Recent advances of hydrogel electrolytes in flexible energy storage devices

Novel flexible storage devices such as supercapacitors and rechargeable batteries are of great interest due to their broad potential applications in flexible electronics and implants. Hydrogels are crosslinked hydrophilic polymer networks filled with water, and considered one of the most promising electrolyte candidates due to their high-water absorbency and softness that fulfilled the fundamental requirements for flexible energy storage devices. Moreover, diverse properties such as self-healing ability, ultra-stretchability, electrochromism, and extreme-temperature resistance can be achieved by modifying the chemical structures, opening the door to the development of novel flexible energy storage devices with prolonged service life and scintillating functions. In this review, we discuss the design methods of recent hydrogel electrolytes for supercapacitors and batteries regarding their electrochemical performance and highlight those with exceptional breakthrough and additional functions. Finally, challenges and prospects of future development are explored.