Lithium ion batteries have been successful in portable electronics market due to their high energy density, adopting the layered LiCoO₂ as the cathode material in commercial lithium ion cells. However, increasing interest in lithium ion batteries for electric vehicle and hybrid electric vehicle applications requires alternative cathode materials due to the high cost, toxicity, and limited power capability of the layered LiCoO₂ cathode. In this regard, spinel LiMn₂O₄ has become appealing as manganese is inexpensive and environmentally benign, but LiMn₂O₄ is plagued by severe capacity fade at elevated temperatures. This dissertation explores the factors that control and limit the electrochemical performance of spinel LiMn₂O₄ cathodes and focuses on improving the performance parameters such as the capacity, cyclability, and rate capability of various spinel cathodes derived from LiMn₂O₄. From a systematic investigation of a number of cationic and anionic (fluorine) substituted spinel oxide compositions, the improvements in electrochemical properties and performances are found to be due to the reduced manganese dissolution and suppressed lattice parameter difference between the two cubic phases formed during the charge-discharge process. Investigations focused on fluorine substitution reveal that spinel LiMn[subscript 2-yz]LiyZnzO[subscript 4-eta]F[subscript eta] oxyfluoride cathodes synthesized by solid-state reactions at 800 °C employing ZnF₂ as a raw material and spinel LiMn[subscript 2-y-z]Li[subscript y]Ni[subscript z]O[subscript 4-eta]F[subscript eta] oxyfluoride cathodes synthesized by firing the cation-substituted LiMn[subscript 2-y-z]LiyNi[subscript z]O₄ oxides with NH₄HF₂ at a moderate temperature of 450 °C show superior cyclability, increased capacity, reduced Mn dissolution, and excellent storage performance compared to the corresponding oxide analogs and the conventional LiMn₂O₄. Spinel-layered composite cathodes are found to exhibit better electrochemical performance with graphite anode when charged to 4.7 V in the first cycle followed by cycling at 4.3-3.5 V compared to the normal cycling at 4.3 - 3.5 V. The improved performance is explained to be due to the trapping of trace amounts of protons that may be present in the electrolyte within the layered oxide lattice during the first charge to 4.7 V and the consequent reduction in Mn dissolution. Electrochemical performances of 3 V spinel Li₄Mn₅O₁₂ cathodes are also improved by fluorine substitution due to the suppression of the disproportionation of Li4Mn5O12 during synthesis and the formation of the Li₂MnO₃ phase.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Quantitative multielemental analysis using Particle Induced X-ray Emission (PIXE) using 1 and 2 MeV proton bombardment on thin targets has been achieved. The method is based on the calculation of atomic ratios from experimentally determined relative x-ray efficiency curves. Sample preparation techniques involving digestion and homogenous deposition of samples and standards with a minimum of contamination have been investigated. The accuracy of the method has been evaluated using five standard reference materials obtained from the National Bureau of Standards. The elimination of bremsstrahlung associated with the charging effect of non-conducting samples in PIXE analysis has been accomplished using thin carbon foils in the beam path. Applications of the PIXE technique to studies on deep-sea ferromanganese nodules were performed. The utility of PIXE in the analysis of noduoles and in the following of the distribution of a large number of elements through the various stages of a processing scheme were demonstrated.

No description available.

Annual application of N at rates of 118 (118N), 236 (236N), and 354 (354N) kg•ha⁻¹ on 35 year old 'Western Schley' pecan trees during four years had little effect on mineral composition and foliar N. No differences in yield, nut quality, and reproductive characteristics were found. Alternate bearing intensity in four consecutive years was 37, 33 and 28% in 118N, 236N, and 354N, respectively, with a significant linear response. Rates from 118 to 236 kg N•ha⁻¹ satisfy N needs for pecan in irrigated pecan orchard of the southwest of United States. The effect of one-time banding of zinc sulfate (74 kg Zn•ha⁻¹) and zinc-EDTA (19 kg Zn•ha⁻¹) was evaluated over a period of four years on ‘Wichita’ pecans growing in alkaline soil. Significant differences in foliar Zn levels were found one month after application of Zinc-EDTA. Differences also were noted during the next three years on approximately 25% of the sampling dates. Yield, leaflet area, and trunk cross sectional area were not affected. Zinc-EDTA increased Zn uptake by 'Wichita' pecan trees in alkaline conditions during three years. A field study indicated that manure or manure plus Zn increased foliar Zn levels in pecans after two years of annual applications. Manure (24 ton ha⁻¹) plus zinc sulfate (258 kg Zn•ha⁻¹ as zinc sulfate) treatment had the highest foliar Zn levels. No differences were observed in trunk growth, leaf area, leaf weight, nut filling, and yield. Manganese toxicity symptoms are exhibited when leaf Mn levels are higher than 1700 μg•g⁻¹ during the standard date sampling of July and affected reproductive characteristics and leaf and shoot growth. More severe visible symptoms include delayed budbreak and die-back of young shoots. In potted pecan trees, zinc EDTA treated trees had a foliar Zn of 244 μg•g⁻¹, in foliar sprayed trees (eight foliar sprays of a combination of zinc sulfate and UAN32) had 140 μg•g⁻¹, and in control trees had 33 μg•g⁻¹. Soil adsorption isotherms showed that of the three fertilizers evaluated Zn sulfate was adsorbed most strongly by the soil (1.5 mg Zn•g⁻¹ of soil). Soil adsorption from Zn EDTA solutions was insignificant.

No description available.

No description available.

No description available.

This thesis provides a detailed evaluation of different environmentally friendly dispersants in invert-emulsion drilling fluids that can be used to drill wells under difficult conditions such as HPHT. The drilling fluid is weighted by manganese tetraoxide (Mn3O4) particles, which have a specific gravity of 4.8 and a mean particle diameter of ca1 micrometers. Manganese tetraoxide has different wetting properties and surface chemistry than other weighting agents. Hence, there is a need to find dispersants for manganese tetraoxide that give reduced sag, reduced rheology, and low fluid-loss at HPHT conditions. This is particularly important for deep wells with narrow operating windows between pore-pressure and fracture pressure gradients. The stricter global environmental regulations mandated the dispersants to be environmentally friendly, e.g. within OCNS group D or E. First, oil compatibility tests and particle settling time experiments were conducted on 31 dispersants. From the experiments, we identified 3 oil-compatible dispersants that gave the longest settling time in base oil and belonged to OCNS group D. We investigated the effectiveness of selected chemicals in dispersing manganese tetraoxide at HPHT conditions. 1.95 and 2.4 S.G. drilling fluid samples were first prepared and tested without any contaminant and then in the presence of rev dust and cement as contaminants. Drilling fluid samples were statically aged at 400 degrees F and 500 psi for 16 hours. Sag and rheological measurements were taken before and after aging to determine the effect of HPHT conditions on fluid properties. Then, HPHT dynamic filtration tests were done at 500 psi differential pressure and 300 degrees F to determine HPHT dynamic fluid-loss. We have found that one of the dispersants (nonionic) gives low rheology and reduced sag before and after static aging. It also gives the lowest fluid-loss of the selected dispersants. For 2.4 S.G. fluid without contaminants, 10-minute gel strength was reduced from 50 to 32 lb/100 ft^2, plastic viscosity from 37 to 25 cp, sag from 0.249 to 0.135 lbm/gal, and fluid-loss was reduced from 44.4 to 39.6 cm^3 with the addition of dispersant. This dispersant prevents agglomeration of particles, thereby reducing fluid rheology, sag, and fluid-loss.