Toward Self-Supported Bifunctional Air Electrodes for Flexible Solid-State Zn-Air Batteries

The demand for flexibility and rechargeability in tandem with high energy density, reliability, and safety in energy-storage devices to power wearable electronics has translated to significant advances in flexible solid-state Zn-air batteries (FSZABs) technology. FSZABs using self-supported bifunctional air electrodes are currently one of the most attractive alternatives to Li-ion battery technology for next-generation wearable electronics. Unlike the conventional powder-based air electrodes, self-supported bifunctional air electrodes offer higher electron-transfer rate, larger specific surface area (and catalyst-reactant-product interfacial contact area), mechanical flexibility, and better operational robustness. To realize their potential nonetheless, self-supported bifunctional air electrodes should have high and stable bifunctional catalytic activity, low cost, and environmental compatibility. This review first summarizes the three typical configurations and working principles of FSZABs. Then, significant development of self-supported bifunctional air electrodes for FSZABs and efficient synthesis strategies are emphasized. The review concludes by providing perspectives on how to further improve the electrochemical performance of FSZABs and their suitability for next-generation wearable electronic devices.