Activating the Inert Li ₂ S/Li ₂ S ₂ Deposits: A Bifunctional Halogen Electrolyte Additive for Stable Lithium‐Sulfur Batteries

Lithium‐sulfur (Li‐S) batteries represent a promising energy storage technology owing to their high energy density and environmental compatibility. However, their practical implementation has been hindered by the growth of lithium dendrites and the accumulation of inactive sulfur species on lithium anode surfaces. NH 4 I is introduced as a bifunctional electrolyte additive to address these issues. Both theoretical and experimental analyses demonstrate that NH 4 + coordinates with solvent molecules, reduces the desolvation energy barrier of Li + , and promotes uniform lithium deposition. Furthermore, during cycling, the reversible I − /I 3 − redox couple reacts with inert lithium sulfides (Li 2 S/Li 2 S 2 ), dissolving them into the electrolyte to alleviate interfacial issues and reduce irreversible active material loss. Consequently, the NH 4 I‐containing electrolyte enables Li‐S batteries to achieve a high reversible capacity of 1097.78 mAh g −1 , and the corresponding capacity retention ration increases from 62.43% to 80.02% after 100 cycles at 0.5C. Moreover, when cycling at 1C for 500 cycles, the capacity attenuation per cycle was only 0.067%. This work gives a novel electrolyte design strategy for long life Li‐S batteries.