Synthesis Of Highly Activated Carbons For Supercapacitor Electrodes

Electrical double-layer capacitors(EDLCs) have received increasing attention due to their short charging time, high power density, and long cycling life.EDLCs store energy via the adsorption of electrolyte ions in the micropores of electrodes, and the charge separation at electrode/electrolyte interfaces. Therefore, higher specific surface area and smaller pores adapted to electrolyte ions sizes are required for EDLCs. Activated carbons are widely used as EDLCs electrodes due to their low cost, precursor availability and high specific surface area.Porous ACs were prepared by one-step pyrolysis of willow leaves with ZnCl2 activation at 700-900 oC for 2 h under N2 atmosphere, and the electrochemical performance of ACs electrode has been investigated. The specific surface area of ACs increases with increasing the carbonization temperature. When the weight ratio of ZnCl2 to willow leaves is 1 and the carbonization temperature is 900 ?, the AC exhibits the maximum specific surface area of1065 m2/g, and its capacitance reaches 228 F g-1 at current density of 0.1 A g-1. The long term performance maintains at about 97% of the initial capacitance after 1000 cycles,indicating that this AC-1 displays excellent stability as supercapacitor electrode.In this study, we demonstrate a facile and scalable synthesis of CNS with high microporosity based on the previous report. In this method, NaCl was used as a water soluble template to form CNS, and followed by a chemical activation with KOH to produce micropores in a large scale. The resulting carbon sheets possess a thickness of less than 100 nm and micropores smaller than 1 nm. Such thin thickness of the carbon sheets guarantees a short ion-transport path, while the micropores accommodate the electrolyte ion charges.Therefore, it is expectable that carbon materials with such novel structure woulddisplay a high electrochemical performance as EDLCs electrodes.Such nanosheets possess a large specific surface area(up to 2266.6 m2 g-1) and microspores with size of 0.8 nm. The unique structural properties allow the short transport paths of ions, which results in a high electrochemical performance. The special capacitance of PCNS-3 electrode is up to 384 F g-1at the current density of 0.1 A g-1, and even remains 218 F g-1 at 30 A g-1. It also displays an excellent cycling stability that the capacity retention reaches 96.1 % after 3000 successive charging-discharging cycles. These promising results reveal that the as-prepared ACs-NaCl might be a promising candidate for high performance supercapacitors.