In a bid to reduce vehicular emissions, automobile manufacturers are moving towards elec- tric and hybrid vehicles. Most hybrid vehicles use Lithium-ion batteries as energy storage systems. Lithium-ion batteries have a narrow range of temperature within which they can be operated efficiently. Operation of Lithium-ion batteries outside this range decreases the life of batteries and reduces performance of the vehicle. Due to this limitation, it is important to prevent overheating of Lithium-ion batteries. Battery pack studied in this work has a fan system for air-cooling the cells. The battery management system (BMS) in the battery pack functions to keep the temperature of the cells within allowable limits by either regulating the fan speed or communicating with the vehicle controller to adjust magnitude of applied current. BMS used in the work is equipped with limited number of temperature sensors that can measure surface temperature of few cells in the battery pack. Additional temper- ature information can be used for better thermal control of the cells in the battery pack. Lithium-ion cells are known to have a measurable temperature gradient when operating un- der extreme conditions. As a result, the surface temperature of cells as measured by the temperature sensors in BMS is not always representative of the maximum cell temperature. To overcome these limitations, a simplified transient thermal model predicting core and sur- face temperature of cell is presented in this work. This model can be implemented in a BMS for real-time control of cell temperature. The thermal model is validated against data avail- able from testing the battery pack. Different current profiles, representative of real-world driving scenarios, are applied to the thermal model and the temperature rise of cells under those conditions is studied. For an array of cells, the thermal model predicts significant temperature rise along the airflow direction, suggesting the use of last cell temperature for thermal control. For short duration, high magnitude of current pulses, temperature rise is shown to be similar for same thermal energy deposited by different current pulses. The maximum thermal energy that can be deposited in the battery by a current pulse can be determined for given conditions of airflow rate, continuous current and air inlet temperature. The maximum magnitude of thermal energy that can be deposited by a peak current pulse to limit cell temperature is shown to be a function of current magnitude squared and the pulse duration time. For multiple current pulses applied to the battery pack, the model can evaluate the minimum time interval between current pulses to keep the temperature of cells within prescribed limits. The minimum time required between two current pulses is shown to decrease by increasing the airflow rate through the battery pack. By increasing the airflow rate, the battery pack is able to operate at a higher continuous current without exceeding the temperature limit. / Master of Science / In a bid to reduce vehicular emissions, automobile manufacturers are moving towards electric and hybrid vehicles. Most hybrid vehicles have an energy storage system in addition to the conventional Internal Combustion (I.C.) engine. Lithium-ion batteries are used as energy storage systems in most hybrid vehicles due to their high energy density, long life and low self discharge rate. Lithium-ion batteries can be operated efficiently only in a narrow range of temperature. Operating these batteries outside of this temperature range results in their faster degradation which results in lower performance of hybrid vehicle. Due to this limi- tation, prevention of overheating in Lithium-ion batteries is extremely important. To keep the operation of Lithium-ion batteries within specified temperature limits, most batteries in hybrid vehicles are equipped with battery management systems (BMS). The BMS monitors cell voltage, cell temperature and applied current and keeps the temperature of cells within allowable limits. BMS of the battery pack used in this work has fan system for air-cooling the individual cells, and can lower the temperature rise of the cells by varying the fan speed. This BMS has limited temperature sensors that can predict surface temperature of few cells of the battery pack. Additional temperature information can be used to improve thermal control of the battery pack. This work presents a simplified thermal model that can be used in controller of a BMS to improve thermal control of cells and keep the temperature of cells within specified limits.

In the entirety of this project, a power converter is modeled, simulated, designed, and optimized to convert a three-phase AC wind turbine source to charge DC lead-acid batteries, applying new control techniques and an innqvative design to produce the most energy from the small wind turbine. The converter will implement new approaches to power factor correction and maximum power point tracking to capture the most energy under any operating conditions of the wind turbine. Overwind conditions will be protected against using the converter's ability to slow the turbine instead of usual resistive loads or mechanical braking. Other techniques to protect the batteries and the converter will be discussed in the scope of this paper. Through testing the designed converter, supporting evidence is shown whether the topology and control techniques are beneficial by comparing the degree of effectiveness of each method. The goal is to prove that these methods will provide a significant increase in energy converted.

This thesis investigates several approaches to the development of high-performance batteries. A general background to the field and an introduction to the experimental methods used are given in Chapters 1 and 2 respectively. Chapter 3 presents a study of ordered and disordered LiNi₀.₅Mn₁.₅O₄ materials produced using an optimised resorcinol-formaldehyde gel (R-F gel) synthetic technique. Both materials exhibited good electrochemical properties and minimal side reaction with the electrolyte. Structural analyses of the materials in various states of discharge and charge were undertaken, and from these the charge / discharge processes were elucidated. In chapter 4 R-F gel synthesised Li(Ni₁/₃Mn₁/₃Co₁/₃)O₂ is studied and found to exhibit a high degree of structural stability on cycling, as well as excellent capacity, cyclability and rate capability. Photoelectron spectroscopy studies revealed that the R-F gel derived particles have highly stable surfaces. A discussion of the results and their significance, with particular regard to the outstanding electrochemical performance observed, is also presented. Chapter 5 sets out an investigation into the nature of R-F gel synthesised 0.5Li₂MnO₃:0.5LiNi₁/₃Mn₁/₃Co₁/₃O₂. The electrochemical data revealed that, after an initial activation stage, the R-F gel derived material exhibited a high capacity, good cyclability and exceptional rate capability. This chapter also considers some initial structural investigations and the electrochemical processes occurring on charge. In chapter 6 the use of ether-based electrolytes, combined with various cathode materials, in lithium-oxygen batteries is examined. The formation of decomposition products was observed, and a scheme suggesting probable reaction pathways is given. It was noted that significant quantities of the desired discharge product, lithium peroxide, were formed on the 1st cycle discharge, implying some electrolyte / cathode combinations do demonstrate a degree of stability. A summary of the results and a discussion of their significance are also included.

Nanotubes (inner diameter of 8nm and outer diameter of 10nm with a length of up to several hundred nm) and nanowires (diameter 20 – 50nm and up to several μm in length) of TiO₂-B have been synthesised and characterised for the first time. These exhibit excellent properties as a host for lithium intercalation and are able to accommodate lithium up to a composition of Li₀.₉₈TiO₂-B for the nanotubes and Li₀.₈₉TiO₂-B for the nanowires. Following some irreversible capacity on the first cycle, which could be reduced to 4% for the nanowires, capacity retention for the nanowires is 99.9% and for the nanotubes is 99.5% per cycle. In both cases, the cycling occurs at ~1.6V versus lithium. The cycling performance was compared with other forms of bulk and nano-TiO₂, all of which were able to intercalate less lithium. Nanowires of VO₂-B (50 – 100nm in diameter and up to several μm in length) were synthesised by a hydrothermal reaction and characterised. By reducing the pressure inside the hydrothermal bomb, narrower VO₂-B nanowires with a diameter of 2 – 5nm and length of up to several hundred nm were created - some of the narrowest nanowires ever made by a hydrothermal reaction. These materials are isostructural with TiO₂-B and were also found to perform well in rechargeable lithium ion batteries, being able to intercalate 0.84Li for the ultra-thin nanowires and 0.57Li for the standard nanowires. The standard VO₂-B nanowires have a capacity retention of 99.8% and the ultra-thin nanowires have 98.4% per cycle after some irreversible capacity on the first cycle. This was found to improve markedly when different electrolytes were used. Macroporous Co₃O₄ (pore size 400nm with a surface area of 208m²/g) was prepared and cycled in rechargeable lithium cells with capacities of 1500mAh/g being achieved. The structure was found to break down on the first cycle and after this the material behaved in the manner of Co₃O₄ nanoparticles. Finally a new candidate for next generation rechargeable lithium batteries was examined; Li/O₂ cells. The cathode is composed of porous carbon in which Li⁺, e⁻ and O₂ meet to form Li₂O₂ on discharge. The reaction is reversible on charge. Capacities of 2800mAh/g can be achieved when 5%mole of αMnO₂ nanowires catalyst is used. Fade is high at 3.4% per cycle meaning that there is much work to do to develop these into a commercial prospect.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

Currently, automotive batteries use intercalation cathodes such as lithium iron phosphate (LiFePO4) which provide high levels of safety while sacrificing cell voltage and therefore energy density. Lithium transition metal oxide (LiMO2) batteries achieve higher cell voltages at the risk of releasing oxygen gas during charging, which can lead to ignition of the liquid electrolyte. To achieve both safety and high energy density, oxide cathodes must be well characterized under operating conditions. In any intercalation cathode material, the loss of positive lithium ions during charge must be balanced by the loss of negative electrons from the host material. Ideally, the TM ions oxidize to compensate this charge. Alarmingly, the stoichiometry of the latest LiMO2 cathode materials includes more lithium ions than the TM ions can compensate for. Inevitably, peroxide ions or dioxygen gas must form. The former mechanism is vital for lithium-air batteries, while the latter must be avoided. Battery researchers have long sought to completely characterize the intercalation reaction in working batteries. However, the volatile electrolytes employed in batteries are not compatible with vacuum-based characterization techniques, nor are the packaging materials required to contain the liquid. For the first time, a solid state battery (using exposed particles of Li1.17Ni0.25Mn0.58O2) was charged while using soft X-ray absorption spectroscopy to observe the redox trends in nickel, manganese and oxygen. This was combined with innovative hard X-ray absorption spectroscopic studies on the same material to create the most complete picture yet possible of charge compensation.

Although competitive today, traditional PbA (<1500 cycles) and advanced lead-acid batteries (ALAB) (>4000 cycles) will not be able to compete with lithium and flow batteries by 2020. To compete with novel zinc, lithium and flow batteries, the PbA chemistry needs to achieve significant performance improvements, primarily through sustainable increases to specific energy (Wh/kg), while not negatively impacting cycle life. Inverse charging has been examined for its potential in improving PbA cycle life as a battery maintenance procedure, and as a potential technique for improving electrode specific capacity (mAh/kg) during battery manufacturing and formation. A thorough levelized cost of energy (LCOE) shows that for traditional PbA batteries with cycle lives <2000, inverse charging as a maintenance strategy (to increase cycle life) improves battery economics. Inverse charging to increase cycle life for ALAB systems (>4000 cycle life) was proven to worsen battery economics, as additional costs of capital and maintenance fail to outweigh savings achieved through reductions in replacement cost. On the other hand, inverse charging employed as a manufacturing practice to increase specific energy dramatically reduces the cost of the PbA and ALAB systems, ensuring future cost competitiveness. Inverse charging as a maintenance strategy should be restricted to devices with <2000 cycles and to projects with long project lives (20 years) that require frequent replacement. Inverse charging as a manufacturing strategy (to increase specific energy) is highly preferable in all instances. When successful, inverse charging increases the specific capacity and active material utilization of studied battery electrodes significantly. Successful inverse charging of battery electrodes and pure lead rods show improvements in discharge capacities over a range of discharge rates with negligible impact to coulombic and energy efficiency values. The extent of success, however, depends on several important variables. Thorough examination of inverse charging on Pb rods and porous battery electrodes illustrates the importance of the degree of prior electrode sulfation and obstruction of transport of H₂SO₄. Other important factors include the composition of electrode grid alloys, the peak oxidation voltage applied to the negative electrode during inverse charging, initial particle sizes, and electrolyte additives. Significant challenges to inverse charging exist. For heavily sulfated batteries and lead metals, impeded electrolyte transport results in excessive internal pore pH increases, creating semipermeable membranes through an electrode hydration mechanism, resulting in dramatic inverse charging failure. Additionally, impedance, voltage, x-ray and BET data hint that post-inverse charging, agglomeration of finely divided Pb and PbSO₄ particles occurs, coupled with negative electrode conductive pathway destruction. As such, the influence of expander materials and nucleation additives should be investigated to better prevent sulfation failure, and to better control the nucleation and growth of lead and lead sulfate structures during inverse charging. Cycle life studies on flooded lead antimony batteries subjected to periodic inverse charging illustrate that inverse charging is highly successful on all batteries independent of states-of-health. Batteries with poor states-of-health (discharge capacities <15% of initial values) experienced almost perfect discharge capacity restoration post-inverse charging. Traditional methods of extending cycle life (i.e. prolonged overcharging techniques) were demonstrated to be inadequate at appreciably regenerating battery capacities, providing only marginal increases. The benefits of inverse charging, however, are met with significant challenges to battery redesign. Temporary antimony poisoning effects lead to declines in round-trip-efficiency for batteries with antimony-based positive plates. Tin dissolution results in diminished grid to active material conductivity and reduced capacity for batteries with tin-based positives. For the negative electrode, Brunauer–Emmett–Teller (BET) surface area and x-ray measurements indicate that although large PbSO₄ crystals are oxidized during inverse charging, creating extensive micropore networks during conversion from Pb to PbO₂, surface area and capacity gains are lost during reconversion back to sponge lead due to uncontrolled nucleation and particle fusion. Additionally, active material shedding of the positive and negative electrodes is observed to spike during and after inverse charging. Negative electrode active material suffers excessive degradation and loss of cohesion, particularly for electrodes with small initial particle feature sizes, resulting in a loss of structure upon completion of the technique. Positive electrode composition changes to weakly interconnected b-PbO₂, dramatically increasing electrode capacity while simultaneously accelerating electrode failure through shedding. Loss of particle cohesion in both electrodes promotes excessive shedding and sludging, creating intra-cellular short-circuits. In addition, inverse charging aggravates grid growth, promoting inter-cellular short-circuiting by creating pathways for cell-to-cell electrolyte contact upon seal destruction in current monoblock designs.

Lors du fonctionnement des batteries Li-ion, la dégradation progressive de l’électrolyte engendre la génération des gaz qui sont à l’origine du phénomène des surpressions dans ces dispositifs, et a pour conséquence des problèmes de sécurité. Cette thèse aborde l’étude de la solubilité des gaz issus des réactions de dégradation des électrolytes tels que le CO2, CH4, ou encore C2H4 dans plusieurs systèmes simples (solvants purs) ou complexes (mélanges binaires, ternaires et quaternaires avec sel de lithium), en fonction de la température, de la structure des solvants et des sels, ainsi que de leurs concentrations en solution. A cet effet, nous avons mesuré préalablement les propriétés volumétriques, de transport, ainsi que les pressions de vapeur des électrolytes formulés en fonction de la composition et de la température. / The performance and the safety of a lithium-ion battery depend to a great extent on the stability of the electrolyte solution, because the high voltage of the battery may cause the decomposition of lithium salt or organic solvents, which limits then the battery lifetime. During these degradations, several gases are, generally, generated like the CO2, CO, CH4 and C2H4, which induce in fact several problems related to the pressure increase inside the sealed cell. The main objective of this PhD thesis is to understand the key thermodynamic parameters which drive the gas dissolution in classical solvents and electrolytes. For that, several pure solvents and electrolytes have been firstly investigated to determine their volumetric and transport properties, as well as, their vapour pressure as the function of temperature and composition.

A vehicular battery must consist of a large number of cells to provide the necessary energy and power. Management only at the level of the battery pack causes out-of-investigation cells and lack of cell equalization ability. Therefore, in the smart module concept, cells are first grouped into modules, which are then connected to the battery pack. Each module is an independent unit with a controller to investigate and control cells. Based on this concept, the work in this thesis redistributes tasks among module controllers and a central controller, applies a self-power design to enhance module independence, and selects the newly developed automotive ICs and sensors. Finally, a prototype of the BMS has been developed and successfully applied in a series of HEVs. / Cell equalization is a crucial technique to balance the cells inside a battery pack, with the ability to maximize pack capacity and protect cells from damage. For the bi-directional Cuk equalizing circuit, we propose a SoC based, instead of voltage based, fuzzy controller to intelligently determine the equalizing current, with the aim of reducing equalizing duration, enhancing equalizing efficiency, and protecting cells. The inputs to the controller are specially designed as the difference in SoC, the average SoC, and the total internal resistance. Because of the lack of theoretical analysis on equalizing current in the electrochemistry field, we utilize a fuzzy controller to incorporate the experience and knowledge of experts. Simulations and experiments verify its availability and efficacy. Especially for a LiFePO4 battery, a large SoC difference may lead to only a small difference in voltage and cause the failure of a traditional voltage based equalizer. The SoC based method successfully avoids this problem and obtains good performance in equalizing LiFePO4 cells. / Fast charge is intended to charge a battery as fast as possible, without any damage and with high energy efficiency, thus helping to reduce vehicle out-of-service time and promote the commercialization of EVs. Battery safety and charging efficiency are partially reflected by the increase in temperature during the charging process. Therefore, the aims of this thesis were to accelerate charging speed and reduce the temperature increase. We introduce a model predictive control framework to control the charging process. An RC model and the modified enhanced self-correcting model are employed to predict the future SoC in simulations and experiments respectively. A single-node lumped-parameter thermal model and a neural network trained by real experimental data are also applied respectively. In addition, a genetic algorithm is applied to optimize the charging current under multiple objectives and constraints. Simulation and experimental results strongly demonstrate that the Pareto front of the proposed algorithm dominates that of the popular constant current constant voltage charge method. / State of charge (SoC) is a battery state indicating its residual capacity. It is the fundamental state of the battery and is the basis for other battery operations. However, SoC is not a directly measurable state and has to be obtained by estimation techniques. Aiming to enhance the anti-noise ability of SoC estimation in a real vehicle environment, we propose a SoC estimation framework consisting of an adaptive nonlinear diffusion filter to reduce the noise of current measurement, a self-learning mechanism to remove its zero-drift, an open loop coulomb counting estimator and a model based closed loop filter to estimate SoC, and a data fusion unit to reach the final estimation result. In a simulation study, the closed loop filter is implemented based on an RC model and Hinfinity filter. In experiments and application, we modify the enhanced self-correcting model to model a type of LiFePO4 battery and apply an extended Kalman filter to estimate SoC. The framework has been demonstrated to improve accuracy and anti-noise ability, and achieves the technique upgrading goal recently published by the Chinese government. / The automotive industry has experienced a significant boom in recent years, accelerating the problems of energy shortage and environmental disruption around the world. To solve the two problems, electric vehicles (EVs), including battery electric vehicles (BEV), hybrid electric vehicles (HEV), and fuel-cell electric vehicles (FEV), have been proposed and studied in recent years. Despite the efforts devoted to the development of EVs by both the scientific research and industrial communities, there are still many obstacles hindering the mass commercialization of EVs. Among these obstacles, the battery system, the new energy storage component in EVs, is one of the most important yet most difficult parts of EV design, and the battery management system (BMS) is recognized as the single most important technical issue in the successful commercialization of EVs. / Yan Jingyu. / Adviser: Xu Yangsheng. / Source: Dissertation Abstracts International, Volume: 73-03, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 166-182). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Hunting for improved energy storage devices based on rechargeable Li-ion batteries and other advanced rechargeable batteries is one of the hottest topics in today's society. Both Li- ion batteries and Li-O2 batteries have been studied within the thesis. The research work of this thesis contains two different parts. Part 1. The controlled synthesis of the extreme small sized nanoparticles and their application for Li-ion batteries; Part 2. The study of the O2 reduction mechanism in Li-O2 batteries with aprotic electrolytes. In the first part, two different types of extremely small-sized TiO2 nanoparticles with at lease on dimension less than 3 nm was synthesised via solvothermal/hydrothermal reaction, i.e., anatase nanosheets and TiO2(B). These nanoparticles were obtained without any contamination of long chain organic surfactants. A series of systematic characterisation methods were employed to analyse the size, phase purity, and surface condition. These extremely small-sized nanoparticles exhibit improved capacity, rate performance as anode materials for Li-ion batteries. The shapes of load curves of charge and discharge are significantly modified due to the reduced size of TiO2 nanoparticles. In chapter 3, we will see the variation of the capacity and the load curve shape of the anatase nanosheets according to their thickness and surface conditions. The origin of the excessive capacity is analysed based on the electrochemical data. It has been identified that both pseudocapacitive (interfacial) Li+ storage and the excessive Li+ -storage from the bulk contribute to the increased capacity. In chapter 4, the shape and size of the sub-3 nm TiO2(B) nanoparticles are studied, a method based the PXRD data is established. These nanoparticles demonstrate a reversible capacity of 221 mAh/g at a rate of 600 mA/g and remain 135 mAh/g at 18000 mA/g without significant capacity fading during cycling. In the last part, a systematic study of O2 reduction mechanism for aprotic Li-O2 batteries based on the combination of a series of electrochemical and spectroscopic data is presented. The novel mechanism unifies two previous models for the growth of Li2O2 during discharge, i.e., Li2O2 particle formation in the solution phase and Li2O2 film formation on the electrode surface. The new mechanism provides fundamental conceptions for the improvement of Li2O2 batteries and shed light on the future research of Li2O2 batteries.