Date of Award
Doctor of Philosophy (PhD)
Creager , Stephen E
Bruce , David A
Pennington , William T
The chemistry demonstrated in this dissertation is concerned with the synthesis, structure, properties and applications of inorganic solids containing iron(II,II) redox centers. The endeavor in exploratory synthesis is due largely to the employment of molten salt fluxes such as alkali metal chloride. These halide-fluxes act in two parts; 1) as a solvent to lower the reaction temperature and 2) as an in situ source of unavailable alkali oxides through metathesis reactions. Using these halide fluxes has allowed for the discovery of several new transition metal-containing phosphates, arsenates, and vanadates for a structure/property correlation study. From this study the selected compounds were evaluated for their usefulness in ion-exchange and battery applications.
These iron(II,III) phosphates, arsenates, and vanadates with interesting structural frameworks and physical properties have been prepared by exploratory synthesis. Crystal growth was achievable by high-temperature, solid-state reaction in molten-salt media. Characterization was done by single crystal and powder X-ray diffraction, electron microscopy, thermal gravimetric analysis, UV-Vis diffuse reflectance, magnetic susceptibility measurements, IR, inductively coupled plasma optical emission spectroscopy, X-ray photoelectron spectroscopy, neutron diffraction, and electrochemical (battery cell) testing.
In this dissertation, research into several different ion-exchange/insertion characteristics will be discussed by newly discovered iron (II,II)-containing solids. Two new oxyanion-based iron oxides, Cs4.65K4.35Fe7(PO4)10 and A2Fe3(XO4)3; A = Na or K/Na, X = P, As, have shown interesting frameworks for ion-exchange. These compounds demonstrate how the larger the A-site cation, the more Li+ cations can be exchanged into the system owing to the weak A-O bonding. Two other compounds, A3Fe3(XO4)4 and KFe3(AsO4)3; A/X = Cs,K/As, Na/P, are showing the ability to perform concomitant Li+-exchange/redox insertion. This once again demonstrates the effectiveness of the large cations 'templating' large openings, which can allow for additional Li+ cations to be inserted into the structure. Several other new compounds are discussed for their potential applications as electrode materials.
The study of high voltage primary lithium batteries is also investigated. Our idea is to synthesize compounds that contain two high reduction potential transition metals, Ag and Fe, with respect to their choice of oxyanions (polyanions). We also attempt to use the inductive effect of the polyanion to further increase the reduction potential of the Fe3+/Fe2+ couple. Four new compounds, Ag3Fe(VO4)2, AgFeV2O7, Ag4Fe5O2(PO4)5, and Ag3Fe3(PO4)4, were studied for their electrochemical properties, with initial voltages above 3 V. There have also been several new silver iron(III) phosphates that have been synthesized for a systematic study of their structure and electrochemical behavior.
Our study of structure/property correlations should offer insight and a better understanding of battery materials and applications. These findings should lead to a further development of these materials and the future directions of materials discovery for the applications of next generation battery devices.
Becht, Gregory, "EXPLORATORY SYNTHESIS OF NEW OPEN-FRAMEWORK IRON (II,III)-CONTAINING POLYANION SYSTEMS TARGETED FOR LITHIUM-ION BATTERY APPLICATIONS" (2008). All Dissertations. 262.