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)(2)SO4 is designed and shows a freezing point of -46.3 degrees 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 similar to 100% capacitance retention and similar to 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.