A doping strategy to regulate the adsorption energy of Li2S4 and Li2S to promote sulfur reduction on Chevrel phase Mo6Se8 in lithium–sulfur batteries

Atomic doping in catalysts is an effective strategy for adjusting their catalytic activity, which has recently been applied to promote sulfur reduction reactions (SRRs) on the cathode of lithium-sulfur (Li-S) batteries. Herein, the electrocatalytic SRR mechanism of eight metal atom (Ca, Ti, V, Cr, Mn, Fe, Co or Ni) doped Chevrel phase Mo₆Se₈ were investigated using density functional theory (DFT) calculations. The results reveal that the interaction between polysulfides and the catalyst mainly originates from the coupling of d_z² and d_xz orbitals of doped metals and the 3p orbitals of S. The Ti-doped Mo₆Se₈ system significantly reduces the overpotential of the SRR to only 0.21 V. After analyzing SRR processes over doped and undoped Mo₆Se₈, no scalar relationship was found between the adsorption energies (E_ad) of various polysulfides. Instead, a linear relationship is established between 4E_ad-Li2S* - E_ad-Li2S4* and overpotential. Finally, a linear relationship between overpotential and descriptors was established based on a machine learning (ML) method, which can accurately predict the overpotential of the SRR over the Mo₆Se₈ catalyst. This work provides new theoretical insights into the SRR mechanism over metal-selenides and the rational design of a catalyst for Li-S batteries.