A Universal Strategy Toward Low‐Cost Aqueous Sulfur–Iodine Batteries

Abstract Rechargeable aqueous batteries with non‐toxic and non‐flammable features are promising candidates for large‐scale energy storage. However, their practical applications are impeded by the insufficient electrochemical stability windows of aqueous electrolytes and intrinsic drawbacks of current electrodes. Herein, an aqueous sulfur–iodine chemistry that can be deployed in aqueous battery systems by employing water‐in‐bisalt (WiBS) electrolyte, sulfur composite anode, and iodine composite cathode is demonstrated. The freestanding iodine/carbon cloth cathode and halide‐containing WiBS electrolyte can support the continuous I⁺/I⁰ reaction by forming interhalogen. Meanwhile, the highly‐concentrated electrolyte and inorganic‐based solid electrolyte interphase can effectively suppress the dissolution/diffusion of polysulfides, thus realizing S/S_x²⁻ conversion reactions on the anode. Therefore, the as‐assembled aqueous sulfur–iodine batteries based on S/S_x²⁻ and I⁺/I⁰ redox couples can deliver a high energy density of 158.7 Wh kg⁻¹ with a considerable cycling performance and safety. Furthermore, this chemistry can be further extended to multivalent ion‐based battery systems. As demonstration models, Ca‐based and Al‐based aqueous sulfur–iodine batteries are also fabricated, which provide a new avenue towards the development of aqueous batteries for low‐cost and highly safe energy storage.