Atomic level design of single iron atom embedded mesoporous hollow carbon spheres as multi-effect nanoreactors for advanced lithium-sulfur batteries

The practical application of lithium-sulfur (Li-S) batteries is still facing the challenges of lithium polysulfide (LiPS) shuttling and uncontrollable Li2S growth due to the soluble nature and sluggish conversion kinetics of LiPSs. Herein, we propose a universal strategy to synthesize monodisperse iron atom embedded nitrogen-doped mesoporous hollow carbon spheres (Fe-N/MHCS) as multi-effect nanoreactors for sulfur at the atomic level. Using a combination of experimental and theoretical methods, the Fe-N-4 center is found to be an efficient electrocatalyst to propel the reversible conversion between LiPSs and Li2S, inhibit the LiPS shuttling and mediate the deposition of Li2S. As a result, S@Fe-N/MHCS exhibits significantly improved rate properties and cycling stability (only 0.0187% capacity fade in 1000 cycles at 1C) without using conductive carbon. Even at a practical high sulfur loading (5.4 mg cm(-2)) and low E/S ratio (8.0 mL mg(-1)), the areal capacity reaches 6.4 mA h cm(-2) and 81.7% of it is retained after 100 cycles. Furthermore, a S@Fe-N/MHCS pouch cell is also assembled showing exceptional cycling stability with a high capacity retention of 77.1% after 200 cycles. Therefore, this work provides valuable insights into the fundamental understanding of the catalysis mechanism for practical Li-S batteries with high specific energy and prolonged lifespan.