| Lithium-ion batteries, introduced in the early 1990s, powered the explosion of personal electronic devices, such as cell phones, laptops and digital cameras. This success spawned a global research initiative to adapt this technology to more demanding applications, such as low-temperature systems or those relying on pulse-power. The electrodes of these batteries store charge by reversibly intercalating Li-ions. The facile insertion flux of Li-ions into the electrode and sluggish solid-state diffusion from surface to non-surface intercalation sites causes a polarization of charge. Therefore, under demanding conditions, the electrode discharges without fully accessing all charge-storage sites.; The electrode used in these studies is created by template-synthesis . Template-synthesis is a general nanofabrication method capable of creating structures of known geometry. Nanomaterial-based electrodes mitigate the rate-limiting effects of sluggish electron-kinetics and mass-transport. The large surface-area of this design serves to distribute the current density improving electron-kinetics, while the small size ensures that intercalation sites reside close to the surface, minimizing the distance Li-ions must solid-state diffuse.; The intent of this dissertation is to highlight the success of nanomaterials in the study of energy-storage systems. It begins with a discussion of the low-temperature performance of Li-ion battery electrodes. These charge-storage characteristics and reproducible electrode geometries identify the fundamental breakdown of Li-ion batteries at low-temperature as the decrease in solid-state diffusion coefficient of the Li-ion (DLi +). This study then quantifies the value of DLi + as a function of both intercalation-level and temperature. Next, it describes a variation of the previous template-synthesis method, in which the polymer template is pyrolyzed to create a LiFePO4/carbon composite electrode. This composite improves upon the poor electron-conductivity of the otherwise attractive LiFePO4 cathode. Finally, preliminary results from polyvalent-ion (Mg2+) intercalation into the V 2O5 electrode are presented. Polyvalent-ions allow for more charge to be stored than is stoichiometrically possible by singly charged ions.; The advantage of incorporating nanomaterials into the design of energy-storage devices is the recurring theme of this document. While the studies are approached from a fundamental view, conclusions such as those reported here will undoubtedly have profound commercial impact on the increasingly portable world. |
