Title of Invention: Secondary Battery Manufacturing Method technical field [One] Cross Citation with Related Applications [2] This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0117069 dated September 23, 2019, and all contents disclosed in the literature of the Korean patent application are incorporated as a part of this specification. [3] technical field [4] The present invention relates to a method for manufacturing a secondary battery. background [5] Recently, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for small, lightweight and relatively high-capacity secondary batteries is rapidly increasing. In particular, a lithium secondary battery has been in the spotlight as a driving power source for a portable device because it is lightweight and has a high energy density. Accordingly, research and development efforts for improving the performance of lithium secondary batteries are being actively conducted. [6] In general, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, and the like. In addition, the positive electrode and the negative electrode may have an active material layer including a positive electrode active material or a negative electrode active material on a current collector. In general, a lithium-containing metal oxide such as LiCoO 2 , LiMn 2 O 4 is used as a positive electrode active material for the positive electrode, and a carbon-based active material or silicon-based active material that does not contain lithium is used as the negative electrode active material for the negative electrode. [7] In particular, silicon-based active materials are attracting attention in that they have a capacity that is about 10 times higher than that of carbon-based active materials, and due to their high capacity, a high energy density can be realized even with a thin electrode. However, the silicon-based active material is not widely used due to the problems of volume expansion due to charging and discharging, cracking/damage of the active material particles due to this, and deterioration of life-span properties by this. [8] Meanwhile, the secondary battery is manufactured through a process of assembling the secondary battery and a process of activating the secondary battery. In this case, the activation may be performed by injecting an electrolyte into the assembled secondary battery and impregnating it, and charging and discharging the impregnated secondary battery through a charging and discharging device. [9] Through the activation, lithium is inserted into the negative electrode included in the secondary battery, and the electrolyte and lithium salt react on the surface of the negative electrode to generate compounds such as Li 2 CO 3 , Li 2 O, and LiOH. These compounds form a kind of passivation layer on the surface of the anode, and the passivation layer is called a solid electrolyte interface layer (hereinafter referred to as a SEI layer). After the SEI layer is formed, it acts as an ion tunnel to allow lithium ions to pass through, the lithium ions do not react with the negative electrode or other materials again, and the amount of charge consumed in the SEI layer is irreversible and does not react reversibly when discharging. has no characteristics. Therefore, through the formation of the SEI layer, no further decomposition of the electrolyte occurs and the amount of lithium ions in the electrolyte is reversibly maintained, so that stable charging and discharging can be maintained. [10] In this regard, when the activation process is performed on the negative electrode to which the silicon-based active material is applied, as described above, since the silicon-based active material has a large degree of volume expansion/contraction due to charging and discharging, the active material is broken or the contact between the active materials is reduced. A new cathode surface can be continuously created. Accordingly, the SEI layer formation reaction continuously occurs on the surface of the new anode. Excessive SEI layer formation may increase the gas generated during the SEI layer formation reaction, and increase the local resistance of the negative electrode due to this gas generation, lithium There is a problem in that the lifespan characteristics of the battery are deteriorated due to precipitation. [11] Therefore, there is a need to develop a silicon-based active material-applied negative electrode and a secondary battery that realizes the high capacity and energy density of the silicon-based active material while improving the stable formation of the SEI layer, charging and discharging performance, and lifespan characteristics. [12] Korean Patent Laid-Open No. 10-2017-0074030 relates to a negative active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same, and discloses a negative active material including a porous silicon-carbon composite. There is a limit to solving it. [13] [Prior art literature] [14] [Patent Literature] [15] Korean Patent Publication No. 10-2017-0074030 DETAILED DESCRIPTION OF THE INVENTION technical challenge [16] One object of the present invention is to provide a method for manufacturing a secondary battery exhibiting improved lifespan characteristics. means of solving the problem [17] The present invention comprises the steps of: forming an electrode assembly including a negative electrode including a silicon-based active material, a positive electrode facing the negative electrode, and a separator interposed between the negative electrode and the positive electrode; impregnating the electrode assembly by injecting an electrolyte into the electrode assembly; activating the impregnated electrode assembly by first charging and discharging it in at least one cycle while pressing; placing the activated electrode assembly at 40° C. to 80° C. in a state in which the SOC is charged to 70% or more; removing the gas generated from the electrode assembly after the mounting; and at least one cycle of charging and discharging the electrode assembly at 15° C. to 30° C. in a second cycle after removing the gas generated from the electrode assembly. Effects of the Invention [18] According to the method for manufacturing a secondary battery of the present invention, a SEI layer having stable and excellent strength is formed on the negative electrode by performing a process of placing the electrode assembly at a high temperature after charging and discharging for activation of an electrode assembly containing a silicon-based active material. Therefore, it is possible to manufacture a secondary battery with improved lifespan performance. [19] In addition, in the method of manufacturing a secondary battery of the present invention, after charging and discharging for activation of an electrode assembly including a silicon-based active material is performed, a process of mounting the electrode assembly at a high temperature is performed, so that a side reaction caused by residual moisture is accelerated and a lot of gas is generated and then the gas is removed by a degassing process. Since the gas generated by the negative electrode side reaction can be maximally removed through the high temperature setting, the gas generation can be suppressed when the product is subsequently applied to the secondary battery, which is preferable for improving the lifespan performance. Brief description of the drawing [20] 1 is a graph evaluating the capacity retention rate of secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 9; Modes for carrying out the invention [21] The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention. [22] The terminology used herein is used to describe exemplary embodiments only, and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. [23] In the present specification, terms such as "comprise", "comprising" or "have" are intended to designate the presence of an embodied feature, number, step, element, or a combination thereof, but one or more other features or It should be understood that it does not preclude the possibility of the presence or addition of numbers, steps, elements, or combinations thereof. [24] In the present specification, the average particle diameter (D 50 ) may be defined as a particle diameter corresponding to 50% of the cumulative volume in the particle size distribution curve of the particles. The average particle diameter (D 50 ) may be measured using, for example, a laser diffraction method. In general, the laser diffraction method can measure a particle diameter of several mm from a submicron region, and can obtain results of high reproducibility and high resolution. [25] Hereinafter, the present invention will be specifically described. [26] [27] [28] The present invention relates to a method for manufacturing a secondary battery, specifically, to a method for manufacturing a lithium secondary battery. [29] Specifically, the method of manufacturing a secondary battery of the present invention comprises: forming an electrode assembly including a negative electrode including a silicon-based active material, a positive electrode facing the negative electrode, and a separator interposed between the negative electrode and the positive electrode; impregnating the electrode assembly by injecting an electrolyte into the electrode assembly; activating the impregnated electrode assembly by first charging and discharging it in at least one cycle while pressing; placing the activated electrode assembly at 40° C. to 80° C. in a state in which the SOC is charged to 70% or more; removing the gas generated from the electrode assembly after the mounting; and charging and discharging the electrode assembly in at least one cycle at 15° C. to 30° C. in a second cycle after removing the gas generated from the electrode assembly. [30] The method for manufacturing a secondary battery of the present invention forms an SEI layer having stable and excellent strength on the surface of the anode by performing a process of placing the electrode assembly at a high temperature after charging and discharging for activation of an electrode assembly including a silicon-based active material. This makes it possible to manufacture a secondary battery with improved lifespan performance. [31] In addition, in the method of manufacturing a secondary battery of the present invention, after charging and discharging for activation of an electrode assembly including a silicon-based active material is performed, a process of mounting the electrode assembly at a high temperature is performed, so that a side reaction caused by residual moisture is accelerated and a lot of gas is generated and then the gas is removed by a degassing process. Since the gas generated by the negative electrode side reaction can be maximally removed through the high temperature setting, the gas generation can be suppressed when the product is subsequently applied to the secondary battery, which is preferable for improving the lifespan performance. [32] [33] [34] The method of manufacturing a secondary battery of the present invention includes forming an electrode assembly including a negative electrode including a silicon-based active material, a positive electrode facing the negative electrode, and a separator interposed between the negative electrode and the positive electrode. [35] The negative electrode includes a silicon-based active material. Silicon-based active materials have a higher capacity than carbon-based active materials, but due to volume expansion/contraction during charging and discharging, cracking of the active material, and deterioration of contact, excessive generation of SEI layer and gas generation due to side reactions are a problem, which may lead to a decrease in the lifespan of However, since the present invention enables the formation of a stable SEI layer by processes such as activation and posturing at high temperatures, which will be described later, it is possible to realize the capacity characteristics of a silicon-based active material and to manufacture a secondary battery having excellent lifespan performance. . [36] The negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, and the negative electrode active material layer may include the silicon-based active material. [37] The anode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. Specifically, as the negative electrode current collector, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, a surface treatment of copper or stainless steel with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. may be used. can [38] The thickness of the negative electrode current collector may be 3 to 500 μm, preferably 5 to 50 μm, preferably 7 to 20 μm for the thin film implementation of a silicon-based active material-containing negative electrode. [39] The negative electrode current collector may form fine concavities and convexities on the surface to strengthen the bonding strength of the negative electrode active material. For example, the negative electrode current collector may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body, and the like. [40] The silicon-based active material may include a compound represented by SiO x (0≤x<2). In the case of SiO 2 , since lithium cannot be stored because it does not react with lithium ions, x is preferably within the above range. [41] Specifically, the silicon-based active material may be Si. Conventionally, Si is advantageous in that its capacity is about 2.5 to 3 times higher than that of silicon oxide (for example, SiO x (0 [88] The present invention includes the step of impregnating the electrode assembly by injecting an electrolyte into the electrode assembly. As the electrode assembly is immersed in the electrolyte, the electrode assembly may be activated by charging and discharging to be described later. [89] The electrolyte may include an organic solvent and a lithium salt. [90] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, gamma-butyrolactone, ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC); 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; Or sulfolane may be used. Among these, carbonate-based solvents are preferable, and cyclic carbonates (eg, ethylene carbonate, propylene carbonate, fluoroethylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve battery charging and discharging performance, and low viscosity A mixture of a linear carbonate-based compound (eg, ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:9 to about 5:5, the performance of the electrolyte may be excellent. [91] The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAlO 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(C 2 F 5 SO 3 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , LiCl, LiI, or LiB(C 2 O 4 ) 2 , etc. may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, the electrolyte may exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions may move effectively. [92] The electrolyte may further include an additive for forming a stable and flexible SEI layer on a negative electrode using a silicon-based active material. Specifically, the additive is at least one selected from the group consisting of vinylene carbonate (VC), polystyrene (PS), succinonitrile, ethylene glycol bis(propionnitrile) ether, and lithium bis(fluorosulfonyl)imide, preferably For example, in terms of being able to easily and stably form an SEI layer through ring opening polymerization, an additive including vinylene carbonate may be further included. [93] The additive may be included in an amount of 0.1 wt% to 15 wt%, preferably 0.5 wt% to 5 wt% in the electrolyte. [94] The step of impregnating the electrode assembly is 12 hours to 48 hours, more preferably in terms of sufficiently wetting the electrode assembly with the electrolyte solution and enabling the activation according to charging and discharging of the electrode assembly to be performed more smoothly may be performed for 18 to 30 hours. [95] The step of impregnating the electrode assembly may be performed at 15° C. to 30° C., more specifically at 23° C. to 27° C., and can improve the impregnability of the electrode assembly when it is in the above range, and It is preferable because it is possible to prevent the formation of dendrites in the anode and the occurrence of low voltage accordingly. [96] [97] [98] The present invention includes activating the impregnated electrode assembly by first charging and discharging it in at least one cycle while pressurizing the electrode assembly. [99] The first charge/discharge may be performed using an electrochemical charge/discharger. [100] The charging and discharging (first charging/discharging) for activation of the electrode assembly may be preferably performed in two or more cycles, more preferably in 2 to 8 cycles, and still more preferably in 3 to 5 cycles. In general, in the case of a silicon-based active material, the degree of volume expansion/contraction due to charging and discharging is greater than that of a carbon-based active material, and accordingly, a new negative electrode surface may be created by the structural change of the silicon-based active material. Accordingly, it is preferable to perform charging and discharging in the cycle of the above-described range so that the SEI layer by activation can be sufficiently formed on the surface of the newly formed anode as well. [101] The voltage range in which the charging and discharging are performed may be appropriately set in consideration of the type of the positive electrode or positive electrode active material used to face the negative electrode. Specifically, in the activating step, the charging and discharging may be performed in a voltage range of 2.5V to 4.35V. More specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer may include a positive electrode active material including a lithium-nickel-cobalt-manganese composite oxide. And, in the activating step, the charging and discharging may be performed in a voltage range of 2.5V to 4.2V, preferably 3V to 4.2V. In addition, the cathode active material layer may include a cathode active material including a lithium-cobalt-based oxide, and in the activating step, the charging and discharging may be performed in a voltage range of 3V to 4.35V. [102] The first charging/discharging may be performed at 10°C to 80°C. Preferably, the first charge/discharge is 15° C. to 40° C., more preferably 23° C. to 30° C., in terms of preventing excessive volume expansion/contraction during the first charging/discharging and preventing continuous generation of the SEI layer. can be performed in [103] [104] The first charging/discharging is performed while pressing the impregnated electrode assembly. As lithium is inserted/desorbed from the silicon-based active material by the first charge/discharge, volume expansion/contraction of the anode active material is performed. In addition, when the charging and discharging process is performed while pressurizing the electrode assembly, the voids of the negative electrode or the negative electrode active material layer can be realized at an appropriate level, so that the decrease in voids due to excessive pressure is prevented, and the electrolyte is depleted according to the decrease in the voids. can be eliminated, which is preferable for improving the lifespan characteristics. [105] The pressure in the first charge/discharge may be 1.5 MPa to 3.5 MPa, preferably, the pressurization may be performed at 2 MPa to 3 MPa. When pressurized within the above pressure range, the voids of the negative electrode can be maintained at an appropriate level while sufficiently controlling the volume expansion of the silicon-based active material, and thus the lifespan characteristics of the battery can be further improved. [106] [107] [108] The present invention includes mounting the activated electrode assembly at 40° C. to 80° C. in a state in which the activated electrode assembly is charged to 70% or more of SOC. [109] The method of manufacturing a secondary battery of the present invention includes the step of mounting the electrode assembly activated by the first charge/discharge at a high temperature of 40° C. to 80° C., thereby enabling the formation of a stable and strong SEI layer on the surface of the negative electrode. . In addition, the new negative electrode surface formed by volume expansion/contraction of the silicon-based active material by the first charging and discharging may be stably formed of an SEI layer by the high temperature setting. In addition, when performing the high temperature deferment step, it is preferable to increase the movement of the gas generated at the initial stage of activation to release the gas in the SEI layer to the outside of the SEI layer, thereby increasing the density of the SEI layer. If the high-temperature deferment step is not performed, there is a risk that the gas in the SEI layer may remain, so that the SEI layer may not be firmly and stably formed. [110] In addition, in the method of manufacturing a secondary battery of the present invention, after charging and discharging for activation of an electrode assembly including a silicon-based active material, a process of placing the electrode assembly at a high temperature is performed. may be generated, and then the gas is removed by a degassing process. Since the gas generated by the negative electrode side reaction can be maximally removed through the high temperature setting, the gas generation can be suppressed when the product is subsequently applied to the secondary battery, which is preferable for improving the lifespan performance. [111] The mounting step is performed in a state in which the electrode assembly is charged to 70% or more (70% to 100%) of the SOC. When the electrode assembly is charged in the above range, since the mounting is performed in a state in which the volume of the silicon-based active material is expanded, it is preferable for forming a stable SEI layer in that side reactions that may occur in the active material can be generated in advance. If the electrode assembly is mounted in a state in which the SOC is less than 70%, the volume of the silicon-based active material may not be sufficiently expanded, which is not preferable in terms of insufficient reaction surface area. [112] The fermenting step is performed at 40°C to 80°C. When the deferring step is performed at less than 40° C., it is difficult to stably form the SEI layer, it is not possible to sufficiently generate a gas due to a side reaction in the deferring step, and the gas removal in the SEI layer is not sufficient. When the deferring step is performed at more than 80° C., there is a risk of metal elution by increasing the reactivity of the metal in the negative electrode current collector, and the low voltage occurrence probability of the secondary battery increases as dendrites of the metal are formed, which is undesirable, high During storage at a temperature, the adhesive strength of the binder is lowered, causing detachment of the electrode, increasing resistance by increasing the distance between active materials, and decreasing lifespan performance due to local lithium precipitation. [113] Preferably, the fermenting step may be performed at 50 °C to 70 °C. In the above range, since the viscosity of the electrolyte is reduced, gas generation due to a side reaction may be accelerated, so that the gas may be removed as much as possible in the subsequent degassing process. In addition, when it is within the above range, it is preferable that the gas movement is activated to prevent gas trapping in the SEI layer, and the gas can be easily discharged to the outside. [114] The fermenting step may be performed for 12 hours to 36 hours, preferably 18 hours to 30 hours, and while sufficiently generating gas through high temperature fermenting, elution of metal in the negative electrode current collector, generation of dendrites, etc. are prevented It is desirable that it can be [115] [116] [117] The present invention includes the step of removing the gas generated from the electrode assembly after the step of mounting. [118] In the gas removal step, a gas may be generated as a byproduct of the generation of the SEI layer after activation of the electrode assembly, generation of an irreversible capacity, and the like. Accordingly, a process of removing by-products may be performed for use of the activated secondary battery, and the secondary battery may be manufactured in a usable form through the gas removal process. [119] In particular, the present invention can remove the gas generated by acceleration by the high-temperature deferment step described above by the gas removal step, can suppress the gas generation when applying the product to the secondary battery, and improve the life performance of the battery. can [120] As the step of removing the gas, a method generally used in the field of secondary batteries may be performed without limitation. For example, the removing of the gas may be performed by partially opening the electrode assembly to remove the gas and sealing in a vacuum state. [121] [122] [123] After removing the gas generated from the electrode assembly, the present invention includes charging and discharging the electrode assembly at a temperature of 15° C. to 30° C. in at least one cycle a second time. [124] The second charging/discharging step may be performed to uniformly and robustly form the SEI layer after the first charging/discharging step. Specifically, after the side reaction gas formed in the first charging/discharging step is removed by the gas removing step, the SEI layer may be formed in a local area remaining after the gas is removed through the second charging/discharging step. Accordingly, when the first charging/discharging step and the second charging/discharging step are performed, the SEI layer in the negative electrode may be more uniformly and firmly formed. [125] The second charging/discharging step is performed at 15°C to 30°C, preferably at 23°C to 27°C. When the second charging/discharging step is performed at a temperature of more than 30°C, there is a risk of deterioration of the life performance of the cell because gas by the electrolyte in the second charging/discharging is excessively generated, and it is to be performed at a temperature of less than 15°C. In this case, the viscosity of the electrolyte is increased, the resistance is increased, and there is a risk of lithium precipitation in a local area, which is not preferable. [126] The second charging/discharging step may be performed while pressing the electrode assembly. By performing the second charging and discharging while pressing the electrode assembly, volume expansion of the negative active material can be easily controlled, which is more advantageous in improving lifespan characteristics. The pressurization in the second charging/discharging step may be performed at 1.5 MPa to 3.5 MPa, preferably 2 MPa to 3 MPa, and when it is within the above range, the voids of the negative electrode can be maintained at an appropriate level while sufficiently controlling the volume expansion of the negative electrode active material. it is preferable to have [127] [128] The secondary battery manufactured by the manufacturing method of the secondary battery of the present invention is useful in the field of portable devices such as mobile phones, notebook computers, digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs), particularly medium and large-sized batteries It can be preferably used as a component battery of a module. Accordingly, the present invention also provides a medium and large-sized battery module including the secondary battery as described above as a unit battery. [129] These medium and large-sized battery modules can be preferably applied to power sources that require high output and large capacity, such as electric vehicles, hybrid electric vehicles, and power storage devices. [130] [131] Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein. [132] [133] Example [134] Example 1: Preparation of secondary battery [135] [136] 1. Preparation of anode [137] A mixture of silicon-based active material Si (average particle diameter (D 50 ): 3 μm), carbon black (product name: Super C65, manufacturer: TIMCAL) as an anode conductive material, and polyvinyl alcohol and polyacrylic acid in a weight ratio of 66:34 as an anode binder (weight average molecular weight: about 360,000 g/mol) was added to a solvent (distilled water) for forming the negative electrode slurry and mixed to prepare a negative electrode slurry (the solid content was 25% by weight based on the total weight of the negative electrode slurry). The silicon-based active material, the negative electrode conductive material, and the negative electrode binder were mixed in a weight ratio of 75:10:15. [138] As a negative electrode current collector, the negative electrode slurry was coated on one side of a copper current collector (thickness: 8 μm) in a loading amount of 68.4 mg/25 cm 2 , rolled, and dried in a vacuum oven at 130° C. for 10 hours. A negative electrode active material layer (thickness: 44 μm) was formed, and this was used as a negative electrode (thickness of the negative electrode: 52 μm). [139] 2. Preparation of anode [140] LiNi 0.6 Co 0.2 Mn 0.2 O 2 (average particle diameter (D 50 ): 10 μm) as a cathode active material, carbon black (product name: Super C65, manufacturer: TIMCAL) as a cathode conductive material, and polyvinylidene fluoride (PVdF) as a cathode binder ) was added to N-methylpyrrolidone (NMP) solvent in a weight ratio of 97:1.5:1.5 and mixed to prepare a positive electrode slurry. As a positive electrode current collector, the positive electrode slurry was coated on one side of an aluminum current collector (thickness: 12 μm) in a loading amount of 459.4 mg/25 cm 2 , rolled, and dried in a vacuum oven at 130° C. for 10 hours. A positive electrode active material layer (thickness: 110 μm) was formed, and this was used as a positive electrode (anode thickness: 122 μm). [141] 3. Fabrication of the electrode assembly [142] A separator (thickness: 17.5 μm) having a laminated structure of ethylene polymer (PE)/propylene polymer (PP)/ethylene polymer (PE) between the negative electrode and the positive electrode, wherein the negative electrode and the positive electrode prepared above are disposed to face each other to prepare an electrode assembly, and the electrode assembly was accommodated in a pouch. [143] 4. N/P ratio [144] A negative electrode sample was prepared by cutting the prepared negative electrode to a predetermined size. A lithium metal electrode having the same size as that of the negative electrode sample was prepared, and it was opposed to the negative electrode sample. After interposing a polyethylene separator between the negative electrode sample and the lithium metal electrode, an electrolyte was injected to prepare a coin-type half-cell. As the electrolyte, an organic solvent in which ethylene carbonate and ethylmethyl carbonate were mixed in a volume ratio of 50:50 was used as a lithium salt in which LiPF 6 was added at a concentration of 1M. The discharge capacity obtained by charging/discharging the coin-type half-cell at 0.1 C was divided by the weight of the silicon-based active material contained in the negative electrode sample to obtain the discharge capacity of the negative electrode sample per unit weight of the silicon-based active material. [145] In addition, the positive electrode prepared above was cut to a predetermined size to prepare a positive electrode sample. A lithium metal electrode having the same size as the positive electrode sample was prepared, and it was opposed to the positive electrode sample. After interposing a polyethylene separator between the positive electrode sample and the lithium metal electrode, an electrolyte was injected to prepare a coin-type half-cell. As the electrolyte, an organic solvent in which ethylene carbonate and ethylmethyl carbonate were mixed in a volume ratio of 50:50 was used as a lithium salt in which LiPF 6 was added at a concentration of 1M. The discharge capacity obtained by charging/discharging the coin-type half-cell at 0.1 C was divided by the weight of the positive active material contained in the positive electrode sample to obtain the discharge capacity of the positive electrode sample per unit weight of the positive electrode active material. [146] The discharge capacity of the negative electrode sample per unit weight of the negative electrode active material measured above was multiplied by the weight of the silicon-based active material and divided by the area of ​​the negative electrode to obtain the discharge capacity per unit area of ​​the negative electrode. In addition, the discharge capacity of the positive electrode sample per unit weight of the positive electrode active material was multiplied by the weight of the positive electrode active material and divided by the area of ​​the positive electrode to obtain the discharge capacity per unit area of ​​the positive electrode. [147] The N/P ratio (=2) was obtained by dividing the discharge capacity per unit area of ​​the negative electrode by the discharge capacity per unit area of ​​the positive electrode. [148] [149] [150] An electrolyte solution was injected into the pouch and the electrode assembly was impregnated. [151] The electrolyte is an organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) are mixed in a volume ratio of 30:70, and a vinylene carbonate (VC) additive is added in an amount of 3% by weight based on the total weight of the electrolyte, As a lithium salt, LiPF 6 added at a concentration of 1M was used. [152] The temperature when the electrode assembly was impregnated was 25° C., and the impregnation was performed for 24 hours. [153] [154] [155] The electrode assembly was activated by placing the impregnated electrode assembly prepared above between a pair of pressure plates, and performing a first charge/discharge while pressing at a pressure of 2.5 MPa using a torque wrench. [156] The first charging and discharging was activated by charging and discharging at 25° C. in 3 cycles with an electrochemical charger (manufacturer: PNE Solution). [157] The charging and discharging were performed under the following conditions. [158] Charging conditions: 0.2C, CC/CV (4.2V, 0.05C cut-off) [159] Discharge conditions: 0.2C, CC (3.0V cut-off) [160] [161] [162] The electrode assembly on which the first charging and discharging was completed was placed in a fully charged state at 60° C. for 24 hours. [163] [164] [165] A degassing process was performed on the electrode assembly on which the mounting was completed. [166] [167] [168] The electrode assembly on which the gas removal process has been performed is placed between a pair of pressure plates, and a second charge/discharge cycle of one cycle is performed under charging and discharging conditions at a temperature of 25° C. while pressing with a pressure of 2.5 MPa using a torque wrench. carried out. The electrode assembly on which the second charging and discharging was completed was used as the secondary battery of Example 1. [169] Charging conditions: 0.33C, CC/CV (4.2V, 0.05C cut-off) [170] Discharge conditions: 0.33C, CC (3.0V cut-off) [171] [172] Example 2: Preparation of secondary battery [173] A secondary battery of Example 2 was prepared in the same manner as in Example 1, except that the first activation was performed at 45°C. [174] [175] Example 3: Preparation of secondary battery [176] A secondary battery of Example 3 was manufactured in the same manner as in Example 1, except that the first charge/discharge and the second charge/discharge were performed while pressurizing at a pressure of 1.87 MPa. [177] [178] Example 4: Preparation of secondary battery [179] A secondary battery of Example 4 was manufactured in the same manner as in Example 1, except that the first charge/discharge and the second charge/discharge were performed while pressurizing at a pressure of 3.12 MPa. [180] [181] Example 5: Preparation of secondary battery [182] A secondary battery of Example 5 was manufactured in the same manner as in Example 1, except that only one cycle of the first charge/discharge was performed. [183] [184] Comparative Example 1: Preparation of secondary battery [185] A secondary battery of Comparative Example 1 was prepared in the same manner as in Example 1, except that the deferment step was performed at 25°C. [186] [187] Comparative Example 2: Preparation of secondary battery [188] A secondary battery of Comparative Example 2 was prepared in the same manner as in Example 2, except that the deferment step was performed at 25°C. [189] [190] Comparative Example 3: Preparation of secondary battery [191] A secondary battery of Comparative Example 3 was prepared in the same manner as in Example 1, except that the deferment step was performed at 25°C and the second charge/discharge was performed at 45°C. [192] [193] Comparative Example 4: Preparation of secondary battery [194] A secondary battery of Comparative Example 4 was prepared in the same manner as in Example 2, except that the deferment step was performed at 25°C and the second charge/discharge was performed at 45°C. [195] [196] Comparative Example 5: Preparation of secondary battery [197] A secondary battery of Comparative Example 5 was prepared in the same manner as in Example 1, except that the second charge/discharge was performed at 45°C. [198] [199] Comparative Example 6: Preparation of secondary battery [200] A secondary battery of Comparative Example 6 was prepared in the same manner as in Example 2, except that the second charge/discharge was performed at 45°C. [201] [202] Comparative Example 7: Preparation of secondary battery [203] A secondary battery of Comparative Example 7 was prepared in the same manner as in Example 1, except that the second charge/discharge was performed at 10°C. [204] [205] Comparative Example 8: Preparation of secondary battery [206] A secondary battery of Comparative Example 8 was prepared in the same manner as in Example 1, except that the deferment step was performed at 90°C. [207] [208] Comparative Example 9: Preparation of secondary battery [209] A secondary battery of Comparative Example 9 was manufactured in the same manner as in Example 1, except that a pressurization process was not performed in performing the first charge/discharge and the second charge/discharge. [210] [211] Experimental Example 1: Lifespan characteristic evaluation [212] For the secondary batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 9, capacity retention rates were evaluated using an electrochemical charger/discharger. [213] The secondary battery was charged and discharged up to the 200th cycle under the conditions of charging (0.5C CC/CV charging, 4.2V, 0.05C cut) and discharging (0.5C CC, discharging, 3.0V cut) conditions. [214] The capacity retention rate was evaluated by Equation 2 below. 1 is a graph showing the capacity retention rate according to the cycle. In addition, the capacity retention rates in the 200th cycle of Examples and Comparative Examples are shown in Table 1 below. [215] [Equation 2] [216] Capacity retention rate (%) = {(discharge capacity in Nth cycle)/(discharge capacity in 1st cycle)} × 100 [217] (in Equation 2, N is an integer from 1 to 200) [218] [219] [Table 1] [220] [221] Referring to Table 1, in the case of Examples 1 to 5, it can be seen that the capacity retention rate is at an excellent level, and thus the lifespan characteristics are improved. [222] On the other hand, in Comparative Examples 1 and 2, by performing the deferment step at a low temperature, the gas generation during activation was not sufficient, so the gas was not sufficiently removed during the degassing process, and the stable formation of the SEI layer was difficult, resulting in poor lifespan performance. degradation can be seen. [223] In addition, in Comparative Examples 3, 4, 5, and 6, by performing the second charging and discharging at a rather high temperature, it can be seen that excessive side reactions occur in the negative electrode and the lifespan performance is reduced. [224] In addition, it can be seen that Comparative Example 7 exhibits lower lifespan performance compared to Examples. In the case of Comparative Example 7, by performing the deferment step at a rather low temperature, the gas generation by the reaction with the electrolyte is not sufficient, and the degassing step does not sufficiently remove the gas, so it is considered that the life performance improvement effect cannot be exhibited. . [225] In addition, it can be seen that Comparative Example 8 exhibits lower lifespan performance compared to Examples. In the case of Comparative Example 8, it is thought that the adhesion of the binder is reduced and detachment of the electrode occurs by performing the deferment step at a high temperature, resulting in an increase in local resistance, lithium precipitation, and a decrease in life performance. [226] In addition, in the case of Comparative Example 9, since the pressurization process was not performed during charging and discharging, the volume expansion/contraction of the silicon-based active material could not be smoothly controlled, and thus, it could be confirmed that the life performance was rapidly reduced. Claims [Claim 1] forming an electrode assembly including a negative electrode including a silicon-based active material, a positive electrode facing the negative electrode, and a separator interposed between the negative electrode and the positive electrode; impregnating the electrode assembly by injecting an electrolyte into the electrode assembly; activating the impregnated electrode assembly by first charging and discharging it in at least one cycle while pressing; placing the activated electrode assembly at 40° C. to 80° C. in a state in which the SOC is charged to 70% or more; removing the gas generated from the electrode assembly after the mounting; and second charging and discharging of the electrode assembly at 15°C to 30°C in at least one cycle after removing the gas generated from the electrode assembly. [Claim 2] The method according to claim 1, wherein the step of impregnating the electrode assembly is performed at 15 °C to 30 °C. [Claim 3] The method according to claim 1, wherein the step of impregnating the electrode assembly is performed for 12 to 48 hours. [Claim 4] The method according to claim 1, wherein the first charging/discharging is performed in two or more cycles. [Claim 5] The method according to claim 1, wherein the pressure in the first charge/discharge is performed at 1.5 MPa to 3.5 MPa. [Claim 6] The method according to claim 1, wherein the second charging and discharging is performed while pressing the electrode assembly. [Claim 7] The method according to claim 1, wherein the holding step is performed for 12 to 36 hours. [Claim 8] The method according to claim 1, wherein the silicon-based active material is Si. [Claim 9] The method according to claim 1, wherein the negative electrode comprises a negative electrode current collector, and a negative electrode active material layer formed on the negative electrode current collector, wherein the negative electrode active material layer comprises the silicon-based active material, a binder, and a conductive material. [Claim 10] The method according to claim 9, wherein the silicon-based negative active material is included in the anode active material layer in an amount of 60 wt% to 90 wt%, the binder is included in an amount of 5 wt% to 30 wt% in the anode active material layer, and the conductive material is the negative electrode A method of manufacturing a secondary battery included in the active material layer in an amount of 5 wt% to 20 wt%. [Claim 11] The method according to claim 9, wherein the negative active material layer has a thickness of 35 μm to 50 μm. [Claim 12] The method according to claim 1, wherein the N/P ratio calculated by the following Equation 1 of the electrode assembly is 1.5 to 3.5 of the secondary battery manufacturing method: [Equation 1] N/P ratio = discharge capacity per unit area of ​​the negative electrode / of Discharge capacity per unit area.