Hydrogen bond regulating in hydrogel electrolytes for enhancing the antifreeze ability of a flexible zinc-ion hybrid supercapacitor

Abstract

Hydrogel electrolytes have attracted notable attention in the field of flexible supercapacitors, such as flexible zinc-ion hybrid supercapacitors (FZHSCs), for their outstanding flexibility, high safety and superior portability. However, the H₂O molecules in conventional hydrogels unavoidably freeze at subzero temperatures, which restricts the application of hydrogel electrolytes in flexible supercapacitors in extremely cold environments. Herein, we fabricated an anti-freezing hydrogel electrolyte successfully through sol–gel transformation of polyvinyl alcohol (PVA) and cellulose nanofibers (CNFs), which are dissolved in a dimethyl sulfoxide (DMSO)–water binary solvent. The introduction of DMSO into the hydrogel substrate can effectively prevent H₂O molecules from freezing at subzero temperatures, owing to the strong hydrogen bonds between DMSO and water. The hydrogel electrolyte exhibits excellent mechanical performance at −20 °C with a strain of 350%. The FZHSC based on the hydrogel electrolyte shows excellent electrochemical properties at low temperature, delivering a specific capacity of 159.79 F g⁻¹ at −20 °C. Besides, it could also hold a high capacity of 382.02 F g⁻¹ at normal temperature (25 °C) with a coulombic efficiency almost reaching 100%. Meanwhile, even under different bending conditions, the FZHSC could also retain great electrochemical performance. It is believed that the strategy in this work will play a potent role for creating stretchable and anti-freezing hydrogel electrolytes for FZHSCs with high capacity under extreme cold conditions.