Separating Nucleation and Growth: High‐Overpotential Pretreatment Pulses for Sodium‐Metal Electrodes

Sodium metal is capable of unlocking a new sustainable pathway toward electrification thanks to its high energy density and abundant resources. However, uneven metal nucleation and growth during cycling remains a challenge to be fully understood and overcome. In this study, short high‐overpotential pretreatment pulses are applied to enable 2D metal growth. This is achieved by separating the initial nucleation step from reversible sodium metal growth. Electrochemical measurements combined with scanning electron microscopy and image analysis prove that the reductive and oxidative pulses significantly decrease the initial overpotential during galvanostatic cycling, compared to cycling without pulses. The oxidative or reductive pulses activate the entire electrode surface by generating a dense population of single micrometer‐sized pits or nuclei, respectively. This activation of the surface decreases the interfacial impedance and circumvents the generation of mossy sodium and forms a smooth hill‐valley‐like topography. Double pulse pretreatment further improves the 2D sodium growth. This improvement is also seen in full‐cells with Prussian white as the cathode material as an increase in Coulombic efficiency. The results of this study demonstrate that separating the nucleation event from continuous growth and using the optimal conditions for each step is key to obtaining stable 2D sodium metal growth conditions.