Method for manufacturing lithium secondary battery having high capacity and high stability by applying magnetic field

Abstract

The present invention relates to a lithium secondary battery having high capacity and high stability by applying a magnetic field, and a lithium secondary battery capable of maintaining stable battery capacity and being recycled even under fast charging conditions. The method for manufacturing a lithium secondary battery according to the present invention can form a stable SEI film on the surface of an electrode inside a unit battery. Accordingly, the life characteristics of the battery are improved, the output characteristics thereof are improved, the battery capacity can be stably maintained even under fast charging conditions, and the battery resistance is reduced, thereby achieving recycling of the battery.

Description

Technical Field

[0001] The present invention relates to a lithium secondary battery having high capacity and high stability by applying a magnetic field, and a lithium secondary battery which maintains a stable battery capacity even under a fast charging condition and can be recycled. Background Art

[0002] As the IT technology and electric vehicle battery markets grow, the industry's technical research on lithium secondary batteries, which are core components for energy use, is continuing. As lithium secondary batteries have the advantages of high energy density, excellent life characteristics, and low self-discharge, they are being used in various fields as energy sources and are becoming increasingly important as energy storage devices.

[0003] In the manufacturing process of lithium secondary batteries, lithium ions are inserted from the lithium metal oxide of the positive electrode into the negative electrode in the formation process. In this process, the solvent component of the electrolyte for lithium secondary batteries reaches the reduction potential, and organic materials such as Li2CO3, LiO, LiOH are generated as reduction byproducts on the surface of the negative electrode to form a coating. The coating formed on the surface of the negative electrode in this way is called a solid electrolyte interface (SEI, hereinafter referred to as SEI film). The SEI film is a non-conductor that does not have electronic conductivity, and when formed once during the first charge, it prevents the reaction of lithium ions with the negative electrode or other materials on the surface of the negative electrode during repeated charge / discharge, and serves as an ion channel that only allows lithium ions to pass between the electrolyte solution and the negative electrode.

[0004] In addition, the SEI film is a core element that determines battery safety, power capacity, leakage current, shelf life, and life. Since the SEI film stably manufactured in the initial formation process does not cause side reactions with the carbon negative electrode or other materials, it reversibly maintains the amount of inserted / desorbed lithium ions and prevents the structural collapse of the structure of the carbon negative electrode by inserting lithium ions and anions dissolved in an organic solvent together. Therefore, the SEI film, which serves as the entrance of stably formed ions, ensures the reversibility of the charge / discharge reaction of the secondary battery after the formation process and suppresses the further increase of resistance.

[0005] That is, lithium secondary batteries repeatedly shrink and expand with charge / discharge, resulting in the peeling of electrode active materials from the current collector, deterioration of charge / discharge efficiency and cycle characteristics. To prevent this problem, it is necessary to stably form an SEI film.

[0006] Generally, in order to stably form the SEI film, attempts have been made to improve the composition of the electrolyte solution or the negative electrode material, or to improve the manufacturing process of the lithium secondary battery to form a stable SEI film, but the effect is not good. Therefore, it is necessary to develop a recyclable and efficient lithium secondary battery that can maintain a stable battery capacity even under fast charging conditions by forming a stable SEI film on the negative electrode surface of the lithium secondary battery. Summary of the invention

[0007] Technical issues

[0008] An object of the present invention is to provide a method for manufacturing a lithium secondary battery, wherein the lithium secondary battery has improved battery output by designing a formation process.

[0009] Another object of the present invention is to provide a method for manufacturing a lithium secondary battery that can ensure stability even under severe conditions such as rapid charge / discharge.

[0010] Another object of the present invention is to provide a method for manufacturing a lithium secondary battery that can be recycled even when the life retention rate is low due to an increase in battery resistance.

[0011] Technical Solutions

[0012] In one overall scheme, a method for manufacturing a lithium secondary battery includes: (a) an electrode plate process step: manufacturing a positive electrode plate and a negative electrode plate; (b) an assembly process step: assembling by including a separator in the positive electrode plate and the negative electrode plate and injecting an electrolyte solution to manufacture a unit cell; and (c) an activation process step: performing a formation process on the manufactured unit cell, wherein a magnetic field is applied in the formation process of (c).

[0013] In the method for manufacturing a lithium secondary battery according to an exemplary embodiment of the present invention, the applied magnetic field may have an intensity of 0.1 T to 2.0 T and a frequency of 1 Hz to 30 Hz, and the application time of the applied magnetic field may be 1 minute to 60 minutes.

[0014] In the method for manufacturing a lithium secondary battery according to an exemplary embodiment of the present invention, the current applied in (c) may be 0.01C to 1.0C, and the time for which the current is applied in (c) may be 1 hour to 10 hours.

[0015] In another general aspect, a lithium secondary battery manufactured by the manufacturing method is provided.

[0016] In the lithium secondary battery according to the exemplary embodiment of the present invention, the lithium secondary battery may have an initial discharge capacity of 20 mAh / g or more, an initial coulombic efficiency of 85% or more, and a discharge capacity ratio of 18% or more.

[0017] Beneficial Effects

[0018] The manufacturing method of the lithium secondary battery according to the present invention can form a stable SEI film on the electrode surface inside the unit cell, thereby improving the life characteristics of the battery, improving its output characteristics, stably maintaining the battery capacity even under fast charging conditions, and reducing the battery resistance, thereby enabling the battery to be recycled. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 : is a graph showing the discharge capacity of the lithium secondary battery manufactured by the manufacturing method according to Embodiments 1 to 3 in the charge / discharge cycle.

[0020] Figure 2 is a graph showing discharge capacity in charge / discharge cycles of lithium secondary batteries manufactured by the manufacturing methods according to Embodiments 4 to 6.

[0021] Figure 3 : is a graph showing the discharge capacity of the lithium secondary batteries manufactured by the manufacturing methods according to Embodiments 7 to 9 in charge / discharge cycles.

[0022] Figure 4 is a graph showing initial discharge capacity depending on the conditions of a magnetic field applied to a lithium secondary battery manufactured according to the present invention.

[0023] Figure 5 is a graph showing initial coulombic efficiency depending on the conditions of a magnetic field applied to a lithium secondary battery manufactured according to the present invention.

[0024] Figure 6 is a graph showing a discharge capacity ratio depending on the conditions of a magnetic field applied to a lithium secondary battery manufactured according to the present invention.

[0025] Figure 7 is a graph showing the retention rate depending on the conditions of the magnetic field applied to the lithium secondary battery manufactured according to the present invention.

[0026] Figure 8 is a graph showing discharge capacity when a magnetic field is applied during recycling of a lithium secondary battery.

[0027] Best Mode for Carrying Out the Invention

[0028] Hereinafter, a method for manufacturing a lithium secondary battery of the present invention will be described in detail with reference to the accompanying drawings.

[0029] The accompanying drawings provided below are provided by way of example so that the concept of the present invention can be fully conveyed to the technicians in the field to which the present invention belongs. Therefore, the present invention is not limited to the accompanying drawings provided below, but can be implemented in many different forms, and the accompanying drawings proposed below may be exaggerated to clearly illustrate the spirit of the present invention.

[0030] Herein, unless otherwise defined, technical and scientific terms used in the specification have general meanings understood by those skilled in the art to which the present invention belongs, and descriptions of known functions and configurations that unnecessarily obscure the subject matter of the present invention will be omitted in the following description and drawings.

[0031] In addition, singular forms used in the specification and the appended claims may be intended to include plural forms as well, unless the context indicates otherwise.

[0032] In this specification and the appended claims, terms such as “first” and “second” are not used in a limiting sense, but are used for the purpose of distinguishing one constituent element from other constituent elements.

[0033] In this specification and the appended claims, terms such as “comprising” or “having” mean that the features or constituent elements described in the specification are present, and unless specifically defined otherwise, do not preclude the possibility of adding one or more other features or constituent elements.

[0034] In the present specification and claims, when a film (layer), region, constituent element or the like exists on other parts, it includes not only the case where it is in direct contact with other parts, but also the case where other films (layers), other regions, other constituent elements exist between these parts.

[0035] The manufacturing method of the lithium secondary battery of the present invention includes: (a) electrode plate process step: manufacturing positive electrode plate and negative electrode plate; (b) assembly process step: assembling by including a separator in the positive electrode plate and the negative electrode plate and injecting an electrolyte solution to manufacture a unit cell; and (c) activation process step: performing a formation process on the manufactured unit cell, wherein a magnetic field is applied in the formation process of (c). In this article, in the activation process step, an aging process can be further performed before or after the formation process.

[0036] The SEI film formed on the surface of the negative electrode during the formation process is a core element in determining battery safety, power capacity, shelf life, etc., and according to the manufacturing method of the present invention, a magnetic field is applied during the formation process to activate the dissociation reaction of ions generated in the interface and the movement of electrons solvated from the negative electrode to form a uniform and stable SEI film in the electrode interface.

[0037] In a specific example, the electrode plate process step (a) is a process for manufacturing a positive electrode plate and a negative electrode plate. In the electrode plate process step, the positive electrode plate and the negative electrode plate are manufactured by mixing an active material, a conductive material, and a binder, and then coating, pressing, laminating, and cutting the mixture.

[0038] The positive electrode plate may be formed on a positive electrode current collector. Herein, a porous body such as a mesh or net shape may be used as the positive electrode current collector, and a porous metal plate such as stainless steel, nickel, or aluminum may be used, but the present invention is not necessarily limited thereto, and any material may be used as long as it can be used as a current collector in the art. In addition, in order to prevent oxidation, the positive electrode current collector may be coated with a metal or alloy coating film having oxidation resistance.

[0039] The active material used in the manufacture of the positive electrode plate may be a compound capable of reversibly inserting and extracting lithium. Specifically, a lithium-containing transition metal oxide may be used, and more specifically, a compound selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(Ni a Co b Mn c )O2 (0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), LiNi 1-y Co y O2, LiCo 1-y Mn y O2, LiNi 1-y Mn y O2 (0 ≤ y < 1), Li(Ni a Co b Mn c )O4 (0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2), LiMn 2-z Ni z O4, LiMn 2-z Co z O4 (0 < z < 2), LiCoPO4, and LiFePO4, preferably any one or a mixture of two or more of the group consisting of Li(Ni a Co b Mn c )O2 (0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), and more preferably, Li(Ni 0.6 Co 0.2 Mn 0.2 )O2. In addition, in addition to oxides, sulfides, selenides, halides, etc. may also be used. In addition, a positive electrode active material in a Li-free form without lithium may be used initially, and more specifically, TiS2, FeS2, V2O5, etc. may be used.

[0040] The conductive material used in the manufacture of the positive electrode plate may be any material having porosity and conductivity without limitation, and more specifically, may be a porous carbonaceous material. The carbonaceous material may be carbon black, graphite, graphene, activated carbon, carbon fiber, etc. In addition, the conductive material may be a metal conductive material such as metal fiber, metal mesh; metal powder of copper, silver, nickel, aluminum, etc.; or an organic conductive material such as a polyphenylene derivative. The conductive material may be used alone or in combination.

[0041] The positive electrode plate may optionally further include a binder. The binder may be a thermoplastic resin or a thermosetting resin. More specifically, as a binder, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluorochloroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polytrifluorochloroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-trifluorochloroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, etc., can be used alone or in combination, but the present invention is not necessarily limited thereto, and any material used as a binder in the art can be used.

[0042] Therefore, the positive electrode plate can be made by mixing the positive electrode active material, the conductive material and optionally the binder to prepare a composition for forming the positive electrode active material layer, and then applying it on at least one surface of the positive electrode collector, drying and rolling. As another method, the positive electrode plate can be made by casting the composition for forming the positive electrode active material layer on a separate support, peeling it from the support to obtain a film, and laminating the film on the positive electrode collector.

[0043] The thickness of the manufactured positive electrode plate can be 10 μm to 100 μm, preferably 15 μm to 50 μm, and more preferably 20 μm to 30 μm. In addition, the area of ​​the manufactured positive electrode can be 1 cm 2 Up to 40cm 2 , preferably 3cm 2 Up to 30cm 2 , more preferably 5cm 2 Up to 20cm 2 Therefore, the unit area capacity of the manufactured positive electrode can be 1 mAh (milliampere hour) / cm 2 Up to 10mAh / cm 2 , preferably 1.5 mAh / cm 2 Up to 7.5 mAh / cm 2 , more preferably 2 mAh / cm2 to 5 mAh / cm 2 。

[0044] In a specific example, the negative electrode plate may include a current collector and a negative electrode active material layer, and the negative electrode active material layer is formed by applying a negative electrode paste including a negative electrode active material on at least one surface of the current collector.

[0045] The negative electrode active material layer may include a negative electrode active material, and optionally, may further include a binder and a conductive material. Examples of the negative electrode active material may be a carbonaceous negative electrode active material, a silicon-based negative electrode active material, or a mixture thereof, but are not limited thereto. The carbonaceous negative electrode active material may be one or more selected from artificial graphite, natural graphite, and hard carbon. The silicon-based negative electrode active material may be Si, SiO x (0 < x < 2), an Si-Q alloy (Q is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, but not including Si), an Si-carbon composite material, or a mixture of at least one of them and SiO2.

[0046] The current collector, binder, and conductive material used for manufacturing the negative electrode plate are the same as those used for manufacturing the positive electrode plate described above.

[0047] The thickness of the manufactured negative electrode may be 10 μm to 100 μm, preferably 20 μm to 70 μm, more preferably 30 μm to 40 μm. Additionally, the area of the manufactured negative electrode may be 1 cm 2 to 40 cm 2 、preferably 3 cm 2 to 30 cm 2 、more preferably 5 cm 2 to 20 cm 2 。Therefore, the capacity per unit area of the manufactured negative electrode may be 1 mAh / cm 2 to 10 mAh / cm 2 ,preferably 1.5 mAh / cm 2 to 7.5 mAh / cm 2 ,more preferably 2 mAh / cm 2 to 5 mAh / cm 2 。

[0048] In a specific example, the assembly process step (b) is a process of processing and assembling the positive electrode plate, negative electrode plate, and separator to manufacture a unit cell in the form of a battery, and may be a step of manufacturing by inserting the unit cell into a bag and then injecting an electrolyte solution.

[0049] The bag can be formed by laminating an insulating layer, an adhesive layer and a metal film, and as the bag, those commonly used in the art can be adopted. More specifically, the metal film can include aluminum, etc., which can ensure the mechanical rigidity of the bag and also block moisture and oxygen from the outside, but the present invention is not limited thereto.

[0050] In addition, the electrolyte solution may be injected into the pouch and contained therein, and the unit cells may be immersed in the electrolyte solution.

[0051] The electrolyte solution may include an organic solvent and a lithium salt. The organic solvent is used as a medium in which the ions participating in the electrochemical reaction of the battery can move, for example, it can be a carbonate group, an ester group, an ether group, a ketone group, an alcohol group or an aprotic solvent, and can be used alone or in combination of two or more, and the mixing ratio when used in combination of two or more can be appropriately adjusted according to the desired battery performance. More specifically, the organic solvent can be an organic solvent selected from the group consisting of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate, methyl propyl carbonate, dipropyl carbonate, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane and tetrahydrofuran.

[0052] In addition, the lithium salt is a material that is dissolved in an organic solvent and acts as a lithium ion source in a battery to enable the lithium secondary battery to work and promotes the movement of lithium ions between the positive electrode and the negative electrode. More specifically, the lithium salt can be composed of Li + X - Indicates that the anion of the lithium salt (X - ) can choose free F - , Cl - Br - ,I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH -、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - , and (CF3CF2SO2)2N - The group consisting of, and preferably, may be LiPF6.

[0053] Herein, the concentration of the lithium salt in the electrolyte solution may be 0.1M to 10M, preferably 0.3M to 5M, and more preferably 0.5M to 2M.

[0054] The separator may be polyethylene, polypropylene, polyvinylidene fluoride or a multilayer of two or more thereof, and a mixed multilayer such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene triple-layer separator, a polypropylene / polyethylene / polypropylene triple-layer separator may be used.

[0055] In a specific example, the activation process step (c) may be a step of imparting electrical characteristics by charging and discharging the assembled unit cells, and a formation process may be performed on the unit cells manufactured by (b), and then an aging process may be performed.

[0056] In the formation process, in a lithium secondary battery, lithium ions are inserted from the lithium metal oxide of the positive electrode into the negative electrode, and in the process, the solvent component of the electrolyte solution reaches its reduction potential, which results in the generation of organic substances such as Li2CO3, LiO and LiOH as reduction byproducts on the surface of the negative electrode, thereby forming a coating film called SEI film. That is, in order to uniformly and stably form the SEI film, the dissociation reaction of ions generated at the interface should be increased, and the mobility of electrons solvated from the negative electrode should also be increased, and for this purpose, a magnetic field should be applied in the formation process.

[0057] In this article, the intensity of the applied magnetic field can be 0.1T to 2T, preferably 0.2T to 1.5T, and more preferably 0.3T to 1.0T. In addition, the frequency of the applied magnetic field can be 1Hz to 30Hz, preferably 2Hz to 25Hz, and more preferably 3Hz to 15Hz. In addition, the application time of the magnetic field can be 1 minute to 60 minutes, preferably 5 minutes to 40 minutes, and more preferably 10 minutes to 20 minutes. When a magnetic field satisfying the intensity, frequency and time within this range is applied, the dissociation reaction of the ions generated in the interface increases, and the mobility of the ions solvated from the negative electrode also increases, thereby forming a uniform and stable SEI film, and therefore, the lithium secondary battery including the SEI film exhibits excellent electrical properties.

[0058] In addition, the intensity of the current applied in the formation process may be 0.01 C to 1.0 C, preferably 0.03 C to 0.5 C, more preferably 0.05 C to 0.2 C. In addition, in the formation process, the current may be applied for 1 hour to 10 hours, preferably 1 hour to 5 hours, more preferably 1 hour to 3 hours.

[0059] In the formation process, the time point of applying the magnetic field can be simultaneous with the first charging of the positive electrode and the negative electrode immersed in the electrolyte solution. In addition, the time point of ending the application of the magnetic field is the time point when the gas generation is completed in the formation process.

[0060] After the formation process, an aging process may be further performed. The aging process is a process of allowing the battery to stand for a certain period of time to stabilize the SEI coating, and the electrolyte solution inside the battery is uniformly dispersed by storing the battery at a temperature of 10°C to 50°C for 1 hour to 5 hours, thereby optimizing ion movement.

[0061] Hereinafter, the present invention will be described in detail through embodiments. However, the embodiments are used to describe the present invention in more detail, and the scope of the present invention is not limited to the following embodiments.

[0062] <Embodiment 1> Production of lithium secondary battery

[0063] 1-1: Electrode plate process steps

[0064] LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2 A slurry in which O2, polyvinylidene fluoride (PVdF) as a binder and carbon black as a conductive material were mixed in a weight ratio of 95:3:2 was coated on an aluminum foil, dried and rolled to manufacture a positive electrode plate. The thickness of the manufactured positive electrode plate was 25.5 μm and the area of ​​the positive electrode plate was 10.36 cm 2 .

[0065] The negative electrode plate was manufactured using graphite as the negative electrode active material. The thickness of the manufactured negative electrode plate was 33 μm and the area of ​​the negative electrode plate was 12 cm 2 .

[0066] 1-2: Assembly process steps

[0067] 1.0 M LiPF 6 was dissolved in a solvent having a volume ratio of ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 1:1:1 to prepare an electrolyte solution.

[0068] A polypropylene (PP) separator is placed between the positive electrode plate and the negative electrode plate manufactured in the electrode plate process step and wound, and an electrolyte solution is injected to manufacture a unit cell.

[0069] 1-3: Activation process steps

[0070] A current of 0.1 C was applied for 2 hours to perform the formation process. At this time, a magnetic field was further applied, the intensity of the magnetic field was 0.5 T, the frequency was 5 Hz, and the application time of the magnetic field was 5 minutes.

[0071] After the forming process, the aging process was performed at 25° C. for 2 hours.

[0072] <Implementation Method 2>

[0073] A lithium secondary battery was manufactured in the same manner as in Embodiment 1, except that the application time of the magnetic field was 15 minutes instead of 5 minutes.

[0074] <Implementation Method 3>

[0075] A lithium secondary battery was manufactured in the same manner as in Embodiment 1, except that the application time of the magnetic field was 30 minutes instead of 5 minutes.

[0076] <Implementation Method 4>

[0077] A lithium secondary battery was manufactured in the same manner as in Embodiment 1, except that the frequency of the magnetic field was 10 Hz instead of 5 Hz.

[0078] <Implementation method 5>

[0079] A lithium secondary battery was manufactured in the same manner as in Embodiment 2, except that the frequency of the magnetic field was 10 Hz instead of 5 Hz.

[0080] <Implementation Method 6>

[0081] A lithium secondary battery was manufactured in the same manner as in Embodiment 3, except that the frequency of the magnetic field was 10 Hz instead of 5 Hz.

[0082] <Implementation Method 7>

[0083] A lithium secondary battery was manufactured in the same manner as in Embodiment 1, except that the frequency of the magnetic field was 20 Hz instead of 5 Hz.

[0084] <Implementation Method 8>

[0085] A lithium secondary battery was manufactured in the same manner as in Embodiment 2, except that the frequency of the magnetic field was 20 Hz instead of 5 Hz.

[0086] <Implementation Method 9>

[0087] A lithium secondary battery was manufactured in the same manner as in Embodiment 3, except that the frequency of the magnetic field was 20 Hz instead of 5 Hz.

[0088] <Comparative Example>

[0089] Except that the magnetic field was not further applied, a lithium secondary battery was manufactured in the same manner as in Embodiment 1. The results of the comparative example are indicated as "ref" in the drawings shown below.

[0090] <Experimental Example 1> Evaluation of efficiency of lithium secondary battery per cycle

[0091] The electrochemical characteristics of the unit cells manufactured by the manufacturing methods of Embodiments 1 to 9 and Comparative Example were evaluated.

[0092] Changes in discharge capacity and discharge capacity retention rate depending on charge / discharge cycle performance were measured.

[0093] First, a unit cell manufactured by applying a magnetic field having a frequency of 5 Hz to a formation process according to Embodiments 1 to 3 was evaluated. Figure 1 When the discharge capacity after 100 cycles was examined, it was confirmed that when a magnetic field was applied, the discharge capacity retention rate was high compared to the comparative example in which no magnetic field was applied, and among them, it was confirmed that the discharge capacity retention rate was the highest in the unit cell in which the magnetic field was applied for 15 minutes.

[0094] Next, the unit cells manufactured by applying a magnetic field having a frequency of 10 Hz to the formation process according to Embodiments 4 to 6 were evaluated. Figure 2 When the discharge capacity after 100 cycles was examined, it was confirmed that when a magnetic field was applied, the discharge capacity retention rate was high compared to the comparative example in which no magnetic field was applied, and among them, it was confirmed that the discharge capacity retention rate was the highest in the unit cell in which the magnetic field was applied for 15 minutes.

[0095] Next, the unit cells manufactured by applying a magnetic field having a frequency of 20 Hz to the formation process according to Embodiments 7 to 9 were evaluated. Figure 3 When the discharge capacity after 100 cycles was examined, it was confirmed that when a magnetic field was applied, the discharge capacity retention rate was high compared to the comparative example in which no magnetic field was applied, and among them, it was confirmed that the discharge capacity retention rate was the highest in the unit cell in which the magnetic field was applied for 15 minutes.

[0096] That is, it can be confirmed that as the number of charge / discharge cycles increases, the discharge capacity of the lithium secondary battery manufactured according to the manufacturing method of embodiments 1 to 9 decreases less than that of the lithium secondary battery manufactured according to the comparative example, and therefore, it can be confirmed that the lithium secondary battery to which a magnetic field is applied during the formation process has excellent capacity retention performance.

[0097] <Experimental Example 2> Evaluation of electrochemical performance of lithium secondary batteries

[0098] 1. Evaluation of initial (first) discharge capacity

[0099] Refer to Table 1 and Figure 4 , when the magnetic field frequency is 10Hz (as shown in Embodiments 4 to 6), not only compared with the comparative example in which the magnetic field is not applied, but also compared with Embodiments 1 to 3 in which the magnetic field frequency is 5Hz and Embodiments 7 to 9 in which the magnetic field frequency is 20Hz, the initial discharge capacity is high when the magnetic field is applied for the same period of time. In addition, even in the case of applying a magnetic field with the same frequency, when the magnetic application time is 15 minutes (Implementations 2, 5 and 8), it is confirmed that the initial discharge capacity is high. Therefore, when a magnetic field with a frequency of 10Hz is applied for 15 minutes as in Embodiment 5, the initial discharge capacity is the highest, which is 23.6mAh.

[0100] (Table 1)

[0101] Initial discharge capacity (mAh / g) Implementation Method 1 20.1 Implementation Method 2 21.3 Implementation 3 19.8 Implementation 4 22.1 Implementation method 5 23.6 Implementation 6 22.9 Implementation 7 21.8 Implementation 8 22.3 Implementation method 9 21.2 Comparative Example 19.6

[0102] 2. Evaluation of Initial Coulombic Efficiency (ICE)

[0103] Refer to Table 2 and Figure 5 , when the magnetic field frequency is 10 Hz (as shown in Embodiments 4 to 6), not only compared with the comparative example in which the magnetic field is not applied, but also compared with Embodiments 1 to 3 in which the magnetic field frequency is 5 Hz and Embodiments 7 to 9 in which the magnetic field frequency is 20 Hz, the initial Coulomb efficiency is high when the magnetic field is applied for the same period of time. In addition, even in the case of applying a magnetic field with the same frequency, when the magnetic field application time is 15 minutes (Implementations 2, 5 and 8), it is confirmed that the initial Coulomb efficiency is high. Therefore, when a magnetic field with a frequency of 10 Hz is applied for 15 minutes as in Implementation 5, it is determined that the initial Coulomb efficiency is the highest, which is 97.9%.

[0104] (Table 2)

[0105]

[0106]

[0107] 3. Evaluation of discharge capacity ratio (rate performance)

[0108] Refer to Table 3 and Figure 6, when the magnetic field frequency is 5 Hz (as shown in Embodiments 1 to 3), and when the magnetic field frequency is 10 Hz (as shown in Embodiments 4 to 6), it can be confirmed that, when the magnetic field is applied for the same period of time, the discharge capacity ratio is high not only compared with the comparative example in which the magnetic field is not applied, but also compared with Embodiments 7 to 9 in which the magnetic field frequency is 20 Hz. In addition, even in the case of applying a magnetic field with the same frequency, when the magnetic field application time is 15 minutes (Implementations 2, 5 and 8), it is confirmed that the discharge capacity ratio is high. Therefore, when a magnetic field with a frequency of 5 Hz or 10 Hz is applied for 15 minutes as in Embodiments 2 or 5, it is confirmed that the discharge capacity ratio is the highest, which is 27.9% or 27.2%.

[0109] (Table 3)

[0110]

[0111]

[0112] 4. Evaluation of the retention rate after the cycle (cycle retention rate)

[0113] Refer to Table 4 and Figure 7 , when the magnetic field frequency is 5 Hz (as shown in Embodiments 1 to 3), and when the magnetic field frequency is 10 Hz as in Embodiments 4 to 6 (as shown in Embodiments 4 to 6), it can be confirmed that, in the case of applying the magnetic field for the same period of time, the retention rate is high not only compared with the comparative example in which the magnetic field is not applied, but also compared with Embodiments 7 to 9 in which the magnetic field frequency is 20 Hz. In addition, even in the case of applying a magnetic field with the same frequency, when the magnetic field application time is 15 minutes (Implementations 2, 5 and 8), it is confirmed that the retention rate is high. Therefore, when a magnetic field with a frequency of 5 Hz or 10 Hz is applied for 15 minutes as in Implementation 2 or 5, it is determined that the retention rate is the highest, which is 88% or 85.2%.

[0114] 100th cycle retention rate (%) Implementation Method 1 75 Implementation Method 2 88 Implementation 3 82.4 Implementation 4 74.3 Implementation method 5 85.2 Implementation 6 82.9 Implementation 7 74.7 Implementation 8 84.5 Implementation method 9 71.6 Comparative Example 71.1

Claims

1. A method for manufacturing a lithium secondary battery, the method comprising: (a) Electrode plate process steps: manufacturing positive electrode plates and negative electrode plates; (b) an assembly process step of assembling by including a separator in the positive electrode plate and the negative electrode plate and injecting an electrolyte solution to manufacture a unit cell; as well as (c) Activation process step: performing a formation process on the manufactured unit cells, Wherein, a magnetic field is applied during the formation process of (c).

2. The method for manufacturing a lithium secondary battery according to claim 1, wherein: The applied magnetic field has a strength of 0.1T to 2.0T.

3. The method for manufacturing a lithium secondary battery according to claim 1, wherein: The applied magnetic field has a frequency of 1 Hz to 30 Hz.

4. The method for manufacturing a lithium secondary battery according to claim 1, wherein: The applied magnetic field is applied for a period of 1 minute to 60 minutes.

5. The method for manufacturing a lithium secondary battery according to claim 1, wherein: The current applied in (c) is 0.01C to 1.0C.

6. The method for manufacturing a lithium secondary battery according to claim 1, wherein: The time for applying the current in (c) is 1 hour to 10 hours.

7. A lithium secondary battery manufactured by the method of claim 1.

8. The lithium secondary battery according to claim 7, wherein: The lithium secondary battery has an initial discharge capacity of 20 mAh / g or more.

9. The lithium secondary battery according to claim 7, wherein: The lithium secondary battery has an initial coulombic efficiency of 85% or more.

10. The lithium secondary battery according to claim 7, wherein: The lithium secondary battery has a discharge capacity ratio of 18% or more.

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