In-situ observation of the Zn electrodeposition on the planar electrode in the alkaline electrolytes with different viscosities

As the dendrite issue is prominent in Zn-based batteries, the regulation of Zn electrodeposition to inhibit the dendrite formation and growth is crucial. Herein, the in-situ observation of electrodeposition process on a planar electrode is performed in this work. The scenarios of operating conditions and electrolyte viscosities are investigated by adjusting charging currents and adding polymer molecules with different concentrations. It is found that the Zn electrodeposition process can be divided into uniform and non-uniform regions, and high currents and high viscosities can prolong the uniform region. Besides, with the increases of current and viscosity, the deposition Zn becomes thinner and compact in the uniform region. The mechanism is proposed as the high current can provide enough electrons which can make the deposition occur besides the deposition tips. The increase in viscosity hinders ion transport, which makes the effect of distance more obvious. Thus, using a high charging current (e.g., pulse charging) and/or an electrolyte with high viscosity are favorable for the uniform deposition of Zn. This work lays the foundation for the improvement of alkaline Zn-based batteries. The optical in-situ observation technology used here is also favorable to explore the deposition process in other electrochemical systems.