Negative electrode for lithium secondary battery, method for manufacturing a negative electrode for lithium secondary battery, and lithium secondary battery including a negative electrode

Abstract

The present application relates to a negative electrode for a lithium secondary battery, a method for manufacturing the negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode.

Description

TECHNICAL FIELD

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0184859 filed with the Korean Intellectual Property Office on December 26, 2022, the entire content of which is incorporated herein by reference.

[0002] The present application relates to a negative electrode for a lithium secondary battery, a method for manufacturing the negative electrode for a lithium secondary battery, and a lithium secondary battery comprising the negative electrode. BACKGROUND ART

[0003] The rapid increase in fossil fuel consumption has led to growing demand for the use of alternative energy and clean energy, and as part of this effort, the most actively researched field is power generation and electricity storage utilizing electrochemical reactions.

[0004] Currently, secondary batteries are a typical example of electrochemical devices that utilize such electrochemical energy, and their fields of application are continuously expanding.

[0005] With the development of technology for mobile devices and the increase in demand for such devices, demand for secondary batteries as an energy source has increased sharply. 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 are widely used. In addition, as an electrode for such high-capacity lithium secondary batteries, active research has been conducted on methods for manufacturing high-density electrodes with higher energy density per unit volume.

[0006] Generally, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that intercalates and deintercalates lithium ions released from the positive electrode, and silicon-based particles with high discharge capacity may be used as the negative electrode active material.

[0007] In particular, with the recent demand for high-density energy batteries, research is actively being conducted on methods to increase capacity by using silicon-based compounds such as Si / C and SiOx, which have more than 10 times the capacity of graphite-based materials, as negative electrode active materials. However, while silicon-based compounds, being high-capacity materials, have superior capacity characteristics compared to conventionally used graphite, they rapidly expand in volume during the charging process, disrupting conductive paths and degrading battery performance, thus reducing capacity from the start. Furthermore, with silicon-based negative electrodes, lithium ions cannot be uniformly charged in the depth direction of the negative electrode during repeated charge and discharge cycles, and reactions occur at the surface, accelerating surface degradation. Therefore, improvements in battery cycle performance are necessary.

[0008] Therefore, in order to resolve the aforementioned problems when using silicon-based compounds as negative electrode active materials, various methods are being discussed, such as methods to adjust the driving potential, additionally, methods to further coat a thin film on the active material layer, methods to suppress volume expansion itself such as adjusting the particle size of the silicon-based compound, or the development of binders that control the volume expansion of silicon-based compounds to prevent the conduction path from being interrupted. Research is also being conducted to supplement the lifetime characteristics of silicon-based negative electrodes by using a method of pre-lithifying the silicon-based active material layer to limit the ratio of silicon-based active material used during initial charging and discharging, thereby providing a storage (reservoir) role.

[0009] However, the above method has limitations in its application because it may actually degrade the performance of the battery. There are still limitations to the commercialization of manufacturing negative electrode batteries with a high silicon-based compound content. As the proportion of silicon-based active material in the silicon-based active material layer increases, prelithiation concentrates on the negative electrode surface, which can damage the silicon-based active material on the surface and result in uneven prelithiation, thus hindering improvements in lifespan characteristics.

[0010] Therefore, methods using silicon-based active materials and adding a negative electrode active material layer that acts as a buffer layer are being studied. However, the process of adding an even thinner film layer on top of the silicon-based active material layer, which is already thin for rapid charging, is extremely difficult, and there are problems with the actual process and product production.

[0011] Therefore, research is needed on methods that, when using silicon-based compounds as active materials to improve capacitance characteristics, do not cause a decrease in capacitance characteristics, prevent electrode surface degradation during charge and discharge cycles, thereby improving cycle performance, and also enable more uniform and thinner coating when using a double active material layer. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2009-080971 [Overview of the project] [Problems that the invention aims to solve]

[0013] This application relates to a lithium secondary battery anode that uses a silicon-based active material as the negative electrode while achieving the maximization of capacity characteristics, which is the main reason for using a silicon-based active material, and preventing electrode surface degradation during charging and discharging cycles, which is a problem in the conventional method, and further ensures rapid charging performance and processability by having two uniform negative electrode active material layers that can be coated with a thin film, a method for manufacturing a lithium secondary battery anode, and a lithium secondary battery including the anode. [Means for solving the problem]

[0014] One embodiment of the present specification provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a first negative electrode active material layer provided on one surface or both surfaces of the negative electrode current collector layer; and a second negative electrode active material layer provided on a surface of the first negative electrode active material layer opposite to the surface facing the negative electrode current collector layer, wherein the first negative electrode active material layer comprises a first negative electrode active material layer composition containing a first negative electrode active material, the second negative electrode active material layer comprises a second negative electrode active material layer composition containing a second negative electrode active material, the first negative electrode active material comprises one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), contains 95 parts by weight or more of the SiOx (x=0) based on 100 parts by weight of the first negative electrode active material, the second negative electrode active material comprises a mixture of one or more selected from the group consisting of carbon-based active materials, silicon-based active materials, metal-based active materials capable of forming an alloy with lithium, and lithium-containing nitrides, the second negative electrode active material layer comprises a first surface that is opposite to the surface facing the first negative electrode active material layer of the second negative electrode active material layer; and a second surface facing the first negative electrode active material layer of the second negative electrode active material layer, the first surface and the second surface each include an uneven surface, and the second negative electrode active material layer satisfies the non-uniformity of the following formula 1.

[0015] [Formula 1] 0 μm ≦ |C-(A+B / 2)| ≦ 10 μm In the above formula 1, A represents the maximum distance (μm) between the first surface and the second surface, B represents the minimum distance (μm) between the first surface and the second surface, C represents the average thickness (μm) of the second negative electrode active material layer.

[0016] In another embodiment, there is provided a method for producing a negative electrode for a lithium secondary battery, comprising: preparing a negative electrode current collector layer; applying a first negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer using a coater to form a first negative electrode active material layer; and applying a second negative electrode active material layer composition to a surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer using a coater to form a second negative electrode active material layer, wherein the first negative electrode active material contains one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), contains 95 parts by weight or more of the SiOx (x=0) based on 100 parts by weight of the first negative electrode active material, the second negative electrode active material contains one or more mixtures selected from the group consisting of carbon-based active materials, silicon-based active materials, metal-based active materials capable of forming an alloy with lithium, and lithium-containing nitrides, a coater liquid thickness in the step of applying the first negative electrode active material layer composition to form the first negative electrode active material layer is 50 µm or more and 100 µm or less, and a coater liquid thickness in the step of applying the second negative electrode active material layer composition to the surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer to form the second negative electrode active material layer is 10 µm or more and 60 µm or less.

[0017] Finally, there is provided a lithium secondary battery comprising: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separation membrane provided between the positive electrode and the negative electrode; and an electrolyte.

Effects of the Invention

[0018] A negative electrode for a lithium secondary battery according to an embodiment of the present invention has a double-layer active material layer composed of a first negative electrode active material layer and a second negative electrode active material layer. In particular, the first negative electrode active material contained in the first negative electrode active material layer contains one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), contains 95 parts by weight or more of the SiOx (x=0) based on 100 parts by weight of the first negative electrode active material, and the second negative electrode active material contained in the second negative electrode active material layer contains one or more mixtures selected from the group consisting of carbon-based active materials, silicon-based active materials, metal-based active materials capable of forming an alloy with lithium, and lithium-containing nitrides.

[0019] The negative electrode for lithium secondary batteries according to this application has a double-layer active material layer having the specific composition and content described above. In particular, since the first negative electrode active material layer contains a high content of SiOx (x=0), it retains the advantages of high capacity, high density, and rapid charging. Furthermore, since the second negative electrode active material layer contains silicon-based active material and / or carbon-based active material, electrode surface degradation can be prevented during charge and discharge cycles, and uniformity during pre-lithiation can also be improved.

[0020] In particular, the negative electrode for lithium secondary batteries according to this application is characterized in that the second negative electrode active material layer satisfies the non-uniformity of formula 1. That is, the first negative electrode active material layer has a silicon-based negative electrode and is coated in a thin thickness range, but there was a problem in that it was difficult to form a second negative electrode active material layer as a thin film on top of it. However, when coating is performed by a method such as that of this application (adjustment of the liquid thickness and core thickness of the coater), the non-uniformity of formula 1 is satisfied, and the second negative electrode active material layer can be coated more uniformly and thinly on top of the first negative electrode active material layer.

[0021] Therefore, lithium secondary batteries incorporating this technology are primarily characterized by their optimal capacity characteristics, which are an advantage of Si negative electrodes, along with their satisfying cycle characteristics.

[0022] In short, the negative electrode for lithium secondary batteries according to this application has the advantages of an electrode that uses a high content of Si particles as a single layer active material, but in order to solve the disadvantages of such electrodes, namely surface degradation, uniformity issues during pre-lithiation, and lifespan characteristics, the second negative electrode active material layer is coated more uniformly with a thin film on top of the first negative electrode active material layer, and is characterized by being constructed as a double layer. [Brief explanation of the drawing]

[0023] [Figure 1] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 2] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 3] This figure shows an SEM image of a negative electrode for a lithium secondary battery according to one embodiment of this application. [Figure 4] This is a flowchart illustrating a wet-on-dry process according to one embodiment of this application. [Figure 5] This is a flowchart illustrating a wet-on-wet process according to one embodiment of this application. [Modes for carrying out the invention]

[0024] Before describing the present invention, let us first define some terms.

[0025] In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0026] In this specification, "p~q" means "greater than or equal to p and less than or equal to q".

[0027] In this specification, "specific surface area" is measured by the BET method, specifically calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using a BELSORP-mini II manufactured by BEL Japan. In other words, in this application, BET specific surface area can mean the specific surface area measured by the above measurement method.

[0028] In this specification, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size, central particle size) at the 50% point of the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution by particle size. Alternatively, the particle size distribution 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). When the particles pass through the laser beam, the difference in diffraction patterns due to particle size is measured to calculate the particle size distribution.

[0029] In this specification, the meaning of a polymer containing a monomer as a monomer unit means that the monomer participates in the polymerization reaction and is included as a repeating unit within the polymer. In this specification, when a polymer is said to contain a monomer, this is interpreted as being equivalent to the polymer containing a monomer as a monomer unit.

[0030] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise explicitly stated as "homopolymer."

[0031] In this specification, weight-average molecular weight (Mw) and number-average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers of various degrees of polymerization (standard samples) commercially available for molecular weight measurement. In this specification, molecular weight refers to weight-average molecular weight unless otherwise specified.

[0032] The present invention will be described in detail below with reference to the drawings, so that a person with ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0033] One embodiment of the present specification provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a first negative electrode active material layer provided on one surface or both surfaces of the negative electrode current collector layer; and a second negative electrode active material layer provided on a surface of the first negative electrode active material layer opposite to the surface facing the negative electrode current collector layer, wherein the first negative electrode active material layer comprises a first negative electrode active material layer composition containing a first negative electrode active material, the second negative electrode active material layer comprises a second negative electrode active material layer composition containing a second negative electrode active material, the first negative electrode active material comprises one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and contains 95 parts by weight or more of the SiOx (x=0) based on 100 parts by weight of the first negative electrode active material, the second negative electrode active material comprises a mixture of one or more selected from the group consisting of carbon-based active materials, silicon-based active materials, metal-based active materials capable of forming an alloy with lithium, and lithium-containing nitrides, the second negative electrode active material layer comprises a first surface which is opposite to the surface of the second negative electrode active material layer facing the first negative electrode active material layer; and a second surface of the second negative electrode active material layer facing the first negative electrode active material layer, the first surface and the second surface each include a non-uniform surface, and the second negative electrode active material layer satisfies the non-uniformity of the following formula 1.

[0034] [Formula 1] 0μm≦|C-(A+B / 2)|≦10μm In Formula 1 above, A represents the longest distance (μm) between the first surface and the second surface, B represents the shortest distance (μm) between the first surface and the second surface, C represents the average thickness (μm) of the second negative electrode active material layer.

[0035] The negative electrode for lithium secondary batteries according to this application is characterized in that the second negative electrode active material layer satisfies the non-uniformity of formula 1. That is, the first negative electrode active material layer has a silicon-based negative electrode and is coated in a thin thickness range, but there was a problem in that it was difficult to form the second negative electrode active material layer as a thin film on top of it. However, when coating is performed by the method of this application (adjustment of the liquid thickness and core thickness of the coater), the non-uniformity of formula 1 is satisfied, and the second negative electrode active material layer can be coated more uniformly and thinly on top of the first negative electrode active material layer. In other words, the negative electrode for lithium secondary batteries according to this application has the characteristics of a first negative electrode active material layer having a high capacity, and the uniformity and thickness of the second negative electrode active material layer have been optimized to control the problem of reaction non-uniformity in which the reaction is concentrated only on the electrode surface during charging and discharging of the first negative electrode active material layer, as well as the problem of uniformity during pre-lithification, resulting in excellent durability. As a result, lithium secondary batteries containing this technology are characterized by their ability to satisfy both optimal capacity characteristics and lifespan characteristics, which are advantages of Si negative electrodes.

[0036] Figure 1 shows a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery can be seen, which includes a first negative electrode active material layer 20 and a second negative electrode active material layer 10 on one surface of a negative electrode current collector layer 30. Figure 1 shows that the first negative electrode active material layer is formed on one surface, but it may also be included on both sides of the negative electrode current collector layer. As described above, in one embodiment of the present application, the first negative electrode active material layer may be formed on the entire surface of the negative electrode current collector layer, and the second negative electrode active material layer may be formed on the entire surface of the first negative electrode active material layer.

[0037] Figure 2 shows a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of this application. Specifically, as shown in Figure 2, a first negative electrode active material layer 20 and a second negative electrode active material layer 10 may be formed on both sides of the negative electrode current collector layer 30. Alternatively, the arrangement may be 10>20>30>20>10, and additionally, the arrangement on the opposite side is irrelevant as long as the first negative electrode active material layer and the second negative electrode active material layer are sequentially laminated on only one side of the negative electrode current collector layer, such as 10>20>30>20, 10>20>30>10, 10>20>30>10>20. Preferably, both sides of the negative electrode current collector layer have the same composition, and specifically, they may have a structure of 10>20>30>20>10.

[0038] The negative electrode for lithium secondary batteries of the present invention will be described in more detail below.

[0039] One embodiment of this application provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a first negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a second negative electrode active material layer provided on the side of the first negative electrode active material layer opposite to the side in contact with the negative electrode current collector layer.

[0040] In one embodiment of this 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, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy may be used. Furthermore, fine irregularities may be formed on the surface to strengthen the bonding force of the negative electrode active material, and it may be used in various forms such as film, sheet, foil, net, porous body, foam, nonwoven fabric.

[0041] In one embodiment of this application, the thickness of the negative electrode current collector layer may be 1 μm or more and 100 μm or less.

[0042] However, the thickness may vary variously depending on the type and application of the negative electrode used, and is not limited thereto.

[0043] In one embodiment of the present application, the first negative electrode active material includes one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and based on 100 parts by weight of the first negative electrode active material, may contain 95 parts by weight or more of SiOx (x=0).

[0044] In one embodiment of the present application, the first negative electrode active material includes one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and based on 100 parts by weight of the first negative electrode active material, may contain 95 parts by weight or more of SiOx (x=0), preferably 97 parts by weight or more of SiOx (x=0), more preferably 99 parts by weight or more, and may contain 100 parts by weight or less.

[0045] In one embodiment of the present application, pure silicon (Si) particles may be particularly used as the first negative electrode active material. Using pure silicon (Si) as the first negative electrode active material may mean that, as described above, when the first negative electrode active material is based on a total of 100 parts by weight, pure Si particles (SiOx (x=0)) that are not bonded to other particles or elements are contained within the above range.

[0046] In one embodiment of the present application, the first negative electrode active material may consist of SiOx (x=0).

[0047] The first negative electrode active material layer according to the present application contains the first negative electrode active material, and specifically contains pure silicon particles containing 95 parts by weight or more of SiOx (x=0). When a high content of pure silicon particles is contained, the capacity characteristics are excellent, but a decrease in life characteristics occurs due to non-uniform surface reaction caused thereby. Therefore, the problem described above is solved by including the second negative electrode active material layer according to the present invention in a specific loading weight.

[0048] On the other hand, the average particle size (D50) of the first negative electrode active material of the present invention may be 3 μm to 10 μm, more specifically 4 μm to 8 μm, and more specifically 5 μm to 7 μm. When the average particle size falls within the above range, the specific surface area of ​​the particles falls within an appropriate range, and the viscosity of the negative electrode slurry is formed to be within an appropriate range. This facilitates the dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the first negative electrode active material is greater than or equal to the lower limit range, the contact area between the silicon particles and the conductive material is excellent due to the composite of the conductive material and the binder in the negative electrode slurry, increasing the likelihood that the conductive network will be sustained and increasing the capacity retention rate. On the other hand, when the average particle size satisfies the above range, excessively large silicon particles are excluded, and the surface of the negative electrode is formed smoothly, thereby preventing the phenomenon of non-uniform current density during charging and discharging.

[0049] In one embodiment of this application, the first negative electrode active material typically has a specific BET specific surface area. The BET specific surface area of ​​the first negative electrode active material is preferably 0.01 m². 2 / g~150.0m 2 / g, comfortably, 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 The value is / g. The BET specific surface area is measured according to DIN 66131 (using nitrogen).

[0050] In one embodiment of this application, the first negative electrode active material may exist, for example, in a crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or multi-piece particles. Alternatively, the silicon particles may have a fibrous structure or exist in the form of a silicon-containing thin film or coating, but these are less preferred.

[0051] In one embodiment of the present application, the first negative electrode active material may have a non-spherical shape, and the degree of spheroidization 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.

[0052] In the present application, the circularity is determined by the following formula A-1, wherein A is the area and P is the boundary perimeter.

[0053] [Formula A-1] 4πA / P 2

[0054] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the content of the first negative electrode active material is 60 parts by weight or more based on 100 parts by weight of the first negative electrode active material layer composition.

[0055] In another embodiment, the first negative electrode active material may be contained in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and may be contained in an amount of 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 80 parts by weight or less, based on 100 parts by weight of the first negative electrode active material layer composition.

[0056] In the first negative electrode active material layer composition according to the present application, even when the first negative electrode active material with significantly high capacity is used within the above range, by jointly using the second negative electrode active material layer described later, the capacity performance of the entire negative electrode is not reduced, and the problems of surface degradation during charging and discharging, uniformity during prelithiation, and lifetime characteristics are solved.

[0057] Conventionally, it was common to use only graphite-based compounds as the negative electrode active material. Recently, as the demand for high-capacity batteries has increased, attempts to mix and use silicon-based compounds to increase capacity have been increasing. However, in the case of silicon-based compounds, there is a limitation that the volume expands rapidly during charging and discharging, damages the conductive paths formed in the negative electrode active material layer, and conversely reduces the performance of the battery.

[0058] Accordingly, in one embodiment of this application, the first negative electrode active material layer composition may further include one or more selected from the group consisting of a first negative electrode conductive material and a first negative electrode binder.

[0059] In this case, the first negative electrode conductive material and the first negative electrode binder contained in the first negative electrode active material layer composition may be those used in the industry without limitation.

[0060] In one embodiment of this application, the first negative electrode conductive material may be any substance commonly used in the industry, and may specifically include one or more selected from the group consisting of point conductive materials, planar conductive materials, and linear conductive materials.

[0061] In one embodiment of this application, the point-shaped conductive material can be used to improve conductivity in the negative electrode and means a point-shaped or spherical conductive material that is conductive without inducing a chemical change. Specifically, the point-shaped 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 contains carbon black in terms of embodying high conductivity and having excellent dispersibility.

[0062] In one embodiment of this application, the point conductive material has a BET specific surface area of ​​40 m². 2 / g or more 70m 2 It may be less than or equal to / g, preferably 45m 2 / g or more 65m 2 / g or less, more comfortably, 50m 2 / g or more 60m 2 It may be less than / g.

[0063] In one embodiment of this application, the particle size of the dot-like conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0064] In one embodiment of this application, the first negative electrode conductive material may include a planar conductive material.

[0065] The planar conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, and at the same time suppress the disruption of the conductive path due to volume expansion. The planar conductive material may also be referred to as a plate-type conductive material or a bulk-type conductive material.

[0066] In one embodiment of this application, the planar conductive material may include at least one selected from the group consisting of plate-type graphite, graphene, graphene oxide, and graphite flakes, and preferably plate-type graphite.

[0067] In one embodiment of this application, the average particle size (D50) of the planar conductive material may be 2 μm to 7 μm, more specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the above range is satisfied, the particle size is sufficient, so dispersion becomes easy without the viscosity of the negative electrode slurry increasing too much. Therefore, the dispersion effect is superior when dispersion is performed using the same apparatus and time.

[0068] In one embodiment of this application, a negative electrode composition is provided in which the planar conductive material has 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.

[0069] In one embodiment of this application, the planar conductive material may be a planar conductive material with a high specific surface area and a high BET specific surface area; or a planar conductive material with a low specific surface area.

[0070] In one embodiment of this application, the planar conductive material may be any planar conductive material with a high specific surface area or a planar conductive material with a low specific surface area without limitation. In particular, the planar conductive material according to this application may be affected to some extent by dispersion in terms of electrode performance, and it is especially preferable to use a planar conductive material with a low specific surface area that does not cause dispersion problems.

[0071] In one embodiment of this application, the planar conductive material has a BET specific surface area of ​​5 m². 2 It may be more than / g.

[0072] In another embodiment, the planar conductive material has a BET specific surface area of ​​5 m². 2 / g or more 500m 2 It may be less than / g, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 / g is also acceptable.

[0073] In another embodiment, the planar conductive material is a planar conductive material with a high specific surface area, and the BET specific surface area is 50 m². 2 / g or more 500m 2 Less than or equal to / g, preferably 80m 2 / g or more 300m 2 Less than / g, more comfortably, 100m 2 / g or more 300m 2 It can satisfy the range of / g or less.

[0074] In another embodiment, the planar conductive material is a planar conductive material with a low specific surface area, and the BET specific surface area is 5m². 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 It can satisfy the range of / g or less.

[0075] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may contain multiple carbon nanotube units. Specifically, unless otherwise specified, "bundle type" here refers to a secondary shape in which multiple carbon nanotube units are arranged in parallel with substantially the same orientation along their longitudinal axes, or are twisted into a bundle or rope. The carbon nanotube units have a graphite sheet that is cylindrical with a nanoscale diameter and has an sp2 bond structure. In this case, depending on the angle and structure in which the graphite sheet is wound, it can exhibit conductive or semiconductor properties. Compared to entangled type carbon nanotubes, the bundle-type carbon nanotubes can be uniformly dispersed during the manufacture of the negative electrode, smoothly forming a conductive network within the negative electrode and improving the conductivity of the negative electrode.

[0076] In one embodiment of this application, the first negative electrode conductive material can satisfy the requirement of being 10 parts by weight or more and 40 parts by weight or less, based on 100 parts by weight of the first negative electrode active material layer composition.

[0077] In another embodiment, the first negative electrode conductive material may be present in an amount of 1 to 40 parts by weight, preferably 3 to 30 parts by weight, and more preferably 5 to 25 parts by weight, based on 100 parts by weight of the first negative electrode active material layer composition.

[0078] In one embodiment of this application, the first negative electrode conductive material includes a point conductive material, a planar conductive material, and a linear conductive material, wherein the ratio of point conductive material:planar conductive material:linear conductive material can satisfy 1:1:0.01 to 1:1:1.

[0079] In one embodiment of this application, the point-shaped conductive material can satisfy the range of 1 part by weight or more and 60 parts by weight or less, preferably 5 parts by weight or more and 50 parts by weight or less, and more preferably 10 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the first negative electrode conductive material.

[0080] In one embodiment of this application, the planar conductive material can satisfy the range of 1 part by weight or more and 60 parts by weight or less, preferably 5 parts by weight or more and 50 parts by weight or less, and more preferably 10 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the first negative electrode conductive material.

[0081] In one embodiment of this application, the linear conductive material can satisfy the range of 0.01 parts by weight or more and 10 parts by weight or less, preferably 0.05 parts by weight or more and 8 parts by weight or less, and more preferably 0.1 parts by weight or more and 5 parts by weight or less, based on 100 parts by weight of the first negative electrode conductive material.

[0082] In one embodiment of this application, the first negative electrode conductive material may include a linear conductive material and a planar conductive material.

[0083] In one embodiment of this application, the first negative electrode conductive material includes a linear conductive material and a planar conductive material, and the weight ratio of the linear conductive material to the planar conductive material can satisfy 0.01:1 to 0.1:1.

[0084] In one embodiment of this application, by satisfying the above composition and ratio of the first negative electrode conductive material, the life characteristics of the conventional lithium secondary battery are not significantly affected, the number of charge and discharge points increases, and the battery has the characteristic of having excellent output characteristics at a high C-rate.

[0085] In the case of the first negative electrode conductive material according to this application, it has a completely different configuration from the conductive material applied to the positive electrode. That is, in the case of the first negative electrode conductive material according to this application, it plays a role in controlling the contact between silicon-based active materials, which experience very large volume expansion of the electrodes due to charging and discharging, while the positive electrode conductive material plays a role in providing partial conductivity while acting as a buffer when rolled, and its configuration and role are completely different from the negative electrode conductive material of the present invention.

[0086] Furthermore, the first negative electrode conductive material in this application is applied to silicon-based active materials and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes with graphite-based active materials simply have smaller particles compared to the active material, and thus have the properties of improving output characteristics and imparting some conductivity. This is completely different in structure and role from the first negative electrode conductive material applied together with silicon-based active materials as in the present invention.

[0087] In one embodiment of this application, the first negative electrode binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, 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 the hydrogens of these substances are substituted with Li, Na, or Ca, or may contain a variety of copolymers thereof.

[0088] The first negative electrode binder according to one embodiment of this application plays a role in controlling the first negative electrode active material and the first negative electrode conductive material in order to prevent twisting and structural deformation of the negative electrode structure during the volume expansion and relaxation of the first negative electrode active material. Any general binder can be applied as long as it fulfills the above role, and specifically, an aqueous binder may be used, and more specifically, a PAM-based binder may be used.

[0089] In one embodiment of this application, the first negative electrode binder may be included in an amount of 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the first negative electrode active material layer composition, and may be included in an amount of 5 parts by weight or more, or 10 parts by weight or more.

[0090] Compared to conventional carbon-based anodes, when a silicon-based anode is used, a water-based binder may be applied in the aforementioned weight portion, and a point-type conductive material may be used. Due to the aforementioned characteristics, the point-type conductive material has hydrophobic properties, resulting in superior bonding strength with the conductive material / binder.

[0091] In one embodiment of this application, the second negative electrode active material may include a mixture of one or more materials selected from the group consisting of carbon-based active materials, silicon-based active materials, metallic active materials that can be alloyed with lithium, and lithium-containing nitrides.

[0092] In another embodiment, the second negative electrode active material may include a mixture of one to three materials selected from the group consisting of carbon-based active materials, silicon-based active materials, metallic active materials that can be alloyed with lithium, and lithium-containing nitrides.

[0093] In another embodiment, the second negative electrode active material may include a carbon-based active material and a silicon-based active material.

[0094] In another embodiment, the second negative electrode active material may include a silicon-based active material.

[0095] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the second negative electrode active material comprises one or more mixtures selected from the group consisting of carbon-based active materials, silicon-based active materials, metal-based active materials capable of forming an alloy with lithium, and lithium-containing nitrides, and an amount of the silicon-based active material is 50 parts by weight or more and 100 parts by weight or less based on 100 parts by weight of the second negative electrode active material.

[0096] In another embodiment, the second negative electrode active material comprises one or more mixtures selected from the group consisting of carbon-based active materials, silicon-based active materials, metal-based active materials capable of forming an alloy with lithium, and lithium-containing nitrides, and an amount of the silicon-based active material may be 50 parts by weight or more and 100 parts by weight or less, preferably 70 parts by weight or more and 100 parts by weight or less, more preferably 80 parts by weight or more and 100 parts by weight or less based on 100 parts by weight of the second negative electrode active material.

[0097] In one embodiment of the present application, the silicon-based active material contained in the second negative electrode active material may comprise one or more selected from the group consisting of SiOx (0<x<2), SiC, and Si alloys.

[0098] In one embodiment of the present application, the silicon-based active material contained in the second negative electrode active material comprises one or more selected from the group consisting of SiOx (0<x<2), SiC, and Si alloys, and may contain 1 part by weight or more of SiOx (0<x<2) based on 100 parts by weight of the second negative electrode active material.

[0099] In another embodiment, the silicon-based active material contained in the second negative electrode active material comprises one or more selected from the group consisting of SiOx (0<x<2), SiC, and Si alloys, and may contain 1 part by weight or more, 10 parts by weight or more, and 99 parts by weight or less of SiOx (0<x<2) based on 100 parts by weight of the second negative electrode active material.

[0100] In another embodiment, the silicon-based active material contained in the second negative electrode active material may comprise SiOx (0<x<2).

[0101] In another embodiment, the silicon-based active material included in the second negative electrode active material may include SiC.

[0102] As described above, the negative electrode for lithium secondary batteries according to this application includes the second negative electrode active material in the second negative electrode active material layer. This allows the aforementioned first negative electrode active material to be included while maintaining high capacity and high density characteristics, and the second negative electrode active material acts as a buffer layer, thereby solving problems such as surface degradation during charging and discharging, uniformity during pre-lithiation, and lifespan characteristics.

[0103] As an example, the second negative electrode active material layer of this application can act as a buffer layer. Electrodes containing Si active material exhibit superior capacitance characteristics compared to electrodes containing SiO or carbon-based active material. However, electrodes containing Si active material experience concentrated degradation on the surface of the negative electrode active material layer due to rapid reaction with Li ions during charging and discharging. This also occurs during the pre-lithiation process in which lithium ions are pre-included in the negative electrode active material layer. In the pre-lithiation process, a buffer layer is used to prevent direct contact between the Si-based electrode and lithium, thereby preventing surface degradation. Therefore, the second negative electrode active material layer of the present invention has the characteristic of exhibiting the same role and effect as a buffer layer in the pre-lithiation process.

[0104] In one embodiment of this application, the carbon-based active material is typically natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, fullerenes, or activated carbon, and is not limited to those commonly used as carbon materials for lithium secondary batteries. Specifically, it can be processed into spherical or point-like forms.

[0105] In one embodiment of this application, the planar conductive material used as the first negative electrode conductive material has a structure and role different from that of a carbon-based active material generally used as a negative electrode active material. Specifically, the carbon-based active material used as a negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or point-like form to facilitate the storage and release of lithium ions.

[0106] On the other hand, the planar conductive material used as the first negative electrode conductive material is a substance having a planar or plate-like form, and can be represented as plate-type graphite. In other words, it is a substance included to maintain conductive pathways within the negative electrode active material layer, and does not play a role in lithium storage and release, but rather refers to a substance that secures conductive pathways in a planar form within the negative electrode active material layer.

[0107] In other words, the use of plate-shaped graphite as a conductive material in this application means that it was processed into a planar or plate-shaped form and used not to serve as a storage or release mechanism for lithium, but rather as a material to secure a conductive path. In this case, the negative electrode active material included together has high capacity characteristics for lithium storage and release, and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0108] On the other hand, in this application, the use of a carbon-based active material as the active material means that it was processed into a point-like or spherical shape and used as a substance that plays a role in storing or releasing lithium.

[0109] In other words, in one embodiment of this application, the carbon-based active material, artificial graphite or natural graphite, has a BET specific surface area of ​​0.1 m². 2 / g or more 4.5m 2 It can satisfy the range of less than / g. In addition, plate-type graphite, which is a planar conductive material, has a surface form and a BET specific surface area of ​​5m². 2 It may be more than / g.

[0110] The aforementioned metallic active material may be a compound containing one or more metallic elements selected from the group consisting of Al, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt, Ti, Sb, Ga, Mn, Fe, Co, Ni, Cu, Sr, and Ba, as a typical example. These metallic compounds can be used in any form, such as elements, alloys, oxides (TiO2, SnO2, etc.), nitrides, sulfides, borides, or alloys with lithium, but elements, alloys, oxides, and alloys with lithium can be made to have high capacity.

[0111] In one embodiment of this application, the negative electrode for a lithium secondary battery is provided, wherein the second negative electrode active material is present in an amount of 60 parts by weight or more, based on 100 parts by weight of the second negative electrode active material layer composition.

[0112] In another embodiment, the second negative electrode active material may be 60 parts by weight or more, based on 100 parts by weight of the second negative electrode active material layer composition, and can satisfy the requirements of 100 parts by weight or less, or 99 parts by weight or less.

[0113] The second negative electrode active material layer composition according to this application has lower capacity characteristics than the first negative electrode active material, but by using a second negative electrode active material within the aforementioned range that exhibits less particle cracking due to charging and discharging, it is possible to suppress surface reactions of the negative electrode without reducing the capacity performance of the negative electrode and thereby enhance its lifespan characteristics.

[0114] In one embodiment of this application, the second negative electrode active material layer composition further comprises one or more selected from the group consisting of a second negative electrode conductive material and a second negative electrode binder, providing a negative electrode for a lithium secondary battery.

[0115] In this case, the same content as that described above for the first negative electrode conductive material and the first negative electrode binder may be applied to the second negative electrode conductive material and the second negative electrode binder.

[0116] In one embodiment of this application, the second negative electrode active material layer includes a first surface opposite to the surface of the second negative electrode active material layer facing the first negative electrode active material layer; and a second surface of the second negative electrode active material layer facing the first negative electrode active material layer, wherein the first surface and the second surface each include a non-uniform surface.

[0117] In this case, the fact that the first and second surfaces include non-uniform surfaces means that the surface or interface is not formed to be ideally flat without any irregularities, but rather includes some irregularities and curves.

[0118] In other words, when a composition is coated, its surface or interface is not formed to be ideally flat, but rather to have an uneven shape, which can be interpreted as meaning that the first and second surfaces include non-uniform surfaces.

[0119] Figure 3 shows an SEM image of a negative electrode for a lithium secondary battery according to one embodiment of this application. Specifically, the surface indicated by the red dotted line (represented as a triangle) corresponds to the second surface of the second negative electrode active material layer, and the surface indicated by the yellow dotted line (represented as a circle) corresponds to the first surface. In this case, the inclusion of non-uniform surfaces can be interpreted as meaning that the yellow and red dotted lines do not form straight lines but include bends.

[0120] In one embodiment of this application, the second negative electrode active material layer provides a negative electrode for a lithium secondary battery that satisfies the non-uniformity of the following formula 1.

[0121] [Formula 1] 0μm≦│C-(A+B / 2)│≦10μm In the above formula 1, A represents the longest distance (μm) between the first surface and the second surface. B represents the shortest distance (μm) between the first surface and the second surface. C represents the average thickness (μm) of the second negative electrode active material layer.

[0122] In one embodiment of this application, A means the longest distance (μm) between the first surface and the second surface. Specifically, A can mean the longest distance among all distances perpendicular to the thickness direction between the first surface and the second surface.

[0123] In one embodiment of this application, B means the shortest distance (μm) between the first surface and the second surface. Specifically, A can mean the shortest distance among all distances perpendicular to the thickness direction between the first surface and the second surface.

[0124] Furthermore, C is a value measured by averaging all distances perpendicular to the thickness direction of the first and second surfaces, and this is defined as the average thickness of the second negative electrode active material layer.

[0125] In this application, if the first negative electrode active material layer and the second negative electrode active material layer are ideally coated, the first and second surfaces are both formed as uniform surfaces, and in this case, the values ​​of A and B may be the same. That is, it can be said that the shortest distance and the longest distance are both uniformly formed in the same form. In this case, if the first negative electrode active material layer and the second negative electrode active material layer are both uniformly coated, the shortest distance, the longest distance, and the average thickness of the second negative electrode active material layer will all have the same value, and equation 1 will satisfy the value of 0.

[0126] In one embodiment of this application, the fact that the second negative electrode active material layer satisfies the range of formula 1 means that the second negative electrode active material layer is more uniformly coated on top of the first negative electrode active material layer.

[0127] In one embodiment of this application, formula 1 can satisfy 0 μm ≤ │C-(A+B / 2)│ ≤ 10 μm, preferably 0.5 μm ≤ │C-(A+B / 2)│ ≤ 8 μm, and more preferably 0.5 μm ≤ │C-(A+B / 2)│ ≤ 5 μm.

[0128] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein A is 5 μm or more and 25 μm or less in thickness, and C is 5 μm or more and 20 μm or less in thickness.

[0129] In one embodiment of this application, A is 5 μm or more and 25 μm or less, preferably 5.5 μm or more and 20 μm or less, and more preferably 6 μm or more and 19 μm or less.

[0130] In one embodiment of this application, B is 3 μm or more and 10 μm or less, preferably 4 μm or more and 9 μm or less, and more preferably 7 μm or more and 9 μm or less.

[0131] In one embodiment of this application, C can satisfy the range of 5 μm to 20 μm, preferably 5.5 μm to 18 μm, and more preferably 6 μm to 15 μm.

[0132] In particular, the negative electrode for lithium secondary batteries according to this application is characterized in that the second negative electrode active material layer satisfies the non-uniformity of formula 1. That is, the first negative electrode active material layer has a silicon-based negative electrode and is coated in a thin thickness range, but there was a problem in that it was difficult to form the second negative electrode active material layer as a thin film on top of it. However, when coating is performed by the manufacturing method described later (adjustment of the liquid thickness and core thickness of the coater), the non-uniformity of formula 1 is satisfied, and the second negative electrode active material layer can be coated more uniformly and thinly on top of the first negative electrode active material layer. As a result, it is possible to ensure rapid charging performance and to effectively control surface degradation reactions, thereby simultaneously ensuring life characteristics.

[0133] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the average thickness of the second negative electrode active material layer is 10% or more and 40% or less of the total thickness of the first negative electrode active material layer and the second negative electrode active material layer.

[0134] In another embodiment, the thickness of the first negative electrode active material layer may be 10 μm or more and 200 μm or less, more specifically 15 μm or more and 190 μm or less, and more specifically 20 μm or more and 170 μm or less.

[0135] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the average surface roughness (Sa) of the first surface is 700 nm or less.

[0136] In another embodiment, the average surface roughness (Sa) of the first surface may be 700 nm or less, preferably 680 nm or less, more preferably 660 nm or less, and may be 400 nm or more, preferably 500 nm or more, more preferably 600 nm or more.

[0137] In one embodiment of this application, average surface roughness can mean surface roughness. Average surface roughness indicates the degree of surface roughness and can indicate the degree of surface irregularities of the material in question.

[0138] In one embodiment of this application, the viscosity of the first negative electrode active material layer composition is 2,000 cPs or more and 15,000 cPs or less at a shear rate of 2.5 (1 / s), and the viscosity of the second negative electrode active material layer composition is lower than that of the first negative electrode active material layer composition, thereby providing a negative electrode for a lithium secondary battery.

[0139] In another embodiment, the viscosity of the first negative electrode active material layer composition can satisfy a shear viscosity of 2,000 cPs or more and 15,000 cPs or less, preferably 2,300 cPs or more and 14,000 cPs or less, and more preferably 2,500 cPs or more and 12,000 cPs or less, at a shear rate of 2.5 (1 / s).

[0140] In this case, only when the viscosity of the second negative electrode active material layer composition is maintained lower than the viscosity of the first negative electrode active material layer composition can two negative electrode active material layers be formed as in the present application. More specifically, although the viscosity of the second negative electrode active material layer composition is lower than the viscosity of the first negative electrode active material layer composition, it must be formed at the same viscosity level as the first negative electrode active material layer composition.

[0141] In one embodiment of the present application, the negative electrode for a lithium secondary battery may be prelithiated.

[0142] The negative electrode for a lithium secondary battery according to the present application is composed of two layers, and particularly the second negative electrode active material layer that satisfies specific non-uniformity serves as a buffer layer during prelithiation, and also functions to enable uniform lithiation to occur in the depth direction of the electrode during cyclic charging and discharging.

[0143] A method for producing a negative electrode for a lithium secondary battery, comprising: preparing a negative electrode current collector layer; applying a first negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer using a coater to form a first negative electrode active material layer; and applying a second negative electrode active material layer composition to a surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer using a coater to form a second negative electrode active material layer, wherein the first negative electrode active material includes one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and based on 100 parts by weight of the first negative electrode active material, contains 95 parts by weight or more of SiOx (x=0), the second negative electrode active material contains a mixture of one or more selected from the group consisting of carbon-based active materials, silicon-based active materials, metal-based active materials capable of alloying with lithium, and lithium-containing nitrides, the thickness of the coater solution in the step of applying the first negative electrode active material layer composition to form the first negative electrode active material layer is 50 µm or more and 100 µm or less, and the thickness of the coater solution in the step of applying the second negative electrode active material layer composition to the surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer to form the second negative electrode active material layer is 10 µm or more and 60 µm or less.

[0144] In the method for manufacturing the negative electrode, the composition and content included in each step may be as described above.

[0145] In other words, as described above, when each composition is applied using a coater to form the first negative electrode active material layer and the second negative electrode active material layer, and when the liquid thickness of the coater is satisfied as described above, it has been found that the second negative electrode active material layer can be applied thinly and uniformly in the form of a thin film on top of the first negative electrode active material layer, thereby enabling the manufacture of a negative electrode for a lithium secondary battery that satisfies the above-mentioned formula 1.

[0146] In one embodiment of this application, the thickness of the coater liquid can have the same meaning as the thickness of the coating liquid, and can mean the liquid thickness of the first negative electrode active material layer composition and the second negative electrode active material layer composition themselves that are coated.

[0147] In one embodiment of this application, a method for manufacturing a negative electrode for a lithium secondary battery is provided, wherein the core thickness of the coater is 0.4T or more and 2T or less.

[0148] The present invention applies a second negative electrode active material layer to the first negative electrode active material layer, which incorporates the advantages of pure silicon (Pure Si) active material while covering its disadvantages. In particular, the second negative electrode active material layer must embody a thin film coating. However, it is a difficult challenge to coat the second negative electrode active material layer thinly and uniformly on top of the thin first negative electrode active material layer. However, as described above, it can be seen that by adjusting the liquid thickness and core thickness of the coater to the aforementioned range, it is possible to manufacture a negative electrode for lithium secondary batteries that satisfies the uniformity and thickness described in this application.

[0149] In one embodiment of this application, the present invention provides a step of forming a first negative electrode active material layer by applying a first negative electrode active material layer composition to one or both sides of the negative electrode current collector layer using a coater.

[0150] In other words, the aforementioned step is the step of forming an active material layer on the negative electrode current collector layer, and can be said to be the step of forming the active material layer on the surface (lower layer) that is in contact with the negative electrode current collector layer in the double layer structure.

[0151] In one embodiment of this application, applying the first negative electrode active material layer composition includes the step of applying and drying a first negative electrode slurry containing the first negative electrode active material layer composition and a negative electrode slurry solvent.

[0152] In this case, the solid content of the first negative electrode slurry can be within the range of 10% to 40%.

[0153] In one embodiment of this application, the step of forming the first negative electrode active material layer may include the steps of mixing the first negative electrode slurry and coating one or both sides of the negative electrode current collector layer with the mixed first negative electrode slurry using a coater, wherein coating methods commonly used in the industry may be used for the coating.

[0154] In one embodiment of this application, a step is provided in which a second negative electrode active material layer composition is applied using a coater to the surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer to form a second negative electrode active material.

[0155] In other words, the above step is the step of forming a second negative electrode active material layer on the first negative electrode active material layer, and can be said to be the step of forming the active material layer on the surface (upper layer) of the double layer structure that is away from the negative electrode current collector layer.

[0156] In one embodiment of this application, applying the second negative electrode active material layer composition includes the step of applying and drying a second negative electrode slurry containing the second negative electrode active material layer composition and a negative electrode slurry solvent.

[0157] In this case, the solid content of the second negative electrode slurry can be within the range of 10% to 40%.

[0158] In one embodiment of this application, a method for manufacturing a negative electrode for a lithium secondary battery is provided, wherein the step of forming the second negative electrode active material layer includes the steps of: mixing the second negative electrode slurry; and coating the mixed second negative electrode slurry with the surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer.

[0159] The aforementioned coating may be a coating method commonly used in this industry.

[0160] The step of forming the second negative electrode active material layer can be similarly described in the description of the step of forming the first negative electrode active material layer.

[0161] One embodiment of this application provides a method for manufacturing a negative electrode for a lithium secondary battery, wherein the step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet-on-dry step; or a wet-on-wet step.

[0162] In one embodiment of this application, the wet-on-dry step means a step of applying a first negative electrode active material layer composition, partially or completely drying it, and then applying a second negative electrode active material layer composition on top of it.

[0163] Figure 4 is a flowchart showing a wet-on-dry process according to one embodiment of this application. Specifically, in the wet-on-dry process, a first negative electrode slurry mixture (first negative electrode active material, first negative electrode conductive material, first negative electrode binder, first solvent) is prepared and applied to the negative electrode current collector layer. Then, the first negative electrode slurry mixture is dried to form the first negative electrode active material layer. Subsequently, a second negative electrode slurry mixture is prepared, applied to the first negative electrode active material layer, and dried to form the second negative electrode active material layer. After that, each layer can be rolled and pressed to form the negative electrode for a lithium secondary battery according to this application.

[0164] In one embodiment of this application, the wet-on-wet process means a process in which a first negative electrode active material layer composition is applied, and then, without drying, a second negative electrode active material layer composition is applied on top of it.

[0165] Figure 5 is a flowchart showing a wet-on-wet process according to one embodiment of the present application. Specifically, in the wet-on-wet process, a first negative electrode slurry mixture is prepared and applied to the negative electrode current collector layer, and at the same time, a second negative electrode slurry mixture is prepared and applied to the first negative electrode slurry mixture, after which the first and second negative electrode slurry mixtures are dried. After that, each layer can be rolled and pressed to form the negative electrode for a lithium secondary battery according to the present application.

[0166] Subsequently, the negative electrode obtained by the wet-on-dry or wet-on-wet process can be slit twice using a single coating die.

[0167] In particular, the wet-on-dry process involves applying the first negative electrode active material layer composition, allowing it to dry completely, and then applying the second negative electrode active material layer composition on top of it. Through this process, the first negative electrode active material layer and the second negative electrode active material layer can have a clear boundary. This allows the compositions contained in the first and second negative electrode active material layers to remain separate and to form a double layer.

[0168] In one embodiment of this application, the negative electrode slurry solvent can be used without limitation as long as it can dissolve the first negative electrode active material layer composition and the second negative electrode active material layer composition, and specifically, water or NMP may be used.

[0169] As a result of the aforementioned wet-on-wet process, a bonding region can be formed in which the first negative electrode active material layer and the second negative electrode active material layer are mixed. In this case, for the wet-on-wet process to be carried out, the viscosity of the first negative electrode active material layer composition must be lower than the viscosity of the second negative electrode active material layer composition, and in this case, mutual mixing can occur between the bonding region and the process.

[0170] In this application, the interface between the two layers is clearly separated when the second negative electrode active material layer is formed after the first negative electrode active material layer has been dried (wet-on-dry process). Furthermore, when the second negative electrode active material layer is applied while the first negative electrode active material layer composition is not completely dry (the first and second negative electrode active material layer compositions are applied simultaneously), mixing occurs at the interface between the two layers, forming a bonding region.

[0171] One embodiment of this application provides a method for manufacturing a negative electrode for a lithium secondary battery, which includes a step of pre-lithiation of a negative electrode having a first negative electrode active material layer and a second negative electrode active material layer formed on the negative electrode current collector layer, wherein the step of pre-lithiation of the negative electrode includes a lithium electroplating step; a lithium metal transfer step; a lithium metal deposition step; or a stabilized lithium metal powder (SLMP) coating step.

[0172] As described above, by having the second negative electrode active material layer contain the aforementioned second negative electrode active material and be provided with a mixed composition of silicon-based active material and carbon-based active material, the advantages of rapid charging can be retained. In particular, in the case of the second negative electrode active material, since it has a mixed composition and is highly irreversible, it can also have advantageous effects during the pre-lithiation process in which the negative electrode is pre-charged. Compared to simply applying only the first negative electrode active material layer, having the second negative electrode active material having the aforementioned composition in the second negative electrode active material layer allows for a uniform pre-lithiation process at the upper end of the negative electrode, thereby improving the lifespan.

[0173] In one embodiment of this application, the porosity of the first negative electrode active material layer and the second negative electrode active material layer can be in the range of 10% to 60%.

[0174] In another embodiment, the porosity of the first negative electrode active material layer and the second negative electrode active material layer can be in the range of 10% to 60%, preferably 20% to 50%, and more preferably 30% to 45%.

[0175] The porosity is varied by the composition and content of the active material, conductive material, and binder contained in the first negative electrode active material layer and the second negative electrode active material layer, thereby ensuring that the electrical conductivity and resistance at the electrodes are within an appropriate range.

[0176] One embodiment of this application provides a lithium secondary battery comprising: a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separation membrane provided between the positive electrode and the negative electrode; and an electrolyte.

[0177] A secondary battery according to one embodiment of this specification may include the negative electrode for lithium secondary batteries described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator membrane interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed explanation will be omitted.

[0178] The positive electrode may include a positive electrode current collector layer and a positive electrode active material layer formed on the positive electrode current collector layer and containing a positive electrode active material.

[0179] In the positive electrode, the positive electrode current collector layer is not particularly limited as long as it is conductive without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector layer may also have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0180] 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; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented as O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.3); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 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); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples but are not limited to these. The positive electrode may be Li metal.

[0181] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0182] In this case, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitations as long as it has electronic conductivity in the battery without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more may be used.

[0183] Furthermore, the positive electrode binder plays a role in improving adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used.

[0184] The separation membrane separates the negative and positive electrodes and provides a pathway for lithium ions to move. Generally, any membrane used as a separation membrane in secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte and excellent moisture-absorbing capacity for the electrolyte are particularly preferred. Specifically, porous polymer films, such as those made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof, may be used. Alternatively, ordinary porous nonwoven fabrics, such as those made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separation membranes containing ceramic components or polymeric substances to ensure heat resistance or mechanical strength may be used, and they may be selectively used in single-layer or multi-layer structures.

[0185] Examples of the aforementioned electrolytes 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 the manufacture of lithium secondary batteries.

[0186] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0187] As the non-aqueous organic solvent, for example, 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, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate may be used.

[0188] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are suitable for use because they are high-viscosity organic solvents with high dielectric constants that readily dissociate lithium salts. Furthermore, by mixing such cyclic carbonates with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate ratios, electrolytes with high electrical conductivity can be produced, making them even more suitable for use.

[0189] The metal salt may be a lithium salt, which is a substance that dissolves easily in the non-aqueous electrolyte, for example, F as the anion of the lithium salt. - 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 - You may use one or more selected from the group consisting of the following:

[0190] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexalic acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0191] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell, and a battery pack including the same. Since the battery module and battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they may be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems. [Examples]

[0192] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative of the present description, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the present description and the technical concept, and such variations and modifications naturally fall within the scope of the claims.

[0193] <Manufacturing example> <Manufacturing of negative electrodes> [Example 1] [Manufacturing of the first negative electrode active material layer] As a silicon-based active material, Si (average particle size (D50): 5 μm), a first conductive material, a second conductive material, and polyacrylamide as a binder were added to distilled water as a solvent for forming the negative electrode slurry in a weight ratio of 80:9.5:0.5:10 to produce a first negative electrode slurry (solid content concentration 25% by weight).

[0194] The first conductive material is a plate-shaped graphite (specific surface area: 17 m²). 2 The values ​​were ( / g, average particle size (D50): 3.5 μm), and the second conductive material was SWCNT.

[0195] As a mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed using a homo mixer at 2500 rpm for 30 minutes, then the active material was added, and the mixture was dispersed again at 2500 rpm for another 30 minutes to prepare a slurry.

[0196] As the negative electrode current collector, 50-70 mg / 25 cm of the first negative electrode slurry is applied to both sides of a copper current collector (thickness: 8 μm). 2 The material was coated with the specified load and rolled (roll press), then dried in a vacuum oven at 130°C for 10 hours to form the first negative electrode active material layer.

[0197] [Manufacturing of the second negative electrode active material layer] As a silicon-based active material, SiO (average particle size (D50): 3.5 μm), a first conductive material, a second conductive material, and polyacrylamide as a binder were prepared in a weight ratio of 70:19.8:0.2:10 to form the second negative electrode active material layer composition. The composition was added to distilled water as a solvent for negative electrode slurry formation to produce the second negative electrode slurry (solid content concentration 25% by weight).

[0198] The first conductive material is a plate-shaped graphite (specific surface area: 17 m²). 2 The second conductive material is carbon nanotubes, with a density of 3.5 μm (average particle size D50).

[0199] As a mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed using a homo mixer at 2500 rpm for 30 minutes, then the active material was added, and the mixture was dispersed again at 2500 rpm for another 30 minutes to prepare a slurry.

[0200] The second negative electrode slurry is added to the first negative electrode active material layer at a rate of 15-40 mg / 25 cm. 2 The material was coated with the specified load and rolled (roll press), then dried in a vacuum oven at 130°C for 10 hours to form the second negative electrode active material layer (thickness: 15 μm).

[0201] In this case, the core thickness of the coater and the liquid thickness (thickness of the coating liquid) are as shown in Table 1 below, and Equation 1, which is derived from these, is also shown in Table 1 below.

[0202] [Table 1]

[0203] <Manufacturing of secondary batteries> As the positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2A cathode slurry was prepared by adding O2 (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 in a weight ratio of 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for cathode slurry formation (solid content concentration 78% by weight).

[0204] As the positive electrode current collector, 537 mg / 25 cm of the positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12 μm). 2 The cathode was manufactured by coating with the specified load amount, rolling (roll press), and drying in a vacuum oven at 130°C for 10 hours to form a cathode active material layer (thickness: 65 μm) (cathode thickness: 77 μm, porosity: 26%).

[0205] A polyethylene separation membrane was interposed between the positive electrode and the negative electrodes of the above-mentioned examples and comparative examples, and an electrolyte was injected to manufacture a lithium secondary battery.

[0206] The aforementioned electrolyte is prepared by adding vinylene carbonate at a concentration of 3% by weight, based on the total weight of the electrolyte, to an organic solvent mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) in a volume ratio of 30:70, and then adding LiPF6 as a lithium salt at a concentration of 1M.

[0207] [Experimental Example 1: Evaluation of Lifetime Characteristics] The secondary batteries containing the negative electrodes manufactured in the above examples and comparative examples were evaluated for their lifespan using an electrochemical charger / discharger, and their capacity retention rate was assessed. The secondary batteries underwent in-situ cycle testing at 4.2-3.0V and 1C / 0.5C. During the test, the batteries were charged / discharged at 0.33C / 0.33C (4.2-3.0V) every 50 cycles, and the capacity retention rate was measured. Tables 2 and 3 below show the in-situ capacity retention rate, not the RPT capacity retention rate.

[0208] Capacity retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the first cycle)} × 100

[0209] [Experimental Example 2: Measurement and Evaluation of Resistance Increase Rate] In Experimental Example 1, during the test, the battery was charged / discharged at 0.33C / 0.33C (4.2-3.0V) every 50 cycles to measure the capacity retention rate. Then, it was discharged with a 2.5C pulse at SOC50, the resistance was measured, and the resistance increase rate was compared and analyzed.

[0210] Furthermore, data for 200 cycles was calculated for both the lifetime characteristic evaluation and the resistance increase rate measurement evaluation, and the results are shown in Table 2 below.

[0211] [Table 2]

[0212] As can be seen in Tables 1 and 2 above, the negative electrode according to the embodiment of this application is characterized in that the second negative electrode active material layer satisfies the non-uniformity of Formula 1. That is, the first negative electrode active material layer has a silicon-based negative electrode and is coated in a thin thickness range, but there was a problem in that it was difficult to form the second negative electrode active material layer as a thin film on top of it. However, when coating is performed by the method shown in Table 1 (adjustment of the liquid thickness and core thickness of the coater), the non-uniformity of Formula 1 is satisfied, and the second negative electrode active material layer can be coated more uniformly and thinly on top of the first negative electrode active material layer.

[0213] This allowed us to confirm that lithium secondary batteries containing this technology exhibited improved cycle characteristics and resistance growth rate, along with the optimal capacity characteristics that are an advantage of Si negative electrodes.

[0214] Comparative Examples 1 and 2 correspond to cases that exceed the range of Formula 1 of this application. That is, although the structure in which the second negative electrode active material layer is formed is the same, these correspond to cases where the coating is non-uniform compared to Examples 1 to 4. In this case, although the capacity and lifespan can be improved compared to a typical single-layer negative electrode, it was confirmed that the capacity retention rate and resistance increase rate are not as good as those of Examples 1 to 4 of this application. This corresponds to the result of the second negative electrode active material layer, which acts as a buffer layer, being non-uniformly coated on top of the first negative electrode active material layer. [Explanation of Symbols]

[0215] 10...Second negative electrode active material layer 20...first negative electrode active material layer 30 ···Negative electrode current collector layer 100 ···Negative electrode for lithium secondary batteries

Claims

1. A negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a first negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a second negative electrode active material layer provided on the side of the first negative electrode active material layer opposite to the side facing the negative electrode current collector layer; The first negative electrode active material layer comprises a first negative electrode active material layer composition containing a first negative electrode active material, and the second negative electrode active material layer comprises a second negative electrode active material layer composition containing a second negative electrode active material. The first negative electrode active material contains one or more selected from the group consisting of SiOx (x=0) and SiOx (0 < x < 2), and contains 95 parts by weight or more of SiOx (x=0) based on 100 parts by weight of the first negative electrode active material. The second negative electrode active material is SiOx (0 < x < 2), The second negative electrode active material is 60 parts by weight or more, based on 100 parts by weight of the second negative electrode active material layer composition. The second negative electrode active material layer includes a first surface opposite to the surface of the second negative electrode active material layer facing the first negative electrode active material layer; and a second surface of the second negative electrode active material layer facing the first negative electrode active material layer. The first surface and the second surface each include an uneven surface, The second negative electrode active material layer satisfies the non-uniformity of the following formula 1, and is a negative electrode for a lithium secondary battery: [Formula 1] 0μm│C-(A+B) / 2││10μm In the above formula 1, A represents the longest distance (μm) between the first surface and the second surface. B represents the shortest distance (μm) between the first surface and the second surface. C represents the average thickness (μm) of the second negative electrode active material layer. The aforementioned C is between 5 μm and 20 μm in size.

2. The negative electrode for a lithium secondary battery according to claim 1, wherein A is 5 μm or more and 25 μm or less.

3. The negative electrode for a lithium secondary battery according to claim 1, wherein the average thickness of the second negative electrode active material layer is 10% or more and 40% or less of the total thickness of the first negative electrode active material layer and the second negative electrode active material layer.

4. The negative electrode for a lithium secondary battery according to claim 1, wherein the average surface roughness (Sa) of the first surface is 700 nm or less.

5. The negative electrode for a lithium secondary battery according to claim 1, wherein the first negative electrode active material is 60 parts by weight or more, based on 100 parts by weight of the first negative electrode active material layer composition.

6. The viscosity of the first negative electrode active material layer composition is such that, at a shear rate of 2.5 (1 / s), the shear viscosity is 2,000 cPs or more and 15,000 cPs or less. The negative electrode for a lithium secondary battery according to claim 1, wherein the viscosity of the second negative electrode active material layer composition is lower than the viscosity of the first negative electrode active material layer composition.

7. The first negative electrode active material layer is formed over the entire surface of the negative electrode current collector layer. The negative electrode for a lithium secondary battery according to claim 1, wherein the second negative electrode active material layer is formed over the entire surface of the first negative electrode active material layer.

8. The stage of preparing the negative electrode current collector layer; A step of forming a first negative electrode active material layer by applying the first negative electrode active material layer composition to one or both sides of the negative electrode current collector layer using a coater; and A step of forming a second negative electrode active material layer by applying the second negative electrode active material layer composition to the surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer using a coater; A method for manufacturing a negative electrode for a lithium secondary battery, including, The first negative electrode active material contains one or more selected from the group consisting of SiOx (x=0) and SiOx (0 < x < 2), and contains 95 parts by weight or more of SiOx (x=0) based on 100 parts by weight of the first negative electrode active material. The second negative electrode active material is SiOx (0 < x < 2), The second negative electrode active material is 60 parts by weight or more, based on 100 parts by weight of the second negative electrode active material layer composition. The thickness of the coater liquid in the step of applying the first negative electrode active material layer composition to form the first negative electrode active material layer is 62 μm or more and 100 μm or less. In the step of forming the second negative electrode active material layer by applying the second negative electrode active material layer composition to the surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer, the thickness of the coater liquid is 10 μm or more and 60 μm or less. A method for manufacturing a negative electrode for a lithium secondary battery, wherein the core thickness of the coater is 0.4T or more and 2T or less.

9. The process includes a step of pre-lithiation of the negative electrode, on which a first negative electrode active material layer and a second negative electrode active material layer are formed on the negative electrode current collector, The method for manufacturing a negative electrode for a lithium secondary battery according to claim 8, wherein the step of pre-lithifying the negative electrode includes a lithium electroplating step; a lithium metal transfer step; a lithium metal deposition step; or a stabilized lithium metal powder (SLMP) coating step.

10. The step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet-on-dry process. The aforementioned wet-on-dry process is Steps include applying the first negative electrode active material layer composition; The steps of forming the first negative electrode active material layer by partially or completely drying the coated first negative electrode active material layer composition; and Steps include applying the second negative electrode active material layer composition to the first negative electrode active material layer; A method for manufacturing a negative electrode for a lithium secondary battery according to claim 8, including the method described in claim 8.

11. The step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet-on-wet process, The aforementioned wet-on-wet process is Steps include applying the first negative electrode active material layer composition; and A step of applying the second negative electrode active material layer composition to the first negative electrode active material layer composition while the first negative electrode active material layer composition is still wet; A method for manufacturing a negative electrode for a lithium secondary battery according to claim 8, including the method described in claim 8.

12. positive electrode; A negative electrode for a lithium secondary battery according to any one of claims 1 to 7; A separation membrane provided between the positive electrode and the negative electrode; and Electrolyte; Lithium-ion batteries, including lithium-ion batteries.

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