Micro-cracking on the surface of zinc metal improves the cycle performance of aqueous zinc ion batteries

Abstract

The notorious zinc dendrite is a severe constraint to the practical application of zinc-based batteries, as the metal tips growing vertically in two dimensions on the surface of the electrodes during cycling and loosely packed sharp edges may pierce through the diaphragm, posing a safety hazard. In this study, physical stress extrusion was used to generate micron- or submicron-sized cracks on zinc metal anodes, which significantly increased the specific surface area of the electrodes and mitigated the local current density of the electrodes. Zinc ion fluxes were significantly dispersed, producing a dense Zn2SO4(OH)6-xH2O (ZHS) layer, which differed distinctly from the by-products of the loose upright growth on the surface of Raw Zn (RZn). Additionally, three-dimensional structure of cracked zinc composition allows it to adjust the zinc volume variations during electroplating/stripping, and the abundance of nucleation sites significantly reduces the Zn polarization voltage, resulting in uniform Zn deposition. The average cycle life of the symmetric cell was >400 h at 1 mA cm−2 current density, and nearly 500 cycles at 5 mA cm−2 current density for the asymmetric cell, with an average Coulombic efficiency of 99.3 %. The activation energy substantially declined with the increase in Zn ion flux per unit time (29.615 KJ mol−1 vs. 44.041 KJ mol−1), demonstrating efficient desolvation kinetics. Furthermore, the Crack Zn || V2O5 full cell also exhibits outstanding self-discharge performance, with 85 % capacity retention in a 48 h resting charge/discharge testing, superior to the raw zinc foil anode (78.3 %). Herein, a method of creating microcrack configurations on the surface of zinc anodes using stress extrusion was presented, sparing the current density while optimizing the undesirable growth patterns of ZHS by-products.