Sodium Stripping and Plating from Na-β"-Alumina Ceramics Beyond 1000mA/cm²

Dendrite formation limits the cycle life of lithium and sodium metal anodes and remains a major challenge for their integration into next-generation batteries, even when replacing the liquid electrolyte by a solid electrolyte. Recent studies have pointed out that lithium and sodium metal creep rather than lithium and sodium diffusion is the primary mechanism for replenishing the voids forming in solid metal anodes at the interface to a solid electrolyte upon stripping. Void formation upon stripping causes current constrictions upon plating, promoting dendrite formation. Here we investigate plating and stripping of liquid sodium metal from a ceramic Na-β"-alumina electrolyte at 250 °C, thereby eliminating mass transport limitations due to creep. Employing a porous carbon electrode coating to (1) prevent dewetting of plated liquid sodium from and (2) to supply liquid sodium upon stripping to the sodiophobic Na-β"-alumina surface, we demonstrate extremely high current densities above 1000 mA/cm2 and cumulative plated capacities of 10 Ah/cm2 without dendrite formation [1]. These values are two orders of magnitude larger than the corresponding values measured at room temperature [2]. We further show that liquid sodium occupies 60% of the porosity of the carbon coating, while excess sodium accumulates on top of the coating. Increasing the thickness of the carbon coating from 50 μm to 200 μm does not affect the Coulombic efficiency, but reduces the constant current rate capability due to the increased flow resistance for liquid sodium in the porous coating. Our results confirm that eliminating void formation is effective in suppressing dendrite formation. [1] D. Landmann, G. Graeber, M. V. F. Heinz, C. Battaglia, Materials Today Energy, in press [2] M.-C. Bay, M. Wang, R. Grissa, M. V. F. Heinz, J. Sakamoto, C. Battaglia, Adv. Energy Mater. 2019, 201902889