A Low Cost Aqueous Zn–S Battery Realizing Ultrahigh Energy Density

Abstract Rechargeable aqueous zinc ion batteries are enabled by the (de) intercalation chemistry, but bottlenecked by the limited energy density due to the low capacity of cathodes. In this work, carbon nanotubes supported 50 wt% sulfur (denoted as S@CNTs‐50), as a conversional cathode, is employed and a high energy density aqueous zinc–sulfur (Zn–S) battery is constructed. In the electrolyte of 1 m Zn (CH 3 COO) 2 (pH = 6. 5) with 0. 05 wt% I 2 additive where I 2 can serve as medium of Zn 2+ ions to reduce the voltage hysteresis of S@CNTs‐50 and stabilize Zn stripping/plating, S@CNTs‐50 delivers a high capacity of 1105 mAh g −1 with a flat discharge voltage of 0. 5 V, realizing an energy density of 502 Wh kg −1 based on sulfur, which is one of the highest values reported in aqueous Zn‐based batteries that use mild electrolyte. Moreover, the chemical materials cost of this aqueous Zn–S battery can be lowered to be 45 kWh −1 due to the cheap raw materials, reaching to the level of pumped energy storage. Ex situ X‐ray diffraction, Raman spectra, X‐ray photoelectron spectrum, and transmission electron microscopy measurements reveal that sulfur cathode undergoes a conversion reaction between S and ZnS.