Safety-enhanced lithium secondary batteries

Abstract

The present invention relates to a composition containing a) at least one fluorinated acyclic carboxylic acid ester and b) at least one halogenated benzene, and to a lithium secondary battery comprising the composition in a liquid electrolyte. The present invention also relates to the use of the composition in a liquid electrolyte for a lithium secondary battery.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Patent Application No. 22201112.4, filed October 12, 2022, the entire contents of which are incorporated herein by reference for all purposes. [Technical Field]

[0002] The present invention relates to a composition comprising a) at least one fluorinated acyclic carboxylic acid ester and b) at least one halogenated benzene, and to a lithium secondary battery comprising the composition according to the invention in a liquid electrolyte. The present invention also relates to the use of the composition in a liquid electrolyte for a secondary battery, in particular to improve safety performance, more particularly to improve intrusion performance exhibiting a EUCAR (European Council for Automotive R&D) hazard level of 4 or less, preferably 2 or less. [Background technology]

[0003] Lithium-ion batteries have held a dominant position in the market for rechargeable energy storage devices for decades due to their many advantages, such as light weight, reasonable energy density, and good cycle life. Nevertheless, higher energy density has been constantly required with the development of high power applications such as electric vehicles, hybrid electric vehicles, grid energy storage, etc.

[0004] Organic carbonates have traditionally been used as liquid electrolytes for lithium secondary batteries, including 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 decompose relatively easily at high voltages, e.g., above 4.35 V. Typically, driving the electrodes to higher / extreme voltages or subjecting the cell to higher temperatures can accelerate undesirable reactions between the liquid electrolyte and the highly reactive electrodes, resulting in reduced cycle life and reduced capacity. In a worst-case scenario, thermal runaway accompanied by fire / flame can occur, followed by cell rupture / explosion and ultimately cell collapse. In particular, such safety concerns are primarily due to the use of organic carbonates, which have relatively low boiling points and are highly flammable.

[0005] Therefore, various approaches have been taken to overcome the limitations of commonly used liquid electrolytes based on organic carbonates, i.e., to improve safety performance while maintaining cycling performance.

[0006] Hydrofluoroether-based solvents have the advantages of being safer and easier to handle than organic carbonates due to their low GWP (global warming potential) and low flammability. As part of various research efforts underway for this purpose, WO 2015 / 078791A (Solvay Specialty Polymers Italy SpA) reports that liquid electrolytes containing specific hydrofluoroethers with high fluorination rates exhibit advantageous properties such as solubility, ionic conductivity, oxidation stability under high voltage, low flammability, and a wide operating temperature range.

[0007] JP 2010 / 192327A (Sony Corporation) discloses a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent containing a halogenated benzene and a halogenated (cyclic and / or acyclic) carbonate, which exhibits excellent cycle characteristics at low temperatures and improved charge / discharge efficiency at high temperatures.

[0008] US Patent Application Publication No. 2011 / 0311879A1 (Sony Corporation) discloses a non-aqueous electrolyte solution containing a solvent, an electrolyte salt, an aromatic compound, particularly a benzene derivative, and a polyoxometalate, particularly a heteropolyacid, which exhibits improved high-temperature cycle discharge capacity retention and high-temperature storage discharge capacity retention.

[0009] As technology matures, safety requirements continue to increase, especially for electric vehicles, making characterization testing, which evaluates response to harsh environments, more meaningful and necessary than simple "pass / fail" testing. This is because understanding failure mechanisms and their root causes is crucial to improving safety performance. While pass / fail testing cannot quantitatively measure a cell's response, characterization testing evaluates its response to harsh environments, thereby identifying failure modes and harsh conditions.

[0010] Among several characterization tests, intrusion safety has been recognized as a critical evaluation parameter, and various attempts to improve it have been considered. This is because, in the event of an accident, penetration of the battery pack as a result of an external impact could occur, causing the charged electrodes to come into physical contact with each other, resulting in a high current flow in a short period of time, which could lead to thermal runaway. In other words, combustion heat could accumulate within the cell, inducing a thermal decomposition reaction, causing the temperature of the battery pack to continue to rise, ultimately resulting in a fire or explosion. Most importantly, intrusion safety is a critical issue that directly affects the lives of passengers using transportation devices. Therefore, if intrusion safety is not ensured, the application of lithium secondary batteries to electric vehicles will ultimately be restricted, especially considering the current industrial demand for higher-capacity power sources for electric vehicles, which is expected to continue to increase.

[0011] EUCAR is the European Automotive Research and Development Council of major European passenger car and commercial vehicle manufacturers. Its members include major automakers such as BMW Group, FIAT Chrysler Automobiles, Ford Europe, Honda R&D Europe, Hyundai Motor Europe, Renault Group, Toyota Motor Europe, Volkswagen Group, and Volvo Group. EUCAR promotes and coordinates pre-competitive research and development projects, and its members participate in a wide range of European collaborative research and development programs. Vehicle requirements vary significantly from manufacturer to manufacturer due to the wide variety of vehicle sizes and uses within the transportation sector, which means that different requirements must be considered for specific transportation applications. In particular, the hazard levels, from 0 to 7, adopted and revised by EUCAR provide detailed descriptions and classification criteria / impacts, commonly known as the EUCAR hazard levels, shown in Table 1 below.

[0012] [Table 1]

[0013] In this regard, the EUCAR hazard levels are used by many automakers, not just European ones. For example, Sandia National Laboratories, one of three National Nuclear Security Administration R&D laboratories in the United States operated by Sandia Corporation for the Department of Energy, references the EUCAR hazard levels in evaluating the safety performance of its cells and provides a detailed test protocol, SAND2005-3123. In particular, the EUCAR hazard levels allow for a more specific and objective assessment of the level of risk associated with batteries. In this regard, most automakers require a minimum hazard level of 4 or less, preferably 2 or less, which corresponds to the essential requirement that no fire or flames occur even under severe accident conditions.

[0014] In addition to the EUCAR hazard levels, there are several guidelines for the safety assessment of secondary lithium batteries, such as UL1642 (Underwriters Laboratories Inc.) and SBA G1101 (Japan Battery Association), which have different standards and evaluation conditions using various parameters.

[0015] For example, U.S. Patent No. 10,818,885 B2 (SK Innovation) discloses an adhesive pad including a substrate layer, an adhesive layer formed on at least one surface of the substrate layer, and a covering material to which the adhesive pad is adhered via the adhesive layer. The adhesive pad contributes to preventing fires and explosions by improving puncture safety. The puncture safety is evaluated with reference to SBA G1101.

[0016] However, there remains a great need for liquid electrolytes for lithium secondary batteries that have improved safety, particularly intrusion safety, while maintaining good cycling performance. Summary of the Invention

[0017] The first object of the present invention is to a) Formula (I) R 1 -C(O)OR 2 (I) (In the formula, R 1 is a C1-C4 alkyl group, and R 2 is a C1-C4 fluoroalkyl group) and at least one fluorinated acyclic carboxylic acid ester represented by the formula: b) Formula (II) [ka] (wherein X represents a C1-C4 fluoroalkyl group, and each of R3 to R7 represents a hydrogen atom, a halogen atom, an alkyl group, a halogenated alkyl group, an alkoxy group, or a halogenated alkoxy group). and at least one halogenated benzene represented by the formula: The present invention relates to a composition comprising:

[0018] A second object of the invention is a lithium secondary battery comprising a composition according to the invention in a liquid electrolyte.

[0019] A third object of the present invention is the use of the composition in a liquid electrolyte for a lithium secondary battery.

[0020] The present inventors have surprisingly found that the composition according to the invention, which contains a) at least one fluorinated acyclic carboxylic acid ester and b) at least one halogenated benzene, when used in a liquid electrolyte for a secondary battery, can achieve a particularly advantageous combination of properties, namely good cycling performance and excellent safety performance, in particular intrusion performance. DETAILED DESCRIPTION OF THE INVENTION

[0021] Ratios, concentrations, amounts, and other numerical data may be presented herein in a range format. It should be understood that such range formats are used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​expressly recited as the upper and lower limits of the range, but also to include all individual numerical values ​​or subranges subsumed within that range, as if each numerical value and subrange were expressly recited. In the context of the present invention, the term "weight percent" (wt%) refers to the content of a particular component in a mixture, calculated as the ratio of the weight of the component to the total weight of the mixture, and the term "volume percent" (vol%) refers to the content of a particular component in a mixture, calculated as the ratio of the volume of the component to the total volume of the mixture.

[0022] It should 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. Additionally, descriptions of well-known functions and constructions may be omitted for clarity and brevity.

[0023] The present invention provides a) Formula (I) R 1 -C(O)OR 2 (I) (In the formula, R 1 is a C1-C4 alkyl group, and R 2 is a C1-C4 fluoroalkyl group) and at least one fluorinated acyclic carboxylic acid ester represented by the formula: b) Formula (II) [ka] (wherein X represents a C1-C4 fluoroalkyl group, R 3 ~R 7 each represents a hydrogen atom, a halogen atom, an alkyl group, a halogenated alkyl group, an alkoxy group, or a halogenated alkoxy group. and at least one halogenated benzene represented by the formula: A composition comprising:

[0024] In one embodiment, R 2 does not include a -CH2F- group or a -CHF- group.

[0025] In a preferred embodiment, R in formula (I) 1 The number of carbon atoms in

[0026] In another preferred embodiment, R in formula (I) 1 The number of carbon atoms in

[0027] Non-limiting examples of suitable fluorinated acyclic carbonates according to the present invention include, among others: 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-CH2CH2C F2H, 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-CH2CF 3、 CH3CH2-C(O)O-CH2CH2CF3, CH3CH2-C(O)O-CH2CF3, and combinations thereof.

[0028] In certain embodiments, a) 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, and combinations thereof.

[0029] In a more specific embodiment, a) the fluorinated acyclic carboxylic acid ester is CH3-C(O)O-CH2CF2H (2,2-difluoroethyl acetate).

[0030] In one embodiment, R 3 ~R 7 One of them is a halogenated C1-C4 alkoxy group, preferably a C1-C2 fluoroalkoxy group.

[0031] In another embodiment, R 3 ~R 7 At least one of the groups is a halogen atom.

[0032] In certain embodiments, b) the halogenated benzene is selected from the group consisting of 1,1,2,2-tetrafluoroethoxybenzene, 1,1,2,2,2-pentafluoroethoxybenzene, fluoromethoxybenzene, difluoromethoxybenzene, trifluoromethoxybenzene, 1,2-bis(1,1,2,2-tetrafluoroethoxy)benzene, 1,3-bis(1,1,2,2-tetrafluoroethoxy)benzene, 1,4-bis(1,1,2,2-tetrafluoroethoxy)benzene, 4-trifluoromethoxytoluene, 1-fluoro-4-(1,1,2,2-tetrafluoroethoxy)benzene, 1-chloro-4-(1,1,2,2-tetrafluoroethoxy)benzene, 1-bromo-4-(1,1,2,2-tetrafluoroethoxy)benzene, and combinations thereof.

[0033] In a more specific embodiment, b) the halogenated benzene is 1,1,2,2-tetrafluoroethoxybenzene.

[0034] In another more specific embodiment, b) the halogenated benzene is 1-fluoro-4-(1,1,2,2-tetrafluoroethoxy)benzene.

[0035] In another more specific embodiment, b) the halogenated benzene is 1,4-bis(1,1,2,2-tetrafluoroethoxy)benzene.

[0036] In one embodiment, the liquid electrolyte further comprises c) at least one organic carbonate which may be partially or fully fluorinated. In the present invention, c) the organic carbonate may be either cyclic or acyclic.

[0037] c) Non-limiting examples of organic carbonates include, in particular, 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. (1,3-dioxolan-2-one), propylene carbonate, butylene carbonate, trimethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, dimethyl vinylene 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 a combination thereof.

[0038] In a particular embodiment, c) the organic carbonate is a mixture of ethylene carbonate and ethyl methyl carbonate.

[0039] In another particular embodiment, c) the organic carbonate is a mixture of ethylene carbonate, ethyl methyl carbonate, and vinylene carbonate.

[0040] In another embodiment, the liquid electrolyte further comprises d) at least one lithium salt.

[0041] Non-limiting examples of d) lithium salts according to the invention include, inter alia, lithium hexafluorophosphate (LiPF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium hexafluoroantimonate (LiSbF), lithium hexafluorotantalate (LiTaF), lithium tetrachloroaluminate (LiAlCl), lithium tetrafluoroborate (LiBF), lithium chloroborate (LiB 10 Cl 10 ), lithium fluoroborate (Li2B 10 F 10 ), Li2B 12 F x H 12-x (x=0~12), LiPF x (R F ) 6-x and LiBF y (R F ) 4-y (In the formula, R F Perfluoro C1-C 20 alkyl or perfluoroaromatic group, where 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 difluorooxalatoborate, and lithium fluoromalonato(difluoro)borate, LiPF2[O2C(CX2) n CO2]2, LiPF4[O2C(CX2) n CO2] (X is selected from the group consisting of H, F, Cl, C1-C4 alkyl groups and fluorinated alkyl groups, and n = 0-4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide Li(FSO2)2N (LiFSI), LiN(SO2C m F 2m+1 )(SO2C n F 2n+1 ) and LiC(SO2C k F 2k+1 )(SO2C m F 2m+1 )(SO2C n F2n+1 ) (wherein k = 1 to 10, m = 1 to 10, and n = 1 to 10), LiN(SO2C p F 2p SO2) and LiC(SO2C p F 2p SO2)(SO2C q F 2q+1 ) (wherein p=1 to 10, q=1 to 10), or a combination thereof.

[0042] In one embodiment, d) the lithium salt according to the present invention is lithium hexafluorophosphate (LiPF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium hexafluoroantimonate (LiSbF), lithium hexafluorotantalate (LiTaF), lithium tetrachloroaluminate (LiAlCl), lithium tetrafluoroborate (LiBF), lithium chloroborate (LiB 10 Cl 10 ), lithium fluoroborate (Li2B 10 F 10 ), Li2B 12 F x H 12-x (x=0~12), LiPF x (R F ) 6-x and LiBF y (R F ) 4-y (In the formula, R F Perfluoro C1-C 20 alkyl group or perfluoroaromatic group, where x = 0-5 and y = 0-3), lithium bis(oxalato)borate [LiB(C2O4)2], lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide Li(FSO2)2N (LiFSI), LiN(SO2C m F 2m+1 )(SO2C n F 2n+1 ) and LiC(SO2C k F 2k+1 )(SO2C m F 2m+1 )(SO2C n F2n+1 ) (wherein k = 1 to 10, m = 1 to 10, and n = 1 to 10), LiN(SO2C p F 2p SO2) and LiC(SO2C p F 2p SO2)(SO2C q F 2q+1 ) (wherein p=1 to 10, q=1 to 10), and combinations thereof.

[0043] In one particular embodiment, d) the lithium salt is lithium bis(trifluorosulfonyl)imide (LiN(CF3SO2)2) (LiTFSI).

[0044] In another particular embodiment, d) the lithium salt is LiFSI.

[0045] In another particular embodiment, d) the lithium salt is LiPF6.

[0046] 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 a solid electrolyte interface (SEI) layer at the electrode surface by pre-reacting a solvent on the electrode surface. With regard to the SEI layer, the main components therefore comprise decomposition products of the liquid electrolyte and salts, which may include Li2CO3 (in the case of LiCoO2 as the cathode electroactive material), lithium alkyl carbonates, lithium alkyl oxides, and other salt moieties such as LiF in the case of an electrolyte based on LiPF6.

[0047] According to one embodiment, e) the film-forming additive stabilizes the SEI layer at the surface of the positive electrode by preventing structural changes in the positive electrode, especially under high voltage.

[0048] This is because e) the reduction potential of the film-forming additive is higher than that of the liquid electrolyte when the reaction occurs on the negative electrode surface, and the oxidation potential of the film-forming additive is lower than that of the liquid electrolyte when the reaction occurs on the positive electrode.

[0049] In the present invention, e) the film-forming additive is different from d) the lithium salt.

[0050] In the present invention, e) the film-forming additive is different from c) the organic carbonate.

[0051] Non-limiting examples of e) film-forming additives according to the present invention include, among others, cyclic sulfite and sulfate compounds including 1,3-propane sultone, ethylene sulfite, and prop-1-ene-1,3-sultone; sulfone derivatives including dimethyl sulfone, tetramethylene sulfone (also known as sulfolane), ethyl methyl sulfone, and isopropyl methyl sulfone; nitrile derivatives including succinonitrile, adiponitrile, glutaronitrile, and 4,4,4-trifluoronitrile; lithium nitrate, vinyl acetate, biphenylbenzene, isopropylbenzene, tris(trimethylsilyl)phosphate, triphenylphosphine, ethyl diphenylphosphinite, triethyl phosphite, tris(2,2,2-trifluoroethyl)phosphite, maleic anhydride, cesium bis(trifluoromethanesulfonyl)imide, cesium fluoride, or combinations thereof.

[0052] In certain embodiments, the e) film-forming 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-propane sultone, ethylene sulfite, prop-1-ene-1,3-sultone, dimethyl sulfone, tetramethylene sulfone, ethyl methyl sulfone, isopropyl methyl sulfone, succinonitrile, adiponitrile, glutaronitrile, vinyl acetate, biphenylbenzene, isopropyl benzene, tris(trimethylsilyl)phosphate, triphenylphosphine, ethyl diphenylphosphinite, triethyl phosphite, tris(2,2,2-trifluoroethyl)phosphite, maleic anhydride, cesium bis(trifluoromethanesulfonyl)imide, cesium fluoride, and combinations thereof.

[0053] In one preferred embodiment, e) the film-forming additive is 1,3-propane sultone.

[0054] According to another embodiment, e) the film-forming additive is an ionic liquid.

[0055] The term "ionic liquid" as used herein refers to compounds containing positively charged cations and negatively charged anions that are in the liquid state at temperatures below 100°C under atmospheric pressure. While ordinary liquids such as water are made up primarily of electrically neutral molecules, ionic liquids are made up mostly of ions and short-lived ion pairs. As used herein, the term "ionic liquid" refers to compounds that do not contain solvent.

[0056] In a preferred embodiment, the ionic liquid is - One or more C1-C 30 a positively charged cation selected from the group consisting of imidazolium, pyridinium, pyrrolidinium, and piperidinium ions, optionally containing an alkyl group; a negatively charged anion selected from the group consisting of halides, fluorinated anions, and borates; Contains:

[0057] C1~C 30 Non-limiting examples of alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-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, among others.

[0058] In a preferred embodiment, the film-forming additive e) 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), and combinations thereof.

[0059] A second object of the invention is a lithium secondary battery comprising a composition according to the invention in a liquid electrolyte.

[0060] In one embodiment, a lithium secondary battery includes a liquid electrolyte comprising a composition according to the present invention, a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode.

[0061] In the present invention, the term "separator" is intended to mean, in particular, an ion-permeable membrane placed between a positive electrode and a negative electrode. Its function is to allow lithium ions to pass through while blocking electrons and ensuring physical separation between the electrodes. That is, a separator refers to a single-layer or multi-layer polymeric, non-woven cellulose or ceramic material / membrane that electrically and physically separates electrodes of opposite polarity in an electrochemical device and is permeable to ions flowing between them.

[0062] The electrodes of an electrochemical cell are called the anode or the cathode. An anode is defined as the electrode where electrons leave the cell and oxidation occurs, and a cathode is defined as the electrode where electrons enter the cell and reduction occurs. Each electrode can be either an anode or a cathode, depending on the direction of current flow through the cell. A bipolar electrode is one that functions as the anode in one cell and the cathode in another. When the cell is being charged, the anode becomes positive and the cathode becomes negative, while when the cell is being discharged, the anode becomes negative and the cathode becomes positive.

[0063] In the present invention, the term "negative electrode" is intended to denote in particular the electrode of an electrochemical cell where oxidation occurs during discharge.

[0064] In the present invention, the term "positive electrode" is intended to denote in particular the electrode of an electrochemical cell where reduction occurs during discharge.

[0065] In one embodiment, the content of a) the fluorinated acyclic carboxylic acid ester is at least 0.1 wt %, preferably at least 1.0 wt %, more preferably at least 2.0 wt %, and / or at most 80.0 wt %, preferably at most 60.0 wt %, more preferably at most 10.0 wt %, based on the total weight of the liquid electrolyte.

[0066] In a specific embodiment, the content of a) the fluorinated acyclic carboxylic acid ester is 0.1 to 80.0 wt %, preferably 1.0 to 60.0 wt %, and more preferably 2.0 to 10.0 wt %, based on the total weight of the liquid electrolyte.

[0067] In a more specific embodiment, the content of a) the fluorinated acyclic carboxylic acid ester is 2.0 to 3.5 wt % based on the total weight of the liquid electrolyte.

[0068] In one embodiment, the content of b) halogenated benzene is at least 0.1 wt. %, preferably at least 1.0 wt. %, more preferably at least 2.0 wt. %, and / or at most 20.0 wt. %, preferably at most 10.0 wt. %, more preferably at most 5.0 wt. %, based on the total weight of the liquid electrolyte.

[0069] In a specific embodiment, the content of b) the halogenated benzene is 0.1 to 20.0 wt %, preferably 1.0 to 10.0 wt %, and more preferably 2.0 to 5.0 wt %, based on the total weight of the liquid electrolyte.

[0070] In a more specific embodiment, the content of b) the halogenated benzene is 2.0 to 3.5 wt % based on the total weight of the liquid electrolyte.

[0071] In the present invention, the total amount of c) organic carbonate is 0 to 95.0% by weight, preferably 0 to 80.0% by weight, and more preferably 0 to 60.0% by weight, based on the total weight of the liquid electrolyte.

[0072] c) When contained in the liquid electrolyte of the present invention, the total amount of organic carbonate is 10.0 to 95.0% by weight, preferably 20.0 to 80.0% by weight, based on the total weight of the liquid electrolyte.

[0073] In one embodiment, the molar concentration (M) of d) the lithium salt in the liquid electrolyte according to the present invention is 0.5M to 8.0M, preferably 0.7M to 3.0M, and more preferably 1.0M to 2.0M.

[0074] In the present invention, the total amount of the film-forming additives e) may be 0 to 30.0% by weight, preferably 0 to 20.0% by weight, more preferably 0 to 15.0% by weight, and even more preferably 0 to 5.0% by weight, relative to the total weight of the liquid electrolyte.

[0075] When contained in the liquid electrolyte of the present invention, the total amount of e) film-forming additives is 0.05 to 10.0 wt %, preferably 0.05 to 5.0 wt %, more preferably 0.05 to 2.0 wt %, based on the total weight of the liquid electrolyte.

[0076] In a preferred embodiment, the total amount of e) film-forming additives accounts for at least 0.5% by weight of the liquid electrolyte.

[0077] A third object of the invention relates to the use of the composition according to the invention in a liquid electrolyte for a lithium secondary battery.

[0078] In one embodiment, a composition containing a) at least one fluorinated acyclic carboxylic acid ester and b) at least one halogenated benzene contributes to improved safety performance when used in a liquid electrolyte for a lithium secondary battery.

[0079] In certain embodiments, the composition exhibits a hazard level of 4 or less, preferably 2 or less, according to EUCAR (European Council for Automotive Research and Development) hazard levels.

[0080] In one embodiment, the total amount of a) the fluorinated acyclic carboxylic acid ester and b) the halogenated benzene is 0.2 to 20.0 wt %, preferably 2.0 to 15.0 wt %, more preferably 3.0 to 10.0 wt %, and most preferably 4.0 to 7.0 wt %, based on the total weight of the liquid electrolyte.

[0081] To the extent that the disclosure of any patents, patent applications, and publications incorporated herein by reference contradicts the statements of this application to the extent that a term may be unclear, the statements of this application shall control.

[0082] The present invention will now be described in more detail with reference to the following examples, the purpose of which is illustrative only and is not intended to limit the scope of the invention. [Example]

[0083] raw materials - DFEA: Fluorinated acyclic carboxylic acid ester of CH3-C(O)O-CH2CF2H, synthesized in-house at Solvay - NP08: 1,1,2,2-tetrafluoroethoxybenzene, synthesized in-house at Solvay - EC: Ethylene carbonate, commercially available from Soulbrain - EMC: Ethyl methyl carbonate, commercially available from Soulbrain - VC: Vinylene carbonate, commercially available from Soulbrain - PS: 1,3-propane sultone, commercially available from Soulbrain - Lithium salt: Lithium hexafluorophosphate (LiPF6), commercially available from Soulbrain

[0084] Liquid electrolyte formulation: The reference liquid electrolyte (hereafter "reference") was prepared by adding a 30:70 (volume %) mixture of EC and EMC to a reactor, then adding 2.0 wt% VC and 0.5 wt% PS to the mixture and stirring for 16 hours until the solution became clear. The wt% values ​​are relative to the total weight of the mixture. Then, 1 M LiPF6 was dissolved in the solution.

[0085] When preparing the liquid electrolyte for Example (E1) of the present invention, a mixture of 3.0 wt% NP08 and 2.0 wt% DFEA based on the total weight of the liquid electrolyte was further added to the reference solution while stirring for 2 hours.

[0086] The reference was used as the liquid electrolyte in Comparative Example 1 (CE1).

[0087] The liquid electrolyte of Comparative Example 2 (CE2) was prepared in the same manner as E1, except that 5 wt % NP08 (without DFEA) was added.

[0088] The liquid electrolyte of Comparative Example 3 (CE3) was prepared in the same manner as E1, except that 5 wt % DFEA (without NP08) was added.

[0089] Electrolyte filling and first aging The prepared liquid electrolyte was injected into a dry pouch cell (1500 mAh at 4.2 V) by pipetting. After injection, the dry cell was stored in a vacuum container to improve wettability, sealed using a vacuum sealer, and then stored at room temperature for another 24 hours (first aging).

[0090] Formation (second aging / activation of electrochemical cell) After the first aging, the pouch cells were charged to a 30% charge level (30% state of charge (SOC)), after which the cells were stored at room temperature for an additional 24 hours (second aging).

[0091] Degassing Gas generated within the pouch cell during formation was removed by opening the cell and then resealing it.

[0092] Electrochemical cell evaluation The cells were evaluated under the test conditions described below: Cyclic test at room temperature - Charging: 1C / 4.2V / 0.05C (constant current / constant voltage) - Discharge: 1C / 3.0V (constant current) Nail penetration tests (mechanical abuse tests) were performed according to SAND2005-3123. - A separate steel rod of 3 mm diameter is pierced at a speed of 8 cm / s at 4.35 V (test voltage at 100% SOC). - Minimum penetration depth: the cell must be completely pierced. - Hazard Level: The results of the nail penetration test were classified into EUCAR hazard levels from 0 to 7.

[0093] result The initial discharge capacity, 90% capacity retention, and nail penetration test results for E1 and CE1-CE3 are shown in Table 1 below. The cycling of E1 and CE1-CE3 continues to estimate the 80% capacity retention upon cycling.

[0094] E1 showed good initial discharge capacity, 90% capacity retention, and excellent penetration performance. EUCAR hazard level 2 corresponds to a state in which the cell is irreversibly damaged and requires repair, but does not result in leakage, eruptions, ignition / fire, exothermic reaction, or thermal runaway. On the other hand, hazard level 5 includes ignition / fire.

[0095] CE1 and CE3 exhibited initial discharge capacities and 90% capacity retention rates comparable to E1, but both CE1 and CE3 ignited and caught fire in the nail penetration test (equivalent to hazard level 5). Among the comparative examples, CE2 only exhibited hazard level 2. However, CE2 exhibited inferior 90% capacity retention rates and initial discharge capacities to E1.

[0096] Therefore, it was clearly demonstrated that only E1 according to the present invention can exhibit excellent performance in both cycling safety and intrusion safety.

[0097]

Table 2

Claims

1. 1. A composition comprising: a) Formula (I) R １ -C(O)O-R ２ (I) (In the formula, R １ is C １ ~C ４ is an alkyl group, and R ２ is C １ ~C ４ is a fluoroalkyl group) and at least one fluorinated acyclic carboxylic acid ester represented by the formula: b) Formula (II) 【Chemical 1】 (Wherein, X is C １ ~C ４ represents a fluoroalkyl group, R ３ ~R ７ each represents a hydrogen atom, a halogen atom, an alkyl group, a halogenated alkyl group, an alkoxy group, or a halogenated alkoxy group. and at least one halogenated benzene represented by the formula: A composition comprising:

2. R ２ is CH ２ The composition of claim 1, which does not contain any F- or -CHF- groups.

3. a) the fluorinated acyclic carboxylic acid ester is CH ３ —C(O)O—CH ２ CF ２ H, CH ３ —C(O)O—CF ２ CF ２ H, CH ３ —C(O)O—CH ２ CF ３ , C.H. ３ —C(O)O—CH ２ CH ２ CF ２ H, CH ３ —C(O)O—CH ２ CF ２ CF ２ H, CH ３ —C(O)O—CH ２ CH ２ CF ２ CF ３ , C.H. ３ CH ２ —C(O)O—CH ２ CF ２ H, CH ３ CH ２ —C(O)O—CH ２ CF ３ , C.H. ３ CH ２ —C(O)O—CH ２ CH ２ CF ２ H, CH ３ CH ２ —C(O)O—CH ２ CH ２ CF ３ 3. The composition of claim 1, wherein the compound is selected from the group consisting of:

4. b) The composition of any one of claims 1 to 3, wherein the halogenated benzene is selected from the group consisting of 1,1,2,2-tetrafluoroethoxybenzene, 1,1,2,2,2-pentafluoroethoxybenzene, fluoromethoxybenzene, difluoromethoxybenzene, trifluoromethoxybenzene, 1,2-bis(1,1,2,2-tetrafluoroethoxy)benzene, 1,3-bis(1,1,2,2-tetrafluoroethoxy)benzene, 1,4-bis(1,1,2,2-tetrafluoroethoxy)benzene, 4-trifluoromethoxytoluene, 1-fluoro-4-(1,1,2,2-tetrafluoroethoxy)benzene, 1-chloro-4-(1,1,2,2-tetrafluoroethoxy)benzene, 1-bromo-4-(1,1,2,2-tetrafluoroethoxy)benzene, and combinations thereof.

5. The composition of any one of claims 1 to 4, further comprising c) at least one organic carbonate.

6. c) The organic carbonate is 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, 6. The composition of claim 5, wherein the alkyl ester is selected from the group consisting of 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, and combinations thereof.

7. The composition of any one of claims 1 to 6, further comprising d) at least one lithium salt.

8. d) The lithium salt is lithium hexafluorophosphate (LiPF ６ ), lithium perchlorate (LiClO ４ ), lithium hexafluoroarsenate (LiAsF ６ ), lithium hexafluoroantimonate (LiSbF ６ ), lithium hexafluorotantalate (LiTaF ６ ), lithium tetrachloroaluminate (LiAlCl ４ ), lithium tetrafluoroborate (LiBF ４ ), lithium chloroborate (Li ２ B １０ Cl １０ ), lithium fluoroborate (Li ２ B １０ F １０ ), Li ２ B １２ F ｘ H １２－ｘ (x=0-12), LiPF ｘ (R Ｆ ) ６－ｘ and LiBF ｙ (R Ｆ ) ４－ｙ (In the formula, R Ｆ is Perfluoro C １ ~C ２０ represents an alkyl group or a perfluoroaromatic group, and x=0 to 5 and y=0 to 3), lithium bis(oxalato)borate [LiB(C ２ O ４ ) ２ ], LiBF ２ [O ２ C (CX ２ ) ｎ CO ２ ], LiPF ２ [O ２ C (CX ２ ) ｎ CO ２ ] ２ , and LiPF ４ [O ２ C (CX ２ ) ｎ CO ２ ] (X is H, F, Cl, C １ ~C ４ alkyl groups and fluorinated alkyl groups, where n=0 to 4), lithium trifluoromethanesulfonate (LiCF ３ SO ３ ), lithium bis(fluorosulfonyl)imide Li(FSO ２ ) ２ N(LiFSI), LiN(SO ２ C ｍ F ２ｍ＋１ ) (SO ２ C ｎ F ２ｎ＋１ ) and LiC(SO ２ C ｋ F ２ｋ＋１ ) (SO ２ C ｍ F ２ｍ＋１ ) (SO ２ C ｎ F ２ｎ＋１ ) (wherein k = 1 to 10, m = 1 to 10, and n = 1 to 10), LiN(SO ２ C ｐ F ２ｐ SO ２ ) and LiC(SO ２ C ｐ F ２ｐ SO ２ ) (SO ２ C ｑ F ２ｑ＋１ 8. The composition of claim 7, wherein the compound is selected from the group consisting of: wherein p=1 to 10, q=1 to 10, and combinations thereof.

9. The composition of any one of claims 1 to 8, further comprising e) at least one film-forming additive.

10. 10. The composition of claim 9, wherein e) the film-forming additive is selected from the group consisting of 1,3,2-dioxathiolane-2,2-dioxide, 1,3,2-dioxathiane-2,2-dioxide, 1,3-propane sultone, ethylene sulfite, prop-1-ene-1,3-sultone, dimethyl sulfone, tetramethylene sulfone (also known as sulfolane), ethyl methyl sulfone, isopropyl methyl sulfone, succinonitrile, adiponitrile, glutaronitrile, vinyl acetate, biphenylbenzene, isopropyl benzene, tris(trimethylsilyl)phosphate, triphenylphosphine, ethyl diphenylphosphinite, triethyl phosphite, tris(2,2,2-trifluoroethyl)phosphite, maleic anhydride, cesium bis(trifluoromethanesulfonyl)imide, cesium fluoride, and combinations thereof.

11. A lithium secondary battery comprising the composition according to any one of claims 1 to 10 in a liquid electrolyte.

12. a) The lithium secondary battery according to claim 11, wherein the content of the fluorinated acyclic carboxylic acid ester is at least 0.1 to 80.0 wt %, preferably 1.0 to 60.0 wt %, more preferably 2.0 to 10.0 wt %, based on the total weight of the liquid electrolyte.

13. b) The lithium secondary battery according to claim 11 or 12, wherein the content of the halogenated benzene is 0.1 to 20.0 wt %, preferably 1.0 to 10.0 wt %, and more preferably 2.0 to 5.0 wt %, relative to the total weight of the liquid electrolyte.

14. Use of the composition according to any one of claims 1 to 10 in a liquid electrolyte for a lithium secondary battery.

15. The use according to claim 14, wherein the total amount of a) the fluorinated acyclic carboxylic acid ester and b) the halogenated benzene is 0.2 to 20.0 wt %, preferably 2.0 to 15.0 wt %, more preferably 3.0 to 10.0 wt %, and most preferably 4.0 to 7.0 wt %, based on the total weight of the liquid electrolyte.

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