Insight into potential oscillation behaviors during Zn electrodeposition: Mechanism and inspiration for rechargeable Zn batteries

Abstract

Tremendous efforts are devoted to improving the utilization and stability of Zn electrodes for rechargeable Zn batteries, while the charging behaviors under high current density are rarely spotlighted. Herein, the mechanism of the potential oscillation during Zn electrodeposition in an alkaline solution is investigated in detail. The in-situ observation reveals a three-step process, involving Zn precipitation, hydrogen bubble evolution, and separation. A mathematical model considering the influence of bubble coverage and the hydrogen evolution reaction (HER) current is built to examine the electrochemically active surface area (ECSA). The results illustrate that convective disturbance of bubbles and the recovery of the ECSA lead to the drop back of the oscillating potential in the initial charging process. Then, the whole electrodeposition process is divided into the oscillating stage, the irregular stage, and the steady stage, of which the evolution may be attributed to the growth of microscopic Zn secondary structures. Based on the mechanism, a concept of the optimal charging curve is introduced, which not only guarantees safe charging without the hydrogen bubble evolution issue but also realizes efficient time-saving. Besides, a pulsed current strategy is also proposed to inhibit potential oscillation by offering sufficient time for ions to diffuse uniformly, and the efficiency is carefully evaluated. This work provides an insightful understanding of potential oscillation during Zn electrodeposition, which will favor the practical application of high-performance rechargeable Zn batteries.