First-principles calculations to investigate the impact of fluorine doping on electrochemical properties of Li-rich Li2MnO3 layered cathode materials

Li-rich layered oxides are promising candidates for high-capacity Li-ion battery cathode materials. In this study, we employ first-principles calculations to investigate the effect of F doping on Li-rich Li₂MnO₃ layered cathode materials. Our findings reveal that both Li₂MnO₃ and Li₂MnO_2.75F_0.25 exhibit significant volume changes (greater than 10%) during deep delithiation, which could hinder the cycling of more Li ions from these two materials. For Li₂MnO₃, it is observed that oxygen ions lose electrons to compensate for charge during the delithiation process, leading to a relatively high voltage plateau. After F doping, oxidation occurs in both the cationic (Mn) and anionic (O) components, resulting in a lower voltage plateau at the beginning of the charge, which can be attributed to the oxidation of Mn³⁺ to Mn⁴⁺. Additionally, F doping can somewhat suppress the release of oxygen in Li₂MnO₃, improving the stability of anionic oxidation. However, the increase of the activation barriers for Li diffusion can be observed after F doping, due to stronger electrostatic interactions between F^- and Li⁺, which adversely affects the cycling kinetics of Li₂MnO_2.75F_0.25. This study enhances our understanding of the impact of F doping in Li₂MnO₃ based on theoretical calculations.