High-voltage and wide temperature aqueous supercapacitors aided by deep eutectic solvents

For water supercapacitors, how to realize high voltage and wide temperature range operation is of great theoretical and practical significance. In this work, introducing a deep eutectic solvent (DES) composed of choline chloride (ChCl, as hydrogen bond acceptor) and ethylene glycol (EG, as hydrogen bond donor) into H2O (as co-hydrogen bond donor) produces DES-H2O electrolyte. Furthermore, density functional theory (DFT) can design and verify the DES system. The experimental results show that the molar ratio of DES plays a decisive role in the solvent structure and supercapacitor performance. When the molar ratio of ChCl, EG and H2O is 1:2:2, the DES structure is the most stable, the total energy is the largest (49.93 eV), also exhibiting the high voltage window of 2.4 V, and the wide temperature range of − 40 to 80 °C. In the meanwhile, superior capacitive performance also occurs with specific capacity of 202 F g−1, energy density of 40.3 Wh kg−1 and cyclability (98.51% after 10,000 cycles) The present DES-H2O electrolyte has the advantages of low price, easy synthesis, good water resistance and high electrochemical performance, which makes it have large application potential in the field of supercapacitors.