Studies On Properties Of Coal-Series Needle Coke Prepared In Magnetic Field

As a new type of carbon materials, needle coke is applied to industrial, defense, energy, environmental protection and other fields based on its excellent comprehensive performance. At present, it mainly used as skeleton materials of high power electrode and ultra high power electrode. Furthermore the research on its application in lithium ion battery and super electrochemical capacitor obtained some achievements. In recent years, there is certain capacity interiorly, but the performance index is difficult to satisfy the demand of high power electrode.Therefore, it is very important to study the influence of various external factors during the carbonization, which have important significance and practical value in improving the comprehensive performance.Taking medium temperature coal tar pitch removed the QI as raw material, the needle coke was made in a pressure vessel under the condition of exerting magnetic field. By changing the heating mode, heating rate, delayed coking temperature, polymerization pressure, the stage of carbonization when applied magnetic field and magnetic induction, to research the influence of all factors in the process of preparing needle coke comprehensively. The morphology and optical anisotropy organizations of needle coke were observed by Scanning Electron Microscope (SEM) and Polarizing Microscope,and the microcrystalline structure parameters was researched by X-Ray Diffractomer(XRD). The needle cokes prepared in different condition are made into work electrodes(WE) respectively.Then the capacitance characteristics, reversibility and interface stability of WE was researched by Cyclic Voltammetry(CV) and Electrochemical Impedance Spectroscopy (EIS) in Three-electorde system formed by needle coke electrode, platinum electrode(CE) and calomel electrode(RE).The conclusions are drawn as follows:(1)The continuous heating with constant rate is beneficial to the forming of optical anisotropy organizations of needle coke, and the lower rate, the more regular of microstructure, the larger size of microcrystal.(2)If the delayed coking temperature is too high, the forming of carbon layer was inhibited.Conversely, the lower temperature will produce immature coke easily.Research shows that 460℃is more appropriate for delayed coking.(3)The pressure play a significant role in formation of orderly structure that can not be ignored.A proper pressure can promote polymerization, and provide enough energy to pull the coke by airflow which produce contributes to forming steamline organzations.The viscosity will change when the pressure is too high or too low, and have negative impact on condensation polymerization.To obtain needle coke with better microstructure, the pressure should be kept in 0.4 MPa.(4)The magnetic field promote the transforming of mosaic into micro-region organization,and help to form the optical anisotropy organizations.Applying the magnetic field in the stage of forming of mesophase is more advantageous to generate fibrous texture structure. Magnetic field has different effects to the size of microcrystalline plane and vertical piling, Zeeman effect and Magnetic field oriented effect are two type of action modes of magnetic field in the process of carbonization.The former can effect free radical in the early stage of carbonization, and facilitated the polymerization of aromatic molecule, however, the latter can improve the order degree of whole system, reduce the steric hindrance of vertical piling and improve Z-axial dimensions.(5)Magnetic field applied during the preparation of needle coke has obvious influence on the electrochemical properties of coke.Owing to the influence of magnetic field, the capacitance of WE was reduced, the solution resistance was increased, but the reversibility of capacitance was improved.As a result of magnetic field, the reducing of active groups in needl coke made the stability of electrode surface ascended.