Critical challenges and solutions: quasi-solid-state electrolytes for zinc-based batteries

Zinc-based batteries are regarded as promising power sources for flexible and wearable electronics due to their merits of low cost, durability, intrinsic safety, satisfactory theoretical energy density, and simple structure. Electrolytes, as a key component of batteries, have been widely investigated with the aim of performance improvement and lifespan extension, and the research trend has shifted from liquid-state toward solid-state for higher stability during deformation and easy fabrication and encapsulation. Quasi-solid-state electrolytes (QSSEs) stand out for mitigating the conflict between electrochemical and mechanical performance. Thus, this review comprehensively reviews the progress of QSSEs (including both hydrogel and colloidal electrolytes), starting from the fundamental properties of QSSE materials with tuning mechanisms summarized, followed by the contribution of QSSEs to the performance of batteries with engineering strategies illustrated, finally extending to modern applications and evaluation protocols with wearable and biocompatible electronics included. So far, the research on functional hydrogel electrolytes is still in its infancy, and the practical application of colloidal electrolytes needs further study. Finally, we summarize those unsolved challenges in current studies and provide guidelines for future research with the hope of accelerating the development and practical application of QSSEs. QSSEs are emerging in aqueous ZBs and modern applications. By summarizing the fundamentals of materials properties, battery performance and applications of QSSEs, this review provides insight into the future development and optimization of ZBs in wider application fields.