Interfacial ionic effects in aqueous zinc metal batteries

Zn metals anodes (ZMAs) are most attractive for emerging aqueous zinc metal batteries (AZMBs). However, the practical application of AZMBs is still impeded by various formidable issues like uncontrolled Zn dendritic growth, hydrogen evolution reaction, and severe corrosion of ZMAs. This review delves into the pivotal role of interfacial ionic effects in AZMBs. We elucidate how ionic additives can reshape the electric double layer (EDL), thereby mitigating the issues for AZMBs. Given the different influences on the EDL behavior including the water dipoles, local electric field, solvation structure, electrochemical reaction, etc., we divide it into five primary interfacial effects of the steric effect, electrostatic shielding effect, entropy effect, chemical effect, and other miscellaneous effects, respectively. Nevertheless, since the EDL is highly inhomogeneous and dynamic, we underscore the tremendous challenge of understanding the exact mechanisms behind these interfacial ionic effects. We thus advocate for the significance of combining advanced Operando characterization techniques and multiscale modelling to uncover the mysteries. Besides, we highlight the development of multifunctional ionic additives and the exploration of interfacial ionic effects in non-aqueous electrolytes. This review arouses the rational design and utilization of ionic additives to design effective electrolytes for more efficient and durable AZMBs.