Abstract

Zinc-ion batteries (ZIBs) have attracted intensive attention over the last five years due to the high volumetric capacity (5855 mAh cm⁻³) of zinc metals and the robust fabrication process under ambient conditions. With the development of ZIBs, flexible zinc-ion batteries (FZIBs) are deemed as potential candidates for powering flexible devices, especially wearable and implantable medical devices. Different from flexible Li-ion, Na-ion, and K-ion batteries, polymer/hydrogel electrolytes are widely utilized in FZIBs providing flexibility and biocompatibility. Currently, polymer electrolytes can be categorized into three clusters: solid polymer electrolytes (SPEs); hydrogel polymer electrolytes (HPEs), and hybrid polymer electrolytes (HBPEs). With the application of polymer electrolytes, electrochemical properties can be enhanced, and additional functionalities can be provided. Although FZIBs are still in their infancy, substantial efforts have been applied to enhance both electrochemical and structural performance. This chapter comprehensively illustrates the recent progress in FZIBs, with an emphasis on ZIB mechanisms, polymer electrolytes, and different functionalities achieved by polymer electrolytes, such as anti-freezing, thermo-response, and self-healing abilities. Energy storage mechanisms and ionic transportation mechanisms for ZIBs are discussed in detail in this chapter. It concludes with coverage of flexible device configurations, fabrication strategies, and current challenges and perspectives.