Gelation mechanisms of gel polymer electrolytes for zinc-based batteries

Zinc-based batteries (ZBs) have been deemed as a potential substitute for lithium-ion batteries due to its unique advantages of abundant resources, low cost and acceptable energy density. Despite great progress in designing electrode materials has been made, the development of high-performance ZBs still remain challenges, such as the dendrite growth of zinc anode, hydrogen evolution reaction, limited electrochemical stability window, water evaporation and liquid leakage. Gel polymer electrolytes (GPEs), including hydrous GPEs with low content of active water and anhydrous GPEs without the presence of water, are proposed to avoid these problems. Furthermore, employing GPEs is conductive to fabricate flexible devices owing to the good mechanical strength. To date, most of researches focus on discovering new GPEs and exploring its application on flexible or wearable devices. Recent reviews also have outlined the polymer matrixes and advances of GPEs in various battery systems. Given this, herein, we seek to summarize the gelation mechanisms of GPEs, involving physical gel of polymer, chemical crosslinking of polymer and chemical polymerization of monomers. Peculiarly, the preparation methods are also classified. In addition, not only the features and central conundrum of GPEs are analyzed but also the corresponding strategies are discussed, contributing to design GPEs with ideal properties for high-performance ZBs.