Competitive Redox Chemistries in Vanadium Niobium Oxide for Ultrafast and Durable Lithium Storage

Niobium pentoxide (Nb₂O₅) anodes have gained increasing attentions for high-power lithium-ion batteries owing to the outstanding rate capability and high safety. However, Nb₂O₅ anode suffers poor cycle stability even after modified and the unrevealed mechanisms have restricted the practical applications. Herein, the over-reduction of Nb⁵⁺ has been demonstrated to be the critical reason for the capacity loss for the first time. Besides, an effective competitive redox strategy has been developed to solve the rapid capacity decay of Nb₂O₅, which can be achieved by the incorporation of vanadium to form a new rutile VNbO₄ anode. The highly reversible V³⁺/V²⁺ redox couple in VNbO₄ can effectively inhibit the over-reduction of Nb⁵⁺. Besides, the electron migration from V³⁺ to Nb⁵⁺ can greatly increase the intrinsic electronic conductivity for VNbO₄. As a result, VNbO₄ anode delivers a high capacity of 206.1 mAh g^-1 at 0.1 A g^-1, as well as remarkable cycle performance with a retention of 93.4% after 2000 cycles at 1.0 A g^-1. In addition, the assembled lithium-ion capacitor demonstrates a high energy density of 44 Wh kg^-1 at 5.8 kW kg^-1. In summary, our work provides a new insight into the design of ultra-fast and durable anodes.