 50.0 wt%, based on the total weight of the negative electroactive material. Metallic silicon may consist of either between 3.0 and 20.0 wt%, or between 20.0 and 50.0 wt%, or between 50.0 and 90.0 wt% of the negative electroactive material. Silicon oxide, i.e. SiOa (with 0<a<2), may preferably consist of between 3.0 and 90.0 wt%, more preferably between 3.0 and 50.0 wt%, based on the total weight of the negative electroactive material. Silicon oxide may consist of between 3.0 and 40.0 wt%, or between 40.0 and 70.0 wt%, or between 70.0 and 90.0 wt% of the negative electroactive material.

[0035] A composite material of at least a carbon material and at least a silicon material, i.e. silicon carbon composite (SiC), may preferably consist of between 3.0 and 90.0 wt%, more preferably between 3.0 and 50.0 wt%, based on the total weight of the negative electroactive material.

[0036] In one embodiment, b) the negative electrode comprises metallic lithium as a negative electroactive material.

[0037] The negative electrode may comprise a composite material selected from the group consisting of Si / C, SiOa / C and Si / SiOa / C (0<a<2) as a negative electroactive material.

[0038] Methods to make such composite materials are based on mixing the individual ingredients (e.g. C and Si and / or SiOa, or a precursor for the intended matrix material) while preparing an electrode-forming composition, or by a separate composite manufacturing step that is then carried out via dry milling / mixing of at least a carbon material and at least a silicon material (which may be followed by a firing step), or via wet milling / mixing of at least a carbon material and at least a silicon material (followed by removal of the liquid medium and possibly by a firing step).

[0039] In one embodiment, a) the positive electrode and / or b) the negative electrode further comprise as a conductive aid, at least one carbon material having a specific surface area of 100 to 1200 m2 / g, preferably 300 to 1000 m2 / g, measured pursuant to the method ISO9277.

[0040] Advantageously, a conductive agent is a carbon material having a specific surface area of at least 200 m2 / g, at least 250 m2 / g, at least 300 m2 / g, at least 400 m2 / g, or at least 500 m2 / g, and / or at most 1100 m2 / g, at most 1000 m2 / g, at most 900 m2 / g, or at most 800 m2 / g, measured pursuant to the method ISO9277.

[0041] Specific surface area (SSA) is a physical property that may be used to determine the type / property of a solid and is defined as the total surface area of a material per unit mass (m2 / kg or m2 / g). SSA of a carbon material is determined by the most commonly used adsorption-based method, i.e. BET (Brunauer-Emmett-Teller) adsorption method as stipulated in ISO9277.

[0042] In another embodiment, a) the positive electrode and / or b) the negative electrode further comprise as a conductive aid, at least one carbon material having a ratio (ID / IG ratio) between the intensity of the D-band (ID) and the intensity of the G-band (IG) of 0.01 or more, characterized by Raman spectroscopy defined in the ISO / TS 80004-13.

[0043] In a particular embodiment, the ID / IG ratio is from 0.01 to 2.0.

[0044] In a more particular embodiment, the ID / IG ratio is from 0.01 to 1 .0.

[0045] In a preferred embodiment, a) the positive electrode and / or b) the negative electrode further comprise as a conductive aid, at least one carbon material having a specific surface area of 100 to 1200 m2 / g, preferably 300 to 1000 m2 / g, measured pursuant to the method ISO9277 and having a ratio (ID / IG) between the intensity of the D-band (ID) and the intensity of the G-band (IG) of 0.01 or more, characterized by Raman spectroscopy defined in the ISO / TS 80004-13.

[0046] Raman spectroscopy is a spectroscopic technique typically used to determine vibrational modes of molecules and hence to provide a chemical and structural fingerprint by which molecules can be identified. When light is scattered by molecules, the oscillating electromagnetic field of a photon induces a polarization of the molecular electron cloud which leaves the molecule in a higher energy state with the energy of the photon transferred to the molecule. Such a so-called virtual state of the molecule is unstable and the phon is re- emited almost immediately, as scattered light.

[0047] In particular, the G-band refers to the primary mode in carbon materials, for instance graphene, which represents the planar configutation of sp2-bonded carbon that constitutes graphene, in other words, graphite-type lattice vibrations. The D-band is also known as the disorder band or the defect band, which represents the presence of defects in graphitic structure which results from out-of-plane vibration. Notably, the intensity of the D-band (ID) is directly proportional to the level of defects in the structure of carbon materials.

[0048] In the present invention, the term “conductive aid” is intended to denote, in particular, a material which is used to ensure electrodes have good charging and discharging performance and to provide additional electrical conductivity.

[0049] Non-limiting examples of the conductive aid are carbonaceous materials and metals in powders or in fibers, for instance carbon nanotubes (CNT), vapor- grown carbon fibers (VGCF), graphite, graphene, graphite fibers and the like.

[0050] In some embodiments, the conductive aid is at least one selected from the group consisting of carbon nanotube (CNT), graphene, and graphene oxide.

[0051] In a particular embodiment, the conductive aid is at least one selected from the group consisting of mono-layer graphene, multi-layer graphene, mono- layer graphene oxide and multi-layer graphene oxide.

[0052] In another particular embodiment, the conductive aid is CNT.

[0053] In one preferred embodiment, the conductive aid is single-walled CNT (SWCNT).

[0054] In the other preferred embodiment, the conductive aid is multi-walled CNT (MWCNT).

[0055] In some embodiments, the conductive aid is included in an electrode in an amount of from 0.01 to 2.0 wt%, preferably from 0.1 to 1 .5 wt%, based on the total weight of the electrode.

[0056] In a particular embodiment, the conductive aid is included in an electrode in an amount of from 0.5 to 1 .0 wt%, based on the total weight of the electrode.

[0057] In the present invention, c) a liquid electrolyte comprises at least one lithium salt dissolved in a solvent mixture comprising at least one fluorinated acyclic carboxylic acid ester represented by the formula (II)R1-C(O)O-R2(II) wherein R1and R2represent an alkyl group respectively; the sum of carbon atoms in R1and R2is from 2 to 7; R1does not contain fluorine, and R2contains fluorine; and wherein the fluorinated acyclic carboxylic acid ester is in an amount of from 5.0 to 80.0 vol%, based on the total volume of the solvent mixture.

[0058] In one embodiment, R2contains neither a CH2F- group nor a -CHF- group.

[0059] In a preferred embodiment, the number of carbon atom in R1in the formula (II) is 1.

[0060] In another preferred embodiment, the number of carbon atom in R1in the formula (II) is 2.

[0061] Non-limitative examples of suitable fluorinated acyclic carboxylic acid ester according to the present invention include, notably, the followings: CH3-C(O)O-CH2CF2H, CH3-C(O)O-CF2CF3, CH3-C(O)O-CH2CF3, CH3- C(O)O-CF2CF2CF3, (CH3)2CH-C(O)O-CF3, CH3CH2-C(O)O-CF2H, CH3CH2- C(O)O-CF2CH3, CH3-C(O)O-CH(CF3)CH3, CH3CH2-C(O)O-CH2CF2H, CH3-C(O)O-CH2CH2CF2H, CH3-C(O)O-CH2CF2CF2H, CH3CH2-C(O)O- CH2CH2CF2H, CH3CH2-C(O)O-CH2CH2CF2H, CH3-C(O)O-CF2CF2H, CH3- C(O)O-CF2CF2CF2CF2H, CH3CH2-C(O)O-CH2CF2H, CH3CH2CH2-C(O)O- CH2CF3, CH3-C(O)O-CH2CH2CF2CF3, (CH3)2CH-C(O)O-CH2CF2H, CH3CH2CH2-C(O)O-CF2H, (CH3)2CH-C(O)O-CF2H, CH3-C(O)O-CH2CF2H, CH3-C(O)O-CH2CF3, CH3CH2-C(O)O-CH2CH2CF3, CH3CH2-C(O)O-CH2CF3, CH3-C(O)O-CF2CH3, CH3-C(O)O-CH2CF2CH3, CH3CH2-C(O)O-CF2CF2H, and combinations thereof.

[0062] In a particular embodiment, the fluorinated acyclic carboxylic acid ester is selected from the group consisting of CH3-C(O)O-CH2CF2H, CH3-C(O)O- CF2CF2H, CH3-C(O)O-CH2CF3, CH3-C(O)O-CH2CH2CF2H, CH3-C(O)O- CH2CF2CF2H, CH3-C(O)O-CH2CH2CF2CF3, CH3CH2-C(O)O-CH2CF2H, CH3CH2-C(O)O-CH2CF3, CH3CH2-C(O)O-CH2CH2CF2H, CH3CH2-C(O)O- CH2CH2CF3, CH3-C(O)O-CF2CH3, CH3-C(O)O-CH2CF2CH3, CH3CH2-C(O)O- CF2CF2H, and combinations thereof.

[0063] In a more particular embodiment, the fluorinated acyclic carboxylic acid ester is CH3-C(O)O-CH2CF2H (2,2-difluoroethyl acetate).

[0064] In another more particular embodiment, the fluorinated acyclic carboxylic acid ester is CH3CH2-C(O)O-CH2CF2H (2,2-difluoroethyl propionate).

[0065] In one particular embodiment, the the fluorinated acyclic carboxylic acid ester is in an amount of from 5.0 to 50.0 vol%, based on the total volume of the solvent mixture.

[0066] In another particular embodiment, the the fluorinated acyclic carboxylic acid ester is in an amount of from 10.0 to 50.0 vol%, based on the total volume of the solvent mixture.

[0067] In the other particular embodiment, the the fluorinated acyclic carboxylic acid ester is in an amount of from 10.0 to 40.0 vol%, based on the total volume of the solvent mixture.

[0068] In some embodiments, the the fluorinated acyclic carboxylic acid ester is in an amount of from 60.0 to 80.0 vol%, based on the total volume of the solvent mixture.

[0069] According to one embodiment, the solvent mixture further comprises at least one organic carbonate, which may be partially or fully fluorinated. In the present invention, the organic carbonate may be either cyclic or acyclic.

[0070] In a particular embodiment, the organic carbonate is at least one selected from the group consisting of a fluorinated cyclic carbonate, a non-fluorinated cyclic carbonate and a non-fluorinated acyclic carbonate.

[0071] Non-limiting examples of the organic carbonate include, notably, 4- fluoroethylene carbonate (4-fluoro-1 ,3-dioxolan-2-one), 4,5-difluoro-1 ,3- dioxolan-2-one, 4,5-difluoro-4-methyl-1 ,3-dioxolan-2-one, 4,5-difluoro-4,5- dimethyl-1 ,3-dioxolan-2-one, 4,4-difluoro-1 ,3-dioxolan-2-one, 4,4,5-trifluoro- 1 ,3-dioxolan-2-one, 4-fluoromethyl-1 ,3-dioxolan-2-one, tetrafluoroethylene carbonate, 4-(2,2-difluoroethoxy)ethylene carbonate, 4-(2,2,2- trifluoroethyoxy)ethylene carbonate, ethylene carbonate (1 ,3-dioxolan-2-one), propylene carbonate, butylene carbonate, trimethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, dimethylvinylene carbonate, ethyl propyl carbonate, cyclohexene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl-2,2-difluoroethyl carbonate, methyl- 2,2,2-trifluoroethyl carbonate, methyl-2,2,3,3-tetrafluoropropyl carbonate, ethyl-2,2-difluoroethyl carbonate, ethyl-2,2,2-trifluoroethyl carbonate, or combinations thereof.

[0072] In some embodiment, the organic carbonate is at least one selected from the group consisting of 4-fluoroethylene carbonate (4-fluoro-1 ,3-dioxolan-2-one),4.5-difluoro-1 ,3-dioxolan-2-one, 4,5-difluoro-4-methyl-1 ,3-dioxolan-2-one,4.5-difluoro-4,5-dimethyl-1 ,3-dioxolan-2-one, 4,4-difluoro-1 ,3-dioxolan-2-one,4.4.5-trif luoro-1 ,3-dioxolan-2-one, 4-fluoromethyl-1 ,3-dioxolan-2-one, tetrafluoroethylene carbonate, 4-(2,2-difluoroethoxy)ethylene carbonate, 4- (2,2,2-trifluoroethyoxy)ethylene carbonate, ethylene carbonate (1 ,3-dioxolan- 2-one), propylene carbonate, butylene carbonate, trimethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, dimethylvinylene carbonate, ethyl propyl carbonate, cyclohexene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and mixtures thereof.

[0073] In one particular embodiment, the organic carbonate is propylene carbonate.

[0074] In another particular embodiment, the organic carbonate is a mixture of propylene carbonate and ethyl methyl carbonate.

[0075] In the other particular embodiment, the organic carbonate is a mixture of ethylene carbonate and ethyl methyl carbonate.

[0076] The term “lithium salt” is hereby intended to denote a substance which needs to be dissolved in a solvent to ensure ionic conduction.

[0077] In a lithium secondary battery, a liquid electrolyte consists mainly of lithium salts in a non-aqueous organic solvent where lithium ions (i.e. Li+cations) are used as charge carriers such that the liquid electrolyte acts as a conductive pathway for the movement of cations, i.e. Li+cations passing from the cathode to anode during the charge. The dissolution of a lithium salt is through solvent- Li+interactions, i.e. the dissociation of Li+cation-(counter)anion interaction is critical. Accordingly, many simple lithium salts are excluded from electrolyte usage because of their strong cation-anion interactions resulting in high lattice energies and thus poor solubility in relevant aprotic solvents, e.g. LiCI, LiF, l_i2O, etc.

[0078] The Li+cation conductivity originates from both the total ionic conductivity and the cation transference number. Given that the cation transference number in a non-aqueous organic solvent is low, e.g. usually smaller than 0.5, the ionic conductivity plays a critical role in the battery performance.

[0079] In a nutshell, a liquid electrolyte where at least one lithium salt is dissolved in at least one non-aqueous organic solvent plays a pivotal role as one of the major components of a conventional lithium secondary battery.

[0080] Non-limitative examples of the lithium salt according to the present invention include, notably, a lithium ion complex such as lithium hexafluorophosphate (LiPFe), lithium perchlorate (LiCICU), lithium hexafluoroarsenate (LiAsFe), lithium hexafluoroantimonate (LiSbFe), lithium hexafluorotantalate (LiTaFe), lithium tetrachloroaluminate (LiAICk), lithium tetrafluoroborate (LiBF4), lithium chloroborate (Li2BioC o), lithium fluoroborate (Li2BioFio), Li2Bi2FxHi2-x wherein x=0-12, LiPFx(RF)6-x and LiBFy(RF)4-y wherein RF represents perfluorinated Ci- C20 alkyl groups or perfluorinated aromatic groups, x=0-5 and y=0-3, lithium bis(oxalato)borate [LiB(C2O4)2], lithium bis(malonato)borate [LiB(O2CCH2CO2)2], lithium bis(difluoromalonato) borate [LiB(O2CCF2CO2)2],lithium difluorooxalato borate, and lithium fluoromalonato (difluoro)borate, LiRF2[O2C(CX2)nCO2]2, LiPF4[O2C(CX2)nCO2] wherein X is selected from the group consisting of H, F, Cl, C1-C4 alkyl groups and fluorinated alkyl groups, and n=0-4, lithium trifluoromethane sulfonate (LiCFsSOs), lithium bis(fluorosulfonyl)imide Li(FSO2)2N (LiFSI), LiN(SO2CmF2m+i)(SO2CnF2n+i) and LiC(SO2CkF2k+i)(SO2CmF2m+i) (SO2CnF2n+i) wherein k=1 -10, m=1 -10 and n=1-10, LiN(SO2CPF2pSO2) and LiC(SO2CPF2PSO2)(SO2CqF2q+i) wherein p=1 - 10 and q=1 -10, or combinations thereof.

[0081] In one embodiment, the lithium salt according to the present invention is selected from the group consisting of lithium hexafluorophosphate (LiPFe), lithium perchlorate (LiCIC ), lithium hexafluoroarsenate (LiAsFe), lithium hexafluoroantimonate (LiSbFe), lithium hexafluorotantalate (LiTaFe), lithium tetrachloroaluminate (LiAICk), lithium tetrafluoroborate (LiBF4), lithium chloroborate (Li2BioC o), lithium fluoroborate (Li2BioFio), Li2Bi2FxHi2-x wherein x=0-12, LiPFx(RF)e-x and LiBFy(RF)4-y wherein RF represents perfluorinated Ci- 020 alkyl groups or perfluorinated aromatic groups, x=0-5 and y=0-3, lithium bis(oxalato)borate [LiB(C2O4)2], lithium trifluoromethane sulfonate (LiCFsSOs), lithium bis(fluorosulfonyl)imide Li(FSO2)2N (LiFSI), LiN(SO2CmF2m+l)(SO2CnF2n+l) and LiC(SO2CkF2k+l)(SO2CmF2m+l) (SO2CnF2n+i) wherein k=1 -10, m=1 -10 and n=1 -10, LiN(SO2CPF2PSO2) and LiC(SO2CpF2pSO2)(SO2CqF2q+i) wherein p=1 -10 and q=1 -10, and combinations thereof.

[0082] In one particular embodiment, the lithium salt is lithium b / s(trifluoromethanesulfonyl) imide (LiN(CF3SO2)2) (LiTFSI).

[0083] In another particular embodiment, the lithium salt is LiFSI.

[0084] In the other particular embodiment, the lithium salt is LiPFe.

[0085] As used herein, the molar concentration or the molarity is a measure of the concentration of a chemical species, in particular of a solute in a solution, in terms of the amount of substance per unit volume of solution. The most commonly used unit for molarity is the number of moles per liter, having the unit of mol / L. A solution with a concentration of 1 mol / L is indicated as 1 molar and designated as 1 M.

[0086] In one embodiment, a molar concentration (M) of a lithium salt in the liquid electrolyte according to the present invention is from 1 M to 4 M, preferably from 1 M to 2 M.

[0087] According to one embodiment, c) the liquid electrolyte further comprises at least one additive. The additive may contain solid electrolyte interface (SEI)- forming additive. SEI-forming additive promotes the formation of the SEI layer on the surface of the electrodes by reacting in advance of the solvents on the surface of the electrodes. For the SEI layer, the main components hence comprise the decomposed products of liquid electrolytes and salts, lithium alkyl carbonate, lithium alkyl oxide and other salt moieties such as Li F in case of LiPFe-based electrolytes.

[0088] The term “SEI”, as used herein, refers to a solid electrolyte interphase layer formed on the active material of an electrode. A lithium secondary battery is assembled in an uncharged state and must be activated (a process called formation) for use. During the first few charging events (battery formation) of a lithium secondary battery, components of the electrolyte are reduced or otherwise decomposed or incorporated onto the surface of the negative electroactive material and oxidized or otherwise decomposed or incorporated onto the surface of the positive electroactive material, electrochemically forming a solid-electrolyte interphase on the active materials. These layers, which are electrically insulating but ionically conducting, help prevent decomposition of the electrolyte and can extend the cycle life and improve the performance of the battery. On the negative electrode, the SEI can suppress the reductive decomposition of the electrolyte; on the positive electrode, the SEI can suppress the oxidation of the electrolyte components.

[0089] In one embodiment, the film-forming additive stabilizes the SEI layer at the surface of a positive electrode by preventing the structural change of the positive electrode, notably under high voltage.

[0090] This is because the reduction potential of the film-forming additive is higher than that of the liquid electrolyte when a reaction occurs at the surface of a negative electrode, and the oxidation potential of the film-forming additive is lower than that of the liquid electrolyte when the reaction occurs at the positive electrode.

[0091] In the present invention, the additive is different from the lithium salt.

[0092] In the present invention, the additive is different from the organic carbonate.

[0093] Non-limitative examples of the additive according to the present invention include, notably, cyclic sulfite and sulfate compounds comprising 1 ,3- propanesultone, ethylene sulfite and prop-1 -ene-1 ,3-sultone; sulfone derivatives comprising dimethyl sulfone, tetramethylene sulfone (also known as sulfolane), ethyl methyl sulfone, and isopropyl methyl sulfone; nitrile derivatives comprising succinonitrile, adiponitrile, glutaronitrile, and 4,4,4- trifluoronitrile; lithium nitrate, vinyl acetate, biphenyl benzene, isopropyl benzene, fr / s(trimethylsilyl)phosphate, triphenyl phosphine, ethyl diphenyl phosphinite, triethyl phosphite, f / 7s(2,2,2-trifluoroethyl) phosphite, maleic anhydride, cesium b / s(trifluoromethanesulfonyl)imide, cesium fluoride, or combinations thereof.

[0094] In a particular embodiment, the additive according to the present invention is selected from the group consisting of 1 ,3,2-dioxathiolane-2,2-dioxide, 1 ,3,2- dioxathiane-2,2-dioxide, 1 ,3-propanesultone, ethylene sulfite, prop-1 -ene-1 ,3- sultone, dimethyl sulfone, tetramethylene sulfone, ethyl methyl sulfone, isopropyl methyl sulfone, succinonitrile, adiponitrile, glutaronitrile, vinyl acetate, biphenyl benzene, isopropyl benzene, fr / s(trimethylsilyl)phosphate, triphenyl phosphine, ethyl diphenyl phosphinite, triethyl phosphite, fr / s(2,2,2- trifluoroethyl) phosphite, maleic anhydride, cesium b / s(trifluoromethanesulfonyl)imide, cesium fluoride, and combinations thereof.

[0095] In the present invention, the total amount of the additive may be from 0 to 10.0 wt%, preferably from 0 to 8.0 wt%, and more preferably from 0 to 5.0 wt%, with respect to the total weight of the liquid electrolyte.

[0096] The total amount of the additive, if contained in the liquid electrolyte of the present invention, is from 0.05 to 5.0 wt%, preferably from 0.05 to 3.0 wt%, and more preferably from 0.05 to 2.0 wt% with respect to the total weight of the liquid electrolyte.

[0097] In a preferred embodiment, the total amount of e) the additive accounts for at least 1.0 wt% of the electrolyte composition.

[0098] The lithium secondary battery as disclosed herein can be unsed in a variety of applications. For instance, the lithium secondary battery can be used forgrid storage or as a power source in various electronically powered or assisted devices (electronic devices) such as a computer, a camera, a power tool, etc., a telecommunication device or a transporation device including a motor vehicle, an electric vehicle, an airplane, etc. The present invention also relates to an electronic device, a transportation device or a telecommunication device comprising a lithium secondary battery according to the present invention.

[0099] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0100] The invention will be now explained in more detail with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the invention.

[0101] EXAMPLES

[0102] Raw Materials :- DFEA: a fluorinated acyclic carboxylic acid ester of CH3-C(O)O-CH2CF2H, synthesized within Solvay;- PC: propylene carbonate, commercially available from Soulbrain;- EMC: ethyl methyl carbonate, commercially available from Soulbrain;- TTE: 1 , 1 ,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, commercially available from SynQyest;- LiPO2F2: lithium difluorophosphate, commercially available from Soulbrain;- Li salt: lithium hexafluorophosphate (LiPFe), commercially available from Soulbrain

[0103] Formulation of the liquid electrolyte:

[0104] The liquid electrolyte for the Inventive Example 1 (E1 ) was prepared by adding a mixture of PC and DFEA in 20:80 (in vol%) in a reactor, followed by introducing 0.5 wt% of LiPO2F2 into the solvent mixture and by mixing under stirring for one hour until the solution became transparent. 1 M of LiPFe was then dissolved in the solution. The wt% was relative to the total weight of the liquid electrolyte.

[0105] The liquid electrolyte for the Inventive Example 2 (E2) was prepared in the same manner as E1 , except that a mixture of PC, DFEA and EMC in 20:40:40 (in vol%) was added.

[0106] The liquid electrolyte for the Inventive Example 3 (E3) was prepared in the same manner as E1 , except that a mixture of PC, DFEA and EMC in 20:10:70 (in vol%) was added.

[0107] The liquid electrolyte of Comparative Example 1 (CE1 ) was prepared in the same manner as E1 , except that EMC was added instead of DFEA.

[0108] The liquid electrolytes of Comparative Example 2 & 3 (CE2 & CE3) were prepared in the same manner as E2 & E3, except that TTE was added instead of DFEA.

[0109] The contituents of the liquid electrolyte are summarized in Table 1 below:Table 1*: vol% with respect to the total volume of the solvent mixture wherein 1M of Li PF 6 is dissolved and 0.5 wt% of Li PO2F2 is added, wt% being with respect to the total weight of the liquid electrolyte.

[0110] Coin cell preparation:

[0111] A positive electrode was prepared with LiNio.8CoO.1Mno.1O2, i.e. NCM811 (commercially available from Cosmo AM&T Co., ltd.) as a cathode electroactive material, carbon nanotubes (commercially available from Advanced NanoProducts Co,, ltd.) as a conductive aid, and polyvinilidene difuoride (PVDF) as a binder (SOLEF®5130, commercially available from Solvay Specialty Polymers Italy) in a weight ratio of 97.6 / 0.9 / 1 .5.

[0112] All the tests were performed with the coin half cells. All coin parts of CR2032 specification were commercially available from Wellcos. A coil cell wasassembled with the positive electrode, lithium metal as a negative electrode and polyethylene porous film as a separator. Each element was first cut by a circle disc. The disc size of the positive electrode, the negative electrode and the separator was 015, 016, and 019, respectively. The discs were then assembled to the coin cells. The separator was located between the positive electrode and the negative electrode, and the liquid electrolyte was subsequently injected into the coin cells. After sealing, the cells were kept at 25°C for 24 hours. Cells were cycled between 3.0 and 4.3V at 45°C. Cells were charged and discharged at a rate of 0.2C / 0.33C.

[0113] Results

[0114] Coulombic efficiency (CE)

[0115] CE refers to a percentage of the ratio of charging capacity and discharging capacity, i.e. CE = [discharging capacity / charging capacity]*100.

[0116] CE at its first cycle is indicated in Table 2, wherein the liquid electrolytes for the inventive examples (E1 -E3) comprising a fluorinated acyclic carboxylic acid ester exhibited better CE.

[0117] Electrochemical impedance spectroscopy (EIS)

[0118] EIS analysis enabled to confirm the degree of resistance of each component in the total resistance of a cell (Rceii), which is indicated also in Table 2, representing the resistance of the cell after formation.

[0119] It was clearly demonstrated that the liquid electrolyte according to the present invention (E1 -E3) exhibited lower resistance of the cell than CE1 -CE3.Table 2

[0120] Cycling performance (at 45°C)

[0121] The discharge capacity (in mAh / g) of E1 -E3 and CE1 -CE3 at 1stcycle, 5thcycle, 10thcycle and 20thcycle was indicated respectively in Table 3.

[0122] E1-E3 showed better discharging capacity than CE1 -CE3. Though CE1 exhibited good discarging capacity at 1stcycle (comparable to, or even better than E1 -E3), as the cycles increased, its discharging capacity decreased rapidly, notably quicker than E1 -E3.

[0123] In a nutshell, it was clearly demonstrated that E1 -E3 according to the present invention can exhibit oustanding performances, i.e. higher colulombic efficiency, lower resistance, and better discharging capacity, notably in comparison to the comparative examples (CE1-CE3).Table 3

Claims

1 . A lithium secondary battery comprising a) a positive electrode comprising, as a positive electroactive material, a lithium transition metal oxide represented by the following formula (I)LiNii-x-y-zMnxCoyAlzO2 (I) wherein x>0; y>0; z>0; 0<x+y+z<0.40; and Ni, Mn, Co, and / or Al are optionally doped with at least one metal selected from the group consisting of Sc, Ti, V, Cr, Fe, Cu, Zn, Mg, Al, Sn, B, Ga, Sr, Ca, In, Si, Zr, La, P, Nb, and Ge, respectively; b) a negative electrode; and c) a liquid electrolyte comprising at least one lithium salt dissolved in a solvent mixture comprising at least one fluorinated acyclic carboxylic acid ester represented by the formula (II)R1-C(O)O-R2(II) wherein R1and R2represent an alkyl group respectively; the sum of carbon atoms in R1and R2is from 2 to 7; R1does not contain fluorine, and R2contains fluorine; wherein the fluorinated acyclic carboxylic acid ester is in an amount of from 5.0 to 80.0% by volume (vol%), based on the total volume of the solvent mixture; and wherein a) the positive electrode and / or b) the negative electrode comprise, as a conductive aid, at least one carbon material having a specific surface area of 100 to 1200 m2 / g, measured pursuant to the method ISO9277 and having a ratio (ID / IG ratio) between the intensity of the D-band (ID) and the intensity of the G-band (IG) of 0.01 or more, characterized by Raman spectroscopy defined in the ISO / TS 80004- 13.

2. The lithium secondary battery according to claim 1 , wherein 0.05<x+y+z<0.30, preferably 0.08<x+y+z<0.25.

3. The lithium secondary battery according to claim 1 or 2, wherein the carbon material has a specific surface area of at least 200 m2 / g, at least 250 m2 / g, at least 300 m2 / g, at least 400 m2 / g, or at least 500 m2 / g, and / or at most 1100 m2 / g, at most 1000 m2 / g, at most 900 m2 / g, or at most 800 m2 / g, measured pursuant to the method ISO9277.

4. The lithium secondary battery according to any one of claims 1 to 3, wherein the conductive aid is included in a cathode or an anode in an amount of from 0.01 to 2.0% by weight (wt%), preferably from 0.01 to 1 .5 wt%, based on the total weight of the cathode or the anode.

5. The lithium secondary battery according to any one of claims 1 to 4, wherein the conductive aid is at least one selected from the group consisting of carbon nanotube (CNT), graphene, and graphene oxide.

6. The lithium secondary battery according to any one of claims 1 to 5, wherein the fluorinated acyclic carboxylic acid ester is in an amount of from 10.0 to 50.0 vol%, based on the total volume of the solvent mixture.

7. The lithium secondary battery according to any one of claims 1 to 6, wherein the fluorinated acyclic carboxylic acid ester is at least one selected from the group consisting of CH3-C(O)O-CH2CF2H, CH3-C(O)O-CF2H, CH3-C(O)O-CF2CF3, CH3-C(O)O-CH2CF3, CH3-C(O)O-CF3, CH3-C(O)O-CF2CF2CF3, (CH3)2CH-C(O)O- CF3, CH3CH2-C(O)O-CF2H, CH3CH2-C(O)O-CF3, CH3CH2-C(O)O-CF2CH3, CH3- C(O)O-CH(CF3)CH3, CH3CH2-C(O)O-CH2CF2H, CH3-C(O)O-CH2CH2CF2H, CH3- C(O)O-CH2CF2CF2H, CH3CH2-C(O)O-CH2CH2CF2H, CH3-C(O)O-CF2CF2H, CH3- C(O)O-CF2CF2CF2CF2H, CH3CH2CH2-C(O)O-CH2CF3, CH3-C(O)O- CH2CH2CH2CF2CF3, (CH3)2CH-C(O)O-CH2CF2H, CH3CH2CH2-C(O)O-CF2H, (CH3)2CH-C(O)O-CF2H, CH3CH2-C(O)O-CH2CF3, CH3-C(O)O-CF2CH3, CH3-C(O)O- CH2CF2CH3, CH3CH2-C(O)O-CF2CF2H, and mixtures thereof.

8. The lithium secondary battery according to any one of claims 1 to 7, wherein the solvent mixture further comprises at least one organic carbonate.

9. The lithium secondary battery according to claim 8, wherein the organic carbonate is at least one selected from the group consisting of a fluorinated cyclic carbonate, a non-fluorinated cyclic carbonate and a non-fluorinated acyclic carbonate.

10. The lithium secondary battery according to claim 8 or 9, wherein the organic carbonate is at least one selected from the group consisting of 4- fluoroethylene carbonate (4-fluoro-1 ,3-dioxolan-2-one), 4,5-difluoro-1 ,3-dioxolan-2- one, 4,5-difluoro-4-methyl-1 ,3-dioxolan-2-one, 4,5-difluoro-4,5-dimethyl-1 ,3-dioxolan- 2-one, 4,4-difluoro-1 ,3-dioxolan-2-one, 4,4,5-trifluoro-1 ,3-dioxolan-2-one, 4- fluoromethyl-1 ,3-dioxolan-2-one, tetrafluoroethylene carbonate, 4-(2,2- difluoroethoxy)ethylene carbonate, 4-(2,2,2-trifluoroethoxy)ethylene carbonate, ethylene carbonate (1 ,3-dioxolan-2-one), propylene carbonate, butylene carbonate, trimethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, dimethylvinylene carbonate, ethyl propyl carbonate, cyclohexene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and mixtures thereof.11 . The lithium secondary battery according to any of claims 1 to 10, wherein the lithium salt is at least one selected from the group consisting of lithium hexafluorophosphate (LiPFe), lithium perchlorate (LiCICU), lithium hexafluoroarsenate (LiAsFe), lithium hexafluoroantimonate (LiSbFe), lithium hexafluorotantalate (LiTaFe), lithium tetrachloroaluminate (LiAICk), lithium tetrafluoroborate (LiBF4), lithium chloroborate (Li2BioC o), lithium fluoroborate (Li2BioFio), Li2Bi2FxHi2-x wherein x=0- 12, LiPFx(RF)6-x and LiBFy(RF)4-y wherein RF represents perfluorinated C1-C20 alkyl groups or perfluorinated aromatic groups, x=0-5 and y=0-3, LiBF2[O2C(CX2)nCO2], LiPF2[O2C(CX2)nCO2]2, LiPF4[O2C(CX2)nCO2] wherein X is selected from the group consisting of H, F, Cl, C1-C4 alkyl groups and fluorinated alkyl groups, and n=0-4, lithium trifluoromethane sulfonate (LiCFsSOs), lithium bis(fluorosulfonyl)imide Li(FSO2)2N (LiFSI), LiN(SO2CmF2m+i)(SO2CnF2n+i) and LiC(SO2CkF2k+i)(SO2CmF2m+i)(SO2CnF2n+i) wherein k=1-10, m=1-10 and n=1-10, LiN(SO2CPF2pSO2) and LiC(SO2CPF2PSO2)(SO2CqF2q+i) wherein p=1 -10 and q=1 -10, and mixtures thereof.

12. The lithium secondary battery according to any of claims 1 to 11 , wherein c) the liquid electrolyte further comprises at least one additive selected from the group consisting of sulfur compounds such as 1 ,3,2-dioxathiolane-2,2-dioxide,1 ,3,2-dioxathiane-2,2-dioxide, 1 ,3-propanesultone, ethylene sulphite and prop-1 -ene- 1 ,3-sultone; sulfone derivatives such as dimethyl sulfone, tetramethylene sulfone (also known as sulfolane), ethyl methyl sulfone and isopropyl methyl sulfone; nitrile derivatives such as succinonitrile, adiponitrile, and glutaronitirle; and lithium nitrate (LiNOs); boron derivatives salt such as lithium difluoro oxalato borate (LiDFOB), lithium bis(oxalato)borate (LiB(C2O4)2; LiBOB), lithium fluoromalonato (difluoro)borate (LiB(O2CCHFCO2)2; LiFMDFB), lithium bis(malonato)borate [LiB(O2CCH2CO2)2], lithium bis(difluoromalonato) borate [LiB(O2CCF2CO2)2], lithium (malonatooxalato) borate [LiB(C2O4)(O2CCH2CO2)], lithium (difluoromalonatooxalato) borate [LiB(C2O4)(O2CCF2CO2)], lithium tris(oxalato) phosphate [LiP(C2O4)3], lithium tris(difluoromalonato) phosphate [LiP(O2CCF2CO2)3], lithium difluorophosphate (IJPO2F2), vinyl acetate, biphenyl benzene, isopropyl benzene, hexafluorobenzene, tris(trimethylsilyl)phosphate, triphenyl phosphine, ethyl diphenylphosphinite, triethyl phosphite, tris(2,2,2-trifluoroethyl) phosphite, maleic anhydride, cesium bis(trifluoromethanesulfonyl)imide (CsTFSI), cesium fluoride (CsF), and mixtures thereof.

13. The lithium secondary battery according to any of claims 1 to 12, wherein b) the negative electrode comprises, as a negative electroactive material, metallic lithium or a composite material of at least a carbon material and a silicon material.

14. The lithium secondary battery according to claim 13, wherein the composite material is at least one selected from the group consisting of Si / C, SiOa / C, and Si / SiOa / C, with 0<a<2.

15. An electronic device, a transportation device or a telecommunication device comprising a lithium secondary battery according to any one of claims 1 to 14.

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