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

Abstract

The present invention relates to an electrolyte for a lithium secondary battery capable of improving the charging rate and lifespan characteristics of a lithium secondary battery, and a lithium secondary battery comprising same. The electrolyte for a lithium secondary battery comprises: a lithium salt; a solvent; and an additive, wherein the additive comprises a chlorine-substituted cyclic carbonate-based compound and a sulfone-based compound.

Description

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

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0146533 filed October 24, 2024 and Korean Patent Application No. 10-2025-0146279 filed October 10, 2025, and all contents disclosed in the documents of said Korean patent applications are incorporated herein as part of this specification.

[0003] The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery containing the same.

[0004] Lithium metal batteries, which use lithium metal as the anode, are attracting attention as next-generation batteries that can overcome the low capacity of conventional lithium-ion batteries. However, lithium metal batteries have the problem of rapid lifespan reduction when charged at high speeds, and during the cycle, lithium dendrites form on the surface of the anode, and as a result, the electrolyte for forming the SEI layer is continuously consumed, which shortens the cycle life of the battery.

[0005] Therefore, there is a need to develop an electrolyte that can enable high-speed charging and improve lifespan characteristics when applied to secondary batteries.

[0006] The present invention provides an electrolyte for a lithium secondary battery capable of improving the charging speed and lifespan characteristics of a lithium secondary battery, and a lithium secondary battery including the same.

[0007] One embodiment of the present invention provides an electrolyte for a lithium secondary battery comprising a lithium salt; a solvent; and an additive, wherein the additive comprises a chlorine-substituted cyclic carbonate compound and a sulfone compound.

[0008] The present invention also provides a lithium secondary battery comprising: a positive electrode comprising a positive active material; a negative electrode; a separator between the positive electrode and the negative electrode; and an electrolyte of the present invention.

[0009] The electrolyte of the present invention simultaneously includes a chlorine-substituted cyclic carbonate compound and a sulfone compound as additives, so that when applied to a lithium secondary battery, particularly a lithium metal secondary battery, a stable CEI (Cathode Electrolyte Interphase) layer is formed on the surface of the positive electrode and a stable SEI (Solid Electrolyte Interphase) layer is formed on the surface of the negative electrode, thereby enabling high-speed charging and obtaining a battery with improved lifespan characteristics.

[0010] Figure 1 shows the measured results of evaluating the capacity retention rate according to the cycle of the lithium secondary battery manufactured in Experimental Example 1.

[0011] Figures 2 and 3 show the results of measuring the voltage according to the capacity of the lithium secondary battery manufactured in Experimental Example 1.

[0012] Hereinafter, an electrolyte for a lithium secondary battery according to a specific embodiment of the invention and a lithium secondary battery including the same will be described.

[0013] Terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0014] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0015] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0016] According to one embodiment of the present invention, an electrolyte for a lithium secondary battery is provided, comprising a lithium salt; a solvent; and an additive, wherein the additive comprises a chlorine-substituted cyclic carbonate compound and a sulfone compound.

[0017] The electrolyte according to this embodiment includes chlorine-substituted cyclic carbonate compounds and sulfone compounds as additives to form a stable SEI (Solid Electrolyte Interphase) layer and a CEI (Cathode Electrolyte Interphase) layer. Accordingly, when the above electrolyte is used, a robust and stable SEI layer and CEI layer are formed on the surfaces of the anode and cathode, respectively, so that a lithium secondary battery with excellent lifespan performance is obtained without a rapid reduction in lifespan even during high-speed charging.

[0018] As described above, the electrolyte of the present invention comprises a chlorine-substituted cyclic carbonate compound, thereby forming a robust and stable interfacial structure and exhibiting excellent lifespan characteristics. On the other hand, fluorine-substituted cyclic carbonate compounds, such as FEC, instead of chlorine-substituted cyclic carbonate compounds, cause wasteful chemical reactions during the formation of the SEI and CEI layers, resulting in a sudden voltage drop within the battery, which can lead to a rapid deterioration in battery performance.

[0019] Meanwhile, in the electrolyte of the above-mentioned embodiment, the lithium salt is used as a medium for transferring ions within a lithium secondary battery. The lithium salt is, for example, Li as a cation + Includes, and F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - and SCN - It may include anions selected from the group consisting of

[0020] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 It may include one or more selected from the group consisting of LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (Lithium bis(fluorosulfonyl) imide, LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl) imide, LiN(SO2CF2CF3)2), LiDFOB (lithium difluoro(oxalate)borate, LiC2BF2O4) and LiTFSI (lithium bis(trifluoromethanesulfonyl) imide, LiN(SO2CF3)2).

[0021] According to one embodiment of the present invention, the electrolyte may contain three or more of the aforementioned lithium salts, specifically three types of salts. In this case, the three or more types of lithium salts are divided into one main salt and two or more salts as additives (sub-salts), and among these, the two or more salts acting as additives react with the chlorine-substituted cyclic carbonate compounds and sulfone compounds contained in the electrolyte to form a stable CEI layer and SEI layer, thereby preventing loss of the electrolyte and contributing to the improvement of battery performance.

[0022] Considering the performance of the lithium secondary battery, the concentration of the lithium salt may be included in the electrolyte at a concentration of 1.0 to 2.5 M or 1.0 to 2.0 M. When the concentration range of the lithium salt is satisfied, the desolvation of lithium ions may be further accelerated, and the performance of the lithium secondary battery may be improved. In this case, when three or more types of lithium salts are included in the electrolyte of the present invention, the molar ratio of one main salt and two or more salts as additives (sub-salts) may be 3:1 to 5:1, specifically 3:1 to 4:1.

[0023] In an electrolyte according to one embodiment of the present invention, the solvent may include a carbonate-based solvent, and specifically, may consist of a carbonate-based solvent. As the carbonate-based solvent, one or more selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate (FEC), methyl propyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate, and methyl(2,2,2-trifluoroethyl) carbonate may be used. When a carbonate-based solvent is included as the solvent of the electrolyte, excellent battery performance can be maintained even at high voltage.

[0024] According to another embodiment, the electrolyte may further include other organic solvents as solvents.

[0025] The above-mentioned other organic solvents may be used without special restrictions as long as they can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above-mentioned other organic solvents include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; and nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double aromatic ring or ether bond). Amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used.

[0026] According to one embodiment of the present invention, when the solvent of the electrolyte includes a carbonate-based solvent and other organic solvents, the volume ratio of the carbonate-based solvent and other organic solvents (volume of carbonate-based solvent:volume of other organic solvent) may be 1:0.1 to 1:0.5.

[0027] In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., the electrolyte may be further enriched with, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene may be further enriched, and to improve high-temperature storage characteristics, carbon dioxide gas may be further enriched, and FEC (Fluoro-Ethylene Carbonate), PRS (Propene Sultone), etc. may be further enriched.

[0028] An electrolyte according to one embodiment of the present invention comprises a chlorine-substituted cyclic carbonate compound and a sulfone compound as additives. When the chlorine-substituted cyclic carbonate compound and the sulfone compound are simultaneously included in the electrolyte, a stable CEI layer is formed on the anode surface and a stable SEI layer is formed on the cathode surface.

[0029] Generally, in the case of lithium secondary batteries, such as lithium metal batteries, a CEI layer is formed on the surface of the positive electrode and an SEI layer is formed on the surface of the negative electrode during initial charging, and as the cycle progresses, the CEI layer and SEI layer gradually break down. At this time, if the CEI layer and SEI layer are not robust, the lithium metal or the surface of the positive electrode rapidly re-reacts with the electrolyte in the gaps created by the breakdown, forming byproducts such as dendrites. Consequently, the problem arises where the cycle performance of the battery deteriorates along with electrolyte consumption, leading to a shortened lifespan.

[0030] Since the electrolyte of the present invention forms a stable CEI layer and SEI layer, it can suppress the formation of dendrites on the surface of the negative electrode, thereby improving the lifespan of the battery, and has the advantage that a rapid reduction in lifespan does not occur even when high-speed charging (approx. 0.5C charging) is performed.

[0031] According to another embodiment, the chlorine-substituted cyclic carbonate compound may specifically be chloroethylene carbonate (ClEC).

[0032] According to another embodiment, the sulfone compound may be a benzene-substituted sulfone compound, specifically diphenyl sulfone (DPS).

[0033] At this time, the above additive may be included in an amount of 5 parts by weight or less based on 100 parts by weight of the total electrolyte, specifically 0.1 parts by weight to 5 parts by weight, and more specifically 0.5 parts by weight to 4 parts by weight.

[0034] According to one embodiment of the present invention, the weight ratio (weight of chlorine-substituted cyclic carbonate compound:weight of sulfone compound) of the chlorine-substituted cyclic carbonate compound added to the electrolyte may be 1:0.5 to 1:1.5, more specifically 1:0.7 to 1:1.2, and even more specifically 1:1.

[0035] According to one embodiment of the present invention, the electrolyte may further include other additives such as lithium nitrate (LiNO3), lithium difluorooxalate phosphate (LiDFOP), lithium tetrafluoride borate (LiBF4), lithium bis-oxalate borate (LiBOB), lithium difluorooxalate borate (LiDFOB), lithium hexafluorophosphate (LiPF6), or fluoroethylene carbonate (FEC).

[0036] Meanwhile, according to another embodiment of the invention, a lithium secondary battery comprising the electrolyte of the above-described embodiment is provided. The lithium secondary battery comprises a positive electrode comprising a positive electrode active material; a negative electrode; a separator between the positive electrode and the negative electrode; and the electrolyte of the above-described embodiment.

[0037] According to the above embodiment, the negative electrode may be in the form of a lithium metal secondary battery including a lithium metal layer.

[0038] First, in the above lithium secondary battery, the negative electrode may have a lithium metal layer formed on one or both sides of a planar negative current collector according to the general configuration of the lithium secondary battery, and the lithium metal layer may be manufactured by depositing lithium metal on one or both sides of the negative current collector or by rolling a lithium foil.

[0039] Here, the negative current collector is a metal having high conductivity that does not cause chemical changes in the battery, and can be formed using any metal previously known to be usable as a negative current collector.

[0040] Specific examples of this include metals such as stainless steel, aluminum, nickel, titanium, or copper, or surfaces of copper, aluminum, or stainless steel treated with carbon, nickel, titanium, silver, etc. Such cathode current collectors can be formed in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

[0041] In addition, the negative current collector may have a thickness of 3 μm to 100 μm, and the lithium metal layer may have a thickness of, for example, 1 μm to 300 μm.

[0042] The lithium metal layer may have a thickness of 1 μm to 300 μm, more specifically 1 to 200 μm, and more specifically 1 to 100 μm.

[0043] Alternatively, the above cathode may be composed of a lithium metal layer without a cathode current collector.

[0044] At this time, the lithium metal layer may be a lithium metal foil and may have a thickness of 1 μm to 300 μm, more specifically 1 to 200 μm, and more specifically 1 to 100 μm.

[0045] Meanwhile, the above positive electrode may include a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector.

[0046] Such anodes can be manufactured by preparing an anode slurry composition by mixing an anode active material and a binder, and in some cases, a conductive material and a filler, in a dispersion medium, and applying the composition to an anode current collector.

[0047] The above positive current collector may generally have a thickness of 3 to 500 μm. In addition, the above positive current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive current collector may also increase the adhesion of the positive active material by forming fine irregularities on its surface, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.

[0048] In addition, the positive electrode active material may include lithium; and a lithium transition metal oxide comprising one or more transition metals selected from the group consisting of nickel, manganese, cobalt, and iron.

[0049] Specifically, the lithium transition metal oxide is a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese oxide (e.g., LiNi1-Y Mn Y O2(here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2(here, 0 <Y2<1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(where, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4(where, 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2), etc.), lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of independent elements, respectively, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, p2 + q2 + r2 + s2 = 1), etc.), or lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (Here, M is one or more selected from Al, Mg and Ti, and X is one or more selected from F, S and N, -0.5≤a≤+0.5, 0≤x≤0.5, 0≤b≤0.1) etc., and any one or more of these oxides may be included.

[0050] The above-described positive active material may be included in an amount of 60 to 99 weight%, or 70 to 99 weight%, or 80 to 98 weight% based on the total weight of the positive active material layer.

[0051] Meanwhile, the conductive material included in the above-mentioned positive electrode active material layer is a component intended to further improve the conductivity of the positive electrode active material. Such conductive material is not particularly limited as long as it possesses conductivity without causing chemical changes in the battery. For example, carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive nanomaterials such as carbon nanofibers or carbon nanotubes; fluorinated carbon powder; conductive powders such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used. Among these, the conductive material may include conductive nanomaterials such as carbon nanotubes or carbon nanofibers to further lower the resistance of the lithium metal secondary battery and further improve output characteristics.

[0052] Typically, the conductive material may be included in an amount of 1 to 20 weight%, or 1 to 15 weight%, or 1 to 10 weight% based on the total weight of the positive active material layer.

[0053] The binder optionally included in the above positive active material layer is a component that assists in the bonding of the positive active material and the conductive material, and in the bonding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, nitrile-based rubber, styrene-butadiene rubber, or fluororubber, and a mixture or copolymer of two or more selected from these may also be used.

[0054] Typically, the binder may be included in an amount of 1 to 20 weight%, or 1 to 15 weight%, or 1 to 10 weight% based on the total weight of the positive active material layer.

[0055] In addition, a filler may be optionally added to the anode as a component that inhibits expansion. Such a filler is not particularly limited as long as it can inhibit the expansion of the electrode without causing chemical changes in the battery, and for example, olifin-based polymers such as polyethylene and polypropylene; fibrous materials such as glass fibers and carbon fibers; etc. may be used.

[0056] The above dispersion medium may be NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof, but is not necessarily limited thereto.

[0057] Meanwhile, the above-described lithium secondary battery may further include a porous separator interposed between the positive electrode and the negative electrode.

[0058] Such porous membranes may be used in the form of sheets, multilayer membranes, microporous films, woven fabrics, and nonwoven fabrics, using olefin-based polymers such as polyethylene (PE) and polypropylene (PP), glass fibers, etc., but are not necessarily limited thereto. However, it may be preferable to use porous polyethylene or porous glass fiber nonwoven fabric (glass filter) as the membrane, and it may be even more preferable to use porous glass filter (glass fiber nonwoven fabric) as the membrane. The membrane may be an insulating thin film having high ion permeability and mechanical strength, and the pore diameter of the membrane may generally be in the range of 0.01 to 10 μm, and the thickness may generally be in the range of 5 to 300 μm, but is not limited thereto.

[0059] Alternatively, the porous membrane may be an SRS membrane having a structure in which an organic-inorganic mixed layer containing inorganic particles and a binder is formed on one or both sides of a polymer substrate.

[0060] Meanwhile, the above-described lithium secondary battery can be manufactured according to conventional methods in the field. For example, it can be manufactured by housing an electrode assembly including a positive electrode, a negative electrode, and a separator in a case and injecting and impregnating the above-described electrolyte.

[0061] These lithium secondary batteries can be applied to battery cells used as power sources for small devices, and are particularly suitable for use as unit cells in battery modules that serve as power sources for medium to large devices. Furthermore, considering the appropriate discharge rate for each application, the battery of the above-mentioned embodiment or another embodiment can be selectively used.

[0062]

[0063] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily practice the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0064]

[0065] Example 1 and Comparative Examples 1 to 4: Preparation of Electrolytes

[0066] Example 1.

[0067] Fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 1:3, dissolved in lithium salts at concentrations of 0.8M LiTFSI, 0.2M LiDFOB, and 0.05M LiPF6, and chloroethylene carbonate (ClEC) and diphenyl sulfone (DPS) were added as additives at 0.5 parts by weight each based on 100 parts by weight of the total electrolyte to prepare the electrolyte.

[0068]

[0069] Comparative Example 1.

[0070] An electrolyte was prepared in the same manner as in Example 1, except that no additives were added in Example 1.

[0071]

[0072] Comparative Example 2.

[0073] An electrolyte was prepared in the same manner as in Example 1, except that diphenyl sulfone (DPS) was excluded as an additive in Example 1, and only chloroethylene carbonate (ClEC) was added at a amount of 0.5 parts by weight based on a total of 100 parts by weight of the electrolyte.

[0074]

[0075] Comparative Example 3.

[0076] An electrolyte was prepared in the same manner as in Example 1, except that diphenyl sulfone (DPS) and bis(4-fluorophenyl)sulfone (BFS) were added as additives in an amount of 0.5 parts by weight each based on 100 parts by weight of the total electrolyte.

[0077]

[0078] Comparative Example 4.

[0079] An electrolyte was prepared in the same manner as in Example 1, except that chloroethylene carbonate (ClEC) was excluded as an additive in Example 1, and only diphenyl sulfone (DPS) was added at a amount of 0.5 parts by weight based on 100 parts by weight of the total electrolyte.

[0080]

[0081] Experimental Example 1: Lithium Secondary Battery Manufacturing and Performance Evaluation

[0082] (1) Lithium secondary battery manufacturing

[0083] A positive electrode slurry was prepared by adding and mixing lithium nickel-manganese-cobalt-aluminum composite oxide (NCMA) as a positive electrode active material, a conductive material (carbon black), and a binder (polyvinylidene fluoride, PVDF) in a weight ratio of 97.0:1.5:1.5 to N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was applied to a positive electrode current collector (Al thin film) with a thickness of 12 μm, dried, and then subjected to a roll press to produce a positive electrode.

[0084] A negative electrode was manufactured by attaching lithium metal foils with a thickness of 20㎛ to each side of a copper current collector with a thickness of 8㎛.

[0085] An electrode assembly was manufactured by sequentially laminating the positive and negative electrodes manufactured as described above together with a polyethylene porous film using a conventional method, and then the assembly was placed in a pouch-type secondary battery case and the electrolyte of Example 1 was injected to manufacture a lithium secondary battery.

[0086] In addition, a lithium secondary battery was manufactured in the same manner as above, except that in the process of manufacturing the lithium secondary battery above, the electrolyte of Comparative Example 1, the electrolyte of Comparative Example 2, the electrolyte of Comparative Example 3, or the electrolyte of Comparative Example 4 was injected instead of the electrolyte of Example 1.

[0087]

[0088] (2) Performance evaluation

[0089] For the five lithium secondary batteries manufactured above, 1 to 10 mA / cm² under constant current / constant voltage (CC / CV) conditions 2 After charging to 4.3 V with constant current, and then terminating charging with a 0.05C current cut, the current density is 1 to 10 mA / cm² 2 Discharge was carried out to 3.0 V under constant current (CC) conditions (discharge temperature: 25 ℃). At this time, the lithium secondary battery was discharged at 8 kgf / cm² 2 Charging and discharging were performed while applying pressure, and a silicone pad was attached to the inner surface of the pressure plate to ensure even pressure was applied.

[0090] Afterwards, charge / discharge (0.5C / 2C) was performed for up to about 350 cycles to measure the capacity retention rate, and the results are shown in FIG. 1. The voltage according to the capacity was measured, and the results are shown in FIG. 2 and FIG. 3.

[0091] From the results of Figure 1, it was confirmed that in the case of the battery using the electrolyte of Example 1, there was no drastic reduction in lifespan even when charging was performed at a rate of 0.5C, and that it was superior to the lifespan of the batteries using the electrolytes of Comparative Examples 1 to 4.

[0092] In addition, referring to FIGS. 2 and 3, it can be seen that when the electrolyte of Example 1 is used, the on-set potential is reduced compared to the batteries using the electrolytes of Comparative Examples 1 to 4. This is expected to be because, although a stable interfacial structure cannot be formed if one or more of chlorine-substituted cyclic carbonate compounds and sulfone compounds are not included, Example 1 of the present invention forms stable SEI and CEI layers on the surfaces of the anode and cathode, contributing to the reduction of overpotential. Furthermore, since Comparative Examples 3 and 4 do not contain chlorine-substituted cyclic carbonate compounds such as ClEC, it can be seen that a rapid voltage drop occurred due to a wasteful chemical reaction with FEC during the formation of the SEI and CEI layers.

Claims

1. comprising a lithium salt; a solvent; and an additive, The above additive is an electrolyte for a lithium secondary battery comprising a chlorine-substituted cyclic carbonate compound and a sulfone compound.

2. In Paragraph 1, The above sulfonate compound is an electrolyte for a lithium secondary battery, which is a benzene-substituted sulfonate compound.

3. In Paragraph 1, The above-mentioned chlorine-substituted cyclic carbonate compound is an electrolyte for a lithium secondary battery, which is chloroethylene carbonate (ClEC).

4. In Paragraph 1, The above sulfone-based compound is a lithium secondary battery electrolyte, which is diphenyl sulfone (DPS).

5. In Paragraph 1, The above additive is an electrolyte for a lithium secondary battery containing 5 parts by weight or less based on 100 parts by weight of the total electrolyte.

6. In Paragraph 1, An electrolyte for a lithium secondary battery in which the weight ratio of the chlorine-substituted cyclic carbonate compound and the sulfone compound (weight of chlorine-substituted cyclic carbonate compound: weight of sulfone compound) is 1:0.5 to 1:1.

5.

7. In Paragraph 1, The above solvent is an electrolyte for a lithium secondary battery comprising a carbonate-based solvent.

8. In Paragraph 1, The above lithium salt is an electrolyte for a lithium secondary battery comprising three or more types of salts.

9. In Paragraph 8, The above lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB 10 Cl 10 An electrolyte for a lithium secondary battery comprising three or more salts selected from the group consisting of LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (Lithium bis(fluorosulfonyl) imide, LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl) imide, LiN(SO2CF2CF3)2), LiDFOB (lithium difluoro(oxalate)borate, LiC2BF2O4) and LiTFSI (lithium bis(trifluoromethanesulfonyl) imide, LiN(SO2CF3)2).

10. In Paragraph 1, The above lithium salt is an electrolyte for a lithium secondary battery included in the above electrolyte at a concentration of 1.0 to 2.5 M.

11. Anode comprising a positive active material; cathode; Separator between the anode and cathode; and A lithium secondary battery comprising an electrolyte according to any one of claims 1 to 10.

12. In Paragraph 11, The above negative electrode is a lithium secondary battery comprising a lithium metal layer.

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