Lithium secondary battery manufacturing method and lithium secondary battery

Abstract

The present application relates to a method for producing a lithium secondary battery and a lithium secondary battery.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0026509, filed with the Korean Intellectual Property Office on March 2, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a method for manufacturing a lithium secondary battery and a lithium secondary battery. [Background technology]

[0003] The rapid increase in the use of fossil fuels has led to an increasing demand for alternative and clean energy, and as part of this, the most actively researched field is the field of power generation and storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that utilizes such electrochemical energy is a secondary battery, and the range of its use is tending to expand more and more.

[0005] As technological development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and widely used. In addition, active research is being conducted on methods for manufacturing high-density electrodes with higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and extracts lithium ions from the positive electrode. The negative electrode active material may be silicon-based particles with a high discharge capacity.

[0007] In recent years, in response to the demand for high-density energy batteries, Si / C and SiO2, which have capacities 10 times larger than those of graphite-based materials, have been used as negative electrode active materials. xActive research is being conducted into methods of increasing capacity by using silicon-based compounds such as those mentioned above. However, silicon-based compounds, which are high-capacity materials, have a problem in that while they have a large capacity compared to conventionally used graphite, they suddenly expand in volume during charging, cutting off the conductive path and reducing battery performance.

[0008] This problem also occurs during the manufacturing process of lithium secondary batteries. During the manufacturing process of lithium secondary batteries, a positive electrode, a negative electrode, and a separator are stacked to form an electrode assembly, which is then impregnated with an electrolyte solution and then subjected to an activation process to enable the battery to function as a lithium secondary battery. The activation process is a necessary process in which the lithium secondary battery is charged and discharged under certain conditions to thoroughly disperse the electrolyte solution inside the lithium secondary battery, optimize ion movement, and screen for defects and capacity issues.

[0009] When using a carbon-based anode, the activation process is a simple process of forming an SEI on the anode to prepare the cell for operation. On the other hand, when using a silicon-based anode, the activation C-rate determines the formation of silicon within the electrode, which significantly affects the performance of the lithium secondary battery. Specifically, as described above, the activation process is performed during the lithium secondary battery manufacturing process, during which the lithium secondary battery undergoes charging and discharging. While increasing the C-rate can shorten the activation process time, the characteristics of silicon-based anodes can lead to more unevenness within the anode, resulting in surface cracks and volume changes, which can actually have adverse effects. Simply lowering the C-rate solves these problems, but it also significantly increases the activation process time, resulting in reduced productivity.

[0010] To solve the above problems, methods such as simply increasing or decreasing the C-rate or decreasing the proportion of silicon-based active materials have been considered, but these methods still have limitations in terms of maximizing capacity characteristics and increasing productivity.

[0011] Therefore, in the process of fabricating a lithium secondary battery including a silicon-based anode to maximize capacity characteristics, research is needed on a method that can prevent uneven charging within the anode during the activation process, minimize surface cracks and volume changes, and improve performance characteristics. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0013] As a result of research into methods for minimizing the surface particle cracking phenomenon that occurs during charging and discharging during the activation process of lithium secondary batteries containing silicon-based anodes and improving productivity, it was found that the problem can be solved by adjusting the charge level during the early and later stages of charging.

[0014] Therefore, the present application relates to a method for manufacturing a lithium secondary battery that can solve the above problems, and a lithium secondary battery manufactured by the method. [Means for solving the problem]

[0015] One embodiment of the present specification provides a method for manufacturing a lithium secondary battery, the method including: preparing an electrode assembly including a silicon-based negative electrode, a positive electrode, and a separator; and activating a lithium secondary battery including the electrode assembly, wherein the activation step includes charging and discharging the lithium secondary battery, the charging step including multi-stage charging from a high-rate charge to a low-rate charge, the multi-stage charging step including a first charging step up to an SOC of 25% and a second charging step after charging to an SOC of 25%, and the first charging step includes charging at a constant current of 0.5 C or more.

[0016] In yet another embodiment, there is provided a lithium secondary battery manufactured by the method for manufacturing a lithium secondary battery according to the present application. [Effects of the Invention]

[0017] The lithium secondary battery according to the present invention has a modified charging condition during the activation process, that is, the charging during the activation process includes multi-stage charging from high to low charging rates, which minimizes surface particle cracking and increases productivity.

[0018] Specifically, the higher the charge C-rate during the activation process, the more surface particle cracking occurs due to non-uniformity within the electrode. However, the activation process according to the present application is carried out by applying a high-rate charge during the initial charge followed by a low-rate charge. That is, it was confirmed that there is no difference in surface particle cracking whether the initial charge is a high-rate or low-rate charge during the activation process, and that particle cracking occurs when a high-rate charge is performed after the initial charge. Therefore, by applying a high-rate charge during the initial charge followed by a low-rate charge, it is possible to minimize the surface particle cracking that occurs during charge and discharge, and since it takes the same amount of time as the existing activation process, it has the advantage of not reducing productivity. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present application. [Figure 2] FIG. 10 is a diagram showing the degree of particle cracking on the electrode surface depending on SOC % during the activation process at high and low filling rates. [Explanation of symbols]

[0020] 10 Negative electrode current collector layer 20...Negative electrode active material layer 30...Separation membrane 40...Cathode active material layer 50 Positive electrode current collector layer 100: Negative electrode for lithium secondary batteries 200: Positive electrode for lithium secondary batteries DETAILED DESCRIPTION OF THE INVENTION

[0021] Prior to describing the present invention, some terms will first be defined.

[0022] In this specification, when a part is said to "comprise" a certain component, this means that it may further include other components, rather than excluding other components, unless specifically stated to the contrary.

[0023] In this specification, "p to q" means a range of "not less than p and not more than q."

[0024] In this specification, the "specific surface area" is measured by the BET method, and specifically, is calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using a BELSORP-mino II manufactured by BEL Japan Co., Ltd. That is, in the present application, the BET specific surface area may mean the specific surface area measured by the above-mentioned measurement method.

[0025] In this specification, "Dn" refers to particle size distribution, and refers to the particle size at the n% point in the cumulative particle number distribution by particle size. That is, D50 is the particle size (median particle size, average particle size) at the 50% point in the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution by particle size. Meanwhile, the median particle size may be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in diffraction patterns due to particle size when the particles pass through a laser beam.

[0026] In one embodiment of the present application, the particle size or particle diameter may refer to the average diameter or representative diameter of each particle constituting the particle.

[0027] In this specification, when a polymer contains a certain monomer as a monomer unit, it means that the monomer is involved in a polymerization reaction and is contained as a repeating unit in the polymer. In this specification, when a polymer contains a monomer, this is interpreted as the same as when a polymer contains a monomer as a monomer unit.

[0028] It is understood that the term "polymer" is used in the broad sense herein to include copolymers unless "homopolymer" is specifically stated.

[0029] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) with various degrees of polymerization that are commercially available for molecular weight measurement as standard substances. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0030] The present invention will now be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the present invention. However, the present invention may be embodied in various different forms and is not limited to the following description.

[0031] One embodiment of the present specification provides a method for manufacturing a lithium secondary battery, the method including: preparing an electrode assembly including a silicon-based negative electrode, a positive electrode, and a separator; and activating a lithium secondary battery including the electrode assembly, wherein the activation step includes charging and discharging the lithium secondary battery, the charging step including multi-stage charging from a high-rate charge to a low-rate charge, the multi-stage charging step including a first charging step up to an SOC of 25% and a second charging step after charging to an SOC of 25%, and the first charging step including charging at a constant current of 0.5 C or more.

[0032] That is, it was confirmed that there is no difference in surface particle cracking whether the initial charging rate is high or low during the activation process, and that particle cracking occurs when the initial charging rate is high after the initial charging rate. Therefore, the present invention relates to a method for manufacturing a lithium secondary battery that applies a high-rate charge during the initial charging and then a low-rate charge, which can minimize the surface particle cracking phenomenon that occurs during charge and discharge, and does not reduce productivity by taking the same time as the existing activation process.

[0033] The method for producing a lithium secondary battery will be described in more detail below.

[0034] The method for manufacturing a lithium secondary battery according to the present application provides a step of manufacturing an electrode assembly including a silicon-based negative electrode, a positive electrode, and a separator.

[0035] The negative electrode according to the present application contains a silicon-based negative electrode material, and the performance of the lithium secondary battery is significantly affected by the C-rate during the activation process compared to when carbon-based or other negative electrode materials are used. Therefore, the method for manufacturing a lithium secondary battery according to the present application is characterized by including specific multi-stage charging in the activation process.

[0036] In one embodiment of the present application, the silicon-based negative electrode includes a negative electrode current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, the negative electrode active material layer including a negative electrode active material layer composition including a silicon-based active material.

[0037] In this case, the negative electrode active material layer composition may include at least one selected from the group consisting of a silicon-based active material; a negative electrode conductive material; and a negative electrode binder.

[0038] In one embodiment of the present application, the silicon-based negative electrode includes a negative electrode current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, the negative electrode active material layer including a negative electrode active material layer composition containing a silicon-based active material, and the silicon-based active material is SiO x (x=0) and SiO xContaining one or more selected from the group consisting of (0 < x < 2), based on 100 parts by weight of the silicon-based active material, the SiO x Provided is a method for manufacturing a lithium secondary battery containing 50 parts by weight or more of (x = 0).

[0039] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Also, fine irregularities can be formed on the surface to strengthen the binding force of the negative electrode active material, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabric bodies, etc.

[0040] In one embodiment of the present application, the thickness of the negative electrode current collector layer may be 1 μm or more and 100 μm or less.

[0041] However, the thickness can be variously deformed according to the type and use of the negative electrode used, and is not limited thereto.

[0042] In one embodiment of the present application, the negative electrode active material layer includes a negative electrode slurry containing a negative electrode active material layer composition, and the negative electrode active material layer composition may include a silicon-based active material; a negative electrode conductive material; and a negative electrode binder.

[0043] In one embodiment of the present application, the silicon-based negative electrode can be formed by applying and drying a negative electrode slurry containing the negative electrode active material layer composition on one or both sides of the negative electrode current collector layer.

[0044] At this time, the negative electrode slurry may include the aforementioned negative electrode active material layer composition; and a slurry solvent.

[0045] In one embodiment of the present application, the solid content of the negative electrode slurry may satisfy 5% or more and 40% or less.

[0046] In another embodiment, the solid content of the negative electrode slurry may satisfy a range of 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

[0047] The solid content of the negative electrode slurry can mean the content of the negative electrode active material layer composition contained in the negative electrode slurry, and can mean the content of the negative electrode active material layer composition based on 100 parts by weight of the negative electrode slurry.

[0048] When the solid content of the negative electrode slurry satisfies the above range, the viscosity during the formation of the negative electrode active material layer is appropriate, and it has the characteristic that the phenomenon of particle agglomeration of the negative electrode active material layer composition can be minimized and the negative electrode active material layer can be efficiently formed.

[0049] In one embodiment of the present application, the slurry solvent can be used without limitation as long as it can dissolve the negative electrode active material layer composition. Specifically, water, acetone or NMP can be used.

[0050] In one embodiment of the present application, the silicon-based active material includes at least one selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and may contain 50 parts by weight or more of the SiO x (x = 0) based on 100 parts by weight of the silicon-based active material.

[0051] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) contains 50 parts by weight or more, preferably 60 parts by weight or more, more preferably 70 parts by weight or more, and most preferably 80 parts by weight or more, and may contain 100 parts by weight or less, preferably 99 parts by weight or less, and more preferably 95 parts by weight or less.

[0052] In one embodiment of the present application, the silicon-based active material may be, in particular, pure silicon (Si). The use of pure silicon (Si) as the silicon-based active material means that, based on 100 parts by weight of the silicon-based active material, pure Si (SiO x (x=0)) may be included in the range.

[0053] Meanwhile, the average particle size (D50) of the silicon-based active material of the present invention may be 5 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle size is within this range, the specific surface area of the particles is within an appropriate range, and the viscosity of the negative electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the silicon-based active material is equal to or greater than the lower limit of the range, the composite of the conductive material and the binder in the negative electrode slurry has an excellent contact area between the silicon particles and the conductive material, increasing the likelihood of maintaining a conductive network, and thereby increasing the capacity retention rate. On the other hand, when the average particle size is within this range, excessively large silicon particles are excluded, resulting in a smooth negative electrode surface, thereby preventing non-uniform current density during charge and discharge.

[0054] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of the silicon-based active material is preferably 0.01 to 150.0 m 2 / g, more preferably 0.1 to 100.0 m 2 / g, particularly preferably 0.2 to 80.0 m 2 / g, most preferably 0.2 to 18.0 m 2 / g. The BET specific surface area is determined in accordance with DIN 66131 (using nitrogen).

[0055] In one embodiment of the present application, the silicon-based active material may be, for example, in crystalline or amorphous form, and is preferably not porous.The silicon particles are preferably spherical or shard-like particles.Alternatively, but less preferably, the silicon particles may also have a fibrous structure or be in the form of a silicon-containing film or coating.

[0056] In one embodiment of the present application, the silicon-based active material may be 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0057] In yet another embodiment, the silicon-based active material may comprise 60 parts by weight or more, preferably 65 parts by weight or more, and more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode active material layer composition, and may comprise 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 85 parts by weight or less.

[0058] The negative electrode active material layer composition according to the present application includes a conductive material and a binder that can suppress the volume expansion rate during charge and discharge even when a silicon-based active material with extremely high capacity is used within the above range. In particular, the charging conditions during the activation process are adjusted to prevent cracking of the particle surface, thereby maximizing capacity characteristics.

[0059] In one embodiment of the present application, the silicon-based active material may have a non-spherical morphology, and the sphericity thereof is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0060] In this application, the circularity is determined by the following formula 1, where A is the area and P is the perimeter. [Formula 1] 4πA / P 2

[0061] In one embodiment of the present application, there is provided a method for producing a lithium secondary battery, wherein the negative electrode active material layer composition includes at least one selected from the group consisting of a negative electrode conductive material; and a negative electrode binder.

[0062] While graphite-based compounds have traditionally been used exclusively as negative electrode active materials, attempts to incorporate silicon-based active materials into negative electrode active materials to increase capacity have been increasing in recent years as demand for high-capacity batteries has grown. However, even if the properties of silicon-based active materials are partially adjusted as described above, the volume of silicon-based active materials can rapidly expand during charge / discharge processes, potentially damaging the conductive paths formed within the negative electrode active material layer.

[0063] Therefore, in one embodiment of the present application, the negative electrode conductive material may include at least one selected from the group consisting of dot-like conductive materials, planar conductive materials, and linear conductive materials.

[0064] In one embodiment of the present application, the dot-like conductive material refers to a spherical or dot-like conductive material that can be used to improve the conductivity of a negative electrode and has conductivity without undergoing a chemical change. Specifically, the dot-like conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black, which realizes high conductivity and excellent dispersibility.

[0065] In one embodiment of the present application, the point-like conductive material has a BET specific surface area of 40 m 2 / g or more 70m 2 / g or less, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 / g or less.

[0066] In one embodiment of the present application, the dot-like conductive material may have a volatile matter content of 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, and more preferably 0.01% or more and 0.1% or less.

[0067] In particular, when the functional group content of the dot-shaped conductive material satisfies the above range, there are functional groups present on the surface of the dot-shaped conductive material, and when water is used as the solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent.

[0068] In one embodiment of the present application, the silicon-based active material is characterized by including a dot-like conductive material having a functional group content within the above range, and the functional group content can be adjusted depending on the degree of heat treatment of the dot-like conductive material.

[0069] In one embodiment of the present application, the particle size of the dotted conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0070] In one embodiment of the present application, the conductive material may include a planar conductive material.

[0071] The planar conductive material increases the surface contact between silicon particles in the negative electrode to improve conductivity, and at the same time, prevents the conductive path from being broken due to volume expansion. The planar conductive material may be referred to as a plate-type conductive material or a bulk-type conductive material.

[0072] In one embodiment of the present application, the sheet conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and may be preferably platelet graphite.

[0073] In one embodiment of the present application, the average particle size (D50) of the sheet conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the average particle size is within this range, the sufficient particle size facilitates dispersion without excessively increasing the viscosity of the negative electrode slurry. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is excellent.

[0074] In one embodiment of the present application, the sheet conductive material provides a negative electrode active material layer composition having a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0075] In one embodiment of the present application, the sheet conductive material may be a high-specific surface area sheet conductive material having a high BET specific surface area; or a low-specific surface area sheet conductive material.

[0076] In one embodiment of the present application, the planar conductive material may be a high-specific surface area planar conductive material or a low-specific surface area planar conductive material without any restrictions. However, the planar conductive material of the present application may be affected to some extent by dispersion in terms of electrode performance, and it may be particularly preferable to use a low-specific surface area planar conductive material that does not cause dispersion problems.

[0077] In one embodiment of the present application, the sheet conductive material has a BET specific surface area of 5 m 2 / g or more.

[0078] In another embodiment, the sheet conductive material has a BET specific surface area of 5 m 2 / g or more 500m 2 / g or less, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 / g or less.

[0079] In another embodiment, the sheet conductive material is a high specific surface area sheet conductive material having a BET specific surface area of 50 m 2 / g or more 500m 2 / g or less, preferably 80m 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 / g or less.

[0080] In another embodiment, the sheet conductive material is a sheet conductive material with a low specific surface area, and has a BET specific surface area of 5 m 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 / g or less.

[0081] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include multiple carbon nanotube monomers. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape in the form of a bundle or rope in which multiple carbon nanotube units are arranged side by side or entangled with their longitudinal axes aligned in substantially the same direction. The carbon nanotube monomer has a graphite sheet in the form of a cylinder with a nanosized diameter and an sp2 bonding structure. Depending on the angle and structure of the graphite sheet, the carbon nanotube may exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during negative electrode fabrication and can smoothly form a conductive network within the negative electrode, improving the conductivity of the negative electrode.

[0082] In one embodiment of the present application, the linear conductive material may include SWCNTs; or MWCNTs.

[0083] In one embodiment of the present application, the negative electrode conductive material may be 5 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode active material layer composition.

[0084] In another embodiment, the negative electrode conductive material may contain 5 parts by weight or more and 40 parts by weight or less, preferably 10 parts by weight or more and 30 parts by weight or less, and more preferably 10 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0085] In one embodiment of the present application, the negative electrode conductive material may include a sheet conductive material and a linear conductive material.

[0086] In one embodiment of the present application, the negative electrode conductive material includes a sheet conductive material and a linear conductive material, and may include 0.01 parts by weight or more and 10 parts by weight or less of the linear conductive material and 90 parts by weight or more and 99.99 parts by weight or less of the sheet conductive material based on 100 parts by weight of the negative electrode conductive material.

[0087] In another embodiment, the linear conductive material may be 0.01 parts by weight or more and 10 parts by weight or less, preferably 0.05 parts by weight or more and 5 parts by weight or less, and more preferably 0.1 parts by weight or more and 3 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material.

[0088] In another embodiment, the sheet conductive material may be 90 parts by weight or more and 99.99 parts by weight or less, preferably 95 parts by weight or more and 99.95 parts by weight or less, and more preferably 97 parts by weight or more and 99.9 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material.

[0089] In particular, in one embodiment of the present application, the negative electrode conductive material includes a planar conductive material and a linear conductive material, each of which satisfies the above-mentioned composition and ratio, thereby not significantly affecting the life characteristics of existing lithium secondary batteries, increasing the number of points at which charging and discharging are possible, and providing the characteristic of excellent output characteristics at a high C-rate.

[0090] The negative electrode conductive material according to the present application has a completely different structure from the positive electrode conductive material used in the positive electrode. That is, the negative electrode conductive material according to the present application serves to form a contact point between silicon-based active materials, which undergo a large volume expansion during charging and discharging, while the positive electrode conductive material serves to provide some conductivity while acting as a buffer during rolling, and is completely different in structure and role from the negative electrode conductive material of the present invention.

[0091] Furthermore, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes having graphite-based active materials simply have smaller particles than the active material, and therefore have the properties of improving output characteristics and imparting some conductivity, and their structure and role are completely different from those of negative electrode conductive materials applied together with silicon-based active materials as in the present invention.

[0092] In one embodiment of the present application, the planar conductive material used as the negative electrode conductive material has a structure and function different from that of a carbon-based active material generally used as a conventional negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or dot-like shape to facilitate the storage and release of lithium ions.

[0093] Meanwhile, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape and may be referred to as plate-shaped graphite. That is, it is a material contained in the negative electrode active material layer to maintain a conductive path within the layer, and does not play a role in storing and releasing lithium, but rather serves to ensure a planar conductive path within the negative electrode active material layer.

[0094] That is, in this application, the use of plate-shaped graphite as a conductive material means that it is processed into a planar or plate-like shape and used as a material to ensure a conductive path rather than to store or release lithium. In this case, the negative electrode active material contained therein has high capacity characteristics for storing and releasing lithium, and plays a role in storing and releasing all lithium ions transferred from the positive electrode.

[0095] Meanwhile, in the present application, the use of a carbon-based active material as an active material means that the carbon-based active material is processed into a dotted or spherical shape and is used as a material that stores or releases lithium.

[0096] That is, in one embodiment of the present application, the carbon-based active material, artificial graphite or natural graphite, is in a dotted form and has a BET specific surface area of 0.1 m 2 / g or more 4.5m 2 The plate-shaped graphite, which is a planar conductive material, may be planar and have a BET specific surface area of 5 m 2 / g or more.

[0097] In one embodiment of the present application, the negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0098] The negative electrode binder according to one embodiment of the present application plays a role in holding down the active material and conductive material to prevent twisting and deformation of the negative electrode structure during volume expansion and relaxation of the silicon-based active material. Any common binder can be used as long as it fulfills this role. Specifically, a water-based binder can be used, and more specifically, a PAM-based binder can be used.

[0099] In one embodiment of the present application, the negative electrode binder may include a water-based binder, and the amount of the negative electrode binder may be 5 parts by weight to 15 parts by weight based on 100 parts by weight of the negative electrode active material layer composition.

[0100] In another embodiment, the amount of the negative electrode binder may be 5 parts by weight or more and 15 parts by weight or less, preferably 7 parts by weight or more and 13 parts by weight or less, and more preferably 10 parts by weight or more and 12 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0101] The negative electrode for a lithium secondary battery according to the present application uses a silicon-based active material to maximize capacity characteristics, and exhibits greater volume expansion during charge and discharge than conventional carbon-based active materials. Compared to conventional carbon-based negative electrodes, when a silicon-based negative electrode is used, a water-based binder is added in the above weight percentage, resulting in superior bonding strength between the conductive material and the binder.

[0102] In one embodiment of the present application, the porosity of the negative electrode active material layer may be in the range of 10% or more and 60% or less.

[0103] In another embodiment, the porosity of the negative electrode active material layer may be in the range of 10% to 60%, preferably 20% to 50%, and more preferably 30% to 45%.

[0104] The porosity varies depending on the composition and content of the silicon-based active material, the negative electrode conductive material, and the negative electrode binder contained in the negative electrode active material layer. In particular, the silicon-based active material and the negative electrode conductive material according to the present application are contained in specific compositions and content portions to satisfy the above range, thereby providing the electrode with appropriate ranges of electrical conductivity and resistance.

[0105] In one embodiment of the present application, 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 including the positive electrode active material.

[0106] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector typically has a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. It may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0107] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; or a compound having the chemical formula Li 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 O2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.3 is satisfied); 2-c3 M c3 Examples of suitable lithium manganese composite oxides include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li-metal.

[0108] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-mentioned positive electrode active material.

[0109] The positive electrode conductive material is used to impart conductivity to the electrode, and can be any material that has electronic conductivity without causing chemical changes in the battery. Specific examples include graphite such as natural graphite and artificial graphite; carbonaceous materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These materials may be used alone or in combination.

[0110] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0111] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitations. In particular, a separator that exhibits low resistance to electrolyte ion movement and excellent electrolyte humidification capability is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be used in a single-layer or multi-layer structure.

[0112] In one embodiment of the present application, after the step of preparing an electrode assembly including a silicon-based anode, a cathode, and a separator, the method may further include the step of placing the electrode assembly in a battery outer can and then injecting an electrolyte.

[0113] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

[0114] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0115] Examples of the non-aqueous organic solvent that may be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0116] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferred because they are high-viscosity organic solvents with high dielectric constants and can dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be produced, and these cyclic carbonates are more preferred.

[0117] The metal salt can be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt can be F - , Cl - , 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 - One or more selected from the group consisting of:

[0118] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purposes of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0119] In one embodiment of the present application, there is provided a method for manufacturing a lithium secondary battery, the method including: manufacturing the electrode assembly, and then activating a lithium secondary battery including the electrode assembly.

[0120] In one embodiment of the present application, there is provided a method for manufacturing a lithium secondary battery, wherein the activating step includes charging and discharging the lithium secondary battery, and the charging includes multi-stage charging from a high rate charge to a low rate charge.

[0121] In one embodiment of the present application, charging and discharging may be performed in CC (Constant Current)-CV (Constant Voltage) mode. Specifically, CC (Constant Current) is a method of charging and discharging up to a voltage set at a constant current value, and CV (Constant Voltage) is a method of charging and discharging up to a current set at a constant voltage value.

[0122] The method for manufacturing a lithium secondary battery according to the present application is characterized in that it can eliminate unevenness within the electrode and suppress surface cracks and volume changes through multi-step charging from high rate charging to low rate charging during the activation process while maintaining the same activation process time as conventional methods.

[0123] That is, the main feature of the present invention is that the durability of the lithium secondary battery manufactured from the above-mentioned activation process under the specific conditions can be improved without reducing productivity.

[0124] In one embodiment of the present application, C-rate refers to a measure of the rate at which a battery is discharged and is defined as the discharge current divided by the theoretical current draw at which the battery delivers its nominal rated capacity in 1 hour. For example, a C-rate of 1C may represent a discharge current that will discharge the battery in 1 hour, a rate of 2C may represent a discharge current that will discharge the battery in 1 / 2 hour, and a rate of C / 2 may represent a discharge current that will discharge the battery in 2 hours.

[0125] Figure 2 shows the degree of particle cracking on the electrode surface as a function of SOC% during the activation process at high and low rates of charging. Specifically, as can be seen from Figure 2, no particle cracking occurred on the electrode surface at either 0.33C (low rate charging) or 1C (high rate charging) in the early SOC period. However, in the middle and late SOC periods, the particle cracking on the electrode surface became more severe at high rate charging than at low rate charging.

[0126] That is, in Figure 2, it was confirmed that there was no difference in surface particle cracking whether the initial charging rate was high or low during the activation process, and that particle cracking occurred when a high rate was applied after the initial charging. Therefore, it was confirmed that the activation process according to the present application can minimize the surface particle cracking phenomenon that occurs with charging and discharging by applying a high rate charge during the initial charging and then a low rate charge. Furthermore, by introducing a high rate charge in the initial stage, it takes the same time as the existing activation process, and does not reduce productivity.

[0127] In one embodiment of the present application, there is provided a method for manufacturing a lithium secondary battery, wherein the multi-stage charging includes a first charging step up to SOC 25% and a second charging step after charging to SOC 25%, and the first charging step includes charging at a constant current of 0.5 C or more.

[0128] That is, the first charging stage may refer to an initial high-rate charge.

[0129] In one embodiment of the present application, the first charging step may include charging at a constant current of 0.9 C or more.

[0130] In one embodiment of the present application, the first charging step includes charging at a constant current of 0.5C or more, preferably 0.7C or more, more preferably 0.9C or more, and can satisfy the range of 1.2C or less.

[0131] By applying a high-rate constant current range within the above range during the first charging step, as described above, particle surface cracking does not occur regardless of whether the charging rate is high or low at the beginning of the SOC, so the activation process time itself can be shortened through the high-rate charging, and therefore, even if low-rate charging is performed at the later stage of the SOC, productivity issues do not arise. Also, by charging at a constant current that meets the above range during the first charging step, if the current is reduced during the first charging step, a more stable battery can be formed, but this can cause problems due to the increased process time.

[0132] In one embodiment of the present application, there is provided a method for manufacturing a lithium secondary battery, wherein the charging after charging to SOC 25% (second charging step) includes charging at a constant current of 0.5 C or less. In the present application, the charging after charging to SOC 25% may be the same as the second charging step.

[0133] That is, the second charging step may refer to low-rate charging.

[0134] In one embodiment of the present application, the charging after charging to SOC 25% includes a step of charging at a constant current of 0.5 C or less, preferably 0.4 C or less, more preferably 0.35 C or less, and can satisfy the range of 0.1 C or more.

[0135] That is, it was confirmed that cracking of the electrode surface particles occurs depending on the activation C-rate after charging to 25% SOC, and by controlling the charging after charging to 25% SOC within the constant current range, it is possible to minimize the cracking of the electrode surface particles.

[0136] In one embodiment of the present application, the multi-stage charging may include a first charging step to SOC 25%, a second-first charging step from SOC 25% to SOC 75%, and a second-second charging step after charging to SOC 75%; the second-first charging step may include charging at a constant current of 0.3 C or more and 0.5 C or less, and the second-second charging step may include charging at a constant current of 0.1 C or more and 0.3 C or less.

[0137] In conclusion, the main feature of the present invention is that the filling step in the activation process of the present application is divided into multiple stages at step rates, and the degree of filling is changed from high to low depending on the degree of filling, thereby solving the existing problems.

[0138] In one embodiment of the present application, there is provided a method for manufacturing a lithium secondary battery, wherein the activation time of the activation step is 10 hours or less.

[0139] In another embodiment, the activation time in the activation step may be 10 hours or less, preferably 9 hours or less, more preferably 8 hours or less, and may be in the range of 3 hours or more, preferably 3.5 hours or more.

[0140] That is, the lithium secondary battery according to the present application is characterized in that the charging conditions in the activation process are changed as described above, and the charging in the activation process includes multi-stage charging from high-rate charging to low-rate charging, thereby minimizing the phenomenon of surface particle cracking and satisfying the above-mentioned activation time, thereby increasing productivity.

[0141] In one embodiment of the present application, there is provided a lithium secondary battery manufactured by the method for manufacturing a lithium secondary battery according to the present application.

[0142] 1 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a lithium secondary battery anode 100 including an anode active material layer 20 on one side of an anode current collector layer 10 can be seen, and a lithium secondary battery cathode 200 including a cathode active material layer 40 on one side of a cathode current collector layer 50 can be seen, and the lithium secondary battery anode 100 and lithium secondary battery cathode 200 are shown stacked with a separator 30 sandwiched between them.

[0143] One embodiment of the present invention provides a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same. The battery module and battery pack include the secondary battery having high capacity, excellent rate-limiting characteristics, and excellent cycle characteristics, and can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. [Example]

[0144] In the following, preferred examples are presented to aid in understanding the present invention, but these examples are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description. Such changes and modifications are naturally intended to fall within the scope of the appended claims.

[0145] <Production example> <Lithium secondary battery manufacturing> Anode manufacturing A silicon-based active material, Si (average particle size (D50): 3.5 μm), a first conductive material, a second conductive material, and polyacrylamide (PAM) as a binder were added to distilled water as a solvent for forming a negative electrode slurry in a weight ratio of 70:10:0.315:9.685 to prepare a negative electrode slurry (solid concentration 25 wt%).

[0146] The first conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the second conductive material was SWCNT.

[0147] As a specific mixing method, the first conductive material, the second conductive material, the binder, and the water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the silicon-based active material was added and dispersed at 2500 rpm for 30 minutes to prepare a negative electrode slurry.

[0148] The negative electrode current collector was a copper current collector (thickness: 8 μm) and the negative electrode slurry was applied to both sides of the copper current collector at a rate of 85 mg / 25 cm. 2 The coated layer was rolled and dried in a vacuum oven at 130° C. for 10 hours to form a negative electrode active material layer.

[0149] Cathode manufacturing LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added in a weight ratio of 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for forming the cathode slurry to prepare a cathode slurry (solid concentration: 78 wt%).

[0150] The positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12 μm) at a rate of 537 mg / 25 cm. 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 65 μm), and a positive electrode was fabricated (positive electrode thickness: 77 μm, porosity: 26%).

[0151] Lithium secondary battery manufacturing An electrolyte was injected between the positive electrode and the negative electrode via a polyethylene separator to prepare a lithium secondary battery, and an activation process was carried out under the activation process conditions shown in Table 1 below.

[0152] [Table 1]

[0153] Table 2 below shows the results of evaluating the activation process time and the capacity retention rate (%) after 200 cycles of the batteries manufactured under the conditions shown in Table 1 for the Examples and Comparative Examples.

[0154] [Table 2]

[0155] As can be seen from the results in Table 2, the activation processes according to Examples 1 and 2 of the present application are carried out by applying a high-rate charge during the initial charge and then a low-rate charge. That is, by applying a high-rate charge during the initial charge and then a low-rate charge during the activation process, it was confirmed through the evaluation of the capacity retention that the surface particle cracking phenomenon that occurs during charge and discharge is minimized. Furthermore, it takes the same time as the existing activation process, and it was confirmed that there is no decrease in productivity when evaluating the activation process time.

[0156] As can be seen in Table 1, Comparative Examples 1 and 3 correspond to cases where single charging (high-rate or heavy-rate single charging) was performed at a CC current of 0.33 C or 1 C, rather than step-rate charging, until the voltage reached 4.2 V. In these cases, the activation process time was similar to that of the Examples, but charging was performed at a high C-rate even at the beginning of the activation process, which resulted in particle cracking on the surface of the electrode and a decrease in capacity retention.

[0157] In Comparative Example 2, the activation process was performed in a multi-stage manner as in the present invention, but the charging process proceeded in reverse from low-rate charging to high-rate charging. In this case, the activation process took the same amount of time, but as in Comparative Example 1, it was confirmed that the capacity retention rate decreased due to a high C-rate even at the beginning of the activation process.

[0158] Comparative Example 4 corresponds to a case where a single charge was performed at a low C-rate during the activation process to improve the capacity retention rate. In this case, particle cracking on the electrode surface was minimized and the capacity retention rate was excellent, but the activation process time was prolonged to 15 hours, which was confirmed to cause problems in mass production of batteries.

[0159] Comparative Example 5 corresponds to a case where the activation process proceeded from high-rate charging to low-rate charging, but the constant current in the first charging step was less than 0.5 C. In this case, the capacity retention rate was high after 200 cycles, but the process time increased to 20 hours when charging up to 4.2 V due to the constant current of less than 0.5 C, which was not suitable for mass production and significantly reduced process efficiency.

[0160] That is, it was confirmed through comparison between the Examples and Comparative Examples that the activation process of the lithium secondary battery according to the present application includes a multi-stage charging process from a low rate to a high rate, which can minimize the activation process time, minimize cracking on the surface of the negative electrode active material layer, and maintain a high capacity retention rate.

Claims

1. preparing an electrode assembly including a silicon-based negative electrode; a positive electrode; and a separator; and activating a lithium secondary battery including the electrode assembly; A method for producing a lithium secondary battery, comprising: the activating step includes charging and discharging the lithium secondary battery; The charging includes multi-stage charging from a high rate charge to a low rate charge, The multi-stage charging includes a first charging step up to an SOC of 25% and a second charging step after charging to an SOC of 25%; the first charging step includes charging at a constant current of 0.5 C or more; the silicon-based negative electrode includes a negative electrode current collector layer; and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer, the negative electrode active material layer includes a negative electrode active material layer composition including a silicon-based active material, The silicon-based active material includes SiOx (x=0).

2. The method of claim 1 , wherein the first charging step comprises charging at a constant current of 0.9 C or more.

3. The method of claim 1 , wherein the second charging after charging to 25% SOC comprises charging at a constant current of 0.5 C or less.

4. 2. The method of claim 1, wherein the activation time is 10 hours or less.

5. The silicon-based active material is a silicon-based active material having a content of SiO based on 100 parts by weight of the silicon-based active material. ｘ The method for producing a lithium secondary battery according to claim 1 , wherein the battery contains 50 parts by weight or more of (x=0).

6. The method for manufacturing a lithium secondary battery according to claim 1 , wherein the silicon-based active material is present in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

7. 6. The method for producing a lithium secondary battery according to claim 5, wherein the negative electrode active material layer composition comprises at least one selected from the group consisting of a negative electrode conductive material and a negative electrode binder.

8. The method for producing a lithium secondary battery according to claim 7 , wherein the negative electrode conductive material comprises a sheet conductive material and a linear conductive material.

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