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.