Towards Sustainable Energy Storage: Evaluating Polymer Electrolytes for Zinc Ion Batteries

Abstract: Polymer electrolytes present a promising solution to the challenges posed by aqueous electrolytes in energy storage systems, offering the flexibility needed for wearable electronics. Despite the increasing interest in polymer electrolyte-based zinc ion batteries (ZIBs), their development is still in its early stages due to various challenges. In this study, we fabricated three promising polymer electrolytes: CSAM (carboxyl methyl chitosan with acrylamide monomer), PAM (polyacrylamide monomer hydrogel electrolyte), and p-PBI (Phosphoric acid (PA)-doped polybenzimidazole) with Zn(ClO4)2 and Zn(OTf)2, for their application in zinc ion batteries. Our results demonstrated that PAM hydrogel electrolyte exhibited very low LDH formation after a long cycle, demonstrating effective protection for zinc foil, and the high mechanical stability of the p-PBI membrane provided prolonged durability against short circuits through the formation of LDH. The presence of carboxyl groups in CSAM and the formation of O-H bonding facilitated ion movement, resulting in enhanced ionic conductivity, and preventing dendrite formation. Incorporating these hydrogels with high-performance zinc salts, such as zinc triflate (Zn(OTf)2), resulted in impressive stability, with the symmetric cell demonstrating over 4000 hours of uniform and stable voltage profile under 1 mA/cm2 and low overpotential of around 53 mV cycling with CSAM. The full-cell battery with PBI-T membrane showed the highest durability and capacity compared to CSAM-T and PAM-T, due to the greater availability of free protons for storing zinc in the cathode.