Negative electrode for lithium secondary battery, method for manufacturing negative electrode for lithium secondary battery, and lithium secondary battery including the 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, and all of its content is incorporated herein by reference.

[0002] This 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.

Background Art

[0003] Due to the rapid increase in the use of fossil fuels, the demand for alternative and clean energy has been increasing. As part of this, the fields of power generation and energy storage using electrochemical reactions are among the most actively studied.

[0004] Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its usage area is showing a trend of continuous expansion.

[0005] With the development of technologies related to mobile devices and the increasing demand, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density, a high voltage, a long cycle life, and a low self-discharge rate have been commercialized and widely used. In addition, research on methods for manufacturing high-density electrodes with a higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries has been actively conducted.

[0006] Generally, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and desorbs lithium ions emitted from the positive electrode, and silicon-based particles having a large discharge capacity may be used as the negative electrode active material.

[0007] In particular, in recent years, in response to the demand for high-density energy batteries, active research has been conducted into methods of increasing capacity by using silicon-based compounds such as Si / C and SiOx, which have a capacity 10 times larger than that of graphite-based materials, as anode active materials. However, in the case of silicon-based compounds, which are high-capacity materials, they have excellent capacity characteristics as materials with a large capacity compared to conventionally used graphite, but their volume expands rapidly during charging, cutting off the conductive path and reducing battery characteristics, resulting in a decrease in capacity from the beginning. In addition, when silicon-based anodes are repeatedly charged and discharged, lithium ions cannot be charged uniformly in the depth direction of the anode, and reactions occur on the surface, accelerating surface deterioration, so performance needs to be improved in terms of battery cycles.

[0008] In order to solve the above problems when using silicon-based compounds as negative electrode active materials, various methods are being discussed, such as a method of adjusting the driving potential, a method of further coating a thin film on the active material layer, a method of suppressing the volume expansion itself, such as a method of adjusting the particle size of the silicon-based compound, or the development of a binder that controls the volume expansion of the silicon-based compound to prevent the conductive path from being broken. In addition, research is being conducted to improve the life characteristics of silicon-based negative electrodes by limiting the usage ratio of silicon-based active materials used during initial charging and discharging and giving them a reservoir role by using a method of pre-lithiating the silicon-based active material layer.

[0009] However, in the case of the above method, there is a risk of warping and reducing the performance of the battery, so there is a limit to its application, and there is still a limit to the commercialization of the manufacture of negative electrode batteries with a high content of silicon-based compounds. As the ratio of silicon-based active material contained in the silicon-based active material layer increases, pre-lithiation is concentrated on the surface of the negative electrode, causing warping and damage to the silicon-based active material on the surface side, and non-uniform pre-lithiation occurs, resulting in problems in improving life characteristics.

[0010] Therefore, a method of using a silicon-based active material and additionally using a negative electrode active material layer that serves as a buffer layer has been studied. However, even without rapid charging, the process of placing an even thinner thin film layer on top of the silicon-based active material layer, which is already formed thinly, is extremely difficult, and there is a problem that the actual process and product production are difficult.

[0011] Therefore, in order to improve the capacity characteristics, even when using a silicon-based compound as the active material, it does not cause a decrease in the capacity characteristics, and when performing charge and discharge cycles, it is possible to prevent electrode surface deterioration and improve the cycle performance. In addition, research is needed on a method that can coat more uniformly and thinly even when using a dual active material layer.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0013] This application relates to a negative electrode for a lithium secondary battery, a method for manufacturing a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode, which can maximize the capacity characteristics, which is the main reason for using a silicon-based active material, while using a silicon-based active material for the negative electrode, prevent electrode surface deterioration during charge and discharge cycles, which is a conventional problem, and further ensure rapid charging performance and processability, with two layers of negative electrode active material layers being uniform and capable of thin film coating.

Means for Solving the Problems

[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 or both surfaces of the negative electrode current collector layer; and a second negative electrode active material layer provided on the opposite surface of the first negative electrode active material layer facing the negative electrode current collector layer. The first negative electrode active material layer contains a first negative electrode active material layer composition containing a first negative electrode active material. The second negative electrode active material layer contains 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 contains a mixture of one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride. The second negative electrode active material layer includes a first surface which is the opposite of the surface of the second negative electrode active material layer facing the first 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 a non-uniform surface. The second negative electrode active material layer satisfies the non-uniformity of Formula 1 below.

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

[0016] In yet another embodiment, a method for manufacturing a negative electrode for a lithium secondary battery includes the steps of preparing a negative electrode current collector layer; applying a first negative electrode active material layer composition using a coater on one or both surfaces of the negative electrode current collector layer to form a first negative electrode active material layer; and applying a second negative electrode active material layer composition using a coater on the opposite surface of the first negative electrode active material layer that contacts the negative electrode current collector layer to form a second negative electrode active material layer. In the method, 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, the SiOx (x = 0) is included in an amount of 95 parts by weight or more. The second negative electrode active material includes a mixture of one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride. The 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 the coater liquid thickness in the step of applying the second negative electrode active material layer composition on the opposite surface of the first negative electrode active material layer that contacts 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. A method for manufacturing a negative electrode for a lithium secondary battery is provided.

[0017] Finally, a lithium secondary battery is provided, which includes a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

Advantages of the Invention

[0018] In the case of the negative electrode for a lithium secondary battery according to an embodiment of the present invention, it 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 included in the first negative electrode active material layer 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, the SiOx (x = 0) is included in an amount of 95 parts by weight or more. The second negative electrode active material included in the second negative electrode active material layer includes a mixture of one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride.

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

[0020] Among them, in particular, the negative electrode for a lithium secondary battery according to the present application is characterized in that the second negative electrode active material layer satisfies the non-uniformity of the above formula 1. That is, there has been a problem that the first negative electrode active material layer has a silicon-based negative electrode and is thinly coated, but it is difficult to form a second negative electrode active material layer as a thin film on top of it. However, when coating is performed by the method (adjusting the liquid thickness and core thickness of the coater) as in the present application, it has the characteristic that it can satisfy the non-uniformity of the above formula 1 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, a lithium secondary battery including this has the main feature of satisfying cycle characteristics together with the optimal capacity characteristics that are the advantages of the Si negative electrode.

[0022] Ultimately, the negative electrode for a lithium secondary battery according to the present application has the advantages of an electrode that applies a high content of Si particles as a single-layer active material, and to solve the problems of surface deterioration, the problem of uniformity during pre-lithiation, and the problem of life characteristics, which are the disadvantages when having this, it is characterized in that the second negative electrode active material layer is coated more uniformly as a thin film on top of the first negative electrode active material layer to form a double layer.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

[0024] Before describing the present invention, first, some terms will be defined.

[0025] In this specification, when a certain part "includes" a certain component, this means that, unless otherwise specified, it does not exclude other components, but may further include other components.

[0026] In this specification, "p to q" means "p or more and q or less".

[0027] In this specification, the "specific surface area" is measured by the BET method. Specifically, it is calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II manufactured by BEL Japan, Inc. That is, in the present application, the BET specific surface area can mean the specific surface area measured by the above measurement method.

[0028] In this specification, "Dn" means the particle size distribution and the particle size at the n% point of the cumulative particle number distribution according to the particle size. That is, D50 is the particle size (average particle size, median particle size) at the 50% point of the cumulative particle number distribution according to the particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution according to the particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution according to the particle size. On the other hand, the particle size distribution may be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500). When the particles pass through the laser beam, the difference in the diffraction pattern due to the particle size is measured to calculate the particle size distribution.

[0029] In this specification, the meaning that a polymer contains a certain monomer in monomer units means that the monomer participates in the polymerization reaction and is included as a repeating unit in the polymer. In this specification, when a polymer is said to contain a monomer, this is interpreted to be the same as the polymer containing the monomer in monomer units.

[0030] In this specification, it is understood that the term "polymer" is used in a broad sense including copolymers unless otherwise specified as "homopolymer".

[0031] In this specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are the polystyrene equivalent molecular weights measured by Gel Permeation Chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as the standard substance. In this specification, the molecular weight means the weight average molecular weight unless otherwise specified.

[0032] Hereinafter, with reference to the drawings, a detailed description will be given so that a person having ordinary knowledge in the technical field to which the present invention pertains can easily implement the present invention. 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 is a negative electrode for a lithium secondary battery including a negative electrode current collector layer; a first negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer; and a second negative electrode active material layer provided on the opposite surface of the first negative electrode active material layer facing the negative electrode current collector layer. The first negative electrode active material layer includes a first negative electrode active material layer composition containing a first negative electrode active material. The second negative electrode active material layer includes a second negative electrode active material layer composition containing a second negative electrode active material. 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, it contains 95 parts by weight or more of SiOx (x = 0). The second negative electrode active material includes a mixture of one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride. The second negative electrode active material layer includes a first surface that 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. 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.

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

[0035] The negative electrode for a lithium secondary battery according to the present application is characterized in that the second negative electrode active material layer satisfies the non-uniformity of the above formula (1). That is, there has been a problem that the first negative electrode active material layer has a silicon-based negative electrode and is thinly coated, but it is difficult to form a second negative electrode active material layer as a thin film on top of it. However, when coating is performed by the method (adjusting the liquid thickness and core thickness of the coater) as in the present application, it is possible to satisfy the non-uniformity of the above formula (1), 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. That is, the negative electrode for a lithium secondary battery according to the present application controls the problem of reaction non-uniformity in which the reaction is concentrated only on the electrode surface during charge and discharge of the high-capacity first negative electrode active material layer, and the problem of uniformity during pre-lithiation, and optimizes the uniformity and thickness of the second negative electrode active material layer with excellent durability. As a result, a lithium secondary battery including this has the main feature of satisfying the life characteristics together with the optimal capacity characteristics which are the advantages of the Si negative electrode.

[0036] FIG. 1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to an embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery including a first negative electrode active material layer 20 and a second negative electrode active material layer 10 can be confirmed on one surface of a negative electrode current collector layer 30. FIG. 1 shows that the first negative electrode active material layer is formed on one surface, but it may be included on both surfaces 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] FIG. 2 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to an embodiment of the present application. Specifically, as shown in FIG. 2, the first negative electrode active material layer 20 and the second negative electrode active material layer 10 may be formed on both surfaces of the negative electrode current collector layer 30. Further, it may have an arrangement of 10>20>30>20>10, and additionally, such as 10>20>30>20, 10>20>30>10, 10>20>30>10>20, etc., as long as the first negative electrode active material layer and the second negative electrode active material layer are sequentially laminated on only one surface of the negative electrode current collector layer, the arrangement on the opposite surface can be laminated regardless of the relationship. Preferably, both surfaces of the negative electrode current collector layer preferably have the same composition, and specifically, may have a structure of 10>20>30>20>10.

[0038] Hereinafter, the negative electrode for a lithium secondary battery of the present invention will be described in more detail.

[0039] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery including: a negative electrode current collector layer; a first negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer; and a second negative electrode active material layer provided on the opposite surface of the first negative electrode active material layer in contact with the negative electrode current collector layer.

[0040] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. may be used. Further, fine irregularities may be formed on the surface to strengthen the binding force of the negative electrode active material, and it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

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

[0042] However, the thickness may vary diversely depending on the type and use of the negative electrode to be 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, the SiOx (x = 0) may be included in an amount of 95 parts by weight or more.

[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, the SiOx (x = 0) may be included in an amount of 95 parts by weight or more, preferably 97 parts by weight or more, more preferably 99 parts by weight or more, and may be included in an amount of 100 parts by weight or less.

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

[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 a 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 the life characteristics due to the surface non-uniform reaction occurs. Therefore, the problem has been solved by including the second negative electrode active material layer according to the present invention in a specific weight loading amount.

[0048] On the one hand, the average particle size (D50) of the first negative electrode active material of the present invention may be 3 μm to 10 μm, specifically, it may be 4 μm to 8 μm, and more specifically, it may be 5 μm to 7 μm. When the average particle size is within the above range, the specific surface area of the particles is within an appropriate range, and the viscosity of the negative electrode slurry is formed to be within an appropriate range. Thereby, the dispersion of the particles constituting the negative electrode slurry becomes smooth. Further, since the size of the first negative electrode active material has a value equal to or greater than the lower limit value of the range, the contact area between the silicon particles and the conductive material by the composite composed of the conductive material and the binder in the negative electrode slurry is excellent, and the possibility of maintaining the conductive network is increased, and the capacity retention rate is increased. On the other hand, when the average particle size satisfies the above range, silicon particles that are too large are excluded, and the surface of the negative electrode is smoothly formed, thereby preventing the non-uniformity phenomenon of the current density during charge and discharge.

[0049] In one embodiment of the present application, the first negative electrode active material has a generally specific BET specific surface area. The BET specific surface area of the first negative electrode active material is preferably 0.01 m 2 / g to 150.0 m 2 / g, more preferably 0.1 m 2 / g to 100.0 m 2 / g, particularly preferably 0.2 m 2 / g to 80.0 m 2 / g, most preferably 0.2 m 2 / g to 18.0 m 2 / g. The BET specific surface area is measured in accordance with DIN 66131 (using nitrogen).

[0050] In one embodiment of the present application, the first negative electrode active material may exist in, for example, a crystalline form or an 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 may exist in the form of a silicon-containing thin film or coating, but this is not so preferable.

[0051] In one embodiment of the present application, the first negative electrode active material may have a non-spherical form, and its degree of sphericity may be, 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, where A is the area and P is the boundary line.

[0053] [Formula A-1] 4πA / P 2

[0054] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, 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.

[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] Even when the first negative electrode active material layer composition according to the present application uses a first negative electrode active material with a significantly high capacity within the above range, by using the second negative electrode active material layer described later together, the capacity performance of the entire negative electrode is not reduced, and problems such as surface deterioration during charging and discharging, uniformity problems during pre-lithiation, and life characteristics problems are solved.

[0057] Conventionally, it has been common to use only graphite-based compounds as the negative electrode active material. However, recently, as the demand for high-capacity batteries has increased, attempts to mix and use silicon-based compounds to increase the capacity have been increasing. However, in the case of silicon-based compounds, there is a limit in that the volume rapidly expands during the charge / discharge process, damaging the conductive paths formed in the negative electrode active material layer and conversely reducing the performance of the battery.

[0058] Therefore, in one embodiment of the present 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] At this time, the first negative electrode conductive material and the first negative electrode binder included in the first negative electrode active material layer composition may be used without being limited to those used in the art.

[0060] In one embodiment of the present application, the first negative electrode conductive material may be used without being limited to substances generally used in the art, and specifically, may include one or more selected from the group consisting of a dot-shaped conductive material, a planar conductive material, and a linear conductive material.

[0061] In one embodiment of the present application, the dot-shaped conductive material can be used to improve the conductivity of the negative electrode, and means a dot-shaped or spherical conductive material having conductivity without inducing a chemical change. Specifically, the dot-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 derivative, and preferably may include carbon black in terms of realizing high conductivity and excellent dispersibility.

[0062] In one embodiment of the present application, the dot-shaped conductive material has a BET specific surface area of 40 m 2 / g or more and 70 m 2 / g or less, preferably 45 m 2 / g or more and 65 m 2 / g or less, more preferably 50 m 2 / g or more and 60 m 2 / g or less.

[0063] In one embodiment of the present application, the particle size of the dot-shaped 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 the present application, the first negative electrode conductive material may include a planar conductive material.

[0065] The planar conductive material can play a role in increasing the surface contact between silicon particles in the negative electrode to improve conductivity, and at the same time suppressing the interruption of the conductive path due to volume expansion. The planar conductive material may be expressed as a plate-shaped conductive material or a bulk conductive material.

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

[0067] In one embodiment of the present application, the average particle size (D50) of the planar conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the above range is satisfied, since the particle size is sufficient, the viscosity of the negative electrode slurry does not increase too much, and at the same time, dispersion becomes easy. Therefore, when dispersing using the same device and time, the dispersion effect is excellent.

[0068] In one embodiment of the present application, the planar conductive material provides a negative electrode composition in which D10 is 0.5 μm or more and 1.5 μm or less, D50 is 2.5 μm or more and 3.5 μm or less, and D90 is 7.0 μm or more and 15.0 μm or less.

[0069] In one embodiment of the present application, as the planar conductive material, a high specific surface area planar conductive material having a high BET specific surface area or a low specific surface area planar conductive material may be used.

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

[0071] In one embodiment of the present application, the planar conductive material may have a BET specific surface area of 5 m 2 / g or more.

[0072] In another embodiment, the planar conductive material may have a BET specific surface area of 5 m 2 / g or more and 500 m 2 / g or less, preferably 5 m 2 / g or more and 300 m 2 / g or less, more preferably 5 m 2 / g or more and 250 m 2 / g.

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

[0074] In another embodiment, the planar conductive material is a planar conductive material with a low specific surface area and can satisfy the range of having a BET specific surface area of 5 m 2 / g or more and 40 m 2 / g or less, preferably 5 m 2 / g or more and 30 m 2 / g or less, more preferably 5 m 2 / g or more and 25 m 2 / g or less.

[0075] In addition, as the conductive material, there may be a linear conductive material such as a carbon nanotube. The carbon nanotube may be a bundled carbon nanotube. The bundled carbon nanotube may include a plurality of carbon nanotube units. Specifically, here, unless otherwise mentioned, the 'bundle type' refers to a secondary shape in which a plurality of carbon nanotube units are arranged in parallel with substantially the same orientation of the longitudinal axis of the carbon nanotube unit or are twisted into a bundle or rope shape. The carbon nanotube unit has a graphite sheet with a nanosize diameter in a cylindrical shape and has an sp2 bonding structure. At this time, depending on the angle and structure by which the graphite sheet is wound, it can exhibit the characteristics of a conductor or a semiconductor. The bundled carbon nanotube can be uniformly dispersed during the production of the negative electrode compared to the entangled type carbon nanotube, and can smoothly form a conductive network in the negative electrode, improving the conductivity of the negative electrode.

[0076] In one embodiment of the present application, the first negative electrode conductive material can satisfy 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 included in an amount of 1 part by weight or more and 40 parts by weight or less, preferably 3 parts by weight or more and 30 parts by weight or less, more preferably 5 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the first negative electrode active material layer composition.

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

[0079] In one embodiment of the present application, the dot-shaped conductive material can satisfy the range of 1 to 60 parts by weight, preferably 5 to 50 parts by weight, more preferably 10 to 50 parts by weight, based on 100 parts by weight of the first negative electrode conductive material.

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

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

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

[0083] In one embodiment of the present 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:planar conductive material can satisfy 0.01:1 to 0.1:1.

[0084] In one embodiment of the present application, when the first negative electrode conductive material satisfies the above composition and ratio, it has no significant impact on the life characteristics of conventional lithium secondary batteries, has more charging and discharging points, and has the characteristic of excellent output characteristics at a high C-rate.

[0085] In the case of the first negative electrode conductive material according to the present 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 the present application, it plays a role in controlling the contacts between silicon-based active materials with a very large volume expansion of the electrode during charging and discharging. The positive electrode conductive material plays a role in imparting some conductivity while acting as a buffer with a buffering effect when rolled. The negative electrode conductive material of the present invention has a completely different configuration and role.

[0086] Also, the first negative electrode conductive material according to the present application is applied to silicon-based active materials and has a completely different configuration from the conductive material applied to graphite-based active materials. That is, the conductive material used in an electrode having a graphite-based active material simply has smaller particles compared to the active material and has the characteristics of improving output characteristics and imparting some conductivity. It has a completely different configuration 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 the present application, the first negative electrode binder may include at least any one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, poly acrylic acid, and substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., and may also include these various copolymers.

[0088] According to one embodiment of the present application, the first negative electrode binder 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 volume expansion and relaxation of the first negative electrode active material. If the above role is satisfied, any general binder can be applied. Specifically, an aqueous binder may be used. More specifically, a PAM-based binder may be used.

[0089] In one embodiment of the present application, based on 100 parts by weight of the first negative electrode active material layer composition, the first negative electrode binder may be contained 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, and may also be contained in an amount of 5 parts by weight or more and 10 parts by weight or more.

[0090] Compared with conventional carbon-based negative electrodes, when a silicon-based material is used as the negative electrode, an aqueous binder may be applied in the above parts by weight and a dot-shaped conductive material may be used. Due to the above characteristics, the dot-shaped conductive material has hydrophobicity, and thus has the characteristic that the bonding strength between the conductive material and the binder is excellent.

[0091] In one embodiment of the present application, the second negative electrode active material may include one or more mixtures selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride.

[0092] In another embodiment, the second negative electrode active material may include one or more and three or less mixtures selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride.

[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, the second negative electrode active material includes one or more mixtures selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride, and 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, and a negative electrode for a lithium secondary battery is provided.

[0096] In another embodiment, the second negative electrode active material includes one or more mixtures selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride, and the silicon-based active material may be contained in an amount of 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 include one or more selected from the group consisting of SiOx (0 < x < 2), SiC, and Si alloy.

[0098] In one embodiment of the present application, the silicon-based active material contained in the second negative electrode active material includes one or more selected from the group consisting of SiOx (0 < x < 2), SiC, and Si alloy, and may include 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 includes one or more selected from the group consisting of SiOx (0 < x < 2), SiC, and Si alloy, and may include 1 part by weight or more, 10 parts by weight or more, and may include 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 include SiOx (0 < x < 2).

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

[0102] As described above, the negative electrode for a lithium secondary battery according to the present application includes the second negative electrode active material in the second negative electrode active material layer. As a result, while including the first negative electrode active material described above, high capacity and high density characteristics are maintained, and the second negative electrode active material serves as a buffer layer, solving the problems of surface deterioration during charge and discharge, the problem of uniformity during pre-lithiation, and the problem of life characteristics.

[0103] As an example, the second negative electrode active material layer of the present application can act as a buffer layer. An electrode containing a Si active material has excellent capacity characteristics compared to an electrode containing SiO or a carbon-based active material. However, in an electrode containing a Si active material, during charge and discharge, deterioration concentrates on the surface of the negative electrode active material layer due to a rapid reaction with Li ions. This also occurs during the pre-lithiation process when lithium ions are pre-contained in the negative electrode active material layer. In the pre-lithiation process, the buffer layer is used to prevent direct contact between the Si-based electrode and lithium and prevent surface deterioration. Therefore, the second negative electrode active material layer of the present invention has the characteristic that it can exhibit the same role and effect as the buffer layer in the pre-lithiation process.

[0104] In one embodiment of the present application, typical examples of the carbon-based active material include natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotube, fullerene, or activated carbon, etc. As long as it is commonly used in carbon materials for lithium secondary batteries, it can be used without limitation. Specifically, it can be processed into a spherical or dot-like form and used.

[0105] In one embodiment of the present application, the planar conductive material used as the aforementioned first negative electrode conductive material has a structure and role different from those of the carbon-based active material generally used as the negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and means a material processed into a spherical or dot-like form in order 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 material having a planar or plate-like form, and can be represented by plate-shaped graphite. That is, it is a material included to maintain a conductive path within the negative electrode active material layer, and means a material for securing a conductive path in a planar form within the negative electrode active material layer, rather than having a role in the storage and release of lithium.

[0107] That is, in the present application, the fact that plate-shaped graphite is used as the conductive material means that it is processed into a planar or plate-like shape and used as a material for securing a conductive path, rather than having a role in the storage or release of lithium. At this time, the negative electrode active material included together has a high capacity characteristic for the storage and release of lithium and plays a role of storing and releasing all lithium ions transmitted from the positive electrode.

[0108] On the other hand, in the present application, the fact that the carbon-based active material is used as the active material means that it is processed into a dot-like or spherical shape and used as a material for playing a role in storing or releasing lithium.

[0109] That is, in one embodiment of the present application, artificial graphite or natural graphite, which is a carbon-based active material, can satisfy the range of a BET specific surface area of 0.1 m 2 / g or more and 4.5 m 2 / g or less. Further, the plate-shaped graphite, which is a planar conductive material, may have a BET specific surface area of 5 m 2 / g or more in a planar form.

[0110] The metal-based active material may be a compound containing any one or two or more metal elements selected from the group consisting of, for example, Al, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt, Ti, Sb, Ga, Mn, Fe, Co, Ni, Cu, Sr, and Ba. These metal compounds can be used in any form such as a single substance, an alloy, an oxide (such as TiO2, SnO2), a nitride, a sulfide, a boride, an alloy with lithium, etc. However, a single substance, an alloy, an oxide, and an alloy with lithium can have a higher capacity.

[0111] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the second negative electrode active material is contained 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, and may satisfy 100 parts by weight or less and 99 parts by weight or less based on 100 parts by weight of the second negative electrode active material layer composition.

[0113] By using the second negative electrode active material having a lower capacity characteristic than the first negative electrode active material but less particle cracking during charge and discharge within the above range, the capacity performance of the negative electrode is not reduced, the surface reaction of the negative electrode is suppressed, and the life characteristic enhancement feature can be achieved.

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

[0115] At this time, the same content as that of the first negative electrode conductive material and the first negative electrode binder described above can be applied to the content of the second negative electrode conductive material and the second negative electrode binder.

[0116] In one embodiment of the present application, the second negative electrode active material layer includes a first surface that 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, and the first surface and the second surface each include a non-uniform surface.

[0117] At this time, the fact that the first surface and the second surface include non-uniform surfaces means that the surface or interface is not ideally flat without uneven portions, but includes some unevenness and bending.

[0118] That is, generally when coating a composition, its surface or interface is not ideally flat, but is formed in a bumpy form, which can be interpreted as meaning that the first surface and the second surface include non-uniform surfaces.

[0119] Figure 3 is a diagram showing a SEM photograph of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, the surface indicated by the red dotted line (triangle display) corresponds to the second surface of the second negative electrode active material layer, and the surface indicated by the yellow dotted line (circular display) corresponds to the first surface. At this time, including a non-uniform surface can mean that the yellow and red dotted lines do not form a straight line and include bending.

[0120] In one embodiment of the present 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 means the longest distance (μm) between the first surface and the second surface, B means the shortest distance (μm) between the first surface and the second surface, C means the average thickness (μm) of the second negative electrode active material layer.

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

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

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

[0125] In the present application, when the first negative electrode active material layer and the second negative electrode active material layer are ideally coated, both the first surface and the second surface are formed as uniform surfaces, and at this time, the values of A and B may be formed identically. That is, it can be meant that both the shortest distance and the longest distance are uniformly formed in the same form. At this time, when both the first negative electrode active material layer and the second negative electrode active material layer are uniformly coated, the shortest distance, the longest distance, and the average thickness of the second negative electrode active material layer all have the same value, and the formula 1 satisfies a value of 0.

[0126] In one embodiment of the present application, the fact that the second negative electrode active material layer satisfies the range of the formula 1 can mean that the second negative electrode active material layer is more uniformly coated on the upper part of the first negative electrode active material layer.

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

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

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

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

[0131] In one embodiment of the present application, C is 5 μm or more and 20 μm or less, preferably satisfying the range of 5.5 μm or more and 18 μm or less, more preferably 6 μm or more and 15 μm or less.

[0132] Particularly, the negative electrode for a lithium secondary battery according to the present application is characterized in that the second negative electrode active material layer satisfies the non-uniformity of the formula (1). That is, there has been a problem that although the first negative electrode active material layer has a silicon-based negative electrode and is thinly coated in terms of thickness range, it is difficult to form a second negative electrode active material layer as a thin film on the upper part thereof. However, when coating is performed by the manufacturing method (adjusting the liquid thickness and core thickness of the coater) described later, it becomes possible to satisfy the non-uniformity of the formula (1) and to coat the second negative electrode active material layer more uniformly and thinly on the upper part of the first negative electrode active material layer. As a result, it is possible to ensure rapid charging performance, effectively control the surface deterioration reaction, and simultaneously ensure the life characteristics.

[0133] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, 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, 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 the present application, there is provided a negative electrode for a lithium secondary battery, in which 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 the present application, the average surface roughness can mean the surface roughness. The average surface roughness indicates the degree of surface roughness and can indicate the degree of unevenness of the surface of the target substance.

[0138] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, in which 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 the viscosity of the first negative electrode active material layer composition.

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

[0140] At this time, only when the viscosity of the second negative electrode active material layer composition is kept lower than that of the first negative electrode active material layer composition, can two-layer negative electrode active material layers be formed as in the present application. More specifically, the viscosity of the second negative electrode active material layer composition is lower than that of the first negative electrode active material layer composition, but it must be formed at the same viscosity level as that of the first negative electrode active material layer composition.

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

[0142] The negative electrode for the lithium secondary battery according to the present application is composed of a double layer, and a second negative electrode active material layer satisfying specific non-uniformity serves as a buffer layer during pre-lithiation, and also serves to enable uniform lithiation in the depth direction of the electrode during cycle charging and discharging.

[0143] In one embodiment of the present application, a method for manufacturing a negative electrode for a lithium secondary battery includes the steps of 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 the surface opposite to the surface of the first negative electrode active material layer that contacts the negative electrode current collector layer using a coater to form a second negative electrode active material layer. 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, it contains 95 parts by weight or more of SiOx (x = 0). The second negative electrode active material includes a mixture of one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride. 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 50 μm or more and 100 μm or less, and the thickness of the coater liquid in the step of applying the second negative electrode active material layer composition to the surface opposite to the surface of the first negative electrode active material layer that contacts 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 applied to the above-described content.

[0145] That is, as described above, in order to form the first negative electrode active material layer and the second negative electrode active material layer, each composition is applied using a coater. At this time, when the liquid thickness of the coater satisfies the above-described conditions, it can be seen that the second negative electrode active material layer can be thinly and uniformly applied in the form of a thin film on the upper part of the first negative electrode active material layer. Thereby, a negative electrode for a lithium secondary battery satisfying the above-described Formula 1 can be manufactured.

[0146] In one embodiment of the present application, the thickness of the coater liquid may have the same meaning as the thickness of the coating liquid, and may mean the liquid thickness of the first negative electrode active material layer composition and the second negative electrode active material layer composition itself to be coated.

[0147] In one embodiment of the present application, there is provided 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.

[0148] The present invention incorporates the advantages of a pure silicon (Pure Si) active material in the first negative electrode active material layer and applies a second negative electrode active material layer that can cover the disadvantages. In particular, the second negative electrode active material layer must implement a thin film coating. However, it is a difficult problem to thinly and uniformly coat the second negative electrode active material layer on the upper part of the thin first negative electrode active material layer. However, as described above, when the liquid thickness and the core thickness of the coater are adjusted within the above ranges, it can be seen that a negative electrode for a lithium secondary battery satisfying the uniformity and thickness according to the present application can be manufactured.

[0149] In one embodiment of the present application, there is provided a step of applying a first negative electrode active material layer composition using a coater on one or both surfaces of the negative electrode current collector layer to form a first negative electrode active material layer.

[0150] That is, the step may mean the step of forming an active material layer on the negative electrode current collector layer, specifically, the step of forming the active material layer on the surface (lower layer part) in contact with the negative electrode current collector layer in the double layer structure.

[0151] In one embodiment of the present application, applying the first negative electrode active material layer composition includes the steps 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] At this time, the solid content of the first negative electrode slurry can satisfy the range of 10% to 40%.

[0153] In one embodiment of the present application, the step of forming the first negative electrode active material layer may include the step of mixing the first negative electrode slurry; and the step of coating the mixed first negative electrode slurry on one or both sides of the negative electrode current collector layer using a coater; for the coating, a coating method generally used in the art may be used.

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

[0155] That is, the step is the step of forming a second negative electrode active material layer on the first negative electrode active material layer, and may mean the step of forming an active material layer on the surface (upper layer part) away from the negative electrode current collector layer in the double layer structure.

[0156] In one embodiment of the present application, applying the second negative electrode active material layer composition includes the steps 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] At this time, the solid content of the second negative electrode slurry can satisfy the range of 10% to 40%.

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

[0159] For the coating, a coating method generally used in the art may be used.

[0160] The description of the step of forming the first negative electrode active material layer may be similarly applied to the step of forming the second negative electrode active material layer.

[0161] In one embodiment of the present application, 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; or a wet on wet process. A method for manufacturing a negative electrode for a lithium secondary battery is provided.

[0162] In one embodiment of the present application, the wet on dry process means a process 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] FIG. 4 is a flowchart showing a wet on dry process according to an embodiment of the present 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 a first negative electrode active material layer. Then, a second negative electrode slurry mixture is prepared and applied to the first negative electrode active material layer and dried to form a second negative electrode active material layer. Then, each layer can be rolled and pressed to form a negative electrode for a lithium secondary battery according to the present application.

[0164] In one embodiment of the present application, the wet-on-wet process means applying a second negative electrode active material layer composition on top of a first negative electrode active material layer composition without drying after the application of the first negative electrode active material layer composition.

[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 a negative electrode current collector layer. At the same time, a second negative electrode slurry mixture is prepared and applied to the first negative electrode slurry mixture, and then the first and second negative electrode slurry mixtures are dried. Thereafter, each layer can be rolled and pressed to form a negative electrode for a lithium secondary battery according to the present application.

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

[0167] In particular, in the wet-on-dry process, after applying the first negative electrode active material layer composition, it is completely dried, and then the second negative electrode active material layer composition is applied on top of it. By the above-described process, the first negative electrode active material layer and the second negative electrode active material layer can have a clear boundary. Accordingly, the compositions contained in the first negative electrode active material layer and the second negative electrode active material layer are not mixed and can be configured as a double layer.

[0168] In one embodiment of the present 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. Specifically, water or NMP may be used.

[0169] As a result of the above-described wet-on-wet process, a joint region in which the first negative electrode active material layer and the second negative electrode active material layer are mixed can be formed. At this time, in order to perform the wet-on-wet process, it is necessary that the viscosity of the first negative electrode active material layer composition is lower than the viscosity of the second negative electrode active material layer composition, and at that time, mutual mixing can occur in the joint region and the process.

[0170] In the present application, after the first negative electrode active material layer is dried (wet-on-dry process), the second negative electrode active material layer is formed, whereby the interfaces of the two layers are clearly separated and formed. Further, when the second negative electrode active material layer is applied in a state where the first negative electrode active material layer composition is not completely dried (the first negative electrode active material layer composition and the second negative electrode active material layer composition are applied simultaneously), mixing occurs at the interfaces of the two layers and a joint region is formed.

[0171] In one embodiment of the present application, a step of pre-lithiation of a negative electrode in which a first negative electrode active material layer and a second negative electrode active material layer are formed on the negative electrode current collector layer is included, and the step of pre-lithiation of the negative electrode includes a lithium electrolytic plating process; a lithium metal transfer process; a lithium metal vapor deposition process; or a stabilized lithium metal powder (SLMP) coating process; A method for manufacturing a negative electrode for a lithium secondary battery is provided.

[0172] As described above, since the second negative electrode active material layer contains the above-described second negative electrode active material and is provided with a mixed composition of a silicon-based active material and a carbon-based active material, the advantages of rapid charging can be maintained as they are. In particular, in the case of the second negative electrode active material, since it has a mixed composition and a large irreversibility, it can also exhibit an advantageous effect during the pre-lithiation process of pre-charging the negative electrode. Simply having the second negative electrode active material having the above composition in the second negative electrode active material layer enables a uniform pre-lithiation process at the upper end portion of the negative electrode, whereby the life can be improved.

[0173] In one embodiment of the present application, the porosity of the first negative electrode active material layer and the second negative electrode active material layer can satisfy the range of 10% or more and 60% or less.

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

[0175] The porosity varies depending on the composition and content of the active material, conductive material, and binder included in the first negative electrode active material layer and the second negative electrode active material layer, whereby the electrical conductivity and resistance in the electrode have an appropriate range.

[0176] In one embodiment of the present application, a lithium secondary battery is provided, which includes a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0177] The secondary battery according to one embodiment of the present specification may particularly include the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, specific descriptions are 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 has conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of aluminum or stainless steel surfaces with carbon, nickel, titanium, silver, etc. may be used. Further, the positive electrode current collector layer may usually have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0180] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; chemical formula Li 1+c1 Mn 2-c1 O4 (0 ≦ c1 ≦ 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ c2 ≦ 0.3) represented by Ni-site type lithium nickel oxide; chemical formula LiMn 2-c3 M c3 O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≦ c3 ≦ 0.1) or lithium manganese composite oxide represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); examples include LiMn2O4 in which a part of the Li in the chemical formula is substituted with an alkaline earth metal ion, but it is not limited thereto. The positive electrode may be Li metal.

[0181] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder together with the above-described positive electrode active material.

[0182] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery to be configured, it can be used without particular limitation as long as it has electron conductivity without causing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances 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. Among these, one kind alone or a mixture of two or more kinds may be used.

[0183] Also, the positive electrode binder plays a role in improving the adhesion between the positive electrode active material particles and the adhesive force 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. Among these, one kind alone or a mixture of two or more kinds may be used.

[0184] The separator membrane separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Generally, any separator membrane that can be used in a secondary battery can be used without particular limitation. In particular, a separator membrane with low resistance to the ion migration of the electrolyte and excellent moisture retention ability of the electrolyte solution is preferred. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, a coated separator membrane containing a ceramic component or a polymer substance to ensure heat resistance or mechanical strength may be used, and it may be selectively used in a single-layer or multi-layer structure.

[0185] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

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

[0187] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-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 derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. may be used.

[0188] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate which are cyclic carbonates are high-viscosity organic solvents with high dielectric constants and can preferably be used because they can well dissociate lithium salts. If such cyclic carbonates are mixed and used with linear carbonates having low viscosity and low dielectric constant such as dimethyl carbonate and diethyl carbonate at an appropriate ratio, an electrolyte having high electric conductivity can be produced, and thus they can be more preferably used.

[0189] As the metal salt, a lithium salt may be used. The lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte. For example, as the anion of the lithium salt, F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 -, CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0190] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc.

[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 the battery pack include the secondary battery having a high capacity, high rate characteristics and cycle characteristics, they may be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

Examples

[0192] Hereinafter, preferred embodiments are presented to assist in understanding the present invention. However, these embodiments are merely illustrative of the description, and it is obvious to those skilled in the art that various changes and modifications can be made within the scope of the description and the scope of the technical idea. It is natural that such variations and modifications belong to the scope of the claims.

[0193] <Production Example> <Manufacture of Negative Electrode> 〔Example 1〕 〔Manufacture 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 a negative electrode slurry at 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 was plate-shaped graphite (specific surface area: 17 m 2 / 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 at 2500 rpm for 30 minutes using a homo mixer, then the active material was added, and then dispersed at 2500 rpm for 30 minutes to prepare a slurry.

[0196] As a negative electrode current collector, the first negative electrode slurry was coated on both sides of a copper current collector (thickness: 8 μm) at a loading amount of 50 to 70 mg / 25 cm 2 and rolled, and dried in a vacuum oven at 130 °C for 10 hours to form a first negative electrode active material layer.

[0197] 〔Manufacture 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 used to prepare a second negative electrode active material layer composition at a weight ratio of 70:19.8:0.2:10. It was added to distilled water as a solvent for forming the negative electrode slurry to produce a second negative electrode slurry (solid content concentration: 25% by weight).

[0198] The first conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the second conductive material is carbon nanotubes.

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

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

[0201] At this time, the core thickness and liquid thickness (thickness of the coating liquid) of the coater were as shown in Table 1 below, and Equation 1 based on this was also described in Table 1 below.

[0202]

Table 1

[0203] <Manufacture of secondary battery> As a positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2O2 (average particle size (D50): 15 μm), carbon black as the conductive material (product name: Super C65, manufacturer: Timcal), polyvinylidene fluoride (PVdF) as the binder were added to N-methyl-2-pyrrolidone (NMP) as the solvent for forming the positive electrode slurry at a weight ratio of 97:1.5:1.5 to produce a positive electrode slurry (solid content concentration: 78 wt%).

[0204] As the positive electrode current collector, the positive electrode slurry was coated on both sides of an aluminum current collector (thickness: 12 μm) at a loading of 537 mg / 25 cm 2 and rolled (roll press), and dried in a vacuum oven at 130 °C for 10 hours to form a positive electrode active material layer (thickness: 65 μm), thereby producing a positive electrode (positive electrode thickness: 77 μm, porosity: 26%).

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

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

[0207] 〔Experimental Example 1: Evaluation of Life Characteristics〕 For the secondary batteries including the negative electrodes manufactured in the examples and comparative examples, life evaluation was performed using an electrochemical charge / discharge device, and the capacity retention rate was evaluated. The secondary batteries were subjected to an in-situ cycle test at 4.2 - 3.0 V, 1C / 0.5C. During the test, charging / discharging (4.2 - 3.0 V) was performed at 0.33C / 0.33C every 50 cycles, and the capacity retention rate was measured. In Tables 2 and 3 below, the in-situ capacity retention rate rather than the RPT capacity retention rate is shown.

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

[0209] [[Experiment Example 2: Measurement and Evaluation of Resistance Increase Rate]] In the above Experiment Example 1, during the test, charging / discharging was performed at 0.33C / 0.33C every 50 cycles (4.2 - 3.0V), and after measuring the capacity retention rate, discharging was performed at 2.5C pulse at SOC50 to measure the resistance, and the resistance increase rate was compared and analyzed.

[0210] In addition, for the above life characteristic evaluation and the measurement and evaluation of the resistance increase rate, data at 200 cycles were calculated respectively, and the results are as shown in Table 2 below.

[0211] [[Table 2]]

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

[0213] As a result, it was confirmed that the lithium secondary battery including this has improved cycle characteristics and resistance increase rate together with the optimal capacity characteristics which are the advantages of the Si negative electrode.

[0214] In the cases of Comparative Example 1 and Comparative Example 2, they respectively correspond to the cases where the scope of the formula 1 of the present application is exceeded. That is, although the structure in which the second negative electrode active material layer is formed is the same, it corresponds to the case where the coating is uneven compared to Examples 1 to 4. In this case, compared with a general single-layer structure negative electrode, the capacity and life can be improved, but it was confirmed that the capacity retention rate and the resistance increase rate are not good compared with Examples 1 to 4 of the present application. This corresponds to the result that the second negative electrode active material layer serving as the buffer layer is unevenly coated on the upper part of the first negative electrode active material layer.

Explanation of Signs

[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 battery

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 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 contains a first negative electrode active material layer composition containing a first negative electrode active material, and the second negative electrode active material layer contains 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 SiO x (x = 0) and SiO x (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 the SiO x (x = 0), the second negative electrode active material contains a mixture of one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride, the second negative electrode active material layer includes a first surface that 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, the second negative electrode active material layer satisfies the non-uniformity of the following formula 1, a negative electrode for a lithium secondary battery: [Formula 1] 0 μm ≤ │C - (A + B / 2)│≤ 10 μm In the formula 1, A means the longest distance (μm) between the first surface and the second surface, B means the shortest distance (μm) between the first surface and the second surface, C means the average thickness (μm) of the second negative electrode active material layer.

2. A is 5 μm or more and 25 μm or less, C is 5 μm or more and 20 μm or less, the negative electrode for a lithium secondary battery according to claim 1.

3. 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, the negative electrode for a lithium secondary battery according to claim 1.

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

5. The second negative electrode active material contains a mixture of one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride, and 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, the negative electrode for a lithium secondary battery according to claim 1.

6. The negative electrode for a lithium secondary battery according to claim 1, wherein the silicon-based active material contains one or more selected from the group consisting of SiO x (0 < x < 2), SiC, and Si alloys.

7. The negative electrode for a lithium secondary battery according to claim 1, wherein the silicon-based active material contains SiO x (0 < x < 2).

8. 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.

9. 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 the viscosity of the first negative electrode active material layer composition. The negative electrode for a lithium secondary battery according to claim 1.

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

11. 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 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 to form a second negative electrode active material layer; A method for manufacturing a negative electrode for a lithium secondary battery, comprising: The first negative electrode active material contains one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and contains 95 parts by weight or more of SiO x (x = 0) based on 100 parts by weight of the first negative electrode active material, The second negative electrode active material contains a mixture of one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride, 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 50 μm or more and 100 μm or less, The thickness of the coater liquid 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. A method for manufacturing a negative electrode for a lithium secondary battery.

12. The manufacturing method of the negative electrode for a lithium secondary battery according to claim 11, wherein the core thickness of the coater is 0.4 T or more and 2 T or less.

13. The method 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. The step of pre-lithiating the negative electrode includes a lithium electroplating process; a lithium metal transfer process; a lithium metal vapor deposition process; or a stabilized lithium metal powder (SLMP) coating process, and is the manufacturing method of the negative electrode for a lithium secondary battery according to claim 11.

14. 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 wet-on-dry process includes a step of applying a first negative electrode active material layer composition; a step of partially drying or fully drying the applied first negative electrode active material layer composition to form a first negative electrode active material layer; and a step of applying the second negative electrode active material layer composition to the first negative electrode active material layer. This is the manufacturing method of the negative electrode for a lithium secondary battery according to claim 11.

15. 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 wet-on-wet process includes a step of applying a 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 in an undried state. This is the manufacturing method of the negative electrode for a lithium secondary battery according to claim 11.

16. A positive electrode; The negative electrode for a lithium secondary battery according to any one of claims 1 to 10; A separator provided between the positive electrode and the negative electrode; and An electrolyte; A lithium secondary battery including these.

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