Carbon based anode materials for lithium-ion batteries

A systematic investigation of carbon based anode materials has been made in this Master’s thesis project. The physical, structural and electrochemical properties of these anode materials have been characterized by a variety of techniques. A literature review summarizes the principles of lithium-ion battery operation, cathode materials, anode materials and electrolytes. Multiwall carbon nanotubes (MWNTs) were synthesized by chemical vapor deposition (CVD) method, using nanocrystalline iron powders as the catalyst. The diameter of the as-prepared MWNTs is about 20-50nm. Electrochemical testing shows that the MWNT electrodes had a reversible lithium storage capacity of 340-350mAh/g. The kinetics of Li-ion insertion in carbon nanotube electrodes were characterized by a.c. impedance measurements. The electrochemical properties of graphitized mesocarbon microbeads (MCMB) anode materials were studied. SEM observation shows that MCMB agglomerates have a spherical shape with an average particle size of 13?m. Cyclic voltammetry measurements demonstrated a pair of redox peaks, corresponding to lithium insertion and extraction in the MCMB structure. MCMB anodes delivered a reversible capacity of ~325mAh/g with good cyclability. In order to improve the capacity of bare graphite, Sn-coated graphite composites were prepared by using electroless deposition. Cyclic voltammograms show additional redox reaction peaks, which are related to the reaction of Sn with lithium. Sn-graphite composites demonstrated a much higher lithium storage capacity than the bare graphite electrode. Since MCMB anode materials are very stable for lithium-ion insertion and extraction, Sn-coated MCMB composites were developed by combining the high lithium storage, elemental Sn and MCMB to obtain stable cyclability. The Sn-MCMB electrodes show improved capacity and good cyclability within a 15wt% loading of Sn.