Abstract
Lithium-ion batteries have come a long way from its inception to widespread deployment in a multitude of applications ranging from micro electronic devices to large scale deployment. However, the story of this technology is far from ending as technology continues to improve and demand higher portable energy storage. Despite decades of research and development, the technology remains bogged down by high cost, insufficient energy storage capacity, and safety. Motivated by these issues, the work set out in this thesis strived to contribute incremental knowledge and understanding of materials that are able to move the technology forward. A systematic study of several novel conversion (MoO2 and CoS2) and alloy (SnS2 and SnSe2) based materials with intrinsic high lithium storage capacities was carried out. These materials were incorporated into carbonaceous materials such as CNTs and graphene through a rational design and synthesis process to obtain hierarchical nanostructured composites. The synthetic strategies proved to be successful where the composites exhibited enhanced electrochemical properties with high capacities (up to 1000 mAh g-1), high rate capability (up to 5 A g-1), and long life time (up to 3000 cycles). Detailed electrochemical and physical characterizations were carried out to uncover the underlying causes to the improved lithium storage properties. Regarding battery safety, thermoresponsive Polyethylene was developed to act as an in situ cell shut down mechanism. At high temperatures, the polymer melts to form an insulating film that prevents further flow of Li-ions. Optimisation and improvements were made through the incorporation of thermally and electrically conductive CNTs as well as deposition of the additive via 3D printing methods. Rapid cell shutdown was achieved using only 1mg cm-2 of the additive.