Electrolytes for lithium secondary batteries and lithium secondary batteries containing the same

Abstract

To provide a lithium secondary battery with improved high-temperature storage performance under high-voltage conditions. [Solution] The electrolyte for lithium secondary batteries according to the embodiment of the present disclosure comprises a butyrolactone compound containing at least one alkenyl group and a lithium salt. As a result, a lithium secondary battery containing the electrolyte for lithium secondary batteries can have improved high-temperature storage performance at high voltage.

Description

Technical Field

[0001] The present disclosure relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same, and more particularly, to an electrolyte for a lithium secondary battery including an electrolyte salt, and a lithium secondary battery including the same.

Background Art

[0002] A secondary battery is a battery capable of repeated charging and discharging, and has been widely applied as a power source for portable electronic communication devices such as camcorders, mobile phones, and notebook computers as the information communication and display industries have developed. Recently, battery packs including secondary batteries have also been developed and applied as power sources for environmentally friendly vehicles such as hybrid cars.

[0003] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, nickel-metal hydride batteries, etc. Among them, lithium secondary batteries are actively researched and developed because of their high operating voltage and energy density per unit weight, and advantages in charging speed and weight reduction.

[0004] For example, a lithium secondary battery can include an electrode assembly including a positive electrode, a negative electrode, and a separator, and an electrolyte that impregnates the electrode assembly. The lithium secondary battery can further include, for example, an exterior material in the form of a pouch that houses the electrode assembly and the electrolyte.

[0005] As the application range of lithium secondary batteries expands, longer life, higher capacity, and operational stability are required. For this reason, there is a need for a lithium secondary battery that provides uniform output and capacity even when charging and discharging are repeated.

[0006] However, repeated charging and discharging can lead to a decrease in output and capacity due to surface damage to the nickel-based lithium metal oxide used as the positive electrode active material, and side reactions between the nickel-based lithium metal oxide and the electrolyte may occur. Furthermore, the stability of the battery may deteriorate under harsh environments of high or low temperatures. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] One of the objectives of this disclosure is to provide a lithium secondary battery with improved high-temperature storage performance under high-voltage conditions. [Means for solving the problem]

[0008] An electrolyte for a lithium secondary battery according to an exemplary embodiment may include a butyrolactone compound containing at least one alkenyl group and a lithium salt.

[0009] In some embodiments, the butyrolactone compound may be a gamma-butyrolactone compound.

[0010] In some embodiments, the butyrolactone compound may further contain at least one alkyl group.

[0011] In some embodiments, the butyrolactone compound can be represented by the following chemical formula 1. [ka] In chemical formula 1, R1 to R6 are each independently hydrogen, C1-C 10 A substituted or unsubstituted alkyl group, or C2-C 10 A substituted or unsubstituted alkenyl group, where at least one of R1 to R6 is C2-C 10 The alkenyl group may be substituted or unsubstituted.

[0012] In some embodiments, at least one of R1 to R6 may be a C1-C6 substituted or unsubstituted alkyl group.

[0013] In some embodiments, one or two of R1 to R6 are C1-C6 substituted or unsubstituted alkyl groups, and the remaining one is C2-C 10 The alkenyl group may be substituted or unsubstituted.

[0014] In some embodiments, R1 to R6 are each independently hydrogen, a C1-C6 substituted or unsubstituted alkyl group, or a C2-C6 substituted or unsubstituted alkenyl group, and at least one of R1 to R6 may be a C2-C6 substituted or unsubstituted alkenyl group.

[0015] In some embodiments, R1 to R6 are each independently hydrogen, a C1-C4 substituted or unsubstituted alkyl group, or a C2-C4 substituted or unsubstituted alkenyl group, and at least one of R1 to R6 may be a C2-C4 substituted or unsubstituted alkenyl group.

[0016] In some embodiments, at least one of R1 and R2 is C2-C 10 The alkenyl group may be substituted or unsubstituted.

[0017] In some embodiments, either R1 or R2 is C1-C 10 The other is a substituted or unsubstituted alkyl group, and the other is C2-C 10 The alkenyl group may be substituted or unsubstituted.

[0018] In some embodiments, the compound represented by chemical formula 1 may include any one of the following compounds represented by chemical formulas 2-1 to 2-3. [ka] [ka] [ka]

[0019] In some embodiments, the content of the butyrolactone compound may be greater than 0% by weight and 10% by weight or less relative to the total weight of the electrolyte.

[0020] In some embodiments, the electrolyte for the lithium secondary battery may further contain an organic solvent, which may include at least one selected from the group consisting of carbonate organic solvents, ester organic solvents, ether organic solvents, ketone organic solvents, alcohol organic solvents, and aprotic organic solvents.

[0021] In some embodiments, the electrolyte may further include at least one auxiliary additive selected from the group consisting of cyclic carbonate compounds, fluorine-containing carbonate compounds, lithium phosphate compounds, sultone compounds, borate compounds, sulfate compounds, and sulfite compounds.

[0022] In some embodiments, the content of the auxiliary additive may be 0.01% to 5% by weight relative to the total weight of the electrolyte.

[0023] An exemplary embodiment of a lithium secondary battery may include an electrode assembly comprising a positive electrode and a negative electrode, and the aforementioned electrolyte for a lithium secondary battery.

[0024] In some embodiments, the positive electrode may include lithium metal oxide particles having a single particle structure.

[0025] In some embodiments, the nickel content in the elements other than lithium and oxygen of the lithium metal oxide particles may be 50 mol% to 70 mol%.

[0026] In some embodiments, the lithium secondary battery can have a drive voltage of 4.35V to 4.5V.

[0027] In some embodiments, the negative electrode includes a solid electrolyte interface (SEI) coating on its surface, and the solid electrolyte interface coating may be produced from the aforementioned lithium secondary battery electrolyte. [Effects of the Invention]

[0028] The lithium secondary battery according to the exemplary embodiment can have improved high-temperature storage performance in a high-voltage environment by including an additive in the electrolyte.

[0029] According to exemplary embodiments, the resistance and thickness increase rates of lithium secondary batteries can be reduced even during high-temperature storage and in high-voltage environments. This improves the energy efficiency, stability, and lifespan characteristics of lithium secondary batteries.

[0030] The electrolyte for lithium secondary batteries according to exemplary embodiments can be widely applied in green technology fields such as electric vehicles, battery charging stations, and other battery-powered applications like solar and wind power generation. Furthermore, the lithium secondary battery can be used in environmentally friendly electric vehicles, hybrid vehicles, and the like to reduce air pollution and greenhouse gas emissions and prevent climate change. [Brief explanation of the drawing]

[0031] [Figure 1] Figure 1 is a schematic plan view showing a lithium secondary battery according to an exemplary embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment. [Modes for carrying out the invention]

[0032] An electrolyte for a lithium secondary battery according to an exemplary embodiment 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.

[0033] In some embodiments, the compound may be an additive.

[0034] In some embodiments, the additive may be present in amounts greater than 0% and less than or equal to 10% by weight of the total weight of the electrolyte.

[0035] An exemplary embodiment of 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 consist of repeated stacking of positive and negative electrodes, and the electrolyte may impregnate the electrode assembly.

[0036] In some embodiments, a solid electrolyte interface (SEI) coating may be included on the surface of the negative electrode. The solid electrolyte interface coating may be produced from the electrolyte for the lithium secondary battery. The solid electrolyte interface coating may include moieties derived from the compound in the electrolyte. For example, the solid electrolyte interface coating may include functional groups derived from the additive. This can improve the high-voltage, high-temperature storage performance of the lithium secondary battery.

[0037] In this specification, "high voltage" may mean operating a battery in the range of 4.3V to 4.7V, specifically in the range of 4.35V to 4.5V or higher.

[0038] In this specification, "A-type compound" may mean a compound containing functional group A and derivatives of that compound.

[0039] As used herein, the term "substituted or unsubstituted" means, for example, a deuterium atom, a halogen atom, a cyano group, a nitro group, an amino group, a silyl group, an oxy group, a thio group, a sulfinyl group, a sulfonyl group, a carbonyl group, an ester group, boron, a phosphine oxide group, a phosphine sulfide group, an alkyl group (e.g., C1-C 60 , C1-C 10 alkyl group), an alkenyl group (e.g., C2-C 60 , C2-C 10 alkenyl group), an alkynyl group (e.g., C2-C 60 , C2-C 10 alkynyl group), an alkoxy group (e.g., C1-C 60 , C1-C 10 alkoxy group), a hydrocarbon ring group, an aryl group (e.g., C6-C 60 aryl group), a heterocyclic group (e.g., C1-C 60 heterocyclic group), and can refer to being substituted or unsubstituted with one or more substituents selected from the group consisting of. For example, a "substituted alkyl group" can refer to a group in which at least one hydrogen atom of the alkyl group is substituted with the aforementioned substituent, and a substituent is further bonded to the carbon atom of the alkyl group.

[0040] The substituents can include combinations selected from the aforementioned groups. For example, at least one hydrogen atom of an alkyl group, an aryl group, etc. included as a substituent can be substituted with a deuterium atom, a halogen atom, a cyano group, a nitro group, an amino group, a silyl group, an oxy group, a thio group, a sulfinyl group, a sulfonyl group, a carbonyl group, an ester group, boron, a phosphine oxide group, a phosphine sulfide group, an alkyl group, an alkenyl group, an alkynyl group, a hydrocarbon ring group, an aryl group, or a heterocyclic group.

[0041] Among the substituents, multivalent substituents such as an amino group, a phosphine sulfide group, a phosphine oxide group, a sulfinyl group, a sulfonyl group, a sulfanyl group, an oxy group, a carbonyl group, an ester group, etc. are C1-C 10 alkyl group, C1-C10 alkenyl group, C1-C 10 The alkynyl group, or C6-C 10 It may be substituted with an aryl group.

[0042] The term "substitutable or non-substitutable C" as used herein a -C b In the Y group of C a -C b This refers to the number of carbon atoms in the unsubstituted Y group and does not include the number of carbon atoms in substituents.

[0043] Alkyl groups are monovalent hydrocarbon groups formed by the removal of one hydrogen atom from a linear or branched hydrocarbon group. For example, alkyl groups can include methyl, ethyl, propyl, sec-butyl, tert-butyl, iso-butyl, pentyl, neopentyl, 2-ethylbutyl, 3,3-dimethylbutyl, hexyl, heptyl, and octyl groups.

[0044] An alkenyl group refers to a monovalent unsaturated hydrocarbon group containing a carbon-carbon double bond, formed by the removal of one hydrogen atom from a linear or branched hydrocarbon group. For example, alkenyl groups can include ethenyl (vinyl) groups, propenyl groups, 1-butenyl groups, 2-butenyl groups, pentenyl groups, neopentenyl groups, hexenyl groups, 2-methylpropenyl groups, 3-methylbutenyl groups, and 3,3-dimethylpentenyl groups.

[0045] The embodiments of this disclosure will be described more specifically below with reference to specific embodiments and drawings. However, these are merely illustrative, and this disclosure is not limited to the specific embodiments described illustratively.

[0046] The electrolyte for a lithium secondary battery according to an exemplary embodiment may include a butyrolactone compound containing at least one alkenyl group.

[0047] In some embodiments, the alkenyl group is C2-C 10It may be a substituted or unsubstituted alkenyl group, a C2-C6 substituted or unsubstituted alkenyl group, or a C2-C4 substituted or unsubstituted alkenyl group.

[0048] For example, if the electrolyte for a lithium secondary battery contains a butyrolactone compound containing at least one alkenyl group, the reactivity of the alkenyl group during high-voltage charging and discharging can easily form a solid electrolyte interface (SEI) film on the electrode active material layer. Furthermore, by forming a film containing alkenyl group-based double bonds, the negative electrode can be stably driven under high voltage.

[0049] For example, the solid electrolyte interface film can be formed on the surface of the negative electrode.

[0050] In some embodiments, the butyrolactone compound may be a gamma-butyrolactone compound.

[0051] In some embodiments, the butyrolactone compound may further comprise at least one alkyl group, wherein the alkyl group is C1-C 10 This may be a substituted or unsubstituted alkyl group, a C1-C6 substituted or unsubstituted alkyl group, a C1-C4 substituted or unsubstituted alkyl group, a C1 or C2 substituted or unsubstituted alkyl group, or a substituted or unsubstituted methyl group.

[0052] In some embodiments, the butyrolactone compound can be represented by the following chemical formula 1.

[0053] [ka]

[0054] In chemical formula 1, R1 to R6 are each independently hydrogen, C1-C 10 A substituted or unsubstituted alkyl group, or C2-C 10A substituted or unsubstituted alkenyl group, where at least one of R1 to R6 is C2-C 10 The alkenyl group may be substituted or unsubstituted.

[0055] In some embodiments, C1-C of R1-R6 10 The substituted or unsubstituted alkyl group may specifically be a C1-C6 substituted or unsubstituted alkyl group, a C1-C4 substituted or unsubstituted alkyl group, a C1 or C2 substituted or unsubstituted alkyl group, or a substituted or unsubstituted methyl group.

[0056] In some embodiments, C2-C of R1-R6 10 The substituted or unsubstituted alkenyl group may specifically be a C2-C6 substituted or unsubstituted alkenyl group, a C2-C4 substituted or unsubstituted alkenyl group, or a substituted or unsubstituted ethenyl group.

[0057] In some embodiments, at least one of R1 to R6 may be a C1-C6 substituted or unsubstituted alkyl group.

[0058] In some embodiments, one or two of R1 to R6 may be C1-C6 substituted or unsubstituted alkyl groups.

[0059] In some embodiments, R1 to R6 are each independently hydrogen, C1-C 10 A substituted or unsubstituted alkyl group, or C2-C 10 A substituted or unsubstituted alkenyl group, where one or two of R1 to R6 are C1-C6 substituted or unsubstituted alkyl groups, and the remaining one is C2-C 10 The alkenyl group may be substituted or unsubstituted.

[0060] In some embodiments, R1 to R6 are each independently hydrogen, a C1-C6 substituted or unsubstituted alkyl group, or a C2-C6 substituted or unsubstituted alkenyl group, and at least one of R1 to R6 may be a C2-C6 substituted or unsubstituted alkenyl group.

[0061] In some embodiments, R1 to R6 are each independently hydrogen, a C1-C4 substituted or unsubstituted alkyl group, or a C2-C4 substituted or unsubstituted alkenyl group, and at least one of R1 to R6 may be a C2-C4 substituted or unsubstituted alkenyl group.

[0062] In some embodiments, at least one of R1 and R2 is C2-C 10 The alkenyl group may be substituted or unsubstituted.

[0063] In some embodiments, either R1 or R2 is C1-C 10 The other is a substituted or unsubstituted alkyl group, and the other is C2-C 10 The alkenyl group may be substituted or unsubstituted.

[0064] In some embodiments, either R1 or R2 may be a C1-C6 substituted or unsubstituted alkyl group, and the other may be a C2-C6 substituted or unsubstituted alkenyl group.

[0065] In some embodiments, either R1 or R2 may be a C1-C4 substituted or unsubstituted alkyl group, and the other may be a C2-C4 substituted or unsubstituted alkenyl group.

[0066] In some embodiments, either R1 or R2 may be a substituted or unsubstituted methyl group or a substituted or unsubstituted ethyl group, and the other may be a C2-C4 substituted or unsubstituted alkenyl group.

[0067] In some embodiments, R3-R6 are hydrogen or C1-C 10 These may be substituted or unsubstituted alkyl groups.

[0068] In some embodiments, R3 to R6 may be hydrogen or C1-C6 substituted or unsubstituted alkyl groups.

[0069] In some embodiments, R3 to R6 may be hydrogen or C1-C4 substituted or unsubstituted alkyl groups.

[0070] In some embodiments, R3 to R6 may be hydrogen, a substituted or unsubstituted methyl group, or a substituted or unsubstituted ethyl group.

[0071] In some embodiments, R3-R6 are all hydrogen; either R3 or R4 is C1-C 10 R5 is a substituted or unsubstituted alkyl group, and the other is hydrogen; or either R5 or R6 is C1-C 10 R3 is a substituted or unsubstituted alkyl group, and the other may be hydrogen. In some embodiments, R3 to R6 are all hydrogen; either R3 or R4 is a C1-C6 substituted or unsubstituted alkyl group, and the other is hydrogen; or either R5 or R6 is a C1-C6 substituted or unsubstituted alkyl group, and the other is hydrogen.

[0072] In some embodiments, R3 to R6 may all be hydrogen; one of R3 and R4 may be a C1-C4 substituted or unsubstituted alkyl group and the other hydrogen; or one of R5 and R6 may be a C1-C4 substituted or unsubstituted alkyl group and the other hydrogen.

[0073] In some embodiments, R3 to R6 may all be hydrogen; one of R3 and R4 may be a substituted or unsubstituted methyl group and the other a hydrogen; or one of R5 and R6 may be a substituted or unsubstituted methyl group and the other a hydrogen.

[0074] In some embodiments, the butyrolactone compound can be represented by any one of the following chemical formulas 2-1 to 2-3.

[0075] [ka]

[0076] [ka]

[0077] [ka]

[0078] In some embodiments, when a butyrolactone compound substituted with an alkenyl group is included in the electrolyte for a lithium secondary battery, a uniform and stable solid electrolyte interface (SEI) film can be formed on the electrode surface. This allows the compound represented by chemical formula 1 to stably protect the active material, improving the high-temperature storage performance of the secondary battery under high-voltage conditions. This effect can be further enhanced when an alkyl group is also substituted in addition to the alkenyl group.

[0079] For example, the SEI coating stably protects the electrode surface, thereby stabilizing the electrode interface and suppressing side reactions with the electrolyte, and also suppressing the increase in the battery's internal resistance even during high-temperature storage.

[0080] For example, by forming an SEI coating with a stable structure even at high temperatures using the butyrolactone-based compound, side reactions on the electrode surface can be suppressed, thereby minimizing battery expansion during charging and discharging.

[0081] In some embodiments, the content of the butyrolactone compound may be greater than 0% by weight and 10% by weight or less, or 0.1% to 10% by weight, relative to the total weight of the electrolyte.

[0082] For example, the content of the butyrolactone compound may be 0.2% to 8% by weight, 0.3% to 5% by weight, 0.4% to 3% by weight, 0.5% to 2% by weight, or 0.1% to 2% by weight, relative to the total weight of the electrolyte.

[0083] Within the aforementioned range, a uniform and stable SEI coating can be formed on the electrode surface, improving the high-temperature storage performance of lithium secondary batteries under high-voltage environments.

[0084] An electrolyte for a lithium secondary battery according to an exemplary embodiment may further include at least one auxiliary additive selected from the group consisting of cyclic carbonate compounds, fluorine-containing carbonate compounds, lithium phosphate compounds, sultone compounds, borate compounds, sulfate compounds, and sulfite compounds.

[0085] By using the aforementioned butyrolactone compound in combination with the aforementioned auxiliary additive, it is possible to efficiently realize a lithium secondary battery with improved low-temperature characteristics and high-temperature storage characteristics.

[0086] For example, the cyclic carbonate compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and the like.

[0087] For example, the fluorine-containing carbonate compound may contain a fluorine atom or a substituent to which a fluorine atom is bonded (e.g., a fluorine-substituted alkyl group such as -CF3) to at least one carbon atom of the carbonate compound.

[0088] In some embodiments, the fluorine-containing carbonate compound may include a fluorine-containing cyclic carbonate compound having a cyclic structure. For example, the fluorine-containing cyclic carbonate compound may have a cyclic structure with 5 to 7 members.

[0089] For example, the fluorine-containing cyclic carbonate compound may include fluoroethylene carbonate (FEC).

[0090] For example, the lithium phosphate compound may include lithium difluorobis-oxalato phosphate, lithium difluoro phosphate, and the like.

[0091] In some embodiments, the sultone compound may include at least one selected from the group consisting of alkylsultone compounds and alkenylsultone compounds.

[0092] In some embodiments, the sultone compound may include both alkylsultone compounds and alkenylsultone compounds.

[0093] For example, the alkylsultone compounds may include 1,3-propane sultone (PS) and 1,4-butane sultone.

[0094] For example, the alkenylsultone compounds may include ethensultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0095] For example, the borate compound may include lithium bis(oxalate)borate.

[0096] In some embodiments, the sulfate compound may include a cyclic sulfate compound containing a cyclic structure. The cyclic sulfate compound may have a cyclic structure with 5 to 7 members.

[0097] For example, the cyclic sulfate compound may include 1,2-ethylene sulfate (ESA), trimethylene sulfate (TMS), 1,2-propylene sulfate, and methyltrimethylene sulfate (MTMS).

[0098] In some embodiments, the sulfite compound may include a cyclic sulfite compound containing a cyclic structure.

[0099] For example, the cyclic sulfite compound may include ethylene sulfite, butylene sulfite, and the like.

[0100] In some embodiments, the content of the auxiliary additive may be 0.01% to 5% by weight relative to the total weight of the electrolyte. For example, the content of the auxiliary additive may be 0.05% to 9% by weight, 0.5% to 8% by weight, 0.8% to 7% by weight, 1.0% to 6% by weight, 1.5% to 5% by weight, or 2% to 4% by weight relative to the total weight of the electrolyte.

[0101] Within the aforementioned range, the durability of the SEI coating can be improved without inhibiting the role of the butyrolactone compound. This makes it possible to further improve the high-voltage, high-temperature storage performance of lithium secondary batteries.

[0102] For example, the secondary battery may contain an organic solvent, and the organic solvent may contain organic compounds that have sufficient solubility in the lithium salt, the additive and the auxiliary additive and that do not react within the lithium secondary battery.

[0103] In some embodiments, the organic solvent may be present in an amount of 50% or more by weight, 60% or more by weight, or 70% or more by weight, relative to the total weight of the electrolyte.

[0104] In some embodiments, the organic solvent may include at least one of a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, and an aprotic solvent.

[0105] In some embodiments, the organic solvent may include a carbonate-based solvent, and the carbonate-based solvent may include linear carbonate-based solvents and cyclic carbonate-based solvents.

[0106] For example, the linear carbonate solvent may include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, and the like.

[0107] For example, the cyclic carbonate solvent may include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, and the like.

[0108] In some embodiments, the organic solvent may contain, by volume, more of the linear carbonate solvent than the cyclic carbonate solvent.

[0109] In some embodiments, the ratio of the volume of the cyclic carbonate solvent to the volume of the linear carbonate solvent in the organic solvent may be 1 / 9 to 1. For example, the volume ratio may be 1 / 9 to 1, 1 / 9 to 2 / 3, 1 / 6 to 2 / 3, or 1 / 4 to 2 / 3. Within this range, the high-temperature storage characteristics and low-temperature characteristics of the lithium secondary battery can be further improved.

[0110] 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, and caprolactone.

[0111] 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), and 2-methyltetrahydrofuran.

[0112] For example, the ketone solvent may include cyclohexanone.

[0113] For example, the alcohol-based solvent may include at least one of ethyl alcohol and isopropyl alcohol.

[0114] For example, the aprotic solvent may include at least one of nitrile solvents, amide solvents (e.g., dimethylformamide), dioxolane solvents (e.g., 1,3-dioxolane), and sulfolane solvents.

[0115] In some embodiments, the electrolyte may include a lithium salt.

[0116] The aforementioned lithium salt is Li + X - It is represented as, for example, the anion (X) of the lithium salt. - ) as 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 - , and (CF3CF2SO2)2N - These are some examples.

[0117] In some embodiments, the lithium salt is LiPF6, LiClO4, LiBF4, LiFSI, LiTFSI, LiSO3CF3, LiBOB, LiFOB, LiDFOB, LiDFBP, LiTFOP, LiPO2F2, LiCl, LiBr, LiI, LiB 10 Cl 10 It may include at least one selected from the group consisting of LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN, and LiC(CF3SO2)3.

[0118] In one embodiment, the lithium salt may include at least one selected from the group consisting of LiPF6, LiFSI, and LiTFSI.

[0119] In some embodiments, the lithium salt may be present in the organic solvent at concentrations of 0.01 M to 5 M, 0.01 M to 4 M, 0.5 M to 3 M, or 0.5 M to 2 M. Within these concentration ranges, lithium ions and / or electrons can move smoothly during charging and discharging of the lithium secondary battery.

[0120] Figures 1 and 2 are schematic plan and cross-sectional views, respectively, of a lithium secondary battery according to an exemplary embodiment. Figure 2 is a cross-sectional view along the line I-I' in Figure 1.

[0121] Referring to Figures 1 and 2, the lithium secondary battery may include an electrode assembly 150 comprising a positive electrode 100 and a negative electrode 130, the electrode assembly may further include a separation membrane 140 interposed between the positive electrode and the negative electrode, a solid electrolyte layer or a semi-solid electrolyte layer.

[0122] For example, the electrode assembly 150 may include repeatedly stacked positive electrodes 100 and negative electrodes 130, and the electrode assembly 150 may be housed and impregnated within the case 160 together with the electrolyte according to the exemplary embodiment described above.

[0123] 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.

[0124] 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 surface-treated with carbon, nickel, titanium, or silver. The thickness of the positive electrode current collector is not limited to, but may be, for example, 10 μm to 50 μm.

[0125] For example, the positive electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0126] In some embodiments, the positive electrode 100 may include a positive electrode active material comprising a lithium metal oxide. The lithium metal oxide may further comprise at least one of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al).

[0127] According to exemplary embodiments, the nickel content in the lithium metal oxide, excluding lithium and oxygen, is 50 mol% to 70 mol%. According to some embodiments, the nickel content in the lithium metal oxide, excluding lithium and oxygen, may be 55 mol% to 65 mol%.

[0128] Within the aforementioned range, a positive electrode with improved stability can be provided without reducing the capacity of the positive electrode.

[0129] When the nickel content exceeds 70 mol%, the crystalline structure stability of lithium metal oxide particles may deteriorate significantly due to battery charging and discharging, potentially reducing battery life characteristics.

[0130] If the nickel content is less than 50 mol%, the capacity of the positive electrode may decrease excessively, which can reduce the energy efficiency of the battery.

[0131] In this specification, unless otherwise defined, “content” may refer to the content based on the total number of moles of each metal contained in the particles as the bulk composition of the lithium metal oxide particles as a whole.

[0132] In some embodiments, the positive electrode active material may include lithium metal oxide particles having a structure represented by the following chemical formula 3.

[0133] [ka]

[0134] 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 may also be applicable. As previously mentioned, M may include Co, Mn, and / or Al.

[0135] The chemical structure represented by chemical formula 3 indicates the bonding relationships contained within the layered or crystalline structure of the positive electrode active material and does not exclude other additional elements. For example, M may include Co and / or Mn, and Co and / or Mn may be provided together with Ni as the main active elements of the positive electrode active material. Chemical formula 3 is provided to represent the bonding relationships of the main active elements and should be understood as a formula that encompasses the introduction and substitution of additional elements.

[0136] In one embodiment, auxiliary elements may be further included in addition to the main active element to improve the chemical stability of the positive electrode active material or the layered / crystalline structure. These auxiliary elements can be mixed together with the layered / crystalline structure to form bonds, and in this case, they should also be understood as being within the range of the chemical structure represented by chemical formula 1.

[0137] The auxiliary element may include, for example, at least one of 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 may also act as an auxiliary active element, such as Al, in conjunction with Co or Mn, contributing to the capacity / power activity of the positive electrode active material.

[0138] For example, the positive electrode active material or the lithium metal oxide may include a layered structure or crystalline structure represented by the following chemical formula 3-1.

[0139] [ka]

[0140] 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 ≤ 0.4, and -0.5 ≤ z ≤ 0.1 may also be true.

[0141] The positive electrode active material may further contain coating elements or doping elements. For example, elements substantially identical or similar to the aforementioned auxiliary elements may be used as coating elements or doping elements. For example, the aforementioned elements may be used individually or in combination of two or more as coating elements or doping elements.

[0142] The coating element or doping element may be present on the surface of the lithium metal oxide particles, or it may penetrate from the surface of the lithium-nickel metal composite oxide particles and be included within the bonding structure represented by chemical formula 3 or chemical formula 3-1.

[0143] The lithium metal oxide may have a single particle structure or a secondary particle structure. According to some embodiments, the lithium metal oxide particles have a single particle structure. As used herein, the term “single particle structure” is used to exclude secondary particles, for example, those formed by the aggregation of multiple primary particles (e.g., more than 10) into substantially one particle.

[0144] For example, lithium metal oxide particles may consist of particles in substantially single-particle form, and secondary particle structures formed by the assembly or aggregation of primary particles may be excluded. Furthermore, the term "single-particle structure" as used herein does not exclude, for example, 2 to 10 single particles adhering to or closely adhering to one another to form a single entity.

[0145] The single particle structure may also include a structure in which multiple primary particles are merged together and converted into a substantially single particle form. According to one embodiment, the lithium metal oxide particle may have a single particle form having a crystallographic single-crystal structure or a polycrystalline structure. If the single particle has a single-crystal structure, the single particle may consist of one single crystal. On the other hand, if the single particle has a polycrystalline structure, the single particle may include two or more single crystals.

[0146] For example, the single-crystal structure and the polycrystalline structure can be distinguished based on the ion image obtained by analyzing the particle cross-section with a focused ion beam (FIB). For example, if a particle has a polycrystalline structure, two crystals can be observed in the FIB analysis image due to differences in crystal orientation. For example, even if a particle is observed as a single particle in a particle cross-sectional image measured by a scanning electron microscope (SEM), it may be observed as a particle containing two or more crystals in the FIB analysis image.

[0147] According to an exemplary embodiment, in the analysis of the cross-sectional image crystal orientation of lithium metal oxide particles obtained using a focused ion beam (FIB), the average particle size with respect to the long axis may be 1 μm or more. For example, in the analysis of the cross-sectional image crystal orientation of 10 or more lithium metal oxide particles obtained using a focused ion beam (FIB), the average particle size with respect to the long axis may be 1 μm to 5 μm.

[0148] For example, a positive electrode slurry can be produced by mixing the positive electrode active material in a solvent. After coating the positive electrode slurry onto a positive electrode current collector, the positive electrode active material layer 110 can be produced by drying and rolling. The coating can be performed by methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting, but is not limited to these. The positive electrode active material layer 110 may further contain a binder and optionally further contain conductive materials, thickeners, etc.

[0149] Solvents used in the production of the positive electrode active material layer 110 include, but are not limited to, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran.

[0150] The binder may include polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) copolymer, polyacrylonitrile, polymethyl methacrylate, acrylonitrile butadiene rubber (NBR), poly(butadiene) rubber (BR), styrene-butadiene rubber (SBR), and the like. In one embodiment, a PVDF-based binder can be used as the positive electrode binder.

[0151] The conductive material may be added to improve the conductivity and / or the mobility of lithium ions or electrons of the positive electrode active material layer 110. For example, the conductive material may include, but is not limited to, carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjenblack, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), and carbon fibers, and / or metallic conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3, as well as perovskite materials.

[0152] The positive electrode active material layer 110 may further contain thickeners and / or dispersants. For example, the positive electrode active material layer 110 may contain a thickener such as carboxymethyl cellulose (CMC).

[0153] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 disposed on at least one surface of the negative electrode current collector 125.

[0154] For example, the negative electrode current collector 125 may be made of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal. The thickness of the negative electrode current collector is not limited to this, but may be, for example, 10 μm to 50 μm.

[0155] The negative electrode active material layer 120 may contain a negative electrode active material. As the negative electrode active material, a material capable of adsorbing and desorbing lithium ions may be used. For example, as the negative electrode active material, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium metal; lithium alloys; silicon (Si)-containing materials or tin (Sn)-containing materials may be used.

[0156] Examples of amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fiber (MPCF).

[0157] Examples of crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0158] Examples of the lithium metal include pure lithium metal or lithium metal with a protective layer formed on it for purposes such as suppressing dendrite growth. In one embodiment, a lithium metal-containing layer deposited or coated on the negative electrode current collector 125 can be used as the negative electrode active material layer 120. In another embodiment, a lithium thin film layer can also be used as the negative electrode active material layer 120.

[0159] The elements contained in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0160] The silicon-containing substance can provide increased capacity characteristics. The silicon-containing substance can include Si, SiO x (0 < x < 2), metal-doped SiO x (0 < x < 2), silicon-carbon composites, etc. The metal can include lithium and / or magnesium, and metal-doped SiO x (0 < x < 2) can include metal silicates.

[0161] For example, the negative electrode active material can be mixed in a solvent to produce a negative electrode slurry. After coating / vapor-depositing the negative electrode slurry on the negative electrode current collector 125, it can be dried and rolled to produce the negative electrode active material layer 120. The coating can be performed by methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc., but is not limited thereto. The negative electrode active material layer 120 can further include a binder, and can selectively further include a conductive material, a thickener, etc.

[0162] In some embodiments, the negative electrode 130 can also include a negative electrode active material layer 120 in the form of lithium metal formed by a vapor deposition / coating process.

[0163] Non-limiting examples of the solvent for the negative electrode active material layer 120 include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, etc.

[0164] As the binder, conductive material, and thickener, the aforementioned substances that can be used during the manufacture of the positive electrode can be used.

[0165] In some embodiments, styrene-butadiene rubber (SBR) binders, carboxymethylcellulose (CMC), polyacrylic acid (PEDOT) binders, and the like can be used as the negative electrode binder.

[0166] A separation membrane 140 can be interposed between the positive electrode 100 and the negative electrode 130. The separation membrane 140 may be configured to prevent electrical short circuits between the positive and negative electrodes and to generate ion flow. For example, the thickness of the separation membrane 140 may be 10 μm to 20 μm, but this disclosure is not limited thereto.

[0167] For example, the separation membrane 140 may include a porous polymer film or a porous nonwoven fabric. The porous polymer film may include polyolefin polymers such as ethylene polymer, propylene polymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer. The porous nonwoven fabric may include high-melting-point glass fibers, polyethylene terephthalate fibers, etc. The separation membrane 140 may also include ceramic materials. For example, inorganic particles may be coated on the polymer film or dispersed within the polymer film to improve heat resistance.

[0168] The separation membrane 140 may have a single-layer or multi-layer structure including the aforementioned polymer film and / or nonwoven fabric.

[0169] According to exemplary embodiments, an electrode assembly 150 can be formed by repeatedly arranging a positive electrode 100, a negative electrode 130, and a separator membrane 140. In some embodiments, the electrode assembly 150 may be of a winding type, stacking type, Z-folding type, or stack-folding type.

[0170] A lithium secondary battery can be defined by housing the electrode assembly 150 in the case 160 together with the electrolyte according to the exemplary embodiment described above.

[0171] For example, electrode tabs (positive electrode tab and negative electrode tab) can protrude from the positive electrode current collector 105 and the negative electrode current collector 125, respectively, and extend to one side of the case 160. The electrode tabs may be fused together with the one side of the case 160 and connected to electrode leads (positive electrode lead 107 and negative electrode lead 127) that extend or are exposed outside the case 160.

[0172] For example, case 160 can be a pouch-type case, a rectangular case, a cylindrical case, a coin-type case, etc.

[0173] The lithium secondary battery can have a drive voltage of 4.3V to 4.7V. For example, the lithium secondary battery can have a drive voltage of 4.35V to 4.5V. This makes it possible to operate the battery in a high-voltage range.

[0174] The embodiments of this disclosure will be further described below with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of this disclosure and do not limit the scope of the attached claims. It will be apparent to those skilled in the art that various changes and modifications can be made to these embodiments within the scope of this disclosure and the technical concept, and that these variations and modifications will naturally fall within the scope of the attached claims.

[0175] <Examples of electrolyte additive synthesis> (1) Synthesis Example 1 (Synthesis of Chemical Formula 2-1) 5-Ethenyldihydro-5-methyl-furan-2-one: Ethyl levulinate (8.5 mL, 60 mmol) and dichloromethane (120 mL) were sequentially added to a round-bottom flask, and the mixture was stirred while cooling to 0°C. While maintaining 0°C, 1 M vinyl magnesium bromide (66 mL, 66 mmol) was slowly added dropwise to the mixture over 1 hour, and the mixture was stirred for 3 hours while raising the temperature to room temperature. After the reaction was complete, the product was washed with saturated aqueous ammonium chloride and distilled water, and the solvent in the remaining organic layer was removed under reduced pressure. The dried product was purified and solvent-dried by silica gel column chromatography to obtain 6 g of the product (chemical formula 2-1) in colorless liquid form. [ka]

[0176] (2) Synthesis Example 2 (Synthesis of Chemical Formula 2-2) 4,5-Dimethyl-5-vinyl-dihydro-furan-2-one: Ethyl 3-methyl-4-oxopentanoate (9.7 mL, 60 mmol) and dichloromethane (120 mL) were sequentially added to a round-bottom flask, and the mixture was stirred while cooling to 0°C. While maintaining 0°C, 1 M vinyl magnesium bromide (66 mL, 66 mmol) was slowly added dropwise to the mixture over 1 hour, and the mixture was stirred for 3 hours while raising the temperature to room temperature. After the reaction was complete, the product was washed with saturated aqueous ammonium chloride and distilled water, and the solvent in the remaining organic layer was removed under reduced pressure. The dried product was purified and solvent-dried by silica gel column chromatography to obtain 6 g of the product (chemical formula 2-2) in colorless liquid form. [ka]

[0177] (3) Synthesis Example 3 (Synthesis of Chemical Formula 2-3) 3,5-Dimethyl-5-vinyl-dihydro-furan-2-one: Ethyl 2-methyl-4-oxopentanoate (9.6 mL, 60 mmol) and dichloromethane (120 mL) were sequentially added to a round-bottom flask, and the mixture was stirred while cooling to 0°C. While maintaining 0°C, 1 M vinyl magnesium bromide (66 mL, 66 mmol) was slowly added dropwise to the mixture over 1 hour, and the mixture was stirred for 3 hours while raising the temperature to room temperature. After the reaction was complete, the product was washed with saturated aqueous ammonium chloride and distilled water, and the solvent in the remaining organic layer was removed under reduced pressure. The dried product was purified and solvent-dried by silica gel column chromatography to obtain 6 g of the product in colorless liquid form (Chemical Formula 2-3). [ka]

[0178] <Examples and Comparative Examples> Example 1 (1) Manufacturing of electrolytes A 1.0 M LiPF6 solution (a 20:80 volume ratio mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC)) was prepared. To the aforementioned LiPF6 solution, 1.5% by weight of fluoroethylene carbonate (FEC), 1.0% by weight of W3, 0.5% by weight of PS, 0.3% by weight of PRS, and 0.5% by weight of ESA were added, based on the total weight (100% by weight) of the electrolyte, and an additional 0.3% by weight of the additive represented by the following chemical formula 2-1 was added to produce the electrolyte. [ka]

[0179] (2) Manufacturing of lithium secondary batteries LiNi with a single particle structure is used as the positive electrode active material. 0.6 Co 0.1 Mn 0.3 A slurry was prepared by mixing O2 (particle size: 3.5 μm), carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 92:5:3. The slurry was uniformly applied to a 15 μm thick aluminum foil, and a positive electrode for a lithium secondary battery was manufactured by vacuum drying and rolling at 130°C. A negative electrode slurry was prepared containing 95% by weight of a negative electrode active material, which was a mixture of artificial graphite and natural graphite in a weight ratio of 7:3; 1% by weight of Super-P as a conductive material; 2% by weight of styrene-butadiene rubber (SBR) as a binder; and 2% by weight of carboxymethylcellulose (CMC) as a thickener. The negative electrode slurry was uniformly applied to a copper foil (15 μm thick) having a protrusion (negative electrode tab) on one side, excluding the protrusion. After drying, the foil was rolled to produce the negative electrode. The positive and negative electrodes manufactured as described above were cut to predetermined sizes and stacked, and an electrode assembly was formed by interposing a separator (polyethylene, 20 μm thick) between the positive and negative electrodes. After that, the tab portions of the positive and negative electrodes were welded together. The electrode assembly was placed in a pouch, and three sides were sealed, excluding the side where the electrolyte solution would be injected. At this time, the portion containing the electrode tabs was included in the sealed area. The electrolyte prepared in (1) was injected through the remaining side excluding the sealed area, and after sealing the remaining side, the assembly was impregnated for 12 hours or more to produce a lithium secondary battery.

[0180] Example 2 Electrolyte and lithium secondary battery samples were prepared in the same manner as in Example 1, except that 0.3% by weight of the additive represented by the following chemical formula 2-2 was used instead of the additive in Example 1. [ka]

[0181] Example 3 Electrolyte and lithium secondary battery samples were prepared in the same manner as in Example 1, except that 0.3% by weight of the additive represented by the following chemical formula 2-3 was used instead of the additive in Example 1. [ka]

[0182] Example 4 Electrolyte and lithium secondary battery samples were prepared in the same manner as in Example 1, except that 0.5% by weight of the additive from Example 1 was used.

[0183] Example 5 Electrolyte and lithium secondary battery samples were prepared in the same manner as in Example 1, except that 0.75% by weight of the additive from Example 1 was used.

[0184] Example 6 Electrolyte and lithium secondary battery samples were prepared in the same manner as in Example 1, except that 1.0% by weight of the additive from Example 1 was used.

[0185] Comparative Example 1 Electrolyte and lithium secondary battery samples were prepared in the same manner as in Example 1, except that the additives used in Example 1 were not added.

[0186] Comparative Example 2 Electrolyte and lithium secondary battery samples were prepared in the same manner as in Example 1, except that 0.3% by weight of the additive represented by the following chemical formula 2-4 was used instead of the additive in Example 1. [ka]

[0187] The electrolyte compositions of the examples and comparative examples are shown in Table 1 below.

[0188] [Table 1]

[0189] The components listed in Table 1 are as follows: Additive 1: Compound represented by the above chemical formula 2-1 Additive 2: Compound represented by the chemical formula 2-2. Additive 3: Compound represented by the above chemical formulas 2-3 Additive 4: Compound represented by the above chemical formulas 2-4 FEC: Fluoroethylene Carbonate W3: Lithium difluorophosphate PS: Propanesultone PRS: Propenesultone ESA: Ethylene Sulfate

[0190] <Example of experiment> The battery performance was evaluated using the method described below, and the results are shown in Table 2.

[0191] Experimental Example 1: Evaluation of Initial Performance (1) Evaluation of initial discharge capacity The lithium secondary batteries of the examples and comparative examples were charged at a rate of 0.5C CC / CV at 25°C (4.35V, 0.05C cutoff), and then discharged at a rate of 0.5C CC (2.7V cutoff) three times. The third discharge capacity value is defined as the initial discharge capacity C1 of the lithium secondary battery, as shown in Table 2 below.

[0192] (2) Evaluation of initial resistance For the lithium secondary batteries of the examples and comparative examples, the C rate was sequentially increased or decreased at the 60% SOC point from 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, and 3.0C. The voltage endpoints for each C rate were calculated using a linear equation, and its slope was adopted as the DCIR. The measured values ​​are shown in Table 2 below.

[0193] Experimental Example 2: Evaluation of high-temperature storage performance (60°C) (1) Evaluation of capacity retention rate 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 60°C constant temperature and humidity chamber for 6 weeks. The lithium secondary batteries of the examples and comparative examples, stored at 60°C for 6 weeks, were discharged at a 0.5C rate CC (2.7V cutoff), and the discharge capacity C2 after high-temperature storage was measured. The capacity retention rate is calculated as follows and is shown in Table 2 below. Capacity maintenance rate (%)=(C2 / C1)×100(%)

[0194] (2) Evaluation of capacity recovery rate After measuring the capacity retention rate 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) and discharged at a rate of 0.5C CC (2.5V cutoff) to measure the discharge capacity C3. The capacity recovery rate is calculated as follows and is shown in Table 2 below. Capacity recovery rate (%)=(C3 / C1)×100(%)

[0195] (3) Evaluation of the resistance increase rate 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 60°C constant temperature and humidity chamber for 6 weeks. At the 60% SOC point, the C rate was sequentially increased or decreased to 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, and 3.0C. The voltage endpoints for each C rate, after 10 seconds of charging and discharging, were constructed using a linear equation, and its slope was adopted as DCIR. The high-temperature internal resistance (DCIR) measured in the lithium secondary battery of Comparative Example 1 was set to 100, and the high-temperature internal resistance (DCIR) measured in the lithium secondary batteries of the Examples and Comparative Examples were converted accordingly.

[0196] (4) Evaluation of the rate of increase in thickness The lithium secondary batteries of the examples and comparative examples were charged at 25°C at 0.5C CC / CV (4.35V 0.05C CUT-OFF), and the battery thickness T1 was measured. The charged lithium secondary batteries were left exposed to air at 60°C for 6 weeks (using a constant temperature device), and the battery thickness T2 was measured. The battery thickness was measured using a flat plate thickness measuring device (Mitutoyo, 543-490B). The battery thickness increase rate was calculated as follows, and the resulting values ​​are shown in Table 2 below. Battery thickness increase rate (%) = T2 / T1 × 100 (%)

[0197] [Table 2]

[0198] As shown in Tables 1 and 2 above, the lithium secondary batteries of the examples showed improved initial performance (increased capacity, decreased D-DCIR) and high-temperature storage performance.

[0199] In contrast, the lithium secondary battery of Comparative Example 1, which did not use an additive containing a butyrolactone compound with at least one alkenyl group, showed high initial resistance, and increased resistance and thickness during high-temperature storage.

[0200] In Comparative Example 2, which used an additive containing a butyrolactone compound that does not contain an alkenyl group, the initial discharge capacity decreased slightly compared to Comparative Example 1, but the high-temperature storage performance improved somewhat. However, in Comparative Example 2, the capacity retention rate and capacity recovery rate during high-temperature storage decreased, while the resistance increase rate and thickness increase rate increased compared to the Examples.

[0201] The foregoing is merely an example of applying the principles of this disclosure, and other configurations may be included without departing from the scope of this disclosure.

Claims

1. A butyrolactone compound containing at least one alkenyl group, An electrolyte for lithium secondary batteries, containing a lithium salt.

2. The electrolyte for a lithium secondary battery according to claim 1, wherein the butyrolactone compound is a gamma-butyrolactone 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 butyrolactone-based compound is represented by the following chemical formula 1, and is an electrolyte for a lithium secondary battery according to claim 1. 【Chemistry 1】 (In Chemical Formula 1, R １ ~R ６ are each independently hydrogen, a substituted or unsubstituted alkyl group of C １ -C １０ , or a substituted or unsubstituted alkenyl group of C ２ -C １０ , and at least one of R １ ~R ６ is a substituted or unsubstituted alkenyl group of C ２ -C １０ ).

5. R １ ~R ６ At least one of them is C １ -C ６ The electrolyte for a lithium secondary battery according to claim 4, wherein the alkyl group is substituted or unsubstituted.

6. R １ ~R ６ One or two of them are C １ -C ６ It is a substituted or unsubstituted alkyl group, and one of the remaining ones is C ２ -C １０ The electrolyte for a lithium secondary battery according to claim 4, wherein the alkenyl group is substituted or unsubstituted.

7. R １ ~R ６ These are hydrogen and C, respectively, independently. １ -C ６ A substituted or unsubstituted alkyl group, or C ２ -C ６ A substituted or unsubstituted alkenyl group, R １ ~R ６ At least one of them is C ２ -C ６ The electrolyte for a lithium secondary battery according to claim 4, wherein the alkenyl group is substituted or unsubstituted.

8. R １ ~R ６ These are hydrogen and C, respectively, independently. １ -C ４ A substituted or unsubstituted alkyl group, or C ２ -C ４ A substituted or unsubstituted alkenyl group, R １ ~R ６ At least one of them is C ２ -C ４ The electrolyte for a lithium secondary battery according to claim 4, wherein the alkenyl group is substituted or unsubstituted.

9. R １ and R ２ At least one of them is C ２ -C １０ The electrolyte for a lithium secondary battery according to claim 4, wherein the alkenyl group is substituted or unsubstituted.

10. R １ and R ２ Either one of them is C １ -C １０ The other is a substituted or unsubstituted alkyl group, and the other is C ２ -C １０ The electrolyte for a lithium secondary battery according to claim 4, wherein the alkenyl group is substituted or unsubstituted.

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 the following chemical formulas 2-1 to 2-3. 【Chemistry 2】 【Transformation 3】 【Chemistry 4】

12. The electrolyte for a lithium secondary battery according to claim 1, wherein the content of the butyrolactone compound is greater than 0% by weight and 10% by weight or less with respect to the total weight of the electrolyte.

13. The electrolyte for a lithium secondary battery according to claim 1, further comprising an organic solvent, wherein the organic solvent comprises at least one selected from the group consisting of carbonate-based organic solvents, ester-based organic solvents, ether-based organic solvents, ketone-based organic solvents, alcohol-based organic solvents, and aprotic organic solvents.

14. The electrolyte for a lithium secondary battery according to claim 1, further comprising at least one auxiliary additive selected from the group consisting of cyclic carbonate compounds, fluorine-containing carbonate compounds, lithium phosphate compounds, sultone compounds, borate compounds, sulfate compounds, and sulfite compounds.

15. The electrolyte for a lithium secondary battery according to claim 14, wherein the content of the auxiliary additive is 0.01% to 5% by weight relative to the total weight of the electrolyte.

16. An electrode assembly including a positive electrode and a negative electrode, A lithium secondary battery comprising the electrolyte for a lithium secondary battery as described in claim 1.

17. The lithium secondary battery according to claim 16, wherein the positive electrode comprises a positive electrode active material containing 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 50 mol% to 70 mol% based on the total number of moles of elements excluding lithium and oxygen in the elements contained in the lithium metal oxide particles.

19. A lithium secondary battery according to claim 16, having a drive voltage of 4.35V to 4.5V.

20. The lithium secondary battery according to claim 16, wherein the negative electrode includes a solid electrolyte interface (SEI) coating formed on its surface from the lithium secondary battery electrolyte.

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