Using Acetone as a Monosolvent for Ultralow Temperature Supercapacitors at −70 °C

The low operating temperature limit of commercial supercapacitor electrolyte (−50 °C) could not satisfy the increasing extreme demands like polar resource exploitation (−60 °C) and near‐space exploration (−70 °C). Although the introduction of cosolvents with low polarities could improve the viscosity and operating temperature range, the multisolvent electrolyte system still endures low conductivity and high desolvation energy as well as the high production cost. This work introduces the acetone (ACT) as monosolvent for low‐temperature electrolyte, which shows the medium dielectric coefficient (ε = 20.9), low donor number (10.67), and ultralow melting point. These properties guarantee its strong ion‐dissociation ability for rapid ion‐transportation in the bulk electrolyte, and weakened ion‐solvent interaction for speeding desolvation process, as well as the outstanding temperature range of liquid phase. The supercapacitor with ACT‐based electrolyte exhibits superior capacitance retention ratio (86.5% from 20 to −70 °C), high cycling stability (97.75% after 13,000 cycles) and preeminent power density and energy density (3776 W kg −1 @ 14.16 W h kg −1 ). Besides, the ACT solvent also displays the merits of low biological toxicity and low production cost, which further enhance its application prospect in the energy storage systems.