Phase Transition Behavior During Sintering Process of Li‐Rich Materials

This work delves into the structure evolution occurring in two-phase Li-rich Mn-based materials during high-temperature calcination process and puts forth a transition mechanism from LiTMO₂ (R3¯${\bar{3}}$m) phase to Li₂MnO₃ (C2/m), indicating that the TM vacancies stemming from interlayer TM migration in LiTMO₂ (R3¯${\bar{3}}$m) phase serve as the root cause of this transformation.

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 R3¯${\bar{3}}$m space group and monoclinic phase Li₂TMO₃ with C2/m space group. Yet to be firmly elucidated is how the precursor transforms into LiTMO₂ (R3¯${\bar{3}}$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.