Highly Puffed Co9S8/Carbon Nanofibers: A Functionalized S Carrier for Superior Li-S Batteries.

Li-S batteries have triggered global research interest because of their higher theoretical energy density and lower cost than popularized Li-ion cells. However, they still do not have practical implementations because of issues induced by intermediate polysulfide dissolution. To better confine both S and polysulfides in cathode regions and prolong the cyclic lifespan, we purposely design the unique highly puffed Co9S8/carbon nanofibers (Co9S8@CNFs) as efficient S carriers. Such fibrous products made of interconnected hollow/porous Co9S8/C nanopolyhedra can provide ample places to load the large amount of S, convenient pathways for both Li+ and electrons transfer, and extra reversible capacity contribution. Particularly, each individual Co9S8 subunit is physically robust, metallic, and polarized, synergistically enabling the spatial confinement and chemical bonding to restrict S volume expansions and anchor the soluble polysulfides during cycling. The as-built highly puffed S⊆Co9S8@CNFs cathodes can exhibit a large specific capacity of ∼1080 mA h g-1, admirable cyclic stability/lifespan (capacity loss rate: ∼0.03% per cycle), and excellent rate capabilities. Our work may hold a great potential in rational design of superior cathodes for applicable Li-S cell systems.