Non-aqueous electrolyte, and lithium secondary battery comprising the same

Abstract

The present invention relates to a non-aqueous electrolyte comprising a lithium salt; an organic solvent; and a compound represented by Formula 1. The non-aqueous electrolyte can control moisture within a lithium secondary battery in which it is used and suppress the generation of by-products resulting from moisture control, and can improve the durability of the lithium secondary battery by improving the durability of the solid electrolyte interface film. [Chemical Formula 1] In the above chemical formula 1, L1 and L2 are independently selected from a single bond and an alkylene group having 1 to 5 carbon atoms, and R1 is selected from hydrogen and an alkyl group having 1 to 5 carbon atoms.

Description

Technology Field

[0001] The present invention relates to a non-aqueous electrolyte and a lithium secondary battery containing the same. Background Technology

[0002] With the recent development of the information society leading to advancements in personal IT devices and computer networks, and the accompanying increase in the overall society's dependence on electrical energy, there is a demand for the development of battery technology to efficiently store and utilize electrical energy.

[0003] In particular, with the growing interest in solving environmental problems and realizing a sustainable circular society, research on energy storage devices such as lithium-ion batteries and electric double-layer capacitors is being conducted extensively. Among these, lithium-ion batteries are receiving attention as battery systems that theoretically have the highest energy density within battery technology.

[0004] The aforementioned lithium secondary battery is largely composed of a positive electrode made of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, an electrolyte that acts as a medium for transporting lithium ions, and a separator. Among these components, the electrolyte is known to have a significant impact on the battery's stability and safety, and as such, extensive research is being conducted on it.

[0005] In this regard, the electrolyte of a lithium secondary battery is generally a non-aqueous electrolyte containing a lithium salt, an organic solvent, etc., and the organic solvent used is a carbonate-based organic solvent, etc. At this time, LiPF6, etc., can be used as the lithium salt, PF6 -In the case of anions, they are very susceptible to heat, so when the battery is exposed to high temperatures, there is a problem in that Lewis acids such as PF5 are generated due to the thermal decomposition of lithium salts. Lewis acids such as PF5 cause the decomposition of the organic solvent itself and destroy the solid electrolyte interface layer (SEI layer) formed on the surface of the negative electrode active material, which causes problems such as increased resistance and reduced lifespan of the lithium secondary battery.

[0006] Therefore, there is an urgent need to develop non-aqueous electrolytes for lithium secondary batteries that can improve lithium ion transport characteristics, electrochemical stability, and battery durability.

[0007] U.S. Patent Publication No. 2018-0316061 discloses an amide-based electrolyte battery, but failed to provide an alternative to the aforementioned problem. Prior art literature

[0008] U.S. Patent Publication No. 2018-0316061 The problem to be solved

[0009] One objective of the present invention is to provide a non-aqueous electrolyte capable of improving high-temperature storage stability and high-temperature life characteristics of a lithium secondary battery.

[0010] In addition, another objective of the present invention is to provide a lithium secondary battery comprising the aforementioned non-aqueous electrolyte. means of solving the problem

[0011] The present invention provides a non-aqueous electrolyte comprising a lithium salt; an organic solvent; and a compound represented by the following chemical formula 1.

[0012] [Chemical Formula 1]

[0013]

[0014] In the above chemical formula 1, L1 and L2 are independently selected from a single bond and an alkylene group having 1 to 5 carbon atoms, and R1 is selected from hydrogen and an alkyl group having 1 to 5 carbon atoms.

[0015] In addition, the present invention provides a lithium secondary battery comprising: a cathode; an anode facing the cathode; a separator interposed between the cathode and the anode; and the aforementioned non-aqueous electrolyte. Effects of the invention

[0016] The non-aqueous electrolyte according to the present invention comprises a lithium salt; an organic solvent; and a compound represented by a specific chemical formula, thereby being capable of improving the high-temperature storage characteristics and high-temperature life characteristics of a lithium secondary battery. Specifically, the compound included in the non-aqueous electrolyte according to the present invention can perform the role of removing Lewis acids of the lithium salt that may occur when the lithium secondary battery is exposed to high temperatures, thus preventing the decomposition of the organic solvent caused by the Lewis acids of the lithium salt, and the destruction of the negative electrode active material or the solid electrolyte interface layer (SEI layer) of the negative electrode. In addition, the compound represented by the specific chemical formula has a low LUMO energy level and can participate in the formation reaction of the solid electrolyte interface layer of the negative electrode, thereby further improving the durability of the solid electrolyte interface layer of the negative electrode.

[0017] Therefore, the lithium secondary battery containing the above-mentioned non-aqueous electrolyte can have improved high-temperature storage characteristics and high-temperature life characteristics. Specific details for implementing the invention

[0018] Hereinafter, the present invention will be described in more detail to aid in understanding the invention. In this case, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should 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.

[0019] Furthermore, in this specification, terms such as “comprising,” “having,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0020] In this specification, the term “alkyl group” may be straight-chain or branched-chain. Additionally, the alkyl group may be optionally substituted. Unless otherwise defined in this specification, the term “substituted” may mean that at least one hydrogen bonded to a carbon is substituted with an element other than hydrogen, for example, with an alkyl group having 1 to 5 carbon atoms or with fluorine.

[0021] In this specification, the average particle size (D 50 ) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. The above average particle size (D 50 ) can be measured, for example, using the laser diffraction method. The laser diffraction method generally enables the measurement of particle sizes ranging from the submicron range to several millimeters, and can obtain results with high reproducibility and high resolution.

[0023] Hereinafter, the non-aqueous electrolyte of the present invention and the lithium secondary battery containing the same will be described in detail.

[0025] Non-aqueous electrolyte

[0026] The present invention provides a non-aqueous electrolyte. Specifically, the non-aqueous electrolyte may be a non-aqueous electrolyte for a lithium secondary battery.

[0027] Specifically, the non-aqueous electrolyte according to the present invention comprises a lithium salt; an organic solvent; and a compound represented by the following chemical formula 1.

[0028] [Chemical Formula 1]

[0029]

[0030] In the above chemical formula 1, L1 and L2 are independently selected from a single bond and an alkylene group having 1 to 5 carbon atoms, and R1 is selected from hydrogen and an alkyl group having 1 to 5 carbon atoms.

[0031] The non-aqueous electrolyte according to the present invention comprises a lithium salt; an organic solvent; and a compound represented by a specific chemical formula, thereby being capable of improving the high-temperature storage characteristics and high-temperature life characteristics of a lithium secondary battery. Specifically, the compound included in the non-aqueous electrolyte according to the present invention can perform the role of removing Lewis acids of the lithium salt that may occur when the lithium secondary battery is exposed to high temperatures, thus preventing the decomposition of the organic solvent caused by the Lewis acids of the lithium salt, and the destruction of the negative electrode active material or the solid electrolyte interface layer (SEI layer) of the negative electrode. In addition, the compound represented by the specific chemical formula has a low LUMO energy level and can participate in the formation reaction of the solid electrolyte interface layer of the negative electrode, thereby further improving the durability of the solid electrolyte interface layer of the negative electrode.

[0032] Therefore, the lithium secondary battery containing the above-mentioned non-aqueous electrolyte can have improved high-temperature storage characteristics and high-temperature life characteristics.

[0034] (1) Lithium salt

[0035] The non-aqueous electrolyte of the present invention comprises a lithium salt. The lithium salt is used as an electrolyte salt in a lithium secondary battery and serves as a medium for delivering lithium ions.

[0036] Typically, the lithium salt may include at least one selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, LiN(CF3SO2)2, CF3SO3Li, LiC(CF3SO2)3, LiC4BO8, LiTFSI, LiFSI, and LiClO4. Specifically, considering the ion transport characteristics and electrochemical stability of the electrolyte, LiPF6 may be included, but is not limited thereto. Meanwhile, the lithium salt may be used as a single type or, if necessary, as a mixture of two or more types.

[0037] The lithium salt may be included in the non-aqueous electrolyte at a concentration of 0.5 M to 5 M, and preferably at a concentration of 0.5 M to 4 M. When the concentration of the lithium salt is within the above range, the concentration of lithium ions in the non-aqueous electrolyte is appropriate so that the charging and discharging of the battery can be properly carried out, and the viscosity of the non-aqueous electrolyte is appropriate so that the wetting in the battery is improved, thereby improving the battery performance.

[0039] (2) Compound represented by Chemical Formula 1

[0040] The present invention includes a compound represented by the following chemical formula 1.

[0041] [Chemical Formula 1]

[0042]

[0043] In the above chemical formula 1, L1 and L2 are independently selected from a single bond and an alkylene group having 1 to 5 carbon atoms, and R1 is selected from hydrogen and an alkyl group having 1 to 5 carbon atoms.

[0044] For example, if the lithium salt is LiPF6, when the lithium salt is exposed to high temperature, PF6 - Lewis acids such as PF5 may be formed due to the thermal decomposition of anions. Since Lewis acids such as PF5 can cause problems such as decomposing organic solvents within the lithium secondary battery or destroying the solid electrolyte interface layer (SEI layer) formed on the negative electrode or the negative electrode active material layer, they can reduce the high-temperature durability of the lithium secondary battery.

[0045] To solve these problems, the non-aqueous electrolyte of the present invention is characterized by comprising a compound represented by Chemical Formula 1. The compound represented by Chemical Formula 1 includes a functional group capable of acting as a Lewis base within its structure, thereby enabling the effective removal of Lewis acids formed from lithium salts, which prevents the decomposition of organic solvents and prevents damage or destruction of the solid electrolyte interface film of the negative electrode. Accordingly, a lithium secondary battery using the non-aqueous electrolyte of the present invention can have significantly improved high-temperature durability, such as high-temperature storage characteristics and high-temperature life characteristics.

[0046] Specifically, since the compound represented by Chemical Formula 1 has a pentagonal ring structure, the energy level of the LUMO (Lowest Unoccupied Molecular Orbital) is low, so it can be easily decomposed at the cathode. This allows the compound represented by Chemical Formula 1 to participate in the formation reaction of the solid electrolyte interface film at the cathode, thereby contributing to the improvement of the durability of the solid electrolyte interface film.

[0047] In addition, the cyano group (-CN) of the compound represented by the above chemical formula 1 can improve the moisture control effect in the non-aqueous electrolyte.

[0049] In the above chemical formula 1, L1 and L2 can be independently selected from a single bond and an alkylene group having 1 to 5 carbon atoms, and specifically, can be a single bond.

[0050] In the above chemical formula 1, R1 can be selected from hydrogen and an alkyl group having 1 to 5 carbon atoms, specifically, in terms of further lowering the possibility of HF generation upon high-temperature exposure, it can be an alkyl group having 1 to 5 carbon atoms, and more specifically, it can be a methyl group.

[0051] The compound represented by the above chemical formula 1 may be a compound represented by the following chemical formula 1A.

[0052] [Chemical Formula 1A]

[0053]

[0054] The above R1 may be selected from hydrogen and an alkyl group having 1 to 5 carbon atoms, specifically an alkyl group having 1 to 5 carbon atoms, more specifically a methyl group.

[0055] Meanwhile, the compound represented by Chemical Formula 1 may include at least one selected from the group consisting of the compound represented by Chemical Formula 2A and the compound represented by Chemical Formula 2B, in which case the moisture control effect of the cyano group may be further enhanced. Specifically, the compound represented by Chemical Formula 1 may include the compound represented by Chemical Formula 2B, in which case the possibility of HF generation upon high-temperature exposure may be further reduced, thereby further improving high-temperature storage performance and high-temperature life performance.

[0056] [Chemical Formula 2A]

[0057]

[0058] [Chemical Formula 2B]

[0059]

[0061] The compound represented by the above chemical formula 1 may be included in the above non-aqueous electrolyte in an amount of 0.01% to 7% by weight, specifically 0.3% to 4% by weight, and more specifically 1.5% to 3.5% by weight. It is desirable that when within this range, the Lewis acid removal effect of the lithium salt described above is sufficiently exhibited to improve the high-temperature durability of the battery.

[0063] (3) Organic solvent

[0064] The non-aqueous electrolyte according to the present invention comprises an organic solvent. The organic solvent is a non-aqueous solvent commonly used in lithium secondary batteries and is not particularly limited as long as it minimizes decomposition due to oxidation reactions, etc., during the charging and discharging process of the secondary battery.

[0065] Specifically, the organic solvent may include at least one selected from linear carbonates, cyclic carbonates, linear esters, cyclic esters, ethers, glymes, and nitriles. The organic solvent may preferably include at least one selected from linear carbonates and cyclic carbonates, and more preferably may include linear carbonates and cyclic carbonates. In particular, conventional non-aqueous electrolytes generally use cyclic carbonates as organic solvents for high dielectric constant and dissociation of lithium salts, and the role of such cyclic carbonates can be partially replaced or substituted by the compound represented by Chemical Formula 1 described above. In particular, the compound represented by Chemical Formula 1 has high oxidation stability, excellent lithium ion transfer performance, and does not generate gaseous byproducts, thereby improving the durability and lifespan characteristics of the lithium secondary battery; thus, superior battery characteristics can be exhibited at a desirable level compared to when cyclic carbonates are used.

[0066] The above linear carbonate may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate.

[0067] The above cyclic carbonate may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, and fluoroethylene carbonate (FEC).

[0068] Specific examples of the above linear esters include, but are not limited to, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0069] Specific examples of the above-mentioned cyclic esters include γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, ε-caprolactone, etc., but are not limited thereto.

[0070] Specific examples of the above ethers include, but are not limited to, dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methylpropyl ether, ethylpropyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL).

[0071] Specific examples of the above-mentioned glyme include dimethoxyethane (glyme, DME), diethoxyethane, diglyme, tri-glyme, and tetra-glyme (TEGDME), but are not limited thereto.

[0072] Specific examples of the above nitriles include, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, etc., but are not limited thereto.

[0073] When the organic solvent comprises the linear carbonate and the cyclic carbonate, the volume ratio of the linear carbonate and the cyclic carbonate may be 20:80 to 80:20, specifically 25:75 to 50:50.

[0075] (4) Additives

[0076] The above-mentioned non-aqueous electrolyte may further include additives.

[0077] Specifically, the above-mentioned non-aqueous electrolyte may further include at least one additive selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, propane sultone, succinonitrile, adiponitrile, ethylene sulfate, propene sultone, fluoroethylene carbonate, LiPO2F2, LiODFB (Lithium difluorooxalatoborate), LiBOB (Lithium bis-(oxalato)borate), TMSPa (3-trimethoxysilanyl-propyl-N-aniline), and TMSPi (Tris(trimethylsilyl) Phosphite), and specifically may further include an additive comprising vinylene carbonate. When the above additive is included in a non-aqueous electrolyte, it is desirable in that it forms a stable solid electrolyte interface layer (SEI layer) on the cathode, thereby suppressing additional decomposition reactions of the electrolyte and improving lifespan characteristics.

[0078] The above additive may be included in the above non-aqueous electrolyte in an amount of 0.1% to 15% by weight, preferably 0.3% to 5% by weight.

[0079] When the above-described additive is included in the above-described non-aqueous electrolyte, the weight ratio of the compound represented by Chemical Formula 1 and the additive may be 0.1:1 to 11:1, specifically 3:1 to 9:1, and when within the above range, the effect of improving high-temperature performance by the combined use of the compound represented by Chemical Formula 1 and the additive can be preferably realized.

[0081] lithium secondary battery

[0082] In addition, the present invention provides a lithium secondary battery comprising the aforementioned non-aqueous electrolyte.

[0083] Specifically, the lithium secondary battery according to the present invention comprises a negative electrode; a positive electrode facing the negative electrode; a separator facing the negative electrode and the positive electrode; and the aforementioned non-aqueous electrolyte.

[0084] At this time, the lithium secondary battery of the present invention can be manufactured according to conventional methods known in the art. For example, it can be manufactured by sequentially stacking a positive electrode, a negative electrode, and a separator between the positive and negative electrodes to form an electrode assembly, inserting the electrode assembly into a battery case, and injecting a non-aqueous electrolyte according to the present invention.

[0086] The above cathode may include a cathode current collector; and a cathode active material layer disposed on at least one surface of the cathode current collector.

[0087] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the above-mentioned negative current collector may be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0088] The above-mentioned cathode current collector can typically have a thickness of 3 to 500 μm.

[0089] The above-mentioned negative current collector may form fine irregularities on its surface to strengthen the bonding force of the negative active material. For example, the above-mentioned negative current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0090] The above-mentioned negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one or both surfaces of the negative electrode current collector.

[0091] The above cathode active material layer may include a cathode active material.

[0092] The above negative electrode active material is a material capable of reversibly inserting / extracting lithium ions, and may include at least one selected from the group consisting of carbon-based active materials, (quasi)metal-based active materials, and lithium metal, and specifically may include at least one selected from carbon-based active materials and (quasi)metal-based active materials.

[0093] The above carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and preferably may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0094] Average particle size (D) of the above carbon-based active material 50 ) can be 10㎛ to 30㎛, preferably 15㎛ to 25㎛, in terms of ensuring structural stability during charging and discharging and reducing adverse reactions with the electrolyte.

[0095] Specifically, the above (quasi)metallic active material may include at least one (quasi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an alloy of lithium with at least one (quasi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an oxide of at least one (quasi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; lithium titanium oxide (LTO); lithium vanadium oxide; etc.

[0096] More specifically, the above (quasi)metallic active material may include a silicon-based active material.

[0097] The above silicon-based active material is SiO x It may include compounds represented by (0≤x<2). Since SiO2 does not react with lithium ions and therefore cannot store lithium, it is preferable that x be within the above range, and more preferably, the silicon-based oxide may be SiO.

[0098] Average particle size (D) of the above silicon-based active material 50 ) can be 1㎛ to 30㎛, preferably 2㎛ to 15㎛, in terms of reducing adverse reactions with the electrolyte while ensuring structural stability during charging and discharging.

[0099] The above-mentioned negative electrode active material may be included in the negative electrode active material layer in an amount of 60% to 99% by weight, preferably 75% to 95% by weight.

[0100] The above cathode active material layer may further include a binder and / or a conductive material together with the cathode active material.

[0101] The binder is used to improve the performance of the battery by enhancing the adhesion between the negative electrode active material layer and the negative electrode current collector, and may include, for example, at least one selected from the group consisting of polyvinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and materials in which hydrogens thereof are substituted with Li, Na, or Ca, etc., and may also include various copolymers thereof. there is.

[0102] The above binder may be included in the cathode active material layer in an amount of 0.5% to 10% by weight, preferably 1% to 5% by weight.

[0103] The above conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, Farnes black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0104] The above conductive material may be included in the above negative electrode active material layer in an amount of 0.5% to 10% by weight, preferably 1% to 5% by weight.

[0105] The thickness of the above negative electrode active material layer may be 10㎛ to 100㎛, preferably 50㎛ to 80㎛.

[0106] The above cathode can be manufactured by coating a cathode slurry comprising a cathode active material, a binder, a conductive material, and / or a solvent for forming a cathode slurry on at least one surface of a cathode current collector, and then drying and rolling.

[0107] The solvent for forming the cathode slurry may include, for example, at least one selected from the group consisting of distilled water, NMP (N-methyl-2-pyrrolidone), ethanol, methanol, and isopropyl alcohol, preferably distilled water, in order to facilitate the dispersion of the cathode active material, binder, and / or conductive material. The solid content of the cathode slurry may be 30% to 80% by weight, specifically 40% to 70% by weight.

[0109] The above positive electrode faces the above negative electrode.

[0110] The above positive electrode may include a positive electrode current collector; and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0111] The above positive current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the above positive current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum-cadmium alloy, preferably aluminum.

[0112] The thickness of the above positive current collector can typically be 3 to 500 μm.

[0113] The above positive current collector may also strengthen the bonding force of the negative active material by forming fine irregularities on its surface. For example, the above positive current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0114] The positive active material layer is disposed on at least one surface of the positive current collector. Specifically, the positive active material layer may be disposed on one or both surfaces of the positive current collector.

[0115] The above positive active material layer may include a positive active material.

[0116] The above-mentioned positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium transition metal composite oxide comprising lithium and at least one transition metal comprising nickel, cobalt, manganese, and aluminum, preferably a lithium transition metal composite oxide comprising lithium and a transition metal comprising nickel, cobalt, and manganese.

[0117] For example, the above lithium transition metal composite oxide includes 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.), and a lithium-nickel-manganese oxide (e.g., LiNi 1-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(Nip Co q Mn r1 )O2(where, 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2 Examples include )O2 (wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are each atomic fractions of independent elements, such that 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc., and any one or more of these compounds may be included. Among these, the lithium transition metal composite oxide is LiCoO2, LiMnO2, LiNiO2, and lithium nickel-manganese-cobalt oxide (for example, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel-cobalt-aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 It may be )O2, etc., and considering the significant improvement effect resulting from controlling the type and content ratio of constituent elements forming the lithium transition metal composite oxide, the lithium transition metal composite oxide is Li(Ni 0.6 Mn 0.2Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 or Li(Ni 0.8 Mn 0.1 Co 0.1 It may be O2, etc., and any one of these or a mixture of two or more may be used.

[0118] More specifically, the positive electrode active material may be a lithium transition metal composite oxide containing 60 mol% or more of nickel based on the total molar amount of the transition metal contained in the lithium transition metal composite oxide. Specifically, the positive electrode active material may be a lithium transition metal composite oxide, wherein the transition metal comprises nickel; and at least one selected from manganese, cobalt, and aluminum, and may contain 60 mol% or more, specifically 60 mol% to 90 mol%, based on the total molar amount of the transition metal. When such a lithium transition metal composite oxide containing a high amount of nickel is used together with the aforementioned non-aqueous electrolyte, it is desirable in that it can reduce gaseous by-products generated by structural collapse.

[0119] In addition, the above positive active material may include a lithium complex transition metal oxide represented by the following chemical formula 5.

[0120] [Chemical Formula 5]

[0121] Li 1+x (Ni a Co b Mn c M d )O2

[0122] In the above chemical formula 5, M is one or more selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and 1+x, a, b, c, and d are each atomic fractions of independent elements, where 0≤x≤0.2, 0.50≤a<1, 0 <b≤0.25, 0<c≤0.25, 0≤d≤0.1, a+b+c+d=1이다.

[0123] Preferably, a, b, c, and d may each be 0.70≤a≤0.95, 0.025≤b≤0.20, 0.025≤c≤0.20, and 0≤d≤0.05.

[0124] In addition, the above a, b, c, and d may each be 0.80≤a≤0.95, 0.025≤b≤0.15, 0.025≤c≤0.15, and 0≤d≤0.05.

[0125] In addition, the above a, b, c, and d may each be 0.85≤a≤0.90, 0.05≤b≤0.10, 0.05≤c≤0.10, and 0≤d≤0.03.

[0126] The above positive active material may be included in the positive active material layer in an amount of 80% to 99% by weight, preferably 92% to 98.5% by weight, taking into consideration the sufficient capacity exertion of the positive active material.

[0127] The above positive active material layer may further include a binder and / or a conductive material together with the aforementioned positive active material.

[0128] The above binder is a component that assists in the binding of active materials and conductive materials, and in binding to current collectors, and specifically may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene ter polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride.

[0129] The above binder may be included in the positive active material layer in an amount of 1% to 20% by weight, preferably 1.2% to 10% by weight, in order to sufficiently secure binding strength between components such as the positive active material.

[0130] The above conductive material can be used to assist and improve conductivity in a secondary battery, and is not particularly limited as long as it is conductive without causing chemical changes. Specifically, the above cathode conductive material may include at least one selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, Farnes black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives, and preferably may include carbon black in terms of improving conductivity.

[0131] The above conductive material may be included in the positive active material layer in an amount of 1% to 20% by weight, preferably 1.2% to 10% by weight, in order to sufficiently ensure electrical conductivity.

[0132] The thickness of the above positive active material layer may be 30㎛ to 400㎛, preferably 40㎛ to 110㎛.

[0133] The above anode can be manufactured by coating an anode slurry comprising an anode active material and optionally a binder, a conductive material, and a solvent for forming an anode slurry onto the above anode current collector, and then drying and rolling.

[0134] The solvent for forming the anode slurry may include an organic solvent such as NMP (N-methyl-2-pyrrolidone). The solid content of the anode slurry may be 40% to 90% by weight, specifically 50% to 80% by weight.

[0136] The above separator is interposed between the anode and the cathode.

[0137] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It can be used without special limitations as long as it is a separator typically used in lithium secondary batteries, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0139] The external shape of the lithium secondary battery of the present invention is not particularly limited and may be, for example, cylindrical, prismatic, pouch, coin, etc.

[0140] The lithium secondary battery according to the present invention can be used as a battery cell used as a power source for a small device, or as a unit cell of a medium-to-large battery module comprising a plurality of battery cells.

[0141] The lithium secondary battery according to the present invention can be usefully used in fields such as portable devices like mobile phones, laptop computers, and digital cameras, and in fields such as electric vehicles like hybrid electric vehicles (HEV) and electric vehicles (EV).

[0143] In addition, the present invention provides a battery module comprising the lithium secondary battery as a unit cell, and a battery pack comprising the battery module.

[0144] The above battery module or battery pack can be used as a power source for medium to large devices selected from the group consisting of power tools; electric vehicles; hybrid electric vehicles; and power storage systems.

[0146] The present invention will be explained in more detail below through specific embodiments. However, the following embodiments are merely examples to aid in understanding the invention and do not limit the scope of the invention. It is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of this description, and it is natural that such variations and modifications fall within the scope of the appended claims.

[0148] Examples

[0149] Example 1: Preparation of non-aqueous electrolyte

[0150] A non-aqueous electrolyte was prepared by mixing LiPF6 as a lithium salt, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) as organic solvents in a volume ratio of 30:70, a compound represented by the following chemical formula 2A, and vinylene carbonate as an additive.

[0151] [Chemical Formula 2A]

[0152]

[0153] The above lithium salt was included at a molar concentration of 1.0 M. The compound represented by Chemical Formula 2A was included in the above non-aqueous electrolyte at 0.5 wt%. The above vinylene carbonate was included in the above non-aqueous electrolyte at 0.5 wt%.

[0155] Example 2: Preparation of non-aqueous electrolyte

[0156] A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that the compound represented by the above chemical formula 2A was included in the non-aqueous electrolyte at a weight of 3%.

[0158] Example 3: Preparation of non-aqueous electrolyte

[0159] A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that the compound represented by the above chemical formula 2A was included in the non-aqueous electrolyte at 0.1% by weight.

[0161] Example 4: Preparation of non-aqueous electrolyte

[0162] A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that the compound represented by the above chemical formula 2A was included in the non-aqueous electrolyte at 5% by weight.

[0164] Example 5: Preparation of non-aqueous electrolyte

[0165] A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that a compound represented by the following chemical formula 2B was used instead of the compound represented by the above chemical formula 2A.

[0166] [Chemical Formula 2B]

[0167]

[0169] Example 6: Preparation of non-aqueous electrolyte

[0170] A non-aqueous electrolyte was prepared in the same manner as in Example 5, except that the compound represented by the above chemical formula 2B was included in the non-aqueous electrolyte at a weight of 3%.

[0172] Example 7: Preparation of non-aqueous electrolyte

[0173] A non-aqueous electrolyte was prepared in the same manner as in Example 5, except that the compound represented by the above chemical formula 2B was included in the non-aqueous electrolyte at 5% by weight.

[0175] Example 8: Preparation of non-aqueous electrolyte

[0176] A non-aqueous electrolyte was prepared in the same manner as in Example 2, except that vinylene carbonate was not included.

[0178] Comparative Example 1: Preparation of non-aqueous electrolyte

[0179] A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that the compound represented by the above chemical formula 2A was not included in the non-aqueous electrolyte.

[0181] Comparative Example 2: Preparation of non-aqueous electrolyte

[0182] A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that a compound represented by the following chemical formula 3 (cis-1,2-dicyanoethylene) was included instead of the compound represented by the above chemical formula 2A.

[0183] [Chemical Formula 3]

[0184]

[0186] Comparative Example 3: Preparation of non-aqueous electrolyte

[0187] A non-aqueous electrolyte was prepared in the same manner as in Example 2, except that a compound represented by Chemical Formula 3 was included instead of the compound represented by Chemical Formula 2A.

[0189] Comparative Example 4: Preparation of non-aqueous electrolyte

[0190] A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that a compound represented by the following chemical formula 4 was included instead of the compound represented by the above chemical formula 2A.

[0191] [Chemical Formula 4]

[0192]

[0194] Comparative Example 5: Preparation of non-aqueous electrolyte

[0195] A non-aqueous electrolyte was prepared in the same manner as in Example 2, except that the compound represented by Chemical Formula 4 was included instead of the compound represented by Chemical Formula 2A.

[0197] Non-aqueous electrolyte Lithium salt (LiPF6) Organic solvent dicyano compounds Vinylene carbonate molar concentration (mol / L) type type Weight % (based on non-aqueous electrolyte) Weight % (based on non-aqueous electrolyte) Example 1 1 EC and EMC (volume ratio 30:70) Chemical formula 2A 0.5 0.5 Example 2 1 EC and EMC (volume ratio 30:70) Chemical formula 2A 3 0.5 Example 3 1 EC and EMC (volume ratio 30:70) Chemical formula 2A 0.1 0.5 Example 4 1 EC and EMC (volume ratio 30:70) Chemical formula 2A 5 0.5 Example 5 1 EC and EMC (volume ratio 30:70) Chemical formula 2B 0.5 0.5 Example 6 1 EC and EMC (volume ratio 30:70) Chemical formula 2B 3 0.5 Example 7 1 EC and EMC (volume ratio 30:70) Chemical formula 2B 5 0.5 Example 8 1 EC and EMC (volume ratio 30:70) Chemical formula 2A 3 - Comparative Example 1 1 EC and EMC (volume ratio 30:70) - - 0.5 Comparative Example 2 1 EC and EMC (volume ratio 30:70) Chemical formula 3 0.5 0.5 Comparative Example 3 1 EC and EMC (volume ratio 30:70) Chemical formula 3 3 0.5 Comparative Example 4 1 EC and EMC (volume ratio 30:70) Chemical formula 4 0.5 0.5 Comparative Example 5 1 EC and EMC (volume ratio 30:70) Chemical formula 4 3 0.5

[0198] Experimental Example

[0199] Experimental Example 1: Measurement of Cathode Reduction Potential

[0200] A coin-type half-cell of Example 1 was manufactured by a conventional method using a graphite electrode as the working electrode, lithium metal as the counter electrode, and the non-aqueous electrolyte of Example 1.

[0201] In addition, coin-type half-cells of Examples 2 to 8 and Comparative Examples 1 to 5 were prepared in the same manner as Example 1, except that the non-aqueous electrolytes of Examples 2 to 8 and Comparative Examples 1 to 5 were used instead of the non-aqueous electrolyte of Example 1.

[0202] For the coin-type half-cells of Examples 1 to 8 and Comparative Examples 1 to 5, cyclic voltammetry was performed between 3V and 0V at a scan rate of 1mA, and the reduction peak voltage measured therefrom is shown in Table 2 below.

[0204] *

[0205] Experimental Example 1 cathodic reduction potential (V) Example 1 2.3 Example 2 2.3 Example 3 2.3 Example 4 2.3 Example 5 2.2 Example 6 2.2 Example 7 2.2 Example 8 2.2 Comparative Example 1 Not observed Comparative Example 2 Not observed Comparative Example 3 Not observed Comparative Example 4 2.7 Comparative Example 5 2.7

[0206] Referring to Table 2, it can be seen that the non-aqueous electrolytes of Examples 1 to 8 undergo reductive decomposition at low potential. This means that the compound of Formula 1 participates in the SEI film formation reaction of the negative electrode and can contribute to improving the durability of the battery.

[0208] Experimental Example 2: Evaluation of High-Temperature Cycle Capacity Retention Rate

[0209] Manufacturing of secondary batteries

[0210] 1. Manufacturing of the cathode

[0211] A cathode slurry was prepared by adding artificial graphite as a cathode active material, carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, an acrylic binder (BM-L302, manufactured by Zeon) as a binder, and carboxymethylcellulose as a thickener to distilled water as a solvent for forming a cathode slurry in a weight ratio of 95:1.5:2.3:1.2.

[0212] As a cathode current collector, the above cathode slurry is applied to one surface of a copper current collector at a rate of 350 mg / 25 cm 2 A negative active material layer was formed by coating with a loading amount, rolling, and drying in a vacuum oven at 130°C for 10 hours, and this was used as the negative electrode.

[0214] 2. Manufacture of the anode

[0215] Li[Ni as a positive electrode active material 0.86 Co 0.05 Mn 0.07 Al 0.02 An anode slurry was prepared by adding O2, carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder to N-methyl-2-pyrrolidone (NMP) as a solvent for forming an anode slurry in a weight ratio of 97.5:1.5:1.0.

[0216] As an anode current collector, the above anode slurry is applied to one surface of an aluminum current collector at a ratio of 607 mg / 25 cm 2A positive electrode active material layer was formed by coating with a loading amount, rolling, and drying in a vacuum oven at 130°C for 10 hours, and this was used as the positive electrode.

[0218] 3. Manufacturing of lithium secondary batteries

[0219] A porous separator was interposed between the anode and cathode prepared above in a battery case, and then the non-aqueous electrolyte prepared in Example 1 was injected to produce the lithium secondary battery of Example 1.

[0221] Lithium secondary batteries of Examples 2 to 8 and Comparative Examples 1 to 5 were each manufactured using the same method as the method for manufacturing the lithium secondary battery of Example 1, except that the non-aqueous electrolyte of Examples 2 to 8 and Comparative Examples 1 to 5 was used instead of the non-aqueous electrolyte of Example 1.

[0223] <High-temperature cycle capacity retention rate evaluation>

[0224] High-temperature cycle capacity retention rate was evaluated using lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5.

[0225] Specifically, the lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 were charged to 4.2V at 45°C under CC / CV and 0.33C conditions using an electrochemical charge / discharger, and then discharged to 3V under CC and 0.33C conditions, with 300 charge / discharge cycles performed as one cycle, and the capacity retention rate was measured.

[0226] The capacity retention rate was calculated using the formula below, and the results are shown in Table 3 below.

[0228] Capacity Retention Rate (%) = (Discharge Capacity after 300 cycles / Discharge Capacity after 1 cycle) × 100

[0230] Experimental Example 3: Evaluation of High-Temperature Cycle Resistance Increase Rate

[0231] Lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 were prepared using the same method as described in Experimental Example 2.

[0232] The lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 were charged to 4.2V at 45°C under CC / CV and 0.33C conditions, and then discharged to 3V under CC and 0.33C conditions, with 300 cycles of charge and discharge being performed.

[0233] After one cycle of charging and discharging, the discharge capacity after one cycle was measured using an electrochemical charge / discharger, and the SOC was adjusted to 50%. Then, a pulse of 2.5C was applied for 10 seconds, and the initial resistance was calculated through the difference between the voltage before and after the pulse application.

[0234] After 300 cycles of charging and discharging, the resistance after 300 cycles was calculated using the same method as above, the resistance increase rate was calculated using the formula below, and the results are shown in Table 3 below.

[0236] Resistance increase rate (%) = (Resistance after 300 cycles - Initial resistance) / Initial resistance × 100

[0238] Experimental Example 4: Evaluation of High-Temperature Cycle Volume Increase Rate

[0239] Lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 were prepared using the same method as described in Experimental Example 2.

[0240] The lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 were subjected to 300 cycles of charge and discharge in the same manner as in Experimental Example 2. At this time, the volume of the lithium secondary battery before charge and discharge (initial volume) and the volume of the lithium secondary battery after 300 cycles were measured, the volume increase rate was calculated using the following formula, and the results are shown in Table 3 below.

[0242] Volume growth rate (%) = (Volume of lithium secondary battery after 300 cycles - Initial volume) / Initial volume × 100

[0244] Experimental Example 2 Experimental Example 3 Experimental Example 4 Capacity retention rate (%) Resistance increase rate (%) Volume increase rate (%) Example 1 95.2 3.5 3.1 Example 2 95.7 2.3 2.8 Example 3 94.7 5.1 4.5 Example 4 93.7 7.5 5.8 Example 5 98.6 0.8 1.2 Example 6 99.2 0.5 0.5 Example 7 97.5 1.5 1.8 Example 8 94.5 4.7 3.6 Comparative Example 1 81.2 17.9 23.2 Comparative Example 2 82.5 15.4 19.5 Comparative Example 3 82.9 15.1 18.3 Comparative Example 4 91.1 10.4 14.5 Comparative Example 5 92.8 9.8 12.1

[0245] Referring to Table 3, it can be seen that the lithium secondary batteries of Examples 1 to 8 using a non-aqueous electrolyte containing a compound represented by Chemical Formula 1 have superior high-temperature cycle life performance compared to the lithium secondary batteries of Comparative Examples 1 to 5, a low rate of increase in resistance with cycles, and a small increase in volume with cycles.

[0247] Experimental Example 5: Evaluation of Capacity Retention Rate After High-Temperature Storage

[0248] Lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 were prepared using the same method as described in Experimental Example 2.

[0249] The lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 were charged to 4.25 V / 55 mA under 0.33 C / 4.25 V constant current / constant voltage (CC / CV) conditions at room temperature and discharged to 2.5 V at 0.33 C to perform initial charge and discharge. Subsequently, they were charged to 4.25 V / 55 mA under 0.33 C / 4.25 V constant current / constant voltage (CC / CV) conditions at room temperature and then stored at 60°C for 12 weeks. After storage, the secondary batteries were charged to 4.25 V / 55 mA under 0.33 C / 4.25 V constant current / constant voltage (CC / CV) conditions at room temperature and discharged to 2.5 V at 0.33 C to measure the capacity at discharge.

[0250] The dosage retention rate was evaluated according to the following formula, and the results are shown in Table 4 below.

[0252] Capacity Retention Rate (%) = (Discharge Capacity after 12 Weeks of Storage / Initial Discharge Capacity) × 100

[0254] Experimental Example 6: Evaluation of Resistance Increase Rate After High-Temperature Storage

[0255] Lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 were prepared using the same method as described in Experimental Example 2.

[0256] The lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 were initially charged and discharged in the same manner as in Experimental Example 5, and after confirming the capacity at room temperature, were charged to an SOC of 50 based on the discharge capacity and discharged for 10 seconds with a current of 3C. The resistance was measured using the difference in voltage drop at that time and set as the initial resistance. After storing at 60°C for 12 weeks, the resistance was measured in the same manner and set as the final resistance. The resistance increase rate was calculated using the following formula. The results are shown in Table 4 below.

[0258] Resistance Increase Rate (%) = (Final Resistance - Initial Resistance) / (Initial Resistance) × 100

[0260] Experimental Example 7: Evaluation of Volume Increase Rate After High-Temperature Storage

[0261] Lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 were prepared using the same method as described in Experimental Example 2.

[0262] The lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 were initially charged and discharged in the same manner as in Experimental Example 5, and each battery was set to SOC 50 based on discharge capacity to measure its volume, which was defined as the initial volume. The volume measured after high-temperature storage at 60°C for 12 weeks at SOC 100% was defined as the final volume, and the volume increase rate of the battery was calculated using the following formula. The results are shown in Table 4 below.

[0264] Volume growth rate (%) = (Final volume - Initial volume) / Initial volume) × 100

[0266] Experimental Example 5 Experimental Example 6 Experimental Example 7 Capacity retention rate (%) Resistance increase rate (%) Volume increase rate (%) Example 1 79.5 27.5 25.7 Example 2 80.2 26.1 23.1 Example 3 78.1 30.2 27.8 Example 4 81.3 24.1 19.7 Example 5 97.2 2.1 2.5 Example 6 98.5 1.6 2.1 Example 7 95.9 2.7 3.7 Example 8 83.7 12.1 10.7 Comparative Example 1 37.5 79.2 80.5 Comparative Example 2 51.4 54.3 57.7 Comparative Example 3 52.1 57.6 55.1 Comparative Example 4 63.2 43.4 40.5 Comparative Example 5 65.0 41.0 38.1

[0267] Referring to Table 4, it can be seen that the lithium secondary batteries of Examples 1 to 8 using a non-aqueous electrolyte containing a compound represented by Chemical Formula 1 have superior high-temperature storage life performance, a lower resistance increase rate, and less volume increase compared to the lithium secondary batteries of Comparative Examples 1 to 5.

[0269] Experimental Example 8: Measurement of water content in electrolyte

[0270] A sample solution of Example 1A was prepared by including 0.5% by weight of a compound represented by the chemical formula 2A in a solvent mixed with ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0271] The amount of water in the electrolyte was measured using a Metrohm 756 Karl Fischer Coulometer with the sample solution of Example 1A, which was 1 hour after the addition of the compound represented by Chemical Formula 2A. The above measurement was performed three times, and the average value of the electrolyte water content was taken as the electrolyte water content of the sample solution of Example 1A and is shown in Table 5 below.

[0273] Except for using the sample solutions of Examples 2A to 7A and Comparative Examples 1A to 3A as described in Table 5 below, the electrolyte moisture content was measured in the same manner as above, and the results are shown in Table 5 below.

[0275] Sample solution Electrolyte moisture content (ppm) menstruum dicyano compounds Types of compounds Content (weight%, based on sample solution weight) Example 1A EC and EMC (volume ratio 30:70) Chemical formula 2A 0.5 15 Example 2A EC and EMC (volume ratio 30:70) Chemical formula 2A 3 10 Example 3A EC and EMC (volume ratio 30:70) Chemical formula 2A 0.1 18 Example 4A EC and EMC (volume ratio 30:70) Chemical formula 2A 5 8 Example 5A EC and EMC (volume ratio 30:70) Chemical formula 2B 0.5 3 Example 6A EC and EMC (volume ratio 30:70) Chemical formula 2B 3 2 Example 7A EC and EMC (volume ratio 30:70) Chemical formula 2B 5 5 Comparative Example 1A EC and EMC (volume ratio 30:70) - - 57 Comparative Example 2A EC and EMC (volume ratio 30:70) Chemical formula 3 0.5 54 Comparative Example 3A EC and EMC (volume ratio 30:70) Chemical formula 3 3 53

[0276] Referring to Table 5, it was confirmed that the sample solutions of Examples 1A to 7A containing the compound represented by Chemical Formula 1 had a much lower amount of water in the electrolyte compared to the sample solutions of Comparative Examples 1A to 3A that did not. This is due to the significantly superior Lewis acid removal ability of the compound represented by Chemical Formula 1, and accordingly, when a non-aqueous electrolyte containing the compound represented by Chemical Formula 1 is applied to a lithium secondary battery, the high-temperature durability, such as high-temperature storage characteristics and high-temperature life characteristics of the lithium secondary battery, can be significantly improved.

Claims

Claim 1 A non-aqueous electrolyte comprising a lithium salt; an organic solvent; and a compound represented by the following chemical formula 1: [Chemical Formula 1] In the above chemical formula 1, L1 and L2 are independently selected from single bonds and alkylene groups having 1 to 5 carbon atoms, and R1 is an alkyl group having 1 to 5 carbon atoms. Claim 2 In claim 1, the compound represented by Chemical Formula 1 is a non-aqueous electrolyte that is a compound represented by the following Chemical Formula 1A: [Chemical Formula 1A] In the above chemical formula 1A, R1 is an alkyl group having 1 to 5 carbon atoms. Claim 3 In claim 1, the compound represented by Chemical Formula 1 is a non-aqueous electrolyte comprising a compound represented by the following Chemical Formula 2B: [Chemical Formula 2B] . Claim 4 In claim 1, the compound represented by Chemical Formula 1 is included in the non-aqueous electrolyte in an amount of 0.01% to 7% by weight. Claim 5 In claim 1, the compound represented by Chemical Formula 1 is included in the non-aqueous electrolyte at a concentration of 1.5% to 3.5% by weight. Claim 6 The non-aqueous electrolyte according to claim 1, wherein the lithium salt comprises at least one selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, LiN(CF3SO2)2, CF3SO3Li, LiC(CF3SO2)3, LiC4BO8, LiTFSI, and LiFSI. Claim 7 In claim 1, the lithium salt is a non-aqueous electrolyte comprising LiPF6. Claim 8 In claim 1, the lithium salt is a non-aqueous electrolyte contained in the non-aqueous electrolyte at a concentration of 0.5 M to 5 M. Claim 9 In claim 1, the organic solvent is a non-aqueous electrolyte comprising at least one selected from linear carbonate and cyclic carbonate. Claim 10 The non-aqueous electrolyte of claim 1 further comprises at least one additive selected from the group consisting of vinylene carbonate, vinylethylene carbonate, propane sulfone, succinonitrile, adiponitrile, ethylene sulfate, propene sulfone, fluoroethylene carbonate, LiPO2F2, LiODFB (Lithium difluorooxalatoborate), LiBOB (Lithium bis-(oxalato)borate), and TMSPi (Tris(trimethylsilyl) Phosphite). Claim 11 In claim 10, the additive is a non-aqueous electrolyte that is vinylene carbonate. Claim 12 In claim 10, the additive is included in the non-aqueous electrolyte in an amount of 0.1% to 15% by weight. Claim 13 A lithium secondary battery comprising: a negative electrode; a positive electrode facing the negative electrode; a separator interposed between the negative electrode and the positive electrode; and a non-aqueous electrolyte according to claim 1.

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