Flexible and anti-freezing quasi-solid-state magnesium-ion hybrid supercapacitor working at -40 °C

The new-generation flexible aqueous magnesium-ion hybrid supercapacitors (MHSCs), applied in flexible devices, need to process high ionic conductivity and great flexibility at low temperatures. Here we report an anti-freezing, high ionic conductivity polyacrylamide (PAAm) hydrogel electrolyte based on low-concentration Mg(ClO4)2 salt. Physical characterizations and theoretical calculations demonstrated that Mg(ClO4)2 salt can effectively disrupt the original hydrogen-bond network among water molecules by the newly formed hydrogen bonds between solvent H2O molecules and solute ClO4-, thus leading to a superior anti-freezing property. A quasi-solid-state MHSC was assembled using PAAm hydrogel electrolyte containing 4M Mg(ClO4)2 salt, which delivers a great energy density of 59.6 Wh/kg and power density of 3.45 kW/kg at -20 °C. This work presented here is a promising strategy for constructing low-temperature energy storage devices for flexible/wearable applications.