Detailed description of the invention
Technical challenge
[12]
An object of the present invention is a novel conductive material capable of improving the capacity of a battery due to its excellent electrical conductivity and excellent electrical conductivity, an electrode including the conductive material, and a secondary battery including the electrode , And to provide a method of manufacturing the conductive material.
Means of solving the task
[13]
According to an embodiment of the present invention, a conductive material having a structure in which a plurality of graphene sheets are connected, an oxygen content of 1% by weight or more based on the total weight of the conductive material, and a D/G peak ratio of 2.0 or less when a Raman spectrum is measured Is provided.
[14]
According to another embodiment of the present invention, the present invention comprises the steps of preparing a preliminary conductive material; And transforming the preliminary conductive material by oxidation treatment, wherein the step of deforming the preliminary conductive material by oxidation treatment includes: a) a heat treatment temperature of 200°C to 800°C in an oxygen atmosphere or air atmosphere First heat treatment with a furnace; And b) reacting the preliminary conductive material with acidic vapor of 120°C to 300°C.
[15]
According to another embodiment of the present invention, an electrode including the conductive material is provided.
[16]
According to another embodiment of the present invention, a secondary battery including the electrode is provided.
Effects of the Invention
[17]
According to the present invention, a novel conductive material having a structure in which a plurality of graphene sheets are connected is easily dispersed in an electrode slurry due to a high oxygen content. In addition, structural stress is eliminated during the manufacturing process of the conductive material, so that the conductive material may have a high degree of graphitization, so that the powder resistance is low and the battery capacity may be improved. In addition, the manufacturing process of the conductive material can be simplified.
Brief description of the drawing
[18]
1 is a schematic diagram and a TEM photograph showing a process of forming a graphene sheet included in a conductive material of the present invention.
[19]
2 is a TEM and STEM (scanning TEM) photograph of the conductive material of Example 1 of the present invention.
[20]
3 is a SEM photograph of the conductive material of Example 1 of the present invention.
[21]
4 is a TEM photograph (a) of the conductive material according to Example 1 of the present invention and a TEM photograph (b) of the conductive material according to Example 2.
[22]
5 is a SEM photograph of carbon black of Comparative Example 2 of the present invention.
Mode for carrying out the invention
[23]
Hereinafter, the present invention will be described in more detail to aid understanding of the present invention. At this time, terms or words used in the present specification and claims should not be construed as being limited to a conventional or dictionary meaning, and the inventor appropriately defines 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 it can be done.
[24]
[25]

[26]
[27]
The conductive material according to an embodiment of the present invention includes a structure in which a plurality of graphene sheets are connected, and the oxygen content is 1% by weight or more based on the total weight of the conductive material, and when a Raman spectrum is measured The D/G peak ratio may be 2.0 or less.
[28]
[29]
In the present invention, the graphene sheet means a carbonaceous structure having a thickness of 20 nm or less, having flexibility, and being in the form of a thin film.
[30]
[31]
The conductive material may include a structure in which a plurality of graphene sheets are connected. Specifically, at least the conductive material may be two or more graphene sheets directly connected to each other or indirectly connected to each other.
[32]
The conductive material may be in the form of secondary particles formed by connecting a plurality of graphene sheets. Specifically, the plurality of graphene sheets may be connected to each other to form a long chain-shaped secondary particle, and more specifically, the chain-shaped secondary particle partially covers a region in which the plurality of graphene sheets are aggregated. Can include. Since the secondary particles have a unique chain-shaped connection structure, the electrical conductivity and thermal conductivity of the conductive material are excellent.
[33]
[34]
The conductive material may further include a connection part connected to at least some of the graphene sheets among the plurality of graphene sheets. In the present invention, when preparing the conductive material, a preliminary conductive material such as carbon black is ruptured by continuous oxidation to form the graphene sheet, and there may be a portion that does not rupture and maintains its original shape. In this case, a portion maintaining the shape may correspond to the connection portion. Accordingly, the connection portion may have a non-graphene form, and the non-graphene form may mean a lump shape having a thickness greater than that of the graphene sheet unlike the above-described graphene sheet.
[35]
[36]
Part of each of the plurality of graphene sheets may be directly connected to each other. Alternatively, at least some of the graphene sheets among the plurality of graphene sheets may be connected to each other through the connection part, and specifically, at least a part of each of the plurality of graphene sheets may be connected to the connection part. The conductive material of the present invention may include both of the above two connection methods.
[37]
[38]
The conductive material is carbon black in the form of particles close to a sphere, such as acetylene black, furnace black, thermal black, channel black, and lamp black. black) may be formed by deforming its shape by oxidation treatment. Referring to the schematic diagram of FIG. 1, the structure of carbon black may be modified by oxidation treatment to form particles including a plurality of graphene sheets. When the carbon black is in the form of secondary particles, a conductive material in the form of secondary particles in which particles including the plurality of graphene sheets are aggregated may be formed.
[39]
[40]
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. If the above range is satisfied, flexibility peculiar to the graphene sheet may be exhibited, and surface contact by the graphene sheet may be improved, so that the electrical conductivity of the conductive material may be excellent. The graphene sheet may be in a form in which 10 or less graphene layers are stacked.
[41]
[42]
The lateral size of the graphene sheet may be 200 nm or less, specifically 150 nm or less, more specifically 10 nm to 100 nm, and, for example, 50 nm to 90 nm. The longest length of the graphene sheet may be controlled according to the degree of heat treatment, for example, after the oxidation treatment process, a separate heat treatment may be additionally performed in an inert atmosphere to control the longest length of the graphene sheet. If the above range is satisfied, ions in the electrolyte may be smoothly diffused within the electrode. Accordingly, the rapid charging characteristic of the battery can be improved, and the rate-limiting characteristic can be improved. The longest length of the graphene sheet means the average of the longest lengths of 100 graphene sheets observed through SEM or TEM, where the longest length refers to a line connecting one point in one graphene sheet to another. It represents the longest length assumed.
[43]
[44]
The oxygen content of the conductive material may be 1% by weight or more based on the total weight of the conductive material, and specifically 1% by weight to 10% by weight. If the above range is satisfied, since the conductive material can be smoothly dispersed in the electrode slurry formed during electrode manufacturing, the conductivity of the electrode can be improved, and the capacity of the manufactured battery can be improved. The oxygen content can be measured by a method of C, H, O, and N elemental analysis.
[45]
The oxygen content may be achieved in the process of oxidizing carbon black. Specifically, oxygen-containing functional groups may be formed on the surface of the conductive material by the oxidation treatment. The oxygen-containing functional group may be at least any one selected from the group consisting of a carboxyl group, a hydroxy group, and a carbonyl group. After the oxidation treatment process, the oxygen content may be additionally controlled through heat treatment of the conductive material in an inert atmosphere.
[46]
[47]
The conductive material may have a higher degree of graphitization than carbon black before oxidation treatment. Specifically, the high structural stress generated by the surface tension of the carbon black is partially relieved as graphene sheets are formed, so that the graphitization degree of the prepared conductive material may increase.
[48]
The conductive material may have a D/G peak ratio of 2.0 or less when measuring a Raman spectrum, specifically 0.9 to 2.0, and more specifically 1.1 to 1.8. In the Raman spectrum, 1590cm -1 G peak in the neighborhood of the carbon sp 2 E of the coupling 2g will resulting from vibration modes, 1350cm -1 D is a peak in the vicinity of the carbon sp 2 appears when there is a defect in the coupling. That is, when the D/G peak ratio is satisfied, it means that a high degree of graphitization can be obtained. Accordingly, when the conductive material is used, the capacity and electrical characteristics of the battery will be improved based on the high electrical conductivity of the conductive material. I can.
[49]
[50]
The conductive material may have a value calculated by Equation 1 below of 0.2, specifically 0 to 0.15, and more specifically 0 to 0.1.
[51]
[Equation 1]
[52]

[53]
In Equation 1, a is the specific surface area (m 2 /g) of the conductive material measured by the nitrogen adsorption BET method, and b is the iodine adsorption value (mg/g) of the conductive material. When the conductive material has a pore structure inside or between particles, a large number of small-sized nitrogen (N 2 ) molecules may be adsorbed into the pores. On the other hand, iodine (I 2 ) , which is a relatively large molecule, is difficult to enter into the pores than nitrogen, so that the iodine adsorption value is not large. That is, when the void structure exists, the value according to Equation 1 increases. In other words, in the conductive material of the present invention, when the value according to Equation 1 is 0.2 or less, it means that the conductive material does not contain micropores. That is, when there is no void, the degree to which iodine is adsorbed and the degree to which nitrogen is adsorbed are similar, and thus the value of Equation 1 is reduced. This means that the surface of the conductive material is a free surface. Specifically, most of the carbon black is transformed into a hollow structure by oxidation treatment, and the structure is destroyed by continuous oxidation treatment, thereby forming graphene sheets. At this time, the graphene sheets may be formed in a shape that opens toward the outside without forming a void structure.
[54]
[55]
The conductive material may have a specific surface area (m 2 /g) of the conductive material measured by a nitrogen adsorption BET method of 200 m 2 /g or more, specifically 300 m 2 /g to 1100 m 2 /g, and more specifically 500 m 2 /g to 900m 2 /g may be. When the specific surface area range is satisfied, it means that the area of ​​the graphene sheet in the conductive material is large, and thus, even if the content of the conductive material in the electrode is small, the conductivity of the electrode can be secured.
[56]
[57]

[58]
[59]
An electrode according to another embodiment of the present invention may include the conductive material of the embodiment described above. The electrode may be an anode or a cathode. The electrode may include a current collector and an active material layer disposed on the current collector.
[60]
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 active material layer disposed on the current collector and including a negative active material. Furthermore, each of the positive active material layer and the negative active material layer may further include a binder.
[61]
The current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, or the like may be used. Specifically, a transition metal such as copper and nickel that adsorbs carbon well can be used as the current collector. The positive active material layer or the negative active material layer may be disposed on one or both surfaces of the current collector, respectively.
[62]
The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may include a layered compound such as lithium cobalt oxide (LiCoO 2 ) or lithium nickel oxide (LiNiO 2 ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as formula Li 1+y1 Mn 2-y1 O 4 (0≦ y1 ≦0.33), LiMnO 3 , LiMn 2 O 3 , and LiMnO 2 ; Lithium copper oxide (Li 2 CuO 2 ); LiV 3 O 8 , V 2 O 5 , Cu 2 V 2 O 7Vanadium oxides such as; Ni site type lithium nickel oxide represented by the formula LiNi 1-y2 M1 y2 O 2 (wherein M1 is Co, Mn, Al, Cu, Fe, Mg, B or Ga, and satisfies 0.01≦y2≦0.3); Formula LiMn 2-y3 M2 y3 O 2 (where M2 is Co, Ni, Fe, Cr, Zn or Ta, and satisfies 0.01≦y3≦0.1) or Li 2 Mn 3 M3O 8 (where M3 is Fe, A lithium manganese composite oxide represented by Co, Ni, Cu, or Zn); Li in the formula may include LiMn 2 O 4 in which a part of Li is substituted with an alkaline earth metal ion, but is not limited thereto.
[63]
The negative active material may be graphite-based active material particles or silicon-based active material particles. The graphite-based active material particles may be one or more selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, and graphitized mesocarbon microbead, and particularly, when using artificial graphite, rate characteristics may be improved. . The silicon-based active material particles are Si, SiO x (0
[67]
[68]
A secondary battery according to another embodiment of the present invention may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and at least one of the positive electrode and the negative electrode is an electrode of the other embodiment described above. Can be
[69]
The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move, and can be used without particular limitation as long as it is used as a separator in a general secondary battery. It is desirable to be excellent. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A stacked structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be optionally used in a single layer or multilayer structure.
[70]
The electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used when manufacturing a lithium secondary battery.
[71]
Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.
[72]
As the nonaqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyllolactone, 1,2-dime Oxyethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, Methyl acetate, phosphoric acid tryster, trimethoxy methane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, pyrofion An aprotic organic solvent such as methyl acid or ethyl propionate may be used.
[73]
Particularly, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, are highly viscous organic solvents and can be preferably used because they dissociate lithium salts well because of their high dielectric constant, and dimethyl carbonate and diethyl carbonate and If the same low viscosity, low dielectric constant linear carbonate is mixed in an appropriate ratio and used, an electrolyte having a high electrical conductivity can be made, and thus it can be more preferably used.
[74]
The metal salt may be a lithium salt, the lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, is in the lithium salt anion F - , Cl - , I - , NO 3 - , N (CN ) 2 - , BF 4 - , ClO 4 - , PF 6 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 - , (CF 3 ) 4 PF 2 - , (CF 3) 5 PF - , (CF 3 ) 6 P - , CF 3 SO 3 - , CF 3 CF 2 SO 3 - , (CF 3 SO 2 ) 2 N - , (FSO 2 ) 2 N - , CF 3 CF 2 ( CF 3 ) 2 CO - , (CF 3SO 2 ) 2 CH - , (SF 5 ) 3 C - , (CF 3 SO 2 ) 3 C - , CF 3 (CF 2 ) 7 SO 3 - , CF 3 CO 2 - , CH 3 CO 2 - , SCN - And (CF 3 CF 2 SO 2 ) 2One type selected from the group consisting of N - can be used.
[75]
In addition to the components of the electrolyte, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and trimethyl, for the purpose of improving battery life characteristics, suppressing reduction in battery capacity, and improving battery discharge capacity. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included.
[76]
[77]
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 same are provided. Since the battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and site characteristics, a mid- to large-sized device selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems It can be used as a power source.
[78]
[79]

[80]
[81]
A method of manufacturing a conductive material according to another embodiment of the present invention includes: preparing a preliminary conductive material; And transforming the preliminary conductive material by oxidation treatment, wherein the step of deforming the preliminary conductive material by oxidation treatment includes: a) a heat treatment temperature of 200°C to 800°C in an oxygen atmosphere or air atmosphere And b) reacting the pre-conductive material with acidic vapor of 120°C to 300°C.
[82]
[83]
In the step of preparing the preliminary conductive material, the preliminary conductive material may be carbon black. Specifically, the preliminary conductive material may be at least one selected from the group consisting of acetylene black, furnace black, thermal black, channel black, and lamp black. More specifically, the preliminary conductive material may be acetylene black having excellent graphitization degree by being manufactured at the highest temperature.
[84]
Preparing the preliminary conductive material may include pyrolyzing acetylene gas, and carbon black, specifically acetylene black may be formed through the pyrolysis. The acetylene gas may be a high-purity acetylene gas, specifically an acetylene gas having a purity of 95% or more, and more specifically, a purity of 98% or more.
[85]
The pyrolysis may be to pyrolyze the acetylene gas at a temperature of 1500°C or higher, specifically 1500°C to 2200°C, and more specifically 1500°C to 2000°C. If the above range is satisfied, the graphitization degree of the prepared preliminary conductive material may be high, and the graphitization degree of the prepared conductive material may also be high. Therefore, the electrical conductivity of the conductive material can be improved.
[86]
The preliminary conductive material may be carbon black, but among them, acetylene black may be preferable from the following points. The graphene sheet included in the conductive material of the present invention may be formed by deforming the surface of the preliminary conductive material by oxidation treatment. Acetylene black formed by the thermal decomposition has a high degree of graphitization of the surface. Therefore, compared to the oxidation treatment of other carbon blacks that inevitably contain some oxygen functional groups on the surface, the structure of the graphene sheet may be smoothly formed when the acetylene black is oxidized.
[87]
The pyrolysis may be an instantaneous pyrolysis by adjusting the temperature inside the reaction furnace within the above temperature range, and then introducing an acetylene gas into the reaction furnace. In addition, in this process, air, oxygen, H 2 O, etc. may be additionally added to control the density of the conductive material and oxygen functional groups, and the connection structure in the conductive material may be controlled.
[88]
[89]
The step of deforming the preliminary conductive material by oxidation treatment may include: a) subjecting the preliminary conductive material to a heat treatment temperature of 200°C to 800°C in an oxygen atmosphere or an air atmosphere (step a); And b) reacting the preliminary conductive material with acidic vapor of 120° C. to 300° C. (step b).
[90]
In step a, the oxygen atmosphere or the air atmosphere may be formed by introducing oxygen or air into a reaction furnace in which the preliminary conductive material is accommodated. Specifically, the graphene sheet structure may be formed by an oxidation process in the reactor according to the setting of an appropriate inflow amount and rate of oxygen or air, a reaction temperature, and a reaction time during the first heat treatment. In addition, the conditions of the oxidation process may vary based on differences in density and oxygen functional group content of the preliminary conductive material.
[91]
In step a, the first heat treatment may be performed by adjusting the temperature of the reaction furnace in the reaction furnace in which the preliminary conductive material is accommodated. The first heat treatment may be heat treatment at a heat treatment temperature of 200°C to 800°C, and specifically, heat treatment at a heat treatment temperature of 200°C to 450°C. When the temperature range is satisfied, excessively rapid oxidation of the pre-conductive material may be prevented, and a graphene sheet having a desired size may be formed. The first heat treatment may be performed for 1 to 50 hours.
[92]
In step b, the preliminary conductive material may be oxidized by reacting with acidic vapor to form graphene. Specifically, the acidic vapor may be vapor derived from an acidic solution such as HCl or HNO 3 . The temperature of the acidic vapor reacting with the preliminary conductive material may be in the range of 120 ℃ to 300 ℃.
[93]
After the step of deforming the preliminary conductive material by oxidation treatment, a second heat treatment process in an inert atmosphere may be additionally performed in order to increase the size of the formed graphene sheet. Specifically, the method of manufacturing the conductive material may further include performing a second heat treatment at a temperature of 500°C or higher on the oxidized and deformed pre-conductive material in an inert atmosphere after the step of oxidizing and deforming the preliminary conductive material. have. In this case, the inert atmosphere may be formed of any one gas selected from the group consisting of vacuum, helium, argon, and nitrogen. The second heat treatment temperature may be 500°C or higher, specifically 500°C to 2800°C, and more specifically 600°C to 1600°C.
[94]
[95]
The mechanism by which the conductive material described in the present invention is formed by the method of manufacturing the conductive material may be as follows. When manufacturing the conductive material, the average size of the spherical primary particles is 50 nm or less, and oxidation treatment is performed under specific conditions for spherical to chain carbon black in which the primary particles share a structure, specifically acetylene black. do. In this case, an oxidizing agent such as oxygen or acidic vapor penetrates and an oxidation reaction occurs from defects such as grain boundaries or dislocations existing in the fine unit structure of the carbon black. When the oxidation treatment is performed for a certain period of time in the temperature range mentioned in the above manufacturing method, the oxidizing agent penetrates to the microstructure inside the carbon black, and oxidation proceeds. At this time, in order to relieve the structural stress of the microstructure inside the primary particles having a radius of curvature larger than the radius of curvature of the surface of the spherical primary particles, an oxidation reaction occurs rapidly inside. Accordingly, the internal carbons are CO, CO 2 , CH 4It is oxidized with a gas such as, and the primary particles are changed into a hollow type. As the surface structure of the hollow primary particles is destroyed by continuous oxidation treatment, most of the structural stress remaining on the spherical primary particles can be relieved, and graphene sheets appear in this process. Accordingly, as the average size of the carbon black, which is the primary particle, is smaller, the internal density of the particle is smaller, and the content of oxygen functional groups inside the primary particle is higher than the surface of the primary particle, the transformation process may be accelerated. In addition, step a is more preferable than step b in that it can further accelerate the transformation process.
[96]
[97]
Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms, and is not limited to the embodiments described herein.
[98]
[99]
Example 1: Preparation of conductive material
[100]
(1) Formation of preliminary conductive material (acetylene black)
[101]
An acetylene gas having a purity of 98% was instantaneously injected into a reaction furnace having an internal temperature of 2000° C. and thermally decomposed to form acetylene black.
[102]
(2) Preparation of conductive material
[103]
Subsequently, after the internal temperature of the reaction furnace in which the acetylene black was accommodated was set to 250°C, oxidation treatment was performed for 30 hours while introducing oxygen. Through this, a conductive material having a secondary particle structure including a form in which a plurality of graphene sheets having a lateral size of 40 nm level are connected to each other was obtained. (See Figs. 2 and 3)
[104]
[105]
Example 2: Preparation of conductive material
[106]
For the conductive material obtained in Example 1, secondary particles including a form in which a plurality of graphene sheets having a lateral size of 65 nm are connected to each other by performing additional heat treatment at 900° C. for 1 hour in an inert atmosphere A structured conductive material was obtained. Referring to FIG. 4, it can be seen that the conductive material of Example 1 shown in FIG. 4(a) was transformed into the conductive material of Example 2 of FIG. 4(b) by heat treatment. Specifically, it can be seen that adjacent graphene sheets are interconnected by the heat treatment to increase the maximum length.
[107]
[108]
Comparative Example 1: Existing conductive material (carbon black) preparation
[109]
Carbon black (acetylene black) in the form of secondary particles in which primary particles are aggregated was prepared. The average particle diameter of the prepared primary carbon black particles was 12 nm. (Denka, SAB (Small Acetylene Black))
[110]
[111]
Comparative Example 2: Existing conductive material (carbon black) preparation
[112]
Carbon black in the form of secondary particles in which primary particles are aggregated was prepared. The average particle diameter of the prepared primary carbon black particles was 23 nm. (Denka, NAB (Normal Acetylene Black)) (See Fig. 5)
[113]
[114]
Comparative Example 3: Existing conductive material (carbon black) preparation
[115]
Carbon black in the form of secondary particles in which primary particles are aggregated was prepared. The average particle diameter of the prepared carbon black secondary particles was 45 nm. (Denka, LAB (Large Acetylene Black))
[116]
[117]
Hereinafter, physical properties of the conductive materials of Examples 1 and 2 and the existing conductive materials of Comparative Examples 1 to 3 are evaluated and shown in Table 1. Specifically, the physical properties were evaluated as follows.
[118]
[119]
1) Longest length of graphene sheet (lateral size) (nm): After measuring the size of 100 graphene sheets in the conductive material by TEM (JEOL, JEM-2010F), the average of these sheets was evaluated.
[120]
2) Nitrogen adsorption specific surface area (m 2 /g): Using a BET measuring equipment (BEL-SORP-MAX, Nippon Bell), degassing at 200°C for 8 hours, and adsorbing N 2 at 77K / Desorption (absorption/desorption) was performed and measured.
[121]
3) Iodine adsorption value (mg/g): Measured according to ASTM D1510 method.
[122]
4) Oxygen content (% by weight): Using elemental analysis equipment (CHN-coder MT-5, Yanako), the content of C, H, and N elements is measured, and oxygen content (differential ) Was calculated.
[123]
5) Raman spectrum D/G ratio: Raman spectrum was analyzed and measured with an Ar-ion laser having a wavelength of 514.5 nm through a Raman spectroscopy equipment (NRS-2000B, Jasco).
[124]
[125]
[Table 1]
Longest length of graphene sheet or average size of primary carbon black particles (nm) Nitrogen adsorption specific surface area (m 2 /g) Iodine adsorption value (mg/g) Oxygen content (% by weight) Raman spectrum D/G ratio
Example 1 41 (graphene sheet) 825 849 8.9 1.42
Example 2 65 (graphene sheet) 712 736 3.2 1.27
Comparative Example 1 12 (Carbon black primary particles) 376 456 4.7 1.68
Comparative Example 2 23 (Carbon black primary particles) 135 152 0.3 1.23
Comparative Example 3 45 (carbon black primary particles) 58 68 0.1 0.96
[126]
Example 3: Preparation of electrode slurry
[127]
Li[Ni 0.6 Mn 0.2 Co 0.2 ]O 2 as a positive electrode active material, polyvinylidene fluoride (PVdF) as a binder, and N-methylpyrrolidone as a solvent in a weight ratio of 96.5:1.5:2.0 to the conductive material of Example 1 ( NMP, N-methylpyrrolidone) to prepare an electrode slurry.
[128]
[129]
Example 4 and Comparative Examples 5 to 8: Preparation of electrode slurry
[130]
Except for using the conductive material of Example 2 and Comparative Examples 1 to 3, respectively, instead of the conductive material of Example 1 as a conductive material, the electrode slurry of Example 4 and Comparative Examples 4 to 6 in the same manner as in Example 3 Was prepared.
[131]
[132]
Experimental Example 1: Evaluation of powder resistance
[133]
The electrode slurries of Examples 3 and 4 and Comparative Examples 4 to 6 were vacuum-dried at a temperature of 130° C. for 3 hours and then pulverized to prepare a powder. Thereafter, using the Loresta GP equipment of Mitsubishi Chem Analytic, the pellets were prepared under a load of 9.8 MPa in an atmosphere of 25° C. and 50% relative humidity. After that, after measuring the powder resistance by the 4-probe method, it is shown in Table 2.
[134]
[135]
[Table 2]
Example 3 Example 4 Comparative Example 4 Comparative Example 5 Comparative Example 6
Powder resistance (Ω) 127 97 148 154 189
[136]
According to Table 2, the powder resistance of Examples 3 and 4 using the conductive material according to the present invention was much lower than the powder resistance of Comparative Examples 4 to 6 using carbon black in the form of secondary particles. That is, it can be seen that the conductive material according to the present invention has the form of secondary particles in which graphene sheets are connected to each other, so that the planar contact between the active materials and the conductive material is increased, so that the electrical conductivity of the slurry or the electrode can be greatly improved. In addition, since the powder resistance of Example 4 is much lower than that of Example 3, it can be seen that controlling the size of the graphene sheet to an appropriate level through additional heat treatment has a great effect on the improvement in conductivity.
[137]
[138]
Example 5: Preparation of secondary battery
[139]
(1) Preparation of positive electrode
[140]
The electrode slurry of Example 3 was applied to a positive electrode current collector (Al) having a thickness of 20 μm, and dried at 130° C. to prepare a positive electrode.
[141]
(2) Secondary battery manufacturing
[142]
A negative electrode slurry was prepared by mixing graphite as a negative active material, carbon black as a negative conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) as negative binders in distilled water at a weight ratio of 96.5:2:1:0.5, respectively. The prepared slurry was applied to a negative electrode current collector (Cu) having a thickness of 10 μm, and dried at 100° C. to prepare a negative electrode.
[143]
Thereafter, a monocell was prepared by combining the prepared negative and positive electrodes, and a 15 μm-thick polyethylene separator interposed therebetween, and then an electrolytic solution (ethylene carbonate (EC)/ethyl methyl carbonate (EMC)) in the monocell. =1/2 (volume ratio), lithium hexafluorophosphate (LiPF 6 1 mol)) was injected to prepare a lithium secondary battery.
[144]
[145]
Example 6 and Comparative Examples 7 to 9: Preparation of secondary battery
[146]
When manufacturing the positive electrode, the electrode slurry of Example 6 and Comparative Examples 7 to 9 was used in the same manner as in Example 5, except that the slurry of Example 4 and Comparative Examples 4 to 6 was respectively used as an electrode slurry. A secondary battery was prepared.
[147]
[148]
Experimental Example 2: Evaluation of discharge capacity according to discharge C rate
[149]
Table 3 shows the evaluation results of the lithium secondary batteries prepared in Examples 5 and 6 and Comparative Examples 7 to 9 for each discharge C-Rate. Specifically, the charging C-Rate was fixed at 0.2C, and the discharge C-Rate was increased from 0.2C to 2.0C, and the 2.0C discharge capacity (%) was evaluated compared to the 0.2C discharge capacity.
[150]
[151]
[Table 3]
Example 5 Example 6 Comparative Example 7 Comparative Example 8 Comparative Example 9
2.0C discharge capacity compared to 0.2C discharge capacity (%) 83.9 86.1 79.8 75.2 71.7
[152]
According to Table 3, the battery capacities of Examples 5 and 6 using the conductive material according to the present invention were higher than those of Comparative Examples 7 to 9 using carbon black in the form of secondary particles. That is, according to the application of the novel conductive material of the present invention in the form of secondary particles in which graphene sheets are connected to each other, it can be seen that the conductivity of the electrode can be greatly improved.
[153]
[154]
[155]
Claims
[Claim 1]
A conductive material comprising a structure in which a plurality of graphene sheets are connected, an oxygen content of 1% by weight or more based on the total weight of the conductive material, and a D/G peak ratio of 2.0 or less when a Raman spectrum is measured.
[Claim 2]
The conductive material according to claim 1, wherein the maximum length of the graphene sheet is 200 nm or less.
[Claim 3]
The method according to claim 1, wherein the conductive material has a value calculated by the following equation 1 of 0.2 or less: [Equation 1] In the equation 1, a is a specific surface area of ​​the conductive material measured by a nitrogen adsorption BET method (m 2 /g) And b is the iodine adsorption value (mg/g) of the conductive material.
[Claim 4]
The conductive material of claim 1, further comprising a connection part connected to at least some of the graphene sheets among the plurality of graphene sheets, and the connection part has a non-graphene form.
[Claim 5]
The conductive material of claim 4, wherein at least a portion of each of the plurality of graphene sheets is connected to the connection part.
[Claim 6]
The conductive material of claim 1, wherein the graphene sheet has an average thickness of 10 nm or less.
[Claim 7]
The conductive material according to claim 1, wherein the specific surface area (m 2 /g) of the conductive material measured by a nitrogen adsorption BET method is 200 m 2 /g or more.
[Claim 8]
Preparing a preliminary conductive material; And deforming the preliminary conductive material by oxidation treatment, wherein the step of deforming the preliminary conductive material by oxidation treatment comprises: a) the preliminary conductive material at a temperature of 200°C to 800°C in an oxygen atmosphere or an air atmosphere. First heat treatment; And b) reacting the preliminary conductive material with acidic vapor of 120°C to 300°C.
[Claim 9]
The method of claim 8, wherein preparing the preliminary conductive material comprises pyrolyzing acetylene gas at a temperature of 1500°C or higher.
[Claim 10]
The method of claim 8, wherein the preliminary conductive material is at least one selected from the group consisting of acetylene black, furnace black, thermal black, channel black, and lamp black.
[Claim 11]
The method of claim 10, wherein the preliminary conductive material is acetylene black.
[Claim 12]
The method of claim 8, wherein the method of manufacturing the conductive material further comprises: after the step of oxidizing the preliminary conductive material to deform the preliminary conductive material, performing a second heat treatment at a temperature of 500°C or higher on the oxidized and deformed preliminary conductive material in an inert atmosphere. A conductive material manufacturing method containing.
[Claim 13]
An electrode comprising the conductive material of any one of claims 1 to 7.
[Claim 14]
anode; cathode; A separator interposed between the anode and the cathode; And an electrolyte, wherein at least one of the positive electrode and the negative electrode is an electrode of claim 13.