Accelerated Sulfur Redox Kinetics on Transition Metal Sulfide Electrocatalysts by Modulating Electronic‐State of Active Sites

Abstract Lithium‐sulfur (Li‐S) batteries are considered a competitive next‐generation electrochemical energy storage device, while the shuttle effect of soluble lithium polysulfides (LiPSs) resulting from the sluggish redox kinetics severely impedes their practical applications. Herein, a novel cation doping strategy is demonstrated for substantially accelerating the sulfur redox kinetics on the transition metal sulfide (TMS) electrocatalysts by partially substituting cobalt atoms with in situ dissolved Ni dopants (Ni x Co 3‐x S 4 , 0<x≤1). Theoretical calculations revealed that the doping of Ni in the spinel Co 3 S 4 phase enables the electronic‐state modulation of metal active sites by realizing the upshift of the d‐orbital center, thus leading to good chemical adsorption of intermediates and low redox conversion barriers between LiPSs and solid Li 2 S products. This is confirmed by in‐depth electrochemical dynamics and in situ Raman characterizations, in which the obtained Ni 0.5 Co 2.5 S 4 with hierarchical nanosheet structure delivers the stronger chemical affinity of Li 2 S 6 and higher precipitation/dissociation capacity of Li 2 S in comparison to monometallic cobalt sulfides. Benefiting from these outstanding attributes, the assembled Li‐S batteries by incorporating Ni 0.5 Co 2.5 S 4 electrocatalysts into S@carbon nanotube cathode (S@Ni 0.5 Co 2.5 S 4 /CNT) exhibit a high specific capacity of 1189 mAh g −1 with excellent rate performance of 596 mAh g −1 at 5 C and long‐term cycling performance over 600 cycles with a capacity decay of 0.06% per cycle at 1 C. More importantly, an ultrahigh reversible areal capacity of 6.6 mAh cm −2 can be achieved for S@Ni 0.5 Co 2.5 S 4 /CNT cathode even with a high sulfur loading of 6.1 mg cm −2 . This work demonstrates a new insight into designing TMS electrocatalysts toward rapid redox conversion kinetics in Li‐S batteries.