Nanosized FeS2 Particles Caged in the Hollow Carbon Shell as a Robust Polysulfide Adsorbent and Redox Mediator

As one of the most promising candidates for next-generation energy storage technology, lithium-sulfur (Li-S) battery has been attracting increasing attention due to its high theoretical specific capacity (1675 mA h g(-1)), natural abundance, and environmental friendliness. However, the notorious shuttle effect caused by the soluble polysulfides as well as the sluggish redox kinetics significantly hinders the practical application. Herein, sulfiphilic iron disulfide (FeS2) nanoparticles caged in the hollow carbon shell have been facilely fabricated as the sulfur host (FeS2@C-S) for Li-S batteries. The deposited amorphous carbon cage with hollow space can provide efficient pathways for electrons, facilitate electrolyte penetration, and effectively accommodate the volume change during the repeated charge/discharge process. In addition, polar FeS2 nanoparticles have strong chemical interaction on the polysulfides and can promote the redox conversion of polysulfides as an electrocatalyst. Visible adsorption and electrochemical analysis have been conducted to confirm the static polysulfide trapping capability and dynamic polysulfide conversion reversibility. Synergistically, the FeS2@C-S cathode with a sulfur loading of similar to 1.5 mg cm(-2) exhibits high cycle stability with a reversible capacity of ca. 800 mA h g(-1) after 200 cycles at a current density of 0.2 C and excellent rate performance. Even at the current density of 5 C, a capacity of ca. 400 mA h g(-1) can still be achieved after 400 cycles. This work provides a feasible approach to provide both physical and chemical protection against polysulfides resulting from the synergistic effects of multifunctional units during the sulfur cathode development.