Negative electrode and secondary battery including the same

Abstract

The present invention relates to a negative electrode 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 binder comprises styrene-butadiene rubber, and the second binder comprises a copolymer including acrylamide-derived units, acrylic acid-derived units, and acrylonitrile-derived units.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0144587, filed on October 27, 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] In recent years, with the rapid spread of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for small, lightweight, and relatively high-capacity secondary batteries has been rapidly increasing. In particular, lithium secondary batteries have been attracting attention as a driving power source for portable electronic devices due to their light weight and high energy density. Therefore, active research, development, and 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 containing 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 particular 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 can cause cracking or damage to the active material particles and reduce lifespan characteristics.

[0006] Furthermore, when used at high voltages, the silicon-based active materials are subject to serious problems such as volume expansion during charge and discharge, deterioration of 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 currently a demand for the development of anodes and secondary batteries using silicon-based active materials that have high energy density and long life characteristics when used at high voltages.

[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 resolving 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 has improved electrode adhesion, prevents the negative electrode from deteriorating due to thickness expansion during charge and discharge, and significantly improves the life performance.

[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 provides a negative electrode 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 binder comprises styrene-butadiene rubber, and the second binder comprises a copolymer including acrylamide-derived units, acrylic acid-derived units, and acrylonitrile-derived units.

[0013] The present invention also provides a secondary battery including 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. [Effects of the Invention]

[0014] The negative electrode of the present invention has a structure in which a negative electrode current collector, a first negative electrode active material layer, and a second negative electrode active material layer are laminated in this order, the first negative electrode active material layer including a first carbon-based active material, a first silicon-based active material, and a first binder, the second negative electrode active material layer including a second silicon-based active material and a second binder, the first binder including styrene-butadiene rubber, and the second binder including a copolymer including an acrylamide-derived unit, an acrylic acid-derived unit, and an acrylonitrile-derived unit. According to the anode of the present invention, the first anode active material layer (lower layer) contains a styrene-butadiene rubber as a first binder, which has low electrolyte absorption and improves adhesion even when impregnated with electrolyte, and the second anode active material layer contains a specific copolymer as a second binder, which has both excellent thickness control and flexibility. This provides excellent adhesion and thickness expansion control, thereby significantly improving the lifespan of anodes and secondary batteries containing carbon-based and silicon-based active materials. In particular, the anode of the present invention can achieve a significant improvement in lifespan when used in a high-voltage range or at high-loading anodes. [Brief explanation of the drawings]

[0015] [Figure 1]FIG. 2 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 in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0017] The terms used in this specification are used only 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] As used herein, the terms "comprises," "comprises," or "having" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the presence or possible addition of one or more other 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, for example, by the laser diffraction method. The laser diffraction method is generally capable of measuring 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, in which: Figure 1 is a schematic side view illustrating the negative electrode according to the present invention;

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

[0022] Referring to FIG. 1, an anode 10 of the present invention includes an anode current collector 100, a first anode active material layer 210 disposed on the anode current collector 100 and including a first carbon-based active material, a first silicon-based active material, and a first binder, and a second anode active material layer 220 disposed on the first anode 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 binder includes styrene-butadiene rubber, and the second binder includes a copolymer including an acrylamide-derived unit, an acrylic acid-derived unit, and an acrylonitrile-derived unit.

[0023] Conventionally, silicon-based active materials have the advantage of having higher capacity than carbon-based active materials, but 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 severe when the negative electrode is used at a high loading or in a high voltage range.

[0024] To solve this problem, the anode of the present invention has a structure in which a anode current collector, a first anode active material layer, and a second anode active material layer are laminated in this order, the first anode active material layer including a first carbon-based active material, a first silicon-based active material, and a first binder, the second anode active material layer including a second silicon-based active material and a second binder, the first binder including styrene-butadiene rubber, and the second binder including a copolymer including an acrylamide-derived unit, an acrylic acid-derived unit, and an acrylonitrile-derived unit. According to the anode of the present invention, the first anode active material layer (lower layer) contains a styrene-butadiene rubber as a first binder, which has low electrolyte absorption and improves adhesion even when impregnated with electrolyte, and the second anode active material layer contains a specific copolymer as a second binder, which has both excellent thickness control and flexibility. This provides excellent adhesion and thickness expansion control, thereby significantly improving the lifespan of anodes and secondary batteries containing carbon-based and silicon-based active materials. In particular, the anode of the present invention can achieve a significant improvement in lifespan when used in a high-voltage range or at high-loading anodes.

[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 μm to 500 μm.

[0027] The negative electrode current collector 100 may have fine irregularities on its surface to strengthen the binding strength of the negative electrode active material. For example, the negative electrode current collector 100 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] 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 is disposed on at least one surface of the negative electrode current collector, and more specifically, it may be disposed on one or both surfaces of the negative electrode current collector.

[0029] The first negative electrode active material layer 210 contains 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. Specifically, it may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0031] The average particle diameter (D 50 ) of the first carbon-based active material may be 5 μm to 35 μm, preferably 10 μm to 20 μm, from the viewpoint of achieving structural stability during charge and discharge and reducing side reactions with the electrolyte.

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

[0033] The first silicon-based active material may include a first silicon-based compound represented by SiO x (0 ≦ x < 2). The first silicon-based compound may be represented by the chemical formula of SiO x (0 ≦ x < 2), and specifically, it may be represented by the chemical formula of SiO x (0 < x < 2). On the other hand, when it is SiO2 (when x = 2), since it does not react with lithium ions, lithium cannot be stored. Therefore, it is preferable that x is within the above range. Specifically, the first silicon-based compound may be represented by the chemical formula of SiO x (0.5 ≦ x ≦ 1.5).

[0034] ​ More specifically, the first silicon-based active material is SiO x The battery may include a first silicon-based compound represented by (0≦x<2) and a first metal doped into the first silicon-based compound. Silicon-based active materials generally suffer from the problem of irreversible sites in the silicon-based active material causing an irreversible reaction in which some of the lithium that migrates to the negative electrode during initial charging does not return to the positive electrode during discharge. To prevent this problem, the first metal is introduced by doping the first silicon-based compound to reduce the irreversible phase of the first silicon-based compound and improve efficiency.

[0035] The first metal is doped into the first silicon-based compound. Specifically, the first metal may be doped into the first silicon-based compound and located inside, on the surface, or inside and on the surface of the first silicon-based compound. The first metal may be doped into the first silicon-based compound and form a metal silicate with silicon oxide contained in the first silicon-based compound.

[0036] 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 the silicon-based oxide particles, preventing damage, and improving initial efficiency.

[0037] The weight of the first metal may be 1 wt% to 30 wt%, specifically 5 wt% to 20 wt%, based on the total weight of the first silicon-based compound and the first metal. When the weight is within this range, the irreversible capacity of the first silicon-based active material can be sufficiently eliminated and a decrease in capacity due to excessive metal doping can be prevented. The content of the first metal can be measured by ICP-AES (inductively coupled plasma atomic emission spectroscopy).

[0038] The first 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 volume expansion of the first silicon-based active material and prevent side reactions with the electrolyte.

[0039] The carbon coating layer may be contained in the first silicon-based active material in an amount of 0.1 wt % to 10 wt %, preferably 3 wt % to 7 wt %, in the above range, which is preferable because the carbon coating layer can effectively control the volume expansion of the first silicon-based active material and prevent side reactions with the electrolyte.

[0040] The carbon coating layer may be an amorphous carbon coating layer. Specifically, the carbon coating layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0041] 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, to prevent the problem of excessive volume expansion / contraction due to excessively large particle size, and to prevent the problem of reduced initial efficiency due to excessively small particle size.

[0042] The first silicon-based active material may be included in the first negative electrode active material layer in an amount of 1 wt % to 20 wt %, specifically 3 wt % to 15 wt %, in order to reduce the effect of volume expansion of the first silicon-based active material and ensure sufficient capacity of the negative electrode.

[0043] When the first silicon-based active material contains the above-mentioned first silicon-based active material and the first metal, the method for manufacturing the first silicon-based active material is not particularly limited. Specifically, the first silicon-based active material is (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 ) may be added as an adjustment step.

[0044] The first carbon-based active material and the first silicon-based active material may be included in the first negative electrode active material layer 210 in an amount of 90% by weight to 99% 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. When the weight ratio is within the above range, the influence 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.

[0045] The first binder is contained in the first negative electrode active material layer 210 to bind the negative electrode current collector 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).

[0046] The first binder may contain styrene-butadiene rubber (SBR). Styrene-butadiene rubber has a low electrolyte absorption rate, and therefore can exhibit excellent adhesive strength even when the negative electrode and secondary battery are immersed in the electrolyte. Therefore, in the negative electrode according to the present invention, by including styrene-butadiene rubber in the first binder, the adhesive strength between the negative electrode current collector and the first negative electrode active material layer can be improved, and detachment of the electrode due to volume expansion of the negative electrode active material, particularly the silicon-based active material, contained in the first negative electrode active material layer can be prevented.

[0047] The average particle size (D 50) may be 150 nm to 550 nm, specifically 200 nm to 400 nm, more specifically 240 nm to 300 nm. When it is in the above range, the contact area between the first binder and the first carbon-based active material, the second silicon-based active material, and the negative electrode current collector can be increased to a suitable level, thereby further improving adhesive strength, preventing an excessive increase in the electrolyte absorption rate, and preventing thickness expansion of the negative electrode.

[0048] The first binder may be included in the first negative electrode active material layer 210 in an amount of 0.5 wt % to 15 wt %, specifically 2.5 wt % to 8.0 wt %, and more specifically 3.5 wt % to 4.5 wt %. This range is preferable in that sufficient adhesive strength is exhibited and a sudden increase in resistance due to the addition of an excessive amount of the first binder is prevented.

[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 is used to improve the conductivity of the first anode active material layer 210 and may be conductive without causing chemical changes. 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. Preferably, 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, in consideration of maintaining the conductive network of the first silicon-based active material.

[0051] The first conductive material may be included in the first negative electrode active material layer 210 at 0.001 wt % to 10 wt %, specifically 0.01 wt % to 1 wt %, in the above range, which is preferable in terms of improving the electrical conductivity of the surface of the first silicon-based active material, eliminating overvoltage during charging, and preventing disconnection of the conductive network due to volume expansion and contraction 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 has a thickness in the above range, it can have excellent adhesive strength and thickness expansion control performance, thereby improving the life performance to an excellent level.

[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 has a loading amount within the above range, it can have excellent adhesive strength and thickness expansion control performance, thereby improving the life performance 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. If the first negative electrode active material layer is disposed on one or both surfaces of the negative electrode current collector, correspondingly, the second negative electrode active material layer 220 can also be disposed on the first negative electrode active material layer 210 disposed on one or both surfaces 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. Specifically, it may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0059] The average particle diameter (D 50 ) of the second carbon-based active material may be 5 μm to 35 μm, preferably 10 μm to 20 μm, in order to achieve structural stability during charge and discharge and reduce side reactions with the electrolyte.

[0060] The second carbon-based active material may 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 may include a second silicon-based compound represented by SiO y (0 ≦ y < 2). The second silicon-based compound is represented by the chemical formula of SiO y (0 ≦ y < 2), and specifically, it may be represented by the chemical formula of SiO y (0 < y < 2). On the other hand, in the case of SiO2 (y = 2), since it does not react with lithium ions, lithium cannot be stored. Therefore, it is preferable that y is within the above range. Specifically, the second silicon-based compound may be represented by the chemical formula of SiO y (0.5 ≦ y ≦ 1.5).

[0062] More specifically, the second silicon-based active material is SiO y The semiconductor device may include a second silicon-based compound represented by (0≦y<2) and a second metal doped into the second silicon-based compound. The second metal is introduced to reduce the irreversible phase of the second silicon-based compound and improve efficiency by doping the second silicon-based compound.

[0063] The second metal is 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.

[0064] The second metal may include at least one metal selected from the group consisting of Li, Mg, Ca, and Al. Specifically, at least one metal selected from the group consisting of Li and Mg, more specifically Mg, may be included, since this can achieve excellent effects such as controlling the volume expansion of the silicon-based oxide particles, preventing damage, and improving initial efficiency.

[0065] The weight of the second metal may be 1 wt% to 30 wt%, specifically 5 wt% to 20 wt%, based on the total weight of the second silicon-based compound and the second metal. When the weight is within this range, the irreversible capacity of the second silicon-based active material can be sufficiently eliminated and a decrease in capacity due to excessive metal doping can be prevented. The content of the second metal can be measured by ICP-AES (inductively coupled plasma atomic emission spectroscopy).

[0066] 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 volume expansion of the second silicon-based active material and prevent side reactions with the electrolyte.

[0067] The carbon coating layer may be contained in the second silicon-based active material in an amount of 0.1 wt % to 10 wt %, preferably 3 wt % to 7 wt %, in the above range, which is preferable because the carbon coating layer can effectively control the volume expansion of the second silicon-based active material and prevent side reactions with the electrolyte.

[0068] The carbon coating layer may be an amorphous carbon coating layer. Specifically, the carbon coating layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0069] 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, to prevent the problem of excessive volume expansion / contraction due to excessively large particle size, and to prevent the problem of reduced initial efficiency due to excessively small particle size.

[0070] 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 %, in order to reduce the effect of volume expansion of the second silicon-based active material and ensure sufficient capacity of the negative electrode.

[0071] When the second silicon-based active material contains the above-mentioned second silicon-based active material and the second metal, the method for manufacturing the second silicon-based active material is not particularly limited. Specifically, the second silicon-based active material is (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) may be added as an adjustment step.

[0072] 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% by weight to 99% by weight, specifically 94% by weight to 98% by weight. 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 the above range, the influence 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.

[0073] The second binder is contained in the second negative electrode active material layer to bind the first negative electrode active material layer 210 and the second negative electrode active material layer 220 and to bind the negative electrode active materials (the second carbon-based active material and the second silicon-based active material).

[0074] The second binder may include a copolymer including an acrylamide-derived unit, an acrylic acid-derived unit, and an acrylonitrile-derived unit. According to the anode of the present invention, by including the second binder in the second anode active material layer, which has high rigidity (tensile strength), strong adhesive strength, and flexibility, structural changes in the anode due to volume expansion of the anode active material, particularly the silicon-based active material, can be minimized, and the charge / discharge characteristics of the electrode can be smoothly maintained.

[0075] Specifically, the acrylamide-derived units contained in the second binder have excellent potential resistance and electrolyte resistance. When thermally cured with the acrylic acid-derived units, they can increase the binder's cohesive strength through hydrogen bonding. Furthermore, they have excellent stiffness, which is advantageous for preventing electrode deformation. The acrylonitrile-derived units can adjust the degree of crosslinking, thereby mitigating brittleness due to the increased stiffness caused by the inclusion of the acrylamide-derived units and acrylic acid-derived units. Therefore, by including a copolymer having the above characteristics, the second binder can effectively control the thickness expansion of the upper layer (second negative electrode active material layer) while preventing negative electrode cracking due to the expansion of the negative electrode active material by adjusting the appropriate degree of crosslinking. If the copolymer does not contain any one of the acrylamide-derived units, acrylic acid-derived units, and acrylonitrile-derived units, the binder's adhesive strength or brittleness may be excessively increased, making it difficult to achieve the above-mentioned effects.

[0076] The acrylic acid-derived units may have at least a portion of the hydrogen atoms of the -OH groups substituted with Na or K, which is preferable in terms of increasing the solubility in a slurry solvent (e.g., water) and controlling the viscosity of the slurry. Specifically, the acrylic acid-derived units may have 1% to 40% of the hydrogen atoms of the -OH groups substituted with Na or K, based on the number of the -OH groups present.

[0077] Specifically, the second binder may include a copolymer containing 55% to 80% by weight of acrylamide-derived units, 10% to 30% by weight of acrylic acid-derived units, and 5% to 20% by weight of acrylonitrile-derived units. More specifically, the second binder may include a copolymer containing 65% to 72% by weight of acrylamide-derived units, 18% to 22% by weight of acrylic acid-derived units, and 7% to 15% by weight of acrylonitrile-derived units. The second binder may include a copolymer containing 67% to 72% by weight of acrylamide-derived units, 18% to 22% by weight of acrylic acid-derived units, and 7% to 13% by weight of acrylonitrile-derived units. A copolymer containing acrylamide-derived units, acrylic acid-derived units, and acrylonitrile-derived units in the above content ranges may further exhibit the effects of improving both adhesive strength and flexibility.

[0078] The glass transition temperature Tg of the copolymer contained in the second binder may be 50° C. to 180° C., specifically 120° C. to 160° C., and more specifically 128° C. to 133° C. When the glass transition temperature Tg is within the above range, the second negative electrode active material layer can be hardened by thermal crosslinking caused by thermal curing of the binder during the drying process in the manufacture of the negative electrode.

[0079] The glass transition temperature Tg can be measured using a DSC device, etc. Examples of such a DSC device include a DSC (DSC823, METTLER TOLEDO) device and a DSC (TA Instrument) device.

[0080] The second binder may be included in the second negative electrode active material layer 220 in an amount of 0.5 wt % to 15 wt %, specifically 0.7 wt % to 3.3 wt %, and more specifically 1.5 wt % to 2.5 wt %. This range is preferable in that it is possible to control the volume expansion of the negative electrode active material due to charge and discharge and to prevent the loss of the conductive network due to the volume expansion of the negative electrode active material.

[0081] 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.

[0082] The second conductive material is used to improve the conductivity of the second negative electrode active material layer and is preferably conductive without causing chemical changes. Specifically, the second 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. Preferably, the second conductive material may include at least one selected from single-walled carbon nanotubes and multi-walled carbon nanotubes, more specifically, single-walled carbon nanotubes, in consideration of maintaining the conductive network of the second silicon-based active material.

[0083] 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 %. This range is preferable in that it is possible to control the volume expansion of the negative electrode active material due to charge and discharge and to prevent the loss of the conductive network due to the volume expansion of the negative electrode active material.

[0084] 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 220 has a thickness in the above range, it can have excellent adhesive strength and thickness expansion control performance, thereby improving the life performance to an excellent level.

[0085] The loading 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 has a loading amount within the above range, it can have excellent adhesive strength and thickness expansion control performance, thereby improving the life performance to an excellent level.

[0086] In the present invention, the ratio of the weight percentage of the first binder to the weight of the first negative electrode active material layer 210 to the weight percentage of the second binder to the weight of the second negative electrode active material layer 220 may be 0.5:1 to 9:1, specifically 0.8:1 to 6:1, and more specifically 1.5:1 to 3:1. 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), which can reduce the adhesive strength of the entire negative electrode. However, when the ratio of the first binder and the second binder is adjusted within the above range, the adhesive strength of the entire negative electrode can be further improved.

[0087] The total weight of the first binder and the second binder may be 0.5 wt % to 15 wt %, specifically 1 wt % to 8 wt %, and more specifically 1.5 wt % to 5.0 wt %, based on 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 the above range, it is possible to realize a negative electrode having excellent capacity in addition to 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, which is preferable in terms of facilitating a slurry coating process during negative electrode fabrication, improving the adhesive strength of the negative electrode, controlling thickness expansion, and improving the overall charge / discharge performance of the negative electrode.

[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 cell thickness expansion control effect can be achieved, and a long life performance can be achieved.

[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 because it can improve the overall charge / discharge performance, adhesive strength, and thickness expansion control effect of the negative electrode.

[0091] The total electrode density of the first and second negative electrode active material layers 210 and 220 may be 1.4 g / cc 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 achieved 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, the negative electrode according to the present invention can be produced 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) to produce a slurry for the first negative electrode active material layer, 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) to produce a slurry for the second negative electrode active material layer, and then applying the resulting slurry to a negative electrode current collector. More specifically, the negative electrode according to the present invention can be produced by applying the slurry for the first negative electrode active material layer prepared above to a negative electrode current collector, rolling, and drying the slurry for the second negative electrode active material layer prepared above on the first negative electrode active material layer, rolling, and drying the slurry for the second negative electrode active material layer. On the other hand, the negative electrode according to the present invention can also be manufactured by applying the slurry for the first negative electrode active material layer to the negative electrode current collector and, substantially simultaneously, applying the slurry for the second negative electrode active material layer onto the applied slurry for the first negative electrode active material layer, 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 μm to 500 μm.

[0098] The positive electrode current collector may have a surface with fine irregularities to enhance the bonding strength of the positive electrode active material. For example, the positive 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.

[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 is a compound capable of reversible intercalation and deintercalation of lithium, and specifically may include 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)、LiMn 2-Z NiZ 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, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2, etc.), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni 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 the atomic fractions of the respective independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2 + q2 + r3 + s2 = 1, etc.), etc. may be mentioned, and any one or two or more of these compounds may be included. Among them, from the point 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 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 Mn 0.1 Co 0.1)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 higher. 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 ) may be 10 μm to 30 μm, specifically 15 μm to 20 μm, and within the above range is preferable from the viewpoints of achieving a high positive electrode energy density and preventing cracks and breakage of 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% by weight to 99% by weight, preferably 92% by weight to 98% by weight, in consideration of the positive electrode active material being able to exhibit sufficient capacity.

[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 assists in binding the active material and conductive material, etc., and in binding them to the current collector, and specifically may contain 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, and 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 is used to assist and improve the conductivity of the secondary battery, and is not particularly limited as long as it does not cause chemical changes and is conductive. Specifically, the conductive material may 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 order to improve conductivity, the conductive material may 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 in an amount of 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 may be 30 μm to 400 μm, 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 may be.

[0113] The positive electrode may be fabricated 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 NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a suitable viscosity when the positive electrode active material, and optionally a binder and a conductive material, are contained therein. For example, the solvent for forming the positive electrode slurry may be contained 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 may be 1.0 to 1.5, preferably 1.0 to 1.2.

[0116] [Mathematical 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 the above 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 life 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 a used negative electrode is prepared. A coin-shaped half-cell is fabricated including 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 a used positive electrode is prepared. A coin-shaped half-cell is fabricated including the positive electrode sample, a lithium metal counter electrode facing the positive 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 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 with low resistance to electrolyte ion movement and excellent electrolyte humidification capacity is preferred. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures 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 coated separator containing a ceramic component or a polymeric material can also be used, and it can be selectively 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 manufacturing 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 is not particularly limited as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specific examples of the organic solvent that may be used include ester-based solvents such as methyl acetate, ethyl acetate, gamma-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 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 can provide excellent electrolyte performance.

[0124] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2 may be used. 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 the above 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 can 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-described secondary battery.

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

[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 the battery pack.

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

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

[0133] In the above mathematical 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 above mathematical formula 2, the V max may be 4.4V to 4.6V, specifically 4.40V to 4.55V, and min may be 2.8 V to 3.3 V, specifically 3.0 V to 3.3 V. According to the present invention, a high life performance of the secondary battery can be exhibited even when used at a high voltage. max , V min This makes it possible to realize a battery system with excellent life performance.

[0135] Although the present invention may be embodied in various different forms, it is not intended to be limited to the embodiments set forth herein, and the present invention is not limited to the embodiments set forth herein.

[0136] [Example] Example 1: Production of negative electrode and secondary battery 1. Manufacturing the negative electrode <Preparation of First Silicon-Based Active Material and Second Silicon-Based Active Material> A silicon-based active material was prepared by doping Mg into SiO and having a carbon coating layer on the surface. 50 The carbon coating layer was contained in the silicon-based active material at 4 wt % and Mg was doped in the silicon-based active material at 9 wt %.

[0137] The silicon-based active material was used as a first silicon-based active material and a second silicon-based active material, which will be described later.

[0138] <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, styrene butadiene rubber (SBR) as a first binder (average particle size (D 50 ) 215 nm), 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 added to water, which was a slurry solvent for the first negative electrode active material layer, to prepare a slurry for the first negative electrode active material layer.

[0139] In this case, the single-walled carbon nanotubes (SWCNTs) were added in the form of a dispersion to a slurry solvent for the first negative electrode active material layer.

[0140] <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, a copolymer containing 70 wt % of acrylamide-derived units, 20 wt % of acrylic acid-derived units, and 10 wt % of acrylonitrile-derived units as a second binder, and single-walled carbon nanotubes (SWCNTs) as a second conductive material were mixed in a weight ratio of 87.0:9.7:3.0:0.3 and added to water as a slurry solvent for a second negative electrode active material layer to prepare a slurry for a second negative electrode active material layer.

[0141] In this case, the single-walled carbon nanotubes (SWCNTs) were added in the form of a dispersion to a slurry solvent for the second negative electrode active material layer.

[0142] The glass transition temperature Tg of the copolymer used as the second binder was 130°C.

[0143] In addition, the acrylic acid-derived units contained in the copolymer were those in which 30% of the hydrogen atoms of the -OH groups present were substituted with Na.

[0144] <Formation of First and Second Negative Electrode Active Material Layers> The slurry for the first negative electrode active material layer prepared above was applied to a copper foil (thickness: 6 μm) serving as a negative electrode current collector, and substantially simultaneously, the slurry for the second negative electrode active material layer prepared above was applied onto the applied slurry for the first negative electrode active material layer, followed by roll pressing and drying in a vacuum oven at 130°C for 10 hours, thereby producing 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 % based on 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 was 2.72 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 5.47 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 The cathode slurry was prepared by adding a mixture of carbon black and multi-walled carbon nanotubes (1:0.5 weight ratio) as a conductive material and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 96:1.5:1.5 to N-methyl-2-pyrrolidone (NMP), a solvent for forming the cathode slurry.

[0151] The positive electrode slurry was applied to an aluminum current collector (thickness: 10 μm) as a positive electrode current collector at 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), thereby producing a positive electrode (thickness: 73.5 μm).

[0152] A polyethylene separator was interposed between the negative electrode and positive electrode prepared as described above, and an electrolyte was injected to prepare a secondary battery of Example 1. The electrolyte used was an organic solvent made by mixing fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethylene propionate (EP) in a volume ratio of 20:20:60, to which 3 wt% vinylene carbonate was added, 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 produced 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, and the second conductive material were mixed in a weight ratio of 87.9:9.8:2.0:0.3.

[0156] <Formation of First and Second Negative Electrode Active Material Layers> The slurry for the first negative electrode active material layer prepared above was applied to a copper foil (thickness: 6 μm) serving as a negative electrode current collector, and substantially simultaneously, the slurry for the second negative electrode active material layer prepared above was applied onto the applied slurry for the first negative electrode active material layer, followed by roll pressing and drying in a vacuum oven at 130°C for 10 hours, thereby producing 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 about 2:1.

[0158] The total weight of the first binder and the second binder was 3 wt % based on 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 was 2.69 mAh / cm 2 The loading of the second negative electrode active material layer is 2.78 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 5.47 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 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 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 84.3:9.4:5.0:1.0:0.3.

[0165] <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, and the second conductive material were mixed in a weight ratio of 88.8:9.9:1.0:0.3.

[0166] <Formation of First and Second Negative Electrode Active Material Layers> The slurry for the first negative electrode active material layer prepared above was applied to a copper foil (thickness: 6 μm) serving as a negative electrode current collector, and substantially simultaneously, the slurry for the second negative electrode active material layer prepared above was applied onto the applied slurry for the first negative electrode active material layer, followed by roll pressing and drying in a vacuum oven at 130°C for 10 hours, thereby producing 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.

[0167] The weight ratio of the first binder in the first negative electrode active material layer (5 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 (1 wt %, based on 100 wt % of the second negative electrode active material layer) was about 5:1.

[0168] The total weight of the first binder and the second binder was 3 wt % based on the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0169] The loading capacity of the first negative electrode active material layer is 2.66 mAh / cm 2 The loading capacity of the second negative electrode active material layer was 2.81 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 5.47 mAh / cm 2 It was.

[0170] 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.

[0171] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0172] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 1, except that the negative electrode manufactured above was used.

[0173] The N / P ratio of the secondary battery of Example 3 was 1.07.

[0174] 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 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 86.7:9.6:2.4:1.0:0.3.

[0175] <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, and the second conductive material were mixed in a weight ratio of 86.5:9.6:3.6:0.3.

[0176] <Formation of First and Second Negative Electrode Active Material Layers> The slurry for the first negative electrode active material layer prepared above was applied to a copper foil (thickness: 6 μm) serving as a negative electrode current collector, and substantially simultaneously, the slurry for the second negative electrode active material layer prepared above was applied onto the applied slurry for the first negative electrode active material layer, followed by roll pressing and drying in a vacuum oven at 130°C for 10 hours, thereby producing 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.

[0177] The weight ratio of the first binder in the first negative electrode active material layer (2.4 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 (3.6 wt %, based on 100 wt % of the second negative electrode active material layer) was about 0.67:1.

[0178] The total weight of the first binder and the second binder was 3.0 wt % based on the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0179] The loading capacity of the first negative electrode active material layer was 2.74 mAh / cm 2 The loading of the second negative electrode active material layer is 2.73 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 5.47 mAh / cm 2 It was.

[0180] 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.

[0181] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0182] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 1, except that the negative electrode manufactured above was used.

[0183] The N / P ratio of the secondary battery of Example 4 was 1.07.

[0184] Example 5: Production of negative electrode and secondary battery 1. Manufacturing the negative electrode <Preparation of Slurry for First Negative Electrode Active Material Layer> The average particle size (D 50 A slurry for a first negative electrode active material layer was prepared in the same manner as in Example 2, except that the thickness of the first negative electrode active material layer was adjusted to 180 nm.

[0185] <Preparation of Slurry for Second Negative Electrode Active Material Layer> A slurry for a second negative electrode active material layer was produced in the same manner as in Example 2.

[0186] <Formation of First and Second Negative Electrode Active Material Layers> A negative electrode was manufactured in the same manner as in Example 2, except that the first negative electrode active material layer slurry and the second negative electrode active material layer slurry prepared above were used.

[0187] 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 about 2:1.

[0188] The total weight of the first binder and the second binder was 3 wt % based on the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0189] The loading capacity of the first negative electrode active material layer was 2.69 mAh / cm 2 The loading of the second negative electrode active material layer is 2.78 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 5.47 mAh / cm 2 It was.

[0190] 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.

[0191] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0192] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 2, except that the negative electrode manufactured above was used.

[0193] The N / P ratio of the secondary battery of Example 5 was 1.07.

[0194] Example 6: Production of negative electrode and secondary battery 1. Manufacturing the negative electrode <Preparation of Slurry for First Negative Electrode Active Material Layer> The average particle size (D 50 A slurry for a first negative electrode active material layer was prepared in the same manner as in Example 2, except that the thickness of the first negative electrode active material layer was adjusted to 270 nm.

[0195] <Preparation of Slurry for Second Negative Electrode Active Material Layer> A slurry for a second negative electrode active material layer was produced in the same manner as in Example 2.

[0196] <Formation of First and Second Negative Electrode Active Material Layers> A negative electrode was manufactured in the same manner as in Example 2, except that the first negative electrode active material layer slurry and the second negative electrode active material layer slurry prepared above were used.

[0197] 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 about 2:1.

[0198] The total weight of the first binder and the second binder was 3 wt % based on the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0199] The loading capacity of the first negative electrode active material layer was 2.69 mAh / cm 2 The loading of the second negative electrode active material layer is 2.78 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 5.47 mAh / cm 2 It was.

[0200] 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.

[0201] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0202] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 2, except that the negative electrode manufactured above was used.

[0203] The N / P ratio of the secondary battery of Example 6 was 1.07.

[0204] Example 7: Production of negative electrode and secondary battery 1. Manufacturing the negative electrode <Preparation of Slurry for First Negative Electrode Active Material Layer> The average particle size (D 50 A slurry for a first negative electrode active material layer was prepared in the same manner as in Example 2, except that the thickness of the first negative electrode active material layer was adjusted to 500 nm.

[0205] <Preparation of Slurry for Second Negative Electrode Active Material Layer> A slurry for a second negative electrode active material layer was produced in the same manner as in Example 2.

[0206] <Formation of First and Second Negative Electrode Active Material Layers> A negative electrode was manufactured in the same manner as in Example 2, except that the first negative electrode active material layer slurry and the second negative electrode active material layer slurry prepared above were used.

[0207] 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 about 2:1.

[0208] The total weight of the first binder and the second binder was 3 wt % based on the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0209] The loading capacity of the first negative electrode active material layer was 2.69 mAh / cm 2 The loading of the second negative electrode active material layer is 2.78 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 5.47 mAh / cm 2 It was.

[0210] 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.

[0211] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0212] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 2, except that the negative electrode manufactured above was used.

[0213] The N / P ratio of the secondary battery of Example 7 was 1.07.

[0214] Example 8: Production of negative electrode and secondary battery <Preparation of Slurry for First Negative Electrode Active Material Layer> A slurry for the first negative electrode active material layer was produced in the same manner as in Example 2.

[0215] <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 a copolymer (glass transition temperature Tg: 124°C) containing 60% by weight of acrylamide-derived units, 25% by weight of acrylic acid-derived units, and 15% by weight of acrylonitrile-derived units was used as the second binder.

[0216] <Formation of First and Second Negative Electrode Active Material Layers> A negative electrode was manufactured in the same manner as in Example 2, except that the first negative electrode active material layer slurry and the second negative electrode active material layer slurry prepared above were used.

[0217] 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 about 2:1.

[0218] The total weight of the first binder and the second binder was 3 wt % based on the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0219] The loading capacity of the first negative electrode active material layer was 2.69 mAh / cm 2 The loading of the second negative electrode active material layer is 2.78 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 5.47 mAh / cm 2 It was.

[0220] 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.

[0221] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0222] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 2, except that the negative electrode manufactured above was used.

[0223] The N / P ratio of the secondary battery of Example 8 was 1.07.

[0224] Example 9: Production of negative electrode and secondary battery <Preparation of Slurry for First Negative Electrode Active Material Layer> A slurry for the first negative electrode active material layer was produced in the same manner as in Example 2.

[0225] <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 a copolymer (glass transition temperature Tg: 138°C) containing 75% by weight of acrylamide-derived units, 15% by weight of acrylic acid-derived units, and 10% by weight of acrylonitrile-derived units was used as the second binder.

[0226] <Formation of First and Second Negative Electrode Active Material Layers> A negative electrode was manufactured in the same manner as in Example 2, except that the first negative electrode active material layer slurry and the second negative electrode active material layer slurry prepared above were used.

[0227] 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 about 2:1.

[0228] The total weight of the first binder and the second binder was 3 wt % based on the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0229] The loading capacity of the first negative electrode active material layer was 2.69 mAh / cm 2 The loading of the second negative electrode active material layer is 2.78 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 5.47 mAh / cm 2 It was.

[0230] 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.

[0231] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0232] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 2, except that the negative electrode manufactured above was used.

[0233] The N / P ratio of the secondary battery of Example 9 was 1.07.

[0234] Example 10: Production of negative electrode and secondary battery <Preparation of Slurry for First Negative Electrode Active Material Layer> A slurry for the first negative electrode active material layer was produced in the same manner as in Example 2.

[0235] <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 a copolymer (glass transition temperature Tg: 128°C) containing 65 wt% acrylamide-derived units, 20 wt% acrylic acid-derived units, and 15 wt% acrylonitrile-derived units was used as the second binder.

[0236] <Formation of First and Second Negative Electrode Active Material Layers> A negative electrode was manufactured in the same manner as in Example 2, except that the first negative electrode active material layer slurry and the second negative electrode active material layer slurry prepared above were used.

[0237] 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 about 2:1.

[0238] The total weight of the first binder and the second binder was 3 wt % based on the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0239] The loading capacity of the first negative electrode active material layer was 2.69 mAh / cm 2 The loading of the second negative electrode active material layer is 2.78 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 5.47 mAh / cm 2 It was.

[0240] 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.

[0241] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0242] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 2, except that the negative electrode manufactured above was used.

[0243] The N / P ratio of the secondary battery of Example 10 was 1.07.

[0244] Comparative Example 1: Production of negative electrode and secondary battery 1. Manufacturing the negative electrode As a carbon-based active material, artificial graphite (average particle size (D 50 ): 18 μm), the same silicon-based active material as the second silicon-based active material of Example 1, the same binder as the second binder of Example 1, and single-walled carbon nanotubes (SWCNTs) as a conductive material were mixed in a weight ratio of 86.1:9.6:4.0:0.3, and the mixture was added to water, which was a slurry solvent for the negative electrode active material layer, to prepare a slurry for the negative electrode active material layer.

[0245] The negative electrode slurry was applied to a copper current collector (thickness: 6 μm) as a negative electrode current collector at a current rate of 5.47 mAh / cm 2 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 (negative electrode thickness: 69.5 μm, electrode density: 1.7 g / cc).

[0246] 2. Secondary battery manufacturing A secondary battery was produced in the same manner as in Example 1, except that the negative electrode produced above was used instead of the negative electrode of Example 1.

[0247] The N / P ratio of the secondary battery of Comparative Example 1 was 1.07.

[0248] Comparative Example 2: Production of negative electrode and secondary battery 1. Manufacturing the negative electrode As a carbon-based active material, artificial graphite (average particle size (D 50 ): 18 μm), the same silicon-based active material as the second silicon-based active material of Example 1, a binder obtained by mixing the first binder and the second binder of Example 1 in a weight ratio of 2:2, carboxymethyl cellulose as a thickener, and single-walled carbon nanotubes (SWCNTs) as a conductive material in a weight ratio of 86.1:9.6:4.0:0.3, and the mixture was added to water as a slurry solvent for the negative electrode active material layer to prepare a slurry for the negative electrode active material layer.

[0249] The negative electrode slurry was applied to a copper current collector (thickness: 6 μm) as a negative electrode current collector at a current rate of 5.47 mAh / cm 2The 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 (negative electrode thickness: 69.5 μm, electrode density: 1.7 g / cc).

[0250] 2. Secondary battery manufacturing A secondary battery was produced in the same manner as in Example 1, except that the negative electrode produced above was used instead of the negative electrode of Example 1.

[0251] The N / P ratio of the secondary battery of Comparative Example 2 was 1.07.

[0252] 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> The first carbon-based active material was artificial graphite (average particle size (D 50 ):18 μm), the same silicon-based active material as the first silicon-based active material of Example 1, a copolymer containing 70 wt % of acrylamide-derived units, 20 wt % of acrylic acid-derived units, and 10 wt % of acrylonitrile-derived units as a first binder, and single-walled carbon nanotubes (SWCNTs) as a first conductive material were mixed in a weight ratio of 85.7:9.5:4.5:0.3 and 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.

[0253] <Preparation of Slurry for Second Negative Electrode Active Material Layer> As the second carbon-based active material, artificial graphite (average particle size (D 50 The silicon-based active material was the same as the second silicon-based active material in Example 1, and styrene-butadiene rubber (average particle size (D 50 ):215 nm), carboxymethyl cellulose (CMC) as a thickener, and single-walled carbon nanotubes (SWCNTs) as a second conductive material were mixed in a weight ratio of 87.5:9.7:1.5:1.0:0.3 and added to water, which was a slurry solvent for the second negative electrode active material layer, to prepare a slurry for the second negative electrode active material layer.

[0254] <Formation of First and Second Negative Electrode Active Material Layers> The slurry for the first negative electrode active material layer prepared above was applied to a copper foil (thickness: 6 μm) serving as a negative electrode current collector, and substantially simultaneously, the slurry for the second negative electrode active material layer prepared above was applied onto the applied slurry for the first negative electrode active material layer, followed by roll pressing and drying in a vacuum oven at 130°C for 10 hours, thereby producing 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.

[0255] The weight ratio of the first binder in the first negative electrode active material layer (4.5 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 (1.5 wt %, based on 100 wt % of the second negative electrode active material layer) was about 3:1.

[0256] The total weight of the first binder and the second binder was 3.0 wt % based on the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0257] The loading capacity of the first negative electrode active material layer was 2.71 mAh / cm 2 The loading of the second negative electrode active material layer is 2.76 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 5.47 mAh / cm 2 It was.

[0258] 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.

[0259] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0260] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 1, except that the negative electrode manufactured above was used.

[0261] The N / P ratio of the secondary battery of Comparative Example 3 was 1.07.

[0262] 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 the first negative electrode active material layer was produced in the same manner as in Example 2.

[0263] <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 a mixture of polyvinyl alcohol (PVA) and polyacrylic acid (PAA) in a weight ratio of 7:3 was used as the second binder.

[0264] <Formation of First and Second Negative Electrode Active Material Layers> A negative electrode was manufactured in the same manner as in Example 2, except that the first negative electrode active material layer slurry and the second negative electrode active material layer slurry prepared above were used.

[0265] 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 about 2:1.

[0266] The total weight of the first binder and the second binder was 3 wt % based on the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0267] The loading capacity of the first negative electrode active material layer was 2.69 mAh / cm 2 The loading of the second negative electrode active material layer is 2.78 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 5.47 mAh / cm2 It was.

[0268] 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.

[0269] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0270] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 2, except that the negative electrode manufactured above was used.

[0271] The N / P ratio of the secondary battery of Comparative Example 4 was 1.07.

[0272] Comparative Example 5: 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 the first negative electrode active material layer was produced in the same manner as in Example 2.

[0273] <Preparation of Slurry for Second Negative Electrode Active Material Layer> A slurry for a second negative electrode active material layer was produced in the same manner as in Example 2, except that a copolymer (polyacrylamide) containing 100% by weight of acrylamide-derived units was used as the second binder.

[0274] <Formation of First and Second Negative Electrode Active Material Layers> A negative electrode was manufactured in the same manner as in Example 2, except that the first negative electrode active material layer slurry and the second negative electrode active material layer slurry prepared above were used.

[0275] 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 about 2:1.

[0276] The total weight of the first binder and the second binder was 3 wt % based on the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0277] The loading capacity of the first negative electrode active material layer was 2.69 mAh / cm 2 The loading of the second negative electrode active material layer is 2.78 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 5.47 mAh / cm 2 It was.

[0278] 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.

[0279] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0280] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 2, except that the negative electrode manufactured above was used.

[0281] The N / P ratio of the secondary battery of Comparative Example 5 was 1.07.

[0282] Comparative Example 6: 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 the first negative electrode active material layer was produced in the same manner as in Example 2.

[0283] <Preparation of Slurry for Second Negative Electrode Active Material Layer> A slurry for a second negative electrode active material layer was produced in the same manner as in Example 2, except that a copolymer containing 70% by weight of acrylamide-derived units and 30% by weight of acrylic acid-derived units was used as the second binder.

[0284] <Formation of First and Second Negative Electrode Active Material Layers> A negative electrode was manufactured in the same manner as in Example 2, except that the first negative electrode active material layer slurry and the second negative electrode active material layer slurry prepared above were used.

[0285] 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 about 2:1.

[0286] The total weight of the first binder and the second binder was 3 wt % based on the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0287] The loading capacity of the first negative electrode active material layer was 2.69 mAh / cm 2 The loading of the second negative electrode active material layer is 2.78 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 5.47 mAh / cm 2 It was.

[0288] 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.

[0289] The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0290] 2. Secondary battery manufacturing A secondary battery was manufactured in the same manner as in Example 2, except that the negative electrode manufactured above was used.

[0291] The N / P ratio of the secondary battery of Comparative Example 6 was 1.07.

[0292] [Experimental Example] [Experimental Example 1: Evaluation of Adhesion Strength] The negative electrode of Example 1 was punched out to a size of 2 cm x 7 cm to prepare a negative electrode sample. The negative electrode sample was then immersed in an electrolyte for 3 hours and washed with dimethyl carbonate. The electrolyte used 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 to which LiPF6 was added as a lithium salt at a concentration of 1 mol / L.

[0293] After attaching double-sided tape to a glass slide, the negative electrode sample was placed so that the active material layer was in contact with the tape-attached surface and rubbed 10 times with a roller. Then, 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.

[0294] Experiments were carried out in the same manner as above on the negative electrodes of Examples 2 to 10 and Comparative Examples 1 to 6. The results are shown in Table 1 below.

[0295] [Experimental Example 2: Evaluation of life characteristics] The secondary batteries produced in Examples 1 to 10 and Comparative Examples 1 to 6 were evaluated for cycle capacity retention using an electrochemical charger / discharger.

[0296] The cycle capacity retention rate was measured at 25°C under the following charge and discharge conditions:

[0297] Charging conditions: CC / CV mode, 4.5V, 0.8C, 0.05C cutoff. Discharge conditions: CC mode, 0.5C, 3.2V cutoff.

[0298] The capacity retention rate was calculated as follows.

[0299] Capacity retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at 1st cycle)} × 100 (In the above formula, N is an integer of 1 or more.)

[0300] The capacity retention rate (%) at the 200th cycle is shown in Table 1 below.

[0301] [Table 1]

[0302] Referring to Table 1, it can be seen that the negative electrodes and secondary batteries of Examples 1 to 10 have significantly improved electrode adhesion and life performance compared to the comparative examples by disposing the first binder and second binder according to the present invention in the first negative electrode active material layer and the second negative electrode active material layer, respectively. [Explanation of symbols]

[0303] 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 as a binder; the first binder is a styrene-butadiene rubber; the second binder is a copolymer consisting of 55% by weight to 80% by weight of acrylamide-derived units, 10% by weight to 30% by weight of acrylic acid-derived units, and 5% by weight to 20% by weight of acrylonitrile-derived units.

2. 2. The negative electrode of claim 1, wherein a ratio of a weight percentage of the first binder to a weight percentage of the second binder to a weight percentage of the second negative electrode active material layer is 0.5:1 to 9:

1.

3. The negative electrode of claim 1 , wherein the first binder is included in the first negative electrode active material layer in an amount of 0.5 wt % to 15 wt %.

4. The negative electrode of claim 1 , wherein the second binder is included in the second negative electrode active material layer in an amount of 0.5 wt % to 15 wt %.

5. 2. The negative electrode of claim 1, wherein a total weight of the first binder and the second binder is 0.5 wt % to 15 wt % based on a total weight of the first negative electrode active material layer and the second negative electrode active material layer.

6. 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.

7. 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 83:17 to 99:

1.

8. 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 83:17 to 99:

1.

9. The first silicon-based active material is SiO ｘ (0≦x<2) and a first metal doped into the first silicon-based compound, 2. The negative electrode according to claim 1, wherein the first metal comprises at least one metal selected from the group consisting of Li, Mg, Ca, and Al.

10. The second silicon-based active material is SiO ｙ (0≦y<2) and a second metal doped into the second silicon-based compound, 2. The negative electrode according to claim 1, wherein the second metal comprises at least one metal selected from the group consisting of Li, Mg, Ca, and Al.

11. 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 The negative electrode according to claim 1 ,

12. 2. The negative electrode of claim 1, wherein a ratio of a loading amount of the first negative electrode active material layer to a loading amount of the second negative electrode active material layer is 1:0.5 to 1:

2.

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

14. 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 13 , wherein the positive electrode active material layer contains a positive electrode active material containing a lithium-cobalt-based oxide.

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