Oxygen-deficient niobium oxides for fast and high-capacity lithium-ion batteries

Niobium oxides with crystallographic shear structures are under investigation as promising anode materials for advanced lithium-ion batteries (LIBs) aimed at high-energy and high-power applications. However, controlling the intrinsic structures to obtain new phases with increased electronic and ionic conductivities remains a significant challenge in enhancing performance. Here we present a new micro-sized oxygen-deficient Nb₂₅O_62-δ particle material with a typical crystallographic shear structure, resulting in an outstanding Li⁺ intercalation characteristics. When evaluated as a LIB anode, Nb₂₅O_62-δ demonstrates lower charge transfer resistance, faster ionic diffusion, and higher structural stability than H-Nb₂O₅, achieving a high capacity of 262.5 mA h g^-1 (1.29 Li⁺ per Nb ion) at 0.25 C and retaining approximately 96.9 % of its initial capacity at a high cycling rate of 25 C. Additionally, the integrated LiFePO₄‖Nb₂₅O_62-δ full cells exhibit a high reversible capacity over 110 mAh g^-1 and maintain a high retention over 97.5 % during more than 500 long-term cycles at a fast rate of 5 C. Density functional theory computations indicate that the excellent performance is attributed to its enhanced electrical conductivity, reduced Li⁺ adsorption energy, and diminished barriers for ion diffusion. This work paves the way for further exploration of innovative non-stoichiometric niobium oxides as promising alternatives for high-power rechargeable LIBs.