Anode for lithium secondary battery, method for manufacturing lithium secondary battery, and lithium secondary battery comprising anode

Abstract

The present application relates to an anode for a lithium secondary battery, a method for manufacturing a lithium secondary battery, and a lithium secondary battery comprising the anode.

Description

Anode for a lithium secondary battery, a method for manufacturing a lithium secondary battery, and a lithium secondary battery including the anode

[0001] This application claims the benefit of Korean Patent Application No. 10-2024-0030609, filed with the Korean Intellectual Property Office on March 4, 2024, the entire contents of which are incorporated herein by reference.

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

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

[0004] A representative example of an electrochemical device that currently utilizes this electrochemical energy is the secondary battery, and its application area is gradually expanding.

[0005] With the increasing technological development and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which boast high energy density and voltage, long cycle life, and low self-discharge rates, are commercialized and widely used. Furthermore, active research is being conducted on methods for manufacturing high-density electrodes with even higher energy density per unit volume as electrodes for these high-capacity lithium secondary batteries.

[0006] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and deintercalates lithium ions from the positive electrode. Silicon particles with a high discharge capacity can be used as the negative electrode active material.

[0007] In particular, due to the recent demand for high-density energy batteries, active research is being conducted on methods to increase capacity by using silicon-based compounds, such as Si / C or SiOx, as anode active materials, which have a capacity more than 10 times greater than graphite-based materials. However, in the case of silicon-based compounds, which are high-capacity materials, compared to the graphite used in the past, the capacity characteristics themselves are excellent, but the volume rapidly expands during the charging process, which cuts off the conductive path, deteriorating the battery characteristics, and consequently, the capacity drops from the beginning. In addition, when the silicon-based anode is repeated, lithium ions are not uniformly charged in the depth direction of the anode, and the reaction proceeds on the surface, accelerating surface degradation, so performance improvement in terms of the battery cycle is necessary.

[0008] Accordingly, in order to solve the above problems when using silicon-based compounds as negative electrode active materials, various methods are being discussed, such as a method of controlling the driving potential, a method of additionally coating a thin film on the active material layer, a method of suppressing the volume expansion itself such as a method of controlling the particle size of the silicon-based compound, or the development of a binder that will control the volume expansion of the silicon-based compound to prevent the conductive path from being cut off. In addition, research is also being conducted to supplement the life characteristics of silicon-based negative electrodes by limiting the proportion of silicon-based active materials used during initial charge and discharge and providing a reservoir role through a method of prelithiating the silicon-based active material layer.

[0009] However, in the case of the above methods, since they may rather lower the performance of the battery, there are limitations in their application, and there are still limitations in the commercialization of negative electrode batteries with a high content of silicon compounds. In addition, as the proportion of silicon-based active materials included in the silicon-based active material layer increases, the pre-lithiation is concentrated on the surface of the negative electrode, which causes damage to the silicon-based active material on the surface, and as uneven pre-lithiation occurs, problems arise in improving the life characteristics.

[0010] Accordingly, in a structure where the negative active material layer is applied in two layers (DLD), research is being conducted to change the composition included in the upper layer. However, when only silicon-based materials such as SiOx are used in the upper layer, the lifespan performance is still not secured due to the concentration of reaction at the surface. In addition, when carbon-based active materials are combined and used, the problem of rapid charging performance deteriorating as the thickness increases to achieve the same capacity continues to be raised.

[0011] Therefore, even when using a silicon-based compound as an active material, it is necessary to study how to prevent electrode surface degradation during charge and discharge cycles, secure rapid charging performance, and improve uniformity during prelithiation, thereby improving cycle performance along with capacity characteristics of lithium secondary batteries.

[0012] <Prior Art Literature>

[0013] (Patent Document 1) Japanese Patent Publication No. 2009-080971

[0014] The present application has found that when a silicon-based active material is used in the negative electrode and a silicon-based active material with a controlled crystal grain size is used in the second negative electrode active material layer, a negative electrode for a lithium secondary battery can be provided that maximizes capacity characteristics, while preventing electrode surface degradation during charge and discharge cycles, which is a problem in the past, and furthermore, secures rapid charging performance.

[0015] Accordingly, this invention relates to a negative electrode for a lithium secondary battery, a method for manufacturing a lithium secondary battery, and a lithium secondary battery including the negative electrode.

[0016] One embodiment of the present specification is a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a first negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a second negative electrode active material layer provided on the opposite side of the side of the first negative electrode active material layer facing the negative electrode current collector layer; wherein the first negative electrode active material layer includes a first negative electrode active material layer composition including a first negative electrode active material, and the second negative electrode active material layer includes a second negative electrode active material layer composition including a second negative electrode active material, and the first negative electrode active material comprises Si and SiOx (0 <x<2)로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 제1 음극 활물질 100 중량부 기준 상기 Si를 95 중량부 이상 포함하고, 상기 제2 음극 활물질은 실리콘계 활물질을 포함하며, 상기 실리콘계 활물질은 결정립 크기가 250nm 이하인 것인 리튬 이차 전지용 음극을 제공한다.

[0017] In another embodiment, a method for manufacturing a lithium secondary battery, comprising: a step of preparing an anode for a lithium secondary battery; and a step of assembling the anode for the lithium secondary battery; a cathode; a separator; and an electrolyte; wherein the step of preparing an anode for a lithium secondary battery comprises a step of preparing an anode current collector layer; a step of applying a first anode active material layer composition to one or both sides of the anode current collector layer to form a first anode active material layer; and the first anode active material layer comprises a first anode active material layer composition including a first anode active material, and the second anode active material layer comprises a second anode active material layer composition including a second anode active material, wherein the first anode active material comprises Si and SiOx (0 <x<2)로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 제1 음극 활물질 100 중량부 기준 상기 Si를 95 중량부 이상 포함하고, 상기 제2 음극 활물질은 실리콘계 활물질을 포함하며, 상기 실리콘계 활물질은 결정립 크기가 250nm 이하인 것인 리튬 이차 전지의 제조 방법을 제공한다.

[0018] Finally, a lithium secondary battery is provided, including: a cathode; an anode for a lithium secondary battery according to the present application; a separator provided between the cathode and the anode; and an electrolyte.

[0019] In the case of a negative electrode for a lithium secondary battery according to one embodiment of the present invention, it has a double layer active material layer composed of a first negative electrode active material layer and a second negative electrode active material layer. In particular, the first negative electrode active material included in the first negative electrode active material layer is Si and SiOx (0 <x<2)로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 제1 음극 활물질 100 중량부 기준 상기 Si를 95 중량부 이상 포함하고, 제2 음극 활물질은 실리콘계 활물질을 포함하며, 상기 실리콘계 활물질은 결정립 크기가 250nm 이하인 것을 사용한다.

[0020] As described above, by using a silicon-based active material with a crystal grain size adjusted as described above in the second negative electrode active material layer, the grain boundaries are widely distributed, so that lithium ions are more uniformly distributed when inserted, thereby reducing the stress generated when lithium ions are inserted into silicon particles, and thereby mitigating breakage of the particles on the surface. As a result, the negative electrode has the characteristic of further improving its life stability.

[0021] The negative electrode for a lithium secondary battery according to the present application has a double-layer active material layer having the specific composition and content as described above, and in particular, since the first negative electrode active material layer contains a high content of Si, it can have the advantages of high capacity, high density, and rapid charging. Furthermore, since a silicon-based active material is used as the second negative electrode active material, it has the characteristics of securing rapid charging performance and high energy density compared to a negative electrode using a carbon-based or a combination of carbon-based and silicon-based second negative electrode active materials.

[0022] That is, in order to secure rapid charging performance, the silicon-based active material contained in the first negative electrode active material layer and the second negative electrode active material layer must be included in a high content, but simply including a high content caused a problem in that the life performance rapidly decreased. Therefore, by including a silicon-based active material having a crystal grain size of 250 nm or less in the second negative electrode active material layer, the surface reaction concentration phenomenon was controlled and the life performance was improved.

[0023] In addition, when controlled in this manner, the thickness of the first negative electrode active material layer and the second negative electrode active material layer can be formed small enough to satisfy the capacity characteristics, thereby ensuring rapid charging performance.

[0024] In conclusion, the negative electrode for a lithium secondary battery according to the present application is characterized by controlling the composition and crystal grain size included in the negative electrode active material layers (first and second) in order to take advantage of an electrode that uses a high content of Si particles as a single-layer active material and solve the disadvantages of having the same, such as surface degradation problems, uniformity problems during prelithiation, and life characteristics problems.

[0025] Figure 1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application.

[0026] Figure 2 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application.

[0027] Figure 3 is a flowchart showing a wet on dry process according to one embodiment of the present application.

[0028] Figure 4 is a flowchart showing a wet on wet process according to one embodiment of the present application.

[0029] Figure 5 shows an enlarged view of a silicon-based active material according to one embodiment of the present application.

[0030] <Explanation of symbols>

[0031] 10: Second negative electrode active material layer

[0032] 20: First negative electrode active material layer

[0033] 30: Negative current collector layer

[0034] Before explaining the present invention, some terms are first defined.

[0035] When a part of this specification is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0036] In this specification, ‘p to q’ means a range of ‘p or more and q or less.’

[0037] In this specification, "specific surface area" is measured by the BET method, and specifically, is calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan. That is, in this application, the BET specific surface area may mean the specific surface area measured by the above measurement method.

[0038] In this specification, "Dn" means particle size distribution, and means the particle size at the n% point of the cumulative distribution of particle numbers according to particle size. That is, D50 is the particle size (average particle size, center particle size) at the 50% point of the cumulative distribution of particle numbers according to particle size, D90 is the particle size at the 90% point of the cumulative distribution of particle numbers according to particle size, and D10 is the particle size at the 10% point of the cumulative distribution of particle numbers according to particle size. Meanwhile, the particle size distribution can be measured using the laser diffraction method. Specifically, after the target powder is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the difference in diffraction pattern according to particle size is measured when the particles pass through a laser beam, thereby calculating the particle size distribution.

[0039] As used herein, the term "a polymer comprises a monomer as a monomer unit" means that the monomer participates in a polymerization reaction and is included as a repeating unit within the polymer. As used herein, "a polymer comprises a monomer" is interpreted to mean that the polymer comprises the monomer as a monomer unit.

[0040] In this specification, the term 'polymer' is understood to be used in a broad sense including copolymers unless 'homopolymer' is specified.

[0041] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-converted molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as standard materials. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0042] Hereinafter, the present invention will be described in detail with reference to the drawings so that those skilled in the art can easily practice it. However, the present invention can be implemented in various different forms and is not limited to the following description.

[0043] One embodiment of the present specification is a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a first negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a second negative electrode active material layer provided on the opposite side of the side of the first negative electrode active material layer facing the negative electrode current collector layer; wherein the first negative electrode active material layer includes a first negative electrode active material layer composition including a first negative electrode active material, and the second negative electrode active material layer includes a second negative electrode active material layer composition including a second negative electrode active material, and the first negative electrode active material comprises Si and SiOx (0 <x<2)로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 제1 음극 활물질 100 중량부 기준 상기 Si를 95 중량부 이상 포함하고, 상기 제2 음극 활물질은 실리콘계 활물질을 포함하며, 상기 실리콘계 활물질은 결정립 크기가 250nm 이하인 것인 리튬 이차 전지용 음극을 제공한다.

[0044] In order to secure rapid charging performance, this device must contain a high content of silicon-based active material in the first negative electrode active material layer and the second negative electrode active material layer. However, simply containing a high content caused a problem in that the lifespan performance rapidly decreased. Therefore, by including a silicon-based active material with a crystal grain size of 250 nm or less in the second negative electrode active material layer, the surface reaction concentration phenomenon was controlled and the lifespan performance was improved.

[0045] FIG. 1 is a diagram showing a laminated structure of an anode for a lithium secondary battery according to one embodiment of the present application. Specifically, a lithium secondary battery anode (100) including a first anode active material layer (20) and a second anode active material layer (10) on one surface of a cathode current collector layer (30) can be confirmed. Although FIG. 1 shows that the first anode active material layer is formed on one surface, it may be included on both surfaces of the cathode current collector layer. As described above, in one embodiment of the present application, the first anode active material layer may be formed on the entire surface of the cathode current collector layer, and the second anode active material layer may be formed on the entire surface of the first anode active material layer.

[0046] In addition, FIG. 2 is a diagram showing a laminated structure of an anode for a lithium secondary battery according to one embodiment of the present application. Specifically, as illustrated in FIG. 2, a first anode active material layer (20) and a second anode active material layer (30) may be formed on both sides of a negative electrode current collector layer (30). In addition, it may have an arrangement of 10>20>30>20>10, and additionally, if the first anode active material layer and the second anode active material layer are sequentially laminated on only one side of the negative electrode current collector layer, such as 10>20>30>20, 10>20>30>10, 10>20>30>10>20, etc., the arrangement on the opposite side may be laminated regardless. Preferably, both sides of the negative electrode current collector layer have the same composition, and specifically, it may have a structure of 10>20>30>20>10.

[0047] Below, the negative electrode for a lithium secondary battery of the present invention is described in more detail.

[0048] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, including: a negative electrode current collector layer; a first negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a second negative electrode active material layer provided on the opposite side of the side of the first negative electrode active material layer that is in contact with the negative electrode current collector layer.

[0049] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. The negative electrode current collector layer is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the bonding strength of the negative electrode active material can be strengthened by forming fine unevenness on the surface, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0050] In one embodiment of the present application, the thickness of the negative electrode current collector layer may be 1 μm or more and 100 μm or less.

[0051] However, the thickness can be varied depending on the type and purpose of the cathode used and is not limited thereto.

[0052] In one embodiment of the present application, the first negative electrode active material is Si and SiOx (0 <x<2)로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 제1 음극 활물질 100 중량부 기준 상기 Si를 95 중량부 이상 포함할 수 있다.

[0053] In one embodiment of the present application, the first negative electrode active material is Si and SiOx (0 <x<2)로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 제1 음극 활물질 100 중량부 기준 상기 Si를 95 중량부 이상, 바람직하게는 Si를 97 중량부 이상, 더욱 바람직하게는 99 중량부 이상을 포함할 수 있고, 100 중량부 이하를 포함할 수 있다.

[0054] In one embodiment of the present application, the first negative electrode active material may particularly use pure silicon (Si) particles. Using pure silicon (Si) as the first negative electrode active material may mean that, based on the total of 100 parts by weight of the first negative electrode active material, pure Si particles (SiOx (x=0), Si) that are not combined with other particles or elements are included within the above range.

[0055] In one embodiment of the present application, the first negative electrode active material may be made of Si.

[0056] The first negative electrode active material layer according to the present invention comprises a first negative electrode active material, specifically, pure silicon particles containing 95 parts by weight or more of silicon. While high content of pure silicon particles provides excellent capacity characteristics, the resulting surface unevenness results in reduced lifespan. Therefore, the second negative electrode active material layer according to the present invention is included at a specific weight loading amount to address the above-described problem.

[0057] Meanwhile, the average particle diameter (D50) of the first negative electrode active material of the present invention may be 3 μm to 10 μm, specifically 4 μm to 8 μm, and more specifically 5 μm to 7 μm. When the average particle diameter is within the above range, the specific surface area of ​​the particles is within an appropriate range, so that the viscosity of the negative electrode slurry is formed within an appropriate range. Accordingly, the particles constituting the negative electrode slurry are smoothly dispersed. In addition, when the size of the first negative electrode active material is greater than or equal to the lower limit, the contact area between the silicon particles and the conductive material is excellent due to the composite composed of the conductive material and the binder in the negative electrode slurry, so that the possibility of the conductive network continuing increases, thereby increasing the capacity retention rate. Meanwhile, when the average particle diameter satisfies the above range, excessively large silicon particles are excluded, so that the surface of the negative electrode is formed smoothly, and thus the phenomenon of uneven current density during charge and discharge can be prevented.

[0058] In one embodiment of the present application, the first negative electrode active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the first negative electrode active material is preferably 0.01 m 2 / g to 150.0 m 2 / g, more preferably 0.1m 2 / g to 100.0 m 2 / g, especially preferably 0.2m 2 / g to 80.0 m 2 / g, most preferably 0.2m 2 / g to 18.0 m 2 / g. BET surface area is measured according to DIN 66131 (using nitrogen).

[0059] In one embodiment of the present application, the first negative electrode active material may exist in a crystalline or amorphous form, for example, and is preferably non-porous. The silicon particles are preferably spherical or fragment-shaped. Alternatively, but less preferably, the silicon particles may also have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0060] In one embodiment of the present application, the first negative electrode active material may have a non-spherical shape and its sphericity is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0061] In the present application, the circularity is determined by the following formula A-1, where A is an area and P is a boundary line.

[0062] [Formula A-1]

[0063] 4πA / P 2

[0064] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the first negative electrode active material is 80 parts by weight or more based on 100 parts by weight of the first negative electrode active material layer composition.

[0065] In another embodiment, the first negative electrode active material may comprise 82 parts by weight or more, preferably 85 parts by weight or more, more preferably 87 parts by weight or more, and may comprise 95 parts by weight or less, preferably 95 parts by weight or less, more preferably 93 parts by weight or less, based on 100 parts by weight of the first negative electrode active material layer composition.

[0066] The first negative electrode active material layer composition according to the present application uses a first negative electrode active material having a significantly high capacity within the above range, and by using a second negative electrode active material layer described later together, the capacity performance of the entire negative electrode is not lowered, and the problems of surface degradation during charging and discharging, uniformity during lithiation, and life characteristics are solved.

[0067] In particular, by increasing the amount of the active material included in the first negative electrode active material layer as described above and using the first negative electrode conductive material described later in a reduced amount, the thickness of the first negative electrode active material layer itself can be formed thinly, thereby ensuring rapid charging performance.

[0068] Traditionally, graphite compounds were used exclusively as anode active materials. However, with the increasing demand for high-capacity batteries, attempts to blend silicon-based compounds to increase capacity are increasing. However, silicon-based compounds have limitations: their rapid volume expansion during charge / discharge processes damages the conductive paths formed within the anode active material layer, thereby degrading battery performance.

[0069] Therefore, in one embodiment of the present application, the first negative electrode active material layer composition may further include at least one selected from the group consisting of a first negative electrode conductive material; and a first negative electrode binder.

[0070] At this time, the first negative electrode conductive material and the first negative electrode binder included in the first negative electrode active material layer composition can be used without limitation as those used in the art.

[0071] In one embodiment of the present application, the first cathode conductive material may be any material generally used in the art without limitation, and specifically may include at least one selected from the group consisting of point-shaped conductive materials, planar conductive materials, and linear conductive materials.

[0072] In one embodiment of the present application, the dot-shaped conductive material can be used to improve conductivity of the negative electrode, and refers to a conductive material having a dot-shaped or spherical shape that has conductivity without causing chemical change. Specifically, the dot-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may include carbon black in terms of implementing high conductivity and excellent dispersibility.

[0073] In one embodiment of the present application, the dot-shaped conductive material has a BET specific surface area of ​​40 m 2 / g or more than 70m 2 / g or less, preferably 45m 2 / g or more than 65m 2 / g or less, more preferably 50m 2 / g or more than 60m 2 / g can be less.

[0074] In one embodiment of the present application, the particle size of the dot-shaped conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0075] In one embodiment of the present application, the first cathode conductive material may include a planar conductive material.

[0076] The above-mentioned planar conductive material can improve conductivity by increasing planar contact between silicon particles within the cathode, and at the same time, can suppress disconnection of the conductive path due to volume expansion, and can be expressed as a plate-shaped conductive material or a bulk conductive material.

[0077] In one embodiment of the present application, the planar conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and may preferably be plate-shaped graphite.

[0078] In one embodiment of the present application, the average particle diameter (D50) of the surface-shaped conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the above range is satisfied, the sufficient particle size facilitates dispersion without causing excessive viscosity increase in the negative electrode slurry. Therefore, the dispersion effect is excellent when dispersion is performed using the same equipment and time.

[0079] In one embodiment of the present application, the surface-shaped conductive material provides a negative electrode composition having a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0080] In one embodiment of the present application, the planar conductive material may be a high-specific surface area planar conductive material having a high BET surface area; or a low-specific surface area planar conductive material.

[0081] In one embodiment of the present application, a high surface area surface conductive material or a low surface area surface conductive material can be used without limitation as the surface conductive material. However, in particular, the surface conductive material according to the present application may be affected to some extent by dispersion in electrode performance, and therefore, it may be particularly preferable to use a low surface area surface conductive material that does not cause dispersion problems.

[0082] In one embodiment of the present application, the surface-shaped conductive material has a BET specific surface area of ​​5 m 2 / g can be more than that.

[0083] In another embodiment, the surface-shaped conductive material has a BET surface area of ​​5 m 2 / g or more than 500m 2 / g or less, preferably 5m 2 / g or more than 300m 2 / g or less, more preferably 5m 2 / g or more than 250m 2 / g can be less.

[0084] In another embodiment, the surface-shaped conductive material is a high surface area surface-shaped conductive material, and has a BET surface area of ​​50 m 2 / g or more than 500m 2 / g or less, preferably 80m 2 / g or more than 300m 2 / g or less, more preferably 100m 2 / g or more than 300m 2 / g can satisfy the range below.

[0085] In another embodiment, the surface-shaped conductive material is a low surface area surface-shaped conductive material, and has a BET surface area of ​​5 m 2 / g or more than 40m 2 / g or less, preferably 5m 2 / g or more than 30m 2 / g or less, more preferably 5m 2 / g or more than 25m 2 / g can satisfy the range below.

[0086] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may include a plurality of carbon nanotube units. Specifically, the term "bundle type" herein refers to a secondary shape in the form of a bundle or rope, in which a plurality of carbon nanotube units are arranged in a substantially identical orientation in parallel or entangled with their longitudinal axes in the carbon nanotube unit direction, unless otherwise specified. The carbon nanotube units have a cylindrical shape of a graphite sheet with a nano-sized diameter and an sp2 bonding structure. At this time, the graphite sheets may exhibit conductor or semiconductor properties depending on the curling angle and structure. The above bundled carbon nanotubes can be uniformly dispersed during the manufacture of a cathode compared to entangled type carbon nanotubes, and can smoothly form a conductive network within the cathode, thereby improving the conductivity of the cathode.

[0087] In one embodiment of the present application, the first negative electrode conductive material can satisfy 0.1 parts by weight or more and 5 parts by weight or less based on 100 parts by weight of the first negative electrode active material layer composition.

[0088] In another embodiment, the first negative electrode conductive material may include 0.1 parts by weight or more and 5 parts by weight or less, preferably 0.3 parts by weight or more and 3 parts by weight or less, and more preferably 0.5 parts by weight or more and 1 part by weight or less, based on 100 parts by weight of the first negative electrode active material layer composition.

[0089] In one embodiment of the present application, the first cathode conductive material may include a linear conductive material alone.

[0090] That is, the first negative electrode active material layer according to the present application contains a high content of the first negative electrode active material at an optimal content in order to secure capacity characteristics and rapid charging, and the content of the first negative electrode conductive material is reduced, and among them, a linear conductive material capable of securing a long-distance conductive network is included in the weight portion to secure a conductive network.

[0091] In one embodiment of the present application, when the first negative electrode conductive material satisfies the above composition and ratio, it does not have a significant effect on the life characteristics of an existing lithium secondary battery, and the number of points at which charging and discharging are possible increases, resulting in excellent output characteristics at a high C-rate.

[0092] The first negative electrode conductive material according to the present application has a completely separate composition from the conductive material applied to the positive electrode. That is, the first negative electrode conductive material according to the present application serves to secure the contact between silicon-based active materials, which undergo a significant volume expansion of the electrode due to charging and discharging, and the positive electrode conductive material serves to provide some conductivity while acting as a buffer during rolling, and is completely different in composition and role from the negative electrode conductive material of the present invention.

[0093] In addition, the first negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different composition from the conductive material applied to a graphite-based active material. That is, the conductive material used in an electrode having a graphite-based active material simply has smaller particles than the active material, and thus has the characteristics of improving output characteristics and imparting some conductivity, and is completely different in composition and role from the first negative electrode conductive material applied together with a silicon-based active material as in the present invention.

[0094] In one embodiment of the present application, the first negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and materials in which hydrogens thereof are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0095] The first negative electrode binder according to one embodiment of the present application serves to hold the first negative electrode active material and the first negative electrode conductive material in order to prevent distortion and structural deformation of the negative electrode structure when the volume of the first negative electrode active material expands and relaxes. If the above-mentioned role is satisfied, all general binders can be applied, and specifically, an aqueous binder can be used, and more specifically, a PAM binder can be used.

[0096] In one embodiment of the present application, the first negative electrode binder may include 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 10 parts by weight or less, and may include 1 part by weight or more, or 3 parts by weight or more, based on 100 parts by weight of the first negative electrode active material layer composition.

[0097] Compared to the existing carbon-based cathode, when a silicon-based cathode is used, an aqueous binder is applied in the above weight portion to control volume expansion and secure life performance.

[0098] In the present application, a negative electrode for a lithium secondary battery is provided, wherein the second negative active material includes a silicon-based active material, and the silicon-based active material has a crystal grain size of 250 nm or less.

[0099] Fig. 5 is an enlarged view of a silicon-based active material according to one embodiment of the present application. Specifically, the silicon-based active material (1) is composed of a plurality of crystal structures (2), and at this time, it can be confirmed that the crystal structures have a crystal grain distribution of 1 nm or more and 250 nm or less. In addition, the space between crystal structures can be defined as a grain boundary. In addition, the crystal structure can generally be expressed as a crystal grain.

[0100] As described above, by using a silicon-based active material with a crystal grain size adjusted as described above in the second negative electrode active material layer, the grain boundaries are widely distributed, so that lithium ions are more uniformly distributed when inserted, thereby reducing the stress generated when lithium ions are inserted into silicon particles, and thereby mitigating breakage of the particles on the surface. As a result, the negative electrode has the characteristic of further improving its life stability.

[0101] Figure 1 is an enlarged view of a silicon-based active material according to one embodiment of the present application. Specifically, the silicon-based active material (1) is composed of a plurality of crystal structures (2), and at this time, it can be confirmed that the crystal structures have a crystal grain distribution of 1 nm or more and 250 nm or less. In addition, the space between crystal structures can be defined as a grain boundary. In addition, the crystal structure can generally be expressed as a crystal grain.

[0102] In one embodiment of the present application, the crystal grain size of the silicon-based active material may be 250 nm or less.

[0103] In another embodiment, the crystal grain size of the silicon-based active material may be 250 nm or less, preferably 240 nm or less, more preferably 230 nm or less, even more preferably 225 nm or less, and specifically 220 nm or less. The crystal grain size of the silicon-based active material may have a range of 1 nm or more, preferably 2 nm or more, and more specifically 3 nm or more.

[0104] The above silicon-based active material has the above crystal grain size, and satisfies the above range so that the grain boundaries are widely distributed, so that when lithium ions are inserted, they are uniformly inserted, thereby reducing the stress applied when lithium ions are inserted into silicon particles, and thus alleviating particle breakage. As a result, it has a characteristic that can improve the life stability of the negative electrode. When the crystal grain size exceeds the above range, the grain boundaries within the particles become narrowly distributed, and in this case, lithium ions within the particles are inserted unevenly, so that the stress due to ion insertion is large, resulting in particle breakage.

[0105] In one embodiment of the present application, the silicon-based active material includes a crystal structure having a crystal grain distribution of 1 nm or more and 200 nm or less, and an anode active material is provided in which the area ratio of the crystal structure is 5% or less based on the total area of ​​the silicon-based active material.

[0106] In another embodiment, the area ratio of the crystal structure based on the total area of ​​the silicon-based active material may be 5% or less, 3% or less, or 0.1% or more.

[0107] That is, the silicon-based active material according to the present application has a crystal grain size of 200 nm or less, so that a single crystal structure can be formed with a small size and satisfy the above-mentioned area ratio. Accordingly, the distribution of grain boundaries can be broadened, and thus the aforementioned effects can be exhibited.

[0108] In one embodiment of the present application, a negative electrode active material is provided in which the number of crystal structures included in the silicon-based active material is 20 or more.

[0109] The number of crystal structures included in the silicon-based active material may refer to the number of each crystal structure in Fig. 1. That is, the silicon-based active material itself may be composed of a plurality of crystal structures, and in this case, the number of crystal structures may include 20 or more.

[0110] In another embodiment, the number of crystal structures included in the silicon-based active material may be 20 or more, 30 or more, or 35 or more, and may satisfy a range of 60 or less, or 50 or less.

[0111] That is, as described above, when the silicon-based active material has a crystal grain size that satisfies the above range and the number of crystal structures that satisfies the above range, the strength of the silicon-based active material itself has an appropriate range, so that when included in an electrode, it can provide flexibility and also has the characteristic of efficiently suppressing volume expansion.

[0112] In the present application, a crystal grain means a crystal particle that is a collection of irregularly shaped microscopic particles in a metal or material, and the crystal grain size may refer to the diameter of an observed crystal grain. That is, in the present application, the crystal grain size refers to the size of a domain that shares the same crystal direction within a particle, and is a different concept from the particle size or particle diameter that expresses the size of a material.

[0113] In one embodiment of the present application, the crystal grain size can be calculated as the FWHM (Full Width at Half Maximum) value through XRD analysis. The remaining values, excluding L, are measured through XRD analysis of a silicon-based active material, and the crystal grain size can be measured through the Debey-Scherrer equation, which states that the FWHM and the crystal grain size are inversely proportional. In this case, the Debey-Scherrer equation is as shown in Equation 1-1 below.

[0114] [Formula 1-1]

[0115] FWHM=(Kλ) / (LCOSθ)

[0116] In the above formula 1-1,

[0117] L represents the grain size, K is a constant, θ is the bragg angle, and λ is the wavelength of the X-ray.

[0118] In addition, the shape of the crystal grains is diverse and can be measured three-dimensionally, and the size of the crystal grains can generally be measured using the commonly used circle method and diameter measurement method, but is not limited thereto.

[0119] The above diameter measurement method can be measured by drawing 5-10 equilibrium lines, each of which is L mm long, on a microscopic photograph of the target particle, counting the number of grains z on the lines, and averaging them. At this time, only those that are completely included are counted, and those that cross are excluded. If the number of lines is P and the magnification is V, the average grain diameter can be calculated using the following equations 1-2.

[0120] [Formula 1-2]

[0121] Dm = (L*P*10 3 ) / (zV) (um)

[0122] In addition, the above circle method is a method of calculating the average area of ​​crystal grains by drawing a circle of a set diameter on a microscopic photograph of the target particle and calculating the number of crystal grains within the circle and the number of crystal grains that fall on the boundary line using the following equation 1-3.

[0123] [Formula 1-3]

[0124] Fm = (Fk * 10 6 ) / ((0.67n + z) V 2 )(um 2 )

[0125] In the above equation 1-3, Fm represents the average particle area, Fk represents the measured area on the photograph, z represents the number of particles inside the circle, n represents the number of particles in the circular arc, and V represents the magnification of the microscope.

[0126] Meanwhile, the average particle diameter (D50 particle size) of the silicon-based active material of the present invention is 1 μm or more and 10 μm or less, specifically 2 μm to 8 μm, and more specifically 3 μm to 8 μm. When the average particle diameter is within the above range, the specific surface area of ​​the particles is within an appropriate range, so that the viscosity of the negative electrode slurry is formed within an appropriate range. Accordingly, the dispersion of the particles constituting the negative electrode slurry is smooth. In addition, since the size of the silicon-based active material is greater than the range of the lower limit, the contact area between the silicon particles and the conductive material is excellent due to the composite composed of the conductive material and the binder in the negative electrode slurry, so that the possibility of the conductive network continuing increases, thereby increasing the capacity retention rate. Meanwhile, when the average particle diameter satisfies the above range, excessively large silicon particles are excluded, so that the surface of the negative electrode is formed smoothly, and thus the phenomenon of uneven current density during charge and discharge can be prevented.

[0127] In particular, the negative active material according to the present application is characterized by controlling the average particle diameter (D50) and crystal grain size of the silicon-based active material. It is generally known that when a silicon-based active material with a large average particle diameter is used, it is easy to secure a path for lithium ions. However, as the average particle diameter increases, the adhesion with the contacting surface decreases, and accordingly, a problem occurs in which the life performance rapidly decreases. Accordingly, when an active material with a small average particle diameter (D50) of the silicon-based active material is simply applied, the life performance is secured, but the problem occurs in which resistance increases because it is difficult to secure a lithium ion path.

[0128] Accordingly, in the present application, the average particle diameter (D50) of the silicon-based active material is controlled within the above range to secure life characteristics, and at the same time, the crystal grain size of the silicon-based particles is controlled as described above to ensure a wide distribution of grain boundaries, so that lithium ions are uniformly inserted when inserted, thereby reducing the stress applied when lithium ions are inserted into the silicon particles, thereby mitigating particle breakage, and as a result, the life stability of the negative electrode is further improved.

[0129] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET surface area. The BET surface area of ​​the silicon-based active material is preferably 0.01 to 150 m 2 / g, more preferably 0.1 to 100 m 2 / g, particularly preferably 0.2 to 80 m 2 / g, most preferably 0.2 to 18 m 2 / g. BET surface area is measured according to DIN 66131 (using nitrogen).

[0130] In one embodiment of the present application, the silicon-based active material may exist in a crystalline or amorphous form, for example, and is preferably non-porous. The silicon particles are preferably spherical or fragment-shaped. Alternatively, but less preferably, the silicon particles may also have a fibrous structure or be present in the form of a silicon-containing film or coating.

[0131] In one embodiment of the present application, the silicon-based active material may have a non-spherical shape and its sphericity is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0132] In the present application, the circularity is determined by the following equation 1-A, where A is an area and P is a boundary line.

[0133] [Formula 1-A]

[0134] 4πA / P 2

[0135] In one embodiment of the present application, the silicon-based active material included in the second negative electrode active material is Si, SiOx (0 <x<2), SiC, 및 Si 합금으로 이루어진 군에서 선택되는 1 이상을 포함할 수 있다.

[0136] In one embodiment of the present application, the silicon-based active material included in the second negative electrode active material is Si, SiOx (0 <x<2), SiC, 및 Si 합금으로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 제2 음극 활물질 100 중량부 기준 Si를 1 중량부 이상 포함할 수 있다.

[0137] In another embodiment, the silicon-based active material included in the second negative electrode active material is Si, SiOx (0 <x<2), SiC, 및 Si 합금으로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 제2 음극 활물질 100 중량부 기준 Si를 1 중량부 이상, 50 중량부 이상 포함할 수 있으며, 100 중량부 이하 포함할 수 있다.

[0138] In another embodiment, the silicon-based active material included in the second negative electrode active material is SiOx (0 <x<2)를 포함할 수 있다.

[0139] In another embodiment, the silicon-based active material included in the second negative electrode active material may include Si.

[0140] The negative electrode for a lithium secondary battery according to the present application includes the second negative electrode active material in the second negative electrode active material layer as described above. Accordingly, while maintaining high capacity and high density characteristics by including the first negative electrode active material described above, the second negative electrode active material acts as a buffer layer, thereby having the characteristics of solving problems of surface degradation during charge and discharge, uniformity during full lithiation, and life characteristics.

[0141] In particular, in the second negative active material layer according to the present application, the crystal grain size of the silicon-based active material was controlled to satisfy the optimal range from the viewpoint of rapid charging, while simultaneously solving the problem of life performance.

[0142] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the second negative electrode active material is included in an amount of 60 parts by weight or more based on 100 parts by weight of the second negative electrode active material layer composition.

[0143] In another embodiment, the second negative electrode active material may be 60 parts by weight or more based on 100 parts by weight of the second negative electrode active material layer composition, and may be 100 parts by weight or less and 99 parts by weight or less.

[0144] The second negative electrode active material layer composition according to the present application has lower capacity characteristics than the first negative electrode active material, but uses a second negative electrode active material with less particle breakage due to charge and discharge within the above range, so that the capacity performance of the negative electrode is not lowered and the surface reaction of the negative electrode is suppressed, thereby having the characteristic of enhanced life characteristics.

[0145] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the second negative electrode active material layer composition further includes at least one selected from the group consisting of a second negative electrode conductive material; and a second negative electrode binder.

[0146] In one embodiment of the present application, the second negative electrode conductive material may be present in an amount of 1 part by weight or more and 40 parts by weight or less based on 100 parts by weight of the second negative electrode active material layer composition.

[0147] In another embodiment, the second negative electrode conductive material may include 1 part by weight or more and 40 parts by weight or less, preferably 3 parts by weight or more and 30 parts by weight or less, and more preferably 5 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the second negative electrode active material layer composition.

[0148] In one embodiment of the present application, the second cathode conductive material includes a dot-shaped conductive material; a planar conductive material; and a linear conductive material, and the dot-shaped conductive material: planar conductive material: linear conductive material can satisfy a ratio of 1:1:0.01 to 1:1:1.

[0149] In one embodiment of the present application, the dot-shaped conductive material can satisfy a range of 1 part by weight or more and 60 parts by weight or less, preferably 5 parts by weight or more and 50 parts by weight or less, and more preferably 10 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the second cathode conductive material.

[0150] In one embodiment of the present application, the surface-shaped conductive material can satisfy a range of 1 part by weight or more and 60 parts by weight or less, preferably 5 parts by weight or more and 50 parts by weight or less, and more preferably 10 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the second cathode conductive material.

[0151] In one embodiment of the present application, the linear conductive material can satisfy a range of 0.01 parts by weight or more and 10 parts by weight or less, preferably 0.05 parts by weight or more and 8 parts by weight or less, and more preferably 0.1 parts by weight or more and 5 parts by weight or less, based on 100 parts by weight of the second cathode conductive material.

[0152] In one embodiment of the present application, the second cathode conductive material may include a linear conductive material and a planar conductive material.

[0153] In one embodiment of the present application, the second cathode conductive material includes a linear conductive material and a planar conductive material, and the weight ratio of the linear conductive material: planar conductive material can satisfy 0.01:1 to 0.1:1.

[0154] In one embodiment of the present application, when the second negative electrode conductive material satisfies the above composition and ratio, it does not have a significant effect on the life characteristics of an existing lithium secondary battery, and the number of points at which charging and discharging are possible increases, resulting in excellent output characteristics at a high C-rate.

[0155] In particular, in one embodiment of the present application, the second cathode conductive material may include at least a linear conductive material.

[0156] As described above, the second negative electrode active material layer has a porosity range within a certain range to secure rapid charging and life performance. In this case, since the porosity is loose, a linear conductive material with a long conductive structure within the second negative electrode active material layer must be included to ensure a conductive path.

[0157] The second negative electrode conductive material according to the present application has a completely separate composition from the conductive material applied to the positive electrode. That is, the second negative electrode conductive material according to the present application serves to secure the contact between silicon-based active materials, which undergo a large volume expansion of the electrode due to charging and discharging, and the positive electrode conductive material serves to provide some conductivity while acting as a buffer when rolled, and is completely different in composition and role from the negative electrode conductive material of the present invention.

[0158] In addition, the second negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different composition from the conductive material applied to a graphite-based active material. That is, the conductive material used in an electrode having a graphite-based active material simply has smaller particles than the active material, and thus has the characteristics of improving output characteristics and imparting some conductivity, and is completely different in composition and role from the second negative electrode conductive material applied together with a silicon-based active material as in the present invention.

[0159] In one embodiment of the present application, the second negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and a material in which hydrogens thereof are substituted with Li, Na, Ca, or the like, and may also include various copolymers thereof.

[0160] The second negative electrode binder according to one embodiment of the present application serves to hold the first negative electrode active material and the first negative electrode conductive material in order to prevent distortion and structural deformation of the negative electrode structure during volume expansion and relaxation of the second negative electrode active material. If the above-mentioned role is satisfied, all general binders can be applied, and specifically, an aqueous binder can be used, and more specifically, a PAM binder can be used.

[0161] In one embodiment of the present application, the second negative electrode binder may include 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, and may include 5 parts by weight or more, or 10 parts by weight or more, based on 100 parts by weight of the second negative electrode active material layer composition.

[0162] In one embodiment of the present application, the thickness of the first negative electrode active material layer may be 10 μm or more and 25 μm or less, and the thickness of the second negative electrode active material layer may be 10 μm or more and 25 μm or less.

[0163] In another embodiment, the thickness of the second negative electrode active material layer may be 10 μm or more and 25 μm or less, specifically, the thickness of the second negative electrode active material layer may be 15 μm or more and 20 μm or less.

[0164] As described above, the present application can form the thickness as described above by optimizing the content of the Si-based active material included in each negative electrode active material layer, and in particular, rapid charging performance can be secured as the thickness of the second negative electrode active material layer satisfies the above range.

[0165] In one embodiment of the present application, the porosity of the first negative electrode active material layer and the porosity of the second negative electrode active material layer may be 20% or more and 50% or less.

[0166] In one embodiment of the present application, a lithium secondary battery negative electrode is provided, wherein the viscosity of the first negative electrode active material layer composition is 2,000 cPs or more and 15,000 cPs or less at a shear rate of 2.5 (1 / s), and the viscosity of the second negative electrode active material layer composition is lower than the viscosity of the first negative electrode active material layer composition.

[0167] In another embodiment, the viscosity of the first negative electrode active material layer composition can satisfy a shear viscosity of 2,000 cPs or more and 15,000 cPs or less, preferably 2,300 cPs or more and 14,000 cPs or less, and more preferably 2,500 cPs or more and 12,000 cPs or less at a shear rate of 2.5 (1 / s).

[0168] At this time, the viscosity of the second negative electrode active material layer composition must be maintained lower than the viscosity of the first negative electrode active material layer composition so that two negative electrode active material layers can be formed as in the present application. More specifically, the viscosity of the second negative electrode active material layer composition must be lower than the viscosity of the first negative electrode active material layer composition, but the viscosity levels must be formed similarly.

[0169] In one embodiment of the present application, the negative electrode for the lithium secondary battery can be fully lithiated.

[0170] The negative electrode for a lithium secondary battery according to the present application is composed of a double layer, and in particular, the second negative electrode active material layer satisfying a specific degree of non-uniformity acts as a buffer layer during prelithiation, thereby also helping to ensure that uniform lithiation occurs in the electrode depth direction during cycle charging and discharging.

[0171] In one embodiment of the present application, a method for manufacturing a lithium secondary battery, comprising: a step of preparing an anode for a lithium secondary battery; and a step of assembling the anode for a lithium secondary battery; a cathode; a separator; and an electrolyte; wherein the step of preparing an anode for a lithium secondary battery comprises a step of preparing an anode current collector layer; a step of forming a first anode active material layer by applying a first anode active material layer composition to one or both sides of the anode current collector layer; and the first anode active material layer comprises a first anode active material layer composition including a first anode active material, and the second anode active material layer comprises a second anode active material layer composition including a second anode active material, wherein the first anode active material comprises Si and SiOx (0 <x<2)로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 제1 음극 활물질 100 중량부 기준 상기 Si를 95 중량부 이상 포함하고, 상기 제2 음극 활물질은 실리콘계 활물질을 포함하며, 상기 실리콘계 활물질은 결정립 크기가 250nm 이하인 것인 리튬 이차 전지의 제조 방법을 제공한다.

[0172] In the above method for manufacturing the cathode, the composition and content included in each step may be applied as described above.

[0173] In one embodiment of the present application, applying the first negative electrode active material layer composition includes applying and drying a first negative electrode slurry comprising the first negative electrode active material layer composition; and a negative electrode slurry solvent.

[0174] At this time, the solid content of the first cathode slurry can satisfy a range of 10% to 40%.

[0175] In one embodiment of the present application, the step of forming the first negative electrode active material layer may include the step of mixing the first negative electrode slurry; and the step of coating the mixed first negative electrode slurry on one or both sides of the negative electrode current collector layer using a coater, and the coating may be performed using a coating method generally used in the art.

[0176] In one embodiment of the present application, a step of forming a second negative electrode active material is provided by applying a second negative electrode active material layer composition through a coater to the opposite surface of the first negative electrode active material layer that is in contact with the negative electrode current collector layer.

[0177] That is, the above step may mean a step of forming a second negative electrode active material layer on the first negative electrode active material layer, and a step of forming an active material layer on a surface (upper layer) away from the negative electrode current collector layer among the double layer structures.

[0178] In one embodiment of the present application, applying the second negative electrode active material layer composition includes applying and drying a second negative electrode slurry comprising the second negative electrode active material layer composition and a negative electrode slurry solvent.

[0179] At this time, the solid content of the second cathode slurry can satisfy a range of 10% to 40%.

[0180] In one embodiment of the present application, a method for manufacturing a negative electrode for a lithium secondary battery is provided, wherein the step of forming the second negative electrode active material layer includes the steps of mixing the second negative electrode slurry; and the step of coating the mixed second negative electrode slurry on the surface opposite to the surface of the first negative electrode active material layer that is in contact with the negative electrode current collector layer.

[0181] The above coating can be made using a coating method commonly used in the art.

[0182] The step of forming the second negative electrode active material layer may be identically applied to the description of the step of forming the first negative electrode active material layer.

[0183] In one embodiment of the present application, a method for manufacturing a negative electrode for a lithium secondary battery is provided, wherein the step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet on dry process; or a wet on wet process.

[0184] In one embodiment of the present application, the wet-on-dry process means a process of applying a first negative electrode active material layer composition, then partially or completely drying it, and then applying a second negative electrode active material layer composition thereon.

[0185] Figure 4 is a flowchart showing a wet-on-dry process according to one embodiment of the present application. Specifically, in the wet-on-dry process, a first negative electrode slurry mixture (a first negative electrode active material, a first negative electrode conductive agent, a first negative electrode binder, and a first solvent) is prepared and applied to a negative electrode current collector layer. Thereafter, the first negative electrode slurry mixture is dried to form a first negative electrode active material layer. Thereafter, a second negative electrode slurry mixture is prepared, applied to the first negative electrode active material layer, and dried to form a second negative electrode active material layer. Thereafter, each layer may be rolled and pressed to form an anode for a lithium secondary battery according to the present application.

[0186] In one embodiment of the present application, the wet-on-wet process means a process of applying a second negative electrode active material layer composition on top of the first negative electrode active material layer composition without drying it.

[0187] Figure 5 is a flowchart illustrating a wet-on-wet process according to one embodiment of the present application. Specifically, in the wet-on-wet process, a first negative electrode slurry mixture is prepared and applied to a negative electrode current collector layer, and simultaneously, a second negative electrode slurry mixture is prepared, applied to the first negative electrode slurry mixture, and the first and second negative electrode slurry mixtures are dried. Thereafter, each layer is rolled and pressed to form a negative electrode for a lithium secondary battery according to the present application.

[0188] Afterwards, the cathode can be slit twice using a single coating die according to the wet-on-dry process or wet-on-wet process.

[0189] In particular, the wet-on-dry process involves applying a first negative electrode active material layer composition, completely drying it, and then applying a second negative electrode active material layer composition thereon. Through the above process, the first negative electrode active material layer and the second negative electrode active material layer can have a clear boundary. Accordingly, the compositions included in the first negative electrode active material layer and the second negative electrode active material layer do not mix, and can have the characteristic of being configured as a double layer.

[0190] In one embodiment of the present application, the negative electrode slurry solvent can be used without limitation as long as it can dissolve the first negative electrode active material layer composition and the second negative electrode active material layer composition, and specifically, water or NMP can be used.

[0191] As a result of the aforementioned wet-on-wet process, a bonding region in which the first negative electrode active material layer and the second negative electrode active material layer are mixed can be formed. In order for the wet-on-wet process to occur, the viscosity of the first negative electrode active material layer composition must be lower than the viscosity of the second negative electrode active material layer composition, so that mutual mixing can occur in the bonding region and during the process.

[0192] In the present application, after the first negative electrode active material layer is dried (wet-on-dry process), the second negative electrode active material layer is formed, thereby forming a clearly separated interface between the two layers. In addition, when the second negative electrode active material layer is applied while the first negative electrode active material layer composition is not completely dried (the first negative electrode active material layer composition and the second negative electrode active material layer composition are applied simultaneously), mixing occurs at the interface of the two layers, thereby forming a bonding region.

[0193] In one embodiment of the present application, a method for manufacturing an anode for a lithium secondary battery is provided, comprising a step of pre-lithiating an anode having a first anode active material layer and a second anode active material layer formed on the anode current collector layer, wherein the step of pre-lithiating the anode includes a lithium electrolytic plating process; a lithium metal transfer process; a lithium metal deposition process; or a stabilized lithium metal powder (SLMP) coating process.

[0194] As described above, the second negative electrode active material layer includes the aforementioned second negative electrode active material and is provided with a mixed composition of a silicon-based active material and a carbon-based active material, so that the advantage of rapid charging can be directly obtained. In particular, since the second negative electrode active material has a mixed composition and has a large irreversibility, it can also be advantageously effective in the pre-lithiation process of pre-charging the negative electrode. Compared to the case where only the first negative electrode active material layer is applied, the second negative electrode active material having the above composition in the second negative electrode active material enables a uniform pre-lithiation process on the upper part of the negative electrode, and thus has the characteristic of improving the lifespan.

[0195] In one embodiment of the present application, a lithium secondary battery is provided, including: a positive electrode; an anode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0196] A secondary battery according to one embodiment of the present specification may particularly include the negative electrode for a lithium secondary battery as described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is identical to the negative electrode described above. Since the negative electrode has been described above, a detailed description thereof will be omitted.

[0197] The above positive electrode is formed on the positive electrode current collector layer and the positive electrode current collector layer, and may include a positive electrode active material layer including a positive electrode active material.

[0198] In the above positive electrode, the positive electrode current collector layer is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector layer may typically have a thickness of 3 to 500 ㎛, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0199] The above positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound having the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4(0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2Ni-site type lithium nickel oxide represented by O2 (wherein, 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); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxide represented by O2 (wherein, 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 (wherein, M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4, etc., in which a part of Li in the chemical formula is replaced with an alkaline earth metal ion, but is not limited thereto. The positive electrode may be Li-metal.

[0200] The above-described positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above.

[0201] At this time, the positive electrode conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more may be used.

[0202] In addition, the positive electrode binder plays a role of improving the adhesion between positive electrode active material particles and the adhesiveness between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0203] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. Any separator commonly used in secondary batteries can be used without any particular restrictions, and in particular, one that has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0204] Examples of the above electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0205] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0206] As the above non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate, ethyl propionate, etc. can be used.

[0207] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be preferably used because they easily dissociate lithium salts. In addition, when low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed and used in an appropriate ratio with these cyclic carbonates, an electrolyte with high electrical conductivity can be produced, so that they can be used even more preferably.

[0208] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, for example, the anion of the lithium salt is F - , Cl - , I - , NO3 -, N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0209] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as, for example, a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery.

[0210] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell and a battery pack including the same. The battery module and battery pack include the secondary battery having high capacity, high rate characteristics, and cycle characteristics, and thus can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0211] Hereinafter, preferred embodiments are presented to help understand the present invention, but the above embodiments are only illustrative of the present disclosure, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0212] <Manufacturing Example>

[0213] <Manufacturing of the cathode>

[0214] Example 1: Preparation of the cathode

[0215] Manufacturing of the first negative electrode active material layer

[0216] A first negative electrode active material layer composition was prepared using Si (average particle diameter (D50): 5 μm) as a silicon-based active material, first conductive agent, second conductive agent, third conductive agent, and polyacrylamide as a binder in a weight ratio of 70:9.8:10:0.2:10. A first negative electrode slurry was prepared by adding it to distilled water as a solvent for forming a negative electrode slurry (solid content concentration: 25 wt%).

[0217] The first challenge material is carbon black C (specific surface area: 58 m 2 / g, diameter: 37 nm), and the second conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle diameter (D50): 3.5 um), and the third challenge material is a carbon nanotube.

[0218] As a mixing method, the first conductive agent, the second conductive agent, the third conductive agent, the binder, and water were dispersed using a homo mixer at 2500 rpm for 30 min, and then the active material was added and dispersed at 2500 rpm for 30 min to produce a first negative electrode slurry.

[0219] The first negative electrode slurry was applied at 2.75 mg / cm on both sides of a copper current collector (thickness: 8 μm) as a negative electrode current collector. 2 The first negative electrode active material layer (thickness: 33 μm) was formed by coating with a loading amount, rolling (roll pressing), and drying in a vacuum oven at 130°C for 10 hours.

[0220] Manufacturing of the second negative electrode active material layer

[0221] A second negative electrode active material layer composition was prepared using Si / C (average particle diameter (D50): 3.5 μm, crystal grain size 200 nm) as a silicon-based active material, a second conductive agent, a third conductive agent, and polyacrylamide as a binder in a weight ratio of 70:19.8:0.2:10. A second negative electrode slurry was prepared by adding it to distilled water as a solvent for forming a negative electrode slurry (solid content concentration 25 wt%).

[0222] The second challenge material is a plate-shaped graphite (specific surface area: 17 m 2 / g, average particle diameter (D50): 3.5 um), and the third conductive material is a carbon nanotube.

[0223] As a mixing method, the second conductive agent, the third conductive agent, the binder, and water were dispersed using a homo mixer at 2500 rpm for 30 min, and then the active material was added and dispersed at 2500 rpm for 30 min to produce a second negative electrode slurry.

[0224] The second negative electrode slurry is added to the first negative electrode active material layer at 1 mg / cm 2 The second negative electrode active material layer (thickness: 15 μm) was formed by coating with a loading amount, rolling (roll pressing), and drying in a vacuum oven at 130°C for 10 hours.

[0225] In the above Example 1, it was manufactured in the same manner as in Table 1 below, except that it was changed.

[0226] First negative electrode active material layerSecond negative electrode active material layerReference negative electrode active material D50 (μm)Negative electrode active material grain size (nm)Example 1Si5Si / C200DL structureExample 2Si5SiO200DL structureExample 3Si5Si200DL structureExample 4Si5Si / C3DL structureExample 5Si5Si / C220DL structureComparative example 1Si5--SL structure(negative electrode active material layer total thickness 50 μm)(crystal grain 200 nm)Comparative example 2Si5Si / C400DL structureComparative example 3Si5Si / C350DL structureComparative example 4Si5SiO400DL structureComparative example 5Si5Si400DL structure

[0227] Experimental Example 1: Life Characteristics Evaluation

[0228] The secondary batteries containing the negative electrodes manufactured in the above examples and comparative examples were subjected to a life evaluation using an electrochemical charger / discharger, and the capacity retention rate was evaluated. The secondary batteries were subjected to a cycle test at 4.2-3.0 V 1C / 0.5C, and the capacity retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0 V) every 50 cycles during the test.

[0229] Capacity retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at first cycle)} Υ 100

[0230] Experimental Example 2: Measurement and Evaluation of Resistance Increase Rate

[0231] In the above experimental example 1, the capacity retention rate was measured by performing 0.33C / 0.33C charge / discharge (4.2-3.0V) every 50 cycles during the test, and then the resistance increase rate was compared and analyzed by measuring the total resistance by discharging at 2.5C pulse at SOC50.

[0232] In addition, for the above life characteristic evaluation and the above resistance increase rate measurement evaluation, data at 200 cycles were calculated, and the results were as shown in Table 2 below.

[0233] Capacity retention rate evaluation (%, @200 cycle Resistance increase rate (%, @200 cycle Example 190.30.75 Example 2901.2 Example 3882.3 Example 4921.5 Example 590.70.7 Comparative example 17723.4 Comparative example 2853.8 Comparative example 385.75.2 Comparative example 484.84.5 Comparative example 583.66.3

[0234] As can be seen in Table 2 above, in the case of the negative electrode according to the present application, the second negative electrode active material layer uses a silicon-based active material with a grain size adjusted as described above, so that the grain boundaries are widely distributed, and when lithium ions are inserted, they are distributed more uniformly, so that the stress generated when lithium ions are inserted into silicon particles can be reduced, and thus, the breakage of the particles on the surface is mitigated. As a result, it was confirmed that it has the characteristic of further improving the life stability of the negative electrode.

[0235] In the case of Comparative Example 1, it corresponds to a single layer structure having a single layer of silicon-based negative electrode active material layer, and in the cases of Comparative Examples 2 to 5, all have a DL structure like the present invention, but the crystal grain size is outside the scope of the present application.

[0236] In this case, it was confirmed that the crystal grain size in the second negative electrode active material layer was large, so that the reaction was concentrated on the surface, and particle breakage progressed on the surface of the second negative electrode active material layer, resulting in a decrease in life stability and a high resistance increase rate. In particular, in the case of the SL structure, it was confirmed that the reaction was concentrated on the surface, resulting in a high resistance increase rate.

Claims

1. A negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a first negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a second negative electrode active material layer provided on the opposite side of the side of the first negative electrode active material layer facing the negative electrode current collector layer; The first negative electrode active material layer includes a first negative electrode active material layer composition including a first negative electrode active material, and the second negative electrode active material layer includes a second negative electrode active material layer composition including a second negative electrode active material. The above first negative electrode active material is Si and SiOx (0 <x<2)로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 제1 음극 활물질 100 중량부 기준 상기 Si를 95 중량부 이상 포함하고, The above second negative active material includes a silicon-based active material, The above silicon-based active material is a negative electrode for a lithium secondary battery having a crystal grain size of 250 nm or less.

2. In claim 1, A negative electrode for a lithium secondary battery, wherein the first negative electrode active material is at least 80 parts by weight based on 100 parts by weight of the first negative electrode active material layer composition.

3. In claim 1, A negative electrode for a lithium secondary battery, wherein the thickness of the first negative electrode active material layer is 10 μm or more and 25 μm or less.

4. In claim 1, The above silicon-based active material is Si, SiOx (0 <x<2), SiC, 및 Si 합금으로 이루어진 군에서 선택되는 1 이상을 포함하는 것인 리튬 이차 전지용 음극.

5. In claim 1, The above silicon-based active material is a negative electrode for a lithium secondary battery containing Si.

6. In claim 1, A negative electrode for a lithium secondary battery, wherein the central particle diameter (D50) of the above silicon-based active material is 1 μm or more and 10 μm or less.

7. In claim 1, A negative electrode for a lithium secondary battery, wherein the thickness of the second negative electrode active material layer is 10 μm or more and 20 μm or less.

8. In claim 1, A negative electrode for a lithium secondary battery, wherein the porosity of the first negative electrode active material layer and the porosity of the second negative electrode active material layer are 20% or more and 50% or less.

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

10. Bipolar; A negative electrode for a lithium secondary battery according to any one of claims 1 to 9; A separator provided between the anode and the cathode; and A lithium secondary battery comprising an electrolyte.

11. Step of preparing a negative electrode for a lithium secondary battery; and A method for manufacturing a lithium secondary battery, comprising the steps of assembling a negative electrode; a positive electrode; a separator; and an electrolyte for the lithium secondary battery; The step of preparing the negative electrode for the lithium secondary battery includes the step of preparing a negative electrode current collector layer; the step of applying a first negative electrode active material layer composition to one or both sides of the negative electrode current collector layer to form a first negative electrode active material layer; and The first negative electrode active material layer includes a first negative electrode active material layer composition including a first negative electrode active material, and the second negative electrode active material layer includes a second negative electrode active material layer composition including a second negative electrode active material. The above first negative electrode active material is Si and SiOx (0 <x<2)로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 제1 음극 활물질 100 중량부 기준 상기 Si를 95 중량부 이상 포함하고, The above second negative active material includes a silicon-based active material, A method for manufacturing a lithium secondary battery, wherein the above silicon-based active material has a crystal grain size of 250 nm or less.

12. In claim 11, A step of pre-lithiating a negative electrode in which a first negative electrode active material layer and a second negative electrode active material layer are formed on the negative electrode current collector layer, A method for manufacturing a lithium secondary battery, wherein the step of prelithiating the negative electrode includes a lithium electrolytic plating process; a lithium metal transfer process; a lithium metal deposition process; or a stabilized lithium metal powder (SLMP) coating process.

13. In claim 11, The step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet on dry process, The above wet-on-dry process comprises a step of applying a first negative electrode active material layer composition; A step of forming a first negative electrode active material layer by partially drying or completely drying the first negative electrode active material layer composition applied above; and A method for manufacturing a lithium secondary battery, comprising: a step of applying the second negative electrode active material layer composition to the first negative electrode active material layer.

14. In claim 11, The step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet on wet process, The above wet-on-wet process comprises the steps of applying a first negative electrode active material layer composition; and A method for manufacturing a lithium secondary battery, comprising: a step of applying the second negative electrode active material layer composition to the first negative electrode active material layer composition while the first negative electrode active material layer composition is in an undried state.

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