Cells were assembled under Argon atmosphere. Before assembly, all cell parts were dried at 60°C for at least 12 h. As separators Whatman™ GF/A glass microfiber filters were used, those were dried at 110°C under vacuum overnight. A piece of sodium metal serves as reference electrode. For the counter electrode sodium metal was roll-pressed to a flat foil using a standard kitchen pasta machine. The working electrode was put in the top of the cell towards the current collector with the gas flow field. 1.6 mL of 1 M electrolytes were used in each cell. A resting time of 24h was applied before the cycling started. The cycling for all the cells was performed at 20 mA g -1 in reference to the NaMNO active material. For the symmetric Na|Na cells the same current as for the PC cell with 4.25 V cut-off was used. This current is in the same range as all cells shown in this work. The duration of a half-cycle was set to be 10 h, which is just a little longer as the expected for the NaMNO at 20 mA g -1 .