Fabrication and Characterization of Nanostructured Oxides for Energy Storage
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Materials for energy storage have become increasingly important in the modern world as alternatives to petrochemical energy sources. Although technology such as lithium-ion batteries and solid oxide fuel cells are in commercial use, improvements must still be made to increase widespread adoption. To this end, nanostructured materials have emerged as potentially impactful solutions, as they can greatly improve the performance of the energy storage device. One goal of this dissertation was to fabricate nanostructured materials through solution-based processing, electrospinning, and controlled annealing for lithium-ion battery electrodes. This project resulted in the formation of porous fibers from inexpensive, nontoxic materials that can be used as high capacity electrodes. Another component of this dissertation was to deposit thin film noble metals and metal oxides via sputtering for metal-air battery cathodes. The results from these experiments indicate that nanostructured thin films could have improved catalytic activity compared to polycrystalline bulk structures, and also were lower cost due to the decrease in material used. The other major portion of this dissertation was to study the fundamental behavior of nanostructured materials for energy storage at a localized level using electrochemical strain microscopy, a technique that is still in its infancy. The measured responses using electrochemical strain microscopy tended to be difficult to interpret, as they contained many different chemical and mechanical contributions. A series of experiments were devised to distinguish among the different mechanisms, comparing differing responses from Vegard strain, ferroelectric behavior, and electrostrictive effects. Given this framework, inhomogeneous lithium iron phosphate was characterized using electrochemical strain microscopy. From these results, it was found that nanocrystalline particles had higher lithium ion diffusivity as compared to microcrystalline particles, which correlates with macroscopic electrochemical performance. Furthermore, this technique could be applied to measure local lithium ion concentration in samples at different states of charge. Electrochemical strain microscopy was also applied to study samarium doped ceria, a solid oxide fuel cell electrolyte. In this case, the measured behavior was found to be due to the motion of small polarons, supporting the space-charge model of mixed ionic and electronic conductivity in nanostructured electrolytes. Electrochemical strain microscopy was found to be a strong and versatile technique that can fundamentally characterize local behavior of ions, vacancies, electrons, and holes in an energy storage material, and can guide future research in this area.
- Mechanical engineering