Design Principles of Flexible Substrates and Polymer Electrolytes for Flexible Zinc Ion Batteries.

Flexible ZIBs are gaining significant attention as a cost-effective and inherently safe energy storage technology with promising applications in next-generation flexible and wearable devices. The rising demand for flexible electronics has spurred the advancement of flexible batteries. However, the widespread adoption of liquid electrolytes in zinc-ion batteries has been hindered by persistent challenges, including liquid leakage, water evaporation, and parasitic water-splitting reactions, which pose significant obstacles to commercialization. Free-standing flexible substrates and solid-state polymer electrolytes are key to enhancing the energy density, ionic conductivity, power density, mechanical strength, and flexibility of ZIBs. Herein, this review highlights recent progress and strategies for developing high-efficiency flexible ZIBs as energy storage systems, focusing on advancements in flexibility (transitioning from rigid to flexible), electrolytes (shifting from liquid to solid), adaptability (from non-portable to portable designs), and the transition from laboratory research to practical industrial applications. Critical assessments of advanced modification approaches for flexible substrates and solid-state electrolytes are presented, emphasizing their role in achieving safe, flexible, stretchable, wearable, and self-healing ZIBs. Finally, future research directions and development strategies for designing effective solid-state polymer electrolytes and flexible substrates for next-generation flexible ZIBs are discussed.