Solid Oxide Ionic Materials For Electrochemical Energy Conversion And Storage
Ruth, Ashley Lidie
Wachsman, Eric D
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Solid state ionic materials can be utilized in components of both solid oxide fuel cells and lithium ion batteries. Solid oxide fuel cells (SOFCs) are devices used to convert chemical energy into useful electrical energy. The higher temperatures required to effectively conduct oxygen vacancies is a material limitation that prevents the implementation of this technology in today's society. Our group has developed the novel incorporation of a bilayer electrolyte utilizing the high conductivity properties of the cubic fluorite bismuth oxide material in the low temperature regime at 650 °C and below. This phase is stabilized by single and double doping of Er, Dy-W, Dy-Ce, and Dy-Gd chemistries in this study. Conductivity measurements through electrochemical impedance spectroscopy champion (Bi0.88Dy0.08Gd0.04)2O3 as the most suitable electrolyte for future testing in SOFCs. Using the bilayer system in button type cells, the layer thickness ratio is optimized for highest open circuit voltage. Using neutron diffraction was used to better understand the activation energy change in conductivity in DWSB due to phase transformation that masked oxygen ordering at lower temperatures. Stabilized bismuth oxides are incorporated into a suitable composite cathode via an in-situ nano-scale mixing with La0.8Sr0.2MnO3-δ, improving the oxygen reduction reaction kinetics. Utilizing lessons from ceramic materials synthesis in SOFCs, cathode materials for Li-ion batteries were synthesized. In previous work, LixMn2O4-yClz spinel demonstrated enhanced charge potential and discharge potential while maintaining reversibility. However the original method for synthesis was extremely cumbersome. Using the simple glycine-nitrate reaction, we could fabricate an operating button cell starting from raw powders in less than 8 hours. X-ray diffraction and x-ray fluorescence confirm spinel structure and maintenance of chlorine through ignition respectively. In demonstrating favorable charge/discharge performance and cyclability, we considered the benefits of B-site doping of the spinel. For the first time LixMn2-wFewO4-yClz was also easily synthesized and tested for more than 250 charge-discharge cycles with 98% capacity retention. Similarly, Ni is introduced to the LixMn2O4-yClz spinel in order to take advantage of the intrinsic redox couple of Ni2+/Ni4+ at 4.7V and demonstrate reversibility from 5.0 V to 2.0 V.