How the Kinetic Balance Between Charge-Transfer and Mass-Transfer Influences Zinc Anode Stability: An Ultramicroelectrode Study.

Aqueous zinc-metal batteries (AZMBs) represent a promising frontier in battery technology, offering sustainable and safe alternatives to traditional non-aqueous batteries. Despite their potential, understanding the kinetics of zinc electrodeposition-a critical factor in AZMB performance-remains underexplored. Utilizing voltammetry on ultramicroelectrodes, we investigate how scan rate influences key processes of nucleation and growth during Zn²⁺ electrodeposition. The findings highlight the efficacy of the Butler-Volmer formulation in capturing electron-transfer kinetics, contrasting with complex electron transfer kinetic models used for non-aqueous battery chemistries. We clearly demonstrate that there is a strong dependence of scan rate on the measured value of kinetic parameters (exchange current). To accurately probe the charge transfer kinetics, it is essential to apply fast scan voltammetry to decouple the influence of mass transfer, ensuring that the measured current is independent of the scan rate. Furthermore, by studying a model electrolyte additive, the intricate balance between charge transfer and mass transfer dynamics is unveiled, and this information is crucial for enhancing the stability of zinc metal anodes. These insights pave the way for developing advanced electrolyte and current collector formulations, promising enhanced cyclability and sustainability in zinc metal batteries.