Ammonium Silicofluoride as Bifunctional Electrolyte Additive to Regulate the Electrode Interface in Lithium-Sulfur Battery

The passivation and corrosion of active interface of cathode and lithium anode caused by the uncontrollable deposition of discharged product (Li2S2/Li2S) in lithium-sulfur (Li-S) batteries lead to deterioration cycling stability and increase voltage polarization. Herein, ammonium silicofluoride (NH4)2SiF6 is demonstrated as an effective soluble ammonium salt to enhance the solvation of Li2S, resulting from the inductive effect of NH4+ cation. In particular, the addition of (NH4)2SiF6 stabilizes the lithium metal interface through the formation of LiF-rich robust SEI. Due to these advantages, excellent cyclic stability is shown in the Li-S cells with (NH4)2SiF6-based electrolyte and the long cycle tests of 0.5 C and 2 C. The proposal of (NH4)2SiF6 provides a new avenue to solve the interface problem of Li-S cells and stimulates the research enthusiasm for developing soluble ammonium salt.