Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
  • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0567—Liquid materials characterised by the additives
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0568—Liquid materials characterised by the solutes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0569—Liquid materials characterised by the solvents
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
  • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
  • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/028—Positive electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2300/00—Electrolytes
  • H01M2300/0017—Non-aqueous electrolytes
  • H01M2300/0025—Organic electrolyte
  • H01M2300/0028—Organic electrolyte characterised by the solvent
  • H01M2300/0034—Fluorinated solvents
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention pertains to a lithium secondary battery comprising a cathode comprising a lithium-manganese-rich layered oxide as a cathode electroactive material and a liquid electrolyte comprising at least one fluorinated acyclic carboxylic acid ester.
• the present invention also relates to use of a liquid electrolyte comprising at least one fluorinated acyclic carboxylic acid ester in a lithium secondary battery, for improving the cycling performance, comprising a cathode comprising a lithium-manganese-rich layered oxide as a cathode electroactive material according to the present invention.
• Lithium secondary batteries have retained a dominant position in the market of rechargeable energy storage devices thanks to their many benefits comprising light-weight, reasonable energy density, and good cycle life.
• LiCoCL was found to have drawbacks such as low practical capacity and relatively high cost of Co; and hence a layered LiNiCL was proposed as an alternative solution.
• LiNiCL has poor thermal stability and its production is difficult due to the Li/Ni disorder, as a result of Li/Ni exchange in octahedral sites, notably when Ni content increases to high values, as it leads to a detrimental effect on Li diffusibility, cycling stability, first-cycle efficiency and overall electrode performance. Accordingly, another solution was required despite the low cost and high rechargeable capacity of LiNiCL in comparison with LiCoCL.
• layered oxides hence have been further investigated, e.g., a binary oxide, such as LiNio.5Mno.5O2, which is a solid solution between LiNiO2 and LiMnO2, and a ternary oxide, such as LiCoi/3Nii/3Mm/3O2, among which LiCoi/3Nii/3Mm/3O2 showed the best electrochemical performance with high reversible capacity and became a promising cathode electroactive materials for high power lithium secondary batteries.
• a binary oxide such as LiNio.5Mno.5O2
• LiMnO2 LiMnO2
• a ternary oxide such as LiCoi/3Nii/3Mm/3O2
• LiCoi/3Nii/3Mm/3O2 showed the best electrochemical performance with high reversible capacity and became a promising cathode electroactive materials for high power lithium secondary batteries.
• LMRO Li- and Mn-rich layered oxide
• Li2MnOs phase can enhance the electrochemical capacity of the cathode because it transforms into an active LiMnCL phase after the first cycle.
• Li2MnOs phase can enhance the electrochemical capacity of the cathode because it transforms into an active LiMnCL phase after the first cycle.
• LMRO cathode electroactive materials are economically competitive and environmentally compatible.
• the present invention pertains to a lithium secondary battery comprising a) a cathode comprising, as a cathode electroactive material, a lithium transition metal oxide represented by the following formula (I)
• R 1 -C(O)O-R 2 (III) wherein R 1 and R 2 represent an alkyl group respectively; the sum of carbon atoms in R 1 and R 2 is from 2 to 7; and R 1 does not contain fluorine, and R 2 contains fluorine.
• the cathode electroactive material according to the present invention corresponds to a lithium-manganese-rich layered transition metal oxide.
• the present invention also pertains to use of a liquid electrolyte comprising at least one fluorinated acyclic carboxylic acid ester in a lithium secondary battery, for improving the cycling performance, comprising a cathode comprising, as a cathode electroactive material, a lithium-manganese-rich layered transition metal oxide according to the present invention.
• 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.
• 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.
• 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.
• anode is intended to denote, in particular, the electrode of an electrochemical cell, where oxidation occurs during discharging.
• cathode is intended to denote, in particular, the electrode of an electrochemical cell, where reduction occurs during discharging.
• the nature of the “current collector” depends on whether the electrode thereby provided is either a cathode or anode.
• 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.
• 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.
• electroactive material is intended to denote an electroactive 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 electroactive material will depend on whether it will be used to form a cathode or an anode.
• the electroactive materials can thus be selected from cathode electroactive materials and anode electroactive materials.
• (C n -C m ) 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.
• 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.
• 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%).
• the present invention relates to a lithium secondary battery comprising a) a cathode comprising, as a cathode electroactive material, a lithium transition metal oxide represented by the following formula (I)
• R 1 -C(O)O-R 2 (III) wherein R 1 and R 2 represent an alkyl group respectively; the sum of carbon atoms in R 1 and R 2 is from 2 to 7; and R 1 does not contain fluorine, and R 2 contains fluorine.
• the cathode electroactive material according to the present invention corresponds to a lithium-manganese-rich layered oxide.
• the cathode electroactive material according to the present invention does not contain Co, i.e. c is zero.
• the cathode electroactive material contains more manganese than nickel, wherein a*(l-d) ⁇ [x/(l-x)] + b(l-d).
• Non-limitative examples of suitable cathode electroactive materials according to the present invention include, notably the followings:
• Li1.09Mn0.91O2 (identical to 0.2[Li2Mn03]-0.8[LiMn02]), Lii.25Mno.625Nio.i2502, Li1.15Mno.56Nio.29O2 and Li1.17Mno.54Nio.28O2.
• the cathode electroactive material is selected from the group consisting of Li1.15Mno.56Nio.29O2 and Li1.17Mno.54Nio.28O2.
• R 2 contains neither a CH2F- group nor a -CHF- group.
• the number of carbon atoms in R 1 in the formula (III) is 1, 2, 3, 4, or 5. In a preferred embodiment, the number of carbon atoms in R 1 in the formula (III) is 1.
• Non-limitative examples of suitable fluorinated acyclic carboxylic acid ester according to the present invention include, notably, the followings: C(O)O-CF 2 H, (CH 3 )2CH-C(O)O-CF 2 H, CH 3 CH2-C(O)O-CH 2 CF3, and mixtures thereof.
• the fluorinated acyclic carboxylic acid ester is CH3-C(O)O- CH2CF2H (2,2-difluoroethyl acetate). In one embodiment, the fluorinated acyclic carboxylic acid ester is in an amount of from 20 to 90% by weight (wt%), preferably from 40 to 80 wt%, and more preferably from 50 to 75 wt% based on the total weight of the liquid electrolyte.
• liquid electrolyte further comprises a fluorinated acyclic carbonate represented by the formula (IV)
• R 3 -OC(O)O-R 4 (IV) wherein R 3 and R 4 represent an alkyl group respectively; the sum of carbon atoms in R 3 and R 4 is from 2 to 7; and at least one hydrogen in R 3 and/or R 4 is replaced by fluorine
• R 3 and R 4 contain neither a CH2F- group nor a -CHF- group.
• R 3 and R 4 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 R 3 are replaced by fluorines, or at least two hydrogens in R 4 are replaced by fluorines, or at least two hydrogens in R 3 and at least two hydrogens in R 4 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 (2,2-difluoroethyl 2,2,2-trifluoroethyl carbonate), CH3CH2-OC(O)O- CH2CF2H (ethyl 2,2-difluoroethyl carbonate), CF3CH2-OC(O)O-CH2CH3 (ethyl 2,2,2- trifluoroethyl carbonate), and mixtures thereof.
• the fluorinated acyclic carbonate is CH3-OC(O)O-CH2CF3 (methyl 2,2,2-trifluoroethyl carbonate).
• liquid electrolyte further comprises at least one fluorinated acyclic diether represented by the formula (V)
• R 5 -O-R 6 -O-R 7 (V) wherein R 5 and R 7 represent a fluorinated straight-chain alkyl group respectively; R 6 represents an optionally fluorinated straight-chain alkyl group; and the sum of carbon atoms in R 5 , R 6 , and R 7 is from 5 to 8, and preferably 6.
• the boiling point of 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.
• the molar ratio F/H in the fluorinated acyclic diether is from 1.3 to 13.0, preferably from 2.5 to 6.0.
• the fluorinated acyclic diether contains 6 carbon atoms. In a more preferred embodiment, the fluorinated acyclic diether is CHF2CF2-O- CH2CH2-O-CF2CF2H.
• Non-limitative examples of suitable fluorinated acyclic diether according to the present invention include, notably the followings:
• CF2HCF2-O-CF2CH2-O-CF2CF2H CF 3 CF2-O-CH2CH2-O-CF2CF3, CF2HCF 2 -O-CHFCHF-O- CF2CF2H, CF3CF2-O-CHFCH2-O-CF2CF2H, CF3CF2-O-CH2CHF-O-CF2CF2H, CF3-0- 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, and mixtures thereof.
• the fluorinated acycic diether contains 7 carbon atoms.
• the fluorinated acyclic diether contains 8 carbon atoms.
• the liquid electrolyte according to the present invention comprises neither a non- fluorinated ether nor a fluorinated mono-ether.
• non-fluorinated ether is intended to denote an ether compound, where no fluorine atom is present.
• fluorinated mono-ether is intended to denote a mono-ether compound, wherein at least one hydrogen atom is replaced by fluorine.
• fluorine One, two, three or a higher number of hydrogen atoms may be replaced by fluorine.
• 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.
• liquid electrolyte further comprises at least one organic carbonate.
• the organic carbonate comprises a fluorinated cyclic carbonate, a non-fluorinated cyclic carbonate and a non-fluorinated acyclic carbonate.
• Non-limitative examples of the organic carbonate according to the present invention include, notably the followings:
• 4-fluoroethylene carbonate (4-fluoro-l,3-dioxolan-2-one), 4, 5 -difluoro- 1,3 -di oxolaneone, 4, 5-difluoro-4-methyl- 1 ,3 -dioxolan-2-one, 4, 5-difluoro-4, 5-dimethyl- 1 ,3 -dioxolan-2- one, 4,4-difluoro-l,3-dioxolan-2-one, 4,4,5-trifluoro-l,3-dioxolan-2-one, 4-fluoromethyl-l,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, dimethylviny
• the organic carbonate is a mixture of fluoroethylene carbonate, propylene carbonate and ethylene carbonate.
• the organic carbonate is a mixture of fluoroethylene carbonate and propylene carbonate.
• the total amount of the at least one organic carbonate is from 0 to 80 wt%, preferably from 0 to 60 wt%, and more preferably from 0 to 50 wt% with respect to the total weight of the liquid electrolyte.
• the total amount of the at least one organic carbonate, if contained in the liquid electrolyte of the present invention is from 10 to 80 wt%, preferably from 20 to 60 wt%, and more preferably from 25 to 50 wt%, with respect to the total weight of the liquid electrolyte.
• the liquid electrolyte further comprises at least one lithium salt.
• the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiN(CF 3 SO 2 )2; LiTFSI).
• the lithium salt is LiPFe.
• the lithium salt is LiFSI.
• 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).
• a heterocyclic ring such as an imidazole, e.g., lithium 2- trifluoromethyl-4,5-dicyanoimidazole (LiTDI).
• the liquid electrolyte according to the present invention further comprises 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.
• SEI solid electrolyte interface
• the main components hence comprise the decomposed products of electrolyte solvents and salts, which may include Li2CO3, lithium alkyl carbonate, lithium alkyl oxide and other salt moieties such as LiF for LiPFe-based electrolytes.
• 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.
• 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.
• the film-forming additive is different from the lithium salt.
• 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, l,3,2-dioxathiolane-4-ethynyl-2,2-dioxide, l,3,2-dioxathiolane-4- ethenyl-2,2-dioxide, l,3,2-dioxathiolane-4,5-diethenyl-2,2-dioxide, l,3,2-dioxathiolane-4- methyl-2,2-dioxide, l,3,2-dioxathiolane-4,5-dimethyl-2,2-dioxide, l,3,2-dioxathiane-2,2- dioxide, l,3,2-dioxathiane-4-ethynyl-2,2-dioxide, l,3,2-dioxathiane-5-ethynyl-2,2-dioxide,2-d
• the film-forming additive is selected from the group consisting of sulfur compounds comprising l,3,2-dioxathiolane-2,2-dioxide, 1,3,2- dioxathiane-2,2-dioxide, 1,3-propanesultone, ethylene sulphite and prop-l-ene-l,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 (LiNCh); boron derivatives salt comprising lithium difluoro oxalato borate (LiDFOB), lithium bis(oxalato)borate (LiB(C2O4)2; LiBOB), lithium fluoride, LiF
• the film-forming additive according to the present invention is LiBOB.
• the film-forming additive according to the present invention is LiDFOB.
• the film-forming additive according to the present invention is an ionic liquid.
• ionic liquid 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.
• Non-limitative examples of the ionic liquid according to the present invention include, notably, N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl) imide (PYR13FSI), N-butyl-N- methylpyrrolidinium bis(fluorosulfonyl) imide (PYR14FSI), N-methyl-N- propylpyrrolidinium bi s(trifluorom ethanesulfonyl) imide (PYR13TFSI), and N-butyl-N- methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR14TFSI).
• the total amount of the 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 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.
• the total amount of the film-forming additive accounts for at least 1.0 wt% of the liquid electrolyte.
• the liquid electrolyte according to the present invention further comprises at least one HF scavenger.
• HF generated by hydrolysis of a lithium salt for instance LiPFe, may dissolve transition metal components in the interface between cathode and electrolyte; negatively affect the stability of SEI layers that protect the electrodes upon repeated cycling; promote the leaching of SEI components; and facilitating electrolyte decomposition at the reactive electrode. This eventually results in poor cycling lifetime of the cathode electroactive materials.
• the HF scavenger is a nitrile compound, e.g. adiponitrile (AN), succinonitrile (SN), hexane tri-cyanide (1,3,6-HTCN), etc.
• AN adiponitrile
• SN succinonitrile
• HTCN hexane tri-cyanide
• the anode electroactive material is not particularly limited and may comprise:
• lithium typically existing in forms such as powders, flakes, fibers or spheres (e.g., mesocarbon microbeads) hosting lithium;
• Li ⁇ TisOii lithium titanates, generally represented by formula Li ⁇ TisOii: these compounds are generally considered as “zero-strain” insertion materials, having low level of physical expansion upon taking up the mobile ions, i.e. Li + ;
• lithium silicides with high Li/Si ratios in particular lithium silicides of formula Li ⁇ Si;
• the anode comprises silicon or silicon-carbon composite as the anode electroactive material.
• the present invention also relates to use of a liquid electrolyte comprising at least one fluorinated acyclic carboxylic acid ester represented by the formula (III)
• R 1 -C(O)O-R 2 (III) wherein R 1 and R 2 represent an alkyl group respectively; the sum of carbon atoms in R 1 and R 2 is from 2 to 7; and R 1 does not contain fluorine, and R 2 contains fluorine.
• a lithium secondary battery for improving the cycling performance, comprising a lithium transition metal oxide represented by the formula (I) as a cathode electroactive material
• M comprises 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.
• the liquid electrolyte comprises from 20 to 90 wt%, preferably from 40 to 80 wt%, and more preferably from 50 to
• the fluorinated acyclic carboxylic acid ester is CH3-C(O)O- CH2CF2H (2,2-difluoroethyl acetate).
• the organic carbanate is a mixture of fluoroethylene carbonate, propylene carbonate and ethylene carbonate.
• the liquid electrolyte comprises a mixture of a fluorinated acyclic carboxylic acid ester, a fluorinated acyclic diether and an organic carbonate.
• the liquid electrolyte comprises a mixture of a fluorinated acyclic carboxylic acid ester, a fluorinated acyclic carbonate, a fluorinated acyclic diether and an organic carbonate.
• the liquid electrolyte comprises a mixture of a fluorinated acyclic carboxylic acid ester, a fluorinated acyclic carbonate and an organic carbonate.
• the liquid electrolyte for lithium secondary batteries according to the present invention comprises
• CF2HCF2-O-CH2CH2-O-CF2CF2H as a fluorinated acyclic diether
• a mixture of PC, FEC and/or EC as an organic carbonate
• liquid electrolyte for lithium secondary batteries according to the present invention comprises
• CF2HCF2-O-CH2CH2-O-CF2CF2H as a fluorinated acyclic diether
• a mixture of PC, FEC and/or EC as an organic carbonate
• the liquid electrolyte for lithium secondary batteries according to the present invention comprises
• CH3-OC(O)O-CH2CF3 (methyl 2,2,2-trifluoroethyl carbonate) as a fluorinated acyclic carbonate; a mixture of PC, FEC and/or EC as an organic carbonate; IM of LiPF 6 as a lithium salt;
• FEC 4-fluoro-l,3-dioxolan-2-one, commercially obtained from Soulbrain;
• EMC ethyl methyl carbonate, commercially obtained from Enchem
• SA076 a fluorinated acyclic carboxylic acid ester of 2,2-difluoroethyl acetate, i.e. CH3-C(O)O-CH2CF2H, synthesized within Solvay;
• SA024 fluorinated acyclic carbonate of methyl 2,2,2-trifluoroethyl carbonate, i.e. CH3-OC(O)O-CH2CF3, synthesized within Solvay;
• BP160 a fluorinated acyclic diether of CeFgHeCE (CHF2CF2-O-CH2CH2-O- CF2CF2H), synthesized within Solvay;
• LiBOB a film- forming additive of lithium bis(oxalato)borate, commercially obtained from Enchem.
• LiPFe a Li salt of lithium hexafluorophosphate, commercially obtained from Enchem.
• liquid electrolytes were prepared for the Inventive Examples of E1-E3 and Comparative Example of CE1, wherein 1 M of LiPFe was used as a Li salt and 0.5 wt% of LiBOB was incorporated as a film-forming additive with respect to the total weight of the liquid electrolyte.
• the constituents of liquid solvents are summarized in Table 1 below:
• the liquid electrolyte of E2 was prepared by mixing 58 wt% of SA076, 30 wt% of FEC and 12 wt% of SA024 together under stirring to form a liquid solvent; subsequently introducing 0.5 wt% of LiBOB using a magnetic stirrer until the solution became transparent. Lastly, 1 M of LiPFe was dissolved in the solution.
• the liquid electrolyte of CE1 was prepared in the same manner as El, except that 70 wt% of EMC was used instead of 70 wt% of SA076.
• the cathode, anode, and separator were prepared.
• Cathode electroactive material i.e. NM13 of Li1.2Nio.2Mno.6O2
• the cathode consiste of NM13, carbon black, and PVDF binder (polyvinilidene difluoride; SOLEF®5130 commercially available from Solvay Specialty Polymers Italy), the ratio was 95/3/2 wt%.
• the anode consisted of artificial graphite, carbon black, and PVDF binder, the ratio was 90/4/6 wt%. Polyethylene porous film was used as a separator.
• the electrolyte test was performed by the coin cells. All coin parts, CR2032 specification, were commercially available from Wellcos.
• the test components of coin cells were the cathode electrode, anode electrode, and separator. Each element was first cut by a circle disc, which disc size was that the cathode was 015, the anode was 016, and the separator was 019. Subsequently, the elements were dried under vacuum overnight, i.e. at 100°C for the electrodes and 60°C for the separator. After drying, all components were moved to a glove box, and the coin cells were assembled. The separator was located between the cathode and the anode, and the electrolyte was injected with separator.
• the cells were kept at 25°C for 24 hours.
• Cells were cycled between 2.0 and 4.7 V at 25°C by using a PEBC050.1 cycler from WONK PNE Co. Ltd. to perform SEI formation. Cells were charged and discharged at a rate of C/10 for 3 cycles.
• Liquid electrolytes according to the invention E1-E3 showed excellent cycling performance at 25°C, much higher than CEL
• CE1 i.e. liquid electrolyte containing only organic carbonates without fluorinated acyclic carboxylic acid ester showed much inferior cycle retention than E1-E3.

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