Bronze titanium dioxide nanowires with N-rich pseudocapacitive surfaces toward improved lithium kinetics and charge storage

Pseudocapacitive processes involve faradaic charge transfers for the energy storage of electrode materials. As the number of charge storage locations on the surface of electrode materials increases upon nano-sizing active particles, such processes have become increasingly important with advancements in nanotechnology. To improve the electrochemical performance of bronze titanium dioxide (TiO₂(B)), a promising pseudocapacitive anode material for Li-ion batteries, namely, TiO₂(B) nanowires, with N-rich pseudocapacitive surfaces is developed through mild thermal nitridation. Preserving the bronze phase of TiO₂(B) nanowires during nitridation is generally challenging because the crystal structure of TiO₂(B) is metastable, and nanowire-shaped active particles with large surface areas are highly reactive. Nevertheless, the resulting TiO₂(B) nanowires retain their original bronze phase and exhibit remarkable electrochemical performance (charge capacity: 92 mA h g⁻¹ @ 20 C; capacity retention: 76.4% @ 1 C after 100 cycles). Moreover, the initial coulombic efficiency of the TiO₂(B) nanowires is improved because the N-rich surface can suppress the reductive decomposition of electrolyte. This work demonstrates that an N-rich pseudocapacitive surface can promote the Li kinetics of TiO₂(B) nanowires and that newly formed O-Ti-N linkages developed via surface nitridation can improve the electronic conduction and enhance the structural/electrochemical stability of the surface.