Revealing the role of Mn/Li disordered mixing in Li-rich cathode Li2MnO3 by first-principles calculations

Abstract

${\mathrm{Li}}_{2}{\mathrm{MnO}}_{3}$ is considered as one of the candidates for Li-rich cathode material of next-generation lithium-ion batteries because of its high energy density. Due to the synthesis environments and migration of Mn in the charging/discharging cycles, Mn/Li disordered mixing in Li/transition-metal layers of ${\mathrm{Li}}_{2}{\mathrm{MnO}}_{3}$ is frequently observed and breaks the uniformity of the original structure. Nevertheless, the role of Mn/Li disordered mixing in ${\mathrm{Li}}_{2}{\mathrm{MnO}}_{3}$ has not been well understood, preventing the rational design of better Li-rich Mn-based cathode materials. In this work, we study the energetic and electronic properties involving local Mn/Li disordered mixing in ${\mathrm{Li}}_{2}{\mathrm{MnO}}_{3}$ through first-principles calculations. A Mn/Li disordered mixing model is created, in which the Li-rich and Mn-rich regions are utilized to describe the structural inhomogeneity. The results indicate that O ions in the Li-rich area are of more isolated $2p$ states, which show higher energy in the electronic structure. Hence, O ions in the Li-rich region possess a higher electrochemical activity and suffer more severe oxidation during the subsequent charging process, which eventually leads to the earlier destabilization of O ions. The Li-rich region facilitates the diffusion of Li in the Li layer, but the close-packed arrangement of Mn in the Mn-rich region impedes the interlayer and intralayer diffusion of Li near it. Furthermore, the misplaced Mn ion in the Mn-rich region is more prone to diffuse into the Li layer. The identification of the role of Mn/Li disordered mixing in ${\mathrm{Li}}_{2}{\mathrm{MnO}}_{3}$ provides a further understanding for the better design of Li-rich Mn-based cathode materials.