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

ABSTRACT

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 Li2MnO2.75F0.25 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 Li2MnO2.75F0.25. This study enhances our understanding of the impact of F doping in Li2MnO3 based on theoretical calculations.