Mo‐Incorporated Magnetite Fe₃O₄ Featuring Cationic Vacancies Enabling Fast Lithium Intercalation for Batteries

Abstract Transition metal oxides (TMOs) as high‐capacity electrodes have several drawbacks owing to their inherent poor electronic conductivity and structural instability during the multi‐electron conversion reaction process. In this study, the authors use an intrinsic high‐valent cation substitution approach to stabilize cation‐deficient magnetite (Fe₃O₄) and overcome the abovementioned issues. Herein, 5 at% of Mo⁴⁺‐ions are incorporated into the spinel structure to substitute octahedral Fe³⁺‐ions, featuring ≈1.7 at% cationic vacancies in the octahedral sites. This defective Fe_2.93▫_0.017Mo_0.053O₄ electrode shows significant improvements in the mitigation of capacity fade and the promotion of rate performance as compared to the pristine Fe₃O₄. Furthermore, physical‐electrochemical analyses and theoretical calculations are performed to investigate the underlying mechanisms. In Fe_2.93▫_0.017Mo_0.053O₄, the cationic vacancies provide active sites for storing Li⁺ and vacancy‐mediated Li⁺ migration paths with lower energy barriers. The enlarged lattice and improved electronic conductivity induced by larger doped‐Mo⁴⁺ yield this defective oxide capable of fast lithium intercalation. This is confirmed by a combined characterization including electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT) and density functional theory (DFT) calculation. This study provides a valuable strategy of vacancy‐mediated reaction to intrinsically modulate the defective structure in TMOs for high‐performance lithium‐ion batteries.