Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery comprising: an electrode assembly including a cathode, an anode and a separator; an electrolyte; and a battery case for accommodating the electrode assembly and the electrolyte, wherein the anode comprises an anode active material layer including graphite and a Si / C composite, the cathode comprises a cathode active material layer including a lithium transition metal oxide represented by chemical formula 1, the electrolyte comprises a non-fluorinated saturated cyclic carbonate and a fluorine-based compound in a ratio of 40:1 to 40:20 by weight, the fluorine-based compound is included in an amount of 1-5 wt% on the basis of the total weight of the electrolyte, and the graphite and the Si / C are included in a ratio of 93.1:6.9 to 99.9:0.1 by weight in the anode active material layer. [Chemical formula 1] Li1+x1[Niy1Coz1Mnw1M1 v1]O2 All variables in chemical formula 1 are the same as those described in the specification.

Description

Lithium secondary battery Cross-citation with related applications This application claims the benefit of priority to Korean Patent Application No. 10-2023-0190463, filed December 22, 2023, and Korean Patent Application No. 10-2024-0190555, filed December 18, 2024, the entire contents of which are incorporated herein by reference. Technical field The present invention relates to a lithium secondary battery, and more specifically, to a lithium secondary battery having excellent capacity characteristics, as well as excellent life characteristics and high-temperature life characteristics. Due to the rapid increase in fossil fuel use, the demand for alternative or clean energy is increasing, and as part of this, the field being most actively researched is power generation and storage using electrochemical reactions. Currently, a representative example of an electrochemical device that utilizes such electrochemical energy is a secondary battery, and its application area is expanding more and more. Recently, as the technological development and demand for portable devices such as portable computers, portable phones, and cameras increase, the demand for secondary batteries as an energy source is rapidly increasing, and among such secondary batteries, lithium secondary batteries with high energy density, that is, high capacity, have been studied extensively, and they are also commercialized and widely used. Lithium secondary batteries are generally manufactured by forming an electrode assembly by interposing a separator between a positive electrode including a positive electrode active material made of a transition metal oxide containing lithium and a negative electrode including an negative electrode active material capable of storing lithium ions, inserting the electrode assembly into a battery case, injecting a non-aqueous electrolyte that serves as a medium for transferring lithium ions, and then sealing the electrode assembly. The non-aqueous electrolyte is generally composed of a lithium salt and an organic solvent capable of dissolving the lithium salt. Previously, carbon-based materials such as natural graphite or artificial graphite were mainly used as negative electrode active materials for lithium secondary batteries. However, since such carbon-based negative electrode active materials have small capacities and slow reaction rates with lithium, secondary batteries using them have limitations in implementing high capacity and rapid charging performance. Accordingly, silicon oxide (SiOx, 0) with a large theoretical capacity <x<2)과 같은 실리콘계 소재를 탄소계 음극 활물질과 혼합하여 적용한 리튬 이차 전지의 개발이 시도되고 있다. 실리콘계 소재는 탄소계 소재와 비교하여 이론 용량이 높고, 리튬과의 반응 속도가 빠르기 때문에 이를 적용할 경우, 용량 특성 및 급속 충전 성능을 향상시킬 수 있다는 장점이 있다. However, SiO x (0≤x<2) Silicon oxide of silicon particles such as silicon oxide reacts with Li ions generated from the positive electrode during charging to form lithium silicate, which is an irreversible phase. Therefore, there is a problem of low initial efficiency of the battery. In addition, silicon particles such as Pure Si change volume excessively during the charge / discharge process, and this volume change of silicon particles reduces the durability of the already formed SEI film, or causes many problems such as continuous electrolyte consumption and increased thickness of the SEI film due to the generation of a new negative electrode active material surface, which causes capacity degradation and reduced lifespan. The present invention is intended to solve the above problems, and to provide a lithium secondary battery in which an SEI film is stably formed on a negative electrode active material layer, and which has excellent life characteristics and high-temperature life characteristics as well as excellent capacity characteristics. [1] The present invention provides a lithium secondary battery comprising: an electrode assembly including a cathode, an anode, and a separator interposed between the cathode and the anode; an electrolyte; and a battery case accommodating the electrode assembly and the electrolyte, wherein the anode includes a cathode active material layer including graphite and a Si / C composite, the cathode includes a cathode active material layer including a lithium transition metal oxide represented by the following chemical formula 1, the electrolyte includes a non-fluorine-containing saturated cyclic carbonate and a fluorine-containing compound in a weight ratio of 40:1 to 40:20, the fluorine-containing compound is included in an amount of 1 wt% to 5 wt% based on the total weight of the electrolyte, and the graphite and Si / C are included in the anode active material layer in a weight ratio of 93.1:6.9 to 99.9:0.1. [Chemical Formula 1] Li 1+x1 [Ni y1 Co z1 Mn w1 M 1 v1 ]O2 In the above chemical formula 1, M 1 is at least one doping element selected from the group consisting of Al, W, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and 0≤x1≤0.2, 0.50≤y1<1, 0 <z1<0.35, 0<w1<0.4, 0≤v1≤0.1이다. [2] The present invention provides a lithium secondary battery, wherein, in the above [1], the Si / C composite is included in an amount of 1 to 15 wt% based on the total weight of the negative electrode active material layer. [3] The present invention provides a lithium secondary battery, wherein, in the above [1] or [2], the Si / C composite contains silicon (Si) and carbon (C) in a weight ratio of 1:10 to 23:10. [4] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to [3], the graphite and Si / C composite are included in the negative electrode active material layer at a weight ratio of 94:6 to 99:1. [5] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to [4], the Si / C composite includes silicon particles embedded within a carbon matrix. [6] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to [5], the non-fluorinated saturated cyclic carbonate is contained in an amount of 10 to 40 wt% based on the total weight of the electrolyte. [7] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to [6], the non-fluorinated saturated cyclic carbonate includes at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate. [8] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to [7], the fluorine-based compound is fluoroethylene carbonate (FEC). [9] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to [8], the electrolyte includes a lithium salt, and the lithium salt is included in the electrolyte at a concentration of 0.5 M to 2.0 M.

[0010] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to [9], a non-fluorinated linear carbonate solvent is contained in an amount of 40 to 90 wt% or less based on the total volume of the electrolyte.

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

[0010] , the battery case is a pouch-type battery case.

[0012] The present invention provides a lithium secondary battery including an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case accommodating the electrode assembly and the electrolyte, wherein the negative electrode includes a negative electrode active material layer and an SEI film (solid electrolyte interphase layer) positioned on the negative electrode active material layer, and the negative electrode includes a negative electrode active material layer including graphite and a Si / C composite, wherein the graphite and Si / C are included in the negative electrode active material layer at a weight ratio of 93.1:6.9 to 99.9:0.1, and the SEI film includes Li2CO3 and LiF at a weight ratio of 1:1 to 3:1. According to the present invention, a lithium transition metal oxide containing nickel, cobalt and manganese is included as a positive electrode active material, graphite and a Si / C composite are mixed and used at a specific weight ratio as a negative electrode active material, a non-fluorine-based saturated cyclic carbonate and a fluorine-based compound are mixed and used at a specific weight ratio as an electrolyte, and the fluorine-based compound is included at a specific content, thereby suppressing destruction of the SEI film due to volume expansion of the negative electrode active material during battery operation, preventing electrolyte side reactions, and preventing an increase in resistance due to an increase in the thickness of the electrode SEI film, and accordingly, the capacity characteristics of the lithium secondary battery can be excellent, while the life characteristics, particularly the high-temperature life characteristics, can be excellent. Figure 1 is an exploded assembly diagram of a lithium secondary battery according to the present invention. Figure 2 is a graph showing the results of a high-temperature life characteristic experiment according to Experimental Example 1 of lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 5. Hereinafter, the present invention will be described in more detail. The terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as having meanings and concepts 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 explain his or her own invention in the best manner. The terminology used in this specification is for the purpose of describing exemplary embodiments only and is not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, it should be understood that the terms “include,” “comprising,” or “having” are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof. In the present invention, a “single-particle particle” means a particle composed of 30 or fewer sub-particles. The sub-particle unit constituting the single-particle particle is referred to as a “nodule.” The single-particle particle includes a single particle composed of one single nodule and a pseudo-single particle which is a composite of 30 or fewer nodules. The above “nodule” refers to a sub-particle unit body constituting a single particle and a quasi-single particle, and the nodule may be a single crystal lacking a crystalline grain boundary, or a polycrystal in which no grain boundary exists in appearance when observed with a scanning electron microscope (SEM) at a magnification of 5,000 to 20,000 times. In the present invention, “secondary particle” means a particle formed by agglomeration of more than 30 sub-particles. In order to distinguish it from the sub-particles constituting the single particle type particle, each lower particle unit constituting the secondary particle is called a “primary particle.” The expression “particle” used in the present invention may include any one or all of a single particle, a quasi-single particle, a primary particle, a nodule, and a secondary particle. In the present invention, "average particle diameter D 50 "It refers to the particle size at 50% of the volume cumulative particle size distribution of the positive electrode active material powder, and can be measured using the laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves of about 28 kHz with an output of 60 W, obtaining a volume cumulative particle size distribution graph, and then finding the particle size corresponding to 50% of the volume cumulative amount. Hereinafter, the present invention will be described in more 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 A lithium secondary battery according to the present invention comprises: an electrode assembly including a cathode, an anode, and a separator interposed between the cathode and the anode; an electrolyte; and a battery case accommodating the electrode assembly and the electrolyte; wherein the anode comprises a cathode active material layer including graphite and a Si / C composite, the cathode comprises a cathode active material layer including a lithium transition metal oxide represented by the following chemical formula 1 as a cathode active material, and the electrolyte comprises a non-fluorine-containing saturated cyclic carbonate and a fluorine-containing compound in a weight ratio of 40:1 to 40:20. [Chemical Formula 1] Li 1+x1 [Ni y1 Co z1 Mn w1 M 1 v1 ]O2 In the above chemical formula 1, M 1 is at least one doping element selected from the group consisting of Al, W, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and 0≤x1≤0.2, 0.50≤y1<1, 0 <z1<0.35, 0<w1<0.35, 0≤v1≤0.1이다. Previously, carbon-based materials such as natural graphite or artificial graphite were mainly used as negative active materials for lithium secondary batteries. However, since such carbon-based negative active materials have small capacities and slow reaction rates with lithium, secondary batteries using them have limitations in implementing high capacity and rapid charging performance. Therefore, development of silicon-based active materials as negative electrode active materials has been carried out recently, and silicon-based particles, SiO, which are commonly used as negative electrode active materials, are used. x (0≤x<2) has the advantage of having a capacity about 10 times higher than that of carbon-based negative electrode active materials. However, the SiO xIn the case of silicon-based particles, since the volume change according to charge and discharge is large, it may cause the disconnection of the conductive connection within the negative electrode, which may cause an increase in resistance and a decrease in life performance. In addition, the use of the silicon-based particles may affect the SEI (Solid Electrolyte Interface) film. The SEI film is formed on the negative electrode active material layer due to the reaction between electrolyte molecules and lithium salts during the activation process of the lithium secondary battery. The activation process refers to the process of performing charging and / or discharging on a lithium secondary battery that has not yet been charged and discharged, and electrical characteristics are imparted to the lithium secondary battery according to the activation process, and the battery can be stabilized by forming an SEI film on the electrode, and as a result, the lithium secondary battery can be made into a state in which it can be actually used. The SEI film refers to a passive film formed as a byproduct due to the chemical reaction between the electrolyte and the negative electrode during charging during the activation process of the lithium secondary battery. The above SEI film protects the electrolyte from further decomposition, but if the thickness of the SEI film increases, the mobility of lithium ions may be restricted, thereby lowering the performance of the battery. Therefore, the formation of a stable SEI film is required. From this perspective, the volume change due to the use of silicon-based particles causes the SEI film to continuously decompose and regenerate. Accordingly, the side reaction of the electrolyte is promoted, the thickness of the SEI film increases, which increases the resistance, and the electrolyte is depleted, which may result in the deterioration of the battery's life performance and storage characteristics. To solve these problems, the present invention uses a mixture of graphite and Si / C composite as a negative electrode active material, thereby producing SiO xWhen silicon-based particles are used, the physical strength and chemical stability are superior, so that the degree of volume expansion of the battery during charge and discharge can be smaller, and the capacity characteristics can be superior compared to when a carbon-based active material is used alone. In addition, the present invention combines a positive electrode including a lithium transition metal oxide including nickel, cobalt, and manganese, a negative electrode including a mixture of graphite and a Si / C composite at a specific weight ratio, and an electrolyte including a non-fluorine-based saturated cyclic carbonate and a fluorine-based compound at a specific weight ratio, thereby forming an SEI film having superior stability and durability in terms of thickness and composition on the negative electrode, and accordingly, an increase in the thickness of the SEI film due to a change in the volume of the Si / C composite during charge and discharge can be suppressed, electrolyte side reactions and electrolyte depletion can be prevented, side reactions between the electrolyte and the negative electrode active material can be reduced, so as to suppress degradation of the negative electrode active material, and improve a swelling phenomenon of the battery. Therefore, the lithium secondary battery according to the present invention can have excellent capacity characteristics, as well as excellent life characteristics and high-temperature life characteristics. Hereinafter, each component of the lithium secondary battery according to the present invention will be described in detail. (1) Electrode assembly An electrode assembly according to the present invention includes an anode, a cathode, and a separator interposed between the anode and the cathode. Specifically, the electrode assembly can be formed by sequentially stacking an anode, a separator, and a cathode, and the anode and cathode can be mutually insulated by the separator. The types of electrode assemblies may include, but are not limited to, stacked, jellyroll, and stack-and-folded. Hereinafter, each component of the electrode assembly according to the present invention will be described in detail. 1) Bipolar The above positive electrode may include a positive electrode active material layer, and specifically, a positive electrode current collector; and a positive electrode active material layer positioned on the positive electrode current collector. As the positive electrode collector, various positive electrode collectors used in the relevant technical field can be used. For example, as the positive electrode collector, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode collector can typically have a thickness of 3 to 500 ㎛, 5 to 300 ㎛, or 8 to 100 ㎛, and fine unevenness can be formed on the surface of the positive electrode collector to increase the adhesion of the positive electrode active material. The positive electrode collector can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, or a non-woven fabric. The above-mentioned positive electrode active material layer may be positioned on the positive electrode current collector, and specifically, may be positioned on one side or both sides of the positive electrode current collector. The above-mentioned positive electrode active material layer may have a single layer or a multilayer structure of two or more layers. The above positive electrode active material layer includes a lithium transition metal oxide represented by the following chemical formula 1 as a positive electrode active material. [Chemical Formula 1] Li 1+x1 [Ni y1 Co z1 Mn w1 M 1 v1 ]O2 In the above chemical formula 1, M 1 is at least one doping element selected from the group consisting of Al, W, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and 0≤x1≤0.2, 0.50≤y1<1, 0 <z1<0.35, 0<w1<0.4 0≤v1≤0.1이다. In the above chemical formula 1, M 1may be at least one doping element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, or may be at least one doping element selected from the group consisting of W, Y, Ba, Ca, Ti, Mg, Ta, and Nb. The above 1+x1 may mean a molar ratio of lithium (Li) in the lithium transition metal oxide represented by the above chemical formula 1, and may be 0≤x1≤0.2, 0≤x1≤0.15, or 0≤x1≤0.1. When the above range is satisfied, the capacity characteristics of the lithium transition metal oxide are significantly improved according to the Li content control, and at the same time, the sinterability during the manufacture of the lithium transition metal oxide can be improved. The above y1 may mean the molar ratio of nickel among the total metal excluding lithium in the lithium transition metal oxide represented by the above chemical formula 1, and may be 0.50≤y1<1, 0.52≤y1<0.9, 0.55≤y1<0.8, or 0.57≤y1<0.75. When the above range is satisfied, the content of nickel (Ni) in the lithium transition metal oxide is secured in a sufficient amount to contribute to charge and discharge, so that high capacity can be achieved, and the structural stability is excellent, so that thermal stability can be excellent. The above z1 may mean the molar ratio of cobalt among the total metals excluding lithium in the lithium transition metal oxide represented by the above chemical formula 1, and 0 <z1<0.35, 0<z1≤0.25, 0.01≤z1≤0.20, 또는 0.03≤z1≤0.15일 수 있다. 상기 범위를 만족할 경우, 리튬 전이금속 산화물이 코발트를 적은 함량으로 포함하여 비용적인 이점을 가지면서도 양호한 저항 특성 및 출력 특성을 구현할 수 있다. The above w1 may mean the molar ratio of Mn among the total metals excluding lithium in the lithium transition metal oxide represented by the above chemical formula 1, and 0 <w1<0.4, 0.01≤w1≤0.37, 0.05≤w1≤0.35, 또는 0.1≤w1≤0.32일 수 있다. 상기 범위를 만족할 경우, 리튬 전이금속 산화물의 구조적 안정성을 향상시킬 수 있다. The above v1 is M among all metals except lithium in the lithium transition metal oxide represented by the above chemical formula 1. 1 It can mean the molar ratio of v1 and can be 0≤v1≤0.1, 0≤v1≤0.08, 0≤v1≤0.05, or v1=0. When the above range is satisfied, the structural stability of the lithium transition metal oxide can be improved. Additionally, the lithium transition metal oxide may include single-particle particles. Alternatively, the lithium transition metal oxide may be a single-particle particle. Specifically, when the lithium transition metal oxide includes secondary particles composed of more than 30 sub-particles (primary particles), particle breakage increases during electrode manufacturing, and internal cracks occur more frequently due to volume expansion / contraction of the primary particles during charge / discharge, which may reduce the effects of improving high-temperature life characteristics and high-temperature storage characteristics. Accordingly, when using a lithium transition metal oxide including single-particle particles as described above, the particle strength is higher than that of a conventional lithium transition metal oxide including secondary particles in which tens to hundreds of primary particles are aggregated, so particle breakage is less during rolling. In addition, in the case of a lithium transition metal oxide including single particle-type particles according to the present invention, since the number of primary particles constituting the particles is small, changes due to volume expansion and contraction of the primary particles during charging and discharging are small, and accordingly, occurrence of cracks inside the particles is significantly reduced, and as a result, the life characteristics of a lithium secondary battery can be excellent. Meanwhile, the average particle diameter (D) of the lithium transition metal oxide 50 ) may be 2 μm to 10 μm. Specifically, the average particle diameter (D) of the lithium transition metal oxide 50 ) may be 2 ㎛ or more, 2.5 ㎛ or more, 3 ㎛ or more, 3.5 ㎛ or more, 4 ㎛ or more, 4.5 ㎛ or more, 5 ㎛ or more, 5.5 ㎛ or more, 6 ㎛ or more, 10 ㎛ or less, 9.5 ㎛ or less, 9 ㎛ or less, 8.5 ㎛ or less, 8 ㎛ or less, 7.5 ㎛ or less, 7 ㎛ or less, 6.5 ㎛ or less, or 6 ㎛ or less. For example, the average particle diameter (D of the lithium transition metal oxide 50 ) may be 2 ㎛ to 10 ㎛, 2.5 ㎛ to 9.8 ㎛, 2.6 ㎛ to 9.7 ㎛, 2.7 ㎛ to 9.6 ㎛, 3 ㎛ to 9 ㎛, 4 ㎛ to 8 ㎛, or 5 ㎛ to 7 ㎛. When the above range is satisfied, side reactions with the electrolyte can be minimized while preventing an increase in resistance and a decrease in output characteristics. The above-described positive electrode active material layer may contain 80 wt% to 99 wt%, 90 wt% to 99 wt%, or 95 wt% to 98 wt% of the lithium transition metal oxide. When the above range is satisfied, the energy density and capacity characteristics of the lithium secondary battery can be improved. Meanwhile, the positive electrode active material layer may optionally further include at least one of a positive electrode conductive material and a positive electrode binder. The above-described positive electrode 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 examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more may be used. The positive electrode conductive material may be included in an amount of 0.1 to 30 wt%, 0.3 to 20 wt%, 0.5 to 10 wt%, or 0.8 to 5 wt% with respect to the total weight of the positive electrode active material layer. The above positive electrode binder serves to improve the adhesion between positive electrode particles and the adhesive strength between the positive electrode and the positive electrode current collector, and specific examples thereof include a fluorine resin binder including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); 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 polyimide binder; and a polyester binder. And silane binders, etc. can be mentioned, and one of these can be used alone or a mixture of two or more can be used. The positive electrode binder can be included in an amount of 0.1 to 30 wt%, 0.5 to 20 wt%, 0.8 to 10 wt%, or 1 to 5 wt% based on the total weight of the positive electrode active material layer. Meanwhile, the positive electrode can be manufactured by a method of applying positive electrode slurry to one side or both sides of a long sheet-shaped positive electrode collector, removing the solvent of the positive electrode slurry through a drying process, and then rolling. Meanwhile, a positive electrode including a non-coated portion can be manufactured by a method of not applying the positive electrode slurry to some area of ​​the positive electrode collector, for example, one end of the positive electrode collector, during the application of the positive electrode slurry. Additionally, the positive electrode slurry can be manufactured by dispersing the positive electrode active material in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. 2) Cathode The above negative electrode may include a negative electrode active material layer, and specifically, may include a negative electrode current collector; and a negative electrode active material layer positioned on the negative electrode current collector. The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery, and for example, 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. can be used. The above negative electrode current collector can typically have a thickness of 3 to 500 ㎛, 5 to 300 ㎛, or 8 to 100 ㎛. In addition, the negative current collector, like the positive current collector, can form fine irregularities on the surface of the negative current collector to strengthen the bonding strength of the negative active material. For example, it can be used in various forms such as a film, sheet, foil, net, porous body, foam, and non-woven fabric. The negative electrode active material layer may be positioned on the negative electrode current collector, and specifically, may be positioned on one side or both sides of the negative electrode current collector. The negative electrode active material layer may have a single layer or a multilayer structure of two or more layers. The above negative electrode active material layer includes graphite and a Si / C composite as negative electrode active materials. The lithium secondary battery according to the present invention can suppress the deterioration of life characteristics due to volume change of silicon particles during charge and discharge while implementing a high-capacity battery by including both graphite and a Si / C composite as negative active materials. The above graphite may be at least one selected from the group consisting of artificial graphite and natural graphite. The graphite may be a combination of artificial graphite and natural graphite, or may be artificial graphite. When the above graphite includes artificial graphite and natural graphite, the artificial graphite and the natural graphite may be included in a weight ratio of 9:1 to 6:4. When the above range is satisfied, the output characteristics and life characteristics may be excellent while improving the capacity characteristics. The above Si / C composite may be formed in a form in which silicon particles are evenly dispersed in an atomic state within a carbon (C) matrix. Specifically, in the present specification, “composite” means a material in which two or more materials are combined to form physically and chemically different phases and exhibit more effective functions, and the “Si / C composite” does not mean a state in which Si and carbon (C) are simply aggregated or mixed, but rather a state in which silicon particles are embedded within a carbon matrix. The carbon matrix may be a porous carbon matrix. When only Si is used as a silicon-based active material, the negative active material may deteriorate and resistance may increase due to volume shrinkage / expansion of Si particles during charge / discharge, which may cause a deterioration in the lifespan, and SiO x There is a problem that high capacity of lithium secondary batteries cannot be sufficiently achieved when only (0≤x<2) is used. Accordingly, the lithium secondary battery according to the present invention has excellent capacity characteristics by using a Si / C composite as a silicon-based active material, and further improves electrical conductivity by having carbon with excellent conductivity dispersed in an atomic state inside Si particles, and can reduce volume expansion of the negative electrode active material compared to a case where a silicon-based active material composed only of Si particles is used, thereby improving the life characteristics of the lithium secondary battery. The above Si / C composite may contain silicon (Si) and carbon (C) in a weight ratio of 1:10 to 23:10, 1.5:10 to 15:10, 2:10 to 10:10, or 3:10 to 6:10. When the above range is satisfied, the electrical conductivity of the negative electrode active material can be improved while achieving high capacity. The above Si / C composite may be included in an amount of 1 wt% to 15 wt%, 2 wt% to 10 wt%, 3 wt% to 8 wt%, 3.5 wt% to 6.5 wt%, 4 wt% to 6 wt%, or 4.5 wt% to 5.5 wt% based on the total weight of the negative electrode active material layer. When the above range is satisfied, the durability of the negative electrode may be excellent, so that the life characteristics of the lithium secondary battery may be excellent, and production may be performed without changing process conditions and process equipment, so that the processability and productivity may be excellent. The above graphite and Si / C composite may be included in the negative electrode active material layer in a weight ratio of 93.1:6.9 to 99.9:0.1, 93.5:6.5 to 99.5:0.5, 94:6 to 99:1, 94.2:5.8 to 98.5:1.5, 94.5:5.5 to 98:2, and 94.8:5.2 to 97.5:2.5. When the above range is satisfied, the volume change of the negative electrode during charge and discharge can be improved while seeking high capacity, so that the life characteristics can be excellent. Meanwhile, the negative electrode active material layer may optionally further include at least one of a negative electrode conductive material and a negative electrode binder in addition to the negative electrode active material. The above negative 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 examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more may be used. The negative conductive material may be included in an amount of 0.1 to 30 wt%, 0.3 to 20 wt%, 0.5 to 10 wt%, or 0.8 to 5 wt% based on the total weight of the negative active material layer. The above negative electrode binder serves to improve the adhesion between negative electrode active material particles and the adhesive strength between the negative electrode active material and the negative electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof may be used. The above negative electrode binder may be included in an amount of 0.1 to 30 wt%, 0.5 to 20 wt%, 0.8 to 10 wt%, or 1 to 5 wt% based on the total weight of the negative electrode active material layer. Meanwhile, when activating the lithium secondary battery according to the present invention, the negative electrode may include a negative electrode active material layer and an SEI (solid electrolyte interphase layer) film positioned on the negative electrode active material layer. The activation refers to a process of charging and / or discharging a lithium secondary battery that has been manufactured but has not been charged or discharged to impart electrical characteristics, and forming an SEI film on the electrode to stabilize the battery, thereby making the battery in a state where it can actually be used. The SEI film refers to a passive film formed as a byproduct of a chemical side reaction between an electrolyte and an negative electrode during a charging process during an activation process of a lithium secondary battery. The above SEI film can contain Li2CO3 and LiF in a weight ratio of 1:1 to 3:1, 1.2:1 to 3:1, 1.5:1 to 3:1, 2:1 to 3:1, or 2.3:1 to 2.5:1. When the above range is satisfied, a stable SEI film can be formed, thereby improving the life characteristics. The above activation may include charging and discharging. The above charging can be up to 4.3 V at 0.3 C, CC / CV conditions. The above discharge can be from 4.3 V to 2.5 V under 0.3 C, CC conditions. 3) Membrane The above separator is interposed between the positive electrode and the negative electrode to separate the negative electrode and the positive electrode and to provide a passage for lithium ions to move. If it is commonly used as a separator in a lithium secondary battery, it can be used without special restrictions. Specifically, the separator may be 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, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength. (2) Electrolyte The electrolyte according to the present invention comprises a non-fluorinated saturated cyclic carbonate and a fluorinated compound in a weight ratio of 40:1 to 40:20, 40:2 to 40:15, 40:2.5 to 40:10, or 40:3 to 40:7. The lithium secondary battery according to the present invention contains a non-fluorine-based saturated cyclic carbonate and a fluorine-based compound together in the electrolyte, thereby improving the strength and flexibility of an SEI film formed on an anode, thereby forming a stable and durable SEI film, and thereby suppressing destruction of the SEI film even when the volume change of the anode active material is large during charge and discharge, thereby improving the deterioration of the life characteristics of the lithium secondary battery. Meanwhile, if the electrolyte contains an excessively small amount of a fluorine-containing compound relative to the non-fluorine-containing saturated cyclic carbonate, there may be a limit to improving the life performance of the lithium secondary battery, and if the electrolyte contains an excessively large amount of a non-fluorine-containing saturated cyclic carbonate relative to the fluorine-containing compound, when the lithium secondary battery is operated at a high temperature, gas may be generated due to decomposition of the electrolyte, which may deteriorate the high-temperature life characteristics. Therefore, the present invention can stably form an SEI film by including a non-fluorine-containing saturated cyclic carbonate and a fluorine-containing compound at the above weight ratio, thereby preventing destruction of the SEI film due to volume expansion of the Si / C composite during charge and discharge, improving the high-temperature life characteristics of the lithium secondary battery, and improving the swelling phenomenon of the battery. The above non-fluorinated saturated cyclic carbonate is an organic solvent that serves to strengthen the SEI film formed on the cathode, and may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate, and preferably may include ethylene carbonate. The non-fluorinated saturated cyclic carbonate may be included in an amount of 5 to 60 wt%, 10 to 40 wt%, 15 to 37 wt%, 20 to 35 wt%, or 25 to 33 wt% based on the total weight of the electrolyte. When the non-fluorinated saturated cyclic carbonate is included in the above range, the strength of the SEI film formed on the negative electrode can be improved. The above fluorine-based compound serves to protect the interface of the Si / C composite, and may be at least one selected from the group consisting of 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, fluorobenzene, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, lithium oxalyldifluoroborate, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF3)2 (lithium bis(trifluoromethane sulfonyl)imide, LiTFSI), LiPO2F2, LiODFB, LiBF4, and fluoroethylene carbonate (FEC), and preferably fluoroethylene carbonate (FEC). The fluorine-based compound may be included in an amount of 1 wt% to 5 wt%, 2 wt% to 4.5 wt%, or 2.5 wt% to 4 wt% based on the total weight of the electrolyte. When the fluorine-based compound is included in the above range, the interface between the Si / C composite and the electrolyte can be protected without increasing the amount of gas generated. Meanwhile, the electrolyte may further include a non-fluorinated linear carbonate as a solvent. The non-fluorinated saturated cyclic carbonate and the non-fluorinated linear carbonate may have a volume ratio of 1:9 to 5:5. The above-mentioned non-fluorinated linear carbonate solvent is an organic solvent having low viscosity and low dielectric constant, and for example, at least one solvent 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 can be used, and specifically, at least one solvent selected from the group consisting of ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC), more specifically, ethyl methyl carbonate (EMC) can be included. When the above-mentioned non-fluorinated linear carbonate solvent is included, the viscosity of the electrolyte can be prevented from becoming excessively high, thereby further improving the electrolyte impregnation property. The above non-fluorinated linear carbonate solvent may be included in an amount of 40 to 90 wt%, 45 to 75 wt%, or 50 to 70 wt% based on the total volume of the electrolyte. The above electrolyte may include a lithium salt. The above lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be at least one selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, and LiB(C2O4)2, preferably, LiPF6. The above lithium salt may be included in the electrolyte at a concentration of 0.5 M to 2.0 M, 0.7 M to 1.8 M, or 1.0 M to 1.5 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate ionic conductivity and viscosity, so that excellent electrolyte performance can be exhibited, and lithium ions can move effectively, so that the life characteristics, rapid charge characteristics, and high-temperature life characteristics of the cylindrical lithium secondary battery can be improved. Meanwhile, the electrolyte may additionally include additives for the purposes of improving the ion conductivity of the battery, improving the cation transport rate, improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, in addition to the electrolyte components. For example, the additive may include at least one additive selected from the group consisting of non-fluorinated unsaturated cyclic carbonate compounds, sultone compounds, sulfate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds different from the lithium salt included in the electrolyte. Specifically, the additives are vinylene carbonate (VC), vinylethylene carbonate, 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, 1-methyl-1,3-propene sultone, ethylene sulfate (Esa), trimethylene sulfate (TMS), methyl trimethylene sulfate (MTMS), tetraphenylborate, succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, phenylacetonitrile, triethanolamine, ethylene diamine, It may be at least one selected from the group consisting of tetravinylsilane, and LiBOB (lithium bisoxalatoborate (LiB(C2O4)2)), and preferably vinylene carbonate. The above electrolyte may contain the additive in an amount of 1.5 wt% or less, 1.2 wt% or less, or 1.0 wt% or less. If the content of the additive is less than 0.01 wt%, the effects of improving the low-temperature output of the battery and the high-temperature storage characteristics and high-temperature life characteristics are minimal, and if the content of the additive exceeds 1.5 wt%, there is a possibility that side reactions may occur excessively in the electrolyte during charge and discharge of the battery. In particular, when the additives for forming the SEI film are added in excessive amounts, they may not be sufficiently decomposed at high temperatures and may exist as unreacted substances or in a precipitated state in the electrolyte at room temperature. Accordingly, side reactions that reduce the life or resistance characteristics of the secondary battery may occur. When the content of the above additive satisfies the above range, the low-temperature output characteristics, high-temperature storage characteristics, and high-temperature life characteristics of the battery can be improved, and side reactions within the electrolyte can be suppressed during battery charging and discharging, thereby improving the life characteristics and resistance characteristics. (3) Battery case The above battery case can serve to accommodate the electrode assembly and the electrolyte. Specifically, the battery case is for housing the electrode assembly, injecting the electrolyte, and then sealing it, and is manufactured from a material having a predetermined flexibility in which a housing portion can be formed, and although there is no limitation on its shape, it may preferably be cylindrical, coin-shaped, square, or pouch-shaped. The upper case and the lower case constituting the battery case may be independent members, or may be substantially one member with one end connected. The outer shape of the battery case may be manufactured in various ways, and the present invention does not limit this. For example, the battery case may be a pouch-type battery case. The pouch-type battery case may be manufactured by molding a pouch film laminate. The pouch-type battery case may accommodate the electrode assembly inside an outer material manufactured by molding a pouch film laminate. The above pouch film laminate may be formed by sequentially laminating a substrate layer, a gas barrier layer, and a sealant layer, but is not limited thereto. Specifically, the substrate layer is formed on the outermost layer of the pouch film laminate to protect the secondary battery from friction and collision with the outside. The substrate layer is made of a polymer and can electrically insulate the electrode assembly from the outside. The above-mentioned substrate layer may be made of one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, and Teflon. Among these, the substrate layer is preferably made of polyethylene terephthalate (PET), nylon, or a combination thereof, which have wear resistance and heat resistance. The above gas barrier layer is laminated between the substrate layer and the sealant layer to secure the mechanical strength of the pouch, block the ingress or egress of gas or moisture from outside the secondary battery, and prevent electrolyte leakage from inside the pouch-type battery case. The gas barrier layer may be formed of a metal. For example, the gas barrier layer may be a metal thin film including at least one metal selected from the group consisting of aluminum (Al), copper (Cu), stainless steel (SUS), nickel (Ni), titanium (Ti), and invar (INVAR), but is not limited thereto. The above sealant layer is intended to completely seal the inside of the pouch-shaped battery case by mutually thermally bonding at the sealing portion when the pouch-shaped battery case containing the electrode assembly (270) inside is sealed. To this end, the sealant layer may be formed of a material having excellent thermal bonding strength. The sealant layer may be formed of a material having insulating, corrosion-resistant, and sealing properties. Specifically, since the sealant layer is in direct contact with the electrode assembly (270) and / or the electrolyte (not shown) inside the pouch-shaped battery case, it may be formed of a material having insulating and corrosion-resistant properties. In addition, since the sealant layer must completely seal the inside of the pouch-shaped battery case to block material movement between the inside and the outside, it may be formed of a material having high sealing properties (e.g., excellent thermal bonding strength). In order to secure such insulating, corrosion-resistant, and sealing properties, the sealant layer may be formed of a polymer material. Specifically, the sealant layer may be made of one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, nylon, polyester, polyparaphenylenebenzobisoxazole, polyarylate, and Teflon, and preferably may be made of a polyolefin resin such as polypropylene (PP) and / or polyethylene (PE). In this case, the polypropylene may be composed of cast polypropylene (CPP), acid modified polypropylene (Acid Modified Polypropylene, PPa), a polypropylene-ethylene copolymer, and / or a polypropylene-butylene-ethylene terpolymer. Figure 1 is an exploded assembly diagram of a lithium secondary battery according to the present invention. The pouch film laminate can be drawn and stretched by a punch or the like to manufacture a pouch-shaped battery case. As a result, referring to FIG. 1, the pouch-shaped battery case can include a cup portion (232) and a receiving portion (234). The receiving portion (234) is a place for receiving an electrode assembly (270), and can mean a receiving space formed in a pocket shape on the inside of the cup portion (232) as the cup portion (232) is formed. Meanwhile, the pouch-type battery case may include a first case (230) and a second case (240). The first case (230) includes a receiving portion (234) that can receive an electrode assembly (270), and the second case (240) may cover the receiving portion (234) from above to prevent the electrode assembly (270) from falling out of the battery case. The first case (230) and the second case (240) may be manufactured with one side connected to each other, but are not limited thereto, and may be manufactured in various ways, such as being manufactured separately from each other. According to another embodiment of the present invention, when forming cup parts (232, 242) on a pouch film laminate, two symmetrical cup parts (232, 242) can be drawn and formed adjacent to each other on one pouch film laminate. In this case, a cup part (242) can be formed on each of the first case (230) and the second case (240). After the electrode assembly (270) is accommodated in the receiving part (234) provided in the cup part (232) of the first case (230), the bridge part (250) formed between the two cup parts (232, 242) can be folded so that the two cup parts (242) face each other. In this case, the cup part (242) of the second case (240) can accommodate the electrode assembly (270) from above. Accordingly, since two cup parts (232, 242) accommodate one electrode assembly (270), an electrode assembly (270) having a thicker thickness can be accommodated than when there is only one cup part. In addition, since one corner of the secondary battery is formed by folding the pouch-type battery case, the number of corners to be sealed can be reduced when performing a sealing process later. Accordingly, the process speed of the pouch-type secondary battery (200) can be improved, and the number of sealing processes can be reduced. The pouch-type battery case can be sealed while housing the electrode assembly (270) so that a part of the electrode lead (10) described later, i.e., a terminal part, is exposed. Specifically, when the electrode lead (10) is connected to the electrode tab (280) of the electrode assembly (270) and the lead film (290) is attached to a part of the electrode lead (10), the electrode assembly (270) is housed in the receiving portion (234) provided in the cup portion (232) of the first case (230), and the second case (240) can cover the receiving portion (234) from above. Then, an electrolyte (not shown) can be injected into the receiving portion (234), and the sealing portion (260) formed on the edges of the first case (230) and the second case (240) can be sealed. The sealing portion (260) can perform a function of sealing the receiving portion (234). Specifically, the sealing portion (260) can seal the receiving portion (234) while being formed along the edge of the receiving portion (234). The temperature for sealing the sealing portion (260) can be 180° C. to 250° C., specifically 200° C. to 250° C., and more specifically 210° C. to 240° C. When the sealing temperature satisfies the above numerical range, the pouch-type battery case can secure sufficient sealing strength by heat bonding. At this time, the sealing portion (260) may be formed by folding toward the receiving portion (234) to secure the energy density of the lithium secondary battery. The lithium secondary battery according to the present invention is useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs). In addition, a battery module or battery pack including the lithium secondary battery as a unit cell can be used as a power source for one or more medium- to large-sized devices among a power tool; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system. The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells. Examples of the above medium and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. Hereinafter, the present invention will be described in more detail through specific examples. Example 1 <Cathode Manufacturing> A negative electrode slurry was prepared by mixing negative active material, conductive material, and binder in a weight ratio of 97:1:2 in distilled water. At this time, an artificial graphite:Si / C composite was used as a negative active material by mixing it in a weight ratio of 95:5, and the Si / C composite contained silicon (Si) and carbon (Si) in a weight ratio of 4:10, and Super C / SWCNT was used as a conductive material, and styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were used as a binder by mixing them in a weight ratio of 6:4. After applying the above cathode slurry to a copper thin film, it was dried and rolled to manufacture a cathode. <Electrolyte manufacturing> A mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7 was used as an organic solvent. An electrolyte was prepared by adding LiPF6 as a lithium salt to the above organic solvent and adding fluoroethylene carbonate (FEC). The LiPF6 was included in the non-aqueous electrolyte at a molar concentration of 1.2 M, the ethylene carbonate was included in the electrolyte at 30 wt%, and the fluoroethylene carbonate was included in the electrolyte at 3 wt%. <Lithium secondary battery manufacturing> A cathode slurry was prepared by mixing cathode active material, conductive material, and binder in a weight ratio of 97:1:2 in distilled water. At this time, Li[Ni 0.6 Co 0.1 Mn 0.3 ]O2 was used, carbon black was used as the challenge material, and polyvinylidene fluoride (PVDF) was used as the binder. After applying the above positive electrode slurry to an aluminum thin film, it was dried and rolled to manufacture a positive electrode. A polyethylene porous film separator was interposed between the positive and negative electrodes manufactured as described above in a dry room, and then the electrolyte manufactured as described above was injected to manufacture a lithium secondary battery. Example 2 <Cathode Manufacturing> The cathode was manufactured using the same method as in Example 1. <Electrolyte manufacturing> A mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 5:5 was used as an organic solvent. An electrolyte was prepared by adding LiPF6 as a lithium salt to the above organic solvent. The LiPF6 was included in the non-aqueous electrolyte at a molar concentration of 1.2 M, the ethylene carbonate was included in the electrolyte at 50 wt%, and the fluoroethylene carbonate was included in the electrolyte at 3 wt%. <Lithium secondary battery> A lithium secondary battery was manufactured using the same method as in Example 1, except that the electrolyte manufactured above was used. Example 3 <Cathode Manufacturing> The cathode was manufactured using the same method as in Example 1. <Electrolyte manufacturing> A mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:9 was used as an organic solvent. An electrolyte was prepared by adding LiPF6 as a lithium salt to the above organic solvent. The LiPF6 was included in the non-aqueous electrolyte at a molar concentration of 1.2 M, the ethylene carbonate was included in the electrolyte at 10 wt%, and the fluoroethylene carbonate was included in the electrolyte at 5 wt%. <Lithium secondary battery> A lithium secondary battery was manufactured using the same method as in Example 1, except that the electrolyte manufactured above was used. Comparative Example 1 <Cathode Manufacturing> The cathode was manufactured using the same method as in Example 1. <Electrolyte manufacturing> A mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7 was used as an organic solvent. An electrolyte was prepared by adding LiPF6 as a lithium salt to the above organic solvent. The above LiPF6 was included in the non-aqueous electrolyte at a molar concentration of 1.2 M, and the above ethylene carbonate was included in the electrolyte at 30 wt%. <Lithium secondary battery> A lithium secondary battery was manufactured using the same method as in Example 1, except that the electrolyte manufactured above was used. Comparative Example 2 <Cathode Manufacturing> The cathode was manufactured using the same method as in Example 1. <Electrolyte manufacturing> A mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 2:8 was used as an organic solvent. An electrolyte was prepared by adding LiPF6 as a lithium salt to the above organic solvent. The LiPF6 was included in the non-aqueous electrolyte at a molar concentration of 1.2 M, the ethylene carbonate was included in the electrolyte at 20 wt%, and the fluoroethylene carbonate was included in the electrolyte at 0.5 wt%. <Lithium secondary battery> A lithium secondary battery was manufactured using the same method as in Example 1, except that the electrolyte manufactured above was used. Comparative Example 3 <Cathode Manufacturing> A negative electrode slurry was prepared by mixing negative active material, conductive material, and binder in a weight ratio of 97:1:2 in distilled water. At this time, artificial graphite:SiO was mixed at a weight ratio of 95:5 as the negative active material, Super P / SWCNT was used as the conductive material, and styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were used as the binder at a weight ratio of 6:4. After applying the above cathode slurry to a copper thin film, it was dried and rolled to manufacture a cathode. <Electrolyte manufacturing> The electrolyte was prepared using the same method as in Example 1. <Lithium secondary battery manufacturing> A lithium secondary battery was manufactured using the same method as in Example 1, except that the negative electrode manufactured above was used. Comparative Example 4 <Cathode Manufacturing> The cathode was manufactured using the same method as in Example 1. <Electrolyte manufacturing> A mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 2:8 was used as an organic solvent. An electrolyte was prepared by adding LiPF6 as a lithium salt to the above organic solvent. The LiPF6 was included in the non-aqueous electrolyte at a molar concentration of 1.2 M, the ethylene carbonate was included in the electrolyte at 20 wt%, and the fluoroethylene carbonate was included in the electrolyte at 6 wt%. <Lithium secondary battery> A lithium secondary battery was manufactured using the same method as in Example 1, except that the electrolyte manufactured above was used. Comparative Example 5 <Cathode Manufacturing> A negative electrode slurry was prepared by mixing negative active material, conductive material, and binder in a weight ratio of 97:1:2 in distilled water. At this time, an artificial graphite:Si / C composite was used as a negative active material by mixing it in a weight ratio of 93:7, and the Si / C composite contained silicon (Si) and carbon (Si) in a weight ratio of 4:10, and Super C / SWCNT was used as a conductive material, and styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were used as a binder by mixing them in a weight ratio of 6:4. After applying the above cathode slurry to a copper thin film, it was dried and rolled to manufacture a cathode. <Electrolyte manufacturing> The electrolyte was prepared using the same method as in Example 1. <Lithium secondary battery manufacturing> A lithium secondary battery was manufactured using the same method as in Example 1, except that the negative electrode manufactured above was used. Experimental Example 1: Analysis of SEI film components After activating the lithium secondary batteries of Example 1 and Comparative Example 1, they were pretreated and subjected to CE (Capillary electrophoresis) analysis to analyze the components of the SEI film, and the weight ratio of Li2CO3:LIF within the SEI film was analyzed. The weight ratio of Li2CO3:LIF within the SEI film measured by the above analysis is shown in Table 1. The above pretreatment was performed by disassembling the lithium secondary battery in a glove box, washing one electrode with methyl propionate for 30 minutes, and then extracting it overnight with 2 to 3 mL of D2O. The above CE analysis was performed according to the CE-based inorganic SEI film content analysis method using 'AMT-5591-0k, a novel anion coating system (CTAB)' by a CE analysis device (EQC-02999, P / ACE MDQ plus, SCIEX). Li2CO3:LIF(weight ratio) Example 171:29 Comparative example 192:8 Referring to Table 1 above, it can be confirmed that the SEI film formed in the lithium secondary battery manufactured in Example 1 contained Li2CO3:LIF so as to satisfy a weight ratio of 1:1 to 3:1, and that the SEI film formed in the lithium secondary battery manufactured in Comparative Example 1 contained Li2CO3:LIF so as not to satisfy a weight ratio of 1:1 to 3:1. Experimental Example 2: Evaluation of high temperature (45℃) life characteristics The life characteristics of the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 5 were measured at 45°C. Specifically, each of the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 5 was charged at 45°C at a constant current of 0.33 C to 4.3 V with a cut off of 0.025 C. Then, discharge was performed at a constant current of 0.33 C to 2.5 V. The above charge and discharge behavior was considered as one cycle, and these cycles were repeated 350 times. The capacity retention rate after 350 cycles was measured to evaluate the high-temperature life characteristics. The measurement results are shown in Table 2 and Fig. 2 below. At this time, the capacity maintenance rate was calculated by the following formula. Capacity retention rate (%) = {(discharge capacity after 350 cycles / discharge capacity after 1 cycle)} Х 100 Capacity retention rate [%] (@350 cycle)Example 192.7Example 288.2Example 390.1Comparative example 187.4Comparative example 288.1Comparative example 387.3Comparative example 487.5Comparative example 583.7 Referring to Table 2 and FIG. 2 above, it can be confirmed that the lithium secondary batteries manufactured in Examples 1 to 3 have a superior capacity retention rate at high temperature (45°C) than the lithium secondary batteries manufactured in Comparative Examples 1 to 5. Experimental Example 3: Evaluation of Life Characteristics The lithium secondary batteries manufactured in the above Examples 1 to 3 and Comparative Examples 1 to 5 were charged to 4.3 V at 0.33 C at 25°C and then discharged to 2.5 V at 0.05 C for 350 cycles, which constituted one cycle. Then, the capacity retention rate and resistance increase rate were measured. The measurement results are shown in Table 3 below. At this time, the capacity maintenance rate was calculated according to the following formula. - Capacity retention rate (%) = (discharge capacity after 350 cycles / initial discharge capacity) × 100 Capacity retention rate [%] (@350 cycle)Example 193.1Example 288.1Example 392.2Comparative Example 165.1Comparative Example 288.5Comparative Example 390.1Comparative Example 488.2Comparative Example 5Not measurable Referring to Table 3 above, it can be confirmed that the lithium secondary batteries manufactured in Examples 1 and 3 have a better capacity retention rate at room temperature than the lithium secondary batteries manufactured in Comparative Examples 1 to 4. Experimental Example 4: Swelling Evaluation The lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 5 were charged to 4.3 V at 0.33 C at 25°C and then discharged to 2.5 V at 0.05 C for 350 cycles, which constituted one cycle, and then the swelling ratio was measured. The measurement results are shown in Table 4 below. At this time, the swelling ratio was calculated according to the following formula. - Swelling ratio [%] = (Thickness of lithium secondary battery after 350 cycles / Initial thickness of lithium secondary battery before cycling) × 100 Swelling ratio [%] (@350 cycles)Example 15.1Example 26.5Example 38.5Comparative example 110.5Comparative example 27.1Comparative example 39.1Comparative example 48.3Comparative example 512.4 Referring to Table 4 above, it can be confirmed that the lithium secondary batteries manufactured in Examples 1 to 2 have a smaller swelling ratio than the lithium secondary batteries manufactured in Comparative Examples 1 to 5. (Explanation of symbols) 10: Electrode Leads 20: Positive Lead 30: Negative lead 200: Secondary battery 210: Battery Case 220: Pouch film laminate 221: Substrate layer 222: Gas barrier layer 223: Sealant layer 230: Case 1 232: Cup part 234: Reception area 240: Case 2 242: Cup part 250: Bridge section 260: Sealing part 270: Electrode assembly 280: Electrode tab 282: Bipolar tab 284: Negative tab 290: Lead Film

Claims

1. A lithium secondary battery comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case accommodating the electrode assembly and the electrolyte; The above negative electrode comprises a negative electrode active material layer including graphite and a Si / C composite, The above positive electrode includes a positive electrode active material layer including a lithium transition metal oxide represented by the following chemical formula 1 as a positive electrode active material, The above electrolyte contains a non-fluorinated saturated cyclic carbonate and a fluorinated compound in a weight ratio of 40:1 to 40:20, The above fluorine compound is included in an amount of 1 to 5 wt% based on the total weight of the electrolyte. A lithium secondary battery, wherein the graphite and Si / C are included in the negative electrode active material layer in a weight ratio of 93.1:6.9 to 99.9:0.

1. [Chemical Formula 1] Li 1+x1 [Ni y1 Co z1 Mr w1 M 1 v1 ]O2 In the above chemical formula 1, M 1 is at least one doping element selected from the group consisting of Al, W, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and 0≤x1≤0.2, 0.50≤y1<1, 0 <z1<0.35, 0<w1<0.4, 0≤v1≤0.1이다.

2. In paragraph 1, A lithium secondary battery, wherein the Si / C composite is included in an amount of 1 to 15 wt% based on the total weight of the negative electrode active material layer.

3. In paragraph 1, A lithium secondary battery, wherein the Si / C composite contains silicon (Si) and carbon (C) in a weight ratio of 1:10 to 23:

10.

4. In paragraph 1, A lithium secondary battery, wherein the graphite and Si / C composite are included in the negative electrode active material layer at a weight ratio of 94:6 to 99:

1.

5. In paragraph 1, A lithium secondary battery, wherein the Si / C composite includes silicon particles embedded within a carbon matrix.

6. In paragraph 1, A lithium secondary battery, wherein the non-fluorinated saturated cyclic carbonate is contained in an amount of 10 to 40 wt% based on the total weight of the electrolyte.

7. In paragraph 1, A lithium secondary battery, wherein the non-fluorinated saturated cyclic carbonate comprises at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate.

8. In paragraph 1, A lithium secondary battery, wherein the above fluorine compound is fluoroethylene carbonate (FEC).

9. In paragraph 1, The above electrolyte contains a lithium salt, A lithium secondary battery, wherein the lithium salt is included in the electrolyte at a concentration of 0.5 M to 2.0 M.

10. In paragraph 1, A lithium secondary battery, wherein a non-fluorinated linear carbonate solvent is contained in an amount of 40 to 90 wt% based on the total volume of the electrolyte.

11. In paragraph 1, The above battery case is a pouch-type battery case, a lithium secondary battery.

12. A lithium secondary battery comprising an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case accommodating the electrode assembly and the electrolyte; The above negative electrode includes a negative electrode active material layer and a solid electrolyte interphase layer (SEI) located on the negative electrode active material layer, The above negative electrode comprises a negative electrode active material layer including graphite and a Si / C composite, The above graphite and Si / C are included in the negative electrode active material layer in a weight ratio of 93.1:6.9 to 99.9:0.1, The above SEI film contains Li2CO3 and LiF in a weight ratio of 1:1 to 3:

1. Lithium secondary battery.

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