High-Spin Cobalt Enables Strong Metal-Sulfur Orbital Hybridization for Accelerated Polysulfide Conversion in Lithium-Sulfur Batteries.

Abstract

The development of electrocatalysts to mitigate polysulfide shuttling and enhance the kinetics of sulfur species conversion is pivotal for the advancement of lithium-sulfur (Li-S) batteries. In this study, the fabrication of porous, undercoordinated titanium dioxide nanosheets adorned with high-spin state cobalt atoms (HSCo/TiO2-x) as efficient electrocatalysts is presented. The undercoordinated TiO2-x nanosheets provide a profusion of edge active sites conducive to Co atom attachment, firmly embedded within the lattice structure, thereby ensuring heightened structural stability throughout repetitive cycling processes. Furthermore, the high-spin state Co atoms contribute abundant unpaired electrons, occupying distinct 3d orbitals. This configuration facilitates electron transfer and orbital hybridization upon interaction with polysulfides, leading to suppressed shutting effect and enhanced polysulfide conversion kinetics. Consequently, the Li-S cell equipped with an HSCo/TiO2-x modified separator exhibits an impressive capacity of 8.05 mAh cm-2 under elevated sulfur loading of 10.9 mg cm-2. Additionally, the fabricated Li-S pouch cell delivers a substantial initial discharge capacity of 0.47 Ah with a high energy density of 379.3 Wh kg-1. This study serves as a valuable reference for exploring the intricate relationship between spin state regulation and electrochemical performance, and holds great promise for the design of highly efficient future electrocatalysts.