Strong Correlation between Ion-Migration Generated Vacancies and Anion Redox Activity in Layered Oxides

Abstract

The role of dynamically generated vacancies associated with cation migrations in activating or facilitating the anion redox reaction (ARR) in layered oxides is still unknown. By taking P2-type Na_2/3Zn_xMn_1–xO₂ as a model system, we herein showcase that Zn-migration induced vacancies are responsible for the ARR activity through first-principles calculations. Remarkably, we reveal a quasi-quantitative connection between Zn-migration induced vacancies and ARR activity in a series of Na_2/3Zn_xMn_1–xO₂ (x = 0.1–0.3) materials by an arsenal of characterizations. The partially reversible Zn migration will divide the ARR beyond the activation cycle into “reversible ion-migration induced” and “irreversible ion-migration induced” types. We further highlight that a stable cyclic performance can be achieved via balancing these two types of ARR and transition-metal (TM) redox, securing both a high reversible capacity and stable discharge voltage. These insights represent a conceptual breakthrough toward the role of dynamically generated vacancies in activating and stabilizing ARR.