Electrochemical Conversion of Confined 1D Sulfur Chains in Li-S Battery

Lithium-sulfur (Li-S) batteries are prospective as one of the most promising candidates for next-generation energy storage systems owing to high energy density and cost-effectiveness. Compared with normal bulk sulfur, the electrochemistry behaviors of sulfur chains inside single-wall carbon nanotubes (SWCNTs) have rarely been investigated. Herein, one type of 1D sulfur chain encapsulated in SWCNTs (S@SWCNTs) is designed as the cathode for Li-S batteries. Experimental studies and density functional theory (DFT) calculations reveal the suppressed shuttle effect and the accelerated sulfur reduction kinetics in S@SWCNTs cathodes, benefiting from the spatial confinement effect of SWCNTs. The S@SWCNTs electrode possesses an excellent rate performance and highly reversible discharge capacity of 1123 mAh g-1 at 1 C with 0.07% capacity fade rate per cycle over 500 cycles. Moreover, the S@SWCNTs as the self-supporting cathodes can still exhibit capacity retention of 94% after 100 cycles with a high sulfur loading of 5.84 mg cm-2 and low E/S (electrolyte/sulfur) ratio of 4.3 mu L mg-1, promising for high energy-density full batteries. This work helps the understanding of sulfur chain redox reaction and electrochemistry behaviors inside SWCNTs and provides a path-breaking vision to develop the cathodes of Li-S batteries. In this work, 1D sulfur chain encapsulated in SWCNTs is synthesized and they exhibit superior electrochemical performance in Li-S batteries. Density functional theory calculations reveal that the spatial confinement effect of SWCNTs can suppress the shuttle effect and accelerate sulfur reduction kinetics in designed cathodes.image