Mild synthesis of superadhesive hydrogel electrolyte with low interfacial resistance and enhanced ionic conductivity for flexible zinc ion battery

Flexible aqueous battery is considered to be one of the most promising energy storage devices for powering flexible electronics. However, inferior interfacial compatibility in electrode–electrolyte interfaces and inefficient ionic channel of electrolytes usually result in potential troubles when applied in practical applications. Herein, we report a mild synthetic route to a sodium lignosulfonate-polyacrylamide hydrogel electrolyte with a high adhesiveness to achieve low electrode–electrolyte interfacial resistance and fast ionic conduction. Comprehensive experiments show that the catechol groups from sodium lignosulfonate demonstrate strong interactions with both cathode and anode materials, and thus greatly reduce the contact resistances across the electrodes. Meanwhile, the existence of sulfonate groups significantly enhances the ionic conductivity of the hydrogel electrolyte. Benefiting from this design, a low ohmic resistance of 3.8 Ω (i.e., 11.4 Ω cm2 ), a low charge transfer resistance of 22.5 Ω (i.e., 67.5 Ω cm2 ), a high ionic conductivity of 31.1 mS cm−1 as well as a 100% capacity retention upon harsh bending deformation can be realized in the flexible zinc ion battery, which are significantly superior to those in the traditional candidates. The present investigation provides new insight into addressing the interfacial issue plaguing flexible energy storage devices.