Thesis (Ph. D.)--University of Rhode Island, 2005. / Typescript. Includes bibliographical references (leaves 74-76).

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Graduation date: 1995

Thesis (Ph. D.)--State University of New York at Binghamton, Materials Science and Engineering Program, 2009. / Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 161-171). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 281-283).

Not available / text

Lithium ion batteries, due to their relatively high energy density, are now widely used as the power source for portable electronics. Commercial lithium ion cells currently employ layered LiCoO₂ as a cathode but only 50% of its theoretical capacity can be utilized. The factors that cause the limitation are not fully established in the literature. With this perspective, prompt gamma-ray activation analysis (PGAA) has been employed to determine the hydrogen content in various oxide cathodes that have undergone chemical extraction of lithium (delithiation). The PGAA data is complemented by data obtained from atomic absorption spectroscopy (AAS), redox titration, thermogravimetric analysis (TGA), and mass spectroscopy to better understand the capacity limitations and failure mechanisms of lithium ion battery cathodes. As part of this work, the PGAA facility has been redesigned and reconstructed. The neutron and gamma-ray backgrounds have been reduced by more than an order of magnitude. Detection limits for elements have also been improved. Special attention was given to the experimental setup including potential sources of error and system calibration for the detection of hydrogen. Spectral interference with hydrogen arising from cobalt was identified and corrected for. Limits of detection as a function of cobalt mass present in a given sample are also discussed. The data indicates that while delithiated layered Li[subscript 1-x]CoO₂, Li[subscript 1-x]Ni[subscript 1/3]Mn[subscript 1/3]Co[subscript 1/3]O₂, and Li[subscript 1-x]Ni[subscript 0.5]Mn[subscript 0.5]O₂ take significant amounts of hydrogen into the lattice during deep extraction, orthorhombic Li[subscript 1-x]MnO₂, spinel Li[subscript 1-x]Mn₂O₄, and olivine Li[subscript 1-x]FePO₄ do not. Layered LiCoO₂, LiNi[subscript 0.5]Mn[subscript 0.5]O₂, and LiNi[subscript 1/3]Mn[subscript 1/3]Co[subscript 1/3]O₂ have been further analyzed to assess their relative chemical instabilities while undergoing stepped chemical delithiation. Each system takes increasing amounts of protons at lower lithium contents. The differences are attributed to the relative chemical instabilities of the various cathodes that could be related to the position of the transition metal band and the top of the O²-:2p band. Chemically delithiated layered Li[Li[subscript 0.17]Mn[subscript 0.33]Co[subscript0.5-y]Ni[subscript y]]O₂ cathodes have also been characterized. The first charge and discharge capacities decrease with increasing nickel content. The decrease in the capacity with increasing nickel content is due to a decrease in the lithium content present in the transition metal layer and a consequent decrease in the amount of oxygen irreversibly lost during the first charge. / text

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.