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 NaClO4 for Co(OH)(2) electrode, which can still fully function at -30 degrees C. At this temperature, the energy density of a Co(OH)(2)-active carbon hybrid capacitor can reach 16.52 Whkg(-1), which has a 72% energy-density retention at 20 degrees C. The hybrid capacitor shows excellent cyclability with the anti-freezing electrolyte at -30 degrees 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.