Surface Overpotential as a Key Metric for the Discharge-Charge Reversibility of Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are receiving increasingattentionfor power-grid energy storage systems. Nevertheless, warranting long-termreversible operation is not trivial owing to uncontrolled interfacialphenomena related to zinc dendritic growth and parasitic reactions.Herein, the addition of hexamethylphosphoramide (HMPA) to the electrolyterevealed the surface overpotential (|& eta;(s)|) to be akey metric of the reversibility. HMPA adsorbs onto active sites onthe zinc metal surface, raising the surface overpotential toward loweringthe nucleation energy barrier and decreasing the critical size (r (crit)) of nuclei. We also correlated the observedinterface-to-bulk properties by the Wagner (Wa) dimensionless number.The controlled interface enables a Zn|V6O13 fullcell to retain 75.97% capacity for 2000 cycles, with a capacity lossof only 1.5% after 72 h resting. Our study not only delivers AZIBswith unparalleled cycling and storage performance but also proposessurface overpotential as a key descriptor regarding the sustainabilityof AZIB cycling and storage.