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

Abstract

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.

Flexible Supercapacitor Based on Organohydrogel Electrolyte with Long‐Term Anti‐Freezing and Anti‐Drying Property

“…Specifically, the surface of OHE and HE is roughened through gently rubbing with a toothbrush as described by Fang et al [ 17 ] After the rubbing, OHE and HE display better adhesion with the electrode materials owing to the microcavity topography as well as the interlocking effect, which could improve the interfacial charge transport and endow electrochemical stability upon mechanical deformation. [ 17 ] Figure a shows the cyclic voltammetry (CV) curves of OHEC in the range of 0–1.0 V at various scan rates at room temperature. The CV curves exhibit a quasi‐rectangular shape at all scan rates, even 200 mV s −1 , indicating remarkable rate capability, excellent capacitive behavior, and low contact resistance.…”

Fundamental Concepts of Hydrogels: Synthesis, Properties, and Their Applications

“…There are many hosts for polymer which have been explored to build up polymer hydrogel electrolytes. For example, chitosan, sodium alginate, agar, cellulose, starch, poly (ethylene oxide) (PEO), poly (acrylic acid) (PAA), poly (acrylamide), poly (ether ether ketone) (PEEK), and poly (vinyl alcohol) (PVA) [140,[178][179][180][181][182][183][184][185][186].…”

A Regenerable Hydrogel Electrolyte for Flexible Supercapacitors

“…This indicates a greater application prospect of PAA-PAH/LiCl than PVA-based gel electrolytes. At the same time, its ionic conductivity is comparable with and even greater than most of modified PAA and PAM-based gel electrolytes (e.g., gelatin-g-PAAm [ Li et al., 2018 ], PAA-co-PAAm [ Dai et al., 2019 ], agar/PAAm [ Fang et al., 2019 ], alginate/PAAm [ Liu et al, 2019b ] and Li-agar/PAAm [ Lin et al., 2018 ]) and other gel electrolytes (e.g., poly (vinylimidazole-hydroxypropyl acrylate) [ Wang et al., 2017 ], Li-alginate [ Ye et al., 2018 ] and chitosan-alginate [ Zhao et al., 2018 ]) with same level of salt addition. Considering its unique molecular structure, the high ionic conductivity is inferred to occur in a synergistic manner: (1) easy separation of the cationic and anionic counter ions within this polyelectrolyte gel electrolyte during ion migration process ( Peng et al., 2016 ; Lee et al., 2018 ); (2) large amounts of carboxylate and ammonium on polymer chains enabling a high electrolyte adsorption capacity and thus a high ion conductivity of the gel electrolyte; (3) 3D porous network structure of PAA-PAH/LiCl ( Figure 1 B inset) that facilitates ion transport, further ensuring a high ionic conductivity ( Guo et al., 2016 ).…”