Tetrahedral‐Field Distortion Engineering of Redox‐Active Orbital Energy Levels Enables Low‐Voltage Delithiation of Li 6 MnO 4

ABSTRACT Cathode lithium‐supplementing materials offset irreversible lithium loss in high‐capacity anode lithium‐ion batteries. Li 6 MnO 4 stands out for its high lithium capacity and low cost. However, its ultrahigh delithiation potential severely hinders practical use, reducing Li utilization and supplement efficiency. Herein, a tetrahedral‐field distortion strategy is developed through partial Co 2+ substitution to elevate the energy levels of redox‐active orbitals in Li 6 MnO 4 , thereby narrowing the energy gap between the cathode redox states and the Li/Li + chemical potential for low‐voltage delithiation. Combined spectroscopic analyses and density functional theory calculations reveal that the distorted tetrahedral coordination reconstructs the local electronic structure, promotes oxygen charge compensation, weakens Li–O interactions, and facilitates Li + diffusion, enabling efficient lithium extraction with high prelithiation capacity. As a result, the optimized Li 6 Mn 0.8 Co 0.2 O 4 exhibits a main delithiation plateau within 3.0–4.3 V (vs Li/Li + ) and delivers an effective lithium‐supplementing capacity of 775.6 mAh g −1 . In NCM||Si/C full cells, it increases the initial reversible specific capacity by 16 mAh g −1 and improves the long‐term capacity retention by 19.4%. This work establishes tetrahedral‐field distortion as an effective strategy for engineering redox‐orbital energy levels to lower the delithiation potential of anti‐fluorite lithium‐supplementing materials, providing a general design principle for next‐generation high‐energy‐density lithium‐ion batteries.