Electrospun polyetherimide nanofiber mat-reinforced, permselective polyvinyl alcohol composite separator membranes: A membrane-driven step closer toward rechargeable zinc-air batteries

Abstract

Despite the commercial success of primary Zinc (Zn)-air batteries, rechargeable Zn-air batteries are still far behind meaningful performance levels. Among numerous challenges facing rechargeable Zn-air batteries, from the material point of view, separator membranes should not be underestimated, along with other battery components such as anodes, cathodes and electrolytes. More particularly, crossover of soluble zincate (Zn(OH4 2-)) ions through separator membranes from Zn anode to air cathode, which significantly affects electrochemical performance of Zn-air cells, has hardly been addressed. Here, as a facile and scalable strategy to resolve the separator membrane-related issues, we demonstrate a new class of electrospun nanofiber mat-reinforced permselective composite membranes (referred to as ERC membranes) and explore their potential contribution to development of rechargeable Zn-air cells in terms of transport phenomena of hydroxyl (OH-) and (Zn(OH4 2-)) ions. The ERC membrane is fabricated by impregnating polyvinyl alcohol (PVA) into electrospun polyetherimide (PEI) nanofiber mat. The PEI nanofiber mat acts as a compliant framework to endow dimensional stability and mechanical strength. The PVA matrix, after being swelled with electrolyte solution, provides ion size (OH- vs. (Zn(OH4 2-)))-dependent conductive pathways. This architecture/material uniqueness of the ERC membrane effectively suppresses permeation of bulky (Zn(OH4 2-)) ions without impairing OH- conduction, thereupon achieving exceptional cycle capacity retention of Zn-air cells far beyond those accessible with conventional microporus polyolefin separators. The ERC membrane featuring the ion size exclusion-based permselectivity opens a new membrane-driven opportunity that leads us closer toward rechargeable Zn-air batteries.