Synergistic crosslinking effect of illite and hydroxyethyl cellulose on improving the properties of PVA based hydrogels

Abstract

Flexible solid-state supercapacitors show great potential in the field of portable wearable electronic devices. However, the preparation of hydrogel electrolytes with high mechanical properties and ionic conductivity remains a challenge. In this paper, hydroxyethyl cellulose (HEC) and illite were used as organic and inorganic additives, respectively, for the polyvinyl alcohol (PVA) matrix to prepare composite hydrogels using the cyclic freeze–thaw method. A dense and uniform three-dimensional network structure of hydrogels was formed through the synergistic action of hydrogen bonding between PVA, HEC, and illite. When the contents of HEC and illite were 3 wt% and 6 wt%, respectively, the composite hydrogel (PH₃I₆) exhibited excellent mechanical properties, achieving a fracture stress of 1.41 MPa and a fracture strain of 500%. Its compressive strength was increased by 423% compared to that of the PVA hydrogel. The ionic conductivity of the PH₃I₆ hydrogel electrolyte reached 29.72 mS cm⁻¹. The supercapacitor assembled with the PH₃I₆ hydrogel electrolyte exhibited a specific capacitance of 292 F g⁻¹ and an energy density of 10.14 Wh kg⁻¹ at a current density of 1 A g⁻¹. Furthermore, the PH₃I₆ supercapacitor maintained a capacity retention rate of 96.52% and demonstrated a coulombic efficiency of 99.28% after 10 000 cycles at 1 A g⁻¹. Additionally, this PH₃I₆ supercapacitor possessed excellent flexibility and stability, functioning normally even when subjected to bending, hammering, and puncturing, thereby demonstrating broad application prospects.