Spontaneous Formation of Porous Zinc in Rechargeable Zinc Batteries

Abstract

The stability of Zn anodes in Ni-Zn and Zn-air batteries is dictated by the electrochemical transition between Zn and ZnO, the complexity of which has long obscured the micro-structural roots of anode failures such as shape changes, passivation, and dendrite formation. Here we reveal that in this phase transition evolves porous Zn, a structure that underpins the rechargeability of the anode. At sequential stages of charging and discharging cycles, we retrieved over one hundred anodes initially made of ZnO particles. At their cross-sections, we observe the progressive, spontaneous evolution of connected curvy Zn ligaments, explained by the continuum percolation theory and structural self-organization. The growth and consumption of ZnO spikes on the porous structure become a steady state until being upended by the growth of large Zn granules via the long-range transport of zincate. More conductive additive promotes the formation of porous Zn, which improves the cycle life to 230 cycles at 30% utilization of the zinc mass, among the best reported for an alkaline Zn anode. The work underlines the importance of micro-structural evolution for the fulfillment of cheap, safe energy storage by Zn.