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

•DES can expand the voltage and operating temperature range of aqueous supercapacitors;•DFT is applied for electrolyte design, optimization and theoretical calculation;•Adjusting the molar ratio of DES and water can influence on the structure and performance of electrolyte;•DES exhibits important potential for high-performance aqueous supercapacitors. 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.