Mechanically robust hydrophobic association hydrogel electrolyte with efficient ionic transport for flexible supercapacitors

Abstract

Hydrogel electrolytes are attracting increasing interest and have made great progress in flexible supercapacitors (SCs). However, the unsatisfactory ionic conductivities and mechanical properties of traditional hydrogel electrolytes greatly limit their use in the flexible SCs, which is hard to run a long-term operation and repeated-deformation for energy devices. Here a hydrophobic association hydrogel electrolyte (HA-GPE) for flexible supercapacitors was successfully prepared by a facile and effective polymerization process. The stable hydrophobic association physical crosslinking design can disperse external stress effectively, provides HA-GPE robust mechanical properties with a tensile strength of 431.9 kPa, an elongation at break of 1150.2% and a compressive stress of 4.8 MPa, much better than those hydrogel electrolytes recently reported. While methodical molecular design enables abundant ion-conductive amine (–NH2) and ethylene oxide (EO) functional groups distributed in HA-GPE network, together with the interconnected porous network structures, allowing for more efficient Li+ ions transport, bring the ionic conductivity achieves as high as 31.1 mS cm−1 at room temperature, which is 3 times higher than the corresponding liquid electrolyte (10.5 mS cm−1). The flexible supercapacitor using this HA-GPE as the electrolyte and the activated carbon as the electrode exhibits excellent electrochemical performance with the specific capacitance of 130.3 F g−1 at 0.5 A g−1 and capacitance retention of 90.1% after 5000 cycles, superior to that of supercapacitor with liquid electrolyte and commercial separator. Additionally, the device associated with the HA-GPE possesses outstanding electrochemical stability under both bending states and durability test. All these results suggest that the HA hydrogel electrolyte is a promising candidate for portable electronics.