Preparation And Properties Of Two Kinds Of Capacitive Carbon For Supercapacitors

Supercapacitors are new energy storage devices with intermediate performance between batteries and dielectric capacitors, which have high power density, long cyclic life and high charge/discharge capability, etc. They have multiple applications including aeronautics and astronautics, electronic communication, automobiles, military, etc. Engrgy density plays a key role in improving the performance of supercapacitor, and the volumetric specific capacities have a significant effect on energy density of supercapacitor.This paper studies the preparation technology and its properties of capacitive carbon, coconut and mesophase pitch microbeads (MPMB) as raw material. The coconut shell is activated by ZnCl2, and MPMB are activated by compound activator, KOH and NaOH, and microwave as the heating method, which both obtain the capacitive carbon with more favorable performances for using in supercapacitors. Also the influences on micro-structure and capacitance characteristics of capacitive carbon after preparation processes are systematically studied, and then the mechanism of activation was explored. The main contents are as follows:For ZnCl2 activated coconut shell, this paper studies that the ratio of ZnCl2 to shell and the activation temperature plays an important role on the performances of activated carbon, and the optimized process is: the ratio of ZnCl2 to shell is 1.5:1, the activation temperature is 700℃, the activation time is 1 hour. The activated carbon is obtained by that process, the tap density reaches 0.53 g/cm3, the specific capacitance is 150 F/g, the volumetric specific capacitance reaches 80 F/cm3. Then X-ray diffraction, scanning electron microscopy, specific surface area tester were used to observe their structure. Finally, the constant current charge-discharge tests on activated carbon show that the capacitive carbon based on coconut shell has a good charge and discharge efficiency, charge and discharge stability at high current and a good discharge characteristics, which is suitable as carbon supercapacitors.With KOH/NaOH as activator compound, using microwave heating, MPMB are prepared the activated carbon used in the supercapacitor, which we called Activated mesocarbon microbeads (A-MCMBs). In this paper, we find that the proportion of activating agent and heating methods played an important role on the capacitance performance of A-MCMBs, and the optimized activation process is : KOH: NaOH: MPMB = 5:1:1, by microwave heating, activation time is 15min. its tap density is 0.36 g/cm3, the specific capacitance reaches 335 F/g, the volumetric specific capacitance reaches 120 F/cm3. Also then the X-ray diffraction, scanning electron microscopy, BET, infrared spectroscopy instrument were used to observe their micro-structure, pore structure, surface functional groups and other properties, and we found that A-MCMBs activated by microwave have much higher degree of graphitization and less surface oxygen groups, which is compared with A-MCMBs activated by conventional heating. Thus, A-MCMBs prepared by microwave are more suitable for electrodes of supercapacitors.