Modulating electrocatalytic activity of zinc sulfides by cation-doping strategy for enhanced sulfur redox kinetics

Lithium-sulfur (Li-S) batteries are considered promising next-generation energy-storage systems, owing to their ultrahigh theoretical energy density, low cost, and environmental benignity. Nevertheless, their practical application is hindered by the sluggish redox kinetics and shuttle effect of soluble lithium polysulfides (LiPSs). Herein, a facile cation doping strategy is proposed to modulate the electrocatalytic activity of zinc sulfide (ZnS) by partially substituting the inert Zn sites with ruthenium (Ru) and further boost the redox kinetics of LiPSs. Informed by the density functional theory calculations and systematic experimental analysis, the open-shell 4d 6 configuration of Ru cation dopants introduces high-energy electronic states into ZnS electrocatalysts, which can effectively optimize the electronic and/or geometric configurations of metal active sites, thereby enhancing chemical adsorption of LiPSs intermediates and their electrocatalytic conversion kinetics characterized by a low rate-limiting step barrier. As a result, the optimized Ru 0.125 Zn 0.875 S electrocatalysts with a particle size of about 50 nm are incorporated into the sulfur cathode of Li-S batteries, delivering a high specific capacity of 1227 mAh g ‒1 at 0.1C and excellent rate capability of 683.2 mAh g ‒1 at 2C. Furthermore, a long-term stability over 700 cycles at 1C with a low capacity decay rate of about 0.023% per cycle is obtained. Even under a high sulfur loading of about 6.1 mg cm ‒2 , the assembled Li-S batteries still exhibit a high reversible areal capacity of 5.1 mAh cm ‒2 after 60 cycles. This work provides valuable insights into designing metal sulfide electrocatalysts by a cation-doping strategy toward accelerating the sulfur redox kinetics in Li-S batteries.