Hierarchical Nb@Nbn Core-Shell-Like Nanocolumns for Asymmetric Supercapacitors

Rational design and facile preparation of electrode materials with unique nanostructure are the key to developing high-performance supercapacitors, which are another important member of energy storage systems complementary to batteries. Herein, we proposed a two-step approach of magnetron sputtering at oblique angle deposition configuration to fabricate hierarchical Nb@NbN core-shell-like nanocolumns for asymmetric supercapacitors. The unique core-shell-like nanocolumn heterostructure not only creates lattice defects, increases active surface area, promotes ion diffusion and charge transfer, but also optimizes the electronic structure and enhances the conductivity. As a result, the hierarchical Nb@NbN core-shell-like nanocolumn electrodes exhibit a high areal capacitance of 53.3 mF cm-2 at 1 mA cm-2 and an excellent capacitance retention of 93.5% after 20,000 cycles, outperforming pristine NbN thin film and most of previously reported transition metal nitride-based electrodes. Furthermore, the assembled Nb@NbN nanocolumns//VN thin films asymmetric supercapacitor device can deliver a maximum energy density of 49.8 mWh cm-3 and power density of 82 W cm-3. This work provides a facile and green strategy for the preparation of transition metal nitride core-shell-like nanocolumns with promising applications in energy storage.