‘Breathing-Crystals’ The Origin of Electrochemical Activity of Mesoporous Li-MnO2

Akin to Le Chatalier’s principle, we show that a mesoporous material can mitigate the effect of stress by expanding or contracting elastically into the pore space; we simulate this ‘breathing-crystal’ phenomenon using MD simulation. In particular, our simulations reveal that mesoporous Li-MnO2 is electrochemically active because the stress, associated with charge cycling, does not influence the structure or dimensions of the (unlithiated) 1x1 tunnels in which the lithium ions intercalate and reside. Conversely, the parent bulk material suffers structural collapse and blockage of the 1x1 tunnels under stress. The mechanism associated with Li deintercalation is presented together with the activation energy barriers, which are calculated to be 0.4eV - irrespective of whether the mesoporous host is un-strained or under considerable (1.6 GPa) tensile or compressive stress

Synthesis and applications of porous non-silica metal oxide submicrospheres

© 2016 Royal Society of Chemistry. Nowadays the development of submicroscale products of specific size and morphology that feature a high surface area to volume ratio, well-developed and accessible porosity for adsorbates and reactants, and are non-toxic, biocompatible, thermally stable and suitable as synergetic supports for precious metal catalysts is of great importance for many advanced applications. Complex porous non-silica metal oxide submicrospheres constitute an important class of materials that fulfill all these qualities and in addition, they are relatively easy to synthesize. This review presents a comprehensive appraisal of the methods used for the synthesis of a wide range of porous non-silica metal oxide particles of spherical morphology such as porous solid spheres, core-shell and yolk-shell particles as well as single-shell and multi-shell particles. In particular, hydrothermal and low temperature solution precipitation methods, which both include various structure developing strategies such as hard templating, soft templating, hydrolysis, or those taking advantage of Ostwald ripening and the Kirkendall effect, are reviewed. In addition, a critical assessment of the effects of different experimental parameters such as reaction time, reaction temperature, calcination, pH and the type of reactants and solvents on the structure of the final products is presented. Finally, the practical usefulness of complex porous non-silica metal oxide submicrospheres in sensing, catalysis, biomedical, environmental and energy-related applications is presented

Impact of Structure and Defect Modification on Vanadium Oxide for Alkali-ion Battery Electrodes

Thesis (Ph.D.)--University of Washington, 2015The 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

Training Care Partners in the Re-Motivation Process for Individuals Living with moderate Dementia: A Single Subject Design

This research study aims to contribute to the field of occupational therapy through a focus on understanding an intervention focused on increasing volition to promote re-engagement in meaningful occupations for community dwelling individuals living with dementia. Dementia may contribute to a lack of motivation for engaging in goal directed tasks and meaningful occupations in people living with dementia; Professionals and care partners identify motivating loved ones with dementia to engage in daily occupations as a challenge. One proven approach found to be beneficial to stave off premature decline and maintain the individual’s performance of activities of daily living is use of occupational therapy interventions. The research seeks to amplify the understanding of the use of the Remotivation Process and Volitional Questionnaire, specifically, to educate care partners in the use of this intervention for individuals with dementia as a way to motivate the individual to engage in occupations once more

Elucidating the Role of Defects for Electrochemical Intercalation in Sodium Vanadium Oxide

Na_{1.25+<i>x</i>}V₃O₈ (with <i>x</i> < 0, = 0, and > 0) was synthesized via a wet chemical route involving the reduction of V₂O₅ in oxalic acid and NaNO₃ followed by calcination. It was possible to control the sodium composition in the final product by adjusting the amount of sodium precursor added during synthesis. It was revealed that deficient and excessive sodium contents, with respect to the ideal stoichiometry, are accommodated or compensated by the respective generation of oxygen vacancies and partial transition metal reduction, or cation disordering. When examined as NIB electrode material, the superior performance of the cation disordered material with excessive sodium was clearly demonstrated, with more than 50% higher storage capacity and superior rate capacity and cyclic stability. The formation of oxygen vacancies initially seemed promising but was coupled with stability issues and capacity fading upon further cycling. The disparity in electrochemical performance was attributed to variations in the electronic distribution as promoted through Na–ion interactions and the direct influence of such on the oxygen framework (sublattice); these factors were determined to have significant impact on the migration energy and diffusion barriers

Surface engineering and design strategy for surface-amorphized TiO 2 @graphene hybrids for high power Li-Ion battery electrodes

Electrode materials with battery-like high capacity and capacitorlike rate performance are highly desirable, since they would signifi cantly advance next-generation energy storage technology. [ 1 ] TiO 2 has received increasing attention as an anode material for lithium-ion batteries (LIBs) due to its good reversible capacity and low volume expansion upon lithiation, as well as its low cost and safe lithiation potential. [ 2 ] The low lithium-ion mobility within the crystalline phase TiO 2 , however, together with its poor electrical conductivity, means that only a thin surface layer of the host material is available for Li intercalation at high rates. [ 3 ] These issues are still challenges that hinder the electrochemical performance of this material

Polyol-Mediated Solvothermal Synthesis and Electrochemical Performance of Nanostructured V₂O₅ Hollow Microspheres

Hollow vanadyl glycolate nanostructured microspheres were synthesized via a highly scalable and template-free polyol-induced solvothermal process. Subsequent calcination transformed the precursor material into vanadium pentoxide, a well-studied transition metal oxide. The vanadyl glycolate nanoparticles were synthesized through a self-seeding process and then aggregated around N₂ microbubbles formed during the reaction that acted as “quasi-micelles” due to the large polarization discrepancy between nitrogen and water. The proposed formation mechanism provides a firm understanding of the processes leading to the observed hollow microsphere morphology. The thermally treated material was tested as a cathode for lithium-ion battery and showed excellent cycle stability and high rate performance. The exceptional electrochemical performance was attributed to the relatively thin-walled structure that ensured fast phase penetration between the electrolyte and active material and shortened lithium-ion migration distance. The prolonged cycling stability is ascribed to the inherent morphological void that can readily accommodate volume expansion and contraction upon cycling