Molecular Bridging Induced Anti‐Salting‐Out Effect Enabling High Ionic Conductive ZnSO4‐Based Hydrogel for Quasi‐Solid‐State Zinc Ion Batteries

Abstract

AbstractHydrogel electrolytes (HEs) hold great promise in tackling severe issues emerging in aqueous zinc‐ion batteries, but the prevalent salting‐out effect of kosmotropic salt causes low ionic conductivity and electrochemical instability. Herein, a subtle molecular bridging strategy is proposed to enhance the compatibility between PVA and ZnSO4 from the perspective of hydrogen‐bonding microenvironment re‐construction. By introducing urea containing both an H‐bond acceptor and donor, the broken H‐bonds between PVA and H2O, initiated by the SO42−‐driven H2O polarization, could be re‐united via intense intermolecular hydrogen bonds, thus leading to greatly increased carrying capacity of ZnSO4. The urea‐modified PVA‐ZnSO4 HEs featuring a high ionic conductivity up to 31.2 mS cm−1 successfully solves the sluggish ionic transport dilemma at the solid‐solid interface. Moreover, an organic solid‐electrolyte‐interphase can be derived from the in situ electro‐polymerization of urea to prohibit H2O‐involved side reactions, thereby prominently improving the reversibility of Zn chemistry. Consequently, Zn anodes witness an impressive lifespan extension from 50 h to 2200 h at 0.1 mA cm−2 while the Zn‐I2 full battery maintains a remarkable Coulombic efficiency (>99.7 %) even after 8000 cycles. The anti‐salting‐out strategy proposed in this work provides an insightful concept for addressing the phase separation issue of functional HEs.