The influence of ethylene glycol on the low-temperature electrochemical performance of carbon-based supercapacitors

Inadequate ionic conductivity and freezing of the electrolyte are considered one of the main problems in low-temperature electrochemical energy storage. Mixing two or more solvents can reduce the overall freezing point of the solution and also increase the ionic conductivity at low temperatures. Therefore, using the co-solvent method to prepare electrolytes is crucial for preventing electrolyte freezing and improving ion conductivity. In this paper, ethylene glycol (EG) was used as a low-temperature co-solvent and an electrolyte with a freezing point lower than − 80 ℃ was obtained by the introduction of a volume fraction of 20% ethylene glycol in 4.5 mol L⁻¹ LiCl aqueous solution. The resulting electrolyte exhibited high ionic conductivity (1.143 mS·cm⁻¹) at − 60 ℃ and low viscosity (1.391 mPa·s) at 20 ℃. The molecular dynamics (MD) simulations and FITR results indicate that hydrogen bonds can be effectively formed between ethylene glycol and water molecules, which facilitate the electrolyte to operate at low temperatures. Additionally, the supercapacitor was able to operate better even at − 60 °C by introducing ethylene glycol into the electrolyte.