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.