Two-dimensional Mo-based compounds for the Li-O2 batteries: Catalytic performance and electronic structure studies

Rechargeable Li-O2 batteries have captured increasing attention owing to their ultra-high theoretical specific energy. However, this promising system is confronted with the large overpotential, limited discharge capacity and low cyclic life. Herein, three two-dimensional (2D) molybdenum-based compounds of MoN, MoO3 and MoS2 are used as cathode catalysts in Li-O2 batteries. The catalytic performance and electronic structures of these catalysts are compared comprehensively. Electrochemical test results reveal the superior battery performance of MoN cathodes, which deliver the highest specific discharge capacity of approximately 7400 mAh g−1 and the lowest discharge/charge overpotential of 0.19/0.72 V. Density functional theory (DFT) calculations demonstrate the metallic property of MoN whereas MoO3 and MoS2 are poor conductive. Besides, interface properties between MoN and Li2O2 products as well as reaction pathways of the Li-O2 battery with MoN cathode are also investigated detailedly by DFT calculations, explaining the excellent catalytic properties of MoN at the atomic level. The present work provides intrinsic insights into designing high-performance cathode catalysts for Li-O2 batteries with fine-tuned morphology and electronic characteristics.