Crystallographic Insight of Reduced Lattice Volume Expansion in Mesoporous Cu2+‐Doped TiNb2O7 Microspheres during Li+ Insertion

TiNb2O7 represents a promising anode material for lithium‐ion batteries (LIBs), but its practical applications are currently hampered by the non‐negligible volumetric expansion and contraction during the charge/discharge process and the sluggish ion/electron kinetics. A combination technique is reported by systematically optimizing the porous and spherical morphology, crystal structure, and surface decoration of mesoporous Cu2+‐doped TiNb2O7 microspheres to enhance the electrochemical Li+ storage performance and stability simultaneously. The Cu2+ dopants preferentially replace Ti4+ in crystal lattices, which decreases the Li+ diffusion barrier and increases the electronic conductivity, as confirmed by density functional theory (DFT) calculation and demonstrated by diverse electrochemical characterizations. The successful Cu2+ doping significantly reduces the lattice expansion coefficient from 7.26% to 4.61% after Li+ insertion along the b‐axis of TiNb2O7, as visualized from in situ and ex situ XRD analysis. The optimal 5% Cu2+‐doped TiNb2O7 with surface coating of N‐doped carbon exhibits significantly enhanced specific capacity and rate and cyclic performances in both half‐ and full‐cell configurations, demonstrating an excellent electrochemical behavior for fast‐charging LIB applications. The successful Cu2+ doping and surface N‐doped carbon coating significantly reduce the lattice expansion coefficient after Li+ insertion of mesoporous TiNb2O7 spheres. The resulting half‐ and full‐cells exhibit enhanced specific capacity and superior rate and cyclic performances.