The Origin of Li2S2 Reduction Mechanism Modulated by Single-Atom Catalyst for all Solid-State Li-S Batteries

Abstract

All solid-state lithium-sulfur batteries (ASSLSBs) demonstrate tremendous potential in the next-generation energy storage system. Nevertheless, the incomplete conversion of Li₂S₂ to Li₂S within the sulfur electrode imposes a substantial impediment on the capacity release. Herein, the nickel single-atom catalyst (NiNC) materials are employed to ameliorate the sluggish reaction kinetics of polysulfides. Moreover, the unknown origin of the catalytic activity of NiNC materials on the ASSLSBs is revealed by using the ligand-field theory. The results show that the $d_{z^2}$ orbital of Ni exhibits a significant vertical hybridization phenomenon from the inert dsp² hybridization state to the active d²sp³ hybridization state, which exerts a catalytic effect on the reduction of Li₂S₂ to Li₂S. As a result, the assembled ASSLSBs attain a capacity release of 1506.9 mAh g⁻¹ at 0.05 C and more than 70% retention ratio after 600 cycles at a high rate of 2 C. The in-depth study of the d-orbitals of nickel single-atom catalysts in this work offers deep insights into the relationship between the catalytic substrate and active substance and a novel perspective for the realization of ASSLSB with high energy density.