Phase Transition Behavior During Sintering Process of Li-Rich Materials

Abstract

Phase transition serves as an ordinary behavior occurring during the high-temperature calcination process, while it becomes quite complicated in Li-rich materials composed of rhombohedral phase LiTMO₂ (TM: Ni, Mn) with R$\overline{3}$m space group and monoclinic phase Li₂TMO₃ with C2/m space group. Yet to be firmly elucidated is how the precursor transforms into LiTMO₂ (R$\overline{3}$m)-Li₂TMO₃ (C2/m) compound and what is the precise conversion mechanism between these two phases. This work systematically elaborates the structural evolution with Li/O incorporation during calcination, and proposes a LiTMO₂ to Li₂TMO₃ phase transition mechanism. A series of characterizations on structural rearrangement and detailed analysis provide insights into the comprehension of this transition, i.e., the transition metal (TM) vacancies induced by interlayer TM ions migration function as the primary reason driving the transformation from LiTMO₂ to Li₂TMO₃. This work offers a novel concept for the structural regulation in Li-rich cathodes.