Lithium secondary battery with enhanced safety

Abstract

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 in a liquid electrolyte. The invention also relates to the use of the composition in a liquid electrolyte for a lithium secondary battery.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from European patent application No. 22201112.4 filed on October 12, 2022, the entire contents of which are incorporated herein by reference for all purposes. Technical Field

[0003] 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 for improving safety performance, more particularly for improving penetration performance, thereby exhibiting a hazard level of 4 or lower, preferably 2 or lower, according to EUCAR (European Council for Automotive R&D). Background Art

[0004] Lithium-ion batteries have maintained their dominance in the rechargeable energy storage device market for decades due to their multiple advantages such as light weight, reasonable energy density, and good cycle life. Nevertheless, with the development of high-power applications such as electric vehicles, hybrid electric vehicles, grid energy storage, etc., there is a constant demand for higher energy density.

[0005] Organic carbonates have been conventionally used as liquid electrolytes for lithium secondary batteries, such as non-cyclic 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 are relatively easy to decompose at high voltages (e.g., higher than 4.35V). Typically, driving the electrode to a higher / extreme voltage or exposing the battery cell to a higher temperature accelerates the undesirable reaction between the liquid electrolyte and the highly reactive electrode, which may result in reduced cycle life and reduced capacity. In the worst case, thermal runaway may occur, which is accompanied by fire / flame, followed by battery cell rupture / explosion and final battery cell disintegration. In particular, such safety issues are mainly due to the use of organic carbonates with relatively low boiling points and high flammability.

[0006] Therefore, various approaches have been conducted to overcome the limitations of commonly used liquid electrolytes based on organic carbonates, namely, to improve the safety performance while maintaining the cycling performance.

[0007] Compared with organic carbonates, hydrofluoroether-based solvents are advantageous because they have low GWP (global warming potential) and low flammability, and are therefore safe and easy to handle. As one of the various research works with such a purpose, WO 2015 / 078791 A (Solvay Specialty Polymers Italy SpA) reports a liquid electrolyte comprising a certain hydrofluoroether with a high fluorination rate, which exhibits favorable properties in terms of solubility, ionic conductivity, oxidation stability at high voltage, low flammability, etc., as well as a wide operating temperature range.

[0008] JP 2010 / 192327 A (Sony Corp.) 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 non-cyclic) carbonate, which exhibits excellent cycle characteristics at low temperatures and improved charge / discharge efficiency at high temperatures.

[0009] US2011 / 0311879 A1 (Sony Corporation) discloses a non-aqueous electrolyte comprising 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.

[0010] As technology matures and safety requirements continue to increase, especially in electric vehicles, characterization testing that evaluates the response to an abuse environment becomes more important and necessary than simple pass / fail testing. This is because understanding failure mechanisms and their root causes is critical to improving safety performance. While pass / fail testing does not provide a quantitative measure of the response of a battery cell, characterization testing evaluates the response to an abuse environment, through which failure modes and abuse conditions can be identified.

[0011] Among several characterizations, penetration safety has been considered an important evaluation parameter, and various attempts have been studied for improving penetration safety. This is because in the event of an accident, penetration of the battery pack may occur due to an impact applied from the outside, and then the electrodes in a charged state are physically in contact with each other, so that if a high current flows in a short period of time, thermal runaway may occur, that is, the temperature of the battery pack continues to rise as the heat of combustion inside the battery cell accumulates and triggers a pyrolysis reaction, ultimately leading to ignition / explosion. Most importantly, penetration safety is a critical issue that is directly related to the lives of passengers using transportation devices. Therefore, when penetration safety is not guaranteed, the application of lithium secondary batteries in electric vehicles should eventually be limited, especially considering that the current industrial demand, that is, electric vehicles require higher capacity power sources, is increasing.

[0012] EUCAR is the European automotive research and development committee of the major European passenger car and commercial vehicle manufacturers, and has major automobile manufacturers as its members, including BMW Group, FIATChrysler 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 R&D projects, and its members participate in a wide range of European cooperative R&D programs. Due to the wide variety of vehicle sizes and applications in the transportation industry, the automotive requirements of each manufacturer vary greatly, and therefore different requirements need to be considered in the context of specific transportation applications. In particular, the hazard levels of 0 to 7 adopted and modified by EUCAR provide detailed descriptions and classification criteria / impacts, which are generally referred to as EUCAR hazard levels, as shown in Table 1 below.

[0013] Table 1

[0014]

[0015]

[0016] In this regard, many automobile manufacturers (not limited to European players) use the EUCAR hazard level as a reference. For example, Sandia National Laboratories, one of the three National Nuclear Security Administration R&D laboratories in the United States and operated by Sandia Corporation for the Department of Energy, refers to the EUCAR hazard level when evaluating the safety performance of battery cells and provides a detailed test scheme SAND 2005-3123. In particular, the EUCAR hazard level enables the hazard level associated with the battery to be evaluated in a more specific / objective manner. In this regard, most automobile companies require a hazard level of 4 or lower as a minimum requirement, preferably a hazard level of 2 or lower, which corresponds to the necessary requirement of no fire or flame even under severe accident conditions.

[0017] In addition to the EUCAR hazard levels, there are several guidelines for safety assessment of secondary lithium batteries, such as UL1642 (Underwriters Laboratories Inc.), SBAG1101 (Japan Storage Battery Association), etc., which have different standards and assessment conditions using various parameters.

[0018] For example, US10818885 B2 (SK Innovation) discloses an adhesive pad comprising a substrate layer and an adhesive layer formed on at least one surface of the substrate layer, and the adhesive pad is adhered to at least one surface of an external material through the adhesive layer. The adhesive pad helps prevent ignition or explosion by improving penetration safety. The penetration safety is evaluated with reference to SBA G1101.

[0019] However, there is still an outstanding need for liquid electrolytes for lithium secondary batteries with improved safety performance, especially penetration safety performance, while maintaining good cycling performance. Summary of the invention

[0020] A first object of the present invention is a composition comprising:

[0021] a) at least one fluorinated acyclic carboxylic acid ester represented by formula (I)

[0022] R 1 -C(O)OR 2(I)

[0023] Where R 1 is a C1-C4 alkyl group, and R 2 is C1-C4 fluoroalkyl; and

[0024] b) at least one halogenated benzene represented by formula (II)

[0025]

[0026] wherein X represents a C1-C4 fluoroalkyl group, and R 3 To R 7 Each of represents a hydrogen atom, a halogen atom, an alkyl group, a halogenated alkyl group, an alkoxy group, or a halogenated alkoxy group.

[0027] A second object of the invention is a lithium secondary battery comprising a composition according to the invention in a liquid electrolyte.

[0028] A third object of the present invention is the use of the composition in a liquid electrolyte for lithium secondary batteries.

[0029] The inventors have surprisingly found that the composition according to the invention comprising a) at least one fluorinated acyclic carboxylic acid ester and b) at least one halogenated benzene can provide a particularly advantageous combination of properties, namely good cycling performance and excellent safety properties, in particular penetration performance, when used in a liquid electrolyte for a secondary battery. DETAILED DESCRIPTION

[0030] Ratios, concentrations, amounts and other numerical data may be presented in range format herein. It should be understood that such range format is used only for convenience and brevity, and should be flexibly interpreted to include not only the values ​​explicitly mentioned as range limits, but also all individual values ​​or sub-ranges encompassed within this range, as if each value and sub-range were explicitly mentioned. In the context of the present invention, the term 'percent by weight (wt%)' indicates the content of a specific component in a mixture calculated as the ratio between the weight of the component and the total weight of the mixture, and the term 'percent by volume (vol%)' indicates the content of a specific component in a mixture calculated as the ratio between the volume of the component and the total volume of the mixture.

[0031] It should be understood that the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the claimed invention. Therefore, various changes and modifications described herein will be apparent to those skilled in the art. In addition, for the sake of clarity and brevity, descriptions of well-known functions and configurations may be omitted.

[0032] The present invention provides a composition comprising:

[0033] a) at least one fluorinated acyclic carboxylic acid ester represented by formula (I)

[0034] R 1 -C(O)OR 2 (I)

[0035] Where R 1 is a C1-C4 alkyl group, and R 2 is C1-C4 fluoroalkyl; and

[0036] b) at least one halogenated benzene represented by formula (II)

[0037]

[0038] wherein X represents a C1-C4 fluoroalkyl group, and R 3 To R 7 Each of represents a hydrogen atom, a halogen atom, an alkyl group, a halogenated alkyl group, an alkoxy group, or a halogenated alkoxy group.

[0039] In one embodiment, R 2 It contains neither CH2F- nor -CHF- groups.

[0040] In a preferred embodiment, R in formula (I) 1 The number of carbon atoms in is 1.

[0041] In another preferred embodiment, R in formula (I) 1 The number of carbon atoms in is 2.

[0042] Non-limiting examples of suitable fluorinated acyclic carboxylic acid esters according to the present invention include, inter alia, the following:

[0043] 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.

[0044] In specific 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, CH3-C(O)O-CH2CH2CF2CF3, CH3CH2-C(O)O-CH2CF2H, CH3CH2-C(O)O-CH2CF3, CH3CH2-C(O)O-CH2CH2CF2H, CH3CH2-C(O)O-CH2CF3, CH3CH2-C(O)O-CH2CH2CF2H, CH3CH2-C(O)O-CH2CH2CF3, and combinations thereof.

[0045] In a more specific embodiment, a) the fluorinated acyclic carboxylic acid ester is CH3-C(O)O-CH2CF2H (2,2-difluoroethyl acetate).

[0046] In one embodiment, R 3 To R 7 One of them is a halogenated C1-C4 alkoxy group, preferably a C1-C2 fluoroalkoxy group.

[0047] In another embodiment, R3 To R 7 At least one of them is a halogen atom.

[0048] In a specific embodiment, b) 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.

[0049] In a more specific embodiment, b) the halobenzene is 1,1,2,2-tetrafluoroethoxybenzene.

[0050] In another more specific embodiment, b) the halobenzene is 1-fluoro-4-(1,1,2,2-tetrafluoroethoxy)benzene.

[0051] In another more specific embodiment, b) the halogenated benzene is 1,4-bis(1,1,2,2-tetrafluoroethoxy)benzene.

[0052] 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 cyclic or acyclic.

[0053] c) Non-limiting examples of organic carbonates include, inter alia, 4-fluoroethylene carbonate, 4,5-difluoro-1,3-dioxolane-2-one, 4,5-difluoro-4-methyl-1,3-dioxolane-2-one, 4,5-difluoro-4,5-dimethyl-1,3-dioxolane-2-one, 4,4-difluoro-1,3-dioxolane-2-one, 4,4,5-trifluoro-1,3-dioxolane-2-one, 4-fluoromethyl-1,3-dioxolane-2-one, tetrafluoroethylene carbonate, 4-(2,2-difluoroethoxy)ethylene carbonate, 4-(2,2,2 -trifluoroethoxy)ethylene carbonate, ethylene carbonate (1,3-dioxolane-2-one), propylene carbonate, butylene carbonate, trimethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, dimethyl vinylene carbonate, ethylpropyl carbonate, cyclohexenyl 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.

[0054] In a specific embodiment, c) the organic carbonate is a mixture of ethylene carbonate and ethyl methyl carbonate.

[0055] In another specific embodiment, c) the organic carbonate is a mixture of ethylene carbonate, ethyl methyl carbonate and vinylene carbonate.

[0056] In another embodiment, the liquid electrolyte further comprises d) at least one lithium salt.

[0057] Non-limiting examples of d) lithium salts according to the present invention include lithium ion complexes, such as lithium hexafluorophosphate (LiPF6); lithium perchlorate (LiClO4); lithium hexafluoroarsenate (LiAsF6); lithium hexafluoroantimonate (LiSbF6); lithium hexafluorotantalate (LiTaF6); lithium tetrachloroaluminate (LiAlCl4); lithium tetrafluoroborate (LiBF4); lithium chloroborate (Li2B4); lithium fluoride (LiF6 ... 10 Cl 10 ); Lithium fluoroborate (Li2B 10 F 10 ); Li2B 12 F x H 12-x , where x = 0-12; LiPF x (R F ) 6-x and LiBF y (R F ) 4-y , where R F represents a perfluorinated C1-C 20Alkyl or perfluorinated aromatic group, x = 0-5 and y = 0-3; Lithium bis(oxalato)borate [LiB(C2O4)2]; Lithium bis(malonate)borate [LiB(O2CCH2CO2)2]; Lithium bis(difluoromalonate)borate [LiB(O2CCF2CO2)2]; Lithium difluorooxalatoborate and lithium fluoromalonate (difluoro)borate; LiPF2[O2C(CX2) n CO2]2, LiPF4[O2C(CX2) n CO2], wherein X is selected from the group consisting of H, F, Cl, C1-C4 alkyl and fluorinated alkyl, 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 F 2n+1 ), wherein k = 1-10, m = 1-10 and n = 1-10; LiN(SO2C p F 2p SO2) and LiC(SO2C p F 2p SO2)(SO2C q F 2q+1 ), wherein p=1-10 and q=1-10; or a combination thereof.

[0058] In one embodiment, the lithium salt d) according to the present invention is selected from the group consisting of: lithium hexafluorophosphate (LiPF6); lithium perchlorate (LiClO4); lithium hexafluoroarsenate (LiAsF6); lithium hexafluoroantimonate (LiSbF6); lithium hexafluorotantalate (LiTaF6); lithium tetrachloroaluminate (LiAlCl4); lithium tetrafluoroborate (LiBF4); lithium chloroborate (Li2B4); lithium fluoride (Li2B6 ... 10 Cl 10 ); Lithium fluoroborate (Li2B 10 F 10 ); Li2B 12 F x H 12-x , where x = 0-12; LiPF x (R F ) 6-x and LiBF y (R F ) 4-y , where RF represents a perfluorinated C1-C 20 Alkyl or perfluorinated aromatic group, 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 F 2n+1 ), wherein k = 1-10, m = 1-10 and n = 1-10; LiN(SO2C p F 2p SO2) and LiC(SO2C p F 2p SO2)(SO2C q F 2q+1 ), wherein p=1-10 and q=1-10; and combinations thereof.

[0059] In a specific embodiment, d) the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2 (LiTFSI).

[0060] In another specific embodiment, d) the lithium salt is LiFSI.

[0061] In another specific embodiment, d) the lithium salt is LiPF6.

[0062] 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 on the surface of the electrode by reacting on the surface of the electrode before the solvent. Thus, the main components of the SEI layer comprise the decomposition products of the liquid electrolyte and the salt, which may include Li2CO3 (in the case of LiCoO2 as the cathode electroactive material), alkyl lithium carbonate, alkyl lithium oxide and other salt moieties such as LiF in the case of LiPF6-based electrolytes.

[0063] In one embodiment, e) the film-forming additive stabilizes the SEI layer at the surface of the cathode by preventing structural changes of the cathode, especially at high voltages.

[0064] This is because e) the reduction potential of the film-forming additive is higher than that of the liquid electrolyte when reacting on the surface of the negative electrode, and the oxidation potential of the film-forming additive is lower than that of the liquid electrolyte when reacting on the positive electrode.

[0065] In the present invention, e) the film-forming additive is different from d) the lithium salt.

[0066] In the present invention, e) the film-forming additive is different from c) the organic carbonate.

[0067] 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 diphenylphosphite, triethyl phosphite, tris(2,2,2-trifluoroethyl)phosphite, maleic anhydride, cesium bis(trifluoromethanesulfonyl)imide, cesium fluoride, or a combination thereof.

[0068] In a specific embodiment, e) the 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-dioxathiolane-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, isopropylbenzene, tris(trimethylsilyl)phosphate, triphenylphosphine, ethyl diphenylphosphite, triethyl phosphite, tris(2,2,2-trifluoroethyl)phosphite, maleic anhydride, cesium bis(trifluoromethanesulfonyl)imide and cesium fluoride, and combinations thereof.

[0069] In a preferred embodiment, e) the film-forming additive is 1,3-propane sultone.

[0070] According to another embodiment, e) the film-forming additive is an ionic liquid.

[0071] As used herein, the term "ionic liquid" refers to a compound containing positively charged cations and negatively charged anions, which is in a liquid state at 100°C or lower at atmospheric pressure. While ordinary liquids such as water are mainly composed of electrically neutral molecules, ionic liquids are mainly composed of ions and short-lived ion pairs. As used herein, the term "ionic liquid" indicates a compound that does not contain a solvent.

[0072] In a preferred embodiment, the ionic liquid comprises:

[0073] - a positively charged cation selected from the group consisting of imidazolium, pyridinium, pyrrolidinium and piperidinium, optionally containing one or more C1-C 30 Alkyl, and

[0074] - Negatively charged anions selected from the group consisting of halides, fluorinated anions and borates.

[0075] 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, among others.

[0076] In a preferred embodiment, the e) 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), and combinations thereof.

[0077] A second object of the invention is a lithium secondary battery comprising a composition according to the invention in a liquid electrolyte.

[0078] In one embodiment, a lithium secondary battery includes a liquid electrolyte including a composition according to the present invention, a positive electrode, a negative electrode, and a separator positioned between the positive electrode and the negative electrode.

[0079] In the present invention, the term "separator" is intended to refer in particular to an ion-permeable membrane placed between the positive electrode and the negative electrode. Its function is to allow lithium ions to pass through while blocking electrons and ensuring physical isolation between the electrodes. That is, a separator refers to a single or multilayer in the form of a polymer, non-woven cellulose or ceramic material / film that electrically and physically separates electrodes of opposite polarity in an electrochemical device and is permeable to ions flowing between the electrodes.

[0080] The electrodes in an electrochemical cell are called anodes or cathodes. The anode is defined as the electrode where electrons leave the cell and oxidation occurs, and the cathode is defined as the electrode where electrons enter the cell and reduction occurs. Each electrode can become either an anode or a cathode, depending on the direction of the current through the cell. A bipolar electrode is an electrode that acts as the anode for one cell and the cathode for another cell. When the cell is charged, the anode becomes the positive electrode and the cathode becomes the negative electrode, while when the cell is discharged, the anode becomes the negative electrode and the cathode becomes the positive electrode.

[0081] In the present invention, the term “negative electrode” is intended to denote in particular the electrode of an electrochemical cell at which oxidation occurs during discharge.

[0082] In the present invention, the term "positive electrode" is intended to denote in particular the electrode of an electrochemical cell at which reduction takes place during discharge.

[0083] In one embodiment, a) the content of 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%, relative to the total weight of the liquid electrolyte.

[0084] In a specific embodiment, the content of a) the fluorinated non-cyclic carboxylic acid ester is 0.1 to 80.0 wt %, preferably 1.0 to 60.0 wt %, more preferably 2.0 to 10.0 wt %, relative to the total weight of the liquid electrolyte.

[0085] In a more specific embodiment, a) the content of the fluorinated acyclic carboxylic acid ester is 2.0 to 3.5 wt % relative to the total weight of the liquid electrolyte.

[0086] 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%, relative to the total weight of the liquid electrolyte.

[0087] 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 % relative to the total weight of the liquid electrolyte.

[0088] In a more specific embodiment, the content of b) the halogenated benzene is 2.0 to 3.5 wt % relative to the total weight of the liquid electrolyte.

[0089] In the present invention, the total amount of c) the organic carbonate is 0 to 95.0 wt %, preferably 0 to 80.0 wt %, more preferably 0 to 60.0 wt % relative to the total weight of the liquid electrolyte.

[0090] If c) an organic carbonate is contained in the liquid electrolyte of the present invention, the total amount thereof is 10.0 to 95.0 wt %, preferably 20.0 to 80.0 wt %, relative to the total weight of the liquid electrolyte.

[0091] 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.

[0092] In the present invention, the total amount of e) the film-forming additive may be 0 to 30.0 wt%, preferably 0 to 20.0 wt%, more preferably 0 to 15.0 wt%, and even more preferably 0 to 5.0 wt% relative to the total weight of the liquid electrolyte.

[0093] If e) a film-forming additive is contained in the liquid electrolyte of the present invention, the total amount thereof is 0.05 to 10.0 wt%, preferably 0.05 to 5.0 wt%, and more preferably 0.05 to 2.0 wt%, relative to the total weight of the liquid electrolyte.

[0094] In a preferred embodiment, the total amount of e) the film-forming additive is at least 0.5 wt % of the liquid electrolyte.

[0095] A third object of the invention relates to the use of the composition according to the invention in a liquid electrolyte for lithium secondary batteries.

[0096] In one embodiment, a composition comprising 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.

[0097] In a specific embodiment, the composition exhibits a hazard level of 4 or lower, preferably 2 or lower, according to the EUCAR (European Council for Automotive Research and Development) hazard level.

[0098] In one embodiment, the total amount of a) fluorinated acyclic carboxylate and b) halogenated benzene is 0.2 to 20.0 wt %, preferably 2.0 to 15.0 wt %, more preferably 3.0 to 10.0 wt %, most preferably 4.0 to 7.0 wt % relative to the total weight of the liquid electrolyte.

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

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

[0101] Examples

[0102] raw material

[0103] -DFEA: Fluorinated acyclic carboxylate CH3-C(O)O-CH2CF2H, synthesized in-house at Solvay

[0104] -NP08: 1,1,2,2-Tetrafluoroethoxybenzene, synthesized in-house at Solvay

[0105] -EC: ethylene carbonate, commercially available from Soulbrain

[0106] -EMC: ethyl methyl carbonate, commercially available from Sobo Ruiyin Corporation

[0107] -VC: vinylene carbonate, commercially available from Sobo Ruiyin Co., Ltd.

[0108] -PS: 1,3-propane sultone, commercially available from Sobo Ruiyin Co., Ltd.

[0109] -Li salt: lithium hexafluorophosphate (LiPF6), commercially available from Sobo Ruiyin

[0110] Preparation of liquid electrolyte:

[0111] A reference liquid electrolyte (hereinafter referred to as 'reference') was prepared by adding a mixture of EC and EMC in a ratio of 30:70 (in vol%) to a reactor, followed by introducing 2.0 wt% of VC and 0.5 wt% of PS into the mixture and mixing under stirring for 16 hours until the solution became transparent. The wt% is relative to the total weight of the mixture. 1 M LiPF6 was then dissolved in the solution.

[0112] When preparing the liquid electrolyte for the inventive example (E1), a mixture of 3.0 wt % of NP08 and 2.0 wt % of DFEA relative to the total weight of the liquid electrolyte was further added to the reference under stirring for 2 hours.

[0113] This reference was used as the liquid electrolyte for Comparative Example 1 (CE1).

[0114] The liquid electrolyte of Comparative Example 2 (CE2) was prepared in the same manner as E1, except that 5 wt % of NP08 (without DFEA) was added.

[0115] The liquid electrolyte of Comparative Example 3 (CE3) was prepared in the same manner as E1, except that 5 wt % of DFEA was added (without NP08).

[0116] Electrolyte filling and first aging

[0117] The liquid electrolyte as prepared was injected into a dry pouch cell (1500 mAh at 4.2 V) by pipetting. After injection, the dry cell was kept in a vacuum container for better wettability, sealed using a vacuum sealer, and then kept at room temperature for another 24 hours (1st aging).

[0118] Formation (secondary aging / activation of electrochemical cells)

[0119] The pouch cell was charged to a 30% charge level (state of charge (SOC) 30%) after the 1st aging, and then the cell was kept at room temperature for another 24 hours (2nd aging).

[0120] Degassing

[0121] Gases generated in the pouch cell during formation are removed by opening the cell and subsequently resealing.

[0122] Electrochemical Cell Evaluation

[0123] The battery cells were evaluated under the test conditions described below:

[0124] ◆Cyclic test at room temperature

[0125] -Charging: 1C / 4.2V / 0.05C (constant current / constant voltage)

[0126] -Discharge: 1C / 3.0V (constant current)

[0127] ◆Nail penetration test (mechanical abuse test) is implemented according to SAND 2005-3123:

[0128] - Penetration with an insulating steel rod with a diameter of 3 mm at a speed of 8 cm / s at 4.35 V (test voltage at SOC 100%).

[0129] - Minimum penetration depth: The battery cell must be fully penetrated.

[0130] - Hazard level: The results of the nail penetration test are classified according to the EUCAR hazard level from 0 to 7.

[0131] result

[0132] The initial discharge capacity, 90% capacity retention, and nail penetration test results of E1 and CE1-CE3 are shown in the following Table 1. Cycling of E1 and CE1-CE3 was continued to estimate the 80% capacity retention (in terms of cycles).

[0133] E1 shows good initial discharge capacity and 90% capacity retention, as well as excellent penetration performance. Hazard level 2 under EUCAR corresponds to cells that are irreversibly damaged and require repair, but with no leakage, no venting, no fire / flame, no exothermic reaction or thermal runaway, while fire / flame is associated with hazard level 5.

[0134] Although CE1 and CE3 exhibited initial discharge capacities and 90% capacity retention rates comparable to E1, nail penetration tests of both CE1 and CE3 resulted in flames and fires (corresponding to hazard level 5). Among these comparative examples, CE2 exhibited only hazard level 2. However, CE2 showed 90% capacity retention and initial discharge capacity inferior to E1.

[0135] Therefore, it is clearly demonstrated that only E1 according to the present invention can exhibit excellent performance in terms of both circulation and penetration safety.

[0136] Table 2

[0137]

Claims

1. A composition comprising: a) at least one fluorinated acyclic carboxylic acid ester represented by formula (I) R 1 -C(O)O-R 2 (I) Where R 1 is a C1-C4 alkyl group, and R 2 is C1-C4 fluoroalkyl; and b) at least one halogenated benzene represented by formula (II) wherein X represents a C1-C4 fluoroalkyl group, and R 3 To R 7 Each of represents a hydrogen atom, a halogen atom, an alkyl group, a halogenated alkyl group, an alkoxy group, or a halogenated alkoxy group.

2. The composition according to claim 1, wherein R 2 It contains neither CH2F- nor -CHF- groups.

3. The composition according to claim 1 or 2, wherein a) The fluorinated non-cyclic 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, 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.

4. The composition according to any one of claims 1 to 3, wherein 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.

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

6. The composition according to claim 5, wherein c) the organic carbonate is selected from the group consisting of 4-fluoroethylene carbonate, 4,5-difluoro-1,3-dioxolane-2-one, 4,5-difluoro-4-methyl-1,3-dioxolane-2-one, 4,5-difluoro-4,5-dimethyl-1,3-dioxolane-2-one, 4,4-difluoro-1,3-dioxolane-2-one, 4,4,5-trifluoro-1,3-dioxolane-2-one, 4-fluoromethyl-1,3-dioxolane-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, dimethyl vinylene carbonate, ethylpropyl carbonate, cyclohexenyl 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, and combinations thereof.

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

8. The composition according to claim 7, wherein d) The lithium salt is selected from the group consisting of: lithium hexafluorophosphate (LiPF6); lithium perchlorate (LiClO4); lithium hexafluoroarsenate (LiAsF6); lithium hexafluoroantimonate (LiSbF6); lithium hexafluorotantalate (LiTaF6); lithium tetrachloroaluminate (LiAlCl4); lithium tetrafluoroborate (LiBF4); lithium chloroborate (Li2B 10 Cl 10 ); Lithium fluoroborate (Li2B 10 F 10 ); Li2B 12 F x H 12-x , where x = 0-12; LiPF x (R F ) 6-x and LiBF y (R F ) 4-y , where R F represents a perfluorinated C1-C 20 Alkyl or perfluorinated aromatic group, x = 0-5 and y = 0-3; Lithium bis(oxalato)borate [LiB(C2O4)2]; LiBF2 [O2C(CX2) n CO2]、LiPF2[O2C(CX2) n CO2]2 and LiPF4[O2C(CX2) n CO2], wherein X is selected from the group consisting of H, F, Cl, C1-C4 alkyl and fluorinated alkyl, 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 F 2n+1 ), wherein k = 1-10, m = 1-10 and n = 1-10; LiN(SO2C p F 2p SO2) and LiC(SO2C p F 2p SO2)(SO2C q F 2q+1 ), wherein p=1-10 and q=1-10; and combinations thereof.

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

10. The composition according to 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-dioxathiolane-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, isopropylbenzene, tris(trimethylsilyl)phosphate, triphenylphosphine, ethyl diphenylphosphite, 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. The lithium secondary battery according to claim 11, wherein a) the content of the fluorinated acyclic carboxylic acid ester is at least 0.1 to 80.0 weight % (wt %), preferably 1.0 to 60.0 wt %, more preferably 2.0 to 10.0 wt % relative to the total weight of the liquid electrolyte.

13. The lithium secondary battery according to claim 11 or 12, wherein: b) 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 carboxylate 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%, most preferably 4.0 to 7.0 wt%, relative to the total weight of the liquid electrolyte.

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