Non-porous activated mesophase carbon microbeads as a negative electrode material for asymmetric electrochemical capacitors

Abstract

Non-porous activated (mesophase carbon microbeads) MCMBs have been prepared by calcinations at 1100 °C and then activated with KOH at 800 °C in a nitrogen flow. This spherical carbon material could store a large number of ions after having been subjected to an “extra” electrochemical activation. It has been used as the negative electrode for asymmetric electrochemical capacitors of MCMB/activated carbon. The charge storage mechanism at the MCMB negative electrode has been investigated by XRD and TEM. The results demonstrate that the intercalation of quaternary alkyl ammonium cations from the electrolytes causes an irreversible expansion of interlayer spaces between adjacent carbon layers, which provides accommodation for subsequent ion adsorption. A series of quaternary alkyl ammonium-based electrolytes have been tested in the capacitors and the effect of the cation has been studied. Spiro-(1,1′)-bipyrrolidinium increases the storage ability most significantly although it is not the lightest quaternary alkyl ammonium cation.