Since the transportation sector wants to move away from fossil fuels and become more dependen ton clean and green energy, the use of rechargeable batteries is a good solution. Lithium-based batteries work very well as rechargeable batteries in electric vehicles. To extend the cycle life of lithium-based batteries a reversed Li+-trapping protocol has been implemented to extract lostcapacity. Prior to the start of this project, reversed Li+-trapping has been used on a proof-of-concept level and no specific protocol has been utilised in conjunction with full cells. With a protocol that uses constant voltage discharge steps on every fifth cycle, trapped Li+ can diffuse out from the graphite (anode) and travel back to the NMC811 (cathode). This will result in a lower capacity loss than if it only had cycled with constant current, using a C-rate of 1C. If a cell is operated with a constant voltage discharge step on every cycle, high capacity can be maintained for many cycles. This could potentially be used as a formation cycle protocol. The capacity is higher in the long run if the constant voltage discharge step is applied on every fifth cycle rather than every cycle. With a constant voltage discharge cell voltage of 2.8 V good results are obtained. A constant voltage discharge cell voltage of 0 V will however destroy the cell due to Cucurrent collector dissolution.

The work presented in this thesis can be divided into two research areas. First, two sets of organic-inorganic hybrid nanocomposites containing phenolic resin/trisilanolphenyl-POSS and phenolic resin/octa(aminophenyl)-T8-POSS nanocomposites were synthesized and the morphology and properties were investigated. Octa(aminophenyl)-T8-polyhedral silsesquioxane is an octafunctional-T8-POSS containing eight aniline-like amino groups, one on each corner silicon atom. It was synthesized in our laboratory by an improved two-step reaction sequence; nitration (HNO3) and reduction (HCOOH/Et3N). Varying amounts of POSS were codissolved with a resole phenolic resin in organic solvent. This was followed by solvent removal and thermal curing. Intermolecular interactions in these nanocomposites were probed by FT-IR. The micro-morphology and aggregation state of POSS were investigated using SEM, TEM, and WAXD studies. The thermal and mechanical properties and thermal stabilities of these composites were investigated by DMTA, DSC, and TGA. Second, two types of carbon-covered mono- and bimetallic (Sn, and Sn/Sb alloy) nanorods for use as anode materials in lithium ion batteries were synthesized by a thermal chemical vapor deposition method. Commercial antimony and tin oxide (Sb3O4/SnO2) nanopowders and added tin (IV) oxide (SnO2) nanoparticles (~19 nm) were used as the precursors for the growth of bimetallic Sn/Sb alloy and monometallic Sn nanorods, respectively. In addition, the shape of the products recovered were different when different hydrocarbon gas flow rates were used for growing intermetallic nanorods in carbon templates. Acetylene and methane were the gases tried. The morphologies and structures of the intermetallic nanorods in carbon templates were investigated using SEM and TEM and proved by X-EDS, XRD, and XPS studies.

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Recently, Electric Vehicles (EVs) have received extensive consideration since they offer a more sustainable and greener transportation alternative compared to fossil-fuel propelled vehicles. Lithium-ion batteries are increasingly being considered in EVs due to their high energy density, slow loss of charge when not in use, and for lack of hysteresis effect. Conventionally, the batteries are connected in series to achieve the load voltage requirements. However, for the batteries with intrinsic discrepancies or different initial states, cell balancing is a concern because it is the weakest cell that determines the empty point for the battery and an undercharged series cell will shorten the lifetime of the entire pack. The imbalance potential of the battery behaves as the way of State-of-Charge (SOC) mismatch and it’s also temperature dependent. Therefore, in this thesis, an active cell balancing optimization was proposed and conducted in MATLAB to optimize battery unused capacity and thermal effect simultaneously based on bi-directional balancing system and pre-estimated SOC. The bi-directional balancing system was physically built based on “Fly-back” converter to compare balancing performance in discharging, idle, and plug-in charging mode. Moreover, a battery combined model worked collaboratively with robust state and parameter estimation strategies, namely Extended Kalman Filter (EKF) and Smooth Variable Structure Filter (SVSF) in order to estimate SOC for cell balancing. As a result, the proposed method can effectively optimize SOC mismatch around 2.5%. Meanwhile, more uniform temperature was achieved and the maximum temperature can be reduced about 7 ℃. / Thesis / Master of Applied Science (MASc)

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The thesis presents a modeling framework for simulating three dimensional effects in lithium-ion batteries. This is particularly important for understanding the performance of large scale batteries used under high power conditions such as in hybrid electric vehicle applications. While 1D approximations may be sufficient for the smaller scale batteries used in cell phones and laptops, they are severely limited when scaled up to larger batteries, where significant 3D gradients can develop in concentration, current, temperature, and voltage. Understanding these 3D effects is critical for designing lithium-ion batteries for improved safety and long term durability, as well as for conducting effective design optimization studies. The model couples an electrochemical battery model with a thermal model to understand how thermal effects will influence electrochemical behavior and to determine temperature distributions throughout the battery. Several modeling example results are presented including thermal influences on current distribution, design optimization of current collector thickness and current collector tab placement, and investigation of lithium plating risk in three dimensions. / text

Chemical Engineering / The successful commercialization of lithium-ion batteries is responsible for the ubiquity of personal electronics. The continued development of battery technology, as well as its application to new emerging markets such as electric vehicles, is dependent on developing safer, higher energy density, and cheaper electrode materials and battery chemistries. The focus of this dissertation is on identifying, characterizing and optimizing new materials for lithium- and sodium-ion batteries. Batteries are incredibly complex engineered systems with each electrode composed of conductive additive and polymeric binder in addition to the active material. All of these components must work together for the electrode system to function properly. In this work, glancing angle deposition (GLAD) and reactive ballistic deposition (RBD) are employed to grow thin films of novel materials with reproducible morphology for use as battery electrodes. The use of these thin film electrodes eliminated the need for conductive additives and polymer binders allowing for the active materials themselves to be studied rather than the whole electrode system. Two techniques are employed to modify the chemical properties of the electrode materials grown by RBD and GLAD: Alloying (Si-Ge alloys for Li-ion batteries and Sn-Ge alloys for Na-ion batteries) and partial chalcogenation (partial oxidation of silicon, and partial sulfidation and selenidation of germanium for Li-ion batteries). Both of these techniques are successfully employed to enhance the electrochemical properties of the materials presented in this dissertation. / text