Thin-carbon-layer-enveloped cobalt-iron oxide nanocages as a high-efficiency sulfur container for Li-S batteries

Lithium-sulfur (Li-S) batteries are regarded as one of the most promising candidates for next-generation energy storage systems due to their advantages of its high specific capacity and low material cost. Regrettably, the electrical insulation nature of sulfur, the volume expansion during lithiation, and the internal shuttle effect aroused by the polysulfides dissolution are the central issues for sulfur cathodes. Here, CoFe2O4@C nanocages derived from Prussian blue analogues and polydopamine were utilized as a sulfur host to address these problems. The polar Co-Fe oxide afforded chemical adsorption sites for anchoring polysulfides to reduce the shuttling effect. The hollow core structure of the nanocages could withstand the large volume change during lithiation and delithiation processes. The conductive carbon layer on the nanocages could ameliorate the extremely low electrical conductivity of S and Li2S. The S/CoFe2O4@C cathode demonstrated high capacity and excellent cyclability (821 mA h g-1 after 100 cycles at 0.5C). More importantly, the combinational strategies of good conductivity, physical space encapsulation, and chemical adsorption provide a means of resolving the current cathode issues in Li-S batteries.