Negative electrode and secondary battery including the same

Abstract

The present invention relates to a negative electrode current collector, a first negative electrode active material layer disposed on the negative electrode current collector and including a first carbon-based active material, a first silicon-based active material, and a first binder, and a second negative electrode active material layer disposed on the first negative electrode active material layer and including a second carbon-based active material, a second silicon-based active material, and a second binder, wherein the first silicon-based active material is SiO x (0≦x<2) and a first metal doped into the first silicon-based compound, and the second silicon-based active material is SiO y (0≦y<2) and a second metal doped into the second silicon-based compound, wherein a weight ratio of the first metal to a sum of weights of the first silicon-based compound and the first metal is greater than a weight ratio of the second metal to a sum of weights of the second silicon-based compound and the second metal, and a ratio of a weight percentage of the first binder based on the weight of the first negative electrode active material layer to a weight percentage of the second binder based on the weight of the second negative electrode active material layer is 0.9:1 to 5.5:1.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0157520, filed November 16, 2021, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a negative electrode and a secondary battery including the same. [Background technology]

[0003] Recently, with the rapid spread of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for secondary batteries that are small, lightweight, and have relatively high capacity has been rapidly increasing. In particular, lithium secondary batteries, which are lightweight and have high energy density, have been attracting attention as a driving power source for portable electronic devices. Therefore, active research and development efforts are being made to improve the performance of lithium secondary batteries.

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, an electrolyte, an organic solvent, etc. The positive electrode and the negative electrode may have an active material layer including a positive electrode active material or a negative electrode active material formed on a current collector. The positive electrode typically uses a lithium-containing metal oxide such as LiCoO2 or LiMn2O4 as the positive electrode active material, while the negative electrode typically uses a lithium-free carbon-based or silicon-based active material as the negative electrode active material.

[0005] Among negative electrode active materials, silicon-based active materials have attracted attention because they have a capacity approximately 10 times higher than carbon-based active materials, and have the advantage of being able to achieve high energy density even with thin electrodes. However, silicon-based active materials are not widely used due to the problem of volume expansion during charging and discharging, which causes cracks / damage to the active material particles and reduces lifespan characteristics.

[0006] Furthermore, when used at high voltages, the silicon-based active materials are subject to serious problems such as volume expansion during charging and discharging, deterioration in the structural stability of the negative electrode, excessive formation of a solid electrolyte interfacial film (SEI layer), and electrolyte depletion. Therefore, they are currently only used in automotive batteries, which have a lower operating voltage range than portable electronic devices.

[0007] Therefore, there is a demand for the development of a negative electrode and a secondary battery using a silicon-based active material that have high energy density and long life characteristics when used at high voltage.

[0008] Korean Patent Publication No. 10-2017-0074030 relates to a negative electrode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same, and discloses a negative electrode active material including a porous silicon-carbon composite, but there are limitations in solving the above-mentioned problems. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Publication No. 10-2017-0074030 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a negative electrode that significantly improves the life performance of a battery, particularly when used in a high voltage range, by preventing deterioration due to non-uniformity of components within the negative electrode.

[0011] Another object of the present invention is to provide a secondary battery including the above-mentioned negative electrode. [Means for solving the problem]

[0012] The present invention relates to a negative electrode active material comprising: a negative electrode current collector; a first negative electrode active material layer disposed on the negative electrode current collector and including a first carbon-based active material, a first silicon-based active material, and a first binder; and a second negative electrode active material layer disposed on the first negative electrode active material layer and including a second carbon-based active material, a second silicon-based active material, and a second binder, wherein the first silicon-based active material is SiO x (0≦x<2) and a first metal doped into the first silicon-based compound, and the second silicon-based active material is SiO y (0≦y<2) and a second metal doped into the second silicon-based compound, wherein a weight ratio of the first metal to a total weight of the first silicon-based compound and the first metal is greater than a weight ratio of the second metal to a total weight of the second silicon-based compound and the second metal, and a ratio of a weight percentage of the first binder based on the weight of the first negative electrode active material layer to a weight percentage of the second binder based on the weight of the second negative electrode active material layer is 0.9:1 to 5.5:1.

[0013] The present invention also provides a secondary battery including the above-mentioned negative electrode, a positive electrode facing the negative electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte. [Effects of the Invention]

[0014] The anode of the present invention has a sequentially stacked structure including a negative electrode current collector, a first negative electrode active material layer, and a second negative electrode active material layer, wherein the metal doping ratio of a first silicon-based active material included in the first negative electrode active material layer is higher than the metal doping ratio of a second silicon-based active material included in the second negative electrode active material layer, and the weight ratio of a first binder included in the first negative electrode active material layer to a second binder included in the second negative electrode active material layer is adjusted to be within a specific range. In the anode of the present invention, the first silicon-based active material and the second silicon-based active material, which have different metal doping ratios, are disposed in the first negative electrode active material layer and the second negative electrode active material layer, respectively, thereby enabling uniform lithium insertion / extraction throughout the anode and significantly reducing thickness expansion of the anode. In addition, according to the anode of the present invention, by adjusting the weight ratio of the first binder and the second binder, uneven distribution of the binder throughout the anode can be prevented, and the bonding or adhesion between the current collector and the first anode active material layer, and between the first anode active material layer and the second anode active material layer, can be improved, and the overall adhesion of the anode containing a silicon-based active material can be improved, and the degree of thickness expansion of the anode can be significantly reduced, resulting in a significant improvement in the life performance of the anode and a secondary battery including the same. In particular, the anode of the present invention can exhibit an outstanding improvement in life performance when used in a high voltage range or at a high loading anode. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic side view illustrating a negative electrode according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that an inventor can appropriately define the concepts of terms in order to best explain his or her invention.

[0017] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0018] It should be understood that in this specification, the terms "comprises," "includes," "has," and the like specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possible presence or addition of one or more different features, numbers, steps, components, or combinations thereof.

[0019] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 ) can be measured using, for example, a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0020] The present invention will be described in detail below with reference to the drawings, specifically, Fig. 1 is a schematic side view for explaining a negative electrode according to the present invention.

[0021] <Negative electrode> The present invention relates to a negative electrode, specifically to a negative electrode for a lithium secondary battery.

[0022] Referring to FIG. 1, the negative electrode 10 of the present invention includes a negative electrode current collector 100, a first negative electrode active material layer 210 disposed on the negative electrode current collector 100 and including a first carbon-based active material, a first silicon-based active material, and a first binder, and a second negative electrode active material layer 220 disposed on the first negative electrode active material layer 210 and including a second carbon-based active material, a second silicon-based active material, and a second binder, wherein the first silicon-based active material is SiO x(0≦x<2) and a first metal doped into the first silicon-based compound, and the second silicon-based active material is SiO y The negative electrode active material layer 220 includes a second silicon-based compound represented by (0≦y<2) and a second metal doped into the second silicon-based compound, wherein a weight ratio of the first metal to a sum of the weights of the first silicon-based compound and the first metal is greater than a weight ratio of the second metal to a sum of the weights of the second silicon-based compound and the second metal, and a ratio of a weight percentage of the first binder based on the weight of the first negative electrode active material layer 210 to a weight percentage of the second binder based on the weight of the second negative electrode active material layer 220 is 0.9:1 to 5.5:1.

[0023] Although silicon-based active materials have the advantage of having higher capacity than carbon-based active materials, they have not been widely used due to the large degree of volume expansion and contraction caused by lithium insertion and extraction. This problem becomes more serious when the negative electrode is loaded at a high level or when the negative electrode is used in a high voltage range.

[0024] To solve these problems, the anode of the present invention has a sequentially stacked structure of a negative electrode current collector, a first negative electrode active material layer, and a second negative electrode active material layer, wherein the metal doping ratio of a first silicon-based active material contained in the first negative electrode active material layer is higher than the metal doping ratio of a second silicon-based active material contained in the second negative electrode active material layer, and the weight ratio of a first binder contained in the first negative electrode active material layer to a second binder contained in the second negative electrode active material layer is adjusted to be within a specific range. In the anode of the present invention, the first silicon-based active material and the second silicon-based active material having different metal doping ratios are disposed in the first negative electrode active material layer and the second negative electrode active material layer, respectively, thereby enabling uniform lithium insertion / extraction throughout the entire anode and significantly reducing thickness expansion of the anode. In addition, according to the anode of the present invention, by adjusting the weight ratio of the first binder and the second binder, uneven distribution of the binder throughout the anode is prevented, the bonding or adhesion between the current collector and the first anode active material layer and between the first anode active material layer and the second anode active material layer is improved, the overall adhesion of the anode containing a silicon-based active material is improved, and the degree of thickness expansion of the anode is significantly reduced, thereby significantly improving the life performance of the anode and a secondary battery including the same. As a result, the anode of the present invention can exhibit excellent life performance when used in a high voltage range or at a high loading anode.

[0025] Negative electrode current collector 100 The negative electrode current collector 100 is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the negative electrode current collector 100 may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and an aluminum-cadmium alloy, and may specifically include copper.

[0026] The negative electrode current collector 100 may generally have a thickness of 3 to 500 μm.

[0027] The negative electrode current collector 100 may have fine irregularities on its surface to enhance the binding strength of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, or a nonwoven fabric.

[0028] First negative electrode active material layer 210 The first negative electrode active material layer 210 is disposed on the negative electrode current collector 100. Specifically, the first negative electrode active material layer may be disposed on at least one surface of the negative electrode current collector, more specifically, on one or both surfaces of the negative electrode current collector.

[0029] The first negative electrode active material layer 210 includes a first carbon-based active material, a first silicon-based active material, and a first binder.

[0030] The first carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and specifically may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0031] The average particle size (D 50 ) can be 5 μm to 35 μm, preferably 10 μm to 20 μm, in order to ensure structural stability during charge and discharge and reduce side reactions with the electrolyte.

[0032] The first carbon-based active material may be included in the first negative electrode active material layer 210 in an amount of 65% to 98% by weight, specifically 80% to 95% by weight.

[0033] The first silicon-based active material is SiO x The silicon-based compound may include a first silicon-based compound represented by (0≦x<2) and a first metal doped into the first silicon-based compound.

[0034] Generally, in the case of silicon-based active materials, due to the existence of irreversible sites in the silicon-based active materials, there is a problem that a part of the lithium that moves to the negative electrode during the initial charging causes an irreversible reaction in which it does not return to the positive electrode during discharging. In order to prevent such a problem, the first metal can be introduced by being doped into the first silicon-based compound to reduce the irreversible phase of the first silicon-based compound and improve the efficiency. On the other hand, as will be described later, the weight ratio of the first metal to the total weight of the first silicon-based compound and the first metal is larger than the weight ratio of the second metal to the total weight of the second silicon-based compound and the second metal. Thereby, the initial efficiency of the silicon-based active material existing in the lower layer portion of the negative electrode increases, and the phenomenon that an excessive overvoltage is applied to the upper layer portion of the negative electrode close to the separator during the negative electrode charging process can be alleviated, and the insertion / desorption of lithium can be uniformly performed without being unevenly distributed in the upper part of the negative electrode, and the degree of volume expansion of the negative electrode due to charge and discharge can be significantly reduced. Thereby, the life performance of the negative electrode and the secondary battery including the same is improved.

[0035] The first silicon-based compound can be represented by the chemical formula of SiO x (0 ≦ x < 2), and specifically, it can be represented by the chemical formula of SiO x (0 < x < 2). On the other hand, in the case of SiO2 (when x = 2 in the chemical formula 1), since it does not react with lithium ions and cannot store lithium, x is preferably within the above range. Specifically, the first silicon-based compound can be represented by the chemical formula of SiO x (0.5 ≦ x ≦ 1.5).

[0036] The first metal is doped into the first silicon-based compound. Specifically, the first metal can be doped into the first silicon-based compound and can be located inside, on the surface, or inside and on the surface of the first silicon-based compound. The first metal is doped into the first silicon-based compound and can form silicon oxides and metal silicates contained in the first silicon-based compound.

[0037] The first metal may include at least one metal selected from the group consisting of Li, Mg, Ca, and Al. Specifically, the first metal may include at least one metal selected from the group consisting of Li and Mg, more specifically, Mg, in order to achieve excellent effects such as controlling the volume expansion of silicon-based oxide particles, preventing damage, and improving initial efficiency.

[0038] The weight of the first metal may be 8 wt% to 20 wt%, specifically 10 wt% to 16 wt%, based on the total weight of the first silicon-based compound and the first metal. Within this range, lithium insertion and desorption can occur smoothly in relation to the second silicon-based active material, improving the overall charging performance of the negative electrode. Lithium insertion and desorption can occur uniformly throughout the negative electrode, reducing the degree of expansion of the negative electrode thickness and preventing a decrease in capacity due to excessive metal doping. The content of the first metal can be measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0039] The first silicon-based active material may further include a carbon coating layer disposed on a surface thereof, which may function as a protective layer to suppress volumetric expansion of the first silicon-based active material and prevent side reactions with the electrolyte.

[0040] The carbon coating layer may be included in the first silicon-based active material in an amount of 0.1 wt % to 10 wt %, preferably 3 wt % to 7 wt %, and when included in this range, the carbon coating layer is preferred in that it can effectively control the volume expansion of the first silicon-based active material and prevent side reactions with the electrolyte.

[0041] The carbon coating layer may be an amorphous carbon coating layer, and may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0042] The average particle size (D 50 ) may be 1 μm to 15 μm, more preferably 2 μm to 8 μm, in order to achieve structural stability of the active material during charge and discharge, prevent the problem of increased volume expansion / contraction caused by excessively large particle size, and prevent the problem of reduced initial efficiency caused by excessively small particle size.

[0043] The first silicon-based active material may be included in the first negative electrode active material layer 210 in an amount of 1 wt % to 20 wt %, specifically 3 wt % to 15 wt %, to reduce the effect of the first silicon-based active material on volume expansion and ensure sufficient capacity of the negative electrode.

[0044] The method for producing the first silicon-based active material is not particularly limited. Specifically, the first silicon-based active material is a silicon-based active material comprising: (a) SiO a (0≦a<2) to generate a first vapor, vaporizing the first metal to generate a second vapor, mixing the first vapor and the second vapor to cause a gas-phase reaction, and cooling the gas-phase reaction to obtain a powder. The first silicon-based active material can be manufactured by a method including the steps of forming a carbon coating layer, an average particle size (D 50 ) adjustment step can be added.

[0045] The first carbon-based active material and the first silicon-based active material may be included in the first negative electrode active material layer in an amount of 90% by weight to 98% by weight, specifically 94% by weight to 98% by weight. The weight ratio of the first carbon-based active material to the first silicon-based active material may be 83:17 to 99:1, specifically 88:12 to 93:7. This range reduces the effect of volume expansion of the silicon-based active material and ensures sufficient capacity of the negative electrode, enabling a high-loading negative electrode to be achieved.

[0046] The first binder is contained in the first negative electrode active material layer 210 to bind the negative electrode current collector 100 and the first negative electrode active material layer 210, and to bind the negative electrode active materials (the first carbon-based active material and the first silicon-based active material).

[0047] The first binder can further improve electrode adhesive strength and provide sufficient resistance to volume expansion / contraction of the active material. The first binder can include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, acrylic rubber, butyl rubber, fluororubber, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyacrylamide (PAM), and specifically can include styrene butadiene rubber (SBR).

[0048] The first binder may be included in the first negative electrode active material layer 210 in an amount of 1 wt % to 15 wt %, specifically 2 wt % to 8 wt %, and more specifically 3.5 wt % to 4.5 wt %. However, the content of the first binder should be adjusted in consideration of the weight ratio of the first binder to the second binder, which will be described later.

[0049] The first negative electrode active material layer 210 may further include a first conductive material in addition to the first carbon-based active material, the first silicon-based active material, and the first binder.

[0050] The first conductive material may be used to improve the conductivity of the first negative electrode active material layer and may be conductive without causing a chemical change. Specifically, the first 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, single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives. In consideration of maintaining the conductive network of the first silicon-based active material, the first conductive material may include at least one selected from single-walled carbon nanotubes and multi-walled carbon nanotubes, more specifically, single-walled carbon nanotubes.

[0051] The first conductive material may be included in the first negative electrode active material layer 210 in an amount of 0.001 wt % to 10 wt %, specifically 0.01 wt % to 1 wt %, and when included in this range, it is preferable in that it improves the electrical conductivity of the surface of the first silicon-based active material, eliminates overvoltage during charging, and prevents the conductive network from being broken due to the expansion and contraction of the volume of the first silicon-based active material.

[0052] The first negative electrode active material layer 210 may further include a thickener, which may include carboxymethyl cellulose (CMC).

[0053] The thickener may be included in the first negative electrode active material layer 210 in an amount of 0.5 wt % to 5 wt %, but is not limited thereto.

[0054] The thickness of the first negative electrode active material layer 210 may be 10 μm to 100 μm, specifically 15 μm to 45 μm. According to the present invention, even if the first negative electrode active material layer 210 has a thickness in this range, it may have excellent adhesive strength and thickness expansion controllability, and may have an excellent lifespan.

[0055] The loading amount of the first negative electrode active material layer 210 is 1 mAh / cm 2 ~5mAh / cm 2 , specifically 2mAh / cm 2 ~4mAh / cm 2 According to the present invention, even if the first negative electrode active material layer 210 has a loading amount within the above range, it may have excellent adhesive strength and thickness expansion controllability, and the lifespan performance may be improved to an excellent level.

[0056] Second negative electrode active material layer 220 The second negative electrode active material layer 220 is disposed on the first negative electrode active material layer 210. When the first negative electrode active material layer is disposed on one or both sides of the negative electrode current collector, the second negative electrode active material layer may also be disposed on the first negative electrode active material layer disposed on one or both sides of the negative electrode current collector.

[0057] The second negative electrode active material layer 220 includes a second carbon-based active material, a second silicon-based active material, and a second binder.

[0058] The second carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and specifically may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0059] The average particle size (D 50 ) can be 5 μm to 35 μm, preferably 10 μm to 20 μm, in order to ensure structural stability during charge and discharge and reduce side reactions with the electrolyte.

[0060] The second carbon-based active material can be contained in the second negative electrode active material layer 220 at 65% to 98% by weight, specifically 80% to 95% by weight.

[0061] The second silicon-based active material is SiO y It can contain a second silicon-based compound represented by (0 ≦ y < 2) and a second metal doped into the second silicon-based compound. The second metal can be doped into the second silicon-based compound and introduced to reduce the irreversible phase of the second silicon-based compound and improve the efficiency.

[0062] According to the negative electrode of the present invention, the weight ratio of the first metal to the total weight of the first silicon-based compound and the first metal is greater than the weight ratio of the second metal to the total weight of the second silicon-based compound and the second metal. Thereby, the insertion and desorption of lithium are prevented from concentrating on the upper part of the negative electrode (the part in contact with the separator), and can be uniformly performed throughout the negative electrode, and the expansion of the thickness of the negative electrode is prevented. When the weight ratio of the first metal to the total weight of the first silicon-based compound and the first metal is the same as or smaller than the weight ratio of the second metal to the total weight of the second silicon-based compound and the second metal, the insertion and desorption of lithium concentrate on the upper part of the negative electrode, or the problem that the insertion and desorption of lithium are not uniformly performed throughout the negative electrode occurs. Therefore, the charge-discharge performance of the negative electrode deteriorates, and there is a problem that the degree of expansion of the volume of the negative electrode increases and the life performance rapidly deteriorates.

[0063] The second silicon-based compound is SiO y It can be represented by the chemical formula of (0 ≦ y < 2), specifically, it can be represented by the chemical formula of SiO y It can be represented by the chemical formula of (0 < y < 2). More specifically, the second silicon-based compound can be represented by the chemical formula of SiO y It can be represented by the chemical formula of (0.5 ≦ y ≦ 1.5).

[0064] The second metal may be doped into the second silicon-based compound. Specifically, the second metal may be located inside, on the surface, or both inside and on the surface of the second silicon-based compound. The second metal may form a metal silicate with silicon oxide contained in the second silicon-based compound.

[0065] The second metal may include at least one metal selected from the group consisting of Li, Mg, Ca, and Al. Specifically, the second metal may include at least one metal selected from the group consisting of Li and Mg, more specifically, Mg, in order to achieve excellent effects such as controlling the volume expansion of silicon-based oxide particles, preventing damage, and improving initial efficiency.

[0066] The weight of the second metal may be 3 wt % or more and less than 10 wt %, specifically 6.5 wt % to 9.5 wt %, based on the total weight of the second silicon-based compound and the second metal. When the weight is within this range, lithium insertion and desorption can be uniformly performed throughout the negative electrode, the degree of expansion of the negative electrode thickness can be reduced, and a decrease in capacity due to excessive metal doping can be prevented.

[0067] The second silicon-based active material may further include a carbon coating layer disposed on the surface thereof, which may function as a protective layer to suppress volumetric expansion of the second silicon-based active material and prevent side reactions with the electrolyte.

[0068] The carbon coating layer may be included in the second silicon-based active material in an amount of 0.1 wt % to 10 wt %, preferably 3 wt % to 7 wt %, and when included in this range, the carbon coating layer is preferred in that it can effectively control the volume expansion of the second silicon-based active material and prevent side reactions with the electrolyte.

[0069] The carbon coating layer may be an amorphous carbon coating layer, and may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0070] The average particle size (D 50 ) may be 1 μm to 15 μm, more preferably 2 μm to 8 μm, in order to achieve structural stability of the active material during charge and discharge, prevent the problem of increased volume expansion / contraction caused by excessively large particle size, and prevent the problem of reduced initial efficiency caused by excessively small particle size.

[0071] The second silicon-based active material may be included in the second negative electrode active material layer 220 in an amount of 1 wt % to 20 wt %, specifically 3 wt % to 15 wt %, to reduce the effect of the second silicon-based active material on volume expansion and ensure sufficient capacity of the negative electrode.

[0072] The method for producing the second silicon-based active material is not particularly limited. Specifically, the second silicon-based active material is a silicon-based active material comprising: (a) SiO b (0≦b<2) to generate a first vapor, vaporizing the second metal to generate a second vapor, mixing the first vapor and the second vapor to cause a gas-phase reaction, and cooling the gas-phase reaction to obtain a powder. The second silicon-based active material can be manufactured by a method including the steps of forming a carbon coating layer, an average particle size (D 50 ) adjustment step can be added.

[0073] The second carbon-based active material and the second silicon-based active material may be included in the second negative electrode active material layer 220 in an amount of 90 wt % to 99 wt %, specifically 94 wt % to 98 wt %. The weight ratio of the second carbon-based active material to the second silicon-based active material may be 83:17 to 99:1, specifically 88:12 to 93:7. When the weight ratio is within this range, the effect of volume expansion of the silicon-based active material is reduced, and sufficient capacity of the negative electrode can be secured, thereby realizing a high-loading negative electrode.

[0074] The second binder is contained in the second negative electrode active material layer 220 to bind the first negative electrode active material layer 210 and the second negative electrode active material layer 220 together, and to bind the negative electrode active materials (the second carbon-based active material and the second silicon-based active material).

[0075] The second binder can further improve electrode adhesive strength and provide sufficient resistance to volume expansion / contraction of the active material. The second binder can include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, acrylic rubber, butyl rubber, fluororubber, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyacrylamide (PAM), and specifically can include styrene butadiene rubber (SBR).

[0076] The second binder may be included in the second negative electrode active material layer 220 in an amount of 1 wt % to 15 wt %, specifically 1.5 wt % to 5.0 wt %, and more specifically 2.5 wt % to 3.5 wt %. However, the content of the second binder should be adjusted in consideration of the weight ratio of the first binder and the second binder, which will be described later.

[0077] The second negative electrode active material layer 220 may further include a second conductive material in addition to the second carbon-based active material, the second silicon-based active material, and the second binder.

[0078] The second conductive material may be used to improve the conductivity of the second negative electrode active material layer and may be conductive without causing a chemical change. Specifically, the first 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, single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives. In consideration of maintaining the conductive network of the second silicon-based active material, the first conductive material may include at least one selected from single-walled carbon nanotubes and multi-walled carbon nanotubes, more specifically, single-walled carbon nanotubes.

[0079] The second conductive material may be included in the second negative electrode active material layer 220 in an amount of 0.001 wt % to 10 wt %, specifically 0.01 wt % to 1 wt %, and when included in this range, volume expansion during charging and discharging can be controlled, which is preferable in terms of preventing the conductive network from being broken due to the volume expansion of the negative electrode active material.

[0080] The second negative electrode active material layer 220 may further include a thickener, which may include carboxymethyl cellulose (CMC).

[0081] The thickener may be included in the second negative electrode active material layer 220 in an amount of 0.5 wt % to 5 wt %, but is not limited thereto.

[0082] The second negative electrode active material layer 220 may have a thickness of 10 μm to 100 μm, specifically, 15 μm to 45 μm. According to the present invention, even if the second negative electrode active material layer has a thickness in this range, it may have excellent adhesive strength and thickness expansion controllability, and may have an excellent lifespan.

[0083] The loading amount of the second negative electrode active material layer 220 is 1 mAh / cm 2 ~5mAh / cm 2 , specifically 2mAh / cm 2 ~4mAh / cm 2 According to the present invention, even if the second negative electrode active material layer 220 has a loading amount within the above range, it may have excellent adhesive strength and thickness expansion controllability, and the life performance may be improved to an excellent level.

[0084] In the present invention, the ratio of the weight percentage of the first binder based on the weight of the first negative electrode active material layer 210 to the weight percentage of the second binder based on the weight of the second negative electrode active material layer 220 is 0.9:1 to 5.5:1. Generally, when manufacturing a single-layer negative electrode, the binder is unevenly distributed in the upper part of the negative electrode (the part in contact with the separator), resulting in a decrease in the overall adhesive strength of the negative electrode. However, in the present invention, the ratio of the first binder to the second binder is adjusted within the above range, thereby improving the overall adhesive strength of the negative electrode. In particular, the first and second binders having the above-mentioned characteristics are disposed in the first and second negative electrode active material layers, respectively, along with the first and second binders having the above-mentioned characteristics, and the first and second silicon-based active materials having different metal doping ratios are disposed in the first and second negative electrode active material layers, thereby simultaneously improving the overall charge / discharge performance, adhesive strength, and thickness expansion control effect of the negative electrode.

[0085] If the weight percentage of the first binder relative to the weight percentage of the second binder relative to the weight of the second negative electrode active material layer is less than 0.9, a binder deficiency phenomenon occurs in the first negative electrode active material layer, causing excessive thickness expansion during charge and discharge of the negative electrode, and the life performance of the secondary battery may be significantly reduced.If the weight percentage of the first binder relative to the weight percentage of the second binder relative to the weight of the second negative electrode active material layer is more than 5.5, the adhesive strength between the first negative electrode active material layer and the second negative electrode active material layer may be reduced, causing excessive thickness expansion during charge and discharge of the negative electrode, and the life performance of the secondary battery may be significantly reduced.

[0086] Specifically, the ratio of the weight percentage of the first binder based on the weight of the first negative electrode active material layer 210 to the weight percentage of the second binder based on the weight of the second negative electrode active material layer 220 may be 1.5:1 to 2.5:1, and when the ratio is in this range, the above-mentioned effects may be more effectively achieved.

[0087] The total weight of the first binder and the second binder may be 0.1 wt % to 10 wt %, specifically 2 wt % to 8 wt %, of the total weight of the first negative electrode active material layer 210 and the second negative electrode active material layer 220. When the weight is within this range, it is possible to achieve a negative electrode having excellent capacity, as well as the aforementioned effects of improving adhesive strength and controlling thickness expansion of the negative electrode, which is preferable.

[0088] The ratio of the thickness of the first negative electrode active material layer 210 to the thickness of the second negative electrode active material layer 220 may be 1:0.5 to 1:2, specifically 1:0.8 to 1:1.3. This range is preferable in that the overall charge / discharge performance, adhesive strength, and thickness expansion control effect of the negative electrode can be improved simultaneously.

[0089] The sum of the loading amount of the first negative electrode active material layer 210 and the loading amount of the second negative electrode active material layer 220 is 4 mAh / cm 2 ~8mAh / cm 2, specifically 4.0mAh / cm 2 ~7.5mAh / cm 2 , more specifically 4mAh / cm 2 ~7mAh / cm 2 According to the present invention, even in the case of a high loading negative electrode as described above, a high level of adhesive strength and a control effect on cell thickness expansion can be achieved, resulting in a long life performance.

[0090] The ratio of the loading amount of the first negative electrode active material layer 210 to the loading amount of the second negative electrode active material layer 220 may be 1:0.5 to 1:2, specifically 1:0.8 to 1:1.3. This range is preferable in that the overall charge / discharge performance, adhesive strength, and thickness expansion control effect of the negative electrode can be improved simultaneously.

[0091] The total electrode density of the first negative electrode active material layer 210 and the second negative electrode active material layer 220 may be 1.4 to 2.0 g / cc, specifically 1.5 g / cc to 1.9 g / cc, and more specifically 1.6 g / cc to 1.8 g / cc. According to the present invention, excellent life performance can be exhibited even at high electrode density and energy density.

[0092] The method for producing the negative electrode is not particularly limited as long as it can produce the first and second negative electrode active material layers having the above-described characteristics. For example, a first negative electrode active material layer slurry can be prepared by dispersing a first carbon-based active material, a first silicon-based active material, a first binder, a first conductive material, and / or a thickener in a solvent (e.g., water), and a second negative electrode active material layer slurry can be prepared by dispersing the second carbon-based active material, the second silicon-based active material, a second binder, and / or a second conductive material in a solvent (e.g., water), and then applying the resulting slurry to a negative electrode current collector. More specifically, a negative electrode according to the present invention can be produced by applying the first negative electrode active material layer slurry prepared as described above to a negative electrode current collector, rolling and drying the slurry, and then applying the second negative electrode active material layer slurry prepared as described above to the first negative electrode active material layer, rolling and drying the slurry. Meanwhile, the anode according to the present invention can also be manufactured by applying the first anode active material layer slurry to the anode current collector, and substantially simultaneously applying the second anode active material layer slurry onto the first anode active material layer slurry, followed by rolling and drying.

[0093] <Secondary battery> The present invention also provides a secondary battery, specifically a lithium secondary battery, including the above-described negative electrode. Specifically, the secondary battery may include the above-described negative electrode, a positive electrode facing the negative electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte.

[0094] The negative electrode has been described above.

[0095] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector.

[0096] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the positive electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and an aluminum-cadmium alloy, and may specifically include aluminum.

[0097] The positive electrode current collector may generally have a thickness of 3 to 500 μm.

[0098] The positive electrode current collector may have a surface with fine irregularities to enhance the bonding strength of the negative electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0099] The positive electrode active material layer may be disposed on the positive electrode current collector, specifically, on one or both surfaces of the positive electrode current collector.

[0100] The positive electrode active material layer may include a positive electrode active material.

[0101] The positive electrode active material may include, as a compound capable of reversible intercalation and deintercalation of lithium, specifically, a lithium transition metal composite oxide containing lithium and at least one transition metal selected from nickel, cobalt, manganese, and aluminum, preferably a lithium transition metal composite oxide containing lithium and a transition metal including nickel, cobalt, and manganese.

[0102] More specifically, the lithium transition metal composite oxides include lithium-manganese oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt oxides (e.g., LiCoO2, etc.), lithium-nickel oxides (e.g., LiNiO2, etc.), and lithium-nickel-manganese oxides (e.g., LiNi 1-Y Mn Y O2 (where 0 <Y<1)、LiMn2-z Ni z O4 (where 0 < Z < 2, etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1, etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2, etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, p2 p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are, as atomic fractions of independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.) and the like can be mentioned, and any one or two or more of these compounds can be included. Among them, in terms of being able to enhance the capacity characteristics and stability of the battery, the lithium transition metal composite oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel-manganese-cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 or Li(Ni 0.8 0.1 Mn 0.1 Co0.1 )O2), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 ) O2, etc.)

[0103] More specifically, the positive electrode active material may include a lithium-cobalt-based oxide, which exhibits excellent stability even at a high voltage range, for example, a charging voltage of 4.4 V or more. In particular, when the negative electrode according to the present invention is combined with a positive electrode containing a lithium-cobalt-based oxide, excellent life performance can be achieved at a high charging voltage.

[0104] The average particle size (D 50 ) can be 10 μm to 30 μm, specifically 15 μm to 20 μm, and when it is in this range, it is possible to achieve a high positive electrode energy density, and it is preferable in terms of preventing cracks and damage to the positive electrode active material.

[0105] The positive electrode active material may be contained in the positive electrode active material layer in an amount of 80 to 99% by weight, preferably 92 to 98% by weight, in consideration of the sufficient capacity of the positive electrode active material.

[0106] The positive electrode active material layer may further include a positive electrode binder and a positive electrode conductive material in addition to the positive electrode active material.

[0107] The positive electrode binder is a component that helps bind the active material and conductive material together and to the current collector, and specifically may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride.

[0108] The positive electrode binder may be contained in the positive electrode active material layer in an amount of 0.1 wt % to 10 wt %, preferably 0.1 wt % to 3 wt %, more specifically 0.5 wt % to 2.5 wt %, in order to ensure sufficient binding strength between components such as the positive electrode active material.

[0109] The positive electrode conductive material can be used to supplement and improve the conductivity of a secondary battery, and is not particularly limited as long as it does not undergo chemical changes and is conductive. Specifically, the conductive material can include at least one selected from the group consisting of graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon nanotubes such as single-walled carbon nanotubes and multi-walled carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives. Specifically, in terms of improving conductivity, the conductive material can include carbon black and carbon nanotubes, more specifically, carbon black and multi-walled carbon nanotubes.

[0110] In order to ensure sufficient electrical conductivity, the positive electrode conductive material may be contained in the positive electrode active material layer at 0.1 wt % to 10 wt %, specifically 0.1 wt % to 3.0 wt %, and more specifically 0.5 wt % to 2.5 wt %.

[0111] The thickness of the positive electrode active material layer can be 30 μm to 400 μm, and preferably 50 μm to 200 μm.

[0112] The loading amount of the positive electrode active material layer is 3.5 mAh / cm 2 ~7.5mAh / cm 2 , specifically 4.5mAh / cm 2 ~6.5mAh / cm 2 It can be.

[0113] The positive electrode may be manufactured by coating a positive electrode slurry containing a positive electrode active material and, optionally, a binder, a conductive material, and a solvent for forming the positive electrode slurry on the positive electrode current collector, followed by drying and rolling.

[0114] The solvent for forming the positive electrode slurry may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount that provides a desired viscosity when the positive electrode active material, and optionally a binder and a conductive material, are included. For example, the solvent for forming the positive electrode slurry may be included in the positive electrode slurry so that the concentration of the solids, including the positive electrode active material, and optionally a binder and a conductive material, is 50 wt % to 95 wt %, preferably 70 wt % to 90 wt %.

[0115] In the secondary battery of the present invention, the N / P ratio calculated by the following mathematical formula 1 can be 1.0 to 1.5, and preferably 1.0 to 1.2.

[0116] [Formula 1] N / P ratio={(discharge capacity per unit area of ​​the negative electrode) / (discharge capacity per unit area of ​​the positive electrode)}.

[0117] Within this range, the silicon-based active material can exhibit high capacity and charging characteristics, and the influence of volume expansion / contraction of the silicon-based active material on the battery can be minimized, thereby further improving the lifespan characteristics of the secondary battery.

[0118] Specifically, the discharge capacity per unit area of ​​the negative electrode can be determined by the following method. First, a negative electrode sample identical to the negative electrode used is prepared. A coin-shaped half-cell is fabricated containing the negative electrode sample, a lithium metal counter electrode facing the negative electrode, a separator interposed between the negative electrode and the lithium metal counter electrode, and an electrolyte, and the discharge capacity is determined. The discharge capacity per unit area of ​​the negative electrode can be determined by dividing the discharge capacity by the area of ​​the negative electrode sample.

[0119] The discharge capacity per unit area of ​​the positive electrode can be determined by the following method. First, a positive electrode sample identical to the positive electrode used is prepared. A coin-shaped half-cell is fabricated containing the positive electrode sample, a lithium metal counter electrode facing the positive electrode, a separator interposed between the positive electrode and the lithium metal counter electrode, and an electrolyte, and the discharge capacity is determined. The discharge capacity per unit area of ​​the positive electrode can be determined by dividing the discharge capacity by the area of ​​the positive electrode sample.

[0120] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. In particular, a separator that exhibits low resistance to electrolyte ion movement and excellent electrolyte humidification is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can also be used, and can be used in a single-layer or multi-layer structure.

[0121] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of secondary batteries, but are not limited to these.

[0122] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0123] The organic solvent can be any organic solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent that can be used include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether and tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, which allows the electrolyte to exhibit excellent performance.

[0124] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, examples of the lithium salt include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, and LiB(C2O4)2. The lithium salt is preferably used at a concentration in the range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0125] The secondary battery may further include a battery case that accommodates the negative electrode, the positive electrode, the separator, and the electrolyte.

[0126] The secondary battery may be manufactured by placing an electrode assembly, in which a separator is interposed between the negative electrode and the positive electrode, inside the battery case and injecting an electrolyte solution, according to a typical method for manufacturing a secondary battery.

[0127] <Battery system> The present invention also provides a battery system including the above-mentioned secondary battery.

[0128] Specifically, the battery system includes the above-mentioned secondary battery and a control unit capable of setting the voltage range of the secondary battery during charging and discharging.

[0129] The secondary battery has been described above.

[0130] The control unit is not particularly limited as long as it can control the voltage range during charging and discharging of the secondary battery, and may be, for example, an electrochemical charger / discharger. Specifically, the control unit may be built into a BMS (Battery Management System) included in a battery pack.

[0131] The voltage range set by the control unit may be set to satisfy the following equation 2.

[0132] [Formula 2] 0.60≦(V max -X) / Y≦0.67

[0133] In the above formula 2, V max is the maximum voltage set by the control unit, and Y is the voltage V max -V min / 1.47, where V min is the minimum voltage set by the control unit, and X is V max and V min is the average voltage when the secondary battery is charged and discharged.

[0134] In the formula 2, the V max may be 4.4V to 4.6V, specifically 4.40V to 4.55V, and the V min According to the present invention, the secondary battery can exhibit a long life even when used at a high voltage, and the V max , V min It is possible to realize a battery system with excellent life performance.

[0135] Although the present invention may be embodied in many different forms, it is to be understood that the invention is not limited to the embodiments set forth herein, and that the invention may be embodied in various different forms, without departing from the spirit or scope of the present invention.

[0136] Example Example 1: Production of negative electrode and secondary battery 1. Manufacturing the negative electrode <Production of first silicon-based active material> SiO as the first silicon-based compound was placed on the first tray and subjected to a first heat treatment at 1,400°C in a reduced pressure atmosphere of -100 torr to generate a first vapor. Mg as the first metal was placed on the second tray and subjected to a second heat treatment at 900°C in a reduced pressure atmosphere of -100 torr to generate a second vapor. The first and second heat treatments on each tray were carried out independently. The weight ratio of SiO placed on the first tray to the metal placed on the second tray was 86.1:13.9.

[0137] The first vapor and the second vapor were mixed in one reactor and subjected to a gas phase reaction for 8 hours.

[0138] After the gas phase reaction was completed, the mixture was cooled from 900° C. to prepare a Mg-doped silicon-based compound. The cooling was carried out for 8 hours.

[0139] The Mg-doped silicon-based compound was pulverized in a jet mill.

[0140] Next, the Mg-doped silicon-based compound was subjected to CVD treatment in a mixed gas of argon (Ar) and methane (CH4) at 950°C for 4 hours to form a carbon coating layer on the surface of the Mg-doped silicon-based compound, which was used as the first silicon-based active material of Example 1. In the first silicon-based active material, the weight of Mg was 13.9 wt% relative to the total weight of SiO and Mg. The first silicon-based active material had an average particle size (D 50 ) was 7 μm and contained 4 wt % of the carbon coating layer.

[0141] <Production of second silicon-based active material> A second silicon-based active material was prepared in the same manner as the first silicon-based active material, except that the weight ratio of SiO placed on the first tray to the metal placed on the second tray was adjusted to 91.7:8.3. In the second silicon-based active material, the weight of Mg was 8.3 wt % relative to the total weight of SiO and Mg. The second silicon-based active material had an average particle size (D 50 ) was 7 μm and contained 4 wt % of the carbon coating layer.

[0142] <Preparation of Slurry for First Negative Electrode Active Material Layer> The first carbon-based active material was artificial graphite (average particle size (D 50 ): 18 μm), the first silicon-based active material prepared as described above, styrene butadiene rubber (SBR) as a first binder, carboxymethyl cellulose (CMC) as a thickener, and single-walled carbon nanotubes (SWCNTs) as a first conductive material were mixed in a weight ratio of 86.1:9.6:3.0:1.0:0.3, and the mixture was added to water as a slurry solvent for a first negative electrode active material layer to prepare a slurry for a first negative electrode active material layer.

[0143] <Preparation of Slurry for Second Negative Electrode Active Material Layer> As the second carbon-based active material, artificial graphite (average particle size (D 50 ): 18 μm), the second silicon-based active material prepared as described above, styrene butadiene rubber (SBR) as a second binder, carboxymethyl cellulose (CMC) as a thickener, and single-walled carbon nanotubes (SWCNTs) as a second conductive material were mixed in a weight ratio of 86.1:9.6:3.0:1.0:0.3, and the mixture was added to water as a slurry solvent for the second negative electrode active material layer to prepare a slurry for the second negative electrode active material layer.

[0144] <Formation of First and Second Negative Electrode Active Material Layers> The slurry for the first negative electrode active material layer prepared as described above was coated on a copper foil (thickness: 6 μm) as a negative electrode current collector. At substantially the same time, the slurry for the second negative electrode active material layer prepared as described above was coated on the coated first negative electrode active material layer slurry, rolled, and dried in a vacuum oven at 130°C for 10 hours to prepare a negative electrode in which the negative electrode current collector, the first negative electrode active material layer, and the second negative electrode active material layer were sequentially stacked.

[0145] The weight ratio of the first binder in the first negative electrode active material layer (3 wt %, based on 100 wt % of the first negative electrode active material layer) to the weight ratio of the second binder in the second negative electrode active material layer (3 wt %, based on 100 wt % of the second negative electrode active material layer) was approximately 1:1.

[0146] The total weight of the first binder and the second binder was 3 wt % of the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0147] The loading capacity of the first negative electrode active material layer is 2.75 mAh / cm 2 The loading of the second negative electrode active material layer is 2.75 mAh / cm 2 the sum of the loading amounts of the first negative electrode active material layer and the second negative electrode active material layer is 5.5 mAh / cm 2 It was.

[0148] The first negative electrode active material layer had a thickness of 31.75 μm, the second negative electrode active material layer had a thickness of 31.75 μm, and the sum of the thicknesses of the first negative electrode active material layer and the second negative electrode active material layer was 63.5 μm.

[0149] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0150] 2. Secondary battery manufacturing As the positive electrode active material, LiCoO2 (average particle size (D 50): 16.5 μm), a conductive material made of a mixture of carbon black and multi-walled carbon nanotubes in a weight ratio of 1:0.5, and a binder made of polyvinylidene fluoride (PVdF) in a weight ratio of 96.0:1.5:1.5 were added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a cathode slurry to prepare a cathode slurry.

[0151] The positive electrode slurry was applied to an aluminum current collector (thickness: 10 μm) as a positive electrode current collector at a rate of 5.2 mAh / cm. 2 The coated film was rolled and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 63.5 μm) to prepare a positive electrode (thickness: 73.5 μm).

[0152] A polyethylene separator was placed between the negative electrode and the positive electrode prepared as described above, and an electrolyte was injected to prepare a secondary battery of Example 1. The electrolytes used were fluoroethylene carbonate (FEC), ethylene carbonate (EC), ethyl The organic solvent was mixed with propionate (EP) at a volume ratio of 20:20:60, to which vinylene carbonate was added at 3 wt %, and LiPF6 was added as a lithium salt at a concentration of 1 mol / L.

[0153] The N / P ratio of the secondary battery of Example 1 was 1.07.

[0154] Example 2: Production of negative electrode and secondary battery 1. Manufacturing the negative electrode <Preparation of Slurry for First Negative Electrode Active Material Layer> A slurry for a first negative electrode active material layer was prepared in the same manner as in Example 1, except that the first carbon-based active material, the first silicon-based active material, the first binder, the thickener, and the first conductive material were mixed in a weight ratio of 85.2:9.5:4.0:1.0:0.3.

[0155] <Preparation of Slurry for Second Negative Electrode Active Material Layer> A slurry for a second negative electrode active material layer was prepared in the same manner as in Example 1, except that the second carbon-based active material, the second silicon-based active material, the second binder, the thickener, and the second conductive material were mixed in a weight ratio of 87.0:9.7:2.0:1.0:0.3.

[0156] <Formation of First and Second Negative Electrode Active Material Layers> The slurry for the first negative electrode active material layer prepared as described above was coated on a copper foil (thickness: 6 μm) as a negative electrode current collector. At substantially the same time, the slurry for the second negative electrode active material layer prepared as described above was coated on the coated first negative electrode active material layer slurry, rolled, and dried in a vacuum oven at 130°C for 10 hours to prepare a negative electrode in which the negative electrode current collector, the first negative electrode active material layer, and the second negative electrode active material layer were sequentially stacked.

[0157] The weight ratio of the first binder in the first negative electrode active material layer (4 wt %, based on 100 wt % of the first negative electrode active material layer) to the weight ratio of the second binder in the second negative electrode active material layer (2 wt %, based on 100 wt % of the second negative electrode active material layer) was approximately 2:1.

[0158] The total weight of the first binder and the second binder was 3 wt % of the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0159] The loading capacity of the first negative electrode active material layer is 2.75 mAh / cm 2 The loading of the second negative electrode active material layer is 2.75 mAh / cm 2 the sum of the loading amounts of the first negative electrode active material layer and the second negative electrode active material layer is 5.5 mAh / cm 2 It was.

[0160] The first negative electrode active material layer had a thickness of 31.75 μm, the second negative electrode active material layer had a thickness of 31.75 μm, and the sum of the thicknesses of the first negative electrode active material layer and the second negative electrode active material layer was 63.5 μm.

[0161] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0162] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 1, except that the negative electrode manufactured as described above was used.

[0163] The N / P ratio of the secondary battery of Example 2 was 1.07.

[0164] Example 3: Production of negative electrode and secondary battery A second silicon-based active material was prepared in the same manner as in Example 2, except that the weight ratio of SiO placed on the first tray to the metal placed on the second tray was adjusted to 90.2:9.8. In the second silicon-based active material, the weight of Mg was 9.8 wt % relative to the total weight of SiO and Mg. The second silicon-based active material had an average particle size (D 50 ) is 7 μm and contains 4 wt % of the carbon coating layer.

[0165] A negative electrode and a secondary battery were manufactured in the same manner as in Example 2, except that the second silicon-based active material prepared as described above was used instead of the second silicon-based active material used in Example 2.

[0166] The loading capacity of the first negative electrode active material layer is 2.75 mAh / cm 2 The loading of the second negative electrode active material layer is 2.75 mAh / cm 2 the sum of the loading amounts of the first negative electrode active material layer and the second negative electrode active material layer is 5.5 mAh / cm 2 It was.

[0167] The first negative electrode active material layer had a thickness of 31.75 μm, the second negative electrode active material layer had a thickness of 31.75 μm, and the sum of the thicknesses of the first negative electrode active material layer and the second negative electrode active material layer was 63.5 μm.

[0168] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0169] The N / P ratio of the secondary battery of Example 3 was 1.07.

[0170] Example 4: Production of negative electrode and secondary battery A second silicon-based active material was prepared in the same manner as in Example 2, except that the weight ratio of SiO placed on the first tray and the metal placed on the second tray was adjusted to 94.2:5.8. In the second silicon-based active material, the weight of Mg was 5.8 wt % relative to the total weight of SiO and Mg. The second silicon-based active material had an average particle size (D 50 ) is 7 μm and contains 4 wt % of the carbon coating layer.

[0171] A negative electrode and a secondary battery were manufactured in the same manner as in Example 2, except that the second silicon-based active material prepared as described above was used instead of the second silicon-based active material used in Example 2.

[0172] The loading capacity of the first negative electrode active material layer is 2.75 mAh / cm 2 The loading of the second negative electrode active material layer is 2.75 mAh / cm 2 the sum of the loading amounts of the first negative electrode active material layer and the second negative electrode active material layer is 5.5 mAh / cm 2 It was.

[0173] The first negative electrode active material layer had a thickness of 31.75 μm, the second negative electrode active material layer had a thickness of 31.75 μm, and the sum of the thicknesses of the first negative electrode active material layer and the second negative electrode active material layer was 63.5 μm.

[0174] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0175] The N / P ratio of the secondary battery of Example 4 was 1.07.

[0176] Example 5: Production of negative electrode and secondary battery The first silicon-based active material was manufactured in the same manner as in Example 2, except that the weight ratio of SiO placed on the first tray and the metal placed on the second tray was adjusted to 79.6:20.4. In the first silicon-based active material, the weight of Mg was 20.4 wt % relative to the total weight of SiO and Mg. The first silicon-based active material had an average particle size (D 50 ) is 7 μm and contains 4 wt % of the carbon coating layer.

[0177] A negative electrode and a secondary battery were manufactured in the same manner as in Example 2, except that the first silicon-based active material prepared as described above was used instead of the first silicon-based active material used in Example 2.

[0178] The loading capacity of the first negative electrode active material layer is 2.75 mAh / cm 2 The loading of the second negative electrode active material layer is 2.75 mAh / cm 2 the sum of the loading amounts of the first negative electrode active material layer and the second negative electrode active material layer is 5.5 mAh / cm 2 It was.

[0179] The first negative electrode active material layer had a thickness of 31.75 μm, the second negative electrode active material layer had a thickness of 31.75 μm, and the sum of the thicknesses of the first negative electrode active material layer and the second negative electrode active material layer was 63.5 μm.

[0180] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0181] The N / P ratio of the secondary battery of Example 5 was 1.07.

[0182] Example 6: Production of negative electrode and secondary battery The first silicon-based active material was manufactured in the same manner as in Example 2, except that the weight ratio of SiO placed on the first tray and the metal placed on the second tray was adjusted to 89.7:10.3. In the first silicon-based active material, the weight of Mg was 10.3 wt % relative to the total weight of SiO and Mg. The first silicon-based active material had an average particle size (D 50 ) is 7 μm and contains 4 wt % of the carbon coating layer.

[0183] A negative electrode and a secondary battery were manufactured in the same manner as in Example 2, except that the first silicon-based active material prepared as described above was used instead of the first silicon-based active material used in Example 2.

[0184] The loading capacity of the first negative electrode active material layer is 2.75 mAh / cm 2 The loading of the second negative electrode active material layer is 2.75 mAh / cm 2 the sum of the loading amounts of the first negative electrode active material layer and the second negative electrode active material layer is 5.5 mAh / cm 2 It was.

[0185] The first negative electrode active material layer had a thickness of 31.75 μm, the second negative electrode active material layer had a thickness of 31.75 μm, and the sum of the thicknesses of the first negative electrode active material layer and the second negative electrode active material layer was 63.5 μm.

[0186] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0187] The N / P ratio of the secondary battery of Example 6 was 1.07.

[0188] Comparative Example 1: Production of negative electrode and secondary battery 1. Manufacturing the negative electrode A slurry for a negative electrode active material layer identical to the slurry for a second negative electrode active material layer prepared in Example 2 was prepared.

[0189] The negative electrode slurry was applied to a copper current collector (thickness: 6 μm) at a rate of 5.5 mAh / cm2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 63.5 µm), which was used as a negative electrode (electrode density: 1.7 g / cc).

[0190] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 1, except that the negative electrode prepared as described above was used instead of the negative electrode of Example 1.

[0191] The N / P ratio of the secondary battery of Comparative Example 1 was 1.07.

[0192] Comparative Example 2: Production of negative electrode and secondary battery 1. Manufacturing the negative electrode <Preparation of Slurry for First Negative Electrode Active Material Layer> A slurry for a first negative electrode active material layer was prepared in the same manner as in Example 2, except that the first carbon-based active material, the first silicon-based active material, the first binder, the thickener, and the first conductive material were mixed in a weight ratio of 87.0:9.7:2.0:1.0:0.3.

[0193] <Preparation of Slurry for Second Negative Electrode Active Material Layer> A slurry for a second negative electrode active material layer was prepared in the same manner as in Example 2, except that the second carbon-based active material, the second silicon-based active material, the second binder, the thickener, and the second conductive material were mixed in a weight ratio of 85.2:9.5:4.0:1.0:0.3.

[0194] <Formation of First and Second Negative Electrode Active Material Layers> The slurry for the first negative electrode active material layer prepared as described above was coated on a copper foil (thickness: 6 μm) as a negative electrode current collector. At substantially the same time, the slurry for the second negative electrode active material layer prepared as described above was coated on the coated first negative electrode active material layer slurry, rolled, and dried in a vacuum oven at 130°C for 10 hours to prepare a negative electrode in which the negative electrode current collector, the first negative electrode active material layer, and the second negative electrode active material layer were sequentially stacked.

[0195] The weight ratio of the first binder in the first negative electrode active material layer (2 wt %, based on 100 wt % of the first negative electrode active material layer) to the weight ratio of the second binder in the second negative electrode active material layer (4 wt %, based on 100 wt % of the second negative electrode active material layer) was approximately 0.5:1.

[0196] The total weight of the first binder and the second binder was 3 wt % of the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0197] The loading capacity of the first negative electrode active material layer is 2.75 mAh / cm 2 The loading of the second negative electrode active material layer is 2.75 mAh / cm 2 the sum of the loading amounts of the first negative electrode active material layer and the second negative electrode active material layer is 5.5 mAh / cm 2 It was.

[0198] The first negative electrode active material layer had a thickness of 31.75 μm, the second negative electrode active material layer had a thickness of 31.75 μm, and the sum of the thicknesses of the first negative electrode active material layer and the second negative electrode active material layer was 63.5 μm.

[0199] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0200] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 2, except that the negative electrode manufactured as described above was used.

[0201] The N / P ratio of the secondary battery of Comparative Example 2 was 1.07.

[0202] Comparative Example 3: Production of negative electrode and secondary battery 1. Manufacturing the negative electrode <Preparation of Slurry for First Negative Electrode Active Material Layer> A slurry for a first negative electrode active material layer was prepared in the same manner as in Example 2, except that the first carbon-based active material, the first silicon-based active material, the first binder, the thickener, and the first conductive material were mixed in a weight ratio of 84.0:9.3:5.4:1.0:0.3.

[0203] <Preparation of Slurry for Second Negative Electrode Active Material Layer> A slurry for a second negative electrode active material layer was prepared in the same manner as in Example 2, except that the second carbon-based active material, the second silicon-based active material, the second binder, the thickener, and the second conductive material were mixed in a weight ratio of 88.3:9.8:0.6:1.0:0.3.

[0204] <Formation of First and Second Negative Electrode Active Material Layers> The slurry for the first negative electrode active material layer prepared as described above was coated on a copper foil (thickness: 6 μm) as a negative electrode current collector. At substantially the same time, the slurry for the second negative electrode active material layer prepared as described above was coated on the coated first negative electrode active material layer slurry, rolled, and dried in a vacuum oven at 130°C for 10 hours to prepare a negative electrode in which the negative electrode current collector, the first negative electrode active material layer, and the second negative electrode active material layer were sequentially stacked.

[0205] The weight ratio of the first binder in the first negative electrode active material layer (5.4 wt %, based on 100 wt % of the first negative electrode active material layer) to the weight ratio of the second binder in the second negative electrode active material layer (0.6 wt %, based on 100 wt % of the second negative electrode active material layer) was approximately 9:1.

[0206] The total weight of the first binder and the second binder was 3 wt % of the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0207] The loading capacity of the first negative electrode active material layer is 2.75 mAh / cm 2 The loading of the second negative electrode active material layer is 2.75 mAh / cm 2 the sum of the loading amounts of the first negative electrode active material layer and the second negative electrode active material layer is 5.5 mAh / cm 2 It was.

[0208] The first negative electrode active material layer had a thickness of 31.75 μm, the second negative electrode active material layer had a thickness of 31.75 μm, and the sum of the thicknesses of the first negative electrode active material layer and the second negative electrode active material layer was 63.5 μm.

[0209] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0210] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 2, except that the negative electrode manufactured as described above was used.

[0211] The N / P ratio of the secondary battery of Comparative Example 3 was 1.07.

[0212] Comparative Example 4: Production of negative electrode and secondary battery 1. Manufacturing the negative electrode <Preparation of Slurry for First Negative Electrode Active Material Layer> A slurry for a first negative electrode active material layer was prepared in the same manner as in Example 2, except that the second silicon-based active material prepared in Example 2 was used instead of the first silicon-based active material prepared in Example 2.

[0213] <Preparation of Slurry for Second Negative Electrode Active Material Layer> A slurry for a second negative electrode active material layer was prepared in the same manner as in Example 2, except that the first silicon-based active material prepared in Example 2 was used instead of the second silicon-based active material prepared in Example 2.

[0214] <Formation of First and Second Negative Electrode Active Material Layers> The slurry for the first negative electrode active material layer prepared as described above was coated on a copper foil (thickness: 6 μm) as a negative electrode current collector. At substantially the same time, the slurry for the second negative electrode active material layer prepared as described above was coated on the coated first negative electrode active material layer slurry, rolled, and dried in a vacuum oven at 130°C for 10 hours to prepare a negative electrode in which the negative electrode current collector, the first negative electrode active material layer, and the second negative electrode active material layer were sequentially stacked.

[0215] The loading capacity of the first negative electrode active material layer is 2.75 mAh / cm 2 The loading of the second negative electrode active material layer is 2.75 mAh / cm 2 the sum of the loading amounts of the first negative electrode active material layer and the second negative electrode active material layer is 5.5 mAh / cm 2 It was.

[0216] The first negative electrode active material layer had a thickness of 31.75 μm, the second negative electrode active material layer had a thickness of 31.75 μm, and the sum of the thicknesses of the first negative electrode active material layer and the second negative electrode active material layer was 63.5 μm.

[0217] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0218] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 1, except that the negative electrode manufactured as described above was used.

[0219] The N / P ratio of the secondary battery of Comparative Example 4 was 1.07.

[0220] Experimental example Experimental example 1: Adhesion strength evaluation The negative electrode of Example 1 was punched out to a size of 2 cm x 7 cm to prepare a negative electrode sample. Next, the negative electrode sample was immersed in an electrolyte for 3 hours and washed with dimethyl carbonate. The electrolyte used here was an organic solvent containing fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethylene propionate (EP) mixed in a volume ratio of 20:20:60, to which 3 wt% vinylene carbonate had been added, and LiPF6 was added as a lithium salt at a concentration of 1 mol / L.

[0221] After attaching double-sided tape to a glass slide, the negative electrode sample was positioned so that the active material layer was in contact with the tape-attached surface and rubbed 10 times with a roller. Next, the sample was peeled off at a speed of 10 cm / min at a 90° angle using a peel tester, and the peel force (unit: gf / 20 mm) was measured.

[0222] The same experiment as above was carried out on the negative electrodes of Examples 2 to 6 and Comparative Examples 1 to 4. The results are shown in Table 1 below.

[0223] Experimental example 2: Life characteristics evaluation The secondary batteries produced in Examples 1 to 6 and Comparative Examples 1 to 4 were evaluated for cycle capacity retention using an electrochemical charger / discharger.

[0224] The measurement of the cycle capacity retention rate was carried out at a temperature of 25° C., and the charge / discharge conditions were as follows.

[0225] Charging conditions: CC / CV mode, 4.5V, 0.8C, 0.05C cut off Discharge conditions: CC mode, 0.5C, 3.2V cut off

[0226] The capacity retention rate was calculated as follows.

[0227] Capacity retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at first cycle)} × 100 In the above formula, N is an integer of 1 or more.

[0228] The capacity retention rate (%) at the 200th cycle is shown in Table 1 below.

[0229] [Table 1]

[0230] Referring to Table 1, it can be seen that the anodes and secondary batteries of Examples 1 to 6 exhibit superior adhesive strength and life performance compared to Comparative Examples 1 to 4 because the ratios of the first binder and the second binder are adjusted to preferred levels and the metal doping ratios of the first silicon-based active material and the second silicon-based active material are adjusted to preferred levels. [Explanation of symbols]

[0231] 10 negative electrode 100 Negative electrode current collector 210 First negative electrode active material layer 220 Second negative electrode active material layer

Claims

1. a negative electrode current collector; a first negative electrode active material layer disposed on the negative electrode current collector and including a first carbon-based active material, a first silicon-based active material, and a first binder; a second negative electrode active material layer disposed on the first negative electrode active material layer, the second negative electrode active material layer including a second carbon-based active material, a second silicon-based active material, and a second binder; The first silicon-based active material is SiO ｘ (0≦x<2) and a first metal doped into the first silicon-based compound, The second silicon-based active material is SiO ｙ (0≦y<2) and a second metal doped into the second silicon-based compound, a weight ratio of the first metal to the sum of the weights of the first silicon-based compound and the first metal is greater than a weight ratio of the second metal to the sum of the weights of the second silicon-based compound and the second metal; a ratio of a weight percentage of the first binder based on the weight of the first negative electrode active material layer to a weight percentage of the second binder based on the weight of the second negative electrode active material layer is 0.9:1 to 5.5:1; a weight of the first metal is 10% by weight to 25% by weight with respect to the total weight of the first silicon-based compound and the first metal; a weight of the second metal is 3 wt % or more and less than 10 wt % of the total weight of the second silicon-based compound and the second metal;

2. 2. The negative electrode according to claim 1, wherein the first metal and the second metal each independently comprise at least one metal selected from the group consisting of Li, Mg, Ca, and Al.

3. the first carbon-based active material and the first silicon-based active material are contained in the first negative electrode active material layer in an amount of 90 wt % to 99 wt %; 2. The negative electrode according to claim 1, wherein a weight ratio of the first carbon-based active material to the first silicon-based active material is 85:15 to 99:

1.

4. the second carbon-based active material and the second silicon-based active material are contained in the second negative electrode active material layer in an amount of 90 wt % to 99 wt %; 2. The negative electrode according to claim 1, wherein a weight ratio of the second carbon-based active material to the second silicon-based active material is 85:15 to 99:

1.

5. The negative electrode of claim 1 , wherein the first binder is contained in the first negative electrode active material layer in an amount of 1 wt % to 15 wt %.

6. The negative electrode of claim 1 , wherein the second binder is contained in the second negative electrode active material layer in an amount of 1 wt % to 15 wt %.

7. 2. The negative electrode according to claim 1, wherein a total weight of the first binder and the second binder is 1 wt % to 15 wt % of a total weight of the first negative electrode active material layer and the second negative electrode active material layer.

8. 2. The negative electrode according to claim 1, wherein the first binder and the second binder each independently comprise at least one selected from the group consisting of polyvinylidene fluoride, styrene butadiene rubber, acrylonitrile butadiene rubber, acrylic rubber, butyl rubber, fluororubber, polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polyacrylonitrile, and polyacrylamide.

9. The negative electrode according to claim 1 , wherein the first binder and the second binder comprise styrene butadiene rubber.

10. 2. The negative electrode according to claim 1, wherein a thickness ratio of the first negative electrode active material layer to the second negative electrode active material layer is 1:0.5 to 1:

2.

11. A negative electrode current collector; a first negative electrode active material layer disposed on the negative electrode current collector and including a first carbon-based active material, a first silicon-based active material, and a first binder; a second negative electrode active material layer disposed on the first negative electrode active material layer, the second negative electrode active material layer including a second carbon-based active material, a second silicon-based active material, and a second binder; the first silicon-based active material includes a first silicon-based compound represented by SiO x (0≦x<2) and a first metal doped into the first silicon-based compound; the second silicon-based active material includes a second silicon-based compound represented by SiO y (0≦y<2) and a second metal doped into the second silicon-based compound; a weight ratio of the first metal to the sum of the weights of the first silicon-based compound and the first metal is greater than a weight ratio of the second metal to the sum of the weights of the second silicon-based compound and the second metal; a ratio of a weight percentage of the first binder based on the weight of the first negative electrode active material layer to a weight percentage of the second binder based on the weight of the second negative electrode active material layer is 0.9:1 to 5.5:1; The sum of the loading amount of the first negative electrode active material layer and the loading amount of the second negative electrode active material layer is 4 mAh / cm ２ ~8mAh / cm ２ That is, the negative electrode.

12. The negative electrode according to any one of claims 1 to 11, a positive electrode facing the negative electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte.

13. the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, The secondary battery according to claim 12, wherein the positive electrode active material layer contains a positive electrode active material containing a lithium-cobalt-based oxide.

Images