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

Abstract

The electrolyte for a lithium secondary battery according to exemplary embodiments comprises a compound having a specific structure and a lithium salt, and comprises an organic solvent comprising ethylene carbonate and ethylmethyl carbonate in specific amounts. Accordingly, a lithium secondary battery comprising the electrolyte for a lithium secondary battery has improved high voltage characteristics and high temperature stability.

Description

Technology Field

[0001] The present disclosure relates to an electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same. More specifically, it relates to an electrolyte for a lithium secondary battery comprising a solvent and an electrolyte salt, and a lithium secondary battery comprising the same. Background Technology

[0002] Rechargeable batteries are batteries capable of repeated charging and discharging, and are widely used as power sources for portable electronic devices such as mobile phones and laptop PCs. Among rechargeable batteries, lithium-ion batteries are being actively developed and applied due to their high operating voltage and energy density per unit weight, as well as their advantages in charging speed and weight reduction.

[0003] A lithium secondary battery may include, for example, an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and an electrolyte impregnating the electrode assembly.

[0004] A lithium secondary battery may further include, for example, an outer casing in the form of a pouch that accommodates the electrode assembly and the electrolyte.

[0005] The positive electrode of a lithium secondary battery can be manufactured by, for example, applying, drying, and rolling a positive electrode slurry comprising a positive electrode active material, a binder, and, if necessary, a conductive material, onto a positive electrode current collector.

[0006] When a lithium secondary battery is subjected to repeated charging and discharging, side reactions may occur between the positive electrode active material and the electrolyte, which can degrade the stability and lifespan characteristics of the lithium secondary battery. The problem to be solved

[0007] One objective of the present disclosure is to provide an electrolyte for a lithium secondary battery having improved high voltage and high temperature characteristics.

[0008] One objective of the present disclosure is to provide a lithium secondary battery having improved high voltage and high temperature characteristics. means of solving the problem

[0009] An electrolyte for a lithium secondary battery according to exemplary embodiments comprises a compound represented by the following chemical formula 1; a lithium salt and an organic solvent comprising ethylene carbonate and ethyl methyl carbonate, wherein, based on the total volume of the organic solvent, the ethylene carbonate is 10 vol% to 30 vol% and the ethyl methyl carbonate is 40 vol% to 80 vol%.

[0010] [Chemical Formula 1]

[0011]

[0012] In Chemical Formula 1, L is a substituted or unsubstituted C1-C10 alkylene group.

[0013] In some embodiments, the organic solvent further comprises propylene carbonate, and the propylene carbonate may be 5 vol% to 15 vol% based on the total volume of the organic solvent.

[0014] In some embodiments, the organic solvent further comprises diethyl carbonate, and the diethyl carbonate may be 5 vol% to 30 vol% based on the total volume of the organic solvent.

[0015] In some embodiments, L may be a substituted or unsubstituted hexylene group.

[0016] In some embodiments, L may be a hexylene group.

[0017] In some embodiments, the compound represented by Formula 1 may be included in an amount greater than 0 weight% and 5 weight% based on the total weight of the electrolyte for the lithium secondary battery.

[0018] In some embodiments, the electrolyte for the lithium secondary battery may further include at least one auxiliary additive selected from the group consisting of cyclic carbonate compounds, fluorine-containing carbonate compounds, lithium phosphate compounds, sulfone compounds, borate compounds, and sulfate compounds.

[0019] In some embodiments, the electrolyte for the lithium secondary battery may further include at least one auxiliary additive selected from the group consisting of fluorine-containing carbonate-based compounds, lithium phosphate-based compounds, sulfone-based compounds and sulfate-based compounds.

[0020] In some embodiments, the fluorine-containing carbonate compound comprises fluoroethylene carbonate, the lithium phosphate compound comprises lithium difluorophosphate, the sulfone compound comprises at least one of 1,3-propane sulfone, 1,4-butane sulfone, ethene sulfone, 1,3-propene sulfone, 1,4-butene sulfone and 1-methyl-1,3-propene sulfone, and the sulfate compound may comprise at least one of ethylene sulfate, trimethylene sulfate and methyl trimethylene sulfate.

[0021] In some embodiments, the auxiliary additive may be included in an amount of 1% to 15% by weight based on the total weight of the electrolyte for the lithium secondary battery.

[0022] In some embodiments, the weight ratio of the auxiliary additive based on the weight of the compound represented by Formula 1 may be 10 to 30.

[0023] A lithium secondary battery according to exemplary embodiments may include an electrode assembly comprising a positive electrode and a negative electrode and an electrolyte for the lithium secondary battery.

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

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

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

[0027] In some embodiments, the surface of the anode or cathode includes a solid electrolyte interphase (SEI) film, and the solid electrolyte interphase film may be formed from the electrolyte for the lithium secondary battery. Effects of the invention

[0028] A lithium secondary battery according to exemplary embodiments can have improved high voltage characteristics and high temperature storage characteristics by including the electrolyte for the lithium secondary battery.

[0029] The above electrolyte can be widely applied in green technology fields such as electric vehicles, battery charging stations, and solar and wind power generation utilizing batteries. In addition, the above lithium secondary battery can be used in eco-friendly electric vehicles, hybrid vehicles, etc., to prevent climate change by suppressing air pollution and greenhouse gas emissions. Brief explanation of the drawing

[0030] FIG. 1 is a schematic plan view of a lithium secondary battery according to exemplary embodiments. FIG. 2 is a schematic cross-sectional view of a lithium secondary battery according to exemplary embodiments. Specific details for implementing the invention

[0031] The electrolyte for a lithium secondary battery according to exemplary embodiments may include a compound having a specific structure and a lithium salt, and may include an organic solvent containing ethylene carbonate and ethylmethyl carbonate in specific amounts.

[0032] Additionally, a lithium secondary battery according to exemplary embodiments may include an electrode assembly comprising a positive electrode and a negative electrode, and an electrolyte for said lithium secondary battery. The electrode assembly may have a positive electrode and a negative electrode repeatedly stacked, and the electrolyte may impregnate said electrode assembly.

[0033] In this specification, "high voltage" refers to driving the battery in a range of 4.3V to 4.7V, specifically 4.35V to 4.5V or higher.

[0034] In this specification, "A-type compound" may mean a compound containing functional group A and a derivative of the compound.

[0035] As used herein, the term “substituted or unsubstituted” refers to, 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, a boron, a phosphine oxide group, a phosphine sulfide group, an alkyl group (for example, C1-C 60 , C1-C 10 alkyl groups), alkenyl groups (e.g., C2-C 60 , C2-C 10 alkenyl group), alkenyl group (e.g., C2-C 60 , C2-C 10 alkynyl group), alkoxy group (e.g., C1-C 60 , C1-C 10 alkoxy groups), hydrocarbon ring groups, aryl groups (e.g., C6-C 60 aryl group), heterocyclic group (e.g., C1-C 60It may refer to one that is substituted or unsubstituted with one or more substituents selected from the group consisting of heterocyclic groups. For example, "substituted alkyl group" may refer to one in which at least one of the hydrogen atoms of the alkyl group is substituted with the substituent described above, thereby further bonding a substituent to a carbon atom of the alkyl group.

[0036] The above substituent may include a combination selected from the groups described above. For example, at least one of the hydrogen atoms, such as alkyl groups and aryl groups included as substituents, may 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, a 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.

[0037] Among the above substituents, multivalent substituents such as amino groups, phosphine sulfide groups, phosphine oxide groups, sulfinyl groups, sulfonyl groups, sulfanyl groups, oxy groups, carbonyl groups, and ester groups are C1-C 10 alkyl group of, C1-C 10 alkenyl group of, C1-C 10 It can be substituted with an alkynyl group or an aryl group having 6 to 10 carbon atoms.

[0038] In the term "substituted or unsubstituted Y group having carbon a to b" as used in this specification, carbon a to b refers to the number of carbons in the unsubstituted Y group and does not include the number of carbons in the substituent.

[0039] An alkyl group refers to a monovalent hydrocarbon group from which one hydrogen atom has been removed from a straight-chain or branched-chain hydrocarbon group. For example, the alkyl group may include a methyl group, an ethyl group, a propyl group, a sec-butyl group, a tert-butyl group, an iso-butyl group, a pentyl group, a neopentyl group, a 2-ethylbutyl group, a 3,3-dimethylbutyl group, a hexyl group, a heptyl group, an octyl group, etc.

[0040] An alkylene group may refer to a divalent hydrocarbon group from which two hydrogen atoms have been removed from a straight-chain or branched-chain hydrocarbon group.

[0041] An aryl group may refer to a monovalent hydrocarbon group from which one hydrogen atom has been removed from a hydrocarbon group having an aromatic structure. An aryl group may include a group in which multiple aromatic rings are directly connected, such as a biphenyl group. The aryl group may include, for example, phenyl, naphthyl, anthracenyl, phenanthrenyl, pyrenyl, fluorenyl, tetracenyl, biphenyl, terphenyl, quarterphenyl, pyrenyl group, chrysenyl, etc.

[0042] Groups in which two or more aryl rings are condensed / connected to each other by a hydrocarbon ring, such as fluorenyl groups, are also included in the category of aryl groups.

[0043] For example, the biphenyl group can be interpreted as an aryl group, or as a phenyl group substituted with a phenyl group.

[0044] Embodiments of the present disclosure will be described in more detail below with reference to specific embodiments and drawings. However, this is merely illustrative and the present disclosure is not limited to the specific embodiments described illustratively.

[0046] Electrolyte for Lithium Secondary Batteries

[0047] An electrolyte for a lithium secondary battery according to exemplary embodiments (hereinafter abbreviated as electrolyte) may include a compound represented by the following chemical formula 1 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.

[0049] The components of the present disclosure will be described in more detail below.

[0050] additives

[0051] The electrolyte for a lithium secondary battery according to exemplary embodiments may include a compound represented by the following chemical formula 1 and a lithium salt.

[0052] [Chemical Formula 1]

[0053]

[0054] In Chemical Formula 1, L is a substituted or unsubstituted C1-C10 alkylene group.

[0055] The compound represented by the above chemical formula 1 may be an additive.

[0056] In this specification, the additive may be included in an amount greater than 0 weight% and less than or equal to 5 weight% of the total weight of the electrolyte.

[0057] In one embodiment, the compound represented by Chemical Formula 1 is included in the electrolyte for the lithium secondary battery and forms a stable solid electrolyte interface film on the surface of the positive electrode interface, thereby stably protecting the electrode surface and stabilizing the electrode interface to suppress adverse reactions with the electrolyte.

[0058] Accordingly, further decomposition of the lithium salt is suppressed, so the decomposition of the organic solvent at high temperatures can be effectively prevented, and the gas generation and resistance increase rate are reduced, thereby improving the performance of the battery.

[0059] In addition, although not bound by any specific theory, the electrode film formed by the compound represented by Chemical Formula 1 above has low resistance, can facilitate the movement of Li between the electrode and the electrolyte, and can improve the cycle life of the secondary battery by minimizing performance degradation during repeated charging and discharging in a high-voltage environment.

[0060] In some embodiments, L may be a substituted or unsubstituted C1-C9 alkylene group, a substituted or unsubstituted C1-C8 alkylene group, or a substituted or unsubstituted C1-C7 alkylene group.

[0061] In some embodiments, L may be a substituted or unsubstituted straight-chain or branched-chain C1-C9 alkylene group, a substituted or unsubstituted straight-chain or branched-chain C1-C8 alkylene group, or a substituted or unsubstituted straight-chain or branched-chain C1-C7 alkylene group.

[0062] In some embodiments, L may be a substituted or unsubstituted straight-chain or branched-chain C1-C7 alkylene group.

[0063] In some embodiments, L may be a straight-chain or branched-chain C1-C7 alkylene group.

[0064] In some embodiments, L may be a substituted or unsubstituted hexylene group.

[0065] In some embodiments, L may be a hexylene group.

[0066] In some embodiments, the compound represented by Formula 1 may be included in an amount greater than 0 weight% and 5 weight% based on the total weight of the electrolyte for the lithium secondary battery.

[0067] In some embodiments, the compound represented by Formula 1 may be 0.1 wt% or more, 0.2 wt% or more, 0.3 wt% or more, 0.4 wt% or more, 0.5 wt% or more, or 1 wt% or more based on the total weight of the electrolyte for the lithium secondary battery. Additionally, the compound represented by Formula 1 may be 5 wt% or less, 4 wt% or less, 3 wt% or less, 1 wt% or less, 0.7 wt% or less, or 0.6 wt% or less based on the total weight of the electrolyte for the lithium secondary battery.

[0068] Within the above range, a uniform and highly ion-conductive solid electrolyte interface (SEI) film can be formed, and the movement of lithium ions and the activity of the positive electrode active material may not be inhibited.

[0070] Organic solvents and lithium salts

[0071] In some embodiments, the secondary battery may include an organic solvent, and the organic solvent may include ethylene carbonate and ethyl methyl carbonate.

[0072] Based on the total volume of the organic solvent, the ethylene carbonate may be 10 vol% to 30 vol%, and the ethyl methyl carbonate may be 40 vol% to 80 vol%. Here, the organic solvent may be included in an amount of more than 5 weight%, 6 weight% or more, 7 weight% or more, 8 weight% or more, 9 weight% or more, or 10 weight% or more of the total weight of the electrolyte.

[0073] The above organic solvent may include an organic compound that has sufficient solubility for the compound represented by Chemical Formula 1, the lithium salt, and the auxiliary additive to be described later, and does not have reactivity in the lithium secondary battery.

[0074] The content of the total organic solvent included in the above-mentioned electrolyte for the lithium secondary battery may be 50% by weight or more, 60% by weight or more, or 70% by weight or more based on the total weight of the above-mentioned electrolyte for the lithium secondary battery, and may be 90% by weight or less.

[0075] By satisfying the aforementioned ranges for the content of the ethylene carbonate and the ethylmethyl carbonate based on the total volume of the organic solvent, the compound represented by Chemical Formula 1 can be sufficiently dissolved to suppress side reactions caused by the electrolyte, and in particular, the capacity retention rate at high voltage can be improved, and the effect of preventing an increase in internal resistance and an effect of preventing an increase in battery thickness at high temperatures can be improved.

[0076] In some embodiments, the organic solvent further comprises propylene carbonate, and the propylene carbonate may be 5 vol% to 15 vol% based on the total volume of the organic solvent.

[0077] For example, based on the total volume of the organic solvent, the propylene carbonate may be 5 vol% to 14 vol%, 5 vol% to 11 vol%, 5 vol% to 10 vol%, or 5 vol% to 8 vol%.

[0078] In some embodiments, the organic solvent further comprises diethyl carbonate, and the diethyl carbonate may be 5 vol% to 30 vol% based on the total volume of the organic solvent.

[0079] For example, based on the total volume of the organic solvent, the diethyl carbonate may be 5 vol% to 25 vol%, 5 vol% to 20 vol%, 5 vol% to 15 vol%, or 5 vol% to 10 vol%.

[0080] In some embodiments, the lithium salt is Li + X - It is expressed as, for example, the anion (X) of the above 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 - Examples of the back can be given.

[0081] 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.

[0082] In one embodiment, the lithium salt may include at least one selected from the group consisting of LiPF6, LiFSI, and LiTFSI.

[0083] In some embodiments, the lithium salt may be included in the organic solvent at a concentration 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 the concentration range, lithium ions and / or electrons can move smoothly during charging and discharging of the lithium secondary battery.

[0085] auxiliary additives

[0086] The electrolyte for a lithium secondary battery according to exemplary embodiments may further include at least one auxiliary additive selected from the group consisting of cyclic carbonate compounds, fluorine-containing carbonate compounds, lithium phosphate compounds, sulfone compounds, borate compounds, and sulfate compounds.

[0087] The electrolyte for a lithium secondary battery according to exemplary embodiments may further include at least one auxiliary additive selected from the group consisting of fluorine-containing carbonate-based compounds, lithium phosphate-based compounds, sulfone-based compounds and sulfate-based compounds.

[0088] In this specification, the auxiliary additive may be included in an amount greater than 0 weight% and less than or equal to 5 weight% of the total weight of the electrolyte.

[0089] In exemplary embodiments, the fluorine-containing carbonate compound comprises fluoroethylene carbonate, the lithium phosphate compound comprises lithium difluorophosphate, the sulfone compound comprises at least one of 1,3-propane sulfone, 1,4-butane sulfone, ethene sulfone, 1,3-propene sulfone, 1,4-butene sulfone and 1-methyl-1,3-propene sulfone, and the sulfate compound may comprise at least one of ethylene sulfate, trimethylene sulfate and methyltrimethylene sulfate.

[0090] When a compound represented by the above chemical formula 1 and the above auxiliary additive are used in combination, a lithium secondary battery having improved low-temperature characteristics and high-temperature storage characteristics can be efficiently realized.

[0091] For example, the above-mentioned cyclic carbonate compounds may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0092] For example, the above fluorine-containing carbonate compound may include a fluorine atom or a substituent (e.g., a fluorine-substituted alkyl group such as -CF3) bonded to at least one carbon atom of the carbonate compound.

[0093] 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 5-7 cyclic structure.

[0094] For example, the above fluorine-containing cyclic carbonate compound may include fluoroethylene carbonate (FEC), etc.

[0095] In some embodiments, the lithium phosphate-based compound may include a fluorine-containing lithium phosphate-based compound.

[0096] For example, the above fluorine-containing lithium phosphate compound may include a fluorine atom bonded to a phosphorus atom of the lithium phosphate compound or a substituent bonded to a fluorine atom (e.g., a fluorine-substituted alkyl group such as CF3).

[0097] In some embodiments, the fluorine-containing lithium phosphate-based compound may include lithium difluorophosphate (LiPO2F2) and lithium difluoro(bis-oxalato) phosphate, etc. For example, the fluorine-containing lithium phosphate-based compound may include lithium difluorophosphate (LiPO2F2), etc.

[0098] In some embodiments, the sulfonate compound may include at least one selected from the group consisting of alkyl sulfonate compounds and alkenyl sulfonate compounds.

[0099] In some embodiments, The above sulfonate compound may include alkyl sulfonate compounds and alkenyl sulfonate compounds together.

[0100] For example, the above alkyl sulfone compounds may include 1,3-propane sultone (PS) and 1,4-butane sultone, etc.

[0101] For example, the above alkenyl sultone compounds may include ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0102] 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 cyclic structure.

[0103] For example, the above-mentioned cyclic sulfate compounds may include 1,2-ethylene sulfate (ESA), trimethylene sulfate (TMS), 1,2-propylene sulfate (1,2-propylene sulfate), and methyltrimethylene sulfate (MTMS).

[0104] For example, the above-mentioned cyclic sulfite compounds may include ethylene sulfite, butylene sulfite, etc.

[0105] For example, the above borate-based compound may include lithium bis(oxalate) borate, etc.

[0106] In some embodiments, the auxiliary additive may include fluoroethylene carbonate, lithium difluorophosphate, 1,3-propane sulfone, and ethylene sulfate.

[0107] In one embodiment, the content of the total auxiliary additive included in the electrolyte for the lithium secondary battery may be 1% to 15% by weight based on the total weight of the electrolyte for the lithium secondary battery.

[0108] For example, the content of the total auxiliary additive included in the electrolyte for the lithium secondary battery may be 1% or more by weight, 1.5% or more by weight, 2% or more by weight, or 3% or more by weight based on the total weight of the electrolyte for the lithium secondary battery, and may be 15% or less by weight, 14% or less by weight, 13% or less by weight, 12% or less by weight, or 11% or less by weight.

[0109] Within the above range, the durability of the solid electrolyte interface film formed on the electrode surface can be enhanced without hindering the role of the compound represented by Chemical Formula 1.

[0110] In one embodiment, the weight ratio of the auxiliary additive based on the weight of the compound represented by Chemical Formula 1 may be 10 to 30.

[0111] For example, the weight ratio of the auxiliary additive based on the weight of the compound represented by the above chemical formula 1 may be 10 to 28, 10 to 27, or 11 to 26.

[0112] Within the above range, excellent high-temperature storage characteristics of the lithium secondary battery can be stably secured.

[0114] Lithium secondary battery

[0115] FIGS. 1 and FIGS. 2 are a schematic plan view and a cross-sectional view, respectively, showing a lithium secondary battery according to exemplary embodiments. FIGS. 2 is a cross-sectional view cut along line II' of FIGS. 1.

[0116] Referring to FIGS. 1 and 2, a 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 separator (140) interposed between the positive electrode and the negative electrode, a solid electrolyte layer, or a semi-solid electrolyte layer.

[0117] For example, the electrode assembly (150) may include a repeatingly stacked positive electrode (100) and negative electrode (130), and the electrode assembly (150) may be received and impregnated with an electrolyte for a lithium secondary battery according to the exemplary embodiments described above within a case (160).

[0118] 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).

[0119] For example, the positive current collector (105) may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive current collector may include carbon, nickel, titanium, aluminum or stainless steel surface-treated with silver. The positive current collector may be, for example, 10 μm to 50 μm, although not limited thereto.

[0120] For example, the above positive active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0121] In some embodiments, the anode may include lithium metal oxide particles having a single particle structure.

[0122] The term "single particle structure" as used in this specification is used to mean excluding secondary particles formed by the aggregation of a plurality of primary particles, for example. For example, in a particle having a single particle structure included in the lithium metal oxide particle, a secondary particle structure formed by the assembly or aggregation of primary particles (e.g., 20 or more, 30 or more, 40 or more, 50 or more, etc.) may be excluded.

[0123] The term “single particle structure” as used herein does not exclude having a monolithic structure in which, for example, two or more and fewer than 20, or a range of two to 10 single particles are observed attached or closely bonded to each other (for example, in scanning electron microscope (SEM) images).

[0124] In some embodiments, the lithium metal oxide may have a structure in which a plurality of primary particles are merged together as a single unit and converted into a substantially single particle.

[0125] For example, the lithium metal oxide may have a granular or spherical single particle form.

[0126] For example, the single particle structure described above can be distinguished based on an ion image obtained by analyzing the particle cross-section using a Focused Ion Beam (FIB). For example, if the particle has a single particle structure, a single crystal may be observed in the FIB analysis image depending on the difference in crystal orientation.

[0127] According to exemplary embodiments, in the cross-sectional image determination orientation analysis of the lithium metal oxide particles obtained using a focused ion beam (FIB), the average value of the long axis reference particle diameters may be 1 μm or more. For example, in the cross-sectional image determination orientation analysis of 10 or more lithium metal oxide particles obtained using a focused ion beam (FIB), the average value of the long axis reference particle diameters may be 1 μm to 20 μm.

[0128] In some embodiments, the average particle size (D50, based on the major axis) of the single particle may be 2 μm to 20 μm. According to some embodiments, the average particle size (D50, based on the major axis) of the single particle may be 2 μm to 10 μm, 3 μm to 10 μm, or 3 μm to 5 μm.

[0129] In some embodiments, the positive electrode comprises a positive electrode active material, and the positive electrode active material may comprise a lithium nickel metal oxide.

[0130] The lithium nickel metal oxide may further comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al). In some embodiments, the lithium nickel metal oxide may further comprise cobalt (Co) and manganese (Mn).

[0131] In some embodiments, the nickel content among the elements excluding lithium and oxygen of the lithium metal oxide particles may be 50 mol% or more to less than 70 mol%, 50 mol% to 65 mol%, or 55 mol% to 65 mol%. Within the nickel content range, sufficient capacity of the lithium secondary battery can be secured.

[0132] In some embodiments, the positive active material or the lithium nickel metal oxide may comprise a layered structure or a crystalline structure represented by the following chemical formula A.

[0133] [Chemical Formula A]

[0134] Li x Ni a M b O 2+z

[0135] In chemical formula A, 0.9≤x≤1.2, 0.5≤a<0.7, 0.01≤b≤0.5, and -0.5≤z≤0.1 may be present. As described above, M may include Co, Mn and / or Al, and may further include Co and Mn.

[0136] In some embodiments, the formula A may be 0.5≤a≤0.65 or 0.55≤a≤0.65.

[0137] The chemical structure represented by Chemical Formula A represents the bonding relationships contained within the layered or crystal structure of the positive electrode active material and does not exclude other additional elements. For example, M includes Co and / or Mn, and Co and / or Mn may be provided as the main active element of the positive electrode active material together with Ni. Chemical Formula A is provided to express the bonding relationships of the main active elements and should be understood as encompassing the introduction and substitution of additional elements.

[0138] In one embodiment, auxiliary elements may be further included in addition to the main active element to enhance the chemical stability of the anode active material or the layered structure / crystalline structure. The auxiliary elements may be incorporated together within the layered structure / crystalline structure to form bonds, and in this case, it should be understood that they are also included within the range of the chemical structure represented by Chemical Formula A.

[0139] The above 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, and Zr. The above auxiliary element may also act as an auxiliary active element that contributes to the capacity / output activity of the cathode active material together with Co or Mn, such as Al.

[0140] In some embodiments, the auxiliary element may further include at least one element among Al, W, Zr, Ti, Y, and B. In this case, the stability of the chemical structure / crystal structure of the lithium metal oxide may be enhanced.

[0141] In one embodiment, the auxiliary element may include at least three elements selected from Al, W, Zr, Ti, and Y. In one embodiment, the auxiliary element may include at least four elements selected from Al, W, Zr, Ti, and Y. For example, the auxiliary element may include Al, W, and Zr, and optionally may further include Y and Ti.

[0142] In one embodiment, the auxiliary element may include Al, W, Zr, and Y.

[0143] For example, the positive electrode active material or the lithium metal oxide may include a layered structure or a crystal structure represented by the following chemical formula A-1.

[0144] [Chemical Formula A-1]

[0145] Li x Ni a M1 b1 M2 b2 O 2+z

[0146] In chemical formula A-1, M1 may include Co, Mn and / or Al. M2 may include the aforementioned auxiliary element. In chemical formula A-1, 0.9≤x≤1.2, 0.5≤a<0.7, 0.01≤b1+b2≤0.5, and -0.5≤z≤0.1.

[0147] In some embodiments, the formula A-1 may be 0.5≤a≤0.65 or 0.55≤a≤0.65.

[0148] The above-described positive active material may further include a coating element or a doping element. For example, elements substantially identical or similar to the auxiliary elements described above may be used as coating elements or doping elements. For example, any of the elements described above may be used alone or in combination of two or more as coating elements or doping elements.

[0149] The above coating element or doping element may be present on the surface of the lithium metal oxide particles or penetrate through the surface of the lithium metal composite oxide particles and be included within the bonding structure represented by Formula A or Formula A-1.

[0150] The above-mentioned positive electrode active material may include a nickel-cobalt-manganese (NCM)-based lithium oxide. Ni may be provided as a transition metal associated with the output and capacity of the lithium secondary battery.

[0151] For example, the positive electrode active material can be dispersed in a solvent to produce a positive electrode composite. The positive electrode composite can be coated onto a positive electrode current collector (105), and then dried and rolled to produce a positive electrode (100). The coating process can be carried out 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 thereto. The positive electrode composite may further include a binder and optionally may further include a conductive material, a thickener, etc.

[0152] Non-limiting examples of solvents used in the preparation of the above anode composite include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0153] The above binder may include polyvinylidenefluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (Poly(vinylidene fluoride-co-hexafluoropropylene), polyacrylonitrile, polymethylmethacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, a PVDF-based binder may be used as the anode binder.

[0154] The above conductive material may be added to enhance the conductivity of the anode composite layer and / or the mobility of lithium ions or electrons. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, acetylene black, ketjenblack, graphene, carbon nanotubes, VGCF (vapor-grown carbon fiber), carbon fiber, etc., and / or metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc.

[0155] As the above-mentioned thickener, for example, carboxymethyl cellulose (CMC) may be used.

[0156] The cathode (130) may include a cathode current collector (125) and a cathode active material layer (120) disposed on at least one surface of the cathode current collector (125).

[0157] For example, non-limiting examples of the negative current collector (125) include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and a polymer substrate coated with a conductive metal. The negative current collector is not limited to these, but may be, for example, 10 μm to 50 μm.

[0158] The cathode composite layer may include a cathode active material. As the cathode active material, a material capable of adsorbing and desorbing lithium ions may be used. For example, the cathode active material may be a carbon-based material such as crystalline carbon, amorphous carbon, carbon composite, or carbon fiber; lithium metal; lithium alloy; silicon (Si)-containing material or tin (Sn)-containing material.

[0159] Examples of the above-mentioned amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fiber (MPCF).

[0160] Examples of the above-mentioned crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0161] The above lithium metal may be pure lithium metal or lithium metal with a protective layer formed thereon for inhibiting dendrite growth, etc. In one embodiment, a lithium metal-containing layer deposited or coated on a negative electrode current collector may be used as a negative electrode active material layer. In one embodiment, a lithium thin film layer may be used as a negative electrode active material layer.

[0162] Examples of elements included in the above lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0163] The above silicon-containing active material can provide increased capacity characteristics. The above silicon-containing active material is Si, SiO x (0 <x<2), 실리콘-탄소 복합체, 금속 도핑된 실리케이트 혹은 SiO x (0 <x<2) 등을 포함할 수 있다. 상기 금속은 리튬 및 / 또는 마그네슘을 포함할 수 있다.

[0164] For example, a cathode composite can be prepared by dispersing the cathode active material in a solvent. A cathode can be manufactured by coating the cathode composite onto a cathode current collector, followed by drying and rolling. The coating process may be carried out using 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 thereto. The cathode composite may further include a binder and optionally may further include a conductive material, a thickener, etc.

[0165] In some embodiments, the cathode may include a cathode active material layer in the form of lithium metal formed through a deposition / coating process.

[0166] Non-limiting examples of solvents for the above-mentioned cathode mixture include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, etc.

[0167] The above-described materials that can be used in the manufacture of the anode as the binder, conductive material, and thickener may be used.

[0168] In some embodiments, styrene-butadiene rubber (SBR) based binder, carboxymethyl cellulose (CMC), polyacrylic acid based binder, poly(3,4-ethylenedioxythiophene), PEDOT based binder, etc. may be used as the cathode binder.

[0169] In one embodiment, a separator (140) may be interposed between the anode (100) and the cathode (130). The separator prevents an electrical short circuit between the anode and the cathode and maintains the flow of ions. According to the embodiment, the thickness of the separator may be 10 μm to 20 μm, but the present disclosure is not limited thereto.

[0170] The separator may include a porous polymer film or a porous nonwoven fabric. The porous polymer film may include polyolefin-based 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.

[0171] The separator may include ceramic-based materials. For example, inorganic particles may be coated on the polymer film or dispersed within the polymer film to improve heat resistance.

[0172] The separator may have a single-layer or multi-layer structure comprising the aforementioned polymer film and / or nonwoven fabric.

[0173] According to exemplary embodiments, the lithium secondary battery may have a driving voltage of 4.3 V to 4.7 V. According to some embodiments, the lithium secondary battery may have a driving voltage of 4.35 V to 4.5 V. Accordingly, the battery may be able to operate in a high voltage range. According to exemplary embodiments, an electrode assembly (150) may be formed by repeating a positive electrode (100), a negative electrode (130), and a separator (140). In some embodiments, the electrode assembly (150) may have a jelly roll shape formed by winding, stacking, zigzag folding, or stack-folding of the separator (140).

[0174] In one embodiment, the electrode assembly (150) may have a jelly roll shape formed by winding together an anode (100), a cathode (130), and a separator (140). In one embodiment, the electrode assembly (150) may have a jelly roll shape in which anodes and cathodes are placed in a space formed by repeatedly z-folding the separator (140).

[0175] In one embodiment, the electrode assembly may be formed by repeatedly stacking an anode, a cathode, and a separator, with each layer cut or separated from one another.

[0176] For example, electrode tabs (positive tabs and negative tabs) may protrude from the positive current collector (105) and the negative 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 leads and negative leads) that extend or are exposed to the outside of the case (160).

[0177] For example, pouch-type cases, rectangular cases, cylindrical cases, coin-type cases, etc., may be used.

[0178] A lithium secondary battery can be defined by housing an electrode assembly (150) together with the aforementioned electrolyte within a case (160).

[0179] In the following, embodiments of the present disclosure are further described with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are merely illustrative of the present disclosure and are not intended to limit the appended claims. It is obvious to those skilled in the art that various changes and modifications to the embodiments are possible within the scope and spirit of the present disclosure, and that such variations and modifications fall within the scope of the appended claims.

[0181] Example 1

[0182] (1) Preparation of electrolyte for lithium secondary batteries

[0183] A 1.2M LiPF6 solution (a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC) in a 30:70 volume ratio) was prepared.

[0184] To the above LiPF6 solution, based on the total weight (100 wt%) of the electrolyte for a lithium secondary battery, 0.4 wt% of hexamethylene diisocyanate (HDI), 5 wt% of fluoroethylene carbonate (FEC), 1 wt% of LiPO2F2 (W3), 2 wt% of 1,3-propane sulfone (PS), and 2 wt% of ethylene sulfonate (ESA) were added to prepare the electrolyte for a lithium secondary battery of Example 1.

[0186] (2) Preparation of lithium secondary battery samples

[0187] LiNi with a single-particle structure as the positive active material 0.6 Co 0.1 Mn 0.3 An anode slurry was prepared by mixing and dispersing O2 (diameter: 3.5 μm), carbon nanotubes as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in NMP at a weight ratio of 97:1:2.

[0188] The above anode slurry was uniformly applied to an area excluding the protrusion of an aluminum foil (15 μm thickness) having a protrusion (anode tab) on one side, dried, and then rolled to manufacture an anode.

[0189] A cathode slurry was prepared by mixing a cathode active material, artificial graphite and natural graphite mixed in a weight ratio of 7:3, a binder, graphite as a conductive material, styrene-butadiene rubber (SBR), and a thickener mixed in a weight ratio of 1:1, with distilled water in a weight ratio of 95:3:2.

[0190] The above cathode slurry was uniformly applied to an area excluding the protrusion of a copper foil (15 μm thickness) having a protrusion (cathode tab) on one side, dried, and then rolled to manufacture a cathode.

[0191] An electrode assembly was formed by interposing a polyethylene separator (thickness 20 μm) between the anode and the cathode. Next, an anode lead and a cathode lead were welded and connected to the anode tab and the cathode tab, respectively.

[0192] The electrode assembly is housed inside a pouch (case) so that a portion of the positive lead and the negative lead are exposed to the outside, and three sides excluding the surface of the electrolyte injection part are sealed.

[0193] A lithium secondary battery sample was prepared by injecting the electrolyte prepared in (1) above, sealing the surface of the electrolyte injection part, and then impregnating it for 12 hours.

[0195] Example 2

[0196] In Example 1, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Example 1, except that a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC):propylene carbonate (PC) with a volume ratio of 10:75:15 was applied.

[0198] Example 3

[0199] In Example 1, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Example 1, except that a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC) with a volume ratio of 20:80 was applied.

[0201] Example 4

[0202] In Example 1, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Example 1, except that a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC):diethyl carbonate (DEC) with a volume ratio of 25:45:30 was applied.

[0204] Example 5

[0205] In Example 1, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Example 1, except that a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC):propylene carbonate (PC) with a volume ratio of 15:79:6 was applied.

[0207] Example 6

[0208] In Example 1, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Example 1, except that a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC):diethyl carbonate (DEC) with a volume ratio of 25:72:8 was applied.

[0210] Example 7

[0211] In Example 3, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Example 3, except that 0.3 wt% hexamethylene diisocyanate, 1 wt% fluoroethylene carbonate (FEC), 1 wt% LiPO2F2(W3), 1 wt% 1,3-propane sulfone (PS), and 0.45 wt% ethylene sulfonate (ESA) were applied.

[0213] Example 8

[0214] In Example 3, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Example 3, except that 1 wt% of fluoroethylene carbonate (FEC), 1 wt% of LiPO2F2(W3), 2 wt% of 1,3-propane sulfone (PS), and 2 wt% of ethylene sulfonate (ESA) were applied.

[0216] Example 9

[0217] In Example 3, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Example 3, except that 0.5 wt% hexamethylene diisocyanate, 5 wt% fluoroethylene carbonate (FEC), 1 wt% LiPO2F2(W3), 2 wt% 1,3-propane sulfone (PS), and 2.75 wt% ethylene sulfonate (ESA) were applied.

[0219] Comparative Example 1

[0220] In Example 4, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Example 4, except that a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC):diethyl carbonate (DEC) with a volume ratio of 5:70:25 was applied.

[0222] Comparative Example 2

[0223] In Comparative Example 1, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Comparative Example 1, except that a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC):diethyl carbonate (DEC) with a volume ratio of 5:85:10 was applied.

[0225] Comparative Example 3

[0226] In Comparative Example 1, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Comparative Example 1, except that a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC):diethyl carbonate (DEC) with a volume ratio of 5:35:60 was applied.

[0228] Comparative Example 4

[0229] In Example 1, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Example 1, except that a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC) with a volume ratio of 35:65 was applied.

[0231] Comparative Example 5

[0232] In Comparative Example 1, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Comparative Example 1, except that a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC):diethyl carbonate (DEC) with a volume ratio of 35:35:30 was applied.

[0234] Comparative Example 6

[0235] In Comparative Example 1, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Comparative Example 1, except that a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC):propylene carbonate (PC):diethyl carbonate (DEC) with a volume ratio of 15:35:20:20 was applied.

[0237] Comparative Example 7

[0238] In Comparative Example 4, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Example 1, except that a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC) with a volume ratio of 15:85 was applied.

[0240] Comparative Example 8

[0241] In Example 1, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Example 1, except that a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC) with a volume ratio of 20:80 was applied and no separate additives were applied.

[0243] Comparative Example 9

[0244] In Comparative Example 8, an electrolyte and a lithium secondary battery sample were prepared in the same manner as in Comparative Example 8, except that a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC):propylene carbonate (PC) with a volume ratio of 10:75:15 was applied.

[0246] The compositions of the organic solvents and additives of the examples and comparative examples are listed in Table 1 below.

[0247] EC(v%) EMC(v%) PC(v%) DEC(v%) HDI(wt%) FEC(wt%) W3(wt%) PS(wt%) ESA(wt%) Additive / HDI weight ratio Example 1 30 70 - - 0.4 5 1 2 2 25 Example 2 10 75 15 - 0.4 5 1 2 2 25 Example 3 20 80 - - 0.4 5 1 2 2 25 Example 4 25 45 - 30 0.4 5 1 2 2 25 Example 5 15 79 6 - 0.4 5 1 2 2 25 Example 6 20 72 - 8 0.4 5 1 2 2 25 Example 7 20 80 - - 0.3 1 1 1 0.45 11.5 Example 8 20 80 - - 0.4 1 1 2 2 15 Example 9 20 80 - - 0.5 5 1 2 2.75 21.5 Comparative Example 1 5 70 - 25 0.4 5 1 2 2 25 Comparative Example 2 5 85 - 10 0.4 5 1 2 2 25 Comparative Example 3 5 35 - 60 0.4 5 1 2 2 25 Comparative Example 4 35 65 - - 0.4 5 1 2 2 25 Comparative Example 5 35 35 - 30 0.4 5 1 2 2 25 Comparative Example 6 15 35 20 30 0.4 5 1 2 2 25 Comparative Example 7 15 85 - - 0.4 5 1 2 2 25 Comparative Example 8 20 80 - - - - - - - - Comparative Example 9 10 75 15 - - - - - - -

[0248] The components listed in Table 1 are specifically as follows.

[0249] EC: Ethylene carbonate

[0250] EMC: Ethylmethyl carbonate

[0251] PC: Propylene Carbonate

[0252] DEC: Diethyl carbonate

[0253] HDI: Hexamethylene diisocyanate

[0254] FEC: Fluoroethylene carbonate

[0255] W3: Lithium difluorophosphate (LiPO2F2)

[0256] PS: 1,3-propane sulfonate

[0257] ESA: Ethylene sulfonate

[0258] Auxiliary Additives: FEC+W3+PS+ESA

[0260] Experimental Example: Evaluation of High Temperature Storage Characteristics (60℃)

[0261] (1) Evaluation of capacity retention rate after high-temperature storage

[0262] The lithium secondary batteries of the examples and comparative examples were subjected to 0.5C CC / CV charging (4.35V, 0.05C CUT-OFF) and 0.5C CC discharging (2.7V CUT-OFF) three times at 25℃, and the third discharge capacity C1 was measured.

[0263] After storing a lithium secondary battery charged to 100% SOC at 60°C for 2 weeks, it was left at room temperature for an additional 30 minutes, and the discharge capacity C2 was measured by discharging 0.5C CC (2.7V CUT-OFF). The capacity retention rate was calculated as follows and is listed in Tables 2 and 3 below.

[0264] Capacity retention rate (%) = C2 / C1 * 100

[0266] (2) Evaluation of resistance increase rate after high-temperature storage

[0267] After leaving the lithium secondary batteries of the examples and comparative examples exposed to an atmosphere at 60°C for 2 weeks (using a constant temperature device), the C-rate was increased and decreased to 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, and 2.5C at 25°C and SOC 60%, and the terminal point of the voltage when charging and discharging at the corresponding C-rate was performed for 10 seconds was constructed using a linear equation, and the slope was adopted as DCIR.

[0268] The DCIR measured during the initial resistance evaluation was set as R1, and the DCIR measured during the resistance evaluation after high-temperature storage was set as R2. The resistance increase rate was calculated as follows, and the results are listed in Table 2 below.

[0269] Resistance increase rate (%) = {(R2-R1) / R1 + 1} * 100

[0271] (3) Evaluation of the rate of increase in battery thickness after high-temperature storage

[0272] After charging the lithium secondary batteries of the examples and comparative examples to 100% SOC at 25°C with 0.5C CC / CV (4.35V 0.05C CUT-OFF), the battery thickness T1 was measured. After leaving the charged lithium secondary batteries of the examples and comparative examples exposed to air at 60°C for 2 weeks (using a constant temperature device), the battery thickness T2 was measured.

[0273] 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 results are listed in Table 2 below.

[0274] Battery thickness increase rate (%) = {(T2-T1) / T1 + 1} * 100

[0275] Dose recovery rate (%) = C3 / C1 * 100

[0276] Capacity retention rate (%) Resistance increase rate (%) Thickness increase rate (%) Example 1 84 114 103 Example 2 86 114 102 Example 3 86 110 101 Example 4 85 114 104 Example 5 85 111 102 Example 6 84 112 102 Example 7 84 115 105 Example 8 84 114 105 Example 9 85 113 103 Comparative Example 1 75 138 115 Comparative Example 2 73 139 118 Comparative Example 3 79 127 116 Comparative Example 4 77 135 115 Comparative Example 5 75 131 122 Comparative Example 6 77 127 113 Comparative Example 7 79 125 115 Comparative Example 8 77 130 117 Comparative Example 9 79 138 121

[0277] Referring to Table 2 above, it can be seen that the initial performance capacity and high temperature (60°C) storage characteristics of the lithium secondary batteries of the examples are superior to those of the comparative examples.

[0278] That is, lithium secondary batteries of comparative examples that do not satisfy the condition that, based on the total volume of organic solvent included in the electrolyte for lithium secondary batteries, ethylene carbonate is 10 vol% to 30 vol% and ethylmethyl carbonate is 40 vol% to 80 vol%, or do not include the compound represented by Chemical Formula 1, had low high-temperature storage characteristics.

[0279] The above description is merely an example of applying the principles of the present disclosure, and other configurations may be included without departing from the scope of the present disclosure. Explanation of the symbols

[0280] 100: Anode 105: Positive current collector 110: Positive active material layer 120: Cathode active material layer 125: Cathode current collector 130: Cathode 140: Separator 150: Electrode assembly 160: Case

Claims

Claim 1 Electrolyte for a lithium secondary battery comprising: a compound represented by the following chemical formula 1; a lithium salt; and an organic solvent comprising ethylene carbonate and ethylmethyl carbonate, wherein, based on the total volume of the organic solvent, the ethylene carbonate is 10 vol% to 30 vol% and the ethylmethyl carbonate is 40 vol% to 80 vol%: [Chemical Formula 1] (In Chemical Formula 1, L is a substituted or unsubstituted C1-C10 alkylene group). Claim 2 An electrolyte for a lithium secondary battery according to claim 1, wherein the organic solvent further comprises propylene carbonate, and the propylene carbonate is 5 vol% to 15 vol% based on the total volume of the organic solvent. Claim 3 An electrolyte for a lithium secondary battery according to claim 1, wherein the organic solvent further comprises diethyl carbonate, and the diethyl carbonate is 5 vol% to 30 vol% based on the total volume of the organic solvent. Claim 4 An electrolyte for a lithium secondary battery according to claim 1, wherein L is a substituted or unsubstituted hexylene group. Claim 5 An electrolyte for a lithium secondary battery according to claim 1, wherein L is a hexylene group. Claim 6 An electrolyte for a lithium secondary battery according to claim 1, wherein the compound represented by Formula 1 is included in an amount greater than 0 weight% and 5 weight% based on the total weight of the electrolyte for a lithium secondary battery. Claim 7 The electrolyte for a lithium secondary battery according to claim 1, wherein the electrolyte for a lithium secondary battery further comprises at least one auxiliary additive selected from the group consisting of a cyclic carbonate-based compound, a fluorine-containing carbonate-based compound, a lithium phosphate-based compound, a sulfone-based compound, a borate-based compound, and a sulfate-based compound. Claim 8 The lithium secondary battery electrolyte of claim 1, wherein the lithium secondary battery electrolyte further comprises at least one auxiliary additive selected from the group consisting of a fluorine-containing carbonate-based compound, a lithium phosphate-based compound, a sulfone-based compound, and a sulfate-based compound. Claim 9 An electrolyte for a lithium secondary battery according to claim 8, wherein the fluorine-containing carbonate-based compound comprises fluoroethylene carbonate, the lithium phosphate-based compound comprises lithium difluorophosphate, the sulfone-based compound comprises at least one of 1,3-propane sulfone, 1,4-butane sulfone, ethene sulfone, 1,3-propene sulfone, 1,4-butene sulfone and 1-methyl-1,3-propene sulfone, and the sulfate-based compound comprises at least one of ethylene sulfate, trimethylene sulfate and methyl trimethylene sulfate. Claim 10 The lithium secondary battery electrolyte of claim 7, wherein the auxiliary additive is included in an amount of 1% to 15% by weight based on the total weight of the lithium secondary battery electrolyte. Claim 11 An electrolyte for a lithium secondary battery according to claim 7, wherein the weight ratio of the auxiliary additive based on the weight of the compound represented by Formula 1 is 10 to 30. Claim 12 A lithium secondary battery comprising an electrode assembly including a positive electrode and a negative electrode; and an electrolyte for a lithium secondary battery according to any one of claims 1 to 11. Claim 13 A lithium secondary battery according to claim 12, wherein the anode comprises lithium metal oxide particles having a single particle structure. Claim 14 A lithium secondary battery according to claim 13, wherein the nickel content among the elements excluding lithium and oxygen of the lithium metal oxide particles is 50 mol% or more and less than 70 mol%. Claim 15 A lithium secondary battery according to claim 12, having a driving voltage of 4.35 V to 4.5 V. Claim 16 A lithium secondary battery according to claim 12, wherein the surface of the anode or cathode comprises a solid electrolyte interphase (SEI) film, and the solid electrolyte interphase film is formed from the electrolyte for the lithium secondary battery.

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