Niobium oxide nanoparticle core–amorphous carbon shell structure for fast reversible lithium storage

Highlights: • Nb₂O₅ nanoparticle core-amorphous carbon shell materials were prepared by a simple method. • Amorphous carbon shell was formed by one-step process with annealing. • Pyrolysis reaction can significantly influence the structural evolution of Nb₂O₅. • The materials show fast Li storage kinetics for hybrid supercapacitors. • The electrodes exhibit excellent long-term cycling stability. - Abstract: The hybrid supercapacitor concept involving a battery electrode and a supercapacitor electrode was recently introduced to meet the demand for high energy and power electrochemical energy storage devices. To successfully apply this device, high-capacity and rate electrode materials for Li storage should be developed. Niobium pentoxide (Nb₂O₅) has recently attracted considerable attention owing to its reasonable capacity, excellent rate capability, and cycling stability. However, the low electronic conductivity of the material is a major limitation. To address this issue, carbon incorporation is usually performed. Herein, we report Nb₂O₅ nanoparticle core-amorphous carbon shell materials prepared by hydrothermal reaction and one-step carbon formation with annealing. During the one-step process, it was found that pyrolysis of a carbon precursor could significantly influence the structural evolution of Nb₂O₅ with increasing temperature. In addition, Nb₂O₅ is reduced to NbO₂ in Ar atmosphere with further increase in temperature. The niobium oxide-carbon core-shell structure was thoroughly examined by using transmission electron microscopy. It was demonstrated that the proposed carbon-coated materials exhibited excellent electrochemical properties in terms of rate and cycle performances.