With carbon dioxide levels in our atmosphere reaching record highs and 2020 quickly approaching, California is expected to pave the way for the United States in terms of replacing fossil fuel generation facilities with various renewable energy power plants. It is well documented that the inherent variability and limited duty cycle of renewables has hindered their growth. Energy storage technologies represent the bridge that can help us cross the divide from where we stand to where we must stand in the next 6 years. Utility companies value services such as peak shaving, voltage support, and frequency regulation, all of which energy storage technologies can provide. Commercial and residential clients’ of the utility will begin to install their own storage systems once properly incentivized. In this paper, a control algorithm for Sodium Sulfur batteries is proposed with hopes that the aforementioned services will be provided to the utilities while system owners realize profit.

The increased demand for electric vehicles in recent years has driven the development of Li ion battery technology, yielding interesting trends in cathode materials. The layered cathode material Li(Ni1/3Mn1/3Co1/3)O2 gives 30% more reversible lithium extraction than the earlier LiCoO2 and the “overlithiated” material Li(Li0.2Mn0.54Ni0.13Co0.13)O2 gives a semi-reversible capacity 25% higher than Li(Ni1/3Mn1/3Co1/3)O2.1,2 6,7Li MAS NMR and 7Li MATPASS NMR were used to investigate the relation between the lithium ion and metal positions within these materials. It was found that Li(Ni1/3Mn1/3Co1/3)O2 showed a preference for Li ions to associate with Co at high voltages, that Mn4+ and Ni2+ showed some association and that the metals were not highly ordered. Li(Li0.2Mn0.5Ni0.13Co0.13)O2 showed a decrease in transition metal layer lithium upon cycling, in agreement with previous models, an ordering of the metal ions with the reinsertion of the lithium ions and a significant change in structure on deep discharge.3 These results will hopefully lead to more accurate modelling of the materials, understanding of reversibility and to increased reversible capacities in future cathode materials. Additionally work was done to enable high rate in-situ NMR spectra in which spectra are obtained from a cell while cycling in the bore of an NMR spectrometer. A Teflon Swagelok-style cell was designed and the effectiveness of solenoid and saddle coils were tested. It was found that for a 6 mm diameter cathode with a Li metal anode, at least half of the signal intensity could be obtained with a saddle coil whereas the signal was not detected when using a solenoid coil. / Thesis / Master of Science (MSc)

The invention of Li-ion batteries (LIBs) marks a new era of energy storage and allows for the large-scale industrialization of electric vehicles. However, the flammable organic electrolyte in LIBs raises significant safety concerns and has resulted in numerous fires and explosion accidents. In the pursuit of more reliable and stable battery solutions, interests in aqueous batteries composed of high-energy cathodes and water-based electrolytes are surging. Limited by the narrow electrochemical stability window (ESW) of water, conventional aqueous batteries only achieve inferior energy densities. Current development mainly focuses on manipulating the properties of aqueous electrolytes through introducing excessive salts or secondary solvents, which enables an unprecedentedly broad ESW and more selections of electrode materials while also resulting in some compromises. On the other hand, the interaction between electrodes and aqueous electrolytes and associated electrode failure mechanism, as the key factors that govern cell performance, are of vital importance yet not fully understood. Owing to the high-temperature calcination synthesis, most electrode materials are intrinsically moisture-free and sensitive to the water-rich environment. Therefore, compared to the degradation behaviors in conventional LIBs, such as cracking and structure collapse, the electrode may suffer more severe damage during cycling and lead to rapid capacity decay. Herein, we adopted multi-scale characterization techniques to identify the failure modes at cathode–electrolyte interface and provide strategies for improving the cell capacity and life during prolonged cycling. In Chapter 1, we first provide a background introduction of conventional non-aqueous and aqueous batteries. We then show the current development of modern aqueous batteries through electrolyte modification and their merits and drawbacks. Finally, we present typical electrode failure mechanism in non-aqueous electrolytes and discuss how water can further impact the degradation behaviors. In Chapter 2, we prepare three types of aqueous electrolytes and systematically evaluate the electrochemical performance of LiNixMnyCo1-x-yO2, LiMn2O4 and LiFePO4 in the aqueous electrolytes. Combing surface- and bulk-sensitive techniques, we identify the roles played by surface exfoliation, structure degradation, transition metal dissolution and interface formation in terms of the capacity decay in different cathode materials. We also provide fundamental insights into the materials selection and electrolyte design in the aqueous batteries. In Chapter 3, we select LiMn2O4 as the material platform to study the transition metal dissolution behavior. Relying on the spatially resolved X-ray fluorescence microscopy, we discover a voltage-dependent Mn dissolution/redeposition (D/R) process during electrochemical cycling, which is confirmed to be related to the Jahn–Teller distortion and surface reconstruction at different voltages. Inspired by the findings, we propose an approach to stabilize the material performance through coating sulfonated tetrafluoroethylene (i.e., Nafion) on the particle, which can regulate the proton diffusion and Mn dissolution behavior. Our study discovers the dynamic Mn D/R process and highlights the impact of coating strategy in the performance of aqueous batteries. In Chapter 4, we investigate the diffusion layer formed by transition metals at the electrode–electrolyte interface. With the help of customized cells and XFM technique, we successfully track the spatiotemporal evolution of the diffusion layer during soaking and electrochemical cycling. The thickness of diffusion layer is determined to be at micron level, which can be readily diminished when gas is generated on the electrode surface. Our approach can be further expanded to study the phase transformation and particle agglomeration at the interfacial region and provide insights into the reactive complexes. In Chapter 5, we reveal the correlation between the electrolytic water decomposition and ion intercalation behaviors in aqueous batteries. In the Na-deficient system, we discover that overcharging in the formation process can introduce more cyclable Na ions into the full cell and allows for a boosted performance from 58 mAh/g to 124 mAh/g. The mechanism can be attributed to the water oxidation on the cathode and Na-ion intercalation on the anode when the charging voltage exceeds the normal oxidation potential of cathode. We emphasize the importance of unique formation process in terms of the cell performance and cycle life of aqueous batteries. In Chapter 6, we summarize the results of our work and propose perspectives of future research directions. / Doctor of Philosophy / Li-ion batteries (LIBs) have dominated the market for portable devices and electric vehicles owing to their high energy density and good cycle life. However, frequent battery explosion accidents have raised significant safety concerns for all customers. The root cause can be attributed to the flammable organic electrolytes in conventional LIBs. To address this issue, aqueous batteries based on water-rich electrolytes attract intensive attention recently. Recent research progress has dramatically improved the energy density of aqueous batteries dramatically by modifying the properties of electrolytes. However, most electrode materials are incompatible with water, leading to severe side reactions and an unstable cycle life. Therefore, understanding the failure mechanism of electrode materials in the presence of water is crucial while not fully studied yet. Our projects systematically evaluate the degradation behavior of various electrodes in aqueous electrolytes and uncover the root cause of transition metal dissolution in the electrodes. Our studies shed light on improving battery capacity and cycle life through a specialized formation cycle and polymer coating process. Furthermore, we also provide new approaches to investigate the dynamic process occurring at electrode–electrolyte interface, which is applicable to other solid–liquid systems. In summary, our research reveals the correlation between the failure mechanism and the capacity decay in various electrode materials, proposing effective approaches to enhance the battery performance.

Lithium ion batteries (LIBs) are crucial for modern electronics and electric vehicles (EV). However,their electrochemical performance is facing challenges at low temperatures (e.g ≤ 0 °C) due to reducedLi+ kinetics and increased charge-transfer resistance. Given the growing dependence on LIBs for bothelectronics and EVs, especially in cold environments, it is imperative to address the low-temperaturelimitations. Thus, improving the low-temperature performance of LIBs is essential for the broaderadoption and further advancement of LIBs. To address these challenges, this thesis demonstrates thatsignificant improvement of electrochemical performance at low temperatures can be achieved by in-corporating Lithium difluoro(oxalato)borate (LiDFOB) as an additive into the baseline electrolyte forthe Li(Ni0.8Mn0.1Co0.1)O2(NMC811)∥Li cell.At a low temperature of -20 °C, the NMC811∥Li cell with the electrolyte containing 4 wt% LiDFOBexhibited an impressive discharge capacity of 125 mAh/g at 0.1C (1C = 2.0 mAh cm−2), representingabout 61.6% of the capacity delivered at 20 °C. In contrast, the cell with the baseline electrolyte de-livered negligible discharge capacity under the same conditions. This result emphasizes the functionsof LiDFOB as an electrolyte additive in enhancing the low-temperature performance of NMC811∥Licells. This work reveals the kinetics bottleneck of Li+ transport during charge/discharge processes atlow temperatures can be mitigated by tuning cathode-electrolyte interphase (CEI) through introducingadditive into the baseline electrolyte.To substantiate these findings, Electrochemical Impedance Spectroscopy (EIS) was employed to re-veal the significant decrease of interface resistance resulting from the addition of LiDFOB into thebase electrolyte. X-ray Photoelectron Spectroscopy (XPS) further confirmed the benefits of LiDFOB,indicating that a B-rich, more conductive and thinner CEI formed on the NMC811 cathode induced byLiDFOB. The results indicate that the inclusion of LiDFOB in the baseline electrolyte is advantageousin tuning CEI at the cathode for reducing charge-transfer resistance and enhancing electrochemicalperformance.In conclusion, the tuned CEI induced by LiDFOB additive plays an important role in improving thelow-temperature performance of the NMC811∥Li cells. This improvement in the capacity delivery at-20 °C can be attributed to the formation of a highly conductive and uniform and thinner CEI layer,which in turn facilitates reduced charge-transfer resistance at low temperatures. This work sheds newlight on the electrolyte design with additives to develop high-performance LIBs operating at extremeconditions.2

<p>  </p> <p>Nowadays, clean and renewable energy sources like wind and solar power have been rapidly growing for the goal of phasing out traditional fossil fuels, achieving carbon neutrality, and realizing sustainable development. Long-duration and large-scale energy storage is needed to address the intermittent nature of these sources. Especially, redox flow battery (RFB) is an attractive energy storage device for large scale applications because of its high scalability, design flexibility, and intrinsic safety. The all vanadium redox flow battery stands for the state-of-the-art system, but the high vanadium cost and limited energy density are among the limiting factors for wide commercialization. Therefore, it is necessary to develop new RFB materials that are cost-effective and highly soluble. Organic redox-active molecules (redoxmers) hold great potential to satisfy these requirements due to structural diversity, tunable chemical and electrochemical properties, and earth-abundant sources. With rational structural design, organic redoxmers can show favorable properties such as high solubility, suitable redox potential, and good chemical stability. However, current efforts are mainly on the development of anolyte redoxmers, e.g. phenazine, anthraquinone and viologen. Only limited types of catholyte candidates have been reported such as ferrocene and TEMPO. The major reason for such slow-paced progress is the limited chemical stability of these catholyte redoxmers. To bridge this critical gap, my efforts are focused mainly on the design and development of promising catholyte redoxmers for both aqueous organic (AORFBs) and non-aqueous organic redox flow batteries (NRFBs).</p> <p>Phenoxazine functionalized with a hydrophilic tetraalkylammonium group demonstrates good water solubility and suitable redox potential. Cyclic voltammograms (CV) and flow cell testing were used to evaluate the electrochemical properties and battery performance, respectively. Besides, the battery fading mechanism was systematically investigated by CV, liquid chromatography mass spectra (LC-MS) and electron paramagnetic resonance (EPR) spectroscopy. The redoxmer decomposition mechanism analysis will benefit future redoxmer development by guiding the molecular design of more stable structure candidates. </p> <p>A structural design strategy for the development of novel TMPD-based (tetramethyl-<em>p</em>-phenylenediamine) catholyte redoxmers for NORFBs is presented. Two categories of functional groups, including oligo(ethylene glycol) (EG) either chains and phenyl rings, were incorporated into the TMPD core to improve solubility and stability in non-aqueous electrolytes, respectively. EPR characterization and bulk electrolyte (BE) analysis were carried out to evaluate the redoxmers stability. In addition, DFT studies were conducted to understand the impacts of functional groups on redox potential and chemical stability. The present work demonstrates the feasibility of constructing promising redoxmers from TMPD and provides insights into molecular designing of catholytes to achieve high solubility and excellent stability for non-aqueous redox flow batteries.</p>

To reduce the negative impacts of climate change, electric vehicles (EVs) have emerged as a viable solution in the mobility sector, leading to an increase in battery production and use. For electric vehicle batteries (EVBs) to be sustainable, the total impact of the supply and value chain has to be as low as possible, making the implementation of circular economy (CE) principles a key element in the transition. There is currently limited research regarding circularity implementation in the value chains of EVBs, and especially in developing countries. This thesis explores the key stakeholders in the EVB ecosystem in Nairobi, Kenya, and identifies barriers and enablers for CE implementation. The objective of the thesis is to analyze, based on literature and empirical findings, what activities are deemed necessary to facilitate a circular value chain (CVC) for EVBs in Nairobi. To enable a realistic and thus relatively comprehensive analysis, a case study was conducted involving a literature study, interview study, document review, and workshop. Findings indicate that the Nairobi EVB ecosystem is largely unexplored but that currently, the most important stakeholders can be seen as EV manufacturers and consumers, as well as waste management actors, and second life actors. The key enablers of the ecosystem are government, government agencies, energy providers and suppliers, as well as importers and distributors. The findings indicate the possibility of new essential stakeholders in the future including battery original equipment manufacturers (OEMs), new EV manufacturers and original equipment manufacturers (OEMs), public transport companies, and second life actors. Potential ecosystem enablers include financial actors, research institutions, and insurance companies. Identified barriers and enablers of CE implementation can be divided into five areas, namely technology and infrastructure, supply chain and management, economic, policy and regulation, and social. The findings indicate that barriers identified within the different areas are interconnected, requiring coinciding strategies to be solved and making it difficult to rate them in terms of importance. The findings further suggest that for a CVC for EVBs to be initiated and supported by stakeholders, actors within the ecosystem have to adopt CE strategies to create a closed loop supply and value chain. Battery design needs to enable CE strategies, such as reuse, repair, refurbish, remanufacture, repurpose, and recycle. Furthermore, innovative business models that extend the life cycle of products need to be developed to facilitate the transition to CE. This requires collaboration between the stakeholders in the ecosystem, as well as working with the barriers and enablers identified. To create favorable and enabling system conditions, there is a need for policies and regulations to facilitate the implementation of CE strategies at end-of-life (EoL).

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