Crystallization evoked surface defects in layered titanates for high-performance sodium storage

Layered titanates (LT) have aroused considerable attention as advanced anodes for high-performance Na-ion batteries. However, their intrinsic issues including low electronic conductivity and sluggish sodiation kinetic hinder the implementation of achieving superior rate capability and long cycle stability simultaneously. Herein, a crystallization-induced surface defect engineering to promote the electrochemical activity of LT by electronic structure modulation and diffusion kinetics regulation is proposed. As evidenced by electrochemical characterization, this surface defect modification strategy can effectively reduce the polarization and facilitate fast electronic/ionic diffusion of titanates. Thereby, the targeted low-crystalline layer modified layered titanate (LC-LT) unfolds enhanced rate capability and cycle stability (8000 cycles, 88%). Theoretical calculations reveal that the LC-LT is equipped with narrower bandgap originated from the 3d orbital of oxygen vacancies-induced defective Ti atoms on the surface. Moreover, reduced Na+ migration energies and interconnected Na+ diffusion pathways are predicted in LC-LT by density functional theory (DFT) calculations and bond valence site energy (BVSE) analysis. When applied in Na-ion full cell with NASICON-type Na3V2(PO4)2F3 cathode, the configuration exhibits comparable rate performance and cycle stability (800 cycles, 81.6%).