High‐Voltage Aluminium‐Sulfur Batteries with Functional Polymer Membrane

Abstract A high‐voltage aluminium‐sulfur (Al‐S) battery is developed by employing the reversible electrochemical oxidation of S, favoring a high discharge voltage of around 1.8 V (vs Al 3+ /Al). The reversible multiple‐electron transformation between positive‐ and negative‐valence S compounds is further realized for activating a high‐capacity Al‐S battery. The formation of sulfur chlorides as charge products of S, including S 2 Cl 2 (l) as the dominant one, has been clearly identified. Benefiting from a functional polymer membrane infiltrated with AlCl 3 /acetamide electrolyte, which can suppress unwanted electrolyte reactions, restrict the shuttling of sulfur chlorides across the separator, and stabilize the Al anode against degradation, the Al‐S battery can deliver largely enhanced performance, with a capacity of 861 mAh g −1 , capacity retentions of 92.1%/79.0% within 50/200 cycles, and durability of 490 cycles. The new electrochemistry scenarios shed light on the development of S‐based secondary batteries with higher energy densities for future.