A KO2-Based Solid Superoxide Reservoir for Irreversible Capacity Compensation in Superoxide-Based Na-O2 Batteries.

Sodium-oxygen (Na-O2) batteries are plagued by persistent discharge-charge capacity imbalances stemming from parasitic reactions and the incompletely reversible oxygen redox chemistry induced by the reactive superoxide species. Herein, we propose the integration of commercial potassium superoxide (KO2) as a sacrificial solid reservoir to actively compensate for the rechargeable superoxide loss in sodium superoxide (NaO2)-based Na-O2 batteries. Mechanistic and spectroscopic investigations reveal that the preloaded KO2 serves a dual function: it acts as an extra superoxide source to directly replenish early stage capacity losses while simultaneously functioning as a promoter to mediate the formation of NaO2. Benefiting from this reservoir-mediated regulation, the KO2-configured Na-O2 cells exhibit unprecedented cyclability, delivering a near-unity Coulombic efficiency (98.5% on average) and sustaining a prolonged lifespan of over 600 cycles. This work establishes a robust paradigm for active capacity compensation, offering a highly scalable design principle to unlock the full potential of alkali metal-air battery systems.