Hybrid cathode composed of pyrite-structure CoS2 hollow polyhedron and Ketjen black@sulfur materials propelling polysulfide conversion in lithium sulfur batteries

Abstract Lithium-sulfur (Li–S) batteries are considered to have great prospects in advanced energy storage devices in the future and have been considered in recent years. However, the shuttling of Li-polysulfides in electrolytes and sluggish electrochemical kinetics of polysulfides hinder the development of Li–S batteries. To address these stumbling blocks, we introduced pyrite-structure CoS2 hollow polyhedron modification of Ketjen black@sulfur (CoS2/KB@S) composite that adsorbs and provides sufficient sites with Li-polysulfides interaction. The CoS2 hollow polyhedron has a pivotal effect on the adsorption and catalysis performance of the polysulfides, which further accelerates the redox kinetics. Consequently, the CoS2/KB@S cathode with 3.1 mg cm−2 sulfur loading attained a high discharge capacity of 0.5 C current density and reversible capacity was 437 mA h g−1 after 500 cycles, which displayed great stability and the capacity attenuation rate of per cycle was only 0.1%. Meanwhile, it also shows excellent rate capabilities and still maintains a high capacity of 527 mA h g−1 at 2 C current density. Even at high sulfur loading of 5.1 mg cm−2, the CoS2/KB@S electrode still delivers a high initial area capacity of 4.36 mA h cm−2 at 0.3 C with capacity retention capacity of 3.63 mA h cm−2 after 100 cycles. The cyclic and rate properties of CoS2/KB@S were greatly improved over that of KB@S. The results suggest the multifunction pyrite-structure CoS2 hollow polyhedron that anchors effectively and catalysis is beneficial to realize the goal of large-scale application for Li–S batteries.