Electrode and secondary battery including the same

Abstract

The present invention relates to an electrode and a secondary battery comprising the same, the electrode comprising an electrode active material layer, the electrode active material layer comprising an electrode active material and a conductive agent, the conductive agent comprising: graphene; a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other; and carbon black, in which the average diameter of the single-walled carbon nanotube units is from 0.5 nm to 5 nm, and in which the average diameter of the carbon nanotube structure is from 2 nm to 200 nm.

Description

[0001] This application is a divisional application of an application with an application date of September 29, 2020, application number 202080048906.4, and invention name “Electrode and Secondary Battery Including the Electrode” (PCT / KR2020 / 013394, national phase entry date January 3, 2022).

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of priority from Korean Patent Application No. 10-2019-0123261, filed on October 4, 2019, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0004] The present invention relates to an electrode and a secondary battery including the electrode, wherein the electrode includes an electrode active material layer, the electrode active material layer includes an electrode active material and a conductive agent, the conductive agent including: graphene; a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other; and carbon black, wherein the carbon nanotube structure is included in the electrode active material layer in an amount of 0.01 wt % to 0.5 wt %. Background Art

[0005] With the recent technological development and increased demand for mobile devices, the demand for batteries as energy sources has significantly increased, and as a result, various studies have been conducted on batteries that can meet various needs. In particular, lithium secondary batteries, which have excellent lifespan characteristics and cycle characteristics and high energy density, have been actively studied as power sources for such devices.

[0006] A lithium secondary battery refers to a battery that includes a non-aqueous electrolyte containing lithium ions in an electrode assembly, wherein the electrode assembly includes: a positive electrode including a positive electrode active material capable of intercalating / deintercalating lithium ions, a negative electrode including a negative electrode active material capable of intercalating / deintercalating lithium ions, and a microporous separator disposed between the positive electrode and the negative electrode.

[0007] At the same time, since the conductivity of the electrode cannot be ensured solely by the electrode active material, the battery resistance may be too high. Therefore, the electrode generally also includes a conductive agent. Generally, point-type conductive agents such as carbon black are mainly used, and linear conductive agents such as carbon nanotubes and carbon nanofibers have also been used to further improve the conductivity and thus increase the battery capacity.

[0008] Single-walled carbon nanotubes are one type of linear conductive agent and improve the conductivity in the electrode active material layer due to their thin and elongated shape. Therefore, in general, single-walled carbon nanotubes are completely dispersed to prepare a dispersion comprising single-walled carbon nanotube units, wherein the single-walled carbon nanotube units exist in a single chain form, and then an electrode slurry is prepared by the dispersion, and the electrode active material layer is prepared by the electrode slurry. Therefore, single-walled carbon nanotubes exist in the electrode active material layer as units (single chains). However, when the battery is repeatedly charged and discharged, the surface of the single-walled carbon nanotube unit is damaged or the single-walled carbon nanotube unit is broken, and therefore, there is a limitation that it is difficult to maintain a conductive network in the electrode active material layer. Therefore, the conductive network is blocked or reduced, and this reduces the life characteristics of the battery.

[0009] To this end, there is a method of using multi-walled carbon nanotubes to ensure conductivity even when the carbon nanotube surface is damaged. However, due to the structure formed by node growth, the multi-walled carbon nanotubes are cut into too short lengths during dispersion preparation, which has limitations in improving the conductivity of the electrode.

[0010] Meanwhile, planar conductive agents such as graphene also have excellent electrical conductivity, but there are limitations, namely, it is difficult to produce a single layer of graphene with a relatively thin thickness, and if a thicker graphene is used, the battery efficiency is reduced. In addition, in the case of planar conductive agents, there are limitations, namely, due to the wide planar contact, the mobility of the electrolyte in the battery is limited. In addition, graphene mainly exists in the form of covering the surface of the electrode active material, and is therefore not suitable for forming a long conductive network between the electrode active materials.

[0011] Furthermore, when a linear conductive agent or a planar conductive agent is used, there is a limitation in that the electrode active material is easily damaged in the process of winding the electrode.

[0012] Therefore, there is a need for a method of suppressing damage to electrode active materials, reducing the resistance of the electrodes, and thus improving the life characteristics of the battery. Summary of the Invention

[0013] Technical issues

[0014] One aspect of the present invention provides an electrode capable of suppressing damage to an electrode active material and reducing resistance of the electrode, thereby improving life characteristics of a battery.

[0015] Another aspect of the present invention provides a secondary battery comprising the electrode

[0016] Technical Solution

[0017] According to one aspect of the present invention, there is provided an electrode including an electrode active material layer, the electrode active material layer including an electrode active material and a conductive agent, the conductive agent including: graphene; a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other; and carbon black, wherein the carbon nanotube structure is included in the electrode active material layer in an amount of 0.01 wt % to 0.5 wt %.

[0018] According to another aspect of the present invention, a secondary battery including the electrode is provided.

[0019] Beneficial effects

[0020] The electrode according to the present invention includes a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded together, thus smoothly maintaining a conductive network. Consequently, the electrode's resistance can be kept low, improving the battery's lifespan. Furthermore, because the carbon nanotube structure exists in the electrode in the form of long ropes, even when the battery is continuously charged and discharged, the decrease in conductivity due to damage to the carbon nanotube structure is suppressed, and a long conductive network can be formed. Furthermore, because the electrode includes graphene, its excellent conductivity can further reduce the electrode's resistance. Furthermore, because graphene helps form a short conductive network by covering the surface of the electrode active material, the combined use of graphene and the carbon nanotube structure allows for a uniform conductive network to be formed across the entire electrode. Furthermore, because the graphene simultaneously covers at least a portion of the carbon nanotube structure, a tight conductive network can be maintained even during repeated charge and discharge cycles. Consequently, the battery's lifespan can be improved. Furthermore, because the electrode according to the present invention includes carbon black, its low hardness can suppress damage to the electrode active material during winding. Therefore, the life performance of the battery can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 These are SEM photographs of a commonly used multi-walled carbon nanotube unit (A) and carbon nanotube structures (B and C) used in examples of the present invention.

[0022] Figure 2 TEM images of the carbon nanotube structure (A) used in the examples of the present invention and the completely dispersed single-walled carbon nanotube unit (B) commonly used.

[0023] Figure 3 This is a SEM photograph of an electrode in an example of the present invention. DETAILED DESCRIPTION

[0024] The terms or words used in the specification and the claims should not be construed as being limited to the ordinary meaning or dictionary meaning, but should be construed as meanings and concepts consistent with the technical spirit based on the principle that the inventor can appropriately define the concept of the terms in order to interpret the present invention in the best manner.

[0025] The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting of the present invention. Terms in the singular may include plural forms unless the context clearly indicates otherwise.

[0026] It will be understood that when used in this specification, the terms "comprises", "comprising" or "having" specify the presence of stated features, numbers, steps, elements or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, elements or combinations thereof.

[0027] In this specification, unless otherwise specifically stated, the expression "%" means % by weight.

[0028] In this specification, the expression "specific surface area" is measured by the BET method, wherein, in particular, the specific surface area can be calculated from the nitrogen adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II manufactured by Bell Japan.

[0029] In this specification, the average particle size (D 50 ) can be defined as the particle size at which the cumulative volume in the particle size distribution curve is 50%. For example, the average particle size (D 50 Laser diffraction is generally capable of measuring particle sizes ranging from submicron to several millimeters, and can obtain results with high repeatability and high resolution.

[0030] In the present invention, a single-walled carbon nanotube unit refers to a tubular unit having a single wall composed of carbon atoms, and a multi-walled carbon nanotube unit refers to a tubular unit having multiple walls composed of carbon atoms in one tube.

[0031] The term graphene herein refers to a carbonaceous structure in the form of a thin film, which has a form in which one graphite plane or a plurality of graphite planes are stacked and has flexibility.

[0032] Hereinafter, the present invention will be described in detail.

[0033] electrode

[0034] The electrode according to the present invention includes an electrode active material layer, the electrode active material layer includes an electrode active material and a conductive agent, the conductive agent includes: graphene; a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other; and carbon black, wherein the carbon nanotube structure is included in the electrode active material layer in an amount of 0.01% to 0.5% by weight.

[0035] The electrode may include an electrode active material layer. The electrode may further include a current collector, and in this case, the electrode active material layer may be provided on one surface or both surfaces of the current collector.

[0036] The current collector is not particularly limited as long as the material of the current collector has conductivity and does not cause adverse chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, their alloys, these materials surface-treated with one of carbon, nickel, titanium, silver, etc., or calcined carbon, etc. may be used.

[0037] The current collector generally may have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to improve the adhesion of the electrode active material. In addition, the electrode current collector may be used in various shapes such as a film, sheet, foil, net, porous body, foam body, non-woven fabric body, etc.

[0038] The electrode active material layer may include an electrode active material and a conductive agent.

[0039] The electrode active material may be a positive electrode active material or a negative electrode active material commonly used in the art, and its type is not particularly limited.

[0040] For example, a lithium oxide containing at least one metal such as cobalt, manganese, nickel or aluminum may be used as the positive electrode active material. More particularly, the lithium oxide may include: lithium manganese-based oxides (such as LiMnO2, LiMn2O, etc.); lithium cobalt-based oxides (such as LiCoO2, etc.); lithium nickel-based oxides (such as LiNiO2, etc.); lithium nickel manganese-based oxides (such as LiNi 1-Y1 Mn Y1 O2 (where 0 < Y1 < 1), LiNi Z1 Mn 2-Z1 O4 (where 0 < Z1 < 2), etc.); lithium nickel cobalt-based oxides (such as LiNi 1-Y2 Co Y2 O2 (where 0 < Y2 < 1), etc.); lithium manganese cobalt-based oxides (such as LiCo 1-Y3 Mn Y3 O2 (where 0 < Y3 < 1), LiMn 2-Z2 Co z2O4 (where 0 < Z2 < 2, etc.); lithium nickel cobalt manganese-based oxides (such as Li(Ni P1 Co Q1 Mn R1 )O2 (where 0 < P1 < 1, 0 < Q1 < 1, 0 < R1 < 1, and P1 + Q1 + R1 = 1) or Li(Ni P2 Co Q2 Mn R2 )O4 (where 0 < P2 < 2, 0 < Q2 < 2, 0 < R2 < 2, and P2 + Q2 + R2 = 2), etc.); or lithium nickel cobalt manganese-other metal (M) oxides (such as Li(Ni P3 Co Q3 Mn R3 M 1 S )O2 (where M 1 is selected from the group consisting of aluminum (Al), copper (Cu), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), zirconium (Zr), zinc (Zn), tantalum (Ta), niobium (Nb), magnesium (Mg), boron (B), tungsten (W), and molybdenum (Mo), and P3, Q3, R3, and S are the atomic fractions of each independent element, where 0 < P3 < 1, 0 < Q3 < 1, 0 < R3 < 1, 0 < S < 1, and P3 + Q3 + R3 + S = 1), etc.), and may include any one of them or a mixture of two or more.

[0041] Meanwhile, the negative electrode active material may include, for example, carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds that can alloy with lithium such as silicon (Si), aluminum (Al), tin (Sn), lead (Pb), zinc (Zn), bismuth (Bi), indium (In), magnesium (Mg), gallium (Ga), cadmium (Cd), Si alloy, Sn alloy, or Al alloy; metal oxides that may or may not be doped with lithium such as SiO v (0 < v < 2), SnO2, vanadium oxides, and lithium vanadium oxides; or composites including metal compounds and carbonaceous materials such as Si-C composites or Sn-C composites, and any one of them or a mixture of two or more may be used. In addition, a thin film of metallic lithium may be used as the negative electrode active material. Moreover, both low-crystalline carbon and high-crystalline carbon can be used as carbonaceous materials.

[0042] The electrode active material may be included in an amount of 70 wt% to 99.5 wt%, preferably 80 wt% to 99 wt%, based on the total weight of the electrode active material layer. When the content of the electrode active material satisfies the above range, excellent energy density, electrode adhesion, and conductivity can be achieved.

[0043] The conductive agent may include graphene, carbon nanotube structures, and carbon black.

[0044] (1) Graphene

[0045] Graphene is mainly disposed on the surface of the electrode active material to help form a conductive network between adjacent electrode active materials.

[0046] Graphene may include a structure in which 1 to 1,000 graphite planes are stacked, and in particular, the number of stacked graphite planes may be 1 to 500, and more particularly 1 to 100. When the above range is met, the characteristics of high-quality graphene, which is flexible due to its thin thickness, can be utilized, and the graphene is easily and uniformly dispersed in the electrode active material layer. In addition, even when a low content of graphene is used, the conductivity of the electrode active material layer can be significantly improved.

[0047] The average length of graphene can be 1 μm to 100 μm, particularly 0.1 μm to 10 μm, and more particularly 0.1 μm to 5 μm. When the above range is met, graphene can be present while appropriately covering the electrode active material. In addition, graphene covers at least a portion of the carbon nanotube structure, so the carbon nanotube structure can be further inhibited from being spaced apart from the electrode active material. Therefore, the conductivity of the electrode active material and the electrode active material can be improved. In the electrode observed by SEM or TEM, the average length corresponds to the average value of the lengths of the first 100 graphenes with longer lengths and the lengths of the last 100 graphenes with shorter lengths. In this article, the expression "graphene length" represents the longest length when it is assumed that there is a line from one point to another in a graphene.

[0048] The average thickness of graphene can be 0.3nm to 300nm, particularly 1nm to 100nm, and more particularly 1nm to 50nm. When the above range is met, the characteristics of high-quality graphene with flexibility due to its thin thickness can be utilized to better cover the electrode active material, and graphene is easily and evenly dispersed in the electrode active material layer. In addition, even with a low content of graphene, the conductivity of the electrode active material layer can be significantly improved. In the electrode observed by SEM or TEM, the average thickness corresponds to the thickness of the first 100 graphenes with thicker thickness and the thickness average of the last 100 graphenes with thinner thickness.

[0049] The BET specific surface area of ​​graphene can be 100m 2 / g to 500m 2 / g, especially 100m 2 / g to 400m 2 / g, and more particularly 100m 2 / g to 300m 2When the above range is met, the graphene has good dispersion in the electrode slurry, and even with a small amount of graphene, the conductivity of the electrode active material layer can be significantly improved. The BET specific surface area can be measured by the nitrogen adsorption BET method.

[0050] Graphene can be included in the electrode active material layer in an amount of 0.01 to 1.0 weight %, particularly 0.05 to 0.5 weight %, and more particularly 0.1 to 0.5 weight %. When the above range is met, applying only a small amount of graphene can significantly improve the adhesion and conductivity of the electrode, and can improve the input / output characteristics and life characteristics of the battery.

[0051] (2) Carbon nanotube structure

[0052] The carbon nanotube structure may include a plurality of single-walled carbon nanotube units. Specifically, the carbon nanotube structure may be one in which 2 to 5,000 single-walled carbon nanotube units are bonded side by side. More specifically, considering the durability of the electrode and the conductive network, it is most preferred that the carbon nanotube structure be one in which 2 to 4,500, preferably 50 to 4,000, and more preferably 1,000 to 4,000 single-walled carbon nanotube units are bonded side by side.

[0053] In a carbon nanotube structure, single-walled carbon nanotube units can be arranged side by side and bonded (with their long axes parallel to each other to have a flexible cylindrical structure) to form a carbon nanotube structure. The carbon nanotube structure can be connected to each other to represent a network structure in an electrode.

[0054] Conventional electrodes containing carbon nanotubes are typically manufactured by dispersing bundle-type or entangled-type carbon nanotubes (single-walled carbon nanotube units or multi-walled carbon nanotube units attached or entangled to each other) in a dispersion medium to prepare a conductive agent dispersion, which is then used. In this case, the carbon nanotubes are completely dispersed in the conventional conductive agent dispersion, existing in the form of a conductive agent dispersion in which single-chain carbon nanotube units are dispersed. In conventional conductive agent dispersions, the carbon nanotube units are easily cut due to excessive dispersion processes, resulting in the length of the carbon nanotube units being shorter than the initial length. In addition, the carbon nanotube units may be easily cut during the rolling process of the electrode, and another limitation is that the carbon nanotube units (particularly single-walled carbon nanotube units) are cut or their surfaces are damaged due to excessive changes in the volume of the electrode active material during battery operation. As a result, due to the deterioration of the conductivity of the electrode, there is a limitation that the input / output characteristics and life characteristics of the battery are deteriorated. Furthermore, regarding the multi-walled carbon nanotube unit, the structure has high defects due to the node growth mechanism (not a smooth linear shape, but nodes exist due to defects generated during the growth process). Therefore, the multi-walled carbon nanotube unit is more easily cut during the dispersion process (see Figure 1 (A)), and the short-cut multi-walled carbon nanotube units are likely to aggregate with each other through π-π stacking based on the carbon surface bonding structure (sp2) of the units. Therefore, it is difficult to make the multi-walled carbon nanotube units more uniformly dispersed and present in the electrode slurry.

[0055] Alternatively, regarding the carbon nanotube structure included in the electrode of the present invention, since the carbon nanotube structure is in the form of a rope in which 2 to 5,000 single-walled carbon nanotube units maintaining relatively high crystallinity without structural defects are arranged side by side and bonded to each other (see Figure 1 (B) and (C) and Figure 2(A)), even if the volume of the electrode active material changes, the length of these single-walled carbon nanotube units can be well maintained without being cut, so that the conductivity of the electrode can be maintained even in the continuous charge / discharge process of the battery. In addition, since the high conductivity of the single-walled carbon nanotube units with high crystallinity leads to an increase in the conductivity of the electrode, the input / output characteristics and life characteristics of the battery can be significantly improved. In addition, since the carbon nanotube structures can be connected to each other and have a network structure in the electrode, the generation of cracks can be prevented by suppressing excessive changes in the volume of the electrode active material, and a strong conductive network can be ensured at the same time. In addition, even if cracks are generated in the electrode active material, the conductive network can be maintained because the carbon nanotube structure can connect the electrode active material while passing through the cracks. In addition, since the carbon nanotube structure is not easily broken and can maintain its long shape, the conductive network can be enhanced throughout the electrode active material layer. In addition, the peeling of the electrode active material can be suppressed, thereby significantly improving the electrode adhesion.

[0056] In particular, from the perspective of combined use with graphene, graphene is primarily provided on the surface of the electrode active material to help ensure conductivity over short lengths, while the carbon nanotube structure can help ensure conductivity over long lengths through its long length and network structure. Furthermore, because graphene is present when covering at least a portion of the carbon nanotube structure, a tight conductive network can be maintained even during repeated charge and discharge cycles of the battery. Therefore, when graphene is used in combination with the carbon nanotube structure, a tight and uniform conductive network can be formed across the entire electrode active material layer even with a reduced total amount of conductive agent, significantly improving the battery's input / output characteristics and lifespan.

[0057] In a carbon nanotube structure, the average diameter of the single-walled carbon nanotube units can be 0.5 nm to 5 nm, particularly 1 nm to 5 nm. When this average diameter is met, the conductivity of the electrode is maximized even with a minimal amount of conductive agent. When the fabricated electrode is observed using a TEM, the average diameter corresponds to the average of the diameters of the first 100 single-walled carbon nanotube units with larger diameters and the last 100 single-walled carbon nanotube units with smaller diameters.

[0058] In the carbon nanotube structure, the average length of the single-walled carbon nanotube units can be 1 μm to 100 μm, particularly 5 μm to 50 μm. When this average length is met, a long conductive path for conductive connection between the electrode active material particles can be formed, and a unique network structure can be formed. Therefore, even with a very small amount of conductive agent, the conductivity of the electrode can be maximized. When the fabricated electrode is observed by TEM, the average length corresponds to the average of the lengths of the first 100 single-walled carbon nanotube units with longer lengths and the last 100 single-walled carbon nanotube units with shorter lengths.

[0059] The specific surface area of ​​a single-walled carbon nanotube unit can be 500m 2 / g to 1,000m 2 / g, especially 600m 2 / g to 800m 2 / g. When the above range is met, the large specific surface area ensures a smooth conductive path in the electrode, thus maximizing the conductivity of the electrode even with a very small amount of conductive agent. The specific surface area of ​​a single-walled carbon nanotube unit can be calculated from the amount of nitrogen adsorbed at liquid nitrogen temperature (77K) using Bell Japan's BELSORP-mini II.

[0060] The average diameter of the carbon nanotube structure can be 2 nm to 200 nm, particularly 5 nm to 150 nm, and more particularly 50 nm to 120 nm. When the above range is met, excellent conductivity can be achieved because it effectively forms a conductive network structure and is conducive to the connection between active material particles. When the manufactured electrode is observed by SEM, the average diameter corresponds to the average of the diameters of the first 100 carbon nanotube structures with larger diameters and the last 100 carbon nanotube structures with smaller diameters.

[0061] The average length of the carbon nanotube structure may be 1 μm to 500 μm, particularly 5 μm to 100 μm, and more particularly 10 μm to 70 μm. When the above range is met, excellent conductivity can be achieved because it effectively forms a conductive network structure and is conducive to the connection between active material particles. When the manufactured electrode is observed by SEM, the average length corresponds to the average value of the lengths of the first 100 carbon nanotube structures with longer lengths and the last 100 carbon nanotube structures with shorter lengths.

[0062] The carbon nanotube structure can be included in the electrode active material layer in an amount of 0.01 wt % to 0.5 wt %, particularly 0.01 wt % to 0.15 wt %, and more particularly 0.01 wt % to 0.1 wt %. When the above range is met, since the conductive path of the electrode can be ensured, the battery life characteristics can be improved while the electrode resistance is kept at a low level. During the preparation of the conductive agent dispersion, when the bundle-type carbon nanotubes are completely dispersed (as a general dispersion method, the dispersion is performed so that the single-chain carbon nanotube units are separated from each other as much as possible), the carbon nanotube structure will not be formed, or even if the carbon nanotube structure is accidentally formed, only a very small amount (e.g., 0.0005 wt %) of the carbon nanotube structure will be formed. That is, the above amount range may never be reached with a general method. Since the carbon nanotube structure has a form in which 2 to 5,000 single-walled carbon nanotube units are arranged side by side and combined with each other, even if the volume of the electrode active material changes, the carbon nanotube structure will not be cut and its length can be well maintained. Therefore, due to the high conductivity of the carbon nanotube structure, the conductivity of the electrode can be maintained and the conductivity of the electrode can be smoothly ensured. Therefore, even if the content of the carbon nanotube structure in the electrode is small, the input / output characteristics and life characteristics of the battery can be excellent.

[0063] In some cases, the single-walled carbon nanotube units can be surface-treated by oxidation or nitridation to increase affinity with the dispersion.

[0064] (3) Carbon black

[0065] Carbon black can be used to reduce the resistance of the electrode and, at the same time, can be used to suppress damage to the electrode active material when the electrode is wound.

[0066] The average particle size of carbon black (D 50 ) can be 1 nm to 500 nm, particularly 10 nm to 250 nm, and more particularly 20 nm to 200 nm. When the above range is met, when the electrode is wound, damage to the electrode active material can be minimized by the carbon black, and a short conductive network can be easily formed.

[0067] Carbon black may be included in the electrode active material layer in an amount of 0.01 to 1% by weight, particularly 0.05 to 1% by weight, and more particularly 0.05 to 0.5% by weight. When the above range is met, the carbon black can minimize damage to the electrode active material when the electrode is wound, and a short conductive network can be easily formed.

[0068] The weight ratio of graphene, carbon nanotube structure, and carbon black can be 0.01 to 3:0.01 to 0.5:0.1 to 10, particularly 0.01 to 2:0.03 to 0.5:0.1 to 5, and more particularly 0.05 to 1:0.05 to 0.5:0.1 to 1. When the above range is met, a dense and uniform conductive network can be formed, and when the electrode is wound, damage to the electrode active material can be effectively suppressed. Therefore, the life characteristics of the battery can be improved.

[0069] Graphene, carbon nanotube structures and carbon black can form Figure 3 The electrode active material in the electrode has the same structure. In particular, the carbon nanotube structure has a long length, connecting the electrode active material particles and connecting to each other to form a network structure. Graphene covers a portion of the nanotube structure, thereby enhancing the conductive connection through the carbon nanotube structure and forming a dense conductive network. Carbon black is arranged on the electrode active material, graphene, and carbon nanotube structure, and acts as a buffer to prevent damage to the electrode active material when winding the electrode.

[0070] The electrode active material layer may further include a binder. The binder is used to ensure the adhesion between the electrode active material particles or the adhesion between the electrode active material and the current collector, wherein the common binder used in the art can be used, and its type is not particularly limited. The binder may include, for example: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile (polyacrylonitrile), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, carboxymethyl cellulose (carboxymethyl cellulose: CMC), styrene-butadiene rubber (SBR), fluororubber or various copolymers thereof, and one of them can be used alone or a mixture of two or more of them can be used.

[0071] The binder may be included in an amount of 10 wt % or less, for example 0.1 wt % to 5 wt %, based on the total weight of the electrode active material layer. When the binder content satisfies the above range, excellent electrode adhesion can be achieved while minimizing the increase in electrode resistance.

[0072] Method for manufacturing electrodes

[0073] Next, a method of manufacturing the electrode of the present invention will be described.

[0074] The method for preparing an electrode of the present invention may include the following steps: preparing a graphene dispersion, a carbon black dispersion, and a carbon nanotube structure dispersion (S1), and forming an electrode slurry including the graphene dispersion, the carbon black dispersion, the carbon nanotube structure dispersion, and an electrode active material (S2). Since the graphene, carbon black, and carbon nanotube structure are the same as those in the above-mentioned embodiment, a detailed description will be omitted.

[0075] (1) Step (S1) for preparing graphene dispersion, carbon black dispersion and carbon nanotube structure dispersion

[0076] 1) Preparation of graphene dispersion

[0077] After preparing a mixed solution containing the graphene of the above embodiment, a dispersion medium, and a dispersant, a graphene dispersion can be prepared by a method such as a homogenizer, a bead mill, a ball mill, a basket mill, an attritor, a universal stirrer, a transparent mixer, a pin mill, a TK mixer, and ultrasonic dispersion. The dispersion medium and dispersant can be the same as those used in the preparation of the carbon nanotube structure dispersion described below, and thus will be described below.

[0078] 2) Preparation of carbon black dispersion

[0079] After preparing a mixed solution containing the carbon black of the above embodiment, a dispersion medium, and a dispersant, a carbon black dispersion can be prepared by a method such as a homogenizer, a bead mill, a ball mill, a basket mill, an attritor, a universal stirrer, a transparent mixer, a pin mill, a TK mixer, and ultrasonic dispersion. The dispersion medium and dispersant can be the same as those used in the preparation of the carbon nanotube structure dispersion described below, and thus will be described below.

[0080] 3) Preparation of carbon nanotube structure dispersion

[0081] The preparation of a carbon nanotube structure dispersion may include the following steps: preparing a mixed solution containing a dispersion medium, a dispersant, and bundled single-walled carbon nanotubes (bonded bodies or aggregates of single-walled carbon nanotubes) (S1-1); and dispersing the bundled single-walled carbon nanotubes by applying a shear force to the mixed solution, thereby forming a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded side by side (S1-2).

[0082] In step S1-1, a mixed solution can be prepared by adding bundled single-walled carbon nanotubes and a dispersant to a dispersion medium. In the bundled single-walled carbon nanotubes, the single-walled carbon nanotube units are combined to exist in the form of a bundle, wherein the bundled single-walled carbon nanotubes generally include 2 or more, substantially 500 or more, for example, 5,000 or more single-walled carbon nanotube units.

[0083] The specific surface area of ​​bundled single-walled carbon nanotubes can be 500m 2 / g to 1,000m 2 / g, especially 600m 2 / g to 800m 2 When the above range is satisfied, since a conductive path in the electrode can be smoothly ensured by a large specific surface area, the conductivity of the electrode can be maximized even with a very small amount of the conductive agent.

[0084] The bundled single-walled carbon nanotubes may be included in the mixed solution in an amount of 0.1 to 1.0 wt %, for example, 0.2 to 0.5 wt %. When the above range is met, the bundled single-walled carbon nanotubes are dispersed at an appropriate level, thereby forming a carbon nanotube structure of an appropriate level and improving dispersion stability.

[0085] The dispersion medium may include, for example, an amide-based polar organic solvent such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc) and N-methylpyrrolidone (NMP); an alcohol such as methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol or octanol; a diol such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,5-pentanediol or Hexylene glycol; polyhydric alcohols such as glycerol, trimethylolpropane, pentaerythritol or sorbitol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether or tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone or cyclopentanone; esters such as ethyl acetate, γ-butyrolactone and ε-propiolactone, and any one of them or a mixture of two or more thereof may be used, but are not limited thereto. More particularly, the dispersion medium may be N-methylpyrrolidone (NMP).

[0086] The dispersant may include at least any one of hydrogenated nitrile rubber, polyvinylidene fluoride, and carboxymethyl cellulose, particularly hydrogenated nitrile rubber or polyvinylidene fluoride.

[0087] The weight ratio of the bundled carbon nanotubes to the dispersant in the conductive agent dispersion may be in the range of 1:0.1 to 1:7, particularly 1:1 to 1:6. When the above range is satisfied, the bundled single-walled carbon nanotubes are dispersed at an appropriate level, thereby forming a carbon nanotube structure at an appropriate level and improving dispersion stability.

[0088] The solid content of the mixed solution can be in the range of 0.1% to 20% by weight, particularly 1% to 10% by weight. When the above range is met, the bundled single-walled carbon nanotubes are dispersed at an appropriate level, thereby forming a carbon nanotube structure of appropriate levels and improving dispersion stability. Furthermore, the electrode slurry can have a viscosity and elasticity suitable for the electrode preparation process, and this also helps increase the solid content of the electrode slurry.

[0089] In step S1-2, the process of dispersing the bundle-type carbon nanotubes in the mixed solution can be performed by using a mixing device such as a homogenizer, a bead mill, a ball mill, a basket mill, an attritor, a universal stirrer, a transparent mixer, a pin mill, a TK mixer, or an ultrasonic (sonification) dispersion device. Among them, the bead mill method is preferred because it can control the diameter size of the carbon nanotube structure, can achieve uniform distribution of the carbon nanotube structure, and has cost advantages.

[0090] The bead milling method can be as follows: the mixed solution is added to a container containing beads, and the container is rotated to disperse the bundled single-walled carbon nanotubes.

[0091] In this case, the conditions for performing the bead milling method are as follows.

[0092] The average diameter of the beads may be 0.5 mm to 1.5 mm, particularly 0.5 mm to 1.0 mm. Within this range, the carbon nanotube structure is not destroyed during the dispersion process, the diameter of the carbon nanotube structure can be appropriately controlled, and a dispersed solution with a uniform composition can be prepared.

[0093] The rotation speed of the container may be 500 to 10,000 RPM, particularly 2,000 to 6,000 RPM. Within this range, the carbon nanotube structure is not damaged during the dispersion process, the diameter of the carbon nanotube structure can be appropriately controlled, and a dispersed solution with a uniform composition can be prepared.

[0094] The bead milling time can be 0.5 to 2 hours, particularly 0.5 to 1.5 hours, and more particularly 0.8 to 1 hour. When this range is met, the carbon nanotube structure is not damaged during the dispersion process, the diameter of the carbon nanotube structure can be appropriately controlled, and a dispersed solution with a uniform composition can be prepared. The bead milling time refers to the total time the bead mill is used. For example, if the bead milling is performed several times, the time refers to the total time spent performing the several bead millings.

[0095] Bead milling conditions are used to appropriately disperse bundled single-walled carbon nanotubes, specifically conditions that exclude complete dispersion of the bundled single-walled carbon nanotubes into single-stranded single-walled carbon nanotubes. Specifically, bead milling conditions are used to appropriately disperse the bundled single-walled carbon nanotubes to form a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bound side by side within the prepared conductive agent dispersion. This can only be achieved by strictly controlling the composition of the mixed solution, the conditions of the dispersion process (e.g., the bead milling process), and so on.

[0096] By using the method, a carbon nanotube structure dispersion can be formed.

[0097] (2) Step (S2) for forming an electrode slurry comprising a graphene dispersion, a carbon black dispersion, a carbon nanotube structure dispersion, and an electrode active material

[0098] By the above method, when preparing the graphene dispersion, carbon black dispersion and carbon nanotube structure dispersion, an electrode slurry including the dispersion and the electrode active material is formed. In this case, the above electrode active material can be used as the electrode active material.

[0099] In addition, as needed, the electrode slurry may further include a binder and a solvent. In this case, the binder of the above embodiment may be used as a binder. The solvent may include, for example, dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc) and N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol or octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,5-pentanediol or hexanediol; polyhydroxy alcohols such as Such as glycerol, trimethylolpropane, pentaerythritol or sorbitol; glycol ethers, such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether or tetraethylene glycol monobutyl ether; ketones, such as acetone, methyl ethyl ketone, methyl propyl ketone or cyclopentanone; esters, such as ethyl acetate, γ-butyrolactone and ε-propiolactone, and any one of them or a mixture of two or more thereof can be used, but the present invention is not limited thereto. The solvent may be the same as or different from the dispersion medium used in the pre-dispersion, and the solvent may preferably be N-methylpyrrolidone (NMP, N-methylpyrrolidone).

[0100] Next, the electrode slurry prepared as described above is dried to form an electrode active material layer. Specifically, the electrode active material layer can be formed by coating the electrode slurry on an electrode current collector and then drying the coated current collector, or can be formed by casting the electrode slurry on a separate support and then laminating the film separated from the support on the current collector. If necessary, after the electrode active material layer is formed by the above method, a rolling process can be further performed. In this case, taking into account the physical properties of the electrode finally prepared, drying and rolling can be performed under appropriate conditions without particular limitation.

[0101] secondary batteries

[0102] A secondary battery according to another embodiment of the present invention may include a negative electrode, a positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, and at least one of the positive electrode and the negative electrode may be the electrode of the above-mentioned other embodiment. More specifically, the electrode of the above-mentioned other embodiment may be the positive electrode of this embodiment.

[0103] Separator separates the negative electrode and the positive electrode and provides a mobile path for lithium ions, wherein any separator can be used as a separator, without particular limitation, as long as it is commonly used for secondary batteries, and in particular, a separator having high moisture retention capacity and low resistance to the transmission of electrolyte ions can be used. Specifically, a porous polymer film can be used, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure with two or more layers thereof can be used. In addition, conventional porous non-woven fabrics can be used, for example, a non-woven fabric formed of high melting point glass fiber or polyethylene terephthalate fiber. In addition, a coated separator including a ceramic component or a polymer component can be used to ensure heat resistance or mechanical strength, and a separator with a single layer or multilayer structure can be selectively used.

[0104] The electrolyte may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a melt-type inorganic electrolyte that can be used in the preparation of a lithium secondary battery, but is not limited thereto.

[0105] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0106] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate can be used.

[0107] In particular, cyclic carbonates among carbonate-based organic solvents, ethylene carbonate and propylene carbonate, as high-viscosity organic solvents, are well able to dissociate lithium salts in the electrolyte due to their high dielectric constants, and therefore cyclic carbonates can be preferably used. Since cyclic carbonates can be mixed with low-viscosity, low-dielectric-constant linear carbonates such as dimethyl carbonate and diethyl carbonate in an appropriate ratio, an electrolyte with high conductivity can be prepared, and therefore cyclic carbonates can be more preferably used.

[0108] As the metal salt, a lithium salt can be used. The lithium salt is a material that is easily soluble in a non-aqueous electrolyte. For example, as an anion of the lithium salt, one selected from the group consisting of: F- 、Cl - , I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - .

[0109] In order to improve the life characteristics of the battery, suppress the reduction of the battery capacity, and improve the discharge capacity of the battery, in addition to the electrolyte components, at least one additive may be further included in the electrolyte, for example, a halogenated alkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum chloride.

[0110] According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the battery module are provided. Since the battery module and the battery pack include secondary batteries having high capacity, high rate characteristics, and high cycle characteristics, the battery module and the battery pack can be used as a power source for medium-sized and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0111] Hereinafter, the present invention will be described in more detail with reference to specific examples and comparative examples.

[0112] Preparation Example 1: Preparation of graphene dispersion

[0113] Chemically expanded graphene (in powder form), hydrogenated nitrile rubber (H-NBR) as a dispersant, and N-methylpyrrolidone (NMP) as a dispersion medium were mixed in a weight ratio of 3.6:1.2:95.2 to form a mixture. The mixture was added to a pin mill filled with 80% beads having a diameter of 0.65 mm, dispersed, and discharged at a discharge rate of 2 kg / min. By performing this process twice, the chemically expanded graphene was completely dispersed to prepare a graphene dispersion (see Figure 3 ).

[0114] Preparation Example 2: Preparation of Carbon Nanotube Structure Dispersion

[0115] Bundle-type single-walled carbon nanotubes (specific surface area 650 m2) consisting of single-walled carbon nanotube units with an average diameter of 1.5 nm and an average length of 5 μm or more 2 / g) and polyvinylidene fluoride (PVdF, KF9700, weight average molecular weight: 880,000 g / mol) were mixed in N-methylpyrrolidone (NMP) as a solvent to prepare a mixture having a solid content of 2.4 wt %.

[0116] The mixture was stirred by a bead mill method, thereby dispersing the bundle-type single-walled carbon nanotubes in the solvent, thereby preparing a carbon nanotube structure dispersion. In this case, the diameter of the beads was 1 mm, the rotation speed of the stirring container containing the beads was 3,000 RPM, and stirring was performed for 60 minutes. The carbon nanotube structure dispersion includes a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are combined side by side (see Figure 2 (A)).

[0117] In the carbon nanotube structure dispersion, the amount of the carbon nanotube structure was 0.4 wt %, and the amount of the polyvinylidene fluoride was 2.0 wt %.

[0118] Preparation Example 3: Preparation of carbon black dispersion

[0119] The specific surface area is 240m 2 / g of carbon black (in the form of secondary particles consisting of primary particles with an average diameter of 25 nm) and hydrogenated nitrile rubber (weight average molecular weight: 260,000 g / mol) were mixed in N-methylpyrrolidone (NMP) as a solvent to prepare a mixture with a solid content of 16.5 wt%.

[0120] The mixture was stirred by a bead mill method to disperse the carbon black in the solvent to prepare a carbon black dispersion. In this case, the diameter of the beads was 1 mm, the rotation speed of the stirring container containing the beads was 3,000 RPM, and stirring was performed for 60 minutes.

[0121] In the carbon black dispersion, the amount of carbon black was 15 wt % and the amount of hydrogenated nitrile rubber was 1.5 wt %.

[0122] Example 1: Preparation of positive electrode

[0123] The graphene dispersion of Preparation Example 1, the carbon nanotube structure dispersion of Preparation Example 2, the carbon black dispersion of Preparation Example 3, and the LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622) and a binder (PVDF, KF9700) were mixed with N-methylpyrrolidone (NMP) to prepare a positive electrode slurry with a solid content of 70.4%. This positive electrode slurry was coated on a 20 μm thick aluminum (Al) film current collector, dried at 130°C, and then roll-pressed to prepare a positive electrode including a positive electrode active material layer.

[0124] In the positive electrode active material layer, LiNi 0.6 Co 0.2 Mn 0.2 The content of O2 (NCM622) is 97.5 weight%, the content of binder is 1.04 weight%, the content of hydrogenated nitrile rubber is 0.06 weight%, the content of polyvinylidene fluoride is 0.4 weight%, the content of graphene is 0.3 weight%, the content of carbon nanotube structure is 0.1 weight%, and the content of carbon black is 0.6 weight%.

[0125] Comparative Example 1: Preparation of positive electrode

[0126] A positive electrode was manufactured in the same manner as in Example 1, except that the graphene dispersion of Preparation Example 1 was not used.

[0127] Comparative Example 2: Preparation of positive electrode

[0128] A positive electrode was manufactured in the same manner as in Example 1, except that the carbon nanotube structure dispersion of Preparation Example 2 was not used.

[0129] Comparative Example 3: Preparation of positive electrode

[0130] A positive electrode was manufactured in the same manner as in Example 1, except that the carbon black dispersion of Preparation Example 3 was not used.

[0131] Test example

[0132] For the positive electrodes of Example 1 and Comparative Examples 1 to 3, the active material resistance and the interface resistance were measured using a MP tester (manufacturer: Hioki) using a 4-probe method. The results are shown in Table 1.

[0133] [Table 1]

[0134]

[0135] Each content is based on 100% by weight of the total amount of the positive electrode active material layer.

[0136] The following content corresponds to the original claims in the parent application and is incorporated herein as part of the specification:

[0137] 1. An electrode comprising an electrode active material layer,

[0138] The electrode active material layer includes an electrode active material and a conductive agent,

[0139] The conductive agent includes:

[0140] graphene;

[0141] A carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other; and

[0142] carbon black,

[0143] The carbon nanotube structure is included in the electrode active material layer in an amount of 0.01 wt % to 0.5 wt %.

[0144] 2. The electrode according to item 1, wherein the average length of the graphene is 0.1 μm to 100 μm.

[0145] 3. The electrode according to item 1, wherein the average thickness of the graphene is 0.3 nm to 300 nm.

[0146] 4. The electrode according to claim 1, wherein the BET specific surface area of ​​the graphene is 100 m 2 / g to 500m 2 / g.

[0147] 5. The electrode according to item 1, wherein the graphene is included in the electrode active material layer in an amount of 0.01 wt% to 1.0 wt%.

[0148] 6. The electrode according to item 1, wherein the carbon nanotube structures are connected to each other to form a network structure in the electrode.

[0149] 7. The electrode according to item 1, wherein, in the carbon nanotube structure, the single-walled carbon nanotube units are arranged side by side and bonded.

[0150] 8. The electrode according to item 1, wherein the average length of the carbon nanotube structure is 1 μm to 500 μm.

[0151] 9. The electrode according to item 1, wherein the average length of the carbon nanotube structure is 10 μm to 70 μm.

[0152] 10. The electrode according to item 1, wherein the average diameter of the carbon nanotube structure is 2 nm to 200 nm.

[0153] 11. The electrode according to item 1, wherein the average diameter of the carbon nanotube structure is 50 nm to 120 nm.

[0154] 12. The electrode according to claim 1, wherein the average particle size (D 50 ) is 1nm to 500nm.

[0155] 13. The electrode according to item 1, wherein the carbon black is included in the electrode active material layer in an amount of 0.01 wt% to 1 wt%.

[0156] 14. The electrode according to item 1, wherein the weight ratio of the graphene, the carbon nanotube structure and the carbon black is 0.01 to 3:0.01 to 0.5:0.1 to 10.

[0157] 15. The electrode according to item 1, wherein the carbon nanotube structure is a carbon nanotube structure in which 50 to 4,000 single-walled carbon nanotube units are bonded to each other.

[0158] 16. A secondary battery comprising the electrode according to item 1.

Claims

1. An electrode comprising an electrode active material layer, The electrode active material layer includes an electrode active material and a conductive agent, The conductive agent includes: graphene; a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other; and carbon black, The average diameter of the single-walled carbon nanotube unit is 0.5 nm to 5 nm. The average diameter of the carbon nanotube structure is 2 nm to 200 nm. 2 . The electrode according to claim 1 , wherein the average length of the graphene is 0.1 μm to 100 μm. The electrode according to claim 1 , wherein the graphene has an average thickness of 0.3 nm to 300 nm.

4. The electrode according to claim 1, wherein the BET specific surface area of ​​the graphene is 100 m 2 / g to 500m 2 / g. 5 . The electrode according to claim 1 , wherein the graphene is included in the electrode active material layer in an amount of 0.01 wt % to 1.0 wt %. The electrode according to claim 1 , wherein the carbon nanotube structures are connected to each other to form a network structure in the electrode.

7. The electrode according to claim 1, wherein In the carbon nanotube structure, the single-walled carbon nanotube units are arranged side by side and combined. The electrode according to claim 1 , wherein the carbon nanotube structure has an average length of 1 μm to 500 μm. 9 . The electrode according to claim 1 , wherein the carbon nanotube structure has an average length of 10 μm to 70 μm. 10 . The electrode according to claim 1 , wherein the carbon nanotube structure has an average diameter of 50 nm to 120 nm.

11. The electrode according to claim 1, wherein the average particle size (D 50 ) is 1nm to 500nm. 12 . The electrode according to claim 1 , wherein the carbon black is included in the electrode active material layer in an amount of 0.01 wt % to 1 wt %. 13 . The electrode according to claim 1 , wherein a weight ratio of the graphene, the carbon nanotube structure, and the carbon black is 0.01 to 3:0.01 to 0.5:0.1 to 10. 14 . The electrode according to claim 1 , wherein the carbon nanotube structure is a carbon nanotube structure in which 50 to 4,000 single-walled carbon nanotube units are bonded to each other. 15 . A secondary battery comprising the electrode according to claim 1 .

Images