Electrochemical Characterization Techniques to Systematically Study Mechanically Rechargeable Zinc Air Battery

The mechanically rechargeable zinc-air battery (MRZAB) shows great potential for the next generation of batteries, suitable for both grid-scale long-duration energy storage and electric vehicle applications. Recently, high battery performance has been demonstrated on a lab scale using novel slurry electrode materials and a new cell configuration. However, further efforts are required to understand the limiting factors that contribute to performance losses in the cell. This understanding is essential for identifying which components need immediate engineering and optimization. In the first study, we systematically analyzed and decomposed the electrochemical losses of MRZABs through polarization curves, utilizing a pseudo-reference electrode. By varying the position of this pseudo-reference electrode between different components within the cell, we could isolate specific components or electrochemical losses of interest. It was found that the zinc slurry electrode is more limited in the mass transport region, while the air electrode shows more sluggish behavior in the kinetic region. In the second study, we explored the lack in zinc utilization within MRZABs. Zinc utilization can be improved by optimizing the zinc slurry composition, specifically through adjustments to KOH concentration and zinc loading. In-situ three-electrode electrochemical impedance spectroscopy (EIS) revealed that the specific resistance of the zinc slurry initially increases and then decreases during the discharge process. This suggests slurry viscosity, passivation layer growth and morphologic effects plays the important roles. An empirical model was developed to account for the conductivity in lowpercolation slurries, capturing the phenomenon where zinc particles are sparsely distributed in suspension. Additionally, cell-scale MRZAB design advancements have shown promising directions towards achieving practically complete removal of discharged zinc slurry. Finally, a stopped-flow experiment, combined with potential step measurements as a new approach to characterizing mass transport within porous electrodes in a vanadium redox flow battery, demonstrated its effectiveness in characterizing quasi-stable diffusion-controlled currents.