Eutectogel with (NH4)2SO4-Based Deep Eutectic Solvent for Ammonium-Ion Supercapacitors

The ammonium-ion supercapacitor (AISC) with nonmetal charge carriers exhibits merits of element abundance and compatibility with aqueous electrolytes. However, it still suffers from severe performance degradation at low temperatures. Herein, a novel deep eutectic solvent (DES) containing H2O, ethylene glycol, and (NH4)2SO4 is designed and shows a freezing point of −46.3 °C. The DES is further incorporated in poly(vinyl alcohol)/gelatin gels to prepare a eutectogel that demonstrates favorable mechanical flexibility and a high ionic conductivity of 45.6 mS cm–1 at room temperature. Furthermore, the eutectogel also shows an excellent self-extinguishing property. The AISC consisting of an optimized eutectogel and carbon electrodes indicates remarkable cycling stability with ∼100% capacitance retention and ∼100% Coulombic efficiency after 30 000 charge–discharge cycles. Moreover, the flexible AISC also exhibits excellent electrochemical performance under harsh conditions, such as bending deformation, a damaged state, and low-temperature environments. Therefore, this work provides an innovative DES and a promising eutectogel platform for next-generation electrochemical energy storage systems.