Negative electrode for secondary battery and lithium secondary battery comprising same

Abstract

A negative electrode for a secondary battery according to one embodiment may include: a negative electrode current collector; a first negative electrode mixture layer formed on at least one surface of the negative electrode current collector and including a first silicon-based active material; and a second negative electrode mixture layer formed on the first negative electrode mixture layer and including a second silicon-based active material, in which the first silicon-based active material may include composite particles including silicon, the second silicon-based active material may include a silicon oxide (SiOx, 0lt; xlt; and 2) the content of the second silicon-based active material contained by taking the total weight of the second negative electrode mixture layer as the reference can be greater than or equal to the content of the first silicon-based active material contained by taking the total weight of the first negative electrode mixture layer as the reference.

Description

Negative electrode for secondary batteries and lithium secondary batteries including the negative electrode Technical Field

[0001] This invention relates to a negative electrode for a secondary battery and a lithium secondary battery including the negative electrode. Background Technology

[0002] In recent years, extensive research has been conducted on electric vehicles (EVs), which are fossil fuel-powered vehicles such as gasoline and diesel vehicles, which can replace one of the main causes of air pollution. These EVs primarily use lithium-ion batteries with high discharge voltage and power stability as their power source. Therefore, the demand for high-energy-density lithium-ion batteries is constantly increasing, and the development and research of high-capacity negative electrodes for these batteries are also actively underway.

[0003] To achieve high-capacity and high-energy-density rechargeable batteries, active research is underway to develop technologies that utilize silicon-based active materials (approximately 1500 mAh / g), with a discharge capacity far exceeding that of graphite (approximately 350 mAh / g), in the anode of rechargeable batteries. When silicon-based active materials with such high discharge capacity are used together with carbon-based active materials such as graphite, the load weight (LW) of the anode mixture layer can be reduced, thereby enabling the fabrication of anodes with excellent energy density and fast-charging characteristics.

[0004] However, silicon-based active materials shrink / expand much more during charging / discharging than carbon-based active materials. Therefore, silicon particles between the active materials in the negative electrode mixture layer are more prone to cracking, leading to a relative decrease in lifespan and other characteristics. Thus, there is a need to develop a negative electrode for rechargeable batteries with superior capacity, fast charging, and lifespan characteristics. Summary of the Invention

[0005] (a) Technical problem to be solved One aspect of the present invention is to provide a negative electrode for a secondary battery and a lithium secondary battery with excellent fast charging life characteristics.

[0006] Another aspect of the present invention is to provide a negative electrode for a secondary battery and a lithium secondary battery with excellent room temperature life characteristics.

[0007] Another aspect of the present invention is to provide a negative electrode for a secondary battery with excellent energy density and a lithium secondary battery.

[0008] Another aspect of the present invention is to provide a negative electrode for a secondary battery and a lithium secondary battery with excellent capacity characteristics.

[0009] Another aspect of the present invention is to provide a negative electrode for a secondary battery and a lithium secondary battery with excellent resistance characteristics.

[0010] (2) Technical Solution The negative electrode for a secondary battery according to a specific embodiment of the present invention may include: a negative electrode current collector; a first negative electrode mixture layer formed on at least one surface of the negative electrode current collector and containing a first silicon-based active material; and a second negative electrode mixture layer formed on the first negative electrode mixture layer and containing a second silicon-based active material, where the first silicon-based active material may include composite particles containing silicon, and the second silicon-based active material may contain silicon oxide (SiO x , 0 < x < 2). The content of the second silicon-based active material based on the total weight of the second negative electrode mixture layer may be greater than or equal to the content of the first silicon-based active material based on the total weight of the first negative electrode mixture layer.

[0011] The composite particles containing silicon may include carbon-based particles and a silicon-containing coating formed on the surface of the carbon-based particles.

[0012] Based on the total weight of the first negative electrode mixture layer, the content of the first silicon-based active material may be 0.01 - 20% by weight.

[0013] Based on the total weight of the second negative electrode mixture layer, the content of the second silicon-based active material may be 0.01 - 30% by weight.

[0014] The first negative electrode mixture layer may further include a first carbon-based active material, and the second negative electrode mixture layer may further include a second carbon-based active material.

[0015] The OI value of the second carbon-based active material according to the following formula 1 may be less than or equal to the OI value of the first carbon-based active material.

[0016] [Formula 1] OI = I 004 / I 110 In the formula 1, OI is the crystal orientation index measured by XRD, I 004 is the peak intensity of the (004) plane in the XRD measurement of the carbon-based active material, and I 110 is the peak intensity of the (110) plane in the XRD measurement of the carbon-based active material.

[0017] The OI value of the first carbon-based active material may be 1 to 10, and the OI value of the second carbon-based active material may be 1 to 3.

[0018] The thickness of the second negative electrode mixture layer may be greater than or equal to the thickness of the first negative electrode mixture layer.

[0019] The thickness ratio of the first negative electrode mixture layer to the second negative electrode mixture layer may be 1:9 to 5:5.

[0020] The first negative electrode mixture layer and the second negative electrode mixture layer may further contain an adhesive.

[0021] The adhesive may include at least one selected from styrene-butadiene rubber (SBR), fluoropolymer rubber, ethylene propylene rubber, butyl acrylate rubber, butadiene rubber, isoprene rubber, acrylonitrile rubber, acrylic rubber, silane rubber, carboxymethyl cellulose (CMC), hydroxypropyl methylcellulose, methylcellulose, polyacrylic acid (PAA) based adhesive, polyvinyl alcohol (PVA) based adhesive, and polyvinyl alcohol-polyacrylic acid copolymer (PVA-PAA Copolymer) based adhesive.

[0022] Another specific embodiment of the lithium secondary battery of the present invention may include: a positive electrode; the negative electrode for the secondary battery described above; and a separator disposed between the positive electrode and the negative electrode.

[0023] (III) Beneficial Effects One aspect of the present invention can provide a negative electrode for a secondary battery and a lithium secondary battery with excellent fast-charging life characteristics.

[0024] Another aspect of the present invention can provide a negative electrode for a secondary battery and a lithium secondary battery with excellent room temperature life characteristics.

[0025] Another aspect of the present invention can provide a negative electrode for a secondary battery with excellent energy density and a lithium secondary battery.

[0026] Another aspect of the present invention can provide a negative electrode for a secondary battery and a lithium secondary battery with excellent capacity characteristics.

[0027] Another aspect of the present invention can provide a negative electrode for a secondary battery and a lithium secondary battery with excellent resistance characteristics.

[0028] Another aspect of the present invention provides a multilayer negative electrode for a secondary battery and a lithium secondary battery including the negative electrode. By appropriately adjusting the composition of each electrode mixture layer, a negative electrode for a secondary battery and a lithium secondary battery with excellent capacity characteristics, resistance characteristics, etc., can be provided. Attached Figure Description

[0029] Figure 1 is a schematic cross-sectional view showing the structure of a negative electrode for a secondary battery according to a specific embodiment.

[0030] Figure 2 is a conceptual diagram showing the basal planes (Basal Planes) and the edge planes (Edge Planes) formed by the aggregation of the edges of the basal planes in a carbon-based active material with a parallel stacked structure. Detailed Implementation

[0031] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. However, this is merely exemplary, and the present invention is not limited to the specific embodiments described exemplarily.

[0032] In the present invention, the "orientation" of the active material refers to the property represented by the "crystallographic orientation index (Orientation Index; OI)" value determined by the peak intensity ratio, and the peak intensity ratio is based on the peak intensity (I 004 ) of the (004) plane and the peak intensity (I 110 ) of the (110) plane measured by XRD. Exemplarily, the smaller the OI value of the active material, the lower the orientation of the active material with small orientation, and the larger the OI value, the higher the orientation of the active material with large orientation.

[0033] Negative electrode 100 for secondary battery Hereinafter, the negative electrode according to the present invention will be described more specifically with reference to the accompanying drawings. Fig. 1 is a cross-sectional view schematically showing the structure of a negative electrode for a secondary battery according to a specific embodiment of the present invention. As shown in Fig. 1, the negative electrode 100 according to the present invention may include: a negative electrode current collector 10; a first negative electrode mixture layer 21 formed on at least one surface of the negative electrode current collector 10 and containing a first silicon-based active material; and a second negative electrode mixture layer 22 formed on the first negative electrode mixture layer and containing a second silicon-based active material, wherein the first silicon-based active material may include composite particles containing silicon, and the second silicon-based active material may contain silicon oxide (SiO x , 0 < x < 2), and the content of the second silicon-based active material contained based on the total weight of the second negative electrode mixture layer may be greater than or equal to the content of the first silicon-based active material contained based on the total weight of the first negative electrode mixture layer.

[0034] Non-limiting examples of the negative electrode current collector 10 may include copper foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper, a polymer substrate coated with a conductive metal, etc. The thickness of the negative electrode current collector is not particularly limited, and for example, it may be 10 - 50 μm.

[0035] The composite particles containing silicon may include carbon-based particles and a silicon-containing coating formed on the surface of the carbon-based particles.

[0036] The composite particles containing silicon may contain silicon (Si). For example, the cross-section of the carbon-based particles may also randomly deform from a circle. In addition, the silicon-containing coating may be partially formed on the pores and surface of the carbon-based particles, or may be formed as a plurality of discontinuous islands or patterns.

[0037] The composite particles may include carbon-based particles having a plurality of pores and a silicon-containing coating.

[0038] According to some implementation schemes, the volume expansion of silicon contained in the silicon-based coating can be mitigated through the porosity of the carbon-based particles. Therefore, while utilizing the relatively high capacity characteristics of silicon, cracking caused by the difference between the volume expansion rate of carbon during charging and discharging (e.g., less than about 150 vol%) and the volume expansion rate of silicon (e.g., more than about 400 vol%) can be prevented. Thus, gas generation caused by side reactions between the negative electrode active material and the electrolyte can be suppressed, and the lifespan characteristics of the secondary battery can be improved.

[0039] The pores of carbon-based particles can include a shape that bends inward from the outermost part of the carbon-based particle towards the interior of the carbon-based particle. For example, pores can include holes (open pores) that are open to the outside of the carbon-based particle.

[0040] The terms "surface of carbon-based particles" and / or "surface of carbon-based particles" as used in this invention can refer to the outer surface of carbon-based particles, the inner surface of pores, or both the outer surface of carbon-based particles and the inner surface of pores. The inner surface of pores refers to the surface of the pores that bend into the interior of the carbon-based particles.

[0041] For example, a silicon-containing coating can be formed on at least a portion of the outer surface of carbon-based particles.

[0042] For example, a silicon-containing coating can be formed on at least a portion of the inner surface of the pores of carbon-based particles.

[0043] For example, a silicon-containing coating can be formed on at least a portion of the outer surface of carbon-based particles and at least a portion of the inner surface of the pores.

[0044] In some implementations, carbon-based particles may include activated carbon, carbon nanotubes, carbon nanowires, graphene, carbon fibers, carbon black, graphite, porous carbon, cryogel, xerogel, aerogel, etc. These can be used alone or in combination of two or more.

[0045] In some embodiments, the aforementioned carbon-based particles may include an amorphous or crystalline structure.

[0046] In some embodiments, the pore size of the carbon-based particles can be 0.1 nm to 20 nm, 0.5 nm to 15 nm, or 1 nm to 10 nm. Within these ranges, excessive silicon deposition can be prevented, and the formation of cracks in the negative electrode active material during the charging and discharging process of the secondary battery can be further suppressed.

[0047] The size of the pores can refer to the diameter of the pore inlet formed on the surface of the carbon-based particles.

[0048] Compared with existing silicon oxide-based active materials, the silicon-containing composite particles can have high-capacity and low-resistance characteristics. In addition, in the silicon-containing composite particles, silicon exists in the porous carbon structure, so the phenomenon of electrode cracking caused by the volume expansion of the active material containing silicon-based oxide can be alleviated, and conductivity can be ensured. By applying the first negative electrode mixture layer 21 containing the silicon-containing composite particles to the side of the negative electrode current collector 10, the resistance generated between the negative electrode current collector 10 and the negative electrode mixture layer 20 can be minimized, which can achieve effects beneficial to battery performance such as fast charging.

[0049] In addition, in addition to the silicon-containing composite particles, the first negative electrode mixture layer 21 may further contain at least one silicon-based active material selected from silicon oxide-based active materials represented by chemical formulas of SiO x (0 < x < 2), metal-doped silicon oxide-based active materials, carbon-coated silicon oxide-based active materials, etc.

[0050] Based on the total weight of the first negative electrode mixture layer 21, the content of the first silicon-based active material may be 0.01-20% by weight, specifically 4-16% by weight, and more specifically 6-12% by weight. By including the first silicon-based active material within the above range, the resistance generated between the negative electrode current collector 10 and the negative electrode mixture layer 20 can be minimized, and effects beneficial to battery performance such as fast charging can be achieved.

[0051] The second negative electrode mixture layer 22 may contain a second silicon-based active material, and the second silicon-based active material may be a silicon oxide-based active material represented by a chemical formula of SiO x (0 < x < 2).

[0052] For the silicon oxide-based active material represented by the chemical formula of SiO x (0 < x < 2), the smaller the x value, the higher the battery capacity and the lower the battery life. The larger the x value, the lower the battery capacity, so there is a problem of reduced energy density of the electrode. Therefore, in one specific embodiment, by providing the x value of the silicon oxide-based active material represented by the chemical formula within the above range, the energy density can be ensured while ensuring the battery capacity. x

[0053] In addition, in addition to the silicon oxide-based active material, the second negative electrode mixture layer 21 may further contain at least one silicon-based active material selected from silicon-containing composite particles, metal-doped silicon oxide-based active materials, carbon-coated silicon oxide-based active materials, etc.

[0054] Based on the total weight of the second negative electrode mixture layer 22, the content of the second silicon-based active material can be 0.01-30% by weight, specifically 5-25% by weight, and more specifically 10-20% by weight. When the content of the second silicon-based active material is within the above range, the fast charging characteristics of the negative electrode for secondary batteries can be maintained at an excellent level, while increasing the content of silicon-based active material based on the overall negative electrode can further improve the capacity characteristics.

[0055] The first silicon-based active material and the second silicon-based active material may each include a carbon coating formed on the silicon-based active material particles. Therefore, contact between the first silicon-based active material and the second silicon-based active material particles and moisture in the atmosphere and / or water in the negative electrode slurry can be prevented, thereby suppressing the reduction of the discharge capacity of the secondary battery.

[0056] For example, the carbon coating may include at least one selected from amorphous carbon, carbon nanotubes, carbon nanofibers, graphite, graphene, graphene oxide, and reduced graphene oxide.

[0057] For example, at least one of the first silicon-based active material and the second silicon-based active material may be provided with the carbon coating on its outermost periphery.

[0058] The content of the second silicon-based active material contained in the second negative electrode mixture layer 22, based on the total weight, can be greater than or equal to the content of the first silicon-based active material contained in the first negative electrode mixture layer 21, based on the total weight. When the content of silicon-based active material contained in the second negative electrode mixture layer (upper layer), which is adjacent to an electrolyte containing a large number of lithium ions, is relatively high, the silicon-based active material, which has a relatively slow lithium ion diffusion rate, comes into contact with a large number of lithium ions, thereby facilitating the entry and exit of lithium ions. Therefore, while maintaining the fast-charging characteristics of the negative electrode for secondary batteries at an excellent level, the content of silicon-based active material based on the overall negative electrode for secondary batteries can be increased, thereby further improving the capacity characteristics.

[0059] The weight ratio of the content of the first silicon-based active material in the first negative electrode mixture layer 21 to the content of the second silicon-based active material in the second negative electrode mixture layer 22 can be from 1:99 to 50:50. Specifically, the weight ratio of the content of the silicon-based active material in the first negative electrode mixture layer 21 to the content of the silicon-based active material in the second negative electrode mixture layer 22 can be from 1:99 to 30:70.

[0060] When the content and ratio of the respective silicon-based active materials contained in the first negative electrode mixture layer 21 and the second negative electrode mixture layer 22 are within the aforementioned range, by adjusting the content of silicon-based active materials in the first negative electrode mixture layer (lower layer) formed on the side adjacent to the negative electrode current collector to a relatively low level, problems such as the shedding of the mixture layer due to volume expansion can be alleviated, and lifetime characteristics can be improved. Furthermore, in the second negative electrode mixture layer (upper layer), by adjusting the content of silicon-based active materials, whose lithium-ion diffusion rate is lower than that of carbon-based active materials, to a relatively high level, high capacity characteristics and fast charging characteristics of the electrode can be ensured.

[0061] The first negative electrode mixture layer 21 and the second negative electrode mixture layer 22 included in the negative electrode mixture layer 20 may further contain a first carbon-based active material and a second carbon-based active material, respectively. The crystal orientation index (OI) and other properties of the carbon-based active materials contained in the negative electrode mixture layer 20 will be described in more detail below.

[0062] The crystal orientation index (OI) is the peak intensity (I004) that appears on the (004) plane when the active material is measured by XRD. 004 ) and the peak intensity (I) appearing on the (110) plane 110 The ratio of I to OI refers to the crystal orientation index (OI) value. Specifically, I... 004 It can be the peak intensity value of the (004) plane appearing at an angle of 2θ = 54.7 ± 0.2° when XRD measurements of active materials are performed using CuKα lines. 110 It can be the peak intensity value of the (110) plane appearing at an angle of 2θ = 77.5 ± 0.2° when XRD measurements of active substances are performed using CuKα lines. Typically, the peak intensity value refers to the peak height or the integrated area of ​​the peak. 004 and the I 110 It can be calculated using the integral area of ​​the peak.

[0063] Additionally, Figure 2 is a conceptual illustration of the base surface (base plane) and the edge surface formed by the aggregation of the edges of the base surfaces in a carbon-based active material having a parallel stacked structure. Referring to Figure 2, a carbon-based active material 1, such as artificial graphite, typically comprises a carbon layer consisting of hexagonal rings of six carbon atoms connected in a plane, the carbon layers being stacked parallel to each other. In this carbon-based active material, the base surface 2 corresponds to the base surface in the carbon layer having a parallel stacked structure, and the edge surface 3 is a surface formed by the aggregation of the edges of the base surface.

[0064] During the charging / discharging process of a secondary battery, the intercalation and deintercalation of lithium ions in the carbon-based active material are mainly achieved through the edge facets 3. Therefore, as the number of these edge facets 3 increases, the intercalation and deintercalation of lithium ions during charging becomes easier, and the fast charging characteristics can also be improved.

[0065] Furthermore, during battery charging, carbon-based active materials primarily expand along their orientation direction. The more highly oriented the carbon-based active material, the more concentrated the expansion in a single direction, potentially resulting in a relatively high expansion rate. Conversely, the less oriented and less oriented carbon-based active materials expand in an unbiased direction, potentially resulting in a relatively low expansion rate.

[0066] Relatedly, the crystal orientation index (OI) value determined by XRD measurement of the carbon-based active material refers to the peak intensity relative to the (004) plane of the (110) plane. As the OI value of the carbon-based active material decreases, the disorder of the crystal arrangement increases, and the carbon-based active material has a structure in which the number of edge faces 3 into which lithium ions can enter and exit is greater than the number of basal faces 2. Therefore, the carbon-based active material can be a low-orientation carbon-based active material with a near-spherical morphology and a non-uniform orientation direction during charging. On the other hand, as the OI value of the carbon-based active material increases, the disorder of the crystal arrangement decreases, and the carbon-based active material has a structure in which the number of basal faces 2 is greater than the number of edge faces 3. Therefore, the carbon-based active material can be a high-orientation carbon-based active material with a uniform orientation direction and a wide plate-like morphology.

[0067] Therefore, the lower the orientation index (OI) of the carbon-based active material in the negative electrode, the easier it is for lithium ions to enter and exit through many edge faces, thus exhibiting excellent fast charging characteristics. Furthermore, the active material's orientation is unbiased, and it can contain a large number of sites that act as buffers during charging / discharging, effectively mitigating the expansion of the active material and resulting in superior lifespan characteristics.

[0068] However, as orientation decreases, the hardness of carbon-based active materials increases, making it practically difficult to roll low-orientation carbon-based active materials into high-density anodes. Therefore, it is difficult to increase the rolling density of anodes containing low-orientation carbon-based active materials, thus limiting the manufacture of high-energy-density anodes for secondary batteries.

[0069] On the other hand, highly oriented carbon-based active materials with relatively large OI values ​​have relatively low hardness and can be rolled into high density, which can help to manufacture anodes with high energy density.

[0070] Therefore, the negative electrode 100 for a secondary battery according to a specific embodiment has a multilayer structure. By including carbon-based active materials with different orientations in each layer in an appropriate distribution, it can have excellent fast charging characteristics and energy density.

[0071] Specifically, the OI value of the second carbon-based active material according to Formula 1 can be less than or equal to the OI value of the first carbon-based active material.

[0072] [Equation 1] OI=I 004 / I 110 In Equation 1, OI is the crystal orientation index measured by XRD, and I... 004 It is the peak intensity of the (004) plane in the XRD measurement of carbon-based active materials, I 110 It is the peak intensity of the (110) plane in the XRD measurement of carbon-based active materials.

[0073] More specifically, the first negative electrode mixture layer 21, which is the lower layer, can contain a large amount of highly oriented first carbon-based active material with a relatively high crystal orientation index (OI) value, while the second negative electrode mixture layer 22, which is the upper layer, can contain a large amount of low-oriented second carbon-based active material with a relatively low crystal orientation index (OI) value.

[0074] That is, the content of the first carbon-based active material in the first negative electrode mixture layer 21 can be greater than the content of the first carbon-based active material in the second negative electrode mixture layer 22, and the content of the second carbon-based active material in the first negative electrode mixture layer 21 can be less than the content of the second carbon-based active material in the second negative electrode mixture layer 22.

[0075] Relatedly, according to one specific embodiment, the first negative electrode mixture layer 21 may contain only a first carbon-based active material as the carbon-based active material, and the second negative electrode mixture layer 22 may contain only a second carbon-based active material as the carbon-based active material. According to another specific embodiment, the first negative electrode mixture layer 21 and the second negative electrode mixture layer 22 may each contain both a first carbon-based active material and a second carbon-based active material. In this case, the content of the first carbon-based active material in the first negative electrode mixture layer 21 may be greater than or equal to the content of the second carbon-based active material, and the content of the first carbon-based active material in the first negative electrode mixture layer 21 may be greater than the content of the first carbon-based active material in the second negative electrode mixture layer 22. Furthermore, the content of the second carbon-based active material in the second negative electrode mixture layer 22 may be greater than or equal to the content of the first carbon-based active material, and the content of the second carbon-based active material in the second negative electrode mixture layer 22 may be greater than the content of the second carbon-based active material in the first negative electrode mixture layer 21.

[0076] The negative electrode 100 for the secondary battery contains a large amount of low-orientation second carbon-based active material in the upper second negative electrode mixture layer 22, which makes it easy for lithium ions to enter / exit / release in the negative electrode mixture layer adjacent to the negative electrode current collector, thereby ensuring excellent fast charging characteristics and alleviating the expansion of the active material, thereby helping to suppress electrical short circuits between the negative electrode current collector and the negative electrode mixture layer.

[0077] Furthermore, the first negative electrode mixture layer 21, which is the lower layer, contains a highly oriented first carbon-based active material that can be rolled into a high density, thus helping to ensure a high energy density.

[0078] The OI value of the first carbon-based active material can be from 1 to 10, and the OI value of the second carbon-based active material can be from 1 to 3. Specifically, the OI value of the first carbon-based active material of the negative electrode for the secondary battery can be from 2 to 8, and the OI value of the second carbon-based active material can be from 1.5 to 3.

[0079] When the crystal orientation index (OI) values ​​of the first carbon-based active material and the second carbon-based active material are within the above-mentioned ranges, in the multilayer structure of the negative electrode, the orientation, hardness, etc. of the carbon-based active materials contained in each mixture layer can be appropriately adjusted within different ranges, thereby achieving excellent fast charging characteristics and energy density of the negative electrode.

[0080] The first and second carbon-based active materials are not particularly limited as long as they meet the aforementioned OI values, etc. For example, the first and second carbon-based active materials may be one or more carbon-based active materials selected from artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, acetylene black, Ketjen black, Super P, graphene, and fibrous carbon. Specifically, considering the ease of adjusting the orientation of the active materials, the first and second carbon-based active materials may each contain artificial graphite.

[0081] The content of the first carbon-based active material in the first negative electrode mixture layer 21 can be 80-95% by weight. In addition, the content of the second carbon-based active material in the second negative electrode mixture layer 22 can be 70-90% by weight.

[0082] The thickness of the second negative electrode mixture layer 22 can be greater than or equal to the thickness of the first negative electrode mixture layer 21. Specifically, the thickness ratio of the first negative electrode mixture layer to the second negative electrode mixture layer can be from 1:9 to 5:5.

[0083] In addition to the porous silicon-based active material and the first carbon-based active material, the first negative electrode mixture layer 21 may also contain a negative electrode binder, conductive material and / or dispersion material.

[0084] In addition to the silicon-based active material coated with magnesium and the second carbon-based active material, the second negative electrode mixture layer 22 may be mixed with negative electrode binder, conductive material and / or dispersion material, etc.

[0085] The adhesive is a compound that serves to firmly bond the components within the negative electrode mixture layer 20 to each other and to firmly bond the negative electrode mixture layer 20 to the current collector. For example, it may be a rubber-based adhesive selected from at least one of styrene-butadiene rubber (SBR), fluoropolymer rubber, ethylene propylene rubber, butyl acrylate rubber, butadiene rubber, isoprene rubber, acrylonitrile rubber, acrylic rubber, and silane rubber; a cellulose-based adhesive such as carboxymethyl cellulose (CMC), hydroxypropyl methylcellulose, methylcellulose, or their alkali metal salts; or a water-soluble polymer-based adhesive such as polyacrylic acid (PAA)-based adhesive, polyvinyl alcohol (PVA)-based adhesive, or polyvinyl alcohol-polyacrylic acid copolymer-based adhesive. Specifically, the first negative electrode mixture layer 21 and the second negative electrode mixture layer 22 may further comprise a rubber-based adhesive. More specifically, the first negative electrode mixture layer 21 and the second negative electrode mixture layer 22 may independently comprise a rubber-based adhesive and a cellulose-based adhesive, respectively.

[0086] The content of the binder in the first negative electrode mixture layer 21 can be greater than or equal to the content of the binder in the second negative electrode mixture layer 22. Specifically, the ratio of the content of the binder in the first negative electrode mixture layer 21 to the content of the binder in the second negative electrode mixture layer 22 can be from 9:1 to 5:5. More specifically, the ratio of the content of the binder in the first negative electrode mixture layer 21 to the content of the binder in the second negative electrode mixture layer 22 can be from 8.5:1.5 to 7:3.

[0087] When the amount of adhesive is too low, the adhesion of the first negative electrode mixture layer 21 adjacent to the current collector decreases, which may lead to problems such as scrap and layer detachment during the cutting process. On the other hand, when the amount of adhesive in the overall negative electrode is too high, it may increase resistance and reduce battery characteristics. Therefore, by adjusting the amount of adhesive in the lower first negative electrode mixture layer 21 to a relatively high level, the above problems can be substantially alleviated while reducing the amount of adhesive in the overall negative electrode, thereby mitigating the increase in resistance.

[0088] The adhesive content in the first negative electrode mixture layer 21 can be 2.0-5.0% by weight. Furthermore, the adhesive content in the second negative electrode mixture layer 22 can be 0.1-2.0% by weight. Specifically, the adhesive content in the first negative electrode mixture layer 21 can be 2.0-3.0% by weight, and the adhesive content in the second negative electrode mixture layer 22 can be 0.3-0.7% by weight.

[0089] When the binder content in each negative electrode mixture layer is within the above range, the multilayer electrode structure can have excellent flexibility and adhesion, thereby substantially alleviating problems such as electrode detachment or cracking during charging / discharging, and ensuring low resistance characteristics.

[0090] The conductive material is used to impart conductivity to the electrode and maintain its structure, and it can be a conductive material that does not undergo side reactions with other components of the secondary battery and is conductive. Examples include graphite such as natural or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, and carbon fiber; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these materials can be used alone or in a mixture of two or more. Specifically, the conductive material may contain carbon nanotubes (CNTs). Compared to existing conductive materials such as carbon black, carbon nanotubes (CNTs) have high electron mobility, thus achieving high energy density even with small amounts, high strength due to their stable structure, and can substantially alleviate the volume expansion of silicon-based active materials. Therefore, when the conductive material contains carbon nanotubes (CNTs), the electrode can have superior energy density, lifetime characteristics, and resistance characteristics.

[0091] The load weight (LW) ratio of the first negative electrode mixture layer 21 to the second negative electrode mixture layer 22 can be from 2:8 to 8:2. Furthermore, the load weight of the first negative electrode mixture layer 21 can be 1.5-9.5 mg / cm³. 2 The loading weight of the second negative electrode mixture layer 22 can be 1.5-9.5 mg / cm³. 2 .

[0092] The load weight (LW) refers to the amount of negative electrode mixture layer formed on the current collector, i.e., a layer containing active materials, binders, conductive materials, etc., formed on the current collector, expressed as the weight per unit area. Here, the area is based on the area of ​​the current collector, and the weight is based on the weight of the entire negative electrode mixture layer formed.

[0093] When the load weight (LW) value and ratio of the first negative electrode mixture layer 21 and the second negative electrode mixture layer 22 are within the above range, a multilayer negative electrode with excellent capacity characteristics, lifetime characteristics, and fast charging characteristics can be provided.

[0094] The method for manufacturing the negative electrode for the above-mentioned secondary battery is not particularly limited, and can be carried out by a "double coating" process in which the upper and lower slurries are coated sequentially; or by a "simultaneous coating" process in which the upper and lower slurries are coated simultaneously. For example, the "double coating" process can be carried out by coating a first negative electrode slurry containing a first solvent, a first carbon-based active material, a silicon-based active material, a binder and a conductive material onto a current collector by means of rod coating, casting or spraying, and drying it at 70-100°C to form a first negative electrode mixture layer 21, and then coating a second negative electrode slurry containing a second solvent, a second carbon-based active material, a silicon-based active material, a binder and a conductive material onto the first negative electrode mixture layer 21 by means of rod coating, casting or spraying, and drying it at 70-100°C.

[0095] The solvent can be, for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. The amount of solvent used can be determined by considering the coating thickness and manufacturing yield of the composition for forming the negative electrode mixture layer to dissolve or disperse the active material, conductive material, and binder. When subsequently coated to form the negative electrode mixture layer, the solvent only needs to have a viscosity that can exhibit excellent thickness uniformity.

[0096] A lithium secondary battery, according to one specific embodiment, may include a positive electrode, a negative electrode for the secondary battery, and a separator disposed between the positive electrode and the negative electrode. The negative electrode may be any of the negative electrodes for the secondary battery described in the above-described embodiments.

[0097] The positive electrode may include a positive electrode current collector and a positive electrode mixture layer disposed on at least one side of the positive electrode current collector. The positive electrode current collector may include stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive electrode current collector may also include a material used to surface-treat aluminum or stainless steel with carbon, nickel, titanium, or silver. The thickness of the positive electrode current collector is not limited thereto, and may be, for example, 10-50 μm.

[0098] The positive electrode mixture layer may contain a positive electrode active material. The positive electrode active material may contain compounds that enable reversible insertion and extraction of lithium ions.

[0099] According to an exemplary embodiment, the positive electrode active material may comprise a lithium-nickel metal oxide. The lithium-nickel metal oxide may further comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0100] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or a crystal structure represented by the following chemical formula 1.

[0101] [Chemical Formula 1]Li x Ni a M b O 2+z In chemical formula 1, the values ​​can be 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, and -0.5≤z≤0.1. As mentioned above, M can contain Co, Mn, and / or Al.

[0102] The chemical structure represented by Formula 1 indicates the bonding relationships contained in the layered or crystalline structure of the positive electrode active material, and does not exclude other additional elements. For example, M may contain Co and / or Mn, and Co and / or Mn may be provided together with Ni as the main active element of the positive electrode active material. Formula 1 is provided to represent the bonding relationships of the main active elements and should be understood as including the introduction and substitution of additional elements.

[0103] In one embodiment, in addition to the primary active element, auxiliary elements may be further included to enhance the chemical stability of the positive electrode active material or the layered / crystal structure. These auxiliary elements may be incorporated into the layered / crystal structure and form bonds; this should be understood to also include the chemical structures represented by Formula 1.

[0104] The auxiliary element may include at least one of, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. The auxiliary element may function as an auxiliary active element, together with Co or Mn, to contribute to the capacity / power activity of the positive electrode active material; for example, Al.

[0105] For example, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or a crystal structure represented by the following chemical formula 1-1.

[0106] [Chemical Formula 1-1]Li x Ni a M1 b1 M2 b2 O 2+zIn chemical formula 1, M1 may contain Co, Mn, and / or Al. M2 may contain the aforementioned auxiliary elements. In chemical formula 1-1, the values ​​can be 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, and -0.5≤z≤0.1.

[0107] The positive electrode active material may further include coating elements or doping elements. For example, elements that are substantially the same as or similar to the auxiliary elements described above can be used as coating elements or doping elements. For example, one or more combinations of the elements described above can be used as coating elements or doping elements.

[0108] The coating element or doping element may exist on the surface of the lithium-nickel metal oxide particles, or may penetrate through the surface of the lithium-nickel metal composite oxide particles and be contained in the bonding structure represented by chemical formula 1 or chemical formula 1-1.

[0109] The positive electrode active material may comprise nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, NCM-based lithium oxide with increased nickel content can be used.

[0110] Nickel (Ni) can be provided as a transition metal related to the power and capacity of lithium secondary batteries. Therefore, as described above, by using a high-content (high-Ni) composition in the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0111] However, with increasing Ni content, the long-term storage stability and lifetime stability of the cathode or secondary battery may relatively decrease, and side reactions with the electrolyte may also increase. However, according to an exemplary embodiment, conductivity can be maintained by including Co, while lifetime stability and capacity retention characteristics can be improved by including Mn.

[0112] The Ni content in the NCM-based lithium oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) can be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the Ni content can be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0113] In some embodiments, the positive electrode active material may also include lithium cobalt oxide-based active material, lithium manganese oxide-based active material, lithium nickel oxide-based active material, or lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0114] In some embodiments, the positive electrode active material may include, for example, a Mn-rich based active material having a chemical structure or crystal structure represented by Chemical Formula 2, a Li rich layered oxide (LLO) / Over Lithiated Oxide (OLO) based active material, or a Co-less based active material.

[0115] [Chemical Formula 2] p[Li2MnO3]·(1-p)[Li q JO2] In Chemical Formula 2, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may include at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0116] A separator may be disposed between the positive electrode and the negative electrode. The separator may be configured to prevent an electrical short circuit between the positive electrode and the negative electrode and allow the flow of ions. According to an embodiment, the thickness of the separator may be 10 μm to 20 μm, but the present invention is not limited thereto.

[0117] For example, the separator may include a porous polymer film or a porous non-woven fabric. The porous polymer film may include polyolefin-based polymers such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers. The porous non-woven fabric may include glass fibers with a high melting point, polyethylene terephthalate fibers, etc. The separator may also include a ceramic-based material. For example, inorganic particles may be coated on the polymer film or dispersed inside the polymer film to improve heat resistance.

[0118] The separator may have a single-layer or multi-layer structure including the above polymer film and / or non-woven fabric.

[0119] The lithium secondary battery as described above has excellent fast charging characteristics, life characteristics, resistance characteristics, etc., and thus has very excellent practicality as a power source for electric vehicles (EVs), etc.

[0120] The embodiments of the present invention will be further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only for illustrating the present invention and are not intended to limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and its technical concept, which will be obvious to those skilled in the art, and such variations and modifications also fall within the scope of the claims.

[0121] Preparation Example 1 (1) Preparation of the composite 1) Preparation of carbon-based particles i) Synthesis of methyl phenolic resin oligomer: Phenol and formaldehyde were mixed in a molar ratio of 1:2, and 1.5% by weight of triethylamine was added. The reaction was carried out at 85°C, 4 hours and 160 rpm (stirring).

[0122] ii) Suspension stabilization of the first-order phenolic resin oligomer: 1 g of polyvinyl alcohol (PVA) is dispersed in an aqueous dispersion medium, and then the first-order phenolic resin oligomer is added.

[0123] iii) Curing of methyl phenolic resin oligomers: 3g of hexamethylenetetramine (HMTA) as a curing agent was added, and the reaction was carried out at 98°C, 12 hours and 400 rpm (stirring).

[0124] iv) Obtaining carbon materials: The cured methyl phenolic resin oligomers were classified using a sieve and then washed with water using H2O.

[0125] v) Using ethanol, remove unreacted monomers and oligomers from the water-washed methyl phenolic resin oligomers and then dry them.

[0126] vi) Carbonization and activation: The dried methyl phenolic resin oligomer is calcined at 900°C for 1 hour under a nitrogen atmosphere. During the calcination process, CO2 gas is introduced at a rate of 1 L / min, and carbonization is carried out at 900°C to prepare porous carbon.

[0127] 2) Formation of silicon-containing coating: Silane gas is injected into the CVD coating machine at a flow rate of 50 mL / min to 100 mL / min, and the temperature is increased to 550°C at a heating rate of 5°C to 20°C. The temperature is then maintained at this temperature for about 120 minutes to prepare silicon-containing composite particles, which are marked as "composite particles" in Table 2 below.

[0128] (2) Preparation of carbon-based active materials: First to third artificial graphite were used as carbon-based active materials. The physical properties of the first to third artificial graphite are shown in Table 1 below.

[0129] At this time, the peak intensity value for calculating the crystallographic orientation index (OI) value of the carbon-based active material was measured using an XRD device (Empyrean from PANalytical) with the CuKα line as the target line. At this time, the measurement conditions were 2θ = 10° to 80°, scanning speed (° / sec) = 3, and step size = 0.025° / step.

[0130] [Table 1] (3) Fabrication of the negative electrode Prepare the first negative electrode paste, which contains, based on solids: 84.2 wt% of the second artificial graphite as the carbon-based active material, 12 wt% of the silicon-containing composite particles as the silicon-based active material, 1 wt% of single-walled carbon nanotubes (SWCNT) as the conductive material, and 2.8 wt% of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as the binder.

[0131] Prepare the second negative electrode paste, which contains, based on solids: 84.2 wt% of the first artificial graphite as the carbon-based active material, 12 wt% of SiO x (0 < x < 2), 1 wt% of single-walled carbon nanotubes (SWCNT) as the conductive material, and 2.8 wt% of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), and it is shown in Table 2 below.

[0132] After that, coat the first negative electrode paste on a copper foil as the negative electrode current collector, then coat the second negative electrode paste on the first negative electrode paste, and then dry at 80 °C to form the first negative electrode mixture layer and the second negative electrode mixture layer, thereby fabricating the negative electrode for the secondary battery, and it is shown in Table 2. At this time, the load weight (LW) ratio of the applied first negative electrode mixture layer and the second negative electrode mixture layer is 5:5.

[0133] (4) Fabrication of the secondary battery Coat a paste containing Li[Ni 0.8 Co 0.1 Mn 0.1 O2 on an aluminum foil and dry it to fabricate the positive electrode. Place the secondary battery cell fabricated by inserting a polyolefin separator between the positive electrode and the negative electrode fabricated above into a soft package for the secondary battery, then inject an electrolyte solution in which 1 M LiPF6 is dissolved in a solvent mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) into the soft package for the secondary battery, and then seal it, thereby fabricating a pouch-type lithium secondary battery, and it is shown in Table 2. The fabricated pouch-type lithium secondary battery is used as the secondary battery sample for Example 1.

[0134] 2. Examples 2 to 3 and Comparative Examples 1 to 4 were manufactured using the same method as in Example 1, except that the types and contents of the first carbon-based active material, the second carbon-based active material, the first silicon-based active material, and the second silicon-based active material contained in the negative electrode mixture layer were changed according to Table 2 below.

[0135] [Table 2] Evaluation of the internal resistance (DC-IR) characteristics of the evaluation examples: For the secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 4, at a SOC of 50%, the C-rate was adjusted to 0.2C, 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, and 3.0C. After charging and discharging at this C-rate for 10 seconds, the voltage termination point was fitted to a linear equation, and its slope was taken as DC-IR. The resulting values ​​are recorded in Table 3 below.

[0136] 2. Evaluation of General (Room Temperature) Lifetime Characteristics: At 25°C, within a SOC range of 4% to 98%, the general lifetime characteristics of the secondary battery samples from Examples 1 to 3 and Comparative Examples 1 to 4 were evaluated. Specifically, the secondary battery samples were charged at 0.3C to the voltage corresponding to 98% SOC under constant current / constant voltage (CC / CV) conditions, then cut off at 0.05C, and then discharged at 0.3C to the voltage corresponding to 4% SOC under constant current (CC) conditions. This cycle was repeated 300 times. The discharge capacity retention rate relative to the initial discharge capacity was calculated as a percentage, and the results are shown in Table 3 below. A sharp decrease in capacity retention rate after a specific number of cycles was marked as "sharp decrease after ~ cycles".

[0137] 3. Evaluation of fast charging life characteristics: At 25°C, within the range of 8% to 80% SOC, the secondary battery samples of Examples 1 to 3 and Comparative Examples 1 to 4 were charged for 25 minutes and discharged at 0.3C. The above cycle was repeated 200 times. The discharge capacity retention rate relative to the initial discharge capacity was then calculated as a percentage, and the results are shown in Table 3 below.

[0138] [Table 3] Referring to Table 3, it can be confirmed that in the multilayer structure of the negative electrode, the resistance characteristics and lifespan characteristics of the secondary battery differ depending on the type and content of the silicon-based active material. Specifically, Examples 1 to 3 include a negative electrode in which the first silicon-based active material comprises silicon-containing composite particles, the second silicon-based active material comprises silicon oxide-based active material, and the content of the second silicon-based active material is greater than or equal to the content of the first silicon-based active material. It can be confirmed that Examples 1 to 3 have low resistance and excellent general lifespan characteristics and fast-charging lifespan characteristics.

[0139] Furthermore, Comparative Example 1 did not contain a first silicon-based active material, and included a silicon oxide-based active material as a second silicon-based active material. However, the content of the silicon oxide-based active material was greater than 20% by weight, which confirmed that Comparative Example 1 had a higher resistance and a generally poorer lifespan.

[0140] In Comparative Example 2, both the first silicon-based active material and the second silicon-based active material use composite particles containing silicon. It can be confirmed that Comparative Example 2 has a higher resistance and poorer fast charging life characteristics. In Comparative Example 3, both the first silicon-based active material and the second silicon-based active material use silicon oxide-based active materials. It can be confirmed that Comparative Example 3 has a poorer general life.

[0141] Comparative Example 4 includes a negative electrode in which the first silicon-based active material comprises silicon-containing composite particles and the second silicon-based active material comprises silicon oxide-based active material. However, the content of the second silicon-based active material is less than or equal to the content of the first silicon-based active material. It can be confirmed that the lifetime characteristics of Comparative Example 4 are poor.

[0142] Therefore, as in Examples 1 to 3, when using a negative electrode with a multilayer structure containing silicon-based active materials that are different from each other and have different contents, it is determined that a lithium secondary battery with excellent resistance characteristics, lifespan characteristics, and fast charging characteristics can be provided.

[0143] The above description is merely an example of applying the principles of the present invention, and other configurations may be included without departing from the scope of the present invention.

[0144] Aspect 1) The negative electrode for a secondary battery may include: a negative electrode current collector; a first negative electrode mixture layer formed on at least one side of the negative electrode current collector and comprising a first silicon-based active material; and a second negative electrode mixture layer formed on the first negative electrode mixture layer and comprising a second silicon-based active material, wherein the first silicon-based active material may comprise composite particles comprising silicon, and the second silicon-based active material comprises silicon oxide (SiO2). x, where 0 < x < 2), the content of the second silicon-based active material included based on the total weight of the second negative electrode mixture layer can be greater than or equal to the content of the first silicon-based active material included based on the total weight of the first negative electrode mixture layer.

[0145] Aspect 2) According to Aspect 1, the silicon-containing composite particles may include carbon-based particles and a silicon-containing coating formed on the surface of the carbon-based particles.

[0146] Aspect 3) According to Aspect 1 or Aspect 2, based on the total weight of the first negative electrode mixture layer, the content of the first silicon-based active material may be 0.01 - 20% by weight.

[0147] Aspect 4) According to any one of Aspects 1 to 3, based on the total weight of the second negative electrode mixture layer, the content of the second silicon-based active material may be 0.01 - 30% by weight.

[0148] Aspect 5) According to any one of Aspects 1 to 4, the first negative electrode mixture layer may further include a first carbon-based active material, and the second negative electrode mixture layer may further include a second carbon-based active material.

[0149] Aspect 6) According to Aspect 5, the OI value of the second carbon-based active material according to Formula 1 below may be less than or equal to the OI value of the first carbon-based active material.

[0150] [Formula 1] OI = I 004 / I 110 In Formula 1, OI is the crystal orientation index measured by XRD, and I 004 is the peak intensity of the (004) plane in the XRD measurement of the carbon-based active material, and I 110 is the peak intensity of the (110) plane in the XRD measurement of the carbon-based active material.

[0151] Aspect 7) According to Aspect 6, the OI value of the first carbon-based active material may be 1 to 10, and the OI value of the second carbon-based active material may be 1 to 3.

[0152] Aspect 8) According to any one of Aspects 1 to 7, the thickness of the second negative electrode mixture layer may be greater than or equal to the thickness of the first negative electrode mixture layer.

[0153] Aspect 9) According to any one of Aspects 1 to 8, the thickness ratio of the first negative electrode mixture layer to the second negative electrode mixture layer may be 1:9 to 5:5.

[0154] Aspect 10) According to any one of Aspects 1 to 9, the first negative electrode mixture layer and the second negative electrode mixture layer may further include an adhesive.

[0155] Aspect 11) According to aspect 10, the adhesives contained in the first negative electrode mixture layer and the second negative electrode mixture layer may each independently include at least one selected from styrene-butadiene rubber (SBR), fluororubber, ethylene propylene rubber, butyl acrylate rubber, butadiene rubber, isoprene rubber, acrylonitrile rubber, acrylic rubber, silane rubber, carboxymethyl cellulose (CMC), hydroxypropyl methylcellulose, methylcellulose, polyacrylic acid (PAA) based adhesives, polyvinyl alcohol (PVA) based adhesives, and polyvinyl alcohol-polyacrylic acid copolymer based adhesives.

[0156] Aspect 12) A lithium secondary battery may include: a positive electrode; a negative electrode for a secondary battery according to any one of Aspects 1 to 11; and a separator disposed between the positive electrode and the negative electrode.

[0157] <Explanation of reference numerals> 1: Carbon-based active material 2: Base surface 3: Edge surface 100: Negative electrode for secondary batteries 10: Negative electrode current collector 20: Negative electrode mixture layer 21: First negative electrode mixture layer 22: Second negative electrode mixture layer Industrial applicability As described above, the features of the present invention can be applied in whole or in part to negative electrodes for secondary batteries and lithium secondary batteries including the negative electrode.

Claims

1. A negative electrode for a secondary battery, comprising: Negative electrode current collector; A first negative electrode mixture layer is formed on at least one side of the negative electrode current collector and contains a first silicon-based active material; and a second negative electrode mixture layer formed on the first negative electrode mixture layer and containing a second silicon-based active material, wherein the first silicon-based active material includes composite particles containing silicon, and the second silicon-based active material contains silicon oxide SiO x , where 0 < x < 2, and the content of the second silicon-based active material contained based on the total weight of the second negative electrode mixture layer is greater than or equal to the content of the first silicon-based active material contained based on the total weight of the first negative electrode mixture layer.

2. The negative electrode for a secondary battery according to claim 1, wherein, The silicon-containing composite particles include carbon-based particles and a silicon-containing coating formed on the surface of the carbon-based particles.

3. The negative electrode for a secondary battery according to claim 1, wherein, Based on the total weight of the first negative electrode mixture layer, the content of the first silicon-based active material is 0.01-20% by weight.

4. The negative electrode for a secondary battery according to claim 1, wherein, Based on the total weight of the second negative electrode mixture layer, the content of the second silicon-based active material is 0.01-30% by weight.

5. The negative electrode for a secondary battery according to claim 1, wherein, The first negative electrode mixture layer further comprises a first carbon-based active material, and the second negative electrode mixture layer further comprises a second carbon-based active material.

6. The negative electrode for a secondary battery according to claim 5, wherein, The OI value of the second carbon-based active material according to Equation 1 is less than or equal to the OI value of the first carbon-based active material, [Equation 1] OI=I 004 / I 110 In Equation 1, OI is the crystal orientation index measured by XRD, and I... 004 It is the peak intensity of the (004) plane in the XRD measurement of carbon-based active materials, I 110 It is the peak intensity of the (110) plane in the XRD measurement of carbon-based active materials.

7. The negative electrode for a secondary battery according to claim 6, wherein, The first carbon-based active material has an OI value of 1 to 10, and the second carbon-based active material has an OI value of 1 to 3.

8. The negative electrode for a secondary battery according to claim 1, wherein, The thickness of the second negative electrode mixture layer is greater than or equal to the thickness of the first negative electrode mixture layer.

9. The negative electrode for a secondary battery according to claim 1, wherein, The thickness ratio of the first negative electrode mixture layer to the second negative electrode mixture layer is 1:9 to 5:

5.

10. The negative electrode for a secondary battery according to claim 1, wherein, The first negative electrode mixture layer and the second negative electrode mixture layer further comprise an adhesive.

11. The negative electrode for a secondary battery according to claim 10, wherein, The adhesive includes at least one selected from styrene-butadiene rubber (SBR), fluoropolymer rubber, ethylene propylene rubber, butyl acrylate rubber, butadiene rubber, isoprene rubber, acrylonitrile rubber, acrylic rubber, silane rubber, carboxymethyl cellulose (CMC), hydroxypropyl methylcellulose, methylcellulose, polyacrylic acid (PAA) based adhesive, polyvinyl alcohol (PVA) based adhesive, and polyvinyl alcohol-polyacrylic acid copolymer based adhesive.

12. A lithium secondary battery, comprising: positive electrode; The negative electrode for a secondary battery according to any one of claims 1 to 11; And a diaphragm disposed between the positive electrode and the negative electrode.

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