Optimizing Lithium-Ion Storage in Single-Crystalline Cu₂Nb₃₄O₈₇ Anode via Aliovalent In³⁺ Doping: Enhanced Diffusion...

Cu₂Nb₃₄O₈₇ (CNO) with the Wadsley-Roth monoclinic structure has emerged as a promising candidate for lithium storage due to its considerable theoretical capacity and unique lithium-ion transport mechanism. However, its poor electronic conductivity and slow lithium-ion diffusion kinetics hinder its practical application as an anode material. To address these challenges, an In³⁺ ion doping strategy is implemented here to optimize the performance of CNO, yielding the single-crystalline In-doped CNO (ICNOx) compounds with In³⁺ substitutes Cu²⁺ lattice sites. Electrochemical characterizations reveal that the optimized ICNO5 delivers the superior rate performance and maintains an exceptional capacity retention of 95.7% after 1000 cycles at 2.0 A g^-1. Theoretical calculation demonstrates the optimized electronic structure and lower Li⁺ diffusion energy barriers of ICNOx. Furthermore, lithium-ion capacitor configured with ICNO5 as the anode and activated carbon as the cathode obtains an energy density of 24.75 Wh kg^-1 at a high-power density of 4.30 kW kg^-1. The findings here underscore the potential of lattice-engineered niobium-based oxides for high-performance, long-life energy storage applications.