Key approaches and challenges in fabricating advanced flexible zinc-ion batteries with functional hydrogel electrolytes

Recent years, a great deal of investigation has been performed on the design and fabrication of the flexible zinc-ion batteries ascribing to their decent capacity, affordable, intrinsic safety, and functional controllability. As the most critical component of flexible zinc-ion batteries, hydrogel electrolytes feature aqueous electrolytes-like ionic conductivity and solid polymer electrolytes-like dimensional stability, integrating the superiority of both. Nevertheless, conventional hydrogel electrolytes only supply a physical framework for facilitating ion transport, encountering tremendous challenges for fabricating the flexible zinc-ion batteries. Functional hydrogel electrolytes can overcome aforementioned issues, which provide the satisfactory electrochemical performance while endowing other functions to work continuously under harsh conditions like high temperature, extreme cold, bending, stretching, strong impact, and even fracture. So far, the study on functional hydrogel electrolytes for flexible zinc-ion batteries is still in an early stage, and the issues encountered with hydrogel electrolytes remain to be addressed. Herein, this comprehensive review aims to summarize the latest advances of functional hydrogel electrolytes for flexible zinc-ion batteries. From the perspective of fabrication, the targeted approaches reported so far to fabricate functional hydrogel electrolytes for flexible zinc-ion batteries are systematically discussed and evaluated. Next, interactions between electrodes and functional hydrogel electrolytes for ZIBs is comprehensively reviewed. Eventually, a series of critical challenges, constructive solutions, and future trends of functional hydrogel electrolytes for flexible zinc-ion batteries are dedicatedly proposed.