Ultrahigh‐Efficiency Zinc‐Air Batteries Enabled by Defect‐Engineered Biomass Carbon and Dynamic Nickel Redox Mediation

Coupled zinc-air batteries (CZABs) are promising in future energy storage and conversion solutions because of their potential for enhanced energy efficiency and boosted power density. However, sluggish reaction kinetics at the cathode remain a key challenge, leading to cycling instability and insufficient battery performance. In this study, a rational interfacial etching method is developed to fabricate nitrogen-doped and defect-rich carbon catalysts from the low-cost eucalyptus waste. The precise formation of carbon vacancies, driven by synergistic spatial confinement domains and oxygen-containing functional groups exposed on eucalyptus precursors, promotes the reconstruction of pyridinic nitrogen (Py-N) coordination. This induces local electron redistribution, enhancing charge transfer efficiency at adjacent Py-N sites, and optimizing *O/*OH adsorption-desorption kinetics, thereby significantly boosting the electrocatalytic activity for the oxygen reduction reaction. Additionally, the integration of self-adaptive Ni2+/Ni3+ redox pair into the cathode effectively mitigates the oxygen evolution reaction and thus reduces voltage delay by 0.12 V. The resulting CZABs achieve 82% energy efficiency at 5 mA cm-2 and 77% after 400 h, which is rarely reported. This work elucidates the intricate mechanism of defect formation during biomass pyrolysis and presents a scalable, cost-effective strategy for producing high-efficiency catalysts, offering a promising strategy toward advanced energy storage systems.