Effect of Calcination Temperature on Electrochemical Performance of Niobium Oxides/carbon Composites

Orthorhombic niobium pentoxide (T-Nb2O5) possesses an intercalation pseudocapacitive behavior, which is a promising candidate of high-rate anodes for Li-ion capacitors. However, its low electric conductivity hinders the realization of this property. In our study, niobium oxides/carbon composites were prepared by calcinating a niobium peroxo-PAA complex (NbPAA) precursor to improve the electric conductivity. It has been found that the calcination temperature played an important role on the chemical compositions of obtained composites. A reduction phenomenon of niobium oxides by carbon was observed at high temperatures. At the medium temperature of 900 °C, the sample was composed of T-Nb2O5, monoclinic Nb2O5 (M-Nb2O5), amorphous carbon and niobium dioxide (NbO2). Due to the high conductivity of carbon, semi-conductivity of NbO2, and high specific capacity of M-Nb2O5, this sample exhibits a good specific capacity of 142 mAh g−1 (0.25 C) and a high-rate capability (capacity retention of 33.1%, 0.25 C to 25 C). It could be used as one of high-rate anodes for Li-ion capacitors.