A freezing-tolerant superior proton conductive hydrogel comprised of sulfonated poly(ether-ether-ketone) and poly(vinyl-alcohol) as a quasi-solid-state electrolyte in a proton battery

Aqueous proton batteries (APBs) are regarded as one of the most promising energy storage devices for the next-generation batteries owing to their high safety, high power density and environmental friendliness, while the study of their electrolytes is still in the infancy regarding metal-based batteries. Herein, we present a double-network hydrogel as a quasi-solid-state electrolyte in a proton battery. Sulfonated poly(ether-ether-ketone) and an ethylene glycol/water solvent are incorporated within the poly(vinyl alcohol) hydrogel network to enhance the mechanical properties, resulting in a tensile strength of 4.37 MPa and a toughness strain of 663%. This composite also exhibits remarkable proton conductivity (8.8 × 10⁻³/1.1 × 10⁻¹ S cm⁻¹ at −35/70 °C, ambient humidity) and low temperature tolerance (−50 °C). A quasi-solid-state proton “rocking-chair” battery demonstrates stable cycling and high rate capability (77% capacity retention after 500 cycles at 1 A g⁻¹ at 25 °C and 95% capacity retention rate over 100 cycles at −20 °C). This study provides a new possible practical application of hydrogel as a proton battery electrolyte, which could advance the development of proton electrochemical devices.