Effects of Valence States of Working Cations on the Electrochemical Performance of Sodium Vanadate.

Supercapacitors have received much attention as large-scale energy storage devices for high power density and ultralong cycling life. In this work, sodium vanadate Na 0.76 V 6 O 15 /poly(3,4-ethylenedioxythiophene) (PEDOT) nanocables with deficient bridge oxygen at the interface (denoted Vo •• -PNVO) have been tailored for supercapacitors through the in situ polymerization of 3,4-ethylenedioxythiophene and studied using three different electrolytes. Experiments and theoretical calculations reveal that all Na + , Zn 2+ , and Al 3+ ions appear as hydrates in aqueous solutions but insert into the crystal structure as Na + ions and Zn 2+ -H 2 O and Al 3+ -H 2 O hydrates, respectively. In comparison with the Zn 2+ -H 2 O and Al 3+ -H 2 O hydrates, Na + ions with a smaller radius diffuse more quickly in Vo •• -PNVO. Thus, Vo •• -PNVO delivers better charge storage capability and stability when an electrolyte with Na + ions is used. The results strongly suggest that an electrostatic interaction is significant in determining transport properties and storage capacities, rather than hydrate radii or valence states.