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

Sodium–oxygen cells with NaO2 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. NaO2 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.