A Low-Concentration and High Ionic Conductivity Aqueous Electrolyte toward Ultralow-Temperature Zinc-Ion Hybrid Capacitors

Aqueous electrochemical energy storage devices have attracted tremendous attention because of its high safety, low cost, and environmental friendliness. However, their low-temperature operation is plagued by the freeze of electrolytes. Herein, a 3 mol kg(-1) Zn(ClO4)(2) electrolyte without adding any organic solvents or antifreezing additives is proposed, which yields a high ionic conductivity of 9.4 mS cm(-1) even at ultralow temperatures of -60 degrees C. The strong electrostatic interaction between Zn2+ ion and water molecules and the structure breaking effect of ClO4- ions to destroy the hydrogen bond network between water molecules in Zn(ClO4)(2) electrolyte is revealed by spectroscopic characterization and theoretical simulation. This low-temperature electrolyte renders the zinc-ion hybrid capacitor to exhibit a high energy density of 40.91 Wh kg(-1) at -60 degrees C and a long-cycle life (over 200 days) at -30 degrees C. This study provides a new path to develop low-concentration antifreezing electrolytes for aqueous electrochemical energy storage devices.