Encapsulating Various Sulfur Allotropes within Graphene Nanocages for Long-Lasting Lithium Storage

The encapsulation of sulfur within carbon matrices is widely utilized in the cathode of a rechargeable lithium-sulfur battery, whose energy density largely depends on the design of the carbon structure. Here, an advanced graphene nanocage structure with the capability of hosting both cyclo-S-8 and smaller sulfur molecules (S2-4) is reported. The cage inner cavity is partially filled with S-8 to form a yolk-shell structure that enables free volumetric variation of S-8 during (de)lithiation. In the graphene shell of the cage, S-8 are downsized to S2-4 to activate extra sulfur loading sites within graphene layers. Importantly, the graphene shell exhibits inward volumetric variation upon (de)lithiation of the loaded S2-4, and the overall electrode strain is thus minimized. This prototyped design promises an ultimate solution to maximize sulfur loading in carbon matrices as well as to circumvent the polysulfide dissolution problem and boost the commercialization of lithium-sulfur batteries in the future.