Super-resolved dynamics of isolated zinc formation during extremely fast electrochemical deposition/dissolution processes.

The development of zinc-air batteries with high-rate capability and long lifespan is critically important for their practical use, especially in smart grid and electric vehicle application. The formation of isolated zinc (i-Zn) on the zinc anode surface, however, could easily lead to deteriorated performance, such as rapid capacity decay. In particular, under the fast charging/discharging conditions, the electrochemical activities on the anode surface are complicated and severely suppressed. Thus, it is highly desirable to deeply understand the formation mechanism of i-Zn and its relationship with the electrochemical performance during extremely high-rate cycling. Herein, we employed a super-resolution dark-field microscope to in situ analyze the evolution dynamics of the electrolyte-Zn interface during the extremely fast electrochemical deposition/dissolution processes. The unique phenomenon of nanoscopic i-Zn generation under the condition is unveiled. We discovered that the rapid conversion of nanoscopic i-Zn fragments into passivated products could greatly exacerbate the concentration polarization process and increase the overpotential. In addition, the role of large-sized i-Zn fragments in reducing the coulombic efficiency is further elucidated. This information could aid the rational design of highly effective anodes for extremely high-rate zinc-based batteries and other battery systems.