Revealing the Role of Ion Transport Properties through Ion-Exchange Membranes for Aqueous Zinc-Ion Battery

The separator material is a critical component that governs the cycling performance of aqueous zinc-ion batteries (AZIBs); however, how its ion transport properties dictate specific electrochemical behaviors remains poorly understood. Here, we investigated the relationship between ion transport properties and AZIB performance using Zn2+-substituted Nafion® (Zn-Nafion®) membranes as model ion-exchange membranes. By separately characterizing electric-field-driven ion migration and concentration-gradient-driven diffusion, we identified that rate capability is primarily influenced by ion conductivity, while long-term stability is governed by ion permeability, as further confirmed by numerical simulation. Guided by this principle, we chemically activated a Zn-Nafion® membrane optimized for both parameters, which demonstrated exceptional cycling stability even under high-rate operation (5.0 A/g). These findings clarify the distinct roles of ion transport in AZIBs and offer a rational strategy for designing advanced membrane materials.