NaCl-Gly deep eutectic electrolyte for stable and high-voltage electrochemical double layer capacitor

The pressing need for alternative energy sources has driven the improvement of electrochemical energy storage systems (EESS), including metal-ion batteries and electrochemical double layer capacitors, to enable the widespread adoption of electric vehicles and intermittent technologies like photovoltaic. However, EESS still rely on electrolytes based on organic carbonates, which are flammable, toxic and not environmentally friendly. To address these issues, Deep Eutectic Solvents (DESs) have been proposed as a novel class of electrolytes, due to their several advantages, i.e. low volatility, low flammability and good thermal and electrochemical stability. The aim of our work is to design truly green electrolytes, specifically metal-polyol DESs, for EESS. Through a combination of thermal analysis (DSC) and vibrational spectroscopy (Raman and FIR), we successfully classified the mixture NaCl-Gly 1:10 as Deep Eutectic Solvent. Moreover, our findings allowed us to correlate both the molecular structure of the components and the intermolecular interactions with the mass transport and electrochemical behaviour of the mixture. Finally, the developed DES electrolyte was successfully tested in an electrochemical double-layer capacitor (EDLC) yielding remarkable results and demonstrating the potential of these cost-effective and eco-friendly electrolytes for EDLC applications.