Anti‐Freezing Aqueous Electrolyte for High‐Performance Co(OH)₂ Supercapacitors at −30 °C

Cobalt hydroxide (Co(OH) 2 ) is a promising electrode material for hybrid devices because of its intrinsic battery‐mimic mechanism for energy storage. However, conventional electrolytes suitable for Co(OH) 2 will lead to performance failure in a harsh environment, which hinders its industrial application at ambient temperature. Here, we propose an anti‐freezing aqueous electrolyte composed of NaOH and a high concentration of NaClO 4 for Co(OH) 2 electrode, which can still fully function at −30 °C. At this temperature, the energy density of a Co(OH) 2 –active carbon hybrid capacitor can reach 16.52 Wh kg −1 , which has a 72 % energy‐density retention at 20 °C. The hybrid capacitor shows excellent cyclability with the anti‐freezing electrolyte at −30 °C, presenting only 3.5 % drop of the capacitance after 500 cycles. This designed anti‐freezing electrolyte may put more pseudocapacitive materials into more practical use, particularly in northern harsh climates.