Illite/Poly(vinyl alcohol) Hydrogel Electrolytes with High Mechanical Strength and Ionic Conductivity for Flexible Energy Storage Devices

Poly(vinyl alcohol) (PVA) hydrogel electrolytes are widely used in flexible energy storage devices because of their high safety, excellent flexibility and biocompatibility. However, PVA hydrogels suffer from low mechanical strength and poor electrochemical properties. To address this issue, in this study, a green composite hydrogel was prepared by introducing Illite, a silicate clay with a lamellar structure, into PVA hydrogel using a cyclic freeze-thaw method. Illite interacts with PVA molecular chains to form hydrogen bonds, leading to a robust cross-linked network structure, which significantly enhances the mechanical properties of the compliant hydrogels. The composite hydrogel prepared by adding 2% Illite to PVA (denoted as P-I_2%) has a tensile strength of 1.52 MPa, elongation at break of 524%, and compressive strength of 0.97 MPa. Moreover, the lamellar structure of Illite generates directional channels in the PVA gel matrix, enabling the P-I_2% hydrogel electrolyte to exhibit high ionic conductivity (41.9 mS cm^-1). The specific discharge capacity of the supercapacitor assembled using the P-I_2% hydrogel electrolyte was 116.97 mF cm^-2 at a current density of 1 mA cm^-2, and the capacitance retention rate of the P-I_2%-based supercapacitor was 86.61% after 5000 working cycles at a current density of 5 mA cm^-2. This work provides new ideas for clay minerals in the pathway to enhance the performance of hydrogel electrolytes.