Conductive agent, electrode including the same, and secondary battery including the electrode

Abstract

The present invention relates to a conductive agent comprising a first particle and a second particle, an electrode comprising the conductive agent, and a secondary battery comprising the electrode, in which the first particle comprises a secondary particle structure in which graphene sheets are connected to each other, the first particle comprises a plurality of graphene sheets arranged in different directions, and the second particles are carbon nanotubes.

Description

[0001] This application is a divisional application of a Chinese patent application filed on May 12, 2020, with application number 202080031595.0, and invention name “Conductive agent, electrode comprising the conductive agent, and secondary battery comprising the electrode”.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of Korean Patent Application No. 10-2019-0056920, filed on May 15, 2019, the disclosure of which is incorporated herein by reference. Technical Field

[0004] The present invention relates to a conductive agent, an electrode including the conductive agent, and a secondary battery including the electrode. Specifically, the conductive agent includes first particles and second particles, wherein the first particles include a secondary particle structure in which graphene sheets are connected to each other, the graphene sheets include a plurality of graphene sheets arranged in different directions, and the second particles are carbon nanotubes. Background Art

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

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

[0007] The positive electrode and / or the negative electrode may include a conductive agent to improve conductivity. Conventionally, a point-type conductive agent such as carbon black is mainly used, and in order to further improve conductivity, a linear conductive agent such as carbon nanotubes is being studied.

[0008] However, for carbon nanotubes, the conductivity is excellent, but due to the nature of the material grown in a bundle type and / or entangled type, it is not easy to disperse in the slurry used to form the electrode, so there is a problem of uneven resistance of the electrode. In order to solve the dispersibility problem, functional groups can be introduced into linear conductive agents, but since this will cause side reactions on the surface of the conductive agent, actual mass production and application are difficult. In addition, since point contact is the main contact method between carbon nanotubes in the electrode, it is limited in improving conductivity.

[0009] In order to improve this, carbon nanotubes can be used together with graphene as a planar conductive agent, in which case the line contact between carbon nanotubes and graphene increases. However, when graphene is prepared by exfoliating graphite, it is difficult to prepare thin graphene, and in the case of using thick graphene, due to the reduction of the conductive path, the battery efficiency is significantly reduced. In addition, even if thin graphene is used, the area of ​​typical graphene is too large, so the diffusion of lithium ions is also suppressed and the output characteristics are reduced. In addition, since graphene has a planar shape, the carbon of carbon nanotubes and the carbon of graphene tend to have sp2 bonds with adjacent carbon. Therefore, π-π bonds can be easily formed between the surface of carbon nanotubes and the surface of graphene, and since most of the carbon nanotubes to be connected to the surface of the electrode active material are easily aggregated (aggregation) on the surface of graphene, especially on the basal plane of graphene, there is a problem of reduced conductivity of the electrode. Furthermore, since a single graphene existing in an electrode has only one planar direction, there is a problem in that the conductivity is further reduced because the directionality of the carbon nanotubes bonded to the graphene is restricted.

[0010] Therefore, there is a need for a conductive agent that does not inhibit the diffusion of lithium ions and can minimize the aggregation of carbon nanotubes while increasing the contact between conductive agent particles. Summary of the invention

[0011] Technical issues

[0012] One aspect of the present invention provides a conductive agent, an electrode including the conductive agent, and a secondary battery including the electrode, which can ensure conductivity between electrode active material particles while increasing contact between conductive agent particles, not inhibiting diffusion of lithium ions, and minimizing aggregation of carbon nanotubes.

[0013] Technical Solution

[0014] According to one aspect of the present invention, there is provided a conductive agent including first particles and second particles, wherein the first particles include a secondary particle structure in which graphene sheets are connected to each other, the first particles include a plurality of graphene sheets arranged in different directions, and the second particles are carbon nanotubes.

[0015] According to another aspect of the present invention, there is provided an electrode including the conductive agent.

[0016] According to another aspect of the present invention, a secondary battery including the electrode is provided.

[0017] Beneficial Effects

[0018] According to the present invention, a first particle including a secondary particle structure in which a plurality of graphene sheets are connected to each other in the form of a chain and having a high dispersion level due to a high oxygen content and a second particle including a carbon nanotube are used in combination as a conductive agent. Therefore, since the conductive contact in the electrode is improved by the composite application of two different types of conductive agents (such as a planar type (first particle) and a linear type (second particle)), the conductivity in the electrode can be improved. In addition, since the first particle includes a short-length graphene sheet different from a typical graphene, the first particle does not interfere with the direct connection between the carbon nanotube and the electrode active material. In addition, since the first particle exists in the form of a chain (a three-dimensional shape rather than a planar shape) and the graphene sheets of the first particle are randomly arranged, the diffusion degree of lithium ions in the electrode can be increased. In addition, since the first particle has a high oxygen content, the repulsive force caused by the unshared electron pairs contained in the oxygen-containing functional group prevents the aggregation of the first particle and / or the second particle, and therefore, the first particle and the second particle can be effectively dispersed and present in the electrode. The conductivity of the electrode can then be further improved, and this can lead to an increase in the high-rate discharge capacity of the battery. In addition, since the graphene sheets of the first particles have different directions, the carbon nanotubes bonded to the graphene sheets can be arranged in different directions. Therefore, since the graphene sheets of the first particles act as a kind of hub, a conductive network consistent with the composite application of carbon nanotubes can be effectively formed, and the conductivity of the electrode can be further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram showing a formation process of a graphene sheet included in the first particles of the conductive agent of the present invention, a transmission electron microscope (TEM) image, and a scanning electron microscope (SEM) image;

[0020] Figure 2 TEM and scanning TEM (STEM) images of the first particle of Preparation Example 1 of the present invention;

[0021] Figure 3 is a SEM image of the first particle of Preparation Example 1 of the present invention;

[0022] Figure 4 (a) is a TEM image of the first particle of Preparation Example 1 of the present invention, and (b) is a TEM image of the first particle of Preparation Example 2;

[0023] Figure 5 is a SEM image of carbon black used in a comparative example of the present invention;

[0024] Figure 6 are SEM images of (a) graphene used in a comparative example of the present invention and (b) a positive electrode using the graphene; and

[0025] Figure 7 This is a SEM image of the positive electrode of Example 1 of the present invention. DETAILED DESCRIPTION

[0026] Hereinafter, the present invention will be described in more detail to allow a clearer understanding of the present invention. In this case, it will be understood that the terms or words used in this specification and claims should not be interpreted as the meanings defined in commonly used dictionaries, and it will be further understood that, based on the principle that the inventor can appropriately define the meanings of terms or words to best explain the present invention, these terms or words should be interpreted as having a meaning consistent with the meaning in the context of the technical concept of the present invention and the related technology.

[0027] In the present invention, the expression "graphene sheet" refers to a carbonaceous structure having a thickness of 10 nm or less, having flexibility and in a thin film form, and the graphene sheet exists in a form included in the first particle. In contrast, the expression "graphene sheet" used in the comparative example refers to a carbonaceous structure that is not included in the first particle and exists as a single particle in a thin film form.

[0028] In the present invention, the oxygen content may be measured by elemental analysis of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), and may be measured using an elemental analyzer (CHN-coder MT-5, Yanako).

[0029] In this specification, the average particle size (D 50 ) can be defined as the particle size when the cumulative volume in the particle size distribution curve is 50%. The average particle size (D 50 ) can be determined, for example, by using a laser diffraction method. The laser diffraction method can generally measure particle sizes ranging from submicron to several millimeters, and can obtain results with high repeatability and high resolution.

[0030] <Conductive Agent>

[0031] The conductive agent according to an embodiment of the present invention includes first particles and second particles, wherein the first particles include a secondary particle structure in which graphene sheets are connected to each other, the first particles include a plurality of graphene sheets arranged in different directions, and the second particles may be carbon nanotubes.

[0032] The conductive agent may include first particles and second particles.

[0033] (1) First particle

[0034] The first particle may include a structure in which a plurality of graphene sheets are connected. Specifically, in the first particle, at least two graphene sheets may be directly connected to each other or may be indirectly connected.

[0035] The first particles may be in the form of secondary particles formed by connecting a plurality of graphene sheets. Specifically, a plurality of graphene sheets may be interconnected to form secondary particles in the form of long chains, and more specifically, the secondary particles in the form of chains may partially include aggregation regions of a plurality of graphene sheets. Since the secondary particles have a unique connection structure in the form of chains, the electrical conductivity and thermal conductivity of the conductive agent including the first particles may be excellent.

[0036] When described in more detail, typical planar graphene has a two-dimensional arrangement due to its small thickness compared to the width of the plane. Therefore, most of the conductive networks formed in the electrode are formed based on a two-dimensional arrangement. In contrast, the graphene sheets included in the first particle include a plurality of graphene sheets with a random arrangement. Specifically, the graphene sheets included in the first particle include a plurality of graphene sheets with different directions (directions perpendicular to the plane of the graphene sheets). That is, the first particle can be in the form of a secondary particle with a three-dimensional arrangement formed by connecting the graphene sheets arranged in various directions to each other, and more specifically, since the graphene sheets are in the form of chains arranged longitudinally with a predetermined length and a three-dimensional arrangement at the same time, a conductive network formed in the electrode can be formed based on a three-dimensional arrangement. Therefore, since a conductive network in various directions can be formed, and a conductive connection between a linear second particle and the first particle can be effectively formed, the conductivity in the electrode can be significantly improved. In particular, considering the combined use with the carbon nanotubes described later, since the graphene sheets of the first particles have different directivities, the carbon nanotubes connected to the graphene sheets can also exist in different directions in the electrode. Therefore, a conductive network in the electrode can be formed more efficiently. Here, the first particle may also include a plurality of graphene sheets arranged in the same direction, but in this case, the first particle also includes a plurality of graphene sheets arranged in different directions.

[0037] The first particle may further include a connection portion connected to at least a portion of the graphene sheets in the plurality of graphene sheets. In the present invention, during the preparation of the first particle, the initial first particle (such as carbon black) is broken by continuous oxidation to form a graphene sheet, and there may also be a portion that maintains its original shape without being broken. In this case, the portion that maintains its shape may correspond to the connection portion. Therefore, the connection portion may have a non-graphene shape, and unlike the above-mentioned graphene sheet, the expression "non-graphene shape" may mean a block having a thickness greater than the graphene sheet, and more specifically may be in an incompletely broken block.

[0038] A portion of each of the plurality of graphene sheets may be directly connected to each other. Alternatively, at least a portion of the plurality of graphene sheets may be connected to each other through a connecting portion, and specifically, at least a portion of each of the plurality of graphene sheets may be connected to a connecting portion. The first particle of the present invention may include two connection methods.

[0039] The first particles can be formed by modifying carbon black (e.g., acetylene black, furnace black, thermal black, channel black, and lamp black) in the form of particles that are approximately spherical by oxidation treatment. Figure 1 Schematic diagram of the invention, the structure of carbon black can be modified by oxidation treatment to form particles including a plurality of graphene sheets. In the case where the carbon black is in the form of secondary particles, first particles in the form of secondary particles can be formed in which particles including a plurality of graphene sheets are aggregated.

[0040] The average thickness of the graphene sheet may be 10 nm or less, specifically 0.34 nm to 10 nm, and more specifically 0.34 nm to 5 nm. In the case where the average thickness of the graphene sheet satisfies the above range, since the flexibility unique to the graphene sheet can be exhibited, the surface contact is improved due to the graphene sheet, and thus the conductivity of the conductive agent can be excellent. The graphene sheet may have a shape in which 30 or less graphene layers are stacked. The average thickness of the graphene sheet may correspond to an average value of the thickness of 100 graphene sheets measured by identifying electrodes with a transmission electron microscope (TEM).

[0041] The lateral size of the graphene sheet may be 200 nm or less, specifically 10 nm to 200 nm or less, and more specifically 10 nm to 100 nm, for example 50 nm to 90 nm. The lateral size of the graphene sheet can be controlled according to the degree of heat treatment, and, for example, the lateral size of the graphene sheet can be controlled by further performing an additional heat treatment in an inert atmosphere after the oxidation treatment. When the lateral size of the graphene sheet satisfies the above range, the ions in the electrolyte solution can diffuse smoothly in the electrode. Therefore, the fast charging characteristics of the battery can be improved, and the rate performance can also be improved. The lateral size of the graphene sheet refers to the average value of the lateral sizes of 100 graphene sheets observed by a scanning electron microscope (SEM) or TEM, and, herein, the expression "lateral size" refers to the longest length when a line from one point to another is assumed in one graphene sheet.

[0042] The lateral dimensions of the graphene sheet are much smaller than those of typical graphene. Generally, for graphene with large lateral dimensions used as a conductive agent, the direct contact between the carbon nanotubes and the electrode active material is blocked because the graphene excessively covers the surface of the electrode active material. In contrast, since the lateral dimensions of the graphene sheet of the present invention are small, it does not interfere with the direct contact between the carbon nanotubes and the electrode active material, and is therefore effective in reducing the resistance of the electrode. These characteristics indicate that the typical graphene of the present invention and the first particle form a conductive network using completely different mechanisms, and mean that the typical graphene of the present invention and the first particle are completely different materials.

[0043] The first particles may have an oxygen content of 1 wt % or more, for example, 1 wt % to 10 wt %, based on the total weight of the first particles. When the oxygen content of the first particles satisfies the above range, since the first particles can be smoothly dispersed in the electrode slurry formed during the preparation of the electrode, the conductivity of the electrode can be improved and the capacity of the prepared battery can be increased. The oxygen content can be measured by elemental analysis of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N).

[0044] The oxygen content can be achieved during the oxidation treatment of the carbon black. Specifically, oxygen-containing functional groups can be formed on the surface of the first particles by the oxidation treatment. The oxygen-containing functional groups can be at least one selected from the group consisting of carboxyl, hydroxyl and carbonyl. After the oxidation treatment, the oxygen content can be further controlled by heat treating the first particles in an inert atmosphere.

[0045] The first particles may have a higher degree of graphitization than the carbon black before the oxidation treatment. Specifically, since the high structural stress caused by the surface tension of the spherical carbon black can be partially eliminated by forming a planar graphene sheet, and the structural defects caused by the curvature can be minimized to form a stable sp 2 structure, thus the graphitization degree of the prepared conductive agent can be improved.

[0046] During Raman spectroscopy measurement, the D / G peak ratio of the first particles may be 2.0 or less, specifically 0.9 to 2.0, and more specifically 1.1 to 1.8. In Raman spectroscopy, due to the sp 2 Key E 2g Vibration mode at 1590cm -1 G peak appears near the carbon sp 2 When the bond is defective, at 1350cm -1 That is, when the D / G peak ratio is satisfied, it indicates that a high degree of graphitization can be obtained, and therefore, when the first particles are used, the capacity and electrical characteristics of the battery can be improved due to the high conductivity of the first particles.

[0047] The first particle may have a value calculated by the following Equation 1 of 0.2 or less, specifically 0 to 0.20, and more specifically 0 to 0.15, for example, 0 to 0.1.

[0048] [Equation 1]

[0049]

[0050] In Equation 1, a is the specific surface area (m2) of the first particles measured by the nitrogen adsorption Brunauer-Emmett-Teller (BET) method. 2 / g), b is the iodine adsorption value (mg / g) of the first particle. In the case where the first particle includes a pore structure inside or between the particles, small-sized nitrogen (N2) molecules may be adsorbed in the pores in large quantities. In contrast, since iodine (I2) is a relatively large molecule and is difficult to enter the pores compared to nitrogen, the iodine adsorption value is not large. That is, when there is a pore structure, the value according to equation 1 increases. In other words, in the first particle, the value of 0.2 or less according to equation 1 means that the first particle does not include micropores or includes a small amount of micropores. That is, in the absence of micropores, since the adsorption of iodine and nitrogen are similar to each other, the value of formula 1 decreases. This means that the surface of the first particle is a free surface. Specifically, most carbon black is modified into a hollow structure by oxidation treatment, and the structure is destroyed by continuous oxidation treatment to form a graphene sheet. In this case, the graphene sheet can be formed to open outward without forming a pore structure.

[0051] The first particle may have a diameter of 200 m 2 / g or more specific surface area (m 2 / g), specifically 200m 2 / g to 1,100m 2 / g, and more specifically 300m 2 / g to 1,100m 2 / g, for example, 500m 2 / g to 900m 2 When the above-mentioned specific surface area range is satisfied, it means that the area of ​​the graphene sheet in the first particles is large, and therefore, even if the amount of the first particles in the electrode is small, the conductivity of the electrode can be ensured.

[0052] The average particle size of the first particles (D 50 ) may be 0.5 μm to 2.5 μm, specifically 0.7 μm to 2.3 μm, and more specifically 0.9 μm to 2.1 μm. When the above range is satisfied, since the first particles act as hubs of a conductive network in the electrode, electrons may be uniformly distributed in the electrode.

[0053] (2) Second particle

[0054] The second particle may be a carbon nanotube. If only the first particle is used, the viscosity of the electrode slurry is excessively increased due to the excessive specific surface area and oxygen content, thereby reducing the processability during electrode preparation. In addition, since the conductive agent is mainly composed of planar graphene sheets, the diffusion of lithium ions is hardly improved. In contrast, when carbon nanotubes are used as second particles and used in combination with the first particles, the total specific surface area and oxygen content of the conductive agent are maintained at an appropriate level, so the processability can be improved. In addition, since planar graphene sheets and linear carbon nanotubes can form a conductive network more effectively in the electrode, the diffusion of lithium ions is improved, and the rate performance and life characteristics of the battery can be improved.

[0055] The graphite sheet of carbon nanotube has a cylindrical shape with a nanometer-scale diameter and has an sp2 bonding structure. In this case, the carbon nanotube can exhibit the characteristics of a conductor or a semiconductor according to the structure and angle at which the graphite surface is rolled. According to the number of bonds forming the wall, carbon nanotubes can be divided into single-walled carbon nanotube (SWCNT, single-walled carbon nanotube) units, double-walled carbon nanotube (DWCNT, double-walled carbon nanotube) units and multi-walled carbon nanotube (MWCNT, multi-walled carbon nanotube) units.

[0056] The carbon nanotube may be a multi-walled carbon nanotube. In the case where the carbon nanotube is a single-walled carbon nanotube or a double-walled carbon nanotube, the conductivity may be reduced because the manufacturing cost of the battery is too high and the carbon nanotube unit exists in an over-aggregated state in the electrode. In contrast, in the case where the carbon nanotube is a multi-walled carbon nanotube, it can be evenly distributed in the electrode because the manufacturing price is relatively low and it is easy to disperse in the electrode slurry. Therefore, the rate performance and life characteristics of the battery can be improved.

[0057] The average diameter of the carbon nanotubes may be 1 nm to 200 nm, specifically 5 nm to 100 nm, and more specifically 5 nm to 50 nm. When the average diameter of the carbon nanotubes satisfies the above range, the carbon nanotubes can be easily dispersed in a slurry for forming an electrode, and the conductivity of the electrode can be improved. The average diameter can be confirmed by obtaining the average diameter of 100 carbon nanotubes in the electrode observed by SEM or TEM.

[0058] The Brunauer-Emmett-Teller (BET) specific surface area of ​​carbon nanotubes can be 50 m 2 / g to 500m 2 / g, specifically 100m2 / g to 400m 2 / g, and more specifically 150m 2 / g to 300m 2 When the BET specific surface area of ​​the carbon nanotubes satisfies the above range, the carbon nanotubes can be appropriately dispersed to maintain manufacturing processability, and even with a small amount of conductive agent, the formation of a conductive network can be maximized. The BET specific surface area can be measured by a nitrogen adsorption BET method.

[0059] The average length of the carbon nanotubes can be 0.1 μm to 100 μm, specifically 0.5 μm to 50 μm, and more specifically 1 μm to 20 μm. The carbon nanotubes can be appropriately dispersed, and an electrode slurry with a high solid content can be used in the preparation process of the electrode to maintain manufacturing processability. In addition, even with a small amount of conductive agent, the formation of the conductive network can be maximized. The average length can be confirmed by obtaining the average length of 100 carbon nanotubes in the electrode observed by SEM or TEM.

[0060] The weight ratio of the first particle to the second particle may be in the range of 1:9 to 9:1, specifically 2:8 to 5:5, and more specifically 3:7 to 4:6. In the case of satisfying the above range, the first particle and the second particle can be appropriately dispersed, and an electrode slurry with a high solid content can be used in the preparation process of the electrode to maintain manufacturing processability. In addition, even with a small amount of conductive agent, the formation of a conductive network can be maximized. Therefore, the rate performance and life characteristics of the battery can be improved.

[0061] <Electrode>

[0062] An electrode according to another embodiment of the present invention may include the conductive agent of the above embodiment. The electrode may be a positive electrode or a negative electrode. The electrode may include a current collector and an active material layer disposed on the current collector.

[0063] The conductive agent may be included in the active material layer in an amount of 0.1 wt % to 3.0 wt %, for example 0.5 wt % to 2.0 wt %. This corresponds to a level lower than the amount of a typical conductive agent. That is, this means that when a conductive agent according to an embodiment of the present invention is used, sufficient conductivity can be ensured even with a small amount of the conductive agent.

[0064] The positive electrode may include a current collector and a positive electrode active material layer disposed on the current collector and including a positive electrode active material. The negative electrode may include a current collector and a negative electrode active material layer disposed on the current collector and including a negative electrode active material. In addition, the positive electrode active material layer and the negative electrode active material layer may each further include a binder.

[0065] The current collector is not particularly limited as long as it has conductivity and does not cause adverse chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, or silver can be used as the current collector. Specifically, transition metals (such as copper and nickel) that can well adsorb carbon can be used as the current collector. The positive electrode active material layer or the negative electrode active material layer can be provided on one surface or both surfaces of the current collector, respectively.

[0066] The positive electrode active material can be a commonly used positive electrode active material. Specifically, the positive electrode active material can include layered compounds such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or compounds substituted by one or more transition metals; lithium manganese oxides such as Li 1+y1 Mn 2-y1 O4 (0 ≤ y1 ≤ 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; lithium nickel oxides of Ni-site type represented by the chemical formula LiNi 1-y2 M1 y2 O2 (where M1 is cobalt (Co), manganese (Mn), aluminum (Al), copper (Cu), iron (Fe), magnesium (Mg), boron (B), or gallium (Ga), and y2 satisfies 0.01 ≤ y2 ≤ 0.3); lithium manganese composite oxides represented by the chemical formula LiMn 2-y3 M2 y3 O2 (where M1 is Co, Ni, Fe, chromium (Cr), zinc (Zn), or tantalum (Ta), and y3 satisfies 0.01 ≤ y3 ≤ 0.1) or Li2Mn3M3O8 (where M3 is Fe, Co, Ni, Cu, or Zn); and LiMn2O4 in which Li is partially replaced by alkaline earth metal ions, but the positive electrode active material layer is not limited thereto.

[0067] The negative electrode active material can include graphite-based active material particles or silicon-based active material particles. At least one selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, and graphitized mesocarbon microbeads can be used as the graphite-based active material particles, and particularly when artificial graphite is used, the rate performance can be improved. At least one selected from the group consisting of silicon (Si), SiO x (0 < x < 2), Si-C composite materials, and Si-Y alloys (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, group 13 elements, group 14 elements, rare earth elements, and combinations thereof) can be used as the silicon-based active material particles, and particularly when Si is used, a battery with high capacity can be obtained.

[0068] The binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylate, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, poly acrylic acid, and materials in which hydrogen is substituted by lithium (Li), sodium (Na) or calcium (Ca), or may include various copolymers thereof.

[0069] <Secondary Battery>

[0070] A secondary battery according to another embodiment of the present invention includes a negative electrode, a positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode may be the electrode of the above-mentioned another embodiment.

[0071] The separator separates the negative electrode and the positive electrode and provides a transmission path for lithium ions, wherein any separator can be used as a separator without particular limitation, as long as it is generally used for secondary batteries, and in particular, a separator having high moisture retention capacity for electrolytes 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 having two or more layers thereof can be used. In addition, a typical porous nonwoven fabric can be used, for example, a nonwoven fabric formed by 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 having a monolayer or multilayer structure can be selectively used.

[0072] 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 molten-type inorganic electrolyte that may be used in the preparation of a lithium secondary battery, but the present invention is not limited thereto.

[0073] Specifically, the electrolyte may include a nonaqueous organic solvent and a metal salt.

[0074] As the nonaqueous 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, ethers, methyl propionate, and ethyl propionate can be used.

[0075] Specifically, in carbonate-based organic solvents, ethylene carbonate and propylene carbonate as cyclic carbonates are well dissociated lithium salts due to high dielectric constant as high viscosity organic solvents, so cyclic carbonates can be preferably used. Because when the above-mentioned cyclic carbonates are mixed with low viscosity, low dielectric constant straight-chain carbonates (such as dimethyl carbonate and diethyl carbonate) in an appropriate ratio and used, an electrolyte with high conductivity can be prepared, so cyclic carbonates can be more preferably used.

[0076] A lithium salt may be used as the metal salt, and the lithium salt is a material that is easily dissolved in a nonaqueous electrolyte solution, wherein, for example, one selected from the group consisting of the following anions may be used as an anion of the lithium salt: 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 - .

[0077] In order to improve the life characteristics of the battery, inhibit the reduction of the battery capacity, and increase the discharge capacity of the battery, in addition to the electrolyte components, the electrolyte may further include at least one of the following additives: for example, a halogenated alkylene carbonate-based compound, such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-ethylene glycol dimethyl ether (glyme), hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0078] 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 performance, and high cycle characteristics, the battery module and the battery pack can be used as a power source for medium and large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0079] <Method for preparing conductive agent>

[0080] According to another embodiment of the present invention, a method for preparing a conductive agent includes: preparing first particles; and mixing the first particles and second particles, wherein the preparation of the first particles includes preparing initial first particles; and modifying the initial first particles by oxidation treatment, wherein modifying the initial first particles by oxidation treatment includes at least one of the following: a) performing a first heat treatment on the initial first particles at a temperature of 200°C to 800°C in an oxygen atmosphere or an air atmosphere; and b) reacting the initial first particles with acidic vapor at 120°C to 300°C, and the second particles may be carbon nanotubes.

[0081] In the preparation of the initial first particles, the initial first particles may be carbon black. Specifically, the initial first particles may include at least one selected from the group consisting of acetylene black, furnace black, thermal black, channel black, and lamp black. More specifically, the initial first particles may be acetylene black, which is produced at the highest temperature to substantially have an excellent degree of graphitization.

[0082] The preparation of the initial first particles may include pyrolysis of acetylene gas, and carbon black (eg, acetylene black) may be formed by pyrolysis. The acetylene gas may be high purity acetylene gas, and specifically may be acetylene gas having a purity of 95% or more, such as 98% or more.

[0083] The pyrolysis of acetylene gas may be performed at a temperature of 1,500° C. or higher, specifically 1,500° C. to 2,200° C., and more specifically 1,500° C. to 2,000° C. When the temperature satisfies the above range, the degree of graphitization of the prepared initial first particles may be high, and the degree of graphitization of the first particles prepared thereby may also be high. Therefore, the conductivity of the conductive agent may be improved.

[0084] The initial first particles may be carbon black, but acetylene black is preferred in terms of the following aspects. The graphene sheets included in the conductive agent of the present invention may be formed by modifying the surface of the initial first particles by oxidation treatment. The surface of acetylene black formed by pyrolysis may have a high degree of graphitization. Therefore, when acetylene black is subjected to oxidation treatment, the structure of the graphene sheet can be smoothly formed, compared with the case where other carbon blacks that inevitably include some oxygen functional groups on their surfaces are subjected to oxidation treatment.

[0085] The pyrolysis can be performed in the following manner: after the internal temperature of the reaction furnace is adjusted to the above temperature range, acetylene gas is introduced into the reaction furnace and the pyrolysis is immediately performed. In addition, in this process, air, oxygen and H2O can be further added to control the density of the conductive agent and the oxygen functional group, and the connection structure in the conductive agent can be controlled.

[0086] Modification of the initial first particles by oxidation treatment may include at least one of: a) subjecting the initial first particles to a first heat treatment at a temperature of 200°C to 800°C in an oxygen atmosphere or an air atmosphere (step a); and b) reacting the initial first particles with acidic vapor at 120°C to 300°C (step b).

[0087] In step a, an oxygen atmosphere or an air atmosphere may be formed by introducing oxygen or air into a reaction furnace containing the initial first particles. Specifically, a graphene sheet structure may be formed by oxidation treatment in the reaction furnace according to the setting of an appropriate flow rate and rate of oxygen or air during the first heat treatment, a reaction temperature, and a reaction time. In addition, the conditions of the oxidation treatment may vary according to the difference in the density of the initial first particles and the amount of oxygen functional groups.

[0088] In step a, the first heat treatment may be performed by controlling the temperature of the reaction furnace in the reaction furnace containing the initial first particles. The first heat treatment may be performed at a heat treatment temperature of 200° C. to 800° C., and specifically may be performed at a heat treatment temperature of 200° C. to 450° C. When the heat treatment temperature satisfies the above range, excessive oxidation of the initial first particles may be prevented, and a graphene sheet having a desired size may be formed. The first heat treatment may be performed for 1 hour to 50 hours.

[0089] In step b, the initial first particles may react with the acidic vapor to be oxidized to form graphene sheets. Specifically, the acidic vapor may be vapor derived from an acidic solution such as HCl and HNO3. The temperature of the acidic vapor reacting with the initial first particles may be in the range of 120°C to 300°C.

[0090] After the initial first particles are modified by oxidation treatment, a second heat treatment process may be further performed in an inert atmosphere to increase the size of the formed graphene sheets. Specifically, the method for preparing a conductive agent may further include: after the initial first particles are modified by oxidation treatment, a second heat treatment is performed on the initial first particles modified by oxidation treatment in an inert atmosphere at a temperature of 500°C or higher. In this case, the inert atmosphere may be formed by a vacuum or any one gas selected from the group consisting of helium, argon and nitrogen. The second heat treatment temperature may be 500°C or higher, specifically 500°C to 2,800°C, and more specifically 600°C to 1,600°C.

[0091] The mechanism of forming the first particle described in the present invention can be as follows. During the preparation of the first particle, spherical or chain carbon black (e.g., acetylene black) is subjected to oxidation treatment under specific conditions, wherein the average diameter of the spherical primary particles is 50nm or less, and the primary particles share the structure. In this case, the penetration and oxidation reaction of the oxidant (such as oxygen and acidic vapor) from the defects (defect) such as grain boundary (grain boundary) or dislocation (dislocation) present in the unit microstructure of the carbon black partially occurs. When the oxidation treatment is carried out for a predetermined time within the temperature range described in the preparation method, the oxidant penetrates into the internal microstructure of the carbon black, thereby causing oxidation. In this case, in order to alleviate the structural stress of the microstructure of the primary particles with a radius of curvature larger than the radius of curvature of the surface of the spherical primary particles, oxidation reaction occurs rapidly in the primary particles. Therefore, the internal carbon atoms are oxidized into gases such as CO, CO2 and CH4, and the primary particles are transformed into hollow types (hollow type). While the surface structure of the hollow primary particles is destroyed by continuous oxidation treatment, most of the structural stress remaining in the spherical primary particles is also relieved, and graphene sheets appear in the process. Therefore, as the average diameter of the carbon black as the primary particles decreases, the internal density of the particles decreases, and the amount of oxygen functional groups in the primary particles is greater than the amount of oxygen functional groups on the surface of the primary particles, the modification process can be accelerated. In addition, in terms of the fact that step a can further accelerate the modification process, step a is more preferable than step b.

[0092] The second particles may be carbon nanotubes. The second particles are the same as the second particles of the above embodiment.

[0093] The second particles can be prepared by dispersing bundle-type or entangled-type carbon nanotubes in a state of dispersion. The expression "bundle-type carbon nanotubes" means a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotubes are arranged side by side in substantially the same direction as the longitudinal axis of the carbon nanotubes. The expression "entangled-type carbon nanotubes" means that a plurality of carbon nanotubes are entangled with each other.

[0094] Thereafter, a step of mixing the first particles and the second particles is performed. The first particles and the second particles may be mixed by mixing a first particle dispersion containing the first particles and a second particle dispersion containing the second particles. The mixing may be performed during the preparation of an electrode slurry for forming an electrode.

[0095] Hereinafter, embodiments of the present invention will be described in detail in a manner that can be easily implemented by those skilled in the art. However, the present invention can be implemented in many different forms and should not be construed as limited to the embodiments set forth herein.

[0096] Preparation Example 1: Preparation of the first particle

[0097] (1) Formation of initial first particles (acetylene black)

[0098] Acetylene black is formed by thermal decomposition of 98% pure acetylene gas by instantaneously injecting acetylene gas into a reaction furnace with an internal temperature of 2,000°C.

[0099] (2) Preparation of the first particle

[0100] Subsequently, the internal temperature of the reaction furnace containing acetylene black was set to 250° C., and then an oxidation treatment was performed for 30 hours while introducing oxygen. As a result, first particles having a secondary particle structure including a chain of graphene sheets having a lateral size of about 40 nm connected to each other were obtained, wherein the graphene sheets included a plurality of graphene sheets arranged in different directions. (See Figure 2 and Figure 3 ).

[0101] Preparation Example 2: Preparation of the first particle

[0102] The conductive agent obtained in Preparation Example 1 was subjected to an additional heat treatment at 900° C. for 1 hour in an inert atmosphere to obtain first particles having a secondary particle structure including a plurality of graphene sheets having a lateral size of about 65 nm connected to each other in a chain shape, wherein the graphene sheets include a plurality of graphene sheets arranged in different directions. Figure 4 It can be understood that by heat treatment Figure 4The first particle of Preparation Example 1 shown in (a) is modified to Figure 4 (b) The first particle of Preparation Example 2. Specifically, it can be understood that since adjacent graphene sheets are interconnected by heat treatment, the lateral size increases.

[0103] Example 1: Preparation of a battery

[0104] (1) Preparation of the first particle dispersion

[0105] The first particles of Preparation Example 1, hydrogenated nitrile rubber (H-NBR) as a dispersant, and N-methylpyrrolidone (NMP) as a dispersion medium were mixed in a weight ratio of 5.7:1.7:92.6 to prepare a mixture. The mixture was added to a pin mill in which 80% was filled with beads having a diameter of 0.65 mm, dispersed, and discharged at a discharge rate of 2 kg / min. This procedure was performed 4 times to prepare a first particle dispersion containing first particles having a controlled particle size distribution.

[0106] (2) Preparation of Second Particle Dispersion

[0107] The bundled multi-walled carbon nanotubes, hydrogenated nitrile rubber (H-NBR) as a dispersant, and N-methylpyrrolidone (NMP) as a dispersion medium were mixed in a weight ratio of 4:0.8:95.2 to prepare a mixture. The mixture was added to a pin mill in which 80% was filled with beads having a diameter of 0.65 mm, dispersed, and discharged at a discharge rate of 2 kg / min. This process was performed twice to prepare a second particle dispersion containing second particles (carbon nanotubes) having a controlled particle size distribution.

[0108] (3) Preparation of positive electrode slurry

[0109] As the positive electrode active material, Li[Ni 0.6 Mn 0.2 Co 0.2 ]O2, polyvinylidene fluoride (PVdF) as a binder, a first particle dispersion, a second particle dispersion, and NMP as a solvent were mixed and stirred to prepare a positive electrode slurry with a solid content of 72%. The weight ratio of the positive electrode active material, PVdF, the first particles of Preparation Example 1, and the second particles in the positive electrode slurry was 96.5:1.5:0.8:1.2.

[0110] (4) Preparation of positive electrode

[0111] The positive electrode current collector (Al) with a thickness of 20 μm was coated with the positive electrode slurry so that the solid loading was 21 mg / cm 2Then, the positive electrode current collector on which the positive electrode slurry was placed was rolled by a rolling method so that the total thickness of the positive electrode slurry and the positive electrode current collector was 77 μm. Then, the positive electrode slurry and the positive electrode current collector were dried at 130° C. for 6 hours to prepare a positive electrode.

[0112] (5) Preparation of secondary batteries

[0113] Artificial graphite as a negative electrode active material, carbon black as a negative electrode conductive agent, styrene butadiene rubber (SBR) as a negative electrode binder, and carboxymethyl cellulose (CMC) were mixed in distilled water at a weight ratio of 96.1:0.5:2.3:1.1 to prepare a negative electrode slurry. A negative electrode current collector (Cu) having a thickness of 20 μm was coated with the prepared slurry so that the loading amount was 10 mg / cm 2 Then, the negative electrode current collector on which the negative electrode slurry was placed was rolled by a rolling method so that the total thickness of the negative electrode slurry and the negative electrode current collector was 80 μm. Then, the negative electrode slurry and the negative electrode current collector were dried at 110° C. for 6 hours to prepare a negative electrode (see Figure 7 ).

[0114] Thereafter, after preparing a single cell by combining the above-prepared negative electrode and positive electrode with a 15 μm thick polyethylene-based separator disposed therebetween, an electrolyte solution (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 1 / 2 (volume ratio)) and lithium hexafluorophosphate (1M LiPF6) were injected into the single cell to prepare a lithium secondary battery.

[0115] Example 2: Preparation of a battery

[0116] A battery was prepared in the same manner as in Example 1, except that in the preparation of the positive electrode slurry, the weight ratio of the positive electrode active material, PVdF, the first particles of Preparation Example 1, and the second particles was 96.5:1.5:0.2:1.8.

[0117] Example 3: Preparation of battery

[0118] A battery was prepared in the same manner as in Example 1, except that in the preparation of the positive electrode slurry, the weight ratio of the positive electrode active material, PVdF, the first particles of Preparation Example 1, and the second particles was 96.5:1.5:1.8:0.2.

[0119] Example 4: Preparation of battery

[0120] A battery was prepared in the same manner as in Example 1, except that in the preparation of the positive electrode slurry, the first particles of Preparation Example 2 were used instead of the first particles of Preparation Example 1.

[0121] Comparative Example 1: Preparation of a battery

[0122] (1) Preparation of positive electrode slurry

[0123] As the positive electrode active material, Li[Ni 0.6 Mn 0.2 Co 0.2 ]O2, polyvinylidene fluoride (PVdF) as a binder, a first particle dispersion (the same as the first particle dispersion used in Example 1) and NMP as a solvent were mixed and stirred to prepare a positive electrode slurry with a solid content of 72%. The weight ratio of the positive electrode active material, PVdF, and the first particles of Preparation Example 1 in the positive electrode slurry was 96.5:1.5:2.0.

[0124] (2) Preparation of batteries

[0125] A battery was prepared in the same manner as in Example 1, except that the above-mentioned positive electrode slurry was used.

[0126] Comparative Example 2: Preparation of a battery

[0127] (1) Preparation of positive electrode slurry

[0128] As the positive electrode active material, Li[Ni 0.6 Mn 0.2 Co 0.2 ]O2, polyvinylidene fluoride (PVdF) as a binder, a second particle dispersion (the same as the second particle dispersion used in Example 1) and NMP as a solvent were mixed and stirred to prepare a positive electrode slurry with a solid content of 72%. The weight ratio of the positive electrode active material, PVdF, and the second particles in the positive electrode slurry was 96.5:1.5:2.0.

[0129] (2) Preparation of batteries

[0130] A battery was prepared in the same manner as in Example 1, except that the above-mentioned positive electrode slurry was used.

[0131] Comparative Example 3: Preparation of a battery

[0132] A battery was prepared in the same manner as in Example 1, except that the first and second particles were not used and the average particle size (D 50 ) is 23nm carbon black (see Figure 5 ) was used as a conductive agent. In this case, the weight ratio of the positive electrode active material, PVdF, and carbon black in the positive electrode was 96.5:1.5:2.0.

[0133] Comparative Example 4: Preparation of a battery

[0134] A battery was prepared in the same manner as in Example 1, except that the first and second particles were not used, and graphene (BTR New Energy Materials, Inc.) having an average thickness of more than 100 nm and an average size of 5.5 μm (see Figure 6 ) was used as a conductive agent. In this case, the weight ratio of the positive electrode active material, PVdF and graphene in the positive electrode was 96.5:1.5:2.0. The average thickness and average size were calculated as the average of 100 graphenes observed by SEM or TEM.

[0135] Comparative Example 5: Preparation of a battery

[0136] A battery was prepared in the same manner as in Example 1, except that carbon black was used instead of the first particles. In this case, the weight ratio of the positive electrode active material, PVdF, carbon black, and carbon nanotubes (second particles) in the positive electrode was 96.5:1.5:0.8:1.2.

[0137] Comparative Example 6: Preparation of a battery

[0138] The battery was prepared in the same manner as in Example 1, except that graphene (BTR New Energy Materials, Inc.) having an average thickness of more than 100 nm and an average size of 5.5 μm was used instead of the first particles. In this case, the weight ratio of the positive electrode active material, PVdF, graphene, and carbon nanotubes (second particles) in the positive electrode was 96.5:1.5:0.8:1.2.

[0139] Hereinafter, physical properties of the conductive agents used in Examples 1-4 and Comparative Examples 1-6 (first particles of Preparation Examples 1 and 2, carbon nanotubes, carbon black and graphene, respectively) were evaluated and shown in Tables 1 to 5. Specifically, the physical properties were evaluated by the following methods.

[0140] 1) Lateral size (nm) of graphene sheets included in first particles: After measuring the sizes of 100 graphene sheets included in the first particles in the positive electrode using TEM (JEOL, JEM-2010F), evaluation was performed from the average value of the sizes.

[0141] 2) Lateral size of graphene: After measuring the sizes of 100 graphene sheets included in the positive electrode with TEM (JEOL, JEM-2010F), evaluation was performed from the average value of the sizes.

[0142] 3) Nitrogen adsorption specific surface area (m 2 / g): measured by degassing at 200°C for 8 hours and performing N2 adsorption / desorption at 77K using a BET measuring instrument (BEL-SORP-MAX, Nippon Bell).

[0143] 4) Iodine adsorption value (mg / g): measured according to ASTM D1510.

[0144] 5) Oxygen content (wt%): The amounts of C, H, and N elements were measured by an element analyzer (CHN-coder MT-5, Yanako), and the oxygen (Oxygen) content (differential) was calculated to reflect the amount of residual ash.

[0145] 6) Raman spectrum D / G ratio: The ratio was measured by analyzing the Raman spectrum obtained by using an Ar-ion laser with a wavelength of 514.5 nm using a Raman spectrometer (NRS-2000B, Jasco).

[0146] 7) Average particle diameter of carbon black: After measuring the first particle diameters of 100 carbon black particles in the positive electrode using TEM (JEOL, JEM-2010F), evaluation was performed from the average value of the diameters.

[0147] [Table 1]

[0148]

[0149] [Table 2]

[0150] Average diameter(nm) Average length (μm) <![CDATA[Specific surface area (m 2 / g)]]> Carbon Nanotubes 12 15 184

[0151] [Table 3]

[0152] Average particle size (μm) <![CDATA[Specific surface area (m 2 / g)]]> Carbon Black 23 135

[0153] [Table 4]

[0154]

[0155] Test Example 1: Evaluation of discharge capacity based on discharge C-rate

[0156] The results of evaluating the lithium secondary batteries prepared in Examples 1-4 and Comparative Examples 1-6 for each discharge C-rate are given in Table 5. Specifically, the charge C-rate was fixed to 0.2C, and while increasing the discharge C-rate from 0.2C to 2.0C, the 2.0C discharge capacity (%) relative to the 0.2C discharge capacity was evaluated.

[0157] [Table 5]

[0158] 2.0C discharge capacity relative to 0.2C discharge capacity (%) Example 1 94.6 Example 2 92.8 Example 3 90.5 Example 4 96.1 Comparative Example 1 83.9 Comparative Example 2 87.4 Comparative Example 3 75.2 Comparative Example 4 68.3 Comparative Example 5 88.2 Comparative Example 6 89.7

[0159] According to Table 5, it can be understood that the rate performance of the embodiment in which the first particles and the second particles (carbon nanotubes) are used together is significantly better than the rate performance of the comparative example in which the first particles and the second particles (carbon nanotubes) are not used together. In addition, it can be understood that the rate performance of Example 1 in which the weight ratio of the first particles to the second particles satisfies 2:8 to 5:5 is higher than the rate performance of Examples 2 and 3 in which the weight ratio of the first particles to the second particles is outside the above range.

[0160] Furthermore, it can be understood that the rate performance of Example 4, in which first particles including graphene sheets having a larger lateral size are used, is higher than that of Example 1.

[0161] The present invention also relates to the following technical solutions:

[0162] 1. A conductive agent comprising first particles and second particles,

[0163] wherein the first particle comprises a secondary particle structure in which graphene sheets are connected to each other,

[0164] The first particle includes a plurality of graphene sheets arranged in different directions, and

[0165] The second particles are carbon nanotubes.

[0166] 2. The conductive agent according to item 1, wherein the oxygen content of the first particles is in the range of 1 wt % to 10 wt % based on the total weight of the first particles.

[0167] 3. The conductive agent according to item 1, wherein the lateral dimension of the graphene sheet is 10 nm to 200 nm.

[0168] 4. The conductive agent according to item 1, wherein during Raman spectroscopy measurement, a D / G peak ratio of the first particles is 0.9 to 2.0.

[0169] 5. The conductive agent according to item 1, wherein the first particles have a value calculated by equation 1 of 0 to 0.2:

[0170] [Equation 1]

[0171]

[0172] Wherein, in equation 1, a is the specific surface area (m2) of the first particle measured by the nitrogen adsorption Brunauer-Emmett-Teller (BET) method. 2 / g), and b is the iodine adsorption value of the first particles (mg / g).

[0173] 6. The conductive agent according to item 1, further comprising a connecting portion connected to at least a portion of the plurality of graphene sheets,

[0174] Wherein, the connecting portion has a non-graphene shape.

[0175] 7. The conductive agent according to item 6, wherein at least a portion of each of the plurality of graphene sheets is connected to the connecting portion.

[0176] 8. The conductive agent according to item 1, wherein the average thickness of the graphene sheet is 0.34 nm to 10 nm.

[0177] 9. The conductive agent according to claim 1, wherein the first particles have a diameter of 200 m 2 / g to 1,100m 2 The specific surface area (m 2 / g).

[0178] 10. The conductive agent according to item 1, wherein the average diameter of the carbon nanotubes is 1 nm to 200 nm.

[0179] 11. The conductive agent according to item 1, wherein the carbon nanotubes are multi-walled carbon nanotubes.

[0180] 12. The conductive agent according to item 1, wherein the average length of the carbon nanotubes is 0.1 μm to 100 μm.

[0181] 13. The conductive agent according to item 1, wherein a weight ratio of the first particles to the second particles is in the range of 1:9 to 9:1.

[0182] 14. The conductive agent according to item 1, wherein a weight ratio of the first particles to the second particles is in the range of 2:8 to 5:5.

[0183] 15. An electrode, comprising the conductive agent described in item 1.

[0184] 16. A secondary battery comprising:

[0185] positive electrode;

[0186] negative electrode;

[0187] A separator disposed between the positive electrode and the negative electrode; and

[0188] Electrolytes,

[0189] Wherein at least one of the positive electrode and the negative electrode is the electrode described in item 15.

Claims

1. An electrode comprising a conductive agent, The conductive agent includes first particles and second particles, wherein the first particle comprises a secondary particle structure in which graphene sheets are connected to each other, The first particle includes a plurality of graphene sheets arranged in different directions, and The second particles are carbon nanotubes. 2 . The electrode according to claim 1 , wherein the oxygen content of the first particles is in the range of 1 wt % to 10 wt % based on the total weight of the first particles.

3. The electrode according to claim 1, wherein the lateral size of the graphene sheet is 10 nm to 200 nm. The electrode according to claim 1 , wherein during Raman spectroscopy measurement, a D / G peak ratio of the first particles is 0.9 to 2.

0.

5. The electrode according to claim 1, wherein the first particles have a value calculated by Equation 1 of 0 to 0.2: [Equation 1] in, In Equation 1, a is the specific surface area (m2) of the first particle measured by the nitrogen adsorption Brunauer-Emmett-Teller (BET) method. 2 / g), and b is the iodine adsorption value of the first particles (mg / g).

6. The electrode according to claim 1, further comprising a connection portion connected to at least a portion of the plurality of graphene sheets, in, The connecting portion has a non-graphene shape. 7 . The electrode according to claim 6 , wherein at least a portion of each of the plurality of graphene sheets is connected to the connection portion. 8 . The electrode according to claim 1 , wherein the average thickness of the graphene sheet is 0.34 nm to 10 nm.

9. The electrode according to claim 1, wherein the first particles have a diameter of 200 m 2 / g to 1,100m 2 The specific surface area (m 2 / g). 10 . The electrode according to claim 1 , wherein the carbon nanotubes have an average diameter of 1 nm to 200 nm.

11. The electrode according to claim 1, wherein the carbon nanotubes are multi-walled carbon nanotubes. 12 . The electrode according to claim 1 , wherein the carbon nanotubes have an average length of 0.1 μm to 100 μm. 13 . The electrode according to claim 1 , wherein a weight ratio of the first particles to the second particles is in a range of 1:9 to 9:

1. 14 . The electrode according to claim 1 , wherein a weight ratio of the first particles to the second particles is in a range of 2:8 to 5:

5.

15. A secondary battery comprising: positive electrode; negative electrode; a separator disposed between the positive electrode and the negative electrode; and Electrolytes, At least one of the positive electrode and the negative electrode is the electrode according to claim 1.

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