Porous MOx/MNx (M: Fe, Co, and Ni) Hybrid Nanosheet Arrays and their Application as a Sulfur Host in Lithium–Sulfur Batteries

Description

As the most successful electrochemical energy storage devices to date, lithium-ion batteries (LIBs) have substantially facilitated the advances of consumer electronic devices and revolutionized our lives in the past 30 years. Nowadays, the applications of energy storage devices are shifting to the ever-growing large-scale energy storage systems, such as passenger electric vehicles and smart stationary grids. Nonetheless, the energy densities of state-of-the-art LIBs based on the intercalation energy storage mechanism have reached their theoretical limitation, and thus, novel electrode materials with high energy density are required. As an emerging alternative, lithium–sulfur (LiS) batteries are considered one of the most promising next-generation batteries because of their high theoretical energy density, eco-friendliness, and low cost. However, the poor conductivity of sulfur and Li2S, high solubility and shuttling effect of lithium polysulfides (LiPSs), and sluggish interconversion kinetics of LiPSs to Li2S have severely impeded the practical applications of Li-S batteries.In the proposed project, we will synthesize hybrid nanosheets comprising MOx/MNx (M: Fe, Co, and Ni) heterojunctions on a carbon cloth (MOx/MNx@cc) by using microwave plasma-enhanced nitridation, and study their application as a sulfur host in Li-S batteries. This project is based on the following concepts. 1) The combined high polarity and catalytic activity of MOx/MNx heterostructures enable enhanced adsorption and conversion of LiPSs. 2) The plasma-enhanced nitridation allows control of the chemical composition and defects (e.g., oxygen and nitrogen vacancies) in the heterostructures, and defect engineering can further tune their adsorption and catalytic capability toward LiPSs. 3) The direct growth of hybrids on carbon cloth, as well as the networked structure and porous nature of nanosheets, are merited with high conductivity, enlarged surface area, and intimate contact with the electrolyte, which are favorable for improving the sulfur loading efficiency and rate performance. In the proposed project, a series of MOx/MNx heterostructures will be synthesized and the impacts of chemical composition, morphology, porosity, microstructure, and defect states on suppressing the shuttling effects of LiPSs will be systematically investigated and optimized to improve the energy density and cycling stability of Li-S batteries. Meanwhile, various in situ characterizations and theoretical simulations will be performed to identify the active sites/paths of MOx/MNx heterostructures for the immobilization and conversion of LiPSs. The implementation of the proposed project will provide further understanding of, and insight into, the design and development of new sulfur host materials for Li-S batteries.