Author: Gang LIU (The Hong Kong Polytechnic University) - The emergence of aqueous zinc-based batteries presents a promising alternative for lithium-ion batteries. Zinc metal exhibits notable advantages, including a high volumetric capacity, a suitable redox potential of 1.65 V, and a low cost of $160 per kW h. Additionally, the use of an aqueous electrolyte enhances intrinsic safety. Despite these benefits, the zinc metal in aqueous batteries still faces a few challenges such as dendrite formation and side reaction (i.e., hydrogen bubble production) during charging. Recent studies have explored various strategies to mitigate dendrite growth and promote uniform deposition of zinc, as well as bubbles removal. These approaches include the introduction of porous electrodes, the addition of electrolyte modifiers, external magnetic field and surface modification of the electrode. Another effective approach is to include flow architecture to inhibit dendrite formation.
In this work, to correlate the relationship between zinc dendrite growth and hydrogen bubble behavior under flow conditions, an in-situ electrochemical system has been developed. This setup enables simultaneous field observations of bubble behavior and dendrite growth while continuously monitoring real-time voltage and current signals. The findings reveal that bubble formation during the zinc deposition process follows a pulsatile sequence: initial accumulation, steady growth, desorption, and discharge. The electrolyte solution (pH=13) is composed of 6 M KOH and 0.2 M Zn(Ac)2. The test was conducted at room temperature. Experimental results show that the attachment-detachment process of hydrogen bubbles is a key factor influencing voltage oscillations and the location of dendrite growth. Under suitable forced convection conditions (90 mL min-1), zinc deposition morphology can be transformed from mossy to layered, and deposition thickness is reduced. At a high current density of 30 mA·cm⁻² and an area capacity of 5 mAh·cm⁻², forced convection enables 500 cycles.