First-Principles Studies Of Blacl Phosphorus And LiMn₂O₄ As Electrode Material For Lithium Ion Batteries

Based on density functional theory (DFT), we mainly investigated lithium ionic dynamics performance in black phosphorus and oxidation states of Mn atoms at LiMn₂O₄ (001) surfaces.1. Electronic and atomic structures of LiP5, Li₃P₇ and LiP, which are formed in the process of lithium intercalation into black phosphorus, have been systematically studied and analyzed using first-principles ultrasoft pseudopotentials method based on the density functional theory. We simulated the diffusion of lithium ions in the LiP5, Li₃P₇ and LiP materials using CINEB(Climbing Images Nudged Elastic Band)method, and the diffusion activation energy of lithium ions are obtained through theoretical calculation. Through the analysis of the diffusion barrier and diffusion pathways, we predicted the lithium ion conduction behavier in black phosphorus during charge and discharge process, and this provides useful information for future theoretical and experimental research.2. The electronic structures of bulk and (001) surfaces ofλ-MnO₂ and LiMn₂O₄ have been studied with density functional theory. Inλ-MnO₂, the Mn oxidation state is +4 both in the bulk and at the (001) surface. In LiMn₂O₄, however, Mn atoms exhibit mixed Mn3+/Mn4+ oxidation states in the bulk, while only Mn3+ at the (001) surface, due to lower coordination with O atoms. The technically undesired Mn3+ ions form at LixMn₂O₄ (001) even for very small Li concentrations. Upon covering the LiMn₂O₄ (001) surface with Al2O3, the oxidation state of surface Mn atoms changes from +3 to +4, which explains the improved performance of coated LiMn₂O₄ cathodes in Li-ion batteries.