Gradient Quasi-Solid Electrolyte Enables Selective and Fast Ion Transport for Robust Aqueous Zinc-Ion Batteries.

The quasi-solid electrolytes (QSEs) have attracted extensive attentions due to their improved ion transport properties and high stability, which is synergistically based on tunable functional groups and confined solvent molecules among polymetric networks. However, the trade-off effect between the polymer content and ionic conductivity exists in QSEs, limiting their rate performance. In this work, the epitaxial polymerization strategy is used to build the gradient hydrogel networks (GHNs) covalently fixed on zinc anode. Then we reveal that the asymmetric distribution of negative charges benefits GHNs with fast and selective ionic transport properties, realizing a higher Zn 2+ transference number of 0.65 than the homogeneous networks (0.52) at same polymer content. Meanwhile, the high-density networks formed at GHNs/Zn interface can efficiently immobilize free water and homogenize the Zn 2+ flux, greatly inhibiting the water-involved parasitic reactions and dendrites growth. Thus, the GHNs enable dendrite-free stripping/plating over 1000 h at 8 mA cm -2 and 1 mAh cm -2 in Zn||Zn symmetric cell, as well as the evidently prolonged cycles in various full cells. This work will shed light on asymmetric engineering of ion transport channels in advanced quasi-solid battery systems to achieve high energy and safety. This article is protected by copyright. All rights reserved.