Transition metal sulfides and energy application in lithium ion battery

• Main Author: Song, Yang
• Other Authors: Alex Yan Qingyu
• Format: Final Year Project
• Language: English
• Published: 2015
• Subjects: DRNTU::Engineering::Materials
• Online Access: http://hdl.handle.net/10356/62526
• Institution: Nanyang Technological University

To meet the ever-increasing energy demands, lithium ion batteries (LIBs) has become one of the most promising energy storage devices for many consumer products, especially in portable electronics, and even for hybrid electric/plug in hybrid (HEV/PHEV) vehicles nowadays. Recently, transition metal sulfides with tailored nanostructures have drawn much attention as anode materials for LIBs. This is because they have great potential to achieve better cycling performance, much higher specific capacity and excellent rate capability in comparison with conventional graphite material for next generation of LIBs in high power applications. In this Final Year Project, different nanostructures of transition metal sulfides such as MnS/C hollow sphere nanoparticles, FeS2/C nanosheets and FeS2/C sphere nanoparticles have been successfully synthesized by a thermal decomposition method. A series of reaction parameters have been tuned to investigate their effects on the phase and morphologies of the final products. After that, the electrochemical test was carried out using these transition metal sulfides and the results showed that their performance is highly dependent on the structures. In particular, their unique structures of nanosheets and hollow sphere nanoparticles have shown much improved performance compared to nanoparticles. The MnS/C hollow sphere nanoparticles showed that relatively high reversible capacity of 680mAh/g and excellent cycling performance during 100th cycle at current density 0.1Ag-1. Moreover, FeS2/C nanosheets demonstrated a much enhanced cycling performance and lithium storage capacity of 800mAh/g during 50th cycle at current density 0.1Ag-1 as compared with FeS2/C nanoparticles. The excellent Li ions storage performance and stable cyclibity are mainly attributed to the large surface area (e.g. nanosheets), better accommodation of large volumetric changes (e.g. hollow spheres), abundant accessible reaction sites between anode and electrolyte for charge storage, and shortened diffusion path of Li ions and electrons. In addition, the carbon layer generated during the annealing process also played an important role on the performance of these materials. It can not only provide excellent electrical conductivity, but also offer more active sites for the electrochemical reactions and prevent the dissolution of polysulfides in the electrolyte during the conversion reaction.