Aqueous Zinc Ion Battery with Potassium Selective Hyper Cross-Linked Dibenzo-18-Crown-6-Ether Membrane

Nonselective ion transport across the separator in zinc-iodine flow batteries (ZIFBs) alters concentration gradients, precipitates insoluble iodine, and generates uneven zinc nucleation on the anode surface. Here, we report the synthesis of a K+ ion-selective hyper-cross-linked dibenzo-18-crown-6-ether-containing polymer (HCP) that allows transfer of the K+ ion while avoiding the crossover of electroactive species. The sulfonated HCP was blended with SPEEK in compositions of 5, 10, and 15%, designated as SHCP1, SHCP2, and SHCP3, respectively. The blending of SHCP results in increases in ion exchange capacity (IEC), water uptake, ionic conductivity, and K+ ion selectivity. The best membrane, SHCP3, showed 7.6 times higher K+ ion selectivity than the neat SPEEK membrane. The galvanostatic charging/discharging over 200 cycles at 20 mA cm(-2) current density showed 96% CE, 88% VE, and 84% EE for the SHCP3 membrane. It delivered 37.5 Ah l(-1) capacity at 20 mA cm(-2) current density, whereas Nafion-117 delivered 22 Ah l(-1) capacity. The OCV of the cell with SHCP3 membranes remains at 1 V over 20 h. The results suggest that K+ ion selectivity is significantly helping in mitigating dendrite formation and enhancing the stability of the ZIFB battery, thus increasing its potential use. (c) 2023 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.