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

Abstract

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

Description

Technical Field

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0184204, filed with the Korean Intellectual Property Office on December 26, 2022, and all of its content is incorporated herein by reference.

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

Background Art

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

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

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

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

[0007] In particular, in response to the recent demand for high-density energy batteries, active research has been conducted into methods for increasing capacity by using silicon-based compounds such as Si / C and SiOx as anode active materials, which have capacities more than 10 times greater than graphite-based materials. However, while silicon-based compounds, which are high-capacity materials, have superior capacity characteristics compared to conventional graphite, their rapid volume expansion during charging can disrupt conductive pathways, degrading battery performance and resulting in a decrease in capacity from the start. Furthermore, silicon-based anodes face challenges in that lithium ions cannot be uniformly charged throughout the anode depth during repeated charge and discharge cycles, and reactions occur on the surface, accelerating surface degradation. This calls for improved performance in terms of battery cycles.

[0008] Therefore, various methods are being discussed to solve the problems associated with using silicon-based compounds as negative electrode active materials, such as adjusting the driving potential, coating a thin film on the active material layer, suppressing volume expansion itself by adjusting the particle size of the silicon-based compound, or developing a binder that controls the volume expansion of the silicon-based compound to prevent the conductive path from being broken. Research is also being conducted to improve the lifespan characteristics of silicon-based negative electrodes by limiting the proportion of silicon-based active material used during initial charge and discharge and providing a reservoir role through the use of a method of prelithiating the silicon-based active material layer.

[0009] However, in the case of the above method, there is a risk that the performance of the battery may be deteriorated, and therefore there is a limit to its applicability, and there is still a limit to the commercialization of the production of negative electrode batteries with a high content of silicon-based compounds. As the proportion of silicon-based active material in the silicon-based active material layer increases, pre-lithiation is concentrated on the surface of the negative electrode, which in turn causes damage to the silicon-based active material on the surface side and causes non-uniform pre-lithiation, resulting in problems in improving life characteristics.

[0010] In the case of a silicon-based negative electrode, during the activation process, one charge and discharge cycle is performed. At this time, due to the influence of the highly reactive silicon-based active material, charging cannot be performed at a high rate, the time of the activation process increases, and problems occur in the manufacturing process.

[0011] Therefore, in order to improve the capacity characteristics, when using a silicon-based compound as the active material, it does not cause a decrease in the capacity characteristics, and when performing charge and discharge cycles, it is possible to prevent electrode surface degradation and improve the cycle performance. In addition, the process time can be shortened in the activation process, and research on a negative electrode having an optimal silicon phase arrangement by the activation process is necessary.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0013] This application relates to a negative electrode for a lithium secondary battery, a method for manufacturing a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode, which can maximize the capacity characteristics, which is the main purpose of using a silicon-based active material, while using a silicon-based active material for the negative electrode, and can prevent electrode surface degradation when performing charge and discharge cycles, and can form an optimal arrangement of silicon phases in the negative electrode active material layer by a high-rate activation process.

[0014] That is, the negative electrode for a lithium secondary battery according to this application is mainly characterized in that it defines the state of the silicon phase of the negative electrode for a lithium secondary battery that can show a capacity retention rate and resistance characteristics equal to or higher than those of a negative electrode with an increased process time by applying a low-rate activation process and can ensure processability.

Means for Solving the Problems

[0015] One embodiment of the present specification is a negative electrode for a lithium secondary battery, including a negative electrode current collector layer; and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer. The negative electrode active material layer includes a first negative electrode active material layer provided on the negative electrode current collector layer; and a second negative electrode active material layer provided on the opposite surface of the first negative electrode active material layer facing the negative electrode current collector layer. The first negative electrode active material layer includes a first negative electrode active material layer composition containing a first negative electrode active material. The second negative electrode active material layer includes a second negative electrode active material layer composition containing a second negative electrode active material. The first negative electrode active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and based on 100 parts by weight of the first negative electrode active material, contains 95 parts by weight or more of SiOx (x = 0). The second negative electrode active material includes a mixture of one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride. The ratio of amorphous silicon contained in the first negative electrode active material layer is lower than the ratio of amorphous silicon contained in the second negative electrode active material layer. The ratio of the silicon phase contained in the negative electrode active material layer satisfies the following formula 1, and a negative electrode for a lithium secondary battery is provided.

[0016] [Formula 1] 5 ≤ B / (A + B)×100(%) ≤ 30 In the above formula 1, A is the part by weight of the crystalline phase based on 100 parts by weight of the silicon phase contained in the negative electrode active material layer, and B is the part by weight of the amorphous phase based on 100 parts by weight of the silicon phase contained in the negative electrode active material layer.

[0017] In another embodiment, a lithium secondary battery is provided, including a positive electrode; the negative electrode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0018] Finally, a step of preparing a lithium secondary battery including a positive electrode, a negative electrode for a lithium secondary battery, a separator, and an electrolyte; and a step of activating the lithium secondary battery; A method for manufacturing a lithium secondary battery, wherein the activating step includes a high C-rate activation step (high-rate charging), and the step of preparing the negative electrode for the lithium secondary battery includes: preparing a negative electrode current collector layer; applying a first negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer using a coater to form a first negative electrode active material layer; and applying a second negative electrode active material layer composition to the opposite surface of the first negative electrode active material layer that contacts the negative electrode current collector layer using a coater to form a second negative electrode active material layer, wherein the first negative electrode active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and based on 100 parts by weight of the first negative electrode active material, the SiOx (x = 0) includes 95 parts by weight or more, and the second negative electrode active material includes one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride. A method for manufacturing a lithium secondary battery is provided.

Effect of the Invention

[0019] In the case of the negative electrode for a lithium secondary battery according to an embodiment of the present invention, it has a double-layer active material layer composed of a first negative electrode active material layer and a second negative electrode active material layer. In particular, the first negative electrode active material included in the first negative electrode active material layer includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and based on 100 parts by weight of the first negative electrode active material, the SiOx (x = 0) includes 95 parts by weight or more, and the second negative electrode active material included in the second negative electrode active material layer includes one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride.

[0020] The negative electrode for a lithium secondary battery according to the present application has a double-layer active material layer having the specific composition and content as described above. In particular, since the first negative electrode active material layer contains a high content of SiOx (x = 0), it can have the advantages of high capacity, high density, and rapid charging as they are. Further, since the second negative electrode active material layer contains a silicon-based and / or carbon-based active material, etc., it is possible to prevent electrode surface degradation during charge and discharge cycles, and the uniformity during pre-lithiation can also be improved.

[0021] Among them, in particular, the negative electrode for a lithium secondary battery according to the present application can enable high C-rate charging in the activation process, thereby forming an optimal arrangement of the silicon phase in the negative electrode active material layer and satisfying the range of Formula 1.

[0022] Therefore, a lithium secondary battery including this mainly features satisfying cycle characteristics along with the optimal capacity characteristics that are the advantages of a Si negative electrode.

[0023] Ultimately, the negative electrode for a lithium secondary battery according to the present application has the advantages of an electrode that applies a high content of Si particles as a single-layer active material, and at the same time, to solve the problems of surface degradation, the problem of uniformity during pre-lithiation, and the problem of life characteristics, which are the disadvantages when having this, the second negative electrode active material layer is coated on top of the first negative electrode active material layer, and by adjusting the conditions of the activation process, an optimal arrangement of the silicon phase in the negative electrode active material layer (in particular, the arrangement of the silicon phase in the first negative electrode active material layer) is formed, and it mainly features satisfying the range of Formula 1.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0025] Before describing the present invention, first, several terms will be defined.

[0026] In this specification, when a part "includes" a certain component, this means that, unless otherwise stated, it does not exclude other components, but may further include other components.

[0027] In this specification, "p to q" means "p or more and q or less".

[0028] In this specification, the "specific surface area" is measured by the BET method. Specifically, it is calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II manufactured by BEL Japan, Inc. That is, in the present application, the BET specific surface area can mean the specific surface area measured by the above measurement method.

[0029] In this specification, "Dn" means the particle size distribution and represents the particle size at the n% point of the cumulative particle number distribution according to the particle size. That is, D50 is the particle size (average particle size, median particle size) at the 50% point of the cumulative particle number distribution according to the particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution according to the particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution according to the particle size. On the other hand, the particle size distribution may be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500). When the particles pass through the laser beam, the difference in the diffraction pattern due to the particle size is measured to calculate the particle size distribution.

[0030] In this specification, the meaning that a polymer contains a certain monomer in monomer units means that the monomer participates in the polymerization reaction and is included as a repeating unit in the polymer. In this specification, when it is said that a polymer contains a monomer, this is interpreted to be the same as the polymer containing the monomer in monomer units.

[0031] In this specification, the term "polymer" is understood to be used in a broad sense including copolymers unless otherwise specified as "homopolymer".

[0032] In this specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are the polystyrene equivalent molecular weights measured by Gel Permeation Chromatography (GPC) using a variety of monodisperse polystyrene polymers (standard samples) with different degrees of polymerization commercially available for molecular weight measurement as the standard substance. In this specification, the molecular weight means the weight average molecular weight unless otherwise specified.

[0033] Hereinafter, with reference to the drawings, a detailed description will be given so that a person having ordinary knowledge in the technical field to which the present invention pertains can easily implement the present invention. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0034] One embodiment of the present specification is a negative electrode for a lithium secondary battery including a negative electrode current collector layer; and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer, wherein the negative electrode active material layer includes a first negative electrode active material layer provided on the negative electrode current collector layer; and a second negative electrode active material layer provided on the opposite surface of the first negative electrode active material layer facing the negative electrode current collector layer, the first negative electrode active material layer includes a first negative electrode active material layer composition including a first negative electrode active material, the second negative electrode active material layer includes a second negative electrode active material layer composition including a second negative electrode active material, the first negative electrode active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), based on 100 parts by weight of the first negative electrode active material, it contains 95 parts by weight or more of the SiOx (x = 0), the second negative electrode active material includes a mixture of one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride, the ratio of amorphous silicon contained in the first negative electrode active material layer is lower than the ratio of amorphous silicon contained in the second negative electrode active material layer, and the ratio of the silicon phase in the negative electrode active material layer satisfies the following formula 1, and a negative electrode for a lithium secondary battery is provided.

[0035] [Formula 1] 5 ≦ B / (A + B)×100(%) ≦ 30 In the above formula 1, A is the part by weight of the crystalline phase based on 100 parts by weight of the silicon phase contained in the negative electrode active material layer, and B is the part by weight of the amorphous phase based on 100 parts by weight of the silicon phase contained in the negative electrode active material layer.

[0036] The negative electrode for a lithium secondary battery according to the present application has the advantages of an electrode that applies Si particles with a high content as a single-layer active material, and at the same time, solves the surface degradation problem, the uniformity problem during pre-lithiation, and the life characteristic problem, which are the disadvantages when having this. To achieve this, a second negative electrode active material layer is coated on top of the first negative electrode active material layer, and by adjusting the conditions of the activation process, an optimal arrangement of the silicon phase within the negative electrode active material layer is achieved, mainly characterized by satisfying the range of Formula 1.

[0037] Figure 1 is a diagram showing the laminated structure of the negative electrode for a lithium secondary battery according to an embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery including a first negative electrode active material layer 20 and a second negative electrode active material layer 10 can be confirmed on one surface of the negative electrode current collector layer 30. Figure 1 shows that the first negative electrode active material layer is formed on one surface, but it may be included on both surfaces of the negative electrode current collector layer. As described above, in an embodiment of the present application, the first negative electrode active material layer may be formed on the front surface of the negative electrode current collector layer, and the second negative electrode active material layer may be formed on the front surface of the first negative electrode active material layer.

[0038] Also, Figure 2 is a diagram showing the laminated structure of the negative electrode for a lithium secondary battery according to an embodiment of the present application. Specifically, as shown in Figure 2, the first negative electrode active material layer 20 and the second negative electrode active material layer 10 may be formed on both surfaces of the negative electrode current collector layer 30. Also, it may have an arrangement of 10>20>30>20>10. Additionally, if the first negative electrode active material layer and the second negative electrode active material layer are sequentially laminated only on one surface 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 surface can be laminated regardless of the relationship. Preferably, both surfaces of the negative electrode current collector layer preferably have the same composition. Specifically, it may have a structure of 10>20>30>20>10.

[0039] Hereinafter, the negative electrode for a lithium secondary battery of the present invention will be described in more detail.

[0040] In one embodiment of the present application, a negative electrode for a lithium secondary battery includes: a negative electrode current collector layer; and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer. The negative electrode active material layer includes a first negative electrode active material layer provided on the negative electrode current collector layer; and a second negative electrode active material layer provided on the surface of the first negative electrode active material layer opposite to the surface facing the negative electrode current collector layer. A negative electrode for a lithium secondary battery is provided.

[0041] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, a surface-treated product of copper or stainless steel with carbon, nickel, titanium, silver, etc. on the surface, an aluminum-cadmium alloy, etc. may be used. Further, fine irregularities may be formed on the surface to strengthen the binding force of the negative electrode active material, and it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0042] 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.

[0043] However, the thickness may vary variously depending on the type and application of the negative electrode used, and is not limited thereto.

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

[0045] In one embodiment of the present application, the first negative electrode active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2). Based on 100 parts by weight of the first negative electrode active material, SiOx (x = 0) may be included in an amount of 95 parts by weight or more, preferably 97 parts by weight or more, more preferably 99 parts by weight or more, and may be included in an amount of 100 parts by weight or less.

[0046] In one embodiment of the present application, the first negative electrode active material may particularly use pure silicon (Si) particles. Using pure silicon (Si) as the first negative electrode active material can mean, as described above, that the first negative electrode active material contains pure Si particles (SiOx (x = 0)) that are not combined with other particles or elements within the above range based on a total of 100 parts by weight.

[0047] In one embodiment of the present application, the first negative electrode active material may consist of SiOx (x = 0).

[0048] The first negative electrode active material layer according to the present application contains the first negative electrode active material, and specifically includes pure silicon particles containing 95 parts by weight or more of SiOx (x = 0). When a high content of pure silicon particles is included, the capacity characteristics are excellent, but the life reduction characteristics due to surface non-uniform reaction occur. Accordingly, the problem has been solved by including the second negative electrode active material layer according to the present invention in a specific weight loading amount.

[0049] On the one hand, the average particle size (D50) of the first negative electrode active material of the present invention may be 3 μm to 10 μm, specifically, it may be 4 μm to 8 μm, and more specifically, it may be 5 μm to 7 μm. When the average particle size is within the above range, the specific surface area of the particles is within an appropriate range, and the viscosity of the negative electrode slurry is formed within an appropriate range. As a result, the dispersion of the particles constituting the negative electrode slurry becomes smooth. In addition, since the size of the first negative electrode active material has a value equal to or greater than the lower limit value of the range, the contact area between the silicon particles and the conductive material by the composite composed of the conductive material and the binder in the negative electrode slurry is excellent, and the possibility of maintaining the conductive network is increased, and the capacity retention rate is increased. On the other hand, when the average particle size satisfies the above range, silicon particles that are too large are excluded, and the surface of the negative electrode is smoothly formed, whereby it is possible to prevent the non-uniform current density phenomenon during charge and discharge.

[0050] In one embodiment of the present application, the first negative electrode active material has a normally specific BET specific surface area. The BET specific surface area of the first negative electrode active material is preferably 0.01 m 2 / g to 150.0 m 2 / g, more preferably 0.1 m 2 / g to 100.0 m 2 / g, particularly preferably 0.2 m 2 / g to 80.0 m 2 / g, most preferably 0.2 m 2 / g to 18.0 m 2 / g. The BET specific surface area is measured according to DIN 66131 (using nitrogen).

[0051] In one embodiment of the present application, the first negative electrode active material may exist, for example, in a crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or multi-piece particles. Alternatively, the silicon particles may have a fibrous structure, or may exist in the form of a silicon-containing thin film or coating, but this is not so preferable.

[0052] In one embodiment of the present application, the first negative electrode active material may have a non-spherical shape, and its sphericity may be, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0053] In the present application, the circularity is determined by the following formula A-1, where A is the area and P is the boundary line.

[0054] [Formula 1-1] 4πA / P 2

[0055] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the first negative electrode active material is 60 parts by weight or more based on 100 parts by weight of the first negative electrode active material layer composition.

[0056] In another embodiment, the first negative electrode active material may contain 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and may contain 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 80 parts by weight or less, based on 100 parts by weight of the first negative electrode active material layer composition.

[0057] The first negative electrode active material layer composition according to the present application uses a first negative electrode active material with a significantly high capacity within the above range, and even when used together with the second negative electrode active material layer described later, it does not reduce the capacity performance of the entire negative electrode, and solves the problems of surface degradation during charging and discharging, the problem of uniformity during pre-lithiation, and the problem of life characteristics.

[0058] Conventionally, it has been common to use only graphite-based compounds as the negative electrode active material. However, recently, as the demand for high-capacity batteries has increased, in order to increase the capacity, attempts have been increasing to use a silicon-based compound by mixing. However, in the case of a silicon-based compound, there is a limit that the volume rapidly expands during the charge / discharge process, damaging the conductive path formed in the negative electrode active material layer and reducing the performance of the battery instead.

[0059] Therefore, in one embodiment of the present application, the first negative electrode active material layer composition may further include one or more selected from the group consisting of a first negative electrode conductive material and a first negative electrode binder.

[0060] At this time, the first negative electrode conductive material and the first negative electrode binder included in the first negative electrode active material layer composition may be used without being limited to those used in the art.

[0061] In one embodiment of the present application, the first negative electrode conductive material may be used without being limited to substances generally used in the art, and specifically, may include one or more selected from the group consisting of a dot-shaped conductive material, a planar conductive material, and a linear conductive material.

[0062] In one embodiment of the present application, the dot-shaped conductive material can be used to improve the conductivity of the negative electrode, and means a dot-shaped or spherical conductive material having conductivity without inducing a chemical change. Specifically, the dot-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivative, and preferably may include carbon black in terms of realizing high conductivity and excellent dispersibility.

[0063] In one embodiment of the present application, the BET specific surface area of the dot-shaped conductive material is 40 m 2 / g or more and 70 m 2 / g or less, preferably 45 m 2 / g or more and 65 m 2 / g or less, more preferably 50 m 2 / g or more and 60 m 2 / g or less.

[0064] 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.

[0065] In one embodiment of the present application, the first negative electrode conductive material may include a planar conductive material.

[0066] The planar conductive material can play a role in increasing the surface contact between silicon particles in the negative electrode to improve conductivity, and at the same time suppressing the interruption of the conductive path due to volume expansion. The planar conductive material may be expressed as a plate-shaped conductive material or a bulk conductive material.

[0067] In one embodiment of the present application, the planar conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and preferably may be plate-shaped graphite.

[0068] In one embodiment of the present application, the average particle size (D50) of the planar conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the above range is satisfied, since the particle size is sufficient, the viscosity of the negative electrode slurry does not increase too much, and at the same time, dispersion becomes easy. Therefore, when dispersing using the same equipment and time, the dispersion effect is excellent.

[0069] In one embodiment of the present application, the planar conductive material provides a negative electrode composition in which D10 is 0.5 μm or more and 1.5 μm or less, D50 is 2.5 μm or more and 3.5 μm or less, and D90 is 7.0 μm or more and 15.0 μm or less.

[0070] In one embodiment of the present application, as the planar conductive material, a high specific surface area planar conductive material with a high BET specific surface area or a low specific surface area planar conductive material may be used.

[0071] In one embodiment of the present application, as the planar conductive material, a planar conductive material with a high specific surface area or a planar conductive material with a low specific surface area may be used without limitation. In particular, the planar conductive material according to the present application may be affected to some extent by dispersion in terms of electrode performance, and it is particularly preferable to use a planar conductive material with a low specific surface area that does not cause problems in dispersion.

[0072] In one embodiment of the present application, the planar conductive material may have a BET specific surface area of 5 m 2 / g or more.

[0073] In another embodiment, the planar conductive material may have a BET specific surface area of 5 m 2 / g or more and 500 m 2 / g or less, preferably 5 m 2 / g or more and 300 m 2 / g or less, more preferably 5 m 2 / g or more and 250 m 2 / g or less.

[0074] In another embodiment, the planar conductive material is a planar conductive material with a high specific surface area, and can satisfy the range of having a BET specific surface area of 50 m 2 / g or more and 500 m 2 / g or less, preferably 80 m 2 / g or more and 300 m 2 / g or less, more preferably 100 m 2 / g or more and 300 m 2 / g or less.

[0075] In another embodiment, the planar conductive material is a planar conductive material with a low specific surface area, and can satisfy the range of having a BET specific surface area of 5 m 2 / g or more and 40 m 2 / g or less, preferably 5 m 2 / g or more and 30 m 2 / g or less, more preferably 5 m 2 / g or more and 25 m 2 / g or less.

[0076] In addition, as the conductive material, there may be a linear conductive material such as a carbon nanotube. The carbon nanotube may be a bundled carbon nanotube. The bundled carbon nanotube may include a plurality of carbon nanotube unit bodies. Specifically, here, the 'bundle type' refers to a secondary shape in which a plurality of carbon nanotube unit bodies are arranged in parallel or twisted in a bundle or rope shape with the axes in the longitudinal direction of the carbon nanotube unit bodies being substantially the same orientation, unless otherwise mentioned. The carbon nanotube unit body has a graphite sheet in a nanosize diameter cylinder shape and has an sp2 bonding structure. At this time, depending on the winding angle and structure of the graphite sheet, it can exhibit conductor or semiconductor characteristics. The bundled carbon nanotube can be uniformly dispersed during the production of the negative electrode compared to the entangled type carbon nanotube, and can smoothly form a conductive network in the negative electrode, improving the conductivity of the negative electrode.

[0077] In one embodiment of the present application, the first negative electrode conductive material can satisfy 10 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the first negative electrode active material layer composition.

[0078] In another embodiment, the first 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, more preferably 5 parts by weight or more and 25 parts by weight or less based on 100 parts by weight of the first negative electrode active material layer composition.

[0079] In one embodiment of the present application, the first negative electrode conductive material includes a dot-shaped conductive material, a planar conductive material, and a linear conductive material, and the ratio of the dot-shaped conductive material: planar conductive material: linear conductive material can satisfy a ratio of 1:1:0.01 to 1:1:1.

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

[0081] In one embodiment of the present application, the planar conductive material can satisfy the range of 1 to 60 parts by weight, preferably 5 to 50 parts by weight, more preferably 10 to 50 parts by weight, based on 100 parts by weight of the first negative electrode conductive material.

[0082] In one embodiment of the present application, the linear conductive material can satisfy the range of 0.01 to 10 parts by weight, preferably 0.05 to 8 parts by weight, more preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the first negative electrode conductive material.

[0083] In one embodiment of the present application, the first negative electrode conductive material may include a linear conductive material and a planar conductive material.

[0084] In one embodiment of the present application, the first negative electrode conductive material includes a linear conductive material and a planar conductive material, and the weight ratio of the linear conductive material: planar conductive material can satisfy 0.01:1 to 0.1:1.

[0085] 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 great impact on the life characteristics of conventional lithium secondary batteries, and there are more points where charging and discharging are possible, and it has the characteristic of excellent output characteristics at a high C rate. In the case of the first negative electrode conductive material according to the present application, it has a completely different configuration from the conductive material applied to the positive electrode. That is, in the case of the first negative electrode conductive material according to the present application, it plays a role in controlling the contacts between silicon-based active materials with very large volume expansion of the electrode during charging and discharging. When the positive electrode conductive material is rolled, it plays a role of imparting partial conductivity while having a buffering effect of a buffer role, and the negative electrode conductive material of the present invention has completely different configurations and roles.

[0086] Also, the first negative electrode conductive material according to the present application is applied to silicon-based active materials and has a completely different configuration from the conductive material applied to graphite-based active materials. That is, the conductive material used for 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 partial conductivity. It has completely different configurations and roles from the first negative electrode conductive material applied together with silicon-based active materials as in the present invention.

[0087] In one embodiment of the present application, the first negative electrode binder may include at least any one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, poly acrylic acid, and substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0088] According to one embodiment of the present application, the first negative electrode binder plays a role in controlling the first negative electrode active material and the first negative electrode conductive material in order to prevent the twisting and structural deformation of the negative electrode structure during the volume expansion and relaxation of the first negative electrode active material. If the above role is satisfied, general binders can all be applied. Specifically, an aqueous binder may be used. More specifically, a PAM-based binder may be used.

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

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

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

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

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

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

[0095] In one embodiment of the present application, the second negative electrode active material includes one or more mixtures selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride, and the silicon-based active material is 50 parts by weight or more and 100 parts by weight or less based on 100 parts by weight of the second negative electrode active material, and a negative electrode for a lithium secondary battery is provided.

[0096] In another embodiment, the second negative electrode active material includes one or more mixtures selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride.

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

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

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

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

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

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

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

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

[0105] In one embodiment of the present application, the planar conductive material used as the first negative electrode conductive material has a structure and role different from those of the carbon-based active material generally used as the negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and means a material processed into a spherical or dot-like form for facilitating the storage and release of lithium ions.

[0106] On the one hand, the sheet-like conductive material used as the first negative electrode conductive material is a substance having a sheet or plate-like form and can be represented by plate-like graphite. That is, it is a substance contained to maintain a conductive path within the negative electrode active material layer, meaning a substance for securing a conductive path in a planar form within the negative electrode active material layer that does not play a role in the storage and release of lithium.

[0107] That is, in the present application, the fact that plate-like graphite was used as the conductive material means that it was processed into a sheet-like or plate-like form and used as a substance for securing a conductive path that does not play a role in the storage or release of lithium. At this time, the negative electrode active material contained together has high capacity characteristics for the storage and release of lithium and plays a role of being able to store and release all lithium ions transmitted from the positive electrode.

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

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

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

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

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

[0113] The second negative electrode active material layer composition according to the present application uses a second negative electrode active material having a lower capacity characteristic than the first negative electrode active material but less particle cracking due to charge and discharge within the above range, so that the capacity performance of the negative electrode is not reduced, the surface reaction of the negative electrode is suppressed, and the life characteristic enhancement can be achieved.

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

[0115] At this time, the contents regarding the second negative electrode conductive material and the second negative electrode binder may be the same as the contents of the first negative electrode conductive material and the first negative electrode binder described above.

[0116] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the ratio of amorphous silicon contained in the first negative electrode active material layer is lower than the ratio of amorphous silicon contained in the second negative electrode active material layer, and the ratio of the silicon phase contained in the negative electrode active material layer satisfies the following formula (1).

[0117] [Formula (1)] 5 ≦ B / (A + B) × 100 (%) ≦ 30 In the above formula (1), A is the part by weight of the crystalline phase based on 100 parts by weight of the silicon phase contained in the negative electrode active material layer. B is the part by weight of the amorphous phase based on 100 parts by weight of the silicon phase contained in the negative electrode active material layer.

[0118] In one embodiment of the present application, the formula 1 can satisfy 5 ≤ B / (A + B)×100(%) ≤ 30, preferably 6 ≤ B / (A + B)×100(%) ≤ 25, more preferably 7 ≤ B / (A + B)×100(%) ≤ 20.

[0119] Compared with the case of using a conventional single-layer silicon-based active material layer, the negative electrode for a lithium secondary battery according to the present application can include high-C-rate charging in the activation process, can shorten the activation process itself, and can adjust the ratio of the silicon phase in the negative electrode active material layer to the range of the formula 1 described above. Thereby, it is possible to shorten the manufacturing process time of the negative electrode for a lithium secondary battery, and to have the characteristics of ensuring high-capacity characteristics and life characteristics at room temperature.

[0120] In one embodiment of the present application, the second negative electrode active material layer includes amorphous silicon and crystalline silicon, and based on 100 parts by weight of the silicon phase contained in the second negative electrode active material layer, the amorphous phase contains 90 parts by weight or more, and a negative electrode for a lithium secondary battery is provided.

[0121] In still another embodiment, the second negative electrode active material layer includes amorphous silicon and crystalline silicon, and based on 100 parts by weight of the silicon phase contained in the second negative electrode active material layer, the amorphous phase may be 90 parts by weight or more, preferably 91 parts by weight or more, and specifically, can satisfy 99 parts by weight or less and 95 parts by weight or less.

[0122] That is, the second negative electrode active material layer (upper layer portion) serves as a buffer layer, is coated so that a minimum thickness can be applied and high-rate activation can be applied, and outside that, a high-capacity and high-density first negative electrode active material layer has an important influence on the negative electrode performance.

[0123] In one embodiment of the present application, the first negative electrode active material layer contains amorphous silicon and crystalline silicon, and based on 100 parts by weight of the silicon phase contained in the first negative electrode active material layer, the crystalline phase contains 50 parts by weight or more, providing a negative electrode for a lithium secondary battery.

[0124] In another embodiment, the first negative electrode active material layer contains amorphous silicon and crystalline silicon, and based on 100 parts by weight of the silicon phase contained in the first negative electrode active material layer, the crystalline phase may be 60 parts by weight or more, preferably 65 parts by weight or more, and specifically, may satisfy 99 parts by weight or less and 95 parts by weight or less.

[0125] In one embodiment of the present application, when the total thickness of the negative electrode active material layer is defined as T, the negative electrode active material layer includes a first region in a range of 0.2T or less and a second region in a range of more than 0.5T and T or less, based on the opposite surface of the surface facing the negative electrode current collector layer. The amorphous phase in the first region contains 90 parts by weight or more based on 100 parts by weight of the silicon phase in the negative electrode active material layer, and the crystalline phase in the second region contains 60 parts by weight or more based on 100 parts by weight of the silicon phase in the negative electrode active material layer, providing a negative electrode for a lithium secondary battery.

[0126] In one embodiment of the present application, the total thickness T of the negative electrode active material layer can mean the combined thickness of the thickness of the first negative electrode active material layer and the thickness of the second negative electrode active material layer, and may be expressed by dividing it into regions as described above based on the total thickness. At this time, the surface used as a reference for thickness measurement can be the opposite surface of the surface of the second negative electrode active material layer facing the first negative electrode active material layer.

[0127] That is, the negative electrode active material layer according to the present application is characterized in that it is formed as a double layer in which a first negative electrode active material layer and a second negative electrode active material layer are laminated. By including the second negative electrode active material layer, high-rate charging becomes possible during the activation process, and as a result, the ratio of the silicon phase in the negative electrode for a lithium secondary battery falls within the aforementioned range.

[0128] In the present application, the arrangement of the silicon phase can be confirmed for changes in the silicon phase in the depth direction by Raman analysis of the negative electrode for a lithium secondary battery, and the ratio of the weight distribution of the silicon phase in the negative electrode can be confirmed by this analysis. At this time, the activation process is performed on the surface portion of the negative electrode active material layer. When the surface portion of the negative electrode active material layer (the region far from the negative electrode current collector layer) contains an amorphous phase and the inside of the negative electrode active material layer (the region close to the negative electrode current collector layer) contains a crystalline phase, it is divided into respective regions according to the thickness T based on the weight ratio of the silicon phase.

[0129] Broadly speaking, it may be divided into an amorphous phase region, a crystalline phase region, and a mixed region of the amorphous phase and the crystalline phase. The aforementioned first region may be shown as the amorphous phase region, the second region may be shown as the crystalline phase region, and the intermediate region within the aforementioned range (that is, more than 0.2T and 0.5T or less) may be shown as the mixed region of the amorphous phase and the crystalline phase.

[0130] By adjusting the distribution of the crystalline phase and the amorphous phase as described above, it is possible to achieve a high capacity and a high energy density, and also to have the characteristic of excellent room temperature cycle life.

[0131] In one embodiment of the present application, the viscosity of the first negative electrode active material layer composition is 2,000 cPs or more and 15,000 cPs or less in shear viscosity 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, providing a negative electrode for a lithium secondary battery.

[0132] In yet another embodiment, the viscosity of the first negative electrode active material layer composition satisfies 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, more preferably 2,500 cPs or more and 12,000 cPs or less at a shear rate of 2.5 (1 / s).

[0133] At this time, the viscosity of the second negative electrode active material layer composition must be kept lower than that 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 is lower than that of the first negative electrode active material layer composition, but must be formed at an equivalent viscosity level.

[0134] In one embodiment of the present application, the negative electrode for the lithium secondary battery may be pre-lithiated.

[0135] The negative electrode for the lithium secondary battery according to the present application is composed of a double layer, and in particular, can include high-rate charging in the activation process, adjust the ratio of the silicon phase in the negative electrode active material layer, and subsequently play a role in enabling uniform lithiation in the depth direction of the electrode during cycle charging and discharging.

[0136] In one embodiment of the present application, a lithium secondary battery is provided, including a positive electrode; the negative electrode for the lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0137] The secondary battery according to one embodiment of the present specification may particularly include the negative electrode for the lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a specific description thereof will be omitted.

[0138] In one embodiment of the present application, a step of preparing a lithium secondary battery including a positive electrode, a negative electrode for a lithium secondary battery, a separator, and an electrolyte; and a step of activating the lithium secondary battery; A method for manufacturing a lithium secondary battery, wherein the activation step includes a high C-rate activation step (high-rate charging), and the step of preparing the negative electrode for the lithium secondary battery includes: preparing a negative electrode current collector layer; applying a first negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer using a coater to form a first negative electrode active material layer; and applying a second negative electrode active material layer composition to the opposite surface of the first negative electrode active material layer that contacts the negative electrode current collector layer using a coater to form a second negative electrode active material layer; wherein the first negative electrode active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), based on 100 parts by weight of the first negative electrode active material, SiOx (x = 0) is included in an amount of 95 parts by weight or more, and the second negative electrode active material includes one or more mixtures selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride. A method for manufacturing a lithium secondary battery is provided.

[0139] In the manufacturing method, the composition and content included in each step may be applied to the above-described content.

[0140] That is, as described above, by forming a second negative electrode active material layer, not the first negative electrode active material layer alone, and having the feature that a high-rate charge can be included in the activation step to arrange the silicon phase of Formula 1 described above, the life characteristics can be ensured.

[0141] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the thickness of the second negative electrode active material layer is 25% or more and 45% or less of the total thickness of the first negative electrode active material layer and the second negative electrode active material layer.

[0142] In yet another embodiment, the thickness of the first negative electrode active material layer may be 10 μm or more and 200 μm or less, specifically, 15 μm or more and 190 μm or less, and more specifically, 20 μm or more and 170 μm or less.

[0143] In yet another embodiment, the thickness of the second negative electrode active material layer may be 5 μm or more and 150 μm or less, specifically, 6 μm or more and 145 μm or less, and more specifically, 7 μm or more and 140 μm or less.

[0144] In one embodiment of the present application, there is provided a step of applying a first negative electrode active material layer composition onto one or both surfaces of the negative electrode current collector layer using a coater to form the first negative electrode active material layer.

[0145] That is, the step may mean a step of forming an active material layer on the negative electrode current collector layer, specifically, a step of forming an active material layer on the surface (lower layer portion) in contact with the negative electrode current collector layer in a double layer structure.

[0146] In one embodiment of the present application, applying the first negative electrode active material layer composition includes steps of applying and drying a first negative electrode slurry including the first negative electrode active material layer composition and a negative electrode slurry solvent.

[0147] At this time, the solid content of the first negative electrode slurry can satisfy the range of 10% to 40%.

[0148] In one embodiment of the present application, the step of forming the first negative electrode active material layer may include a step of mixing the first negative electrode slurry; and a step of coating the mixed first negative electrode slurry onto one or both surfaces of the negative electrode current collector layer using a coater; and the coating may use a coating method generally used in the art.

[0149] In one embodiment of the present application, a step of applying a second negative electrode active material layer composition to the surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer to form a second negative electrode active material is provided.

[0150] That is, the step can mean a step of forming a second negative electrode active material layer on the first negative electrode active material layer, and forming an active material layer on the surface (upper layer part) away from the negative electrode current collector layer in the double layer structure.

[0151] 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 including the second negative electrode active material layer composition and a negative electrode slurry solvent.

[0152] At this time, the solid content of the second negative electrode slurry can satisfy the range of 10% to 40%.

[0153] In one embodiment of the present application, the step of forming the second negative electrode active material layer includes a step of mixing the second negative electrode slurry; and a step of coating the mixed second negative electrode slurry on the surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer, and provides a method for manufacturing a lithium secondary battery.

[0154] For the coating, a coating method generally used in the art can be used.

[0155] For the step of forming the second negative electrode active material layer, the description of the step of forming the first negative electrode active material layer can be similarly applied.

[0156] In one embodiment of the present application, the step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet on dry process; or a wet on wet process; and provides a method for manufacturing a lithium secondary battery.

[0157] In one embodiment of the present application, the wet-on-dry process means a process of applying a first negative electrode active material layer composition, partially or completely drying it, and then applying a second negative electrode active material layer composition on top of it.

[0158] Figure 3 is a flowchart showing the 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 (first negative electrode active material, first negative electrode conductive material, first negative electrode binder, first solvent) is prepared and applied to the negative electrode current collector layer. Then, the first negative electrode slurry mixture is dried to form a first negative electrode active material layer. Then, a second negative electrode slurry mixture is prepared and applied to the first negative electrode active material layer and dried to form a second negative electrode active material layer. Then, each layer can be rolled and pressed to form a negative electrode for a lithium secondary battery according to the present application.

[0159] In one embodiment of the present application, the wet-on-wet process means a process of applying a first negative electrode active material layer composition and then, without drying it, applying a second negative electrode active material layer composition on top of it.

[0160] Figure 4 is a flowchart showing the wet-on-wet process according to one embodiment of the present application. Specifically, in the wet-on-wet process, a first negative electrode slurry mixture is prepared and applied to the negative electrode current collector layer, and at the same time, a second negative electrode slurry mixture is prepared and applied to the first negative electrode slurry mixture, and then the first and second negative electrode slurry mixtures are dried. Then, each layer can be rolled and pressed to form a negative electrode for a lithium secondary battery according to the present application.

[0161] In particular, in the wet on dry process, after applying the first negative electrode active material layer composition, it is completely dried, and then the second negative electrode active material layer composition is applied on top of it. By the above-described process, the first negative electrode active material layer and the second negative electrode active material layer can have a clear boundary. As a result, the compositions contained in the first negative electrode active material layer and the second negative electrode active material layer are not mixed and can have the characteristic of being configured as a double layer.

[0162] In one embodiment of the present application, the negative electrode slurry solvent can be used without limitation as long as it can dissolve the first negative electrode active material layer composition and the second negative electrode active material layer composition. Specifically, water or NMP may be used.

[0163] As a result of the wet on wet process described above, a joined region in which the first negative electrode active material layer and the second negative electrode active material layer are mixed can be formed. At this time, in order to perform the wet on wet process, it is necessary that the viscosity of the first negative electrode active material layer composition is lower than the viscosity of the second negative electrode active material layer composition, and at that time, mutual mixing can occur in the joined region and the process. Only by satisfying such a viscosity range can a stable double layer coating be achieved in the wet on wet process.

[0164] In the present application, after the first negative electrode active material layer is dried (wet on dry process), when the second negative electrode active material layer is formed, the interfaces of the two layers are clearly separated and formed. Also, when the second negative electrode active material layer is applied in a state where the first negative electrode active material layer composition is not completely dried (the first negative electrode active material layer composition and the second negative electrode active material layer composition are applied simultaneously), mixing occurs at the interface of the two layers and a joined region is formed. At this time, in the wet on dry process, it is not preferable to form a mixed region. In order to ensure this wet on wet processability, as described above, when the viscosity of the second negative electrode active material layer composition is lower than the viscosity of the first negative electrode active material layer, coating can be performed well up to the coating edge portion in terms of coating processability.

[0165] In one embodiment of the present application, a method for manufacturing a lithium secondary battery is provided, which includes 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. The step of pre-lithiating the negative electrode includes a lithium electroplating process; a lithium metal transfer process; a lithium metal evaporation process; or a stabilized lithium metal powder (SLMP) coating process.

[0166] As described above, since the second negative electrode active material layer contains 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, the advantages of rapid charging can be maintained. In particular, in the case of the second negative electrode active material, since it has a mixed composition and a large irreversibility, it can also exhibit an advantageous effect in the pre-lithiation process of pre-charging the negative electrode. Simply having the second negative electrode active material having the aforementioned composition in the second negative electrode active material layer enables a uniform pre-lithiation process at the upper end portion of the negative electrode electrode compared to the case where only the first negative electrode active material layer is applied, and thereby has the characteristic that the lifespan can be improved.

[0167] In one embodiment of the present application, the porosity of the first negative electrode active material layer and the second negative electrode active material layer can satisfy the range of 10% or more and 60% or less.

[0168] In another embodiment, the porosity of the first negative electrode active material layer and the second negative electrode active material layer can satisfy the range of 10% or more and 60% or less, preferably 20% or more and 50% or less, more preferably 30% or more and 45% or less.

[0169] The porosity varies depending on the composition and content of the active material, conductive material, and binder included in the first negative electrode active material layer and the second negative electrode active material layer, and thereby has the characteristic that the electrical conductivity and resistance in the electrode have an appropriate range.

[0170] In one embodiment of the present application, the positive electrode may include a positive electrode current collector layer and a positive electrode active material layer formed on the positive electrode current collector layer and containing a positive electrode active material.

[0171] In the positive electrode, the positive electrode current collector layer is not particularly limited as long as it has conductivity while not inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. Further, the positive electrode current collector layer may usually have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc.

[0172] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; the chemical formula Li 1+c1 Mn 2-c1 O4 (0 ≦ c1 ≦ 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; the chemical formula LiNi 1-c2 Mc2O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ c2 ≦ 0.3) represented by Ni-site type lithium nickel oxide; the chemical formula LiMn 2-c3 M c3O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≦ c3 ≦ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn), and lithium manganese composite oxides represented thereby; examples include, but are not limited to, LiMn2O4 in which part of Li in the chemical formula is substituted with alkaline earth metal ions. The positive electrode may be Li metal.

[0173] The 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.

[0174] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery to be configured, it can be used without particular limitation as long as it has electron conductivity without causing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these or a mixture of two or more thereof may be used.

[0175] In addition, the positive electrode binder plays a role in improving the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. Among these, one kind alone or a mixture of two or more kinds may be used.

[0176] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, any separator that can be used in a secondary battery can be used without particular limitation, and in particular, one with low resistance to the ion migration of the electrolyte and excellent moisture retention ability of the electrolyte solution is preferred. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Also, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, a coated separator containing a ceramic component or a polymer substance to ensure heat resistance or mechanical strength may be used, and it may be selectively used in a single-layer or multilayer structure.

[0177] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0178] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0179] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc.

[0180] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and can preferably be used because they can well dissociate lithium salts. If such cyclic carbonates are mixed with linear carbonates such as dimethyl carbonate and diethyl carbonate having low viscosity and low dielectric constant at an appropriate ratio, an electrolyte having high electrical conductivity can be produced, so it can be more preferably used.

[0181] The metal salt may be a lithium salt. The lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte. For example, as the anion of the lithium salt, F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2- , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0182] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc.

[0183] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell, and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they can be used as a power source for medium to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

Examples

[0184] Hereinafter, preferred embodiments are presented to facilitate understanding of the present invention. However, the following embodiments are merely illustrative of the present description, and it is obvious to those skilled in the art that various changes and modifications can be made within the scope of the present description and the scope of the technical idea. It is natural that such variations and modifications belong to the scope of the claims.

[0185] <Manufacturing Example> <Manufacture of Negative Electrode> Manufacture of the First Negative Electrode Active Material Layer As a silicon-based active material, Si (average particle size (D50): 5 μm), a first conductive material, a second conductive material, and polyacrylamide as a binder were added to distilled water as a solvent for forming a negative electrode slurry at a weight ratio of 70:10:10:10 to produce a first negative electrode slurry (solid content concentration: 25% by weight).

[0186] The first conductive 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 size (D50): 3.5 μm).

[0187] As a mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed at 2500 rpm for 30 minutes using a homo mixer, and then the active material was added. Thereafter, it was dispersed at 2500 rpm for 30 minutes to produce a slurry.

[0188] As a negative electrode current collector, the first negative electrode slurry was coated on both sides of a copper current collector (thickness: 8 μm) and roll-pressed, and dried in a vacuum oven at 130 °C for 10 hours to form a first negative electrode active material layer.

[0189] Manufacture of the Second Negative Electrode Active Material Layer As a silicon-based active material, SiO (average particle size (D50): 3.5 μm), as a carbon-based active material, artificial graphite, a first conductive material, a second conductive material, and polyacrylamide as a binder were added to distilled water as a solvent for forming a negative electrode slurry at a weight ratio of 50:30:5.5:10 to produce a second negative electrode slurry (solid content concentration: 25% by weight).

[0190] The first conductive 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 size (D50): 3.5 μm).

[0191] As a mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed at 2500 rpm for 30 minutes using a homo mixer, then the active material was added, and then dispersed at 2500 rpm for 30 minutes to produce a slurry.

[0192] The second negative electrode slurry was coated on the first negative electrode active material layer and roll-pressed, and dried in a vacuum oven at 130 °C for 10 hours to form a second negative electrode active material layer.

[0193] <Manufacture of secondary battery> As a positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry at a weight ratio of 97:1.5:1.5 to produce a positive electrode slurry (solid content concentration: 78% by weight).

[0194] As a positive electrode current collector, the positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12 μm) at 537 mg / 25 cm 2Coated with the loading amount and roll-pressed, then dried in a vacuum oven at 130 °C for 10 hours to form a positive electrode active material layer (thickness: 65 μm), and a positive electrode was manufactured (thickness of the positive electrode: 77 μm, porosity 26%).

[0195] A polyethylene separator was interposed between the positive electrode and the negative electrodes of the examples and comparative examples, and an electrolyte was injected to manufacture a lithium secondary battery.

[0196] The electrolyte is an organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) are mixed at a volume ratio of 30:70, with vinylene carbonate added at 3% by weight based on the total weight of the electrolyte, and as a lithium salt, LiPF6 is added at a concentration of 1 M.

[0197] Hereinafter, an activation process was performed under the conditions shown in Table 1 below, and the results are shown in Table 2 below.

[0198]

Table 1

[0199]

Table 2

[0200] Figure 5 is a diagram showing the distribution of silicon phases by Raman analysis for the negative electrodes of Lithium secondary batteries of Examples 1 to 4 according to the present application, and Figure 6 is a diagram showing the distribution of silicon phases by Raman analysis for the negative electrodes of Lithium secondary batteries of Comparative Examples 1 to 4 according to the present application.

[0201] Specifically, for the above-described Examples and Comparative Examples, with respect to the first negative electrode active material layer for the cross-section electrode, the change in the silicon phase in the electrode depth direction was confirmed by Raman analysis. Specifically, red (upper part) indicates the amorphous phase, blue (lower part) indicates the crystalline phase, and green (middle end part) can mean a mixture of the amorphous phase and the crystalline phase. In the case of the second negative electrode active material layer, based on the silicon phase of the entire second negative electrode active material layer, the ratio of the amorphous phase contains 95 parts by weight or more. However, since the thickness of the second negative electrode active material layer is formed thinner than that of the first negative electrode active material layer, when looking at the entire negative electrode for the lithium secondary battery, there is only an increase in a certain amount of the amorphous phase (an increase of 5 to 7 parts by weight in the overall comparison) in the Raman analysis of the first negative electrode active material layer, and there is no significant difference.

[0202] <Comparative Example 5> As the silicon-based active material, Si (average particle size (D50): 5 μm), a first conductive material, a second conductive material, and polyacrylamide as a binder were added to distilled water as a solvent for forming a negative electrode slurry at a weight ratio of 70:10:10:10 to produce a negative electrode slurry (solid content concentration: 25% by weight).

[0203] The first conductive 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 size (D50): 3.5 μm).

[0204] As the mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed at 2500 rpm for 30 minutes using a homo mixer, then the active material was added, and then dispersed at 2500 rpm for 30 minutes to produce a slurry.

[0205] As the negative electrode current collector, the negative electrode slurry was coated on both sides of a copper current collector (thickness: 8 μm) and roll-pressed, and dried in a vacuum oven at 130 °C for 10 hours to form a negative electrode active material layer. Then, a positive electrode was manufactured as in Example 1 above, and a lithium secondary battery was similarly manufactured.

[0206] Thereafter, an activation step was performed under the same conditions as in Example 1.

[0207] FIG. 7 is a diagram showing an SEM photograph of a cross-section of a negative electrode for a lithium secondary battery according to Comparative Example 5 of the present application. Specifically, as in Example 1, a charging process was performed at a high rate of 1C, and it was confirmed that the reaction was concentrated on the surface portion of the electrode made of pure silicon (Pure Si), and a surface degradation phenomenon occurred. It was also confirmed that the surface degradation reaction could be easily observed only from the SEM photograph even before the Raman analysis was performed.

[0208] Experimental Example 1: Evaluation of life characteristics For the secondary batteries including the negative electrodes manufactured in the above Examples and Comparative Examples, life evaluation was performed using an electrochemical charge / discharge device, and the capacity retention rate was evaluated. The secondary batteries were subjected to an in-situ cycle test at 4.2 - 3.0 V and 1C / 0.5C. During the test, charging / discharging (4.2 - 3.0 V) was performed at 0.33C / 0.33C every 50 cycles, and the capacity retention rate was measured. In Table 3 below, the in-situ capacity retention rate rather than the RPT capacity retention rate is shown.

[0209] Capacity retention rate (%) = {(discharge capacity at the Nth cycle) / (discharge capacity at the first cycle)} × 100

[0210] Experimental Example 2: Measurement and evaluation of resistance increase rate In Experimental Example 1, during the test, charging / discharging (4.2 - 3.0 V) was performed at 0.33C / 0.33C every 50 cycles, and after measuring the capacity retention rate, discharging was performed at a 2.5C pulse at SOC50 to measure the resistance, and the resistance increase rate was compared and analyzed.

[0211] Also, for the life characteristic evaluation and the measurement and evaluation of the resistance increase rate, data at 200 cycles were calculated respectively, and the results are as shown in Table 3 below.

[0212]

Table 3

[0213] As can be confirmed in Table 3 above, the lithium secondary battery according to the present application includes a second negative electrode active material layer, and it was found that a lithium secondary battery satisfying an optimal silicon phase can be manufactured when performing an activation process under the activation conditions of Table 1 above.

[0214] Specifically, Examples 1 to 4 according to the present application are cases where high-rate charging of 1C or more is performed. They include a second negative electrode active material layer, and as can be confirmed in Table 2, it was found that the ratio of the amorphous silicon phase to the crystalline phase can satisfy a specific formula 1. That is, even when performing activation conditions at a high rate (1C or more), it was confirmed that the capacity retention rate and the resistance increase rate satisfy a specific range during battery operation, and the activation time is minimized, making it suitable for mass production processes.

[0215] That is, in the case of the negative electrodes of Examples 1 to 4 according to the present application, they include a second negative electrode active material layer, and it is possible to ensure the processability of mass production including an activation process at a high rate (1C or more). Despite having an activation process at a high rate (1C or more), they satisfy the capacity characteristics as in the prior art, and are characterized by defining the ratio of the amorphous silicon phase to the crystalline phase with a low resistance increase rate.

[0216] In the case of Comparative Examples 1 to 4, it corresponds to the case where the activation conditions are changed as in Table 2 above for the same negative electrode as in the examples and then measured. That is, in the activation process, when charging for a long time under low charging conditions (low rate), the capacity characteristics and the resistance increase rate are excellent. However, as in Comparative Examples 1 to 4, when the activation process time corresponds to a range exceeding 2 hours, it was confirmed that problems occur in mass production and it is not suitable for the process.

[0217] Also, the higher the content of SiO contained in the second negative electrode active material layer, the better the retention tends to be, and the SiO content in the composition of the second negative electrode active material layer can be adjusted to such an extent that the performance can be improved compared to a negative electrode containing Si as a single active material layer, and it may be below or above the content of Example 1.

[0218] For reference, in the case of Comparative Example 5, it corresponds to the case where only the first negative electrode active material layer according to the present application is used, that is, a negative electrode having a single active material layer structure is manufactured. In this case, the second negative electrode active material layer is not included. When passing through a high-rate activation process as in Example 1, the processability can be ensured in the same manner as in Example 1. However, as shown in Table 3, it can be seen that the capacity retention rate is partially reduced compared to Examples 1 to 4 of the present application, and the resistance increase rate is also higher than that of the examples. This confirmed that the reaction was concentrated during activation on the surface of the negative electrode containing only pure silicon, and the life characteristics deteriorated rapidly due to the surface degradation phenomenon. That is, in such a case, it is necessary to adjust the activation process conditions to a low rate or another method of activation process.

[0219] That is, as can be confirmed in Table 3, the batteries of Examples 1 to 4 according to the present application show a capacity retention rate and resistance characteristics equivalent to or higher than those of Comparative Examples 1 to 4 in which the activation process time was increased by applying a low-rate activation process, and at the same time, the state of the silicon phase of the negative electrode for a lithium secondary battery that can ensure processability corresponds to the feature of the present invention.

Explanation of symbols

[0220] 10 ··· Second negative electrode active material layer 20 ··· First negative electrode active material layer 30 ··· Negative electrode current collector layer 100 ·· Negative electrode for lithium secondary battery

Claims

1. A negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer, wherein the negative electrode active material layer includes a first negative electrode active material layer provided on the negative electrode current collector layer; and a second negative electrode active material layer provided on the opposite surface of the first negative electrode active material layer facing the negative electrode current collector layer; the first negative electrode active material layer includes a first negative electrode active material layer composition containing a first negative electrode active material, and the second negative electrode active material layer includes a second negative electrode active material layer composition containing a second negative electrode active material, the first negative electrode active material includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the first negative electrode active material, the SiO x (x = 0) contains 95 parts by weight or more, the second negative electrode active material includes a mixture of one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride, the ratio of amorphous silicon contained in the first negative electrode active material layer is lower than the ratio of amorphous silicon contained in the second negative electrode active material layer, a negative electrode for a lithium secondary battery, wherein the ratio of the silicon phase contained in the negative electrode active material layer satisfies the following formula 1: [Formula 1] 5 ≤ B / (A + B) × 100 (%) ≤ 30 In the formula 1, A is the part by weight of the crystalline phase based on 100 parts by weight of the silicon phase contained in the negative electrode active material layer, B is the part by weight of the amorphous phase based on 100 parts by weight of the silicon phase contained in the negative electrode active material layer.

2. The second negative electrode active material layer includes amorphous silicon and crystalline silicon, The negative electrode for a lithium secondary battery according to claim 1, wherein based on 100 parts by weight of the silicon phase contained in the second negative electrode active material layer, the amorphous phase contains 90 parts by weight or more.

3. The first negative electrode active material layer includes amorphous silicon and crystalline silicon, The negative electrode for a lithium secondary battery according to claim 1, wherein based on 100 parts by weight of the silicon phase contained in the first negative electrode active material layer, the crystalline phase contains 50 parts by weight or more.

4. When the total thickness of the negative electrode active material layer is defined as T, The negative electrode active material layer includes a first region in the range of 0.2 T or less and a second region in the range of more than 0.5 T and T or less, based on the opposite surface of the surface facing the negative electrode current collector layer. The amorphous phase in the first region contains 90 parts by weight or more based on 100 parts by weight of the silicon phase in the negative electrode active material layer. The crystalline phase in the second region contains 60 parts by weight or more based on 100 parts by weight of the silicon phase in the negative electrode active material layer. The negative electrode for a lithium secondary battery according to claim 1.

5. The second negative electrode active material includes one or more mixtures selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride. The silicon-based active material is 65 parts by weight or more and 100 parts by weight or less based on 100 parts by weight of the second negative electrode active material. The negative electrode for a lithium secondary battery according to claim 1.

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

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

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

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

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

11. Positive electrode; A negative electrode for a lithium secondary battery according to any one of claims 1 to 10; A separator provided between the positive electrode and the negative electrode; and Electrolyte; A lithium secondary battery comprising the same.

12. Preparing a lithium secondary battery including a positive electrode, a negative electrode for a lithium secondary battery, a separator, and an electrolyte; and Activating the lithium secondary battery; A method for manufacturing a lithium secondary battery, comprising the same. The activating step includes a high-C-rate activation process (high-rate charging), 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 surfaces of the negative electrode current collector layer using a coater to form a first negative electrode active material layer; and The step of applying a second negative electrode active material layer composition to the opposite surface of the first negative electrode active material layer in contact with the negative electrode current collector layer using a coater to form a second negative electrode active material layer; including The first negative electrode active material includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the first negative electrode active material, the SiO x (x = 0) includes 95 parts by weight or more, The second negative electrode active material includes a mixture of one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride, and a method for manufacturing a lithium secondary battery.

13. including the step of pre-lithiation of the negative electrode on which the first negative electrode active material layer and the second negative electrode active material layer are formed on the negative electrode current collector layer, The step of pre-lithiating the negative electrode includes a lithium electroplating process; a lithium metal transfer process; a lithium metal evaporation process; or a stabilized lithium metal powder (SLMP) coating process, and a method for manufacturing a lithium secondary battery according to claim 12.

14. The step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet-on-dry process, The wet-on-dry process includes the step of applying a first negative electrode active material layer composition; the step of partially drying or completely drying the applied first negative electrode active material layer composition to form a first negative electrode active material layer; and the step of applying the second negative electrode active material layer composition to the first negative electrode active material layer; including the method for manufacturing a lithium secondary battery according to claim 12.

15. The step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet-on-wet process, The wet-on-wet process includes the step of applying a first negative electrode active material layer composition; and the step of applying the second negative electrode active material layer composition to the first negative electrode active material layer composition in an undried state; including the method for manufacturing a lithium secondary battery according to claim 11.

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