Electrolyte for lithium secondary battery and lithium secondary battery comprising the same

Abstract

An electrolyte for a lithium secondary battery and a lithium secondary battery are provided. The electrolyte for the lithium secondary battery comprises a butyrolactone compound containing at least one alkenyl group and a lithium salt. The lithium secondary battery includes: an electrode assembly containing a positive electrode and a negative electrode; and the electrolyte for the lithium secondary battery.

Description

Cross-reference to related applications and priority claims

[0001] This application claims priority to Korean Patent Application No. 10-2024-0199294, filed on December 27, 2024, the entire disclosure of which is incorporated herein by reference. Technical Field

[0002] This disclosure relates to batteries such as lithium secondary batteries. Background Technology

[0003] Rechargeable batteries have been widely used as power sources for mobile electronic devices such as cameras, mobile phones, and laptops. In recent years, battery packs, including rechargeable batteries, have been developed and applied to power environmentally friendly vehicles such as all-battery-powered electric vehicles and hybrid vehicles. Summary of the Invention

[0004] This disclosure relates to the technical features of secondary batteries, including the composition of an electrolyte for lithium secondary batteries, the electrolyte comprising a butyrolactone-based compound and an electrolyte salt.

[0005] The technical features of this disclosure can be implemented in a variety of applications to provide an electrolyte with improved properties at high temperatures.

[0006] The technical features disclosed herein can also be used to provide a lithium secondary battery with improved electrochemical storage characteristics at high temperatures.

[0007] According to an exemplary embodiment of this disclosure, the electrolyte for a lithium secondary battery may include: a butyrolactone compound containing at least one alkenyl group; and a lithium salt.

[0008] In some embodiments, the butyrolactone-based compound may include a γ-butyrolactone-based compound.

[0009] In some embodiments, the butyrolactone compound may also include at least one alkyl group.

[0010] In some embodiments, the butyrolactone compound may be represented by chemical formula 1.

[0011] [Chemical Formula 1]

[0012]

[0013] In chemical formula 1, R1 to R6 can each be hydrogen, substituted or unsubstituted C1-C. 10 Alkyl, or substituted or unsubstituted C2-C 10 Alkenyl group, and at least one of R1 to R6 may be a substituted or unsubstituted C2-C group.10 Alkenyl group.

[0014] In some embodiments, at least one of R1 to R6 may be a substituted or unsubstituted C1-C6 alkyl group.

[0015] In some embodiments, one or both of R1 to R6 may be substituted or unsubstituted C1-C6 alkyl groups, and one of the remaining groups may be substituted or unsubstituted C2-C6 alkyl groups. 10 Alkenyl group.

[0016] In some embodiments, R1 to R6 may each be independently hydrogen, substituted or unsubstituted C1-C6 alkyl, or substituted or unsubstituted C2-C6 alkenyl, and at least one of R1 to R6 may be substituted or unsubstituted C2-C6 alkenyl.

[0017] In some embodiments, R1 to R6 may each be independently hydrogen, substituted or unsubstituted C1-C4 alkyl, or substituted or unsubstituted C2-C4 alkenyl, and at least one of R1 to R6 may be substituted or unsubstituted C2-C4 alkenyl.

[0018] In some embodiments, at least one of R1 and R2 may be substituted or unsubstituted C2-C. 10 Alkenyl group.

[0019] In some implementations, one of R1 and R2 may be substituted or unsubstituted C1-C. 10 Alkyl group, and the other may be a substituted or unsubstituted C2-C group. 10 Alkenyl group.

[0020] In some embodiments, the butyrolactone compound may include compounds represented by any one of chemical formulas 2-1 to 2-3.

[0021] [Chemical Formula 2-1]

[0022]

[0023] [Chemical Formula 2-2]

[0024]

[0025] [Chemical Formula 2-3]

[0026]

[0027] In some embodiments, the content of butyrolactone compounds may be greater than 0 wt% and less than 10 wt% based on the total weight of the electrolyte.

[0028] In some embodiments, the electrolyte for a lithium secondary battery may also include an organic solvent. The organic solvent may include at least one selected from carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, or aprotic solvents.

[0029] In some embodiments, the electrolyte for lithium secondary batteries may further include at least one auxiliary additive selected from cyclic carbonate compounds, fluorine-containing carbonate compounds, lithium phosphate compounds, sultone compounds, borate compounds, sulfate compounds, or sulfite compounds.

[0030] In some embodiments, the content of auxiliary additives may range from 0.01 wt% to 5 wt% based on the total weight of the electrolyte.

[0031] A lithium secondary battery may include: an electrode assembly comprising a positive electrode and a negative electrode; and the electrolyte described above for a lithium secondary battery.

[0032] In some embodiments, the positive electrode may comprise a positive electrode active material including lithium metal oxide particles having a single particle structure.

[0033] In some embodiments, the nickel content in the lithium metal oxide particles can be in the range of 50 mol% to 70 mol% based on the total molar number of elements other than lithium and oxygen in the lithium metal oxide particles.

[0034] In some implementations, the operating voltage of the lithium secondary battery can be from 4.35V to 4.5V.

[0035] In some embodiments, the negative electrode surface may include a solid electrolyte interphase (SEI) film, and the SEI film may be formed from an electrolyte for a lithium secondary battery.

[0036] According to some exemplary embodiments, lithium secondary batteries may include additives in the electrolyte to improve high-temperature storage performance under high-pressure environments.

[0037] According to an exemplary embodiment, even after high-temperature storage, the resistance increase ratio and thickness increase ratio of the lithium secondary battery can be reduced during high-voltage operation. Therefore, the energy efficiency, stability, and lifespan characteristics of the lithium secondary battery can be improved.

[0038] According to this disclosure, the electrolyte for lithium secondary batteries and the lithium secondary batteries themselves can be widely used in green technology fields that utilize batteries, such as electric vehicles, battery charging stations, solar power generation, and wind power generation. According to this disclosure, lithium secondary batteries can be used in environmentally friendly electric vehicles and hybrid vehicles to prevent climate change by suppressing air pollution and / or greenhouse gas emissions. Attached Figure Description

[0039] Figure 1 and Figure 2 These are a plan view and a cross-sectional view of a lithium secondary battery according to an exemplary embodiment. Detailed Implementation

[0040] Examples of secondary batteries include lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among these, lithium-ion batteries are being actively developed and widely used due to their high operating voltage, high energy density per unit weight, high charging rate, and compact size.

[0041] A lithium secondary battery may include an electrode assembly and an electrolyte immersed in the electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator (membrane). A lithium secondary battery may also include a casing, for example, a pouch-shaped casing, for housing the electrode assembly and the electrolyte.

[0042] As the applications of lithium-ion batteries expand, there is a growing demand for longer lifespans, higher capacity, and improved operational stability. Therefore, lithium-ion batteries that can provide uniform power and capacity even during repeated charge-discharge cycles are being developed.

[0043] However, with repeated charge and discharge cycles, power and capacity may decrease due to surface damage, for example, to nickel-based lithium metal oxide particles used as positive electrode active materials, and side reactions between the nickel-based lithium metal oxide and the electrolyte may occur. Furthermore, battery stability may deteriorate in harsh environments such as high or low temperatures.

[0044] The technology disclosed herein can be used to develop electrolytes for lithium secondary batteries in a variety of applications, achieving stable high-voltage and high-temperature storage performance.

[0045] According to an exemplary embodiment, the electrolyte for a lithium secondary battery may include a butyrolactone compound containing at least one alkenyl group and a lithium salt. The electrolyte may be a liquid electrolyte or a semi-solid electrolyte, and the semi-solid electrolyte may include a gel-polymer electrolyte.

[0046] In some embodiments, butyrolactone compounds may be present as electrolyte additives.

[0047] In some implementations, the concentration of the additive may be greater than 0 wt% and less than 10 wt% based on the total weight of the electrolyte.

[0048] In an exemplary embodiment, a lithium secondary battery may include: an electrode assembly comprising a positive electrode and a negative electrode; and an electrolyte for the lithium secondary battery. For example, the electrode assembly may include repeatedly stacked positive and negative electrodes, and the electrolyte may immerse the electrode assembly.

[0049] In some embodiments, the surface of the negative electrode may include a solid electrolyte interphase (SEI) film. The SEI film can be generated from an electrolyte used in lithium-ion secondary batteries. The SEI film may include moiety derived from compounds in the electrolyte. For example, the SEI film may include functional groups derived from additives. This improves the high-voltage, high-temperature storage performance of the lithium-ion secondary battery.

[0050] The term "high voltage" as used in this article can refer to a battery driving voltage or operating voltage in the range of 4.3V to 4.7V or in the range of 4.35V to 4.5V.

[0051] The term "A-based compound" as used in this article can refer to compounds containing the functional group A or its derivatives.

[0052] As used herein, the term "substituted or unsubstituted" refers to, for example, substitution with at least one group selected from: deuterium, halogen, cyano, nitro, amino, silyl group, oxygen, thio, sulfinyl, sulfonyl, carbonyl, ester, boron, phosphine oxide group, phosphinesulfide group, alkyl (e.g., C1-C) 60 Alkyl, C1-C 10 Alkyl), alkenyl (e.g., C2-C) 60 alkenyl, C2-C 10 alkenyl), alkynyl (e.g., C2-C) 60 alkynyl group, C2-C 10 alkynyl), alkoxy (e.g., C1-C) 60 Alkoxy, C1-C 10 Alkoxy, hydrocarbon cyclic, aryl (e.g., C6-C)60 Aryl groups), and heterocyclic groups (e.g., C1-C). 60 (Heterocyclic groups), or those not substituted by the aforementioned groups. For example, "substituted alkyl" can refer to an alkyl group in which at least one hydrogen atom is substituted by the aforementioned substituents, thus the substituents are further bonded to the carbon atoms of the alkyl group.

[0053] Substituents may include combinations selected from the above groups. For example, at least one hydrogen atom in the alkyl, aryl, etc., substituents may be replaced by the following groups: deuterium atom, halogen atom, cyano, nitro, amino, silyl, oxy, thio, sulfinyl, sulfonyl, carbonyl, ester, boron, phosphoxy group, phosphosulfur group, alkyl, alkenyl, alkynyl, cycloalkyl, aryl, heterocyclic group or other groups.

[0054] Among the substituents mentioned above, polyvalent substituents such as amino, phosphorus sulfide, phosphoroxy group, sulfinyl, sulfonyl, oxygen, carbonyl, and ester groups can be C1-C2. 10 Alkyl, C1-C 10 alkenyl, C1-C 10 alkynyl or C6-C 10 Aryl substitution.

[0055] The term "substituted or unsubstituted C" used in this article a -C b In "Y-based", C a -C b This refers to the number of carbons in the unsubstituted Y group, and may include the number of carbons without substituents.

[0056] Alkyl groups refer to monovalent hydrocarbon groups that have had one hydrogen atom removed from a straight-chain or branched hydrocarbon group. For example, alkyl groups can include methyl, ethyl, propyl, sec-butyl, tert-butyl, isobutyl, pentyl, neopentyl, 2-ethylbutyl, 3,3-dimethylbutyl, hexyl, heptyl, octyl, etc.

[0057] Alkenyl refers to a monovalent unsaturated hydrocarbon group that has had one hydrogen atom removed from a straight-chain or branched hydrocarbon group and contains a carbon-carbon double bond. For example, alkenyl can include vinyl (vinyl group), propenyl, 1-butenyl, 2-butenyl, pentenyl, neopentenyl, hexenyl, 2-methylpropenyl, 3-methylbutenyl, 3,3-dimethylpentenyl, etc.

[0058] The embodiments of this disclosure will be described in detail below with reference to the examples and accompanying drawings. However, the disclosed embodiments are merely examples, and this disclosure is not limited to these specific embodiments.

[0059] According to an embodiment, the electrolyte for a lithium secondary battery may include a butyrolactone compound containing at least one alkenyl group.

[0060] In some embodiments, the alkenyl group may be a substituted or unsubstituted C2-C group. 10 Alkenyl, substituted or unsubstituted C2-C6 alkenyl, or substituted or unsubstituted C2-C4 alkenyl.

[0061] For example, using butyrolactone compounds containing at least one alkenyl group, a solid electrolyte interphase (SEI) film can be readily formed on the electrode active material due to the reactivity of the alkenyl group during high-voltage charge / discharge. Furthermore, films containing alkenyl-based double bonds can be formed, enabling the negative electrode to operate stably under high voltage.

[0062] For example, a solid electrolyte interfacial film can be formed on the surface of the negative electrode.

[0063] In some embodiments, the butyrolactone-based compound may include a γ-butyrolactone compound.

[0064] In some embodiments, the butyrolactone compound may further include at least one alkyl group. The alkyl group may be substituted or unsubstituted C1-C. 10 Alkyl, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C1 or C2 alkyl, or substituted or unsubstituted methyl.

[0065] In some embodiments, the butyrolactone compound may be represented by chemical formula 1.

[0066] [Chemical Formula 1]

[0067]

[0068] In chemical formula 1, R1 to R6 can each be hydrogen, substituted or unsubstituted C1-C. 10 Alkyl, or substituted or unsubstituted C2-C 10 Alkenyl group, and at least one of R1 to R6 may be a substituted or unsubstituted C2-C group. 10 Alkenyl group.

[0069] In some embodiments, the substituted or unsubstituted C1-C of R1 to R6 10 The alkyl group may be a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted C1-C4 alkyl group, a substituted or unsubstituted C1 or C2 alkyl group, or a substituted or unsubstituted methyl group.

[0070] In some embodiments, the substituted or unsubstituted C2-C of R1 to R6 10 The alkenyl group can be a substituted or unsubstituted C2-C6 alkenyl group, a substituted or unsubstituted C2-C4 alkenyl group, or a substituted or unsubstituted vinyl group.

[0071] In some embodiments, at least one of R1 to R6 may be a substituted or unsubstituted C1-C6 alkyl group.

[0072] In some embodiments, one or both of R1 to R6 may be substituted or unsubstituted C1-C6 alkyl groups.

[0073] In some embodiments, R1 to R6 may each be independently hydrogen, substituted or unsubstituted C1-C. 10 Alkyl, or substituted or unsubstituted C2-C 10 Alkyl; and one or both of R1 to R6 may be substituted or unsubstituted C1-C6 alkyl, and one of the remaining groups may be substituted or unsubstituted C2-C6 alkyl. 10 Alkenyl group.

[0074] In some embodiments, R1 to R6 may each be independently hydrogen, substituted or unsubstituted C1-C6 alkyl, or substituted or unsubstituted C2-C6 alkenyl, and at least one of R1 to R6 may be substituted or unsubstituted C2-C6 alkenyl.

[0075] In some embodiments, R1 to R6 may each be independently hydrogen, substituted or unsubstituted C1-C4 alkyl, or substituted or unsubstituted C2-C4 alkenyl, and at least one of R1 to R6 may be substituted or unsubstituted C2-C4 alkenyl.

[0076] In some embodiments, at least one of R1 and R2 may be substituted or unsubstituted C2-C. 10 Alkenyl group.

[0077] In some implementations, one of R1 and R2 may be substituted or unsubstituted C1-C. 10 Alkyl group, and the other may be a substituted or unsubstituted C2-C group. 10 Alkenyl group.

[0078] In some embodiments, one of R1 and R2 may be a substituted or unsubstituted C1-C6 alkyl group, and the other may be a substituted or unsubstituted C2-C6 alkenyl group.

[0079] In some embodiments, one of R1 and R2 may be a substituted or unsubstituted C1-C4 alkyl group, and the other may be a substituted or unsubstituted C2-C4 alkenyl group.

[0080] In some embodiments, one of R1 and R2 may be a substituted or unsubstituted methyl group or a substituted or unsubstituted ethyl group, and the other may be a substituted or unsubstituted C2-C4 alkenyl group.

[0081] In some embodiments, R3 to R6 may each be hydrogen, or substituted or unsubstituted C1-C. 10 alkyl.

[0082] In some embodiments, R3 to R6 may each be hydrogen, or substituted or unsubstituted C1-C6 alkyl groups.

[0083] In some embodiments, R3 to R6 may each be hydrogen, or substituted or unsubstituted C1-C4 alkyl groups.

[0084] In some embodiments, R3 to R6 may each be hydrogen, substituted or unsubstituted methyl, or substituted or unsubstituted ethyl.

[0085] In some embodiments, R3 to R6 may be all hydrogen; or, one of R3 and R4 may be a substituted or unsubstituted C1-C. 10 Alkyl group, and the other is hydrogen; or, one of R5 and R6 may be a substituted or unsubstituted C1-C group. 10 Alkyl group, and the other is hydrogen.

[0086] In some embodiments, R3 to R6 may all be hydrogen; or, one of R3 and R4 may be a substituted or unsubstituted C1-C6 alkyl group and the other may be hydrogen; or, one of R5 and R6 may be a substituted or unsubstituted C1-C6 alkyl group and the other may be hydrogen.

[0087] In some embodiments, R3 to R6 may all be hydrogen; or, one of R3 and R4 may be a substituted or unsubstituted C1-C4 alkyl group and the other may be hydrogen; or, one of R5 and R6 may be a substituted or unsubstituted C1-C4 alkyl group and the other may be hydrogen.

[0088] In some embodiments, R3 to R6 may all be hydrogen; or, one of R3 and R4 may be a substituted or unsubstituted methyl group and the other may be hydrogen; or, one of R5 and R6 may be a substituted or unsubstituted methyl group and the other may be hydrogen.

[0089] In some embodiments, the butyrolactone compound may be represented by any of chemical formulas 2-1 to 2-3.

[0090] [Chemical Formula 2-1]

[0091]

[0092] [Chemical Formula 2-2]

[0093]

[0094] [Chemical Formula 2-3]

[0095]

[0096] In some embodiments, when the alkenyl-substituted butyrolactone compound is included in the electrolyte for lithium secondary batteries, a uniform and stable solid electrolyte interphase (SEI) film can be formed on the electrode surface. Therefore, the compound represented by Formula 1 can stably protect the active material, thereby improving the high-temperature storage performance of the secondary battery under high-voltage conditions. When alkyl substituents are included in addition to the alkenyl group, the above effects can be further enhanced.

[0097] For example, the SEI film can stably protect the electrode surface, thereby stabilizing the electrode interface to suppress side reactions with the electrolyte, thus suppressing the increase in battery internal resistance even during high-temperature storage.

[0098] For example, butyrolactone compounds can form an SEI film that remains structurally stable even at high temperatures, thereby suppressing side reactions on the electrode surface and also suppressing battery swelling during charging and discharging.

[0099] In some embodiments, the content of butyrolactone compounds may be greater than 0 wt% and less than 10 wt%, or in the range of 0.1 wt% to 10 wt%, based on the total weight of the electrolyte.

[0100] For example, based on the total weight of the electrolyte, the content of butyrolactone compounds can be in the range of 0.2wt% to 8wt%, 0.3wt% to 5wt%, 0.4wt% to 3wt%, 0.5wt% to 2wt%, or 0.1wt% to 2wt%.

[0101] Within the aforementioned range, a uniform and stable SEI film can be formed on the electrode surface, which can improve the high-temperature storage performance of lithium secondary batteries under high-voltage conditions.

[0102] In an exemplary embodiment, the electrolyte for a lithium secondary battery may further include at least one auxiliary additive selected from cyclic carbonate compounds, fluorocarbonate compounds, lithium phosphate compounds, sulcinolone compounds, borate ester compounds, sulfate ester compounds, or sulfite ester compounds.

[0103] When using a combination of butyrolactone-based compounds and auxiliary additives, lithium secondary batteries with improved low-temperature performance and high-temperature storage performance can be efficiently achieved.

[0104] For example, cyclic carbonate compounds may include vinylene carbonate (VC), ethylene carbonate (VEC), etc.

[0105] For example, fluorocarbonate compounds may include fluorine atoms or fluorine-containing substituents (e.g., fluorine-substituted alkyl groups, such as -CF3) bonded to at least one carbon atom in the carbonate compound.

[0106] In some embodiments, the fluorocarbonate compound may include a fluorinated cyclic carbonate compound having a cyclic structure. For example, the fluorinated cyclic carbonate compound may have a 5-7 member cyclic structure.

[0107] For example, fluorinated cyclic carbonate compounds may include fluoroethylene carbonate (FEC), etc.

[0108] For example, lithium phosphate compounds may include lithium difluorobis-oxalatophosphate, lithium difluorophosphate, or others.

[0109] In some embodiments, the sulfonyl compound may include at least one selected from alkyl sulfonyl compounds or alkenyl sulfonyl compounds.

[0110] In some embodiments, the sulfonyl compound may simultaneously include alkyl sulfonyl compounds, alkenyl sulfonyl compounds, etc.

[0111] For example, alkyl sulpholactone compounds may include 1,3-propane sulpholactone (PS), 1,4-butane sulpholactone, etc.

[0112] For example, alkenyl sultone compounds may include ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, 1-methyl-1,3-propene sultone, etc.

[0113] For example, borate compounds may include lithium bis(oxalate) borate.

[0114] In some embodiments, the sulfate compound may include a cyclic sulfate compound having a cyclic structure. The cyclic sulfate compound may have a 5-7 member cyclic structure.

[0115] For example, cyclic sulfate compounds may include 1,2-ethylene sulfate (ESA), trimethylene sulfate (TMS), 1,2-propylene sulfate, methyltrimethylene sulfate (MTMS), etc.

[0116] In some embodiments, the sulfite compound may include a cyclic sulfite compound having a cyclic structure.

[0117] For example, cyclic sulfite-based compounds may include ethyl sulfite, butyl sulfite, etc.

[0118] In some embodiments, the content of auxiliary additives may range from 0.01 wt% to 5 wt% based on the total weight of the electrolyte. For example, the content of auxiliary additives may range from 0.05 wt% to 9 wt%, 0.5 wt% to 8 wt%, 0.8 wt% to 7 wt%, 1.0 wt% to 6 wt%, 1.5 wt% to 5 wt%, or 2 wt% to 4 wt% based on the total weight of the electrolyte.

[0119] Within the aforementioned range, the durability of the SEI film can be improved without reducing the functionality of the butyrolactone-based compound. Therefore, the high-temperature storage performance of lithium-ion batteries under high voltage can be further improved.

[0120] For example, the secondary battery or electrolyte may include an organic solvent. The organic solvent may include an organic compound that has sufficient solubility for lithium salts, additives, and auxiliary additives and does not react within the lithium secondary battery. In this case, the electrolyte may be provided in the form of a non-aqueous electrolyte (including the organic solvent).

[0121] In some embodiments, the content of organic solvent may be at least 50 wt%, at least 60 wt%, or at least 70 wt%, based on the total weight of the electrolyte.

[0122] In some embodiments, the organic solvent may include at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, or aprotic solvents.

[0123] In some embodiments, the organic solvent may include a carbonate solvent, which may include linear carbonate solvents and / or cyclic carbonate solvents.

[0124] For example, linear carbonate solvents may include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, or others.

[0125] For example, cyclic carbonate solvents may include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, or others.

[0126] In some embodiments, the volume-based content of linear carbonate solvent in the organic solvent may be higher than the volume-based content of cyclic carbonate solvent.

[0127] In some embodiments, the volume ratio of the cyclic carbonate solvent to the linear carbonate solvent in the organic solvent can be in the range of 1 / 9 to 1. For example, the volume ratio can be in the range of 1 / 9 to 2 / 3, 1 / 6 to 2 / 3, or 1 / 4 to 2 / 3. Within the above ranges, the high-temperature storage performance and low-temperature performance of the lithium secondary battery can be further improved.

[0128] For example, the ester solvent may include at least one of methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), gamma-butyrolactone (GBL), decanolide, valerolactone, mevalonolactone, or caprolactone.

[0129] For example, the ether-based solvent may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), or 2-methyltetrahydrofuran.

[0130] For example, ketone solvents may include cyclohexanone, etc.

[0131] For example, alcohol-based solvents may include at least one of ethanol or isopropanol.

[0132] For example, aprotic solvents may include nitrile solvents, amide solvents (such as dimethylformamide), dioxolane solvents (such as 1,3-dioxolane), sulfolane solvents, or at least one of the following.

[0133] In some implementations, the electrolyte may include a lithium salt.

[0134] Lithium salts can be represented as Li + X - Its anion (X - Examples include F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - 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 - , or others.

[0135] In some embodiments, the lithium salt may include those selected from LiPF6, LiClO4, LiBF4, LiFSI, LiTFSI, LiSO3CF3, LiBOB, LiFOB, LiDFOB, LiDFBP, LiTFOP, LiPO2F2, LiCl, LiBr, LiI, and LiB. 10 Cl 10 At least one of LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN, or LiC(CF3SO2)3.

[0136] In one embodiment, the lithium salt may include at least one selected from LiPF6, LiFSI, or LiTFSI.

[0137] In some embodiments, the concentration of the lithium salt in the organic solvent can be 0.01M-5M, 0.01M-4M, 0.5M-3M, or 0.5M-2M. Within these concentration ranges, the migration of lithium ions and / or electrons during the charging and discharging of the lithium secondary battery can be accelerated.

[0138] Figure 1 and Figure 2 The figures shown are a plan view and a cross-sectional view of a lithium secondary battery according to an exemplary embodiment. Figure 2 For along Figure 1 A cross-sectional view cut off by the I-I' line.

[0139] refer to Figure 1 and Figure 2 The lithium secondary battery may include an electrode assembly 150, which includes a positive electrode 100 and a negative electrode 130; and the electrode assembly may also include a separator 140, a solid electrolyte layer or a semi-solid electrolyte layer sandwiched between the positive electrode and the negative electrode.

[0140] For example, electrode assembly 150 may include repeatedly stacked positive electrode 100 and negative electrode 130, and electrode assembly 150 may be housed in housing 160 and immersed in electrolyte according to the above embodiment.

[0141] The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110 disposed on at least one surface of the positive electrode current collector 105.

[0142] For example, the positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive electrode current collector may also include aluminum or stainless steel with a surface treated with carbon, nickel, titanium, or silver. The thickness of the positive electrode current collector may be from 10 μm to 50 μm, but is not limited thereto.

[0143] For example, positive electrode active materials may include compounds capable of reversibly inserting and deintercalating lithium ions.

[0144] In some embodiments, the positive electrode 100 may include a positive electrode active material containing a lithium metal oxide. The lithium metal oxide may also include at least one of nickel (Ni), cobalt (Co), manganese (Mn), or aluminum (Al).

[0145] In an exemplary embodiment, the nickel content in the lithium metal oxide, excluding lithium and oxygen, may be in the range of 50 mol% to 70 mol%. In some embodiments, the nickel content in the lithium metal oxide, excluding lithium and oxygen, may be in the range of 55 mol% to 65 mol%.

[0146] Within the aforementioned range, a positive electrode with improved stability can be provided without reducing its capacity.

[0147] If the nickel content exceeds 70 mol%, the stability of the crystal structure of lithium metal oxide may decrease during battery charging and discharging, thereby reducing battery life characteristics.

[0148] If the nickel content is less than 50 mol%, the capacity of the positive electrode may be excessively reduced, and the energy efficiency of the battery may also be reduced.

[0149] As described herein, unless otherwise defined, “content” can be the total number of moles of various metals contained in the bulk composition of the entire particle of lithium metal oxide.

[0150] In some embodiments, the positive electrode active material may include lithium metal oxide particles having the structure shown in Formula 3.

[0151] [Chemical Formula 3]

[0152] Li x Ni a M b O 2+z

[0153] In chemical formula 3, 0.9 ≤ x ≤ 1.2, 0.5 ≤ a ≤ 0.9, 0.01 ≤ b ≤ 0.4, and -0.5 ≤ z ≤ 0.1. As mentioned above, M may include Co, Mn, and / or Al.

[0154] The chemical structure represented by Formula 3 can indicate the bonding relationships contained in the layered or crystalline structure of the cathode active material, and does not exclude other additional elements. For example, in Formula 3, M can include Co and / or Mn, and Co and / or Mn can be used together with Ni as the main active elements of the cathode active material. Formula 3 is used to express the bonding relationships of the main active elements and should be understood as a chemical formula that includes the introduction and substitution of additional elements.

[0155] In one embodiment, in addition to the main active element, auxiliary elements may be added to enhance the chemical stability of the positive electrode active material or the layered / crystalline structure. The auxiliary elements may be incorporated into the layered / crystalline structure to form bonds; this should also be understood as being included in the chemical structure of Formula 3.

[0156] The auxiliary element may include at least one selected from Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. The auxiliary element can serve as an auxiliary active element, contributing to the capacity / power activity of the positive electrode active material.

[0157] For example, lithium metal oxides may include layered or crystalline structures represented by chemical formula 3-1.

[0158] [Chemical Formula 3-1]

[0159] Li x Ni a M1 b1 M2 b2 O 2+z

[0160] In chemical formula 3-1, M1 may include Co, Mn and / or Al. M2 may include the aforementioned auxiliary elements. In chemical formula 3-1, 0.9≤x≤1.2, 0.5≤a≤0.9, 0.01≤b1+b2≤0.5, and -0.5≤z≤0.1.

[0161] In some embodiments, the lithium metal oxide may further include coating elements or doping elements. For example, elements that are substantially the same as or similar to the auxiliary elements described above may be used as coating elements or doping elements. For example, the elements described above may be used alone, or two or more of them may be used in combination as coating elements or doping elements.

[0162] The coating or doping elements may be present on the surface of the lithium metal oxide particles or may penetrate the surface of the lithium metal oxide particles to be contained in the bonding structure represented by chemical formula 3 or chemical formula 3-1.

[0163] Lithium metal oxide particles can have a single particle structure or a secondary particle structure.

[0164] In some implementations, the lithium metal oxide particles may have a single-particle structure. The term "single-particle structure" as used herein is intended to exclude secondary particles formed by the aggregation of multiple primary particles (e.g., more than 10 particles) into a single particle.

[0165] For example, lithium metal oxide particles may consist primarily of particles with a single particle structure or a single particle shape, while secondary particle structures formed by the aggregation or agglomeration of primary particles can be excluded. The term "single particle structure" as used herein does not exclude, for example, a single particle structure in which 2 to 10 single particles are interconnected or attached to form a single individual or integral structure.

[0166] A single-particle structure can also include structures that combine multiple primary particles into a substantially single particle.

[0167] In one embodiment, from a crystallographic perspective, the single-particle structure of the lithium metal oxide particles has a monocrystalline structure or a polycrystalline structure.

[0168] For example, if a single particle has a single-crystal structure, then the single particle may actually consist of one single crystal. If a single particle has a polycrystalline structure, that single particle may include two or more single crystals.

[0169] For example, single-crystal and polycrystalline structures can be distinguished based on ion images obtained by analyzing particle cross-sections using focused ion beam (FIB). For instance, if a particle has a polycrystalline structure, two or more single crystals may be observed in the FIB analysis image due to differences in crystal orientation. For example, although a single particle may be observed in a scanning electron microscope (SEM) cross-sectional image, the particle may contain two or more crystals in the FIB analysis image.

[0170] In an exemplary embodiment, in crystal orientation analysis of cross-sectional images of lithium metal oxide particles obtained using FIB, the average particle diameter along the major axis can be 1 μm or greater. For example, in crystal orientation analysis of 10 or more cross-sectional images of lithium metal oxide particles obtained using FIB, the average particle diameter along the major axis can be in the range of 1 μm to 5 μm.

[0171] For example, a positive electrode slurry is prepared by mixing the positive electrode active material in a solvent. The positive electrode slurry is coated onto a positive electrode current collector, then dried and pressed to form a positive electrode active material layer 110.

[0172] Coating processes can be carried out through methods such as gravure coating, slot die coating, multi-layer simultaneous coating, embossing, doctor blade coating, dip coating, bar coating, and casting, but are not limited to these.

[0173] The positive electrode active material layer 110 may also include a binder, and may optionally also include conductive materials, thickeners, etc.

[0174] Non-limiting examples of solvents used in the preparation of the positive electrode active material layer 110 include: N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0175] The binder may include: polyvinylidene fluoride (PVDF), vinylidene fluoride-co-hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, acrylonitrile butadiene rubber (NBR), poly(butadiene) rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, the PVDF-based binder can be used as a positive electrode binder.

[0176] Conductive materials can be added to enhance the conductivity and / or lithium-ion or electron mobility of the positive electrode active material layer 110. For example, conductive materials may include carbon-based conductive materials (such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), carbon fiber, etc.), and / or metal-based conductive materials (such as tin, tin oxide, titanium oxide), perovskite materials (such as LaSrCoO3 and LaSrMnO3), etc.

[0177] The positive electrode active material layer 110 may further include a thickening agent and / or a dispersing agent, etc. For example, the positive electrode active material layer 110 may include a thickening agent, such as carboxymethyl cellulose (CMC).

[0178] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 provided on at least one surface of the negative electrode current collector 125.

[0179] For example, non-limiting examples of the negative electrode current collector 125 include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, etc. The thickness of the negative electrode current collector may be in the range of 10 μm to 50 μm, but is not limited thereto.

[0180] The negative electrode active material layer 120 may include a negative electrode active material. A material capable of adsorbing and desorbing lithium ions may be used as the negative electrode active material. For example, the negative electrode active material may be a carbon-based material (such as crystalline carbon, amorphous carbon, carbon composite material, carbon fiber, etc.), lithium metal, lithium alloy, a silicon (Si)-containing material, or a tin (Sn)-containing material, etc.

[0181] Examples of amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbead (MCMB), pitch-based carbon fiber (MPCF), etc.

[0182] Examples of crystalline carbon include graphite-based carbon, such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0183] The lithium metal may be pure lithium metal or lithium metal formed with a protective layer to inhibit dendrite growth. In one embodiment, a lithium metal-containing layer deposited or coated on the negative electrode current collector 125 may serve as the negative electrode active material layer 120. In one embodiment, a lithium thin film layer may also serve as the negative electrode active material layer 120.

[0184] Elements included in the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0185] The silicon-containing material may provide increased capacity characteristics. The silicon-containing material may include silicon, SiO x (0 < x < 2), metal-doped SiO x (0 < x < 2), silicon-carbon composite material, etc. The metal may include lithium and / or magnesium, and the metal-doped SiO x (0 < x < 2) may include metal silicate.

[0186] For example, negative electrode active materials can be mixed in a solvent to prepare a negative electrode slurry. The negative electrode slurry can be coated / deposited onto the negative electrode current collector 125, then dried and pressed to form a negative electrode active material layer 120.

[0187] Coating processes can be carried out through methods such as gravure coating, slot die coating, multi-layer simultaneous die coating, embossing, doctor blade coating, dip coating, bar coating, and casting, but are not limited to these.

[0188] The negative electrode active material layer 120 may also include a binder, and may optionally also include conductive materials, thickeners, etc.

[0189] In some embodiments, the negative electrode 130 may include a negative electrode active material layer 120 in the form of lithium metal formed by a deposition / coating process.

[0190] Non-limiting examples of solvents for the negative electrode active material layer 120 include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, tert-butanol, or others.

[0191] The materials mentioned above used to form the positive electrode can also be used as binders, conductive materials, and thickeners to form the negative electrode.

[0192] In some embodiments, the negative electrode binder may include styrene-butadiene rubber (SBR) based binder, carboxymethyl cellulose (CMC), polyacrylic acid-based binder, poly(3,4-ethylenedioxythiophene) (PEDOT) based binder, etc.

[0193] The separator 140 can be sandwiched between the positive electrode 100 and the negative electrode 130. The separator 140 can maintain the ion flow between the positive and negative electrodes while preventing electrical short circuits between them. For example, the thickness of the separator 140 can be in the range of 10 μm to 20 μm, but is not limited thereto.

[0194] For example, the diaphragm 140 may include a porous polymer membrane or a porous nonwoven fabric. The porous polymer membrane may include polyolefin-based polymers, such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methyl acrylate copolymers, etc. The porous nonwoven fabric may include high-melting-point glass fibers, polyethylene terephthalate fibers, or others.

[0195] The diaphragm 140 may also include ceramic materials. For example, inorganic particles may be coated on or dispersed in the polymer membrane to improve heat resistance.

[0196] The diaphragm 140 may have a single-layer or multi-layer structure including the aforementioned polymer membrane and / or nonwoven fabric.

[0197] In an exemplary embodiment, the positive electrode 100, the negative electrode 130, and the separator 140 may be repeatedly arranged to form the electrode assembly 150. In some embodiments, the electrode assembly 150 may be a wound type, a stacked type, a Z-folded type, a stacked folded type, or others.

[0198] According to the above embodiments, the electrode assembly 150 can be housed together with the electrolyte in the casing to form a lithium secondary battery.

[0199] For example, electrode tabs (positive and negative tabs) included in each electrode unit may protrude from the positive current collector 105 and the negative current collector 125 to one side of the housing 160, respectively. The electrode tabs may be fused to one side of the housing 160 to connect to electrode pins (positive pin 107 and negative pin 127) extending or exposed outside the housing 160.

[0200] For example, bag-shaped shells, prismatic shells, cylindrical shells, coin-shaped shells, etc. can all be used as shells 160.

[0201] Lithium-ion secondary batteries can operate within a voltage range of 4.3V to 4.7V. For example, the operating voltage of a lithium-ion secondary battery can be between 4.35V and 4.5V. Therefore, the battery can operate within a high voltage range.

[0202] Exemplary experimental embodiments will be presented below to describe this disclosure in more detail. However, the following embodiments are merely illustrative of this disclosure, and those skilled in the art will understand that various substitutions and modifications can be made within the scope and spirit of this disclosure.

[0203] Example 1

[0204] Synthesis Example 1 (Synthesis of Chemical Formula 2-1): 5-vinyldihydro-5-methyl-furan-2-one (5- ethenyldihydro-5-methyl-furan-2-one)

[0205] Ethyl levulinate (8.5 mL, 60 mmol) and dichloromethane (120 mL) were added sequentially to a round-bottom flask. The mixture was cooled to 0 °C and stirred. Over 1 hour, 1 M vinyl magnesium bromide (66 mL, 66 mmol) was slowly added dropwise to the mixture while maintaining the temperature at 0 °C; the temperature was then raised to room temperature while stirring for 3 hours.

[0206] The product was then washed with a saturated aqueous solution of ammonium chloride and distilled water, and the solvent in the remaining organic layer was removed under reduced pressure. The dried product was purified by silica gel column chromatography, and the solvent was dried to give 6 g of the product as a colorless liquid (Chemical Formula 2-1).

[0207] [Chemical Formula 2-1]

[0208]

[0209] Electrolyte preparation:

[0210] Prepare a 1.0 M LiPF6 solution (including a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 20:80).

[0211] Based on the total weight (100wt%) of the electrolyte, 1.5wt% of fluoroethylene carbonate (FEC), 1.0wt% of W3, 0.5wt% of PS, 0.3wt% of PRS, 0.5wt% of ESA, and 0.3wt% of the additive shown in Formula 2-1 were added to a LiPF6 solution to prepare the electrolyte.

[0212] Manufacturing of lithium secondary batteries:

[0213] A slurry was prepared by mixing the following substances in a weight ratio of 92:5:3: LiNi, a single-particle structure (particle size: 3.5 μm) used as the positive electrode active material. 0.6 Co 0.1 Mn 0.3 O2, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder. The slurry was uniformly coated onto an aluminum foil with a thickness of 15 μm, vacuum dried at 130°C, and pressed to manufacture the positive electrode for lithium secondary batteries.

[0214] A negative electrode slurry was prepared comprising 95 wt% of a negative electrode active material (a mixture of artificial graphite and natural graphite in a weight ratio of 7:3), 1 wt% of Super-P as a conductive material, 2 wt% of styrene-butadiene rubber (SBR) as a binder, and 2 wt% of carboxymethyl cellulose (CMC) as a thickener. The negative electrode slurry was uniformly coated onto a copper foil (thickness: 15 μm), then dried and pressed to form the negative electrode.

[0215] The prepared positive and negative electrodes are cut to predetermined sizes and stacked together with a separator (polyethylene, thickness: 20 μm) sandwiched in between to form an electrode assembly. The tabs of the positive and negative electrodes are then welded on.

[0216] The electrode assembly is placed in a bag (all sides are sealed except for the electrolyte injection side). The area around the electrode tabs is included in the sealed portion. The electrolyte prepared above is injected through the electrolyte injection side, and then the electrolyte injection side is sealed. Subsequently, it is immersed for more than 12 hours to obtain a lithium secondary battery.

[0217] Example 2

[0218] Synthesis Example 2 (Synthesis of Chemical Formula 2-2): 4,5-Dimethyl-5-vinyldihydrofuran-2-one (4,5- dimethyl-5-vinyl-dihydro-furan-2-one):

[0219] Ethyl 3-methyl-4-oxopentanoate (9.7 mL, 60 mmol) and dichloromethane (120 mL) were added sequentially to a round-bottom flask. The mixture was cooled to 0 °C and stirred. 1 M vinyl zinc bromide (66 mL, 66 mmol) was slowly added dropwise to the mixture over 1 hour while maintaining the temperature at 0 °C; the mixture was then heated to room temperature while stirring for 3 hours.

[0220] The product was then washed with a saturated aqueous solution of ammonium chloride and distilled water, and the solvent in the remaining organic layer was removed under reduced pressure. The dried product was purified by silica gel column chromatography, and the solvent was dried to give 6 g of the product as a colorless liquid (Chemical Formula 2-2).

[0221] [Chemical Formula 2-2]

[0222]

[0223] Electrolyte and lithium secondary battery samples were prepared using the same method as in Example 1, except that 0.3 wt% of the additive represented by chemical formula 2-2 was used instead of the additive in Example 1.

[0224] Example 3

[0225] Synthesis Example 3 (Synthesis of Chemical Formulas 2-3): 3,5-Dimethyl-5-vinyldihydrofuran-2-one (3,5- dimethyl-5-vinyl-dihydro-furan-2-one) :

[0226] Ethyl 2-methyl-4-oxopentanoate (9.6 mL, 60 mmol) and dichloromethane (120 mL) were added sequentially to a round-bottom flask. The mixture was cooled to 0 °C and stirred. While maintaining the temperature at 0 °C, 1 M vinyl magnesium bromide (66 mL, 66 mmol) was slowly added dropwise to the mixture over 1 hour, and the temperature was raised to room temperature while stirring for 3 hours.

[0227] The product was then washed with a saturated aqueous solution of ammonium chloride and distilled water, and the solvent in the remaining organic layer was removed under reduced pressure. The dried product was purified by silica gel column chromatography, and the solvent was dried to give 6 g of the product as a colorless liquid (chemical formula 2-3).

[0228] [Chemical Formula 2-3]

[0229]

[0230] Electrolyte and lithium secondary battery samples were prepared using the same method as in Example 1, except that 0.3 wt% of the additives represented by chemical formulas 2-3 were used instead of the additives in Example 1.

[0231] Example 4

[0232] Electrolyte and lithium secondary battery samples were prepared using the same method as in Example 1, except that 0.5 wt% of the additives from Example 1 were used.

[0233] Example 5

[0234] Electrolyte and lithium secondary battery samples were prepared using the same method as in Example 1, except that 0.75 wt% of the additives from Example 1 were used.

[0235] Example 6

[0236] Electrolyte and lithium secondary battery samples were prepared using the same method as in Example 1, except that 1.0 wt% of the additives from Example 1 were used.

[0237] Comparative Example 1

[0238] Electrolyte and lithium secondary battery samples were prepared using the same method as in Example 1, except that the additives of Example 1 were not added.

[0239] Comparative Example 2

[0240] Electrolyte and lithium secondary battery samples were prepared using the same method as in Example 1, except that 0.3 wt% of the additives represented by chemical formulas 2-4 were used instead of the additives in Example 1.

[0241] [Chemical Formula 2-4]

[0242]

[0243] The composition of the electrolytes in the examples and comparative examples is shown in Table 1 below.

[0244] Table 1

[0245]

[0246] The components listed in Table 1 are as follows.

[0247] Additive 1: The compound shown in chemical formula 2-1

[0248] Additive 2: The compound shown in chemical formula 2-2

[0249] Additive 3: The compound shown in chemical formula 2-3

[0250] Additive 4: Compounds represented by chemical formula 2-4

[0251] FEC: Fluorinated vinyl carbonate

[0252] W3: Lithium difluorophosphate

[0253] PS: Propanesulfonyl lactone

[0254] PRS: Propesultone

[0255] ESA: Ethylene sulfate

[0256] The battery performance was evaluated as follows, and the results are shown in Tables 2 and 3.

[0257] Initial performance evaluation:

[0258] (1) Evaluation of initial discharge capacity

[0259] The lithium secondary batteries of the examples and comparative examples were charged at 25°C at a rate of 0.5C and a discharge rate of CC / CV (4.35V, 0.05C cutoff) and discharged at a rate of 0.5C and a discharge rate of CC (2.7V cutoff) for three charge-discharge cycles.

[0260] The discharge capacity of the third cycle is defined as the initial discharge capacity C1 of the lithium secondary battery, and the results are shown in Tables 2 and 3.

[0261] (2) Evaluation of initial resistance

[0262] For the lithium secondary batteries in the examples and comparative examples, the C-rate was increased sequentially from 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, and 3.0C at 60% state of charge (SOC), while simultaneously performing a charge-discharge cycle of 10 seconds at each C-rate. A linear equation was established using the terminal voltage point, and the slope was used as the DCIR.

[0263] Evaluation of high-temperature storage performance (60℃):

[0264] (1) Assessment of capacity retention

[0265] The lithium secondary batteries of the examples and comparative examples were charged at 25°C at a rate of 0.2C and a CC / CV (4.35V, 0.05C cutoff) and then stored in a constant temperature and humidity chamber at 60°C for 6 weeks.

[0266] The lithium secondary batteries of the examples and comparative examples, which were stored at 60°C for 6 weeks, were subjected to 0.5C rate, CC discharge (2.7V cutoff), and the discharge capacity C2 after high-temperature storage was tested.

[0267] The capacity retention rate is calculated as follows, and the results are shown in Tables 2 and 3.

[0268] Capacity retention rate (%) = (C2 / C1) × 100 (%)

[0269] (2) Assessment of capacity recovery rate

[0270] After measuring the capacity retention of the lithium secondary batteries of the examples and comparative examples as described in (1) above, they were charged at a rate of 0.5C, CC / CV (4.35V, 0.05C cutoff), discharged at a rate of 0.5C, CC (2.5V cutoff), and then the discharge capacity C3 was measured.

[0271] The capacity recovery rate is calculated as follows:

[0272] Capacity recovery rate (%) = (C3 / C1) × 100 (%)

[0273] (3) Evaluation of resistance growth rate

[0274] The lithium secondary batteries of the examples and comparative examples were charged at 25°C at a rate of 0.2C, CC / CV (4.35V, 0.05C cutoff), and then stored in a constant temperature and humidity chamber at 60°C for 6 weeks.

[0275] With a SOC of 60%, the C-rate is increased sequentially from 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, and 3.0C, while simultaneously performing a 10-second charge-discharge cycle at each C-rate. A linear equation is established using the terminal voltage point, and the slope is used as the DCIR.

[0276] The high-temperature internal resistance (DCIR) measured from the lithium secondary battery of Comparative Example 1 was set to 100 to convert the high-temperature internal resistance (DCIR) measured from the lithium secondary batteries of the Examples and Comparative Examples.

[0277] (4) Assessment of thickness growth rate

[0278] The lithium secondary batteries of the examples and comparative examples were charged at 25°C at 0.5C, CC / CV (4.35V 0.05C cutoff), and the battery thickness T1 was measured. The charged lithium secondary batteries were exposed to air at 60°C for 6 weeks (using a thermostat), and then the battery thickness T2 was measured.

[0279] The battery thickness was measured using a flat plate thickness measuring device (Mitutoyo, 543-490B). The battery thickness growth rate was calculated as follows, and the results are shown in Tables 2 and 3 below.

[0280] Battery thickness growth rate (%) = T2 / T1 × 100 (%)

[0281] Table 2

[0282]

[0283] Table 3

[0284]

[0285] Referring to Tables 1 to 3, in the lithium secondary batteries of the embodiments, both the initial performance (increased capacity, reduced DCIR) and high-temperature storage performance are comprehensively improved.

[0286] In the lithium secondary battery of Comparative Example 1, which did not use an additive including a butyrolactone compound containing at least one alkenyl group, the initial resistance was high, and the resistance growth rate and thickness growth rate also increased after high-temperature storage.

[0287] In Comparative Example 2, which used an additive including an alkenyl-free butyrolactone compound, the initial discharge capacity was slightly lower than that of Comparative Example 1, but the high-temperature storage performance was slightly improved. However, compared to the examples, in Comparative Example 2, the capacity retention and capacity recovery rates after high-temperature storage were lower, and the resistance growth rate and thickness growth rate were higher.

[0288] The above description provides only embodiments for implementing specific implementations of the disclosed technology. Modifications to the disclosed embodiments and other embodiments can be made based on this disclosure.

Claims

1. An electrolyte for lithium secondary batteries, comprising: Butyrolactone compounds, which include at least one alkenyl group; and Lithium salts.

2. The electrolyte for a lithium secondary battery according to claim 1, wherein the butyrolactone-based compound comprises a γ-butyrolactone-based compound.

3. The electrolyte for a lithium secondary battery according to claim 1, wherein the butyrolactone compound further comprises at least one alkyl group.

4. The electrolyte for a lithium secondary battery according to claim 1, wherein the butyrolactone-based compound is represented by chemical formula 1: [Chemical Formula 1] in, In chemical formula 1, R1 to R6 are each independently hydrogen, substituted or unsubstituted C1-C. 10 Alkyl, or substituted or unsubstituted C2-C 10 Alkenyl group, wherein at least one of R1 to R6 is a substituted or unsubstituted C2-C group. 10 Alkenyl group.

5. The electrolyte for a lithium secondary battery according to claim 4, wherein at least one of R1 to R6 is a substituted or unsubstituted C1-C6 alkyl group.

6. The electrolyte for a lithium secondary battery according to claim 4, wherein one or both of R1 to R6 are substituted or unsubstituted C1-C6 alkyl groups, and one of the remaining groups is a substituted or unsubstituted C2-C6 alkyl group. 10 Alkenyl group.

7. The electrolyte for a lithium secondary battery according to claim 4, wherein R1 to R6 are each independently hydrogen, substituted or unsubstituted C1-C6 alkyl, or substituted or unsubstituted C2-C6 alkenyl, and at least one of R1 to R6 is substituted or unsubstituted C2-C6 alkenyl.

8. The electrolyte for a lithium secondary battery according to claim 4, wherein R1 to R6 are each independently hydrogen, substituted or unsubstituted C1-C4 alkyl, or substituted or unsubstituted C2-C4 alkenyl, and at least one of R1 to R6 is substituted or unsubstituted C2-C4 alkenyl.

9. The electrolyte for a lithium secondary battery according to claim 4, wherein at least one of R1 and R2 is a substituted or unsubstituted C2-C. 10 Alkenyl group.

10. The electrolyte for a lithium secondary battery according to claim 4, wherein one of R1 and R2 is a substituted or unsubstituted C1-C. 10 Alkyl group, and the other is a substituted or unsubstituted C2-C group. 10 Alkenyl group.

11. The electrolyte for a lithium secondary battery according to claim 1, wherein the butyrolactone-based compound comprises a compound represented by any one of chemical formulas 2-1 to 2-3: [Chemical Formula 2-1] [Chemical Formula 2-2] [Chemical Formula 2-3] 。 12. The electrolyte for a lithium secondary battery according to claim 1, wherein the content of the butyrolactone compound is greater than 0 wt% and less than 10 wt% based on the total weight of the electrolyte.

13. The electrolyte for lithium secondary batteries according to claim 1, further comprising an organic solvent, in, The organic solvent includes at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, or aprotic solvents.

14. The electrolyte for lithium secondary batteries according to claim 1 further comprises at least one auxiliary additive selected from cyclic carbonate compounds, fluorocarbon compounds, lithium phosphate compounds, sulfonyl lactone compounds, borate compounds, sulfate compounds, or sulfite compounds.

15. The electrolyte for a lithium secondary battery according to claim 14, wherein the content of the auxiliary additive is in the range of 0.01 wt% to 5 wt% based on the total weight of the electrolyte.

16. A lithium secondary battery, comprising: An electrode assembly, comprising a positive electrode and a negative electrode; and The electrolyte for lithium secondary batteries according to claim 1.

17. The lithium secondary battery according to claim 16, wherein the positive electrode comprises a positive electrode active material, the positive electrode active material comprises lithium metal oxide particles, the lithium metal oxide particles having a single particle structure.

18. The lithium secondary battery according to claim 17, wherein the nickel content in the lithium metal oxide particles is in the range of 50 mol% to 70 mol% based on the total molar number of elements other than lithium and oxygen in the lithium metal oxide particles.

19. The lithium secondary battery according to claim 16, wherein the operating voltage of the lithium secondary battery is 4.35V to 4.5V.

20. The lithium secondary battery of claim 16, wherein the surface of the negative electrode comprises a solid electrolyte interface phase film formed by the electrolyte.

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