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 producing a 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 dates of Korean Patent Application No. 10-2021-0090580, filed with the Korean Intellectual Property Office on July 9, 2021, and Korean Patent Application No. 10-2021-0189600, filed with the Korean Intellectual Property Office on December 28, 2021, and all of its content is incorporated herein by reference.

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

Background Art

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

[0004] Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its usage area is increasingly expanding.

[0005] As the technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is 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 is actively underway.

[0006] Generally, a secondary battery is composed of 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 can be used as the negative electrode active material.

[0007] Especially in recent years, in response to the demand for high-energy-density batteries, as anode active materials, Si / C and SiO, etc., which have a capacity more than 10 times greater than that of graphite-based materials, are used together to increase the capacity, and research on related methods has been actively carried out. However, in the case of silicon-based compounds, which are high-capacity materials, compared with the conventionally used graphite, although the material with a large capacity has excellent capacity characteristics itself, during the charging process, the volume expands rapidly, the conductive path is interrupted, and the battery characteristics deteriorate, resulting in a decrease in capacity from the beginning. In addition, in the case of a silicon-based anode, when repeating the charge and discharge cycles, uniform charging of lithium ions does not occur in the depth direction of the anode, and the reaction proceeds on the surface, accelerating surface deterioration, so performance improvement is required on the side of the battery cycle. x Therefore, various solutions have been discussed, such as a solution to adjust the driving potential to solve the above problems when using a silicon-based compound as the anode active material, a method of further coating a thin film on the active material layer, and a method of suppressing the volume expansion itself, such as a method of adjusting the particle size of the silicon-based compound, or the development of a binder that suppresses the volume expansion of the silicon-based compound to prevent the interruption of the conductive path. In addition, through the method of pre-lithiation of the silicon-based active material layer, the use ratio of the silicon-based active material used during the initial charge and discharge is limited, giving it the role of a reservoir, and research on complementing the life characteristics of the silicon-based anode is also underway.

[0008] However, in the case of the above solutions, it may conversely reduce the performance of the battery, so there are limitations in application, and there are still limitations in the commercialization of the production of anode batteries with a high content of silicon-based compounds. The higher the ratio of the silicon-based active material contained in the silicon-based active material layer, the more concentrated the pre-lithiation on the anode surface, conversely causing damage to the silicon-based active material on the surface side and non-uniform pre-lithiation, resulting in problems in improving the life characteristics.

[0009]

[0010] ​Therefore, even when a silicon-based compound is used as the active material, it is possible to prevent deterioration of the electrode surface during the charge and discharge cycles, improve the uniformity during prelithiation, and there is a need for research on improving the cycle performance along with the capacity characteristics of the lithium secondary battery.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] 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, which can prevent deterioration of the electrode surface during the charge and discharge cycles, which is an existing problem, while using a silicon-based active material for the negative electrode, and can further improve the uniformity during prelithiation and improve the cycle performance along with the capacity characteristics of the lithium secondary battery.

Means for Solving the Problems

[0013] One embodiment of the present specification is a negative electrode for a lithium secondary battery including a negative electrode current collector layer; a first negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer; and a second negative electrode active material layer provided on a surface opposite to the surface of the first negative electrode active material layer in contact with the negative electrode current collector layer, wherein 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; a second negative electrode conductive material; and a second negative electrode binder-containing second negative electrode active material layer composition, and the first negative electrode active material includes SiO x (x = 0) and SiO x (0 < x < 2), and at least one selected from the group consisting of, based on 100 parts by weight of the first negative electrode active material, the SiO xIt contains 95 parts by weight or more of (x = 0), the second negative electrode conductive material contains at least one selected from the group consisting of a dot-shaped conductive material, a linear conductive material, and a planar conductive material, the second negative electrode active material contains at least one 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.

[0014] Also, in one embodiment of the present application, the first negative electrode active material layer may be formed on a part or all of the surface of the negative electrode current collector layer, and the second negative electrode active material layer may be formed on a part or all of the surface of the first negative electrode active material layer.

[0015] Also, in another embodiment, a step of preparing a negative electrode current collector layer; a step of applying a first negative electrode active material layer composition containing a first negative electrode active material on one or both surfaces of the negative electrode current collector layer to form a first negative electrode active material layer; and a step of applying a second negative electrode active material layer composition containing a second negative electrode active material, a second negative electrode conductive material, and a second negative electrode binder on the surface opposite to the surface of the first negative electrode active material layer in contact with the negative electrode current collector layer to form a second negative electrode active material layer; a method for manufacturing a negative electrode for a lithium secondary battery, wherein the first negative electrode active material is 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 conductive material contains at least one selected from the group consisting of a dot-shaped conductive material, a linear conductive material, and a planar conductive material, the second negative electrode active material contains at least one 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 method for manufacturing a negative electrode for a lithium secondary battery is provided.

[0016] Also, in one embodiment of the present application, the first negative electrode active material layer may be formed on a partial surface or the entire surface of the negative electrode current collector layer, and the second negative electrode active material layer may be formed on a partial surface or the entire surface of the first negative electrode active material layer.

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

Advantages of the Invention

[0018] The negative electrode for a lithium secondary battery according to one embodiment of the present invention has a double-layer active material layer composed of a first negative electrode active material layer and a second negative electrode active material layer. In particular, the first negative electrode active material contained in the first negative electrode active material layer is SiO x (x = 0) and SiO x (0 < x < 2), and contains at least one selected from the group consisting of, based on 100 parts by weight of the first negative electrode active material, 95 parts by weight or more of the SiO x (x = 0). The second negative electrode active material contained in the second negative electrode active material layer is at least one 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 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.

[0019] In particular, the second negative electrode active material contains at least one selected from the group consisting of a carbon-based active material, SiO x (0 < x < 2), SiC, and Si alloy, and may particularly contain SiO x (0 < x < 2).

[0020] The negative electrode for a lithium secondary battery according to the present application has a double-layer active material layer having the above-described specific composition and content. In particular, the first negative electrode active material layer is SiO xIt can contain a high content of (x = 0) and directly have advantages beneficial for high capacity, high density, and rapid charging. Furthermore, the second negative electrode active material layer contains a silicon-based, carbon-based active material, etc., which can prevent the deterioration of the electrode surface during the charging and discharging cycle progress, and can also improve the uniformity during pre-lithiation.

[0021] Also, the second negative electrode conductive material contains at least one selected from the group consisting of a dot-shaped conductive material; a linear conductive material; and a planar conductive material, and particularly necessarily contains a linear conductive material, which does not significantly affect the life characteristics of existing lithium secondary batteries, increases the number of points where charging and discharging are possible, and has the characteristic of excellent output characteristics at a high C-rate (C-rate).

[0022] In particular, it has a second negative electrode active material layer with the above composition, which can reduce the deterioration of the negative electrode surface during charge and discharge. Also, during the pre-lithiation process of pre-charging the negative electrode for a lithium secondary battery, it can be given the role of a buffer layer, solving the problems in the case of using a single-layer silicon-based active material layer, and having a negative electrode for a lithium secondary battery with excellent life characteristics in addition to high capacity, high density, and rapid charging is the main feature of the present invention.

[0023] As an example, the second negative electrode active material layer of the present application can act as a buffer layer. An electrode containing a Si active material has excellent capacity characteristics compared to an electrode containing SiO or a carbon-based active material. However, in an electrode containing a Si active material, the deterioration of the surface of the negative electrode active material layer is concentrated due to the rapid reaction with Li ions during charge and discharge. This also occurs during the pre-lithiation process when lithium ions are pre-contained in the negative electrode active material layer. In the pre-lithiation process, the buffer layer is used to prevent the 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 of being able to exhibit the same role and effect as the buffer layer in the pre-lithiation process.

[0024] Ultimately, 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 using a single layer of active material, and to solve the problems of surface deterioration, which is a drawback when having this, the problem of uniformity during pre-lithiation, and the problem of life characteristics, the first negative electrode active material layer and the second negative electrode active material layer are configured as a double layer to which specific compositions and content parts are applied.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0026] Before explaining the present invention, first, several terms are defined.

[0027] In this specification, when a part is said to "include" a certain component, this means that, unless otherwise specified to the contrary, it does not exclude other components, but may further include other components.

[0028] In this specification, "p to q" means the range of "p or more and q or less".

[0029] 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 BEL Japan's BELSORP-mini II. That is, in this application, the BET specific surface area may mean the specific surface area measured by the above measurement method.

[0030] In this specification, "Dn" means the particle size distribution and means the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution by particle size. 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), and the difference in the diffraction pattern due to the particle size when the particles pass through the laser beam is measured to calculate the particle size distribution.

[0031] 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 in the same way as the polymer containing the monomer in monomer units.

[0032] In this specification, it is understood that the term "polymer" is used in a broad sense including copolymers unless otherwise specified as "homopolymer".

[0033] In this specification, the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) are the polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as the standard substances. In this specification, the molecular weight means the weight-average molecular weight unless otherwise specified.

[0034] Hereinafter, for those with ordinary knowledge in the technical field to which the present invention pertains to easily implement the present invention, a detailed description will be given with reference to the drawings. However, the present invention can be implemented in various different forms and is not limited to the following description.

[0035] One embodiment of this specification is a negative electrode for a lithium secondary battery including: a negative electrode current collector layer; a first negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer; and a second negative electrode active material layer provided on a surface opposite to the surface of the first negative electrode active material layer that contacts 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, a second negative electrode conductive material, and a second negative electrode binder. The first negative electrode active material includes at least one 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, it contains 95 parts by weight or more of SiO x (x = 0). The second negative electrode conductive material includes at least one selected from the group consisting of a dot-shaped conductive material, a linear conductive material, and a planar conductive material. The second negative electrode active material includes at least one 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 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.

[0036] The negative electrode for a lithium secondary battery according to the present application is a single-layer active material, taking advantage of the electrode with a high content of Si particles, and solving the problems of surface deterioration, which is a drawback when having this, the uniformity problem during pre-lithiation, and the life characteristic problem. It is characterized in that the first negative electrode active material layer and the second negative electrode active material layer are constituted by a double layer to which specific compositions and content parts are applied.

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

[0038] Further, FIG. 4 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to an embodiment of the present application. Specifically, as shown in FIG. 4, the first negative electrode active material layer 20 and the second negative electrode active material layer 10 can be formed on both surfaces of the negative electrode current collector layer 30. Also, it can have an arrangement of 10>20>30>20>10, and further, like 10>20>30>20, 10>20>30>10, 10>20>30>10>20, etc., as long as the first negative electrode active material layer and the second negative electrode active material layer are sequentially laminated only on one surface of the negative electrode current collector layer, the arrangement on the opposite surface may be laminated regardless of the relationship. Preferably, both surfaces of the negative electrode current collector layer preferably have the same composition, and 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, there is provided a negative electrode for a lithium secondary battery, including: a negative electrode current collector layer; a first negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer; and a second negative electrode active material layer provided on a surface opposite to the surface of the first negative electrode active material layer in contact with the negative electrode current collector layer.

[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, those obtained by surface treatment of the surface of copper or stainless steel with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. may be used. Further, fine irregularities can 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, sheet, foil, net, porous body, foam, 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 can be variously deformed according to the type and use of the negative electrode used, and is not limited thereto.

[0044] In one embodiment of the present application, the first negative electrode active material contains at least one selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and may contain 95 parts by weight or more of SiO x (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 contains at least one 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) is 95 parts by weight or more, preferably SiO x (x = 0) contains 97 parts by weight or more, more preferably 99 parts by weight or more, and may contain 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 means that, as described above, when based on 100 parts by weight in total of the first negative electrode active material, pure Si particles (SiO x (x = 0)) may be included within the above range.

[0047] The first negative electrode active material used in the first negative electrode active material layer of the present invention involves very complex crystal changes in the reaction of electrochemically absorbing, storing, and releasing lithium atoms. As the reaction of electrochemically absorbing, storing, and releasing lithium atoms proceeds, the composition and crystal structure of the silicon particles change to Si (crystal structure: Fd3m), LiSi (crystal structure: I41 / a), Li 2 Si (crystal structure: C2 / m), Li 7 Si 2 (Pbam), Li 22 Si 5 (F23), etc. Further, along with the change in the complex crystal structure, the volume of the silicon particles expands by about four times. Therefore, when the charge-discharge cycle is repeated, the silicon particles are destroyed, and a bond is formed between the lithium atoms and the silicon particles, so that the lithium atom insertion sites initially possessed by the silicon particles are damaged, and the cycle life may be significantly reduced.

[0048] In one embodiment of the present application, the first negative electrode active material may consist of SiO x (x = 0).

[0049] The first negative electrode active material layer according to the present application contains the first negative electrode active material, specifically SiO xIt contains pure silicon particles containing 95 parts by weight or more of (x = 0). At this time, when a high content of pure silicon particles is contained, the capacity characteristics are excellent. In order to solve the characteristic of life reduction due to surface non-uniform reaction accompanying this, it includes the second negative electrode active material layer according to the present invention, and solves the above problems.

[0050] On the other hand, the average particle size (D50) of the first negative electrode active material of the present invention is 3 μm to 10 μm, specifically 4 μm to 8 μm, and more specifically 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 included in 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. Further, since the size of the first negative electrode active material has a value equal to or greater than the lower limit value of the above 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 conductive network is likely to continue, increasing the capacity retention rate. On the other hand, when the average particle size satisfies the above range, silicon particles that are too large are excluded, and the surface of the negative electrode is smoothly formed, thereby preventing the non-uniformity phenomenon of the current density during charge and discharge.

[0051] In one embodiment of the present application, the first negative electrode active material has a generally characteristic BET specific surface area. The BET specific surface area of the first negative electrode active material is preferably 0.01 m 2 / g to 150.0 m 2 / g, more preferably 0.1 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 DIN66131 (using nitrogen).

[0052] In one embodiment of the present application, the first negative electrode active material may exist in a crystalline or amorphous form, for example, and is preferably not porous. The silicon particles are preferably spherical or flaky particles. Alternatively, the silicon particles may also have a fibrous structure or exist in the form of a silicon-containing film or coating, but this is not recommended.

[0053] In one embodiment of the present application, the first negative electrode active material may have a non-spherical form, and its circularity is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0054] In the present application, the circularity is determined by the following formula 1, where A is the area and P is the boundary line. [Formula 1] 4πA / P 2

[0055] In one embodiment of the present application, the first negative electrode active material provides a negative electrode for a lithium secondary battery that 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 be 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, based on 100 parts by weight of the first negative electrode active material layer composition, and may be 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 80 parts by weight or less.

[0057] The first negative electrode active material layer composition according to the present application uses the first negative electrode active material with a significantly high capacity within the above range, and together with the second negative electrode active material layer described later, solves the problems of surface deterioration during charging and discharging, the uniformity problem during pre-lithiation, and the life characteristic problem without degrading the capacity performance of the entire negative electrode.

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

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

[0060] At this time, as the first negative electrode conductive material and the first negative electrode binder included in the first negative electrode active material layer composition, those used in the art can be used without limitation.

[0061] In one embodiment of the present application, as the first negative electrode conductive material, substances generally used in the art can be used without limitation. Specifically, it may include at least one selected from the group consisting of a dot-shaped conductive material, a planar conductive material, and a linear conductive material.

[0062] The content regarding the first negative electrode conductive material is the same as that of the second negative electrode conductive material described later and will be described later.

[0063] In one embodiment of the present application, the first negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, poly acrylic acid, and substances obtained by substituting hydrogen thereof with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0064] The first negative electrode binder according to one embodiment of the present application serves to suppress the active material and the conductive material in order to prevent twisting and structural deformation of the negative electrode structure in the volume expansion and relaxation of the first negative electrode active material. If the above role is satisfied, all general binders can be applied. Specifically, an aqueous binder can be used, and more specifically, a PAM-based binder may be used.

[0065] In one embodiment of the present application, the first negative electrode binder is 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the first negative electrode active material layer composition, and may be 5 parts by weight or more, 10 parts by weight or more.

[0066] In one embodiment of the present application, the second negative electrode active material may include one or more selected from the group consisting of carbon-based active materials, silicon-based active materials, metal-based active materials capable of alloying with lithium, and lithium-containing nitrides.

[0067] At this time, the silicon-based active material may be 50 parts by weight or more and 100 parts by weight or less, preferably 60 parts by weight or more and 100 parts by weight or less, more preferably 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.

[0068] In the second negative electrode active material layer, when the part by weight of the silicon-based active material is less than the above range, during the progress of charge and discharge cycles, rather, the second negative electrode active material layer acts as a resistance layer and the capacity retention rate decreases, thereby causing a problem that the resistance increase rate of the negative electrode becomes high.

[0069] In one embodiment of the present application, the silicon-based active material contained in the second negative electrode active material is SiO x (0 < x < 2), SiC, and at least one selected from the group consisting of Si alloys may be included.

[0070] In one embodiment of the present application, the silicon-based active material is SiO x (0 < x < 2); or, a negative electrode for a lithium secondary battery containing SiC is provided.

[0071] In still another embodiment, the silicon-based active material contained in the second negative electrode active material may contain SiO x (0 < x < 2).

[0072] In still another embodiment, the silicon-based active material contained in the second negative electrode active material may contain SiC.

[0073] The negative electrode for a lithium secondary battery according to the present application is composed of a double layer, and by including the second negative electrode active material in the second negative electrode active material layer as described above, it includes the first negative electrode active material described above, retains high-capacity and high-density characteristics, and solves the problems of surface deterioration during charge and discharge, the problem of uniformity during pre-lithiation, and the problem of life characteristics.

[0074] In one embodiment of the present application, typical examples of the carbon-based active material include natural graphite, artificial graphite, expanded graphite, carbon fiber, graphitizable carbon, carbon black, carbon nanotube, fullerene, activated carbon, etc. Any material commonly used for carbon materials in lithium secondary batteries can be used without limitation, and specifically, it may be processed into a spherical or dot-like form for use.

[0075] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the carbon-based active material contains graphite, the graphite contains artificial graphite and natural graphite, and the weight ratio of the artificial graphite to the natural graphite is 5:5 to 9.5:0.5.

[0076] The artificial graphite according to one embodiment of the present invention may be in the form of primary particles, or may be in the form of secondary particles in which a plurality of the primary particles are aggregated.

[0077] The term "initial particle" used in the present invention means the original particle when other types of particles are formed from a certain particle, and a plurality of initial particles can aggregate, combine, or be granulated to form secondary particles.

[0078] The term "secondary paricles" used in the present invention means a physically separable large particle formed by aggregating, combining, or granulating individual primary particles.

[0079] The artificial graphite of the primary particles may be manufactured by heat-treating one or more selected from the group consisting of needle cokes, mosaic cokes, and coaltar pitch.

[0080] The artificial graphite is generally produced by carbonizing raw materials such as coal tar, coal tar pitch, and petroleum middle distillate at 2,500 °C or higher, and can be used as a negative electrode active material after such graphitization through particle size adjustment such as pulverization and secondary particle formation. In the case of artificial graphite, the crystals are randomly distributed within the particles, and it has a lower roundness and a somewhat pointed shape compared to natural graphite.

[0081] The artificial graphite used in one embodiment of the present invention may be commercially widely used mesophase carbon microbeads (MCMB), mesophase pitch-based carbon fiber (MPCF), artificial graphite carbonized in block form, artificial graphite carbonized in powder form, etc. The roundness of the artificial graphite may be 0.91 or less, or 0.6 to 0.91, or 0.7 to 0.9.

[0082] Also, the artificial graphite may have a particle size of 5 μm to 30 μm, preferably 10 μm to 25 μm.

[0083] Specifically, the D50 of the artificial graphite primary particles may be 6 μm to 15 μm, or 6 μm to 10 μm, or 6 μm to 9 μm. When the D50 of the primary particles satisfies such a range, the primary particles can be formed to have a high degree of graphitization, the orientation index of the negative electrode active material particles can be appropriately ensured, and the rapid filling performance can be improved.

[0084] The artificial graphite secondary particles may be formed by granulating the primary particles. That is, the secondary particles may be a structure in which the primary particles are aggregated with each other through a granulation process. The secondary particles may contain a carbonaceous matrix that aggregates the primary particles. The carbonaceous matrix may contain at least one of soft carbon and graphite. The soft carbon may be formed by heat-treating pitch.

[0085] The carbonaceous matrix may be contained in the secondary particles at 8 wt% to 16 wt%, and specifically may be contained at 9 wt% to 12 wt%. This range is at a level lower than the content of the carbonaceous matrix used in normal artificial graphite secondary particles. This is because the particle size of the primary particles in the secondary particles is controlled, and even if the content of the carbonaceous matrix required for granulation is small, structurally stable secondary particles can be manufactured, and the amount of primary particles constituting the secondary particles can also be uniform.

[0086] The surface of the artificial graphite secondary particles includes a carbon coating layer, and the carbon coating layer may include at least one of amorphous carbon and crystalline carbon.

[0087] The crystalline carbon can further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least any one selected from the group consisting of fullerene and graphene.

[0088] The amorphous carbon can appropriately maintain the strength of the coating layer and suppress the expansion of the natural graphite. The amorphous carbon may be at least one carbide selected from the group consisting of tar, pitch and other organic substances, or a carbon-based substance formed using a hydrocarbon as a source in a chemical vapor deposition method.

[0089] The carbide of the other organic substances may be a carbide of an organic substance selected from the group consisting of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or ketohexose, and combinations thereof.

[0090] The D50 of the artificial graphite secondary particles is 10 μm to 25 μm, specifically 12 μm to 22 μm, and more specifically may be 13 μm to 20 μm. When this range is satisfied, the artificial graphite secondary particles can be uniformly dispersed in the slurry, and the charging performance of the battery can also be improved.

[0091] The tap density of the artificial graphite secondary particles may be 0.85 g / cc to 1.30 g / cc, specifically may be 0.90 g / cc to 1.10 g / cc, and more specifically may be 0.90 g / cc to 1.07 g / cc. When the above range is satisfied, it means that the packing of the artificial graphite secondary particles in the negative electrode can be smoothly performed, and thus the negative electrode adhesion can be improved.

[0092] The natural graphite may generally be in the form of plate-like aggregates before being processed, and the plate-like particles may be manufactured in a spherical form with a smooth surface by post-treatment processes such as particle pulverization and re-granulation processes for use as an active material for electrode manufacturing.

[0093] The natural graphite used in one embodiment of the present invention may have a circularity of more than 0.91 and 0.97 or less, or 0.93 to 0.97, or 0.94 to 0.96.

[0094] The natural graphite may have a particle size of 5 μm to 30 μm, or 10 μm to 25 μm.

[0095] According to one embodiment of the present invention, the weight ratio of the artificial graphite and the natural graphite may be 5:5 to 9.5:0.5, or 5:5 to 9.3:0.7, or 5:5 to 9:1, or 6:4 to 9:1. When the weight ratio of the artificial graphite and the natural graphite satisfies such a range, it can exhibit more excellent output and can be advantageous in terms of life and rapid charging performance.

[0096] In one embodiment of the present application, the sheet-like conductive material used as the negative electrode conductive material described above generally 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 to facilitate the storage and release of lithium ions.

[0097] On the other hand, the sheet-like conductive material used as the negative electrode conductive material is a substance having a sheet or plate-like form and can be expressed as plate-like graphite. That is, it is a substance contained to maintain a conductive path within the negative electrode active material layer, and it does not play a role in the storage and release of lithium, but rather means a substance for ensuring a sheet-like conductive path inside the negative electrode active material layer.

[0098] 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 ensuring a conductive path, rather than for the role of storing or releasing lithium. At this time, the negative electrode active material contained together has high capacity characteristics for lithium storage and release and plays a role of being able to store and release all lithium ions transmitted from the positive electrode.

[0099] 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 shape and used as a substance for playing a role of storing or releasing lithium.

[0100] That is, in one embodiment of the present application, artificial graphite or natural graphite, which is a carbon-based active material, may 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 sheet-like form.

[0101] The metal-based active material may be, as a representative example, 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, an alloy, an oxide (TiO 2 、SnO 2 etc.), a nitride, a sulfide, a boride, an alloy with lithium, etc., but a single substance, an alloy, an oxide, and an alloy with lithium may have the possibility of increasing the capacity.

[0102] In one embodiment of the present application, the second negative electrode active material includes one or more and two or less 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 may be 50 parts by weight or more and 100 parts by weight or less, 60 parts by weight or more and 100 parts by weight or less, or 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.

[0103] In one embodiment of the present application, the second negative electrode active material includes two 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 silicon-based active material provides a negative electrode for a lithium secondary battery that is 50 parts by weight or more and 95 parts by weight or less based on 100 parts by weight of the second negative electrode active material.

[0104] In another embodiment, the second negative electrode active material includes two 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 silicon-based active material may include 50 parts by weight or more and 95 parts by weight or less, preferably 60 parts by weight or more and 90 parts by weight or less, and more preferably 65 parts by weight or more and 80 parts by weight or less based on 100 parts by weight of the second negative electrode active material.

[0105] In one embodiment of the present application, the negative electrode for a lithium secondary battery has a second negative electrode active material including a silicon-based active material. The silicon-based active material may be 50 parts by weight or more and 100 parts by weight or less, preferably 60 parts by weight or more and 100 parts by weight or less, and more preferably 70 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 composition.

[0106] In one embodiment of the present application, the negative electrode for the lithium secondary battery includes a silicon-based active material and a carbon-based active material as the second negative electrode active material, and the silicon-based active material may be 40 parts by weight or more and 95 parts by weight or less, preferably 45 parts by weight or more and 80 parts by weight or less, more preferably 50 parts by weight or more and 75 parts by weight or less based on 100 parts by weight of the second negative electrode active material composition.

[0107] As described above, when the second negative electrode active material satisfies the above composition and content, a lithium secondary battery with improved various performances such as cycle life characteristics can be manufactured. That is, in the present application, the second negative electrode active material layer serves as a buffer layer, and in order to solve the surface deterioration problem during charge and discharge, the uniformity problem during pre-lithiation, and the life characteristic problem, the above-mentioned SiO x (0 < x < 2) and / or a carbon-based active material is included, and intense reaction with lithium ions on the surface of the second negative electrode active material layer can be suppressed.

[0108] Ultimately, the second negative electrode active material layer according to the present application has the above composition and content, solves the surface deterioration problem during charge and discharge cycle continuation, and can have the effect of pre-lithiation even if pre-lithiation is not performed up to the first negative electrode active material layer during pre-lithiation, and has the characteristic of being able to provide a negative electrode for a high-capacity and high-density lithium secondary battery.

[0109] 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 60 parts by weight or more based on 100 parts by weight of the second negative electrode active material layer composition.

[0110] In another embodiment, the second negative electrode active material may be 60 parts by weight or more, preferably 63 parts by weight or more, and 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 70 parts by weight or less based on 100 parts by weight of the second negative electrode active material layer composition.

[0111] The second negative electrode active material layer composition according to the present application uses a second negative electrode active material having lower capacity characteristics than the first negative electrode active material but less particle cracking during charge-discharge cycle progress or prelithiation within the above range, thereby not degrading the capacity performance of the negative electrode and having the characteristic of enhancing the life characteristics.

[0112] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery including a second negative electrode active material layer composition including a second negative electrode active material, a second negative electrode conductive material, and a second negative electrode binder.

[0113] At this time, the second negative electrode conductive material may include at least one selected from the group consisting of a dot-shaped conductive material, a linear conductive material, and a planar conductive material.

[0114] In one embodiment of the present application, the dot-shaped conductive material may be used to improve the conductivity of the negative electrode, and has conductivity without inducing a chemical change, and means a conductive material having a dot shape or a spherical shape. Specifically, the dot-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal 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 having excellent dispersibility.

[0115] In one embodiment of the present application, the dot-shaped conductive material has a BET specific surface area of 40 m 2 / g or more and 70 m 2 / g or less, preferably 45 m 2 / g or more and 65 m 2 / g or less, more preferably 50 m 2 / g or more and 60 m 2 / g or less.

[0116] In one embodiment of the present application, the particle size of the dot-shaped conductive material is 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0117] In one embodiment of the present application, the second negative electrode conductive material may include a planar conductive material.

[0118] 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, and can be represented by a plate-shaped conductive material or a bulk-type conductive material.

[0119] In one embodiment of the present application, the planar conductive material can 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.

[0120] In one embodiment of the present application, the average particle size (D50) of the planar conductive material is 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically may be 4 μm to 5 μm. When the above range is satisfied, the excessive viscosity increase of the negative electrode slurry is not caused by the sufficient particle size, and the dispersion is easy. Therefore, when dispersing using the same equipment and time, the dispersion effect is excellent.

[0121] 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.

[0122] In one embodiment of the present application, as the planar conductive material, a high specific surface area planar conductive material having a high BET specific surface area; or a low specific surface area planar conductive material may be used.

[0123] In one embodiment of the present application, as the planar conductive material, a high specific surface area planar conductive material or a low specific surface area planar conductive material can be used without limitation. However, particularly for the planar conductive material according to the present application, the electrode performance may be affected by dispersion to some extent, and it is particularly preferable to use a low specific surface area planar conductive material that does not have problems with dispersion.

[0124] 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.

[0125] In another embodiment, the planar conductive material has 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.

[0126] In another embodiment, the planar conductive material is a high specific surface area planar conductive material, and has 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.

[0127] In another embodiment, the planar conductive material is a low specific surface area planar conductive material, and has 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.

[0128] As other conductive materials, there may be linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may include a plurality of carbon nanotube unit bodies. Specifically, here, the "bundle type" refers to a secondary shape in the form of a bundle or a rope in which a plurality of carbon nanotube unit bodies are arranged side by side with substantially the same orientation of the longitudinal axis of the carbon nanotube unit body or are intertwined, unless otherwise specified. The carbon nanotube unit body has a cylindrical form with a nanosize diameter of a graphite sheet and has an sp2 bonding structure. At this time, the characteristics of a conductor or a semiconductor can be exhibited depending on the winding angle and structure of the graphite sheet. The bundle-type carbon nanotubes can be uniformly dispersed during the production of the negative electrode as compared with entangled-type carbon nanotubes, and can smoothly form a conductive network in the negative electrode to improve the conductivity of the negative electrode.

[0129] In particular, the linear conductive material according to an embodiment of the present application may be a single-walled carbon nanotube (SWCNT).

[0130] The single-walled carbon nanotube is a substance in which carbon atoms arranged in a hexagonal shape are in a tubular form, and exhibits the properties of an insulator, a conductor, or a semiconductor according to its specific chirality. The carbon atoms are connected by strong covalent bonds, and the tensile strength is about 100 times or more greater than that of steel. It has excellent flexibility and elasticity, and also has chemically stable properties.

[0131] The average diameter of the single-walled carbon nanotubes is from 0.5 nm to 15 nm. According to an embodiment of the present invention, the average diameter of the single-walled carbon nanotubes may be from 1 nm to 10 nm, or from 1 nm to 5 nm, or from 1 nm to 2 nm. When the average diameter of the single-walled carbon nanotubes satisfies such a range, the electrical conductivity of the negative electrode can be maintained even when the single-walled carbon nanotubes are included in a very small content, and a preferable viscosity and solid content can be obtained during the production of the conductive material dispersion. In the conductive material dispersion, the single-walled carbon nanotubes may exist in an entangled state (aggregate) where they are intertwined with each other. Therefore, the average diameter can be derived by confirming the diameter of any entangled single-walled carbon nanotube aggregate extracted from the conductive material dispersion by SEM or TEM and then dividing the diameter of the aggregate by the number of single-walled carbon nanotubes constituting the aggregate.

[0132] The BET specific surface area of the single-walled carbon nanotubes is 500 m 2 / g to 1,500 m 2 / g, or 900 m 2 / g to 1,200 m 2 / g, and specifically may be 250 m 2 / g to 330 m 2 / g. When the above range is satisfied, a conductive material dispersion having a preferable solid content can be obtained, and an excessive increase in the viscosity of the negative electrode slurry can be prevented. The BET specific surface area can be measured by the nitrogen adsorption BET method.

[0133] The aspect ratio of the single-walled carbon nanotube may be 50 to 20,000, or the length of the single-walled carbon nanotube may be 5 μm to 100 μm, or 5 to 50 μm. When the aspect ratio or length satisfies such a range, since the specific surface area is at a high level, the single-walled carbon nanotube can be adsorbed to the active material particles with a strong attractive force in the negative electrode. Thereby, the conductive network can be smoothly maintained even during the volume expansion of the negative electrode active material. The aspect ratio can be confirmed by obtaining the average of the aspect ratios of 15 single-walled carbon nanotubes with a large aspect ratio and 15 single-walled carbon nanotubes with a small aspect ratio when observing the single-walled carbon nanotube powder through SEM.

[0134] Compared with multi-walled carbon nanotubes and double-walled carbon nanotubes, the single-walled carbon nanotube is advantageous in that it has a large aspect ratio, a long length, and a large volume, so that an electrical network can be constructed even when only a small amount is used.

[0135] In one embodiment of the present application, the second negative electrode conductive material may satisfy 1 part by weight or more and 40 parts by weight or less based on 100 parts by weight of the second negative electrode active material layer composition.

[0136] In another embodiment, the second negative electrode conductive material may be 1 part by weight or more and 40 parts by weight or less, preferably 10 parts by weight or more and 30 parts by weight or less, and more preferably 15 parts by weight or more and 25 parts by weight or less based on 100 parts by weight of the second negative electrode active material layer composition.

[0137] In one embodiment of the present application, the second negative electrode conductive material includes a dot-shaped conductive material, a planar conductive material, and a linear conductive material, and the dot-shaped conductive material: planar conductive material: linear conductive material may satisfy a ratio of 1:1:0.01 to 1:1:1.

[0138] In one embodiment of the present application, the dot-shaped conductive material may satisfy the range of 1 part by weight or more and 60 parts by weight or less, preferably 5 parts by weight or more and 50 parts by weight or less, and more preferably 10 parts by weight or more and 50 parts by weight or less based on 100 parts by weight of the second negative electrode conductive material.

[0139] In one embodiment of the present application, the planar conductive material may satisfy the range of 1 part by weight or more and 60 parts by weight or less, preferably 5 parts by weight or more and 50 parts by weight or less, and more preferably 10 parts by weight or more and 50 parts by weight or less based on 100 parts by weight of the second negative electrode conductive material.

[0140] In one embodiment of the present application, the linear conductive material may satisfy the range of 0.01 part by weight or more and 10 parts by weight or less, preferably 0.05 part by weight or more and 8 parts by weight or less, and more preferably 0.1 part by weight or more and 5 parts by weight or less based on 100 parts by weight of the second negative electrode conductive material.

[0141] In one embodiment of the present application, the second negative electrode conductive material may include a linear conductive material and a planar conductive material.

[0142] In one embodiment of the present application, the second negative electrode conductive material includes a linear conductive material and a planar conductive material, and the ratio of the linear conductive material to the planar conductive material may satisfy 0.01:1 to 0.1:1.

[0143] In one embodiment of the present application, when the second negative electrode conductive material particularly includes a linear conductive material and a planar conductive material and satisfies the respective compositions and ratios, it does not significantly affect the life characteristics of existing lithium secondary batteries, and there are more points where charging and discharging are possible, and it has the characteristics of excellent output characteristics at a high C-rate.

[0144] The first negative electrode conductive material according to the present application provides a negative electrode for a lithium secondary battery including at least a linear conductive material.

[0145] The second negative electrode conductive material according to the present application provides a negative electrode for a lithium secondary battery including at least a linear conductive material.

[0146] In one embodiment of the present application, the second negative electrode conductive material may be composed of a linear conductive material.

[0147] At this time, based on 100 parts by weight of the second negative electrode active material, the linear conductive material may be 0.1 part by weight to 2 parts by weight, or 0.1 part by weight to 0.7 part by weight, or 0.1 part by weight to 0.3 part by weight. When the content of the linear conductive material satisfies such a range, an electrical network can be sufficiently constructed in the negative electrode active material layer, which is advantageous in terms of the mixing and coating processability during electrode manufacturing. Further, in the negative electrode according to an embodiment of the present invention, since the linear conductive material is included in both the first negative electrode active material layer and the second negative electrode active material layer, the conductive network between the active materials accompanying the volume expansion and contraction of the Si electrode can be maintained, which is also advantageous in terms of life, and the rapid charging performance can be maintained. Basically, the rapid charging performance is advantageous because the Si-based negative electrode can be thinly film-coated compared to graphite. However, the linear conductive material helps in rapid charging by firmly maintaining the conductive network, and can further help improve the initial rapid drop and maintain the life of the Si-based negative electrode.

[0148] In the case of the second negative electrode conductive material according to the present application, it has a completely different configuration from the positive electrode conductive material applied to the positive electrode. That is, in the case of the second negative electrode conductive material according to the present application, it serves to take contact points between silicon-based active materials with a very large volume expansion of the electrode during charging and discharging. The positive electrode conductive material serves to provide partial conductivity while playing a buffering role when rolled, and its configuration and role are completely different from those of the negative electrode conductive material of the present invention.

[0149] Further, the second negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different configuration from the conductive material applied to a graphite-based active material. That is, the conductive material used for an electrode having a graphite-based active material has characteristics of improving output characteristics and providing partial conductivity because it simply has smaller particles than the active material, and its configuration and role are completely different from those of the first negative electrode conductive material applied together with a silicon-based active material as in the present invention.

[0150] At this time, the content regarding the first negative electrode conductive material may be the same as the content of the second negative electrode conductive material described above.

[0151] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the thickness of the first negative electrode active material layer is 10 μm or more and 200 μm or less, and the thickness of the second negative electrode active material layer is 10 μm or more and 100 μm or less. The first negative electrode active material layer and the second negative electrode active material layer may be formed on both sides of the negative electrode current collector layer, and the thickness may be the same as described above.

[0152] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the loading amount (a) of the first negative electrode active material layer composition satisfies that it is 2 times or more the loading amount (b) of the second negative electrode active material layer composition.

[0153] In another embodiment, the loading amount (a) of the first negative electrode active material layer composition may satisfy the range of 2 times or more and 10 times or less, preferably 2.2 times or more and 6 times or less the loading amount (b) of the second negative electrode active material layer composition.

[0154] The loading amount can mean the weight of the composition for forming the negative electrode active material layer. Specifically, the loading amount of the composition may have the same meaning as the loading amount of the slurry containing the composition.

[0155] In one embodiment of the present application, the loading amount (a) of the first negative electrode active material layer composition is 2 mg / cm 2 or more and 5 mg / cm 2 or less, preferably 2.2 mg / cm 2 or more and 4 mg / cm 2 or less.

[0156] In one embodiment of the present application, the loading amount (b) of the second negative electrode active material layer composition is 0.5 mg / cm 2 or more and 1.5 mg / cm 2Hereinafter, it may preferably satisfy the range of 0.8 mg / cm 2 or more and 1.3 mg / cm 2 or less.

[0157] By the first negative electrode active material layer composition and the second negative electrode active material layer composition having the loading amount, the ratio of the active materials contained in the first negative electrode active material layer and the second negative electrode active material layer can be adjusted. That is, the amount of the first negative electrode active material contained in the first negative electrode active material layer can be adjusted to optimize the capacity characteristics, and the amount of the second negative electrode active material contained in the second negative electrode active material layer can be adjusted together so as not to reduce the capacity characteristics, suppressing the surface reaction of the negative electrode, and enabling the negative electrode to have the characteristic of enhancing the life characteristics.

[0158] In one embodiment of the present application, the negative electrode for a lithium secondary battery is composed of a double layer, and particularly, the second negative electrode active material layer serves as a buffer layer during pre-lithiation, and the first negative electrode active material layer is characterized in that pre-lithiation is not performed.

[0159] In one embodiment of the present application, the negative electrode for a lithium secondary battery may be a pre-lithiated negative electrode.

[0160] In one embodiment of the present application, the first negative electrode active material layer may be formed on the entire surface of the negative electrode current collector layer, and the second negative electrode active material layer may be formed on the entire surface of the first negative electrode active material layer.

[0161] In one embodiment of the present application, a method for manufacturing a negative electrode for a lithium secondary battery includes the steps of preparing a negative electrode current collector layer; applying a first negative electrode active material layer composition containing a first negative electrode active material to one or both surfaces of the negative electrode current collector layer to form a first negative electrode active material layer; and applying a second negative electrode active material layer composition containing a second negative electrode active material, a second negative electrode conductive material, and a second negative electrode binder 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 layer. The first negative electrode active material is SiO x (x = 0) and SiO xincluding at least one selected from the group consisting of (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 conductive material includes at least one selected from the group consisting of a dot-shaped conductive material, a linear conductive material, and a planar conductive material. The second negative electrode active material includes at least one 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 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. Provided is a method for manufacturing a negative electrode for a lithium secondary battery.

[0162] In the method for manufacturing the negative electrode, the composition and content included in each step may be applied to the foregoing content.

[0163] In one embodiment of the present application, provided is a step of applying a first negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer to form a first negative electrode active material layer.

[0164] That is, the step is a step of forming an active material layer on the negative electrode current collector layer, and can mean a step of forming an active material layer on the surface (lower layer part) in contact with the current collector layer in a double layer structure. Also, when the first negative electrode active material layer is formed on both surfaces of the negative electrode current collector layer, the second negative electrode active material layer may be applied to one or both surfaces of such a first negative electrode active material layer.

[0165] In one embodiment of the present application, applying the first negative electrode active material layer composition includes applying and drying a first negative electrode slurry including the first negative electrode active material layer composition and a negative electrode slurry solvent.

[0166] At this time, the solid content of the first negative electrode slurry may satisfy the range of 10% to 40%.

[0167] In one embodiment of the present application, the step of forming the first negative electrode active material layer may include the step of mixing the first negative electrode slurry; and the step of coating the mixed first negative electrode slurry on one or both surfaces of the negative electrode current collector layer, and a coating method generally used in the art may be used for the coating.

[0168] In one embodiment of the present application, there is provided 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.

[0169] That is, the step is a step of forming a second negative electrode active material layer on the first negative electrode active material layer, and can mean a step of forming an active material layer on the surface (upper layer part) away from the current collector layer in a double layer structure.

[0170] 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.

[0171] At this time, the solid content of the second negative electrode slurry may satisfy the range of 10% to 40%.

[0172] In one embodiment of the present application, the step of forming the second negative electrode active material layer includes the step of mixing the second negative electrode slurry; and the step of coating the mixed second negative electrode slurry on the surface opposite to the surface in contact with the negative electrode current collector layer of the first negative electrode active material layer; and provides a method for manufacturing a negative electrode for a lithium secondary battery.

[0173] The coating may use a coating method generally used in the art.

[0174] The description of the step of forming the first negative electrode active material layer may be similarly applied to the step of forming the second negative electrode active material layer.

[0175] 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 negative electrode for a lithium secondary battery.

[0176] In one embodiment of the present application, the wet on dry process may mean 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.

[0177] FIG. 5 is a flowchart showing a wet on dry process according to one embodiment of the present application. Specifically, in the wet on dry process, a first negative electrode slurry mixture (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 crimped to form a negative electrode for a lithium secondary battery according to the present application.

[0178] 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.

[0179] FIG. 6 is a flowchart showing a wet on wet process according to one embodiment of the present application. Specifically, in the wet on wet process, a first negative electrode slurry mixture is prepared and applied to the negative electrode current collector layer. At the same time, after preparing a second negative electrode slurry mixture, it is applied to the first negative electrode slurry mixture, and the first and second negative electrode slurry mixtures are dried. Then, each layer can be rolled and crimped to form a negative electrode for a lithium secondary battery according to the present application.

[0180] 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, and the wet on dry process includes: applying a first negative electrode active material layer composition; partially or completely drying the applied first negative electrode active material layer composition to form a first negative electrode active material layer; and applying the second negative electrode active material layer composition to the first negative electrode active material layer. A method for manufacturing a negative electrode for a lithium secondary battery is provided.

[0181] 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 wet process, and the wet on wet process includes: applying a first negative electrode active material layer composition; and applying the second negative electrode active material layer composition to the first negative electrode active material layer composition in an undried state. A method for manufacturing a negative electrode for a lithium secondary battery is provided.

[0182] In particular, in the wet on dry process, after applying the first negative electrode active material layer composition and partially or completely drying it, the second negative electrode active material layer composition is applied on top of it. Through the above 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 do not mix, and it has the characteristic of being composed of a double layer.

[0183] In one embodiment of the present application, the negative electrode slurry solvent can be used without limitation as long as the first negative electrode active material layer composition and the second negative electrode active material layer composition can be dissolved. Specifically, water or NMP can be used.

[0184] As a result of the above-described wet-on-wet process, a joint region in which the first negative electrode active material layer and the second negative electrode active material layer are mixed can be formed. At this time, in order for the wet-on-wet process to occur, if the viscosity of the first negative electrode active material layer composition is not lower than the viscosity of the second negative electrode active material layer composition, mutual mixing cannot occur in the joint region and the process.

[0185] As shown in FIG. 7, after the first negative electrode active material layer is dried (wet-on-dry process), it can be confirmed that the interface between the two layers is clearly separated by forming the second negative electrode active material layer.

[0186] On the other hand, as shown in FIG. 8, by applying the second negative electrode active material layer 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), it can be confirmed that mixing occurs at the interface between the two layers and a joint region is formed.

[0187] In one embodiment of the present application, a method for manufacturing a negative electrode for a lithium secondary battery is provided, including a step of pre-lithiation of a negative electrode in which a first negative electrode active material layer and a second negative electrode active material layer are formed on the negative electrode current collector, and the step of pre-lithiating the negative electrode includes a lithium electrolytic plating process; a lithium metal transfer process; a lithium metal vapor deposition process; or a stabilized lithium metal powder (SLMP) coating process.

[0188] The negative electrode for a lithium secondary battery as described above has SiO for enhancing capacity characteristics as the first negative electrode active material layer x(x = 0) is included, and it is provided with a specific composition of the silicon-based active material and / or the carbon-based active material described above as the second negative electrode active material layer, and can have the merits of rapid charging as it is. Furthermore, since the second negative electrode active material has the above composition and has a large irreversibility, it can exhibit particularly advantageous effects even during the pre-lithiation process of pre-filling the negative electrode. Compared to the case where only the first negative electrode active material layer is applied, it has a second negative electrode active material having the above composition in the second negative electrode active material, and a uniform pre-lithiation process is possible at the upper end portion of the negative electrode electrode, and thus the life can be further improved.

[0189] In one embodiment of the present application, the porosity of the first and second negative electrode active material layers may satisfy the range of 10% or more and 60% or less.

[0190] In another embodiment, the porosity of the first and second negative electrode active material layers may satisfy the range of 10% or more and 60% or less, preferably 20% or more and 50% or less, and more preferably 30% or more and 45% or less.

[0191] The porosity varies according to the composition and content of the active material, conductive material, and binder contained in the first and second negative electrode active material layers, and thereby the electric conductivity and resistance in the electrode have an appropriate range.

[0192] In one embodiment of the present application, a lithium secondary battery is provided, which includes a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0193] The secondary battery according to one embodiment of the present specification may particularly include the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, specific description thereof is omitted.

[0194] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0195] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Further, the positive electrode current collector may usually have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0196] 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 (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe 3 O 4 ; lithium manganese oxides with chemical formulas Li 1+c1 Mn 2-c1 O 4 (0 ≦ c1 ≦ 0.33), LiMnO 3 , LiMn 2 O 3 , LiMnO 2 ; lithium copper oxide (Li 2 CuO 2 ); vanadium oxides such as LiV 3 O 8 , V 2 O 5 , Cu 2 V 2 O 7 ; and compounds with chemical formulas LiNi 1-c2 M c2 O 2(Here, 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) Nickel site-type lithium nickel oxide represented by; chemical formula LiMn 2-c3 M c3 O 2 (Here, 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 Li 2 Mn 3 MO 8 (Here, M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn.) Lithium manganese composite oxide represented by; a part of Li in the chemical formula is substituted with an alkaline earth metal ion, LiMn 2 O 4 and the like can be mentioned, but it is not limited only to these. The positive electrode may be Li metal (Li-metal).

[0197] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder together with the above-described positive electrode active material.

[0198] 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, and one kind alone or a mixture of two or more kinds of these may be used.

[0199] In addition, the positive electrode binder serves to improve 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), vinylidene 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.

[0200] As the separator, it separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, it can be used without particular limitation as long as it is used as a separator in a secondary battery. In particular, those with low resistance to the ion migration of the electrolyte and excellent electrolyte moisture retention ability are preferred. Specifically, a porous polymer film, for example, a porous polymer film made from polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be selectively used in a single-layer or multi-layer structure.

[0201] 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 during the manufacture of lithium secondary batteries.

[0202] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0203] 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 pyruvate, ethyl propionate, etc. may be used.

[0204] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, have a high dielectric constant as high-viscosity organic solvents and can be preferably used to dissociate lithium salts well. When such cyclic carbonates are mixed with low-viscosity and low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate in an appropriate ratio, an electrolyte having a high electrical conductivity can be made and can be more preferably used.

[0205] The metal salt can use 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 - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , PF 6 - , (CF 3) 2 PF 4 - 、(CF 3 ) 3 PF 3 - 、(CF 3 ) 4 PF 2 - 、(CF 3 ) 5 PF - 、(CF 3 ) 6 P - 、CF 3 SO 3 - 、CF 3 CF 2 SO 3 - 、(CF 3 SO 2 ) 2 N - 、(FSO 2 ) 2 N - 、CF 3 CF 2 (CF 3 ) 2 CO - 、(CF 3 SO 2 ) 2 CH - 、(SF 5 ) 3 C - 、(CF 3 SO 2 ) 3 C - 、CF 3 (CF 2 ) 7 SO 3 - 、CF 3 CO 2 - 、CH 3 CO 2 - 、SCN - および(CF 3 CF 2 SO 2 ) 2 N - One or more selected from the group consisting of can be used.

[0206] In addition to the electrolyte constituent components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, triamide hexaline, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, 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, and improving the discharge capacity of the battery.

[0207] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having a high capacity, high rate characteristics, and cycle characteristics, they 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.

[0208] Hereinafter, preferred examples are presented to assist in understanding the present invention. It is obvious to those skilled in the art that the examples are illustrative of the description and that various changes and modifications are possible within the scope of the description and the scope of the technical idea. It goes without saying that such variations and modifications belong to the scope of the appended claims.

[0209] <Example> <Manufacture of negative electrode> [Example 1: Manufacture of negative electrode] (Manufacture of the first negative electrode active material layer) Si (average particle size (D50): 5 μm) as a silicon-based active material, a first conductive material, a second conductive material, a third conductive material, and polyacrylamide as a binder were used to prepare a first negative electrode active material layer composition at a weight ratio of 70:9.8:10:0.2:10. It was added to distilled water as a solvent for forming a negative electrode slurry to produce a first negative electrode slurry (solid content concentration: 25% by weight).

[0210] The first conductive material is carbon black C (specific surface area: 58 m 2 / g, diameter: 37 nm), the second conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the third conductive material is a carbon nanotube.

[0211] As a mixing method, the first conductive material, the second conductive material, the third conductive material, the binder, and water were dispersed at 2500 rpm for 30 minutes using a homomixer, and then the active material was added and dispersed at 2500 rpm for 30 minutes to prepare a first negative electrode slurry.

[0212] The first negative electrode slurry was coated on both sides of a copper current collector (thickness: 8 μm) as a negative electrode current collector at a loading amount of 2.75 mg / cm 2 and rolled (roll press), and dried in a vacuum oven at 130 °C for 10 hours to form a first negative electrode active material layer (thickness: 33 μm).

[0213] (Manufacture of the second negative electrode active material layer) SiO (average particle size (D50): 3.5 μm) as a silicon-based active material, a second conductive material, a third conductive material, and polyacrylamide as a binder were used to prepare a second negative electrode active material layer composition at a weight ratio of 70:19.8:0.2:10. It was added to distilled water as a solvent for forming a negative electrode slurry to produce a second negative electrode slurry (solid content concentration: 25% by weight).

[0214] The second conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the third conductive material is a carbon nanotube.

[0215] As a mixing method, after dispersing the second conductive material, the third conductive material, the binder, and water at 2500 rpm for 30 minutes using a homomixer, the active material was added, and then dispersed at 2500 rpm for 30 minutes to prepare the second negative electrode slurry.

[0216] The second negative electrode slurry was coated on the first negative electrode active material layer at a loading amount of 1 mg / cm 2 , rolled (roll press), and dried in a vacuum oven at 130 °C for 10 hours to form a second negative electrode active material layer (thickness: 15 μm).

[0217] Thereafter, lithium metal was transferred onto the upper part of the second negative electrode active material layer to proceed with prelithiation. The prelithiation ratio was 10% - 15% prelithiated based on the negative electrode filling capacity.

[0218] [Example 1-1: Fabrication of Negative Electrode] In Example 1, a negative electrode was fabricated in the same manner as in Example 1, except that the negative electrode was not prelithiated.

[0219] [Example 2: Fabrication of Negative Electrode] In the fabrication of the second negative electrode active material layer of Example 1, a second negative electrode active material layer composition was prepared with SiC (average particle size (D50): 3.5 μm) as the silicon-based active material, the second conductive material, the third conductive material, and polyacrylamide as the binder at a weight ratio of 70:19.8:0.2:10, and a negative electrode was fabricated under the same conditions as in Example 1 (solid content concentration 25 wt%) except that it was added to distilled water as a solvent for forming the negative electrode slurry to produce the second negative electrode slurry.

[0220] [Example 3: Fabrication of Negative Electrode] In the production of the second negative electrode active material layer of Example 1, except that SiO (average particle size (D50): 3.5 μm) as the silicon-based active material, the second conductive material, the third conductive material, and polyacrylamide as the binder were prepared into a second negative electrode active material layer composition at a weight ratio of 63:17:0.3:19.7 and added to distilled water as the solvent for forming the negative electrode slurry to produce the second negative electrode slurry, a negative electrode was produced under the same conditions as in Example 1 (solid content concentration: 25% by weight).

[0221] [Example 4: Production of Negative Electrode] (Production of the First Negative Electrode Active Material Layer) The first negative electrode active material layer was produced in the same manner as in Example 1.

[0222] (Production of the Second Negative Electrode Active Material Layer) As the silicon-based active material, SiO (average particle size (D50): 3.5 μm), artificial graphite, the second conductive material, the third conductive material, and polyacrylamide as the binder were prepared into a second negative electrode active material layer composition at a weight ratio of 50:20:10:10:10. It was added to distilled water as the solvent for forming the negative electrode slurry to produce the second negative electrode slurry (solid content concentration: 25% by weight).

[0223] The second conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the third conductive material is carbon nanotubes.

[0224] As the mixing method, the second conductive material, the third conductive material, the binder, and water were dispersed at 2500 rpm for 30 min using a homomixer, then the active material was added, and then dispersed at 2500 rpm for 30 min to prepare a slurry.

[0225] The second negative electrode slurry was coated on the first negative electrode active material layer at a loading amount of 2.8 mg / cm 2 , rolled (roll press), and dried in a vacuum oven at 130 °C for 10 hours to form a second negative electrode active material layer (thickness: 15 μm).

[0226] Thereafter, lithium metal was transferred onto the upper part of the second negative electrode active material layer to proceed with prelithiation.

[0227] [Example 5: Production of Negative Electrode] 100 parts by weight of Si with a D50 of 5 μm, 13 parts by weight of carbon black as the first conductive material, 0.3 parts by weight of single-walled carbon nanotubes (SWCNT) with an average diameter of 1 nm, 15 parts by weight of polyacrylic acid (PAA) as the first binder polymer, and 1.1 parts by weight of carboxymethyl cellulose (CMC) were mixed, and water was added as the first dispersion medium to produce a first negative electrode slurry. At this time, the solid content of the first negative electrode slurry was 25% by weight.

[0228] SiO 63 parts by weight, 7 parts by weight of natural graphite, The artificial graphite of secondary particles with a D50 of 16.7 μm and a tap density of 0.91 g / cc 30 parts by weight, 1.0 part by weight of carbon black as the second conductive material, 3.0 parts by weight of styrene-butadiene rubber (SBR) as the second binder polymer, and 1.1 parts by weight of carboxymethyl cellulose (CMC) were mixed, and water was added as the second dispersion medium to produce a second negative electrode slurry. At this time, the solid content of the second negative electrode slurry was 49% by weight.

[0229] Using a double slot die, while coating the first negative electrode slurry on one side of a copper (Cu) thin film, which is a negative electrode current collector with a thickness of 10 μm, at the same time, the second negative electrode slurry was coated on the first negative electrode slurry. At this time, the loading amounts of the first negative electrode slurry and the second negative electrode slurry were 3 mg / cm 2 and 1 mg / cm 2 respectively.

[0230] Thereafter, using a device in which a hot air drying and an infrared drying method were combined, the coated first negative electrode slurry and the second negative electrode slurry were dried simultaneously to form an active material layer.

[0231] The thus-formed negative electrode active material layer was simultaneously rolled by a roll pressing method to produce a negative electrode having an active material layer with a bilayer structure having a thickness of 78 μm.

[0232] [Example 6: Production of Negative Electrode] A negative electrode was produced in the same manner as in Example 5, except that the negative electrode active material in the second negative electrode slurry of Example 5 was changed to "31.5 parts by weight of artificial graphite, 3.5 parts by weight of natural graphite, and 65 parts by weight of SiO".

[0233] [Example 7: Production of Negative Electrode] In the second negative electrode slurry of Example 5, except that the negative electrode active material was changed to " SiC 63 parts by weight, 7 parts by weight of natural graphite, Artificial graphite 30 parts by weight", a negative electrode was produced in the same manner as in Example 5.

[0234] [Example 8: Production of Negative Electrode] A negative electrode was produced in the same manner as in Example 5, except that the negative electrode active material in the second negative electrode slurry of Example 5 was changed to "31.5 parts by weight of artificial graphite, 3.5 parts by weight of natural graphite, and 65 parts by weight of SiC".

[0235] (Method for Measuring Average Diameter of Single-Walled Carbon Nanotubes) Using a transmission electron microscope (TEM) (manufacturer: HITACHI, model name: H7650), the sample was magnified at a magnification of 150,000 times or more for measurement. Then, the average diameter of the single-walled carbon nanotubes confirmed in an arbitrarily sampled range within the measured photograph was measured. At this time, the number of measurements was at least 10 or more, and after measurement, the average diameter was obtained.

[0236] [Comparative Example 1: Production of Negative Electrode] As a silicon-based active material, Si (average particle size (D50): 5 μm), a first conductive material, and polyacrylamide as a binder were used to produce an active material layer composition at a weight ratio of 70:20:10. It was added to distilled water as a solvent for forming the negative electrode slurry to produce a negative electrode slurry (solid content concentration: 25% by weight).

[0237] The first conductive material uses carbon black C (specific surface area: 58 m 2 / g, diameter: 37 nm).

[0238] As a mixing method, the first conductive material, the binder, and water were dispersed at 2500 rpm for 30 min using a homomixer, and then, after adding the active material, they were dispersed at 2500 rpm for 30 min to prepare a slurry.

[0239] The negative electrode slurry was coated on both sides of a copper current collector (thickness: 8 μm) as a negative electrode current collector at a loading amount of 85 mg / 25 cm 2 and rolled (roll press), and then dried in a vacuum oven at 130 °C for 10 hours to form a negative electrode active material layer (thickness: 33 μm).

[0240] Thereafter, lithium metal was transferred onto the upper part of the negative electrode active material layer to promote prelithiation.

[0241] [Comparative Example 2: Production of Negative Electrode] In the Comparative Example 1, a negative electrode was produced in the same manner as in the Comparative Example 1, except that prelithiation did not proceed.

[0242] [Comparative Example 3: Production of Negative Electrode] In the Example 1, a negative electrode was produced in the same manner as in the Example 1, except that the lamination order of the first negative electrode active material layer and the second negative electrode active material layer was changed.

[0243] [Comparative Example 4: Production of Negative Electrode] In Example 1 above, except that SiO (average particle size (D50): 3.5 μm) as the silicon-based active material, artificial graphite as the carbon-based active material, the first conductive material, the second conductive material, and polyacrylamide as the binder were added to distilled water as the solvent for forming the negative electrode slurry at a weight ratio of 30:50:5:5:10 to produce the second negative electrode slurry, the negative electrode was produced in the same manner as in Example 1 above.

[0244] [Comparative Example 4-1: Production of Negative Electrode] In Comparative Example 4 above, except that pre-lithiation did not proceed, the negative electrode was produced in the same manner as in Comparative Example 4.

[0245] [Comparative Example 5: Production of Negative Electrode] In Comparative Example 1 above, except that the active material layer composition was produced at a weight ratio of 52.5:17.5:9.8:10:0.2:10 with Si (average particle size (D50): 5 μm), SiO (average particle size (D50): 3.5 μm), the first conductive material, the second conductive material, the third conductive material, and polyacrylamide as the binder, the negative electrode was produced in the same manner as in Comparative Example 1.

[0246] The first conductive material is carbon black C (specific surface area: 58 m 2 / g, diameter: 37 nm), the second conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the third conductive material is carbon nanotube.

[0247] [Manufacture of Secondary Battery] As the positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2 O 2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were added to N-methyl-2-pyrrolidone (NMP) as the solvent for forming the positive electrode slurry at a weight ratio of 97:1.5:1.5 to produce the positive electrode slurry (solid content concentration: 78% by weight).

[0248] The positive electrode slurry was coated on both sides of an aluminum current collector (thickness: 12 μm) as the positive electrode current collector at a loading amount of 537 mg / 25 cm 2 , rolled (roll press), and dried in a vacuum oven at 130 °C for 10 hours to form a positive electrode active material layer (thickness: 65 μm) to fabricate a positive electrode (thickness of the positive electrode: 77 μm, porosity 26%).

[0249] An electrolyte was injected between the positive electrode and the negative electrode of Example 1 through a polyethylene separator to fabricate the secondary battery of Example 1.

[0250] The electrolyte was prepared by adding vinylene carbonate at 3 wt% based on the total weight of the electrolyte to an organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) were mixed at a volume ratio of 30:70, and adding LiPF 6 at a concentration of 1 M as a lithium salt.

[0251] Secondary batteries were fabricated in the same manner as above, except that the negative electrodes of the above Examples and Comparative Examples were used.

[0252] [Experimental Example 1: Evaluation of Life Characteristics] Regarding the secondary batteries including the negative electrodes manufactured in Examples 1 to 8, Example 1-1, and Comparative Examples 4-1, 1 to 5, life evaluation was carried out using an electrochemical charger / discharger, and the capacity retention rate was evaluated. The secondary batteries were subjected to a cycle test at 4.2 - 3.0 V at 1C / 0.5C, and charged / discharged at 0.33C / 0.33C (4.2 - 3.0 V) every 50 cycles during the test to measure the capacity retention rate. Capacity retention rate (%) = {(Discharge capacity at the Nth cycle) / (Discharge capacity at the 1st cycle)} × 100

[0253] Figure 2 shows the RPT capacity retention rate graphs according to the Examples and Comparative Examples.

[0254] [Experimental Example 2: Measurement and Evaluation of Resistance Increase Rate] During the test in the above Experimental Example 1, after measuring the capacity retention rate by charging and discharging at 0.33C / 0.33C (4.2 - 3.0V) every 50 cycles, the resistance was measured by discharging at 2.5C pulse at SOC50, and the resistance increase rate was compared and analyzed.

[0255] Figure 3 shows the RPT resistance increase rate graphs according to the examples and comparative examples.

[0256] Also, for the above life characteristic evaluation and the resistance increase rate measurement evaluation, the data at 200 cycles were calculated respectively, and the results were as shown in Table 1 below.

[0257]

Table 1

[0258] As can be confirmed from Table 1 above, in the case of the negative electrodes of Examples 1 to 8 and Example 1-1, it was confirmed that they were superior to the negative electrodes of Comparative Examples 1 to 5 and Comparative Example 4-1 in the evaluation of capacity retention rate and resistance increase rate.

[0259] In particular, the negative electrodes of Examples 1 to 8 and Example 1-1 have a double-layer active material layer with a specific composition and content. In particular, the first negative electrode active material layer contains a high content of SiO x (x = 0), and it was confirmed that it can have the advantages of high capacity, high density, and being advantageous for rapid charging as they are. Furthermore, it was confirmed that the second negative electrode active material layer contains one or more selected from the group consisting of silicon-based and carbon-based active materials, and the uniformity of the negative electrode surface during charge and discharge can be adjusted, and the cycle characteristics are improved.

[0260] In addition, in Example 1 and Example 1-1, although the composition of the negative electrode is the same, it is a comparison between the case where pre-lithiation proceeded and the case where it did not proceed. When pre-lithiation did not proceed as in Example 1-1, the capacity retention rate was inferior to that of Example 1. However, when the composition of the double-layer negative electrode according to the present application was satisfied, it was confirmed that the capacity retention rate was superior to those of Comparative Examples 1 to 5 and Comparative Example 4-1, and the resistance increase rate was also low. This is because it is possible to prevent the acceleration of deterioration on the surface of the negative electrode even when the charge and discharge cycles proceed. Furthermore, when pre-lithiation proceeds as in Example 1, it was confirmed that the above advantages are further improved, and the capacity retention rate is formed extremely high.

[0261] That is, from the results of Examples 1 to 8 and Example 1-1 of the present invention, the negative electrode having a double-layer structure with the specific composition and content of the present invention can prevent deterioration on the surface during charge and discharge compared to other negative electrodes (Comparative Examples 1 to 5 and Comparative Example 4-1), and it was confirmed that it is excellent in capacity retention and resistance characteristics. Furthermore, when Examples 1 and 1-1 were compared, even when pre-lithiation proceeds, the negative electrode of the present application includes a second negative electrode active material layer, can prevent non-uniform pre-lithiation on the surface, and has a very high capacity retention rate formed, and it was confirmed that the resistance increase rate shows an equivalent level.

[0262] In Comparative Example 1, a single-layer active material layer containing Si particles as a negative electrode active material was used. Although the initial capacity was excellent, it was confirmed that the capacity retention rate decreased due to the cracking phenomenon of the Si particles on the electrode surface, and the resistance increase rate was high. From this, the role of the second negative electrode active material layer according to the present application, which plays the role of a buffer layer, could be confirmed.

[0263] In Comparative Example 2, a single-layer active material layer containing Si particles as a negative electrode active material was used, and it is a negative electrode in which pre-lithiation did not proceed. In this case, it was confirmed that the capacity retention rate and the resistance increase rate due to the cracking phenomenon of the Si particles on the electrode surface during charge and discharge were also inferior to those of the examples.

[0264] Comparative Example 3 corresponds to a negative electrode in which the order of the first negative electrode active material layer and the second negative electrode active material layer of the present application is changed. In this case, it was confirmed that the cracking phenomenon of Si particles on the electrode surface portion still occurred, resulting in a decrease in the capacity retention rate and a high resistance increase rate.

[0265] Comparative Example 4 corresponds to the case where the content of the silicon-based active material contained in the second negative electrode active material layer of the present application is less than the lower limit value. That is, it is the case where the second negative electrode active material layer contains more graphite-based active material than the silicon-based active material. In this case, as can be confirmed from Table 1, during charging and discharging, the second negative electrode active material layer acts as a resistance layer, and the capacity retention rate is inferior to that of Examples 1 to 8, and it was confirmed that the resistance increase rate is high.

[0266] Comparative Example 5 is a negative electrode having a single-layer negative electrode active material layer in which Si active material and SiO active material are blended. In this case, it was confirmed that, compared with the case where the negative electrode active material layer is provided in two layers as in the present invention, the optimum Si and SiO contents are not satisfied, the capacity retention rate is decreased, and the resistance increase rate is also high.

Explanation of Reference Numerals

[0267] 10 ··· Second negative electrode active material layer 20 ··· First negative electrode active material layer 30 ··· Negative electrode current collector layer

Claims

1. A negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a first negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer; and a second negative electrode active material layer provided on a surface opposite to the surface of the first negative electrode active material layer that contacts the negative electrode current collector layer, wherein the first negative electrode active material layer contains a first negative electrode active material layer composition containing a first negative electrode active material, and the second negative electrode active material layer contains a second negative electrode active material; a second negative electrode conductive material; and a second negative electrode binder. A second negative electrode active material layer composition, The first negative electrode active material contains SiO ｘ (x = 0) and SiO ｘ (0 < x < 2), and contains one or more selected from the group consisting of them. 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 conductive material includes at least one selected from the group consisting of a dot-shaped conductive material; a linear conductive material; and a planar conductive material, 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, the silicon-based active material is one or more selected from the group consisting of SiO x (0 < x < 2), SiC, and Si alloys, 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, a negative electrode for a lithium secondary battery.

2. The silicon-based active material is SiO ｘ where (0 < x < 2); or the negative electrode for a lithium secondary battery according to claim 1, which contains SiC.

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

4. The thickness of the first negative electrode active material layer is 10 μm or more and 200 μm or less, The negative electrode for a lithium secondary battery according to claim 1, wherein the thickness of the second negative electrode active material layer is 10 μm or more and 100 μm or less.

5. The negative electrode for a lithium secondary battery according to claim 1, wherein the loading amount (a) of the first negative electrode active material layer composition satisfies 2 times or more the loading amount (b) of the second negative electrode active material layer composition.

6. The negative electrode for a lithium secondary battery according to claim 1, wherein the first negative electrode active material layer composition further includes at least one selected from the group consisting of a first negative electrode conductive material; and a first negative electrode binder.

7. The carbon-based active material includes graphite, the graphite includes artificial graphite and natural graphite, The negative electrode for a lithium secondary battery according to claim 1, wherein the weight ratio of the artificial graphite to the natural graphite is 5:5 to 9.5:0.

5.

8. The negative electrode for a lithium secondary battery according to claim 1, wherein the second negative electrode conductive material includes at least a linear conductive material.

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

10. Preparing a negative electrode current collector layer; Coating a first negative electrode active material layer composition containing a first negative electrode active material on one or both surfaces of the negative electrode current collector layer to form a first negative electrode active material layer; and Coating a second negative electrode active material layer composition containing a second negative electrode active material, a second negative electrode conductive material, and a second negative electrode binder on 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 layer; A method for manufacturing a negative electrode for a lithium secondary battery, comprising: The first negative electrode active material contains SiO ｘ (x = 0) and SiO ｘ (0 < x < 2), and contains one or more selected from the group consisting of, 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 conductive material includes at least one selected from the group consisting of a dot-shaped conductive material, a linear conductive material, and a planar conductive material. 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. The silicon-based active material is one or more selected from the group consisting of SiO x (0 < x < 2), SiC, and Si alloys. The method for manufacturing a negative electrode for a lithium secondary battery, wherein 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.

11. Pre-lithiation of the negative electrode on which a first negative electrode active material layer and a second negative electrode active material layer are formed on the negative electrode current collector; The step of pre-lithiating the negative electrode includes a lithium electrolytic plating process, a lithium metal transfer process, a lithium metal evaporation process, or a stabilized lithium metal powder (SLMP) coating process. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 10.

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

13. 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 coating a first negative electrode active material layer composition; Partially drying or completely drying the coated first negative electrode active material layer composition to form a first negative electrode active material layer; and Coating the second negative electrode active material layer composition on the first negative electrode active material layer. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 10.

14. 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 while the first negative electrode active material layer composition is in an undried state; The method for manufacturing a negative electrode for a lithium secondary battery according to claim 10.

15. A positive electrode; The negative electrode for a lithium secondary battery according to any one of claims 1 to 9; A separator provided between the positive electrode and the negative electrode; and An electrolyte; A lithium secondary battery comprising.

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