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.

<p>The lithium ion battery is today mainly used in cell phonesand laptops. In the future, this kind of battery might beuseful in hybrid electric vehicles as well.</p><p>In this work, the main focus has been to gain more knowledgeabout the lithium ion battery in the hybrid electric vehicle(HEV) and more precisely to examine what processes of thebattery that are limiting at HEV currents. Both experiments andmathematical modelling have been used. In both cases, highrate, pulsed currents typical for the HEV, have been used.</p><p>Two manuscripts have been written. Both of them concern thebehaviour of the battery at HEV load, but from different pointsof view. The first one concerns the electrochemical behaviourof the battery at different ambient temperatures. Theexperimental results of this paper were used to validate amathematical model of a Li-ion battery. Possiblesimplifications of the model were identified. In this work itwas also concluded that the mass transfer of the electrolyte isthe main limiting process within the battery. The mass transferof the electrolyte was further studied in the second paper,where the concentration of lithium ions was measured indirectlyusing in situ Raman spectroscopy. This study showed that themathematical description of the mass transfer of theelectrolyte is not complete. One main reason of this issuggested to be the poor description of the physical parametersof the electrolyte. These ought to be further studied in orderto get a better fit between concentration gradients predictedby experiments and model respectively.</p>

The demand for high performance Lithium-ion batteries (LIBs) is increasing due to widespread use of portable devices and electric vehicles. Silicon (Si) is one of the most attractive candidate anode materials for the next generation LIBs because of its high theoretical capacity (3,578 mAh/g) and low operation potential (~0.4 V vs Li+/Li). However, the high volume change (>300%) during Lithium ion insertion/extraction leads to poor cycle life. The goal of this work is to improve the electrochemical performance of Si/C composite anode in LIBs. Two strategies have been employed: to explore spatial arrangement in micro-sized Si and to use Si/graphene nanocomposites. A unique branched microsized Si with carbon coating was made and demonstrated promising electrochemical performance with a high active material loading ratio of 2 mg/cm2, large initial discharge capacity of 3,153 mAh/g and good capacity retention of 1,133 mAh/g at the 100th cycle at 1/4C current rate. Exploring the spatial structure of microsized Si with its advantages of low cost, easy dispersion, and immediate compatibility with the prevailing electrode manufacturing technology, may indicate a practical approach for high energy density, large-scale Si anode manufacturing. For Si/Graphene nanocomposites, the impact of particle size, surface treatment and graphene quality were investigated. It was found that the electrochemical performance of Si/Graphene anode was improved by surface treatment and use of graphene with large surface area and high defect density. The 100 nm Si/Graphene nanocomposites presented the initial capacity of 2,737 mAh/g and good cycling performance with a capacity of 1,563 mAh/g after 100 cycles at 1/2C current rate. The findings provided helpful insights for design of different types of graphene nanocomposite anodes.

Lithium ion battery systems are promising solutions to current energy storage needs due to their high operating voltage and capacity. Numerous efforts have been conducted to model these systems in order to aid the design process and avoid expensive and time consuming prototypical experiments. Of the numerous processes occurring in these systems, solid state transport in particular has drawn a large amount of attention from the research community, as it tends to be one of the rate limiting steps in lithium ion battery performance. Recent studies have additionally indicated that purposeful design of battery electrodes using 3D microstructures offers new freedoms in design, better use of available cell area, and increased battery performance. The following study is meant to serve as a first principles investigation into the behaviors of 3D electrode architectures by monitoring concentration and cycle behaviors under realistic operating conditions. This was accomplished using computational tools to model the solid state diffusion behavior in several generated electrode morphologies. Developed computational codes were used to generate targeted structures under prescribed conditions of particle shape, size, and overall morphology. The diffusion processes in these morphologies were simulated under conditions prescribed from literature. Primary results indicate that parameters usually employed to describe electrode geometry, such as volume to surface area ratio, cannot be solely relied upon to predict or characterize performance. Additionally, the interaction between particle shapes implies some design aspects that may be exploited to improve morphology behavior. Of major importance is the degree of particle isolation and overlap in 3D architectures, as these govern gradient development and lithium depletion within the electrode structures. The results of this study indicate that there are optimum levels of these parameters, and so purposeful design must make use of these behaviors.

The Li-ion field of battery research has in the latest decades made substantial progress and is seen to be the most promising battery technology due to the high volume and specific energy densities of Li-ion batteries. However, in order to achieve a battery capable of competing with the energy density of a combustion engine, further research into new electrode materials is required. As the cathode materials are the limiting factor in terms of capacity, this is the main area in need of further research. The introduction of 3-D electrodes brought new hope as the ion transportpath is decreased as well as an increased electrode area leading to an increased capacity. This thesis work has focused on the development of aluminium 3-D current collectors in order to improve the electrode area and shorten the Li-ion transportpath. By using a template assisted electrodeposition technique, nanorods of controlled magnitude and order can be synthesized. Furthermore, the electrodeposition brings excellent possibilities of upscaling for future industrial manufacturing of the batterycells. A polycarbonate template material which showed interesting properties,was used in the electrodeposition of aluminium nanorods. As the template pores were nonhomogeneously ordered a number of nonordered nanorods were expected to arise during the deposition. However, a surplus of nanorods in reference to the template pores was acquired. This behavior was investigated and a hypothesis was formed as to the mechanism of the nanorod formation. In order to achieve acomplete cathode electrode, a coating of an ion host material on the nanorods isneeded. Due to its high capacity and voltage, vanadium oxide was selected. Based on previous work with electrodeposition of V2O5 on platinum, a series of experiments were performed to mimic the deposition on an aluminium sample. Unfortunately, the deposition was unsuccessful as the experimental conditions resulted in aluminium corrosion which in turn made deposition of the cathode material impossible. The pH dependence of the deposition was evaluated and the conclusion was drawn, that electrodeposition of vanadium oxide on aluminium is not possible using this approach.

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Lithium-ion batteries are the most promising rechargeable battery system for both vehicle applications and stationary storage of electricity produced from renewable sources such as solar and wind energies. However, the current lithium ion technology does not fully meet the requirements of these applications in terms of energy and power density. One approach to realizing a combination of high energy and power density is to use a composite cathode that consists of the high-capacity lithium-rich layered oxide Li[Li,Mn,Ni,Co]O2 and the high-voltage spinel oxide LiMn1.5Ni0.5O4. This dissertation explores the unique structural characteristics and their effect on the electrochemical performance of the layered-spinel composite oxide cathodes along with individual layered and spinel oxides over a wide voltage range (5.0 – 2.0 V). Initially, the effect of cation ordering on the electrochemical and structural characteristics of LiMn1.5Ni0.5O4 during cycling between 5.0 and 2.0 V were investigated by an analysis of the X-ray diffraction (XRD) and electrochemical data. Structural studies revealed that the cation ordering affects the size of the empty-octahedral sites in the spinel lattice. The differences in the size of the empty-octahedral sites affect the discharge profile below 3 V due to the variation in lattice distortion during lithium ion insertion into 16c octahedral sites. With the doped LiMn1.5Ni0.5-xMxO4 (M = Cr, Fe, Co, and Ga) spinels, different dopant ions have different effects on the degree of cation ordering due to the differences in ionic radii and surface-segregation characteristics. The compositional and wt.% variations of the layered and spinel phases from the nominal values in the layered-spinel composites were obtained by employing a joint XRD and neutron diffraction (ND) Rietveld refinement method. With the obtained composition and ex-situ XRD data, the mechanism for the increase in capacity and the facile phase transformation of the layered phase in the composite cathodes to a 3 V spinel-like phase during cycling was proposed. Investigations focused on synthesis temperature revealed that the electrochemical characteristics of the composites are highly affected by the synthesis temperature due to the change in the surface area of the sample and cation ordering of the spinel phase. In addition, the electrochemical performance of the lithium-rich layered oxide Li[Li,Mn,Ni,Co]O2 could be improved by blending it with a lithium-free insertion host VO2(B) and by controlling the amount of lithium ions extracted from the layered lattice during the first charge process. / text

Lithium-ion batteries have revolutionized the portable electronics market, and they are currently pursued intensively for vehicle applications and storage of renewable energies (solar and wind energy). Cost, safety, cycle life, and energy and power densities are the critical parameters for these applications. With this perspective, there has been immense interest to develop new cathode and anode materials as well as to develop novel synthesis and processing approaches. This dissertation explores the use of novel synthesis approaches to obtain high-performance, nanostructured phosphate and silicate cathodes and iron oxide nanowire anodes and investigates their structure-property relationships. First, a novel microwave-solvothermal (MW-ST) approach has been developed to synthesize phase-pure, highly crystalline LiFePO₄ nanorods within 5-15 minutes at low temperatures of < 300 °C, without requiring reducing gas atmospheres. The LiFePO₄ nanorods, after forming a nanocomposite with conducting polymer or multi-walled carbon nanotubes or coating with conductive carbon, offer excellent cycle life and rate performance when implemented as cathodes in lithium-ion cells. In addition, other LiMPO₄ (M = Mn, Co, and Ni) olivine nanorods have also been synthesized by the MW-ST approach and characterized. The MW-ST process has then been extended to prepare a new class of carbon-coated, nanostructured silicates of the formula Li₂MSiO₄ (M = Fe and Mn). These materials have two times higher theoretical capacities (~ 330 mAh/g) than olivine phosphates (~ 170 mAh/g). Li₂FeSiO₄ exhibits practical discharge capacities of 148 mAh/g at room temperature and 203 mAh/g at 55 °C, with good rate capability and stable cycle life. Li₂MnSiO₄, on the other hand, shows higher discharge capacities of 210 mAh/g at room temperature and 250 mAh/g at 55 °C, but it exhibits poor rate performance and rapid capacity fade during cycling. In addition, carbon-coated olivine solid solution nano-particles of the formula LiM[subscript 1-y]M[subscript y]PO₄ (M = Fe, Mn, Co, and Mg), synthesized by a facile, high-energy mechanical milling process (HMME), have also been investigated. The electrochemical data reveal a systematic shift in the redox potential (open-circuit voltage) of the M²⁺/³⁺ couples in the LiM[subscript 1-y]M[subscript y]PO₄ solid solutions compared to those of the pristine LiMPO₄. The shifts in the redox potentials have been explained by the changes in the M-O covalence (inductive effect), which are caused by changes in the electronegativity of M or the M-O bond length or M-O-M interactions. Finally, a two-step microwave-hydrothermal process has been developed to synthesize carbon-decorated, single-crystalline Fe₃O₄ nanowires. The resulting iron oxide nanowires exhibit capacity values > 800 mAh/g with stable cycle life and high rate performance as an anode in lithium-ion cells. / text

Electric Vehicles (EVs) have gained acceptance as low or zero emission means of transportation. This thesis deals with the design of a battery cell testing platform and Lithium-Ion (Li-Ion) battery modeling for EVs. A novel regenerative cell testing platform is developed for cell cycling applications. A 300 W - 5 V cell cycler consisting of a buck and a boost converter is designed. Furthermore, a novel battery modeling approach is proposed to accurately predict the battery performance by dynamically updating the model parameters based on the battery temperature and State of Charge (SOC). The comparison between the experimental and the model simulation results of an automotive cell under real-world drive-cycle illustrates 96.5% accuracy of the model. In addition, the model can be utilized to assess the long-term impact of battery impedance on performance of EVs under real-world drive-cycles.

Electric Vehicles (EVs) have gained acceptance as low or zero emission means of transportation. This thesis deals with the design of a battery cell testing platform and Lithium-Ion (Li-Ion) battery modeling for EVs. A novel regenerative cell testing platform is developed for cell cycling applications. A 300 W - 5 V cell cycler consisting of a buck and a boost converter is designed. Furthermore, a novel battery modeling approach is proposed to accurately predict the battery performance by dynamically updating the model parameters based on the battery temperature and State of Charge (SOC). The comparison between the experimental and the model simulation results of an automotive cell under real-world drive-cycle illustrates 96.5% accuracy of the model. In addition, the model can be utilized to assess the long-term impact of battery impedance on performance of EVs under real-world drive-cycles.