Choline chloride-based deep eutectic solvents as electrolytes for wide temperature range supercapacitors

Deep eutectic solvents (DESs) are a promising new class of environmentally friendly versatile solvent systems. In this work, a new approach for applying choline chloride-based DESs as cost-effective, and anti-corrosion electrolytes for activated carbon-based electrochemical capacitors (ECs) is proposed for the first time. In this regard, DESs of choline chloride/glycerol and choline chloride/propionic acid were prepared with molar ratios of 1:2. Important properties such as viscosity, electrical conductivity, and electrochemical measurements were studied in the range of room temperature up to 373 K. With the rising temperature, the viscosity of DESs decreased and their electrical conductivity increased. High energy is provided by the symmetric ECs in the choline chloridebased electrolytes, which exhibit excellent electrochemical stability at a maximum voltage up to 2.5 V. The electrolyte with DES ChCl/PA under 373 K has a specific capacitance of 198 F g-1 (with an energy density of 110 Wh kg- 1), which can be reduced to 145 F g-1 (with an energy density of 16.3 Wh kg- 1) at room temperature. In addition, 93 % capacity retention was achieved in the supercapacitor prepared based on DES ChCl/PA up to 5000 cycles at 373 K. According to the results, important implications are presented for expanding the application of green, non-toxic and cheap electrolytes for high-performance ECs with wide voltage windows and superior lifetime.