Unveiling Oxygen Redox Activity in P2-Type NaxNi0.25Mn0.68O2 High-Energy Cathode for Na-Ion Batteries

Na-ion batteries are emerging as convenient energy-storage devices for large-scale applications. Enhanced energy density and cycling stability are key in the optimization of functional cathode materials such as P2-type layered transition metal oxides. High operating voltage can be achieved by enabling anionic reactions, but irreversibility of O2-/O-2(n-)/O-2 evolution still limits this chance, leading to extra capacity at first cycle that is not fully recovered. Here, we dissect this intriguing oxygen redox activity in Mn-deficient NaxNi0.25Mn0.68O2 from first-principles, by analyzing the formation of oxygen vacancies and dioxygen complexes at different stages of sodiation. We identify low-energy intermediates that release molecular O-2 at high voltage, and we show how to improve the overall cathode stability by partial substitution of Ni with Fe. These new atomistic insights on O-2 formation mechanism set solid scientific foundations for inhibition and control of this process toward the rational design of new anionic redox-active cathode materials.

Automated summary

This study dissects the oxygen redox activity mechanism in Mn-deficient NaxNi0.25Mn0.68O2 from first-principles and proposes partial substitution of Ni with Fe to improve cathode stability. These findings provide a solid scientific foundation for rational design of new anionic redox-active cathode materials.