Negative electrode for lithium secondary battery, method for manufacturing negative electrode for lithium secondary battery, and lithium secondary battery comprising negative electrode

Abstract

The present invention provides a negative electrode for a lithium secondary battery, the negative electrode comprising: a negative electrode current collector layer; a first negative electrode active material layer provided on one surface of the negative electrode current collector layer; and a second negative electrode active material layer disposed on the other surface of the negative electrode current collector layer, in which the first and second negative electrode active material layers each include upper and lower negative electrode active material layers, the first lower negative electrode active material layer and the second upper negative electrode active material layer having the same composition, and the first upper negative electrode active material layer and the second lower negative electrode active material layer have the same composition.

Description

Technical Field

[0001] This application claims priority and benefit to Korean Patent Application No. 10-2023-0158202, filed with the Korean Intellectual Property Office on November 15, 2023, the entire contents of which are incorporated herein by reference.

[0002] This application relates to a negative electrode for lithium secondary batteries, a method for manufacturing a negative electrode for lithium secondary batteries, and a lithium secondary battery including a negative electrode. Background Technology

[0003] Due to the rapid increase in the use of fossil fuels, the demand for alternative or clean energy sources is growing, and as part of this, the most active research area is in the field of power generation and energy storage using electrochemical reactions.

[0004] Currently, secondary batteries are a representative example of electrochemical devices that utilize this type of electrochemical energy, and their application scope is gradually expanding.

[0005] With the technological development and increasing demands of mobile devices, the demand for secondary batteries as an energy source has increased dramatically. Among these secondary batteries, lithium-ion batteries, characterized by high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used. Furthermore, methods for manufacturing high-density electrodes with even higher energy density per unit volume are being actively researched for use in these high-capacity lithium-ion batteries.

[0006] Typically, a secondary battery comprises a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material for inserting and deintercalating lithium ions from the positive electrode, and silicon-based particles with high discharge capacity can be used as the negative electrode active material.

[0007] Lithium-ion batteries are used in various industrial sectors such as automobiles, small modules, and mobile phones. The performance of lithium-ion batteries targeted in each sector involves various factors, but generally, it essentially requires the development of technologies aimed at increasing energy density while ensuring stability, fast charging, and lifespan performance.

[0008] In particular, while carbon-based materials such as graphite exhibit excellent stability and reversibility as anode materials, their capacity is limited. Therefore, in fields aiming for high capacity, i.e., maximizing energy density, there is an increasing trend towards using Si-based materials with high theoretical capacity as anode materials. However, simply incorporating high amounts of Si-based materials for high capacity purposes results in a rapid degradation in lifetime performance due to volume expansion compared to carbon-based materials, making it difficult to apply Si-based materials in practical applications.

[0009] To address the challenges encountered when using Si-based materials as anodes, various methods have been discussed, such as controlling the driving potential, additionally coating the active material layer with a thin film, suppressing volume expansion (e.g., controlling the particle size of the silicon compound), or developing adhesives capable of suppressing volume expansion of the silicon compound to prevent the conductive path from being interrupted. Furthermore, the lifetime characteristics of silicon-based anodes have been supplemented by limiting the proportion of silicon-based active material used during the initial charge-discharge phase through pre-lithiation of the silicon active material layer, thereby imparting reservoir functionality.

[0010] However, the above methods have limitations in their application because they may actually reduce battery performance, thus limiting their commercialization in negative electrode batteries with high silicon compound content.

[0011] Furthermore, to address the aforementioned issues, research has been conducted on using bilayer anode active materials, such as carbon-based active materials that can serve as a buffer layer on top of silicon-based active materials, to prevent volume expansion and surface concentration degradation. However, recently, this type of anode has also encountered a problem: the heat applied to the battery is rapidly transferred to other batteries, causing safety concerns.

[0012] Therefore, in the development of lithium secondary batteries aimed at increasing energy density and ensuring fast charging and lifespan performance, research is needed to ensure thermal safety.

[0013] Existing technical documents

[0014] Japanese Patent Application Publication No. 2009-080971 Summary of the Invention

[0015] Technical issues

[0016] This application relates to a negative electrode for lithium secondary batteries, and more particularly, to a negative electrode for lithium secondary batteries that can prevent electrode surface degradation during charge-discharge cycles (a problem present in existing silicon-based active materials), improve the cycle performance and capacity characteristics of lithium secondary batteries, and ensure thermal safety (preventing heat propagation), and relates to a method for manufacturing a negative electrode for lithium secondary batteries and a lithium secondary battery including the negative electrode.

[0017] Technical solution

[0018] An exemplary embodiment of this specification provides a negative electrode for a lithium secondary battery, the negative electrode comprising: Negative electrode current collector layer; A first negative electrode active material layer is disposed on one surface of the negative electrode current collector layer; and The second negative electrode active material layer is disposed on another surface of the negative electrode current collector layer, wherein... The first negative electrode active material layer includes a first lower negative electrode active material layer that contacts the negative electrode current collector layer and a first upper negative electrode active material layer disposed on a surface of the first lower negative electrode active material layer opposite to the surface that contacts the negative electrode current collector layer. The second negative electrode active material layer includes a second lower negative electrode active material layer that contacts the negative electrode current collector layer and a second upper negative electrode active material layer disposed on a surface of the second lower negative electrode active material layer opposite to the surface that contacts the negative electrode current collector layer. One of the first lower negative electrode active material layer and the first upper negative electrode active material layer contains a silicon-based active material. The first lower negative electrode active material layer and the second upper negative electrode active material layer have the same composition, and The first upper negative electrode active material layer and the second lower negative electrode active material layer have the same composition.

[0019] An exemplary embodiment of this application provides a method for manufacturing a negative electrode for a lithium secondary battery, the method comprising: Prepare the first negative electrode slurry and the second negative electrode slurry; The first negative electrode slurry is coated onto one surface of the negative electrode current collector layer, and the second negative electrode slurry is coated onto the first negative electrode slurry coated on one surface of the negative electrode current collector layer; and The second negative electrode slurry is coated onto the opposite surface of the negative electrode current collector layer, and the first negative electrode slurry is coated onto the second negative electrode slurry coated on the opposite surface of the negative electrode current collector layer. One of the first negative electrode slurry and the second negative electrode slurry contains a silicon-based active material.

[0020] Finally, a lithium secondary battery is provided, comprising: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0021] Beneficial effects

[0022] In the development of automotive batteries, heat transfer is the most critical safety issue. It involves assessing how quickly and explosively heat generated in one battery can be transferred to other batteries, and ensuring thermal safety is a major part of this development process.

[0023] In particular, due to the recent use of silicon-based materials to achieve high capacity, the issue of thermal stability has become more prominent. Therefore, a negative electrode for a lithium secondary battery according to an exemplary embodiment of the present invention is characterized by having a double-layered structure of negative electrode active material layers disposed on the upper and lower surfaces (a first negative electrode active material layer and a second negative electrode active material layer) of the negative electrode current collector layer, specifically, the first lower negative electrode active material layer and the second upper negative electrode active material layer have the same composition, and the first upper negative electrode active material layer and the second lower negative electrode active material layer have the same composition.

[0024] By improving the structure of the negative electrode for lithium secondary batteries as described above, the explosive force of the negative electrode when heat is applied can be reduced. Specifically, the bilayer active materials contained in the first and second negative electrode active material layers are arranged in a structure that is asymmetrical to each other. Thus, even if thermal runaway occurs in the negative electrode active material layer containing the silicon-based active material, the thermal runaway can be controlled because of the other negative electrode active material layer that can act as a barrier. Attached Figure Description

[0025] Figure 1 This is a view showing a stacked structure of a negative electrode for a lithium secondary battery according to an exemplary embodiment of this application.

[0026] <Explanation of Figure Symbols and Markings>

[0027] 10-1: First lower negative electrode active material layer

[0028] 10-2: First upper negative electrode active material layer

[0029] 20: Negative electrode current collector layer

[0030] 30-1: Second lower negative electrode active material layer

[0031] 30-2: Second upper negative electrode active material layer Detailed Implementation

[0032] Before describing the present invention, some terms will be defined.

[0033] In this specification, unless otherwise specifically described, when a part "contains", "includes", or "has" a constituent element, it does not mean that other constituent elements are excluded, but rather that other constituent elements may be further included.

[0034] In this specification, "p to q" means the range of "above p and below q".

[0035] In this specification, "specific surface area" is measured by the BET method, specifically calculated by using the BELSORP-mini II, available from BEL Japan, Inc., from the amount of nitrogen adsorbed at liquid nitrogen temperature (77K). In other words, in this application, BET specific surface area can refer to the specific surface area measured by the above method.

[0036] In this specification, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution based on particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative particle number distribution based on particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution based on particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution based on particle size. Note that the particle size distribution can be measured using laser diffraction. Specifically, after dispersing the powder to be measured in a dispersion medium, the resulting dispersion is introduced into a commercially available laser diffraction particle size measurement device (e.g., Microtrac S3500), where the difference in the diffraction pattern based on particle size is measured as the laser beam passes through the particles, and the particle size distribution is then calculated.

[0037] In this specification, the statement "the polymer contains a monomer as a monomeric unit" means that the monomer participates in the polymerization reaction and is included in the polymer as a repeating unit. In this specification, when the polymer contains a monomer, it is interpreted in the same way as when the polymer contains a monomer as a monomeric unit.

[0038] In this specification, the term "polymer" is to be understood in a broad sense and includes copolymers unless otherwise stated as "homogeneous polymer".

[0039] In this specification, weight-average molecular weight (Mw) and number-average molecular weight (Mn) are converted molecular weights of polystyrene measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) of various degrees of polymerization as standard materials. Unless otherwise specified, molecular weight in this specification refers to weight-average molecular weight.

[0040] In the following, exemplary embodiments of the invention will be described in detail with reference to the accompanying drawings, enabling those skilled in the art to readily implement the invention. However, the invention can be implemented in various different forms and is not limited to the following description.

[0041] An exemplary embodiment of this specification provides a negative electrode for a lithium secondary battery, the negative electrode comprising: Negative electrode current collector layer; A first negative electrode active material layer is disposed on one surface of the negative electrode current collector layer; and The second negative electrode active material layer is disposed on another surface of the negative electrode current collector layer, wherein... The first negative electrode active material layer includes a first lower negative electrode active material layer that contacts the negative electrode current collector layer and a first upper negative electrode active material layer disposed on a surface of the first lower negative electrode active material layer opposite to the surface that contacts the negative electrode current collector layer. The second negative electrode active material layer includes a second lower negative electrode active material layer that contacts the negative electrode current collector layer and a second upper negative electrode active material layer disposed on a surface of the second lower negative electrode active material layer opposite to the surface that contacts the negative electrode current collector layer. One of the first lower negative electrode active material layer and the first upper negative electrode active material layer contains a silicon-based active material. The first lower negative electrode active material layer and the second upper negative electrode active material layer have the same composition, and The first upper negative electrode active material layer and the second lower negative electrode active material layer have the same composition.

[0042] By improving the structure of the negative electrode for lithium secondary batteries as described above, the explosive force of the negative electrode when heat is applied can be reduced. Specifically, the bilayer active materials contained in the first and second negative electrode active material layers are arranged in a structure that is asymmetrical to each other. Therefore, even if thermal runaway occurs in the negative electrode active material layer containing the silicon-based active material, the explosive pressure can be reduced and the acceleration of thermal runaway of the positive electrode can be controlled due to the arrangement of the other negative electrode active material layer, which can act as a barrier.

[0043] Figure 1 This is a view illustrating the stacked structure of a negative electrode for a lithium secondary battery according to an exemplary embodiment of this application. Specifically, the negative electrode 100 for a lithium secondary battery can be seen, which includes a first negative electrode active material layer comprising a first lower negative electrode active material layer 10-1 and a first upper negative electrode active material layer 10-2, and a second negative electrode active material layer comprising a second lower negative electrode active material layer 30-1 and a second upper negative electrode active material layer 30-2, on one surface of the negative electrode current collector layer 20. In this case, one of the first lower negative electrode active material layer and the first upper negative electrode active material layer contains a silicon-based active material, and the first lower negative electrode active material layer and the second upper negative electrode active material layer have the same composition, and the first upper negative electrode active material layer and the second lower negative electrode active material layer have the same composition.

[0044] Existing negative electrode structures have a configuration where the first lower negative electrode active material layer 10-1 and the second lower negative electrode active material layer 30-1 have the same composition, the first upper negative electrode active material layer 10-2 and the second upper negative electrode active material layer 30-2 have the same composition, and at least one of the first lower negative electrode active material layer 10-1 and the second lower negative electrode active material layer 30-1 contains a silicon-based active material. That is, in existing double-layer structures, symmetrical structures have been developed, wherein the silicon-based active material is concentrated towards the negative electrode current collector layer or towards the outside. However, when the silicon-based active material is formed simultaneously towards the negative electrode current collector, the negative electrode current collector layer is prone to melting, increasing the explosive force. Furthermore, it is known that when the silicon-based active material is formed simultaneously towards the outside, the thermal runaway mechanism begins at the negative electrode and accelerates the thermal runaway at the positive electrode. In this respect, when the silicon-based active material is formed simultaneously with the concentration towards the outer side of the negative electrode as described above, it causes problems by acting as a thermal trigger, accelerating thermal runaway at the positive electrode and thus reducing safety. However, this application is able to solve the above-mentioned problems.

[0045] In this application, the first negative electrode active material layer includes a first lower negative electrode active material layer in contact with the negative electrode current collector layer and a first upper negative electrode active material layer disposed on the surface of the first lower negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer. This configuration can mean that the negative electrode current collector layer, the first lower negative electrode active material layer and the first upper negative electrode active material layer are stacked sequentially.

[0046] In this application, the second negative electrode active material layer comprises a second lower negative electrode active material layer in contact with the negative electrode current collector layer and a second upper negative electrode active material layer disposed on a surface of the second lower negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer. This configuration can mean that the negative electrode current collector layer, the second lower negative electrode active material layer and the second upper negative electrode active material layer are stacked sequentially.

[0047] In one exemplary embodiment of this application, the first negative electrode active material layer and the second negative electrode active material layer may be formed on the entire surface of the negative electrode current collector layer.

[0048] The negative electrode for lithium secondary batteries of the present invention will be described in more detail below.

[0049] The negative electrode for lithium secondary batteries includes: Negative electrode current collector layer; A first negative electrode active material layer is disposed on one surface of the negative electrode current collector layer; and The second negative electrode active material layer is disposed on another surface of the negative electrode current collector layer, wherein... The first negative electrode active material layer includes a first lower negative electrode active material layer in contact with the negative electrode current collector layer and a first upper negative electrode active material layer disposed on a surface of the first lower negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer. The second negative electrode active material layer includes a second lower negative electrode active material layer that is in contact with the negative electrode current collector layer and a second upper negative electrode active material layer disposed on the surface of the second lower negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer.

[0050] In one exemplary embodiment of this application, the negative electrode current collector layer typically has a thickness of 1 μm to 100 μm. This negative electrode current collector layer is not particularly limited, as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloys, etc., can be used. Furthermore, the negative electrode current collector layer may have fine irregularities formed on its surface to improve the adhesion of the negative electrode active material, and can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, or nonwoven fabrics.

[0051] In one exemplary embodiment of this application, the thickness of the negative electrode current collector layer may be more than 1 μm and less than 100 μm.

[0052] However, the thickness can be modified in various ways depending on the type and purpose of the negative electrode used, and is not limited thereto.

[0053] In one exemplary embodiment of this application, one of the first lower negative electrode active material layer and the first upper negative electrode active material layer contains a silicon-based active material, the first lower negative electrode active material layer and the second upper negative electrode active material layer have the same composition, and the first upper negative electrode active material layer and the second lower negative electrode active material layer have the same composition.

[0054] In this application, "having the same composition" can mean that the composition and content of each active material layer are the same, and in this case, "same" can allow for some errors that are permissible in the art. However, in this application, "having the same composition" means only the composition, and the physical properties (thickness, loading, etc.) can be different.

[0055] In one exemplary embodiment of this application, the first lower negative electrode active material layer comprises a silicon-based active material, the first lower negative electrode active material layer and the second upper negative electrode active material layer have the same composition, and the first upper negative electrode active material layer and the second lower negative electrode active material layer have the same composition.

[0056] In one exemplary embodiment of this application, the first upper negative electrode active material layer comprises a silicon-based active material, the first lower negative electrode active material layer and the second upper negative electrode active material layer have the same composition, and the first upper negative electrode active material layer and the second lower negative electrode active material layer have the same composition.

[0057] In other words, as described above, the negative electrode for lithium secondary batteries of this application is characterized by containing a silicon-based active material, which is not continuously contained in the negative electrode, but is discontinuously disposed together with another layer of negative electrode active material or a negative electrode current collector layer that acts as a barrier. Therefore, even in the event of thermal runaway, thermal stability is ensured because the barrier prevents heat transfer.

[0058] In other words, this application provides a negative electrode for a lithium secondary battery, wherein the first negative electrode active material layer and the second negative electrode active material layer are asymmetrical relative to the negative electrode current collector layer.

[0059] Furthermore, this application provides a negative electrode for a lithium secondary battery, wherein the first lower negative electrode active material layer and the second lower negative electrode active material layer have different compositions, and the first upper negative electrode active material layer and the second upper negative electrode active material layer have different compositions.

[0060] In this context, "having different compositions" can be defined as having different compositions when the types or amounts of active materials contained in each active material layer are different.

[0061] In this application, a negative electrode for a lithium secondary battery is provided, wherein the first lower negative electrode active material layer comprises a first lower negative electrode active material layer composition, the first upper negative electrode active material layer comprises a first upper negative electrode active material layer composition, the first lower negative electrode active material layer composition comprises a first lower negative electrode active material, a first lower negative electrode conductive material and a first lower negative electrode binder, and the first upper negative electrode active material layer composition comprises a first upper negative electrode active material, a first upper negative electrode conductive material and a first upper negative electrode binder.

[0062] In this application, a negative electrode for a lithium secondary battery is provided, wherein one of the first lower negative electrode active material and the first upper negative electrode active material comprises one or more selected from the group consisting of carbon-based active materials, silicon-based active materials, metal-based active materials capable of alloying with lithium, and lithium-containing nitrides, and the other of the first lower negative electrode active material and the first upper negative electrode active material comprises a carbon-based active material.

[0063] In this application, a negative electrode for a lithium secondary battery is provided, wherein the first lower negative electrode active material comprises one or more selected from the group consisting of carbon-based active materials, silicon-based active materials, metal-based active materials capable of alloying with lithium, and lithium-containing nitrides, and the first upper negative electrode active material comprises a carbon-based active material.

[0064] In addition, a negative electrode for a lithium secondary battery is provided, wherein the first upper negative electrode active material comprises one or more selected from the group consisting of carbon-based active materials, silicon-based active materials, metal-based active materials capable of alloying with lithium, and lithium-containing nitrides, and the first lower negative electrode active material comprises a carbon-based active material.

[0065] This application provides a negative electrode for a lithium secondary battery, wherein one of the first lower negative electrode active material and the first upper negative electrode active material comprises a carbon-based active material and a silicon-based active material, and the other of the first lower negative electrode active material and the first upper negative electrode active material comprises a carbon-based active material.

[0066] In this application, the first lower negative electrode active material may include carbon-based active material and silicon-based active material, the first upper negative electrode active material may include carbon-based active material, and based on 100 parts by weight of the first lower negative electrode active material, the content of silicon-based active material may be more than 1 part by weight and less than 50 parts by weight.

[0067] In another exemplary embodiment, the first lower negative electrode active material may comprise carbon-based active material and silicon-based active material, the first upper negative electrode active material may comprise carbon-based active material, and based on 100 parts by weight of the first lower negative electrode active material, the content of the silicon-based active material may be more than 1 part by weight and less than 50 parts by weight, preferably more than 3 parts by weight and less than 40 parts by weight, more preferably more than 5 parts by weight and less than 20 parts by weight.

[0068] In this application, the first upper negative electrode active material may include carbon-based active material and silicon-based active material, the first lower negative electrode active material may include carbon-based active material, and based on 100 parts by weight of the first upper negative electrode active material, the content of silicon-based active material may be more than 1 part by weight and less than 50 parts by weight.

[0069] In another exemplary embodiment, the first upper negative electrode active material may comprise a carbon-based active material and a silicon-based active material, the first lower negative electrode active material may comprise a carbon-based active material, and based on 100 parts by weight of the first upper negative electrode active material, the content of the silicon-based active material may be more than 1 part by weight and less than 50 parts by weight, preferably more than 3 parts by weight and less than 40 parts by weight, more preferably more than 5 parts by weight and less than 20 parts by weight.

[0070] As described above, the first lower negative electrode active material or the first upper negative electrode active material contains the aforementioned amount of silicon-based active material by weight, thereby ensuring high energy density and minimizing lifetime performance issues related to volume expansion, thus providing a high-capacity negative electrode with improved lifetime performance. In other words, the negative electrode active material layer composition according to this application uses a silicon-based active material with very high capacity within the aforementioned range, while also using another negative electrode active material layer stacked together, thereby solving the problems of surface degradation during charge and discharge, uniformity during pre-lithiation, and lifetime characteristics without compromising the overall capacity performance of the entire negative electrode.

[0071] This application provides a negative electrode for a lithium secondary battery, wherein the silicon-based active material comprises SiO₂. x (x=0), SiO x (0 < x < 2) or SiC.

[0072] In one exemplary embodiment of this application, pure silicon (SiO2) can be used as the silicon-based active material. x (x=0) particles.

[0073] Note that the average particle size (D50) of the silicon-based active material of the present invention can be from 3 μm to 10 μm, specifically from 4 μm to 8 μm, and more specifically from 5 μm to 7 μm. When the average particle size is within the above range, the specific surface area of ​​the particles is within a suitable range, resulting in a negative electrode slurry viscosity within an appropriate range. Therefore, the particles constituting the negative electrode slurry are smoothly dispersed. Furthermore, when the size of the first negative electrode active material has a value equal to or greater than the lower limit of the above range, due to the composite material made of conductive material and binder in the negative electrode slurry, the contact area between the silicon particles and the conductive material is excellent, increasing the likelihood of a continuous conductive network and thereby increasing the capacity retention rate. Note that when the average particle size falls within the above range, excessively large silicon particles are excluded, resulting in a smooth surface for forming the negative electrode. Therefore, it is possible to prevent uneven current density during charging and discharging.

[0074] In one exemplary embodiment of this application, the silicon-based active material typically has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is preferably 0.1 m². 2 / g to 150.0m 2 / g, more preferably 0.1m 2 / g to 100.0m 2 / g, with a particularly preferred value of 0.2m 2 / g to 80.0m 2 / g, the optimal value is 0.2m 2 / g to 18.0m 2 / g. BET specific surface area is measured according to DIN 66131 (using nitrogen).

[0075] In one exemplary embodiment of this application, the silicon-based active material may exist, for example, in crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or fragmented particles. Alternatively, but less preferably, the silicon particles may also have a fibrous structure, or may exist in the form of a silicon-containing film or coating.

[0076] In one exemplary embodiment of this application, the silicon-based active material may have a non-spherical shape, and its sphericity (circularity) is, for example, below 0.9, such as 0.7 to 0.9, such as 0.8 to 0.9, such as 0.85 to 0.9.

[0077] In this application, the sphericity is determined by the following formula 1, where A is the area and P is the boundary line.

[0078] [Formula 1]

[0079] 4πA / P 2

[0080] In one exemplary embodiment of this application, representative examples of the carbon-based active materials include natural graphite, artificial graphite, expandable graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, fullerenes, activated carbon, etc., and the carbon-based active materials can be used without limitation, as long as the carbon-based active materials are generally used in carbon materials for lithium secondary batteries, specifically, they can be processed into spherical or dot-shaped forms for use.

[0081] In one exemplary embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the carbon-based active material includes graphite, the graphite includes artificial graphite and natural graphite, and the weight ratio of artificial graphite to natural graphite is 5:5 to 9.5:0.5.

[0082] According to an exemplary embodiment of the present invention, artificial graphite may be in the form of primary particles, or it may be in the form of secondary particles in which a plurality of primary particles are aggregated.

[0083] As used in this invention, the term "primary particle" means the original particle from which different types of particles are formed, and multiple primary particles can be aggregated, combined, or assembled to form secondary particles.

[0084] As used in this invention, the term "secondary particle" refers to a physically distinguishable large particle formed by aggregating, combining, or assembling individual primary particles.

[0085] The primary particle-based artificial graphite can be manufactured by heat treatment of one or more selected from the group consisting of needle coke, mosaic coke, and coal tar pitch.

[0086] The artificial graphite is typically manufactured by carbonizing raw materials (such as coal tar, coal tar pitch, and petroleum-based heavy oil) at temperatures above 2,500°C. After this graphitization, the artificial graphite can be particle-sized, such as by crushing and forming secondary particles, and then used as a negative electrode active material. In the case of artificial graphite, crystals are randomly distributed within the particles, have a lower roundness than natural graphite, and are slightly sharper in shape.

[0087] Examples of the artificial graphite used in one exemplary embodiment of the present invention include commercially widely used mesophase carbon microspheres (MCMB) and mesophase pitch-based carbon fibers (MPCF), block graphitized artificial graphite, powdered graphitized artificial graphite, etc. The artificial graphite may have a sphericity of less than 0.91, or 0.6 to 0.91, or 0.7 to 0.9.

[0088] Furthermore, the artificial graphite may have a particle size of 5 to 30 μm, preferably 10 to 25 μm.

[0089] Specifically, the artificial graphite primary particles can have a D50 of 6 μm to 15 μm, 6 μm to 10 μm, or 6 μm to 9 μm. When the D50 of the primary particles meets this range, the primary particles can be formed with high graphitization, appropriately ensuring the orientation index of the negative electrode active material particles, thereby improving fast charging performance.

[0090] The artificial graphite secondary particles can be formed by assembling primary particles. That is, the secondary particles can be structures formed by aggregating the primary particles together through an assembly process. The secondary particles may contain a carbonaceous matrix that aggregates the primary particles. The carbonaceous matrix may contain at least one of soft carbon and graphite. The soft carbon can be formed by heat-treating pitch.

[0091] The carbonaceous matrix can be included in the secondary particles in an amount of 8% to 16% by weight, specifically 9% to 12% by weight. This range is lower than the level of carbonaceous matrix content used in typical artificial graphite secondary particles. Within this range, the particle size of the primary particles in the secondary particles can be controlled, so that structurally stable secondary particles can be produced even with a small amount of carbonaceous matrix required for assembly, and the amount of primary particles constituting the secondary particles can also be uniform.

[0092] The surface of the artificial graphite secondary particles may contain a carbon coating, and the carbon coating may contain at least one of amorphous carbon and crystalline carbon.

[0093] The crystalline carbon can further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerenes and graphene.

[0094] The amorphous carbon can appropriately maintain the strength of the coating to suppress the expansion of the natural graphite. The amorphous carbon can be a carbide selected from at least one of the group consisting of tar, pitch and other organic materials, or a carbon-based material formed using hydrocarbons as a source for chemical vapor deposition.

[0095] Other organic materials may be carbonized from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldose, or ketose, as well as carbonized from organic materials selected from combinations thereof.

[0096] The artificial graphite secondary particles can have a D50 of 10 μm to 25 μm, specifically 12 μm to 22 μm, and more specifically 13 μm to 20 μm. When the above range is met, the artificial graphite secondary particles can be uniformly dispersed in the slurry and can also improve the charging performance of the battery.

[0097] The artificial graphite secondary particles can have a tap density of 0.85 g / cc to 1.30 g / cc, specifically 0.90 g / cc to 1.10 g / cc, and more specifically 0.90 g / cc to 1.07 g / cc. When the above range is met, the artificial graphite secondary particles can be smoothly filled into the negative electrode, which means that the adhesion of the negative electrode can be improved.

[0098] The natural graphite is typically in the form of plate-like aggregates before processing, and the plate-like particles can be manufactured into spheres with smooth surfaces through post-processing (such as particle crushing and reassembly processes) for use as active materials in the manufacture of electrodes.

[0099] In one exemplary embodiment of the invention, the natural graphite used may have a roundness greater than 0.91 and less than 0.97, or 0.93 to 0.97, or 0.94 to 0.96.

[0100] The natural graphite may have a particle size of 5 to 30 μm or 10 to 25 μm.

[0101] According to an exemplary embodiment of the present invention, the weight ratio of the artificial graphite to the natural graphite can be 5:5 to 9.5:0.5, or 5:5 to 9.3:0.7, or 5:5 to 9:1, or 6:4 to 9:1. When the weight ratio of the artificial graphite to the natural graphite meets such a range, better output can be exhibited, which can be advantageous in terms of lifespan and fast charging performance.

[0102] In one exemplary embodiment of this application, the planar conductive material used as the negative electrode conductive material has a different structure and function than the carbon-based active material typically used as the negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material can be artificial graphite or natural graphite, and refers to a material processed into spherical or dot-like shapes for use to promote the storage and release of lithium ions.

[0103] On the other hand, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape, and can be described as plate-like graphite. That is, the planar conductive material is a material included to maintain the conductive path in the negative electrode active material layer, and refers to a material used to ensure the conductive path in a planar shape within the negative electrode active material layer rather than to store and release lithium.

[0104] In other words, in this application, using plate-shaped graphite as a conductive material means processing graphite into planar or plate-like forms and using it as a material to ensure a conductive path rather than to store or release lithium. In this case, the negative electrode active material included together has high capacity properties regarding the storage and release of lithium and is used to store and release all lithium ions transferred from the positive electrode.

[0105] On the other hand, in this application, using carbon-based active materials as active materials means processing the carbon-based active materials into dots or spheres and using them as materials for storing or releasing lithium.

[0106] In other words, in one exemplary embodiment of this application, the BET specific surface area of ​​artificial graphite or natural graphite, which is a carbon-based active material, can meet the requirement of 0.1 m². 2 / g or more and 4.5m 2 The range is below / g. Furthermore, plate-shaped graphite, as a planar conductive material, has a planar shape, and its BET specific surface area can be 5m².2 / g or more.

[0107] Representative examples of metal-based active materials can be compounds containing one or more metallic elements selected from the group consisting of Al, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt, Ti, Sb, Ga, Mn, Fe, Co, Ni, Cu, Sr, and Ba. These metal compounds can be used in any form, such as elements, alloys, oxides (TiO2, SnO2, etc.), nitrides, sulfides, borides, and alloys with lithium; however, the elements, alloys, oxides, and alloys with lithium can increase capacity.

[0108] In one exemplary embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the composition of the first lower negative electrode active material layer is based on 100 parts by weight, and the content of the first lower negative electrode active material is 60 parts by weight or more.

[0109] In another exemplary embodiment, based on 100 parts by weight of the first lower negative electrode active material layer composition, the content of the first lower negative electrode active material may be 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and may be 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 80 parts by weight or less.

[0110] In one exemplary embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the composition is based on 100 parts by weight of the first upper negative electrode active material layer, and the content of the first upper negative electrode active material is 60 parts by weight or more.

[0111] In another exemplary embodiment, based on 100 parts by weight of the first upper negative electrode active material layer composition, the content of the first upper negative electrode active material may be 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and may be 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 80 parts by weight or less.

[0112] In existing technologies, graphite-based compounds are typically used as the negative electrode active material. However, in recent years, with the increasing demand for high-capacity batteries, attempts to mix and use silicon-based compounds to increase capacity are increasing. However, a limitation of silicon-based compounds is that their volume expands rapidly during charge and discharge, leading to damage to the conductive paths formed in the negative electrode active material layer, thereby reducing battery performance.

[0113] Therefore, in an exemplary embodiment of this application, the first lower negative electrode active material layer composition may include a first lower negative electrode active material, a first lower negative electrode conductive material and a first lower negative electrode adhesive, and the first upper negative electrode active material layer composition may include a first upper negative electrode active material, a first upper negative electrode conductive material and a first upper negative electrode adhesive.

[0114] In this case, the following description of the negative electrode conductive material can be equally applied to the description of the first lower negative electrode conductive material and the first upper negative electrode conductive material, and the following description of the negative electrode adhesive can be equally applied to the description of the first lower negative electrode adhesive and the first upper negative electrode adhesive.

[0115] In one exemplary embodiment of this application, the negative electrode conductive material may be any material commonly used in the art without limitation, and may specifically include one or more selected from the group consisting of point conductive materials, planar conductive materials and linear conductive materials.

[0116] In one exemplary embodiment of this application, the dot-shaped conductive material refers to a conductive material that can be used to improve the conductivity of the negative electrode, has conductivity without causing chemical changes, and has a dot-shaped or spherical shape. 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 cracking black, conductive fibers, fluorocarbons, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may contain carbon black for high conductivity and excellent dispersibility.

[0117] In one exemplary embodiment of this application, the dot-shaped conductive material may have a density of 40m. 2 / g or more and 70m 2 / g or less, preferably 45m 2 / g or more and 65m 2 / g or less, more preferably 50m 2 / g or more and 60m 2 BET specific surface area below / g.

[0118] In one exemplary embodiment of this application, the particle size of the dot-shaped conductive material can be from 10 nm to 100 nm, preferably from 20 nm to 90 nm, and more preferably from 20 nm to 60 nm.

[0119] In one exemplary embodiment of this application, the second negative electrode conductive material may comprise a planar conductive material.

[0120] The planar conductive material can improve conductivity by increasing the surface contact between silicon particles in the negative electrode, while suppressing the breakage of the conductive path caused by volume expansion, and can be described as a plate-shaped conductive material or a bulk-shaped conductive material.

[0121] In one exemplary embodiment of this application, the planar conductive material may comprise at least one selected from the group consisting of plate graphite, graphene, graphene oxide, and graphite flakes, and preferably plate graphite.

[0122] In one exemplary embodiment of this application, the average particle size (D50) of the planar conductive material can be 2 to 7 μm, specifically 3 to 6 μm, and more specifically 4 to 5 μm. When the above range is met, sufficient particle size leads to easy dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is excellent.

[0123] In one exemplary embodiment of this application, a negative electrode composition is provided, wherein the planar conductive material has a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0124] In one exemplary embodiment of this application, the planar conductive material can be a planar conductive material with a high specific surface area (BET specific surface area) or a planar conductive material with a low specific surface area (BET specific surface area).

[0125] In one exemplary embodiment of this application, the planar conductive material can be used without limitation either a planar conductive material with a high specific surface area or a planar conductive material with a low specific surface area. However, in particular, the planar conductive material according to this application may be affected to some extent by the dispersion effect in terms of electrode performance, making it particularly preferable to use a planar conductive material with a low specific surface area that does not cause dispersion problems.

[0126] In one exemplary embodiment of this application, the BET specific surface area of ​​the planar conductive material may be 5m². 2 / g or more.

[0127] In another exemplary embodiment, the BET specific surface area of ​​the planar conductive material may be 5m². 2 / g or more and 500m 2 Below / g, 5m is preferred. 2 / g or more and 300m 2 / g or less, preferably 5m 2 / g or more and 250m 2 / g or less.

[0128] In another exemplary embodiment, the planar conductive material is a planar conductive material with a high specific surface area, and the BET specific surface area can fall within 50m². 2 / g or more and 500m 2 / g or less, preferably 80m 2 / g or more and 300m 2 / g or less, more preferably 100m 2 / g or more and 300m 2 Within the range of / g and below.

[0129] In another exemplary embodiment, the planar conductive material is a planar conductive material with a low specific surface area, and the BET specific surface area can fall within 5m². 2 / g or more and 40m 2 / g or less, preferably 5m 2 / g or more and 30m 2 / g or less, preferably 5m 2 / g or more and 25m 2 Within the range of / g and below.

[0130] Other conductive materials may include linear conductive materials, such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. A bundled carbon nanotube may comprise multiple carbon nanotube units. Specifically, unless otherwise stated, the term "bundled" herein refers to a bundle-like or rope-like secondary shape in which multiple carbon nanotube units are aligned or entangled side-by-side with substantially the same orientation along their longitudinal axes. The carbon nanotube units have cylindrical graphite sheets with nanometer-sized diameters and sp2 bonding structures. In this case, the properties of a conductive or semi-conductive material can be exhibited depending on the winding angle and structure of the graphite sheets. Compared to entangled carbon nanotubes, bundled carbon nanotubes can be more uniformly dispersed during the fabrication of the negative electrode and can more readily form a conductive network within the negative electrode, thereby improving the conductivity of the negative electrode.

[0131] In particular, the linear conductive material according to an exemplary embodiment of this application may be a single-walled carbon nanotube (SWCNT).

[0132] In this application, a negative electrode for a lithium secondary battery is provided, wherein the first lower negative electrode conductive material and the first upper negative electrode conductive material comprise at least linear conductive materials.

[0133] The single-walled carbon nanotubes are tubular materials formed by hexagonally arranged carbon atoms. Due to their unique chirality, they exhibit non-conductor, conductor, or semiconductor properties. Furthermore, because the carbon atoms are connected by strong covalent bonds, they have tensile strength that is more than 100 times higher than that of steel, excellent flexibility and elasticity, and chemical stability.

[0134] The average diameter of the single-walled carbon nanotubes is 0.5 nm to 15 nm. According to an exemplary embodiment of the invention, the average diameter of the single-walled carbon nanotubes can be 1 nm to 10 nm, 1 nm to 5 nm, or 1 nm to 2 nm. When the average diameter of the single-walled carbon nanotubes falls within the above range, the conductivity of the negative electrode can be maintained even when the content of single-walled carbon nanotubes is very low, while the desired viscosity and solids content are achieved during the preparation of the conductive material dispersion solution. In the conductive material dispersion solution, the single-walled carbon nanotubes aggregate with each other, and therefore can exist in an entangled state (aggregate). Therefore, by measuring the diameter of any entangled single-walled carbon nanotube aggregate extracted from the conductive material dispersion solution using SEM or TEM, and then dividing the diameter of the aggregate by the number of single-walled carbon nanotubes constituting the aggregate, the average diameter can be determined.

[0135] The BET specific surface area of ​​the aforementioned single-walled carbon nanotubes can be 500 m². 2 / g to 1,500m 2 / g or 900m 2 / g to 1,200m 2 / g, specifically 250m 2 / g to 330m 2 / g. When the above range is met, a conductive material dispersion solution with a preferred solid content is obtained, and excessive increase in viscosity of the negative electrode slurry is prevented. The BET specific surface area can be measured by the nitrogen adsorption BET method.

[0136] The aspect ratio of the single-walled carbon nanotubes can be from 50 to 20,000, or the length of the single-walled carbon nanotubes can be from 5 to 100 μm or from 5 to 50 μm. When the aspect ratio or length is within such a range, the specific surface area is at a high level, allowing the single-walled carbon nanotubes in the negative electrode to be adsorbed onto the active material particles by strong attraction. Therefore, the conductive network can be successfully maintained even during the volume expansion of the negative electrode active material. When observing the single-walled carbon nanotube powder by SEM, the aspect ratio can be confirmed by obtaining the average aspect ratio of 15 single-walled carbon nanotubes with a large aspect ratio and 15 single-walled carbon nanotubes with a small aspect ratio.

[0137] The single-walled carbon nanotubes mentioned above are superior to multi-walled or double-walled carbon nanotubes because their larger aspect ratio, greater length and larger volume allow them to form electrical networks even when used in small quantities.

[0138] In one exemplary embodiment of this application, based on 100 parts by weight of the first lower negative electrode active material layer composition, the first lower negative electrode conductive material can be in the range of more than 1 part by weight and less than 40 parts by weight.

[0139] In another exemplary embodiment, based on 100 parts by weight of the first lower negative electrode active material layer composition, the content of the first lower negative electrode conductive material may be more than 1 part by weight and less than 40 parts by weight, preferably more than 10 parts by weight and less than 30 parts by weight, and more preferably more than 15 parts by weight and less than 25 parts by weight.

[0140] In one exemplary embodiment of this application, based on 100 parts by weight of the first upper negative electrode active material layer composition, the first upper negative electrode conductive material can be in the range of more than 1 part by weight and less than 40 parts by weight.

[0141] In another exemplary embodiment, based on 100 parts by weight of the first upper negative electrode active material layer composition, the content of the first upper negative electrode conductive material may be more than 1 part by weight and less than 40 parts by weight, preferably more than 10 parts by weight and less than 30 parts by weight, and more preferably more than 15 parts by weight and less than 25 parts by weight.

[0142] In one exemplary embodiment of this application, the negative electrode conductive material may comprise dot-shaped conductive material, planar conductive material, and linear conductive material, and the dot-shaped conductive material, the planar conductive material, and the linear conductive material may satisfy a ratio of 1:1:0.01 to 1:1:1.

[0143] In one exemplary embodiment of this application, based on 100 parts by weight of the negative electrode conductive material, the content of the dot-shaped conductive material may be more than 1 part by weight and less than 60 parts by weight, preferably more than 5 parts by weight and less than 50 parts by weight, and more preferably more than 10 parts by weight and less than 50 parts by weight.

[0144] In one exemplary embodiment of this application, based on 100 parts by weight of the negative electrode conductive material, the content of the planar conductive material may be more than 1 part by weight and less than 60 parts by weight, preferably more than 5 parts by weight and less than 50 parts by weight, and more preferably more than 10 parts by weight and less than 50 parts by weight.

[0145] In one exemplary embodiment of this application, based on 100 parts by weight of the negative electrode conductive material, the content of the linear conductive material may be 0.01 parts by weight or more and 10 parts by weight or less, preferably 0.05 parts by weight or more and 8 parts by weight or less, and more preferably 0.1 parts by weight or more and 5 parts by weight or less.

[0146] In one exemplary embodiment of this application, the negative electrode conductive material may include linear conductive materials and planar conductive materials.

[0147] In one exemplary embodiment of this application, the negative electrode conductive material may comprise linear conductive material and planar conductive material, and the ratio of the linear conductive material to the planar conductive material may be from 0.01:1 to 0.1:1.

[0148] In an exemplary embodiment of this application, since the negative electrode conductive material specifically includes the linear conductive material and the planar conductive material, and satisfies the above composition and ratio respectively, it will not significantly affect the life characteristics of existing lithium secondary batteries, and the number of charge and discharge points increases, resulting in excellent output characteristics at high C-rate.

[0149] In one exemplary embodiment of this application, the negative electrode conductive material may be composed of a linear conductive material.

[0150] In this case, based on 100 parts by weight of the negative electrode active material, the content of the linear conductive material can be 0.1 to 2 parts by weight, 0.1 to 0.7 parts by weight, or 0.1 to 0.3 parts by weight. When the content of the linear conductive material meets such a range, an electrical network can be sufficiently constructed in the negative electrode active material layer, which is advantageous in terms of mixing and coating processability in electrode manufacturing. Furthermore, in the negative electrode according to an exemplary embodiment of the invention, since both the first and second negative electrode active material layers contain linear conductive material, the conductive network between the active materials can be maintained according to the volume expansion and contraction of the Si electrode, which is advantageous in terms of lifetime and can maintain fast charging performance. Basically, fast charging performance is advantageous because Si-based negative electrodes can be coated in thin films compared to graphite, but the linear conductive material also contributes to fast charging by firmly maintaining the conductive network, and can further help improve the initial drop in the lifetime of the Si-based negative electrode and maintain its lifetime.

[0151] The negative electrode conductive material according to this application has a completely different structure from the positive electrode conductive material used in the positive electrode. That is, the second negative electrode conductive material according to this application is used to maintain contact between silicon-based active materials that expand greatly in electrode volume due to charging and discharging, while the positive electrode conductive material is used to impart a certain conductivity and to act as a buffer during rolling, and is completely different from the negative electrode conductive material of this invention in terms of structure and function.

[0152] Furthermore, the negative electrode conductive material according to this application is applied to a silicon-based active material and has a completely different structure from the conductive material applied to a graphite-based active material. That is, since the conductive material used in the electrode with the graphite-based active material has only particles smaller than those of the active material, the conductive material is characterized by improved output characteristics and imparts a certain degree of conductivity, and is completely different in structure and function from the negative electrode conductive material used in this invention together with the silicon-based active material.

[0153] In one exemplary embodiment of this application, the negative electrode adhesive may comprise at least one material 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, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and the above materials in which hydrogen is replaced by Li, Na, Ca, etc., and may also comprise various copolymers thereof.

[0154] According to an exemplary embodiment of this application, the negative electrode adhesive is used to support the active material and the conductive material to prevent twisting and structural deformation of the negative electrode structure during the volume expansion and relaxation of the negative electrode active material. When the above-mentioned function is satisfied, all common adhesives can be applied; specifically, water-based adhesives can be used, and more specifically, polyacrylamide (PAM) based adhesives can be used.

[0155] In one exemplary embodiment of this application, based on 100 parts by weight of the first lower negative electrode active material layer composition, the content of the first lower negative electrode adhesive may be less than 30 parts by weight, preferably less than 25 parts by weight, more preferably less than 20 parts by weight, and may be more than 5 parts by weight or more than 10 parts by weight.

[0156] In one exemplary embodiment of this application, based on 100 parts by weight of the first upper negative electrode active material layer composition, the content of the first upper negative electrode adhesive may be less than 30 parts by weight, preferably less than 25 parts by weight, more preferably less than 20 parts by weight, and may be more than 5 parts by weight or more than 10 parts by weight.

[0157] In this application, a negative electrode for a lithium secondary battery is provided, wherein the second lower negative electrode active material layer comprises a second lower negative electrode active material layer composition, the second upper negative electrode active material layer comprises a second upper negative electrode active material layer composition, the second lower negative electrode active material layer composition comprises a second lower negative electrode active material, a second lower negative electrode conductive material, and a second lower negative electrode binder, and the second upper negative electrode active material layer composition comprises a second upper negative electrode active material, a second upper negative electrode conductive material, and a second upper negative electrode binder.

[0158] In this case, the first lower negative electrode active material layer and the second upper negative electrode active material layer differ only in the layers used (the second and the first), and the same description can be applied. Furthermore, the first upper negative electrode active material layer and the second lower negative electrode active material layer differ only in the layers used (the second and the first), and the same description can be applied.

[0159] An exemplary embodiment of this application provides a method for manufacturing a negative electrode for a lithium secondary battery, the method comprising the following steps: Prepare the first negative electrode slurry and the second negative electrode slurry; The first negative electrode slurry is coated onto one surface of the negative electrode current collector layer, and the second negative electrode slurry is coated onto the first negative electrode slurry coated on one surface of the negative electrode current collector layer; and The second negative electrode slurry is coated onto the opposite surface of the negative electrode current collector layer, and the first negative electrode slurry is coated onto the second negative electrode slurry coated on the opposite surface of the negative electrode current collector layer. One of the first negative electrode slurry and the second negative electrode slurry contains a silicon-based active material.

[0160] In one exemplary embodiment of this application, the first negative electrode slurry may comprise a first composition and a negative electrode slurry solvent.

[0161] In this case, the above description of the first lower negative electrode active material layer composition or the second upper negative electrode active material layer composition can be applied to the first composition.

[0162] In one exemplary embodiment of this application, the second negative electrode slurry may comprise a second composition and a negative electrode slurry solvent.

[0163] In this case, the description of the first upper negative electrode active material layer composition or the second lower negative electrode active material layer composition can be applied to the second composition.

[0164] In this application, the solid content of the first negative electrode slurry and the second negative electrode slurry can fall within the range of 10% to 40%.

[0165] For the slurry solvent, solvents used in the art can be used without limitation; specifically, NMP or water can be used.

[0166] In one exemplary embodiment of this application, a method for manufacturing a negative electrode for a lithium secondary battery is provided, wherein the steps of coating a first negative electrode slurry onto a surface of the negative electrode current collector layer and coating a second negative electrode slurry onto the first negative electrode slurry coated on a surface of the negative electrode current collector layer include the following steps: after coating the first negative electrode slurry, partially or completely drying the first negative electrode slurry and coating the second negative electrode slurry onto the first negative electrode slurry.

[0167] The coating method is a wet-on-dry process, specifically involving preparing a first negative electrode slurry and coating it onto the negative electrode current collector layer. The first negative electrode slurry mixture is then dried to form a first lower negative electrode active material layer. A second negative electrode slurry mixture is then prepared, coated onto the first lower negative electrode active material layer, and dried to form a first upper negative electrode active material layer. The layers can then be calendered and pressed to form the negative electrode for a lithium secondary battery according to this application.

[0168] In one exemplary embodiment of this application, a method for manufacturing a negative electrode for a lithium secondary battery is provided, wherein the steps of coating a second negative electrode slurry onto the opposite surface of the negative electrode current collector layer and coating a first negative electrode slurry onto the second negative electrode slurry coated on the opposite surface of the negative electrode current collector layer include the following steps: after coating the second negative electrode slurry, partially or completely drying the second negative electrode slurry and coating the first negative electrode slurry onto the second negative electrode slurry.

[0169] In one exemplary embodiment of this application, a method for manufacturing a negative electrode for a lithium secondary battery is provided, wherein the steps of coating a first negative electrode slurry onto one surface of the negative electrode current collector layer and coating a second negative electrode slurry onto the first negative electrode slurry coated on one surface of the negative electrode current collector layer include the following steps: after coating the first negative electrode slurry, coating the second negative electrode slurry onto the first negative electrode slurry in an undried state.

[0170] The coating method is a wet-on-wet process, specifically involving preparing a first negative electrode slurry and coating it onto the negative electrode current collector layer. Then, while the first negative electrode slurry mixture is still wet, a second negative electrode slurry mixture is prepared, and the second negative electrode slurry mixture is coated onto the first negative electrode slurry and dried to form a first negative electrode active material layer. The layers can then be calendered and pressed to form the negative electrode for a lithium secondary battery according to this application.

[0171] In one exemplary embodiment of this application, a method for manufacturing a negative electrode for a lithium secondary battery is provided, wherein the steps of coating a second negative electrode slurry onto the opposite surface of the negative electrode current collector layer and coating a first negative electrode slurry onto the second negative electrode slurry coated on the opposite surface of the negative electrode current collector layer include the following steps: after coating the second negative electrode slurry, coating a first negative electrode slurry onto the second negative electrode slurry in an undried state.

[0172] Specifically, the wet-drying process involves coating and partially or completely drying the first negative electrode slurry composition, followed by coating the second negative electrode slurry composition thereon. Through this process, the first lower negative electrode active material layer and the first upper negative electrode active material layer can have clear boundaries. Therefore, the components contained in the first lower negative electrode active material layer and the first upper negative electrode active material layer do not mix, thereby achieving a two-layer characteristic structure.

[0173] On the other hand, as a result of the aforementioned wet-on-wet process, a bonding region can be formed where the first lower negative electrode active material layer and the first upper negative electrode active material layer are mixed. In this case, in order to perform the wet-on-wet process, the viscosity of the first lower negative electrode active material layer composition must be lower than the viscosity of the first upper negative electrode active material layer composition, so that they can mix with each other in the bonding region during the process.

[0174] An exemplary embodiment of this application provides a lithium secondary battery comprising: a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0175] A secondary battery according to an exemplary embodiment of this specification may specifically 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 inserted 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 already been described above, its detailed description is omitted.

[0176] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0177] In the positive electrode, the positive electrode current collector is not particularly limited, as long as it is conductive and will not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, and aluminum or stainless steel that have undergone surface treatments with carbon, nickel, titanium, silver, etc., can be used. Furthermore, the positive electrode current collector can typically have a thickness of 3 to 500 μm, and its surface can be formed with fine irregularities to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0178] The positive electrode active material can be a commonly used positive electrode active material. Specifically, the positive electrode active material can be a layered compound, such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or a compound replaced by one or more transition metals; lithium iron oxide, such as LiFe3O4; lithium manganese oxide, such as Li 1+c1 Mn 2-c1 O4 (0≤c1≤0.33), LiMnO3, LiMn2O3 and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides, such as LiV3O8, V2O5 and Cu2V2O7; Ni-site type lithium nickel oxides, consisting of the 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) represents the lithium manganese composite oxide, represented by the 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 Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4, wherein a portion of the Li in the chemical formula is replaced by alkaline earth metal ions; etc., but not limited thereto. The positive electrode may be Li metal.

[0179] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, in addition to the aforementioned positive electrode active material.

[0180] In this context, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular restriction, as long as the positive electrode conductive material has electronic conductivity without causing a chemical change in the battery to be constructed. Specific examples may include graphite, such as natural graphite and artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking 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, etc., and any one or a mixture of two or more thereof may be used.

[0181] Furthermore, the positive electrode adhesive is used to improve the bonding between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof may be used.

[0182] The separator is used to separate the negative electrode and the positive electrode and provide a migration path for lithium ions. Any separator can be used without particular limitation, as long as it is typically used in secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to electrolyte ion movement are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers; or membranes having two or more layers. Alternatively, common porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymer materials can be used, and separators with single-layer or multi-layer structures can be selectively used.

[0183] Examples of the electrolyte may include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used in the manufacture of the lithium secondary battery.

[0184] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0185] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butyl 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, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, or ethyl propionate can be used.

[0186] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, as cyclic carbonates, are high-viscosity organic solvents and are preferred for use because they have high dielectric constants that allow for good dissociation of lithium salts. When cyclic carbonates are mixed with linear carbonates such as dimethyl carbonate and diethyl carbonate, which have low viscosity and low dielectric constants, in a suitable ratio, an electrolyte with high conductivity can be prepared, and therefore can be used more preferably.

[0187] Lithium salts can be used as the metal salt, and the lithium salt is a material that is readily soluble in the non-aqueous electrolyte. The anion of the lithium salt can be, for example, one or more selected from the group consisting of: 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 - .

[0188] To improve battery lifespan, suppress capacity reduction, and improve discharge capacity, the electrolyte may further contain one or more of the following additives in addition to the electrolyte components described above: alkylene carbonate compounds such as difluorocarbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0189] An exemplary embodiment of the present invention provides a battery module comprising the secondary battery as a unit battery and a battery pack comprising the same. Because the battery module and the battery pack comprise a secondary battery with high capacity, high rate performance, and high cycle characteristics, they can be used as a power source for medium to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems.

[0190] Preferred embodiments will be provided below to better understand the invention. It will be apparent to those skilled in the art that these embodiments are provided merely to illustrate the invention, and that various modifications and variations can be made within the scope and spirit of the invention. Such modifications and variations naturally fall within the scope of the claims included herein.

[0191] Invention Model

[0192] <Preparation Example>

[0193] <Preparation of the negative electrode>

[0194] <Example 1>

[0195] <Preparation of the first negative electrode slurry>

[0196] As the active material of the first negative electrode slurry, artificial graphite (average particle size (D50) = 19 μm) and spherical natural graphite (average particle size (D50) = 11 μm) are uniformly mixed at a weight ratio of 8:2. Then, the active material, carbon black as the first conductive material, SBR as the binder, and carboxymethyl cellulose (CMC) as the thickener are mixed at a weight ratio of 95:1.5:2.3:1.2, respectively. The mixture is then mixed with water (H2O) as the first solvent to prepare the first negative electrode slurry.

[0197] <Preparation of the Second Negative Electrode Slurry>

[0198] As the active material for the second negative electrode slurry, artificial graphite (average particle size (D50) = 19 μm), spherical natural graphite (average particle size (D50) = 11 μm), and SiO were uniformly mixed at a weight ratio of 56:14:30. Then, the active material, CNT as the first conductive material, SBR as the binder, and carboxymethyl cellulose (CMC) as the thickener were mixed at a weight ratio of 96.293:0.043:3.6:0.065, respectively. The mixture was then mixed with water (H2O) as the first solvent to prepare the second negative electrode slurry.

[0199] The second negative electrode slurry prepared as described above is coated onto the upper surface of Cu, which serves as the negative electrode current collector layer, and the first negative electrode slurry is coated on top of the second negative electrode slurry to form a first negative electrode active material layer. In this case, the coating is performed such that the respective loading amounts (mAh / cm³) are... 2 The ratio is 1:1.

[0200] After coating as described above, the first negative electrode slurry prepared as described above is coated onto the back side of Cu, which serves as the negative electrode current collector layer, and the second negative electrode slurry is coated onto the top of the first negative electrode slurry and dried to form the second negative electrode active material layer.

[0201] Information regarding the slurry coated onto the first negative electrode active material layer and the second negative electrode active material layer in Example 1 is shown in Table 1 below.

[0202] [Table 1]

[0203] In Table 1 above, DL indicates double layer, meaning that the negative electrode active material layer has a double layer, and SL indicates single layer, meaning that the negative electrode active material layer has a single layer.

[0204] For reference, the preparation method of Comparative Example 4 in Table 1 above is as follows.

[0205] <Preparation of the Third Anode Slurry>

[0206] As the active material for the third negative electrode slurry, artificial graphite (average particle size (D50) = 19 μm), spherical natural graphite (average particle size (D50) = 11 μm), and SiO were uniformly mixed at a weight ratio of 68:17:15. Then, the active material, CNTs as the first conductive material, SBR as the binder, and carboxymethyl cellulose (CMC) as the thickener were mixed at a weight ratio of 96.293:0.043:3.6:0.065, respectively. The mixture was then combined with water (H2O) as the first solvent to prepare the third negative electrode slurry.

[0207] Prepare Cu as the negative electrode current collector layer, and coat the third negative electrode slurry onto both surfaces of the Cu to create a single layer.

[0208] <Preparation of Secondary Batteries>

[0209] By using LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent used to form the positive electrode slurry in a weight ratio of 97:1.5:1.5 to prepare a positive electrode slurry (solid concentration: 78 wt%).

[0210] The positive electrode slurry was prepared at 537 mg / 25 cm⁻¹ 2 The loading amount was coated on both surfaces of an aluminum current collector (thickness: 12 μm) used as the positive electrode current collector, then rolled and dried in a vacuum oven at 130 °C for 10 hours to form a positive electrode active material layer (total thickness of the positive electrode active material layer: 65 μm), thereby preparing the positive electrode (thickness of the positive electrode: 77 μm, porosity: 26%).

[0211] The secondary battery of Example 1 was prepared by inserting a polyethylene diaphragm between the positive electrode and the negative electrode of Example 1 and injecting an electrolyte.

[0212] The electrolyte is obtained by adding vinylene carbonate in an amount of 3 wt% based on the total weight of the electrolyte to an organic solvent and adding LiPF6 as a lithium salt to a concentration of 1M, wherein fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) are mixed in a volume ratio of 30:70 in the organic solvent.

[0213] Except for using the negative electrode of the examples and comparative examples, each secondary battery was manufactured in the same manner as described above.

[0214] Experimental Example 1: Evaluation of Service Life Characteristics

[0215] For the secondary batteries containing the negative electrodes manufactured in the examples and comparative examples, lifetime and capacity retention were evaluated using an electrochemical charge-discharge apparatus. The secondary batteries were cycle-tested at 4.2–3.0 V at 1C / 0.5C, and capacity retention was measured during the test by performing charge-discharge cycles (4.2–3.0 V) at 0.33C / 0.33C every 50 cycles.

[0216] Capacity retention (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the 1st cycle)} x 100

[0217] Experiment Example 2: Measurement and Evaluation of Resistance Increase Rate

[0218] In the test in Experimental Example 1, the capacity retention rate was measured by charging and discharging the battery at 0.33C / 0.33C (4.2~3.0V) every 50 cycles, and the resistance was measured by discharging the battery at SOC50 under a 2.5C pulse to compare and analyze the rate of increase in resistance.

[0219] In addition, for the evaluation of lifetime characteristics and the measurement of resistance increase rate, data were calculated at 200 cycles, and the results are shown in Table 2 below.

[0220] Experiment Example 3: TP Evaluation

[0221] For the lithium secondary batteries prepared in the above embodiments and comparative examples, the thermal pad in contact with the battery is heated to induce thermal runaway of the battery.

[0222] The experiment was conducted in an autoclave (isolated from the external environment / atmosphere) under a N2 atmosphere, and the pressure of the gas released when thermal runaway occurred was measured using a pressure gauge in the autoclave, and the TR rate was determined, as shown in Table 2 below.

[0223] TR rate = (Maximum pressure - Pre-ignition pressure) / (Battery capacity) / (Time before ignition - Time to reach maximum pressure)

[0224] [Table 2]

[0225] As can be seen from Tables 1 and 2 above, it is confirmed that by improving the structure of the negative electrode for lithium secondary batteries according to this application, the explosive force of the negative electrode during heating can be reduced. Specifically, the double-layer active materials contained in the first negative electrode active material layer and the second negative electrode active material layer are arranged to have a structure that is asymmetrical with each other, so that even if thermal runaway occurs in the negative electrode active material layer containing silicon-based active materials, thermal runaway can be controlled because another negative electrode active material layer that can act as a barrier is arranged.

[0226] In Comparative Examples 1 and 2, it was confirmed that the negative electrodes of the DL structures were identical, but the upper and lower surfaces (i.e., the first and second negative electrode active material layers) had a symmetrical form relative to the negative electrode current collector layer. In this case, in Comparative Example 1, the negative electrode active material layer containing silicon-based active material was disposed on the negative electrode current collector side, and in Comparative Example 2, the negative electrode active material layer containing silicon-based active material was concentrated on the side facing the positive electrode. As a result, the evaluation results for lifetime and resistance were slightly worse than those in the examples, and the evaluation results for thermal stability were particularly poor. This corresponds to the result described above where another negative electrode active material layer capable of acting as a barrier was not arranged.

[0227] Comparative Examples 3 and 4 illustrate negative electrodes with an SL structure. Specifically, Comparative Example 3 illustrates a negative electrode having a carbon-based active material (first negative electrode active material layer) on the upper surface and a silicon-based active material (second negative electrode active material layer) on the back side, and Comparative Example 4 illustrates a negative electrode mixed with silicon and carbon-based active materials. In these cases, it was also confirmed that the thermal stability evaluation was inferior to that of Examples 1 and 2 of the present invention. Furthermore, it was confirmed that the lifetime and resistance increase rate were inferior to those of the embodiments of the present application.

Claims

1. A negative electrode for a lithium secondary battery, the negative electrode comprising: a negative electrode current collector layer; a first negative electrode active material layer provided on one surface of the negative electrode current collector layer; and a second negative electrode active material layer provided on the other surface of the negative electrode current collector layer, wherein the first negative electrode active material layer comprises a first lower negative electrode active material layer in contact with the negative electrode current collector layer and a first upper negative electrode active material layer provided on the surface of the first lower negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer, the second negative electrode active material layer comprises a second lower negative electrode active material layer in contact with the negative electrode current collector layer and a second upper negative electrode active material layer provided on the surface of the second lower negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer, one of the first lower negative electrode active material layer and the first upper negative electrode active material layer comprises a silicon-based active material, the first lower negative electrode active material layer and the second upper negative electrode active material layer have the same composition, and the first upper negative electrode active material layer and the second lower negative electrode active material layer have the same composition.

2. The negative electrode for a lithium secondary battery according to claim 1, wherein the first negative electrode active material layer and the second negative electrode active material layer are asymmetric to each other with respect to the negative electrode current collector layer.

3. The negative electrode for a lithium secondary battery according to claim 1, wherein the first lower negative electrode active material layer and the second lower negative electrode active material layer have different compositions, and the first upper negative electrode active material layer and the second upper negative electrode active material layer have different compositions.

4. The negative electrode for a lithium secondary battery according to claim 1, wherein the first lower negative electrode active material layer comprises a first lower negative electrode active material layer composition, the first upper negative electrode active material layer comprises a first upper negative electrode active material layer composition, the first lower negative electrode active material layer composition comprises a first lower negative electrode active material, a first lower negative electrode conductive material, and a first lower negative electrode binder, and the first upper negative electrode active material layer composition comprises a first upper negative electrode active material, a first upper negative electrode conductive material, and a first upper negative electrode binder.

5. The negative electrode for a lithium secondary battery according to claim 4, wherein one of the first lower negative electrode active material and the first upper negative electrode active material comprises 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 other of the first lower negative electrode active material and the first upper negative electrode active material comprises a carbon-based active material.

6. The negative electrode for a lithium secondary battery according to claim 5, wherein the silicon-based active material comprises SiO x (x = 0), SiO x (0 < x < 2), or SiC.

7. The negative electrode for a lithium secondary battery according to claim 5, wherein the content of the silicon-based active material is 1 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the first lower negative electrode active material.

8. The negative electrode for a lithium secondary battery according to claim 1, wherein the thickness of the first negative electrode active material layer is 10 μm or more and 200 μm or less, and the thickness of the second negative electrode active material layer is 10 μm or more and 200 μm or less. The thickness of the second negative electrode active material layer is 10 μm or more and 200 μm or less.

9. The negative electrode for lithium secondary batteries according to claim 4, wherein the first lower negative electrode conductive material and the first upper negative electrode conductive material comprise at least a wire-shaped conductive material.

10. A lithium secondary battery comprising: a positive electrode; the negative electrode for lithium secondary batteries according to any one of claims 1 to 9; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

11. A method of manufacturing a negative electrode for lithium secondary batteries, the method comprising: preparing a first negative electrode slurry and a second negative electrode slurry; applying the first negative electrode slurry to one surface of a negative electrode current collector layer and applying the second negative electrode slurry to the first negative electrode slurry applied to one surface of the negative electrode current collector layer; and applying the second negative electrode slurry to an opposite surface of the negative electrode current collector layer and applying the first negative electrode slurry to the second negative electrode slurry applied to the opposite surface of the negative electrode current collector layer, wherein one of the first negative electrode slurry and the second negative electrode slurry comprises a silicon-based active material.

12. The method according to claim 11, wherein the applying the first negative electrode slurry to one surface of the negative electrode current collector layer and the applying the second negative electrode slurry to the first negative electrode slurry applied to one surface of the negative electrode current collector layer comprises: after applying the first negative electrode slurry, applying the second negative electrode slurry to the first negative electrode slurry in a non-dried state.

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