Hygroscopic Chemistry Enables Fire‐Tolerant Supercapacitors with a Self‐Healable “Solute‐in‐Air” Electrolyte

High‐temperature‐induced fire is an extremely serious safety risk in energy storage devices; which can be avoided by replacing their components with nonflammable materials. However; these devices are still destroyed by the high‐temperature decomposition; lacking reliability. Here, a fire‐tolerant supercapacitor is further demonstrated that recovers after burning with a self‐healable “solute‐in‐air” electrolyte. Using fire‐tolerant electrodes and separator with a semiopen device configuration; hygroscopic CaCl 2 in the air (“CaCl 2 ‐in‐air”) is designed as a self‐healable electrolyte; which loses its water solvent at high temperatures but spontaneously absorbs water from the air to recover by itself at low temperatures. The supercapacitor is disenabled at 500 °C; while it recovers after cooling in the air. Especially; it even recovers after burning at around 647 °C with enhanced performance. The study offers a self‐healing strategy to design high‐safety; high‐reliability; and fire‐tolerant supercapacitors; which inspires a promising way to deal with general fire‐related risks.