Cobalt single-atom catalyst helps high-sulfur lithium-sulfur batteries

by:CTECHi     2021-07-20

Lithium-sulfur (Li-S) battery has a higher theoretical energy density and lower cost, and is an ideal choice for next-generation energy storage devices. Its electrochemical performance largely depends on the effective and reversible conversion of lithium polysulfide (LiPS) to Li2S and to elemental sulfur (S8) during charging. However, the slow kinetics of the liquid-solid phase transition process limits the rate performance of the battery, and also causes more serious shuttle effects and active surface passivation. Finding efficient catalysts to accelerate the conversion process of soluble LiPS to insoluble S8 or Li2S is an important way to improve the electrochemical performance of batteries. The single-atom catalyst supported on a solid substrate has theoretically 100% atom utilization and combines the dual advantages of heterogeneous and homogeneous catalysts. Due to high conductivity and excellent activity, single-atom catalysts have been widely used in oxygen reduction, hydrogen evolution and CO2 reduction reactions, and it can be expected that they should also play a highly effective catalytic role in the conversion of sulfur-containing species.

[Introduction of Achievements]

Recently, Associate Professor Kong Xianghua, Hefei University of Technology, Professor Ji Hengxing and Professor Wu Xiaojun, University of Science and Technology of China The team published a paper entitled 'Cobalt in Nitrogen-Doped Graphene as Single-Atom Catalyst for High-Sulphur Content Lithium-Sulphur Batteries' in the JACS journal. This work uses monodisperse cobalt atoms on a nitrogen-doped graphene substrate to promote the surface-mediated reaction of LiPS. Combined with in-situ X-ray absorption spectroscopy (XAS) and first-principles calculations, it is proved that the Co-N-C coordination center as a bifunctional electrocatalyst can promote the formation and decomposition of Li2S during discharge and charging, respectively. The S@Co-N/C composite material can provide a specific capacity of 1210 mAh g–1 and an areal capacity of 5.1 mAh cm–2. When the sulfur loading is increased to 6 mg cm–2, the capacity decay rate is reduced to 0.029%/ ring.

[Research Highlights]

This work introduces single-atom catalysts into lithium-sulfur batteries for the first time, and through high-angle ring-shaped darkening Field-spherical aberration corrected scanning transmission electron microscope (HAADF-STEM) imaging, in-situ XAS spectra and first-principles calculations reveal the principle of single-atom catalysis. This work provides ideas for the design of single-atom catalysts and opens up new methods for the development of high-performance Li-S batteries and other electrochemical energy storage devices.

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