Unraveling the mechanism of non-uniform zinc deposition in rechargeable zinc-based batteries with vertical orientation

Secondary zinc-based batteries demonstrate a bright prospect as a candidate for next-generation electrochemical energy storage devices. However, the inhomogeneous zinc deposition with vertical orientation during electrochemical stripping/platting cycles leads to battery failure quickly and thereby limits commercial applications of zinc-based batteries. In this work, the deposited electrochemical reaction is deeply investigated and the mechanism of inhomogeneous electrochemical deposition is proposed via in-situ optical observation and numerical analysis. During the deposited reaction, zinc atoms prefer to deposit on the nucleation sites on the electrode surface, changing the morphology of nucleation sites and leading to possible fractures. The fractural zinc fragments then accumulate at the bottom and connect to the bulk electrode, which initiate the inhomogeneous distribution in the vertical direction where the protrusion appears at the bottom, and the middle and top parts have rare deposited zinc. The inhomogeneity is exacerbated during stripping/platting reaction cycles due to the non-uniform local current density distribution on the emerging protrusion. Besides, the generated bubbles caused by hydrogen evolution exacerbate the inhomogeneous distribution via changing the ion distribution. Based on the conclusions, a uniform deposition behavior is achieved via modulating the ion distribution by the flowing electrolyte as a demonstration. The unraveled mechanisms can serve as a reference for the design of advanced zinc-based batteries with stable electrodes.