Fabricating low-temperature-tolerant and durable Zn-ion capacitors via modulation of co-solvent molecular interaction and cation solvation

Aqueous Zn-based energy-storage devices have aroused much interest in recent years. However, uncontrollable dendrite growth in the Zn anode significantly limits their cycle life. Moreover, the poor low-temperature performance arising from the freezing of aqueous electrolytes at sub-zero temperatures restricts their practical applications in cold regions. Here, we fabricated low-temperature-tolerant and durable Zn-ion hybrid supercapacitors (ZHSCs) via modulating a co-solvent water/ethylene glycol electrolyte. The interaction of intermolecular hydrogen bonds between water and ethylene glycol as well as cation solvation was systematically investigated by tuning the co-solvent composition. The results illustrate that the ZnSO4/water/ethylene glycol (65%) electrolyte possesses high ionic conductivity at low temperatures and effectively prevents the dendrite formation of the Zn anode. The as-fabricated ZHSCs exhibit long-term cyclability and are capable of working at sub-zero temperatures as low as −40°C. The present ZHSCs are anti-freezing and cost-effective, which may find new applications in the fields of next-generation electrochemical energy storage devices.