Hofmeister Effect Mediated Conductivity of Hydrogel Electrolytes for High Performance Supercapacitor

Regulating the performance of hydrogel electrolytes by Hofmeister effect has attracted great interest. However, the Hofmeister effects of cations on the conductivity of hydrogel electrolytes are rarely reported. Here, hydrogel electrolytes (polySA) have been fabricated by random copolymerization of zwitterionic monomers in the presence of NH₄Cl, NaCl and LiCl. The weak interaction between NH₄⁺ with water and molecular chains makes polySA-NH₄⁺ electrolyte have high conductivity at room temperatures, whereas the strong interaction between Li⁺ with water and molecular chains makes polySA-Li⁺ electrolyte possess good anti-freezing properties and high mechanical strength. The polySA-Li⁺ hydrogel electrolyte can have a conductivity of 9.63 mS cm⁻¹ at −35 °C. Supercapacitors assembled with polySA-Li⁺ offers high specific capacitance of 52.25 F g⁻¹ at 25 °C and 47.75 F g⁻¹ at −35 °C. The capacitance retention is 94.64 % after 10 days at −35 °C. Our work shows that different properties of hydrogel electrolytes can be achieved by regulating Hofmeister effect, which provides a new way to prepare high-performance energy storage materials.