Mitigation of Dendrite Growth in Zinc-iodide Flow Battery with Tröger’s Base Anion Exchange Membrane

Abstract

Tröger’s base anion exchange membrane (TB-AEM) was readily prepared by condensation polymerization of biphenyl diamine and dimethoxymethane in the presence of trifluoroacetic acid followed by quaternization with methyl iodide. The film cast from N-Methyl-2-Pyrrolidone (NMP) solvent displayed good mechanical strength, a tensile modulus of 1.18 GPa with elongation at break of 17%, and a glass transition temperature (Tg) at 248 °C. It exhibited OH− ion conductivity of 108 mS cm−1 by impedance measurement at 80 °C in 1M KOH. The membrane exhibited good affinity toward I2, resulting in the formation of I2Br− ions in the membrane matrix. Over 300 charge/discharge cycles at a 50 mA cm−2 current density, the battery exhibited 95.5% Coulombic efficiency (CE), 76.4% voltage efficiency (VE), and 74.0% energy efficiency (EE) and delivered a capacity of 24.8 Ah L−1. Over a span of 60 h, the open-circuit voltage (OCV) of the cell remained constant at 1.2 V. Collectively, our findings suggest that the anion exchange membrane's charge and porosity tuning are key factors in the design of new generation separators for zinc-iodide flow batteries.