Tetrathiafulvalene as a multifunctional electrolyte additive for simultaneous interface amelioration, electron conduction, and polysulfide redox regulation in lithium-sulfur batteries

Numerous efforts can improve reversible capacity and long cycling stability for lithium-sulfur (Li–S) batteries, however, challenges remain in achieving high sulfur utilization and suppressing the shuttle effect, especially for cells with a low electrolyte/sulfur (E/S) ratio. In this research, we utilize tetrathiafulvalene (TTF) as multifunctional catalyst for high-performance Li–S batteries through optimizing electrolyte chemistry for the first time. With TTF additive in electrolyte, it acts as π-electron donor molecule to improve the electron transport of Li2Sx due to the van der Waals interaction, and promote LiNO3 to Li3N to form highly conductive passivation layer on lithium anode (Li-anode). Furthermore, TTF functions as a catalyst to improve the redox kinetics of Li2Sx thus slowing down the "shuttle effect", improve the utilization of sulfur, and protect the Li-anode. As a result, the cell with TTF exhibits excellent performances with high discharge capacity (1359 mAh g−1 at 0.1C), long-term cycling stability (509 mAh g−1 after 500 cycles at 0.5C), and excellent cycling performance even at low E/S ratio (5.5 μL mg−1) (initial discharge capacity of 1129 mAh g−1 with a capacity decay rate of 0.20% per cycle at 0.1C for 200 cycles).