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Title: Chemical investigations of spinel lithium manganese oxides
Author: Albadran, J.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2004
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In this work, a preparation method has been developed to obtain a pure, single-phase, and high surface area spinel LiMn2O4. Characterisation of the product confirmed that it is a thermally stable, single-phase spinel LiMn2O4 with surface area of 7.6 m2 g-1. The relatively high surface area found for samples prepared during the course of this study indicates a positive step when compared with those prepared using other techniques. Another member of the spinel family, l-MnO2, has been prepared by the topotactic extraction of lithium from the previously prepared LiMn2O4. The spinel l-MnO2 has further chemically reduced to yield the oxide hydroxide form of manganese. The manganese oxide hydroxide obtained above has not been reported before and has been designated l-MnOOH to indicate the relationship to its precursor oxide. Both manganese oxides were thoroughly characterised using various analysis techniques. Surface area measurements of the oxides gave 6.3 and 11.2 m2 g-1 for l-MnO2 and l-MnOOH respectively. Kinetic investigation of the oxidation of normal spinel LiMn2O4 by chemical extraction of Li+ revealed that the extraction process is diffusion-controlled with a diffusion coefficient of 2.01 x 10-9 cm2 s-1 and activation energy of 22.2 - 28.2 kJ mol-1. It was found that due to the low activation energy of reaction, Li+ is the only diffusing cation in the system and the process is taking place using the lattice’s tetrahedral interstitial sites. The reversibility of the extraction of lithium from LiMn2O4 in aqueous solutions was investigated. It has been found that it is possible to re-introduce lithium ions into the Mn2O4 framework only if Mn2+ is present in the solution. It was confirmed by X-ray diffraction that the result of the insertion reaction is the spinel LiMn2O4. Other members of the Li-Mn-O system were investigated. Various oxide members were obtained by varying the Li:Mn ratio of the reactants. Some oxide members were successfully synthesised by mixing stoichiometric amounts of Li2CO3 and Mn2O3. A method to prepare the electrochemically active LiMnO2 was proposed. The oxide was positively identified as orthorhombic LiMnO2 with unit cell dimensions a = 2.790 Å, b = 5.614 Å and c = 4.564 Å. Other oxide members were prepared and characterised by means of X-ray diffraction and thermal analysis techniques.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available