High-Voltage Hybrid Electrolytes for Fast Charging Devices

Developing high-voltage electrolytes to extend the cell voltage has been regarded as an efficient strategy to increase the energy density of supercapacitors (SCs) since energy density is proportional to the square of the cell voltage. Recently, deep eutectic solvent (DES), as an ionic liquid analog, has been regarded as a green liquid media and novel alternative for non-aqueous type electrolytes for SCs due to its unique features of non-flammability, low cost, wide ESW, low vapor pressure, biodegradability, renewability, and compositional tunability. Unfortunately, due to the strong molecular interaction of DES, it shows high viscosity and low ionic conductivity behavior, resulting in a diminished capacitive performance at high current densities.<br/>To overcome these issues, a novel hybrid DES electrolyte was developed by simply introducing the appropriate amount of water and acetonitrile co-solvents. The as-fabricated symmetric SC device using the optimized DES hybrid electrolyte showed an impressive cell voltage of 2.2 V and delivered a high energy density of 21.4 Wh kg^-1 at the power density of 1100 W kg^-1, and also achieved excellent capacity retention of 86.8% after 120-h floating test. As a consequence, this work should definitely enlarge the application of the DES electrolyte systems consisting of water/acetonitrile towards high-performance energy storage devices.