Transmission Electron Microscopy Investigation of Ion Intercalation in Vanadium Pentoxide Polymorphs

Ever increasing demands for batteries with higher energy densities, faster cycling times, as well as safer and more economical options have motivated scientists to explore better cathodes for existing Lithium ion (Li-ion) batteries, as well as develop alternative battery technologies. Among possible alternative technologies, Magnesium (Mg) ion based multivalent batteries are an exciting prospect. However, one of the primary challenges in the field is the complicated nature of intercalation reactions into oxide cathodes, such as V2O5. There is a lack of systematic characterization work, especially in the field of Mg-ion batteries that can determine phase evolution upon intercalation and reveal intercalation sites directly. In my thesis, I examine Li-ion and Mg-ion intercalation into two different V2O5 polymorphs using in situ TEM, aberration-corrected scanning transmission electron microscopy (STEM) imaging, electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDX) that can directly capture structural changes induced by ionic intercalation process. To elucidate the diverse nature of electrochemical reactions into oxide cathodes, the case of calcium (Ca) ion insertion into α-MnO2 cathode host will also be briefly discussed. Finally, I will highlight the significance of implementing in-situ, multimodal studies in a liquid environment inside the TEM to learn more about some of the overarching scientific challenges going forward, such as the formation and evolution of the solid-electrolyte interphase (SEI) in case of Mg-ion batteries.