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

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 ZnSO 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 HO, initiated by the SO -driven HO polarization, could be re-united via intense intermolecular hydrogen bonds, thus leading to greatly increased carrying capacity of ZnSO. The urea-modified PVA-ZnSO HEs featuring a high ionic conductivity up to 31.2 mS cm 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 HO-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 while the Zn-I 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.