Synergistic Regulation of Surface and Defects Enabling High-Performance Li-Rich Mn-Based Cathode Materials for Lithium-ion Battery

The practical commercialization of Li-rich Mn-based oxides (LRMOs) is severely impeded by intrinsic structural degradation stemming from irreversible lattice oxygen release and intense interfacial side reactions at high voltages. Herein, we report a highly innovative "interface-defect" synergistic engineering strategy to concurrently stabilize the bulk structure and interface of the Li1.2Mn0.56Ni0.16Co0.08O2 cathode via a facile, one-step ammonium dihydrogen phosphate (NH4H2PO4) thermal treatment. From a theoretical and mechanistic perspective, we demonstrate that this modification exerts a dual-protective effect: (1) the in-situ conversion of surface residual lithium forms a dense, ion-conductive Li3PO4 coating that effectively suppresses deleterious electrolyte side reactions and transition metal dissolution; and (2) the simultaneous generation of near-surface oxygen vacancies (OVs) fundamentally regulates the anionic redox chemistry, serving as dynamic trapping sites that buffer lattice oxygen evolution and structurally inhibit the detrimental layered-to-spinel phase transition. As a result of this synergistic regulation, the optimally modified cathode achieves a remarkably enhanced initial Coulombic efficiency of 87.6% (compared to 72.6% for the pristine material) and exhibits outstanding cycling stability with 93% capacity retention after 100 cycles at 1.0 C, alongside significantly mitigated voltage decay. This study provides profound theoretical insights into coupling surface passivation with intrinsic defect engineering, offering a scalable and robust paradigm for designing next-generation high-energy-density cathodes.