Lithium secondary battery and method for evaluating thermal safety of lithium secondary battery

Abstract

The present invention relates to: a lithium secondary battery having improved safety when high heat is applied from an external heat source, since the relationship among the size of the secondary battery, the content of remaining ethylene carbonate, and the reaction area of a negative electrode satisfies specific conditions; and to a method for evaluating thermal safety of a lithium secondary battery, whereby, through the information, thermal safety of a cylindrical lithium secondary battery can be evaluated.

Description

Lithium secondary battery and method for evaluating thermal safety of lithium secondary battery The present invention relates to a lithium secondary battery and a method for evaluating the thermal safety of a lithium secondary battery. Lithium secondary batteries are generally manufactured by applying electrode active material slurry to a positive electrode current collector and a negative electrode current collector to manufacture a positive electrode and a negative electrode, laminating them on both sides of a separator to form an electrode assembly of a predetermined shape, then storing the electrode assembly in a pouch and injecting electrolyte. Secondary batteries are classified into pouch types and can types depending on the material of the case that accommodates the electrode assembly. Among these, pouch type secondary batteries are manufactured by performing press processing on a flexible pouch film laminate to form a cup portion, accommodating the electrode assembly in the cup portion, injecting an electrolyte, and then sealing the seal portion. Can type secondary batteries are manufactured by accommodating the electrode assembly in a can made of a metal material, injecting an electrolyte, and then assembling a top cap on the top of the can to seal it. The 4680 cylindrical secondary battery, which has emerged as a next-generation secondary battery among can-type secondary batteries, is a cylindrical secondary battery with a diameter of 46 mm and a height of 80 mm. Compared to existing cylindrical secondary batteries, its diameter and height have increased, so it has the advantages of high energy density and output. However, as the energy density and output are high, heat generation increases, making internal heat dissipation difficult. As the diameter and height of the cylindrical secondary battery increase, its internal volume also increases, making safety in high-temperature environments an increasingly important issue. The problem that the present invention seeks to solve is to provide a lithium secondary battery in which safety is ensured when high heat is applied from an external heat source. Another problem to be solved by the present invention is to provide a method for evaluating the thermal safety of a lithium secondary battery, which can evaluate whether the lithium secondary battery is safe when exposed to high heat from an external heat source. To solve the above problem, the present invention provides a lithium secondary battery. [1] 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 including ethylene carbonate as a solvent; and a cylindrical battery case accommodating the electrode assembly and the electrolyte, and satisfying the following formula 1: [Formula 1] In the above equation 1, R is the diameter of the battery (mm), H is the height of the battery (mm), dEC is the amount of ethylene carbonate remaining in the lithium secondary battery after activation (g), and AA is the area of ​​the negative electrode (cm). 2 ), LA is the loading amount of the cathode (g / cm 2 ), RA is the ratio of the negative active material, BA is the BET (g / m) of the negative active material. 2 ), wherein R is 45 to 47 and H is 78 to 130. [2] The present invention provides a lithium secondary battery according to the above [1], wherein R and H are the diameter and height of a 4680 lithium secondary battery, a 4695 lithium secondary battery, a 46120 lithium secondary battery, or a 46125 lithium secondary battery, respectively. [3] The present invention provides a lithium secondary battery according to [1] or [2], wherein the dEC is 2.0 to 10.0. [4] The present invention provides a lithium secondary battery according to any one of the above [1] to [3], wherein AA is 2,800 to 2,900. [5] The present invention provides a lithium secondary battery according to any one of the above [1] to [4], wherein the LA is 0.1000 to 0.2000. [6] The present invention provides a lithium secondary battery according to any one of the above [1] to [5], wherein the RA is 0.80 to 0.99. [7] The present invention provides a lithium secondary battery according to any one of the above [1] to [6], wherein BA is 0.01 to 100. [8] The present invention provides a lithium secondary battery, wherein in any one of [1] to [7], the electrolyte further comprises an organic solvent other than ethylene carbonate, and the organic solvent comprises at least one selected from the group consisting of ester solvents, ether solvents, ketone solvents, aromatic hydrocarbon solvents, carbonate solvents other than ethylene carbonate, alcohol solvents, nitriles, amides, dioxolanes, and sulfolanes. [9] The present invention provides a lithium secondary battery, wherein in any one of the above [1] to [8], the electrolyte further comprises an electrolyte additive, and the electrolyte additive comprises at least one selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0010] The present invention provides a lithium secondary battery according to any one of the above [1] to [9], wherein the positive electrode includes a positive electrode active material, and the positive electrode active material includes a lithium transition metal containing Ni at 60 mol% or more of all metals excluding lithium. In addition, the present invention provides a method for evaluating the thermal safety of a lithium secondary battery to solve the other problems mentioned above.

[0011] The present invention provides a method for evaluating the thermal safety of a cylindrical lithium secondary battery, comprising: (s1) a step of measuring the diameter and height of a lithium secondary battery; (s2) a step of measuring the amount of ethylene carbonate (EC) remaining in the lithium secondary battery after activation; (s3) a step of measuring the reaction area of ​​a negative electrode active material layer of an anode included in the lithium secondary battery; and (s4) a step of determining that the battery has thermal safety if the following equation 1 is satisfied: [Formula 1] In the above equation 1, R is the diameter of the battery (mm), H is the height of the battery (mm), dEC is the amount of ethylene carbonate remaining in the lithium secondary battery after activation (g), and AA is the area of ​​the negative electrode (cm). 2 ), LA is the loading amount of the cathode (g / cm 2 ), RA is the ratio of the negative active material, BA is the BET (g / m) of the negative active material. 2 ), and the reaction area of ​​the negative active material layer is calculated as AA × LA × RA × BA, where R is 45 to 47 and H is 78 to 130.

[0010] The present invention provides a method for evaluating the thermal safety of a lithium secondary battery, wherein in the above [9], R and H are the diameter and height of a 4680 lithium secondary battery, a 4695 lithium secondary battery, a 46120 lithium secondary battery, or a 46125 lithium secondary battery, respectively. When the relationship among the size of the battery, the content of residual ethylene carbonate after activation, and the reaction area of ​​the negative electrode satisfies specific conditions, such as in the lithium secondary battery according to the present invention, safety can be improved when high heat is applied from an external heat source, and thus a lithium secondary battery with improved thermal safety can be provided. In addition, according to the method for evaluating thermal safety of a lithium secondary battery of the present invention, the thermal safety of a lithium secondary battery can be predicted and evaluated from the size of the battery, the content of residual ethylene carbonate after activation, and the reaction area of ​​the negative electrode. 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 that conform to 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. Hereinafter, the present invention will be described in more detail. The lithium secondary battery of the present invention comprises an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte including ethylene carbonate as a solvent; and a cylindrical battery case accommodating the electrode assembly and the electrolyte, and satisfies the following formula 1. [Formula 1] In the above equation 1, R is the diameter of the battery (mm), H is the height of the battery (mm), dEC is the amount of ethylene carbonate remaining in the lithium secondary battery after activation (g), and AA is the area of ​​the negative electrode (cm). 2 ), LA is the loading amount of the cathode (g / cm 2 ), RA is the ratio of the negative active material, BA is the BET (g / m) of the negative active material. 2 ), wherein R is 45 to 47 and H is 78 to 130. Recently, as the demand for high-capacity batteries, such as those for electric vehicles, has increased, the rated capacity of secondary battery cells has increased, and accordingly, the size and weight of electrode assemblies have increased. As the size and weight of the electrode assembly increase, it has the advantage of high energy density and output, but as the energy density and output increase, heat generation increases, making internal heat dissipation difficult, and accordingly, the influence of heat transfer by external heat sources further affects the thermal stability of the battery. Factors affecting the thermal stability and safety of cylindrical secondary batteries with larger diameter and height than conventional cylindrical secondary batteries include the internal space and electrolyte injection amount of the cylindrical secondary battery, and also the effect of the formation of a SEI (Solid Electrolyte Interphase) film due to the electrolyte additive. Among the above factors, the effect of the SEI film is greater than that of the electrolyte injection amount, and therefore, the decrease in the SEI film as the absolute amount of the electrolyte additive decreases rather than the increase in the internal space due to the decrease in the electrolyte injection amount has a greater effect on the thermal stability and safety of the secondary battery. Therefore, in order to secure the thermal stability and safety of the 4680 cylindrical secondary battery, a certain amount of electrolyte additive must be included in the cylindrical secondary battery so that the SEI film is sufficiently formed. In a lithium secondary battery, when Li ions diffuse from the positive electrode during initial activation, they are deposited on the surface of the negative electrode to form an SEI film. In the process of forming the SEI film, the electrolyte additive reacts first, and then the electrolyte solvent, ethylene carbonate (EC), reacts. Therefore, the degree of SEI film formation can be confirmed by the degree of decomposition of ethylene carbonate included in the lithium secondary battery. That is, based on the fact that the sufficient formation of the SEI film has a great impact on the thermal stability and safety of a lithium secondary battery, by confirming the degree of decomposition of ethylene carbonate included in the lithium secondary battery during the activation process, it is possible to confirm whether the SEI film is sufficiently formed within the lithium secondary battery, thereby confirming the thermal stability and safety of the lithium secondary battery. A lithium secondary battery according to the present invention includes a sufficiently formed SEI film, wherein the size of the lithium secondary battery, the content of ethylene carbonate remaining in the lithium secondary battery after activation, and the reaction area of ​​the negative electrode satisfy the following Equation 1. [Formula 1] In the above equation 1, R is the diameter of the battery (mm), H is the height of the battery (mm), dEC is the amount of ethylene carbonate remaining in the lithium secondary battery after activation (g), and AA is the area of ​​the negative electrode (cm). 2 ), LA is the loading amount of the cathode (g / cm 2 ), RA is the ratio of the negative active material, BA is the BET (g / m) of the negative active material. 2 ) is. In addition, in the above equation 1, AA × LA × RA × BA represents the reaction area of ​​the cathode. A lithium secondary battery satisfying the above equation 1 is a lithium secondary battery after activation. In one embodiment of the present invention, Equation 1 can be specifically represented by Equation 1-1 below, and more specifically can be represented by Equation 1-2 below. [Formula 1-1] [Formula 1-2] In the above equations 1-1 and 1-2, R is the diameter of the battery (mm), H is the height of the battery (mm), dEC is the amount of ethylene carbonate remaining in the lithium secondary battery after activation (g), and AA is the area of ​​the negative electrode (cm). 2 ), LA is the loading amount of the cathode (g / cm 2 ), RA is the ratio of the negative active material, BA is the BET (g / m) of the negative active material. 2 )am. In addition, in one embodiment of the present invention, the value of the above formula 1 can satisfy 5.00 to 10.00, specifically, the value of the above formula 1 can satisfy 5.00 to 8.00, and more specifically, the value of the above formula 1 can satisfy 5.00 to 6.00. When the above lithium secondary battery satisfies the above formula 1-1, it can exhibit even better battery performance and thermal safety, and when it satisfies the above formula 1-2, it can exhibit even better battery performance and thermal safety. In one embodiment of the present invention, R is a diameter (mm) of the battery, which may be the diameter of a lithium secondary battery or the diameter of a cylindrical battery case. R may be 45 to 47, specifically, R may be 45.5 to 46.5, and more specifically, R may be 46. In addition, in one embodiment of the present invention, H is the height (mm) of the battery, which may be the height (length) of the lithium secondary battery or the height (length) of the cylindrical battery case. H may be 78 to 130, and specifically, H may be 79.0 to 126.0, 79.0 to 121.0, 79.0 to 82.0, 94.0 to 96.0, 119.0 to 121.0, or 124.0 to 126.0, and more specifically, H may be 79.5 to 80.5, 94.5 to 95.5, 119.5 to 120.5, or 124.5 to 125.5. The above R (diameter of the battery) and H (height of the battery) may be the diameter and height measured from the outer surface of the lithium secondary battery or the cylindrical battery case. In addition, in one embodiment of the present invention, R (diameter of battery) and H (height of battery) may specifically represent the diameter and height of a cylindrical lithium secondary battery, and more specifically, may represent the diameter and height of a 4680 lithium secondary battery, a 4695 lithium secondary battery, a 46120 lithium secondary battery, or a 46125 lithium secondary battery. In one embodiment of the present invention, the dEC represents the amount (g) of residual ethylene carbonate, which represents the amount of ethylene carbonate contained in the lithium secondary battery. In addition, it may mean the weight (g) of ethylene carbonate remaining in the electrolyte injected into the lithium secondary battery after activation of the lithium secondary battery. In one embodiment of the present invention, the lithium secondary battery satisfies the above formula 1, and the dEC may be 2.0 to 10.0, specifically 2.4 to 7.5, and more specifically 4.95 to 5.83. In one embodiment of the present invention, the AA is the area of ​​the cathode (cm 2 ) and may be the total area of ​​one side of the negative electrode included in the lithium secondary battery. In one embodiment of the present invention, the lithium secondary battery satisfies the above formula 1, and the AA may be 2,800 to 2,900, and specifically 2,820. It can be between 2,880 and 2,841.3, more specifically between 2,855.3 and 2,880. In one embodiment of the present invention, the LA is a negative electrode loading amount (g / cm 2 ) is the available capacity of the cathode per unit area. In one embodiment of the present invention, the lithium secondary battery satisfies the above formula 1, and the LA may be 0.1000 to 0.2000, specifically 0.1400. It can be 0.1600, more specifically 0.1468 It could be 0.1512. In one embodiment of the present invention, the RA represents the weight ratio of the negative electrode active material to the total weight of the negative electrode active material layer. In one embodiment of the present invention, the lithium secondary battery satisfies the above formula 1, and the RA may be 0.80 to 0.99, specifically 0.82 to 0.99, and more specifically 0.84 to 0.99. In one embodiment of the present invention, the BA has a BET surface area (m) of the negative electrode active material. 2 / g), and the above “BET specific surface area” is measured by the BET method, and specifically, can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan. In one embodiment of the present invention, the lithium secondary battery satisfies the above formula 1, and the BA may be 0.01 to 100, specifically 0.01 to 50, and more specifically 0.5 to 3.0. A lithium secondary battery satisfying the above equation 1 can exhibit excellent thermal stability and thermal safety because an SEI film is sufficiently formed upon initial activation. Meanwhile, in one embodiment of the present invention, the electrolyte may further include an organic solvent other than ethylene carbonate while including ethylene carbonate as a solvent. The above organic solvent may include at least one selected from the group consisting of ester solvents, ether solvents, ketone solvents, aromatic hydrocarbon solvents, carbonate solvents other than ethylene carbonate, alcohol solvents, nitriles, amides, dioxolanes, and sulfolanes. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Examples of solvents that can be used include carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, which may include a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes. More specifically, a carbonate solvent can be used, and a solvent that can constitute a mixture of a cyclic carbonate having high ionic conductivity and high dielectric constant capable of improving the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) can be used. In addition, in one embodiment of the present invention, the electrolyte may additionally include a known electrolyte additive in the non-aqueous electrolyte as needed to prevent the non-aqueous electrolyte from being decomposed in a high-power environment and causing cathode collapse, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and high-temperature battery expansion suppression effects. The above electrolyte additive may be an additive for forming an SEI film, and may be, for example, at least one selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds. When the above electrolyte additive is included, it participates in the formation of the SEI film by decomposing earlier than the ethylene carbonate during the initial activation of the lithium secondary battery, thereby forming a more uniform and sufficient SEI film and improving the thermal stability of the SEI film. The above cyclic carbonate compound may be vinylene carbonate (VC) or vinylethylene carbonate. The above halogen-substituted carbonate compound may be fluoroethylene carbonate (FEC). The above sultone compound may be at least 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 sulfate compound may be ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS). The above phosphate compound may be at least one compound selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyl trimethyl silyl phosphate, trimethyl silyl phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl) phosphite. The above borate compound may be tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), or lithium bisoxalatoborate (LiB(C2O4)2, LiBOB). The above nitrile compound may be at least 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 be tetravinylsilane. The above lithium salt compound is a compound different from the lithium salt included in the non-aqueous electrolyte, and may be lithium difluorophosphate (LiDFP), LiPO2F2, or LiBF4. In one embodiment of the present invention, the electrolyte may include one selected from the group consisting of vinylene carbonate (VC), 1,3-propane sultone (PS), ethylene sulfate (Esa), and lithium difluorophosphate (LiDFP) as an electrolyte additive. The above electrolyte may also contain a lithium salt. The 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 LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable to use the concentration of the lithium salt in the range of 0.1 to 5.0 M, preferably 0.1 to 3.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively. In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxy ethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. In this case, the additives may be contained in an amount of 0.1 to 5 wt% with respect to the total weight of the electrolyte. The above positive electrode includes a positive electrode current collector and a positive electrode active material layer positioned on the positive electrode current collector. In one embodiment of the present invention, the positive electrode active material is a material capable of causing an electrochemical reaction and may be a lithium transition metal oxide. For example, the positive electrode active material may be a layered compound such as lithium cobalt oxide, lithium nickel oxide, etc. substituted with one or more transition metals; lithium manganese oxide substituted with one or more transition metals; Li a [Ni b Co c Mn d M 1 1-(b+c+d) ]O2(M 1 is at least one element selected from the group consisting of Na, K, Mg, Al, Fe, Cr, Y, Sn, Ti, B, P, Zr, Ru, Nb, W, Ba, Sr, La, Ga, Mg, Gd, Sm, Ca, Ce, F, Ta, Mo, Sc, V, Zn, Nb, Cu, In, S, B and Bi, and 0.9≤a≤1.1, 0.6≤b<1, 0 <c<0.4, 0<d<0.4, 0.6<b+c+d≤1이다)로 표현되는 리튬 니켈 코발트 망간 복합 산화물; Li[Ni 1-y M 2 y ]O2(where, M 2 Lithium nickel-based oxide expressed as Li is at least one selected from Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn, and Ga, and 0.01≤y≤0.7; 1+x [M 3 1-q M 4 q ]PO 4-r X r (Here, M 3 is at least one selected from the group consisting of Fe, Mn, Co, and Ni, and M 4wherein X is at least one selected from the group consisting of Al, Mg, and Ti, and may include at least one selected from the group consisting of olivine-based lithium metal phosphates represented by (-0.5≤x≤0.5, 0≤q≤0.5, 0≤r≤0.1). In addition, the positive electrode may include a lithium nickel cobalt manganese composite oxide as a positive electrode active material, and specifically, the positive electrode active material may include a lithium transition metal oxide containing Ni at 60 mol% or more among all metals excluding lithium. In addition, in one embodiment of the present invention, the positive electrode may include a lithium transition metal oxide having a composition represented by the following chemical formula 1 as a positive electrode active material. [Chemical Formula 1] Li a [Ni b Co c Mn d M 1 1-(b+c+d) ]O2 M 1 is at least one element selected from the group consisting of Na, K, Mg, Al, Fe, Cr, Y, Sn, Ti, B, P, Zr, Ru, Nb, W, Ba, Sr, La, Ga, Mg, Gd, Sm, Ca, Ce, F, Ta, Mo, Sc, V, Zn, Nb, Cu, In, S, B and Bi, and 0.9≤a≤1.1, 0.6≤b<1, 0 <c<0.4, 0<d<0.4, 0.6<b+c+d≤1이다. Also, in the chemical formula 1, 0.9≤a≤1.1, 0.8≤b<1, 0 <c<0.2, 0<d<0.2, 0.8<b+c+d≤1일 수 있다. The above-described positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it is easily adhered to a positive electrode active material layer but does not react in the voltage range of the battery. The positive electrode current collector may be, for example, made of stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. In addition, the positive electrode current collector may typically have a thickness of 3 ㎛ to 500 ㎛, and fine unevenness may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, the 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, and a non-woven fabric. The above positive electrode can be manufactured by a conventional method known in the art. For example, a slurry is manufactured by mixing and stirring a positive electrode active material with a solvent, a binder, a conductive agent, and a dispersant as needed, and then the slurry is applied (coated) to a current collector made of a metal material, compressed, and then dried to manufacture the positive electrode. At this time, the positive electrode active material may be included in an amount of 80 wt% to 99 wt%, more specifically 90 wt% to 98 wt%, based on the total weight of the positive electrode active material layer. The conductive material is used to provide conductivity to the electrode, and can be used without special restrictions as long as it does not cause a chemical change in the battery to be formed and has electronic conductivity. Specific examples thereof include graphite such as natural graphite or artificial graphite; carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and other carbon-based materials; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.01 wt% to 10 wt%, specifically, 0.1 wt% to 9 wt%, and more specifically, 0.1 wt% to 5 wt%, based on the total weight of the positive electrode active material layer. The above binder serves to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylalcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and polymers in which hydrogens of these are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The above binder may be included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%, based on the total weight of the positive electrode active material layer. The solvent may be a solvent generally used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water. One of these may be used alone or a mixture of two or more may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity during subsequent coating for manufacturing the positive electrode. Alternatively, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, and then peeling the resulting film from the support and laminating it onto a positive electrode current collector. The above negative electrode includes 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, heat-treated carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and, like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can 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 active material layer optionally includes a binder and a conductive material together with the negative electrode active material. As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, and Al alloy; metallic oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these can be used. In addition, a metallic lithium thin film can be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon can be used as the carbon material. Representative examples of low-crystallization carbon include soft carbon and hard carbon, and representative examples of high-crystallization carbon include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase pitches, mesophase pitches, and high-temperature heat-treated carbon such as petroleum or coal tar pitch derived cokes. The negative electrode active material may be included in an amount of 80 wt% to 99 wt%, 82 wt% to 99 wt%, or 84 wt% to 99 wt% based on the total weight of the negative electrode active material layer. The above binder is a component that assists in bonding between the conductive agent, the active material, and the current collector, and is typically added in an amount of 0.1 to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, various copolymers thereof, and the like. The conductive agent is a component for further improving the conductivity of the negative electrode active material, and may be included in an amount of 1 wt% to 30 wt%, 1 wt% to 20 wt%, or 1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used. The above negative electrode active material layer can be manufactured by applying and drying a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent, on a negative electrode current collector, or by casting the negative electrode slurry composition on a separate support and then laminating the obtained film by peeling it off from the support on a negative electrode current collector. Accordingly, according to another embodiment of the present invention, a battery module including a plurality of the lithium secondary batteries and a battery pack including a plurality of the battery modules are provided. The above battery module refers to a battery assembly (assembly) in which a certain number of lithium secondary batteries are bundled and placed in a frame to protect them from external shock, heat, vibration, etc. The above battery pack refers to the final form of a battery system installed in electric vehicles, etc. The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, including power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems. A battery module and battery pack including a lithium secondary battery according to the present invention have excellent resistance to external heat, and maximize safety by thermal propagation in the event of an actual fire, thereby enabling high capacity and large area batteries to be realized. In addition, the present invention provides a method for evaluating the thermal safety of a cylindrical lithium secondary battery. The method for evaluating the thermal safety of a cylindrical lithium secondary battery of the present invention comprises the steps of (s1) measuring the diameter and height of the lithium secondary battery; (s2) measuring the amount of ethylene carbonate (EC) remaining in the lithium secondary battery; (s3) measuring the reaction area of ​​the negative electrode active material layer of the negative electrode included in the lithium secondary battery; and (s4) determining that the battery has thermal safety if the following equation 1 is satisfied. [Formula 1] In the above equation 1, R is the diameter of the battery (mm), H is the height of the battery (mm), dEC is the amount of ethylene carbonate remaining in the lithium secondary battery after activation (g), and AA is the area of ​​the negative electrode (cm). 2 ), LA is the loading amount of the cathode (g / cm 2 ), RA is the ratio of the negative active material, BA is the BET (g / m) of the negative active material. 2 ), and the reaction area of ​​the negative active material layer is calculated as AA × LA × RA × BA, where R is 45 to 47 and H is 78 to 130. In one embodiment of the present invention, the method for evaluating the thermal safety of the cylindrical lithium secondary battery can be applied to a cylindrical lithium secondary battery of a certain standard. The diameter of the cylindrical lithium secondary battery can be 45 mm to 47 mm, specifically, the diameter can be 45.5 mm to 46.5 mm, and more specifically, the diameter can be 46 mm. In addition, the height of the cylindrical lithium secondary battery may be 78 mm to 130 mm, and specifically, the height may be 79.0 mm to 126.0 mm, 79.0 mm to 121.0 mm, 79.0 mm to 82.0 mm, 94.0 mm to 96.0 mm, 119.0 mm to 121.0 mm, or 124.0 mm to 126.0 mm, and more specifically, may be 79.5 mm to 80.5 mm, 94.5 mm to 95.5 mm, 119.5 mm to 120.5 mm, or 124.5 mm to 125.5 mm. Specifically, the thermal safety evaluation method of the above cylindrical lithium secondary battery can be applied to a 4680 lithium secondary battery, a 695 lithium secondary battery, a 46120 lithium secondary battery, or a 46125 lithium secondary battery. By using the above method for evaluating the thermal safety of a cylindrical lithium secondary battery, it is possible to determine whether the cylindrical lithium secondary battery to be evaluated satisfies Equations 1 and 2, thereby determining whether the cylindrical lithium secondary battery to be evaluated has an appropriate level of thermal safety. In addition to the electrolyte components, the electrolyte may further contain additives for the purposes of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. As the additives, for example, one or more additives may be further contained, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxy ethanol, or aluminum trichloride. In this case, the additives may be contained in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the total weight of the electrolyte. Hereinafter, the present invention will be described in more detail through specific examples. Hereinafter, preferred embodiments are presented to help understand the present invention, but the above embodiments are only illustrative of the present disclosure, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims. Example 1 Surface area 2.1 m 2 / g of natural graphite with a surface area of ​​0.7 m 2The negative electrode slurry was prepared by mixing the negative electrode active material, conductive agent, additive, and binder in a weight ratio of 97.0:1.0:1.0:1.0 in NMP solvent, and applying it to one surface of a copper current collector, drying, and rolling to prepare a negative electrode. The negative electrode had an area of ​​2855.3 cm 2 , the loading of the cathode is 0.01468 g / cm 2 This was done to make it happen. A cathode slurry was prepared by mixing the cathode active material (NCM65 1520), conductive agent (Li-435), and PVDF binder (KF9700, AD-c01) in a weight ratio of 96.5:1.5:2.0 in N-methylpyrrolidone. After applying the positive electrode slurry to one surface of the above-mentioned manufactured electrode collector, it was dried at 140°C and then rolled to manufacture a positive electrode. An electrode assembly was manufactured by interposing a separator between the positive and negative electrodes manufactured by the above-described method, and then the assembly was placed inside a 4680 cylindrical battery case (diameter 46 mm, height 80 mm), and an electrolyte was injected into the case to manufacture a battery cell. The electrolyte was manufactured by dissolving 0.7 M LiPF6 in a mixed organic solvent of ethylene carbonate (EC): propylene carbonate (PC): ethyl methyl carbonate (EMC) = 2:1:7 by volume. The above battery cell was charged at a constant current (CC) of 0.2 C at 24°C to an SOC of 60%, and then stored at 60°C for one day. Thereafter, the battery cell was charged at a constant current (CC) of 0.2 C at 24°C to 4.2 V, and then charged at a constant voltage (CV) of 4.2 V for the first time until the charge current became 0.05 C (cut-off current). After leaving it for 20 minutes, it was discharged at a constant current of 0.2 C for the first time to complete the activation process, thereby completing a 4680 lithium secondary battery. Examples 2 to 4 A battery cell was manufactured in the same manner as in Example 1, except that the amount of electrolyte injected was gradually increased in Examples 2, 3, and 4, and the activation process was completed to complete a 4680 lithium secondary battery. Example 5 The area of ​​the cathode is 2841.3 cm 2 , the loading of the cathode was 0.01512 g / cm 2 A battery cell was manufactured in the same manner as in Example 1, except that the amount of electrolyte injected was the same as in Example 4, and the activation process was completed to complete a 4680 lithium secondary battery. Example 6 The area of ​​the cathode is 6102.8275 cm 2 , the loading of the cathode was 0.00644 g / cm 2 An electrode assembly was manufactured in the same manner as in Example 1, except that it was manufactured in this manner. The manufactured electrode assembly was placed inside a 4695 cylindrical battery case (diameter 46 mm, height 95 mm), and an electrolyte was injected to complete the activation process, thereby completing a 4695 lithium secondary battery. Example 7 The area of ​​the cathode is 5557.5 cm 2 , the loading of the cathode was 0.00644 g / cm 2 An electrode assembly was manufactured in the same manner as in Example 1, except that it was manufactured in this manner. The manufactured electrode assembly was placed inside a 4695 cylindrical battery case (diameter 46 mm, height 95 mm), and an electrolyte was injected to complete the activation process, thereby completing a 4695 lithium secondary battery. Comparative examples 1 and 2 A battery cell was manufactured and the activation process was completed in the same manner as in Example 1, except that the amount of electrolyte injected was reduced compared to Example 1, thereby completing a 4680 lithium secondary battery. The amount of electrolyte reduced in Comparative Example 1 was increased compared to Comparative Example 2. Comparative Example 3 The area of ​​the cathode is 2841.3 cm 2 , the loading of the cathode was 0.01512 g / cm 2 Except for this, a battery cell was manufactured in the same manner as in Example 1, and the activation process was completed to complete a 4680 lithium secondary battery. Reference Example 1 The area of ​​the cathode is 58.6148 cm 2 , the loading of the cathode was 0.0132 g / cm 2 The activation process was completed in the same manner as in Example 1, except that the electrode assembly was positioned inside a 2170 battery case (diameter 21 mm, height 70 mm) and an electrolyte was injected into the case to manufacture a battery cell, thereby completing a 2170 lithium secondary battery. Reference example 2 A 2170 lithium secondary battery was completed in the same manner as in Reference Example 1, except that the amount of electrolyte injected was reduced compared to Reference Example 1. Experimental example (1) Measurement of the amount of residual ethylene carbonate A portion of the battery case of each of the 4680 lithium secondary batteries, 4695 lithium secondary batteries, or 2170 lithium secondary batteries manufactured in Examples 1 to 7, Comparative Examples 1 to 3, and Reference Examples 1 and 2 was cut open to collect the electrolyte contained within the lithium secondary battery case. The content of residual ethylene carbonate in the electrolyte was measured using Varian's 500MHz 1H, 470MHz 19F NMR as described in the literature (KR 10-2362162 B1). 1 H and 19 Measurements were made using F as the measuring nuclide. (2) Calculation of the value of Equation 1 For each of the 4680 lithium secondary battery, 4695 lithium secondary battery, or 2170 lithium secondary battery manufactured in Examples 1 to 7, Comparative Examples 1 to 3, and Reference Examples 1 and 2, the satisfaction of the following Equation 1 value was calculated. [Formula 1] In the above equation 1, R is the diameter of the battery (mm), H is the height of the battery (mm), dEC is the amount of ethylene carbonate remaining in the lithium secondary battery after activation (g), and AA is the area of ​​the negative electrode (cm). 2 ), LA is the loading amount of the cathode (g / cm 2 ), RA is the ratio of the negative active material, BA is the BET (g / m) of the negative active material. 2 )am. (3) High temperature safety evaluation Each of the 4680 lithium secondary batteries, 4695 lithium secondary batteries, or 2170 lithium secondary batteries manufactured in Examples 1 to 7, Comparative Examples 1 to 3, and Reference Examples 1 and 2, respectively, was charged at 24°C with a constant current (CC) of 0.2 C until the battery reached 4.2 V, and then charged at a constant voltage (CV) of 4.2 V until the charge current became 0.05 C (cut-off current). Each of the 4680 lithium secondary batteries, 4695 lithium secondary batteries, and 2170 lithium secondary batteries manufactured in Examples 1 to 7, Comparative Examples 1 to 3, and Reference Examples 1 and 2, respectively, was placed in a hot box at room temperature (25°C), and the temperature was increased at a heating rate of 5°C / min. When the temperature of the hot box reached 130°C, the temperature of the hot box was maintained at 130°C. The temperature of 130°C was maintained for 30 minutes, and thereafter, heating to maintain the temperature of the hot box was stopped. After maintaining a temperature of 130℃ for 30 minutes, if ignition occurred in the lithium secondary battery, it was evaluated as fail, and if no ignition occurred, it was evaluated as pass. R(mm)h(mm)dEC(g)AA(cm2 )LA(g / cm 2 )RABA (m 2 / g) Artificial graphite Natural graphite Artificial graphite Natural graphite Example 146804.95 2855.30.01 4680.4850.4850.72.1 Example 246805.30 2855.30.01 4680.4850.4850.72.1 Example 346805.52 2855.30.01 4680.4850.4850.72.1 Example 446805.83 2855.30.01 4680.4850.4850.72.1 Example 546805.83 2841.30.015120.4850.4850.72.1 Example 646956.116102.830.006440.4850.4850.72.1Example 746955.825557.50.006440.4850.4850.72.1Comparative Example 146804.642855.30.014680.4850.4850.72.1Comparative Example 246804.782855.30.014680.4850.4850.72.1Comparative Example 346804.952841.30.015120.4850.4850.72.1Reference Example 121701.29758.6150.013200.4850.4850.72.1Reference Example 221701.15858.6150.013200.4850.4850.72.1 R / hdEC(g)Reaction area(m) 2) Value of Equation 1 (≥5.00) Hot Box Results Artificial Graphite Natural Graphite Union System Example 10.5754.95 14.2304242.69 12556.92 1665.00 Pass Example 20.5755.30 14.2304242.69 12556.92 1665.35 Pass Example 30.5755.52 14.2304242.69 12556.92 1665.58 Pass Example 40.5755.83 14.2304242.69 12556.92 1665.89 Pass Example 50.5755.8314.5850743.7552258.340305.75PassExample 60.4846.1113.3431040.0293053.372405.54PassExample 70.4845.8212.1508136.4524248.603235.80PassComparative Example 10.5754.6414.2304242.6912556.921664.69FailComparative Example 20.5754.7814.2304242.6912556.921664.83FailComparative Example 30.5754.9514.5850743.7552258.340304.88FailReference Example 10.31.300.2626760.7880291.05070537.03-Reference Example 20.31.160.2626760.7880291.05070533.06- First, referring to Reference Examples 1 and 2 in Tables 1 and 2 above, it can be seen that these are for 2170 lithium secondary batteries and that the values ​​of Equation 1 are very large, at 37.03 and 33.06, respectively. In the case of the 2170 lithium secondary battery, Equation 1 can be satisfied even when the dEC value has a very small value, so it can be confirmed that Equation 1 can be appropriately applied to lithium secondary batteries having certain specifications. Referring to Tables 1 and 2 above, Examples 1 to 7 satisfy the value of Equation 1 and are evaluated as pass in the hot box test, confirming that the safety is excellent when high temperature is applied from outside the battery. On the other hand, Comparative Examples 1 to 3 do not satisfy the value of Equation 1 and are evaluated as fail in the hot box test, confirming that the safety is inferior when high temperature is applied from outside the battery. Comparative Examples 1 and 2 had a smaller amount of electrolyte injected than Examples 1 to 4, and thus the dEC value, which is the amount (g) of ethylene carbonate remaining in the lithium secondary battery after activation, also showed a smaller value due to the smaller amount of electrolyte injected. As a result, Comparative Examples 1 and 2 showed a relatively small value in the amount of ethylene carbonate remaining in the lithium secondary battery after activation compared to the reaction area of ​​the negative electrode active material layer calculated by AA × LA × RA × BA, and could not satisfy Equation 1. It was confirmed that Comparative Examples 1 and 2, which did not satisfy Equation 1 in this way, had inferior high-temperature safety. Comparative Example 3 is an example in which, compared to Example 1, the loading amount of the negative electrode is relatively large, so that the area of ​​the negative electrode is relatively small, but the reaction area of ​​the negative electrode active material layer calculated as AA × LA × RA × BA is larger. Comparative Example 3 and Example 1 were injected with the same amount of electrolyte, and the dEC value, which is the amount (g) of ethylene carbonate remaining in the lithium secondary battery after activation, was the same. However, unlike Example 1 which satisfies Equation 1, Comparative Example 3 did not satisfy Equation 1 because the reaction area of ​​the negative electrode active material layer was relatively large. Referring to Table 2, Example 1 which satisfies Equation 1 was evaluated as Pass in the hot box test, but Comparative Example 1 which does not satisfy Equation 1 was evaluated as Fail in the hot box test. That is, although Example 1 and Comparative Example 3 are 4680 lithium secondary batteries of the same specifications and contain the same amount of residual ethylene carbonate in the lithium secondary battery, it can be confirmed that the relative ratio between the residual ethylene carbonate and the reaction area of ​​the negative electrode active material layer is different due to the difference in the reaction area of ​​the negative electrode active material layer, resulting in a difference in high-temperature safety.

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 including ethylene carbonate as a solvent; and a cylindrical battery case accommodating the electrode assembly and the electrolyte, and satisfying the following formula 1: [Formula 1] In the above equation 1, R is the diameter of the battery (mm), H is the height of the battery (mm), dEC is the amount of ethylene carbonate remaining in the lithium secondary battery after activation (g), and AA is the area of ​​the negative electrode (cm). 2 ), LA is the loading amount of the cathode (g / cm 2 ), RA is the ratio of the negative active material, BA is the BET (g / m) of the negative active material. 2 ) and The above R is 45 to 47 and the above H is 78 to 130.

2. In paragraph 1, A lithium secondary battery, wherein the above R and H are the diameter and height of a 4680 lithium secondary battery, a 4695 lithium secondary battery, a 46120 lithium secondary battery or a 46125 lithium secondary battery, respectively.

3. In paragraph 1, A lithium secondary battery having the above dEC of 2.0 to 10.

0.

4. In paragraph 1, The above AA is a lithium secondary battery of 2,800 to 2,900.

5. In paragraph 1, The above LA is a lithium secondary battery having a value of 0.1000 to 0.2000.

6. In paragraph 1, A lithium secondary battery having an RA of 0.80 to 0.

99.

7. In paragraph 1, A lithium secondary battery wherein the above BA is 0.01 to 100.

8. In paragraph 1, The above electrolyte additionally contains an organic solvent other than ethylene carbonate, A lithium secondary battery, wherein the organic solvent comprises at least one selected from the group consisting of ester solvents, ether solvents, ketone solvents, aromatic hydrocarbon solvents, carbonate solvents other than ethylene carbonate, alcohol solvents, nitriles, amides, dioxolanes, and sulfolanes.

9. In paragraph 1, The above electrolyte additionally contains an electrolyte additive, A lithium secondary battery, wherein the electrolyte additive comprises at least one selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

10. In paragraph 1, The above positive electrode contains a positive electrode active material, A lithium secondary battery comprising a lithium transition metal oxide in which the positive electrode active material contains Ni at 60 mol% or more among all metals excluding lithium. 11.(s1) Step of measuring the diameter and height of a lithium secondary battery; (s2) A step of measuring the amount of ethylene carbonate (EC) remaining in a lithium secondary battery; (s3) a step of measuring the reaction area of ​​the negative electrode active material layer of the negative electrode included in the lithium secondary battery; and (s4) A method for evaluating the thermal safety of a cylindrical lithium secondary battery, comprising a step of determining that the battery has thermal safety if the following equation 1 is satisfied: [Formula 1] In the above equation 1, R is the diameter of the battery (mm), H is the height of the battery (mm), dEC is the amount of residual ethylene carbonate (g), and AA is the area of ​​the negative electrode (cm 2 ), LA is the loading amount of the cathode (g / cm 2 ), RA is the ratio of the negative active material, BA is the BET (g / m) of the negative active material. 2 ) and, The reaction area of ​​the above negative active material layer is calculated as AA × LA × RA × BA. The above R is 45 to 47 and the above H is 78 to 130.

12. In paragraph 11, A method for evaluating thermal safety of a lithium secondary battery, wherein the above R and H are the diameter and height of a 4680 lithium secondary battery, a 4695 lithium secondary battery, a 46120 lithium secondary battery or a 46125 lithium secondary battery, respectively.

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