A hydrogel electrolyte with ultrahigh ionic conductivity and transference number benefit from Zn2+ “highways” for dendrite-free Zn-MnO2 battery

Abstract

Aqueous zinc ion batteries (AZIBs) have been regarded as promising energy storage devices owing to high safety and abundant resources. However, it still remains a great challenge to solve the issue of Zn dendrites. So far, some efforts have been made to inhibit dendrites using hydrogels as electrolytes. Nevertheless, it’s more challenging to improve ionic conductivity of hydrogel electrolyte to ensure it’s high enough to provide an environment for rapid transmission of Zn2+. Therefore, new strategies that can simultaneously solve above problems must be explored. Herein, a semi-interpenetrating network P(PEGMEA-AM)/PAM hydrogel electrolyte (s-PPMHE) with molecular chain designability was innovatively constructed. Abundant functional C-O-C groups in linear polymer chain of s-PPMHE can reduce the electrostatic potential of hydrated Zn2+ and release trapped Zn2+, thus significantly accelerating Zn2+ migration with an ultrahigh transference number (tZn2+ = 0.82). Thanks to the unique structural design, s-PPMHE has good mechanical stability and coordination ability with Zn2+, which is conducive to constructing ion migration channels and immobilizing water molecules, thus alleviating water-related parasitic reactions. The theoretical calculation results reveal that s-PPMHE can regulate Zn2+ electric field distribution and boost desolvation kinetics. Therefore, the Zn||s-PPMHE||MnO2 cells exhibit excellent electrochemical performance involving high average coulombic efficiency of 98.9% and ultrahigh specific capacity of ∼ 300 mAh/g at 0.05C (97% of theoretical capacity). Furthermore, s-PPMHE delivers excellent ionic conductivity of 82.65 mS/cm and over 350 h zinc stripping/plating cycling properties. Moreover, the flexible pouch AZIBs based on s-PPMHE show stable voltage under different conditions. This work provides a novel and exploratory strategy for design of hydrogel electrolyte at molecular chain level, and opens up a new avenue to design functional hydrogel matrix for high-performance electrochemical devices.