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

Abstract

Hydrogel 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 SO₄ ^2--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.