Enhancing Bidirectional Sulfur Conversion Through p-d Orbital Hybridization via Vacancy Engineering

Lithium-sulfur batteries (LSBs) have garnered significant concern as materials with high energy density for energy storage. Nevertheless, their severe shuttle effect and delayed redox kinetics limit their practical application. Herein, a strategy based on the regulation of oxygen vacancy concentration in CoWO₄ has been proposed to accelerate polysulfide kinetics. Experiments and density functional theory calculations reveal that catalytic materials with the appropriate number of oxygen vacancies (CWO-M) have moderate adsorption energy and optimal catalytic capacity for polysulfides due to strong p-d orbital hybridization. More importantly, CWO-M not only accelerates the reduction of sulfur during discharge but also significantly accelerates the oxidation of Li₂S during charging, showing a favorable bidirectional catalytic effect. Benefiting from these unique advantages, the CWO-M/S-based battery exhibits an excellent rate performance of 768 mAh g^-1 at 2 C and a capacity retention of 91.1% after 100 cycles at 0.2 C. Stable cycling performance with a high capacity of nearly 4 mAh cm^-2 was achieved even after 100 cycles at a high sulfur loading of 8.02 mg cm^-2 and a low electrolyte/sulfur (E/S) ratio of 8 µL mg S^-1. This work provides significant insights into bidirectional catalysts by modulating the oxygen vacancy concentration for application in LSBs.