A zwitterionic hydrogel with a surprising function of increasing the ionic conductivity of alkali metal chloride or sulfuric acid water-soluble electrolyte

Polymer hydrogel electrolytes combine the advantages of solvent-free solid electrolytes and liquid electrolytes, with a specific ion migration rate, excellent flexibility and safety. However, the critical limitation to the application of hydrogel electrolytes is that their ionic conductivity hardly rivals that of liquid electrolytes. In this work we design zwitterionic hydrogel (PMH) electrolytes with ultrahigh ionic conductivity, whose ionic conductivity is 140-160% that of alkali metal chloride solutions (LiCl, NaCl and KCl) and 130% that of sulfuric acid solution. This fascinating discovery is attributed to the ice-like clathrate structure formed via electrostatic induction between zwitterionic groups and water molecules. This delicate structure affects the hydration state of nearby ions and improves ion mobility. Meanwhile, the dipole-dipole interaction facilitates the dissociation of ion clusters, further increasing the ionic conductivity. This work provides an effective way to obtain electrolytes with ultrahigh ionic conductivity, representing an important step forward for practical applications in energy storage.