Lithium ion batteries have become one of the most popular types of battery in consumer electronics as well as aerospace and automotive applications. The efficient use of Li-ion batteries in automotive applications requires well designed battery management systems. Low order Li-ion battery models that are fast and accurate are key to well- designed BMS. The control oriented low order physics based model developed previously cannot predict the temperature and predicts inaccurate voltage dynamics. This thesis focuses on two things: (1) the development of a thermal component to the isothermal model and (2) the development of a hybrid neural net and physics based battery model that corrects the output of the physics based model. A simple first law based thermal component to predict the temperature model is implemented. The thermal model offers a reasonable approximation of the temperature dynamics of the battery discharge over a wide operating range, for both a well-ventilated battery as well as an insulated battery. The model gives an accurate prediction of temperature at higher SOC, but the accuracy drops sharply at lower SOCs. This possibly is due to a local heat generation term that dominates heat generation at lower SOCs. A neural net based modeling approach is used to compensate for the lack of knowledge of material parameters of the battery cell in the existing physics based model. This model implements a neural net that corrects the voltage output of the model and adds a temperature prediction sub-network. Given the knowledge of the physics of the battery, sparse neural nets are used. Multiple types of standalone neural nets as well as hybrid neural net and physics based battery models are developed and tested to determine the appropriate configuration for optimal performance. The prediction of the neural nets in ventilated, insulated and stressed conditions was compared to the actual outputs of the batteries. The modeling approach presented here is able to accurately predict voltage output of the battery for multiple current profiles. The temperature prediction of the neural nets in the case of the ventilated batteries was harder to predict since the environment of the battery was not controlled. The temperature predictions in the insulated cases were quite accurate. The neural nets are trained, tested and validated using test data from a 4.4Ah Boston Power lithium ion battery cell. / text

Today’s information-centered world leads the ever-increasing consumer demand for more powerful, multifunctional portable devices. Additionally, recent developments on long-lasting energy sources and compliant, flexible systems, have introduced new required features to the portable devices industry. For example, wireless sensor networks are in urgent need of self-sustainable, easy-to-deploy, mobile platforms, wirelessly interconnected and accessible through a cloud computing system. The objective of my doctoral work is to develop integration strategies to effectively fabricate mechanically flexible, energy-independent systems, which could empower sensor networks for a great variety of new exciting applications. The first module, flexible electronics, can be achieved through several techniques and materials. Our main focus is to bring mechanical flexibility to the state-of-the-art high performing silicon-based electronics, with billions of ultra-low power, nano-sized transistors. Therefore, we have developed a low-cost batch fabrication process to transform standard, rigid, mono-crystalline silicon (100) wafer with devices, into a thin (5-20 m), mechanically flexible, optically semi-transparent silicon fabric. Recycling of the remaining wafer is possible, enabling generation of multiple fabrics to ensure lowcost and optimal utilization of the whole substrate. We have shown mono, amorphous and poly-crystalline silicon and silicon dioxide fabrics, featuring industry’s most advanced high-/metal-gate based capacitors and transistors. The second module consists on the development of efficient energy scavenging systems. First, we have identified an innovative and relatively young technology, which can address at the same time two of the main concerns of human kind: water and energy. Microbial fuel cells (MFC) are capable of producing energy out the metabolism of bacteria while treating wastewater. We have developed two micro-liter MFC designs, one with carbon nanotubes (CNT)-based anode and the second with a more sustainable design and easy to implement. Power production ranges from 392 to 100 mW/m3 depending on design. Additionally we have explored a flexible thermoelectric generator (0.139 μW/cm2) and a lithium-ion battery (~800 μAh/m2) for back-up energy generation and storage. Future work includes the implementation of a self-powered System-on-Package which gathers together energy generation, storage and consumption. Additionally we are working to demonstrate Complementary Metal-Oxide-Semiconductor (CMOS) circuitry on our flexible platform, as well as memory systems.

The power requirement for the soldier's equipment is largely supplied by batteries. Situational awareness is critical for a soldier to perform his tasks. Therefore the radio used by the soldier is a key element in situational awareness and also consumes the most power. The South African National Defence Force (SANDF) uses the A43 tactical radio specifically designed for them. The radios are regarded as old technology but will be in use for about another five years. The radios still use non-rechargeable alkaline batteries which do not last very long and are not cost effective. The purpose of this study is to research the new generation secondary batteries as a possible replacement for the alkaline battery packs. The new generation batteries investigated in this study are the latest rechargeable batteries, also called secondary batteries. They include nickel cadmium, nickel metal hydride, lithium ion, rechargeable alkaline manganese and zinc air. The main features of rechargeable cells are covered and the cell characteristics are defined to allow the technology to be matched to the user requirement. Li-ion technology was found to be the best choice. This research also showed that international trends in battery usage are towards Li-ion. A new Li-ion battery was designed based on commercial cells. Tests showed that commercial Li-ion cells can be used in the radio and that they outperform the current battery by far. The study also examined the design of a New Generation Battery System consisting of an intelligent battery, a charger which uses a Systems Management Bus and a battery 'state of health" analyser to assist the user to maintain the batteries. Tests were done to demonstrate that the battery can withstand typical military environmental conditions. Expected military missions for a battery system were defined and used to compare the cost between the existing batteries and the new batteries system. Important usage factors which will influence the client when using a New Generation Battery System were addressed. To summarise, this study showed that by using a New Generation Battery System, the SANDF could relieve the operational cost of the A43 radio while saving on weight and enabling the soldier to carry out longer missions. / Thesis (M.Ing. (Electronical Engineering))--North-West University, Potchefstroom Campus, 2008.

The layered transition metal oxide composition series of Li1+xV1-xO2 was synthesized using the solid state synthesis technique. X-ray diffraction was used to determine the dependence of structure on composition and clearly indicated a structural anomaly at x = 0 caused by the unusual magnetic ordering on the triangular lattice of the V3+ layer. To prevent magnetic frustration V3+ cations undergo orbital ordering and subsequent periodic displacent to form “trimers”. The periodicity of this phenomena results in a superlattice structure that can be observed as a faint peak in XRD spectra. The relationship between composition, superlattice peak intensity and lattice parameters was clearly documented for the first time. Li/Li1+xV1-xO2 cells were made and tested. Recent literature has shown that the transformation to 1T Li2VO2 upon lithiation is dependant on a nonzero x (ideally x = 0.07 for maximum capacity) to make a small number of tetrahedrally coordinated Li sites accessible. These sites then act as a trigger for shearing into the 1T phase. The cells described within this work intercalated significant amounts of lithium at a higher potential than the to 1T transition, possibly signifying occupation of a large number of the tetrahedral sites. LiVO2 is known to undergo delithiation even in ambient conditons and this can lead to cationic disorder. Cationic disorder is an inhibitor of anion sheet shearing and this suggests that sample handling could be a cause of the observed electrochemical behaviour. The effects of air and water exposure were investigated.

La prédiction de l'évolution du vieillissement de la batterie lithium-ion est source d'un grand défi, dans les applications liées aux véhicules électriques et hybrides. Sa méconnaissance est un risque considérable compromettant la viabilité d'un tel système. Invoquant les coûts substantiels de la densité d'énergie, liée à la dégradation considérable des performances de la batterie au cours de sa durée de vie, il devient important d'en tenir compte dès le processus de conception. La dépendance de la stratégie de contrôle du véhicule aux paramètres de la batterie justifie aussi la nécessité d'une telle prédiction. Il est connu que le vieillissement, sensible aux facteurs tels que le courant, la température et la profondeur de décharge, a un impact considérable sur la perte de capacité de la batterie ainsi que sur l'augmentation de la résistance interne. Le premier est directement lié à l'autonomie électrique du véhicule, alors que le second mène à une surchauffe de la batterie, à une augmentation des pertes en puissance qui se manifeste par une diminution de la tension de bus. À cet égard, impliqué dans la conception d'un véhicule récréatif hybride branchable à trois roues, le Centre de Technologies Avancées s'intéresse à l'étude du vieillissement de la batterie Li-ion pour une telle application. Pour ce faire, au contraire de la plupart des estimations empiriques de la durée de vie, basées sur des profils de décharge à courant constant, un profil de courant plus approprié pour l'application donnée, basé sur un cycle de vitesse représentatif de la conduite d'une motocyclette, a été utilisé. Par le biais d'un simulateur complet du véhicule, le cycle de courant a été extrait du cycle de vitesse. Ainsi, les travaux menés impliquent l'analyse expérimentale de la décharge cyclique de quatre cellules LiFePO 4 . Pendant plus de 1400 cycles, un banc d'essai complet a permis l'acquisition de la capacité, de la résistance interne, du courant, de la tension ainsi que de la température de surface. [symboles non conformes]

No description available.

Applications of biotechnology in drug delivery and medical instrumentation and energy storage have been gaining popularity. Especially, utilization of biotechnology for energy storage is attracting attention due to its environmentally friendly nature and cost efficiency. In this project, a filamentous bacteriophage, M13, to fabricate metal oxide battery electrodes. M13 phage is 6.5 nm wide and 800 nm long, and can act as a template to produce nano-sized metal oxide particles. A method to prepare manganese oxide electrodes was developed, where the phage is integrated with the oxide into a nanocomposite. The composite material was used to make a high capacity electrode for lithium ion batteries. The M13 templated manganese oxide, Mn3O4, could deliver a high initial capacity of 766 mAh/g, and recorded a stabilized discharge capacity of ~800 mAh/g even after 60 cycles.

Lithium ion batteries (LIBs) play an essential role in modern life. Although relatively unknown throughout past decades, LIBs have supplanted several categories of chemically rechargeable batteries including lead-acid, nickel-cadmium and nickel-hydrogen batteries. Nowadays, LIBs dominate the market of portable electronic devices such as mobile phones, digital cameras and laptops. As the price of petroleum keeps increasing, electrically powered or assisted vehicles using LIBs are similarly gaining in the automotive market. However, current state-of-art LIBs using graphite as their electrical anode and Li metal oxides as the cathode are facing major challenges. For example, the current LIBs are approaching their capacity limit. Batteries that can maintain high charge and discharge rates are in great demand, which has not been adequately addressed by modern LIBs. Safety issues with these current batteries are being reported even from some market leaders such as Boeing and Tesla. Herein, several categories of novel anode materials have been investigated in a search for promising candidates to enable evolution of the next generation of lithium ion batteries. This research included silicon-carbon based materials, especially silicon-graphene (Si-G) materials and their derivatives, and transitional metal based materials, e.g., cobalt oxide (Co3O4). In this proposed work, Si-G composites were synthesized via a freeze-drying method; the conditions of the synthesis were controlled and adjusted to obtain a Si-G composite with the most promising morphology as well as battery performance. Based on preliminary results, graphene wrapped silicon electrodes showed significantly improved cycling performance than bare silicon electrodes. At high charge and discharge rates it was found that Si-G composites also showed superior stability and capacity retention over bare silicon electrodes. After 200 cycles, the optimized Si-G composite maintained a capacity retention close to 100%, with a capacity of 800 mAh g-1 at a 0.2 C rate and 600 mAh g-1 at a 1 C rate. This observation was a prominent increase from the performance of commercial graphite-based batteries at a theoretical capacity 372 mAh g-1. Considering the facile fabrication method and increasing use of commercial silicon nano-particles (Si-NPs) into account, Si-G composites could be a promising candidate for the anode material in LIBs. Extended work on the Si-G project also involved further decorations based on the Si-G composite synthesized from the method previously mentioned, as well as improvement on the synthesis method to make it more applicable for industrial purposes. Cobalt Oxide (Co3O4), a transitional metal oxide which has a theoretical capacity of 890 mAh g-1, draws attention as an anode material in LIBs due to its capacity compared to graphite and heavily reduced degradation compared to silicon. A novel electrode fabrication procedure was adopted in this research together with a simple material-synthesizing methodology. Similar to common silicon electrodes, Co3O4 suffers from poor electron conductivity volume change upon cycling. Herein the Co3O4 active material is directly deposited on stainless steel mesh, serving as both a current collector and a substrate for the active material. Through adapting the electrode fabrication process by directly depositing on the stainless steel electron conductor, the traditional conductive carbon material and binder requirements can be avoided. As a result, the process is reduced in both cost and complexity. The presented novel electrode design facilitates both ion diffusion and electron transportation, improving the overall performance of the material in LIBs. After 100 cycles of charge and discharge, Co3O4 on stainless steel mesh shows a capacity around 770 mAh g-1, which is more than twice that of graphite. The capacity retention was around 90% in this case.

The power requirement for the soldier's equipment is largely supplied by batteries. Situational awareness is critical for a soldier to perform his tasks. Therefore the radio used by the soldier is a key element in situational awareness and also consumes the most power. The South African National Defence Force (SANDF) uses the A43 tactical radio specifically designed for them. The radios are regarded as old technology but will be in use for about another five years. The radios still use non-rechargeable alkaline batteries which do not last very long and are not cost effective. The purpose of this study is to research the new generation secondary batteries as a possible replacement for the alkaline battery packs. The new generation batteries investigated in this study are the latest rechargeable batteries, also called secondary batteries. They include nickel cadmium, nickel metal hydride, lithium ion, rechargeable alkaline manganese and zinc air. The main features of rechargeable cells are covered and the cell characteristics are defined to allow the technology to be matched to the user requirement. Li-ion technology was found to be the best choice. This research also showed that international trends in battery usage are towards Li-ion. A new Li-ion battery was designed based on commercial cells. Tests showed that commercial Li-ion cells can be used in the radio and that they outperform the current battery by far. The study also examined the design of a New Generation Battery System consisting of an intelligent battery, a charger which uses a Systems Management Bus and a battery 'state of health" analyser to assist the user to maintain the batteries. Tests were done to demonstrate that the battery can withstand typical military environmental conditions. Expected military missions for a battery system were defined and used to compare the cost between the existing batteries and the new batteries system. Important usage factors which will influence the client when using a New Generation Battery System were addressed. To summarise, this study showed that by using a New Generation Battery System, the SANDF could relieve the operational cost of the A43 radio while saving on weight and enabling the soldier to carry out longer missions. / Thesis (M.Ing. (Electronical Engineering))--North-West University, Potchefstroom Campus, 2008.

Rechargeable lithium sulfur (Li-S) batteries are potentially safe, environmentally friendly and economical alternative energy storage systems that can potentially be combined with renewable sources including wind solar and wave energy. Sulfur has a high theoretical specific capacity of ~1680 mAh/g, attainable through the reversible redox reaction denoted as S8+16Li ↔8Li¬2S, which yields an average cell voltage of ~2.2 V. However, two detrimental factors prevent the achievement of the full potential of the Li-S batteries. First, the poor electrical/ionic conductivity of elemental sulfur and Li2S severely hampers the utilization of active material. Second, dissolution of intermediate long-chain polysulfides (Li2Sn, 2<n<7) into the electrolyte and their shuttle between cathode and anode lead to fast capacity degradation and low Coulombic efficiency. As a result of this shuttle process, insoluble and insulating Li2S/Li2S2 precipitate on the surface of electrodes causing loss of active material and rendering the electrode surface electrochemically inactive. Extensive research efforts have been devoted to overcome the aforementioned problems, such as combination of sulfur with conductive polymers, and encapsulation or coating of elemental sulfur in different nanostructured carbonaceous materials. Noteworthy, sulfur-polyacrylonitrile (SPAN) composites, wherein sulfur is chemically bond to the polymer backbone and PAN acts as a conducting matrix, have shown some success in suppressing the shuttle effect. However, due to the limited electrical conductivity of polyacrylonitrile, the capacity retention and rate performance of the SPAN systems are still very modest, which shows only 67 % retention of the initial capacity after 50 cycles for the binary system. Recently, graphene has been intensively investigated for enhancing the rate and cycling performance of lithium sulfur batteries. Graphene, which has a two-dimensional, one-atom-thick nanosheet structure, offers extraordinary electronic, thermal and mechanical properties. Herein, a sulfur-polyacrylonitrile/reduced graphene oxide (SPAN/RGO) composite with unique electrochemical properties was prepared. PAN is deposited on the surface of RGO sheets followed by ball milling with sulfur and heat treatment. Infrared spectroscopy and microscopy studies indicate that the composite consists of RGO decorated with SPAN particles of 100 nm average size. The PAN/RGO composite shows good overall electrochemical performance when used in Li/S batteries. It exhibits ~85% retention of the initial reversible capacity of 1467 mAh/g over 100 cycles at a constant current rate of 0.1 C and retains 1100 mAh/g after 200 cycles. In addition, the composite displays excellent Coulombic efficiency and rate capability, delivering up to 828 mAh/g reversible capacity at 2 C. The improved performance stems from composition and structure of the composite, wherein RGO renders a robust electron transport framework and PAN acts as sulfur/polysulfide absorber.