Internally Connected Porous Polymer Electrolyte Membrane for Long-Lasting Flexible Zinc-Air Batteries

Abstract

The market of various wearable devices is rapidly growing in the recent. Accordingly, a light, safe, and flexible power source is also required to operate. The lithium-ion batteries (LIBs) are optimized for portable devices and can be miniaturized, but they are vulnerable due to the use of organic electrolytes and have limited theoretical energy density. The zinc-air battery (ZAB), as a next-generation battery, have garnered attention for its specific energy density (~1350 Wh/kg) and price competitiveness compared to the LIB. In particular, the use of an aqueous-based polymer electrolyte can provide safety and flexibility, making it a promising energy source for wearable devices. However, the open cathode structure of ZABs for breathing air as an active material leads to gradual loss of liquid components in the polymer electrolyte, resulting in decreased performance.Herein, we developed a porous hybrid polymer membrane to overcome the aforementioned issues by means of the introduction of superabsorbent polymer (SAP) and the formation of internal network design of the membrane. First, a polyacrylic acid (PAA), one of the SAP, based fibrous network was constructed through an electrospinning process. Second, polyvinyl alcohol (PVA) as an ion conductive polymer was cast on the PAA framework, and subsequently impregnated with KOH electrolyte to form a gel-polymer electrolyte (GPE). Interestingly, the sacrificial PAA framework forms internal pores along with the fiber network, which can act as water pockets affording fast ionic conduction through the membranes and providing a higher electrolyte retention effect. As a result, the hybrid GPE had approximately three times higher ionic conductivity compared to pure PVA and better retention, resulting in outstanding electrochemical performance and cycle-life of the ZAB cell. We believe that our unique design approach for GPE can accelerate the commercialization of flexible ZABs and extend the market of wearable devices. Figure 1