Anion‐Transferring Electrolyte Enables In Situ Construction of Uniform LiF‐Rich Interphases for Long‐Cycling Lithium–Sulfur Batteries

Stabilizing electrode/electrolyte interphases is crucial for high‐performance lithium–sulfur batteries; however, simultaneously fabricating robust interphases on both the lithium anode and sulfur cathode is challenging. Here, we report an anion‐transferring functional electrolyte containing non‐expendable tetramethylammonium (TMA) bromide that enables the in situ formation of LiF‐rich interphases on both electrodes. The TMA + cations act as ion carriers that electrostatically shuttle PF 6 − anions from the bulk electrolyte to the electrode/electrolyte interfaces in the form of ion pairs. This localized enrichment of PF 6 − facilitates its electrochemical decomposition, leading to the formation of a uniform LiF‐rich solid electrolyte interphase on the anode and a cathode‐electrolyte interphase on the sulfur cathode. The LiF‐rich interphases show a high Young's modulus, which help suppress interfacial parasitic reactions and Li dendrite formation. The adsorbed TMA + cations form an electrostatic shielding layer that mitigates local Li + flux heterogeneity, further suppressing dendrite growth. When applied to Li‐SPAN batteries, they maintain a 92% capacity retention after 350 cycles at 1 C and deliver a high reversible capacity of 1039 mAh g −1 after 300 cycles at 0.5 C. This work provides an innovative alternative to conventional interphase engineering for stabilizing lithium battery interphases.