Antifreezing zwitterionic hydrogel electrolyte with high conductivity at subzero temperature for flexible sensor and supercapacitor

The presence of large amounts of water in hydrogel electrolyte makes it inevitable freezing at low temperatures, causing it to lose properties such as flexibility or electrical conductivity. It restricts the application of hydrogel electrolyte in subzero temperatures. Here, an antifreezing hydrogel electrolyte is designed and prepared by using zwitterionic and the hydrophilic monomer. The introduction of ethylene glycol (EG) into the hydrogel results in improving the mechanical properties of the hydrogel due to the interaction between EG and the polymer chain. The addition of LiCl not only makes the hydrogel conductive but also enhances the antifreezing and anti-drying properties of the hydrogel, which made the hydrogel exhibit a high ionic conductivity of 1.84 mS cm−1 at −30 °C. The great mechanical properties and electrical conductivity of hydrogels lead to excellent responsiveness in temperature and strain at both ambient and low temperatures. In addition, the electrolyte assembled supercapacitors can be operated normally at low and high temperatures, and their specific capacitance at 60 °C and −20 °C is 108.0% and 48.8% of that at room temperature, respectively.