Core-Shell Structured S@Co(OH)2 with a Carbon-Nanofiber Interlayer: A Conductive Cathode with Suppressed Shuttling Effect for High-Performance Lithium-Sulfur Batteries.

Rechargeable lithium-sulfur batteries are potential candidates for storing electrochemical energy because of their extremely high energy density. However, their practical applications are prohibited by the sluggish charge transfer, the retarding Li ion diffusion, and the shuttle effect of lithium polysulfides. We report here a high-performance cathode material in which a S submicrosphere with a mass fraction of 80% was encapsulated within a permeable Co(OH)2 nanoshell which functions as a physical barrier preventing the sulfur and polysulfides from leaking into the electrolyte and also contributes to the catalytic decomposition of polysulfides during the charge and discharge process. When an interlayer of carbon nanofibers is introduced between the S@Co(OH)2 cathode and the separator, the performance of the Li-S batteries can be further significantly enhanced. Specifically, the S@Co(OH)2 cathode possesses good cycling stability over 1000 cycles with an initial discharge capacity of 1100 mAh g-1 at 2 C and a reversible capacity of 606 mAh g-1. In particular, without the LiNO3 additive, this S@Co(OH)2 cathode also exhibits a Coulombic efficiency as high as 85%, just a little lower than that of commercial electrolyte with LiNO3 additive. Relevant mechanistic studies revealed that such superior performances are attributed to the enhanced internal electrical and ionic conductivity and suppressed shuttling effect, owing to the presence of the Co(OH)2 shell and the carbon-nanofiber interlayer. Theoretical simulations based on density functional theory were also carried out to figure out the interaction between the Co(OH)2 nanosheets and the polysulfides. It revealed that the Co(OH)2 nanoshell, rather than merely working as a physical barrier to trap the polysulfides, could also adsorb polysulfides and catalyze their decomposition during the cycling process, further helping to suppress the shuttling effect.