<p>The widespread commercialization of electric vehicles is currently hindered by their inability to compete with conventional gasoline-powered vehicles in terms of refueling time. The main barrier to achieving fast charge of lithium-ion batteries is the plating of metallic lithium on the surface of the graphite negative electrode, which is known to occur most prevalently at high C-rates, low temperatures, and high states of charge (SOC). While it is accepted that the lithium plating process is largely reversible, the factors affecting the reversibility of lithium plating have not been thoroughly investigated. This work seeks to determine the most influential factors affecting the reversibility of lithium plating in order to devise strategies to mitigate long-term damage to the cell if lithium plating has been detected. It was determined that the temperature during the rest phase following plating has the most significant influence on plating reversibility, with cells undergoing rest at 30 ℃ exhibiting nearly twice the Coulombic inefficiency of cells undergoing rest at 0 ℃. Additionally, a novel technique was developed to observe the relaxation processes directly in a graphite electrode just after lithium plating has occurred. The occurrence of electrochemical stripping and the dissolution of overshooting phases in graphite were verified through direct <i>in-situ</i> observation. A two-part model is presented to describe the progression of the relaxation processes in graphite after lithium plating occurs under high rate operation.</p>

Advancements in Li-ion batteries are needed especially for the development of electric vehicles and stationary energy storage. Prior research has shown mesoscale variations in electrode electronic conductive properties, which can cause capacity loss and uneven electrochemical behavior of Li-ion batteries. A micro-four-line probe (μ4LP) was used to measure electronic conductivity and contact resistance over mm-length scales in that prior work. This work describes improvements to overcome the challenge of unreliable surface contact between theμ4LP and the sample. Ultimately a second generation flexible probe called the micro-radial-surface probe (μ4LP) was designed and produced. The test fixture was also optimized to obtain consistent contact with the new measurement probe and to perform measurements at a lower force. The μ4LP was then used to study the effect of heterogeneity on calendering, which is the compression of electrode films to obtain a uniform thickness and desired porosity. The thickness, electronic conductivity and contact resistance of two cathodes and one anode were measured before and after calendering. The the spatial standard deviation divided by the mean was used as a measure of heterogeneity. The results show variability in conductive properties increased for two of the three samples after calendering, despite the increased uniformity in thickness of the electrodes. This suggests that additional quality control metrics are needed besides thickness to be able to identify uneven degradation and produce longer lasting batteries.

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. 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. 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 predicted growth in demand for electric vehicles (EVs) has given rise to increasing use of lithium-ion batteries (LIBs), which are the source of energy used in all EVs. Recycling of spent LIBs not only can supply more materials to manufacturing new LIBs, but also can mitigate haz-ardous waste disposal in the environment. Direct recycling focuses on separating cathode materials to be re-purposed or remanufactured. Delamination of cathode materials is the necessary first step; however, it is fraught with difficulties due to the strong adhesive forces provided by the polyvi-nylidene fluoride (PVDF) binder that is widely used in LIBs. The widely accepted delamination methods are N-Methyl-2-pyrrolidone (NMP) solvent dissolution and direct calcination, which are not desirable due to either environmental and health concerns or high energy consumption.</p> <p>The lithium chemical systems (LiCl, LiNO₃, and LiOH) and their binary eutectic systems, were systematically studied to recover heterogeneous cathode active materials (NMC 111 and LMO) from spent LIBs of EVs. The LiOH-LiNO₃ eutectic system showed 98.3% peel-off effi-ciency under preferable conditions. The recycled products were characterized using ICP-OES, XPS, SEM, and XRD. There were minimal changes in chemical composition, morphology, or crystal structure of the recycled cathode materials after LiOH-LiNO3 eutectic treatment, compared with those recycled with an AlCl₃-NaCl eutectic molten salt treatment that introduces more Al contamination and morphological defects.  </p> <p>In order to avoid corrosive chemicals and minimize particle agglomeration, additional lith-ium salts were investigated, including LiOAc (lithium acetate), Li₂CO₃, and Li₂SO₄. A peel-off efficiency of up to 98.5% was achieved at a LiOAc to LiNO₃ molar ratio of 3:2, salt to cathode mass ratio of 10:1, temperature of 300° C, and a holding time of 30 minutes. To validate the effect of the cations, the recycled products from the molten sodium salt system (NaOAc-NaNO3) were tested. The lithium salt system achieved separation at a lower temperature. Use of LiOAc-LiNO₃ minimized morphological changes compared with direct calcination.</p> <p>The effective separation in LiOH-LiNO3 or LiOAc-LiNO3 molten salt systems was based on promotion of PVDF decomposition, and these two systems may be feasible for recycling other typical cathodes (LCO and LFP) where PVDF is used as the binder. Use of molten lithium salts as alternatives to direct calcination or use of other solvents, may help facilitate recycling of spent LIBs, and even achieve a way for closed loop direct recycling of materials.</p> <p> Additionally, a chemical-free pressure washing system was studied to overcome the adhe-sion provided by PVDF. Although the pressure washing system was not able to remove PVDF from the cathode materials, nearly instant separation from the aluminum backing was achieved when the shear stress and normal stress provided by the impacting of high-pressure waterjet was stronger than the binding forces. Factors investigated included water pressure, distance between the nozzle and cathode, the incident angle of the water jet, and the nozzle type (sprayer angle). A 34-1 fractional factorial design was used to evaluate the parameters and find the optimal operating conditions. A small amount of Al and consistent morphology (of nearly pristine cathode active materials) were detected. Three kinds of recycled cathode materials (NMC&LMO, LCO, and LFP) were used as inputs to investigate a sulfuric acid leaching process, indicating high leaching effi-ciencies (lithium > 90% and cobalt > 85%).</p> <p>The degradation of cathode active materials or PVDF affects the adhesion force between cathode materials layer and Al current collector. Because delamination replies on inactivation of bonding forces provided by PVDF, it is believed that the storage environment (air, O₂ or H_{<strong>2</strong>}O) will affect the performances of delamination to some extent. Three representative methods (direct cal-cination, solvent extraction, and pressure washing system) of delamination were selected to eluci-date the effect from air exposure time. Direct calcination was barely influenced and stably sepa-rated CAMs in terms of peel-off efficiency. The pressure washing system or solvent extraction exhibited high peel-off efficiency using control samples, but the performance regarding either Al contamination or separation efficiency  significantly worsened after long air exposure time. This hypothesis could explain lack of reproducibility of some results in different studies and highlight the importance of strict storage condition of spent LIBs to direct recycling technology. </p> <p>Overall, this thesis examines innovative delamination methods for the development of cost-efficient and environmentally friendly direct recycling of spent LIBs. Application of the eutectic molten lithium salt system (LiOH-LiNO₃ and LiOAc-LiNO₃) or pressure washing system indicates promising benefits to reduce toxic gas emission and energy consumption, and accelerate the cir-cular economy.</p>

A behavioral battery modeling approach aimed at large format batteries is the topic of this dissertation. Drawing from the development of cell - level electrical analogue battery models, the comprehensive modeling approach described here shows how to scale a high fidelity battery cell model to a computationally fast battery model of large format batteries for system level design and simulation. The accurate behavioral battery model is performance - driven and tailored for stringent system simulation requirements. A novel bandwidth - based parameter extraction algorithm and advanced State of Charge (SOC) - Open Circuit Voltage (OCV) profile identification method are presented. While a real-world battery system is non-linear and time varying, a truncated representation of the system is provided by a commonly studied non-physical "electrical analogue" battery model. However, the limited bandwidth characteristic of the electrical analogue battery model is often overlooked. The reported algorithm starts by assessing a desired battery application, followed by modeling the battery according to the application bandwidth, and then estimating the model parameters using the sequential quadratic programming method. This approach recognizes and makes use of the limited bandwidth of the battery model by reconciling the bandwidth of the application into the bandwidth of the electrical analogue battery model. The model will help in vehicle concept development, and provide an analytical tool during the process of selecting the most appropriate battery during system design but before a prototype system is built. Another application is to represent the plant in realtime model-based battery management and control systems embedded in actual application controllers. This modeling approach is independent of the battery chemistry and therefore it is applicable to lithium-ion, nickel-metal-hydride (NiMH), and lead-acid batteries, among others.

The objective of this project is to present a Lithium Ion battery voltage model derived using systems engineering principles. This paper will describe the details of the model and the implementation of the model in practical use in a power system. Additionally, the model code is described and results of the model output are compared to battery cell test data. Finally, recommendations for increased model fidelity and capability are summarized. The modeling theory has been previously documented in the literature but detailed implementation and application of the modeling theory is shown. The detailed battery cell test voltage profiles are proprietary; as such this project will not include axis values, often used in presentation of proprietary data in the public domain. The objective of this presentation is still achieved, as the modeling implementation and results are clearly demonstrated.

<p> Ceramic samples of Li2+xYxZr1-xO3 with x=0 to 0. 1, Li8+xYxZr1-xO6 with x=0 to 0.2, Li1-xYxZr1-xO2 with x=0 to 0.5 and Li1+xZrxY1-xO2+x with x=0 to 0. 3 were prepared via conventional solid reactions. The solubilities, crystal structures and microstructures in these samples were studied by x-ray diffraction(XRD), infrared spectra, differential thermal analysis(DTA) and scanning electron microscopy(SEM). The results show that the solubilities are 0.05≤X<0.1 for Li2+xYxZr1-xO3 and Li8+xYxZr1-xO6, 0.1≤x<0.15 for Li1-xYxZr1-xO2, and x≥0.3 for Li1+xZrxY1-xO2+x, respectively. The crystal structures of the solid solutions of Li2+xYxZr1-xO3 and Li8+xYxZr1-xO6 are the same as Li2ZrO3 and Li8ZrO6, respectively but the cell constants change slightly with x, while the structure of Li1-xYxZr1-xO2 and Li1+xZrxY1-xO2+x changes from monoclinic for pure LiYO2 (x=0) to tetragonal (x≥0.005). The sinterability of Li2ZrO3 improves greatly with yttrium additions to Li2ZrO3. </p> <p> The conductivities of the samples were measured by complex impedance spectroscopy and dc polarization. The results show that lithium conductivity in Li2+xYxZr1-xO3 samples increases slightly from 3.9x10^-6 to 5.0x10^-6 S/cm at 400°C as x increases from 0 to 0.05 and the corresponding conduction activation energy decreases slightly from 0.99 to 0.92 eV. Based on the effective medium theory, the conductivity increase in the solid solution was estimated to be 3% for x=0.05 compared with pure Li2ZrO3 crystal.</p> <p>For Li8+xYxZr1-xO6 samples, a mixture of LiOH and Li2CO3, which melts at about 430°C, can be formed during the processing and measurements. The ionic conductivity depends to a large degree on the microstructure(the amount and distribution of the mixture) below 430°C. The lithium conductivity at 435°C increases from 1.0x10^-2 to 6.9x10^-2 S/cm as x increases from 0 to 0.05. The electronic contribution to total conductivity is lower than 1% below 435°C.</p> <p> The ionic conductivity in the tetragonal phase of Zr-doped LiYO2 is much lower than in pure monoclinic LiYO2. The conductivity values at 500°C are 1.3x10^-2 for pure LiYO2 and 1.2x10^-4 for Li1.3Zr0.3Y0.7O2.3. The ionic conduction activation energy in the tetragonal Zr-doped LiYO2 is much higher than pure LiYO2.</p> <p> The thermal stability and the hydrolysis tendency for Li2ZrO3, Li8ZrO6 and LiYO2 were examined by thermodynamic calculations and by experiments.</p> / Thesis / Master of Engineering (MEngr)

Additives used in the cathode of a Lithium-ion (Li-ion) battery to improve electrical conductivity can negatively impact the ionic conductivity and specific capacity. Therefore, recent focus on the design of Li-ion battery is on the additive-free cathodes. This research work aims to provide a simple rule for the design of cathode microstructure using extensive study of the effect of particle size and volume fraction on effective electrical conductivity. Most design methods used to model the effective transport properties of lithium ion battery electrodes utilize the approximations based on Bruggeman’s formula. However, this formula does not consider the microstructure geometry and hence cannot accurately predict the effective transport properties of complicated microstructure like those of Li-ion battery electrodes. In this thesis, based on the principles of mathematical homogenization, an extensive analysis of randomly generated two-phase microstructures idealized for li-ion battery cells is carried out to obtain more accurate estimates of the effective electrical conductivity. To this end, a wide range of values of particle size, volume fraction and conductivity ratios are considered to evaluate the effective conductivity values. From these results, an explicit formulation based on these three parameters to predict the effective conductivity is provided to establish a framework for a simple design rule for additive-free cathode microstructures. Finally, the significance of the microstructural information is highlighted by studying the discharge characteristics of a battery for a theoretical battery model using the Brugemman’s formulation as well as the proposed formulation based on the mathematical homogenization technique. / Thesis / Master of Applied Science (MASc)

Major vehicle manufacturers are committed to expand their electrified vehicle fleet in upcoming years to meet fuel efficiency goals. Understanding the effect of the charge/discharge cycle profiles on battery durability is important to the implementation of batteries in electrified vehicles and to the design of appropriate battery testing protocols. In this work, commercial high-power prismatic lithium ion cells were cycled using a pulse-heavy profile and a simple square-wave profile to investigate the effect of cycle profile on the capacity fade of the battery. The pulse-heavy profile was designed to simulate on-road conditions for a typical hybrid electric vehicle, while the simplified square-wave profile was designed to have the same charge throughput as the pulse-heavy profile, but with lower peak currents. The batteries were cycled until each battery achieved a combined throughput of 100 kAh. Reference Performance Tests were conducted periodically to monitor the state of the batteries through the course of the testing. The results indicate that, for the batteries tested, the capacity fade for the two profiles was very similar and was 11 % ± 0.5 % compared to beginning of life. The change in internal resistance of the batteries over the course of the testing was also monitored and found to increase 21% and 12% compared to beginning of life for the pulse-heavy and square-wave profiles respectively. Cycling tests on coin cells with similar electrode chemistries as well as development of a first principles, physics based model were done in order to understand the underlying cause of the observed degradation. The results from the coin cells and the model suggest that the loss of active material in the electrodes due to the charge transfer process is the primary cause of degradation while the loss of cyclable lithium due to side reactions plays a secondary role. These results also indicate that for high power cells, the capacity degradation associated with the charge-sustaining mode of operation can be studied with relatively simple approximations of complex drive cycles. / Ph. D. / Major vehicle manufacturers are committed to expand their electrified vehicle fleet in upcoming years to meet fuel efficiency goals. Understanding the effect of the charge/discharge cycle profiles on battery durability is important to the implementation of batteries in electrified vehicles and to the design of appropriate battery testing protocols. In this work, commercial lithium ion cells were tested using two profiles with the same energy transfer; a pulse-heavy profile to simulate on-road conditions for a typical hybrid electric vehicle, and a simplified square-wave profile with the same charge flow as the pulse-heavy profile, but with lower currents. Cycling tests on coin cells with similar electrode chemistries as well as development of a first principles, physics based model were done in order to understand the underlying cause of the degradation. The results suggest that the degradation observed is not dependent on the type of profile used. These results also indicate that for high power cells, the capacity degradation associated with the charge-sustaining mode of operation can be studied with relatively simple approximations of complex drive cycles.

Advance Vehicle Technology Competitions (AVTCs) have been around for 30 years. Since 1994, the Hybrid Electric Vehicle Team (HEVT) at Virginia Tech has participated in AVTCs to pursue hybrid technologies. HEVT participated in a four-year AVTC called EcoCAR 3. At the beginning of the competition, HEVT introduced an ultra-rapid onboarding process, the Independent Study (IS) program, to involve non-seniors with the team. Although the IS program provides an incredible experience to non-seniors, it lacks hands-on experience related to the actual work students do once they become full-fledged team members. The challenge is to introduce two hands-on supplemental projects: the energy storage system (ESS) and the motor system. Each project is considered low voltage (LV) for safety and simplicity, however high voltage techniques are used for learning purposes. The LV ESS is used to power up an LV motor system. To limit depletion of the battery energy, another LV motor system is used as a generator to recharge the LV ESS. The lead faculty advisor, Dr. Douglas Nelson, and the project manager, Andres Coello, are working in congruence to introduce a smooth transition of the projects into HEVT's IS program. The hands-on projects are expected to last one semester. The goals are to guide students in the design, construction and testing of both systems. The hands-on supplemental projects are also meant to aid the Applied Automotive Engineering (AAE) curriculum by filling important knowledge gaps current AAE modules are missing. / Master of Science / The Hybrid Electric Vehicle Team of Virginia Tech has participated in Advanced Vehicle Technology Competitions since its inception in 1994. These competitions challenge universities to reengineer and convert a vehicle into a hybrid vehicle. The goal is to train the next generation of automotive students by providing real world engineering experiences. The latest Advanced Vehicle Technology Competition is a four-year competition called EcoCAR 3. Due to complexity of the project, the Hybrid Electric Vehicle Team introduced an onboarding process to recruit and teach students the required knowledge of hybrid vehicles. To further improve the program, two projects are created to provide hands-on experience and visual learning about the electric layout of a hybrid vehicle. The first project is a low voltage battery pack and the second project is a low voltage motor dynamometer system. Both projects complement each other, meaning the battery pack acts as a power supply to the motor system. Overall, these projects are chosen to provide a good understanding to incoming students in the onboarding process about batteries and motors. Finally, practices used by the Hybrid Electric Vehicle Team are implemented in the project designs to improve the overall experience of students in the onboarding process and to improve knowledge transfer.