Multi‐Effect Ionic Liquid Additives Achieve High Cycle Stability Lithium‐Sulfur Batteries by Constructing an Electrostatic Shielding Layer and Eliminating ‘Dead Sulfur’

Abstract Lithium‐sulfur (Li‐S) batteries are considered the most promising alternative for energy storage, however, their practical applications are still limited by lithium dendrites growth, slow lithium polysulfides (LiPSs) conversion kinetics, shuttle effect, and deposition of “dead sulfur” at Li anode surface. Herein, a novel ionic liquid tetrabutylammonium triiodide (TBAI 3 ) is adopted as a multi‐effect electrolyte additive to solve low coulombic efficiency and short life issues of Li‐S batteries. A series of in situ characterization technologies, theoretical calculations, potentiostatic Li 2 S deposition experiments, and different kinds of symmetric and asymmetric cells are conducted to reveal the multifunctional electrochemical work mechanism. It is found that the TBA + cations can coordinate with solvent molecules, reduce desolvation barrier, and accelerate Li + transport kinetics; they can also form a dynamic electrostatic shielding layer at the lithium protrusions and induce uniform lithium deposition. The I 3 − /I − redox pairs continuously eliminate “dead sulfur” by transforming Li 2 S deposits into soluble LiPSs and release active substances during cycling, while the reduzate I − can be electrochemically rejuvenated into I 3 − when charged to 2.89 V. Therefore, Li‐S batteries with TBAI 3 additives exhibit a ultra‐long cycle performance of 503 mAh g −1 at 2 C after 1000 cycles with an average coulombic efficiency of 99.99%.