Hollow nanoparticle-assembled hierarchical NiCo₂O₄nanofibers with enhanced electrochemical performance for lithium-ion batteries

Significant capacity degradation and a dramatic volume change call for effective strategies to address the intrinsic issues of transition metal oxide anodes of lithium-ion batteries. Rational nanostructural design has shown great promise in improving structural stability and electrochemical performance. We here report the fabrication of hollow nanoparticle-assembled hierarchical NiCo2O4 nanofibers via a facile electrospining technique and annealing process. A set of control experiments and systematic characterization demonstrate that the presence of polymers and an appropriate annealing procedure are key to form a novel nanostructured anode. The hollow nanostructure and abundant mesopores centered at about 20 nm in the nanofibers could effectively suppress severe volume variations in the lithiation/delithiation process. Furthermore, the novel nanoparticle-nanofiber hierarchical architecture could shorten the lithium diffusion length, increase the contact areas between the electrode and electrolyte, and accordingly promote fast electron/charge transfer. As expected, the optimized hierarchical NiCo2O4 nanofibers exhibit excellent performance for Li-ion batteries, delivering a capacity of 926.2 mA h g-1 at 0.1 A g-1 and 687 mA h g-1 at a high current density of 2 A g-1. This work may provide an attractive and promising strategy for advancing transition metal oxide anodes.