Electrodissolution-driven enhancement in Zn electrode reversibility.

Abstract

Current strategies to enhance Zn reversibility in aqueous Zn batteries (AZBs) primarily focus on inducing planar deposition. However, electrodissolution, as the initial operational step in AZBs, significantly affects deposition behavior and reversibility, yet it is surprisingly overlooked. Herein, the crucial electrodissolution behavior of Zn electrodes and its impact on irreversibility are comprehensively elucidated. First, the dissolution pathways at different current densities are investigated at the microscopic level. As the current density increases, the electrodissolution behavior evolves from "point dissolution" to "line dissolution" and ultimately to "surface dissolution". Meanwhile, the proportion of dissolution area and depth changes at different operating protocols are quantitatively analyzed. Then, Combining theoretical calculations and experimental tests, dissolution differences among various crystal planes are unveiled with the sequence from weakest to toughest being (110), (101), (103), (102), (100), and (002). Additionally, morphological characterization and electrochemical-mass transport coupling models demonstrate that dissolution reshapes the surface morphology and interfacial microenvironment for deposition, which in turn determines nucleation and growth sites. More importantly, the mechanism of "dead Zn" formation is clarified by considering the internal structural heterogeneity of the dendrites and the external concentration distribution. As a proof of concept, Zn electrodes with preferred orientations constructed via epitaxial growth demonstrated uniform dissolution and achieved over a 46 % improvement in cycling lifespan compared to Zn electrodes with random orientations. This work provides a profound comprehension of the largely overlooked electrodissolution, opening a novel avenue for improving the reversibility of metal electrodes.