Synergistic ionic and hydrogen-bond locking in hydrogel electrolytes for all-climate high-performance flexible supercapacitors

Abstract

The practical implementation of flexible supercapacitors at sub - zero temperatures is impeded by the performance deterioration of hydrogel electrolytes induced by freezing. In this study, we present a synergistic "ionic and hydrogen - bond locking" strategy to surmount this limitation via a rationally engineered hydrogel electrolyte (Hy-p(AA/AM)_1/2-(NaAc/LiCl)_2.5). This design incorporates two complementary confinement mechanisms: an ionic lock stemming from a hydration-optimized dual-salt (NaAc/LiCl) system, which disrupts the hydrogen-bond network of water and inhibits ice nucleation, and a hydrogen-bond lock originating from a hyperbranched polymer network, which further confines water and restricts the growth of ice crystals. The resultant electrolyte demonstrates an ultra-low freezing point of −67.4 °C, high ionic conductivity of 3.01 S m⁻¹ at −30 °C, and outstanding self-healing (92.7 % efficiency) and self-adhesive (11.38 kPa) properties. Flexible supercapacitors assembled with this electrolyte attain a wide voltage window of 1.6 V, yield an energy density of 21.8 Wh kg⁻¹ at −30 °C, and retain 70.7 % of the initial capacitance after 15,000 cycles at −30 °C. A comparison with recent reports reveals that this work achieves an unparalleled equilibrium of ionic conductivity, low-temperature tolerance, and mechanical robustness. This dual-lock strategy offers a generalizable design principle for advanced energy storage materials for all - climate wearable electronics and other applications.