Title of the invention: conductive material, slurry for electrode formation including the same, electrode, and lithium secondary battery manufactured using the same Technical field [One] Mutual citation with related applications [2] This application claims the benefit of priority based on Korean Patent Application No. 2018-0009777 filed on January 26, 2018, and all contents disclosed in the documents of the Korean patent application are included as part of this specification. [3] [4] Technical field [5] The present invention relates to a conductive material and a lithium secondary battery manufactured using the same, and more particularly, a conductive material including graphene flakes having excellent dispersibility and electrical conductivity, a slurry for electrode formation including the same, It relates to an electrode and a lithium secondary battery manufactured using the same. [6] Background [7] As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self-discharge rate have been commercialized and widely used. In addition, as such an electrode for a high-capacity lithium secondary battery, research is being actively conducted on a method for manufacturing a high-density electrode having a higher energy density per unit volume. [8] In general, a high-density electrode is manufactured through a process of forming a mixture layer by applying a slurry containing electrode active material particles having a size of several µm to several tens of µm on a substrate, drying, and then rolling. However, the shape of the electrode active material particles may be deformed by the high pressure press applied in the rolling step, and the space between the particles may also decrease, so that the permeability of the electrolyte solution in the mixture layer may be reduced. [9] In order to solve the above problems, in the process of forming the mixture layer of the electrode, in addition to the electrode active material particles, a conductive material having excellent strength and electrical conductivity is used together. When a conductive material is used in manufacturing an electrode, the conductive material is dispersed between the compressed electrode active material, thereby maintaining micropores between the active material particles, thereby improving permeability of the electrolyte. In addition, since the conductive material has high conductivity, the resistance within the electrode can be reduced. Recently, research has been conducted to use carbon nanotubes (CNT), graphene, carbon black, etc. as conductive materials. [10] Carbon nanotubes, which are a kind of fine carbon fiber, are tubular carbons with a diameter of less than 1 µm, and are increasingly used due to high conductivity, tensile strength, and heat resistance due to their specific structure. However, carbon nanotubes have a problem in that they are easily aggregated due to the strong van der Waals attraction between them, and thus there is a problem in that solubility and dispersibility are low. In order to solve this problem, a method of introducing a functional group to the surface of a carbon nanotube has been devised, but side reactions may occur, so it is still difficult to commercialize it as a conductive material. [11] Graphene is a semi-metallic material with a layered structure formed by forming an arrangement in which carbon atoms are connected in a hexagonal shape by sp2 bonds in two dimensions. Graphene not only has excellent electrical conductivity, but also has structural and chemical stability and excellent thermal conductivity. In addition, it is easy to process a one-dimensional or two-dimensional nano pattern made of only carbon, which is a relatively light element. Above all, the graphene sheet is an inexpensive material and has excellent price competitiveness compared to conventional nanomaterials. [12] Due to such excellent properties of graphene, various methods for more effectively mass-producing graphene from carbon-based materials such as graphite have been proposed or studied. [13] For example, a method of manufacturing graphene by pulverizing graphite with a dispersant has been devised, but it is difficult to obtain graphene of the desired size and shape due to excessive pulverization of graphite, and types of dispersant that can be used There is also a problem of being limited. [14] Therefore, it is necessary to develop graphene having high dispersibility and electrical conductivity of a certain level or higher and a conductive material using the same. [15] (Patent Document 1) Korean Patent Application Publication No. 10-2011-0077606 [16] Detailed description of the invention Technical challenge [17] The present invention is to solve the above problems, a conductive material including graphene flakes that can significantly improve dispersibility while having excellent electrical conductivity, slurry for electrode formation including the same, an electrode, and It is to provide a lithium secondary battery manufactured using this. [18] Means of solving the task [19] In one aspect, the present invention includes graphene flakes in which the maximum peak is observed in the range of 24.5° to 26° in the data graph obtained by X-ray diffraction (XRD) analysis, and the graphene flakes It provides a conductive material having an aspect ratio of 500 to 50,000 with respect to the average thickness of graphene flakes in a direction perpendicular to the plane relative to the average long axis length of the plane. [20] At this time, the average thickness of the graphene flakes may be 1 ㎚ to 10 ㎚. [21] On the other hand, the graphene flakes were obtained by Raman spectroscopy using a laser having a wavelength of 532 nm with respect to the maximum peak intensity of the G band at 1580 ± 50 cm -1 , the maximum peak intensity of the D band at 1360 ± 50 cm -1 The average value of the ratio of may be 0.06 to 0.5. [22] In another aspect, the present invention is an electrode active material; bookbinder; Dispersion medium; And it provides an electrode forming slurry containing the conductive material, an electrode manufactured using the same, and a lithium secondary battery. [23] Effects of the Invention [24] The conductive material according to the present invention includes graphene flakes in which the maximum peak is observed in the range of 24.5° to 26° in the data graph obtained by X-Ray Diffraction (XRD) analysis, so peelability and crystallinity This is excellent. In addition, including graphene flakes in which the aspect ratio to the thickness of the graphene flakes in the vertical direction of the plane to the long axis length of the plane of the graphene flakes satisfies an appropriate level, it has high dispersibility and is uniform within the electrode. It can be positioned so that the electrical conductivity in the electrode can be improved. [25] In addition, even when a small amount of the electrode forming slurry containing the conductive material is used, the electrical conductivity is maintained at a certain level or higher, and the dispersibility and viscosity are high, so that the electrode adhesion can be improved. [26] Brief description of the drawing [27] 1 is a graph of data obtained by X-ray diffraction (XRD) of graphene flakes prepared in Example 1 and Comparative Examples 1 and 2 of the present invention. [28] 2 is a graph of data obtained by XPS analysis of graphene flakes of Example 1 and Comparative Examples 1 and 2 of the present invention. [29] 3 is a graph observing a change in powder resistance according to the press density of the electrode forming slurry according to Examples 2 to 4 and Comparative Examples 3 to 6 of the present invention. [30] 4 is a graph measuring adhesion when the electrode-forming slurry according to Examples 2 to 4 and Comparative Examples 3 to 6 of the present invention is peeled off at 90°. [31] 5 is a graph showing the capacity retention rate (capacity retention%) according to the cycle at 45° C. of the manufactured secondary battery manufactured according to the manufacturing example of the present invention. [32] FIG. 6 is a graph showing the capacity retention% and resistance increase (%) measured in weeks at 60° C. of a manufactured secondary battery manufactured according to Preparation Example of the present invention. . [33] Best mode for carrying out the invention [34] Hereinafter, the present invention will be described in more detail to aid understanding of the present invention. [35] The terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of ​​the present invention based on the principle that there is. [36] The terms used in the present specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. [37] In the present specification, terms such as "comprise", "include", or "have" are intended to designate the presence of implemented features, numbers, steps, elements, or a combination thereof, and one or more other features or It is to be understood that the possibility of the presence or addition of numbers, steps, components, or combinations thereof is not preliminarily excluded. [38] [39] Conductive material [40] The conductive material according to the present invention includes graphene flakes whose maximum peak is observed in the range of 24.5° to 26° in the data graph obtained by X-ray diffraction (XRD) analysis, and the graphene flake surface The aspect ratio for the average thickness of the graphene flakes in the direction perpendicular to the plane relative to the average long axis length of is 500 to 50,000. [41] [42] In general, in order to manufacture an electrode for a secondary battery including a conductive material, a slurry for forming an electrode including a conductive material is prepared, and then the electrode forming slurry is applied to a substrate, followed by drying and rolling processes to manufacture an electrode. Therefore, only when the conductive material is uniformly dispersed in the electrode forming slurry and the slurry can maintain a certain level of viscosity, the conductive material is uniformly dispersed on the surface of the substrate to improve electrical conductivity. [43] However, in the case of graphene, which is conventionally used as a conductive material, there is a problem that the dispersibility and viscosity of the electrode forming slurry including the same are deteriorated because the peeling is not properly performed as a single layer. [44] On the other hand, in the present invention, in the data graph obtained by X-Ray Diffraction (XRD) analysis, graphene flakes in which the maximum peak is observed in the range of 24.5° to 26° of 2θ (2theta) is the conductive material of the present invention. Was used as (see Fig. 1). [45] The X-ray diffraction analysis can be derived from the results measured using a thin film X-ray diffraction analyzer (Rigaku Ultima IV). The applied voltage can be set to 40 kV and the applied current can be set to 40 mA, and the measured range of 2 θ is 24° to 28°, and can be measured by scanning at 0.2° intervals. At this time, the slit may use a variable divergence slit 2 mm. [46] Referring to FIG. 1, when the range of 2θ is 24.5° to 26°, the graphene flake according to the present invention shows a broad peak in a wide shape around 25° to 26°. In this specification, the maximum peak is defined as a peak having the highest intensity value within the 2θ range. [47] The reason that the graphene flakes of the present invention have the maximum peak within the 2θ range is that when the single-layer thin film peeled off from graphite is re-laminated, the interlayer gap between the single-layer thin films re-laminated by a dispersant adsorbed between the layers or a newly formed pore structure is Because it has increased. Therefore, it can be seen that the graphene flakes according to the present invention are sufficiently peeled off and formed in a single layer form. [48] On the other hand, graphene flakes in which peeling has not sufficiently progressed have a maximum peak observed around 26.5°, similar to graphite before peeling. [49] [50] Meanwhile, the graphene flake has a full width at half-maximum (FWHM) of the maximum peak in the range of 24.5° to 26° of 2θ in the data graph obtained by an X-ray diffraction analyzer (Rigaku Ultima IV). It may be from 0.5° to 5°. [51] In the present invention, the half width (FWHM) is the peak width at the position of 1/2 of the maximum peak intensity in the range of 24.5° to 26° of 2θ (theta) obtained from X-ray diffraction of the graphene flake. I did it. Even if the thin film peeled off from graphite is re-laminated during the production of graphene flakes, if the interlayer spacing to be re-laminated is not constant, the value of the corresponding half width increases. At this time, since the degree of peeling is higher as the interlayer spacing is re-laminated without being uniform, the value of the half width is preferably 0.5° to 5°. [52] [53] Meanwhile, an aspect ratio to the thickness of the graphene flake in a direction perpendicular to the surface of the graphene flake relative to the long axis length of the surface of the graphene flake may be 500 to 50,000, preferably 1,000 to 50,000. This is when the graphene flakes of the present invention exist in the form of a plate, the average lateral size of the plane is 5 µm to 50 µm, and the average thickness of the graphene flakes is 1 It is due to being in the range of nm to 10 nm. [54] At this time, the long axis length and thickness of the graphene flakes can be measured with an atomic force microscope (AFM), and the average long axis length and average thickness can be statistically calculated through measurement directly from the image acquired during AFM measurement. For example, after observing hundreds or thousands of graphene flakes, the length and thickness of the long axis of the observed graphene flakes were measured, respectively, and then the upper part and the lower part were collected in order of length. Thereafter, the average long axis length and average thickness of the graphene flakes can be measured by taking an average of the collected long axis length and thickness, respectively. [55] [56] If the aspect ratio is less than 500, the peelability of graphene flakes may not be excellent, so it may be difficult to form a minimum conductive network for expressing electrical conductivity. If it exceeds 50,000, the area of ​​graphene flakes is too large, It is difficult to access into this active material, and there is a possibility of increasing the diffusion resistance of electrolytic ions. [57] [58] On the other hand, in the case of the graphene flake of the present invention , the D band at 1360 ± 50 cm -1 for the maximum peak intensity of the G band at 1580 ± 50 cm -1 obtained by Raman spectroscopy using a laser having a wavelength of 532 nm The average value of the ratio of the maximum peak intensity of may be 0.06 to 0.5, more preferably 0.06 to 0.4. [59] Raman spectroscopy is a method of analyzing the crystallinity of graphene flakes, and is a useful method for analyzing the surface state of graphene flakes. The peak present in the region near the wavenumber of 1580 ± 50 cm -1 in the Raman spectrum is referred to as the G peak, which is a peak indicating sp 2 binding of graphene flakes . On the other hand, the Raman frequency of 1360 ± 50 cm spectrum -1 is called a peak present in the region in the vicinity of the D peak, which Yes pin sp of flakes 3 as a peak indicating a bond, sp for mangmyeon hexagonal graphite layer 2 bonds are broken It increases when sp 3 is bonded. Therefore, in the case of having a ratio of the maximum peak intensity of the D band at 1360 ± 50 cm -1 to the maximum peak intensity of the G band within 1580 ± 50 cm -1 , the intrinsic crystalline destruction is minimized and the peeling is remarkable. Can provide graphene flakes. [60] [61] In addition, the oxygen content of the graphene flakes may be 5 atomic% to 10 atomic%, preferably 5.5 atomic% to 10 atomic%, more preferably 6 atomic% to 10 atomic%. The oxygen content in graphene flakes is measured by X-ray photoelectron spectroscopy (XPS). Oxygen is contained in the graphene flakes because a surfactant including an oxygen functional group is adsorbed on the surface of the graphene flakes in the process of being peeled from the graphite. On the other hand, when oxygen is contained in the graphene flakes within the above range, electrical repulsion is generated, so that it can be more evenly dispersed in the slurry for forming an electrode. [62] [63] The conductive material according to the present invention may further include other conductive materials in addition to the graphene flakes. For example, graphite; Carbon-based materials such as carbon black, carbon nanotube, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used. Specific examples of commercially available conductive materials include acetylene black-based Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, EC The group (Armak Company), Vulcan XC-72 (Cabot Company) and Super P (Timcal). [64] [65] Hereinafter, a method of manufacturing a conductive material will be described. The conductive material may be prepared through (1) preparing an ionic solution, (2) preparing a graphite mixture solution, and (3) obtaining graphene flakes. Each step will be described below. [66] (1) Ionic solution preparation step [67] The ionic solution may be prepared by mixing an organic solvent, naphthalene, and potassium (K). [68] The naphthalene and potassium (K) are used to form the potassium (K) complex, and as electrons of the potassium (K) are transferred to naphthalene, they become ionized and coordinate with the organic solvent molecules to form the potassium (K) complex. The potassium (K) may be contained in a concentration of 0.1 to 2 M, preferably 1 to 2 M, in the ionic solution to form a complex. When the potassium (K) is included in the above range, the intercalation reaction of the potassium complex may proceed between the layers of the mixed graphite. [69] The organic solvent is used as a constituent of the potassium (K) complex while dispersing the potassium (K) complex and graphite added to the ionic solution, and does not cause a side reaction with the potassium (K) complex and graphite. If so, it may be used without limitation, and preferably an aprotic organic solvent may be used. [70] For example, the organic solvent is tetrahydrofuran (THF), acetonitrile, dimethylformamide (DMF), dimethylacetamide (DMA), n-methyl-2-pyrrolidone (N -Methyl-2-pyrrolidone: NMP, methyl ethyl ketone (MEK), pyridine, quinoline, xylene, chloroform, ammonia, toluene, benzene, dimethylsulfoxide (DMSO), propylene carbonate (propylene carbonate) ), etc. Each of these may be used alone or in combination. More preferably, the organic solvent may include tetrahydrofuran. [71] [72] (2) Graphite mixed solution preparation step [73] The graphite mixture solution is prepared by mixing graphite in the ionic solution prepared through step (1). [74] More specifically, after preparing the ionic solution in a temperature condition of 25°C to 40°C in an argon (Ar) atmosphere glove box, 30 mg/ml to 150 mg/ml of the graphite in the ionic solution , Preferably 35 mg/ml to 150 mg/ml, more preferably 35 mg/ml to 145 mg/ml. [75] At this time, the graphite that may be used may be natural graphite or artificial graphite. The graphite may be used in a processed form such as powder, lump, or foil. The graphite is added at a concentration within the above range in consideration of the solubility and viscosity in the ionic solution, and the concentration of graphite added may vary according to experimental conditions. [76] When graphite is added to the ionic solution, the potassium (K)-complex dissolved in the ionic solution is inserted between the layers of the graphite to weaken the Van der Waals bonds between the layers, thereby improving the peelability of the graphite. [77] [78] (3) Step of obtaining graphene flakes [79] The graphite mixture solution can be stirred to obtain the graphene flakes. The agitation includes all processes such as stirring, sonication dispersion, and centrifugation. [80] More specifically, the graphene flake can be obtained through the following steps. [81] First, the graphite mixture solution was stirred in a glove box for 5 to 10 hours, and then the potassium (K)-complex was removed from the ionic solution except for solids such as graphite and the like. After that, it can be washed using a non-polar or low-polar solvent capable of dissolving the remaining naphthalene. For example, tetrahydrofuran (THF) or cyclohexane may be used, and the solid content is preferably washed with cyclohexane. [82] After mixing the washed solid content and polyvinylpyrrolidone (PVP) in a dimethyl sulfoxide (DMSO) solvent, graphite is single-layered through sonication dispersion for 10 to 60 minutes using a water bath type ultrasonic equipment. Separated into the structure. [83] In order to separate only the detached single-layer structure, centrifugation at 2000 rpm for 30 minutes to 1 hour using a centrifuge (Hanil Science Combi-514R), and then only the upper layer is separated. [84] The separated upper layer materials were centrifuged once more for 30 minutes to 1 hour at 10000 rpm using a centrifuge (Hanil Science Combi-514R), and then the solvent remaining in the upper layer was removed, and graphene flakes were obtained. [85] Meanwhile, the graphene flakes were injected into n-methyl-2-pyrrolidone (NMP) solvent to a concentration of 0.5 mg/ml to 5 mg/ml, and then ultrasonicated for 5 to 20 minutes using a water bath type ultrasonic equipment. It can be prepared in a state of being dispersed in a solvent through sonication dispersion. [86] [87] Slurry for electrode formation [88] Hereinafter, the slurry for electrode formation will be described. The electrode formation slurry contains an electrode active material, a binder, a dispersion medium, and the conductive material. Since the conductive material is the same as described above, detailed descriptions are omitted. [89] [90] Meanwhile, the conductive material may be included in an amount of 0.05 to 2.0 parts by weight, preferably 0.3 to 1.5 parts by weight, more preferably 0.5 to 1.3 parts by weight, based on 100 parts by weight of the solid content excluding the dispersion medium in the electrode forming slurry. have. When the conductive material is included within the above range, the conductivity can be improved and the viscosity can be maintained at a certain level or higher. [91] [92] In the slurry for forming an electrode, the electrode active material may be used as a positive or negative active material of a secondary battery. [93] Specifically, when the electrode forming slurry is for forming a positive electrode, the electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, at least one type of cobalt, manganese, nickel, or aluminum. It may include a lithium composite metal oxide containing metal and lithium. [94] More specifically, the lithium composite metal oxide is a lithium-manganese oxide (eg, LiMnO 2 , LiMn 2 O 4, etc.), a lithium-cobalt oxide (eg, LiCoO 2, etc.), a lithium-nickel oxide (E.g., LiNiO 2 ), lithium-nickel-manganese oxide (e.g., LiNi 1-Y1 Mn Y1 O 2 (here, 0