Dual functional coordination interactions enable fast polysulfide conversion and robust interphase for high-loading lithium-sulfur batteries.

Abstract

The stable operation of high-capacity lithium-sulfur batteries (LSBs) has been hampered by slow conversion kinetics of lithium polysulfides (LiPSs) and instability of the lithium metal anodes. Herein, 6-(dibutylamino)-1,3,5-triazine-2,4-thiol (DTD) is introduced as a functional additive for accelerating the kinetics of cathodic conversion and modulating the anode interface. We proposed that a coordination interaction mechanism drives the polysulfide conversion and modulates the Li⁺ solvated structure during the binding of the N-active site of DTD to LiPSs and lithium salts. The results show that DTD effectively promotes the redox of LiPSs and the formation of an inorganic-organic synergistic solid electrolyte interface (SEI). This suppresses the parasitic reaction of LiPSs and confers uniform lithium deposition. Therefore, the capacity decay rate per cycle of the DTD-added LSBs is only 0.066% after 600 cycles at 1C. Moreover, Li-Li symmetric batteries exhibited smaller overpotentials during long cycling and a 41% increment in cycle life. Even with high sulfur loading (5.38 mg cm^-2) and a depleted electrolyte sulfur ratio (E/S = 5 μL mg^-1), the capacity retention of the battery is 71.5%. This work provides a new reference for elucidating the mechanisms of polysulfide conversion and SEI interface regulation for high-energy-density lithium-sulfur batteries.