Hybrid electrolyte using dimethylformamide as additive to achieve outstanding low temperature performance for Zn-ion hybrid supercapacitors

The development of electrolytes with low cost and wide temperature range is important for the practical application of Zn-ion hybrid supercapacitors (ZHSCs). Low concentration electrolytes have significant advantages in terms of cost and viscosity, however, the ease of water electrolyte solidification at low temperatures and poor cycling stability hinder its application. Here, we developed a hybrid electrolyte with a reduced concentration to inhibit freezing of water at low temperatures using a polar small molecule cosolvent, and which can promote uniform deposition of Zn-ion and inhibit side reactions at the same time due to its strong interaction with Zn-ion. Based on the results, ZHSCs with relatively low concentration hybrid electrolyte have good cycle stability with more than 500 h of cycling and high specific capacities of 44 mAh g−1 at −20 °C, while maintaining the low-cost advantage of water electrolyte. This work provides a reasonable method for designing relatively low concentration electrolytes and is expected to realize the practical application of Zn-based energy storage equipment. The low viscosity of the 1 M ZnSO4/H2O/DMF at low temperature is conducive to the rapid migration of Zn-ion, and the participation of DMF in the solvation structure of Zn-ion significantly stabilizes the electrode/electrolyte interface. [Display omitted] •A relatively low concentration hybrid electrolyte formula was developed.•The freezing point of 1 M ZnSO4/H2O/DMF electrolyte is reduced to −20 °C.•The electrolyte formula can maintain ionic conductivity of 8.33 ms cm−1 at −20 °C.•The hybrid supercapacitor delivers exceeds 5000 cycles at −20 °C.•The action mechanism of DMF on Zn-ion and water molecules is revealed.