Real-Time Imaging of the Electrochemical Process in Na–O₂ Nanobatteries Using Pt@CNT and Pt_0.8Ir_0.2@CNT Air Cathodes

Compared to lithium–oxygen batteries, sodium–oxygen (Na–O₂) batteries exhibit a number of advantages: extremely low cost, low charging overpotential, and stability under nitrogen. However, accumulation of insoluble discharge products and failure of catalysts often result in poor performance of Na–O₂ batteries and limit their cycling life. In this work, electrochemical reactions of Na–O₂ batteries were directly investigated in situ by assembling a solid-state Na–O₂ nanobattery in an aberration-corrected environmental transmission electron microscope. During discharge, NaO₂ hollow spheres formed and expanded continuously, accompanying their partial decomposition into Na₂O₂. These spheres shrank and collapsed into Na₂O₂ nanoparticles during the charging process. Carbon nanotubes doped with Pt and bimetallic Pt/Ir nanoscale catalyst can promote product formation and reversible evolution. In-depth investigation of the electrochemical reaction mechanism in Na–O₂ cells helps to accelerate the development of metal–air devices.