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

- 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.

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.