Quantification of the voltage losses in the minimal architecture zinc-bromine battery using GITT and EIS

The sources of voltage loss in the minimal architecture zinc bromine battery are characterized using the galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) on a cell with a three electrode setup. Monitoring of the electrode voltages during charge/discharge indicate the full cell capacity is limited by the Zn/Zn²⁺ negative electrode. From GITT, the losses in voltage due to mass transport are shown to be relatively small in comparison to the IR resistance in the cell. In addition, it is shown that decreases in the open circuit voltage with respect to theory are likely caused by the complexation of Br₂ into Br_X⁻. Using EIS, the charge transfer resistances at each electrode and ohmic resistances of each component are determined. Overall, the main factors restricting the voltage of the cell are the ohmic resistances in the carbon cloth current collectors and in the electrolyte. Additionally, significant charge transfer resistances are observed at the negative electrode near the start of charge and end of discharge, when the amount of zinc plated on the carbon cloth electrode is minimal.