Interfacial Molecule Mediator in Cathode for Advanced Li-S Battery

The complicated reactions at the cathode–electrolyte interface in Li–S batteries are a large barrier for their successful commercialization. Herein, we developed a molecular design strategy and employed three small molecules acting as interfacial mediators to the cathodes of Li–S batteries. The theoretical calculation results show that the incorporation of tris(4-fluorophenyl)phosphine (TFPP) has a strong binding performance. The experimental results demonstrate that the strong chemical interactions between polysulfides and the F, P atoms in TFPP not only modify the kinetics of the electrochemical processes in the electrolyte but also promote the formation of short-chain clusters (Li2Sx, x = 1, 2, 3, and 4) at the interface during the charge–discharge process. As a result, an optimized electrode exhibits a low capacity decay rate of 0.042% per cycle when the current rate is increased to 5 C over 1000 cycles.