Atomic-level design rules of metal-cation-doped catalysts: manipulating electron affinity/ionic radius of doped cations for accelerating sulfur redox kinetics in Li-S batteries

Although metal-cation doping into transition-metal dichalcogenides (TMDCs) has been investigated for promoting stepwise sulfur redox in lithium-sulfur batteries (LSBs), a rational design principle and a systematic theoretical study on how to select a suitable metal-cation dopant for doping into TMDCs to tune their catalytic activity are lacking in LSBs. Herein, we demonstrate a general electron affinity/ionic radius (E-A/r) rule as a new selection criterion of metal-cation dopants to guide the design of efficient metal-cation-doped Li-S catalysts. And a series of metal-cation dopants with different E-A/r values into WSe2 as a model to engineer their electronic structure and catalytic activity for manipulating sulfur redox kinetics are systematically investigated. Theoretical and experimental results reveal that a low E-A/r value of metal-cation dopant easily induces more Se vacancies and lattice defects, increases active sites and more electron accumulation on surface Se sites for stronger binding with lithium polysulfides (LiPSs), but it also weakens the competing Li-S bonds in LiPSs/Li2S captured on the host surface, thereby increasing LiPSs adsorption yet decreasing the Li2S nucleation and decomposition energy barrier. As expected, the V-doped WSe2/MXene catalyst with a minimum E-A/r value as a high-efficiency sulfur host exhibits the highest reversible capacity (1402.5 mAh g(-1)), a long-term cycling stability with 800 cycles (similar to 70% retention), and a large areal capacity (6.4 mAh cm(-2)). This work provides a general design rule as the selection criterion of metal-cation dopants to tune the catalytic activity for designing advanced Li-S catalysts.