Recent advances in flexible alkaline zinc-based batteries: Materials, structures, and perspectives

The development of wearable electronic systems has generated increasing demand for flexible power sources. Alkaline zinc (Zn)-based batteries, as one of the most mature energy storage technologies, have been considered as a promising power source owing to their exceptional safety, low costs, and outstanding electrochemical performance. However, the conventional alkaline Zn-based battery systems face many challenges associated with electrodes and electrolytes, causing low capacity, poor cycle life, and inferior mechanical performance. Recent advances in materials and structure design have enabled the revisitation of the alkaline Zn-based battery technology for applications in flexible electronics. Herein, we summarize the up-to-date works in flexible alkaline Zn-based batteries and analyze the strategies employed to improve battery performance. Firstly, we introduce the three most reported cathode materials (including Ag-based, Ni-based, and Co-based materials) for flexible alkaline Zn-based batteries. Then, challenges and modifications in battery anodes are investigated. Thirdly, the recently advanced gel electrolytes are introduced from their properties, functions as well as advanced fabrications. Finally, recent works and the advantages of sandwich-type, fiber-type and thin film-type flexible batteries are summarized and compared. This review provides insights and guidance for the design of high-performance flexible Zn-based batteries for next-generation electronics.