Deciphering the electrocatalysis essence of cobalt diselenide in lithium-sulfur electrochemistry from crystal-phase engineering

Polysulfide shuttle effect and sluggish sulfur reaction kinetics severely impede the cycling stability and sulfur utilization of lithium-sulfur (Li-S) batteries. Precisely designing effective electrocatalysts to accelerate sulfur conversion kinetics and suppress polysulfide migration is urgently needed. Generally, electrocatalytic activity is highly dependent on the electronic structures of catalysts, while the crystal phases play a pivotal role in governing the electronic structures. However, the "crystal phase - electronic structure - catalytic capability" relation chain of Li-S batteries catalysts usually lacks clear elucidation. Herein, crystal-phase engineering is reported by regulating phases of CoSe2 to enhance the electrochemical performance of Li-S batteries. Experimental investigations and atomic level analyses reveal that the orthorhombic CoSe2 can trap and accelerate the conversion of sulfur species more effectively than cubic one. Electronic structure analysis further demonstrates that the superior electrocatalytic activity is originated from the strong Jahn-Teller distortion. As a result, the Li-S batteries with orthorhombic CoSe2 modified separator exhibit a high initial capacity of 1390.7 mAh g−1 at 0.1C and outstanding rate performance with a specific capacity of 738.4 mAh g−1 at 3C. Moreover, even at a high sulfur loading of 10.09 mg cm−2, a favorable initial areal capacity of 12.0 mAh cm−2 is achieved at 0.05C, and the battery still maintains at 7.9 mAh cm−2 over 50 cycles under 0.1C. This work may provide a new strategy for effective catalyst design in Li-S batteries.