Flexible solid-state Zn-air battery based on polymer-oxygen-functionalized g-C₃N₄ composite membrane

Personalized healthcare devices require an energy storage system that is flexible and has good mechanical strength and stability for long periods. Zn-air batteries show promise as an alternative to Li-air batteries for this purpose. Zn-air batteries with a high theoretical specific energy density of 1350 W h kg^-1 have the potential to replace other metal-air batteries but faces the challenges, such as dendrite formation and Zn corrosion, hindering their successful commercialization. In this work, we report the design and performance optimization of a solid-state flexible Zn-air battery with superior performance and good mechanical property. In addition, we focused on the development of a gel-polymer composite membrane as the electrolyte. The main advantage of the flexible electrolyte is its optimum combination of good ionic conductivity and mechanical strength. Thus, we attempted to address the above-mentioned issues by modifying poly(vinyl alcohol) (PVA) with o-g-C₃N₄ through the in situ formation of a composite. The interaction between the functional groups of o-g-C₃N₄ and PVA increased the conductivity without compromising the mechanical behavior of the composite. According to the optimization of the composite composition, it was concluded that 0.32 wt% o-g-C₃N₄ in PVA showed the highest conductivity and excellent mechanical strength (increase from 25 MPa for pristine PVA membrane to 35 MPa for g-C₃N₄-PVA composite membrane). The performance of the solid-state battery was better (40 hours) than the standard PVA KOH (13 hours) membrane. Moreover, the stability of the battery was retained at various bending angles, demonstrating its potential to be used in flexible electronic devices.