Integrating Bulk Nb Doping and F Surface Layer to Construct a Robust Li-Rich Mn-Based Layered Cathode with Stable...

Li-rich Mn-based layered oxides (LLOs) are among one of the most promising cathode materials for next generation lithium-ion batteries (LIBs) owing to their ultrahigh specific capacity and low cost. However, their practical deployment remains hindered by severe voltage decay, interfacial instability, and structural degradation during cycling. Herein, we propose a synergistic optimization strategy that combines high-valence heteroionic Nb⁵⁺ doping with surface fluorine modification to effectively stabilize the crystal and interfacial structures of xLi₂MnO₃·(1-x)LiMO₂ (M = Ni, Co, Mn) cathodes. The cooperative incorporation of Nb⁵⁺ and F^- induces the formation of a mixed-phase surface reconstruction layer rich in oxygen vacancies, which accelerates Li⁺ diffusion, suppresses oxygen release, and enhances interfacial stability. Comprehensive analyses based on Rietveld refined XRD, HRTEM/EDS, in situ XRD and DEMS, and EIS measurements reveal that the modified M-LLO exhibits superior phase stability, lower charge transfer resistance, and alleviated surface phase transitions compared with the pristine sample. Benefiting from these structural and interfacial optimizations, the M-LLO delivers remarkable electrochemical performance, achieving 89.7% capacity retention after 100 cycles at 1 C/1 C, 78.4% after 300 cycles at 3 C/3 C, and a minimal voltage decay rate of only 3.3 mV·cycle^-1. This study proposes an effective core-surface cooperative engineering strategy for developing structurally robust, energy-dense Li-rich layered cathode materials.