Improvement of Redox Kinetics of Dendrite-Free Lithium–Sulfur Battery by Bidirectional Catalysis of Cationic Dual-Active Sites

Abstract

The practical application of lithium–sulfur batteries (LSBs) is hampered by the slow lithium polysulfide (LIPS) conversion kinetics and the uncontrollable anode-metal lithium dendrites. Herein, a three-dimensional cation dual-active-site eggshell structure compound (3DCS-FMO@C) was synthesized by soft template, ion exchange, and pyrolysis to modify the commercial separator. Experimental and theoretical analysis results showed that Mn 2+ and Fe 2+ sites in 3DCS-FMO@C can synergistically adsorb LIPSs, effectively regulate the bidirectional conversion dynamics of intermediate liquid-phase LIPSs and solid-phase lithium sulfide, and reduce the energy barrier of the reaction. The 3DCS-FMO@C-modified separator with high mechanical stability and no reduction in ion diffusion also had a lithiophilic central core that can homogenize the lithium-ion flow, thereby inhibiting the dendrite growth of lithium. Based on the above advantages, 3DCS-FMO@C-modified separator LSBs had better electrochemical performance, including an initial capacity of 1530 mAh g –1 at 0.1C and an ultralow decay rate of 0.029% for 1000 cycles at 0.5C. A high area capacity of 8.7 mAh cm –2 was achieved even with high sulfur loading and poor electrolyte. This work provided a basis for understanding the bidirectional catalysis for practical application in LSBs and simultaneously solved the problem of lithium dendrites.