Patent Application
20240243364
This application claims priority to European patent application No. 21167334.8 filed on Apr. 8, 2021, the whole content of this application being incorporated herein by reference for all purposes.
The present invention pertains to a liquid electrolyte for lithium secondary batteries comprising:
The present invention also relates to a lithium secondary battery comprising an anode, a cathode, a separator and a liquid electrolyte according to the present invention.
For more than two decades, lithium secondary batteries including lithium-ion batteries have retained a dominant position in the market of rechargeable energy storage devices due to their many benefits comprising light-weight, reasonable energy density, and good cycle life. Nevertheless, current lithium secondary batteries still suffer from relatively low energy densities with respect to the required energy density, which keeps increasing for high power applications such as electrical vehicles (EVs), hybrid electrical vehicles (HEVs), grid energy storage, etc.
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 (up to 5.0 V) is desired in the art, and accordingly the developments of electrolyte suitable for the high-voltage batteries, and/or the component for such an electrolyte have been consistently required in the art. In terms of the charge cut-off voltage, such high-voltage batteries have a charge cut-off voltage of higher than 4.2 V, in particular at least 4.35 V.
As electrolyte solvents for lithium secondary batteries, organic carbonates have been conventionally used comprising 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 can easily decompose above 4.35V and there are also safety concerns with the use of organic carbonates because of their relatively low boiling point and high flammability, which may result in a degradation of battery performance.
Accordingly, various approaches have been investigated to overcome the limitations of commonly used liquid electrolytes based on the organic carbonates, to increase the energy density, notably at higher voltage, to improve the cycle performance at elevated temperature, and to reduce the swelling of the batteries, while ensuring high safety.
As one of the diverse research efforts with such purposes, a particular solvent mixture for use as a liquid electrolyte in lithium secondary batteries, which comprises ethylene carbonate and a fluorine-containing carboxylic acid ester in certain concentrations, was reported in WO 2013/033579 (E.I.DUPONT DE NEMOURS AND COMPANY), to contribute to the improved cycling performance at high temperature, particularly with a high voltage cathode.
Besides, there have been several approaches with the same purpose, consisting of using particular hydrofluoroethers as an essential component of the electrolyte for lithium ion batteries. For instance, U.S. Pat. No. 5,916,708 (HOESHST AKTIENGESELLSCHAFT) discloses particular hydroflouroethers represented by the formulae (i) and/or (ii),
WO 2015/078791 (Solvay Specialty Polymers Italy S.p.A) discloses that the liquid electrolyte comprising certain hydrofluoroethers having a high fluorination rate, which are obtainable with the process disclosed in the WO 2012/084745A (Solvay Specialty Polymers Italy S.p.A), exhibit favorable properties in terms of solubility of a lithium salt, working temperature range, ionic conductivity, oxidative stability at high voltage and low flammability.
Despite the efforts in this field as briefly described above, there still exists the outstanding needs for a liquid electrolyte for lithium secondary batteries having improved cycling performance at high temperature, particularly with a high voltage cathode.
The present invention pertains to a liquid electrolyte for lithium secondary batteries comprising:
It was surprisingly found by the inventors that the above-mentioned technical problems can be solved by using a liquid electrolyte according to the present invention, which is clearly evidenced by the excellent capacity retention and Coulombic efficiency.
Throughout this specification, unless the context requires otherwise, the word “comprise” or “include”, or variations such as “comprises”, “comprising”, “includes”, including” will be understood to imply the inclusion of a stated element or method step or group of elements or method steps, but not the exclusion of any other element or method step or group of elements or method steps. According to preferred embodiments, the word “comprise” and “include”, and their variations mean “consist exclusively of”.
As used in this specification, the singular forms “a”, “an” and “the” include plural aspects unless the context clearly dictates otherwise. The term “and/or” includes the meanings “and”, “or” and also all the other possible combinations of the elements connected to this term.
The term “between” should be understood as being inclusive of the limits.
The term “aliphatic group” includes organic moieties characterized by straight or branched-chains, typically having between 1 and 18 carbon atoms. In complex structures, the chains may be branched, bridged, or cross-linked. Aliphatic groups include alkyl groups, alkenyl groups, and alkynyl groups.
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, e.g., type of cathode or anode.
As used herein, the terminology “(Cn-Cm)” in reference to an organic group, wherein n and m are integers, respectively, indicates that the group may contain from n carbon atoms to m carbon atoms per group.
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. For example, a temperature range of about 120° C. to about 150° C. should be interpreted to include not only the explicitly recited limits of about 120° C. to about 150° C., but also to include sub-ranges, such as 125° C. to 145° C., 130° C. to 150° C., and so forth, as well as individual amounts, including fractional amounts, within the specified ranges, such as 122.2° C., 140.6° C., and 141.3° C., for example.
Unless otherwise specified, in the context of the present invention the amount of a component in a composition is indicated as the ratio between the volume of the component and the total volume of the composition multiplied by 100, i.e., % by volume (vol %) or as the ratio between the weight of the component and the total weight of the composition multiplied by 100, i.e., % by weight (wt %). 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.
The present invention relates to a liquid electrolyte for lithium secondary batteries comprising:
In one embodiment, R4 and R5 contain neither a CH2F— group nor a —CHF— group.
In one embodiment, the number of carbon atoms in R4 in the formula (II) is 1, 3, 4, or 5. In a preferred embodiment, the number of carbon atoms in R4 in the formula (II) is 1.
In the present invention, the term “alkyl” is intended to denote saturated hydrocarbons having one or more carbon atoms, including straight-chain alkyl groups, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, cyclic alkyl groups (or “cycloalkyl” or “alicyclic” or “carbocyclic” groups), such as cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl, branched-chain alkyl groups, such as isopropyl, tert-butyl, sec-butyl, and isobutyl, and alkyl-substituted alkyl groups, such as alkyl-substituted cycloalkyl groups and cycloalkyl-substituted alkyl groups.
In the present invention, the term “fluorinated ayclic diether” is intended to denote an acyclic diether compound, wherein at least one hydrogen atom is replaced by fluorine. One, two, three or a higher number of hydrogen atoms may be replaced by fluorine.
In the present invention, the term “boiling point” is intended to denote the temperature at which the vapour pressure of a liquid substance equals to the pressure surrounding the liquid and the liquid changes its physical status into a vapour. The boiling point of a liquid substance varies depending on the surrounding environmental pressure and the boiling point according to the invention corresponds to the boiling point when the liquid is at atmospheric pressure, also known as the atmospheric boiling point.
In one embodiment, the boiling point of a) the fluorinated acyclic diether is at least 80° C., preferably from 80° C. to 160° C., and more preferably from 120° C. to 160° C.
In one embodiment, a) the fluorinated acyclic diether is in an amount of from 0.05 to 45% by weight (wt %), and preferably from 0.5 to 40 wt %, based on the total weight of the liquid electrolyte.
In another embodiment, a) the fluorinated acyclic diether is in an amount of from 10 to 45 wt %, and preferably from 20 to 40 wt %, based on the total weight of the liquid electrolyte.
In one embodiment, the molar ratio F/H in a) the fluorinated acyclic diether is from 1.3 to 13.0, preferably from 2.5 to 6.0.
In a preferred embodiment, a) the fluorinated acyclic diether contains 6 carbon atoms.
In a more preferred embodiment, a) the fluorinated acyclic diether is CHF2CF2—O—CH2CH2—O—CF2CF2H.
Non-limitative examples of suitable a) fluorinated acyclic diether according to the present invention include, notably, the followings:
CF3CH2—O—CF2CHF—O—CF3, CHF2CH2—O—CF2CF2—O—CF3, CF3CF2—O—CHFCHF—O—CHF2, CHF2CF2—O—CHFCHF—O—CF3, CF3CHF—O—CHFCF2—O—CHF2, CF3CHF—O—CF2CHF—O—CHF2, CH3CF2—O—CF2—O—CF2CF3, CFH2CHF—O—CF2—O—CF2CF3, CF3CF2—O—CHF—O—CHFCHF2, CF3CF2—O—CHF—O—CHFCHF2, CF3CH2—O—CF2CF2—O—CF3, CHF2CHF—O—CF2CF2—O—CF3, CH2FCF2—O—CF2CF2—O—CF3, CF3CF2—O—CHFCHF—O—CF3, CF3CF2—O—CF2CH2—O—CF3, CF3CF2—O—CH2CF2—O—CF3, CF3CF2—O—CF2CFH—O—CHF2, CF3CHF—O—CHFCF2—O—CF3, CF3CHF—O—CF2CHF—O—CF3, CHF2CF2—O—CF2CHF—O—CF3, CHF2CF2—O—CHFCF2—O—CF3, CHF2CF2—O—CF2CF2—O—CHF2, CF3CHF—O—CF2CF2—O—CHF2, CF3CF2—O—CF2—O—CHFCF3, CF2HCF2—O—CF2—O—CF2CF3, CF3CHF—O—CF2—O—CF2CF3, CF3CF2—O—CHF—O—CF2CF3, CF3CF2—O—CF2—O—CF2CHF2, CF2HCF2—O—CF2CH2—O—CF2CF2H, CF3CF2—O—CH2CH2—O—CF2CF3, CF2HCF2—O—CHFCHF—O—CF2CF2H, CF3CF2—O—CHFCH2—O—CF2CF2H, CF2HCF2—O—CHFCHF—O—CF2CF2H, CF3CF2—O—CH2CHF—O—CF2CF2H, CF3—O—CHFCF2CH2—O—CF2CF2H, CF2HCF2—O—CF2CF2—O—CF2CF2H, CF3CF2—O—CF2CHF—O—CF2CF2H, CF3CF2—O—CHFCF2—O—CF2CF2H, CF3CF2—O—CF2CH2—O—CF2CF3, CF3CF2—O—CHFCHF—O—CF2CF3, CF3CF2—O—CHFCHF—O—CF2CF3, and mixtures thereof.
In another embodiment, a) the fluorinated acycic diether contains 7 carbon atoms.
In another embodiment, a) the fluorinated acyclic diether contains 8 carbon atoms.
In one embodiment, the liquid electrolyte according to the present invention comprises neither a non-fluorinated ether nor a fluorinated mono-ether.
In the present invention, the term “non-fluorinated ether” is intended to denote an ether compound, wherein no fluorine atom is present.
In the present invention, the term “fluorinated mono-ether” is intended to denote a mono-ether compound, wherein at least one hydrogen atom is replaced by fluorine. One, two, three or a higher number of hydrogen atoms may be replaced by fluorine.
Non-limitative examples of suitable fluorinated acyclic carboxylic acid ester according to the present invention include, notably, the followings:
CH3—C(O)O—CH2CF2H, CF3—C(O)O—CH2CF3, CH3—C(O)O—CH2CF3, CF3—C(O)O—CH2CF2CF2H, CH3—C(O)O—CH2CH2CF2H, CH3—C(O)O—CH2CF2CF2H, CH3CH2—C(O)O—CH2CH2CF2H, CF2H—C(O)O—CH2CF2H, CH3CH2—C(O)O—CH2CF2H, CH3—C(O)O—CH2CH2CH2CF2CF3, CH3—C(O)O—CH2CF2H, CH3—C(O)O—CH2CF3, CH3CH2—C(O)O—CH2CF2H, CH3CH2—C(O)O—CH2CF3, and mixtures thereof.
In a preferred embodiment, b) the fluorinated acyclic carboxylic acid ester comprises CH3—C(O)O—CH2CF2H, CH3—C(O)O—CH2CH2CF2H, CH3CH2—C(O)O—CH2CH2CF2H, CH3—C(O)O—CH2CF3, CH3CH2—C(O)O—CH2CF2H, CH3CH2—C(O)O—CH2CF3, CH3CH2—C(O)O—CH2CF2H, or mixtures thereof.
In a more preferred embodiment, b) the fluorinated acyclic carboxylic acid ester is CH3—C(O)O—CH2CF2H (2,2-difluoroethyl acetate).
In one embodiment, b) the fluorinated acyclic carboxylic acid ester is in an amount of from 10 to 50 wt %, and preferably from 20 to 45 wt %, based on the total weight of the liquid electrolyte.
The liquid electrolyte according to the present invention does not comprise a fluorinated cyclic carboxylic acid ester, e.g., a fluorinated lactone containing a 1-oxacycloalkan-2-one structure.
Non-limitative examples of c) the organic carbonate according to the present invention include, notably, the followings:
4-fluoroethylene carbonate, 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, propylene carbonate, butylene carbonate, trimethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, dimethylvinylene carbonate, ethyl propyl carbonate, cyclohexene carbonate, bisphenol A, B and F carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and mixtures thereof.
In one embodiment, the total amount of c) the at least one organic carbonate is from 10 to 80 wt %, and preferably from 15 to 60 wt %, with respect to the total weight of the liquid electrolyte.
In a particular embodiment, c) the organic carbonate comprises a fluorinated cyclic carbonate in an amount of from 1 to 15 wt %, preferably from 2 to 12 wt %, and more preferably from 4 to 10 wt %, based on the total weight of the liquid electrolyte.
In one embodiment, c) the organic carbonate comprises a fluorinated acyclic carbonate represented by the formula (III)
wherein R6 and R7 represent an alkyl group respectively; the sum of carbon atoms in R6 and R7 is from 2 to 7; and at least one hydrogen in R6 and/or R7 is replaced by fluorine.
In one embodiment, R6 and R7 contain neither a CH2F— group nor a —CHF— group.
In a particular embodiment, R6 in the formula (III) does not contain fluorine and R7 contains fluorine.
In another particular embodiment, R6 and R7 independently represent a straight-chain or branched alkyl group having from 2 to 7 carbon atoms, where at least two hydrogens are replaced by fluorines (that is, at least two hydrogens in R6 are replaced by fluorines, or at least two hydrogens in R7 are replaced by fluorines, or at least two hydrogens in R6 and at least two hydrogens in R7 are replaced by fluorines).
Non-limitative examples of suitable fluorinated acyclic carbonate according to the present invention include, notably, the followings:
CH3—OC(O)O—CH2CF2H (methyl 2,2-difluoroethyl carbonate), CH3—OC(O)O—CH2CF3 (methyl 2,2,2-trifluoroethyl carbonate), CH3—OC(O)O—CH2CF2CF2H (methyl 2,2,3,3-tetrafluoropropyl carbonate), CF2HCH2—OC(O)O—CH2CF3 (ethyl 2,2-difluoroethyl carbonate), CF3CH2—OC(O)O—CH2CH3 (ethyl 2,2,2-trifluoroethyl carbonate), CF3CH2—OC(O)O—CH2CF3 (bis(2,2,2-trifluoroethyl) carbonate), CF2HCH2—OC(O)O—CH2CF2H (bis(2,2-difluoroethyl) carbonate), CH3—OC(O)O—CH2CF2H (methyl 2,2-difluoroethyl carbonate), CF3—OC(O)O—CF3, CFH2—OC(O)O—CH3, CF3CHF—OC(O)O—CF3, CH3CH2—OC(O)O—CHFCH3, CH3CHF—OC(O)O—CHFCH3, CH3CHF—OC(O)O—CH2CF3, CH3CHF—OC(O)O—CH2CH2CH3, and mixtures thereof.
Non-limitative examples of d) the lithium salt according to the present invention include, notably, the followings:
a lithium ion complex such as lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiCIO4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroantimonate (LiSbF6), lithium hexafluorotantalate (LiTaF6), lithium tetrachloroaluminate (LiAlCl4), lithium tetrafluoroborate (LiBF4), lithium chloroborate (Li2B10Cl10), lithium fluoroborate (Li2B10F10), Li2B12FxH12-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 (LiCF3SO3), lithium bis(fluorosulfonyl)imide Li(FSO2)2N (LiFSI), LiN(SO2CmF2m+1)(SO2CnF2n−1) and LiC(SO2CkF2k−1)(SO2CmF2m−1)(SO2CnF2n+1) wherein k=1-10, m=1-10 and n=1-10, LiN(SO2CpF2pSO2) and LiC(SO2CpF2pSO2)(SO2CqF2q−1) wherein p=1-10 and q=1-10, and mixtures thereof.
In one embodiment, d) the lithium salt is lithium bis(trifluorosulfonyl)imid (LiN(CF3SO2)2; LiTFSI).
In another embodiment, d) the lithium salt is LiPF6.
In another embodiment, d) the lithium salt is LiFSI.
In one embodiment, a molar concentration (M) of the lithium salt in the liquid electrolyte according to the present invention is from 1 M to 8 M, preferably from 1 M to 4 M, and more preferably from 1 M to 2 M.
The lithium salt according to the present invention does not comprise lithium salts having nitrogen atoms on a heterocyclic ring such as an imidazole, e.g., lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI).
According to one embodiment, the liquid electrolyte according to the present invention further comprises e) at least one film-forming additive, which promotes the formation of the solid electrolyte interface (SEI) layer at the negative electrode surface by reacting in advance of the solvents on the electrode surfaces. For the SEI layer, the main components hence comprise the decomposed products of electrolyte solvents and salts, which may include Li2CO3 (in case of LiCoO2 as a positive electrode), lithium alkyl carbonate, lithium alkyl oxide and other salt moieties such as LiF for LiPF6-based electrolytes. According to another embodiment, e) the film-forming additive stabilizes the cathode electrolyte interface (CEI) layer at the positive electrode surface by preventing the structural change of the positive electrode, notably under high voltage. Usually, the reduction potential of the film-forming additive is higher than that of the solvent when a reaction occurs at the negative electrode surface, and the oxidation potential of the film-forming additive is lower than that of the solvent when the reaction occurs at the positive electrode side.
In one embodiment, e) the film-forming additive according to the present invention is selected from the group consisting of sulfur compounds comprising 1,3,2-dioxathiolane-2,2-dioxide, 1,3,2-dioxathiolane-4-ethynyl-2,2-dioxide, 1,3,2-dioxathiolane-4-ethenyl-2,2-dioxide, 1,3,2-dioxathiolane-4,5-diethenyl-2,2-dioxide, 1,3,2-dioxathiolane-4-methyl-2,2-dioxide, 1,3,2-dioxathiolane-4,5-dimethyl-2,2-dioxide, 1,3,2-dioxathiane-2,2-dioxide, 1,3,2-dioxathiane-4-ethynyl-2,2-dioxide, 1,3,2-dioxathiane-5-ethynyl-2,2-dioxide, 1,3,2-dioxathiane-4-ethenyl-2,2-dioxide, 1,3,2-dioxathiane-5-ethenyl-2,2-dioxide, 1,3,2-dioxathiane-4,5-diethenyl-2,2-dioxide, 1,3,2-dioxathiane-4,6-diethenyl-2,2-dioxide, 1,3,2-dioxathiane-4,5,6-triethenyl-2,2-dioxide, 1,3,2-dioxathiane-4-methyl-2,2-dioxide, 1,3,2-dioxathiane-5-methyl-2,2-dioxide, 1,3,2-dioxathiane-4,5-dimethyl-2,2-dioxide, dioxathiane-4,6-dimethyl-2,2-dioxide, dioxathiane-4,5,6-trimethyl-2,2-dioxide; 1,3-propane sultone, 3-fluoro-1,3-propane sultone, 4-fluoro-1,3-propane sultone, 5-fluoro-1,3-propane sultone, 1,4-butane sultone, 3-fluoro-1,4-butane sultone, 4-fluoro-1,4-butane sultone, 5-fluoro-1,4-butane sultone, 6-fluoro-1,4-butane sultone, preferably 1,3,2-dioxathiolane-2,2-dioxide, 1,3,2-dioxathiane-2,2-dioxide, oxathiolane-2,2-dioxide (1,3-propane sultone), 1,3,2-dioxathiolane-2-oxide (ethylene sulfite) and prop-1-ene-1,3-sultone, dimethyl sulfone, tetramethylene sulfone (also known as sulfolane), ethyl methyl sulfone and isopropyl methyl sulfone; nitrile derivatives comprising succinonitrile, adiponitrile, and glutaronitrile; lithium nitrate (LiNO3); boron derivatives salt comprising lithium difluoro oxalato borate 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 (LiPO2F2), vinyl acetate, biphenyl benzene, isopropyl benzene, hexafluorobenzene, tris(trimethylsilyl)phosphate, triphenyl phosphine, ethyl diphenylphosphinite, triethyl phosphite, tris(2,2,2-trifluoroethyl) phosphite, maleic anhydride, vinylene carbonate, vinyl ethylene carbonate, cesium bis(triflulorosulfonyl)imide (CsTFSI), cesium hexafluorophosphate (CsPF6), cesium fluoride (CsF), trimethylboroxine (TMB), tributyl borate (TBB), 2-(2,2,3,3,3-pentafluoropropoxy)-1,3,2-dioxaphospholane (PFPOEPi), 2-(2,2,3,3,3-pentafluoropropoxy)-4-(trifluormethyl)-1,3,2-dioxaphospholane (PFPOEPi-1CF3), lithium hexafluorophosphate (LiPF6), silver nitrate (AgNO3), silver hexafluorophosphate (AgPF6), tris(trimethylsilyl)phosphine (TMSP), 1,6-divinylperfluorohexane, and mixtures thereof.
In a preferred embodiment, e) the film-forming additive is selected from the group consisting of sulfur compounds comprising 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 comprising dimethyl sulfone, tetramethylene sulfone (also known as sulfolane), ethyl methyl sulfone and isopropyl methyl sulfone; nitrile derivatives comprising succinonitrile, adiponitrile, and glutaronitirle; and lithium nitrate (LiNO3); boron derivatives salt comprising 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 (LiPO2F2), 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(triflulorosulfonyl)imide (CsTFSI), cesium fluoride (CsF), and mixtures thereof.
In a more preferred embodiment, the e) film-forming additive according to the present invention is LiBOB.
In another more preferred embodiment, the e) film-forming additive according to the present invention is maleic anhydride.
In another more preferred embodiment, the e) film-forming additive according to the present invention is a mixture of maleic anhydride and LiBOB.
In another embodiment, e) the film-forming additive according to the present invention is an ionic liquid.
The term “ionic liquid” as used herein refers to a compound comprising a positively charged cation and a negatively charged anion, which is in the liquid state at the temperature of 100° C. or less under atmospheric pressure. While ordinary liquids such as water are predominantly made of electrically neutral molecules, ionic liquids are largely made of ions and short-lived ion pairs. As used herein, the term “ionic liquid” indicates a compound free from solvent.
The term “onium cation” as used herein refers to a positively charged ion having at least part of its charge localized on at least one non-metal atom such as O, N, S, or P.
In the present invention, the ionic liquid has a general formula of An−Ql+(n/l), wherein
The cation(s) may be selected, independently of one another, from metal cations and organic cations. The cation(s) may be mono-charged cations or polycharged cations.
As metal cation, mention may preferably be made of alkali metal cations, alkaline-earth metal cations and cations of d-block elements.
In the present invention, Ql+(n/l) may represent an onium cation. Onium cations are cations formed by the elements of Groups VB and VIB (as defined by the old European IUPAC system according to the Periodic Table of the Elements) with three or four hydrocarbon chains. The Group VB comprises the N, P, As, Sb and Bi atoms. The Group VIB comprises the O, S, Se, Te and Po atoms. The onium cation can in particular be a cation formed by an atom selected from the group consisting of N, P, O and S, more preferably N and P, with three or four hydrocarbon chains.
The onium cation Ql+(n/l) can be selected from:
In the above formulas, each “R” symbol represents, independently of one another, a hydrogen atom or an organic group. Preferably, each “R” symbol can represent, in the above formulas, independently of one another, a hydrogen atom or a saturated or unsaturated and straight-chain, branched or cyclic C1 to C18 hydrocarbon group optionally substituted one or more times by a halogen atom, an amino group, an imino group, an amide group, an ether group, an ester group, a hydroxyl group, a carboxyl group, a carbamoyl group, a cyano group, a sulfone group or a sulfite group.
The cation Ql+(n/l) can more particularly be selected from ammonium, phosphonium, pyridinium, pyrrolidinium, pyrazolinium, imidazolium, arsenium, quaternary phosphonium and quaternary ammonium cations.
The quaternary phosphonium or quaternary ammonium cations can more preferably be selected from tetraalkylammonium or tetraalkylphosphonium cations, trialkylbenzylammonium or trialkylbenzylphosphonium cations or tetraarylammonium or tetraarylphosphonium cations, the alkyl groups of which, either identical or different, represents a straight-chain or branched alkyl chain having from 4 to 12 carbon atoms, preferably from 4 to 6 carbon atoms, and the aryl groups of which, either identical or different, represents a phenyl or naphthyl group.
In a specific embodiment, Ql+(n/l) represents a quaternary phosphonium or quaternary ammonium cation.
In one preferred embodiment, Ql+(n/l) represents a quaternary phosphonium cation. Non-limiting examples of the quaternary phosphonium cation comprise trihexyl(tetradecyl)phosphonium, and a tetraalkylphosphonium cation, particularly the tetrabutylphosphonium (PBu4) cation.
In another embodiment, Q′(n/l) represents an imidazolium cation. Non-limiting examples of the imidazolium cation comprise 1,3-dimethylimidazolium, 1-(4-sulfobutyl)-3-methyl imidazolium, 1-allyl-3H-imidazolium, 1-butyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-octyl-3-methylimidazolium
In another embodiment, Ql+(n/l) represents a quaternary ammonium cation which is selected in particular from the group consisting of tetraethylammonium, tetrapropylammonium, tetrabutylammonium, trimethylbenzylammonium, methyltributylammonium, N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium, N,N-dimethyl-N-ethyl-N-(3-methoxypropyl) ammonium, N,N-dimethyl-N-ethyl-N-benzyl ammonium, N, N-dimethyl-N-ethyl-N-phenylethyl ammonium, N-tributyl-N-methyl ammonium, N-trimethyl-N-butyl ammonium, N-trimethyl-N-hexyl ammonium, N-trimethyl-N-propyl ammonium, and Aliquat 336 (mixture of methyltri(C8 to C10 alkyl)ammonium compounds).
In one embodiment, Ql+(n/l) represents a piperidinium cation, in particular N-butyl-N-methyl piperidinium, N-propyl-N-methyl piperidinium.
In another embodiment, Ql+(n/l) represents a pyridinium cation, in particular N-methylpyridinium.
In a more preferred embodiment, Ql+(n/l) represents a pyrrolidinium cation. Among specific pyrrolidinium cations, mention may be made of the following: C1-12alkyl-C1-12alkyl-pyrrolidinium, and more preferably C1-4alkyl-C1-4alkyl-pyrrolidinium. Examples of pyrrolidinium cations comprise, but not limited to, N,N-dimethylpyrrolidinium, N-ethyl-N-methylpyrrolidinium, N-isopropyl-N-methylpyrrolidinium, N-methyl-N-propylpyrrolidinium, N-butyl-N-methylpyrrolidinium, N-octyl-N-methylpyrrolidinium, N-benzyl-N-methylpyrrolidinium, N-cyclohexylmethyl-N-methylpyrrolidinium, N-[(2-hydroxy)ethyl]-N-methylpyrrolidinium. More preferred are N-methyl-N-propylpyrrolidinium (PYR13) and N-butyl-N-methylpyrrolidinium (PYR14).
Non-limiting examples of an anion of the ionic liquid comprise iodide, bromide, chloride, hydrogen sulfate, dicyanamide, acetate, diethyl phosphate, methyl phosphonate, fluorinated anion, e.g., hexafluorophosphate (PF6−) and tetrafluoroborate (BF4−), and oxalatooborate of the following formula.
In one embodiment, An− is a fluorinated anion. Among the fluorinated anions that can be used in the present invention, fluorinated sulfonimide anions may be particularly advantageous. The organic anion may, in particular, be selected from the anions having the following general formula:
(Ea-SO2)N−R
in which:
Preferably, Ea may represent F or CF3.
According to a first embodiment, R represents a hydrogen atom.
According to a second embodiment, R represents a straight-chain or branched, cyclic or non-cyclic hydrocarbon-based group, preferably having from 1 to 10 carbon atoms, which can optionally bear one or more unsaturations, and which is optionally substituted one or more times with a halogen atom, a nitrile function, or an alkyl group optionally substituted one of several times by a halogen atom. Moreover, R may represent a nitrile group —CN.
According to a third embodiment, R represents a sulfinate group. In particular, R may represent the group —SO2—Ea, Ea being as defined above. In this case, the fluorinated anion may be symmetrical, i.e. such that the two Ea groups of the anion are identical, or non-symmetrical, i.e. such that the two Ea groups of the anion are different.
Moreover, R may represent the group —SO2—R′, R′ representing a straight-chain or branched, cyclic or non-cyclic hydrocarbon-based group, preferably having from 1 to 10 carbon atoms, which can optionally bear one or more unsaturations, and which is optionally substituted one or more times with a halogen atom, a nitrile function, or an alkyl group optionally substituted one of several times by a halogen atom. In particular, R′ may comprise a vinyl or allyl group. Furthermore, R may represent the group —SO2—N—R′, R′ being as defined above or else R′ represents a sulfonate function —SO3.
Cyclic hydrocarbon-based groups may preferably refer to a cycloalkyl group or to an aryl group. “Cycloalkyl” refers to a monocyclic hydrocarbon chain, having 3 to 8 carbon atoms. Preferred examples of cycloalkyl groups are cyclopentyl and cyclohexyl. “Aryl” refers to a monocyclic or polycyclic aromatic hydrocarbon group, having 6 to 20 carbon atoms. Preferred examples of aryl groups are phenyl and naphthyl. When a group is a polycyclic group, the rings may be condensed or attached by σ (sigma) bonds.
According to a fourth embodiment, R represents a carbonyl group. R may, in particular, be represented by the formula —CO—R′, R′ being as defined above.
The organic anion that can be used in the present invention may advantageously be selected from the group consisting of CF3SO2N−SO2CF3 (bis(trifluoromethane sulfonyl)imide anion, commonly denoted as TFSI), FSO2N−SO2F (bis(fluorosulfonyl)imide anion, commonly denoted as FSI), CF3SO2N−SO2F, and CF3SO2N−SO2N−SO2CF3.
In a preferred embodiment, the ionic liquid contains:
Non-limiting examples of C1-C30 alkyl groups include, notably, methyl, ethyl, propyl, iso-propyl, n-butyl, isobutyl, sec-butyl, t-butyl, pentyl, isopentyl, 2,2-dimethyl-propyl, hexyl, 2,3-dimethyl-2-butyl, heptyl, 2,2-dimethyl-3-pentyl, 2-methyl-2-hexyl, octyl, 4-methyl-3-heptyl, nonyl, decyl, undecyl and dodecyl groups.
In one preferred embodiment, the film-forming additive according to the present invention is selected from the group consisting of N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl) imide (PYR13FSI), N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl) imide (PYR14FSI), N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR13TFSI), and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR14TFSI).
In the present invention, the total amount of the e) film-forming additive may be from 0 to 10 wt %, preferably from 0 to 8 wt %, and more preferably from 0 to 5 wt % with respect to the total weight of the liquid electrolyte.
The total amount of e) the film-forming additive, if contained in the liquid electrolyte of the present invention, is from 0.05 to 5.0 wt %, and preferably from 0.05 to 3.0 wt %, with respect to the total weight of the liquid electrolyte.
In a more preferred embodiment, the total amount of e) the film-forming additive accounts for at least 1.0 wt % of the electrolyte composition.
In one embodiment, the liquid electrolyte for lithium secondary batteries according to the present invention comprises:
wherein R1 and R3 represent a fluorinated straight-chain alkyl group respectively; R2 represents an optionally fluorinated straight-chain alkyl group; and the sum of carbon atoms in R1, R2, and R3 is from 5 to 8, and preferably 6;
wherein R4 and R5 represent an alkyl group respectively; the sum of carbon atoms of R4 and R5 is from 2 to 7; at least one hydrogen in R5 is replaced by fluorine, and R4 and R5 contain neither a CH2F— group nor a —CHF— group;
In a particular embodiment, the liquid electrolyte for lithium secondary batteries according to the present invention comprises
The present invention also provides a lithium secondary battery comprising:
In the present invention, the term “anode” is intended to denote, in particular, the electrode of an electrochemical cell, where oxidation occurs during discharging.
In the present invention, the term “cathode” is intended to denote, in particular, the electrode of an electrochemical cell, where reduction occurs during discharging.
In the present invention, the nature of the “current collector” depends on whether the electrode thereby provided is either a cathode or anode. Should the electrode of the invention be a cathode, the current collector typically comprises, preferably consists of at least one metal selected from the group consisting of Aluminium (Al), Nickel (Ni), Titanium (Ti), and alloys thereof, preferably Al. Should the electrode of the invention be an anode, the current collector typically comprises, preferably consists of at least one metal selected from the group consisting of Lithium (Li), Sodium (Na), Zinc (Zn), Magnesium (Mg), Copper (Cu) and alloys thereof, preferably Cu.
In the present invention, the term “areal capacity” of the electrodes, i.e., an node and a cathode, is intended to denote, in particular, the area-normalized specific capacity of the electrodes.
Selection and preparation of the electrodes, components contained therein and other possibly existing components in the batteries are known in the art, and therefore, can be suitably constructed depending on the purpose.
For instance, the electrodes of batteries, such as cathode and anode, can be formed from an electrode-forming composition comprising an active-electrode material, a binder, a solvent, and optionally one or more additives.
In the present invention, the term “electro-active material” is intended to denote an electro-active material that is able to incorporate or insert into its structure and substantially release therefrom lithium ions during the charging phase and the discharging phase of a battery. The nature of the electro-active material will depend on whether it will be used to form a cathode or an anode. The electro-active materials can thus be selected from cathode electro-active materials and anode electro-active materials.
In the case of forming a cathode for a lithium ion battery, the cathode electro-active material is not particularly limited. It may comprise a composite metal chalcogenide of formula LiMQ2, wherein M is at least one metal selected from transition metals such as Co, Ni, Fe, Mn, Cr, and V and Q is a chalcogen such as O or S. Among these, it is preferred to use a lithium-based composite metal oxide of formula LiMO2, wherein M is the same as defined above. The lithium-based composite metal oxide, such as LiCoO2, may comprise or consist of the layered structure. The composite metal chalcogenide, such as the lithium-based composite metal oxide, may comprise or consist of nano-structure.
Preferred examples thereof may include LiCoO2, LiNiO2, LiNixCO1−xO2 (0<x<1), and spinel-structured LiMn2O4. Another preferred examples thereof may include lithium-nickel-manganese-cobalt-based metal oxide of formula LiNixMnyCozO2 (x+y+z=1, referred to as NMC), for instance LiNi0.8Mn0.1Co0.1O2, LiNi0.5Mn0.2Co0.3O2, LiNi1/3Mn1/3Co1/3O2, LiNi0.6Mn0.2Co0.2O2, preferably LiNi0.8Mn0.1Co0.1O2, and lithium-nickel-cobalt-aluminum-based metal oxide of formula LiNixCoyAlzO2 (x+y+z=1, referred to as NCA), for instance LiNi0.8Co0.15Al0.05O2. Nonetheless, a broader range of chalcogenides may be considered, including those represented by formulae:
wherein:
Another preferred examples may include lithium-nickel-manganese-based metal oxide (referred to as LNMO), for instance LiNi0.5Mn0.5O2, and LiNi0.5Mn1.5O4.
As an alternative, still in the case of forming a cathode for a lithium ion battery, the cathode electro-active material may comprise a lithiated or partially lithiated transition metal oxyanion-based electro-active material of formula M1M2(JO4)fE1−f, wherein M1 is lithium, which may be partially substituted by another alkali metal representing less than 20% of the M1 metals, M2 is a transition metal at the oxidation level of +2 selected from Fe, Mn, Ni or mixtures thereof, which may be partially substituted by one or more additional metals at oxidation levels between +1 and +5 and representing less than 35% of the M2 metals, including 0, JO4 is any oxyanion wherein J is either P, S, V, Si, Nb, Mo or a combination thereof, E is a fluoride, hydroxide or chloride anion, f is the molar fraction of the JO4 oxyanion, generally comprised between 0.75 and 1. The M1M2(JO4)fE1−f electro-active material as defined above is preferably phosphate-based and may have an ordered or modified olivine structure. More preferably, the cathode electro-active material has formula Li3−xM′yM″2−y(JO4)3 wherein 0≤x≤3, 0≤y≤2, M′ and M″ are the same or different metals, at least one of which being a transition metal, JO4 is preferably PO4 which may be partially substituted with another oxyanion, wherein J is either S, V, Si, Nb, Mo or a combination thereof. Still more preferably, the cathode electro-active material is a phosphate-based electro-active material of formula Li(FexMn1−x)PO4 wherein 0≤x≤1, wherein x is preferably 1 (i.e., lithium iron phosphate of formula LiFePO4).
In a preferred embodiment, the cathode electro-active material is selected from the group consisting of LiMQ2, wherein M is at least one metal selected from Co, Ni, Fe, Mn, Cr and V and Q is O or S; LiNixCo1−xO2 (0<x<1); spinel-structured LiMn2O4; lithium-nickel-manganese-cobalt-based metal oxide (NMC), for instance LiNi0.8Mn0.1Co0.1O2, LiNi0.6Mn0.2Co0.2O2, lithium-nickel-cobalt-aluminum-based metal oxide (NCA), for instance LiNi0.8Co0.15Al0.05O2, and LiFePO4.
In one embodiment, the cathode comprises lithium-nickel-manganese-cobalt-based metal oxide of formula LiNixMnyCozO2 (x+y+z=1), lithium-nickel-cobalt-aluminum-based metal oxide of formula LiNixCoyAlzO2 (x+y+z=1), lithium-cobalt-based metal oxide, or lithium-nickel-manganese-based metal oxide (LNMO) as the cathode electro-active material.
In a preferred embodiment, the cathode comprises LiNi0.8Mn0.1Co0.1O2, LiNi0.6Mn0.2Co0.2O2, LiNi0.8Co0.15Al0.05O2, LiNi0.5Mn0.5O2, LiNi0.5Mn1.5O4, and LiCoO2 as the cathode electro-active material.
In the case of forming an anode for a lithium ion battery, the anode electro-active material is not particularly limited and may comprise:
In one embodiment, the anode comprises silicon or silicon-carbon composite as the anode electro-active material.
The batteries of the present invention may be lithium secondary batteries, including a lithium-ion battery, a lithium sulfur battery, and a lithium air battery, and sodium secondary batteries, such as a sodium ion battery, and a sodium sulfur battery, in particular a lithium-ion battery. In the present invention, the batteries having the high charge cut-off voltage are preferably secondary batteries, in particular secondary lithium-ion batteries.
By the term “separator”, it is hereby intended to denote a monolayer or multilayer polymeric, nonwoven cellulose or ceramic material/film, which electrically and physically separates the electrodes of opposite polarities within an electrochemical device and is permeable to ions flowing between them.
In the present invention, the separator can be any porous substrate commonly used for a separator in an electrochemical device.
In one embodiment, the separator is a porous polymeric material comprising at least one material selected from the group consisting of polyester such as polyethylene terephthalate and polybutylene terephthalate, polyphenylene sulphide, polyacetal, polyamide, polycarbonate, polyimide, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, polyethylene oxide, polyacrylonitrile, polyolefin such as polyethylene and polypropylene, or mixtures thereof, optionally coated with inorganic nanoparticles.
Non-limitative examples of the inorganic nanoparticles comprise SiO2, TiO2, Al2O3, and ZrO2.
In one particular embodiment, the separator is a polyester film coated with SiO2.
In another particular embodiment, the separator is a polyester film coated with Al2O3.
In another particular embodiment, the separator is a porous polymeric material coated with polyvinylidene difluoride (PVDF).
Should the disclosure of any patents, patent applications, and publications that 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.
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.
The liquid electrolytes were prepared for the Inventive Examples of E1-E2 and Comparative Examples of CE1-CE3. Their constituents are summarized in Table 1 below:
When preparing the liquid electrolyte of E1, DFEA and BP160 were first mixed and FEC and PC were then added under stirring. 0.85 wt % of LiBOB was subsequently mixed using a magnetic stirrer within a glove box until the solution became transparent. 1M of LiPF6 was subsequently added. After the solution became transparent, 0.5 wt % of MA was finally added to the solution.
The liquid electrolyte of E2 was prepared in the same manner as E1, except that BP120 was used instead of BP160.
The liquid electrolyte of CE1 was prepared in the same manner as E1, except that FC4 was used instead of BP160.
When preparing the liquid electrolyte of CE2, FEC and PC were added to DFEA and 0.85 wt % of LiBOB was mixed together under stirring until the solution became transparent. 1M of LiPF6 was then dissolved in the solution. After the solution became transparent, 0.5 wt % of MA were subsequently added to the solution.
The liquid electrolyte of CE3 was prepared by mixing DMC and TTE first, followed by FEC under stirring. 1M of LiPF6 was dissolved in the solution until the solution became transparent. 2 wt % of TMSPa was subsequently added to the solution.
Before use, the pouch cells were cut below the heat seal and dried under vacuum at 55° C. for 96 hours to remove any excess moisture. After drying, cells were filled with 3.077 ml of electrolyte solution, sealed at −95 kPa pressure using a vacuum sealer. After that, the cells were kept at 25° C. for 24 hours. Cells were then connected to a Maccor 4000 series cycler to perform SEI formation by charging cells at C/10 for 3 hours. The cells were then kept at 25° C. and 60° C. for 24 hours consecutively. Cells were then degassed by cutting the pouch open and resealed using the vacuum sealer. Cells were cycled between 3.0 and 4.35V at 25° C. Cells were charged and discharged at a rate of C/2 for 3 cycles.
The cycle retention of the liquid electrolytes E1-E2 and CE1-CE3 at room temperature (25° C.) and at high temperature (45° C.) is shown in Table 2 below and in
Liquid electrolytes according to the invention E1-E2 shows excellent cycling performance both at 25° C. and at 45° C., much higher than CE2 and CE3. In particular, CE1, i.e. liquid electrolyte containing a C4 fluorinated di-ether of CF3—O—CH2CH2—O—CF3 (C4F6H4O2) instead of BP160 (or BP120) showed inferior cycle retention (95% at 25° C.) than E1. In addition, the cycle retention (90% at 45° C.) of E1 was 370 cycles, while that of CE1 was 90 cycles.
Moreover, the storage swelling performance of E1-E2 and CE1-CE3 after storage at 60° C. (difference in thickness between initial and after 4 weeks of storage at 60° C.) are shown in view of thickness increase rate (in %) in Table 3 below and in thickness changes (in mm) in
It was clearly demonstrated that the liquid electrolytes according to the invention E1-E2 provides higher capacity retention and less swelling than the liquid electrolytes of CE1-CE3.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21167334.8 | Apr 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/059024 | 4/5/2022 | WO |
