Study On The Preparation And Electrochemical Performances Of Activated Carbon For Non-aqueous Supercapacitors

Supercapacitors are new energy store devices which developed rapidly recently. Carbon materials are the most important. In this work, the activated carbons for non-aqueous supercapacitors were prepared from nut shell by NaOH activation, and their electrochemical performances were evaluated in detail. The influence of thermal treatment on the microstructure and the capacitive performances of the carbon were also investigated.Activated carbons for supercapacitors were prepared from nut shell by NaOH activation. The influence of granularity size, type of the nut shell, carbonization temperature and activated temperature on the microstructure and their electrochemical performances were investigated in detail. The results show that granularity of the nut shell has not obvious effect, but the type of the nut shell, carbonization temperature and activated temperature have dramatic effect on both the structure and the capacitive performances of the activated carbon. Some nut shells are difficult to activate because of their compact structure, although their carbon content are nearly similar each other. Activated carbons prepared from nut shell A have excellent capacitance and rate capability. As the carbonization temperature increases,the activation reaction becomes more difficult.As a result, the surface area and the pore volume of the carbon decrease dramatically, and the gravimetric capacitance decreases too,while the apparent density of the carbon electrode shows an increasing tendency. The volumetric capacitance, which is the combination of the gravimetric capacitance and apparent density of the carbon, increases first and then decreases.The activated carbon prepared at a moderate carbonization temperature of600℃has both higher volumetric capacitance and rate capability. As the activated temperature increase, the activation reaction becomes more easily. The capacitance at low current density becomes higher as the activated temperature increases. There is no obvious change when the activated temperature is higher than600℃. Take the cost and performance into account, the activatation temperature of650℃is the optimal one.The surface area of the activated carbons reaches1992m2/g which prepared by nut shell A, carbonization at600℃for1h, then activated at650℃with a alkali to carbon ratio of2:1.The gravimetric capacitance and volumetric capacitance in1mol.L-1Et4NBF4/PC is162F·g-1and84F·cm-3respectively, much higher than YP15(110F.g-1,63F·cm-3).The rate capability is also excellent. Thermal treatment can affect the microstructure, surface chemistry and capacitance of the carbon in1mol.L-1Et4NBF4/PC.The specific surface area and the surface oxygen content decreases after thermal treatment.Though the specific capacitance decreases slightly, the cycling performances and the coulomb efficiency in the first charge-discharge cycle are enhanced, and the self-discharge during24h reduced evidently.