Sodium Nitrate/Formamide Deep Eutectic Solvent as <scp>Flame‐Retardant</scp> and Anticorrosive Electrolyte Enabling 2.6 V Safe Supercapacitors with Long Cyclic Stability

Safe operation of electrochemical capacitors (supercapacitors) is hindered by the flammability commercial organic electrolytes. Non-flammable Water-in-Salt (WIS) electrolytes are promising alternatives; however, they plagued limited voltage window (typically ≤2.3 V) and inherent corrosion current collectors. Herein, a novel deep eutectic solvent (DES)-based electrolyte which uses formamide (FMD) as hydrogen-bond donor sodium nitrate (NaNO3) acceptor demonstrated. The exhibits wide stability (3.14 V), high electrical conductivity (14.01 mS cm−1), good flame-retardance, anticorrosive property, ultralow cost (7% 2% WIS). Raman spectroscopy Density Functional Theory calculations reveal that hydrogen bonds between FMD molecules NO 3 − $$ {{\mathrm{NO}}_3}^{-} ions primarily responsible for superior conductivity. developed NaNO3/FMD-based coin cell supercapacitor among best-performing state-of-art DES WIS devices, evidenced (2.6 outstanding energy power densities (22.77 Wh kg−1 at 630 W 17.37 kW 12.55 kg−1), ultralong cyclic (86% after 30 000 cycles), negligible collector corrosion. NaNO3/FMD industry adoption potential demonstrated fabricating 100 F pouch supercapacitors using aluminum