Polyacrylonitrile-induced formation of core-shell carbon nanocages: Enhanced redox kinetics towards polysulfides by confined catalysis in Li-S batteries

Slow redox kinetics of polysulfides (PSs) on sulfur cathode remains a grand challenge for achieving high rate, high capacity and long cycling performance of Li-S batteries, especially in lean electrolyte condition. Herein, we demonstrate the preparation of cobalt (Co) nanoparticles-decorated and nitrogen-doped carbon nanocages confined in a carbon shell (denoted [email protected]) through carbonization of polyacrylonitrile (PAN)-encapsulated ZIF-67 ([email protected]) prepared by a simple “phase-inversion” method. The Co nanoparticles supported on nitrogen-doped carbon frame and confined in the carbon shell can efficiently promote the redox kinetics of PSs due to the confined catalysis, as demonstrated by density functional theory (DFT) calculation and electrochemical measurements. Therefore, the sulfur cathode based on such confined hollow core/shell nanocages delivers a capacity of 635.8 mAh g−1 at 5 C and an outstanding cycling stability with an ultralow capacity decay of 0.018% per cycle for 2700 cycles at 1 C. Furthermore, a reversible capacity of 552.9 mAh g−1 was delivered at a current density of 0.2 C over 500 cycles at a high sulfur loading of 5.7 mg cm−2 under lean electrolyte condition. Meanwhile, a high areal capacity of 9.5 mAh cm−2 was achieved at a sulfur loading of 10.2 mg cm−2. More intriguingly, a soft-packaged Li-S batteries based on this composite cathode material also exhibited superior cycling stability in folding conditions, demonstrating a high potential for practical application in wearable electronic devices.