Functionalized Quasi-Solid-State Electrolytes in Aqueous Zn-Ion Batteries for Flexible Devices: Challenges and Strategies

The rapid development of wearable and intelligent flexible devices has posed strict requirements for power sources, including excellent mechanical strength, inherent safety, high energy density, and eco-friendliness. Zn-ion batteries with aqueous quasi-solid-state electrolytes (AQSSEs) with various functional groups that contain electronegative atoms (O/N/F) with tunable electron accumulation states are considered as a promising candidate to power the flexible devices and tremendous progress has been achieved in this prospering area. Herein, this review proposes a comprehensive summary of the recent achievements using the AQSSE in flexible devices by focusing on the significance of different functional groups. The fundamentals and challenges of the ZIBs are introduced from a chemical view in the first place. Then, the mechanism behind the stabilization of the flexible ZIBs with the functionalized AQSSE is summarized and explained in detail. Then the recent progress regarding the enhanced electrochemical stability of the ZIBs with the AQSSE is summarized and classified based on the functional groups on the polymer chain. The advanced characterization methods for the AQSSE are briefly introduced in the following sections. Last but not least, current challenges and future perspectives for this promising area are provided from the authors' point of view.