Poly(acrylic acid)-Based Composite Gel Polymer Electrolytes with High Mechanical Strength and Ionic Conductivity toward Flexible Zinc–Air Batteries with Long Cycling Lifetime

The rapid development of portable, flexible, and wearable devices motivates the requirement for flexible zinc–air batteries (FZABs) not only to provide high energy density but also to have sufficient deformability for wearer comfort. The gel polymer electrolyte (GPE) serves as the core part of the FZABs, playing a key function in the battery’s practical output performance such as discharge voltage, energy density, and cycling life. Unfortunately, ascribed to its high water absorption, the GPE regularly shows comparatively poor mechanical strength, which is difficult to offer sufficient physical support between electrodes. Herein, we report an optimized poly(acrylic acid) (PAA)-based composite GPE with the aluminum oxide (Al2O3) filler and apply it for FZAB. The mechanical strength, electrolyte absorption capacity, electrolyte retention ability, and ionic conductivity of the PAA–Al2O3 gel polymers and corresponding GPEs were investigated. The results indicate that the above performances of polymers and corresponding GPEs depend to a considerable extent on the content of the addition of Al2O3 particles. When 20 wt.% Al2O3 is added to the PAA polymer, the obtained PAA–20 wt.% Al2O3 gel polymer exhibits improved mechanical strength. The corresponding PAA–20 wt.% Al2O3 GPE shows a high ionic conductivity of 186 mS cm–1 and pleasurable electrolyte retention capability. This optimized GPE enables the assembled FZAB to display a long cycling lifetime of 384 h, a large power density of 77.7 mW cm–2, and excellent discharge performance. Moreover, the integrated FZAB can power various electronic devices, demonstrating its outstanding practicability and extensibility as a flexible power source.