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

Abstract

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 Sn2–, 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.

Boosting Polysulfide Transformation by NiCo2S4 Hollow Dodecahedra@Nitrogen-Doped Carbon Core/Shell Nanostructures as Cathodes for Lithium–Sulfur Batteries

“…Figure h shows that both samples have three pairs of redox peaks. Due to better electrical conductivity and adsorption of polysulfides, the NiCo 2 S 4 @NC symmetric cell not only has a larger redox peak area but also exhibits three distinct pairs of redox peaks attributed to the reduction of S 8 to Li 2 S 6 , Li 2 S 6 to Li 2 S 4 and Li 2 S 4 to Li 2 S 2 /Li 2 S during the reduction reaction . However, NiCo 2 S 4 symmetric cell possesses a smaller reduction/oxidation peak potential difference and three pairs of redox peaks, indicating that the N-doped carbon shell does not improve the catalytic conversion of polysulfides.…”

Understanding the Catalytic Kinetics of Polysulfide Redox Reactions on Transition Metal Compounds in Li–S Batteries

“…The reduction–oxidation peaks of polysulfides were retained as the CV scan rates of the symmetric cell increased, which indicated a fast catalytic redox reaction (Figure g). The corresponding full batteries endured 1000 cycles with a high initial capacity of 961 mAh/g at 1 C. Recently, Li et al obtained NiCo 2 (O–S) 4 by doping O atoms into NiCo 2 S 4 , which outperformed both the pristine NiCo 2 O 4 and naturally oxidized NiCo 2 S 4 . Combining high stability, conductivity, and strong interactions with polysulfides through polar Li–O–Co/Ni and Co/Ni–S bonds, the NiCo 2 (O–S) 4 as separator coating achieved a high area capacity of 8.68 mAh/cm 2 with a sulfur loading of 8.75 mg/cm 2 and an electrolyte content of 3.8 μL/g.…”

“…The reduction− oxidation peaks of polysulfides were retained as the CV scan rates of the symmetric cell increased, which indicated a fast catalytic redox reaction (Figure 6g). The corresponding full batteries endured 1000 cycles with a high initial capacity of 961 mAh/g at 1 C. Recently, Li et al 109 2 and an electrolyte content of 3.8 μL/g. These studies provide ways to prepare catalysts with high sulfur loading and lean E/S ratio.…”

A 3D-printed Al metal–organic framework/S cathode with efficient adsorption and redox conversion of polysulfides in lithium–sulfur batteries

“…3–9 However, Li–S batteries still suffer from low conductivity, polysulfide shuttling, limited reaction kinetics, huge electrode expansion, and side reaction. 10–15 To address these issues, many functional materials, such as carbonous materials, 16–18 conductive polymers, 19,20 metal carbides, 21,22 and metal compounds, 23–25 have been utilized as sulfur hosts in the cathodes of Li–S batteries.…”