Skin-Inspired Surface-Microstructured Tough Hydrogel Electrolytes for Stretchable Supercapacitors.

Double-network tough hydrogels have raised increasing interest in stretchable electronic applications as well as electronic skin (e-skin) owing to their excellent mechanical properties and functionalities. While hydrogels have been extensively explored as solid-state electrolytes, stretchable energy storage devices based on tough hydrogel electrolytes are still limited despite their high stretchability and strength. A key challenge remains in the robust electrode/electrolyte interface under large mechanical strains. Inspired by the skin structure that involves the microstructured interface for the tight connection between the dermis and epidermis, we demonstrated that a surface-microstructured tough hydrogel electrolyte composed of agar/polyacrylamide/LiCl (AG/PAAm/LiCl) could be exploited to allow stretchable supercapacitors with enhanced mechanical and electrochemical performance. The prestretched tough hydrogel electrolyte was treated to generate surface microstructures with a roughness of tens of micrometers simply via mechanical rubbing followed by the attachment of activated carbon electrodes on both sides to realize the fabrication of the stretchable supercapacitor. Through investigating the properties of the tough hydrogel electrolyte and the electrochemical performance of the as-fabricated supercapacitors under varied strains, the surface-microstructured hydrogel electrolyte was shown to enable robust adhesion to electrodes, improving electrochemical behavior and capacitance, as well as having better performance retention under repeated stretching cycles, which surpassed the pristine hydrogel with smooth surfaces. Our approach could provide an alternative and general strategy to improve the interfacial properties between the electrode and the hydrogel electrolyte, driving new directions for functional stretchable devices based on tough hydrogels.