Electrolyte solution for a lithium secondary battery and lithium secondary battery containing this

Abstract

An electrolyte solution for a lithium secondary battery according to embodiments of the present disclosure comprises a lithium salt, an organic solvent, a phosphate-based additive, and a radical scavenger. The flame retardancy and high-temperature stability of the electrolyte solution are improved, and a lithium secondary battery containing the electrolyte solution, exhibiting improved high-temperature lifetime and improved storage properties, is provided.

Description

CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY

[0001] This application claims priority to Korean Patent Application No. 10-2023-0075639, filed on June 13, 2023, with the Korea Intellectual Property Office (KIPO), the entire disclosure of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present disclosure relates to an electrolyte solution for a lithium secondary battery and a lithium secondary battery containing the same. More specifically, the present disclosure relates to an electrolyte solution for a lithium secondary battery containing an additive and a lithium secondary battery containing the same. BACKGROUND

[0003] A secondary battery that can be repeatedly charged and discharged is widely used as a power source for mobile electronic devices such as camcorders, mobile phones, laptops, etc. Recently, a battery pack containing a secondary battery is being developed and used as a power source for an environmentally friendly vehicle such as an electric car, a hybrid vehicle, etc.

[0004] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, nickel-hydrogen batteries, etc. The lithium secondary battery, for example, is widely used and widely used due to its high working voltage and energy density per unit weight, high charging speed, compact size, etc.

[0005] The secondary battery may, for example, include an electrode assembly with a cathode, an anode, and a separator, as well as an electrolyte solution in which the electrode assembly is immersed. The lithium secondary battery may further include an outer casing, e.g., in the form of a bag, for accommodating the electrode assembly and the electrolyte solution.

[0006] With the expansion of the application range of lithium secondary batteries, the development of lithium secondary batteries with improved cycle life, capacity and operational stability is being promoted.

[0007] However, during repeated charging and discharging processes, surface damage, such as that of a nickel-based lithium metal oxide used as the active cathode material, can lead to deterioration in performance and capacity, and a side reaction can occur between the nickel-based lithium metal oxide and an electrolyte. Furthermore, the battery's stability can be compromised in harsh environments with high or low temperatures. SUMMARY

[0008] According to one aspect of the present disclosure, an electrolyte solution for a lithium secondary battery is provided which has improved high-temperature stability.

[0009] According to one aspect of the present invention, there is provided a lithium secondary battery containing the electrolyte solution and having improved high-temperature stability.

[0010] An electrolyte solution for a lithium secondary battery contains a lithium salt, an organic solvent, a phosphate-based additive containing a compound represented by chemical formula 1, and a radical scavenger containing a compound represented by chemical formula 2. The content of the phosphate-based additive is in a range of 1 wt% to 10 wt% based on the total weight of the electrolyte solution.

[0011] In chemical formula 1, R 1 to R 3 each independently represents a C6 to C18 aryl group, a halogenated C6 to C18 aryl group, a C1 to C10 alkyl group, a halogenated C1 to C10 alkyl group or a C2 to C10 alkenyl group,

[0012] In chemical formula 2, R 4 to R 6each independently of one another represents a C1 to C10 alkyl group, a C3 to C12 cycloalkyl group, a C2 to C10 alkenyl group or a C6 to C18 aryl group.

[0013] In some embodiments, in chemical formula 1, R 1 and R 2 be equal, and each of R 1 and R 2 not equal to R 3 be, can R 1 and R 3 be equal and each of R 1 and R 3 not equal to R 2 be, or R 1 , R 2 and R 3 are not equal to each other.

[0014] In some embodiments, in chemical formula 1, R 1 and R 2 each independently of one another is a C6 to C18 aryl group, a halogenated C6 to C18 aryl group, a C1 to C10 alkyl group, a halogenated C1 to C10 alkyl group, or a C2 to C10 alkyl group, R 3may be a C6 to C18 aryl group, a halogenated C6 to C18 aryl group or a halogenated C1 to C10 alkyl group, and at least one of R 1 and R 2 cannot equal R 3 be.

[0015] In some embodiments, in chemical formula 1, R 1 a C6 to C18 aryl group or a C6 to C18 halogenated aryl group, and R 2 can be a C1 to C5 halogenated alkyl group.

[0016] In some embodiments, in chemical formula 1, R 1 a phenyl group or a fluorophenyl group, R 2 may be a trifluoromethyl group, a 2,2,2-trifluoroethyl group, a 3,3,3-trifluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group or a 2,2,3,3,4,4,4-heptafluorobutyl group, and R 3is a phenyl group, a fluorophenyl group, a trifluoromethyl group, a 2,2,2-trifluoroethyl group, a 3,3,3-trifluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group or a 2,2,3,3,4,4,4-heptafluorobutyl group.

[0017] In some embodiments, the content of the phosphate-based additive may be in a range of 5 to 10 wt.% based on the total weight of the electrolyte solution.

[0018] In some embodiments, in the chemical formula 2, R 4 and R 5 each independently be a branched C3 to C10 alkyl group.

[0019] In some embodiments, in the chemical formula 2, R 6 a linear C1 to C10 alkyl group.

[0020] In some embodiments, the radical scavenger may contain 2,6-di-tert-butyl-p-cresol.

[0021] In some embodiments, the content of the radical scavenger may be in the range of 0.1 wt% to 2 wt% based on the total weight of the electrolyte solution.

[0022] In some embodiments, the ratio between the content of the phosphate-based additive and the content of the radical scavenger, based on the total weight of the electrolyte solution, is greater than 1 and less than or equal to 50.

[0023] In some embodiments, the ratio between the content of the phosphate-based additive and the content of the radical scavenger, based on the total weight of the electrolyte solution, is in a range of 2 to 20.

[0024] In some embodiments, the electrolyte solution may further contain at least one auxiliary additive selected from the group consisting of a cyclic unsaturated carbonate-based compound, a fluorine-substituted cyclic carbonate-based compound, a sultone-based compound, a cyclic sulfate-based compound, a fluorine-substituted phosphate-based compound, and an oxalatoborate-based compound.

[0025] In some embodiments, the auxiliary additive may be present in an amount of 0.01 wt% to 5 wt% based on the total weight of the electrolyte solution.

[0026] A lithium secondary battery includes a case, an electrode assembly including a cathode and an anode opposite to the cathode and housed in the case, and the electrolyte solution for a lithium secondary battery according to the previously described embodiments.

[0027] An electrolyte solution for a lithium secondary battery according to embodiments of the present disclosure may contain a phosphate-based additive and a radical scavenger. The phosphate-based additive can improve the flame-retardant properties and high-temperature stability of the electrolyte solution, and the radical scavenger can prevent components of the electrolyte solution from decomposing or side reactions occurring at high temperatures. Accordingly, the amount of gas generated during high-temperature storage of the electrolyte solution and the battery containing it can be reduced.

[0028] In addition, when the lithium secondary battery containing the electrolyte solution is repeatedly charged and discharged at high temperature, an increase in capacity and internal resistance can be suppressed.

[0029] The electrolyte solution for a lithium secondary battery according to embodiments of the present disclosure may contain the phosphate-based additive and the radical scavenger in a desired amount. Furthermore, the electrolyte solution for a lithium secondary battery according to embodiments of the present disclosure may contain the phosphate-based additive and the radical scavenger in a desired ratio.

[0030] Accordingly, the lithium secondary battery containing the electrolyte solution can exhibit further improved high-temperature storage properties (e.g., reduced gas formation in the battery during storage at high temperatures) and high-temperature life characteristics (e.g., increased capacity and resistance retention).

[0031] The lithium secondary battery of the present disclosure can be widely used in green technology, such as electric vehicles, battery charging stations, solar and wind power systems, etc. that use a battery. The lithium secondary battery according to the present disclosure can be used for green electric vehicles and hybrid vehicles to prevent climate change by suppressing air pollution and greenhouse gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 and Fig. 2 are a schematic plan view and a schematic cross-sectional view showing a lithium secondary battery according to embodiments, respectively. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] According to embodiments of the present disclosure, an electrolyte solution for a lithium secondary battery is provided, which contains a phosphate-based additive and a radical scavenger. Furthermore, a lithium secondary battery with the electrolyte solution is provided, which has improved high-temperature storage properties and high-temperature life characteristics. <Elektrolytlösung für Lithium-Sekundärbatterie>

[0033] An electrolyte solution for a lithium secondary battery (hereinafter abbreviated as electrolyte solution) according to embodiments of the present disclosure may contain a lithium salt, an organic solvent, a phosphate-based additive, and a radical scavenger.

[0034] In embodiments, the organic solvent may be present in a residual amount excluding solid components such as the lithium salt, the phosphate-based additives, the radical scavenger, and an auxiliary additive. In some embodiments, the organic solvent content may range from 90 weight percent (wt%) to 96 wt%, based on the total weight of the electrolyte solution.

[0035] The organic solvent may contain an organic compound capable of providing sufficient solubility for the lithium salt, phosphate-based additive, radical scavenger, auxiliary additive, etc., and non-reactive with the elements of the lithium secondary battery. In some embodiments, a non-aqueous organic solvent may be used, and the electrolyte solution may be provided as a non-aqueous electrolyte solution.

[0036] In one embodiment, the organic solvent may include a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, an aprotic solvent, etc. These may be used alone or in combination of two or more thereof.

[0037] Examples of carbonate-based solvent include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, diethyl carbonate (DEC), dipropyl carbonate, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, etc.

[0038] Examples of the ester-based solvent include methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), 2,2-difluoroethyl acetate (DFEA), 3,3,3-trifluoroethyl acetate, methyl propionate (MP), ethyl propionate (EP), gamma-butyrolactone (GBL), decanolide, valerolactone, mevalonolactone, caprolactone, etc.

[0039] Examples of the ether-based organic solvent include dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc.

[0040] Examples of ketone-based solvents include cyclohexanone. Examples of alcohol-based solvents include ethyl alcohol and isopropyl alcohol.

[0041] The aprotic solvent may include a nitrile-based solvent, an amide-based solvent such as dimethylformamide (DMF), a dioxolane-based solvent such as 1,3-dioxolane, a sulfolane-based solvent, etc.

[0042] In one embodiment, the carbonate-based solvent can be used as the organic solvent. The organic solvent can include, for example, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or a combination thereof.

[0043] In one embodiment, a combination of at least two of the following substances can be used as the organic solvent: ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) and diethyl carbonate (DEC).

[0044] In embodiments, the lithium salt may contain one or more lithium salt compounds. For example, the lithium salt may be Li + X- and non-limiting examples of the anion (X - ) of the lithium salt contain PF6 - , F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , (CF3CF2SO2)2N - , BF4 - , BF2(C2O4) - , B(C3H2O4)2 - , BF2(C3H2O4) - , B(C3HO4F)2 - , B(C3F2O4)2 - , etc. These can be used individually or in a combination of two or more of them.

[0045] In one embodiment, the concentration of the lithium salt in the electrolyte solution may be in a range from 0.01 M to 2 M or from 0.5 M to 1.5 M. In the above-mentioned range, the transfer of lithium ions and / or electrons during charging and discharging of the lithium secondary battery may be promoted, and improved capacity may be provided.

[0046] In embodiments, the electrolyte solution may contain the phosphate-based additive. The phosphate-based additive can improve the flame retardancy of the electrolyte solution and enhance the high-temperature lifespan and high-temperature storage properties of the lithium secondary battery by improving high-temperature stability.

[0047] The phosphate-based additive may contain a compound of the following chemical formula 1.

[0048] In the chemical formula 1, R 1 to R 3each independently be a C6 to C18 aryl group, a halogenated C6 to C18 aryl group, a C1 to C10 alkyl group, a halogenated C1 to C10 alkyl group or a C2 to C10 alkenyl group.

[0049] The term “Ca to Cb” as used herein means that the number of carbon atoms in a hydrocarbon group is in a range from a to b.

[0050] The term “aryl group” as used herein refers to a group containing at least one aromatic ring and may include, for example, a phenyl group, a naphthyl group, an anthracene group, etc.

[0051] As used herein, the term "alkyl group" refers to a chain-like saturated hydrocarbon that may contain a linear or branched alkyl group. For example, a C1 to C10 alkyl group may contain a linear C1 to C10 alkyl group and a branched C3 to C10 alkyl group.

[0052] The term “halogenated” as used herein means that at least one of the hydrogen atoms bonded to the carbon of an alkyl group or an aryl group is replaced by a halogen atom such as Cl, Br, F or I.

[0053] The term “alkenyl group” as used herein refers to a chain-like unsaturated hydrocarbon group containing a carbon-carbon double bond in the middle or at one end of the chain.

[0054] The terms “alkyl group”, “alkenyl group” and “aryl group” as used herein may refer broadly to a substituted or an unsubstituted group.

[0055] For example, the alkyl group, the cycloalkyl group, the alkenyl group, and the aryl group may each contain a substituent that replaces at least one hydrogen atom bonded to carbon.

[0056] Non-limiting examples of the substituent may include functional groups such as halogen, a hydroxy group, a carboxyl group, an amine group, an amide group, a cyano group, a thiol group, a sulfonic acid group, etc.

[0057] The halogenated alkyl group or halogenated aryl group can have 2 to 6 hydrogen atoms bonded to a carbon atom. For example, if the halogenated alkyl group is a 2,2,3,3,4,4,4-heptafluorobutyl group, two hydrogen atoms are bonded to the carbon. If the halogenated aryl group is a fluorophenyl group, four hydrogen atoms are bonded to the carbon.

[0058] In exemplary embodiments, R 1 to R 3each independently be a C6 to C18 aryl group such as a phenyl group, a naphthyl group, an anthracene group, etc.; a halogenated C6 to C18 aryl group such as a fluorophenyl group, a difluorophenyl group, a trifluorophenyl group, a chlorophenyl group, a dichlorophenyl group, a trichlorophenyl group, a fluoronaphthyl group, etc.; a C1 to C10 alkyl group such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an n-pentyl group, a neopentyl group, an isopentyl group; a halogenated C1 to C10 alkyl group such as a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a 2-fluoroethyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, a 3-fluoropropyl group, a 3,3-difluoropropyl group, a 3,3,3-trifluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group, a 4-fluorobutyl group, a 4,4-difluorobutyl group, a 4,4,4-trifluorobutyl group, a 3,3,4,4,4-pentafluorobutyl group, a 2,2,3,3,4,4,4-heptafluorobutyl group, etc.; or a C2 to C10 alkenyl group such as a vinyl group, a 1-propenyl group, a 2-propenyl group, an isopropenyl group, a 1-butenyl group, a 2-butenyl group, a 3-butenyl group, an isobutenyl group, a 2-methyl-2-butenyl group, etc.

[0059] In the chemical formula 1, R 1 to R 3 be equal. In some embodiments, R 1 to R 3 be the same and can be a C6 to C18 aryl group, a C6 to C18 halogenated aryl group, or a C1 to C10 halogenated alkyl group. For example, R 1 to R 3 each be a phenyl group or a 2,2,2-trifluoroethyl group.

[0060] In chemical formula 1, at least one of R 1 and R 2 not be the same as R 3 . In chemical formula 1, for example, R 1 and R 2 be equal but not equal to R 3 be.

[0061] For example, R 1 and R 2 the same C1 to C10 alkyl group or the same C2 to C10 alkenyl group. R 3may be a C6 to C18 aryl group, a halogenated C6 to C18 aryl group or a halogenated C1 to C10 alkyl group and may be different from R 1 and R 2 differentiate.

[0062] For example, R 1 to R 3 C6 to C18 aryl groups. R 1 and R 2 can be equal and different from R 3 For example, R 1 and R 2 a phenyl group and R 3 a naphthyl group.

[0063] For example, R 1 and R 2 be the same C6 to C18 aryl group, and R 3 can be a halogenated C6 to C18 aryl group different from R 1 and R 2 For example, R 1 and R 2 a phenyl group and R 3 a fluorophenyl group.

[0064] For example, R 1 and R 2be the same halogenated C6 to C18 aryl group, and R 3 can be a C6 to C18 aryl group different from R 1 and R 2 For example, R 1 and R 2 a fluorophenyl group and R 3 can be a phenyl group.

[0065] For example, R 1 and R 2 be the same C6 to C18 aryl group, and R 3 can be a halogenated C6 to C18 aryl group different from R 1 and R 2 For example, R 1 and R 2 a phenyl group and R 3 a fluorophenyl group.

[0066] For example, R 1 to R 3 halogenated C6 to C18 aryl groups. R 1 and R 2 can be equal and different from R 3 distinguish. R 1 and R 2 can be, for example, a fluorophenyl group and R3 can be a difluorophenyl group.

[0067] For example, R 1 and R 2 be the same C1 to C10 alkyl group, and R 3 can be a C6 to C18 aryl group different from R 1 and R 2 For example, R 1 and R 2 be a methyl group and R 3 can be a phenyl group.

[0068] For example, R 1 and R 2 be the same C2 to C10 alkenyl group, and R 3 can be a C6 to C18 aryl group different from R 1 and R 2 For example, R 1 and R 2 be a vinyl group and R 3 can be a phenyl group.

[0069] For example, R 1 and R 2 be the same halogenated C1 to C10 alkyl group, and R 3 can be a C6 to C18 aryl group different from R1 and R 2 For example, R 1 and R 2 a 2,2,2-trifluoroethyl group and R3 can be a phenyl group.

[0070] For example, R 1 to R 3 halogenated C1 to C10 alkyl groups. R 1 and R 2 can be equal and different from R 3 distinguish. R 1 and R 2 can be, for example, a 2,2,2-trifluoroethyl group and R 3 can be a 3,3,3-trifluoropropyl group.

[0071] In some embodiments, in chemical formula 1, R 1 and R 3 be equal and different from R 2 distinguish, or R 1 , R 2 and R 3 cannot be the same.

[0072] In embodiments, in the chemical formula 1, R 1 a C6 to C18 aryl group or a C6 to C18 halogenated aryl group, and R2 can be a C1 to C5 halogenated alkyl group.

[0073] In embodiments, in the chemical formula 1, R 1 a phenyl group or a fluorophenyl group, R 2 can be a trifluoromethyl group, a 2,2,2-trifluoroethyl group or a 3,3,3-trifluoropropyl group, and R 3 can be a phenyl group, a fluorophenyl group, a trifluoromethyl group, a 2,2,2-trifluoroethyl group or a 3,3,3-trifluoropropyl group.

[0074] For example, in the chemical formula 1 R 1 be a phenyl group, R 2 can be a 2,2,2-trifluoroethyl group and R 3 can be a phenyl group or a 2,2,2-trifluoroethyl group.

[0075] In embodiments, the electrolyte solution may contain the phosphate-based additive containing an aryl group or a halogenated alkyl group. The phosphate-based additive can increase the flame retardancy of the electrolyte solution and improve the high-temperature stability of the electrolyte solution and the battery.

[0076] In embodiments, the phosphate-based additive may contain 50 weight percent (wt%) or more, 60 wt%, 70 wt%, 80 wt% or more, or 90 wt% or more of the compound represented by Chemical Formula 1, based on the total weight of the phosphate-based additive. In some embodiments, the phosphate-based additive may consist essentially of the compound represented by Chemical Formula 1.

[0077] In embodiments, the phosphate-based additive may contain two or more different compounds in which at least one of the radicals R 1 , R 2and R 3 in the compound represented by chemical formula 1. For example, the phosphate-based additive may be a mixture of a compound in which in chemical formula 1 R 1 and R 2 a 2,2,2-trifluoroethyl group and R 3 is a phenyl group, and a compound in which in the chemical formula 1 R 1 and R 2 a phenyl group and R 3 a 2,2,2-trifluoroethyl group.

[0078] In embodiments, the content of the phosphate-based additive may range from 1 wt% to 10 wt% based on the total weight of the electrolyte solution. For example, the content of the phosphate-based additive may be 1 wt% or more, 2 wt% or more, 3 wt% or more, 4 wt% or more, 5 wt% or more, and 10 wt% or less, 9 wt% or less, 8 wt% or less, 7 wt% or less, or 6 wt% or less based on the total weight of the electrolyte solution.

[0079] In the above-mentioned range, the flame retardancy of the electrolyte solution can be achieved, and excessive side reactions of the electrolyte solution at high temperatures can be suppressed.

[0080] If the content of the phosphate-based additive is less than 1 wt%, the side reactions of the electrolyte solution may increase and cause excessive gas formation inside the battery. Accordingly, the battery may expand, leading to an increase in battery thickness, and the energy density and stability of the battery may deteriorate.

[0081] If the content of the phosphate-based additive exceeds 10 wt%, the capacity may decrease when the battery is repeatedly charged and discharged under high temperatures, resulting in deterioration of the cycle life characteristics.

[0082] In embodiments, the electrolyte solution may contain the radical scavenger. The radical scavenger can remove radicals that arise when the electrolyte solution decomposes at high temperatures or when a side reaction occurs between the electrolyte solution and an electrode material. Accordingly, damage to the battery can be suppressed by preventing an additional side reaction or resulting heat generation / explosion.

[0083] When the electrolyte solution contains only the phosphate-based additive, the flame retardancy of the electrolyte solution can be achieved, but components of the electrolyte solution may decompose at high temperatures or gas may be generated due to the side reaction of the electrolyte solution. The electrolyte solution according to embodiments of the present disclosure contains the radical scavenger, so that the amount of gas evolution from the battery in the high-temperature environment can be reduced, and the battery has improved storage and life characteristics at high temperatures.

[0084] In embodiments, the radical scavenger may contain a compound of chemical formula 2.

[0085] In the chemical formula 2, R 4 to R 6 each independently be a C1 to C10 alkyl group, a C3 to C12 cycloalkyl group, a C2 to C10 alkenyl group or a C6 to C18 aryl group.

[0086] The term “cycloalkyl group” as used herein refers to a cyclic saturated hydrocarbon and may include a structure in which at least two ends of a linear alkyl group or a branched alkyl group are connected.

[0087] The alkyl group, the alkenyl group, and the aryl group may be the same as those described with reference to Chemical Formula 1. In addition, the alkyl group, the cycloalkyl group, the alkenyl group, and the aryl group may each contain a substituent replacing at least one hydrogen atom bonded to carbon.

[0088] Non-limiting examples of the substituent may include functional groups such as halogen, a hydroxy group, a carboxyl group, an amine group, an amide group, a cyano group, a thiol group, a sulfonic acid group, etc.

[0089] For example, in the chemical formula 2 R 4to R 6 each independently represents a C1 to C10 alkyl group such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an n-pentyl group, a neopentyl group, an isopentyl group, etc.; a C3 to C12 cycloalkyl group such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, etc.; a C2 to C10 alkenyl group such as a vinyl group, a 1-propenyl group, a 2-propenyl group, an isopropenyl group, a 1-butenyl group, a 2-butenyl group, a 3-butenyl group, an isobutenyl group, a 2-methyl-2-butenyl group, etc.; or a C6 to C18 aryl group such as a phenyl group, a naphthyl group, an anthracene group, etc.

[0090] In some embodiments, at least one alkylene group (-CH2-) contained in the alkyl group or the alkenyl group may be substituted with S, O, an amine group such as -NH- or -NR- (R is a C1 to C5 alkyl group), a phosphanyl group such as -PH- or -PR- (R is a C1 to C5 alkyl group), an ester group, a carbonyl group, a disulfide group, a sulfonyl group, an azo group, an amide group, an imine group, a peroxy group, a carbonate group, a phosphate group, etc.

[0091] In embodiments, in the chemical formula 2 R 4 and R 5 each independently a branched C3 to C10 alkyl group. In some embodiments, R 4 and R 5 a branched C3 to C5 alkyl group, for example a tert-butyl group.

[0092] In chemical formula 2, R 6be attached to a position para to a hydroxy group. In this case, the substituent is attached to the position with less steric hindrance and must not inhibit the radical scavenging activity of the hydroxy group.

[0093] In embodiments, in the chemical formula 2 R 6 a linear C1 to C10 alkyl group. In some embodiments, R 6 a linear C1 to C3 alkyl group, e.g. a methyl group.

[0094] In embodiments, the radical scavenger may contain 2,6-di-tert-butyl-p-cresol of the following chemical formula 2-1.

[0095] In exemplary embodiments, the content of the radical scavenger can be in a range from 0.1 wt.% to 2 wt.%, based on the total weight of the electrolyte solution. In some embodiments, the content of the radical scavenger can be in a range from 0.1 wt.% to 1 wt.% or from 0.1 wt.% to 0.5 wt.%, based on the total weight of the electrolyte solution. In the aforementioned range, radicals generated in the electrolyte solution at high temperatures can be more effectively scavenged by the radical scavenger. This can further improve the high-temperature stability of the electrolyte solution.

[0096] In embodiments, the radical scavenger may contain a compound containing a di-tert-butylhydroxyphenyl group in an amount of 50 wt.% or more, 60 wt.% or more, 70 wt.% or more, 80 wt.% or more, or 90 wt.% or more, based on the total weight of the radical scavenger. In some embodiments, the radical scavenger may consist essentially of the compound containing a di-tert-butylhydroxyphenyl group.

[0097] In embodiments, the ratio between the content (wt%) of the phosphate-based additive and the content (wt%) of the radical scavenger may be greater than 1 and less than or equal to 50. In some embodiments, the ratio of the content of the phosphate-based additive to the content of the radical scavenger may be in a range from 2 to 20 or from 5 to 17.

[0098] In the above-mentioned range, volume expansion of the battery can be prevented by reducing gas formation while adequately maintaining the flame retardancy of the electrolyte solution.

[0099] In embodiments, the electrolyte solution may further contain an auxiliary additive. The auxiliary additive may be present in an amount of 0.01 wt% to 5 wt%, based on the total weight of the electrolyte solution. In some embodiments, the content of the auxiliary additive may be in a range of 0.1 wt% to 4 wt%.

[0100] The auxiliary additive may contain, for example, a cyclic unsaturated carbonate-based compound, a fluorine-substituted cyclic carbonate-based compound, a sultone-based compound, a cyclic sulfate-based compound, a fluorine-substituted phosphate-based compound, an oxalatoborate-based compound, etc.

[0101] The cyclic unsaturated carbonate-based compound may be a different compound than the organic solvent and may contain vinylethylene carbonate (VEC). The cyclic unsaturated carbonate-based compound may contain a double bond and may contain, for example, vinylene carbonate (VC).

[0102] The fluorine-substituted cyclic carbonate-based compound may contain fluoroethylene carbonate (FEC).

[0103] The sultone-based compound may contain 1,3-propanesultone, 1,3-propenesultone, 1,4-butanesultone, etc.

[0104] The cyclic sulfate-based compound may contain 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0105] The fluorine-substituted phosphate-based compound may contain lithium difluorophosphate (LiPO2F2). The fluorine-substituted phosphate-based compound may contain a fluorine-substituted oxalatophosphate-based compound, e.g., lithium difluorobis(oxalato)phosphate (LiPF2(C2O4)2).

[0106] The oxalatoborate-based compound may contain lithium bis(oxalato)borate (LiB(C2O4)2).

[0107] In one embodiment, the fluorine-substituted cyclic carbonate-based compound, the sultone-based compound, and the oxalatoborate-based compound may be used together as an auxiliary additive.

[0108] The auxiliary additive can be added to further improve the durability and stability of the electrode. The auxiliary additive can be added in an appropriate amount within a range that does not affect the mobility of lithium ions in the electrolyte solution. <Lithium-Sekundärbatterie>

[0109] According to embodiments of the present disclosure, a lithium secondary battery is provided that contains the electrolyte solution described above.

[0110] Fig. 1 and Fig.2 are a schematic plan view and a cross-sectional view, respectively, showing a lithium secondary battery according to embodiments. For example, Fig. 2 a cross-sectional view along a line II' of Fig. 1 in one thickness direction.

[0111] As in Fig. 1 and Fig. 2, a lithium secondary battery may include an electrode assembly including a cathode 100, an anode, and a separator 140 disposed between the cathode and the anode.

[0112] The electrode assembly may be housed in a housing 160 with the electrolyte solution according to the previously described embodiments to be impregnated therein.

[0113] The cathode 100 may include a cathode active material layer (110) formed by applying a cathode active material to a cathode current collector (105). The cathode active material may contain a compound capable of reversibly intercalating and deintercalating lithium ions.

[0114] In embodiments, the cathode active material may contain a lithium transition metal oxide. The lithium transition metal oxide may, for example, contain nickel (Ni) and, in addition, at least one of cobalt (Co) or manganese (Mn).

[0115] For example, the lithium transition metal oxide can be represented by the chemical formula 3 below. Li 1+a Ni 1-(x+y) Co x M y O2 [Chemical Formula 3]

[0116] In chemical formula 3, -0.05≤a≤0.2, 0.01≤x≤0.3, 0.01≤y≤0.3, and M can be at least selected from Mn, Mg, Sr, Ba, B, Al, Si, Ti, Zr and W.

[0117] As expressed in Chemical Formula 3, the lithium transition metal oxide can contain Ni in the highest content or molar ratio among Ni, Co, and M. Ni can essentially serve as a metal related to the performance and / or capacity of the lithium secondary battery. Ni can be contained in the largest amount among the transition metals, so that the lithium secondary battery with high capacity and high power output can be realized.

[0118] In one embodiment, in Chemical Formula 3, 0.01≤x≤0.2 and 0.01≤y≤0.2. In one embodiment, the molar ratio of Ni may be 0.7 or more, or 0.8 or more.

[0119] A slurry can be prepared by mixing and stirring the cathode active material with a binder, a conductive material, and / or a dispersant in a solvent. The slurry can be applied to the cathode current collector 105 and then dried and pressed to form the cathode 100.

[0120] The cathode current collector 105 may comprise stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof. For example, the cathode current collector 105 may comprise aluminum or an aluminum alloy.

[0121] The binder may contain an organic binder such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate or an aqueous binder such as styrene-butadiene rubber (SBR) and may be used with a thickener such as carboxymethylcellulose (CMC).

[0122] For example, a PVDF-based binder can be used as the cathode binder. In this case, the amount of binder required to form the cathode active material layer can be reduced and the amount of cathode active material can be relatively increased. This can further improve the capacity and performance of the lithium secondary battery.

[0123] The conductive material can be added to facilitate electron mobility between the active material particles. The conductive material can, for example, include a carbon-based material such as graphite, carbon black, graphene, carbon nanotubes, etc., and / or a metal-based material such as tin, tin oxide, titanium oxide, a perovskite material such as LaSrCoO3 or LaSrMnO3, etc.

[0124] The anode 130 may include an anode current collector 125 and an anode active material layer 120 formed by applying anode active material to the anode current collector 125.

[0125] As the anode active material, a material capable of adsorbing and desorbing lithium ions, as is generally known in the relevant art, can be used without particular limitation. For example, a carbon-based material such as crystalline carbon, amorphous carbon, a carbon composite, carbon fiber, etc., a lithium alloy, a silicon (Si)-based compound, or tin can be used.

[0126] Examples of amorphous carbon include hard coal, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers (MPCF), etc.

[0127] Examples of crystalline carbon include graphite-based carbon such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc. The elements contained in lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0128] The silicon-based compound may contain, for example, silicon, a silicon oxide or a silicon-carbon compound such as silicon carbide (SiC).

[0129] For example, the anode active material may be mixed and stirred with the previously described binder, conductive material, thickener, etc. in a solvent to form a slurry. The slurry may be applied to at least one surface of the anode current collector 125 and then dried and pressed to form the anode 130.

[0130] The separator 140 can be inserted between the cathode 100 and the anode 130. The separator 140 can include a porous polymer film made, for example, from a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, or the like. The separator 140 can also include a nonwoven fabric formed from a high-melting-point glass fiber, a polyethylene terephthalate fiber, etc.

[0131] In some embodiments, an area and / or volume of the anode 130 (e.g., a contact area with the separator 140) may be larger than that of the cathode 100. In this way, the lithium ions generated by the cathode 100 may be easily transferred to the anode 130 without loss, e.g., through precipitation or sedimentation.

[0132] In embodiments, an electrode cell may be defined by the cathode 100, the anode 130, and the separator 140, and a plurality of electrode cells may be stacked to form the electrode assembly 150, which may, for example, have the shape of a jelly roll. The electrode assembly 150 may be formed, for example, by winding, stacking, or folding the separator 140.

[0133] The electrode assembly 150 may be housed in the housing 160 together with the electrolyte solution according to the previously described embodiments of the present disclosure.

[0134] As in Fig.As shown in Figure 1, electrode strips (a cathode strip and an anode strip) may protrude from the cathode current collector 105 and the anode current collector 125 included in each electrode cell to one side of the housing 160. The electrode strips may be welded to one side of the housing 160 to connect to an electrode lead (a cathode lead 107 and an anode lead 127), which may be extended or exposed to the outside of the housing 160.

[0135] The lithium secondary battery can be manufactured in a cylindrical container shape, a prismatic shape, a bag shape, a coin shape, etc.

[0136] Exemplary experimental examples are proposed below to more concretely describe the present disclosure. However, the following examples are only illustrative of the present invention, and those skilled in the art will naturally understand that various changes and modifications are possible within the scope and spirit of the present invention. Such changes and modifications are properly encompassed in the appended claims. Synthesis example 1

[0137] Phenylbis(trifluoroethyl)phosphate was synthesized as a compound of chemical formula 1-1.

[0138] 100 ml of dichloromethane was measured and added to a 500 ml round-bottom flask, then cooled to 0 °C. 10 g (47.4 mmol) of phenyldichlorophosphate and 12 g (118 mmol) of triethylamine were weighed and mixed. Then, while maintaining the temperature at 0 °C in a nitrogen atmosphere, 10.4 g (104.3 mmol) of 2,2,2-trifluoroethanol was slowly added over 20 minutes and stirred at room temperature for 24 hours.

[0139] After the reaction, the organic layer was mixed and extracted once with an aqueous hydrochloric acid solution and twice with distilled water. The organic layer was then dried in vacuo to remove solvent and moisture. The resulting solution was purified using a silica gel column to obtain 11.7 g with a yield of 73%.

[0140] 1H-NMR chemical shift (500 MHz, acetone-d6), δ: 7.46-7.48 (m, 2H), 7.28-7.33 (m, 3H), 4.79-4.85 (m, 4H)

[00159] Synthesis Example 2

[0141] Diphenyl trifluoroethyl phosphate was synthesized as a compound of chemical formula 1-2.

[0142] After 100 ml of dichloromethane was added to a 500 ml round-bottom flask and cooled to 0 °C, 10 g (37.2 mmol) of diphenyl chlorophosphate and 8.3 g (81.8 mmol) of triethylamine were quantified and mixed. Then, 7.7 g (76.3 mmol) of 2,2,2-trifluoroethanol was slowly added over 20 minutes under a nitrogen atmosphere, followed by stirring at room temperature for 24 hours.

[0143] After the reaction described above, an organic layer was mixed and extracted once with an aqueous hydrochloric acid solution and twice with distilled water. The organic layer was then dried in vacuo to remove solvent and moisture. The resulting solution was purified through a silica gel column to obtain 9.89 g with a yield of 80%.

[0144] 1H-NMR chemical shift (500 MHz, acetone-d6), δ: 7.44–7.48 (m, 4H), 7.28–7.37 (m, 6H), 4.88–4.91 (m, 2H)

[00166] Synthesis Example 3

[0145] Tris(4-fluorophenyl)phosphate was synthesized as a compound of chemical formula 1-3.

[0146] After measuring 300 ml of toluene into a 500 ml round-bottom flask, 50 g (446 mmol) of 4-fluorophenol and 19.6 g (491 mmol) of sodium hydroxide were measured and mixed. The mixture was then vigorously stirred for 1.5 hours at 0 °C in a nitrogen atmosphere. Then, 20.7 g (135 mmol) of phosphorus oxychloride (POCl3) was slowly added and stirred at room temperature for 21 hours.

[0147] After the reaction described above, 200 ml of a 10% aqueous sodium hydroxide solution was added and stirred for 15 minutes, then the organic solvent layer was separated. The resulting organic solvent layer was mixed and extracted three times with distilled water, and then the organic solvent layer was dried in vacuo to remove the solvent and moisture, yielding 46.7 g with a yield of 87.8%.

[0148] 1H-NMR chemical shift (500 MHz, acetone-d6), δ: 7.32-7.38 (m, 6H), 7.18-7.26 (m, 6H) Synthesis example 4

[0149] Bis(2,2,3,3,3-pentafluoro-1-propyl)phenyl phosphate was synthesized as a compound of chemical formula 1-4.

[0150] After measuring and pouring 100 ml of tetrahydrofuran into a 500 ml round-bottom flask, the mixture is cooled to 0°C, and 10 g (66.7 mmol) of pentafluoropropanol and 1.64 g (68.3 mmol) of sodium hydride are measured and mixed. The mixture is then stirred at 0°C in a nitrogen atmosphere for 2 hours. Then, 6.9 g (32.5 mmol) of phenyl dichlorophosphate is slowly added over 10 minutes and stirred at 60°C for 24 hours.

[0151] After the reaction described above, the organic solvent was removed by cooling to room temperature and drying under reduced pressure. 100 ml of dichloromethane was added and dissolved, neutralized with an aqueous hydrogen chloride solution and an aqueous sodium hydroxide solution, and the organic layer was mixed and extracted twice with distilled water. The organic layer was dried under vacuum to remove solvent and moisture. The resulting solution was purified on a silica gel column to obtain 7.3 g with a yield of 66%.

[0152] 1H-NMR chemical shift (500 MHz, acetone-d6), δ: 7.46-7.47 (m, 2H), 7.30-7.32 (m, 3H), 4.86-4.94 (m, 4H) Synthesis example 5

[0153] Bis(2,2,3,3,4,4,4-heptafluoro-1-butyl)phenyl phosphate was synthesized as a compound of chemical formula 1-5.

[0154] After quantification and filling 100 ml of dichloromethane into a 500 ml round-bottom flask, 10 g (47.4 mmol) of phenyldichlorophosphate and 10.6 g (105 mmol) of triethylamine were quantified and mixed. Subsequently, 19.9 g (99.5 mmol) of hexafluorobutanol was slowly added over 30 minutes under a nitrogen atmosphere, and the mixture was stirred at room temperature for 72 hours.

[0155] After the reaction described above, neutralization was performed with an aqueous hydrogen chloride solution and an aqueous sodium hydroxide solution. Then, an organic layer was mixed and extracted twice with distilled water. The organic layer was dried under vacuum to remove solvent and moisture. The resulting solution was purified on a silica gel column to obtain 14.1 g with a yield of 55%.

[0156] 1H-NMR chemical shift (500 MHz, acetone-d6), δ: 7.47–7.51 (m, 2H), 7.30–7.33 (m, 3H), 4.90–4.99 (m, 4H)

[00187] Synthesis Example 6

[0157] Triphenyl phosphate was synthesized as a compound of chemical formula 1-6.

[0158] After quantification and filling a 500-mL round-bottom flask with 200 mL of dichloromethane, 20 g (213 mmol) of phenol and 22.2 g (219 mmol) of triethylamine were quantified and mixed. After vigorous stirring for 1 hour at 0°C in a nitrogen atmosphere, 10.5 g (69 mmol) of phosphorus oxychloride (POCl3) was slowly added dropwise to the reactor. The mixture was stirred for a further 18 hours at room temperature while maintaining a nitrogen atmosphere.

[0159] After mixing 100 ml of 10% NaOH aqueous solution and 100 ml of water twice with the resulting organic solvent layer and extracting, the organic solvent layer was dried in vacuo to remove solvent and moisture. The resulting solution was purified on a silica gel column to obtain 13.9 g with a yield of 62%.

[0160] 1H-NMR chemical shift (500 MHz, acetone-d6), δ: 7.44-7.19 (m, 15H).

[00194] Synthesis Example 7

[0161] Tris(trifluoroethyl)phosphate was synthesized as a compound of chemical formula 1-7.

[0162] After quantification and filling 200 mL of dichloromethane into a 500 mL round-bottom flask, 20 g (200 mmol) of 2,2,2-trifluoroethanol and 14.0 g (206 mmol) of imidazole were weighed and mixed. After vigorous stirring for 1.5 hours at 0 °C in a nitrogen atmosphere, 9.89 g (64 mmol) of phosphorus oxychloride (POCl3) was slowly added dropwise to the reactor. The mixture was stirred for 21 hours at room temperature while maintaining the nitrogen atmosphere.

[0163] After the reaction described above, 200 ml of 10 wt% NaOH was mixed to quench any remaining starting material, and an organic solvent layer was separated. The resulting organic solvent layer was mixed and extracted three times with 200 ml of water, and then the organic solvent layer was dried in vacuo to remove solvent and moisture. The resulting solution was purified using a silica gel column to obtain 11.98 g with a yield of 54%.

[0164] 1H-NMR chemical shift (500 MHz, acetone-d6), δ: 4.26-4.15 (m, 6H) Example 1(1) Preparation of the electrolyte solution

[0165] A 1M LiPF6 solution (using a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC), volume ratio EC:EMC=25:75) was prepared. Based on the total weight of the electrolyte solution, 1 wt% of fluoroethylene carbonate, 0.5 wt% of 1,3-propanesultone (PS), 0.5 wt% of 1,3-propenesultone (PRS), and 0.3 wt% of lithium bis(oxalato)borate were added to the 1M LiPF6 solution. 5 wt% of the compound synthesized in Synthesis Example 1 was added as a phosphate-based additive and 0.5 wt% of 2,6-di-tert-butyl-p-cresol (Sigma Aldrich), represented by Chemical Formula 2-1 below, was added as a radical scavenger.

[00206] (2) Preparation of lithium secondary battery samples

[0166] A cathode active material in which Li[Ni 0,6 Co 0,2 Mn 0,2 ]O2 and Li[Ni 0,8 Co 0,1 Mn 0,1]O2 were mixed in a weight ratio of 6:4, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in a weight ratio of 92:5:3 to prepare a slurry. The slurry was evenly coated on a 15 µm thick aluminum foil, vacuum dried, and pressed at 130 °C to prepare a cathode for a lithium secondary battery.

[0167] An anode slurry containing 95 wt% of an anode active material in which artificial graphite and natural graphite were mixed in a weight ratio of 7:3, 1 wt% Super-P as a conductive material, 2 wt% styrene-butadiene rubber (SBR) as a binder, and 2 wt% carboxymethyl cellulose (CMC) as a thickener was prepared. The anode slurry was evenly coated on a 15 µm thick copper foil, dried, and pressed to prepare an anode.

[0168] The previously prepared cathode and anode were cut into a predetermined size and stacked with a separator (polyethylene, thickness of 20 µm) inserted between them to form an electrode assembly, and strip portions of the cathode and anode were welded.

[0169] The electrode assembly was placed in a bag, and three sides were sealed, except for one side for electrolyte injection. The areas around the strips were included in the sealing section. The electrolyte solution prepared as above in (1) was injected through the electrolyte injection side, and then the electrolyte injection side was also sealed. Afterward, the electrode assembly was impregnated for 12 hours or more to prepare a lithium secondary battery sample. Example 2

[0170] A secondary battery sample was prepared by the same method as in Example 1, except that the compound synthesized in Synthesis Example 2 was used instead of the compound synthesized in Synthesis Example 1 to prepare the electrolyte solution. Example 3

[0171] A secondary battery sample was prepared by the same method as in Example 1, except that the compound synthesized in Synthesis Example 3 was used instead of the compound synthesized in Synthesis Example 1 to prepare the electrolyte solution. Example 4

[0172] A secondary battery sample was prepared by the same method as in Example 1, except that the compound synthesized in Synthesis Example 4 was used instead of the compound synthesized in Synthesis Example 1 to prepare the electrolyte solution. Example 5

[0173] A secondary battery sample was prepared by the same method as in Example 1, except that the compound synthesized in Synthesis Example 5 was used instead of the compound synthesized in Synthesis Example 1 to prepare the electrolyte solution. Example 6

[0174] A secondary battery sample was prepared by the same method as in Example 1, except that the compound synthesized in Synthesis Example 6 was used instead of the compound synthesized in Synthesis Example 1 to prepare the electrolyte solution. Example 7

[0175] A secondary battery sample was prepared by the same method as in Example 1, except that the compound synthesized in Synthesis Example 7 was used instead of the compound synthesized in Synthesis Example 1 to prepare the electrolyte solution. Example 8

[0176] A secondary battery sample was prepared by the same method as in Example 1, except that 1 wt% of the compound synthesized in Synthesis Example 6 was added instead of the compound synthesized in Synthesis Example 1 in the preparation of the electrolyte solution. Example 9

[0177] A secondary battery sample was prepared by the same method as in Example 1, except that 10 wt% of the compound synthesized in Synthesis Example 6 was added instead of the compound synthesized in Synthesis Example 1 in the preparation of the electrolyte solution. Example 10

[0178] A secondary battery sample was prepared by the same procedure as in Example 6, except that 0.1 wt% of the radical scavenger was added during preparation of the electrolyte solution. Example 11

[0179] A secondary battery sample was prepared by the same procedure as in Example 6, except that 0.3 wt% of the radical scavenger was added during preparation of the electrolyte solution. Example 12

[0180] A secondary battery sample was prepared by the same procedure as in Example 6, except that 0.7 wt% of the radical scavenger was added during preparation of the electrolyte solution. Comparison example 1

[0181] A secondary battery sample was prepared by the same method as in Example 1, except that the compound synthesized in Synthesis Example 6 was used instead of the compound synthesized in Synthesis Example 1 and the radical scavenger was not added in the preparation of the electrolyte solution. Comparison example 2

[0182] A secondary battery sample was prepared by the same method as in Example 1, except that the compound synthesized in Synthesis Example 7 was used instead of the compound synthesized in Synthesis Example 1 and the radical scavenger was not added in the preparation of the electrolyte solution. Comparison example 3

[0183] A secondary battery sample was prepared by the same method as in Example 1, except that 0.5 wt% of the compound synthesized in Synthesis Example 6 was added instead of the compound synthesized in Synthesis Example 1 in the preparation of the electrolyte solution. Comparison example 4

[0184] A secondary battery sample was prepared by the same method as in Example 1, except that 12 wt% of the compound synthesized in Synthesis Example 6 was added instead of the compound synthesized in Synthesis Example 1 in the preparation of the electrolyte solution. Comparison example 5

[0185] A secondary battery sample was prepared by the same procedure as in Example 1, except that 0.05 wt% of the radical scavenger was added during preparation of the electrolyte solution. Comparison example 6

[0186] A secondary battery sample was prepared by the same procedure as in Example 1, except that the compound synthesized in Synthesis Example 1 and the radical scavenger were not added during the preparation of the electrolyte solution.

[0187] Table 1 below shows the compositions of the electrolyte solution in the examples and comparative examples. The type of phosphate-based additive was expressed by the synthesis example number, and the content was given in wt% based on the total weight of the electrolyte solution. [Table 1] Phosphate-based additive radical scavengers Type (synthesis example) Content (wt%) Addition Content (wt%) Example 1 1 5 O 0,5 Example 2 2 5 O 0,5 Example 3 3 5 O 0,5 Example 4 4 5 O 0,5 Example 5 5 5 O 0,5 Example 6 6 5 O 0,5 Example 7 7 5 O 0,5 Example 8 6 1 O 0,5 Example 9 6 10 O 0,5 Example 10 6 5 O 0,1 Example 11 6 5 O 0,3 Example 12 6 5 O 0,7 Comparison example 1 6 5 X - Comparison example 2 7 5 X - Comparison example 3 6 0,5 O 0,5 Comparison example 4 6 12 O 0,5 Comparison example 5 6 5 O 0,05 Comparison example 6 - - X - Experimental example

[0188] The high-temperature storage properties of the battery samples were evaluated according to the following experimental method, and the results are shown in Table 2. (1) Measurement of the DCIR increase rate

[0189] For each of the secondary battery samples of Examples and Comparative Examples, before high-temperature storage, a C-rate was increased to 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, and 3.0C at 60% of SOC, and the endpoints of the voltages were configured as a straight line equation when a discharge was performed at each corresponding C-rate for 10 seconds, and a slope thereof was taken as the initial DCIR.

[0190] Each of the secondary battery samples of Examples and Comparative Examples was left at a temperature of 60 °C and stored at high temperature for 13 weeks, and the DCIR was measured at room temperature after completion of the high temperature storage, and a DCIR increase rate was calculated as a percentage compared to the initial DCIR. DCIR increase rate (%) = (DCIR after high-temperature storage / initial DCIR) × 100 (2) Measurement of capacity maintenance

[0191] Each of the secondary battery samples of Examples and Comparative Examples was charged at 0.5C CC / CV (4.2V, 0.05C cut-off) before high-temperature storage and then discharged at 0.5C CC (2.7V cut-off) at 25°C to measure the discharge capacity. The above cycle was performed three times to calculate an average value as the initial capacity.

[0192] As described in (1) above, the secondary battery samples of Examples and Comparative Examples were stored at 60°C for 13 weeks at high temperature. Then, after the high-temperature storage, they were discharged at a rate of 0.5C CC (2.7V cut-off) at room temperature. The discharge capacity was then measured.

[0193] Capacity retention was calculated as a percentage of discharge capacity after high-temperature storage relative to initial capacity. Capacity retention (%) = (discharge capacity after high-temperature storage / initial capacity) × 100 (3) Measurement of the thickness increase rate

[0194] For each of the secondary battery samples of the Examples and Comparative Examples, the thickness was measured at a central location before high-temperature storage. The secondary battery samples were stored at high temperature as described in (1) above, and then the thickness of the same location was measured again.

[0195] The thickness increase rate was calculated as a percentage of the battery thickness after high-temperature storage relative to the initial thickness.

[0196] Thickness increase rate (%) = (battery thickness after high temperature storage / initial thickness) × 100

[00263] [Table 2] 60°C high temperature storage properties, 13 weeks Thickness (mm) Thickness increase rate (%) Capacity maintenance (%) DCIR increase rate (%) Example 1 8,25 140 82 117 Example 2 7,44 133 83 115 Example 3 9,32 152 83 109 Example 4 7,04 128 87 110 Example 5 7,13 129 86 111 Example 6 10,24 172 87 107 Example 7 6,84 109 83 119 Example 8 9,97 164 88 108 Example 9 8,18 136 83 96 Example 10 10,95 184 85 107 Example 11 10,97 186 83 112 Example 12 8,94 150 85 114 Comparison example 1 13,4 216 85 119 Comparison example 2 11,09 179 82 124 Comparison example 3 12,55 209 83 116 Comparison example 4 10,49 176 80 117 Comparison example 5 11,86 197 85 116 Comparison example 6 14,60 238 85 116

[0197] Table 2 shows that in the secondary batteries of the examples using electrolyte solutions containing the phosphate-based additive and the free radical scavenger, internal gas generation was reduced even after high-temperature storage, thereby reducing the battery thickness increase ratio. Furthermore, even during high-temperature storage, a low resistance increase rate and high capacity retention were provided, and the original battery properties were maintained.

[0198] In the secondary batteries of Comparative Examples 1 and 2, which did not contain a radical scavenger, the side reactions in the electrolyte solution were not sufficiently suppressed at high temperatures, and the battery expanded due to gas formation, resulting in an increase in battery thickness. Furthermore, the resistance increase rate increased during high-temperature storage, leading to a deterioration in battery performance.

[0199] In the batteries of Comparative Example 3, which contained the electrolyte solution with the phosphate-based additive in an amount of less than 1 wt%, and Comparative Example 4, which contained the electrolyte solution with the phosphate-based additive in an amount of more than 10 wt%, the side reactions in the electrolyte solution were not effectively suppressed.

[0200] For the secondary battery of Comparative Example 6, which did not contain the phosphate-based additive or the radical scavenger, the battery thickness increase ratio during high-temperature storage was the highest. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] KR 10-2023-0075639

[0001]

Claims

[1] An electrolyte solution for a lithium secondary battery, comprising: a lithium salt; an organic solvent; a phosphate-based additive containing a compound represented by chemical formula 1; and a radical scavenger containing a compound represented by the chemical formula 2, wherein the content of the phosphate-based additive is in a range of 1 wt% to 10 wt%, based on the total weight of the electrolyte solution: where in the chemical formula 1 R 1 to R 3 each independently represents a C6 to C18 aryl group, a halogenated C6 to C18 aryl group, a C1 to C10 alkyl group, a halogenated C1 to C10 alkyl group or a C2 to C10 alkenyl group, where in the chemical formula 2 R 4 to R 6each independently represents a C1 to C10 alkyl group, a C3 to C12 cycloalkyl group, a C2 to C10 alkenyl group or a C6 to C18 aryl group. [2] The electrolytic solution for a lithium secondary battery according to claim 1, wherein in the chemical formula 1, R 1 and R 2 are equal, and R 1 and R 2 each not equal to R 3 are, R 1 and R 3 are equal, and R 1 and R 3 each not equal to R 2 are, or R 1 , R 2 and R 3 are not equal to each other. [3] The electrolyte solution for a lithium secondary battery according to claim 1 or 2, wherein in the chemical formula 1, R 1 and R 2each independently represents a C6 to C18 aryl group, a halogenated C6 to C18 aryl group, a C1 to C10 alkyl group, a halogenated C1 to C10 alkyl group or a C2 to C10 alkyl group, R 3 a C6 to C18 aryl group, a halogenated C6 to C18 aryl group or a halogenated C1 to C10 alkyl group, and at least one of R 1 and R 2 not the same as R 3 is. [4] An electrolyte solution for a lithium secondary battery according to any one of claims 1 to 3, wherein in the chemical formula 1 R 1 a C6 to C18 aryl group or a halogenated C6 to C18 aryl group and R 2 is a halogenated C1 to C5 alkyl group. [5] An electrolyte solution for a lithium secondary battery according to any one of claims 1 to 4, wherein in the chemical formula 1 R 1 a phenyl group or a fluorophenyl group, R 2a trifluoromethyl group, a 2,2,2-trifluoroethyl group, a 3,3,3-trifluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group or a 2,2,3,3,4,4,4-heptafluorobutyl group, and R 3 a phenyl group, a fluorophenyl group, a trifluoromethyl group, a 2,2,2-trifluoroethyl group, a 3,3,3-trifluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group or a 2,2,3,3,4,4,4-heptafluorobutyl group. [6] The electrolytic solution for a lithium secondary battery according to any one of claims 1 to 5, wherein the content of the phosphate-based additive is in a range of 5 wt% to 10 wt% based on the total weight of the electrolytic solution. [7] An electrolyte solution for a lithium secondary battery according to any one of claims 1 to 6, wherein in the chemical formula 2 R 4 and R 5 each independently represents a branched C3 to C10 alkyl group. [8] An electrolyte solution for a lithium secondary battery according to any one of claims 1 to 7, wherein in the chemical formula 2 R 6 is a linear C1 to C10 alkyl group. [9] The electrolyte solution for a lithium secondary battery according to any one of claims 1 to 8, wherein the radical scavenger contains 2,6-di-tert-butyl-p-cresol. [10] The electrolytic solution for a lithium secondary battery according to any one of claims 1 to 9, wherein the content of the radical scavenger is in a range of 0.1 wt% to 2 wt% based on the total weight of the electrolytic solution. [11] The electrolytic solution for a lithium secondary battery according to any one of claims 1 to 10, wherein a ratio of the content of the phosphate-based additive to the content of the radical scavenger, based on the total weight of the electrolytic solution, is greater than 1 and less than or equal to 50. [12] The electrolytic solution for a lithium secondary battery according to any one of claims 1 to 11, wherein the ratio of the content of the phosphate-based additive to the content of the radical scavenger, based on the total weight of the electrolytic solution, is in a range of 2 to 20. [13] The electrolytic solution for a lithium secondary battery according to any one of claims 1 to 12, further comprising at least one auxiliary additive selected from the group consisting of a cyclic unsaturated carbonate-based compound, a fluorine-substituted cyclic carbonate-based compound, a sultone-based compound, a cyclic sulfate-based compound, a fluorine-substituted phosphate-based compound, and an oxalatoborate-based compound. [14] The electrolytic solution for a lithium secondary battery according to claim 13, wherein the auxiliary additive is contained in an amount of 0.01 wt% to 5 wt% based on the total weight of the electrolytic solution. [15] Lithium secondary battery, comprising: a housing; an electrode assembly housed in the housing, comprising a cathode and an anode opposite the cathode; and the electrolytic solution for a lithium secondary battery according to any one of claims 1 to 14, which is housed in the casing together with the electrode assembly.

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