Impact of Structure and Defect Modification on Vanadium Oxide for Alkali-ion Battery Electrodes
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The proliferation of portable electronics and electric vehicles paired with the updating of an antiquated grid system has driven the rapid progression of improved technologies related to energy distribution and storage. However, energy storage materials and devices have come to be viewed as a crux impeding advanced device development. Alkali-ion, namely lithium and sodium, batteries are a robust technology that has seen gains in performance based on materials chemistry over the past several decades. Despite years of intensive research accompanied with significant progress, the cathode remains a limiting factor towards improved battery performance because of its low capacity and exasperated degradation over long term cycling; the cathode is also one of the most expensive material components of the overall cell. Thus, research concerning new cathode material development and the improvement of already well-established cathode materials should be a top priority. Within this context, vanadium oxide is an ideally suited model material showcasing how structural or chemical alterations can have tremendous impact on device performance. As a means towards improving electrochemical performance, the role of kinetics and thermodynamics were investigated through structural and defect chemistry manipulation in the vanadium oxide system. Structural modification, as a means towards achieving kinetic stabilization, can be utilized to develop electrodes with the chemical stability of microsized particles that simultaneously exploit the beneficial properties associated with nanoparticles. Defect modification is a powerful means towards improving material intercalation capabilities by reducing the stress and localized electrostatic contributions which directly alter the migration energy and diffusion barriers the alkali-ion must overcome. Lithium-ion was chosen for structural (kinetic) examination as it is a mature technology that has been extensively investigated; sodium-ion was chosen for defect manipulation because the larger size and different transport characteristics of sodium ions influence the thermodynamic (and to a lesser extent the kinetic properties) of sodium-ion batteries, and can lead to unexpected electrochemical behavior. The findings gained are by no means limited to the originally investigated systems, and should be taken into consideration for an assortment of electrode materials.