Highly Isolated Cobalt Sulfide Nanoparticles Encapsulated in 3D Hollow Nitrogen Doped Carbon Sheells for Superior Lithium and Sodium Storage

Abstract

Highly Isolated Cobalt Sulfide Nanoparticles Encapsulated in 3D Hollow Nitrogen Doped Carbon Sheells for Superior Lithium and Sodium StorageWei Huang, a, b Huihui Shangguan, b Christian Engelbrekt, a Xiaowen Zheng, b Fei Shen, a Xinxin Xiao, a Lijie Ci, b Pengchao Si b, * and Jingdong Zhang a, * a Department of Chemistry, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark. b SDU & Rice Joint Center for Carbon Nanomaterials, Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials, Ministry of Education, School of Materials Science and Engineering, Shandong University, Jinan 250061, P. R. China.Hollow materials derived from metal-organic frameworks (MOFs) present a class of promising electrode materials for energy storage technology. Herein, we report the design and nanoengineering of highly isolated cobalt sulfide nanoparticles embedded in hollow nitrogen-doped carbon shells (Co9S8/HNCS) for superior lithium and sodium storage. Initially, hollow intermediates with preserved cobalt component were prepared by simultaneously dissociating cobalt containing zeolitic-imidazolate-frameworks-67 (ZIF-67), and polymerizing dopamine in a Tris-HCl solution (pH = 8.5). The poly-dopamine (PDA) wrapped intermediates inherited the polyhedron structure of the ZIF-67 crystals. The final Co9S8/HNCS composite was obtained via a combined carbonization and sulfurization treatment of the intermediates, allowing the formation of hollow polyhedrons of nitrogen-doped carbon layers (900 ± 100 nm) derived from PDA and the encapsulation of highly monodispersed cobalt sulfide nanoparticles (11 ± 2 nm). This configuration not only shortened the ionic diffusion distance, and accommodated volume expansion during lithium or sodium ion insertion/extraction, but also promoted the overall electronic conductivity, and provided more active sites during cycling. As a result, Co9S8/HNCS composite exhibited an impressive reversible capacity of 755 mA h g-1 at 500 mA g-1 after 200 cycles for lithium ion storage, and capacities of 327 mA h g-1 at 500 mA g-1 after 200 cycles and 224 mA h g-1 at 1000 mA g-1 after 300 cycles for sodium ion storage. Essential factors associated with the structural stability and changes during cycling have been identified and the discharge/charge mechanism has been discussed. Figure 1