Formation and Discharge of Zn Sponge Anodes, Followed by Synchrotron Hard X-ray Imaging

The fabrication of engineered Zn anodes often relies on different forms of ZnO as the material in direct contact with the alkaline aqueous electrolyte in the pristine assembled cell state. Of course, in this case, the as-assembled cell is in the discharged state and requires an initial charging step, or "formation", to generate active metallic Zn. The formation of ZnO-based anodes is a complex process the control of which calls for an in-depth understanding of electrochemical phase growth. In fact, formation gives rise to morphochemical imprinting, profoundly impacting the electrode functional performance. The present work contributes to the understanding of the formation of Zn sponge electrodes, combining electrochemistry and synchrotron-based X-ray imaging. Specifically, we employed dynamic <i>in operando</i> radiography to select the potentiostatic formation conditions that exclude hydrogen-induced damaging of the sponge structure. Subsequently, formation and the subsequent first discharge are followed by time-lapse <i>in situ</i> tomography, allowing to track the early structural evolution of the sponge electrode and the Zn/ZnO phase distribution.