Decoding the Mechanisms of Reversibility Loss in Rechargeable Zinc-Air Batteries

Attaining high reversibility of the electrodes and electrolyteis essential for the longevity of secondary batteries. Rechargeablezinc-air batteries (RZABs), however, encounter drastic irreversiblechanges in the zinc anodes and air cathodes during cycling. To uncoverthe mechanisms of reversibility loss in RZABs, we investigate theevolution of the zinc anode, alkaline electrolyte, and air electrodethrough experiments and first-principles calculations. Morphologydiagrams of zinc anodes under versatile operating conditions revealthat the nanosized mossy zinc dominates the later cycling stage. Suchanodic change is induced by the increased zincate concentration dueto hydrogen evolution, which is catalyzed by the mossy structure andresults in oxide passivation on electrodes and eventually leads tolow true Coulombic efficiencies and short life spans of batteries.Inspired by these findings, we finally present a novel overcharge-cyclingprotocol to compensate for the Coulombic efficiency loss caused byhydrogen evolution and significantly extend the battery life.

Automated summary

Achieving high reversibility between the electrodes and electrolyte is crucial for the durability of secondary batteries. Rechargeable zinc-air batteries (RZABs) undergo irreversible changes in the zinc anodes and air cathodes during cycling. Through experiments and calculations, it was found that nanosized mossy zinc dominates the later cycling stage due to increased zincate concentration caused by hydrogen evolution. This mossy structure catalyzes the hydrogen evolution, resulting in oxide passivation on electrodes, low true Coulombic efficiencies, and short battery life. Inspired by these findings, a novel overcharge-cycling protocol is presented to compensate for the Coulombic efficiency loss and extend battery life significantly.