Constructing a raincoat-like protective layer on sulfur cathode for aqueous Zn–S batteries

The unwanted disproportionation reactions between sulfur and water seriously deteriorate the cycling performance of aqueous Zn−S batteries, but there is not yet effective strategy to address this dilemma. Here, we proposed a concept of putting a "raincoat" on the S cathode to suppress the aforementioned side reactions. Via adding trace amounts of rationally selected organic ligands to the ZnSO4-based electrolyte, a layer of hundreds nanometer thick metal−organic complexes can be in-situ formed on the cathode surface during the charging process. Although the as-formed raincoat-like protecting layer is much thicker than traditional cathode electrolyte interphase (CEI), it has similar functions with CEI, which can not only block the contact between sulfur and aqueous electrolyte, but also effectively transfer Zn2+ during the charging/discharging process. As a result, the obtained aqueous Zn−S batteries delivered a high specific capacity of 1478 mAh g−1 at 0.1 A g−1, and much-improved stability over 300 cycles at 2 A g−1. Moreover, they also delivered an extremely high areal capacity of 4.2 mAh cm−2 and extraordinary cyclic stability even under harsh condition (E/S ratio, 8 μL mg−1, N/P ratio, ∼1.5). We also prove the universality of this strategy to different kinds of S-based cathodes for aqueous Zn−S batteries.