Theoretical study of structural phase transition and soft mode behavior in P2-ATMO₂ (A=Li/Na/K/Mg, TM=Mn/Co/Ni)

Abstract P2-type layered transition metal oxides (P2-ATMO₂, A = Li, Na, K, Mg; TM = Mn, Co, Ni) are promising cathode materials for rechargeable batteries due to their open framework, which facilitates efficient charge carrier diffusion. However, these materials undergo complex phase transitions during charging and discharging cycles, significantly impacting battery performance. Phonon properties provide critical insights into structural stability and phase transitions, thus providing guidance for enhancing cathode stability. In this study, we investigated the phonon and electronic properties of P2-ATMO₂ materials, focusing on the influence of Jahn-Teller (JT) distortion. We identify several soft phonon modes, indicating a propensity for JT -driven transitions to P’2 structures and P2-O2 phase transitions. The evolution of soft modes in these layered oxides exhibits clear regularity. The agreement between our theoretical analysis of these soft modes and the experimental observations validates their role in structural stability and phase transitions. Our findings clarify the relationship between phonon dynamics, JT effects, and electrochemical performance, paving the way for the rational design of stable, high-performance cathode materials.