Synergistic O2/O3 Phase Engineering Suppresses Voltage Fade and Enhances Cycling Stability in Lithium-Rich Layered Oxides

Lithium-rich manganese-based layered oxides are considered next-generation cathode materials due to their ultra-high capacity and voltage plateau. However, the single O3 phase is prone to lattice oxygen loss and irreversible phase transitions during high-voltage cycling, leading to rapid capacity and voltage decay. In this study, a molten salt ion exchange method was used to quantitatively convert the P2 phase into the O2 phase, creating a composite cathode with a precisely adjustable O2/O3 ratio. The effects of phase ratio on microstructure, crystal structure, surface chemistry, and electrochemical performance were systematically investigated. The results show that the introduction of the O2 phase enhances the structural stability of the cathode material. Specifically, the 0.3O2/0.7O3 sample, after 200 cycles at 4.6 V and 1 C, maintained a capacity of 159.8 mAh/g with a capacity retention of 98.8%, a voltage decay rate of only 2.43 mV/cycle, and the smallest shift in the oxidation peak, showing the best overall performance. This work elucidates the synergistic stabilization mechanism of different O2/O3 ratios and provides a reference for phase engineering in lithium-rich manganese-based cathodes.