Synergistic Enhancement of Surface Interlayer Expansion and Bulk Structural Stabilization in Mg/Mo Co-Doped Li-Rich Mn-Based Cathode Materials via Ratio Optimization

Abstract Li-rich Mn-based layered oxides (LMO) are highly susceptible to irreversible phase transitions and lattice oxygen evolution under high voltages, leading to severe voltage decay and rate capability deterioration. To address the asymmetric modification requirements for surface anti-erosion and bulk structural maintenance of LMO, we propose a nanoscale spatially differentiated Mg/Mo bulk-surface synergistic doping strategy in this study. Specifically, large-radius Mo6+ exhibits a gradient distribution primarily within the particle surface layer, accelerating lithium-ion transport by expanding the surface lattice spacing. Simultaneously, small-radius Mg2+ is uniformly distributed throughout the particle bulk, effectively stabilizing the internal lattice skeleton by anchoring lattice oxygen. Within this nanoscale structural regulation, the mechanisms of surface Mo accelerating ion transport and bulk Mg anchoring lattice oxygen generate a bidirectional synergy, effectively suppressing the propagation of structural collapse and ensuring the overall stability of the material. At the optimal Mg/Mo molar ratio of 5:5, the material delivers an initial discharge specific capacity of 297.4 mAh/g and maintains a reversible capacity of 188.9 mAh/g after 200 cycles at a high rate of 5C, with a capacity retention of 76.78%. This nanoscale spatially differentiated synergistic mechanism mitigates the structural degradation of the material, providing an effective perspective for the design of highly stable Li-rich cathodes.