High-Density Oxygen Doping of Conductive Metal Sulfides for Better Polysulfide Trapping and Li₂S-S₈ Redox Kinetics in High Areal Capacity Lithium–Sulfur Batteries

Exploring new materials and methods to achieve high utilization of sulfur with lean electrolyte is still a common concern in lithium-sulfur batteries. Here, high-density oxygen doping chemistry is introduced for making highly conducting, chemically stable sulfides with a much higher affinity to lithium polysulfides. It is found that doping large amounts of oxygen into NiCo₂S₄ is feasible and can make it outperform the pristine oxides and natively oxidized sulfides. Taking the advantages of high conductivity, chemical stability, the introduced large Li–O interactions, and activated Co (Ni) facets for catalyzing S_n^2–, the NiCo₂(O–S)₄ is able to accelerate the Li₂S-S₈ redox kinetics. Specifically, lithium-sulfur batteries using free-standing NiCo₂(O–S)₄ paper and interlayer exhibit the highest capacity of 8.68 mAh cm^–2 at 1.0 mA cm^–2 even with a sulfur loading of 8.75 mg cm^–2 and lean electrolyte of 3.8 µL g^–1. The high-density oxygen doping chemistry can be also applied to other metal compounds, suggesting a potential way for developing more powerful catalysts towards high performance of Li–S batteries.