Toward Better Sodium–Oxygen batteries: A Study on the Performance of Engineered Oxygen Electrodes based on Carbon Nanotubes

Sodium–oxygen cells with NaO 2 as discharge product show very low overvoltages during discharge and charge, and their energy efficiency can be higher than 90 %. In this study the electrochemical behavior of three different free‐standing gas diffusion layers (GDL) is discussed, with each prepared by using a straightforward process from commercial starting materials: A pure carbon nanotube (CNT) electrode, a CNT electrode mixed with carbon fibers (CF) and a CNT electrode mixed with carbon black (CB). A solvent‐free method was applied to the fabrication of these electrodes, which may help to overcome limitations of common slurry‐based processes. NaO 2 formed as the sole discharge product for all electrodes tested. The pure CNT electrode performs best in terms of capacity (1530 mAh g −1 , 4.2 mAh cm −2 ) and cycle life (more than 140 cycles), and the results are superior in comparison to previous studies.