Dual-Confined Flexible Sulfur Cathodes Encapsulated in Nitrogen-Doped Double-Shelled Hollow Carbon Spheres and Wrapped with Graphene for Li-S Batteries

Batteries with high energy and power densities along with long cycle life and acceptable safety at an affordable cost are critical for large-scale applications such as electric vehicles and smart grids, but is challenging. Lithium-sulfur (Li-S) batteries are attractive in this regard due to their high energy density and the abundance of sulfur, but several hurdles such as poor cycle life and inferior sulfur utilization need to be overcome for them to be commercially viable. Li-S cells with high capacity and long cycle life with a dual-confined flexible cathode configuration by encapsulating sulfur in nitrogen-doped double-shelled hollow carbon spheres followed by graphene wrapping are presented here. Sulfur/polysulfides are effectively immobilized in the cathode through physical confinement by the hollow spheres with porous shells and graphene wrapping as well as chemical binding between heteronitrogen atoms and polysulfides. This rationally designed free-standing nanostructured sulfur cathode provides a well-built 3D carbon conductive network without requiring binders, enabling a high initial discharge capacity of 1360 mA h g(-1) at a current rate of C/5, excellent rate capability of 600 mA h g(-1) at 2 C rate, and sustainable cycling stability for 200 cycles with nearly 100% Coulombic efficiency, suggesting its great promise for advanced Li-S batteries.