Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery with improved high-temperature cycle characteristics and, in particular, to a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator; and an electrolyte, wherein the positive electrode includes lithium iron phosphate and lithium nickel cobalt manganese oxide as positive electrode active materials, the positive electrode has a loading amount of 32 mg / cm2 to 60 mg / cm2, the electrolyte includes: a lithium salt; a first organic solvent; a second organic solvent; a first additive; and a second additive, the first organic solvent is a cyclic lactone compound, the second organic solvent is a carbonate-based organic solvent, the first additive is an oligomer including repeating units derived from a monomer represented by chemical formula 1 and repeating units derived from a monomer represented by chemical formula 2, and the second additive is an imidazole-based compound.

Description

Lithium secondary battery Cross-citation with related application(s) This application claims the benefit of priority to Korean Patent Application No. 10-2023-0189771, filed December 22, 2023 and Korean Patent Application No. 10-2024-0171420, filed November 26, 2024, the entire contents of which are incorporated herein by reference. Technical field The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery with improved high temperature and high voltage stability. Recently, lithium secondary batteries are being used in various fields including mobile electronic devices such as mobile phones, PDAs, and laptop computers. In particular, as interest in environmental issues grows, research on lithium secondary batteries with high energy density and discharge voltage as a power source for electric vehicles that can replace vehicles that use fossil fuels such as gasoline and diesel vehicles, which are one of the main causes of air pollution, is being actively conducted, and some are in the commercialization stage. Meanwhile, in order to use the lithium secondary battery as a power source for an electric vehicle, it must be able to stably maintain high output at high temperatures and high voltages. To this end, the lithium secondary battery is considering using carbon materials, lithium metal, sulfur compounds, silicon compounds, tin compounds, etc. as the main components of the negative active material, and lithium-containing cobalt oxide (LiCoO2) or nickel-based lithium transition metal oxide is mainly used as the positive active material. However, in the case of the lithium-containing cobalt oxide, the energy density and output characteristics are reaching their practical limits, and especially when used in high-energy density applications, due to its structural instability, it causes structural transformation at a high temperature under a charged state, oxygen release within the structure, and an exothermic reaction with the electrolyte within the battery, which causes an explosion of the secondary battery. In the case of the nickel-based lithium transition metal oxide, since the output rapidly decreases in a low SOC range (for example, SOC 30% or less), there is a disadvantage in that the usable SOC range is greatly limited, and thus there are limitations in applying it to fields such as electric vehicles where output characteristics are particularly important. In particular, the nickel-based lithium transition metal oxide has low structural stability, and when exposed to high temperatures or high voltage, there is a problem that the transition metal within the positive electrode active material is eluted or a side reaction with the electrolyte is induced, which rapidly deteriorates the battery performance. Recently, to solve these problems, a method of using lithium iron phosphate with an olivine structure that has excellent high-temperature safety instead of nickel-based lithium transition metal oxide is being studied. However, since the above lithium iron phosphate has a lower theoretical capacity than the nickel-based lithium transition metal oxide used previously, it has a disadvantage in that the energy density is relatively lower than that of the nickel-based lithium transition metal oxide when designing an electrode under the same conditions. To solve these problems, high-loading electrodes that increase the amount of electrode active material applied per area (loading amount) when applying lithium iron phosphate have recently been attempted. However, since the high-loading electrode is designed to have a high degree of active material coating and to increase the density of the electrode, the degree of electrode compression is very large, and accordingly, the porous structure inside the electrode is insufficient, which has the disadvantage of reducing electrolyte impregnation. This reduction in electrolyte impregnation can cause a decrease in "charge transfer", which is a reaction between lithium ions and electrons, and this can appear in the form of an increase in battery resistance. Accordingly, there is a demand for the development of a new secondary battery that can improve electrolyte impregnation properties and enhance charge mobility while manufacturing a secondary battery using a high-loading electrode. The present invention is intended to solve the above problems, and to provide a lithium secondary battery which, when applying a high-loading cathode, forms a stable film on the electrode surface by using an electrolyte with improved impregnation properties by a specific composition, thereby increasing the charge transfer phenomenon, thereby suppressing an increase in resistance during high-temperature storage, and ensuring excellent cycle capacity retention. [1] The present invention relates to a lithium secondary battery comprising a cathode, an anode, a separator and an electrolyte, wherein the cathode comprises lithium iron phosphate and lithium nickel cobalt manganese oxide as cathode active materials, and the loading amount of the cathode is 32 mg / cm 2 60 mg / cm 2 and the electrolyte comprises a lithium salt; a first organic solvent; a second organic solvent; a first additive; and a second additive, wherein the first organic solvent is a cyclic lactone compound, the second organic solvent is a carbonate-based organic solvent, the first additive is an oligomer including a repeating unit derived from a monomer represented by the following chemical formula 1 and a repeating unit derived from a monomer represented by the following chemical formula 2, and the second additive is an imidazole-based compound. [Chemical Formula 1] In the above chemical formula 1, R1 is hydrogen or an alkyl group having 1 to 3 carbon atoms, R2 is an alkyl group having 1 to 20 carbon atoms. [Chemical formula 2] In the above chemical formula 2, R3 is hydrogen or an alkyl group having 1 to 3 carbon atoms, R4 and R5 are each independently an alkylene group having 1 to 10 carbon atoms. [2] The present invention provides a lithium secondary battery, wherein, in the above [1], the lithium iron phosphate comprises a compound represented by the following chemical formula 3: [Chemical Formula 3] Li 1+a Fe x M y (PO 4-b )X' b In the above chemical formula 3, M is any one selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X' is any one element selected from the group consisting of F, S, and N, and -0.5≤a≤0.5, 0.5≤x≤1.0, 0≤y≤1.0, and 0≤b≤0.3. [3] The present invention provides a lithium secondary battery, wherein, in the above [1] or [2], the lithium iron phosphate includes lithium iron phosphate (LiFePO4) or lithium manganese iron phosphate (LiMnFePO4). [4] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to [3], the lithium nickel cobalt manganese oxide comprises a compound represented by the following chemical formula 4: [Chemical Formula 4] Li 1+a1 Ni x1 Co y1 M 1 z M 2 w O2 In the above chemical formula 4, M 1 is Mn, Al or a combination of these, and M 2 is at least one selected from the group consisting of Al, Zr, W, Ti, Mg, Ca and Sr, and 0≤a1≤0.5, 0 <x1≤0.6, 0<y1≤0.4, 0<z≤0.4, 0≤w≤0.1이다. [5] The present invention, in at least one of the above [1] to [4], the lithium nickel cobalt manganese oxide is Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.6 Co 0.2 Mn 0.2 )O2, Li(Ni) 0.6 Co 0.1 Mn 0.3 )O 2, Li(Ni) 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O2 and Li(Ni 0.90 Mn 0.05 Co 0.05 ) provides a lithium secondary battery selected from the group consisting of O2. [6] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to [5], the lithium iron phosphate and lithium nickel cobalt manganese oxide are included in a weight ratio of 50:50 to 80:20. [7] The present invention, in at least one of the above [1] to [6], the lithium iron phosphate is lithium iron phosphate (LiFePO4), and the lithium nickel cobalt manganese oxide is Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni) 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.8 Mn 0.1Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O2 and Li(Ni 0.90 Mn 0.05 Co 0.05 ) provides a lithium secondary battery selected from the group consisting of O2. [8] The present invention, in at least one of the above [1] to [9], the lithium iron phosphate is lithium manganese iron phosphate (LiMnFePO4), and the lithium nickel cobalt manganese oxide is Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.6 Co 0.2 Mn 0.2 )O2 and Li(Ni) 0.6 Co 0.1 Mn 0.3 ) provides a lithium secondary battery selected from the group consisting of O2. [9] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to [8], the cyclic lactone compound includes gamma-butyrolactone.

[0010] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to [9], the second organic solvent is a cyclic carbonate-based organic solvent.

[0011] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to

[0010] , the first organic solvent and the second organic solvent are included in a volume ratio of 50:50 to 99:1.

[0012] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to

[0011] , in the chemical formula 1, R1 is hydrogen or an alkyl group having 1 or 2 carbon atoms.

[0013] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to

[0012] , in the chemical formula 1, R2 is an alkyl group having 1 to 10 carbon atoms.

[0014] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to

[0013] , in the chemical formula 2, R3 is hydrogen or an alkyl group having 1 or 2 carbon atoms.

[0015] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to

[0014] , in the chemical formula 2, R4 and R5 are each independently an alkylene group having 1 to 8 carbon atoms.

[0016] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to

[0015] , the oligomer is an oligomer represented by the following chemical formula 5: [Chemical Formula 5] In the above chemical formula 5, n is an integer from 1 to 500, and m is an integer from 1 to 300.

[0017] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to

[0016] , the first additive is included in an amount of 0.01 wt% to 10 wt% based on the total weight of the electrolyte.

[0018] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to

[0017] , the imidazole compound is a compound represented by the following chemical formula 6: [Chemical formula 6] In the above chemical formula 6, R is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, and R6 to R8 are each independently hydrogen, an alkyl group having 1 to 3 carbon atoms, or -CN.

[0019] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to

[0018] , the imidazole compound is a compound represented by the following chemical formula 6A: [Chemical Formula 6A] .

[0020] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to

[0019] , the second additive is included in an amount of 0.01 wt% to 10 wt% based on the total weight of the electrolyte.

[0021] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to

[0020] , the negative electrode includes a carbon-based active material, a silicon-based active material, or a mixture of a carbon-based active material and a silicon-based active material. The lithium secondary battery according to the present invention can realize excellent high temperature and high voltage safety by using a high-loading positive electrode containing lithium iron phosphate and lithium nickel cobalt manganese oxide in a specific composition ratio. In addition, the lithium secondary battery according to the present invention can form a film having low resistance and improved charge mobility on the surface of the high-loading positive electrode by using an electrolyte having a specific composition together when applying the high-loading positive electrode, thereby preventing electrode deterioration, and thereby improving high temperature and high voltage stability, and can realize a lithium secondary battery capable of securing excellent cycle capacity retention. Hereinafter, the present invention will be described in more detail. The terms and words used in this specification and claims are only used to describe exemplary embodiments, and should not be construed as limited to their usual or dictionary meanings, and should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to describe his own invention in the best manner. For example, in this specification, the terms “comprise,” “include,” or “have” should be understood to specify the presence of a feature, number, step, component, or combination thereof, but not to exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof. In addition, in the description of "carbon atoms a to b" in the present specification, "a" and "b" represent the number of carbon atoms included in a specific functional group. That is, the functional group may include "a" to "b" carbon atoms. For example, "an alkylene group having 1 to 5 carbon atoms" refers to an alkylene group including 1 to 5 carbon atoms, namely, -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2(CH2)CH-, -CH2CH2CH2CH2CH2-, and -CH(CH2)CH2CH2-. In addition, in the present specification, the term "alkylene group" means a branched or unbranched aliphatic hydrocarbon group or a functional group in which one hydrogen atom is missing from carbon atoms located at both ends of the aliphatic hydrocarbon group. In one embodiment, the alkylene group can be substituted or unsubstituted. The alkylene group includes, but is not limited to, a methylene group, an ethylene group, a propylene group, an isopropylene group, a butylene group, an isobutylene group, a tert-butylene group, a pentylene group, a 3-pentylene group, and the like, and each of these can be optionally substituted in other embodiments. Additionally, in this specification, unless otherwise defined, “substitution” means that at least one hydrogen bonded to carbon is replaced with another element such as fluorine. Additionally, in this specification, unless otherwise defined, “*” means a connected portion between terminals of a chemical formula. In addition, in this specification, the "loading amount" means the amount of active material per unit area of ​​the positive electrode active material layer including lithium iron phosphate of an olivine structure formed on the current collector, and is expressed as "mg / cm 2 " is expressed as. At this time, in this specification, "loading amount" means the total sum of the loading amounts on both sides of the anode. Hereinafter, the present invention will be described in detail. A lithium secondary battery according to the present invention comprises at least one of the configurations disclosed below, and may comprise any combination between technically possible configurations among the configurations below. Lithium secondary battery The present invention relates to a lithium secondary battery. Specifically, the present invention provides a lithium secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte. The above positive electrode may include lithium iron phosphate and lithium nickel cobalt manganese oxide as positive electrode active materials. The loading amount of the above anode is 32 mg / cm 2 60 mg / cm 2 It could be. The above electrolyte may include a lithium salt; a first organic solvent; a second organic solvent; a first additive; and a second additive. The first organic solvent may include a cyclic lactone compound. The second organic solvent may include a carbonate-based organic solvent. The above first additive may include an oligomer including a repeating unit derived from a monomer represented by the following chemical formula 1 and a repeating unit derived from a monomer represented by the following chemical formula 2. [Chemical Formula 1] In the above chemical formula 1, R1 is hydrogen or an alkyl group having 1 to 3 carbon atoms, R2 is an alkyl group having 1 to 20 carbon atoms. [Chemical formula 2] In the above chemical formula 2, R3 is hydrogen or an alkyl group having 1 to 3 carbon atoms, R4 and R5 are each independently an alkylene group having 1 to 10 carbon atoms. The second additive may include an imidazole compound. (1) Bipolar The positive electrode of the present invention may include lithium iron phosphate as a positive electrode active material. Specifically, the lithium iron phosphate may include a compound represented by the following chemical formula 3. [Chemical Formula 3] Li 1+a Fe x M y (PO 4-b )X' b In the above chemical formula 3, M is one selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y, X' is one or more elements selected from the group consisting of F, S, and N, -0.5≤a≤0.5, 0 <x≤1, 0≤y≤1 및 0≤b≤0.3이다. Lithium iron phosphate represented by the above chemical formula 3 may include, as a representative example, lithium iron phosphate (LiFePO4) or lithium manganese iron phosphate (LiFeMnPO4). The lithium iron phosphate represented by the above chemical formula 3 can use primary particles of nanometer size for high input / output of lithium ions, and it is also possible to use secondary particles, which are aggregates of these primary particles, by assembling them. For example, when using primary particles as the lithium iron phosphate, the particle size may be 50 to 2000 nm, more specifically, 200 to 1100 nm. In addition, when using secondary particles, which are aggregates of these primary particles by assembling them, the average particle diameter (D50) of the secondary particles may be 0.5 ㎛ to 30 ㎛. The lithium iron phosphate represented by the above chemical formula 3 may have an amorphous layer of carbon or metal oxide coated on its surface. In this case, since the amorphous layer of carbon or metal oxide coated on its surface is not crystalline, lithium ions are inserted and deintercalated into the lithium iron phosphate of the core portion through the amorphous layer of the shell. The amorphous layer of carbon or metal oxide coated on its surface allows lithium ions to pass through and also has excellent electron conductivity, so it can act as a current path to the lithium iron phosphate core, which is an active material, and thus can enable charging and discharging at a high rate. In addition, when the surface of the lithium iron phosphate is coated with the amorphous layer of carbon or metal oxide, safety can be further increased in that unnecessary reactions between the core material and the electrolyte can be controlled. The lithium iron phosphate represented by the above chemical formula 3 is structurally stable against volume changes due to charge and discharge and has high thermal stability because phosphorus and oxygen form strong covalent bonds within the tetrahedral structure of PO4. However, compared to lithium transition metal oxides, the movement of lithium ions and the flow of electrons are not smooth due to the strong oxygen bond, so the electrical conductivity is relatively low. Therefore, in the present invention, in order to increase the electrical conductivity of the positive electrode, lithium nickel cobalt manganese oxide is used together with the lithium iron phosphate, thereby further improving the electrical conductivity of the positive electrode. The above lithium nickel cobalt manganese oxide may include a compound represented by the following chemical formula 4. [Chemical Formula 4] Li 1+a1 Ni x1 Co y1 M 1 z M 2 w O2 In the above chemical formula 4, M 1 is Mn, Al or a combination thereof, M 2 is one selected from the group consisting of Al, Zr, W, Ti, Mg, Ca and Sr, and 0≤a1≤0.5, 0 <x1<1.0, 0<y1≤0.4, 0<z≤0.4, 0≤w≤0.1 이다. In the chemical formula 4, the 1+a1 represents the molar ratio of lithium in the lithium nickel cobalt manganese oxide, and may be 0≤a1≤0.5, or 0≤a1≤0.2, and preferably 0≤a1≤0.1. When the molar ratio of lithium satisfies the above range, the layered crystal structure of the lithium nickel cobalt manganese oxide can be stably formed. When the a1 exceeds 0.5, there is a concern that the initial discharge capacity of the battery may decrease or the Li byproduct on the surface of the positive electrode active material may increase too much, which may lead to severe gas generation during high-temperature operation. The above x1 represents the molar ratio of nickel among the total metals excluding lithium in lithium nickel cobalt manganese oxide, and is 0. <x1<1.0일 수 있고, 또는 0.55<x1<1.0 일 수 있다. 상기 x1가 상기 범위를 만족할 때 우수한 용량 특성을 구현할 수 있다. The above y1 represents the molar ratio of cobalt among all metals excluding lithium in lithium nickel cobalt manganese oxide, and is 0. <y1≤0.4, 구체적으로 0<y1≤0.3, 더욱 구체적으로는 0.05≤y1≤0.3일 수 있다. The above z is M among all metals except lithium in the lithium transition metal oxide.1 It represents the molar ratio of elements, 0 <z≤0.4, 바람직하게는 0<z≤0.3, 더 바람직하게는 0.01≤z≤0.3일 수 있다. The above w is M among all metals except lithium in the lithium transition metal oxide. 2 It represents the molar ratio of elements, 0 <w≤0.1, 바람직하게는 0<w≤0.05, 더 바람직하게는 0.01≤w≤0.02일 수 있다. Specifically, the lithium nickel cobalt manganese oxide is Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.6 Co 0.2 Mn 0.2 )O2, Li(Ni) 0.6 Co 0.1 Mn 0.3 )O 2, Li(Ni) 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O2 and Li(Ni 0.90 Mn 0.05 Co 0.05 ) can be any one selected from the group consisting of O2. Meanwhile, in the cathode active material of the present invention, the lithium iron phosphate and lithium nickel cobalt manganese oxide may be included in a weight ratio of 50:50 to 80:20, and specifically, may be included in a weight ratio of 50:50 to 70:30. When the mixing ratio of the above lithium iron phosphate and lithium nickel cobalt manganese oxide satisfies the above range, the high temperature and high voltage safety of the battery can be secured while improving the electrical conductivity. Specifically, when the content ratio of lithium iron phosphate to the lithium nickel cobalt manganese oxide is less than 80 weight ratio, excellent capacity characteristics and electrical conductivity can be secured, and when the content ratio of lithium iron phosphate to the lithium nickel cobalt manganese oxide is 50 weight ratio or more, high temperature and high voltage stability can be secured. In particular, the cathode active material of the present invention, when the lithium iron phosphate is lithium iron phosphate (LiFePO4), in order to implement a high voltage of 4.4 V or higher and a high energy density, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni) 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O2 and Li(Ni 0.90 Mn 0.05 Co 0.05 ) It is preferable to use in combination any one lithium nickel cobalt manganese oxide selected from the group consisting of O2. In addition, in the case where the positive electrode active material of the present invention is lithium manganese iron phosphate (LiFeMnPO4), in order to realize high temperature stability and high energy density, Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.6 Co0.2 Mn 0.2 )O2 and Li(Ni) 0.6 Co 0.1 Mn 0.3 ) It is preferable to use in combination any one of the lithium nickel cobalt manganese oxides selected from the group consisting of O2. In addition, the present invention has a loading amount of 32 mg / cm of the positive electrode including lithium iron phosphate and lithium nickel cobalt manganese oxide for high-capacity design of the electrode. 2 Ideal (cross-sectional loading: 16 mg / cm 2 ) and specifically 32 mg / cm 2 60 mg / cm 2 may be, more preferably 40 mg / cm 2 60 mg / cm 2 If the loading amount of the above positive electrode satisfies the above range, a high energy density battery design is possible. The above positive electrode may include a positive electrode current collector; and a positive electrode composite layer disposed on at least one surface of the positive electrode current collector. In this case, the positive electrode composite layer may include a mixture of lithium iron phosphate and lithium nickel cobalt manganese oxide as the positive electrode active material. The thickness of the above positive electrode collector can typically have a thickness of 3 to 500 μm. The above-mentioned positive electrode current collector may form fine irregularities on the surface to strengthen the bonding strength of the positive electrode active material. For example, the above-mentioned positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc. The above positive electrode composite layer is disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode composite layer may be disposed on one surface or both surfaces of the positive electrode current collector. In addition, lithium iron phosphate represented by the chemical formula 3 may be included in the positive electrode composite layer at 80 to 99 wt% in consideration of sufficient capacity, etc. Meanwhile, the positive electrode composite layer may further include a binder and / or a conductive material together with the positive electrode active material described above. The above binder serves to improve the adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the current collector. Examples of such binders include: a fluorine resin binder such as polyvinylidene fluoride (PVDF); a rubber binder including styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; a cellulose binder including carboxyl methyl cellulose (CMC), starch, hydroxy propyl cellulose, and regenerated cellulose; a polyalcohol binder including polyvinyl alcohol; a polyolefin binder including polyethylene and polypropylene; a polyimidazole binder; a polyester binder; and a silane binder, one of which alone or a mixture of two or more thereof may be used. The above binder may be included in the positive electrode composite layer at 0.1 to 15 wt%, preferably 0.1 to 10 wt%. Next, the conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without special restrictions. Specific conductive materials that can be used include carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as fluorinated carbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives. The above-mentioned challenging agent can be added in an amount of 1 to 30 wt% in the positive electrode composite layer. The above positive electrode can be manufactured by coating a positive electrode slurry containing a positive electrode active material and optionally a binder, a conductive material, and a solvent for forming a positive electrode slurry on the positive electrode current collector, and then drying and rolling. Alternatively, a positive electrode can be manufactured by mixing a positive electrode active material and optionally a binder, a conductive material, etc. to manufacture a film, and then laminating the film on a positive electrode current collector. The solvent for forming the positive electrode slurry may include at least one selected from the group consisting of distilled water, N-methyl pyrrolidone, ethanol, methanol and isopropyl alcohol, preferably N-methyl pyrrolidone, in terms of facilitating dispersion of the positive electrode active material, binder and / or conductive agent. (2) Cathode Next, let's explain the cathode. The above negative electrode may include a negative electrode active material. As the above negative active material, a carbon-based active material, a silicon-based active material, or a mixture of a carbon-based active material and a silicon-based active material can be used. As the carbon-based active material, various carbon-based active materials used in the art, for example, graphite-based materials such as natural graphite, artificial graphite, and Kish graphite; high-temperature calcined carbon such as pyrolytic carbon, mesophase pitch based carbon fiber, carbon microbeads, mesophase pitches, and petroleum or coal tar pitch derived cokes, soft carbon, and hard carbon, etc. can be used. The shape of the carbon-based active material is not particularly limited, and materials of various shapes such as amorphous, plate-like, flaky, spherical, or fibrous can be used. Specifically, the carbon-based active material may be either natural graphite or artificial graphite, and natural graphite and artificial graphite may be used together to increase adhesion to the current collector and suppress desorption of the active material. In addition, the silicon-based active material may be, for example, metal silicon (Si), silicon oxide (SiO). x, here 0 <x<2) 실리콘 탄화물(SiC) 및 Si-Y 합금(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님)로 이루어진 군으로부터 선택된 1종 이상을 포함할 수 있다. 상기 원소 Y로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db (dubnium), Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, 및 이들의 조합으로 이루어진 군에서 선택될 수 있다. The average particle diameter (D) of the above silicon-based active material 50 ) may be 1 ㎛ to 30 ㎛, preferably 2 ㎛ to 15 ㎛, in order to reduce side reactions with the electrolyte while ensuring structural stability during charging and discharging. In addition, the negative electrode of the present invention may include at least one selected from the carbon-based active material and the silicon-based active material. Specifically, the negative electrode of the present invention may include the carbon-based active material and the silicon-based active material. At this time, the weight ratio of the silicon-based active material and the carbon-based active material may be 1:99 to 30:70, specifically 3:97 to 15:85. When the mixing ratio of the silicon-based active material and the carbon-based active material satisfies the above range, the capacity characteristics can be improved while the volume expansion of the silicon-based active material is suppressed, thereby ensuring excellent cycle performance. The above negative electrode may include a negative electrode current collector; and a negative electrode composite layer disposed on at least one surface of the negative electrode current collector. In this case, the negative electrode active material may be included in the negative electrode composite layer. The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. The above negative electrode collector may typically have a thickness of 3 to 500 μm. The above negative electrode current collector may form fine irregularities on the surface to strengthen the bonding strength of the negative electrode active material. For example, the above negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc. The above negative electrode composite layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode composite layer may be disposed on one surface or both surfaces of the negative electrode current collector. The above negative active material may be included in the negative electrode composite layer at 60 wt% to 99 wt% in order to sufficiently express the capacity in the secondary battery while minimizing the effect of volume expansion / contraction on the battery. The above negative electrode composite layer may further include a conductive material and / or a binder together with the above negative electrode active material. The conductive agent is a component for further improving the conductivity of the negative electrode active material, and is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as fluorinated carbon powder, aluminum powder, 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, etc. can be used. The above-mentioned challenging agent may be added to the cathode composite layer in an amount of 10 wt% or less, preferably 5 wt% or less. The above binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and typically includes a fluorine resin binder such as polyvinylidene fluoride (PVDF); a rubber binder including styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; a cellulose binder including carboxymethyl cellulose (CMC), starch, hydroxy propyl cellulose, and regenerated cellulose; a polyalcohol binder including polyvinyl alcohol; a polyolefin binder including polyethylene and polypropylene; a polyimidazole binder; a polyester binder; and a silane binder. The above binder may be included in the cathode composite layer at 0.1 to 15 wt%, preferably 0.1 to 10 wt%. The above negative electrode can be manufactured by coating a negative electrode slurry including a negative electrode active material and optionally a binder, a conductive material, and a solvent for forming a negative electrode slurry on the negative electrode current collector, and then drying and rolling. Alternatively, the negative electrode can be manufactured by mixing a negative electrode active material and optionally a binder, a conductive material, etc. to manufacture a film, and then laminating the film on the negative electrode current collector. The solvent for forming the negative electrode slurry may include at least one selected from the group consisting of distilled water, N-methyl pyrrolidone, ethanol, methanol and isopropyl alcohol, preferably distilled water, in terms of facilitating dispersion of the negative electrode active material, binder and / or conductive agent. (3) Membrane The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. If it is a separator commonly used in lithium secondary batteries, it can be used without any special restrictions. In particular, it is preferable that it have low resistance to the movement of ions in a non-aqueous electrolyte and excellent non-aqueous electrolyte wetting ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used as the separator. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, or the like can be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure. (4) Electrolyte Next, the electrolyte of the present invention may include a lithium salt; a first organic solvent; a second organic solvent; a first additive; and a second additive, and specific examples of each component are as described below. (4-1) Lithium salt First, the lithium salt can be used without limitation as an electrolyte for lithium secondary batteries, for example, Li as a cation. + , and the anion is F - , Cl - , Br - , I - , 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 - Any one selected from the group consisting of may be mentioned. Specifically, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, LiB10 Cl 10 , LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2(lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2(lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), and LiN(SO2CF3)2(lithium bis(trifluoromethane sulfonyl)imide, LiTFSI), and specifically, LiBF4, LiPF6, LiN(SO2F)2(lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2(lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), and LiN(SO2CF3)2(lithium bis(trifluoromethane sulfonyl)imide, LiTFSI) may be included. In addition to these, lithium salts commonly used in electrolytes of lithium secondary batteries may be used without limitation. The above lithium salt may be appropriately changed within a normally usable range, but in order to obtain an optimal effect of forming a film for preventing corrosion of the electrode surface, it may be included in the electrolyte at a concentration of 0.8 M to 3.0 M, specifically, at a concentration of 1.0 M to 2.0 M, and preferably at a concentration of 1.0 M to 1.8 M. When the concentration of the lithium salt is within the above range, the viscosity of the electrolyte can be controlled to achieve optimal impregnation, and the mobility of lithium ions can be improved, thereby improving the capacity characteristics and cycle characteristics of a lithium secondary battery. (4-2) First organic solvent Next, the first organic solvent is described. The first organic solvent may include a cyclic lactone compound. The above cyclic lactone compound is a compound having high dielectric constant and ionic conductivity, and can improve the charge transfer degradation phenomenon caused when operating a high-loading electrode. The above cyclic lactone compound may include gamma-butyrolactone. The first organic solvent may be included in an amount of 39 wt% to 80 wt% based on the total weight of the electrolyte, specifically, in an amount of 48 wt% to 80 wt%, and more preferably, in an amount of 52 wt% to 70 wt%. When the content of the first organic solvent satisfies the above range, the lithium ion transfer characteristics can be improved, thereby achieving a battery resistance reduction effect. (4-3) Second organic solvent Next, the second organic solvent is explained. The above second organic solvent may include a carbonate-based organic solvent so that decomposition due to oxidation reactions, etc. during the charging and discharging process of the secondary battery can be minimized and the desired characteristics can be exhibited together with an additive. Specifically, it is preferable that the carbonate-based organic solvent include one selected from the group consisting of a cyclic carbonate-based organic solvent having high ionic conductivity and high dielectric constant and a linear carbonate-based organic solvent having low viscosity and low dielectric constant, and specifically may include a cyclic carbonate-based organic solvent. The above cyclic carbonate-based organic solvent may specifically include one or two or more organic solvents 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), and among these, ethylene carbonate capable of maintaining a stable SEI film passivation ability may be mentioned. In addition, the linear carbonate-based organic solvent may be one or two or more organic solvents selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, and among these, ethyl methyl carbonate (EMC) or dimethyl carbonate (DMC) having a small molecular size and low viscosity characteristics among the linear carbonate-based organic solvents may be exemplified. When the cyclic carbonate and linear carbonate are mixed and used as the second organic solvent, in order to secure low viscosity characteristics, the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent may be mixed and used in a volume ratio of about 1:99 to 50:50, or may be mixed and used in a volume ratio of 20:80 to 40:60. Meanwhile, in the present invention, the first organic solvent and the second organic solvent may be included in a volume ratio of 50:50 to 99:1, and specifically, may be included in a volume ratio of 80:20 to 99:1. When the mixing ratio of the first organic solvent and the second organic solvent satisfies the above range, a high ion transfer characteristic effect can be achieved, and battery performance with low resistance characteristics can be secured. That is, when the volume ratio of the first organic solvent is 50 or more, the ion transfer characteristic effect can be secured, and when the volume ratio is 99 or less, a stable film can be formed, thereby improving the battery life characteristics. (4-4) First additive Next, the first additive will be described. The above first additive may include an oligomer comprising a repeating unit derived from a monomer represented by the following chemical formula 1 and a repeating unit derived from a monomer represented by the following chemical formula 2: [Chemical Formula 1] In the above chemical formula 1, R1 is hydrogen or an alkyl group having 1 to 3 carbon atoms, R2 is an alkyl group having 1 to 20 carbon atoms. [Chemical formula 2] In the above chemical formula 2, R3 is hydrogen or an alkyl group having 1 to 3 carbon atoms, R4 and R5 are each independently an alkylene group having 1 to 10 carbon atoms. The present invention includes an oligomer including a repeating unit derived from a monomer based on an acrylate structure containing an ether group and a terminal nitrile group as a first additive, thereby improving the effect of forming a low-resistance CEI (cathode electrolyte interphase) film by adsorbing an ether group, a nitrile group, and an ester functional group on the surface of the positive electrode, thereby reducing the interfacial resistance. In addition, since the oligomer can form a high-ion conductive film through the ether group, the nitrile group, and the ester functional groups in the structure, the electrolyte impregnation property and the ion transfer capability can be improved, thereby preventing electrode deterioration. At this time, since the nitrile group or the ester functional group can chelate a metal ion such as Fe or Mn, the elution of the metal ion from the positive electrode can be effectively suppressed. Accordingly, the high-temperature life characteristics and high-temperature durability of a lithium secondary battery can be further improved. Meanwhile, in the chemical formula 1, R1 may be hydrogen or an alkyl group having 1 or 2 carbon atoms, and specifically, may be an alkyl group having 1 or 2 carbon atoms. In addition, in the chemical formula 1, R2 may be an alkyl group having 1 to 10 carbon atoms, or an alkyl group having 1 to 5 carbon atoms, and specifically, may be an alkyl group having 1 to 5 carbon atoms. In addition, in the chemical formula 2, R3 may be hydrogen or an alkyl group having 1 or 2 carbon atoms, and specifically, R1 may be an alkyl group having 1 or 2 carbon atoms. In addition, in the chemical formula 2, R4 may be an alkylene group having 1 to 8 carbon atoms, or an alkylene group having 1 to 5 carbon atoms, and specifically, an alkylene group having 2 to 5 carbon atoms. In addition, in the chemical formula 2, R5 may be an alkylene group having 1 to 8 carbon atoms, or an alkylene group having 1 to 5 carbon atoms, and specifically, an alkylene group having 2 to 5 carbon atoms. More specifically, the oligomer of the present invention may be an oligomer represented by the following chemical formula 5. [Chemical Formula 5] In the above chemical formula 5, n is an integer from 1 to 500, and m is an integer from 1 to 300. In the above chemical formula 5, n can be an integer from 1 to 300, or can be an integer from 1 to 200, and specifically can be an integer from 1 to 100. Additionally, in the chemical formula 5, m can be an integer from 1 to 300, or can be an integer from 1 to 200, and specifically can be an integer from 1 to 100. The weight average molecular weight (Mw) of the oligomer of the present invention can be controlled by the number of repeating units, and can be about 3,000 g / mol to 300,000 g / mol, specifically 5,000 g / mol to 50,000 g / mol. When the weight average molecular weight of the oligomer is within the above range, the oligomer property itself is prevented from becoming rigid, so that the affinity with a non-aqueous electrolyte solvent is increased and can be easily dissolved, so that uniform and excellent electrolyte formation can be expected. The above weight average molecular weight can be measured using a gel permeation chromatography (GPC) device, and unless otherwise specified, the molecular weight may mean the weight average molecular weight. For example, in the present invention, the measurement is performed using the Agilent 1200 series under GPC conditions, and the column used at this time can be an Agilent PL mixed B column, and the solvent can be THF or DMF. Meanwhile, the first additive may be included in an amount of 0.01 wt% to 10 wt% based on the total weight of the electrolyte. When the content of the first additive of the present invention satisfies the above range, a stable film formation effect on the surfaces of the positive and negative electrodes can be obtained, and the anion stabilization of the lithium salt and the dissolution of the transition metal (Fe) can be suppressed. When the content of the first additive is 0.01 wt% or more, the anion stabilization can be maintained more stably due to the formation of a complex with the anion of the lithium salt during the battery operation time, and the metal ion dissolution can be suppressed due to the film formation caused by the adsorption on the positive electrode surface and the complex formation with the metal ion. In addition, when the content of the first additive is 10 wt% or less, the viscosity of the electrolyte caused by the excess compound can be prevented, while the mobility of ions in the battery can be improved, the cell swelling suppression effect can be significantly improved, and the excessive film formation can be suppressed to effectively prevent the increase in battery resistance, thereby preventing the deterioration of the capacity and cycle characteristics. Specifically, the first additive may be included in an amount of 0.01 wt% to 7.0 wt% based on the total weight of the non-aqueous electrolyte for a lithium secondary battery, preferably in an amount of 0.1 wt% to 7.0 wt%, and more preferably in an amount of 0.5 wt% to 7.0 wt%. (4-5) Second additive Additionally, the additive of the present invention may include an imidazole compound as a second additive. The above imidazole compound may be a compound represented by the following chemical formula 6. [Chemical formula 6] In the above chemical formula 6, R is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, R6 to R8 are each independently hydrogen, an alkyl group having 1 to 3 carbon atoms, or -CN. The compound represented by the chemical formula 6, which is the second additive, can suppress the generation of Lewis acids by removing Lewis acids such as HF and PF5, which are decomposition products of lithium salts, by the unshared electron pair of the nitrogen element included in the structure acting as a Lewis base, and stabilizing lithium salt anions. As a result, the deterioration behavior of the film on the surface of the positive or negative electrode caused by the Lewis acid can be suppressed, and additional electrolyte decomposition caused by this can be prevented. As a result, the self-discharge of the secondary battery can be alleviated, and the high-temperature storage characteristics can be improved. In addition, the compound represented by the chemical formula 6 contains a propargyl functional group that is easily reduced on the cathode surface within its structure, so that it can form an SEI film having a high passivation ability on the cathode surface, thereby preventing additional reduction and decomposition reactions of the electrolyte caused by the instability of the SEI film, and improving the high-temperature durability of the cathode itself, thereby suppressing the self-discharge reaction of the cathode. In particular, the propargyl group included in the compound represented by the chemical formula 1 can be adsorbed on the surface of metallic impurities included in the cathode, thereby suppressing the elution of the impurities, thereby suppressing the deposition of metal ions on the cathode surface, thereby preventing internal short circuit. In the above chemical formula 6, R may be a substituted or unsubstituted alkylene group having 1 to 3 carbon atoms, and specifically, may be an unsubstituted alkylene group having 1 or 2 carbon atoms. In addition, in the chemical formula 6, R6 may be hydrogen, an alkyl group having 1 carbon atom, or -CN, or may be hydrogen, an alkyl group having 1 carbon atom, or -CN, and specifically may be hydrogen or -CN. In addition, in the above chemical formula 6, R7 may be hydrogen, an alkyl group having 1 carbon atom, or -CN, or may be hydrogen, an alkyl group having 1 carbon atom, or -CN, and specifically may be hydrogen or -CN. In addition, in the above chemical formula 6, R8 may be hydrogen, an alkyl group having 1 carbon atom, or -CN, or may be hydrogen, an alkyl group having 1 carbon atom, or -CN, and specifically may be hydrogen or -CN. Preferably, the compound represented by the chemical formula 6 may be a compound represented by the following chemical formula 6A. [Chemical Formula 6A] . Meanwhile, the second additive may be included in an amount of 0.01 wt% to 10 wt% based on the total weight of the electrolyte. When the second additive is included in the above content range, an anion stabilization improvement effect and a stable film formation effect can be implemented. When the content of the second additive is 0.01 wt% or more, the stabilization of the anion can be maintained more stably due to the formation of a complex with the anion during the battery operation time, and the formation of a film due to adsorption on the positive electrode surface and the formation of a complex with the metal ion can suppress the elution of the metal ion. In addition, when the content of the second additive is 10 wt% or less, the viscosity of the electrolyte due to the excess compound can be prevented, while the mobility of ions in the battery can be improved, the cell swelling suppression effect can be significantly improved, and the excessive formation of a film can be suppressed to effectively prevent an increase in battery resistance, thereby preventing a decrease in capacity and cycle characteristics. Specifically, the second additive may be included in an amount of 0.01 wt% to 7.0 wt% based on the total weight of the non-aqueous electrolyte for a lithium secondary battery, preferably in an amount of 0.1 wt% to 7.0 wt%, and more preferably in an amount of 0.5 wt% to 7.0 wt%. (4-6) Other additives Meanwhile, the lithium secondary battery of the present invention may additionally include other additives in the electrolyte as needed to prevent the electrolyte from being decomposed and causing cathode collapse in a high-power environment, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and high-temperature battery expansion suppression effects. When such other additives are included, the other additives may be named a third additive. These other additives may include, as representative examples, any one selected from the group consisting of cyclic carbonate compounds, sulfate compounds, sultone compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds, and preferably any one of cyclic carbonate compounds, sulfate compounds, and sultone compounds. The above cyclic carbonate compound may include vinylene carbonate (VC). The above sulfate compounds may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), methyl trimethylene sulfate (MTMS), etc. The above sultone compound may be any one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone. The above phosphate compound may include at least one compound selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphate. The above borate compounds include tetraphenylborate and lithium oxalyldifluoroborate. The above nitrile compound may include any one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile. The benzene compound may include fluorobenzene, the amine compound may include triethanolamine or ethylene diamine, and the silane compound may include tetravinylsilane. The above lithium salt-based compound is a compound different from the lithium salt included in the electrolyte, and may include at least one compound selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate borate (LiB(C2O4)2), LiBF4, and LiDFOP. Meanwhile, two or more of the above other additives may be mixed and used, and may be included in an amount of less than 10 wt%, specifically 0.01 wt% or more and less than 8.0 wt%, and preferably 0.05 wt% to 5.0 wt%, based on the total weight of the electrolyte. When the content of the above other additives satisfies the above range, side reactions caused by unreacted additives can be suppressed, and the effects of improving low-temperature output and high-temperature storage characteristics and high-temperature life characteristics of the battery can be further enhanced. The lithium secondary battery according to the present invention as described above can be usefully used in portable devices such as mobile phones, laptop computers, digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs). There is no particular limitation on the external shape of the lithium secondary battery of the present invention, but it may be in the shape of a cylinder, a square, a pouch, or a coin using a can. The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells. Hereinafter, the present invention will be described in detail by way of examples in order to specifically explain the present invention. However, the examples according to the present invention may be modified in various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided in order to more completely explain the present invention to a person having average knowledge in the art. [Example] Example 1. (Electrolyte manufacturing) LiPF6 was dissolved to a concentration of 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 80:20, and then 0.01 wt% of an oligomer of chemical formula 5 (n is 30, m is 70, weight average molecular weight: 12,000 g / mol) as a first additive and 0.01 wt% of a compound represented by chemical formula 6A as a second additive were added to manufacture an electrolyte for a lithium secondary battery of the present invention. (Polar manufacturing) Cathode active materials (LiFeMnPO4 and Li(Ni 0.6 Co 0.1 Mn 0.3 )O2 = 70:30 in weight ratio), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) were added to the solvent N-methyl-2-pyrrolidone (NMP) in a weight ratio of 90:5:5 to prepare a positive electrode active material slurry (solid content 48 wt%). The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film) having a thickness of 15 ㎛, dried, and roll pressed to prepare a positive electrode (double-sided loading: 48 mg / cm2, single-sided loading: 24 mg / cm2). (Cathode manufacturing) A negative active material slurry (solid content: 70 wt%) was prepared by adding a negative active material (artificial graphite), a binder, CMC-SBR, and a conductive material, in a weight ratio of 95:2:3, to a solvent, distilled water. The negative active material slurry was applied to a negative current collector (Cu thin film) having a thickness of 8 ㎛, dried, and roll pressed to prepare a negative electrode. (Secondary battery manufacturing) An electrode assembly was manufactured by a conventional method of sequentially laminating the positive and negative electrodes manufactured by the above-described method together with a polyethylene porous film, and then this was placed in a pouch-type secondary battery case, and the lithium secondary battery electrolyte manufactured as described above was injected to manufacture a lithium secondary battery. Example 2. (Electrolyte manufacturing) LiPF6 was dissolved to a concentration of 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 80:20, and then 0.1 wt% of an oligomer of chemical formula 5 (n is 30, m is 70, weight average molecular weight: 12,000 g / mol) as a first additive and 0.1 wt% of a compound represented by chemical formula 6A as a second additive were added to manufacture an electrolyte for a lithium secondary battery of the present invention. (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the manufactured electrolyte was injected. Example 3. (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 80:20, and then 1.0 wt% of an oligomer of chemical formula 5 (n is 30, m is 70, weight average molecular weight: 12,000 g / mol) as a first additive and 1.0 wt% of a compound represented by chemical formula 6A as a second additive were added to manufacture an electrolyte for a lithium secondary battery of the present invention. (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the manufactured electrolyte was injected. Example 4. (Electrolyte manufacturing) LiPF6 was dissolved to a concentration of 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 80:20, and then 5.0 wt% of an oligomer of chemical formula 5 (n is 30, m is 70, weight average molecular weight: 12,000 g / mol) as a first additive and 5.0 wt% of a compound represented by chemical formula 6A as a second additive were added to manufacture an electrolyte for a lithium secondary battery of the present invention. (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the manufactured electrolyte was injected. Example 5. (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 50:50, and then 1.0 wt% of an oligomer of chemical formula 5 (n is 30, m is 70, weight average molecular weight: 12,000 g / mol) as a first additive and 1.0 wt% of a compound represented by chemical formula 6A as a second additive were added to manufacture an electrolyte for a lithium secondary battery of the present invention. (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the manufactured electrolyte was injected. Example 6. (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 40:60, and then 1.0 wt% of an oligomer of chemical formula 5 (n is 30, m is 70, weight average molecular weight: 12,000 g / mol) as a first additive and 1.0 wt% of a compound represented by chemical formula 6A as a second additive were added to manufacture an electrolyte for a lithium secondary battery of the present invention. (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the manufactured electrolyte was injected. Example 7. (Polar manufacturing) Cathode active materials (LiFeMnPO4 and Li(Ni 0.6 Co 0.1 Mn 0.3)O2 = 70:30 in weight ratio), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) were added to the solvent N-methyl-2-pyrrolidone (NMP) in a weight ratio of 90:5:5 to prepare a positive electrode active material slurry (solid content 48 wt%). The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film) having a thickness of 100 ㎛, dried, and roll pressed to prepare a positive electrode (double-sided loading: 32 mg / cm2, single-sided loading: 16 mg / cm2). (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-mentioned manufactured positive electrode was applied. Example 8. (Polar manufacturing) Cathode active materials (LiFeMnPO4 and Li(Ni 0.6 Co 0.1 Mn 0.3 )O2 = 70:30 in weight ratio), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) were added to the solvent N-methyl-2-pyrrolidone (NMP) in a weight ratio of 90:5:5 to prepare a positive electrode active material slurry (solid content 48 wt%). The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film) having a thickness of 100 ㎛, dried, and roll pressed to prepare a positive electrode (double-sided loading: 60 mg / cm2, single-sided loading: 30 mg / cm2). (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-mentioned manufactured positive electrode was applied. Comparative example 1. (Electrolyte manufacturing) LiPF6 was dissolved to a concentration of 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 80:20, and then 1.0 wt% of an oligomer of the chemical formula 5 (n is 30, m is 70, weight average molecular weight: 12,000 g / mol) as a first additive was included, except that no second additive was included, and a lithium secondary battery electrolyte was manufactured in the same manner as in Example 1. (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the manufactured electrolyte was injected. Comparative example 2. (Electrolyte manufacturing) LiPF6 was dissolved to a concentration of 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 80:20, and an electrolyte for a lithium secondary battery was manufactured in the same manner as in Example 1, except that the first additive was not included and 1.0 wt% of the compound represented by the chemical formula 6A was included as the second additive. (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the manufactured electrolyte was injected. Comparative example 3. (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing ethyl methyl carbonate and ethylene carbonate in a volume ratio of 80:20, and then 1.0 wt% of an oligomer of chemical formula 5 (n is 30, m is 70, weight average molecular weight: 12,000 g / mol) as a first additive and 1.0 wt% of a compound represented by chemical formula 6A as a second additive were added to manufacture an electrolyte for a lithium secondary battery of the present invention. (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the manufactured electrolyte was injected. Comparative example 4. (Polar manufacturing) Cathode active materials (LiFeMnPO4 and Li(Ni 0.6 Co 0.1 Mn 0.3 )O2 = 70:30 in weight ratio), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) were added to the solvent N-methyl-2-pyrrolidone (NMP) in a weight ratio of 90:5:5 to prepare a positive electrode active material slurry (solid content 48 wt%). The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film) having a thickness of 100 ㎛, dried, and roll pressed to prepare a positive electrode (double-sided loading: 64 mg / cm2, single-sided loading: 32 mg / cm2). (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-mentioned manufactured positive electrode was applied. [Experimental example] Experimental Example 1. Evaluation of high temperature (45℃) cycle characteristics The lithium secondary batteries manufactured in the examples above and the lithium secondary batteries manufactured in the comparative examples were each charged to 4.2 V at a constant current / constant voltage condition at a 0.33 C rate at room temperature (25°C), discharged for 10 seconds at a 0.33 C rate condition, and then the initial capacity and the initial internal resistance of the batteries were measured by the 10s-DCIR (direct current internal resistance) method at room temperature using a PNE-0506 charger / discharger (manufacturer: PNE solution). Then, the battery was charged to 4.2 V under constant current / constant voltage conditions at a high temperature (45℃) at a rate of 0.33 C, and discharged to 2.5 V under constant current conditions at a rate of 0.33 C for 100 cycles, which was considered one cycle, and then the discharge capacity was measured. In addition, the internal resistance of the battery after the high-temperature cycle was measured by the 10s-DCIR method. The capacity retention rate (%) was calculated using the initial capacity obtained at room temperature (25°C) and the discharge capacity obtained after the high-temperature cycle, and the results are shown in Table 1. In addition, the resistance increase rate (%) was calculated using the internal resistance of the initial battery obtained at room temperature and the internal resistance of the battery obtained after the high-temperature cycle, and the results are shown in Table 1 below. Capacity retention rate (%) Resistance increase rate (%) Example 194.554.3 Example 294.154.6 Example 393.855.4 Example 493.654.3 Example 591.057.8 Example 691.457.6 Example 790.957.4 Example 890.857.7 Comparative Example 181.163.2 Comparative Example 280.964.2 Comparative Example 379.765.2 Comparative Example 479.866.1 Referring to Table 1 above, it can be confirmed that the capacity retention rate (%) after high-voltage, high-temperature cycling of the lithium secondary batteries manufactured in Examples 1 to 8 of the present invention is improved compared to the lithium secondary batteries of Comparative Examples 1 to 4. In particular, in the case of the lithium secondary battery of Comparative Example 4, the capacity and resistance characteristics after high-temperature cycling seem to be inferior to those of the Examples as the electrolyte impregnation property decreases and the resistance increases due to the increase in loading. Experimental Example 2. Evaluation of high temperature (45℃) storage characteristics The lithium secondary batteries manufactured in the examples above and the lithium secondary batteries manufactured in the comparative examples were fully charged at room temperature at a constant current-constant voltage of 0.33 C / 4.15 V, discharged for 10 seconds, and then the initial capacity and the initial internal resistance of the batteries were measured by the 10s-DCIR (direct current internal resistance) method at room temperature using a PNE-0506 charger / discharger (manufacturer: PNE solution). Then, after storage at 60℃ for 10 weeks (SOC (state of charge) 100%), the discharge capacity was measured by charging to 4.2 V under constant current / constant voltage conditions at 0.33 C rate and discharging to 2.5 V under constant current conditions at 0.33 C rate. In addition, the internal resistance of the battery after high-temperature cycling was measured by the 10s-DCIR method. The capacity retention rate (%) was calculated using the initial capacity obtained before the high-temperature storage and the discharge capacity obtained after the high-temperature storage, and the results are shown in Table 2. In addition, the resistance increase rate (%) was calculated using the internal resistance of the initial battery obtained at room temperature and the internal resistance of the battery obtained after high-temperature storage, and the results are shown in Table 2 below. Capacity retention rate (%) Resistance increase rate (%) Example 193.555.3 Example 293.155.6 Example 392.856.4 Example 492.657.3 Example 590.058.8 Example 690.458.6 Example 789.958.4 Example 889.858.7 Comparative Example 180.164.2 Comparative Example 279.965.2 Comparative Example 378.766.2 Comparative Example 478.867.1 Referring to Table 2 above, it can be confirmed that the capacity retention rate (%) and resistance increase rate (%) after high-temperature storage of the lithium secondary batteries manufactured in Examples 1 to 8 of the present invention are improved compared to the lithium secondary batteries of Comparative Examples 1 to 4. In particular, in the case of the lithium secondary battery of Comparative Example 4, the capacity retention rate and resistance increase rate after high-temperature storage seem to be inferior to those of the Examples because the electrolyte impregnation property decreases and the resistance increases due to the increase in loading. Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood by those skilled in the art or having ordinary knowledge in the art that various modifications and changes may be made to the present invention without departing from the spirit and technical scope of the present invention as set forth in the claims below. Accordingly, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

Claims

1. In a lithium secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte, The above positive electrode contains lithium iron phosphate and lithium nickel cobalt manganese oxide as positive electrode active materials, The loading amount of the above anode is 32 mg / cm 2 60 mg / cm 2 And, The electrolyte comprises a lithium salt; a first organic solvent; a second organic solvent; a first additive; and a second additive. The above first organic solvent is a cyclic lactone compound, The above second organic solvent is a carbonate-based organic solvent, The above first additive is an oligomer comprising a repeating unit derived from a monomer represented by the following chemical formula 1 and a repeating unit derived from a monomer represented by the following chemical formula 2, A lithium secondary battery wherein the second additive is an imidazole compound: [Chemical Formula 1] In the above chemical formula 1, R1 is hydrogen or an alkyl group having 1 to 3 carbon atoms, R2 is an alkyl group having 1 to 20 carbon atoms. [Chemical formula 2] In the above chemical formula 2, R3 is hydrogen or an alkyl group having 1 to 3 carbon atoms, R4 and R5 are each independently an alkylene group having 1 to 10 carbon atoms.

2. In paragraph 1, A lithium secondary battery, wherein the lithium iron phosphate comprises a compound represented by the following chemical formula 3: [Chemical Formula 3] Li 1+a Fe x M y (PO 4-b )X' b In the above [chemical formula 3], M is one selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y, X' is one or more elements selected from the group consisting of F, S, and N, -0.5≤a≤0.5, 0 <x≤1, 0≤y≤1 및 0≤b≤0.3이다.

3. In paragraph 2, A lithium secondary battery, wherein the lithium iron phosphate is lithium iron phosphate (LiFePO4) or lithium manganese iron phosphate (LiFeMnPO4).

4. In paragraph 1, A lithium secondary battery, wherein the lithium nickel cobalt manganese oxide comprises a compound represented by the following chemical formula 4: [Chemical Formula 4] Li 1+a1 Ni x1 Co y1 M 1 z M 2 w O2 In the above [chemical formula 4], M 1 is Mn, Al or a combination thereof, M 2 is one selected from the group consisting of Al, Zr, W, Ti, Mg, Ca and Sr, 0≤a1≤0.5, 0 <x1<1.0, 0<y1≤0.4, 0<z≤0.4, 0≤w≤0.1 이다.

5. In paragraph 4, The above lithium nickel cobalt manganese oxide is Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.6 Co 0.2 Mn 0.2 )O2, Li(Ni) 0.6 Co 0.1 Mn 0.3 )O 2, Li(Ni) 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O2 and Li(Ni 0.90 Mn 0.05 Co 0.05 )A lithium secondary battery, wherein the lithium secondary battery is one selected from the group consisting of O2.

6. In paragraph 1, A lithium secondary battery, wherein the lithium iron phosphate and lithium nickel cobalt manganese oxide are contained in a weight ratio of 50:50 to 80:

20.

7. In paragraph 1, The above lithium iron phosphate is lithium iron phosphate (LiFePO4). The above lithium nickel cobalt manganese oxide is Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni) 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O2 and Li(Ni 0.90 Mn 0.05 Co 0.05 )A lithium secondary battery, wherein the lithium secondary battery is one selected from the group consisting of O2.

8. In paragraph 1, The above lithium iron phosphate is lithium manganese iron phosphate (LiFeMnPO4). The above lithium nickel cobalt manganese oxide is Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.6 Co 0.2 Mn 0.2 )O2 and Li(Ni) 0.6 Co 0.1 Mn 0.3 )A lithium secondary battery, wherein the lithium secondary battery is one selected from the group consisting of O2.

9. In paragraph 1, A lithium secondary battery, wherein the above cyclic lactone compound comprises gamma-butyrolactone.

10. In paragraph 1, A lithium secondary battery, wherein the above carbonate-based organic solvent is a cyclic carbonate-based organic solvent.

11. In paragraph 1, A lithium secondary battery, wherein the first organic solvent and the second organic solvent are included in a volume ratio of 50:50 to 99:

1.

12. In paragraph 1, A lithium secondary battery, wherein in the chemical formula 1 above, R1 is hydrogen or an alkyl group having 1 or 2 carbon atoms, and R2 is an alkyl group having 1 to 10 carbon atoms.

13. In paragraph 1, A lithium secondary battery, wherein in the chemical formula 2 above, R3 is hydrogen or an alkyl group having 1 or 2 carbon atoms, and R4 and R5 are each independently an alkylene group having 1 to 8 carbon atoms.

14. In paragraph 1, A lithium secondary battery wherein the above oligomer is an oligomer represented by the following chemical formula 5: [Chemical Formula 5] In the above chemical formula 5, n is an integer from 1 to 500, and m is an integer from 1 to 300.

15. In paragraph 1, A lithium secondary battery, wherein the first additive is included in an amount of 0.01 wt% to 10 wt% based on the total weight of the electrolyte.

16. In paragraph 1, The above imidazole compound is a lithium secondary battery represented by the following chemical formula 6: [Chemical formula 6] In the above chemical formula 6, R is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, R6 to R8 are each independently hydrogen, an alkyl group having 1 to 3 carbon atoms, or -CN.

17. In paragraph 16, The above imidazole compound is a lithium secondary battery represented by the following chemical formula 6A: [Chemical Formula 6A] .

18. In paragraph 1, A lithium secondary battery, wherein the second additive is included in an amount of 0.01 wt% to 10 wt% based on the total weight of the electrolyte.

19. In paragraph 1, A lithium secondary battery, wherein the negative electrode comprises a carbon-based active material, a silicon-based active material, or a mixture of a carbon-based active material and a silicon-based active material.

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