Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery having improved high-temperature cycle characteristics and, more specifically, 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 as a positive electrode active material, and the electrolyte includes a lithium salt, a first organic solvent, a second organic solvent, and an additive. The first organic solvent is a cyclic lactone compound, the second organic solvent is a carbonate-based organic solvent, and the additive is lithium nitrate (LiNO3). The lithium secondary battery satisfies equation 1. [Equation 1]. In equation 1, A is the total injection amount (g) of the electrolyte injected into the lithium secondary battery, B is the content (wt%) of lithium nitrate (LiNO3) contained in the injected electrolyte, C is the loading amount (g / cm2) of the positive electrode, and D is the total area (cm2) of the surface of a positive electrode current collector.

Description

Lithium secondary battery Cross-citation with related application(s) This application claims the benefit of priority to Korean Patent Application No. 10-2023-0189753, filed December 22, 2023, and Korean Patent Application No. 10-2024-0165719, filed November 19, 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 cycle characteristics. Recently, as the application areas of lithium secondary batteries have rapidly expanded to include not only power supply for electronic devices such as electric, electronic, communication, and computers, but also power storage for large-area devices such as automobiles and power storage devices, the demand for high-capacity, high-output, and high-stability secondary batteries is increasing. In particular, in order to use lithium secondary batteries as a power source for electric vehicles, they must be able to stably produce high output at high temperatures and high voltages. To this end, negative electrode active materials such as lithium metal, carbon compounds, and silicon compounds, as well as positive electrode active materials with high energy density and high nickel content, are being considered for use. However, in the case of the above-mentioned high nickel content cathode active material, since the output decreases rapidly in the low SOC range (for example, SOC 30% or less), there is a disadvantage that the usable SOC range is greatly limited, which limits its application to fields where output characteristics are particularly important, such as electric vehicles. Furthermore, in the case of the above-mentioned high nickel content cathode active material, since the stability is low, when a lithium secondary battery is operated in an environment such as high voltage or high temperature, as charge and discharge progress, structural instability may cause structural transformation, or the film formed on the surface of the cathode and / or anode may deteriorate due to a side reaction with the electrolyte, thereby causing transition metal ions to be eluted from the cathode surface. In this way, the eluted transition metal ions deteriorate the passivation ability of the SEI as they are electro-deposited on the cathode, which causes a problem of deterioration of the cathode. Recently, to solve these problems, a method of using lithium iron phosphate with an olivine structure that has excellent high-temperature safety instead of a high-nickel content cathode active material has emerged. However, since the above lithium iron phosphate has a lower theoretical capacity than the existing high nickel content cathode active material, it has a disadvantage in that the energy density is relatively lower than that of the high nickel content cathode active material when designing an electrode under the same conditions. Therefore, 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 been attempted recently. However, since these high-loading electrodes have a high degree of active material coating and are designed 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. If the electrolyte impregnation is reduced in this way, the "charge transfer", which is the reaction between lithium ions and electrons, is reduced, and this causes the battery resistance to increase, which may deteriorate the battery capacity characteristics. 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 to solve the above problems, and to provide a lithium secondary battery which improves electrolyte impregnation property by using an electrolyte in which the content range of a specific electrolyte additive is controlled according to the amount of anode loading when applying a high-loading cathode, and at the same time forms a stable film on the electrode surface to increase the charge transfer phenomenon, thereby suppressing an increase in resistance during high-temperature storage and ensuring excellent cycle capacity retention. [1] The present invention provides a lithium secondary battery including a cathode, an anode, a separator, and an electrolyte, wherein the cathode includes lithium iron phosphate as a cathode active material, the electrolyte includes a lithium salt; a first organic solvent; a second organic solvent; and an additive, wherein the first organic solvent is a cyclic lactone compound, the second organic solvent is a carbonate-based organic solvent, and the additive is lithium nitrate (LiNO3), and the lithium secondary battery satisfies the following formula 1. [Formula 1] 0.0001≤ ≤0.050 In the above equation 1, A is the total amount of electrolyte (g) injected into the lithium secondary battery, B is the content (weight%) of lithium nitrate (LiNO3) contained in the above-mentioned electrolyte, C is the loading of the anode (g / cm 2 ) and D is the total area of ​​the positive electrode surface (cm 2 )am. [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 1: [Chemical Formula 1] Li 1+a Fe x M y (PO 4-b )X' b In the above [chemical formula 1], 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] The present invention provides a lithium secondary battery, wherein, in the above [1] or [2], the lithium iron phosphate is lithium iron phosphate (LiFePO4) or lithium manganese iron phosphate (LiFeMnPO4). [4] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to [3], the cyclic lactone compound includes gamma-butyrolactone. [5] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to [4], the carbonate-based organic solvent is a cyclic carbonate-based organic solvent. [6] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to [5], the first organic solvent and the second organic solvent are included in a volume ratio of 50:50 to 99:1. [7] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to [6], in the above formula 1, A is 3.0 g to 8.5 g. [8] The present invention, in at least one of the above [1] to [7], in the above formula 1, C is 0.032 g / cm 2 Within 0.064 g / cm 2 It provides a lithium secondary battery. [9] The present invention, in at least one of the above [1] to [8], in the above formula 1, D is 310 cm 2 450 cm inside 2 It provides a lithium secondary battery.

[0010] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to [9], 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.

[0011] The present invention provides a lithium secondary battery having a capacity of 1,000 mAh to 3,000 mAh, in at least one of the above [1] to

[0010] . The lithium secondary battery according to the present invention improves the electrolyte impregnation property for a positive electrode with a high loading by applying an electrolyte including an organic solvent containing a cyclic lactone compound as a main solvent and lithium nitrate (LiNO3) as an additive whose content range is controlled according to the positive electrode loading amount, and at the same time forms a film having a low resistance on the surface of the positive electrode with a high loading, thereby improving the charge mobility on the surface of the positive electrode with a high loading. Therefore, the lithium secondary battery of the present invention can have improved cycle characteristics and high-temperature storage characteristics. 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. In addition, in this specification, "loading amount" means the amount of active material per unit area of ​​a positive electrode active material layer including lithium iron phosphate formed on a current collector, and is expressed as "g / cm 2 " is expressed as. At this time, in this specification, "positive electrode loading amount" means the total sum of the loading amounts on both sides of the positive electrode. 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 as a positive electrode active material. The above electrolyte may include a lithium salt; a first organic solvent; a second organic solvent; and an additive. The first organic solvent may include a cyclic lactone compound. The second organic solvent may include a carbonate-based organic solvent. The above additive is lithium nitrate (LiNO3) and can satisfy the following equation 1. [Formula 1] 0.0001≤ ≤0.050 In the above equation 1, A is the total amount of electrolyte (g) injected into the lithium secondary battery, B is the content (weight%) of lithium nitrate (LiNO3) contained in the above-mentioned electrolyte, C is the loading of the anode (g / cm 2 ) and D is the total area of ​​the positive electrode surface (cm 2 )am. Below, each component of the lithium secondary battery of the present invention is specifically described. (1) Bipolar The positive electrode of the present invention may include lithium iron phosphate as a positive electrode active material, and the lithium iron phosphate may be represented by the following chemical formula 1. [Chemical Formula 1] Li 1+a Fe x M y (PO 4-b )X' b In the above [chemical formula 1], 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 1 may include, as a representative example, lithium iron phosphate (LiFePO4, LFP) or lithium manganese iron phosphate (LiFeMnPO4, LFMP). The lithium iron phosphate represented by the above chemical formula 1 can use primary particles of nanometer size for high input / output of lithium ions, and it is also possible to use these primary particles by assembling them into secondary particles, which are aggregates thereof. 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 these primary particles by assembling them into secondary particles, which are aggregates thereof, the average particle diameter (D50) of the secondary particles may be 0.5 ㎛ to 30 ㎛. The lithium iron phosphate represented by the chemical formula 1 above can secure structural stability and thermal stability even in volume changes due to charge and discharge because phosphorus and oxygen form strong covalent bonds within the tetrahedral structure of PO4. In addition, the lithium iron phosphate represented by the chemical formula 1 may have an amorphous layer of carbon or metal oxide coated on the surface. In this case, since the amorphous layer of carbon or metal oxide coated on the 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 the 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, thereby enabling high-rate charging and discharging. 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. Meanwhile, the present invention has a high capacity design of the electrode, and the loading amount of the anode is 0.032 g / cm. 2 Ideal (loading of the anode on the cross-section basis: 0.016 g / cm 2 ) can be more than 0.032 g / cm2, specifically 2 Within 0.064 g / cm 2 may be, more preferably 0.040 g / cm 2 Within 0.060 g / cm 2 It can be done. When the loading amount of the above positive electrode active material satisfies the above range, a high energy density battery design is possible. The positive electrode of the present invention 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 the lithium iron phosphate described above as a 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 1 may be included in the positive electrode composite layer at 80 to 99 wt% in consideration of sufficient capacity, etc. Additionally, the porosity of the cathode composite layer measured by the BET method can be 20% to 40%, and specifically 20% to 30%. When the porosity of the above-mentioned positive electrode composite layer satisfies the above-mentioned range, the electrode density can be secured while the interface resistance of the positive electrode can be lowered, thereby improving the output characteristics of the battery. 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 porosity of the anode composite layer measured by the BET method after the above rolling may be 20% to 40%, and specifically 20% to 30%. 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. Additionally, the porosity of the cathode composite layer measured by the BET method may be 20% to 40%, and specifically 20% to 30%. When the porosity of the negative electrode composite layer satisfies the above range, the interfacial resistance of the negative electrode can be reduced, thereby improving the output characteristics of the battery. Meanwhile, the negative electrode composite layer may further include a conductive material and / or a binder together with the 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 porosity of the cathode composite layer measured by the BET method after the above rolling may be 20% to 40%, and specifically 20% to 30%. 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; and an 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, LiB 10 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 for 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 obtaining the effect of 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 reduction 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 of the present invention 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 organic solvent so that decomposition due to oxidation reaction, 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 organic solvent include one selected from the group consisting of a cyclic carbonate organic solvent having high ionic conductivity and high dielectric constant and a linear carbonate organic solvent having low viscosity and low dielectric constant, and specifically may include a cyclic carbonate 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. The linear carbonate 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. Among these, dimethyl carbonate (DMC), which has a small molecular size and low viscosity characteristics, may be exemplified. Specifically, the second organic solvent may be ethylene carbonate, propylene carbonate or a mixed solvent thereof. 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 organic solvent and the linear carbonate 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. The electrolyte of the present invention may additionally include a linear ester-based organic solvent as a third organic solvent, if necessary. Representative examples of the linear ester organic solvent include at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, and specifically, may include at least one of methyl acetate and ethyl acetate. Meanwhile, in the electrolyte of 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 70:30 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) Additives Additionally, the electrolyte of the present invention may include lithium nitrate (LiNO3) as an additive. Lithium nitrate (LiNO3) included as the above additive can form an inorganic film including lithium-nitrogen and lithium-oxygen bonds on the surface of the negative electrode during the activation step. Since this inorganic film increases surface energy and acts as an ion transporter capable of uniformly transporting lithium ions, it can improve the electrode impregnation property of the electrolyte and induce a more effective charge transfer reaction. In addition, lithium nitrate (LiNO3) included as the additive forms a coordination bond with a transition metal eluted from the positive electrode under a high-temperature environment, or forms a coordination bond with a Lewis acid generated by a decomposition product of a lithium salt, thereby inhibiting the deposition of transition metal ions on the negative electrode surface, thereby preventing reversible lithium loss, and thus improving the deterioration of cycle characteristics. The content (weight %) of the above additive lithium nitrate (LiNO3) may vary depending on the loading amount of the positive electrode, and for example, it is preferable to satisfy the following equation 1. [Formula 1] 0.0001≤ ≤0.050 In the above equation 1, A is the total amount of electrolyte (g) injected into the lithium secondary battery, B is the content (weight%) of lithium nitrate (LiNO3) contained in the above-mentioned electrolyte, C is the loading of the anode (g / cm 2 ) and D is the total area of ​​the positive electrode surface (cm 2 )am. Specifically, in the above formula 1, A may be 3.0 g to 8.5 g. When A is 3.0 g or more, the impregnation property of the electrode assembly for the electrolyte can be easily controlled, and when A is 8.5 g or less, the amount of gas generated inside the cell during battery operation can be controlled, thereby preventing the impregnation property of the electrolyte and an increase in the thickness of the battery. Also, for the high-capacity design of the electrode, in the above equation 1, C is 0.032 g / cm 2 Within 0.064 g / cm 2 It could be. In addition, in the above formula 1, D represents the total area of ​​both surfaces of the positive electrode current collector coated with the positive electrode active material, and is specifically 310 cm so that it can be applied to small batteries. 2 450 cm inside 2 It could be. Meanwhile, the above 0.02 is a constant, and is a value determined by multiplying 0.01, an integer value for expressing the percentage of the content of the additive in the electrolyte as a decimal, and 2, an integer value for converting the loading amount of the positive electrode of B into a cross-sectional loading amount. When the content (weight %) of lithium nitrate (LiNO3), which is an additive in the electrolyte of the present invention, satisfies the above formula 1, the electrolyte impregnation property for the electrode can be increased, and an inorganic film including lithium-nitrogen and lithium-oxygen bonds capable of improving ion transport characteristics on the surface of the negative electrode is uniformly formed, thereby ensuring excellent battery performance. That is, when the value of the above formula 1 satisfies 0.0001 or more, or 0.0005 or more, and preferably 0.001 or more, a film that does not operate as a resistor but as an effective ion transporter is uniformly formed, thereby suppressing an increase in battery resistance, thereby preventing the deterioration of battery performance and preventing the deterioration of life performance at low temperatures (film temperature). In addition, when the value of the above formula 1 satisfies 0.050 or less, or 0.040 or less, preferably 0.030 or less, side reactions can be suppressed to prevent unnecessary activation gases, etc. from being generated, and thus deterioration of high-temperature cycle and high-temperature storage characteristics can be prevented. (4-5) Other additives Meanwhile, the lithium secondary battery of the present invention may further 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 other additives are additionally included in the electrolyte of the present invention, the lithium nitrate (LiNO3) may be referred to as a first additive, and the other additives may be referred to as second additives. The above other additives may include any one other additive selected from the group consisting of, for example, cyclic carbonate compounds, sulfate compounds, sultone compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds. Specifically, the cyclic carbonate compound may include vinylene carbonate (VC). The above sulfate compounds may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS). 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. The above other additives may be used in a mixture of two or more, and may be included in an amount of less than 10 wt%, specifically 0.01 wt% to less than 8.0 wt%, and preferably 0.05 wt% to 5.0 wt%, based on the total weight of the electrolyte. Preferably, in the electrolyte of the present invention, the additive lithium nitrate (LiNO3) and other additives may be included in a weight ratio of 1:0.01 to 1:50, may be included in a weight ratio of 1:0.1 to 1:10, and more preferably may be included in a weight ratio of 1:0.1 to 1:6. When the electrolyte of the present invention includes the additive and other additives in the above ranges, a stable film can be formed simultaneously on the surfaces of the positive and negative electrodes. That is, when the other additives are included in an amount of 50 weight percent or less, a uniform film can be formed on the surface of the negative electrode, thereby preventing it from acting as a resistor, and by suppressing the elution of transition metals, the deposition of metal materials on the negative electrode can be prevented, thereby preventing an increase in the film thickness and resistance. On the other hand, when the other additives are included in a relatively large amount, the content of the other additives that are reduced and decomposed on the surface of the negative electrode increases, thereby increasing the film thickness, and as a result, the additives cannot operate effectively and act as resistors, so that the cell performance can be significantly deteriorated. Meanwhile, there is no particular limitation on the external shape of the lithium secondary battery of the present invention, and it may be cylindrical, square, pouch-shaped, or coin-shaped. In addition, the lithium secondary battery of the present invention can be usefully used in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs). In addition, the lithium secondary battery according to the present invention can be applied not only to a battery cell used as a power source for a small device, but also to a unit battery of a medium- to large-sized battery module including a plurality of battery cells. Specifically, the lithium secondary battery of the present invention can be applied to a battery cell for a small device having a capacity of 1,000 mAh to 3,000 mAh and a volume of width (33 to 39 mm) × length (80 to 96 mm) × thickness (3.0 mm to 5.0 mm). 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. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.048 mg / cm2, loading amount based on cathode cross-section: 0.024 mg / cm2, porosity of cathode composite layer: 24%). (Cathode manufacturing) A slurry of positive active material (solid content: 53 wt%) was prepared by adding negative active material (100% artificial graphite), CMC-SBR as a binder, and carbon black as a conductive material to distilled water as a solvent in a weight ratio of 96:3.5:0.5. 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 (porosity of the negative electrode composite layer: 26%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 1.0 wt% of lithium nitrate (LiNO3) was added to prepare an electrolyte for a lithium secondary battery of the present invention. (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 3.65 g of the lithium secondary battery electrolyte manufactured as described above was injected to manufacture a lithium secondary battery (see Table 1 below). Example 2. (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 1.0 wt% of lithium nitrate (LiNO3) was added to prepare 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 4.98 g of the lithium secondary battery electrolyte manufactured above was injected (see Table 1 below). 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 70:30, and then 1.0 wt% of lithium nitrate (LiNO3) was added to prepare 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 6.64 g of the lithium secondary battery electrolyte manufactured above was injected (see Table 1 below). Example 4. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.064 mg / cm2, loading amount based on cathode cross-section: 0.032 mg / cm2, porosity of cathode composite layer: 24%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 1.0 wt% of lithium nitrate (LiNO3) was added to prepare 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 positive electrode manufactured by the above-described method was used and 4.65 g of the lithium secondary battery electrolyte manufactured above was injected (see Table 1 below). 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 70:30, and then 1.0 wt% of lithium nitrate (LiNO3) was added to prepare 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 4, except that 6.43 g of the lithium secondary battery electrolyte manufactured above was injected (see Table 1 below). 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 70:30, and then 1.0 wt% of lithium nitrate (LiNO3) was added to prepare 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 4, except that 8.45 g of the lithium secondary battery electrolyte manufactured above was injected (see Table 1 below). Example 7. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 312 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.048 mg / cm2, loading amount based on cathode cross-section: 0.024 mg / cm2, porosity of cathode composite layer: 24%). (Cathode manufacturing) A slurry of positive active material (solid content: 53 wt%) was prepared by adding negative active material (100% artificial graphite), CMC-SBR as a binder, and carbon black as a conductive material to distilled water as a solvent in a weight ratio of 96:3.5:0.5. 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 (porosity of the negative electrode composite layer: 26%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 0.5 wt% of lithium nitrate (LiNO3) was added to prepare an electrolyte for a lithium secondary battery of the present invention. (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 3.10 g of the lithium secondary battery electrolyte manufactured as described above was injected to manufacture a lithium secondary battery (see Table 1 below). Example 8. (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 0.5 wt% of lithium nitrate (LiNO3) was added to prepare 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 7, except that 3.57 g of the lithium secondary battery electrolyte manufactured above was injected (see Table 1 below). Example 9. (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 0.5 wt% of lithium nitrate (LiNO3) was added to prepare 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 7, except that 4.77 g of the lithium secondary battery electrolyte manufactured above was injected (see Table 1 below). Example 10. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.064 mg / cm2, loading amount based on cathode cross-section: 0.032 mg / cm2, porosity of cathode composite layer: 24%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 0.5 wt% of lithium nitrate (LiNO3) was added to prepare 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 7, except that the positive electrode manufactured by the above-described method was used and 3.43 g of the lithium secondary battery electrolyte manufactured above was injected (see Table 1 below). Example 11. (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 0.5 wt% of lithium nitrate (LiNO3) was added to prepare 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 10, except that 4.55 g of the lithium secondary battery electrolyte manufactured above was injected (see Table 1 below). Example 12. (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 0.5 wt% of lithium nitrate (LiNO3) was added to prepare 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 10, except that 6.07 g of the lithium secondary battery electrolyte manufactured above was injected (see Table 1 below). Example 13. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.048 mg / cm2, loading amount based on cathode cross-section: 0.024 mg / cm2, porosity of cathode composite layer: 24%). (Cathode manufacturing) A slurry of positive active material (solid content: 53 wt%) was prepared by adding negative active material (100% artificial graphite), CMC-SBR as a binder, and carbon black as a conductive material to distilled water as a solvent in a weight ratio of 96:3.5:0.5. 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 (porosity of the negative electrode composite layer: 26%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 0.25 wt% of lithium nitrate (LiNO3) was added to prepare an electrolyte for a lithium secondary battery of the present invention. (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 4.86 g of the lithium secondary battery electrolyte manufactured as described above was injected to manufacture a lithium secondary battery (see Table 1 below). Example 14. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.064 mg / cm2, loading amount based on cathode cross-section: 0.032 mg / cm2, porosity of cathode composite layer: 24%). (Cathode manufacturing) A slurry of positive active material (solid content: 53 wt%) was prepared by adding negative active material (100% artificial graphite), CMC-SBR as a binder, and carbon black as a conductive material to distilled water as a solvent in a weight ratio of 96:3.5:0.5. 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 (porosity of the negative electrode composite layer: 26%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 0.25 wt% of lithium nitrate (LiNO3) was added to prepare an electrolyte for a lithium secondary battery of the present invention. (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 4.86 g of the lithium secondary battery electrolyte manufactured as described above was injected to manufacture a lithium secondary battery (see Table 1 below). Example 15. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.048 mg / cm2, loading amount based on cathode cross-section: 0.024 mg / cm2, porosity of cathode composite layer: 24%). (Cathode manufacturing) A slurry of positive active material (solid content: 53 wt%) was prepared by adding negative active material (100% artificial graphite), CMC-SBR as a binder, and carbon black as a conductive material to distilled water as a solvent in a weight ratio of 96:3.5:0.5. 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 (porosity of the negative electrode composite layer: 26%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 3.0 wt% of lithium nitrate (LiNO3) was added to prepare an electrolyte for a lithium secondary battery of the present invention. (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 4.65 g of the lithium secondary battery electrolyte manufactured as described above was injected to manufacture a lithium secondary battery (see Table 1 below). Example 16. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.064 mg / cm2, loading amount based on cathode cross-section: 0.032 mg / cm2, porosity of cathode composite layer: 24%). (Cathode manufacturing) A slurry of positive active material (solid content: 53 wt%) was prepared by adding negative active material (100% artificial graphite), CMC-SBR as a binder, and carbon black as a conductive material to distilled water as a solvent in a weight ratio of 96:3.5:0.5. 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 (porosity of the negative electrode composite layer: 26%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 3.0 wt% of lithium nitrate (LiNO3) was added to prepare an electrolyte for a lithium secondary battery of the present invention. (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 4.65 g of the lithium secondary battery electrolyte manufactured as described above was injected to manufacture a lithium secondary battery (see Table 1 below). Example 17. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.048 mg / cm2, loading amount based on cathode cross-section: 0.024 mg / cm2, porosity of cathode composite layer: 24%). (Cathode manufacturing) A slurry of positive active material (solid content: 53 wt%) was prepared by adding negative active material (100% artificial graphite), CMC-SBR as a binder, and carbon black as a conductive material to distilled water as a solvent in a weight ratio of 96:3.5:0.5. 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 (porosity of the negative electrode composite layer: 26%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 0.5 wt% of lithium nitrate (LiNO3) was added to prepare an electrolyte for a lithium secondary battery of the present invention. (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 8.29 g of the lithium secondary battery electrolyte manufactured as described above was injected to manufacture a lithium secondary battery (see Table 1 below). Example 18. (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 1.0 wt% of lithium nitrate (LiNO3) was added to prepare 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 17, except that 8.29 g of the lithium secondary battery electrolyte manufactured above was injected (see Table 1 below). Example 19. (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 2.0 wt% of lithium nitrate (LiNO3) was added to prepare 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 17, except that 8.29 g of the lithium secondary battery electrolyte manufactured above was injected (see Table 1 below). Example 20. (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 3.0 wt% of lithium nitrate (LiNO3) was added to prepare 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 17, except that 8.29 g of the lithium secondary battery electrolyte manufactured above was injected (see Table 1 below). Example 21. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 280 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.048 mg / cm2, loading amount based on cathode cross-section: 0.024 mg / cm2, porosity of cathode composite layer: 24%). (Cathode manufacturing) A slurry of positive active material (solid content: 53 wt%) was prepared by adding negative active material (100% artificial graphite), CMC-SBR as a binder, and carbon black as a conductive material to distilled water as a solvent in a weight ratio of 96:3.5:0.5. 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 (porosity of the negative electrode composite layer: 26%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 1.0 wt% of lithium nitrate (LiNO3) was added to prepare an electrolyte for a lithium secondary battery of the present invention. (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 3.65 g of the lithium secondary battery electrolyte manufactured as described above was injected to manufacture a lithium secondary battery (see Table 1 below). Example 22. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was placed on a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 465 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.048 mg / cm2, loading amount based on cathode cross-section: 0.024 mg / cm2, porosity of cathode composite layer: 24%). (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 21 except that the above-mentioned manufactured positive electrode was used (see Table 1 below). Example 23. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.030 mg / cm2, loading amount based on cathode cross-section: 0.015 mg / cm2, porosity of cathode composite layer: 24%). (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 21 except that the above-mentioned manufactured positive electrode was used (see Table 1 below). Example 24. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.072 mg / cm2, loading amount based on cathode cross-section: 0.036 mg / cm2, porosity of cathode composite layer: 24%). (Secondary battery manufacturing) A lithium secondary battery was manufactured in the same manner as in Example 21 except that the above-mentioned manufactured positive electrode was used (see Table 1 below). Example 25. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.048 mg / cm2, loading amount based on cathode cross-section: 0.024 mg / cm2, porosity of cathode composite layer: 24%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 1.0 wt% of lithium nitrate (LiNO3) was added to prepare 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 21, except that the positive electrode manufactured above was used and 2.98 g of the lithium secondary battery electrolyte manufactured above was injected (see Table 1 below). Example 26. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm.2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.048 mg / cm2, loading amount based on cathode cross-section: 0.024 mg / cm2, porosity of cathode composite layer: 24%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 1.0 wt% of lithium nitrate (LiNO3) was added to prepare 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 21, except that the positive electrode manufactured above was used and 9.95 g of the lithium secondary battery electrolyte manufactured above was injected (see Table 1 below). Comparative example 1. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 312 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.032 mg / cm2, loading amount based on cathode cross-section: 0.016 mg / cm2, porosity of cathode composite layer: 24%). (Cathode manufacturing) A slurry of positive active material (solid content: 53 wt%) was prepared by adding negative active material (100% artificial graphite), CMC-SBR as a binder, and carbon black as a conductive material to distilled water as a solvent in a weight ratio of 96:3.5:0.5. 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 (porosity of the negative electrode composite layer: 26%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 4.0 wt% of lithium nitrate (LiNO3) was added to prepare an electrolyte for a lithium secondary battery of the present invention. (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 8.50 g of the lithium secondary battery electrolyte manufactured as described above was injected to manufacture a lithium secondary battery (see Table 1 below). Comparative example 2. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 312 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.064 mg / cm2, loading amount based on cathode cross-section: 0.032 mg / cm2, porosity of cathode composite layer: 24%). (Cathode manufacturing) A slurry of positive active material (solid content: 53 wt%) was prepared by adding negative active material (100% artificial graphite), CMC-SBR as a binder, and carbon black as a conductive material to distilled water as a solvent in a weight ratio of 96:3.5:0.5. 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 (porosity of the negative electrode composite layer: 26%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 11.0 wt% of lithium nitrate (LiNO3) was added to prepare an electrolyte for a lithium secondary battery of the present invention. (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 4.77 g of the lithium secondary battery electrolyte manufactured as described above was injected to manufacture a lithium secondary battery (see Table 1 below). Comparative example 3. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.048 mg / cm2, loading amount based on cathode cross-section: 0.024 mg / cm2, porosity of cathode composite layer: 24%). (Cathode manufacturing) A slurry of positive active material (solid content: 53 wt%) was prepared by adding negative active material (100% artificial graphite), CMC-SBR as a binder, and carbon black as a conductive material to distilled water as a solvent in a weight ratio of 96:3.5:0.5. 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 (porosity of the negative electrode composite layer: 26%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 0.025 wt% of lithium nitrate (LiNO3) was added to prepare an electrolyte for a lithium secondary battery of the present invention. (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 3.48 g of the lithium secondary battery electrolyte manufactured as described above was injected to manufacture a lithium secondary battery (see Table 1 below). Comparative example 4. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.048 mg / cm2, loading amount based on cathode cross-section: 0.024 mg / cm2, porosity of cathode composite layer: 24%). (Cathode manufacturing) A slurry of positive active material (solid content: 53 wt%) was prepared by adding negative active material (100% artificial graphite), CMC-SBR as a binder, and carbon black as a conductive material to distilled water as a solvent in a weight ratio of 96:3.5:0.5. 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 (porosity of the negative electrode composite layer: 26%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 6.5 wt% of lithium nitrate (LiNO3) was added to prepare an electrolyte for a lithium secondary battery of the present invention. (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 8.29 g of the lithium secondary battery electrolyte manufactured as described above was injected to manufacture a lithium secondary battery (see Table 1 below). Comparative Example 5. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.064 mg / cm2, loading amount based on cathode cross-section: 0.032 mg / cm2, porosity of cathode composite layer: 24%). (Cathode manufacturing) A slurry of positive active material (solid content: 53 wt%) was prepared by adding negative active material (100% artificial graphite), CMC-SBR as a binder, and carbon black as a conductive material to distilled water as a solvent in a weight ratio of 96:3.5:0.5. 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 (porosity of the negative electrode composite layer: 26%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 0.02 wt% of lithium nitrate (LiNO3) was added to prepare an electrolyte for a lithium secondary battery of the present invention. (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 3.00 g of the lithium secondary battery electrolyte manufactured as described above was injected to manufacture a lithium secondary battery (see Table 1 below). Comparative example 6. (Polar manufacturing) A slurry of positive electrode active material (LiFePO4), a conductive agent (carbon black), and a binder (polyvinylidene fluoride, PVDF) was prepared by adding a solvent, N-methyl-2-pyrrolidone (NMP), at a weight ratio of 96:1:3. The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film, total area of ​​the positive electrode current collector surface: 435 cm) having a thickness of 15 μm. 2 ) was applied, dried, and roll pressed to manufacture a cathode (loading amount of cathode: 0.064 mg / cm2, loading amount based on cathode cross-section: 0.032 mg / cm2, porosity of cathode composite layer: 24%). (Cathode manufacturing) A slurry of positive active material (solid content: 53 wt%) was prepared by adding negative active material (100% artificial graphite), CMC-SBR as a binder, and carbon black as a conductive material to distilled water as a solvent in a weight ratio of 96:3.5:0.5. 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 (porosity of the negative electrode composite layer: 26%). (Electrolyte manufacturing) LiPF6 was dissolved to 1.0 M in an organic solvent containing gamma-butyrolactone and ethylene carbonate in a volume ratio of 70:30, and then 12.0 wt% of lithium nitrate (LiNO3) was added to prepare an electrolyte for a lithium secondary battery of the present invention. (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 6.43 g of the lithium secondary battery electrolyte manufactured as described above was injected to manufacture a lithium secondary battery (see Table 1 below). Total area of ​​the positive electrode surface (cm) 2 )Positive loading amount (g / cm) 2) Total electrolyte volume (g) Content of lithium nitrate (LiNO3) (%) When substituted into Equation 1, the calculated value is Example 14350.0483.6510.0035 Example 20.0484.980.0048 Example 30.0486.640.0064 Example 40.0644.650.0033 Example 50.0646.430.0046 Example 60.0648.450.0061 Example 73120.0483.100.50.0021 Example 80.0483.570.0024 Example 90.0484.770.0032 Example 100.0643.430.0017 embodiment 110.0644.550.0023 embodiment 120.0646.070.0030 embodiment 134350.0484.860.250.0012 embodiment 140.0644.860.250.0009 embodiment 150.0484.653.00.0134 embodiment 160.0644.653.00.0100 embodiment 170.0488.290.50.0040 embodiment 181.00.0079 embodiment 192.00.0159 embodiment 203.00.0238 embodiment 212800.0483.6510.0054 Example 224650.0483.650.0033 Example 234350.0303.650.0056 Example 244350.0723.650.0023 Example 254350.0482.980.0029 Example 264350.0489.950.0095 Comparative Example 13120.0328.504.00.0681 Comparative Example 23120.0644.7711.00.0526 Comparative Example 34350.0483.480.0250.00008 Comparative Example 44350.0488.296.50.0516Comparative Example 54350.0643.000.020.00004Comparative Example 64350.0646.4312.00.0554 [Experimental example] Experimental Example 1. Evaluation of high temperature (45℃) cycle characteristics The lithium secondary batteries manufactured in the above examples and comparative examples were each charged to 64% SOC at a high temperature (55°C) at a C rate of 0.1, and then subjected to an aging (48 hours) and degassing process to perform an activation process. After the activation process was completed, each lithium secondary battery was charged to 3.8 V under constant current / constant voltage conditions at 0.1 C rate at room temperature (25°C), and discharged to 2.5 V under constant current conditions at 0.33 C rate to confirm the initial capacity. Then, each lithium secondary battery was charged to 3.8 V under constant current / constant voltage conditions at a high temperature (45°C) at a 0.33 C rate, and discharged to 2.5 V under constant current conditions at a 0.33 C rate for 100 cycles, which was considered one cycle, and then the discharge capacity was measured. The lithium secondary battery operation was performed using a PNE-0506 charger / discharger (manufacturer: PNE solution). The capacity retention rate (%) after high temperature cycling was calculated using the 100th discharge rate of the obtained initial capacity dash, and the results are shown in Table 2 below. Experimental Example 2. Evaluation of low temperature (-10℃) cycle characteristics The lithium secondary batteries manufactured in the above examples and comparative examples were each charged to 64% SOC at a high temperature (55°C) at a C rate of 0.1, and then subjected to an aging (48 hours) and degassing process to perform an activation process. After the activation process was completed, each lithium secondary battery was charged to 3.8 V under constant current / constant voltage conditions at 0.1 C rate at room temperature (25°C), and discharged to 2.5 V under constant current conditions at 0.33 C rate to confirm the initial capacity. Then, each lithium secondary battery was charged to 3.8 V under constant current / constant voltage conditions at a low temperature (-10℃) at a 0.2 C rate, and discharged to 2.0 V under constant current conditions at a 0.33 C rate for 200 cycles, which was considered one cycle, and then the discharge capacity was measured. The lithium secondary battery operation was performed using a PNE-0506 charger / discharger (manufacturer: PNE solution). The capacity retention rate (%) after the low-temperature cycle was calculated using the obtained initial capacity and the 200th discharge capacity, and the results are shown in Table 2 below. Capacity retention rate after high temperature cycle (%) Capacity retention rate after low temperature cycle (%) Example 195.199.0 Example 294.899.1 Example 395.398.8 Example 495.498.4 Example 596.098.9 Example 694.998.5 Example 794.798.2 Example 895.798.7 Example 994.399.1 Example 1094.897.9 Example 1194.798.0 Example 1295.097.8 Example 1394.695.5 Example 1494.596.3 Example 1594.295.7 Example 1694.996.6 Example 1795.097.1Embodiment 1894.897.7Embodiment 1995.196.2Embodiment 2094.596.0Embodiment 2193.178.4Embodiment 2293.279.8Embodiment 2393.677.3Embodiment 2493.571.8Embodiment 2592.880.2Embodiment 2693.380.1Comparative Example 190.164.4Comparative Example 289.950.1Comparative Example 388.345.0Comparative Example 489.567.7Comparative Example 589.738.5Comparative Example 688.965.9 Referring to Table 2 above, it can be confirmed that in the case of the lithium secondary batteries manufactured in Examples 1 to 26 of the present invention, both the capacity retention rate (%) after a high-temperature cycle and the capacity retention rate (%) after a low-temperature cycle were improved compared to the lithium secondary batteries of Comparative Examples 1 to 6. 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 as a positive electrode active material, The above electrolyte comprises a lithium salt; a first organic solvent; a second organic solvent; and an additive. The above first organic solvent is a cyclic lactone compound, The above second organic solvent is a carbonate-based organic solvent, The above additive is lithium nitrate (LiNO3), and a lithium secondary battery satisfying the following formula 1: [Formula 1] 0.0001≤ ≤0.050 In the above equation 1, A is the total amount of electrolyte (g) injected into the lithium secondary battery, B is the content (weight%) of lithium nitrate (LiNO3) contained in the above-mentioned electrolyte, C is the loading of the anode (g / cm 2 ) and D is the total area of ​​the positive electrode surface (cm 2 )am.

2. In paragraph 1, A lithium secondary battery, wherein the lithium iron phosphate comprises a compound represented by the following chemical formula 1: [Chemical Formula 1] Li 1+a Fe x M y (PO 4-b )X' b In the above [chemical formula 1], 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 above cyclic lactone compound comprises gamma-butyrolactone.

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

6. 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.

7. In paragraph 1, A lithium secondary battery, wherein in the above formula 1, A is 3.0 g to 8.5 g.

8. In paragraph 1, In the above equation 1, C is 0.032 g / cm 2 0.064 g / cm 2 A lithium secondary battery.

9. In paragraph 1, In the above equation 1, D is 310 cm 2 450 cm inside 2 A lithium secondary battery.

10. 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.

11. In paragraph 1, A lithium secondary battery having a capacity of 1,000 mAh to 3,000 mAh.

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