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

Abstract TiNb 2 O 7 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 Cu 2+ ‐doped TiNb 2 O 7 microspheres to enhance the electrochemical Li + storage performance and stability simultaneously. The Cu 2+ dopants preferentially replace Ti 4+ 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 Cu 2+ doping significantly reduces the lattice expansion coefficient from 7.26% to 4.61% after Li + insertion along the b ‐axis of TiNb 2 O 7 , as visualized from in situ and ex situ XRD analysis. The optimal 5% Cu 2+ ‐doped TiNb 2 O 7 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.