The original MA-ZBB is composed of two carbon based electrodes, which are spatially separated in the vertical direction, in an aqueous electrolyte containing zinc-bromide salt. The battery does not contain any passive components for controlling bromine/zinc interaction. Instead, the electrodes are vertically separated to utilize the variations in density between bromine and the aqueous electrolyte as an advantage to minimize self-discharge. At the negative electrode on top of the cell, zinc ions are reduced (Zn) and oxidized (Zn2+) on a carbon cloth during charge and discharge, respectively. At the positive electrode, which is located on the bottom of the cell, bromide ions are oxidized (Br2) and reduced (Br-) within a carbon foam electrode.
To date, a proof-of-concept cell on the lab-scale has demonstrated an energy efficiency of over 60% for over 1000 cycles at an energy density of ~10 Wh/L. In this work, we present recent efforts aimed at improving the efficiency and capacity of the system. Galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) are utilized to determine the relative importance of ohmic overpotential, charge transfer overpotential, and mass transport limitations on the performance of the cell. Based on these results, variations in cell and electrode design/materials selection are investigated, which minimize the main sources of overpotential in the system and maximize the cell capacity (Figure 1).
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