| Description |
Lithium batteries are widely used in consumer electronic products, including laptop computers, cellular phones, cameras, camcorders, and medical devices. Applications in electric and hybrid electric vehicles have been steadily increasing in the past few years by virtue of their high energy and power density. Research and development in this area have attracted the interests of researchers all around the world. One of the major challenges is the safety issue related to liquid electrolytes. Polymer-based ion conducting materials have been of great interest to researchers in the field of lithium batteries in the past decades. The use of solid polymer electrolytes (SPEs), such as the polyethylene oxide (PEO)-based SPE, instead of the conventional liquid or gel electrolyte, can significantly improve the safety aspects of lithium batteries. However, existing PEO-based solid electrolytes do not meet functional performance requirements, especially at ambient temperature. The ionic conductivity is low, since PEO exists in crystalline form at low temperatures, which restricts the lithium ion mobility. Further, the cycling evaluation of batteries assembled with such solid polymer electrolytes does not show good performance when batteries are charged/discharged at relatively high current densities. In this thesis, four different clay-mineral-based SPEs were prepared using the solvent casting technique to achieve improved electrolyte systems for lithium batteries. Among all the clay minerals, halloysite nanotubes (HNTs) generated the optimal properties. iv HNT-based SPEs (HNT/SPEs) were further tested and modified. The ambient temperature ionic conductivity observed at room temperature was noteworthy (1.52×10-4 S·cm-1) due to the decrease of the glass transition temperature of the polymer. The cycling performances of HNT/SPEs for lithium-sulfur batteries show that the battery systems demonstrate extraordinary stability and long cycle life at 25°C and 0.1 C and at 100 °C and 2 C (1C= 1672 mA·g-1). Finally, the HNT/SPE was further modified to form a new electrolyte system (HNT-LFP/SPE) and effectiveness demonstrated for the lithium iron phosphate batteries. The lithium iron phosphate battery systems display stable cycling performance at room temperature in the C-rate range of 0.1~0.5 C and at 60 °C and 1 C (1C= 172 mA·g-1). |
