Large specific gravimetric/volumetric energy density, environmental benignity and safe low working voltage. All of these points have been used to describe the lithium sulfur (Li-S) battery in the past, but often times it is short cycle life and poor capacity retention that is associated with the Li-S battery. In order to realize the full potential of the Li-S battery in society today, many obstacles must be overcome. In a typical Li-S cell with an organic liquid electrolyte sulfur is reduced by lithium during discharge and subsequent lithium polysulfide species (Li2Sx where x, 2 < x < 8) are formed. These species are readily soluble in typical organic electrolytes and can lead to low Coulombic efficiency and most challenging: active mass loss. Through the loss of active mass, rapid capacity fading occurs over long-term cell cycling. Overcoming the loss of active mass and stabilizing cell capacity at high rates is pivotal to the realization of practical Li-S cells. In this thesis, four separate concepts and materials were studied and prepared with the aim to improve the Li-S batteries capacity, cycle life and capacity retention.

Thesis (doctoral)--Universität Heidelberg, 1912. / Includes bibliographical references (p. [vii]-viii).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 112-113). Also available via the Internet.

Thesis (doctoral)--Friedrich-Alexander-Universität zu Erlangen.

Thesis (M.Sc.)--City University of Hong Kong, 2004. / At head of title: City University of Hong Kong, Department of Physics and Materials Science, Master of Science in materials engineering & nanotechnology dissertation. Title from title screen (viewed on Sept. 4, 2006) Includes bibliographical references.

This thesis describes an investigation of some of the factors which govern the operation of the commercially important Li-SOCl2 cell. Electrode processes at lithium anodes and C-SOCl2 cathodes have been studied using the technique of Faradaic impedance. A kinetic interpretation of the results has been advanced. Additionally some aspects of the formation and nature of LiCl films, which frequently cover the anode surface have been revealed from the decomposition of the numerical data. The impedance study further yielded kinetic data relating to the lithium dissolution process. Complementary preliminary studies of the impedance of glassy carbon-SOCl2 cathodes have shown that the cathode process is complicated.

Increasing energy demands world-wide must be met with more effective systems to produce, store, and distribute energy. Ideally, these systems should avoid fossil fuels and incorporate renewable technologies. To accommodate for the intermittent nature of renewable energies, a rechargeable gallium-air flow battery system for electrical grid applications is suggested. Using liquid gallium-air flow batteries could meet the rigorous world-wide demands for storage capacity, discharge duration, and durability necessary for the electrical grid. Toward this goal, a batch gallium-air battery was build and investigated. The performance of the system has been incrementally improved to a 30 hour discharge duration. Some insights into the mechanism of the gallium-air reaction was also obtained. However, recharging experiments were mostly unsuccessful. Despite the failures caused by carbonation and the separator drying, the Ga-Air system remains promising.

Increasing energy demands world-wide must be met with more effective systems to produce, store, and distribute energy. Ideally, these systems should avoid fossil fuels and incorporate renewable technologies. To accommodate for the intermittent nature of renewable energies, a rechargeable gallium-air flow battery system for electrical grid applications is suggested. Using liquid gallium-air flow batteries could meet the rigorous world-wide demands for storage capacity, discharge duration, and durability necessary for the electrical grid. Toward this goal, a batch gallium-air battery was build and investigated. The performance of the system has been incrementally improved to a 30 hour discharge duration. Some insights into the mechanism of the gallium-air reaction was also obtained. However, recharging experiments were mostly unsuccessful. Despite the failures caused by carbonation and the separator drying, the Ga-Air system remains promising.

The effect of elevated temperatures on the phase transformation mechanisms in electrodes for lithium-ion batteries (LIBs) is an important but – to date – only less studied subject in battery research. In real-life applications, LIBs usually function at non-ambient conditions and especially increased temperatures give rise to safety concerns. This thesis focuses to gain deeper insights into the phase transformations at high temperatures (HTs) by tackling both the challenging hardware development of a HT in situ synchrotron X-ray diffraction (XRD) battery testing system as well as its application to study two important cathode materials: LiFePO4 and V6O13. This allows unprecedented insights into the structural changes and its influence on electrochemical performance at variable temperatures (VTs). LiFePO4 was investigated for various battery cycling rates and temperatures. Electrochemical cycling of LiFePO4 in the newly designed in situ XRD setup proved that the in situ XRD cells work from low to high cycling rates between 25 to 150oC. The current induced non-equilibrium solid solution metastable LiFePO4 phase, present at room temperature during high rate cycling, was found to be less pronounced at temperatures above 125oC. This is possibly due to faster Li-ion diffusion at HT, leading to faster phase separations in the solid solution phases. In a next step, V6O13, a promising cathode material for HT applications, especially for oil field applications, was tested using the in situ HT XRD setup. The material exhibits a very high capacity with a complex voltage profile. The underlying asymmetric discharge and charge phase transition mechanisms, which include a six-step discharge and five-step charge process, are unravelled by in situ XRD. The LixV6O13 unit cell expands sequentially in c, b, and a directions during discharge and reversibly contracts back during charge. The process is associated with a change of occupied lithium sites as well as charge ordering in LixV6O13. Density functional theory (DFT) calculations and nuclear magnetic resonance spectroscopy gave further insight into the electronic structures and preferred Li positions in the different structures formed upon cycling, particularly at high lithium contents. At HT, V6O13 exhibits an even greater capacity, as well as a more symmetric discharge and charge profile. Combining the results from the HT in situ XRD study and the DFT calculation, the most Li puckered phase was found to be able to open further along the b axis, with a new Li site getting (partially) occupied. The new Li site corresponds to more Li intercalation into the LixV6O13 structure and, therefore, more electrode charge storage capacity. The more symmetric discharge and charge process was attributed to the disappearance of phase 2 (present at room temperature for 1.7 < x ≤ 2.1 in LixV6O13) at HT.

Doctor of Philosophy / Department of Chemical Engineering / Placidus B. Amama / Advances in synthesis and processing of nanocarbon materials, particularly graphene, have presented the opportunity to design novel Li-ion battery (LIB) anode materials that can meet the power requirements of next-generation power devices. This thesis presents three studies on electrochemical behavior of three-dimensional (3D) nanostructured anode materials formed by pure graphene sheets and graphene sheets coupled with conversion active materials (metal oxides). In the first project, a microgel-templated approach for fabrication of 3D macro/mesoporous reduced graphene oxide (RGO) anode is discussed. The mesoporous 3D structure provides a large specific surface area, while the macropores also shorten the transport length of Li ions. The second project involves the use of a novel magnetic field-induced method for fabrication of wrinkled Fe3O4@RGO anode materials. The applied magnetic field improves the interfacial contact between the anode and current collector and increases the stacking density of the active material. The magnetic field treatment facilitates the kinetics of Li ions and electrons and improves electrode durability and the surface area of the active material. In the third project, poly (methacrylic acid) (PMAA)-induced self-assembly process was used to design super-mesoporous Fe3O4@RGO anode materials and their electrochemical performance as anode materials is also investigated. To establish correlations between electrode properties (morphological and chemical) and LIB performance, a variety of techniques were used to characterize the samples. The significant improvement in LIB performance of the 3D anodes mentioned above is largely attributed to the unique properties of graphene and the resulting 3D architecture.