High-Density Oxygen Doping of Conductive Metal Sulfides for Better Polysulfide Trapping and Li 2 S-S 8  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 NiCo 2 S 4 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 NiCo 2 (O-S) 4 is able to accelerate the Li 2 S-S 8 redox kinetics. Specifically, lithium-sulfur batteries using free-standing NiCo 2 (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.