Multiwalled carbon nanotubes coated with a thin carbon layer for use as composite electrodes in supercapacitors

Submicron-thick films of composite (CSN) electrodes were prepared by the simple spin-coating of a multiwalled carbon nanotube (MWCNT) suspension with sucrose as the precursor to form a thin carbon layer; this was followed by heat treatment at 1000 degrees C for 2 h. Thin carbon layers were coated onto the outer surface of the MWCNTs and the resulting CSN electrode was shown to be an interconnected open network structure. This binder-free thin-film CSN electrode with a unique architecture has a large areal capacitance of similar to 723 mu F cm(-2) at a constant current of 0.23 mu A cm(-2) in a Na2SO4 aqueous electrolyte. About 81% of the initial capacitance is preserved, even at high specific currents. Based on the results of electrochemical impedance spectroscopy, the CSN electrode was shown to concurrently optimize ion and electron transport for high power delivery. It also shows good cycle stability after prolonged operation (up to 3000 charge/discharge cycles).