A self-healable and highly flexible supercapacitor integrated by dynamically cross-linked electro-conductive hydrogels based on nanocellulose-templated carbon nanotubes embedded in a viscoelastic polymer network

Recent development of flexible and self-healable electro-conductive hydrogels (ECHs) are considered as promising soft materials towards intelligent applications. Nonetheless, realizing the integrated features of high electro-conductivity, viscoelasticity and mechanical toughness, as well as inherent mouldability, fast self-healing ability, and ideal electrochemical properties is still challenging. Herein, we report a kind of multifunctional ECHs based on a polyvinyl alcohol-borax (PVAB) hydrogel and carbon nanotube-cellulose nanofiber (CNT-CNF) nanohybrids that combines the conductivity of CNTs and template function of CNFs. CNFs serve as dispersant to uniformly stabilize CNTs in suspension. As-prepared CNT-CNF nanohybrids are uniformly dispersed into PVAB to construct freeze-standing CNT-CNF/PVAB composite hydrogels. Owing to a conductive and reinforcing dual-network structure, the compression stress (∼93 kPa) and storage modulus (∼7.12 kPa) of CNT-CNF/PVAB are 2.7 and 1.9-fold larger than those of CNF/PVAB. CNT-CNF/PVAB also exhibits low density (∼1.1 g cm−3), high water content (∼95%), pH sensitivity, intrinsic mouldability and 20s self-healing capability. The solid-state supercapacitor assembled by PVAB-based hydrogels has a specific capacitance of 117.1 F g−1 and a capacitance retention of 96.4% after 1000 cycles. The self-healable and flexible supercapacitor demonstrates an ideal capacitance retention (∼98.2%) after ten damaging/self-healing cycles and a capacitance retention (∼95%) after 1000 cycles under various deformation.