Thesis (M. Phil.)--University of Hong Kong, 1974. / Mimographed. Also available on microfilm.

Nowadays personal small electronic devices like cellphones are more and more popular, but the various batteries in need of charging become a problem. This thesis aims to explain a Lithium-ion charger which can control the current and voltage so that it can charge most kinds of popular batteries. More specifically, Li-ion battery charging is presented. The charging circuit design, simulation and the measurements will also be included.

Entering a new era of green energy, several criteria such as cost, cycle life, safety, efficiency, energy, and power need to be considered in developing electrical energy storage systems for transportation and grid storage. Lithium-sulfur (Li-S) batteries are one of the prospective candidates in this regard as sulfur offers a high theoretical capacity of 1675 mAh g⁻¹ at a safer operating voltage range of ~ 2.1 V and low-cost benefit. This dissertation explores various original designs of novel electrodes, new cell configurations, and recharge strategies that can boost the cycle performance of Li-S cells. An in situ sulfur deposition route has been developed for synthesizing sulfur-carbon composites as cathode materials. This facile synthesis method involves the precipitation of elemental sulfur at the interspaces between carbon nanoparticles in aqueous solution at room temperature. Thus, a sulfur/multi-wall carbon nanotube (MWCNT) composite cathode with high-rate cyclability has been synthesized by the same process. Due to the self-weaving behavior of MWCNTs, extra cell components such as binders and current collectors are rendered unnecessary, thereby streamlining the electrode manufacturing process and decreasing the cell weight. A novel Li-S cell configuration with a carbon interlayer inserted between the separator and cathode has been designed to enhance the battery cyclability as well. A conductive MWCNT interlayer acting as a pseudo-upper current collector not only reduces the charge transfer resistance of sulfur cathodes significantly, but also localizes and retains the dissolved active material during cycling. Moreover, with a bi-functional microporous carbon paper intrerlayer, we observe a significant improvement not only in the active material utilization but also in capacity retention, without involving complex synthesis or surface modification. The kinetics of the sulfur/long-chain polysulfide redox couple (S₈ [double-sided arrow] Li₂S₄, theoretical capacity = 419 mAh g⁻¹) is experimentally proven to be very fast in the Li-S system. The Li-S cell with a blended carbon interlayer retains excellent cycle stability and possesses a high percentage of active material utilization over 250 cycles at high C rates (up to 15C). The meso-/micro- pores in the interlayer are in charge of accommodating the shuttling polysulfides and offering sufficient electrolyte accessibility. An appropriate and applicable way to recharge Li-S cells within the lower plateau region has been designed to offer tremendous improvement with various Li-S battery systems. Adjusting the charging condition led to long cycle life (over 500 cycles) with excellent capacity retention (> 99%) by inhibiting the electrochemical reactions along with polysulfide dissolution. In addition, the redox products determined by ex situ x-ray photoelectron spectroscopy (XPS) further clarify the mechanism of polysulfide formation upon cycling, which is partially different from the general consensus. These approaches of novel electrode designs, new cell configurations, charging strategy, and understanding of the reactions in different discharge steps could progress the development and advancement of Li-S batteries. / text

No description available.

Lithium-ion (Li-ion) batteries are critically important for portable electronics, electric vehicles, and grid-level energy storage. The development of next-generation Li-ion batteries requires high-capacity electrodes with a long cycle life. However, the high capacity of Li storage is usually accompanied by large volume changes, dramatic morphological evolution, and mechanical failures in the electrodes during charge and discharge cycling. To understand the degradation of electrodes and resulting loss of capacity, this thesis aims to develop mechanistic-based models for predicting the chemo-mechanical processes of lithiation and delithiation in high-capacity electrode materials. To this end, we develop both continuum and atomistic models that simulate mass transport, interface reaction, phase and microstructural evolution, stress generation and damage accumulation through crack or void formation in the electrodes. The modeling studies are tightly coupled with in-situ transmission electron microscopy (TEM) experiments to gain unprecedented mechanistic insights into electrochemically-driven structural evolution and damage processes in high-capacity electrodes. Our models are successfully applied to the study of the two-phase lithiation and associated stress generation in both crystalline and amorphous silicon anodes, which have the highest known theoretical charge capacity, as well as the lithiation/sodiation-induced structural changes and mechanical failures in silicon-based multilayer electrodes. The modeling studies have uncovered unexpected electrochemical reaction mechanisms and revealed novel failure modes in silicon-based nanostructured anodes. Our modeling research provides insights into how to mitigate electrode degradation and enhance capacity retention in Li-ion batteries. More broadly, our work has implications for the design of nanostructured electrodes in next-generation energy storage systems.

This thesis investigates the mechanical behavior of electrodes in Li-ion batteries. Each electrode in a Li-ion battery consists of host atoms and guest atoms (Li atoms). The host atoms form a framework, into which Li atoms are inserted via chemical reactions. During charge and discharge, the amount of Li in the electrode varies substantially, and the host framework deforms. The deformation induces in an electrode a field of stress, which may lead to fracture or morphological change. Such mechanical degradation over lithiation cycles can cause the capacity to fade substantially in a commercial battery. We study fracture of elastic electrodes caused by fast charging using a combination of diffusion kinetics and fracture mechanics. A theory is outlined to investigate how material properties, electrode particle size, and charging rate affect fracture of electrodes in Li-ion batteries. We model an inelastic host of Li by considering diffusion, elastic-plastic deformation, and fracture. The model shows that fracture is averted for a small and soft host—an inelastic host of a small feature size and low yield strength. We present a model of concurrent reaction and plasticity during lithiation of crystalline silicon electrodes. It accounts for observed lithiated silicon of anisotropic morphologies. We further explore the microscopic deformation mechanism of lithiated silicon based on first-principles calculations. We attribute to the microscopic mechanism of large plastic deformation to continuous Li-assisted breaking and reforming of Si-Si bonds. In addition, we model the evolution of the biaxial stress in an amorphous Si thin film electrode during lithiation cycle. We find that both the atomic insertion driven by the chemomechanical load and plasticity driven by the mechanical load contribute to reactive flow of lithiated silicon. In such concurrent process, the lithiation reaction promotes plastic deformation by lowering the stress needed to flow. Li-ion battery is an emerging field that couples electrochemistry and mechanics. This thesis aims to understand the deformation mechanism, stresses and fracture associated with the lithiation reaction in Li-ion batteries, and hopes to provide insight on the generic phenomenon that involves interactive chemical reactions and mechanics. / Engineering and Applied Sciences

"Yuewang Goujian shijia," the forty-first chapter of the Shiji, is one of the most important sources for the history of the ancient state of Yue. However, this chapter has not received serious scholarly examination in the West. Unlike those chapters of the Shiji which have been translated in the Shiji translation project headed by William Nienhauser, "Yuewang Goujian shijia" has not yet been translated into English. This thesis provides an annotated translation of the "Yuewang Goujian shijia." In addition, it has been argued that the history of the Spring and Autumn period in the Shiji is a compilation of earlier sources. The introduction to the translation will specifically look at the relationship of the "Yuewang Goujian shijia" to one of its proposed sources, the "Yueyu xia," which is the twenty-first chapter of the Guoyu. In comparing these two texts, it will be shown that dependence cannot be definitely demonstrated.

No description available.

Li-Fraumeni Syndrome (LFS) is a rare cancer predisposition syndrome, typically involving germline mutations in the TP53 gene. Despite the high penetrance of TP53 mutations, LFS patients display striking phenotypic differences, suggesting the presence of secondary risk loci. To date, all genetic modifiers in LFS have been shown to map to either TP53 or its principal negative regulator, Mdm2. Given this strong association, we set out to interrogate the contribution of a recently-described miRNA regulator of the p53-MDM2 loop, called miR-605. We hypothesized that, if functional, the miR-605 gene and its variant (rs2043556) could impact cancer risk in TP53 mutation carriers. Consistent with this proposition, the variant allele of miR-605 was associated with a significant acceleration in tumor onset and caused a decrease in the processing efficiency of its host miRNA. We also demonstrate that miR-605 overexpression activates the MAPK pathway and leads to tumor suppression in TP53 mutant cell lines.

Li-Fraumeni Syndrome (LFS) is a rare cancer predisposition syndrome, typically involving germline mutations in the TP53 gene. Despite the high penetrance of TP53 mutations, LFS patients display striking phenotypic differences, suggesting the presence of secondary risk loci. To date, all genetic modifiers in LFS have been shown to map to either TP53 or its principal negative regulator, Mdm2. Given this strong association, we set out to interrogate the contribution of a recently-described miRNA regulator of the p53-MDM2 loop, called miR-605. We hypothesized that, if functional, the miR-605 gene and its variant (rs2043556) could impact cancer risk in TP53 mutation carriers. Consistent with this proposition, the variant allele of miR-605 was associated with a significant acceleration in tumor onset and caused a decrease in the processing efficiency of its host miRNA. We also demonstrate that miR-605 overexpression activates the MAPK pathway and leads to tumor suppression in TP53 mutant cell lines.