A Comprehensive Formulation of Aqueous Electrolytes for Low-Temperature Supercapacitors.

Safer-by-design and sustainable energy storage devices are envisioned to be among the required 2.0 solutions to satisfy the fast growing energy demands. Responding to this evolution cannot be freed from a global and synergetic approach to design the requisite electrolytes taking into account the toxicity, the eco-compatibility and the cost of their constituents. To target low-temperature applications, a non-toxic and cost-efficient eutectic system comprising LiNO in water with 1,3-propylene glycol as co-solvent was selected to design a ternary electrolyte with a wide liquid range. By using this electrolyte in an electrochemical double-layer capacitor (EDLC), the operating voltage of the device reaches an optimum of 2.0 V at -40 °C over more than 100 h of floating. Moreover, after being set up at 20 °C, the temperature resilience of the capacitance is near total, demonstrating thus a promising feature related to the suitable thermal and electrochemical behaviours of the tested EDLC devices.