Chitosan hydrogel polyelectrolyte-modified cotton pad as dendrite-inhibiting separators for stable zinc anodes in aqueous zinc-ion batteries

Aqueous Zn-ion batteries have lately attracted much interest due to their high theoretical capacity, low redox potential, excellent safety, and low cost of zinc metal; yet, their widespread use is hampered by a substantial bottleneck caused by dendrite formation and side reactions. Although adapting the widely-used glass fiber (GF) separator for dendrite-free Zn anodes is a successful method, GF-based separators are currently uneconomical due to their high cost and labor-intensive preparation procedure, which makes them unsuitable for large-scale manufacturing. Herein, scalable Janus separators are designed via simply coating and gelating accessible chitosan (CS) directly on one side of a commercial cotton pad (CP, consisting of natural cellulose fibers). The zincophilic surface of the CS-CP separator affords abundant functional groups, which can lock water molecules, buffer protons and change the transport manner of zinc ions by beneficial adsorption. Furthermore, CP displays good mechanical properties and superior electrolyte wettability. Therefore, the synergistic effect of CP and gelated CS can effectively suppress the Zn dendrites and side reactions and ensure excellent electrochemical performance. Accordingly, Zn//Zn symmetric cells equipped with CS-CP separators reveal exceptional cycling longevity of 1500 h at 1 mA cm−2/1 mAh cm−2 and 600 h at 4 mA cm−2/1 mAh cm−2.