Distinct Charge Compensation Induced by Cationic Ordering-Disordering Transition in Layered Oxide Cathode.

Abstract

Constructing in-plane cationic ordering in layered oxide cathodes can mitigate the adverse effects associated with the anionic redox reaction to achieve high energy density, while recent studies reveal that cationic disordering may also stabilize oxygen redox by tuning the local coordination environment of lattice oxygen. These findings underscore the pivotal role of local coordination and raise a further question regarding how the structural evolution of the transition metal sequence during electrochemical cycling dynamically dictates the charge compensation pathway. Herein, we unraveled the charge compensation evolution of P2-type Na0.6Li0.2Mn0.8O2 (NLMO) upon cationic ordering-disordering transition. During the initial cycle process, the electron holes are delocalized over oxygen ions coordinated to two Mn (O-Mn2) units arranged in the ribbon superstructure within the TM layers of NLMO, enabling a reversible anionic redox reaction. Upon extended cycles, the irreversible chemical depletion of Li and O serves as the thermodynamic driving force that destabilizes the ribbon superstructure. This structural instability facilitates in-plane Mn migration as a kinetic pathway, converting O-Mn2 units to O-Mn3 configurations and driving the macroscopic ordering-to-disordering transition. This fundamental structural disordering uniquely activates the bulk Mn2+/Mn3+ redox couple, which compensates for the diminished anionic redox contribution. By revealing the dynamic coupling between superstructure evolution and redox behavior, this work identifies irreversible cationic transitions as the root cause of structural degradation, underscoring the necessity of constructing rigid TM frameworks in high-capacity layered cathodes.