Surface Codoping and Defect Construction through Gas Treatment to Address Voltage Attenuation of Li-Rich Layered Oxide Cathodes

Li-rich layered oxide (LLO) cathodes are considered promising candidates for next-generation lithium-ion batteries. However, LLO still faces primary challenges such as low initial Coulombic efficiency and severe capacity and voltage attenuation. These issues are primarily attributed to the irreversible loss of lattice oxygen and the degradation of the layered structure. In this study, to address these problems, LLO (Li1.2Mn0.54Ni0.13Co0.13O2) cathode materials are codoped with boron and fluorine at the surface using a gas–solid reaction strategy. The codoped LLO cathode has a capacity retention of 91.9% and a voltage decay of 0.344 V after 450 cycles at 1 C. After 800 cycles at 10 C, it retains 92.6% of its capacity and 0.276 V of voltage degradation. At a temperature of 55 °C, the codoped LLO maintains 92.7% of its initial capacity after 100 cycles at 1 C. A calculation based on density functional theory indicates that the codoping of boron and fluorine can reduce the unhybridized states and energy barrier, which improve the efficiency of ion diffusion. These results demonstrate that the codoping modification by a gas–solid reaction strategy effectively mitigates capacity and voltage degradation of LLO cathodes, inhibits the surface side reactions, and therefore significantly enhances their cycling stability.