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

Abstract

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 °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.

A Flexible and Safe Aqueous Zinc–Air Battery with a Wide Operating Temperature Range from −20 to 70 °C

“…Various approaches have been used to enhance the performance of hydrogel electrolytes at extreme temperatures, such as the incorporation of ionic liquids, − novel ethylene glycol polymers, , high concentrations of electrolyte solution (such as NaClO 4 solution), and organic solvents. , However, ionic liquids have low ion mobility and high viscosity. More importantly, ionic liquids are unstable in the air and thus the preparation of batteries with ionic liquid gels requires highly controlled conditions .…”

Ions Transport in Electrochemical Energy Storage Devices at Low Temperatures

“…And the aqueous LIBs using saturated LiCl solution as the electrolyte can work at −40 °C due to the small electrolyte resistance (Figure 3a, b). [50] Besides, some inorganic salts and acids, such as KOH, [66] CsOH, [67] NaClO 4 , [68][69][70] NaNO 3 , [71] Zn(BF 4 ) 2 , [72] H 2 SO 4 , [51,73] H 3 PO 4 , [74] and some organic salts, such as choline chloride [52] and (1-butyl-3-methylimidazole) [75] have also been used to prepare high-concentration electrolytes. It should be pointed out that salt precipitation can occur easily in high-concentration electrolytes at low temperatures, resulting in performance degradation and even failure of the EES devices.…”

“…And the aqueous LIBs using saturated LiCl solution as the electrolyte can work at −40 °C due to the small electrolyte resistance ( Figure a, b). [ 50 ] Besides, some inorganic salts and acids, such as KOH, [ 66 ] CsOH, [ 67 ] NaClO 4 , [ 68–70 ] NaNO 3 , [ 71 ] Zn(BF 4 ) 2 , [ 72 ] H 2 SO 4 , [ 51,73 ] H 3 PO 4 , [ 74 ] and some organic salts, such as choline chloride [ 52 ] and (1‐butyl‐3‐methylimidazole) [ 75 ] have also been used to prepare high‐concentration electrolytes.…”

Rational Design of Antifreezing Organohydrogel Electrolytes for Flexible Supercapacitors

“…Various strategies have been used to improve the antifreezing performance of the hydrogel electrolytes for flexible SCs. One common strategy is increasing the electrolytic salts concentration of hydrogel electrolytes to bestow them cold resistance. , For example, Pan and co-workers developed a salt-tolerance hydrogel electrolyte, and its freezing point was significantly reduced to −10.2 °C . However, such highly concentrated electrolytic salt might cause serious erosion and side reactions, which therefore result in electrochemical performance deterioration and even devices failure. , In addition, it is necessary to extend the working temperature window of the hydrogel electrolytes for flexible SCs to satisfy more harsh conditions.…”

“…One common strategy is increasing the electrolytic salts concentration of hydrogel electrolytes to bestow them cold resistance. 20,21 For example, Pan and co-workers developed a salt-tolerance hydrogel electrolyte, and its freezing point was significantly reduced to −10.2 °C. 22 However, such highly concentrated electrolytic salt might cause serious erosion and side reactions, which therefore result in electrochemical performance deterioration and even devices failure.…”