Aqueous zinc-iodine (Zn-I 2 ) batteries are promising candidates for gridscale energy storage due to their safety and cost-effectiveness. However, the shuttle effect of polyiodides, Zn corrosion, and accumulation of by-products restrict their applications. Herein, a simple vermiculite nanosheets (VS) suspension electrolyte is designed for simultaneous confinement of polyiodides and stabilization of Zn anode. It is found that the generation of I 5 − as dominant intermediate and the precipitation reaction between I 5 − and alkaline by-products should cause irreversible iodine species loss. Benefiting from the high binding energy between polyiodides and silica-oxygen bonds of VS, dissolved polyiodides are effectively anchored on the surface of VS suspended in the bulk electrolyte to suppress the shuttle effect, which is confirmed by in situ Raman, Ultraviolet-visible characterizations and theoretical calculations. Furthermore, the self-assembly VS interfacial layer on the surface of Zn anode hinders side reactions induced by polyiodides. Meanwhile, the interlayer and surface excess negative charges of VS tend to be compensated by Zn 2+ from diffuse layer, which serves as ion accelerators for transferring Zn 2+ at the interface immediately, rendering dendrite-free Zn plating/stripping behavior. Consequently, the Zn-I 2 battery with VS electrolyte achieves an ultra-long lifespan of 40000 cycles with a negligible capacity decay at 20 C.
ZnÀ I 2 batteries stand out in the family of aqueous Zn-metal batteries (AZMBs) due to their lowcost and immanent safety. However, Zn dendrite growth, polyiodide shuttle effect and sluggish I 2 redox kinetics result in dramatically capacity decay of ZnÀ I 2 batteries. Herein, a Janus separator composed of functional layers on anode/cathode sides is designed to resolve these issues simultaneously. The cathode layer of Fe nanoparticles-decorated single-wall carbon nanotubes can effectively anchor polyiodide and catalyze the redox kinetics of iodine species, while the anode layer of cation exchange resin rich in À SO 3 À groups is beneficial to attract Zn 2 + ions and repel detrimental SO 4 2À / polyiodide, improving the stability of cathode/anode interfaces synergistically. Consequently, the Janus separator endows outstanding cycling stability of symmetrical cells and high-areal-capacity ZnÀ I 2 batteries with a lifespan over 2500 h and a high-areal capacity of 3.6 mAh cm À 2 .
The Zn dendrite issue, which is closely related to the creation of the space-charge region upon local anion depletion during cycling, has plagued the practical applications of aqueous Zn metal batteries (ZMBs). Herein, we propose a Kevlar-derived hydrogel (KevlarH) electrolyte with immobilized anions to diminish the space-charge layer effect. SO 4 2− anions are strongly tethered to amide groups of polymer chains, which mitigates the concentration polarization of interfacial Zn 2+ ions by preventing the anion depletion. Furthermore, the relatively weak interaction between Zn 2+ cations and carbonyl groups can redistribute Zn 2+ -ion flux without sacrificing the ion diffusion rate. The synergistic "zincophilic" and "anionphilic" building blocks enable dendrite-free Zn deposition behavior and suppressed side reactions, thereby extending the lifespan of a Zn metal anode up to 3500 h with an ultrahigh Coulombic efficiency of 99.87%. Importantly, the KevlarH electrolyte can be directly used to assemble high-voltage bipolar ZMBs and break the 2 V barrier in aqueous ZMBs.
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