MXene-Doped Supramolecular Hydrogel Electrolyte for High-Voltage Symmetric Supercapacitors with Wide-Temperature Tolerance

Ionic conductive hydrogels are promising flexible electrolyte for flexible energy storage devices based on good conductivity and flexibility. However, conventional hydrogel electrolytes face fundamental limitations: the narrow electrochemical stability window imposed by water’s electrolysis voltage (1.23 V) restricts operating voltages. In addition, the freezing or drying problems caused by the high content of water in the hydrogel seriously decrease its electrochemical performance. To address these challenges, we developed a feasible method to prepare MXene-doped ionic conductive hydrogel electrolyte (MSAH). The MSAH simultaneously achieves good flexibility (56.57 kPa, under 50% deformation), high ionic conductivity (247.35 mS/cm at 20 °C), freeze resistance (200.13 mS/cm at −25 °C), and exceptional water retention (<0.8% mass loss after 30 days). The MSAH electrolyte was used as an electrolyte to assemble a symmetric supercapacitor with carbon electrodes (MSAH-s). The MSAH-s displayed a wide working voltage window from 0 to 2.2 V, delivering an energy density of 141.06 Wh/kg at a power density of 1999.5 W/kg. More importantly, the good water-retaining and antifreezing of MSAH endowed the MSAH-s with an excellent stability (−25 to 50 °C), preventing freezing and drying issues. This work provides a practical pathway toward robust flexible energy storage under demanding operational conditions.