A self-supporting graphitic carbon nanocage network confining high-loading sulfur for high performance potassium-sulfur batteries

Potassium-sulfur (K-S) battery is a promising candidate for high-energy and low-cost energy storage system. However, the development of K-S battery is challenged by the sluggish kinetics, low utilization of sulfur and serious shuttle effect. Herein, a novel self-supporting carbon/sulfur composite cathode (S@GCNs) was developed by infusing sulfur into an interconnected graphitic carbon nanocage (GCNs) network. Typically, the small GCNs (<10 nm) provide a large amount of space for sulfur storage, the sulfur content could reach more than 80 wt%. In addition, the interconnected GCNs network with high conductivity provide fast transport pathways for electrons/ions, and the strong confinement of GCNs on sulfur will buffer the volume expansion of sulfur and alleviate shuttle effect. The unique microstructure of S@GCNs boosts the rate capability and cycle stability of K-S battery, the initial capacity was 452.7 mAh/g, which remained 270.6 mAh/g and 205.9 mAh/g after 10 and 20 cycles, the capacity can reach 97.7 mA h g −1 even at 2000 mA g −1 . Characterizations of the phase and structural evolution of S@GCNs revealed the reversible conversion mechanism of sulfur: S 0 ↔ $\leftrightarrow$ K 2 S x (x = 5, 6) ↔ $\leftrightarrow$ K 2 S x (x = 4) ↔ $\leftrightarrow$ K 2 S 3 .